Purpose and significance
On modern cars, steering system is the indispensable one of the most basic system, is to determine the key assembly of automobile active safety, vehicle steering characteristics, keep the car has better control performance, it is always an important topic of auto detection technology. In particular, the design of automotive steering system is of great importance in the modern day when the vehicle is highspeed, the driver is not professional and the traffic flow is densified. The design of automotive steering system can help students master the principles and methods of designing the steering system. Training theory combined with practical skills. The design is closely related to the professional, and can make use of the specialized courses of automobile construction, mechanical design, engineering materials and CAD drawing.

There are two cores in the design of gear rack steering gear: the first is the reasonable matching of gear and rack to meet the correct transmission ratio and strength requirement of the steering gear; The second is to adjust the design of the steering mechanism to properly match the spring stiffness to ensure the starting torque and meshing characteristics of the steering gear. So this topic in considering the above requirements and factors on the basis of the research using the rotation of the steering wheel drive pinion and rack steering shaft steering transmission mechanism, through the universal joint steering gear shaft rotates, steering gear shaft and rack joint, steering rack to linear motion, realize steering. The simple and compact structure of the steering gear is realized, and the advantages of short axial size and small number of parts can increase the power, thus achieving the stability and sensitivity of the vehicle steering. In this article mainly has carried on the steering gear and rack design and check of steering gear shaft, main method and theory of using the experience of the auto design parameters and college design of mechanical design course content, the result meet the strength requirement, safe and reliable.

