Abs systems in cars pdf

Deceleration Sensor During braking on four-wheel-drive vehicles, it detects the vehicle's deceleration rate and sends these signals to the ECU. The ECU uses these signals to determine precisely the road surface conditions and make the required control measurements. The deceleration speed sensor is located in the luggage compartment in passenger cars and in the engine compartment in other vehicles.

Deceleration sensor contains two pairs of LEDs light emitting diode and one channel with photo transistor plate and a signal conversion circuit. When the vehicle's deceleration rate changes, the channel plate is rocked along the longitudinal direction of the vehicle in accordance with the deceleration rate.

Channels on the channel plate open and close the photo transistor by cutting off the light coming from the photo-transistor from the LEDs. The rate at which these transistors turn on and off is divided into four levels, which are signaled to the ECU. Valves The Hydraulic Control Unit controls these valves which are continuously active in the system. The main tasks of valves are; In the first position, valve open; the pistons in the caliper are braked by giving full power to them.

In the second position cuts the valve line; it cuts off the hydraulic flow on the line leading to the piston and no power is transmitted even when the pedal is pressed. Hydraulic Pump When the flow of the valve line is stopped, the hydraulic pressure is released from the pump to regain the lost pressure. This process is repeated every time when the hydraulic pressure decreased due to opening of valves. It is located on the hydraulic unit.

ABS Control Module ABS Control Module is a microprocessor that evaluates the information transmitted by the wheel speed sensors and with this information it controls the ABS system by giving the necessary commands to the actuators. Generally, it is located under the hydraulic unit.

In some vehicles the hydraulic unit may have been mounted at a different location. In the event of a fault, the ABS and the connected systems are disabled, some failures may cause problems with other systems, and the ABS warning lamp is turn on. Types of ABS 5. On vehicles with ABS on all four wheels, the braking systems of the cars prevent the wheels from locking on all four wheels. The driver can control the vehicle better and it is easier to keep the vehicle under control.

At this time, the braking pressure required for braking is set. If only the rear two wheels have ABS; this situation is usually found in trucks, minibuses and sports cars. The car is prevented from locking only on the rear wheels. In this case, the driver must manually adjust the pressure on the brake pedal. Thus, the driver can conveniently orient the car in the desired direction and provide safe driving.

Figure 5. Each wheel is controlled independently. Steering safety and stopping distance on all road conditions are protected. In front-wheel drive vehicles, most of the weight is on the front wheels due to engine and transmission system located in front of the vehicle.

For this reason, vehicles with four- channel ABS have a low-logic choice on the rear wheels to maintain the balance of the vehicle in the majority. Three-channel Three-sensor ABS The three speed sensors measure the number of revolutions of both the wheel and differential sun gear.

The braking force on the front wheel is adjusted separately by solenoid valves. The braking force of the rear wheels is regulated by a single solenoid valve. This type hydraulic units are used in parallel brake circuits. Two-channel ABS This type of hydraulic unit is used on heavy vehicles or on vehicles such as trucks.

Only the rear two wheels are controlled. There is only one valve and one sensor, which controls the rear wheels. It is similar to the three-channel ABS system for the way of operation.

The distinctive feature of the system is that there is no independent speed sensor for each wheel. ABS Failures and Signs If the warning light of the ABS brake system does not extinguish within three seconds of applying the voltage, or if the lamp lights up during driving, there is a fault and the system is switched off.

Figure 6. In the meantime, the normal operation of the brakes remains unaffected. The investigation of the faults is extremely easy with the diagnostic facility.

Faults are detected according to the fault code appropriate to the fault type. Determination of the fault location in the faulty line can also be done by conventional methods. If the ABS warning light is on; In order to provide separate testing of the parts in the system, this diagnostic method is divided into stages. In any kind of fault diagnosis, the test should be started from the first stage until the fault is corrected. If the ABS warning light is on after the engine has started, sensor cables and isolations should be checked.

All sensor cabling in the system and their insulation should be checked one by one. First, the system's members should be tested one by one, then complaints should be followed up to the developer. If the ABS warning lamp lights up intermittently; It is also possible to investigate the fault in this case again at various stages. The handbrake is released; if the light remains on, the hand brake setting is checked.

Hydraulic level warning lamp operation check; The ignition is switched off, the pedal is pumped at least 20 times. The ignition is switched on and the hydraulic level is checked immediately when the engine has stopped running; It should be between 'max' and 'min' lines. If the ABS warning light is not lit at all; All the recommended operations are performed so that all parts in the system can be tested one by one.

If the ABS warning light is not lit at all, fuses, light bulbs and wiring should be checked. If the brake pedal goes too deep While ABS warning light is off ; After all the parts in the system have been checked, external leaks are checked, and air is taken from the system.

Central pump internal hydraulic leaks are also checked, and necessary actions and changes are performed. This operation is followed by electrical control of the main valve. If the operation of ABS is weak; After all elements are checked in the system, diode operation control is performed.

Then an external leak check is carried out and air in the system is removed. After that, resistance control of the inlet and outlet valves is performed, and the hydraulic duty controls of the inlet and outlet valves are performed. As a result of the checks made, necessary actions are taken.

