Rolling bearing device

A rolling bearing device includes a bearing portion and an oil supply unit provided adjacent, in the axial direction, to an annular space between an inner ring and an outer ring of the bearing portion to supply lubricating oil to the annular space. The oil supply unit includes an oil chamber that accommodates lubricating oil, a nozzle that discharges lubricating oil in the oil chamber, a pump body that applies a discharge force for causing lubricating oil in the oil chamber to fly from the nozzle toward the annular space, and a detection portion that detects gathering of lubricating oil at a discharge port of the nozzle. The detection portion includes a pair of electrodes disposed with the discharge port of the nozzle interposed therebetween, and a measurement portion that measures the capacitance of the pair of electrodes.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2016-232224 filed on Nov. 30, 2016 including the specification, drawings and abstract, is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a rolling bearing device that includes an oil supply unit.

2. Description of the Related Art

In recent years, various types of machine tools are requested to increase the speed of a main spindle in order to improve the processing efficiency and the production efficiency. When the main spindle is rotated at a high speed, the lubricating property of a bearing portion that supports the main spindle is particularly important. Therefore, there is proposed a rolling bearing device that includes an oil supply unit configured to supply lubricating oil and provided adjacent to a bearing portion in the axial direction (see Japanese Patent Application Publication No. 2004-108388 (JP 2004-108388 A)).

The oil supply unit described in JP 2004-108388 A includes a pump that discharges lubricating oil in an oil chamber from a nozzle and that supplies the lubricating oil to an annular space between an inner ring and an outer ring. In order to efficiently supply oil using such an oil supply unit, it is requested to supply a minute amount of lubricating oil that is necessary to lubricate the bearing portion at predetermined oil supply timings. To this end, it is conceivable to form the nozzle so as to have a very small inside diameter of several micrometers to several tens of micrometers, and to supply lubricating oil by causing a minute amount of lubricating oil to fly from the nozzle by actuating the pump.

In this case, however, a part of the lubricating oil which is discharged from the nozzle flies as oil droplets, but the remaining lubricating oil is occasionally gathered in a drop-like form around a discharge port of the nozzle because of the surface tension of the lubricating oil. The lubricating oil which has been gathered may block the discharge port to cause clogging, and oil may not be supplied appropriately.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a rolling bearing device that includes an oil supply unit that can detect gathering of lubricating oil at a discharge port of a nozzle due to clogging etc.

An aspect of the present invention provides a rolling bearing device including: a bearing portion that has an inner ring, an outer ring, and a plurality of rolling elements interposed between the inner ring and the outer ring; and an oil supply unit provided adjacent, in an axial direction, to an annular space between the inner ring and the outer ring to supply lubricating oil to the annular space, in which: the oil supply unit includes an oil chamber that accommodates lubricating oil, a nozzle that discharges lubricating oil in the oil chamber, a pump body that applies a discharge force for causing lubricating oil in the oil chamber to fly from the nozzle toward the annular space, and a detection portion that detects gathering of oil at a discharge port of the nozzle; and the detection portion includes a pair of electrodes disposed with the discharge port of the nozzle interposed therebetween, and a measurement portion that measures a capacitance of the pair of electrodes.

DETAILED DESCRIPTION OF EMBODIMENTS

A rolling bearing device according to an embodiment of the present invention will be described below.FIG. 1is a sectional view illustrating a rolling bearing device according to an embodiment. A rolling bearing device10rotatably supports a main spindle (shaft7) of a main spindle device of a machine tool, and is housed in a housing8of the main spindle device. InFIG. 1, the shaft7and the housing8are indicated by the long dashed double-short dashed lines. In the following description, the direction which is parallel to a center line C of the rolling bearing device10is referred to as an “axial direction”, and the direction which is orthogonal to the axial direction is referred to as a “radial direction”. The rolling bearing device10is also applicable to devices other than machine tools.

The rolling bearing device10includes a bearing portion20and an oil supply unit40. The bearing portion20has an inner ring21, an outer ring22, a plurality of balls (rolling elements)23, and a cage24that holds the plurality of balls23, and constitutes a ball bearing (rolling bearing). The rolling bearing device10further includes an inner ring spacer17and an outer ring spacer18in a cylindrical shape.

In the embodiment, the outer ring22, the outer ring spacer18, and the oil supply unit40are attached to the bearing housing8so as not to be rotatable. The inner ring21and the inner ring spacer17are rotatable together with the shaft7. Thus, the outer ring22serves as a stationary ring that is not rotatable, and the inner ring21serves as a rotary ring that is rotatable together with the shaft7.

