Patent Application
20070222287
The present invention relates to an automotive vehicle having both a friction braking subsystem and a regenerative braking subsystem, as well as at least one software-based controller for running the braking subsystems in a series configuration during normal operation, and in a parallel configuration in the event that a brake system controller becomes inoperative.
Vehicles having either full or partial electrodrive capability, such as purely battery powered vehicles on the first hand, and hybrid gasoline-electric vehicles on the other hand, typically utilize regenerative braking as a principal means for enhancing vehicle fuel economy. Regenerative braking is almost always combined with friction braking, because regenerative braking is usually not adequate for all situations, for a host of reasons.
A principle reason militating in favor of supplementing regenerative braking with friction braking exists because regenerative brakes are usually not available on all of the wheels of a vehicle. This is simply due to the fact that motor drives are usually applied to only one axle of a vehicle. On the other hand, friction brakes are readily applied to all the wheels of the vehicle. A second reason limiting the capability of regenerative brakes deals with the need to store energy. Thus, if a battery is fully charged, the regenerative system cannot be employed unless a resistance load bank is incorporated within the vehicle at added cost, weight, complexity and thermodynamic load. Also, regenerative braking in some modes is limited by the status of the heat build within the traction motor.
Vehicles having regenerative friction braking subsystems may be operated either as a parallel system, in which both the friction and regenerative brakes are applied simultaneously, or as a series system, in which regenerative brakes are applied first, followed by friction braking to fill in the required braking amount. The term “coordinated braking” is sometimes used to refer to series braking. In general, parallel braking systems are less expensive, but suffer from inferior brake pedal feel, including inconsistent brake pedal feel. Parallel systems also offer a lesser fuel economy improvement than do series braking systems. Series braking systems on the other hand, offer, albeit at a higher price, a better, more consistent, pedal feel and more regenerative capability, which yields a higher fuel economy improvement. In addition, series systems require coordinated braking control between the friction brake actuator controllers(s) and the powertrain actuator controller(s).
Vehicle systems designers have attempted to provide controls to prevent lock up of driving wheels due to regenerative braking system operation, as well as control of regenerative and friction braking systems so as to present a transparent operating characteristic to the operator of a vehicle. U.S. Pat. No. 6,724,165 and U.S. Pat. No. 6,655,754 illustrate typical regenerative braking systems.
The present invention deals with an issue tied to the use of braking systems having regenerative and friction subsystems. Namely, in the event that the controller required for the coordination of the friction brakes and the regenerative brakes becomes inoperative, regenerative braking becomes unavailable. Such inoperativeness could be due to loss of a communication link between controllers of the friction brake subsystem and the powertrain control module, or for a variety of system fault reasons. The present system operates friction braking and regenerative braking subsystems in a parallel fashion using only a powertrain control module to operate the regenerative braking in the event that a brake system control module becomes inoperative.
An automotive regenerative and friction braking system includes a friction braking subsystem having at least one power absorber and a plurality of braking system sensors. A brake system control module operates the friction braking subsystem. A regenerative braking subsystem is operated by at least one powertrain control module which is operatively connected with the brake system control module. The powertrain control module operates the regenerative braking system according to commands including at least one command, or other information, from the brake system control module. A software routine sited within the powertrain control module operates the regenerative braking subsystem in parallel with the friction braking subsystem in the event that either coordinated braking becomes inoperative, or the brake system control module exhibits degraded control over friction braking. Those skilled in the art will appreciate in view of this disclosure that a powertrain module useful for practicing the present invention could comprise either a traditional powertrain control module for controlling operating parameters such as fuel delivery, spark timing, gear selection, torque converter lockup and other variables, or an engine torque and brake controller primarily used for other purposes, such as an adaptive cruise control module.
The software routine within the powertrain control module uses an output of at least one braking parameter sensor to control the regenerative braking subsystem in the event that the brake system control module becomes inoperative. The sensor output used by the software routine may include output from a motorist-controlled device such as a brake pedal switch, a brake pedal position sensor, or a friction braking system pressure sensor.
