Method for operating an internal combustion engine

The invention concerns a method of operating an internal-combustion engine, in particular a vehicle engine, in which air is fed to the combustion chambers through an induction manifold in which different induction-pipe lengths and/or volumes for resonance-mode or pulse-mode supercharging can be included, a switchover unit monitoring operation and initiating corrective measures in the event of an out-of-adjustment condition occurring.

BACKGROUND OF THE INVENTION 
The invention relates to a method for operating an internal combustion 
engine, especially in a motor vehicle. 
To enable efficient operation of internal combustion engines with as little 
pollution as possible, especially in motor vehicles, their control 
sophistication is being continuously increased. Thus, among other things, 
ignition control and fuel metering are becoming more and more complicated 
and the induction systems are being improved. It is known by DE-A-35 29 
388, for example, that to achieve good filling of the combustion chambers 
over the rpm range of the internal combustion engine, an induction 
manifold can be provided, in which--in the lower rpm and load range--long 
induction pipes (tuned induction pressure charging [resonance mode]) 
and--in the upper rpm range--short induction pipes take effect with an 
increased induction volume. Switching over in the form of throttle valves 
generally takes place depending on rpm and/or depending on induction pipe 
pressure. However, it is of decisive importance that these measures for 
improving the power and efficiency with favorable pollutant values 
interact without problems. 
In addition, by virtue of DE-A-39 04 412, an induction system is known with 
an air flow rate and--associated with it--fuel metering, on the one hand, 
which are controlled via a main throttle valve, and in the idle range are 
controlled via a bypass system which bypasses the main throttle valve. 
There is a memory which stores a numerous reference values of the pressure 
in the induction area which are derived in agreement with the engine rpm 
and the degree of opening of the throttle valve. Furthermore, there is a 
pressure transducer for sampling the pressure in the induction port, and 
an engine rpm sensor. A throttle valve position transducer samples the 
degree of opening of the throttle valve; another position transducer 
determines the degree of opening of the valve in the bypass. To monitor 
the systems, there are comparator means which compare the pressure value 
measured by the pressure transducer to a reference pressure derived from 
the memory and which deliver an error signal when the sampled pressure 
does not match the computed reference pressure. The error signal can thus 
lead, for example, to cutoff of fuel feed. 
SUMMARY OF THE INVENTION 
The object of the invention is to demonstrate a method of the generic type 
with which faults in the switching-over of the efficient induction areas 
can be recognized, and (if necessary) at least partially offset. 
According to the invention, it is therefore proposed that the switching 
function of the induction manifold be monitored, and, in case of 
maladjustment of the switching means, measures be initiated. In the 
simplest case these measures can be the triggering of a warning display 
which indicates to the operator that the internal combustion engine is not 
operating in a regular and proper manner. However the measures can 
preferably be the triggering of a error memory from which, for example, 
the type of problem and (if necessary) its duration can be retrieved in a 
service station by readout of the error memory. Alternatively or in 
addition to this, in the course of control of the internal combustion 
engine, for example by ignition intervention (shifting of the ignition 
point), or by intervention in the fuel metering or in the exhaust gas 
recirculation, measures can be initiated which compensate for the adverse 
effects on engine operation and/or exhaust gas emissions caused by 
maladjustment of the switching means. 
Electrical (potentiometer) or electromechanical position sensors which 
deliver a fault signal when the switching means are maladjusted can be 
placed on the switching means of the induction manifold. 
In a preferred embodiment, the combustion air flow rate or capacity of the 
internal combustion engine is used as the monitored parameter. In doing 
so, it must be taken into account that (for example) for fuel metering, 
the capacity of the internal combustion engine is computed anyway, so that 
the control sophistication necessary for this purpose is generally already 
present. 
By comparing these desired values--which are present in regular engine 
operation for the combustion flow rate or capacity--to the actual values, 
it can thus be determined at relatively low structural cost whether the 
switching means in the induction manifold are maladjusted, because then 
the actual values are below the desired values in any case. In doing so it 
can be advisable to take into account the absolute air pressure at the 
same time in order to preclude incorrect error messages during major air 
pressure fluctuations.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to the illustration of the present invention shown in FIGS. 1-3, 
FIG. 1 schematically shows the cylinder head 10 of a four cylinder 
reciprocating internal combustion engine with two exhaust valves 12 and 
two intake valves 14 per cylinder. The intake valves 14 control one 
induction port 16 per cylinder for which one induction manifold 18 is 
connected in the conventional manner to the induction ports 16. 
