Motor bearing system

Abstract

To prevent vibration and abnormal sound by whirling of a rotation shaft when switching a bearing from a sliding bearing to a rolling bearing.SOLUTION: A motor bearing system 20 includes: a bearing 4 configured to support a rotation shaft 2 of a motor 1; a clutch 10 configured to switch the state between a fixed state in which the bearing is fixed to the rotation shaft and functions as a rolling bearing and a released state in which the bearing is released from the rotation shaft and functions as a sliding bearing (gas bearing) using gas lubrication; a shaft center position sensor 37 for detecting a shaft center position of the rotation shaft; and a control device 50 configured to control the clutch to switch the state between the fixed state and the released state. In a situation where the state of the clutch is switched from the released state to the fixed state, the control device controls an actuator 15 to switch the clutch from the released state to the fixed state gradually according to the eccentricity of the rotation shaft corresponding to the shaft center position detected by the shaft center position sensor.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to a bearing system for a motor.

Background Art

[0002] Conventionally, for example, rolling bearings and sliding bearings have been used as bearings for supporting the rotating shafts of power sources (engines or motors) of vehicles. A rolling bearing has low friction in a low rotation region, while a sliding bearing has high friction in a low rotation region. On the other hand, a rolling bearing has a finite lifespan due to rolling fatigue, while a sliding bearing has a permanent lifespan under appropriate lubrication conditions.

[0003] Here, a technique has been proposed in which a system is configured to have both a rolling bearing and a sliding bearing, and the bearing to be applied is switched according to the characteristics of each bearing as described above. For example, Patent Document 1 describes a sliding bearing that supports a rotating body housed in a housing, a rolling bearing that is arranged in parallel with the sliding bearing and supports the rotating body, and a moving mechanism that switches the bearing that functions to support the rotating body by axially moving the inner ring or outer ring of the rolling bearing. In particular, in this system, the radial clearance of the rolling bearing is changed by relatively moving the inner ring or outer ring axially by driving a moving device. When the radial clearance of the rolling bearing is larger than the radial clearance of the sliding bearing, only the sliding bearing functions, while when the radial clearance of the rolling bearing is smaller than the radial clearance of the sliding bearing, only the rolling bearing functions.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a general engine (internal combustion engine), it is effective to apply a sliding bearing in the high rotation region. Usually, fluid lubrication with lubricating oil is used for this sliding bearing. By the way, in a motor that operates at a higher rotation speed than an engine, if such a sliding bearing is applied in the high rotation region of the motor, there is a problem that the fluid friction and resistance of the lubricating oil increase, and the electricity cost of the motor decreases.

[0006] Due to the above problems, the inventor of the present case considered applying a gas bearing (typically an air bearing) that uses gas lubrication (gas lubrication) with a lower viscosity than lubricating oil as a sliding bearing. In order to realize such a sliding bearing, it is necessary to surely form a gas layer between the bearing and the rotating shaft in order to prevent contact between the bearing and the rotating shaft. It is considered good to utilize the so-called wedge effect and throttling effect that occur between the bearing and the rotating shaft for the formation of this gas layer. However, since the wedge effect and the throttling effect can basically be obtained only in the high rotation region of the motor, in the method of utilizing these effects, there is a possibility that the bearing and the rotating shaft come into contact (solid contact) in the low rotation region of the motor.

[0007] From the above, the inventor of the present case considered switching the bearing to be applied between a rolling bearing and a sliding bearing according to the rotation speed (shaft rotation speed) of the motor. That is, it was considered to use a rolling bearing in the low rotation region and a sliding bearing in the high rotation region. However, as a result of intensive research, the inventor of the present case found that when switching the bearing from a sliding bearing (gas bearing) to a rolling bearing, that is, when fixing the rotating shaft with the bearing, if the axis of the rotating shaft is eccentric, the rotating shaft will wobble. Such wobbling of the rotating shaft may cause vibrations and abnormal noises.

[0008] Therefore, the present invention has been made to solve the above-described problems of the prior art, and an object thereof is to provide a bearing system for a motor capable of preventing vibrations and abnormal noises caused by the wobbling of the rotating shaft when switching the bearing from a sliding bearing to a rolling bearing.

Means for Solving the Problems

[0009] To achieve the above object, the present invention provides a bearing system for a motor, comprising a bearing configured to support the rotating shaft of the motor, a switching mechanism configured to be switchable between a first state in which the bearing is fixed to the rotating shaft and functions as a rolling bearing, and a second state in which the bearing is released from the rotating shaft and functions as a sliding bearing using gas lubrication, a shaft center position sensor for detecting the shaft center position of the rotating shaft, and a control device configured to control the switching mechanism so as to switch between the first state and the second state. The control device is configured to control the switching mechanism to gradually switch from the second state to the first state according to the eccentricity of the rotating shaft corresponding to the shaft center position detected by the shaft center position sensor in a situation of switching from the second state to the first state.

