JP2015002610A - On-vehicle structure of inverter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress influences of noise generated by an inverter upon radio regarding an inverter on-vehicle structure supporting the inverter on a motor unit.SOLUTION: In an inverter on-vehicle structure, an inverter 6 is mounted to a case 3a of a motor unit 3 via a vibration-proof member 9 formed by overlapping coil springs which are wound inversely to each other. Each of the coil springs are conducted with both the case of the motor unit and the inverter, and the coil springs are insulated from each other. When a noise current flows in two coil springs, induced magnetic fields are canceled by each other, thereby reducing inductance. A noise current which is propagated from the inverter to the motor and returns from the motor to the inverter via the case of the motor unit and the vibration-proof member can be increased, such that a noise component to flow to a body ground with the high risk of influences upon radio can be reduced as a result.

Description

  The present invention relates to an in-vehicle structure of an inverter in an electric vehicle. The inverter in this specification is a device that supplies electric power to a motor for traveling. In addition, the “electric vehicle” in this specification includes a hybrid vehicle and a fuel cell vehicle having both a motor and an engine.

  The electric vehicle includes an inverter that converts the DC power of the battery into AC power having a frequency suitable for driving the traveling motor. In a circuit that generates an alternating current with an inverter, the switching element repeatedly turns on and off at a high frequency, so a high-frequency noise current is generated. Since the inverter that supplies power to the traveling motor has a large output, the generated noise current is also large.

  Patent Document 1 discloses a technique for propagating noise current from an inverter to the ground and reducing radiation noise from a switching element. In the technique disclosed in Patent Document 1, a control unit (inverter) including a switching element is supported on a case of a motor unit via a vibration isolating means having conductivity. The noise current generated in the control unit propagates to the case of the motor unit through the conductive vibration isolating means. In the case of a vehicle, the body is normally regulated to the ground potential, and the case of the motor unit is electrically connected to the vehicle body. When the body of the vehicle is represented as a connection destination of an electrical ground potential, it is referred to as “body ground”. The technology of Patent Document 1 is a technical idea that a vibration isolating member that supports a control unit is provided with conductivity, and that the vibration isolating member is used as a propagation path of noise current to the body ground. The motor unit is typically a housing that houses a motor for driving and a gear set (gear mission), but may be a simple motor case in the case of an electric vehicle with a simple drive mechanism.

  In addition, an example in which a control unit (inverter) is mounted on the upper part of a transaxle (motor unit) case via an anti-vibration rubber is also exemplified in Patent Document 2. The structure in which the control unit is mounted on the upper part of the motor unit can shorten the cable for supplying power from the inverter to the motor, and has an effect of reducing power transmission loss.

JP 2004-215343 A JP 2004-215348 A

  The present specification relates to an improvement of the technique of Patent Document 1. That is, the technology disclosed in this specification effectively suppresses the influence of the noise current by further effectively utilizing the vibration isolating member that supports the control unit (inverter) on the motor unit.

  The technology disclosed in this specification includes a set of two coil springs as a vibration isolation member. The two coil springs are combined so that one pitch of the other coil spring enters between the pitches of one coil spring, and is fitted between the case of the motor unit and the inverter. Further, the two coil springs are combined so that the winding directions are opposite to each other. The two coil springs are electrically connected to the case of the motor unit and the inverter, respectively, but are insulated from each other. Coil springs are typically made of steel and have an insulating coating except at the ends.

  According to the above-described in-vehicle structure, a noise current flows from the case of the motor unit to the inverter (or from the inverter to the case of the motor unit) through each of the two coil springs. The noise current flowing through the coil spring induces a magnetic field, but the induction magnetic fields cancel each other because the coil winding directions are opposite to each other. As a result, the inductance caused by the induced magnetic field is reduced. Switching noise is a high frequency, and if the inductance is small, current flows easily. That is, by adopting a vibration isolating member in which two coil springs wound in opposite directions are overlapped, a noise current can easily pass between the case of the motor unit and the casing of the inverter.

