Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Indication or control of braking – acceleration – or deceleration
Reexamination Certificate
2000-03-24
2001-08-14
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Indication or control of braking, acceleration, or deceleration
C701S070000, C303S152000, C303S191000, C318S376000, C180S165000, C188SDIG001
Reexamination Certificate
active
06275763
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a regenerative braking system for a motor vehicle used to recapture vehicle kinetic energy during a braking event. More particularly, the present invention relates to a control strategy for a vehicle equipped with both a regenerative braking system and an anti-lock brake system for selectively controlling the regenerative braking effort provided by the regenerative braking system.
DESCRIPTION OF THE RELATED ART
Electric motor vehicles typically incorporate regenerative braking, delivered to the drive wheels by the electric motor, to supplement the friction brake system and to recover a portion of the vehicle's kinetic energy during the braking event to increase vehicle range. Regenerative braking may be applied whenever the driver deactivates the accelerator pedal, sometimes referred to as compression regeneration, and is applied more aggressively when the driver presses the brake pedal, commonly referred to as service brake regeneration.
It is also common in recent years to provide vehicles with anti-lock brake systems adapted to detect and modulate excessive vehicle slip, which typically occurs when the vehicle is operated upon a low coefficient of friction surface. Upon application of the vehicle's friction service brakes and detection of wheel slip, the anti-lock braking system modulates the brake forces applied by the friction brake system, typically by intermittently removing the hydraulic pressure applied to the friction service brakes at a desired frequency and amplitude. This feature prevents the wheels from locking and allows the vehicle driver to maneuver the vehicle during what otherwise would have been a purely skidding event. Since the anti-lock braking system controls only the friction brake system when wheel slip has been detected, service brake and/or compression regeneration must be selectively terminated to give the anti-lock braking system full control of vehicle braking. Thus, the prior solution, employing a constant rate of removal of a fixed regenerative braking effort across all temperatures, was biased toward a cold weather/slick road setting, which required rapid removal of regenerative braking for good anti-lock braking system control.
However, apparent wheel slippage can arise in at least two contexts. In the first context are the events noted above, where the braking force developed by one or more wheels exceeds the available surface friction of the road surface, such as on snow or ice. Anti-lock braking intervention is beneficial in this context because it optimizes braking system performance and improves vehicle control. In the second context are non-slippage events, which occur when the wheel travels over a bump and loses contact with the road surface. Without contact with the road surface, the wheels will rapidly decelerate if braking force is applied. To a vehicle provided with an anti-lock braking system, this rapid acceleration appears as excessive wheel slip. The anti-lock braking system is thus placed in control of the braking event, which leads to an unnecessary termination in service brake regeneration. Also, the undesired harshness of bump activation through an anti-lock braking system is aggravated by the rapid reduction in service brake and/or compression regeneration. Thus, solutions were sought that would allow a reduction in regenerative braking upon activation of an anti-lock braking system during actual slippage, but incorporate a strategy that did not aggravate wheel bump-activation harshness when slippage is erroneously detected.
SUMMARY OF THE INVENTION
According to the present invention, a temperature dependent regenerative braking strategy adapts the regenerative braking parameters based upon the ambient temperature. By employing temperature dependence, the regenerative braking system control provides lower overall regenerative braking levels during cold weather driving and a faster service brake regeneration removal rate (also known as slew-out rate). This provides improved anti-lock braking system control on slick surfaces. The temperature dependence also allows for higher service brake regeneration levels at warmer temperatures, when very slick surfaces are less likely. In addition, a slower slew-out rate employed at warmer temperatures further reduces the harshness of wheel bump activation events.
Thus, a brake system for a motor vehicle has a friction braking system and a service brake regeneration system, controlled by a braking system controller, where the friction brake system is operative upon actuation of a brake pedal by the motor vehicle operator. The friction brake system further includes an anti-skid brake system controlled through the anti-skid braking system controller, in communication with the braking system controller, for selectively controlling braking effort to the wheels upon detection of slippage of one or more wheels relative to the road surface. The service brake regeneration brake system is operated at a first effective applied regeneration braking force upon application of the brake pedal at a temperature above a first predetermined temperature and operative at a second, lower applied regeneration braking force at a temperature below a second predetermined temperature. The service brake and/or compression regeneration system is also controlled to apply a high rate of reduction in the current flow from the electric motor to the battery and applied regenerative braking force at ambient temperatures below a predetermined temperature and a relatively low rate of reduction in current flow to the battery from the electric motor and applied regenerative braking force at ambient temperatures above a predetermined temperature.
In its preferred form, the present service brake regeneration is applied at 100% effectiveness at ambient temperatures above 60° F. and at 10% or less effectiveness at ambient temperatures below 40° F. For ambient temperatures between 60° F. and 40° F., the effectiveness of the service brake regeneration is reduced in a linear relationship with the ambient temperature. Thus, the service brake regeneration is not as biased toward cold weather operation as with previous systems.
Also, the rate at which the service brake and/or compression regeneration is removed as a consequence of wheel slippage is reduced at warmer temperatures, such as above 60° F., where true skidding is less likely to occur. Similarly, the rate at which service brake regeneration is removed is accelerated at a lower temperature, such as below 45° F., where true skidding is more likely to occur. For ambient temperatures between 60° F. and 45° F., the rate of removal of the service brake and/or compression regeneration is gradually increased as the ambient temperature decreases. The result is a system where service brake and/or compression regeneration is removed far more slowly during warmer temperatures, where it is more likely that wheel bounce only is the triggering event for activation of the anti-lock braking system and where application of as high a level of service brake and/or compression regeneration as possible is most desired.
The above brief description sets forth rather broadly the more important features of the present disclosure so that the detailed description that follows may be better understood and so that the present contributions to the art may be better appreciated. There are, of course, additional features of the disclosure that will be described hereinafter which will form the subject matter of the claims appended hereto.
In this respect, before explaining the preferred embodiment of the disclosure in detail, it is to be understood that the disclosure is not limited in its application to the details of the following description or drawings. The regenerative braking system of the present disclosure is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for description and not limitation. Where specific dimensional ma
Lotito David James
Sagan Clement Newman
Xu Jack H.
Beaulieu Yonel
Cuchlinski Jr. William A.
Ford Global Technologies Inc.
Price Heneveld Cooper DeWitt & Litton
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