Rolling bearing device

Abstract

The objective is to create a rolling bearing device that can efficiently discharge lubricating oil with a simple structure, allowing for miniaturization and simplification of the lubrication mechanism, while also enabling efficient and stable discharge of lubricating oil in accordance with the rotational speed of the rolling bearing. [Solution] The lubricating oil supply device B includes a tank 5 that holds lubricating oil O, and a discharger 6 such as a pump equipped with a discharge mechanism that discharges the lubricating oil supplied from the tank 5 into the bearing space between the inner ring 1 and the outer ring 2. By opening a ventilation hole 10 in the wall of the tank 5 that connects the inside of the tank 5 to the bearing space, the pressure of the airflow that is guided into the tank 5 via the ventilation hole 10 from the swirling airflow generated in the bearing space is used to supply the lubricating oil O from the oil supply passage 9 to the discharger 6.

Description

Technical Field

[0001] The present invention relates to a rolling bearing device provided with a lubricating oil supply device for supplying lubricating oil to a rolling bearing.

Background Art

[0002] Generally, as a lubricating means for a rolling bearing, air-oil lubrication, oil mist lubrication, etc. are adopted for a rolling bearing that holds a main shaft of a machine tool such as a spindle for a machine tool that requires high-speed rotation (improvement of lubrication durability) instead of grease lubrication.

[0003] Air-oil lubrication and oil mist lubrication are provided with injection ports and oil passages for supplying lubricating oil into the bearing adjacent to the rolling bearing, and it is necessary to attach a supply device for compressed air and oil to the machine body to transfer the oil. These injection devices cause the machine body to become larger and increase the initial cost and operating cost.

[0004] Therefore, as a means for supplying lubricating oil to a rolling bearing that is small and does not require an injection device, a bearing device incorporating a lubricating oil supply unit is known. The lubricating oil supply unit includes a holding unit that holds lubricating oil, a supply unit that supplies lubricating oil from the holding unit, and a power generation unit that generates electric power, and operates a micropump with the electric power from the power generation unit to supply lubricating oil into the rolling bearing (Patent Document 1).

[0005] Also, as a diaphragm-type pump in a lubricating oil supply unit used for a rolling bearing device, a pump using a piezoelectric element in a drive unit is known, and it is known that felt or sponge is provided in a tank that holds lubricating oil to hold the lubricating oil (Patent Document 2).

[0006] Also, in order to facilitate replenishment of lubricating oil, it is known that a lubricating oil tank is constituted by a flexible bag body capable of filling lubricating oil (Patent Document 3).

[0007] Furthermore, in high-speed rotating rolling bearings, a swirling airflow (swirling flow) is generated in the annular space between the outer and inner rings, and the oil droplets of the injected lubricating oil are easily repelled by the swirling flow. Therefore, there are known techniques to provide a windbreak of the required shape and to generate airflow in the required direction, so that as many oil droplets of lubricating oil floating around the nozzle that injects the lubricating oil as possible reach targets such as rolling elements and raceways (Patent Documents 4 and 5). [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Patent No. 6495700 [Patent Document 2] Patent No. 6446887 [Patent Document 3] Patent No. 6054095 [Patent Document 4] Patent No. 6750296 [Patent Document 5] Patent No. 6677070 [Overview of the project] [Problems that the invention aims to solve]

[0009] However, with the conventional technology described above, it is not easy to deliver a sufficient amount of lubricating oil droplets to the target. In order to efficiently deliver the oil droplets to targets such as rolling elements and tracks, it is necessary to increase the output of the oil supply mechanism, such as the pump. This requires larger pumps and more complex discharge mechanisms to improve the functionality of the discharge mechanism.

[0010] Furthermore, incorporating complex mechanisms and structures into the pump unit would require the entire lubrication unit and machinery to become larger, which would lead to higher manufacturing costs.

