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HILL LAUNCH ASSIST (HLA)

HILL LAUNCH ASSIST (HLA)

SM2334034

id041500104700



Purpose/Function

• The hill launch assist (HLA) is a function which assists the driver in accelerating the vehicle on a slope by activating the traction control solenoid valve in the DSC HU/CM when the vehicle begins accelerating on a slope, and maintaining/reducing brake fluid pressure to prevent the vehicle from rolling for a specified time.
• 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)

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)
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• The selector/shift lever position is in the R position, the hill launch assist (HLA) operates on a downslope.
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• The hill launch assist (HLA) operates constantly without affecting the DSC OFF switch operation.
• When the parking brake is applied, the hill launch assist (HLA) does not operate.
• When the DSC HU/CM has malfunction, the hill launch assist (HLA) does not operate.



Structure

• The hill launch assist (HLA) constantly controls the brake fluid pressure in accelerating the vehicle on a slope by determining the hill launch assist (HLA) operation based on the signals input from each module via CAN communication, wheel speed signals from the ABS wheel-speed sensor.

Block diagram
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Hydraulic circuit diagram
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Operation

• If all of the following conditions are met while the vehicle is stopped on a slope, the DSC HU/CM performs controls to maintain brake fluid pressure (control the traction control solenoid valve) even if the driver has released the brake pedal.


Hold control

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

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
― The highest brake fluid pressure is maintained as the maximum hold pressure while fluctuating.
― 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).
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― When releasing the brake pedal, the brake fluid pressure (stored 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.
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Slow release control

• Control condition (one or more of following conditions are met):
― Parking brake applied
― Clutch pedal released (MTX)
― Shift lever is in neutral position (MTX)
― Selector lever is in P or N position (ATX)
― DSC HU/CM has malfunction (performs slow release control only if solenoid valve control is available)
― 0.2 s has elapsed on slope of 1.0 % or less
― Approx. 1.5 s (MTX) or approx. 2 s (ATX) has elapsed after the driver releases the brake pedal during hold control
• Control description
― Maintained brake fluid pressure is decreased gradually
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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