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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a turbocharger, and, more
specifically, to a device for controlling the supercharging pressure of
the turbocharger.
2. Description of the Present Art
In an internal combustion engine equipped with a turbochager, the
turbocharger is usually controlled by means of an exhaust gas bypass
mechanism which reduces the volume of exhaust gas flowing to the turbine
by bypassing this exhaust gas. The pressure at the throttle throat of the
turbine is determined by the capacity of the turbine. Accordingly, when a
turbine with a small flow capacity is used, the torque is increased at low
engine speed and decreased at high engine speed. When a turbine with a
large flow volume is used, the torque is increased at high speed, but is
reduced at medium and low engine speeds. Therefore, proposals have been
put forward in the past for a variable capacity turbocharger in which it
is possible to increase the torque from low engine speed to high engine
speed by varying the geometry of the turbine in conformance with the
operating conditions of the engine.
As a conventional variable capacity turbocharger and its control device,
the device known from the Japanese Utility Model for opposition No.
53-50310 is given as an example. This proposal device is illustrated in
FIGS. 1 to 4, in which a turbocharger is provided with a variable geometry
device 3 comprising a movable member 4, a rod 5, and an actuator 6. The
variable geometry device 3 is regulated by the degree of opening of a
scroll throttle throat 2A according to the detected revolutions per minute
of the engine and the position of an accelerator rack 9.
However, in the control device of this type of conventional variable
capacity turbocharger, the degree of opening of the scroll throttle throat
2A is specifically determined from the engine RPM and the position of the
accelerator rack 9. As a result, a change in the supercharging pressure
will result, conforming to any change in the temperature of the inlet air,
atmospheric pressure, and octane rating of the fuel, or a change in the
intake air flow volume resulting from the individual characteristics of
the engine. Therefore, the optimum supercharging pressure corresponding to
the operating conditions of the engine cannot be obtained.
Accordingly, in order to obviate this type of problem, a supercharging
pressure control device for a turbocharger, such as the device illustrated
in FIG. 5, has been considered. This supercharging pressure control device
for a turbocharger has a control unit 55 for providing revised control of
the engine supercharging pressure based on the detected supercharging
pressure value obtained from a supercharging pressure sensor 27 provided
in an engine 24. The control unit 55 comprises a plurality of calculating
means 61 and 66, a table look-up means 62, an adder 63, a plurality of
setting means 64 and 69 for setting the objective supercharging pressure,
a plurality of subtractors 65 and 70, and a compensating control means 68.
More particularly, in the variable geometry mechanism of the turbine, a
feedforward control system which comprises the control means 61, the table
look-up means 62, the adder 63, a solenoid valve 47, and the engine 24,
compensates for the supercharging pressure control which has been
performed with a first feed back control system comprising an objective
supercharging pressure setting means 64, a subtractor 65, and a
calculating means 66. On the other hand, in the exhaust gas bypass
mechanism, the previously mentioned feed forward control system performs
compensating control on the supercharging pressure control which has been
performed, with a second feed back control system comprising a target
supercharging pressure setting device 69, a subtractor 70, a compensating
control means 68, and a solenoid valve 51.
However, in a supercharging pressure control device for a turbocharger,
such as is described above, the supercharging pressure sensor 27, in the
case where a breakdown such as a broken wire, etc. is produced, and the
correct detected value cannot be outputted to a control unit 55, there is
the problem that normal supercharging pressure control becomes impossible.
In addition to this, in a high pressure, high load region, such as the
region (C) illustrated in FIG. 6, when the actual supercharging pressure
exceeds the normal value, the supercharging pressure sensor 27 breaks
down. In the case where a detected value lower than the actual
supercharging pressure is given to the control unit 55, the control system
activates the supercharging pressure to an even higher value. In the worst
case, engine damage can occur.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a supercharging pressure
control device for a turbocharger with which an almost optimum
supercharging pressure control is possible and no damage is caused to the
engine from an abnormally high supercharging pressure even when the
supercharging pressure control sensor breaks down.
