Method of controlling power output apparatus

Prime-mover dynamo plants – Electric control – Engine control

Reexamination Certificate

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C310S114000

Reexamination Certificate

active

06380640

ABSTRACT:

INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Application No. HEI 11-287256 filed on Oct. 7, 1999 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of controlling a power output apparatus including a prime mover, such as an engine, and an electric motor or motors, as power sources, and more particularly to a method of controlling such a power output apparatus that is provided with a coupling device capable of coupling a rotary shaft of the electric motor to at least one of a drive shaft and an output shaft of the prime mover.
2. Discussion of Related Art
In recent years, hybrid vehicles, such as that as disclosed in Japanese laid-open Patent Publication No. HEI 9-47094, have been proposed wherein a power output apparatus having an engine and an electric motor(s) as power sources is installed on the vehicle. In such a hybrid vehicle, the power output apparatus installed on the vehicle transmits a part of the power generated by the engine to a drive shaft through a power adjusting device, and converts the remaining power into electric power in a regenerative manner. The electric power may be stored in a battery, or used for driving the electric motor as a power source other than the engine. During the power transmitting process as described above, the power output apparatus controls the power adjusting device and the electric motor so as to output the power generated by the engine to the drive shaft at a desired rotation speed with desired torque. This makes it possible to operate the engine with a high operating efficiency by selecting an appropriate engine operating point, irrespective of the required output to be transmitted from the drive shaft, and therefore the hybrid vehicle is excellent in terms of energy saving or resource conservation and exhaust emission control, as compared with a conventional vehicle having only an engine as a power source.
In the power output apparatus as described above, the rotary shaft of the electric motor may be coupled to the drive shaft or the output shaft of the engine. In a first coupling state in which the rotary shaft of the electric motor is coupled to the drive shaft, so-called power circulation, or transmission of power from the downstream side to the upstream side, occurs during overdrive operations (overdrive running) in which the rotation speed of the drive shaft is higher than the engine speed, with a result of a reduced amount of power being generated by the engine and effectively transmitted to the drive shaft. Thus, the power output apparatus placed in the above coupling state exhibits a higher operating efficiency during underdrive operations (underdrive running) in which the rotation speed of the drive shaft is lower than the engine speed, as compared with the operating efficiency during overdrive operation. In a second coupling state in which the rotary shaft of the electric motor is coupled to the output shaft of the engine, on the other hand, the power effectively transmitted to the drive shaft is reduced due to the above-described power circulation occurring during underdrive operations (underdrive running). Thus, the power output apparatus exhibits a higher operating efficiency during overdrive operations (overdrive running), as compared with that during underdrive operations (underdrive running).
In view of the above situations, a power output apparatus has been proposed which is capable of switching the coupling state of the rotary shaft of the electric motor, namely, coupling the rotary shaft to a selected one of the drive shaft and the output shaft of the engine, and an example of such an apparatus is disclosed in Japanese laid-open Patent Publication No. HEI 10-271749. The power output apparatus of this type includes a first clutch that permits coupling and uncoupling of the rotary shaft of the electric motor to and from the output shaft of the engine, and a second clutch that permits coupling and uncoupling of the rotary shaft of the electric motor to and from the drive shaft. Where the rotation speed of the drive shaft becomes lower than the engine speed (during underdrive running), the first clutch is released while the second clutch is engaged or applied, so that the rotary shaft of the electric motor is coupled to the drive shaft. Where the rotation speed of the drive shaft becomes higher than the engine speed (during overdrive running), on the other hand, the first clutch is engaged while the second clutch is released, so that the rotary shaft of the electric motor is coupled to the output shaft of the engine. In this manner, the power output apparatus operates with a sufficiently high efficiency during both underdrive operations and overdrive operations.
In the following description, the coupling state in which the rotary shaft of the electric motor is coupled to the drive shaft will be called “underdrive (UD) coupling”, and the coupling state in which the rotary shaft of the electric motor is coupled to the output shaft of the engine will be called “overdrive (OD) coupling”.
In the hybrid vehicle on which the power output apparatus as described above is installed, the coupling state of the rotary shaft of the electric motor is changed in the following manner depending upon running conditions of the vehicle.
When the vehicle is started from its rest state, the vehicle is always started while UD coupling is established, so that the drive shaft can generate a large driving torque. With UTD coupling thus established, the sum of the torque from the engine and the torque from the electric motor is applied as driving torque to the drive shaft.
While the vehicle is running at a high-speed, on the other hand, OD coupling is established so as to reduce loss in the power output apparatus (i.e., loss in the engine, electric motor, power adjusting device and others), and improve the fuel economy during high-speed running.
When the vehicle starts from rest with UTD coupling established as described above, the vehicle keeps running only by means of the electric motor, without starting the engine. More specifically, the electric motor produces driving torque to be applied to the drive shaft, using electric power stored in a battery. With this arrangement, the vehicle is able to run without using a low-speed operating region in which the engine operates with a poor efficiency, thus assuring improved fuel economy.
Here, the mode in which the vehicle runs only by means of the electric motor without using the engine will be called “EV mode” (or “EV running”), and the mode in which the engine is started and the vehicle runs using both the engine and the electric motor will be called “HV mode” (or “HV running”).
FIG. 26
is a diagram showing operating patterns in which a hybrid vehicle starts from its rest state. In
FIG. 26
, the vertical axis indicates torque, and the horizontal axis indicates rotation speed.
FIG. 26
shows operating characteristics of a power output apparatus.
In
FIG. 26
, curve LIM is the maximum output line of the power output apparatus. Accordingly, a region defined by the vertical axis indicating the torque, the horizontal axis indicating the rotation speed, and the curve LIM indicates a range in which the operating point of the drive shaft can be located, namely, the operating region of the power output apparatus. The operating point is expressed as a combination of the torque and the rotation speed.
The curve EL is an operating line used when determining the target operating point of the engine. The engine exhibits the highest efficiency on this operating line EL, and the engine operates with optimum fuel economy if the target operating point of the engine is determined according to this operating line EL.
In general, the operating line of the engine is a boundary on which the engine speed and the rotation speed of the drive shaft are equal to each other. Accordingly, the engine operates with the rotary shaft of the electric motor held in

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