DE10351685A1 - Operating process for internal combustion engine involves altering through flow cross section, recording reaction of lambda regulating circuit, and assessing reaction - Google Patents

Abstract

The internal combustion engine operating process uses a control apparatus (56) to control the engine (10). It has a lambda regulating circuit, tank venting system and low pressure damper (30) in a low pressure circuit for a high-pressure pump (22) the damper is connected to the tank venting system and to a control cross section in the hydraulic connection (39, 40). The through flow cross section is altered, the reaction of the lambda regulating circuit is recorded, and the reaction is assessed for a check on the functional capability of the damper.

Description

State of technology

The The invention relates to a method for operating an internal combustion engine with lambda control circuit, tank ventilation system and low pressure damper in a low-pressure circuit for a high-pressure pump of the internal combustion engine, with a hydraulic Connection of a partial volume of the low-pressure damper with the tank ventilation system and with a controllable arranged in the hydraulic connection Flow cross-section.

Furthermore the invention relates to a control device for operating an internal combustion engine, that performs such a procedure.

One such method and such control device are known per se.

Today's internal combustion engines, in particular internal combustion engines with direct injection of fuel into combustion chambers of the internal combustion engines are operated with high injection pressures in the order of magnitude of 10 ¹ to more than 10 ² bar. These injection pressures are provided by periodically operating high pressure pumps which are supplied with fuel from a tank via a low pressure circuit with a low pressure pump. Due to the retroactive effect of a periodically operating high-pressure pump, there are pressure pulsations in the low-pressure circuit, which can load components of the low-pressure circuit and cause unwanted noise.

By se known internal combustion engines have to damp the pulsations in the low pressure circuit a pressure damper on. This pressure damper has one or two membranes containing a fuel-filled low pressure part, the hydraulically connected to a low pressure side of the high pressure pump is from a filled with air Partial volume of the pressure damper separate. The partial volume is usually designed as spring chamber, in which an elastic element against against a fuel pressure exerts on the membrane directed counterforce.

Of the Spring chamber is for ventilation with running low-pressure pump, usually an electric fuel pump, connected to a leakage line of the high pressure pump to increase the pressure Fuel vapors avoid that diffuse through the membrane (s). at switched Niederduckpumpe is the vent line of the spring chamber the pump by a switching valve from the leakage line of the high-pressure pump separated and with a tank vent line connected. Modern internal combustion engines have such tank vent lines on to fuel vapors from the tank to the internal combustion engine, so that the vapors do not unburned can get into the environment.

By avoids the connection of the spring chamber with the tank vent line, that the pressure damper by cooling and by the associated condensation with fuel fills and after a restart of the internal combustion engine is not functional.

Now tear one or both membranes, liquid fuel penetrates into the spring chamber and is, with the low pressure pump, over the Spring chamber vent line which now opens into the leakage line of the high-pressure pump, in the tank returned. Therefore When the low-pressure pump is running, no liquid fuel can escape to the outside or in the normally fuel vapor leading tank vent line reach.

Becomes the engine and thus the low pressure pump switched off and the changeover valve switched, then the fuel heats up in the then still warm spring air vent line on and evaporates in part. He enlarges it its volume by about a factor of 1000 and still drives liquid fuel from the spring ventilation duct in the tank ventilation line, which is supposed to transport only fuel vapor. The liquid fuel can be in front of a tank vent valve, which is to control the fuel vapor supply to the engine, collect. At an opening Driving the tank ventilation valve after a restart can then so much liquid fuel through the tank vent line get to the internal combustion engine that this because of a mixture superfatting emanates. Even if the internal combustion engine does not go out, it can to soot formation and come to a lubricating oil dilution, the wear of the Internal combustion engine promotes and in extreme cases can lead to engine damage.

In front In this background, the object of the invention in the specification a method and a control device for operating an internal combustion engine, with which these consequences can be avoided.

