GB1560603A

GB1560603A - Safety belt retractor

Info

Publication number: GB1560603A
Application number: GB2619/78A
Authority: GB
Original assignee: Britax Ltd
Current assignee: Britax Ltd
Priority date: 1978-01-23
Filing date: 1978-01-23
Publication date: 1980-02-06
Also published as: IT1114381B; FR2414930B3; IT7947729A0; FR2414930A1; ES240893Y; ES240893U; JPS54113120A; JPS6157222B2; DE7900774U1

Description

(54) SAFETY BELT RETRACTOR (71) We, BRITAX (WINGARD) LI MITED, a British Company of Chandler Road, Chichester, Sussex PO19 2UG, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to a safety belt retractor comprising a pair of coaxial toothed wheels which are mounted for synchronous rotation when a safety belt is extracted, one of the toothed wheels having a smaller radius than the other toothed wheel, a locking member which includes a locking portion and a sensing portion, and a socalled "inertia mechanism" which is responsive to an accelerational above a predetermined value to cause engagement between the sensing portion and the toothed wheel of smaller radius whereby the locking portion is caused to engage and to lock the toothed wheel of larger radius, the locking member being pivoted about an axis outside the radius of the latter toothed wheel.

In a known safety belt retractor of the latter type, the sensing portion phases the locking portion into correct engagement with a space between two adjacent teeth of the larger wheel. Such phasing avoids collisions between the tip of the locking portion and the teeth of the wheel. However, if contact is maintained between the sensing portion and the smaller wheel after the locking portion fully engages the larger wheel, the sensing portion will be loaded by the torque on the safety belt storage shaft.

The sensing portion is usually an arm and there is a risk that the tip of the arm will, in time, snap off due to fatigue. If this occurs, the retractor will not be locked after the inertia mechanism responds to sudden vehicle deceleration. This highly dangerous situation must be avoided to provide adequate safety for the vehicle occupant.

One attempt to mitigate this problem depends on using a flexible sensing portion or arm for resiliently absorbing any load imposed thereon when the locking portion fully engages the larger wheel. However, this does not solve the problem since there is still an element of risk that the tip of the flexible portion or arm will snap off, or become deformed due to continued flexing and fatigue. Whether a rigid, or flexible arm is used, the above-mentioned risks increase if there is any movement. strain or wear which has the effect of advancing the rotation of the larger wheel before it is stopped by the tip of the locking portion or arm, thereby increasing the load of flexible portion or arm.

There is also usually a degree of slackness in the components of the retractor, such as bearing play, as in most mechanical linkages, this slackness being taken up under load. Moreover, some relative movement between the components may occur due to tne resilience or deformation of plastic bearings used in the retractor, this is usually more prevalent to wear and it can adversely effect the operation of the retractor when the sensing portion or arm is under heavy load.

The present invention solves the above problem by providing a safety belt retractor of the latter-mentioned type wherein the locking portion is fast with the sensing portion, and the locking portion is spaced from the sensing portion so that a gap exists between the engagement surfaces of the sensing portion and the toothed wheel of smaller radius when the locking portion is fully engaged with the toothed wheel of larger radius.

The locking and sensing portions can be respective arms of a bell crank lever and the sensing portion or arm is preferably lighter than the locking portion or arm. For example, the sensing portion can be made of plastics material, such as acetal resin and be keyed to the locking portion, which may be made of metal, on a common fixed shaft.

In a position of rest (i.e. under no accelerational or decelerational forces), the sensing portion is closer to the axis of rotation of the toothed wheels than the locking portion. For example, when the locking portion engages and locks the larger toothed wheel, if the distance measured radially from the axis of rotation to the tip or engagement surface of the sensing portion is d, then the radial distance to the tip or engagement surface of the locking portion is greater than d, for example, 1.ld to 1.5d. This creates a velocity ratio between the sensing and locking portions whereby the tip or engagement surface of the locking portion has a component of movement over a shorter distance, in a direction tangential to the teeth of the larger wheel, than the component of movement of the sensing portion, in a direction tangential to the teeth of the smaller wheel. This velocity ratio may be achieved with either a bell crank lever having sensing and locking arms, or a straight lever with sensing and locking portions at different radial distances from the lever pivot axis.

