CONSTRUCTION SPECIFICATIONS
VIEW OF ASSEMBLY
1 - ABS/ESP control unit
2 - Steering angle sensor built into the EPS (electric steering)
3 - Engine management control unit
4 - Yaw/lateral/longitudinal acceleration sensor
5 - Right front wheel sensor
6 - ASR off button
7 - Right rear wheel sensor
8 - Left rear wheel sensor
9 - ESP warning light
10 - EBD warning light
11 - ABS warning light
12 - Front wheel sensor Left
13 - HHC warning light
SPECIFICATIONS
The BOSCH 8.1 ABS braking system currently used is the most advanced available to guarantee safe driving. To achieve this, an ESP system which includes ASR/MSR/HBA/HHC functions has been added to the ABS/EBD hydraulic control unit.
µ - Wheel grip
S - Slip
A - EBD intervention area
A - ABS intervention area
C - ESP intervention area
1 - Lateral force curve
2 - Longitudinal force curve
As can be seen from the hold versus slip graph, the area covered by the ESP system is larger than that covered by a conventional ABS/EBD system.
The ESP system switches on automatically when the vehicle is started up and cannot be switched off by the user; the button in the centre console only switches off the ASR/MSR function and only when advisable (see ASR/MSR function).
INPUT SIGNALS:
- Wheel speed sensors (from direct line) (3)
- Brake pedal sensor normally open (from direct line) (4)
- Brake pedal sensor normally closed (from C-CAN line) (5)
- ASR off button (from direct line) (6)
- Engine management control unit (from C-CAN line) (2)
- Throttle angle position (from NCM C-CAN line) (8)
- Body computer (14)
- Handbrake lever position (from C-CAN line)
- Warning light status signal (from C-CAN line) (11)
- Yaw sensor (Z) (rotation of vehicle on vertical axis) (from C-CAN line) (10)
- Lateral acceleration sensor (Y) (from C-CAN line) (10)
- Longitudinal acceleration sensor (X) (from C-CAN line) (10)
- Steering angle/steering wheel rotation sensor in electric steering (from C-CAN line) (12)
- Robotised transmission control unit on versions where fitted (gear engaged status) (from C-CAN line) (13)
- Hydraulic system pressure sensor (from direct line) (1)
- Reverse gear engagement sensor (16)
OUTPUT SIGNALS:
- Brake pressure modulation control (15)
- Ignition advance reduction control (from C-CAN line) (9)
- Engine power management control (from C-CAN line) (8)
- Gear change inhibition on versions with robotised gearbox (from C-CAN line) (13)
- Wheel speed signal for speedometer and mileometer (from C-CAN) (14)
- VSO signal (vehicle speed) (14)
- ABS/ASR/ESP/HHC warning light in panel (from C-CAN line) (11)
- ASR off LED (7)
ESP SYSTEM
Introduction
The ESP (Electronic Stability Program) is an active safety system for the control of the vehicle during dynamic manoeuvres, which intervenes in emergency conditions. The ESP system, as well as including the ASR/MSR/HBA/HHC functions described previously, keeps the vehicle stable in the event of brisk manoeuvres, especially on slippery surfaces. It reacts quickly to both vehicle oversteer and understeer, restoring stability and allowing the driver to maintain full control of the vehicle.
This has been achieved through the addition of special sensors: steering angle sensor and yaw/lateral acceleration/longitudinal acceleration sensor.
The ESP system is managed by the A.B.S. electronic control unit, built into a special hydraulic control unit which allows action on the braking system, independent of the user''s action.
The control unit processes the following signals:
- steering angle/steering wheel rotation speed sensor
- yaw/lateral/longitudinal acceleration sensor
- motorised throttle position
- wheel RPM sensors
- hydraulic braking system pressure sensor
and uses special algorithms in the electronic control unit software to obtain the figures for the dynamic control of the vehicle:
- longitudinal and transverse slip between the wheels and the road surface
- axle drift.
Using these figures, the system interprets the effective dynamics of the vehicle; having identified all the critical conditions resulting from environmental factors (e.g. surface with poor grip) or any errors made by the user (e.g. panic situations) and with subsequent intervention on the brakes and the drive torque, the vehicle is restored to good driving conditions.