These The object is achieved by a method of the type mentioned by the following steps: Change the flow cross-section, detecting a reaction of the Lambda control loop, and evaluating the reaction for an exam the functionality of the pressure damper.

Further This object is achieved by a control unit of the type mentioned solved, which controls such a process.

Advantages of invention

By these features can be detected a defective pressure damper and at taken into account the control of the internal combustion engine and / or the driver are displayed and / or an error message in a fault memory of the controller for later evaluation be stored in a workshop. The consideration at the other Operation of the internal combustion engine, for example, in a limitation or a ban on openings of the tank ventilation valve consist.

It it is preferred that the method further comprises a step of opening Activation of the tank ventilation valve outside a normal tank ventilation function performs.

These Design allows a control of the tank ventilation valve with a for a detection of a defective pressure damper suitable control pattern.

Further it is preferred that the step of the opening control before a Start the normal tank ventilation function carried out becomes.

By this embodiment is achieved that a review of the pressure damper with a suitable drive pattern for the tank vent valve maybe one before full opening of the tank ventilation valve as part of the normal tank ventilation function he follows. This reduces the undesirable consequences of a defective pressure damper.

Prefers is also that the tank vent valve just so far and so long opening is controlled, that the internal combustion engine, even with a defective pressure damper not emanates.

These Design prevents going out of the engine at defective pressure damper and increased thus the operational safety of the internal combustion engine.

Further it is preferred that the pressure damper then as functional is judged when the reaction of the Lambda control loop below of a predetermined threshold after the driving pattern for the Tank ventilation valve for the detection of the pressure damper state was passed through.

These Design allows reliable detection of a non-defective Pressure damper. A That is, above-threshold reaction provides a kind of a necessary, but not a sufficient condition for recognition a defective pressure damper because a big one Lambda reaction also from a large, regular fuel vapor stream the tank ventilation system could be caused. To distinguish a defective pressure damper from such a regular effect would be more Steps necessary (see below), their processing in the determination a comparatively small response of the lambda control loop is eliminated can. This allows the operation of the internal combustion engine with proper pressure damper without further diagnostic steps are optimized.

A Another preferred embodiment is characterized in that when the response of the lambda control loop is above a predetermined one Threshold, further steps are taken to distinguish whether the reaction of the Lambda control circuit from a normal function of the tank ventilation system or caused by a malfunction of the pressure damper.

Also Here is the advantage in that such further steps only then done Need to become, if a reasonable one There is a suspicion of a malfunction of the pressure damper.

Prefers is also that the normal function of the tank ventilation system in a further step at least reduced.

By This refinement will achieve that impact defective pressure damper be limited to uncritical orders of magnitude in any case can. The opening of the tank ventilation valve For example, in such a case, it may be limited to the extent that A departure of the engine is avoided in any case.

Further it is preferred that the following further steps are carried out: opening Driving the tank ventilation valve at a level above a predetermined threshold Air flow rate through the internal combustion engine, determining a measure of one Partial fuel flow to the internal combustion engine via the tank ventilation, Compare the measure for the Partial fuel flow with a predetermined threshold, and closing the Tank ventilation valve then when the measure of the partial fuel flow over the tank ventilation falls below the predetermined threshold.

By These features can affect the influence of a regular function of the tank venting on a subsequent further review of the Function of the pressure damper be minimized.

It is also preferred that the controllable flow cross-section after closing the Tank vent valve is opened.

By this embodiment, the pressure damper is then checked again, if the influence of the regular tank ventilation has fallen away.

A Another preferred embodiment is characterized in that a reaction of the lambda control to the opening of the flow cross section as a sufficient condition for a decision over the functionality of the pressure damper is evaluated. It is also preferable that one is above a predetermined one Threshold lying reaction of the lambda control as confirmation for a defective pressure damper is valued.

On this way you can influences a defective pressure damper distinguished with sufficient certainty from regular influences from the tank ventilation become.