According to another aspect of the present invention, a method for operating an automotive regenerative and friction braking system includes the steps of normally operating a friction braking subsystem and a regenerative braking subsystem in a series configuration using a brake system control module and a powertrain control module. The friction braking subsystem and the regenerative braking subsystem are operated in a parallel configuration under the sole control of a control module independent of the brake module, such as a powertrain control module, in the event that the brake system control module is inoperative. The powertrain control module receives input from a plurality of vehicle sensors including at least a braking parameter sensor.
In addition to operating at least one traction motor attached to an associated traction battery, a powertrain control module according to present invention may also operate an internal combustion engine shown at 40 in
It is an advantage of a method and system according to the present invention that regenerative braking may be maintained on a vehicle having both regenerative and friction braking capability, even if coordinated braking becomes inoperative or the brake system control module exhibits an indication of degraded friction braking performance capability.
It is a further advantage of a method and system according to the present invention that a vehicle operating according to this method will maintain regenerative operation at a safe level notwithstanding the absence of an effective brake system controller.
It is yet another advantage of a method and system according to the present invention that a redundant braking system is provided, so as to increase the availability of braking notwithstanding control system malfunctions.
Other advantages, as well as features and objects of the present invention, will become apparent to the reader of this specification.
As shown in
Brake system control module 12 communicates with powertrain control module 24, which is operatively connected with traction motor 28, traction battery 36, and a plurality of sensors, 32. The functions of brake system control module 12 and powertrain control module 24 may be housed within any control module(s) which coordinate brake control between the regenerative and friction braking subsystems. Thus, one of the duties of powertrain control module 24 is to function as a regenerative control module. This duty could be handled by another control module, such as a freestanding, dedicated regenerative controller. This detail is consigned to those wishing to employ the present invention.
At least some of sensors 20 may be the same as sensors 32. In other words, the sensors are shared by the regenerative and friction braking subsystems. The regenerative braking subsystem includes at least traction motor 28 and traction battery 36. Powertrain control module 24 operates in response to commands from brake system control module 12 during normal, or series, operation of the present regenerative and friction braking system. In the event that brake system control module 12 exhibits an indication of degraded brake system control capability, or if communication is lost between brake system control module 12 and powertrain control module 24, such as because of a wiring fault, or if brake system control module 12 ceases to function, powertrain control module 24 will initiate operation of the braking system in a parallel function. In essence, a software routine sited within powertrain control module 24 operates the regenerative braking subsystem in parallel with the friction braking subsystem.
Operation of the present system in a parallel mode is facilitated by at least one braking parameter sensor which may or may not be shared by the friction and regenerative braking subsystems. Such a sensor, which preferably comprises a brake pedal position sensor, or a brake system pressure sensor, both of which may be included in sensor groups 20 and 32, produces a signal which is indicative of the extent to which a motorist has either depressed a brake pedal in a vehicle, or otherwise requested braking, such as by activating a retarder switch. This information is communicated to powertrain control module 24, which uses the information as an indication of the extent to which the regenerative braking subsystem should be applied. This is shown in
If module 12 is operative at block 52, the system operates according to series braking rules at block 54. If, however, brake system control module 12 is not operative, the routine moves to block 56.
At block 56 the controller gives a command to operate according to parallel braking rules. Then, at block 58 at least one friction brake operating parameter is sensed and at block 60, the value of this operating parameter is used by powertrain control module 24 to operate the regenerative braking system. Then, the routine continues at block 62.
When the present braking system is being operated by powertrain control module 24, a true parallel system is in operation, because the brake line hydraulic pressure created by a motorist pressing on the brake pedal is allowed to flow through to at least one of friction brakes 16, while powertrain control module 24 simultaneously provides control of the regenerative braking system. A shared or independent sensor feature, as described above, allows the powertrain control module to use brake pedal position as an input variable.
Although the present invention has been described in connection with particular embodiments thereof, it is to be understood that various modifications, alterations, and adaptations may be made by those skilled in the art without departing from the spirit and scope of the invention set forth in the following claims.
