HILL LAUNCH ASSIST (HLA)

id041500104700

Purpose/Function

• The Hill Launch Assist (HLA) functions to assist in accelerating the vehicle from a stop on uphill slopes. When the vehicle is held at a stop by depressing the brake pedal on a slope with a grade of 6% or more, the brake fluid pressure is maintained even after the foot is released from the brake pedal to prevent the vehicle from rolling backwards. However, during i-stop control (engine off), the Hill Launch Assist (HLA) does not operate. Instead, the Vehicle Roll Prevention Function operates.

ac5wzn00001120

ac5wzn00001121

• The system automatically operates when the vehicle is stopped on a slope of approx. 3 % or more (changes slightly depending on load and vehicle conditions such as tire wear and air pressure). (MTX)

• The system automatically operates when the vehicle is stopped on a slope of approx. 6 % or more (changes slightly depending on load and vehicle conditions such as tire wear and air pressure). (ATX)

Structure

Block diagram

ac5wzn00001122

Hydraulic circuit diagram

ac5wzn00000248

Operation

• If all of the operationg conditions are met while the vehicle is stopped on a slope, the Hill Launch Assist (HLA) maintains brake fluid pressure to maintain vehicle stop condition (hold control).

• After the accelerator pedal is depressed, the required engine torque for accelerating vehicle on a slope is produced, the Hill Launch Assist (HLA) decreases brake fluid pressure according to road slope and engine torque for smooth startability. (release control)

• If the DSC system malfunction occurs, the Hill Launch Assist (HLA) operates the the slow release control or the fast release control depending on malfunction contents.

Note

• The shift lever position is in the other than R position, the Hill Launch Assist (HLA) operates on a upslope. (MTX)

• The selector lever position is in the D/M position, the Hill Launch Assist (HLA) operates on a upslope. (ATX)

• The selector/shift lever position is in the R position, the Hill Launch Assist (HLA) operates on a downslope.

• The Hill Launch Assist (HLA) operates constantly without affecting the TCS OFF switch operation.

• When the parking brake is applied, the Hill Launch Assist (HLA) does not operate.

• When the DSC indicator light illuminates, the Hill Launch Assist (HLA) does not operate.

Hold control

• Control conditions (all of the following conditions met):

― Engine speed is at a certain value or more

― All doors are fully closed

― Slope of approx. 3 % or more (MTX)

― Slope of approx. 6 % or more (ATX)

― Wheel speed is 0 km/h {0 mph}

― Parking brake not operated

― Accelerator pedal not depressed

― Not fail-safe mode is present

― Upslope: The selector lever position is in the D/M position (ATX)

― Upslope: The shift lever position is in the position other than R (MTX)

― Downslope: The selector/shift lever position is in the R position

― Brake pedal is depressed and brake fluid pressure is at a certain value or more

― Clutch pedal depressed (MTX)

• Control description:

― If all of the control conditions are met, the DSC HU/CM controls the traction control solenoid valve and maintains brake fluid pressure (driver can depress brake pedal more at this time)

ac5uun00000974

― If the brake pedal is released, brake fluid pressure (hold-pressure stored in memory) is maintained for a maximum of 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 condition (one or more of following conditions are met):

― Parking brake applied

― Clutch pedal released (MTX)

― DSC HU/CM has malfunction (performs slow release control only if solenoid valve control is available)

― Slope of 1.0 % or less (MTX)

― Slope of 4.0 % or less (ATX)

― 2 s have elapsed with brake pedal released

• Control description

― Brake fluid pressure being maintained is lowered in 1 s

ac5wzn00000251

Fast release control

• Control condition

― DSC HU/CM has malfunction and solenoid valve control is not available

• Control description

― Brake fluid pressure being maintained is reduced to 0 kPa {0 mmHg, 0 inHg} immediately