Lubricant deterioration detection device and lubricant deterioration state evaluation method

A lubricant deterioration detection device of the present invention includes a gas sensor that selectively detects a carbonyl compound. The gas sensor is configured to detect the carbonyl compound from at least one of formaldehyde, acetaldehyde, propanal, butanal, pentanal, n-hexanal, n-heptanal, formic acid, and acetic acid. The detection deterioration device further includes an oil removal portion that removes an oil mist generated from the lubricant.

TECHNICAL FIELD

The present invention relates to a lubricant deterioration detection device and a lubricant deterioration state evaluation method.

BACKGROUND ART

In devices lubricated with a lubricant such as lubricating oil and grease, including rolling devices (for example, rolling bearings, ball screws, and linear guides), lubricant deterioration can increase the torque, the abrasion, the temperature, or the like of a device to cause abnormal events.

Deterioration of a lubricant is mainly caused by thermal decomposition and oxidation (oxidative deterioration), for example. Lubricant deterioration can lead to generation of acids, decomposition of lubricant components to generate volatile (low-molecular weight) hydrocarbons, generation of compounds having a carbonyl group (including a ketone group and an aldehyde group) or a similar group, and a reduction in thickness of a lubricating film to increase the abrasion amount of a lubrication-receiving member, for example.

Hence, measurement of the abrasion amount, the acid amount, the volatilization amount of hydrocarbons, and the amount of compounds having a carbonyl group or a similar group generated by deterioration enables determination of the deterioration state of a lubricant.

Conventionally, a lubricant is periodically sampled from a rolling device during operation, and the deterioration state of the lubricant is examined by the following method, for example. The method includes a method of measuring the abrasion amount by quantitative determination of a metal by atomic absorption analysis or the like, a method of measuring the acid amount by determination of the total acid value in accordance with “ASTM D3242”, and a method of measuring the absorbance arising from a carbonyl group around 1,710 cm−1by infrared spectrophotometry.

Chemical deterioration of a lubricant proceeds from (1) peroxy radicals, (2) hydroperoxides, (3) carbonyl compounds, to (4) polymers (gum) and lower fatty acids, in this order. The method of measuring the acid amount is a method of detecting the deterioration in the step (4).

The method of periodically sampling a lubricant to examine the deterioration state, however, cannot prevent abnormal events when deterioration suddenly proceeds between examinations. Hence, there is a demand for enabling continuous monitoring of the deterioration degree of a lubricant in a rolling device.

PTL 1 discloses, as a device capable of continuous monitoring the deterioration state of a lubricant in a rolling bearing, a lubricant deterioration detection device including a gas sensor that detects at least any gas of hydrocarbons, hydrogen sulfide, and ammonia in a bearing. Specifically, a rolling bearing has a shield plate and is lubricated with a lubricant, a circular plate of the shield plate has an opening, and the gas sensor is attached to the opening through a ceramic filter.

PTL 1 also discloses a lubricant deterioration detection device in which an infrared generator and an infrared detector included in an infrared spectrometer are placed at opposite positions interposing a lubricant flowing pipe, and a sample cell through which infrared light passes is provided at a position of the pipe interposed between the infrared generator and the infrared detector. An example of the device is disclosed as a device that continuously monitors the deterioration state of a lubricating oil flowing in a pipe from a reservoir toward an oil supply opening for reuse of the lubricating oil discharged from a rolling bearing, by measuring the absorbance arising from a carbonyl group around 1,710 cm−1.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

The lubricant deterioration detection device for a rolling bearing disclosed in PTL 1 includes a gas sensor that is directly attached to a shield plate and thus may malfunction by vibration or heat generated during operation of a bearing.

The lubricant deterioration detection device including an infrared spectrophotometer is difficult to accurately determine the absorbance of a carbonyl group generated by deterioration, directly from a lubricating oil in a pipe, and cannot be used when the lubricant is a grease.

In other words, the lubricant deterioration detection device disclosed in PTL 1 has room for improvement inaccurate determination of the lubricant deterioration.

The present invention is intended to enable determination of the deterioration state of a lubricant in a rolling bearing with high accuracy.

Solution to Problem

To solve the problems, a first aspect of the present invention provides a lubricant deterioration detection device including a gas sensor configured to detect a carbonyl compound.

A second aspect of the invention provides a lubricant deterioration detection device including a gas sensor configured to detect at least one of n-hexanal and n-heptanal.

A third aspect of the invention provides a lubricant deterioration state evaluation method including in situ determining an amount of a gaseous carbonyl compound generated from a lubricant in a rolling bearing lubricated with the lubricant to evaluate a deterioration state of the lubricant.

A fourth aspect of the invention provides a lubricant deterioration detection device that includes a housing rotatably storing a rolling bearing, a gas sensor located outside the housing, and a gas inlet pipe connecting a gas outlet port formed on the housing to a gas inlet port of the gas sensor and configured to introduce a gas in the housing into the gas sensor, and a deterioration state of a lubricant in the rolling bearing is detected by a detected value of the gas sensor.

Advantageous Effects of Invention

The lubricant deterioration detection device of the first aspect includes a gas sensor configured to detect a carbonyl compound that predicts deterioration of a lubricant, and thus more accurately determines lubricant deterioration than a device that determines lubricant deterioration by detection of hydrocarbons, which are generated even when a lubricant does not deteriorate yet.

The lubricant deterioration detection device of the second aspect includes a gas sensor configured to detect at least one of n-hexanal and n-heptanal that predicts deterioration of a lubricant, and thus more accurately determines lubricant deterioration than a device that determines lubricant deterioration by detection of hydrocarbons, which are generated even when a lubricant does not deteriorate yet.

According to the third aspect, a method capable of determining the deterioration state of a lubricant in a rolling bearing with high accuracy can be provided.

The lubricant deterioration detection device of the fourth aspect includes a gas sensor outside a housing that rotatably stores a rolling bearing, and thus the gas sensor is unlikely to be affected by vibration or heat generated during operation of the rolling bearing. Accordingly, the lubricant deterioration detection device can determine the deterioration state of a lubricant in a rolling bearing with higher accuracy than a lubricant deterioration detection device in which the housing of a gas sensor is directly attached to a rolling bearing.

DESCRIPTION OF EMBODIMENTS

First Aspect

The lubricant deterioration detection device disclosed in PTL 1 includes a gas sensor that detects at least any gas of hydrocarbons, hydrogen sulfide, and ammonia in a bearing.

However, the inventors of the present application have analyzed gases generated by thermal deterioration under long-term heating of a mineral oil, a poly-α-olefin oligomer oil, and a polyol ester oil used as a lubricant for bearings, with a gas chromatograph-mass spectrometer, revealing that the main component of smelling components is a carbonyl compound.

FIG. 1is a chart illustrating the analysis result of the mineral oil,FIG. 2is a chart illustrating the analysis result of the poly-α-olefin oligomer oil, andFIG. 3is a chart illustrating the analysis result of the polyol ester oil. Compounds of peaks 1 to 8 inFIG. 1toFIG. 3and physical properties thereof are listed in Table 1.

As apparent fromFIG. 1toFIG. 3and Table 1, different types of lubricants yield common carbonyl compounds (aldehydes, a ketone, an organic peroxide, organic acids) as smelling components. Although this analysis recorded the result from 5 minutes as the elution time, smelling components probably also includes formaldehyde, acetaldehyde, propanal, butanal, pentanal, formic acid, and the like, which have lower boiling points than those of the compounds listed in Table 1.

The molecular weights, the boiling points, and the vapor pressures of formaldehyde, acetaldehyde, propanal, butanal, pentanal, and formic acid are listed in Table 2.

Such low-molecular weight carbonyl compounds have low boiling points of 118° C. to 195° C., usually have high vapor pressures, easily volatilize when a lubricant deteriorates, thus are easily collected, and are preferred as components for examining lubricant deterioration (detection targets). Such highly volatile compounds quickly absorb to/desorb from a detector of a gas sensor (a film formed on the resonator surface in the case a quartz resonator sensor) and are unlikely to be left, resulting in satisfactory responsivity of the gas sensor.

Of the above compounds, formaldehyde, acetaldehyde, propanal, butanal, pentanal, n-hexanal, n-heptanal, formic acid, and acetic acid are particularly preferred as the detection target, in terms of boiling points and vapor pressure values.

Hence, it has been thought that by using a gas sensor capable of highly accurately detecting a minute amount of a carbonyl compound (at least one of formaldehyde, acetaldehyde, propanal, butanal, pentanal, n-hexanal, n-heptanal, formic acid, and acetic acid) as a main smelling component generated by deterioration of a lubricant in a rolling bearing, the determination accuracy of lubricant deterioration can be improved.

Hydrogen sulfide and ammonia as the detection targets of the lubricant deterioration detection device in PTL 1 are gases derived from additive components and are not contained in some lubricants. Hydrocarbons are generated when a rolling bearing is at a high temperature but a lubricant does not deteriorate yet, and thus use of a device of detecting hydrocarbons to determine lubricant deterioration is likely to lead to an incorrect result.

First Embodiment

An embodiment in a first aspect of the present invention will now be described, but the invention is not limited to the following embodiment. The following embodiment includes technically preferred limitations for carrying out the invention, but the limitations are not essential requirements of the invention.

<Structure of Lubricant Deterioration Detection Device>

As illustrated inFIG. 4, a lubricant deterioration detection device10in the present embodiment includes a gas sensor1, a radio transmitter2, a display device (receiver)20, and a thermoelectric conversion element3. The gas sensor1, the radio transmitter2, and the thermoelectric conversion element3are fixed onto the outer peripheral surface of a cylinder5. The cylinder5is a bearing housing in which outer rings of rolling bearings are fitted. To the cylinder5, two identical rolling bearings4are attached.