  According to the inventors' investigation, the noise current generated in the switching element of the inverter propagates to the motor as common mode noise via a cable (power cable) that supplies power from the inverter to the motor. It propagates to the body ground via The common mode noise generally means noise generated between a power supply line (in this case, a power cable) and ground (in this case, body ground).

  The common mode noise that flows to the body ground affects the sound quality of the radio mounted on the vehicle. Specifically, the common mode noise interferes with the antenna ground, or when the common mode noise flows through the muffler or the drive shaft, the radio wave is emitted and interferes with the radio wave. Therefore, it is preferable that the common mode noise generated by the inverter should not flow to the body ground as much as possible.

  If the vibration isolation member interposed between the motor unit case and the inverter is made conductive, the noise current of common mode noise that flows from the inverter to the motor unit through the power cable flows back to the inverter through the vibration isolation member. there is a possibility. The low-inductance vibration-isolating member disclosed in the present specification makes it easy for noise current to flow back from the case of the motor unit to the casing of the inverter, and as a result, the influence of noise current on the radio is suppressed.

  On the other hand, the vibration isolating member in which two coil springs are stacked contributes to the vibration isolation. In order to enhance the vibration isolation effect, a rubber vibration isolation material may be disposed at the center of the coil spring.

  Details and further improvements of the technology disclosed in this specification will be described in the following “DETAILED DESCRIPTION”.

It is a typical structure figure of the inverter vehicle-mounted structure of an Example. It is a perspective view of a vibration isolator. It is a typical perspective view of the inverter vehicle-mounted structure of a modification.

  An in-vehicle structure 2 of an inverter according to an embodiment will be described with reference to the drawings. In this embodiment, a hybrid vehicle is targeted. FIG. 1 shows a block diagram of main drive system components in a hybrid vehicle. In FIG. 1, only parts necessary for explaining the reduction of noise current generated by the inverter are illustrated, and some other parts are not shown. FIG. 1 is a diagram for explaining a propagation path of noise, and schematically shows a structural connection relationship of main drive system components. It should be noted that the inverter 6 and the motor unit 3 are hatched to represent a cross section of the case in order to emphasize the case. Reference numeral 3a represents a motor unit case, and reference numeral 6a represents an inverter case.

  The drive system components shown in FIG. 1 will be described. The vehicle of the embodiment is a hybrid vehicle, and includes an engine 22 and a motor 4 for traveling. The motor 4 is stored in the case 3 a together with a gear group that synthesizes / distributes the output torque of the engine 22 and the output torque of the motor 4. The motor 4 and the aforementioned gear group are collectively referred to as a motor unit 3. This type of motor unit is sometimes called a transaxle.

  A drive shaft 21 is connected to the motor unit 3, and the output torque of the engine 22 and the output torque of the motor 4 are appropriately fused / distributed by a gear set in the motor unit 3 and transmitted to the drive shaft 21. Although not shown, a drive wheel is connected to the tip of the drive shaft 21, and the drive wheel is rotated by the rotational force of the drive shaft 21. A muffler 25 is connected to the engine 22.

  The engine 22 and the motor unit 3 are mounted in the front compartment of the vehicle. An air conditioner compressor 23 is fixed on the engine 22, and an inverter 6 is fixed on the motor unit 3. The inverter 6 is fixed on the motor unit 3 via a vibration isolation member 9. The vibration isolation member 9 reduces the influence of the vibration of the motor unit 3, the vibration of the engine 22, or the traveling vibration on the inverter 6.

  The inverter 6 and the compressor 23 are electrically connected by an electric cable 24. The inverter 6 and the battery 27 are electrically connected by an electric cable 26. The battery 27 is a large-capacity power storage device that stores electric power for driving the motor 4, and is not disposed in the front compartment, but under the seat or in the luggage room. It is drawn near 6.

