When vehicle wheels are about to lock the abs
Abs and wheel lock are two safety technologies widely used in automotive steering systems. The smooth running of the steering wheel, allowing it to return to approximately the same point after a movement in one or another direction, contributes to increasing safety on the road. In this chapter, we will analyze some ABS problems that can occur, how they appear on a mechanic’s diagnostic machine, what should be done if they happen and how vehicles are equipped with ABS.
Multiple wheels apply the brake multiple times per second
When a vehicle is about to lock the ABS, multiple wheels apply the brake multiple times per second. ABS uses two strategies to prevent locking: pumping and modulating. When one wheel locks, the ABS switches to pumping mode by releasing the pressure on that wheel and reapplying it at a higher rate.
When all four wheels are close to locking, it switches to modulating mode by releasing pressure on all four wheels and reapplying it at a lower rate. Pumping is used when one wheel locks, while modulating is used when multiple wheels lock up.
Allowing some wheels to lock reduces overall braking power
When the brakes are applied, the ABS system monitors wheel speed and applies the brakes to the wheels that are rotating fastest. This allows them to lock up (and skid) slightly so that the other wheels can continue to turn freely.
When all four wheels lock, there is no movement of the vehicle and it skids sideways with no directional control. If you apply the brakes hard enough, you may be able to regain control by releasing pressure on the brake pedal and reapplying it until you feel some braking action again.
When vehicle wheels are about to lock the abs activates and pulsates
This is a safety function of the ABS system. The pulsing you feel is the activation of the anti-lock braking system (ABS). This is done to prevent the wheels from locking up and skidding during hard braking situations.
The ABS will be activated when you apply the brakes hard enough that one or more of your wheels is about to lock up. The ABS will then pulse in order to prevent any wheel from locking up completely.
When the vehicle begins to accelerate
This is not the same as when you step on the brakes, which locks the wheels and causes a skid. When the wheels lock, it means that your car has reached its maximum possible speed. The ABS system is designed to use a combination of brake pressure and engine power to control how much braking force is applied to each wheel.
If you press on the brakes too hard, you can experience what’s known as “brake fade.” This happens when too much heat builds up in the brake pads (or discs) while they are working hard to slow down your vehicle during hard braking. If this happens, then eventually the brakes will stop working altogether especially if you continue pressing them down hard enough to apply pressure to those hot pads at all times.
This can be dangerous because if there isn’t enough friction between your tires and the road surface, then your vehicle won’t be able to stop as quickly as it should be able to do under normal circumstances (and perhaps even at all).
The faster the wheels turn the more pressure will build on the brake pedal
The ABS system is designed to prevent locking of the wheels. When it senses that this might happen, it applies the brakes on each wheel in turn very quickly. This can produce a pulsing or pulsating feeling in the brake pedal, and/or a slight vibration through the steering wheel, which might be felt by passengers.
It’s important to understand that when you select a higher gear, such as when accelerating up a steep hill or cresting a humpback bridge, you will need more time to slow down than when you’re travelling at lower speeds or have a longer distance to stop. This is because your vehicle’s engine has less power at higher RPMs and will take longer to slow down your vehicle as it approaches a complete stop.
The wheels will lock again and again until the brakes are no longer needed or the vehicle is stopped
When the ABS system is active, the wheels are prevented from locking by a hydraulic brake pressure modulation system that uses wheel speed sensors to measure the rotational speed of each wheel.
The controller compares the measured speed to a threshold value and modulates brake pressure to maintain the required braking effort. This prevents the wheels from locking up while maintaining enough braking torque to stop the vehicle.
This modulation provides better control than conventional brakes because it distributes brake force evenly between all four wheels and keeps them from locking up. The ABS system is also capable of detecting when one or more wheels have stopped rotating under heavy braking conditions. When this happens, the ABS system will automatically apply maximum braking effort at each wheel until either the brakes are no longer needed or the vehicle comes to a complete stop.
Conclusion
The ability to identify when your vehicle is about to completely lock a brake is essential. The faster you can react and move your foot to a different position, the less likely you are to get rear-ended. In some cases, a certain part will vibrate while it approaches complete lock up, giving you enough time to react once you feel the vibrations. In other vehicles, however, there is no such indicator or warning, so knowing and recognizing this potential setup allows you to react accordingly.
