Electricity: motive power systems – Positional servo systems – 'reset' systems
Reexamination Certificate
2003-05-16
2004-12-28
Masih, Karen (Department: 2837)
Electricity: motive power systems
Positional servo systems
'reset' systems
C318S599000, C318S560000, C318S804000, C388S800000
Reexamination Certificate
active
06836091
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a servo control device of a DC motor for controlling an object to be controlled of a servomechanism for controlling a mechanical position or an angle, for example, an exhaust gas recirculation (hereinafter referred to as EGR) valve provided in a recirculation system of an exhaust gas, a throttle valve, an actuator of a turbocharger and the like.
BACKGROUND ART
FIG. 1
shows a diagram in which a valve
11
of an EGR valve arranged in an exhaust gas return passage (c) for making an exhaust gas passage (a) of an engine E communicate with an intake gas passage (b) thereof is an object to be controlled and in which a DC motor
21
is driven by the output of a control section
50
to control the opening of the valve
11
.
FIG. 2
is a longitudinal cross sectional view to show a constitution of the EGR valve to which a servo control device is applied having a DC motor
21
as a driving source. In
FIG. 2
, a reference numeral
1
denotes a valve body in which a passage communicating with the exhaust gas return passage (c) is disposed in a recirculation system of an exhaust gas. When the valve
11
is moved up as shown in the drawing, it is put into contact with a seat
12
to close the exhaust gas return passage c and when the valve
11
is moved down, it is separated from the seat
12
to open the exhaust gas return passage (c).
A reference numeral
21
denotes a DC motor to be a driving unit (torque generating source) of a valve for opening/closing an exhaust gas passage,
22
denotes a motor case mounted on the valve body
1
,
23
denotes a rotor rotatably supported in the motor case
22
via bearings
24
,
25
, and the rotor
23
has a screw hole
23
a
made through the central portion of a shaft. A reference numeral
26
denotes a magnet mounted on the outer peripheral portion of the rotor
23
,
27
denotes a stator core surrounding the outer periphery of the magnet
26
, and a predetermined gap is formed between this stator core
27
and the above mentioned magnet
26
.
A reference numeral
28
denotes a coil arranged in the stator core
27
and constituting a stator,
29
denotes a motor shaft to be a valve driving shaft, and this motor shaft
29
is made in a screw shaft and screwed into the screw hole
23
a
of the above mentioned rotor
23
and moved in an axial direction by the rotation of the above mentioned rotor
23
.
A reference numeral
30
denotes a valve shaft abutting member integrally formed with the motor shaft
29
. By making the top end of a valve shaft
13
having the above mentioned valve
11
at its top end abut against the tip (bottom end in
FIG. 1
) of this valve shaft abutting member
30
, the valve shaft
13
is made to follow a movement in an axial direction of the above mentioned motor shaft
29
to thereby open/close the above mentioned valve
11
.
A reference numeral
31
denotes a cover mounted on an end surface on the valve shaft abutting member
30
side in the motor case
22
,
32
denotes a spring retaining member mounted on the tip side of the valve shaft abutting member
30
,
33
denotes a spring hung between the spring retaining member
32
and the above mentioned cover
31
for urging the valve, and this spring
33
urges the valve
11
at the tip of the valve shaft via the valve shaft abutting member
30
in a direction that opens the valve
11
. A reference numeral
34
denotes a commutator rotating integrally with the rotor
23
and having a shaft hole
34
a
at its central portion.
A reference numeral
35
denotes a power source side case mounted on an opening end on the commutator
34
side of the motor case
22
. This power source side case
35
is an integrally molded part made of synthetic resin and constitutes a main body of a device for passing current through the DC motor
21
and is an integral combination of a built in sensor portion
36
in which a position sensor (not shown) for detecting the opening of the above mentioned valve is built and an input/output connector portion
37
in which a connector terminal is built.
A reference numeral
38
denotes a brush holding cylindrical portion integrally molded with a wall opposed to the commutator
34
in the power source side case
35
, and
39
denotes a brush slidably inserted into the brush holding cylindrical portion
38
for passing a current. This brush
39
is made of carbon powder and copper powder and is connected via a lead wire (not shown) to the connector terminal of the above mentioned input/output connector portion
37
.
Next, an operation will be described. Passing a current through the coil
28
via the brush
39
and the commutator
34
generates a rotational torque in the rotor
23
by an interaction between a magnetic field generated by the coil
28
and the magnetic field of the magnet
26
. When the rotor
23
is rotated by the rotational torque, the motor shaft
29
screwed into the screw hole
23
a
of the rotor
23
is fed by the screw and moved straight in an axial direction.
Here, in a case where the motor shaft
29
is moved downward in
FIG. 1
, the valve shaft abutting member
30
is pushed by the motor shaft
29
in the direction of an urging force of the spring
33
to open the control valve
11
via the valve shaft
13
against which the valve shaft abutting member
30
abuts. Then, when the valve
11
moves near to a target position and a difference between a present position and a target position becomes nearly equal to zero, an electric power required to hold the valve
11
at its position against the restoring force of the return spring
18
is supplied to the DC motor
21
.
On the other hand, when the rotor
23
of the DC motor
21
is rotated in a direction opposite to the above mentioned direction, the motor shaft
29
is moved upward in FIG.
1
and the valve shaft
13
abutting against the valve shaft abutting member
30
integral with the motor shaft
29
follows the motor shaft
29
by the restoring force of the return spring
18
to close the valve.
FIG. 3
is a diagram of one example of a circuit constitution to show a servo control device for controlling the driving of the above mentioned DC motor
21
. In
FIG. 3
, a reference numeral
41
denotes a position sensor and this position sensor
41
has a movable contact
43
moving on a resistor
42
to which a constant voltage is applied by a power supply terminal and when the movable contact
43
moves with the rotation of the rotor
23
, a voltage responsive to its moving position, that is to say, a voltage in compliance with the valve position is outputted as a detection signal.
A reference
44
denotes a controller block and this controller block
44
has an A/D input port
45
inputted with the detection signal from the valve position sensor
41
, a filter
46
for reading the output of the A/D input port
45
, a PI control computing section
48
for performing a PI control computation based on the output of the filter
46
and the output of a target value determining section
47
, an excitation switching and duty computing section
49
for performing an excitation duty computation based on the output of the PI control computing section
48
, a digital output port
50
for outputting an ON/OFF signal based on the output of the excitation switching and duty computing section
49
and a PWM output port
51
for outputting a PWM signal.
A reference numeral
52
denotes a switching circuit for controlling the passing of a current through the DC motor
21
. A (+) side end of the DC motor
21
is connected to a connection point of semiconductor switching devices (hereinafter referred to as switch device)
53
,
54
connected in series and a (−) side end thereof is connected to a connection point of semiconductor switching devices (hereinafter referred to as switch device)
55
,
56
connected in series.
To each of the above mentioned switch devices
53
,
55
is connected each of transistors
57
,
58
which is turned ON by the output of the digital output port
50
, and to each of the above mentioned switch devices
54
,
5
Fujita Youichi
Kawamura Satoshi
Miyoshi Sotsuo
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