Electronic device

Abstract

Electronic device for controlling a drive operation of an electric motor (3), comprising: a printed circuit board (20); a connector terminal (30) installed on the circuit board (20) and receiving an electric current provided from an external electric power source (32) to a coil (7) of the electric motor (3); a plurality of heat generating devices (24, 25) installed on the circuit board (20) and generating heat when the electric current to be supplied to the coil (7) is passed through the plurality of heat generating devices (24, 25); a drive line (21) installed on the circuit board (20) and carrying the electrical current between: a motor line (8) connected to the coil (7); the plurality of heat generating devices (24, 25); and the connector terminal (30); a heat sink main body (41) that absorbs the heat generated from the plurality of heat generating devices (24, 25); a primary support (42, 43) extending integrally from the heat sink main body (41) and supporting the circuit board (20) at a location between: the connector terminal (30); and one of the plurality of heat generating devices (24, 25), the drive line (21) or the motor line (8); a secondary support (44, 45) extending integrally from the heat sink main body (41) and supporting the circuit board (20) at a location that is an opposite side of the plurality of heat generating devices (24, 25), the drive line (21) and the motor line (8) opposite to the connector terminal (30); a temperature sensor (27) installed on the circuit board (20) at a location spaced from the primary support (42, 43), the plurality of heat generating devices (24, 25), the drive line (21) and the motor line (8), and wherein the temperature sensor (27) measures a temperature of the secondary support (44, 45); a control device (28) that limits the electric current supplied to the plurality of heat generating devices (24, 25) while using the temperature measured by the temperature sensor (27) as a reference temperature;. a control connector terminal (31) installed on the circuit board (20) and receiving an electrical current to be provided to the control device (28); and a control line (22) installed on the circuit board (20) and electrically connecting between the control connector terminal (31), the control device (28) and the temperature sensor (27), wherein: the drive line (21) is not connected to the secondary support (44, 45) and is connected to the primary support (42, 43); and the control line (22) is not connected to the primary support (42, 43) and is connected to the secondary support (44, 45).

Description

TECHNICAL FIELD

[0001] The present disclosure relates to an electronic device that controls a driving operation of an electric motor. BACKGROUND

[0002] A known electronic device controls a driving operation of an electric motor of, for example, an electric power steering system through a plurality of drive circuits constituting a plurality of systems. In the event that one of the drive circuits fails, the electronic control device stops the failed drive circuit and performs the control operation for driving the electric motor through the remaining normal one of the drive circuits.

[0003] For example, an electronic device of JP 2008-230540 A (equivalent to US 2008 / 0230302 A1) has a thermistor that functions as a temperature sensor. The electronic device limits the amount of electric current supplied to electronic components such that the temperature of the electronic components is maintained within a temperature range in which the electronic components are operable, while the temperature measured with the thermistor is used as a reference temperature. In this way, the electronic device limits thermal destruction of the electronic components.

[0004] However, in the electronic device of JP 2008-230540 A (corresponding to US 2008 / 0230302 A1), the location of the thermistor on the circuit board is not defined. Therefore, in the case of the electronic device having multiple drive circuits constituting multiple systems, the following disadvantages may possibly occur depending on the location of the thermistor.

[0005] For example, assume that the thermistor is placed in a location where one of the drive circuits constituting the multiple systems has a significant impact on the thermistor. In such a case, if one of the drive circuits fails, the temperature measured by the thermistor will decrease. In such a case, the amount of electric current that can be supplied to the remaining normal drive circuit(s) is determined based on the reference temperature, which is lower than the actual temperature of the electronic components of the normal drive circuit(s).Therefore, if the excess amount of electric current that may cause an increase in the temperature of the electronic components beyond the operating temperature of the electronic components is supplied to the electronic components of the normal drive circuit, the normal drive circuit may possibly fail due to the excess amount of heat generated by the electronic components of the normal drive circuit.

[0006] To address the above drawback, it is desirable to provide a plurality of thermistors corresponding to the drive circuits constituting the plurality of systems. However, in such a case, the size of the electronic device is disadvantageously increased, and the cost of the electronic device is disadvantageously increased.

[0007] Reference is also made to DE 10 2016 205 202 A1 and JP 2011 - 182 614 A, which were identified as prior art. OVERVIEW

[0008] The present disclosure has been made in view of the above disadvantages. Thus, an object of the present disclosure is to provide an electronic device that enables stable temperature measurement.

