System and method for using all wheel drive coupling to enhance electronic parking brake function on a motor vehicle

A system and method is disclosed for applying a counter torque to at least one axle of a motor vehicle, wherein the motor vehicle has an electronic parking brake (EPB) subsystem, to thus enhance a braking action of the vehicle while the EPB subsystem is engaged. In one embodiment the system may have an all wheel drive (AWD) system configured to process electronic information received by the AWD system that informs the AWD system that the EPB subsystem has been engaged, and to then apply a counter torque to the at least one axle of the vehicle. The system may also at least one of release the counter torque after receiving electronic information informing the AWD system that the EPB subsystem has been disengaged, or return to a torque value required for AWD system operation.

FIELD

The present disclosure relates to electronic parking brake systems used on motor vehicles such as cars and light trucks, and more particularly to a system and method for integrating the use of an all wheel drive coupling system with an electronic parking brake to significantly enhance the braking ability of the vehicle when the electronic parking brake is engaged.

BACKGROUND

Electronic parking brakes are now commonly employed on various motor vehicles such as cars and light trucks. Typically the electronic parking brake activates the brakes on the rear wheels of the vehicle when it is engaged. Some present day vehicles use the electronic parking brake to assist the driver of the vehicle during hill-start situations. With a hill-start situation, the hydraulic brakes of the vehicle may be programmed to remain active for a calibratable amount of time, and then the electronic parking brake may be automatically engaged to provide additional braking action during the hill-start maneuver.

The effectiveness of the electronic parking brake in either hill-start situations or in simply holding the vehicle stationary while the vehicle is parked, can be somewhat reduced when the vehicle is parked on a hill with a moderate or steep grade or the rear axle is located on a lower friction surface (ex: gravel, snow, ice). This is particularly so if the vehicle is orientated on a decline, that is with the front axles of the vehicle at an elevation which is lower than the rear end of the vehicle. In this instance the weight of the vehicle may biased significantly toward the front end of the vehicle, and thus well less than 50% of the vehicle's weight may be present on the rear wheels of the vehicle. As a result, the electronic parking brake, which is engaging the brakes on the rear wheels, may be limited in effectiveness due to the reduced weight that the tires at the rear end of the vehicle are experiencing. In this example, if the vehicle has an all wheel drive (“AWD”) system, there ordinarily would not be any counteracting torque applied to the front axles of the vehicle while the electronic parking brake is engaged. But being able to use the vehicle's AWD system to apply a counteracting torque to the front axles of the vehicle would significantly enhance the ability to hold the vehicle stationary, especially when the vehicle is parked on a decline with its front end lower than its rear end or the rear wheels are located on a lower friction surface (ex: gravel, snow, ice). The use of the vehicle's AWD system to apply a counteracting torque to the front axles (or possibly to all axles) of the vehicle during an emergency braking operating could also be highly beneficial in augmenting the vehicle's electronic parking brake's antilock braking function in bringing the vehicle to a rapid and controlled stop.

SUMMARY

In one aspect the present disclosure relates to a system for applying a counter torque to at least one axle of a motor vehicle, wherein the motor vehicle includes an electronic parking brake (EPB) subsystem, to enhance a braking action of the vehicle while the EPB subsystem is engaged. The system may comprise an all wheel drive (AWD) system which is configured to perform a plurality of operations. The AWD system may process electronic information received by the AWD system that informs the AWD system that the EPB subsystem has been engaged. The AWD system may then apply a counter torque to the at least one axle of the vehicle. The AWD system may also release the counter torque after receiving electronic information informing the AWD system that the EPB subsystem has been disengaged.

In another aspect the present disclosure relates to a system for applying a counter torque to at least one axle of a motor vehicle, wherein the motor vehicle includes an electronic parking brake (EPB) subsystem, to enhance a braking action of the vehicle while the EPB subsystem is engaged. The system may comprise an all wheel drive (AWD) system including a controller and software. The AWD system may be configured to perform a plurality of operations including communicating over a communications bus of the vehicle with the EPB subsystem, and receiving information over the communications bus. The received information may indicate when the EPB subsystem has been engaged. The AWD may act to apply a counter torque to the at least one axle of the vehicle to augment a braking action being applied by the EPB subsystem. The AWD may release the counter torque after receiving additional information over the communications bus informing the AWD system that the EPB subsystem has been disengaged. In one embodiment the AWD System may be configured so that it receives a single or combination of signals from another vehicle control module, such as the EPB or Electronic Stability Control System, which commands the AWD System clutch torque to a torque value when the EPB System is active. Once the vehicle's control module is no longer commanding the AWD system to a torque value, the AWD system's clutch torque returns to a torque value commanded by the AWD System.

