Patent Application
20150377203
The present invention is directed to automotive electrical systems and, more particularly, to a system for controllably implementing a motoring mode and a generating mode.
Electric generators used in automotive vehicles include multiphase alternators that generate alternating current (AC) electric power when a rotor of the alternator is mechanically rotated, such as by a belt coupled to a motor of the vehicle. A rectifier bridge is typically used to convert the AC electric power output to direct current (DC) electric power for charging one or more vehicle batteries and for powering DC loads. Commonly used rectifier bridges for automotive alternators are formed with diodes and/or metal-oxide-semiconductor field-effect transistors (MOSFETs) and allow for current flow in one direction only. The current flow in a diode is determined by the voltage differential between the anode and cathode, such that when the anode voltage overcomes the forward diode drop and any voltage present on the cathode, a current will flow through the diode. Since the current flow in a diode is based only on voltage differentials, no external controls or circuitry are required for determining when the current should flow. Accordingly, a given rectifier diode bridge configuration may easily be adapted for a chosen phase configuration. When the diodes of a rectifier bridge are replaced with MOSFETs, the efficiency of the rectification is significantly increased because electrical power losses of MOSFETs are much less than those of diodes.
An automotive alternator-starter is typically configured to operate in a generating mode for charging one or more batteries, and to operate in a motoring mode. The rotor of the alternator-starter is mechanically connected to the internal combustion engine (ICE), whereby mechanical rotational power is transferred from the ICE to the rotor in generating mode and from the rotor to the ICE in the motoring mode. The mechanical connection may include a direct connection, a pulley, a belt, and/or other mechanism(s) such as gears, clutch assemblies, etc. In the generating mode, rotation of the ICE causes the rotor of the alternator-starter to rotate, thereby generating a battery charging current. In the motoring mode, the alternator-starter operates as a high torque motor for starting an ICE and/or for use at a lower torque as an auxiliary motor, such as for driving an air conditioning compressor, for preventing the ICE from stalling, and/or for powering the vehicle over short distances. Modern automotive alternators are generally required to supply ever-greater amounts of electrical current. For example, hybrid vehicles may use electricity instead of internal combustion for driving the wheels. A variety of different hybrid vehicles are known. One type of known hybrid vehicle employ a belted alternator starter (BAS) to provide assistance to the ICE. Other electrical loading from air conditioning, electric power steering, and other vehicle systems further increases the required alternator electrical capacity.
An automotive alternator-starter is typically an electric machine having a multiple-phase stator winding that acts as an armature in alternator/generating mode. The stator may receive an AC voltage from an inverter when operating in a motoring mode. The electric machine has a rotor that may be in electrical communication with a DC power source in a traditional alternator design that utilizes excitation windings, brushes, and a commutator. In various forms, the electric machine may be brushless and may include permanent magnets. An alternator-starter typically is operated with one or more sensors, a voltage regulator, and a controller. For example, a battery state of charge, temperature, and/or voltage may be monitored for adjusting a charging current being output in a generating mode, for determining whether sufficient battery power is available for an auxiliary motoring function, and for other operations.
In electrical automotive applications such as those implemented in hybrid vehicles, an alternator-starter may be integrated into battery charging that includes regenerative braking, solar panels, plug-in and/or inductive powering of a separate battery charger, and other devices. An alternator-starter may operate in a so-called start-stop mode. For example, a hybrid automotive vehicle's ICE may be turned off during an ‘idle’ event such as when the vehicle is stopped at a traffic light, and then the alternator-starter is required to quickly and efficiently re-start the ICE after the idle event is over. In particular, mechanically driving the gears that cold start or re-start the ICE requires that the alternator-starter operate in motoring mode with a high torque at low rotation speeds. In order to increase the torque for a starting event, a conventional alternator-starter might be formed with a reduced number of stator turns, but this is typically undesirable for the voltage generation in generating mode. Alternatively, a conventional alternator-starter may increase voltage excitation of the rotor, but this is also undesirable for voltage generation in the generating mode. Another conventional alternator-starter has utilized two separate batteries, where the inverter is connected by a MOSFET switch to the positive terminal of a second battery in motoring mode, and where the rectifier bridge is connected by another MOSFET switch to the positive terminal of the main battery when the alternator-starter is operating in generating mode. However, conventional alternator-starters are not optimized for both start-stop and charging operations.
