SEAT BELT RETRACTOR

Abstract: A seat belt retractor has a winding shaft (20) for winding a seat belt. A motive spring (26) biases the winding shaft in the winding direction of the seat belt. A drive unit (60) provides at least partial relaxation of the motive spring when the seat belt is at least partially unwound. A bridging device (40) can also be provided, by means of which the winding shaft can be driven more directly by the drive unit during a process of winding the seat belt.

Description: SEAT BELT RETRACTOR The present invention relates to a seat belt retractor. It is well known to use a motive spring, for example a spiral spring, to rotate the winding shaft of a seat belt retractor. One end of the motive spring is connected in a non-rotatable manner to the winding shaft and the other end of the motive spring rests on a fixed point, for example the casing of the retractor fixed to the vehicle structure. While the seatbelt is in use the spiral spring constantly applies a force to the seatbelt webbing in the retracting direction. While handling the seatbelt, the vehicle occupant will feel a constant pull on the seatbelt webbing, and when the vehicle occupant releases the unbuckled seatbelt, the seatbelt will return to its fully retracted position. A vehicle occupant may experience some discomfort because the seatbelt could be too snug or tight. DE 41 12 620 Al teaches a so-called comfort retractor, to overcome the above-described problem. An electric motor is provided for the winding process in addition to the motive spring. If the belt webbing is unwound or pulled out by hand, the electric motor increases the bias of the motive spring until a blocking device responds and prevents further rotations of the motor. If the tongue is pulled out of the buckle, a switch closes and restarts the electric motor. The winding spring is then biased again by rotation of the spring casing to such an extent that it reliably retracts and re-winds the belt webbing . The foregoing solution from the prior art is unsatisfactory in so far as a certain amount of time elapses after release of the tongue from the buckle, until the actual winding process that is brought about by the motive spring. This problem is solved by a the seat belt retractor of claim 1 Brief Description of the Drawings Fig. 1 is a cross-section through a schematically reproduced retractor. Fig. 2 is a section through the retractor according to the invention reproduced in Fig. 1. Detailed Description of the Invention The terms "top", "bottom", "left" and "right" used in connection with the description relate to the invention as it is shown in the accompanying figures. A seat belt retractor 10 according to the invention shown in Fig. 1 comprises a winding shaft 20 arranged horizontally in a spring cartridge 22 that also forms the casing of the retractor. With its left end 20a, the winding shaft passes through the left vertical wall 22a of the spring cartridge. A winding drum, not shown in detail, for the belt webbing of a seat belt is arranged in a non-rotatable manner at the left end 20a of the winding shaft. A spring casing 24 that accommodates a motive spring 26 in the form of a spiral spring is provided in the interior of the spring cartridge 22 on the left vertical wall 22a of the spring cartridge. The motive spring is connected in a non-rotatable manner to the winding shaft 20 at its inner end and is fastened on a fixing point 24a on the internal periphery of the spring casing 24 at its outer end. The motive spring 26 exerts a winding bias on the belt webbing when the belt webbing has been unwound by a vehicle occupant. At the outer periphery of the spring casing 24 there are external teeth 28 that mesh with a gear 30 that is a component of a drive unit 60 of the retractor . At the right end of the spring casing 24 is a covering disc 32 that is connected in a non-rotatable manner to the spring casing 24 by pegs 34 that are pressed into holes 35 (Fig. 2) . In Fig. 1 one of the pegs 34 is shown m one of the holes 35. In Fig. 1, the winding shaft 20 completely penetrates the spring casing 24 and the covering disc 32. At the right end 20b of the winding shaft adjoining the covering disc 32 there is provided an annular clutch member 36 that is connected to the winding shaft and has an external diameter that is greater than the external diameter of the winding shaft. The clutch member surrounds a receiving space 36a that is open toward the right end 20b of the winding shaft and has an internal diameter greater than the external diameter of the winding shaft . A variety of structures can be provided as a spring element. It is advantageous if the spring element is a helical wrap spring having one end connected in a non-rotatable manner to the drive unit and the other end connected m a non-rotatable manner to the damping element. A bridging device 40 comprises a helical wrap spring 42 and a damping element 44 that acts on the covering disc 32 of the spring casing 24. The helical wrap spring is provided on the outer periphery of the clutch member 36 coaxial with the winding shaft 20. One end 42a of the helical wrap spring 42 is fastened m the cover disc 32 whereas the other end 42b of the helical wrap spring 42 engages an annular extension 46 of the damping element 44. Each end 42a, 42b of the wrap spring 42 is connected m a non-rotatable manner to its associated components 32, 46. When a torque is exerted on the helical wrap spring at one end and the other end is simultaneously held by the damping element, the diameter of the wrap spring decreases resulting in frictional contact with the winding shaft . Owing to the bridging device (40) it is possible, even with a motive spring having only low, or no, spring tension to begin the winding process immediately after release of the tongue from the buckle, by using the force of the motor drive unit for the winding process. In contrast to the current state of the art, the motive spring (26) is not used for the winding process, but instead the drive unit (60), in particular the motor contained therein, which is preferably an electric motor, in the retractor according to the invention. If the bridging device (40) is to act directly between drive unit (60) and the winding shaft the drive unit would have to be arranged in the vicinity of the winding shaft (20) . This requires an additional configuration to enable the drive unit to be used for relaxing the motive spring when the tongue is inserted into the buckle. In user-friendly retractors, the motive spring is frequently accommodated in a rotatable spring casing to which the torque of the drive unit can be transmitted. In such a case it is advantageous for a compact construction of the retractor if the bridging device, on the one hand, is connected in a non-rotatable manner to the spring casing and, on the other hand, can be brought into rotational engagement with the winding shaft for transmitting a torque of the drive unit. In principle, the bridging device (40) can have different designs. A particularly advantageous solution can be achieved if the bridging device is a centrifugal clutch (switched according to the number of revolutions) . This has the advantage that the bridging device is only "connected" when a specific, predetermined speed is exceeded. The drive unit can be used both during the relaxation process of the motive spring when the seat belt is applied and during the winding process. If the speed of the drive unit is lower than the aforementioned limit value, the bridging device remains "disconnected" and the drive unit can rotate the spring casing into the load releasing direction of the motive spring. If the speed of the drive unit exceeds the limit value, the bridging device is automatically switched and the drive unit drives the winding shaft for winding the belt webbing. In the switched state the centrifugal clutch can produce an interlocking fit or frictional contact for torque transmission between the drive unit and the winding shaft, frictional contact being preferred. The construction of the centrifugal clutch can, in turn, be quite different. It is particularly advantageous if the centrifugal clutch comprises at least one spring element 4) that changes shape elastically under the influence of the torque and is formed by at least one damping element 4) . The damping element bringing about speed-dependent switching in such a way that the centrifugal clutch remains disconnected at a speed of the drive unit below a predetermined limit but the centrifugal clutch produces frictional contact with the winding shaft when the limit value is exceeded. The spring element can annularly surround the winding shaft 20. As shown m Fig. 1, the damping element 44 is arranged on the right vertical wall 22b of the spring cartridge 22. The damping element 44 has an output shaft 50 that extends horizontally to the left and is aligned axially with the central axis of the winding shaft 20. For achieving a compact construction of the retractor 10, the distance between the two shafts 20, 50 is so small that the two mutually opposed shaft ends 20a, 50a do not contact one another. Teeth 52 are provided on the left end 50a of the output shaft 50 for non-rotatable connection to the annular extension 46. The annular extension of the damping element 44 is connected m a non-rotatable manner to the output shaft 50 via these teeth 52. In Fig. 1 the annular extension 46 has an external diameter that is smaller than the internal diameter of the clutch member 36. The annular extension 46 extends into the clutch member 36. To prevent the helical wrap spring 42 from spreading radially outwardly, an axially extending centering cage 24b is provided on the cover disc 24. The centering cage 24a has an internal diameter that is greater than the external diameter of the helical wrap spring 42 and an axial length that is slightly greater than the axial length of the clutch member 36. To avoid axial spreading, m particular to the right, an axially extending projection 46a is also shaped on the annular extension 46, the external diameter of the projection being greater than the external diameter of the centring cage 24b. The radial projection 46a is at only a small distance from the face end of the centring cage, so that the helical wrap spring 42 is securely encapsulated. To support for the motive spring, it is advantageous if the drive unit is self-locking . This can be achieved, for example, by providing a worm gear 64 between the motor of the drive unit and the spring casing. The drive unit 60 comprises an electric motor 62. A worm gear 64 is connected to the output shaft of the motor 62. An intermediate shaft 66 that extends substantially perpendicularly to the worm gear 64 is mounted m a rotatable manner but axially rigidly m the spring cartridge 22. A gear 68 meshing with the worm gear 64 attached m a non- rotatable manner on the intermediate shaft 66 as well as the aforementioned gear 30 are provided m the spring cartridge 22 below the spring casing 24. The gear 30 is mounted m a non-rotatable manner on the intermediate shaft 66 to the left of the gear 68. The drive unit 60, m particular the motor 62, is connected to a controller, not shown m detail, that controls the operation of the drive unit. In describing the operation of the seat belt retractor of the invention it is initially assumed that the belt webbing is located m the stored, or fully retracted, position, i.e. the belt webbing is wound completely on the winding drum and substantially relaxes the motive spring 26. If the belt webbing is drawn out manually for application, the winding shaft 20 rotates, as does the end of the motive spring 26 connected m a non-rotatable manner to the winding shaft. As, on the other hand, the drive device 60 is self-locking, the other end of the motive spring 26 connected to the spring casing 24 at the fixing point 24a is not rotated, so the motive spring is tensioned. Once the tongue has latched into the buckle, this state is relayed to the controller of the drive unit 60 via a switch located in the buckle. The motor 62 is then set into operation and the spring casing 24 displaced via the drive unit. The external teeth 28 are moved at low speed into a position such that the motive spring 26 is located in a so-called user- friendly position, i.e. in a state of spring tension lower than the state of tension caused by the unwinding process. The belt webbing now lies