WO1989001430A1

WO1989001430A1 - Seat belt pretensioner

Info

Publication number: WO1989001430A1
Application number: PCT/GB1988/000673
Authority: WO
Inventors: Peter Michael Frederick Watson
Original assignee: The Secretary Of State For Transport In Her Britan
Priority date: 1987-08-17
Filing date: 1988-08-15
Publication date: 1989-02-23
Also published as: AU2231588A; GB8719415D0

Abstract

A vehicle seat belt (20) pretensioner is actuated by relative movement between a resiliently mounted unit such as an engine (11) and gearbox assembly and body structure (12). Actuation may occur during heavy braking, and the system is self re-setting after actuation occurs as a result of events which have not caused permanent movement between unit (11) and structure (12).

Description

SEAT BELT PRETENSIONER

The present invention relates to seat belt pretensioners and to the derivation of motive power for the operation thereof.

Motor manufacturers are continuously striving to reduce the fuel consumption of vehicles they produce. One method of reducing the fuel consumption is minimisation of vehicle drag, and to aid the achievement of this aim it is usual for windscreens to be raked. Inevitably in a car carrying a hi y raked windscreen the top of the screen is closer to the head of a front seat occupant than is the case with a lesser raked windscreen.

The provision and use of front seat safety belts in cars is, with fe^'w exceptions, mandatory in the UK. Most new cars are now fitted with seat belts which allow the wearer some freedom of movement but which lock'automatically in the event of a deceleration larger than a preset threshold value. The locking mechanism of the belts is most commonly an inertia reel system. The lock mechanism operates on the reel and not on the belt, and the belt wearer is still free to move until the slack in the belt and around the reel has been taken up by motion of the wearer. The belt also tends to stretch under tension. In the event of an impact the belt wearer is thrown forwards in the car towards the windscreen, and in a car with a steeply raked windscreen the movement may be sufficient to allow his head to strike the windscreen or its surround. There is also a danger that similar misfortune may occur to a belt wearer, par- ticularly a passenger, in the event of heavy braking.

There is a requirement, therefore, for slack in the belt to be eliminated in the event of an impact, or on heavy braking, so that movement of the belt wearer is limited to that allowed by stretch of the belt. Methods for pretensioning a seat belt in the event of an impact have been suggested. For example UK patent number 1384988 (Daimler-Benz) describes a radar proximity-measuring device pro¬ grammed to detect an imminent impact and to vary the restraining force on a safety belt accordingly. The system operates by supply¬ ing pneumatic or hydraulic pressure, by means of a pump, stored energy device, or combination thereof to a piston and cylinder arrangement. This arrangement is clearly expensive, prone to operation at times inconvenient to a seat belt wearer, such as when a vehicle is in a slow moving traffic stream or entering a garage, and can also be contrary to national laws as being liable to interfere with police speed measuring devices. Another type of known belt tensioner, also made by Daimler-Benz and fitted to some Mercedes cars, is described in detail in Paper Number 26AGARD Conference Proceeding Number 322, 26-29 April 1982, Cologne, Federal Republic of Germany. This tensioner is actuated either by an impact accelerometer or by the crushing of part of a vehicle forward structure. A pyrotechnic charge is fired and drives a hydraulic turbine which turns a belt reel through a clutch. To prevent over- ighten ng of the bel the clutch is set to slip at a preset torque. The system is available in some production cars but does have several disadvantages associated with cost, complexity of the necessary electronics to prevent inadvertent firing, and the impossibility of testing the system without having to replace the pyrotechnic charge. Tensioning only occurs after impact of the vehicle, and must be set at a level where heavy braking cannot actuate the system.

UK Patent 1528908 describeeyet another pretensioning device wherein a bumper is mounted on a piston and cylinder arrangement whereby motion of the bumper relative to the vehicle body results in pretensioning of the seat belts and also in movement of the steering wheel to prevent this being contacted by a driver.

A more recent development as described, inter alia, in an Audi News release on 17 September 1986 and. in the edition of

Autocar on the same date involves the use of a preset cable system to drag the steering wheel forward and to tighten the seat belts. This sustem is actuated by rearward movement of the engine and gearbox relative to the passenger compartment. Clearly this system is designed only for very serious accidents involving major structural damage, as the type of movement required to actuate the system occurs comparatively late in the progress of the damage.

The pretensioning systems described in AGARD Paper 322, in UK Patent 1528908 and in the Audi News Release all require actual impact to occur and also (apart from the use of an accelerometer as one option in the AGARD Paper) require actual physical deformation of vehicle structure before pretensioning occurs. Also none of these systems is self re-setting. In practice, in heavy braking and in minor accidents, which can be severe enough to cause injury to driver or passengers, the initial movement of equipment such as an engine is forward relative to the vehicle bodywork. Also in some major accidents where a vehicle impacts on a corner, rather than head on, there may be insignificant rearward movement of the engine relative to the passenger compartment.