[0011] Therefore, the objective of this invention is to solve the above-mentioned problems, to provide a rolling bearing device that can discharge lubricating oil as efficiently as possible with a simple structure for the lubricating oil supply device attached to the rolling bearing, to accommodate miniaturization and simplification of the lubrication mechanism, and moreover, to provide a rolling bearing device that can efficiently and stably discharge lubricating oil in accordance with the rotational speed of the rolling bearing. [Means for solving the problem]

[0012] To solve the above problems, this invention provides a rolling bearing comprising a rolling bearing with a plurality of rolling elements interposed between an inner ring and an outer ring, and a lubricating oil supply device attached to the rolling bearing for supplying lubricating oil. The lubricating oil supply device comprises a tank for holding lubricating oil and a discharger equipped with a discharge mechanism for discharging the lubricating oil supplied from the tank into the bearing space between the inner ring and the outer ring of the rolling bearing. The rolling bearing device contains lubricating oil in the tank and has a ventilation hole that opens in the wall of the tank to connect the inside of the tank with the bearing space.

[0013] As described above, the rolling bearing device of this invention has ventilation holes opening in the wall of the tank that connect the inside of the tank and the bearing space. This allows the swirling flow generated by the rotation of the rolling bearing, which causes the air in the bearing space between the outer ring and the inner ring to swirl, to be taken into the tank through the ventilation holes.

[0014] As the air pressure inside the tank increases in response to the air pressure of the swirling flow taken in, the oil pressure of the lubricating oil contained in the tank is increased, and the pressurized lubricating oil is supplied to the discharge mechanism.

[0015] Furthermore, in order to allow as much of the swirling airflow generated in the bearing space by the rotation of the rolling bearing as possible to flow into the tank, it is preferable to provide an enclosure or duct at the opening edge of the ventilation hole opening into the wall surface to guide the airflow swirling around the axis in the bearing space from the opening into the tank.

[0016] Further, the discharge machine may be a rolling bearing device including a discharge mechanism driven by an actuator and having a power source unit and a control unit of the actuator. The discharge machine may employ a pump in a well-known form, or may be a valve (such as a pressure release valve) adjusted to open the discharge port at a predetermined pressure or higher, or may be a discharge machine equipped with both such a pump and a valve.

[0017] The discharge machine is driven by an actuator such as a piston, a gear, or a diaphragm by a power source unit and its control unit. By driving these, regardless of the rotational speed of the rolling bearing, a necessary minimum amount of lubricating oil can be stably and constantly discharged from the discharge port into the bearing space.

[0018] The amount of lubricating oil supplied to the discharge machine changes according to the pressure received by the lubricating oil due to an air flow (swirling flow) corresponding to the rotational speed of the rolling bearing. Thus, the higher the rotational speed, the more lubricating oil is supplied, and at low rotational speeds, it is adjusted to be supplied in a small amount or not at all. In this way, an appropriate amount of lubricating oil corresponding to the rotational speed of the bearing is supplied to the bearing space by a very simple adjustment mechanism.

[0019] It is also possible to accommodate a lubricating oil holding member in the tank that changes in volume as the air pressure in the tank changes. This can divide the area in the tank where lubricating oil exists from the area with an air pocket, and by opening a vent hole in the latter area, the air pressure of the air flow can be efficiently applied to the lubricating oil.

[0020] As the lubricating oil holding member, it is also preferable to employ a porous body or a bag-shaped container capable of holding lubricating oil. Such a lubricating oil holding member changes in volume as the air pressure changes, that is, it contracts when pressurized, and the contracted volume of lubricating oil is supplied to the discharge mechanism.

[0021] When the lubricant holding member is a flexible porous body having lubricant permeability and elasticity, the lubricant in the tank is held in a state of being infiltrated into the pores of the porous body in advance by capillary action, and the amount of lubricant having a volume contracted by atmospheric pressure against the elasticity of the porous body is supplied from the tank to the discharge machine.

[0022] Also, when the lubricant holding member is a bag-shaped container capable of accommodating lubricant, as the bag-shaped container whose volume changes with the change in atmospheric pressure and which is the lubricant holding member shrinks, the amount of lubricant having a reduced volume flows out from the bag-shaped container into the tank and is supplied to the discharge mechanism.

[0023] Further, in order to be able to adjust the discharge amount of the lubricant by the discharge machine according to the usage conditions, purpose or application of the rolling bearing device, it is preferable to provide a flow rate adjusting valve in one or more selected from the oil supply passage for supplying lubricant from the tank to the discharge machine and the discharge machine.

[0024] By providing a valve for adjusting the flow rate in the vent hole or the oil supply passage for the lubricant from the tank to the discharge mechanism and adjusting the flow rate of the lubricant, the supply amount of the lubricant to the discharge machine can be adjusted.

