Multi-mode hybrid electric transfer case for four-wheel drive vehicle

A hybrid transfer case can include first and second output shafts adapted for connection to respective rear and front drivelines, a first input shaft adapted for connection to a transmission and for selective connection to the first output shaft, and a second input shaft that can be rotatably supported on the first input shaft and selectively connected to the first output shaft. The transfer case can further include a planetary gearset, a transfer system and an electric motor/generator. The planetary gearset can include a first member fixed for rotation with the first input shaft, a second member fixed for rotation with the second input shaft, and a third member. The transfer system can couple the second input shaft to the second output shaft, and the electric motor can selectively drive the third member.

INTRODUCTION

The present disclosure relates generally to hybrid drive systems for motor vehicles and, more particularly, to a transfer case for use in four-wheel drive hybrid vehicles.

BACKGROUND

Automobile manufacturers are actively working to develop alternative powertrain systems in an effort to reduce the level of pollutants exhausted into the air by conventional powertrains equipped with internal combustion engines. Significant development has been directed to electric vehicles and fuel cell vehicles. Unfortunately, these alternative powertrain systems may suffer from several disadvantages and, for all practical purposes, are still under development. However, several different hybrid electric vehicles have recently been offered for sale. Some of the hybrid vehicles are equipped with an internal combustion engine and an electric motor that can be operated independently or in combination to drive the vehicle.

There are generally two types of hybrid vehicles, namely, series hybrid and parallel hybrid. In a series hybrid vehicle, power is delivered to the wheels by the electric motor which draws electrical energy from the battery. The engine is used in series hybrid vehicles to drive a generator which supplies power directly to the electric motor or charges the battery when the state of charge falls below a predetermined value. In parallel hybrid vehicles, the electric motor and the engine can be operated independently or in combination pursuant to the running conditions of the vehicle. Typically, the control strategy for such parallel hybrid vehicles utilizes a low-load mode where only the electric motor is used to drive the vehicle, a high-load mode where only the engine is used to drive the vehicle, and an intermediate assist mode where the engine and electric motor are both used to drive the vehicle. Regardless of the type of hybrid drive system used, hybrid vehicles are highly modified versions of conventional vehicles that may be expensive due to the componentry, required control systems, and specialized packaging requirements.

Hybrid vehicles have also been adapted to four-wheel drive vehicles and typically utilize the above-noted parallel hybrid powertrain to drive the primary wheels and a second electric motor to drive the secondary wheels. Such a four-wheel drive system may be extremely expensive and difficult to package. Thus, a need exists to develop hybrid powertrains for use in four-wheel drive vehicles that utilize many conventional powertrain components so as to minimize specialized packaging and reduce cost.

SUMMARY

In one form, a transfer case for a vehicle having an engine, a transmission, and front and rear drivelines is provided. The transfer case can include a first output shaft adapted for connection to the rear driveline, a second output shaft adapted for connection to the front driveline, and first and second input shafts. The first input shaft can be adapted for connection at a first end to the transmission and for selective connection at a second end to the first output shaft. The second input shaft can be rotatably supported on the first input shaft for rotation relative thereto and can be adapted for selective connection to the first output shaft. The transfer case can further include a planetary gear set, a transfer system and an electric motor. The planetary gear set can include a first member fixed for rotation with the first input shaft, a second member fixed for rotation with the second input shaft, and a third member. The transfer system can rotatably couple the second input shaft to the second output shaft, and the electric motor can selectively drive the third member.

In another form, a hybrid vehicle is provided. The hybrid vehicle can include a powertrain, first and second drivelines and a transfer case. The powertrain can include an internal combustion engine and an electric motor as motive power sources. The first driveline can transfer power to a first wheel and can include a first disconnect arranged to drivingly connect and disconnect the motive power sources and the first wheel. The second driveline can transfer power to a second wheel and can include a second disconnect arranged to drivingly connect and disconnect the motive power sources and the second wheel. The transfer case can include first and second output shafts and first and second input shafts. The first output shaft can be adapted for connection to the first driveline and the second output shaft can be adapted for connection to the second driveline. The first input shaft can be adapted for connection at a first end to the internal combustion engine, and for selective connection at a second end to the first output shaft. The second input shaft can be adapted for selective connection to the first input shaft. The transfer case can further include a planetary gear set and a transfer system. The planetary gear set can include a first member fixed for rotation with the first input shaft, a second member fixed for rotation with the second shaft, and a third member. The transfer system can rotatably couple the second input shaft to the second output shaft, and the electric motor can selectively drive the third member.

