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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 1

Part 1





Anti-Lock Control - Traction Control

NOTE:
A = Hardwired; D = High speed CAN (controller area network) bus; O = LIN (local interconnect network) bus; U = Private high speed CAN (controller area network) bus.









ANTI-LOCK BRAKE SYSTEM
The ABS (anti-lock brake system) controls the speed of all road wheels to ensure optimum wheel slip when braking at the adhesion limit. The wheels are prevented from locking to retain effective steering control of the vehicle.
The front and rear brake pressures are modulated separately for each wheel.

CORNER BRAKE CONTROL
CBC influences the brake pressures, below and within ABS (anti-lock brake system) thresholds, to counteract the yawing moment produced when braking in a corner. CBC produces a correction torque by limiting the brake pressure on one side of the vehicle, to assist the vehicle in achieving the turn radius the driver is requesting.

DYNAMIC STABILITY CONTROL
DSC uses brakes and powertrain torque control to assist in maintaining the lateral stability of the vehicle. While the ignition is energized the DSC function is permanently enabled, unless selected off using the DSC switch.
DSC enhances driving safety in abrupt maneuvers and in under-steer or over-steer situations that may occur in a bend. The ABS (anti-lock brake system) module monitors the yaw rate and lateral acceleration of the vehicle and the steering input, then selectively applies individual brakes and signals for powertrain torque adjustments to reduce under-steer or over-steer.
In general:
- In an under-steer situation; the inner wheels are braked to counteract the yaw movement towards the outer edge of the bend.
- In an over-steer situation; the outer wheels are braked to prevent the rear end of the vehicle from pushing towards the outer edge of the bend.
The ABS (anti-lock brake system) module monitors the tracking stability of the vehicle using inputs from the wheel speed sensors, the steering angle sensor, and the yaw rate sensor. The tracking stability is compared with stored target data. Whenever the tracking stability deviates from the target data, the ABS (anti-lock brake system) module intervenes by applying the appropriate brakes.
The following interactions occur in an intervention situation:
- High speed CAN (controller area network) signal to the ECM (engine control module), to reduce engine torque.
- High speed CAN (controller area network) signal to the active on-demand coupling module, to open the locking torque of the center coupling.
- Application of braking to the appropriate corner of the vehicle.

ELECTRONIC BRAKE FORCE DISTRIBUTION
Only the rear brakes are controlled by the EBD (electronic brake force distribution) function. EBD (electronic brake force distribution) limits the brake pressure applied to the rear wheels. When the brakes are applied, the weight of the vehicle transfers forwards, reducing the ability of the rear wheels to transfer braking effort to the road surface. This may cause the rear wheels to slip and make the vehicle unstable.
EBD (electronic brake force distribution) uses the anti-lock braking hardware to automatically optimize the pressure of the rear brakes, below the point where ABS (anti-lock brake system) is normally invoked.

ELECTRONIC TRACTION CONTROL
ETC attempts to optimize forward traction by reducing engine torque, or by applying the brake of a spinning wheel until traction is regained.
ETC is activated if an individual wheel speed is above that of the vehicle reference speed (positive slip) and the brake pedal is not pressed. The brake is applied to the spinning wheel, allowing the excess torque to be transmitted to the non-spinning wheels through the drive line. If necessary, the ABS (anti-lock brake system) module also sends a high speed CAN (controller area network) bus message to the ECM (engine control module) to request a reduction in engine torque.
When the DSC function is selected off using the DSC switch, the engine torque reduction feature is disabled.

