Simulation and optimization of steering drive shaf

Simulation and optimization of steering drive shaft arrangement in independent suspension

1 preface

in order to ensure that the vehicle has better power and handling, the front wheel of front drive car must have two functions of steering and driving. As a steering wheel, the wheel is required to be within a certain angle range, and the angle can be deflected arbitrarily; As the driving wheel, the axle shaft is required to continuously transfer the power from the main reducer to the wheel at the same angular speed in the process of wheel deflection. Constant velocity university joint (CVJ) connects the wheel and axle shaft, so that the two shafts transmit motion at the same angular speed

the drive shaft of non independent suspension only needs to install a centering constant velocity universal joint (hereinafter referred to as the outer universal joint) near the wheel hub. In modern vehicles, the drive (axle) shaft cannot be made into a whole but needs to be segmented, while the drive shaft of independent suspension also needs an axial sliding constant velocity universal joint (hereinafter referred to as the inner universal joint) near the differential

for the steering drive wheel, since the included angle between the left and right half shafts changes with the steering needs, the maximum included angle is often more than 30 degrees. This makes the axial slip and angle change of the universal joint in the drive shaft very large. Axial slip and angle change will not only produce sliding resistance, but also affect power transmission. It will also bring vibration and noise, affect the ride and driving comfort, and shorten the service life of the universal joint. In addition to selecting constant velocity universal joints with different structures, the position of the universal joint can also be optimized to reduce the vibration and noise of the drive shaft

some people in China have done research on the drive shaft, but they mainly studied the performance of a single drive shaft, rather than designing the drive shaft from the perspective of suspension assembly or even the whole vehicle. In this paper, MSC Adams is used to establish the dynamic analysis model of the front suspension of a front drive vehicle. The factors affecting the motion characteristics of the drive shaft are comprehensively considered, the motion characteristics of the inner universal joint of the drive shaft are investigated, and then the position of the outer universal joint of the drive shaft is optimized, so as to obtain the optimal position of the drive shaft

by introducing multi-body dynamics analysis software to simulate and analyze the motion performance of the drive shaft, and optimizing the position of the drive shaft on the basis of the analysis results, we can quickly understand the technical performance of the designed drive shaft and guide the design work according to the optimization results

2 Establishment of suspension multi-body dynamics analysis model

multi-body dynamics is the theoretical basis of virtual prototyping technology. Among the multi-body dynamics modeling methods, Lagrange multiplier method is one of the commonly used methods. The Cartesian coordinates of the centroid of each rigid body and the Euler angle describing the orientation of the rigid body are selected as the generalized coordinates Q of the system. According to the topological structure of the system, the following constraint equations are established:

Φ (q,t)=0 Φ ∈Rm （1）

θ (q, q,t)=0 θ ∈ RM (2)

where m is the number of constraint equations

for holonomic constraint equations, Φ (q,t)=0 ； For nonholonomic constraint equations, θ (q, q,t)= 0。

and calculate the Jacobian matrix of the system Φ Q and θ q. Then the dynamic equation of the system is:

where: t is the kinetic energy of the system; Q is the generalized coordinate vector of the system; FQ is the generalized force sequence vector; λ 1 is the Lagrange multiplier column vector corresponding to the complete constraint; λ 2 is the Lagrange multiplier column vector corresponding to the nonholonomic constraint; Φ Q is the transpose matrix of the Jacobian matrix corresponding to the complete constraint; Φ TQ is the transpose matrix of the Jacobian matrix corresponding to the nonholonomic constraint

by simplifying formula (3) with bavmgrade stabilization method of constraint equation, the advantages Q of high specific strength and large specific elastic modulus can be obtained at the same time, and then the acceleration of the member can be obtained through appropriate transformation, so as to obtain the parameters such as velocity and displacement of the member through time integration

based on the above multi-body dynamics theory (4), the influence of suspension system, steering system, tire and elastic bushing between connections is considered in detail by using MSC Adams/car module. Based on the modeling data, the simulation analysis model of the vehicle's front suspension is established, as shown in Figure 1

