GB2251369A

GB2251369A - Ratchet and clamping mechanism in a seat belt tightening system

Info

Publication number: GB2251369A
Application number: GB9202576A
Authority: GB
Inventors: Hiroshi Tabata; Shizuyo Nakao; Yoshihiko Kinoshita; Atsushi Katsuki
Original assignee: Honda Motor Co Ltd
Current assignee: Honda Motor Co Ltd
Priority date: 1988-03-11
Filing date: 1992-02-06
Publication date: 1992-07-08
Anticipated expiration: 2012-02-06
Also published as: JP2607256B2; GB2251369B; JPH01229746A; GB9202576D0

Abstract

The mechanism comprises a fixed member 13 having sawteeth 28 and a movable member 21 having complementary sawteeth 27. Moreover, the member 21 is provided with clamping elements 22, 23 for the seat belt (not shown). Normally, the member 21 is held in its disengaged position shown by the cooperation of breakable projections (29, Fig. 2) with holes 29a. However during emergency operation of the tightening system, the projections (29) become broken and the seat belt is clamped by the relative movement of the elements 22, 23 and is tightened by successive engagement with ridges 24a, 24b, 24c on element 23 during clockwise rotation of member 21. When the tightening operation is finished, the tension in the tightened belt causes the member 21 to move radially to engage the sawteeth 27, 28 thereby prevent reverse rotation of member 21. <IMAGE>

Description

RATCHET MECHANISM The present invention relates to a ratchet mechanism for preventing a reverse rotation of a rotary mechanism, which in particular can bemused in vehicle seat belt tightening systems.

A vehicle seat is typically equipped with a seat belt to restrain the vehicle occupant from being thrown forward in case of a vehicle crash, and such a seat belt is sometimes provided with an emergency locking retractor (which is referred to as ELR device hereinafter) for locking the winding spool of a seat belt in case of a sudden stop or a crash, but without restraining the movement of the occupant under normal conditions.

An ELR device typically detects a deceleration level indicative of a vehicle crash or a rapid pay out of the seat belt before it locks up the winding spool in a very short period of time. Therefore, if the amount of the slack of the seat belt in the initial stage is excessive, there is a possibility that the seat belt may be inadequate to restrain the occupant to a necessary extent.

Furthermore, these ELR devices are typically provided with a reversal preventing device consisting of a ratchet wheel and a ratchet pawl for permitting free unwinding and winding of the seat belt under normal condition and locking up the winding spool only in case of an emergency (refer to Japanese Patent Publication No. 53-21574 and Japanese Utility Model Publication No. 53-25943). However, according to such conventional arrangements, the ratchet pawl is urged into engagement with the ratchet wheel by a spring to prevent the rotation of the ratchet wheel in the reverse direction, and the reliability of such a reversal preventing device is inevitably much dependent on elasticity of the spring which causes the necessary movement of the ratchet pawl.Therefore, the operation of the reversal preventing device is not entirely free from the chance of failure if the ratchet pawl should be jammed or mechanically frozen.

According to the present invention there is provided a ratchet mechanism comprising a fixed engagement member and a movable engagement member which is movable relative to the fixed engagement member between a released position and an engaged position, the engagement members having teeth which are cooperable when the movable member is in an engaged position, to permit displacement of the movable engagement member in one direction relative to the fixed engagement member but to prevent displacement of the movable engagement member in an opposite direction, in which the movable engagement member is provided with clamping means for clamping an elongate flexible member, whereby movement of the movable engagement member into the engaged position is achieved by tension applied to the elongate flexible member clamped by the clamping means.

The movable engagement member may be mounted for rotation relative to the fixed engagement member, and the clamping means provided on the movable engagement member may be adapted to clamp an elongate flexible member in the form of a seat belt.

The fixed engagement member may comprise a frame part having an opening provided with sawtooth shaped inner teeth and the movable engagement member may comprise a gear member which has saw tooth shaped outer teeth, the movable engagement member being positioned in the opening so that, in the released position, rotation of the movable engagement member in either direction is not opposed by interference between the inner and outer teeth. When the inner and outer teeth are in meshing engagement, rotation of the movable engagement member in the direction corresponding to paying out of a seat belt is prevented.

The movable engagement member may be retained in the released position by means of a breakable member which is adapted to be broken upon activation of the clamping means.