Advantages and Disadvantages of ABS 7. Advantages of ABS The advantage of the anti-lock braking system is that the vehicle under all kinds of braking conditions; stabilize and ensure optimum braking without losing control of the steering wheel. Optimum braking means optimizing the braking distance by achieving maximum road holding, thus bringing it to the optimum distance. If emergency braking is necessary, must be able to avoid an obstacle, lose dominance during bends, and lose steering dominance even if the wheels have different levels of grip.

When the wheel or differentials of the vehicle rotates, it induces magnetic field around the sensor. The fluctuation in this magnetic field generates voltage in the sensor.

This voltage generated sends signals to the controller. With the help of the voltage the controller reads the acceleration and deceleration of the wheel. Each brake line which is controlled by the ABS has a valve. In some of the systems, the valve works on three positions. The clogging of the valve is the major problem in ABS. When the valve is clogged, it becomes difficult for the valve to open, close or change position.

When the valve is in inoperable condition, it prevents the system form modulating the valves and controlling pressure to the brakes. Pump is used to restore the pressure to the hydraulic brakes after the valve releases the pressure. When the controller detects wheel slip, it sends signals to release the valve. After the valve releases the pressure supplied from the driver, it restore a desired amount of pressure to the braking system. The controller modulates adjust the status of the pump so as to provide desired amount of pressure and reduce slipping of the wheel.

Related Posts: What is Heat Exchanger? Leave a Comment Cancel Reply Your email address will not be published. ABS simply gets the pumping job done much faster and in much precise manner than the fastest human foot.

A simple braking system consists of a master cylinder, and four wheel cylinders. Every wheel cylinder contains two pistons which move out words when the hydraulic fluid flows from the master cylinder to the wheel cylinders through the suitable pipes or lines. Springs are used to hold the brake shoes on all four wheels. When the brake pedal is pressed the piston in the master cylinder forces the liquid out of the cylinder.

This liquid presses the two pistons in the wheel cylinders outwards. These two pistons push the brake shoes out words. The brake shoes in turn press against the brake drums; this stops the brake drum which will be rotating.

When the brake pedal is released the master cylinder is pushed backwords. This is done by a spring fitted in the master cylinder. The liquid in the wheel cylinder is pushed outwards through the pipes. It returns through the pipes to the master cylinder.

This is how the hydraulic system of the four wheels operates 3. The liquid in the reservoir flows through bypass port to the master cylinder.

When the pedal is pressed the primary piston moves to the left. When the pedal is released the primary piston is moved back wards. At the same time a partial vacuum is developed in the space previously occupied by the spring. In this case the vehicle slides rather than rolls to a stop. The skidding and lack of control was caused by the locking of wheels. The release and reapply of the brake pedal will avoid the locking of the wheels which in turn avoid the skidding.

This is exactly what an antilock braking system does. This is called pressure modulation. Pressure modulation works to prevent the wheel locking. ABS can modulate the pressure to the brake as often as 15 times per seconds.

By modulating the pressure to the brakes the friction between the tires and the road is maintained and the vehicle is able to come to the controllable stop. But once it is skid it has little or no directional stability. The Maneuverability of the vehicle is reduced if the front wheels are locked and the stability of the vehicle is reduced if the rear wheels are locked. ABS precisely controls the slip rate of the wheels to ensure maximum grip force from the tyre and it there by ensures maneuverability and stability of the vehicle.

ABS control module calculates the slip rate of the wheels based on the vehicle speed and speed of the wheels, and then it controls the brake fluid pressure to attain the target slip rate. These designs are varied by their basic layout, operation and components. The ABS components can be divided into two categories. Hydraulic components 2. Normally the accumulator is charged with nitrogen gas and is an integral part of the modulator unit. It may be of integral type and non integral type.

In integral type the unit is combined with the power boost and master cylinder unit into one assembly. Both types generally contain solenoid valve that control the releasing, holding and applying of brake system pressure. The booster pump is used to provide pressurized hydraulic fluid ABS. The pumps motor is controlled by systems control unit. This fluid is then used by pump to build pressure for the brake hydraulic system.

The unit may have one pump and one motor or it have one motor and two pumps. When open pressurized brake fluid from the booster circuit is directed into the master circuit to prevent excessive pedal travel. This unit may also be called the hydraulic actuator, hydraulic power unit or the electro hydraulic control valve. The control module switches the solenoids on or off to increase, decrease, or maintain the hydraulic pressure to the individual wheel units.

One controls the inlet valve of the circuit, the controls the outlet valve. Outlet valves are normally closed and inlet valves are normally open. Valves are activated when abs control module switches 12 volts to the circuit solenoids. During normal driving the circuits are not activated. It monitors system operation and controls antilock function when needed.

The module relies on input from the wheel speed sensors and feedback from the hydraulic unit to determine if the abs is operating correctly and to determine when the anti lock mode is required. When the brake pedal exceeds the antilock brake pedal sensor switch setting during an antilock stop, the antilock brake control module senses that the antilock brake pedal sensor switch is open and grounds the pump motor relay coil. When the pump motor is running, the hydraulic reservoir is filled with high pressure brake fluid and the brake pedal will be pushed up until antilock brake pedal sensor switch closes.

This switch sends a signal to the control module whenever there is an undesirable difference in the hydraulic pressures with in the brake system.