GB2386873A

GB2386873A - Safety arrangement having pedestrian detection system

Info

Publication number: GB2386873A
Application number: GB0207480A
Authority: GB
Inventors: Vincent Mathevon
Original assignee: Autoliv Development AB
Current assignee: Autoliv Development AB
Priority date: 2002-03-28
Filing date: 2002-03-28
Publication date: 2003-10-01
Anticipated expiration: 2022-03-28
Also published as: GB2386873B; GB0207480D0

Abstract

A safety arrangement on a vehicle includes a pedestrian detection system. The system has a first accelerometer (9) mounted on a item such as a bumper which is yieldably mounted to the chassis of the vehicle at the front of the vehicle. There is a second accelerometer (12) located on a second structure which forms part of, or which is less yieldably mounted on the chassis of the vehicle. An evaluation unit (17) receives signals from the two accelerometers to generate a control signal which can be used to deploy the safety arrangement.

Description

DESCRIPTION OF INVENTION

"IMPROVEMENTS IN OR RELATING TO A SAFETY

ARRANGEMENT"

THE PRESENT INVENTION relates to a safety arrangement, and more particularly relates to a safety arrangement provided on a motor vehicle.

It has been proposed to provide a vehicle with a safety arrangement, the safety arrangement being intended to protect a pedestrian struck by the vehicle.

Typically such a safety arrangement incorporates a pedestrian detector which is adapted to detect a pedestrian and, in particular, to detect an impact with a pedestrian. Typically the detector is associated with a mechanism which performs a particular function such as, for example, inflating an air-bag provided on the exterior of the vehicle to protect the pedestrian or, alternatively, a mechanism which raises the hood or bonnet of the vehicle to a position in which the hood or bonnet may deform, when struck by the pedestrian, thus decelerating the pedestrian gradually rather than suddenly.

The present invention relates primarily to the detector portion of such a safety arrangement.

It is, of course, to be understood that if a vehicle is provided with a safety arrangement to provide protection for a pedestrian, the safety arrangement should only be actuated or deployed if there is actually an impact with a pedestrian. If there is an impact with a lighter object, such as a bird or a traffic cone, then the safety arrangement should not be actuated. Similarly, if there is an impact with an object which is heavier than a pedestrian, such as another vehicle, then again the safety arrangement should not be actuated.

Also, the arrangement should be such that the safety arrangement should not be actuated by driving along a rough road, or by the wheels of the vehicle hitting an object such as, for example, a curb. Thus, if accelerometers are used, care must be taken that the accelerometers are arranged in such a way that inadvertent actuation of the safety arrangement, by driving on a rough road or by hitting a curb is prevented.

It would be possible to consider using one accelerator in the bumper or fender of a motor vehicle, and another accelerometer mounted on the chassis of the vehicle. By comparing the signals generated by the two accelerometers it may be possible to distinguish between an impact with a pedestrian and an impact with a lighter object, such as a bird or cone and a heavier object such as another vehicle. However, it has been found that if only two accelerometers are used in this manner, there is a substantial risk that the safety arrangement will be actuated when driving along a rough road. Whilst it would be possible to add a contact sensor in the bumper or fender, which would give an arrangement which would not be deployed simply by driving along a rough road, it has been found that contact sensors in the bumper or fender are generally unreliable, and are also relatively complex.

The present invention seeks to provide an improved safety arrangement.

According to this invention there is provided a safety arrangement provided on a vehicle, the arrangement incorporating a pedestrian detection system, the system comprising at least one first accelerometer mounted on a first structure located at the front of the vehicle, the first structure being yieldably mounted to the chassis of the vehicle, and at least one second accelerometer mounted on a second structure located adjacent the first structure and forming part of, or being less yieldably mounted on, the chassis of the vehicle, and an evaluation unit connected to receive signals from said at least one first accelerometer and said at least one second accelerometer, and to generate a control signal.

Preferably the first structure is a bumper or fender.

