ESP Electronic Stability Programme Design and function SE LF -S TU DY PR OG RAM ME N o . 204 ESP is the abbreviation for “Electronic stability programme”. The system’s task is to assist the driver in demanding driving situations, e. g. if a wild animal suddenly runs across path of vehicle, and also to compensate for overreaction on the part of the driver and to prevent loss of vehicle stability. However, ESP is not intended for speed manics to try and defy the laws of physics. A responsible driving style adapted to the prevailing road and traffic conditions is therefore still essential.
In the course of this booklet, we will explain how ESP is based on the proven anti-lock braking system (ABS) and its related systems – TCS, EDL, EBD and EBC – and we will describe the various versions of ESP which we use in our vehicles. 204_095 NEW Important Note The Self-Study Programme is not a Workshop Manual. Please always refer to the relevant Service Literature for all inspection, adjustment and repair instructions.
Even in the early days, designers were confronted with the question of how to keep this technology manageable for the average driver. In other words: What systems would be required to ensure maximum braking safety and assist the driver? Purely mechanical precursors to the modern-day anti-lock braking system were first conceived as long ago as the 1920s and 1940s. However, these systems were not suited to the task in hand because they were too slow. The electronics revolution in the 1960s made antilock braking systems feasible. Such systems have become more and more efficient with the further development of digital technology.
Today, we regard not only ABS, but also systems such as EDL, EBD, TCS and EBC, as everyday technology. Today’s state of the art is reflected in ESP, which is now ready for production. However, our engineers are already thinking one step further. 204_069 What does ESP do? The electronic stability programme is one of the vehicle’s active safety features. It is also known as a “driving dynamic control system”. Expressed in simple terms, ESP is an anti-skid programme. It recognises when the vehicle is in danger of skidding and compensates when the vehicle breaks out.
Plus-points: – ESP is not an independent system. In fact it is based on other traction control systems. That is why it also includes the performance features of these systems. – It relieves the burden on the driver. – The vehicle remains manageable. – It reduces the accident risk if the driver overreacts. 4 Brevity is the soul of wit However, since there are so many vehicle systems that sound alike, abbreviations can be confusing. That is why we have summarised the most commonly used concepts for you below. ABS Anti-lock Braking System This system prevents the wheels from locking while braking.
Despite the system’s powerful braking effect, track stability and steerability are re-tained. ESP Electronic Stability Programme This system prevents the vehicle from skidding by selectively intervening in the brake and engine management systems. The following abbreviations are used also: – ASMS (Automatic Stability Management System), – DSC (Dynamic Stability Control), – DDC (Driving Dynamic Control), – VSA ( Vehicle Stability Assist) and – VSC ( Vehicle Stability Control). TCS Traction Control System This system prevents the driven wheels from spinning, e. g. on ice or gravel, by intervening in the brake and engine management systems.
EBC Engine Braking Control This system prevents the driven wheels from locking due to the engine braking effect when the accelerator pedal is released suddenly or when the vehicle is braked with a gear engaged. EBD Electronic Brake Pressure Distribution This system prevents overbraking of the rear wheels before ABS takes effect or if ABS is unavailable, due to specific fault states. EDL Electronic Differential Lock This system makes it possible to drive away on road surfaces where each wheel has a different degree of traction by braking the wheel which is spinning. Introduction These two different systems used are within the Group for various vehicle types. BOSCH Audi A8 Audi A6 Audi A4 Passat ‘97 ITT AUTOMOTIVE Golf ‘98 Audi A3, Audi TT Skoda Oktavia New Beetle Seat Toledo To prevent skidding, a driving dynamic control system such as ESP must be able to control brake activation within a fraction of a second. The return flow pump for the anti-lock braking system produces the pressure required. To improve the delivery rate of the pump, there must be sufficient pre-pressure provided on the suction side.
The fundamental difference between the systems made by BOSCH and ITT Automotive is how this prepressure is built up. BOSCH ITT Automotive 204_085 204_086 In the Bosch system, the pre-pressure is generated by a charge pump. This pump is known as the hydraulic pump for driving dynamic control and is attached to a common bracket located below the hydraulic unit. The ESP control unit and the hydraulic unit are separated. In the ITT system, the pre-pressure is generated by an active brake servo. It is also known as a booster. The hydraulic unit and the control unit form a single module. 6
Basic physical principles Forces and moments A body is subjected to different forces and moments. If the total of the forces and moments acting on the body equals zero, the body is at rest. If this total does not equal zero, the body is moving in the direction of the resultant force of this total. F = 9. 81 N The most widely known force to man is that of gravity. The force of gravity acts in the direction of the centre of the earth. If you suspend a 1 kilogram weight from a spring balance in order to measure the forces that occur, the balance will give a reading of 9. 81 Newtons for the force of gravity. 04_002 1 Additional forces which act on a vehicle are: – Tractive force (1 ) – Brake pressure (2) which counteracts tractive force – Lateral forces (3) which preserve the vehicle’s steerability and – Adhesion forces (4) resulting from friction and gravity, among other things. 2 4 3 204_003 Vehicles are also subjected to the following forces: I II II – Yaw moments (I) which try to rotate the vehicle about its vertical axis as well as – Wheel moments and moments of inertia (II) which try to retain the direction in which the vehicle is moving – Plus other forces such as aerodynamic drag. 204_019 Basic physical principles Interaction between some of these forces can be described using of the Kamm friction circle. The radius of the circle is defined by the adhesion force between the road surface and the tyres. In other words, the lower the adhesion force, the smaller the radius (a): the higher the adhesion force, the larger the radius (b). The basis of the friction circle is a forceparallelogram comprising lateral force (S), brake power or tractive force (B) and a resultant total force (G). As long as the total force lies within the circle, the vehicle is in a stable state (I).