In still another aspect the present disclosure relates to a method for applying a counter torque to at least one axle of a motor vehicle, wherein the motor vehicle includes an electronic parking brake (EPB) subsystem, to enhance a braking action of the vehicle while the EPB subsystem is engaged. The method may comprise using an all wheel drive (AWD) system to process electronic information received by the AWD system. The electronic information may inform the AWD system that the EPB subsystem has been engaged. The AWD system may apply a counter torque to the at least one axle of the vehicle. The AWD may also release the counter torque after receiving electronic information informing the AWD system that the EPB subsystem has been disengaged.

DETAILED DESCRIPTION

InFIG. 1a system10in accordance with one embodiment of the present disclosure is shown integrated into a motor vehicle12. The motor vehicle12may be any type of motor vehicle, but the system10is expected to find particularly utility on passenger cars and light trucks. The system10may also find utility on all-terrain vehicles (“ATVs”). A 4×4 ATV could be a potential application, as well as virtually any vehicle that makes use of a transfer case (e.g., a pick-up truck). As such, it will be appreciated that the system10is not limited to use with any one particular type or style of motor vehicle.

The system10may include an all wheel drive (“AWD”) system14having a controller16with software18. The AWD system14may communicate over a communications bus20of the vehicle12to receive and/or send electronic messages, commands or status information, or other types of information in the form of electronic messages. In this example the communications bus is a controller area network (“CAN”) bus, although it will be understood that the system10may make use of virtually any type of communications bus that permits status electronic messages, commands, status information, or any other type of electronic information to be relayed between the various subsystems of the vehicle12in real time. Simply for convenience, the communications bus20will be referred to throughout the following discussion as “CAN bus”20.

The AWD system14may communicate over the CAN bus20with a wide range of electronic and electromechanical subsystems of the vehicle12, for example an electronic parking brake (“EPB”) subsystem22, an on-board vehicle computer24, an antilock braking system (“ABS”)26, and a transaxle28. The ABS26may control the braking force applied by rear brakes30and front brakes32.

It is a principal advantage of the system10that the AWD system14, and particularly the controller16thereof, is able to monitor the CAN bus20and determine when the EPB subsystem22is engaging the rear brakes30. The EPB subsystem22is typically deployed by the user of the vehicle engaging a parking brake lever or switch inside the vehicle. This action is detected by the EPB subsystem22, and in response, the EPB subsystem causes engagement of the rear brakes30. Typically, the EPB subsystem22is used to apply a braking force to the rear wheels31of the vehicle in situations where an additional braking force is desired, such as when the vehicle is parked on an incline or decline or if the conventional hydraulic brakes have failed. As noted above, when the vehicle12is parked on a decline (i.e., front wheels at lower elevation than rear wheels), the weight that the rear wheels of the vehicle will be experiencing may be significantly reduced or the rear wheels are located on a lower friction surface (e.g., gravel, snow, ice). This will depend in large part on the severity of the angle of decline. In such instances the front wheels of the vehicle12may be experiencing significantly added weight (e.g., well more than 50% of the vehicle's total curb weight), which may make performing braking using the front brakes32significantly more advantageous than using the rear brakes30.

The system10takes advantage of this condition by using the controller16and its associated software18to first detect when the EPB subsystem22is active. This detection may be accomplished by the controller16recognizing a signal or command that has been transmitted on the CAN bus20by the EPB subsystem22. The controller16may control or command the AWD system14to signal the transaxle28to apply a counter torque to a pair of front axles34associated with the transaxle28. The counter torque applied to the front axles34is a torque that counteracts the torque being experienced by the front axles34as a result of the vehicle being on a decline. The counter torque acts as a braking force, applied by the front axles34, on the front wheels36of the vehicle12. This, coupled with the added weight being experienced by the front wheels36as a result of the vehicle12being on a decline, provides a potential braking force to the front wheels36. Thus, a braking force may be applied to the front wheels36by the AWD system14while a braking force is applied to the rear wheels31by the EPB subsystem22. The braking force applied to the front wheels36by using the AWD system14may be especially helpful if the vehicle is parked on a slight grade (i.e., slight decline), where the rear wheels are on a low friction surface (e.g., snow) and the front wheels are on a high friction surface (e.g., dry pavement).

It will be appreciated that the system10could be modified so that the on-board vehicle computer24recognizes a message or command on the CAN bus that the EPB subsystem22is being engaged to brake the rear wheels31, or alternatively if the on-board computer24or the ABS26determines that the EPB subsystem22should be applied. In either instance, the on-board vehicle computer24may command the AWD system14to apply the counter torque to the front axles34. Put differently, the sensing action which determines the need for the AWD system14to generate the counter torque can be performed either by the AWD system14itself, as depicted inFIG. 1and described in detail above, or by the on-board vehicle computer24, or potentially by some other sensing device/subsystem.

