Motor bearing system

Abstract

To prevent contact of a bearing and a rotation shaft when switching the bearing from a rolling bearing to a sliding 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; and a control device 50 configured to control the clutch so as to switch the state between the fixed state and the released state. In a situation where the state is switched from the fixed state to the released state, the control device is configured to determine load capacity when the bearing is caused to function as a sliding bearing, and, according to the result of the determination, control the clutch to switch the state from the fixed state to the released state gradually.SELECTED DRAWING: Figure 10

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. Rolling bearings have low friction in the low rotation region, while sliding bearings have high friction in the low rotation region. On the other hand, rolling bearings have a finite lifespan due to rolling fatigue, while sliding bearings have 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 axially moving the inner ring or outer ring relative to each other 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, when 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 invention 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 these 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 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 invention 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 repeated intensive research, the inventor of the present invention found that when switching the bearing from a rolling bearing to a sliding bearing (gas bearing), if the load capacity (in other words, the load capacity) when the bearing functions as a sliding bearing is not sufficient, the bearing and the rotating shaft will come into contact.

[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 that can prevent contact between the bearing and the rotating shaft when switching the bearing from a rolling bearing to a sliding 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 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, 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 determine the load capacity when the bearing functions as a sliding bearing in a situation of switching from the first state to the second state, and control the switching mechanism to gradually switch from the first state to the second state according to the determination result.

[0010] According to the present invention configured as described above, it is possible to gradually switch from the first state in which the bearing functions as a rolling bearing to the second state in which the bearing functions as a sliding bearing (gas bearing) when the load capacity when the bearing functions as a sliding bearing is sufficient. Therefore, according to the present invention, it is possible to prevent contact (solid contact) between the bearing and the rotating shaft when switching the bearing from a rolling bearing to a sliding bearing.

[0011] Preferably, the present invention further includes an axial center position sensor for detecting the axial center position of the rotating shaft. The control device determines whether the load capacity is in a state where the bearing can function as a sliding bearing based on the eccentricity of the rotating shaft corresponding to the axial center position, and controls the switching mechanism in the switching direction from the first state to the second state when it is determined that the load capacity is in a state where the bearing can function as a sliding bearing. The eccentricity of the above rotating shaft is a factor causing a wedge effect generated between the bearing and the rotating shaft, and this wedge effect affects the load capacity of the sliding bearing. Therefore, according to the present invention that takes such eccentricity into consideration, the load capacity when the bearing functions as a sliding bearing can be accurately determined.

[0012] In the present invention, preferably, the control device further uses the axial load applied to the rotating shaft, and is configured to determine whether the load capacity is in a state where the bearing can function as a sliding bearing based on the relationship between the eccentricity and the axial load. According to the present invention configured as described above, by considering the axial load in addition to the eccentricity, it is possible to more accurately determine the load capacity when the bearing functions as a sliding bearing.

[0013] In the present invention, preferably, it further includes a shaft rotation speed sensor that detects the shaft rotation speed of the rotating shaft and a bearing rotation speed sensor that detects the bearing rotation speed of the bearing, and the control device determines whether the load capacity is in a state where the bearing can function as a sliding bearing based on the relationship between the shaft rotation speed and the bearing rotation speed. When it is determined that the load capacity is in a state where the bearing can function as a sliding bearing, the control device is configured to control the switching mechanism in the direction of switching from the first state to the second state. Specifically, the shaft rotation speed of the rotating shaft and the bearing rotation speed of the bearing, that is, the relative rotation speed between the rotating shaft and the bearing, are factors that cause the wedge effect generated between the bearing and the rotating shaft. This wedge effect affects the load capacity of the sliding bearing. Therefore, according to the present invention that considers such a relationship between the shaft rotation speed and the bearing rotation speed, it is possible to accurately determine the load capacity when the bearing functions as a sliding bearing.

[0014] 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 movably provided in the axial direction. The clutch moves toward the bearing side in the axial direction and presses the bearing, thereby fixing the inner ring of the bearing to the rotating shaft to form a first state. On the other hand, the clutch moves to the side opposite to the bearing in the axial direction and separates from the bearing, thereby releasing the inner ring from the rotating shaft to form a second state. The control device is configured to perform control to gradually weaken the pressing force applied from the clutch to the bearing based on the load capacity in a situation where the control device switches from the first state to the second 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.

[0015] In a preferred example of the present invention, the control device is configured to control the switching mechanism so as to gradually switch from the first state to the second state based on the load capacity when the vehicle equipped with the bearing system of the motor accelerates.

