Electricity: motive power systems – Constant motor current – load and/or torque control
Reexamination Certificate
2000-03-28
2001-09-04
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Constant motor current, load and/or torque control
C318S254100, C318S434000, C318S701000, C318S721000
Reexamination Certificate
active
06285148
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to an energization control device for an electric motor and in particular to a chopping control device of a switched reluctance motor which is driven such that switching the energization for each of the phase coils is made.
In electric motors, particularly switched reluctance motors (SR motors), for controlling the amount or level of current which flows through a load or phase coil, an H-type switching circuit is used as disclosed in Japanese Patent Laid-open print No. Hei.8-172793 published without examination in 1996. In the conventional electric motor device, the H-type switching circuit is interposed between the phase coil and a DC power supply and the actual current flowing through the phase coil is measured by using a resistor. The resultant current is compared to the target current in binary mode and the H-type switching element is turned on and turned off when the target current ≧ the actual current and the target current < the actual current, respectively. Thus, repeating the tuning on and off the switching element in alternative fashion changes the actual current flowing through the phase coil, thereby adjusting the actual current to the target current as precise as possible.
In the conventional motor, controlling the output torque, the rotational number, and the current flowing through the phase coil is established by the switching element. On the other hand, a control data map is prepared inside a microprocessor which is made up of a plurality of control data items and one of the control data items is selected for energizing the motor. Each of the control data items includes an ON-angle at which the switching element is turned on, an OFF-angle at which the switching element is turned off and a target current. The larger the number of the control data items (or the higher the resolving power of the data), the more precise the control of the motor.
However, such a resolving power is limited. On the other hand, the output of the motor depends on the resolving power of the ON-angle/OFF-angle. For example, within a range of intermediate-high speed of 5000 rpm or above, according to the motor characteristics, though the current flowing through the phase coil is increased in a gradual manner after the angular position of the rotor passes the ON-angle, the angular position of the rotor reaches the OFF-angle, which sometimes causes turning off the switching element before the actual current reaches the target current. In this case, for example, advancing the ON-angle by the minimum resolution power, a several percent increase of the output of the motor is attained. However, in an intermediate range between the advanced ON-angle and the original ON-angle, it is impossible to change the output of the motor or the torque derived from the motor.
In view of the foregoing circumstances, a need exists to establish an optimum control of the motor in such a manner that the output of the motor coincides with the target output of the motor without improving the resolution power.
SUMMARY OF THE INVENTION
It is, therefore, a principal object of the present invention to provide an improved energization control device for an electric motor which satisfies the need noted above.
In order to attain the foregoing object, the present invention provides an energization control device for an electric motor which is comprises
(a) detecting means for detecting an angle of rotation of a rotor of the motor,
(b) control data storage means for storing therein a plurality of control data items corresponding to rotational conditions of the rotor, and
(c) control means for controlling the energization of the motor, the control means obtaining first control data items for deriving a first torque from the motor and second control data items for a second torque, when a target torque intended to be derived from the motor is smaller and larger than the first torque and the second torque, respectively,
the control means, when establishing an energization control for deriving the target torque from the motor, using the first control data items and the second control data items in such a manner that a ratio of the second control data items to the first control data items is the ratio of a first deviation between the first torque and the target torque to a second deviation between the target torque and the second torque.
In accordance with the present invention, based on the deviation ratio, the weighted average of the first control data item and the second control data item makes it possible to derive an intermediate torque from the motor which lies between the first torque and the second torque, with the result that a more precise control of energizing the phase coil of the motor is possible using the conventional control data map.
REFERENCES:
patent: 5282401 (1994-02-01), Hebbale et al.
patent: 5747962 (1998-05-01), Fulton
patent: 5754024 (1998-05-01), Sugiyama
patent: 6051942 (2000-04-01), French
Aisin Seiki Kabushiki Kaisha
Leykin Rita
Nappi Robert E.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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