GB2353362A

GB2353362A - Coil Transducer With Magnetic Field Compensating Means

Info

Publication number: GB2353362A
Application number: GB9919535A
Authority: GB
Inventors: Yan Lu; Marcus Weidner
Original assignee: Bayerische Motoren Werke AG
Current assignee: Bayerische Motoren Werke AG
Priority date: 1999-08-19
Filing date: 1999-08-19
Publication date: 2001-02-21
Anticipated expiration: 2019-08-19
Also published as: GB2353362B; GB9919535D0

Abstract

A transducer 10 is disclosed which is suitable for a side intrusion detection system of a vehicle. The transducer 10 is a ferro-magnetic transducer and includes a flat wound spiral form coil 12 which is arranged in use to provide self-compensation against magnetic fields which might be induced in the transducer 10, such as could arise from eddy currents in a target member like a door skin 20.

Description

2353362 A Transducer This invention relates to transducers and in

particular to a transducer which is suitable for detecting the deformation or relative movement of at least a portion of an associated target member.

It is known to provide transducers for detecting the deformation or relative movement of associated target members. These transducers have been found to be suitable for use in detection systems such as those used for, but not limited to, side intrusion systems of vehicles. One general arrangement of this type can be seen with particular reference to Figure 1.

1 In Figure 1 an arrangement is provided for detecting the deformation of a door skin 3 of a vehicle (not shown further). The side intrusion detection arrangement comprises a plurality of coils 1 which are wound in a conventional bundle form with, in this case, a ferrite core 2. If the door skin 3 deforms in a side impact, it induces an inductance change in the coils 1 which is used to determine whether or not side airbags (not shown) should be deployed.

Because of their construction, these transducers 1, 2 have only a limited range, somewhat similar to the radius of the winding of their coils 1. They are therefore suitable only for measuring short distances, by which is meant that the transducer may have to be substantially in the immediate vicinity of the object 3.

It is a problem with such arrangements that eddy currents induced in the target object door skin 3 can induce a magnetic field in the transducer coils 1 such that their inductance, and therefore also their sensitivity, is altered.

The change in sensitivity can be represented in a simplified form by the ratio given below:

A5/ L LoAD in which AL is the change in inductance for the change in the distance AD to the door skin and L is the mean inductance in the change in distance AD.

For transducers of this type, one way to increase their range is to increase the diameter of their coils 1. The maximum possible coil diameter, however, may be constrained by the space available between the transducer 1, 2 and the sensed object 3. This means that, at the extreme of their range, such prior art transducers 1,2 exhibit only a low sensitivity.

The yeduced range and lower sensitivity of the prior art transducers 1, 2 is particularly disadvantageous when you are trying to detect side intrusion, as this should be detected as early as possible and is especially important in vehicles in which there is a large distance between the side impact transducer and the outer door skin or relevant door reinforcing structure.

It is an object of this invention to provide an improved transducer.

Accordingly, the invention provides a transducer suitable for detecting a deformation or relative movement of at least a portion of an associated target member, the transducer comprising a coil wound on a bobbin means, wherein said coil is wound in substantially a single plane as a substantially flat coil and said transducer is disposed in use such that the plane of winding of said coil is substantially parallel to the plane of said portion.

Said coil may be wound in a substantially spiral form and may be arranged to provide self-compensation of a magnetic field which may be induced therein from a source external to said transducer. Said self-compensation may be a function of the ratio of the spacing between substantially proximate windings of said coil and the diameter of said proximate windings themselves.

In use, said coil may be provided with a constant current.

Said bobbin means may comprise a ferro-magnetic core.

The invention also provides a detection system suitable for use as a side intrusion detection system of a vehicle, the system including a transducer according to the invention.

The invention will now be described by way of example only and with I reference to the remainder of the accompanying drawings, in which:

Figure 2 is a sectional side view of a transducer arrangement according to the invention; and Figure 3 is a plan view of the transducer of Figure 2.

Referring to Figures 2 and 3, a ferro-magnetic transducer 10 comprises a coil 12 which is wound as a substantially flat coil onto a bobbin means in the form of a ferro-magnetic core 14. The coil 12 is wound in a spiral form and has an inner coil end 16 and an outer coil end 18 which are connected to a side intrusion detection control means (not shown).

In use, the transducer 14 is disposed spaced apart from a portion of a door skin 20 in such a manner that the plane of winding of the coil 12 is substantially parallel to the plane of the portion of the door skin 20 which it uses as a target member.

In use, the coil 12 is supplied with a constant current by the control means and sets up a magnetic field which is disturbed if the door skin 20 closes the gap, as might occur rapidly in a side impact crash. The rapid approach of the door skin 20, will alter the magnetic field and cause an alteration in the inductance sensed by the control means so that it can make its decision on whether or not to deploy side airbags (not shown).

The coil 12 is arranged to provide localised self-compensation of its magnetic field against a magnetic field which might be induced therein as a result of eddy currents in the target member 20. The transducer inductivity, and therefore its sensitivity, is a function of the ratio between the spacing 60 of substantially proximat windings and the diameter 50 of the coil winding wire itself.

Winding Spacing 60 Winding Diameter 50 The compensation results in a damping of the magnetic field induced in the transducer 10 by eddy currents in the sensed object 20. This in turn leads to improved sensitivity and, the greater the ratio between the spacing 60 and the winding diameter 50, the higher will be the sensitivity.

The maximum sensitivity achievable can best be obtained by employing a particular number or range of windings, preferably after substantially all the other parameters have been fixed. Such values are best obtained by simulation or experimentation, as they will at least in part depend on the particular properties of the transducer materials, target materials and installation chosen.

A transducer according to the present invention provides better sensitivity at a particular range than a transducer including conventional bundle-form windings and, furthermore, our transducer delivers this advantage in a more compact package. This is especially advantageous in installations where space is limited.

The more compact nature of transducers made in accordance with our invention also means that less material is used to manufacture each unit and thus 5 costs can be saved.

It is not essential that the target member 20 is actually deformed. Relative movement between the target member 20 and the transducer 10 is all that is required to induce a signal change.

Claims

-6CLAIMS

1. A transducer suitable for detecting a deformation or relative movement of at least a portion of an associated target member, the transducer comprising a coil wound on a bobbin means, wherein said coil is wound in substantially a single plane as a substantially flat coil and said transducer is disposed in use such that the plane of winding of said coil is substantially parallel to the plane of said portion.

2. A transducer according to Claim 1, wherein said coil is wound in a substantially spiral form.

3. A transducer according to Claim I or Claim 2, wherein said coil is arranged to provide self-compensation of a magnetic field which may be induced therein from a source external to said transducer.

4. A transducer according to Claim 3, wherein said self-compensation is a function of the ratio of the spacing between substantially proximate windings of said coil and the diameter of said proximate windings themselves.

5. A transducer according to any preceding claim, wherein in use said coil is provided with a constant current.

6. A transducer according to any preceding claim, said bobbin means comprising a ferro-magnetic core.

7. A transducer substantially as described herein and with reference to Figures 2 and 3 of the accompanying drawings.

8. A detection system suitable for use as a side intrusion detection system of a vehicle, the system including a transducer according to any preceding claim.