Hydraulic impulse storage, automatic transmission

The hydraulic impulse storage allows the automatic engine start-stop on vehicles with automatic transmission. The hydraulic impulse storage provides the required pressure to be able to activate the shift elements during an automatic engine start.

Fig 1: Identifying 8HP Automatic Transmission And Hydraulic Impulse Storage

Courtesy of BMW OF NORTH AMERICA, INC.

System pressure is applied to the hydraulic impulse storage when driving. The piston is pressed back against the spring pressure. The electromagnetic locking unit keeps the piston in this position. The hydraulic impulse storage is ready for the engine start.

At an engine start the electromagnetic locking unit is released by the automatic engine start-stop. Spring force presses the piston into its original position. This makes the pressure required for the shift elements immediately available.

Fig 2: Identifying Electromagnetic Locking Unit Components

Courtesy of BMW OF NORTH AMERICA, INC.

During the engine start the hydraulic impulse storage fills system pressure into the shift elements of the drive-off gear. The engine start can therefore be carried out for selector lever position D. The automatic engine start-stop is deactivated if the selector lever is in the shift gate M/S.