Motor bearing system

Abstract

To properly avoid resonance of a gas bearing in a motor bearing system in which switching between a rolling bearing and the gas bearing is performed.SOLUTION: A motor bearing system 20 includes: a bearing 3 that includes an inner ring 4, an outer ring 5, a plurality of rolling elements 6, and a sleeve 7 and supports a rotation shaft 2 of a motor 1; a brake mechanism 9 that can switch between fixing and releasing of the sleeve of the bearing; and a control device 50 that controls the brake mechanism based on a motor rotation speed. When the motor rotation speed is less than a prescribed value, the control device operates the brake mechanism to fix the sleeve in order to cause the bearing to function as a rolling bearing. When the motor rotation speed is equal to or greater than the prescribed value, the control device stops the brake mechanism to release the sleeve in order to cause the bearing to function as a gas bearing. Further, when the motor rotation speed is equal to or greater than the prescribed value and within a prescribed rotation region corresponding to a resonant rotation region of the gas bearing, the control device operates the brake mechanism.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a motor bearing system that is switchable between a rolling bearing and a sliding bearing. [Background technology]

[0002] Conventionally, rolling bearings and plain bearings have been used as bearings to support the rotating shaft of, for example, a vehicle's power source (engine or motor). Rolling bearings have low friction at low rotation speeds, while plain bearings have high friction at low rotation speeds. On the other hand, rolling bearings have a finite lifespan due to rolling fatigue, but plain bearings have an indefinite lifespan under appropriate lubrication conditions.

[0003] Here, a technology has been proposed in which a system is configured to include both rolling bearings and plain bearings, and the bearing to be applied is switched depending on the characteristics of each bearing as described above. For example, Patent Document 1 describes a system that includes a plain bearing that supports a rotating body housed in a housing, a rolling bearing that is arranged in parallel to the plain bearing and supports the rotating body, and a movement mechanism that switches the bearing that functions to support the rotating body by moving the inner ring or outer ring of the rolling bearing in the axial direction. In particular, in this system, the radial clearance of the rolling bearing is changed by driving the movement device to move the inner ring or outer ring relative to the rolling bearing in the axial direction, and only the plain bearing functions when the radial clearance of the rolling bearing is larger than that of the plain bearing, but only the rolling bearing functions when the radial clearance of the rolling bearing is smaller than that of the plain bearing. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-19728 Summary of the Invention [Problem to be solved by the invention]

[0005] Generally, sliding bearings such as those described above use fluid lubrication with lubricating oil. However, in sliding bearings that use fluid lubrication, the fluid friction and resistance of the lubricating oil increase at high rotational speeds. Therefore, in systems that operate sliding bearings at high rotational speeds, it is effective to use gas bearings (typically air bearings) that use gas lubrication, which has a lower viscosity than lubricating oil. However, at low rotational speeds, the load capacity of gas bearings tends to be insufficient. On the other hand, at high rotational speeds, the load capacity of gas bearings can be ensured due to wedge effects and throttle effects. Therefore, the present inventors conceived of building a system that allows the bearings to be switched depending on the rotational speed, so that rolling bearings function at low rotational speeds and gas bearings function at high rotational speeds.

[0006] On the other hand, as a result of extensive research, the present inventors have discovered that gas bearings experience relatively large resonances in a certain range of rotation within the high rotational speed range in which they are used. In other words, gas bearings have a resonance rotation range (resonance frequency range) in a relatively high rotational speed range. When resonance occurs in a gas bearing, its load capacity decreases, and it may not be possible to properly implement the gas bearing.

[0007] The present invention has been made to solve the problems of the conventional technology described above, and aims to appropriately avoid resonance of gas bearings in a motor bearing system that switches between rolling bearings and gas bearings. [Means for solving the problem]

[0008] In order to achieve the above object, the present invention provides a motor bearing system, comprising: a bearing provided on the outer periphery of a rotating shaft of a motor to support the rotating shaft, the bearing comprising first and second raceway portions each formed to extend circumferentially and arranged at a distance so as to face each other in the radial direction, and a plurality of rolling elements interposed between the first and second raceway portions; a brake mechanism configured to switch between a state in which the bearing can function as a rolling bearing by fixing the first raceway portion of the bearing, and a state in which the bearing can function as a gas bearing by releasing the first raceway portion of the bearing; The control device has a motor rotation speed sensor that detects the motor rotation speed of the motor, and a control device configured to control the brake mechanism based on the motor rotation speed detected by the motor rotation speed sensor, and the control device is configured to: when the motor rotation speed is less than a predetermined value, activate the brake mechanism to fix the first raceway ring portion in order to allow the rolling bearing to function; when the motor rotation speed is equal to or greater than the predetermined value, stop the brake mechanism to release the first raceway ring portion in order to allow the gas bearing to function; and when the motor rotation speed is equal to or greater than the predetermined value and is within a predetermined rotation range corresponding to the resonant rotation range (resonant frequency range) of the gas bearing, activate the brake mechanism.

[0009] In the present invention configured as described above, the control device generally stops the brake mechanism to allow the gas bearing to function when the motor rotation speed is equal to or greater than a predetermined value. However, the control device exceptionally activates the brake mechanism when the motor rotation speed is equal to or greater than the predetermined value but within a predetermined rotation range. This allows the gas bearing rotation speed to be controlled independently of the motor rotation speed by adjusting the rotation speed of the first bearing ring portion with the brake mechanism when the motor rotation speed is within the predetermined rotation range. In particular, by decelerating the first bearing ring portion with the brake mechanism, the gas bearing rotation speed can be temporarily set to a rotation speed lower than the motor rotation speed. As a result, the gas bearing rotation speed can be quickly moved out of the resonance rotation range without stagnation within the resonance rotation range. This makes it possible to avoid resonance in the gas bearing.

[0010] In the present invention, the control device is preferably configured to control the brake mechanism so as to maintain the rotation speed of the first raceway ring portion below the resonance rotation speed range when the motor rotation speed or the rotation speed of the first raceway ring portion enters a predetermined rotation range while the motor rotation speed is increasing, and to stop the brake mechanism so as to rapidly increase the rotation speed of the first raceway ring portion when the motor rotation speed leaves the predetermined rotation range. According to the present invention configured in this manner, when the motor rotation speed increases, the rotation speed of the gas bearing can be quickly caused to leave the resonance rotation range, making it possible to effectively avoid resonance of the gas bearing.

[0011] In the present invention, preferably, when the motor rotation speed is decreasing, the control device is configured to control the brake mechanism so that when the motor rotation speed or the rotation speed of the first raceway ring portion enters a predetermined rotation range, the rotation speed of the first raceway ring portion is rapidly decreased to maintain it below the resonance rotation range, and to stop the brake mechanism when the motor rotation speed leaves the predetermined rotation range. According to the present invention configured in this manner, when the motor rotation speed decreases, the rotation speed of the gas bearing can be quickly caused to leave the resonance rotation range, making it possible to effectively avoid resonance of the gas bearing.

[0012] In the present invention, preferably, the brake mechanism is configured to apply a braking force to the first raceway ring portion in order to fix the first raceway ring portion, and the control device is configured to perform duty control on the brake mechanism in order to adjust the braking force applied to the first raceway ring portion from the brake mechanism when the motor rotation speed is within a predetermined rotation range. According to the present invention configured in this manner, the braking force applied to the first bearing ring portion from the brake mechanism can be adjusted with a simple control configuration.

