Patent Application
20100155157
The present invention relates to drive systems for vehicles; more particularly, to hybrid input differential engine systems; and most particularly, to a hybrid input differential engine system incorporating a supercharger.
The Toyota® Prius® is generally and presently regarded in the automotive world as a state-of-the-art high efficiency vehicle. In the Prius® drivetrain architecture, referred to hereinafter as the “Prior Art drivetrain” a naturally aspirated “Atkinson” Cycle gasoline internal combustion engine (ICE) is combined with two motor/generators and a planetary power split device (PSD). A single planetary gear set is used in an electrically-controlled Continuously Variable Transmission (eCVT). Control of the speed and torque of the two motor/generators has the effect of varying the gear ratio from the ICE to the output shaft through the PSD.
Although the Prior Art drivetrain offers a significant fuel economy improvement compared to current non-hybrid vehicles, especially on urban stop-and-go driving cycles, there are some notable drawbacks to its system.
First, the cost of the Prior Art drivetrain is significantly higher than that of a standard non-hybrid powertrain, because of the relatively high-power electric machines (also referred to herein as “motor/generators”), the associated power electronics, and the large high-power battery system.
Second, because of this same content plus an ICE having a relatively low power density, the Prior Art drivetrain weight is also much higher than that of a standard vehicle.
A trend in the automotive industry is the use of ICEs that have relatively low power (“downsized”) but are boosted by an exhaust-powered turbocharger using “free” energy. Such engines can reduce engine weight and improve fuel economy on typical light-duty driving cycles. Small-displacement direct-injection engines can have efficiency similar to that of the Prior Art drivetrain by using a turbocharger to boost torque and power.
Turbochargers are very efficient at constant high-speed high-load conditions where the volume and driving force of engine exhaust is also high. However, in lower speed stop-and-go driving, turbocharger efficiency is lower and there is no inherent ability in such engine configurations to use regenerative braking, as there is in a Prior Art drivetrain configuration. Engine torque tends to be low at and just above idle speed, resulting in low initial acceleration performance, non-linearity of torque response, and pollution challenges with transient emissions.
What is needed in the art is a lower-cost, lower-weight powertrain system for a vehicle that retains the attractive attributes of the Prior Art drivetrain, but which is compatible with the trend to downsized boosted engines, and which mitigates the poor low engine speed performance of prior art downsized turbocharged systems.
It is a principal object of the present invention to provide an improved powertrain system for a vehicle.
Briefly described, a hybrid input differential engine system in accordance with the present invention comprises a planetary gear set having two inputs and one output. The planetary gear set includes a sun gear, a plurality of planet gears engaged by the sun gear and tied together by a gear carrier, and a ring gear engaged by the planet gears. An ICE is connected to the gear carrier (in a currently-preferred embodiment), and the output is connected to the ring gear, as in the Prior Art drivetrain system. However, the sun gear is connected to a supercharger/expander. An electric or hydraulic motor-generator optionally may also be connected to the sun gear. When the supercharger alone is used, the steady state speed and torque are fixed by the preumatic load on the supercharger, which load is a function of the speed ratio of the supercharger to the ICE, as this determines the pressure ratio across the supercharger. Thus, as engine torque increases, the supercharger speeds up relative to the engine speed and operates at a higher pressure ratio, increasing engine torque still further. This effect is similar to, but enhanced over, the effect a Prior Art drivetrain has in acceleration from low vehicle speeds. This effect allows a suitably designed engine to have very high torque at low RPM, enabling good driveability with a small displacement engine.
In cruise conditions, the sun gear is motored in reverse to normal direction or, optionally, may be braked (stopped) or slowed down to a free-wheeling state using an optional clutch. With the case of motoring, the supercharger may act as an expander. With appropriate valving or porting of the supercharger, the pressure drop across the expander generates a torque to cause the reverse rotation. A first optional motor/generator may be used to modulate the speed/torque relationships between the ICE and the supercharger/expander and to manage transient conditions smoothly. A second optional motor/generator may be used on the output shaft (analogous to the prior art system). The motor/generator machines may be downsized significantly over their prior art counterparts because substantially less power is needed for the operation of the eCVT (net of the supercharger/expander load).
