In this paper we propose a new multi-functional steering wheel switch for HVAC and audio systems. This new switch has five buttons on the front side of the spoke area and one button with vibration on the backside of it. Drivers can operate either HVAC or audio functions with the front switches, and HVAC or audio mode can be alternatively selected by pressing the back switch. Since different vibration modes are assigned for the HVAC and audio mode, drivers can also easily recognize which function can be operated. By changing the assignment of the mode in this way, the switch can operate more than 10 functions with 6 buttons allocated on the spoke area. Several kinds of evaluations were performed in order to develop this multi-functional switch.
At first, to optimize the positions of the buttons, the behaviors of thumbs and fingers were measured. Also the physical workload of the thumb motion and middle fingers' postures was evaluated when subjects operated the switches. Secondly, tactile sensibility of humans was investigated, and sensory evaluations concerned with vibration sensitivity were performed to decide the specification of the vibration. Thirdly, functions for operating the HVAC and audio systems with this switch were selected by considering driving situations. Finally, the switch that was developed based on the results of these evaluations was re-evaluated by using a driving simulator to verify the operability of the switch.
As a result of this evaluation, it was shown that the new switch with the functions for both the HVAC and audio systems performs well compared to the conventional switches.