Electric power steering apparatus

Abstract

To improve the heat dissipation effect of the heat generated by a field effect transistor in an electronic control unit that controls a motor outputting steering assist force in an electric power steering apparatus.SOLUTION: A recess 71 accommodating field effect transistors (Q1, Q2, QA1) mounted on the mounting surface of the substrate, is formed on the opposing surface of a heat sink 70 facing the mounting surface of a substrate 60, copper foil patterns 61 to 63 connected to drain pads (D1, D2, D3) provided on the surface of the substrate facing the field effect transistors are formed on the substrate, and in the vertical view of the mounting surface, the copper foil patterns are formed such that they extend from the position where the drain pads connect to the copper foil patterns within the region where the recess is formed, to the outside of the region where the recess is formed.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] Patent Document 1 below describes an electronic control unit that drives and controls a motor that generates assist torque for an electric power steering device. This electronic control unit includes a substrate, a high-heat-generating component that is mounted on at least one of one or the other surfaces of the substrate and that generates a heat amount equal to or greater than a predetermined value when in operation, a control unit that can control a control target by controlling the operation of the high-heat-generating component, a heat sink that is provided with one surface facing the one surface of the substrate and recessed from the one surface to accommodate the high-heat-generating component mounted on the one surface of the substrate, and a heat conduction member that is provided between the substrate and the heat sink so as to be in contact with at least the high-heat-generating component and the recess, and that conducts heat from the high-heat-generating component to the heat sink.

[0003] The recesses are formed in a shape corresponding to the shapes of the high-heat-generating components mounted on one side of the board, a plurality of high-heat-generating components are provided and mounted on one side of the board, a plurality of recesses are formed to correspond to all or part of the plurality of high-heat-generating components mounted on one side of the board, each of the plurality of recesses has five rectangular inner walls and all have the same depth from one side of the heat sink, and each of the plurality of high-heat-generating components housed in the recesses has five rectangular outer walls facing the five inner walls of the recesses, and all have the same height from one side of the board, and the thermally conductive member includes an insulating heat dissipation sheet. The insulating heat dissipation sheet is a single sheet formed to correspond to the plurality of high-heat-generating components housed in the recesses, and a plurality of portions of the insulating heat dissipation sheet are located between the five inner walls of the recesses and the five outer walls of the high-heat-generating components. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6115465 Summary of the Invention [Problem to be solved by the invention]

[0005] In the electronic control unit of Patent Document 1, the heat from the high heat generating components that is transferred to the board side cannot be efficiently dissipated from the heat sink. The present invention has been made in light of the above-mentioned problems, and aims to improve the heat dissipation effect of heat generated by a field effect transistor provided in an electronic control unit that controls a motor that outputs steering assist force for an electric power steering device. [Means for solving the problem]

[0006] To achieve the above object, one aspect of the present invention provides an electric power steering device including an electronic control unit and a motor controlled by the electronic control unit to output a steering assist force to assist steering by a driver. The electronic control unit includes a substrate on which a field-effect transistor is mounted, a heat sink provided so as to face the mounting surface on which the field-effect transistor is mounted on the substrate, and a thermally conductive member provided between the substrate and the heat sink. A recess is formed on the surface of the heat sink facing the mounting surface of the substrate to accommodate the field-effect transistor mounted on the mounting surface of the substrate. A copper foil pattern is formed on the substrate to connect to a drain pad provided on the surface of the field-effect transistor facing the substrate, and the copper foil pattern is formed so as to extend from a position where the drain pad and the copper foil pattern are connected within the region where the recess is formed to outside the region where the recess is formed, when viewed perpendicular to the mounting surface. [Effects of the Invention]

[0007] According to the present invention, it is possible to improve the heat dissipation effect of heat generated by a field effect transistor provided in an electronic control unit that controls a motor that outputs a steering assist force of an electric power steering device. [Brief explanation of the drawings]

[0008] [Figure 1]1 is a configuration diagram illustrating an overview of an example of an electric power steering device according to an embodiment; [Figure 2] 1 is a configuration diagram illustrating an outline of an example of an electronic control unit (ECU) according to an embodiment. [Figure 3] FIG. 2 is a block diagram illustrating an example of a functional configuration of a control arithmetic device. [Figure 4] FIG. 2 is a schematic diagram illustrating a part of an electronic control unit according to the embodiment. [Figure 5] FIG. 2 is a cross-sectional view showing a part of the electronic control unit according to the embodiment. [Figure 6] FIG. 1 is a layout diagram of an example of a drain pad, a source pad, and a gate pad of a field effect transistor and a copper foil pattern. [Figure 7] FIG. 2 is an explanatory diagram of an example of dimensions of a copper foil pattern. [Figure 8] FIG. 2 is a configuration diagram showing an outline of a first modified example of an electric power steering device. [Figure 9] FIG. 10 is a configuration diagram showing an outline of a second modified example of an electric power steering device. [Figure 10] FIG. 10 is a configuration diagram showing an outline of a third modified example of an electric power steering device. DETAILED DESCRIPTION OF THE INVENTION

[0009] Embodiments of the present invention will be described in detail with reference to the drawings. Note that the embodiments of the present invention shown below are merely examples of devices and methods for embodying the technical concept of the present invention, and the technical concept of the present invention does not limit the configuration, arrangement, etc. of component parts to those described below. Various modifications can be made to the technical concept of the present invention within the technical scope defined by the claims.