[0010] In the present invention configured as described above, the switching from the second state in which the bearing functions as a sliding bearing (gas bearing) to the first state in which the bearing functions as a rolling bearing is gradually performed according to the eccentricity, without immediately performing the switching. Therefore, according to the present invention, it is possible to switch the bearing from a sliding bearing to a rolling bearing at a timing when the eccentricity becomes small, that is, when the shaft center of the rotating shaft is sufficiently close to the center. Thus, according to the present invention, it is possible to prevent vibrations and abnormal noises caused by the wobbling of the rotating shaft when switching the bearing from a sliding bearing to a rolling bearing.

[0011] In the present invention, preferably, when the eccentricity is equal to or greater than a threshold value, in addition to the first control for shifting the switching mechanism in the direction from the second state to the first state, the control device performs a second control for shifting the switching mechanism in the direction from the first state to the second state, and repeats the first and second controls until the eccentricity becomes less than the threshold value. According to the present invention configured as described above, it is possible to accurately perform the complete fixing of the bearing at a timing when the shaft center of the rotating shaft is sufficiently close to the center. In other words, it is possible to accurately perform the switching of the switching mechanism to the complete fixed state, and effectively prevent the wobbling of the rotating shaft.

[0012] In the present invention, preferably, the threshold value is set in advance based on the centrifugal force generated on the rotating shaft according to the rotational speed and eccentricity of the rotating shaft. According to the present invention, by determining the current eccentricity using such a threshold value, it is possible to accurately determine whether the axis of the rotating shaft has approached the center to such an extent that the rotating shaft does not wobble.

[0013] In the present invention, preferably, the bearing includes an outer ring provided so as to surround the outer periphery of the rotating shaft, an inner ring disposed inside the outer ring and provided with a gap between the inner ring and the rotating shaft, and a plurality of rolling elements interposed between the outer ring and the inner ring. The switching mechanism includes a clutch provided on the outer periphery of the rotating shaft in parallel with the bearing along the axial direction of the rotating shaft and provided so as to be movable in the axial direction. The clutch forms a first state by moving axially toward the bearing side and pressing the bearing, thereby fixing the inner ring of the bearing to the rotating shaft, and forms a second state by moving axially away from the bearing and separating from the bearing, thereby releasing the inner ring from the rotating shaft. The control device is configured to perform control to gradually switch the clutch from the second state to the first state according to the eccentricity in a situation where the clutch is switched from the second state to the first state. In the present invention configured as described above, by moving the clutch axially on the rotating shaft and changing the fixing (first state) and release (second state) of the inner ring of the bearing with respect to the rotating shaft, the bearing can be switched between a rolling bearing and a sliding bearing and made to function. Therefore, according to the present invention, unlike the technique described in Patent Document 1 above, a separately configured sliding bearing and rolling bearing are not used, and the inner or outer ring of the rolling bearing is not relatively moved in the axial direction. Thus, the switching between the rolling bearing and the sliding bearing can be performed with a simple configuration.

[0014] In a preferred example of the present invention, the control device is configured to control the switching mechanism to gradually switch from the second state to the first state according to the eccentricity when the vehicle equipped with the bearing system of the motor decelerates.

Advantages of the Invention

[0015] According to the bearing system of the motor according to the present invention, it is possible to prevent vibrations and abnormal noises caused by the wobbling of the rotating shaft when switching the bearing from a sliding bearing to a rolling bearing.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0017] Hereinafter, with reference to the accompanying drawings, a bearing system of a motor according to an embodiment of the present invention will be described.

[0018] [Device Configuration] FIG. 1 is a schematic configuration diagram of a motor system to which a bearing system of a motor according to an embodiment of the present invention is applied. FIG. 1 is a cross-sectional view of the motor system 100 taken along the axial direction. As shown in FIG. 1, the motor system 100 is a system for driving a vehicle, and mainly includes a motor (electric motor) 1 including a rotor 1a and a stator 1b, a rotating shaft 2 of the motor 1, and a pair of bearings 4 (only one bearing 4 is shown in FIG. 1, and the illustration of the other bearing 4 is omitted) that support the rotating shaft 2. The motor 1, the rotating shaft 2, and the bearing 4 are housed in a housing (not shown).

[0019] The bearing 4 is a radial bearing that supports the rotating shaft 2, and includes an outer ring 6 provided so as to surround the outer periphery of the rotating shaft 2, an inner ring 7 disposed inside (radially inside) the outer ring 6 and provided with a gap between the inner ring 7 and the rotating shaft 2, and a plurality of rolling elements (typically “rollers”) 5 interposed between the outer ring 6 and the inner ring 7. Further, the bearing 4 has an inner ring fixing portion 8 provided inside (radially inside) the inner ring 7. The inner ring fixing portion 8 is preferably configured integrally with the inner ring 7, but may be configured separately from the inner ring 7.