For a better understanding of the present invention and to show how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 is a perspective view of a seat belt arrangement; Figure 2 shows a partly sectioned view of a seat belt tightening system for the arrangement of Figure 1; Figures 3 and 4 show right and left side views of the seat belt tightening system shown in Figure 2; Figure 5 is a sectional side view taken along line V-V of Figure 2; Figures 6 to 8 are sectional views of a seat belt tightening system showing the process of taking up slack'on the seat belt with a seat belt tightening unit; and Figures 9 to 11 are schematic side views showing the operation of a device in accordance with the present invention for preventing the reverse rotation of the seat belt tightening unit.

Figure 1 shows the structure surrounding a seat belt system,to which the present invention is applied, and the seat belt 3 extending upwardly from a webbing retractor 2 fixedly attached to a lower part of a center pillar 1 of a passenger compartment is passed through a through ring 4 attached to an upper part of the center pillar 1, and passed downward therefrom.

The free end portion 6 of the seat belt 3 is attached to a rear part of a side portion of the seat 5. A tongue plate 7 is provided in the part of the seat belt 3 extending between the through ring 4 and the end portion 6 so as to be slidable along the seat belt 3.

When the vehicle occupant seated in the seat 5 pulls the seat belt 3 out of the webbing retractor 2 and engages the tongue plate 7 with a buckle 8 provided on the side of the seat 5 opposite to the anchor point of the end portion 6 of the seat belt 3, the seat belt 3 will be passed over the shoulder, chest and waist of the vehicle occupant.

As shown in Figures 2 through 4, the webbing retractor 2 is provided with an ELR unit 9 for permitting the pay-out and take-up of the seat belt 3 under normal condition, a seat belt tightening unit 10 for removing slack from the seat belt 3 in case of a vehicle crash, a drive unit 11 for supplying rotational power to the seat belt tightening unit 10, and a deceleration sensor 12 for detecting the occurrence of a vehicle crash.

The ELR unit 9 imparts a rotational force to the webbing winding spool for winding the seat belt 3 thereon by means of a spring incorporated therein in the same way as a conventional ELR device, and, in particular in case of a sudden deceleration, prevents the pay-out of the seat belt 3 by means of a conventional inertia locking mechanism not shown in the drawings.

The casing 13 of the seat belt tightening unit 10 is made by bending metallic plate, and one of its mutually opposing side walls 13a rotatably supports a pulley 15 via a journal bearing 14 consisting of a synthetic resin having a self-lubricating property. A wire 16 is passed around this pulley 15, and one of the ends of the wire 16 is connected to the drive unit 11 while the other end thereof is connected to a suitable location of the pulley 15.

The drive unit 11 comprises a cylinder 17 extending in a tangential direction with respect to the pulley 15, a piston 18 slidably received in the cylinder 17, and a propellant 19 accommodated in the base end of the cylinder 17 for applying a propelling force to the piston 18 when ignited, and is securely attached to the upper end of the casing 13 of the seat belt tightening unit 10. And, by the action of the deceleration sensor 12 integrally incorporated in the base end of the cylinder 17, the propellant 19 is ignited for explosion, and the resulting combustion pressure causes the piston 18 to be pushed through the cylinder 17 and the wire 16 by to be drivingly pulled, thereby drivingly rotating the pulley 15.

The other side wall 13b of the casing 13 is provided with an opening 20 for receiving a ratchet wheel 21 so as to be rotatable therein without any interference as described hereinafter. A fixed clamp member 22 having an elliptic cross section is interposed between the opposing surfaces of the pulley 15 and the ratchet wheel 21 so as to extend between the two opposing side walls 13a and 13b and so as to be slightly displaced from the center of the pulley 15.

further, a moveable clamp member 23 is rotatably interposed between the pulley 15 and the ratchet wheel 21 by way of a pivot shaft 23a so as to oppose the fixed clamp member 22. Thus, the assembly consisting of the ratchet wheel 21, the clamp members 22 and 23, and the pulley 15 is rotatably supported by the journal bearing 14 in the manner of a cantilever. The external side surface of the ratchet wheel 21 is covered by a resin cover 30 having a pair of projections 29 fitted into corresponding openings 29a provided in the ratchet wheel 21. The moveable clamp member 23 is provided with three ridges 24a, 24b and 24c projecting radially from the center of the pivot shaft 23a thereof and extending laterally between the opposing two walls 13a and 13b.Each of these ridges 24a, 24b and 24c has a length along the axial direction corresponding to the width of the seat belt 3.