[0009] The problem is solved by the features of independent claim 1. Advantageous further developments can be found in the dependent claims.

[0010] According to the present disclosure, an electronic device for controlling a driving operation of an electric motor is provided. The electronic device includes a circuit board, a connector terminal, a plurality of heat generating devices, a drive line, a heat sink main body, a primary support, a secondary support, a temperature sensor, and a controller. The connector terminal is installed on the circuit board and receives an electric current supplied from an external electric power source to a coil of the electric motor. The plurality of heat generating devices are installed on the circuit board and generate heat when the electric current to be supplied to the coil is passed through the plurality of heat generating devices.The drive line is installed on the circuit board and conducts the electric current between a motor line connected to the coil, the plurality of heat generating devices, and the connector terminal. The heat sink main body absorbs the heat generated from the plurality of heat generating devices. The primary support extends integrally from the heat sink main body and supports the circuit board at a location between: the connector terminal; and one of the plurality of heat generating devices, the drive line, or the motor line. The secondary support extends integrally from the heat sink main body and supports the circuit board at a location that is an opposite side of the plurality of heat generating devices, the drive line, and the motor line, or opposite the connector terminal.at a location that is a side opposite the connector terminal with respect to the plurality of heat generating devices, the drive line, and the motor line. The temperature sensor is installed on the circuit board at a location spaced apart from the primary support, the plurality of heat generating devices, the drive line, and the motor line, and at which the temperature sensor measures a temperature of the secondary support. The control device restricts the electric current supplied to the plurality of heat generating devices while using the temperature measured by the temperature sensor as a reference temperature. The electronic device further includes a control connector terminal and a control line. The control connector terminal is installed on the circuit board and receives an electric current to be supplied to the control device.The control line is installed on the circuit board and electrically connects the control connector terminal, the control device, and the temperature sensor. The drive line is not connected to the secondary support and is connected to the primary support. The control line is not connected to the primary support and is connected to the secondary support. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The drawings described herein are for illustrative purposes and are not intended to limit the scope of the present disclosure in any way. Fig. 1 is a cross-sectional view of a drive device of an electric power steering system in which an electronic device of a first embodiment of the present disclosure is implemented. Fig. 2 is a cross-sectional view along line II-II of Fig. 1; Fig. 3 is a schematic diagram of a surface wiring in an area III of Fig. 2; Fig. 4 is a cross-sectional view along a line IV-IV of Fig. 3; Fig. 5A to Fig. 5C are graphs indicating a change in a measured temperature of a temperature sensor and a change in an exothermic temperature of heat generating devices according to the first embodiment; Fig. 6 is a schematic diagram of a circuit board of an electronic device according to a comparative example; Fig. 7 is a cross-sectional view along line VII-VII of Fig. 6; Fig. 8A to Fig. 8C are graphs indicating a change in a measured temperature of a temperature sensor and a change in an exothermic temperature of heat generating devices with time according to the comparative example; Fig. 9 is a schematic diagram of a circuit board of an electronic device according to a second embodiment of the present disclosure; Fig. 10 is a schematic diagram of a surface wiring in an area X of Fig. 9; and Fig. 11 is a cross-sectional view along line XI-XI of Fig. 10. DETAILED DESCRIPTION

[0012] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Furthermore, in a case where a plurality of structures (components) that are substantially identical to each other are shown in each of the drawings, only one of the plurality of structures (components) is indicated by a corresponding reference numeral. (First embodiment)

[0013] A first embodiment of the present disclosure will be described with reference to Fig. 1 to Fig. 5C. An electronic device of the present embodiment is used in a drive device that generates a steering assist torque in an electric power steering system of a vehicle (for example, an automobile).

[0014] As in Fig. 1, the drive device 2 includes the electronic device 1 and an electric motor 3. The electronic device 1 controls a drive operation of the electric motor 3.

[0015] Hereinafter, a structure of the electric motor 3, a structure of the electronic device 1 and a characteristic structure of the electronic device 1 will be described sequentially. (Structure of electric motor)

[0016] The electric motor 3 includes a stator 4 and an armature 5. The stator 4 is formed in a cylindrical tubular shape. One axial end of the stator 4 is fixed to a frame end 6, and another axial end of the stator 4 is fixed to a heat sink 40. Coils 7 are wound around slots of the stator 4. A motor lead (the motor lead including a plurality of motor leads) 8 extending from the coil 7 is connected to a drive lead (the drive lead including a plurality of drive leads) 21 of a circuit board 20 of the electronic device 1 (see Fig. 2).