DETAILED DESCRIPTION

Referring toFIG. 1of the drawings, a hybrid four-wheel drive powertrain system5for a hybrid motor vehicle is shown and can include a first power source10, a transmission14, a rear driveline16, a front driveline18, and a second power source20. The first power source may include an internal combustion engine12and the second power source may include an electric motor/generator22. Transmission14can be of any known type including, but not limited to, an automatic, manual, automated manual or continuously variable transmission. The vehicle can further include a powertrain control system24generally shown to include a battery26, a group of vehicle sensors28, and a controller30. Rear driveline16can include a first pair of wheels32connected to a rear axle assembly34having a differential unit36and a pair of rear axle or wheel disconnects38. Differential unit36can be connected to one end of a rear prop shaft40, the opposite end of which can be connected to a first or rear output shaft42of a transfer case44. Similarly, front driveline18can include a second pair of wheels46connected to a front axle assembly48having a differential unit50and a pair of front axle or wheel disconnects52. Differential unit50can be connected to one end of a front prop shaft54, the opposite end of which can be connected to a second or front output shaft56of transfer case44.

Referring now primarily toFIGS. 2-5, transfer case44is shown schematically and can include a housing assembly58of the type normally adapted for bolted mounting to a casing of transmission14, a first input shaft60, a second input shaft62, and a planetary gear set64. Planetary gear set64can include a ring gear66in constant meshing engagement with a plurality of planet gears68which can be in constant meshing engagement with a sun gear70. Ring gear66can be fixed for rotation with first input shaft60at one end adjacent to transmission14. Planet gears68can be rotatably supported by pins72which can be fixed to a carrier74. Carrier74can be fixed for rotation with second input shaft62. While not intended to be limiting, it is contemplated that a reduction ratio of about 3 to 1 can be established by planetary gear set64.

First input shaft60can be rotatably supported in housing58by bearing assemblies and adapted for direct connection at one end to an output shaft of transmission14. First input shaft60can also include a hub76at a second end fixed for rotation with first input shaft60and for facilitating selective engagement with rear output shaft42as will be detailed herein. A plurality of teeth77are formed on hub76. Second input shaft62can be concentrically supported on first input shaft60for rotation relative thereto and can include a toothed hub78for facilitating selective engagement with rear output shaft42as will also be detailed herein.

A transfer system80can be provided in transfer case44for transferring torque from second input shaft62to front output shaft56. Transfer system80can include a first sprocket82fixed for rotation with second input shaft62and a second sprocket fixed84for rotation with front output shaft56. A flexible member, such as a power chain86, can couple the first and second sprockets82,84so as to transfer drive torque from first sprocket82to second sprocket84and thus from second input shaft62to second output shaft56.

Transfer case44can further include a first mode clutch assembly90and a second mode clutch assembly92, each controlled by controller30. First mode clutch90, shown as an exemplary dog clutch, can include a mode sleeve94for selectively coupling one of the first input shaft60and the second input shaft62with rear output shaft42. Mode sleeve94is fixed for rotation with and axially moveable relative to rear output shaft42via a splined hub96. To selectively couple the first input shaft60, mode sleeve94can be controlled to couple hub76with hub96of rear output shaft42. Similarly, to selectively couple the second input shaft62, mode sleeve94can be translated to couple hub78and96. Second mode clutch92, also shown as an exemplary dog clutch, can include a mode sleeve98operable to selectively couple the front output shaft56to a ground100so as to restrict front output shaft56from rotating.

A motor/generator clutch assembly102and first and second sleeves104,106can also be provided in transfer case44for selectively coupling motor/generator22with sun gear70. First and second sleeves104,106can be concentrically supported on second input shaft62for relative rotation thereto. First sleeve104can be connected at one end to sun gear70and arranged for selective engagement by motor/generator clutch102at an opposite end. Second sleeve106can be connected to a rotor108of motor/generator22at one end and arranged for selective engagement by motor/generator clutch102at an opposite end. Motor/generator clutch102, shown as an exemplary dog clutch, can be controlled by controller30to selectively fix rotor108for rotation with sun gear70via mode sleeve110. It should be appreciated that while first and second mode clutches90,92and electric motor/generator clutch102are shown as exemplary dog clutch arrangements, other suitable clutch arrangements, such as friction plate clutches or synchronizers, can be used in place of the dog clutches.