[0020] Further, the motor system 100 further includes a clutch 10 configured to be able to switch between a fixed state (first state) in which the inner ring 7 of the bearing 4 is fixed (connected) to the rotating shaft 2 and a released state (second state) in which the inner ring 7 is separated from the rotating shaft 2, and a pedestal 12 fixed to the rotating shaft 2 and provided facing the inner ring fixing portion 8 of the bearing 4. In the motor system 100, the bearing system 20 of the motor according to the present embodiment mainly includes the bearing 4 and the clutch 10. The clutch 10 is also provided for the other bearing 4 whose illustration is omitted in FIG. 1.

[0021] Specifically, the clutch 10 is provided on the outer periphery of the rotating shaft 2 and is arranged in parallel with the bearing 4 along the axial direction. Also, a pair of clutches 10 are provided so as to sandwich the bearing 4 in the axial direction. Further, the clutch 10 is attached to the rotating shaft 2 so as to rotate together with the rotating shaft 2 and is provided so as to be axially movable on the rotating shaft 2 (the white arrow in FIG. 1). For example, the clutch 10 moves on a pedestal 12 fixed to the rotating shaft 2. Note that the clutch 10 may be directly moved on the rotating shaft 2 without providing the pedestal 12.

[0022] The clutch 10 configured as described above forms a fixed state in which the inner ring 7 is fixed to the rotating shaft 2 by moving axially toward the bearing 4 side and biasing the bearing 4 (pressed by an actuator 15 described later), while forming a released state in which the inner ring 7 is separated from the rotating shaft 2 by moving axially to the side opposite to the bearing 4 and separating from the bearing 4. When the clutch 10 is in the fixed state, the bearing 4 functions as a rolling bearing, and when the clutch 10 is in the released state, the bearing 4 functions as a sliding bearing. In particular, in the present embodiment, the bearing 4 functions as a sliding bearing using gas lubrication, typically an air bearing. Details thereof will be described later.

[0023] Specifically, the outer wall surface of the clutch 10 facing the bearing 4 abuts against the outer wall surface of the inner ring fixing portion 8 facing the clutch 10, thereby forming a fixed state in which the clutch 10 fixes the inner ring 7 to the rotating shaft 2. More specifically, the bearing 4 has a first inclined surface 8a inclined with respect to the radial direction and the axial direction of the rotating shaft 2 when viewed in a cross-section along the axial direction, formed at the end on the inner ring 7 side, that is, the inner ring fixing portion 8. The clutch 10 has a second inclined surface 10a inclined with respect to the radial direction and the axial direction so as to be able to abut against the first inclined surface 8a of the bearing 4, formed to face the first inclined surface 8a when viewed in a cross-section along the axial direction. Then, a fixed state is formed by the abutment of the first inclined surface 8a of the inner ring fixing portion 8 and the second inclined surface 10a of the clutch 10, and a released state is formed by the separation of the first inclined surface 8a and the second inclined surface 10a.

[0024] Figure 1 shows a conceptual diagram schematically showing a bearing 4, a clutch 10, etc. Hereinafter, with reference to FIGS. 2 to 4, the specific configuration of the bearing system 20 of the motor according to the present embodiment will be described. FIG. 2 shows a perspective view of the bearing system 20 of the motor according to the present embodiment, FIG. 3 shows a cross-sectional view of the bearing system 20 of the motor in the released state, and FIG. 4 shows a cross-sectional view of the bearing system 20 of the motor in the fixed state.

[0025] As shown in FIG. 2, the bearing system 20 of the motor further has an actuator 15 configured to be movable to move the clutch 10 so as to switch between the fixed state and the released state (in FIGS. 3 and 4, for convenience of explanation, the illustration of the actuator 15 is omitted). Specifically, the actuator 15 moves the clutch 10 so as to switch the clutch 10 between the fixed state and the released state, and operates so as to press the clutch 10 against the bearing 4 in the fixed state, that is, generates a pressing force. Further, a pair of actuators 15 are provided to face each other on the outer periphery of the rotating shaft 2, and another pair of these are provided with the bearing 4 interposed therebetween, and each of the pair of clutches 10 is configured to be axially movable. Note that various known mechanisms can be applied to the actuator 15 as a mechanism for axially moving the clutch 10. Further, the clutch 10 and the actuator 15 correspond to the "switching mechanism" in the present invention.

[0026] Also, as shown in FIG. 2, the bearing system 20 of the motor has a detent 17 for reliably fixing the clutch 10 to the rotating shaft 2. Typically, this detent 17 is constituted by a convex portion and a concave portion provided on each of the clutch 10 and the rotating shaft 2, and these convex portion and concave portion are engageable with each other and are formed to be relatively slidable in the axial direction. With the detent 17 configured in this way, the clutch 10 can rotate together (interlockingly) with the rotating shaft 2, while being axially movable on the rotating shaft 2.

