Interpretation of the most popular automotive powe

2022-08-15
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Interpretation of common automobile power steering system

power steering, as the name suggests, is to resist the steering resistance by increasing external force, so that the driver can complete the steering with less force. It is also called power steering, which is called power steering in English. Initially, it was to make some heavy vehicles easier to operate, but now it is very popular, which makes driving easier and easier, It also makes the vehicle more responsive and improves the safety to a certain extent. According to the different sources of power, power steering can be divided into two categories - hydraulic power and electric power

hydraulic power

the origin of hydraulic power steering dates back to February 1902. Frederick W. Lanchester of Britain invented "cause the steering mechanism to be activated by hydraulic power", that is, hydraulic drive steering mechanism. Later, similar inventions were patented by inventors in the United States and Canada. Among automobile manufacturers, Chrysler took the lead in realizing the commercial production of hydraulic power steering system, named it hydraguide hydraulic steering system, and carried it on Chrysler's sixth generation imperial (translated as emperor) model in 1951. With the development of technology, electronic hydraulic power steering system with electronic pump instead of mechanical pump has appeared, so at present, hydraulic power is mainly divided into mechanical hydraulic power and electronic hydraulic power. In addition, on the basis of mechanical hydraulic power, electronic servo hydraulic power steering system has also been derived

mechanical hydraulic power steering

let's look at the main principle of mechanical hydraulic power steering. It is based on the mechanical rack and pinion steering mechanism, and adds a complete set of hydraulic system, including fluid reservoir, hydraulic power pump, mechanical valve connected to the steering column, hydraulic cylinder on the steering mechanism and piston that can push the steering rod, etc

schematic diagram of mechanical hydraulic power assistance

front view structure diagram of mechanical hydraulic power assistance

the hydraulic pump providing hydraulic pressure for mechanical power steering is driven by the engine through the belt, that is, only when the engine is running, the steering pump can operate, which is why the steering wheel power assistance disappears after the engine is stopped. On the steering gear, there is a mechanical valve that can rotate with the steering column. When the steering wheel does not rotate left and right, the pressure in the chambers on both sides of the piston is consistent and in a balanced state. When the steering wheel rotates, the mechanical valve connected to the steering column will be opened or closed accordingly. The oil on one side will no longer flow through the hydraulic cylinder and directly return to the oil storage tank. The oil on the other side will continue to be injected into the hydraulic cylinder. The pressure difference between the two sides of the piston will be pushed under the action of hydraulic pressure, and then an auxiliary force will be generated to push the steering rod to turn the wheel, which greatly reduces the force we need to rotate the steering wheel

when steering, the opening and closing of the mechanical valve makes it flexible. Due to the different construction of waterproof engineering and structural engineering, the hydraulic pressure difference between the two sides of the square plug will push the piston and drive the steering rod

the hydraulic power steering system has another advantage, which is to improve the comfort and safety. When the wheels jump violently and the tires turn involuntarily when encountering potholes, the effect of hydraulic pressure on the piston can well buffer and absorb vibration, The vibration transmitted to the steering wheel is greatly reduced. At the same time, this structure also improves the safety. For example, when the tires of vehicles using traditional gear and rack mechanism suddenly change direction when they encounter potholes during steering, the rack will drive the gear to reverse the steering wheel, resulting in a "thug" situation. It is very easy to have no impact on the use of most workpieces, and it is easy to damage the driver's hands. There will be no such problem on hydraulic assisted vehicles

mechanical hydraulic power assist features: the whole system is of mechanical structure, from the mechanical hydraulic pump driven by the belt to the hydraulic mechanical valve body on the steering column, without any electronic system. The technology is mature and stable, with high reliability and a wide range of applications. Even if the vehicle's hydraulic system fails and loses power, it can still rely on the traditional gear and rack mechanism for steering. The disadvantage is that the structure is complex, takes up a large space, and the manufacturing cost is high, which also makes the maintenance more difficult and costly. And because the hydraulic pump is driven by the engine belt, it will consume part of the power of the engine, affecting the fuel economy and the power of the vehicle, especially for the small displacement vehicle with relatively weak power itself. In addition, the power of a simple mechanical hydraulic power assist system cannot be adjusted, so it is difficult to take into account the different requirements for pointing accuracy at low speed and high speed

electronic hydraulic power assistance

the so-called electronic hydraulic power assistance, referred to as EHPS, has the same principle as mechanical hydraulic assistance, and the biggest difference with mechanical hydraulic assistance is that it no longer uses the hydraulic pump driven by the engine through the belt, but replaces it with an electric driven electronic pump

the advantage of electro-hydraulic power is first reflected in energy consumption. First, the electronic pump driven by electric energy uses the electric energy output of the generator and battery, which no longer consumes the power of the engine itself. The start and shutdown of the electronic pump are all controlled by the electronic system. When the steering action is not done, the electronic pump is turned off, unlike the mechanical hydraulic power pump, which is always linked with the engine, further reducing energy consumption

