How Brakes Work ?
#1
03-02-2010, 03:33 PM
How Brakes Work ?
What's behind your car's binders?
Created by Jeff Karr
Your vehicle's brake system is one of those things you only think about when it fouls up (or you do). Like when the service guy says, "You need your rotors ground and it's gonna cost $200," or you're surprised by a yellow light at an intersection. Suddenly your brakes are of acute interest. Why wait for unpleasant surprises? A general understanding of your vehicle's brake system can save you money, and may allow you to drive more safely and save a lot more than just cash. After all, the more you know, the better you can care for your car.
Braking Theory Your vehicle's brake system is one of those things you only think about when it fouls up (or you do). Like when the service guy says, "You need your rotors ground and it's gonna cost $200," or you're surprised by a yellow light at an intersection. Suddenly your brakes are of acute interest. Why wait for unpleasant surprises? A general understanding of your vehicle's brake system can save you money, and may allow you to drive more safely and save a lot more than just cash. After all, the more you know, the better you can care for your car.
Ask any of your physicist pals, and they'll tell you that brakes convert the kinetic energy of vehicle motion into heat. Translation: Brakes stop the car—or more accurately, brakes stop the wheels. There's a big difference, because the most powerful brakes in the world will not stop your vehicle effectively if the road surface has little or no traction. Mash the brake pedal and the wheels will stop turning sure enough, but the vehicle will skid along happily. You, on the other hand, will be a lot less happy. Many drivers tend to think of a skid as "brake failure" when in fact the situation is really a failure of the driver to understand the traction conditions and to drive accordingly.
Brake Basics The typical passenger-vehicle brake system is relatively simple. When you step on the brake pedal, the force your leg exerts is applied to a device called a master cylinder. The master cylinder contains a piston that pressurizes a network of hydraulic brake lines that lead to each of the vehicle's wheels. At each wheel, that brake fluid pressure operates the brakes by driving pistons that force replaceable linings against a rotating drum or disc. Friction is what slows the wheel, and in turn, the entire vehicle.
When the friction material (a.k.a. pads, linings, shoes) is almost worn out, metallic tabs are designed to create a squealing noise when the brakes are applied to (hopefully) alert the driver that the brake linings are due for replacement. Heed the warning. Worn linings have less fade-resistance than new linings. Plus, if you ignore the warnings long enough, you can do costly damage to the rotors, drums and other components. Even with regular replacement of the linings, some additional service is typically required over the long haul. The surfaces of drums and discs wear unevenly in normal use and eventually need to be re-machined to work properly.
All modern braking systems are many times more powerful than the vehicle's engine, so at full throttle, even a very powerful vehicle can be easily stopped with the brakes. All vehicles also have a parking brake (sometimes called the emergency brake) that works independently of the regular brake system. The parking brake typically acts on only the rear wheels and is mechanically operated to work in case of a hydraulic problem with the regular service brakes.
Better Braking When the friction material (a.k.a. pads, linings, shoes) is almost worn out, metallic tabs are designed to create a squealing noise when the brakes are applied to (hopefully) alert the driver that the brake linings are due for replacement. Heed the warning. Worn linings have less fade-resistance than new linings. Plus, if you ignore the warnings long enough, you can do costly damage to the rotors, drums and other components. Even with regular replacement of the linings, some additional service is typically required over the long haul. The surfaces of drums and discs wear unevenly in normal use and eventually need to be re-machined to work properly.
All modern braking systems are many times more powerful than the vehicle's engine, so at full throttle, even a very powerful vehicle can be easily stopped with the brakes. All vehicles also have a parking brake (sometimes called the emergency brake) that works independently of the regular brake system. The parking brake typically acts on only the rear wheels and is mechanically operated to work in case of a hydraulic problem with the regular service brakes.
Many engineering refinements over the history of the automobile have spectacularly improved the function and reliability of braking systems. Power brakes are standard on virtually all modern passenger vehicles, and they use energy supplied by the engine to help power the brakes so that the strength of your right leg doesn't have to do all the work. To eliminate the possibility of sudden, complete brake failure, modern vehicles actually have two parallel brake systems, with each system controlling two of the vehicle's wheels. This way, even if one system has a major failure, the other system can still stop the vehicle (albeit less effectively).
Brakes themselves have dramatically improved over the years, too. A few decades ago, drum brakes were in wide usage, and they're still used on the rear wheels of many vehicles. This type of brake employs a drum-shaped assembly that spins with the wheel. Inside the drum, stationary "shoes" faced with replaceable friction material are forced against the drum when you push the brake pedal. Drum brakes work well, but they have a hard time shedding heat well enough to prevent fade when used really hard. Brake fade occurs when the brake overheats dramatically; braking power is vastly reduced, and the brake components and linings can be damaged.
A significant advancement came in the form of disc brakes, which today are used almost universally on front wheels (which do most of the work under braking) and on many rear wheels. Disc brake systems have a metal (or exotic material in some racing applications) disc (or rotor) that spins along with the wheel, and a stationary "caliper" that squeezes the disc with replaceable friction material when the brakes are applied. With plenty of airflow on the exposed discs, these types of brakes are much less fade-prone.
Additionally, the discs are often internally vented to allow even greater airflow. Back when brake fade was a common problem on long mountainous descents, drivers would shift the transmission into a lower gear to allow engine braking to take some of the load off of the brakes. With modern brakes, this is usually no longer required, except in situations such as towing a heavy load downhill.
