ANTI - LOCK BRAKING and TRACTION CONTROL SYSTEMS

Anti - Lock Braking Systems were first developed in the aircraft industry to aid and further improve the landing capabilities of the aircraft.

Anti - Lock Braking Systems were first developed in the aircraft industry to aid and further improve the landing capabilities of the aircraft. This improved the following : the stopping distance of the plane.

Anti - Lock Braking Systems were first developed in the aircraft industry to aid and further improve the landing capabilities of the aircraft. This improved the following : the stopping distance of the plane. control of the plane on landing.

Anti - Lock Braking Systems were first developed in the aircraft industry to aid and further improve the landing capabilities of the aircraft. This improved the following : the stopping distance of the plane. control of the plane on landing. safety in poor weather conditions.

Anti - Lock Braking Systems were first developed in the aircraft industry to aid and further improve the landing capabilities of the aircraft. This improved the following : the stopping distance of the plane. control of the plane on landing. safety in poor weather conditions. directional stability.

Anti - lock braking systems on vehicles provide the same advantages as with aircraft. Any system must fulfil the following criteria : maintenance of manoeuvrability (lateral guiding of the front wheels).

Anti - lock braking systems on vehicles, provide the same advantages as with aircraft. Any system must fulfil the following criteria : maintenance of manoeuvrability (lateral guiding of the front wheels). maintenance of directional stability (lateral guiding of the rear wheels).

Anti - lock braking systems on vehicles, provide the same advantages as with aircraft. Any system must fulfil the following criteria : maintenance of manoeuvrability (lateral guiding of the front wheels). maintenance of directional stability (lateral guiding of the rear wheels). reduction in braking distance in comparison with a conventional system.

Anti - lock braking systems on vehicles provide the same advantages as with aircraft. Any system must fulfil the following criteria : maintenance of manoeuvrability (lateral guiding of the front wheels). maintenance of directional stability (lateral guiding of the rear wheels). reduction in braking distance in comparison with a conventional system. Guarantee of low regulation amplitudes (pedal reactions and comfort). OVERALL IMPROVED SAFETY OF THE VEHICLE.

Brake Pressure Unit PUMP UNIT This diagram shows an INTEGRATED ABS system. Brake Pressure Unit Brake Servo ABS Unit High Pressure Pump PUMP UNIT

Brake Pressure Unit PUMP UNIT This diagram shows an INTEGRATED ABS system. Brake Pressure Unit Brake Servo ABS Unit High Pressure Pump This system comprises of : - a brake pressure unit : functional INTEGRATION of the master cylinder and brake servo with the ABS regulation unit. PUMP UNIT

Brake Pressure Unit PUMP UNIT This diagram shows an INTEGRATED ABS system. Brake Pressure Unit Brake Servo ABS Unit High Pressure Pump This system comprises of : - a brake pressure unit : functional INTEGRATION of the master cylinder and brake servo with the ABS regulation unit. PUMP UNIT - a pump unit : source of high pressure (180 bars) for the hydraulic servo.

This diagram shows ADDITIONAL ABS system. ADDITIONAL REGULATION UNIT (ABS)

This diagram shows ADDITIONAL ABS system. ADDITIONAL REGULATION UNIT (ABS) An additional ABS system comprises : - a tandem master cylinder with servo (vacuum or hydraulic) which produces the brake pressure and distributes it to the callipers through the brake pipes.

This diagram shows ADDITIONAL ABS system. ADDITIONAL REGULATION UNIT (ABS) An additional ABS system comprises : - a tandem master cylinder with servo (vacuum or hydraulic) which produces the brake pressure and distributes it to the callipers through the brake pipes. - an additional regulation unit, modulating the brake pressure in each calliper independently of the effort applied to the brake pedal.

Schematic Diagram Bosch 2SE system

Hydraulic Circuit A The ABS system contains a : - hydraulic circuit. - electrical circuit. B This circuit has 4 callipers (A) connected to the tandem master cylinder which generates the brake pressure.

Hydraulic Circuit C A load sensitive compensator (C) modifies the braking pressure to the rear callipers according to body movement.

