Controller of exhaust gas recirculation valve

Details Controller of exhaust gas recirculation valve Controller of exhaust gas recirculation valve

2001-10-23

2003-04-15

Moulis, Thomas N. (Department: 3747)

Internal-combustion engines

Charge forming device

Exhaust gas used with the combustible mixture

C251S129110

Reexamination Certificate

active

06546920

ABSTRACT:

This application is the national phase under 35 U.S.C. § 371 of PCT International Application No. PCT/JP00/01130 which has an International filing date of Feb. 25, 2000, which designated the United States of America and was not published in English.
TECHNICAL FIELD
This invention relates to an exhaust gas recirculation (referred to as EGR, hereinafter) valve controller provided in an exhaust gas recirculation system.
BACKGROUND ART
FIG. 1
is a constitutional view of an engine exhaust system, in which the control valve
11
of an EGR valve is arranged in an exhaust recirculation passage c for communicating the exhaust passage a and the intake passage b of an engine E with each other. This EGR valve controller is adapted to control the opening/closing of the control valve
11
by, for example, a stepping motor M of a hybrid PM 4-phase type or the like. The EGR valve controller controls the.opening angle of the control valve
11
by subjecting.the stepping motor M to open loop control in steps of a stepping angle.
The controller using such a stepping motor M is capable of controlling the opening angle of the control valve
11
only in steps of the stepping angle of the stepping motor M. Thus, there is a limit to the resolving power of the control valve
11
to control the opening angle. In addition, in the open control of the stepping motor M, a power swing phenomenon sometimes occurs, placing a limit on responsiveness. Once power swing occurs, a difference occurs in controlled variables, and this difference is maintained, consequently reducing reliability.
EGR valve controllers designed to deal with the foregoing problem have been available in the related art. For example, Japanese Patent Laid-Open Application Hei 10 (1998)-122059 discloses a controller for an EGR valve, which opens/closes on a torque balance between a predetermined return torque applied in the opening/closing direction of the control valve
11
by pressing means, and a variable motor torque applied in the closing/opening direction of the control valve
11
by the energization of a direct current motor (referred to as a DC motor, hereinafter) in one direction. This controller comprises: an open loop control system for open-loop controlling the DC motor in such a way as to generate a motor torque corresponding to the target opening/closing position of the control valve
11
; and a feedback control system for feedback-controlling the DC motor based on deviation between input data indicative of the target opening/closing position of the control system
11
, and detection data indicative of the actual opening/closing position of the control valve
11
.
First, a driving system using the above DC motor will be described. To feedback-control the opening angle of the control valve by a DC servo motor system, the opening angle of the control valve
11
is continuously detected and fed back by using a position sensor of a sliding resistance type or the like. Thus, by continuously controlling the torque generated by the DC motor, the resolving power of the control valve
11
to control an opening angle can be infinitely reduced theoretically. In the DC motor, unlike the case of the stepping motor M, there are no control errors caused by a power swing phenomenon. Accordingly, responsiveness can be improved compared with a case in which the stepping motor M is used, thus enhancing reliability.
The EGR valve driving system using such a DC motor employs a so-called torque balance system, which is adapted to control valve opening/closing on a torque balance between a predetermined return torque applied in a closing direction (or opening direction) by a spring as pressing means, and a variable motor torque applied in an opening direction (or closing direction) by the energization of the DC motor in one direction. In the case of such a driving system, since the return torque is always applied to the EGR valve, the inclinations of lines A and B undergoing a hysteresis caused by friction exhibits a difference, as shown in FIG.
2
.
Referring to
FIG. 2
, the line A indicates an operation characteristic when the control valve
11
is opened by increasing the motor torque; and the line B an operation characteristic when the control valve
11
is closed by reducing the motor torque. The inclinations of the lines A and B are changed by a spring constant of the spring applying the return torque, and the lines A and B are shifted left and right in
FIG. 2
according to the magnitude of a set torque.
It is now assumed that the mere PI control is employed to control the control valve
11
of the foregoing operation characteristics, wherein the DC motor is subject to proportion and integration (PI) control based on a deviation between input data indicative of the target opening/closing position of the control valve
11
, and detection data indicative of the actual opening/closing position of the same. In this case, because of the operation characteristics shown in
FIG. 2
, it is difficult to maintain the control valve
11
in the target opening/closing position.
Specifically, proportion (P) and integration (I) gains must be increased in order to execute control along the line A, considering the operation characteristics shown in FIG.
2
. However, under such setting, when the motor torque is increased based on the PI control, the deviation from the target opening position becomes “0” immediately after the control valve
11
is opened to the target opening position, setting a P component equal to “0” and clearing an I component, and the closing of the control valve
11
is immediately started by the return torque. In an initial stage when the valve closing has just started (small deviation), the motor torque cannot overcome the return torque because the P and I components are both small, thus enlarging deviation. Thereafter, even if the deviation grows to a point that the motor torque and the return torque are balanced, the closing operation of the control valve
11
cannot be stopped suddenly due to the inertia of the DC motor, and consequently the opening operation of the control valve
11
cannot be immediately started. If a gain is increased in such a way as to generate relatively large motor torque even when the deviation is small, as shown in
FIG. 3
, the process is brought into a vicious cycle of increased overshoots and undershoots.
A description will be given of one related-art construction of the controller of the control valve based on a so-called torque balance driving system using the DC motor, by referring to
FIGS. 4
to
7
. In
FIG. 4
, a reference numeral
1
denotes a valve body having an exhaust recirculation passage c formed in the recirculation system of exhaust gas. The control valve
11
is raised as shown to be brought into contact with a seat
12
, thereby closing the exhaust passage c. The control valve
11
is lowered to be separated from the seat
12
, thereby opening the exhaust passage c.
A reference numeral
2
denotes a motor case for housing a DC motor
20
. This DC motor
20
includes a rotor
21
having a coil
22
wound thereon, and a yoke
23
having a magnet
24
. The upper end part of the rotor
21
is rotatably supported in the motor case
2
by a slide ball
25
and a rotor shaft
26
. The lower end part of the rotor
21
is rotatably supported in the valve body
1
by a bearing
27
. A commutator
28
is attached to the upper end of the rotor
21
, and the motor brush
30
of the motor case
2
side is pressed against the commutator
28
by a brush spring
29
.
A reference numeral
40
denotes a position sensor for detecting the rotational position of the rotor
21
, a resistance value of the position sensor
40
varying according to the rotational position of the rotor
21
. The position sensor
40
and the motor brush
30
are connected to the controller (described later) by a connector terminal
3
.
A motor shaft
31
is engaged inside the rotor
21
, and the motor shaft
31
is prevented from being rotated by the guide bush
13
of the body
1
. Accordingly, the motor shaft
31
is raised an

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