Seat belt retractor

Details Seat belt retractor Seat belt retractor

2000-03-01

2001-07-24

Nguyen, John Q. (Department: 3653)

Winding, tensioning, or guiding

Reeling device

With spring motor

C280S805000, C280S807000

Reexamination Certificate

active

06264127

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a seat belt retractor having load limiting capability.
BACKGROUND OF THE INVENTION
Load limiting seat belt retractors are used to reduce the effect on a vehicle occupant of forces generated during a crash. They are designed to absorb some of the initial impact forces to minimize injury caused to the vehicle occupant by interaction with the safety restraint itself, for example by sudden impact of the vehicle occupant with the seat belt webbing. In a severe crash the effect of the vehicle occupant's forward momentum being stopped by a relatively narrow band of webbing can cause injuries. The initial forces of a crash on the vehicle occupant have been reduced by load limiting seat belt retractors and particularly those incorporating torsion bars in the seat belt retractor. Torsion bars are connected in the force transmission path and twist under the forces of a crash thus allowing a limited payout of seat belt webbing and dissipating some of the initial energy of the crash pulse. However, they do not break and when the initial peak of the crash pulse is passed, then the torsion bar holds fast and the seat belt retractor locks against webbing payout in the normal way, restraining the vehicle occupant against impact with internal parts of the vehicle.
The ideal load profile of a load limiting seat belt retractor is an initial steep rise in the force of the torque with a smooth transition to a generally flat, i.e. constant force, line. In practice the load profile tends to rise too slowly and to exhibit undesirable peaks and troughs of torque, with the forces rising over an undesirably long period instead of reaching a plateau quickly. This is due to the combination of elastic and plastic deformation exhibited by a torsion bar.
One arrangement to improve the load profile is to introduce shear pins between the spool of the seat belt retractor and the torsion bar. This raises the gradient of the initial part of the force curve due to the additional force needed to shear the pins. The force is dependent upon the rigidity of the pins.
However shear pins are extra components and increase production times and costs. They must be manufactured to close tolerances to produce the desired performance.
DISCUSSION OF THE PRIOR ART
WO 96/32303 A1 shows shear pins in FIG. 1.
U.S. Pat. No. 5,820,058 shows shear pins in FIG. 1.
U.S. Pat. No. 5,779,177 shows a deformable portion in FIGS. 1 to 4.
SUMMARY OF THE INVENTION
The present invention aims to achieve an improved load profile in a load limiting seat belt retractor using less components and at lower cost.
According to the present invention there is provided a seat belt retractor comprising a spool on which seat belt webbing is wound, arranged for rotation about its longitudinal axis, for payout and winding in of seat belt webbing, a torsion bar coaxial with the spool and having one end fixed to the spool, a ratchet fixed to the other end of the torsion bar, a toothed wheel fixed to the spool, to rotate with the spool, a toothed wheel fixed to the spool, to rotate with the spool, a pivoting lock bar extending across the length of the spool, having at least one pawl fixed at each end, to engage with the toothed wheel and with the ratchet respectively, wherein the pawl on the spool side is arranged to be weaker than the other pawl so as to shear under a predetermined force to allow the spool to rotate and the torsion bar to twist.
At the onset of a crash, the lock bar pivots to bring the locking teeth into engagement with the toothed wheel and with the ratchet respectively, thus locking the spool against rotation and against payout of webbing. Thus the vehicle occupant is securely restrained against forward movement at the earliest possible moment in the crash.
As the crash pulse progresses and the forces increase, the force on the locking pawls of the lock bar increases. At a predetermined force level the weaker pawl on the toothed wheel (spool) side of the lock bar shears and allows the toothed wheel, and thus the spool, to rotate under the force of the forward momentum of the vehicle occupant. Rotation of the spool allows limited additional payout of seat belt webbing, and thus a limited additional controlled forward movement of the vehicle occupant, thus reducing the force transferred to the vehicle occupant from the seat belt. Rotation of the toothed wheel allows rotation of one end of the torsion bar while the other end of the torsion bar is held fast by the other, locking, pawl engaging the ratchet. The torsion bar twists under the force of the crash pulse and absorbs some of the energy of the crash, until the force of the crash has dissipated to a level less then that required to twist the bar. At this stage the spool is locked and no further webbing payout occurs.
Optionally more than one shearable tooth is arranged on the spool side pawl and the teeth may shear simultaneously or in staggered arrangement so as to more accurately define the absorbed forces.
The invention has the benefit of bringing double sided locking of the spool into effect at the beginning of a crash pulse in a load limiting seat belt retractor and thus ensuring stronger initial locking of the spool, and a steeper force gradient at the onset of the crash pulse.
The shearable lock bar pawl, on the ratchet, i.e. spool, side of the lock bar is preferably die cast since this method of manufacture allows the load level at which the tooth breaks to be more accurately determined.
On the ratchet side of the lock bar, there may be one or more than one locking tooth on the pawl and these must be strong enough not to shear under the crash forces.
The shearable lock bar pawl may be inherently weaker because of its material or its construction. It may be constructed to be relatively thin or may be weakened by a notch. The design must be such that the fracture load level is repeatable and predictable.


REFERENCES:
patent: 5779177 (1998-07-01), Kielwein
patent: 5820058 (1998-10-01), Hirzel et al.
patent: 0297537 (1989-01-01), None
patent: WO96/32303 (1996-10-01), None

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