DE4126376A1 - Monitoring sensor for temp.-dependent wear and ageing - uses material, e.g. layers of zircon and nickel@, whose speed of ageing depends on temp. and is electrically measurable - Google Patents

Abstract

The sensor includes a section having an electrically measurable material property (pref. electrical conductivity) which changes irreversibly at a rate dependent on temp. The sensor pref. has at least one pair of adjacent layers of different materials, one of which is capable of temp-dependent diffusion into the other to produce a permanent conductivity change in the diffusion zone. Pref. the materials are transition metals, esp. Zr and Ni, in the form of vapour deposited layers on a substrate or in the form of foils which are pref. wound into a coil. The layers are pref. at least 0.5 microns thick. The sensor part is pref. gas-impreviously encapsulated, esp. in a protective gas or vacuum. USE/ADVANTAGE - Components subjected to heavy thermal loading, e.g. motor vehicle clutch or brakes. Reliability achieved by using solid state amorphisation effect with inherent measurement storage requiring no external circuitry.

Description

The invention relates to a sensor for wear and / or aging monitoring of temperature-dependent wearing and / or aging objects.

Numerous mechanical or thermal loads Components of machines, electrical systems or power vehicles show faster with increasing temperature progressive material aging or wear ver hold on. Examples of this are motor vehicle couplings called lungs and brakes, which are comparatively in operation are exposed to high temperatures and rise with it the temperature shows increasing wear.

Are such components in addition to normal operation thermally stressed in a special way, so it can unexpected operational impairments or even too Breakdowns come. On the one hand, this can be met that the components in sufficient short safety time intervals or where that is not possible to exchange timely. The maintenance is however, as a rule, with a complex intervention connected to the component in question, whereby often only then it turns out that the component is still unrestricted is operational and therefore does not require maintenance. In the event of a routine replacement of components Security reasons, such as electrical Components whose aging condition without destroying the Component is not detectable, it often happens Elimination of quite a long time operational components.

There is therefore a need for a way that Aging or wear behavior of components or  other temperature-dependent objects with simple means to monitor.

In the physical journals "Physical Review Letters "51, No. 5, pages 415 ff (1983) and" Physics Reports "(Review Section of Physics Letters (161, No. 1, Pages 1-41 (1988)) is a "solid state amorphization "physical effect described, which is that at the interface two adjacent layers of certain different crystalline transition metals one of the Layer materials or both in the other diffuse in. This forms in the diffusion zone an amorphous alloy layer from the two transitions metals. This amorphous alloy layer has one compared to the originally pure crystalline areas changed electrical conductivity.

The physical effect mentioned was, for example, at Layer combinations demonstrated in which one Layer of a so-called early transition metal and the other layer from a so-called late over gear metal exists. As early transition metals, the in the periodic table of elements as subgroup elements classified metals, the second extreme Electron shell compared to the maximum border number of electrons are occupied. These include for example the elements titanium (Ti), yttrium (Y), Zircon (Zr), Niobium (Nb), Lantan (La) and Hafnium (Hf). Late transition metals are such sub-group elements the second outermost electron shell already with one larger number of electrons is occupied. These include for example the subgroup elements iron (Fe), cobalt (Co), nickel (Ni), copper (Cu) and gold (Au).  

The layer structures were obtained by evaporating the relevant materials on a layer support in obtained an ultra high vacuum system.

In an article by L. Schultz in "Amorphous Metals and Non-Equilibrium Processing ", ed. M. v. Allmen (Les Editions de Physique, Les Ulis (1984), page 135 ff) the manufacture of an essentially completely amorphous Wire with macroscopic dimensions based on the Amorphization process explained above beat. The wire is obtained by over interlaced foils of nickel and zircon in one Winding rolls and this winding along its winding axis pulls through a lace shape to make the wrap radial to compress while keeping the layers in close contact bring together. Another compression can can be achieved by pulling the winding wire. From that obtained wire can be formed into a bundle of wires which again in a lacing form to a wire structure is deformed. According to the technical contribution mentioned above such a wire takes one essentially completely amorphous structure if it is used for a long time, e.g. B. 150 Hours, a high temperature, e.g. B. 300 ° C exposed becomes.