The system10may also be configured to apply a counter torque to the front axles34and/or rear axles38(seeFIG. 1) of the vehicle12in real time during an emergency braking situation, or possibly if a condition is detected in which the front brakes32or rear brakes30fail while the vehicle12is moving. By applying a counter torque while some limited braking of the vehicle12is taking place, this action may augment the action of the ABS26and thus potentially help to bring the vehicle12to a controlled stop.

Still another potential application of the teachings of the present disclosure may be in connection with aiding the driver during hill-start situations. At the present time some vehicle manufacturers provide a feature that allows the driver to remove his/her foot from the brake pedal and have the vehicle remain stationary for a limited, calibratable amount of time. This can be helpful in allowing the driver to better begin transitioning the vehicle from a parked condition up to a cruising speed when the vehicle begins moving up or down a hill. This function may be implemented by having the hydraulic brakes active for a calibratable amount of time, and then having the vehicle's EPB system engage to keep the vehicle stationary. This “brake-hold” function could be enhanced by using the system10so that the vehicle's AWD system applies a counter torque to the front axles when the EPB is active. This would allow for the potential transfer of the EPB torque to the front axles, depending on conditions. This feature would allow the driver to transition his/her foot from the brake pedal to the throttle pedal, without vehicle roll-back. In the case of a manual transmission vehicle, this would allow the driver to remove his/her foot from the brake pedal to use the vehicle's clutch and throttle pedal without vehicle roll-back.

With brief reference toFIG. 2, a graph100is shown to illustrate the potential braking enhancement that may be achieved using the system10when initiating a braking event at various speeds. The curves102,104and106shown on the graph100were generated using CARSIM® mechanical dynamic simulation software which is available from Mechanical Simulation Corporation of Ann Arbor, Mich. Curve102illustrates the stopping distance for a 4Wheel ABS equipped vehicle. Curve104illustrates the stopping distance using just the vehicle's EPB system, and curve106illustrates the stopping distance using both the vehicle's EPB system and the system10of the present disclosure. In this simulation, the stopping distance has been reduced by more than 30 meters, which is a significant reduction in stopping distance.

Referring toFIG. 3, a graph200is shown which illustrates curves202,204and206to illustrate an estimated reduction in braking time (in seconds) to bring a vehicle to a dead stop after a braking event is initiated. Curve202represents the estimated braking time using only the vehicle's 4Wheel ABS system. Curve204represents the estimated braking time using the vehicle's EPB system, and curve206represents the estimated braking time when using both the vehicle's EPB system and the system10of the present disclosure. Again, a significant time reduction is experienced (about 5 seconds) when the system10is used to help brake the vehicle.

FIG. 4shows a flowchart300to illustrate one example of various operations that may be performed by the system10. At operation302sensing for activation of the vehicle's EPB subsystem22is performed. This may be performed in any suitable manner, for example by sensing for appropriate signals transmitted on the vehicle's CAN bus20from the EPB subsystem22. Sensing may be performed by the AWD system14, the on-board vehicle computer24or a different subsystem.

At operation304the vehicle's AWD system14is controlled to apply a counter torque to the front axles34of the vehicle's transaxle28. At operation306disengagement of the EPB subsystem22is detected. Again, this detection may be accomplished by the AWD system14, or possibly by the on-board vehicle computer24or by different subsystem of the vehicle12. At operation308the AWD system14is controlled to remove the counter torque. At operation310, torque control may be returned to the AWD system14that is not dependent on the EPB state (i.e., torque control may or may not be applied by the AWD system14depending on vehicle conditions). Again, it will be appreciated that the sensing actions, as well as the activation and removal of the counter torque, are carried out in real time.

The present system10and methodology of operation described herein thus enables an AWD system to be used to apply a counter torque to the axles of a vehicle to enhance a braking action on the vehicle's wheels when the EPB subsystem of the vehicle is activated. While the various embodiments have been described in connection with applying a counter torque to the front axles of a transaxle, it will be appreciated that the present disclosure could readily be implemented such that the AWD system applies a counter torque to all four axles of a vehicle (i.e., both pairs of front and rear axles), or possibly to either just the front axles or just the rear axles, depending on specific conditions. The system10of the present disclosure could also be configured such that the AWD system14applies a ramped up counter torque, or a modulated counter torque, or possibly even both, to best meet the needs of a particular driving situation.