IE41700B1

IE41700B1 - Improvements in and relating to a measuring probe for measuring wear

Info

Publication number: IE41700B1
Application number: IE2013/75A
Authority: IE
Original assignee: Burmeister & Wains Motor Og As
Priority date: 1974-09-20
Filing date: 1975-09-15
Publication date: 1980-02-27
Also published as: SE406124B; JPS5651562B2; BE833450A; IE41700L; GB1518165A; DK133915B; DK413375A; FI752629A; IT1047193B; NO753154L; PL104502B1; DE2445111A1; JPS5157467A; ES441087A1; FI58837C; NL7510956A; FR2285594B1; YU237075A; DE2445111B2; FR2285594A1

Abstract

1518165 Measuring wear BURMEISTER & WAIN'S MOTOR O G MASKINFABRIK AF 1971 A/S 18 Sept 1975 [20 Sept 1974] 38365/75 Heading G1N A measuring probe for measuring the wear in the cylinder wall 8 of a diesel engine comprises a central, cylindrical magnetic core 1 in a jacket 6 also of high magnetic permeability; a coil 5 wound on the core and a gap 12 between the core and jacket which gap is filled with a plastics material and of which the area is reduced by wear. The jacket is tapered to be pressed into a matching bore in the cylinder wall so the end faces of the jacket 6a and of the core are in the plane of the cylinder wall. Preferably a further coil 4 is wound on the core and a constant area gap 13 is provide whereby the further coil may be connected as a reference in a bridge circuit with the coil 5. The coil 5 may, alternatively, be connected in a resonance circuit of which the resonant frequency provides the measure of wear.

Description

The invention relates to a measuring probe for measuring wear on mechanical parts of engines or other machines by means of a self-inductance measurement.

For measuring the thicknesses of ferromagnetic materials it is known to use inductive measuring probes comprising a magnetic circuit which is placed on the body, the thickness of whioh is to be measured. The body forms part of the magnetic circuit, and when the thickness of this body is changed, for example by wearing action, a corresponding change in the reluctance in the magnetic circuit occurs, and this change in the reluctance gives a measure of the wear occurred.

Particularly in the case that it is desired to measure for example cylinder wear in an engine such an arrangement has the drawback that the measuring probe cannot be very sensitive, since it has to SS placed externally on the cylinder wall. The reduction occurring in the thickness of the body, that is to say in the thickness of the cylinder wall, has only a slight influence on the magnetic reluctance, and since the cylinder wall usually has a rather large thickness the resulting change in the reluctance in the magnetic circuit will be relatively small. Another drawback of the prior art arrangement is that the cylinder wall or another mechanical part is not necessarily intended for having such a measuring probe mounted on it, and special measures must therefore be taken to make it possible to mount the measuring probe in a suitable place on the cylinder wall or the mechanical part.

It is an object of the invention to overcome at least some of these drawbacks.

The present invention provides a measuring probe for measuring wear of a surface of a mechanical part of an engine or other machine comprising a magnetic circuit of a first material having a gap defined by confronting pole faces and sealed with a second material, said first material having a substantially higher magnetic permeability than said second material, said probe having a measuring surface disposable, in use of the probe, in said surface of the mechanical part, said gap extending from said measuring surface and being so disposed relative to said measuring surface that the pole faces are oriented generally normally to the measuring surface so that, in use of the probe, the magnetic flux flowing in said magnetic circuit traverses said poles faces and said gap generally orthogonally and the surface area of said confronting pole faces is reduced by the wearing of said measuring surface taking place during wearing of said surface of the mechanical part.

Preferably the gap is in the form of an annulus sealed with the second material and disposed between a core and a jacket of the first material providing cylindrical pole faces defining the gap.

By having the gap in the magnetic circuit arranged so that the gap is exposed directly to the wearing action occurring a notably higher sensitivity is achieved, since the reluctance is changed markedly by a reduction of the surface area of the confronting pole faces due to the wear. - 4 Incidentally, there has also been previously known for measuring the wear on mechanical parts, for example cylinder wear in an engine, the use of a resistor body which is placed in a gap between elec5 trodes and which is mounted in the mechanical part exposed to wear and to perform a measurement of the change in the ohmic resistance in this body due to the wearing action occurring. Usually a d.c. measurement is performed in this method.

However, this previously known method too has various drawbacks. Thus there is a risk of mechanical damage to, even possible breakage of, the resistor body when the latter is inserted into the mechanical part.

The value of the resistance, which varies With the wear, depends on for instance the temperature in the measuring zone and may be influenced chemically or corrosively by the lubricant in the engine. There is the additional risk that the lubricant penetrates between the resistor body and the insulating material, which must necessarily be placed between the probe and the mechanical part, and here forms perturbing alternative current paths resulting in misleading measuring results. These drawbacks are substantially avoided in the measuring probe according to the present invention.