If the total force exceeds the circle, the vehicle is no longer controllable (II). I a S B II S G B G B 204_004 1 Consider the inter-relationships between the forces at play: 1. The magnitudes the brake pressure and lateral force are such that the total force lies within the circle. The vehicle is steerable without any problem. S G B 204_005 2 2. Now brake pressure is increased. Lateral force is low. S 3. Total force equals brake pressure. The wheel locks up. The vehicle can no longer be controlled since there are no lateral forces.
A similar relationship exists between input power and lateral force. If the lateral forces are zero because input power is fully utilised, the driven wheels will spin. G B 204_006 3 S=0 B=G 204_007 8 Driving dynamic control Control process Before ESP can respond to a critical driving situation, it must answer two questions: a – In what direction is the driver steering? b – In what direction is the vehicle moving? The system obtains the answer to the first question from the steering angle sensor (1) and the speed sensors at the wheels (2).
The answer to the second question is supplied by measuring the yaw rate (3) and lateral acceleration (4). 1 3 4 2 If the information received provides two different answers to questions a and b, ESP assumes that a critical situation can occur and that intervention is necessary. I A critical situation may manifest itself in two different types of behaviour of the vehicle: I. The vehicle threatens to understeer. By selectively activating the rear brake on the inside of the corner and intervening in the engine and gearbox management systems, ESP prevents the vehicle fromovershooting the corner. II II.
The vehicle threatens to oversteer By selectively activating the front brake on the outside of the corner and intervening in the engine and gearbox management systems, ESP prevents the vehicle from skidding. 204_008 9 Driving dynamic control As you can see, ESP can counteract both oversteer and understeer. For this purpose, it is also necessary to initiate a change of direction without direct intervention in the steering. The basic principle is the same as for tracked vehicles. When a bulldozer wants to negotiate a left-hand bend, the track on the inside of the corner is braked and the outer track is accelerated. 04_009 To return to the original direction of travel, the track which was previously on the inside of the corner and now on the outside of the corner is accelerated and the other track is braked. 204_010 ESP intervenes along much the same lines. Here is an example of how such a situation is handled by a vehicle without ESP. The vehicle must avoid an obstacle which suddenly appears. At first, the driver steers very quickly to the left and to then immediately to the right. 204_011 The vehicle swerves due to the driver’s steering wheel movements and the rear end breaks away.
The driver is no longer able to control the resulting rotation about the vertical axis. 204_012 10 Now let us observe how a vehicle handles the same situation with ESP. The vehicle attempts to avoid the obstacle. From the data provided by the sensors, ESP recognises that the vehicle is losing stability. The system calculates its counteraction measures: ESP brakes the left-hand rear wheel. This promotes the turning motion of the vehicle. The lateral force acting on the front wheels is retained. 204_013 As the vehicle swerves to the left, the driver steers to the right.
To help the driver steer into the over-steer, the front right wheel is braked. The rear wheels roll freely in order to ensure an optimal build-up of lateral forces acting on the rear axle. 204_014 The preceding lane change can cause the vehicle to roll about its vertical axis. To prevent the rear end from breaking away, the front left wheel is braked. In highly critical situations, the wheel may be braked very heavily in order to limit the build-up of lateral forces on the front axle (Kamm circle). 204_016 Once all instabile operating states have been corrected, ESP ends its corrective intervention. 204_017 1 Overview The system and its components As mentioned already, the electronic stability programme is based on the proven traction control system. However, it has several key additional features: q The system can recognise and compensate for instable vehicle operating states at an early stage, such as skidding. Control unit For this purpose, several additional components are required. Before we explain ESP in greater detail, here is an overview of these components. BOSCH 204_061 Brake servo ITT 204_073 Brake pressure sensor BOSCH / ITT 204_071 Two makes of ESP system are fitted to VOLKSWAGEN vehicles.
One system is supplied by BOSCH and the other by ITT Automotive. Even though both systems have identical tasks and basic principles, they differ from one another in their component parts. When ordering spare parts, you should note the system on which you are working. 12 BOSCH/ITT Automotive Longitudinal acceleration sensor (only Quattro/Syncro) Steering angle sensor Wheel sensors at front and rear wheels ITT 204_067 BOSCH / ITT 204_064 BOSCH / ITT 204_084 Yaw rate sensor 204_001 BOSCH 204_058 Charge pump Hydraulic unit Lateral acceleration sensor BOSCH 204_062 BOSCH 204_072 BOSCH 204_068 13 System overview BOSCH
Sensors Probe for TCS/ESP E256 Brake light switch F ABS control unit with EDL/TCS/ESP J104, in footwell on front right at engine bulkhead Brake pedal switch F47 speed sensors rear right G44 front right G45 rear left G46 front left G47 Steering angle sender G85 Lateral acceleration sender G200 Brake pressure sender G201 Yaw rate sender G202, in footwell on front left in front of central control system for convenience system Auxiliary signals Engine management Gearbox management system 14 BOSCH Actuators Return flow pump relay – ABS J105, in protective housing for control units, in engine compartment on front left
Return flow pump for ABS V39 Solenoid valve relay – ABS J106, in protective housing for control units, in engine compartment on front left ABS intake valves N99, N101, N133, N134 ABS exhaust valves N100, N102, N135, N136 Driving dynamic control valve -1- N225 Driving dynamic control valve -2- N226 Driving dynamic control high-pressure valve -1N227 Driving dynamic control high-pressure valve -2N228 Hydraulic pump for driving dynamic control V156 Control unit for display unit in dash panel insert J285 ABS warning lamp K47 Warning lamp for brake system K118 TCS/ESP warning lamp K155
Auxiliary signals Engine management system Gearbox management system Navigation management system Diagnosis plug connection 204_087 15 Design and function of ESP Control cycle 1 ABS control unit with EDL/TCS/ESP 2 Hydrualic unit with charge pump 3 Brake pressure sender 11 12 3 4 Lateral acceleration sender 2 5 Yaw rate sender 6 Button for TCS/ESP 7 Steering angle sender 8 Brake light switch 9-12 Speed sensor 18 MONITORING 4 5 6 7 17 8 ABS TCS EDL EBD MSR CONTROL ESP 13 Diagnosis wire 14 Warning lamp for brake system 15 ABS warning lamp 16 TCS/ESP warning lamp 17 Vehicle and driver behaviour 18 Intervention in engine management
MONITORING 9 10 13 1 19 19 Intervention in gearbox control unit (vehicles with automatic gearbox only) 14 15 16 204_018 The speed sensors provide a continuous stream of data on speeds for each wheel. The steering angle sensor is the only sensor which supplies data directly via the CANbus to the control unit. The control unit calculates the desired steering direction and the required handling performance of the vehicle from both sets of information. The lateral acceleration sensor signals to the control unit when the vehicle breaks away to the side, and the yaw rate sensor signals when the vehicle begins to skid.