Conveniently the first structure is mounted on a said second structure and the second structure is mounted on the chassis.

Preferably the first structure is resiliently mounted on the second structure and the second structure is mounted on the chassis by at least one plastically yieldable element.

Conveniently a subtracter is provided to determine the difference between signals derived from the said at least one first accelerometer and said at least one second accelerometer, the subtracter forming a part of the evaluation unit.

Preferably an integrator arrangement is provided between the said accelerometers and the evaluation unit.

Conveniently said at least one first accelerometer is associated with a f rst integrator to provide a first integrated signal to be passed to the subkactor and said at least one second accelerometer is associated with a second integrator to provide a second integrated signal t be passed to the subtracter.

Alternatively an integrator is provided to integrate the output of the subtracter. Conveniently there is a further accelerometer mounted to the chassis of the vehicle.

Preferably the second structure is behind the first structure and is mounted in front of the front wheels of the vehicle.

Conveniently first accelerometer is associated with a first integrator to provide a first integrated signal to be passed to the evaluation unit and said at least one second accelerometer is associated with a second integrator to provide a second integrated signal to be passed to the evaluation unit.

Preferably a speed sensor is provided to supply a signal representative of vehicle speed to the evaluation unit, vehicle speed being one of said conditions.

Conveniently the evaluation unit is adapted to generate the control signal only if vehicle speed is above a predetermined threshold.

Preferably the evaluation unit is adapted to generate the control signal only when the output of the subtracter exceeds a predetermined value.

Conveniently said predetermined value is a calculated value dependence on vehicle speed.

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 diagrammatic view of part of a motor vehicle provided '^^ with a safety arrangement in accordance with the invention, FIGURE 2 is a diagrammatic plan view of part of the vehicle shown in Figure 1, FIGURE 3 is a view corresponding to part of Figure 1 illustrating the vehicle when a low energy impact occurs,...

FIGURE 4 comprises four graphical figures used to explain the operation of the safety arrangement when the vehicle is subjected to a low energy impact as shown in Figure 3, FIGURE 5 is a view corresponding to Figure 3 illustrating a higher energy impact, for example hitting a pedestrian, FIGURE 6 is a series of graphical figures corresponding to the graphical figures of Figure 4, for use in explaining the operation of the safety arrangement when subject to a higher energy impact as shown in Figure S.

FIGURE 7 is a view corresponding to Figure 3 illustrating the situation in which the vehicle wheel is subjected to a force, for example due to the wheel hitting a curb, FIGURE 8 is a set of graphical figures corresponding to Figure 4 for use in explaining operation of the system when a wheel is subjected to a force, as shown in Figure 7, FIGURE 9 is a view corresponding to Figure 3 illustrating the vehicle when subjected to a severe impact, for example an impact with another vehicle, FIGURE 10 is a set of graphical figures used in explaining the operation of the safety arrangement when subjected to a severe impact as shown in Figure 9, and FIGURE 11 is a further graphical figure used for explanatory purposes.

Referring initially to Figures 1 and 2 of the accompanying drawings, a motor vehicle 1 is illustrated. The motor vehicle 1 incorporates a chassis 2.

The chassis is of conventional design and supports wheels 3 (only the front wheels are illustrated) and a conventional body-work, the body-work including a hood or bonnet 4 and a windscreen or windshield 5.

Provided at the front of the vehicle is a bumper or fender 6. The bumper or fender 6 comprises a structure including an internal rigid element 7, which may be of hollow box section, which extends transversely of the vehicle, and an outer skin 8. Mounted on the rear of the element 7 is at least one first accelerometer 9. As shown in Figure 2, two such accelerometers are provided.

The transverse element 7 is mounted, by resilient mountings 10, on a second structure 11 constituted by a rigid supporting element 11 which extends transversely of the vehicle. The supporting element 11 is located behind the bumper or fender 6. Mounted to the rigid supporting element 11 is at least one second accelerometer 12. The rigid supporting element 11 is mounted, by a plurality of plastically deformable elements 13 on a forward part of the chassis 2 of the vehicle.