An advantage of the latter velocity ratio, at least with a bell crank lever, is that if there is any wear in the bearings which respectively support a belt storage shaft and the bell crank lever, which wear effectively moves apart the centres of rotation of said shaft and said lever, there is a tendency for said gap to increase between the engagement surfaces of the sensing portion and the respective tooth of the smaller wheel.

Suitably, the tip of the locking portion or arm and the teeth of the larger wheel are matingly shaped so as to facilitate engagement. For example, each tooth on the wheel may have the leading edge (engaged by the locking portion) wbhich is substantially radial to the axis of wheel rotation, and a trailing edge which makes an angle of approximately 45C with the leading edge.

The apex of the included angle between said leading and trailing edges and the corresponding corner of the V-shaped end of the locking portion are preferably rounded.

The safety belt retractor of the preferred embodiment of the invention comprises a shaft including a safety belt storage portion; a first toothed wheel fast with said shaft; a second toothed wheel rotatably mounted on an extension of said shaft; and a third toothed wheel axially displaceable on said shaft extension but mounted for rotation with said shaft, said third toothed wheel being of a smaller diameter than said first toothed wheel. Biassing means urges said third toothed wheel into engagement with said second toothed wheel whereby said second and third toothed wheels normally rotate together with said shaft when the belt is extracted slowly. The second and third toothed wheels have a camming arrangement which operates to displace the third toothed wheel axially on the shaft extension when the second toothed wheel lags behind rotation of the third toothed wheel, due to its inertia, when the belt is suddenly extracted. The axial displacement of the third toothed wheel brings it to a position to engage a sensing portion of a locking member which is pivoted outside the diameter of said first toothed wheel, the locking member having a locking portion which engages the first toothed wheel, when the locking member pivots, to lock the shaft of the retractor. The sensing and locking portions are fast on a common shaft which is pivoted outside the diameter of the first toothed wheel. An inertia mechanism is provided, which responds above a predetermined accelerational force, to cause a pawl to engage the second toothed wheel and prevent it from rotating with the shaft thereby causing the third toothed wheel to be axially displaced by the camming arrangement.

This leads to engagement between the sensing portion and the third toothed wheel wheel and hence locking of the first toothed wheel by the locking portion. When the locking portion fully engages the teeth of the first toothed wheel, there is a gap between the engagement surfaces of the sensing portion and the respective tooth of the third wheel so that no load is exerted on the sensing portion. The third toothed wheel, which is axially displaceable on the shaft extension, is preferably much lighter than the second toothed wheel which is rotatably mounted on the shaft. For exam ple, the third toothed wheel may be made of plastics material, such as acetal resin, and be in the form of a thin disc from the surface of which its teeth project in the axial direction of said shaft. On the other hand, the second toothed wheel may be made of metal and be several times as thick as the third teethed wheel. The second toothed wheel needs to be relatively massive since it is intended to lag when the shaft rotates rapidly due to sudden belt extraction. It is also preferable to provide a relatively strong second toothed wheel, the teeth of which directly engage the pawl which is moved by the inertia mechanism, for example, a so-called ball-insaucer mechanism. However, the main advantage of providing a relatively light third toothed wheel is in reducing the interval between the onset of a force which operates the inertia sensitive mechanism (e.g. when the vehicle decelerates) and the instant at which the first toothed wheel, and hence the safety belt storage shaft, is locked against rotation. In this respect, it is advan tageous to reduce the weight of the linkage between the inertia mechanism and the locking mechanism of the retractor. There is a further advantage associated with retractors in which a toothed wheel is displaced axially of the belt storage shaft in response to the inertia mechanism. Such an axially displaced toothed wheel is relatively massive in some known retractors and the axial movement is adversely affected by the position of the retractor in the vehicle. for example, the retractor may be fitted so that said axial displacement is against the direction of vehicle movement. In such a case, when the vehicle decelerates, the decelarational forces act on the massive toothed wheel and reduce its speed of axial displacement. This reduces the speed of locking the retractor. However, in the preferred embodiment of the invention the third toothed wheel is a relatively light construction, compared with the prior art (and the mass of the second toothed wheel) and it is much less affected by vehicle decelerational forces when it is axially displaced counter to the direction of vehicle movement. The camming engagement between the second and third toothed wheels can be provided by arcuate cams or ramps on one of the toothed wheels which engage corresponding arcuate slots or recesses in the other one of the toothed wheels. This provides a so-called "belt sensitive" locking mechanism wherein the retractor is locked when the safety belt is suddenly extracted. The third toothed wheel is suitably keyed to the shaft extension to enable its axial movement. When the safety belt is suddenly extracted, the third toothed wheel rides over the cams or ramps and is thereby axially displaced on keys on the shaft extension and moves away from the second toothed wheel. A spring mounted on the shaft extension, between the first and third toothed wheel, is provided for returning the third toothed wheel to its starting position. All of the toothed wheels, the inertia mechanism and Locking mechanism, together with a rewinding spring attached to one end of the belt storage shaft, are suitably mounted in a housing adjacent one end of the belt storage shaft.