The control unit calculates the actual state of the vehicle from these two sets of information. If the nominal value and actual value do not match, ESP performs corrective intervention calculations. ESP decides: – what wheel to brake or accelerate and to what extent, – whether engine torque is reduced and – whether the gearbox control unit is activated on vehicles with automatic gearbox. The system then checks to see if intervention was successful from the data it receives from the sensors. If this is the case, ESP ends intervention and continues to monitor the vehicle’s handling characteristics.
If this is not the case, the intervention cycle is repeated. When corrective intervention is taking place, this is indicated to the driver by the flashing ESP lamp. 16 BOSCH ABS control unit with EDL/TCS/ESP J104 In the Bosch version, the control unit and the hydraulic unit are separated. The control unit is located on the right in the front footwell. Design and function The ABS control unit comprises a high-performance microcomputer. Since a high level of fail-safety is required, the system has two processing units as well as its own voltage monitoring device and a diagnoscs interface.
The two processing units utilise identical software for information processing and monitoring one another. Dual-processor systems of this type have what is known as active redundancy. 204_061 Electric circuit The control unit J104 obtains its power supply via the positive connection in the dash panel wiring loom. A/+ S Effects of failure In the unlikely event of the control unit failing, the driver will only have use of the standard brake system without ABS, EBS, TCS and ESP. Self-diagnosis 204_100 J104 The following faults are detected: Control unit defective Power supply failure 17 Design and function of ESP
Steering angle sender G85 is mounted on the steering column between the steering column switch and the steering wheel. The centring ring with slip ring for the airbag is integrated in the steering angle sender and located on the base of the steering angle sender. Task The sender transfers the steering wheel lock angle to the ABS control unit with EDL/TCS/ESP. An angle of ±720° corresponds to four full turns of the steering wheel. Centring ring with slip ring for driver’s airbag 204_064 Effects of failure Without the information supplied by the steering angle sensor, ESP would be unable to determine the desired direction of travel.
The ESP function fails. Self-diagnosis After replacing the control unit or the sensor, the zero position must be re-calibrated. Electric circuit G85 is the only sensor of the ESP system which transfers information direct via CANbus to the control unit. After turning on the ignition, the sensor initialises itself as soon as the steering wheel has been rotated through an angle of 4. 5°. This is equivalent to a turning movement of approx. 1. 5 cm. – Steering angle sender – no communication Wrong setting Mechanical fault Defective Implausible signal J104 S 204_101 J105 J106 G85 Faults can occur if the track has become maladjusted.
Make sure that the sensor is connected securely to the steering wheel. 18 BOSCH Design The angle is measured using the principle of the light barrier. The basic components are: a light source (a) an encoding disc (b) optical sensors (c+d) and a counter (e) for full revolutions B e 204_024 d c a The encoding disc comprises two rings: the absolute ring and the incremental ring. Both rings are scanned by two sensors each. 4 3 Function 5 1 204_025 2 We can simplify the setup by arranging an incremental hole template ( 1) and an absolute hole template ( 2) side by side. The light source (3) is positioned in between the hole templates.
The optical sensors (4+5) are located on the outside. Light impinging on a sensor through a gap generates a signal voltage. If the light source is covered, the voltage breaks down again. Moving the hole templates produces two different voltage sequences. The incremental sensor supplies a uniform signal, since the gaps follow each other at regular intervals. The absolute sensor generates an irregular signal, since light passes through the gaps in the template at irregular intervals. By comparing both signals, the system can calculate how far the hole template has moved. The absolute part determines the starting point of the movement.
Designed for only one turning motion, the steering angle sender uses the same principle. 204_026 204_027 19 Design and function of ESP Lateral acceleration sender G200 For physical reasons, this sensor should be located as closely as possible to the vehicle’s centre of gravity. This is why it is installed in the footwell below the driver’s seat. Task G200 determines whether and to what extent lateral forces are causing the vehicle to lose directional stability. 204_068 Effects of failure Without the lateral acceleration measurement, the actual vehicle operating state cannot be calculated in the control unit.
The ESP function fails. Self-diagnosis The diagnosis establishes whether an open circuit has occurred, or a short circuit to positive or GND exists. The system is also able to determine whether the sensor is defective or not. Electric circuit The lateral acceleration sender is connected to control unit J104 by three wires. J104 G200 204_102 This sensor is highly sensitive to damage. 20 BOSCH Design Expressed in simple terms, the lateral acceleration sender comprises a permanent magnet (1), a spring (2), a damper plate (3) and a Hall sensor (4). The permanent magnet, spring and damper form a magnetic system.