[0013] In the present invention, the control device is preferably configured to set the duty ratio applied in the duty control for a predetermined period immediately after the motor rotation speed enters a predetermined rotation range to a smaller value as the absolute value of the rate of change of the motor rotation speed becomes smaller. According to the present invention configured as described above, when the rate of change of the motor rotation speed is small, the braking force applied by the brake mechanism can be limited, thereby making it possible to suppress the discomfort felt by the driver, particularly the feeling of deceleration, during slow acceleration.

[0014] In the present invention, preferably, the motor bearing system further has one or more vibration sensors that detect vibrations generated in the bearing, and has a plurality of brake mechanisms that are arranged to apply braking forces to a plurality of circumferential positions on the first raceway ring portion in order to fix the first raceway ring portion, and the control device is configured to control the activation of one or more brake mechanisms among the plurality of brake mechanisms that correspond to the direction of vibration based on the direction of vibration detected by the one or more vibration sensors. According to the present invention configured as described above, vibrations in various directions that occur due to resonance in the gas bearing can be effectively suppressed.

[0015] In the present invention, preferably, the first raceway ring portion is arranged radially outside the plurality of rolling elements, and the second raceway ring portion is arranged radially inside the plurality of rolling elements, and the motor bearing system further has a fixed member having an inner circumferential surface extending along the outer circumferential surface of the first raceway ring portion and arranged with a gap between it and the outer circumferential surface, and fixed so as not to rotate with rotation of the rotating shaft, and when the brake mechanism releases the first raceway ring portion, the outer circumferential surface of the first raceway ring portion is spaced apart from the inner circumferential surface of the fixed member, and the entire bearing rotates relative to the fixed member with rotation of the rotating shaft, so that the bearing functions as a gas bearing. According to the present invention configured as described above, when the first raceway ring portion is fixed by the brake mechanism, the bearing functions as a rolling bearing, while by releasing the brake mechanism from fixing the first raceway ring portion, the bearing can accurately function as a gas bearing. In other words, according to the present invention, by using the brake mechanism to switch between fixing and releasing the first raceway ring portion, it is possible to easily switch between a rolling bearing and a sliding bearing. Therefore, according to the present invention, since it does not use a sliding bearing and a rolling bearing configured as separate bodies or move the inner or outer ring of the rolling bearing relative to each other in the axial direction, as in the technology described in Patent Document 1 above, it is possible to switch between a rolling bearing and a gas bearing with a simple configuration.

[0016] In the present invention, preferably, the motor bearing system further includes a gas passage for supplying gas to a gap between the outer peripheral surface of the first raceway ring portion and the inner peripheral surface of the fixed member, and a pump provided on the gas passage for pressurizing the gas, and the control device is configured to control the pump to supply gas from the gas passage to the gap when the motor rotation speed is equal to or greater than a predetermined value. According to the present invention configured in this manner, a gas layer is formed in the gap between the outer peripheral surface of the first raceway ring portion and the inner peripheral surface of the fixed member using gas supplied from a pump, thereby making it possible to effectively realize a gas bearing. [Effects of the Invention]

[0017] According to the present invention, resonance of the gas bearing can be appropriately avoided in a motor bearing system that switches between a rolling bearing and a gas bearing. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a schematic configuration diagram of a motor system to which a motor bearing system according to an embodiment of the present invention is applied; [Figure 2] 1 is a cross-sectional view of a motor bearing system according to an example embodiment of the present invention. [Figure 3]FIG. 2 is a block diagram showing the electrical configuration of the motor bearing system according to the embodiment of the present invention. [Figure 4] FIG. 1 is an explanatory diagram illustrating a basic concept of bearing switching control according to an embodiment of the present invention. [Figure 5] 4 is a time chart showing bearing switching control according to an embodiment of the present invention. [Figure 6] FIG. 2 is an explanatory diagram of resonance occurring in a gas bearing. [Figure 7] 4 is a time chart showing resonance avoidance control according to an embodiment of the present invention. [Figure 8] 4 is a flowchart showing resonance avoidance control according to an embodiment of the present invention. [Figure 9] 10 is an explanatory diagram of resonance avoidance control according to a second modified example of the embodiment of the present invention. FIG. [Figure 10] FIG. 10 is a schematic cross-sectional view of a motor bearing system according to a third modified example of an embodiment of the present invention. [Figure 11] FIG. 10 is an explanatory diagram illustrating an example of resonance avoidance control according to a third modified example of the embodiment of the present invention. [Figure 12] FIG. 10 is an explanatory diagram of another example of resonance avoidance control according to the third modification of the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, a motor bearing system according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0020] [Device configuration] First, the basic device configuration of a motor bearing system according to this embodiment will be described with reference to Fig. 1. Fig. 1 is a schematic configuration diagram of a motor system to which a motor bearing system according to this embodiment is applied. Specifically, Fig. 1 is a cross-sectional view of a motor system 100 as viewed along the axial direction.

[0021] As shown in Fig. 1, the motor system 100 mainly comprises a motor (electric motor) 1 including a rotor 1a and a stator 1b, a rotating shaft 2 connected to the rotor 1a, and a pair of motor bearing systems 20 (only one of which is shown in Fig. 1, the other is omitted) that support the rotating shaft 2. The motor 1, rotating shaft 2, and motor bearing system 20 are housed in a housing (not shown). The motor system 100 is used to drive a vehicle (not shown), such as an electric car.

[0022] Specifically, the motor bearing system 20 has a bearing (rolling bearing) 3 including an inner ring (raceway) 4 fixed to the outer periphery of the rotating shaft 2, an outer ring (raceway) 5 arranged radially outward of the inner ring 4 with a gap between it and the inner ring 4, a plurality of rolling elements (balls or rollers) 6 interposed between the inner ring 4 and the outer ring 5, and a sleeve 7 fixed to the outer periphery of the outer ring 5. The sleeve 7 also includes an outer circumferential surface 7s and a protrusion (in other words, a flange portion) 7p provided at an end in the axial direction and protruding radially outward.

[0023] The outer ring 5 and sleeve 7 of the bearing 3 correspond to an example of the "first raceway portion" in the present invention, and the inner ring 4 corresponds to an example of the "second raceway portion" in the present invention. Here, the "first raceway portion" in the present invention is formed by the outer ring 5 and the sleeve 7, which are separate members, but in other examples, this "first raceway portion" may be formed by a member in which the outer ring 5 and the sleeve 7 are integrated.

[0024] The motor bearing system 20 also includes a fixed member 8 that surrounds the bearing 3 and is fixed so as not to rotate with the rotation of the rotating shaft 2, and a brake mechanism 9 that is fixed to the fixed member 8 and configured to fix the sleeve 7 of the bearing 3 to the fixed member 8. The fixed member 8 is formed, for example, from the housing (case) of the motor 1, and includes an inner circumferential surface 8s that extends along the outer circumferential surface 7s of the sleeve 7 and is provided with a small gap SP between it and the outer circumferential surface 7s. The brake mechanism 9 also includes an actuator (not shown) that applies a braking force to the protruding portion 7p of the sleeve 7, thereby fixing the sleeve 7 to the fixed member 8 so as not to rotate with the rotating shaft 2. In this case, the outer ring 5 fixed to the sleeve 7 is also fixed to the fixed member 8.

