Patent ID: 12234904

DETAILED DESCRIPTION

A vehicle is provided with a gear mechanism such as a rear differential gear. The gear mechanism is air-cooled by, for example, fins disposed in a gear case that houses the gear mechanism. In a vehicle in the related art, a cooling structure for a power conversion apparatus such as an inverter and a cooling structure for a gear mechanism are provided separately (that is, for respective cooling targets). Therefore, spaces occupied by the cooling structures are increased, and as a result, it is not easy to improve a degree of freedom of vehicle design.

Accordingly, it is desirable to provide a simplified vehicle cooling structure.

In the following, an embodiment of the disclosure is described in detail with reference to the accompanying drawings. Note that the following description is directed to an illustrative example of the disclosure and not to be construed as limiting to the disclosure. Factors including, without limitation, numerical values, shapes, materials, components, positions of the components, and how the components are coupled to each other are illustrative only and not to be construed as limiting to the disclosure. Further, elements in the following example embodiment which are not recited in a most-generic independent claim of the disclosure are optional and may be provided on an as-needed basis. The drawings are schematic and are not intended to be drawn to scale. Throughout the present specification and the drawings, elements having substantially the same function and configuration are denoted with the same numerals to avoid any redundant description.

FIG.1is a schematic diagram illustrating a part of a vehicle1according to the present embodiment. A vehicle cooling structure2is applied to the vehicle1. InFIG.1, front-rear and left-right directions of the vehicle1are indicated by solid arrows.FIG.2is a schematic diagram illustrating a power supply system of the vehicle1according to the present embodiment.

The vehicle1is, for example, an engine vehicle provided with an engine as a drive source for traveling. The vehicle1may be an electric vehicle provided with a motor as the drive source for traveling, or may be a hybrid vehicle provided with an engine and a motor as driving sources.

As illustrated inFIG.1, the vehicle1includes a propeller shaft11, a rear differential gear12, a gear case13, a motor14, an inverter15, and a step-down converter16. One end of the propeller shaft11is coupled to the drive source for traveling (for example, the engine) through a transmission. The rear differential gear12corresponds to an example of a gear mechanism according to the disclosure. Further, as illustrated inFIG.2, the power supply system of the vehicle1includes a battery17in addition to the motor14, the inverter15, and the step-down converter16.

The rear differential gear12includes an input shaft21, a ring gear22, a frame23, a first side gear24, a second side gear25, a first output shaft26, a second output shaft27, a first pinion shaft28, a second pinion shaft29, a first pinion gear30, and a second pinion gear31.

In one example, the input shaft21is a drive pinion shaft. The other end of the propeller shaft11is coupled to the input shaft21. The input shaft21extends in the front-rear direction. A bevel gear21ais formed at a tip of the input shaft21. The bevel gear21ameshes with the ring gear22. The frame23protrudes from one side surface of the ring gear22. The frame23is hollow. The frame23rotates permanently affixed with the ring gear22.

The first side gear24, the second side gear25, the first pinion gear30, and the second pinion gear31are housed in the frame23. The first side gear24and the second side gear25are disposed parallel to the ring gear22, and face each other with a gap therebetween. The first side gear24is coupled to the first output shaft26. The first output shaft26extends leftward through the ring gear22and is coupled to a left rear wheel. The second side gear25is coupled to the second output shaft27. The second output shaft27extends rightward through the frame23and is coupled to a right rear wheel.

Each of the first pinion shaft28and the second pinion shaft29protrudes from an inner surface of the frame23. The first pinion gear30is rotatably supported by the frame23via the first pinion shaft28. The second pinion gear31is rotatably supported by the frame23via the second pinion shaft29. The first pinion gear30and the second pinion gear31mesh with the first side gear24and the second side gear25, respectively.

The gear case13is configured with a case main body41and a cover42. A space41ais formed inside the case main body41. An opening41bis provided on a rear side of the case main body41. The cover42closes the opening41bof the case main body41from the rear side. When the cover42is attached to the case main body41, the gear case13is sealed. The gear case13is sealed while housing the rear differential gear12and oil. The oil lubricates the components of the rear differential gear12.

In the rear differential gear12, frictional heat is generated between the gears in accordance with rotation of the gears. For example, relatively large frictional heat is generated between the bevel gear21aof the input shaft21and the ring gear22. The oil in the gear case13is heated by such frictional heat.

The motor14outputs power for assisting rotation of the rear wheels. The motor14is, for example, a three-phase AC motor. The motor14is arranged side by side with the gear case13, and is coupled to the rear differential gear12. Although not illustrated, the motor14is coupled to, for example, the ring gear22or the frame23.