The system interfaces with:
- E.C.M. (Engine Control Module) for regulating drive torque,
- BCM (Body Computer Node) for the transmission of the vehicle speed and the control of the warning lights.
The exchange of information between these components takes place via the C-CAN line.
The K serial line is used to diagnose the system.
The system is combined with a power unit with a specific brake pump; in addition, the pipes between the brake pump and the A.B.S. control unit have a larger diameter (6 mm) than normal pipes (4 mm); this is designed to prevent adverse effects on the operation of the ESP at low brake fluid temperatures.
Operating strategies
As described previously, in addition to controlling longitudinal vehicle slip, the ESP system also controls transverse slip and thus the vehicle''s lateral stability.
The lateral stability of a vehicle depends on the reaction of the tyres to lateral forces, and on the adhesion force of the wheel to the road surface.
It should be remembered that wheel grip depends on the vertical load and the wheel condition (loaded or unladen) and on the friction coefficient, which is in turn determined by the road surface and tyre conditions.
When the vehicle is travelling in a straight line, the lateral forces do not really have an effect unless outside factors intervene (e.g. a gust of wind or a change to a different surface) and increase their intensity, unlike when driving round a bend where there is a strong increase in lateral forces due to the increase in centrifugal force.
The action of the lateral forces produces a variation in the drift angle of the wheels and, consequently, a variation in the axle drift (drift angle = difference between the desired route and the actual route).
The lateral forces do not, however, act equally on all four wheels because they are not subject to the same load conditions. In fact, the load on the wheel differs according to the situation the wheel is in, namely:
- acceleration (lightening of the front axle and loading of the rear axle)
- braking (loading of the front axle and lightening of the rear axle)
- bend to the right/left (loading of the outer wheels and lightening of the inner wheels)
- accelerating/decelerating round a bend (combination of the cases mentioned above).
It is obvious that if the lateral forces acting on the individual wheels vary, there will also be a variation in the forces acting on the vehicle axles; consequently the lateral forces acting on the front axle overcome those on the rear axle and vice versa, determining a rotation (moment) on the vertical axis of the vehicle (yaw axis).
The yaw moment affects the behaviour of the vehicle, producing either understeer or oversteer.
UNDERSTEER:
understeer for a vehicle is when, with increasing lateral acceleration, the drift angle for the front axle increases greatly compared with that of the rear axle. When this happens, the vehicle tends to go straight ahead (taking the curve wide) when cornering.
OVERSTEER:
oversteer for a vehicle is when, with increasing transverse acceleration, the drift angle for the rear axle increases greatly compared with that of the front axle. In this case the vehicle tends to turn around on itself (the rear axle tends to go straight on, causing the vehicle to cut the corner).
To keep the effect of lateral forces under control and limit the yaw moment, the ABS control unit calculates the nominal behaviour of the vehicle by means of:
- steering angle sensor
- accelerator pedal position
- brake pedal pressure
the control unit compares these parameters with the actual behaviour of the vehicle by means of:
- vehicle speed sensor (active sensors on the wheels),
- yaw/lateral acceleration sensor
if the values differ from the normal operation of the vehicle, the control unit is capable of:
- detecting actions carried out by the user, i.e. the steering wheel reveals the number of degrees (wide radius or narrow radius bends) and the rotation speed of the drive wheels (abrupt or gradual turns) and the throttle position and the brake pressure when accelerating or braking indicates how the user is taking the bend or deviating from a straight line.
- detecting the actual behaviour of the vehicle given the environmental variables, e.g. slippery surface, gusts of wind, reaction of the vehicle to incorrect manoeuvres by the user, etc., in order to identify the yaw moment and the lateral sliding of the axles via the sensors on the four wheels and the yaw/lateral acceleration sensor.
These operations are necessary to superimpose the mathematical model mapped in the control unit on the effective behaviour of the vehicle, in order to identify the vehicle''s state (understeer or oversteer) and to decide the action for the brakes and the engine management
UNDERSTEER ON CORNERS
The control unit detects the presence of understeer (mainly from the drift of the front axle), corrects the behaviour of the vehicle, braking the inner front and rear wheels round the bend in order to create an opposing moment which will lead the vehicle towards the centre of the bend and, possibly, reduce the drive torque.
