There have been many forms of steering gears throughout history, but many have been obsolete. According to the classification of power assist forms, steering gears can be divided into mechanical (non-assisted) and powered (assisted).
According to the different structural forms, mechanical steering gear can be divided into rack and pinion type, recirculating ball type, worm crank finger pin type, recirculating ball crank finger pin type, worm roller type, etc. Commonly used are rack and pinion type, recirculating ball type, and worm crank finger pin type.
The rack and pinion steering gear is one of the simplest types of steering gear. Its advantages are simple structure, compact, high stiffness, low cost, sensitive steering, high positive and counterattack rates, easy to arrange, and especially suitable for candle suspension and MacPherson suspension, can also directly drive the tie rod, simplify the steering transmission mechanism. Therefore, it is widely used in cars and micro and light trucks.
The recirculating ball steering gear has a high positive and counterattack rate, so it is light to operate, has a long service life, and works stably and reliably, but due to the high counterattack rate, it is easy to transmit the road impact force to the steering wheel.
The power steering gear is actually a combination of a mechanical steering gear and a steering afterburner device. According to the different energy transmission medium, there are two types of power steering gear: pneumatic type and hydraulic type. The hydraulic power steering can be divided into three structural types: integral (mechanical steering gear, steering power cylinder and steering control valve are designed as one), semi-integral (mechanical steering gear and steering control valve are designed together, and the steering power cylinder is independent) and separated (mechanical steering gear is independent, and the steering control valve and steering power cylinder are designed as one).
It is worth noting that the truck with a large loading mass should not use the pneumatic power steering gear, because the working pressure of the pneumatic system is low (generally not higher than 0.7MPa), and when used on heavy vehicles, its component size will be too large. The working pressure of the hydraulic power steering can be as high as 10MPa or more, so its component size is very small. The hydraulic system works without noise, has a short working lag time, and can absorb the impact from uneven road surfaces. Therefore, hydraulic power steering has been widely used in all kinds of automobiles at all levels.