[0010] (composition) 1 is a schematic diagram showing an example of an electric power steering (EPS) device according to an embodiment. A steering shaft (steering shaft, steering shaft) 2 of a steering wheel (steering handle) 1 is connected to steered wheels 8L, 8R via reduction gears (worm gears) 3, universal joints 4a and 4b, a pinion-rack mechanism 5, tie rods 6a and 6b, and hub units 7a and 7b, which constitute a reduction mechanism.

[0011] The pinion rack mechanism 5 has a pinion 5a connected to a pinion shaft to which steering force is transmitted from the universal joint 4b, and a rack 5b that meshes with this pinion 5a, and converts the rotational motion transmitted to the pinion 5a into linear motion in the vehicle width direction by the rack 5b. The steering shaft 2 is provided with a torque sensor 10 that detects the steering torque Th. The steering shaft 2 is also provided with a steering angle sensor 14 that detects the steering angle θh of the steering wheel 1. A motor 20 that assists the steering force of the steering wheel 1 is connected to the steering shaft 2 via a reduction gear 3.

[0012] An electronic control unit (ECU) 30 that controls the electric power steering device is supplied with power from a battery 13 and receives an ignition key signal via an ignition switch 11. The ECU 30 calculates a current command value of the assist control command based on the steering torque Th detected by the torque sensor 10, the vehicle speed Vh detected by the vehicle speed sensor 12, and the steering angle θh detected by the steering angle sensor 14, and controls the currents (A-phase current I1a, B-phase current I1b, and C-phase current I1c) supplied to the motor 20 using a voltage control command value obtained by performing compensation, etc. on the current command value.

[0013] The steering angle sensor 14 is not essential, and the steering angle θh may be calculated by adding the torsion angle of the torsion bar of the torque sensor 10 to the product of the motor rotation angle θm obtained from a rotation angle sensor 23a that detects the rotation angle of the rotating shaft of the motor 20 and the gear ratio of the reduction gear 3. The rotation angle sensor 23a may be, for example, a resolver that detects the rotation position of the motor, or a magnetic sensor that detects the magnetic field of a magnet attached to the rotating shaft of the motor 20. Furthermore, the steering angle of the steered wheels 8L, 8R may be used instead of the steering angle θh. For example, the steering angle may be detected by detecting the displacement of the rack 5b.

[0014] The ECU 30 includes, for example, a computer including a processor and peripheral components such as a storage device, etc. The processor may be, for example, a CPU (Central Processing Unit) or an MPU (Micro-Processing Unit). The storage device may include any of a semiconductor storage device, a magnetic storage device, and an optical storage device. The storage device may include a register, a cache memory, a memory such as a ROM (Read Only Memory) used as a main memory, and a RAM (Random Access Memory). The functions of the ECU 30 described below are realized, for example, by the processor of the ECU 30 executing a computer program stored in a storage device.

[0015] The ECU 30 may be formed of dedicated hardware for executing each of the information processes described below. For example, the ECU 30 may include a functional logic circuit configured in a general-purpose semiconductor integrated circuit. For example, the ECU 30 may have a programmable logic device (PLD) such as a field-programmable gate array (FPGA).

[0016] 2 is a block diagram showing an example of an outline of the ECU 30 according to the embodiment. The ECU 30 includes an electronic control unit 40A having a motor rotation angle detection circuit 23, a control and arithmetic device 31a, a motor current cutoff circuit 33A, a gate drive circuit 41A, a power conversion circuit 42A, and a power cutoff circuit 44A. A power line PWa that transmits power from the battery 13 is connected to the ECU 30 via a connector CNT. A positive power line Lpa of the power line PWa passes through a noise filter circuit such as an EMC (Electromagnetic Compatibility) filter formed by a choke coil La and ceramic capacitors Ca1 and Ca2, and is then connected to a control arithmetic device 31a and a power supply cutoff circuit 44A.

[0017] One end of the choke coil La is connected to the positive power supply line Lpa and one end of the ceramic capacitor Ca1, the other end of the choke coil La is connected to one end of the ceramic capacitor Ca2, and the other ends of the ceramic capacitors Ca1 and Ca2 are grounded. Meanwhile, the negative line of the power wiring PWa is connected to the ground line of the ECU 30 and the ground line of the power conversion circuit 42A.

