Patent Application
20120197472
1. Field of the Invention
This invention pertains to a powertrain and method of a kinetic hybrid vehicle, such as a gas and/or electric powered vehicle that includes a flywheel. The powertrain and method may be used to store and use energy of the flywheel device for vehicle propulsion and optimizing fuel efficiency.
2. Description of the Related Art
Improving fuel economy is an important objective in vehicle design, since it enables reduced fuel consumption and reduced emissions. Especially with the current situation of dwindling fossil fuel resources and worsening environmental conditions, the end goal of reducing fuel consumption and emissions becomes particularly important. Although automotive technology has been advancing and there have been improvements in fuel economy, there still exists an inherent conflict between fuel economy and accelerative power in conventional vehicles. In a conventional vehicle powered by an internal combustion engine, fuel economy is generally inversely related to vehicle performance, as the engine generally cannot be downsized to be run at its optimal efficiency without sacrificing performance. This inverse relationship is due to the characteristics of the internal combustion engine. IC engines are at their highest efficiency within a certain speed range and at a fairly high load, but these conditions constitute only a small region in the map of all loads and speeds the engine is operable at. Both gasoline engines and diesel engines exhibit this characteristic. As a non-limiting example, an engine may be most efficient running at 2000 RPM and seventy-five percent of its maximum load. Thus an IC engine achieves its best efficiency at relatively high power; automotive vehicles, however, require only low power most of the time. Acceleration performance is seen in how much reserve power the vehicle has to overcome its own inertia and increase its speed. The more reserve power, the more quickly the desired acceleration or speed can be achieved, and the better the performance of the vehicle. Hence for performance considerations, the bigger the engine in conventional vehicles, the more reserve power there is to accelerate the vehicle relatively quickly and overcome inertia. On the other hand, this means that when the vehicle is not accelerating, its engine is operating at a lower load level and lower efficiency state, wasting the maximum efficiency potential of the engine. If a smaller engine is used, then the engine will be working at a higher efficiency to improve fuel consumption, but there will be less reserve power, which means poorer performance in acceleration. In addition, much of the vehicle's kinetic energy is dissipated as heat in the brakes when decelerating, reducing the vehicle's potential fuel efficiency.
Hybrid vehicle technologies have taken a large step forward in resolving the compromise between performance and fuel economy. Hybrid electric vehicles (HEVs), which are equipped with another power source and energy storage, may recover a portion of the vehicle's kinetic energy during deceleration, and can use a downsized engine operating at optimal efficiency consuming the least fuel for each unit of work done for increased fuel efficiency. By supplementing the power from a smaller engine with power from a traction motor, HEVs can run the engine at increased efficiency compared to conventional vehicles without sacrificing performance. HEVs can also recover a portion of the vehicle's kinetic energy during deceleration. Although more efficient and environment friendly than some conventional vehicles, these electric hybrids may be difficult to produce without the added costs of a large traction motor, controller, and electrochemical and/or electric storage devices. These costs, which may outweigh the amount of money saved from consuming less fuel, may result in an increased price to consumers that limits market penetration.
Aside from cost, a main disadvantage of electric hybrids is that they are greatly limited in the fuel economy improvements they can provide. Part of conventional electric hybrids' efficiency limitations comes from the fact that energy is not stored in the same form it is used in. When energy from the engine or the vehicle is stored as electricity, there are multiple conversions from mechanical to electric, from electric to electrochemical, from electrochemical to electric, and from electric to mechanical. There are typically four energy transformations by the time the energy is used, each resulting in a conversion loss. These conversion losses typically comprise above one-third the original amount of energy initially recovered, such as from braking. Another part of conventional electric hybrids' efficiency limitations comes from the inherent characteristics of motor/generators and batteries—namely, their power transfer limitations and reduced efficiency at high rates of charge and discharge. Even when the electric storage consists of ultracapacitors, which are highly efficient at high rates of charge and discharge, the energy regenerated from deceleration is limited by the power of the traction motor. Thus only a small portion of the vehicle's kinetic energy may be recovered via regenerative braking in electric hybrids.
To avoid conversion losses and improve fuel economy, an alternative energy storage device is available: the flywheel, which can also serve as a power source. As an energy storage device the flywheel is analogous to electrical storage devices like batteries and supercapacitors, and as a power source the flywheel can function similarly to motors. Flywheels have much higher power density and can give and receive much higher power than motor/generators, and since flywheels store energy in the same form that it is to be used in for vehicle propulsion, they are more efficient than electrical energy storage devices used in hybrid electric vehicles if the energy is released via a direct mechanical path. The challenge with flywheels is how to control the amount of energy transferred. Flywheel systems may use Continuously Variable Transmissions (CVTs), traditionally mechanical, to store and release energy. Mechanical CVTs typically achieve only about a 6:1 transmission ratio, and cost quite a bit. In the early days of flywheel vehicle development and even now in some industrial applications and Uninterruptible Power Supply (UPS) systems, energy is stored into and released from the flywheel via one or more motor/generator(s), traveling a 100 percent electromagnetic path from source to destination; these flywheel systems also suffer multiple energy conversions and limited efficiency due to conversion losses. With these methods the flywheel was used only as an energy storage device. More recently, flywheels have been used with electrically controlled CVTs that have a direct mechanical path as well as an electromagnetic path for the transfer of power, increasing efficiency.
U.S. Pat. No. 7,341,534 by Schmidt discloses an electrically variable hybrid transmission and powertrain equipped with a flywheel energy storage device. In this configuration, based on modifying a conventional Internal Combustion Engine (ICE) driveline, the engine is coupled to the final drive through a torque converter, an automatic transmission, and the transmission shaft. The final drive may include a drive shaft, a differential, a set of fixed gears, and wheels, but does not include a transmission. Meanwhile, the flywheel is coupled to the final drive through a three way power split transmission wherein a first input/output port is coupled to the flywheel, a second is coupled to a motor/generator, and the third is coupled to the transmission output shaft. The motor/generator and the planetary gear set comprise a CVT between the flywheel and the transmission output shaft so that part of the energy recovered by the flywheel from the wheels is transferred through a purely mechanical path The motor/generator controls the transfer of energy between the flywheel and the vehicle by adjusting the speed of the port to which the motor/generator is connected, which in turn affects the speeds of the other two ports of this CVT for the flywheel. The placement of the flywheel and its CVT is after the transmission of the engine, so the variator motor/generator in the flywheel's CVT must operate over a wide range and needs two planetary gear sets to perform the right function. Also, two transmissions are required; an automatic transmission for the engine and the three port power split CVT for the flywheel.
Document US2010/0184549 by Sartre, et. al discloses a similar configuration for the same purpose of energy recovery. Unlike Schmidt, the flywheel energy recovery system for Sartre is located between the engine and the engine's transmission. It takes advantage of the engine's transmission so that the energy recovery system is more independent from the vehicle speed than that in U.S. Pat. No. 7,341,534. The variator motor/generator for the flywheel operates over a narrower range than in Schmidt.
In both the configurations of Schmidt and Sartre, the CVT for the flywheel is a three way power split transmission embodied by planetary gears and at least one motor/generator to vary the CVT ratio for the aforementioned power split transmission. Both use three-port power split devices as transmissions only for the flywheel, so the engine needs a separate transmission. Another disadvantage is that both systems may have critical points where the variator motor/generator approaches zero speed (stall state, maximum current) and the system has poor efficiency unless the effect is mitigated through other means such as by mechanically braking the variator port when the motor/generator approaches zero speed. In the prior art, the electrically controlled CVTs used to control the flywheel comprised planetary gear systems with three input/output ports. Even where there was more than one planetary gear system used, one of the ports of the additional planetary gear system was fixed, with the remaining two ports functioning as fixed gears, and only one planetary gear set was used to vary speed.
Both the configurations of Schmidt and Sartre have coupled the engine and the final drive on the same port of the power split transmission. With the engine and the final drive both connected to the same port on the power split transmission, another transmission may be needed between the engine and the final drive to vary the relative speeds of the engine and the final drive. In these configurations, the CVT only serves the flywheel, so the engine needs its own separate transmission.
The conventional power split CVTs used in conjunction with a flywheel have three input/output ports, and may include an additional planetary gear set for gear reduction rather than as part of the CVT. In other words, the conventional three-port CVT is for use with only the flywheel, and a separate transmission is needed for the engine.
In the present invention, a number of kinetic hybrid systems and methods are demonstrated. Three-port power split CVTs and four-port compound power split CVTs that do not require a separate engine transmission are used in configurations and methods distinct from the prior art. Only in retrofit systems that make use of the existing transmission for the engine does the present invention use two transmissions. A power split transmission may be a transmission that includes at least two paths that power can travel through. A compound power split transmission may be a power split transmission where the inputs can be split and the outputs can be split.