The rolling bearings4(4A,4B) are sealed deep groove ball bearings each including an inner ring41, an outer ring42, balls43, a retainer44, and shield plates45. At both axial ends on the inner peripheral surface of the cylinder5, grooves51,52are formed for fitting the outer rings42of the rolling bearings4A,4B.

The gas sensor1, the radio transmitter2, and the thermoelectric conversion element3are located on the cylinder5at positions where the outer ring42of the rolling bearing4A is fixed in the axis direction. The gas sensor1, the radio transmitter2, and the thermoelectric conversion element3are located on the cylinder5at positions different in the circumferential direction. The gas sensor1and the radio transmitter2are connected through a wiring60, and the radio transmitter2and the thermoelectric conversion element3are connected through a wiring70. The display device20is located at a position apart from the cylinder5.

As the gas sensor1, a micro gas sensor array produced by MEMS (micro electro mechanical systems) technology can be used, for example. An example of the micro gas sensor array is illustrated inFIG. 5. The micro gas sensor array inFIG. 5includes seven rows each including four channels11to14. The number of rows can be optional. A larger number of rows can improve detection sensitivity. The first channel11selectively detects n-hexanal and n-heptanal. The second channel12selectively detects hydrocarbons. The third channel13selectively detects water. The fourth channel14selectively detects oxygen.

As each sensor included in the micro gas sensor array, a quartz resonator sensor can be used. In the case, for example, a film of polyethylene glycol2000is formed on the resonator surface in the first channel11. In the second channel12, for example, a polyvinyl chloride (PVC) film is formed on the resonator surface.

In the third channel13, for example, a poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS: polythiophene-based electrically conductive polymer) film is formed on the resonator surface. In the fourth channel14, for example, a tin oxide (SnO2) film is formed on the resonator surface. Each film can be formed by spin coating or sputtering, and the film thickness is preferably 50 nm, for example.

As the radio transmitter2, a radio transmitter including a circuit board21can be used, for example. In the case, the circuit board21includes a signal processing circuit211, a transmission circuit212, an antenna213, a charging circuit214, and a secondary battery215. An input power line22of the radio transmitter2is connected through the wiring70to the thermoelectric conversion element3. An output power line23and an input signal processing line24of the radio transmitter2are connected through the wiring60to the gas sensor1.

As the thermoelectric conversion element3, a thermoelectric conversion element including a flexible substrate32and a plurality of thermoelectric conversion units310of a printed pattern formed on the substrate32can be used, as illustrated inFIG. 6andFIG. 7. In the case, a cross-sectional shape of a unit formation portion321of the substrate32on which a thermoelectric conversion unit310is formed includes a projection portion3211, a first base portion part3212, and a second base portion3213. The first base portion3212and the second base portion3213are located at the respective sides of the projection portion3211, are lower than the projection portion, and are as high as non-formation portions322on which no thermoelectric conversion unit310is formed.

In the case, as illustrated inFIG. 6, the thermoelectric conversion unit310includes a first layer331from the first base portion3212of the unit formation portion321to a top3211aof the projection portion3211and a second layer332from the top3211ato the second base portion3213. The unit formation portion321is separated in the whole region of the projection portion3211from a non-formation portion322A (seeFIG. 7) behind the plane ofFIG. 6(appearing below the projection portion3211). The first layer331is formed from a p-type electrically conductive polymer (thermoelectric conversion material), and the second layer332is formed from a cured product of silver paste (electrically conductive material).

As the thermoelectric conversion element3, a thermoelectric conversion element in which 100 of the thermoelectric conversion units310illustrated inFIG. 6are arranged in a 10×10 matrix can be used. In the case, these thermoelectric conversion units310are connected in series.FIG. 7illustrates a thermoelectric conversion element3in which 14 thermoelectric conversion units310are formed in two columns and seven rows on a substrate32, for simple explanation.FIG. 6is a cross-sectional view taken along the line A-A inFIG. 7.

In the case, lower wirings341are formed above the first base portions3212and the second base portions3213through the first layers331and the second layers332and each connect a first layer331and a second layer332of the adjacent thermoelectric conversion units310.

In the case, the first layer331and the second layer332are formed from different materials, and thus an upper wiring342for connecting the first layer331and the second layer332in each thermoelectric conversion unit310is formed at the top3211aof the projection portion3211. The ends of the series connection are located on one edge of the substrate32, and at each position, an external connection terminal343is formed.

In the case, each thermoelectric conversion unit310has a height difference between a lower part331athat is a part of the first layer331on the first base portion3212or a lower part332athat is a part of the second layer332on the second base portion3213and upper parts331b,332bof the first layer331and the second layer332on the top3211a, and the height difference is not less than the thicknesses of the first layer331and the second layer332.

In the case, the substrate32of the thermoelectric conversion element3is fixed to the cylinder5, and the pair of connection terminals343of the thermoelectric conversion element3are connected through the wiring70to the power line22of the radio transmitter2.

<Operation of Lubricant Deterioration Detection Device>

When heat generated by rotation of the rolling bearings4heats the cylinder5, a temperature difference is caused between the lower parts331a,332aand the upper parts331b,332bof each thermoelectric conversion unit310included in the thermoelectric conversion element3. Accordingly, the thermoelectric conversion element3generates electricity, and electric current signals produced by the electricity flow through the power line22into the charging circuit214on the circuit board21and are charged in the secondary battery215.

The electric current in the secondary battery215drives the signal processing circuit211and the transmission circuit212and is supplied through the power line23to the gas sensor1.

Accordingly, the radio transmitter2processes detection data input from the gas sensor1, with the signal processing circuit211and the transmission circuit212and transmits the result as radio waves from the antenna213. The display device20receives the detection data transmitted as radio waves from the antenna213of the radio transmitter2and displays the detection result.

<Sensed Result by Sensor Array and Determination Method>

A virtual example prepared for explanation of a determination method using the sensor array is illustrated inFIG. 8. The case in which a peak of the first channel (n-hexanal and n-heptanal)11and a peak of the second channel (hydrocarbons)12are observed at the initial state of rotation will be described. In this case, the peaks are supposed to be formed in the process in which a lubricant is widely spread in and fits with the whole bearing at the initial state of rotation. In other words, at this time point, n-hexanal and/or n-heptanal produced by decomposition of a lubricant that is being spread in the whole bearing and hydrocarbons produced by evaporation of low-molecular weight substances contained in the lubricant in association with a temperature increase are considered to be detected.

The case in which a peak of the first channel11, a peak of the second channel12, and a peak of the third channel (water)13are subsequently observed will be described. In this case, air (air in the space where the tester is installed) enters a sensor attachment position at this time point, and n-hexanal and/or n-heptanal, hydrocarbons, and water contained in the air are considered to be detected.

The case in which peaks of the first channel11and the second channel12and peaks of the third channel13and the fourth channel (oxygen)14are subsequently observed will be described. In this case, exhaust gas from gasoline-fueled cars or the like passing near the tester enters a sensor attachment position at this time point, and oxygen, water, hydrocarbons, and n-hexanal and/or n-heptanal contained in the exhaust gas are considered to be detected.

The case in which only a peak of the first channel11is subsequently observed just before seizing up will be described. From the case, detection of only the peak of the first channel11, or detection of only n-hexanal and/or n-heptanal can be considered to indicate a prediction of seizing up. Hence, if the rotation of a bearing is stopped upon this detection, the breakage of a bearing due to seizing up or damage to other devices can be minimized, and the operation of an apparatus can be safety stopped.

<Effect of Lubricant Deterioration Detection Device>

The lubricant deterioration detection device disclosed in PTL 1 uses a gas sensor that detects at least any gas of hydrocarbons, hydrogen sulfide, and ammonia, whereas the lubricant deterioration detection device in the present embodiment can use a gas sensor1that includes a highly sensitive micro gas sensor array prepared by MEMS technology and includes a plurality of channels including a channel for detecting n-hexanal and n-heptanal (first channel11).

Detection of hydrocarbons indicates evaporation of low-molecular weight substances in association with a temperature increase of a lubricant but does not directly indicate lubricant deterioration.

Hence, the lubricant deterioration detection device of the embodiment should improve the determination accuracy of lubricant deterioration as compared with the lubricant deterioration detection device disclosed in PTL 1.

To attach the lubricant deterioration detection device disclosed in PTL 1 to a rolling bearing, an opening is formed on a circular plate of a shield plate, and a detector including a gas sensor is attached to the opening. The detector and the device main body (display device) are connected through a wiring. In contrast, in the lubricant deterioration detection device of the embodiment, the gas sensor1, the radio transmitter2, and the thermoelectric conversion element3are fixed onto the outer peripheral surface of the cylinder5, and the detection result is displayed on the display device20wirelessly connected to the gas sensor1.

In other words, the lubricant deterioration detection device of the embodiment neither damages the rolling bearings4nor has any wiring extending from the rolling bearings4to the display device20. Lubricant deterioration can be continuously monitored on the display device20located apart from the rolling bearings4.

<Method for Producing Thermoelectric Conversion Element>

A method for producing the thermoelectric conversion element3will be described with a thermoelectric conversion element including 14 thermoelectric conversion units310in two columns and seven rows.

The thermoelectric conversion element3is produced by performing a slit forming step illustrated inFIG. 9, a former step in a first print step illustrated inFIG. 10, a latter step in the first print step illustrated inFIG. 11, a second print step illustrated inFIG. 7, and a projection forming step of making the state inFIG. 12into the state inFIG. 6, in this order.

In the method for producing the thermoelectric conversion element3in the embodiment, 28 slits325corresponding to 14 thermoelectric conversion units310illustrated inFIG. 7are first formed on a substrate32, as illustrated inFIG. 9. The slits325are formed to have the same length as the formation distance of a pair of lower wirings341in a thermoelectric conversion unit310. In other words, slits325are formed in the entire region of the substrate32in which projection portions3211are formed.

