Land vehicles – Wheeled – Attachment
Reexamination Certificate
1999-11-16
2001-05-29
Culbreth, Eric (Department: 3611)
Land vehicles
Wheeled
Attachment
C180S371000
Reexamination Certificate
active
06237958
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a pretensioner for a vehicle seat belt and particularly to a locking device for such a pretensioner.
BACKGROUND OF THE INVENTION
A pretensioner is used with a vehicle seat belt to rapidly tension a length of seat belt webbing at the onset of a crash to more securely restrain the vehicle occupant by restricting his forward movement. This places the vehicle occupant in a more effective position for protection by a secondary restraint such as an airbag.
A modern pretensioner comprises a piston driven along a cylinder by gas from a pyrotechnically detonated gas generator. The piston is connected to a cable, that in turn is connected through a buckle to the webbing of a restraint retractor. On activation, the piston pulls the cable which in turn tensions the retractor webbing, pulling the webbing tight around the vehicle occupant. At the end of the pretensioning stroke it is necessary to stop the piston and prevent it moving back down the cylinder which would loosen the webbing again.
Various forms of locking mechanisms for the piston have been devised. An elliptical disc may be attached to the piston in such a way that it slides easily along the tube in a pretensioning direction but is tilted to jam into the sides of the tube in the reverse direction. This locks the piston against reverse movement.
Alternatively it has been proposed to place loose locking balls around a groove in the piston, on a tapering surface arranged such that the balls are located in the deepest part of the groove when the piston is moving in the pretensioning direction. However, when the piston is pulled back by the inertia of the occupant at the end of the pretensioning pulse, the balls slide to a shallower part of the groove and consequently engage the inner surface of the cylinder providing the requisite braking effect.
These prior art designs are expensive since they require many component parts that must be manufactured to close tolerances.
SUMMARY OF THE INVENTION
According to the present invention there is provided a locking mechanism for a pretensioner in a vehicle safety restraint, the pretensioner comprising: a cylinder; a piston mounted for movement within and along the cylinder; and a cable connected at one end to the piston and at its other end to the safety restraint, wherein the locking mechanism comprises: a locking block and means for resiliently biasing the block away from the piston toward the inside wall of the cylinder.
Preferably the block is tapered, in the form of a wedge, in that it has a surface which is inclined at an angle to the longitudinal axis of the cylinder. Advantageously the block is slidably located on an angular sloping surface of the piston, i.e. on a surface inclined at an angle to the longitudinal axis of the cylinder, and the resilient biasing means acts in the longitudinal direction. There may be a plurality of blocks, for example three wedges circumferentially spaced around the piston.
In a first embodiment, the piston surface is inclined towards the nearest inner wall of the cylinder, and in a second embodiment it is inclined towards the cable, in the direction of travel of the piston in the pretensioning direction.
According to the first embodiment the inclined surface or surfaces on the piston and on the block are such that the resilient bias, provided for example by spring pressure, tends to push the block towards the inside surface of the cylinder. Frictional forces between the block and the inside cylinder surface will enhance this effect and when the piston is urged in one direction (i.e. that opposite to the pretensioning direction), then the blocks are forced into locking contact with the wall, preventing reverse movement of the piston. Movement of the piston in the opposite direction, i.e. the pretensioning direction, is not inhibited because in this direction the friction between the inner wall of the cylinder and the block tends to push the wedge down the sloping surface and out of contact with the cylinder wall.
According to the second embodiment of the invention the inclined surface or surfaces are in the piston housing and are such that the resilient bias, e.g. spring pressure, pushes the block or blocks towards the cable to grip the cable to prevent reverse movement of the cable after pretensioning. In this embodiment the blocks preferably have teeth on their surface which faces the cable, to improve the grip.
The resilient bias may be provided by a pressure ring with one or more spring legs arranged at positions corresponding to the position of the wedge or wedges.
REFERENCES:
patent: 3942819 (1976-03-01), Schwanz et al.
patent: 4023427 (1977-05-01), Beier
patent: 4917210 (1990-04-01), Danicek et al.
patent: 5207618 (1993-05-01), Nishizawa
patent: 5358275 (1994-10-01), Fohl
patent: 5586677 (1996-12-01), Kopetzky et al.
patent: 5924730 (1999-07-01), Burrow et al.
patent: 5971488 (1999-10-01), Pedronno et al.
patent: 6068664 (2000-05-01), Meyer et al.
patent: 2364235 (1975-06-01), None
patent: 4020600 (1991-01-01), None
patent: 1417665 (1974-07-01), None
patent: 9613409 (1996-05-01), None
Breed Automotive Technology Inc.
Culbreth Eric
Drayer Lonnie
LandOfFree
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