One thing is common to all the embodiments of the present invention: the final drive is connected to its own independent port and does not share its port with any other power source. The various power sources (flywheel, motor, and/or engine) may share the remaining ports in one way or another. In contrast, the conventional power split CVT's connect the engine and the final drive to the same port through an additional transmission. For embodiments using a three-port power split CVT, the present invention connects and uses the three-port power split CVT in ways that are distinct from the conventional system and methods.
In preferred embodiments of the present invention, one port manipulated by a variator can change the speed ratio between the other two or three ports. This allows the flywheel of the present invention to exchange energy with the vehicle, and it can also change the speed ratio between the engine and the final drive, allowing the engine to effectively transfer power to the vehicle's wheels across a full range of vehicle speeds. In other words, the flywheel and the engine can share a single CVT.
In one aspect, a flywheel hybridizes a single motor electric vehicle. The flywheel (the kinetic power source and kinetic energy storage), the motor (the variator and electric power source), and the final drive each have their own independent input/output port.
In another aspect, a flywheel hybridizes a dual motor electric vehicle. One motor, as variator, is connected to a third port, the final drive is connected to a second port, and the other motor serving as the electric power source and the flywheel serving as the kinetic power source and energy storage share the first port.
In further aspects, a conventional vehicle with an IC engine is hybridized into a kinetic-gas hybrid system. The variator and the final drive each has its own independent port while the flywheel and engine can either share the first port and use the same transmission simultaneously in a four-port configuration, or connect to the CVT in a three-port configuration through clutches, using the CVT in turns. The final drive is connected to a second port and the other motor, as variator, is connected to a third port. None of the above configurations need a second transmission, reducing cost.
In a preferred aspect of the present invention, a four-port compound split transmission, as used in the present invention, ensures that there are enough independent ports for the engine, the final drive, the flywheel and the variator motor/generator to be separately coupled. However, the engine and the motor/generator used for propulsion may share a port. The compound split CVT can be considered as comprised of two CVTs, one for the engine and the other for the flywheel. No other transmission is needed. It should be noted that the compound split CVT of the preferred embodiments of this invention is not equivalent to two separate CVTs that do not have direct feedback.
In a further aspect, the invention consists of a flywheel, an electrically controlled continuously variable transmission with preferably four ports for input/output, a prime mover, a control unit, and a plurality of gears working together to provide the vehicle with a powertrain, an additional power source, energy storage, and an energy recovery system. The prime mover used with the invention may be either an internal combustion engine or a motor/generator. The prime mover, the flywheel, the CVT variator, and the final drive are coupled to separate ports, allowing the CVT to be used for both the prime mover and the flywheel. As a kinetic energy storage device, the flywheel stores energy in the same form it is used in. When provided a direct mechanical path by the CVT for transfer of energy between the flywheel and the vehicle, the flywheel can recover the vehicle's kinetic energy during deceleration as well as directly power the drivetrain to drive the vehicle during acceleration or cruise, all with minimal energy conversion and conversion losses because of the direct mechanical transfer of energy. Using the flywheel as a secondary mover can also result in higher performance since flywheels have a much higher power density than motors or batteries. In an embodiment where the prime mover is a traction motor, an engine may be coupled to the same port to extend the vehicle's range. In an embodiment where the prime mover is an internal combustion engine, a torquer motor/generator may share the same port to improve efficiency.
When the IC engine is configured to be the primary power source and the flywheel is configured to be the secondary power source and energy storage, the system is configured as a kinetic hybrid vehicle. When the IC engine is not used, the torquer motor is configured to be the primary power source, and the flywheel is configured to be the secondary power source and energy storage, the system is configured as a kinetic-electric hybrid vehicle. In a four port compound CVT, the speed change in any input/output port may cause speed changes in the other ports; therefore, with appropriate methods to control the variator motor/generator, both the engine and the torquer motor/generator can be controlled as well so as to exchange energy between the flywheel and the vehicle's wheels, to pass energy from the engine and/or torquer motor/generator to the vehicle's wheels, to pass energy from the engine and/or torquer motor/generator to the flywheel, and even to pass energy from the flywheel through a motor/generator to charge the battery pack. Besides physical embodiments or configurations, good control methods are also important to achieving fuel economy. The vehicle's operation during driving can typically be classified into two states: a first state where the vehicle's speed is significantly changing, such as during acceleration and deceleration, where inertia and change in the vehicle's kinetic energy are involved, and a second state where the vehicle's speed is not changing significantly, such as during cruise. In the first state both high efficiency and high performance are desired, whereas in the second state only high efficiency is desired, since there is no appreciable change in the vehicle's speed.
In yet another aspect of the invention, a “de-inertia operation” method is provided for controlling the flywheel with the powertrain so that the vehicle's inertial effects are drastically reduced. The flywheel can be precharged so that when the vehicle's kinetic energy is low (vehicle speed is low or zero), the flywheel is at its maximum energy level. The flywheel provides most of the power used to launch the vehicle from rest, starts the engine, and continues to participate in accelerating the vehicle, thus helping the vehicle overcome its rest inertia. There is an inverse relationship between the kinetic energy in the flywheel and the kinetic energy in the vehicle's wheels: the higher the vehicle speed, the lower the amount of energy stored in the flywheel. When deceleration is desired, the energy in the flywheel may be at a relatively low level, and the flywheel can be charged back up to a higher energy level using the vehicle's kinetic energy. The lower the vehicle speed, the higher the amount of energy recovered in the flywheel. Once deceleration is over, the recovered energy in the flywheel may be used to accelerate the vehicle in the next acceleration maneuver. In doing so, the flywheel helps the vehicle to decelerate, helping reduce the effects of the vehicle's moving inertia, which improves performance. It also improves efficiency by recovering energy during deceleration and reusing that energy for the next acceleration. This method provides optimal efficiency and performance while the vehicle speed is changing, enabling downsizing of the engine and the motor/generators compared to conventional vehicles and hybrids. More specific steps to this method will be described later with reference to the drawings.
Still another aspect of the invention provides a optimized efficiency cruise method for controlling the powertrain to provide power to the vehicle during cruise (when the vehicle's operator does not desire acceleration or deceleration). In conventional vehicles, when there is no need for acceleration, such as during cruise, when there is no appreciable speed or kinetic energy change, the engine load is relatively low, since there are only air drag and rolling resistance to overcome, and efficiency is low. The system and methods of the present invention can raise the engine load and splits excess power generated from raising the load to the flywheel. The flywheel can be charged while the vehicle is in motion, and the engine is continuously run in its most efficient state (e.g. within a range of speeds and within a range of load that correspond to the engine's maximum efficiency). With the engine running at its optimal efficiency, its output is suitably divided between the flywheel and the vehicle. When the energy in the flywheel reaches a certain level, the engine is turned off and decoupled from the rest of the powertrain; the vehicle is then driven by the flywheel until the energy in the flywheel reaches a lower level or setting. At that point, the engine is coupled to the powertrain again to charge the flywheel. This method of alternatively using the engine to simultaneously charge the flywheel and drive the vehicle, and then decoupling the engine to let the flywheel drive the vehicle, allows for the engine to be run in a start-stop manner. Although electric hybrids may also operate the engine in a start-stop manner, it is often not practical for them to do so because of multiple stage energy conversion losses. Since the system of the present invention minimizes conversion losses, it is beneficial to operate the engine this way more often.
Whenever the engine is on, it is run in its highest efficiency state within a certain speed range and preferably a certain load, which can be adjusted or shared by the optional but beneficial torque motor/generator on the same port. Whenever the flywheel is driving the vehicle, the engine is off, and the vehicle consumes no fuel. The speeder motor/generator, or the variator, ensures that a constant power is delivered to the wheels so that the vehicle remains in cruise, regardless of whether it is driven by the engine or the flywheel. Hence, this method optimizes efficiency during cruise. Cruise includes situations where the vehicle operator does not intentionally accelerate or decelerate; in one non-limiting example, the vehicle speed might change slightly with road conditions such as a slope or incline that does not lead the vehicle operator to appreciably change the position of the throttle. Variations for a vehicle powered by a traction motor as the prime mover are also provided.
