Graduation Design (Dissertation) of Wuhan University of Technology

Steering system design of

1.6 litre car

(School): International Education College

Specialty amp; Class: Vehicle engineering gj1302

Student name: Liu Yiding

Tutor: Han Aiguo

Statement of Originality

I solemnly declare that the thesis I submit is a piece of writing I completed independently based on my own research under the guidance of my supervisor. Except for the quotations, this paper does not include any writings published or completed by other individuals or groups. I am fully aware that the legal consequences of this statement are borne by me.

Signature of the author: 刘一丁

Date:2017.5.29

Copyright Letter of Authorization to The Dissertation

The author of this dissertation fully understands provisions stipulated by this school on keeping and using dissertations. The author agrees that the school can reserve and send photocopies and electronic versions of this thesis to relevant departments or institutions managing dissertations. This thesis can be read and borrowed. I hereby authorize excellent provincial institutions appraising bachelor dissertations to incorporate all or any part of this dissertation into relevant databases for retrieval, as well as to preserve and compile this dissertation by photocopying, scanning or reprinting it in a reduced format.

This dissertation is: 1. Confidential until(year) and then this authorization letter will apply. 囗

2. Non-confidential. 囗

(Please tick "√" the corresponding box above)

Signature of the author:刘一丁 Date;2017.5.29

(Not: this page shall be stapled together with this dissertation as its title page)

Abstract

Electric Power Steering system, as a new direction of power steering, because it has the advantages of energy saving, environmental protection, small space occupation, sensitive response and so on. So automotive companies and researchers always use it for automotive design. There is no doubt that electric power will replace the traditional hydraulic steering system in the future. The application of automobile steering system can be divided into mechanical steering system, hydraulic power steering system, electronic control hydraulic power steering system, electric power steering system.

This article mainly studies the rack power steering device. The design of the steering gear rack is mainly composed of steering mechanism design, gear rack transmission design, steering trapezium mechanism design and hardware selection of control system. when the driver turns the steering wheel, in the process of electric power steering system. The torque sensor and the speed sensor will transmit the information to the controller which sends out commands to control the positive and negative output torque of the motor, so that the driver can easily drive the car and increase the steering sensitivity of the car.

Key words: Steering system; Gear – rack; Automatic control.

Contents

Statement of Originality ii

Copyright Letter of Authorization to The Dissertation iii

Abstract iii

Contents v

1 Introduction 1

1.1 Automobile steering system 1

1.1.1 The development of EPS at home and abroad 2

1.1.2 Comparison of EPS with other automotive steering systems 3

1.1.3 Characteristics of EPS steering system 4

1.2 Design idea of automobile steering system 4

1.3 The significance of EPS research 5

2 Hardware analysis of EPS control device 6

2.1 The mechanism and classification of automotive electric power steering system 6

2.1.1 Mechanism of electric power assisted system 6

2.1.2 Categories of electric power steering systems: 8

2.2 Main components of electric power steering mechanism 10

2.2.1 Motor 10

2.2.2 Reduction mechanism 10

2.2.3 P87C591 microcontroller 10

2.2.4 Vehicle Speed Sensor 10

2.2.5 The torque sensor 11

3 Design of electric power steering system 12

3.1 Performance requirements of power steering mechanisms 12

3.2 Efficiency of steering system 13

3.2.1 Positive efficiency of steering system 13

3.2.2 Inverse efficiency of steering system 14

3.3 Change characteristics of transmission ratio 14

3.3.1 Composition of transmission ratio of steering system 14

3.3.2 Relationship between force ratio and angle ratio of steering system 14

3.3.3 Calculation of transmission ratio of transmission system 16

3.4 Gear and rack design 17

3.4.1 The characteristics of transmission gear rack 17

3.4.2 Selection of gear parameters 18

3.4.3 Allowable stress of contact fatigue 19

3.4.4 Bending strength design of gear root 20

3.4.5 Determine the main parameters and geometric dimensions of the gear 21

3.4.6 Determine the main parameters and geometric dimensions of the rack 22

3.4.7 Checking the fatigue strength of tooth surface contact 24

3.5 Gear shaft design 24

3.5.1 Force analysis of rack drive 24

3.5.2 Determination of minimum shaft diameter of gear shaft 25

3.5.3 Strength check of gear shaft 26

4 Determination of main parameters of speed reduction mechanism 31

4.1 Power assist characteristics of electric power steering system 31

4.2 The choice of EPS electric power assisted motor 32

4.2.1 Selection of rated speed of motor 32

4.2.2 Calculation of motor output power 33