Land vehicles – Wheeled – Attachment
Reexamination Certificate
2000-05-26
2001-04-03
Dickson, Paul N. (Department: 3618)
Land vehicles
Wheeled
Attachment
C297S470000
Reexamination Certificate
active
06209916
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a load limiting device for use with a seat belt.
BACKGROUND OF THE INVENTION
Modern seat belts comprise a length of webbing arranged to pass diagonally across the torso of a vehicle occupant and generally, horizontally across the hip region of the vehicle occupant (the so-called lap portion of the belt). This is known as a three point belt system. One end of the belt webbing is firmly attached to a structural part of the vehicle, such as the floor, and the other end is attached to the spool of a retractor which itself is firmly attached to a structural part of the vehicle, usually the side, B-pillar. The retractor automatically keeps any slack in the belt wound onto the spool and thus keeps tension in the belt. Between the retractor and the other fixed point, a fastening element such as a metal tongue is fixed to the belt with which it can be fastened into a buckle which itself is attached to a fixed part of the vehicle on the other side of the seat.
A clock spring in the retractor allows pay out of webbing under the influence of relatively gentle forwardly directed inertia of the vehicle occupant, for example to allow for normal movement of the vehicle occupant such as reaching forward to activate in-car controls, glove compartments or door pockets.
In the event of a crash the sudden high forward momentum of the vehicle occupant activates a crash sensor which locks the spool against rotation and prevents forward motion of the vehicle occupant to prevent him colliding with the internal structure of the vehicle such as the steering wheel, dashboard or windscreen.
However, it has been found in high velocity crashes that the sudden locking of the seat belt can itself cause injury to the vehicle occupant due to the sudden impact of the torso with the belt webbing.
In recent years it has been proposed to introduce a load limiting effect into the seat belt system so as to allow a limited and controlled forward motion of the vehicle occupant after the retractor has locked. This decreases the forces exerted by the belt on the vehicle occupant's torso.
DISCUSSION OF THE PRIOR ART
Load limiting proposals are described in EP 0297537 wherein a plastically deformable member is used in the retractor, and particularly between the spool and inner most winding of the belt webbing. Alternative load limiting proposals are known in which crushable bushings or nuts or deformable torsion bars are placed in the retractor in the force path between the spool locking mechanism and belt webbing. These proposals are complex and expensive and require the retractor to be specially designed and constructed to incorporate them.
SUMMARY OF THE INVENTION
The present invention proposes improved, simpler and more cost effective load limiting devices for seat belts.
According to one aspect of the present invention there is provided a vehicle safety restraint comprising seat belt webbing, for restraining a vehicle occupant, the webbing being attached to a structural part of the vehicle via a load limiting device, the load limiting device comprising a container defining a flow path for a fluid, an actuator arranged within the container and operable to act on the fluid, and a restriction in the flow path of the fluid, wherein the actuator is movable within the container under the action of load transmitted to the webbing from the vehicle occupant under extreme acceleration or deceleration conditions, to move the fluid through the restriction in the flow path thereby to dissipate a predetermined portion of the load on the webbing.
According to one embodiment of the invention the actuator comprises a piston and the container comprises a cylinder, and either the piston or cylinder is attached to an end of the belt webbing and the other is attached to the structural part of the vehicle.
The restriction may comprise one or more holes in the piston itself so that under pressure fluid is forced from one part of the cylinder, on the high pressure side of the piston, to the other part of the cylinder, on the low pressure side. Alternatively, there is a feedback pipe external to the cylinder to feed fluid under pressure from the high pressure side of the piston to the low pressure side. This feedback pipe may have a further restriction or a valve. The valve may be adjustable to offer a predetermined resistance to fluid flow in dependence upon the force damping characteristics required for the particular seat belt. The valve may be actively controllable, for example in response to a gauge constantly monitoring the pressure of the fluid in the cylinder. In this way the load perceived by the vehicle occupant can be actively tailored, not only to the vehicle concerned, but also to the circumstances which generated the load: the severity of the crash pulse, the weight of the vehicle occupant and the activation of a secondary restraint such as an airbag, or the occurrence of a second crash.
The piston may be arranged so that the cross sectional area which it presents to the fluid is variable. For example, it can be formed of a series of concentric tubes which are picked up by the core piston with increasing belt payout as the load increases. This increases the predetermined load at which the load limiting effect comes into operation and thus increases the restraining effect of the belt with increasing belt extension. This is particularly appropriate for example, in a severe crash and/or with a heavy vehicle occupant. In this case it would be important to ensure that the occupant is stopped completely from his forward motion before the end of the load limiting device is reached.
On the other hand, there are circumstances in which it is desirable to decrease the restraining effect as the crash pulse progresses. This can be done by decreasing the predetermined load at which load limiting becomes operational as the belt payout increases. For example, if an airbag is fitted to the vehicle, then that will take over the restraining effect and stopping the seat belt completely at an early stage of the crash pulse is not important. In this case the piston can be arranged to lose sections of its effective cross section as it travels down the cylinder. The exact arrangement can thus be easily adapted to obtain the required effect.
In an alternative embodiment the actuator is a rotary paddle or vane member or an array of such members, mounted for rotation in a housing containing the fluid. This embodiment may, for example, take the general form of an eccentric vane pump or a peristaltic pump or a swash plate pump, though many other suitable forms of pump arrangement will be evident to those skilled in the art. In each case the fluid flow path within the pump housing is arranged with one or more restrictions to absorb some of the energy of a crash pulse.
REFERENCES:
patent: 2680476 (1954-06-01), Saffell
patent: 3343874 (1967-09-01), Hildebrandt
patent: 3889969 (1975-06-01), Otani
patent: 5037132 (1991-08-01), Borlinghaus et al.
patent: 568327 (1993-11-01), None
Blackadder David
Downie Andrew
Harte Joe
Park Andrew
Rees Elizabeth
Breed Automotive Technology Inc.
Dickson Paul N.
Drayer Lonnie
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