Pistons for automatic gearboxes

In an automatic gearbox, the setting in motion and the changing of gears are done by clutches on which pistons, moved by oil pressure, act.

Up to the present, these pistons were in moulded aluminium alloy or steel. The sealing for aluminium pistons was done by elastomer seals of various shapes fitted into the grooves or, for steel pistons, kept in position by outer rings.

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Since the seal had to be both interior and exterior, each piston was made up of from 3 to 5 parts, which meant high stocks along with and fitting problems, quite apart from being of mediocre efficiency under pressures of 10 to 20 bars.

The type of piston produced by PAULSTRA consists of only one piece of stamped steel on to which are bonded 2 sealing lips. The shape of these lips is adapted to ensure a good seal with little friction and to avoid extrusion.