In initial condition, a gap 25 (Figure 3) is defined between the opposing surfaces of the fixed and moveable clamp members 22 and 23 so as to define a vertical slot through which the seat belt not shown in the drawing can pass freely. Further, the opposing surfaces of the clamp members 22 and 23 at the ELR unit end of the gap 25 are provided with a plurality of axial clamp grooves 26a and 26b extending the entire axial length thereof in a substantially complementary fashion relative to each other.

As shown ln Figure 4, three quarters of the outer periphery of the ratchet wheel 21 is provided with sawtooth shaped outer ratchet teeth 27 which are inclined rearwardly as seen along the direction of normal rotation thereof. Five eighths of the inner periphery of the opening 20 is provided with inner ratchet teeth 28 which are complementary to the outer atchet teeth 27. The inner and outer diameters of the opening 20 and the ratchet wheel 21 are determined in such a manner that the ratchet wheel 21 may rotate relative to the opening 20 with the tips of the outer ratchet teeth 27 and the inner ratchet teeth 28 barely contacting each other or entirely out of contact with each other when the ratchet wheel 21 is placed coaxially with the opening 20.

The seat belt tightening unit 10 is normally in the state shown in Figure 5, and the pay out and the take up of the seat belt 3 can be made freely through the gap 25 defined between the fixed clamp member 22 and the moveable clamp member 23. In order to maintain this state, the projections 29 provided ix side resin cover 30 of the ratchet wheel 21 are fitted into the corresponding holes 29a provided in the ratchet wheel 21. These projections 29 are adapted to be easily broken by the torque produced by the drive unit 11 when the latter is activated.

When the propellant 19 is ignited, the resulting explosive increase in pressure pushes up the piston 18.

When the piston 18 is thus driven, the wire 16 is pulled in the direction indicated by the arrow P in Figure 3, and the pulley 15, along with the ratchet wheel 21, is rotated in the direction indicated by the arrow B in Figure 6.

Thereby, the ridge 24a of the moveable clamp member 23 abuts the seat belt 3. It then follows that the moveable clamp member 23 rotates in the direction indicated by the arrow C by being pressed by the seat belt 3 until the seat belt 3 is firmly wedged between the clamp grooves 26a and 26b as shown in Figure 7.

Further rotation of the pulley 15 and the moveable clamp member 23 causes the clamp member 23 to act as a lever having a fulcrum at its rotary shaft 23a and its point of application of force at the end portion of the ridge 24a thereby further urging the clamp grooves 26b against the corresponding clamp grooves 26a of the fixed clamp member 22, whereby the seat belt 3 is pulled in the direction indicated by the arrow D as shown in Figure 8.

During this process, due to the reaction force acting upon the clamp members 22 and 23, the ratchet wheel 21 tends to be pulled downward and the projections 29 are broken. However, because the sawtooth shaped ratchet teeth 27 and 28 of the opening 20 and the ratchet wheel 21 are so selected that the outer ratchet teeth 27 and the inner ratchet teeth 28 can slip relative to each other, this permits the seat belt tightening unit 10 to rotate in the direction to take up slack from the seat belt 3. In particular, since the initial contact between the peripheral edges of the opening 20 and the ratchet wheel 21 takes place at the smooth parts of the edges where no teeth are formed, the initial rotational motion of the ratchet wheel 21 immediately after breakage of the projections 26 can be started substantially without obstruction.

This is advantageous in ensuring the quick response of the seat belt tightening unit 10.

The further the wire 16 is pulled, the more the seat belt 3 is drawn by the ridges 24a and 24b of the fixed clamp member 22 (Figure 8').