Advantages of the Invention

[0016] According to the bearing system of the motor according to the present invention, it is possible to prevent contact between the bearing and the rotating shaft when switching the bearing from a rolling bearing to a sliding bearing.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0018] Hereinafter, a bearing system of a motor according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0019] [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 (in FIG. 1, only one bearing 4 is shown, and the illustration of the other bearing 4 is omitted) that support the rotating shaft 2. These motor 1, rotating shaft 2, and bearing 4 are housed in a housing (not shown).

[0020] 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.

[0021] In addition, 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. Note that the clutch 10 is also provided for the other bearing 4 whose illustration is omitted in FIG. 1.

[0022] Specifically, the clutch 10 is provided on the outer periphery of the rotating shaft 2 and arranged in parallel with the bearing 4 along the axial direction. Further, a pair of clutches 10 are provided so as to sandwich the bearing 4 in the axial direction. Also, 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.

[0023] 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). On the other hand, by moving axially to the side opposite to the bearing 4 and separating from the bearing 4, a released state in which the inner ring 7 is separated from the rotating shaft 2 is formed. 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 in a gas bearing (typically an air bearing). Details thereof will be described later.

[0024] 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, and is formed at the end on the inner ring 7 side, that is, at 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 when viewed in a cross section along the axial direction, and is formed to face the first inclined surface 8a. 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.

[0025] FIG. 1 showed 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.

[0026] As shown in FIG. 2, the bearing system 20 of the motor further has an actuator 15 configured to be movable to switch the clutch 10 between a fixed state and a 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 a fixed state and a released state, and operates to press the clutch 10 against the bearing 4 in the fixed state, that is, to generate a pressing force. Further, a pair of the actuators 15 are provided to face each other on the outer periphery of the rotating shaft 2, and another pair of the actuators 15 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.

[0027] Also, as shown in FIG. 2, the bearing system 20 of the motor has a detent 17 for securely fixing the clutch 10 to the rotating shaft 2. Typically, the 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.

[0028] Subsequently, 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, the first inclined surfaces 8a are formed on the surfaces (i.e., both end surfaces) facing each of the pair of clutches 10. 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. Further, 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, the second inclined surface 10a is formed on the surface facing the bearing 4. 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. 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.

[0029] Next, with reference to FIG. 5, the electrical configuration of the bearing system 20 of the motor according to the present 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 a CPU), 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).

[0030] 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.

[0031] 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 a fixed state and a 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 control"). Typically, the control device 50 executes such motor shaft control 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").

[0032] [Motor Shaft Control] Next, the motor shaft control according to this embodiment will be specifically described.

[0033] First, the basic concept of the motor shaft control 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, and the electricity cost of the motor decreases.

[0034] Therefore, in the present embodiment, a gas bearing (typically an air bearing) that uses lubrication with a gas having a lower viscosity than the lubricating oil is applied 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 come into contact with each other 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).

[0035] 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 frictional torque on the vertical axis.

[0036] 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.

[0037] 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 greatly 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.

[0038] On the other hand, in the present embodiment, as described above, the control device 50 controls the actuator 15 so as 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 the region R11 where the motor rotation speed is low, since almost no wedge effect and throttle 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.

[0039] Subsequently, when the motor rotation speed exceeds the region R11, that is, when entering the region R12 higher than the region R11, a certain degree of wedge effect and throttle effect can be obtained. Therefore, the control device 50 attempts to make the bearing 4 function as a gas bearing. Specifically, in the region R13 on the low rotation side in the region R12, since the wedge effect and the throttle 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 the region R14 on the high rotation side in the region R12, since the wedge effect and the throttle 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.

[0040] 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. When 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.

[0041] 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 increases from the first speed to the second speed and the vehicle accelerates.

[0042] 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 the bearing 4 is regarded as a rolling bearing decreases, the rotation speed when the bearing 4 is regarded 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 the bearing 4 is regarded as a rolling bearing becomes very small, the rotation speed when the bearing 4 is regarded as a gas bearing becomes stable at a large speed, that is, the bearing 4 stably functions as a gas bearing. After that, at time t3, the motor rotation speed reaches the second speed.

