Anti-lock braking (AB) systems are designed to maintain driver control and car stability during emergency braking. Locked wheels will slow the car but will not provide steering ability. ABS allows you to apply maximum braking while maintaining the ability to "steer out of trouble." The theory behind anti-lock brakes is simple. A slipping wheel (where the contact patch of the tire slips relative to the road) has less traction than a non-slip wheel. By preventing your wheels from spinning as you slow down, anti-lock brakes benefit you in two ways: You'll stop faster and you'll be able to steer while stopping. An ABS system monitors four-wheel speed sensors to evaluate wheel slip. Slip can be determined by calculating the ratio of wheel speed to vehicle speed, which is continuously calculated from the four individual wheel speeds. During a braking event, the function of the control system is to maintain as much grip as possible of the wheels on the road - without the wheels locking - by regulating the pressure of the hydraulic fluid on each brake via electronically controlled solenoid valves. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an original essay Automobile manufacturers around the world are competing with each other to imagine more reliable devices, thus approaching the fantasy of the 'Propelled Welfare Vehicle' or 'Extreme Safety Vehicle', on which innovative work has been going on for some years now Most modern vehicle models offer ABS as a standard or optional feature. Locking of the wheels during braking causes skidding which then causes loss of support and control of the vehicle the route. So the car slides wildly it is possible to steer the road wheel still swiveling. This is the purpose of the ABS, the driver can brake sharply, make cunning movements and still be responsible of the vehicle in any road condition, at any speed and under any load. ABS does not decrease separation when stopping, but rather compensates for changing trim or stacking the tires by avoiding wheel lockup. During cold braking, when the wheels are about to lock, the sensors detect that the wheel has recently started to spin more slowly than the others on the vehicle. They then rapidly decrease the braking power on the affected wheel. This prevents the wheels from slipping on the asphalt. The moment the wheel starts moving again, full braking power is connected again. The ABS repeats the procedure until balanced braking is no longer required. The ABS works faster than any driver could, pumping the brakes a few times per second. Depending on the type of system, ABS changes the braking power at each wheel or set of wheels, although the driver's foot on the brake pedal applies all the brakes without a moment's delay in typical braking. The theory behind anti-lock brakes is simple. A slipping wheel (where the contact patch of the tire slips relative to the road) has less traction than a non-slip wheel. If the vehicle is stuck on ice and the wheels slip, the vehicle has no traction. This is because the contact patch slips relative to the ice. By preventing your wheels from spinning as you slow down, anti-lock brakes benefit you in two ways: You'll stop faster and you'll be able to steer while stopping. Good drivers always havepress the brake pedal during panic braking to avoid locking of the wheels and loss of steering control. ABS simply does the pumping work much faster and very precisely than the fastest human foot. The brakes of the vehicle not equipped with ABS lock the wheels very quickly when the driver suddenly applies the brake. In this situation, the vehicle slides instead of stopping. The skidding and loss of control was caused by wheel locking. Relieving and reapplying the brake pedal will prevent wheel locking which will thus prevent skidding. This is exactly what an electronically monitored slowdown mechanism does. When the brake pedal is pumped or pulsed, pressure is quickly applied and released to the wheels. This is called pressure modulation. Pressure modulation works to prevent wheel lockup. ABS can modulate brake pressure up to 15 times per second. By modulating brake pressure, friction between the tires and the road is maintained and the vehicle is able to come to a controllable stop. Steering is another important consideration. As long as a tire doesn't slip, it only goes in the direction it's turned. But once skidded it has little or no directional stability. The maneuverability of the vehicle decreases if the front wheels are blocked and the stability of the vehicle decreases if the rear wheels are blocked. ABS precisely controls the wheel slip speed to ensure maximum tire grip force and thus ensures vehicle handling and stability. Many different ABS are found on today's vehicles. These designs vary in basic layout, operation, and components. ABS components can be divided into two categories. Hydraulic Components Electrical/Electronic Components In addition to these normal and conventional brake components are part of the entire braking system. Accumulator: An accumulator is used to store hydraulic fluid to maintain high pressure in the brake system and provide residual pressure for power-assisted braking. Normally the accumulator is charged with nitrogen and is an integral part of the modulator unit. Anti-Lock Hydraulic Control Valve Assembly: This assembly controls the release and application of brake system pressure to the wheel brake assemblies. It can be of the integral type and of the non-integral type. In the integral type, the unit is combined with the power booster and the master cylinder unit into one assembly. The non-integral type is mounted externally to the master cylinder/power amplifier and is positioned between the master cylinder and the wheel brake assembly. Both types generally contain a solenoid valve that controls the release, hold and application of brake system pressure. Booster Pump: The booster pump is a set of electric motor and pump. The booster pump is used to supply pressurized hydraulic fluid to the ABS. The pump motor is controlled by the system control unit. Brake Booster/Master Cylinder Assembly: Called the hydraulic unit, it contains the valves and pistons necessary to modulate the hydraulic pressure in the wheel circuit during ABS operations. Fluid accumulator: Different from a pressure accumulator, fluid accumulator, temporarily stores brake fluid, which is removed from the wheel brake unit during the ABS cycle. This fluid is then used by the pump to create pressure for the hydraulic brake system. Hydraulic Control Unit: This assembly contains solenoid valve, fluid accumulator, pump and electric motor. The unit can have one