Land Rover Discovery: Parking Brake and Actuation - Operation

Operation

When the park brake is applied with the EPB switch, the ABS control module uses the wheel speed inputs to determine when to use the static and dynamic modes of operation. It uses the static mode at vehicle speeds up to 3km/h (2mph) and the dynamic mode at vehicle speeds greater than 3km/h (2mph).

STATIC APPLY/RELEASE

For the static apply to operate, the ignition can be on or off. When the EPB switch is pulled up, the ABS control module activates both EPB actuators to apply the brakes and signals the IC to turn on the park brake indicator lamp.

The warning indicator remains on continuously while the ignition is on, and for 30 seconds after the ignition is switched off.

For the static release to operate the ignition must be on and either the brake, clutch or accelerator pedal pressed. When the EPB switch is pressed down, the ABS control module then activates both EPB actuators to release the brakes and signals the IC to turn off the park brake indicator lamp.

IGNITION OFF APPLY (MANUAL TRANSMISSION VEHICLES ONLY)

The EPB is automatically applied when the ignition is switched off.

The ABS control module inhibits the ignition off apply operation if the EPB switch is held down, the ignition is turned off within 5 seconds, and the EPB switch is then held down for a further 2 seconds.

DRIVE AWAY RELEASE

With the vehicle static and the park brake applied, the drive away release mode releases the EPB when the accelerator pedal is pressed, without the EPB switch being set to the release position, to assist with a smooth drive away. This mode is only active if either the driver door is closed, or if the driver seatbelt is buckled and the engine is running.

The point at which the ABS control module releases the brakes is determined by the following factors:

• Tilt angle - from the longitudinal accelerometer sensor in the RCM
• Engine torque - from the ECM
• Accelerator pedal applied - from the APP sensor
• Clutch pedal releasing - from the clutch pedal position sensor (manual transmission vehicles)
• 1st or reverse gear selected - from the 1st and reverse gear switch (manual transmission vehicles)
• D (drive) or R (reverse) selected - from the TCM (automatic transmission vehicles)

The drive away release operation can be delayed by holding the EPB switch in the applied position, then releasing it back to its neutral position at the required time.

AUTOMATIC TRANSMISSION APPLY/RELEASE

The park brake is automatically applied on vehicles with automatic transmission when park (P) is selected (shift into park apply).

The park brake is automatically released when the transmission selector is taken out of P, provided the brake pedal is applied and the engine is running (shift from park release).

HIGH TEMPERATURE RE-CLAMP

After heavy use of the brakes the disc temperatures can be extremely high.

At high brake disc temperatures, if the vehicle is stationary and the park brake is applied, the ABS control module automatically re-applies the park brake as the brake discs cool down. A temperature model in the ABS control module software calculates the brake disc temperature from brake application force, the time the brake force is applied and vehicle speed.

High temperature re-clamp occurs at brake disc temperatures of 250ºC (482ºF) and above, or at any temperature when parked on a 20% slope or steeper. Depending on the temperature and tilt angle up to three re-clamps can occur, at varying time intervals, in the 10 minutes following the initial application of the park brake. To limit the number of re-clamps, the ignition status as well as the current tilt angle of the vehicle is considered.

DRIVER EXIT WARNING

If the driver attempts to exit the vehicle with the park brake off and the ignition on or the engine running, the following warning signals occur when the driver door opens:

• A warning chime sounds
• A message center warning is displayed.

ROLL AWAY RE-CLAMP

The roll away re-clamp function is used in order to ensure safe park even in worst case conditions (undetected actuator efficiency loss, extreme low friction between pads and disc, etc.).

Conditions for activation:

• Accelerator pedal not pressed (or invalid) OR engine not running (or invalid)
• Both brakes have been statically applied
• Mode is STATIC (vehicle speed < 4/5km/h)
• RAR not inhibited (e.g. due to fault entries)
• EPB reference speed (2nd fastest wheel speed) valid and > 0, or
• At least one wheel pulse counter (only rear wheels) > 12 pulses).
• ABS control module must be awake

DYNAMIC APPLY

While the vehicle is moving, the dynamic apply mode provides emergency braking. At a vehicle speed greater than 3km/h (2mph), pulling up and holding the EPB switch produces a gradual deceleration of the vehicle. The red park brake warning indicator illuminates, accompanied by a warning in the message center and a warning chime. The vehicle stop lamps also illuminate, activated by a CAN bus message from the ABS control module to the CJB. Dynamic apply operation is cancelled if the EPB switch is either released or pressed down to the release position, or the accelerator pedal is pressed.

There are four modes of dynamic apply, which the ABS control module uses in the following order of preference:

1. Hydraulic Dynamic Brake Function (HDBF)
2. Degraded Dynamic Brake Function (DDBF).
3. Actuator Dynamic Brake Function (ADBF).

The HDBF and DDBF modes use hydraulic braking on all four wheels to decelerate the vehicle. The ADBF mode uses the EPB actuators to operate the rear brakes to decelerate the vehicle.

HYDRAULIC DYNAMIC BRAKE FUNCTION (HDBF)

The braking operation is controlled by the ABS control module. The ABS control module monitors the deceleration rate using the wheel speed sensor signals, and adjusts the hydraulic pressure to the brakes as necessary to achieve the required deceleration. All of the anti-lock control - traction control system brake modes remain enabled.

DEGRADED DYNAMIC BRAKE FUNCTION (DDBF)

The braking operation is controlled by the ABS control module. The ABS control module monitors the deceleration rate using the wheel speed sensor signals if available, and adjusts the hydraulic pressure to the brakes as necessary to achieve the required deceleration. If all wheel speed sensors have failed, the longitudinal acceleration sensor is used to monitor vehicle deceleration.

ACTUATOR DYNAMIC BRAKE FUNCTION (ADBF)

The ADBF mode is used if the ABS control module cannot operate the brakes hydraulically, but still has wheel speeds available. The wheel speed inputs allow the ABS control module to adjust the clamp load on the rear brakes as necessary to produce maximum deceleration without locking the wheels. When the vehicle speed decreases to 3km/h (2mph), the ABS control module fully applies the electric park brake.

ADBF uses the EPB actuators to apply the rear brakes only, there is no hydraulic brake application and the front brakes are not applied.

SERVICE

Functional Test

The EPB incorporates a vehicle inspection mode that allows a functional test of the park brake to be performed on a rolling brake tester. For additional information, refer to: park Brake and Actuation (206-05, General Procedures).

Brake Pad Replacement

To change the rear brake pads it is necessary to fully retract the ball screw drive to allow retraction of the caliper piston. This can be done using one of the following methods: For additional information, refer to: Electronic Parking Brake Service Mode Activation and Deactivation (206-05 Parking Brake and Actuation, General Procedures).

• Putting the ABS control module into the maintenance mode using Land Rover approved diagnostic equipment
• Putting the ABS control module into the maintenance mode without diagnostic equipment
• Remove the actuators from the calipers.

CONTROL DIAGRAM

NOTE:

A = Hardwired; AN = High Speed (HS) Computer Area Network (CAN) Powertrain bus.

1. ABS control module
2. IC
3. TCM (automatic transmission vehicles only)
4. CJB
5. ECM
6. Diagnostic connector (J1962)
7. Left EPB actuator
8. Right EPB actuator
9. Ground
10. Power supply
11. EPB switch

Clutch Pedal Position Sensor (Manual Ransmission Vehicles Only)Parking Brake and Actuation / Diagnosis and Testing

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