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Description  |
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STATE OF THE ART
The invention is based on a device or a method for influencing control of
operational magnitudes of internal combustion engines having exhaust gas
recirculation.
In order to lower the impact on the environment due to the emission of
harmful substances from internal combustion engines, a number of measures
are available for reducing these harmful substance emissions. All these
measures are directed to obtain an optimum exhaust gas quality with
smallest changes of serviceability like, for example, fuel consumption,
drive capacity, drive characteristic and price. Apart from other methods,
in particular the exhaust gas return had been shown to be reliable for
reduding the harmful substance emission. Thereby, a portion of the exhaust
gases is returned from the exhaust to the intake, whereby the returned
amount of exhaust gas is regulated by pneumatic or electrically controlled
exhaust gas return valves. As a result of this measure the temperature and
the peak pressures are reduced in the combustion chamber and thereby a
reduced emission in particular of nitric oxides is achieved.
For example, for the fuel feeding in an internal combustion engine with
exhaust gas return a control device is known which is provided with an
intake or suction pressure measuring transmitter or sensor for measuring
the intake underpressure, a differential pressure-measuring transmitter or
sensor for measuring the pressure differential of the pressures in the
exhaust gas return conduit and in the intake pipe, a rotary speed meter
for picking up the rotary speed of the motor and a device for determining
the required amount of fuel which is fed to the motor in dependency on
these three measuring magnitudes.
It has been shown to be disadvantageous in this known control device that
in addition to the conventional load sensor, which is designed as a
pressure sensor, a further sensor must be used for picking up the amount
of the returned exhaust gas. This very expensive additional sensor, which
is designed as a differential pressure senor, requires additional
constructive adjustments on the exhaust gas return pipe, so that its
operability be assured.
ADVANTAGES OF THE INVENTION
In contrast thereto, the inventive device for the inventive method of
affecting operational magnitudes of internal combustion engines is
advantageous in that only a single pressure sensor is used. Such a
pressure sensor is anyway provided in pressure-rotary-speed-controlled
systems, so that the constructive and mechanical expenditures for
installing an exhaust gas return system are reduced to a minimum.
A further advantage when using only a single pressure sensor results from
the reduced susceptibility to breakdown of the system.
A very flexible data analysis is made possible by the use of only a single
pressure sensor in combination with a control device, wherein the
measuring values are further processed. Thereby an uncomplicated
adaptation, high reliability and accuracy is assured for different types
of internal combustion engines.
Further advantages of the invention are the result of the embodiments of
the invention stated in the subclaims. Due to the timely successive
measuring of at least two pressure values, in particular during switched
on and switched off exhaust gas return the further processing of the
measuring signals is simplified, on the one hand, and a control function
with respect to the operability of the pressure sensor is exerted, on the
other hand.
The averaging of a plurality of pairs of measuring values has to be
considered to be very advantageous, because in this manner possible errors
caused by dynamic processes can be eliminated. A further advantage is
obtained by introducing an adaptive adjustment of the control values
responsible for the amount of the return exhaust gas in dependency on
operational parameters of the engine. Thus, long time drifting due to
aging and contamination, for example, of the exhaust gas return valve, is
corrected.
These advantages and further special features or advantageous further
embodiments and improvements of the invention are disclosed in the claims
in conjunction with the specification of the exemplified embodiment and
the drawing.
DRAWING
One exemplified embodiment of the invention is illustrated in the drawing
and explained in more detail in the subsequent specification. The drawings
show in
FIG. 1 a simplified block diagram of the device in accordance with the
invention, and
FIG. 2 a flow diagram for explaining the method in accordance with the
invention.