The magnet is securely connected to the spring and can oscillate back and forth over the damper plate. 4 1 3 2 204_029 Function When lateral acceleration (a) acts on the vehicle, the permanent magnet tracks this movement after a time lag caused by its mass moment of inertia. This means that the damper plate, together with the sensor housing and the vehicle as a whole, moves away below the permanent magnet which initially remains at rest. 204_031 a U This movement generates electrical eddy currents within the damper plate. These eddy currents in turn build up a field opposing the magnetic field of the permanent magnet.
The strength of the overall magnetic field is reduced in this way. This causes the Hall voltage (V) to change. The voltage change is directly proportional to lateral acceleration. U That means that the more movement there is between the damper and magnet, the weaker the magnetic field will become and the more the Hall voltage will change. The Hall voltage remains constant if no lateral acceleration exists. a 204_032 204_030 U 21 Design and function of ESP Yaw rate sender G202 This sensor should also be located as closely as possible to the vehicle’s centre of gravity.
In the Passat ‘98, this sensor is housed in the footwell on the front left in front of the central control unit for the convenience system. Task 204_058 The yaw rate sender incorporates space technology. Its task is to determine whether torque is acting on a body. Depending on its installation position, it can detect rotation about one of the axes in space. In the ESP, the sensor must determine whether the vehicle is rotating about its vertical axis. This process is known as measuring the yaw rate. A sensor which operates according to a gyroscopic principle has been used in the BOSCH system until ow. However, this sensor will be superseded by a combined transverse acceleration and steering yaw rate sensor which functions according to a different principle. Design and function An integral component is a small, metallic hollow cylinder (1 ). Eight piezoelectric elements (2) are attached to the hollow cylinder. Four of these elements induce resonance vibration (a) in the hollow cylinder. The other four elements “observe” whether the vibration nodes of the cylinder change. This is precisely what happens when torque acts on the hollow cylinder. The vibration nodes shift (b).
This is measured by the piezo elements and is signalled to the control unit which calculates the yaw rate based on this data. Vibration node 1 a B 2 204_047 22 BOSCH Combined Sensor Lateral acceleration sender G200 Yaw rate sender G202 In future, both senders will be combined in a housing. The advantages of this are: – smaller fitting dimensions, – exact alignment of both sensors face to face – this alignment cannot be changed – and – stronger design 204_075 The components are mounted on a printed circuit board and operate according to micromechanical principles. The sensor is connected by a six-pin connector.
Lateral acceleration is measured according to a capacitive principle. The yaw rate is determined by measuring the Coriolis acceleration which occurs. Here is an example: If you fire a canon ball horizontally in the northern hemisphere, for example, it will no longer appear to travel in a straight line to an observer rotating with the earth. This is caused by a force which accelerates the ball against the direction of rotation of the earth and causes it to deviate from its straight path –or what is known as the Coriolis force. Coriolis force Direction of rotation of earth 204_126 23 Design and function of ESP
Design of lateral acceleration sender The sender is a tiny component on the printed circuit board of the combined sensor. Expressed in simple terms, the lateral acceleration sender is a capacitor plate with a moving mass which is suspended so that it can move back and forth. Two additional, permanently mounted capacitor plates enclose the movable plate in such a way as to form two series-connected capacitors (K1 and K2). The quantity of electricity which the two capacitors can absorb can now be measured by means of electrodes. This quantity of electricity is known as capacitance C.
Stationary plate K1 Direction of travel Suspension Capacitor plate with movable mass 204_125 K2 Stationary plate Electrode Function As long as no acceleration acts on this system, the measured quantities of electricity (C1 and C2) of the two capacitors are of equal magnitude. If lateral acceleration acts on the system, the inertia of the movable mass at the centre plate causes this part opposite the fixed plate to move against the direction of acceleration. This causes the spacing between the plates to change and this also changes the quantities of electricity of the partial capacitors.
The spacing of the plates at capacitor K1 increases and the associated capacitance C1 decreases. The spacing of the plates of K2 decreases and capacitance C2 therefore increases. C2 C1 C1 = C2 204_120 C1 ;lt; C2 204_121 24 BOSCH Design of yaw rate sender The yaw rate sender is mounted on the same board, but is physically separate from the lateral acceleration sensor. This design can also be explained in simple terms. Imagine a vibrating mass suspended in a support in a constant magnetic field located between the north pole and south pole. Printed circuits representing the actual sensor are attached to this vibrating mass.
In the actual sender, this configuration exists twice for reasons of reliability. North pole Direction of travel Substrate Conductors Vibrating mass South pole Function 204_123 If you apply an AC voltage (V~), the part containing the conductors begins to oscillate in the magnetic field. V~ Linear vibration corresponding to AC voltage applied 204_124 If angular acceleration acts on this structure, the oscillating mass behaves like the canon ball described above due to its inertia. It ceases to oscillate back and forth because a Coriolis acceleration occurs.
Since this occurs in a magnetic field, the electrical behaviour of the conductors changes. When measured, this change therefore shows the magnitude and direction of the Coriolis acceleration. The evaluation electronics calculate the yaw rate from this data. Yaw rate Coriolis acceleration 25 Design and function of ESP Brake pressure sender G201 is bolted to the hydraulic pump for driving dynamic control. Task The brake pressure sender signals the momentary pressure in the brake circuit to the control unit. From this, the control unit calculates the wheel braking forces and the longitudinal forces acting on the vehicle.