The present invention provides an alternator-starter system having a plurality of batteries that can be operated in a manner to efficiently start a combustion engine and charge the batteries.
The invention comprises, in one form thereof, an alternator-starter system mechanically coupled with an internal combustion engine which includes an electric machine; an inverter/rectifier operably coupled with the electric machine; a plurality of batteries operably coupled with the inverter/rectifier; a plurality of switches operably coupled the system; and a controller operably coupled with the system. At least one controller selectively operates the system in a generating mode wherein the alternator-starter system generates an electrical current or a motoring mode wherein the alternator-starter system generates a mechanical torque. The at least one controller selectively operates the switches to connect the plurality of batteries in series or in parallel. The system is operated such that, when the system is operated in the motoring mode to supply a torque to the engine to start the engine, the plurality of batteries are connected in series and, under at least some conditions when the system is operated in the generating mode, the batteries are connected in parallel.
In some embodiments of the alternator-starter system, under at least some conditions when the system is operated in the generating mode, the batteries are connected in series. Such an embodiment may be further configured such that the at least one controller is selectively operable to individually connect the plurality of batteries with the inverter/rectifier and, under at least some conditions when the system is operated in the generating mode, the plurality of batteries are connected individually.
In other embodiments, when the rotational speed of the electric machine is between a first predetermined threshold and a second predetermined threshold and the system is in the generating mode, the plurality of batteries are connected in parallel. In such an embodiment wherein the second predetermined threshold is greater than the first predetermined threshold, when the rotational speed of the electric machine exceeds the second predetermined and the system is in the generating mode, the plurality of batteries are advantageously connected in series.
The invention comprises, in another form thereof, an alternator-starter system mechanically coupled with an internal combustion engine that includes an electric machine; an inverter/rectifier operably coupled with the electric machine; a plurality of batteries operably coupled with the inverter/rectifier; a plurality of switches operably coupled with the system; and at least one controller operably coupled with the system. The at least one controller selectively operates the system in a generating mode wherein the system generates an electrical current or a motoring mode wherein the system generates a mechanical torque. The at least one controller also selectively operates the plurality of switches to connect the plurality of batteries in series or in parallel. When the system is operated in the motoring mode to supply a torque to the engine to start the engine, the plurality of batteries are connected in series. When the rotational speed of the electric machine exceeds a first predetermined threshold, the system is operated in the generating mode and, under at least some conditions when the system is operated in the generating mode, the plurality of batteries connected in parallel.
In some embodiments of such an alternator-starter system, the batteries are connected in series under at least some conditions when the system is operated in the generating mode. Such embodiments may further be configured such that the at least one controller is selectively operable to individually connect the plurality of batteries with the inverter/rectifier and, under at least some conditions when the system is operated in the generating mode, the plurality of batteries are connected individually.
In other embodiments of such an alternator-starter system, when the engine is operating and the rotational speed of the electric machine exceeds a second predetermined threshold greater than the first predetermined threshold, the alternator-starter system is operated in the generating mode with the plurality of batteries connected in series. Such embodiments may be further configured such that, when the rotational speed of the electric machine is between the first and second predetermined thresholds, the plurality of batteries are always connected in parallel.
The invention comprises, in yet another embodiment thereof, a method of operating an alternator-starter system. The method includes mechanically coupling an electric machine with an internal combustion engine; coupling an inverter/rectifier with the electric machine; coupling a plurality of batteries with the inverter/rectifier; and coupling a plurality of switches with the system wherein the switches are operable to connect the plurality of batteries in different configurations. The method additionally includes operably connecting the plurality of batteries in series to supply electrical power to the electric machine when operating the system in a motoring mode and thereby supply a torque to the engine to start the engine, and operably connecting the plurality of batteries in parallel to charge the plurality of batteries when operating the system in a generating mode.