It can be seen, from Figures 1 and 2, that the bumper or fender 6 is located at the very front of the vehicle, and the structure constituted by thee transverse element 11 is located behind the bumper or fender 6, but in front of the front wheel 3 of the vehicle.

The first accelerometer 9 provides an output signal which is passed to a first integrator 14, and the second accelerometer 12 provides an output which is connected to a second integrator 1S. The integrators are provided to integrate the output signals from the accelerometers.

The outputs from the two integrators 14 and 15 are passed to a subtractor circuit 16 which forms part of an evaluation unit. Another part of the evaluation unit is constituted by a central processor 17 which receives a signal from the subtracter.

A further accelerometer 18 which is a chassis accelerometer, is provided mounted on the chassis 2 of the vehicle, at a position behind the front wheel.

Preferably the chassis accelerometer 18 is centrally located within the floor pan of the vehicle. The chassis accelerometer measures the acceleration of the entire chassis. The output of the chassis accelerometer 18 passes to an integrator 19, and the output of the integrator 19 passes to the central

processor 17. A speed sensor 20 is provided. The speed sensor may, of course, be the conventional speed sensor provided to actuate the speedometer of the vehicle. The output of the speed sensor is connected to the central processor 17.

At this stage it should be mentioned that whilst, in the described embodiment, the subtracter 16 subtracts two signals which have been integrated by integrators 14 and 15, in a modified embodiment of the invention, the two signals from the first accelerometer 9 and the second accelerometer 12 may initially be subtracted, and the resultant difference signal can be integrated.

As will become more clear from the following description, the central

processor 17 is adapted, in response to the various inputs that it receives, to generate a control signal, the control signal being passed to a device, such as the device 21, which is to be actuated to provide protection for a pedestrian when the vehicle strikes a pedestrian. The device 21, in the embodiment shown, may be adapted, for example, to raise the hood or bonnet of the vehicle.

Alternatively, the device 21 could comprise one or more air-bags adapted to be inflated in response to the control signal, the inflated air-bags then overlying part of the hood or bonnet, and the "A"-Posts of the vehicle. In embodiments of the invention, the device 21 which is to provide protection for a pedestrian may take different forms.

It is to be appreciated that the central processor 17 receives input signals, in the described embodiments, from a number of sources.

As it is undesirable for the safety device 21 to be deployed in a very low speed impact, the central processor unit 17 may be adapted to that a control signal can only be generated if the speed of the vehicle is above a certain

predetermined threshold, such as, for example, 5 kilometres per hour. This will avoid the safety device being deployed in a very low speed impact.

Referring now to Figures 3 and 4 consideration will be given to the situation that exists if the vehicle is travelling in excess of the predetermined threshold, and impacts with an item such as a bird or a traffic cone. Only a low force is generated in such an impact. Because the vehicle is travelling at a speed in excess of the threshold speed, the central processor 17 of the evaluation unit may generate a control signal to actuate the device 21 if an appropriate predetermined set of conditions should be detected. i If the vehicle strikes a bird or a traffic cone, a relatively low level force 30 is applied to the bumper or fender 6. This will cause the structure constituting the bumper or fender 6 to move towards the transverse supporting element 11, with a resilient yielding of the resilient mountings 10. Since the supporting element 11 is mounted to the chassis 1 by means of the plastically deformable elements 13 which are much less "yielding" than the resilient mountings 10, the structure constituting the bumper or fender will move rearwardly relative to the chassis, but the transverse supporting element 11 will not move rearwardly relative to the chassis.

Thus, as can be seen from Figure 4, over the relevant period of time, the accelerometer 9 will provide an output signal representative of a very low acceleration, whereas the accelerometer 12 will provide an output indicating no acceleration. The difference signal, as determined by the subtracter 16 is thus of a relatively low value. The acceleration signal received from the chassis accelerometer 18 shows no acceleration. The central processor 17 will be adapted, in response to input signals of this type, not to actuate the safety device.

