developed from a rectangular sash made by riveting industrial angle iron side members to transverse angle iron girders or from a wooden frame of the same simple The arrangements and proportions of the vehicle body, springs, fenders and even of the power equipment and transmission elements were made to suit this form. The modern frame be gan its evolution when, about the year 1900, large strips of sheet steel were first shaped for this purpose in hydraulic presses. By degrees it has become practicable to bend the sheet steel in all three directions. Nearly all the side reaches of frames are of [ section. Most of the frames are contracted at the front to allow a large turning angle for the front wheels and many are also bent upward at the rear to make room for spring and axle movements. Re cently, by using straight but converging side members, as in Fig. 1, cost is saved and such frames readily meet varying design require Motor Cars.— The motor car chassis (Figs. 1 and 2) comprises a frame, a power equipment, means for power transmission from engine to road wheels, axles, vehicle springs, means for transmitting a driving-thrust from the road wheels to the vehicle frame, a steering gear, a system of brakes, road wheels and tires. In nearly all motor cars the means for trans mitting power from the engine to road wheels are purely mechanical, but in a minority these means are electrical. In a still smaller minor ity of cases they are hydraulic, which, however, is only a special form of mechanical transmis sion. i Nearly all engines are kept from reach ing inadmissible temperatures by the circula tion of water which in turn is cooled by air, but in some instances the engine is cooled di rectly by air. In nearly all motor cars the engine power is transmitted to the rear road wheels only, and the front road wheels are rotated by the push from the rear wheels against the vehicle frame and are utilized for steering, but in a few instances the front wheels are driven from the engine and steered as well, or all four wheels are driven and steered. These variations in construction are indicated when a motor car is referred to as a "gas-elec tric" car, a "hydraulic-transmission° car or truck, an "air-cooled" car, a "front-drive)) car, cab or truck, a "four-wheel-drive" vehicle.
The Frame.— The motor car frame has been ments by compromise. Large vehicle manu facturers, however, have the frames designed throughout to suit the rest of their construction after the latter has been determined. In a few instances steps and running-boards are in corporated in the frame .to strengthen it with out adding weight. Practically all frames are now hot-pressed and hot-riveted. The riveting formerly done by a hammering process is now often accomplished by pressure, with less noise and more rapidly. The strength of the frames depends not only on design and dimensions, but largely upon the skillful shaping of the dies in which they are hydraulically pressed.
The Power Equipment.—The arrangements for fuel supply, the automobile engine and the means for starting and controlling the engine constitute the power equipment. The fuel tank, made of sheet copper or plated sheet steel, is either suspended at the rear end of the frame (Figs. 1 and 2) or supported over a transverse member of the frame underneath the driver's seat. In the first case its position is low, and a light pressure is maintained over the fuel in the tank by means of a small air pump operated optionally from the engine or by hand, in order to make sure that the fuel will be piped to the engine as needed in whatever position the car stands or moves. In the other case the fuel is fed naturally by gravity from the tank to the float-chamber of the carburetor, but the flow is less active when the car goes uphill than when it moves on the level or downhill. To combine the advantages of both methods, a system is now frequently used by which a small suction from the intake manifold of the engine. Fig. 3 shows the latter arrangement. Formerly pressure above the fluid in the main tank at the rear was often maintained by piping a portion i of the exhaust gas from the engine into the tank. The fuel piping should have few joints, no sharp downward or upward bends where impurities may settle or air bubbles may lodge. The automobile engine may be considered as a development of the as engine, which was the first internal-combustion engine, so called, when it made its first appearance, to distinguish its nature from that of steam engines. The fuel
is burned inside of the cylinders which are util ized for transforming the expansion of gases into mechanical movement, instead of outside of them. Gas engines, stationary and marine hydrocarbon (gasoline or oil) engines, Diesel engines and automobile engines are the four large varieties of the internal-combustion type and each of them has characteristics which overshadow their similarity on the point men tioned. In France and Germany the automobile engine is rarely mentioned as an internal-com bustion engine, this distinction from steam en gines being apparently considered superfluous.
auxiliary tank is placed near the engine and higher than the carburetor, supplying the latter by a gravity flow with practically unvarying head of pressure while the auxiliary tank is supplied from the main tank at the rear by The German term Verbrennungsmaschine is a simplification. The term "explosion engine" (French: Moteur a explosion), an equivalent for internal-combustion engine, is now seldom used. (See INTERNAL-COMBUSTION ENGINE; GAS ENGINE; DIESEL ENGINE; AUTOMOBILE ENGINE). The typical automobile engine is operated with gasoline as fuel, the equivalent of which is called petrol (pet-rol) in Great Britain, Benzin in Germany and essence de parole (or more commonly essence only) in France.
It has four cylinders usually bored in a single iron casting and is bolted to an aluminum crank casing and mounted to stand lengthwise and upright in the front portion of the auto mobile frame. Four pistons connect by "con necting-rods," without crossheads, with a crank shaft machined from a single drop-forging. It draws a spray of fuel, fuel-vapor and air through a carburetor (q.v.) by means of the suction caused by downward strokes of the pistons, admits the mixture to the cylinders by poppet valves which are opened mechanically and closed by valve springs, ignites the mixture with a spark generated by means of a magneto (q.v.) or other electrical machine at the in terior terminals of a spark plug (or esparking plug") screwed into the head of each cylinder, expels burnt gases by poppet valves which are opened mechanically and closed by springs. It has one camshaft geared to open, and hold open, both intake and exhaust valves at the proper periods. It detonates and burns an ex plosive gas mixture at every fourth piston stroke in each cylinder. The rear end of the crankshaft carries a small flywheel which is arranged to be used as one member of the coupling between the engine and the power transmission mechanism, and to which is also frequently applied the effort by which the en gine is started, unless this is done by hand power by applying a crank to the front end of the crankshaft. The upper portion of each cylinder is cast with hollow walls forming a water jacket, and the water jackets are placed in a water circulation circuit by piping to the upper and lower portions of a °radiator° which is mounted upright and transversely at the front end of the automobile frame. Between the radiator and the camshaft gearing, in front of the foremost cylinder, a rotary fan is operated by gearing or belting to increase the flow of air in the interstices of the radiator structure. A centrifugal pump gear-driven in the lower branch of the water circuit often assists in ef fecting the circulation. External piping gathers the exhaust from the cylinders and is continued rearward underneath the frame, supported at an intermediate point in a muffler or silencer where the flow of hot exhaust gases, already cooled somewhat on the way, is further baffled and cooled before it is allowed to reach the atmosphere. Of the descriptive statements here made not a single one holds true for all auto mobile engines. Those which come nearest to representing universal practice refer to the use of a carburetor operated by suction from the engine and to the ignition of the fuel mixture by means of an electrically generated spark. The world-wide demand for an automobile en gine in which liquid fuels less volatile and costly than gasoline may be used with equal facility already foreshadows the eventual dis appearance of the carburetor operated by engine suction, a more positive and more accurately predetermined preliminary action upon the less volatile fuels being required to make them readily inflammable in the cylinders when the engine is cold and under other adverse condi tions of operation, as are bound to obtain in practice occasionally.