Motor Control System

Abstract

A motor control system capable of suppressing oil from entering an air gap in a radial gap motor is provided. [Solution] A motor control system 1 includes a motor 10 including a rotor 11, a stator 17 disposed across an air gap from the rotor 11, and a motor housing 25, and a motor ECU 30. The motor control system 1 further includes a cooling device 40 that supplies oil O to the motor 10, a suction pump 50 that sucks oil O accumulated at the bottom of the motor housing 25, and a temperature sensor 60 attached to the lower end of the coil end 20. When the temperature T detected by the temperature sensor 60 exceeds an upper limit temperature ULT, the motor ECU 30 increases the suction force of the suction pump 50 so that the oil level of the oil O accumulated in the motor housing 25 does not exceed the lowest end of the air gap.

Description

[Technical Field]

[0001] The present invention relates to a motor control system. [Background technology]

[0002] When the stator coil attached to the stator becomes hot due to the passage of current, the rotational efficiency of the motor decreases. Therefore, various methods have been proposed to cool the coil ends, which are the parts of the stator coil that are most likely to become hot, using cooling oil or the like.

[0003] For example, Patent Document 1 discloses a cooling device for a rotating electric machine in which a cooling medium is discharged toward a coil end from a discharge hole of a cooling medium passage arranged along the direction of the rotation axis inside a device case. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-115650 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in a method of directly supplying oil to the stator coil, etc., as in Patent Document 1, the oil accumulates at the bottom of the motor housing (corresponding to the device case).For this reason, if this method is applied to a radial gap motor in which the stator core is arranged with a gap (air gap) in the radial direction from the outer circumferential surface of the cylindrical rotor core, the oil may seep into the air gap when the air gap is immersed in the oil accumulated at the bottom of the motor housing.

[0006] If oil penetrates (intervenes) in the air gap in this way, frictional resistance occurs between the rotor core and stator core, which are rotating at high speed, due to the viscosity of the oil, causing the rotor core and stator core to heat up. Furthermore, if the oil is compressed in the air gap, cavitation occurs, which suddenly increases the frictional resistance, and this may further heat the rotor core and stator core. In addition, if the stator core heats up, it may lead to a sudden rise in temperature of the stator coil that passes through the slots formed in the stator core near the location where frictional resistance is occurring.

[0007] Here, it is possible to reduce the amount of oil supplied to the stator coil, etc., in order to lower the oil level that accumulates at the bottom of the motor housing so that the air gap is not submerged in oil. However, this would reduce the motor's cooling performance and ultimately lead to a decrease in the motor's rotational efficiency.

[0008] Another possible method is to install an oil level sensor inside the motor housing and manage the oil level so that the air gap is not submerged in oil. However, in motors mounted on vehicles, the oil level tilts inside the motor housing, and oil supplied to the rotor rotating at high speed splashes, causing air bubbles to form on the oil surface, which can cause the oil level sensor to mistakenly detect the surface of the air bubbles as the oil level, making it difficult to adopt a method using an oil level sensor.

[0009] The present invention has been made in consideration of the above points, and an object of the present invention is to provide a motor control system that can suppress oil from entering the air gap in a radial gap motor. [Means for solving the problem]

[0010] To achieve the above object, the motor control system according to the present invention controls the oil level of the oil pooled at the bottom of the motor housing based on the temperature of the coil ends of the stator coil.

[0011] Specifically, the present invention is directed to a motor control system comprising a motor including a rotor having a cylindrical rotor core, a stator having a stator core arranged to surround the rotor core with an air gap radially spaced from the outer peripheral surface of the rotor core, a motor housing that accommodates the rotor and stator, and a control device that controls the motor.

[0012] The motor control system further includes a cooling device that supplies oil to the motor, a pump that sucks up oil that has accumulated at the bottom of the motor housing, and a temperature sensor that detects the temperature of a stator coil attached to the stator, wherein the temperature sensor is attached to a portion of the coil end of the stator coil that is lower than the lowest end of the air gap, and the control device is configured to control the pump to increase its suction force when the temperature detected by the temperature sensor exceeds a predetermined upper limit temperature so that the height of the oil level of the oil that has accumulated at the bottom of the motor housing does not exceed the lowest end of the air gap.