[0017] The armature 5 is formed in a cylindrical tubular shape and is placed on a radially inner side of the stator 4 such that the armature 5 is rotatable with respect to the stator 4. A shaft 9 is fixed to a center of the armature 5. One end portion of the shaft 9, located on a side where an output end 10 of the shaft 9 is located, is rotatably supported by a ball bearing 11 installed on the frame end 6. Another end portion of the shaft 9, opposite to the one end portion of the shaft 9, is rotatably supported by a ball bearing 12 installed on the heat sink 40.

[0018] When the electronic device 1 feeds the coils 7 of the electric motor through the motor cable 8, a rotating magnetic field is generated in the stator 4. This causes the armature 5 and the shaft 9 to rotate about their rotational axes. (Structure of electronic device)

[0019] As in Fig. 1 and Fig. As shown in Fig. 2, the electronic device 1 includes a circuit board (a single circuit board) 20, various electronic components 24-28, the heat sink 40, and a cover 50. The electronic components 24-28 are installed on the circuit board 20. The circuit board 20 is installed on the heat sink 40.

[0020] The printed circuit board 20 is a multilayer printed circuit board including the lines 21, 22 formed in layers and via holes (or simply vias, which are holes with metallization) 23, as shown in Fig. 4 is shown.

[0021] The electronic components installed on the circuit board 20 include, for example, switching devices 24 (also referred to as switching elements such as MOSFETs), shunt resistors 25, a position sensor 26, a temperature sensor 27, a microcomputer 28, and ICs.

[0022] Some of the electronic components of the present embodiment, such as the switching devices 24 and the shunt resistors 25, which generate heat from their power supply, serve as heat generating devices (also referred to as heat generating elements) of the present disclosure.

[0023] Furthermore, some of the electronic components of the present embodiment, such as the microcomputer 28 and the ICs, serve as control devices (also referred to as control elements) of the present disclosure.

[0024] Furthermore, a connector 29 is installed on the circuit board 20. The connector 29 includes connector terminals (also referred to as coil-side connector terminals) 30 and control connector terminals 31. A large current to be supplied from an external electrical power source 32 to the coils 7 of the electric motor 3 is supplied through the connector terminals 30.

[0025] The connector terminals 30, the switching devices 24, the shunt resistors 25, and the motor line 8 are electrically connected by the drive line 21 formed on the circuit board 20. The drive line 21 serves to conduct the large current to be provided to the coils 7 of the electric motor 3 by the corresponding electronic components discussed above. Fig. 2, a region where the drive line 21 is formed is indicated by a dotted line A. Further, in this specification, the drive line 21 refers to the drive line 21 on both the electric power source side and the ground side.

[0026] Corresponding ones of the switching devices 24, corresponding ones of the shunt resistors 25 and a section of the drive line 21, which are arranged in an area B on the right side in Fig. 2 form a first drive circuit 51. Corresponding ones of the switching devices 24, corresponding ones of the shunt resistors 25 and another section of the drive line 21, which are arranged in an area C on the left side in Fig. 2, form a second drive circuit 52. Each of the first drive circuit 51 and the second drive circuit 52 of the present embodiment is configured as, for example, a three-phase inverter circuit. That is, the electronic device 1 of the present embodiment drives the electric motor 3 through the drive circuits 51, 52, which form a plurality of systems (two systems in this embodiment).

[0027] The switching devices 24 discussed above include switching devices constituting the three-phase inverter circuit for supplying power to the electric motor 3, and a switching device capable of switching on and off the electrical power to be supplied to the three-phase inverter circuit from the connector terminal 30. The shunt resistors 25 are used to measure the electrical current flowing through the switching devices 24 of the three-phase inverter circuit.

[0028] Electrical power for operating the position sensor 26, the temperature sensor 27, the microcomputer 28, and the IC is supplied through the control connector terminals 31 of the connector 29. The control connector terminals 31, the position sensor 26, the temperature sensor 27, the microcomputer 28, and the ICs are electrically connected by a control line (the control line including a plurality of control lines, i.e., conductive control lines) 22 formed on the circuit board 20. The control line 22 conducts a relatively small electric current between the electronic components such as the position sensor 26, the temperature sensor 27, the microcomputer 28, and the ICs. Fig. 2, a region where the control line 22 is formed is indicated by a dotted line D. Further, in this specification, the control line 22 refers to the control line 22 on both the electric power source side and the ground side.

