Circuit unit

Abstract

Disclosed is a circuit unit capable of stably controlling an inrush current while suppressing an increase in the mounting space for a pre-charge resistor.　A circuit unit 10 is connected between an in-vehicle power supply 12 and a load 14 and includes: a main relay 18 that performs switching between supplying and not supplying power between the in-vehicle power supply 12 and the load 14; and a pre-charge relay 22 and a pre-charge resistor 24 that constitute a pre-charge circuit 20 connected in parallel with the main relay 18. The pre-charge resistor 24 is constituted using a metal clad resistor, and a metal case 54 of the metal clad resistor has a thermal contact part 56 in thermal contact with an object 80 for heat dissipation.

Description

Circuit Unit

[0001] The present disclosure relates to a circuit unit.

[0002] Patent Document 1 discloses a circuit unit that is housed within a battery pack mounted on a vehicle and switches between energization and de-energization between the battery and a load. The circuit unit has a case that houses a relay and a pre-charge resistor, which is a ceramic resistor. The pre-charge resistor is connected in series with a pre-charge relay and forms a pre-charge circuit that is connected in parallel with the relay. The pre-charge circuit pre-charges a capacitor in the vehicle load to control inrush current that flows through the load (e.g., an inverter circuit) when the vehicle starts, thereby protecting circuit components such as the capacitor and relay.

[0003] JP 2009-181737 A

[0004] However, inrush currents have become larger due to the trend toward higher voltages in vehicles in recent years, and multiple pre-charge resistors are often required to control the inrush current. Meanwhile, there is also a demand for smaller circuit units, making it difficult to secure space for installing pre-charge resistors.

[0005] Therefore, a circuit unit is disclosed that can stably control inrush current while suppressing an increase in the mounting space for a precharge resistor.

[0006] The circuit unit of the present disclosure is a circuit unit connected between an on-board power supply and a load, and includes a main relay that switches between energization and de-energization between the on-board power supply and the load, and a pre-charge relay and a pre-charge resistor that form a pre-charge circuit connected in parallel to the main relay, wherein the pre-charge resistor is constructed using a metal-clad resistor, and the metal case of the metal-clad resistor has a thermal contact portion that is in thermal contact with a heat dissipation target.

[0007] According to the circuit unit of the present disclosure, it is possible to control the inrush current while suppressing an increase in the mounting space for the precharge resistor.

[0008] Fig. 1 is a perspective view showing a circuit unit according to a first embodiment fixed to a heat dissipation target. Fig. 2 is a perspective view showing the circuit unit shown in Fig. 1 with an upper case constituting an insulating case removed. Fig. 3 is a plan view of the circuit unit shown in Fig. 2. Fig. 4 is a cross-sectional view taken along line IV-IV in Fig. 3. Fig. 5 is a cross-sectional view taken along line V-V in Fig. 3. Fig. 6 is a perspective view showing the circuit unit shown in Fig. 1 fixed to another heat dissipation target, with an upper case constituting an insulating case removed.

[0009] <Description of Embodiments of the Present Disclosure> First, embodiments of the present disclosure will be listed and described. The circuit unit of the present disclosure is: (1) a circuit unit connected between an on-board power supply and a load, the circuit unit including: a main relay that switches between energization and de-energization between the on-board power supply and the load; a pre-charge relay and a pre-charge resistor that form a pre-charge circuit connected in parallel to the main relay; the pre-charge resistor being configured using a metal clad resistor; and a metal case of the metal clad resistor having a thermal contact portion that thermally contacts a heat dissipation target.

[0010] According to the circuit unit of this aspect, the precharge resistor of the precharge circuit that controls the inrush current when the vehicle starts is configured using a metal-clad resistor, which is an insulated wire-wound resistor enclosed in a metal case. Because metal-clad resistors are used for large currents, they can handle large currents without increasing the number of resistors, as is the case with conventional ceramic resistors. In other words, by using a metal-clad resistor, it is possible to suppress an increase in the mounting space for the precharge resistor or to reduce the mounting space while stably controlling the inrush current.

[0011] Furthermore, since the metal clad resistor itself has a metal case, it has excellent heat dissipation properties, and by thermally contacting the thermal contact part of the metal case with the heat dissipation target, it is possible to easily ensure a heat dissipation path for the metal clad resistor, thereby improving the heat dissipation properties of the metal clad resistor, which also ensures the operational stability of the metal clad resistor and allows for more stable control of inrush current.