The inverter15is disposed on an outer surface42aof the cover42of the gear case13. As illustrated inFIG.2, the inverter15is electrically coupled to the motor14through a power line. The step-down converter16is disposed on the outer surface42aof the cover42of the gear case13. As illustrated inFIG.2, the step-down converter16is electrically coupled to the inverter15through the power line. The battery17(for example, a secondary battery such as a lithium ion battery or a nickel hydrogen battery) is electrically coupled to the step-down converter16through the power line. Although simplified inFIG.2for ease of understanding, various devices (for example, various inverters for devices other than the motor14; not illustrated) may be further coupled to the battery17.

The step-down converter16steps down power stored in the battery17(that is, lowers a voltage) and supplies the stepped-down power to the inverter15. The inverter15converts supplied DC power into AC power and supplies the AC power to the motor14. In this way, the power is supplied from the battery17to the motor14via the power conversion apparatus including the inverter15and the step-down converter16. The motor14is driven by the power supplied from the battery17. The inverter15and the step-down converter16generate heat in response to supply of a current to the motor14.

The vehicle cooling structure2includes a cooling passage61formed inside the cover42of the gear case13. The cooling passage61is formed between an inner surface42bof the cover42of the gear case13(that is, an inner surface of the gear case13) and the inverter15, and between the inner surface42band the step-down converter16. That is, the cooling passage61is formed in a portion of the gear case13where the inverter15and the step-down converter16are disposed. A coolant flows through the cooling passage61. As will be described in detail later, the coolant flowing through the cooling passage61cools both the oil in the gear case13and the power conversion apparatus (that is, the inverter15and the step-down converter16), which are cooling targets of the vehicle cooling structure2.

The vehicle1is provided with a heat exchanger62and a cooling pump63. Positions of the heat exchanger62and the cooling pump63are not limited to the rear side of the gear case13, and may be a front side of the gear case13. As indicated by dashed arrows inFIG.1, the cooling passage61, the heat exchanger62, and the cooling pump63form a cooling circuit through which the coolant circulates. The heat exchanger62cools the coolant delivered from the cooling passage61of the gear case13. The cooling pump63feeds the coolant cooled by the heat exchanger62to the cooling passage61of the gear case13.

FIG.3is a schematic cross-sectional view of the cover42. InFIG.3, up-down and front-rear directions of the vehicle1are indicated by solid arrows. In addition, dashed arrows inFIG.3indicate that the cooling passage61is connected. As illustrated inFIG.3, the cover42is attached to the case main body41by fastening members71such as bolts.

The inverter15includes a capacitor15aand a power module15b. The power module15bincludes a plurality of semiconductor switching elements such as insulated gate bipolar transistors (IGBTs). For example, in the power module15b, six semiconductor switching elements are coupled in a three-phase bridge between DC terminals coupled to the step-down converter16. The capacitor15ais, for example, an electrolytic capacitor. The capacitor15ais, for example, coupled in parallel between the DC terminals of the power module15b. The capacitor15aand the power module15bgenerate heat when a current is supplied to the motor14.

The step-down converter16includes a reactor16aand a power module16b. The step-down converter16includes, for example, a chopper circuit. The reactor16ais coupled in series to a DC terminal coupled to the battery17in the chopper circuit. The power module16bis a portion including semiconductor switching elements such as IGBTs in the chopper circuit. The reactor16aand the power module16bgenerate heat when a current is supplied to the motor14.

The inverter15(specifically, the capacitor15aand the power module15b) and the step-down converter16(specifically, the reactor16aand the power module16b) are fixed to the outer surface42aof the cover42. The inverter15and the step-down converter16are fixed such that heat dissipation surfaces thereof are in contact with the cover42. Electrical terminals of the inverter15and the step-down converter16are disposed, for example, on surfaces different from the surfaces in contact with the cover42, such as side surfaces thereof. Further, the inverter15and the step-down converter16are surrounded and covered by a protector72. The inverter15and the step-down converter16are sealed by the cover42and the protector72.

The outer surface42aof the cover42is formed with a feed inlet61aand a feed outlet61bthat are open rearward. The cooling passage61communicates from the feed inlet61ato the feed outlet61b. The feed inlet61ais coupled to the cooling pump63through a pipe or the like. The feed outlet61bis coupled to the heat exchanger62through a pipe or the like.

As described above, the cooling passage61is formed between the inner surface42bof the cover42and the inverter15, and between the inner surface42band the step-down converter16. In one example, the cooling passage61is formed so as to pass between the inner surface42bof the cover42and the capacitor15a, between the inner surface42bof the cover42and the power module15b, between the inner surface42bof the cover42and the power module16b, and between the inner surface42bof the cover42and the reactor16a.