[0029] In Fig. 2, in an overlapped region where the drive line 21 and the control line 22 overlap each other (that is, an overlapped region where the dotted line A region and the dotted line D region overlap), the drive line 21 and the control line 22 are each formed in different layers.

[0030] The position sensor 26 measures a magnetic field of a magnet 13 installed at an end portion of the shaft 9 of the electric motor 3 to measure a rotation angle of the armature 5. The microcomputer 28 controls the amount of electric current flowing through the switching devices 24 based on the rotation angle of the armature 5 measured by the position sensor 26 and the required assist torque for the steering operation to control the supply of electric current from the first drive circuit 51 and the second drive circuit 52 to the coils 7.

[0031] The temperature sensor 27 is a single temperature sensor installed on the circuit board 20. The temperature sensor 27 is, for example, a thermistor that changes its electrical resistance depending on the temperature. The temperature sensor 27 is electrically connected to the microcomputer 28 through the control line 22. The microcomputer 28 can measure the temperature of the temperature sensor 27 and its surroundings by powering the temperature sensor 27. With respect to the temperature measured by the temperature sensor 27, the microcomputer 28 limits the amount of electrical current supplied to the electronic components (for example, the switching devices 24) such that a temperature that is a sum of the exothermic temperatures of the electronic components is maintained within a temperature range in which the electronic components are operable.The sum of the exothermic temperatures of the electronic components is calculated based on an integral value of the amounts of electric current supplied to each of the electronic components.

[0032] In a case where one of the first drive circuit 51 and the second drive circuit 52 fails, the microcomputer 28 can stop supplying electric power to the failed one of the first drive circuit 51 and the second drive circuit 52, and can drive the other of the first drive circuit 51 and the second drive circuit 52, which is normal. Even in such a case, the microcomputer 28 limits the amount of electric power supplied to the normal one of the first drive circuit 51 and the second drive circuit 52 so that the temperature is maintained within a range that allows the operation of, for example, the switching devices 24 of the normal one of the first drive circuit 51 and the second drive circuit 52. This point will be described later.

[0033] The heat sink 40 is made of a material such as aluminum, which has high thermal conductivity and a large heat capacity. The heat sink 40 absorbs the heat generated by the switching devices 24 and / or the shunt resistors 25 at the time of power supply thereto. The heat sink 40 includes a heat sink main body 41 and four supports 42-45. The supports 42-45 are integrally formed with the heat sink main body 41 (specifically, the supports 42-45 are integrally formed and seamless with the heat sink main body 41) such that the supports 42-45 extend from the heat sink main body 41 toward the circuit board 20 side. The circuit board 20 is fixed to the four supports 42-45, for example, with screws.

[0034] In the present embodiment, the four supports 42-45 of the heat sink 40 include two primary supports 42, 43 and two secondary supports 44, 45. The primary supports 42, 43 support the circuit board 20 at a location between the connector terminals 30 and one (or more) of the switching devices 24, the drive line 21, or the motor line 8. The secondary supports 44, 45 support the circuit board 20 at a location that is on an opposite side of the switching device 24, the drive line 21, and the motor line 8, which is opposite the connector terminals 30 in a plane of the circuit board 20.

[0035] As shown by a dotted line in Fig. 2, the drive line 21 is connected to the primary supports 42, 43 and is not connected to the secondary supports 44, 45. Accordingly, the heat generated from, for example, the drive line 21 and the switching devices 24 is absorbed by the heat sink main body 41 through the primary supports 42, 43. The heat sink main body 41 has a large heat capacity, so the temperature of the heat sink main body 41 is largely stable except in the vicinity of the primary supports 42, 43.

[0036] As indicated by the dotted line in Fig. 2, the control line 22 is connected to the secondary support 44 and is not connected to the primary supports 42, 43. The temperature of the secondary support 44 is substantially the same as the temperature of the portion of the heat sink main body 41 having the substantially stable temperature. (Characteristic structure of the electronic device)

[0037] Next, the characteristic structure of the electronic device 1 of the present embodiment will be described with reference to FIG. Fig. 3 to Fig. 5 described.

[0038] Fig. Figure 3 schematically shows an outer layer of the printed circuit board 20 in a section III of Fig. 2. In Fig. 3, the location of the secondary support 44 is indicated by a dotted line. Furthermore, Fig. 4 schematically shows a cross section along line IV-IV of Fig. 3 on.