[0012] The heat dissipation target with which the thermal contact portion of the metal case of the metal-clad resistor comes into thermal contact may be a component provided in the circuit unit itself (e.g., the case of the circuit unit, etc.), or a component other than the circuit unit (e.g., the housing of the battery pack in which the circuit unit is mounted, etc.).

[0013] (2) In the above (1), it is preferable that the device further includes an insulating case that holds the main relay, the pre-charge relay, and the pre-charge resistor, and the insulating case has an opening that exposes the thermal contact portion of the metal case of the metal-clad resistor so that it can be in thermal contact with the heat dissipation target. While the main relay, pre-charge relay, and pre-charge resistor are stably held in the insulating case, the thermal contact portion of the metal case can be brought into thermal contact with the heat dissipation target through the opening provided in the insulating case, making it possible to simultaneously ensure insulation between the main relay, pre-charge relay, and pre-charge resistor, and a heat dissipation path for the metal-clad resistor.

[0014] (3) In the above (1) or (2), it is preferable that the thermal contact portion of the metal case contacts the heat dissipation target via an elastic heat dissipation sheet or a gap filler, which advantageously prevents a gap from being formed between the thermal contact portion formed by the surface of the metal case of the metal clad resistor and the heat dissipation target, thereby advantageously preventing a reduction in the heat dissipation performance of the metal clad resistor.

[0015] (4) In any one of (1) to (3) above, it is preferable that the heat dissipation target with which the thermal contact portion of the metal-clad resistor is in thermal contact is a heat sink in thermal contact with the main relay. The main relay generates heat when current is applied between the power source and the load, while the metal-clad resistor generates heat when the vehicle starts, which is different from the heat generation time of the main relay. Therefore, by skillfully using the heat sink for the main relay as the heat dissipation target for the metal-clad resistor, it is possible to ensure a heat dissipation path for the metal-clad resistor while suppressing an increase in the number of parts.

[0016] The heat sink may be a metal plate that is in close contact with the insulating case described in (2) above that constitutes the circuit unit, or may be a metal housing of a battery pack on which the insulating case described in (2) above is placed.

[0017] (5) In any one of the above (1) to (4), it is preferable that the heat dissipation target with which the thermal contact portion of the metal-clad resistor is in thermal contact is a metal plate that constitutes the housing of the on-board power supply and has a refrigerant flow path through which a refrigerant flows. This is because by using a metal plate with a refrigerant flow path in the housing of the on-board power supply to which the circuit unit is connected as the heat dissipation target, the heat dissipation performance of the metal-clad resistor can be further advantageously increased.

[0018] <Details of Embodiments of the Present Disclosure> Specific examples of the circuit unit of the present disclosure will be described below with reference to the drawings. Note that the present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0019] First Embodiment A circuit unit 10 according to a first embodiment of the present disclosure will be described below with reference to FIGS. 1 to 5 . The circuit unit 10 is mounted, for example, on an electric vehicle or a hybrid vehicle and is connected between an on-board power supply and a load. In the first embodiment, the circuit unit 10 is connected between a battery 12, which is an example of an on-board power supply, and an inverter 14, which is an example of a load. Note that the circuit unit 10 can be arranged in any orientation within the vehicle; however, in the following description, the upper side will be referred to as the upper side in FIG. 4 , the lower side as the lower side in FIG. 4 , the left side as the left side in FIG. 3 , the right side as the right side in FIG. 3 , the front side as the lower side in FIG. 3 , and the rear side as the upper side in FIG. 3 . Note that, in some cases, when multiple identical components are shown, only some of the components will be designated by reference numerals, and the reference numerals will be omitted for the other components.

[0020] The battery 12 may be a known battery, and its structure is not limited, but may be, for example, a battery module made up of a plurality of battery cells (not shown). The battery 12 (battery module) may be housed in, for example, a metal housing 16 (see FIG. 6 , which will be described later), and the battery 12 and the circuit unit 10 are housed together in the housing 16 to form a battery pack (not shown).

