GB2371780A

GB2371780A - A safety-belt arrangement

Info

Publication number: GB2371780A
Application number: GB0102926A
Authority: GB
Inventors: Fredrik Wigstrom; Anders Ingemarsson
Original assignee: Autoliv Development AB
Current assignee: Autoliv Development AB
Priority date: 2001-02-06
Filing date: 2001-02-06
Publication date: 2002-08-07
Also published as: GB0102926D0; GB2371782A; GB2371782B; GB0114284D0; GB2371781A; DE10296133T5; GB0114285D0; GB2371781B; DE10296133B4

Abstract

A safety-belt arrangement for use in a motor vehicle has a safety-belt (5), one end of which is connected to a retractor (8). A sensor (11) generates a signal representative of the amount of safety-belt paid-out from the retractor. A force limiter (10) is associated with the retractor to permit safety-belt to be paid-out with a variable force limiting effect. A control arrangement (12) changes the level of force applied by the force limiter (10) in dependence upon the length of safety-belt paid-out from the retractor.

Description

DESCRIPTION OF INVENTION "IMPROVEMENTS IN OR RELATING TO A SAFETY-BELT ARRANGEMENT" THE PRESENT INVENTION relates to a safety-belt arrangement, and more particularly relates to a safety-belt arrangement intended for use in a motor vehicle.

A simple safety-belt arrangement, as in widespread use, comprises a lapand-diagonal safety-belt arrangement, with one end of the safety-belt being anchored to part of the vehicle, an intermediate part of the safety-belt being provided with a tongue releasably engageable with a fixed buckle, and the other end of the safety-belt being wound on to the spindle of a retractor. The retractor incorporates a mechanism which locks the spindle of the retractor to prevent further safety-belt being paid out from the retractor when an accident or a potential accident situation is sensed. If the safety-belt is locked in this way, however, the safety-belt can, in certain circumstances, apply a very great retarding force to the occupant of the vehicle, decelerating the occupant very swiftly, and also possibly injuring the occupant. Thus it has been proposed to provide a force limiter in a safety-belt system, the force limiter being adapted to enable certain length of safety-belt to be paid-out, with a force limiting or energy absorbing effect, when very high forces are applied to the safety-belt.

It has been proposed to provide an arrangement in which the force limiting effect can be varied, at the start of or during an accident situation, in dependence upon the load applied to the safety-belt. An arrangement of this type is disclosed in WO 9749583-A in which the reel of a retractor is provided with a torsion bar arrangement which provides the force limiting effect. The torsion bar arrangement includes an axially extending torsion bar and a co-axial torsion sleeve. The torsion bar and the torsion sleeve each terminate with a portion having a toothed periphery which can be releasably engaged by a respective ratchet element. In this way the level of force of the force limiting effect can be selected.

It is desirable, in a typical accident situation, for the force limiter to provide a high force limiting effect during the initial stages of the accident, as the occupant of the seat begins to move forwardly, and to provide a lower force limiting effect at a subsequent stage in the accident when the occupant has moved forwardly and begins to impact with the inflating air-bag. It has, therefore, been proposed to have an arrangement in which the force level (or energy absorbing level) of the force limiter is adjusted after a predetermined period of time has elapsed following the sensing of an accident or a potential accident situation, and thus after the pretensioner has been triggered. However, an arrangement of this type suffers from various disadvantages.

Many accidents start with minor or short interaction with a first object, such as an impact with a car having a relatively low speed, or an impact at the edge of the road, with this minor or short interaction being followed, some moments later, by a severe impact with a second object, such as an on-coming high speed car, a tree or a building. In such a situation the first interaction would be sensed by the sensors provided in the motor vehicle to detect an accident or a potential accident situation. The sensor may control various safety devices within the motor vehicle, such as a pre-tensioner and an air-bag, but would also start the timer associated with the force limiter.

