HILL LAUNCH ASSIST (HLA)

id041900702200

Purpose, Function

• Hill Launch Assist (HLA) functions to assist in accelerating the vehicle from a stop on uphill slopes. When the vehicle accelerates from a stop on a slope, the brake fluid pressure is maintained/decreased to prevent the vehicle from rolling backwards by operating the pressure feed valve built into the electronically controlled brake unit.

• Hill Launch Assist (HLA) operates automatically when the vehicle is stopped on a slope with a grade of approx. 6% (grade on which system operates changes slightly depending on vehicle conditions such as load, tire wear, tire air pressure).

Note

• Hill Launch Assist (HLA) operates when the selector lever is in the D (forward)/R (reverse) position.

a30zzn00001457

a30zzn00001458

• Hill Launch Assist (HLA) operates continuously without effect on the TCS OFF switch / Off-Road Traction Assist switch operation.

• While the electric parking brake is operating, Hill Launch Assist (HLA) does not operate.

• If a malfunction occurs in the DSC system, Hill Launch Assist (HLA) does not operate.

Construction

• Hill Launch Assist (HLA) controls the brake fluid pressure constantly when on a slope. This control is performed based on the signal input from each module via CAN communication and the wheel speed signal input from the ABS wheel-speed sensor.

Block diagram

a30zzn00001459

Hydraulic circuit diagram

a30zzn00001591

Operation

• When all of the following control conditions are met while the vehicle is stopped on a slope, the electronically controlled brake unit controls the linear actuator and maintains the brake fluid pressure even after the driver’s foot is released from the brake pedal.

• If a malfunction occurs in the DSC system during hold control, the electronically controlled brake unit decreases the brake fluid pressure immediately.

Hold control

• Control conditions (all of the following conditions must be met)

― The road inclination is approx. 6%.

― The wheel speed is 0 km/h {0 mph}.

― The parking brake is not operating.

― The accelerator pedal is not depressed.

― Forward: Selector lever is in D position

― Reverse: Selector lever is in R position

― The brake fluid pressure of a certain value or more is input after depressing the brake pedal.

• Control description

Note

• Brake fluid pressure is maximum hold pressure or more

― If the brake fluid pressure decompresses to the maximum hold pressure when the driver releases the brake pedal without performing hold control, the brake pedal pressure is maintained at the maximum hold pressure position.

• Brake fluid pressure fluctuates when it is bellow the maximum hold pressure

― If the brake fluid pressure does not reach the required hold pressure, the electronically controlled brake unit continues to increase the brake fluid pressure to the required hold pressure.

― When all of the following control conditions are met, the electronically controlled brake unit controls the pressure feed valve and maintains the brake fluid pressure. In addition, if the driver depresses the brake pedal and the brake fluid pressure increases, the increased brake fluid pressure is maintained.

a30zzn00001592

― When releasing the brake pedal, the brake fluid pressure (maximum hold pressure) is maintained for maximum of approx. 2 s.

Release control

• Control condition

― After the accelerator pedal is depressed, the required engine torque for accelerating vehicle on a slope is produced

• Control description

― Brake fluid pressure being maintained is lowered depending on produced engine torque.

ac5wzn00000250

Slow release control

• Control conditions (any one or more of the following conditions must be met)

― The parking brake is operating.

― Selector lever is in N position

― 0.2 s have elapsed on a slope with a grade of 1.0% or less.

― Approx. 2 s have elapsed after the driver releases the brake pedal during hold control.

• Control description

― Maintained brake fluid pressure is decreased gradually

a30zzn00001460