DESCRIPTION OF THE EXEMPLIFIED EMBODIMENT
The exemplified embodiment relates to a device for influencing operating
magnitudes of internal combustion engines. In FIG. 1 an internal
combustion engine is desdignated with the reference numeral 10, whereby
the fresh air required for combusting the fuel is fed into the engine
through an inlet conduit 11. A throttle valve 12 is disposed in the inlet
conduit 11. A throttle valve sensor 13 picks up the full load or idling
position of the throttle valve and the output of sensor 13 is connected to
a signal input LL/VL of a control device 14. Further input magnitudes from
a pressure sensor 15, a rotary speed sensor 16, a temperature sensor 17
and a non-specified sensor 18 are fed to corresponding inputs n, p, T of
the control device 14. The non-specified sensor 18 may be a knock sensor,
an exhaust gas sensor, or the like. The air-fuel-mixture after combustion
in the internal combustion engine is discharged through an exhaust conduit
19 into outer atmosphere. An exhaust gas return conduit 20 branches from
exhaust conduit 19 and opens into the intake conduit 11 downstream of
throttle valve 12. A valve 21 is provided in the exhaust gas return
conduit 20 for controlling the amount of exhaust gas being returned from
the exhaust conduit 19 to the intake conduit 11.
From the magnitude of underpressure signal delivered by the pressure sensor
15 which is mounted in the intake conduit 11 downstream of the opening of
the exhaust gas return conduit 20, of speed proportional signals detected
by the rotary speed sensor 16, as well as from other correction magnitudes
indicated by arrows 22 and 23 or signals of detected by sensors 17, 18 the
control device 14 calculates or selects values for the amounts of fuel to
be supplied, which in the special case of an injection system is
determined as the opening times t.sub.i for the injection valves 24.
However, the invention is not limited to injection systems, be if intake
pipe injection or individual cylinder injection, but may also be used for
carburetor systems. In addition to other output magnitudes, such as for
example, the time of ignition 25 or control magnitudes 26 for an automatic
transmission, the control device 14 also determines values for the
position of the exhaust gas return valves 21 and outputs corresponding
signals.
Referring to the electronic fuel metering systems, which are known for a
long time; and which measure the amount of fuel to be allocated in
dependency on underpressure in the intake pipe and on rotary speed, in
furtherance only the modifications will be explained which in accordance
with the invention are designed such as to integrate the additional
function of the exhaust gas return feeding. Since the exhaust gas return
is completely shut off during many frequently occuring motor operating
conditions, for example, during idling, warming up and full load,
naturally no operational differences occur under these conditions with
respect to a system without an exhaust gas return. When the exhaust gas
return is switched off the intake pipe pressure is accordingly picked up
and the required amount of fuel is fed to the internal combustion engine
10 by means of the injection valve 24 in condependency on the momentary
rotary speed. After switching on the exhaust gas return, in particular
during the partial load of the engine, the intake pipe pressure is again
picked up and the difference with respect to the previous pressure value
without exhaust gas return is determined. The time difference between
picking up the two pressure values with and without the exhaust gas return
is minute and is only fractions of a second. The two pressure values or
the difference thereof are stored in a storage (RAM, EE Prom) and are
available for further processing. The difference between the two pressure
values not only determines the amount of the required exhaust gas, but
also the value of the fresh air as a difference between the total amount
of air fed into the internal combustion engine and the amount of returned
exhaust gas. By means of this difference value indicative of the amount of
fresh air, the amount of fuel to be supplied to the internal combustion
engine can be determined. By experimentally picking up the intake pipe
pressure with or without exhaust gas return by means of a single pressure
sensor one can determine the two unknowns, namely both fresh air and
exhaust gas. Moreover, it had been shown to be very advantageous to repeat
the aforementioned process several times and to store the obtained pairs
of pressure value or differences of the pressure value pairs for a
subsequent statistical averaging over a certain period of time depending
on operational parometers. This averaging is required primarily to correct
dynamic processes which may occur during the switching on of the exhaust
gas return. Moreover, it had been shown to be advantageous to store the
difference values of the pressure value pairs only in the case when a
stationary or substantially stationary operative condition of the engine
was present before and after the switching on of the exhaust gas return.
In addition, the determination of the actual value of the returned amount
of exhaust gas by the aforedescribed device, permits a transition from a
pure control of the exhaust gas return to a regulation of the exhaust gas
return. For this purpose adaptive methods are particularly useful,
wherein, by way of example, preliminary control values obtained in
dependency on operational parameters and stored in a storage readjust by a
superimposed regulation the long term drifting of the regulating path.
