GB2314755A - Safety belt pretensioner with energy absorbing means - Google Patents

Abstract

A safety-belt pretensioner comprises a spool 6 on which part of a safety-belt is wound, connected for co-rotation with a reversible motor 21. In operation, a crash sensor 12 triggers a gas generator 13, discharging a large volume of gas at high velocity into one portion 14 of a cylinder, driving a piston 15 and forcing a hydraulic fluid from a first reservoir 16 to a second reservoir 23 via a flow passage 17 and through a reversible motor 21. The reversible motor 21 and spool 6 thus rotate and pretension the safety-belt. A fluid flow control means, comprising a non-return valve 18 connected in parallel across a reduction valve 19, allows substantially unrestricted fluid flow from the reservoir 16 towards the reversible motor 21 but restricts the flow in the opposite direction to allow a controlled pay-out of the safety belt from the spool 6.

Description

2314755 PATENTS ACT 1977 Agents Ref: P10659GB-NHF/SP/er Title:

IMPROVEMENTS IN OR RELATING TO A SAFETY-BELT PRETENSIONER THE PRESENT INVENTION RELATES TO a safety-belt pretensioner and, more particularly, relates to a safety-belt pretensioner intended f or use with a saf ety-belt in a motor vehicle such as a motor car.

It has been proposed previously to provide a safety-belt in a motor car with a pretensioner mechanism adapted to apply an initial tension to the safety-belt when an accident occurs.

The advantage of providing the safety-belt with a pretensioner mechanism is that, when an accident occurs, the safety-belt is drawn tightly across the chest and lap of the occupant of the vehicle, with the mechanism taking up any slack in the safety-belt, holding the occupant firmly in the seat.

It has been proposed to use a f luid motor in a pretensioner mechanism. For example, GB-A-1,587,460 discloses an arrangement in which a Pelton wheel is connected to one end of a spool around which the saf etybelt is wound, and water is directed towards the Pelton wheel, when an accident arises, to rotate the wheel and the spool, thus tensioning the safetybelt. The water is not retained within the system when an accident occurs, but is simply wasted.

DE-A-2,814,487 discloses an alternative arrangement in which a motor is again provided at the end of the spool.

2 The motor comprises a housing which def ines a chamber of circular cross- section which receives a rotatable element. This rotatable element is provided with outwardly biassed scraper elements which engage the inner wall of the chamber. Gas is supplied to the chamber causing the element to rotate, thus applying tension to the safetybelt.

A significant disadvantage of the prior art arrangements is that when the pretensioners are activated, they reel in the safety-belt drawing it tightly across the chest and lap of the occupant and lock the safety-belt in this tight position. In the event of an accident, an occupant of a motor vehicle will have a substantial degree of inertia. Whilst the motor vehicle is usually brought to an abrupt halt, the occupant, due to inertia, will continue to move forwardly relative to the vehicle seat, against the tensioned safety-belt. Thus, the tensioned safety-belt exerts a substantial pressure on certain areas of the occupant's body which may result in serious injury. Whilst most safety-belts have a certain degree of inherent elasticity due to the nature of their construction, this may not prove to be capable of absorbing the kinetic energy of the occupant of a vehicle in certain situations.

It is an object of the present invention to provide an improved safetybelt pretensioner.

According to this invention there is provided a safety-belt pretensioner comprising a spool on which part of a safety-belt is wound, and means responsive to an indication that an accident is occurring or is likely to occur, said means being adapted to drive an hydraulic fluid from a first reservoir to a second reservoir through a flow passage arrangement which incorporates a rotating means to 3 reversibly convert linear fluid flow to rotary motion, the rotating means being connected to co-rotate with the spool, and which also incorporates a fluid flow control means adapted to allow substantially unrestricted fluid flow from the first reservoir to the second reservoir, and to restrict fluid flow in the opposite direction.

Conveniently said fluid flow control means comprises a non-return valve connected in parallel across a reduction valve.

Advantageously said means responsive to an indication that an accident is occurring or is about to occur comprises a gas generator adapted to supply gas to drive said hydraulic fluid.

Preferably said gas is directed to a cylinder containing a piston adapted to drive the hydraulic fluid from the first reservoir to the second reservoir.

Conveniently said second reservoir comprises a resilient bladder.

Advantageously said rotary means comprises a reversible rotary motor.

Preferably the pretensioner further comprises a sensor adapted to provide an output signal in response to one or more parameters that indicate that an accident is occurring or is likely to occur, to provide said indication that an accident is occurring or is likely to occur, the sensor being connected to the driving means.

4 In a preferred embodiment the gas generator comprises a pyrotechnic device, but alternatively it may comprise a source of compressed gas.