A preferred embodiment of the invention will now be described with reference to the accompanying drawings, in which; Figure 1 is a sectioned side elevation, on line aa of Figure 2, of a safety belt retractor according to the invention Figure 2 is a side elevation of the retractor with an end cover and rewinding spring assembly removed, Figures 3-5 each illustrate a pawl locking device and a toothed wheel for locking the retractor, the views illustrating different stages in a locking sequence. and Figure 6 shows the effect of bearing wear.

Referring to Figure 1, the safety belt retractor comprises a reel frame 1 in which a first shaft 2 is rotatably mounted in special bushes 3, 4 supported by respective frame members. Shaft 2, which is made of metal has a hollow which contains a plastics pin 2' for retention of the webbing of a safety belt (not shown), this pin being retained in a substantially parallel portion of the hollow of shaft 2 by means of a thin conical flange.

The disc 5 covers the end of bush 3 and is retained in position by a number of stops 6 on shaft 2. The cover 7 houses a rewinding spring 8 and a reel locking mechanism adjacent the left hand member 1' (as illustrated) of the frame 1. One end of the spring 8 is retained in a formed recess 9 in cover 7, the inner end of the spring 8 being located in slots 10 at one end of shaft 2.

The locking mechanism comprises a first ratchet type wheel 11 preferably made of metal, which is made fast with shaft 2 by keys or teeth 11'. Wheel 11, and hence the shaft 2, can be locked by a locking portion or lever arm 12 (see Figure 2) of a pawl locking device including a bell crank lever 29. This lever 29 is pivotally mounted on a shaft 13 supported by the same frame members which support the shaft 2.

A second ratchet-type wheel 14, preferably made of metal and having a predetermined mass, is rotatably mounted a part 2" of shaft 2 having a reduced diameter. Its teeth are engageable by a pawl 15 of a known "ball-in-saucer" inertia sensitive mechanism 16. This mechanism is well known wherein the ball 17 rides up the sloping side of the saucer 18, when a predetermined acceleration is exceeded to raise the pawl 15 into engagement with a rotating toothed wheel. In this case, pawl 15 engages the teeth of tPe second toothed wheel 14 whereby further rotation with shaft 2 is prevented. Wheel 14 normally rotates with shaft 2 by virtue of its engagement with a third ratchet-type wheel 19 as described below.

The third toothed wheel 19, which is preferably made of plastics, such as acetal resin, and is thinner and much lighter than wheel 14, is axially displaceable on the reduced diameter part 2" of shaft 2 on at least one keyway or spline 20. The keyway or spline 20 enables axial displacement of wheel 19 but holds it fast for rotation with shaft 2". The wheel 19 is biased towards the wheel 14 by a coil compression spring 21.

Spring 21 is located on shaft 2" between wheel 11 and wheel 19.

