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when in proper condition, and is as easily controlled after it is set in motion as either the steam or electric motor. Modern gasoline automobile engines have great flexibility, and have a range of speed from 150 to 1,200 or more revolutions per minute, by simple movement of the spark and throttle control levers.

Once the gasoline engine is set in motion, it requires no more attention from the operator, and it will continue to run as long as the fuel supply, lubricating oil, and electrical ignition will hold out. Its range or touring radius is not limited by conditions which make it necessary to frequently replenish the supply of water, as is the case with the steam engine, and it is independent of the central charging station on which the electric automobile depends. It will carry fuel enough in a tank of small size so it is possible to go several hundred miles without a stop, and then this is only a stop of a few minutes duration or just long enough to refill the gasoline and oil tanks.

The internal combustion motor is the most economical form to operate, and as a rule, automobiles equipped with this form of power require less attention than either steam or electric automobiles. Some of the disadvantages advanced against the gasoline power plant are: lack of overload capacity which necessitates the use of change speed gears; inability to reverse engine, which means that reversing gearing is necessary to allow the automobile to run backward; inability to start engine under load, which means that a separate clutching mechanism is needed so the motor may be started independent of the vehicle and to permit it to run fast enough to develop its full power before the car is started. Electric motors and steam engines start as soon as the automobile to which they are fitted does, and as no clutch is necessary, they may be directly connected to the driving wheels by some form of positive gearing. Owing to its lack of overload capacity, reduction gearing must be used whenever a gasoline car is made to climb a steep hill, whereas the power of the electric or steam motor may be increased by permitting more energy to flow from the container where it is stored under pressure to the motor, thus no change speed gears are necessary on these types of vehicles. The disadvantages mentioned are more apparent than real, as with the highly developed form of gasoline engines of the present day, there is no need of constant gear changing or speed

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Fig. 1.-Chassis of the Pleasure Car Type Fitted With Various Forms of Delivery Bodies. A-Stake Platform Body. B-Wire Side

Delivery. C—Panel Side Delivery.

shifting, and practically all the variations of speed that are desired on average highways may be obtained by simply manipulating the throttle lever which supplies more gas to the engine. The speed changing lever is left in its direct drive position and is not moved to the lower gear ratio except when starting the car or when ascending steep grades. The modern gasoline automobile is just as suitable for city work as either the steam or electric cars and is much superior as a touring conveyance.

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Fig. 2.—Side View of Typical Heavy Truck Design With Power Plant

Placed Under Operator's Seat.

Q. Into what classes may automobiles be divided ?

A. The two main classes of automobiles are pleasure vehicles and commercia cars.

Q. How do they differ from each other?

A. Pleasure cars generally are built for high speed and are much lighter than the commercial vehicles which must carry heavy loads. In a pleasure car as a rule, everything is sacrificed to speed and comfort. In a commercial vehicle, the parts are large and substantial and everything is designed with a view to maximum carrying capacity and minimum operating expense. The parts of automobiles are the same in general principle, whether used in a touring car or truck, except that they are made heavier, and of greater strength when used in the vehicle carrying the greatest loads. Pleasure cars

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Fig. 3.- Sectional View of Natco Truck Chassis, Outlining_Disposition of Important Chassis Components

and Their Relation to Each Other.

are usually mounted on pneumatic tires, as air filled tires are called, while motor trucks which travel at slower speeds use solid rubber tires.

Motor trucks may be divided into two classes: those which utilize chassis patterned after pleasure types, but fitted with delivery bodies, as shown at Fig. 1, and those types of which a typical example is shown at Fig. 2, in which the motor is carried under the driver's seat and where the general design is such that the chassis can be used only for commercial purposes. There are classes of commercial cars, such as taxicabs, light delivery wagons, ambulances and vehicles of this nature, which are practically pleasure car chassis fitted with forms of bodies adapting it to a commercial use.

Q. What are the essential elements of the automobile?

A. The principal parts of automobiles are shown at Figs. 3, 4, 5, these outlining the chassis of pleasure cars and a typical truck. The foundation for the entire mechanism is the frame, which is attached to and supported by springs which are bolted to the axles on which the wheels are mounted. The power p ant, which consists of the gasoline engine and a number of other parts, is usually carried at the front end of the frame, where it is housed under a hood, or in a special compartment under the body where it can be easily reached.

The clutch and gear set form part of the transmission system, as does the chain or propeller shaft used to transmit the engine power from the change speed gearing to the rear axle. A steering gear by which the direction of car is controlled and levers for shifting the change speed gears, for controlling the brake and for operating the spark and throttle of the engine, complete the chassis assembly. An automobile may be said to consist of the following main groups: the power plant; the clutch and change speed gearing; the power transmission system; the supporting frame and springs; the axle and wheels; the controlling elements; and the load carrying or body member. (Figs. 4 and 5.)

Q. What is the function of the power plant?

A. The purpose of the power plant is to generate enough power so that when this is transmitted to the rear wheels thru the medium of suitable reduction gearing, it will propel the vehicle.

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