Ride has always been an important aspect in vehicle design, driven by the customer’s increasing demand for vehicles with better comfort. The vibrational response of the vehicle is one of many factors contributing to the overall ride perception, with road inputs being the major excitation source. The improved capabilities of vehicle simulation models and virtual proving grounds have supplemented experimental prototype testing for tuning suspensions. Final tuning, and ride evaluation, is however still done through physical on-road testing. Four-post rig tests hold potential cost and time savings when used appropriately in the development process.

The four-post rig imposes only vertical inputs at the tire contact patches and thus it is expected for the vertical response of the vehicle to be the dominant component. The objective of this paper is to determine whether ride comfort can sufficiently be evaluated on the four-post rig using only the vertical seat Component Ride Value (CRV). The response of an instrumented vehicle on the four-post rig was measured by a tri-axial seat pad accelerometer. Vertical, longitudinal and lateral seat CRVs as well as the seat Point Ride Value (PRV) were calculated from the measured seat acceleration in the three translational directions using the BS6841 (1987) standard. The PRV is the square root of the sums of squares of the three CRVs. The CRVs and PRV, obtained from tests at various speeds and road roughnesses, were analyzed to determine whether the vertical seat CRV is sufficient in capturing the perceived ride comfort.

Results showed that the longitudinal and lateral CRVs are in excess of 26% and 63%, respectively of the dominant vertical seat CRV over the various tests. This implies that the vertical seat CRV underestimated the discomfort when compared to the seat PRV. It was also observed that the three CRVs had different sensitivities to test parameters and conditions. For example, at different speeds over the same road roughness the longitudinal CRV increased significantly more than the other two components. The differences in sensitivities may be due to the specific boundary conditions imposed on the vehicle by the four-post rig. It is concluded that the vertical seat CRV may not be sufficient to evaluate the ride comfort on a four-post rig.

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