[0027] Next, as shown in FIGS. 3 and 4, the inner ring fixing portion 8 of the bearing 4 is formed in a substantially cylindrical shape as a whole so as to surround the rotating shaft 2, and when viewed in a cross section along the axial direction, on the surfaces (i.e., both end surfaces) facing each of the pair of clutches 10, the above-described first inclined surface 8a is formed. This first inclined surface 8a is inclined in a direction away from the rotating shaft 2 as it advances toward the clutch 10 side when viewed in a cross section along the axial direction. Also, each of the pair of clutches 10 is formed in a substantially cylindrical shape (in other words, substantially annular shape) as a whole so as to surround the rotating shaft 2, and when viewed in a cross section along the axial direction, on the surface facing the bearing 4, the above-described second inclined surface 10a is formed. This second inclined surface 10a is inclined in a direction approaching the rotating shaft 2 as it advances toward the bearing 4 side when viewed in a cross section along the axial direction. As shown in FIG. 4, the first inclined surface 8a of the inner ring fixing portion 8 and the second inclined surface 10a of the clutch 10 are in contact with each other without a gap, and by the contact of these first inclined surface 8a and second inclined surface 10a, the fixed state of the bearing 4 by the clutch 10 is formed. In this case, due to the pressing force applied from the actuator 15 to the clutch 10, the second inclined surface 10a is biased against the first inclined surface 8a. Note that if the angles of the first inclined surface 8a and the second inclined surface 10a with respect to the axial direction are set to relatively large angles (i.e., steep inclinations), it is advantageous in ensuring the load capacity of the gas bearing described later.

[0028] Next, with reference to FIG. 5, the electrical configuration of the bearing system 20 of the motor according to this embodiment will be described. As shown in FIG. 5, the bearing system 20 of the motor includes various sensors indicated by reference numerals 31 to 40, a control device 50 into which various signals are input from these various sensors, and an actuator 15 that is controlled by a control signal supplied from the control device 50. The control device 50 is composed of a computer including one or more processors 50a (typically CPUs), a memory 50b such as a ROM and a RAM that stores various programs (including basic control programs such as an OS and application programs that are launched on the OS and realize specific functions) and various data interpreted and executed on the processor 50a. Note that the control device 50 controls not only the actuator 15 but also the motor 1 via an inverter (not shown).

[0029] Specifically, the bearing system 20 of the motor mainly includes a vehicle speed sensor 31 that detects the speed of the vehicle (vehicle speed), an acceleration sensor 32 that detects the acceleration of the vehicle, an accelerator opening sensor 33 that detects the accelerator opening corresponding to the depression amount of the accelerator pedal, a brake sensor 34 that detects the depression amount of the brake pedal, a shaft rotation speed sensor 35 that detects the rotation speed (unambiguously the number of revolutions) of the rotating shaft 2 of the motor 1, a bearing rotation speed sensor 36 that detects the rotation speed (unambiguously the number of revolutions) of the bearing 4, a shaft center position sensor 37 that detects the position in the radial direction of the center axis of the rotating shaft 2, a shaft load sensor 38 that detects the load (shaft load) applied to the rotating shaft 2, an outer bearing load sensor 39 that detects the load applied to the outer ring 6 of the bearing 4, and an inner bearing load sensor 40 that detects the load applied to the inner ring 7 of the bearing 4.

[0030] In this embodiment, based on the detection signals from the various sensors 31 to 40 described above, the control device 50 controls the actuator 15 to switch the clutch 10 between the fixed state and the released state so as to cause the bearing 4 to function by switching between a rolling bearing and a sliding bearing (hereinafter, this control is referred to as "motor shaft controlled operation"). Typically, the control device 50 executes such motor shaft controlled operation based on the rotational speed of the rotating shaft 2 of the motor 1 detected by the shaft rotational speed sensor 35 (hereinafter, appropriately referred to as "shaft rotational speed" or "motor rotational speed").

[0031] [Motor shaft controlled operation] Next, the motor shaft controlled operation according to this embodiment will be specifically described.

[0032] First, the basic concept of the motor shaft controlled operation according to this embodiment will be described. Conventionally, rolling bearings and sliding bearings have been used as bearings for supporting the rotating shaft of a vehicle's power source. A rolling bearing has low friction in the low rotation region, while a sliding bearing has high friction in the low rotation region. On the other hand, a rolling bearing has a finite lifespan due to rolling fatigue, while a sliding bearing has a permanent lifespan under appropriate lubrication conditions. In a general engine (internal combustion engine), it is effective to apply a sliding bearing in the high rotation region. Usually, fluid lubrication with lubricating oil is used for this sliding bearing. However, in the motor 1 that operates at a higher rotation speed than the engine, if such a sliding bearing is applied in the high rotation region of the motor 1, there is a problem that the fluid friction and resistance of the lubricating oil increase, resulting in a decrease in the electricity cost of the motor.