Next, as the former step in the first print step, a first layer331is formed for each thermoelectric conversion unit310in the width between two adjacent slits325in each column, as illustrated inFIG. 10. Adjacent first layers331in a column or between columns of 14 thermoelectric conversion units310in the two columns are provided at opposite positions in the length direction of the slits325. An end of each first layer331along the slits325protrudes outward from the slits325.

Next, as the latter step in the first print step, a second layer332is formed for each thermoelectric conversion unit310in the width between two adjacent slits325in each column, as illustrated inFIG. 11. The second layer332is formed in contact with the adjacent first layer331to have the same thickness as that of the first layer331.

Through the process, a thermoelectric conversion pattern including all the first layers331and the second layers332constituting 14 thermoelectric conversion units310in two columns are formed on the substrate32. In the state ofFIG. 11, the portions including the first layers331and the second layers332on the substrate32are unit formation portions, and the other portions are non-formation portions.

Next, as the second print step, a conductive layer pattern including lower wirings341, connection terminals343, and upper wirings342is formed as illustrated inFIG. 7, on the thermoelectric conversion pattern illustrated inFIG. 11. The thermoelectric conversion units310in the state are formed in a planar shape on the planar substrate32, as illustrated inFIG. 12.

Next, as the projection forming step, a mold having male portions corresponding to the projection portion3211inFIG. 6is pressed against the back face of the substrate32where the slits325are formed (face without the thermoelectric conversion units310). This pressing draws and deforms the first layers331, the second layers332, and portions of the substrate32with the first layers331and the second layers332, forming projection portions3211. For the pressing, a mold having male portions corresponding to the projection portions3211of all the unit formation portions321is used to form the projection portions3211for all the thermoelectric conversion units310at once.

In the thermoelectric conversion element3produced in this manner, each thermoelectric conversion unit310has a height difference between the lower part331athat is a part of the first layer331on the first base portion3212or the lower part332athat is a part of the second layer332on the second base portion3213and the upper parts331b,332bof the first layer331and the second layer332on the top3211a, and the height difference is not less than the thicknesses of the first layer331and the second layer332.

Hence, even when the thermoelectric conversion element3is placed on a planar heating element (for example, a hot plate) while the non-formation portion322of the substrate32is horizontally held and the lower parts331aof the first layers331and the lower parts332aof the second layers332are heated through the substrate32, high electric power generation performance can be achieved. In addition, the substrate32with the printed pattern can be simply, stably installed on a heating element.

The whole region of the projection portion3211in each unit formation portion321is separated from non-formation portions322A. Lower spaces K of the projection portions3211thus continue to form an air flow path in each column of the thermoelectric conversion units310. Hence, by flowing air through the flow paths including the lower spaces K to cool the tops3211aat the time of heating of the substrate32, a larger temperature difference can be produced between the lower parts331a,332aand the upper parts331b,332bof the thermoelectric conversion units310.

[Selective Adsorption Film of Gas Sensor]

Examples of the material of the film selectively adsorbing at least one of n-hexanal and n-heptanal include polynaphthylamine, high-density polyethylene, EVOH (ethylene-vinyl alcohol copolymer), dinitrophenylhydrazine, nitroterephthalic acid-modified polyethylene glycol, polyethyleneimine, and ABS resins, in addition to the above polyethylene glycol.

When a polynaphthylamine film is compared with a polyethylene glycol film as the film formed on the resonator surface of a quartz resonator sensor, the quartz resonator sensor using the polyethylene glycol film achieves higher sensitivity of detecting n-hexanal and n-heptanal than that using the polynaphthylamine film. Hence, the polyethylene glycol film is preferably used.

When a method using molecular template technology is used to form a selective adsorption film for a carbonyl compound on a quartz crystal microblance (QCM) sensor, a strain sensor, a pressure sensor, or the like, a sensor having higher selectivity can be prepared.

As an example, a selective adsorption film for acetic acid was prepared by molecular template technology, and the performance of the sensor was examined. Specifically, a polymer thin film selectively adsorbing acetic acid was formed on a quartz crystal microblance (QCM) sensor by the following procedure.

First, 1.44 g of tertiary-butyl methacrylate and 1.98 g of ethylene glycol dimethacrylate were placed in a container, then, 0.22 g of acetic acid was added into the container, and 0.18 g of 1-hydroxycyclohexyl phenyl ketone as a radical generator and 10 ml of chloroform were further added, giving a monomer solution. With a micropipette, 0.5 μl of the monomer solution was taken and dropped on a round blank of a QCM (nominal frequency: 9 MHz) sensor manufactured by Nihon Dempa Kogyo Co., Ltd.

Next, to the liquid film on the blank formed by the dropping, ultraviolet light was applied at only an integrated light quantity of 4,200 mJ to cure the liquid film. Next, the cured film was washed with water, warm water, and distilled water to elute acetic acid from the film, and the resulting film was dried. Consequently, a polymer thin film having the template of acetic acid was formed on the QCM sensor.

The resulting QCM sensor having the acetic acid-selective film was attached to a QCM measurement apparatus “NAPICOS twin sensor system” manufactured by Nihon Dempa Kogyo Co., Ltd., and was brought into contact with gases each containing 1 ppm acetic acid (AcOH), n-heptanal (C6CHO), n-heptanol (C7OH), n-heptane (C7H16), or toluene (Tol), in this order, determining relative detection intensities. Subsequently, the effect by water was eliminated. The result is illustrated inFIG. 13. As illustrated inFIG. 13, a gas containing acetic acid showed a phenomenon in which acetic acid was adsorbed by the film on the QCM sensor to greatly reduce the oscillating frequency. Gases containing the compounds other than acetic acid hardly changed the oscillating frequency, and this indicates that the compounds other than acetic acid were not adsorbed by the film on the QCM sensor.

Next, the QCM sensor having the acetic acid-selective film was attached to a QCM measurement apparatus “NAPICOS twin sensor system” and was brought into contact with a gas generated by thermal deterioration of a poly-α-olefin oligomer oil at 120° C. for 1,500 hours, determining the detection intensity of acetic acid. The result is illustrated inFIG. 14.FIG. 14illustrates that use of the QCM sensor enables detection of acetic acid from smelling components of an oil after thermal deterioration to determine lubricant deterioration.

The smell generated by the thermal deterioration was such a degree as to be slightly sensed by a human, but quantitative determination with a prepared calibration curve revealed that the acetic acid concentration was 500 ppb. Acetic acid at the concentration can be detected at a certain position apart from the machine lubrication position lubricated by a lubricant, and thus the QCM sensor is thought to have acetic acid detection performance for practical use.

Selective adsorption films for carbonyl compounds other than acetic acid can also be prepared by the above procedure using corresponding carbonyl compounds in place of acetic acid.

Preferred Embodiment

The lubricant deterioration detection device in the first aspect of the present invention includes a gas sensor configured to detect a carbonyl compound. The carbonyl compound to be detected is preferably at least one of formaldehyde, acetaldehyde, propanal, butanal, pentanal, n-hexanal, n-heptanal, formic acid, and acetic acid. The gas sensor preferably has a plurality of channels including a channel that selectively detects a carbonyl compound.

An example of the lubricant deterioration detection device in the first aspect of the invention is a lubricant deterioration detection device further including a radio transmitter that wirelessly transmits a detection result by the gas sensor to a receiver and a stand-alone power supply that includes a thermoelectric conversion element and supplies electric power to the gas sensor and the radio transmitter.

The thermoelectric conversion element included in the stand-alone power supply preferably has the following structures (a) to (d) or (a) to (e).

(a) A substrate and a plurality of thermoelectric conversion units formed on the substrate are included.

(b) A cross-sectional shape of a unit formation portion with each thermoelectric conversion unit on the substrate includes a projection portion, a first base portion, and a second base portion, the first base portion and the second base portion are located at the respective sides of the projection portion and are lower than the projection portion, and a non-formation portion without the thermoelectric conversion unit on the substrate is at a lower position than the top of the projection.

(c) The thermoelectric conversion unit includes a first layer from the first base portion of the unit formation portion to the top of the projection portion and a second layer from the top to the second base portion. At least one of the first layer and the second layer is formed from a thermoelectric conversion material. The first layer and the second layer are formed from the same material or different materials. The plurality of thermoelectric conversion units are connected in series.

(d) Lower wirings are formed above the first base portion and the second base portion and each connect the first layer and the second layer of the adjacent thermoelectric conversion units. When the first layers and the second layers are formed from different materials, an upper wiring connecting the first layer and the second layer in each thermoelectric conversion unit is formed at the top. External connection terminals are provided at the respective ends of the series connection.

(e) Each unit formation portion is separated in the region of the projection from the non-formation portion.

Second Aspect

The lubricant deterioration detection device disclosed in PTL 1 includes a gas sensor that detects at least any gas of hydrocarbons, hydrogen sulfide, and ammonia in a bearing.

However, the inventors of the application have performed a rotation test of a rolling bearing to analyze gases generated from the rolling bearing immediately before seizing up, with a gas chromatograph and have revealed that the main components of the smelling components were n-hexanal and n-heptanal and the concentrations thereof were several tens of parts per million.FIG. 15is a chart illustrating the analysis result with a gas chromatograph. InFIG. 15, it was ascertained that the peak 1 was n-hexanal and the peak 2 was n-heptanal.

Specifically, the rotation test was performed by continuously rotating a deep groove ball bearing with an inner diameter of 50 mm, an outer diameter of 110 mm, and a width of 27 mm and including noncontact seals in conditions of inner ring rotation, grease lubrication, a rotation speed of 10,000 rpm, and an axial load of 98 N, until seizing up was caused. The grease used was a commercially available grease containing lithium soap as a thickener and mineral oil as a base oil.

