Electric power steering device

Abstract

This electric power steering device (1, 1A, 1B) comprises: a motor (2); a heatsink (32) provided with a bearing (33) that rotatably supports a rotary shaft (21) of the motor; and a circuit substrate (31) which is provided with an inverter circuit (4, 4A, 4B) for driving the motor and which is disposed on a surface of the heatsink on the side opposite to the motor. Heater elements (8, 8A, 8B, 9, 9A, 9B) constituting the inverter circuit are arranged within a projection domain (42) which is formed on the circuit substrate and onto which the outer shape of the heatsink is projected, as viewed from the axial direction of the rotary shaft. The inverter circuit is configured to be driven at a first voltage of 20 V or higher.

Description

[Technical Field]

[0001] The present disclosure relates to an electric power steering device. [Background technology]

[0002] Patent Document 1 discloses an electric power steering device that is installed in a vehicle and assists the driver's steering operation. The electric power steering device includes a control device configured with an inverter circuit that drives a motor and a control circuit that controls the inverter circuit, mounted on a circuit board, and the control device is integrated with the motor. The inverter circuit includes power semiconductor elements such as switching elements, which are heat-generating elements that generate heat when the motor is driven. In addition, electronic components mounted on the circuit board may have an upper limit on their operating temperature. If this upper limit is reached, measures such as suspending the operation of the electric power steering device may be taken to prevent malfunction or damage to the electronic components. In this case, the continuous use time of the electric power steering device may be shortened, which may lead to a decrease in steering assist force. Therefore, the electric power steering device is provided with a heat dissipation structure that dissipates heat from the heat-generating elements. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent No. 6146380 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 employs a heat dissipation structure in which a heat dissipation material is provided between one side of a circuit board on which a heat generating element is mounted and a heat sink that forms part of the motor housing, and the circuit board is fixed to the housing with screws to bring the heat dissipation material into close contact with the circuit board and the heat sink, thereby dissipating heat generated by the heat generating elements on the circuit board to the heat sink via the heat dissipation material. While this structure is intended to efficiently dissipate heat from the heat generating elements, it is necessary to ensure that the circuit board and the heat sink have sufficient area to be in close contact with the heat dissipation material, and the use of the heat dissipation material poses issues such as an increase in the size of the device and an increase in product weight.

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to provide an electric power steering device with an integrated control device that reduces the heat generation amount of the heating element, thereby miniaturizing and simplifying the heat dissipation structure, reducing product weight, and enabling low-cost manufacturing. [Means for solving the problem]

[0006] The electric power steering device of the present disclosure comprises a motor, a heat sink provided with bearings that rotatably support the rotating shaft of the motor, and a circuit board provided with an inverter circuit that drives the motor and arranged on the side of the heat sink opposite the motor, wherein a heat-generating element that constitutes the inverter circuit is arranged within a projection area on the circuit board that is a projection of the outline of the heat sink when viewed from the axial direction of the rotating shaft, and the inverter circuit is configured to be driven by a first voltage of 20 V or more. [Effects of the Invention]

[0007] According to the present disclosure, it is possible to provide an electric power steering device with an integrated control device that can reduce the amount of heat generated by the heating element, thereby enabling the heat dissipation structure to be made smaller and simpler, reducing product weight and enabling low-cost manufacturing. [Brief explanation of the drawings]

[0008] [Figure 1]1 is a block diagram showing an electric power steering device according to a first embodiment. [Figure 2] 1 is a cross-sectional view of an electric power steering device according to a first embodiment. [Figure 3] FIG. 2 is a plan view of the circuit board according to the first embodiment. [Figure 4] FIG. 10 is a plan view of a circuit board according to a first modification of the first embodiment. [Figure 5] FIG. 5 is a cross-sectional view taken along the line VV in FIG. 4. [Figure 6] FIG. 10 is a plan view of a circuit board according to a second modification of the first embodiment. [Figure 7] FIG. 7 is a cross-sectional view taken along the line VII-VII in FIG. 6. [Figure 8] FIG. 10 is a plan view of a circuit board according to a third modification of the first embodiment. [Figure 9] FIG. 9 is a cross-sectional view taken along line IX-IX in FIG. 8. [Figure 10] FIG. 10 is a block diagram showing an electric power steering device according to a fourth modification of the first embodiment. [Figure 11] FIG. 10 is a block diagram showing an electric power steering device according to a second embodiment. [Figure 12] FIG. 10 is a plan view of a circuit board according to a second embodiment. [Figure 13] FIG. 10 is a block diagram showing an electric power steering device according to a modified example of the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Embodiment 1 FIG. 1 is a block diagram showing an electric power steering device 1 according to a first embodiment. The electric power steering device 1 shown in FIG. 1 includes a motor 2 that generates a steering assist force and a control device 3 that controls the motor 2. The motor 2 in this embodiment is a three-phase brushless motor. The control device 3 is electrically connected to a vehicle-side power supply 50 and a vehicle-side sensor 51 that are mounted on the vehicle. That is, the vehicle-side power supply 50 and the vehicle-side sensor 51 are provided outside the electric power steering device 1. The vehicle-side power supply 50 is, for example, a battery, and supplies DC power of 24 V (first voltage) to the control device 3. Specific examples of the vehicle-side sensor 51 include a vehicle speed sensor that detects the speed of the vehicle and a torque sensor that detects the steering torque of the steering wheel.