An additional aspect of the invention provides a motorless configuration, also capable of directing the storage and release of energy to and from a flywheel to benefit vehicle propulsion. Instead of using motors or a more complicated mechanical transmission, this configuration uses just planetary gearing and either a set of brakes or a slip clutch and a brake as variators.
a) illustrates one possible way of combining the embodiment of
b) illustrates a wheel hub implementation of the system described in
a) shows a possible way of placing the dual motor embodiment into an existing vehicle with an engine to form a hybrid vehicle with three power sources;
b) illustrates a wheel hub implementation of the system described in
a) presents an embodiment of the invention for a vehicle having an engine as its prime mover, wherein the engine shares a port of the CVT with the flywheel through a clutch;
b) presents a variation upon
a) illustrates a unique motorless embodiment of the present invention where a pair of brakes act as variators to store energy to and release energy from the flywheel;
b) is an equivalent embodiment that is also motorless, using a clutch and a brake instead as the method of control for storing and releasing energy to and from the flywheel;
c) shows how the motorless brake-based embodiment of
d) is a mechanical schematic of the brake-based embodiment of
a), 20(b), and 20(c) are flowcharts depicting stationary, reverse, and restore operations of a preferred embodiment;
Embodiment(s) of the present invention are described herein with reference to the drawings. In the drawings, like reference numerals represent like elements.
Although both fuel efficiency and performance are desired in vehicles, they are conflicting goals in the design of a conventional vehicle powered by an internal combustion engine. High performance vehicles are equipped with large engines but suffer from poor efficiency, whereas fuel efficient vehicles lack performance.
Gas-electric hybrid vehicle technologies have made considerable advances in resolving the deadlock conflict between fuel efficiency and accelerative performance. These hybrid electric vehicles, or HEVs, rely on a downsized engine that works at a better efficiency converting fuel to mechanical power, while a motor, as a secondary mover, supplements power to compensate for a smaller engine's lack of reserve power for acceleration. In addition, HEVs can recover part of the vehicle's kinetic energy with a generator during deceleration, which is typically wasted and completely dissipated as heat in the brakes when conventional vehicles are decelerated.
Yet there still remains a core problem in vehicle propulsion using electric power. Powering the vehicle with an electric machine requires an electrical energy storage (henceforth referred to as a battery pack, with the understanding that the “battery pack” can be any combination of different electrical energy storage devices, such as batteries and/or supercapacitors). The disadvantage to using an electric power source is that energy is not stored in the same form that it is used in. Even if each energy conversion can be performed at a high efficiency each stage, having multiple stages of energy conversion (such as in vehicle propulsion, where energy is converted from a mechanical form to an electric form and then to electrochemical form when energy from the engine or from regenerative braking is stored into the battery pack through a generator and inverter, then released and used to the vehicle's drivetrain, undergoing conversion from electrochemical to electric to mechanical form) results in considerable conversion losses. Conversion losses significantly limit fuel efficiency; this is a problem common to electric vehicles as well as to the electric system components of hybrid vehicles. Another problem frequently encountered by electric hybrid vehicles and by many electric vehicles is that the higher the rate of charge and discharge of power to and from the batteries, the less efficient the transformation of energy will be.
Acceleration—accelerative vehicle demands include overcoming inertia and various resistive forces acting on the vehicle, and a large amount of accelerative power is desired. In order to provide such power, the battery pack 05 would typically be discharged at a relatively high rate, as shown by point a on the inset curve 07; conversion efficiency as the energy stored in electrochemical form is transformed into electricity is 77 percent as the inverter 03 supplies current to the motor 01. Because the motor 01 typically works at high torque and low RPM when converting electrical energy to a mechanical form during acceleration, around point d on the inset curve 08, the combined efficiency of the inverter 03 and the motor 01 is around 80 percent. Overall efficiency is then 62 percent (0.77*0.80=0.62).
Steady speed (cruise)—during cruise, the vehicle need only overcome air drag and rolling resistance, as the kinetic energy of the vehicle need not change. Thus the demand on electrical current is low and the motor 01 would work at moderate speed and torque. The battery pack 05 can work near point b and achieve 96 percent efficiency, while the motor 01 and inverter 03 can work around point f and reach 84 percent efficiency. Overall efficiency is then 81 percent (0.96*0.84=0.81).
Regenerative braking—when the vehicle needs to be decelerated, the power demand on the generator 01 and the battery pack 05 is usually greater than acceleration power demands. For simplicity, however, assuming that the charge rate of the battery pack 05 and torque demands of the motor/generator 01 are symmetrical to the case for acceleration, the battery pack 05 works again around point a, and the generator 01 would work near point h. In regenerative braking, kinetic energy from the vehicle's wheels 34 is transmitted through the wheel axes 36 and the final drive 32 to the transmission 11 and the generator 01 to be converted into electricity. From the generator 01, the electricity is passed to the inverter 03 and the battery pack 05, where electricity is transformed into a chemical form and stored. In the next acceleration maneuver, this energy conversion process is reversed, and the chemical energy in the battery pack 05 must be converted into an electrical form and then a mechanical form before it can accelerate the wheels 34. The path energy recovered from deceleration must traverse (through the motor 01 operating around point d) to reach the wheels 34 again thus involves four energy transformations, and the resulting efficiency is 38 percent (0.80*0.77*0.77*0.80). If other mechanical transmission losses and the use of other means to slow down the vehicle are considered, then efficiency is even lower.
It should be noted that the highest efficiency does not occur where the motor/generator 01 or the battery pack 05 is most efficient, but where the multiplicative product of their efficiencies is maximum, as it is unlikely that the motor/generator 01 and the battery pack 05 will both operate at optimal efficiency simultaneously. For example, when the motor/generator 01 works close to its most efficient around point e or g, the battery pack 05 may be operating around point c, so that the overall system efficiency is highest at 86 percent (0.94*0.91=0.86).
Thus it can be seen that in vehicles relying upon electric machines for propulsion, efficiency can fluctuate quite a bit. Especially in situations calling for acceleration or deceleration, the amount of energy lost to conversion is significantly, particularly when large currents are needed or produced. Another factor to consider is that battery lifespan is inversely proportional to the number of charge/discharge cycles and the “depth” to these cycles. Reducing the rates of charge and discharge also prolongs battery life. In summary, to improve efficiency in electric systems for vehicle propulsion, it is important to use the motor/generator 01 and the battery pack 05 under conditions resulting in high efficiency, and it is important to avoid converting energy to be stored into the battery pack as much as possible, by reducing the rate (electric current) and the number of cycles of charge and discharge in the battery pack.
Supercapacitors and ultracapacitors can directly store energy in the electrical form, which is an improvement upon battery alone, because capacitors only require two energy conversions instead of the typical four conversions with batteries. These capacitors have higher power density than batteries, but their disadvantage is low energy density. The combination of capacitors and batteries into a battery pack can increase efficiency and extend battery life.
Should it be possible to directly store and release kinetic energy and minimize energy conversions, efficiency can be improved.
When it comes to vehicle propulsion, there is a fundamental truth: the ultimate form of energy the vehicle gains and uses is mechanical, and to be more specific, kinetic. If a kinetic power source and energy storage replace electric machines and electrical storage as a secondary power source or the secondary mover, then the vehicle would become a kinetic-gas hybrid. Furthermore, if the prime mover is not an internal combustion engine but an electric system, then the resulting combination of a kinetic secondary mover with an electric prime mover produces a kinetic-electric hybrid. (Note that the definition of hybrid used here refers to any vehicle having two or more sources of power for propulsion. There is a prime mover or primary power source, and a secondary mover or secondary power source, along with an energy storage that is used by the secondary power source; the energy supplied to the secondary power source generally comes from the prime mover, or from recovering the kinetic energy of the vehicle.) With a kinetic power source, the vehicle may directly use the stored energy without need for energy conversion, at least in a portion of the stored energy, or a majority of the stored energy, to move the vehicle, improving overall efficiency. (100 percent of the energy the vehicle uses from electric power sources must undergo conversion.)
Flywheels make for both a kinetic energy storage and a kinetic power source; a flywheel is analogous in function to both a battery pack (energy storage) and a motor/generator (power source and a means for recovering energy) combined into one device. A major benefit of a flywheel is that the form of the energy stored is kinetic, which is the same form of energy that the vehicle needs to use. Hence there are no energy conversion losses, only energy transmission losses. This characteristic provides the basis for improving fuel economy.
Another important characteristic of the flywheel is its extremely high power density, easily over ten times the power density of electric machines for vehicle propulsion. As flywheels can output or absorb large rates of power while still remaining lightweight, they can vastly improve the vehicle's performance. Flywheels have considerable energy density as well, which is an often neglected fact. Some flywheels may have more energy stored per unit weight than any type of battery. Unlike batteries, flywheels do not suffer degradation from use, and can easily outlast vehicle lifetimes. They do not create hazardous byproducts or wastes either in the manufacturing process or disposal. Flywheels also have a simple, cost-effective structure; they are simply a solid mass of material in a simple shape.
Owing to the aforementioned advantages, effective use of flywheels for vehicle propulsion may increase efficiency, reduce emissions, improve the vehicle's performance, and reduce cost of manufacture compared to electric hybrids comparable in power and size. The challenge is in how to utilize a flywheel just so to make the best use of the flywheel's characteristics for vehicle propulsion.
