Belt tensioner

Details Belt tensioner Belt tensioner

1997-09-15

2001-12-04

Mai, Lanna (Department: 3619)

Land vehicles

Wheeled

Attachment

C297S480000, C242S374000

Reexamination Certificate

active

06325416

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a belt tensioner.
BACKGROUND OF THE INVENTION
Known belt tensioners comprise a linear piston and cylinder drive, whose piston may be driven by a compressed gas entering a working space and moves a part engaging the safety belt via a traction means attached to the piston.
A belt tensioner of this type is disclosed in the European patent publication 0 616 928 A1. The piston provided in this case is composed of a plurality of parts, between which a preferably plastically deformable damping element is arranged. On one part at the face end thereof facing the working space a bead is provided which is conically formed outward and constitutes a rigid sealing edge. A cylinder is manufactured by cutting off a suitable portion of a tube which is made by drawing and, therefore, could be of indefinite length. Since the bore diameter of the tube varies owing to wear of the tools employed for machining it, substantial variations are also liable to occur in the bore diameter from one cylinder to another. Therefore, it is not in every cylinder that a rigid sealing edge can ensure an optimum sealing effect so that in the case of a cylinder with a large bore diameter compressed gas is able to flow past the piston out of the working space, something which reduces the performance of the belt tensioner.
BRIEF DESCRIPTION OF THE INVENTION
The invention provides a more effective belt tensioner, in the case of which leakage flow from the working space may be reduced while nevertheless adhering to a simple design. The belt tensioner according to the invention comprises a cylinder with an inner shell surface, a piston with a piston head, a working space in the cylinder into which compressed gas enters upon activation of the tensioner to drive the piston, a part engaging the safety belt, and a traction means attached to the piston and to the belt engaging part. The piston head delimits the working space and is formed by an annular sealing plate on which an essentially axially extending thin sealing lip is formed. The lip is adapted to resiliently yield radially and contact the inner shell surface of the cylinder in a biased condition.
The sealing lip has a relatively large overall axial length and may consequently be readily bent elastically and adapt itself to the course of the barrel face of the cylinder and to the variations in the bore diameter so that hardly any leakage will occur.
In the preferred embodiment of the invention the sealing lip widens out conically toward its free edge resting against the shell surface with the result that the introduction of the piston into the cylinder in the course of assembly is facilitated. If the free edge externally, furthermore, has an axially short collar, same may be so designed that during fitting the piston in the cylinder it is partly abraded or cut back and accordingly adapts itself to the cylinder's inner shell surface. This operation may be likened to so-called grinding in. If the annular sealing plate is made of aluminum and the cylinder is made of steel, excellent sealing results can be achieved by the “grinding-in-effect”.
In the case of the preferred embodiment the sealing plate is made concave toward the working space and increases the size of the working space, into which compressed gas flows from a container for the storage of compressed gas or from a pyrotechnical gas generator. Accordingly the piston and cylinder linear drive may be made with a generally shorter overall length, something which is aimed for in view of the in any case limited amount of space available in vehicles. The sealing lip is formed by the peripheral wall left on the sealing plate.
A further provision is that the piston is composed of only a few readily-manufactured parts. In the case of the preferred embodiment of the invention a guide sleeve is provided to the side of the sealing plate, such sleeve having a central opening conically narrowing toward the working space, such opening being adjoined without any intervening ledge by an opening which is provided in the sealing plate and also narrows conically. The locking body is designed in the form of a conical sleeve and press fitted in the openings so that owing to the wedging effect the parts are connected together by friction. In this design the frictional force between parts is even further increased by the pressure of the gas acting on the sealing plate so that there is a self-reinforcing effect.


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