Patent Description:
Inverters are known which convert direct current to alternating current. The inverters include power modules including switching elements.

Since an inverter of this type deals with a large amount of power, a high voltage is applied and large current flows in the inverter. The inverter requires cooling because it generates a large amount of heat when activated. A large surge voltage also occurs. Individual electronic components of the inverter, therefore, tend to be large in size and weight. The presence of such an inverter of the related art has been a hindrance to achieving better fuel economy and lower power consumption.

To shorten the distance of power transmission, an inverter is typically disposed near a drive motor. Since an automobile requires many components to be installed, the space for accommodating the inverter is limited. The balance of the vehicle body also needs to be considered. Therefore, it is difficult to properly position a large size, heavy weight inverter in the automobile.

As an inverter structure in an alternating current motor combined with an inverter, for example, a structure is known where a positive (+) bus bar and a negative (-) bus bar are molded of resin as an integral part of a doughnut-shaped inverter case, and are connected to a switching element, see, e.g., <CIT>.

An inverter includes, for example, power modules including switching elements, and a smoothing capacitor. Generally, such electronic components of an inverter that supports a high-voltage power supply are large in size and weight, as described above.

Metal strips (bus bars), which are electronic components for connecting the power modules and the smoothing capacitor described above, also allow large current to flow therein and thus are large in size and weight. As the wiring length of bus bars increases, the electric resistance also increases and this results in copper loss when current flows. The bus bars generate a large amount of heat. Moreover, since large current in the inverter is switched on and off at high speed by switching control, significant magnetic changes occur in the bus bars.

When the inverter is activated, the magnetic changes cause noise, vibration, and electromagnetic interference in the bus bars. This leads to energy loss and negatively affects the performance of the automobile in various ways. Necessary measures need to be taken to avoid this. If the bus bars have a complex shape, the resulting impact is more significant.

In the technique described in <CIT>, the switching element and the smoothing capacitor are connected through the positive bus bar and the negative bus bar that are molded of resin as an integral part of the inverter case. With this configuration, due to constraints in wiring length and width, it is not easy to equalize the inductances of the bus bars while reducing them.

Inverter structures suitable for automotive applications are also disclosed in <CIT>, <CIT>, <CIT> and <CIT>.

The present invention has been made in view of the points described above. An object of the present invention is to facilitate equalization of the inductances of wires connected to the smoothing capacitor while reducing the inductances.

The invention is defined by the features of claim <NUM>. The dependent claims recite advantageous embodiments of the invention.

To achieve the object described above, a first aspect of the present invention, according to claim <NUM>, provides an inverter structure of an inverter including a smoothing capacitor and a plurality of power modules. The smoothing capacitor includes a plurality of columnar unit capacitors each having electrodes at both ends thereof, a plate-shaped one-end-side bus plate connected to the electrode at one end of each unit capacitor, and a plate-shaped other-end-side bus plate connected to the electrode at the other end of the unit capacitor. The columnar unit capacitors are connected together by being held from both sides in the axial direction by the one-end-side bus plate and the other-end-side bus plate. The power modules are arranged side by side in a circumferential direction of the inverter, on an outer side of the smoothing capacitor, at positions, on a circular arc, equally distant from a center of the inverter, and equally distant from the smoothing capacitor.

The unit capacitors are arranged, with axes thereof parallel to each other, side by side in a direction along a plane perpendicular to the axes. This can reduce the size of the inverter in the axial direction. The smoothing capacitor includes the plate-shaped one-end-side bus plate and the plate-shaped other-end-side bus plate that are connected to the electrodes at one end and the other end of each unit capacitor. The power modules can thus be easily arranged in such a way as to reduce the distance to the smoothing capacitor. That is, the degree of freedom in the layout of the power modules can be improved. The power modules are arranged at positions equally distant from a predetermined center of the inverter and equally distant from the smoothing capacitor. This can further reduce the size of the inverter in the axial direction. It is also possible to reduce inductance because of the reduced distance between the smoothing capacitor and the power modules, easily equalize the inductances because of the uniform distance between each power module and the smoothing capacitor, and offer greater control over the motor.

A second aspect of the present invention is characterized in that in the inverter structure according to the first aspect of the present invention, a pattern of arrangement of each of the power modules and at least some unit capacitors close to the power module is set to be constant.

The power modules are thus equally positioned with respect to their corresponding unit capacitors, and this further facilitates equalization of inductances.

A third aspect of the present invention is characterized in that in the inverter structure according to the first or second aspect of the present invention, the one-end-side bus plate and the other-end-side bus plate are circular in outer shape.

This allows, for example, extension and connection of terminals at any position in the circumferential direction of the smoothing capacitor, and thus can easily increase the degree of freedom in the layout of the power modules.

A fourth aspect of the present invention is characterized in that in the inverter structure according to any one of the first to third aspects of the present invention, the inverter further includes an input bus bar configured to connect one of an outer edge of the one-end-side bus plate and an outer edge of the other-end-side bus plate to the power modules.

A fifth aspect of the present invention is characterized in that in the inverter structure according to any one of the first to third aspects of the present invention, an outer edge of at least one of the one-end-side bus plate and the other-end-side bus plate is connected to the power modules.

It is thus possible to facilitate connection of the smoothing capacitor to the power modules while reducing and equalizing inductances.

A sixth aspect of the present invention is characterized in that in the inverter structure according to any one of the first to fifth aspects of the present invention, an outer surface of at least one of the one-end-side bus plate and the other-end-side bus plate is disposed in the same plane as one of outer surfaces of the power modules.

This further facilitates size reduction in the axial direction of the inverter.