In some embodiments of the method, the method further includes connecting the plurality of batteries in series to charge the plurality of batteries under at least some conditions when the system is operated in the generating mode. In such embodiments, the method may additionally include connecting an individual one of the plurality of batteries to charge the individual battery under at least some conditions when the system is operated in the generating mode.
In another embodiment of the method, the method additionally includes connecting the plurality of batteries in series to charge the plurality of batteries when the rotational speed of the electric machine exceeds a second predetermined threshold and the system is in the generating mode. In such an embodiment, the plurality of batteries are advantageously connected in parallel when the rotational speed of the electric machine is between a first predetermined threshold and the second predetermined threshold and the system is in the generating mode, the second predetermined threshold being greater than the first predetermined threshold.
In alternative embodiments of the method, the method further includes operating the system in the generating mode whenever the rotational speed of the electric machine exceeds a first predetermined threshold. Such an embodiment may further include connecting the plurality of batteries in series to charge the plurality of batteries whenever the rotational speed of the electric machine exceeds a second predetermined threshold greater than the first predetermined threshold. In still another variant, such an embodiment may involve connecting the plurality of batteries in parallel whenever the rotational speed of the electric machine is between the first and second predetermined thresholds.
The above-mentioned aspects of exemplary embodiments will become more apparent and will be better understood by reference to the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding or similar parts throughout the several views.
The embodiments described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of these teachings.
The Drain terminals of MOSFETs 5, 7, 9 are connected in common as a first rail 11. The Source terminals of MOSFETs 6, 8, 10 are connected in common as a second rail 12. The Source terminal of MOSFET 5 and the Drain terminal of MOSFET 6 are connected to one another and to a phase winding 13 of stator 3. The Source terminal of MOSFET 7 and the Drain terminal of MOSFET 8 are connected to one another and to a phase winding 14 of stator 3. The Source terminal of MOSFET 9 and the Drain terminal of MOSFET 10 are connected to one another and to a phase winding 15 of stator 3. Although illustrated in a wye configuration having three phases, stator 3 may alternatively include a delta configuration and/or any number of phases (e.g., 5, 6, or 7 phases).
In a generating mode, controller 16 may duty-cycle the voltage being provided to the excitation windings of rotor 2, thereby adjusting the induced AC voltage of stator coils 13-15 that is being provided to inverter/rectifier 4 and the resultant DC voltage across rails 11, 12. For example, such DC voltage may be around 14.0 to 14.7 volts for charging an automotive type battery having a 12 volt rating or label.
In a motoring mode, inverter/rectifier 4 acts as an inverter by providing electrical power as separate phases to coils 13-15, whereby stator 3 causes rotor 2 to rotate and drive the pulley(s) or other mechanical connections to the ICE. For example, MOSFETs 5-10 may be sequentially driven by controller 16 to provide three respective voltages to coils 13-15 that are 120 degrees out of phase with one another. Controller 16 may receive rotor information from a first sensor 17, a second sensor 18, and other sensors and/or devices. For example, sensor 17 and/or 18 may provide a signal to controller 16 indicative of the rotational speed of the rotor typically measured in revolutions per minute (rpm) and also referred to herein as the rotational speed of electric machine 62. Sensors 17, 18 may be Hall-effect, magneto-resistive, resolver, or other sensor type suitable for providing speed and angular position information. Such rotation information, for example, may be utilized for timing the switching of MOSFETs 5-10 to implement the inverter function.
Although not shown in
A first battery 19 includes a positive (+) terminal 21 and a negative (−) terminal 22, and a second battery 20 includes a positive (+) terminal 23 and a negative (−) terminal 24. Batteries 19, 20 are connected in series with a heavy gauge conductor 25 that joins (−) terminal 22 and (+) terminal 23. Although the exemplary embodiment of
Positive (+) terminal 21 of battery 19 is connected to the Source terminal of a MOSFET switch “D” and negative (−) terminal 22 of battery 19 is connected to the Drain terminal of a MOSFET switch “B.” Positive (+) terminal 23 of battery 20 is connected to the Source terminal of a MOSFET switch “C” and negative (−) terminal 24 of battery 20 is connected to the Drain terminal of a MOSFET switch “A.” The respective Drain terminals of MOSFETs D and C are connected to positive rail 11. The respective Source terminals of MOSFETs B and A are connected to negative rail 12. The respective Gate terminals of MOSFETs A-D are each connected to individual driver outputs of controller 16. Each MOSFET A-D is independently switchable by controller 16. Negative rail 12 is typically vehicle ground (chassis).