[0010] As shown in FIG. 1, the control device 3 includes an inverter circuit 4, a control circuit 5, a voltage dividing circuit 6 (voltage step-down circuit), and a rotation angle sensor . The inverter circuit 4 is controlled by a control circuit 5 and configured to supply and cut off current to the motor 2. In this embodiment, the inverter circuit 4 is configured to receive 24V power from a vehicle-side power supply 50 and be driven by this power. However, due to the charging and discharging states of the vehicle-side power supply 50, the voltage supplied from the vehicle-side power supply 50 is not necessarily constant. The inverter circuit 4 is configured to operate appropriately at a voltage between 20V and 32V, for example. The inverter circuit 4 includes multiple power semiconductor elements 8 functioning as switching elements and a current detection element 9 that detects the magnitude of the current. Although not shown, the inverter circuit 4 also includes multiple ripple capacitors that absorb ripples in the current flowing through the motor 2. An example of the power semiconductor element 8 is a field effect transistor (FET). Multiple bridge circuits are configured by the multiple switching elements, and each bridge circuit is configured to supply current to each of the three-phase (U, V, W) windings of the motor 2. The current detection element 9 may be, for example, a shunt resistor.

[0011] The control circuit 5 has a CPU 10 that performs arithmetic processing. Although not shown, the control circuit 5 may also have a drive circuit used by the CPU 10 to control the switching of the inverter circuit 4, an input circuit that transmits signals from the rotation angle sensor 7 and the vehicle-side sensor 51 to the CPU 10, a regulator circuit that adjusts voltage, and the like. The functions of the CPU 10, the drive circuit, the input circuit, and the regulator circuit may be realized by, for example, an integrated circuit (IC) or an application-specific integrated circuit (ASIC). The CPU 10 is configured to acquire various input signals, and specific examples of the input signals include information from the vehicle-side sensor 51, voltages at various parts in the inverter circuit 4, the magnitude of the drive current of the motor 2 detected by the current detection element 9, and the rotation angle detected by the rotation angle sensor 7.

[0012] The voltage divider circuit 6 is a circuit (step-down circuit) that generates a lower voltage of 12 V (second voltage) from the 24 V voltage supplied from the vehicle-side power supply 50. The voltage divider circuit 6 is composed of, for example, two resistors. The voltage divider circuit 6 is electrically connected to the control circuit 5 and supplies the generated 12 V voltage to the control circuit 5. In place of the voltage divider circuit 6, for example, a regulator or a step-down DC / DC converter may be provided to generate a lower voltage (second voltage) from the 24V voltage (first voltage) supplied from the vehicle-side power supply 50.

[0013] The rotation angle sensor 7 is used to detect the rotation angle of the motor 2. In this embodiment, the rotation angle sensor 7 detects the rotation angle of the motor 2 by changes in magnetism. The rotation angle sensor 7 is supplied with power that has been adjusted to an appropriate voltage by the voltage divider circuit 6 or the regulator circuit.

[0014] Although not shown, the control device 3 may also have a power supply relay capable of cutting off the power supply to the inverter circuit 4 and a noise filter connected to the vehicle-side power supply 50. The power supply relay is used to protect the inverter circuit 4 from incorrect connection of the vehicle-side power supply 50 to the control device 3. A field effect transistor (FET) which is a switching element may also be used for the power supply relay. When a noise filter is provided, the power supplied from the vehicle-side power supply 50 passes through the noise filter before being supplied to the inverter circuit 4 and the voltage divider circuit 6. The noise filter may be composed of a multilayer ceramic capacitor and a choke coil.

[0015] The operation of the control circuit 5 will now be described in outline. Based on the acquired input signals, the CPU 10 calculates the magnitude of the drive current to be supplied to each winding of the motor 2, etc. Based on the calculation results, the CPU 10 controls the switching of the inverter circuit 4. More specifically, the CPU 10 issues control instructions to the drive circuit. Based on the control instructions from the CPU 10, the drive circuit controls the power semiconductor elements 8 that function as switching elements. Control by the CPU 10 via the drive circuit is performed for each phase (U, V, W) of the motor 2. In other words, when the power semiconductor elements 8 of each phase (U, V, W) are driven by the drive circuit, a predetermined current flows to each winding of the motor 2.

[0016] The magnitude of the current value supplied to each winding of the motor 2 is provided to the CPU 10 as an actual current value via the current detection element 9. The CPU 10 performs feedback control according to the deviation between the calculated value (target value) and the actual current value. Furthermore, the CPU 10 utilizes the rotation angle information obtained by the rotation angle sensor 7 to control the rotation of the motor 2. Specifically, the CPU 10 uses the rotation angle information obtained by the rotation angle sensor 7 to calculate the rotation angle (phase) or rotation speed of the rotating shaft 21 of the motor 2.

[0017] Next, the structure of each part of the electric power steering device 1 equipped with the control device 3 and the motor 2 will be described with reference to FIG. FIG. 2 is a cross-sectional view showing the electric power steering device 1 according to the first embodiment. In the following description, the direction in which the central axis O of the rotary shaft 21 of the motor 2 extends may be referred to as the axial direction. The axial direction is also the thickness direction of the circuit board 31 of the control device 3. In addition, in the axial direction, the side where the control device 3 is located may be referred to as the upper side, and the side where the motor 2 is located may be referred to as the lower side. The view from the axial direction may be referred to as a plan view. In the plan view, the direction intersecting the central axis O may be referred to as the radial direction, and the direction going around the central axis O may be referred to as the circumferential direction.