[0013] While spraying oil onto the coil ends is an effective way to cool hot coil ends, it is generally believed that immersing the coil ends in oil accumulated at the bottom of the motor housing is an even more effective way to cool hot coil ends. However, when oil is sprayed onto the coil ends, the oil that absorbs heat from the coil ends splashes away from the coil ends, whereas when the coil ends are immersed in oil, the hot oil that absorbs heat from the coil ends remains near the coil ends. The inventors have discovered that if hot oil remains near the coil ends, the temperature of the coil ends will actually rise above the expected temperature, even if the coil ends are immersed in oil.

[0014] Based on this knowledge, with this configuration, the portion of the coil end that is lower than the lowest point of the air gap will always be submerged in oil before the oil level accumulated at the bottom of the motor housing reaches the lowest point of the air gap. Therefore, when the oil level attempts to rise to reach the lowest point of the air gap, the temperature sensor attached to the coil end that is lower than the lowest point of the air gap can reliably detect an unexpected temperature rise in the oil-submerged coil end.

[0015] When the temperature detected by the temperature sensor exceeds a predetermined upper limit, the control device increases the suction force of the pump so that the oil level at the bottom of the motor housing does not exceed the lowest point of the air gap. This reliably prevents the air gap from being submerged in oil, thereby suppressing oil penetration into the air gap. This prevents a rapid temperature rise in the rotor core, stator core, and stator coil due to frictional resistance of the oil.

[0016] In the motor control system, the temperature sensor may be attached to a lower end of the coil end.

[0017] With this configuration, the temperature sensor is attached to the lower end of the lowest coil end among the parts of the coil end that are lower than the lowest end of the gap, so that a rise in the oil level can be detected early, thereby more reliably preventing oil from entering the air gap.

[0018] Furthermore, in the motor control system, the control device may be configured to stop control to increase the suction force of the pump when the temperature detected by the temperature sensor exceeds the predetermined upper limit temperature and then falls below a predetermined lower limit temperature that is set lower than the predetermined upper limit temperature.

[0019] According to this configuration, the control to increase the suction force of the pump is stopped not when the temperature detected by the temperature sensor falls below a predetermined upper limit temperature, but when it falls below a predetermined lower limit temperature that is set lower than the predetermined upper limit temperature.This makes it possible to prevent hunting, in which the suction force repeatedly increases and stops around the predetermined upper limit temperature.

[0020] In the motor control system, the rotor core may be formed with a recess by recessing its outer circumferential surface.

[0021] With this configuration, unlike a rotor without undulations on the outer peripheral surface of the rotor core, a rotor with recesses formed in the outer peripheral surface of the rotor core rotates, causing an air flow (wind) to be generated within the air gap. Since the wind generated within the air gap has nowhere to go, it flows toward both axially outer sides of the rotor, which increases the pressure at both axial ends of the air gap, creating a state in which a barrier is formed as if to prevent oil from entering the air gap.

[0022] Therefore, it is possible to reliably prevent not only oil accumulated at the bottom of the motor housing, but also oil splashed from the oil accumulated at the bottom and oil supplied directly to the stator coil, etc. from penetrating into the air gap. [Effects of the Invention]

[0023] As described above, the motor control system according to the present invention can prevent oil from entering the air gap in a radial gap motor. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a diagram schematically illustrating a motor control system according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a diagram schematically illustrating a cross section perpendicular to the rotation axis of a rotor and a stator. [Figure 3]FIG. 2 is a front view schematically showing a rotor and a stator housed in a motor housing. [Figure 4] FIG. 2 is a side view schematically showing a rotor and a stator housed in a motor housing. [Figure 5] 10 is a flowchart illustrating an example of oil level control in a motor control system. [Figure 6] FIG. 1 is a diagram for explaining a mechanism for generating wind in an air gap. [Figure 7] FIG. 2 is a diagram illustrating a schematic view of the flow of air in an air gap. [Figure 8] FIG. 3 is a diagram illustrating a schematic diagram of pressure distribution around the rotor. [Figure 9] 10 is a flowchart showing an example of oil level control in the motor control system according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0026] (Embodiment 1) - Motor control system overview - FIG. 1 is a diagram schematically illustrating a motor control system 1 according to this embodiment. This motor control system 1 is mounted on an electrically powered vehicle, such as an electric vehicle or a hybrid vehicle, and is used as a driving power source for the vehicle. As shown in FIG. 1, the motor control system 1 includes a motor 10, a motor ECU 30 that controls the motor 10, a cooling device 40 that cools the motor 10, a suction pump 50, and a temperature sensor 60. The motor control system 1 is configured to prevent the rotor 11 and stator 17 from heating up rapidly through control by the motor ECU 30 and the structure of the motor 10 itself. This motor control system 1 will be described in detail below.