In order that the invention may be more readily understood, and so that further features thereof may be appreciated, the invention will now be described by way of example, with reference to the accompanying drawings in which:

FIGURE 1 is a perspective view of part of a safetybelt pretensioner in accordance with the invention; FIGURE 2 is a schematic view illustrating some operative parts of the pretensioner of Figure 1; FIGURE 3 is an elevational view of part of the pretensioner of Figures 1 and 2; FIGURE 4 is a perspective view of another part of the pretensioner of Figures 1 and 2; and FIGURE 5 is an elevational view corresponding to Figure 3 illustrating components of the pretensioner in a subsequent position.

Referring initially to Figure 1, a pretensioner for a safety-belt comprises a substantially U-shaped metal frame 1 having a base 2 and two spaced-apart side arms 3,4. The base 2 is provided with a plurality of apertures 5 to enable the frame 1 to be secured in position.

Extending between the two side arms 3,4 is a spool 6 upon which is wound a reel 7 of safety-belt 8. The spool is mounted for rotation about its axis by the arms 3,4.

The side arm 3 carries a housing 9 which contains a conventional locking mechanism adapted to lock the spool 6 in response to a rapid deceleration of the vehicle, or in response to the safety-belt being withdrawn rapidly from the spool, thus preventing the safety-belt 8 being substantially withdrawn from the reel 7 on the spool 6. Such locking mechanisms are well-known, and so will not be described in detail here.

The side arm 4 carries, on its outer surface, a housing 10 which contains a conventional spring mechanism adapted to provide a torsional force tending to rotate the spool 6 to retract the safety-belt 8 on to the spool 6 to form the reel 7. Such spring mechanisms are well-known and so will not be described in detail here.

Adjacent the housing 10, there is provided a further housing 11 containing a pretensioning device, the essential components of which are illustrated schematically in Figure 2.

Turning now to Figure 2, there is provided a sensor 12 adapted to provide an output signal in response to one or more parameters that indicate that an accident is occurring or is likely to occur. The sensor 12 may comprise one or more accelerometers adapted to respond to deceleration of the vehicle in excess of a predetermined limit.

The output of the sensor 12 is applied as a triggering input to a gas generator 13, which may comprise a pyrotechnic charge. A conduit extends from the gas generator to one end of a cylinder 14 that forms part of a hydraulic system. Spaced slightly from that end of the cylinder is a piston 15 which is slidable within the 6 cylinder. The portion 16 of the cylinder, on the side of the piston remote from the conduit extending to the gas generator, operates as a reservoir containing an hydraulic fluid, such as oil. The portion 16 of the cylinder communicates with a flow passage 17.

The flow passage 17 is connected to a non-return valve 18 which permits a substantially unrestricted fluid f low in one direction, that is to say a flow direction leading away from the cylinder 14. The flow passage 17 is also connected to a reduction valve 19 which is connected in parallel with the non-return valve 18, and which permits a restricted fluid flow at least in a flow direction opposite to said one direction. The non- return valuve 18 and the reduction valve 19 are both connected to a single conduit which is sealed by a breakable foil 20. The foil 20 retains the hydraulic fluid initially in the part of the system comprising the cylinder 14 and the valves 18 and 19.

The valve arrangement comprising the combination of the non-return valve 18 and the reduction valve 19 will operate as a fluid flow control means and is connected, via the flow passage containing the breakable foil 20, to a reversible hydraulic motor 21. A reversible hydraulic motor is a motor which reversibly converts a fluid flow into a rotary motion. Thus, if a fluid flow is directed to the motor, an operative part of the motor is rotated. Also, if the operative part of the motor is rotated (for example by an external force), a fluid flow is created. The reversible motor 21 is associated with the spool 6 such that the operative parts of the reversible motor 21 and the spool 6 co-rotate.

The reversible motor 21 is provided with a further flow passage 22 which leads to a second reservoir 23 for 7 hydraulic fluid. In its initial condition, the flow system defined by the portion 16 of the cylinder 14, flow passage 17, non-return valve 18 and reduction valve 19, is primed with hydraulic fluid. The reversible motor 21, flow passage 22 and second reservoir 23 are initially empty of hydraulic fluid, the breakable foil 20 acting as a barrier to the fluid.

In the event of an accident occurring, the sensor 12 provides an output signal in response to one or more parameters indicating that an accident is occurring or is likely to occur. The output of the sensor 12 is then applied to the gas generator 13, triggering the gas generator 13.

Upon activation, the gas generator 13 discharges a large volume of gas at high velocity through the associated conduit and into one end of the cylinder 14. Due to the initial proximity of the piston 15 to said end of the cylinder, the effective volume of the space within the cylinder 14 into which the gas passes is significantly less than the volume of gas produced by the gas generator. The resultant pressure of the gas upon the piston 15 drives the piston 15 in a direction away from said end of the cylinder as illustrated in Figure 2.

