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Home >> Land Rover >> 2012 >> Range Rover Evoque (LV) L4-2.0L Turbo >> Repair and Diagnosis >> Brakes and Traction Control >> Antilock Brakes / Traction Control Systems >> Description and Operation >> Description >> Part 2

Part 2





Anti-Lock Control - Traction Control

ROLL STABILITY CONTROL
The RSC function uses the brakes and the engine to attempt to restore vehicle stability if the vehicle is forced into a harsh maneuver that risks it tipping over.
The ABS (anti-lock brake system) module monitors driver inputs and vehicle behavior using various powertrain signals and inputs of wheel speed, steering angle, yaw rate, roll rate and lateral acceleration. These inputs are compared with modeled behavior and, if the vehicle behavior reaches a given risk level, the ABS (anti-lock brake system) module cuts the engine power, or brakes one or more wheels sufficiently to allow the vehicle to regain stability and help the driver remain in control.
While the ignition is energized, RSC is permanently enabled even if the DSC function is selected off.

TERRAIN RESPONSE SYSTEM INTEGRATION
The terrain response function integrates the ABS (anti-lock brake system) and other vehicle system control modules to assist the vehicle when driving off-road or during difficult surface conditions. Terrain response is activated when a terrain response special program is selected.
When a terrain response special program is activated, the ABS (anti-lock brake system) module, along with other vehicle system control modules, will operate in accordance with programmed software maps. The software maps allow the ABS (anti-lock brake system) system to function with a threshold that will assist the selected terrain response special program. For additional information, refer to Ride and Handling Optimization Ride and Handling Optimization

TRAILER STABILITY ASSIST
When the trailer electrical socket is connected, the trailer stability assist function operates automatically to enhance the existing DSC and terrain response functions of the vehicle when towing. The system detects sway movements caused by trailer oscillations at speeds in excess of 50 km/h (31 mph) and acts to eliminate them. It does this through braking and engine management. Braking the vehicle asymmetrically counterbalances the sway movement, thereby slowing the vehicle and eliminating the oscillations. Engine management adapts engine torque output to support the braking management in stabilizing the vehicle and trailer.
Typical conditions when sway can occur include:
- Changing highway lanes.
- Traversing a lengthy bend.
- Acceleration.
- Braking.
- Incorrectly laden trailers.
The capability of trailer stability assist to respond early to the beginning of trailer-sway makes the system almost unnoticeable under normal driving conditions and keeps the vehicle and trailer under safe control. Trailer stability assist requires no input from the driver and operates up to the maximum vehicle speed.
Trailer stability assist will not operate while DSC is switched off.

DYNAMIC STABILITY CONTROL SWITCH









The DSC switch is a non-latching switch installed in the floor console, forward of the gear selector. Pressing the DSC switch connects an ignition power feed to the ABS (anti-lock brake system) module. With the first press of the DSC switch, the ABS (anti-lock brake system) module disables the DSC functions. When the DSC switch is pressed again, the ABS (anti-lock brake system) module re-enables the DSC functions. The DSC switch must be pressed for a minimum of 0.3 second for the ABS (anti-lock brake system) module to react. The DSC function is re-enabled at the beginning of each ignition cycle.
To confirm that the DSC function is selected off, the amber colored DSC OFF warning indicator in the instrument cluster is continuously illuminated. A message is also displayed in the message center to confirm that DSC is selected off. When the DSC function is selected on again, the DSC OFF warning indicator and message go off.
Although Land Rover recommend that DSC is selected on for all normal driving conditions, it may be beneficial to deselect DSC in order to maximize traction under the following conditions:
- To rock the vehicle out of a hollow or a soft surface.
- When driving on loose surfaces or with snow chains installed.
- When driving in deep sand, snow or mud.
- When driving on tracks with deep longitudinal ruts.
Even when DSC is deselected, driving maneuvers with extreme yaw or lateral acceleration may trigger RSC activity to assist the vehicle stability.
To prevent mis-use of, or in the event of a broken DSC switch, a DTC (diagnostic trouble code) is stored in the ABS (anti-lock brake system) module memory if the input from the DSC switch is held high for more than 1 minute.

HILL DESCENT CONTROL SWITCH









The HDC switch controls the selection of the HDC function.
The HDC switch is a non-latching switch installed in the floor console, forward of the gear selector. Momentarily pressing and releasing the HDC switch connects an ignition power feed to the ABS (anti-lock brake system) module. With the first press and release of the HDC switch, the ABS (anti-lock brake system) module enables operation of the HDC function. When the HDC switch is pressed and released again, the ABS (anti-lock brake system) module disables operation of the HDC function.
To prevent mis-use of, or in the event of a broken HDC switch, if the switch is pressed for more than 10 seconds no change of state occurs. A DTC (diagnostic trouble code) is stored in the ABS (anti-lock brake system) module memory if the input from the HDC switch is held high for more than 1 minute.

