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Design of stamping parts for the base plate of combined spring mechanism for automobile suspension

    In this paper, the structure and performance of the bottom plate of the new combined spring mechanism for vehicle are analyzed. The static analysis and modal analysis are carried out by using ANSYS software. The results show that the first-order modal frequency of the bottom plate is low. Therefore, it is proposed to increase the stiffener, increase the local size and increase the local step structure. The modal simulation calculation shows that the scheme of increasing the local step structure can effectively improve the mechanical performance of the bottom plate.
    There are researches on the recovery of vehicle suspension vibration in foreign countries. Audi demonstrated the Erot concept car in 2015, and its improved electric damper has been able to recover suspension vibration energy well. A university in Canada reported the research on suspension vibration energy recovery. Yu Changmiao of Jilin University in China transformed the linear displacement of the suspension into the rotary motion of the generator by means of a series rack and pinion mechanism, so as to realize the damping required by the suspension and recover the vibration energy of the suspension at the same time. Cao min of Shanghai Jiaotong University studied the characteristics of the improved active suspension as well as the recovery of suspension vibration energy. These studies show that the recovery of suspension vibration energy can significantly improve vehicle efficiency and comfort under most road conditions. Therefore, a combined spring for vehicle suspension is proposed, which changes the linear displacement motion of the suspension into the rotary motion of the generator to realize the elastic deformation and damping function required by the suspension. Its structure is shown in Figure 1. The generator is connected with the spring in parallel, which can meet the requirements of the generator’s internal shaft displacement. When the suspension is deformed, the generator turns to generate electricity and controls the output of the generator to adjust the damping. Therefore, the spring mechanism flattens the elastic elements and damping elements of the suspension, and has the function of recovering the suspension vibration energy.
    Figure 1 combined spring mechanism for vehicle suspension
    The base plate of the prototype is made of aluminum alloy, which is obtained by NC machining center, which leads to long processing time and low production efficiency. Changing the bottom plate into stamping parts can greatly improve the production efficiency and material utilization, and further improve the lightweight and compact structure of the spring mechanism.Analysis of mechanical properties of base plate
    The base plate is designed for stamping parts, and the mounting hole of the spring is calendered and stretched, which makes the strength of the mounting hole strengthened. The outer groove of the spring is made of blind groove to strengthen the strength of this part of the area. The peripheral of the motor is of through hole structure, which is compatible with the shape of the motor. Because the local size is small, it is thin-walled parts. In order to improve the accuracy of the simulation results, local encryption is carried out for the motor. The improved simulation model is shown in Figure 2.
    Figure 2 stamping part model of base plate
    The force and constraint imposed by the simulation model are shown in Figure 3. The center of the simulation model has six spring with a circumference, whose size is limited by the size of the inner ring gear and the height. If the inner ring gear of the transmission is taken as a small size, there will be no need for the corresponding parts of the body to have a large space to accommodate the suspension spring, so that the volume of the body will increase. The extended spring is used to supplement the spring force of the strip, and the transverse arrangement is to make it easier to arrange in the car.
    In Figure 3, a is constrained at the mounting bolt, B is constrained at the small bearing, and C is installed at the big bearing. The section height of the central striped spring is 0.65mm and the section width is 7mm. The calculated maximum force applied by the center strip spring D, e, F, G, h and I is 20n, and the maximum force applied by J and K expanding spring is 30n.
    The material is 5mm thick 304 stainless steel plate, its elastic modulus is 195gpa and Poisson ratio is 0.247. Figure 4a is the stress and strain diagram. From the static analysis results, it can be seen that the structural strength of the bottom plate meets the requirements. Fig. 4b is the free mode of the bottom plate, the first mode vibration frequency is 140.75hz, and the results of local modal analysis are unreasonable, so it is necessary to improve the local structure to improve its mechanical performance.
    Figure 3 simulation model of force and constraint
    Figure 4 static and modal analysis results

    Structural improvement and modal analysis
    In order to improve the local structural strength of the base plate and obtain better modal analysis results, the parts are improved, and there are two schemes. Scheme 1 increases the edge dimension of the mounting motor hole and sets the reinforcement. The motor hole of scheme 2 transformer is of counterbore structure, as shown in Fig. 5. Because the area with large deformation in first mode is the thin side of the big hole side of the motor, the local structural strength needs to be strengthened. In scheme 1, the method of enlarging size and setting reinforcement is adopted. The modal analysis results show that the frequency of first order bending mode is slightly lower. Scheme 2 uses to press the large hole of the installation motor into step hole, and at the same time, the reinforcement is set locally. According to the results of other people and previous experience, the width of reinforcement is 5mm, the depth is 3mm, the depth of step is 5mm, and the average edge width is 12mm. The four corners of the bottom plate are all rounded, with a radius of 3mm.
    Figure 5 floor of improved local structure
    The mode simulation analysis is carried out for scheme 2. The constraints of X, y and Z are set at the middle six small holes, so the modal analysis is a constrained modal analysis. The results of modal analysis are shown in Figure 6.
    Analysis of simulation results
    The vibration of general vehicles mainly comes from engine and road surface, among which the engine vibration frequency is related to its maximum speed, and the vibration of road surface is related to its speed and road condition. The speed V is 120km/h, and the space frequency n of the better road is 5, and the vibration frequency of the road surface is 166.67hz. Although the vibration of road passes the attenuation of tire, the vibration of the road does not pass the attenuation of suspension system, so the frequency is safe to take the road vibration frequency. From table 1, it can be seen that the first mode frequency of the initial model can not meet the needs, while the first mode frequency of the improved model reaches 214.34hz, which meets the requirements. It is of reference significance in the subsequent design and production.