13 Vehicle Driveline Benchmarking to Support Predictive CAE Modeling Development 147 (a) (c) (b) (d) Fig. 13.7 Step relaxation results for cold tire time data (a) and linear spectrum (b) as well as hot tire time data (c) and corresponding linear spectrum(d) 13.4 Conclusion The aim of this study was to use experimental modal analysis to derive stiffness and damping estimates for use in a CAE lumped parameter model for vehicle development. The lumped parameter model is used for reduced computational load compared with FEA methods, however it requires several assumptions to be made for lumped parameter distribution. With the values extracted from MPE, the number of assumptions is reduced in the CAE model and drives towards better correlation with experimental results. Testing was performed on three different lumped components; the powerplant, differential, and propeller shaft. Each component was evaluated for either the first rigid body roll mode or first torsional mode. An updated material selection for the propeller shaft required a closed form solution to estimate the first torsional mode. The solution identified the mode to be between 133 and 1790 Hz based on estimates for boundary condition and/or coupled stiffness or inertia. This was used to set the bandwidth of the experimental testing to ensure the torsional mode was captured within the dataset. Results from experimental testing identified the roll modes at 9.5 Hz and 132 Hz for the power plant and differential respectively while the propeller shaft torsional mode was found at 1546 Hz. Static testing was performed on the entire vehicle body to estimate the stiffness and damping of the fore-aft suspension mode. This was done by shifting the transmission into park such that the driveline cannot rotate (other than through the lash zone). The frame was then loaded in tension with a cable and released such that a step relaxation force was input to the body. This resulted in a vehicle oscillation like that of a pluck test and showed the frequency of oscillation to be 1 Hz with cold tires and 1.13 Hz with warm tires. The decay of the output data was also used to estimate damping of 3.71% to 2.73% when the tires were cold and warm respectively. The combination of roll modes, torsional modes, and fore-aft body mode parameters were all used as vehicle parameters for building a lumped parameter CAE model of the test vehicle.
RkJQdWJsaXNoZXIy MTMzNzEzMQ==