In accordance with a preferred embodiment of the invention the measuring probe is characterized in that the probe is in the shape of a pin having a free end provided with said measuring surface and insertable in the mechanical part with said measuring surface in said surface of the mechanical part, said probe comprising an elongated, central core of the first material, at least one coil placed around the core, a jacket disposed to surround the coil and the core which jacket is of a material having a higher magnetic permeability than the second material, the gap being disposed between the core and the jacket adjacent the measuring surface and extending from said free end of the probe and filled with said second material, the coil being connected to an inductance measuring circuit arrangement, the core and jacket being formed and disposed relative to each other and to the coil so that the magnetic flux flowing in the magnetic circuit through the core and jacket traverses the pole faces and said gap generally orthogonally.

When the end face of the pin in the plane of the surface of the mechanical part, i.e. the measuring surface of the probe, is subjected to wear, the surface area of the confronting pole faces and hence the area of the gap is reduced. Since the self-inductance of the coil in said magnetic circuit depends on the number of turns of the coil, and on the area and width of the gap, and since the area of the gap is the only quantity which is here changed by wear, the selfinductance of the coil will be reduced proportionally to the wear. Consequently, the measuring probe will, via the inductance measuring circuit arrangement, directly provide an indication of the wear that has taken place. With the compact and robust construction that can be used for the probe of the invention, the probe can be inserted into the mechanical part substantially free of any risk of being mechanically damaged. Also the probe will be substantially free of any influence by any lubricant present on the wearing surface. In addition, the risk of chemical attack from the lubricant can be substantially avoided. Consequently the risks of erroneous wear measurements are substantially minimised.

Advantageously there may around the core and inside the jacket be provided an additional coil which is separated from the first mentioned coil, the magnetic - 6 circuit associated with the additional coil extending substantially through a part of the core, a part of the jacket and a further gap of a constant size between said part of the core and part of the jacket. This second coil and associated magnetic circuit have a constant reluctance, since the gap has a constant size, and consequently this second coil can be used as reference coil in the measuring circuit means, which may for example be a measuring bridge circuit. With such a reference coil it is thus possible to compensate for the influence of temperature on the probe.

Below, the invention is explained with reference to the accompanying diagrammatical drawing which illustrates an embodiment of a measuring probe according to the present invention.

The measuring probe comprises a central, substantially cylindrical, elongated core 1 which is provided with two annular flanges 2 and 3 which are located at a predetermined separation from each other and one of which, 3, is situated at one end of the core 1. The core 1 is made of a material having a high magnetic permeability.

Around the core 1 and between the other flange 2 and the other, free, end of the core, a coil 5 is provided wound around the core, and on the other side of the other flange 2 between the flanges 2 and 3, an additional coil 4 Is placed around the core 1.

The core 1 and the two coils 4 and 5 placed around the core are surrounded by a circumferential jacket 5 which is also made of a material having a high magnetic permeability. The jacket 6, the outside 7 of which has a slight taper which is somewhat exaggerated in the drawing, is adapted to be pressed into a hole, with a corresponding taper, in the mechanical part 8, which may be, for example the cylinder wall in a Diesel - Ί engine, which is exposed to wear and the wearing of which is to be measured by means of the probe.

The jacket 6 is so dimensioned that its end face 6a is located in the same plane as the surface 11 of the mechanical part 8 exposed to wear.

The coil 5 extends over only part of the length of the core from said other flange 2 to the free end of the core 1, leaving the end part la of the core free. The jacket 6 is so designed that its inner diameter within the zone around the coil 5 is slightly larger than the outer diameter of the coil 5 and within the zone around the free end part la of the core is significantly smaller than its inner diameter around the coil 5 but slightly larger than the outer diameter of the core, so that the magnetic circuit (through which the magnetic flux flows in use of the probe) extending through the jacket 6 and core 1 extend substantially through the reduced inner diameter portion of the jacket 6 around the free end part la of the core, the free end part la of the core and the resulting gap 12 therebetween, the inner surface of the reduced inner diameter portion and the outer surface of end part la of the core constituting confronting pole faces. In use of the probe the magnetic flux flowing in the magnetic circuit traverses these pole faces and the gap generally orthogonally.

This gap 12, in the magnetic circuit associated with the coil 5 between the inner surface of the jacket and the end part la of the core, and the clearance between the inner surface of the jacket and the coil 5 are filled with a substantially non-maghetic material, for example plastics material. The end face · of the end part la of the core and the end face of the gap are located in the same plane as the end face 6a of the jacket 6 (that is to say in the same plane as the surface 11 exposed to wear) and together constitute the measuring surface of the probe, i.e. the surface of the probe subjected to the same wearing forces as mechanical part surface 11 and whose wearing is measured.

In the opposite end of the probe there is, between the end face of the jacket and said one flange 3, inserted a ring of for example plastic or preferably a ductile, substantially non-magnetic material, such as copper, which forms a gap 13 in the magnetic circuit associated with the additional coil 4.

At the rear end of the probe, that is to say at the end facing away from the measuring surface of the probe, the jacket 6 is provided with a cap 15 of electrically insulating material of for example the same kind as the material in the gap 12 which is cast onto said end or is a push-fit onto said end. Leads 14 to and from the coils 4 and 5, respectively, are passed for example through said one flange 3 and through the cap 15. For stress relieving, these leads may be clamped to said flange 3 by means of a clamping device, not shown, and then passed through the cap 15.