With Reference to the controller it is preferred that the controller at least one of the above controls mentioned.

Further Advantages will be apparent from the description and the attached figures.

It it is understood that the above and the following yet to be explained features not only in the specified combination, but also in other combinations or alone, without to leave the scope of the present invention.

drawings

embodiments The invention are illustrated in the drawings and in the following description explained. Show it:

1 the technical environment of the invention;

2 schematically a lambda control loop;

3 Reactions of a manipulated variable of the lambda control loop in qualitative form,

4 A first embodiment of a method according to the invention,

5 a first supplement of the first embodiment to a second embodiment; and

6 a further supplement to a third embodiment.

description the embodiments

The 1 shows an internal combustion engine 10 , via a suction tube 12 Air is supplied. Via an injection valve arrangement 14 a metering of fuel to match the amount of air supplied. The fuel gets out of a tank 16 from a low pressure pump 18 sucked in and over a low pressure line 20 on a high pressure pump 22 delivered. The low pressure pump 18 typically produces a pressure of a few bar. The high pressure pump 22 , for example one from the combustion engine 10 driven piston pump, the fuel is under a pressure in the order of 10 ¹ to over 10 ² bar and supplies this under injection pressure fuel to a high-pressure fuel storage 24 from which the injection valve assembly 14 is supplied with the high-pressure fuel. Exceeds the pressure in the high-pressure fuel storage 24 due to a malfunction of the high-pressure pump 22 or, when the internal combustion engine is turned off, by fuel heating up a threshold value, this fuel is via a pressure relief valve 26 and a return 28 to the tank 16 recycled.

The high pressure pump 22 generates during operation pressure pulsations on the low pressure side, ie in the low pressure line 20 , These pressure pulsations are controlled by a pressure damper 30 attenuated. For this purpose, the pressure damper 30 a membrane 32 on, which is a first partial volume 34 of the pressure damper 30 from a second partial volume 36 separates. The first partial volume 34 is hydraulic with the low pressure line 20 connected and therefore filled with fuel. In the second subvolume 36 is an elastic element 38 , For example, a spring element arranged. Pressure pulsations in the low pressure line 20 direct the membrane 32 against the restoring force of the elastic element 38 and are muted in this way. Fuel vapors, that of the fuel-filled first partial volume 34 over the membrane 32 in the second subvolume 36 diffuse, be with the internal combustion engine 10 and stationary low-pressure pump 18 via a vent line 39 and a controllable passage cross section in a hydraulic connection 40 to a tank vent line 44 directed.

The controllable flow cross section is preferred as a changeover valve 42 realized, in the de-energized state with shut off internal combustion engine 10 the in the 1 drawn switching position occupies. With running low-pressure pump 18 becomes the switching valve 42 switched to its second, not shown switching position in which the vent line 39 with a leakage line 46 the high pressure pump 22 is connected. The tank vent line 44 is part of a tank ventilation system that has a gas space 47 of the tank 16 about one controllable tank vent valve 50 with the suction pipe 12 of the internal combustion engine 10 combines. As a rule, the tank ventilation system also has an activated carbon filter 48 up, over a fuel vapor line 52 with the gas space 47 of the tank 16 is connected and caches fuel vapor. With the internal combustion engine running 10 and opening controlled tank vent valve 50 the internal combustion engine sucks 10 Air over a ventilation opening 54 of the activated carbon filter 48 in the activated carbon filter 48 stored fuel vapor travels and via the intake manifold 12 combustion in the internal combustion engine 10 supplies.

The tank vent valve 50 will, as well as the switching valve 42 , from a control unit 56 This also controls the fuel metering to the internal combustion engine 10 via the injection valve arrangement 14 controls. In addition gets the control unit 56 Signals about operating parameters of the internal combustion engine 10 fed. These operating parameters include, for example, the signal of an air mass meter 58 passing the suction pipe 12 to the internal combustion engine 10 flowing air mass measures, and the signal of an exhaust gas sensor 60 which provides a signal about the composition of the burned fuel / air mixture. The fuel metering takes place in a control circuit also referred to as lambda control from the exhaust gas probe 60 as control sensor, control unit 56 as a regulator, injector arrangement 14 as an actuator and internal combustion engine 10 as a controlled system.