pump and one motor or one motor and twopumps. Main valve: This is a two-position valve, also controlled by the ABS control module and is only open in the ABS model. When pressurized brake fluid is opened from the booster circuit it is directed into the main circuit to prevent excessive pedal travel. Modulator Unit: The modulator unit controls the flow of pressurized brake fluid to individual wheel circuits. Typically the modulator consists of the solenoid that opens and closes the valves, several valves that control the flow of fluid to the wheel brake units, and electrical relays that turn the solenoids on or off through commands from the control module. This unit may also be called a hydraulic actuator, hydraulic power pack or electro-hydraulic control valve. Solenoid valves: Solenoid valves are located in the modulator unit and are electrically operated by signals from the control module. The control module activates or deactivates solenoids to increase, decrease or maintain hydraulic pressure on individual wheel units. Wheel Circuit Valves: Two solenoid valves are used to control each circuit or channel. One controls the circuit's inlet valve, the other controls the outlet valve. The position is determined by the control module. The outlet valves are normally closed and the inlet valves are normally open. The valves are activated when the ABS control module supplies 12 volts to the circuit's solenoids. During normal driving, the circuits are not activated. ABS Control Module: This small computer is normally mounted inside the boot on the wheel arch, mounted on the master cylinder or is part of the hydraulic control unit. Monitor system operation and check the anti-lock function when necessary. The module relies on input from the wheel speed sensors and feedback from the hydraulic unit to determine whether the abs are working properly and to determine when anti-lock mode is required. Brake Pedal Sensor: The anti-lock brake pedal sensor switch is normally closed. When the brake pedal exceeds the anti-lock brake pedal sensor switch setting during an anti-lock stop, the anti-lock brake control module detects that the anti-lock brake pedal sensor switch is open and grounds the pump motor relay coil. This energizes the relay and turns on the pump motor. When the pump motor is running, the hydraulic reservoir is filled with high-pressure brake fluid, and the brake pedal is pushed up until the anti-lock brake pedal sensor switch closes. when the anti-lock brake pedal sensor switch closes, the pump motor is turned off and the brake pedal is depressed slightly with each ABS control cycle until the anti-lock brake pedal sensor switch closes opens and the pump motor is turned back on. This minimizes pedal feedback during ABS. cycle.Pressure differential switch: This is located in the modulator unit. This switch sends a signal to the control module whenever there is an unwanted difference in hydraulic pressures within the brake system. Relays: Relays are electromagnetic devices used to control a high-current circuit with a low-current switching circuit. In ABS, relays are used to switch motors and solenoids. A low-current signal from the control module energizes the relays that complete the electrical circuit of the motor or solenoid. It can be placed on a half shaft, a differential or the hub of a wheel. This ring comesused together with the wheel speed sensor. The ring has a number of teeth around its circumference. As the ring rotates and each tooth passes the wheel speed sensor, an AC voltage signal is generated between the sensor and the tooth. It is mounted next to the different toothed ring. When the ring teeth rotate past the sensor, an AC voltage is generated. as the teeth move further away from the sensor, the signal is interrupted until the next tooth moves closer to the sensor. The end result is a pulsating signal that is sent to the control module. The control module translates the signal into wheel speed. The sensor is normally a small coil of wire with a permanent magnet in the center. One of the classifications of ABS is integral and non-integral type. In the integral type they combine the main cylinder, the hydraulic multiplier and the hydraulic circuit in a single hydraulic group. In the non-integral type they use a conventional booster with vacuum assistance and a master cylinder. Additionally, they can be classified based on the control they provide. This is the best scheme. 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 ensure it is achieving maximum braking force. This scheme is commonly found on pickup trucks with four-wheel ABS, it has one speed sensor and one valve for each of the front wheels, with one valve and one sensor for both rear wheels. The speed sensor for the rear wheel is located on the rear axle. This system provides individual control of the wheels, so that both can achieve maximum braking force. The rear wheels, however, are monitored together, both must begin to lock before the rear ABS activates. With this system, it is possible for one of the rear wheels to lock during a stop, reducing the effectiveness of the brakes. This system is commonly found on pickup trucks with ABS on the rear wheels. It has a valve that controls both rear wheels and a speed sensor, located in the rear axle. This system works the same way as the rear end of the rear channel system. The rear wheels are monitored together and both must begin to lock before the ABS kicks in. In this system it is also possible that one of the rear wheels locks, reducing the effectiveness of the brakes. ABS Improvements Some systems that work with ABS are Automatic Traction Control and Automatic Stability Control, discussed below. Automatic Traction Control (ATC) Automatic traction control systems apply the brakes when a drive wheel attempts to slip and lose traction. The system works best when one drive wheel works on a good traction surface and the other does not. The system also works well when the vehicle accelerates on slippery road surfaces, especially uphill. ATC is especially useful on four-wheel or all-wheel-drive vehicles where loss of traction on one wheel could impede driver control. When driving on the road, the ATC system uses an electronic control module to monitor the wheel speed sensors. If a wheel enters a situation of loss of traction, the module applies braking force to the wheel in difficulty. Loss of traction is identified by comparing vehicle speed to wheel speed. If a loss of traction occurs, the wheel speed will be greater than expected for the particular vehicle speed. ABS and ATC systems can be integral and use common valves. These systems are designed.