The transmission in
(k+1)ωc=kωr+ωs (1)
Where ωc, ωr, and ωs are respectively the speeds of the planetary carrier C, the ring gear R, and the sun gear S, and the constant k represents the physical gear ratio between the ring gear R and sun gear S.
Even with an appropriate physical embodiment, the hybrid system must have an appropriate method of control to increase fuel efficiency effectively using a flywheel.
At the start of the drive or when stopped at an intersection, the hybrid system can pre-charge the flywheel F, as shown in
b) shows that once the flywheel F is charged and acceleration is desired, the vehicle's brakes are released, and the motor/generator G reverses the direction of its torque to act as a generator, reducing the speed of the ring gear R by providing a braking torque in the direction opposite that of motion. The sun gear S obtains a reaction torque from the ring gear R, allowing for the release of energy from the flywheel F. Energy from the flywheel F is split into two paths: the majority of the power flows from S to C to accelerate the vehicle's wheels W, while a small portion is used by the generator G to produce the braking torque on R, which also charges the battery pack B in the process. In this operation state for acceleration the speeds of the flywheel F and the generator G, as well as the sun gear port of the sun gear S and the ring gear port of the ring gear R they are connected to, decrease, while the speeds of the planetary carrier port and the wheels W increase. Aside from the small portion of power supplied to the speed ratio variator G, the transfer of accelerative power from the flywheel F to the wheels W is extremely efficient, and the drivability of the vehicle at low speeds is improved by supplying accelerative power from the flywheel F, which has very high power density.
The first acceleration state portrayed in
From the pre-charge phase to the acceleration phase, the motor stores energy into the flywheel at a high efficiency and the flywheel can be controlled to release energy at a high power and a high efficiency, which explains why the flywheel can increase both the vehicle's efficiency and performance.
It should be mentioned that the acceleration at the start of a journey or drive can also occur without a flywheel pre-charge phase. In that scenario, although the forward or CW motion of the motor/generator M (causing the ring gear R to also rotate CW) would otherwise cause the sun gear S and flywheel F to spin in the reverse or CCW direction, the one-way cltuch 24 locks down this port so that ωs=0. The planetary gear set 12 then becomes a fixed ratio transmission with (k+1)/k as the transmission ratio. To accelerate the vehicle without pre-charging the flywheel F would therefore involve the motor M working alone at a larger current and torque (lower efficiency and also lower performance, since the power density of motor/generators are lower, compared to operation states 3(a) through 3(c). If the flywheel F is not pre-charged as in 3(a), then it must wait for the next deceleration maneuver to be charged and be of use in the subsequent acceleration maneuver.
d) depicts the cruise operation state. In the latter part of acceleration or during cruise, the energy of the flywheel F will eventually be released to zero. By then, the motor M will have already started rotating CW to provide power directly to the wheels W, no longer serving as the variator for the flywheel F. After ωs reaches zero, the one-way clutch 24 locks the flywheel F and the port S, preventing them from spinning in the reverse direction, so ωs remains at zero. The motor M alone provides power to the wheels W, but since during cruise the vehicle only has to overcome air drag and rolling resistance, the power required to maintain cruise is not high, and the motor M by itself can drive the vehicle with a relatively high system efficiency (the combined efficiency of the battery pack B and the motor M).
If the flow of energy from the battery pack B to the motor/generator M/G is stopped, the rotor of the motor/generator M/G and the ring gear R it is connected to can spin freely without transmitting torque. Thus both the vehicle's wheels W and the flywheel F can remain in the same state, and do not affect one another (as there is no torque on the ring gear R). This is equivalent to a neutral state, seen in
During deceleration, if the speed of the flywheel F is less than k+1 times the vehicle speed (also expressed as ωs<(k+1)ωc) then the motor/generator G acts as a generator, applying a torque in the CCW direction opposite the CW direction of motion, reducing the speed ωr of the ring gear R, depicted in
The second deceleration state, shown in
To drive in reverse, the operation state depicted in
At the end of the drive, indicated by
With a flywheel as the secondary power source and energy storage, the motor/generator can work consistently in a high efficiency state. Especially during acceleration and deceleration, the motor/generator is not responsible for the entire vehicle's power, but only a small portion of the total power; because a much larger portion of the vehicle's power comes from the flywheel, the power requirements of the motor/generator are lowered. Furthermore, because the flywheel can handle a significant portion of energy storage and release at a high rate, the portion of energy that passes through the battery pack is reduced, not only increasing the efficiency (less energy conversions) but also extending the battery pack's life.
In summary, compared to conventional electric vehicles, a kinetic-electric hybrid vehicle has the following advantages. It increases fuel efficiency by enabling the motor/generator and the battery pack to continuously work at high efficiency, through decreasing the charge or discharge rate of the battery pack. It also increases accelerative performance, since the flywheel has a much higher power density than a motor/generator, and for acceleration both the flywheel and motor/generator can contribute their power. A kinetic-electric hybrid vehicle can also reduce the cost of the vehicle since it allows for downsizing of the motor/generator and extends the life of the battery pack (it uses the flywheel as an energy storage buffer, decreasing the number of charge/discharge cycles).
As a variation, the kinetic-electric hybrid system described in
b) illustrates another implementation where the basic kinetic-electric hybrid configuration of
There is room for improvement for the basic hybrid system configuration.
To pre-charge the flywheel F, the dual motor configuration of
For acceleration, illustrated in
By the time the ring gear R is turning CW, the variator M1 is no longer functioning as a generator, but as a motor; this marks the second acceleration state, which can be seen in
The neutral or coasting state shown in
During cruise, the dual motor configuration seen in
In the second cruise state depicted in
The third cruise state illustrated in
A fourth cruise state shown in
Which of these four cruise states is best for efficiency depends on many conditions and may be determined in real-time by the vehicle's ECU 62, which can generate signals needed to control the hybrid system.
For the first deceleration state, shown in
The ring gear R will at some point be completely braked by the torque produced by the variator G1, and will start to turn in the opposite direction as the planetary carrier C and the wheels W. This marks the beginning of the second deceleration phase, illustrated in
When it is desired to drive the vehicle in reverse, the motor M1 turns the planetary carrier port in the reverse direction while the generator G2 acts as a variator to produce a braking torque, so that energy is passed from the ring gear port to the planetary carrier port, shown in
m) demonstrates how energy may be restored from the flywheel F to the battery pack B. The motor/generator G2 simply works as a generator, absorbing the energy from the flywheel F and regenerating it as electricity to store into the battery pack B while the motor/generator G1 is off. Since there is no torque on R, there is no influence to the speed of the vehicle's wheels W. Thus flywheel energy restoration may be performed when the vehicle is moving (coasting) as well as when the vehicle is stopped.
In summary, the dual motor hybrid configuration demonstrated by
A powertrain in an automobile may be the collection of components that work as a system to generate and transmit power from a power source to the road surface (e.g., the engine, motor, flywheel, gears, transmission, and wheels). As shown in
Another implementation is illustrated in
As seen in
On the basis of the dual motor kinetic-electric hybrid system, the configuration of
The configuration of
When the clutch 22 is disengaged, decoupling the engine 20 from the drivetrain, while the clutch 16 is engaged, coupling the flywheel 10 to the drivetrain, the system is in the kinetic-electric mode seen in
When the clutch 16 is disengaged, decoupling the flywheel 10 from the drivetrain, but the clutch 22 is engaged, the system is in the fuel-electric hybrid mode. The planetary gear set 12 and the motor/generator 02 comprise an electrically variable CVT for the engine 20 controlling the speed ratio and energy transfer from the ring gear port R to the planetary carrier port C. In this mode the variator 02 acts as a generator, and the motor 01 reuses the electricity from the variator 02 to produce torque back to the powertrain to avoid conversion losses in the battery pack 05. The motor 01's power supplements that of the engine 20.