The induction manifold 18 is composed essentially of a first header 20, a 
second header 22, one short individual pipe 24 and one long individual 
pipe 26 per cylinder of the internal combustion engine. The individual 
pipes 24 empty into the header 22 in this case, while the individual pipes 
26 enter the header 20. The individual pipes 24, 26 combine into a common 
single pipe in front of the connection to the induction ports 16. The 
headers 20, 22 are interconnected via a connecting pipe 28. 
In the header 20, in its induction connection 32 is an arbitrarily 
controllable throttle valve 32 which is connected to the gas pedal of the 
motor vehicle (this is not shown) and which is used to control the 
performance of the internal combustion engine. 
In addition, in the short individual pipes 24 are butterfly valves 34 
which, in one of their positions (as shown), close the short individual 
pipes 24, while in the other end position completely open them. 
The butterfly valves 34 are actuated via a rod assembly 36, which is only 
partially shown, and an electric motor 38. The electric motor 38 has a 
two-armed lever 40 here; the actuating rod 36 engages one end of the two 
armed-lever, while the other end interacts with two position sensors 42, 
44. 
The electric motor 38 is triggered via a control device 46 which, among 
others, processes a rpm signal n of the internal combustion engine. 
Butterfly valves 34 are controlled in this process such that they are 
closed at a speed n&lt;3000 rpm, and at a switching speed ns of 3000/minute, 
they are swivelled into their open position by a corresponding signal to 
the electric motor 38. In the open or closed position of the butterfly 
valves 34 the free arm of lever 40 lies either against the position sensor 
42 or position sensor 44 so that the actual position of the butterfly 
valves 34 is indicated to the control device 46 via these sensors. 
If the butterfly valves are out of adjustment, i.e., for example when the 
electric motor 38 fails at a speed of &gt;3000/minute the butterfly valves 34 
are still closed, the problem is recognized via the control device 46, and 
an error message is output to a warning indication 48. Maladjustments can 
also be caused by only partially closed butterfly valves 34 (position 
sensors 42 and 44 not actuated). 
FIGS. 2 and 3 show another version in which the same parts are labeled with 
the same reference symbols. 
Instead of position sensors 42, 44, the position of the butterfly valves 34 
in the short individual pipes 24 is monitored depending on the capacity of 
the internal combustion engine. To do this there is a central computer 50 
(commercial name, for example, Motronic) which first calculates the 
ignition control and fuel metering to the injection valves 52 in the 
conventional manner. Among others, the following valves are sent to the 
central computer 50 in this process: 
P.sub.A =absolute air pressure 
P=pressure in the induction manifold 18 
m=air mass/amount (determined, for example, by means of a hot wire or a 
swing-out butterfly valve in the induction area) 
n=engine rpm 
.alpha.=load state (for example, by opening of throttle valve 32) 
T=temperature of the internal combustion engine. 
The capacity .lambda.a is computed using the following equation 
EQU .lambda.a=K.multidot.(m/n) 
in which K is a constant. .lambda.a is the basis of the calculation of the 
injection amount per work cycle of the internal combustion engine. 
In the induction manifold 18 which is shown with switching ns of the 
butterfly valves 34 at, for example, 3000/minute, in the full load 
position (throttle valve 30 fully opened) there is a capacity curve as 
shown in FIG. 3 in the solid lines. For regular switching of butterfly 
valves 34, the curve segment .lambda.aL (below the revolutions per minute 
ns) for ns changes into curve segment .lambda.aK, which is rising again, 
while when butterfly valves 34 are out of adjustment the underlying solid 
curve segments would be relevant. 
The curve behavior shown in FIG. 3 (for regular operation) is stored as a 
setpoint in the central computer 50 in an operating map in addition to the 
other curve behaviors for other load states and is continually compared to 
the actual values in engine operation. If the actual values do not reach a 
specific threshold (broken line), maladjustment of butterfly valves 34 is 
recognized, and an error message is delivered to a read-out error memory 
54. 
In addition, an auxiliary program with changed ignition and fuel metering 
measurement values is started in the central computer 50 with the error 
message. 
To prevent incorrect error reports during larger air pressure fluctuations, 
the absolute air pressure P.sup.a.sub.bs is also processed in the central 
computer at the same time, and the setpoint curve or threshold curve is 
shifted down in the operating map as the air pressure decreases (for 
example, as is indicated with the dot-dash line). However, the actual 
values can also be modified with an air pressure-dependent correction 
factor. 
Differing from the version described last, the flow rate of combustion air 
in the induction manifold 18 can also be used to assess the operation of 
butterfly valves 34, for example, by the corresponding pressure sensors or 
by butterfly valves which can be swung out by the air flow within the 
induction manifold 18.