The chassis usually is made of angle iron riveted together in form convenient for supporting the other parts. This rests upon the springs which take up the road shocks in part, and the springs rest upon the axles.
The rear axles—there is a separate axle for each rear wheel—are fixed, that is, they keep the wheels from oscillating, and they are joined in the center by the differential, a device driving the axle shafts by which one wheel is permitted to revolve at a differing speed as compared with the other, in turning a corner. Since, in turning, the outer wheel must travel a much longer distance than the inside wheel, if no device were installed to take up this difference, the outer wheel would scrape over the ground on every curve, or the inner wheel would spin without forward motion. In either event it would be disastrous to tires.
To keep the differential housing from twisting, a torque rod or tube connects it to the frame; to keep the rear axles at right angles to the frame and to transmit the driving thrust to the load, radius rods connect the axles to the frame forward.
The forward axle, unlike in an ordinary wagon, is fastened to the chassis frame, through springs, and does not turn. On either end is a yoke from which is suspended a steering knuckle, the wheel turning on a tapered spindle forged with the knuckle. The two knuckles are fastened together by a tie rod, which has some form of a turn buckle by which the wheels may be made to run parallel, or practically so. As a matter of fact the wheels are not parallel. They foregather slightly, so that the lines, projected forward far enough, would meet and make a pointed effect, like the bow of a boat. Its effect is to bring a slight but constant pressure upon both wheels and makes them less likely to swerve through contact with road unevenness. Also the wheels undergather, so that the load is brought over the center of knuckle support, minimizing the strain.
This deviation of the wheels from true produces a very slight wear on the tires, but it is more than compensated for by the other advantages noted. The deviation is worked out scientifically and the owner need not trouble himself about it. His only concern is that the tie rod be not bent so that the foregather is increased, when there would be excess wear of tires.
Courtesy of Allen Motor Co.
CHASSIS OF A MODERN AUTOMOBILE WITH FOUR-CYLINDER ENGINE
The brake drums are attached to the rear wheels and have inside and outside bands with mechanism to tighten them against the drum providing the necessary friction. The levers which connect the bands to the brake pedal or emergency lever are termed the brake linkage.
The motor, or engine, rests upon the chassis frame forward, being fastened thereto by bolts. Forward of it is a radiator, if it is a water-cooled motor, to which it is connected by pipes; the cooling system may be either pump or thermo-syphon type. Some few motors are air-cooled. The principle of cooling is that the motor should be kept just cool enough to prevent the lubricating oil from burning off the cylinder walls.