Hydraulic Circuit D The Additional Regulator Unit (D), modifies the brake pressure in the callipers in such a way as to prevent the wheel locking.

Electrical Circuit This circuit comprises of : - 4 wheel speed sensors (E) which generate electrical impulses whose frequency depends on the speed of rotation of the wheel. E E E E

Electrical Circuit F An electronic control unit (F) which uses the signals from the wheel sensors and controls the solenoid valve in the regulation unit.

H Electrical Circuit A warning lamp (G) located in the instrument panel and a connector (H) enabling fault diagnosis. G

Electrical Circuit - The Wheel Sensor Nearly all modern ABS systems have four channel operation. That is to say that there is a wheel sensor fitted on each of the road wheels. The ECU can monitor up to 8000 sensor signals per second and can take action within a few milliseconds.

Electrical Circuit - The Wheel Sensor Nearly all modern ABS systems have four channel operation. That is to say that there is a wheel sensor fitted on each of the road wheels. The ECU can monitor up to 8000 sensor signals per second and can take action within a few milliseconds. PERMANENT MAGNET

Electrical Circuit - The Wheel Sensor Nearly all modern ABS systems have four channel operation. That is to say that there is a wheel sensor fitted on each of the road wheels. The ECU can monitor up to 8000 sensor signals per second and can take action within a few milliseconds. PERMANENT MAGNET SOFT IRON CORE

Electrical Circuit - The Wheel Sensor Nearly all modern ABS systems have four channel operation. That is to say that there is a wheel sensor fitted on each of the road wheels. The ECU can monitor up to 8000 sensor signals per second and can take action within a few milliseconds. PERMANENT MAGNET SOFT IRON CORE WINDING

Electrical Circuit - The Wheel Sensor The wheel sensor is known as a PASSIVE sensor.

Electrical Circuit - The Wheel Sensor Reluctor tooth on driveshaft Pick up coil in wheel sensor with permanent magnet

+ 0.3v Electrical Circuit - The Wheel Sensor As the reluctor tooth approaches the pick up coil tooth, a magnetic field increases in strength, thus generating a voltage in the pick up coil. + 0.3v Amp Volt Ohm Farad VOLTAGE

+ 0.7v Electrical Circuit - The Wheel Sensor Just before the tooth is in line with the pick up coil tooth, maximum voltage is generated. + 0.7v Amp Volt Ohm Farad MAXIMUM VOLTAGE

0.0v Electrical Circuit - The Wheel Sensor ZERO VOLTAGE Amp Volt Ohm Farad ZERO VOLTAGE The reluctor tooth is now in line with the pick up coil tooth, the magnetic field is longer growing (moving) thus no voltage is generated in the pick up coil.

- 0.7v Electrical Circuit - The Wheel Sensor Amp Volt Ohm Farad NEGATIVE VOLTAGE The reluctor tooth is now moving away from the pick up coil tooth and the magnetic field is collapsing (moving in the opposite direction). The voltage has become negative.

Electrical Circuit - The Wheel Sensor ZERO VOLTAGE The reluctor tooth has moved some distance from the pick up coil tooth and the voltage generated voltage has dropped back to ZERO.

Electrical Circuit - The Wheel Sensor With an oscilloscope an AC waveform should be produced with the wheel rotating.

Electrical Circuit - The Wheel Sensor Experiment : Using the computer program Crocodile Clips produce a simple ABS layout with wheel sensors. Use the oscilloscope to test the wheel sensors. You must carry out the following tests : 1. Set the motor speed to 50 rpm and the wheel sensor to 1 Hz. 2. Using the oscilloscope test each wheel sensor for operation. 3. Does the polarity of the waveform change. If so why? 4. Set the motor speed to 100 rpm and the sine wave generator to 3Hz. What do you notice about the waveform signal? One the next screen is an example.

