An automotive hill descent control includes a friction-braking subsystem and a non-friction braking subsystem with engine-based braking and regenerative braking. The regenerative and engine-based braking systems may be controlled according to the position of a manual switch, as well as inversely proportionally to the slope upon which a vehicle is being operated, and according to the speed of the vehicle
According to an embodiment of the present invention, an automotive braking system includes a friction braking subsystem, a non-friction braking subsystem, and an incline detection system for determining when a vehicle equipped with the present braking system is being operated on an incline. In several embodiments, the incline sensor system further determines the magnitude of an incline.
A controller operates the non-friction braking subsystem based upon at least the output of the incline detection system. The controller provides a first maximum amount of non-friction braking when the vehicle is being operated upon a surface having an inclination less than a predetermined threshold inclination, as detected either by the vehicle's operator, or by a sensor, and a second maximum amount of non-friction braking when the vehicle is being operated on a surface having an inclination greater than the predetermined threshold inclination. The second maximum amount of non-friction braking is generally less than the first maximum amount of non-friction braking. In an embodiment of the invention, the second amount of non-friction braking may be generally inversely proportional to the magnitude of an incline upon which the vehicle is being operated, or may be a fixed amount of maximum non-friction braking.
According to another aspect of the present invention, a non-friction braking system may include a regenerative braking system and an engine-based braking system. A vehicle speed sensor may be operatively connected with the controller, to permit the controller to operate the engine-based braking system so as to limit engine and/or regenerative braking at speeds below a predetermined speed threshold.
In another embodiment according to the present invention, the controller limits both engine braking and regenerative braking at speeds below a predetermined speed threshold.
According to another embodiment of the present invention, a second maximum amount of non-friction braking, which is employed in the event that the vehicle is being operated at an incline greater than a predetermined threshold, is a null, or zero amount of regenerative braking.
According to another aspect of the present invention, a method for operating an automotive braking system having a friction braking subsystem and a non-friction braking subsystem including an engine-based braking system and a regenerative braking system includes: detecting operation of a vehicle equipped with the braking system upon an incline, including detecting the magnitude of the incline, and providing a first maximum permissible amount of non-friction braking when a vehicle equipped with the braking system is being operated upon a surface having a magnitude of inclination less than a first predetermined threshold inclination, while providing a second maximum permissible amount of non-friction braking when the vehicle is being operated upon a surface having a magnitude of inclination greater than the first predetermined threshold. The second maximum permissible amount of braking is less than the first maximum permissible amount of braking, and the second amount may be reduced to zero in the case of both the engine-based braking system and regenerative braking system.
The present hill descent control system provides the advantage that wheel slip due to both engine-based braking and regenerative braking is avoided.
The present hill descent control system advantageously uses well-established friction braking techniques at higher angles of inclination, so as to provide well-modulated descent control.
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