GB1586594A

GB1586594A - Safety belt retractors

Info

Publication number: GB1586594A
Application number: GB2409577A
Authority: GB
Original assignee: Britax Wingard Ltd
Current assignee: SMR Automotive Mirrors UK Ltd
Priority date: 1978-05-09
Filing date: 1978-05-09
Publication date: 1981-03-25

Description

(54) IMPROVEMENTS IN SAFETY BELT RETRACTORS (71) We, BRITAX (WINGARD) LIMITED, 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. In a typical safety belt retractor having a spring to rewind a safety belt on a storage reel or shaft, the reel or shaft is locked in response to movement of an inertial mass due to vehicle acceleration, or in response to suddenly extracting the belt from the retractor housing due to occupant movement, or in response to both.

The user's body moves forwards, for example, on vehicle deceleration, and it acts as an inertial mass to provide the force for suddenly extracting the belt. In this case, two types of mechanism may be employed for locking the retractor. One of these includes a mass which lags, or is left behind when the belt storage shaft or reel rotates with an acceleration above a predetermined minimum. The other includes a mass or masses which are thrown outwardly due to centrifugal force when the belt storage shaft or reel rotates at a speed or velocity above a predetermined minimum. These two types of mechanism will be herinafter referred to as belt acceleration responsive and belt velocity responsive mechanisms respectively. Both types of mechanism can be designed to provide an acceptable performance although our investigations show that each has its own advantages in different types of accidents.

This is best explained with reference to Fig.

1 which is a graph relating three parameters namely, belt or webbing acceleration, in units of "g" (the vertical ordinate), belt or webbing travel, in inches (horizontal abcissa), and acceleration onset rate, in "g/seconds" (superimposed as a grid of curved lines representing constant rates of onset of acceleration which intersect curved lines which give the acceleration after specified distances of travel from rest). The graph enables the acceleration to be calculated given the rate of acceleration onset and the distance travelled by the belt or webbing.

For example, if a belt starts from rest and is subjected to an increasing rate of acceleration of 10g per second, it will reach an acceleration of 1.5 g after two inches of travel. After 10 inches of travel, it will reach an acceleration of 2.5g.

If a belt acceleration responsive mechanism is designed to operate when the belt or webbing is withdrawn at an acceleration of 1.5g and if the acceleration onset rate of 35g/seconds, the mechanism will respond to lock the safety belt retractor when the belt or webbing has moved only 0.1 inches. This is clearly a very good performance. However, if the acceleration onset rate is only 2glseconds, an acceleration of 1.5g is not achieved, to commence locking, until over 50 inches of belt or webbing has been extracted. Clearly, this is totally unacceptable.

The line A which intersects the webbing acceleration ordinate at 1.5g represents a typical required acceleration response.

In accidents, an actual collision is often preceded by light, then heavy braking. If the belt occupant starts to move forwards during this period, possibly because he is asleep, a low acceleration onset rate occurs which may lead to a large forward movement. In such circumstances, the belt acceleration responsive mechanism is not sensitive enough, as explained above, to restrain the occupant. However, this problem may be overcome by designing velocity responsive mechanism which will respond sooner to an acceleration of 1.5 g.

Line B represents points of equal belt or webbing withdrawal velocity. It is possible to draw a family of such lines but, for reasons which will later become clear, the line which passes through an acceleration of 1.5g and 1.0 inches of belt or webbing travel has been illustrated. A safety belt retractor including a belt velocity responsive mechanism could be designed to operate when the g level on this line is reached.

To the left of the intersection of lines A and B, the belt acceleration responsive mechanism has the best performance, although a belt velocity responsive mechanism will begin to lock the retractor before one inch of belt is extracted. To the right of the intersection, a belt velocity responsive mechanism is superior having regard to the example mentioned above wherein locking commences after more than 50 inches of belt extraction. The belt velocity responsive mechanism will start to lock after about 4 inches of belt extraction.

The present invention relates to a safety belt retractor which exploits the advantages of both belt acceleration and belt velocity responsive mechanisms. Thus, better protection will be afforded to the user at both high and low acceleration onset rate.

Regarding the effect of a vehicle acceleration responsive mechanism, such as the so-called ball-in-saucer mechanism, and assuming that the belt user accelerates from his seat at the same rate as the vehicle is brought to rest (not necessarily a good assumption), the vehicle sensitive locking acceleration can be plotted on the graph of Fig. 1. In Europe, vehicle acceleration responsive mechanisms are designed to operate at 0.4g, whilst in the U.S.A., 0.6g is the standard. Both levels are plotted on the graph of Fig.