In an accident of this type, the force limiter would exhibit a high level of force for a period of time following the minor or short interaction, but the occupant of the vehicle may not move forwardly at all, or may move forwardly only by a very short distance during this period of time. Before the severe impact with the second object, the timer may have timed-out, and thus the force limiter would only have the lower level of force. Then, when the severe impact occurs, which will cause the occupant to move forwardly, the level of force provided by the force limiter might well be too low to absorb all of the energy of the occupant before the occupant hits the steering wheel or the dashboard.

A further disadvantage of using an arrangement which incorporates a timer is that the instant of recognition of a crash by the crash algorithm associated with the crash sensor (i. e. normally the moment to triggering the pretensioner) varies considerably (typically 2 ms) relative the main crash pulse, or the most severe deceleration experienced during the accident, which will cause the occupant to move forward relative to the vehicle compartment.

This will cause the same problem as above.

The present invention seeks to provide an improved safety-belt arrangement.

According to this invention there is provided a safety-belt arrangement for use in a motor vehicle, the safety-belt arrangement comprising a safety-belt, one end of which is connected to a retractor, a sensor adapted to generate a signal representative of the amount of the safety-belt paid-out from the retractor, a force limiter associated with the retractor adapted to permit the safety-belt to be paid-out with a variable force limiting effect, means to change the level of force applied by the force limiter, and a control unit to receive a signal from the sensor and to generate, at least partially in response to said signal, an output signal to control the means which change the level of force.

Preferably the retractor incorporates a pretensioner.

Conveniently the control unit generates said output signal in response to the amount of webbing paid-out in excess of the amount of webbing paid-out prior to activation of the pretensioner.

Alternatively the control unit generates said output signal in response to the amount of webbing paid-out in excess of the amount of webbing paid-out immediately after the pretensioner has been activated.

In a preferred embodiment means are provided to lock the safety-belt in response to a sensed parameter and the control unit generates said output signal in response to the amount of webbing paid-out in excess of a reference length, means being provided to determine the reference length at or about the instant of locking of the safety-belt.

Conveniently a further sensor is provided to generate a signal representative of a parameter of the occupant, which signal is supplied to the control unit, the output signal of the control unit also being related to the signal from the second sensor.

In one embodiment the further sensor determines the weight of the occupant of the seat.

In another embodiment the further sensor is a capacitative sensor adapted to determine the water content of the occupant of the seat.

In a further embodiment the further sensor is an optical sensor adapted to determine a size parameter of the occupant of the seat.

Preferably the control unit is adapted to categorise an occupant, in response to the signal representative of a parameter, into one of a plurality of categories, the length of safety-belt necessary to be withdrawn to cause the change in the force limiting effect being dependent upon the category of the occupant of the seat.

Conveniently the said variable force limiting effect comprises a plurality of discrete force levels.

Preferably the force levels comprise two discrete force levels.

Advantageously a crash sensor is provided adapted to generate a signal representative of the crash severity, and the force limiting effect is adjusted to be a function of crash severity.

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 I is a diagrammatic figure illustrating one embodiment of the invention, FIGURE 2 is a graphical figure showing a plot of force applied to a safety-belt against the length of belt withdrawn for a typical person provided for purposes of explanation, FIGURE 3 is a graphical figure showing a plot of force applied to a safety-belt and length of belt extracted against time for a situation equivalent to that shown in Figure 1, FIGURE 4 is a further graphical figure corresponding to Figure 2 for a heavy person, and FIGURE 5 is further graphical figure corresponding to Figures 2,3 and 4 for a light person Referring initially to Figure 1 of the accompanying drawings, a vehicle seat 1 having a seat squab 2 and a back-rest 3 is illustrated. The seat is occupied by an occupant 4. The occupant 4 is illustrated wearing a safety-belt that forms a safety-belt arrangement in accordance with the invention. The safety-belt comprises a webbing strap, one end of which is anchored to part of the vehicle seat. Not shown in Figure 1 is a tongue which is mounted on the safety-belt and which is engaged releasably in a buckle provided on the other side of the seat. Part of the safety-belt 5 passes through a pillar-loop 7, and the other end of the safety-belt is connected to a floor mounted retractor 8. The retractor 8 is adapted to respond to an accident situation to lock a spool within the retractor to prevent further safety-belt being paid-out from the retractor, by locking in response to a sensed parameter such as a predetermined deceleration of the vehicle and/or in response to the speed of withdrawal of the safety-belt from the retractor. The retractor is provided with a pretensioner 9 which is adapted, in response to an accident situation being sensed, to rotate the spool of the retractor to wind in part of the safety-belt. Safety-belt arrangements having the features described above are well known and in common use. However, alternative mechanisms which lock the safety-belt in response to a sensed parameter may be used.

