Motor integrated parallel hybrid transmission

A motor-integrated transmission mechanism for use in parallel hybrid electric vehicles. The transmission can provide five basic modes of operation that can be further classified into sixteen sub-modes: one electric motor mode, four engine modes, four engine/charge modes, three power modes and four regenerative braking modes. Each of these sub-modes can be grouped into like clutching conditions, providing the functional appearance of a conventional 4-speed automatic transmission, with electric launch, engine-only, engine/charge, power-assist, and regeneration capability. CVT capability is provided with one of the engine/charge modes. The transmission can be incorporated in front-wheel drive and in rear-wheel drive vehicles.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention disclosed herein relates generally to parallel hybrid electric vehicle (HEV) transmissions, and more particularly to parallel hybrid electric vehicle transmissions capable of providing one- or two-degree-of-freedom operation in order to couple and transmit torque from two power sources to the drive wheels of the automobile, or to split the torque from one power source into two parts, one for driving the automobile and the other for charging the vehicle batteries.

2. Description of the Background

Internal combustion engines are widely used for driving passenger cars. Typically, the size of an engine used in a vehicle is several times greater than the average power requirement of the vehicle in order to meet various operating conditions. As a result, the engine cannot run at its optimal operating condition most of the time which leads to poor fuel economy and emissions. This problem is particularly important in large cities where stop-and-go driving is common and pollution is a major problem.

One approach to reduce pollutants is to utilize electric vehicles. In an electric vehicle, an electric motor derives its power from a battery pack to drive the vehicle. The batteries are charged by an external power source when the vehicle is off duty. However, electric vehicles suffer the problems of limited driving range, typically around 200 miles, insufficient acceleration and hill climbing performance, and prolonged battery charging time.

Another approach is to employ hybrid vehicles. There are two types of hybrid vehicles, namely, series hybrid and parallel hybrid. In a series hybrid, an electric motor converts chemical energy stored in a battery pack into mechanical power to drive the vehicle whereas an engine is used to drive a generator for charging the batteries. Power is transmitted from the engine to the electric generator, the battery pack, and the electric motor, and then to the wheels. This arrangement permits the engine to run near its optimal operating condition on demand. Hence, the problems of limited driving range and prolonged battery charging time can be avoided. In a parallel hybrid, two or more power sources such as an engine and an electric motor are used to drive the vehicle simultaneously. Through the use of a non-conventional transmission and an electronic control unit, the electric motor can sometimes be converted into a generator for charging the batteries. In this regard, a parallel hybrid provides a more direct transfer of energy from the engine to the driving wheels. In addition, the size of the electric motor can be much smaller than that of a series hybrid, and there is no need for a separate generator. Hence, a parallel hybrid is more efficient and more economical than a series hybrid.

Attempts have been made in the past to provide parallel hybrid electric vehicle transmissions, but with limited success. For example, U.S. Pat. No. 5,577,973 to Schmidt describes a two-degree-of-freedom hybrid transmission in which a compound planetary gear set having two planetary gear subsets is provided, with two gear members of each subset being conjoined with two gear members of the opposing subset. This arrangement allows the electric motor to supplement the torque supplied by the heat engine to enable a two-degree-of-freedom transmission, but fails to enable engine-only or motor-only operation, thus limiting the utility of the transmission to one having two modes of forward driving operation.

Likewise, U.S. Pat. No. 5,558,175 to Sherman describes a hybrid transmission comprising two compound planetary gear train arrangements, one for combining torque outputs from an internal combustion engine with the torque outputs from an electric motor, and the other for providing a multi-range transmission capability. Thus, the Sherman '175 system requires two separate planetary gear train assemblies in order to accomplish the combined functions of torque combination with multi-speed capability.

It would therefore be advantageous to provide a hybrid electric vehicle transmission which combines the features of torque combination from a heat engine and electric motor and multi-speed capability in a single compound planetary gear train assembly, while enabling combined engine and motor operation, engine-only operation, or motor-only operation as the need arises to meet varying torque and engine efficiency requirements. It would be even more advantageous to provide these features in a configuration where a single motor/generator unit can be integrated coaxially with the planetary gear set.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a parallel hybrid transmission which avoids the disadvantages of the prior art.

It is another object of the present invention to provide a parallel hybrid transmission having the ability to sum torque from two power sources and transmit the combined torque to the vehicle wheels.

It is another object of the present invention to provide a parallel hybrid transmission operable by a single heat engine and a single electric motor/generator unit.

It is yet another object of the present invention to provide a parallel hybrid transmission that enables selective operation of engine-only, motor-only, and combined engine and motor torque transmission to an output shaft.