The basic function of such a control loop 64 is in the 2 shown. The control loop 64 has a block 66 which outputs a base value for an injection pulse width. This underlying is in a link 68 linked to a manipulated variable by a controller 70 is issued. The result of this linkage is the injection valve arrangement 14 driven. That from the control of the injection valve assembly 14 in the internal combustion engine 10 resulting fuel / air mixture ratio is above that in the exhaust pipe 62 arranged exhaust gas sensor 60 captured and in a link 72 compared with a target value. The comparison result, for example, the deviation of the exhaust gas sensor 60 supplied actual value of the setpoint SW, is as a control deviation to the controller 70 fed, which forms the control variable, usually a multiplicative-acting control factor.

In the 3 is qualitatively the mean value of the regulator 70 applied control value plotted over time. In the period from t_0 to t_1 the internal combustion engine works 10 initially with closed tank vent valve 50 and activated lambda control. When the control is steady, the mean value in the example of the 3 multiplicatively acting manipulated variable of the controller 70 only slightly off the neutral value of 1. At time t_1 then the tank ventilation valve 50 opening controlled. In this case, an opening control means any type of control, which is a flow through the tank vent valve 50 allowed. For clocked controllable tank ventilation valves 50 an opening control takes place, for example, by outputting a specific duty cycle. By varying the duty cycle can be the amount of the tank vent valve 50 controlling the flow of gas.

If on the left side of the tank vent valve 50 in the 1 Fuel or fuel vapor is present, the internal combustion engine 10 with the tank vent valve open 50 additional fuel is supplied, which is enrichment of the internal combustion engine 10 burned fuel / air mixture causes. The lambda control loop 64 responds with a reduction of the injection pulse widths for driving the injection valve assembly 14 that are in the 3 in a reduction of the control factor from the time t_1 map. With functional pressure damper 30 The fuel comes from the tank ventilation valve 50 to the internal combustion engine 10 is metered, exclusively from the gas space 47 of the tank 18 and the optionally present activated carbon filter 48 , Once the charcoal filter 48 by sufficiently long intake of fresh air through the ventilation opening 54 is regenerated, the fuel vapor stream from the tank vent via the tank vent valve 50 dry up and the control factor returns to its neutral value 1 back. This is in the 3 at time T_2 the case.

there It should be noted that in some systems when flushing the Activated carbon container over the Tank ventilation valve no permanent deviation of the manipulated variable of the lambda control loop from its neutral value occurs. This is done by an adaptation method that's the fault the tank ventilation For example, by averaging the control value learns and in an additional Correction intervention takes over. The additional Correction intervention reduces the over Injectors metered amount of fuel to the fuel flow through the tank vent valve to compensate. Will continue with regenerated activated carbon filter flushed with air, flows additional, lean-acting air to the combustion engine.

Such an adaptation is deactivated for diagnosis. According to the invention, the behavior of the lambda control loop described in connection with the tank ventilation 64 also for the diagnosis of the pressure damper 30 exploited. As already mentioned, it can damage the membrane 32 happen that fuel from the Low-pressure line 20 in the second subvolume 36 of the pressure damper 30 arrives. When the engine is running, this is not a problem because of this fuel through the vent line 39 and the switching valve 42 into the leakage line 46 the high pressure pump 22 and with it to the tank 18 is returned. With the internal combustion engine switched off 10 and stationary low-pressure pump 18 takes the switching valve 42 however in the 1 shown switching position in which a connection of the second sub-volume 36 over the hydraulic connection 40 to the tank ventilation line 44 consists.

