anti lock brake system ( tata motors information )


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Model : All LCVs, M/HCVs with air brakes

Group: 42

January 2008


SUBJECT: Introduction of Anti Lock Braking System (ABS) on LCV & M/HCVvehicles with air brake system.We are pleased to inform you about introduction of Anti Lock Braking System (ABS) on commercial vehicles. This is to meet requirement of CMVR regulation which makes Anti Lock Braking System (ABS) conforming to IS: 11852:2003 (Part 9) mandatory on the following type/class of vehicles (i) N2 category of vehicles (GVW >3.5 Ton & < 12 Ton) and N3 category of vehicles (GVW more than 12 Tons) other than tractor-trailer combination manufactured on and after the 1st day of October, 2006 meant for carrying hazardous goods and liquid petroleum gas; (ii) N3 category vehicles manufactured on and after the 1st day of October, 2007, which are double decked transport vehicles; (iii) N3 category vehicles used as tractor-trailer combinations which are manufactured on and after the 1st day of October, 2007, they are used as tractor-trailer combinations. (iv) M3 category of buses (vehicle having more than 25 seats and GVW greater than 5 Tons) that ply on All India Tourist permit, manufactured on and after the 1st day of October, 2007 We are attaching details on following topics on ABS for air brake system for your ready reference: 1. 2. 3. 4. 5. 6. 7. 8. 9. Introduction, advantages & Working principle of ABS Suppliers of ABS system ABS Instructions to User (Operator) General Instructions to Mechanics (Working with ABS) ABS configuration Functions of individual components of ABS Troubleshooting with Blink Code Diagnostics Diagnostic Kit & diagnostic software installation. List of service representatives from Knorr Bremse & WABCO.

Please bring this information to the notice of all concerned in your workshop and educate customers.

1) Introduction, advantages & working principle of ABSAnti Lock braking system is an electronically controlled an add on system, to existing air brake system, used to prevent vehicle skidding during wheel lock under all circumstances of load, tyre/road grip coefficient. The ABS modulates the air pressure in the brake actuator to prevent wheel lock and provides precise vehicle control during braking.


Improves Stability

Prevents vehicle skidding by avoiding front & rear wheel lock. Helps driver to steer around obstacles during panic braking even on slippery roads. Helps to stop the vehicle at lesser stopping distance on dry as well as slippery roads. Prevents tractor swinging around the fifth wheel coupling in tractor trailer combination.

Improves Steerability while braking Shorter stopping distance Prevents Jack Knifing


Working Principle :ABS consists of an Electronic Control Unit (ECU), pressure modulator valves, sensing rings or pole wheel, wheel speed sensors, Diagnostic switch, Warning lamp and associated electrical wiring. ABS system takes over the control of the air pressure whenever a wheel is about to lock. Each rotating wheel hub is fitted with a Sensing ring or Polewheel. A Wheel Speed Sensor (magnetic sensor) which is mounted on each wheel in close proximity to the Sensing ring or Polewheel generates electrical pulses when the wheel rotates. The electric pulses generated will be in the form of sinusoidal pulses. The frequency at which the pulses are generated is a measure of the wheel speed. The generated electrical pulse signal is sent to Electronic Control Unit (ECU) for processing.

Diagnostics Switch Electronic Control Unit Warning Lamp

Wheel Speed Sensors

Modulator Valve



The ECU after receiving the input signals from all wheel speed sensors processes and compares the sensor signals and detects an impending wheel lock situation. When a wheel is about to lock, the ECU sends an electrical signal to the corresponding modulator valve solenoid (Modulator Valve is fitted in the delivery pipeline coming from dual brake valve), which releases pressure from the brake actuator. When the wheel recovers sufficiently, the brake pressure is reapplied by the ECU by switching off the signal to the modulator valve. This signal is sent to the Electronic Control Unit (ECU) through connecting cables and processed by the ECU. The modulator valve has an additional 'HOLD' state, which maintains pressure in the brake actuator, in order to optimize the braking process. The cycling of the modulator valve is continued till the vehicle comes to a controlled stop. During ABS operation, ECU switches the modulator valve to the above three states (Pressure release, Pressure hold and Pressure re-apply) five six times per second to regulate the brake pressure.