The object of the present invention is to provide a belt pretensioner which avoids the disadvantages of pyrotechnics, is self testing in use, which can in certain circumstances provide belt pretensioning before impact, which is relatively cheap, and which is preferably self re-setting.

According to the present invention a seat belt pretensioner in a vehicle having body structure and equipment resiliently mounted in the body structure is characterised in having fluid powered pretensioning means actuated by forward movement,of the equipment relative to the body structure, hich exceeds a predetermined level.

In one embodiment of the invention motive power for the pretensioner is derived from movement of a resiliently mounted engine and gear box relative to vehicle bodywork. The motive power may be transmitted by pneumatic or by hydraulic means.

The pretensioner may be used in conjunction with a static seat belt, in which case a seat belt wearer can be allowed more freedom of movement whilst wearing the belt under normal conditions than would otherwise be possible. Preferably, however, the pretensioner is used in conjunction with a locking system such as an inertia reel, and when used with an inertia reel seat belt the pretensioner can be arranged either to pull directly on the belt or to pull the belt via the inertia reel whilst the latter stays in the locked position.

The pretensioner can conveniently include a fluid displacer supplying fluid to a piston and cylinder arrangement which acts to pretension the seat belt.

To prevent seat belt induced injuries the pretensioner can be allowed to control forward motion of the seat belt wearer if the seat belt tension exceeds a threshold value. This can be achieved by means of a pressure release valve in the fluid circuit. The fluid circuit may also include a bleed valve which allows the belt tension, after an initial application, to be progressively reduced. In this way an excessive duration of a belt tension, which may be necessary to restrain an occupant in the event of a crash but which may be potentially dangerous to a human frame,can be avoided.

Maximum belt tension may be necessary for no more than about 100 milliseconds.

The belt pretensioner can be arranged to be self testing and to provide pre-impact belt slack removal by initiating the operation of the pretensioner at braking decelerations that are commonly experienced in normal driving. With a static seat belt this deceleration may be set at O.lg and with an inertia reel belt this deceleration should be above 0.3g, the dece/gcation at which the inertia reel locks, and below 0.5g_ja not excessive braking deceleration for every day driving.

When motive power is transmitted by pneumatic means the pretensioner can be reset, on release of tension, by allowing air from atmosphere to re-enter the displacer and by venting the piston and cylinder arrangement to atmosphere. WHen motive power is transmitted by hydraulic means a closed system, similar to that used in braking and clutch systems, can be used.

Some embodiments of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, of which: Figure 1 is an elevation, in section, of a car with an engine movement driven seat belt pretensioner.

Figure 2 is an elevation, in section, of a pneumatic displacer, and

Figures 3, 4, 5 and Figures 6a, b are details of various piston and cylinder arrangements for use in seat belt pretensSoners according to the invention.

A car, of which part is shown at 10 in Figure 1, has an engine 11 mounted on resilient supports 14, and structure 12. A pneumatic displacer 13 is connected by struts 15 to the engine 11 and to structure 12. The displacer 13 is connected by a pipe 16 to a piston and cylinder arrangement 17. The piston of the piston and cylinder arrangement 17 is secured by a connecting rod 18 to an inertia reel mechanism 19 on which is mounted one end of a seat belt system 20 securing a car occupant 21.

In operation, when heavy braking or impact occurs, the engine 11 moves on the resilient mounting 14 relative to the fixed structure 12 causing the pneumatic displacer 13 to pump air 16 to the piston and cylinder arrangement 17. Movement of the piston in the cylinder moves the inertia reel 19 (which is by this time locked) pretensioning the seat belt 20 and holding the occupant 21 securely in his seat. Details of pneumatic displacers and piston and cylinder arrangements as used in the invention will now be described.

A pneumatic displacer 13 (Figure 2) has a cylinder portion 40 secured by a strut 15 to the engine 11 (not shown in this figure) and a piston portion 41 connected by a strut 15 to structure 12 (not shown in this figure). A pipe 16 leads away from the cylinder portion 40 and a space 42 within the cylinder portion 40 and bounded by piston 41 is connected to atmosphere via a bore 43 in piston 41 and non return valve 44. In operation relative movement of engine 11 and structure 12 caused by heavy braking or impact moves struts 15 and hence piston 14 relative to cylinder 40 thus reducing the area of space 42 and forcing air along the pipe 16. When the relative motion has been induced by heavy braking release of the braking allows piston 41 and cylinder 40 to return to their original position increasing the area 42. Air is not allowed to return along the pipe 16 (as described below) but is allowed to enter chamber 42 through the bore 43 and non return valve 44.