Disengaging both clutches 16 and 22 permits operation in a pure electric mode. Either motor/generator may act as a traction motor or as a variator for the other motor/generator in the CVT. Either one or both motors may be used for vehicle propulsion. With 01 as the variator and 02 propelling the vehicle, the transmission speed ratio is greater than (k+1), suitable for low vehicle speeds; with 02 as the variator and 01 propelling the vehicle, the transmission speed ratio is greater than (k+1)/k, more suitable for moderate vehicle speeds; with both 01 and 02 acting as motors propelling the vehicle, the transmission speed ratio is adjustable and less than (k+1)/k, suitable for high vehicle speeds. Additionally, there are single motor modes available for use with the configuration of
The methods used to control the system of
d) depicts the system starting the engine E during acceleration. Since the ring gear R is already rotating in the forward direction from the second acceleration state in
e) depicts a first cruise state, wherein the flywheel F is disengaged, and the engine E provides the power that the vehicle needs while the variator G2 manipulates the speed ratio of the CVT to control vehicle speed. The motor M1 reuses the electricity generated by the variator G2 to also propel the vehicle, reducing the number of charge/discharge cycles for the battery pack B, extending battery life. In a second cruise state shown in
The deceleration states demonstrated by
Fuel-electric hybrids save fuel primarily by virtue of running a small engine in a fuel efficient region of operation. Although the downsized engine has low reserve power, performance is not compromised because the hybrid relies upon the electric power source and energy storage to compensate for the engine's poor performance. The electric power source and energy storage also enable regenerative braking to recover a portion of the vehicle's kinetic energy that is normally completely lost when a conventional vehicle is decelerated. As analyzed and discussed in
Power split fuel-electric hybrid vehicle powertrains are well known, but if a flywheel is integrated into the powertrain, the vehicle becomes a kinetic-fuel-electric hybrid like the one shown in
Another arrangement is possible while maintaining the principle of keeping the final drive 32 independent on its own input/output port in a three-port power split CVT. Placing a power plant on the same port as the final drive 32 may result in an additional transmission being needed for that power plant. Thus, the engine 20 and the flywheel 10 may either each command one of the remaining two ports, as with the configuration of
For the configuration of
Apart from propelling the vehicle, an important function of the engine 20 is to charge the flywheel 10, maintaining the flywheel 10's RPM within a certain range. The RPM range of the flywheel 10 can be controlled dynamically, for example, as a function of the current vehicle speed. The flywheel 10's speed can be inversely related to the vehicle speed, so that the sum of the vehicle's kinetic energy and the flywheel 10's kinetic energy at any given moment is approximately a constant value, which in one non-limiting example can be equal to the maximum safe energy storage capacity of the flywheel 10. Should the flywheel 10 drop below a lower speed or energy setting at any moment, the engine 20 may be engaged with the clutch 22 to charge the flywheel 10; when the flywheel 10 is above some higher speed or energy setting, the engine 20 may be disengaged and turned off or in idle. The engine 20 can be operated in a start-stop manner, either driving the vehicle and charging the flywheel 10 at the engine's maximum efficiency, or using no fuel when the engine 20 is disengaged and shut off. The flywheel 10 may be thought of as an energy buffer for the engine 20, gradually releasing the excess energy generated as a result of running the engine 20 in its most fuel efficient state. In comparison, HEVs may use the same control strategy at times with electric storage devices as buffers for the excess energy generated by the engine, but electric storage results in more energy conversion losses and lower overall system efficiency.
The configuration portrayed in
a)-11(m) provide more detail on how to control the equivalent embodiments of
When pre-charging the flywheel, illustrated in
During cruise, the configurations of
Once the flywheel F's energy reaches a certain level or setting, the engine E can be disengaged and either turned off or in idle, allowing the vehicle to be propelled primarily by power from the flywheel F, shown in
The first and second deceleration states, presented in
k) and
Conventional vehicles dissipate all of the kinetic energy of the vehicle every time the vehicle is braked to a full stop. For converting existing vehicles into hybrids, or for new vehicles where the primary focus of fuel efficient design is to recover the vehicle's kinetic energy during deceleration, an embodiment of the present invention includes a brake-based, motorless hybrid system configuration in
The flywheel 10 in the configuration of
When deceleration (kinetic energy recovery) or acceleration (kinetic energy release) is desired, the slipping brakes 50 and 52 are the means to change the speed of port-3 and port-4, replacing the motor variator of the previous embodiments and the prior art. They will and should slip when engaging. Only one of the slipping brakes 50 or 52 is used at a time; 50 for vehicle deceleration, and 52 for vehicle acceleration.
During deceleration, if the brake 50 is engaged, the interaction between the torques on port-3 (ring gear R1) and port-2 (planetary carriers C1 and C2) leads to torque being passed to port-4 (sun gear S1 and ring gear R2). S1 receives torque in the opposite direction of the motion of C1 and causes R2 to rotate in the reverse direction. Consequently, the sun gear S2 on port-4 accelerates, storing energy into the flywheel 10, while the vehicle decelerates. When the brake 50 has completely braked port-4, the flywheel 10's maximum speed can reach −(k1k2−1) times the speed of port-2, where k1 and k2 respectively represent the physical gear ratio of the ring gear to the sun gear in the planetary gear sets 12 and 14. Once this maximum ratio between the speeds of port-1 and port-2 is reached, or perhaps when the speed of port-1 compared to the speed of port-2 is close enough to this ratio, the brake 50 should be released or disengaged, or else the flywheel 10 would actually prevent the vehicle from further decelerating. After this maximum speed ratio is reached (when the energy stored in the flywheel 10 is at a maximum) and the brake 50 disengaged (to prevent releasing energy from the flywheel 10, which would interfere with further deceleration), the vehicle must be further decelerated by another braking mechanism if further deceleration is desired.
The brake 52 should be engaged if it is desired to release the energy stored in the flywheel 10 for accelerating the vehicle. Braking port-4 with the slipping brake 52 can release energy in the flywheel 10 all the way down to zero to propel the vehicle. The brake 52 should be disengaged immediately thereafter, or else the flywheel 10 may start spinning in the reverse direction, negatively impacting the vehicle's drivability.
b) demonstrates a variation on the configuration of
ωs=(k3k4+k3+1)ωc (2)
can be derived for when the clutch 51 is completely engaged. The flywheel 10 can therefore be charged up to (k3k4+k3+1) times the vehicle speed ωc before the clutch 51 should be disengaged. Releasing the energy stored in the flywheel 10 involves only the brake 52, and the flywheel 10's energy can be totally released to zero before disengaging the brake 52.
c) illustrates an actual implementation of the configuration of
d) is a mechanical schematic of
This configuration yields a four-port power split system, with port-G coming off the sun gear S1 of the planetary gear set 12 that is connected to the variator motor/generator 01, port-F coming off the sun gear S2 of the planetary gear set 14 that is connected to the kinetic power source flywheel 10 through the clutch 16, port-W that is connected to C1 and R2 and to the wheels 34 through the final drive 32, and port-EM, which is connected to the ring gear R1 and the planetary carrier C2 as well as the electric power source motor/generator 02 and the IC engine 20 through the clutch 22 and secured with the one-way clutch 24. The system mainly functions as a flywheel hybrid, and with an adequately large battery pack 05 it can also function as a plug-in flywheel hybrid electric vehicle. The interface to the system 62 may contain a series of sensors generating signals to the ECU 60, including sensors to detect RPM of various ports of the CVT, the engine load, and the state of charge of the battery pack 05, and etc. The interface 62 also processes the control signals from the ECU 60 to perform operations to the system, such as providing signals to the controller/inverters 03 and 04 or generating signals to couple or decouple the flywheel 10 and/or the engine 20.
The compound CVT is the key to controlling the system's three power sources. The motion of the rotational components in the compound CVT is governed by the following planetary gear equations:
(k1+1)ωc1=k1ωr1+ωs1 (3)
(k2+1)ωc2=k2ωr2+ωs2 (3)
The constant k1 is the physical gear ratio of the ring gear R1 to the sun gear S1, chosen to fit high efficiency RPM ranges for the motor/generators 01 and 02. The constant k2 is the physical gear ratio of the ring gear R2 to the sun gear S2, chosen in consideration of the energy level of the flywheel 10.
ωc1 and ωr2 represent the angular speed of port-W, directly related to the vehicle speed. ωr1 and ωc2 represent the angular speed of port-EM, which is the angular speed of both the motor/generator 02 and the engine 20. ωs1 is the angular speed of port-G and represents the speed of the motor/generator 01, and ωs2 is the angular speed of port-F, which is the speed of the flywheel 10. Supposing that ωw is the speed of the wheels 34 (disregarding the final drive 32), ωem is the speed of both the engine 20 and motor/generator 02, ωg is the speed of the motor/generator 01, and ωf is the speed of the flywheel 10, we can rewrite equations (3) and (4) as follows.
(k1+1)ωw=k1ωem+ωg (5)
(k2+1)ωem=k2ωw+ωf (6)
The speed change(s) of any port(s) will affect the speed(s) of the others. The planetary gear set 12 governed by equation (5) allows the engine 20 and motor/generator 02 to drive the wheels 34, with the motor/generator 01 acting as the variator of the planetary gear set 12 and the compound CVT 40. Changing the speed of the motor/generator 01 varies the transmission speed ratio, which is ωem/ωw, which can be used to control the vehicle speed. The planetary gear set 14 governed by equation (6) is for the control of the flywheel 10 to store and release its kinetic energy when the clutch 16 is in the engaged position. The speed of the vehicle, ωw, is used as the variator in the planetary gear set 14 to control the exchange of kinetic energy between the flywheel 10 and the vehicle.