[0018] Signals of the steering torque Th detected by the torque sensor 10, the vehicle speed Vh detected by the vehicle speed sensor 12, and the steering angle θh detected by the steering angle sensor 14 are transmitted to the control calculation device 31a via a connector CNT. The control calculation device 31a calculates a current command value, which is a control target value of the drive current of the motor 20, based on at least the steering torque Th, and outputs voltage control command values ​​V1a, V1b, and V1c obtained by performing compensation on the current command value to the gate drive circuit 41A. The voltage control command values ​​V1a, V1b, and V1c are the A-phase voltage control command value, B-phase voltage control command value, and C-phase voltage control command value of the motor 20.

[0019] The power supply interruption circuit 44A has a series circuit configuration in which two power supply interruption field effect transistors (FETs) QC1 and QC2 have their sources connected to each other, forming parasitic diodes facing in opposite directions, and connects or disconnects the positive power supply line Lpa and the power conversion circuit 42A. The drain of the power supply interruption FET QC1 is connected to the positive power supply line Lpa, and the drain of the power supply interruption FET QC2 is connected to the drains of the high-side FETs Q1, Q3, and Q5 of the power conversion circuit 42A. The control and arithmetic device 31a outputs control signals SsA and SpA to the gate drive circuit 41A, which respectively control the conduction and interruption of the power supply interruption FETs QC1 and QC2. The gate drive circuit 41A outputs gate signals for the power supply interruption FETs QC1 and QC2 in response to the control signals SsA and SpA, thereby controlling the on / off of the power supply interruption FETs QC1 and QC2. The power supply cutoff FETQC2 is connected between the DC power supply and the inverter to function as a reverse connection protection field effect transistor that blocks current from flowing from the inverter side to the DC power supply side, in order to prevent a malfunction that may occur if the polarity of the battery 13, which is a DC power supply, is mistakenly connected in reverse.

[0020] When the gate drive circuit 41A receives voltage control command values ​​V1a, V1b, and V1c from the control arithmetic device 31a, it generates six gate signals by pulse width modulation (PWM) based on the voltage control command values ​​V1a, V1b, and V1c and a triangular wave carrier signal, and outputs these gate signals to the power conversion circuit 42A.

[0021] The power conversion circuit 42A includes an inverter having three switching arms SWAa, SWAb, and SWAc configured by FETs, which are switching elements, and electrolytic capacitors CA1 and CA2. The switching arms SWAa, SWAb, and SWAc are connected in parallel with one another. The A-phase switching arm SWAa includes a high-side FET Q1 and a low-side FET Q2 connected in series, the B-phase switching arm SWAb includes a high-side FET Q3 and a low-side FET Q4 connected in series, and the C-phase switching arm SWAc includes a high-side FET Q5 and a low-side FET Q6 connected in series.

[0022] A gate signal output from the gate drive circuit 41A is input to the gate of each of the FETs Q1 to Q6, and this gate signal causes an A-phase current I1a, a B-phase current I1b, and a C-phase current I1c to flow from the connection points between the FETs of each of the switching arms SWAa, SWAb, and SWAc to the A-phase winding, B-phase winding, and C-phase winding of the motor 20 via the motor current cut-off circuit 33A. The electrolytic capacitors CA1 and CA2 have a noise removal function and a power supply auxiliary function for the power conversion circuit 42 A. The electrolytic capacitors CA1 and CA2 may be hybrid capacitors that use an electrolyte that combines a conductive polymer and an electrolytic solution, for example.

[0023] Current detection circuits 39A1, 39B1, and 39C1 are provided on the source sides of low-side FETs Q2, Q4, and Q6, which form the lower arms of switching arms SWAa, SWAb, and SWAc of the power conversion circuit 42A. The current detection circuits 39A1, 39B1, and 39C1 include shunt resistors through which downstream currents of switching arms SWAa, SWAb, and SWAc flow, respectively. The current detection circuits 39A1, 39B1, and 39C1 detect the A-phase current, B-phase current, and C-phase current of the coil of motor 20 based on the voltage drop across the shunt resistors, and output the detected values ​​I1ad, I1bd, and I1cd.

[0024] The motor current interruption circuit 33A has three phase interruption FETs QA1, QA2, and QA3 for interrupting the phase current of the motor. The source of the phase interruption FET QA1 is connected to the junction of FETs Q1 and Q2 of the switching arm SWAa of the power conversion circuit 42A, and its drain is connected to the A-phase winding of the motor 20. The source of the phase interruption FET QA2 is connected to the junction of FETs Q3 and Q4 of the switching arm SWAb, and its drain is connected to the B-phase winding of the motor 20. The source of the phase interruption FET QA3 is connected to the junction of FETs Q5 and Q6 of the switching arm SWAc, and its drain is connected to the C-phase winding of the motor 20.