Such adaptive regulating methods are described in detail in German patent
application P No. 34 08 215.9 and will not be explained in all detail. In
particular the specific structure of the control device provided with a
microcomputer and peripheral units for performing such adaptive functions
is already known, so that a person skilled in the field of electronic
control and regulation of engines can realize such a regulating concept by
means of software without problems, once he has knowledge of the subject
invention.
In conjunction with the flow diagram of FIG. 2, a schematic plan for the
realization of the method in accordance with the invention is provided.
At the start of the program in block 40 the pressure difference Dp(AGR, p)
is set to zero. After determination of the condition of the motor, for
example, the rotary speed, the load or the different shift positions
(block (41), these data are stored in the microcomputer (block 42). After
picking up the next motor condition (block 43) the fresh air-pressure is
determined in block 44 in accordance with the equation stated in block 44.
The microcomputer calculates in block 45 as a function of the fresh air
pressure the amount of injection to be supplied and indicates the same as
a time duration, for example. The decision making block 46 examines
whether the exhaust gas return-valve is closed and if the answer is NO,
the program jumps back to block 42 and passes again through the
aforedescribed stages up to block 46. However, if the exhaust gas
return-valve is closed the pressure differential Dp will be zero (block
47) and in block 48 it is examined whether a stationary or quasi
stationary operating condition of the internal combustion engine is
present. If this is not the case the program again jumps back to block 42.
However, if a stationary or quasi stationary operating condition of the
internal combustion engine is present and if the exhaust gas return-valve
should be activated (block 49), then value of the instantaneous suction or
intake pipe-pressure p (block 50) is stored. If the exhaust gas
return-valve should not be actuated the program jumps back to block 42.
After storing the intake pipe-pressure (block 50), the rotary speed value
and values of different gear shift positions (block 51) and after
expiration of a programmable or adjustable delay time, which corresponds
approximately to the duration of the exhaust gas return-valve movement
(block52), the motor condition is again ascertained in accordance with
block 53. After an examination whether the operating parameters of the
internal combustion engine remained substantially uniform before or after
the actuation of the exhaust gas return-valve, that means, whether a
stationary or quasi stationary operation had been present (block 54), the
intake pipe pressure p is again stored in accordance with program block
55, provided that a stationary or quasi stationary operating condition had
been present. If no stationary or quasi stationary operating condition had
been present in the internal combustion engine the program jumps back from
block 54 to block 41 and the program starts again. According to block 56
the pressure difference in the intake pipe vacuum pressure with and
without exhaust gas return is ascertained and according to block 57 it is
stored after a plausibility test in dependency on the exhaust gas
return-valve movement and the intake pipe pressure. This plausibility test
is required to eliminate measuring errors caused by dynamic processes
which may have occurred during the switching on of the exhaust gas return.
This plausibility, in its simplest form consists in comparing the values
of the difference pressure with predetermined threshold values and
eliminating pressure values outside of a certain tolerance range from
further processing. Furthermore, it had been shown to be advantageous to
store the actual pressure difference values Dp in a performance graph or
field of characteristics by means of an adaptive regulating method. In
this context reference is made to German patent application P No. 34 08
215.9. Subsequently, a comparison of the instantaneous with the preceding
pressure differential Dp (EGR, p) is made followed by a statistic
averaging, for example. Thereafter, the program jumps back to block 42 and
the described program flow starts again from the beginning.
Since the drifting of the amount of the exhaust gas return is noticeable
only over a long period of time (contamination of the exhaust gas return
valve) and since the absolute the returned amount of exhaust gas up to 20%
to 30% still represents only a correcting magnitude, a very rapid
converging of such an adaptive process can be expected. In particular,
this is due to the fact that the switching on and switching off of the
exhaust gas return occurs very frequently during normal driving operation.
In general, it is advantageous in the inventive device or the inventive
method that the determination of load pick up is made possible by means of
a single, very simple and thereby costeffective sensor, and that the exact
amount of the returned exhaust gas can be determined, which has not always
been possible even with exhaust gas return valves which are equipped with
position sensors.
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