8.1.7 Rack and pinion steering gear
Now let’s describe a rack-and-pinion steering gear (figure 8.4). It consists of a gear and a rack/ The gear is connected to the steering column shaft, and the rail through the rods - with the rotary fists of the wheels.
Figure 8.4 Pack-and-pinion steering gear.
Interesting
Sometimes the teeth are made on the rack with a variable step (Figure 8.5). Designers do this in order to get the semblance of active steering for achieving the optimal combination of conflicting performance such as handling and comfort. Thus, for the sake of ease, it is desirable to reduce quantity of turns from a stop to a stop to one, and even to a half-turn. This is done so during parking the driver would not turn a steering wheel on 5 - 10 turns. But in case if there is only one turn from the right extreme position of the steering wheel to the left, the steering will be quite sensitive to each movement. This is dangerous while driving at high speeds, because it will be hard to perform all maneuvers, and this might have consequences. That’s why the designers came to such a fairly simple compromise solution: the step of the central teeth of the steering rack is small, and the gear ratio is slightly higher. Therefore, the sensitivity to the deviation of the steering wheel is small. But from the center the pitch of the teeth increases in order to reduce the gear ratio and the total speed of the steering wheel.
Figure 8.5 Example of steering gear toothed rack with variable teeth pitch.
Note
The pitch of the teeth is the distance between the centers of the vertices of the teeth.
Interesting
By the way, there may be a reverse situation when the pitch of the rack teeth decreases closer to the ends of the rack.
The rack-and-pinion steering gear replaced the worm-type gear and was firmly established as the most actual design. Its advantages speak for themselves: control of the car, which is even not equipped with the power steering, simple, small number of links of all steering mechanism, simplicity of installation on the car and reduction to a minimum of operations of service.
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