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.
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.
Teflon has the following advantages:
– a very low coefficient of friction.
– resistance to aggressive products.
The mini-lip has many advantages:
– Reduced dimensions
The decrease in height and the difference between the internal and external diameters allow type IE seals to be used for applications where only type IO used to be possible. The reduced dimensions also mean less weight.
– Less energy loss due to friction
The radial load is smaller, which leads to a decrease of about 30% of the friction torque, which results in:
– a gain in power for the prime mover.
– less heating.
– Increased life
The decrease in heating due to friction results in a lower temperature, which:
– improves the life of the elastomer.
– slow carbonisation, which causes leaks by producing irregularities and stiffening the lip.
This type of seal has its own friction track.
Its main advantages are:
-reduces the need to grind the shaft,
-treatment of only one part,
-no shaft wear,
– protection of the lip in storage and handling,
– in a bearing, it can serve as a supporting element until it is fitted in the unit.
A moulded lip guarantees a better geometrical fit of the sealing lip by eliminating the machining tolerances on:
– the lip angle on the fluid side,
– the distance between the edge of the lip and the axis of the spring,
– the length of the lip (i.e. the distance between the fixing rim and the sealing edge).
