摘 要

本文对多轴纯电动小车的悬架进行了系统的设计，设计内容包括悬架的选型，基本参数的确定，弹性元件以及减振器的设计。针对多轴车的特点，本次悬架使用的是双横臂悬架系统，上下横臂采用V型臂，并让螺旋弹簧与减振器一体式安装，使布置更为方便。并比较了双横臂的不同布置方案，计算了悬架侧倾中心以及纵倾中心。

本文是为了设计出一辆小型的八轴车以便研究其控制特性，可靠性展示等汽车相关特性，因原车尺寸过大，占用面积大不便于研究。

关键词：悬架设计；双横臂悬架；螺旋弹簧；减振器

Abstract

In this thesis, the suspension of multi-axis pure electric vehicle is systematically designed. The design includes the selection of suspension, the determination of basic parameters, the design of elastic element and shock absorber. For the characteristics of multi-axle, the suspension uses double wishbone suspension system and the upper and lower arms are designed with V-arm. And the coil spring and shock absorber are installed integrally, so that the layout is more convenient. And this thesis compares the different arrangement of the double wishbone, at the same time the center of the suspension roll and the center of the trim are calculated.

The study was designed to design a small eight-axle vehicle to study its control characteristics, reliability, and other related characteristics of the vehicle, because the original vehicle size is too large to study.

Key words: suspension design; double wishbone suspension; coil spring; shock absorber

