The present invention relates to a brake control system. It finds particular application in conjunction with controlling brakes to assist a heavy vehicle backing down a slope and will be described with particular reference thereto. It will be appreciated, however, that the invention is also amenable to other applications.
Heavy vehicles (e.g., trucks) are frequently used in heavy industry and for construction jobs. For example, trucks are commonly used at construction sites for carrying and delivering heavy materials. It is not uncommon that a truck is required to back down a steep sloped surface (e.g., a hill having a grade of 20% to 30%) for unloading the material.
When the truck is backed down a sloped surface, weight is transferred from the front axles to the rear axles. Furthermore, when backing down the slope, the truck is typically traveling at less than about 5 miles per hour (mph). An anti-lock braking system (ABS) is typically designed to be inoperative at speeds less than about 5-6 mph. Therefore, the ABS on a truck backing down a slope likely becomes inoperative or “cuts-out.” Because the ground at a construction site on which a heavy vehicle operates often times includes mud or other substances that may increase the likelihood of wheel slippage, the wheels associated with the steering axle (e.g., the front wheels) tend to lock when the service brakes are applied if the ABS cuts-out. Once the wheels associated with the steering axle lock, the driver's ability to steer the vehicle is impeded. Therefore, it is not uncommon for a driver of a truck backing down a slippery slope at a low speed (e.g., less than about 5 mph) to experience difficulty steering because the wheels associated with the steering axle lock when the service brake is applied.
One method drivers of heavy vehicles currently employ for preventing the wheels associated with the steering axle from locking while backing down a surface having a steep grade includes using the vehicle's hand brake in place of the service brakes to slow down the vehicle. More specifically, the operator does not activate the service brakes by depressing the foot pedal but, instead, activates the hand brake to control the speed of the vehicle. Since hand brakes on heavy vehicles typically only control the rear brakes, the front (steering) wheels do not lock. Therefore, the steering capacity of the vehicle is not degraded by locked wheels on the steering axles.
Although the operator has more control over steering the vehicle, there are drawbacks when using the hand brake to control the vehicle speed under the circumstances described above. For example, high hysteresis associated with use of the hand brake makes it difficult to control the speed of the vehicle. Furthermore, while operating the hand brake, one of the operator's hands cannot be used for steering the vehicle. Therefore, the operator's ability to steer the vehicle is compromised.