1 as lines C and D respectively. Thus, it can be seen that whilst a typical vehicle acceleration responsive mechanism gives a better locking performance (at a low acceleration onset rate) than a belt acceleration responsive mechanism a belt velocity responsive mechanism offers additional protection at very low acceleration onset rate and, of course, an additional degree of protection against failure of the vehicle acceleration responsive mechanism.

The present invention provides a safety belt retractor comprising a safety belt, a member which rotates when the safety belt is extracted, and locking means including first and second sensing mechanisms, the first mechanism being responsive to belt acceleration and to a greater extent than the second mechanism and the second mechanism being responsive to belt velocity to a greater extent than the first mechanism.

According to one embodiment of the invention, the locking means comprises an actuator which is responsive to both the rotational acceleration and the rotational velocity of said member. Preferably, the actuator moves a pawl or pawls into engagement which a fixed ring of ratchet teeth to lock the retractor. Preferably, the actuator comprises flywheel means connected by biassing means to said member, said biassing means being provided for exerting a force between said flywheel means and said member. The latter force is overcome on exceeding a predetermined minimum rotational acceleration of said member so that relative rotational displacement occurs between said flywheel means and said member to provide actuator movement to acceleration response.

Also, the flywheel has a plurality of portions which are displaceable by a centrifugal force, on exceeding a predetermined minimum rotational velocity of said member, to provide actuator movement due to velocity response.

The locking means preferably includes a plurality of pawls mounted for rotation with said member and which are moved, by the actuator, into engagement with a ring of ratchet teeth fixed to the retractor housing. The pawls are preferably provided on a diameter passing through the rotary axis of said member, for example, on a disc which is fast for rotation with said member.

According to another embodiment of the invention, the actuator comprises a flywheel which is displaceable with respect to said member, when the rotational acceleration of said member overcomes a predetermined biassing force as explained above, to operate a pawl which is pivotally mounted on a disc fast for rotation with said member, the pawl having a shape and a mass with respect to its pivot to cause it to move outwardly due to centrifugal force. Thus, the acceleration response is provided by rotational movement of the flywheel relative to said member as before, and the velocity response is provided by the cenrtrifugal movement of the pawl. However, the actuator may include flywheel portions, as before, which move outwardly due to centrifugal force to augment the velocity response.

According to another embodiment of the invention, the locking means comprises separate mechanisms which respond respectively when a minimum rotational acceleration and rotational velocity of said member is exceeded. Said mechanisms may comprise first and second pivoted pawls. The first pawl is circumferentially but not radially balanced on its pivot so as to provide the acceleration responsive. The second pawl is radially but not circumferentially balanced on its pivot to provide the velocity response. A ring of fixed ratchet teeth are provided for engagement by said pawls for locking the retractor. Suitably, the pawls are pivotally mounted on a supporting disc and are biassed away from the ring of ratchet teeth by respective springs, the springs being attached to the pawls so that one end of each spring approaches an over-centre position as the pawls move outwardly away from the centre of rotation of the supporting disc. This arrangement reduces the force resisting movement of each respective pawl as it is caused to pivot by rotation of said member. In such an arrangement, the ratchet assists return of each respective pawl to its starting position when the supporting disc rotates in the opposite direction due to a spring in the retractor which rewinds the belt.

Suitably, said member is a reel or shaft on which the safety belt is normally stored. However, it may be a wheel or a gear which is rotated by a reel or shaft on which the safety belt is stored. When flywheel means are employed for displacement with respect to said member to provide the acceleration response, it is suitably in the form of a circular discshaped mass, or semi-circular masses which define a disc-shape, the mass or masses being centred on the rotating axis of said member.

However, the flywheel means may take other forms wherein masses are provided which are balanced with respect to the axis of rotation of said member. Moreover, by way of an alternative to respective pawls for providing acceleration and velocity response for directly locking the retractor, suitably shaped and pivoted masses may be employed to actuate respective locking pawls, or to actuate a common locking pawl, for locking the retractor. Generally speaking, the acceleration and velocity responses may be used to operate either respective locking pawls or a common locking pawl.

Embodiments of the invention will now be described with reference to Figs. 2-5 of the accompanying drawings, in which: Fig. 2 illustrates a belt withdrawal responsive actuator for locking a safety belt retractor, Fig. 3 illustrates the actuator of Fig. 2 in conjunction with a locking mechanism, Fig. 4 schematically illustrates a locking mechanism according to a second embodiment, Figs. 5 and 6 are views of respective circumferentially and radially balanced pawls used in the second embodiment, and Fig. 7 schematically illustrates a locking mechanism according to a further embodiment.