The oil in the gear case13is in contact with the inner surface42bof the cover42. Therefore, the oil in the gear case13is cooled by heat exchange with the coolant in the cooling passage61through the inner surface42bof the cover42. The capacitor15aand the power module15bare in contact with the outer surface42aof the cover42. Therefore, the capacitor15aand the power module15bare cooled by the heat exchange with the coolant in the cooling passage61through the outer surface42aof the cover42. Further, the reactor16aand the power module16bare in contact with the outer surface42aof the cover42. Therefore, the reactor16aand the power module16bare cooled by the heat exchange with the coolant in the cooling passage61through the outer surface42aof the cover42.

In this way, in the vehicle cooling structure2, both the oil in the gear case13and the power conversion apparatus (that is, the inverter15and the step-down converter16) can be cooled by the common coolant flowing through the cooling passage61. Accordingly, for example, in the vehicle cooling structure2, air cooling fins of the gear case13can be omitted. Therefore, in the vehicle cooling structure2, it is possible to reduce the increase in the space occupied by the cooling structure.

Therefore, according to the vehicle cooling structure2of the present embodiment, the cooling structure can be simplified, and the degree of freedom of the vehicle design can be improved.

A heat-resistant temperature of the oil in the gear case13exceeds, for example, 100° C. Meanwhile, heat-resistant temperatures of the capacitor15a, the power module15b, the reactor16a, and the power module16bare less than 100° C., for example, about 80° C. In some cases, a temperature of the oil in the gear case13may be higher than the heat-resistant temperatures of the capacitor15a, the power module15b, the reactor16a, and the power module16b.

However, in the vehicle cooling structure2, the coolant flows between the oil in the gear case13and each one among the capacitor15a, the power module15b, the reactor16a, and the power module16b. Accordingly, in the vehicle cooling structure2, the coolant prevents heat of the oil in the gear case13from being transmitted to the capacitor15a, the power module15b, the reactor16a, and the power module16b.

Therefore, in the vehicle cooling structure2, even when the temperature of the oil in the gear case13is equal to or higher than the heat resistant temperatures of the capacitor15a, the power module15b, the reactor16a, and the power module16b, temperatures of the capacitor15a, the power module15b, the reactor16a, and the power module16bcan be made lower than the heat-resistant temperatures of the capacitor15a, the power module15b, the reactor16a, and the power module16b. As a result, in the vehicle cooling structure2, even though the inverter15and the step-down converter16are disposed on the outer surface42aof the gear case13, the inverter15and the step-down converter16can be prevented from being damaged.

Further, the cooling passage61communicates in an up-down direction in the vicinity of the inverter15and the step-down converter16. Accordingly, for example, even when a small amount of air is mixed into the coolant, the air is moved upward. Therefore, in the vehicle cooling structure2, it is possible to prevent the air in the coolant from staying in the vicinity of the inverter15and the step-down converter16, and it is possible to prevent a reduction in a cooling effect of the inverter15and the step-down converter16.

As illustrated inFIG.3, the gear case13includes a plurality of fins81protruding from an inner surface of the cooling passage61into the cooling passage61. The fins81are formed in a region of the inner surface of the cooling passage61on a side opposite to a region where the inverter15and the step-down converter16are in contact with the gear case13. That is, the fins81are disposed at positions corresponding to installation positions of the inverter15and the step-down converter16(specifically, positions facing the inverter15and the step-down converter16) in the cooling passage61.

In one example, the fins81are formed in a region of the inner surface of the cooling passage61on a side opposite to a region where the capacitor15ais in contact with the gear case13. The fins81are formed in a region of the inner surface of the cooling passage61on a side opposite to a region where the power module15bis in contact with the gear case13. The fins81are formed in a region of the inner surface of the cooling passage61on a side opposite to a region where the reactor16ais in contact with the gear case13. Further, the fins81are formed in a region of the inner surface of the cooling passage61on a side opposite to a region where the power module16bis in contact with the gear case13. Each fin81is formed in, for example, a prismatic shape extending from the inner surface of the cooling passage61. A shape of the fin81is not limited to the prismatic shape, and may be appropriately designed, such as a pyramidal shape.

In the vehicle cooling structure2, since the fins81are formed at positions close to the inverter15and the step-down converter16, an area of the heat exchange between the coolant flowing through the cooling passage61and the inverter15and the step-down converter16is widened. Therefore, in the vehicle cooling structure2, the cooling effect of the inverter15and the step-down converter16can be improved.

