Chassis - Overview: Other MINI Cooper I

Suspension

The suspension system used on MINI provides a firm and responsive ride with superb levels of comfort and good acoustic properties. The weight distribution between the front and rear axles is biased to the front due the front wheel drive configuration.

Adjustment to the camber at the front and rear suspension is not possible, only the front and rear toe is adjustable.

Power assisted steering using an electric pump and ABS is standard, with DSC available as an option on MINI COOPER. ASC is standard on the COOPER S, DSC is optional.

Front Suspension

The front suspension design features anti-dive and anti-squat geometry via the anti-roll bar and 1:1 strut movement ratio. The layout of the design minimizes camber loss due to side forces, thus improving handling and steering response.

Scheme 58

The front suspension consists of the following main components

1. Front Subframe
2. Lower Control Arms
3. Anti-Roll Bar and Links
4. McPherson Struts
5. Front Shocks
6. Front Springs
7. Front Top Mount
8. Front Hubs

Scheme 59

A main component of the front suspension is the Subframe. It is made from hydro-formed steel tubing and bolts directly to the body. The subframe provides the location for all suspension and steering components with the exception of the upper strut mounts. Attached between the front of the subframe and the bumper are the crush tubes. These tubes are attached with two bolts to the subframe and are designed to deform in an accident.

Scheme 60

Lower Control Arms

The pressed steel lower control arm links the subframe to the hub assembly via two ball joints. The inner joint is bolted to the subframe and the outer joint to the hub assembly. The rear of the lower control arm has a hexagonal shaft onto which the compliance bushing is press fit. The compliance bushing is attached to the body with a single mounting and to the subframe with two bolts, which also secure the anti-roll bar.

Scheme 61

As the suspension moves, the lower control arm pivots on the inner ball joint. The linear movement of the suspension is changed to rotational movement of the lower control arm, which is controlled by the radial stiffness of the compliance bushing.

Should replacement be necessary a new bushing and housing assembly will be required. Both ball joints are available as separate service parts.

Anti-Roll Bar and Links

Two sizes of anti-roll bar are used at the front axle: 19 mm for MINI COOPER and 24 mm for the COOPER S.

The anti-roll bar bushings clamped to the top of the compliance bushing housings are manufactured from low friction PTFE. This material requires no additional lubrication. This allows the anti-roll bar to rotate freely and quietly. It also allows the anti-roll bar to respond quickly to roll inputs and the use of stiffer bushings, as there is no compression or twisting as found on conventional bushings. Washers attached to the anti-roll bar located on the inside of each bushing prevent sideways movement.

The anti-roll bar links have ball joints fitted at each end. The ball joint attached to the strut is mounted on the same axis as the link. The ball joint attached to the anti-roll bar is mounted at 90° to the axis of the link and is attached to the front of the anti-roll bar with the nut facing rearwards.

Scheme 62

Workshop Hint

At this time it is not possible to remove the rear mounting bolt from the front anti-roll bar without lowering the subframe.

Scheme 63

McPherson Struts

Two MacPherson struts control the damping of the front suspension. Each strut assembly consists of a damper unit, a coil spring and a top mount assembly. The coil spring is retained in a compressed condition between the strut spring seat and the top mount. Isolators at each end of the spring reduce noise transmission from the suspension to the cabin. A bearing is fitted to the top spring mount that allows the spring to rotate as the steering is operated. The coil spring axis is offset to the axis of the damper. This arrangement reduces friction between the damper and piston during cornering. A dust cover protects the piston rod from dirt ingress. No provision is made for camber adjustment at the top mounting.

Scheme 64

Front Shocks

The front shocks are designed as twin-tube gas pressure shocks, similar to the E46. The lower end of the damper is inserted into a cylindrical sleeve on the swivel hub. The damper bracket determines the correct orientation of the damper; the bracket slides into a machined slot in the swivel hub cylindrical sleeve and is secured with a pinch bolt. A label is adhered to the damper for side identification.

The top mounts attach to the body with three studs and are replaced as a complete assembly. There is no provision for adjustment of the camber at the front top mounts.

Scheme 65

Scheme 66

Front Springs

The spring mounts between the seat on the damper body and the top mount, and is color coded to suit the suspension type and equipment level of the car.