[0043] Next, the motor shaft control performed when switching the bearing 4 from a rolling bearing to a sliding bearing (gas bearing) will be described. As described above, when switching the bearing 4 from a rolling bearing to a gas bearing, if the load capacity (in other words, the load capacity) when the bearing 4 functions as a gas bearing is not sufficient, there is a problem that the bearing 4 and the rotating shaft 2 come into contact (solid contact). Such contact occurs when the load capacity when the bearing 4 functions as a gas bearing is smaller than the actual load due to gravity or pushing up. Therefore, in the present embodiment, the control device 50 determines the load capacity when the bearing 4 functions as a gas bearing in the situation of switching the bearing 4 from a rolling bearing to a gas bearing, that is, in the situation of switching the clutch 10 from the fixed state to the released state, and controls the actuator 15 to gradually weaken the pressing force applied to the bearing 4 from the clutch 10 according to the determination result.

[0044] When the pressing force is gradually weakened in this way, the position of the axis of the rotating shaft 2 deviates from the center due to the load, increasing the wedge effect. Also, the wedge effect increases because the bearing rotation speed of the bearing 4 becomes relatively lower than the shaft rotation speed (motor rotation speed) of the rotating shaft 2. Therefore, in the present embodiment, the control device 50 considers the axis of the rotating shaft 2 (which affects the shape of the wedge) and the shaft rotation speed and the bearing rotation speed (which affect the speed of entraining the gas), and determines whether the load capacity of the bearing 4 is in a state where the bearing 4 can function as a gas bearing. Then, while the load capacity is in a state where the bearing 4 can function as a gas bearing, the control device 50 performs control to gradually weaken the pressing force applied from the clutch 10 to the bearing 4.

[0045] Here, with reference to FIGS. 8 and 9, a method for determining the load capacity of the gas bearing will be specifically described.

[0046] FIG. 8 shows the load capacity of the gas bearing defined based on the eccentricity ratio (horizontal axis) of the bearing 4 and the axial load applied to the rotating shaft 2 (vertical axis). Here, the eccentricity ratio indicates the degree of eccentricity of the axial position (position in the radial direction of the axis) of the rotating shaft 2. When the value is 0, the axis is located at the center. 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 ratio is obtained from the axial position detected by the axial position sensor 37. Also, the axial load is detected by the axial load sensor 38. Note that the axial load is not limited to being detected by the axial load sensor 38, and may be obtained based on the bearing loads detected by the bearing load sensors 39 and 40, the running state of the vehicle (typically the road surface state), etc.

[0047] The first reference line shown in FIG. 8 corresponds to a reference that can determine that the load capacity can function as a gas bearing for bearing 4 if it is below this line, and is defined based on the eccentricity and the axial load. The first reference line is defined such that as the eccentricity increases (as it approaches 1), the range of the axial load for which the load capacity is sufficient to function as a gas bearing for bearing 4 expands. In the present embodiment, in the situation where the control device 50 switches bearing 4 from a rolling bearing to a gas bearing, when the currently obtained eccentricity and axial load are within the range defined by the first reference line (that is, when it is below the first reference line), it is determined that the load capacity is in a state where it can function as a gas bearing for bearing 4.

[0048] Subsequently, FIG. 9 shows the load capacity of the gas bearing defined based on the axial rotation speed (motor rotation speed) of the rotating shaft 2 and the bearing rotation speed of bearing 4. Here, the axial rotation speed is detected by the axial rotation speed sensor 35, and the bearing rotation speed is detected by the bearing rotation speed sensor 36. The second reference line shown in FIG. 9 corresponds to a reference that can determine that the load capacity can function as a gas bearing for bearing 4 if it is below this line, and is defined based on the axial rotation speed and the bearing rotation speed. The second reference line is defined such that as the axial rotation speed increases, the range of the bearing rotation speed for which the load capacity is sufficient to function as a gas bearing for bearing 4 expands. In the present embodiment, in the situation where the control device 50 switches bearing 4 from a rolling bearing to a gas bearing, when the currently obtained axial rotation speed and bearing rotation speed are within the range defined by the second reference line (that is, when it is below the second reference line), it is determined that the load capacity is in a state where it can function as a gas bearing for bearing 4.

[0049] In particular, in the present embodiment, when the control device 50 switches the bearing 4 from a rolling bearing to a gas bearing, for example, when the vehicle accelerates, if the eccentricity and the axial load are within the ranges defined by the first reference line (Fig. 8), and the shaft rotation speed and the bearing rotation speed are within the ranges defined by the second reference line (Fig. 9), the control device 50 determines that the load capacity is in a state where the bearing 4 can function as a gas bearing. Then, when the control device 50 determines that the load capacity is in a state where the bearing 4 can function as a gas bearing, the control device 50 controls the actuator 15 to gradually weaken the pressing force applied from the clutch 10 to the bearing 4 so as to switch the clutch 10 from the fixed state to the released state. In this case, until the clutch 10 is switched from the fixed state to the released state, that is, while the clutch 10 is in the fixed state, the control device 50 repeatedly performs control to reduce the pressing force applied from the clutch 10 to the bearing 4 by a predetermined amount.

