The development of theeconomy has made the proportion of automobiles in people's lives more and morelarge, while medium-sized cargo vehicles have a large share in the productionof automobiles, and the demand for simple structures and low-cost drivingbridges has increased. It can reduce the total cost of production and promotethe development of the cargo car economy^[1].

The role of the truck drivebridge is to get the torque from the car engine^[2] .By passing themain speed reducer, differential, drive shaft and other parts to the frontdrive wheel of the truck, the main speed reducer will reduce the transmissionspeed and obtain a relatively high output torque. The main speed reducer double-sidedgear pair and the bevel gear pair can change the torque transmission direction^[3]. During the journey of the truck, the drive bridge uses the differentialto make the wheels on both sides of the truck produce differential effects whenturning and turning, so that the wheels on the outside and inside sides of thetruck turn at different speeds at the same time. The Effect of Load andTransfer Power on the Shell Body of Carbridge and the Wheel of Truck^[4].

Domesticdrive bridges mostly use hoof type or disc type dry type brake, disc type brakeis divided into two types: clamp disc type and total type^[5].Comparedwith foreign advanced products, the domestic technology level of driving bridgegear transmission is still relatively low, and there are two main shortcomings:First, there is a certain gap between gear, shaft, shell and other parts andmaterials compared with foreign products. There are defects such as largeoverall weight and volume, short service life, etc.. Second, the technicalperformance is relatively backward, and there is generally no advanced devicesuch as self-locking Anti-Slip differential and wet brake^[6]. Thepromotion of self-locking Anti-Slip differential and wet brake in the tire typeengineering mechanical drive bridge is one of the ways to improve the technicallevel of the engineering mechanical drive bridge, and it is also an inevitabletrend of the development of domestic mechanical drive bridge technology.

Domestic truck-driven bridge productionenterprises are mainly concentrated in several enterprises such as EastWindmill Bridge, Jinan Bridge Box Factory, Shaanxi Hande Bridge, ChongqingHongyan and Ankai^[7].These companies account for almost 90 % or moreof the domestic truck bridge market; There are two main technical sources oftruck bridge in China: First, the truck bridge introduced by FAW and Dongfengis the representative; The second is represented by the Steyr series trainbridge introduced by heavy steam^[8].There is a big gap between thequality of domestic commercial vehicle bridges and the international level.There are problems of oil leakage, gear noise, early failure, and low brakequality. The user's serious overload needs to bear the high quality insurancecompensation; Malignant market competition produces "reinforced products"with reinforced shell and thick half axis^[9].Nearly 60 miles oftrucks matching the wheel side deceleration bridge, the structure is complex,low efficiency, high fuel consumption, and the newly introduced product 485,498 single-stage deceleration bridge stability is not enough^[10,11].Andthe cost is high; Mechanical efficiency of the bridge will become the target ofenterprises, such as Dina's two-speed bridge^[12],

twospeed ratios are available. The large speed ratio can increase the torque whenfull load, and the small speed ratio can save fuel when empty load. Disc brakeheat dissipation good, light quality. Trucks in Europe and the United Stateshave widely used disc brakes, electronic system assisted braking technologywill be gradually extended to the truck industry^[13].

At present, a lot of achievements have beenmade in the study of automobile driven bridge shell, but there are still manydefects in the design of the bridge shell^[14].From the uncertaintyof the traditional research methods to the limitations of the finite elementmethods at present, there are various degrees of defects in the research of CAEmodeling, performance analysis, and process design. If the analysis is onlyfrom a single process point of view, it can not meet the accuracy requirementsof the overall design. The focus of future research should be to seek designmethods that consider complex factor analysis to improve the accuracy of thebridge shell manufacturing process ^[15].

The purpose and significance of this designis to meet the demand of consumers for improving the performance of automotiveproducts by designing a driving bridge with good economy, high quality andsuperior performance. The main reduction ratio of the designed drive bridgeshould ensure that the vehicle has the best power and fuel economy drivingbridge shape size is small, the necessary distance from the ground isguaranteed, and it has sufficient stiffness and strength, and its qualityshould be minimized. Smooth work, low noise, easy to unpack and adjust, lowcost. The drive bridge is one of the most important systems of the car. It isdesigned for the transmission and distribution of power in the car. The speedreducer is an important part of the drive bridge, and the most important partof the deceleration is the deceleration Bevel gear Heqi. The differentialeffect of planetary gears. Therefore, the machining technology and heattreatment ability of the gear greatly determine the stability and reliabilityof the bridge. The material and machining precision of the gear determine thebearing capacity and service life of the bridge. The key of the driving bridgelies in the bridge shell, which is one of the main load-bearing parts in theautomobile assembly. It is not only a part of the transmission system but alsoa part of the running system. The driving bridge shell is an important safetypart in the vehicle.

2. 研究的基本内容与方案

2.1Basic content, objectives of the study