Even the best physical configuration for a hybrid vehicle needs to be controlled appropriately to achieve the desired characteristics. For control strategies, the two key considerations are performance and efficiency. The present invention also provides two operation methods that optimize these two key considerations; which method is used depends upon whether the vehicle's speed is changing (acceleration, deceleration) or steady (cruise).
The energy consumed by the vehicle can generally be categorized into two portions: one portion is used for overcoming frictional forces such as drag and rolling resistance, and is unrecoverable; the other portion of the energy used goes into the kinetic and/or potential energy of the vehicle. When the vehicle is either accelerating or decelerating, the kinetic energy of the vehicle must either increase or decrease. Inertia always plays a negative or resistive role in changing the vehicle's speed. It takes energy to speed the vehicle up, and when the vehicle needs to be slowed or stopped, the vehicle's kinetic energy is dissipated as heat when braking in conventional vehicles. The energy wasted to braking during deceleration is a result of having to overcome the vehicle's inertia. Most of the reserve power from the vehicle's prime mover is for performance during acceleration, also driven by the need to overcome the vehicle's inertia. In other words, a conventional vehicle must be equipped with an engine powerful enough to overcome inertia in short periods of time for acceleration, but this means that for the remainder of the drive, since relatively little power is needed, the vehicle operates at low engine load and, consequently, low efficiency. The tradeoff in performance and efficiency is necessary because of inertia. If there was no inertia, then fuel or electricity used for vehicle propulsion would only be expended for overcoming drag, rolling resistances, and other frictional forces. Removing inertia from the vehicle is the motivation for the method of performing a “de-inertia operation” enabled by the present invention. The system of the present invention offers both improved performance and efficiency while drastically reducing the vehicle's inertial effects.
The de-inertia process starts from an initial state wherein the speed of ωw on port-W is zero (the vehicle is stationary), and the speed of the flywheel or port-F, ωf, is high (it is assumed the flywheel 10 was pre-charged or charged from the last deceleration maneuver). By equation (6), therefore, the speed of port-EM equals ωf/(k2+1), and by equation (5) the speed of port-G can be expressed as −k1ωem or −k1ωf/(k2+1). The variator 01 in the planetary gear set 12 thus rotates in the negative direction at the speed ωg=−k1ωf/(k2+1). The engine 20 and the motor/generator 02 rotate in the positive direction at the speed ωem=ωf/(k2+1), which is controlled within a relatively stable range around the engine 20's RPM that corresponds to its best efficiency state for maximum efficiency. Because k1 and k2 are constant, and ωem, is near-constant, the k1ωem, and (k2+1)ωem, in equations (5) and (6) are near-constant. The variator 01 meanwhile rotates in the negative direction, acting as a generator most of the time to provide the reaction force needed to transmit the power from the movers 20 and 02 to the wheels 34 through the direct mechanical path from port-EM to port-W of the CVT (R1 to C1 of 12).
When acceleration is desired, by decreasing the speed ωg of the variator 01 in the negative direction and having the motor/generator 02 hold ωem, to be relatively steady, the speed ωw of the vehicle's wheels increases, since k1 in equation (5) is constant. In the planetary gear set 14, described by equation (6), k2 is also a constant, and the rise of ωw while ωem is constant will cause ωf to drop, also releasing energy to port-W and serving to increase ωw. This is the process of acceleration, whereby the engine 20, whereby the flywheel 10, the motor 02, and/or the engine 20 exchange energy with port-W to accelerate the vehicle. Under the control of the variator 01, the vehicle accelerates, which increases its kinetic energy, while the flywheel 10 decelerates as its kinetic energy decreases. Most of the flywheel 10's energy is transferred from port-F to port-W to accelerate the vehicle via a mechanical path, and approaching 100 percent efficiency. A smaller portion of the flywheel 10's energy travels an electrical path through the variator 01 on port-G, and is reused by the motor 02 on port-EM to also accelerate the vehicle at port-W. This process, governed by the speed relationships of equations (5) and (6), is such that decreasing the speed of the variator 01 releases kinetic energy stored in the flywheel 10 to the vehicle's wheels 34, thereby accelerating the vehicle. Conversely, increasing ωg in the negative direction will cause a decrease in ωw and an increase in ωf when ωem is maintained to be constant or near constant, resulting in deceleration while also charging the vehicle's energy into the flywheel 10.
To prevent the flywheel 10 from reducing drivability when vehicle speed is low and there is not enough energy in the flywheel 10, the flywheel 10 can be pre-charged; alternatively, it can also be decoupled from the drivetrain by keeping the clutch 16 in the disengaged position if it is desired to charge the flywheel 10 later, during deceleration. In the pre-charge state (which is also explained in detail later with
Note that the speed ωw of the wheels 34 is the speed of the vehicle, which directly relates to the kinetic energy level of the vehicle; similarly, the speed ωf of the flywheel 10 determines the flywheel 10's kinetic energy level. During acceleration, the vehicle's kinetic energy increases and the flywheel 10's kinetic energy decreases. During deceleration, the vehicle's kinetic energy decreases and the flywheel 10's kinetic energy increases. The speed of the flywheel 10 is inversely related to the vehicle's speed. The vehicle's kinetic energy level and the flywheel 10's kinetic energy level are related, but they change in opposite directions, so that during acceleration kinetic energy is released from the flywheel 10 to speed up the vehicle's wheels 34, and during deceleration the kinetic energy of the vehicle is recovered and stored back into the flywheel 10. Therefore, accelerating and decelerating the vehicle simply entails energy exchange between the flywheel 10 and the vehicle, and little to no external energy need be provided to accelerate the vehicle, as long as the vehicle's speed is in the range covered by the flywheel 10. The engine 20, therefore, does not need to work at higher power to overcome the vehicle's inertia, and is primarily used to overcome resistive forces such as drag and rolling resistance. The effect is that the flywheel 10 always acts against the vehicle's inertia and reduces or eliminates inertial effects, thus achieving “de-inertia” operation. In the configuration of the present invention, adjusting the speed ωg of the motor/generator 01 to suitably control vehicle speed automatically performs the de-inertia function described above during acceleration or deceleration. When a change in the vehicle's speed is desired, the vehicle's kinetic energy can be recovered and reused with little loss, increasing both efficiency and performance.
In the lower speed range depicted in the diagram, the vehicle can be boosted to over 30 km/h solely through the energy released from the flywheel 10, while the engine 20 is off and/or decoupled from the hybrid powertrain. Since at and below 30 km/h the flywheel 10 of this example can totally cover the kinetic energy gained by the vehicle, and the motor 02 covers drag and rolling forces, and since the flywheel 10 has a tremendous power density, the vehicle is easily accelerated, and the resulting effect is that it is as though the vehicle has little or no inertia.
As the speed of the vehicle ωw gets higher and higher, 02 gradually increases its power to contribute to the vehicle's acceleration. The IC engine 20 may be started to supply power to accelerate the vehicle as ωw enters higher speed ranges. The speed of the motor 02 is then controlled to be held at the speed of the engine's ideal efficiency, which is assumed to be 2000 RPM for the purpose of this example. The speed of the variator 01, ωg, can be controlled to increase ωw and accelerate the vehicle (also see
It is feasible for the present invention to release the energy in the flywheel 10 entirely to zero; for the sake of performance, however, it is better to reserve a certain level of kinetic power in the flywheel 10 even as the vehicle speed increases. In the case of heavier acceleration to a higher speed, the torquer motor/generator 02 can help share the engine load to optimize efficiency. In cases where the heaviest acceleration is desired, the engine 20, motor 02, motor 01, and the flywheel 10 may all contribute driving power for maximum performance of the vehicle (also see
“De-inertia operation” methods use the flywheel 10 to diminish the effects of inertia, which comes into play during acceleration and deceleration. Using the flywheel in this manner improves the system's efficiency and increases performance. When a steady vehicle speed is desired, without significant demand for change in vehicle speed, or when vehicle speed changes only slightly, as during cruise, inertia is no longer an issue, and the main concern is fuel efficiency. (Steady vehicle speeds may be considered to mean constant, near-constant, or fluctuating only a little within a certain speed range based off a percentage of the vehicle's current speed; for instance, in a non-limiting example, if the current vehicle speed is 100 km/h, a steady speed may fluctuate within a 10 percent vehicle speed range, or 5-15 percent of the current speed, such as 95 km/h to 105 km/h.) For optimized fuel efficiency, it would be undesirable to not take advantage of the flywheel's capabilities and to let it sit there as “dead weight.” During a period of driving where steady speed is desired, the flywheel 10 can still be used to improve the vehicle's fuel efficiency. The difference between the steady speed optimized efficiency method of the present invention and the “de-inertia operation” explained earlier is that during a preferred implementation of steady speed (cruise) operation the flywheel 10 is charged by the engine 20 and then transfers the energy to the vehicle, whereas in a preferred implementation of “de-inertia operation” the flywheel 10 exchanges energy with the vehicle only.