[0018] The lower end of the rotating shaft 21 of the motor 2 is used as the output end 21a. A boss 22 is attached to the output end 21a and is connected to a driven object (for example, a steering system of a vehicle). A reducer or the like may be interposed between the output end 21a and the driven object. The output of the motor 2 is transmitted to the driven object via the output end 21a. When the electric power steering device 1 is used, the axial direction of the rotating shaft 21 does not have to coincide with the vertical direction.

[0019] The motor 2 includes a motor main body M and a motor case 23. The motor case 23 has a cylindrical portion 23a, a bottom portion 23b, and a protruding portion 23c. The cylindrical portion 23a extends axially. The bottom portion 23b is provided to close an opening at the lower end of the cylindrical portion 23a. The protruding portion 23c protrudes radially outward from the upper end of the cylindrical portion 23a. The motor main body M is housed inside the cylindrical portion 23a of the motor case 23. The motor case 23 is made of metal. Considering heat dissipation and ease of molding, an aluminum-based alloy is a suitable specific material for the motor case 23. The motor case 23 is fabricated, for example, by cutting a molded body obtained by die-casting or the like from an aluminum-based alloy. A through-hole is formed in the center of the bottom portion 23b of the motor case 23, through which the rotating shaft 21 passes. A first bearing 25 that rotatably supports the rotary shaft 21 is attached to the through hole in the bottom portion 23b.

[0020] The motor main body M includes a rotor 26 and a stator 27. The rotor 26 includes a cylindrical rotor core 26a disposed around the rotating shaft 21 and fixed to the rotating shaft 21, and a plurality of permanent magnets 26b disposed on the outer circumferential surface of the rotor core 26a. The plurality of permanent magnets 26b are arranged such that the polarities (south poles and north poles) on the outer circumferential surface of the rotor 26 alternate along the circumferential direction. The stator 27 is disposed radially outside the rotor 26, with a gap therebetween. The stator 27 includes a stator core 27a formed by laminating steel plates, and a winding 27b wound around the stator core 27a with an insulator 27c interposed therebetween. The stator 27 is fixed in the cylindrical portion 23a of the motor case 23 by press-fitting, shrink-fitting, or the like. The rotating shaft 21, the rotor 26, and the stator 27 are arranged coaxially.

[0021] An annular connection ring 28 is disposed above the stator 27, close to the windings 27b. The connection ring 28 has a structure in which bus bars 29 (see FIG. 3) for electrical wiring are insert-molded into insulating resin. An end of each winding 27b is connected to the bus bars 29 of the connection ring 28, thereby forming a three-phase winding. The bus bars 29 for each phase protrude from the connection ring 28 and extend toward the control device 3. Three bus bars 29 are provided on the connection ring 28, one for each phase (U, V, W). Each bus bar 29 protrudes upward from the connection ring 28 and is disposed so as to penetrate a circuit board 31 of the control device 3.

[0022] A disk-shaped heat sink 32 is fitted into the upper end of the cylindrical portion 23a of the motor case 23. The heat sink 32 is disposed with its central axis parallel to the axial direction. The height of the upper surface of the heat sink 32 is equal to the height of the upper surface of the protruding portion 23c of the motor case 23. In this embodiment, the upper surface of the heat sink 32 is formed flat and is flush with the upper surface of the protruding portion 23c. The heat sink 32 is made of metal (for example, an aluminum-based alloy). In order to ensure a relatively large heat capacity, the motor case 23 has a thickness greater than the axial thickness of the bottom portion 23b of the motor case 23, for example.

[0023] A through-hole 32a is formed in the center of the heat sink 32 in the plate thickness direction, and a second bearing 33 (bearing) is attached to this through-hole 32a to rotatably support the rotating shaft 21. The second bearing 33 supports the end 21b (upper end in this embodiment) of the rotating shaft 21 opposite the output end 21a of the rotating shaft 21. The end 21b of the rotating shaft 21 is disposed in the through-hole 32a of the heat sink 32. The rotation angle sensor 7 is provided on the lower surface of the circuit board 31 and is disposed in a position facing the through-hole 32a of the heat sink 32. Although the rotation angle sensor 7 protrudes downward from the lower surface of the circuit board 31, it is disposed within the through-hole 32a of the heat sink 32 and does not interfere with the heat sink 32. Furthermore, the heat sink 32 is formed with three through-holes (not shown) through which the bus bars 29 of each phase (U, V, W) pass.

[0024] Both ends of the rotating shaft 21 are rotatably supported by a first bearing 25 and a second bearing 33. Therefore, the rotor 26 fixed to the rotating shaft 21 is also rotatable radially inside the stator 27. A sensor magnet 34 is attached to the end 21b of the rotating shaft 21 opposite the output end 21a. The sensor magnet 34 is at least partially formed of a permanent magnet and emits a magnetic field. The sensor magnet 34 rotates together with the rotating shaft 21. As the rotating shaft 21 rotates, the sensor magnet 34 also rotates, causing a change in the magnetic field. The sensor magnet 34 is disposed axially opposite the rotation angle sensor 7. Therefore, the rotation angle sensor 7 detects the rotation angle of the rotating shaft 21 of the motor 2 based on changes in the magnetic field emitted by the sensor magnet 34, which rotates together with the rotating shaft 21.