[0025] Additionally, the fixed member 8 is formed with a portion of a gas passage 11 for supplying gas (typically air) to a gap SP between an inner peripheral surface 8s of the fixed member 8 and an outer peripheral surface 7s of the sleeve 7. A pump 12 for pumping the gas is provided on the gas passage 11.

[0026] In the motor bearing system 20 according to this embodiment, when the brake mechanism 9 fixes the sleeve 7, the outer ring 5 is fixed via the sleeve 7, and the bearing 3 functions as a rolling bearing (the original function of the bearing 3). In contrast, when the brake mechanism 9 releases the sleeve 7, the entire bearing 3 (including the sleeve 7) rotates together with the rotating shaft 2, thereby providing a sliding bearing, particularly a gas bearing (gas-lubricated bearing). When this gas bearing is provided, the bearing 3 rotates relative to the fixed member 8 with the outer peripheral surface 7s of the sleeve 7 spaced apart from the inner peripheral surface 8s of the fixed member 8. In addition, in this embodiment, when the brake mechanism 9 releases the sleeve 7, gas from the pump 12 is supplied to the gap SP between the sleeve 7 and the fixed member 8, forming a gas layer in this gap SP, thereby providing a gas bearing.

[0027] As described above, the motor bearing system 20 according to this embodiment is configured to be able to selectively implement a rolling bearing or a gas bearing by switching between fixing and releasing the sleeve 7 using the brake mechanism 9.

[0028] An example of the motor bearing system 20 will now be described with reference to Fig. 2. Fig. 2 is a cross-sectional view of a motor bearing system according to one embodiment of this invention.

[0029] In the example of motor bearing system 20 shown in Fig. 2, sleeve 7 is fixed to an end in the axial direction and has protrusion 7a protruding radially outward and armature 7b attached to protrusion 7a (these correspond to protrusion 7p described above). Brake mechanism 9 also has mounting portion 9a for mounting brake mechanism 9 to fixed member 8, coil 9b fixed to mounting portion 9a and generating an electromagnetic force for attracting armature 7b of sleeve 7, and lining (friction material) 9c provided opposite armature 7b. Brake mechanism 9 is configured by an electromagnetic brake.

[0030] In such a motor bearing system 20, in the brake mechanism 9, the coil 9b is energized to generate an electromagnetic force, which attracts the armature 7b of the sleeve 7 and causes it to abut against the lining 9c, thereby fixing the sleeve 7 with the brake mechanism 9. In this way, the sleeve 7 can be reliably fixed with the brake mechanism 9 by utilizing the electromagnetic force of the coil 9b.

[0031] The configuration of the motor bearing system 20, the sleeve 7, and the brake mechanism 9 shown in FIG. 2 is an example, and various other configurations are also applicable.

[0032] [Electrical configuration] Next, the electrical configuration of the motor bearing system 20 according to this embodiment will be described with reference to Fig. 3. As shown in Fig. 3, in addition to the motor 1, brake mechanism 9, and pump 12 described above, the motor bearing system 20 includes various sensors indicated by reference numerals 31 to 36, a control device 50 to which various signals are input from the various sensors, and a display device 40 that displays various information via the control device 50. The control device 50 is configured as a computer that includes one or more processors 50a (typically a CPU) and memory 50b such as ROM and RAM that stores various programs interpreted and executed by the processor 50a (including basic control programs such as an OS and application programs that are run on the OS to realize specific functions) and various data.

[0033] Specifically, the motor bearing system 20 mainly includes a motor rotation speed sensor 31 that detects the motor rotation speed (the rotation speed of the rotor 1a, the rotating shaft 2, which is synonymous with rotational speed) of the motor 1, a sleeve rotation speed sensor 32 that detects the sleeve rotation speed (synonymous with rotational speed) of the sleeve 7, a vibration sensor 33 that detects vibration of the bearing 3 (including the sleeve 7), a vehicle speed sensor 34 that detects the speed of the vehicle (vehicle speed), an acceleration sensor 35 that detects the acceleration occurring in the vehicle, and an accelerator opening sensor 36 that detects the accelerator opening corresponding to the amount of depression of the accelerator pedal in the vehicle.

[0034] The control device 50 controls the motor 1, the brake mechanism 9, the pump 12, the display device 40, and the like, based on detection signals from the various sensors 31 to 36. In particular, in this embodiment, the control device 50 controls the brake mechanism 9 to switch between locking and releasing the sleeve 7 so that the bearing 3 can function as either a rolling bearing or a gas bearing, based on the motor rotation speed detected by the motor rotation speed sensor 31 (hereinafter, this control will be referred to as "bearing switching control"). Specifically, when the motor rotation speed is below a predetermined value (hereinafter, referred to as the "switching threshold"), i.e., in the low rotation range, the control device 50 operates the brake mechanism 9 to lock the sleeve 7 so that the bearing 3 functions as a rolling bearing, whereas when the motor rotation speed is equal to or greater than the switching threshold, i.e., in the high rotation range, the control device 50 stops the brake mechanism 9 so that the sleeve 7 is released so that the bearing 3 functions as a gas bearing. In addition, in such bearing switching control, when the motor rotation speed is equal to or greater than the switching threshold, that is, when the bearing 3 is made to function as a gas bearing, the control device 50 controls the pump 12 to supply gas from the gas passage 11 to the gap SP between the sleeve 7 and the fixed member 8.

[0035] Furthermore, in this embodiment, control device 50 also performs control to avoid resonance that occurs in the gas bearing as described above in the "Problem to be Solved by the Invention" section (hereinafter referred to as "resonance avoidance control"). Specifically, when the motor rotation speed is equal to or greater than the switching threshold but is within a predetermined rotation range corresponding to the resonance rotation range (a rotation range higher than the switching threshold), control device 50 operates brake mechanism 9 to perform resonance avoidance control so that the gas bearing rotation speed (corresponding to the sleeve rotation speed) avoids the resonance rotation range, more specifically so that the sleeve rotation speed quickly passes through the resonance rotation range without stagnating within it.

[0036] [Bearing switching control] Next, the bearing switching control according to this embodiment will be specifically described.

[0037] First, the basic concept of bearing switching control according to this embodiment will be described. Conventionally, rolling bearings and plain bearings have been used as bearings to support the rotating shaft of a vehicle's power source. Rolling bearings have low friction in the low rotation range, while plain bearings have high friction in the low rotation range. On the other hand, rolling bearings have a finite lifespan due to rolling fatigue, while plain bearings have a permanent lifespan under appropriate lubrication conditions. In a typical engine (internal combustion engine), it is effective to use plain bearings in the high rotation range. These plain bearings typically use fluid lubrication with lubricating oil. However, in a motor 1 that operates at a higher rotation speed than an engine, using such plain bearings in the high rotation range of the motor 1 increases the fluid friction and resistance of the lubricating oil, resulting in a problem of reduced motor power consumption.