[0039] As discussed above, the electronic device 1 of the present embodiment is characterized by the location of the temperature sensor 27 on the circuit board 20.

[0040] The temperature sensor 27 is placed adjacent to the secondary support 44, which is one of the two secondary supports 44, 45 located on the side where the first drive circuit 51 is placed. However, the secondary support 44 is placed at a location spaced apart from the drive line 21 and the switching devices 24. Accordingly, the temperature of the secondary support 44 is stable, like that of the heat sink main body 41.

[0041] The control line 22, which is connected to the temperature sensor 27, is connected to the secondary support 44. Accordingly, as indicated by arrows F1, F2 in Fig. 4, the heat of the heat sink main body 41 is conducted from the secondary support 44 to the temperature sensor 27 through the control line 22. Thus, the microcomputer 28 can measure the temperature of the secondary support 44, which has the stable temperature like the heat sink main body 41, through the temperature sensor 27.

[0042] In Fig. 5A, Fig. 5B, Fig. 5C, a lower solid line L, M, N indicates the temperature of the temperature sensor 27 measured by the microcomputer 28. In Fig. 5A, Fig. 5B, Fig. In Fig. 5C, an upper solid line O, P, Q indicates the temperature of the switching devices 24 estimated by the microcomputer 28. The microcomputer 28 estimates the temperature of the switching devices 24 based on the temperature measured by the temperature sensor 27 and the sum of the exothermic temperatures of the switching devices 24 calculated based on the integral value of the amounts of electric current supplied to the switching devices 24.

[0043] The graph of Fig. 5A indicates a change in the temperature L of the temperature sensor 27 and a change in the estimated temperature O of the switching devices 24 in the case where both the first drive circuit 51 and the second drive circuit 52 of the electronic device 1 are operating normally. In this case, during the time period between time t1 and time t2, the temperature L of the temperature sensor 27 changes from temperature α to temperature β, and the estimated temperature O of the switching devices 24 changes from temperature γ to temperature δ. Note that temperature δ is the operating temperature of the switching devices 24.

[0044] The graph of Fig. 5B indicates a change in the temperature M of the temperature sensor 27 and a change in the estimated temperature P of the switching devices 24 of the second drive circuit 52 in the case where the first drive circuit 51 fails. In this case, during the time period between time t1 and time t2, the temperature M of the temperature sensor 27 changes from temperature α to temperature β, and the estimated temperature P of the switching devices 24 changes from temperature γ to temperature δ. That is, the temperature M of the temperature sensor 27 is substantially the same as the temperature L of the temperature sensor 27 in the case where the first drive circuit 51 and the second drive circuit 52 of the electronic device 1 are operating normally. Accordingly, the microcomputer 28 can accurately estimate the estimated temperature P of the switching devices of the second drive circuit 52.

[0045] The graph of Fig. 5C indicates a change in the temperature N of the temperature sensor 27 and a change in the estimated temperature Q of the switching devices 24 of the first drive circuit 51 in a case where the second drive circuit 52 fails. In this case, during the time period between time t1 and time t2, the temperature N of the temperature sensor 27 changes from temperature α to temperature β, and the estimated temperature Q of the switching devices 24 changes from temperature γ to temperature δ. That is, the temperature N of the temperature sensor 27 is substantially the same as the temperature L of the temperature sensor 27 in the case where the first drive circuit 51 and the second drive circuit 52 of the electronic device 1 are both normally operated. Accordingly, the microcomputer 28 can accurately estimate the estimated temperature Q of the switching devices 24 of the first drive circuit 51.

[0046] In the present embodiment, as shown in the graphs of Fig. 5B and Fig. 5C, even in the case where one of the first drive circuit 51 and the second drive circuit 52 fails, the microcomputer 28 can accurately estimate the temperature of the switching devices 24 of the other of the first drive circuit 51 and the second drive circuit 52. Accordingly, the microcomputer 28 can limit the amount of electric current supplied to the switching devices 24 of the first drive circuit 51 and the second drive circuit 52 so that the temperature does not exceed the operating temperature of the switching devices 24 of the first drive circuit 51 or the second drive circuit 52.

[0047] Hereinafter, an electronic device 100 of a comparative example will be described with reference to Fig. 6 to Fig. 8C.

