Worm and Roller

Figure 8-20.—Worm and sector steering gear. An adjusting nut or plug is provided for adjusting the end play of the worm gear. Worm and Roller The worm and rotter steering gear (fig. 8-21) is quite similar to the worm and sector, except a roller is supported by ball or rotter bearings within the sector mounted on the pitman arm shaft. These bearings assist in reducing sliding friction between the worm and sector. As the steering wheel turns the worm, the roller turns with it, forcing the sector and pitman arm shaft to rotate. The hourglass shape of the worm, which tapers from both ends to the center, affords better contact between the worm and roller in all positions. This design provides a variable steering ratio to permit faster and more efficient steering. Figure 8-21.—Worm and roller steering gear. "Variable steering ratio" means that the ratio is larger at one position than another. Therefore the wheels are turned faster at certain positions than at others. At the center or straight-ahead position, the steering gear ratio is high, giving more steering control. However, as the wheels are turned, the ratio decreases so that the steering action is much more rapid. This design is very helpful for parking and maneuvering the vehicle. Cam and Lever The cam and lever steering gear. in which the worm is known as a cam and the sector as the lever, is shown in figure 8-22. The lever carries two studs that are mounted in bearings and engage the cam. As the steering wheel is turned, the studs move up and down on the cam. This action causes the lever and pitman arm shaft to rotate. The lever moves more rapidly as it nears either end of the cam. This action is caused by the increased angle of the lever in relation to the cam. Like the worm and roller, this design allows for variable steering ratio. Worm and Nut The worm and nut steering gear is made in several different combinations. A nut is meshed with and screws up and down on the worm gear. The nut may operate the pitman arm directly through a lever or through a sector on the pitman arm shaft. Figure 8-22.—Cam and lever steering gear 8-19