Generally speaking, the actuator shown in Fig. 2 is used in the embodiment of Fig. 3 to provide locking means sensitive to both the acceleration and velocity of a belt storage shaft 1. Figs. 4-6 schematically illustrate another embodiment for giving the same effect but which employs respective locking mechanisms, in the form of pivoting pawls, to provide the acceleration and velocity response. Fig. 7 schematically illustrates a further embodiment which may employ the actuator of Fig. 2, or part of it, and in which, at high acceleration onset of rates locking of the retractor is a compromise between the acceleration and velocity response of the rotating shaft, whilst at low acceleration onset rates, locking is due to the velocity response.

In each of the illustrated embodiments, only the retractor locking mechanism has been illustrated because the construction and operation of the usual parts of the retractor are well known. Typically, shaft 1 extends through a housing and has a safety belt wound on it. The housing includes a clock-type spring connected to the shaft for rewinding the belt. An inertia sensitive locking mechanism incorporating a so-called "ball-in-saucer" mechanism, or incorporating a pendulum operated mechanism, may also be included to lock the retractor due to sudden vehicle deceleration. Such a vehicle acceleration responsive mechanism may be housed on one side of the belt storage shaft, the belt acceleration and velocity responsive mechanisms being housed on the other side of said shaft.

Referring to Fig. 2, a safety belt reel spindle or belt storage shaft 1 supports a flywheel carrier 2 which can be rotatably displaced with respect to the shaft 1. Carrier 2 is in the form of a short cylindrical sleeve having a pair of equally spaced cylindrical pegs 3 and 3' projecting radially outwardly. A spiral spring 4 connects the carrier to shaft 1 and stops 5 and 6 are provided so that the spring can be initially pretensioned and the tension maintained between shaft 1 and carrier 2. The tension is selected with respect to a predetermined minimum rotational acceleration of shaft 1. If this minimum acceleration is exceeded, the resultant force overcomes the tension in the spring 4 whereby the carrier 2 lags behind the shaft 1. A pair of semicircular flywheel halves 7 and 8 are mounted, one on each peg, so that radial sliding can take place. Pretensioned springs 9 and 10 connect the flywheel halves 7 and 8, the tension being determined with respect to a predetermined minimum rotational velocity of shaft 1 which, when exceeded, results in a centrifugal force to overcome the tension in springs 9 and 10. Each flywheel half carries a respective driving pin 11 or 12.

When the shaft 1 is suddenly rotated by rapid belt extraction, the tension in spiral spring 4 will be overcome on exceeding the predetermined minimum acceleration and the carrier 2 will lag with respect to shaft 1. When the rotational velocity of shaft 1 exceeds the predetermined minimum value, the tension in springs 9 and 10 will be overcome and the flywheel halves 7 and 8 will move radially outwardly on pegs 3 and 3'. The spring rates are such that there will be a "take-over band" when both effects take place, so that there will not be a sharp kink as indicated by the graph of Fig. 1.

There will be a smooth transition from acceleration control to velocity control.

The actuator of Fig. 2 is employed in the embodiment of Fig. 3 to cause a pair of pawls 25 and 26 to engage a ring of ratchet teeth 30, fast with the retractor housing, for locking the retractor. The drive pins 11 and 12 of the actuator are located in respective and inclined slots or recesses 23, 24 in the respective pawls 25,26. Each pawl is pivotally mounted on a disc 20 which is fast for rotation with the belt storage shaft 1.The disc 20 has two cut-outs 21 and 22 through which the driving pins 11 and 12 project. The pawls are pivotally mounted on disc 20 and are shaped so that they are balanced about their respective pivots both radially and circumferentially. Such balancing is best understood having regard to Figs. 5 and 6 which illustrate pawls used in the embodiment of Fig. 4. By comparison, pawls 25,26 have a shape and mass evenly distributed with regard to the respective pivots to provide both radial and circumferential balancing.

The slots or recesses in pawls 25, 26 are shaped so that when the driving pins move relative to disc 20, or when they move outwardly, the pawls move outwardly to engage the teeth 30. The teeth 30 may be part of, or attached to the housing of the retractor to provide the stop for each respective pawl 25, 26. Alternatively, the ring of ratchet teeth 30 may move so as to drive a much more substantial pawl (not shown) into engagement with a set of secondary teeth (not shown) attached to or forming part of the retractor housing. The pawls 25, 26 are balanced so that they do not themselves contribute to inertia sensing, for example, as in a locking mechanism which employs the so-called "ball-in-saucer" mechanism or a pendulum mechanism for locking the retractor due to vehicle deceleration.

