Pretensioner

Abstract: A pretensioner for use with a retractor for a vehicle safety restraint to rapidly take up slack in a safety belt system at the onset of a crash situation so as to more correctly and securely restrain the vehicle occupant and to more correctly position him for maximum effect of an inflatable safety device such as an air bag. The pretensioner comprises a piston-cylinder arrangement in which a piston is driven along the inside of a cylinder under force provided, for example, by a spring or by a gas generator. The pretensioner has a resilient seal around the piston and the cylinder to provide load limiting at the start of the pretensioner stroke. Safety arrangements are provided for ensuring that the pretensioner is not activatable before installation in the vehicle, and the gas generator is constructed to ensure that there are no loose parts after detonation, which could cause damage. A bearing for the cylinder is provided for use when the piston-cylinder forms the crash sensor.

Description: The present invention relates to a pretensioner for use with a retractor for a vehicle safety restraint. Pretensioners are used to rapidly take up slack in a safety belt system at the onset of a crash situation so as to more correctly and securely restrain the vehicle occupant and to more correctly position him for maximum effect of an inflatable safety device such as an air bag. Known pretensioners comprise piston-cylinder arrangements in which a piston is driven along the inside of a cylinder under force provided, for example, by a spring or by a gas generator. The piston is attached to one end of a cable, the other end of which may be attached to a rewind mechanism of a safety restraint retractor so that movement of the piston rewinds the belt webbing by an appropriate amount. A pretensioner according to the preamble of claim 1 is known from US 5.310.219. Various problems arise with such pretensioners and it is an object of the present invention to provide an improved pretensioner arrangement. Aspects which the present invention particularly addresses include the seals around the piston and the cylinder, load limiting at the start of the pretensioner stroke, safety arrangements for ensuring that the pretensioner is not activatable before installation in the vehicle, and construction of the gas generator to ensure that there are no loose parts after detonation, which could cause damage to vehicles or their occupants. Pretensioners incorporate crash sensors and this is often effected by inertial means such as a pendulum sensor. In one known type of pretensioner the piston-cylinder itself acts as an inertial crash sensor by being weighted with an additional mass and mounted on a bearing at one end of the tube in which the cylinder is housed. Usually movement is restricted to one dimension (the forward-backward dimension of the vehicle). The present invention addresses aspects of such a bearing. Thus according to one aspect of the present invention there is provided a pretensioner arrangement for a vehicle safety restraint retractor, the pretensioner comprising: a piston movable along a cylinder under action of gas from a gas generator, the piston being connected to one end of a cable, the other end of which is connected to means for shortening the effective length of belt webbing available to the vehicle occupant, wherein an elastomeric seal is provided on the piston at one end characterised in that the seal seals the piston to the cable, such that the elastomeric seal is compressed and temporarily absorbs some of the force generated by the gas generator on detonation of the pretensioner when a crash situation is sensed.A pretensioner arrangement for a vehicle safety restraint retractor, the pretensioner comprising: a piston movable along a cylinder under action of gas from a gas generator, the piston being connected to one end of a cable, the other end of which is connected to means for shortening the effective length of belt webbing available to the vehicle occupant, wherein an elastomeric seal is provided on the piston at one end characterised in that the seal seals the piston to the cable, such that the elastomeric seal is compressed and temporarily absorbs some of the force generated by the gas generator on detonation of the pretensioner when a crash situation is sensed. This has the advantage that a smaller initial force is applied to the piston than would otherwise be the case making sudden breakages of the cable less likely. However the resilient nature of the seal of the invention allows it to be compressed and prevents any overall lost force and so there is no significant overall loss of gas pressure in the cylinder, giving improved performance over known systems. Preferably the seal is made of Elastollan, a