[0050] Next, with reference to Fig. 10, the specific flow of the motor shaft control performed when switching the bearing 4 from a rolling bearing to a gas bearing will be described. Fig. 10 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.

[0051] 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 stopped. For example, the control device 50 determines whether the motor 1 is stopped 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 stopped (step S11: Yes), it proceeds to step S12, and when it does not determine that the motor 1 is stopped (step S11: No), it ends the motor shaft control.

[0052] Next, in step S12, the control device 50 determines whether there is a start request for the motor 1. For example, the control device 50 determines whether there is a start request for the motor 1 based on the depression 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 start request for the motor 1 (step S12: Yes), it proceeds to step S13 and starts the motor 1, while when it does not determine that there is a start request for the motor 1 (step S12: No), it ends the motor shaft control.

[0053] 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 equal to or higher than the first speed, that is, whether the shaft rotation speed has entered from region R11 to region R13 (FIG. 6). Here, the control device 50 determines whether the situation has become such that the bearing 4 should be switched from a rolling bearing to a gas bearing as the vehicle accelerates. As a result, when the control device 50 determines that the shaft rotation speed is equal to or higher than the first speed (step S14: Yes), it proceeds to step S15 and acquires various signals from the various sensors 31 to 40. On the other hand, when it does not determine that the shaft rotation speed is equal to or higher than the first 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 equal to or higher than the first speed.

[0054] Next, in step S16, the control device 50 determines whether the load capacity of the bearing 4 is in a state where the bearing 4 can function as a gas bearing, that is, whether the above-described conditions of the first and second reference lines regarding the load capacity are satisfied. Specifically, the control device 50 determines whether the eccentricity and the axial load are within the ranges defined by the first reference line (FIG. 8), and whether the shaft rotation speed and the bearing rotation speed are within the ranges defined by the second reference line (FIG. 9). In this case, the control device 50 uses the eccentricity obtained from the shaft center position detected by the shaft center position sensor 37, and also uses the axial load, the shaft rotation speed, and the bearing rotation speed detected by the axial load sensor 38, the shaft rotation speed sensor 35, and the bearing rotation speed sensor 36, respectively.

[0055] As a result of step S16, when the control device 50 determines that the conditions of the first and second reference lines are satisfied (step S16: Yes), it proceeds to step S17 and controls the actuator 15 to weaken the pressing force applied from the clutch 10 to the bearing 4. Specifically, the control device 50 performs control to reduce the pressing force applied from the clutch 10 to the bearing 4 by a predetermined amount. On the other hand, when the control device 50 determines that the conditions of the first and second reference lines are not satisfied (step S16: No), it returns to step S15. In this case, the control device 50 does not perform control to weaken the pressing force applied from the clutch 10 to the bearing 4.

[0056] After the above step S17, the control device 50 proceeds to step S18 to determine whether the fixation of the bearing 4 is released, that is, whether the clutch 10 has switched from the fixed state to the released state. For example, the control device 50 determines whether the pressing force applied from the clutch 10 to the bearing 4 by the actuator 15 has become zero based on, for example, the control amount for the actuator 15, thereby making the determination in step S18. As a result, when the control device 50 determines that the fixation of the bearing 4 is released (step S18: Yes), it ends the motor shaft control, and when it does not determine that the fixation of the bearing 4 is released (step S18: No), it returns to step S15. In the latter case, the control device 50 repeatedly performs control to weaken the pressing force applied from the clutch 10 to the bearing 4 according to the load capacity of the bearing 4.

[0057] [Operation and Effect] Next, the operation and effect of the motor bearing system 20 according to the present embodiment will be described. In the present embodiment, when the control device 50 switches the clutch 10 from the fixed state to the released state, it determines the load capacity when the bearing 4 functions as a sliding bearing (gas bearing), and controls the actuator 15 so as to gradually switch the clutch 10 from the fixed state to the released state according to the determination result. Thereby, such a switch can be made when the load capacity when the bearing 4 functions as a sliding bearing is sufficient, and it becomes possible to prevent contact (solid contact) between the bearing 4 and the rotating shaft 2.