It is yet another object of the present invention to provide a parallel hybrid transmission having the ability to split torque from a heat engine such that a portion of the torque derived from the heat engine is used to power a generator that charges the vehicle batteries, while the remaining portion of the torque derived from the heat engine is transmitted to the vehicle wheels.

It is still yet another object of the present invention to provide a parallel hybrid transmission having the ability to operate two power sources individually, and to control such power sources independently from one another.

It is still even yet another object of the present invention to provide a parallel hybrid transmission having the ability to operate as a continuous variable transmission.

It is still yet another object of the present invention to provide a parallel hybrid transmission having regenerative braking capability.

It is even yet another object of the present invention to provide a parallel hybrid transmission having a single motor/generator unit mounted coaxially with a planetary gear set.

It is even yet another object of the present invention to provide a parallel hybrid transmission exhibiting small mechanical and electrical losses.

It is still even yet another object of the present invention to provide a parallel hybrid transmission of reliable and simplified design over prior art transmissions.

In accordance with the above objects, a novel parallel hybrid transmission is provided comprising a compound planetary gear set, an engine, an engine input shaft, a combined electric motor and generator assembly, a motor input shaft, an output shaft, and four torque transfer devices. In a preferred embodiment of the invention, the four torque transfer devices comprise two multi-disk clutches and two band clutches. The compound planetary gear set comprises two planetary gear trains that conjoin two gear members from each gear train. In a preferred embodiment of the invention, the two planetary gear trains share a compound sun gear and conjoin the ring gear of the input planetary gear train with the planet carrier of the output planetary gear train. Also in a preferred embodiment of the invention, the combined electric motor and generator assembly is integrated coaxially with the compound planetary gear set, with the central rotational axes of the motor and planetary gear set aligning with the rotational axes of the engine input shaft and output shaft. Through the use of the torque transfer devices, the engine input shaft may be selectively coupled to various members of the compound planetary gear set and various members of the compound planetary gear set may be selectively grounded to the transmission case in order to provide 16 operational modes, namely: an electric motor driving mode for moving the vehicle from a standstill and for low speed driving in city traffic; three power modes which combine the torque provided from the engine and the motor; three engine charge modes which use power from the engine to simultaneously drive the vehicle and charge the batteries; a continuous variable transmission/charging mode which uses power from the engine to simultaneously drive the vehicle and charge the batteries while enabling continuous variable transmission through regulation of the speed of the generator; four engine modes which power the vehicle directly from the heat engine with no power assist from the motor for use in highway cruising conditions; and four regenerative modes experienced during vehicle braking in which the electric motor is operated as a generator to charge the batteries.

Thus, the combination of the torque transfer devices and compound planetary gear train of the instant invention provide increased versatility of a hybrid vehicle transmission over prior art hybrid vehicle transmissions, while maintaining a simplified, reliable transmission construction operable through engine-only, motor-only, and combined engine and motor torque transmission to the transmission output shaft.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in the schematic representation ofFIG. 1, the parallel hybrid electric vehicle transmission of the instant invention comprises a compound planetary gear set (shown generally at10), an engine20, an engine input shaft21, a combined electric motor and generator30, an output shaft50, and four torque transfer devices61,62,63, and64. Torque transfer devices61and62preferably comprise multi-disk clutches, and torque transfer devices63and64preferably comprise band clutches. However, other similarly configured torque transfer devices, such as one-way clutches, may likewise be used without departing from the spirit and scope of the instant invention.

Compound planetary gear set10more particularly comprises an input planetary gear train (shown generally at100) and an output planetary gear train (shown generally at200). Each of planetary gear trains100and200share a compound sun gear101. Input planetary gear train100further comprises a ring gear102and a plurality of planetary gears103. Likewise, output planetary gear train200further comprises a ring gear202and a plurality of planetary gears203. The output shaft50interconnects ring gear102of input planetary gear train100with the carrier204of planetary gears203of output planetary gear train200. Electric motor30is integrated coaxially with compound sun gear101.

Engine input shaft21is affixed to hub151, which may in turn be operatively connected to the compound planetary gear train10by engaging either or both of multi-disk clutches61and62. When clutch61is engaged, engine input shaft21is coupled to the compounded sun gear101of input planetary gear train100and output planetary gear train200through hub152. Likewise, when clutch62is engaged, engine input shaft21is coupled to carrier104of input planetary gear train100. Band clutches63and64are used to ground ring gear202and sun gear101to the transmission case (not shown), and can be used to reduce the mobility of the transmission from the two degree-of-freedom to one degree-of-freedom operation.