The present disclosure can facilitate equalization of inductances of wires connected to the smoothing capacitor.

Hereinafter, embodiments of the present invention will be described in detail on the basis of the drawings. The following description of preferred embodiments is merely illustrative in nature and is in no way intended to limit the present invention, its application, or uses. In the embodiments and modifications described below, components having the same functions as those of the other embodiments or modifications are assigned the same reference numerals and their description will be omitted.

<FIG> illustrates a vehicle <NUM> including drive units A according to a first embodiment, as viewed from below the vehicle <NUM>. The vehicle <NUM> transmits power from at least one of an engine <NUM> and a drive motor <NUM> disposed at the front of the vehicle <NUM> to rear wheels <NUM> disposed at the rear of the vehicle <NUM>. That is, the vehicle <NUM> is a front-engine, rear-wheel drive (FR) hybrid vehicle.

As illustrated in <FIG>, the vehicle <NUM> includes the engine <NUM>, a transmission <NUM> coupled to the engine <NUM>, a drive motor <NUM> interposed between the engine <NUM> and the transmission <NUM>, a propeller shaft <NUM> coupled to the transmission <NUM> and configured to transmit power from the engine <NUM> and the drive motor <NUM> to the rear wheels <NUM>, and a differential gear <NUM> coupled to the propeller shaft <NUM> and configured to transmit power from the engine <NUM> and the drive motor <NUM> to the rear wheels <NUM> on the right and left sides.

The propeller shaft <NUM> extends in the vehicle front-rear direction on the underside of a floor panel <NUM>. A tunnel <NUM> is provided in the center of the floor panel <NUM> in the vehicle width direction. The propeller shaft <NUM> is disposed inside the tunnel <NUM>.

The vehicle <NUM> includes an exhaust pipe <NUM> that extends from the engine <NUM> in the vehicle front-rear direction. A catalytic device <NUM> is disposed on the upstream side of the exhaust pipe <NUM>. While not shown, a silencer is disposed on the downstream side of the exhaust pipe <NUM>.

The vehicle <NUM> includes a fuel tank (not shown) that stores fuel to be supplied to the engine <NUM>, and a battery <NUM> that stores power to be supplied to the motor <NUM>. The drive motor <NUM> transmits power to the rear wheels <NUM>. During deceleration of the vehicle <NUM>, the drive motor <NUM> generates regenerative power by being rotationally driven by the propeller shaft <NUM>, and supplies the generated power to the battery <NUM>. The battery <NUM> is composed of a first battery unit 12a and a second battery unit 12b arranged on both sides in the vehicle width direction. The second battery unit 12b is longer than the first battery unit 12a in the vehicle front-rear direction. The battery units 12a and 12b each include a plurality of battery cells. The battery cells are, for example, lithium-ion batteries.

An in-wheel motor <NUM> is connected to each of front wheels <NUM> on the right and left sides. The in-wheel motors <NUM> function as assist motors that generate power at the start of the vehicle <NUM> and transmit the power to the front wheels <NUM>. The in-wheel motors <NUM> also function as regenerative brakes that generate power during deceleration of the vehicle <NUM>. Like the drive motor <NUM>, the in-wheel motors <NUM> are supplied with power from the battery <NUM>.

As illustrated in <FIG>, an inverter <NUM> is interposed between the drive motor <NUM> and the transmission <NUM>. The drive motor <NUM> and the inverter <NUM> are arranged adjacent to each other in the axial direction of the drive motor <NUM> (or in the vehicle front-rear direction). An inverter <NUM> is disposed inside each of the in-wheel motors <NUM> in the vehicle width direction. The in-wheel motor <NUM> and the inverter <NUM> are arranged adjacent to each other in the axial direction of the in-wheel motor <NUM> (or in the vehicle width direction). The drive motor <NUM> and the inverter <NUM> constitute a drive unit A. Similarly, the in-wheel motor <NUM> and the inverter <NUM> constitute a drive unit A.

The inverters <NUM> and <NUM> convert direct-current power stored in the battery <NUM> to alternating-current power and supply the alternating-current power to the motors <NUM> and <NUM>. During deceleration of the vehicle <NUM>, the inverters <NUM> and <NUM> convert alternating-current power generated by the motors <NUM> and <NUM> to direct-current power and charge the battery <NUM>.

The drive unit A of the vehicle <NUM> will be described by using one that includes the drive motor <NUM> and the inverter <NUM> as an example. <FIG> is a perspective view of the drive unit A. As described above, the drive unit A is constituted by the motor <NUM> and the inverter <NUM>. The motor <NUM> and the inverter <NUM> are coaxially arranged adjacent to each other in the axial direction of the motor <NUM>. Specifically, a central axis O of the motor <NUM> coincides with a central axis O of the inverter <NUM>. The motor <NUM> (specifically, a casing of the motor <NUM>) is cylindrically shaped. The inverter <NUM> (specifically, a casing of the inverter <NUM>) is cylindrically shaped to fit the motor <NUM>. A rotary shaft 3a of the motor <NUM> penetrates the inverter <NUM> in the axial direction. The inverter <NUM> is a thin member that has, for example, a thickness Wiv of <NUM> or less (preferably <NUM> or less). The inverter <NUM> has an internal cooling passage <NUM> (described below). An inlet pipe <NUM> and an outlet pipe <NUM> for cooling are connected to the upper part of the inverter <NUM> and communicate with the cooling passage <NUM>.