OVERSTEER ON CORNERS
The control unit detects the presence of understeer (mainly from the drift of the rear axle) and corrects the behaviour of the vehicle, braking the outer front wheel round the bend in order to create an opposite yaw moment. In certain cases, in addition to the action on the brakes, there is also an increase in the speed of the inner drive wheel round the bend.
The system intervenes before the oversteer and understeer values are too high, in order to prevent the countersteering manoeuvre from making handling difficult.
ABRUPT VARIATIONS FROM A STRAIGHT PATH (SLALOM/OVERTAKING)
In the event of sharp variations from the path (e.g. overtaking, slalom), the control unit identifies possible oversteer and understeer conditions and corrects the path of the vehicle, acting as described previously.
Sharp variation from the straight path (gusts of wind, driving on different surfaces)
The control unit is capable of detecting deviations in the path and the prevalence of axle drift, and correcting the path through suitable action on the brakes and the engine.
ABRUPT ACCELERATION/DECELERATION
The control unit deploys the ASR/MSR strategy, while also controlling vehicle lateral acceleration and, as a result, the action on the brakes and drive torque.
Exclusion of ASR/MSR system
If the ASR/MSR function is cut out, the following functions remain activated:
- ABS/EBD
- T.C. up to a speed of 40 km
- ESP with intervention of the brakes only
- HHC
ESP INTERVENTION DISPLAY
The intervention of the ESP system is shown by the flashing of the special warning light on the instrument panel (5 Hz d.c. 50%).
the ESP system improves driving safety but there are limited situations which cannot be controlled by the ESP system. It is, therefore, not seen as a device which improves the vehicle''s performance, but as a device that improves its safety.
Asr/msr function
This system, in addition to the normal anti-lock and brake force distribution functions controlled by the ABS with EBD, also carries out the following functions:
- acceleration slipping adjustment (A.S.R.)
- adjustment of the engine braking torque (M.S.R.)
- locking the differential through action on the brakes (T.C.).
These functions are carried out through action on the drive torque (ASR/MSR) and the application of a braking force on one or both the drive wheels (TC).
If, during acceleration, one or both the drive wheels tend to slip, the ASR system asks the engine management control unit to reduce the torque transmitted to the wheels. Almost simultaneously, it brakes the wheel or wheels without any intervention by the user (TC)
If the wheels tend to lock during heavy deceleration, the MSR system requests that the engine management control unit adjusts the engine braking torque in order to prevent the vehicle becoming unstable.
The system can be bypassed by operating the button on the dashboard next to the Hazard pushbutton (hazard lights).
The LED in the button comes on and the display in the instrument panel signals that the ASR/MSR system has been switched off.
The warning light in the panel coming on indicates that the system is excluded on account of a fault recorded by the control unit.
The intervention of the ASR/MSR is signalled by the flashing of the warning light in the instrument panel.
Each time the vehicle is started up, the ASR/MSR function is activated even if the function was switched off when the vehicle was switched off.
The system works through signals coming from the active sensors for the four wheels, from the brake light switch and from the ASR on/off button.
It continuously compares the speed of the wheels on the same side of the vehicle (right front with right rear and left front with left rear) and when a difference in speed of more than 2-6 km/h (intervention level) is detected between two wheels on the same side, it intervenes with the ASR logic.
The ABS/ASR control unit communicates continuously with the engine management control unit via the C-CAN line.
Slipping of the drive wheels
Intervention - intervention times for good road grip conditions
Drive torque reduction by the engine management control unit through the alteration of the ignition advances, 6/100 of a second after the slipping limit is exceeded.
A further reduction in torque through a decrease in the throttle opening (by the engine management control unit through the motorised throttle body after 15/100 of a second).
Intervention of the hydraulic system (braking force on the drive wheels) after 2/10 of a second.