If ESP intervention is necessary, the control unit allows for this value when calculating the lateral forces. 204_071 Electric circuit The brake pressure sender is connected to the control unit J104 by three wires. Effects of failure Without values for current brake pressure, the system is no longer able to calculate the lateral forces correctly. The ESP function fails. Self-diagnosis The diagnosis establishes whether an open circuit exists or whether a short circuit to positive or earth has occurred. The system is also able to recognise whether the sensor is defective. J104 G201 204_105
Do not remove the pressure sensor from the hydraulic pump. It must be replaced together with the pump. 26 BOSCH Design The core of the sensor is a piezoelectric element (a) on which the brake fluid pressure can act plus the sensor electronics (b). b a 204_033 Function When the brake fluid applies pressure to the piezoelectric element, the charge distribution in the element changes. If the piezoelectric element is not subjected to pressure, the electric charges are distributed uniformly (1 ). If the piezoelectric element is subjected to pressure, the electric charges are shifted in space (2). An electrical voltage is generated.
The higher the pressure, the greater the extent to which the charges are separated. The voltage rises. This voltage is amplified by the built-in electronics and transmitted to the control unit in the form of a signal. The voltage level is therefore a direct measure of the brake pressure applied. 1 204_034 2 204_035 27 Design and function of ESP Button for TCS/ESP E256 This button is located on the dash panel insert, depending on the vehicle type. It allows the driver to de-activate the ESP function. When the driver depresses the brake pedal or presses the button again, it re-activates the ESP function.
If the driver forgets to reactivate ESP, the system re-activates itself when the engine is restarted. It makes sense to de-activate the ESP function in the following situations: – when trying to free the vehicle from deep snow or loose surfaces by rocking the car back and forth, – when driving with snow chains fitted, and – to run the vehicle on a dynamometer. The system cannot be de-activated while ESP intervention is in progress or above a certain speed. 204_060 Effects of failure If the ESP button is defective, the ESP function cannot be de-activated. A malfunction is indicated on the dash panel insert by the TCS/ ESP warning lamp.
Self-diagnosis The self-diagnosis cannot detect a defective button. Electric circuit + S L71 E256 J104 204_113 28 BOSCH The hydraulic pump for driving dynamic control V156 is mounted below the hydraulic unit in the engine compartment on a common support. Task In an ABS system, a small quantity of brake fluid must be pumped through the brake pedal against a high pressure. This task is performed by the return flow pump. However, the return flow pump cannot provide a large quantity of brake fluid at low or zero pedal pressure because the brake fluid has a viscosity that is too high at low temperature.
The ESP system therefore requires an additional hydraulic pump in order to build up the necessary pre-pressure on the suction side of the return flow pump. The pressure for pre-charging is limited by a nozzle in the master cylinder. The hydraulic pump for driving dynamic control itself is not regulated. 204_062 Electric circuit Both lines of the hydraulic pump are connected to control unit J104. J104 204_106 V156 Effects of failure The ESP function can no longer be executed. ABS, EDL and TCS are not impaired. Self-diagnosis The self-diagnosis indicates open circuit as well as short circuit to positive and GND.
Do not repair the hydraulic pump. It must be replaced as a whole. As a replacement part, the pump is already filled with brake fluid. Do not remove the plug prematurely. Do not use an empty hydraulic pump. 29 Design and function of ESP The hydraulic unit It is mounted on a support in the engine compartment. The exact fitting location may vary depending on vehicle type. In the Passat 97, for example, it is located on the driver’s side on the suspension strut tower. Task The hydraulic unit has two diagonally split brake circuits.
Compared with older ABS units, the hydraulic unit has been extended by the addition of a changeover valve and an intake valve per brake circuit. The return flow pump is now self-priming. The changeover valves are as follows: Driving dynamic control valve -1- N225 and Driving dynamic control valve -2- N226. The intake valves are as follows: Driving dynamic control high-pressure valve -1N227, and Driving dynamic control high-pressure valve -2N228. Electric circuit 204_072 J104 N99 N100 N101 N102 N133 N134 N135 N136 N225 N226 N227 N228 V39 204_107 The individual wheel brake cylinders are activated by the valves in the hydraulic unit.
Three states are possible by activating the intake and exhaust valves of a wheel brake cylinder in the hydraulic unit: – Raise pressure – Hold pressure – Reduce pressure Effects of failure If proper functioning of the valves cannot be assured, the complete system is de-activated. Self-diagnosis Control valves N225 and N226 as well as the high-pressure control valves N227 and N228 are checked for open circuit and short circuit to positive/GND. 30 BOSCH Functional diagram G B h F e d a c Let us now examine a single brake circuit and one particular wheel in the combination.
