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1、400 Commonwealth Drive, Warrendale, PA 15096-0001 U.S.A. Tel: (724) 776-4841 Fax: (724) 776-5760 Web: www.sae.org SAE TECHNICAL PAPER SERIES 2006-01-0991 Suspension Tuning Parameters Affecting Impact Harshness Performance Evaluation Xiaobo Yang, Dajun Zhang, Sudhakar Medepalli and Mohammed Malik Dai
2、mlerChrysler Corporation Reprinted From: Load Simulation some free edges are captured forming 1.32 million elements for animation purpose. 1020304050 2 4 6 8 PSD-Fx kN2/Hz 1020304050 0.02 0.04 0.06 0.08 0.1 0.12 0.14 PSD-Tx kNm2/Hz 1020304050 0.5 1 1.5 2 2.5 PSD-Fy kN2/Hz 1020304050 0.005 0.01 0.015
3、 0.02 0.025 PSD-Ty kNm2/Hz 1020304050 10 20 30 Frequency (Hz) PSD-Z Disp cm2/Hz 1020304050 0.05 0.1 0.15 0.2 0.25 Frequency (Hz) PSD-Tz kNm2/Hz LF RF LR RR Figure 3: Input data PSD plots. COMPREHENSIVE EVALUATION INDEX FOR IMPACT HARSHNESS So far from literature, a standardized criterion to objectiv
4、ely evaluate the impact harshness performance hasnt been found. The usual evaluation practices among major automotive manufacturers are mainly through subjective evaluations. Due to the nature of human drivers, different drivers may give different evaluation results more or less for the same vehicle
5、 on the same impact harshness event. They may also focus on different aspects/points of acceleration responses under the same situation. Therefore, in order to make the analytical objective evaluation consistently and eventually correlate statistically with actual subjective evaluation, certain anal
6、ytical comprehensive evaluation index is needed. Therefore, in this study, a comprehensive evaluation index is proposed. Response Variables Considerations Since the objective of this study is to evaluate the effects of various design tuning parameters on impact harshness performance, the response ob
7、jective needs to be established. As mentioned earlier, it is not determined where the drivers focus on to evaluate the impact harshness, thus various locations are selected to cover possible locations that majority of drivers may be cautious about. These locations are listed in Table 1, where the we
8、ighting factors will be discussed later. Table 1: Weighting factors for impact harshness performance objective evaluation. XW110.026W410.026 YW210.026W510.026 ZW310.026W610.026 XW120.026W420.026 YW220.026W520.026 ZW320.026W620.026 XW130.026W430.026 YW230.026W530.026 ZW330.026W630.026 XW140.03W440.03
9、 YW240.03W540.03 ZW340.03W640.03 XW150.026W450.026 YW250.026W550.026 ZW350.026W650.026 XW160.026W460.026 YW260.026W560.026 ZW360.026W660.026 XW170.026W470.026 YW270.026W570.026 ZW370.026W670.026 XW180.026W480.026 YW280.026W580.026 ZW380.026W680.026 XW190.03W490.03 YW290.03W590.03 ZW390.03W690.03 XW1
10、100.032W4100.032 YW2100.03W5100.03 ZW3100.032W6100.032 XW1110.03W4110.03 YW2110.03W5110.03 ZW3110.03W6110.03 XW1120.03W4120.03 YW2120.03W5120.03 ZW3120.03W6120.03 11 Driver Seat Track Front 12 Driver Seat Track Rear 9 Steer Wheel 12 Oclock 10 Steer Wheel 9 Oclock 7 Rear seat front left 8 Rear seat f
11、ront right 5 Floor front seat left 6 Floor front seat right 3 Steering Column Tilt 4Front Pedal Weighting Factors for RMS 1 Front Passenger Seat Front Inboard 2 Front Passenger Seat Rear Outboard Response Point # Response Point Name Directions Weighting Factors for Peak- to-Peak Range Since impact h
12、arshness is a short term transient event, peak-to-peak range and RMS values of the acceleration response time histories are selected as the performance 4 measure. The range values, characterized as the peak-to- peak difference, may indicate the impact severity effects (higher the range value, higher
13、 the impact response), while the RMS values may include the information of overall acceleration response level including the after impact effect, etc. This can be clearly demonstrated in Figure 4, where the acceleration responses D and E are of almost the same peak-to-peak range values over the enti
14、re time history, but Response D has larger RMS value showing greater oscillations after impact. Figure 4: Illustration of two acceleration responses with same peak-to-peak range but different RMS values. Comprehensive Evaluation Index In this study, the evaluation of impact harshness event includes
15、both peak-to-peak range and RMS values. The evaluation index is formulated as shown in Equation (1) below: RMSrange JJJ+= (1) where, range n k zkkykkxkk range a awawaw J max_ 1 321 )(Range)(Range)(Range = + = rms n k zkkykkxkk RMS a awawaw J max_ 1 654 )(RMS)(RMS)(RMS = + = 0 . 1 1 3 1 = = n ki ik w
16、 and 0 . 1 1 6 4 = = n ki ik w, n is the total number of acceleration response points observed, wik are the weighting factors, axk, ayk and azk are the acceleration response at kth point in x, y and z directions, respectively. amax_range and amax_rms are the maximum values of the peak-to-peak range
17、and RMS acceleration responses at nominal design condition, respectively, they should be constants for a specific vehicle. It should be noted that ultimately the determination of the weighting factors should statistically represent the entire human drivers evaluation characteristics, which, to some