[0027] -Motor- 2 is a schematic diagram showing a cross section perpendicular to the rotation axis of the rotor 11 and the stator 17. As shown in FIG. 1, the motor 10 includes the rotor 11, the stator 17, a rotor shaft 21, and a motor housing 25. As shown in FIG. 2, the motor 10 is configured as a radial gap motor in which the stator 17 is disposed radially away from the rotor 11 with an air gap G therebetween.

[0028] The rotor 11 has a cylindrical rotor core 13 and permanent magnets 15 embedded in the rotor core 13. As shown in Fig. 1, an oil passage 13a is formed inside the rotor core 13 for flowing oil O introduced via a rotor shaft 21. The oil passage 13a extends radially outward from a central hole 13b of the rotor core 13, then branches outward in both axial directions, extends radially outward again at a position corresponding to the coil end 20 of the stator 17, and opens at an outer peripheral surface 13c of the rotor core 13.

[0029] The stator 17 has a cylindrical stator core 19 and a stator coil attached to the stator core 19. Note that each drawing shows only the coil ends 20 of the stator coil. The stator core 19 has a cylindrical yoke 19a and a plurality of teeth 19b that protrude radially inward from the inner peripheral surface of the yoke 19a and are arranged circumferentially at intervals, with the stator coil housed in slots 19c defined by adjacent teeth 19b.

[0030] As shown in the enlarged upper view circled in Figure 2, the stator core 19 is arranged to surround the rotor core 13 so that an air gap G is created between the tip surfaces (radially inner surfaces) of the teeth 19b and the outer peripheral surface 13c of the rotor core 13.

[0031] The rotor shaft 21 is inserted into the central hole 13b of the cylindrical rotor core 13 so as not to be rotatable relative to the rotor 11, and is rotatably supported by the motor housing 25 via bearings 23, thereby enabling the rotor 11 to rotate relative to the motor housing 25 and also serving to introduce oil O into the rotor 11 through the oil inlet passage 21a formed therein.

[0032] The motor housing 25 accommodates the rotor 11, the stator 17, and the rotor shaft 21 in its hollow portion. As shown in FIG. 1, the motor housing 25 is formed with first and second oil supply holes 25a, 25b and an oil discharge hole 25c. The first oil supply hole 25a is formed above the coil end 20. The second oil supply hole 25b is formed to communicate with an oil chamber 29 that communicates with the oil introduction passage 21a of the rotor shaft 21. The oil discharge hole 25c is formed so that its lower end is flush with the upper surface of the bottom wall portion 27 of the motor housing 25.

[0033] -Motor ECU- The motor ECU (control device) 30 is configured as a microcomputer centered around a CPU (Central Processing Unit), and in addition to the CPU, includes a ROM (Read Only Memory) that stores processing programs, a RAM (Random Access Memory) that temporarily stores data, and input / output ports for communicating various types of data.

[0034] The motor ECU 30 is configured to rotate and drive the motor 10 by controlling the switching of multiple switching elements of an inverter (not shown) based on commands from a higher-level ECU (Electronic Control Unit) that controls the entire vehicle, for example. The motor ECU 30 is also configured to control the cooling device 40 and the suction pump 50 to adjust the amount of cooling oil O supplied to the motor 10 according to the state of the motor 10.

[0035] -Cooling device- 1, the cooling device 40 has an oil cooler 41, an oil tank 43, a discharge pump 45, and a flow rate adjustment valve 47, and is configured to supply oil O to various locations within the motor housing 25. The oil cooler 41 is provided adjacent to, for example, a radiator (not shown), and is configured to cool the oil O, which is discharged from the oil discharge hole 25c of the motor housing 25 and has become hot through heat exchange with the rotor core 13 and the coil ends 20, by heat exchange with the outside air. The oil tank 43 is connected to the oil cooler 41 so as to store the oil O, which has been cooled by passing through the oil cooler 41.

[0036] The discharge pump 45 is configured to suck and discharge low-temperature oil O stored in the oil tank 43 based on a command from the motor ECU 30, and send the oil O to the flow rate adjustment valve 47. The flow rate adjustment valve 47 is configured to be able to adjust the flow rate of the oil O supplied to the first oil supply hole 25a side and the flow rate of the oil O supplied to the second oil supply hole 25b side based on the oil pressure output from a solenoid valve (not shown) controlled by the motor ECU 30, for example.

[0037] -Suction pump- The suction pump 50 is configured to suck in and discharge high-temperature oil O accumulated at the bottom of the motor housing 25 through the oil discharge hole 25c and send it to the oil cooler 41 based on commands from the motor ECU 30.

