The rack and pinion steering gear consists of a steering gear integrated with the steering shaft and a rack that is often integrated with the steering tie rod. Compared with other types of steering gears, the main advantages of the rack and pinion steering gear are: simple and compact structure; the shell is die-casted from aluminum alloy or magnesium alloy, the quality of the steering gear is relatively small; the transmission efficiency is up to 90%; After the gap occurs between the rack and the rack due to wear, the spring can be adjusted by the pressing force attached to the back of the rack and close to the active pinion, which can automatically eliminate the inter-tooth gap, which can not only improve the rigidity of the steering system, but also Prevents impact and noise during operation; the volume occupied by the steering gear is small; there is no steering rocker and straight rod, so the steering wheel angle can be increased; the manufacturing cost is low.
The main disadvantages of rack and pinion steering gear are:
Due to the high reverse efficiency (60% to 70%), when the car is driving on uneven roads, the impact force between the steering wheel and the road surface can be transmitted to the steering wheel, which is called backlash. The recoil phenomenon will make the driver nervous, and it is difficult to accurately control the direction of the car. The sudden rotation of the steering wheel will cause a thug and cause damage to the driver.
According to the input gear position and output characteristics, the rack and pinion steering gear has four forms: intermediate input, output at both ends; side input, output at both ends; side input, intermediate output; side input, one end output.
With the side input and intermediate output schemes, the left and right tie rods that are attached to the rack extend close to the longitudinal symmetry plane of the vehicle. As the length of the drawbar increases, the swing angle of the drawbar decreases when the wheel is bouncing up and down, which is beneficial to reduce the motion interference between the steering system and the suspension system when the wheel is bouncing up and down. The tie rod and the rack are fixedly coupled by bolts, so that the two tie rods and the rack move to the left or the right at the same time, so that a long groove in the axial direction is opened on the steering gear housing, thereby reducing its strength.
When the output scheme of both ends is adopted, since the length of the steering rod is limited, it is easy to cause motion interference with the guiding mechanism of the suspension system.
A rack-and-pinion steering gear with a side input and an output at one end is often used on a head minivan.
If the rack and pinion steering gear is meshed with the spur gear, the running smoothness is reduced, the impact is large, and the working noise is increased. Furthermore, the angle between the gear axis and the axis of the rack can only be a right angle, which is eliminated due to the incompatibility with the overall arrangement. The rack and pinion steering gear with helical gear and mesh gear mesh increases the degree of coincidence, runs smoothly, the impact and working noise are reduced, and the angle between the gear axis and the rack axis is easy to meet the overall design. Claim.
The cross-sectional shape of the rack has three types: circular, V-shaped and Y-shaped. The manufacturing process of the circular section rack is relatively simple. Compared with the circular section, the V-shaped and Y-shaped cross-section racks consume less material, save about 20%, so the quality is small; the two inclined surfaces located under the teeth are in contact with the rack holder, which can be used to prevent the rack from rotating about the axis; The tooth width of the Y-shaped cross-section rack can be made wider and the strength is increased; a spacer made of an anti-friction material (such as Teflon) is usually installed between the rack and the bracket to reduce sliding friction.
Depending on the position of the rack and pinion steering gear and the steering trapezoid relative to the front axle, the rack and pinion steering gear has four arrangements in the car: the steering gear is located behind the front axle and the rear trapezoid; the steering gear is located behind the front axle. Front trapezoid; the steering gear is located in front of the front axle, rear trapezoidal; the steering gear is located in front of the front axle, front trapezoidal.
Rack and pinion steering gears are widely used in miniature, general-grade, mid-range and mid- to high-class cars, even in premium cars. Some trucks and buses with small loads and independent suspensions on the front wheels also use rack and pinion steering gear.
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