18、extent, are unknown. In reality, the weighting factors can be collected from various customers including some professional evaluators and ordinary drivers, and then established from statistic models. In this study, one set of weighting factors are proposed as shown in Table 1. It can be seen that th
19、e proposed weighting factors for peak-to-peak range and RMS values are the same for the same acceleration response, indicating that the on- impact response and after-impact response are treated equally important. Furthermore, the maximum weighting factors of 0.032 are put on the steering wheel 9 Ocl
20、ock position at fore/aft (X) and Vertical/Tangential (Z), and the second maximum weighting factors of 0.03 are put on the front pedal, driver seat track, steering wheel 12 Oclock, and steering wheel 9 Oclock position lateral direction, respectively. Since the weighting factors directly affect the ov
21、erall evaluation index, their choice needs to be correlated with the sets of subjective evaluations in the future studies. INFLUENCE OF SUSPENSION TUNING PARAMETERS ON IMPACT HARSHNESS PEROFRMANCE EVALUATION During the entire development process of a vehicle program, several phases, ranging from pro
22、totype, pre- production and production, need to tune the vehicle design to improve the vehicle performances. The suspension and steering systems are usually the critical sub-systems affecting directly the vehicle performances, such as ride and handling, NVH, durability, etc. Thus tuning suspension a
23、nd steering system parameters frequently happens. Although there are different types of suspensions and steering system, all suspension and steering system parameters contain the spring stiffness, shock damping, unsprung mass, bushing stiffness, trackwidth, steer gear ratio, etc. When tuning suspens
24、ion and steering system parameters, understanding their effects to various performance attributes is essential. Thus in this study, a series of sensitivity analyses are performed to illustrate their independent effects on impact harshness performance. The observation variable is the relative change
25、in the evaluation index to the relative change in the concerned parameter, defined as shown in Equation (2). n n n n r r x xx J JJ x J S = (2) where Jr and xr are the relative change of the evaluation index J and design parameter x, respectively. Jn is the evaluation index at nominal design paramete
26、r xn. The result of the calculated sensitivity S directly reflects the amount of relative change in the performance index J Response D Response E Time Acceleration Response Impact Occurs After Impact 5 corresponding to the amount of relative change in the concerned parameter x. Since the sensitivity
27、 S is non- dimensional, it may be used to compare different parameters sensitivities. A positive value of S indicates that the impact harshness evaluation index increases with an increase in the parameter, meaning that the impact harshness performance becomes worse when the parameter value is increa
28、sed. If the value of S is close to zero, which indicates the impact harshness performance is not sensitive to the corresponding parameters variation. The performance evaluation indices, calculated using Equation (1) and weighting factors from Table 1, under nominal design parameters are illustrated
29、in Table 2. Table 2: Evaluation index at nominal design. Max Range of Acceleration at nominal design amax_range (g) Max RMS of Acceleration at nominal design amax_rms (g) JrangeJRMSJ 2.960.420.320.310.63 In this study, the suspension and steering system parameters concerned are listed in Table 3, wh
30、ere their nominal values and corresponding relative changes up to 20% are illustrated, except for the trackwidth, for which only 4% range of change is considered due to practical reason. It should be noted that the front unsprung mass only includes the front tires, wheels, rotors, brake calipers and
31、 knuckles, and the rear unsprung mass only cover rear tires, wheels, brake rotors and axle with differential and driveline shafts. When the unsprung mass changes, only the mass change is considered in the current study, the CG locations and mass moment of inertia are assumed to be unchanged. The sho
32、ck damping listed in Table 3 only represents the linear region in the rebound condition. When changing the shock rebound linear damping, the damping in the other regions will change proportionally. Table 3: Suspension and steering tuning parameters. FrontRearFrontRearFrontRear mm/radian Relative Cha
33、nge from Nominal mm -20%88.243.484.890.6156.46.1-4%1525.25 -15%93.746.28.55.196.3166.26.5-3%1541.14 -10%99.248.995.4102.0176.06.9-2%1557.02 -5%104.751.69.55.7107.6185.87.3-1%1572.91 0%110.254.3106113.3195.57.60%1588.8 5%115.757.010.56.3119.0205.38.01%1604.69 10%121.259.7116.6124.6215.18.42%1620.58 1