[0038] For this reason, in this embodiment, a gas bearing (typically an air bearing) that uses lubrication with a gas that has a lower viscosity than lubricating oil is used as the sliding bearing. To achieve this gas bearing, it is necessary to reliably form a gas layer in the gap SP between the sleeve 7 and the fixed member 8 to prevent the sleeve 7 and the fixed member 8 from coming into contact without ensuring the load capacity of the gas bearing. In this embodiment, to reliably form such a gas layer, gas is supplied to the gap SP between the sleeve 7 and the fixed member 8 by a pump 12, and the wedge effect and throttling effect that occur in this gap SP are utilized. Because these wedge and throttling effects are only obtained in the high rotation speed range of the motor 1, methods that attempt to utilize these effects may not ensure sufficient load capacity of the gas bearing in the low rotation speed range of the motor 1, resulting in contact between the sleeve 7 and the fixed member 8.

[0039] In view of the above, in this embodiment, the control device 50 performs bearing switching control to switch between locking and releasing the sleeve 7 by the brake mechanism 9 depending on the motor rotation speed, as described above, so that the bearing 3 functions as a rolling bearing in the low rotation range, while the bearing 3 functions as a gas bearing in the high rotation range.

[0040] Next, the basic concept of the bearing switching control according to this embodiment will be explained in more detail with reference to Fig. 4. Here, the bearing switching control according to this embodiment will be compared with the bearing switching control according to a comparative example. In Fig. 4, the horizontal axis represents the motor rotation speed, and the vertical axis represents the shaft friction torque.

[0041] In the bearing switching control according to the comparative example, the bearing that functions to support the rotating shaft of the motor is switched between a rolling bearing and a sliding bearing that uses fluid lubrication with lubricating oil. Specifically, in the comparative example, in region R11 (low rotation range) where the motor rotation speed is low, a rolling bearing is used as the bearing that functions to support the rotating shaft 2, while in region R12 where the motor rotation speed is higher than region R11, a sliding bearing is used as the bearing that functions to support the rotating shaft 2. This control corresponds to the technology described in Patent Document 1.

[0042] In Figure 4, graph G11 shows the axial friction torque generated in a rolling bearing, i.e., boundary lubrication friction due to direct contact, and graph G12 shows the axial friction torque generated in a sliding bearing that uses fluid lubrication with lubricating oil, i.e., fluid lubrication friction of the lubricating oil. Therefore, the axial friction torque generated in the bearing switching control of the comparative example described above is the sum of the axial friction torque shown in graph G11 and the axial friction torque shown in graph G12, i.e., the torque shown in graph G21. In this case, the axial friction torque increases significantly as the motor rotation speed increases in region R12. This is due to increased friction caused by deformation of the rolling elements in the rolling bearing, as shown in graph G13.

[0043] In contrast to this, in this embodiment, as described above, the control device 50 controls the brake mechanism 9 to switch between locking and releasing the sleeve 7 so that the bearing 3 can function by switching between a rolling bearing and a gas bearing. First, in the region R11 where the motor rotation speed is low, the wedge effect and throttle effect cannot be obtained, so the control device 50 locks the sleeve 7 using the brake mechanism 9 to cause the bearing 3 to function as a rolling bearing, that is, to cause the bearing 3 to perform its original function (function as a rolling bearing).

[0044] Next, when the motor rotation speed exceeds region R11, that is, when it enters region R12 which is higher than region R11, the wedge effect and throttle effect gradually begin to be obtained, so control device 50 causes bearing 3 to function as a gas bearing. Specifically, control device 50 releases sleeve 7, which had been fixed by brake mechanism 9, and supplies gas from pump 12 to gap SP between sleeve 7 and fixed member 8, thereby causing bearing 3 to function as a gas bearing and not as a rolling bearing. In this case, outer peripheral surface 7s of sleeve 7 is separated from inner peripheral surface 8s of fixed member 8, and a gas bearing is realized in which the entire bearing 3 (including sleeve 7) rotates together relative to fixed member 8.

[0045] In Figure 4, graph G14 shows the shaft friction torque generated in the gas bearing, i.e., gas-lubricated friction. The shaft friction torque generated in the bearing switching control according to the present embodiment described above is the sum of the shaft friction torque shown in graph G11 and the shaft friction torque shown in graph G14, i.e., the torque shown in graph G22. When comparing the shaft friction torque according to the present embodiment shown in graph G22 with the shaft friction torque according to the comparative example shown in graph G21, it can be seen that the shaft friction torque is significantly reduced according to the present embodiment. Therefore, it can be said that the present embodiment can effectively improve electricity consumption compared to the comparative example.

[0046] Next, the flow of bearing switching control according to this embodiment will be described with reference to Fig. 5. Fig. 5 is a time chart showing bearing switching control according to this embodiment. From top to bottom, Fig. 5 shows the motor rotation speed, on / off of the brake mechanism 9, and on / off of the pump 12. Note that "Nm0" in Fig. 5 is the threshold value for switching the motor rotation speed described above, and corresponds to the motor rotation speed at the boundary between region R11 and region R12 in Fig. 4. Also, Fig. 5 assumes a situation in which the motor rotation speed increases and the vehicle accelerates.

[0047] 5, between times t0 and t1 when the motor rotation speed is below the switching threshold, the control device 50 turns on the brake mechanism 9 to fix the sleeve 7 and turns off the pump 12, causing the bearing 3 to function as a rolling bearing. Then, from time t1 when the motor rotation speed becomes equal to or greater than the switching threshold, the control device 50 turns off the brake mechanism 9 to release the sleeve 7 and turns on the pump 12 to supply gas into the gap SP between the sleeve 7 and the fixed member 8, thereby switching the bearing 3 from a rolling bearing to a gas bearing.

[0048] [Resonance avoidance control] Next, the resonance avoidance control according to this embodiment will be specifically described.

[0049] First, with reference to Figure 6, we will explain resonance that occurs in gas bearings. In Figure 6, the horizontal axis represents the rotational speed of the gas bearing, and the vertical axis represents vibration intensity (vibration level). As Figure 6 shows, gas bearings experience relatively large resonance between rotational speeds N1 and N2 (rotational speeds N1 and N2 are greater than the switching threshold Nm0). The rotational speed range from the rotational speed (lower limit) N1 to the rotational speed (upper limit) N2 is the resonant rotational range (resonant frequency range) of the gas bearing. When such resonance occurs in a gas bearing, its load capacity decreases, and it may not be possible to properly implement the gas bearing.

[0050] Therefore, in this embodiment, in order to avoid resonance occurring in the gas bearing, control device 50 performs resonance avoidance control using brake mechanism 9 when the motor rotation speed is within a predetermined rotation range corresponding to the resonance rotation range. Specifically, when the motor rotation speed is within the predetermined rotation range, control device 50 adjusts the braking force applied from brake mechanism 9 to sleeve 7 of bearing 3, thereby intentionally controlling the relative rotation speed between sleeve 7 and fixed member 8, i.e., the rotation speed of the gas bearing (equivalent to the sleeve rotation speed). This allows the rotation speed of the gas bearing to quickly pass through the resonance rotation range without stagnating within the resonance rotation range.

[0051] The predetermined rotational speed range used in resonance avoidance control (hereinafter referred to as the "resonance avoidance rotational speed range") is a wide range that provides a margin relative to the resonance rotational speed range. Specifically, the lower limit of the resonance avoidance rotational speed range is set to a value somewhat smaller than the lower limit N1 of the resonance rotational speed range, and the upper limit of the resonance avoidance rotational speed range is set to a value somewhat larger than the upper limit N2 of the resonance rotational speed range.