When the wire 16 is substantially completely pulled in, and the rotational torque acting upon the pulley 15 and the ratchet wheel 21 disappears, the torque arising from the tension of the seat belt 3 starts acting upon the ratchet wheel 21 so as to pull it upwardly and rotate it in the reverse direction (Figure /9). Thus, the inner ratchet tooth 28T located substantially at the top is engaged by the most adjacent outer ratchet tooth 28T. As a result, a rotational moment M acts upon the ratchet wheel 21 around the point of first engagement 27T and 28T (Figure 16). Thus, as shown in Figure 11, the outer ratchet teeth 27 in the region E located ahead of the above mentioned point are brought into meshing engagement with the corresponding inner ratchet teeth 27 so as to positively prevent the reverse rotation of the seat belt tightening unit 10.

The seat belt tightening system disclosed herein is also disclosed and claimed in our copending Patent Application No. 8905576.8 (Serial No. 2216391).

Claims

1. A ratchet mechanism comprising a fixed engagement member and a movable engagement member which is movable relative to the fixed engagement member between a released position and an engaged position, the engagement members having teeth which are cooperable when the movable member is in an engaged position, to permit displacement of the movable engagement member in one direction relative to the fixed engagement member but tu prevent displacement ot the movable engagement member in an opposite direction, in which the movable engagement member is provided with clamping means for clamping an elongate flexible member, whereby movement of the movable engagement member into the engaged position is achieved by tension applied to the elongate flexible member clamped by the clamping means.

2. A ratchet mechanism as claimed in claim 1, in which the clamping means is adapted to clamp an elongate flexible member in the form of a seat belt.

3. A ratchet mechanism as claimed in claims 1 or 2, in which the movable engagement member is mounted for rotation relative to the fixed engagement member.

4. A ratchet mechanism as claimed in claim 4, in which the fixed engagement member comprises a frame part having a opening provided with inner teeth, and the movable engagement member comprises a gear member having outer teeth which is positioned in the opening so that, in the released position, rotation of the movable engagement member in either direction is not opposed by interference between the inner and outer teeth.

5. A ratchet mechanism as claimed in claim 4, when appendant to claim 2, in which the inner and outer teeth are sawtooth shaped so as to prevent rotation of the movable member in the direction corresponding to paying out of the seat belt, when the inner and outer teeth are in meshing engagement.

6. A ratchet mechanism substantially as described herewith with reference to, and as shown in, Figures 2 to 11 of the accompanying drawings.

6. A ratchet mechanism as claimed in any one of claims 3 to 5, in which the movable engagement member is movable from the released position to .the engaged position in any radial direction and the fixed and movable engagement members are provided with smooth peripheral edge portions, at which they are brought into mutual contact in an initial stage of the operation of said clamping means.

7. A ratchet mechanism as claimed in any preceding claim in which the movable engagement member is retained in the released position by means of a breakable member which is adapted to be broken upon activation of said clamping means.

8. A ratchet mechanism substantially as described herewith with reference to, and as shown in, Figures 2 to 11 of the accompanying drawings. Amendments to the claims have been filed as follows

1. A ratchet mechanism suitable for use in vehicle seat belt tightening systems comprising a fixed engagement member and a movable engagement member which is radially movable relative to the fixed engagement member between a released position and an engaged position, the engagement members having teeth which are cooperable when the movable member is in an engaged position, to permit rotation of the movable engagement member in one direction relative to the fixed engagement member but to prevent rotation of the movable engagement member in an opposite direction, in which the movable engagement member is provided with clamping means for clamping a seat belt, wherein movement of the movable engagement member into the engaged position is achieved by tension applied to the seat belt when clamped by the clamping means.

2. A ratchet mechanism as claimed in claim 1, in which the fixed engagement member comprises a frame part having an opening provided with inner teeth, and the movable engagement member comprises a gear member having'outer teeth which is positioned in the opening so that, in the released position, rotation of the movable engagement member in either direction is not opposed by interference between the inner and outer teeth.

3. A ratchet mechanism as claimed in claim 2, in which the inner and outer teeth are sawtooth shaped so as to prevent rotation of the movable member in the direction corresponding to paying out of the seat belt, when the inner and outer teeth are in meshing engagement.

4. A ratchet mechanism as claimed in any preceding claim, in which the movable engagement member is movable from the released position to the engaged position in any radial direction and the fixed and movable engagement members are provided with smooth peripheral edge portions, at which they are brought into mutual contact in an initial stage of the operation of said clamping means.

5. A ratchet mechanism as claimed in any preceding claim in which the movable engagement member is retained in the released position by means of a breakable member which is adapted to be broken upon activation of said clamping means.