We usually drive, control the steering wheel to get the car in the direction we want, and rarely explore how the steering wheel turns the wheels. I often hear the terms “hydraulic power steering”, “electric power steering” and “active steering”. How do they work? What is the difference?
● What is the power steering?
The so-called power steering means that the driver can complete the steering with less force by means of external force. Initially applied to some large cars, it is easy to complete the steering without much effort. It has been widely used in various types of vehicles, making driving easier and more agile, and driving safety to a certain extent. Power steering can be divided into hydraulic power and electric power according to the source of power.
● Mechanical hydraulic power steering
The mechanical hydraulic assist system mainly includes two parts: a rack and pinion steering structure and a hydraulic system (hydraulic booster pump, hydraulic cylinder, piston, etc.). The working principle is to provide hydraulic pressure to push the piston through a hydraulic pump (driven by the engine belt), thereby generating an auxiliary force to push the steering rod to assist the steering of the wheel.
How does that move specifically? Firstly, the mechanical valve body (which can rotate with the steering column) is located on the steering gear. When the steering wheel is not rotating, the valve body remains in the original position, and the oil pressure on both sides of the piston is the same and in equilibrium. When the steering wheel rotates, the steering control valve will open or close accordingly. One side of the oil will not directly flow back to the oil storage tank without passing through the hydraulic cylinder, and the other side of the oil will continue to be injected into the hydraulic cylinder, so that both sides of the piston will be generated. The pressure difference is pushed, which in turn generates an auxiliary force to push the steering rod, making steering easier.
In the hydraulic steering system, such as the violent jumping of the wheel and the involuntary steering of the tire caused by the pitted road surface, the hydraulic pressure on the piston can well buffer and absorb the vibration, so that the vibration transmitted to the steering wheel is greatly cut back. The mechanical hydraulic assist technology is mature and stable, with high reliability and wide application. However, the structure is more complicated and the maintenance cost is higher. Moreover, the mechanized hydraulic assist system is not adjustable, and it is difficult to balance the different requirements for pointing accuracy at low speeds and high speeds.
● Electronic hydraulic power steering
The structural principle of the electronic hydraulic booster is basically the same as that of the mechanical hydraulic boost. The biggest difference is that the hydraulic oil pump is driven differently. The mechanical hydraulically assisted hydraulic pump is driven directly by the engine belt, while the electronic hydraulic boost uses an electrically driven electronic pump.
The electro-hydraulic-assisted electronic pump does not consume the power of the engine itself, and the electronic pump is controlled by the electronic system. When the steering is not required, the electronic pump is turned off, further reducing energy consumption. The electronic control unit of the electro-hydraulic power steering system utilizes information processing of sensors such as a vehicle speed sensor and a steering angle sensor, and can change the magnitude of the steering assist force by changing the flow rate of the electronic pump.
● Electric power steering
The electric power is mainly composed of a sensor, a control unit and a booster motor. There is no hydraulic pump, hydraulic line, steering column valve body and the like of the hydraulic assist system, and the structure is very simple.
The main working principle is that when the steering wheel rotates, the torque sensor at the position of the steering column transmits the rotation signal to the controller, and the controller provides an appropriate voltage to the motor through the operation correction to drive the motor to rotate. The torque output from the motor is amplified by the speed reduction mechanism to push the steering column or the steering rod to provide steering assistance. The electric power steering system can change the amount of power according to the speed, which makes the steering wheel lighter at low speeds and more stable at high speeds.
There are two ways to realize electric power steering. One is to apply power to the steering column. The assist motor is directly connected to the steering column after being decelerated and twisted. The auxiliary torque output from the motor is directly applied to the steering column, which is equivalent to the motor directly. Help us turn the steering wheel. The other is to apply a boost to the steering rod. The assist motor is mounted on the steering rod, and the lever is directly pushed by the assist motor to steer the wheel. The latter structure is more compact and easy to arrange, and is currently widely used.
● What is the variable power steering at speed?
Variable speed steering at speed means that the amount of steering assist can vary with the speed of the vehicle. What are the benefits of this? When driving at low speeds such as parking and parking, it is convenient to turn the steering wheel lightly. However, if the steering wheel is too light at high speed, it is a hazard because it is not conducive to the stability of the vehicle at high speed.
The speed-variable power steering can do this. When the car is running at low speed, it can provide a large boost to ensure that the steering wheel is light and flexible. When the vehicle speed is high, it will provide less boost to enhance. Driving safety and stability.
● What is a variable steering ratio steering system (active steering system)?
The so-called variable steering ratio can be simply understood as the ratio of the angle of rotation of the steering wheel to the corresponding angle of rotation of the wheel. In the aforementioned variable-speed variable-power steering system, what can be changed is only the assisting force, that is, only the assisting force when the steering wheel is rotated, but the steering ratio is immutable, and the steering ratio of the variable steering ratio is only The power of the steering can be changed. In different situations, the angle of rotation of the wheel corresponding to the steering wheel angle can also be changed.