In other words, the inventors of the present application have found that n-hexanal and n-heptanal are components predicting lubricant deterioration.

n-Hexanal, which have a boiling point of 130° C., and n-heptanal, which have a boiling point of 152° C., are highly volatile components of the smelling components in a grease after deterioration and thus can be easily collected. Such highly volatile compounds quickly absorb to/desorb from a detector of a gas sensor (a film formed on the resonator surface in the case a quartz resonator sensor) and are unlikely to be left, resulting in satisfactory responsivity of the gas sensor.

Hence, it has been thought that by using a gas sensor capable of highly accurately detecting minute amounts of n-hexanal and/or n-heptanal, which are main smelling components generated by deterioration of a lubricant in a rolling bearing, the determination accuracy of lubricant deterioration can be improved.

Hydrogen sulfide and ammonia as the detection targets of the lubricant deterioration detection device in PTL 1 are gases derived from additive components and are not contained in some lubricants. Hydrocarbons are generated when a rolling bearing is at a high temperature but a lubricant does not deteriorate yet, and thus use of a device of detecting hydrocarbons to determine lubricant deterioration is likely to lead to an incorrect result.

Second Embodiment

An embodiment in a second aspect of the present invention will now be described, but the invention is not limited to the following embodiment. The following embodiment includes technically preferred limitations for carrying out the invention, but the limitations are not essential requirements of the invention.

<Structure of Lubricant Deterioration Detection Device>

As illustrated inFIG. 16, a lubricant deterioration detection device10in the present embodiment includes a gas sensor1, a radio transmitter2, a display device (receiver)20, and a thermoelectric conversion element3. The gas sensor1, the radio transmitter2, and the thermoelectric conversion element3are fixed onto the outer peripheral surface of a cylinder5. The cylinder5is a bearing housing in which outer rings of rolling bearings are fitted. To the cylinder5, two identical rolling bearings4are attached.

The rolling bearings4(4A,4B) are sealed deep groove ball bearings each including an inner ring41, an outer ring42, balls43, a retainer44, and shield plates45. At the respective axial ends of the cylinder5on the inner peripheral surface, grooves51,52are formed for fitting the outer rings42of the rolling bearings4A,4B.

The gas sensor1, the radio transmitter2, and the thermoelectric conversion element3are located on the cylinder5at positions where the outer ring42of the rolling bearing4A is fixed in the axis direction. The gas sensor1, the radio transmitter2, and the thermoelectric conversion element3are located on the cylinder5at positions different in the circumferential direction. The gas sensor1and the radio transmitter2are connected through a wiring60, and the radio transmitter2and the thermoelectric conversion element3are connected through a wiring70. The display device20is located at a position apart from the cylinder5.

As the gas sensor1, a micro gas sensor array produced by MEMS (micro electro mechanical systems) technology can be used, for example. An example of the micro gas sensor array is illustrated inFIG. 17. The micro gas sensor array inFIG. 17includes seven rows each including four channels11to14. The number of rows can be optional. A larger number of rows can improve detection sensitivity. The first channel11selectively detects n-hexanal and n-heptanal. The second channel12selectively detects hydrocarbons. The third channel13selectively detects water. The fourth channel14selectively detects oxygen.

As each sensor included in the micro gas sensor array, a quartz resonator sensor can be used. In the case, for example, a film of polyethylene glycol2000is formed on the resonator surface in the first channel11. In the second channel12, for example, a polyvinyl chloride (PVC) film is formed on the resonator surface.

In the third channel13, for example, a poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS: polythiophene-based electrically conductive polymer) film is formed on the resonator surface. In the fourth channel14, for example, a tin oxide (SnO2) film is formed on the resonator surface. Each film can be formed by spin coating or sputtering, and the film thickness is preferably 50 nm, for example.

As the radio transmitter2, a radio transmitter including a circuit board21can be used, for example. In the case, the circuit board21includes a signal processing circuit211, a transmission circuit212, an antenna213, a charging circuit214, and a secondary battery215. An input power line22of the radio transmitter2is connected through the wiring70to the thermoelectric conversion element3. An output power line23and an input signal processing line24of the radio transmitter2are connected through the wiring60to the gas sensor1.

As the thermoelectric conversion element3, a thermoelectric conversion element including a flexible substrate32and a plurality of thermoelectric conversion units310of a printed pattern formed on the substrate32can be used, as illustrated inFIG. 18andFIG. 19. In the case, a cross-sectional shape of a unit formation portion321of the substrate32on which a thermoelectric conversion unit310is formed includes a projection portion3211, a first base portion part3212, and a second base portion3213. The first base portion3212and the second base portion3213are located at the respective sides of the projection portion3211, are lower than the projection portion, and are as high as non-formation portions322on which no thermoelectric conversion unit310is formed.

In the case, as illustrated inFIG. 18, the thermoelectric conversion unit310includes a first layer331from the first base portion3212of the unit formation portion321to a top3211aof the projection portion3211and a second layer332from the top3211ato the second base portion3213. The unit formation portion321is separated in the whole region of the projection portion3211from a non-formation portion322A (seeFIG. 19) behind the plane ofFIG. 18(appearing below the projection portion3211). The first layer331is formed from a p-type electrically conductive polymer (thermoelectric conversion material), and the second layer332is formed from a cured product of silver paste (electrically conductive material).

As the thermoelectric conversion element3, a thermoelectric conversion element in which 100 of the thermoelectric conversion units310illustrated inFIG. 18are arranged in a 10×10 matrix can be used. In the case, these thermoelectric conversion units310are connected in series.FIG. 19illustrates a thermoelectric conversion element3in which 14 thermoelectric conversion units310are formed in two columns and seven rows on a substrate32, for simple explanation.FIG. 18is a cross-sectional view taken along the line A-A inFIG. 19.

In the case, lower wirings341are formed above the first base portions3212and the second base portions3213through the first layers331and the second layers332and each connect a first layer331and a second layer332of the adjacent thermoelectric conversion units310.

In the case, the first layer331and the second layer332are formed from different materials, and thus an upper wiring342for connecting the first layer331and the second layer332in each thermoelectric conversion unit310is formed at the top3211aof the projection portion3211. The ends of the series connection are located on one edge of the substrate32, and at each position, an external connection terminal343is formed.

In the case, each thermoelectric conversion unit310has a height difference between a lower part331athat is a part of the first layer331on the first base portion3212or a lower part332athat is a part of the second layer332on the second base portion3213and upper parts331b,332bof the first layer331and the second layer332on the top3211a, and the height difference is not less than the thicknesses of the first layer331and the second layer332.

In the case, the substrate32of the thermoelectric conversion element3is fixed to the cylinder5, and the pair of connection terminals343of the thermoelectric conversion element3are connected through the wiring70to the power line22of the radio transmitter2.

<Operation of Lubricant Deterioration Detection Device>

When heat generated by rotation of the rolling bearings4heats the cylinder5, a temperature difference is caused between the lower parts331a,332aand the upper parts331b,332bof each thermoelectric conversion unit310included in the thermoelectric conversion element3. Accordingly, the thermoelectric conversion element3generates electricity, and electric current signals produced by the electricity flow through the power line22into the charging circuit214on the circuit board21and are charged in the secondary battery215.

The electric current in the secondary battery215drives the signal processing circuit211and the transmission circuit212and is supplied through the power line23to the gas sensor1.

Accordingly, the radio transmitter2processes detection data input from the gas sensor1, with the signal processing circuit211and the transmission circuit212and transmits the result as radio waves from the antenna213. The display device20receives the detection data transmitted as radio waves from the antenna213of the radio transmitter2and displays the detection result.

<Sensed Result by Sensor Array and Determination Method>

A virtual example prepared for explanation of a determination method using the sensor array is illustrated inFIG. 20. The case in which a peak of the first channel (n-hexanal and n-heptanal)11and a peak of the second channel (hydrocarbons)12are observed at the initial state of rotation will be described. In this case, the peaks are supposed to be formed in the process in which a lubricant is widely spread in and fits with the whole bearing at the initial state of rotation. In other words, at this time point, n-hexanal and/or n-heptanal produced by decomposition of a lubricant that is being spread in the whole bearing and hydrocarbons produced by evaporation of low-molecular weight substances contained in the lubricant in association with a temperature increase are considered to be detected.

The case in which a peak of the first channel11, a peak of the second channel12, and a peak of the third channel (water)13are subsequently observed will be described. In this case, air (air in the space where the tester is installed) enters a sensor attachment position at this time point, and n-hexanal and/or n-heptanal, hydrocarbons, and water contained in the air are considered to be detected.

The case in which peaks of the first channel11and the second channel12and peaks of the third channel13and the fourth channel (oxygen)14are subsequently observed will be described. In this case, exhaust gas from gasoline-fueled cars or the like passing near the tester enters a sensor attachment position at this time point, and oxygen, water, hydrocarbons, and n-hexanal and/or n-heptanal contained in the exhaust gas are considered to be detected.

The case in which only a peak of the first channel11is subsequently observed just before seizing up will be described. From the case, detection of only the peak of the first channel11, or detection of only n-hexanal and/or n-heptanal can be considered to indicate a prediction of seizing up. Hence, if the rotation of a bearing is stopped upon this detection, the breakage of a bearing due to seizing up or damage to other devices can be minimized, and the operation of an apparatus can be safety stopped.

<Effect of Lubricant Deterioration Detection Device>

The lubricant deterioration detection device disclosed in PTL 1 uses a gas sensor that detects at least any gas of hydrocarbons, hydrogen sulfide, and ammonia, whereas the lubricant deterioration detection device in the present embodiment can use a gas sensor1that includes a highly sensitive micro gas sensor array prepared by MEMS technology and includes a plurality of channels including a channel for detecting n-hexanal and n-heptanal (first channel11).

