SEAT BELT RETRACTOR

Abstract: A seat belt rectractor has a rotatable spool (2) mounted in a frame (1), a primary locking mechanism (6) for arresting rotation ofthe spool and a load absorbing mechanism (7) arranged to come into effect at a predetermined load for absorbing a portion of the spool locking load. The load absorbing mechanism may be a section of an inwardly facing peripheral edge of the frame having a serrated or roughened texture (7) which is positioned and adapted so that above a predetermined load it co-operates with a smooth surfaced spool bearing face to absorb some of the load. Spool rotationis prevented on engagement of the primary locking mechanism andthe load on the primary locking mechanism rises causing the frame sidewalls (3) to deform and the serrated or roughened section is pushed against the spool bearing face.

Description: SEAT BELT RETRACTOR The present invention relates to a seat belt retractor and particularly to a locking mechanism for a seat belt retractor. A seat belt retractor typically comprises a spool on which seat belt webbing is wound and which is mounted in a frame to rotate about its longitudinal axis to pay out or wind in webbing as required by movement of the vehicle occupant. In the event of a crash the spool is locked against rotation and thus payout is prevented and the vehicle occupant is securely restrained against forward motion. The spool is usually locked by engagement of ratchet teeth at its ends with at least one toothed pawl mounted in a load-bearing manner to the frame (e.g., on a lockbar extending across the width of the spool) . The locking pawl is under considerable strain during a crash and must be constructed to be very strong. It is not unusual for the teeth on the locking pawl to shear under particularly high crash forces . In some known seat belt retractors, a secondary locking arrangement is used to lock the spool with the frame using complementary locking formations, (e.g., inter-engaging teeth) . This arrangement has disadvantages because the loads are very high and the teeth can shear if the locking is not suitably phased. The problems left unsolved in the prior art are solved by the seat belt retractor of claim 1. Brief Description of the Drawings Fig. 1 is an isometric view of a seat belt retractor according to a first embodiment of the invention. Fig. 2 is a cross-sectional side view of the seat belt retractor of Fig. 1 showing the primary locking pawl engaged under relatively low loads . Fig. 3 is a cross-sectional side view of the seat belt retractor of Fig. 1 showing the primary locking pawl engaged under relatively high loads. Detailed Description of the Invention In the drawings like parts are referenced accordingly. A seat belt retractor is shown comprising a U-shaped frame 1 with a spool 2 mounted for rotation between sidewalls 3 of the frame. A primary locking mechanism arrests rotation of the spool and a load absorbing mechanism comes into effect at a predetermined load for absorbing a portion of the spool locking load. At least one end of the spool 2 is a toothed ratchet wheel 4 as is well known in the art ' and more clearly shown in Figs . 2 and 3. A toothed pawl 6 is mounted to pivot about a pivot point 5 in the event of a crash to engage the teeth on the pawl 6 with the teeth on the ratchet wheel 4 to lock the spool against further rotation and thus against payout of seat belt webbing to restrain a vehicle occupant. According to a preferred embodiment of the invention, the load absorbing mechanism comprises a section of an inwardly facing peripheral edge of the frame having a serrated or roughened texture and which is positioned and adapted so that above the predetermined load it co-operates with a smooth surfaced spool bearing face to absorb some of the load. A load absorbing mechanism is shown comprising serrations 7 formed on a section of the inner peripheral edge of a cutout in at least one of the sidewalls 3 of the frame 1. Preferably at least the serrated or roughened section of the frame is of a stronger material than the spool . The serrations 7 are in the plane of a smooth bearing face 9 at one end of the spool 2. A bearing face 9 may be provided at each end of the spool if serrations are incorporated into both sidewalls of the frame 1. In embodiments with the load absorbing mechanism at the same end of the spool as on the ratchet wheel 4, the bearing face 9 is axially adjacent the teeth on the ratchet wheel or wheels. The roughened or serrated section is preferably arranged diametrically opposite the pivot point of the primary locking pawl. The serrations may be in the form of rough irregularly shaped small teeth placed at irregular or random intervals or in the form of grooves in the peripheral surface. In this way the loads may be transferred from the relatively weak spool to the stronger frame and thus the primary locking pawl does not need to be so strong and can, for example be made of a weaker, less costly, material such as aluminum. Spool rotation is prevented on engagement of the primary locking mechanism and the load on the primary mechanism rises causing the frame side walls to deform and the serrated or roughened section is pushed closer to, and eventually against the spool bearing face, roughening the smooth surface and increasing its coefficient of friction to absorb some of the load and resist rotation of the spool. The primary locking mechanism may comprise a locking pawl 6 for engaging with ratchet teeth on the outer periphery of the spool. This is activated by the vehicle sensor in a traditional seat belt retractor. In operation, after a crash is detected the primary locking pawl 6 pivots and engages the ratchet wheel 4 to lock the spool 2 against rotation. As the crash force increases, the spool 2 moves so that one or both ends makes contact with the frame 1. The bearing face 9 is forced against the serrations 7 which etch into the face and thus increase the co- efficient of the friction of the bearing face thus increasing friction between the bearing face and the frame 1 and consequently absorbing some of the load. Fig. 1 shows the seat belt retractor in perspective and Figs. 2 and 3 are cross-sectional side views. In Fig. 2 the spool 2 is shown in its normal operative position relative to the frame 1. The locking pawl 6 has engaged the teeth on the ratchet wheel 4 thus preventing rotation of the spool 2. The torque T exerted on the spool 2 from the forward momentum of the restrained vehicle occupant is counteracted by the force FV on the lockbar in stopping spool rotation. As the force, specifically that exerted by the webbing, increases the spool 2 rotates about the pivot point 5 and moves into contact with the frame as shown in Fig. 3. The resulting resisting force is shown as FV. By increasing the coefficient of friction between the contacting surfaces, the resisting force FV is increased thus taking some of the load of the locking pawl. It will be seen that the resisting force FV is a relatively small force and could not alone hold the spool against rotation: the pawl 6 is necessary to lock the seat belt retractor. The serrations 7 reduce the effective surface contact area between the inner periphery of the frame cutout and the spool bearing face. This concentrates the vertical loading over a smaller area of the spool causing the spool to yield locally and thus increasing the coefficient of friction of the bearing face. It will be noted that any part of the bearing face may engage the frame to equal effect. It is entirely random and not repeatable. The load absorbing mechanism does not effect locking of the seat belt retractor but instead effectively shares the load which would otherwise be placed on the locking pawl and the spool and may be used to spread the load around at least part of the periphery of the frame aperture. Therefore the seat belt retractor can take greater loads than was hitherto possible and/or can make use of lighter and less costly materials.