Briefly described, this object of the present invention is accomplished by
the provision of a supercharging pressure control device for a
turbocharger comprising a valve mechanism 105, for driving the valve of a
variable geometry mechanism to vary the area of a flow channel in an
exhaust gas channel; a valve mechanism 117, for driving a valve provided
in a channel which causes the exhaust gases to be bypassed; a detection
means 109 for detecting the supercharging pressure of the inlet air to an
internal combustion engine; a detection means 103 for detecting the drive
condition of the internal combustion engine; a control-value-obtaining
means 101 for obtaining a value for controlling the opening and closing of
a valve for the previously mentioned variable geometry mechanism based on
the detected drive condition; a first control system 107 for controlling a
valve mechanism which drives a valve of the variable geometry mechanism
using a revised control value based on a first objective supercharging
pressure set value and a detected value obtained by the detection means
109, at the time when the control value obtained by the control value
obtaining means 101 relates to a prescribed operating region of the
internal combustion engine; a second control system 111 for controlling a
valve mechanism which drives a valve for the exhaust bypass channel using
a revised control valve based on a second objective supercharging pressure
set value and the detected value obtained by the detection means 109 at
the time when the control value obtained by the control value obtaining
means 101 relates to non-prescribed operating region of the internal
combustion engine; a cutoff means 115, for cutting off the compensated
control by means of the first control system; and a recording control
means 113 for controlling a valve mechanism which drives a valve for the
exhaust gas bypass channel from a revised value recorded when an
abnormality of the previously mentioned supercharging pressure control
detection means is recognized and when the cutoff means is activated at
the time when a malfunction or abnormality of the supercharging pressure
detection means is recognized, and the compensated value calculated by
means of the second control system is recorded.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects, features and advantages of the present invention
will become more apparent from the following description of a preferred
embodiment taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a sectional drawing of a scroll of a supercharging pressure
control device for a turbocharger in accordance with conventional
technology
FIG. 2 is a block diagram of the supercharging pressure control device
shown in FIG. 1;
FIG. 3 and FIG. 4 are graphs illustrating the relationship between the
degree of opening of the scroll intake port and the RPM of the engine;
FIG. 5 is a block diagram of a supercharging pressure control device shown
in FIG. 2;
FIG. 6 is a graph illustrating the characteristics of an internal
combustion engine equipped with a turbochager;
FIG. 7 is a block diagram of a supercharging pressure control device
according to the present invention;
FIG. 8 is a drawing showing one embodiment of the supercharging pressure
control device for a turbocharger in accordance with the present
invention.
FIG. 9 is a sectional drawing of a variable capacity turbocharger shown in
FIG. 8;
FIG. 10 is a block diagram of a supercharging pressure control device for a
turbocharger in accordance with the present invention;
FIG. 11 is a graph showing the output characteristics of a supercharging
pressure sensor shown in FIG. 8; and
FIG. 12 is a flow chart for control process of the device shown in FIG. 10.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIGS. 7-12, there is shown a supercharging pressure control
device embodying the present invention.
As shown in FIG. 8, intake air is introduced into an engine 24 through an
intake air tube 13 and an intake air manifold 25. An air flowmeter 11, a
compressor impeller housing 17 for a turbocharger 16, throttling valve 23,
and a relief valve 19 are provided in the intake air tube 13. The air
flowmeter 11 measures an intake air flow volume Qa and outputs this value
to a control unit 55. A crank angle sensor 21 detects the RPM Ne of the
engine 24 and outputs this value to the control unit 55. The intake air is
pressurized by means of a compressor impeller 15 provided in the
compressor impeller housing 17, and, after being regulated by the
throttling valve 23, this intake air is divided and fed into the air tubes
of the engine 24 by way of the intake air manifold 25. A supercharging
pressure sensor 27, which will be subsequently described, is mounted in
the intake air manifold 25.
The exhaust gas from the engine 24 is collected in exhaust gas manifold 36
and exhausted through an exhaust gas pipe 40. A variable geometry means 42
and a turbine impeller housing 29 for the turbocharger 16 are provided in
the exhaust gas pipe 40. A turbine impeller 41 which is linked to the
compressor impeller 15 is housed in the turbine impeller housing 29. The
flow velocity of the exhaust gas used in the turbine impeller 41 is varied
by the variable geometry means 42. The variable geometry mechanism 42
comprises a movable tongue section 35 disposed at the inlet of scroll 57;
a shaft 37 linked to a rod 39; an atmospheric chamber 45, a positive
pressure chamber 48, and a diaphragm 46 which together form an actuator
for opening and closing the movable tongue section 35; a solenoid valve 47
which controls air pressure in a channel 14 which accesses both the
downstream side of the compressor impeller casing 17 of the intake air
tube 13 and the positive pressure chamber 48. The solenoid valve 47 is
controlled by a duty signal from the control unit 55. Within the
atmospheric chamber 45 a spring 43 which energizes the diaphragm 46 is
installed in the contracted position in the positive pressure chamber 48.