The retractor 8 incorporates a variable force limiter 10. The force limiter 10 may be a continuously variable force limiter, such as an adjustable brake mechanism which acts on a disc or drum which co-rotates with the spool of the retractor mechanism, or may be a variable force limiter which provides a plurality of discrete force levels, such as a torsion bar force limiter of the type disclosed in WO 9749583-A.

The retractor 8 is provided with a sensor 11 adapted to sense the amount of safety-belt that has been withdrawn from the sensor. Various types of sensor which perform this function have been proposed before. EP 0 723 895 A discloses an arrangement in which a gear train is provided, driven by the spool of a retractor, which causes the rotation of an element which has a part spiral outer edge. A sensor has a spring-biased probe which engages the part spiral outer edge, so that as safety-belt is withdrawn from the retractor, the element with the part spiral outer edge rotates and the degree of movement of the probe is indicative of the length of safety-belt that has been withdrawn. In another prior proposed arrangement, an element which co-rotates with the spool is provided with a plurality of evenly spaced markings which are sensed by an optical sensor. The optical sensor generates a discrete pulse for each marking that passes the sensor. Appropriate circuitry connected to the sensor can determine the length of safety-belt that has been paid-out by determining the number of rotations, or part rotations, of the spool. A Hall effect sensor can also be used to determine the rotations of the spool when the spool is provided with a number of appropriately located magnets. In preferred embodiments, the sensor senses when withdrawal of safety-belt from the retractor stops as a consequence of the retractor becoming locked.

The output from the sensor 11 is provided to a central control unit 12.

The central control unit 12, in the described embodiment, also receives signals from other sources. The control unit 12 receives signals from an accident sensor 13 in the form of an accelerometer. The accelerometer provides an output signal whenever deceleration in excess of a predetermined threshold is sensed. The accelerometer may also provide a signal which indicates the severity of the crash. Such an accident sensor 13 is conventional. The control unit 12 also receives signals from a further sensor arrangement, which signals are representative of a parameter of the occupant of the seat. In the described embodiment of the invention, a weight sensor 14 is provided which is incorporated within the squab 2 of the seat adapted to generate a signal indicative of the weight of the occupant 4. Such a sensor may include piezoelectric sensor devices. In alternative embodiments of the invention, the seat 1 may include a plurality of capacitative plates which are connected to appropriate circuitry, and which are adapted to determine the change in capacitance between the capacitative plates when the occupant of the seat positions himself on the seat. The change in capacitance is a function of the total water content of the occupant of the seat, which is closely related to the total weight of the occupant of the seat. Thus, by using an arrangement of this type, it is again possible to generate a signal which is at least approximately related to the weight of the occupant of the seat.

In yet a further embodiment of the invention, instead of determining the weight of the occupant of the seat, an optical system may be used which determines, optically, the size of the occupant or the size of at least part of the occupant. This, again, will generate a signal which is at least proportional to the weight of the occupant of the seat.

In the presently described embodiment, the control unit 1 is adapted to control not only the pre-tensioner and the force limiter, but also an air-bag 15, which is located in front of the occupant.

Whilst, in the described embodiment, the single control unit 12 controls a number of different items, in alternative embodiments of the invention, the control function may be divided up between a number of different independent control units.

As will become clear from the following description, in a safety-belt arrangement in accordance with the invention, a variable force limiting effect is provided, with the variation in the force limiting effect being controlled in response to the length of safety-belt that has been paid-out, rather than the time from the commencement of the accident or potential accident situation. Also, in preferred embodiments of the invention, the length of safety-belt that has to be paid-out to effect a change in the force limiting effect is determined in dependence upon sensed parameters of the occupant, and also possibly in response to a signal from the accelerometer indicating the degree of severity of the accident.