The inner ring21is a cylindrical member that is externally fitted with the shaft7. A raceway (hereinafter referred to as an “inner ring raceway25”) is formed on the outer periphery of the inner ring21. In the embodiment, the inner ring21and the inner ring spacer17are separate from each other. However, the inner ring21and the inner ring spacer17may be integral (inseparably integral) with each other. The outer ring22is a cylindrical member fixed to the inner peripheral surface of the bearing housing8. A raceway (hereinafter referred to as an “outer ring raceway26”) is formed on the inner periphery of the outer ring22. In the embodiment, the outer ring22and the outer ring spacer18are separate from each other. However, the outer ring22and the outer ring spacer18may be integral (inseparably integral) with each other.

The balls23and the cage24are provided in an annular space11formed between the inner ring21and the outer ring22. The balls23are interposed between the inner ring21and the outer ring22, and rolled on the inner ring raceway25and the outer ring raceway26.

The cage24has an annular shape as a whole, and has an annular portion28aon one side, in the axial direction, of the balls23, an annular portion28bon the other side, in the axial direction, of the balls23, and a plurality of cage bars29that couple the annular portions28aand28bto each other. Spaces between the annular portions28aand28band between the cage bars29and29which are adjacent to each other in the circumferential direction serve as pockets27. One ball23is housed in each of the pockets27. With this configuration, the cage24can hold the plurality of balls23at intervals in the circumferential direction.

The annular portion28aon one side (side of the oil supply unit40), in the axial direction, of the cage24can be brought into slide contact with a shoulder portion30of the outer ring22. Consequently, the cage24is positioned in the radial direction by the outer ring22. That is, the cage24of the bearing portion20is guided by the outer ring (guided by the bearing ring). The cage24is made of a resin (e.g. a phenol resin), for example. The inner ring21and the outer ring22are made of steel such as bearing steel. The balls23may be made of steel such as bearing steel, or may be made of a ceramics.

FIG. 2is a cross-sectional view of the oil supply unit40as seen in the axial direction. The oil supply unit40is formed in a circular ring shape as a whole. The oil supply unit40includes a tank42and a pump43. The tank42and the pump43are provided in an annular body portion41of the oil supply unit40. The oil supply unit40includes a control portion44and a power source portion45, and further includes various sensors (not illustrated).

The body portion41is attached to the inner peripheral side of the outer ring spacer18, and has a function as a frame that holds the pump43etc. The body portion41is a circular ring member, and is formed with internal spaces. The pump43, the control portion44, and the power source portion45are provided in the spaces. One of the spaces serves as the tank42. Consequently, the oil supply unit40which includes the body portion41, the tank42, the pump43, the control portion44, the power source portion45, etc. is constituted integrally.

InFIG. 2, the tank42stores lubricating oil (oil), and is connected to the pump43through piping46in order to cause the lubricating oil to flow to the pump43. A holding material (porous member) that holds lubricating oil may be provided in the tank42. Some or all of the tank42, the control portion44, and the power source portion45may be provided outside the rolling bearing device10(housing8). In this case, such components are connected to the pump43etc. through piping and a communication line.

As illustrated inFIG. 1, the pump43includes a pump case48and a pump body51. The pump body51is provided in the internal space of the pump case48. The pump body51is constituted of a micro pump of a diaphragm type, and includes a piezoelectric element43aand a diaphragm47. The diaphragm47and a wall portion of the pump case48form an oil chamber43b. Lubricating oil from the tank42flows into the oil chamber43bto be stored. A nozzle50in the shape of a hole that penetrates a wall portion49of the pump case48on the bearing portion20side is formed in the wall portion49along the axial direction. The nozzle50communicates between the oil chamber43band the outside of the pump case48. The inside diameter of the nozzle50is ten micrometers or so to several tens of micrometers, e.g. 25 μm.

The pump body51drives the piezoelectric element43ato reciprocally deform the diaphragm47to vary the capacity of the oil chamber43b. When the capacity of the oil chamber43bis decreased, a compression force acts on lubricating oil in the oil chamber43b. With the compression force turned into a discharge force, the lubricating oil flies from the nozzle50toward the annular space11of the bearing portion20as a minute amount of oil droplets P to be supplied to the annular space11(seeFIG. 1). In other words, lubricating oil is discharged from the nozzle50as the oil droplets P at an initial velocity.

