Almost all modern vehicles use an anti-lock braking system (ABS), which prevents accidents by allowing drivers to steer properly and reducing braking distance. But what exactly is ABS, and how does it prevent accidents?
To understand ABS, it’s important to first understand the principles of steering and braking. When you apply the brake pedal, brake pads on the wheel disks will activate and press against the disks, stopping the wheel rotation and causing friction between the road and wheels to stop the vehicle. The steering mechanism, on the other hand, depends on the simple principle of wheels rolling. The wheels rotate on their axis and move along the direction of the car. For non-slip rolling conditions, the sum of the translational and rotational velocities at the contact point should be zero.
In automobiles, all four wheels should be rolling at all times to avoid the vehicle slipping. If the wheels are turned but the car carries straight on, the car will slip. The translation velocity needs to be inclined to avoid this, which is possible when the whole car makes a turn. When the car makes a turn, all four wheels can satisfy the condition of rolling, and the velocity at the contact point of all four wheels becomes zero.
During braking, due to the brake pads being activated, the wheels stop spinning. Even if the wheels are turned, since they are not rotating, there will be no rotational velocity. Therefore, the vehicle does not need to turn, and the vehicle will slide in a straight line, which can cause an accident. Apart from losing control of the steering, cars without ABS face another big issue of braking on surfaces with different traction levels. When the left and right wheels are on different traction surfaces, applying the brakes will generate different frictional forces on the wheels, producing torque, and the car will go into an uncontrollable spin.
This is where ABS comes in. ABS prevents the wheels from completely locking up by partially releasing the brake pad on the wheel when the speed sensors detect that a wheel is about to lock up. This way, the wheels will be allowed to spin intermittently during braking, allowing steering to function, and drivers will be able to steer the vehicle even during braking.
The key benefit of ABS is reducing the braking distance. The frictional coefficient between the tire and the road varies with respect to slip. During braking without ABS, the frictional coefficient which comes into effect is predominantly sliding friction. However, in ABS braking, the clever algorithm adjusts the brake pressure to keep the slip ratio near to 12%, where the frictional value is at the maximum. This significantly reduces the braking distance.
In addition to reducing braking distance, modern ABS also includes intelligent electronic braking distribution (EBD), a subsystem that measures the yaw rate of the car and the relative slip of each wheel. By reducing brake pressure on the wheels with higher grip, we can reduce the frictional force produced by these wheels, keeping the yaw torque and the whole car under control.
In conclusion, ABS is a crucial system that all drivers should understand. By understanding its principles, you can see how it prevents accidents and reduces braking distance. So the next time you’re on the road, remember, ABS can make all the difference.