Referring now to Figures 2 and 3, which is a graphical figure, the operation of the safety-belt arrangement of Figure 1 in a typical accident for a person of typical or normal weight will be described. The graph of Figure 2 is a plot of the force of the force limiting effect as plotted against the length of safety-belt withdrawn from the retractor. The graph of Figure 3 is a plot of force and length of safety-belt withdrawn against time.

It can be seen that there are two predetermined retarding forces shown on the graph FI and F2, the force F2 being greater than the force Fl. These forces may, by way of example, be considered to be the forces provided by the torsion bar or the torsion tube, respectively, of an arrangement as shown in WO 9749583-A.

The accident situation commences at point 20 on the graph. At this stage a predetermined length of safety-belt has been withdrawn from the retractor as the occupant places the safety-belt in the position illustrated in Figure 1. This length of safety-belt is the length of safety-belt ordinarily deployed when the occupant who is of normal or typical size, is sitting comfortably in an upright position, and is identified as Lo. When an accident, or potential accident situation is sensed by the accelerometer 13, at time to, a signal from the control unit 12 is passed to the pretensioner 9 which is activated to wind in safety-belt on to the spool of the retractor 8. The spool of the retractor thus rotates and the sensor 11 senses that safety-belt is being wound in, against a gently increasing resistive force which gradually rises to a level Fp until the point 21 is reached, when the safety-belt is fully tight around the occupant. The length of belt withdrawn from the retractor is now at a minimum Lmin-The time is now tm, n. The period of time between to and tmin is a as shown in Figure 3. This time period represents the time taken for the pretensioner to pretension the webbing.

During a subsequent period of time, running from tmin to tlock at point 22 in Figure 2, the occupant of the seat moves forwardly and safety-belt is withdrawn from the retractor against a resistive force which, during the relevant time period, which has a duration b (as shown in Figure 3), gradually reduces. At time instant t) oek, the retractor becomes locked by the locking mechanism that forms part of the retractor.

It is to be appreciated that the duration of the time period b coud vary to accident-to-accident due to the fact that the recognition of a crash by the sensor, and thus the instant to, could vary, typically by : 2ms, relative to the main crash pulse or main deceleration of the vehicle, which causes the occupant of the seat to move forwardly. flock occurs at or shortly after the main crash pulse.

During a subsequent time interval, which has a duration c, as the occupant continues to move forwardly slightly the resistive force applied by the retractor rises from the level Fp to the level F2. At the end of this particular phase, the point 23 on the graph is reached. During this phase, that is to say during the phase of movement following locking of the spool and the occupant of the seat moving forward to such an extent that the full resistive force F2 of the force-limiter is experienced, the sensor which senses the length of safetybelt that has been paid-out, takes a reference measurement at time tref, and effectively measures a reference length of safety-belt that is paid-out Lref.

The point at which the reference is made is shown as point 24 on the graph of Figure 1.

If the occupant then moves forwardly, the resistive force F2 is experienced as the safety-belt is paid-out. This is shown by the horizontal line 25 of the graph. The time taken for the occupant to move forwardly, against the resistive force, is not of any relevance since the resistive force F2 will be enabled until a predetermined length of belt has been paid-out. When a predetermined length of safety-belt has been paid-out, as measured from the reference length, Lref, at point 26 on the graph, and identified as Loch, the force limiter 10 no longer provides the high resistive force F2, but instead provides the lower resistive force Fl, as shown at point 27 on the graph. This can be visualised as changing from the torsion bar to the torsion tube of the arrangement of WO 9749583-A. Continued forward movement of the occupant is then effected against the much lower resistive force as shown at line 28. In a

typical case, during this phase of movement of the occupant of the seat, energy is also being absorbed, as shown in phantom at line 29, by an inflating air-bag.