More particulary, sixteen useful operational modes are available from the parallel hybrid transmission of the instant invention using different combinations of the four clutches and operating the electric motor as either a motor or generator or allowing it to freewheel in the off condition. The sixteen useful modes of operation may be summarized by the following Table 1, and are discussed in greater detail below:

The first mode of operation of the parallel hybrid transmission of the instant invention is motor-only mode in which the electric motor provides all of the power to drive the vehicle, in the forward or reverse direction, at a low-speed gear reduction. The motor-only mode is used to initially move the vehicle from a standstill and for low speed driving in city traffic. Band clutch member63is the only clutch member engaged, grounding ring gear202to the transmission case. As a result, the transmission becomes a single degree-of-freedom transmission operable solely through the torque produced by electric motor30. As shown, power is directed from electric motor30, sun gear101, and planetary gears203(and their carrier204) to output shaft50. Ring gear202serves as a reaction member. In this operational mode, the input planetary gear train spins freely.

Another feature of the motor-only mode of operation of the transmission of the instant invention is that a vehicle operator may start engine20without an electric starter, as is traditionally required. When operating in motor-only mode, the vehicle operator need only engage clutch61, and thus shift from the motor-only mode to the first combined engine and motor mode, which process will in turn pull the engine up to operating speed as would a traditional, separate electric starter.

The next group of modes of operation of the parallel hybrid transmission of the instant invention are power-summing combination modes which combine torque from the engine and motor to drive the vehicle, at different gear reductions. The power-summing combination modes are used for maximum acceleration or hill climbing.

In the first power-summing combination mode, band clutch63and multi-disk clutch61are engaged, and all other clutches are disengaged. Ring gear202is grounded to the transmission case and serves as a reaction member. With multi-disk clutch61engaged, torque from the engine enters through sun gear101to output planetary gears203and carrier204to output shaft50. Likewise, torque from the motor enters through sun gear101to output planetary gears203and carrier204to output shaft50. Thus, the torque from the engine and motor are summed at the sun gear and directed to output shaft50.

In the second power-summing combination mode, multi-disk clutch62is engaged, along with band clutch63, and all others are disengaged. With clutch62engaged, torque from the engine enters from shaft21through input carrier104, to planetary gears103, where it is split between the sun gear101and the ring gear102. The portion of engine power entering sun gear101is combined with the motor power at sun gear101. The combined torque on the sun gear enters planetary gears203and carrier204to the output shaft50. The remainder of the engine power entering ring gear102is added to the other combined engine and motor power on the output shaft50to power the vehicle, at less gear reduction than the first combined power-summing mode.

In the third power-summing combination mode, multi-disk clutches61and62are engaged and all other clutches are disengaged. Under this condition, the input and output planetary gear trains lock together and rotate as a single unit, providing a direct drive power-summing mode. Torque from the engine is transferred from hub151to both input planetary gear carrier104and hub152. From planetary gear carrier104, torque is transferred to planetary gears103, and in turn to ring gear102and sun gear101, and ultimately to output shaft50. Torque from hub152is likewise transferred through sun gear101, ultimately to output shaft50. Finally, motor torque is also transferred through sun gear to output shaft50. The engine torque and motor torque are summed in the locked planetary gear set10to power the output shaft50. Under this configuration, the engine and motor rotate at the same speed.

The next group of modes of operation of the parallel hybrid transmission of the instant invention are engine-only modes which are utilized during highway cruising conditions in which it is highly desirable to power the vehicle directly from the heat engine with no power assist from the motor. The varying clutch arrangements made available by the configuration of the instant invention offer four distinct engine-only modes, namely, two reduction modes, one direct drive mode, and one overdrive gear ratio mode.

In the first reduction gear ratio engine-only mode, multi-disk clutch61and band clutch63are engaged, and the motor is free-wheeling in the off condition. With band clutch63engaged, ring gear202serves as a reaction member, and the input shaft21is coupled to the output planetary gear train200. The electric motor is switched to a neutral condition. In this configuration, engine torque is transferred through hub151, then hub152, through sun gear101, to output planetary gear train carrier204, to output shaft50.

In the second reduction gear ratio engine-only mode, clutches62and63are engaged and all others are disengaged. With clutch62engaged, torque from the engine enters from shaft21through input carrier104, to planetary gears103, where it is split between the sun gear101and the ring gear102. The motor30is free-wheeling in the off condition. The portion of engine power entering sun gear101is transferred through planetary gears203to output shaft50. The remainder of the engine power entering ring gear102is added to the other engine power on output shaft50to power the vehicle, at less gear reduction than the first engine-only mode.