Detection of hydrocarbons indicates evaporation of low-molecular weight substances in association with a temperature increase of a lubricant but does not directly indicate lubricant deterioration.

Hence, the lubricant deterioration detection device of the embodiment should improve the determination accuracy of lubricant deterioration as compared with the lubricant deterioration detection device disclosed in PTL 1.

To attach the lubricant deterioration detection device disclosed in PTL 1 to a rolling bearing, an opening is formed on a circular plate of a shield plate, and a detector including a gas sensor is attached to the opening. The detector and the device main body (display device) are connected through a wiring. In contrast, in the lubricant deterioration detection device of the embodiment, the gas sensor1, the radio transmitter2, and the thermoelectric conversion element3are fixed onto the outer peripheral surface of the cylinder5, and the detection result is displayed on the display device20wirelessly connected to the gas sensor1.

In other words, the lubricant deterioration detection device of the embodiment neither damages the rolling bearings4nor has any wiring extending from the rolling bearings4to the display device20. Lubricant deterioration can be continuously monitored on the display device20located apart from the rolling bearings4.

Examples of the material of the film selectively adsorbing at least one of n-hexanal and n-heptanal include polynaphthylamine, high-density polyethylene, EVOH (ethylene-vinyl alcohol copolymer), dinitrophenylhydrazine, nitroterephthalic acid-modified polyethylene glycol, polyethyleneimine, and ABS resins, in addition to polyethylene glycol.

When a polynaphthylamine film is compared with a polyethylene glycol film as the film formed on the resonator surface of a quartz resonator sensor, the quartz resonator sensor using the polyethylene glycol film achieves higher sensitivity of detecting n-hexanal and n-heptanal than that using the polynaphthylamine film. Hence, the polyethylene glycol film is preferably used.

<Method for Producing Thermoelectric Conversion Element>

A method for producing the thermoelectric conversion element3will be described with a thermoelectric conversion element including 14 thermoelectric conversion units310in two columns and seven rows.

The thermoelectric conversion element3is produced by performing a slit forming step illustrated inFIG. 21, a former step in a first print step illustrated inFIG. 22, a latter step in the first print step illustrated inFIG. 23, a second print step illustrated inFIG. 19, and a projection forming step of making the state inFIG. 24into the state inFIG. 18, in this order.

In the method for producing the thermoelectric conversion element3in the embodiment, 28 slits325corresponding to 14 thermoelectric conversion units310illustrated inFIG. 19are first formed on a substrate32, as illustrated inFIG. 21. The slits325are formed to have the same length as the formation distance of a pair of lower wirings341in a thermoelectric conversion unit310. In other words, slits325are formed in the entire region of the substrate32in which projection portions3211are formed.

Next, as the former step in the first print step, a first layer331is formed for each thermoelectric conversion unit310in the width between two adjacent slits325in each column, as illustrated inFIG. 22. Adjacent first layers331in a column or between columns of 14 thermoelectric conversion units310in the two columns are provided at opposite positions in the length direction of the slits325. An end of each first layer331along the slits325protrudes outward from the slits325.

Next, as the latter step in the first print step, a second layer332is formed for each thermoelectric conversion unit310in the width between two adjacent slits325in each column, as illustrated inFIG. 23. The second layer332is formed in contact with the adjacent first layer331to have the same thickness as that of the first layer331.

Through the process, a thermoelectric conversion pattern including all the first layers331and the second layers332constituting 14 thermoelectric conversion units310in two columns are formed on the substrate32. In the state ofFIG. 23, the portions including the first layers331and the second layers332on the substrate32are unit formation portions, and the other portions are non-formation portions.

Next, as the second print step, a conductive layer pattern including lower wirings341, connection terminals343, and upper wirings342is formed as illustrated inFIG. 19, on the thermoelectric conversion pattern illustrated inFIG. 23. The thermoelectric conversion units310in the state are formed in a planar shape on the planar substrate32, as illustrated inFIG. 24.

Next, as the projection forming step, a mold having male portions corresponding to the projection portion3211inFIG. 18is pressed against the back face of the substrate32where the slits325are formed (face without the thermoelectric conversion units310). This pressing draws and deforms the first layers331, the second layers332, and portions of the substrate32with the first layers331and the second layers332, forming projection portions3211. For the pressing, a mold having male portions corresponding to the projection portions3211of all the unit formation portions321is used to form the projection portions3211for all the thermoelectric conversion units310at once.

In the thermoelectric conversion element3produced in this manner, each thermoelectric conversion unit310has a height difference between the lower part331athat is a part of the first layer331on the first base portion3212or the lower part332athat is a part of the second layer332on the second base portion3213and the upper parts331b,332bof the first layer331and the second layer332on the top3211a, and the height difference is not less than the thicknesses of the first layer331and the second layer332.

Hence, even when the thermoelectric conversion element3is placed on a planar heating element (for example, a hot plate) while the non-formation portion322of the substrate32is horizontally held and the lower parts331aof the first layers331and the lower parts332aof the second layers332are heated through the substrate32, high electric power generation performance can be achieved. In addition, the substrate32with the printed pattern can be simply, stably installed on a heating element.

The whole region of the projection portion3211in each unit formation portion321is separated from non-formation portions322A. Lower spaces K of the projection portions3211thus continue to form an air flow path in each column of the thermoelectric conversion units310. Hence, by flowing air through the flow paths including the lower spaces K to cool the tops3211aat the time of heating of the substrate32, a larger temperature difference can be produced between the lower parts331a,332aand the upper parts331b,332bof the thermoelectric conversion units310.

Preferred Embodiment

The lubricant deterioration detection device in the second aspect of the present invention includes a gas sensor configured to detect at least one of n-hexanal and n-heptanal. The gas sensor preferably has a plurality of channels including a channel that selectively detects at least one of n-hexanal and n-heptanal.

An example of the lubricant deterioration detection device in the second aspect of the invention is a lubricant deterioration detection device further including a radio transmitter that wirelessly transmits a detection result by the gas sensor to a receiver and a stand-alone power supply that includes a thermoelectric conversion element and supplies electric power to the gas sensor and the radio transmitter.

The thermoelectric conversion element included in the stand-alone power supply preferably has the following structures (a) to (d) or (a) to (e).

(a) A substrate and a plurality of thermoelectric conversion units formed on the substrate are included.

(b) A cross-sectional shape of a unit formation portion with each thermoelectric conversion unit on the substrate includes a projection portion, a first base portion, and a second base portion, the first base portion and the second base portion are located at the respective sides of the projection portion and are lower than the projection portion, and a non-formation portion without the thermoelectric conversion unit on the substrate is at a lower position than the top of the projection.

(c) The thermoelectric conversion unit includes a first layer from the first base portion of the unit formation portion to the top of the projection portion and a second layer from the top to the second base portion. At least one of the first layer and the second layer is formed from a thermoelectric conversion material. The first layer and the second layer are formed from the same material or different materials. The plurality of thermoelectric conversion units are connected in series.

(d) Lower wirings are formed above the first base portion and the second base portion and each connect the first layer and the second layer of the adjacent thermoelectric conversion units. When the first layers and the second layers are formed from different materials, an upper wiring connecting the first layer and the second layer in each thermoelectric conversion unit is formed at the top. External connection terminals are provided at the respective ends of the series connection.

(e) Each unit formation portion is separated in the region of the projection from the non-formation portion.

Third Aspect

With the method of evaluating the deterioration state of a lubricant in a rolling bearing by the amount of hydrocarbons contained in a gas in the rolling bearing, different amounts of hydrocarbons may be detected even when the deterioration state of a lubricant is the same because different operation conditions of a rolling bearing (rotation speed or changes in load) may result in various temperature increases of the lubricant. Hence, the threshold of the hydrocarbon detection amount indicating deterioration is required to be changed depending on operation conditions of a rolling bearing. The threshold change is a complicated operation, and deviation of the threshold from an appropriate value may cause misjudgment of lubricant deterioration.

The inventors of the present application have studied to solve the problem and have revealed that the amount of carbonyl compounds (aldehydes and ketones) contained in the gas in a rolling bearing is substantially 0 before lubricant deterioration regardless of operation conditions of the rolling bearing, gradually increases just before seizing up by the lubricant, and then increases sharply.

On the basis of the findings, it has been thought that a lubricant deterioration detection device including a gas sensor that selectively detects carbonyl compounds can determine the deterioration state of a lubricant in a rolling bearing with higher accuracy than a lubricant deterioration detection device including a gas sensor that detects hydrocarbons, and the invention is achieved.

Third Embodiment

An embodiment in a third aspect of the present invention will now be described, but the invention is not limited to the following embodiment. The following embodiment includes technically preferred limitations for carrying out the invention, but the limitations are not essential requirements of the invention.

As illustrated inFIG. 25andFIG. 26, the lubricant deterioration detection device10of the embodiment includes a gas sensor1, a filter201, gas inlet pipes301,401, and a suction pump50. The gas inlet pipe301connects a gas inlet port of the gas sensor1and a gas outlet port of the filter201. One end of the gas inlet pipe401is a gas inlet portion410of the lubricant deterioration detection device, and the other end is connected to a gas inlet port of the filter201.

In the example inFIG. 25, the gas inlet pipe401includes three straight pipes and two elbow pipes, extends through an elbow pipe402in the direction perpendicular to the extending direction of the gas inlet portion410, and extends through an elbow pipe403in the same direction as the extending direction of the gas inlet portion410. The suction pump50is connected to a point between the elbow pipes402,403of the gas inlet pipe401. In the example inFIG. 26, the gas inlet pipe401includes two straight pipes and an elbow pipe and extends through an elbow pipe404to a direction perpendicular to the extending direction of the gas inlet portion410. The suction pump50is connected to a point between the elbow pipe404of the gas inlet pipe401and the filter201.