The partial brake circuit comprises: Control valve N225 (a), High-pressure valve N227(b), Intake valve (c), Exhaust valve (d), Wheel brake cylinder (e), Return flow pump (f), Hydraulic pump for driving dynamic control (g) and brake servo (h). Raise pressure When the ESP performs corrective intervention, the hydraulic pump for driving dynamic control begins to convey brake fluid from the reservoir to the brake circuit. As a result, brake pressure is quickly available at the wheel brake cylinders and return flow pump. The return flow pump begins to convey brake fluid in order to continue raising the brake pressure. 04_036 204_037 Hold pressure The intake valve closes. The exhaust valve remains closed. The pressure cannot escape from the wheel brake cylinders . The return flow pump stops and N227 closes. 204_038 Reduce pressure N225 switches to the opposite direction. The intake valve remains closed while the exhaust valve opens. The brake fluid can flow back through the tandem master cylinders into the reservoir. 204_039 31 Functional diagram BOSCH A/+ D S S S A/+ S G44 G45 G46 G47 L71 E256 F F47 J104 S J106 J105 N99 N100 N101 N102 N133 N134 N135 N136 N225 N226 N227 N228 V39 204_092
Components A/+ D E256 F F47 G44 G45 G46 G47 G85 G200 G201 Positive connection Ignition switch Button for TCS/ESP Brake light switch Brake pedal switch Rear right speed sensor Front right speed ssensor Rear left speed sensor Front left speed sensor Steering angle sender Lateral acceleration sender Brake pressure sender G202 Yaw rate sender, in footwell on front left, in front of central control system for convenience system J104 ABS control unit with EDL/TCS/ESP, in footwell on front right, at engine bulkhead J105 Relay for return flow pump – ABS, in protective housing for control units, in engine compartment on front left J106 Relay for solenoid valves – ABS, in protective housing for control units, in engine compartment on front left J285 Control unit for display unit in dash panel insert K47 K118 K155 ABS warning lamp Warning lamp for brake system TCS/ESP warning lamp 32 BOSCH E K47 J285 B K155 K118 A C D V156 J104 S G85 G200 G201 G202 Input signal Output signal Positive terminal Earth CANbus 204_092A
N99 N100 N101 N102 N133 N134 N135 N136 N225 N226 N227 N228 S V39 V156 ABS intake valve, front right ABS exhaust valve, front right ABS intake valve, front left ABS exhaust valve, front left ABS intake valve, rear right ABS intake valve, rear left ABS exhaust valve, rear right ABS exhaust valve, rear left Driving dynamic control valve -1Driving dynamic control valve -2Driving dynamic control high pressure valve -1Driving dynamic control high pressure valve -2Fuse Return flow pump for ABS Hydraulic pump for driving dynamic control A B C D E Handbrake warning switch connection Navigation system (only on vehicles with navigation system) Engine management system Gearbox management system (only vehicles with automatic gearbox) Diagnosis wire 33 Self-diagnosis Self-diagnosis can be performed with fault readers V. A. G 1551 and V. A. G 1552.
The following functions are available: 00 01 02 04 05 06 08 11 Automatic test procedure, Interrogate control unit version, Interrogate fault memory, Start basic adjustment, Erase fault memory, End of output, Read measured value block and Login procedure. The interface between the diagnostic unit and ESP system is the diagnosis plug connection. The exact fitting location is dependent on the vehicle type. 34 BOSCH Warning lamps and buttons in the diagnosis If a fault occurs while corrective intervention is in progress, the system tries its best to complete corrective intervention. At the end of the corrective process, the subsystem is de-activated and the warning lamp is activated. Faults and activation of warning lamps are always saved to the fault memory.
The ESP function can be de-activated by pressing the button for TCS/ESP. Warning lamps Warning lamp for brake system K118 ABS warning lamp K47 TCS/ESP warning lamp K155 K118 Ignition “on” K47 K155 System OK TCS/ESP intervention TCS/ESP button off ABS remains active, ESP is de-activated when coasting and accelerating, but remains active during ABS intervention TCS/ESP failure Fault at yaw rate sender, lateral acceleration sender, steering angle sender or brake pressure sender; in eventof ABS failure, emergency ESP function remains active. EBD remains active. ABS failure All systems switch off 204_900 35 System overview ITT Automotive Sensors Button for TCS/ESP E256 Brake light switch F
ABS control unit with EDL/TCS/ESP J104, in engine compartment on left ESP brake recognition switch F83, in brake servo Speed sensor G44, G45, G46, G47 Steering angle sender G85 Lateral acceleration sender G200 Brake pressure sender -1- G201 at master brake cylinder Yaw rate sender G202, in footwell on front left, in front of central control system for convenience system Brake pressure sender -2- G214, at master brake cylinder Longitudinal acceleration sender G249, at right-hand A pillar (only 4-wheel drive vehicles) Auxiliary signals Engine management system Gearbox management system system 36 ITT Automotive Actuators Return flow pump for ABS V64
ABS intake valve N99, N101, N133, N134 ABS exhaust valve N100, N102, N135, N136 Driving dynamic contro valve -1- l N225 Driving dynamic contro valve -2- N226 Driving dynamic control high pressure valve -1N227 Driving dynamic control high pressure valve -2N228 Magnetic coil for brake pressure N247, in brake servo Relay for brake light suppression J508, on auxiliary relay carrier above relay plate Control unit with display unit in dash panel insert J285 ABS warning lamp K47 Warning lamp for brake system K118 TCS/ESP warning lamp K155 Auxiliary signals Engine management system Gearbox management system Navigation management system 204_093 Diagnosis plug connection 37 Design and function of ESP Control circuit 1 Hydraulic unit with control unit for ABS with EDL/TCS/ESP 2 Active booster with 11 12 2 rake pressure sender and release switch 3 Longitudinal acceleration sender (quattro/syncro only) 4 Lateral acceleration sender 5 Yaw rate sender MONITOR 3 4 5 6 17 7 8 ABS TCS EDL EBD EBC CONTROL ESP 18 6 Button for TCS/ESP 7 Steering angle sender 8 Brake light switch 9-12 Speed sensor MONITOR 9 10 13 14 15 1 19 13 Diagnosis wire 14 Warning lamp for brake system 15 ABS warning lamp 16 16 TCS/ESP warning lamp 17 Vehicle and driver behaviour 18 Intervention in engine management 19 Intervention in gearbox control unit (only vehicles with automatic gearbox) 204_074 The only differences between the control circuits are the way in which the pre-pressure is built up and the inclusion of an additional brake pressure sender on the tandem master cylinder.
