Wuhan University of Technology Graduation Design (Thesis)

Design of steering system

of Yutong ZK6579 School bus

School: School of International Education

Specialty amp; Class: Automotive Engineering gj1501

Name: Chen Ming

Tutor: Yuan Xiaohong

Statement of Degree Thesis originality

I solemnly declare：The thesis submitted is the research result independently obtained by myself under the guidance of my tutor. Except for the contents specifically quoted in this thesis, this thesis does not include any other works that have been published or written by individuals or groups. I fully understand that the legal consequences of this statement are borne by me.

Author’s Signature：陈明

Date:2019.6.10

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Author’s Signature：陈明 Date:2019.6.1

Tutor’s Signature： Date:

Abstract​

With the increasing popularity of school buses, people pay more and more attention to the safety of school buses. The design of a reasonable school bus steering system is of great significance to ensure the safety of students.

This paper takes the Yutong school bus as the research object and compares the advantages and disadvantages of different steering systems. And then according to the actual situation of the school bus. The hydraulic power steering system of gear and rack is designed.

The main contents of this paper include comparing different types of steering gear and power system, the design scheme is selected according to the specific situation of Yutong school bus, and finally the gear rack steering gear and hydraulic power system are selected. It also includes the selection and calculation of the parameters of gear rack steering gear. The hydraulic cylinder, steering valve and piston stroke in the assist system are calculated. Finally, the strength of the main components in the steering system is carried out. It includes checking the tooth surface contact fatigue strength and the tooth root bending fatigue strength of the gear rack. Finally, the assembly drawing and part drawing of the whole steering system are drawn.

Key words: school bus; steering system; hydraulic power; rack and pinion; strength check

Catalogue

Chapter 1: Introduction 1

1.1 The purpose and significance of subject Research 1

1.2 Research status at home and abroad 1

1.2.1 Research status of steering system 1

1.2.2 Research status of steering gear 4

1.3 Requirements for steering systems 5

1.4 The research content of this subject 5

1.5 Expected target 6

Chapter 2: Determination of main body Design Scheme and parameters 7

2.1 Requirements for power steering mechanisms 7

2.2 Selection of Gear and Rack steering gear 7

2.3 Main parameters of design target vehicle 8

2.4 Calculation of steering angle and steering system angle transmission ratio 8

2.5 Summary of this chapter 9

Chapter 3 Design of Mechanical part of steering Gear 10

3.1 Design of geometric size structure of Gear and Rack 10

3.2 The relationship between Gear and Rack geometric Transmission 10

3.3 Summary of basic parameters of gear and rack 12

3.4 Gear strength check 13

3.4.1 Tooth surface contact strength 13

3.4.2 Check of contact fatigue strength of tooth surface 14

3.4.3 Tooth root bending fatigue strength 14

3.4.4 Check of tensile strength of rack compression bar 15

3.5 Summary of this chapter 16

Chapter 4 Design of hydraulic assist system 17

4.1 Composition and principle of hydraulic Power steering system 17

4.11 Composition of rotating Valve hydraulic Power steering system 17

4.12 Principle of hydraulic Power steering system 18

4.2 Design and calculation of Power cylinder of hydraulic Auxiliary system 18

4.2.1 Rated pressure of hydraulic system p_n 18

4.2.2 Total efficiency of hydraulic cylinder 19

4.2.3 Theoretical Force of hydraulic cylinder F 19

4.2.4 Cylinder inner diameter D 19

4.2.5 Calculation of Wall thickness of Power cylinder 19

4.2.6 Piston stroke S 20

4.2.7 Minimum guide length 20

4.3 Design and calculation of rotating Valve Control Valve 20

4.3.1 Factors affecting the characteristics of rotating valve 20

4.3.2 Design of spool edge 21

4.3.3 Limiting mechanism 21

4.4 Design of steering bar and its end 22

4.5 Rack clearance adjusting device 22

4.6 Torsion bar design 23

4.7 Steering control mechanism design 24

4.8 Summary of this chapter 25

Conclusion 26

Reference 27

Thanks 29

Chapter 1 Introduction

1.1 The purpose and significance of subject Research

With the increasing popularity of school buses, people pay more and more attention to the safety of school buses. The school bus steering system is an important part of the school bus, and its performance directly affects the safety of the whole school bus. It ensures the Passability of the school bus to the complex road surface and protects the safety of students and drivers. It is of great significance to reduce students' traffic accidents and improve students' traffic efficiency. Especially today, with the high speed of traffic, the popularization of vehicles and the diversification of roads, the research and development of school bus steering system is particularly important. A reasonable steering system can perfectly solve the contradiction between light operation and steering sensitivity. The design of a school bus steering system with good maneuverability and safety has always been a hot research topic for automobile manufacturers and scientific research institutions.

1.2 Research status at home and abroad

1.2.1 Research status of steering system

Since modern times, the automobile industry has obtained the long-term development, the automobile steering system has also made the huge breakthrough in the technology, the first is the pure mechanical steering system, later in order to meet the higher use requirements, people invented the power steering system. The power steering system adds a power mechanism on the basis of the mechanical steering system. According to the different sources of power, the power steering system can be divided into hydraulic power and electric power. The hydraulic power steering system can be subdivided into mechanical hydraulic power steering system and electric hydraulic power steering system, and the electric power steering system is derived from the line control power steering system.

Since modern times, the automobile industry has obtained the long-term development, the automobile steering system has also made the huge breakthrough in the technology, the first is the pure mechanical steering system, later in order to meet the higher use requirements, people invented the power steering system. The power steering system adds a power mechanism on the basis of the mechanical steering system. According to the different sources of power, the power steering system can be divided into hydraulic power and electric power. The hydraulic power steering system can be subdivided into mechanical hydraulic power steering system and electric hydraulic power steering system, and the electric power steering system is derived from the line control power steering system.