The channel 14, which leads into the positive pressure chamber 48, is
opened to atmosphere by the action of the solenoid valve 47. The diaphragm
46 drives the rod 39 and shaft 37 by an increase in pressure in the
positive pressure chamber 48, and activates the movable tongue section 35
in the direction which increases the throat area of an exhaust gas
introduction channel 59 in a scroll 57 which is illustrated in FIG. 9. The
movable tongue section 35 is constructed so that it can be returned to its
original position by the reversion of the pressure in the positive
pressure chamber 48 to atmospheric pressure.
A waste gate valve 33 is provided in the exhaust gas bypass channel in the
engine 24. The valve 33 is linked to an activating member 49 which is in
turn linked to a diaphragm activator 53, and is constructed so that it
controls the degree of opening of the exhaust gas bypass channel 38 by the
duty control of the solenoid valve 51 provided near the diaphragm actuator
53 of the channel 14. The waste gate valve 33 functions as a supercharging
pressure control means when the RPM of the engine 24 is in the region (C)
illustrated in FIG. 6.
Referring to FIG. 9, there is shown the relationship of the variable
geometry means 42 comprising the movable tongue 35 and the shaft 37, the
turbine impeller 41, the scroll 57, and the exhaust-gas-introduction
channel 59. The turbine impeller housing 29 contains the scroll 57 which
is formed to surround the turbine impeller 41. The cross-sectional area of
the scroll 57 gradually becomes smaller in the downstream direction
(indicated by the arrows in the drawing) from the exhaust-gas-introducing
channel 59. The movable tongue 35 is provided at the confluence of the
exhaust-gas-introduction channel 59 and a scroll end-section 58, and this
movable tongue 35 pivots on the shaft 37 in such a way as to expand or
contract the introduction channel 59. The supercharging pressure decreases
as the movable tongue 35 swings toward the scroll end-section 58, and
increases as the tongue 35 swings in the direction of the
exhaust-gas-introduction channel 59.
Referring to FIG. 10, as previously noted, there is shown a block diagram
of one embodiment of a supercharging pressure control device for a
turbocharger in accordance with the present invention. The control unit 55
comprises a microprocessor, a memory, and an input-output interface, and
its basic action may be identical to the microcomputer for engine control.
The control unit 55 comprises a plurality of calculating means 61 and 66,
a table look-up means 62, an adder 63, a plurality of target supercharging
pressure setting means 64 and 69, a plurality of subtractors 65 and 70, a
compensating control means 68, a recording control means 71, and a cutout
means 72. The calculating means 61 calculates a parameter Tp which
represents the added load on the engine 24, based on the detected value Qa
for intake air flow volume outputted from the air flowmeter 11 and the
detected value Ne for the engine RPM outputted from the crank angle sensor
21. The parameter Tp indicates a time band of the ontime for the fuel flow
volume control pulse for the electronically controlled gasoline injection
device (EGI). The calculating means 61 calculates Tp in accordance with
the equation:
Tp=KQa/Ne (where K is a constant)
When the calculating device 61 has calculated Tp in accordance with the
above equation, it outputs the value to the table look-up means 62.
The table look-up means 62 receives the calculated value Tp outputted from
the calculating means 61, the detected value Ne outputted from the crank
angle sensor 21, for obtaining a duty value from a table such as that
illustrated in FIG. 6, based on the values Tp and Ne, to drive the
solenoid valve 47. This table contains the duty values for the solenoid
valve 47 arranged as data to get the optimum supercharging pressure for
each operating point. The duty values for the solenoid valve 47,
corresponding to the optimum supercharging pressure at each engine
operating point, are obtained experimentally.
