Electricity: motive power systems – Automatic and/or with time-delay means – Responsive to thermal conditions
Reexamination Certificate
2000-04-26
2001-11-27
Ip, Paul (Department: 2837)
Electricity: motive power systems
Automatic and/or with time-delay means
Responsive to thermal conditions
C318S139000, C318S472000, C165S091000, C361S699000
Reexamination Certificate
active
06323613
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to a drive unit in which an electric motor is used as a power source, and more particularly, to a cooling system in a drive unit for an electric vehicle or a hybrid drive unit.
2. Related Art
When an electric motor is used as a power source for a vehicle, the load exerted on the electric motor varies significantly with running conditions. Accordingly, in order to manage the heat generation with a heavy load, cooling is necessary. Therefore, conventionally, as disclosed in Japanese Patent Application Laid-Open No. 7-288949, the drive unit case is provided with a water passage for cooling the electric motor.
However, in the conventional system, the coolant passage is formed as tubing held in a spiral groove on the outer surface of the casing, with substantially half of the circular section of the tubing exposed and extending from the outer surface of the casing. Such structure is complicated, and is disadvantageous in terms of cost and space.
SUMMARY OF THE INVENTION
Therefore, a first object of the present invention is to provide a drive unit including a casing, an electric motor housed in the casing, and a simplified cooling structure incorporated into the drive unit casing.
An electric motor requires a controller which is an inverter in the case of an alternating current electric motor. Since a controller such as an inverter is connected to the electric motor by a power cable, it can be mounted anywhere, separate from the electric motor. However, for convenience of mounting on a vehicle, such a controller may be integrated with the electric motor. However, when the controller is integrated with the electric motor, the controller receives heat both as heat generated by its own elements and as heat from the electric motor transferred through the drive unit case. Therefore, such controllers require cooling.
Thus, a second object of the present invention is to provide a cooling system whereby both the inverter and the electric motor can be effectively cooled, even in the case of an inverter integrated with the drive unit case.
In order to achieve the first object as above, the present invention provides a drive unit including an electric motor, a drive unit case housing the electric motor, and a circulation passage for a first coolant for cooling the electric motor formed in the drive unit case. A circulation passage is provided for a second coolant separate from the circulation passage for first coolant and the circulation passage for the second coolant has a section which serves as a heat exchanger for heat exchange with the first coolant. The first coolant for cooling the electric motor is cooled by the heat transferred to the second coolant in the heat exchanger.
Where an inverter for controlling the electric motor is included, the circulation passage for the second coolant should include a portion for cooling the inverter.
Preferably, the heat exchanger portion is disposed downstream of the portion for cooling of the inverter in the circulation passage for the second coolant.
In order to attain the second object, the drive unit further includes an inverter panel for fixing the inverter to the case, and a flow passage for the second coolant is formed between the inverter panel and the drive unit case and is divided by a partition wall into first (upper) and second (lower) flow chambers.
The first chamber and the second chamber may be interconnected in series with the first chamber upstream of the second chamber. Alternatively, the first and second chambers may be connected in parallel to the circulation passage for the second coolant.
Furthermore, in any of the above-described embodiments, the drive unit may include an electric generator, a circulation passage for the first coolant for cooling the generator in the drive unit case, and an inverter for controlling the electric generator, the generator inverter being fixed to the inverter panel together with the motor inverter.
The drive unit case may have a coolant reservoir for the first coolant positioned facing the flow passage for the second coolant and the coolant reservoir may be divided into a coolant container for the electric motor and a coolant container for the electric generator. Orifices may be employed in the flow passage of the first coolant for distributing different proportions of coolant to the coolant container for the electric motor and to the coolant container for the electric generator. Each coolant container may have a dam in the vicinity of its exit. Further, a coolant container may be partially defined by the stator of the electric motor and/or the electric generator.
The first coolant may be passed through the rotor of the electric motor downstream of the coolant container, and discharged through a discharge hole provided in the rotor. Because the first coolant is brought into direct contact with the stator of the electric motor or the electric generator without being mediated by the drive unit case, the electric motor or the electric generator can be cooled more effectively.
By using as the first coolant a lubricant oil or ATF (automatic transmission fluid) which does not adversely affect, by corrosion or the like, the electric motor, very efficient heat transfer can be obtained through direct contact between the electric motor and the coolant, and moreover, the heat conveyed to the coolant by heat transfer can be discharged efficiently to the second coolant at one heat exchanger. Accordingly, the motor can be cooled efficiently without a complicated circulation passage for the first coolant passing through the drive unit case.
The first coolant for cooling the electric motor may be cooled by the second coolant which also cools the inverter(s) required for motor and/or generator control. In such a structure, the second coolant for cooling the inverter is also used for the (indirect) cooling of the electric motor, thereby making it possible to simplify the cooling structure of the drive unit. Where the area of heat exchange between the first and second coolants is downstream of the area of heat exchange between the second coolant and the inverter it is possible to prevent the heat of the first coolant, received from the electric motor, from being transferred to the inverter which has a heat tolerance lower than that of the electric motor.
Where the second coolant does not directly cool the electric motor, but simultaneously cools both the inverter and the first coolant which cools the motor, the heat from the electric motor is reduced, relative to direct heat transfer, by heat exchange between the second coolant and the first coolant, and thus it is possible to prevent the temperature of the second coolant from rising above the maximum temperature tolerated by the inverter.
In an alternative embodiment, the second coolant does not simultaneously cool the electric motor and the inverter. Instead, it first cools the inverter through the inverter panel and then cools the electric motor and (optionally) generator through the drive unit case. Therefore, it becomes possible to conduct cooling according to the individual cooling requirements of the inverter, electric motor and (optionally) generator, respectively, by a single coolant. Thus, it is possible to cool the inverter, the electric motor and (optionally) generator efficiently by a simple flow passage construction. Also, since the space between the integrated inverter and the drive unit case is used as a space for flow of coolant for cooling the inverter and the electric motor, it is possible to avoid the conventional complicated construction which include a coolant passage around the drive unit case, thereby improving space efficiency and reducing costs.
In yet another embodiment with parallel and independent coolant flows through the first chamber and the second chamber, it is possible to cool the inverter simultaneously with the motor, and (optionally) the generator, and further it is possible to prevent the heat from the electric motor and generator from
Agata Hiromichi
Hara Takeshi
Hotta Yutaka
Kido Takahiro
Kutsuna Naruhiko
Aisin Aw Co. Ltd.
Ip Paul
Lorusso & Loud
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