Anti-Lock Braking Systems Brakes themselves have dramatically improved over the years, too. A few decades ago, drum brakes were in wide usage, and they're still used on the rear wheels of many vehicles. This type of brake employs a drum-shaped assembly that spins with the wheel. Inside the drum, stationary "shoes" faced with replaceable friction material are forced against the drum when you push the brake pedal. Drum brakes work well, but they have a hard time shedding heat well enough to prevent fade when used really hard. Brake fade occurs when the brake overheats dramatically; braking power is vastly reduced, and the brake components and linings can be damaged.
A significant advancement came in the form of disc brakes, which today are used almost universally on front wheels (which do most of the work under braking) and on many rear wheels. Disc brake systems have a metal (or exotic material in some racing applications) disc (or rotor) that spins along with the wheel, and a stationary "caliper" that squeezes the disc with replaceable friction material when the brakes are applied. With plenty of airflow on the exposed discs, these types of brakes are much less fade-prone.
Additionally, the discs are often internally vented to allow even greater airflow. Back when brake fade was a common problem on long mountainous descents, drivers would shift the transmission into a lower gear to allow engine braking to take some of the load off of the brakes. With modern brakes, this is usually no longer required, except in situations such as towing a heavy load downhill.
A vehicle's tires generate the maximum deceleration when braking power is brought right to the brink of wheel lock-up—but not beyond. Once the brakes lock and the wheels skid, actual deceleration is reduced and directional control via the steering is lost. Electronically controlled anti-lock braking systems (ABS) have netted great advances in vehicle controllability and reduced stopping distances in most real-world situations, particularly in rain or when cornering. ABS uses a combination of electronics and hydraulic controls to allow normal braking right up to the point of wheel lock-up, then the system intervenes to reduce fluid pressure to the brakes to keep vehicle deceleration at its maximum given the road conditions.
Typical ABS systems have speed sensors at each wheel that continuously feed information to a centrally located ABS computer. The computer uses this data to determine overall vehicle speed, and to detect when a wheel begins to lock. Since each wheel is independently controlled (in a four-channel ABS system), pressure is automatically limited or reduced to only the wheel that is locking.
Three-channel ABS is a slightly less complex system used on some vehicles; it allows for independent control of each of the front wheels, but applies the same braking pressure to both rear wheels. Measurable performance differences between these two types of ABS are slight, and both types of ABS have a significant advantage over non-ABS brakes. When one wheel locks on a non-ABS car, the only way to allow it to spin again and regain full directional control is by the driver reducing the brake pedal pressure, which reduces the braking force at all four wheels at once. ABS is capable of providing shorter stopping distances in difficult situations than would a conventional system, even with an expert doing the driving.
Driving with ABS requires no special training, though you might need to un-learn a technique that makes some sense with non-ABS brakes. With old-style brakes, drivers were commonly told to "pump" the brakes when they were approaching wheel lockup. This rule of thumb was meant to help the average driver avoid fully locking the brakes and skidding straight ahead without steering control. With ABS, you simply push on the brake pedal as hard as necessary to make the stop. If traction is marginal, you may feel a pulsing sensation through the brake pedal, which is completely normal. Throughout the stop, you have steering control, so you can swerve or turn if required to avoid an obstacle.
Member's, what did you think of
above article ? Helpful ?
Typical ABS systems have speed sensors at each wheel that continuously feed information to a centrally located ABS computer. The computer uses this data to determine overall vehicle speed, and to detect when a wheel begins to lock. Since each wheel is independently controlled (in a four-channel ABS system), pressure is automatically limited or reduced to only the wheel that is locking.
Three-channel ABS is a slightly less complex system used on some vehicles; it allows for independent control of each of the front wheels, but applies the same braking pressure to both rear wheels. Measurable performance differences between these two types of ABS are slight, and both types of ABS have a significant advantage over non-ABS brakes. When one wheel locks on a non-ABS car, the only way to allow it to spin again and regain full directional control is by the driver reducing the brake pedal pressure, which reduces the braking force at all four wheels at once. ABS is capable of providing shorter stopping distances in difficult situations than would a conventional system, even with an expert doing the driving.
Driving with ABS requires no special training, though you might need to un-learn a technique that makes some sense with non-ABS brakes. With old-style brakes, drivers were commonly told to "pump" the brakes when they were approaching wheel lockup. This rule of thumb was meant to help the average driver avoid fully locking the brakes and skidding straight ahead without steering control. With ABS, you simply push on the brake pedal as hard as necessary to make the stop. If traction is marginal, you may feel a pulsing sensation through the brake pedal, which is completely normal. Throughout the stop, you have steering control, so you can swerve or turn if required to avoid an obstacle.
Member's, what did you think of
above article ? Helpful ?
#2
03-02-2010, 04:32 PM
Monte Of The Month -- August 2009
Join Date: Jan 2009
Location: Highland, IN
Posts: 5,827
#5
03-02-2010, 08:38 PM
It looks like 'Space is trying to fill the 'space again!! o.O! I was a great student in school and still am in college, but I don't think engines, brakes, transmissions, or cars in general are something you can read and know about. The only way that I have ever been able to learn about cars is by getting out there and working on them. Getting the impact guns and wrenches in my hands has always been the only way I could learn about them... I can't speak for everyone else though!
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