[YesAuto technology] I believe everyone is familiar with steering wheels, but do you really understand such a seemingly accustomed thing? Why does it turn so easily? Why is the vehicle's “turning direction” heavy when it is stalled? Is the mechanical hydraulic assist and the electro-hydraulic assist written on the configuration sheet the same thing? Is electro-hydraulic assist and electric assist a concept? These seemingly tangled problems are solved in this issue of “Helping You to Understand the Parameter Configuration Table Article-Power Steering Part”.
The definition of power-assisted steering in the textbook is to increase the external force to resist the steering resistance. In fact, it is a configuration that allows us to easily complete the steering when driving. We felt that the steering wheel was heavy when we were driving at school and learning, the light steering wheel of our own car, and the feeling that the seemingly cute MINI is driving but like fitness are all due to the difference in the power steering system. Below, let us classify and look at these power steering systems that often appear in the configuration table.
■The steering is basically relying on the “no assist”
The mechanical power steering system uses the driver’s physical strength as the main power source of the steering system. Simply put, most of the power comes from the strength of the user’s shoulders and arms. All the power-transmitting components are mechanical. At present, it is almost in passenger use. The car field is extinct, and it is only in service on the micro-face model.
Although its structure is simple and the cost is low, its power assistance is extremely limited, so it has almost disappeared from passenger cars at present, only occasionally appearing on micro-face models. Of course, if you want to experience this “primitive mechanical feel”, you can also go to the karting hall to experience it.
■ “Special for the old three” mechanical hydraulic assistance
Although mechanical power steering already has a certain boosting effect, people obviously will not be satisfied with the power-assisted feeling comparable to fitness. Therefore, mechanical hydraulic power with more obvious power-assisted effects was born. While retaining the mechanical power steering structure, it adds a hydraulic pump as a power source. Many years ago, the “old three” Fukang, Jetta, and Santana generally used mechanical hydraulic power.
In principle, it is very similar to the pure mechanical assist we mentioned earlier, except that the steering energy source is not only the driver himself, but also the power from the engine. Vividly speaking, one monk carried water to eat, and two monks carried water to eat. Therefore, the models that we drive with mechanical hydraulic power steering will feel lighter than the models that use pure mechanical power steering as mentioned above.
When the steering wheel is not rotating, 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 control valve connected to the steering column will open or close accordingly. The oil on one side will no longer pass through the hydraulic cylinder but will directly return to the oil storage tank, and the oil on the other side will continue to be injected into the hydraulic cylinder and the piston There is a pressure difference between the two sides, which will be pushed under the action of hydraulic force, and then produce auxiliary force. At this time, we will feel that turning the steering wheel is not so laborious.
Since most of its entire system is mechanical structure and few electronic systems, it is also characterized by maturity and stability, high reliability, and wide application range. In addition, even if the vehicle's hydraulic system fails and loses power, it can still rely on the traditional rack and pinion mechanism for steering.
Advantages: There are few electronic systems, mature and stable technology, and high reliability. Even if the vehicle hydraulic system fails and loses power, it can still rely on the traditional rack and pinion mechanism for steering.
Disadvantages: It takes up a lot of space, consumes the power output of the engine, and in order to ensure the boosting effect, high pressure must be maintained in the pipeline at all times, and there may be a hidden danger of oil leakage in the later period.
■ Common electro-hydraulic power assist in household cars
Electro-hydraulic power steering is often called Electro-hydraulic power steering in English. The biggest difference between it and mechanical hydraulic power steering is that the power source no longer directly consumes engine power, but is provided by the motor.
The start and shutdown of the booster pump in this system are all controlled by the electronic control system. When not steering, the booster pump is turned off, unlike the mechanical hydraulic booster pump that is always linked with the engine, so it consumes less engine power. .
In addition to consuming less engine power, the greater advantage of electronic hydraulic power steering is that it can analyze the information collected by the vehicle speed sensor, lateral acceleration sensor, steering angle and other sensors to change the power of the power pump in real time and change the power of the steering. That is, the steering wheel is lighter when the vehicle is driving at low speed and moving, and the steering wheel is heavier when the vehicle is at high speed, which gives the driver confidence with the variable speed assist function.