resilient plastics material. In some known systems an initial load limiting is achieved by providing a leakage path which dissipates the power applied to the piston but obviously this lowers the gas pressure, and reduces overall efficiency. For example in US 5 310 219 an annular piston seal only becomes fully effective after the gas pressure takes full effect and moves the annular seal axially along a comically rising bottom of an annular groove of the piston, to stretch it and fame it against the cylinder wall. The safety of the device during transport and storage before it is fitted into a vehicle is of paramount importance. This is particularly so with a pyrotechnic pretensioner since this contains a small amount of explosive substance. There are known systems to hold a pretensioner in a de-activated state before fitting but they are complex requiring several steps in the de-activation procedure. The present invention aims for a simpler and safer safety mechanism and being deflectable therefrom to allow movement of the pendulum sensor when a mounting bolt is inserted through a mounting hole in the housing to mount the pretensioner in a vehicle. In a preferred embodiment in which the crash sensor is formed by the piston-cylinder arrangement itself, the restraining abutment is formed by an extension attached to the free end of the cylinder and there is a slot on the retractor frame blocked by the lever in the restraining position and through which the extension can pass when the lever is deflected. According to a preferred embodiment of the invention the gas generator comprises a burst disc at one end through which the gas is released on detonation, the burst disc being circumscribed by a line of weakness around a substantial part of its periphery and having a segment of its periphery reinforced so that on detonation of the gas generator, the opened burst disc in retained attached to the gas generator by the reinforced segment. The gas generator is usually formed of aluminium and a fourth aspect of the invention provides for one end of the gas generator to be reinforced by a steel ring with a diameter slightly larger than the diameter of the one end. According to a preferred embodiment a sensor lever rests against the gas generator in the region of the steel ring and in this case the sensor lever is preferably reinforced with a steel pin incorporated into its structure. This Particularly for the embodiment in which the piston cylinder arrangement forms the crash sensor; a bearing may be provided. The bearing may be formed of a hollow square of plastics material having two opposite sides formed with crush ribs on their inner faces, structured and dimensioned to provide a close fit with co-operating recessed surfaces of the cylinder. The other two sides of the square have internal faces which do not grip the cylinder. The co-operating surface of the cylinder may be formed with a circumferential channel of semi-circular cross-section. The bearing may allow pivoting of the cylinder in a direction parallel to the engaging bearing faces (the crush ribs) but not in a direction perpendicular to the crush ribs since in that direction the bearing is held fast in the recess in the cylinder. Preferably the outer facing four surfaces of the bearing are arranged to co-operate with internal features of a cylinder housing. For example, two opposite outward facing surfaces may each have an upwardly facing ledge to co-operate with respective inwardly deformable cut-outs on corresponding faces of the cylinder housing. The other two outwardly facing surfaces may be provided with downwardly facing ledges to rest on projections from the other two internal faces of the cylinder housing. In this way the bearing is held fast in the housing and prevented from longitudinal and lateral movement. Preferably the bearing is formed of two identical moulded plastics L-shaped parts, one of which is turned through 180° and the two of which are clipped together by tight fitting peg and hole connections. For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made to the accompanying drawings in which: Figure 1 is an exploded view of a safety restraint retractor incorporating a pretensioner according to the present invention. Figure 2 is an enlarged view of part of Figure 1 showing the cylinder mass and cable arrangement in more detail. Figure 3 is an enlarged view of part of the pretensioner shown in Figure 2 giving more detail. Figure 4 shows various cross-sectional views of the bearing used in the pretensioner shown in Figure 2. Figure 5 is an exploded cross-sectional view illustrating the piston cylinder mass and cable arrangement of Figure 2. Figure 6 is a cross-sectional side view of the retractor pretensioner of Figure 1. Figure 7 is a