[0052] Next, the flow of resonance avoidance control according to this embodiment will be described with reference to Fig. 7. Fig. 7 is a time chart showing resonance avoidance control according to this embodiment. Fig. 7 shows, from top to bottom, the motor rotation speed, the on / off state of the brake mechanism 9, and the sleeve rotation speed. Here, the behavior of the vehicle during normal driving is shown, where the motor rotation speed increases to accelerate the vehicle, and then the motor rotation speed decreases to decelerate the vehicle.

[0053] 7, first, the motor rotation speed increases from time t10, but between times t10 and t11, the motor rotation speed is less than the switching threshold Nm0, so the control device 50 turns on the brake mechanism 9 to fix the sleeve 7, causing the bearing 3 to function as a rolling bearing. Then, at time t11, the motor rotation speed becomes equal to or greater than the switching threshold Nm0, so the control device 50 turns off the brake mechanism 9 to release the sleeve 7, causing the bearing 3 to function as a gas bearing.

[0054] After this, at time t12, the motor rotation speed reaches the lower limit Nm1 of the resonance avoidance rotation range, that is, it begins to enter the resonance avoidance rotation range. At this time, the sleeve rotation speed reaches the lower limit Ns1 corresponding to the lower limit Nm1 of the resonance avoidance rotation range (note that at this time, the sleeve rotation speed is approximately equal to the motor rotation speed, and the lower limit Ns1 is also approximately equal to the lower limit Nm1). Therefore, from time t12, the control device 50 controls the brake mechanism 9 to maintain the sleeve rotation speed below the resonance rotation range.

[0055] Specifically, the control device 50 performs duty control on the brake mechanism 9 to adjust the braking force applied from the brake mechanism 9 to the sleeve 7 so as to maintain the sleeve rotation speed at a lower limit value Ns1 that is below the resonance rotation range. In this case, the control device 50 repeatedly switches on and off the voltage applied to an actuator (such as the coil 9b in FIG. 2) of the brake mechanism 9, and thereby controls the pulse width (corresponding to the duty ratio) of the applied voltage to adjust the braking force of the brake mechanism 9. Furthermore, the control device 50 performs feedback control on the brake mechanism 9 based on the sleeve rotation speed detected by the sleeve rotation speed sensor 32 so as to maintain the sleeve rotation speed at the lower limit value Ns1.

[0056] Then, at time t13, the motor rotation speed exceeds the upper limit Nm2 of the resonance avoidance rotation range, i.e., it leaves the resonance avoidance rotation range. Therefore, from time t13, control device 50 stops brake mechanism 9, i.e., releases brake mechanism 9 from fixing sleeve 7. This causes the sleeve rotation speed to rise sharply to value Ns2, which corresponds to upper limit Nm2 of motor rotation speed. Due to this control of brake mechanism 9 from time t12 to t13 (resonance avoidance control), as the motor rotation speed increases, the gas bearing rotation speed does not stagnate within the resonance rotation range, but quickly leaves the resonance rotation range.

[0057] Subsequently, after time t13, the motor rotation speed stops increasing and becomes constant. Then, the motor rotation speed decreases, and at time t14, the motor rotation speed reaches the upper limit Nm2 of the resonance avoidance rotation range, i.e., begins to enter the resonance avoidance rotation range. At this time, the sleeve rotation speed reaches the upper limit Ns2 corresponding to the upper limit Nm2 of the resonance avoidance rotation range (at this time, the sleeve rotation speed is approximately equal to the motor rotation speed, and the upper limit Ns2 is also approximately equal to the upper limit Nm2). Therefore, from time t14, the control device 50 controls the brake mechanism 9 to rapidly decrease the sleeve rotation speed and maintain it below the resonance rotation range. In this case, too, the control device 50 performs the duty control described above to adjust the braking force applied to the sleeve 7 from the brake mechanism 9 so as to maintain the sleeve rotation speed at the lower limit Ns1, which is below the resonance rotation range. Furthermore, the control device 50 feedback-controls the brake mechanism 9 based on the sleeve rotation speed detected by the sleeve rotation speed sensor 32 to maintain the sleeve rotation speed at the lower limit Ns1.

[0058] Then, at time t15, the motor rotation speed falls below the lower limit value Nm1 of the resonance avoidance rotation range, i.e., it leaves the resonance avoidance rotation range. Therefore, from time t15, control device 50 stops brake mechanism 9, i.e., releases the brake mechanism 9 from fixing the sleeve 7. By controlling brake mechanism 9 in this way from time t14 to t15 (resonance avoidance control), the rotation speed of the gas bearing does not stagnate within the resonance rotation range when the motor rotation speed decreases, and quickly leaves the resonance rotation range. After this, at time t16, the motor rotation speed falls below switching threshold value Nm0, so control device 50 turns on brake mechanism 9 to fix the sleeve 7, causing bearing 3 to function as a rolling bearing.

[0059] Next, a flowchart illustrating resonance avoidance control according to this embodiment will be described with reference to FIG. 8. This flow is repeatedly executed at a predetermined cycle by the control device 50. More specifically, the processor 50a in the control device 50 reads out a program stored in the memory 50b and executes the program, thereby realizing the control related to this flow. In FIG. 8, the motor rotation speed is represented as "Nm" and the sleeve rotation speed is represented as "Ns". "Nm1", "Nm2", "Ns1", and "Ns2" are as shown in FIG. 7.

[0060] First, in step S10, the control device 50 acquires various pieces of information from the sensors 31 to 36 (FIG. 3) described above. Then, the control device 50 proceeds to step S11, where it determines whether the change over time (dNm / dt) in the motor rotation speed detected by the motor rotation speed sensor 31 is greater than 0, i.e., whether the motor rotation speed is increasing. As a result, if the control device 50 determines that the motor rotation speed is increasing (step S11: Yes), it proceeds to step S12. On the other hand, if the control device 50 does not determine that the motor rotation speed is increasing (step S11: No), it proceeds to step S21, where it determines whether the motor 1 will stop based on the motor rotation speed detected by the motor rotation speed sensor 31 and the like. As a result, if the control device 50 determines that the motor 1 will stop (step S21: Yes), it ends the control of this flow. However, if it does not determine that the motor 1 will stop (step S21: No), it returns to step S11.

[0061] Next, in step S12, the control device 50 determines whether the sleeve rotation speed detected by the sleeve rotation speed sensor 32 has become equal to or greater than the lower limit Ns1 that defines the resonance avoidance rotation range. Here, the control device 50 determines whether resonance avoidance control should be started. As a result, if the control device 50 determines that the sleeve rotation speed has become equal to or greater than the lower limit Ns1 (step S12: Yes), the control device 50 proceeds to step S13. If the control device 50 does not determine that the sleeve rotation speed has become equal to or greater than the lower limit Ns1 (step S12: No), that is, if the sleeve rotation speed is less than the lower limit Ns1, the control device 50 returns to step S11. Note that the determination of whether resonance avoidance control should be started is not limited to comparing the sleeve rotation speed with the lower limit Ns1 as described above. Instead, the control device 50 may compare the motor rotation speed with the lower limit Nm1 that defines the resonance avoidance rotation range.