[0021] <Circuit Unit 10> The circuit unit 10 includes a positive-side relay 18 as a main relay that switches between energization and de-energization between the battery 12, which is a power source, and the inverter 14, which is a load, and a pre-charge relay 22 and a pre-charge resistor 24 that constitute a pre-charge circuit 20 that are connected in parallel to the positive-side relay 18. In the first embodiment, the circuit unit 10 includes a negative-side relay 19 in addition to the positive-side relay 18, and these positive and negative-side relays 18, 19, pre-charge relay 22, and pre-charge resistor 24 are fixed by bolts or screws to a lower case 62 that constitutes an insulating case 58, which will be described later.

[0022] <Main Relay (Positive Relay 18)> In the first embodiment, a pair of relays 18, 19 are provided in the circuit unit 10 and are arranged spaced apart from each other in the left-right direction. One relay (the left relay in the first embodiment) is the positive relay 18 serving as the main relay, and the other relay (the right relay in the first embodiment) is the negative relay 19. The positive and negative relays 18, 19 each have a pair of terminals 26, 26 (one of which is shown in FIG. 4 ) on their front sides (the positive relay 18 is at the front, and the negative relay 19 is at the rear) that are spaced apart from each other in the left-right direction, and each terminal 26 is exposed on the surface of each relay 18, 19.

[0023] The terminals 26 are input and output terminals for the relays 18 and 19. For example, in the positive relay 18, the left terminal 26 is an input terminal on the positive side, and the right terminal 26 is an output terminal on the positive side. In the negative relay 19, the left terminal 26 is an output terminal on the negative side, and the right terminal 26 is an input terminal on the negative side.

[0024] A current-carrying bus bar 28 is overlapped with each terminal portion 26 of each of the relays 18, 19 and fixed with a bolt 30. That is, the circuit unit 10 includes first and second current-carrying bus bars 28a, 28b connected to the input and output terminal portions 26, 26 of the positive-side relay 18, and third and fourth current-carrying bus bars 28c, 28d connected to the output and input terminal portions 26, 26 of the negative-side relay 19. When the circuit unit 10 is assembled, the ends of the first to fourth current-carrying bus bars 28a to 28d are exposed to the outside through through windows 68a to 68d provided in an insulating case 58 (upper case 60) described below, and form input and output connection portions 32a, 32b on the positive side and output and input connection portions 32c, 32d on the negative side, respectively.

[0025] 1, the input connection portion 32a on the positive electrode side and the input connection portion 32d on the negative electrode side are electrically connected to positive and negative terminal portions (not shown) of the battery 12, respectively, by conductive members 34 made of bus bars, electric wires, etc. Furthermore, the output connection portion 32b on the positive electrode side and the output connection portion 32c on the negative electrode side are electrically connected to positive and negative terminal portions (not shown) of the inverter 14, respectively, by conductive members 34. These connections 32a to 32d and the conductive members 34 can be fixed by bolts 35.

[0026] As a result, a main circuit 36 ​​between the battery 12 and the inverter 14 is configured, including the relays 18, 19, the first to fourth current-carrying bus bars 28a to 28d, and the conductive members 34. In the main circuit 36, by switching the relays 18, 19 between ON and OFF, the main circuit 36 ​​between the battery 12 and the inverter 14 can be switched between a conducting state and a non-conducting state.

[0027] In addition to the first to fourth current-carrying bus bars 28a to 28d, first to fourth heat-dissipating bus bars 38a to 38d are fastened to the terminals 26 of the positive and negative relays 18, 19 by bolts 30. Each of the first to fourth heat-dissipating bus bars 38a to 38d is generally L-shaped and has a portion that extends vertically and a portion that bends from the lower end of the vertically extending portion and expands horizontally. The upper ends of the heat-dissipating bus bars 38a to 38d are fixed to the terminals 26 of the relays 18, 19 by bolts 30, and their lower ends extend in the front-to-rear direction and are located below the relays 18, 19.

[0028] As will be described later, the portion extending in the front-rear direction at the lower end of each of these heat dissipation bus bars 38a to 38d is a heat dissipation portion 40 that is in thermal contact with a heat sink 80, which is the heat dissipation target, via an insulating sheet 76 and an elastic heat dissipation sheet (or gap filler) 78. With this structure, each terminal portion 26 of each relay 18, 19 is in thermal contact with the heat sink 80 via each of the heat dissipation bus bars 38a to 38d, the insulating sheet 76, and the elastic heat dissipation sheet (or gap filler) 78, and heat generated when current is applied to each relay 18, 19 can be dissipated from the heat sink 80.

