Seat belt retractor with automatic locking mechanism

Abstract: According to the present invention there is provided a retractor (1) comprising a rotatably mounted spool (3) for supporting seat belt webbing, an emergency locking mechanism for selectively locking the spool (3) against rotation, an automatic locking mechanism for selectively locking the spool against pay out of webbing, a switch having a first position (2) for activating the automative locking mechanism in dependence upon a predetermined amount of webbing being wound off the spool, and a second position for deactivating the automatic locking mechanism, in dependence upon a predetermined amount of webbing being wound back onto the spool, a gear for connecting the spool with the switch mechanism comprising a first (28) and a second actuator tab (29) on the gear and a pivotally mounted actuator member (12) having an actuator pawl (15) for locking the spool and parts (16,17) intergaging with the first (28) and second tabs (29) to move the switch between the first and second positions. The tabs and the interengaging parts are radially oriented in line one with the other.

Description: The present invention relates to a seat belt retractor with an automatic locking mechanism. A conventional seat belt retractor passes around an occupant's body in a vehicle seat and effects a positive restraining force in an emergency by locking to prevent belt protraction when emergency conditions are detected by sensors in the retractor. Under non-emergency conditions the retractor allows seat belt webbing to be paid out permitting the vehicle occupant to move relatively freely in the seat. A problem arises when a child seat is to be attached in a vehicle seat fitted with such a retractor since safety regulations require the child seat to be fixedly mounted in the vehicle and thus the retractor must be permanently in a locked condition. Thus retractors have been produced with an automatic locking mechanism which can be engaged when a child seat is to be installed. Usually the automatic locking mechanism is engaged by pulling out a predetermined amount of webbing: generally of the order of at least 90% of the webbing wound on the retractor. This action switches in the automatic locking mechanism which locks the retractor against payout but allows the webbing to be retracted so that the belt can be adjusted to the correct size for the child seat. The automatic locking mechanism is disengaged when the webbing is fully wound back onto the retractor. Various mechanisms for an automatic locking mechanism have been proposed. All require some form of step-down gearing to translate a large number of turns of a retractor spool, as the webbing is unwound, into a much smaller number of turns of a member which actuates the automatic locking mechanism. A cycloidal gear arrangement is particularly suitable. US 4 811 912 describes the use of a planetary gear train, responsive to rotation of a spool, for pivoting an actuating pawl into and out of an automatic locking position in engagement with a ratchet wheel. A further arrangement is described in US 5 518 197 which uses a cycloidal gear arranged to rotate at a slower speed than the retractor spool. An actuator pawl is biased by a spring to two separate positions. One position moves a locking pawl to engage a ratchet and stop further protraction of the webbing from the spool. In the other position the actuator pawl has no effect and the retractor is free to operate in an emergency locking mode as normal. An axially extending actuator tab on the cycloidal gear moves the actuator lever between the two positions. The present invention aims to improve on this arrangement. According to the present invention there is provided a retractor comprising a rotatably mounted spool for supporting seat belt webbing, an emergency locking mechanism for selectively locking the spool against rotation, an automatic locking mechanism for selectively locking the spool against pay out of webbing, a switch mechanism having a first position for activating the automatic locking mechanism in dependence upon a predetermined amount of webbing being wound off the spool, and a second position for deactivating the automatic locking mechanism, in dependence upon a predetermined amount of webbing being wound back onto the spool, a gear for connecting the spool with the switch mechanism, the switch mechanism comprising a first and a second actuator tab on the gear and a pivotally mounted actuator member having an actuator pawl for locking the spool and parts intergageing with the first and second tabs to move the switch between the first and second positions wherein the tabs and the interengageing parts are radially oriented in line one with the other. According to one embodiment the gear is a cycloidal gear