<FIG> is a horizontal cross-sectional view of the motor <NUM>, as viewed from the inverter <NUM>. The motor <NUM> includes coils <NUM>. Specifically, U-phase, V-phase, and W-phase coils 17u, 17v, and 17w are each formed by concentrated winding on the stator of the motor <NUM>. Two U-phase coils 17u are arranged opposite each other in the radial direction of the motor <NUM>. Similarly, two V-phase coils 17v are arranged opposite each other in the radial direction of the motor <NUM>. Similarly, two W-phase coils 17w are arranged opposite each other in the radial direction of the motor <NUM>.

The motor <NUM> has three motor-side terminal blocks <NUM> on the outer periphery thereof. The three motor-side terminal blocks <NUM> correspond to the U-phase, V-phase, and W-phase coils 17u, 17v, and 17w. A lead wire (not shown) is extended from each of the two U-phase coils 17u. The two lead wires are tied into a bundle and connected to the corresponding one of the motor-side terminal blocks <NUM>. The same applies to the V-phase coil 17v and the W-phase coil 17w. An iron core <NUM> and N-pole and S-pole permanent magnets <NUM>, which constitute a rotor, are secured to the rotary shaft 3a.

<FIG> is a circuit diagram of the inverter <NUM>. The inverter <NUM> includes a smoothing capacitor <NUM> and a plurality of power modules <NUM>. The smoothing capacitor <NUM> smooths a voltage applied to the power modules <NUM>. The plurality of power modules <NUM> constitute an inverter circuit and convert a direct-current voltage to an alternating-current voltage.

The plurality of power modules <NUM> include a U-phase power module 20u, a V-phase power module 20v, and a W-phase power module 20w. The U-phase power module 20u is connected to the U-phase coil 17u of the motor <NUM>. The V-phase power module 20v is connected to the V-phase coil 17v of the motor <NUM>. The W-phase power module 20w is connected to the W-phase coil 17w of the motor <NUM>.

The power modules <NUM> are each composed of two arm elements, a lower arm element <NUM> and an upper arm element <NUM>, each serving as a switching element. When one of the lower arm element <NUM> and the upper arm element <NUM> opens in the power module <NUM> of each phase, the other of the lower arm element <NUM> and the upper arm element <NUM> closes. This allows three-phase alternating current to be supplied to the motor <NUM>.

The power module <NUM> includes a metal-oxide-semiconductor field-effect transistor (MOSFET) containing silicon carbide (SiC) (hereinafter referred to as SiC-MOSFET). <FIG> compares a SiC-MOSFET and an insulated gate bipolar transistor (IGBT). The SiC-MOSFET constitutes a chip <NUM> including the lower arm element <NUM>, the upper arm element <NUM>, and other control elements. The lower surface of the chip <NUM> is secured by soldering to a silicon substrate. A copper block <NUM> serving as a heat transfer block is secured by soldering to the upper surface of the chip <NUM>. The same applies to the IGBT.

As illustrated in <FIG>, the surface area of the chip <NUM> constituted by the SiC-MOSFET is smaller than the surface area of a chip <NUM>' constituted by the IGBT. Accordingly, the size of the copper block <NUM> disposed on the upper side of the SiC-MOSFET (chip) <NUM> is smaller than the size of a copper block <NUM>' disposed on the upper side of the IGBT (chip) <NUM>'. The SiC-MOSFET has better heat resistance than the IGBT.

<FIG> gives a perspective view and a circuit diagram illustrating a detailed structure of the power module <NUM>. Each power module <NUM> has a wide flat shape. Specifically, each power module <NUM> is longer in a width direction W than in a thickness direction t. The power module <NUM> is substantially in the shape of a rectangular parallelepiped. The width direction W includes a first width direction W1 and a second width direction W2 orthogonal to each other. Hereinafter, one side of the power module <NUM> in the thickness direction t may be referred to as a lower side, and the other side of the power module <NUM> in the thickness direction t may be referred to as an upper side.

The power module <NUM> has a lower surface <NUM> to be cooled (first cooled surface), on the lower side thereof (or on one side thereof in the thickness direction t). The power module <NUM> has an upper surface <NUM> on the upper side thereof. The power module <NUM> has a first end face <NUM> on one side thereof in the first width direction W1. The power module <NUM> has a second end face <NUM> on the other side thereof in the first width direction W1.

A negative-side input terminal <NUM> is connected to the lower side of the first end face <NUM>, on one side of the first end face <NUM> in the second width direction W2. A positive-side input terminal <NUM> is connected to the upper side of the first end face <NUM>, on the other side of the first end face <NUM> in the second width direction W2. The negative-side input terminal <NUM> and the positive-side input terminal <NUM> are spaced apart in the up and down direction (thickness direction t). An output terminal <NUM> is connected to the center of the second end face <NUM>.

The lower arm element <NUM> and the upper arm element <NUM> are housed in a package (housing) of the power module <NUM>. The negative-side input terminal <NUM> is connected to the lower arm element <NUM>, and the positive-side input terminal <NUM> is connected to the upper arm element <NUM>. The output terminal <NUM> is connected between the lower arm element <NUM>.

<FIG> is a horizontal cross-sectional view of the inverter <NUM>, as viewed from the side opposite the motor <NUM>. <FIG> is a vertical cross-sectional view taken along line VIII-VIII in the inverter <NUM> illustrated in <FIG>. As illustrated in <FIG>, the inverter <NUM> has, in the center thereof, a shaft through-hole <NUM> that allows the rotary shaft 3a of the motor <NUM> to pass therethrough. The shaft through-hole <NUM> is defined by a cylindrical boss <NUM> formed therearound. The smoothing capacitor <NUM> is disposed along the boss <NUM>.