As the piston 15 moves along the cylinder 14, it reduces the effective volume of the portion 16 of the cylinder 14 that acts as a reservoir. Due to the incompressible nature of the hydraulic fluid within the cylinder, said fluid is driven out of the cylinder and along the flow passage 17. The majority of the hydraulic fluid is allowed to pass as a substantially unrestricted fluid flow through the non-return valve 18 towards the second reservoir 23. It is to be appreciated, however, 8 that a small proportion of the hydraulic fluid may also be allowed to pass through the reduction valve 19 towards the second reservoir 23.

After passing through the valve arrangement, the hydraulic fluid then breaks the breakable foil 20 and passes into the reversible motor 21,1 rotating the operative part of the reversible motor 21 which in turn rotate the spool 6 such that the safety-belt 8 is wound onto the reel 7 on the spool 6, thus tightening the safety-belt across the occupant of the vehicle. Fluid outflow from the reversible motor 21 passes along flow passage 22 and into reservoir 23 which has sufficient volume to accommodate this inflow of fluid.

As the occupant of the vehicle begins to move forwardly with inertia relative to the vehicle, as a result of the accident, the occupant applies a force to the safety-belt which tends to unwind the safety-belt from the reel 7 on the spool 6. As the spool 6 begins to rotate in the counter-clockwise direction as illustrated in Figure 2, the associated operative part of the reversible motor 21 begin to co-rotate in the same sense. The reversible motor 21 thus draws hydraulic fluid from the reservoir 23 as it rotates and ejects hydraulic fluid towards the valve arrangement.

The presence of the non-return valve 18 within the valve arrangement prevents fluid flow through the valve 18 in the direction from the reversible motor 21 towards the reservoir 16. Thus, the entire fluid flow from the reversible motor 21 is driven through the reduction valve 19. This reduction valve 19 presents a constriction through which the fluid is driven, resulting in a dampening effect which restricts the rotation of the reversible motor 9 21 and thus the spool 6. In this way, the pay-out of the safety-belt from the reel 7 on the spool 6 is controlled, thus absorbing a substantial proportion of the kinetic energy of the moving occupant.

The presence of the piston 15 between the gas from the gas generator and the hydraulic fluid prevents any debris that may be in the gas, from the pyrotechnic charge, contaminating the hydraulic fluid.

Referring now to Figure 3, a preferred reversible motor 21 is illustrated. The reversible motor comprises a substantially cylindrical housing 25 which defines a cylindrical recess 26 therein. Within recess 26, there is provided a rotatable annular element 27 of circular outer cross-section, the outer cross-section being of slightly smaller diameter than the cylindrical recess 26. The annular element 27 defines a central aperture 28 having a cross-section in the form of a five-pointed star with concave sides and radially convex corners.

Within the aperture 28, there is provided a rotor 29 of substantially square cross-section having convex sides, and radially concave corners 30. The corners 30 of rotor 29 each have a radius substantially equal to that of a corner of aperture 28. The top faces of the housing 25, the rotatable annular element 27 and the rotor 29 are substantially co-planar.

The rotor 29 is connected to the shaft of the spool 6 which passes through an aperture formed in the base of the recess 26 formed in the housing 25. The rotor 29 can rotate about an axis formed by the shaft of the spool 6, the corners 30 of the rotor 29 being constantly in contact with the sides of aperture 28. As the rotor 29 rotates, the annular element 27 also rotates in the same direction but with a lower speed of rotation.

Turning now to Figure 4, there is provided a cover plate 31 of substantially the same external cross-section as the housing 25. The cover plate 31 and the housing 25 are each provided with four mounting apertures 32. The cover plate 31 may be engaged with the housing 25, with the apertures 32 in the housing and the cover plate co-aligned. Fastening bolts may pass through the co-aligned apertures to retain the cover in sealing engagement with the housing.

The inner face of the cover plate is substantially planar and is in contact with the top faces of the housing 25, the rotatable annular element 27 and the rotor 29.

The cover plate 31 is provided with a pair of diametrically opposed apertures 33,34 formed in oppositely outwardly directed side edges of the cover plate. The apertures 33,34 communicate with radially inwardly directed flow passages 35,36 respectively, which flow passages subsequently communicate with respective inwardly facing apertures 37,38 formed in the inner face of the cover plate. The positioning of the flow passages 35,36 and the apertures 37,38, when the cover plate 31 is engaged with the housing 25, are illustrated by dotted lines on Figures 3 and 5. As can be seen, each aperture 37,38 is offset slightly from the central horizontal axis of the pump.

The reversible motor 21, as shown in Figures 3 to 5, has the aperture 33 connected to the valve arrangement and the aperture 34 connected to the further flow passage 22.