[0048] In the comparative example, the temperature sensor 27 is placed adjacent to the primary support 43, which is one of the two primary supports 42, 43 placed adjacent to the second drive circuit 52. The drive line 21 of the comparative example is formed in an area indicated by a dotted line in Fig. 6. Accordingly, the drive line 21 of the comparative example is connected to the secondary supports 44, 45 and is not connected to the primary support 43. In contrast, the control line 22 of the comparative example, which is connected to the temperature sensor 27, is formed in an area indicated by a dotted line H in Fig. 6. As in Fig. 6, the control line 22 of the comparative example is connected to the primary support 43.

[0049] In this case, as shown by arrows J1-J7 in Fig. 7, the heat generated by the switching devices 24 and the drive line 21 is conducted to the primary supports 42, 43 through the resin of the circuit board 20 and a line pattern of an internal layer of the circuit board 20, and is also conducted to the temperature sensor 27 by the control line 22 connected to the primary support 43.

[0050] In each of the graphs of Fig. 8A, Fig. 8B and Fig. 8C, a lower solid line R, S, T indicates the temperature of the temperature sensor 27 measured by the microcomputer 28. Furthermore, in each of the graphs of Fig. 8A, Fig. 8B, Fig. 8C, an upper solid line U, V, W indicates the temperature of the switching device 24, which is estimated by the microcomputer 28. In the graph of Fig. 8C, a solid line X indicates the actual temperature of the switching devices 24 of the first drive circuit 51.

[0051] The graph of Fig. 8A indicates a change in the temperature R of the temperature sensor 27 and a change in the estimated temperature U of the switching devices 24 with time in the case where the first drive circuit 51 and the second drive circuit 52 of the electronic device 100 of the comparative example are both operating normally. In this case, during the time period from time t1 to time t2, the temperature R of the temperature sensor 27 changes from temperature ε to temperature ζ, and the estimated temperature U of the switching devices 24 changes from temperature η to temperature θ. It should be noted that temperature θ is the operating temperature of the switching devices 24.

[0052] The graph of Fig. 8B indicates a change in the temperature S of the temperature sensor 27 and a change in the estimated temperature V of the switching devices 24 of the second drive circuit 52, which is normally operated, according to time in the case where the first drive circuit 51 fails. In this case, during the time period between time t1 and time t2, the temperature S of the temperature sensor 27 changes from temperature ε to temperature ζ, and the estimated temperature V of the switching devices 24 changes from temperature η to temperature θ.

[0053] The temperature sensor 27 of the comparative example is placed adjacent to the primary support 43, which is placed adjacent to the second drive circuit 52 that is normally operated. Thus, the temperature S of the temperature sensor 27 changes synchronously with the temperature of the switching devices 24 of the second drive circuit 52. Therefore, in this case, the temperature S of the temperature sensor 27 is substantially the same as the temperature R of the temperature sensor 27 in the case where both the first drive circuit 51 and the second drive circuit 52 of the electronic device 1 are normally operated. Thus, the microcomputer 28 can accurately estimate the estimated temperature V of the switching devices 24 of the second drive circuit 52.

[0054] In contrast, the graph of Fig. 8C shows a change in the temperature T of the temperature sensor 27, a change in the estimated temperature W of the switching devices 24 of the first drive circuit 51 operating normally, and a change in the actual temperature X of the switching devices 24 of the first drive circuit 51 with time in the case where the second drive circuit 52 fails. In this case, during the time period between time t1 and t2, the temperature T of the temperature sensor 27 changes from the temperature ε to the temperature and the estimated temperature W of the switching devices 24 changes from the temperature η to the temperature κ.

[0055] The temperature sensor 27 of the comparative example is placed adjacent to the primary support 43, which is placed adjacent to the failed second drive circuit 52. Accordingly, the temperature T of the temperature sensor 27 is Fig. 8C, which is measured by the microcomputer 28, below the temperature R of the temperature sensor 27 of Fig. 8A or the temperature S of the temperature sensor 27 of Fig. 8B after the lapse of time. Therefore, the estimated temperature W of the switching devices 24 of the first drive circuit 51, which is normally operated, is erroneously estimated as the temperature lower than the actual temperature X of the switching devices 24. Therefore, the microcomputer 28 of the comparative example may supply the electric current, which may cause the temperature of the switching devices 24 to exceed the operative temperature θ of the switching devices 24, to the switching devices 24 of the first drive circuit 51, which is normally operated. Thus, in the comparative example, the actual temperature X of the switching devices 24 of the first drive circuit 51 may exceed the operative temperature θ of the switching devices 24 at a point indicated by a dotted circle Y in Fig. 8C, possibly causing failure of the first drive circuit 51 in addition to the failed second drive circuit 52.