Fig. 4 shows a more simple device. A shaft 1 is rotationally fixed to a disc 32 carrying two pawls 33,34. One of the pawls 33 is shaped so that it is balanced circumferentially, but not radially, so that its tip 53 can move outwardly due to acceleration of shaft 1.

Referring to Fig. 5 which is an enlarged schematic view of pawl 33, the shape of the pawl is such that the mass to the left of radius CO balances the mass to the right of CO. However, the pawl is radially unbalanced because the mass beneath the line AB is much less than the mass above AB. In view of such balancing, rotation of the disc 32 (centred on O) at a con stant velocity will not normally displace the pawl 33 on its pivot 35. Spring 37 extends between a fixed point 38 on the disc 32 and a movable point 39 at one side of a line passing through point 38 and the centre of pivot 35.

This spring provides a bias to hold pawl 33 against stop 50 and hence out of contact with a ring of ratchet teeth 51 fixed to the retractor housing 52. Pawl 33 is initially restrained by the prestressed spring 37. This prevents locking with low values of rotational acceleration and rotational velocity of shaft 1. However, if the belt is rapidly extracted, pawl 33 moves outwardly and the movable point 39 moves towards an over centre position on a line through point 38 and the centre of pivot 35.

The bias on pawl 33 then decreases as the pawl tip 53 approaches the teeth 51 - This occurs as the disc 32 rotates anti-clockwise (as shown) due to belt extraction. The ratchet teeth 51 are shaped and spaced with respect to the disc 32 so that when the disc 32 is caused to rotate in the clockwise direction, that is after releasing any belt tension and allowing the retractor rewinding spring (not shown) to retract the belt, the respect tooth 51 urges the pawl tip 53 radially inwardly away from the over centre position of the spring 37 whereby the bias increases to return the pawl 33 to its starting position. Thus, pawl 33 provides the acceleration response.

Referring to Fig. 6, pawl 34 provides the velocity response. Pawl 34 is radially balanced in that the mass above the arc AB is equal to the mass below the arc AB. However, this pawl is unbalanced circumferentially because the mass to the left of line CO is greater than the mass to the right of the line CO. A spring 37' is equivalent to the spring 37 described with reference to Fig. 5 and it extends between a fixed point 38 and a movable point 39'. The spring 37' normally maintains the pawl 34 in engagement with its stop 50'. If the safety belt is extracted, when the predetermined minimum rotational velocity is exceeded by disc 32, centrifugal force will cause pawl 34 to rotate clockwise on pivot 35'. As before, the bias exerted by spring 37' decreases as the point 39' moves towards an over centre position. Following engagement between the pawl tip 53' and the teeth 51, retraction of the belt causing rotation of disc 32 in the clockwise direction enables the respective tooth 51 to urge the pawl tip 53' radially inwardly and the increasing bias applied by spring 37' returns the pawl to its starting position. Better locking is provided by reducing the bias on the pawls 33, 34 by the respective springs 37, 37 when they approach an over centre position. The reduction in bias also gives a smaller take-over band in which both pawls operate. Stops 50, 50' prevent the respective pawls 33, 34 from pivoting inwardly due to springs 37, 37' respectively.

Fig. 7 shows a variation in the arrangement of Figs. 2 and 3. In Fig. 7, a flywheel 40 is rotatably mounted on a shaft 1 and a disc 41 is fixed on the shaft. A prestressed spiral spring (not shown) such as that indicated by reference 4 in Fig. 2 connects the shaft 1 to the flywheel 40. In this embodiment, the flywheel may not be made as half portions, because the velocity response is provided by a centrifugally displaceable pawl 43 mounted on a disc 41 fast with shaft 1. However, the actuator described with reference to Fig. 2 can alternatively be used, whereby the centrifugal displacement of the flywheel halves 7, 8 augment the velocity response of pawl 43. A driving pin 45 fixed to the flywheel projects through an aperture 42 in the rim of disc 41. Pawl 43 is pivotally mounted on the disc 41 and a cam surface 44 on the pawl is urged into contact with the flywheel driving pin 45 by a spring 46. Pawl 43 has most of its mass to the left (as shown) of pin 45 so that it can move outwardly by centrifugal force.

At high g onset rates, the relative rotation of the flywheel 40 is resisted by both the spiral spring (not shown) and the pawl spring 46.

