The hydraulic impulse accumulator - HIS for short - is an additional component for automatic transmissions that enables a start-stop function. It is a solution that is easy to install, requires hardly any modifications to the transmission and consumes very little energy. The HIS is connected to the transmission's oil circuit and supplies the automatic transmission's shift elements required for starting with oil.
The HIS is an electromagnetically switchable spring-piston accumulator that fills up with oil while driving, tensioning a spring in the process. This reservoir of around 100 centiliters is fed back into the hydraulic system at lightning speed after the spring is released when the engine is started and generates sufficient oil pressure to actuate the shift elements of the automatic transmission required for starting. This accelerates the pressure build-up in the transmission and the car can start up again with virtually no delay after just 350 ms after the engine is switched off.
As the HIS was specifically designed for use in automatic transmissions and is installed transversely behind the hydraulic control unit on the transmission, it does not require any additional installation space.