[0056] In contrast to the comparative example, the electronic device 1 of the present embodiment has the following advantages. (1) In the present embodiment, the temperature sensor 27 is placed at the corresponding location spaced from the primary supports 42, 43, the switching devices 24, the shunt resistors 25, the drive line 21, and the motor line 8, and at which the temperature of the secondary support 44 can be measured with the temperature sensor 27 (that is, the corresponding location at which the temperature of the secondary support 44 is measured with the temperature sensor 27).

[0057] Accordingly, the heat generated by, for example, the switching devices 24 is absorbed by the heat sink main body 21 via the drive line 21 and the primary supports 42, 43. Thus, the temperature change of the primary supports 42, 43 and an adjacent portion of the heat sink main body 41 located adjacent to the primary supports 42, 43 becomes large. In contrast, the temperature change of the secondary supports 44, 45 located on the opposite side of the drive line 21 (the drive line 21 that conducts the large current) and the switching devices 24 with respect to the connector terminals 30 is moderate, and the temperature change of an adjacent portion of the heat sink main body 41 located adjacent to the secondary supports 44, 45 is moderate to maintain the stable temperature.Therefore, even if one (or more) of the switching devices 24 of one of the drive circuits fails, the microcomputer 28 can relatively accurately estimate the temperature of the switching devices 24 of the normal drive circuit(s) by using the stable temperature measured by the temperature sensor 27 as the reference temperature. Therefore, in the electronic device 1, the switching devices 24 of the normal drive circuit(s) can be used within the temperature range in which the switching devices 24 can be safely operated. (2) In the present embodiment, the drive line 21 is connected to the primary supports 42, 43 and is not connected to the secondary supports 44, 45. In contrast, the control line 22 is not connected to the primary supports 42, 43 and is connected to the secondary support 44.

[0058] Accordingly, the heat generated by the switching devices 24 and the drive line 21 is absorbed by the heat sink main body 41 via the primary supports 42, 43. In contrast, the temperature of the secondary support 44, to which only the control line 22 is connected, is stabilized. (3) In the present embodiment, in the case where one of the drive circuits fails, the microcomputer 28 limits the electric current supplied by the switching devices 24 of the other normal drive circuit based on the measured temperature of the temperature sensor 27 and the current value of the electric current supplied to the switching devices 24.

[0059] In this way, in the electronic device 1, even in the case where one of the drive circuits fails, the switching devices 24 of the other normal drive circuit can be used within the temperature range in which the switching devices 24 can be safely operated. (4) In the present embodiment, the temperature sensor 27 is the single temperature sensor installed on the circuit board 20.

[0060] Accordingly, the size of the electronic device 1 can be reduced or minimized. (Second embodiment)

[0061] Fig. 9 to Fig. 11 indicate a second embodiment of the present disclosure. In the second embodiment, each corresponding structure (component) that is the same as that of the first embodiment is denoted by the corresponding reference numeral and will not be redundantly described for simplicity.

[0062] In the second embodiment, the drive line 21 is connected to both the primary supports 42, 43 and the secondary supports 44, 45. In contrast, the control line 22 is connected to the secondary support 44 and is not connected to the primary supports 42, 43. Furthermore, in the second embodiment, as shown in Fig. 10, at a location where the secondary support 44 and the circuit board 20 contact each other, resin 33 forming the circuit board 20 is inserted between the drive line 21 and the control line 22, both of which are connected to the secondary support 44.

[0063] As indicated by arrows K1 to K6 in Fig.11, the heat generated by the drive line 21 and the switching devices 24 is absorbed by the heat sink main body 41 through the primary supports 42, 43 and the secondary supports 44, 45. However, this heat is not directly conducted to the control line 22 due to the presence of the resin 33 located between the drive line 21 and the control line 22.

[0064] Since the heat capacity of the heat sink main body 41 is large, the temperature of the heat sink main body 41 is stabilized. The heat of the heat sink main body 41 is conducted from the secondary support 44 to the temperature sensor 27 through the control line 22, as indicated by arrows K7, K8. Thus, the microcomputer 28 can measure the temperature of a portion of the secondary support 44 that has a relatively stable temperature through the temperature sensor 27.