Top Mount

The top mount assembly includes the top mounting plate, with a bonded rubber bushing and integral metal sleeve; three studs are pressed into the plate to retain the assembly to the body. The steel insert in the bushing prevents the damper rod retaining nut from over compressing the bushing when it is tightened. The bushing is not serviceable and a new top mount plate assembly must be fitted if replacement is required. Three lugs on the underside of the top mount plate provide location for the top mount bearing. The bearing is available as a service part separate from the top mount plate.

Scheme 67

General Suspension Data

GENERAL SUSPENSION DATA

Suspension Loading Information for Alignment

SUSPENSION LOADING INFORMATION FOR ALIGNMENT

Scheme 68

The BMW developed multi-link rear suspension is used for all models of MINI, making it the only car in its class to use such a sophisticated system. Benefits of this suspension are the exceptional handling characteristics and ride comfort, with good acoustic properties. Main components of the rear suspension include

1. Rear Subframe
2. Trailing Arms
3. Lateral Links
4. Anti-Roll Bar
5. Rear Springs
6. Rear Shocks

System Components

The fabricated subframe is attached to the body by four bolts. The inside bolt (3 on illustration) on the left side of the subframe is the master bolt to ensure the subframe is in its correct lateral position. The subframe also provides attachment points for the fuel tank straps and rear suspension lateral links. The anti-roll bar attachment points are on the top of the subframe and cannot be seen on the illustration.

Scheme 69

Trailing Arms

The trailing arms are fabricated from steel with a wall thickness of approximately 4 mm. The trailing arm provides toe-in control; counters brake lift and provides a low roll center. The arm also provides attachment for the brake caliper, damper unit and anti-roll bar. The trailing arms have two attachment points for the upper and lower lateral links to aid in the track control.

Attached to the front of the arm is the compliance bushing and housing. The housing is attached to the trailing arm by a single bolt. This controls side-force steer performance and enhances ride and noise levels. The bushing is located in a fabricated bracket held to the body by three bolts. The bolt holes in the bracket are slotted to allow for toe-in adjustment. Correct orientation of the bracket to the trailing arm is important to ensure correct wind up when fitted to the body.

Scheme 70

Lateral Links

The lateral links control the track of the rear wheels and are made of fabricated steel with elastokinematic bushings at both ends. The bolts locating the lateral links to the subframe and trailing arm should only be torque tightened with the car in curb side condition (full weight of the car on the suspension).

The lateral links are not side specific. The two lower lateral links have protective covers fitted (forward facing) to protect them from becoming damaged by impact.

Scheme 71

Rear Anti-Roll Bar

The anti-roll bar is attached to the top of the rear subframe by two PTFE bushings secured with clamp plates. The low friction PTFE bushings allow the anti-roll bar to rotate freely and quietly and require no additional lubrication. The anti-roll bar is made of solid spring steel. The anti-roll bar links from the anti-roll bar to trailing arm have ball joints at both ends and can be installed only one way, with the ball joints on the inside.

Scheme 72

Rear Springs

Coil springs, manufactured from silicon steel, are fitted to the shock assembly. The springs are retained at the lower end by plates attached to the shock. Between the spring and shock is an isolator. The top of the spring is contained with an isolator and cup that is clamped between the shock rod and rebound plate by a nut.

Rear Shocks and Top Mounts

The shocks at the rear are of the twin-tube gas pressure design, and like the front axle, the rear shocks are side specific. The shock rod is located in a bushing in the top mounting and is secured with a rebound plate and a locknut. The top mounts are side specific and identified by the letter "R" or "L" and attached to the body by two bolts.

Scheme 73

Brake System

The braking system features disc brake and calipers on all four wheels. The hydraulic system has a dual circuit that is split diagonally. A brake booster is fitted to all models. The system incorporates Anti-Lock Brakes (ABS) as a standard with its sub systems of Electronic Brake Force Distribution (EBV), Cornering Brake Control (CBC) and Engine Torque Feedback Control (MSR).

