Apparatus for controlling the ratio of air to fuel quantity in internal combustion engines

An apparatus is proposed which serves to control the ratio of air to fuel quantity of the operational mixture to be introduced into the combustion chambers of an internal combustion engine. The actual fuel quantity supplied via an injection apparatus (2) and the actual air quantity supplied via the intake manifold of the engine are measured and processed in a control apparatus (21) into a correction adjusting variable. The apparatus further functions with exhaust recirculation, with the aspirated fresh air quantity being dosed and the remnant filling of the gaseous filling introduced into the combustion chambers of the engine is replaced by recirculated exhaust gas. For the purpose of dosing the fresh air, a symmetrical throttle valve (14) is disposed in the intake manifold, whose position is transferred by means of pneumatic servomotor (23) to a second throttle device (12, 32), by means of which finally the quantity of the recirculated exhaust gas is determined.

BACKGROUND OF THE INVENTION 
The invention relates to an apparatus which serves to control the ratio of 
air to fuel quantity of the operational mixture to be introduced into the 
combustion chambers of an internal combustion engine. In a known apparatus 
of this kind, the quantity adjustment member of a fuel injection pump is 
actuated in accordance with the correction signal. Acting as a guide value 
for the control apparatus is an adjustable stop which limits the 
deflection of a baffle plate within a portion of an intake manifold which 
narrows opposite the flow direction in the manner of a funnel. The baffle 
plate, which is adjustable in this intake manifold portion by means of 
differential pressure, serves in combination with a constant restoring 
force as an air flow rate meter by means of which a fuel metering cross 
section is adjusted in accordance with the aspirated air quantity. The 
comparison of a set-point fuel quantity, corresponding to this fuel 
metering cross section, with the actual fuel quantity adjusted at the fuel 
injection pump by means of the quantity adjusting device takes place by 
hydraulic means, with the position of the quantity adjusting device being 
corrected in accordance with the result of comparison. Downstream from the 
baffle plate there is a throttle valve in the intake manifold which is 
adjustable by the pressure prevailing between the throttle valve and the 
baffle plate on the one side and the pressure prevailing upstream of the 
baffle plate on the other side, counter to the force of the restoring 
spring. When the throttle valve is opened, the entry of an exhaust 
recirculation line is kept closed by the valve with its portion located 
downstream of the throttle valve shaft. The prior art apparatus has the 
disadvantage that in order to adjust the load an intervention must be made 
at the air flow rate meter, and this intervention must be performed 
counter to the forces, which are not insignificant, acting on the baffle 
plate, especially in the case of reducing the load. Furthermore, a 
correction intervention is made on the fuel side where small errors have a 
very great effect on the resulting composition of the exhaust. 
OBJECT AND SUMMARY OF THE INVENTION 
The apparatus according to the invention which serves to control the ratio 
of air fuel quantity of the operational mixture to be introduced into the 
combustion chambers of an internal combustion engine has the advantage 
over the prior art that the adjustment of fresh air quantity can be 
accomplished virtually force-free with the aid of the throttle valve 
according to the invention. As a result of the features disclosed in the 
present invention, advantageous further embodiments of and improvements to 
the apparatus which serves to control the ratio of air fuel quantity of 
the operational mixture to be introduced into the combustion chambers of 
an internal combustion engine are possible. It is particularly 
advantageous that a valve closing member cooperating with the mouth of the 
exhaust recirculation line, acting as the valve seat, serves as the 
throttle device and has the form of a plate valve which is urged in the 
closing direction by the pressure in the exhaust recirculation line. 
As a result of this embodiment, there is achieved the advantage that the 
exhaust gas counter pressure may substantially be used as the sealing 
force acting on the valve closing member. The disposition of a symmetrical 
throttle valve upstream of the mouth of the exhaust recirculation line 
offers the advantage that first the throttle valve can be adjusted with a 
very small expenditure of force, so that a correction adjustment can also 
be made without a great amount of additional force, in the context of a 
closed control loop, and second that the throttle valve remains free of 
soiling which could limit its function. 
