Patent Application
20080079311
These and other features and advantages of the invention will be apparent from the following detailed description and the appendant claims, taken in conjunction with the accompanying drawings, in which:
By way of example, a preferred system and methodology for implementing the present invention is described below. The provided system and methodology may be adapted, modified or rearranged to best-fit a particular implementation without departing from the scope of the present invention.
The generator 14 can also be used as a motor, outputting torque to a shaft 26 connected to the sun gear 24. Similarly, the engine 12 outputs torque to a shaft 28 connected to the carrier 20. In one embodiment, the shaft 28 is comprised of two separate shafts that are coupled together by the damper (not shown). Having the generator 14 operatively connected to the engine 12, as shown in
The ring gear 18 is connected to a shaft 34, which is connected to vehicle drive wheels 36 (i.e., rear wheels) through a second gear set 38. As recognized by one of ordinary skill, wheels 36 are mechanically connected to a rear axle 36 in a known manner. Additionally, a front axle 37 is mechanically connected to a set of front wheels 33 located on vehicle 10. Wheels 33 are responsive to a steering device 15, which is also connected to axle 37 via a steering shaft.
As recognized by one of ordinary skill, a steering sensor (not shown) may be included in the steering system of vehicle 10. The steering sensor is configured to sense the positioning and re-positioning of steering device 15. Accordingly, when a vehicle operator steers (i.e., positions or re-positions steering device 15) the vehicle 10, a steering command signal is generated through the use of steering device 15 and the steering sensor. As will be described hereinafter, a controller 50 receives and processes the steering command signal in accordance with the present invention.
It is also recognized that in alternative embodiments, the present invention may include steer-by-wire systems without departing from the scope of the present invention. Additionally, it is recognized that the steering system shown on vehicle 10 may include four wheel steering. In such an embodiment, depending upon the steering command signals, wheels 33 and 36 are both configured to respond to the vehicle operator's steering inputs. As used herein, the term “steering” includes, but is not limited to, a change in the vehicle's steered wheels in response to a driver's input. The term “turning” includes, but is not limited to, a change in the vehicle's direction, which may occur independent of the driver's input.
A friction braking system is located on vehicle 10, which includes a brake pedal 30, a braking distribution device 32, a brake disc 41, and a brake caliper 43. Upon engagement of the friction braking system via brake pedal 30, the braking distribution device 32 distributes braking fluid to each braking caliper 43. In response, the caliper 43 exerts braking forces on brake disc 41, thereby causing vehicle 10 to decrease speed or stop. Alternatively, the friction braking system may be embodied as a brake-by-wire system.
In the brake-by-wire embodiment, the braking distribution device 32 may have electronics integrated therein and function as a controller. Accordingly, the braking distribution device 32 generates signals that control the application of friction braking force to wheels 33 and 36. Particularly, in the event a reduction in regenerative braking force occurs, the braking distribution device 32 may generate signals that cause an increase in the applied friction braking force. In one aspect of the invention, the friction braking force is increased an amount that is substantially equal to the amount the regenerative braking force is reduced. Preferably, the increase in friction braking force occurs on an axle other than the axle upon which the regenerative braking force is reduced. It is also recognized that braking distribution device 32 may be configured to cause engagement of the friction braking system independently of whether the brake pedal is engaged.
Vehicle 10 also includes a second electric machine, or motor 40, which can be used to output torque to a shaft 42. Other vehicles within the scope of the present invention may have different electric machine arrangements, such as more or less than two electric machines. In the embodiment shown in
The battery 46 is a high voltage battery that is capable of outputting electrical power to operate the motor 40 and the generator 14. Other types of energy storage devices and/or output devices can be used with a vehicle, such as the vehicle 10. For example, a device such as a capacitor can be used, which, like a high voltage battery, is capable of both storing and outputting electrical energy. Alternatively, a device such as a fuel cell may be used in conjunction with a battery and/or capacitor to provide electrical power for the vehicle 10.
As shown in
It is recognized that although the vehicle 10 is an HEV, it is understood that the present invention contemplates the use of other types of vehicles. In addition, although the vehicle 10 shown in
In both preferred and alternative embodiments, the controller 50 may be a combination vehicle system controller and powertrain control module (VSC/PCM). Although it is shown as a single hardware device, it may include multiple controllers in the form of multiple hardware devices, or multiple software controllers within one or more hardware devices.
A controller area network (CAN) 52 allows the controller 50 to communicate with the transaxle 48 and a battery control module (BCM) 54. Just as the battery 46 has the BCM 54, other devices controlled by the controller 50 may have their own controllers. For example, an engine control unit (ECU) may communicate with the controller 50 and may perform control functions on the engine 12. In addition, the transaxle 48 may include one or more controllers, such as a transaxle control module (TCM) 56, configured to control specific components within the transaxle 48, such as the generator 14 and/or the motor 40.