[0025] In this way, by adjusting the amount of intake of the swirling flow into the tank during the high-speed rotation of the rolling bearing, the excessive supply of lubricant can be controlled. Also, during the low-speed rotation of the rolling bearing, conversely, the flow rate adjusting valve can be loosened to adjust so as to supply as much oil as possible.

Advantages of the Invention

[0026] According to this invention, by providing a vent hole that connects the inside of the tank of the rolling bearing device and the bearing space and opening it on the wall surface of the tank, while making the lubricant supply device attached to the rolling bearing have a simple structure, an appropriate amount of lubricant can be efficiently discharged, enabling miniaturization and simplification of the structure of the lubricant supply device, and moreover, there is an advantage that an appropriate amount of lubricant can be stably discharged corresponding to the rotational speed of the rolling bearing.

Brief Description of the Drawings

[0027] [Figure 1] Axial cross-sectional view of the main part of the rolling bearing device of the first embodiment [Figure 2] Cross-sectional view along line II-II in Figure 1 [Figure 3] Block diagram illustrating the function of the lubricating oil supply device of the first embodiment. [Figure 4] Radial cross-sectional view of the main part of the rolling bearing device of the second embodiment [Figure 5] A perspective view showing a cutaway of the main part of the rolling bearing device of the third embodiment. [Figure 6] A perspective view showing the ventilation holes of the tank of the rolling bearing device of the fourth embodiment. [Figure 7] A perspective view showing the ventilation holes of the tank of the rolling bearing device of the fifth embodiment. [Figure 8] A perspective view showing the ventilation holes of the tank of the rolling bearing device of the sixth embodiment. [Figure 9] A schematic diagram illustrating the operation of a flow control valve. [Modes for carrying out the invention]

[0028] Embodiments of this invention will be described below with reference to the attached drawings. As shown in Figure 1-3, the first embodiment is a rolling bearing device applicable to mechanical devices used in high-speed rotation such as machine tool spindles, and consists of an angular contact ball bearing A, which has a cage 4 that holds the rolling elements 3, which are multiple balls, between an inner ring 1 and an outer ring 2, so that they can rotate freely at regular intervals in the circumferential direction while being guided by the outer ring 2, and a lubricating oil supply device B that is attached in close contact with the axial end face of the outer ring 2 and supplies lubricating oil O.

[0029] As shown in Figures 1 and 2, the lubricating oil supply device B has its required components incorporated between the outer ring spacer B1 and the inner ring spacer B2 and is fixed to the outer ring spacer B1. The lubrication oil supply device B includes a discharger (pump) 6 equipped with a discharge mechanism that discharges lubricating oil O supplied from the tank 5 into the bearing space between the inner ring 1 and the outer ring 2. The casing 8 of the discharger (pump) 6, which is equipped with a discharge nozzle 7, is in communication with the tank 5 via an oil supply passage 9. The oil supply passage 9 may be molded integrally with the casing 8 or the tank 5.

[0030] As shown in Figure 2, a ventilation hole 10 is opened in the wall of the end portion of the semicircular ring-shaped, cylindrical tank 5 that is away from the discharger 6, connecting the inside of the tank 5 to the bearing space. Inside the tank 5, which contains lubricating oil, is a lubricating oil holding member 12a made of a flexible porous material that changes volume in accordance with changes in air pressure inside the tank 5. This lubricating oil holding member (porous material) 12a holds a sufficient amount of lubricating oil O so that it seeps out due to its volume change.

[0031] Such ventilation holes 10 only need to be one or more, and the shape and number of holes may vary. For example, multiple elongated holes, such as slits, may be arranged in parallel, or each elongated hole may be partially covered by an overhang to guide airflow from a predetermined direction.

[0032] As shown in Figure 3, the discharger 6 leading to the tank 5 is equipped with a discharge mechanism such as a diaphragm or a positive displacement pump with a reciprocating piston and cylinder, and further includes an actuator 11 such as a piezoelectric element that drives the discharge mechanism, a power supply 13 which is its power source, and a microcontroller 14 which is its control unit.

[0033] The power supply mechanism of the power source unit 13 is arbitrary and may utilize, for example, a storage battery, a power supply connected to the outside of the lubricating oil supply device B, or electromotive force obtained by incorporating a power generation mechanism into the lubricating oil supply device B.