[0038] -Temperature sensor- The temperature sensor 60 detects the temperature of the coil end 20 of the stator coil and is attached to the lower end of the coil end 20 (see FIG. 3). The temperature of the coil end 20 detected by the temperature sensor 60 (detected temperature T) is output to the motor ECU 30 via, for example, an on-board network.

[0039] -Motor cooling- In the motor control system 1 configured as described above, for example, when the ECU determines the required driving force in accordance with the accelerator operation amount, a signal (command) representing the required driving force is output to the motor ECU 30. Upon receiving this signal, the motor ECU 30 controls the switching of the inverter to rotate and drive the motor 10 so as to realize the motor torque calculated based on the required driving force.

[0040] Here, when the permanent magnets 15 and the stator coils become hot due to current flow as the motor 10 rotates, the rotational efficiency of the motor 10 decreases, and therefore, to suppress this decrease in rotational efficiency, the motor ECU 30 controls the cooling device 40. Specifically, the motor ECU 30 drives the discharge pump 45 to send low-temperature oil O stored in the oil tank 43 to the flow rate adjustment valve 47, and controls the solenoid valve to distribute the low-temperature oil O at an appropriate ratio between the first oil supply hole 25a and the second oil supply hole 25b via the flow rate adjustment valve 47.

[0041] The low-temperature oil O allocated to the first oil supply hole 25a side is supplied from above (radially outward) to the coil ends 20, which are the parts of the stator coil that are most likely to become hot. On the other hand, the low-temperature oil O allocated to the second oil supply hole 25b side flows through the oil chamber 29 into the oil introduction passage 21a of the rotor shaft 21 and is then supplied to the rotor core 13. The oil O supplied to the rotor core 13 flows through the oil passage 13a while cooling the rotor core 13 and permanent magnets 15, and is then supplied to the coil ends 20 from the radially inner side, as shown in FIG. 1. By supplying low-temperature oil O to the permanent magnets 15, coil ends 20, etc. in this way, a decrease in the rotational efficiency of the motor 10 is suppressed.

[0042] The oil O supplied to the coil ends 20 and the like flows down while cooling the rotor 11 and the stator 17, and accumulates at the bottom of the motor housing 25. The oil O accumulated at the bottom of the motor housing 25 and heated to a high temperature due to heat exchange with the rotor core 13 and the coil ends 20 is discharged from the oil discharge hole 25c when the motor ECU 30 drives the suction pump 50, and is sent to the oil cooler 41, where it is cooled by heat exchange with the outside air and is reused as oil O for cooling.

[0043] - Abnormal temperature rise caused by air gap - In a radial gap motor such as the motor 10 of this embodiment, if oil O penetrates (is present) in the air gap G, frictional resistance occurs between the rotor core 13 and stator core 19, which are rotating at high speed, due to the viscosity of the oil O, and this may heat up the rotor core 13 and stator core 19. Furthermore, if the oil O is compressed in the air gap G, cavitation occurs, which suddenly increases the frictional resistance, and this may further heat up the rotor core 13 and stator core 19. Furthermore, if the stator core 19 is heated, this may lead to a sudden rise in temperature of the stator coil passing through the slots 19c formed in the stator core 19 near the location where frictional resistance is occurring.

[0044] Here, one possible case in which oil O penetrates into the air gap G is when oil O supplied to the coil end 20 splashes and penetrates between the rotor core 13 and the stator core 19. However, the overwhelming majority of cases involve oil O penetrating into the air gap G when the air gap G is immersed in oil O that has accumulated at the bottom of the motor housing 25.

[0045] -Preventing oil from penetrating into the air gap- Therefore, in this embodiment, the motor ECU 30 is configured to control the oil level of the oil O to prevent the air gap G from being submerged in the oil O accumulated at the bottom of the motor housing 25. Furthermore, the structure of the rotor 11 is also devised to reliably prevent the oil O from entering the air gap G. In other words, the motor control system 1 according to this embodiment is designed to prevent the oil O from entering the air gap G in terms of both control and structure.

[0046] <Oil infiltration prevention through control> One possible method for lowering the oil level of the oil O accumulated at the bottom of the motor housing 25 so that the air gap G is not submerged in the oil O is to reduce the output of the discharge pump 45 and reduce the amount of oil O supplied to the stator coil, etc. However, this method may reduce the cooling performance of the motor 10, which in turn may reduce the rotational efficiency of the motor 10.