As stated above, controller 50 in combination with TCM 56 are configured to determine the occurrence of a braking imbalance between the braking forces being applied to wheels 33 and 36. The braking imbalance may be caused by an undesirable distribution of braking between wheels on opposite axles (e.g., axles 35 and 37). Upon determination of a braking imbalance, when the vehicle is traveling at or above a speed threshold (e.g., 10 miles per hour), controller 50 generates signals that cause a reduction in the amount of regenerative braking forces being applied to wheels 36 until a braking balance between the wheels 33 and 36 is achieved. Additionally, in combination with reducing the amount of regenerative braking force applied to one set of wheels (e.g., wheels 36 attached to axle 35), the friction braking force applied to wheels on another axle (e.g., wheels 33 attached to axle 37) may be increased to achieve the braking balance.
As shown in
In one embodiment, controller 50 contains a braking distribution map that has data pertaining to levels of braking forces generated by the friction and regenerative braking systems. The braking distribution map provides a braking tolerance band that may be used to indicate and achieve a braking balance. In one aspect of the present invention, an acceptable braking balance includes a variance in the amount of friction and regenerative braking forces being applied to wheels 33 and 36.
Regarding the braking distribution map, which may be embodied as a table of data stored within controller 50, it includes data indicating ideal relative braking levels for the vehicle axles (i.e., axles 35 and 37). Accordingly, when the vehicle operator engages the friction brakes via brake pedal 30, the controller 50 determines whether a braking imbalance exists based on the ideal relative braking levels and/or braking tolerances as provided by the braking distribution map. Controller 50 then generates signals to obtain appropriate levels of regenerative braking and/or friction braking that will reduce braking imbalances between wheels 33 and 36. Additionally, it is recognized that in some embodiments, controller 50 may determine the presence of a braking imbalance irrespective of whether the brake pedal 30 is engaged, so long as the vehicle is traveling at a speed greater than the speed threshold.
In some cases of braking imbalance, the vehicle's steerability and stability may be affected. Thus, as stated above, controller 50 is adapted to receive and process steering command signals while determining whether a braking imbalance exists. In one aspect of the present invention, the steering command signals may be processed to determine a steering angle of at least one of the steering device 15 and wheels 33 (and wheels 36 in alternative embodiments). As such, the controller 50 may generate a time filtered value for the steering angle, which may be utilized by the controller 50 to determine how much turning is occurring in addition to determining whether the braking imbalance exist.
As indicated above, in conjunction with monitoring the application of regenerative and friction braking forces, the controller 50 detects and processes the steering command signals generated via the steering system. The steering command signals may be monitored to determine whether the vehicle 10 is actually turning. In such an embodiment, the controller 50 determines the existence of the braking imbalance when the vehicle 10 is entering or experiencing a turn as indicated by the steering command signals.
Furthermore, controller 50 may also detect steering or turning of the vehicle by determining and processing an angular rotation rate or lateral acceleration of the vehicle. The angular rotation rate or lateral acceleration may also indicate the vehicle's level of turning. In other aspects of the present invention, the turning may be detected by evaluating the speed difference between wheels on the same axle (e.g., axle 35 or 37). If a braking imbalance is detected based on the distribution of friction braking forces and the regenerative braking forces along with a detection of steering commands and/or vehicle turning, the controller 50 generates signals that cause a reduction in regenerative braking forces to achieve a braking balance. Optionally, in conjunction with the reduction in regenerative braking forces, the friction braking forces applied to an axle other than the axle receiving the regenerative braking forces may be increased.
In alternative embodiments, controller 50 may contain one or more braking function algorithms that also provide the braking tolerances for controller 50 to determine the existence of a braking imbalance and a desired braking distribution between wheels 33 and 36. In such an embodiment, controller 50 may have, in memory, a braking function embodied as a mathematical expression containing variables for vehicle speed, relative wheel speeds (i.e., for wheels 33 and 36), friction braking, regenerative braking, and steering angle. Based on calculations through the use of the braking function and the foregoing variables, the existence of a braking imbalance and an appropriate braking force distribution may be determined.
Referring now to
As depicted by block 66, the method determines an ideal rear brake torque and the tolerance band for optimal levels of front and rear braking. As shown by block 68, the method determines whether the rear brake torque is within the tolerance band. In the embodiments shown, the rear wheels of the vehicle may be the set of wheels designated to receive regenerative braking. It is recognized, that in alternative embodiments, the vehicle may be configured to apply regenerative braking to the front wheels without departing from the scope of the present invention. Nevertheless, if the rear brake torque is within the tolerance band, the method returns to block 62. Alternatively, if the brake torque or force being applied to the rear wheels is not within the tolerance band, block 70 occurs.
At block 70, the controller evaluates the existence of a steering command. Accordingly, as depicted by block 72, the method determines whether or not a steering command is being generated by the vehicle operator. If a steering command is being generated by the operator, block 78 occurs wherein at least one of the regenerative braking and the friction braking is adjusted until an acceptable braking balance is achieved. In one embodiment, the regenerative braking is reduced at one axle while the friction braking being applied to an opposite axle is increased to achieve the braking balance.
However, if the steering command is not being generated, block 74 occurs wherein the method determines if the vehicle is actually turning. If the vehicle is turning, the block 78 occurs, wherein the regenerative braking and the friction braking are adjusted until an acceptable braking balance is achieved. If the vehicle is not turning, the method returns to block 62. Following block 78, the method ends at block 80.
While the best mode for carrying out the invention has been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.