cross-sectional front view of the retractor pretensioner shown in Figure 1. In Figure 1 a retractor 1 is shown comprising a frame 2 in which is mounted a spool 3 which holds seat belt webbing 21 which is fixed in the spool by a retaining webbing pin 22. The webbing passes from the spool through the webbing guide 6 through a direction changing loop 23 (also known as a D-ring), through a buckle tongue 24 and is fixed in the vehicle around slider bar 25 which is fastened to the floor or chassis of the vehicle. Upper and lower tie plates 4, 5 hold the frame together and the webbing guide 6 is fixed to the top of the frame 2. On the right-hand side of the frame 2 (as shown in Figure 1) a vehicle sensor 7 and a webbing sensor 8 are mounted between mechanism bush 9 and multi-function piece 10 and protected from ingress of adverse environmental conditions by mechanism cover 11 sealed by cover seal 12. The vehicle sensor 7 comprises vehicle sensor housing 13, mass assembly 14, primary lever 15 and secondary lever 16. Webbing sensor 8 comprises inertial disk 17 and web sensor pawl 18. Activation of either of the sensors causes locking of the spool via lock bar 19. The lock bar is connected via a lock bar bush 50 and a tie bar 51 to a spring side lock bar 52. In this way when either the vehicle sensor or the web sensor operate further pay out of webbing is prevented by locking of the spool on both sides of the mechanism (pawl 19, 52). A lock cup return spring 20 is also provided. The construction and operation of these parts will be evident to a person skilled in the art who will also introduce, as required, screws, shims and any other minor elements such as springs or pins as required. On the left-hand side of the frame 2 is the pretensioner 26. This comprises a piston 27 which is attached by crimping to one end of a cable 28 and is sealed by piston seal 29. The piston 27 is housed in a pressure tube or cylinder 30. The cable 28 passes through a mass 30 to which it is sealed by mass seal 31. In Figure 1 the cable is not shown exiting from the mass 30 since lack of space does not permit. However the course of the cable will be more clearly seen from subsequent Figures. The piston cylinder mass arrangement acts as a pendulum crash sensor. To this end it is mounted in cover 31 and supported therein at its lower end by bearing retainer 32. A swivel bar 33 and sensor lever 34 are located to one side of the mass 30 whereas a sensor spring 35 fitting into a sensor spring cap 36 are located on the other side of the mass 30, within the cover 31. In a top recess of the mass 30 a gas generator 37 mounted within a firing spring 38 is located. A firing pin plate 39 sits on top of the gas cylinder. Movement of the piston cylinder mass pendulum arrangement within the cover 31 will cause detonation or the gas generator and hence activation of the pretensioner. Activation of the pretensioner causes the piston 27 to move down the cylinder 30 and hence to pull the cable 28. The cable passes through the mass 30 and is wound at its other end 40 around a spiral assembly 41. Thus when the piston pulls the cable 28, the spiral assembly 41 is rotated (as shown this would be in a clockwise direction). Rotation of the spiral 41 rotates a steering part 42 and causes a clutch arrangement 43 to move into engagement. Clutch clamping jaws 44 are spiralled outwards by movement of steering part 42 to engage ratchet 45 and thus to rotate the spool in a webbing take-up direction. The clamp jaws 44 are supported by support disk 46 and clutch bearing sleeve 47 and are located within clutch housing 48 by means of a packing element 49. The standard spiral retraction spring 53 is mounted on retraction spring shim 54 and connected to the spool 3 by spring arbour 55. These parts are covered by a spring cover 56. A safety lockout device is also provided for the pretensioner and is indicated at 58. This is a safety device which prevents the pretensioner firing when it is not fixed in a vehicle. This lockout device comprises a lockout lever 59 which is mounted on a lockout shaft 60 inside the frame 2. At one end of the lockout lever 59 is located a lockout pawl 57. A lockout spring 61 is located at the other end of the lockout lever 59 so as to bias to a position where the bulbous head sits adjacent frame mounting hole 62 and the lockout pawl blocks a cutout 63 on the side of frame 2. Insertion of a screw or bolt through the frame mounting hole 62 will act on the bulbous part of the lockout lever 59, against the lockout spring 61, to urge the bulbous part away from the mounting hole 62 and thus to rotate the lockout pawl 57 upwards (i.e. clockwise in Figure 1). In the unmounted state of the retractor pretensioner arrangement, the interlock lever 57 blocks a small cut out 63 in the