Virtual design and optimization of the hottest McP

2022-08-02
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Virtual design and optimization of McPherson front suspension

McPherson independent suspension has many advantages, such as simple structure and convenient maintenance. However, since the kingpin axis is located on the connecting line between the upper fulcrum of the shock absorber and the outer fulcrum of the lower arm, when the suspension is deformed, the kingpin axis will also change, and the wheel alignment parameters and track width will also change accordingly. The amount of change may be large, It directly affects the handling stability of the whole vehicle and the wear of tires. In the project of cooperating with a company to develop an electric golf cart, the front suspension adopts McPherson type independent suspension, and the manufacturer prepares self-made parts. In order to save the cost and shorten the development cycle, the virtual design and kinematics analysis of suspension should be done before the design of specific parts

I. model building

(I) overall modeling scheme

the front suspension is to be designed as a McPherson independent suspension with a gear rack transmission steering gear. Some design requirements of the golf cart: the cart adopts 18 ″ tires, with a width of 210mm, a diameter of 457.2mm, and a hub diameter of 220mm, which is larger than that of ordinary cars; Front wheel distance 850mm; The load is small, and the estimated total mass of 2 adults is 550Kg; The vehicle speed is low, and the maximum speed is 25km/h. Using the multi-body kinematics analysis method, firstly, the kinematics simulation system model as shown in Figure 1 is abstracted

McPherson suspension is symmetrical to the longitudinal plane of the vehicle, and is composed of lower swing arm, steering knuckle assembly (including lower body of shock absorber and hub shaft), steering tie rod, upper body of shock absorber, steering rack, wheel assembly and vehicle body. The connection relationship between the rigid bodies is as follows: the upper end of the shock absorber is connected to the ball hinge a of the vehicle body, one end of the lower swing arm (simplified as one point) is connected to the vehicle body through the rotating pair C, and the other end is connected to the steering knuckle assembly through the ball hinge B. the connecting line AB forms the kingpin axis. The steering knuckle assembly and the upper body of the shock absorber are restrained by a cylindrical pair and can only move and rotate along the axis. One end of the tie rod is connected to the steering knuckle assembly through ball joint D, and the other end is connected to the steering rack through ball joint E. During motion analysis, the steering rack is fixed to the vehicle body, the wheel assembly and steering knuckle assembly are also connected through the fixed pair F, and the vehicle body does not move relative to the ground. Since the kinematics does not need to consider the force, the damping of the shock absorber and the stiffness of the spring are not considered. It is assumed that the wheel does not rotate and the wheel is a rigid body

(II) prediction of key points of the model

first determine the design target parameters: kingpin inclination 8.5 °, kingpin caster 2.5 °, and wheel camber 1.5 °. From the ideal relationship between front toe angle and camber angle ε ≈ c/2d and c=2d Φ L/Φ r+4 α L α [1] According to the design parameters, the toe in angle of the front wheel is calculated to be about 0.5 °. In the trial production design stage of the first production line of virtual DuPont Hongji new materials, these parameters need not be completely accurate, and can be adjusted through subsequent optimization design. Use CAD software to pre design the spatial coordinates of some key points (only the parameters of the right half suspension are designed due to the symmetry of the suspension). The coordinate system adopts the default coordinate system in adams/view modeling. See Table 1

(III) establish simulation model

according to the position of points in Table 1, establish the multi-body kinematics analysis model of McPherson front suspension system in adams/view module. Due to symmetry, only the right half suspension model is established. As shown in Figure 2

II. Simulation analysis of the model

carry out parallel runout simulation of both sides of the wheels to analyze the change law of kingpin inclination, kingpin caster, camber, front wheel toe in and wheel side slip

set the measurement functions of the required measurement parameters in ADAMS. Take the moving pair between the ground and the test platform as the driving pair, create the driver, and the driving function is: disp (time) =40 × sin(360d × Time), that is, the range of wheel runout is ± 40mm. Draw the suspension characteristic curve with the wheel runout as the x-axis, as shown in figure 3:

it can be seen from the figure that the change of kingpin inclination is 6.665 ° to 10.351 °, and the change is 2.706 °; Caster angle of kingpin is from 2.311 ° to 2.725 °, which increases slightly with suspension compression, and the state is ideal; The camber angle changes from 3.600 ° to 0.303 °, with a change of 3.297 °, slightly larger; The toe in angle of the front wheel changes greatly, from -4.568 ° to 1.723 °, with a change of 6.291 °; The wheel slip varies greatly from 19.35mm for 40mm down jump to -9.235mm for 40mm up jump, especially when the tire jumps down

the analysis results are as follows: (1) the change state of kingpin inclination and kingpin caster is relatively normal, indicating that the establishment of the model is generally successful; (2) If the wheel offset is too large, the wheel track changes greatly when driving, which will lead to serious tire wear; (3) The unreasonable toe change will further increase the tire wear and affect the handling performance

put forward the optimization objective: under the premise of ensuring the ideal state of kingpin caster angle and appropriately reducing the changes of kingpin inclination angle and wheel camber angle, improve the change state of front wheel toe angle and control the wheel slip

III. optimization design

laying a 500mm wide vacuum insulation board on the balcony plate can play a role in isolating the heat bridge. Analyze the problems raised above and refer to the previous research [2], further narrow the scope of the problem, and mainly solve the problem by adjusting the height of the swing arm hinge point C and the position of the pull rod hinge point E. Parameterize the coordinates of these two points, design relevant variables, and use the powerful analysis ability of adams/insight module to evaluate the impact of various factors on wheel alignment parameters and wheel side slip, as shown in Table 2

it can be seen from table 2 that the height of swing arm hinge point C is very important and needs to be reduced, and the resulting increase in front wheel toe angle can be optimized by adjusting the Y coordinate of tie rod hinge point E. After analysis, optimization and some related adjustments, the new coordinates of the key points listed in Table 3 are obtained

repeat the wheel parallel runout simulation to obtain the suspension characteristic diagram as shown in Figure 4. It can be seen from the figure that the optimization results meet the requirements, which proves that the optimization plan is suitable for testing the shear stress and shear elastic modulus by using sandwich structure or core samples; The experimental types are divided into compressive shear and tensile shear. It can be seen from the figure that: (1) the caster angle continues to maintain an ideal change state, the caster angle changes from 7.069 ° to 9.481 °, and the change amount decreases to 2.422 °; (2) The change state of front wheel toe in angle is obviously improved, and the camber angle of the wheel is optimized, as shown in Figure 5; (3) The side slip of the wheel is significantly reduced, from -2.65mm to 12.72mm. Combined with the optimization of the front toe angle, the wear condition of the tire can be better improved

IV. conclusion

through the modeling and kinematics simulation analysis of Adams, the virtual design before the design of specific parts and components is well completed and the process of optimizing the cost of purchasing parts and components is reduced, which shortens the development cycle of golf cart, improves the performance of suspension, better controls the variation range of positioning parameters and avoids serious wear of tires. After the parameterization of this virtual design platform, it lays a foundation for the subsequent design of related products

in the optimization analysis of suspension layout, the following conclusions are drawn: (1) the height of the link hinge between the swing arm and the vehicle body has a great impact on the positioning parameters, which should be taken into account; (2) The arrangement of steering tie rod only affects the toe in of front wheel, but has little effect on other parameters

references

[1] Wei daogao Research and Prospect of front wheel alignment parameters [j] Journal of Hefei University of technology, 2004

[2] Wang Guolin Experimental analysis of the influence of wheel runout on alignment parameters [j] Journal of agricultural machinery, 2005 (7) (end)

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