MXPA00006363A - Seat belt retractor with torsion bar - Google Patents

Abstract

A torsion bar (50) in a seat belt retractor (20) has a circular cross section. The torsion bar is formed as a cold headed extruded part with the grain structure of the metal aligned in the axial direction of the torsion bar in the center of the bar and the grain structure smoothly diverges from the axial direction near an end formation (52a, b) of the torsion bar. The seat belt retractor includes:a frame (22) to rotationally support the torsion bar and spool (30). The torsion bar (50) is characterized by an elastic deformation zone and a sharp onset into a plastic deformation zone. The spool rotates with the torsion bar. The retractor also includes a locking device, activated during a vehicle crash and linked to the torsion bar for preventing one side of the torsion bar from rotating while permitting the other side and the spool to rotate once loaded by the vehicle occupant.

Description

SAFETY BELT RETRACTION DEVICE WITH TORQUE BAR The present invention relates generally to safety belt retraction devices with energy absorbing torsion bars. The classic type of safety belt retraction device comprises a frame with a spool rotatably mounted on said frame. The spool typically includes one or more locking wheels each having several teeth engaged and locked by a corresponding locking catch. The locking latch is rotatably mounted on the frame and can be moved from an unattached position to a position engaged with a tooth of the locking wheel. After locking the spool, any additional rotation of the spool is prevented. All the forward movement of an occupant of a vehicle will not be stopped by this type of retraction device because as the occupant of the vehicle loads the blocked retraction device, the safety belt is strained and stretched and the seatbelt is it slides on itself. However, with a retraction device that absorbs energy, the spool and its associated mechanisms can rotate and the safety belt is extensively controllable in response to the load provided to the safety belt by the occupant. The forward movement of the occupant of the vehicle is restricted by a reaction force or torque generated within the retraction device. In this way, the lengthening of the safety belt and the forward movement of the occupant of the vehicle can be controlled. Power-absorbing safety belt retraction devices often employ a deformable member such as a compressible bushing or torsion bar. In both cases, a bushing is compressed or a torsion bar is twisted beyond its elastic limit in its plastic range to generate the desired reaction torque acting against the torque transferred to the retraction device spool through of the forces provided to the safety belt by the occupant of the moving vehicle. The object of an energy absorbing retraction device is the generation of a generally constant reaction force to oppose the forward movement of the vehicle occupant and to be able to generate this constant force during an accident, that is, during the entire period in which the seat belt is loaded by the occupant of the vehicle. In theory, this can be achieved by using a compressible bushing or a torsion bar that always operates in its constant plastic area. In a torsion bar, a safety belt tensioning device, one end of the torsion bar is clamped on a locking wheel and the other end is clamped on the retraction device reel. During an accident, the locking wheel can not rotate due to the interposition of a locking catch or locking catch on the teeth of the locking wheel. As a seatbelt is loaded by the occupant of the vehicle, the spool tends to rotate in opposition to the torsional reaction torque generated within the torsion bar, as the torsion bar is twisted. The amount of reaction torque that is generated depends on the amount of rotation or torsion of the torsion bar as well as the physical characteristics of the torsion bar. More specifically, the reaction torque generated by a torsion bar varies depending on whether the torsion bar is in its zones or elastic transition ranges or plastics. In an ideal torsion bar, the elastic range is characterized by a steeply sloping slope or preferably an infinite inclination slope or deflection curve, and the plastic range is characterized by a region of perfectly constant torque deviation that it has an abrupt transition in relation to the elastic region. On this ideal torsion bar and on the corresponding safety belt retraction device, once a first end of the torsion bar has been locked and once the reel is loaded, the torsion bar immediately makes a transition from its elastic range (see curve 100 of figure 1) to the plastic range of operation in such a way that generate a constant reaction force through the retraction device as the safety belt lengthens. Torsion bars of the prior art have been made using several different methods of manufacture. In one method, an oversized metal bar is machined to reduce its diameter to a desired dimension. Subsequently, end formations are formed in the machined bar as for example by cold rolling. The machining of the bar can produce stress changes that are not typically uniform and the cold rolling of the machined bar is considered to reorient the granular structure of the metal undesirably. To make the distribution of stress within the torsion bar more uniform, tempering is frequently employed in an oxygen controlled atmosphere, which increases the cost of the final product. However, this type of torsion bar does not achieve the objects of the present invention since it exhibits the characteristic torque deviation curve similar to that illustrated in curve 102 of FIG. 101 having an elastic zone, an extended elastic / plastic transition zone and a plastic zone.