11 In operation of the reversible motor 21 during pretensioning of the saf ety-belt, the aperture 3 3 serves as the fluid inlet to the reversible motor 21. Fluid f lows from the valve arrangement, via aperture 33, into flow passage 35 and then outwardly from aperture 37 and into a space 39 between the rotor 29 and element 27. This fluid flow, being introduced to the rotor 29 through an aperture 37 which is offset from the central axis of the pump, causes counter-clockwise rotation of the rotor 29 which, in turn, causes counter-clockwise rotation of element 27, the rotation of element 27 being in the same sense as, but at a lower annular speed than, that of the rotor 29. As the annular element 27 and the rotor 29 rotate, the effective volume of space 39 increases, while the effective volume of a space 40 which is initially adjacent the aperture 38 decreases, as shown in Figure 5. The decrease in volume of space 40 forces the fluid therein, via aperture 38, into flow passage 36, and then through aperture 34 and into flow passage 22, aperture 34 in the cover plate 31 serving as the outlet port from the pump. As the rotor rotates fluid introduced to the space 39 is moved to occupy the position initially occupied by the fluid in space 40.

Once the safety-belt is fully pretensioned, and the occupant of the vehicle begins to move forwardly with respect to the vehicle, the safetybelt begins to pay out from the reel 7 on the spool 6 which thus reverses the direction of rotation of the reversible motor 21, which also reverses the direction of fluid flow. In operation during the controlled pay out of the safety-belt, aperture 34 serves as the fluid inlet to the reversible motor 21. Fluid flows via aperture 34 into flow passage 36, and then outwardly from aperture 38 and into space 40 between the rotor 29 and the annular element 27. This fluid flow causes clockwise rotation of the rotor 29 which, in turn, 12 cause clockwise rotation of the annular element 27. As the annular element 27 and the rotor 29 rotate, the effective volume of space 40 increases, while the effective volume of space 39 decreases. The decrease in volume of space 39 forces the fluid therein into flow passage 35 via aperture 37. Aperture 33 in the cover plate 31 now serves as the outlet port from the pump, and communicates with the valve arrangement.

It is to be appreciated that whilst the invention has been described with reference to one specific embodiment, various modifications could be effected without departing from the scope of the invention. For example, instead of using a pyrotechnic charge to generate gas, a source of compressed gas could be utilised. A f urther modification may involve replacing the piston 15 with a thin sheet of metallic foil. Upon activation of the gas generator, said metallic foil would be punctured and the pressure of the gas would directly act upon the hydraulic fluid in reservoir 16, driving said fluid towards the second reservoir 23. The reservoir 23 may comprise a closed vessel, a vessel with ventilation valves, or a resilient bladder.

A still further modification may involve positioning the breakable foil 20 between reservoir 16 and the valve arrangement comprising non-return valve 18 and reduction valve 19. In this arrangement, only the reservoir 16 and part of flow passage 17 would initially be primed with hydraulic fluid. It should be appreciated that such an arrangement would require a larger reservoir 16 to accommodate sufficient fluid to drive the reverible motor 21.

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Claims (11)

CLAIMS:

1. A safety-belt pretensioner comprising a spool on which part of a safety-belt is wound, and means responsive to an indication that an accident is occurring or is likely to occur, said means being adapted to drive an hydraulic fluid from a first reservoir to a second reservoir through a flow passage arrangement which incorporates a rotating means to reversibly convert linear fluid flow to rotary motion, the rotating means being connected to co-rotate with the spool, and which also incorporates a fluid flow control means adapted to allow substantially unrestricted fluid flow from the first reservoir to the second reservoir, and to restrict fluid flow in the opposite direction.

2. A pretensioner according to Claim 1, wherein said fluid flow control means comprises a non-return valve connected in parallel across a reduction valve.

3. A pretensioner according to any one of the preceding claims, wherein said means responsive to an indication that an accident is occurring or is about to occur comprises a gas generator adapted to supply gas to drive said hydraulic fluid.

4. A pretensioner according to Claim 3, wherein said gas is directed to a cylinder containing a piston adapted to drive the hydraulic fluid from the first reservoir to the second reservoir.

5. A pretensioner according to any one of the preceding claims, wherein said second reservoir comprises a resilient bladder.

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6. A pretensioner according to any one of the preceding claims, wherein said rotary means comprises a reversible hydraulic motor.

7. A pretensioner according to any one of Claims 3 to 6, wherein the gas generator comprises a pyrotechnic device.

8. A pretensioner according to any one of Claims 3 to 7, wherein the gas generator comprises a source of compressed gas.

9. A pretensioner according to any one of the preceding claims further comprising a sensor adapted to provide an output signal in response to one or more parameters that indicate that an accident is occurring or is likely to occur, the sensor being connected to the driving means.

10. A pretensioner for a safety-belt substantially as herein described with reference to and as shown in the accompanying drawings.

11. Any novel feature or combination of features disclosed herein.