The hybrid four-wheel drive powertrain system5of the present disclosure can include two main power sources, namely internal combustion engine12and electric motor/generator22. Power from engine12can be transmitted to transmission14, which in turn, can be delivered to transfer case44via first input shaft60. First input shaft60can drive rear output shaft42if first mode clutch90is controlled to selectively couple the respective shafts. In a parallel power transmission path, driven ring gear66can drive carrier74through planet gears68which in turn can drive second input shaft62. Second input shaft62can then drive front output shaft56via transfer system80and/or can be selectively coupled to drive rear output shaft42via first mode clutch90. The driven planet gears68can also drive sun gear70which, in turn, can selectively transmit torque to motor/generator22for generation via motor/generator clutch102. Conversely, motor/generator22can be energized to transmit torque via rotor108and motor/generator clutch102to drive sun gear70to drive second input shaft62.

Motor/generator22can be connected to battery26and can be selectively placed in one of a driving state, a charging state, and a no-load or off state by controller30. In the drive state, motor/generator22can function as an electric motor driven by energy supplied by battery26. In the charging state, motor/generator22can function as an electric generator with regenerative braking (brake torque electrically generated by motor/generator22) for providing and storing energy in battery26. In the no-Load or off state, motor/generator can be permitted to rotate freely or can be selectively disconnected from the hybrid four-wheel drive powertrain system5via motor/generator clutch102.

As noted, control system24can be provided for controlling operation of the hybrid four-wheel drive powertrain system5shown inFIG. 1. With reference toFIG. 6, controller30is shown to receive signals from various sensors and input devices previously identified cumulatively inFIG. 1as vehicle sensors28. Controller30can be principally comprised of a microprocessor having a central processing unit, random-access memory, read-only memory, and an input-output actuator interface. Controller30can perform data processing operations to execute various control routines according to control programs and/or maps stored in the read-only memory.

Controller30can receive data from an ignition switch120, an acceleration position sensor122, a brake status sensor124, a battery temperature sensor126, a battery state of charge sensor128, and a throttle position sensor130. In addition, other inputs can include an engine speed sensor132, a motor speed sensor134, a rear output shaft speed sensor136, and a front output shaft speed sensor138. Ignition switch120can be closed when the vehicle key is turned on. Accelerator position sensor122can sense a depression angle of an accelerator pedal. Brake status sensor124can be turned on when a brake pedal is depressed. Battery temperature sensor126can sense a temperature of battery26. Battery state of charge sensor128can sense a charge level of battery26. Throttle position sensor130can sense a degree of opening of the engine throttle valve. Engine speed sensor132can sense a parameter indicative of the rotary speed of a drive shaft of engine12. Motor speed sensor134can sense a parameter indicative of a rotary speed of rotor108of motor/generator22. Rear speed sensor136can sense a rotary speed of either rear output shaft42or rear prop shaft40and can further be used as an indication of vehicle speed. Front speed sensor138can sense a rotary speed of either front output shaft56or front prop shaft54.

Based upon the operating information inputted to controller30, a mode of operation of the hybrid transfer case44can be selected and controller30can send electronic control signals to the various power-operated controlled devices. Specifically, controller30can monitor and continuously control actuation of motor/generator22, engagement of front and rear wheel disconnects52,38, operation of first and second mode clutches90,92, operation of electric motor/generator clutch102, and various operator selected vehicle operation options such as a trailer tow112and traction control114option. Additionally, controller30can monitor and control various engine management systems for controlling the speed and torque generated by engine12. These systems can include a fuel delivery system140, an ignition timing system142, and a valve timing system144. A low voltage auxiliary battery146may serve as the power supply for controller30.

The hybrid four-wheel drive powertrain system5of the present disclosure can include four primary modes of operation, namely a front wheel drive mode (FWD mode), a rear wheel drive mode (RWD mode), an all wheel drive or power augmentation mode (AWD mode), and a part-time four wheel drive mode (4WD mode). With particular reference toFIG. 2, the FWD mode of operation will now be discussed in greater detail. In the FWD mode, motive power can be supplied solely by electric motor/generator22to drive the front output shaft56to drive front axle48and front wheels46. More specifically, engine12can be turned off and transmission14can be in a locked state thereby fixing first input shaft60and ring gear66from rotating. Motor/generator clutch102can be in the engaged state to transmit rotary driving power from rotor108of motor/generator22to drive sun gear70. Driven sun gear70can then drive carrier74through planet gears68against fixed ring gear66. Driven carrier74can drive second input shaft62which in turn can drive transfer system80and front output shaft56. In this configuration, second mode clutch92can be disengaged from ground100to allow front output shaft56to rotate, and first mode clutch90can be disengaged from the first and second input shafts60,62. Front axle disconnects52can be in a connected state to transmit the motive power to the front wheels46and rear axle disconnects38can be in either a connected or a disconnected state. While optional in this mode, opening or disengaging the rear axle disconnects38can allow rear wheels32to rotate without requiring rear axle34to rotate thereby reducing friction and serving to improve fuel economy.