In the direct drive engine-only mode, multi-disk clutches61and62are engaged, and all remaining clutches are disengaged. The motor is allowed to free-wheel in the off condition. Under this condition, the input and output planetary gear trains lock together and rotate as a single unit, providing a direct drive engine-only mode. Torque from the engine is transferred from hub151to both input planetary gear carrier104and hub152. From planetary gear carrier104, torque is transferred to planetary gears103, and in turn to ring gear102and sun gear101, and ultimately to output shaft50. Torque from hub152is likewise transferred through sun gear101, ultimately to output shaft50.

In the overdrive engine-only mode, multi-disk clutch62and band clutch64are engaged, and all other clutches are disengaged. Prevented from rotating due to band clutch64, sun gear101becomes the reaction member, and the output planetary gear train carries no load. Engine torque is transferred through hub151, input planetary gear train carrier104, planetary gears103, ring gear102, to output shaft50.

The next mode of operation of the parallel hybrid transmission of the instant invention is engine charging modes which enable the engine to power the vehicle and power the electric motor generator assembly simultaneously. The generator in turn charges the vehicle batteries when the battery state-of-charge is low and the power requirement for cruising is low. The varying clutch arrangements made available by the configuration of the instant invention offer four distinct engine charge modes, namely two reduction modes, one direct drive mode, and one continuously variable transmission (CVT) mode.

In the first reduction engine charging mode, band clutch63and multi-disk clutch61are engaged, and all other clutches are disengaged. Ring gear202is grounded to the transmission case and serves as a reaction member. The power flow in this mode is similar to that of the first reduction power-summing mode, except motor30is operated as a generator to charge vehicle batteries or power vehicle accessories.

In the second reduction engine charging mode, multi-disk clutch62is engaged, along with band clutch63, and all others are disengaged. Ring gear202is grounded to the transmission case and serves as a reaction member. The power flow in this mode is similar to that of the second power-summing mode, except motor30is operated as a generator to charge vehicle batteries or power vehicle accessories.

In the direct-drive engine charging mode, multi-disk clutches61and62are engaged, and all remaining clutches are disengaged. The power flow in this mode is similar to that of the direct-drive power-summing mode, except motor30is operated as a generator to charge vehicle batteries or power vehicle accessories.

In the continuously variable transmission engine charging mode, multi-disk clutch62is engaged, and torque from the engine is transferred through hub151and input planetary gear train carrier104to input planetary gears103, where the torque is split. Most of the torque is used to drive the vehicle as it is transferred from planetary gears103through ring gear102, and to output shaft50, while the remainder is used to power the motor/generator for charging the batteries and powering vehicle electric accessories through sun gear101. For this operating mode, the motor is operated as a generator. For a given output shaft speed, the engine can be operated at a speed yielding peak efficiency while the vehicle speed is regulated by varying the speed of the generator. In this regard, the transmission functions as a continuous variable transmission.

As indicated in Table 1 above, four regenerative braking modes are also made available through the parallel hybrid transmission of the instant invention. During braking events, the electric motor is operated as a generator to charge the batteries. The output shaft becomes an input shaft, and kinetic energy of the vehicle that would otherwise have been lost through the brakes is stored for later use.

The first regenerative braking mode is identical to the clutch condition in motor-only mode, except that the motor is operated as a generator. In this regenerative braking mode the engine is off. The power flow is the reverse of motor-only mode. In this condition, only the generator provides braking torque.

The second regenerative braking mode is identical to the clutch condition in power-summing combination mode1, except that the motor is operated as a generator. Both the engine and the generator provide braking torque. The power flow is the reverse of power-summing mode1.

The third regenerative braking mode is identical to the clutch condition in power-summing combination mode2, except that the motor is once again operated as a generator. Again, both the engine and generator provide braking torque. The power flow is the reverse of power-summing mode2.

Finally, the fourth regenerative braking mode is identical to the direct-drive power-summing mode, except that the motor is operated as a generator. Again, both the engine and generator provide braking torque. The power flow is the reverse of power-summing mode3.

Alternative similar hybrid transmission mechanisms may also be provided. In general, a hybrid transmission is preferably comprised of two basic planetary gear trains with four torque transfer devices and a coaxially integrated motor/generator unit. Using different combinations of the four clutches and operating the electric motor as either a motor or generator or allowing it to freewheel in the off condition, motor-only, power-summing, engine-only, engine charge, and regenerative braking operating modes are capable.