34、5%126.762.411.56.9130.3224.98.83%1636.46 20%132.265.2127.2136.0234.69.24%1652.35 Note: (1) The front unsprung mass includes tire, wheel, rotor and bearing, caliper and knuckle at left and right sides; (2) The rear unsprung mass includes left- and right-side tire, wheel, rotor and bearing, caliper an
35、d axle; (3) The steer gear ratio is the rack travel in minimeter per radian of pinion rotational angle; (4) All design variables in the table are varied within 20% range except for the trackwidth, for which only 4% range of variations are concerned. (5) The front and rear trackwidths are assumed to
36、be the same. Unsprung Mass kg Steer Gear Ratio Trackwidth Relative Change from nominal Spring Stiffness N/mm Shock Damping Ns/mm SPRING STIFFNESS The sensitivities of impact harshness performance evaluation index to the front and rear coil spring stiffness are illustrated in Figure 5, where the uppe
37、r and lower graphs are for front and rear springs, respectively. It can be seen that the sensitivities for both front and rear springs are positive under 20% change range from their nominal values, indicating that an increase either in front or rear coil spring stiffness will worsen the impact harsh
38、ness performance. Compared with the sensitivity values for front and rear springs, the impact harshness performance is much more sensitive to the front spring stiffness than to the rear spring stiffness. Furthermore, it can be seen that the sensitivity of the rear spring stiffness is fairly constant
39、 over the 20% spring stiffness change, even though a slight increase in the relative sensitivity values with increase in the relative spring stiffness change level can be observed. On the other hand, the sensitivity of front spring stiffness is fairly constant over the 10% spring stiffness changes.
40、The relative sensitivity for the peak-to-peak range value and RMS value as well as the sum, J, are similar in terms of their tendency with the spring stiffness change. This may indicate that using either one as the impact harshness evaluation can reasonably represent the other for the impact harshne
41、ss variation trend as far as spring stiffness concerned. It should be noted that the spring stiffness basically affects the vehicle natural frequencies in bounce, roll and pitch modes, which may directly affect the body acceleration responses under given road inputs. This result may imply that if th
42、e spring stiffness is to be changed for impact harshness performance, reduction in the front spring stiffness from its nominal value by 10% may achieve the most efficient results. 0.30 0.35 0.40 0.45 0.50 -20%-10%0%10%20% Relative Change in Front Spring Stiffness Sensitivity of Evaluation Index (%/%
43、) Jrange Jrms J 0.025 0.035 0.045 0.055 0.065 -20%-10%0%10%20% Relative Change in Rear Spring Stiffness Sensitivity of Evaluation Index (%/%) Jrange Jrms J Figure 5: Sensitivities of front and rear spring stiffness. SHOCK DAMPING The sensitivities of impact harshness performance index to the front a
44、nd rear shock damping are illustrated in Figure 6 upper and lower graphs, respectively. It can be seen that 6 both front and rear shock absorbers yield positive relative sensitivity for all three evaluation indices, which indicates that reduction in either front or rear damping will improve the impa
45、ct harshness performances. Furthermore, the rear shock damping has fairly constant positive sensitivity values within the 20% changes, which indicates that the impact harshness performance will be improved by almost the same amount within 20% change range in the rear shock damping. While the sensiti
46、vity pattern for the front shock damping is much more diversity in the 20% change ranges, than the rear shock damping. The relative sensitivity for RMS value is pretty constant within 20% of the relative front shock damping change. The relative sensitivity of the peak-to-peak range evaluation index
47、decrease with the decease in the relative front shock damping up to 5%, then increase with an increase in the relative shock damping slowly. These results may imply that when changing the front shock damping for improving the impact harshness performance, a nonlinear effect of front shock damping sh
48、ould be aware of and different range of change in the shock damping may result in different efficiencies. 0.076 0.077 0.078 0.079 0.080 0.081 0.082 -20%-10%0%10%20% Relative Change in Front Shock Damping Sensitivity of Evaluation Index (%/%) Jrange Jrms J 0.035 0.045 0.055 0.065 -20%-10%0%10%20% Rel
49、ative Change in Rear Shock Damping Sensitivity of Evaluation Index (%/%) Jrange Jrms J Figure 6: Sensitivities for front and rear shock damping. STEER GEAR RATIO Figure 7 illustrates the impact harshness performance evaluation index relative sensitivities to the relative change in steer gear ratio. Here the steer gear ratio is defined as the amount of steering rack translational displacement per radian of steering wheel angle. Thus higher the steer gear ratio yields more rack travel under the same steering wheel angle. It can be seen
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