[0025] The control device 3 includes a circuit board 31 and an electronic circuit 35 provided on the circuit board 31. The circuit board 31 is, for example, a multilayer printed circuit board in which multiple insulating layers and multiple conductor layers are stacked. The electronic circuit 35 includes the inverter circuit 4, control circuit 5, and voltage divider circuit 6 shown in FIG. 1. Electronic components such as a rotation angle sensor 7, power semiconductor element 8, current detection element 9, and CPU 10 are mounted on the circuit board 31. These electronic components and the circuit pattern formed on the circuit board 31 form the electronic circuit 35. The circuit board 31 is covered from above by a cover 36.

[0026] The cover 36 is configured to cover the circuit board 31. The circuit board 31 is housed in a space surrounded by the cover 36 and the motor case 23. The cover 36 has functions such as protecting the circuit board 31 from external electromagnetic noise and preventing electromagnetic noise generated by the circuit board 31 from leaking out of the cover 36. In order to fulfill these functions, the cover 36 is desirably made of metal. In this embodiment, the cover 36 is made of resin and metal.

[0027] A connector 30 is provided on the underside of the protruding portion 23c of the motor case 23. The connector 30 is used to connect the electric power steering device 1 to a vehicle-side power supply 50 and a vehicle-side sensor 51. A plurality of connector terminals 43 are provided above the connector 30. The connector terminals 43 are electrically connected to terminals (not shown) within the connector 30. The protruding portion 23c of the motor case 23 has an opening (not shown) for passing the connector terminals 43 through, and the connector terminals 43 are inserted into the opening. The connector terminals 43 are inserted into through-holes formed in the circuit board 31, and the circuit pattern of the circuit board 31 and the connector terminals 43 are electrically connected by soldering. Note that the method of connecting the circuit board 31 and the connector terminals 43 is not limited to soldering, and for example, press-fitting may also be used. Power from the vehicle-side power supply 50 and signals from the vehicle-side sensors 51 are transmitted to the circuit board 31 via the connector 30. In this embodiment, the connector 30 is provided on the underside of the protrusion 23c, but this is not limited to this. It is also possible to form a hole in the cover 36 and attach the connector 30 to the upper surface of the circuit board 31 from above through the hole.

[0028] No electronic components other than the rotation angle sensor 7 are mounted on the underside of the circuit board 31. The underside of the circuit board 31 is disposed in contact with the surface of the heat sink 32 opposite the motor 2 (the upper surface in this embodiment). More specifically, the underside of the circuit board 31 is in contact with the upper surface of the heat sink 32 via an applied insulating grease (not shown in FIG. 2). It is preferable to select a grease with high thermal conductivity.

[0029] Fig. 3 is a plan view of the circuit board 31. The top surface of the circuit board 31 is shown in Fig. 3. As shown in Fig. 3, circuit board 31 is fixed to motor case 23 with a plurality of screws 37. Three bus bars 29 corresponding to each phase are connected to circuit board 31 and penetrate the board in the thickness direction. Bus bars 29 are connected to a circuit pattern (not shown) on circuit board 31 by soldering, and this circuit pattern is electrically connected to windings 27b of motor 2 via bus bars 29. Note that the circuit pattern of circuit board 31 and bus bars 29 of each phase may be connected by means other than soldering, for example, by press-fit.

[0030] When viewed in the axial direction, an imaginary area obtained by projecting the outline of the heat sink 32 onto the circuit board 31 is referred to as a projection area 42. When viewed in the axial direction, the circuit board 31 protrudes outside the projection area 42. The protruding portion 23c of the motor case 23 also protrudes radially outward from the cylindrical portion 23a so as to support the portion of the circuit board 31 that protrudes outside the projection area 42.

[0031] Here, the power semiconductor element 8, the current detection element 9, and the like mounted on the circuit board 31 are heat-generating elements that generate heat when a large current flows through them as the motor 2 is driven. In order to prevent a decrease in the steering assist force without shortening the continuous use time of the electric power steering device 1, it is preferable that the heat generated by these heat-generating elements be quickly released to the outside of the electric power steering device 1. In this embodiment, the power semiconductor element 8 and the current detection element 9 are arranged on the upper surface of the circuit board 31. Furthermore, the power semiconductor element 8 and the current detection element 9 are arranged within the projection area 42 of the circuit board 31. That is, the power semiconductor element 8 and the current detection element 9 are arranged side by side with the heat sink 32 in the axial direction. Furthermore, since the lower surface of the circuit board 31 is in contact with the upper surface of the heat sink 32 via grease, heat generated by these heat-generating elements is transferred to the heat sink 32 via the circuit board 31 and the grease, and is then dissipated from the heat sink 32 to the outside.

[0032] The input power to the inverter circuit 4 of the electric power steering device 1 is input power P = current I × voltage V (W). However, the heat generation of the electronic components and motor 2 is calculated as heat generation Q = resistance R × current I^2 × time t, so the current value has a significant effect on heat generation. Conventionally, a 12V voltage was generally supplied to the electric power steering device from the vehicle-side power supply. However, in this embodiment, a 24V voltage is supplied from the vehicle-side power supply 50 to the inverter circuit 4 of the control device 3. Therefore, if the input power to the motor 2 is the same as in the conventional case, the voltage is doubled compared to the conventional case, and the current can be halved. This makes it possible to suppress heat generation from the power semiconductor elements 8, such as FETs, in the inverter circuit 4.

