Electricity: motive power systems – Constant motor current – load and/or torque control
Reexamination Certificate
2002-08-22
2004-05-11
Nappi, Robert (Department: 2837)
Electricity: motive power systems
Constant motor current, load and/or torque control
C318S139000, C318S140000, C318S430000, C318S432000, C318S434000, C318S055000, C318S059000, C318S064000, C056S010800, C056S01020E, C056S010600, C056S011100, C056S011900
Reexamination Certificate
active
06734647
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to working machines which include an engine functioning as a drive source of a machine's working section and an electric motor functioning as a drive source of a machine's moving or transporting section.
BACKGROUND OF THE INVENTION
In recent years, there have been developed new-type working machines where a machine's working section and transporting section are driven by separate drive sources. Typically, the working section is driven by an engine, while the transporting section is driven by an electric motor. Because the rotation of the motor that drives the transporting section can be controlled as desired, the new-type working machines can make relatively sharp small turns and thereby move relatively agilely.
Among examples of such new-type working machines is a “self-propelled lawn mower” disclosed in Japanese Patent Laid-open Publication No. HEI-3-43013 (hereinafter also called a “disclosed prior art mower”). In the disclosed prior art mower, a lawn mowing cutter is driven by an engine, front wheels are driven via a transporting drive motor powered by a battery, and the rotation of the transporting drive motor is controlled by a controller.
However, the disclosed prior art mower, where the transporting drive motor is powered by the battery alone, can work only for a limited time. In addition, the battery must be of a great capacity, which therefore has to be large in size and heavy in weight. Mounting such a large and heavy battery on the working machine of a relatively small size is not advisable.
As one solution to the problem of the disclosed prior art mower, it is thinkable to use the above-mentioned engine to drive not only the mowing cutter but also an electric power generator so that the battery can be charged by the power generator, and use the power generator and battery as the power source for the transporting drive motor. In this case, the transporting drive motor can be driven by the power generated by the power generator alone, and the remainder of the power generated by the power generator can be stored in the battery. This way, the battery may have a smaller size, which can advantageously reduce the necessary space for mounting the battery on the mower and the overall weight of the mower as well. In addition, the mower is allowed to work for a very long time.
Generally, a small-size engine is used to drive the mowing cutter or other working section which is subjected to only small loads. However, the working machine is often operated with its traveling speed greatly varied in accordance with actual working conditions. For example, even when the small-size engine is being rotated at low speed with a small throttle opening, the transporting drive motor may be accelerated rapidly to quickly achieve a high-speed transporting state.
Since the transporting drive motor is driven by the electric power generated by the electric power generator at any time, the generator is required to generate more electric power as necessary acceleration of the transporting drive motor increases. As the necessary electric power increases rapidly, the loads on the engine also increase rapidly. If the loads on the engine rapidly become excessive, the number of rotations of the engine would be reduced to a considerable degree. Further, the reduced number of the engine rotations would reduce the number of rotations of the mowing cutter, so that the working efficiency of the mower would be lowered undesirably.
To maintain a desired number of rotations of the engine, it is only necessary to adjust the throttle valve opening by manually operating an engine throttle lever. In this case, however, operating the engine throttle lever each time the transporting drive motor is to be accelerated or decelerated through operation of a transporting speed lever is very bothersome, and some improvement has to be made to enhance the operability of the working machine.
SUMMARY OF THE INVENTION
In view of the foregoing prior art problems, it is an object of the present invention to provide a working machine where a working section and electric power generator are driven via an engine and the power generator and battery chargeable by the power generator are used as power sources of a transporting electric motor, and which can accelerate the electric motor with necessary acceleration while effectively restricting a rapid increase of loads on the engine.
It is another object of the present invention to provide a working machine where a working section and electric power generator are driven via a small-size engine and the power generator is used as a power source of a transporting electric motor, and which can readily maintain a desired number of rotations of the engine in response to acceleration or deceleration of the electric motor and thereby achieve enhanced operability.
It is still another object of the present invention to provide a working machine where a working section and electric power generator are driven via an engine and the power generator is used as a power source of a transporting drive motor, and which can accelerate the electric motor with necessary acceleration while effectively preventing a rapid increase of loads on the engine.
According to a first aspect of the present invention, there is provided an improved working machine which comprises: a driving section including an engine, an electric power generator driven by the engine, a battery chargeable by the electric power generator, and an electric motor (transporting electric motor) drivable by both of the electric power generator and the battery; a working section driven by the engine to perform desired work; a transporting section driven by the electric motor; and a control section for controlling rotation of the electric motor, on the basis of a comparison between an actual transporting speed and a target transporting speed of the transporting section. In the present invention, the control section performs the operations of: determining necessary acceleration of the transporting section in accordance with a current actual transporting speed of the transporting section; determining a correction coefficient corresponding to a current number of rotations of the engine, from among correction coefficients having a characteristic of becoming closer to a value of one as the number of rotations of the engine increases but becoming closer to zero as the number of rotations of the engine decreases; multiplying the necessary acceleration by the determined correction coefficient, to thereby provide corrected necessary acceleration; and controlling the rotation of the electric motor in accordance with the corrected necessary acceleration.
When the number of rotations of the engine is relatively great, i.e., when the engine is rotating at relatively high speed, the rotation of the electric motor can be accelerated in the present invention in accordance with a value close to the necessary acceleration having been determined in accordance with the current actual transporting speed of the transporting section. When, on the other hand, the number of engine rotations is relatively small, the rotation of the electric motor can be accelerated in accordance with the corrected necessary acceleration of a relatively small value. Therefore, the rotation of the electric motor can be accelerated in accordance with optimum necessary acceleration corresponding to the current number of rotations of the engine.
Thus, even when the electric motor has been accelerated rapidly while the engine is rotating at low speed, the acceleration of the motor can be restricted to an optimal value corresponding to the number of rotations of the engine, and thus the amount of power generated by the power generator can also be restricted appropriately. Consequently, loads on the engine can be lessened appropriately. Namely, in the present invention, it is possible to increase the rotating speed of the electric motor with the necessary acceleration while effectively preventing a rapid increase of the loads on
Inui Tsutomu
Kanke Hiroo
Wakitani Tsutomu
Adams & Wilks
Honda Giken Kogyo Kabushiki Kaisha
Nappi Robert
Smith Tyrone
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