Electricity: motive power systems – Limitation of motor load – current – torque or force
Reexamination Certificate
2000-09-06
2002-01-01
Dang, Khanh (Department: 2834)
Electricity: motive power systems
Limitation of motor load, current, torque or force
C318S811000, C388S903000
Reexamination Certificate
active
06335600
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Application No. 11-252593 filed on Sep. 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 invention relates to a motor drive unit which controls an electric motor through pulse width modulation (PWM) control and to detection of a malfunction for the motor drive unit.
2. Description of the Related Art
At present, there is a motor drive unit which controls an electric motor. The motor drive unit has a bridge circuit composed of four sides that each have a switching element. The electric motor has at least two ends connected to the switching elements that are diagonally positioned in relation to the bridge circuit. At least one of the switching elements is connected to a power line, and at least one of the other switching elements is grounded. The motor unit is driven by applying voltage to the power switching element. By performing pulse width modulation control of the switching elements, drive control of the electric motor is performed. In a drive unit of this type, if the sum of the terminal voltages of the electric motor becomes approximately equal to “0”, i.e., equal to or smaller than a predetermined threshold value (e.g. approximately 3% of the battery voltage), it is determined whether or not the electric motor and the grounded line has been short-circuited (e.g. Japanese Patent Application Laid-Open No. 5-185937).
SUMMARY OF THE INVENTION
However, the aforementioned motor drive unit takes into account nothing but the possibility of the portion between one terminal of the electric motor and the grounded line being short-circuited. Therefore, this motor drive unit is useless when there is a malfunction occurring in a motor drive device, a malfunction detection controller, or the like.
The invention provides a motor drive unit and a method of detecting a malfunction thereof which make it possible to detect a wide variety of malfunctions relating to an electric motor by detecting various malfunctions in the electric motor, the motor drive device and the malfunction detection monitor device.
To achieve the aforementioned and/or other objects, a motor drive unit in accordance with a first exemplary embodiment of the present invention has a bridge circuit composed of four sides that each have a switching element. An electric motor having two ends is connected to the bridge circuit that is diagonally positioned in relation to the electric motor. At least one of the pair of switching elements is connected to a power line, and at least one of the other switching elements is grounded. The motor drive unit is driven by applying voltage to the power terminal. By performing pulse width modulation control of the switching elements, drive control of the electric motor is performed. The motor drive unit has a malfunction judgment controller which judges the occurrence of a malfunction when the sum of the terminal voltages of the electric motor is different from a power voltage by a predetermined value or more during operation of the electric motor.
In the thus-constructed first exemplary embodiment of the invention, if the electric motor, the motor drive device, and its marginal device including a malfunction detection controller are in normal operation, the sum Vm of terminal voltages Vm
1
, Vm
2
at the ends of the electric motor is approximately equal to the power voltage Vb due to the operation of the bridge circuit. If the respective switching elements are short-circuited, the sum Vm assumes a value which is approximately equal to or greater than 3·Vb/2 or a value which is approximately equal to or smaller than Vb/2. Further, even if the portions between respective ends of the electric motor and the grounded line or the power line are short-circuited, the sum Vm assumes a value which is approximately equal to or greater than 3·Vb/2 or a value which is equal to or smaller than Vb/2. As a result, according to the invention, since the malfunction judgment controller judges the occurrence of a malfunction when the sum of the terminal voltages of the electric motor is different from the power voltage by a predetermined value or more, various malfunctions as mentioned above are detected. Thus, it is possible to provide a suitable countermeasure against those malfunctions.
Further, a second exemplary embodiment of the invention is applied to a motor drive unit which controls the electric motor by using the bridge circuit as mentioned above. The motor drive unit has a malfunction judgment controller which judges the occurrence of a malfunction when the electric motor is out of operation and when the sum of the terminal voltages of the electric motor is different from the sum of voltage values which has been determined in advance based on the voltage values at the ends of the electric motor during a turned-off state of all the switching elements by a predetermined value or more.
In the thus-constructed second exemplary embodiment of the invention, if the electric motor, the motor drive device and its marginal device including the malfunction detection controller are in normal operation, the sum Vm of the terminal voltages Vm
1
, Vm
2
at the ends of the electric motor is equal to a predetermined voltage in a turned-off state of all the switching elements. For example, if the electric motor is grounded at one end through a pull-down resistor without connecting the electric motor at another end to the power line through a pull-up resistor, the sum Vm is equal to a ground voltage “0” (hereinafter referred to as a first mode). Further, if at least one of the ends of the electric motor is connected to the power line through the pull-up resistor and at least one of the other ends of the electric motor is grounded through the pull-down resistor, the sum Vm is equal to a value which is twice as great as a predetermined value between the power voltage Vb and the ground voltage “0” (equal to the power voltage Vb if the pull-up resistor and the pull-down resistor assume the same resistance value) (hereinafter referred to as a second mode). In addition, if the electric motor is connected to the power line through the pull-up resistor without grounding the ends of the electric motor through the pull-down resistor, the sum Vm is equal to the power voltage 2·Vb (hereinafter referred to as a third mode).
In the first mode, while the electric motor is out of operation as mentioned above, if portions between the switching elements on the side of the power line of the bridge circuit and the power line have been short-circuited, or if portions between the ends of the electric motor and the power line have been short-circuited, the sum Vm is approximately equal to 2·Vb.
Further, in the second mode, while the electric motor is out of operation as mentioned above, if the switching elements of the bridge circuit have been short-circuited, the sum Vm is approximately equal to 2·Vb or “0”. Further, if portions between the ends of the electric motor and the power line or the grounded line have been short-circuited, the sum Vm is approximately equal to 2·Vb or “0”.
In addition, in the third mode, while the electric motor is out of operation as mentioned above, if portions between the switching elements on the grounded side of the bridge circuit and the grounded line have been short-circuited, or if portions between the ends of the electric motor and the grounded line have been short-circuited, the sum Vm is approximately equal to “0”.
As a result, according to the second exemplary embodiment of the invention, the malfunction judgment controller judges the occurrence of a malfunction when the detected sum of the terminal voltages of the electric motor is different from the sum of voltage values which has been determined in advance based on the voltage values at the ends of the electric motor during a turned-off state of all the switching elements by at least a predetermined value. Thus, various malfunctions as described above are detected. T
Fujita Shuji
Kasai Eiji
Dang Khanh
Oliff & Berridg,e PLC
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