[0033] This effect of suppressing the amount of heat generated is not limited to power semiconductor elements 8 such as FETs mounted on circuit board 31, but also applies to all heat-generating elements that can reduce current, such as current detection elements 9, ripple capacitors, power relays, choke coils, etc. Heat generated by bus bars 29 and windings 27b of motor 2 can be similarly suppressed. Because the heat generation amounts of the power semiconductor element 8 and the current detection element 9 can be suppressed, a simplified heat dissipation structure using the heat sink 32 of this embodiment can be adopted. As described above, the power semiconductor element 8 and the current detection element 9 are arranged on the upper surface of the circuit board 31 and within the projection area 42. Therefore, even in a simplified heat dissipation structure in which the lower surface of the circuit board 31 is in contact with the upper surface of the heat sink 32 via grease, the heat generated by the above-mentioned heat-generating elements can be appropriately dissipated to the outside from the heat sink 32 via the circuit board 31 and the grease. Because the heat generation amounts of the heat-generating elements can be suppressed, the heat dissipation structure can be made smaller and simpler, the weight of the electric power steering device 1 can be reduced, and manufacturing costs can be further reduced.

[0034] In this embodiment, the vehicle-side power supply 50 supplies a voltage of 24 V to the control device 3. However, this is not limiting. For example, the vehicle-side power supply 50 may supply a voltage of 48 V to the control device 3 and the inverter circuit 4. If the input power to the motor 2 is the same as in the past, the voltage is four times higher than in the past, so the current can be reduced to one-fourth, further reducing the amount of heat generated by the heating element. As described above, the voltage supplied from the vehicle-side power supply 50 is not necessarily constant depending on the charging and discharging status of the vehicle-side power supply 50. In this case, the inverter circuit 4 is configured to operate appropriately at a voltage of, for example, 42 V or higher and 56 V or lower. Therefore, to reduce the amount of heat generated, the inverter circuit 4 may be configured to operate at a voltage of 20 V or higher and 56 V or lower. Furthermore, although the control circuit 5 in this embodiment operates on a voltage of 12 V, it is also possible to increase the withstand voltage performance of the electronic components constituting the control circuit 5 and configure it to operate on a voltage of 24 V, similar to the inverter circuit 4. In this case, it becomes unnecessary to supply a voltage of 12 V to the control circuit 5 from the voltage divider circuit 6 described above.

[0035] This embodiment can employ the following modifications. FIG. 4 is a plan view of a circuit board 31 according to a first modification of the first embodiment. FIG. 5 is a cross-sectional view taken along the line VV in FIG. 4. In the configuration of the first embodiment, the current detection element 9 is disposed on the upper surface of the circuit board 31 and within the projection area 42. However, in this modification, the current detection element 9 is disposed within the projection area 42 and on the lower surface of the circuit board 31, i.e., the surface of the circuit board 31 facing the heat sink 32. If the current detection element 9 is disposed on the lower surface of the circuit board 31, it would be difficult to bring the lower surface of the circuit board 31, other than the current detection element 9, close to the heat sink 32. However, in this modification, the heat sink 32 has a recess 41 formed in a position facing the current detection element 9 to accommodate the current detection element 9. Therefore, as in the first embodiment, the lower surface of the circuit board 31, other than the current detection element 9, close to the upper surface of the heat sink 32 can be brought close to the upper surface of the heat sink 32. By employing such a configuration, even when the mounting area of ​​the circuit board 31 is limited, it is possible to mount some of the heat-generating elements on the lower surface of the circuit board 31 and maintain good heat dissipation performance. The gap between the lower surface of the circuit board 31 and the upper surface of the heat sink 32, and the inside of the recess 41, are filled with grease 44 to form a heat dissipation path.

[0036] FIG. 6 is a plan view of a circuit board 31 according to a second modification of the first embodiment. FIG. 7 is a cross-sectional view taken along line VII-VII in FIG. 6. In this modification, a plurality of thermal vias 45 for heat dissipation are arranged around the power semiconductor elements 8 in the circuit board 31. The thermal vias 45 are arranged around the power semiconductor elements 8 in the circuit board 31 at positions different from the power semiconductor elements 8 in a plan view. The thermal vias 45 have a configuration in which the inner surface of a through hole that penetrates the circuit board 31 in the thickness direction is plated with a metal such as copper or gold that has good thermal conductivity. By arranging such thermal vias 45 around the power semiconductor elements 8, heat from the power semiconductor elements 8 can be more efficiently transferred from the upper surface of the circuit board 31 to the heat sink 32 via the metal plating of the thermal vias 45, thereby improving heat dissipation performance.

[0037] Although not shown, a circuit pattern extending in a planar direction along the upper surface of the circuit board 31 may be formed to connect the thermal vias 45 and the power semiconductor elements 8, or a circuit pattern extending in a planar direction from the thermal vias 45 may be formed on the lower surface of the circuit board 31. By forming such a circuit pattern, the heat of the power semiconductor elements 8 can be more efficiently released through the thermal vias 45. Furthermore, the thermal vias 45 may be formed around heat-generating elements other than the power semiconductor elements 8.

