Anti-Lock Braking System
ABS controls the speed of all wheels to ensure optimum wheel slip when braking while maintaining traction. Wheel lock is prevented to maintain control of the vehicle with efficient steering. The pressure in the front brakes is modulated separately for each wheel.
The pressure in the rear brakes is modulated according to the principle "choose less". Principle "choose less" allows the same pressure to be applied to both rear brakes, corresponding to the pressure applied by the wheel located on the lower friction surface. This keeps the rear of the car stable when the wheels are on surfaces with different coefficients of friction.
Corner braking system
CBC influences brake pressure, keeping it below and within the ABS thresholds to counteract the yaw moment generated when cornering braking occurs. CBC produces corrective torque by limiting brake pressure on one side of the vehicle.
Dynamic stability control
DSC uses the brakes and powertrain torque control to help maintain vehicle roll stability. When the ignition is on, the DSC function is permanently available unless the DSC switch is turned off. Even when DSC is disabled, harsh yaw or lateral acceleration maneuvers may trigger RSC action to help maintain vehicle stability.
DSC improves driving safety when performing sharp maneuvers and in situations of understeer or oversteer that can occur when cornering. The ABS module monitors yaw rate, vehicle lateral acceleration, and steering input and then selectively applies individual brakes and provides signals for torque adjustments in the powertrain to reduce understeer or oversteer.
Usually:
- In an understeer situation, the inside wheels are braked to counteract yaw towards the outer edge of the turn.
- In an oversteer situation, the outer wheels are braked to counteract the rear of the vehicle moving towards the outer edge of the corner.
The ABS module monitors the vehicle's directional stability using inputs from the wheel speed sensors, steering angle sensor, lateral acceleration sensor, and yaw sensor. The directional stability is compared with the stored target data. Whenever stability deviates from the set values, the ABS module intervenes by activating the appropriate brakes.
In an intervention situation, the following interactions occur:
- High speed CAN bus signal to ECM to reduce engine torque.
- Signal on the high speed CAN bus to the active clutch module to release the locking torque of the center clutch.
- Application of braking to the corresponding corner of the car.
Electronic brake force distribution
EBD limits the brake pressure applied to the rear wheels. When the brakes are applied, the vehicle's weight is transferred forward, reducing the ability of the rear wheels to transfer braking force to the road surface. This can cause rear wheel slip and make the vehicle unstable.
EBD uses the anti-lock brake system hardware to automatically optimize rear brake pressure below the point where ABS normally kicks in.
NOTE: The EBD function only controls the rear brakes.
Electronic traction control
ETC attempts to optimize forward traction by reducing engine torque or applying the brake on a spinning wheel until traction is restored.
ETC is activated if the speed of an individual wheel is higher than the reference speed of the vehicle (positive slip) and the brake pedal is not depressed. A brake is applied on the spinning wheel, allowing excess torque to be transmitted through the transmission to the non-spinning wheels. If necessary, the ABS module also sends a high speed CAN·message to the ECM to request a reduction in engine torque.
When the DSC function is selected to be disabled using the DSC switch, the engine torque reduction function is disabled.
Emergency Brake Assist
EBA assists the driver in emergency braking situations by automatically increasing the braking force. There are two situations when a module invokes an EBA activation:
- When the brake pedal is quickly depressed.
- When the brake pedal is depressed hard enough to activate the ABS on the front brakes.
When the brake pedal is depressed quickly, the ABS module increases the hydraulic pressure in all brakes until the threshold for ABS operation is reached. This action provides maximum braking force for the available tractive effort. The ABS module controls sudden activation of the brakes using inputs from the brake pedal switch and from the pressure sensor in the HCU. With the brake pedal depressed, if the rate of increase in hydraulic pressure exceeds a pre-set limit, the ABS module will activate emergency braking.
When the brake pedal is depressed hard enough to bring the front brakes into operation with ABS activation, the ABS module increases the hydraulic pressure supplied to the rear brakes up to the ABS threshold.