The power modules <NUM> (U-phase power module 20u, V-phase power module 20v, and W-phase power module 20w) are arranged on the outer side of the smoothing capacitor <NUM>. The power modules <NUM> are arranged side by side in the circumferential direction of the motor <NUM>, on the outer side of the smoothing capacitor <NUM>. That is, the power modules 2C are arranged at positions (on a circular arc) equally distant from the center of the rotary shaft 3a of the motor <NUM>. At the same time, the power modules <NUM> are arranged at positions equally distant from the smoothing capacitor <NUM> (i.e., positions in respective radial directions of the smoothing capacitor <NUM>). More specifically, for example, when x is the distance between the negative-side input terminal <NUM> (or positive-side input terminal <NUM>) of the U-phase power module 20u and the outer edge of the one-end-side bus plate 19c (or the other-end-side bus plate 19d) of the smoothing capacitor <NUM>, the same distance x is set for the V-phase power module 20v and the W-phase power module 20w. The distance between only one of the negative-side input terminal <NUM> and the positive-side input terminal <NUM> and the smoothing capacitor <NUM>, described above, may be equal for all the power modules <NUM>.

The input terminals <NUM> and <NUM> (on the first end face <NUM>) and the output terminal <NUM> (on the second end face <NUM>) of each power module <NUM> are configured to face in the circumferential direction of the motor <NUM> (inverter <NUM>). The power modules <NUM> are arranged on respective lines radially extending from the center O of the inverter <NUM> (motor <NUM>). The power modules <NUM> are each disposed in such a way that the thickness direction t coincides with the axial direction of the motor <NUM>. The smoothing capacitor <NUM> and the power modules <NUM> are arranged in a space defined by an outer peripheral wall <NUM> and the boss <NUM> in the inverter <NUM>.

As illustrated in <FIG> and <FIG>, a heat sink <NUM> is disposed on a side of the inverter <NUM> adjacent to the motor <NUM>. The heat sink <NUM> is mainly used for cooling the power modules <NUM>. The heat sink <NUM> is disposed between the outer peripheral wall <NUM> and the boss <NUM> in the inverter <NUM>. The heat sink <NUM> has an upper wall 60a, an outer peripheral wall 60b, a lower wall 60c, and an inner peripheral wall 60d.

An upper surface <NUM> of the upper wall 60a of the heat sink <NUM> constitutes a mounting surface (which may hereinafter be referred to as "mounting surface <NUM>") orthogonal to the axial direction of the motor <NUM>. The lower surface (first cooled surface) <NUM> of each of the power modules <NUM> (U-phase power module 20u, V-phase power module 20v, and W-phase power module 20w) faces toward the motor <NUM>. Specifically, the lower surfaces (first cooled surfaces) <NUM> of the power modules <NUM> are arranged side by side on the same mounting surface <NUM>.

As illustrated in <FIG> and <FIG>, the smoothing capacitor <NUM> is formed by a group of columnar unit capacitors <NUM> each having electrodes T at both ends (one end 19a and the other end 19b) thereof. The columnar unit capacitors <NUM> are arranged, with axes thereof parallel to each other (i.e., parallel to the rotary shaft 3a of the motor <NUM>), side by side in a direction along a plane perpendicular to the axes, and connected together by being held from both sides in the axial direction by the one-end-side bus plate 19c and the other-end-side bus plate 19d that are circular in outer shape. The one-end-side bus plate 19c on the lower side of the smoothing capacitor <NUM> serves as a surface to be cooled (third cooled surface) and faces toward the motor <NUM>. Specifically, the one-end-side bus plate 19c of the smoothing capacitor <NUM> is mounted on the mounting surface <NUM>.

The configuration of the electrodes T at the one end 19a and the other end 19b of each unit capacitor <NUM> is not particularly limited, and electrodes of various types may be used. For example, the electrodes T may be lead wire electrodes, band electrodes, or plate-shaped electrodes. Also, the way of connecting the electrodes T to the one-end-side bus plate 19c and the other-end-side bus plate 19d is not particularly limited, and various techniques, such as welding, soldering, or mechanical pressure bonding, may be used.

The plurality of unit capacitors <NUM> are arranged in such a way that some of them are equally distant, for example, from the center of the rotary shaft 3a of the motor <NUM>. Also, a pattern of arrangement of each of the power modules <NUM> and at least some unit capacitors <NUM> close to the power module <NUM> is set to be constant. Additionally or alternatively, the distance between each power module <NUM> and at least the unit capacitor <NUM> closest to the power module <NUM> is set to be constant. More specifically, for example, when y is the distance between the negative-side input terminal <NUM> (or positive-side input terminal <NUM>) of the U-phase power module 20u and the electrode T of a unit capacitor <NUM> closest thereto, the same distance y is set for the V-phase power module 20v and the W-phase power module 20w. The distance between only one of the negative-side input terminal <NUM> and the positive-side input terminal <NUM> and the unit capacitor <NUM> closest thereto may be equal for all the power modules <NUM>.

With the configuration described above, the inductances of connecting wires between the smoothing capacitor <NUM> and the power modules <NUM> can be easily reduced, and/or the inductances described above can be easily equalized by making the power modules <NUM> equally distant from the smoothing capacitor <NUM>.

As illustrated in <FIG> and <FIG>, with respect to the smoothing capacitor <NUM>, the power modules <NUM> are arranged side by side in a direction along a plane perpendicular to the axial direction. The smoothing capacitor <NUM> is connected to the power modules <NUM> by a negative-side bus bar <NUM> and a positive-side bus bar <NUM> serving as input bus bars <NUM> (which may hereinafter be simply referred to as "bus bars <NUM>"). The negative-side bus bar <NUM> and the positive-side bus bar <NUM> are plate-shaped. Specifically, the negative-side bus bar <NUM> and the positive-side bus bar <NUM> are longer in the width direction W and the length direction L than in the thickness direction t.