[0038] FIG. 8 is a plan view of a circuit board 31 according to a third modification of the first embodiment. FIG. 9 is a cross-sectional view taken along line IX-IX in FIG. 8. In this modification, a copper inlay 46 is disposed in the circuit board 31 at a position between the power semiconductor element 8 and the heat sink 32 in the axial direction. The copper inlay 46 has a configuration in which an inlay made of copper, which has good thermal conductivity, is disposed in a through hole that penetrates the circuit board 31 in the thickness direction. The upper surface of the copper inlay 46 is preferably in contact with the lower surface of the power semiconductor element 8. By disposing such a copper inlay 46, heat from the power semiconductor element 8 can be more efficiently transferred to the heat sink 32 via the copper inlay 46, thereby improving heat dissipation performance. The copper inlay 46 may also be disposed between a heat-generating element other than the power semiconductor element 8 and the heat sink 32.

[0039] 10 is a block diagram showing an electric power steering device 1 according to a fourth modification of the first embodiment. The configuration of this modification differs from that of the first embodiment in that a vehicle-side power supply 50 supplies 12V power to the control device 3 of the electric power steering device 1, and that the control device 3 includes a boost circuit 11 instead of the voltage divider circuit 6 in the first embodiment.

[0040] A 12V voltage (second voltage) supplied from the vehicle-side power supply 50 is supplied to the control circuit 5 and the boost circuit 11. The control circuit 5 is driven by the externally supplied 12V voltage. The boost circuit 11 generates a higher voltage of 24V (first voltage) from the externally supplied 12V voltage. For example, a DC / DC converter can be used as the boost circuit 11. The 24V voltage generated by the boost circuit 11 is supplied to the inverter circuit 4, which is driven by the 24V voltage generated by the boost circuit 11. As described above, since the amount of heat generated is proportional to the square of the current value, the output voltage of the boost circuit 11 may be further increased to, for example, 48V, while the current in the inverter circuit 4 may be further reduced to further reduce the amount of heat generated. The boost circuit 11 may output a voltage of, for example, 20V or more. Correspondingly, the inverter circuit 4 may also be configured to be driven by a voltage of 20V or more. According to this modification, measures can be taken to reduce the amount of heat generated in the electric power steering device 1 without changing the configuration of the vehicle-side power supply 50 from the conventional configuration.

[0041] In the first embodiment and the first to fourth modifications, the first voltage at which the inverter circuit 4 is driven may be 20 V or higher. On the other hand, the second voltage at which the control circuit 5 is driven may be lower than the first voltage and may be higher than or equal to a voltage at which the control circuit 5 can operate properly.

[0042] As described above, the electric power steering device 1 according to this embodiment includes the motor 2, the heat sink 32 provided with the second bearing 33 that rotatably supports the rotating shaft 21 of the motor 2, and the circuit board 31 that is provided with the inverter circuit 4 that drives the motor 2 and is disposed on the surface of the heat sink 32 opposite to the motor 2. The power semiconductor element 8 and the current detection element 9 that constitute the inverter circuit 4 are disposed within a projection area 42 on the circuit board 31 that is a projection of the outline of the heat sink 32, as viewed in the axial direction of the rotating shaft 21. The inverter circuit 4 is configured to be driven by a first voltage of 20 V or more.

[0043] According to this configuration, the current in the inverter circuit 4 can be reduced, thereby suppressing the amount of heat generated by the power semiconductor element 8 and the current detection element 9, and therefore a simplified heat dissipation structure using the heat sink 32 can be adopted. As described above, the power semiconductor element 8 and the current detection element 9 are arranged within the projection area 42 of the circuit board 31. Therefore, even in a simplified heat dissipation structure in which the lower surface of the circuit board 31 is in contact with the upper surface of the heat sink 32 via grease, the heat generated by the above-mentioned heat-generating element can be appropriately dissipated to the outside from the heat sink 32 via the circuit board 31 and the grease. Because the amount of heat generated by the heat-generating element can be suppressed, the heat dissipation structure can be made smaller and simpler, the weight of the electric power steering device 1 can be reduced, and manufacturing costs can be further reduced.

[0044] The circuit board 31 may also be provided with a voltage divider circuit 6 (step-down circuit) that generates a second voltage lower than a first voltage supplied from an external source, and a control circuit 5 that is driven by the second voltage generated by the voltage divider circuit 6 and controls the inverter circuit 4. With this configuration, the control circuit 5 is driven by the second voltage lower than the first voltage, so that it is possible to employ a configuration that operates at a voltage of, for example, 12 V, which has been conventionally common, without improving the withstand voltage performance of the electronic components that make up the control circuit 5, and it is possible to avoid an increase in the cost of the electronic components due to a change in withstand voltage performance.

[0045] The circuit board 31 may also be provided with a boost circuit 11 that generates the first voltage from a second voltage that is supplied from the outside and is lower than the first voltage, and the inverter circuit 4 may be driven by the first voltage generated by the boost circuit 11. With this configuration, it is possible to obtain the effect of reducing the amount of heat generated in the inverter circuit 4 and the like only with the configuration of the electric power steering device 1, without changing the configuration and output voltage of the external vehicle-side power supply 50 from conventional ones. Furthermore, in this case, the circuit board 31 is provided with a control circuit 5 that controls the inverter circuit 4, and the control circuit 5 may be driven by a second voltage supplied from outside. With this configuration, the control circuit 5 is driven by a second voltage lower than the first voltage, so that it is possible to adopt a configuration that operates at a voltage of, for example, 12 V, which has been conventionally common, without improving the withstand voltage performance of the electronic components that make up the control circuit 5, and it is possible to avoid an increase in the cost of the electronic components due to a change in withstand voltage performance.