[0025] The control calculation device 31a outputs a control signal SmA that controls the conduction and cutoff of the motor current cutoff circuit 33A to the gate drive circuit 41A. The gate drive circuit 41A outputs gate signals of the phase cutoff FETs QA1 to QA3 in response to the control signal SmA, and causes the A-phase current I1a, B-phase current I1b, and C-phase current I1c to flow from the power conversion circuit 42A to the motor 20 and be cut off. It should be noted that, for example, silicon devices or silicon carbide devices may be used as the high-side FETs Q1, Q3 and Q5, the low-side FETs Q2, Q4 and Q6, the phase-blocking FETs QA1 to QA3, and the power-blocking FETs QC1 and QC2.

[0026] The motor rotation angle detection circuit 23 acquires a detection value from the rotation angle sensor 23a and detects the motor rotation angle θm, which is the rotation angle of the rotary shaft of the motor 20. The motor rotation angle detection circuit 23 outputs the motor rotation angle θm to the control and arithmetic device 31a. The control and arithmetic device 31a acquires information on the motor rotation angle θm from the motor rotation angle detection circuit 23. The control and arithmetic device 31a acquires detection values ​​I1ad, I1bd, and I1cd of the A-phase current, B-phase current, and C-phase current of the coil of the motor 20 via an A / D conversion unit (not shown).

[0027] Next, the control arithmetic device 31a will be described. Fig. 3 is a block diagram showing an example of the functional configuration of the control arithmetic device 31a. The control arithmetic device 31a includes a current command value calculation unit 50, a current limiting unit 51, subtractors 52 and 53, a proportional-integral (PI) control unit 54, a two-phase / three-phase conversion unit 55, a three-phase / two-phase conversion unit 56, and an angular velocity conversion unit 57, and drives the motor 20 by vector control.

[0028] The current command value calculation unit 50 calculates a q-axis current command value Iq0 and a d-axis current command value Id0 to be passed through the motor 20 based on the steering torque Th, the vehicle speed Vh, the motor rotation angle θm of the motor 20, and the rotation angular velocity ω of the motor 20. The current limiting unit 51 limits the upper limits of the q-axis current command value Iq0 and the d-axis current command value Id0, and outputs the limited q-axis current command value Iq1 and d-axis current command value Id1.

[0029] The detected values ​​I1ad, I1bd, and I1cd of the A-phase current, B-phase current, and C-phase current of the coil of the motor 20 detected by the current detection circuits 39A1, 39B1, and 39C1 are converted into d-axis and q-axis currents id and iq by the three-phase / two-phase conversion unit 56. Subtractors 52 and 53 calculate the q-axis deviation current Δq and the d-axis deviation current Δd by subtracting the fed-back currents iq and id from the q-axis current command value Iq1 and the d-axis current command value Id1, respectively.

[0030] The PI control unit 54 calculates voltage command values ​​vq, vd such that the q-axis deviation current Δq and the d-axis deviation current Δd are each set to 0. The two-phase / three-phase conversion unit 55 converts the voltage command values ​​vd, vq into an A-phase voltage control command value V1a, a B-phase voltage control command value V1b, and a C-phase voltage control command value V1c for the motor 20, respectively, and outputs them to the gate drive circuit 41A. The angular velocity conversion unit 57 calculates the rotational angular velocity ω of the motor 20 based on the change over time in the motor rotational angle θm. The motor rotational angle θm and rotational angular velocity ω are input to the current command value calculation unit 50 and used for vector control.

[0031] Next, the heat dissipation structure of the electronic control unit 40A will be described. Fig. 4 is a schematic diagram showing a part of the electronic control unit 40A according to the embodiment, and Fig. 5 is a cross-sectional view showing a part of the electronic control unit 40A according to the embodiment. Fig. 4 shows a schematic representation of the parts of the electronic control unit 40A related to FETs Q1, Q2, and QA1. The same is true for Fig. 6. Fig. 5 shows a schematic representation of the parts related to FET Q1.

[0032] FETs Q1, Q2, and QA1 are mounted on a circuit board 60 of electronic control unit 40A. In the following description, circuit board 60 will be referred to simply as "board 60," and one of the two surfaces of board 60 on which FETs Q1, Q2, and QA1 are mounted will be referred to as "mounting surface f1."

[0033] FETs Q1, Q2, and QA1 are sealed in a package 83 made of, for example, resin, and package 83 is formed in the shape of a rectangular plate as shown in Figures 4 and 5. That is, FETs Q1, Q2, and QA1 are each formed in the shape of a hexahedron and have six rectangular, planar outer walls. FETs Q1, Q2, and QA1 are mounted so that one of the six outer walls faces mounting surface f1 of substrate 60 and the surface direction is parallel to mounting surface f1.

[0034] Heat dissipator (e.g., heat sink) 70 is provided such that one surface f2 faces the mounting surface f1 of substrate 60 on which FETs Q1, Q2, and QA1 are mounted. In the following description, one surface f2 of heat dissipator 70 may be referred to as the "facing surface f2." Heat sink 70 is made of a metal with good thermal conductivity, such as an aluminum alloy. As shown in Fig. 5, in the assembled state of electronic control unit 40A, substrate 60 and heat sink 70 are fixed to each other by a fixing member or the like (not shown) so that a predetermined gap (gap) t1 is formed between mounting surface f1 of substrate 60 and opposing surface f2 of heat sink 70.