WHEEL SPEED SENSORS









An active wheel speed sensor is installed in each wheel knuckle, and provides the ABS (anti-lock brake system) module with a rotational speed signal from each road wheel. The head of each wheel speed sensor is positioned close to a magnetic encoder incorporated into the seal of the wheel bearing. Each front axle bearing encoder contains 46 north and south pole pairs; each rear axle bearing encoder contains 48 pole pairs. A fly lead connects each sensor to the vehicle harness.
The wheel speed sensor is supplied with a power supply and a signal connection from the ABS (anti-lock brake system) module. When the ignition switch is in power mode 6 (ignition), the ABS (anti-lock brake system) module supplies power to the wheel speed sensors and monitors the return signals. Rotation of the wheels induces current fluctuations in the speed sensor return signals. The ABS (anti-lock brake system) module subsequently converts the return signals into individual wheel speeds and the overall vehicle speed.
The ABS (anti-lock brake system) module outputs the individual wheel speeds and the overall vehicle speed on the high speed CAN (controller area network) bus for use by other systems. The quality of the vehicle speed signal is also broadcast on the high speed CAN (controller area network) bus. If all wheel speed signals are available to calculate vehicle speed from, the quality of the vehicle speed signal is set to 'data calculated within specified accuracy'. If one or more wheel speed sensors are inoperative, the quality of the vehicle speed signal is set to 'accuracy outside specification'.
The ABS (anti-lock brake system) module monitors the wheel speed sensor circuits for faults. If a fault is detected the ABS (anti-lock brake system) module stores a related DTC (diagnostic trouble code) in memory and illuminates the appropriate brake warning indicators, depending on the system functions affected. A warning chime is also sounded to alert the driver to the fault condition and, if the fault affects the HDC function, a message is displayed in the message center.
As the wheel speed sensors are active devices, a return signal is available when the road wheels are not rotating. This enables the ABS (anti-lock brake system) module to check the condition of the speed sensors while the vehicle is stationary.

YAW RATE SENSOR





The yaw rate sensor is located on the floor tunnel, under the front of the floor console. The sensor is secured by three nuts and connects to the vehicle wiring via a multipin connector.
When the ignition is on, the sensor receives a power feed from the CJB (central junction box). The sensor measures the yaw rate, roll rate, longitudinal acceleration and lateral acceleration of the vehicle, providing values to the ABS (anti-lock brake system) module via a dedicated, private high speed CAN (controller area network) bus connection. The ABS (anti-lock brake system) module broadcasts these values on the high speed CAN (controller area network) bus for use by other systems.
If a sensor fault is detected by the ABS (anti-lock brake system) module, a warning message will be displayed in the instrument cluster message center and the DSC warning indicator will illuminate.

STEERING ANGLE SENSOR









The steering angle sensor is integrated into the clockspring, which is part of the steering wheel module.
The steering wheel module is mounted to the upper steering column with two screws, and receives an electrical supply from the main harness via a multipin connector located on the side of the unit. The module provides the location and electrical connection for the two multifunction switches.
Input signals from the steering angle sensor are received and processed by the steering wheel module to calculate the steering wheel angle, and steering wheel angle speed. The information, together with signal integrity information, is transmitted on the high speed CAN (controller area network) bus for use by the ABS (anti-lock brake system) module and functions such as DSC (dynamic stability control).
A code wheel and 16 optical digital sensors are installed inside the steering angle sensor. Rotation of the code wheel is read by the optical digital sensors to produce steering wheel rotational speed signals. The steering angle sensor is able to measure a rotation range of +/-720 degrees, although the steering mechanism will only allow the steering wheel to rotate a maximum of +/-540 degrees.
If a fault occurs within the steering angle sensor, a DTC (diagnostic trouble code) will be set and stored in the steering angle sensor memory. The steering angle sensor fault is also stored in the ABS (anti-lock brake system) module memory. The ABS (anti-lock brake system) module will also illuminates the appropriate warning indicators, depending on the brake functions affected. A warning chime is also sounded to alert the driver to the fault condition and, if the fault affects the HDC function, a message is displayed in the message center.
The steering angle sensor and ABS (anti-lock brake system) module can be interrogated using Land Rover approved diagnostic equipment.

