What are the hydraulic direction and the assist direction?

You mean hydraulic power and electronic assistance.

The main components of mechanical hydraulic power-assisted system are hydraulic pump, tubing, pressure fluid control valve, V-belt, oil storage tank, etc. This power-assisted method is to convert part of the power output of the engine into the pressure of the hydraulic pump, and apply auxiliary force to the steering system, thus steering the tires. The steering wheel and steering wheel assisted by mechanical hydraulic power are all connected by mechanical parts, with accurate control, direct road feeling and rich information feedback; The hydraulic pump is driven by the engine and has abundant steering power, which is suitable for all vehicles. Mature technology, high reliability and low average manufacturing cost. Because the oil pump is driven by the engine power, the energy consumption is relatively high, so the driving force of the vehicle is consumed invisibly; The pipeline structure of hydraulic system is very complicated, and there are many valves to control oil, so the later maintenance needs cost. The whole oil circuit is always in a high pressure state, and its service life will be affected. These are the shortcomings of the mechanical hydraulic power steering system.

The principle of electro-hydraulic power-assisted system is basically the same as that of mechanical hydraulic power-assisted, but the difference is that the oil pump is driven by a motor, and the power of the power-assisted system is variable. The vehicle speed sensor monitors the vehicle speed, and the electronic control unit changes the oil pressure by controlling the opening of the steering control valve after obtaining the data, so as to realize the adjustment of steering power. Electro-hydraulic power assist has most advantages of mechanical hydraulic power assist, at the same time, it also reduces energy consumption and has more sensitive response. Steering power can also be adjusted according to parameters such as rotation angle and vehicle speed, which is more humanized. However, with the introduction of many electronic units, the manufacturing and maintenance costs will increase accordingly, and the stability of use is not as reliable as that of mechanical hydraulic type. With the continuous maturity of technology, these shortcomings are being gradually overcome, and electro-hydraulic power has become the choice of many household models.