[0035] The opposing surface f2 of the heat sink 70 has a plurality of recesses 71 formed to recess from the opposing surface f2 toward the rear surface f3. The recesses 71 are formed to correspond to the FETs Q1, Q2, and QA1 so as to accommodate the FETs Q1, Q2, and QA1, respectively. A thermally conductive member 73 is interposed between the mounting surface f1 of the substrate 60 and the opposing surface f2 of the heat sink 70. The thermally conductive member 73 may be a thermal interface material (TIM) such as a conductive paste (e.g., thermal grease).

[0036] The heat conducting member 73 is provided between the mounting surface f1 of the substrate 60 and the opposing surface f2 of the heat sink 70 so as to be in contact with the FETs Q1, Q2, and QA1 and the heat sink 70 (see FIG. 5). This allows the heat conducting member 73 to conduct the heat of the FETs Q1, Q2, and QA1 to the heat sink 70.

[0037] In this embodiment, recess 71 of heat sink 70 is formed in a shape corresponding to the shapes of FETs Q1, Q2, and QA1. That is, recess 71 has five rectangular planar inner walls corresponding to (facing) the five outer walls of FETs Q1, Q2, and QA1 other than the outer walls facing substrate 60. Bottom surface 72 is formed parallel to facing surface f2, and four of the inner walls forming recess 71 other than bottom surface 72 are formed perpendicular to facing surface f2 and bottom surface 72 of heat sink 70.

[0038] Note that "the recess 71 is formed in a shape corresponding to the shapes of the FETs Q1, Q2, and QA1" means that, for example, when the electronic control unit 40A is assembled, the distance between the inner wall of the recess 71 and the outer wall of the corresponding FETs Q1, Q2, and QA1 is equal to or less than a predetermined value, that is, the recess 71 is formed to follow the shapes of the FETs Q1, Q2, and QA1.

[0039] 5, recess 71 is formed so that gap t2 between the surface of FETs Q1, Q2, and QA1 facing bottom surface 72 of recess 71 and bottom surface 72 is larger than gap t1 between the mounting surface f1 of substrate 60 and an area of ​​facing surface f2 of heat sink 70 where recess 71 is not formed. This makes it easier for recess 71 accommodating FETs Q1, Q2, and QA1 to tolerate dimensional errors of FETs Q1, Q2, and QA1 in the direction perpendicular to mounting surface f1. For example, gaps t1 and t2 may be approximately 0.25 mm and 0.5 mm, respectively.

[0040] As shown in FIG. 5, FET Q1 has a structure in which a chip 80 body of an electrolytic transistor, a die attach member 81 connecting the chip 80 to a drain pad D1, a wire 82 connecting the source terminal of the chip 80 to a source pad S1, and a wire (not shown) connecting the gate terminal of the chip 80 to a gate pad (not shown) are sealed in a package 83. The drain pad D1, source pad S1, and gate pad (not shown) of the FET Q1 are provided on the surface of the FET Q1 facing the substrate 60.

[0041] Copper foil patterns 61 and 62 are formed on the mounting surface f1 of the substrate 60. A drain pad D1 of the FET Q1 is electrically connected to the copper foil pattern 61 via solder 84. A source pad S1 of the FET Q1 is electrically connected to the copper foil pattern 62 via solder 85.

[0042] When viewed perpendicular to the mounting surface f1 (i.e., when viewed perpendicular to the opposing surface f2), the drain pad D1 is located within the region where the recess 71 that accommodates the FET Q1 is formed (see FIG. 7). Therefore, when viewed perpendicular to the mounting surface f1, the connection point between the drain pad D1 and the copper foil pattern 61 is also located within the region where the recess 71 that accommodates the FET Q1 is formed. Hereinafter, the perpendicular view to the mounting surface f1 will be simply referred to as the "vertical view."

[0043] 6 is a layout diagram of an example of drain pads D1 to D3, source pads S1 to S3, and gate pads G1 to G3 of FETs Q1, Q2, and QA1, and copper foil patterns 61 to 63. The drain pad D1 of FET Q1 is electrically connected to the copper foil pattern 61, and the drain pad D2 of FET Q2 is electrically connected to the copper foil pattern 62. A copper foil pattern 63 is formed on the mounting surface f1 of the substrate 60 in addition to the copper foil patterns 61 and 62. The drain pad D3 of the FET QA1 is electrically connected to the copper foil pattern 63.

[0044] As described above, the source pad S1 of FET Q1 is also electrically connected to the copper foil pattern 62. The source pad S3 of FET QA1 is also electrically connected to the copper foil pattern 62. Therefore, the source terminal of FET Q1, the drain terminal of FET Q2, and the source terminal of FET QA1 are electrically connected via the copper foil pattern 62. The drain terminal of the FET Q1 is electrically connected to the drain of the power cutoff FET QC2 via a copper foil pattern 61, and the drain terminal of the FET QA1 is electrically connected to the A-phase winding of the motor 20 via a copper foil pattern 63.