When the shaft 1 accelerates, there is a tendency for the acceleration and centrifugal force to overcome the springs so that the locking performance is governed by both acceleration and velocity of the rotating shaft 1. More particularly, the tension in the spiral spring (not shown) is overcome by exceeding a predetermined minimum shaft acceleration whereby the flywheel 40, and hence pin 45, move relative to the camming surface of pawl 43 to move it outwardly. When a predetermined shaft velocity is exceeded, the major mass of pawl 43 (to the left of pin 45) provides enough centrifugal force to overcome spring 46 to move the pawl outwardly. At low g onset rates, however, the pawl 43 can move out independently so that velocity control takes over. Spring 46 extends between a fixed point on disc 41 and a movable point on pawl 43, the movable point approaching an over-centre position as with the spring 37 of the embodiment of Fig. 4. Thus, the bias exerted on pawl 43 decreases as it moves outwardly to engage a ring of ratchet teeth 53. The ratchet teeth assist return of the pawl to its starting position as the belt is subsequently retracted. The above described embodiment can be combined with a vehicle responsive inertia locking mechanism, such as the so-called "ball-in-saucer" mechanism, in the same housing.

WHAT WE CLAIM IS: 1. A safety belt retractor comprising a safety belt, a member which rotates when the safety belt is extracted, and locking means inclu ding first and second sensor mechanisms, the first mechanism being responsive to belt acceleration and to a greater extent than the second mechanism and the second mechanism being responsive to belt velocity to a greater extent than the first mechanism.

2. A retractor according to claim 1 wherein said locking means comprises an actuator responsive to both the rotational acceleration and the rotational velocity of said member.

3. A retractor according to claim 2 wherein the actuator moves a pawl or pawls into engagement with a fixed ring of ratchet teeth to lock the retractor.

4. A retractor according to claim 1 wherein said locking means comprises separate mechanisms which respond respectively when a minimum rotational acceleration and rotational velocity of said member is exceeded.

5. A retractor according to claim 4 wherein said mechanisms comprise first and second pivoted pawls, the first pawl being circumferentially but not radially balanced on its pivot so as to provide the acceleration response, the second pawl being radially but not circumferentially balanced on its pivot to provide the velocity response, a ring of ratchet teeth being provided for engagement by the pawls for locking the retractor.

6. A retractor according to claim 2 or 3 wherein said actuator comprises flywheel means connected by biasing means to said member, the force exerted by said biasing means being overcome on exceeding a predetermined minimum rotational acceleration of said member so that relative rotational displacement occurs between said flywheel means and said member to provide actuator movement.

7. A retractor according to claim 6 wherein said flywheel means has a plurality of portions which are displace'able by centrifugal force on exceeding the predetermined minimum rotational velocity of said member to provide actu ator movement.

8. A retractor according to claim 7 wherein said portions are mounted on a carrier, which carrier is connected to said member by a pretensioned spring.

9. A retractor according to claim 8 wherein said portions are semi-circular and define a discshaped flywheel, the portions being held together by springs and being mounted on the carrier for radial movement.

10. A retractor according to claim 8 or 9 wherein a drive pin is located on each of said portions, a pawl corresponding with each drive pin being pivotally mounted on a disc fast with said member, each pawl having an inclined recess or slot for receiving the respective drive pin.

11. A retractor according to claim 4 or 5 wherein said pawls are biassed away from said ring of teeth by respective springs, said springs being attached between a supporting disc fast with said member and each respective pawl, the end of each spring connected to the respective pawl approaching an over-centre position of the spring so that the bias is reduced on the pawl as it moves outwardly into engagement with said teeth, said teeth being such as to assist returning each respective pawl to its starting position when the belt is retracted.

12. A retractor according to claim 6 wherein the actuator co-operates with a pivoted pawl mounted for rotation with said member, said pawl being displaceable by centrifugal force as well as by said actuator to engage a ring of ratchet teeth for locking said retractor.

13. A retractor according to claim 12 wherein said pawl is pivotally mounted on a disc fast with said member and has a camming surface which engages a drive pin on said flywheel means, said flywheel means being displaceable with respect to said member to cam the pawl into engagement with said teeth.

14. A safety belt retractor substantially as herein described with reference to Figs. 2 and 3 of the accompanying drawings.

15. A safety belt retractor substantially as herein described with reference to Figs. 4, 5 and 6 of the accompanying drawings.

16. A safety belt retractor substantially as herein described with reference to Fig. 7 of the accompanying drawings.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. teeth 53. The ratchet teeth assist return of the pawl to its starting position as the belt is subsequently retracted. The above described embodiment can be combined with a vehicle responsive inertia locking mechanism, such as the so-called "ball-in-saucer" mechanism, in the same housing. WHAT WE CLAIM IS:

1. A safety belt retractor comprising a safety belt, a member which rotates when the safety belt is extracted, and locking means inclu ding first and second sensor mechanisms, the first mechanism being responsive to belt acceleration and to a greater extent than the second mechanism and the second mechanism being responsive to belt velocity to a greater extent than the first mechanism.