Touch-sensitive panels make mobile phones easier to use and are central to the appeal of Apple's iPad. But the technical challenges presented by a car interior have so far limited the use of touch panels in cars.
"When you make a touch panel there are two main technical solutions: resistive and capacitive," says Jean-Yves Daurelle of Johnson Controls. "Resistive is very cheap, very robust, but you have to press quite hard. Typically that is what you have in an ATM or when you buy your ticket in a train station. They have been used for several years in automotive applications."
The alternative technology, used in smart phones and the iPad, is a capacitive panel. "You don't have to press very hard. They are very smooth, very responsive," says Daurelle. Unfortunately, capacitive panels are not yet suitable for automotive use thanks to the variation of temperature common in automotive interiors. "This type of touch panel tends to become yellowish and lose their optical quality over time with temperature cycles," says Daurelle (so don't leave your iPad in the sun). Typically a capacitive panel would last a couple of years in a car interior, but automotive manufacturers refuse to accept any system which will not remain in perfect order for at least five years.
Johnson's solution is a development of the resistive panel. "Working with one of our partners we reduced the activation threshold," says Daurelle. Existing panels typically need about 1 Newton of fingertip force to activate, but the new panel reduces that to just 0.1-0.2 Newtons. The improvement in response broadens the options for designers, allowing features like slider controls for audio volume or cabin temperature. As a result touch panels might be more widely used in future interior designs.
The low activation force resistive displays are likely to be in production by 2013. Two European car makers are said to be interested: Johnson won't say who, though rumours suggest PSA and BMW are likely candidates.