secondly, the electronic control unit of the electro-hydraulic power steering system can change the strength of the steering power by processing the information of the speed sensor, lateral acceleration sensor, steering angle sensor and other sensors, and by changing the flow of the electronic pump in real time, that is, the variable power assist function with speed. Of course, electro-hydraulic power is not the only way to achieve variable power with speed. We will introduce various "variable" power steering systems in detail in the following articles

electro hydraulic power has been gradually popularized since the late 1990s. Ford, Volkswagen, Toyota, Honda, Mazda, Peugeot, Citroen and other brands all use electro-hydraulic power systems. Mazda 3, triumph and other models we are familiar with use such systems

why can't electronic hydraulic power assist replace mechanical hydraulic power

in terms of technology, function and economy, electronic hydraulic power has more advantages than mechanical hydraulic power. However, at present, electronic hydraulic power has not been able to replace mechanical hydraulic power. The main reasons are as follows:

1 The cost of electro-hydraulic power is higher. Compared with the mechanical hydraulic power system, after adding the electronic control system and replacing the electronic pump, the manufacturing cost of the electronic hydraulic power system is higher, the technology is more complex, and the difficulty and cost of maintenance and repair are also increased

2. Reliability is inferior to mechanical hydraulic power. In addition to the failure of steering mechanism and hydraulic mechanism, electronic hydraulic power system also increases the possibility of failure of electrical system, so its reliability is not as reliable as traditional hydraulic power system

3. Limited assistance. Although the use of electronic pump has obvious advantages, the electronic pump needs to be driven by the electric energy of the generator, and the power of the on-board generator and the maximum current that the battery can provide are limited, so the power of the electronic pump is also limited, and the load it can carry is also limited. Therefore, at present, most of the vehicles that use electro-hydraulic power are small and medium-sized vehicles. For vehicles that need greater power assistance, the electronic hydraulic power assistance system is out of reach

4. Evolved mechanical hydraulic power assist system. With the development of technology, the variable speed function of electronic hydraulic power has been realized on the evolved mechanical hydraulic power system (using electromagnetic valve body technology), and even the variable ratio active steering system has been derived from the mechanical hydraulic power steering system. Therefore, the mechanical hydraulic power steering system with higher reliability and load-bearing capacity is still welcomed by manufacturers

electric power steering

electric power steering system (EPS or EPAs for short) is also a steering technology gradually applied to mass-produced vehicles since the late 1990s. Like hydraulic power steering system, it is still based on rack and pinion steering mechanism, but the power steering mechanism has changed from a complex hydraulic mechanism to a system that relies on electric motors to generate power

the figure shows ZF's electric power steering system products

from the schematic diagram, we can see that the structure of the electric power steering system is very simple, without the hydraulic pump, reservoir, hydraulic pipeline and steering column valve body structure, but composed of sensors, control units and power motors. A torque sensor is installed at the steering column position. When the steering wheel rotates, the torque sensor detects the rotating torque and converts it into an electrical signal to the controller. The speed sensor also transmits the signal to the controller at the same time. The controller calculates enough to supply the appropriate voltage to the motor to drive the motor to rotate. The motor amplifies the torque through the reduction mechanism to drive the steering column or steering rod to move, so as to achieve power assistance. Its variable assistance based on speed can make the steering wheel lighter at low speed and more stable at high speed

electric power steering has two main structures according to the different action positions. These two structures are used to assist the steering column and steering rod respectively. The electric power assisted structure that applies power to the steering column is to connect the power assisted motor (with a reduction mechanism to amplify torque) directly to the steering column, and the auxiliary torque output by the motor is directly applied to the steering column, which is equivalent to the motor directly helping us turn the steering wheel

the electric power system acting on the steering column is directly connected to the steering column to apply power to the steering column

another structure is to arrange the power assisted motor on the steering rod, and directly use the power assisted motor (1. When the jaw is clamped, it is not properly equipped with a deceleration mechanism, which plays the role of amplifying torque) to push the rod to help the wheel steer. This structure is more compact and easy to arrange. It is widely used at present. Moreover, compared with the first structure, the steering part of the steering wheel is relatively independent of the motor assistance. The information of the road surface can be well fed back to the steering wheel through the tire, gear and rack mechanism. Compared with the first structure, this structure has a clearer "road feel" and better takes into account the driving pleasure. At present, in China, the sixth generation Golf and Ruiyi, which we are familiar with, have adopted the electric power steering system with this structure

the second structure is to use the power assisted motor to drive the steering rod, and the motor and steering column mechanism are separate

Ruiyi's electric power steering system, which uses the second structure

golf 6 uses the electric power steering, which is also the second structure

advantages and disadvantages of the electric power steering system

compared with the hydraulic power steering system, the reflected signal in the frequency range of 12 ~ 18GHz can be attenuated by more than 10dB, Electric power steering has many advantages:

1 The structure is simple and compact, the manufacturing cost is low, the process is relatively simple, and the later maintenance is also simpler

2. The system has low loss (there will be no loss of booster fluid like hydraulic power), low running noise, and no running noise of hydraulic pump or electronic pump, which improves the comfort

3 The power of assistance can be variable with the speed, which can meet the different needs of the vehicle for assistance when driving at high speed and low speed, and the response speed is fast

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