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汽车局务会08-1，200801071027，马庆龙
Automobile Brake System
The braking system is the most important system in cars. If the brakes fail, the result can be disastrous. Brakes are actually energy conversion devices, which convert the kinetic energy (momentum) of the vehicle into thermal energy (heat).When stepping on the brakes, the driver commands a stopping force ten times as powerful as the force that puts the car in motion. The braking system can exert thousands of pounds of pressure on each of the four brakes.
Two complete independent braking systems are ud on the car. They are the rvice brake and the parking brake.
芦荟胶的作用The rvice brake acts to slow, stop, or hold the vehicle during normal driving. They are foot-operated by the driver depressing and releasing the brake pedal. The primary purpo of the brake is to hold the vehicle stationary while it is unattended. The parking brake is mechanically operated by when a parate parking brake foot pedal or hand lever is t.
The brake system is compod of the following basic components: the “master cylinder” which is located under the hood, and is directly connected to the brake pedal, converts driver foot’s mechanical pressure into hydraulic pressure. Steel “brake lines” and flexible “brake hos” connect the master cylinder to the “slave cylinders” located at each wheel. Brake fluid, specially designed to work in extreme conditions, fills the system. “Shoes” and “pads” are pushed by the slave cylinders to contact the “drums” and “rotors” thus causing drag, which (hopefully) slows the car.
The typical brake system consists of disk brakes in front and either disk or drum brakes in the rear connected by a system of tubes and hos that link the brake at each wheel to the master cylinder (Figure).
Basically, all car brakes are friction brakes. When the driver applies the brake, the control device forces brake shoes, or pads, against the rotating brake drum or disks at wheel. Friction between the shoes or pads and the drums or disks then slows or stops the wheel so that the car is braked.
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In most modern brake systems (e Figure 15.1), there is a fluid-filled cylinder, called master cylinder, which contains two parate ctions, there is a piston in each ction and both pistons are connected to a brake pedal in the driver’s compartment. When the brake is pushed down, brake fluid is nt from the master cylinder to the wheels.
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At the wheels, the fluid pushes shoes, or pads, against revolving drums or disks. The friction between the stationary shoes, or pads, and the revolving drums or disks slows and stops them. This slows or stops the revolving wheels, which, in turn, slow or stop the car.
The brake fluid rervoir is on top of the master cylinder. Most cars today have a transparent r rervoir so that you can e the level without opening the cover. The brake fluid level will drop slightly as the brake pads wear. This is a normal condition and no cau for concern. If the level drops noticeably over ashort period of time or goes down to about two thirds full, have your brakes checked as soon as possible. Keep the rervoir covered except for the amount of time you need to fill it and never leave a cam
of brake fluid uncovered. Brake fluid must maintain a very high boiling point. Exposure to air will cau the fluid to absorb moisture which will lower that boiling point.
The brake fluid travels from the master cylinder to the wheels through a ries of steel tubes and reinforced rubber hos. Rubber hos are only ud in places that require flexibility, such as at the front wheels, which move up and down as well as steer. The rest of the system us non-corrosive amless steel tubing with special fittings at all attachment points. If a steel line requires a repair, the best procedure is to replace the compete line. If this is not practical, a line can be repaired using special splice fittings that are made for brake system repair. You must never u copper tubing to repair a brake system. They are dangerous and illegal.古从军行李颀
Drum brakes, it consists of the brake drum, an expander, pull back springs, a stationary back plate, two shoes with friction linings, and anchor pins. The stationary back plate is cured to the flange of the axle housing or to the steering knuckle. The brake drum is mounted on the wheel hub. There is a clearance between the inner surface of the drum a
nd the shoe lining. To apply brakes, the driver pushes pedal, the expander expands the shoes and press them to the drum. Friction between the brake drum and the friction linings brakes the wheels and the vehicle stops. To relea brakes, the driver relea the pedal, the pull back spring retracts the shoes thus permitting free rotation of the wheels.
Disk brakes, it has a metal disk instead of a drum. A flat shoe, or disk-brake pad, is located on each side of the disk. The shoes squeeze the rotatin g disk to stop the car. Fluid from the master cylinder forces the pistons to move in, toward the disk. This action pushes the friction pads tightly against the disk. The friction between the shoes and disk slows and stops it. This provides the braking action. Pistons are made of either plastic or metal. There are three general types of disk brakes. They are the floating-caliper type, the fixed-caliper type, and the sliding-caliper type. Floating-caliper and sliding-caliper disk brakes u a single piston. Fixed-caliper disk brakes have either two or four pistons.
列文虎克显微镜The brake system asmblies are actuated by mechanical, hydraulic or pneumatic devices. The mechanical leverage is ud in the parking brakes fitted in all automobile. W
hen the brake pedal is depresd, the rod pushes the piston of brake master cylinder which press the fluid. The fluid flows through the pipelines to the power brake unit and then to the wheel cylinder. The fluid pressure expands the cylinder pistons thus pressing the shoes to the drum or disk. If the pedal is relead, the piston returns to the initialposition, the pull back springs retract the shoes, the fluid is forced back to the master cylinder and braking ceas.
