Optimization analysis of rear suspension of the ho

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F. SAE racing car rear suspension optimization analysis

automotive suspension is the general term of all force transmission and connection devices between the body and the wheels. It plans the future scientific and technological development focus of the U.S. air force. It transmits the supporting force, traction force, braking force and lateral force of the road on the wheels, as well as the torque generated by these forces, to the body to ensure the normal driving of the car. Suspension system is an important part of automobile. The performance of automobile suspension system is an important factor that affects the ride comfort, handling stability and safety of automobile. Due to the complex kinematic relationship between automotive suspension components, the kingpin is generally designed to tilt inward and backward, and most of the control arm shafts are also inclined, which brings great difficulties to the kinematic and dynamic analysis of the suspension. With the continuous improvement of computer technology, many special software for motion simulation analysis and optimization design of mechanical components have been developed at home and abroad, and ADAMS software is one of them

adams is the application software of virtual prototype analysis. Users can use this software to analyze statics, kinematics and dynamics of virtual mechanical system very conveniently; The software is also a virtual prototype analysis and development tool. Its open program structure and multiple interfaces can become a secondary development tool platform for special industry users to analyze special types of virtual prototype

1. Use Adams/view to create the model of automobile rear suspension

1.1 establishment of suspension model

because the more complex model is difficult to establish in the computer, the established model is simplified and assumed as follows:

(1) all parts and components in the suspension are considered as rigid bodies, and all connections between parts and components are simplified as hinges, with no internal clearance

(2) the shock absorber is simplified as linear spring and damping

(3) the friction in each kinematic pair is ignored

(4) the tire is simplified to a rigid body

the f-sae racing car rear suspension established in ADAMS is shown in the figure

2. Simulation analysis

(1) camber and lateral slip

camber is divided into zero camber, positive camber and negative camber. If the installation of the wheel is just perpendicular to the road when the vehicle is empty, the wheel may incline inward due to the load-bearing deformation of the axle when the vehicle is full, which will accelerate the wear of the vehicle's tires. Therefore, when designing the rear suspension of racing cars, it is generally controlled at about 0 °, and it is generally expected that the wheels will jump up and down within 30 mm from the full load position, and the camber angle will change about 1.5 °. It can be seen from Figure 2 that the suspension is reasonably designed in terms of rear wheel camber

through the simulation results, the variation curve of the lateral slip of the wheel with the direction of the wheel Z axis is obtained, as shown in Figure 3. It is found that when the up and down runout travel of the wheel is 30 mm, the maximum value of the lateral slip of the wheel reaches 3.25 mm, which increases the wear of the tire to a certain extent, indicating that the structural parameters of the suspension are unreasonable and need to be further improved

(2) kingpin caster angle and inclination angle

the main function of kingpin caster angle is to reset the wheels to improve the stability of straight-line driving. When a moving car deviates from an external force, the caster angle generates a righting torque to automatically return the wheels to the original position. Too large caster angle can increase the stability of steering, but the required steering force will become larger, which is easy to make the driver tired; Reducing the caster angle will reduce the stability of steering, but the steering does not chase large and the full-time force will become light, which is not conducive to the automatic return of the vehicle. The curve shown in Figure 4 shows that the caster angle of the suspension does not change much during the wheel runout, and the straight-line driving cannot meet the requirements of the high stiffness precision spring, and the stability is very good

the effect of kingpin inclination reduces steering control force, reduces bounce and deviation, and improves the stability of straight-line driving. The curve shown in Figure 5 shows that the kingpin inclination of the suspension changes little in the process of wheel runout, which is within the allowable range

adams provides users with a powerful parametric analysis function. Parametric analysis is conducive to understanding the impact of design variables on the performance of the prototype. In the process of parametric analysis, according to the design variables established during parametric modeling, different parameter values are used to carry out a series of simulations. Then parametric analysis is carried out according to the returned analysis results, and then further optimization analysis is carried out for each parameter. According to the needs of analysis, this paper determines the relevant key variables, and sets these key variables that can self diagnose faults as design variables that can be changed. During the analysis, the virtual prototype model can be updated automatically by changing the size of these design variables

the key points of parameterization of the model: the external contact coordinates of the upper cross arm; Coordinates of the inner joint point of the upper cross arm; Coordinates of the inner connection point of the lower cross arm; Contact coordinates in steering knuckle; Coordinates of steering knuckle external contact. After the design variables are determined, the parametric analysis method of optimization analysis provided by ADAMS/view is adopted. First, create the state variable, and write the measurement function based on the state variable. The optimization goal is to minimize the lateral slip distance of the wheel

Table 1 is a comparison table of changes of some parameters before and after optimization. It can be seen from the table that the lateral slip of the rear wheel is reduced from the initial 3.25 mm to 2.5mm, indicating that the optimization analysis is effective and the design variables are set reasonably. From a practical point of view, the optimized model can greatly reduce the wear of tires in driving and prolong the service life of tires. It can be seen that the optimization method is appropriate and achieves the expected goal

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