[0065] In the second embodiment, even in the case where one or more of the switching devices 24 of one of the drive circuits fails, the microcomputer 28 can relatively accurately estimate the temperature of the switching devices 24 of the normal drive circuit(s) using the stable temperature measured with the temperature sensor 27 as the reference temperature. (Other embodiments) (1) In the above embodiments, the electronic device 1 that controls the electric motor of the electric power steering system is described. In another embodiment, the application of the electronic device 1 is not necessarily limited to the electric power steering system, and the electronic device of the present disclosure can be applied as an electronic device that controls an electric motor used in other various systems or devices. (2) In the above embodiments, the electronic device 1 has been described as being integrally formed with the electric motor 3. In another embodiment, the electronic device of the present disclosure may be formed as a separate component separated from the electric motor 3. (3) In the above embodiments, the switching devices 24 and the shunt resistors 25 are described as examples of heat generating devices that generate heat when supplied with electric power. In another embodiment, a heat generating device(s) may be another type(s) of electronic component(s), such as a choke coil(s), a capacitor(s), a relay(s), or the like. (4) In the above embodiments, the electronic device is described that includes the drive circuits that constitute the two systems in correspondence. In another embodiment, the electronic device of the present disclosure may be configured to have a single drive circuit that constitutes the single system, or the electronic device of the present disclosure may be configured to have three or more drive circuits that constitute three or more systems in correspondence. (5) In the above embodiments, the multilayer printed circuit board including four layers is described. In another embodiment, the printed circuit board of the present disclosure may be formed as a single-layer printed circuit board or a multilayer printed circuit board including five or more layers.

[0066] As described above, the present disclosure is not limited to the above embodiments, and the structures (components) of the above embodiments can be appropriately combined to implement various other embodiments within a scope of the present disclosure.

Claims

[1] Electronic device for controlling a drive operation of an electric motor (3), comprising: a printed circuit board (20); a connector terminal (30) installed on the circuit board (20) and receiving an electric current provided from an external electric power source (32) to a coil (7) of the electric motor (3); a plurality of heat generating devices (24, 25) installed on the circuit board (20) and generating heat when the electric current to be supplied to the coil (7) is passed through the plurality of heat generating devices (24, 25); a drive line (21) installed on the circuit board (20) and carrying the electrical current between: a motor line (8) connected to the coil (7); the plurality of heat generating devices (24, 25); and the connector terminal (30); a heat sink main body (41) that absorbs the heat generated from the plurality of heat generating devices (24, 25); a primary support (42, 43) extending integrally from the heat sink main body (41) and supporting the circuit board (20) at a location between: the connector terminal (30); and one of the plurality of heat generating devices (24, 25), the drive line (21) or the motor line (8); a secondary support (44, 45) extending integrally from the heat sink main body (41) and supporting the circuit board (20) at a location that is an opposite side of the plurality of heat generating devices (24, 25), the drive line (21) and the motor line (8) opposite to the connector terminal (30); a temperature sensor (27) installed on the circuit board (20) at a location spaced from the primary support (42, 43), the plurality of heat generating devices (24, 25), the drive line (21) and the motor line (8), and wherein the temperature sensor (27) measures a temperature of the secondary support (44, 45); a control device (28) that limits the electric current supplied to the plurality of heat generating devices (24, 25) while using the temperature measured by the temperature sensor (27) as a reference temperature;. a control connector terminal (31) installed on the circuit board (20) and receiving an electrical current to be provided to the control device (28); and a control line (22) installed on the circuit board (20) and electrically connecting between the control connector terminal (31), the control device (28) and the temperature sensor (27), wherein: the drive line (21) is not connected to the secondary support (44, 45) and is connected to the primary support (42, 43); and the control line (22) is not connected to the primary support (42, 43) and is connected to the secondary support (44, 45). [2] Electronic device according to claim 1, wherein: the drive line (21) and the plurality of heat generating devices (24, 25) form a plurality of drive circuits (51, 52) which drive the electric motor (3); when one of the plurality of drive circuits (51, 52) fails, the control device (28) limits the electric current to be provided to a corresponding one or more of the plurality of heat generating devices (24, 25) provided in another of the plurality of drive circuits (51, 52) that is normal, based on: the temperature measured by the temperature sensor (27); and a current value of the electric current supplied to the corresponding one or more of the plurality of heat generating devices (24, 25) provided in the normal of the plurality of drive circuits (51, 52). [3] Electronic device according to one of claims 1 or 2, wherein the temperature sensor (27) is a single temperature sensor on the circuit board (20).

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