Internal-combustion engines – Charge forming device – Exhaust gas used with the combustible mixture
Reexamination Certificate
2000-12-07
2002-05-07
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Charge forming device
Exhaust gas used with the combustible mixture
C123S568240, C701S108000, C702S058000, C702S183000, C324S701000
Reexamination Certificate
active
06382194
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to stepping motors for controlling an exhaust-gas-returning valve in an exhaust gas re-circulation system attached to an internal combustion engine, and in particular relates to a malfunction-detecting device for an EGR stepping motor, which detects the malfunction of the stepping motor.
2. Description of the Related Art
Hitherto, as pollution control in automobile exhaust gas, an exhaust gas re-circulation (EGR) system is known for reducing nitrogen oxides (NO
x
) in exhaust gas of an internal combustion engine. In the EGR system, a part of exhaust gas is returned from an exhaust gas passage to an intake passage via an exhaust gas returning passage connecting the exhaust gas passage to the intake passage of the internal combustion engine so as to be re-circulated in fuel mixture to be sucked into the engine, so that the heat due to the combustion in the engine cylinder is absorbed by the inert gas in the exhaust gas so as to reduce the maximum combustion temperature, thereby reducing NO
x
.
However, the re-circulation of exhaust gas causes reduction in the output of the engine and instability in combustion, resulting in problems of deteriorated operationality and increased hydrocarbons (HC). Therefore, the re-circulating amount of the exhaust gas must be suitably controlled according to operational conditions so as to reduce the problems. For that purpose, an exhaust gas returning valve (EGR valve) is provided in an exhaust gas returning passage and the amount of the valve opening (opening area) is controlled. The EGR valve is conventionally controlled by using a stepping motor (EGR stepping motor) in general, because in the EGR stepping motor, digital control of closed loop can be performed; positional control is excellent; accumulated errors are small. A valve opening adjusting structure in that a valve disc is ascended or descended by the rotation of the stepping motor rotor is known.
FIG. 7
is a schematic illustration showing an overall structure of a commonly used internal combustion engine. In
FIG. 7
, an air flow sensor (AFS)
2
measures the amount of air sucked into an engine
1
which is an internal combustion engine; a throttle valve
3
adjusts the amount of air sucked into the engine
1
by operation linked to an accelerator pedal (not shown) which is generally operated by a driver; a throttle valve opening sensor
4
detects the position of the throttle valve
3
; a clank angel sensor
5
detects the rotational speed and the position of a clank shaft of the engine
1
; a water temperature sensor
6
detects the temperature of cooling water
1
a
as means for detecting warming up conditions of the engine
1
; an O
2
sensor
7
detects the concentration of oxygen in the exhaust gas exhausted from the engine
1
; and a cylinder identifying sensor
13
identifies a combustion cylinder attached to a cam shaft.
An engine controller
8
determines operational conditions of the engine by receiving information from the above-mentioned various sensors arranged in each position of the engine
1
and performs the computation of various controlled variables according to the operational conditions, thereby burn fuel in a desired air-fuel ratio. An air by-pass valve
10
controls an air reservoir by-passing the throttle valve
3
and performs the rotational speed control of the engine during the idling when the throttle valve
3
is perfectly closed and the torque control during the running. An injector
11
supplies fuel to the engine
1
.
An exhaust gas returning passage
23
is the EGR system for returning the exhaust gas exhausted from the engine
1
again to a combustion chamber in the engine
1
so as to burn it again by connecting an exhaust gas passage
22
to an intake passage
21
. An EGR valve
12
is arranged in the exhaust gas returning passage
23
for controlling the amount of the EGR to be burnt again. A sparking plug
9
, the air by-pass valve
10
, the injector
11
, and the EGR valve
12
are controlled by the engine controller
8
.
FIG. 8
is a sectional view showing an example of an EGR valve structure. As shown in the drawing, the EGR valve
12
comprises a stepping motor
12
a
and a valve disc
12
b
. The stepping motor
12
a
comprises a stator
121
and a rotor
122
while the valve disc
12
b
comprises a valve
123
and a rod
124
having the valve
123
at one end affixed thereto and being vertically movable when viewed in the drawing. The exhaust gas flows into an entrance port
125
from the exhaust gas passage
22
and flows out of an exit port
126
toward the intake passage
21
. These ports
125
and
126
form parts of the exhaust gas returning passage
23
.
When the rotor
122
is rotated by a driving signal to the stepping motor
12
a
, the rotation is converted into rectilinear motion by a screw
127
to be transmitted to a motor shaft
128
. At this time, when the rotation of the stepping motor
12
a
is the normal direction, the motor shaft
128
moves the rod
124
upwardly when viewed in the drawing against a spring force of a spring
129
so that the valve
123
is moved in the separating direction from a seat member
130
, thereby opening the EGR valve. On the other hand, when the rotation is the reverse direction, the motor shaft
128
moves the rod
124
downwardly in corroboration of a spring force of the spring
129
so that the valve
123
is moved in the approaching direction toward the seat member
130
, thereby closing the EGR valve.
FIG. 9
shows a schematic connection diagram of a conventional malfunction-detecting device for the EGR stepping motor disclosed in Japanese Unexamined Patent Application Publication No. 3-203599, for example. In
FIG. 9
, a microcomputer
80
corresponds to the engine controller
8
; a motor driving circuit
81
drives the stepping motor
12
a
of the EGR valve
12
. In a break detecting circuit
82
, transistors Tr
1
to Tr
4
are driving and detecting breaks; grounding resistances R
1
to R
4
are grounding emitters of the transistors; excitation coils S
1
to S
4
are the stator
121
of the stepping motor
12
a
; numerals C
1
to C
4
denotes comparators; potential dividing resistors R
5
and R
6
are dividing a power supply voltage V
c
; numerals
511
to
514
denote delay circuits; numerals
521
to
424
denote D type flip-flop circuits; and numeral
53
denotes an AND circuit.
In the circuit of the conventional malfunction-detecting device for the EGR stepping motor shown in
FIG. 9
, when driving signals (symmetrical square-waves) having four phases being 90° out of phase with each other are supplied to each base of the transistors Tr
1
to Tr
4
from the motor driving circuit
81
, as shown in
FIG. 10
, the transistors Tr
1
to Tr
4
are turned on during the base input signal is in the high (“H”) level while are turned off during the low (“L”) level. When the transistor Tr
1
is turned on, the excitation coil S
1
is electrically excited while a non-inversion input terminal of a comparator C
1
is to be the high (“H”) level by a voltage drop due to the resistor R
1
. To the non-inversion input terminal of the comparator C
1
, a dividing voltage due to the potential dividing resistors R
5
and R
6
is applied; since the voltage generated in both ends of the resistor R
1
by the current flowing through the resistor R
1
is set to be higher than the dividing voltage, the output voltage of the comparator C
1
is to be the high (“H”) level.
On the other hand, during the off of the transistor Tr
1
, the above-mentioned current does not pass through the excitation coil S
1
and the resistor R
1
so that the input voltage of the non-inversion input terminal of the comparator C
1
is to be lower than the above-mentioned dividing voltage, thereby the output voltage of the comparator C
1
is to be the low (“L”) level. As for the other transistors Tr
2
to Tr
4
, the same operations are performed. The outputs of the comparators C
1
to C
4
are shown in
FIG. 10
(broken lines show breaks).
The output voltag
Sughrue & Mion, PLLC
Wolfe Willis R.
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