Because the wires 39 . 40 and 44 From the previous operation of the internal combustion engine are usually still warm, evaporates a part of the second part volume 36 with defective membrane 32 existing fuel and drives liquid fuel from the second sub-volume 36 and the line 39 in the tank vent line 44 in front of the tank vent valve 50 , Because the tank vent line 44 and the tank vent valve 50 are designed for controlling vaporous fuel, it may occur in the presence of liquid fuel in front of the tank ventilation valve 50 and then opening the tank vent valve 50 after a restart of the internal combustion engine 10 come to the unwanted effects described above.

The following are with reference to the 4 to 6 Embodiments of inventive method explained. The flowchart follows 4 an embodiment of a method according to the invention in its most elementary form. The step 74 in the 4 corresponds to a main program for controlling the internal combustion engine 10 as it is in the control unit 56 For example, to control the fuel metering via the injection valve assembly 14 without tank venting, ie with the tank venting valve closed 50 , is carried out. In one step 56 then the tank vent valve 50 opening controlled. The changeover valve 42 from the 1 is at this time in a normal position for operation with running internal combustion engine 10 , This normal position corresponds to that in the 1 Switching position, not shown, in which the vent line 39 of the second partial volume 36 on the leakage line 46 the high pressure pump 22 is turned on.

The first time opening the tank ventilation valve 50 in step 76 of the 4 This is done first so that there is a very low flow through the tank vent valve 50 established. This will prevent the presence of liquid fuel on the left side of the tank vent valve 50 so much fuel to the intake manifold 12 and thus to the internal combustion engine 10 that it may die or may result in oil thinning if it occurs repeatedly.

By limiting the normal tank ventilation function is achieved that with a defective pressure damper 30 and resulting liquid fuel before the tank vent valve 50 Fuel in excess over the tank vent line 40 and the suction tube 12 to the internal combustion engine 10 arrives.

Then in one step 78 the flow area in the hydraulic connection 39 . 40 of the second partial volume 36 of the accumulator 30 with the tank vent line 44 changed. In the in the 1 shown system is the switching valve 42 in step 80 controlled in the drawn switching position and then takes place in the step 82 an evaluation of a reaction of the lambda control instead. In principle, in this procedure, the order of the steps 76 and 78 also be turned around. However, it is preferred that the opening of the tank venting valve before changing the flow cross-section, ie before switching the switching valve 42 in the in the 1 drawn position is performed. In this case, a clear reaction of the lambda control can in all probability be attributed to the fact that undesired additional fuel via a defective membrane 32 and the wires 39 . 40 in the tank vent line 44 arrives.

Alternatively, it is preferable that the internal combustion engine 10 after a standstill first in the step 74 is operated with a main program for engine control without tank ventilation and that the change of the flow cross section by switching the valve 42 with the start of the internal combustion engine 10 he follows. The at standstill of the internal combustion engine 10 in the drawn switching position of the switching valve 42 in the 1 existing connection of the second sub-volume 36 with the tank vent line 44 is thus initially interrupted and during operation of the internal combustion engine 10 over the defective membrane 32 in the second subvolume 36 getting fuel is through the vent line 39 and the switching valve 42 into the leakage line 46 the high pressure pump 22 guided. With defective pressure damper 30 has in the previous shutdown phase liquid fuel in the tank vent line 44 in front of the tank ventilation valve 50 accumulated. Will then the tank ventilation valve 50 after the restart of the internal combustion engine 10 triggered opening, it may come to a reaction of the lambda control, which again in the step 80 captured and in step 82 is evaluated.