As illustrated in <FIG>, the negative-side bus bar <NUM> and the positive-side bus bar <NUM> are wide members that extend along the circumferential direction of the motor <NUM> (inverter <NUM>). In other words, the negative-side bus bar <NUM> and the positive-side bus bar <NUM> are wide members that extend along the direction in which the power modules <NUM> are arranged side by side. The width direction W of the negative-side bus bar <NUM> and the positive-side bus bar <NUM> is along the circumferential direction of the motor <NUM> (or along an arc). The negative-side bus bar <NUM> and the positive-side bus bar <NUM> are fan-shaped. The length direction L of the negative-side bus bar <NUM> and the positive-side bus bar <NUM> is along the radial direction of the motor <NUM>.

The negative-side bus bar <NUM> is connected at one end portion 51i thereof to the outer edge of the one-end-side bus plate 19c on the lower side of the smoothing capacitor <NUM>. The negative-side bus bar <NUM> is also connected at the other end portion 51o thereof to the negative-side input terminal <NUM> of each power module <NUM>. The positive-side bus bar <NUM> is connected at one end portion 52i thereof to the outer edge of the other-end-side bus plate 19d on the upper side of the smoothing capacitor <NUM>. The positive-side bus bar <NUM> is also connected at the other end portion 52o thereof to the positive-side input terminal <NUM> of each power module <NUM>. The outer edge of at least one of the one-end-side bus plate 19c and the other-end-side bus plate 19d may be directly connected to the negative-side input terminal <NUM> or the positive-side input terminal <NUM> of the power module <NUM>.

The negative-side bus bar <NUM> may have a lower surface 51a to be cooled (second cooled surface), on the lower side thereof (or on one side thereof in the thickness direction t). The lower surface (second cooled surface) 51a of the negative-side bus bar <NUM> faces toward the motor <NUM>. Specifically, the lower surface (second cooled surface) 51a of the negative-side bus bar <NUM> may be mounted on the mounting surface <NUM>.

As illustrated in <FIG>, an output bus bar <NUM> is connected to the output terminal <NUM> of each power module <NUM>. There are a total of three output bus bars <NUM> corresponding to the U-phase, the V-phase, and the W-phase. The output bus bars <NUM> are each interposed between the power module <NUM> and a corresponding one of the coils <NUM>. The output bus bar <NUM> is plate-shaped. In addition to the output bus bar <NUM>, a wire harness may be interposed between the power module <NUM> and a corresponding one of the coils <NUM>.

The inverter <NUM> has three inverter-side terminal blocks <NUM> on the outer periphery thereof. The inverter-side terminal blocks <NUM> correspond to the respective power modules <NUM>. The output bus bars <NUM> each extend to a corresponding one of the inverter-side terminal blocks <NUM>. Electrically conducting members (such as a bus bar and a wire harness) are interposed between each inverter-side terminal block <NUM> and a corresponding one of the motor-side terminal blocks <NUM>.

<FIG> is a perspective view of the bus bar <NUM>. <FIG> gives graphs each illustrating a relation between a size of the bus bar <NUM> and inductance sensitivity. As a result of dedicated studies, the inventors of the present application made the following discoveries about the relation between the size of the bus bar <NUM> and inductance sensitivity.

As illustrated in <FIG> and <FIG>, the inductance sensitivity (nH) of the bus bar <NUM> decreases as the width dimension W (mm) of the bus bar <NUM> increases.

Basically, the inductance sensitivity (nH) of the bus bar <NUM> increases as the length dimension L (mm) of the bus bar <NUM> increases. However, as shown by the graph in the middle of <FIG>, the relation between the length dimension L (mm) and the inductance sensitivity (nH) of the bus bar <NUM> has a local minimum M. This means that different length dimensions L correspond to the same inductance sensitivity (nH). Specifically, the inductance sensitivity (nH) of the bus bar <NUM> (<NUM> or <NUM>) is a function of the length dimension L (mm) from the one end portion 51i or 52i (i.e., the one-end-side bus plate 19c or other-end-side bus plate 19d of the smoothing capacitor <NUM>) to the other end portion 51o or 52o (i.e., the input terminal <NUM> or <NUM> of each power module <NUM>) of the bus bar <NUM> (<NUM> or <NUM>). The function has the local minimum M such that different lengths, the first length L1 (mm) and the second length L2 (mm), correspond to the same inductance sensitivity K (nH). The second length L2 (mm) is longer than the first length L1 (mm).

The inductance sensitivity (nH) of the bus bar <NUM> shows little change with the change in the thickness dimension t (mm) of the bus bar <NUM>.

As illustrated in <FIG>, the width dimension of the negative-side bus bar <NUM> and the width dimension of the positive-side bus bar <NUM> are substantially the same. As illustrated in <FIG>, the length dimension L- of the negative-side bus bar <NUM> and the length dimension L+ of the positive-side bus bar <NUM> differ from each other. The length dimension L- of the negative-side bus bar <NUM> corresponds to the first length L1. The length dimension L+ of the positive-side bus bar <NUM> corresponds to the second length L2. The length dimension L+ of the positive-side bus bar <NUM> (second length L2) is longer than the length dimension L- of the negative-side bus bar <NUM> (first length L1). Because of the presence of the local minimum M, however, the inductance of the negative-side bus bar <NUM> and the inductance of the positive-side bus bar <NUM> are equal.

