With the increasing popularity of school buses, the safety of schoolbuses is attracting more and more attention. As an important part of schoolbuses, the steering system of school buses is the key assembly for the activesafety of school buses, it plays an important role in ensuring the safety ofvehicles, protecting the safety of drivers and students, and improving theworking conditions of drivers. A suitable steering system can perfectly solvethe contradiction between light handling and sensitive steering. How to designthe steering system of the school bus so that the school bus has goodmaneuverability and safety has always been an important research topic forautomobile manufacturers and research institutions.

Automobile steering system has experienced five basic developmentstages: pure mechanical steering system, mechanical hydraulic power steeringsystem, electronic hydraulic power steering system, electric power steeringsystem and wire-controlled power steering system. The steering wheel control ofpure mechanical steering system is relatively heavy, the driver's burden isheavier, currently in the edge of elimination. Mechanical hydraulic powersteering system can greatly reduce the steering torque, but the hydraulic pumphas been working, a waste of resources. And low speed steering power is notenough, power characteristics cannot be changed, and the hydraulic power systemis easy to damage. Electro-hydraulic power steering system reduces energyconsumption, and the size of steering power can also be adjusted according tothe rotation Angle, speed and other parameters, which has become the choice ofmany household models. The electric power steering system uses the electricmotor as the power source, according to the speed and steering parameters andother factors, by the electronic control unit to complete the power control. Itcan give consideration to the light steering at low speed and the stableoperation at high speed. It has good return-to-normal performance, simpleadjustment, flexible assembly and energy-saving advantages. Wire-controlledpower steering system is a new generation of automotive electronic steeringsystem, which eliminates the mechanical connection between the steering wheeland directive wheel. It can improve the passive safety of automobile, bebeneficial to automobile design and manufacture, and greatly improve the ridecomfort of automobile. But it's still in the research phase.

The pure mechanical steering system is simple in structure andreliable in operation. At present, it is used in some micro cars andagricultural vehicles with large steering force and low requirements forsteering performance. Hydraulic power steering system technology is mature, canprovide large steering power, widely used in heavy vehicles; Electric powersteering system is favored for its unique advantages. It represents thedevelopment direction of power steering technology in the future. Thewire-controlled steering system will become the development direction of thepower steering system because it is beneficial to improve the passive safety,design and manufacture, ride comfort and handling stability of the automobile.

At present, there are four main types of automobile steering gearstructure: rack and pinion type (RP type), ball screw type (BS type), wormroller type (WR type), worm and peg type (WP type). Rackand pinion type structure is simple and compact; transmission efficiency up to90%; can automatically eliminate the gap between the teeth; low manufacturingcost. The ball screw type steering gear has the higher transmission efficiency,the operation is lighter and more comfortable, the mechanical parts wear less,the service life is relatively long. Worm roller type structure is simple,reliable work, long life; negative efficiency is low. but the positiveefficiency is low, the adjustment meshing clearance is difficult, the steeringgear transmission ratio cannot change. worm and peg type steering gear is dividedinto fixed pin type steering gear and rotary pin type steering gear. fixed pinworm pin type wear fast, low efficiency. the structure of rotary pin typesteering gear is complex and less applied.

The ball screw type steering gear and the rack and pinion typesteering gear have become the main two kinds of steering gear in the world.worm roller type steering gear and worm and peg type steering gear are beingphased out or retained a small position.

2. 研究的基本内容与方案

1. Basic contents

(1) according to the requirements of Yutong ZK6579 school bus, theoptimal scheme of steering system is selected

(2) select appropriate steering gear form and carry out dimensionaldesign