[0034] Furthermore, the power source unit 13, which uses a power supply, is connected to the control unit 14 and the actuator 11 so as to be able to supply power to them. The microcontroller of the control unit 14 is connected so as to be able to send commands to the actuator 11.

[0035] In the operating state of the rolling bearing device of the first embodiment configured in this way, when the rolling bearing A is rotating, the airflow generated in the bearing space (for example, the swirling flow shown by the arrow in Figure 2) flows into the tank 5 through the vent hole 10 formed in the part of the tank 5 that has an air reservoir on the end of the lubricating oil supply flow direction. Because the rolling bearing A is equipped with a cage 4 that holds the rolling elements 3, the airflow (swirling flow) generated by the rotation of the rolling bearing A is generated more sufficiently.

[0036] The rotational conditions of the rolling bearing device assumed in the embodiment can range from low speed to high speed, but for example, in the rotational state at high speed, the dn value is 70 × 10 4 Preferably 110 × 10 4 The above can be assumed. The upper limit of the dn value is not particularly limited, but for example, 200 × 10 4 Preferably 180 × 10 4 That is the case.

[0037] When the air pressure inside the tank 5 increases due to the incoming air, the lubricating oil retaining member 12a housed in the tank 5 contracts due to the pressure from the airflow, and the lubricating oil O corresponding to the contracted volume is supplied from the oil supply passage 9 to the discharger 6, which consists of a pump. If the lubricating oil retaining member 12a is omitted and only the lubricating oil O is housed in the tank, the lubricating oil O is directly supplied to the discharger 6 under pressure from the airflow.

[0038] When the actuator 11 operates a discharger 6, such as a positive displacement pump, based on a command from the control unit 14, pressurized lubricating oil O is supplied to the discharger 6, assisting the discharge operation and allowing the discharge mechanism to be operated with less energy.

[0039] In this manner, the lubricating oil, such as lubricating oil, discharged from the discharger 6 is discharged into the bearing space from the tip of the discharge nozzle 7, which extends into the bearing space.

[0040] When the rolling bearing A is rotating its inner ring, liquid lubricating oil O is discharged from the tip of the discharge nozzle 7, moves along the raceway surface of the inner ring 1 (Figure 1) by centrifugal force from the outer circumferential surface of the inner ring 1, and lubricates the raceway surface of the outer ring 2 via the surface of the rolling element 3.

[0041] As in the first embodiment described above, when the outer ring 2 of the rolling bearing is mounted in a fixed state, the rolling bearing device can be used without housing the lubricating oil retaining member 12a inside the tank, provided that the air reservoir a is always positioned at the top of the tank.

[0042] The actuator 11 described above can, for example, use a mechanism that combines a piston or plunger that reciprocates using a diaphragm or solenoid made of piezoelectric ceramic, and an electric motor. For relatively large rolling bearings, a fluid pressure cylinder powered by pneumatics or hydraulics can also be used.

[0043] Specific examples of the discharger 6 include pneumatically or hydraulically driven piston pumps, hydraulic pumps such as gear pumps, diaphragm pumps, and rotary pumps. Alternatively, it may be a pump using an electric motor or a piezoelectric element, such as a micropump using piezoelectric ceramics.

[0044] The lubricating oil retaining member 12a can be made of a nonwoven fabric with continuous gaps between densely packed fibers, or a sponge-like material that has the property of drawing in lubricating oil into interconnected pores, so as to draw it in through capillary action.

[0045] Furthermore, the lubricating oil retaining member 12a may be made of a material that is soft and porous enough to be elastically deformable when pressed by the driving force of the actuator 11. For example, a material with interconnected pores and elastic deformability, such as a soft elastic rubber (elastomer) foam, can be used. Typical examples of such materials include soft urethane foam, soft resin sponge, rubber sponge, felt, nonwoven fabric, and fiber filter material.

[0046] The lubricating oil used in this invention is not particularly limited, and any low-viscosity liquid lubricant that is liquid when used with rolling bearings and can be discharged from a dispenser can be used.

[0047] In other words, depending on the intended use of the rolling bearing device, liquid lubricants can be used, but lubricating greases containing thickeners that separate in response to external forces or temperature increases, and waxes whose phase state changes from solid to liquid depending on the operating environment can also be used.