A piston and cylinder arrangement for use with a belt pretensioner, as shown in Figure 3, has a cylinder 50 divided into chambers 51, 52 by a piston 53 connected by a connecting rod 18 to an inertia reel 19. A seat belt 20 is attached to the inertia reel. A spring 54 in chamber 52 urges piston 53 in a sense tending to increase the area of chamber 52. Pipe 16 from the pneumatic displacer 13 (not shown in this figure) leads via a non return valve 55 into chamber 51. The pneumatic circuit of pipe 16 also includes, downstream of the non return valve 55, a pressure relief valve 56. In operation, when air is supplied from the pneumatic displacer 13 through pipe 16 it is allowed to pass through the non return valve 55 to the chamber 51. The piston 53 is moved against the pressure of spring 54 and the inertia reel 19 is therefore moved, through being connected to piston 53 by connecting rod 18, in a sense tending to tighten the seat belt 20. As the inertia reel 19 locks with this impulse the seat belt 20 is tightened. The pressure release valve 56 is adjusted such that the tension in the seat belt 20 is prevented from reaching a level where it will cause injury to a person wearing the seat belt. The pressure release valve 56 may also contain a time delay which allowfa potentially injurious tension to be maintained for a period (for example 100 milliseconds) to restrain a seat belt wearer during the critical stage of an impact, after which the pressure is released. In cases where the pretensioner is activated by heavy braking, once the heavy braking stops there is no requirement for the seat belt to be pretensioned and air is allowed to escape from the chamber 51, either by leakage past the piston 53 or through pressure release valve 56, but not back through non return valve 55, so allowing spring 54 to return the piston 53 and hence inertia reel 19 to their original positions, and in this way releasing the tension.

In another arrangement of the piston and cylinder 17 (Figure 4) the inertia reel 19 is mounted on structure 61 of the car (not shown) and the piston 53 is connected by connecting rod 18 to a self locking seat belt clamp 60. Other details are as described above with references to Figure 3, as is operation of the arrangement.

In yet another piston and cylinder 17 arrangement (Figure 5) movement of the piston 53 operates via a cord or wire 71 to rotate a cylinder 70 which is secured to the inertia reel-. In yet another embodiment of the invention the inertia reel 19 is mounted on structure 61 and the seat belt 20 passes over a first roller 70 rotatably mounted on car structure (not shown) and a second roller 71 rotatably mounted on connecting rod 18. In operation movement of piston 53 moves the second roller 71 and hence tightens the strap 20. As willbe apparent from Figures 6a and b a given movement of piston 53 results in a double movement of seat belt 20. Many other embodiments of the invention will be readily apparent to those skilled in the art. It will also be realised that whilst the embodiments of the invention have been described as using pneumatic operation the invention can readily be adapted to use hydraulics. Suitable hydraulics systems will be readily apparent to those skilled in the art of car manufacture, being adaptions of conventional braking and clutch systems.

A feature of the invention is, it will be realised, that when pretensioning has resulted, from an event, such as braking, which does not cause permanent dispacement of the engine (11) relative to the structure (12), the system will be self re-setting.

Claims

CLAIMS What is claimed is:

1. A seat belt (20) pretensioner in a vehicle having body structure (12) and equipment (11) resiliently mounted in the body structure (12), characterised in having fluid powered pretentioner (13, 17) means actuated by forward movement,of the equipment relative to the body structure,which exceeds a predetermined level.

2. A seat belt pretensioner as claimed in Claim 1 charaterised in that the equipment (11) is a resiliently mounted engine and gear box.

3. A seat belt pretensioner as claimed in Claim 1 or 2 characterised in that the fluid powered pretensioning means is pneumatic.

4. A seat belt pretensioner as claimed in Claim 1 or 2 characterised in that the fluid powered pretensioning means is hydraulic.

5. A seat belt pretensioner as claimed in any one of Claims 1 to 4 characterised in acting on a static seat belt (20) .

6. A seat belt pretensioner as claimed in any one of Claims 1 to 4 characterised in acting on a locking seat belt (20).

7. A seat belt pretensioner as claimed in Claim 6 characterised in that locking is affected by an inertia reel system (19).

8. A seat belt pretentioner as claimed in Claim 7 characterised in that tension is directly applied to the belt (20) .

9. A seat belt pretensioner as claimed in Claim 7 characterised in that tension is applied to the inertia reel (19).

10. A seat belt pretensioner as claimed in any one of Claims 1 to 9 characterised in having a fluid displacer (13) which supplies fluid to a piston and cylinder arrangement (17) which acts to pretension the seat belt (20).

11. A seat belt pretensioner as claimed in any one of Claims 1 to 10 characterised in having means for allowing forward motion of a seat belt wearer (21) relative to a seat if-the seat belt (20) tension exceeds a threshold value.

12. A seat belt pretensioner as claimed in Claim 11 characterised in that the means include a pressure relief value.

13. A seat belt pretensioner as claimed in any one of Claims 1 to 12 characterised in having bleed means to allow tension, after an initial application, to be progressively reduced. •

14. A seat belt pretensioner as claimed in any one of Claims 1 to 13 characterised in being arranged to operate at braking decelerations experienced in normal driving.

15. A seat belt pretensioner as claimed in any one of Claims 1 to 13 characterised in being self re-setting after being actuated as a result of events not resulting in permanent displacement of the equipment (11) relative to the structure (12).