In the same technical contribution there is another possibility to produce a completely amorphous state transferred macroscopic structure from the concerned Layers suggested. One starts from several folded pairs of foils by cold rolling be pressed together to form a dense structure to get. After an appropriate heat treatment the body obtained in this way also showed an im essentially completely amorphous structure.

Technical applications of the so-called "Solid-state amorphization" effects are in the  aforementioned scientific publications not specified.

The aim of the invention is to provide a sensor for wear and / or aging monitoring of temperature-dependent to indicate wearing and / or aging objects, which works to a high degree without problems.

This object is achieved in that the Sensor has a sensor part, which is a irreversibly changing, electrically measurable material properties shaft, the rate of change in particular which corresponds to a monotonous function of the tempe rature depends.

Is the sensor within a certain time interval exposed to high temperatures for long periods then there was the electrically measurable material property changed significantly in a significant way. The Change is greater the longer the sensor the higher Exposed to temperatures in the specified time interval was and the higher the temperatures were. In this respect, the sensor behaves according to the invention similar to an integrator that measures the temperature load integrated over time.

The state of wear or aging of temperature depending on wear and aging objects qualitatively in a corresponding manner from the "Temperaturge layer "of the object. Is the typical old behavior of the object to be monitored in Dependence on temperature essentially known e.g. B. by empirical studies, you can on hand of the measured values taken at certain points in time connected to the object in question the invention statements about the aging of the  individual object at the specified times do.

Accordingly, the state of wear or aging of temperature-dependent wear or aging Components with an associated sensor after the Invention can be monitored in a simple manner by periodically the electrically measurable material shaft of the sensor part measures. Elaborate interventions in the Components for determining their aging condition can therefore refrain from doing so. Furthermore, with a sensor components of the invention monitored, their aging could not be determined so far without being destroyed, and then routinely at safety intervals were exchanged according to their actual Aging condition are kept in operation longer.

The sensor according to the invention works very reliably, since it stores its measurement information inherently completely self-sufficient and not electrically with external components must interact. In particular, it is not necessary that the sensor constantly with a measuring device for measuring the electrically measurable material property is connected.

The sensor part is preferably made of one material det, whose changing material properties the elec electrical conductivity.

According to a preferred embodiment of the invention the sensor part has at least one pair adjoining one another layers of different materials, at least one depending on the tempe diffuses into the other, the elec permanent conductivity in the diffusion zone changes.  

The layers are preferably made of transition metals, formed in particular from zircon and nickel. One on this Sensor constructed in this way works in accordance with the Principle of introduction mentioned Solid-state amorphization by Diffusion of the layer material. The measured value acquisition is preferably done by measuring the macroscopic electrical resistance R along the layers. The macroscopic electrical resistance R of the sensor part becomes with increasing width of the diffusion zone at the original layer boundary larger because the conductive amorphous alloy material in the diffusion zone is less than the conductivity of the original layered material.

The change in resistance therefore depends on the width the amorphous alloy determined by the diffusion process intermediate layer and changes (at least in one for numerous technical uses of the Sufficiently large temperature range) with a monotonically dependent on the rate of change efficiency.

The sensor part is used to increase the measuring effect from only two preferably from a variety of match other layers formed, so that said Diffusion process can start at every layer boundary.

The layers can, for example, by evaporating the Layer material made on a layer support be.

However, layers of foils are preferred layer material to form the sensor part used.  

To realize a particularly compact sensor part it is proposed to roll up the foils into a roll len. By means of appropriate cold deformation measures, the Then winds compressed so that the individual turns of the Wraps as closely as possible in close contact with each other come to as large an effective interface as possible create where the diffusion process can begin. A such a wound sensor part can be on his End faces comparatively simple with connecting wires to contact.

The layers preferably each have a thickness of at least 0.5 µ. A layer thickness specification is insofar as the life of the Sensor depends on the layer thickness. The sensor is namely essentially consumed when the diffusions fronts have passed through the respective layers. This takes a given temperature at a thick one Layer longer than a thinner layer.