On 4-wheel drive vehicles, a longitudinal acceleration sender is also included in the control circuit. Here, the brake booster assumes the role of the hydraulic pump for driving dynamic control. There is a magnetic coil for brake pressure and a switch for brake recognition in the brake servo. The control process has been described above. If actual and nominal vehicle handling deviate from one another, the system performs corrective intervention calculations until the information supplied by the sensors indicates that vehicle stability has been restored. For a more detailled description of the control process, please turn to page 16. 38 ITT Automotive ABS control unit with EDL/TCS/ESP J104 s combined with the hydraulic unit to form of an assembly; its electronic design is similar to that of the Bosch control unit. Function – Control of ESP, ABS, EDL, TCS, EBD and EBC functions, – Continuous monitoring of all electrical components, and – Diagnostic support during servicing work in the workshop After turning on the ignition, the control units perform a self-test. All electrical connections are continously monitored and the solenoid valves are periodically tested for proper functioning. 204_063 Effects of failure In the unlikely event of the control unit failing completely, the driver only has use of the standard brake system without ABS, EDL, EBD, EBC, TCS and ESP.
Electric circuit Control unit J104 obtains its supply via the positive connection in the dash panel wiring loom. Self-diagnosis The following faults are detected: Control unit defective Control unit incorrectly encoded Fault in power supply Hydraulic pump defective Implausible signals for ABS operation Drive train databus + + S S S A N99 N100 N101 N102 N133 N134 J104 N135 N136 N225 N226 N227 N228 V64 204_117 39 Design and function of ESP Steering angle sender G85 is mounted on the steering column between the steering column switch and the steering wheel. The centring ring and coil spring for the airbag are integrated in the steering angle sender and located on its base. Centring ring and coil spring for driver’s airbag
Task The steering angle sender signals the angle through which the driver turns the steering wheel clockwise or anticlockwise to the ABS control unit with EDL/TCS/ESP. The steering angle sender can measure an angle of ±720°, i. e. four full turns of the steering wheel. 204_064 J104 Effects of failure Without the information supplied by the steering angle sensor, ESP is unable to determine the desired direction of travel. The ESP function fails. Self-diagnosis Electric circuit After replacing the control unit or the sensor, the zero position must be re-calibrated. Steering angle sender – no communication Wrong setting Mechanical fault Defective Implausible signal G85 is the only sensor of the ESP systems which transfers its information directly to the control unit over the CANbus.
After turning on the ignition, the sensor is initialised by turning the steering wheel through 4. 5°. This is equivalent to a turning movement of approx. 1. 5 cm. J217 J… G85 + + J217 J… 204_108 For details of design and function, please turn to page 19. 40 ITT Automotive Lateral acceleration sender G200 For physical reasons, this sensor should be as close to the centre of gravity of the vehicle as possible. Under no circumstances may the fitting location and alignment of the sensor be changed. It is located on the right-hand side next to the steering column and is secured to the yaw rate sender on a bracket. Task G200 determines what lateral forces can be transferred.
G200 therefore provides a sound basis for assessing what vehicle movements are controllable under the prevailing road conditions. 204_065 Electric circuit The lateral acceleration sender is connected to the control unit J104 by three wires. Effects of failure Without the measurement of lateral acceleration, the actual vehicle operating state cannot be calculated in the control unit. The ESP function fails. J104 Self-diagnosis The diagnosis establishes whether an open circuit has occurred or a short circuit to positive or GND exists. The system recognises whether the sensor signal is plausible. G200 204_109 This sensor is also very sensitive to damage. 41 Design and function of ESP Design The lateral acceleration sender operates according to a capacitive principle.
What does this mean? Imagine that the sensor comprises two capacitors connected in series. The common, central capacitor plate can be moved by applying a force. Each capacitor has a capacitance, i. e. it can absorb a certain amount of electric charge. 204_040 Function As long as no lateral acceleration is acting on the central plate, the gap between the central plate and the outer plates remains constant, with the result that the electrical capacitance of the two capacitors is equal. 204_041 If lateral acceleration acts on the central plate, the one gap increases and the other decreases. The capacitance of the partial capacitors also changes.
The electronics can determine the direction and quantity of lateral acceleration from a change in capacitance. 204_042 42 ITT Automotive Yaw rate sender G202 The required installation position close to the vehicle’s centre of gravity was made possible by mounting the yaw rate sender, together with the lateral acceleration sender, on a bracket. Unlike the BOSCH combined sensor system, the ITT uses two separate sensors which can be replaced individually. Task G202 ascertains whether torque is acting on a body. Depending on the installation position, it can detect rotation about one of the axes in space. In the ESP, the sensor must determine whether the vehicle has rotated about its vertical axis. This process is known as measuring the yaw rate. 204_066
Electric circuit The yaw rate sender is connected to the control unit J104 by three wires. Effects of failure Without the measurement of the yaw rate, the control unit is unable to ascertain whether the vehicle has begun to swerve. The ESP function fails. Self-diagnosis The diagnosis establishes whether an open circuit has occurred or a short circuit to positive or GND exists. The system also ascertains whether the sensor signal is plausible. G202 J104 204_110 43 Design and function of ESP Design A basic component of ESP is a micromechanical system with a double tuning fork comprising a silicon crystal housed in a small electronic component on the sensor board. Here is a simplified drawing of the double tuning fork.
Its mid-section is connected to the other silicon element which we have ommited here for the sake of clarity. The double tuning fork comprises an exciter tuning fork and a measuring tuning fork. Measuring tuning fork Exciter tuning fork Connection to other silicon body 204_077 Function Applying an AC voltage induces a sympathetic voltage in the silicon tuning fork. The two halves are matched so that the exciter tuning fork has a resonance vibration at exactly 11kHz and the measuring tuning fork at 11. 33kHz. Applying an AC voltage at a frequency of exactly 11 kHz to the double tuning fork induces sympathetic vibration in the exciter tuning fork, but not in the measuring tuning fork.