In another manufacturing method, the torsion bar is manufactured using a cold forming process wherein the metal bar or the wire (large diameter) has a smaller diameter than the desired dimension. The bar having a diameter smaller than the desired diameter is expanded in a bar having the largest diameter desired. This type of torsion bar has been tested and exhibits or exhibits a torque deflection curve characteristic similar to that of curve 102 of FIG. 1. The prior art has also suggested a method for manufacturing a torsion bar that has a shortened or abrupt elastic / plastic transition zone. In this method, a previously machined or pre-formed torsion bar is hardened (by subjecting it to pre-twisting beyond its level of yield point torque) prior to its installation within a safety belt retraction device. A potential deficiency of this technique is that the pre-torque reduces the useful range in which the torsion bar can be twisted additionally, during an accident, once installed inside a retraction device. It is an object of the present invention to provide a torsion bar that has an abrupt transition from its elastic zone to its plastic zone. A further object of the present invention is to provide a safety belt retraction device that absorbs the energy that this type of torsion bar employs. Many other objects and purposes of the invention will be clear from the following detailed description of the invention. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a torsion-deviation curve for an idealized torsion bar and for a conventional torsion bar having a circular cross-section. Figure 2a shows data illustrating a torsion-deviation curve for a torsion bar that has been cold formed in accordance with the present invention. Figure 2b shows test data for a torsion bar that has been cold formed and then quenched. Figures 3a and 3b show a torsion bar in several processing steps. Figures 4a and 4b are end plan views of the torsion bar. Figure 5 shows a safety belt retraction device incorporating a torsion bar of the present invention. DETAILED DESCRIPTION OF THE INVENTION Figures 3a and 3b show a torsion bar made in accordance with the present invention. The torsion bar 50 includes a central body 52 and two end formations 52a and 52b which allow the torsion bar to be respectively connected with a spring shaft and a ratchet body. The torsion bar is made from a bar (or large diameter wire) of metal having a circular diameter. In the preferred embodiment, rod or wire is made of spherical tempered steel, oxidized by aluminum, 1005 with a Rockwell B classification comprised between 50 and 70 and preferably within a range of 60 to 65. This metal is chosen because it is sufficiently ductile when its granular structure is generally aligned longitudinally. The initial diameter Di (see figure 3a) of the metal bar 110 is approximately (5%) greater than the final desired diameter Dd of the torsion bar 50. The final diameter of the torsion bar is achieved by employing an extrusion process of cold forming wherein the bar 110 (see Figure 3a) is partially pushed through a die (not shown) and then the bar 110 is cut to the desired length. During this process or extrusion step, the granular structure of the metal bar 110 remains oriented in a generally longitudinal direction. The number 53 indicates a diagrammatic illustration of a typical pattern of a longitudinal granular structure. That is, the granular structure is parallel to the axis 112 of the torsion bar 50. Even if the granular structure of the original bar or wire does not have its granular structure longitudinally aligned, this extrusion process will align the granular structure. After reducing the diameter of the bar 110 to the desired dimension, the ends of the bar are subjected to cold head forming to form the end formations 52, 52b. These formations can be formed in a multi-stage process or in a single stage. Figures 4a and 4b show end views of each of the end formations. The end formation 52a includes an enlarged diameter section where a plurality of flutes 56a is formed. The end formation 52b includes an enlarged section having grooves 56 and at least one groove or notch 58 integrally formed which provides a means for receiving the spring shaft 60 as shown in Fig. 5. The cold head forming process which is used to form the larger diameter fluted sections 56a, 56b maintains the longitudinal granular structure in the bar as well as adds a radial component to the granular structure of the material. However, it is believed that the transition radii 55, 57 (see Figure 3b) avoid discontinuities in the granular structure and stress distribution. Accordingly, it is possible to eliminate the hardening process step commonly employed after metal formation. Surprisingly, if the torsion bar is quenched, the resulting torque deflection curve is as shown through the curve 202 of Fig. 2b. Reference is again made to the test data illustrated by the curve 202 of Figure 2a which shows a dramatically reduced transition zone between the elastic behavior and the plastic behavior of the torsion bar 50 and which has been achieved without the need to tune the material after the formation of the torsion bar. If the torsion bar was tempered, the torque deviation curve would look like the data shown in curve 202 of Figure 2b. If this extruded, cold formed torsion bar was installed inside the retraction device, less elongation (less occupant movement) would be required to raise the reaction torque and internal stress in its plastic region and the torque of The reaction generated as the fabric is elongated in a controllable manner would be greater than in the case of a torsion bar that has previously been subjected to stress through the extrusion process with respect to a given amount of torsion. Figure 5 shows the construction of the main components of an energy absorbing safety belt retraction device 20, with torsion bar. The retraction device comprises a frame 22 with a first side 24a and a second side 24b and a rear part 24c, each of the first side and second side includes a respective first opening 28a or 28b. The retraction device also includes a