[0033] Therefore, in the present embodiment, an attempt was made to apply a gas bearing (typically an air bearing) that uses lubrication with a gas having a lower viscosity than the lubricating oil as a sliding bearing. In order to realize this gas bearing, it is necessary to surely form a gas layer between the bearing 4 and the rotating shaft 2 in order to prevent contact (solid contact) between the bearing 4 and the rotating shaft 2. In the present embodiment, in order to surely form such a gas layer, the so-called wedge effect and throttling effect generated between the bearing 4 and the rotating shaft 2 are utilized. However, since the wedge effect and the throttling effect can basically be obtained only in the high rotation region of the motor 1, in the method of utilizing these effects, there is a possibility that the bearing 4 and the rotating shaft 2 may come into contact in the low rotation region of the motor 1. From the above, in the present embodiment, while the bearing 4 functions as a rolling bearing in the low rotation region, the control device 50 switches the above-described clutch 10 between the fixed state and the released state according to the motor rotation speed so that the bearing 4 functions as a gas bearing (sliding bearing) in the high rotation region (FIGS. 3 and 4).

[0034] Next, with reference to FIG. 6, the basic concept of the motor shaft control according to the present embodiment will be described more specifically. Here, the motor shaft control according to the present embodiment and the motor shaft control according to the comparative example will be described in comparison. FIG. 6 shows the motor rotation speed on the horizontal axis and the shaft friction torque on the vertical axis.

[0035] In the motor shaft 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 the region R11 (low rotation region) where the motor rotation speed is low, a rolling bearing is applied as the bearing that functions to support the rotating shaft 2, while in the region R12 where the motor rotation speed is higher than the region R11, a sliding bearing is applied as the bearing that functions to support the rotating shaft 2. This control corresponds to the technique described in Patent Document 1.

[0036] In FIG. 6, graph G11 shows the shaft friction torque generated in a rolling bearing, that is, the boundary lubrication friction due to direct contact, and graph G12 shows the shaft friction torque generated in a sliding bearing using fluid lubrication with lubricating oil, that is, the fluid lubrication friction of the lubricating oil. Therefore, the shaft friction torque generated in the motor shaft control according to the above-described comparative example is the sum of the shaft friction torque shown in graph G11 and the shaft friction torque shown in graph G12, that is, the one shown in graph G21. In this case, the reason why the shaft friction torque increases significantly as the motor rotation speed increases in region R12 is due to the increase in friction caused by the deformation of the rolling elements in the rolling bearing as shown in graph G13.

[0037] On the other hand, in the present embodiment, as described above, the control device 50 controls the actuator 15 to switch the clutch 10 between the fixed state and the released state in order to switch the bearing 4 that supports the rotating shaft 2 of the motor 1 between a rolling bearing and a gas bearing. First, in region R11 where the motor rotation speed is low, since almost no wedge effect and throttling effect can be obtained, the control device 50 sets the clutch 10 in the fixed state so that the bearing 4 functions as a rolling bearing.

[0038] Subsequently, when the motor rotation speed exceeds region R11, that is, when entering region R12 that is higher than region R11, a certain degree of wedge effect and throttling effect can be obtained. Therefore, the control device 50 attempts to make the bearing 4 function as a gas bearing. Specifically, in region R13 on the low rotation side in region R12, since the wedge effect and throttling effect are not sufficient, the control device 50 changes the clutch 10 between the fixed state and the released state so as to switch the bearing 4 between a rolling bearing and a gas bearing. Then, in region R14 on the high rotation side in region R12, since the wedge effect and throttling effect are sufficient, the control device 50 sets the clutch 10 in the released state so that the bearing 4 functions as a gas bearing.

[0039] In FIG. 6, graph G14 shows the shaft friction torque generated by the gas bearing, that is, the gas lubrication friction. The shaft friction torque generated in the motor shaft control according to the above-described embodiment is the sum of the shaft friction torque shown in graph G11 and the shaft friction torque shown in graph G14, that is, the one shown in graph G22. Comparing the shaft friction torque according to this embodiment shown in graph G22 with the shaft friction torque according to the comparative example shown in graph G21, it can be seen that according to this embodiment, the shaft friction torque is significantly reduced. Therefore, according to this embodiment, it can be said that the electricity cost can be effectively improved as compared with the comparative example.

[0040] Next, with reference to FIG. 7, the motor shaft control according to this embodiment will be specifically described. FIG. 7 is a time chart showing the motor shaft control according to this embodiment. FIG. 7 shows, in order from the top, the motor rotation speed, the rotation speed when bearing 4 is regarded as a rolling bearing, the rotation speed when bearing 4 is regarded as a gas bearing (sliding bearing), and the state (fixed state or released state) of clutch 10. In FIG. 7, the “first speed” is the motor rotation speed corresponding to the lower limit value of region R13 in FIG. 6 (in other words, the upper limit value of region R11), and the “second speed” is the motor rotation speed corresponding to the lower limit value of region R14 in FIG. 6 (in other words, the upper limit value of region R13). FIG. 7 assumes a situation where the motor rotation speed rises from the first speed to the second speed and the vehicle accelerates.