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner.
The invention employs a planetary power split device and mounts a supercharger on one of the members of the planetary gear set. In principle, an ICE, a supercharger plus first optional motor/generator, and an output shaft plus second optional motor/generator may be connected respectively in any arrangement to the sun gear, planet gear carrier, and ring gear of a planetary gear set. In one aspect of the invention, as described below, the arrangement includes a twin-screw Lysholm® type supercharger on the “sun” gear of the planetary system, an ICE on the planet gear carrier, and an output shaft on the ring gear. The twin-screw supercharger can inherently be used as an expander wherein it is turned in reverse to a normal direction and with valves or porting used to reverse the flow direction of gas through the rotors. Other supercharger types, such as Roots® type or “Centrifugal” superchargers may use the optional clutch since they are efficient only when turning in one direction.
Referring to
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Either or both of the motor/generators may be electric, hydraulic, pneumatic, or a combination thereof. Electric would be a likely choice for light duty vehicles, but hydraulic may prove to be attractive for heavy duty vehicles and may be simpler and lower cost in some applications.
System 110 defines a low cost drive system which allows a supercharger to be driven at a variable speed relative to the engine. The system may optionally drive other accessories such as an air conditioning compressor (not shown).
A Lysholm®-type supercharger is preferred as it can function as either a compressor or an expander with relatively high efficiency in forward and reverse directions, respectively. Other supercharger types can be used with an optional clutch (not shown), resulting in a CVT system with a smaller range of effective gear ratios.
Referring now to
In the mode shown
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An important benefit of system 110 over prior art system 10 is that supercharger/expander 130 permits significant downsizing of the electric machines (motor/generators) and their associated electronic controls. The corresponding components in the prior art are relatively large, heavy, and expensive, being approximately the size and weight of the engine. Thus system 110 affords a significant reduction in overall vehicle weight.
High power mode during accelerations uses first motor/generator 126 as a generator, and having supercharger 130 operative on the same planetary gear element allows generation of the correct engine torque with much less electric generation than in the prior art, and thus less motoring into second motor/generator 128 and the potential to reduce the size of the battery or equivalent energy storage (not shown).
Cruise modes tend to require lower power, so the generator power required to make system 110 work is the limiting factor for sizing the motor/generators and power electronics. Further, the expander mode of the supercharger allows a modest reduction in motoring power of first motor/generator 126 and generating power of second motor/generator 128, resulting in reduced electrical parasitics in light load operation (such as a moderate speed highway cruise condition).
Refering now to
Some vehicular advantages of a system 110 in accordance with the present invention are:
a) the potential for a large reduction in cost, size, weight, and capacity of the motor/generators and associated power electronics;
b) a similar reduction in the cost, size, weight, and capacity of an energy storage device (not shown), typically a Li-ion or NiMH battery, which can permit use of a small pneumatic energy storage and/or an ultracapacitor as the only significant energy storage capability within system 110;
c) the potential for significant downsizing of engine 122, for example, to three cylinders instead of six, or to two cylinders instead of four, while retaining very high torque at low engine speeds, and excellent powertrain smoothness;
d) the ability to recover energy from lightly throttling the engine by using the supercharger as an expander; modestly- throttled operation is useful for other reasons, e.g., low noise, ability to meter EGR, and ability to modulate torque smoothly and quickly, and system 110 significantly reduces the parasitic pumping loss which is otherwise associated with throttling in the prior art;
e) compatibility with direct injection diesel (compression-ignited) engines, by supplying lots of transient air and mitigating “smoke” and HC emissions associated with operation near the low RPM “lug” line;
f) compatibility with direct injection gasoline (spark-ignited) engines, by manipulating the volumetric efficiency, charge temperature and speed/torque relationship during low RPM transients; and
g) use of pneumatic energy storage, for example, during engine braking, to reduce the effective energy cost of supercharged operation and to mitigate the power levels needed in the optional hybrid (electric or hydraulic) motor/generator devices.
While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.