[0047] Another possible method is to provide an oil level sensor (not shown) inside the motor housing 25 and manage the oil level so that the air gap G is not submerged in the oil O. However, in an on-vehicle motor 10, the oil level tilts inside the motor housing 25, and the oil O supplied to the rotor 11 rotating at high speed splashes, causing air bubbles to form on the oil surface, which can cause the oil level sensor to erroneously detect the surface of the air bubbles as the oil level, making it difficult to adopt a method using an oil level sensor.

[0048] 3 and 4 are a front view and a side view, respectively, that schematically show the rotor 11 and the stator 17 housed in the motor housing 25. Note that the dashed line indicated by the symbol OS1 and the two-dot dashed line indicated by the symbol OS2 in Figs. 3 and 4 represent first and second oil levels, respectively, of the oil O accumulated at the bottom of the motor housing 25. Here, the first oil level OS1 is an oil level at a height such that the lower ends of the coil ends 20 are immersed in the oil O, as shown in Figs. 3 and 4, and the second oil level OS2 is an oil level at a height corresponding to the height of the lowest end of the air gap G.

[0049] Incidentally, spraying oil O onto the coil ends 20 is an effective way to cool the coil ends 20 that have become hot. However, it is generally believed that a more effective way to cool coil ends 20 that are even hotter is to immerse the coil ends 20 in oil O that has accumulated at the bottom of the motor housing 25, as shown in Figures 3 and 4.

[0050] However, when oil O is sprayed onto the coil end 20, the oil O that absorbs heat from the coil end 20 splashes away from the coil end 20, whereas when the coil end 20 is immersed in oil O, the high-temperature oil O that absorbs heat from the coil end 20 continues to remain near the coil end 20. In this way, if high-temperature oil O continues to remain near the coil end 20, the temperature of the coil end 20 will rise above the expected temperature even if the coil end 20 is immersed in oil O. Conversely, if the temperature of the coil end 20 is higher than the expected temperature, there is a high possibility that the coil end 20 is immersed in oil O.

[0051] Therefore, in the motor control system 1 according to this embodiment, the oil level of the oil O accumulated in the bottom of the motor housing 25 is controlled based on the temperature of the coil end 20 of the stator coil.

[0052] Specifically, when the detected temperature T of the temperature sensor 60 that detects the temperature of the coil end 20 exceeds a predetermined upper limit temperature ULT, the motor ECU 30 is configured to perform oil infiltration suppression control that increases the suction force of the suction pump 50 so that the height of the oil level of the oil O accumulated at the bottom of the motor housing 25 does not exceed the lowest end of the air gap G, in other words, so that the oil level of the oil O is below the second oil level OS2.

[0053] More specifically, the portion of the coil end 20 that is lower than the lowest end of the air gap G will be immersed in the oil O before the level of the oil O that has accumulated at the bottom of the motor housing 25 reaches the lowest end of the air gap G. Therefore, when the level of the oil O begins to rise and reaches the first oil level OS1 as shown in Figures 3 and 4, the lower end of the coil end 20 will be immersed in the oil O.

[0054] In this way, when the lower end of the coil end 20 is immersed in oil O, the high-temperature oil O that absorbs heat from the lower end of the coil end 20 remains at the lower end of the coil end 20, causing the temperature of the coil end 20 to rise unexpectedly and reach a predetermined upper limit temperature ULT. Because the temperature sensor 60 is attached to the lower end of the coil end 20, which is a part of the coil end 20 that is lower than the lowest end of the air gap G, the temperature sensor 60 can quickly and reliably detect the unexpected temperature rise (upper limit temperature ULT) of the coil end 20 immersed in oil O, in other words, the fact that the oil level of the oil O is rising so high that it reaches the lower end of the coil end 20.

[0055] When the temperature T detected by the temperature sensor 60 exceeds the upper limit temperature ULT, the motor ECU 30 increases the suction power of the suction pump 50 so that the oil level of the oil O accumulated at the bottom of the motor housing 25 does not exceed the second oil level OS2. By increasing the suction power of the suction pump 50 in this manner, the oil O accumulated at the bottom of the motor housing 25 is discharged from the oil discharge hole 25c, and the oil level of the oil O drops below the first oil level OS1. Therefore, the oil level of the oil O does not exceed the second oil level OS2, which reliably prevents the air gap G from being immersed in the oil O, thereby preventing the oil O from entering the air gap G.

