The higher is the volume of automated transmissions for high load capacity commercial vehicles in the market, the higher is the necessity to develop auxiliary systems capable to reduce the wear of the clutch disc during start-ability performance in slopped plans. The Hill Start Assist System, HSA, is compounded by a set of components in the brake system, disposed in such a way that provides to the driver the possibility of starting to run with comfort and safety by the actuation of the service brakes, without overheating the clutch system and simultaneously avoiding the undesirable effect of composition roll-back. For this, it is only necessary that the vehicle be equipped, besides automated transmission, Anti-lock Braking System, ABS, and an active traction control in, at least, one of the drive axles. The proposal of this work is to present a Hill Start Assist System specially developed to work with an extremely simple electrical and pneumatic logics, by the direct control of the drive axle service brakes and the indirect control of all of the remaining brakes of the vehicle. The system, by the communication with the ABS control unit, keeps the brake forces on the wheels exactly as requested by the driver, without necessity of keeping the brake pedal actuated, during the time necessary for the vehicle to be ready for the start. With this type of configuration, the efficiency of the HSA becomes independent of the grade of the slope, adhesion between tires and road and the temperature of the brakes. It is also presented in this work, technical characteristics of the valves that are part of the pneumatic circuit, its electrical and pneumatics logics and tests, including field durability evaluation and bench tests. Auxiliary devices such as the HSA, certainly add perceptible values to the final customers. This is extremely important in competitive markets, where the comfort and safety are characteristics that are been sought much more than any other.
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