[0041] Before time t0, the motor rotation speed is less than the first speed (i.e., the motor rotation speed is within region R11), the clutch 10 is in a fixed state, and the bearing 4 functions as a rolling bearing. Then, from time t0, the motor rotation speed begins to exceed the first speed (i.e., the motor rotation speed enters region R12). The control device 50 starts controlling the actuator 15 from the subsequent time t1 so that the clutch 10 shifts from the fixed state to the released state. As a result, while the rotation speed when viewing the bearing 4 as a rolling bearing decreases, the rotation speed when viewing the bearing 4 as a gas bearing begins to increase. After that, at time t2, the clutch 10 is completely switched from the fixed state to the released state, and the control device 50 controls the actuator 15 to maintain the clutch 10 in the released state. After this time t2, while the rotation speed when viewing the bearing 4 as a rolling bearing becomes very small, the rotation speed when viewing the bearing 4 as a gas bearing becomes stable at a large speed, that is, the bearing 4 functions stably as a gas bearing. After that, at time t3, the motor rotation speed reaches the second speed.

[0042] Next, the motor shaft control performed when switching the bearing 4 from a sliding bearing (gas bearing) to a rolling bearing will be described.

[0043] As described above, when switching the bearing 4 from a gas bearing to a rolling bearing, that is, when fixing the rotating shaft 2 with the bearing 4, if the axis of the rotating shaft 2 is eccentric, wobbling of the rotating shaft 2 occurs. That is, when fixing the rotating shaft 2 in a state where the axis is eccentric, wobbling occurs when the rotating shaft 2 rotates. When the rotating shaft 2 wobbles in this way, there is a possibility of generating vibrations, abnormal noises, etc.

[0044] Therefore, in the present embodiment, when the control device 50 switches the bearing 4 from a gas bearing to a rolling bearing, in other words, when the clutch 10 is switched from the released state to the fixed state, in order to prevent the wobbling of the rotating shaft 2, the actuator 15 is controlled to gradually switch the clutch 10 from the released state to the fixed state according to the eccentricity of the rotating shaft 2. That is, the clutch 10 is not switched immediately. The eccentricity indicates the degree of eccentricity of the axial center position (the position in the radial direction of the axis) of the rotating shaft 2. When the value is 0, the axis is centered. As the value increases, the axis moves away from the center. When the value is 1, the rotating shaft 2 contacts the bearing 4. This eccentricity is obtained from the axial center position detected by the axial center position sensor 37.

[0045] Here, when the pressing force applied to the bearing 4 from the clutch 10 is increased as described above, the bearing rotation speed increases, and the axial center of the rotating shaft 2 tends to move away from the center. On the contrary, when the pressing force applied to the bearing 4 from the clutch 10 is decreased, the bearing rotation speed decreases, and the axial center of the rotating shaft 2 tends to approach the center. Therefore, by increasing or decreasing the pressing force, the axial center will move at any time. Therefore, during the repeated process of increasing or decreasing the pressing force, it is possible to create a moment when the axial center is exactly near the center (the eccentricity becomes small) when the pressing force is increased, that is, when the rotating shaft 2 is fixed.

[0046] Therefore, in the present embodiment, when the eccentricity of the rotating shaft 2 is equal to or greater than a predetermined threshold value, in addition to the control (first control) for increasing the pressing force applied from the clutch 10 to the bearing 4, the control device 50 performs control (second control) for temporarily weakening the pressing force applied from the clutch 10 to the bearing 4, and repeats these two controls until the eccentricity becomes less than the threshold value. By repeating the control for increasing the pressing force and the control for weakening the pressing force in this way, when the axis of the rotating shaft 2 sufficiently approaches the center (at the timing when the eccentricity becomes less than the threshold value), the bearing 4 is completely fixed, that is, the clutch 10 is switched to a complete fixed state. Thereby, the wobbling of the rotating shaft 2 can be effectively prevented.

[0047] Next, with reference to FIG. 8, a specific flow of the motor shaft control performed when switching the bearing 4 from a gas bearing to a rolling bearing will be described. FIG. 8 is a flowchart showing the motor shaft control performed when switching the bearing 4 from a rolling bearing to a gas bearing in the present embodiment. This flow is repeatedly executed by the control device 50 at a predetermined cycle. More specifically, the processor 50a in the control device 50 reads out the program stored in the memory 50b and executes the program, thereby realizing the motor shaft control according to this flow.

[0048] First, in step S10, the control device 50 acquires various signals from the various sensors 31 to 40 shown in FIG. 5. Then, in step S11, the control device 50 determines whether the motor 1 is operating. For example, the control device 50 determines whether the motor 1 is operating based on the shaft rotation speed (motor rotation speed) corresponding to the signal supplied from the shaft rotation speed sensor 35. As a result, when the control device 50 determines that the motor 1 is operating (step S11: Yes), it proceeds to step S12, and when it determines that the motor 1 is not operating (step S11: No), it ends the motor shaft control.

[0049] Next, in step S12, the control device 50 determines whether there is a deceleration request for the motor 1. For example, the control device 50 determines whether there is a deceleration request for the motor 1 based on the release of the accelerator pedal indicated by the signal supplied from the accelerator opening sensor 33. As a result, when the control device 50 determines that there is a deceleration request for the motor 1 (step S12: Yes), it proceeds to step S13 to decelerate the motor 1. On the other hand, when the control device 50 determines that there is no deceleration request for the motor 1 (step S12: No), it ends the motor shaft controlled state.