EBA operation continues until the driver releases the brake pedal sufficiently for the hydraulic pressure in the HCU to drop below a threshold value stored in the ABS module's memory.
Motor braking torque control
EDC prevents wheel spin caused by any of the following:
- A sudden decrease in engine torque when the accelerator pedal is abruptly released.
- Sudden engagement of the clutch after downshifting on vehicles with a manual transmission.
- Downshifting with the CommandShift function on vehicles with automatic transmission.
When the ABS module detects the effect of wheel spin without applying the brakes, the ABS module sends a high speed CAN signal to the ECM to request an instant increase in engine torque.
Descent control system
HDC uses engine braking and brake intervention to control vehicle speed and acceleration during low-speed descents in off-road conditions and low-traction conditions in off-road conditions. As a rule, equal pressure is applied to all four brakes, but the pressure to individual brakes can be changed by the ABS and DSC systems in order to maintain vehicle directional stability. The selection of the HDC function is controlled by the HDC switch located on the floor console. HDC works at vehicle speeds up to 50 km/h.
WARNING: Improper use of the HDC function can compromise vehicle stability, resulting in a dangerous and uncontrolled hill descent. Depressing the clutch pedal and/or driving with the transmission in neutral when HDC is active prevents engine braking from being applied to assist the vehicle. The brakes will overheat and initiate a de-efficiency strategy for HDC. In this state, there will be no control over the vehicle when descending.
NOTE: When HDC is selected, it works even when the clutch pedal is depressed or the transmission is in neutral. It is not recommended to drive the vehicle further than absolutely necessary with the HDC system selected and the clutch pedal depressed or the transmission in neutral.
On manual transmission vehicles, HDC can only be used in first gear and reverse gear. After the car starts moving, the clutch pedal should be fully released. Do not select the 'N' position in the gearbox while driving with HDC activated.
On automatic transmission vehicles, HDC can only be used in 'D', 'R' and CommandShift '1' positions. In the 'D' position, the TCM automatically selects the most suitable gear. Do not select the 'N' position in the gearbox while driving with HDC activated.
The HDC function can be selected up to 80 km/h but will only be activated below 50 km/h.
When HDC is selected:
- At speeds up to 50 km/h, the HDC status indicator lights up permanently if a valid gear is selected.
- At speeds between 50 and 80 km/h, the HDC warning lamp flashes, and on vehicles with an instrument panel "high series" a message is displayed in the message center notifying you that the speed is too high. If the HDC switch is pressed when the vehicle speed is over 80 km/h, the HDC status indicator lamp will not light and HDC will not be selected.
- If the speed reaches 80 km/h or more, a warning horn sounds, the HDC function turns off, the status indicator lamp goes off and, on vehicles with an instrument cluster "high series", a message is displayed in the message center notifying you that the HDC system has been turned off.
For more information, see the chapter:
- instrument panel (413-01 Instrument panel, Description and function)
- Information and message center (413-08 Information and Message Centre, Description and Operation)
When the HDC system is enabled, the ABS module calculates the set speed and compares it with the actual vehicle speed. The ABS module then activates the HCU in active braking mode, if necessary, to achieve and maintain the set speed. The operation of the vehicle's brake lights during HDC operation is controlled by the CJB.
Activation of the brake pedal during active braking can result in a pulsation perceived through the brake pedal.
The set speed varies between the minimum and maximum values for each gear and transmission range, depending on the driver's commands given through the pedals: If the pedals are not used, the ABS module assumes the default speed:
HDC speed setpoints
Set speed | Transmission in automatic transmission | Transmission in a manual transmission | ||
1st and D | Reverse | 1st | Reverse | |
Default | 10 km/h | 3.5 km/h | 10 km/h | 8 km/h |
Minimum | 6 km/h | 3.5 km/h | 7.5 km/h | 8 km/h |
Maximum | 20 km/h | 3.5 km/h | 20 km/h | 8 km/h |
The set speed is changed between the minimum and maximum values using the accelerator pedal or by pressing the '+' and '-' buttons of the cruise control (depending on vehicle specification). The HDC target speed will also change depending on the selected Terrain Response™ mode.