The amount of lubricating oil discharged from the oil chamber43bin one operation of the piezoelectric element43ais a minute amount (e.g. 50 nL). Therefore, the piezoelectric element43aof the pump body51is caused to operate a plurality of times for one oil supply operation. That is, the piezoelectric element43ais caused to pulse for one oil supply operation. Each time lubricating oil is discharged from the oil chamber43b, the oil chamber43bis automatically replenished with lubricating oil from the tank42.

The power source portion45(seeFIG. 2) supplies power for the pump43to operate. The control portion44can control the timing for the pump43to operate. The power source portion45may be used to supply power to a detection portion60to be described next. The control portion44may be used to control the detection portion60.

The oil supply unit40further includes the detection portion60. The detection portion60detects gathering (accumulation in a drop-like form) of lubricating oil around a discharge port50a. For example, when lubricating oil is discharged from the discharge port50aof the nozzle50by the pump43, a part of the lubricating oil is caused to fly as the oil droplets P. However, the remainder occasionally adheres to the vicinity of the discharge port50a, because of the surface tension, to be gathered gradually. The lubricating oil which has been gathered acts to block the discharge port50a, which obstructs flight of lubricating oil toward the bearing portion20. That is, the discharge port50ais clogged. Therefore, lubricating oil is gathered around the discharge port50amore easily, which makes it difficult to supply oil with lubricating oil unable to fly. That is, a discharge abnormality is caused when lubricating oil is gathered at the discharge port50a. The detection portion60detects a discharge abnormality by detecting gathering of lubricating oil at the discharge port50a.

FIG. 3is a sectional view illustrating the vicinity of the discharge port50aof the nozzle50of the oil supply unit40as enlarged. The right-left direction inFIG. 3indicates the circumferential direction of the bearing portion20. The arrow X indicates the direction of a flow of air generated along with rotation of the inner ring21.

The detection portion60includes a pair of electrodes61and62and a capacitance measurement portion63. The pair of electrodes61and62are provided in the wall portion49of the pump case48on the bearing portion20side. The pair of electrodes61and62are disposed with a clearance from each other in the circumferential direction with the discharge port50aof the nozzle50interposed therebetween. A clearance w1between the pair of electrodes61and62is several millimeters, e.g. two millimeters, and is larger than an inside diameter d of the nozzle50.

The pair of electrodes61and62are disposed so as to be flush with an outer surface49aof the wall portion49of the pump case48in which the discharge port50aof the nozzle50opens. One of the electrodes,61, positioned on the upstream side in the air flow direction X is disposed closer to the discharge port50aof the nozzle50than the other electrode62positioned on the downstream side in the same direction. Specifically, when the distance from a center O of the nozzle50to the one electrode61is defined as w11and the distance from the center O to the other electrode62is defined as w12, the relationship w11<w12is met.

The capacitance measurement portion63measures the capacitance of the pair of electrodes61and62. The capacitance of the pair of electrodes61and62is varied as the dielectric constant between the electrodes61and62is varied. The detection portion60detects variations in the capacitance of the pair of electrodes61and62, that is, variations in the dielectric constant therebetween, by the capacitance measurement portion63measuring the capacitance.

When the nozzle50of the pump is clogged etc. and lubricating oil L is gathered (accumulated in a drop-like form) at the discharge port50aas illustrated inFIGS. 4A and 4B, the dielectric constant between the pair of electrodes61and62is varied. The dielectric constant is also varied between the case where the amount of the lubricating oil L which is gathered at the discharge port50ais small (seeFIG. 4A) and the case where the amount of the lubricating oil L which is gathered at the discharge port50ais large (seeFIG. 4B). In particular, the lubricating oil L can reach the pair of electrodes61and62to extend between the electrodes61and62(so that the electrodes61and62are connected to each other through the lubricating oil L) as illustrated inFIG. 4B. Therefore, the dielectric constant is varied conspicuously compared to the case where there is only air between the pair of electrodes61and62as illustrated inFIG. 3.

Thus, the detection portion60can detect the lubricating oil L which is gathered at the discharge port50aof the nozzle50from variations in the capacitance which is measured by the capacitance measurement portion63. It is possible to detect occurrence of a discharge abnormality due to clogging of the nozzle50etc. on the basis of the detection results. A determination as to whether or not there occurs a discharge abnormality can be made by the control portion44, for example, on the basis of a comparison between the capacitance which is measured by the capacitance measurement portion63and a predetermined threshold.