[0048] The amount of lubricating oil discharged is preferably such that it does not affect the torque fluctuations of the rolling bearing, and may be an extremely small amount. For example, 0.001 mL to 0.1 mL can be discharged using a micropump or the like. The discharge amount may be controlled so that the amount and timing of lubrication are controlled according to the lubrication state of the rolling bearing A. The lubrication state may be detected by sensors installed inside or around the rolling bearing A, for example.

[0049] As shown in Figure 4, the lubricating oil supply device C used in the second embodiment is an example in which a lubricating oil holding member 12b, which is a bag-shaped container, is housed in the tank 5, instead of the lubricating oil supply device B used in the first embodiment. The lubricating oil holding member 12b is formed of a thin-walled sheet-like or film-like resin container or the like so that its volume can change in response to changes in atmospheric pressure. In the second embodiment, the same configuration as the first embodiment is adopted, except that the lubricating oil retaining member 12b, the external shape of the discharger 6a, and the shape (arrangement and length) of the discharge nozzle 7a are different.

[0050] The lubricating oil supply device D used in the third embodiment shown in Figure 5 expands the lubricating oil tank 5a used in the second embodiment to be as long as possible in the circumferential direction of the outer ring 2 to increase its capacity, and for this purpose, the control unit 14 and the power source unit 13 are arranged in parallel with the tank 5a. The components of this third embodiment other than the tank 5a are the same as those of the second embodiment.

[0051] Figure 6 shows the main part of a rolling bearing device as a fourth embodiment, in which a ventilation hole 10 is provided on the inner diameter surface side of the end of the tank 5 of the lubricating oil supply device. In yet another embodiment, a ventilation hole 10 provided on the end face of the tank 5 is shown by a dashed line. The ventilation hole 10 shown is one formed in the tank 5 of each embodiment, but two or more ventilation holes 10 may be provided in the required parts.

[0052] The fifth and sixth embodiment rolling bearing devices shown in Figures 7 and 8, respectively, have ventilation holes 10 in the tank, provided on the side of the end of the tank 5, and an arc-shaped airflow guide enclosure 15 (Figure 7) or an elbow-shaped duct 16 (Figure 8) is provided around the opening periphery of the ventilation hole 10.

[0053] By providing an annular airflow guide enclosure such as an arc-shaped projection enclosure 15 or a duct 16 facing the direction opposite to the swirling flow, the airflow (swirling flow) can be efficiently taken into the tank 5 from the ventilation hole 10.

[0054] Furthermore, as shown in Figure 9, it is preferable to provide one or more flow rate adjustment valves 17, 18, and 19 selected from the vent hole 10, the oil supply passage 9 that supplies lubricating oil from the tank 5 to the discharger 6, and the discharge port of the nozzle 7 of the discharger 6, and to open and close these valves as appropriate and selectively.

[0055] This approach can address the following problems: In other words, when a rolling bearing rotates at high speed, the temperature of the inner ring 1 (see Figure 1) and the outer ring 2 rises due to frictional heat. The heat rise of the inner ring 1 and the outer ring 2 is transferred to the adjacent outer ring spacers B1 and inner ring spacers B2, causing the heated tank 5 to expand thermally, and the air a and lubricating oil O inside the tank 5 also attempt to expand thermally.

[0056] At this time, as shown in Figures 9(c) and 9(d), if the valve 18 of the fuel supply passage 9 is closed and the tank 5 is sealed, the internal pressure of the tank 5 will increase mainly due to the thermal expansion of the air. As a result, the tank 5 may be damaged, and as shown in Figure 9(d), any gaps in the fuel supply mechanism that could not maintain airtightness, or the lubricating oil O, may be forcibly pushed out from the discharge port of the discharge nozzle 7, leading to unintended oil leaks. To address these issues, it is necessary to keep the fuel supply passage 9, which connects the air a inside the tank 5 to the outside of the tank 5, open to prevent an increase in internal pressure inside the tank 5.

[0057] Furthermore, as shown in Figure 9(c), when only the vent hole 10 is open and the fuel supply passage 9 is closed by the valve 18, the path from the vent hole 10 to the fuel supply passage 9 is blocked, so the swirling flow does not flow into the tank 5 from the vent hole 10.