[0046] Furthermore, the heat-generating elements constituting the inverter circuit 4 may include a current detection element 9 provided on the surface of the circuit board 31 facing the heat sink 32, and a recess 41 for accommodating the current detection element 9 may be formed in the heat sink 32 at a position facing the current detection element 9. With this configuration, even if it is difficult to mount the current detection element 9 on the upper surface of the circuit board 31 due to mounting area restrictions or the like and it is mounted on the lower surface of the circuit board 31, accommodating the current detection element 9 in the recess 41 makes it possible to bring the surface of the circuit board 31 other than the current detection element 9 into close contact with the heat sink 32, thereby maintaining high heat transfer efficiency between the circuit board 31 and the heat sink 32.

[0047] Furthermore, thermal vias 45 for heat dissipation may be arranged around heat generating elements such as power semiconductor elements 8 and current detection elements 9 on circuit board 31. With this configuration, heat generated by the heat generating elements can be efficiently transferred from the heat generating element mounting surface of circuit board 31 to the opposite surface via thermal vias 45, thereby improving heat dissipation efficiency.

[0048] Furthermore, a copper inlay 46 may be disposed on the circuit board 31 at a position in the axial direction between the heat sink 32 and heat generating elements such as the power semiconductor elements 8 and the current detection elements 9. With this configuration, heat generated by the heat generating elements can be efficiently transferred from the heat generating element mounting surface of the circuit board 31 to the opposite surface via the copper inlay 46, thereby improving heat dissipation efficiency.

[0049] Embodiment 2 Fig. 11 is a block diagram showing an electric power steering device 1A according to embodiment 2. Fig. 12 is a plan view of a circuit board 31 according to embodiment 2. The structure of the motor 2 in this embodiment is similar to the structure of the motor 2 according to embodiment 1. Therefore, the same components of the motor 2 as those in embodiment 1 are denoted by the same reference numerals and their description will be omitted, with the differences being mainly described.

[0050] 11, the control device 3 in this embodiment includes two control units 3A and 3B. The stator 27 of the motor 2 in this embodiment has two sets of three-phase windings (not shown). The first control unit 3A is configured to control the first three-phase windings, and the second control unit 3B is configured to control the second three-phase windings.

[0051] The control units 3A and 3B have the same circuit configuration. Furthermore, each of the control units 3A and 3B has approximately the same circuit configuration as the control device 3 described in the first embodiment. Therefore, in this embodiment, among the components of the first control unit 3A, the same reference numerals as the corresponding components in the first embodiment are given the suffix "A." Furthermore, among the components of the second control unit 3B, the same reference numerals as the corresponding components in the first embodiment are given the suffix "B."

[0052] In the following, the description of the same structure as in the first embodiment will be omitted, and differences will be mainly described. For example, the control unit 3A includes a control circuit 5A and an inverter circuit 4A. The configurations of the control circuit 5A and the inverter circuit 4A are the same as those of the control circuit 5 and the inverter circuit 4 described in the first embodiment. As shown in FIG. 12, the mounting area of ​​the circuit board 31 in this embodiment is divided into two areas corresponding to the control units 3A and 3B, and the electronic components included in the control units 3A and 3B are also arranged in these two areas. The area designated by reference numeral 3A contains multiple power semiconductor elements 8A, multiple current detection elements 9A, a CPU 10A, and three bus bars 29A. The area designated by reference numeral 3B contains multiple power semiconductor elements 8B, multiple current detection elements 9B, a CPU 10B, and three bus bars 29B. In FIG. 12, electronic components such as a ripple capacitor, a choke coil, and a power relay are not shown.

[0053] Returning to Figure 11, the motor 2 is a brushless motor with two sets of three-phase windings. The electric power steering device 1A is equipped with rotation angle sensors 7A and 7B for detecting the rotation angle of the motor 2. The rotation angle signal output by the first rotation angle sensor 7A is input to the control circuit 5A of the first control unit 3A, and the rotation angle signal output by the second rotation angle sensor 7B is input to the control circuit 5B of the second control unit 3B.

[0054] The control units 3A and 3B can independently drive the motor 2. That is, the inverter circuits 4A and 4B each drive the motor 2. However, the control units 3A and 3B are each supplied with a current obtained by dividing the current output from the vehicle-side power supply 50 into two, and the same signal output from the vehicle-side sensor 51 is input to both of them. For example, in the first control unit 3A, the first control circuit 5A and the first inverter circuit 4A operate based on input information from the vehicle-side sensor 51, the first rotation angle sensor 7A, etc., thereby driving the rotating shaft 21 via the first winding. Similarly, in the second control unit 3B, the second control circuit 5B and the second inverter circuit 4B operate based on input information from the vehicle-side sensor 51, the second rotation angle sensor 7B, etc., thereby driving the rotating shaft 21 via the second winding.

[0055] In this way, redundancy is ensured by configuring the two control units 3A, 3B to be able to drive the motor 2 independently of each other. For example, even if a malfunction occurs in one of the control units 3A, 3B and it becomes impossible to drive the motor 2, the other control unit 3A, 3B can continue to drive the motor 2, preventing the steering assist force from becoming completely zero, and furthermore, the driver can sense the reduction in the steering assist force while operating the steering wheel, allowing the driver to quickly recognize the occurrence of a malfunction.

