With the increasing number of cars with engine front-wheel drive, the increase in the load on the front axle of the car has made steering lightness a common concern. Since the power steering system can not only solve the contradiction between light steering and flexible steering, but also improve driving safety and comfort, the current power steering system is not only widely used in medium-sized trucks, especially heavy-duty trucks , And was gradually transferred to the car.
The traditional hydraulic power steering system needs to consume a certain amount of energy, which will increase the fuel consumption of the car. The fuel consumption caused by the device's hydraulic power steering system accounts for about 3% of the vehicle's fuel consumption. With the development of electronic technology, an electronically controlled mechanical-hydraulic power steering system came into being. The system is superior to the traditional hydraulic power steering system in certain performances, but it still cannot eliminate the inherent shortcomings of the hydraulic power steering system.
Electronically controlled electric power steering system 'lectricPowerSystem), is another kind of power steering system. It completely eliminates the hydraulic device and replaces the hydraulic energy with electrical energy, which reduces the energy consumption of the engine. The research and development of electric power steering systems are in line with the three major themes of safety, environmental protection and energy saving in the development of automobiles, and therefore have certain practical and long-term significance.
Characteristics of electric power steering system The traditional hydraulic power steering system (hereinafter referred to as hydraulic power system) is composed of a steering oil tank, a steering oil pump, a high-pressure fuel pipe, a control valve, and a mechanical steering gear. The system structure is huge and complex; the power steering gear requires high processing accuracy; the steering oil pump is driven by the engine. Whether the car is turned or not needs to consume engine power; the leakage of hydraulic oil is also a big problem, which requires frequent maintenance. Therefore, the hydraulic power system is restricted to a certain extent in terms of system layout, installation, tightness, handling sensitivity, energy consumption, wear and noise.
Electronically controlled electric power steering system (hereinafter referred to as electric power steering system) is based on the mechanical steering mechanism, adding a signal sensor, an electronic control unit and a steering power assist mechanism. It is a schematic diagram of the electric power steering system.
Signal sensors include torque sensors, vehicle speed sensors and steering angle sensors. Through these sensors, the steering force, steering angle, and vehicle speed signals acting on the steering wheel are obtained, thereby providing information for determining the assist control command.
The electronic control unit includes a detection circuit, a microprocessor, a control circuit, etc. The detection circuit shapes and amplifies the signal of the sensor and sends it to the microprocessor, and then the microprocessor calculates the optimal boosting torque. The control circuit sends the current command from the microprocessor to the motor drive circuit.
The steering assist mechanism includes a booster motor, an electromagnetic clutch, and a reduction transmission mechanism. The booster motor generally adopts a DC motor, and its current is controlled by a microprocessor, and corresponding boosting characteristics can be obtained according to different vehicle speeds. Through the reduction transmission mechanism, the power of the motor is transmitted to the steering gear. The electromagnetic clutch is used as a safety device to ensure that when the system fails, the motor and the deceleration transmission mechanism are disconnected, the power transmission is interrupted, and the system is switched from the electric power steering state to the manpower-mechanical steering state.
Compared with the hydraulic power system, the electric power steering system has the following characteristics: energy consumption is reduced. The electric power steering system has no hydraulic device and is an on-demand system, that is, the system only works when steering and consumes less energy. Therefore, compared with the hydraulic power system, it can save 80% energy under various driving conditions ~ 90%. Significant weight reduction. The hydraulic power system has components such as hydraulic cylinders, oil pumps, rotary valves, hydraulic pipes, etc., which makes the system structure complex, the number of parts is large, the space is large, and the layout is inconvenient. Obvious advantages, compact system structure, reduced quality, no oil leakage, easy system layout, etc.
Optimize power control characteristics. There is a certain lag in the increase and decrease of hydraulic power, the response sensitivity is poor, and the follow-up is not enough. Since the electric power steering system adopts electronic control, it can optimize the steering performance of the steering system and enhance the followability.
*) System security protection. When the electric power steering system fails, it cuts off the power transmission between the motor and the deceleration transmission mechanism, and quickly turns into the manual-mechanical steering state.
Development status of electric power steering system 3.1 Types of electric power steering system According to the different positions of the steering power steering system, the electric power steering system is divided into three categories: steering shaft assist type, steering gear pinion assist type and rack assist type. ). The steering assist mechanism is installed on the steering shaft. When the driver turns the steering wheel, the control unit accepts signals such as torque, direction of rotation, and vehicle speed to control the current of the DC booster motor. The power of the motor is transmitted to the steering shaft gear through the clutch and the motor gear, and then transmitted to the steering gear through the universal joint and the intermediate shaft.