<FIG> is a horizontal cross-sectional view of the cooling passage <NUM> in the inverter <NUM>, as viewed from the motor <NUM>. As illustrated in <FIG> and <FIG>, the heat sink <NUM> has therein the cooling passage (cooling jacket) <NUM> constituting a cooling zone. The cooling passage <NUM> is defined by the upper wall 60a, the outer peripheral wall 60b, the lower wall 60c, and the inner peripheral wall 60d. As viewed in the axial direction of the motor <NUM> (inverter <NUM>), the cooling passage <NUM> is a doughnut-shaped (annular or cylindrical) passage that extends throughout the perimeter. The rotary shaft 3a of the motor <NUM> penetrates inside the inner peripheral wall 60d. As described above, the upper surface of the upper wall 60a of the heat sink <NUM> is the mounting surface <NUM>.

The cooling passage <NUM> is disposed closer to the motor <NUM> than the mounting surface <NUM> is. A cooling medium H flows in the cooling passage <NUM>. For example, the cooling medium H is cooling water or cooling oil.

A plurality of fins <NUM> constituting the cooling zone are provided in the interior (cooling passage <NUM>) of the heat sink <NUM>. In the cooling passage <NUM>, the fins <NUM> extend downward from the upper wall 60a. That is, the fins <NUM> are disposed closer to the motor <NUM> than the mounting surface <NUM> is.

As illustrated in <FIG> and <FIG>, as viewed in the axial direction of the motor <NUM> (inverter <NUM>), the cooling passage (cooling zone) <NUM> faces toward the entire area of both the lower surface (first cooled surface) <NUM> of each power module <NUM> and the one-end-side bus plate (third cooled surface) 19c on the lower side of the smoothing capacitor <NUM>.

Similarly, as viewed in the axial direction of the motor <NUM>, the fins (cooling zone) <NUM> face toward the entire area of both the lower surface (first cooled surface) <NUM> of each power module <NUM> and the one-end-side bus plate (third cooled surface) 19c on the lower side of the smoothing capacitor <NUM>.

As illustrated in <FIG>, the inlet pipe <NUM> and the outlet pipe <NUM> are connected to the upper part of the outer peripheral wall <NUM> of the inverter <NUM>. The inlet pipe <NUM> and the outlet pipe <NUM> communicate with the cooling passage <NUM>. The cooling medium H introduced through the inlet pipe <NUM> into the cooling passage <NUM> is guided by the outer peripheral wall <NUM> and the boss <NUM> to circumferentially flow in the cooling passage <NUM>, and is then discharged through the outlet pipe <NUM> to the outside. The inlet pipe <NUM> may be provided with a guide plate <NUM> on the downstream side.

In the present embodiment, increasing the width dimensions of the bus bars <NUM> and <NUM> can reduce the inductances of the bus bars <NUM> and <NUM>.

The smoothing capacitor <NUM> and the power modules 20u, 20v, and 20w are mounted on the same mounting surface <NUM>. Since this reduces the lengths of the bus bars <NUM> and <NUM> that connect the smoothing capacitor <NUM> to the power modules 20u, 20v, and 20w, the inductances of the bus bars <NUM> and <NUM> can be reduced.

The motor <NUM> and the inverter <NUM> are arranged adjacent to each other in the axial direction. This reduces the length of an electric path between each of the power modules 20u, 20v, and 20w and a corresponding one of the coils 17u, 17v, and 17w. It is thus possible to reduce the inductance of the electric path (including the output bus bar <NUM>) that connects each of the power modules 20u, 20v, and 20w to a corresponding one of the coils 17u, 17v, and 17w.

The power modules 20u, 20v, and 20w are arranged side by side in the circumferential direction of the motor <NUM>, on the outer side of the smoothing capacitor <NUM>. This can equalize the distances between the smoothing capacitor <NUM> and each of the power modules 20u, 20v, and 20w. With the bus bars <NUM> and <NUM> that are wide members extending along the circumferential direction of the motor <NUM>, the inductances of the electric paths between the smoothing capacitor <NUM> and each of the power modules 20u, 20v, and 20w can be equalized.

With the local minimum M (see <FIG>), even though the length dimension L- of the negative-side bus bar <NUM> (first length L1) and the length dimension L+ of the positive-side bus bar <NUM> (second length L2) differ from each other, the inductance of the negative-side bus bar <NUM> and the inductance of the positive-side bus bar <NUM> can be equalized.

As described above, a pattern of arrangement of each power module <NUM> and some unit capacitors <NUM> close to the power module <NUM> is set to be constant. Also, the distance between each power module <NUM> and at least the unit capacitor <NUM> closest to the power module <NUM> (i.e., the distance of wiring connection between the electrode and the terminal) is set to be constant. Thus, the inductances of the connecting wires between the smoothing capacitor <NUM> and the power modules <NUM> can be more easily reduced, and/or the inductances described above can be easily equalized by making the power modules <NUM> equally distant from the smoothing capacitor <NUM>.

In each power module <NUM> having a wide and flat shape, the lower surface (first cooled surface) <NUM> having a large area faces toward the cooling passage <NUM> and the fins <NUM> constituting a cooling zone. This increases the area of the power modules <NUM> cooled by the cooling passage <NUM> and fins <NUM> (cooling zone). Thus, even when only one side (lower surface, first cooled surface) <NUM> of the power module <NUM> is cooled by the cooling passage <NUM> and fins <NUM> (cooling zone), it is possible to ensure sufficient cooling performance.

