Analysis of Factors Influencing Steady State Rotation Characteristics In view of the oversteer trend problem, firstly, the calculation method of the axle load difference between the inner and outer wheels during cornering is deduced theoretically, and then the structural parameters that affect the steady state rotation characteristics of the vehicle are discussed.
(a) is a two-track model of a four-wheeled vehicle. The body is replaced by a rod, which is supported on the roll center MZV and MZH of the front and rear suspensions, and is supported on the axle by front and rear springs. The body mass center SPA has a centrifugal force mA (v2/) acting on the mass of mA, and this force generates a moment mA (v2/) h about the roll axis.
When the body rotates around the roll axis and reaches an equilibrium state, the mass center SPA laterally shifts hsin. The body gravity generates a moment GAhsinGAh, so the total torque that causes left and right wheel load transfer is: M=mAv2h+GAh(1)(b) is force In the distribution on the fore and aft axis, the centrifugal force is distributed to the two roll centers by the center of mass force, mA (v2/) (lHA/l) and mA (v2/) (lVA/l). Where lVA and lHA is the distance from the center of the axle to the center of mass of the body. It can be seen that the calculation of the load balance between the inner and outer axles of the two-axle vehicle bends can be seen that the change of the wheel load is related to the following structural parameters when the relative lateral acceleration is given.
Centroid position: lVAl, lHAl, hV, hH Relative roll center height: PVsV, relative height of the PHsH centroid to roll axis: ratio of hsV, hsH roll stiffness coefficient: CVCV+CH-GAh, CHCV+CH-GAh3 physics The determination and implementation of the prototype vehicle improvement program can be seen from the above analysis: the relative positions of the center of mass, the relative height of the roll center, and the center of mass to the roll axis are not easily changed, and the ratio of the roll stiffness coefficient is easy to change. According to equations (7) and (8), the CV can be increased or the CH can be decreased so that CVCV+CH-GAh>CHCV+CH-GAh, and the moment of centrifugal force around the roll axis is taken over by the front axle. Thus, Front wheel slip angle
V increases or the rear wheel slip angle
The decrease of H causes the difference of the wheel's side slip angle to be H> 0. In order to increase the CV or reduce the CH, a harder spring may be installed on the front axle or a softer spring may be installed on the rear axle, but harder. The spring makes the acceleration of the vehicle body larger, resulting in deterioration of comfort; the softer spring cannot satisfy the bearing requirements and this method is not feasible.
Another method is to increase the rigidity of the front suspension stabilizer bar or reduce the stiffness of the rear suspension stabilizer bar. Therefore, on the premise that as few parts as possible are changed, the author proposes to: thicken the front stabilizer bar and adjust the stiffness matching method of the front and rear suspension.
The optimization analysis of multiple matching schemes was performed on a virtual prototype vehicle and found that when the CV/CH increases from 1.2 to 1.8, the oversteering tendency is eliminated, and there is a moderate understeer characteristic. Therefore, it is recommended to use this solution for physical prototypes. To improve the comparison of the physical prototype test results before and after. It can be seen that, in the case of a given lateral acceleration, the ratio R/R0 of the turning radius of the improved physical prototype is greater than that before the improvement, and the ratio rapidly increases when the lateral acceleration is large. Oversteer tends to be eliminated and understeer tends to be more pronounced.
End (1) Using the method of combining multibody dynamics theory with CAE, a virtual prototype car model of SUV was set up and a virtual prototype test was conducted. It was concluded that the car has excessive steering tendency and physics at full load with large lateral acceleration. The problems in the prototype test are consistent, which verifies the correctness of the virtual prototype model.
(2) The structural parameters of the vehicle affecting the steady-state rotation characteristics of the vehicle are discussed. A method for increasing the stiffness of the front suspension lateral stiffness bar and increasing the stiffness of the front suspension lateral angle and then adjusting the stiffness matching of the front and rear suspension side angles is proposed. The prototype vehicle was optimized for a variety of matching schemes. It is concluded that when the CV/CH increases from 1.2 to 1.8, as the lateral acceleration does not increase, the steering tendency increases, and the oversteering tendency during large lateral acceleration is eliminated.
(3) Applying this conclusion to the physical prototype vehicle, the improved steering characteristics of the physical prototype vehicle have been significantly improved, demonstrating the feasibility of the program. If you want to use the opposite of the above to affect the steering characteristic trend, you only need to reduce the value of CV/CH.
(4) Using the method of combination of virtual prototype vehicle test and physical prototype vehicle test, the problem of oversteering of a certain SUV sample vehicle with large lateral acceleration at full load is quickly solved. It saves the design cost and shortens the development cycle. It has important practical significance.
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