It is contemplated that the FWD mode can be used for launching the vehicle as well as for low speed driving and for a city driving cycle that would typically involve start and stop driving. The motor/generator22can also be used in the FWD mode for regeneration when not driving the vehicle, such as during motor braking or coasting. In addition, by using motor/generator22for the city driving cycle, emissions typically generated by an internal combustion engine during acceleration events normally associated with city driving can be substantially reduced, if not completely eliminated.

Turning now toFIG. 3, the AWD mode will now be discussed in greater detail. In the AWD mode, motive power can be supplied by both engine12and motor/generator22to drive rear wheels32and front wheels46. In this configuration, engine12through transmission14can drive first input shaft60. Mode clutch90can be operated to selectively engage mode sleeve94with hub76and hub96to transmit driving power to rear output shaft42. Motor/generator22can drive sun gear70in a manner similar to the FWD mode discussed above, except that motor/generator22can be controlled by controller30to drive sun gear70relative to the driven ring gear66to drive second input shaft62and front wheels46. Torque output from motor/generator22can be controlled as a function of engine12input torque to control torque splitting between front and rear axles48,34. For an exemplary torque split of approximately fifty percent to front axle48and fifty percent to rear axle34, electric motor/generator torque can be approximately twenty percent of engine12input torque. This torque ratio is obtained by the gear ratio provided by planetary gear set64operating in the manner described. Other torque ratios may alternatively be provided. In addition, front and rear wheel disconnects52,38can be in a locked or engaged configuration so as to transmit motive power from front and rear axles48,34to front and rear wheels46,32.

The AWD mode of operation can be manually selected by a vehicle operator, such as by selecting the AWD mode using mode selector switch116, or by selecting the trailer tow112or traction control114operating options when additional traction and/or power augmentation may be desired. Conversely, the AWD mode of operation can also be automatically selected by the controller30based on predetermined criteria or events such as detected wheel slippage, detected hill climbing, and/or for transitioning between the FWD and RWD modes of operation of the hybrid transfer case44as will be detailed. If the AWD mode is selected by controller30as opposed to being manually selected by a vehicle operator, the motor/generator22can be controlled to operate in an on-demand configuration where engine12provides primary input torque to drive front and rear wheels46,32and electric motor/generator22is selectively engaged via electric motor/generator clutch102by controller30for additional torque input. Controller30can also selectively engage/disengage motor/generator22in the AWD on-demand configuration to charge battery26as may be required when electric motor/generator22is not in a driving state.

Turning now toFIG. 4, the RWD mode will now be discussed in greater detail. In the RWD mode, motive power can be supplied solely by engine12to drive rear wheels32. In addition, the RWD mode can also used as a generation mode to charge battery26. In this configuration, motive power can be supplied to rear wheels32in the manner discussed above with respect to the AWD mode. In addition, second mode clutch92can be controlled to selectively engage front output shaft56to ground100via mode sleeve98to provide a reaction for planetary carrier74as will be detailed. Front axle disconnects52can be in the open or disengaged mode to permit front wheels46to rotate while front output shaft56is prevented from rotating. Locking front output shaft56via mode clutch92selectively restricts second input shaft62and thus carrier74from rotation. With carrier74fixed, as ring gear66is driven by engine12, sun gear70can be correspondingly driven which, in turn, can drive motor/generator22via engaged motor/generator mode clutch102. Driven motor/generator22can then charge battery26while being monitored by controller30. When controller30determines that battery26is fully charged via battery state of charge sensor128, motor/generator clutch102can be controlled to selectively disengage motor/generator22from sun gear70, and thereby place motor/generator22in the no-load or off state.

The RWD mode of operation can be used as the primary mode of operation for providing motive power at highway speeds. By having the FWD mode and using motor/generator22for launching the vehicle in the FWD mode as discussed above, engine12can be optimized for economy performance by, for example, using a lower displacement engine. In addition, the electric motor/generator can be selectively used to charge battery26during the RWD mode of operation. Finally, if any power augmentation is needed during RWD operation, either the user can manually select or controller30can automatically call for power augmentation (through one of the previously discussed sensors or switches) thereby transitioning the hybrid transfer case44into the AWD mode with power augmentation by motor/generator22.