Wheel 19 has a ring of teeth 22 which extend axially (with respect to shaft 2) towards wheel 11. The wheel 19 is, in a rest position, housed in a recess 14' in wheel 14 and it has at least a pair, preferably four, arcuate slots or recesses 24 which co-operate with arcuate cams or ramps 25 circumferentially spaced and fixed to an inner face 26 of the wheel 14. The cams 25 normally engage the slots 24, due to the action of spring 21, whereby wheel 19 drives wheel 14 when shaft 2 is rotated on withdrawing or storing a safety belt (not shown). However, the mass of wheel 14 relative to wheel 19 and the shape of cams 25 are such that sudden belt withdrawal causes the slots 24 to ride over the cams, due to the inertia of wheel 14, thereby axially displacing wheel 19 towards wheel 11 against the bias of spring 21. If either the wheel 14 is prevented from rotating (by the inertia sensitive mechanism 16), or the wheel 19 lags with respect to wheel 14 (due to the belt withdrawal sensitive mechanism) the wheel 19 is axially displaced on the shaft 2" so that one of its teeth 22 engage a tooth 27 on the other arm 28 of the bell crank lever 29. This causes the lever 29 to pivot on its shaft 13 whereby the arm 12 is moved between adjacent teeth on the wheel 11. This is described in more detail below, with respect to Figures 3 - 5.

Figure 3 shows the situation with a retractor when normally worn and not subject to any decelerational force above a value which would operate the shaft locking mechanism. The wheel 19 is free to rotate with respect to arm 28 of the bell crank lever 29 and one of the teeth 22 is shown passing by the tooth '7 of the arm 28. The wheel 19 would rotate in this way when, for example, the wearer of the safety belt voluntarily leans forward. It can be seen that the arm 12 is clear of the peripheral teeth on wheel 11 which rotates together with wheel 19.

In Figure 4. either the inertia sensitive mechanism 16 or the belt withdrawal sensitive mechanism which employs wheel 14 and 19 has responded and has caused axial displacement of the wheel 19 towards the arm 28. The tooth 27 has engaged one of the teeth 2 of wheel 19 whereby further rotation of wheel 19 causes lever 29 to rotate anticlockwise on its shaft 13.

As shown in Figure 5, the lever 29 has rotated to a stage where the end of arm 12 is fully engaged with a space 30 between adjacent teeth on wheel 11. At this point, a small gap or clearance 31 exists between tooth 27 and the adjacent tooth 22 of the wheel 19. The gap or clearance 51 ensures that no load is transferred to the sensing arm 28 when the wheel 1' is fully locked by arm 12.

As shown in Figure 2, the angle between the arms 12 and 28 of lever 29 is less than 90" (i.e. about 30 - 40 ). Both arms also extend radially from the same side of shaft 13 so that they tend to disengage. by gravity from the respective toothed wheels 11 and 19 after the accelerational force which actuates inertia sensitive mechanism 16 has fallen below a predetermined minimum value and the tension on a safety belt attached to the retractor has been released. Such gravity return is also assisted by the position of arm 12, which is the heaviest being made of metal, because it extends almost horizontally when the retractor is fitted in the upright position shown in Figure 2 in a vehicle. The arm 28 and the axially displaceable wheel 19 are both made of plastics, such as acetal resin, to improve the response (i.e. locking speed) to actuation by inertia sensing mechanism 16. The teeth on wheel 19 have a profile, seen in the plane of Figure 1, which is substantially a right angled triangle. The leading edge of each tooth (in the direction of rotation of wheel 19 when the safety belt is withdrawn) is substantially horizontal, and the trailing edge is inclined at approximately 45" to the leading edge. The tooth 27 of arm 28 is correspondingly shaped so that it is captured by one of the rotating teeth on wheel 19 when axially displaced.

Referring to Figures 3 - 5, it can be seen that the diameter of the axially displaceable sensing wheel 19 is less than the diameter of the locking wheel 11. The angle between the arms 12 and 28 is also less then 90".

