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
approx. 10 % 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.
• The system automatically operates when the vehicle is stopped on a slope of approx. 10 % or more (changes slightly depending on load and vehicle conditions such as tire wear and air pressure).
Structure
Block diagram
Hydraulic circuit diagram
Operation
• If all of the operation 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 slow release control or the fast release control depending on malfunction contents.
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Note
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• The selector lever position is in the D/M position, the Hill Launch Assist (HLA) operates on a upslope.
• The selector 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
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• Control conditions (all of the following conditions met):
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― Engine speed is at a certain value or more
― All doors are fully closed
― Slope of approx. 10 % or more
― 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
― Downslope: The selector lever position is in the R position
― Brake pedal is depressed and brake fluid pressure is at a certain value or more
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• Control description:
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― 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)
― If the brake pedal is released, brake fluid pressure (hold-pressure stored in memory) is maintained for a maximum of 2 s.
Release control
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• Control condition:
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― After the accelerator pedal is depressed, the required engine torque for accelerating vehicle on a slope is produced
• Control description:
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― Brake fluid pressure being maintained is lowered depending on produced engine torque.
Slow release control
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• Control condition (one or more of following conditions are met):
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― Parking brake applied
― DSC HU/CM has malfunction (performs slow release control only if solenoid valve control is available)
― The selector lever position is in the P/N position
― The vehicle is stopped on a downslope of approx. 8 % or less when the selector lever position is in the R position
― The vehicle is stopped on flat road or upslope when the selector lever position is in the R position
― The vehicle is stopped on a upslope of approx. 8 % or less when the selector lever position is in the D position
― The vehicle is stopped on flat road or downslope when the selector lever position is in the D position
― 2 s have elapsed with brake pedal released
• Control description
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― Brake fluid pressure being maintained is lowered in
1 s
Fast release control
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• Control condition
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― DSC HU/CM has malfunction and solenoid valve control is not available
• Control description
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― Brake fluid pressure being maintained is reduced to 0 kPa {0 mmHg, 0 inHg} immediately