The gas sensor1is a controlled potential electrolysis sensor that detects only aldehydes (carbonyl compounds). The gas sensor1includes a display device that displays a real time aldehyde concentration. As the filter201, a ceramic filter that removes oil mist is provided.

The device to which the lubricant deterioration detection device10is attached includes two identical rolling bearings6, a cylinder portion7, and circular plate portions8,8A each having a central hole81in the example inFIG. 25. In the example inFIG. 26, the device includes two identical rolling bearings6, a cylinder portion7, and two identical circular plate portions8each having a central hole81. The cylinder portion7is a bearing housing in which outer rings of the rolling bearings are fitted.

In the example inFIG. 25, the cylinder portion7and the circular plate portions8,8A constitute a housing that rotatably stores two rolling bearings6. In the example inFIG. 26, the cylinder portion7and the two identical circular plate portions8constitute a housing that rotatably stores two rolling bearings6.

Each of the two rolling bearings6is a sealed deep groove ball bearing including an inner ring61, an outer ring62, balls (rolling elements)63, a retainer64, and shield plates (noncontact seals)65and is lubricated with a lubricant. At the respective axial ends of the cylinder portion7on the inner peripheral surface, grooves71,72are formed for fitting the outer rings62of the two rolling bearings6.

The circular plate portion8A used in the example inFIG. 25has a through hole82penetrating in the axis direction at a position facing a shield plate65. The cylinder portion7A used in the example inFIG. 26has a through hole73penetrating in a direction orthogonal to the axis, at the axial center.

The two rolling bearings6are fixed to the cylinder portion7apart from each other in the axis direction by fitting the outer rings62to the corresponding grooves71,72. The respective axial ends of the cylinder portion7are closed by the circular plate portions8,8A in the example inFIG. 25or by the two circular plate portions8in the example inFIG. 26. A rotating shaft9fitted to the inner rings61of the two rolling bearings6penetrates the central holes81, extends outward from the circular plate portions8,8A in the example inFIG. 25or extends outward from the two circular plate portions8in the example inFIG. 26, and is connected to a rotation device not shown in the drawings.

In the example inFIG. 25, the gas inlet portion410of the lubricant deterioration detection device10is inserted through a cylindrical-shaped rubber member85into the through hole82of the circular plate portion8A, and the gap between the gas inlet portion410and the through hole82is sealed by the rubber member85. In the example inFIG. 26, the gas inlet portion410of the lubricant deterioration detection device10is inserted through a cylindrical-shaped rubber member75into the through hole73of the cylinder portion7A, and the gap between the gas inlet portion410and the through hole73is sealed by the rubber member75.

The lubricant deterioration detection device10functions as follows: By activating the suction pump50concurrently with the rotation start of the rolling bearings6, the gas in the space surrounded by the rolling bearings6, the cylinder portion7, and the circular plate portions8(8A) is sucked. The sucked gas passes through the gas inlet pipe401into the filter201, and the filter201removes oil mist. Subsequently, the gas passes through the gas inlet pipe301into the gas sensor1, then the gas sensor1determines the aldehyde concentration, and the result is displayed.

The aldehyde concentration of a gas sucked into the gas inlet pipe401of the lubricant deterioration detection device10is substantially 0 before deterioration of a lubricant in the rolling bearings6, gradually increases just before seizing up by the lubricant, and then increases sharply. Hence, the deterioration of a lubricant in the rolling bearings6can be identified when the gas sensor1starts to detect increasing aldehyde concentrations.

If a lubricant or components other than the components generated from a lubricant adhere to the gas sensor1, the gas sensor1may malfunction, or the detection accuracy of the gas sensor1may deteriorate. To address this, the lubricant deterioration detection device10in the embodiment includes a filter201between the gas sensor1and the gas inlet portion410. As the filter201, an oil mist-removing filter is provided. In place of the oil mist-removing filter, a wet dust collector or a static oil mist remover may be provided.

Examples of the oil mist-removing filter include a paper filter, a metal filter, a ceramic filter, and a CNP filter. Of these filters, a paper filter is preferably used in terms of easy exchange. As the paper filter, a paper filter having a mesh size of about 200 and capable of collecting oil mist particles having a particle size of 0.3 μm or more is preferably used.

Between the gas sensor1and the gas inlet portion410, a filter that removes smelling components other than aldehydes may be provided. Examples of the filter that removes smelling components other than aldehydes (for example, smelling components generated from industrial wastes of factories) include a photocatalytic filter and an activated carbon filter. Specifically preferred is a filter in which an adsorbent and a photocatalytic powder are packed in the space (cavities) between a nonwoven fabric and a film. The adsorbent is preferably activated carbon and silica gel, and the photocatalyst is preferably titanium oxide and zinc oxide.

Alternatively, the difference between a gas having passed through a filter that adsorbs aldehydes, such as a dinitrophenylhydrazine (DNPH) filter, and a gas not having passed can be analyzed to determine aldehydes.

<Verification Test of Lubricant Deterioration Detection by Lubricant Deterioration Detection Device10: Test1>

The device illustrated inFIG. 27was used to perform the verification test for examining the lubricant deterioration detection result by the lubricant deterioration detection device10. The device illustrated inFIG. 27is prepared as follows: the elbow pipe402that connects a portion of the gas inlet pipe401with the suction pump50to the gas inlet portion410in the example inFIG. 25is replaced with a branch pipe405, and the opposite side of the branch pipe405to the gas inlet pipe401is connected to one end of a gas inlet pipe104included in a lubricant deterioration detection device100of a comparative example. As the electrode included in the controlled potential electrolysis sensor of the gas sensor1, a platinum electrode was used.

The lubricant deterioration detection device100includes a smell sensor101, a filter102, gas inlet pipes103,104, and a suction pump105. The gas inlet pipe103connects a gas inlet port of the smell sensor101and a gas outlet port of the filter102. The other end of the gas inlet pipe104is connected to a gas inlet port of the filter102. The suction pump105is connected to a portion of the gas inlet pipe104connected to the branch pipe405. The smell sensor101is an indium oxide-based heat ray sintered semiconductor sensor and can determine odor index. As the filter102, the same oil mist-removing filter as the filter201was used.

As two rolling bearings6, rolling bearings each having an inner diameter of 25 mm, an outer diameter of 62 mm, and a width of 17 mm were prepared. Each rolling bearing6was lubricated with a grease. The grease used was a commercially available grease containing a lithium soap (consistency: No. 2) as a thickener and a mineral oil (dynamic viscosity at 40° C.: 100 mm2/s) as a base oil.

The outer ring62of each rolling bearing6was fitted to the corresponding groove71,72on the cylinder portion7, a rotating shaft9of a tester is fitted to the inside of the inner ring61of each rolling bearing6, and the gas inlet portion410of the lubricant deterioration detection devices10,100was attached to the circular plate portion8A, giving the state illustrated inFIG. 27. The through hole82in the circular plate portion8A has a diameter of 6.5 mm, and the gas inlet pipe401has an outer diameter of 6 mm and an inner diameter of 4 mm. The gap between the through hole82and the gas inlet pipe401is sealed by a rubber member85.

While a radial load of 98 N and an axial load of 1,470 N were applied to each rolling bearing6, the rotating shaft9was continuously rotated at a rotation speed of 10,000 min−1. Concurrently with the rotation start of the rotating shaft9, the lubricant deterioration detection devices10,100were driven, and the aldehyde concentration detection by the gas sensor1, the odor index measurement by the smell sensor101, and the outer ring temperature measurement were continuously performed. The results are illustrated as the graphs inFIGS. 28A to 28C. The rotation of the rotating shaft9and the driving of the lubricant deterioration detection devices10,100were so controlled as to be stopped when an abnormal increase of the outer ring temperature was detected.

At 208 hours after the test start, an abnormal increase of the outer ring temperature was detected, and the rotation of the rotating shaft9and the driving of the lubricant deterioration detection devices10,100were stopped.

The graphs inFIGS. 28A to 28Creveal the following findings.

FIG. 28Ais a graph illustrating the relation between elapsed time and outer ring temperature. The outer ring temperature increased after the test start, then was almost constant from about 10 hours, and exceeded 125° C. at 208 hours.

FIG. 28Bis a graph illustrating the relation between elapsed time and odor index detected by the smell sensor101. The odor index increased at substantially the same rate as the increase rate of the outer ring temperature and then was almost constant at around 5.0 when the outer ring temperature became almost constant. Subsequently, the odor index slightly increased at around 165 hours, then was constant at about 6.0, and started to increase from 185 hours.

FIG. 28Cis a graph illustrating the relation between elapsed time and aldehyde concentration determined by the gas sensor1. The aldehyde concentration was almost 0 immediately after the test start until 180 hours, then gradually increased from 180 hours, and sharply increased from 206 hours that was immediately before the detection of the abnormal increase of the outer ring temperature.

The test results reveal the following findings.

The lubricant deterioration detection devices10,100can identify lubricant deterioration in advance.

With the lubricant deterioration detection device10of the embodiment, the aldehyde concentration was substantially 0 immediately after the test start until lubricant deterioration was caused in the rolling bearings6, gradually increased just before seizing up by the lubricant, and then increased sharply. Hence, the deterioration of a lubricant in the rolling bearings6can be identified when the gas sensor1starts to detect increasing aldehyde concentrations.

With the lubricant deterioration detection device100of the comparative example, the odor index increased immediately after the test start, then was almost constant before lubricant deterioration was caused in the rolling bearings6, and gradually increased just before seizing up by the lubricant. Hence, by setting the threshold of the odor index at, for example, 7.0, lubricant deterioration in the rolling bearings6can be identified when the odor index reaches the threshold. In other words, the lubricant deterioration detection device100of the comparative example needs previous threshold setting depending on conditions of use. In addition, the odor index varies with conditions of use of a rolling bearing, and thus an apparatus including a plurality of rolling bearings needs threshold setting for the respective bearings, which is a complicated process.

