Brakes stop your vehicle by applying pressure to your wheels. The pressure or resistance applied creates friction. That result of the friction is heat. The friction slows and eventually stops a wheel. The friction creates lots of heat. The speed which a wheel can be stopped depends on things like the vehicles weight, braking force, the total braking surface area, efficiency of creating friction, and removing that heat. The heat needs to be removed or minimized so the system can perform adequately.
Types of Breaks
Drum brakes are designed like a drum. The components are housed in a small drum that rotates with the wheel. Inside are a set of shoes. That would be triggered by pressing the brake peddle. Press the brakes, and the shoes are pressed against the wheel creating friction that slows the wheel. The challenge of drum brakes is that when continually pressed, like slowing on a long hill, heat builds up and the system becomes less effective.
Disc brakes use a rotor and caliper to slow the wheel. Attached on both sides of the caliper are brake pads. When the brake pedal is pressed, the caliper, and pads, press against the wheel. Unlike drum brakes, the mechanism is exposed to air which can cool the system while it operates. This allows the system to work more effectively than drum brakes.
Many vehicles use a combination of brakes: with front disc systems in front and drum brakes in the rear. But four-wheel disc brakes are available on most higher-end models.
If you plan on driving on ice and snow, and if you’re reading this you better be, anti-lock braking systems (ABS) were built for you. When roads are slick, the coefficient of friction goes down increasing your chances of slipping. ABS are designed to minimize the slip by increasing traction. In simplest terms, they automatically start and stop pressure to the brake pads or shoes. ABS are built using machines and computers. These include speed sensors, pumps, valves and controllers.
Speed sensors do what they sound like they do and sense speed. By sensing speed these sensors can “sense” when a wheel is about to lock up. The sensors can be at the wheel, the differential or both.
Valves are placed in the brake line of ABS controlled brakes. The valve manages pressure transmitted between the master cylinder and brake. Valves can be further managed and mediated by placing it in various positions. An open valve allows pressure to freely between the master cylinder and the brake. A closed valve blocks the line, isolating the brake from the master cylinder, preventing the driver from from increasing pressure by pressing harder on the brake pedal. A partially open valve releases some of the pressure from the brake.
The pump allows pressure to be restored after a valve releases pressure. The pump, pumps.
The controller “controls” things like valve position based on sensor information. The controller is a kind of computer.
How do ABS Systems Work?
From your perspective, you press the brake pedal and hold it down. The system does the rest. ABS prevent brakes from locking up. When brakes lock, they create heat and quickly become less effective. When brakes lock, they cause the wheels to skid making steering very difficult and dangerous. There are lots of ABS configurations and control options. Here’s how a basic system works.
The controller monitors speed sensors. When wheels stop functioning, like before they lock up, they decelerate. This deceleration can be picked up by the sensors. Controller algorithms can quickly reduce pressure to the brake before wheel decelerations occur and help the wheel speed match overall vehicle declaration. This creates the pulses you feel when you press and hold the brake pedal. ABS can cycle 5, 10 or 15 times a second.
Do ABS work? An average driver using ABS stops faster than professional drivers.
Anti-Lock Brake Types
There are many ways that manufacturers design and configure ABS. A reasonable way to get your hands around some basic options, and understand how they may benefit you, is to break them up (pun intended) by how many wheels are individually managed. This management is done with combination of valves (that can regulate pressure at individual wheels) and sensors that can operate at the wheel level or the axle level.
Four-channel, four-sensor ABS
These systems manage every wheel of the vehicle. They utilize valves for pressure, and speed sensors for wheel level control. This allows the controller to monitor and manage each wheel individually so that each wheels braking capability is maximized.
Three-channel, three-sensor ABS
This system uses a speed sensor and a valve for each front wheel, and one valve and one sensor for both rear wheels. This configuration is common on 4WD pick-up trucks. The front system have the ability to optimize braking. The rear wheels are not individually managed and both wheels need to start to lock up before ABS initiates.
One-channel, one sensor ABS
This is the three channel system above, minus the front wheel ABS. In other words, its one channel, one sensor, and one valve for the rear wheels.