  The inverter 6 and the motor 4 are electrically connected by an electric cable 8. The motor 4 is an induction motor type motor driven by a three-phase alternating current, and more specifically, the electric cable 8 is composed of three wires for transmitting the UVW three-phase alternating current. An electric cable for passing a large current for driving the wheel is commonly called a power cable. In the case of FIG. 1, the electric cable 26 that connects the inverter 6 and the battery 27 and the electric cable 8 that connects the inverter 6 and the motor 4 correspond to power cables.

  The inverter 6 converts the DC power output from the battery 27 into AC power suitable for driving the motor 4. The main component of the inverter 6 is an inverter circuit 7 in which six sets of power transistors such as IGBTs and anti-parallel circuits of diodes are combined. In FIG. 1, a transistor and a diode are drawn in a rectangle indicated by reference numeral 7 to schematically represent the inverter circuit 7. The inverter 6 may include a boost converter that boosts the output voltage of the battery 27 and supplies the boosted voltage to the inverter circuit 7. The main component of the boost converter is also an antiparallel circuit of a power transistor and a diode. The “inverter” referred to in this specification may include not only a DC / AC conversion circuit but also other electric circuits necessary for the vehicle (for example, the above-described boost converter).

  Since the power transistor is repeatedly turned on / off at a predetermined frequency, switching noise is generated. Next, a transmission path of noise current (noise current) generated mainly by the power transistor of the inverter 6 will be described.

  The noise current generated by the power transistor of the inverter circuit 7 propagates to the motor 4 through the electric cable 8 (power cable) that connects the inverter 6 and the motor 4. The noise current at this time is a noise current called common mode noise that flows in the same direction through a plurality of power cables. Here, since the housing of the motor 4 and the case for housing the motor 4 (that is, the case 3a of the motor unit 3) are also made of metal, noise current propagated to the motor 4 passes through the housing of the motor 4 to the case 3a. Propagate. Note that current does not flow directly from the power cable to the case 3a through the motor casing, but high-frequency noise propagates from the power cable to the motor casing and then to the case 3a. In FIG. 1, a parasitic capacitance 5 schematically represents a propagation path from the power cable to the case 3a.

  The inverter 6 is fixed on the case 3a of the motor unit 3 through a vibration isolating member 9, and in this embodiment, the vibration isolating member 9 also has conductivity. The inverter case 6a is also conductive. Therefore, the noise current propagated to the case 3a of the motor unit propagates to the case 6a of the inverter through the vibration isolating member 9. The substrate of the inverter circuit 7 is connected to the inverter case 6 a through various members, and the noise current flowing through the case 6 a propagates to the substrate of the inverter circuit 7. A parasitic capacitance 12 schematically represents the propagation path. The noise current that has reached the case 6 a of the inverter 6 flows back to the inverter circuit 7 through the parasitic capacitance 12. That is, the noise current generated by the inverter circuit 7 flows back to the inverter circuit 7 through the electric cable 8, the motor 4, the motor unit case 3a, the vibration isolating member 9, and the inverter case 6a. A broken-line arrow shown in FIG. 1 represents this return path of the noise current.

  Various other components are electrically connected to the inverter 6 and the motor unit 3, and the propagation path of the noise current is not limited to the above-described path. For example, the noise current propagated to the case 3a of the motor unit 3 through the electric cable 8 and the motor 4 also flows to the engine 22 that is physically and electrically in contact with the case 3a. The noise current also flows from the engine 22 to the drive shaft 21 or the muffler 25. Note that some in-vehicle components connect the ground to the vehicle body. In FIG. 1, symbol BG represents a body ground. The noise current reaching the engine 22 can also flow through the body ground.

  On the other hand, the noise current generated in the inverter circuit 7 propagates to the battery 27 via the electric cable 26. The battery 27 is also connected to the body ground BG. The noise current generated in the inverter circuit 7 can also propagate to the body ground BG via the electric cable 26 and the battery 27.