The forward power dissipation and related heat of a MOSFET device are typically lower than that of a rectifier diode because MOSFETs generally have a lower on-state impedance. Compared with a diode, the addition of a third terminal provides a MOSFET with the capability of electronic control of the device impedance and of the flow of current. The device impedance may have a very low forward voltage drop (saturation voltage) with the current being limited by an external load, and may have a very low leakage current during its off condition. In a switching mode, a MOSFET is either on or off, where the shortest possible times to accomplish the turn-on and turn-off are desirable. For example, a pair of MOSFETs may be arranged in a Darlington connection to increase gain, saturation voltage, and switching speed. Compared with bipolar transistors, MOSFETs have faster switching speeds with reduced delay, rise, storage, and fall times. MOSFETs are voltage controlled and may be driven by logic level signals. MOSFETs typically have a conduction voltage drop versus temperature characteristic that allows parallel MOSFETs to share current. A MOSFET typically does not block reverse voltage but instead acts as a switch. The “on” resistance of a MOSFET is a function of the gate-source voltage and the minimum rated RdsON channel resistance. The term “MOSFET” has become somewhat generic. For example, the previously metal gate material is now often a layer of polysilicon (polycrystalline silicon), and materials other than oxides may be used, such as different dielectric materials that are structured for obtaining strong channels with smaller applied voltages.
MOSFETs may include enhancement mode MOSFETs and depletion mode MOSFETs. In an enhancement mode MOSFET, a voltage drop across the oxide induces a conducting channel between the source and drain contacts via the field effect. The term “enhancement mode” refers to the increase of conductivity with increase in oxide field that adds carriers to the channel, also referred to as the inversion layer. The channel can contain electrons (called an nMOSFET or nMOS), or holes (called a pMOSFET or pMOS), opposite in type to the substrate, so nMOS is made with a p-type substrate, and pMOS with an n-type substrate. In a depletion mode MOSFET, the channel consists of carriers in a surface impurity layer of opposite type to the substrate, and conductivity is decreased by application of a field that depletes carriers from this surface layer. As used herein, a MOSFET may also refer an insulated-gate field-effect transistor (IGFET). MOSFET devices A-D may each include a diode (not shown) connected between the respective source and drain thereof. Such diodes are commonly referred to as anti-parallel or free-wheeling diodes, and are typically incorporated into the same package as the respective MOSFET. The free-wheeling diodes suppress voltage spikes at turn off/on. In an exemplary embodiment, MOSFETs A-D may be obtained from IXYS Corporation and have a part number IXT—170N075T2.
In operation, alternator-starter system 1 is either in alternator/generating mode or in motoring mode. It is generally desirable for an alternator-starter to operate at a lower voltage in generating mode and at a higher voltage in motoring mode. For example, higher voltage in motoring mode provides higher power and torque when starting an ICE. Lower voltage is generally desirable in generating mode. The voltage generated in generating mode is Vs=Ns*dflux/dt, where Ns is the number of stator turns and dflux/dt is the flux rate of change. When the voltage Vs is increased, the stator turns and/or the rotor speed (dflux/dt) must also be increased. Increasing the number of stator turns is undesirable because this generally creates higher resistance, lower current and lower torque in motoring mode, and increased size, cost and weight. Increasing the gear or pulley ratio to thereby increase the rotor speed is also undesirable because this generally increases noise, inertia, and top end rotor speed.
First and second MOSFET switches are provided for each battery in a series battery string, where each switch may be individually turned on/off by controller 16. In generating mode, this allows the switches to be opened/closed for selectively charging any individual battery at a low voltage. In motoring mode, this allows the higher voltage of a series string of batteries to be applied to and power the alternator-starter.