EMERGENCY BRAKE ASSIST
EBA (emergency brake assist) helps the driver in emergency braking situations by automatically maximizing the applied braking effort. There are two situations when the ABS (anti-lock brake system) module will invoke EBA (emergency brake assist):
- When the brake pedal is rapidly pressed.
- When the brake pedal is pressed hard enough to bring the front brakes into ABS (anti-lock brake system) operation.
When the brake pedal is rapidly pressed, the ABS (anti-lock brake system) module increases the hydraulic pressure to all of the brakes until the threshold for ABS (anti-lock brake system) operation is reached. This action applies the maximum braking effort for the available traction. The ABS (anti-lock brake system) module monitors for the sudden application of the brakes using inputs from the brake pedal switch and from the pressure sensor within the HCU (hydraulic control unit). With the brake pedal pressed, if the rate of increase of hydraulic pressure exceeds the predetermined limit, the ABS (anti-lock brake system) module invokes emergency braking.
When the brake pedal is pressed hard enough to bring the front brakes into ABS (anti-lock brake system) operation, the ABS (anti-lock brake system) module increases the hydraulic pressure to the rear brakes up to the ABS (anti-lock brake system) threshold.
EBA (emergency brake assist) operation continues until the driver releases the brake pedal sufficiently for the hydraulic pressure in the HCU (hydraulic control unit) to drop below a threshold value stored in the ABS (anti-lock brake system) module.

ENGINE DRAG-TORQUE CONTROL
EDC prevents wheel slip caused by any of the following:
- A sudden decrease in engine torque when the accelerator is suddenly released.
- The sudden engagement of the clutch after a downshift on manual transmission vehicles.
- A downshift using the paddle switch on automatic transmission vehicles.
When the ABS (anti-lock brake system) module detects the onset of wheel slip without the brakes being applied, it signals the ECM (engine control module) on the high speed CAN (controller area network) bus to request a momentary increase in engine torque. Also, when the driver is braking and the ABS (anti-lock brake system) module has reduced brake pressure, but the wheels have not accelerated to the vehicle reference speed quickly enough, EDC will increase engine torque to accelerate the wheels up to reference speed and regain stability.

HILL DESCENT CONTROL
HDC uses engine braking and brake intervention to control the vehicle speed and acceleration during low speed off-road descents and in low grip on-road conditions. Generally, equal pressure is applied to all four brakes, but pressure to individual brakes may be modified by the ABS (anti-lock brake system) and HDC functions to retain vehicle stability. Selection of the HDC function is controlled by the HDC switch located on the floor console. HDC operates at vehicle speeds up to 50 km/h (31 mph).

WARNING: Incorrect use of the HDC function may compromise the stability of the vehicle, resulting in a dangerous and uncontrolled hill descent. Pressing the clutch pedal and/or driving with the transmission in neutral while HDC is active, will prevent engine braking from assisting the vehicle. The brakes will overheat and induce the HDC fade out strategy. In this condition there will be no control over the vehicle during a descent.

NOTE:
With the HDC function selected, HDC is operative even when the clutch pedal is pressed or the transmission is in neutral. It is not recommended to drive the vehicle further than is absolutely necessary with HDC selected, and the clutch pedal pressed or the transmission in neutral.
On manual transmission vehicles, HDC may be used in first, second and reverse gears only. Once the vehicle is moving, the clutch pedal is to be fully released. The vehicle is not recommended to be driven with HDC active and the transmission in neutral.
On automatic transmission vehicles, HDC may be used in D (drive), R (reverse) and gears 1 and 2 in sport mode. When in D, the TCM (transmission control module) will automatically select the most appropriate gear. It is not recommended to drive the vehicle with HDC active and the transmission in N (neutral).
HDC can be selected at any speed, but will only be enabled at speeds below 50 km/h (31 mph).
When HDC is selected:
- At speeds up to 50 km/h (31 mph), the HDC active indicator is permanently illuminated if a valid gear is selected.
- At speeds above 50 km/h (31 mph), the HDC active indicator flashes and a message advising that the speed is too high is displayed in the message center.
When HDC is enabled, the driver decides upon a target speed. Initially a default target speed is adopted, then, in any valid gear, the driver can adjust this target speed using the cruise control buttons. The new selected target speed will be indicated to the driver on the HDC display in the message center. The HDC function then compares this target speed with the actual vehicle speed. The ABS (anti-lock brake system) module then operates the HCU (hydraulic control unit) in the active braking mode as required, to achieve and maintain the target speed. Operation of the vehicle stoplamps during HDC is controlled by the CJB (central junction box).
Applying the foot brake during active braking may result in a pulse being felt through the brake pedal.
The target speed can be varied between minimum and maximum values for each gear and transmission range, depending on driver inputs through the cruise control buttons. If no cruise control buttons are pressed the ABS (anti-lock brake system) module adopts the appropriate default target speed:





