Cooling System

Almost all automobiles employ liquid cooling systems for their engines.

For operation at temperatures below 0°C, it is necessary to prevent the coolant from freezing. This is usually done by adding some compound to depress the freezing point of the coolant. Alcohol formerly was commonly used, but it has a relatively low boiling point and evaporates quite easily, making it less desirable than organic compounds with a high boiling point, such as ethylene glycol. By varying the amount of additive, it is possible to protect against freezing of the coolant down to any minimum tem­perature. Coolants contain corrosion inhibitors designed to make it necessary to drain and refill the cooling system only once a year.

Air-cooled cylinders operate at higher, more efficient temperatures, and air- cooling offers the important advantage of eliminating not only freezing and boiling of the coolant at tem­perature extremes but also corrosion damage to the coolant system.

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Brakes

Systems for stopping vehicles have had a long his­tory of development: from mechanical brakes to hydraulic, power and disc systems. 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. (674)

Trucks

A truck, or lorry, is a motor vehicle designed to carry freight or goods or to perform special services. The truck was derived from horse-driven wagon technology. Trucks enjoy an almost total monopoly in intercity freight delivery in some countries.

In 1896 Gottlieb Daimler of Germany built the first motor truck. It was equipped with a 4-horsepower engine and a belt drive with two speeds forward and one in reverse. In 1898 the Winton Company of the US produced a gasoline-powered delivery wagon with a single-cylinder 6-horsepower engine.

Trucks can be classified as either straight or articulated. A straight truck is one in which all axles are attached to a single frame. An articulated vehicle is one that consists of two or more separate frames connected by suitable couplings.

At the beginning of the 1990s light trucks made up more than 92% of all trucks. These vehicles generally have more in common with passenger cars than with larger trucks. More than half of the world production of trucks consists of small pickup trucks and vans. There are also medium trucks, heavy-duty haulers, cross­ country trailers, off-road and mining trucks.

Steering of trucks, with their heavy loads, is difficult. Steering is always by the Ackerman system, which provides a kingpin for each front wheel. Maximum cramp angle of the front wheels is about 35 degrees. The minimum turning radius is de­pendent on the wheelbase.

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Buses

The bus is a self-propelled road vehicle designed to carry more passengers than an automobile, generally on a fixed route. It was developed at the beginning of the 20th century. Today buses are defined as vehicles that accommodate more than 8 passengers.

Until the 1920s the technical history of the bus was the history of the motor truck, since the early bus consisted of a bus body mounted on a truck chassis. The majority of present-day school buses are made in this way. In 1921 the first vehicle with a chassis specifically designed for bus service was made in the US by Fageol Safety Coach Company of Oakland, California.

There are four main types of buses: city or transit, subur­ban, intercity or tour, and school. The city bus operates within the city limits and is characterized by low maximum speed, low-ride platform, provision for standing, and wheelchair passengers, two entrances on the curb side, low-back seats, and no luggage space. The suburban bus is designed for short intercity runs and has high-back seats, luggage compartments and racks, and a single, front entrance. The intercity type has a high-ride platform to provide maximum luggage space under the passengers, high-back seats, overhead luggage racks, individual reading lights, and a wash­room. School buses generally consist of a 50-passenger bus body, with special signal lamp and safety provi­sions, mounted on a long-wheelbase truck chassis.

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