Steering wheel vibration and human perception

is the most significant contributor to car passengers’ comfort. To cool down and warm up the car cabin, a centrifugal fan (also called: blower) blows air at the requested temperature inside the cabin. The air flow provided by the centrifugal fan depends on the wheel speed.
The unbalance of this rotating machine (fan + electric motor) can create unacceptable vibrations for car passengers. The vibration levels depend on the mass unbalance and rotating speed. These vibrations are transmitted from the HVAC to the steering wheel. Even if the wheel and electric motor are balanced to reduce the centrifugal force, the level of vibration can still be unacceptable, especially when the thermal engine of the car is off. This is the case in electric, hybrid or micro-hybrid vehicles. Today for thermal power train, carmakers’ specifications are mainly based on levels of acceleration whatever the fan speed.
This study, based on human vibration perception, was done to review and improve the specifications. In this paper, two approaches based on jury evaluation will be described.
In the first approach, an aluminum steering wheel is used for the test. A jury of 27 participants (female and male, younger and older) was selected. An electrodynamics shaker fixed to the steering wheel creates vibrations at fixed frequencies and fixed levels. The vibration levels are measured by a low mass accelerometer placed on the steering wheel. 8 vibration stimuli are created (4 frequencies and 2 acceleration levels). Each participant gives a quotation from 1 to 5 for each stimulus.
In the second approach the tests are done in the vehicle. An electrodynamics shaker is fixed on the HVAC blower. It creates vibrations and a low mass accelerometer is fixed on the steering wheel to measure vibrations. A jury of 15 participants was selected. They judged different levels of vibrations at fixed frequency. The test is to determine the highest vibration level judged as acceptable.
Based the two approaches it is possible to define new specification of vibration on the steering wheel. Others studies are still ongoing to correlate these results and HVAC Blower unbalance.