[0045] 5, the heat conductive member 73 is provided between the mounting surface f1 of the substrate 60 and the opposing surface f2 of the heat sink 70 so as to be in contact with the copper foil patterns 61 and 62 and the heat sink 70. Similarly, the heat conductive member 73 is provided so as to be in contact with the copper foil pattern 63 and the heat sink 70. Note that the surfaces of the copper foil patterns 61 to 63 may be covered with a protective film (e.g., resist), or may be in contact with the heat conductive member 73 without a protective film therebetween.

[0046] This allows the heat generated from FETs Q1, Q2, and QA1 to be conducted to the heat sink 70 via drain pads D1 to D3, copper foil patterns 61 to 63, and heat conduction member 73. That is, the heat from FETs Q1, Q2, and QA1 that is conducted to the substrate 60 side can be efficiently dissipated from the heat sink 70. As a result, the heat generated by FETs Q1, Q2, and QA1 can be conducted effectively to the heat sink 70 from both the surface of FETs Q1, Q2, and QA1 facing the heat sink 70 and the surface of FETs Q1, Q2, and QA1 facing the substrate 60. This improves the heat dissipation effect of the heat generated from FETs Q1, Q2, and QA1.

[0047] In order to promote the transfer of heat from the copper foil patterns 61-63 to the heat sink 70, the copper foil patterns 61-63 are formed so as to extend from the connection positions where the drain pads D1-D3 are connected to the copper foil patterns 61-63 within the region where the recesses 71 that accommodate the FETs Q1, Q2, and QA1 are formed to the outside of the region where the recesses 71 are formed, as viewed vertically. That is, the copper foil patterns 61-63 are formed so as to have overlapping portions with the region outside the recesses 71, as viewed vertically.

[0048] 7 is an explanatory diagram showing an example of the dimensions of copper foil pattern 61 connected to drain pad D1 of FET Q1. Copper foil patterns 62 and 63 connected to drain pads D2 and D3 of FETs Q2 and QA1 may be similar. Note that FIG. 7 shows FET Q1 and recess 71 as viewed vertically (i.e., from a direction perpendicular to mounting surface f1). The package 83 of the FET Q1 has a rectangular shape when viewed vertically, and the recess 71 is formed in a rectangular shape corresponding to the rectangular shape of the package 83 when viewed vertically.

[0049] In a vertical view, the gate pad G1 and source pad S1 of FET Q1 are provided on only one of the four sides of the rectangular shape of package 83. In a vertical view, the copper foil pattern 61 is formed so as to extend to the outside of the region where the recess 71 is formed on the remaining three sides of the rectangular shape of package 83 on which the gate pad G1 and source pad S1 are not formed. It should be noted that the copper foil pattern 61 does not need to be formed so as to extend outside the area in which the recess 71 is formed on all three remaining sides of the rectangular shape, and may be formed so as to extend outside the area in which the recess 71 is formed on only one or two of these sides.

[0050] 7, the copper foil pattern 61 is formed to extend from the edges of the remaining three sides of the rectangular shape of the package 83 to positions spaced apart by lengths L3, L4, and L5, respectively, outside the area where the recess 71 is formed. The lengths L3, L4, and L5 may be, for example, 3 mm or more. If the gap between the inner walls of the recess 71 other than the bottom surface 72 and the outer wall of the package 83 is t3, the widths of the strip-shaped portions of the copper foil pattern 61 extending to the outside of the recess 71 on three sides of the rectangular shape of the package 83 are L3-t3, L4-t3, and L5-t3, respectively. The gap t3 may be, for example, 1 mm. In these strip-shaped portions, the copper foil pattern 61 and the heat sink 70 are close to each other and are thermally connected to each other via the thermally conductive member 73. The gap t1 between the copper foil pattern 61 and the heat sink 70 is smaller than the gap t2 between the FET Q1 and the bottom surface 72.

[0051] For example, assume that the horizontal and vertical dimensions L1 and L2 of the rectangular shape of the package 83 are 5 mm when viewed vertically, and the lengths L3, L4, and L5 are 3 mm. In this case, the area of ​​the rectangular shape of the package 83 when viewed vertically is 25 mm. 2 The area of ​​the copper foil pattern 61 is (5+3+3)×(5+3)=88 mm 2In this way, the area of ​​the copper foil pattern 61 may be, for example, about (88 / 25) times (about 3.5 times) the area of ​​the rectangular shape of the package 83 when viewed vertically.