[0050] Next, in step S14, the control device 50 determines whether the shaft rotation speed (motor rotation speed) corresponding to the signal supplied from the shaft rotation speed sensor 35 is less than the second speed, that is, whether the shaft rotation speed has entered from region R14 to region R13 (Fig. 6). Here, the control device 50 determines whether the vehicle has decelerated to a situation where the bearing 4 should be switched from a gas bearing to a rolling bearing. As a result, when the control device 50 determines that the shaft rotation speed is less than the second speed (step S14: Yes), it proceeds to step S15. On the contrary, when the control device 50 determines that the shaft rotation speed is not less than the second speed (step S14: No), it returns to step S14. In this case, the control device 50 repeats the determination in step S14 until the shaft rotation speed becomes less than the second speed.

[0051] Next, in step S15, the control device 50 controls the actuator 15 to shift the clutch 10 in the released state to the fixed state. Specifically, the control device 50 shifts the clutch 10 to a state where it abuts against the bearing 4 (a state where the first inclined surface 8a of the clutch 10 abuts against the second inclined surface 10a of the bearing 4). Then, the control device 50 proceeds to step S16 and controls the actuator 15 so that a predetermined pressing force is applied from the clutch 10 to the bearing 4, that is, so as to increase the pressing force applied from the clutch 10 to the bearing 4. After that, it proceeds to step S17 and acquires various signals from the various sensors 31 to 40.

[0052] Next, in step S18, the control device 50 determines whether the eccentricity of the rotating shaft 2 is less than a predetermined threshold value. Here, the control device 50 determines whether the center of the axis of the rotating shaft 2 has approached the center to such an extent that the wobbling of the rotating shaft 2 does not occur by comparing the current eccentricity with the threshold value. In this case, the control device 50 obtains the eccentricity from the axial position detected by the axial position sensor 37. Also, the control device 50 makes the determination in step S18 using a threshold value set in advance.

[0053] Such a threshold value is set in advance based on the centrifugal force generated on the rotating shaft 2 according to the axial rotation speed and eccentricity of the rotating shaft 2. Basically, if the rotating shaft 2 is fixed in a state where the pressing force applied from the clutch 10 to the bearing 4 is greater than the centrifugal force, the rotating shaft 2 will not shift when fixed. Therefore, the threshold value can be determined based on the relationship between the pressing force and the centrifugal force. However, if an attempt is made to align the axis only by the pressing force, the pressing force needs to overcome the centrifugal force and the frictional force (specifically, the frictional force between the clutch 10 and the bearing 4). For this reason, the threshold value may be defined based on the centrifugal force at the boundary between the region of centrifugal force where the axis can be firmly aligned and the region of centrifugal force where the axis cannot be aligned but the rotating shaft 2 can be held (in a region beyond this, the rotating shaft 2 runs wild). Note that the centrifugal force is a force corresponding to the value obtained by multiplying the eccentricity by the square of the axial rotation speed.

[0054] As a result of step S18 above, when the control device 50 determines that the eccentricity is less than the threshold value (step S18: Yes), it proceeds to step S19. In this case, since the center of the axis of the rotating shaft 2 has approached the center sufficiently and the wobbling of the rotating shaft 2 does not occur, the control device 50 controls the actuator 15 to completely fix the bearing 4, that is, to set the clutch 10 to a complete fixed state. Then, the control device 50 ends the motor shaft control.

[0055] On the other hand, when the control device 50 does not determine that the eccentricity is less than the threshold value (step S18: No), that is, when the eccentricity is greater than or equal to the threshold value, it proceeds to step S20 and controls the actuator 15 to weaken the pressing force applied from the clutch 10 to the bearing 4. That is, the control device 50 temporarily weakens the pressing force. After that, the control device 50 returns to step S16. Thus, by repeating steps S16, S17, S18, and S20, the control device 50 repeats the control of strengthening and weakening the pressing force until the eccentricity becomes less than the threshold value.

[0056] [Operation and Effect] Next, the operation and effect of the bearing system 20 of the motor according to the present embodiment will be described. In the present embodiment, when the control device 50 switches the clutch 10 from the released state to the fixed state, the control device 50 controls the actuator 15 to gradually switch the clutch 10 from the released state to the fixed state according to the eccentricity of the rotating shaft 2 corresponding to the axial position detected by the axial position sensor 37. Thereby, such a switch can be made at a timing when the axis of the rotating shaft 2 is sufficiently close to the center (the timing when the eccentricity becomes small), and it is possible to prevent vibrations and abnormal noises caused by the wobbling of the rotating shaft 2.

[0057] Further, in the present embodiment, when the eccentricity is greater than or equal to the threshold value, in addition to the first control (control for strengthening the pressing force) for shifting the clutch 10 from the released state to the fixed state, the control device 50 performs a second control (control for weakening the pressing force) for shifting the clutch 10 from the fixed state to the released state, and repeats these first and second controls until the eccentricity becomes less than the threshold value. Thereby, at a timing when the axis of the rotating shaft 2 is sufficiently close to the center, the bearing 4 can be accurately fixed, in other words, the clutch 10 can be accurately switched to the completely fixed state, and it is possible to effectively prevent the wobbling of the rotating shaft 2.