The target speed is varied between the minimum and maximum values using the speed control '+' and '-' buttons. If the driver brakes during HDC control, the driver generated brake pressure supplements the deceleration and the vehicle will slow further. When the brake pedal is released the previously adopted target speed will be used once again. When the driver presses the accelerator pedal the vehicle will accelerate normally and HDC will not intervene; as soon as the driver releases the accelerator pedal the pre-selected target speed will be maintained once more.
During changes of target speed, the ABS (anti-lock brake system) module limits vehicle deceleration and acceleration to -0.5 m/s2 (-1.64 ft/s2) and +0.5 m/s2 (+1.64 ft/s2) respectively.
To provide a safe transition from active braking to brakes off, the ABS (anti-lock brake system) module invokes a fade out strategy that gradually releases the braking effort during active braking. The fade out strategy occurs if any of the following conditions is detected during active braking:
- HDC is selected off using the HDC switch.
- Failure of a component used by HDC, but not critical to the fade out function.
- Brake overheat.
If fade out is invoked because of HDC de-selection or component failure, the HDC function is cancelled by the ABS (anti-lock brake system) module. If fade out is invoked because of brake overheat, the HDC function remains in standby and resumes operation when the brakes have cooled.
The fade out strategy increases the target speed at a constant acceleration rate of 0.5 m/s2 (1.64 ft/s2), until the maximum target speed is reached, or until no active braking is required for 0.5 second. If the accelerator pedal is positioned within the range that influences target speed, the acceleration rate is increased to 1.0 m/s2 (3.3 ft/s2).
When fade out is invoked because of component failure, a warning chime is sounded and the HDC active indicator is extinguished. A message advising of the fault is displayed in the message center.
When fade out is invoked because of brake overheat, a message advising that HDC is temporarily unavailable is displayed. At the end of fade out, the HDC active indicator flashes. The flashing active indicator lamp and displayed message continue while HDC remains selected, until the brakes have cooled.
To monitor for brake overheat, the ABS (anti-lock brake system) module monitors the amount of braking activity and, from this, estimates the temperature of each brake. If the estimated temperature of any brake exceeds a preset limit, the ABS (anti-lock brake system) module invokes the fade out strategy. After a fade out cycle, the HDC function is re-enabled when the ABS (anti-lock brake system) module estimates that all of the brake temperatures are at less than 64% of the preset temperature limit.

Gradient Release Control
Gradient release control is an automatic system which is always available when HDC is selected.
If the vehicle is brought to a standstill on a slope using the foot brake, gradient release control will become active (except in the terrain response, sand program).
When descending a hill, a brake hold and gradual release is employed to provide a smooth transition into HDC. Gradient release control operates in forward and reverse gears and requires no driver intervention.

Activation of Stoplamps
Operation of the vehicle stoplamps during HDC is controlled by the CJB (central junction box). The ABS (anti-lock brake system) module monitors the brake system hydraulic pressure and requests the CJB (central junction box), via the high speed CAN (controller area network) bus, to energize the stoplamps during active braking.
A pressure threshold and time filter prevents the stoplamps from flickering while HDC is braking.

Stop/Start Vehicles
Activation of HDC will deactivate the stop/start system. If HDC is activated while the engine is shutdown in a stop/start cycle, the engine will automatically restart. However, if the stop/start system cannot detect the driver, for example either the driver safety belt or the driver door is unlatched, the engine will not restart. The stop/start system will then request the driver to depress the clutch, to restart the engine, by displaying an appropriate message in the message center. The driver must respond to this request within a limited time period, otherwise a conventional engine restart using the engine START/STOP switch will be required.

HILL START ASSIST
Regardless of HDC selection, the automatic hill start assist function will aid smooth transition from foot brake release to moving away, on all ascents above a 5% gradient. It does this by holding driver generated brake pressure for a short period of time (2-3 seconds) and then balancing brake torque with the propulsion torque generated when the accelerator pedal is applied, to ensure the vehicle does not roll backwards.
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