1. Design trend of modern automobile steering device.
1.1 adapt to the high speed of the car.
From the Angle of maneuverability, stability and safe driving, the automobile manufacture is widely used in more advanced technology, and it USES the variable speed ratio diverter and the high rigid steering gear. "Variable speed ratio and high rigidity" is the direction of the current steering structure in the world.
1. Fully consider safety and portability.
With the increase of vehicle speed, the driver and the passengers' safety is very important, on many vehicles at home and abroad has generally add energy absorption device, such as collision safety steering column, seat belts, air bags, etc., and gradually popularized. From the point of view of human engineering, it has gradually adopted adjustable steering column and power steering system.
1.3 low cost, low fuel consumption and mass production.
With the deterioration of the international economic situation, oil crisis caused by the recession, car production become more and more importance to economy, therefore, to design low cost, low fuel consumption of cars and low cost, reasonable production line, try to realize the specialization of mass production. The production of spare parts, especially the steering gear, is more outstanding.
1. The computerization of the vehicle steering gear.
The vehicle's steering device must be the only way to develop computers.
The development trend of modern automobile steering device.
2. 1. The use of modern automotive steering devices.
With the rapid development of the automobile industry, the structure of the steering device has changed a lot. The structure of the automobile steering a lot, from the perspective of the prevalence of currently used, there are four main steering type: a worm and worm shaw (WP), roller type (WR), circulating ball type (BS), the rack and pinion type (RP). These four types of steering gear have been widely used in automobiles.
We have learned, in the world, cars accounted for about 45%, circulating ball type steering gear rack and pinion steering gear-component accounted for about 40%, worm wheel type redirector accounted for about 10%, other types of steering accounted for 5%. The circular ball type diverter has been developing steadily. In the Western Europe minibus, rack and gear type steering gear has a great development. The characteristics of the Japanese automotive steering is increasing in proportion of circulating ball type steering gear, equipped with various types of different kinds of engine cars in Japan, using different types of steering gear, the bus used in the circulating ball type steering gear, has been from the '60 s 62. Five percent, to the present 100 percent. (worm wheel type steering gear has been eliminated on the bus.) Large and small trucks mostly adopt circular ball type steering gear, but the rack gear type steering gear has also developed. The minivan USES the circular ball type steering gear to account for 65%, and the rack gear type accounts for 35%.
Based on the above analysis, the following conclusions are drawn:
Circular ball type steering gear and gear rack type steering gear have become the main two kinds of steering gear in the world. The worm gear # 0; Worm type steering gear and worm - type steering gear are gradually being eliminated or retained in a smaller position.
There are different views on the development of the diverter on the minibus, with the United States and Japan focusing on the circular ball type steering gear, which has reached or exceeded 90%. Western Europe focuses on developing pinion steering gear, with a ratio of over 50% and France up to 95%.
Due to the advantages of pinion type steering gear, the application of small car (including minibus, minivan or passenger car) has been developed rapidly. The main structure of the large vehicle is the circular ball type steering device.
2. The characteristics of circular ball type steering gear.
The circular ball type steering gear is characterized by high efficiency, light control and a smooth operating force characteristic curve.
The layout is convenient. Suitable for large, medium and power steering systems; Easy to transmit driver control signal; The reverse efficiency is high, the return position is good, and the action of hydraulic power booster is good.
It can realize the characteristic of variable ratio and meet the requirement of maneuverability. The middle position is small and often used, and requires a sensitive direction, so it is hoped that the speed ratio near the middle position will be smaller to increase the sensitivity. The large Angle turns to the position and the resistance is large, but the use frequency is small, so it is hoped that the large Angle position speed ratio is larger to reduce the steering force. Because of the variable ratio, the application is becoming more and more widely.
Through the rolling contact of a large number of steel balls, the steering force has great strength and good wear resistance. And it can be designed to have equal strength structure, which is one of the reasons why it is widely used.
The variable speed ratio has a higher rigidity than the structure, which is especially suitable for the increase of the vehicle speed. The high speed vehicle needs to have better steering stability at high speed, and it must be guaranteed that the steering gear has a high stiffness.
Clearance adjustable. It is also one of the advantages of this kind of steering gear that it can adjust the clearance after the wear of the rack, so as to make it have the appropriate steering gear clearance.
The production of our country's diverter, in addition to the early production of jiefang automobile with worm #0; Roller type steering gear, dongfeng motor with worm - type steering gear, most of the other vehicles adopt circular ball structure, and all have certain production experience. At present, the liberation and dongfeng are also actively developing the circular ball type steering gear, and the circular ball type diverter is widely used in the second generation. It can be seen from this that our country's diverter is also developing to a large number of circulating ball boaters.
2.3 the production of the steering gear is specialized.
The circular ball type diverter has achieved professional production in foreign countries. Meanwhile, it has carried out the experiment and research mainly with the specialized factory, which has greatly improved the production and quality of the products. In Japan "seiko" (NSK) company's circular ball type steering gear is low cost, good quality, high yield, gradually occupy the Japanese market, and sell its products to the world. Germany's ZF is also known as a major steering gear specialist. It has been producing ZF type steering gear since 1948, with annual output of more than 2 million. There are also a number of large diverter manufacturers, such as the SAGINAW division of Delphi. The British BURM# 0; Company AN is a well-known professional manufacturer, with a large production and sales surface. Specialized production has become a trend. Only by taking this road, can the product quality be high, the output is large, the cost is low, and it is competitive in the market.
2.4 dynamic steering is the direction of development.
The power steering system is widely used, not only in heavy vehicles, but also in advanced cars, and the application of medium cars is also gradually promoted. The main aim is to relieve the fatigue of the driver and improve the maneuverability and stability. Despite the problems of high cost and complex structure, the advantages are obvious and the development is very rapid.
There are three types of power steering: monolithic, semi-detached and connected valve type power steering structure. At present, the three forms have their own characteristics, and the development is relatively fast. The whole body is used for the front axle load of 3 ~ 8t cars, and the combined valve type is mostly used for the front axle load of 5#0; 18t automobile, semi - split is used for the front axle load of 6t to ultra heavy vehicles.
From the perspective of development trend, the foreign integrated steering gear is developing rapidly, and the structure of the integrated steering valve is the current development direction.

2. 研究的基本内容与方案

1) determine the structure layout plan.
2) complete the main structure design of valve body and gear rack mechanism.
3) completed overall design.

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