[0062] Next, in step S13, the control device 50 controls the brake mechanism 9 to maintain the sleeve rotation speed below the resonance rotation range, that is, executes resonance avoidance control. Specifically, the control device 50 performs duty control on the brake mechanism 9 to adjust the braking force applied to the sleeve 7 from the brake mechanism 9 so as to maintain the sleeve rotation speed at the lower limit value Ns1. Furthermore, the control device 50 feedback-controls the brake mechanism 9 based on the sleeve rotation speed detected by the sleeve rotation speed sensor 32 so as to maintain the sleeve rotation speed at the lower limit value Ns1.

[0063] Next, in step S14, the control device 50 determines whether the motor rotation speed detected by the motor rotation speed sensor 31 has exceeded the upper limit value Nm2 that defines the resonance avoidance rotation range. Here, the control device 50 determines whether or not the resonance avoidance control may be terminated. As a result, if the control device 50 determines that the motor rotation speed has exceeded the upper limit value Nm2 (step S14: Yes), the control device 50 proceeds to step S15. In this case, in step S15, the control device 50 stops the brake mechanism 9 and releases the fixation of the sleeve 7 by the brake mechanism 9 to terminate the resonance avoidance control. Then, the control device 50 proceeds to step S16. On the other hand, if the control device 50 does not determine that the motor rotation speed has exceeded the upper limit value Nm2 (step S14: No), that is, if the motor rotation speed is equal to or less than the upper limit value Nm2, the control device 50 returns to step S13. In this case, the control device 50 continues the resonance avoidance control until the motor rotation speed exceeds the upper limit value Nm2.

[0064] Next, in step S16, the control device 50 determines whether the change over time (dNm / dt) of the motor rotation speed detected by the motor rotation speed sensor 31 is less than 0, that is, whether the motor rotation speed is decreasing. As a result, if the control device 50 determines that the motor rotation speed is decreasing (step S16: Yes), the process proceeds to step S17, and if the control device 50 does not determine that the motor rotation speed is decreasing (step S16: No), the process returns to step S16.

[0065] Next, in step S17, the control device 50 determines whether the sleeve rotation speed detected by the sleeve rotation speed sensor 32 has become equal to or less than the upper limit value Ns2 that defines the resonance avoidance rotation range. Here, the control device 50 determines whether resonance avoidance control should be started. As a result, if the control device 50 determines that the sleeve rotation speed has become equal to or less than the upper limit value Ns2 (step S17: Yes), the control device 50 proceeds to step S18. If the control device 50 does not determine that the sleeve rotation speed has become equal to or less than the upper limit value Ns2 (step S17: No), that is, if the sleeve rotation speed is greater than the upper limit value Ns2, the control device 50 returns to step S16. Note that the determination of whether resonance avoidance control should be started is not limited to comparing the sleeve rotation speed with the upper limit value Ns2 as described above. Instead, the control device 50 may compare the motor rotation speed with the upper limit value Nm2 that defines the resonance avoidance rotation range.

[0066] Next, in step S18, the control device 50 controls the brake mechanism 9 to rapidly reduce the sleeve rotation speed and maintain it below the resonance rotation range, that is, executes resonance avoidance control. Specifically, the control device 50 performs duty control on the brake mechanism 9 to adjust the braking force applied to the sleeve 7 from the brake mechanism 9 so as to maintain the sleeve rotation speed at the lower limit value Ns1. Furthermore, the control device 50 feedback-controls the brake mechanism 9 based on the sleeve rotation speed detected by the sleeve rotation speed sensor 32 so as to maintain the sleeve rotation speed at the lower limit value Ns1.

[0067] Next, in step S19, the control device 50 determines whether the motor rotation speed detected by the motor rotation speed sensor 31 has fallen below the lower limit Nm1 that defines the resonance avoidance rotation range. Here, the control device 50 determines whether or not it is acceptable to end the resonance avoidance control. As a result, if the control device 50 determines that the motor rotation speed has fallen below the lower limit Nm1 (step S19: Yes), the control device 50 proceeds to step S20. In this case, in step S20, the control device 50 stops the brake mechanism 9 and releases the brake mechanism 9 from fixing the sleeve 7 to end the resonance avoidance control. Thereafter, the control device 50 makes the determination in step S21 described above. As a result, if the control device 50 determines that the motor 1 will stop (step S21: Yes), the control device 50 ends the control related to this flow. However, if the control device 50 does not determine that the motor 1 will stop (step S21: No), the control device 50 returns to step S11. On the other hand, if the control device 50 does not determine in step S19 that the motor rotation speed has fallen below the lower limit value Nm1 (step S19: No), that is, if the motor rotation speed is equal to or greater than the lower limit value Nm1, the process returns to step S 18. In this case, the control device 50 continues the resonance avoidance control until the motor rotation speed falls below the lower limit value Nm1.

[0068] [Action and effect] Next, the operation and effects of the motor bearing system 20 according to this embodiment will be described. As described above, in this embodiment, the control device 50 in the motor bearing system 20 activates the brake mechanism 9 to lock the sleeve 7 of the bearing 3 so that the rolling bearing functions when the motor rotation speed is below the switching threshold, stops the brake mechanism 9 to release the sleeve 7 so that the gas bearing functions when the motor rotation speed is equal to or greater than the switching threshold, and activates the brake mechanism 9 when the motor rotation speed is equal to or greater than the switching threshold and is in a resonance avoidance rotation range corresponding to the resonance rotation range of the gas bearing.

[0069] According to this embodiment, when the motor rotation speed is equal to or higher than the switching threshold, the control device 50 generally stops the brake mechanism 9 to allow the gas bearing to function. However, when the motor rotation speed is within the resonance avoidance rotation range, the control device 50 exceptionally activates the brake mechanism 9. This allows the brake mechanism 9 to apply a braking force to the sleeve 7 of the bearing 3 when the motor rotation speed is within the resonance avoidance rotation range, thereby enabling the relative rotation speed between the sleeve 7 and the fixed member 8, i.e., the rotation speed of the gas bearing, to be controlled independently of the motor rotation speed. In particular, by decelerating the sleeve 7 with the brake mechanism 9, the gas bearing can be temporarily set to a rotation speed lower than the motor rotation speed. As a result, the rotation speed of the gas bearing can be quickly moved out of the resonance rotation range without stagnation within the resonance rotation range. This makes it possible to avoid resonance of the gas bearing.

[0070] Furthermore, according to this embodiment, when the motor rotation speed is increasing and the motor rotation speed or the sleeve rotation speed enters the resonance avoidance rotation range, control device 50 controls brake mechanism 9 to maintain the sleeve rotation speed below the resonance rotation range, and when the motor rotation speed leaves the resonance avoidance rotation range, stops brake mechanism 9 to cause the sleeve rotation speed to rise sharply. This allows the gas bearing rotation speed to quickly leave the resonance rotation range when the motor rotation speed increases, making it possible to effectively avoid resonance in the gas bearing.

[0071] Furthermore, according to this embodiment, when the motor rotation speed is decreasing and the motor rotation speed or sleeve rotation speed enters the resonance avoidance rotation range, control device 50 controls brake mechanism 9 to rapidly decrease the sleeve rotation speed to maintain it below the resonance rotation range, and when the motor rotation speed leaves the resonance avoidance rotation range, stops brake mechanism 9. In this way, when the motor rotation speed is decreasing, the gas bearing rotation speed can be quickly caused to leave the resonance rotation range, making it possible to effectively avoid resonance in the gas bearing.