[0056] As described above, the control units 3A and 3B are each supplied with a current that is the current output by the vehicle-side power supply 50 divided into two, but since the control units 3A and 3B can each drive the motor 2 independently, the input power P to the motor 2 is P = (voltage V × current I / 2) + (voltage V × current I / 2), so the power input to the motor 2 is the same as in embodiment 1, and the steering assist force output by the motor 2 is also equivalent to that in embodiment 1. On the other hand, the current supplied to the inverter circuits 4A and 4B is half the current in embodiment 1, so the heat generated by the heat-generating elements of the inverter circuits 4A and 4B can be reduced compared to embodiment 1.

[0057] This embodiment can employ the following modifications. FIG. 13 is a block diagram showing an electric power steering device 1B according to a modification of the second embodiment. In the configuration of the second embodiment, the control units 3A and 3B are each supplied with a current obtained by dividing the current output by the vehicle-side power supply 50 into two, and the same signal output by the vehicle-side sensor 51 is input to both. However, in this modification, vehicle-side power supplies 50A and 50B and vehicle-side sensors 51A and 51B corresponding to the control units 3A and 3B are used. The first vehicle-side power supply 50A supplies power to the first control unit 3A, and the second vehicle-side power supply 50B supplies power to the second control unit 3B. In the first control unit 3A, the first control circuit 5A and the first inverter circuit 4A operate based on input information from the first vehicle-side sensor 51A, the first rotation angle sensor 7A, and the like. Similarly, in the second control unit 3B, the second control circuit 5B and the second inverter circuit 4B operate based on input information from the second vehicle-side sensor 51B and the second rotation angle sensor 7B, etc. Although not shown, two connectors are also provided for connecting the circuit board 31 of this modification to the vehicle-side power supplies 50A, 50B and the vehicle-side sensors 51A, 51B.

[0058] In this modification, vehicle-side power supplies 50A, 50B supply power to control units 3A, 3B separately, but the current supplied by each of vehicle-side power supplies 50A, 50B is half the current supplied by vehicle-side power supply 50 shown in Fig. 11. Therefore, in this modification as well, the current supplied to each of inverter circuits 4A, 4B is half the current in the first embodiment, and the heat generated by the heat-generating elements of each of inverter circuits 4A, 4B can be reduced compared to the first embodiment.

[0059] In the second embodiment, two inverter circuits 4A, 4B each drive the motor 2, and a two-system configuration is employed; however, the number of inverter circuits is not limited to two, and three or more inverter circuits may be provided, each driving the motor 2. For example, a four-system configuration may be employed. When maintaining the same output of the motor 2 as before, increasing the number of inverter circuits can further reduce the current supplied to the inverter circuits, and therefore the amount of heat generated by the heating element.

[0060] The present disclosure is not limited to the configurations of the above-described embodiments and modifications, but is limited only by the scope of the claims. The modifications described in each embodiment may be combined with each other, and the configurations of each embodiment may be modified or omitted as appropriate. For example, in embodiment 2, the description is based on the control device 3 shown in FIG. 1 of embodiment 1, but it is also possible to apply the control device 3 described in variants 1 to 4 of embodiment 1 to embodiment 2. [Explanation of symbols]

[0061] 1, 1A, 1B Electric power steering device 2 motors 4, 4A, 4B inverter circuit 5, 5A, 5B control circuit 6 Voltage divider circuit (step-down circuit) 8, 8A, 8B Power semiconductor element (heat generating element) 9, 9A, 9B Current detection element (heating element) 11 Boost circuit 21 Rotation axis 31 Circuit Board 32 Heat sink 33 Second bearing (bearing) 41 Recess 42 Projection area 45 Thermal via 46 Copper Inlay

Claims

1. A motor; a heat sink provided with a bearing that rotatably supports a rotary shaft of the motor; a circuit board having an inverter circuit for driving the motor and disposed on a surface of the heat sink opposite to the motor, a heat generating element constituting the inverter circuit is disposed within a projected area of ​​the circuit board, the projected area being a projection of an outline of the heat sink, as viewed in the axial direction of the rotation shaft; the inverter circuit is configured to be driven by a first voltage of 20 V or more; the heat generating element includes a current detecting element provided on a surface of the circuit board facing the heat sink, a recess for accommodating the current detection element is formed in a position of the heat sink facing the current detection element; The heat generating element includes a switching element disposed on the surface of the circuit board opposite to the heat sink.

2. The circuit board includes: a step-down circuit that generates a second voltage lower than the first voltage from the first voltage supplied from an external source; a control circuit that is driven by the second voltage generated by the step-down circuit and controls the inverter circuit; 2. The electric power steering device according to claim 1, further comprising:

3. a booster circuit that generates the first voltage from a second voltage that is supplied from an external source and is lower than the first voltage is provided on the circuit board; 2. The electric power steering device according to claim 1, wherein the inverter circuit is driven by the first voltage generated by the boost circuit.

4. a control circuit for controlling the inverter circuit is provided on the circuit board; 4. The electric power steering device according to claim 3, wherein the control circuit is driven by the second voltage supplied from an external source.

5. The circuit board is provided with a plurality of the inverter circuits, 2. The electric power steering device according to claim 1, wherein each of the plurality of inverter circuits drives the motor.

6. 2. The electric power steering device according to claim 1, wherein a thermal via for heat dissipation is arranged around the heat generating element in the circuit board.

7. The electric power steering device according to claim 1 , wherein a copper inlay is disposed on the circuit board at a position between the heat generating element and the heat sink in the axial direction.

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