BRAKE WARNING INDICATORS









The instrument cluster contains various warning indicators for the anti-lock control - traction control functions. The warning indicators provide a visual indication of either a system fault or system operating status.

ANTI-LOCK BRAKE SYSTEM MODULE









The ABS (anti-lock brake system) module controls the brake functions by operating the HCU (hydraulic control unit) to modulate hydraulic pressure to the individual wheel brakes.
The ABS (anti-lock brake system) module is attached to the HCU (hydraulic control unit) and forms an integral component. A multipin connector provides the electrical interface between the ABS (anti-lock brake system) module and the vehicle wiring. The ABS (anti-lock brake system) module may be interrogated using Land Rover approved diagnostic equipment.

HYDRAULIC CONTROL UNIT
The HCU (hydraulic control unit) is a four channel unit that modulates the supply of hydraulic pressure to the brakes, under the control of the ABS (anti-lock brake system) module.
The master cylinder primary and secondary circuit outlets are connected to the HCU (hydraulic control unit) primary and secondary circuits. For additional information, refer to Hydraulic Brake Actuation Locations
Each of the HCU (hydraulic control unit) circuits contains the following components to control the supply of hydraulic pressure to the brakes:
- A normally open, solenoid-operated pilot valve, to enable active braking.
- A normally closed, solenoid-operated priming valve, to connect the brake fluid reservoir to the dual circuit hydraulic pump during active braking.
- A hydraulic pump, to generate hydraulic pressure for active braking and return brake fluid to the reservoir.
- Normally open, solenoid-operated inlet valves and normally closed, solenoid-operated outlet valves, to modulate the hydraulic pressure in the individual brakes.
- An accumulator and a relief valve, to allow the fast release of pressure from the brakes.
- Filters, to protect the internal components from contamination.
A pressure sensor in the primary circuit provides the ABS (anti-lock brake system) module with hydraulic pressure signals.
Contact pins on the HCU (hydraulic control unit) mate with contacts on the ABS (anti-lock brake system) module to provide the electrical connections from the ABS (anti-lock brake system) module to the dual circuit hydraulic pump motor and the pressure sensors. The solenoids that operate the valves are installed within the ABS (anti-lock brake system) module.

Hydraulic Control Unit Schematic Diagram









The HCU (hydraulic control unit) features 3 operating modes:
- Normal braking / EBD (electronic brake force distribution).
- ABS (anti-lock brake system) braking.
- Active braking.

Normal Braking / EBD Mode
Initially, all of the solenoid-operated valves are de-energized. Operating the brake pedal produces a corresponding increase or decrease of pressure in the brakes, through the open pilot valves and inlet valves. If the ABS (anti-lock brake system) module determines that EBD (electronic brake force distribution) is necessary, it energizes the inlet valves for both the rear brakes, to isolate the brakes from any further increase in hydraulic pressure. Only the rear brakes are controlled by the EBD (electronic brake force distribution) function.

ABS Braking Mode
If the ABS (anti-lock brake system) module determines that ABS (anti-lock brake system) braking is necessary, it energizes the inlet and outlet valves of the related brake and starts the hydraulic return pump. The inlet valve closes to isolate the brake from pressurized fluid; the outlet valve opens to release pressure from the brake into the accumulator and the return pump circuit. The reduced hydraulic pressure allows the wheel to accelerate. The ABS (anti-lock brake system) module then operates the inlet and outlet valves to modulate the pressure in the brake to apply the maximum braking effort without locking the wheel. Control of the valves for each wheel takes place individually.

Active Braking Mode
The active braking mode is used to generate and control hydraulic pressure to the brakes for functions other than the normal / EBD (electronic brake force distribution) and ABS (anti-lock brake system) braking modes.
For active braking, the ABS (anti-lock brake system) module energizes the pilot valves and priming valves, starts the return pump and energizes all of the inlet valves. Brake fluid, drawn from the reservoir through the master cylinder and priming valve, is pressurized by the hydraulic pump and supplied to the inlet valves. The ABS (anti-lock brake system) module then operates the inlet valves and outlet valves, as required, to modulate the pressure in the individual brakes. Some noise may be generated during active braking.

Service Information
The ABS (anti-lock brake system) module and HCU (hydraulic control unit) form a single component and must not be separated. The ABS (anti-lock brake system) module and HCU (hydraulic control unit) assembly is supplied in a pre-filled state. After installation, the hydraulic brake system only requires a conventional bleed of the system; there is no requirement to pressure bleed the system.
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