INTRODUCTION:

INTRODUCTION:

• Anti-lock braking system (ABS) is an automobile safety system that allows the wheels on a motor vehicle to maintain tractive contact with the road surface according to driver inputs while braking, preventing the wheels from locking up (ceasing rotation) and avoiding uncontrolled skidding.

• ABS generally offers improved vehicle control and decreases stopping distances on dry and slippery surfaces for many drivers; however, on loose surfaces like gravel or snow-covered pavement, ABS can significantly increase braking distance, although still improving vehicle control.

INTRODUCTION:Recent versions not only prevent wheel lock under braking, but also electronically control the front-to-rear brake bias.

OPERATION:

• Typically ABS includes a central electronic control unit (ECU), four wheel speed sensors, and at least two hydraulic valves within the brake hydraulics.

• The ECU constantly monitors the rotational speed of each wheel; if it detects a wheel rotating significantly slower than the others, a condition indicative of impending wheel lock, it actuates the valves to reduce hydraulic pressure to the brake at the affected wheel, thus reducing the braking force on that wheel; the wheel then turns faster.

OPERATION:

• If the ECU detects a wheel turning significantly faster than the others, brake hydraulic pressure to the wheel is increased so the braking force is reapplied, slowing down the wheel.

• Some anti-lock systems can apply or release braking pressure 15 times per second .Because of this, the wheels of cars equipped with ABS are practically impossible to lock even during panic braking in extreme conditions.

OPERATION:

• ABS applies individual brake pressure to all four wheels through a control system of hub-mounted sensors and a dedicated micro-controller.

• A minimum of two additional sensors are added to help the system work: these are a steering wheel angle sensor, and a gyroscopic sensor.

• When the gyroscopic sensor detects that the direction taken by the car does not coincide with what the steering wheel sensor reports, the controller will brake the necessary individual wheel(s) so that the vehicle goes the way the driver intends.

OPERATION:

OPERATION:

ABS IN MOTORCYCLES:

• Different from cars, planes or trains, at a motorcycle rear and front wheel are controlled separately.

• If the rider only brakes with the front or rear wheel, the braked wheel tends to lock up faster as if both brakes would have been applied.

• Motorcycle ABS system uses Combined Braking System.

• CBS helps to reduce the danger of wheel locks and fall downs.

ABS IN MOTORCYCLES:

• A Combined Braking System distributes the brake force also to the non-braked wheel to lower the possibility of a lock up, increase deceleration and reduce suspension pitch.

• At a single CBS the brake pressure applied on the rear brake (pedal) is simultaneously distributed to the front wheel.

• A delay valve cuts the hydraulic pressure to assure that only when strong braking is applied, pressure is also created at the front wheel.

COMPONENTS:

Speed sensors:• A speed sensor is used to determine the acceleration or deceleration of

the wheel .

• These sensors use a magnet and a coil of wire to generate a signal.

• The rotation of the wheel or differential induces a magnetic field around the sensor.

• The fluctuations of this magnetic field generate a voltage in the sensor.

COMPONENTS:

• Since the voltage induced in the sensor is a result of the rotating wheel, this sensor can become inaccurate at slow speeds.

• The slower rotation of the wheel can cause inaccurate fluctuations in the magnetic field and thus cause inaccurate readings to the controller.

COMPONENTS:

Pump:• The pump in the ABS is used to restore the pressure to the hydraulic

brakes after the valves have released it.

• A signal from the controller will release the valve at the detection of wheel slip.

• After a valve release the pressure supplied from the user, the pump is used to restore a desired amount of pressure to the braking system.

COMPONENTS:

• The controller will modulate the pumps status in order to provide the desired amount of pressure and reduce slipping.

Controller:• The controller is an ECU type unit in the car which receives information

from each individual wheel speed sensor, in turn if a wheel loses traction the signal is sent to the controller, the controller will then limit the brake force (EBD) and activate the ABS modulator which actuates the braking valves on and off.

BRAKE TYPES:

They can be differentiated by the number of channels: that is, how many valves that are individually controlled and the number of speed sensors.

Four-channel, four-sensor ABS:

• There is a speed sensor on all four wheels and a separate valve for all four wheels.

• With this setup, the controller monitors each wheel individually to make sure it is achieving maximum braking force.

TYPES:

Three-channel, four-sensor ABS:

• There is a speed sensor on all four wheels and a separate valve for each of the front wheels, but only one valve for both of the rear wheels.

• Older vehicles with four-wheel ABS usually use this type.

• Channel indicates valves in the controller system.

TYPES:

• Three-channel, three-sensor ABS:

• There is a speed sensor and a valve for each of the front wheels, with one valve and one sensor for both rear wheels.

• This system provides individual control of the front wheels, so they can both achieve maximum braking force.

• The rear wheels, however, are monitored together; they both have to start to lock up before the ABS will activate on the rear.

• Commonly found on pickup trucks with four-wheel ABS.

TYPES:

Two-channel, four sensor ABS:

• Uses a speed sensor at each wheel, with one control valve each for the front and rear wheels as a pair.

• If the speed sensor detect lock up at any individual wheel, the control module pulses the valve for both wheels on that end of the car.

• Commonly found on old passenger cars.

TYPES:

One-channel, one-sensor ABS:

• It has one valve, which controls both rear wheels, and one speed sensor, located in the rear axle.

• The rear wheels are monitored together and they both have to start to lock up before the ABS kicks in.

• Commonly found on pickup trucks with rear-wheel ABS.