The lower surfaces (first cooled surfaces) <NUM> of the power modules <NUM> (U-phase power module 20u, V-phase power module 20v, and W-phase power module 20w) are arranged side by side on the same mounting surface <NUM> orthogonal to the axial direction of the motor <NUM>. This can reduce the axial length of the inverter <NUM>. Also, since the cooling passage <NUM> and fins <NUM> (cooling zone) simply need to be provided on one side (lower surfaces, first cooled surfaces) <NUM> of the power modules <NUM>, the inverter <NUM> can be made smaller than when the cooling passage <NUM> and fins <NUM> (cooling zone) are provided on both sides of the power modules <NUM>.

With the configuration described above, it is possible to reduce the size of the drive unit A composed of the motor <NUM> and the inverter <NUM> while sufficiently cooling the power modules <NUM>.

By allowing the cooling medium H to flow in the cooling passage <NUM> constituting a cooling zone, the power modules <NUM> can be more effectively cooled by the cooling zone.

Since the SiC-MOSFET chip <NUM> included in each power module <NUM> is small in size, the copper block <NUM> (heat transfer block) disposed on the SiC-MOSFET chip <NUM> is also small in size (see <FIG>). To enable the power module <NUM> to be effectively cooled on both sides, it is necessary to provide expensive ceramic substrates (e.g., SiN substrates) on both sides of the SiC-MOSFET chip <NUM>. Cooling one side of the power module <NUM> and improving the effectiveness of cooling the one side is more advantageous costwise than cooling both sides of the power module <NUM>.

Together with the power modules <NUM>, the smoothing capacitor <NUM> can also be cooled by the cooling passage <NUM> and fins <NUM> (cooling zone).

The power modules <NUM> are arranged side by side in the circumferential direction of the motor <NUM>, on the outer side of the smoothing capacitor <NUM>. At the same time, by extending the negative-side bus bar <NUM> in the circumferential direction of the motor <NUM>, the negative-side bus bar <NUM> can be easily widened in the width direction W. This can easily increase the area of heat dissipation from the negative-side bus bar <NUM> toward the cooling passage <NUM> and fins <NUM> (cooling zone).

The cooling passage <NUM> and fins <NUM> (cooling zone) are disposed adjacent to the motor <NUM>. This is also advantageous for cooling the wires (e.g., output bus bars <NUM>) that connect the motor <NUM> to the power modules <NUM>.

In the related art, as indicated by a two-dot chain line in <FIG>, an inverter <NUM>' has often been disposed near a second battery unit 12b' of a battery <NUM>'. In the present embodiment, where the inverter <NUM> can be disposed adjacent to the motor <NUM> in the axial direction, the inverter <NUM> does not need to be disposed near the second battery unit 12b. This can increase the degree of freedom in the layout of the second battery unit 12b and can increase the size of the second battery unit 12b.

<FIG> corresponds to <FIG> and illustrates a first modification of the first embodiment. In the present modification, the cooling passage <NUM> and fins <NUM> (cooling zone) do not at all face toward the one-end-side bus plate (third cooled surface) 19c on the lower side of the smoothing capacitor <NUM>.

There may be no problem even when the smoothing capacitor <NUM>, which generates less heat than the power modules <NUM>, is not cooled by the cooling passage <NUM> and fins <NUM> (cooling zone).

<FIG> corresponds to <FIG> and illustrates a second modification of the first embodiment. The inverter <NUM> according to the present modification is disposed adjacent to the in-wheel motor <NUM> in the axial direction of the in-wheel motor <NUM> (or in the vehicle width direction) (see <FIG>). The inverter <NUM> does not have the shaft through-hole <NUM> and the boss <NUM>. In the smoothing capacitor <NUM>, the unit capacitors <NUM> are also provided in and around the center. The heat sink <NUM> does not have the inner peripheral wall 60d. The cooling passage <NUM> is in the shape of a circle without a hole, as viewed in the axial direction of the motor <NUM>.

The cooling medium H flowing in the cooling passage <NUM> may be, for example, air. The cooling zone may not include the cooling passage <NUM>, and may be constituted by the fins <NUM> alone. The cooling zone may be constituted by a solid cooling member.

The cooling zone does not necessarily need to be provided throughout the perimeter, and may be provided only in an area facing toward the power modules <NUM> and extending in the circumferential direction.

Instead of the negative-side bus bar <NUM>, the positive-side bus bar <NUM> may have the second cooled surface on one side thereof (or on one side in the thickness direction t) facing toward the motor <NUM> and mounted on the mounting surface <NUM>.

While not shown, the output bus bars <NUM> may be wide members that extend along the circumferential direction of the motor <NUM>. In other words, the width direction of the output bus bars <NUM> may be along the circumferential direction (or along an arc). The output bus bars <NUM> may be fan-shaped. This makes it easier to widen the output bus bars <NUM>, and thus easier to reduce the inductances of the output bus bars <NUM> (see <FIG>).

The mounting surface <NUM> may be constituted by a plurality of surfaces in the same plane orthogonal to the axial direction of the motor <NUM>.

<FIG> is a horizontal cross-sectional view corresponding to <FIG> and illustrating the inverter <NUM>, as viewed from the side opposite the motor <NUM>, according to a second embodiment. <FIG> is a vertical cross-sectional view corresponding to <FIG> and illustrating the inverter <NUM> according to the second embodiment. Note that the same components as those of the aforementioned embodiment may not be described in detail.

In the present embodiment, the power modules <NUM> (U-phase power module 20u, V-phase power module 20v, and W-phase power module 20w) are arranged on the outer side of the smoothing capacitor <NUM>. The power modules <NUM> are arranged side by side in the circumferential direction of the motor <NUM>, on the outer side of the smoothing capacitor <NUM>.