The mode of operation of the probe is as follows: In the mechanical part, a surface 11 of which is exposed to wear, a frusto-conical hole is provided having such a size that the probe can be pressed into this hole so that the measuring surface of the probe, that is to say the end faces of the core 1, the gap 12 and the jacket 6 are located in the same plane as said surface 11 of the said mechanical part.

The two coils 4 and 5 are connected to an impedance bridge (not shown) to which a.c. voltage of a constant frequency is supplied. The magnetic circuit associated with the additional coil 4 has a constant - 9 reluctance since the dimensions of its gap 13 remain constant, and consequently the coil has a substantially constant impedance. The additional coil 4 thus serves as a reference in the impedance bridge circuit.

When the surface 11 of the mechanical part 8 is worn, the measuring surface of the probe is also exposed to wear. This means that the end face 6a of the jacket, the end face of the gap 12 as well as the end face of the core 1 are worn in the direction indicated by the arrow S in the drawing. Since the selfinductance of the coil 5 depends on the number of turns of the coil and on the area and width of the gap 12 defined by the confronting pole faces, being proportional to the area and inversely proportional to the width of the gap, the self-inductance of the coil 5 will be reduced proportionally to the wear, which reduces only the surface area of the pole faces and hence the area of the gap. Thus, the impedance of the coil 5 is reduced, and the result of this is that on the bridge circuit it is possible to ascertain a change in the equilibrium which to a good approximation indicates the amount of wear occurring.

The change in the reluctance of the magnetic circuit, which comprises the coil 5, can also be used to indicate the wear occurring by connecting the coil 5 into a resonance circuit. In this case, the necessary change of the measuring frequency for restoring the state of resonance will also indicate the amount of wear.

Claims

1. CLAIMS: 10

1. A measuring probe for measuring wear of a surface of a mechanical part of an engine or other machine comprising a magnetic circuit of a first material having a gap defined by confronting pole faces and sealed with a second material, said first material having a substantially higher magnetic permeability than said second material, said probe having a measuring surface dispoable, in use of the probe, in said surface of the mechanical part, said gap extending from said measuring surface and being so disposed relative to said measuring surface that the pole faces are oriented generally normally to the measuring surface so that, in use of the probe, the magnetic flux flowing in said magnetic circuit traverses said pole faces and said gap generally orthogonally and the surface area of said confronting pole faces is reduced by the wearing of said measuring surface taking place during wearing of said surface of the mechanical part.

2. A measuring probe as claimed in claim 1, in the shape of a pin having a free end provided with said measuring surface and insertable in the mechanical part with said measuring surface in said surface of the mechanical part, said probe comprising an elongated, central core of the first material, qt least one coil placed around the core, a jacket disposed to surround the coil and the core which jacket is of a material having a higher magnetic permeability than the second material, the gap being disposed between the core and the jacket adjacent the measuring surface and extending from said free end of the probe and filled with said second material, the coil being connected to an inductance measuring circuit arrangement, the core and jacket being formed and disposed relative to each other and to the coil so that the magnetic flux flowing in the magnetic circuit through the core and jacket traverses the pole faces and said gap generally orthogonally.

3. A measuring probe as claimed in claim 2, wherein around the core and inside the jacket an additional coil, separated from the first mentioned coil is provided, and wherein a magnetic circuit associated with the additional coil extends substantially through a part cf the core, a part of the jacket and a further gap of a constant size between said part of the core and part of the jacket.

4. A measuring probe as claimed in any of claims 1 to 3 wherein the gap and/or the further gap is filled with a plastics material.

5. A measuring probe as claimed in claim 2 or claim 3 or claim 4 when dependent on claim 2 wherein the one end of the pin is frusto-conical with the broader end of the frustum forming the end faces, exposed, in use of the probe, to wear, of the core, gap and jacket.

6. A measuring probe for measuring wear of mechanical parts of engines or machines, substantially as described hereinbefore with reference to the accompanying drawings.

7. A measuring device for measuring wear of mechanical parts of engines or machines which device comprises a measuring probe according to any of claims 1 to 6 together with electric circuit means connected to the coil usable for monitoring changes in the reluctance of the magnetic circuit.

8. A device as claimed in claim 7 when dependent on claim 2 wherein said electric circuit means are connected to the coil.

9. A measuring device as claimed in claim 8 when dependent on claim 3 wherein the coil and additional coil are connected to an impedance bridge. - 12 10. A measuring device according to claim 7 substantially as described hereinbefore with particular reference to the accompanying drawing. 11. A method of measuring wear of a surface in a 5 mechanical part of an engine or machine wherein a measuring probe according to any of claims 1 to 6 is disposed with its measuring surface in the plane of said surface of the mechanical part, and the reluctance of the magnetic circuit monitored.

10. 12. A method according to claim 11 when dependent on claim 2 wherein the monitoring of the reluctance is effected through monitoring of the impedance of the coil.

11. 13. A method of measuring wear of a surface in a

12. 15 mechanical part of an engine or a machine according to claim 12 substantially as described hereinbefore with reference to the accompanying drawings.