Purpose of the System

The Brake System provides the stopping power for the MINI and a cable operated parking brake. System components include

1. Brake Booster
2. Master Cylinder with Reservoir
3. Front Wheel Brake Assemblies
4. Rear Wheel Brake Assemblies
5. Parking Brake

Brake Booster

All cars are fitted with a 10" diameter vacuum brake booster. The booster is vented through an aluminum baffle plate, fitted between the booster and the bulkhead.

Master Cylinder with Reservoir

The tandem master cylinder is available in two versions one for ABS/ASC and one for DSC, both have a piston diameter of 22.2 mm. The visible difference between the two units is the single sensor fitted to the underside of the master cylinder on the DSC unit. This sensor informs the DSC control unit whether the driver has applied the brakes during DSC intervention.

Scheme 74

Scheme 75

The reservoir is secured to the master cylinder by a bolt connecting two mounting tabs. A sensor monitors fluid level, and supplies information to the ABS/DSC control unit. Two "O" rings seal the unit to the master cylinder. The reservoir also supplies fluid to the clutch hydraulics on manual gearbox models. There is an integral filter in the filler neck to prevent dirt contamination of the fluid.

Steering

The MINI features a power assisted steering system (EHPS) on all models. EHPS is a system not previously seen on BMW vehicles. The steering rack is of conventional rack and pinion design. The steering column has two collapsible mechanisms and tilt adjustment. The twin spoke steering wheel is common to all models although there are small differences depending on the model and equipment level. The steering column has 54 mm of tilt adjustment manually controlled by a lever beneath the column. The electrically driven power steering pump is the main difference.

The Steering System is designed to offer smooth operation with maximum feedback to the driver. The Electro Hydraulic Power Steering, driven by an electric motor rather than the conventional belt, conserves valuable engine power and provides a 3% savings in fuel economy.

The main components of the steering system are

1. Electro Hydraulic Power Steering Pump (EHPS)
2. Rack and Pinion
3. Steering Column
4. Steering Wheel

EHPS

All models and derivatives are equipped with Electro Hydraulic Power Steering (EHPS). This system uses an electric motor to drive the hydraulic pump. This replaces the customary design whereby the pump is permanently driven from the engine via the auxiliary belt.

Scheme 76

The EHPS motor weighing 5.5 kg is mounted by four rubber insulators and is positioned in front of the steering rack.

The hydraulic pump displaces 1.25cm 3/revolution developing a pressure of 105 bar at a maximum pump motor speed of 4,200 rpm. The hydraulic pump has an incorporated pressure relief valve. The smaller metal pipe from the aluminum bodied pump is the high pressure side and the flexible pipe fitted to the plastic reservoir on the pump is the low pressure side. There is a small reservoir fitted to the end of the pump with a remote reservoir fitted to the bulkhead. The system is filled with Pentosin CHF 11 S. For top-up and refill use the same oil.

Scheme 77

Scheme 78

Scheme 79

Rack and Pinion

The Steering Rack is mounted on the front subframe and is of conventional power assisted rack design. The rack is 2.56 turns lock to lock.

Scheme 80

Steering Column

The steering column is mounted on a one-piece aluminum bracket attached to the cross car beam. The steering column features two collapsible mechanisms, the upper part sliding away from the driver and the lower part telescoping to allow for movement of the engine and sub-frame during an impact.

Vehicles equipped with DSC have a steering angle sensor fitted to the lower end of the upper column. The data is transmitted to the DSC control unit via the CAN bus.

Scheme 81

A grommet with an integral bearing seals the column to the bulkhead and provides additional support at the bottom of the column. A "Yoke" type joint secured by a nut and bolt secures the column to steering rack pinion.

The ignition switch, steering lock cylinder and gearbox interlock (ECVT cars only) is mounted on the steering column tube. The interlock prevents the ignition key from being removed until the ECVT lever is in the Park position.

A slip clutch is fitted beside the steering lock detent pin. If force is exerted on the steering wheel, this prevents the detent pin from shearing off. This improves anti-theft protection. To reduce weight the column/lock assembly is made from pressure die cast magnesium.

The rotary coupler for the airbag is attached to the steering column switch unit. This is screwed to the top of the column.