[0029] <Precharge Circuit 20> The precharge circuit 20 is connected in parallel to the main relay (positive side relay 18) in the main circuit 36. Specifically, in the precharge circuit 20, a precharge relay 22 and a precharge resistor 24 are connected in series. The precharge relay 22 and the input terminal 26 of the positive side relay 18 are electrically connected by an electric wire 42, and the precharge resistor 24 and the output terminal 26 of the positive side relay 18 are electrically connected by an electric wire 44. The precharge relay 22 and the precharge resistor 24 are also electrically connected by an electric wire 46.

[0030] A terminal 48 is provided on at least one end of each of the electric wires 42, 44, 46, and each terminal 48 is overlapped with each terminal portion 26 of the positive side relay 18 or each terminal portion 50 (described later) of the precharge relay 22, and fixed by a bolt 30 or a screw 52.

[0031] <Pre-charge relay 22> A known pre-charge relay 22 may be employed, and its structure is not limited thereto. However, it includes a pair of terminals 50, 50 (one of which is shown in FIG. 4 ) spaced apart from each other in the left-right direction. In the first embodiment, the pre-charge relay 22 is positioned with its upper front facing upward, and each terminal 50 is exposed on the top surface of the pre-charge relay 22. A terminal 48 provided at the end of an electric wire 42 connecting the positive relay 18 and the pre-charge relay 22 is overlapped with the input terminal 50 (left terminal 50) of the pre-charge relay 22 and secured with a screw 52. Furthermore, a terminal 48 provided at the end of an electric wire 46 connecting the pre-charge relay 22 and the pre-charge resistor 24 is overlapped with the output terminal 50 (right terminal 50) of the pre-charge relay 22 and secured with a screw 52.

[0032] <Pre-charge Resistor 24> The pre-charge resistor 24 is configured using a metal-clad resistor. Because a known type can be used as the pre-charge resistor 24 (metal-clad resistor), detailed description will be omitted. However, the pre-charge resistor 24 is configured by sealing a wire-wound resistor (not shown) in an insulated state in a metal case 54. Note that in FIG. 5, the internal structure of the pre-charge resistor 24 is not shown, and only the metal case 54 is shown. In other words, the metal case 54 of the pre-charge resistor 24 is hollow, and a wire-wound resistor (not shown) is housed inside the metal case 54 in an insulated state. In the first embodiment, the metal case 54 of the pre-charge resistor 24 is hollow and approximately rectangular, and is disposed so as to extend in the front-to-rear direction.

[0033] As described above, the pre-charge resistor 24 is connected to the electric wire 44 connected to the positive relay 18 and the electric wire 46 connected to the pre-charge relay 22. Specifically, the electric wire 44 is connected to one end of a winding provided inside the pre-charge resistor 24, and the electric wire 46 is connected to the other end. The electric wires 44, 46 connected to both ends of the winding extend from the inside of the metal case 54 to the outside. In the first embodiment, the electric wires 44, 46 extend to the outside from one end in the longitudinal direction of the metal case 54 (the front end in the first embodiment). The terminals 48 provided at the ends of the electric wires 44, 46 are overlapped with the output terminal portion 26 of the positive relay 18 and the output terminal portion 50 of the pre-charge relay 22, respectively, and are fixed by the bolts 30 and the screws 52, respectively.

[0034] The metal case 54 of this precharge resistor 24 (metal clad resistor) has a thermal contact portion 56 that is in thermal contact with a heat sink 80 serving as a heat dissipation target, which will be described later. In the first embodiment, the metal case 54 is placed on the heat sink 80 via an elastic heat dissipation sheet (or gap filler) 78, which will be described later, and the thermal contact portion 56 is formed by the lower wall portion that constitutes the hollow metal case 54.

[0035] <Insulating Case 58> The circuit unit 10 has an insulating case 58 that holds the relays 18, 19, including the main relay (positive relay 18), the pre-charge relay 22, and the pre-charge resistor 24. In the first embodiment, the insulating case 58 has a hollow rectangular parallelepiped shape as a whole, and the left-right dimension is larger than the front-rear dimension. In particular, in the first embodiment, the insulating case 58 includes an upper case 60 and a lower case 62 that can be assembled and disassembled relative to each other in the vertical direction. The upper case 60 and the lower case 62 are formed of, for example, synthetic resin. The method of fixing the upper case 60 and the lower case 62 together is not limited, but in embodiment 1, the upper case 60 is placed above the lower case 62 with the lower case 62 sandwiched between them, and the heat sink 80 described below is placed below the lower case 62, and the upper case 60 and the lower case 62 are fixed together by fastening them together with bolts 63 at the four corners of the outer periphery.