As described above, the lubricant deterioration detection device100of the comparative example needs previous threshold setting, and thus a setting error of the threshold may lead to incorrect determination of lubricant deterioration. In contrast, the lubricant deterioration detection device10of the embodiment eliminates the necessity of threshold setting depending on conditions of use. An example of the threshold is 1.0 ppm from the graph inFIG. 28C. Hence, the lubricant deterioration detection device10of the embodiment can determine the deterioration state of a lubricant with higher accuracy than the lubricant deterioration detection device100of the comparative example.

A test of determining aldehyde concentrations in a closed space was performed by heating a closed space containing a grease to increase the grease temperature. The grease used was the same as that used in the test1. The aldehyde concentration was determined by using the gas sensor1and the filter201used in the test1.

Specifically, 20 mg of grease was thinly applied onto an aluminum foil, and the aluminum foil was placed in a closed space having a volume of 25 mL. A pipe was attached to a side wall defining the closed space, and a gas through the filter201was analyzed by the gas sensor1. As a result, an aldehyde was started to be clearly detected when the temperature in the closed space exceeded about 160° C., and the aldehyde concentration sharply increased when the temperature exceeded 190° C. and reached 200° C., as illustrated inFIG. 29.

The test1has revealed that the outer ring temperature when the aldehyde concentration sharply increased was 120° C. to 130° C., and the results of the test1and the test2reveal that the temperature of the grease in the bearing is higher than the temperature of the outer ring when the aldehyde concentration sharply increases.

<Verification of Initial Stage in Test1>

FIGS. 30A to 30Cindicate that, in the initial stage of test1, the odor detection amount increased almost in proportion to the outer ring temperature, whereas almost no aldehyde was detected. The result of the test2indicates that an aldehyde concentration was detected when the grease reached a certain temperature or higher.

These results indicate that detection of both the odor amount and the aldehyde concentration enables simple evaluation of the temperature in a bearing. It is difficult to directly measure the temperature in a bearing, and thus this evaluation method is useful. The reason of the difficult measurement includes rolling elements rolling on an orbital plane through a grease and difficulty in making a hole in a bearing member.

The lubricant deterioration detection device10inFIG. 26was used to continuously monitor the deterioration state of a lubricant in a rolling bearing.

As two rolling bearings6, rolling bearings each having an inner diameter of 70 mm, an outer diameter of 110 mm, and a width of 20 mm and including steel balls63were prepared. Each rolling bearing6was lubricated with a grease. The grease used was a commercially available grease containing a barium complex soap (consistency: No. 2) as a thickener and a mixed oil of mineral oil and ester oil (dynamic viscosity at 40° C.: 23 mm2/s) as a base oil.

While an axial load of 200 N was applied to each rolling bearing6, a rotating shaft9was rotated at a rotation speed of 14,000 min−1for 20 hours and then was rotated at a rotation speed of 2,000 min−1for 4 hours. This cycle was repeated to continuously rotate the rotating shaft9. Concurrently with the rotation start of the rotating shaft9, the lubricant deterioration detection device10was driven, and the aldehyde concentration detection by the gas sensor1and the outer ring temperature measurement were continuously performed.

As a result, an abnormal increase of the outer ring temperature was detected at 303 hours after the test start. At this point, the detected aldehyde concentration was about 20 times as high as the normal concentration. At 500 hours after the test start, the lubricant deterioration detection device10was manually stopped. In the rolling bearing6after the test, damages and discoloration probably resulting from seizing up were observed on the orbital plane.

Alternative Embodiment

A lubricant deterioration detection device of an alternative embodiment illustrated inFIG. 31is prepared as follows: the elbow pipe402that connects a portion of the gas inlet pipe401with the suction pump50to the gas inlet portion410in the lubricant deterioration detection device10inFIG. 25is replaced with a flow path switching pipe47, and the flow path switching pipe47is connected to a plurality of gas inlet portions410. Each of the plurality of gas inlet portions410is inserted into a through hole73(82) formed in a corresponding cylinder portion7(or a circular plate portion8A) through a rubber member75(85), and the gap between the gas inlet portion410and the through hole73(82) is sealed.

In the example illustrated inFIG. 31, by switching the flow path switching pipe47, the aldehyde concentrations contained in gases in the plurality of cylinder portions (bearing housings)7can be determined by a single gas sensor1. In other words, lubricant deterioration of rolling bearings fixed in a plurality of cylinder portions (bearing housings)7can be evaluated by a single lubricant deterioration detection device. Hence, as compared with the case in which lubricant deterioration detection devices are separately installed for a plurality of bearing housings, the install space can be reduced, and periodic filter exchange can be performed for a single filter201to simplify the maintenance.

As apparent from the graph inFIG. 28C, the aldehyde concentration determined by the gas sensor1is substantially 0 for a while after the rotation start of the bearing and exceeds 1.0 ppm only after 195 hours. Hence, by setting the lubricant deterioration detection device illustrated inFIG. 31to switch the flow path switching pipe47in such a way as to enable connection to each gas inlet portion410once or more between 195 hours and 206 hours, the lubricant deterioration can be correctly determined. The same threshold can be used for a plurality of bearings used in different conditions, and thus complicated threshold setting can be simplified. An example threshold is 1.0 ppm as described above.

Fourth Aspect

Fourth Embodiment

An embodiment in a fourth aspect of the present invention will now be described, but the invention is not limited to the following embodiment. The following embodiment includes technically preferred limitations for carrying out the invention, but the limitations are not essential requirements of the invention.

As illustrated inFIG. 32andFIG. 33, the lubricant deterioration detection device10of the embodiment includes a gas sensor1, a filter201, gas inlet pipes301,401, and a suction pump50. The gas inlet pipe301connects a gas inlet port of the gas sensor1and a gas outlet port of the filter201. One end of the gas inlet pipe401is a gas inlet portion410that is a connector to the housing described later, and the other end is connected to a gas inlet port of the filter201.

In the example inFIG. 32, the gas inlet pipe401includes three straight pipes and two elbow pipes, extends through an elbow pipe402in the direction perpendicular to the extending direction of the gas inlet portion410, and extends through an elbow pipe403in the same direction as the extending direction of the gas inlet portion410. The suction pump50is connected to a point between the elbow pipes402,403of the gas inlet pipe401. In the example inFIG. 33, the gas inlet pipe401includes two straight pipes and an elbow pipe and extends through an elbow pipe404to a direction perpendicular to the extending direction of the gas inlet portion410. The suction pump50is connected to a point between the elbow pipe404of the gas inlet pipe401and the filter201.

The gas sensor1is a controlled potential electrolysis sensor that detects only aldehydes (carbonyl compounds). The gas sensor1includes a display device that displays a real time aldehyde concentration. As the filter201, a ceramic filter that removes oil mist (oil removal portion) is provided.

The lubricant deterioration detection device10includes a housing that rotatably stores two rolling bearings6. The housing in the example inFIG. 32includes a cylinder portion7and circular plate portions8,8A each having a central hole81, and the housing in the example inFIG. 33includes a cylinder portion7A and two identical circular plate portions8each having a central hole81.

Each of the two rolling bearings6is a sealed deep groove ball bearing including an inner ring61, an outer ring62, balls (rolling elements)63, a retainer64, and shield plates (noncontact seals)65and is lubricated with a lubricant. At the respective axial ends of the cylinder portion7on the inner peripheral surface, grooves71,72are formed for fitting the outer rings62of the two rolling bearings6.

The circular plate portion8A included in the housing in the example inFIG. 32has a through hole82penetrating in the axis direction at a position facing a shield plate65. The cylinder portion7A included in the housing in the example inFIG. 33has a through hole73penetrating in a direction orthogonal to the axis, at the axial center.

The two rolling bearings6are fixed to the cylinder portion7apart from each other in the axis direction by fitting the outer rings62to the corresponding grooves71,72. The respective axial ends of the cylinder portion7are closed by the circular plate portions8,8A in the example inFIG. 32or by the two circular plate portions8in the example inFIG. 33. A rotating shaft9fitted to the inner rings61of the two rolling bearings6penetrates the central holes81, extends outward from the circular plate portions8,8A in the example inFIG. 32or extends outward from the two circular plate portions8in the example inFIG. 33, and is connected to a rotation device not shown in the drawings.

In the example inFIG. 32, the gas inlet portion410of the gas inlet pipe401is inserted through a cylindrical-shaped rubber member85into the through hole82of the circular plate portion8A, and the gap between the gas inlet portion410and the through hole82is sealed by the rubber member85. In the example inFIG. 33, the gas inlet portion410of the gas inlet pipe401is inserted through a cylindrical-shaped rubber member75into the through hole73of the cylinder portion7A, and the gap between the gas inlet portion410and the through hole73is sealed by the rubber member75.

The lubricant deterioration detection device10functions as follows: By activating the suction pump50concurrently with the rotation start of the rolling bearings6, the gas in the housing is sucked. The sucked gas passes through the gas inlet pipe401into the filter201, and the filter201removes oil mist. Subsequently, the gas passes through the gas inlet pipe301into the gas sensor1, then the gas sensor1determines the aldehyde concentration, and the result is displayed.

The aldehyde concentration of a gas sucked into the gas inlet pipe401of the lubricant deterioration detection device10is substantially 0 before deterioration of a lubricant in the rolling bearings6, gradually increases just before seizing up by the lubricant, and then increases sharply. Hence, the deterioration of a lubricant in the rolling bearings6can be identified when the gas sensor1starts to detect increasing aldehyde concentrations.

In the lubricant deterioration detection device10of the embodiment, the gas sensor1is provided outside the housing rotatably storing the rolling bearings6, thus is unlikely to be affected by vibration or heat generated during operation of the rolling bearings6, and is unlikely to cause malfunction or failure. Accordingly, the lubricant deterioration detection device can determine the deterioration state of a lubricant in a rolling bearing with higher accuracy than a lubricant deterioration detection device in which the housing of a gas sensor is directly attached to a rolling bearing.