To avoid undesirable environmental influences proposed to make the sensor part gas impermeable, in particular encapsulate them in a vacuum and / or protective gas environment. In this way, the oxidation of the Sensor sub-layers can be avoided.

The sensor according to the invention is suitable, for example good for monitoring wear and / or aging of Motor vehicle components that are exposed to high temperatures are. Such a component is, for example friction clutch, in particular the rub the coupling parts a temperature-dependent wear are exposed. It is advisable to arrange the sensor as close as possible to the rubbing to be monitored Coupling parts.  

In a corresponding manner, it is also proposed to Sensor according to the invention for monitoring a force to use vehicle brake.

The invention is explained in more detail below with the aid of the figures explained.

It shows:

Fig. 1 is a partial view of a layer structure of a sensor according to the invention, when new and in the working condition,

Fig. 2 is a plan view of a broken away front side of a spirally wound sensor part of a sensor according to the invention,

Fig. 3 shows a sensor part of a sensor according to the invention according to another embodiment formed from sheets,

Fig. 4 is a sectional view of a sensor according to the invention,

Fig. 5 is a graph showing the reciprocal of the electrical resistance of a sensor according to the invention over the root of time for three different temperature profiles, and

Fig. 6 shows a schematically illustrated motor vehicle clutch with a sensor according to the invention.

Fig. 1 is a schematic partial view showing a layer structure of a sensor according to the invention in the new state (panel a) and in the working condition (panel b). The layer structure consists of a plurality of alternately successive layers 1 , 2 made of nickel ( 2 ) and zirconium ( 1 ), of which three layers are shown in more detail in FIG. 1, looking parallel to the layer planes. The production of a layer structure shown in FIG. 1a can materials carried on a layered support in a vacuum vapor deposition, for example by alternate vapor deposition of the respective layers. For the formation of a layer structure with in particular several μ-thick individual layers, however, it is preferred to alternately stack commercially available foils from the layer materials concerned and then to press them together by cold forming, such as cold rolling, to such an extent that they come into close contact with one another at their interfaces 3 and build cohesion.

If such a layer structure is exposed to correspondingly high temperatures over correspondingly long times, amorphous intermediate layers 4 are formed at the original layer boundaries 3 . As has already been explained at the beginning, the amorphous intermediate layers result from the fact that at least one of the layer materials diffuses into the respective other adjacent layer material and forms an amorphous alloy with the latter. The higher the layer temperature, the faster the respective diffusion front proceeds perpendicular to the layer boundaries 3 . Thus, on the one hand, the thickness of the amorphous intermediate layers 4 increases as a function of the temperature and the time, and the thickness of the crystalline metal layers 1 , 2 decreases.

The amorphous alloy material in the intermediate layers 4 has a lower electrical conductivity than the crystalline layer material of the layers 1 and 2 . With increasing growth of the amorphous intermediate layers 4 , the electrical resistance R of the layer structure increases both along the layers 1 , 2 , 4 and across the layers 1 , 2 , 4 . The change in resistance resulting from the change in conductivity of the material in diffusion zone 4 is irreversible in the zirconium-nickel layer structure shown in FIG. 1 as long as a recrystallization temperature of the layer materials above 350 ° C. is not exceeded over a certain period of time. In accordance with the growth of the amorphous intermediate layers 4 , the resistance of the layer structure changes with a rate of change which depends on the temperature in accordance with a monotonous function.

The sensor part 5 of a sensor according to the invention formed from the layers 1 , 2 is used up when the original crystalline material of the layers 1 , 2 is essentially completely amorphized. In the following, an example calculation is used to show how long it takes for a layer structure of 1 μ thick, alternately successive nickel-zircon layers to be amorphized if they are constantly at a first temperature T ₁ = 90 ° C. or at a second Temperature T ₂ = 150 ° C is maintained.

Sample calculation

The diffusion path x for the diffusing Ni particles in a 1 µm thick Zr layer as a measure of the the path of a diffusion front results in good Approximation from the relationship:

x = 2 √ (1)

where D is the diffusion coefficients and t the time designated.

The diffusion coefficient D can be determined by the relationship

express in the

D _o a material-dependent pre-factor,
Q the enthalpy of activation and
k the Boltzmann constant (natural constant)
is.