  As described above, the noise current generated by the inverter circuit 7 can propagate through various paths. The frequency of the noise current depends on the ON / OFF cycle of the transistor of the inverter circuit 7. Depending on the frequency of the noise current, the noise current affects the AM or FM radio. In particular, a noise current that flows through the body ground BG may affect the ground of the radio antenna. In addition, noise currents flowing through long objects such as the muffler 25 and the drive shaft 21 are radiated as radio waves. This radio wave may interfere with the radio wave. The noise current thus affects the radio noise.

  From the viewpoint of radio performance, it is preferable that the noise current generated by the inverter circuit is not propagated to the body ground as much as possible. Of the noise current propagation paths described above, by introducing more noise current to the path that returns to the inverter circuit 7 through the case 3a of the motor unit, the vibration isolating member 9, and the case 6a of the inverter, the noise current is transferred to the body ground. The flowing noise current can be reduced. In order to increase the ratio of the noise current returning to the inverter circuit 7 as compared with the noise current flowing into the body ground BG, the impedance of the return path may be reduced as compared with the other paths. Since the vibration isolator 9 is narrowed as a current path among the paths of the noise current flowing back to the inverter circuit 7, reducing the impedance of the vibration isolator 9 increases the noise current flowing back to the inverter circuit 7. To contribute. In this embodiment, the structure of the vibration isolation member 9 is devised so that the impedance is reduced. Next, a specific structure of the vibration isolation member 9 will be described.

  FIG. 2 is a perspective view of the vibration isolation member 9. The anti-vibration member 9 has a structure in which a rubber-made cylindrical core member 33 is arranged at the center of a stack of two coil springs 31 and 32. The rubber core material 33 mainly contributes to vibration isolation of the inverter 6, but the two coil springs also contribute to vibration isolation performance.

  The two springs 31, 32 are combined so that the winding of the other coil spring passes between the pitches of the windings of one coil spring. Each coil spring is made of a conductive metal (e.g., steel) but has an insulating coating except at the ends. Reference numerals 31a, 32a, and 31b in FIG. 2 indicate exposed end portions. The end portions 31a and 32a are hatched portions where the metal is exposed. In each of the two coil springs, one end (for example, 31a and 32a) is in contact with the inverter case 6a, and the other end (for example, 31b) is in contact with the case 3a of the motor unit. Although the other end 32b of the coil spring 32 is hidden and not visible in FIG. 2, it is in contact with the case 3a of the motor unit. That is, the two coil springs 31 and 32 are insulated from each other, but are electrically connected to both the case 3a of the motor unit and the inverter 6 (the case 6a).

  The two springs 31 and 32 are combined so that the winding directions are opposite to each other. In FIG. 2, the arrow A indicates the winding direction of the coil spring 31, and the arrow B indicates the winding direction of the coil spring 32.

  The pair of coil springs 31 and 32 which are combined so that the winding of the other coil spring enters between the pitches of the one coil spring and wound in opposite directions have the following effects. That is, the pair of coil springs are electrically connected to the case 3a of the motor unit and the inverter (the case 6a). As described above, the noise current generated by the inverter circuit 7 and propagated to the case 3a of the motor unit 3 flows from the case 3a of the motor unit to the case 6a of the inverter 6 through each of the pair of coil springs. Since the noise current flowing through the coil spring has a high frequency, an induction magnetic field is generated. However, since the winding directions are opposite to each other, the induction magnetic fields generated by the pair of coil springs cancel each other. Eventually, this is equivalent to the fact that a magnetic field is not generated (or a small magnetic field is generated even if it is generated), so that the inductance resulting from the generation of the magnetic field is reduced. The inductance depends on the magnitude of the generated magnetic field, and even if it is a simple plate-like conducting member, when an alternating current flows, an induction magnetic field is generated to generate an inductance. However, in the vibration isolating member 9 in which the pair of coil springs are wound in opposite directions, the induction magnetic fields generated by the pair of coil springs cancel each other out. Becomes smaller. Thus, the vibration isolator 9 has a very small inductance.

