Make a short report in front of the class.

Resources recommended:

www.automobile.com

www.wikeipedia.com

www.motorcars.com

Text 18

I. Read the text about different kinds of brakes.

Brakes

Until the 1930s, most systems for stopping vehicles were mechanically actuated drum brakes with internally expanding shoes; i.e., foot pressure exerted on the brake pedal was carried directly to semicircular brake shoes by a system of flexible cables. Mechanical brakes, however, were difficult to keep adjusted so that equal braking force was applied at each wheel; and, as vehicle weights and speeds increased, more and more effort on the brake pedal was demanded of the driver.

Mechanical brakes were replaced by hydraulic systems, in which the brake pedal is connected to pistons in master cylinders and thence by steel tubing with flexible sections to individual cylinders at the wheels.

Disc brakes, originally developed for aircraft, have become increasingly popular because of their fade resistance. Although there are some four-wheel systems, usually discs are mounted on the front wheels, and conventional drum units are retained at the rear. Disc designs are somewhat more costly but have become increasingly popular. They were fitted on four out of five new cars in 1990. Each wheel has a hub-mounted disc and a brake unit or caliper rigidly attached to the suspension. The caliper employs two friction-pad assemblies, one on each side of the disc. When the brake is applied, hydraulic pressure forces the friction pads against the disc. This arrangement is self-adjusting, and the ability of the discs to dissipate heat rapidly in the open air stream makes them practically immune to fading.

Antilock braking systems (ABS) were available in the late 1980s and subsequently became standard equipment on a growing number of passenger cars. ABS installations consist of wheel-mounted sensors that input wheel rotation speed into a microprocessor. When wheel rotation increases owing to tire slippage or loss of traction, the control unit signals a hydraulic or electric modulator to regulate brake line pressure to forestall impending wheel lockup. The brake continues to function as the system cyclically releases and applies pressure. The wheels continue to roll, retaining the driver's ability to steer the vehicle and stop in a shorter distance. Parking brakes usually are of the mechanical type, applying force only to the rear brake shoes by means of a flexible cable connected to a hand lever or pedal.

On cars with automatic transmissions, an additional lock is usually provided in the form of a pawl that can be engaged, by placing the shift lever in the “park” position, to prevent the drive shaft and rear wheels from turning. The service brake pedal must be applied to permit shifting the transmission out of the “park” position. This eliminates the possibility of undesired vehicle motion that could be caused by accidental movement of the transmission control.

II. Look through the text again and answer the following questions:

1. What was the first for stopping vehicles?

2. What were mechanical brakes then replaced by?

3. Why have disc brakes become very popular?

4. Did ABS become a standard equipment on passenger cars?

5. What are parking brakes?

III. Match the words with their definitions and make up your own sentences with these words:

1. brake	a) having the shape of one half of a circle;
2. semicircular	b) a device for stopping or slowing a car;
3. to adjust	c) to fix smth in position for use, display;
4. to mount	d) to adapt smth.;
5. hydraulic systems	e) the system of gears by which power is passed from the engine to the wheels;
6. pedal	f) a round plate or short cylinder that fits closely inside a tube and moves up and down inside it;
7. piston	g) a flat bar that drives or controls a machine;
8. transmissions	h) a metal support;
9. caliper	i) a bar or rod joining parts of a machine or transmitting power in a machine;
10. drive shaft	j) a system of a mechanism operated by liquid moving in this way;

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Automotive body	\|	IV. Find the information about new brake performance. While looking for information you are free to use the internet sites given below as well as any other online resources.

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