relatively slack on the vehicle occupant. This "relaxation process" of the motive spring 26 is effected by the winding shaft 20 and the end of the motive spring 26 connected to it remaining at rest after the latching of the tongue into the buckle and the spring casing 24 as well as the end of the motive spring connected to the spring casing 26 at the fixing point 26a is rotated in the relaxation direction. During this movement of the spring casing 24, the cover disc 32 is also rotated and the end 42a of the helical wrap spring 42 rigidly connected to the cover disc 32. However, as the speed of the drive unit 60 is low in this case and the damping of the damping element 40 is adjusted in such a way that the other end 42b of the helical wrap spring can also be rotated, there is no change to the shape of the helical wrap spring 42, in particular the helical wrap spring does not come into contact with the clutch member 36 of the winding shaft 20. If the tongue is released from the buckle for a belt-removal, this is detected by the switch located in the buckle and relayed to the control device of the drive unit 60. The drive unit is then set into rotation in a direction opposed to the attainment of the above-mentioned user- friendly position at a speed higher than the speed for the relaxation process of the motive spring 26. This speed is selected and the damping of the damping element 40 adapted to it such that the damping of the damping element is "overcome", i.e. the end 42b of the helical wrap spring 42 is held by the damping element and initially remains at a standstill. On the other hand, the end 42a of the wrap spring 42 is set into rotation together with the cover disc 32. The internal diameter of the wrap spring 42 is thus reduced and comes into contact with the external peripheral face of the clutch member 36. Frictional contact between the helical wrap spring 42 and the external peripheral surface of the clutch member of the winding shaft 20 is thus formed. The motive spring 26 is consequently bridged over and the winding shaft set into rotation by the drive unit 60 via the spring casing 24 and the helical wrap spring, so that a winding process is performed. The motive spring 26 remains at rest. On the other hand, the output shaft 50 of the damping element 40 also rotates after a short time delay. This time delay is sufficient to hold the right end 42b of the helical wrap spring 42 such that frictional contact between the spring and the clutch member 36 is produced. The belt webbing is wound by the drive unit 60 until the parking position is reached. This state can be established by monitoring the power consumption of the motor 62. Further rotation of the winding shaft 20 and of the motor is no longer possible once the belt webbing has reached the parking position. As the motor remains switched on, but can no longer rotate, its power consumption increases. This increase can be detected and the motor can then be switched off. After reaching the stored position of the belt webbing, the drive unit 60 is also used to approach the zero position of the motive spring 26, i.e. to relax it at least almost completely. This takes place at the lower speed of the motor 62 already mentioned. Alternatively, it is also possible to carry out the operation of application only with the user- friendly spring position. The motive spring can also remain in the user- friendly position in the parking position.

Claims: CLAIMS : 1. A seat belt retractor comprising a winding shaft (20) for winding a seat belt webbing thereon, a motive spring (26) for biasing the winding shaft in a direction for winding the seat belt, and a drive unit (60) for the at least partial relaxation of the motive spring when the seat belt is at least partially unwound, wherein a bridging device (40) is provided by means of which the winding shaft can be driven directly by the drive unit during a winding process of the seat belt. 2. The seat belt retractor according to claim 1 wherein the motive spring (26) is located in a rotatable spring casing (24) to which the torque of the drive unit can be transmitted and the bridging device (40) is connected in a non-rotatable manner to the spring casing and can be brought into rotational engagement with the winding shaft (20) for transmitting torque from the drive unit (60) . 3. The seat belt retractor according to claim 1 or 2 wherein the bridging device comprises a clutch (42, 44) . 4. The seat belt retractor according to claim 3 wherein the clutch (42, 44) comprises at least one spring element (42) that changes shape elastically under the influence of a torque and is formed by at least one damping element (44) . 5. The seat belt retractor according to claim 5 wherein the spring element (42) surrounds the winding shaft (20) in an annular manner. 6. The seat belt retractor according to claim 5 wherein the spring element is a helical wrap spring (42) having one end that is connected in a non- rotatable manner to the drive unit (60) and a second end that is connected in a non-rotatable manner to the damping element (44) . 7. The seat belt retractor according to claim 6 wherein the spring element (42) makes frictional contact with a clutch member of the winding shaft (20) to transmit a torque to the winding shaft . 8. The seat belt retractor according to claim 7 wherein the damping element (44) has an output shaft (50) on which one end of the spring element (42b) acts in a non-rotatable manner and that is arranged coaxially with the winding shaft (20) . 9. The seat belt retractor according to claim 8 wherein the output shaft (50) of the damping element (44) has an end with an annular extension (46) having an external diameter that is greater than the external diameter of the output shaft but smaller than the internal diameter of the clutch member (36) . 10. The seat belt retractor according to any of the preceding claims wherein the attainment of the completely wound state of the belt webbing can be monitored via an increase in the power consumption of the drive unit. (60)

Inventors: SPECHT MARTIN, SPECHT, MARTIN
Applicants: BREED AUTOMOTIVE TECH, BREED AUTOMOTIVE TECHNOLOGY, INC.
Application year: 2000
Main classification: B60R22
IPC codes: B60R22