Advantages: Compared with mechanical hydraulic power assistance, the structure is simpler, less engine power consumption, and easy to expand the speed-dependent power steering function.
Disadvantages: Maintenance is still required later.
■ EPS, ESP silly electric power steering
Compared with mechanical hydraulic power assistance and electronic hydraulic power assistance, electric power steering equipment has the shortest mass production time. It was gradually applied to mass production vehicles after the 1990s. It is characterized by abandoning the complex hydraulic mechanism and relying purely on the electric motor to generate power.
In addition, when we operate the steering wheel to rotate, the torque sensor arranged on the steering column detects the rotational torque, converts it into an electrical signal and transmits it to the controller. The vehicle speed sensor also transmits the signal to the controller at the same time, and then it controls the actuator. Boost. That is to say, compared with the hydraulic steering assist mentioned earlier, the boost force is theoretically more “real”.
The use of an electric power steering system can rely on the motor to very accurately control the steering angle of the vehicle. Therefore, it can realize the function of automatic parking and the function of automatically correcting the direction of the lane keeping system.
Advantages: Compared with the hydraulic power steering system, the structure is more simple and compact, and the subsequent maintenance and maintenance are also simpler. At the same time, it is easier to arrange, has low system loss and operating noise, and has strong scalability.
Disadvantages: Under intense driving conditions, the booster motor is prone to overload, which affects the work of the booster system. In addition, affected by the power of the motor, electric power assistance is still somewhat inadequate for large vehicles with large steering loads.
● Only electric power assist can realize speed steering?
After understanding the above content, it is not difficult for you to find that electric power steering is easier to realize the speed steering function. Then the two hydraulic power steering mentioned above can not achieve the speed steering function?
Not only Mercedes-Benz, the BMW 3 Series code-named E90 has also used hydraulic power steering plus electronic valves to realize the speed-dependent steering function, and from the configuration table, they are all named electric power steering. In fact, they are only based on The hydraulic power steering system was developed.
■ “Cutting-edge technology” wire transmission control steering
When we usually drive through potholes, the steering wheel may “beat” with the ups and downs of the road. Is there a technology that can change this phenomenon? This technology called steer by wire can solve the above problems. If you buy a car in a 4S shop, the sales staff will often tell you that this is the world's most advanced technology from the aerospace field.
Wire transmission control steering abandons the mechanical structure under normal circumstances, and the transmission speed of electrical signals is much faster than that of mechanical and hydraulic structures, so it has an extremely fast response speed. However, for safety reasons, it cannot be completely separated from the mechanical structure at this stage.
■ Variable steering system
After understanding the common types of power steering, let's take a look at the system called variable steering that often appears in the configuration table. People not only hope that when the vehicle is parked in a roadside parking space, the steering wheel can be turned more briskly during the normal use of the car; when the vehicle is driving at high speed, the steering wheel will be heavier and bring more peace of mind. We will also greedily hope that in intense driving, the steering system can be more aware of the situation when we turn the steering wheel at the same angle, and control the wheels to rotate at different angles according to the speed of the vehicle. Therefore, the variable steering system came into being.
In addition to BMW and Toyota, Audi also has a variable steering system called Audi Dynamic Steering. In principle, it still uses a superposition method, although its structure is very different from BMW and Toyota systems. The goal is to achieve a variable steering function by changing the gear ratio. Previously, we have performed a detailed interpretation of this part. Friends who are interested in this part may wish to click “Mystery under the steering wheel (2) Detailed explanation of variable steering system” to read.
Full text summary:
This time, we mainly introduced the content related to power steering. The more traditional pure mechanical power assistance has no advantage in power and scalability, and only occasionally appears in the micro-facet market; mechanical hydraulic power assistance with fewer electronic systems, mature and stable technology, and high reliability is currently widely used in the industry. Automotive market; electronic power steering that replaces hydraulic pumps with electronic pumps consumes less energy and can be expanded to speed steering; electric power steering is quieter, simpler in structure, less energy loss, and more expandable. Popularization trend; wire-by-wire control appears as an emerging technology in some high-end models.