(See power steering gear steering type). The steering assist mechanism is installed at the steering gear pinion. Compared with the steering shaft assist type, it can provide a larger steering force and is suitable for medium-sized vehicles. Its power control features increase the difficulty.
For steering gear pinion-assisted electric steering power-assist system, see rack assist. The steering assist mechanism is installed at the steering rack. The motor directly drives the steering rack via a reduction gear mechanism. Compared with the steering gear pinion assist type, it can provide greater steering force and is suitable for large vehicles. There are major changes to the original steering transmission mechanism.
3.2 The development status of electric power steering system Since the first use of electric power steering system in March 1988, it was used in the Selwo car of Suzuki Motor Corporation of Japan, followed by Miller of Daihatsu Motor Co., Ltd. Suzuki Motor's Alto and other cars have been adopted successively. At present, several large foreign companies such as ZF in Germany, Lucas-Wilida in the United Kingdom, Delphi, Saginaw, TRW in the United States, NSK in Japan, Koyo, etc.) have all launched their own electric power steering systems. At the Fifth International Auto Expo in Beijing in 1998 and the Sixth International Auto Expo in Beijing in 2000, the German ZF company exhibited electric power steering systems.
So far, there are only a handful of domestic colleges and universities (continued on page 34) 32% in 2000. Diesel engines have given new life to old models, such as Peugeot 306 or the first-generation Renault Laguna. On the one hand, the price of unleaded gasoline has increased by 20% since the fuel price has risen by 995%. On the other hand, French and German manufacturers have launched new supercharged diesel engine systems that are more efficient, cleaner, and more energy-efficient. These new engines are high-pressure direct-injection diesel engines, which are the focus of Peugeot and Renault's research. Their HDi and dCi diesel vehicles' sales share keeps increasing leaps and bounds. 57% of Renault ’s “Landscape“ cars and kangoo â€cars, 59 / Citroen“ Picasso â€cars, 70.5% Peugeot 406 and 68% Peugeot 607 are diesel cars. Even more surprising is that diesel cars The share of small utility vehicles cannot be underestimated, such as Peugeot 20643.6% diesel vehicles) and Renault Clio. Those manufacturers who launched diesel vehicles late have suffered heavy losses and sales have fallen sharply. For example, Ford ’s sales in France have fallen. 20%, a drop of 10% in Europe, and the same for Opel.
2000 was a good harvest year for French manufacturers. Renault and PSA regained their lost ground in one fell swoop through their own internal reorganization, strict management of policy makers and a keen strategic vision of the market, and began a massive counterattack. In the case of a decline of 0.7% in the entire French sedan market, sales of French manufacturers have increased to 1.26 million units. PSA won a 31% market share with Citroen Picasso ’s “2.8% market share†and Citroen Picasso ’s “2.8% market shareâ€, of which Citroen accounted for 12.3%) while Renault maintained its sales level in 1999, reaching 602 415 Vehicles, occupying a 28.2% market share, and its alliance partner Nissan's sales in France soared 20.9%. At the same time its main competitors began to lose their territory, Volkswagen Golf's sales fell by 2.3%, withdrew from French sales The top ten, while sales of Ford Group and Honda fell by 21% and 42%, respectively. At the same time, in overseas markets, French cars are also everywhere. From 1996 to 2000, French car exports increased by 15% in the United Kingdom, 20% in Germany, and 55% and 90% in Spain and Italy respectively. Editor Gao Hui) continued from page 5) In order to study the electric power steering system, the research work is not in-depth, and no products have been developed.
Research and development key and development trend of electric power steering system The electric power steering system has fully demonstrated its superiority in light handling, energy saving and other aspects, and has broad application prospects. The key to the development of electric power steering systems lies in electronic control technology, including the establishment of appropriate power-assistance characteristics, as well as the sensing technology that collects the main parameters. In addition, the relationship between the electric power steering system and the safety and steering stability of the car, and the reliability of the electric power steering system will become important research topics.
Over the past decade, electric power steering systems have made significant progress in reducing system self-quality and price, reducing system heat, current consumption, internal friction, matching with the vehicle to obtain reasonable power-assistance characteristics, and ensuring good road feel. The future development trend is: to further improve the control performance, so that it can better adapt to different grades of cars. For example, increase the steering feedback signal of the car, and control the return performance of the vehicle.
Improve the reliability of the system. Such as the use of non-contact torque sensors.
Lower the price.
Conclusion With the rapid economic development, the penetration rate of cars will become higher and higher, and the lightness of car steering will become one of the considerations for car buyers. Therefore, the research and development of the system is of great significance to meet the needs of society and keep up with the development of the world's automotive technology.
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