VEHICLE SPRINGS ; SPRINGS ; REBOUND CHECKS ; SHOCK ABSORBERS ; RUBBER TIRES.
Rear Axles are built up from cast and pressed steel sections on the plan typically shown in Fig. 21. The many variations and the distinction between axles with and °semi-floating') wheel shafts are elucidated in textbooks. Both types give excellent results when materials and other mechanical details, such as bearings and the provisions for lubri cation, are suitable. Front axles are drop forged from one piece of steel into shapes such as shown with steering knuckles and drag link added in Fig. 22. The two types indicated in Fig. 23 represent preferred American and European practice, respectively, in front axles.
To convey the driving-thrust from the rear axle of a motor car to its frame it was up to about 1912 universally considered neces sary to employ thrust rods, often termed radius rods, extending from the axle to some portion of the frame near its middle, and in the power transmission system a detail of kindred nature is a torsion rod or tube serving to prevent the power thrust upon the teeth of bevel gears from skewing the axle and causing uneven riding of the frame and body on the springs. Torsion rods or bars are still generally used, and in many cases the thrust rods and the torsion rods are combined in the form of a tubular casing for the drive shaft, forking into two branches at the front end. Figs. 2 and 24 show typical constructions for these poses. In recent years, however, it has been found practicable to transmit the driving effort through the vehicle springs, and to omit special braces for absorbing torque reaction, in which case the construction may be such as shown in Figs. 2 and 20. For small cars equipped with cross springs only, a pair of radius rods con verging toward a transverse girder at the mid dle of the frame is generally employed for the front axle as well as for the rear.
The Steering Gear of motor cars typically comprises the arrangement shown in Fig. 25 by which the front wheels are turned by turning a nearly vertical pivot pin forged in one piece with the wheel spindle, the turning movement being transmitted from the wheel most directly actuated to its mate by a transverse drag-link connecting the pivot pins and provided with adjustment screws and nuts to secure parallel ism of the wheels for driving straight ahead.
The nature of the linkage (known as the Ack erman steering system and invented for use with ordinary vehicles more than 100 years ago) causes the wheels to diverge a trifle forwardly when turned— and the more the more they are turned— with the object of mak ing one wheel turn a shorter curve than the other, as required. In some cases the pivot pin is formed upon the axle end and the knuckle in one piece with the wheel spindle. (Fig. 23).
The operating mechanism, as shown in Fig. 25, actuates a wormwhecl (or a sector of a wormwheel) by means of a worm with treble or quadruple thread of about 30 to 45 degrees pitch, and the steering arm keyed to the worm wheel or sector is thereby turned forward or backward, its lower end describing a short arc. This end is jointed as in Fig. 26 with the rear end of a lengthwise steering rod whose front end is jointed to a short crank arm on the pivot pin or knuckle. This median ism is reversible, as the worm and sector are kept well lubricated within the sub stantial casing enclosing them, and the wheels can readily be turned by applying force against them for that purpose. But in some motor cars, and in a majority of heavy motor trucks and other motor vehicles, a square screwthread takes the place of the worm, and a large nut is moved obliquely up and down to actuate the steering arm. This arrangement is only semi-reversible, or it may be irreversible if the screwthread is of low pitch. Jolts re ceived on the sides of the front wheels on rough roads are with this construction trans mitted only in slight degree to the driver's hands, but the violence of stresses to which the mechanism is subjected from wheel rim to steering gear is correspondingly greater. These stresses are absorbed to some extent in the buffer springs with which the joints of the steering rod are provided.