In order to detect gathering of the lubricating oil L at the discharge port50aof the nozzle50, a certain amount of the lubricating oil L is necessary. Therefore, the clearance w1between the pair of electrodes61and62is determined to be sufficiently larger than the inside diameter d of the nozzle50which is very small. The cause of gathering of the lubricating oil L at the discharge port50aof the nozzle50is considered to include a fact that the discharge force is weakened by an increase in the flow resistance due to residence of foreign matter in the nozzle50or adhesion of foreign matter to the nozzle50, a reduction in the pump performance, or the like. However, such a factor is not limiting.

One of the electrodes61and62disposed on the upstream side in the air flow direction X is disposed closer to the discharge port50aof the nozzle50than the other disposed on the downstream side. The lubricating oil L which is gathered at the discharge port50aof the nozzle50is easily spread in the direction of the arrow X because of the air flow, but is not easily spread in the opposite direction. Therefore, the lubricating oil L can be caused to easily reach the one electrode61, which is positioned on the upstream side in the flow direction X, by providing the electrode61closer to the discharge port50a, and the lubricating oil L can also be caused to easily reach the other electrode62, which is positioned on the downstream side in the flow direction X, by the flow of air. Thus, the lubricating oil L can reach both the electrodes61and62early to extend between the electrodes61and62. Thus, it is possible to detect gathering of lubricating oil L at the discharge port50aof the nozzle50earlier.

The pair of electrodes61and62are disposed so as to be flush with a surface in which the discharge port50aof the nozzle50is formed, that is, the outer surface49aof the wall portion49of the pump case48. Consequently, the flow of air is not hindered by the pair of electrodes61and62, and the flow of air exerts a large effect on the lubricating oil L which is gathered at the discharge port50aof the nozzle50. Therefore, the lubricating oil L also reaches the other electrode62, which is farther from the nozzle50, early.

The pair of electrodes61and62in the oil supply unit40according to modifications will be described below. In a modification illustrated inFIG. 5, the pair of electrodes61and62are disposed at an equal distance from the discharge port50aof the nozzle50(w11=w12). The modification is otherwise the same in configuration as the embodiment, and achieves generally the same function and effect as those of the embodiment. It should be noted, however, that the lubricating oil L which is gathered at the discharge port50aof the nozzle50is not easily spread toward the upstream side in the air flow direction X. Therefore, it takes time before the lubricating oil L reaches the electrode61on the upstream side in this modification. Therefore, it takes time before gathering of the lubricating oil L can be clearly detected with the lubricating oil L extending between the electrodes61and62, compared to the embodiment. Thus, the embodiment is more advantageous in this respect.

In a modification illustrated inFIG. 6, the pair of electrodes61and62are provided so as to project toward the bearing portion20with respect to a surface in which the discharge port50aof the nozzle50is formed (the outer surface49aof the wall portion49). The pair of electrodes61and62are disposed at an equal distance from the discharge port50aof the nozzle50. The modification is otherwise the same in configuration as the embodiment. In this modification, the electrodes61and62project with respect to the outer surface49aof the wall portion49. Therefore, there is less effect of the flow of air, and lubricating oil L can reach both electrodes61and62generally as easily even if the electrodes61and62are provided with an equal clearance from the nozzle50.

In this modification, the pair of electrodes61and62project toward the bearing portion20, and therefore it is difficult to provide the nozzle50close to the bearing portion20. Therefore, lubricating oil L flies over a long distance from the nozzle50toward the annular space11. In the embodiment, in this respect, the discharge port50aof the nozzle50and the electrodes61and62are disposed so as to be flush with each other. Consequently, the nozzle50can be provided as close as possible to the bearing portion20, and lubricating oil L flies over a short distance. Therefore, the discharge force of the pump body51can advantageously be made as small as possible.

The embodiment and the modifications are exemplary in all respects, and not limiting. That is, the rolling bearing device according to the present invention is not limited to the illustrated embodiment, and may be in other embodiments without departing from the scope of the present invention. For example, in the embodiment, the bearing portion20is an angular contact ball bearing. However, the type of the bearing is not limited thereto, and may be a deep-groove ball bearing, or may be a tapered rolling bearing or a cylindrical roller bearing. The rolling bearing device10may be used for usage other than a main spindle of a machine tool. In the bearing portion20, the inner ring21may be a stationary ring, and the outer ring22may be a rotary ring.

With the present invention, it is possible to detect gathering of lubricating oil at a discharge port of a nozzle due to clogging etc.