arrangement. Preferably the first tab comprises a radially extending elongated gear tooth and the second tab comprises a partially filled in space between two gear teeth. However both tabs may comprise partially filled in spaces or elongated radially extending gear teeth. A seat belt retractor according to the present invention can be constructed of a smaller number of parts than a known retractor and also with a smaller overall package size, particularly a slimmer packet size. For a better understanding of the present invention, and to show how the same 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 retractor according to the present invention. Figure 2 is an exploded view of the retractor of figure 1. Figures 3 to 7 are put cut-away side views of the retractor of figures 1 and 2 showing the sequence of operation. Figure 1 shows a retractor 1 of generally known construction comprising a frame 2, a spool 3 and an emergency locking system and an automatic locking system, attached to the left hand side of the frame 2. The emergency locking system is of generally known construction and comprises a vehicle sensor 4 of a type known conventionally as a standing man, a vehicle sensor pawl 5, and a vehicle sensor locking pawl 6. In an emergency situation the standing man 4 tips due to acceleration or deceleration above a predetermined limit. This causes sensor pawl 5 to rise which in turn pivots locking pawl 6 into engagement with teeth on a ratchet wheel fixedly connected to the spool 3. Engagement of the locking pawl 6 with the ratchet wheel brings a load bearing lock dog 7 into engagement to lock the spool in load bearing manner. The lock dog 7 is pivoted on the frame and is brought into engagement by interaction of a cam 8 on the lock dog 7 and a cam slot 9 on a multifunction piece 10 on which the vehicle sensor 4 is mounted. The automatic locking mechanism comprises a cycloidal gear arrangement 11 and an actuator member 12. The cycloidal gear arrangement 11 comprises an internally toothed gear ring 13 and an externally toothed gear wheel 14 mounted off-centre from the gear ring 13 by an eccentric cam 22 cooperating with an eccentric cam drive 23. This translates the rapid movement of the spool 3 into a slower movement of the cycloidal gear wheel 14. The actuator member 12 comprises an actuator pawl 15 at one end which is arranged to engage the ratchet wheel, two spaced teeth 16 and 17 arranged to engage the external toothing on gear wheel 14 and a spring arrangement 18. The spring 18 is moulded as part of the actuator member 12 and comprises a plastic loop with an indentation 19. Inside the loop, abutting the indentation 19 is a pointed post member 20 which provides the working surface against which the spring 18 acts. The indentation 19 can be positioned on either side of the post 20 depending upon the direction of resilient bias required to be applied to the actuator member 12. A spring 21 biases the multifunction piece 10 to a position in which the lock dog 7 is not engaged with the ratchet wheel. In figure 2 these parts are shown in exploded view and like parts are referenced accordingly. The operation of the retractor will now be described with reference to figures 3 to 7. Figure 3 shows a stowed position of the retractor in a vehicle with a full spool of webbing and no engagement of the automatic locking mechanism. The retractor is therefore in emergency locking retractor (ELR) mode. Webbing is being pulled off the spool in the direction of arrow 24. This results in the spool rotating in a clockwise direction as shown by arrow 25. The eccentric cam 22 therefore also rotates clockwise and thus the gear wheel rotates anti-clockwise. The eccentric cam 22 is mounted on the eccentric cam drive 23 fixed to the spool 3. This results in the gear wheel 14 rotating anti-clockwise in the direction of arrow 26. As shown in figure 3 the actuation lever 12 is in such a position that the actuator pawl 15 is out of engagement with the ratchet wheel 27 and the spring arrangement is such that the indentation 19 sits on the right hand side (as shown in figure 3) of the peak of the post 20. Thus the actuator member 12 is biased in an anti-clockwise direction relative to its pivot. In this situation webbing can be pulled in or out freely. In figure 4 webbing is being pulled off the spool in the direction of arrow 22 and the spool 3 and eccentric cam 22 are rotating clockwise in the direction of arrow 25. The gear wheel 14 is rotating anti-clockwise in the direction of arrow 26. The gear wheel 14 has generally evenly spaced teeth with two exceptions. One extra long tooth 28 extends radially beyond the extent of the other teeth and will be referred to as a first actuator tab. In addition the space between two of the normal teeth is partly filled in to provide a second