If you insert the relationship ( 2 ) in (1) and solve the relationship ( 1 ) after the time t, you get the relationship ( 3 ), which gives a good approximation of the time t in which the diffusion front of a Zr layer the thickness x passes through.

With the relevant numerical values:

k = 1.4 x 10 ^-23 J / K
x = 1 µm
D _o ≈ 10 ^-6 m ² / s
Q ≈ 1.2 eV

for the first temperature (T ₁ = 90 ° C) there is a time value of 6.4 · 10 ⁹ s 200 years and for the second temperature a time value of 3.0 · 10 ⁷ s 1 year, after which the layers due to the Diffusion are completely amorphized.

From this it can also be estimated that a sensor part from a corresponding Zr-Ni layer combination having sensor according to the invention very sensitive reacts to high temperatures, but at moderate ones  Temperatures up to approx. 100 ° C comparatively is insensitive.

This property makes the sensor according to the invention particularly suitable for monitoring objects, which only age significantly at high temperatures or wear out.

Fig. 2 shows a section of a sensor part 5 a of an embodiment of the invention. This sensor part 5 a is formed from two superimposed foils 1 a, 2 a made of zircon ( 1 a) and nickel ( 2 a), which are rolled up into a coil. After being rolled up, the winding was subjected to a wire drawing process, whereby it was drawn along the winding axis in order to press the layers 1 a, 2 a in essentially continuous contact with one another. After the wire drawing process, the layers 1 a, 2 a had a thickness of approximately 2 μm and the coil had a diameter of approximately 1 mm. Of course, depending on the layer thickness of the starting foils and the degree of deformation during wire drawing, other layer thicknesses can be obtained. The diameter of the coil also depends on its number of turns.

The sensor part 5 a has the advantage that it is comparatively easy to manufacture and, with a compact structure, offers large-area effective layer boundaries 3 a for the diffusion process.

Fig. 3 is a broken sectional view of a sensor part Sb of a further embodiment of the invention. The sensor part 5 b is formed from two layers of zirconium ( 1 b) and nickel ( 2 b) placed on top of one another, which have been folded around a core surface 6 while maintaining the sense of direction. The structure thus obtained was then cold-rolled, wherein the layers 1 b, 2 b in the direction of arrows were pressed against each other 7, to bring them into close contact with each other.

To form a sensor according to the invention, the sensor parts 5 a and 5 b were formed on their by the narrow sides of the layers 1 a, 2 a and 1 b, 2 b (based on FIG. 2 and FIG. 3 parallel to the plane of the drawing lying) front sides 8 and 8 a with electrical lines 9 ( Fig. 4) contacted.

In FIG. 4, an embodiment of a sensor according to the invention is shown in longitudinal section. The sensor section 5 (5 a, 5 b) is formed from zirconium and nickel foils, and has a structure according to Fig. 1, Fig. 2 or Fig. 3.

A ceramic capsule 10 encapsulates the sensor part 5 ( 5 a, 5 b) in a gas and liquid-tight manner. The electrical lines 9 are led out of the capsule 10 in a corresponding manner in a gastight and liquid-tight manner. The lines 9 shown in dashed lines in FIG. 4 can optionally be provided for a resistance measurement in four-wire circuit technology.

In the diagram in FIG. 5, the reciprocal resistance of the sensor S for two constant temperatures T ₁ and T ₂ and for an arbitrarily assumed time-dependent temperature T (t) over the square root of time is shown qualitatively. The temperature T ₂ is greater than the temperature T ₁ .

At constant temperatures (T ₁ , T ₂ ) the reciprocal resistance R ^-1 or the conductance of the sensor S changes in good approximation proportional to the root of time.

The rate of change of the reciprocal resistance R ^-1 depends essentially on the temperature. The locations in the course of the curve drawn for the changing temperature T (t) in FIG. 5, which have a greater gradient, indicate that the sensor S was exposed to particularly high temperatures during the associated times, whereas the locations with a flat curve Times can be assigned in which the sensor S was exposed to less high temperatures.