As discussed in greater detail below with reference to the embodiment of
In an embodiment having a configuration as shown in
In generating mode, when controller 16 determines that the voltage on Vsense line 27 is low, controller 16 turns on MOSFET switches A and C and turns off MOSFET switches B and D. As a result, positive (+) terminal 23 of battery 20 is connected to positive rail 11 and negative (−) terminal 24 of battery 20 is connected to negative rail 12. Controller 16 and a voltage regulator (not shown) maintain a rail voltage of about 14.0 to 14.7 volts for charging battery 20.
In the generating mode, when controller 16 determines that rotor 2 is rotating at a speed that exceeds a certain high speed, such as by evaluating rotation information obtained from sensors 17, 18, controller 16 turns MOSFET switches A and D on and turns MOSFET switches B and C off. As a result, batteries 19, 20 are charged in series. For example, controller 16 and a voltage regulator (not shown) maintain a rail voltage of about 24.0 to 29.4 volts for charging batteries 19, 20. This high voltage generating mode is possible because the high rotor speed provides sufficient dflux/dt to generate the higher charging voltage across rails 11, 12.
In motoring mode, the
Although system 1 is shown with only two batteries 19, 20 in series, an alternator-starter system in a given embodiment may be formed to have three, four, five, or any number of individual batteries connected in series. In such a case, for example, when each battery has a nominal 12 volt rating, the nominal rail voltage may be 12, 24, 36, 48, 60, etc. volts. Each such series battery has two corresponding MOSFET switches for connecting/disconnecting the respective battery to/from rails 11, 12. Each MOSFET switch may be individually controlled.
Similarly, the embodiment illustrated in
The disclosed alternator-starter system 1 of
Although the embodiments have been described in reference to a motoring mode for cranking the ICE during a starting operation, alternator-starter system 1 may also/alternatively be utilized in motoring mode for supplying motive force to a hybrid automotive engine. Such motive force may be employed as supplemental or short term power for a hybrid vehicle, for example by providing a mechanical power boost to a running ICE at selected times.
In various embodiments, battery(s) at either end of a series connection of batteries may be switched in or out of the series battery string being charged or being used for motoring. A variable series string may be used, for example to adapt a nominal charging or motoring mode to account for additional operations that may affect efficiency or that may otherwise optimize performance of an alternator-starter. For example, in a start-stop hybrid automotive operation, actual machine loading, temperature, performance and operational profile information, and other parameters may be utilized in an adaptive structure. The temperature-related performance of a given battery may vary significantly according to the battery technology, and according to the actual temperature of operation. Accordingly, various embodiments may utilize monitored battery temperature(s) and/or battery performance profile information to adjust charging voltage target value(s) for series-connected batteries, for individual batteries, and/or for selecting which batteries of a series combination may be included by being switched into or out of a series string under use.
Another embodiment is schematically depicted in
The operation of switch E is governed by controller 16. It is noted that the illustrated embodiments schematically depict a single controller 16 controlling the operation of the alternator-starter system 1A. While a single controller may be used, it is also possible for a plurality of controllers to be used with alternator-starter systems disclosed herein.
The inclusion of switch E in line 25 allows batteries 19 and 20 to be connected in parallel with inverter/rectifier 4 of electric machine 62. More specifically, by opening switch E and closing switches A-D, batteries 19 and 20 will be connected in parallel. This allows batteries 19 and 20 be connected individually, in series or in parallel and thereby provides greater versatility in the operation of the system.
This embodiment can be operated in the manner described above with reference to the embodiment of
A significant advantage provided by system 1A is that it allows batteries 19, 20 to be simultaneously charged at a relatively low voltage when the system is operated in generating mode. For example, system 1A can be configured to operate in a manner where batteries 19, 20 are connected in series when starting engine 60, batteries 19, 20 are connected in parallel when the system is operating in the generating mode and electric machine 62 has a relatively low rotational speed and batteries 19, 20 are connected in series when the system is operating in the generating mode with electric machine 62 having a relatively high rotational speed.