actuator tab 29. In the embodiment illustrated first tab 28 is diametrically opposed to second tab 29. In the position shown in figure 4 the first actuator tab 28 on gear wheel 14 is in contact with a first leg 17 on the actuator member 12. This pushes the actuator member 12 against the force of the spring 18 in a clockwise direction about its pivot point. The first tab 28 is dimensioned so as to rotate the actuator member 12 sufficiently far for the overcentre spring to move over the switching point, ie over the apex of the peaked post 20. In this position the overcentre spring engages the other side of the peaked post 20, which biases the actuator member 12 in a generally clockwise direction about its pivot point thus biasing the actuator pawl 15 into engagement with the ratchet wheel teeth. In this position the retractor is in automatic locking retractor (ALR) mode since the spool is locked against further protraction of the webbing. In figure 5 the retractor is working in automatic locking retractor (ALR) mode and webbing can only be drawn back onto the spool. The spool 3 and the eccentric cam 22 can only rotate anticlockwise and the gear wheel can only rotate clockwise. The gear wheel 14 is shown in a position in which it has moved clockwise by about 90° compared to the position in figure 4. The gear wheel 14 continues to rotate clockwise until the second actuator tab 29 has moved around to engage arm 16 of actuator member 12. This is the position shown in figure 6. In this position the second actuator tab 29 pushes against the arm 16 urging the actuator member 12 to rotate anticlockwise against the force of the overcenter spring 18. The geometry of the second actuator tab and the arm 16 is such that the actuator member 12 is pivoted sufficiently far for the actuator pawl 15 to disengage from the ratchet wheel. Thus the spool is released and the ALR mode is switched off. The retractor is now in ELR mode again. It will also be seen that the indentation 19 of the overcentre spring 18 has been pushed over the peak of post 20 and the actuator member 12 is again biased in a generally anticlockwise direction so that pawl 15 is biased out of engagement with the ratchet wheel. In this position webbing can be pulled off the spool or wound back onto the spool, and the eccentric cam together with the gear wheel can rotate freely in any direction. This is the position shown in figure 7. The low number of extra elements required in this arrangement means that the package size of the retractor is much slimmer than previous designs. This is because both activation and deactivation are performed with tabs which are all provided in a single layer. An alternative would be to use elongated teeth for both actuator tabs or to use filled teeth roots for both actuator tabs. A multitude of arrangements can be envisaged by a man skilled in the art with appropriate adjustment to the geometry of the arms of the actuator member 12.

Claims: A retractor (1) comprising: a rotatably mounted spool (3), for supporting seat belt webbing an emergency locking mechanism for selectively locking the spool (3) against rotation; an automatic locking mechanism for selectively locking the spool (3) against pay out of the webbing; a switch having a first position for activating the automatic locking mechanism in dependence upon a predetermined amount of webbing being wound off the spool (3); a second position for deactivating the automatic locking mechanism in dependence upon a predetermined amount of webbing being wound back onto the spool (3); a gear (11) for connecting the spool (3) with the switch mechanism the switch mechanism comprising a first (28) and a second (29) actuator tab on the gear (11); and a pivotally mounted actuator member (12) having an actuator pawl (15) for locking the spool (3) and characterised by parts (16, 17) interengageing with the first (28) and second (29) tabs to move the switch between the first and second positions, wherein the tabs (28, 29) and the interengageing parts (16, 17) are radially oriented in line one with the other. A retractor according to claim 1 wherein the gear (11) is a cycloidal gear arrangement (13, 14, 22, 23). A retractor according to claim 1 or claim 2 wherein the first tab (28) comprises a radially extending elongated gear tooth and the second tab (29) comprises a partially filled in space between the two gear teeth. A retractor according to claim 1 or claim 2 wherein both tabs comprise partially filled in spaces between the adjacent gear teeth. A retractor according to claim 1 or claim 2 wherein both tabs comprise elongated radially extending gear teeth.

Inventors: PALLISER MARTYN NEIL, PALLISER, MARTYN NEIL
Applicants: KEY SAFETY SYSTEMS INC, KEY SAFETY SYSTEMS, INC.
Application year: 2001
Main classification: B60R22
IPC codes: B60R22