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Description  |
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BACKGROUND OF THE INVENTION
The invention relates to a control apparatus. In a known control apparatus
of this kind, in order to maintain a very precise ratio of air to fuel in
an auto-igniting internal combustion engine, the recirculated exhaust gas
quantity is controlled in a very expensive manner in that the recirculated
exhaust gas quantity, after precise apportionment of the air quantity in
relationship to the injected fuel quantity, comprises the remnant charge
of the combustion chambers of the engine.
An exhaust gas recirculation valve control apparatus is also known in which
the control pressure for the pneumatic adjustment device of the exhaust
gas recirculation valve is a mixture of the pressure prevailing in the
Venturi restriction of a carburetor and the pressure prevailing downstream
of the throttle valve of the carburetor. This apparatus thus makes use of
a known carburetor and is thus restricted to use in externally ignited
internal combustion engines. The control pressure can be modified by means
of throttles in the lines leading off from the pressure withdrawal points
in such a manner that the recirculated quantity of exhaust gas corresponds
approximately to particular requirements of the engine at various
operational points.
Another new apparatus for setting a desired exhaust gas recirculation rate
in accordance with the air quantity induced by the carburetor has a
slit-like cross section in the pivoting range of the throttle valve, which
cross section is also partially opened toward the intake manifold upstream
of the throttle valve when the throttle valve is closed. In accordance
with the extent to which the throttle valve is opened, a control pressure
is attained in the work chamber of a pneumatically functioning exhaust gas
recirculation valve which communicates with the slit-like cross section
which pressure varies in accordance with the extent of the throttle valve
opening and with the underpressure prevailing downstream of the throttle
valve. In order to obtain proper proportions of recirculated exhaust gas,
the cross section of the slit-like opening can be appropriately
controlled. This apparatus as well relates to exhaust gas recirculation in
externally ignited internal combustion engines and in particular engines
which are supplied with operational mixture by carburetors.
OBJECTS AND SUMMARY OF THE INVENTION
The apparatus according to the invention has the advantage over this prior
art in that the control of the exhaust gas recirculation quantity can be
performed in a very simple and inexpensive manner. Furthermore, favorable
opportunities for intervention to provide an additional control in
accordance with other operating parameters are created. The fuel quantity
control means combined therewith and arranged to function pneumatically
has the advantage that very satisfactory, smooth driving behavior can be
attained in a vehicle driven by such an engine. A further advantage
resides in the fact that the same guide value is used for the exhaust gas
recirculation rate and for the injection quantity.
The invention will be better understood as well as further objects and
advantages thereof become more apparent from the ensuing detailed
description of two preferred embodiments taken in conjunction with the
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic illustration of one embodiment of a fuel injection
system for an internal combustion engine according to the present
invention wherein exhaust gas recycling is utilized and including details
illustrated partly in cross section which in assembly serve to control the
exhaust gas recycling; and
FIG. 2 is a further schematic illustration of another embodiment of this
invention where dual pressure points straddle the throttle valve.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Shown in simplified form in the drawings are an internal combustion engine
1 with an intake manifold 2, through which air is delivered to the
internal combustion engine, and an exhaust manifold 3, from which an
exhaust gas recirculation line 4 leads to the intake manifold 2 of the
engine. This engine is an auto-igniting internal combustion engine, which
is supplied with fuel by a fuel injection pump 6, which may be, for
example, an in-line injection pump as shown here. The fuel injection pump
6 is driven in a conventional manner by the engine and has a control rod 8
as its quantity adjustment device.
In order to vary the fuel injection quantity, a pneumatic controller 9 is
provided in accordance with the invention, and associated therewith is a
throttle valve 10. This throttle valve 10 is disposed in the intake
manifold 2 and is arbitrarily actuatable via a rod 11, by means of a gas
pedal 12, for instance.
Downstream of the throttle valve 10, which is in its closed position, a
first pressure withdrawal point 14 is disposed in the intake manifold 2,
from which a control pressure line 15 leads to the work chamber 16 of a
first pneumatic adjustment device 17. The first pneumatic adjustment
device 17 is an essential part of the pneumatic controller 9 and comprises
a pressure box in which an adjustment diaphragm 19 is fixed, with the
diaphragm being arranged to separate the working chamber 16 from a
reference pressure chamber 20. The adjustment diaphragm 19 is stressed by
a control spring 21 fixed in the work chamber 16 and is coupled on the
other side with the control rod 8, which thus, with increasing pressure in
the work chamber 16, is adjustable against the force of the control spring
21 in the direction of a smaller fuel injection quantity.