side of frame 2. Adjacent to this cut out 63 and to the lockout pawl 57 is located the conical upper extension of firing pin plate 39. Thus when the retractor pretensioner arrangement is not fitted in the car, for example during assembly and transport, the firing pin plate is prevented from moving (to the left in Figure 1). Since the firing pin plate, is the assembled mechanism, is an integral part of the piston cylinder mass pendulum sensor arrangement, then the pendulum is prevented from moving even under conditions of shock similar to those experienced during a crash. Thus the pretensioner is prevented from firing and is in a safe condition. However, when a bolt or screw is passed through frame mounting hole 62, the lockout lever 59 is rotated (clockwise) and lockout pawl 57 clears the hole 63 so that firing pin plate 39 can move. Thus when the retractor pretensioner is mounted in a vehicle the pretensioner is armed. An interlock lever 67 is provided to prevent rotation of the spiral until or unless the pretensioner is operated. Figure 2 shows the pressure tube and mass arrangement in more detail. Like parts are denoted by like reference numerals. Pressure tube 64 mounted to sensor mass 30 at the top of which can be seen the firing pin plate 39. Cable 28 passes out of the pressure tube 64, through the mass 30 and is wound around spiral member 41. The spiral 41 is housed within clutch housing 48 and held there by the packer clip 49. Bearing retainer 32 fits around the bottom of the pressure tube 64 and is located there by means of a circumferential recess 65. Figure 3 shows the connection of the cable to the piston in more detail. Again like parts are denoted by like reference numerals. Firing pin plate 39 is located on top of gas generator 37 which is mounted in firing spring 38 in a recess 66 of sensor mass 30. In Figure 3 the gas generator can be seen more clearly. It comprises a burst disk 68 at one end through which gases released when the pretensioner is activated. This burst disk is formed with a segment of its circumference reinforced to act as a hinge when the gas is expelled. In this way the burst disk remains attached to the gas generator and there are no loose parts. The other end of the gas generator is reinforced with a steel ring having a diameter slightly larger than the diameter of the end on which it is mounted. The steel ring is denoted by reference 69. The sensor lever 34 mounted on swivel bar 33 rests against the gas generator 37 in the region of this steel ring 69. The sensor lever is reinforced with a steel pin 70 incorporated into its structure. This prevents excessive wear on the sensor lever. Friction between the sensor lever and the swivel bar is reduced by using a coating of molycote on the sensor lever and is further reduced by the curved profile used on the sensor lever where it engages the swivel bar 33. This sensor lever and swivel bar hold the generator in place within the body of the mass 30. A temporary clamp may be used to hold the members in place during assembly of the pretensioner. The firing pin plate 39 is crimped into the top of recess 66 in mass 30. The sensor spring 35 is compressed when assembled into aperture 71 of mass 30 and is held in place by sensor spring cap 36. The cable is sealed into mass 30 by mass seal 31 which is held in place in mass 30 when pressure tube 64 is screwed into the mass. The end of cable 28 passes through piston seal 29 into piston 27 wherein it is crimped. A gap is provided as shown in mass seal 31 to enable gas from gas generator 37 to pass into pressure tube 64. Figure 4 illustrates the bearing retainer 32. This is made in two parts which may be moulded from an identical moulding process. One of the parts is turned through 180° and the two parts are interlocked by means of tabs 72 which provide a snug fit into cooperating holes 73. In its assembled condition the bearing retainer 32 has two opposing internal surfaces formed with crush ribs 74. These crush ribs 74 have the same profile as the generally semi-circular recess or channel 75 at the bottom end of pressure tube 64. This is more clearly shown in Figure 4A which shows a cross-section drawn along line A-A in Figure 4. This engagement means that the bearing retainer 32 cannot move in the dimension defined by the line A-A. However the other two opposing faces of bearing retainer 32 do not, in the assembled condition, contact the surfaces of the pressure tube 64. This is shown in Figure 4C which is a cross-section taken along line C-C of Figure 4. Hence movement in the dimension defined by the line C-C is possible and the bearing retainer 32 pivots on the crush ribs 74. Figure 4B is a side view of one half of the bearing retainer 32-as seen in the direction B and Figure 4D is a side view of one