Electricity: motor control systems – Closed loop speed control system for dc motor with commutator – Armature control by digital or combined analog and digital...
Reexamination Certificate
1999-08-16
2001-05-15
Nappi, Robert E. (Department: 2837)
Electricity: motor control systems
Closed loop speed control system for dc motor with commutator
Armature control by digital or combined analog and digital...
C318S254100, C318S471000, C701S036000
Reexamination Certificate
active
06233396
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application is related to and claims priority from Japanese Patent Application No. Hei. 10-269965 filed on Sep. 24, 1998, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a load control system for preventing an error operation of a driving unit when a signal input line of a driving circuit is short-circuited, more particularly relates to a load control system for a blower motor of a vehicle air conditioner.
2. Description of Related Art
In recent years, a motor without a commutator and a brush (hereinafter, referred to as “motor”) is used as a blower motor of a vehicle air conditioner, and a rotation speed of the motor is controlled by performing a pulse-width modulation control (PWM control) relative to a driving signal of an inverter for controlling electrical power applied to an armature winding of the motor.
For example, in a vehicle air conditioner, an electrical relay
140
which is turned on when an ignition switch
114
of a vehicle engine turns on is disposed between a vehicle battery
113
and a motor driving circuit (MDC)
117
of a blower motor
110
, as shown in FIG.
6
. That is, electrical power is supplied from the vehicle battery
113
to the motor driving circuit
117
through the electrical relay
140
.
Further, as shown in
FIG. 6
, an armature winding
111
of the blower motor
110
is delta-connected, and an air-conditioning control unit (A/C ECU)
115
is connected between the ignition switch
114
and the motor driving circuit
117
. The air-conditioning control unit
115
calculates a target rotation speed of the blower motor
110
and outputs a duty signal Dt. The duty signal Dt output from the air-conditioning control unit
115
is input into the motor driving circuit
117
through a signal input line
116
. In the conventional system, the rotation speed of the blower motor
110
is controlled by the motor driving circuit
117
to be increased in proportion to an increase of the duty signal percentage (ratio) Dt (%), as shown in FIG.
7
. Therefore, when the motor driving circuit
117
of the blower motor
110
or the air-conditioning control unit
115
has a trouble and full-load operation of the blower motor
110
is performed, the ignition switch
114
is turned off by a passenger, so that the electrical relay
140
is turned off and operation of the blower motor
110
can be stopped.
However, when the electrical relay
140
is not provided for reducing cost, the motor driving circuit
117
is directly connected to the vehicle battery
113
. In this case, when the signal input line
116
for inputting signal to the motor driving circuit
117
is short-circuited on a vehicle side (i.e., ground short-circuited), 100% of duty signal Dt is applied to the motor driving circuit
117
. As a result, the full-load operation of the blower motor
110
is continued even when the ignition switch
114
is turned off in this case, and over-discharge of the vehicle battery
113
may be caused.
SUMMARY OF THE INVENTION
In view of the foregoing problems, it is an object of the present invention to provide a load control system for a driving unit, which can automatically prevent full-load operation of the driving unit due to short-circuit of a signal input line for inputting signal from a control circuit to a driving circuit, even when the driving circuit is directly connected to a power source.
According to the present invention, a load control system for a driving unit includes a driving circuit directly connected to an electrical power source to electrically control the driving unit, a control unit for generating a control signal for the driving unit, a signal input line through which the control signal from the control circuit is input to the driving circuit, and a determining unit for determining a short-circuited state of the signal input line. In the load control system, when the determining unit determines that the short-circuited state of the signal input line, the driving circuit stops operation of the driving unit based on an output signal from the determining unit. Thus, even when the signal input line is short-circuited when the driving circuit is directly connected to the power source, the determining unit determines the short-circuited state, and the driving unit is automatically stopped. As a result, over-discharging of the power source is prevented.
Preferably, the control signal from the control circuit is a duty signal in which a duty ratio becomes 100% when the signal input line is short-circuited, and the determining unit determines that the signal input line is short-circuited when the duty ratio is increased to a value proximate to 100%. Therefore, the short-circuited state of the signal input line is readily determined without using a special sensor, and the load control system protects the driving unit with a simple structure.
More preferably, the driving circuit controls the driving unit in such a manner that load applied to the driving unit is increased as the duty ratio of the duty signal increases, until the duty ratio is increased to a predetermined value lower than 100%, and the driving circuit stops operation of the driving unit when the duty ratio becomes more than the predetermined value. Therefore, both of operation control of the driving unit during a normal operation and an automatic stop of the driving unit at an abnormal operation can be accurately performed.
REFERENCES:
patent: 5019757 (1991-05-01), Beifus
patent: 5148092 (1992-09-01), Ishii et al.
patent: 5418676 (1995-05-01), Murakami et al.
patent: 5469032 (1995-11-01), Otake
patent: 5780983 (1998-07-01), Shinkawa et al.
patent: 5915070 (1999-06-01), Takekawa et al.
Konda Shinichi
Kuwada Katsuzi
Denso Corporation
Harness Dickey & Pierce PLC
Leykin Rita
Nappi Robert E.
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