  In the inverter on-vehicle structure of the embodiment, the inverter 6 is fixed to the case 3a of the motor unit 3 through the above-described vibration isolating member 9, so that the above-described noise current is increased and the noise current flowing to the body ground is relatively Can be made smaller. As a result, high-frequency noise that affects the radio can be reduced.

  As an example, when coil springs having an inductance of 46.8 [nH] were stacked in opposite directions, it was confirmed that the total inductance decreased to 7.5 [nH].

  In the schematic diagram of FIG. 1, a structure in which the vibration isolating member 9 is simply sandwiched between the case 3 a of the motor unit 3 and the inverter 6 is shown. The arrangement of the vibration isolation member 9 is not limited to the arrangement shown in FIG. For example, as shown in FIG. 3, an L-shaped bracket 41 is fixed on the case 3a of the motor unit, and the inverter 6 is protected on the side in the vehicle front-rear direction (the X-axis direction of the coordinates shown in FIG. 3). The vibration member 9 may be disposed and the vibration isolation member 9 may be fixed on one side of the L-shaped bracket 41. Note that the X-axis direction of the coordinate system shown in FIG. 3 corresponds to the longitudinal direction of the vehicle, the Y-axis direction corresponds to the vehicle width direction, and the Z-axis direction corresponds to the vertical direction of the vehicle. The in-vehicle structure 2a of FIG. 3 has an advantage that the inverter 6 is difficult to come off against a collision that receives an impact in the front-rear direction.

  As described above, in the inverter on-vehicle structure of this embodiment, the noise current generated by the inverter circuit 7 is such that the power cable to the motor 4, the motor 4, the motor unit case 3a, the vibration isolating member 9, and the inverter case 6a. And it is easy to return to the inverter circuit 7. Therefore, the noise current component flowing to the body ground can be reduced, and the influence of the noise current on the radio is suppressed.

  Points to be noted regarding the technology described in the embodiments will be described. The inverter may include a voltage converter circuit that boosts the voltage of the battery and other circuits in addition to the inverter circuit that converts direct current to alternating current.

  The anti-vibration member of the embodiment has two coil springs wound in opposite directions to each other so that the winding of the other coil spring passes between one pitch and is made of rubber at the axial center. Anti-vibration material is arranged. The rubber vibration isolating member is mainly responsible for the vibration isolating effect of the inverter, but the pair of coil springs also contribute to the vibration isolating.

  In order to reduce the influence of the noise current of the inverter on the radio, it is preferable that the inductance of the vibration isolation member (two coil springs) is small in the AM or FM frequency band. By adjusting the length, diameter, winding thickness, etc. of the coil spring, the inductance can be reduced in a desired frequency band.

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or the drawings can achieve a plurality of objects at the same time, and has technical usefulness by achieving one of the objects.

2, a2: inverter on-vehicle structure 3: motor unit 3a: case 4: motor 5, 12: parasitic capacitance (virtual capacitor)
6: Inverter 6a: Case 7: Inverter circuits 8, 24, 26: Electric cable 9: Anti-vibration member 21: Drive shaft 22: Engine 23: Compressor 25: Muffler 27: Battery 31, 32: Coil spring 33: Core material 41 : Bracket BG: Body ground

Claims (1)

It is an in-vehicle structure of an inverter that attaches an inverter that supplies power to the motor in the case of a motor unit that has a built-in motor for traveling.
The inverter is attached to the case of the motor unit via a vibration isolating member in which coil springs wound in opposite directions are stacked,
Each of the coil springs is electrically connected to both the case of the motor unit and the inverter, and the coil springs are insulated from each other.

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