[0036] The upper case 60 has a generally box-like shape that opens downward overall, and includes an upper bottom wall 64 and an upper peripheral wall 66 that protrudes downward from the outer periphery of the upper bottom wall 64. Rectangular through-windows 68a to 68d that penetrate the upper bottom wall 64 in the thickness direction (vertical direction) are provided at positions that correspond to the connection portions 32a to 32d of the first to fourth current-carrying bus bars 28a to 28d when the circuit unit 10 is assembled.

[0037] The lower case 62 has a bottom wall 70 that is generally flat, and the bottom wall 70 has substantially the same shape as the upper case 60 in a plan view. As a result, when the upper case 60 and the lower case 62 are overlapped and fixed together, the bottom wall 70 of the lower case 62 covers the lower opening of the upper case 60.

[0038] The bottom wall 70 has rectangular opening windows 72 (one of which is shown in FIG. 4 ) penetrating through in the thickness direction (vertical direction) at positions corresponding to the heat dissipation portions 40 of the first to fourth heat dissipation bus bars 38 a to 38 d when the circuit unit 10 is assembled. The bottom wall 70 also has rectangular opening windows 74 penetrating through in the thickness direction (vertical direction) at positions corresponding to the thermal contact portions 56 of the precharge resistors 24 (metal-clad resistors) when the circuit unit 10 is assembled. This allows the opening windows 74 to expose the thermal contact portions 56 of the metal case 54 so that they can be in thermal contact with a heat sink 80 (described later) when the circuit unit 10 is assembled.

[0039] In the first embodiment, an insulating sheet 76 and an elastic heat dissipation sheet 78 are stacked and housed in each opening window 72 provided below each heat dissipation section 40. This allows the first to fourth heat dissipation bus bars 38a to 38d to be in electrically insulated and thermally conductive contact with the heat dissipation plate 80 (described later) that is overlaid on the bottom wall section 70. Known insulating sheets 76 and elastic heat dissipation sheets 78 may be used. In particular, the elastic heat dissipation sheet 78 may be a thermally conductive material that allows the heat dissipation section 40 to contact the heat dissipation plate 80 via the insulating sheet 76 and elastic heat dissipation sheet 78 without an air gap between them. A known gap filler may also be used. Furthermore, the insulating sheet 76 and elastic heat dissipation sheet 78 do not need to be separate members, but may be formed from a single member that is insulating and thermally conductive. These insulating sheets 76 and elastic heat dissipation sheets (or gap fillers) 78 are fixed (e.g., glued) to the underside of each heat dissipation section 40, and are placed inside each opening window 72 when the circuit unit 10 is assembled.

[0040] An elastic heat dissipation sheet (or gap filler) 78 is housed in an opening 74 provided below the thermal contact portion 56. This allows the thermal contact portion 56 to be in thermally conductive contact with a heat sink 80 (described later). Because the wire-wound resistors constituting the pre-charge resistor 24 are housed in an insulated state in the metal case 54, the metal case 54 remains electrically insulated even when the circuit unit 10 is energized, and the insulating sheet 76 does not need to be placed in the opening 74. The elastic heat dissipation sheet (or gap filler) 78 is, for example, fixed (e.g., glued) to the lower surface of the thermal contact portion 56 (the lower wall portion of the metal case 54) and is housed and placed inside the opening 74 when the circuit unit 10 is assembled.

[0041] <Heat Dissipation Target (Heat Dissipation Plate 80)> The heat dissipation plate 80 is made of a metal with excellent heat dissipation properties and is configured as a metal plate with a predetermined thickness. The heat dissipation plate 80 has the same shape as the insulating case 58 in a plan view, and the insulating case 58 and the heat dissipation plate 80 are secured together with bolts 63 in an overlapping state. By securing the insulating case 58 and the heat dissipation plate 80 together in an overlapping state, the heat dissipation portions 40 of the first to fourth heat dissipation bus bars 38a to 38d are secured together with the heat dissipation plate 80 via the insulating sheet 76 and the elastic heat dissipation sheet (or gap filler) 78. Furthermore, by securing the insulating case 58 and the heat dissipation plate 80 together in an overlapping state, the thermal contact portion 56 of the metal case 54 is secured together with the heat dissipation plate 80 via the elastic heat dissipation sheet (or gap filler) 78. As a result, the positive and negative relays 18 and 19 and the precharge resistor 24 are in thermal contact with the same heat sink 80 .