Further, the vehicle1can perform mechanical four-wheel drive using the propeller shaft11. In such a mechanical four-wheel drive vehicle, the rear differential gear12may vibrate due to a phase difference in power transmission between front wheels and rear wheels. Therefore, in the mechanical four-wheel drive vehicle, an inertial mass, that is, a ballast is provided at a position on a rear side of the gear case13of the rear differential gear12.

In the vehicle1, as described above, the inverter15and the step-down converter16are located on a rear side of the vehicle1in the gear case13. The inverter15and the step-down converter16have a considerable mass. Accordingly, the inverter15and the step-down converter16can function as at least a part of the inertial mass described above. Therefore, in the vehicle1, a mass of the inertia mass to be added can be reduced by the mass of the inverter15and the step-down converter16. As a result, in the vehicle1to which the vehicle cooling structure2is applied, an increase in a total weight of the vehicle1can be reduced.

FIG.4is a transparent plan view of the cover42as viewed from the rear side. InFIG.4, the up-down and left-right directions of the vehicle1are indicated by solid arrows. Further, white arrows inFIG.4illustrate a direction in which the coolant flows.

The capacitor15aand the power module15bof the inverter15, and the reactor16aand the power module16bof the step-down converter16are disposed in the vicinity of a center of the outer surface42aof the cover42. The feed inlet61ais located above the capacitor15a, the power module15b, the reactor16a, and the power module16b. The feed outlet61bis located below the capacitor15a, the power module15b, the reactor16a, and the power module16b.

As illustrated inFIG.4, the cooling passage61is spirally spread from an inner portion close to the center of the outer surface42atoward an outer portion far from the center. The feed inlet61ais located at an inner end of the spiral of the cooling passage61. The feed outlet61bis located at an outer end of the spiral of the cooling passage61. The capacitor15a, the power module15b, the reactor16a, and the power module16bare located in the vicinity of the feed inlet61ain a path of the cooling passage61.

The capacitor15ais disposed above the power module15b. That is, the capacitor15ais disposed upstream of the power module15bon the cooling passage61. The reactor16ais disposed below the power module16b. That is, the reactor16ais disposed downstream of the power module16bon the cooling passage61. The power module15bof the inverter15and the power module16bof the step-down converter16are arranged in the left-right direction. That is, a position of the power module15bin the up-down direction and a position of the power module16bin the up-down direction substantially coincide with each other.

The coolant fed from the feed inlet61apasses through the vicinity of the capacitor15a, the vicinity of the power module15band the power module16b, and the vicinity of the reactor16ain this order. The capacitor15a, the power module15b, the reactor16a, and the power module16bare cooled by a coolant having a sufficiently high cooling capacity, in other words, a coolant having a sufficiently low temperature. Therefore, in the vehicle cooling structure2, the inverter15and the step-down converter16can be effectively cooled.

Here, in the inverter15, a heat resistance performance of the capacitor15ais lower than a heat resistance performance of the power module15b. Therefore, by placing the capacitor15aupstream of the power module15bon the cooling passage61, the capacitor15acan be cooled preferentially to the power module15b. Further, in the step-down converter16, a heat resistance performance of the power module16bis lower than a heat resistance performance of the reactor16a. Therefore, by placing the reactor16adownstream of the power module16bon the cooling passage61, the power module16bcan be cooled preferentially to the reactor16a.

The coolant passing through the vicinity of the reactor16acirculates in the vicinity of a peripheral edge of the cover42and reaches the feed outlet61b. Accordingly, the coolant cools a wide range of the inner surface42band the outer surface42aof the cover42. Therefore, the oil in contact with the inner surface42bof the cover42can be effectively cooled. As described above, the capacitor15a, the power module15b, the reactor16a, and the power module16bmay have temperatures lower than that of the oil. Therefore, the coolant after the heat exchange with the capacitor15a, the power module15b, the reactor16a, and the power module16bcan sufficiently cool the oil.

As described above, an example of a positional relationship between the components including the capacitor15a, the power module15b, the reactor16a, and the power module16bhas been described with reference toFIG.4, whereas the positional relationship between the components is not limited to the example ofFIG.4. For example, the positional relationship between the components in the up-down direction may be different from that in the example ofFIG.4.

FIG.5is a diagram illustrating an example of an output characteristic of the motor14. As illustrated inFIG.5, a torque of the motor14increases as a rotational speed decreases, and decreases as the rotational speed increases.

