1. Design purpose and significance

1.1 Design purpose and significance

Suspension is an important assembly of automobile, which connects frame (or body) with axle (or wheel) elastically. Its function is to transfer all the forces or moments between the wheel and the frame (or body) and to alleviate the impact load from the uneven road surface to the frame (or body), attenuate the vibration caused by it and ensure the smooth running of the car. The suspension is mainly composed of elastic elements, guiding mechanism and shock absorber. Some suspensions also have buffer blocks and lateral stabilizers. Independent suspension and non-independent suspension are common suspensions in two-axle automobiles, while independent suspension is the main suspension in modern automobiles. With the development of automotive industry, the demand for comfort, handling and stability of automobile is increasing. Among many kinds of suspension, multi-link independent suspension has become the main suspension structure used in the rear suspension of mid-class and high-class cars by virtue of its excellent performance. [4] In independent suspension, single longitudinal arm and single oblique arm independent suspension are simple in structure and low in cost. They are often used in rear suspension, but there are still some shortcomings such as small lateral stiffness and small roll angle stiffness. This design is the rear suspension design of Toyota's eighth generation Camry. The eighth generation of Camry is based on TNGA, and has redeveloped almost all parts to make it a genuine and thorough new replacement model. Honda chose McPherson independent suspension on the front suspension and double-arm independent suspension on the rear suspension. This design chooses multi-link independent suspension on the rear suspension to obtain the best location of the kingpin caster angle, and minimize the forward and backward direction force to ensure the stability of normal driving, and also improve the ride comfort and comfort when the speed changes. By designing the constraint angle connecting the moving points, the wheel alignment can be adjusted actively when the suspension is compressed, so as to improve the control limit of the vehicle. By reasonably configuring the positions of the connecting rods of the suspension, the suspension can actively adjust the wheel alignment when it jumps, and the design freedom is large. The structure of multi-link suspension is complex, and the cost of material, research and development and manufacturing are much higher than other types of suspension, which occupies large space. However, the comfort of the multi-link suspension is the best of all suspensions, and its maneuverability is similar to that of the double-arm independent suspension.

The lightweight of automobiles of reducing the quality of automobiles as much as possible under the premise of guaranteeing the strength and safety performance of automobiles, so that to improve the power of automobiles, reduce the fuel consumption and reduce exhaust pollution.

Experiments show that if the vehicle weight is reduced by 10%, the fuel efficiency can be increased by 6%-8%. For every 100 kg reduction in vehicle quality, the fuel consumption can be reduced by 0.3-0.6 liters for 100 kilometers. The vehicle weight can be reduced by 1%, and the fuel consumption can be reduced by 0.7%. At present, the lightweight of automobile has become the trend of world automobile development. A considerable part of spring brackets in suspension system are cast brackets. The lightweight of brackets is also one of the key points of lightweight suspension system. The material is changed from QT450-10 to QTD1050-6 to achieve the design effect. The use of high-strength materials can greatly reduce the quality of suspension system bracket, with the gradual widespread application, the price will also be reduced.

1.2 Foreign research status

The traditional suspension system has many disadvantages. The development of multi-link suspension system has a history of more than 20 years. As early as 1977, BMW in Germany began to use the McPherson multi-link suspension system, but there was no such name at that time. Until 1983, Mercedes-Benz series first applied the concept of multi-link suspension system to the W201 model, and greatly improved the performance of the suspension system, so the multi-link suspension system. The term " multi-link suspension system" has only slowly come to the fore. Since 1988, many scholars have begun to study in many ways, including multi-link suspension system derived from double wishbone, multi-link suspension system derived from McPherson and multi-link suspension system with special configuration. The research reached its peak from 1991 to 1995. Since then, due to the performance improvement and design problems of suspension system, its development has gradually focused on multi-link suspension system with separated upper and lower control arms. The suspension system connects the steering knuckle to the body by a number of connecting rods arranged in space. This structure can fully realize the ideal design goals of kinematics and elastic kinematics, and achieve its smaller non-spring mass.

1.3 Domestic research status

For various reasons, most of our automobiles use independent suspension. The research of independent suspension, even multi-link independent suspension, started late in China, and there is a big gap with foreign countries. In the 1990s, it was still only used in luxury cars with high exhaust capacity. In recent years, there have been many studies on various suspensions in China: Ivy Quan of SAIC Automobile Engineering Research Institute and others have modified the McPherson suspension, designed the longitudinal "zero offset" L-shaped lower control arm and the L-shaped lower control arm, so that the lateral and longitudinal forces of the vehicle are controlled through the front and rear bushes respectively, so that the required lateral stiffness is independent of the longitudinal flexibility, so as to make the lateral stiffness independent of the longitudinal flexibility. When lateral force and longitudinal force act simultaneously, there is no coupling between them, which avoids the occurrence of suspension arm resonance and improves vehicle ride comfort. Zhuge Xiaoyu of Automotive Engineering College of Wuhan University of Technology analyzed the motion of McPherson suspension based on CATIA /ADASM, and determined the selection range of wheel alignment parameters, as well as the optimal design method of suspension. Li Jincan of the Technology Center of Shanghai Automobile Group Co., Ltd. analyzed the influence of torsional steering on the front-end vehicle. This study has reference significance for solving the actual torsional steering problem of vehicle and the design optimization in the early stage of vehicle development.

1.4 The future development

Due to the requirements of vehicle ride comfort and handling stability, green intelligent suspension with safety, intelligence and cleanliness will be the development trend of vehicle suspension in the future. Structural optimization, process equipment and the application of new materials are the main ways to realize the lightweight of vehicle chassis. In recent years, the application of new polymer materials and composites in the field of vehicle lightweight, vibration and noise reduction has been increasing. On the premise of continuous optimization of vehicle mainstream specifications and retaining the size of main parameters of specifications, the structural strength of the whole vehicle is improved and the consumption of consumables is reduced by using light materials such as aluminium, magnesium, ceramics, plastics, glass fiber or carbon fiber composite materials. The computer is used for structural design, such as finite element analysis, local strengthening design, etc., and the load-bearing body is used to reduce the thickness of body plate, etc. Among them, the current main measures of automobile lightweight mainly use light materials.

2. 研究的基本内容与方案

2.The basic content and scheme of the design

When designing a suspension for a vehicle, engineers will fully consider the structure, price, location and cost control of the vehicle. Each kind of suspension has its own advantages and disadvantages, but there are many advantages and disadvantages. At the same time, different suspensions have a great impact on the performance of vehicles, leading to strong mobility and comfort.

2.1 Leaf spring type non-independent suspension

Longitudinal leaf spring independent suspension is a suspension which uses leaf spring as an elastic element and is arranged parallel to the longitudinal axis of the vehicle. It also acts as a guide mechanism, which simplifies the suspension system. It is commonly used in commercial vehicles, such as trucks, pickups, vans, etc.