Operation in poor grip conditions
The system is capable of recognising these conditions by comparing the acceleration of the drive wheels with the torque transmitted by the engine (engine load from the engine management control unit).
The system behaves as for both drive wheels slipping in good road grip conditions and the intervention levels are at the lower limit.
Slipping of one drive wheel only
Intervention - intervention times
Torque reduction by the engine management control unit through the alteration of the ignition advances, 6/100 of a second after the slipping limit is exceeded.
A further reduction in torque through a decrease in the throttle opening (by the engine management control unit, through the motorised throttle body) after 15/100 of a second.
Intervention of the hydraulic system: a braking action exerted on the wheel that is slipping to guarantee a resistive force on the side with poor grip (T.C.).
This resistive force allows the differential to transmit an equal torque with good grip.
Slipping of one wheel round bends in good grip conditions
The system recognises the bend from the speed of the rear wheels (driven).
The system implements the same operating mode described for the "Slipping of one drive wheel only" condition, with the intervention levels at the upper limit. The torque reduction is applied gently.
Slipping of one wheel round bends in poor grip conditions
The system implements the same operating mode described for the "Slipping of one drive wheel only" condition, with the intervention levels at the lower limit. The torque reduction is accentuated (to ensure good lateral vehicle hold).
In the ASR intervention conditions with the control unit simultaneously receiving the signal coming from the brake light switch, the system excludes intervention on the brakes. The section relating to the torque reduction remains activated.
With the brake light switch activated and maximum braking pressure (e.g. heel point, switch defective, etc.), if the system detects a difference in speed between the two front and rear wheels which implies the intervention of the ASR, the torque reduction only is implemented. Intervention on the brakes is excluded.
Adjustment of engine braking torque during deceleration
Vehicle instability during deceleration in poor grip conditions
The system recognises this condition from the engine load, from the speed of the front and rear wheels and from the brake pedal sensor. In this case there is an increase in drive torque through the intervention of the engine management control unit opening the motorised throttle to overcome the natural instability of the vehicle owing to the engine braking torque in poor grip conditions.
ASR/MSR function exclusion
If the function is excluded using the button on the dashboard, which is advisable when the vehicle is on certain surfaces (e.g: deep snow, deep mud, thick sand or gravel) or chains are fitted to the drive wheels, the ABS/EBD system remains activated.
Intervention levels
The different intervention levels between 2 and 6 km/h depend on environmental factors; some of the conditions have been described in the operating logics, others are:
- high acceleration level, high threshold
- vehicle speed (see graph)
- type of tyres (normal or winter): with winter tyres and good grip, high intervention levels; with winter tyres and poor grip, low intervention levels. The system is capable of recognising these conditions by comparing the acceleration of the drive wheels with the torque transmitted by the engine (engine load from the engine management control unit).
The ASR/MSR function is active at all vehicle speeds but the braking effect is cut out above 80 km/h.
K - Slipping level
ASR/MSR SYSTEM FAILURE
In the case of a failure of the ABS system, the ASR system is also disabled. The following problems exclude the ASR system only:
- engine C-CAN message errors
- C-CAN bus errors.
When these problems occur, the control unit activates the warning lights on the instrument panel and on the button.
The warning light strategy is shown in the Warning Light Operation table.
The warning lights are operated by the ABS control unit via the C-CAN, as for the ABS/EBD system.
Operation of the hydraulic system
The electrohydraulic unit on the versions equipped with ASR has 4 additional solenoids.
When the (normally closed) intake solenoid is activated, the additional quantity of fluid required to increase the pressure and brake the wheel(s) can be received.
When the (normally open) control solenoid is activated, it allows the modulated pressure produced by the pump - necessary for the intervention of the ASR - to be maintained in the brake calliper-pump circuit.
With the ASR function not switched on, the electronic control unit:
- does not supply the (N.C.) intake solenoid (2).
- does not supply the (N.O.) solenoid (3).
In this way the system operates during the following stages:
- pressure increase;
- pressure maintenance;
- pressure reduction;
- pressure increase and resupply.