A tuning fork vibrating in resonance reacts more slowly to the application of force than a nonoscillating mass. The exciter tuning fork vibrates in resonance AC voltage at a frequency of 11kHz The measuring tuning fork does not vibrate in resonance 204_078 44 BOSCH Sympathetic vibration This means that,whereas angular acceleration causes the other half of the double tuning fork and the remainder of the sensor together with the vehicle to move, the oscillating part of the double tuning fork lags behind this movement. As a result, the double tuning fork becomes twisted like a corkscrew. The twisting effect changes the charge distribution in the tuning fork.
This is measured by electrodes, evaluated by the sensor electrics and transmitted to the control unit in the form of a signal. Torque 204_088 45 Design and function of ESP Longitudinal acceleration sender G249 is located on the A pillar on the right and is only required on 4-wheel drive vehicles. On vehicles that are driven at one axle only, the system calculates the vehicle’s longitudinal acceleration from the data supplied by the sender for brake pressure, the signals supplied by the speed sensors on the wheels and information from the engine management system. On 4-wheel drive vehicles fitted with Haldex viscous coupling, the front and rear wheels are joined by a rigid coupling.
The calculated true vehicle road speed, which is determined from the individual speeds, may be too inaccurate under certain conditions at low coefficients of friction and when the Haldex viscous coupling is closed. The longitudinal acceleration measured is used to verify the calculated vehicle road speed. 204_067 Effects of failure Without the additional measurement of longitudinal acceleration on 4-wheel drive vehicles, it may be impossible under unfavourable conditions to determine the vehicle’s road speed accurately. The ESP and TCS functions fail. The EBD function remains active. Electric circuit The longitudinal acceleration sender is connected to control unit J104 by three wires.
Self-diagnosis The diagnosis establishes whether an open circuit has occurred or a short circuit to positive or GND exists. The system also recognises whether the sensor signal is plausible or not. J104 For further details of design and function, please turn to page 42. This sender is installed rotated through 90° in relation to the lateral acceleration sender. 46 G249 204_111 ITT Automotive Button for TCS/ESP E256 This button is located on the dash panel insert, depending on vehicle type. It enables the driver to de-activate the ESP/TCS function. This is indicated by the TCS/ESP warning lamp. Pressing this button again re-activates the TCS/ ESP function.
If the driver forgets to re-activate the TCS/ESP function, the system re-activates itself when the engine is restarted. It makes sense to de-activate the ESP function in the following situations: 204_060 – when trying to free the vehicle from deep snow or loose surfaces by rocking the car back and forth, – when driving with snow chains fitted and – for running the vehicle on a dynamometer. The system cannot be de-activated while ESP intervention is in progress. Electric circuit + Effects of failure If the ESP button is defective, the ESP function cannot be de-activated. S J104 Self-diagnosis The self-diagnosis does not detect a defective button. 04_113 L71 E256 47 Design and function of ESP Brake pressure sender – 1 – G201 Brake pressure sender – 2 – G214 Both senders are bolted to the tandem master cylinder. Task To ensure maximum safety, there are two brake pressure senders. In this case, too, the system has a redundant design. As with the BOSCH ESP system, the task of this system is to supply measured values for calculating the braking force and for controlling the pre-charging function. 204_070 Effects of failure It is practically impossible for both sensors to fail simultaneously. If the control unit does not receive a signal from one of the two senders, the ESP function is disabled.
Self-diagnosis The diagnosis establishes whether an open circuit has occurred or a short circuit to positive or GND exists. The system also checks whether the signals of the two sensors are plausible or not. Electric circuit Each of the brake pressure senders is connected to control unit J104 by three wires. J104 J104 G201 G214 204_114 204_115 48 ITT Automotive Design a Both sensors are capacitive-type sensors. For the sake of clarity, we are using here a simplified diagram of the plate capacitor in the interior of the sensor (a) on which brake fluid pressure can act. 204_043 Function Due to the gap (s) between the two plates, the capacitor has a defined capacitance C.
This means that it can absorb a certain amount of electric charge. Capacitance is measured is Farady. C 204_044 s One plate is fixed, the other can be moved by brake fluid pressure. s1 When pressure acts on the movable plate, the gap (s1 ) between the two plates becomes smaller and the capacitance C1 increases. C1 204_045 If the pressure drops again, and the plate moves back. The capacitance is again low. A change in capacitance is therefore a direct measure of pressure change. 204_046 49 Design and function of ESP Active brake servo with tandem master cylinder The active brake servo or booster differs fundamentally from the previous model. Over and above the usual function, i. e. ncreasing the foot pressure on the brake pedal by means of a partial vacuum which is generated by the intake manifold or from a vacuum pump, the active brake servo assumes the task of building up the pre-pressure for ESP intervention. This is necessary since the intake capacity of the return flow pump is not always sufficient to generate the required pressure. The reason for this is the high viscosity of the brake fluid at low temperatures. Advantage of the active brake servo: – No additional installation work is necessary 204_073 Effects of failure If the magnetic coil or switch F83 fails, the ESP function will no longer be available. Self-diagnosis Electric circuit The following faults are detected: open circuit, short circuit to positive or GND and defective component. J104 N247 F83 204_116 0 ITT Automotive Design a B First of all, let us observe an overview of the design. The booster comprises a modified tandem master cylinder (a) and the brake servo (b). The brake servo is subdivided into a vacuum part (c) and a pressure part (d) which are separated by a diaphragm. It also has a valve piston and magnet unit (e). e d c 204_050 The valve piston and magnet unit is electrically connected to the ESP system. N247 It comprises: – ESP brake recognition switch F83, – magnetic coil for brake pressure N247, – various air ducting valves which we shall not explain here in greater detail. F83 204_051 switch closed 1 2 switch open 1 2 204_052