subject: Abs Brakes Systems Explained [print this page] ABS uses wheel speed sensors, a hydraulic control unit, and a computerized electronic control module, which is the "brain" of the system. When the brake pedal is applied, the electronic control module monitors the speed of the wheels through the wheel speed sensors.
If the control module detects that one or more wheels are about to lock up, the module signals the hydraulic unit to control hydraulic pressure to that wheel or wheels. This varying of pressure is much like "pumping" the brake; only with the ABS system, the wheel that is locking up (causing a potential loss of control) is the only one being controlled, while the rest of the wheels are free to roll.
This maximizes vehicle steer ability. Here are a few things you may notice the first time you use anti-lock brakes:
- When the pedal is applied and ABS is activated, the pedal may feel harder than usual; this is normal.
- The pedal may seem to ratchet or pulsate (vibrate), or there could be a combination of these sensations; this is also normal.
- Finally, you may hear a noise that sounds like a motorboat engine; this is the hydraulic control unit operating; again, this is normal.
When driving a car with ABS brakes, remember to:
- Maintain the same safe stopping distance from the vehicle ahead as with conventional brakes. ABS will not make the vehicle "stop on a dime."
- Do not pump the brake. Just apply firm, constant pressure and let ABS do the work for you.
You may feel a slight vibration or hear noise as the hydraulic control unit functions. Be ready to push the pedal further if it travels closer to the floor.
Many people wonder how much water it takes before their car will hydroplane? Hydroplaning or aquaplaning is a phenomenon that occurs when a layer of water builds between the footprint of the rubber tires of the vehicle and the road surface. When this happens, the vehicle can't respond to control efforts such as steering and braking.
According to laboratory tests, hydroplaning occurs on a wet road surface at speeds of 50MPH or higher. The deeper the water, the worse it becomes.
You're driving along in the rain, and suddenly your car is out of control, acting as if it were on ice. What is happening?
A thin sheet of water has formed between the tire tread area and the road surface. Your vehicle has become a powerful sled and you're along for a wild ride!
Three main factors that contribute to hydroplaning:
- Vehicle speed: As speed increases, wet traction is reduced, and thus the chance of hydroplaning increases.
- Tire tread depth: The more shallow the depth, the less the tires are able to resist hydroplaning.
- Water depth: The deeper the water, the sooner the tires will lose traction.
If you find your car hydroplaning:
- Do not apply the brakes because braking is ineffective when hydroplaning and will cause the vehicle to skid even more.
- Do not turn the steering wheel. The vehicle is moving uncontrolled on a sheet of water; trying to steer out of it could result in a crash.
- Hold the wheel firmly and do not steer in any other direction but straight ahead. This is the best way to "ride it out."
- Ease your foot off the gas (helps to regain traction) until the car slows and steering returns to normal.
- If you need to brake, do it gently with light pumping actions. If you have ABS brakes, the system will do this for you. Just apply steady, even pressure to the brake pedal and the system will take care of the rest.
Once your vehicle's tires come in contact with the road surface, you should be able to regain control.
