Brakes and Traction Control: Description and Operation
HILL-HOLDER
The hill-holder is a device to make starting on an uphill road easier and permits even a driver not yet familiarized with starting by use of the parking brake to start the vehicle smoothly. When pressing down the clutch pedal with the brake pedal depressed in order to start the vehicle on an uphill road, this device holds the brake temporarily upon taking your toot off the brake pedal (until the clutch pedal is released). Therefore, smooth starting is enabled by usual engagement of the clutch while depressing the accelerator pedal.
Pressure Hold Valve (PHV)
- PHV (Pressure Hold Valve) is connected to one of the service brake pipes and pushrod (8) is pushed in and/or pulled out by cam shaft (2) interlinked with the clutch pedal to change the clearance between ball (3) and seal (5), thereby opening and/or closing the hydraulic circuit.
Normally, on a flat road, ball (3) is located at the front and the valve is kept opened regardless of the position of the pushrod. (This status is the same as on a downhill road.)
- When stopping the vehicle on an uphill road by depressing both brake and clutch pedals, the ball rolls toward the rear and, at the same time, the pushrod retracts to close the valve, so that hydraulic pressure is maintained. Even when taking your foot off the brake pedal, the hydraulic pressure is maintained so far as the clutch pedal is kept depressed. In this status, when engaging the clutch ordinarily while depressing the accelerator pedal, the maintained hydraulic pressure is released simultaneously with the generation of driving force to permit smooth starting.
Fig. 18 Hill Holder Activated:
Activating Condition
This device is activated only when depressing the clutch and brake pedals with the vehicle stopped on an uphill road.
When stopping the vehicle on an uphill road, the ball rolls toward the rear to seal the port and therefore the hydraulic pressure is maintained even by releasing the brake pedal.
Inactive Status
This accessory is not activated in any status other than the above.
1) While driving
Fig. 19 Hill Holder Deactivated:
(1) During acceleration or usual driving
Since the clutch pedal is not depressed, the pushrod is located outside the port. In this status, hydraulic pressure cannot be maintained.
(2) During deceleration
Even when depressing the clutch pedal, the ball is kept at the front by decelerating force. In this status, hydraulic pressure is not maintained.
2) When stopping
Even when stopping on an uphill road, hydraulic pressure is not maintained unless the clutch pedal is depressed.
3) On a flat road
This device is not designed to operate on a flat road, except for reversing.
Operational Precautions
1) The hill-holder is a device used to facilitate starting on an uphill road. When stopping on an uphill road, therefore, you must keep the brake pedal depressed or pull the parking brake.
2) The hill-holder may not be activated on a slope of an extremely small incline.
3) If the brake is not held sufficiently upon releasing the brake pedal with the clutch pedal depressed, press down the brake pedal a little more strongly once again.
4) If the clutch pedal is depressed again in the course of the starting operation, the brake may be released. In this case, depress the brake pedal again. (Because the brake is released when returning the clutch pedal halfway.) (For example, when interrupting starting operation or shifting gear from other than LOW because of misoperation.)
5) Before you leave the driver's seat, be sure to pull the parking lever and confirm that the vehicle is kept stopped upon releasing the clutch pedal.
6) When reversing the vehicle on a flat road, the following phenomena may be felt. These phenomena are caused by the activation of the hill holder, which does not constitute abnormality.
(1) Brake effect remains even after releasing the brake pedal if depressing the clutch and brake pedals when reversing the vehicle.
(2) A slight shock is given to the vehicle when starting the vehicle after stopping the reverse movement.