Electrical Circuit - The Wheel Sensor 250ohms Volt Farad Amp Ohm

250ohms Electrical Circuit - The Wheel Sensor Resistance/continuity check 250ohms Volt Farad Amp Ohm

Control System - Modulator. Over the next few screens you will see the operation of the hydraulic modulator. The solenoid drawn only represents 1 of the 4 in the system. There is 1 solenoid plunger for each separate wheel. Fluid flow through the solenoid valve is determined by the solenoid plunger, the position of which is determined by current supplied by the ECU to the energising coil. The 3 plunger positions needed to control the system are obtained in response to ECU outputs of 0A, 2A and 5A. Solenoid Valve

Hydraulic Modulator - Normal operation ABS not activated. Master Cylinder Pump OFF Solenoid Winding Solenoid Plunger ABS ECU Solenoid Current 0A Brake Calliper When the output from the ECU is 0A the return spring holds the plunger into position. Wheel Sensor Hydraulic Accumulator Hydraulic Modulator - Normal operation ABS not activated.

Hydraulic Modulator - Skid Sensed Pressure Reduction Master Cylinder Pump ON Solenoid Winding Solenoid Plunger ABS ECU Solenoid Current 5A Brake Calliper When 5A is applied from the ECU it is forced to the upper end of its travel. ABS is in use. Wheel Sensor Hydraulic Accumulator Hydraulic Modulator - Skid Sensed Pressure Reduction

Hydraulic Modulator - Pressure Being Held Steady. Master Cylinder Pump ON Solenoid Winding Solenoid Plunger ABS ECU Solenoid Current 2A Brake Calliper The weaker magnetic flux produced by 2A holds the plunger half way. The ECU will increase pressure again until a skid is detected. Wheel Sensor Hydraulic Accumulator Hydraulic Modulator - Pressure Being Held Steady.

Control System (closed loop). Hydraulic Modulator Master Cylinder Control System (closed loop).

Control System (closed loop). brake pressure control unit Hydraulic Modulator Master Cylinder Control System (closed loop).

Control System (closed loop). computes change of speed U brake pressure control unit Hydraulic Modulator Master Cylinder Control System (closed loop).

Control System (closed loop). pressure computes change of speed U C brake pressure control unit Hydraulic Modulator Master Cylinder Control System (closed loop).

Control System (closed loop). monitors system E controls pressure computes change of speed U C brake pressure control unit Hydraulic Modulator Master Cylinder Control System (closed loop).

ABS SYSTEMS - DELCO VI - GM Latest System Block Diagram 30 K200 F38 15 F43 30 F20 15 -Ignition ON 30 - Battery Positive 31 - Ground A 205 - Brake modulation F20 - Fuse F38 - Fuse F43 - Fuse H5 - Tell brake system H26 - tell tale ABS K50 - ABS ECU K61 -Engine ECU K200 ABS relay M205 - ABS motor pack P17 - Wheel sensor FL P18 - Wheel sensor FR P19 - Wheel sensor RL P20 - Wheel sensor RR S8 - Brake light switch WEG -Odometer signal Y205.1 - Solenoid valve FR Y205.3 - Solenoid valve RL X13 - Diagnose Y205.2 - Solenoid valve FL Y205.4 - Solenoid valve RR P17 K50 Y205.1 Y205.2 Y205.3 Y205.4 P18 P19 A 205 P20 M205 K61 S8 WEG H5 31 H26 X13

TRACTION CONTROL It has long been known that safety and vehicle performance is improved if spinning of the road wheels could be prevented under driving conditions. When a wheel spins, traction is lost and vehicle control is jeopardised. This control problem arises because spinning of a rear wheel causes the back of the vehicle to move sideways and loss of adhesion at the front results in loss of steering control. Since many vehicles are now fitted with ABS, the speed sensors on each wheel can also be used to signal when a wheel starts to spin. The existence on the vehicle of this sensing equipment means that it is a comparatively small step to fit a TCS.

TRACTION CONTROL - TCS There are 2 main additional requirements of a tractive control system: throttle controller - varies the output of the engine. ECU - detects spin at any wheel and overcomes it by applying the brake on that wheel and simultaneously reduces engine power. Vehicles with an ABS system have a dual ABS traction control ECU.