[0042] The heat sink 80 may be placed over the battery pack housing 16, for example, so that heat generated in the relays 18, 19 and pre-charge resistor 24 is dissipated from the housing 16 via the heat sink 80. Alternatively, the heat sink 80 does not have to be placed over the battery pack housing 16, and heat generated in the relays 18, 19 and pre-charge resistor 24 may be dissipated into the air via the heat sink 80.

[0043] <Assembly of Circuit Unit 10> A specific example of a method for assembling the circuit unit 10 will now be described. Note that the method for assembling the circuit unit 10 is not limited to the embodiment described below.

[0044] First, the first to fourth current-carrying bus bars 28a to 28d and the first to fourth heat-dissipating bus bars 38a to 38d are placed on the terminal portions 26 of the relays 18, 19, respectively, and are then secured with the bolts 30. At this time, the terminals 48 provided at the ends of the electric wires 42, 44 are also placed on the terminal portions 26 of the positive relay 18, and are fastened together with the bolts 30. Then, the relays 18, 19, pre-charge relay 22, and pre-charge resistor 24 are placed on the lower case 62, which is provided with the opening windows 72, 74, and secured with bolts or screws.

[0045] For example, insulating sheets 76 and elastic heat dissipation sheets (or gap fillers) 78 are superimposed and pre-fixed to the underside of the heat dissipation portions 40 of the first to fourth heat dissipation bus bars 38a to 38d. As a result, when the relays 18, 19 are fixed to the lower case 62, the insulating sheets 76 and elastic heat dissipation sheets (or gap fillers) 78 are housed within the respective opening windows 72. Also, for example, elastic heat dissipation sheets (or gap fillers) 78 are superimposed and pre-fixed to the underside of the lower wall portion of the metal case 54. As a result, when the pre-charge resistor 24 is fixed to the lower case 62, the elastic heat dissipation sheets (or gap fillers) 78 are housed within the opening windows 74.

[0046] Thereafter, the terminals 48 provided at the ends of the electric wires 42, 46 are overlapped with the terminal portions 50 of the pre-charge relay 22, and each is secured with a screw 52. Next, the heat sink 80 is placed on the underside of the lower case 62 (bottom wall portion 70) configured in this manner, and the upper case 60 is brought close to the lower case 62 from above, and the upper case 60 and the heat sink 80 are secured with the bolts 63. This completes the circuit unit 10. In the completed state of the circuit unit 10, the connection portions 32a-32d of the first to fourth current-carrying bus bars 28a-28d are exposed to the outside through the through windows 68a-68d in the upper case 60.

[0047] The circuit unit 10 manufactured as described above is housed in, for example, the housing 16 of a battery pack, and the input connection portion 32a on the positive electrode side and the input connection portion 32d on the negative electrode side are electrically connected to the battery 12 arranged in the housing 16 by respective conductive members 34. Furthermore, the output connection portion 32b on the positive electrode side and the output connection portion 32c on the negative electrode side are electrically connected to the inverter 14 provided outside the battery pack by respective conductive members 34. In this way, the battery 12 and the inverter 14 are electrically connected via the circuit unit 10. Note that when the circuit unit 10 is arranged in the housing 16 of the battery pack, the heat sink 80 may or may not be superimposed on the housing 16.

[0048] Generally, when a vehicle is started, electricity flows from the battery to the inverter to charge the capacitor in the inverter. However, the current (inrush current) generated during vehicle startup is relatively large, and if the inrush current flows through the main circuit, it may damage the main relay. To prevent this damage, a pre-charge resistor is provided. Specifically, when the vehicle is started, the positive relay 18 is turned OFF and the pre-charge relay 22 is turned ON, thereby supplying power from the battery 12 to the capacitor in the inverter 14 via the pre-charge circuit 20, thereby preventing damage to the positive relay 18 and charging the capacitor. After the vehicle is started, the positive relay 18 is turned ON and the pre-charge relay 22 is turned OFF, thereby supplying power from the battery 12 to the inverter 14 through the main circuit 36. Therefore, when the vehicle is started, the pre-charge circuit 20 is energized, causing the pre-charge resistor 24 to heat up, and after the vehicle is started, the main circuit 36 ​​is energized, causing the relays 18 and 19 to heat up. That is, the precharge resistor 24 and the positive relay 18 generate heat at different times.