The steering column has a tilt mechanism that allows the steering wheel to move 27 mm up and down from the center. Thus providing a total tilt adjustment of 54 mm. Adjustment is made by means of a lever located under the column cover. The column is counterbalanced by two springs, one either side of the column.

Steering Wheel

All models feature a two-spoke steering wheel. The MINI COPPER rim is vinyl. The MINI COOPER S (and optional MINI COOPER) steering wheel is leather trimmed. The diameter of the steering wheel is 370 mm. The steering wheel airbag module has a capacity of 57 liters and is a two-stage bag.

There are a number of functions that can be performed without the driver having to remove his/her hands from the steering wheel. Situated on the outside of the two spokes are the horn push buttons, these are on all steering wheels on all derivatives.

Cruise control buttons (if equipped) are laid out on the wheel in the following manner. Cruise on & resume buttons are on the left hand side and speed increase and decrease plus SET on the right hand side, these are located underneath the horn buttons.

Scheme 82

Audio system remote controls (if equipped) are located on the back of the steering wheel. On the left hand side is station search + and - these buttons only search the station presets. On the right is volume + and - and in the middle is a mode button to change to bass, treble, balance and fade. These are rocker type switches.

Traction Control Systems

Safe vehicle handling and braking is primarily achieved by highly developed, State of the Art chassis, suspension and brakes design.

However, even on a perfectly balanced vehicle, critical situations may occur during braking, accelerating and cornering which result in loss of directional stability.

Because the majority of drivers would not be able to maintain control of the vehicle in these situations, MINI has developed the following systems to assist drivers in these extreme situations

1. ABS Anti-lock Braking System EBV Electronic Brake Force Distribution CBC Cornering Brake Control MSR Engine Drag Torque Control
2. ASC Automatic Stability Control
3. DSC Dynamic Stability Control

EBV, CBC and MSR are sub-systems of, and are controlled by, the ABS system. All versions of the MINI are fitted with ABS, and thus EBV, CBC and MSR as standard equipment.

ASC is standard on MINI COOPER S. The ASC option is fitted as a package with ABS, EBV, CBC and MSR systems.

DSC is not standard on any version of the MINI but is available as an option on all versions.

ABS

The ABS system prevents the road wheel lock-up during brake application, thus maintaining vehicle stability and steering control under emergency conditions. The system is fitted to all versions of the MINI.

The ABS function is permanently active when the vehicle is being driven and cannot be disabled by the driver. ABS is always fitted together with EBV, CBC and MSR. Primary system components of the ABS System include

1. Hydraulic/Electronic Control Unit
2. Wheel Speed Sensors
3. Brake Light Switch
4. Brake Fluid Level Switch
5. Warning LED

Automatic Stability Control + Traction (ASC+T)

The ASC system prevents the driven front wheels from spinning when engine torque is applied and maintains an equal torque distribution to both wheels. This ensures that optimum traction and directional stability are maintained. ASC is always fitted together with ABS, EBV, CBC and MSR.

The main tasks of the ASC system are

1. To prevent loss of traction and possible resultant steering veer when engine torque is applied to the driving wheels.
2. To minimize power induced understeer (front end running wide) when driving through a corner and the front (driven) wheels start to slip due to excessive torque application.

Components differing from ABS system are

1. Hydraulic/Electronic Control Unit
2. Interface to EMS2000
3. ASC ON/OFF Switch

Dynamic Stability Control (DSC)

The ABS and ASC systems sense and react purely to wheel slip (longitudinal data) but cannot sense the sideways forces (lateral data) acting on the vehicle. ASC therefore has limited influence on stability when cornering.

DSC is fitted as a package with ABS, EBV, CBC, MSR and ASC. DSC interfaces with all these systems but, additionally, monitors the following items

1. Steering wheel movements via the steering angle sensor.
2. Lateral (sideways) forces via the acceleration sensor in the DSC sensor cluster.
3. Vehicle rotational speed via the yaw rate sensor in the DSC sensor cluster.

Hydraulic/Electronic Control Unit

All versions of MINI are equipped with Teves Mk 60 ABS as standard, which includes the following

1. EBV - Electronic Brake Force Distribution
2. CBC - Corner Brake Control
3. MSR - Engine Drag Torque Control

The ABS Control Unit is mounted in the plenum chamber on the opposite side of the vehicle to the master cylinder. The aluminum body of the unit contains the hydraulic valves that control hydraulic pressure to the individual brake lines.