It is to be appreciated that the change of the force level of the force limiter occurs when a certain amount of safety-belt has been paid-out, and thus occurs when a certain amount of energy has been absorbed. In the arrangement described, the length of safety-belt that is paid-out is measured from a reference point which is the length of safety-belt paid-out at the moment that the retractor is locked due to forward movement of the occupant of the seat as a consequence of the substantial deceleration of the vehicle caused by the main "accident pulse". The instant of this"locking"is uncertain in time as regards the instant of initial sensing of an accident situation, and thus it is appropriate to use the moment at which the retractor becomes blocked, or an instant which is, in time, very close to that moment, as a reference point. Thus, provided that the distance Lref is measured during the time period c, the difference between Lref and Lch will be almost constant, and the energy absorbed before the change of force will therefore also be almost constant.

The safety-belt is withdrawn until a maximum extension Lmax is achieved, at which point all of the kinetic energy of the occupant is absorbed.

The transition between the high energy absorbing level F2 and the low energy absorbing level Fi, as shown at 24 and 25 on the graph, is effected when a predetermined length Lch of safety-belt has been paid out. That predetermined length of safety-belt is, as described, preferably measured from Lier, but could alternatively be measured from Lo, the amount of safety-belt withdrawn from the retractor just before the commencement of the accident situation, or from Lamm, the amount of safety-belt withdrawn from the retractor just after the pretensioner has pre-tensioned the safety-belt.

Lmax is selected so that the kinetic energy of the occupant is absorbed before the occupant actually reaches the steering wheel or windscreen.

It is to be appreciated that during the final part of the withdrawal of the safety-belt, the occupant is restrained, not only by the safety-belt but also by the air-bag, and thus the speed of withdrawal of the safety-belt remains substantially constant, and the total retarding force applied to the occupant remains substantially constant. Figure 3 shows, in phantom, at 30, the situation that would prevail if the air-bag did not inflate.

It is preferred that when the occupant of the seat is a heavy or large occupant, the length of safety-belt is paid-out against the high resistive force should be somewhat greater than for an occupant of normal weight. Figure 4 is therefore a graph corresponding to Figure 2, and in which the same reference numerals have been utilised.

As can be seen from Figure 4, the initial point on the graph shows a length of belt Lob withdrawn from the spool, which is less than the length Lo as withdrawn in Figure 2. The reason for this is that with a heavy or large occupant, the vehicle seat will be moved further away from the steering wheel, meaning that less safety-belt has to be withdrawn initially. However, it can equally be seen that the distance between Lob and Lmax and also the distance between Lref and Lhbis much greater than the equivalent distances in Figure 2.

The distance between Lref and Lchb is greater, to enable more energy to be absorbed. The distances are, however, still such that at Lmax the occupant has not actually reached the steering wheel or windscreen.

Referring now to Figure 5 it is to be understood that for a light-weight occupant it may be desirable to omit the very strong energy absorbing force, and to use only the relatively low force. Thus, referring to Figure 5, it is to be noted that the initial extension Los of safety-belt is greater than the extension Lo of Figure 2. The reason for this is that for a light-weight occupant the vehicle seat will be located closer towards the steering wheel than for an occupant of normal weight, meaning that more safety-belt will have to be withdrawn, initially, from the retractor for the safety-belt to be placed in position.

Following commencement of the accident at point 20, safety-belt is withdrawn from the initial extension Los to an extension Lmm, as shown at point 21. During the main crash pulse, that is to say during the time period c, the safety-belt is pulled out from the retractor and the resistive force rises until it reaches the force level Fl at 23. Subsequently the occupant can move forwardly withdrawing the safety-belt, as shown at 25, against the resistive force Pi until the maximum extension of safety-belt Lmax is achieved. It is to be appreciated that much less energy is absorbed during the described procedure, since only the relatively low resistive force Fi is utilised. However, with a light-weight occupant, this is a sufficient degree of energy absorption, since it is only necessary to use the higher force level F2 for a person of normal, or above normal weight.

Whilst reference has been made, in connection with the graphs of Figures 3 and 4, to different operating characteristics being provided depending upon the weight of the occupant of the seat, it is to be fully understood that these different characteristics may be provided in response to any sensed parameter which is related to the weight of the occupant of the seat such as a sensed parameter of the water content of the occupant of the seat, and a sensed parameter relating to the size of the occupant of the seat.

