Manual steering systems

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Steering Ratio

Construction Mechanic Basic Volume 2

Worm and Nut

MANUAL STEERING SYSTEMS
Manual steering is considered to be entirely adequate for smatter vehicles. It is tight. fast, and accurate in maintaining steering control. However, larger and heavier engines. greater front overhang on larger vehicles, and a trend toward wide tread tires have increased the steering effort required. Steering mechanisms with higher gear ratios were tried, but dependable power steering systems were found to be the answer. There are several different types of manual steering systems, which are as follows:

Worm and sector
Worm and rotter
Cam and lever
Worm and nut
Rack and pinion

Worm and Sector
In the worm and sector steering gear (fig. 8-20), the pitman arm shaft carries the sector gear that meshes with the worm gear on the steering gear shaft. Only a sector of gear is used because it turns through an arc of approximately 70 degrees. The steering wheel turns the worm on the lower end of the steering gear shaft, which rotates the sector and the pitman arm through the use of the shaft. The worm is assembled between tapered rotter bearings that take up the thrust and toad.

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.