Scheme 83

Scheme 84

The purpose of the switched orifices in the inlet valves to the front brakes is to allow a greater volume of fluid to reach the pistons during initial application. When the pad to disc clearances have been eliminated and the required volume of fluid transfer is reduced, the orifices are closed and fluid finds its way through a more restricted path in the inlet valves.

Wheel Speed Sensors

One Wheel Speed Sensor is located in each of the four wheel hubs. The sensors are of the magnetoresistive type.

The active sensing of the Magnetoresistive Sensor is particularly suitable for advanced stability control applications in which sensing at zero or near zero speed is required. A permanent magnet in the sensor produces a magnetic field with the magnetic field stream at a right angle to the sensing element.

The sensor element is a ferromagnetic alloy that changes its resistance based on the influence of magnetic fields. As the high portion of the pulse wheel approaches the sensing element a deflection of the magnetic field stream is created. This creates a resistance change in the thin film ferromagnetic layer of the sensor element.

The sensor element is affected by the direction of the magnetic field, not the field strength. The field strength is not important as long as it is above a certain level. This allows the sensor to tolerate variations in the field strength caused by age, temperature, or mechanical tolerances.

The resistance change in the sensor element affects the voltage that is supplied by the evaluation circuit. The small amount of voltage provided to the sensor element is monitored and the voltage changes (1 to 100mv) are converted into current pulses by the evaluation module.

Scheme 85

1. Signal Low- 7mA
2. Signal High- 14mA

The sensor is supplied 12V by the control unit. Output voltage from the sensor is approximately 10V. The control unit counts the high and low current pulses to determine the wheel speed.

Brake Light Switch

The electronic brake light switch supplies important information in hall effect format to the ABS control unit.

Scheme 86

ABS Warning LED

Located in the instrument cluster the ABS Warning Led is amber in color. The LED is ON during the pre-Drive check or when the system is faulted.

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ASC System

The ASC System, standard on COOPER S and optional on MINI COOPER, adds to the ABS system traction control functions. The Hydraulic/Electronic Control Unit while differing from the ABS unit is similar in appearance and in the same locations as the ABS unit. Additionally, a switch is added to the central switch pack in the center console to enable the driver to turn off the ASC functions.

ASC Switch

The ASC Switch provides an ON/OFF request to the ASC control unit for ASC operation.

Scheme 87

Scheme 88

ASC Warning LED

The ASC Warning LED in located in the instrument cluster and is amber in color. The LED is ON

44-09-34

1. During Pre-Drive Check
2. When the system is switched off by the driver
3. When a system fault is detected

The LED Flashes when the system is active.

Notes

DSC System

The DSC system, optional on both MINI COOPER AND COOPER S, replaces either the ABS or ASC system. Additional inputs allow the DSC control unit to analyze the desired motion of the vehicle and compare it with the actual motion and if instability is detected to take corrective action.

Additional input devices used by the DSC system

Scheme 89

1. Steering Angle Sensor
2. DSC Sensor Cluster
3. Hydraulic Pressure Sensor

Steering Angle Sensor

The steering wheel angle sensor is a potentiometer with two brushes positioned at 90 degrees to each other. The potentiometer provides data to the DSC control unit. When first fitted on the factory assembly line or when replaced in service, the sensor must be calibrated with the wheels in the straight ahead position. Thus, steering wheel angle is identified and analyzed by the DSC control unit.

Scheme 90

Scheme 91

DSC Sensor Cluster

The cluster contains a transverse acceleration sensor and a rotation speed (yaw rate) sensor. The acceleration sensor measures the lateral force acting on the vehicle when cornering. The yaw rate sensor measures the speed at which the vehicle is rotating around its vertical axis.

Scheme 92

The sensor provides fluid pressure information to the DSC control unit in the event of the driver applying the brakes during DSC intervention.

DSC Switch

The DSC Switch provides an ON/OFF request to the DSC control unit for DSC operation.

DSC Warning LED

The DSC Warning LED is located in the instrument cluster and is amber in color.