TRACTION CONTROL Throttle Controller Engine torque is controlled either by fitting an additional throttle (electronically controlled) or using an actuator on the main throttle. When an electronic actuator controls the position of the throttle the traditional mechanical linkage becomes redundant so a drive by wire system is employed. Vehicles fitted with this electronic throttle control have the accelerator pedal connected to a potentiometer.

Throttle and Pedal Position Potentiometer Operation The position sensor contains a potentiometer or variable resistor. The variable resistor has a power supply from the ECU (5 volts), connected at one end of the resistor track, the other end connected to earth via the ECU.

Throttle and Pedal Position Potentiometer Operation The throttle/pedal position sensor contains a potentiometer or variable resistor. The variable resistor has a power supply from the ECU (5 volts), connected at one end of the resistor track, the other end connected to earth via the ECU.

Throttle and Pedal Position Potentiometer Operation A third terminal on the sensor connects to “wiper” contact. The wiper sweeps backwards and forwards along the resistance track when the throttle/pedal is opened and closed.

1 volt Throttle and Pedal Position Potentiometer Amp Volt Ohm Farad Depending on the wiper position the voltage at the wiper contact will vary. On most systems, the voltage will rise as the throttle/pedal is opened.

3 volts Throttle and Pedal Position Potentiometer Amp Volt Ohm Farad Depending on the wiper position the voltage at the wiper contact will vary. On most systems, the voltage will rise as the throttle is opened.

5 volts Throttle and Pedal Position Potentiometer Amp Volt Ohm Farad Depending on the wiper position the voltage at the wiper contact will vary. On most systems, the voltage will rise as the throttle is opened.

5 volts Throttle and Pedal Position Potentiometer Amp Volt Ohm Farad The ECU monitors the signal voltage from the third terminal and therefore has an exact indication of throttle position. The ECU also requires an indication that the throttle is at idle. This may be achieved by having a set voltage range of 0.5 to 0.7 volts when the throttle is closed.

5 volts Throttle and Pedal Position Potentiometer Amp Volt Ohm Farad Wth the multi plug connected, check the following: - power supply, normally 5 volts.

0 volts Throttle and Pedal Position Potentiometer Amp Volt Ohm Farad Wth the multi plug connected, check the following: - power supply, normally 5 volts. - zero volts on earth path (accept up to 0.1 volts).

3 volts Throttle and Pedal Position Potentiometer Amp Volt Ohm Farad Wth the multi plug connected, check the following: - power supply, normally 5 volts. - zero volts on earth path (accept up to 0.1 volts). - check signal voltage at centre terminal. It should rise smoothly as throttle is opened.

3 volts Throttle and Pedal Position Potentiometer Amp Volt Ohm Farad If there is no power supply availiable or the supply voltage is incorrect, then check wiring from the sensor to the ECU. If the voltage on the earth circuit is greater than 0.1 v, then check for a high resistance or poor connection. If the signal from the centre terminal jumps at all, suspect a sensor fault and replace potentiometer.

Experiment : Below is an example of a potentiometer circuit. Task Using Crocodile Clips construct a circuit that would represent both the throttle and pedal position sensors. The ECU is represented by the 5 volt battery (both supply and earth).

M ROTARY ACTUATOR - Throttle Control ECU controls rotary actuator clockwise / anti-clockwise to control engine rpm/power.

M ROTARY ACTUATOR - Throttle Control Vehicle near full throttle ECU detects spin and activates actuator to close throttle.

M ROTARY ACTUATOR - Throttle Control Vehicle near full throttle ECU detects spin and activates actuator to close throttle and simultaneously applies the brake/s ant the spinning wheel.

ELECTRICAL CIRCUIT - TASK Using Crocodile Clips, design a simplified circuit to show and ABS system and Traction control system. Your design should function correctly. It should include the following: 4 wheel sensors (sine wave generator). 1 ECU to be represented by a 5 volt battery. 2 potentiometers (1 throttle and 1 pedal). 4 solenoid valves. 1 rotary actuator (use a motor). 1 diagnostic light. TCS ON light and OFF light. Where necessary use switches to simulate ECU outputs.