As for ABS Description and Operation 3340A SYSTEM (A.B.S.) CONTROL/REGULATION DEVICES
Hba operation
Introduction
It has been demonstrated that in emergency conditions not all drivers manage to produce the best possible performance from their vehicle''s braking system. In effect, although many manage to apply the brakes quickly, the force applied is limited.
There are two effects of this limitation: the first is linked to the fact that the braking force is the same as in normal conditions; the second is linked to the psychological fear of locking the wheels, even knowing that ABS is available. In these conditions, emergency braking assistance is carried out by increasing the pressure in the system in direct proportion to the effort applied by the driver.
The same vehicle deceleration is produced with a load reduced by a third compared with normal braking. In addition, as is known, vehicle stopping distances depend not only on the braking distance but on the distance travelled during the braking reaction time and rest time. By reducing the latter, the device allows the stopping distance to be reduced, especially at high speeds.
Operation
The HBA function (Hydraulic Brake Assist) is carried out electronically by the ABS control unit and is an ESP software module which controls the oil pressure uphill gradient when the driver brakes.
Emergency braking conditions are recognised when this gradient exceeds the set level.
The device''s speed level is set so that it only intervenes in actual emergency conditions without affecting in any way the manoeuvrability of the pedal in normal vehicle usage conditions.
Hhc function
Introduction
The HHC function (Hill Holder Control) is designed to assist the driver during departures in forward gears or reverse when the gradient of the road is more than 2%. In effect, the HHC is capable of automatically providing sufficient braking torque to keep the vehicle stationary until the clutch is fully released and the engine torque is sufficient to start the vehicle comfortably.
Operating strategy
The HHC is automatically activated when the brake pedal is pressed in conjunction with the following conditions:
- vehicle speed equal to zero,
- gradient more than 2%,
- clutch pedal pressed.
The moment the brake pedal is released, with all other conditions being equal, the HHC keeps the braking system pressurised for 1.5 seconds to allow the driver to move his/her foot from the brake pedal to the accelerator pedal, without the vehicle moving and without using the parking brake.
Once the accelerator is pressed, the HHC continues to keep the vehicle still for a further 1.5 seconds or until the engine torque is sufficient to start the vehicle.
The time indicated (1.5 + 1.5 secs.) is a maximum time that the control unit varies (i.e. reduces) if the sequence of driver movements (brake pedal/acceleration/sufficient torque) is quicker.
Conversely, if the driver does not press the accelerator within the first 1.5 seconds following the release of the brake pedal or the necessary torque is not reached within the additional 1.5 seconds, the HHC removes the pressure from the hydraulic circuit, so that the removal is not sudden.
In poor grip conditions the HHC is switched off for better vehicle control. This is because when stopped on an icy incline, if the HHC keeps the wheels locked but the vehicle slips backwards, it does not manage to produce minimum control of the vehicle. If the wheels are released, however, it is possible move backwards, keeping a straight-line path.
A slipping recognition test lasting about 150 ms has been designed for these extreme conditions and is implemented when the ABS or ASR is activated or one of the wheels locks just prior to the engagement of the HHC.
During the test stage the control unit (using the ABS parameters) defines which wheel is the most stable and then discharges the braking pressure for this wheel, keeping the other three braked.
If the speed sensor for the wheel which is not braked reports a speed other than zero, this means that the vehicle is moving even though all the other wheels are locked; this indicates poor grip conditions, therefore the HHC will switch off, releasing the pressure in the entire braking circuit.
Conversely, if the wheel that is not braked remains still, this means that the situation is stable and the HHC will continue to work.
BASIC FEATURES
Specifications:
- automatic engagement with speed at zero and vehicle gradient > 2%
- management of NQS failure warning light
- pressure maintenance time of 1.5 + 1.5 secs.
- automatic switching off prior to acceleration, clutch release or exceeding of maximum time from brake pedal release.
Necessary sensors and signals: :
- reverse gear engaged from C-CAN
- clutch status from C-CAN
- accelerator pedal status from C-CAN
- brake pedal status from C-CAN
- engine torque value from C-CAN
- engine rpm from C-CAN
- longitudinal or tilt sensor
- brake pressure sensor (incorporated in the ESP control unit).
- wheels stationary from rpm sensor signal
