1. 研究目的与意义（文献综述）

in recent years,the construction of road traffic infrastructure in our country developsrapidly, coupled with the year-on-year increase in the number of vehicleownership in china, which has led to frequent road traffic accidents. as aresult, the demand for treatment of illegal vehicles and accident rescues incities has increased rapidly. the road clearing and rescue industry hasgradually been taken seriously by the society and the public. therefore,wreckers have been widely used in roads, urban construction, automobile repairindustry, airports, docks and highway companies. the function of the wrecker ismainly to eliminate road obstacles, clear the accident vehicles, and arrangethe urban environment to provide drivers and vehicles with help and rescueservices. the hydraulic system is the main working system of the wrecker. withthe aid of the hydraulic system, the accident vehicle is dragged onto the boxof the wrecker and towed off the road in order to restore the traffic order assoon as possible. therefore, the design of the hydraulic system directlyaffects the performance of the wrecker and the reliability of the work.

in the 1950s, theworld's first wrecker was born in the united states. with the improvement ofstyle and function, wreckers have evolved from a single structure and functioninto a multi-functional, multi-purpose wrecker. in the near future, wreckerswill have greater work capacity, more advanced operating methods, and a morecomfortable working environment.

the developmentof wreckers is divided into the following stages: the first stage, in the 20thand 50th centuries in the 20th century, has a single function and a simplestructure. at this stage, self-made chassis are often used and pulleys, wireropes and winches are installed on trucks. the hoisting machine is driven bymechanical transmission, supported by tie rods, and one end of the faultyvehicle is pulled off the site. the second stage was the 1950s to the 1970s.represented by challenger, jerr-dan, and wrecker companies in the unitedstates, many wrecker companies with advanced technologies emerged in the world.at this stage, the technology of wreckers has been greatly developed. first ofall, hydraulic transmission and control technologies were introduced at thisstage. secondly, the series of wreckers have increased in variety and scale. inaddition, the structure and chassis are also diversified. the third stage, fromthe 1980s to the present, is the period of rapid development of wreckers. themain characteristics of wreckers at this stage are various structures andcomplete functions, such as lifting, dragging, hauling, maintenance and otherfunctions.

2. 研究的基本内容与方案

the working principle of the hydraulicdrive for wreckers is to use oil as the working medium, to transmit motionsbased on changes in the sealed volume, and to rely on the pressure inside thehydraulic to transmit power. hydraulic transmission is essentially a kind ofenergy conversion device. it first converts mechanical energy into hydraulicenergy that facilitates transportation, and then converts hydraulic energy intomechanical energy to drive the working mechanism to perform various requiredactions.

the road wrecker hydraulic system consistsof hydraulic components, hydraulic pumps, hydraulic cylinders, hydraulicmotors, hydraulic control valves, and hydraulic accessories. these componentsform the power section, execution section, control section, and auxiliarysection of the hydraulic system.

3. 研究计划与安排

the 19th and 20th weeks of 7th semester determine the topic of graduation design,graduation design assignment (related parameters), and collection of information in school

the 1st week of the 8th semester projectidea, literature search, and completion report

the 2nd and 3rd weeks off-campus internship, off-campus information collection,completion of internship report

4. 参考文献（12篇以上）

[1]王望予.汽车设计[m].北京：机械工业出版社，2004.

[2]余志生.汽车理论[m].北京：机械工业出版，2009.

[3]陈家瑞,马天飞.汽车构造[m].北京：人民交通出版社，2005