[0049] In the circuit unit 10 of embodiment 1 having the above-described structure, a metal-clad resistor capable of handling large currents is employed as the pre-charge resistor 24. That is, the metal-clad resistor is an insulated wire-wound resistor housed in a metal case 54, and heat can be dissipated through the metal case 54. As a result, the metal-clad resistor has better heat dissipation properties than, for example, a ceramic resistor, and even when multiple ceramic resistors are required, a smaller number of metal-clad resistors (for example, one) can handle large currents. As a result, the mounting space for the pre-charge resistor can be reduced, allowing the circuit unit 10 to be made smaller.

[0050] The relays 18, 19 including the main relay (positive-side relay 18), the pre-charge relay 22, and the pre-charge resistor 24 are held in an insulating case 58, and a lower case 62 constituting the insulating case 58 has an opening window 74 formed therein that exposes the thermal contact portion 56 of the pre-charge resistor 24 (metal-clad resistor) so that it can come into contact with a heat sink 80. This allows heat generated in the pre-charge resistor 24 to be dissipated from the heat sink 80 through the opening window 74.

[0051] In particular, the thermal contact portion 56 is in contact with the heat sink 80 via an elastic heat dissipation sheet (or gap filler) 78. By providing the elastic heat dissipation sheet (or gap filler) 78 between the thermal contact portion 56 and the heat sink 80 in this manner, no air layer is interposed between the thermal contact portion 56 and the heat sink 80, thereby improving the heat dissipation efficiency.

[0052] The heat sink 80, with which the thermal contact portion 56 is in thermal contact, is also in thermal contact with the positive relay 18. This allows a common heat dissipation path to be formed for the pre-charge resistor 24 and the main relay (positive relay 18), which generate heat at different times, and avoids an increase in the number of parts compared to when separate heat dissipation paths are formed for the pre-charge resistor 24 and the main relay (positive relay 18).

[0053] <Modifications> Although the first embodiment has been described above in detail as a specific example of the present disclosure, the present disclosure is not limited to this specific description. Modifications, improvements, etc. within the scope of achieving the object of the present disclosure are included in the present disclosure. For example, the following modifications of the embodiment are also included in the technical scope of the present disclosure.

[0054] (1) In the above embodiment, the heat dissipation target was the heat sink 80 made of a metal plate. However, this is not limited to this. That is, as shown in FIG. 6 , the heat dissipation target may be a metal plate 92 that constitutes the housing 16 of the battery 12, which is an on-board power source, and that has a refrigerant flow path 90 through which a refrigerant (not shown) flows. Specifically, the metal plate 92 is formed, for example, by the bottom wall of the housing 16, and the refrigerant flow path 90 is formed inside the metal plate 92. Note that a known refrigerant may be used for the refrigerant flowing through the refrigerant flow path 90. Furthermore, the extension direction and length of the refrigerant flow path 90 shown in FIG. 6 are merely exemplary, and the extension direction and length of the refrigerant flow path are not limited. Even if the heat dissipation target is such a metal plate 92, the same effects as those of the above embodiment can be achieved by overlapping and fixing the circuit unit 10 and thermally contacting the thermal contact portion 56 of the pre-charge resistor 24 (metal-clad resistor). Furthermore, even when the circuit unit 10 is placed and fixed on the metal plate 92 formed by the bottom wall portion of the housing 16 in this manner, a heat sink 80 as in the above embodiment may be provided between the circuit unit 10 and the metal plate 92.

[0055] (2) In the above embodiment, the lower case 62 has the openings 72 at positions corresponding to the heat dissipation portions 40 of the heat dissipation bus bars 38a to 38d of the relays 18, 19, and the openings 74 at positions corresponding to the thermal contact portions 56 of the precharge resistors 24. However, this is not limited to this. The openings are not essential to the lower case, and the heat dissipation portions and thermal contact portions may be in thermal contact with the bottom wall of the lower case, which is made of a synthetic resin with good thermal conductivity. In this case, the bottom wall of the lower case constitutes the heat dissipation target. Note that the heat dissipation bus bars, insulating sheets, and elastic heat dissipation sheets (or gap fillers) are not essential to the circuit unit according to the present disclosure.