In order to perform an additionally controlled adjustment of the control
rod 8, for example by means of an additional controller for the purpose of
final rpm control, two control springs may be provided instead of one
control spring 21; that is, as shown, there is a second compression spring
22, which directly engages the control rod 8 through an annular plate and
acts in the direction of full load. The coupling between control rod 8 and
adjustment diaphragm 19 then is effected, as shown, via an oblong slot 24,
which permits an adjustment of the control rod 8 in the direction of a
smaller quantity independently of the position of the adjustment diaphragm
19.
Thus, the pressure prevailing in the work chamber 16 is that which is
established downstream of the throttle valve. This pressure is dependent
on the rpm at a particular time of the engine and on the extent of opening
of the throttle valve by means of which the torque intention is
communicated.
The pressure is a standard for the quantity of fuel injected. The control
rod 8 is brought, at high suction pressure, into a position which
signifies a small fuel injection quantity, and vice versa. Adjustments can
be performed by means of the initial stressing and spring characteristics
of the control spring 21. Furthermore, opportunities for intervention are
provided in that the work chamber 16 can be connected with the surrounding
atmosphere via a connecting line 25, which may also, for example, branch
off from the control pressure line 15. To this end, a valve 26 is disposed
in the connecting line 25 which can be varied by means of a control
apparatus 27 in accordance with operating parameters of the engine. In
special cases it can be efficient to control the fuel quantity not in
accordance with the pressure difference between intake manifold pressure
and atmospheric pressure (i.e., the relative pressure), but rather as a
function of the absolute pressure. In these cases, the diaphragm 19 and
the reference pressure chamber 20 are replaced by an evacuated barometer
box.
From the first pressure withdrawal point 14 or from the control pressure
line 15, a pressure line 33 leads to the work chamber 35 of a second
pneumatic adjustment device 36. The arrangement of elements in this device
serves to actuate a valve closing member 37 in a flow-through cross
section 38 of the exhaust gas recirculation line 4. Similar to the first
pneumatic adjustment device, an adjustment diaphragm 39 is also provided
herein. The diaphragm 39 disposed within the housing of the pneumatic
adjustment device 36 encloses the work chamber 35 and in this work chamber
is provided a control spring 40 that is arranged to stress the adjustment
diaphragm. The adjustment diaphragm 39 is connected firmly to the valve
closing member 37. The other side of the adjustment diaphragm 39 is
exposed to atmospheric pressure, so that with increasing vacuum in the
work chamber 35, the diaphragm 39 urges the valve closing member 37
against the force of the control spring 40 in the opening direction.
Accordingly, the modes of operation of both adjustment devices are such
that they reinforce one another. While with increasing vacuum the fuel
injection quantity is reduced, the exhaust gas recirculation quantity is
simultaneously increased; that is, the fresh air component in the total
quantity induced is reduced. However, in an advantageous manner, this
precisely corresponds to requirements. Thus the fresh air quantity is
adapted to the fuel quantity which enters the combustion chambers, and at
various operational states of the engine the largest possible exhaust gas
quantity which can be permitted at a certain state is supplied on the
intake side.
FIG. 2 illustrates a second form of the embodiment of the invention for the
driving of the exhaust gas recirculation valve. In order to withdraw the
control pressure, the pressure line 33 may also communicate with a
separately provided pressure withdrawal point, which may be provided
either at the same level as the first pressure withdrawal point 14 or, in
order to adapt to the adjustment characteristic of the exhaust gas
recirculation valve or for the purpose of modifying the control pressure
in accordance with the position of the throttle valve, in a position in
the intake manifold which is closer to the pivoting range of the throttle
valve.
In the immediate vicinity of the throttle valve 10, shown in its closed
position, a second pressure withdrawal point 29 is provided on the intake
manifold 2, and downstream of the throttle valve on the intake manifold 2,
a third pressure withdrawal point 30 is provided. A first connecting line
31 leads off from the second pressure withdrawal point 29 which together
with a second connecting line 32 leading from the third pressure
withdrawal point 30 leads via a common pressure line 33 to the work
chamber 35 of a second pneumatic adjustment device 36. The second
pneumatic adjustment device 36 serves to actuate a valve closing member 37
in a flow-through cross section 38 of the exhaust gas recirculation line
4. Similar to the first pneumatic adjustment device, an adjustment
diaphragm 39 is also provided herein. The diaphragm 39 provided in the
housing of the pneumatic adjustment device 36 encloses the work chamber
35, and in this work chamber is disposed a control spring 40 that is
arranged to stress the adjustment diaphragm 39. The adjustment diaphragm
39 is thus firmly connected to the valve closing member 37. The other side
of the adjustment diaphragm 39 is exposed to atmospheric pressure, so that
the diaphragm, at increasing vacuum in the work chamber 35, urges the
valve closing member 37 in the opening direction against the force of the
control spring 40. The higher the vacuum is, the smaller the fuel metering
quantity becomes and thus the higher the exhaust gas recirculation
quantity becomes. The flow-through cross sections of at least one of the
connecting lines 31, 32 or the pressure line 33 can be calibrated by means
of a throttle. In an advantageous manner, a throttle 41 is disposed in the
first connecting line 31 and a throttle 42 is disposed in the second
connecting line 32. As a result of this throttle 41, the penetration
effect on the work chamber 35 of the pressure prevailing upstream of the
throttle valve 10 can be fixed in comparison with the penetration effect
thereon of the pressure prevailing downstream of the throttle valve 10.