The curve marked X in FIG. 5 represents an aging tolerance curve of a motor vehicle clutch monitored by the sensor S. The curve X was obtained from data from empirical studies of the principal temperature-dependent aging or wear behavior of the relevant clutch type. These data were related to the basically known temperature-dependent resistance change behavior of the sensor according to FIG. 4, so that the curve X specifies a limit value for the reciprocal resistance of the sensor S for each point in time, which must not be undercut, if not the risk of an intolerable Wear of the clutch should be accepted. Such a tolerance violation is shown in Fig. 5 at the point t _x ^0.5 Darge, with the curve T (t) the course of the reciprocal resistance R ^{-1 of} the at a defined point of the coupling near the wear-prone parts, such as the Clutch linings, arranged sensor S should represent.

The sensor can, for example, in a corresponding manner also for monitoring the aging or wear ver be used by motor vehicle brakes.

In Fig. 6 is a greatly simplified outlined clutch 11 is shown with a sensor S according to the invention in a sectional view. The clutch 11 comprises a flywheel 12, which is connected in a rotationally fixed manner to the crankshaft of the engine, not shown, with a clutch housing 13 fastened thereon, and a transmission input shaft 14 coupled in the engaged state of the clutch 11 via a frictional connection to the flywheel 12 . To produce the frictional connection, a rotatably but axially movably connected to the transmission input shaft 14 clutch plate 15 is provided in the clutch housing 13 which has friction pads 16 on both sides. A pressure plate 17 guided in a rotationally fixed but axially movable manner on the clutch housing 13 presses the clutch disc 15 against the flywheel 12 , with frictional engagement between the friction linings 16 and the flywheel 12 or the pressure plate 17 . The contact pressure is applied by a pressure plate 17 in front of an exciting plate spring or diaphragm spring 18 , which is held on the clutch housing 13 . To disengage the clutch 11 , an axially displaceable releaser 19 is provided, which is operated by a clutch, not shown, pedal. The clutch 11 shown is a so-called pressed clutch design, in which the diaphragm spring 18 is supported on the clutch housing 13 in such a way that it allows the pressure plate 17 to disengage in the direction of the arrow 20 when the clutch 19 is in the direction of the arrow 21 the diaphragm spring 18 is moved. In the disengaged state, the clutch disc 15 with its friction linings 16 comes free from the flywheel 12 or the pressure plate 17 , so that the transmission input shaft 14 can rotate relative to the flywheel 12 . Particularly exposed to high temperatures and therefore susceptible to wear, the friction linings 16 on the clutch disc 15 and the clutch surfaces 22 which come into frictional engagement with the friction linings 16 on the flywheel 12 or on the pressure plate 17 . The wear of these elements 16 , 22 can increase drastically if the friction linings 16 are grinded against the clutch surfaces 22 in an improper manner over a long period of time, as is the case, for example, when the motor vehicle is overcharged or on gradients is driven for a long time with a sliding clutch. The frictional heat generated in the case of grinding friction linings or clutch linings 16 leads to an increase in temperature and thus to an acceleration of the wear of the respective friction elements 16 , 22 . A sensor S according to the invention fastened in the vicinity of the friction linings 16 on a sensor holder 23 in the non-rotating clutch bell 24 enclosing the clutch is essentially exposed to the temperatures of the elements 16 , 22 which are susceptible to wear.

The temperatures occurring during normal operation of the clutch 11 at the location of the sensor S are usually less than 100 ° C. At such normal operating temperatures, the sensor does not experience any significant change in resistance associated with the layer diffusion process (cf. example calculation above). When the clutch is subjected to extreme loads and the associated increasing risk of wear of clutch elements 16 , 22 , the temperature at the location of the sensor S can rise to over 150 ° C. At such high temperatures, sensor S experiences an accelerated irreversible change in resistance (cf. the example calculation above for temperature T ₂ ).

By measuring the resistance R of the sensor S after certain time intervals, information is therefore obtained as to whether the clutch 11 has been overloaded over a longer period in the relevant time intervals.

For the measurement of the resistance of the sensor S, a resistance measurement device 25 shown in broken lines in FIG. 6 can be provided with a display device in the motor vehicle. To connect the sensor S with a resistance measuring device 25 , connecting wires 9 a of the sensor S are led out of the clutch bell 24 .