half of the bearing retainer 32 as seen in direction D. Figure 5 is an exploded cross-sectional view of the pretensioner arrangement of Figure 1. Like parts are denoted by like reference numerals and thus it will be seen that clutch parts 43 comprise the spiral member, steering part, clamp jaws, clutch bearing and support disk. The clutch is mounted in between clutch housing 48 and ratchet 45. Clutch housing 48 is mounted on sensor mass 30. Firing pin plate 39 is located on top of gas generator 37 which is mounted in spring 38 in the top of mass 30. The sensor lever 34 and swivel bar 33 are mounted at one side of mass 30. Sensor spring 35 is mounted in the other side of mass 30 and retained there by spring cap 36. Mass seal 31 is shown engaging cable 28. In the embodiment of Figure 5 the mass seal 31 is shown inverted compared to its orientation in Figure 1. The cable 28 also passes through piston seal 29 and is crimped into piston 27. Piston 27 is located in pressure tube 64 which is pivotally retained at its lower end in cover 81 by means of bearing retainer 32 which co-operates with the inwardly deformable tabs 75 and projections 76 at the lower end of cover 81. Figure 6a is a cross-sectional side view of the retractor pretensioner arrangement before it is fitted into a vehicle. Figure 6b is a side cross-sectional view of part of Figure 6a with the retractor pretensioner fitted in the vehicle. The difference between Figures 6a and 6b resides in the insertion of bolt 76 through the fixing hole in the frame. Bolt 76 deflects the lockout lever 59 and lifts the lockout pawl 57 away from frame cutout 63. This clears the frame cutout 63 for the upper conical projection of firing pin plate 39 to pass through and thus the pretensioner is armed. The other features of Figures 6a and 6b will be clear from a comparison with previously described Figures. Figure 7a is a front cross-sectional view of the retractor pretensioner. Again like parts are denoted by like reference numerals and the operation of the retractor pretensioner will be evident from a comparison with previously described Figures. Figure 7a illustrates more clearly a connecting passage 77 between the gas generator 37 and the pressure tube 64. Figure 7b is a cross-sectional view through line b-b in Figure 7a and illustrates the bearing retainer 32 and its co-operation with the retaining flaps 75. It can be seen from Figure 7b that the cover 81 is traditionally made from two parts interlocked together by press seems 77.

Claims: A pretensioner arrangement for a vehicle safety restraint retractor, the pretensioner comprising: a piston (27) movable along a cylinder (30)under action of gas from a gas generator (37), the piston (27) being connected to one end of a cable (28), the other end of which is connected to means for shortening the effective length of belt webbing available to the vehicle occupant, wherein an elastomeric seal (29) is provided on the piston (27) at one end, characterised in that the seal seals the piston to the cable (28), such that the elastomeric seal (29)is compressed and temporarily absorbs some of the force generated by the gas generator (37) on detonation of the pretensioner when a crash situation is sensed. A pretensioner according to claim 1 wherein the seal (29) is made of a resilient plastics material. A pretensioner according to claim 2, wherein the seal (29) is made of Elastollan. A pretensioner according to claim 1, 2 or claim 3, wherein the gas generator (37) comprises a burst disc (68) at one end through which the gas is released on detonation, the burst disc (68) being circumscribed by a line of weakness around a substantial part of its periphery and having a segment of its periphery reinforced so that on detonation of the gas generator, the opened burst disc is retained attached to the gas generator by the reinforced segment. A pretensioner according to claim 1, 2, 3 or 4, wherein the gas generator (37) is formed of aluminium and one end of the gas generator (37) is reinforced by a steel ring (69) with a diameter slightly larger than the diameter of said one end. A pretensioner according to claim 5 further comprising a sensor lever (34) which rests against the gas generator in the region of the steel ring (69). A pretensioner according to claim 6, wherein the sensor lever (34) is reinforced with a steel pin (70) incorporated into-its structure. A pretensioner according to claim 6 or 7 wherein the sensor lever (34) is provided with a curved profile. A pretensioner according to claim 7 or 8 wherein the sensor lever (34)is coated with molycote.

Inventors: MARSHALL STEVEN JOHN, MARSHALL, STEVEN JOHN
Applicants: BREED AUTOMOTIVE TECH, BREED AUTOMOTIVE TECHNOLOGY, INC.
Application year: 1997
Main classification: B60R22
IPC codes: B60R22