[0058] Therefore, it is preferable that the vent hole 10, the oil supply passage 9 that supplies lubricating oil to the discharger, and the discharge port of the discharger 6 are all open. In this case, a portion of the swirling flow from the rolling bearing enters through the vent hole 10, and the lubricating oil O inside the tank 5 is pushed in the direction of discharge from the discharge port. As a result, the pushing force from the swirling flow, along with the discharge operation of the discharger 6, acts as an auxiliary to the pressure of the discharge operation, saving the energy required for the discharge operation.

[0059] Furthermore, a flow rate adjustment filter is provided in the vent hole 10 or the lubrication oil supply passage 9 from the tank 5 to the discharger 6, and the mesh size of the filter can be adjusted to separate gas and liquid or solid and liquid. In addition, the flow rate adjustment filter can release the pressure inside the tank 5 while preventing foreign matter and excess lubrication oil from flowing in from outside the tank 5, or it can allow only air or liquid above the required pressure to pass through the filter.

[0060] In the embodiments described above, an angular contact ball bearing applicable to a machine tool spindle was shown as an example of rolling bearing A. However, the rolling bearing in the rolling bearing device of this invention can also be a deep groove ball bearing, cylindrical roller bearing, tapered roller bearing, self-aligning roller bearing, needle roller bearing, thrust cylindrical roller bearing, thrust tapered roller bearing, thrust needle roller bearing, thrust self-aligning roller bearing, etc.

[0061] Furthermore, the rolling bearing device of this invention is not limited to the illustrated configuration. For example, the tank 5 may be extended in an annular shape to follow the entire circumference of the outer ring spacer B1, and the shape, material, and hardness of the tank are not particularly limited. The power source unit 13 and the control unit 14 may be arranged in any configuration within the space between the outer ring spacer B1 and the inner ring spacer B2, and the pump and tank that constitute the lubricating oil supply device B may be placed inside the rolling bearing. In addition, protective partitions may be provided to prevent contact between the power source unit 13 and the control unit 14 and the inner ring spacer B2, or they may be covered with a casing. [Explanation of Symbols]

[0062] 1 Inner ring 2 Outer ring 3 Rolling element 4 Cage 5, 5a Tank 6, 6a discharge machine 7, 7a Discharge nozzle 8 Casing 9. Fueling channel 10 Ventilation holes 11 Actuators 12, 12a, 12b Lubricating oil retaining members 13 Power source section 14 Control Unit 15 Enclosure 16 ducts 17, 18, 19 valves A Rolling bearing B, C, D Lubricating oil supply device B1 Outer wheel spacer B2 Inner Wheel Spacer O Lubricating oil a air pocket

Claims

1. A rolling bearing having multiple rolling elements interposed between the inner and outer rings, This consists of a lubrication oil supply device attached to the rolling bearing to supply lubricating oil, The lubricating oil supply device includes a tank for holding lubricating oil, The system includes a discharger equipped with a discharge mechanism that discharges lubricating oil supplied from this tank into the bearing space between the inner and outer rings of the rolling bearing, A rolling bearing device comprising a tank containing lubricating oil and a ventilation hole opening in the wall of the tank.

2. The rolling bearing device according to claim 1, wherein an enclosure or duct is provided at the opening edge of the ventilation hole opening into the wall surface to guide the airflow swirling around the axis in the bearing space from the opening into the tank.

3. The rolling bearing device according to claim 1 or 2, wherein the discharge device is a discharge device using a pump, a valve, or both.

4. The above-mentioned discharger is equipped with a discharge mechanism driven by an actuator, The rolling bearing device according to claim 3, comprising a power source unit and a control unit for the actuator.

5. The rolling bearing device according to claim 1 or 2, wherein a lubricating oil retaining member, whose volume changes in accordance with changes in air pressure inside the tank, is housed in the above-mentioned tank.

6. The rolling bearing device according to claim 5, wherein the lubricating oil holding member is a porous body or a bag-shaped container capable of holding lubricating oil.

7. The rolling bearing device according to claim 1 or 2, further comprising one or more flow rate adjustment valves selected from the above-mentioned vent holes, the above-mentioned oil supply passage for supplying lubricating oil from the above-mentioned tank to the above-mentioned discharger, and the discharger.

8. The rolling bearing device according to claim 3, further comprising one or more flow rate adjustment valves selected from the above-mentioned vent holes, the above-mentioned oil supply passage for supplying lubricating oil from the above-mentioned tank to the above-mentioned discharger, and the discharger.

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