An Anti-lock Braking System (ABS), the name itself defines it as the system used for braking purposes to slow down the wheel without locking it. In other words, It is also called an anti-skidding braking system. The purpose of ABS is to prevent the wheels from locking up during braking. Therefore, maintains the traction with the road surface for more stability and allows better control over the vehicle. This system uses the principle of Cadence braking and Threshold braking.
The ABS controls the rate at which an individual wheel decelerates with the action of regulating the braking pressure through a pressure-modulating unit. The pressure is controlled by the signal generated by the controller which is derived from the analysis of the output taken from the wheel speed sensors. Many aircraft and land vehicles use ABS. One example of the effectiveness of ABS in a car is shown above.
Components of ABS:
a. Wheel speed sensor:
The components of the Wheel speed sensor normally consist of a toothed ring and a magnet enclosed within the coil. The contact between the ring and the magnet will generate an electric signal. This signal is then sent to the controller which determines the speed of each wheel individually and controls the valve to maintain the pressure depending on the speed of the wheel.
b. Controller:
The controller is the processing unit in ABS, it is also known as the Electronic Control Unit (ECU). It receives the signal from individual wheel speed sensors. When an individual wheel speed is less than the limiting value, the wheel speed sensor will send a signal to the controller. And the controller will decrease the braking force by adjusting the valve. But, when an individual wheel speed is more than the limiting value, the wheel speed sensor will send a signal to the controller. And the controller will increase the braking force by adjusting the valve.
c. Valves:
A valve is an important part of the ABS inside the HCU (Hydraulic control unit). It consists of a solenoid valve that regulates the brake pressure according to the speed of the wheel. When applying force on the brake pedal, the speed of the wheel decreases simultaneously then the valve will limit the pressure on the brake to prevent the locking of the wheel. And, when the wheel tends to rotate, the valve will increase the braking pressure. The operation of limiting and releasing pressure through the valve happens in 3 steps of the valve position. They are,
• In the Open position, the Valve allows the pressure from the master cylinder to pass through the brake.
• In the Block position, the Valve blocks the extra pressure from the master cylinder to the brake and maintains a limited pressure on the brakes.
• In the Release position, Valve releases the pressure held on the brakes
d. Pump:
The function of the pump in ABS is to restore the pressure to the brakes after the release of the valve. The pump is controlled by the controller depending on the signals received from wheel speed sensors to get the desired amount of pressure in the process.
e. Brake fluid:
In every hydraulic system, the fluid is the main applicator of the system. The function of Brake fluid is to transfer pressure from the Brake pedal to the brake mechanism at the wheels. Because the operation of the hydraulic braking system includes the compression of fluid to transfer the pressure and compression produces a lot of heat. The braking fluid should possess some properties like it should have a high boiling point.
Working of ABS:
As we apply pressure on the brake pedal, it will inject fluid pressure from the master cylinder to the HCU. The HCU consists of a Hydraulic chamber, valve, and pump) to each wheel brake. While in hard braking If the sensors detect that a wheel is about to lock up, then the sensor will send the signal to the controller in the HCU system. After that, the system will release the pressure on the brake. The release is only for a moment. But when the sensor detects that the wheel is accelerating. It will send the signal to the controller in the HCU system and the system will apply the pressure.
The process continues till the wheel speed becomes zero, generating the pulse-like force to the brake. This process is so fast that it occurs 15 times a second, depending upon the system. Because of the speed of the system, we may feel a pulsation through the brake pedal as we press it when ABS is active.
Advantages
- ABS helps in stopping the car without losing control in emergency braking.
- Because of ABS, the Cars will be more stable while braking so they are less likely to be involved in crashes.
- We can get Better braking performance in diverse conditions.