The adder 63 adds the duty value obtained for the optimum supercharging
pressure from the table look-up means 62 to the calculated value data
outputted from the calculating means 66 (which will be later described),
and controls the opening and closing of the solenoid valve 47 with the
duty value corresponding to the supercharging pressure value resulting
from this addition. The calculating means 61, the table look-up means 62,
and the adder 63 make up one part of the control unit 55, and with the
solenoid valve 47 and the engine 24 form the feed forward control system.
The target supercharging pressure setting means 64 sets the appropriate
upper limit P set for the supercharging pressure for the engine 24, and
outputs this set value P set to the subtractor 65. The subtractor 65
accepts the target supercharging pressure value P set, and calculates the
difference .DELTA.P between the value P set and the detected value P2
outputted from the supercharging pressure sensor which is mounted in the
engine 24, and outputs this value to the calculating means 66. The
calculating means 66 accepts the value P and performs, for example,
proportional+integral+derivative action (subsequently referred to as PID
action), and outputs the compensating portion of the duty ratio, which
drives the solenoid valve 47 in accordance with the result of the PID
action, to the adder 63. The adder 63 accepts the calculated result from
the calculating device 66, and adds it to revise the drive duty value for
the solenoid valve 47 from the table look-up means 62, and controls the
opening and closing of the solenoid valve 47. The target supercharging
pressure setting means 64, the subtractor 65, and the calculating means 66
make up the feed forward control system, which is an open loop control
system provided in order to eliminate the drawback of lack of
correspondence to variation in the parts. This control system forms the
first feedback control system for compensating the supercharging pressure
control by the feed forward system at the region (A) in FIG. 6, that is,
the region of low rotation of the engine.
The target supercharging pressure setting means 69 sets the appropriate
upper limit value P set for the supercharging pressure in the engine 24,
and outputs this set value P set to the subtractor 70. The subtractor 70
accepts the appropriate upper limit value P set, calculates the difference
.DELTA.Pw between the value P set and the detected value P2 from the
supercharging pressure sensor 27, and outputs this value .DELTA.Pw to a
compensating control means 68. The compensating control means 68 accepts
the value .DELTA.Pw, which is outputted from the subtractor 65, and
applies, for example, a PID action. It then applies compensating control
to the drive duty value of the solenoid valve 51 so that supercharging
pressure P2 of the engine 24 is revised to the target value P set. A
compensated data value S900 which is the drive duty value for the solenoid
valve 51 output by the compensating control means 68, is provided to a
recording control means 71.
The recording control means 71 accepts the revised data value S900 provided
by the compensating control means 68 and records it. The recording control
means 71 maintains the previously recorded data until it is provided with
the newly revised data value S900 from the compensating control means 68.
The recording control means 71 accepts the detected value P2 from the
supercharging pressure sensor 27, and judges whether or not, for example,
a malfunction or abnormality such an abnormal broken line has been
produced in the supercharging pressure sensor 27. The recording control
means 71 controls the opening and closing of the solenoid valve 51 from
the duty value based on the compensated data value S900. When the
recording control means 71 judges that there has been a breakdown in the
supercharging pressure sensor 27, it outputs a signal S901 to cut off the
compensation of the supercharging pressure control being carried out by
the feed forward control system by means of the first feedback control
system. A cutoff means 72 which cuts off the calculating means 66 and the
adder 63 is then activated. After the cutoff means 72 is activated, the
recording control means 71 thereafter controls the opening and closing of
the solenoid valve 51 by using the data S900 obtained immediately before
recognition of an abnormality in the supercharging pressure sensor 27.
A pressure sensor which has characteristics such as those illustraed in
FIG. 11 is used as the supercharging pressure sensor 27. If the output
voltage of the supercharging pressure sensor 27 is in the region a10 to
b10 in FIG. 11, the RPM of the engine 24 is in the region (C) in FIG. 6.
The target supercharging pressure setting means 69, the subtractor 70, the
compensating control means 68, the recording control means 71, and the
solenoid valve 51, form the second feedback control system which revises
the supercharging pressure control of the feed forward control system for
the region (C) in FIG. 6, that is, for the high speed, high load operating
region of the engine.
These control actions will be explained with reference mainly to the
flowchart in FIG. 12.