[0052] (Variation) (1) In the above explanation, an example has been described in which the current control device of the present invention is applied to a column assist type electric power steering device, which is a so-called upstream assist type, but the current control device of the present invention may also be applied to a so-called downstream assist type electric power steering device. Below, configuration examples in which the current control device of the present invention is applied to single pinion assist type, rack assist type, and dual pinion assist type electric power steering devices as examples of downstream assist type electric power steering devices will be explained. In the case of the downstream assist system, the motor 20, rotation angle sensor 23a, and ECU 30 may not be separate components but may be integrated into an MCU (Motor Control Unit) as shown by the dashed lines in FIGS. 8 to 10 for waterproofing purposes.

[0053] 8 shows an example of a configuration in which the current control device of the present invention is applied to a single-pinion assist type electric power steering device. A steering wheel 1 is connected to one universal joint 4a of an intermediate shaft via a steering shaft 2. An input shaft 4c of a torsion bar (not shown) is connected to the other universal joint 4b. The pinion rack mechanism 5 includes a pinion gear (pinion) 5a, a rack bar (rack) 5b, and a pinion shaft 5c. The input side shaft 4c and the pinion rack mechanism 5 are connected by a torsion bar (not shown) that twists due to a difference in rotation angle between the input side shaft 4c and the pinion rack mechanism 5. The torque sensor 10 electromagnetically measures the torsion angle of the torsion bar as the steering torque Th of the steering wheel 1. A motor 20 that assists the steering force of the steering wheel 1 is connected to the pinion shaft 5c via a reduction gear 3, and a rotation angle sensor 23a similarly calculates rotation angle information of the motor rotation shaft of the motor 20.

[0054] (2) Figure 9 shows an example of a configuration in which the current control device of the present invention is applied to a rack-assist type electric power steering device. A spiral groove (not shown) is formed on the outer peripheral surface of the rack bar 5b, and a similar lead spiral groove (not shown) is also formed on the inner peripheral surface of the nut 91. A ball screw is formed by arranging multiple rolling elements in the rolling path formed by these spiral grooves. A belt 94 is wound around a drive pulley 92 connected to a rotary shaft 20a of a motor 20 that assists the steering force of the steering wheel 1, and a driven pulley 93 connected to a nut 91, and the rotational motion of the rotary shaft 20a is converted into linear motion of the rack bar 5b. A rotation angle sensor 23a calculates rotation angle information of the motor rotary shaft of the motor 20.

[0055] (3) Figure 10 shows an example of a configuration in which the current control device of the present invention is applied to a dual pinion assist type electric power steering device. The dual pinion assist type electric power steering device has a second pinion shaft 95 and a second pinion gear 96 in addition to a pinion shaft 5c and a pinion gear 5a, and a rack bar 5b has first rack teeth (not shown) that mesh with the pinion gear 5a and second rack teeth (not shown) that mesh with the second pinion gear 96. A motor 20 that assists the steering force of the steering wheel 1 is connected to the second pinion shaft 95 via a reduction gear 3, and a rotation angle sensor 23a calculates rotation angle information of the motor rotation shaft of the motor 20.

[0056] (Effects of the embodiment) (1) An electric power steering device includes an electronic control unit and a motor that is controlled by the electronic control unit and outputs a steering assist force to assist steering by a driver. The electronic control unit includes a substrate on which a field-effect transistor is mounted, a heat sink provided so as to face the mounting surface on which the field-effect transistor is mounted on the substrate, and a heat conductive member provided between the substrate and the heat sink. A recess is formed on the surface of the heat sink facing the mounting surface of the substrate to accommodate the field-effect transistor mounted on the mounting surface of the substrate. A copper foil pattern is formed on the substrate to connect to a drain pad provided on the surface of the field-effect transistor facing the substrate. When viewed perpendicularly to the mounting surface, the copper foil pattern is formed so as to extend from a position where the drain pad and the copper foil pattern are connected within the region where the recess is formed to outside the region where the recess is formed.

[0057] This allows the heat generated by the field-effect transistor to be conducted to the heat sink via the drain pad, copper foil pattern, and thermally conductive member. As a result, the heat from the field-effect transistor that is conducted to the substrate side can be efficiently dissipated from the heat sink. In this way, the number of transmission paths for conducting the heat generated by the field-effect transistor to the heat sink can be increased, thereby improving the heat dissipation effect of the heat generated by the field-effect transistor.

[0058] (2) The package of the field-effect transistor may have a rectangular shape when viewed perpendicularly to the mounting surface. When viewed perpendicularly, the recess may be formed in a rectangular shape corresponding to the rectangular shape of the package. A gate pad and a source pad of the field-effect transistor may be provided on one side of the rectangular shape of the package. When viewed perpendicularly, the copper foil pattern may be formed so as to extend outside the area where the recess is formed on at least one of the three sides of the rectangular shape of the recess corresponding to the remaining three sides of the rectangular shape of the package on which the gate pad and the source pad are not formed. For example, the copper foil pattern may be formed so as to extend outside the area where the recess is formed on all three sides of the rectangular shape of the recess. This makes it easier to form a copper foil pattern for transferring heat from the drain pad in a sufficient area without contacting the gate pad and the source pad.

