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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.

This paper describes the rationale used in the development of design guidelines for switch controls around the steering wheel in view of relating to the human operating characteristics. The resulting steering wheel control can be operated with ease and without a chance for any misuse. The results are based upon motion study, and relating to the surface area around the controls, where the thumb makes contact. First, a motion study was conducted, which involved recording the motion of the hand while operating the controls. Next, an experimental system was developed to measure the contact area and thumb pressure. A series of experiments was performed to evaluate operational areas, hand postures and thumb contact areas. The experimental results confirmed that the range of thumb movement in the upper location of the steering pad was bigger than the lower location, and the direction of contact area changes with control positions.