The invention will be better understood and further objects and advantages 
thereof will become more apparent from the ensuing detailed description of 
preferred embodiments taken in conjunction with the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the exemplary embodiment of FIG. 1, an internal combustion engine 1 is 
shown in simplified form, which is supplied with fuel by a fuel injection 
pump 2. The fuel injection pump 2 is supplied with fuel via a fuel supply 
line 3 from a fuel supply container 4, and the supplied fuel quantity, 
which then also proceeds to injection into the engine, is measured with 
the aid of a fuel quantity meter 5 disposed in the fuel supply line 3. In 
a conventional manner, the engine 1 has an air intake line 6 and an 
exhaust manifold 7. From the exhaust manifold 7, an exhaust recirculation 
line 9 leads to the air intake line 6 and in the example of FIG. 1 
protrudes freely into the air intake line 6. The mouth 10 of the exhaust 
recirculation line 9 is located in the pivotal range of a second throttle 
valve 12, by means of the throttle valve half of which located downstream 
of the throttle valve shaft 13 the mouth 10 of the exhaust recirculation 9 
is closed when this throttle valve half is opened relative to the air 
intake line cross section. Upstream of the second throttle valve 12 is a 
first, symmetrical throttle valve 14, which is actuatable via a rod 17. In 
FIG. 1 the rod 17 is connected with the gas pedal 18 by way of which the 
torque intention of the driver is indicated. Upstream of the first 
throttle valve 14 and the air intake line 6 is an air flow rate meter 20, 
which furnishes a control apparatus 21. The control apparatus 21 is 
furthermore connected with the fuel quantity meter 5 and compares both 
furnished values relative to a fuel-air mixture which is to be maintained. 
The control apparatus 21 may function electrically or hydraulically as 
well, which depends especially upon the type of quantity meter which is 
used. The acutal air quantity signal can be converted in the control 
device in a known manner into a set-point fuel quantity signal and 
compared with the acutal fuel quantity signal. The correction control 
signal resulting from the result of comparison is used, in the illustrated 
exemplary embodiment, for the purpose of correcting the quantity adjusting 
device (not further shown) of the fuel injection pump. This adjustment can 
also be effected either mechanically or electromechanically. 
The second throttle valve is actuated with the aid of a pneumatic 
servomotor 23, in the housing 24 of which an adjusting diaphragm 25 is 
fastened in a tight manner. The adjusting diaphragm 25 encloses on one 
side a first pressure chamber 26 in the housing 24 which communicates via 
a line 27 with the air intake line 6 upstream of the first throttle valve 
14, preferably with an area of the air intake line between the throttle 
valve 14 and the air flow rate meter 20. On the other said of the 
adjusting diaphragm 25, the diaphragm encloses a second pressure chamber 
28, in which a compression spring 29 is disposed which acts upon the 
adjusting diaphragm 25. A rod 30 is firmly connected to the adjusting 
diaphragm 25 and leads to the shaft 13 of the second throttle valve and 
adjusts it in such a manner that the shaft 13, solely under the influence 
of the compression spring 29, moves into a position in which the cross 
section of the air intake line 6 is opened and the mouth of the exhaust 
recirculation line 9 is closed. The second pressure chamber 28 
communicates with the air intake line 6 in the area between the first 
throttle valve 14 and the second throttle valve 12. 