[0056] At this time, the discharge pump 45 and the like are controlled by the motor ECU 30 according to the state of the motor 10, regardless of the suction pump 50, so the amount of oil O supplied to the stator coil and the like is not affected by the oil infiltration suppression control. Therefore, the cooling performance of the motor 10 is not reduced, and therefore the rotational efficiency of the motor 10 is not reduced.

[0057] Here, it is conceivable to configure the motor ECU 30 so that, when the temperature T detected by the temperature sensor 60 falls below the upper limit temperature ULT, the control to increase the suction power of the suction pump 50 is stopped. However, this results in hunting, in which the suction power of the suction pump 50 repeatedly increases and stops near the upper limit temperature ULT (near the first oil level OS1), as follows: (1) the oil level rises and the lower end of the coil end 20 is immersed in the oil O → (2) the temperature T detected by the temperature sensor 60 exceeds the upper limit temperature ULT → (3) the oil level drops as the suction power of the suction pump 50 is increased → (4) the temperature T detected by the temperature sensor 60 falls below the upper limit temperature ULT → (5) the control to increase the suction power of the suction pump 50 is stopped → (1) the oil level rises and the lower end of the coil end 20 is immersed in the oil O → ...

[0058] Therefore, in the motor control system 1 according to this embodiment, the motor ECU 30 is configured to stop the control to increase the suction force of the suction pump 50 when the detected temperature T of the temperature sensor 60 exceeds the upper limit temperature ULT and then falls below a predetermined lower limit temperature LLT that is set lower than the upper limit temperature ULT.

[0059] In this way, the control to increase the suction force of the suction pump 50 is stopped not when the detected temperature T of the temperature sensor 60 falls below the upper limit temperature ULT, but when it falls below the lower limit temperature LLT which is set lower than the upper limit temperature ULT, thereby preventing hunting from occurring near the upper limit temperature ULT (near the first oil level OS1).

[0060] <Flowchart> Next, a specific example of oil level control executed by the motor ECU 30 will be described with reference to the flowchart of Figure 5. The control routine of Figure 5 starts, for example, when a start switch (not shown) of the vehicle is turned ON, and is executed at predetermined time intervals while the start switch is ON. In addition, when the start switch is turned ON, flag F is set to F=0.

[0061] First, in step SA1, motor ECU 30 reads the detected temperature T of temperature sensor 60, and then proceeds to step SA2. In the next step SA2, motor ECU 30 determines whether the value of flag F is 0. As described above, when the vehicle is started (when the start switch is turned ON), flag F is set to 0, so the determination in step SA2 is YES, and the process proceeds to step SA3.

[0062] In the next step SA3, the motor ECU 30 determines whether the temperature T detected by the temperature sensor 60 is higher than the upper limit temperature ULT. If the determination in step SA3 is NO, the process returns and the flow of steps SA1 to SA3 is repeated at predetermined intervals. On the other hand, if the determination in step SA3 is YES, the process proceeds to step SA4.

[0063] In the next step SA4, the motor ECU 30 increases the suction force of the suction pump 50, and then proceeds to step SA5. In the next step SA5, the motor ECU 30 sets the value of flag F to 1, and then returns.

[0064] In step SA1 after increasing the suction power of the suction pump 50 in step SA4, the motor ECU 30 reads the detected temperature T of the temperature sensor 60, and then proceeds to step SA2. In the next step SA2, the motor ECU 30 determines whether the value of flag F is 0 or not. However, since the value of flag F was set to 1 in step SA5 after increasing the suction power of the suction pump 50, the determination in step SA2 is NO, and the process proceeds to step SA6.

[0065] In the next step SA6, the motor ECU 30 determines whether the temperature T detected by the temperature sensor 60 is equal to or lower than the lower limit temperature LLT. If the determination in step SA6 is NO, the process returns, and the flow of steps SA1, SA2, and SA6 is repeated at predetermined intervals. On the other hand, if the determination in step SA6 is YES, the process proceeds to step SA7.

[0066] In the next step SA7, the motor ECU 30 stops increasing the suction force of the suction pump 50, and then the process proceeds to step SA8, where the value of flag F is set to 0, and then the process returns.

[0067] <Oil penetration prevention through structure> Fig. 6 is a diagram that schematically explains the mechanism by which wind is generated in the air gap G, Fig. 7 is a diagram that schematically explains the flow of wind in the air gap G, and Fig. 8 is a diagram that schematically explains the pressure distribution around the rotor 11. Note that in Fig. 7, the size of the air gap G is exaggerated to make the drawing easier to see. Also, the legend in Fig. 8 indicates that the pressure is higher in the upper section.