Instead of a resistance measuring device 25 , the connecting wires 9 a can also be led to connecting terminals, to which a resistance measuring device external to the vehicle can be connected if required.

The reference symbols S ₁ , S ₂ denote sensors according to the invention, which can be arranged on the coupling 11 as an alternative or in addition to the sensor S. The sensor S ₁ is shown in FIG. 6 attached by means of a bracket 23 a directly to the clutch disc 15. This sensor S ₁ is thermally very well coupled to the wear-prone friction linings 16 , so that it is exposed to the temperatures of the friction linings 16 essentially without delay. The electrical connections of the sensor S ₁ can be connected to a resistance measuring device by means of suitable measures. However, the sensor S ₁ preferably has no electrical connection after connections outside the coupling 11 . In the latter case, the sensor S ₁ is used in particular to provide information about the cause of worn friction linings 16 if necessary. If, for example, the friction linings 16 are worn out in an unusually short time, the resistance of the sensor S ₁ provides information as to whether the friction linings 16 were thermally overloaded over a long period of time or whether material errors were the cause of the wear. The measurement of the resistance R of the sensor S ₁ can be carried out for this purpose with the coupling 11 removed, so that it is not necessary to lead electrical connections out of the coupling.

For a corresponding purpose, the sensor S ₂ can be attached in the vicinity of the friction linings 16 on the pressure plate 17 or, if appropriate, on the flywheel 12 or the clutch housing 13 .

In the described embodiment of the sensor according to the invention, the sensor part is formed from a multiplicity of layers 1 , 2 or 1 a, 2 a or 1 b, 2 b made of zirconium and nickel. Other designs of the sensor part, not shown, have layer combinations of two or more different subgroup metals or transition metals. Preferred material combinations are:

Zr-Ni, Ti-Ni, Zr-Cu, Au-Y, Zr-Co, Au-La, Ni-Hf and Zr-Fe.

Claims (12)

1. Sensor for wear and / or aging monitoring of temperature-dependent wearing and / or aging objects, characterized by a sensor part ( 5 ; 5 a; 5 b) which has an irreversibly changing electrically measurable material property, the rate of change of which depends on the temperature. 2. Sensor according to claim 1, characterized in that the changing material property the electrical Conductivity is. 3. Sensor according to claim 1 or 2, characterized in that the sensor part ( 5 ; 5 a; 5 b) has at least one pair of adjacent layers ( 1 , 2 ; 1 a, 2 a; 16 , 26 ) made of different materials, At least one diffuses into the other depending on the temperature, the electrical conductivity in the diffusion zone ( 4 ) changing permanently. 4. Sensor according to claim 3, characterized in that the layers ( 1 , 2 ; 1 a, 2 a; 1 b, 2 b) of the sensor part ( 5 , 5 a, 5 b) made of transition metals, in particular zirconium and nickel are. 5. Sensor according to claim 3 or 4, characterized in that the layers ( 1 , 2 ) are produced by vapor deposition of the layer material on a layer support. 6. Sensor according to claim 3 or 4, characterized in that the layers ( 1 , 2 ; 1 a, 2 a; 1 b, 2 b) are formed from films of the layer materials. 7. Sensor according to claim 6, characterized in that the films are rolled up into a coil ( Fig. 2; Fig. 3). 8. Sensor according to at least one of claims 3 to 7, characterized in that the layers ( 1 , 2 ; 1 a, 2 a; 1 b, 2 b) each have a thickness of at least 0.5 µm. 9. Sensor according to at least one of the preceding claims, characterized in that the sensor part ( 5 ; 5 a; 5 b) is gas-impermeable - in particular in a vacuum or protective gas environment - encapsulated. 10. Use a sensor according to one of the previous ones the claims for wear and / or aging monitoring chung a motor vehicle component, in particular one Clutch or brake. 11. Motor vehicle clutch with at least one for aging and / or wear monitoring there angeord designated sensor ( 5 ; 5 a; 5 b) according to any one of claims 1-9. 12. Motor vehicle brake with at least one sensor for aging and / or wear monitoring arranged thereon ( 5 ; 5 a; 5 b) according to one of claims 1-9.