In the description that follows regarding optimized efficiency cruise methods, some steps of
If the motor 02 is the prime mover, as in the case for an electric vehicle (EV) embodiment, the most efficient control method when driving at a steady speed is simply to adjust the speeds ωem and ωg so that both the motor/generators 01 and 02 are operating in high efficient RPM regions of a predetermined efficiency map. Alternatively, the motor/generators 01 and 02 can be dynamically controlled and adjusted in real time to minimize electric current while maintaining the same vehicle speed, which also improves the charge/discharge efficiency in the battery pack 05. In electric vehicle mode, with the engine 20 off and the clutch 22 in the engaged position, the one-way clutch 24 can lock the port-EM and prevents the motor 02 and the engine 20 from turning in the negative direction, so that the variator motor/generator 01 alone can drive the vehicle in the lower speed range. In the higher speed range, both the motor/generators 01 and 02 work together to provide more power, with both controlled to work at the optimal efficiency possible.
If the engine 20 is the prime mover, as in hybrid vehicle embodiments, the efficiency of the engine 20 should be the focus. Engine efficiency is determined by engine speed and load. The highest efficiency state for a conventional IC engine is usually constrained within a limited range of engine speed ωem and occurs at a relatively high engine load, close to two-thirds or three-fourths of the maximum torque that the engine 20 can produce. For a conventional vehicle in cruise, only power to overcome air drag and other resistive forces is needed, so the engine is operated at low power, which means lower efficiency; the lower the vehicle speed (less power needed to maintain the speed), the less efficiently the engine runs. When ωem, is controlled to be in the optimal range, as is possible with the present invention, placing a suitably high enough load on the engine 20 is the key to optimizing fuel efficiency. In a non-limiting example for the configuration of
Should the load level be too high for a given vehicle speed (determined in step 1202,
Low engine load means low engine efficiency, and it seems simple to just turn off the engine 20 in a hybrid vehicle and let the motor 02 take over as the power source moving the vehicle. However, since in HEVs electric energy may originally be derived from the fuel for the vehicle or another chemical energy source, which has to go through four energy conversions, it may not always be desirable to turn off the engine 20 and let the motor 02 take over due to conversion losses. Suppose that the efficiency for each conversion is 90 percent and mechanical gear to gear transmission loss is ignored, then the efficiency of the electric energy that gets output to the wheels is 0.9̂4=0.6561, about 66 percent, which means that 34 percent of the energy was lost to energy conversions. It is thus not advisable to turn off the engine 20 and use only the motor 02 to propel the vehicle unless the efficiency drop from the best efficiency region is more than 34 percent (66 percent relative efficiency or lower; relative efficiency is defined as the engine efficiency under current operation conditions divided by the maximum engine efficiency when operating under optimal conditions for efficiency). Using the motor 02 with electric energy from the battery before the engine efficiency has dropped 34 percent from its best efficiency will use more fuel in the long haul, since more energy has been lost through conversion than the energy that was conserved or gained by operating the engine at the maximum efficiency. When the engine load drops below a certain threshold, which is related to 66 percent relative efficiency in the HEV case, which can be calculated by estimating the conversion losses, the engine 20 is turned off and motor 02 takes over until the state of charge in the battery pack 05 drops to a lower state of charge limit. Then, the engine 20 starts and the variator 01 and traction motor 02 can act as generators to increase the load seen by the engine 20, controlling the engine 20 to work at optimal load and optimal efficiency while ωem, is fixed in the most efficient range of the engine 20 by the generator 02, and the CVT ratio is controlled by the generator 01 to maintain the same vehicle speed. The power generated by the variator 01 and the traction motor 02 charge the battery pack 05 until an upper state of charge limit is reached. The engine 20 is then shut off and the motor 02 is then used to drive the vehicle until the lower state of charge limit is reached. Under this control strategy for HEVs, the IC engine 20 is ensured to work at 66 percent relative efficiency or better.
In a preferred embodiment of the present invention, the addition of the flywheel 10 brings a kinetic power source and kinetic energy storage to the vehicle, which will be heretofore referred to as the kinetic hybrid vehicle or KHV. A kinetic hybrid vehicle may be a vehicle that includes a kinetic power source and a kinetic energy storage in addition to having a prime power source (e.g., a prime mover) and the energy source for the prime mover. Since the energy is stored in the flywheel in the same form it is used in, the energy exchange between the flywheel 10 and the wheels 34 of the vehicle takes place along a direct mechanical path, with no energy conversion. There is a mechanic-electric energy split between port-G and port-EM for the control of the CVT ratio. With a compound CVT, typically around 25 or less percent of the total power goes through the electric path, and 75 percent or more of the power is transferred via a direct mechanical path. The same assumptions used for the HEV example, namely that each energy conversion stage is 90 percent efficient and that the mechanical gear to gear loss is negligible, may be used to estimate the percentage of energy lost to storing and releasing energy to and from the flywheel 10 in the KHV.
In the fuel-kinetic hybrid mode of operation, the KHV's strategy during cruise is to keep the engine 20 working within its optimal efficiency region; although more power will be generated as a result, the output power from the engine 20 can be split into two portions, one of which drives the vehicle's wheels 34 to maintain the desired cruise speed, and another which is split to the flywheel 10 to store up to a level either predetermined or calculated in real time. Once the energy in the flywheel 10 has reached that level, the engine 20 is turned off and disengaged, allowing the flywheel 10 to propel the vehicle and maintain the desired cruise speed.
It follows from equation (5) that if the clutch 22 is engaged and the speed of the engine 20 ωem is increased a certain increment, and the speed of the variator 01 ωg in the reverse direction is increased by k1 times that increment, the vehicle speed ωw will remain unchanged. It also follows from equation (6) that if the speed ωem of the engine 20 is increased a certain increment but the vehicle speed ωw remains the same, the speed of the flywheel 10, ωf, must increase by k2+1 times that increment. Thus a steady cruise speed can be maintained while the engine 20 runs at optimal efficiency.
Once the kinetic energy of the flywheel 10 reaches some upper limit, the clutch 22 is disengaged and the engine 20 is turned off; from equation (5), it follows that if the variator 01 decreases its speed ωg in the reverse direction by k1 times a certain decrement and the motor 02 decreases its speed ωem by one time that decrement, the vehicle speed ωw remains unchanged. According to equation (6), if the vehicle speed ωw remains the same, and the motor 02 decreases its speed ωem by a certain decrement, then the speed of the flywheel 10, ωf, must decrease by k2+1 times that decrement. In other words, the system controls the flywheel 10 to release energy to the vehicle's wheels 34 to maintain the desired cruise speed. Once the kinetic energy of the flywheel 10 reaches some lower limit, the clutch 22 is engaged and the engine 20 is started to begin the next cycle; the engine 20 and the flywheel 10 propel the vehicle in turns in this manner. Whenever the engine 20 is on, it works at optimal efficiency, and whenever the flywheel 10 propels the vehicle, it does so at a very high efficiency, since the flywheel 10 transfers kinetic energy to the vehicle mechanically, without conversion loss. With the engine 20 and the flywheel 10 working together in this way, the vehicle's efficiency during cruise can be optimized and can improve significantly.
The flywheel 10 in the preferred embodiment of the KHV is used as a kinetic energy and kinetic power buffer to enable the prime mover engine 20 to be operated in the most efficient manner. Most of the energy transferred into and out of the flywheel 10 is transferred mechanically, and with negligible loss. What energy conversion losses there are in the KHV comes from the portion of energy that travels the electric path, through the variator 01 and the motor 02 (refer to
The right side of
With a preferred embodiment of the KHV of this invention, it is worthwhile to perform start-stop operation as long as the efficiency of the engine has dropped by 9 percent compared to its highest efficiency (100%). For a preferred embodiment of the KHV of the present invention, the IC engine 20 may work at 91 percent relative efficiency or better, and the engine load that corresponds to 91 percent relative efficiency in the speed range of ωem can be used as a threshold load condition to trigger the optimized efficiency cruise operation or start-stop operation of the engine 20. If in cruise the engine 20 would be operating at a “current” load below the threshold load condition (step 1206,
In a slightly more condensed form than was described previously, the preferred method to optimize efficiency of cruise (steady vehicle speed) operation for the preferred embodiment of the KHV of the present invention is as follows. If the load is too high (step 1202) from road conditions for the engine 20, the motor 02 shares the extra load and lets the engine 20 work in its most efficient state (step 1204). When the load is just right (step 1208), the motor 02 maintains the minimum power needed to absorb the electricity from the variator 01, and the engine 20 provides the remaining torque needed. If the engine load is below a threshold (determined by step 1206), the engine load is controlled to increase to the highest efficiency load level of the engine 20 (step 1214) by increasing the engine speed ωem incrementally; the speed of the generator 01, ωg, is increased k1 times the increment of the change in ωem in the opposite direction to keep the speed ωw of the vehicle stable (equation (5)). At the same time, ωf, the speed of the flywheel 10, is increased k2+1 times the incremental change in ωem (equation (6)), so the energy is charged to the flywheel 10 from the engine 20. When the speed ωf of the flywheel 10 reaches a preset upper value (determined by step 1210), the engine 20 is turned off (step 1216), and the flywheel 10 is used to drive the wheels 34. At this point, the control goes as follows: the speed ωg of the generator (and transmission ratio variator) 01 is decreased k1 times an incremental speed in the negative direction, and the speed of the motor/generator 02, ωem, is decreased that incremental speed in the positive direction to keep ωw stable. As a result, the speed ωf of the flywheel 10 is decreased by k2+1 times the incremental speed, and energy is released from the flywheel 10 to drive the wheels 34. When ωf drops to or below a lower preset value (determined by step 1224), the engine 20 is started again (step 1214) to begin another cycle of this operation, where a portion of the energy is delivered to the vehicle at a constant rate, but another portion is transmitted from the engine 20 to the flywheel 10 and stored in the flywheel 10 until used. The flywheel 10 functions as both an energy storage device and as a power source.