[0056] (3) The structure of the precharge resistor (metal clad resistor) is not limited as long as it has a metal case. In the above embodiment, the electric wires 44, 46 extending from the precharge resistor 24 extend from one end (front end) in the longitudinal direction of the precharge resistor 24. However, the two electric wires may extend from both ends in the longitudinal direction of the precharge resistor.

[0057] (4) The shapes, lengths, etc. of the conductive members 34 shown in FIG. 1 are merely examples, and do not limit the manner in which the on-board power supply and the load are connected to the circuit unit.

[0058] (5) In the above embodiment, the heat sink 80 may have a divided structure, and may be composed of, for example, two members separated from each other in the left-right direction. That is, the left heat sink may be in thermal contact with the heat sink portions 40 of the heat sink bus bars 38a, 38b in the main relay (positive relay 18) and the thermal contact portion 56 in the pre-charge resistor 24, and the right heat sink may be in thermal contact with the heat sink portions 40 of the heat sink bus bars 38c, 38d in the negative relay 19. Note that the heat sink (e.g., the heat sink) may simply be provided at a position corresponding to the thermal contact portion of the metal case in the pre-charge resistor.

[0059] (6) In the above embodiment, the precharge circuit 20 is connected in parallel to the positive relay 18. However, the precharge circuit may be connected in parallel to the negative relay. In this case, the main relay is constituted by the negative relay.

[0060] 10 Circuit unit 12 Battery (on-board power supply) 14 Inverter (load) 16 Housing 18 Positive side relay (main relay) 19 Negative side relay 20 Precharge circuit 22 Precharge relay 24 Precharge resistor 26 Terminal portion 28 Current-carrying bus bar 28a First current-carrying bus bar 28b Second current-carrying bus bar 28c Third current-carrying bus bar 28d Fourth current-carrying bus bar 30 Volt 32a (for input on the positive side) Connection portion 32b (for output on the positive side) Connection portion 32c (for output on the negative side) Connection portion 32d (for input on the negative side) 34 Conductive member 35 Volt 36 Main circuit 38a to 38d Heat dissipation bus bars 40 Heat dissipation portion 42, 44, 46 Electric wire 48 Terminal 50 Terminal portion 52 Screw 54 Metal case 56 Thermal contact portion 58 Insulating case 60 Upper case 62 Lower case 63 Bolt 64 Upper bottom wall portion 66 Upper peripheral wall portion 68a to 68d Through window 70 Bottom wall portion 72, 74 Opening window 76 Insulating sheet 78 Elastic heat dissipation sheet (or gap filler) 80 Heat sink (heat dissipation target) 90 Coolant flow path 92 Metal plate (heat dissipation target)

Claims

1. A circuit unit connected between an on-board power supply and a load, comprising: a main relay that switches between energization and de-energization between the on-board power supply and the load; and a pre-charge relay and a pre-charge resistor that constitute a pre-charge circuit connected in parallel to the main relay, wherein the pre-charge resistor is constructed using a metal clad resistor, and the metal case of the metal clad resistor has a thermal contact portion that is in thermal contact with a heat dissipation target.

2. A circuit unit as described in claim 1, comprising an insulating case that holds the main relay, the pre-charge relay, and the pre-charge resistor, the insulating case having an opening window that exposes the thermal contact portion of the metal case of the metal clad resistor so that it can come into thermal contact with the heat dissipation target.

3. The circuit unit according to claim 1 or 2, wherein the thermal contact portion of the metal case is in contact with the heat dissipation target via an elastic heat dissipation sheet or a gap filler.

4. The circuit unit according to claim 1 or 2, wherein the heat dissipation target with which the thermal contact portion of the metal clad resistor is in thermal contact is a heat sink that is in thermal contact with the main relay.

5. A circuit unit as described in claim 1 or 2, wherein the heat dissipation target with which the thermal contact portion of the metal clad resistor is in thermal contact is a metal plate that constitutes the housing of the vehicle-mounted power supply and has a refrigerant flow path through which a refrigerant flows.

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