[0072] Furthermore, according to this embodiment, when the motor rotation speed is in the resonance avoidance rotation range, the control device 50 performs duty control on the brake mechanism 9 to adjust the braking force applied from the brake mechanism 9 to the sleeve 7. This makes it possible to adjust the braking force applied from the brake mechanism 9 to the sleeve 7 with a simple control configuration.

[0073] Furthermore, according to this embodiment, when the brake mechanism 9 releases the sleeve 7, the motor bearing system 20 rotates as a whole relative to the fixed member 8 in conjunction with the rotation of the rotating shaft 2, with the outer peripheral surface 7s of the sleeve 7 spaced apart from the inner peripheral surface 8s of the fixed member 8, thereby realizing a gas bearing. As a result, by releasing the outer ring 5 of the bearing 3 via the sleeve 7 with the brake mechanism 9, it is possible to switch the bearing 3 from a rolling bearing to a gas bearing. Therefore, according to this embodiment, it is not necessary to use a sliding bearing and a rolling bearing that are configured as separate bodies, nor to move the inner ring or outer ring of the rolling bearing relative to one another in the axial direction, as in the technology described in Patent Document 1 above, and therefore switching between a rolling bearing and a gas bearing can be performed with a simple configuration.

[0074] Furthermore, according to this embodiment, motor bearing system 20 further includes gas passage 11 for supplying gas to gap SP between outer peripheral surface 7s of sleeve 7 and inner peripheral surface 8s of fixed member 8, and pump 12 provided on gas passage 11 for pumping the gas, and control device 50 controls pump 12 to supply gas from gas passage 11 to gap SP when the motor rotation speed is equal to or higher than the switching threshold. This makes it possible to accurately form a gas layer in gap SP between sleeve 7 and fixed member 8, making it possible to effectively realize a gas bearing.

[0075] [Variations] Various modifications of the above-described embodiment will be described below. Note that the modifications described below can be implemented in combination with each other.

[0076] (Variation 1) In the above-described embodiment, a configuration was adopted in which the rolling bearing was disposed radially inward and the gas bearing was disposed radially outward ( FIG. 1 ). In this embodiment, the outer ring 5 of the bearing 3 (to which braking force is applied) corresponds to the "first raceway ring portion" in the present invention, and the inner ring 4 of the bearing 3 corresponds to the "second raceway ring portion" in the present invention. In contrast, Modification 1 adopts a configuration in which the rolling bearing is disposed radially outward and the gas bearing is disposed radially inward. In Modification 1, the inner ring of the bearing (to which braking force is applied) corresponds to the "first raceway ring portion" in the present invention, and the outer ring of the bearing corresponds to the "second raceway ring portion" in the present invention. Resonance avoidance control similar to that of the above-described embodiment can also be applied to Modification 1.

[0077] (Variation 2) Next, Modification 2 changes the duty ratio applied in the duty control for the brake mechanism 9 in the resonance avoidance control. Specifically, Modification 2 sets the duty ratio applied in the duty control for a predetermined period immediately after the motor rotation speed enters the resonance avoidance rotation range (hereinafter referred to as the "initial duty ratio") based on the rate of change (absolute value) of the motor rotation speed.

[0078] The resonance avoidance control according to this modified example 2 will be described in detail with reference to Fig. 9. Fig. 9(a) shows a map that determines the initial duty ratio to be applied depending on the rate of change (meaning an absolute value, the same applies hereinafter) of the motor rotation speed. As shown in Fig. 9(a), the smaller the rate of change of the motor rotation speed, the smaller the initial duty ratio that the control device 50 applies. Note that when the rate of change of the motor rotation speed reaches or exceeds a predetermined value, the control device 50 applies a fixed initial duty ratio.

[0079] Next, FIG. 9(b) is a time chart showing a specific example of resonance avoidance control (duty control) according to Modification 2. Here, an example is taken of resonance avoidance control that is performed when the rate of change of the motor rotation speed is small. In this case, the control device 50 limits the braking force applied by the brake mechanism 9 at the beginning of the resonance avoidance control (a predetermined period) by setting the initial duty ratio to a small value. As a result, as shown in FIG. 9(b), the sleeve rotation speed temporarily exceeds the above-mentioned lower limit value Ns1.

[0080] According to variant 2, when the rate of change of the motor rotation speed is small, the initial duty ratio is set to a small value, so that the braking force applied by the brake mechanism 9 can be limited. As a result, it is possible to suppress the discomfort felt by the driver, particularly the sense of deceleration, during slow acceleration.

[0081] (Variation 3) Next, Modification 3 controls the braking force applied from brake mechanism 9 during resonance avoidance control according to the direction of vibration (resonance) generated in the gas bearing. Specifically, Modification 3 provides multiple brake mechanisms 9 to apply braking force to multiple positions in the circumferential direction of sleeve 7, and applies braking force to positions in the circumferential direction of sleeve 7 according to the direction of vibration generated in the gas bearing.

[0082] First, the configuration of the motor bearing system according to Modification 3 will be described with reference to Fig. 10. Fig. 10 is a cross-sectional view that schematically shows the motor bearing system according to Modification 3. In Fig. 10, for ease of explanation, the inner ring 4 and outer ring 5 of the bearing 3 are omitted (the same applies to Figs. 11 and 12).

[0083] As shown in Fig. 10, the motor bearing system 20a according to the third modification includes four brake mechanisms 9x1, 9x2, 9y1, and 9y2 spaced evenly at 90-degree intervals along the circumferential direction, and two vibration sensors 33x and 33y. The brake mechanisms 9x1 and 9x2 are arranged opposite each other in the lateral direction and are capable of applying a braking force to the sleeve 7 in the lateral direction (both leftward and rightward). The brake mechanisms 9y1 and 9y2 are arranged opposite each other in the vertical direction and are capable of applying a braking force to the sleeve 7 in the vertical direction (both upward and downward). The vibration sensor 33x is configured to detect lateral vibrations of the bearing 3, and the vibration sensor 33y is configured to detect vertical vibrations of the bearing 3.

[0084] Next, an example of resonance avoidance control according to Modification 3 will be described with reference to FIG. 11. FIG. 11(a) is a schematic cross-sectional view of motor bearing system 20a similar to FIG. 10, and FIG. 11(b) is a schematic longitudinal cross-sectional view of motor bearing system 20a along the axial direction. Here, as shown in FIG. 11(a), a case where downward vibration (arrow A11) occurs in bearing 3 (i.e., gas bearing) is taken as an example. This vibration is detected by vibration sensor 33y. In this case, as shown in FIG. 11(b), rotating shaft 2 and gas bearing tilt downward (arrow A12). To return the tilted state to its original position, control device 50 controls brake mechanism 9y2, located below, to apply a braking force. That is, brake mechanism 9y2 applies a suction force to the lower portion of sleeve 7 (arrow A13). This suppresses vibration (resonance) of the gas bearing.