It is to be appreciated that in certain embodiments, the actual level of force exhibited by the force limiter may vary continuously, although in preferred embodiments of the invention, the force limit level can only change between a limited number of discrete levels. Whilst embodiments have been disclosed in which the force limit level can be changed between two discrete levels, it is to be understood that the force limit level can be changed between a plurality of discrete levels. It is to be appreciated that the force limit level actually exhibited by the force limiter may be determined as a function of the crash severity. Thus, in a very severe accident, an initial force limit level may be adopted which is a very high level, which can be visualised as using simultaneously both the torsion bar and the torsion tube of WO 9749583-A.

For simplicity of manufacture, the relationship between the weight or other parameter of the occupant and the functioning of the force limiter may be such that the force limiter has a restricted number of discrete modes of operation, such as, for example, three modes of operation as described. Thus, an occupant of a seat will be assessed, by the appropriate sensor, to determine which category of occupant is present in the seat, and thus which mode of operation is to be utilised.

Thus, in the example given, an occupant of a seat may be assessed as being"light","normal weight"or"heavy", and the described arrangement will then function in the appropriate manner.

In the present specification"comprise"means"includes or consists of and"comprising"means"including or consisting of.

The features disclosed in the foregoing description, or the following Claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

CLAIMS: 1. A safety-belt arrangement for use in a motor vehicle, the safety-belt arrangement comprising a safety-belt, one end of which is connected to a retractor, a sensor adapted to generate a signal representative of the amount of the safety-belt paid-out from the retractor, a force limiter associated with the retractor adapted to permit the safety-belt to be paid-out with a variable force limiting effect, means to change the level of force applied by the force limiter, and a control unit to receive a signal from the sensor and to generate, at least partially in response to said signal, an output signal to control the means which change the level of force.
2. An arrangement according to Claim 1 wherein the retractor incorporates a pretensioner.
3. An arrangement according to Claim 2 wherein the control unit generates said output signal in response to the amount of webbing paid-out in excess of the amount of webbing paid-out prior to activation of the pretensioner.
4. An arrangement according to Claim 2 wherein the control unit generates said output signal in response to the amount of webbing paid-out in excess of the amount of webbing paid-out immediately after the pretensioner has been activated.
5. An arrangement according to Claim 2 wherein means are provided to lock the safety-belt in response to a sensed parameter and wherein the control unit generates said output signal in response to the amount of webbing paid-out in excess of a reference length, means being provided to determine the reference length at or about the instant of locking of the safety-belt.
6. An arrangement according to any one of the preceding Claims wherein a further sensor is provided to generate a signal representative of a parameter of the occupant, which signal is supplied to the control unit, the output signal of the control unit also being related to the signal from the second sensor.
7. An arrangement according to Claim 6 wherein the further sensor determines the weight of the occupant of the seat.
8. An arrangement according to Claim 6 wherein the further sensor is a capacitative sensor adapted to determine the water content of the occupant of the seat.
9. An arrangement according to Claim 6 wherein the further sensor is an optical sensor adapted to determine a size parameter of the occupant of the seat.
10. An arrangement according to any one of Claims 6 to 9 wherein the control unit is adapted to categorise an occupant, in response to the signal representative of a parameter, into one of a plurality of categories, the length of safety-belt necessary to be withdrawn to cause the change in the force limiting effect being dependent upon the category of the occupant of the seat.
11. An arrangement according to any one of the preceding Claims wherein the said variable force limiting effect comprises a plurality of discrete force levels.
12. An arrangement according to Claim 11 wherein the force levels comprise two discrete force levels.
13. An arrangement according to any one of the preceding Claims wherein a crash sensor is provided adapted to generate a signal representative of the crash severity, and the force limiting effect is adjusted to be a function of crash severity.
14. A safety-belt arrangement substantially as herein described with reference to and as shown in the accompanying drawings.
15. Any novel feature or combination of features disclosed herein.