Claims: CLAIMS : 1. A seat belt retractor comprising a rotatable spool (2) mounted in a frame (1) , a primary locking mechanism (6) for arresting rotation of the spool and a load absorbing mechanism (7) arranged to come into effect at a predetermined load for absorbing a portion of a spool locking load. 2. The seat belt retractor according to claim 1 wherein the primary locking mechanism (6) comprises a locking pawl for engaging with ratchet teeth on the outer periphery of the spool (2) . 3. The seat belt retractor according to either claim 1 or 2 wherein the load absorbing mechanism (7) comprises a section of an inwardly facing peripheral edge of the frame (1) having a serrated or roughened texture and which is positioned and adapted so that above a predetermined load it co-operates with a smooth surfaced spool bearing face to absorb some of the load. 4. The seat belt retractor according to claim 3 wherein spool rotation is prevented on engagement of the primary locking mechanism (6) and the load on the primary mechanism rises causing the frame sidewalls (3) to deform and the serrated or roughened section (7) is pushed closer to, and eventually against the spool bearing face, roughening the smooth surface and increasing its coefficient of friction to absorb some of the load and resist rotation of the spool (2) . 5. The seat belt retractor according to either of claims 3 or 4 wherein the roughened or serrated section (7) is arranged diametrically opposite the pivot point of the primary locking pawl (6) . 6. The seat belt retractor according to any of claims 3 , 4 or 5 wherein the serrated or roughened section (7) of the frame (1) comprises a stronger material than the spool (2) . 7. The seat belt retractor according to any of claims 3 to 6 wherein the serrations (7) are in the form of rough irregularly shaped small teeth placed at irregular or random intervals. 8. The seat belt retractor according to any of claims 3 to 6 wherein the serrations (7) are in the form of grooves in the peripheral surface. AMENDED CLAIMS [received by the International Bureau on 27 March 2001 (27.03.01); original claims 2 and 4-13 cancelled; original claims 1 and 3 amended; remaining claims unchanged (2 pages)] 1. A temperature measurement apparatus, comprising: a switched sensing circuit for sensing a temperature to be measured based on charging or discharging a capacitor through a temperature-dependent sense resistance, the switched sensing circuit having a common set of electrical components including the capacitor and a multi-pole switch to which the capacitor is connected in series, and also including a substantially temperature-independent reference resistor, wherein the reference resistor and the sense resistance are connected to different poles of the switch, the switched sensing circuit switchable via the switch so as to alter the charging or discharging time of the capacitor by including as an impedance to the charging or discharging of the capacitor either the reference resistor or the sense resistance, the switched sensing circuit for responding to the temperature to be measured via the sense resistance and for providing switched sensing circuit signals containing information about the time to charge or discharge the capacitor alternately through the temperature-dependent sense resistance and the temperature-independent reference resistor; and a detection circuit, including a comparator responding to the switched sensing circuit signals and providing a comparator signal indicating when a comparison of the capacitor voltage to a reference voltage changes, and a controller responding to the comparator signal and to a counter signal and providing a detection circuit output signal containing information about the temperature to be measured taking into account the time for the capacitor to charge or discharge through the reference resistor, wherein the controller provides a detection circuit switch control signal for controlling when the switched sensing circuit switches from charging or discharging the capacitor through either the reference resistor or the sense resistance to charging or discharging the capacitor through the other, the providing of the detection circuit switch control signal being based on the comparator signal, and also wherein the counter signal that is provided by a counter that is reset by the controller using a start/stop signal and conveys information about the time elapsed since the controller last provided the detection circuit switch control signal; whereby, in the sensing circuit, except for the sensing resistance and the reference resistor, all of the operative components are the same when the capacitor charges or discharges, so that a temperature measurement provided by the temperature-measuring apparatus is unaffected by aging of any component except for the reference resistor. 3. A temperature measurement circuit according to claim 1, wherein the temperature-dependent sense resistance is a thermistor.

Inventors: BARBER MATTHEW, BELL JOHN, FOSTER HOWARD, JACK BRIAN, JACK GRAHAM, BARBER, MATTHEW, BELL, JOHN, FOSTER, HOWARD, JACK, GRAHAM,, JACK,_BRIAN
Applicants: BREED AUTOMOTIVE TECH, BREED AUTOMOTIVE TECHNOLOGY, INC.
Application year: 2000
Main classification: B60R22
IPC codes: B60R22