If a lubricant or components other than the components generated from a lubricant adhere to the gas sensor1, the gas sensor1may malfunction, or the detection accuracy of the gas sensor1may deteriorate. To address this, in the lubricant deterioration detection device10of the embodiment, the gas inlet port of the gas sensor1is not directly connected to the through hole82,73as the gas outlet port of the housing through a gas inlet pipe, but the filter201is provided therebetween. The gas inlet port of the gas sensor1is connected to the gas outlet port of the filter201through the gas inlet pipe301, and the through hole82,73of the housing is connected to the gas inlet port of the filter201through the gas inlet pipe401. As the filter201, an oil mist-removing filter is provided.

The gas sensor1is thus unlikely to be affected by oil mist generated during operation of the rolling bearing6and is unlikely to cause malfunction or failure. Accordingly, the lubricant deterioration detection device10of the embodiment can determine the deterioration state of a lubricant in a rolling bearing with higher accuracy than a lubricant deterioration detection device in which the gas inlet port of a gas sensor is directly connected to the gas outlet port of a housing through a pipe.

In place of the oil mist-removing filter, a wet dust collector or a static oil mist remover may be provided.

Examples of the oil mist-removing filter include a paper filter, a metal filter, a ceramic filter, and a CNP filter. Of these filters, a paper filter is preferably used in terms of easy exchange. As the paper filter, a paper filter having a mesh size of about 200 and capable of collecting oil mist particles having a particle size of 0.3 μm or more is preferably used.

Between the gas sensor1and the gas inlet portion410, a filter that removes smelling components other than aldehydes (smell removal portion) may be provided. Examples of the filter that removes smelling components other than aldehydes (for example, smelling components generated from industrial wastes of factories) include a photocatalytic filter and an activated carbon filter. Specifically preferred is a filter in which an adsorbent and a photocatalytic powder are packed in the space (cavities) between a nonwoven fabric and a film. The adsorbent is preferably activated carbon and silica gel, and the photocatalyst is preferably titanium oxide and zinc oxide.

Alternatively, the difference between a gas having passed through a filter that adsorbs aldehydes, such as a dinitrophenylhydrazine (DNPH) filter, and a gas not having passed can be analyzed to determine aldehydes.

<Verification Test of Lubricant Deterioration Detection by Lubricant Deterioration Detection Device10>

The device illustrated inFIG. 34was used to perform the verification test for examining the lubricant deterioration detection result by the lubricant deterioration detection device10. The device illustrated inFIG. 34is prepared as follows: the elbow pipe402that connects a portion of the gas inlet pipe401with the suction pump50to the gas inlet portion410in the example inFIG. 32is replaced with a branch pipe405, and the opposite side of the branch pipe405to the gas inlet pipe401is connected to one end of a gas inlet pipe104included in a lubricant deterioration detection device100of a comparative example. As the electrode included in the controlled potential electrolysis sensor of the gas sensor1, a platinum electrode was used.

The lubricant deterioration detection device100includes a smell sensor101, a filter102, gas inlet pipes103,104, and a suction pump105. The gas inlet pipe103connects a gas inlet port of the smell sensor101and a gas outlet port of the filter102. The other end of the gas inlet pipe104is connected to a gas inlet port of the filter102. The suction pump105is connected to a portion of the gas inlet pipe104connected to the branch pipe405. The smell sensor101is an indium oxide-based heat ray sintered semiconductor sensor and can determine odor index. As the filter102, the same oil mist-removing filter as the filter201was used.

As two rolling bearings6, rolling bearings each having an inner diameter of 25 mm, an outer diameter of 62 mm, and a width of 17 mm were prepared. Each rolling bearing6was lubricated with a grease. The grease used was a commercially available grease containing a lithium soap (consistency: No. 2) as a thickener and a mineral oil (dynamic viscosity at 40° C.: 100 mm2/s) as a base oil.

The outer ring62of each rolling bearing6was fitted to the corresponding groove71,72on the cylinder portion7, a rotating shaft9of a tester is fitted to the inside of the inner ring61of each rolling bearing6, and the gas inlet portion410of the lubricant deterioration detection devices10,100was attached to the circular plate portion8A, giving the state illustrated inFIG. 34. The through hole82in the circular plate portion8A has a diameter of 6.5 mm, and the gas inlet pipe401has an outer diameter of 6 mm and an inner diameter of 4 mm. The gap between the through hole82and the gas inlet pipe401is sealed by a rubber member85.

While a radial load of 98 N and an axial load of 1,470 N were applied to each rolling bearing6, the rotating shaft9was continuously rotated at a rotation speed of 10,000 min−1. Concurrently with the rotation start of the rotating shaft9, the lubricant deterioration detection devices10,100were driven, and the aldehyde concentration detection by the gas sensor1, the odor index measurement by the smell sensor101, and the outer ring temperature measurement were continuously performed. The results are illustrated as the graphs inFIGS. 35A to 35C. The rotation of the rotating shaft9and the driving of the lubricant deterioration detection devices10,100were so controlled as to be stopped when an abnormal increase of the outer ring temperature was detected.

At 208 hours after the test start, an abnormal increase of the outer ring temperature was detected, and the rotation of the rotating shaft9and the driving of the lubricant deterioration detection devices10,100were stopped.

The graphs inFIGS. 35A to 35Creveal the following findings.

FIG. 35Ais a graph illustrating the relation between elapsed time and outer ring temperature. The outer ring temperature increased after the test start, then was almost constant from about 10 hours, and exceeded 125° C. at 208 hours.

FIG. 35Bis a graph illustrating the relation between elapsed time and odor index detected by the smell sensor101. The odor index increased at substantially the same rate as the increase rate of the outer ring temperature and then was almost constant at around 5.0 when the outer ring temperature became almost constant. Subsequently, the odor index slightly increased at around 165 hours, then was constant at about 6.0, and started to increase from 185 hours.

FIG. 35Cis a graph illustrating the relation between elapsed time and aldehyde concentration determined by the gas sensor1. The aldehyde concentration was almost 0 immediately after the test start until 180 hours, then gradually increased from 180 hours, and sharply increased from 206 hours that was immediately before the detection of the abnormal increase of the outer ring temperature.

The test results reveal the following findings.

The lubricant deterioration detection devices10,100can identify lubricant deterioration in advance.

With the lubricant deterioration detection device10of the embodiment, the aldehyde concentration was substantially 0 immediately after the test start until lubricant deterioration was caused in the rolling bearings6, gradually increased just before seizing up by the lubricant, and then increased sharply. Hence, the deterioration of a lubricant in the rolling bearings6can be identified when the gas sensor1starts to detect increasing aldehyde concentrations.

With the lubricant deterioration detection device100of the comparative example, the odor index increased immediately after the test start, then was almost constant before lubricant deterioration was caused in the rolling bearings6, and gradually increased just before seizing up by the lubricant. Hence, by setting the threshold of the odor index at, for example, 7.0, lubricant deterioration in the rolling bearings6can be identified when the odor index reaches the threshold. In other words, the lubricant deterioration detection device100of the comparative example can previously detect lubricant deterioration. In other words, the lubricant deterioration detection device100of the comparative example needs previous threshold setting depending on conditions of use. In addition, the odor index varies with conditions of use of a rolling bearing, and thus an apparatus including a plurality of rolling bearings needs threshold setting for the respective bearings, which is a complicated process.

As described above, the lubricant deterioration detection device100of the comparative example needs previous threshold setting, and thus a setting error of the threshold may lead to incorrect determination of lubricant deterioration. In contrast, the lubricant deterioration detection device10of the embodiment eliminates the necessity of threshold setting depending on conditions of use. An example of the threshold is 1.0 ppm from the graph inFIG. 35C. Hence, the lubricant deterioration detection device10of the embodiment can determine the deterioration state of a lubricant with higher accuracy than the lubricant deterioration detection device100of the comparative example.

Alternative Embodiment

A lubricant deterioration detection device of an alternative embodiment illustrated inFIG. 36is prepared as follows: the elbow pipe402that connects a portion of the gas inlet pipe401with the suction pump50to the gas inlet portion410in the lubricant deterioration detection device10inFIG. 32is replaced with a flow path switching pipe47, and the flow path switching pipe47is connected to a plurality of gas inlet portions410. Each of the plurality of gas inlet portions410is inserted into a through hole73(82) formed in a corresponding housing (a cylinder portion7or a circular plate portion8A) through a rubber member75(85), and the gap between the gas inlet portion410and the through hole73(82) is sealed.

In the example illustrated inFIG. 36, by switching the flow path switching pipe47, the aldehyde concentrations contained in gases in the plurality of housings can be determined by a single gas sensor1. In other words, lubricant deterioration of rolling bearings rotatably stored in a plurality of housings can be evaluated by a single lubricant deterioration detection device. Hence, as compared with the case in which lubricant deterioration detection devices are separately installed for a plurality of housings, the install space can be reduced, and periodic filter exchange can be performed for a single filter201to simplify the maintenance.

As apparent from the graph inFIG. 35C, the aldehyde concentration determined by the gas sensor1is substantially 0 for a while after the rotation start of the bearing and exceeds 1.0 ppm only after 195 hours. Hence, by setting the lubricant deterioration detection device illustrated inFIG. 36to switch the flow path switching pipe47in such a way as to enable connection to each gas inlet portion410once or more between 195 hours and 206 hours, the lubricant deterioration can be correctly determined. The same threshold can be used for a plurality of bearings used in different conditions, and thus complicated threshold setting can be simplified. An example threshold is 1.0 ppm as described above.

REFERENCE SIGNS LIST