The current supplied from the inverter15to the motor14increases as the torque of the motor14increases. Therefore, as illustrated by a broken line A1inFIG.5, an amount of the heat generated by the inverter15and the step-down converter16increases as the torque of the motor14increases.

In contrast, a rotational speed of each gear of the rear differential gear12increases as the rotational speed of the motor14increases. As the rotational speed of each gear increases, an amount of the heat generated by the friction between the gears increases. That is, as illustrated by a broken line A2inFIG.5, an amount of the heat generated by the rear differential gear12increases as the rotational speed of the motor14increases.

In this way, the inverter15supplies the current to the motor14such that a timing at which the amount of the heat generated by the inverter15and the step-down converter16increases is different from a timing at which the amount of the heat generated by the rear differential gear12increases.

Accordingly, in the vehicle cooling structure2, the cooling of the inverter15and the step-down converter16may be reduced when the cooling of the oil in the gear case13is significantly necessary, and the cooling of the oil in the gear case13may be reduced when the cooling of the inverter15and the step-down converter16is significantly necessary. Therefore, in the vehicle cooling structure2, it is possible to cool the oil in the gear case13and the power conversion apparatus (that is, the inverter15and the step-down converter16) while reducing an increase in a size of the heat exchanger62or the cooling pump63.

Here, in the vehicle cooling structure2, since the step-down converter16is provided in addition to the inverter15as the power conversion apparatus, the following various effects are achieved.

For example, since the voltage of the inverter15can be lowered by the step-down converter16, a switching loss in the inverter15can be reduced. As a result, the increase in the size of the inverter15can be reduced.

Further, for example, since a voltage of the battery17can be lowered by the step-down converter16and the power can be supplied to the motor14, it is possible to flexibly cope with a case where the voltage of the battery17is to be changed at a time of designing the vehicle1without reselecting each component. That is, flexibility with respect to system changes is enhanced.

Further, for example, since a voltage of the motor14can be adjusted by the step-down converter16, even when an induced voltage generated in the motor14increases as the rotational speed of the motor14increases, it is possible to prevent the induced voltage from exceeding the voltage of the battery17. Accordingly, it is not necessary to set the voltage of the inverter15to be excessively high in advance such that the induced voltage does not exceed the voltage of the battery17regardless of the rotational speed of the motor14. Therefore, an increase in the switching loss due to the increase in the voltage in the inverter15can be reduced, and the increase in the size of the inverter15can be reduced.

For example, by providing the step-down converter16, it is possible to reduce the switching loss in the inverter15as described above without lowering a carrier frequency. Therefore, deterioration of responsiveness of control of the motor14due to the decrease of the carrier frequency can be reduced, and deterioration of responsiveness of the torque can be reduced.

As described above, according to the vehicle cooling structure2of the present embodiment, it is possible to simplify the cooling structure while benefiting from the various effects described above due to the provision of the step-down converter16.

Although the embodiment of the disclosure has been described above with reference to the accompanying drawings, it is not necessary to say that the disclosure is not limited to such an embodiment. It will be apparent to those skilled in the art that various changes and modifications may be conceived within the scope of the claims, and it is understood that such changes and modifications also fall within the technical scope of the disclosure.

For example, the inverter15and the step-down converter16in the above-described embodiment are disposed on the outer surface42aof the cover42. However, the inverter15and the step-down converter16may be disposed on an outer surface of the case main body41without being limited to the outer surface of the cover42.

Further, the inverter15and the step-down converter16in the above-described embodiment are disposed on the rear side of the gear case13. However, positions of the inverter15and the step-down converter16may be disposed at any positions in the gear case13without being limited to the rear side of the gear case13. Here, when the inverter15and the step-down converter16are caused to function as a part of the inertia mass, the inverter15and the step-down converter16are disposed on the rear side of the gear case13.

In the vehicle cooling structure2of the above-described embodiment, the fins81are provided in the cooling passage61. However, the fins81may be omitted. Here, the cooling effect of the inverter15and the step-down converter16can be increased by providing the fins81.

In the above-described embodiment, the gear case13that houses the rear differential gear12is provided with the inverter15, the step-down converter16, and the cooling passage61. However, the gear case13provided with the inverter15, the step-down converter16, and the cooling passage61is not limited to one that houses the rear differential gear12. The gear case13may house various gear mechanisms such as a front differential gear, a transmission, and a decelerator. Further, oil that lubricates operations of the gear mechanisms is also housed in the gear case13that houses these gear mechanisms. In the vehicle cooling structure2of this aspect, the oil in the gear case13and the power conversion apparatus (that is, the inverter15and the step-down converter16) can be cooled by the common coolant, as in the above-described embodiment.