« НазадПродовжити »
are used in conjunction with the accelerator to vary the rotative speed of the motor and thus regulate the energy produced in proportion to the work to be performed. The emergency brake lever applies a powerful braking effect when it is desired to stop the car quickly and also when one wishes to lock the brakes if the car movement is arrested on a down grade. The change speed lever operates the sliding gearing, which is utilized to produce varying ratios of velocity between the engine shaft and the rear wheel. The steering wheel actuates the mechanism which moves the wheels to the right or left when one wishes to describe the circle, turn a corner, or otherwise deviate from a straight line.
The change speed gear is one of the most important elements of the power transmission system and in connection with the clutch it is much used in operating and controlling the vehicle. The function of the frame has been previously described. The exhaust pipe is employed to convey the inert gases discharged from the motor cylinders to a device known as the muffler, which is designed to reduce the exhaust gas pressure by augmenting the volume and thus diminish the noise made as it issues to the atmosphere. The driving shaft transmits power from the change speed gearset to the bevel gearing in the rear axle. A universal joint is a positive connection which permits a certain degree of movement between two shafts which must be driven at the same speed. One or the other, or both, may move in a lateral or vertical plane to a limited extent without interrupting the drive or cramping the transmission parts. Some cars have one, most 1917 models have two.
The power transmitted by the universally jointed propeller shaft goes to a differential mechanism and driving gearing in the rear axle from which shafts deliver the energy to the traction wheels. All parts are supported by or attached to the frame, made of pressed steel with suitable side members and cross braces held together by rivets. The frame carries springs or yielding members which allow movement of the frame with respect to the axles. The rear wheels are invariably provided with brakes to bring the vehicle to a stop, these being easily operated by the driver. The storage battery carries the current
Fig. 4.—Side View of Chalmers Light Six Engine, Showing Arrangement of Power Plant Auxiliaries and
Mounting of Gear Box as a Unit With the Engine.
for starting the motor, ignition and lighting the lamps used in night driving. The starting motor turns over the engine crank shaft to get the engine going. The generator supplies the storage battery when the engine is running. The gasoline tank carries the fuel needed to run the engine, this being turned into a gas that will explode in the motor cylinders to produce power by a carburetor.
Gasoline Engine Types.—The gasoline engine may have any number of cylinders, though the conventional types used in automobile propulsion seldom use any but an even number, usually four or six and never more than twelve. At one time singlecylinder motors were very popular. These were used in both the horizontal and vertical types. Power plants of this type were, for the most part, of low power and were patterned largely after stationary gasoline engine practice as far as proportion of parts was concerned. They were heavy and operated at low speed. Such engines are seldom employed at the present time, except in cars of ancient construction, some of which are still in use. Though this type of motor was comparatively slow "acting and considerable vibration existed while it was in operation, they were strongly constructed and capable of giving very satisfactory service. Engines of this type were usually installed under the body, the engine cylinder being parallel with the frame side member while the crank shaft was at right angles to it. This permitted a very simple and efficient method of power transmission, as the planetary change speed gearing which was usually carried on the crank shaft extension could be easily coupled to the rear axle by means of a single chain and a pair of sprockets.
The engines of present day automobiles are of the multiple cylinder form because they are more flexible, smoother running and more practical than the simpler types used a decade ago. Six, eight and twelve-cylinder forms are used in many cases. The more cylinders there are, the greater the number of power impulses one obtains to each turn of the rear wheels for a given final drive gear ratio. Few impulses or explosions result in jerky action, more impulses mean steadier power. For instance,
a four-cylinder engine has two explosions each revolution of the crank shaft; a six has three; an eight-cylinder has four, and a twelve-cylinder has six explosions. As the cylinder number is increased, the size can be reduced to secure the same power as obtained with a lesser number of larger cylinders. There is less vibration with small cylinders than with large ones and the working parts are not loaded so much. The power output depends upon the size of the cylinders as well as their number.
Fig. 5.-Sectional View of Dodge Brothers Four Cylinder Motor,
Showing All Important parts of a Gasoline Automobile Engine.
Many six-cylinder engines have more power than twelve-cylinder forms. The essential parts of an eight or twelve-cylinder engine are no different than in simpler types; there are more of them, that is all. A typical six-cylinder power plant is shown at Fig. 4, while the part sectional view of a four-cylinder at Fig. 5 shows the interior parts which produce the power.
The method of installing the power plant varies but slightly on different types of automobiles, and the majority of cars have the engine placed at the extreme front end of the chassis. In