A detailed description of the function of the apparatus is as follows: 
If the free flowthrough cross section of the air intake line 6 is enlarged 
via the first throttle valve 14 at this point, on the basis of an 
initially controlled status of the described system by means of actuation 
of the gas pedal 18, then the pressure in the second pressure chamber 28 
increases. Under the effect of the compression spring 29, the second 
throttle valve 12 also opens to some extent, until such time as the 
underpressure downstream of the second throttle valve 12 has reduced the 
pressure in the area between the first throttle valve 14 and the second 
throttle valve 12 to such a point that there is a balance of forces at the 
adjusting diaphragm 25. Simultaneously the second throttle valve 12 
throttles the quantity of the recirculated exhaust gas. When the first 
throttle valve is completely opened, the second throttle valve 12 is 
accordingly also completely opened and the mouth 10 of the exhaust 
recirculation line 9 is completely closed. 
Thus in an advantageous manner the exhaust recirculation at full load is 
entirely precluded in this apparatus, so that the internal combustion 
engine can produce its maximum power. The second throttle valve 12, as can 
be understood from the description, follows up the adjustment of the first 
throttle valve 14, whereupon by way of the spring characteristic of the 
compression spring 29 influence can still be exerted on the force 
transmission ratio. As in other known embodiments, in this type of engine 
control the fresh air quantity is varied and the remnant filling of the 
cylinders of the engine is accomplished with a quantity of exhaust gas. 
This is particularly true for the partial-load range. 
The measurement of the aspirated air already described and known from other 
embodiments and the measurement of the injected fuel are provided for the 
purpose of precise metering of the fuel with the aid of the control device 
21, a correction adjustment variable is created which represents depending 
on its size the deviation of the fuel-air ratio from a desired air number 
lambda. By means of this control variable, the fuel quantity is made to 
follow up the fresh air quantity adjusted at the throttle valve 14, by 
means of adjusting the quantity adjusting member of the fuel injection 
pump. 
Essential elements of the apparatus of FIG. 2 correspond to those of the 
apparatus shown in FIG. 1. Identical elements are given identical 
reference numerals. Deviating from the embodiment of FIG. 1, a plate valve 
32 is provided here instead of the second throttle valve 12 and its valve 
shaft 33 is firmly connected to the adjusting diaphragm 25. The exhaust 
recirculation line 9' discharges compactly into the air intake line 6 and 
at the mouth 10' has an annular cross-piece 34 acting as a valve seat, 
through the inner opening of which the valve shaft 33 protrudes into the 
exhaust recirculation line 9'. The valve plate 32 is thus located inside 
the exhaust recirculation line 9' and is there urged in the closing 
direction by the exhaust pressure prevailing there. The sealing force of 
the valve is substantially generated by means of the exhaust gas pressure 
acting on the valve surface. This embodiment has the advantage that the 
pneumatic servomotor 23 can be designed as less powerful and that to a 
greater extent than the preceding example the tightness of the closing at 
the mouth 10' of the exhaust recirculation line 9' is assured during 
operation. Disadvantages resulting from soiling of the valve closing 
element are to be expected much less frequently. 
FIG. 2 furthermore shows a different version of the fuel-air quantity 
control embodied in FIG. 1. Deviating therefrom, a correction signal is 
generated by the control device 21' which as in the preceding example 
receives control signals from the fuel meter 5 and the air flow rate meter 
20. The correction signal is furhished to a rotary magnet 36 which 
communicates with the first throttle valve 14'. The fuel injection 
quantity which is adjusted with the aid of a gas pedal 18', which is 
connected with an adjusting lever 37 for the quantity adjusting device of 
the fuel injection pump, acts as the guide variable. Then the supplied 
fresh air quantity is made to follow up the adjusted fuel quantity with 
the aid of the control apparatus 21'. As has been described in the 
preceding example, the plate valve 32 follows up the adjustment movement 
of the first throttle valve 14'. Naturally in this embodiment the control 
principle described in FIG. 1 can be used. Because the first throttle 
valve 14' is balanced as to force, a very small rotary magnet is 
sufficient for actuating the valve. Its position has the advantage that it 
is not exposed to soiling by exhaust gas and further can be located at a 
sufficient distance from points in the intake manifold where high 
temperatures develop. 
The foregoing relates to preferred 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.