Mazda CX-5 Service & Repair Manual: Hill Launch Assist (Hla)

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)

    

    
    

  • 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.

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

Hydraulic circuit diagram

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 linear control solenoid valve) even if the driver has released the brake pedal.

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).

  

  
  

• 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.

  

  
  

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)

• 0.2 s has elapsed on slope of 1.0 % or less

• 2 s have elapsed with brake pedal released

• Control description

• Brake fluid pressure being maintained is lowered in 1 s

  

  
  

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