Contents

Chapter 1 Introduction 1

1.1 Purpose and Meaning 1

1.2 Domestic and International Research Status 2

1.3 Summary of Chapter 3

Chapter 2 Suspension 5

2.1 Vehicle Suspension 5

2.2 Suspension Type 5

2.3 Summary of Chapter 6

Chapter 3 Parameter Design 7

3.1 Suspension Parameter Design 7

3.1.1 Front Beam Change 7

3.1.2 Wheel Camber Angle 7

3.1.3 Kingpin Inclination Angle and Offset 7

3.1.4 Kingpin Caster Angle 8

3.1.5 Suspension Static Deflection Selection 8

3.1.6 Suspension Dynamic Deflection Selection 9

3.1.7 Calculation of Suspension Stiffness 9

3.1.8 Double Wishbone Independent Suspension Roll Center 10

3.1.9 Suspension Trim Center 11

3.2 Guide Mechanism Design 12

3.2.1 Longitudinal Plane of Upper and Lower Arms Arrangement Plan 12

3.2.2 Transverse Plane of Upper and Lower Arms Arrangement Plan 13

3.2.3 Horizontal Plane of Upper and Lower Arms Arrangement Plan 14

3.2.4 Length of Upper and Lower Arm 14

3.3 Summary of Chapter 14

Chapter 4 Elastic Component 15

4.1 Design of Elastic Component 15

4.2 Coil Spring Design 15

4.2.1 Calculation of Main Parameters 15

4.2.2 Check the Strength of The Coil Spring 16

4.2.3 Spring End Shape Design 17

4.3 Summary of Chapter 18

Chapter 5 Shock Absorber 19

5.1 Shock Absorber Design 19

5.2 Shock Absorber Type 19

5.3 Main Performance Parameter Selection 22

5.3.1 Selection of Relative Damping Coefficient 22

5.3.2 Determination of Damping Coefficient 23

5.3.3 Determination of The Shock Absorber Installation Angle 24

5.3.4 Determination of Maximum Unloading Force 25

5.3.5 Main Dimension Parameter 25

5.3.6 Determination of The Shock Absorber Total Stroke 26

5.4 Summary of Chapter 26

Chapter 6 Conclusion 27

References 28

Acknowledgement 30

Chapter 1 Introduction

1.1 Purpose and Meaning

Because the rapid development of the world economy, the continuous improvement of automobile design technology and the rapid growth of automobile sales, the automobile industry is regarded as the key industry of various countries in the world. China's current vehicle sales rise year after year, with the development of the automotive market and the overall demand. The major vehicle brands are also more and more attention to China's auto market, and consumers have a higher demand for vehicle performance, so that scholars pay more attention to the study of the vehicle. After China's reform and opening, multi-axis vehicle has developed more and more quickly in China because of its excellent carrying capacity, efficient carrying characteristics and other advantages, to adapt to more and more rapid economic development needs. Among them, the new energy of the multi-axis vehicle is a trend of the future, and now China also pays more and more attention to the development of new energy vehicles. In the cites holding more vehicles, new energy vehicles can better solve environmental pollution and energy shortages and a series of questions^[1]. New energy vehicles can be divided into pure electric, hybrid, fuel cell and other types. This study is pure electric multi-axis vehicle, whose energy source is wider, prices is lower and has low emissions. Pure electric can effectively protect the environment, and the body noise is low, the overall comfort is better. But during the current development, the main problem is that pure electric vehicle mileage is shorter than traditional fuel vehicles, and the charging equipment in the country's penetration rate is especially less. However, the state vigorously promotes pure electric vehicles. Some vehicle manufacturers have been able to launch mass production of pure electric vehicles, to meet people's daily life in the use of the vehicle. The operation of these vehicles is simpler than the traditional fuel vehicle, which could achieve no emission. In general, the overall development prospects of pure electric vehicles are good, but the current multi-axis vehicle for the pure electric research is less^[2]. Pure electric vehicles can solve the contradiction between the growing vehicle sales and the lack of oil resources, and reduce the environmental pollution caused by fuel vehicles. In addition, the battery technology is more mature, which is a point of entry that could transform China's fuel industry into the new energy automotive industry.

The study of the entire suspension system is not only reflected in the ride comfort, but also a criterion for overall quality of the vehicle. The suspension system connects the wheels to the frame so that the vehicle could safely travel on the road. If a vehicle without installed suspension system drives on the uneven road, the impact of the road will make the driver feel extremely uncomfortable and destroy the goods. In the vehicle driving process, the suspension can also be a certain guiding role on the wheel's trajectory to ensure the stability of the vehicles’ operation. Therefore, the selection of suspension system and parameter have a great impact on the overall performance of the vehicle. One of the multi-axle suspension system due to the gradual increase speed, was constantly improved to adapt to modern vehicles and road conditions. Double wishbone independent suspension is widely used in modern multi-axle vehicle, which is mostly for the front suspension and could freely design structural parameters to obtain better vehicle performance^[12].

1.2 Domestic and International Research Status

Foreign research on suspension in 1901, Henri Fournier's Mors used the shock absorber for the first time, and this new suspension system with shock absorber allowed Henri Fournier to win a famous vehicle game. The coil spring in 1906 for the first time in the Brush Motor company’s Brush Runabout. In 1920, Leo motor in the suspension system using torsion bar spring. In 1922, Lambda created an independent front suspension, and in 1925 TATRA designed an independent suspension truck, but because of the easy damage to the wheel during use, it is no longer used on the truck. During 1970 to 1980, the multi-axle began to use different elastic elements of the independent spring, such as leaf spring independent suspension, variable stiffness of the coil spring-type independent suspension or oil and gas spring type. In 1990 OSHKOSH company designed a double wishbone independent suspension, which was used in large quantities in off-road vehicles.

In 1994, Bauk and Enzo et al. used the standard design method of engineering to set up a set of basic principles for the reasonable development and design of the suspension system of the bus, and described the geometric dynamics method of the suspension in detail. By assuming that the bus is a rigid body model, it calculated the stiffness of the spring and the frequency of bounce and pitch, analyzed the whole equation of motion including the work in order to obtain the primary and the secondary mass values and its center of gravity coordinates. And it also studied the suspension performance which is fron anti-dive, back anti-lift force and anti-squat properties.

2013 Shpetim, LAJQI, Stanislav et al. who designed the suspension mechanism for a four-wheel drive and four-wheeled terrain vehicle to meet the stability, safety and mobility requirements. And McPherson suspension and double wishbone suspension and other active suspension had been comprehensively studied, and then had a kinematic simulation analysis in the 2D work model and MATLAB environment. The results will be more detailed discussion to find the best solution to meet the frame system requirements.

2014 Anand Tandel, A. R. Deshpande, S. P. Deshmukh and K. R. Jagtap describes how to build a quarter models of double wishbone suspension by using SimMinkchan and Simulink in MATLAB. SimMechanics was applied to the physical model of the suspension, while Simulink used a quarter of the mathematical model of the vehicle suspension. Then, the PID controller is implemented on two models to minimize the vertical acceleration of the vehicle body. Finally, the various combinations of spring stiffness and damping coefficient was analyzed to get the acceleration of the vehicle body. The results of the two models was compared.