hollow reel 30 rotatably supported in the frame. The spool 30 includes a center body 32 and opposed flanges 34a, 34b at respective ends of the center body 32. The center body includes a hollow hole 40 having splines 42 formed at one end thereof. The body also includes a device such as a slit (not shown) of known construction for receiving and holding one end of a seatbelt fabric length 36. The number 36a refers to some layers of the safety belt wound around the reel. A torsion bar 50 is received within the hole 40. The torsion bar includes a center body 52 and the end formations 52a, 52b. As mentioned, end formation 52b includes grooves 56 (which engage with grooves 42 of the spool). The notch or groove 58 (see also figure 4b) receives an impulse key 60 from a spring shaft 62. The spring shaft includes a groove 64 where an inner end of a rewind spring 66 is received. The spring is held firmly on a spring cover 68. The spring cover is fixed on one side of the frame 24b and includes a circular projection 70 received within a frame opening 28-b. The projection 70 serves as a bushing to rotatably support the spring shaft 62, 50 torsion bar and spool. The spool 30 includes opposed pockets 38 located adjacent the splines 42 of the torsion bar 50. With the torsion bar in place, a tool is inserted into the bags to locally deform the spool to snap the reel splines 42 and the torsion bar grooves 56b. Emergency blocking retraction devices (ELRs) include several ratchet or lock wheel assemblies. The precise type for use in the present invention is not especially important. As is known in the art, the ratchet wheel assemblies include a sensor for causing a locking latch to engage the teeth in the ratchet or locking wheel to suspend the lengthening of the safety belt. Said sensors typically detect a deceleration of the vehicle above a predetermined level and a tissue sensor that initiates the blocking of the retraction device when the safety belt (tissue) is removed from the reel at a speed that exceeds a predetermined level. The ratchet or locking wheel assemblies may have one or more plastic sensor latches that engage a plastic or metal ratchet wheel which in turn connects a locking cup to the shaft of the retraction device (in the present case to the torsion bar) . After having connected the blocking cup to the shaft (torsion bar), the blocking cup rotates. The movement of the blocking cup displaces a locking lock, typically metal, which absorbs the load, in engagement with a metal wheel that absorbs load, thus suspending, possibly only temporarily (when energy absorbing components are employed). as for example a torsion bar), the lengthening of the safety belt. Such a locking wheel assembly that can be employed with the present invention is disclosed in US 5 529 258 or in EP 0228729. The end formation 52a of the torsion bar 50 is fixed on an assembly of ratchet wheel 80. The assembly includes a ratchet body 82 and a locking wheel or ratchet 84 having teeth 85. The ratchet body includes a tubular portion 86 having internal ribs 88 that engage with bar ridges 56a. 50. The locking wheel may be part of the body or a separate part which, as illustrated, is fixed and knitted. The ratchet body is received within an opening of the frame 28a and is supported by a bushing 90. A locking catch 92 is rotatably supported on the frame side 24a and can move in engagement with the teeth 85 of the wheel. blocking in response to the activation of a vehicle or tissue sensor. The lock wheel assembly 80 includes a fabric sensor 220 which detects the angular acceleration of the rotation of the spool 30. As illustrated, the tissue sensor is connected to the torsion bar 50 through the lock wheel assembly , whose speed (before blocking) is the speed of the reel. The lock wheel assembly further includes a vehicle sensor 222. As mentioned above, the specific implementation of the fabric and vehicle sensors varies, however this is known in the art. When either the vehicle is activated, the locking latch 92 engages to lock the locking wheel 84, through known mechanisms. The operation of the retraction device 20 is generally the same as that presented above. During an accident, the end 52a of the torsion bar 50 is blocked to prevent further rotation and the safety belt is loaded as the occupant of the vehicle moves forward or attempts to move forward. The load is transferred to the spool 30, through the safety belt 36, to whose movement the reaction torque generated by the spring end 52b of the torsion bar rotates. An increased load of the occupant causes the spool and the torsion bar to rotate, as opposed to the reaction force, thereby lengthening the seatbelt and allowing the vehicle occupant to move forward in a controlled manner.

Claims (1)

1. CLAIMS A safety belt retraction device (20) comprising: a spool (30) and a torsion bar (50), the torsion bar includes a first end formation and a second end formation (52b, 52a) , the first of the end formations (52b) is connected to the reel; the torsion bar further includes an elongated body (52), ductile located between the end formations and formed by the extrusion of an oversized metal bar in a bar of reduced diameter with its granular structure in the vicinity of a center of the bar (50) aligned in a longitudinal direction. The safety belt retraction device (20) of claim 1, wherein the end formations (52a, 52b) are formed through a cold head forming process. The safety belt retraction device (20) according to claim 2, wherein the second end formation is connected to a locking wheel assembly device (84). The safety belt retraction device (20) according to claim 1, wherein the torsion bar is subjected to a previous effort before being installed in the retraction device sufficient to longitudinally align the structure of the bar. The safety belt retraction device (20) according to claim 1, wherein the torsion bar is subjected to a previous effort before being installed in the retraction device sufficient to produce an abrupt start in a plastic deformation zone . The belt retraction device (20) according to claim 1, wherein the torsion bar has a circular cross section