Further opportunities for intervention are provided in that a valve 43 is
disposed in the pressure line 33 which is actuatable by a control
apparatus 44 in accordance with engine operating parameters. This valve
may also be disposed in one of the connecting lines 31 or 32.
An adjustment of the resulting control pressure in desired operational
ranges also can be attained by means of fixing the distances of the second
pressure withdrawal point 29 and that of the third pressure withdrawal
point 30 from the shaft 46 of the throttle valve 10. Furthermore, as is
known in carburetors, the pressure withdrawal points 29 and/or 30 can also
be distributed on the intake manifold circumference in the pivoting range
of the throttle valve, or may comprise a plurality of bores disposed in
this region and interconnected downstream with one another, in order to
exploit the geometric cross-sectional relationships in the case of an
opening throttle valve for the purpose of modification of the control
pressure. The pressure withdrawal points 29 and/or 30 can further be
controlled by means of a separate slide apparatus actuatable in common
with the throttle valve.
While in the exemplary embodiment of FIG. 2 a control pressure which is at
first substantially unmodified is thus at the disposal of the first
pneumatic adjustment device 17, the control pressure supplied to the
second pneumatic adjustment device 36 is very much dependent on the
particular setting of the throttle valve 10. In the closing position of
the throttle valve 10, the atmospheric pressure present at the second
pressure withdrawal point 29 predominates, so that the closing device 37
is substantially closed. Accordingly, during idling, little exhaust gas or
none at all is recirculated, which has the advantage that as a result of
an increased inert gas component the mixture appearing in the combustion
chamber of the engine does not rup up against the running limit or the
smoke limit; that is, it ignites only in delayed fashion or not at all.
The connecting line 31 and the connecting line 32 together, in this case,
have the sole function of a bypass line, wherein the quantity of bypass
air can be severely restricted by means of the throttles 41 and 42.
At medium load, the second pressure withdrawal point 29, because of the
throttle valve 10 which then is located in the partially open position,
also enters the effective region of the vacuum arising downstream from the
throttle valve 10. Depending on the extent to which the throttle valve is
opened, however, the atmospheric pressure present upstream of the throttle
valve 10 also has an influence, so that an average pressure is established
between the atmospheric pressure and the maximum suction pressure created.
The valve closing member 37 is accordingly also brought into a middle
position or a completely open position.
When the throttle valve 10 is fully open, the atmospheric pressure
prevailing upstream of the throttle valve can also penetrate into the
intake manifold portions located downstream of the throttle valve 10; that
is, the vacuum existing there previously is broken down. Now, this control
pressure located near the level of atmospheric pressure moves through the
pressure line 33 to the work chamber 35 and causes the valve closing
member 37, under the effect of the control spring 40, to move in the
closing direction. As a result of the initial stressing and the
characteristic of the control spring 40, in combination with the
previously listed possibilities for control pressure modification, the
exhaust gas recirculation rates at various operational states of the
engine may be optimally set in a simple and empirically ascertainable
manner.
Furthermore, in particular in the case of pneumatic controllers, the use of
pressure boxes as pneumatic adjustment devices permits compensation for
the influence of atmospheric pressure fluctuations on the mixture
composition appearing in the combustion chamber. The control apparatuses
27 and 44 may be of either mechanical or electronic type. With the control
apparatus 27, a maximum rpm to be maintained may also be ascertained, for
example, and regulated by means of closing the valve 26 when the rpm is
exceeded.
Furthermore, the pressure withdrawal for the first pneumatic adjustment
device 17 can be undertaken in accordance with the same principle and with
the same features of adjustment to the requirements of the engine
performance graph as is the case in known pneumatic controllers for fuel
injection pumps.
The foregoing relates to preferred exemplary embodiments of the invention,
it being understood that other embodiments and variants thereof are
possible within the spirit and scope of the invention, the latter being
defined by the appended claims.
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