When the set speed changes, the ABS module limits vehicle deceleration and acceleration to -0.5 m/s2 (-1.64 ft/s2) and up to +0.5 m/s2 (+1.64 ft/s2) respectively.
To ensure a safe transition from active braking to releasing the brakes, the ABS module invokes a brake reduction strategy that gradually reduces braking force during active braking. The brake reduction strategy works if any of the following conditions are detected during active braking.
- HDC is disabled by using the HDC switch.
- Malfunction of an element used by HDC, but not critical to the brake reduction function.
- Depressing the accelerator pedal when the transmission is in neutral.
- Overheating of the brakes.
If the reduction in brake performance is caused by HDC disengagement or a component failure, the HDC function is canceled by the ABS module. If the reduction in brake performance is caused by depressing the accelerator pedal while the transmission is in neutral, or due to overheating of the brake, the HDC function remains in a ready state and resumes operation after the accelerator pedal is released or the brakes cool.
Brake reduction strategy increases target speed with a constant acceleration of 0.5 m/s2 (1.64 ft/s2) until the maximum set speed is reached, or until active braking is requested for 0.5 seconds. If the accelerator pedal is located in a range that affects the set speed, the acceleration rate increases to 1.0 m/s2 (3.3 ft/s2).
When there is a reduction in efficiency, a warning chime sounds and the HDC status indicator lamp turns off. Then the HDC indicator lamp goes out (on the instrument panel "low series") or in the message center (on the instrument panel "high series") a message is displayed notifying you of a malfunction.
For more information, see the chapter:
- instrument panel (413-01 Instrument panel, Description and function)
- Information and message center (413-08 Information and Message Centre, Description and Operation)
When efficiency loss is due to overheating of the brakes, on vehicles with an instrument panel "high series" a message is displayed notifying that HDC is temporarily unavailable. On vehicles with instrument panel "low series" the HDC warning lamp flashes. At the end of the efficiency reduction function, the HDC status indicator lamp flashes. The flashing of the warning lights and/or the display of the message continues with the selected HDC system until the brakes have cooled down.
For more information, see the chapter:
- instrument panel (413-01 Instrument panel, Description and function)
- Information and message center (413-08 Information and Message Centre, Description and Operation)
To control overheating of the brakes, the ABS module monitors the effectiveness of braking and, based on this, estimates the temperature of each brake. If the estimated temperature of any of the brakes exceeds a pre-set limit, the ABS module invokes a deceleration strategy. After a deceleration cycle, HDC operation becomes possible again when the ABS module judges that the temperature in all brakes is less than 64% of the set temperature limit.
Maintaining stability with roll elimination
The RSC function uses the brakes and the engine to attempt to restore vehicle stability if the vehicle is involved in a sudden maneuver that threatens to roll over the vehicle.
The ABS module monitors driver input and vehicle behavior using various powertrain signals and inputs from wheel speed sensors, steering wheel angle sensor, roll, yaw and lateral acceleration sensors. These inputs are compared to simulated behavior and if the vehicle's behavior reaches a predetermined risk level, the ABS module limits engine power or brakes one or more wheels just enough to allow the vehicle to regain stability and assist the driver in controlling the vehicle.
When the ignition is on, the RSC function is always available, even if DSC function off is selected.
Terrain Response™ System Integration
The Terrain Response™ feature integrates the ABS module and other vehicle control modules to facilitate driving off-road or in rough road conditions. The Terrain Response system is activated when the rotary control switch is set to the special Terrain Response program.
When the special Terrain Response program is activated, the ABS module, along with other vehicle control modules, will work according to the programmed characteristic tables. Software built-in characterization tables allow the ABS system to operate according to a threshold value that will assist the selected specific Terrain Response program. For more information, see chapter: Optimizing vehicle suspension and handling characteristics (204-06 Optimization of vehicle suspension and handling characteristics, Description and principle of operation).
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