[0068] In cases where oil O seeps into the air gap G, in addition to the case where the air gap G is submerged in oil O accumulated at the bottom of the motor housing 25, there is also a case where oil O supplied to the coil end 20 splashes and seeps into the gap between the rotor core 13 and the stator core 19, as described above. In addition, there is also a case where oil O splashes from the oil surface of the oil O accumulated at the bottom of the motor housing 25 when the vehicle shakes, and seeps into the gap between the rotor core 13 and the stator core 19.

[0069] Therefore, the motor control system 1 according to this embodiment employs a configuration that makes it difficult for oil O to penetrate between the rotor core 13 and the stator core 19. Specifically, as shown in the enlarged view of the lower part circled in Fig. 2, the rotor core 13 is configured to have a plurality of axially extending recesses 13d formed by recessing the outer peripheral surface 13c radially inward.

[0070] As shown by the hollow arrows in Fig. 6, when the rotor 11 rotates, recesses 13d are formed in the outer peripheral surface 13c of the rotor core 13, and as shown by the thick arrows in the enlarged view enclosed by a circle in Fig. 6, the air in the air gap G is pushed, generating an air flow (wind) in the air gap G. Since multiple recesses 13d are formed extending in the axial direction, wind flowing in the circumferential direction is generated throughout the air gap G. Note that although the slots 19c are shown as hollow in Fig. 6, in reality, stator coils are housed in the slots 19c, making it difficult for the generated wind to escape into the slots 19c.

[0071] Therefore, the wind generated in the air gap G has nowhere to go and flows outward in both axial directions, as shown by the solid black arrows in Fig. 7. As a result, as shown in Fig. 8, the pressure at both axial ends of the air gap G increases (see the portions indicated by arrows A, B, C, and D), creating a state in which an air barrier is formed to block the oil O that attempts to infiltrate the air gap G. Therefore, it is possible to reliably prevent not only the oil O that has accumulated at the bottom of the motor housing 25, but also the oil O that is supplied directly to the stator coil, etc., and the oil O that splashes when the vehicle sways, from infiltrating into the air gap G.

[0072] As described above, the motor control system 1 according to this embodiment can prevent oil O from penetrating into the air gap G, thereby preventing a sudden rise in temperature of the rotor core 13, stator core 19, and stator coil caused by the frictional resistance of the oil O.

[0073] (Embodiment 2) This embodiment differs from the first embodiment in the conditions for stopping the control to increase the suction force of the suction pump 50. The following mainly describes the differences from the first embodiment.

[0074] In the first embodiment, when the temperature T detected by the temperature sensor 60 becomes equal to or lower than the lower limit temperature LLT, the control to increase the suction power of the suction pump 50 is stopped. However, in the present embodiment, the motor ECU 30 is configured to stop the control to increase the suction power of the suction pump 50 when a predetermined time has elapsed since the control to increase the suction power of the suction pump 50 was started.

[0075] <Flowchart> An example of a specific oil level control executed by the motor ECU 30 will be described with reference to the flowchart of Fig. 9. Like the control routine of Fig. 5, the control routine of Fig. 9 also starts when the start switch is turned ON, for example, and is executed at predetermined time intervals while the start switch is ON. Also, like the first embodiment, the flag F is set to F = 0 when the start switch is turned ON.

[0076] First, in step SB1, the motor ECU 30 determines whether the value of flag F is 0. As described above, when the start switch is ON, flag F is set to 0, so the determination in step SB1 is YES and the process proceeds to step SB2. In the next step SB2, the motor ECU 30 reads the detected temperature T of the temperature sensor 60, and then the process proceeds to step SB3.

[0077] In the next step SB3, the motor ECU 30 determines whether the temperature T detected by the temperature sensor 60 is higher than the upper limit temperature ULT. If the determination in step SB3 is NO, the process returns, and the flow of steps SB1 to SB3 is repeated at predetermined time intervals. On the other hand, if the determination in step SB3 is YES, the process proceeds to step SB4, where the motor ECU 30 increases the suction power of the suction pump 50, and then proceeds to step SB5. In the next step SB5, the motor ECU 30 sets the value of flag F to 1, and then returns.

[0078] In step SB1 after increasing the suction force of the suction pump 50 in step SB4, the motor ECU 30 determines whether the value of flag F is 0 or not. However, since the value of flag F is set to 1 in step SB5, the determination in step SB1 is NO, and the process proceeds to step SB6.