2) Suppliers for ABS System for Commercial vehicles (with S-Cam brakes)There are two suppliers for ABS system for Tata vehicles. i) Knorr Bremse ii) WABCO The working principle, components and their functions for both the suppliers are same. These systems can be identified by the name of supplier on the individual components. Parts for Knorr Bremse & WABCO are not interchangeable between the two suppliers.

3) ABS instructions to User (Operator)As soon as you switch on the ignition switch, ABS warning lamp on the dash-board should come ON for 5 seconds and go OFF. In case ABS warning lamp does not come ON momentarily or remains ON or comes ON any other time, then it indicates fault in the ABS. In such case, ABS may not function. However the basic brake system will continue to function normally, and will provide normal stopping ability. In case ABS warning lamp remains ON, take the vehicle to the nearest service station for attending to the fault. In case of vehicle being driven with ABS warning lamp in ON condition, applying panic brake or braking on wet road may result in wheel locking, as it would happen in a vehicle without ABS. Do not assume that with ABS fitted to a vehicle, it is safe to drive faster or more aggressively. Under panic braking conditions, press hard on the brakes and continue to hold it down. ABS does not come into action unless wheel is about to lock during brake application. Do not switch 'off' the ignition while driving. This makes ABS non-operational. For any welding job on the vehicle, disconnect all ECU connectors. For removing the electrical connector, do not hold & pull the wires. Hold connector body firmly & then pull it.

4) General Instructions to Mechanics (Working with ABS)Ensure wheel bearings are adjusted appropriately to ensure that the run-out of the pole wheel is within acceptable limits. Always ensure that the wheel run-out is within specified limits To push the sensor, use soft non pointed tool (Nylon bar, plastic bar, etc). Do not use any metallic sharp tool like screw driver After removing the hub, keep the hubs with the pole wheel facing upwards. Dont try repairing any of the ABS parts. Replace with new genuine parts. ABS prevents vehicle skidding/ pulling by avoiding the front & rear wheel lock. However in case of vehicle pulling to one side during partial braking condition is not due to ABS. The reason could be the basic brake system and investigation for brake pulling on vehicle without ABS system needs to be performed. When installing ancillary electrical equipment on the vehicle do not use the electrical supply to the ABS as a power source for the equipment. Do not connect or disconnect any ABS component with the ignition switched on. Never remove the battery while engine is running. Voltage spikes caused by the alternator could possibly damage the ECU if they were not absorbed by the battery. While replacing sensor, replace the sensor bush also and apply recommended grease (part of spares kit) on Sensor.

5) ABS ConfigurationABS configuration is based on the no of Sensors (S) & Modulators (M) used in the system. For twin axle 4 x 2 Truck, 4S /4M (i.e. 4 Sensors & 4 Modulators) system is used. - 4 sensors one on each wheel and - 4 modulator valves, one for each wheel brake actuator For multi axle vehicle 6 x 2 truck, 4S/4M system is used. 4 sensors two for front wheels and two for rear live axle wheels 4 modulator valves, two for front wheel brake actuators one for both rear left brake actuator one for both rear right brake actuator

Please refer the following brake circuit diagrams on ABS configuration for Twin axle & Multi axle vehicles.

Twin axle 4 x 2 Truck, 4S /4M system

Multi axle 6 x 2 Truck, 4S /4M system

6) Functions of individual components of ABS:a) Sensing ring or PolewheelSensing ring or Polewheel is a toothed wheel made of ferrous material. It has 100 evenly spaced teeth. The Sensing ring or Polewheel rotates along with the hub and cuts the magnetic flux generated by the wheel speed sensor. It is fitted on the wheel hub.

b) Sensor ('L' type)

It is a magnetic sensor (passive type) consists of a permanent magnet and a coil assembly. It generates electrical pulses proportional to wheel speed and transmits to the ECU as a sinusoidal signal It is fitted with a sensor bush in a bracket mounted in the carrier plate as a stationery part. The air gap of < 0.2 mm is maintained between Sensing ring or Polewheel and sensor.



< 0.2 mm Air Gap

Wheel Speed Sensor

Pole wheel


Adjustment of Polewheel & sensor Gap The spring-loaded sensor bush is used to hold the wheel speed sensor whilst allowing easy adjustment of the gap between it and the teeth of the sensing ring. The wheel speed sensor can slide in the sensor bush, so the gap between the wheel speed sensor and the teeth of the


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