1. 研究目的与意义（文献综述）

the automobile is not only a means of transportation in the life and industrial production, but also a manifestation of the national level of science and technology and manufacturing capabilities. automobile engineering is a fund-intensive, technology-intensive, talent-intensive, comprehensive, and highly economical industry. all developed countries in the world regard the automobile industry as the key to the development of the national economy. nowadays, with the continuous development of the expressway and the further increase of the vehicle speed, the reliability of the automobile brake system becomes more and more important. decelerating or even stopping the car in motion, keeping the speed of the downhill car stable, and keeping the parked car stationary, these actions are collectively referred to as car braking^[1]. according to relevant information, in the accident caused by the vehicle's own problems, the accident caused by the failure of the braking system accounted for 45% of the total. it can be seen that the braking system is an extremely important system for ensuring the safety of driving. in addition, the braking system has a direct impact on the average vehicle speed and the transportation efficiency of the vehicle, which is also an important factor for ensuring the economic benefits of transportation. therefore, the design of the braking system is one of the important links in the design of automobile.

with the development of china's automobile industry technology, especially the development of the car industry, the introduction of joint ventures, and the entry of foreign advanced technologies, the deployment of disc brakes on automobiles is gradually forming scale in china. in particular, it has played a large role in improving the performance of the entire vehicle, ensuring safety, and improving the comfort of the occupants^[2,3]. statistics shows that only 20% of drum brakes are used in passenger cars in china, and disc brakes have been used in front-wheel brakes. in the past seven years, the application of disc brakes has grown very rapidly and companies engaged in disc brakes are gradually increasing in china^[4]. in foreign countries, after decades of development, the technology for producing gas-liquid pressure disc brakes has matured and formed a series of products. for example: bosch, wabco, and arvinmeritor each have annual output of 200,000 to 500,000 units. in developed countries such as europe, united states, and japan, disc brakes have been used as standard parts equipped on multi-level cars, passenger cars, medium-sized and heavy-duty vehicles^[5,6]

2. 研究的基本内容与方案

the wheel brakes of general vehicles can be divided into two categories: disc brakes, drum brakes. drum brake principle: the drum brake is simply composed of a brake oil pump, a piston, a brake pad and a tympanum. when the brake is braked, the high pressure brake oil of the brake cylinder pushes the piston, and the two half moon shaped brake shoes are used. the force is applied to press against the inner wall of the drum, and the braking force is prevented by the frictional force to prevent the brake drum from rotating. disc brake principle: disc brakes are powered by air pressure. the main components are brake discs, air chambers, brake calipers, and air hoses. brake discs are made of cast iron or alloy steel and are fixed to the wheels and rotate with the wheels. the air chamber is fixed on the bottom plate of the brake, and the two friction plates on the brake caliper are respectively installed on both sides of the brake disk. the piston of the air chamber is acted on by the pneumatic pressure from the trachea to push the friction plate to the brake disk. friction occurs just like clamping a spinning plate with pliers to slow down the brakes^[9-11]. comparing the advantages and disadvantages of these two kinds of brakes: disc brake advantages: (1) generally no frictional helper effect, so the brake performance is less affected by the friction coefficient, that is, the performance is more stable. (2) there is less reduction in performance after soaking, and it only needs to be braked once or twice to return to normal. (3) in the case of the same output braking torque, the size and mass are generally small. (4) the amount of thermal expansion in the thickness direction of the brake disc is extremely small, and the brake pedal stroke does not increase significantly as the thermal expansion of the brake drum does not significantly increase the brake clearance. (5) it is easier to realize automatic gap adjustment, and other maintenance operations are also relatively simple. disadvantages of the disc brake: (1) the performance is low, so the pressure required for the brake actuation line in the hydraulic brake system is high, and the servo device is generally used. (2) when used in parking brakes, the parking brake transmission device that needs to be installed is more complicated than the drum brake, and thus the application on the rear wheel is limited. considering comprehensively, this design selects the disc brake both of the front and the rear^[12,13]

(1) extensively collecting data to understand the development of braking systems at home and abroad, while analyzing the comparative disc type, the advantages and disadvantages of drum brakes.

3. 研究计划与安排

1-2 (7 semester, 19 to 20 weeks) determine the topic of design plan, descriptions of the graduation design selection (parameters), the campus information collection.

3 (8 semester 1 week) design, document retrieval, complete the opening report.

(2-3 weeks) practice outside, the data collection outside, finish internship report.

4. 参考文献（12篇以上）

[1]shi wenku, yao weimin. automotive construction(sixth edition)[m]. china communication press. 2013, 06.

[2]wang zhonghui. car brake system design[a]. texas college. 2016, 12.

[3]li lihi. automotive brake system design[a]. anhui jianghuai company limited. 2016, 08.