Furthermore, the shaft 13, providing the pivot for the bell crank lever 29, is outside the diameter of the locking wheel 19. The geometry of the construction shown in Figures 3 - 5 is such that the tooth 27 is caused to move on a path which is almost parallel with a tangent to the outer ring of teeth 22 of wheel 19. This is indicated by the arrow 32. The end 33 of arm 12 is simultaneously caused to move towards the ring of teeth on wheel 11 and it has a component of movement 34 in the direction of arrow 32.

As tooth 27 is nearer the axis of rotation 35 of the wheels 11, 19 than the end 33 of arm 12, the distance travelled, in the direction of arrows 32 and 34. by tooth 27 is greater than that travelled by end 33. In other words, there is a velocity ratio between the components of movement of tooth 27 and the end 33 of arm 12 with respect to the direction of arrows 32 and 34 which are parallel to tangents to wheels 11 and 19 at the point of contact teeth 22 and 27.

Preferably, the arm 28 is made of more resilient material (such as acetal plastics or resin) than the material of arm 12 (sudh as metal). The arms 12 and 28 are keyed together by a spline or tooth 13'. Alternatively, the arms 12 and 28 may be integral and made of the same material.

Referring to Figure 6, the drawing shows that there is an increase in the gap 31 if there is any play, deformation or wear in bearing 3 (Figure 1) which supports the belt storage shaft 2", and in the bearing surfaces or a bearing (not shown) which support the bell crank lever 29 (Figure 2) on shaft 13. As shown in Figure 6, the end 33 of arm 12 is fully engaged in the space 30 between adjacent teeth on wheel 11. The torquf exerted by wheel 11 will cause a force to act radially, in the direction of the broken line 37, on shaft 2". Any play, deformation or wear in the bearing which supports shaft 2", enables shaft 2" to move from its original position (shown by the broken circular outline) to a new position (shown by the full circular outline) resulting in an effective displacement of the axis of rotation of shaft 2" from point 35 to point 35'. A similar effect in the bearing surfaces or a bearing which supports the bell crank lever 29 on shaft 13 will enable the bell crank lever 29 to be displaced, by a force acting through the arm 12, (and as shown by the broken and full circular outlines) to displace the axis of rotation form point 36 to point 36'.

Such effects result (under load) in moving the axes of rotation of wheel 11 and lever 29 further apart. However, the geometry is such that the gap 31 increases between the tooth 27 of arm 28 and the respective tooth 22 of wheel 19. This is due to the velocity ratio, in the directions of the arrows 32, 34 as described above with reference to Figure 4. In other words, as tooth 27 is closer to the centre of rotation 35, 35' than the tip 33 of arm 12, a few degrees of extra rotation of the bell crank lever 29 causes less effect between tip 33 and the space 30 than between the tooth 27 and the tooth 22.

WHAT WE CLAIM IS: 1. A safety belt retractor comprising a pair of coaxial toothed wheels which are mounted for synchronous rotation when a safety belt is extracted, one of the toothed wheels having a smaller radius than the other toothed wheel, a locking member which includes a locking portion and a sensing portion, and an inertia mechanism which is responsive to an acclerational above a predetermined value to cause engagement between the sensing portion and the toothed wheel of smaller radius whereby the locking portion is caused to engage and to lock the toothed wheel of larger radius, the locking member being pivoted about an axis outside the radius of the latter toothed wheel, the locking portion being fast with the sensing portion, and the locking portion being spaced from the sensing portion so that a gap exists between the engagement surfaces of the sensing portion and the toothed wheel of smaller radius when the locking portion is fully engaged with the toothed wheel of larger radius.

2. A safety belt retractor according to claim 1 wherein the locking and sensing portions are respective arms of a bell crank lever and the sensing portion or arm is lighter than the locking portion or arm.

3. A safety belt retractor according to any one of the preceding claims wherein the sensing portion is keyed to the locking portion on a common fixed shaft.

4. A safety belt retractor according to any one of the preceding claims wherein each tooth of the toothed wheel of larger radius has a leading edge which is substantially radial to its axis of rotation and a trailing edge which makes an angle of approximately 45" with the leading edge, and the apex of the included angle between said leading and trailing edges and the corresponding corner of a V-shaped end of the locking portion are rounded.