In the 5 is an embodiment of the step 82 in the form of a sequence of steps 84 to 88 respectively. 84 to 90 specified. This is done in one step 84 First, the reaction of the lambda control on the opening of the tank vent valve 50 compared with a threshold. This threshold may be, for example, that in the 3 act with the letter S threshold value for a control factor or average control factor of the lambda control. If the control factor remains above the threshold value S, this corresponds to a comparatively small reaction of the lambda control to an opening triggering tank venting valve 50 , Such a reaction will only occur if there is no liquid fuel in front of the tank vent valve 50 is available. Such behavior therefore characterizes a functioning pressure damper 30 with functional membrane 32 that does not contain liquid fuel in the tank vent line 44 reach. In this case, the step becomes 84 in the step 90 branches, in which the proper functioning of the pressure damper 30 determined and, for example, in a memory of the control unit 56 is registered.

If the threshold S in the 3 however, this is equivalent to a large reaction of the lambda control, as it alternatively by a high loading of the activated carbon filter 48 with fuel or a defective pressure damper 30 can be caused. In this case, the step becomes 84 in one step 90 branches, by further steps to distinguish the two possible causes for the large response of the lambda control requested or performed.

With proper function, first in the step 86 branched and in step 88 again branched to the main program for engine control with normal control of the tank ventilation function.

6 shows a sequence of further steps, as in step 90 of the 5 be requested or performed. If in the 5 the step 90 has been achieved, this can be considered a suspicion of a defective pressure damper 30 be interpreted as a strong reaction of the lambda control on a first-time opening of the tank vent valve 50 after a restart of the internal combustion engine 10 it is a necessary condition, if there is a malfunction of the pressure damper 30 is satisfied. Because of this suspicion is in one step 92 initially reduced the extent of normal tank ventilation. This means that the flow through the tank vent valve 50 for the normal tank ventilation function in the further operation of the internal combustion engine 10 initially limited.

In one step 94 is then checked if the air flow through the internal combustion engine 10 exceeds a predetermined threshold. In addition the signal of the mass air flow sensor becomes 58 evaluated. If the air mass flow rate is sufficiently high, ie if the above threshold value is exceeded, the tank venting valve will be activated 50 Carefully open to fuel, located on the left side of the tank vent valve 50 has accumulated, to a sufficiently slow extent to the internal combustion engine 10 to suck. In this case, a sufficiently slow level is characterized by the fact that the tank venting line 44 to the intake manifold 12 reaching amount of fuel from the internal combustion engine 12 still within the permissible manipulated variable fluctuation of the lambda control loop 64 from the combustion engine 10 is processed.

The control loop 64 is then, for example, in the 3 show behavior shown between times t_1 and t_2. First, the control factor or the averaged control factor will decrease and then, when the fuel delivery from the tank ventilation system dries up, return to its normal value near 1, as shown in FIG 3 happened at time t_2. This behavior is in the embodiment of the 6 through the step 98 registered by, for example, the control factor of the lambda control loop is observed. Once it has risen to its neutral value after an initial fall, it can be assumed that on the left side of the tank vent valve 50 neither large amounts of fuel vapor in the activated carbon filter 48 even larger amounts of liquid fuel in the hydraulic connection 40 available.

In this case, with the step 100 the tank vent valve 50 initially closed again. Subsequently, in the step 102 a switching of the switching valve 42 in the in the 1 illustrated switching position in which the second sub-volume 36 of the pressure damper 30 hydraulically with the tank vent line 44 connected is. With defective membrane 32 of the pressure damper 30 can in this switching state of the switching valve 42 be expected to use fuel from the low pressure pump 18 with some bar through the low pressure line 20 to the high pressure pump 22 through the fuel-filled first partial volume 34 and a defective membrane 32 of the pressure damper 30 in the second subvolume 36 of the pressure damper 30 arrives. From there, the liquid fuel through the vent line 39 , the change-over valve 42 and the hydraulic connection 40 in the tank vent line 44 arrive and over the open tank vent valve 50 and the suction tube 12 to the internal combustion engine 10 be sucked. In the internal combustion engine 10 occurs as a result of a strong Gemischanfettung, which is reflected in the lambda control in a strong, almost abrupt drop in the control factor. This is in the 3 shown from the time t_3. If the control factor passes through the threshold value S after the time t_3, this is confirmed as confirmation of the existing suspicion of a defective pressure damper 30 scored. The detection of the reaction of the lambda controller is shown in the flow chart of 6 through the step 104 represents.