The input terminals <NUM> and <NUM> (on the first end face <NUM>) and the output terminal <NUM> (on the second end face <NUM>) of each power module <NUM> are configured to face in the radial direction of the motor <NUM> (inverter <NUM>). Specifically, the input terminals <NUM> and <NUM> (on the first end face <NUM>) of each power module <NUM> face inward, and the output terminal <NUM> (on the second end face <NUM>) of each power module <NUM> faces outward. The power modules <NUM> are arranged on respective lines radially extending from the center O of the inverter <NUM> (motor <NUM>).

As in the embodiments described above, the lower surface (first cooled surface) <NUM> of each power module <NUM> and the one-end-side bus plate (third cooled surface) 19c on the lower side of the smoothing capacitor <NUM> are mounted on the mounting surface <NUM>.

As illustrated in <FIG>, the width dimension of the negative-side bus bar <NUM> and the width dimension of the positive-side bus bar <NUM> are the same. As illustrated in <FIG>, the length dimension L- of the negative-side bus bar <NUM> and the length dimension L+ of the positive-side bus bar <NUM> are the same. Accordingly, the inductance of the negative-side bus bar <NUM> and the inductance of the positive-side bus bar <NUM> are equal.

The other configurations are the same as those of the first embodiment.

<FIG> is a horizontal cross-sectional view corresponding to <FIG> and illustrating the inverter <NUM>, as viewed from the side opposite the motor <NUM>, according to a third embodiment. <FIG> is a vertical cross-sectional view corresponding to <FIG> and illustrating the inverter <NUM> according to the third embodiment. Note that the same components as those of the aforementioned embodiments may not be described in detail.

As illustrated in <FIG> and <FIG>, the negative-side input terminal <NUM> is connected to the lower side of the first end face <NUM> of each power module <NUM>. The positive-side input terminal <NUM> is connected to the lower side of the second end face <NUM> of each power module <NUM>. The output terminal <NUM> is connected to the center of the upper surface <NUM> of each power module <NUM>.

The negative-side bus bar <NUM> connects the one-end-side bus plate 19c of the smoothing capacitor <NUM> to the negative-side input terminal <NUM> of each power module <NUM>. The positive-side bus bar <NUM> connects the other-end-side bus plate 19d of the smoothing capacitor <NUM> to the positive-side input terminal <NUM> of each power module <NUM>.

The positive-side bus bar <NUM> leaves the other-end-side bus plate 19d of the smoothing capacitor <NUM> (one end portion 52i), and extends along the upper surface <NUM> from the first end face <NUM> toward the second end face <NUM> of each power module <NUM>. The positive-side bus bar <NUM> then bends downward and extends along the second end face <NUM> to reach the positive-side input terminal <NUM> (the other end portion 52o) on the lower side. In other words, the positive-side bus bar <NUM> extends along the upper surface <NUM> to wrap the power module <NUM>. Each output bus bar <NUM> leaves the output terminal <NUM> on the upper surface <NUM> of the power module <NUM> and extends upward. The positive-side bus bar <NUM> has three openings that allow passage of the respective output bus bars <NUM> that extend upward.

As illustrated in <FIG>, the width dimension of the negative-side bus bar <NUM> and the width dimension of the positive-side bus bar <NUM> are the same. As illustrated in <FIG>, the length dimension (L-) of the negative-side bus bar <NUM> and the length dimension (sum of La+ and Lb+) of the positive-side bus bar <NUM> differ from each other. The length dimension (L-) of the negative-side bus bar <NUM> corresponds to the first length L1. The length dimension (sum of La+ and Lb+) of the positive-side bus bar <NUM> corresponds to the second length L2. The length dimension (sum of La+ and Lb+, second length L2) of the positive-side bus bar <NUM> is longer than the length dimension (L-, first length L1) of the negative-side bus bar <NUM>. Because of the presence of the local minimum M (see <FIG>), however, the inductance of the negative-side bus bar <NUM> and the inductance of the positive-side bus bar <NUM> are equal.

The conditions (e.g., materials) of the negative-side bus bar <NUM> and the positive-side bus bar <NUM> according to the present embodiment differ from those in the embodiments described above. This means that the mode of the local minimum M (see <FIG>) also differs from that in the embodiments described above. Specifically, the difference between the first length L1 and the second length L2 is greater than in the embodiments described above.

The other configurations are the same as those of the second embodiment.

The embodiments described above show an example where three power modules <NUM> are closely arranged side by side on the circumference, but the arrangement of the power modules <NUM> is not limited to this. For example, as illustrated in <FIG>, the power modules <NUM> may be arranged at intervals of <NUM>° about the central axis, and the unit capacitors <NUM> may accordingly be arranged in a rotationally symmetrical pattern. This arrangement can further facilitate equalization of inductances.

Claim 1:
An inverter structure of an inverter (<NUM>, <NUM>) comprising a smoothing capacitor (<NUM>) and a plurality of power modules (<NUM>),
wherein the smoothing capacitor includes a plurality of columnar unit capacitors (<NUM>) each having electrodes (T) at both ends thereof, a plate-shaped one-end-side bus plate (19c) connected to the electrode at one end of each unit capacitor, and a plate-shaped other-end-side bus plate (19d) connected to the electrode at the other end of the unit capacitor, and the unit capacitors are arranged, with axes thereof parallel to each other, side by side in a direction along a plane perpendicular to the axes; wherein the columnar unit capacitors (<NUM>) are connected together by being held from both sides in the axial direction by the one-end-side bus plate (19c) and the other-end-side bus plate (19d); and
the power modules (<NUM>) are arranged side by side in a circumferential direction of the inverter (<NUM>, <NUM>), on an outer side of the smoothing capacitor (<NUM>), at positions, on a circular arc, equally distant from a center (O) of the inverter and equally distant from the smoothing capacitor.