The key part of semi-trailer: Anti-lock braking system (ABS) is an electronic safety system that controls and monitors wheel speed when brakes are applied. It is also known as an anti-skid braking system.
The system functions with the air brake system that is found in heavy-duty trailers. ABS ensures that wheels maintain their contact with the ground when the driver applies the braking system.
The safety system also prevents uncontrolled wheel skidding and lock-up.
Without the ABS, the driver loses control of the vehicle because the wheels either stop turning or skid on the surface. Many heavy-duty trucks overturn and sometimes cause fatal accidents where their braking systems fail.
The ABS is particularly important for controlling wheel speed on slippery and loose gravel surfaces. Most drivers tend to lose control of heavy trucks on such surfaces. The ABS consists of four wheel speed sensors, an electronic control unit, and two hydraulic valves.
The brake system functions automatically when brake pedal or valve is depressed. A wheel goes through a rapid deceleration before it locks up.
In most cases, the deceleration is faster than the standard deceleration speed of a car especially when the vehicle has no safety system. It takes less than a second for the wheel to stop spinning after it locks up.
How the ABS works
1.The wheel sensors detect when a wheel is about to lock after applying brakes. A wheel could be rotating at a lower speed than the other wheels.
A sensor uses an electromagnet coil, Hall-effect sensor and a magnet to generate and send a signal. Any the rotation on wheel triggers a magnetic field.
Any fluctuations in the magnetic field because of acceleration or deceleration generate a voltage in the wheel sensors. The sensors send readings to the electronic control unit for action.
2.The electronic control unit triggers the hydraulic valve to reduce the amount of pressure applied to the brake of that specific wheel.
3.When the braking force is reduced, the rotation speed of the wheel increases until it rotates at the same speed as other wheels.
4.The pump restores the right amount of pressure required in the braking system. The ABS controller regulates the function of the pump to ensure that it sustains the right pressure amount in the system.
5.In case a wheel is turning at a higher speed than others are, the control unit increases the pressure on the braking system on the affected wheel. The wheel slows down as the braking force increases.
6.The ABS system repeats the process several times. The driver can detect the process on the brake pedal. The rapid opening and closing of hydraulic valves send pulses to the brake valve or pedal.
Sometimes the process sends an audible chattering sound on the pedal. The control unit can repeat the process 15 times in a second in some ABS systems.
7.In case the ABS malfunctions or any of its components develops a mechanical problem, the whole system is disabled. A warning sign or light appears on the instrument panel warning the driver that the ABS has a fault. The system is only activated when the problem is fixed.
The continuous process ensures that a car fitted with an ABS system does not lock up at any time even in case of emergencies. Sometimes the ABS malfunctions when the sensors send inaccurate readings to the control unit.
The sensors generate a voltage based on the rotation of the wheels. When the rotation speed is slow, the fluctuations in the magnetic field are inaccurate. Consequently, the readings or signals sent to the controller are inaccurate.
When the controller in the ABS system is functioning properly, it corrects any possible lock up even before the affected wheel can change its rotation speed significantly.
If the wheel has started decelerating at a faster rate than the vehicle, the controller reduces the wheel’s speed so fast that the wheel and vehicle decelerate at the same speed within seconds.
Drivers must check their ABS systems regularly to ensure that they are functioning properly. Truck drivers should not ignore warning signs that the system sends on the dashboards especially when carrying heavy loads.
If you drive a heavy-duty truck for while without detecting any pulses or chattering sounds on the brake pedal, you need to have your ABS system checked.