The step 106 represents an evaluation of the reaction of the control loop 64 by comparing the control factor or averaged control factor with the threshold S. If the threshold is not undershot, the program branches out of the step 106 in the step 102 in which the pressure damper 30 is judged to be functional. In this case, a corresponding information in a memory of the control unit 56 and previous restrictions on the tank ventilation function are canceled. If the control factor or the averaged control factor falls below in the step 106 however, the threshold S, this is considered as confirmation of the existing suspicion of a defective pressure damper.

Claims (12)

Method for operating an internal combustion engine ( 10 ) with lambda control loop ( 64 ), Tank venting system and low-pressure damper ( 30 ) in a low pressure circuit for a high pressure pump ( 22 ) of the internal combustion engine ( 10 ), with a hydraulic connection ( 39 . 40 ) of a partial volume ( 36 ) of the low-pressure damper ( 30 ) with the tank ventilation system and with one in the hydraulic connection ( 39 . 40 ) arranged controllable flow cross-section, characterized by the steps: changing the flow cross-section, detecting a reaction of the Lambda control circuit ( 64 ), and evaluating the reaction for a test of the functioning of the pressure damper ( 30 ). Method according to Claim 1, characterized by a step of opening a tank-venting valve ( 50 ) outside of a normal tank ventilation function. Method according to claim 2, characterized in that that the step of the opening Control is performed before a start of the normal tank ventilation function. Method according to Claim 3, characterized in that the tank-venting valve ( 50 ) just so far and so long opening is controlled that the internal combustion engine ( 10 ) even with a defective pressure damper ( 30 ) does not go out. Method according to claim 4, characterized in that the pressure damper ( 30 ) is judged to be functional when the reaction of the lambda control loop ( 64 ) is below a predetermined threshold. Method according to at least one of Claims 2 to 5, characterized in that when the reaction of the lambda control loop ( 64 ) is above a predetermined threshold, further steps are performed to distinguish whether the response of the lambda control loop ( 64 ) of a normal function of the tank ventilation system or of a malfunction of the pressure damper ( 30 ) is caused. Method according to Claim 6, characterized that the normal function of the tank ventilation system in another Step is at least reduced. Method according to Claim 6 or 7, characterized by the following further steps: opening of the tank venting valve at an air flow rate above a predetermined threshold value by the internal combustion engine ( 10 ), Determining a measure of a partial fuel flow to the internal combustion engine ( 10 ), which is via the tank venting, comparing the measure of the partial fuel flow with a predetermined threshold, and closing the tank venting valve ( 50 ), when the measure of the partial fuel flow over the tank venting falls below the predetermined threshold value. A method according to claim 8, characterized in that the controllable flow cross-section after closing the tank venting valve ( 50 ) is opened. Method according to Claim 9, characterized in that a reaction of the lambda control loop ( 64 ) on the opening of the flow cross section as a sufficient condition for a decision on the functioning of the pressure damper ( 30 ) is evaluated. A method according to claim 10, characterized in that a lying above a predetermined threshold value of the reaction of the Lambda ( 64 ) as confirmation of a defective pressure damper ( 30 ). Control unit ( 56 ) for operating an internal combustion engine ( 10 ) with lambda control loop ( 64 ), Tank venting system and low-pressure damper ( 30 ) in a low pressure circuit for a high pressure pump ( 22 ) of the internal combustion engine ( 10 ), with a hydraulic connection ( 39 . 40 ) of a partial volume ( 36 ) of the low-pressure damper ( 30 ) with the tank ventilation system and with one in the hydraulic connection ( 39 . 40 ) arranged controllable flow cross-section, characterized in that the control unit ( 56 ) at least one of the above controls mentioned method.