[0085] Next, another example of resonance avoidance control according to Modification 3 will be described with reference to FIG. 12. FIG. 12(a) is a schematic cross-sectional view of motor bearing system 20a similar to FIG. 10, and FIG. 12(b) is a schematic longitudinal cross-sectional view of motor bearing system 20a along the axial direction. Here, as shown in FIG. 12(a), an example is given in which upward vibration (arrow A21) occurs in the gas bearing. This vibration is detected by vibration sensor 33y. In this case, as shown in FIG. 12(b), rotating shaft 2 and the gas bearing tilt upward (arrow A22). To return the tilted state to its original position, control device 50 controls brake mechanism 9y1, located above, to apply a braking force. In other words, brake mechanism 9y1 applies a suction force to the upper portion of sleeve 7 (arrow A23). This suppresses vibration (resonance) in the gas bearing.

[0086] 11 and 12 illustrate resonance avoidance control for dealing with vertical vibrations. However, the control device 50 can also perform similar resonance avoidance control for lateral vibrations. In this case, the control device 50 may perform control to apply a braking force from one of the brake mechanisms 9x1 and 9x2. When vibrations having both lateral and vertical components occur, the control device 50 may perform both control to apply a braking force from one of the brake mechanisms 9x1 and 9x2 and control to apply a braking force from one of the brake mechanisms 9y1 and 9y2. In this case, the control device 50 may determine the relationship between the magnitude of the lateral vibrations and the magnitude of the vertical vibrations from the detection results of the vibration sensors 33x and 33y, and adjust the magnitude of the braking force applied from one of the brake mechanisms 9x1 and 9x2 and the magnitude of the braking force applied from one of the brake mechanisms 9y1 and 9y2, respectively. Specifically, the ratio between the magnitude of the braking force applied from one of the brake mechanisms 9x1, 9x2 and the magnitude of the braking force applied from one of the brake mechanisms 9y1, 9y2 can be set according to the ratio between the magnitude of the lateral vibration and the magnitude of the vertical vibration.

[0087] In this third variation, motor bearing system 20a further includes two vibration sensors 33x, 33y that detect vibrations generated in the gas bearing, and multiple brake mechanisms 9x1, 9x2, 9y1, 9y2 that are provided to apply braking forces to multiple positions around the sleeve 7, and control device 50 controls the operation of one or more of the multiple brake mechanisms 9x1, 9x2, 9y1, 9y2 that correspond to the direction of vibration detected by the two vibration sensors 33x, 33y. This makes it possible to effectively suppress vibrations in various directions that occur in the gas bearing due to resonance.

[0088] (Variation 4) Next, in Modification 4, when it is determined that the vibration is increasing, the position of the resonant rotation range (in other words, the resonant frequency (resonant point)) is changing, or the resonant rotation range is expanding, based on the vibration of bearing 3 detected by vibration sensor 33, a notification to that effect is provided. For example, control device 50 controls display device 40 to display that the gas bearing is deteriorating due to aging. [Explanation of symbols]

[0089] 1 motor 2 rotation axes 3. Bearings 4. Inner Circle 5 outer ring 6 rolling elements 7 Sleeve 7p protrusion 7s outer surface 8 Fixing member 8s Inner surface 9 Brake mechanism 11 Gas passage 12 Pump 20 Motor Bearing System 31 Motor rotation speed sensor 32 Sleeve rotation speed sensor 33 Vibration Sensor 50 Control device 100 Motor System

Claims

1. 1. A motor bearing system comprising: a bearing provided on an outer periphery of a rotating shaft of a motor to support the rotating shaft, the bearing comprising: a first raceway ring portion and a second raceway ring portion each formed to extend circumferentially and arranged at a distance from each other so as to face each other in a radial direction; and a plurality of rolling elements interposed between the first raceway ring portion and the second raceway ring portion; a brake mechanism configured to switch between a state in which the bearing can function as a rolling bearing by fixing the first raceway portion of the bearing, and a state in which the bearing can function as a gas bearing by releasing the first raceway portion of the bearing; and a motor rotation speed sensor for detecting the motor rotation speed of the motor; a control device configured to control the brake mechanism based on the motor rotation speed detected by the motor rotation speed sensor; and The control device When the motor rotation speed is less than a predetermined value, the brake mechanism is operated to fix the first raceway portion so as to allow the rolling bearing to function, and when the motor rotation speed is equal to or greater than the predetermined value, the brake mechanism is stopped to release the first raceway portion so as to allow the gas bearing to function; when the motor rotation speed is equal to or greater than the predetermined value and is within a predetermined rotation range corresponding to a resonance rotation range of the gas bearing, the brake mechanism is activated. A motor bearing system characterized by being configured as follows.

2. 2. The motor bearing system of claim 1, wherein the control device is configured to, when the motor rotation speed or the rotation speed of the first raceway ring portion enters the predetermined rotation range while the motor rotation speed is increasing, control the brake mechanism to maintain the rotation speed of the first raceway ring portion below the resonance rotation range, and when the motor rotation speed leaves the predetermined rotation range, stop the brake mechanism to rapidly increase the rotation speed of the first raceway ring portion.

3. 3. The motor bearing system according to claim 1, wherein the control device is configured to control the brake mechanism so that, when the motor rotation speed or the rotation speed of the first raceway ring portion enters the predetermined rotation range while the motor rotation speed is decreasing, the rotation speed of the first raceway ring portion is rapidly decreased to maintain it below the resonance rotation range, and to stop the brake mechanism when the motor rotation speed leaves the predetermined rotation range.

4. the brake mechanism is configured to apply a braking force to the first race portion to fix the first race portion; 3. The motor bearing system according to claim 1, wherein the control device is configured to perform duty control on the brake mechanism to adjust the braking force applied to the first raceway portion from the brake mechanism when the motor rotation speed is within the predetermined rotation range.

5. 5. The motor bearing system according to claim 4, wherein the control device is configured to set the duty ratio applied in the duty control during a predetermined period immediately after the motor rotation speed enters the predetermined rotation range to a smaller value as the absolute value of the rate of change of the motor rotation speed decreases.

6. the motor bearing system further includes one or more vibration sensors that detect vibrations occurring in the bearing, and includes a plurality of the brake mechanisms that are provided to apply braking forces to a plurality of positions in the circumferential direction of the first raceway portion in order to fix the first raceway portion; The control device is configured to perform control to activate one or more of the brake mechanisms corresponding to the direction of the vibration detected by the one or more vibration sensors, among the plurality of brake mechanisms. The motor bearing system of claim 1 .

7. the first raceway ring portion is provided radially outward of the plurality of rolling elements, and the second raceway ring portion is provided radially inward of the plurality of rolling elements, the motor bearing system a fixed member that includes an inner peripheral surface that extends along an outer peripheral surface of the first raceway ring portion and is provided with a gap between the inner peripheral surface and the outer peripheral surface, and that is fixed so as not to rotate in accordance with the rotation of the rotating shaft; When the brake mechanism releases the first raceway ring portion, the outer peripheral surface of the first raceway ring portion is separated from the inner peripheral surface of the fixed member, and the entire bearing rotates relative to the fixed member in accordance with the rotation of the rotating shaft, thereby causing the bearing to function as the gas bearing.

3. The motor bearing system according to claim 1 or 2.

8. the motor bearing system further includes a gas passage for supplying gas to the gap between the outer circumferential surface of the first raceway ring portion and the inner circumferential surface of the fixed member, and a pump provided on the gas passage for pumping the gas, the control device is configured to control the pump to supply the gas from the gas passage to the gap when the motor rotation speed is equal to or greater than the predetermined value.

8. The motor bearing system of claim 7.

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