Electricity: motive power systems – Limitation of motor load – current – torque or force
Reexamination Certificate
1999-09-07
2001-12-11
Martin, David S. (Department: 2837)
Electricity: motive power systems
Limitation of motor load, current, torque or force
C318S432000, C318S452000, C318S466000, C318S626000
Reexamination Certificate
active
06329777
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application relates to and incorporates herein by reference Japanese Paten Application No. 10-328249 filed on Nov. 18, 1998.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a motor drive control apparatus and method having a motor current limit function, which can be applied to a motor driven throttle valve control in an internal combustion engine.
2. Related Art
In a motor driven throttle control apparatus for vehicles, a direct current motor is coupled to a throttle valve of an internal combustion engine. The motor is driven with an electric current (motor current) of 100% duty at the time of starting the motor drive from one position to another to improve responsiveness of the throttle valve. The motor current is reversed temporarily to brake the motor so that the throttle valve is stopped at a target throttle position or angle, when the throttle valve rotates to a position near the target throttle position. The current increases excessively when the motor locks due to jamming of foreign obstacles with the throttle valve. The current is shut off to protect semiconductor switching devices, when the motor lock is detected based on the condition that the throttle valve does not rotate to the target position within a predetermined time period.
The motor tends to lock slightly when water on the throttle valve freezes. However, the motor will rotate again normally when the supply of the motor current is continued, unless the degree of freezing is substantial. If the time period for the motor lock detection is set short, the current is shut off unnecessarily even when the motor lock is nominal, such as when the degree of freezing is not substantial. If the time period for the motor lock detection is set long, semiconductor switching devices of large size and cost are required.
In U.S. Pat. No. 5,712,550, a motor current is limited to below a predetermined level to reduce the power capacity and cost of semiconductor switching devices. However, the motor drive with the limited motor current will result in insufficiency of the drive torque for starting the motor drive from one rotation position to another and the braking force for braking the motor, thereby lessening the responsiveness of the throttle valve.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a motor drive control apparatus and method, which enables a continued supply of motor current upon detection of a motor lock without lessened responsiveness and increased size and cost of switching devices.
According to the present invention, a motor is driven with a high motor current for a larger torque during the initial stage of motor drive, and thereafter with a low motor current lower than the high motor current. As the high motor current is only for the motor drive starting period, the size and cost of switching devices need not be increased. Thus, the supply of motor current can be continued for some period of time to counter the nominal motor lock.
According to the present invention, a motor is braked with a high motor current for a larger torque during a motor braking, and thereafter with a low motor current lower than the motor current supplied during the motor braking. Thus, the motor braking performance can be improved, and the heating of semiconductor switching devices can be reduced because of reduction of the motor current after the motor braking.
Preferably, the high motor current and the low motor current during the motor drive starting operation and the motor braking operation are limited to predetermined levels, respectively. Further, the motor current in shut off, when a control object driven by the motor does not attain a target position for more than a predetermined reference period.
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Itabashi Toru
Niimi Yukihide
Denso Corporation
Martin David S.
Nixon & Vanderhye P.C.
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