More specifically, when starting engine 60, system 1A can be placed in the motoring mode with switches A, D and E closed and switches B and C open to thereby connect batteries 19, 20 in series with electric machine 62. This will provide a relatively high voltage to electric machine 62 and thus high torque to engine 60.
After engine 60 is started, system 1A can be placed in generating mode. The rotational speed of electric machine 62 can be advantageously used to determine how to connect batteries 19, 20. For example, when the rotational speed of electric machine 62 exceeds a first predetermined threshold, switch E can be opened and switches A, B, C and D closed to connect batteries 19, 20 in parallel with electric machine 62 with system 1A in generating mode. Once the rotational speed of electric machine has exceeded a larger second predetermined threshold, switches B, C can be opened and switch E closed (with switches A and D remaining closed) to place batteries 19, 20 in series with electric machine 62 with system 1A in generating mode.
Operating system 1A in this manner allows for the advantageous use of batteries 19, 20. More specifically, by connecting batteries 19, 20 in series (in the motoring mode) when starting engine 60, the batteries will provide a relatively high voltage to thereby enhance the torque supplied to engine 60 during the starting operation. When the system switches to generating mode, by initially connecting batteries 19, 20 in parallel after a first rotational speed threshold has been exceeded, batteries 19, 20 can be simultaneously charged. The second rotational speed threshold at which batteries 19, 20 are connected in series when the system is operating in generating mode may be set to a speed at which electric machine 62 readily generates a higher voltage.
It is noted that first predetermined threshold may also correspond to speed at which system will always be in generating mode. As a general rule, when using electric machine 62 in the motoring mode to start engine 60, the rotational speed of electric machine 62 will be at a speed that is lower than when engine 60 is already running and driving the rotation of rotor 2 to thereby allow the system to be placed in generating mode. Thus, for some vehicles, system 1A will always be in a generating mode when the rotational speed of electric machine 62 exceeds a predetermined threshold that is set somewhat higher than the speed electric machine 62 will reach when starting engine 60. In such a system, the rotational speed of electric machine 62 can be monitored and when it exceeds the first predetermined threshold, batteries 19, 20 can be connected in parallel to thereby provide for simultaneous charging of the batteries. Such a system might also involve connecting batteries 19, 20 in series for simultaneous charging once the rotational speed of electric machine 62 exceeds a second higher predetermined threshold. Such a system could be configured such that batteries 19, 20 are always connected in parallel with the system in charging mode when the rotational speed of electric machine 62 falls between the first and second predetermined thresholds.
As mentioned above, with system 1A it is also possible to connect an individual battery to electric machine 62. It may be advantageous to connect only one of batteries 19, 20 to electric machine 62. For example, controller 16 might periodically run down the charge and recharge batteries 19, 20 individually to determine if the battery is functioning properly or for calibration purposes. In this regard, it is noted that batteries 19, 20 cannot not only be connected individually and in parallel for purposes of charging the batteries but also when the system is in the motoring mode. For example, in a hybrid vehicle, it might be desirable to connect an individual battery or batteries 19, 20 in parallel when providing an assist to engine 60 when it is already running.
Various other conditions might be employed to determine which arrangement (individual battery, parallel connection, or series connection) is used when system 1A is in generating mode. For example, when electric machine 62 is in generating mode and the rotational speed of electric machine is below a first threshold, an individual battery would be connected, once the first threshold is exceeded, both batteries would be connected in parallel and then after a second, higher, rotational speed threshold is exceeded, the batteries would be connected in series.
While examples of specific conditions have been described for determining when to connect batteries 19, 20 individually, in parallel and in series, alternative embodiments might employ different conditions. For example, temperature could be a factor in such a determination. Moreover, the plurality of batteries might be larger than the illustrated two batteries.
While various embodiments incorporating the present invention have been described in detail, further modifications and adaptations of the invention may occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention.
This is a continuation-in-part of application Ser. No. 13/911,462 filed Jun. 6, 2013 entitled CHARGING IN MULTIPLE VOLTAGE START/STOP BAS SYSTEM the disclosure of which is hereby incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13911462 | Jun 2013 | US |
| Child | 14849496 | US |