[0058] In addition, in the present embodiment, the control device 50 determines whether the load capacity is in a state where the bearing 4 can function as a sliding bearing based on the eccentricity of the rotating shaft 2, and when it is determined that the load capacity is in a state where the bearing 4 can function as a sliding bearing, the actuator 15 is controlled in a direction to switch the clutch 10 from the fixed state to the released state. The eccentricity of the rotating shaft 2 is a factor causing the wedge effect generated between the bearing 4 and the rotating shaft 2, and this wedge effect affects the load capacity of the sliding bearing. Therefore, according to the present embodiment, it is possible to accurately determine the load capacity when the bearing 4 functions as a sliding bearing.

[0059] In addition, in the present embodiment, the control device 50 further uses the axial load applied to the rotating shaft 2 and determines whether the load capacity is in a state where the bearing 4 can function as a sliding bearing based on the relationship between the eccentricity and the axial load. Thereby, by considering the axial load in addition to the eccentricity, it is possible to more accurately determine the load capacity when the bearing 4 functions as a sliding bearing.

[0060] In addition, in the present embodiment, the control device 50 determines whether the load capacity is in a state where the bearing 4 can function as a sliding bearing based on the relationship between the axial rotation speed of the rotating shaft 2 and the bearing rotation speed of the bearing 4, and when it is determined that the load capacity is in a state where the bearing 4 can function as a sliding bearing, the actuator 15 is controlled in a direction to switch the clutch 10 from the fixed state to the released state. The relative rotation speed between the rotating shaft 2 and the bearing 4 is a factor causing the wedge effect generated between the bearing 4 and the rotating shaft 2, and this wedge effect affects the load capacity of the sliding bearing. Therefore, according to the present embodiment, it is possible to accurately determine the load capacity when the bearing 4 functions as a sliding bearing.

[0061] Also, 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 forms a fixed state by moving toward the bearing 4 side in the axial direction and pressing the bearing 4, thereby fixing the inner ring 7 of the bearing 4 to the rotating shaft 2. On the other hand, by moving in the direction opposite to the bearing 4 in the axial direction and separating from the bearing 4, the inner ring 7 is released from the rotating shaft 2 to form a released state. When the control device 50 switches the clutch 10 from the fixed state to the released state, based on the load capacity, the control device 50 performs control to gradually weaken the pressing force applied from the clutch 10 to the bearing 4.

[0062] 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 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

[0063] 1 Motor 2 Rotating shaft 4 Bearing 5 Rolling element 6 Outer ring 7 Inner ring 8 Inner ring fixing portion 10 Clutch 8a First inclined surface 10a Second inclined surface 15 Actuator 20 Bearing system of motor 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; a control device configured to control the switching mechanism so as to switch between the first state and the second state; and the control device is configured to determine a load capacity when the bearing functions as the sliding bearing in a situation of switching from the first state to the second state, and to control the switching mechanism to gradually switch from the first state to the second state according to the determination result. A bearing system for a motor, characterized in that.

2. further comprising an axial position sensor for detecting an axial position of the rotating shaft; the control device determines whether or not the load capacity is in a state where the bearing can function as the sliding bearing based on an eccentricity ratio of the rotating shaft corresponding to the axial position, and when it is determined that the load capacity is in a state where the bearing can function as the sliding bearing, the control device is configured to control the switching mechanism in a direction of switching from the first state to the second state. The bearing system for a motor according to claim 1.

3. The control device is further configured to use an axial load applied to the rotating shaft, and to determine whether or not the load capacity is in a state where the bearing can function as the sliding bearing based on a relationship between the eccentricity ratio and the axial load. The bearing system for a motor according to claim 2.

4. further comprising an axial rotation speed sensor for detecting an axial rotation speed of the rotating shaft and a bearing rotation speed sensor for detecting a bearing rotation speed of the bearing; The control device determines whether or not the load capacity is in a state where the bearing can function as the sliding bearing based on the relationship between the shaft rotation speed and the bearing rotation speed, and when it is determined that the load capacity is in a state where the bearing can function as the sliding bearing, the switching mechanism is controlled in a direction of switching from the first state to the second state. The bearing system of the motor according to claim 1 or 2.

5. 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 the first state by moving toward the bearing side in the axial direction and pressing the bearing to fix the inner ring of the bearing to the rotating shaft, while forming the second state by moving to the side opposite to the bearing in the axial direction and separating from the bearing to release the inner ring from the rotating shaft. The control device is configured to perform control to gradually weaken the pressing force applied from the clutch to the bearing based on the load capacity in a situation of switching from the first state to the second state. The bearing system of the motor according to claim 1 or 2.

6. The control device is configured to control the switching mechanism so as to gradually switch from the first state to the second state based on the load capacity when a vehicle equipped with the bearing system of the motor accelerates. The bearing system of the motor according to claim 1 or 2.

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