When the value Qa detected at the air flowmeter 11, and the value Ne
detected by the crank angle sensor 21, are respectively inputted to the
control unit 55, the calculating unit 61 calculates Tp and outputs this
value to the table look-up device 62. The table look-up device 62
retrieves a table which is based on the input Tp and the value Ne detected
by the crank angle sensor 21. If the operating region obtained from the
detected value Ne and the calculated value Tp falls in the region (A) in
FIG. 6, the control for obtaining an appropriate supercharging pressure is
carried out by combining the control from the feed forward control system
and the control from the first feedback control system or revising the
control carried out by the feed forward control system. That is, in this
case, the opening and closing of the solenoid valve 47 is controlled from
the duty value corresponding to an appropriate supercharging pressure
which corresponds to the engine operating status. If, for example, the
drive duty value obtained at the solenoid valve 47 by the adder 63 is
100%, the solenoid valve 47 would be fully opened. This would cause the
positive pressure chamber 48 to assume atmospheric pressure, and the
movable tongue 35 would cause the cross-sectional area of the introduction
channel 59 to assume minimum status (i.e. completely closed status),
causing the supercharging pressure to increase. Furthermore, in the region
(A) of FIG. 6, since the cross-sectional area of the introduction channel
59 is at its minimum, the supercharging pressure P2 will not reach the set
value, for example, 350 mm Hg.
If the operating region obtained from the detected value Ne, which is
inputted to the table look-up means 62, and from the calculated value Tp
falls within the region (C) in FIG. 6, the control to obtain the
appropriate supercharging pressure is the control from the feed forward
control system combined with the control from the second feedback control
system for compensating the feed forward control. Accordingly, the table
look-up means 62 carries out table retrieval (Step 81) in order to perform
control in region (C) in FIG. 6. The feed forward control system acts to
obtain an appropriate supercharging pressure based on the data retrieved
by the table look-up means 62. The recording control means 71 outputs a
drive instruction signal to the solenoid valve 51 with a duty value based
on the revised data value S900 obtained from the compensating control
means 68. If, for example, a drive duty ratio of 0% is issued to the
solenoid valve 51 from the recording control means 71, the solenoid valve
51 assumes the fully closed position. For this reason, the pressure within
the diaphragm actuator rises, the actuating means 49 moves in the right
hand direction in FIG. 8, the waste gate valve 33 opens, and the
supercharging pressure drops. In this way, the recording control means 71
carries out control by varying the duty value, so that the supercharging
pressure P2 of the engine 24 is controlled to the appropriate
supercharging pressure P set W. The recording control means 71 can
determine if there are any abnormalities present by comparing the detected
value P2, from the supercharging pressure sensor 27, with data previously
stored in memory, such as the sensor characteristics shown in FIG. 11
(Step 83). When the recording control means 71 determines that there are
no abnormalities present in Step 83, it next proceeds to Step 85.
The subtractor 70 calculates the difference .DELTA.Pw between P2 and P set
W and outputs this value to the compensating control means 68 (Step 85).
The compensating control means 68 adds .DELTA.Pw to the supercharging
pressure data value retrieved by the table look-up control means 62, and
outputs this data to the recording control means 71 (Step 87). The
recording control means 71 multiplies the value P set W set by the target
supercharging pressure setting means 69 by a factor such as 3/4. In the
following step, the resulting value is added to the revised data value
from the compensating control means 68 multiplied by a factor of 1/4 (Step
89). The recording control means 71 sets the drive duty value for the
solenoid value 51, using the value obtained from Step 89, and outputs an
open/close control signal to the solenoid valve 51 (Step 93).
When the recording control means 71 determines in Step 83 that
abnormalities are present, it moves to Step 91. The recording control
means 71 subtracts a fixed value .DELTA.x from the revised data value S900
obtained from the compensating control means 68 immediately before an
abnormality was discovered in the supercharging pressure sensor 27, and
outputs a open signal S901 to the cutoff means 72 (Step 91), then proceeds
to Step 93. The fixed value .DELTA.x is subtracted from the revised data
value S900 in Step 91 in consideration of the safety of the engine 24.
Although the above explanation was made with reference to one embodiment of
the present invention, the present invention is not limited to this
embodiment only. For example, a step motor may be used in place of the
variable geometry means 42. In addition, the method of controlling the
supercharging pressure is not limited to that method described in the flow
sheet of FIG. 12.
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