SCHOTT solutions no. 2/2009 > Sensor Technology

Automatic transmissions are becoming progressively smoother. However, despite the duplex clutch, passengers still feel a noticeable jolt while shifting gears and reaccelerating. New transmissions attempt to reduce this by using a clever electronic control system, nevertheless erratic changes in torque can still occur during shifting, especially as the vehicle and transmission ages so that the original calibration becomes less and less accurate. The reason is that it has not yet been possible to produce sensors that are capable of directly measuring the torque inside the drivetrain. The attempts made by various manufacturers to produce torque sensors from two housing parts have failed because, in order to perform exact measurements, this housing must be both elastic, as well as completely hermetic.

”The solution that Transense and SCHOTT have now developed is a unique housing that combines a metal with a high elastic limit for transmitting the torque to the sensor with an annealed metal suitable for hermetic glass-fritted elec- trical feedthroughs,” explains David Vile, Business Manager of Torque Systems at Transense plc. Unlike conventional housings, for the first time ever, this unit consists of three parts: a base, a ring and a cover.

The round base disk consists of a stainless steel that is not hardened by heat treatment, but rather only by mechanical processing. This, in turn, ensures that the metal remains elastic, even when it is subjected to high stresses. As a result, the linear strain is transferred to the torque sensor that is bonded to its inner surface. The second component of the housing made of annealed stainless steel contains openings for the two connector pins that are hermetically sealed by glass fritting inside an oven. The ring is actually welded to the base before the sensor is added. Then, once the sensor has been added, the housing is enclosed with a stainless steel cover welded in place.