With reference toFIG. 5, the 4WD mode will be discussed in greater detail. In this mode, motive power can be supplied to the front wheels46and the rear wheels32by both engine12and motor/generator22or either engine12or motor/generator22. In the 4WD mode, with any configuration of power sources, the first mode clutch90can be controlled to engage second input shaft62with rear output shaft42, and the second mode clutch92can be disengaged from ground100. In addition, the front and rear axle disconnects52,38can be in a locked or engaged state in the 4WD mode. In a 4WD configuration where input torque can be supplied by both engine12and motor/generator22, engine12can drive carrier74through ring gear66and motor/generator22can drive carrier74through sun gear70, with motor/generator clutch102controlled to engage motor/generator22to sun gear70via mode sleeve110. Carrier74can then drive second input shaft62which, in turn, can drive front output shaft56through transfer system80and rear output shaft42through mode clutch90.

In a 4WD mode configuration where torque can be supplied by only engine12, motor/generator clutch102can be controlled to selectively fix sun, gear70by moving mode sleeve110to a position110′ thereby coupling sleeve104to a ground118. Engine12can then drive carrier74through ring gear66which, in turn, can drive second input shaft62and front and rear output shafts56,42as detailed above. In a 4WD mode configuration where torque input can be supplied by only motor/generator22, transmission14can be in a locked state so as to fix ring gear66from rotating. Motor/generator clutch102can also be controlled to engage motor/generator22to sun gear70and motor/generator22can then drive carrier74through sun gear70against fixed ring gear66. Carrier74can then drive second input shaft62to drive front and rear output shafts56,42as detailed above. In this configuration, motor/generator22can be in a drive state when driving sun gear70and in a regeneration state when the vehicle is coasting or braking.

The hybrid vehicle of the present disclosure can advantageously use the operating modes of the hybrid transfer case44under normal or typical driving conditions to launch the vehicle with the FWD mode, transition through the AWD mode, and operate at higher steady-state speeds with the RWD mode. More specifically, the hybrid four-wheel drive powertrain system5can be configured to launch in the FWD mode using only motor/generator22for motive power as discussed above. The vehicle can then continue in the FWD mode through approximately 30 miles per hour, where the hybrid transfer case44can then transition to the AWD mode. During this transition, which can take place between approximately 30-40 miles per hour, engine12can be started and brought up to an appropriate rotational speed by controller30and then first mode clutch90can be controlled to engage first input shaft hub76via mode sleeve94. If the rear wheel disconnects38were optionally disconnected during operation in the FWD mode, they can be reconnected or locked by controller30prior to engaging rear output shaft42with first input shaft60as discussed above.

If the vehicle continues to accelerate above 40 miles per hour, then the hybrid transfer case44can transition to the RWD mode for speeds above approximately 40 miles per hour. For the transition to the RWD mode, electric motor/generator22can be slowed to a stop by controller30while motive power is supplied to rear wheels32by engine12. A command from controller30can then be issued to release front axle disconnects52prior to having second mode clutch92engage front output shaft56via mode sleeve98so as to lock front output shaft56to ground100for the RWD mode configuration. During the RWD mode, electric motor/generator can be selectively engaged and disengaged by controller30to recharge battery26as discussed above.

It should be appreciated that the AWD mode can also be selected at any speed in the FWD or the RWD mode as may be desired for additional traction control and/or power augmentation. For example, if the AWD mode is manually selected by a vehicle operator or automatically selected by controller30responsive to a predetermined threshold condition, such as detected wheel slippage, controller30controls motor/generator22for synchronization to second input shaft62via motor/generator mode clutch102. Controller30can also instruct second mode clutch92to disengage front output shaft56from ground100and instruct front axle disconnects52to reconnect or lock front wheels46to axle48. It should also be appreciated that if the AWD mode or the 4 WD mode is manually selected by the vehicle operator, the vehicle can launch in the manually selected mode (i.e., AWD or 4 WD) in place of the FWD mode.

The foregoing description is merely exemplary in nature and is not intended to limit the present disclosure, its application or uses. While specific examples have been described in the specification and illustrated in the drawings, it will be understood by those of ordinary skill in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure as defined in the claims. Furthermore, the mixing and matching of features, elements and/or functions between various examples is expressly contemplated herein, even if not specifically shown or described, so that one of ordinary skill in the art would appreciate from this disclosure that features, elements and/or functions of one example may be incorporated into another example as appropriate, unless described otherwise, above. Moreover, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular examples illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out the teachings of the present disclosure, but that the scope of the present disclosure will include any embodiments falling within the foregoing description and the appended claims.