The Peerless steering gear (Fig. 178) differs somewhat from those shown above, being of the worm and wheel type with friction controls mounted above the hand wheel. This hand wheel is attached to the steering shaft by means of a taper and key, while the former is made large enough to form both the shaft and the mast.
With inside controls and a mast, there is considerable difficulty in providing a shaft of proper proportions, so that in eliminating the mast, the shaft can be made ample in size. Although it is somewhat more difficult to provide a bracket on the foot boards, owing to the shaft turning with the hand wheel.
In this construction a complete worm wheel is used instead of a sector, and as only about 90 degrees of the worm wheel comes in contact with the worm teeth, while the wheels are moved their entire turning range, and as the shaft is squared, the steering arm can be removed and the wear taken up by turning the wheel through an angle of 90 degrees, and another quarter section brought into action. The thrust is taken on ball bearings in either direction. The controls consist of a stationary tube on top of which is mounted a cylindrical box, with a horizontal slot in one side through which the control levers extend. Each control lever has an extension, which carries a friction segment, being pressed against the inner wall of the cylindrical housing by a spring. The lower end of this stationary tube is rigidly attached to the housing so that it cannot rotate.
A shaft and tube pass through the former to which the upper and lower levers are attached.
Fig. 179. Natco Steering Column.
The Natco steering gear (Fig. 179) is also of the worm and wheel type with suitable ball bearings to take the thrust of the worm, while a thrust button takes care of the wheel thrust. The housing is made in one piece with openings for introducing the worm and wheel. In this construction the steering shaft is also used as the mast; however, the wheel is attached to the shaft by bolts and flanges. But one control is provided, with the lever located above the hand wheel; however, instead of passing the control shaft through the case, the movement of the control lever is transmitted externally by means of a double thread screw or cam. The steering shaft has slots on opposite sides directly above the housing. These are enclosed by a collar which fits over the steering shaft and carries two dowel pointed screws, which set in threads of the cam. A fork rests on this collar and any movement of the control lever will tend to raise or lower this collar. carrying with it the fork which is connected to the carburetor.
Fig. 180. Vulcan Steering Gear. Worm and Sector Type.
Screw and Nut Type (Fig. 177) illustrates a screw and nut type of steering used on the Pierce 5-ton chassis. The solid steering shaft has the hand wheel keyed to its upper end and a multiple square threaded screw at its lower end. This screw net nates a nut with trunnions on its outside which carry die cast trunnion Mocks that slide within the jaws of a forked lever, keyed to the steering ball lever shaft. The housing is divided horizontally and carries suitable ball thrust bearings, which are adjustable from the lower end of the housing. The spark and throttle controls are of the ratchet and sector type mounted outside of the column on the steering column mast.
Another screw and nut type of steering gear which is used on a number of trucks is the Ross, shown in Fig. 181. The hollow steering shaft carries a steel screw at its lower end mounted between two hall bearings to take up its end thrust. This screw is held to the shaft by means of a brazed joint and when the hand wheel is turned a steel block or sleeve is given later movement. This steel block or sleeve has a square external section and thereby is prevented from turning by the housing. On each side of the lower end of this sleeve, cylindrical recesses are turned, and cylinders, which are free to rotate, are placed in these recesses. The cylinders have slots milled in them which receive the projecting arms of the steering ball lever shaft.
The control levers ore mounted above the wheel and their shafts pass through the steering shaft. The motion of these levers is reduced at the lower end by means of bevel gears.
Fig. 181. Ross Strew and Nut Type Steering Gear for Fore and Aft Steering.
All of the gears depicted above are best- adapted to fore and aft steering, alt hough they may in some oases be arranged for cross steering. Fig. 182 illustrates the Rots screw type of gear, especially designed for cross steering on heavy vehicles. The lower end of the steering shaft is integral with a steel screw, which, when turned by the hand wheel, gives a bronze sleeve longitudinal motion. This bronze sleeve is threaded internally to receive the steel screw and has spirals milled upon its external surface. The housing has spirals cut on its internal surface which engage with the spirals on the sleeve. The bronze sleeve in addition to internal threads contains a number of straight key-ways. The steering ball lever which projects half way up into the sleeve has integral keys, so that when the sleeve is given rotative and longitudinal motion, it rotates the hall lever. The gear is provided with hall-thrust bearings and an adjustment to take up wear, and can be made semi-irreversible or irreversible, depending upon the ratio of the threads.
Fig. 182. Ross Screw and Nut Type Steering Gear tor Cross Steering.
In Fig. 179 is shown a type of drag link used on vehicles up to about two tons capacity. It has ball sockets which fit over the ball on the steering arm of the axle. One of the ball sockets is brazed or welded to the drag-link tube and has an opening to receive another socket, which is retained by a nut or cap. The steering gear end has a housing attached to the tube which carries ball sockets and springs. These springs are introduced in the drag link to reduce the shock. The ball end may be introduced through holes in the housing and sockets or through slots which extend to the end of the housing.
The Vulcan drag link (Fig. 183) offers an example of the type used on heavy vehicles. This consists of a link of solid section threaded on both ends into housings which are divided on the ball center. The ball sockets on both ends are provided with cushion springs, while the caps of the housings are retained by long studs. This tends to facilitate assembling especially when the springs are heavy.
Some makers enclose these joints in leather boots, as shown in Fig. 179, to hold grease and prevent dirt and grit from cutting the ball surface.
As mentioned previously, universal joints are necessary at both ends of the drag link, because the steering arm moves in a vertical plane, and the knuckle arm in a horizontal plane, but instead of the ball and socket joints, forked joints are sometimes used. This type of joint was illustrated in the preceding chapter. They are somewhat simpler in construction and present larger bearing surfaces. However, they are more difficult to enclose and cannot take up wear automatically.
Fig. 183. Vulcan Drag Link.