5. A safety belt retractor according to any one of the preceding claims wherein the toothed wheel of larger radius is a first toothed wheel fast with a shaft on which the safety belt is stored, a second toothed wheel is rotatably mounted on an extension of said shaft, and said toothed wheel of smaller radius is a third toothed wheel which is axially displaceable on said shaft extension but is mounted for rotation with said shaft extension; the retractor including biassing means to urge said third toothed wheel into engagement with said second toothed wheel. whereby said second and third toothed wheels normally rotate together with said shaft when the belt is extracted slowly, and said second and third toothed wheels having a camming arrangement which operates to displace the third toothed wheel axially on the shaft extension when the second toothed wheel lags behind rotation of the third toothed wheel, due to its intertia, when the belt is extracted suddently, the axial displacement of the third toothed wheel enabling the engagement to occur between it and the sensing portion of the locking member to cause the locking portion to engage and to lock the first toothed wheel.

6. A safety belt retractor according to claim 5 wherein said inertia mechanism is provided with a pawl, which is engageable with said second toothed wheel, when a predetermimed acceleration is exceeded, whereby said second toothed wheel is prevented from rotating with said third toothed wheel and said third toothed wheel is axially displaced on said shaft extension to engage the sensing portion and hence cause the locking portion to engage and lock the first toothed wheel.

7. A safety belt retractor according to claim 5 or 6 wherein the camming arrangement comprises arcuate cams or ramps on one of said second or third toothed wheels which pass through corresponding arcuate slots or recesses in the other one of said second or third toothed wheels.

8. A safety belt retractor according to any one of claims 5 - 7 wherein said third toothed wheel is much lighter than the second toothed wheel.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. shown in Figure 6, the end 33 of arm 12 is fully engaged in the space 30 between adjacent teeth on wheel 11. The torquf exerted by wheel 11 will cause a force to act radially, in the direction of the broken line 37, on shaft 2". Any play, deformation or wear in the bearing which supports shaft 2", enables shaft 2" to move from its original position (shown by the broken circular outline) to a new position (shown by the full circular outline) resulting in an effective displacement of the axis of rotation of shaft 2" from point 35 to point 35'. A similar effect in the bearing surfaces or a bearing which supports the bell crank lever 29 on shaft 13 will enable the bell crank lever 29 to be displaced, by a force acting through the arm 12, (and as shown by the broken and full circular outlines) to displace the axis of rotation form point 36 to point 36'. Such effects result (under load) in moving the axes of rotation of wheel 11 and lever 29 further apart. However, the geometry is such that the gap 31 increases between the tooth 27 of arm 28 and the respective tooth 22 of wheel 19. This is due to the velocity ratio, in the directions of the arrows 32, 34 as described above with reference to Figure 4. In other words, as tooth 27 is closer to the centre of rotation 35, 35' than the tip 33 of arm 12, a few degrees of extra rotation of the bell crank lever 29 causes less effect between tip 33 and the space 30 than between the tooth 27 and the tooth 22. WHAT WE CLAIM IS:

1. A safety belt retractor comprising a pair of coaxial toothed wheels which are mounted for synchronous rotation when a safety belt is extracted, one of the toothed wheels having a smaller radius than the other toothed wheel, a locking member which includes a locking portion and a sensing portion, and an inertia mechanism which is responsive to an acclerational above a predetermined value to cause engagement between the sensing portion and the toothed wheel of smaller radius whereby the locking portion is caused to engage and to lock the toothed wheel of larger radius, the locking member being pivoted about an axis outside the radius of the latter toothed wheel, the locking portion being fast with the sensing portion, and the locking portion being spaced from the sensing portion so that a gap exists between the engagement surfaces of the sensing portion and the toothed wheel of smaller radius when the locking portion is fully engaged with the toothed wheel of larger radius.

9. A safety belt retractor according to

claim 8 wherein said third toothed wheel is in the form of a thin disc from the surface of which teeth project in the axial direction of said shaft, the disc being made of plastics material, the second toothed wheel being made of metal.

10. A safety belt retractor substantially as herein described with reference to the accompanying drawings.