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Application of adams/car in suspension design

suspension is one of the main assemblies of automobile, and its influence on handling stability and smoothness is very important. McPherson suspension has many advantages, which makes it widely used in the front suspension of cars, light vehicles and so on. During the design, the guide mechanism shall not change the positioning parameters of the kingpin too much during the up and down runout of the wheel, and the wheel and the guide mechanism shall move in coordination. The steering mechanism consists of a spatial lever mechanism. When the position of the steering ladder disconnection point is not selected properly, the movement of the tie rod and the suspension guide mechanism will be uncoordinated, and the front wheel shimmy will occur when the vehicle is driving, damaging the handling stability and aggravating the tire wear. The traditional design generally adopts the methods of empirical design, mathematical derivation and geometric drawing. Although it can meet the design requirements, the accuracy and efficiency are not high. Traditional methods have been difficult to meet the increasingly accelerated design requirements. In order to shorten the development cycle and reduce the development cost, it is necessary to adopt new design methods. There is a special template for suspension kinematics and dynamics analysis in adams/car module, which can easily establish suspension of various structural forms and quickly obtain performance curves of more than 30 parameters of suspension. All the models adopt digital design, which can easily modify and adjust the design parameters to find their impact on various performance parameters, optimize the design objectives, and finally provide the enterprise with product development solutions

1 suspension analysis parameters

the coordinates of wear-resistant components used in household appliances at key points in the suspension system are obtained from the design drawings, the parameters of shock absorber and torsion bar spring are obtained from tests, and the front wheel positioning parameters are provided by the manufacturer. (provisions of the coordinate system: the longitudinal direction of the vehicle is x-axis, and the rear direction is positive; the transverse direction of the vehicle is y-axis, and the right direction is positive; the vertical direction of the vehicle is z-axis, and the upper direction is positive)

2 establishment and verification of the simulation model. As shown in figure 1

Figure 1 McPherson independent suspension

2.2 after the suspension model is built, the suspension model is assembled with the test platform, and then the suspension model is simulated under the condition of parallel runout of left and right wheels with an up and down runout of -125~100mm

Figure 2 setting diagram of parallel runout condition

after clicking apply, the suspension will perform parallel runout condition, and the simulation step is 100 steps

2.3 after calling ams/solver for solution, the system can output dozens of parameters related to suspension performance

front wheel alignment parameters

the following are the simulation results of the wheel alignment parameters of the McPherson front suspension:

2.3.1 camber angle

Fig. 3 change of camber angle

it can be seen from the above figure that the change range of camber angle of the front suspension model is -3.2deg~ 0.75deg

4. Poor oil return of buffer

2.3.2 caster angle

Fig. 4 caster angle change

it can be seen from the above figure that the caster angle of the front suspension model changes between 5.3deg and 5.9deg

2.3.3 kingpin inclination angle

Figure 5 change of kingpin inclination angle

it can be seen from the above figure that the change range of kingpin inclination angle is 8deg~13deg

2.3.4 screw radius

Figure 6 Variation of screw radius

it can be seen from the above figure that the variation range of screw radius is about -6.2mm~ 0.6mm

2.3.5 toe angle

Figure 7 change of toe angle

it can be seen from the above figure that the change range of toe angle is about -1.9deg~ 7.8deg

2.4 optimization of suspension performance parameters

in the process of vehicle movement, due to certain unevenness of the road surface, the relative position between the tire and the vehicle body will change, which will also cause corresponding changes in wheel alignment parameters. If the wheel alignment parameters change too much, it will aggravate the wear of tires and steering parts and reduce the handling stability and other related performance of the whole vehicle. Therefore, in principle, the change of wheel alignment parameters should not be too large

with ams/insight module, users can optimize one or more wheel alignment parameters to achieve an ideal value. This paper is to optimize the positioning parameters by changing the coordinates of some hard points of the suspension

in the insight module, we analyzed the 15 coordinate values (x, y and Z coordinates at each point) of the five coordinate points of the McPherson suspension, including the front and rear points of the lower rocker arm, the inner and outer points of the steering rod, and the ball joint pin of the lower rocker arm, and set the variation range of each coordinate value between -5mm and 5mm. For the analysis of 15 coordinate values, insight will perform 215 iterations. The amount of calculation is extremely huge, so we only perform 64 partial iterations

after the iterative solution, we can use the built-in function of insight to store the optimization results in the interactive page as dynamic data. See figure 8:

it can be seen from this page that the factor item is 15 hard point coordinate values, and the response item is five positioning parameters. The difference between the maximum and minimum values of the factor item and the nominal value is 5 units. This is because we previously set the variation range of the coordinate value to be ± 5mm

when the value of factor (i.e. hard point parameter) is modified within the range of maximum and minimum values, the value of response item (positioning parameter) will change. After modifying the hard point parameters, the change trend of the five positioning parameters may be reversed, for example, modifying the LCA_ After the X coordinate value of the front point, the camber value becomes smaller than the original value, while the caster value is larger than the original value. At this time, although the camber value meets our requirements, the caster value deviates from our design principles. When this happens, in order to balance, we take a compromise value

the following table shows the coordinates of some hard points of the optimized front and rear suspensions

the following is the comparison diagram of the wheel alignment parameters before and after optimization (the solid line is the optimized curve, and the dotted line is the curve before and after optimization:

Figure 9 Comparison of the camber angle before and after optimization

2.4.1 camber angle (.Camberu angle)

in order to prevent excessive understeer or oversteer of the wheel, It is generally expected that the camber angle of the wheel will change by about 1 degree within the range of 40mm from the full load position. It can be seen from the figure that the variation range of camber angle after optimization is 0.03deg~2 37deg, which is a little smaller than the range before optimization. This is because insight gave up some benefits of camber in order to take into account the optimization of other four positioning parameters. However, within the range of 40mm up and down, the change of camber after optimization is basically about 1 degree, which meets the design requirements

2.4.2 caster_angle

Figure 10 comparison of caster angle before and after optimization

when the caster angle is positive, it can restrain the nodding during braking, but if it is too large, the counter torque at the wheel support will be too large, which is easy to cause wheel shimmy or changes in the force on the steering wheel. Therefore, the change range of caster angle is 10 DEG ~40 DEG when the suspension is compressed by 10mm. After optimization, the change range of kingpin caster angle is 2.6deg~5.5deg, which is much smaller than that before optimization (4) and the fair introduction of financial innovation tools. At this time, the change range of caster angle is about 3.68 DEG for every 10mm of suspension compression, which well meets our design requirements

2.4.3 kingpin'inclination'angle

Figure 11 comparison of kingpin'inclination before and after optimization

kingpin'inclination can make the vehicle steering return to normal and easy to operate. When the wheel jumps, the kingpin'inclination changes greatly, which will make the steering heavy and accelerate tire wear. After optimization, the change range of kingpin inclination angle is not much different from that before optimization, but the initial value of kingpin inclination angle is about 0.3deg smaller than the original value, which will reduce the sliding between the wheel and the ground during steering and slow down tire wear

2.4.4 scubu radius

Figure 12 comparison before and after optimization of kingpin offset

when the vehicle is steering, the steering wheel rotates around the kingpin, and the resistance torque of the ground surface steering is directly proportional to the size of kingpin offset. The smaller the kingpin offset is, the smaller the steering resistance moment is. Therefore, it is generally hoped that the kingpin offset is smaller to reduce the steering control force and the impact of the ground on the steering system. The kingpin offset is closely related to the kingpin inclination. Different kingpin offset can be obtained by adjusting the kingpin inclination with the buffer closed. The ideal kingpin offset value is -10~ 30mm. After optimization, the variation range of kingpin offset is -10.02~ 1.5 mm, which is closer to the design value than before optimization

2.4.5 toeu angle

Figure 13 comparison of toe angle before and after optimization

for the front wheel of the car, the toe value when the wheel jumps up is mostly designed to change from zero to negative toe. When the vehicle is driving, the toe in changes too much, which will affect the straight-line driving stability of the vehicle. At the same time, it will increase the rolling resistance between the tire and the ground and aggravate the tire wear. Therefore, the design principle of toe in angle is that the smaller the change is, the better when the wheel jumps. It can be seen from the figure that after optimization, the change of toe angle is roughly the same as before, and the stability of straight-line driving of the vehicle is not improved

3 summary:

using ams/insight, through multiple modification iterations on the hard point coordinates and elastic parameters of the model, one or more performance indicators of the model can be optimized, and the system will automatically find an optimal result. This paper introduces the optimization of some hard point coordinates of McPherson front suspension to optimize the variation of wheel alignment parameters during wheel jumping, so as to improve the kinematic performance of the suspension. However, due to the limitation of body layout, the change of hard point coordinates can only be limited to a certain small range, so the optimal value obtained is only a relative value, not an absolute optimal result

References:

[1] written by chenjiarui Automobile structure [m] People's Communications Press 1994

[2] Lin Yi et al Spatial motion analysis of sliding column swing arm suspension [j] Automobile technology 1998.3

[3] initial lighting, etc Optimization and analysis of trapezoidal breaking point position of steering mechanism of sliding column swing arm suspension [j] automotive engineering 1996.6

[4] zhaoxiaoguang Motion analysis of steering transmission mechanism of disconnected steering trapezoid [j] Automotive Technology 1993

[5] Lu Bo Motion analysis of wheat suspension system [j] Automotive Technology 1994.6

[6] zhanghongxin Vector analysis method of column swing arm suspension [j] Automotive Technology 1989

[7] huangxiaoping Kinematic analysis of steering mechanism [j] Automotive Engineering 1991

[8] wuyuanjie et al Kinematic analysis and parameter optimization design of car strut swing arm independent suspension [j] Journal of Jilin University of technology 1991.3

author profile:

zhutianjun, male, 1977, graduate student, teaching assistant, now engaged in the teaching and research of vehicle engineering in the vehicle engineering department of mechanical and electrical College of Hebei Institute of engineering. (end)

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