[0059] (3) When viewed vertically, the copper foil pattern may be formed so as to extend at least 3 mm from the edge of the rectangular shape of the package to the outside of the area where the recess is formed. This makes it easier to transfer heat generated from the field effect transistor to the heat sink 70 via the copper foil pattern.

[0060] (4) The gap between the bottom surface of the recess and the opposing surface of the field-effect transistor facing the bottom surface of the recess may be larger than the gap between the mounting surface of the substrate and an area of ​​the opposing surface of the heat sink facing the mounting surface of the substrate where no recess is formed. The recess 71 that accommodates the field effect transistor can more easily tolerate dimensional errors of the field effect transistor in the direction perpendicular to the mounting surface. [Explanation of symbols]

[0061] 1...Steering wheel, 2...Steering shaft, 3...Reduction gear, 4a, 4b...Universal joint, 4c...Input side shaft, 5...Pinion rack mechanism, 5a...Pinion gear (pinion), 5b...Rack bar (rack), 5c...Pinion shaft, 6a, 6b...Tie rod, 7a, 7b...Hub unit, 8L, 8R...Steered wheels, 10...Torque sensor, 11...Ignition switch, 12...Vehicle speed sensor, 13...Battery, 14...Steering angle sensor, 20...Motor, 2 0a...rotating shaft, 23...motor rotation angle detection circuit, 23a...rotation angle sensor, 30...electronic control unit (ECU), 31a...control calculation device, 33A...motor current cutoff circuit, 39A1, 39B1, 39C1...current detection circuit, 40A...electronic control unit, 41A...gate drive circuit, 42A...power conversion circuit, 44A...power cutoff circuit, 50...current command value calculation unit, 51...current limiting unit, 52, 53...subtractor, 54...proportional integral (PI) control unit, 55...2-phase / 3-phase conversion unit, 5 6...3-phase / 2-phase conversion section, 57...angular velocity conversion section, 60...circuit board, 61-63...copper foil patterns, 70...heat sink, 71...recess, 72...bottom surface, 73...thermal conduction member, 80...chip, 81...die attach member, 82...wire, 83...package, 84, 85...solder, 91...nut, 92...drive pulley, 93...driven pulley, 94...belt, 95...second pinion shaft, 96...second pinion gear, Ca1, Ca2...ceramic capacitor, CA1, CA2...electrolytic capacitor CNT...connector, D1 to D3...drain pad, f1...mounting surface, f2, f2...opposing surface, f3...back surface, G1 to G3...gate pad, Q1, Q3, Q5...high-side FET, Q2, Q4, Q6...low-side FET, QA1, QA2, QA3...phase interruption FET, QC1, QC2...power interruption FET, La...choke coil, Lpa...positive power line, PWa...power wiring, S1 to S3...source pad, SWAa, SWAb, SWAc...switching arm

Claims

1. An electric power steering device including an electronic control unit and a motor controlled by the electronic control unit to output a steering assist force that assists steering by a driver, the electronic control unit includes a substrate on which a field effect transistor is mounted, a heat sink provided so as to face a mounting surface on which the field effect transistor is mounted on the substrate, and a heat conduction member provided between the substrate and the heat sink, a recess for accommodating the field effect transistor mounted on the mounting surface of the substrate is formed on a surface of the heat sink facing the mounting surface of the substrate, a copper foil pattern is formed on the substrate, the copper foil pattern being connected to a drain pad of the field effect transistor provided on a surface facing the substrate; When viewed perpendicularly to the mounting surface, the copper foil pattern is formed so as to extend from a position where the drain pad and the copper foil pattern are connected within the region where the recess is formed to an outside of the region where the recess is formed. An electric power steering device characterized by:

2. the package of the field effect transistor has a rectangular shape when viewed perpendicularly to the mounting surface, the recess is formed in a rectangular shape corresponding to the rectangular shape of the package when viewed vertically; a gate pad and a source pad of the field effect transistor are provided on one side of the rectangular shape of the package; the copper foil pattern is formed so as to extend to the outside of an area where the recess is formed on at least one of three sides of the rectangular shape of the recess corresponding to the remaining three sides of the rectangular shape of the package on which the gate pad and the source pad are not formed, when viewed from the vertical direction; 2. An electric power steering device according to claim 1.

3. 3. The electric power steering device according to claim 2, wherein the copper foil pattern is formed so as to extend to the outside of the area where the recess is formed on all three sides of the rectangular shape of the recess.

4. 3. The electric power steering device according to claim 2, wherein the copper foil pattern is formed so as to extend from an edge of the rectangular shape of the package to an outside of an area where the recess is formed by at least 3 mm when viewed from the vertical direction.

5. The electric power steering device according to any one of claims 1 to 4, characterized in that a gap between the bottom surface of the recess and an opposing surface of the field effect transistor that faces the bottom surface of the recess is larger than a gap between a region of the opposing surface of the heat sink that faces the mounting surface of the board and the mounting surface of the board, where the recess is not formed.

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