The method of the optimized efficiency cruise operation described above (and described in more detail with
At the beginning of the journey prior to launching the vehicle, it would be desirable to charge up the flywheel F before starting the engine E so that the flywheel F enhances drivability and efficiency. To pre-charge the flywheel F while the vehicle remains stationary and braked at the wheels W (which applies just as the vehicle is started and there is not yet enough energy in the flywheel, or when the vehicle is stopped at a signal light and the energy in the flywheel is not yet at maximum state of charge), the engine E is decoupled from the drivetrain and the motor M2 draws energy from the battery pack B charge the flywheel F at optimal efficiency (at a current maximizing combined efficiency), as shown in
Once the flywheel F is sufficiently charged, the vehicle is ready to be started by the flywheel; the variator G1 reduces its speed in the reverse direction, producing a reaction force enabling the transfer of kinetic energy from the flywheel F and the motor M2 to the wheels W, which is no longer braked, launching the vehicle from rest. Either the motor MG2 or the flywheel F may supply the torque needed to start the engine E, depicted by
Following the start of the engine E, the vehicle is launched from rest by the flywheel F and accelerates. In
Following acceleration, cruising or coasting may be desired for some period of time. In the coasting state shown in
For deceleration, there are also two states. In
The last three states of
In the flow charts, M/G1 refers to the motor/generator 01, M/G2 refers to the motor/generator 02, and both Engine and ICE refer to the engine 20, while CL(E) refers to the clutch 22 connecting the engine 20 to the drivetrain, and CL(F) refers to the clutch 16 connecting the flywheel 10, which is just expressed as Flywheel.
The vehicle is started at step 1002. When the vehicle is first started, it is presumed that the vehicle is first stationary (step 1004), and the flywheel 10 can be pre-charged while it is stationary. The vehicle stationary step 1004 also includes the vehicle state when the vehicle is stopped in traffic. The process represented by step 1004 consists of the steps 1110 through 1132, explained in more detail in
As long as the vehicle remains in the stationary state, the system will make decisions as to whether the battery pack 05 and/or the flywheel 10 should be charged. First, it detects the state of charge in the battery pack 05 and determines in step 1116 whether it needs charging. If so, the system proceeds to step 1118, engaging the clutch 22 to connect the engine 20, which then drives the generator 02 to charge the battery pack 05, as in
Variations on battery charging and flywheel charging. In one conceivable but less preferred variation, the system may determine whether the flywheel 10 needs charging before determining whether the battery pack 05 needs to be charged. In another variation, the steps 1126 and 1128 may be omitted. In another variation, the steps 1130 and 1132 may be omitted. In still another variation, the steps 1126, 1128, 1130, and 1132 may all be omitted. The system would still work with these variations, just at less optimal efficiency.
Of course, another possibility for when the vehicle is stationary is if the end of the drive has been reached (step 1006) and it is time to turn off the vehicle. If so, then the system performs the flywheel restore function that corresponds to the state in
Once again following the logic flow chart in
After the vehicle has been started (step 1004 of
After some period of acceleration has ended (determined in step 1022), the system detects whether it is desired that the vehicle be decelerated, step 1026. The de-inertia deceleration state is represented by step 1028 in
After some period of acceleration, the vehicle can enter into an optimized efficiency cruise state (
In step 1202, the system detects whether the current engine load or torque value is higher than the load corresponding to the engine 20's best efficiency state (encountered when there is strong wind or incline). If so, then the motor 02 shares the load in excess using energy from the battery pack 05 to allow the engine 20 to run at a better efficiency. If the engine load is not too high, then the system detects whether the engine load is too low in the next step, step 1206. If the engine load is neither too high nor too low, then because engine speed ωem is approximately fixed at the ideal speed for efficiency, the system determines that the engine 20 is already running at optimal efficiency, and in step 1208 controls the motor 02 to only reuse the power generated by the variator 01 as the variator 01 behaves mostly as a generator to vary the transmission ratio for the engine 20. Following 1204 or 1208, the system checks whether the operator intends to change the vehicle speed in step 1212: if not, the system returns to step 1202 to keep looping; if yes, the system exits the optimized efficiency cruise loop in step 1226.
If the engine load is too low, as is usually the case when the vehicle is in cruise (inducing low engine efficiency in conventional vehicles), the adjustment of the engine load becomes key. The following steps use the flywheel 10 to increase the load of the engine 20 to ensure the greatest efficiency in operating the engine 20. When the load of the engine 20 is less than the lower limit of the load range for optimal efficiency (determined from steps 1200 to 1206), the system will proceed to step 1210 to determine whether the flywheel 10 has enough energy stored to drive the vehicle on its own for a period of time. During cruise the flywheel speed ωf is controlled to be no lower than a lower setting and no higher than an upper setting. The lower setting represents power reserved in the flywheel 10 in the event that it is desired to stop cruising and accelerate the vehicle. The difference between the maximum safe flywheel speed and the upper setting represents the amount of energy the flywheel 10 can still safely recapture in case of deceleration. These lower and upper speed settings for the flywheel 10 under cruise can be predetermined or dynamically determined according to parameters such as vehicle speed, which can be read from the interface to the system 60 or the vehicle's ECU 62.
Should the flywheel 10 speed ωf be greater than the upper setting in step 1210, it means the flywheel 10 has enough energy stored to drive the vehicle on its own (
After discharging the flywheel in step 1216, the system proceeds to step 1220 to make sure that the vehicle should still be operated in cruise. Then as long as the flywheel speed is above the lower setting in step 1224, the system continues to release energy from the flywheel to maintain a steady vehicle speed while the engine is off, step 1216,
If in step 1210 it is determined that the flywheel speed ωf is not above the upper setting, or if the flywheel speed ωf has already dropped below some lower setting in step 1224, the system then charges the flywheel 10 up to the upper setting (
The optimized efficiency cruise method primarily consists of step 1214, charging the flywheel 10, and step 1216, releasing energy from the flywheel 10. These two steps are alternatively used until there is a demand for a change in vehicle speed. In step 1214, the engine 20 is operated within an optimal efficiency range, simultaneously driving the vehicle's wheels 34 and charging the flywheel 10. The vehicle maintains the same speed since any power in excess of what is needed to maintain the cruise speed is stored into the flywheel 10. In step 1216, the engine 20 is off and consumes no fuel, and the power needed to maintain the same vehicle speed comes from the flywheel 10. Any time the engine 20 is used, it is operated in its best efficiency state, hence optimizing the vehicle's fuel efficiency during cruise.
(k1+1)ωw=k1ωem+ωg (7)
(k2+1)ωw=k2ωem+ωg (8)
The configuration in
For the alternative configurations shown in
For the configuration of
(k1+1)ωw=k1ωg+ωem (9)
(k2+1)ωem=k2ωw+ωf (10)
For the configuration of
(k1+1)ωw=k1ωg+ωem (11)
(k2+1)ωw=k2ωem+ωf (12)
The relationship between the configurations of
This application claims priority from a U.S. Non-provisional patent application Ser. No. 13/193,728, filed Jul. 29, 2011, and from U.S. Provisional Patent Application Ser. Nos. 61/438,267 filed Feb. 1, 2011; 61/471,213, filed Apr. 4, 2011; and 61/495,993, filed Jun. 11, 2011, and which all are incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 61438267 | Feb 2011 | US | |
| 61471213 | Apr 2011 | US | |
| 61495993 | Jun 2011 | US |