Turning now to Figure 5 and the associated Figure 6, reference will now be made to the situation that will exist if the vehicle is travelling in excess of the threshold speed and impacts, for example, with a pedestrian. If this situation should arise, the bumper or fender 6 will be subjected to a force 31 at a much higher level than the force 30 referred to above in connection with Figure 3. The force 31 will move the transverse element 7 of the bumper or fender 6 rearwardly, substantially compressing the resilient mountings 10 which mount the transverse element 7 on the supporting transverse element 11.

However, the force is still not sufficient to deform the plastically deformable mounting elements 13 since, as has been indicated above, the plastically deformable mounting elements 13 are substantially more rigid, and thus less yielding than the resilient mountings 10.

As can be seen from Figure 6, the output signal from accelerometer 9 shows a very substantial amplitude, as the structure of the bumper or fender has been moved rearwardly, relative to the chassis, with a substantial acceleration.

However, the transverse supporting element 11 has not moved relative to the chassis, and thus the output from the accelerometer 12 shows no acceleration.

The difference signal, that is to say the signal present at the output of the subtracter 16, shows a substantial peak. Again in this embodiment, there is no output signal from the chassis accelerometer 18. The central processor unit of the evaluation unit is adapted to generate the control signal in response to this set of conditions.

Referring now to Figure 7, the situation that exists when the wheel of the vehicle strikes an object, such as curb, or part of a rough road, will be considered. Should the wheel 3 of the vehicle strike the curb whilst the vehicle is travelling in excess of the predetermined speed, a force 32 will be applied to

the wheel of the vehicle. This force will tend to decelerate the whole of the vehicle, although the "shock" will be experienced more at the front of the vehicle than at the centre of the vehicle.

The accelerometer 9 and the accelerometer 12 will each be substantially equally effected, as there will be no relative movement between these two accelerometers as a consequence of the force applied to the wheel 3. Thus, as can be seen from Figure 8, the outputs from each of the accelerometers 9 and 12 presents a relatively large peak, but the difference signal, as generated by the subtracter 16, shows that there is no real difference between the sensed accelerations. There is, in this case, however, an output signal from the chassis accelerometer 18. The central processor unit is adapted not to generate the control signal in response to this type of condition.

Figure 9 illustrates the situation that may exist if the vehicle should be involved in an impact with another vehicle. In this situation a very substantial force 33 may be applied to the bumper or fender 6. The bumper or fender- 6 may move rearwardly from its initial position, as shown in phantom, to a final position, with this movement causing not only compression of the resilient mountings 10 which mount the transverse element 7 on the transverse supporting element 11, but also a plastic deformation of the support elements 13 which mount the transverse supporting element 11 on the chassis 2.

Thus, substantial output signals may be generated by the accelerometer 9 and also the accelerometer 12. As indicated in Figure 10, the output signals may fragment as the accelerometers may be destroyed. Generally the difference between the output signals from the accelerometers 9 and 12 is non-existent, and thus there is no significant output from the subtracter 16. There is, however, a substantial output from the chassis accelerometer 18. The central

processor unit will not generate an output signal in response to these conditions, primarily in response to the large output from the chassis accelerometer 18.

It will be clear, from the foregoing description, that the central

processor 17 is adapted to generate the control signal when the difference between the output signals of the accelerometer 9 and the accelerometer 12 is substantial, as shown in Figure 6, but not if the difference is minimal, as shown in Figure 4. Thus the central processor 17 compares the output signal from the subtracter 16 with a predetermined value to determine whether the control signal should, or should not, be generated. The predetermined value may, in a preferred embodiment of the invention, be dependent upon the velocity of the vehicle. Thus the predetermined difference value may be substantial if the speed of the vehicle is high, but may be relatively low if the speed of the vehicle is low.