[0079] In the next step SB6, the motor ECU 30 determines, based on a built-in timer, whether a predetermined time has elapsed since the motor ECU 30 started increasing the suction power of the suction pump 50. If the determination in step SB6 is NO, the process returns, and the flow of steps SB1 and SB6 is repeated every predetermined time. On the other hand, if the determination in step SB6 is YES, the process proceeds to step SB7, where the motor ECU 30 stops increasing the suction power of the suction pump 50, and then the process proceeds to step SB8, where the value of flag F is set to 0, and the process then returns.

[0080] In this way, when a predetermined time has elapsed since the start of control to increase the suction power of the suction pump 50, the control to increase the suction power of the suction pump 50 is stopped, thereby preventing hunting, in which the suction power of the suction pump 50 is repeatedly increased and stopped in a short period of time.

[0081] (Other embodiments) The present invention is not limited to the embodiments, and can be implemented in various other forms without departing from the spirit or main characteristics thereof.

[0082] In each of the above embodiments, the temperature sensor 60 is attached to the lower end of the coil end 20, but this is not limiting, and the temperature sensor 60 may be attached to a location other than the lower end of the coil end 20 as long as the temperature sensor 60 is attached to a portion lower than the lowest end of the air gap G.

[0083] Furthermore, in each of the above embodiments, two pumps, namely, the discharge pump 45 and the suction pump 50, are used. However, this is not limited to this, and only the suction pump 50 may be used, for example, if the portion of the oil O sucked by the suction pump 50 that exceeds the amount required for cooling is temporarily stored in a buffer section (not shown) via the flow control valve 47.

[0084] Furthermore, in each of the above embodiments, the motor ECU 30, which performs switching control, etc., controls the suction pump 50. However, this is not limiting, and for example, another control device may be made to control the suction pump 50. In this case, the other control device also corresponds to the "control device that controls the motor" as defined in the claims.

[0085] Furthermore, in each of the above embodiments, the recess 13d is formed in the outer peripheral surface 13c of the rotor core 13, but this is not limited to this, and as long as oil infiltration suppression control is performed to increase the suction force of the suction pump 50 when the detected temperature T of the temperature sensor 60 exceeds the upper limit temperature ULT, the recess 13d does not need to be formed in the outer peripheral surface 13c of the rotor core 13. In other words, the infiltration of oil O into the air gap G may be suppressed only by oil infiltration suppression control by the motor ECU 30.

[0086] As such, the above-described embodiments are merely examples in all respects and should not be interpreted as limiting. Furthermore, all modifications and changes within the scope of the claims are within the scope of the present invention. [Industrial Applicability]

[0087] According to the present invention, it is possible to prevent oil from entering the air gap in a radial gap motor, and therefore it is extremely useful when applied to a motor control system that cools the motor by supplying oil. [Explanation of symbols]

[0088] 1. Motor control system 10 Motor 11 rotor 13c Outer surface 13d recess 17 Stator 20 Coil end 25 Motor housing 30 Motor ECU (control unit) 40 Cooling device 50 Suction Pump 60 Temperature Sensor G Air Gap LLT lower limit temperature O Oil T Detected temperature ULT upper limit temperature

Claims

1. A motor control system comprising: a motor including a rotor having a cylindrical rotor core; a stator having a stator core arranged to surround the rotor core with an air gap radially spaced from the outer peripheral surface of the rotor core; and a motor housing that accommodates the rotor and the stator; and a control device that controls the motor, a cooling device that supplies oil to the motor; a pump that sucks oil accumulated at the bottom of the motor housing; a temperature sensor that detects the temperature of a stator coil attached to the stator; Furthermore, the temperature sensor is attached to a coil end of the stator coil at a portion lower than the lowest end of the air gap, The motor control system is characterized in that the control device is configured to control the pump to increase its suction force so that the oil level of the oil accumulated at the bottom of the motor housing does not exceed the lowest end of the air gap when the temperature detected by the temperature sensor exceeds a predetermined upper limit temperature.

2. 2. The motor control system of claim 1, A motor control system characterized in that the temperature sensor is attached to a lower end of the coil end.

3. 2. The motor control system of claim 1, The motor control system is characterized in that the control device is configured to stop control to increase the suction force of the pump when the temperature detected by the temperature sensor exceeds the predetermined upper limit temperature and then falls below a predetermined lower limit temperature that is set lower than the predetermined upper limit temperature.

4. 2. The motor control system of claim 1, A motor control system characterized in that the rotor core has a recess formed in its outer circumferential surface.

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