The LED is ON

1. During Pre-Drive Check
2. When the system is switched off by the driver
3. When a system fault is detected

44-09-34

The LED Flashes when the system is active.

The four ABS wheel sensors supply information to the ABS control unit that monitors the rotational speed of each wheel. Should one or more wheels decelerate at a rate that exceeds a predetermined value, the ABS control unit activates the ABS hydraulic unit and in turn reduces the hydraulic brake pressure supplied to the affected wheel(s). The ABS control unit and hydraulic unit are assembled together as a single unit.

When the control unit determines that ABS operation is required, it energizes the inlet and outlet solenoid valves within the hydraulic unit corresponding to the relevant hydraulic brake lines and starts the return pump. The inlet valve closes to isolate the brake line(s) from master cylinder pressure and the outlet valve opens to release pressure from the brake line into the accumulator. Thus the brake is released and the relevant wheel begins to accelerate. The control unit then opens and closes the inlet and outlet valves as necessary to modulate the hydraulic pressure and achieve the maximum possible braking effort without locking the wheel.

The return pump takes its fluid supply from the master cylinder reservoir and maintains pressure behind the inlet valves so that when the inlet valves re-open, the pressure in the brake lines is quickly re-established.

During anti-lock brake operation the driver will experience feed-back' in the form of a pulsating brake pedal that is accompanied by solenoid/pump noise.

Sub-systems of the ABS system are

1. EBV
2. CBC
3. MSR

These Sub-systems are also included in the ASC and DSC Systems.

EBV (Electronic Brake Force Distribution)

EBV is a development of the ABS system which controls the distribution of hydraulic brake pressure between the front and rear wheels. This is necessary to optimize the efficiency of the brakes under varying vehicle load conditions. It also allows larger rear brakes to be specified and ensures that front and rear brake linings wear at a similar rate.

The EBV system is fitted to all versions of the MINI and cannot be disabled by the driver.

If the vehicle is carrying 2 passengers in the rear seats, the luggage compartment is full and the fuel tank is full, the point at which the rear wheels start to lock under braking will correspond approximately with that of the front wheels. Thus a high amount of rear brake force can be applied safely and the vehicle's braking performance optimized.

If, however, a vehicle is carrying only the driver and the fuel tank is nearly empty, the rear brakes will start to lock well before the front brakes. This could result in the vehicle becoming unstable. The EBV system is designed to prevent this situation from occurring.

During braking, the ABS control unit detects a potential rear wheel slip situation and instructs the hydraulic unit to close the rear brake inlet valves. This prevents any further increase in hydraulic pressure being applied to the rear brakes while allowing pressure to the front brakes to increase and maximize the overall braking force. If the relative speed of the front and rear wheels return to within pre-determined limits, the ABS control unit opens the inlet solenoid valves in a series of steps which allows a progressive increase in hydraulic pressure to the rear brakes. The slip limit at which EBV operates varies with vehicle speed.

The ABS control unit manages EBV and, while operation is similar to that of ABS, EBV intervenes at lower wheel slip conditions and operates on the rear wheels only. The driver detects operation of EBV when the inlet valves close as a slightly stiffening pedal and a slight pulsing of the pedal when the valves open.

Scheme 93

CBC

CBC is a further development of the ABS system which, together with EBV, helps to keep the vehicle under control under all braking, vehicle loading and steering conditions.

The CBC system is fitted to all versions of the MINI. It is permanently engaged and cannot be disabled by the driver.

When the brakes are applied, weight is transferred to the front axle of the vehicle. If this occurs during cornering or directional change, the self-steering properties of the vehicle have a tendency to turn the vehicle into the curve (slight oversteer).

This tendency is normally compensated for by the design characteristics (elastokinematics) of the suspension and by intuitive steering adjustment by the driver.

The CBC system adjusts hydraulic pressure to each individual wheel under these circumstances to optimize directional stability.

Application of adequate rear axle brake force is largely responsible for vehicle stability when braking in a corner or during directional changes. The CBC system provides the precondition to enable rear brakes with larger pistons to be fitted to the vehicle (pistons with a greater diameter will apply greater brake forces for a given brake pressure).

