Intermediate shaft assembly is used to connect steering gear to the steering wheel. The primary function of the intermediate shaft is to transfer torsional loads. There is a high probability of noise propagating through the Intermediate shaft to the driver. The current standard for measuring the noise is by performing vehicle level subjective evaluations. If improperly clamped at either of the yokes, a sudden change in the direction of the torsional load on the Intermediate shaft can generate a displeasing noise. Noise can also be generated from the constant velocity joint.
Intermediate shaft noise can be measured using a microphone or can be correlated to acceleration values. The benefit of measuring the acceleration over sound pressure level is the reduction of complexity of the test environment and test set up. The nature of the noise in question requires the filtering of low frequency data.
This paper presents a new test procedure that has been developed by General Motors. The test requires the steering system to be setup in the nominal vehicle position. The steering system is loaded at the inner tie rod while acceleration levels are measured at different locations. As a function of the steering system, the linear tie rod loads are converted to torsional loads on the Intermediate shaft. The torsional loads acting on the intermediate shaft provide the necessary excitation for the displeasing noise to occur.