Referring now to Figure 11, the lower axis of the graph is vehicle velocity, and the vertical axis of the graph represents the value of the difference signal as provided by the subtracter 16.

As can be seen from Figure 11, the vehicle must have a predetermined minimum speed Vat before an output signal can be generated. At that minimum speed Vat, the difference must have a predetermined minimum value Do for the control signal to be generated. As speed increases, so the value of the difference signal, as generated by the subtracter 16 that is necessary for the control signal to be generated increases. In the graph shown in Figure 11, the increase is a substantially linear increase, but the increase may have a predetermined non-linear function. If the speed of the vehicle and the measured value of Do are plotted, and the plotted point is within the shaded area of the graph, the control signal will be generated, unless the output signal from

the chassis accelerometer 18 is such that an indication is given that the vehicle has been subjected to a severe crash or accident situation.

In the present Specification "comprises" 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.

i. A-.

Claims

CLAIMS:

1. A safety arrangement provided on a vehicle, the arrangement incorporating a pedestrian detection system, the system comprising at least one first accelerometer mounted on a first structure located at the front of the vehicle, the first structure being yieldably mounted to the chassis of the vehicle, and at least one second accelerometer mounted on a second structure located adjacent the first structure and forming part of, or being less yieldably mounted on, the chassis of the vehicle, and an evaluation unit connected to receive signals from said at least one first accelerometer and said at least one second accelerometer, and to generate a conko1 signal.

2. A safety arrangement according to Claim 1 wherein the first structure is a bumper or fender.

3. A safety arrangement according to Claim 2 wherein the first skucture is mounted on a said second structure and the second structure is mounted on the chassis.

4. A safety arrangement according to Claim 3 wherein the first skucture is resiliently mounted on the second structure and the second structure is mounted on the chassis by at least one plastically yieldable element.

5. A safety arrangement according to any one of the preceding Claims wherein a subtracter is provided to determine the difference between signals derived from the said at least one first accelerometer and said at least one second accelerometer, the subtracter forming a part of the evaluation unit.

6. A safety arrangement according to any one of the preceding Claims wherein an integrator arrangement is provided between the said accelerometers and the evaluation unit.

7. A safety arrangement according to Claim 6 is dependent upon Claim 5 wherein said at least one first accelerometer is associated with a first integrator to provide a first integrated signal to be passed to the subtracter and said at least one second accelerometer is associated with a second integrator to provide a second integrated signal to be passed to the subtracter. ^

8. A safety arrangement according to Claim 6 as dependent upon Claim 5."r wherein- an integrator is provided to integrate the output ofthe subtracter.

9. A safety arrangement according to any one of the preceding Claims.

wherein there is a further accelerometer mounted to the chassis of the vehicle.

10. A safety arrangement according to any one of the preceding Claims wherein the second structure is behind the first structure and is mounted in front of the front wheels of the vehicle.

11. A safety arrangement according to any one of the preceding Claims wherein the evaluation unit is adapted to generate said control signal in response to a predetermined set of conditions, and the safety arrangement incorporates a device actuated by the control signal to protect a pedestrian.

12. A safety arrangement according to Claim 11, wherein a speed sensor is provided to supply a signal representative of vehicle speed to the evaluation unit, vehicle speed being one of said conditions.

13. A safety arrangement according to Claim 12 wherein the evaluation unit is adapted to generate the control signal only if vehicle speed is above a predetermined threshold.

14. A safety arrangement according to any one of Claims 11 to 13 as directly or indirectly dependent on claim 5 wherein the evaluation unit is adapted to generate the control signal only when the output of the subtracter exceeds a predetermined value.

15. A safety arrangement according to Claim 14 as dependent on claim 12 wherein said predetermined value is a calculated value dependence on vehicle speed.

16. A safety arrangement substantially as herein described with reference to and as shown in the accompanying drawings.

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