Overall braking efficiency and pad life are also optimized with the fitting of larger rear brakes. The CBC system is controlled by the ABS control unit and operates using the same slip detection and brake modulation principles as the ABS system. However, CBC intervenes at relatively lower system pressures.

Note. CBC operates only when the brakes are applied by the driver as opposed to DSC which operates even when the brakes are not applied. CBC operates about 1% of the time during braking operations.

Scheme 94

MSR

If the vehicle is coasting with a low gear selected, or during a downshift, excessive engine braking could be applied resulting in wheel slip. This would result in vehicle instability. In this situation, the MSR system intervenes and sends a command to the engine management system to cancel decel fuel cut-off and open the throttle valve. Thus engine drag torque is converted into positive engine torque and wheel slip is eliminated. The system is controlled by the ABS control unit and uses the same slip detection principles as the ABS system.

ASC

The system is controlled by the ASC control unit (which replaces the ABS control unit) and is permanently active when the vehicle is being driven. The driver can disable ASC through the switch panel mounted switch. ASC is fitted as standard to MINI COOPER S version and is available as a factory fitted option on all other versions of the MINI.

The prevention of wheel spin is achieved by engine torque reduction and/or brake application. To prevent one wheel spinning, brake application to that wheel is employed and to prevent both wheels spinning, engine torque reduction is employed. These processes occur within milliseconds.

The ASC control unit checks for wheel spin by comparing the speed of each front driven wheel with the speed of the rear wheel on the same side. With this information, the ASC control unit determines whether brake application or engine torque reduction is appropriate. If brake application is required, the hydraulic unit isolates the brake line to the appropriate driven wheel and hydraulic pressure is applied in that brake line until the speed of the wheel returns to a value acceptable to the control unit. The return pump that takes its fluid supply from the master cylinder reservoir provides hydraulic pressure.

If engine torque reduction is also required, the ASC control unit sends the necessary command to the Engine Management System (EMS) control unit. A torque change request from the ASC control unit takes priority over any other torque change request received by, or generated internally within, the EMS control unit. Torque reduction is limited to the minimum value necessary to prevent wheel spin. The ASC control unit constantly updates the EMS control unit to ensure that driver demand' for acceleration is restored as soon as conditions permit.

The ASC warning lamp in the instrument cluster will flash when the system is operating. The warning lamp is illuminated permanently if the driver has switched off the ASC system or if the ASC control unit has detected a fault with the system. The need to switch off the ASC system should only be necessary under unusual circumstances such as driving away in snow or muddy conditions. The system must be switched off when snow chains are in use.

Scheme 95

Scheme 96

DSC

When the lateral cornering forces acting on the vehicle overcome the available grip on the road, understeer or oversteer will occur.

If the DSC system senses that understeer is occurring, it will apply brake force to the rear wheel that follows the inside radius of the curve thus applying a counter force which helps to bring the vehicle back onto its original course. (A much lower braking force may also be applied to the front wheel on the inside of the curve.)

If the DSC system senses that oversteer is occurring, it will apply brake pressure to the front wheel that follows the outside radius of the curve. (A much lower braking force may also be applied to the rear wheel on the outside of the curve.)

Scheme 97

Scheme 98

Scheme 99

Scheme 100

At the same time as with ASC, engine torque reduction will be applied.

DSC operates whether or not the driver applies the brakes and, if necessary, during ABS controlled braking.

The DSC warning lamp in the tachometer (or center mounted speedometer for USA vehicles) will flash when the system is operating. This is the same lamp and symbol as that of a vehicle equipped with the ASC system. The warning lamp is illuminated permanently if the DSC control unit has detected a fault with the system. The driver through the switch panel may disable the DCS system. When DSC is disabled, the DSC warning light is illuminated.

Scheme 101

On vehicles equipped with DSC, short lengths of flexible hose are situated in the rigid hydraulic brake lines from the master cylinder to the hydraulic unit. Their purpose is to reduce the rigidity of the master cylinder brake lines (which are of a larger diameter on DSC equipped vehicles) and also to minimize transmission of system noise.

Workshop Hint

The Hydraulic/Electronic Control Units are very similar in appearance for ABS, ASC and DSC.

Be sure the correct replacement unit is being installed.