Figure 1 suspension dynamics simulation model

3 position analysis and optimization of drive shaft

due to the diversity of driving conditions, the wheels will jump and be affected by longitudinal and lateral forces. The biggest influence of automobile drive shaft is the wheel vertical runout and turning conditions. The following is the dynamic analysis of the suspension and the optimization of the drive shaft for the above two working conditions

this study optimizes the position of the drive shaft without changing the mounting mode and position of the powertrain. At this time, the end point of the drive shaft hub is easier to adjust than the end point of the drive shaft differential. Therefore, five schemes are proposed based on the distance between the end point of the drive shaft hub and the wheel center, and the observation objectives are the angle change and axial slip change of the telescopic constant velocity universal joint

automatically calculate the experimental results, apply the established suspension dynamics simulation model, change the distance between the outer point of the drive shaft and the wheel center, formulate five analysis schemes for simulation analysis, and obtain the motion characteristics of the drive shaft under two working conditions, as shown in figures 2 to 5

figures 2 and 3 show the relationship between the angle change and axial slip change of the inner universal joint and the vertical runout of the wheel under the vertical runout test. It can be seen from the figure that as the distance between the outer point of the drive shaft and the wheel center increases, the angle change of the inner universal joint increases and the change of axial slip also increases

Figures 4 and 5 show the transmission of precision lead screw pair under steering test; 2 is the relationship curve between the angle change and axial slip change of the inner universal joint of ordinary belt drive and the steering wheel angle. It can be seen from the figure that with the increase of the distance between the outer point of the drive shaft and the wheel center, the angle change of the inner universal joint increases, while the change of axial slip decreases first and then increases

the analysis results of the above five schemes are sorted out, as shown in Fig. 6 and Fig. 7

Figure 6 shows the maximum angle and maximum axial slip of the inner universal joint corresponding to the five schemes when running out in parallel. It can be seen that the maximum angle and maximum axial slip corresponding to scheme 1 are the smallest of several schemes

Figure 7 shows the maximum angle and maximum axial slip of the inner universal joint corresponding to the five schemes when running out in parallel. It can be seen that the maximum angle corresponding to scheme 1 is the smallest of several schemes. The maximum axial slip is the minimum of scheme 2

if the angle of the universal joint changes too much, the wear of the universal joint will be serious and affect its service life. Therefore, we hope that the initial angle of the universal joint is as small as possible and the variation range is also small. From this point of view, scheme 1 is the optimal drive shaft layout scheme under runout condition and steering condition

the smaller the design change of axial slip, the better the power transmission, the better the NVH performance of the drive shaft, and reduce the abnormal wear of the tire. From this point of view, scheme 1 is the most ideal under runout condition; Under the steering condition, scheme 2 is the most ideal

comprehensively considering the above two working conditions and combined with the actual spatial layout to ensure the NVH performance and stability of the vehicle during high-speed steering, it is recommended to arrange the end point of the drive shaft hub at about 75mm away from the wheel center, which can ensure the change of the angle of the constant velocity universal joint and the change of axial slip within the expected range

4 Conclusion

through the analysis of the motion characteristics of the steering drive shaft of the front drive vehicle, it is found that the axial slip and angle change of the telescopic constant velocity universal joint at the inner end are relatively large, which can not only greatly affect the steering effect, but also produce vibration and noise, so as to reduce the riding comfort. Taking a Chery car as an example, the drive shaft position of the front drive car is optimized, and a more reasonable end position of the drive shaft hub is obtained, which is an important basis for the design of the drive shaft. Finally, in the real vehicle verification, it is found that the optimization result not only improves the NVH performance of the whole vehicle, reduces the abnormal wear of tires, but also improves the service life of the drive shaft