[0058] In addition, in the present embodiment, the above threshold value is set in advance based on the centrifugal force generated on the rotating shaft 2 according to the axial rotation speed and eccentricity of the rotating shaft 2. By determining the current eccentricity using such a threshold value, it is possible to accurately determine whether the wobbling of the rotating shaft 2 has occurred and whether the axis of the rotating shaft 2 has approached the center to the extent that the wobbling does not occur.

[0059] In addition, in the present embodiment, the bearing 4 includes an outer ring 6 provided so as to surround the outer periphery of the rotating shaft 2, an inner ring 7 disposed inside the outer ring 6 and provided with a gap between the inner ring 7 and the rotating shaft 2, and a plurality of rolling elements 5 interposed between the outer ring 6 and the inner ring 7. The clutch 10 is provided on the outer periphery of the rotating shaft 2 in parallel with the bearing 4 along the axial direction of the rotating shaft 2 and is provided so as to be movable in the axial direction. The clutch 10 moves toward the bearing 4 side in the axial direction and presses the bearing 4 to fix the inner ring 7 of the bearing 4 to the rotating shaft 2 to form a fixed state. On the other hand, when the clutch 10 moves to the side opposite to the bearing 4 in the axial direction and separates from the bearing 4, the inner ring 7 is released from the rotating shaft 2 to form a released state. The control device 50 performs control to gradually switch the clutch 10 according to the eccentricity when switching the clutch 10 from the released state to the fixed state.

[0060] According to such a present embodiment, by moving the clutch 10 axially on the rotating shaft 2 and changing the fixed state and the released state of the inner ring 7 of the bearing 4 with respect to the rotating shaft 2, the bearing 4 can be switched between a rolling bearing and a sliding bearing and made to function. Therefore, according to the present embodiment, unlike the technique described in Patent Document 1 above, a separately configured sliding bearing and rolling bearing are not used, and the inner ring or outer ring of the rolling bearing is not relatively moved in the axial direction. Thus, the switching between the rolling bearing and the sliding bearing can be performed with a simple configuration.

Explanation of Reference Numerals

[0061] 1 Motor 2 Rotating shaft 4 Bearing 5 Rolling element 6 Outer ring 7 Inner ring 8 Inner ring fixing part 10 Clutch 8a First inclined surface 10a Second inclined surface 15 Actuator 20 Motor bearing system 50 Control device 100 Motor system

Claims

1. A bearing system for a motor, comprising: a bearing configured to support a rotating shaft of the motor; a switching mechanism configured to be able to switch between a first state in which the bearing is fixed to the rotating shaft and functions as a rolling bearing, and a second state in which the bearing is released from the rotating shaft and functions as a sliding bearing using gas lubrication; an axial position sensor configured to detect an axial position of the rotating shaft; a control device configured to control the switching mechanism so as to switch between the first state and the second state; and in a situation where the control device switches from the second state to the first state, the control device is configured to control the switching mechanism to gradually switch from the second state to the first state according to an eccentricity ratio of the rotating shaft corresponding to the axial position detected by the axial position sensor. A bearing system for a motor, characterized in that.

2. When the eccentricity ratio is equal to or greater than a threshold value, the control device performs a first control to shift the switching mechanism in a direction from the second state to the first state, and in addition, performs a second control to shift the switching mechanism in a direction from the first state to the second state, and repeats the first and second controls until the eccentricity ratio becomes less than the threshold value. The bearing system for a motor according to claim 1.

3. The threshold value is set in advance based on a centrifugal force generated on the rotating shaft according to a rotational speed and an eccentricity ratio of the rotating shaft. The bearing system for a motor according to claim 2.

4. The bearing includes an outer ring provided so as to surround an outer periphery of the rotating shaft, an inner ring disposed inside the outer ring and provided with a gap between the inner ring and the rotating shaft, and a plurality of rolling elements interposed between the outer ring and the inner ring. The switching mechanism includes a clutch provided on an outer periphery of the rotating shaft in parallel with the bearing along an axial direction of the rotating shaft and provided so as to be movable in the axial direction. The clutch forms the first state by moving axially toward the bearing side and pressing the bearing, thereby fixing the inner ring of the bearing to the rotating shaft. On the other hand, the clutch forms the second state by moving axially to the side opposite to the bearing and separating from the bearing, thereby releasing the inner ring from the rotating shaft. The control device is configured to perform control to gradually switch the clutch from the second state to the first state according to the eccentricity in a situation where the clutch is switched from the second state to the first state. The bearing system for a motor according to claim 1 or 2.

5. The control device is configured to control the switching mechanism to gradually switch from the second state to the first state according to the eccentricity when the vehicle equipped with the bearing system of the motor decelerates. The bearing system for a motor according to claim 1 or 2.

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