EP1292764B1 - Method for operating an internal combustion engine - Google Patents

Abstract

The invention relates to an internal combustion engine (1), especially for a motor vehicle. According to the invention, the fuel can be injected into a combustion chamber (4) in at least two operating modes, and an air/fuel mixture can flow via a tank ventilation valve (17) and can be supplied to the combustion chamber (4). A specific set fuel rate of the air/fuel mixture flowing via the tank ventilation valve (17) can be determined by a control device (18).

Description

State of the art

The invention relates to a method for operating an internal combustion engine, in particular a motor vehicle according to the preamble of claim 1. The invention also relates to a corresponding control device for such an internal combustion engine.

Such a method, such an internal combustion engine and such a control unit are, for example, from a so-called. Gasoline direct injection known. There, fuel is injected in a homogeneous operation during the intake phase or in a shift operation during the compression phase in the combustion chamber of the internal combustion engine. The homogeneous operation is preferably provided for the full-load operation of the internal combustion engine, while the stratified operation is suitable for idling and part-load operation. The shift operation is characterized inter alia by a motor operation with excess air, ie by a lean operation. Depending on operating variables of the internal combustion engine, switching is made between the aforementioned operating modes in the case of such a direct injection.

As operating modes of the internal combustion engine and the homogeneous operation with lambda equal to one, a lean homogeneous operation or homogeneous lean operation and possibly further operations of the internal combustion engine to be understood.

Furthermore, in such internal combustion engines is known to provide a tank ventilation, with which an air / fuel mixture from the fuel tank of the internal combustion engine can be performed via a tank vent valve to the combustion chamber of the internal combustion engine. The tank vent can be used to prevent unburned fuel from being released into the atmosphere.

The aforementioned tank ventilation must be incorporated into the entire control and / or regulation of the internal combustion engine. For this purpose, it is particularly necessary to control the tank vent valve such that on the one hand maximum possible ventilation of the fuel tank is achieved, but that on the other hand has no negative impact on the development of pollutants or desired by the driver of the motor vehicle torque.

Further prior art is known from EP 1 106 815 A1.

Purpose and advantages of the invention

The object of the invention is to provide a method for operating an internal combustion engine, with which an optimal tank ventilation can be achieved.

This object is achieved by a method according to claim 1. In a control device for an internal combustion engine the said object is achieved according to the invention accordingly.

With the specific target fuel rate of the air / fuel mixture flowing through the tank ventilation valve, a variable is made available with which the respective current lambda of the internal combustion engine can be taken into account in the control and / or regulation of the tank ventilation. The tank ventilation can thus be used not only at a lambda of 1, but at any air / fuel ratio of the internal combustion engine. Thus, the use of the tank ventilation is also possible in a direct-injection internal combustion engine in which Lambda can also be unequal to 1. On the basis of this specific target fuel rate then the tank ventilation, in particular the control of the tank ventilation valve is made.

The specific target fuel rate is controlled to a desired fuel fraction of the air / fuel mixture flowing through the tank vent valve. The said desired fuel fraction can be taken in particular from a map which is dependent on operating variables of the internal combustion engine. The specific target fuel rate may be weighted by a factor representing the load of an activated carbon filter contained in the fuel tank of the internal combustion engine.

The specific target fuel rate is generated by an integrator when the specific target fuel rate is compared with the desired fuel fraction and when the comparison result is returned to the integrator. This ultimately corrects the comparison result by the integrator. There is thus a regulation of specific target fuel rate on the target fuel fraction. As already mentioned, the specific target fuel rate and thus the entire regulation described above can be used for any air / fuel ratio of the internal combustion engine. The said regulation is thus not limited to a lambda equal to 1.

In an advantageous development of the invention, a desired flow factor of the air flowing through the tank venting air / fuel mixture is generated and damped. The nominal flow factor roughly represents the quotient of set flow and maximum flow. Ultimately, the tank venting valve can be controlled with this target flow factor. By damping the target flow factor, it is achieved that this factor can not change abruptly in the positive direction. This ensures that the tank vent valve can be opened only delayed. In this way, an overall accurate control and / or regulation of the internal combustion engine is ensured.

It is particularly advantageous if the desired flow factor is generated by a positive feedback integrator, and if the target flow factor is limited by a maximum flow factor. This maximum flow factor can be determined in particular from the specific target fuel rate. In this way it is achieved that the desired flow factor can only be controlled delayed, but can be abruptly deactivated. This prevents a sudden opening of the tank venting valve, but at the same time a sudden closing of the tank venting valve is possible.

In a further advantageous embodiment of Invention is generated and damped a desired mass flow through the tank vent valve. This in turn ensures that the desired mass flow can not change abruptly, at least in the positive direction. This positive jumps in the context of control and / or regulation of the entire internal combustion engine can be safely avoided.

It is particularly advantageous if the desired flow factor is converted into a maximum mass flow via the tank ventilation valve, if the desired mass flow is generated by a positive feedback integrator, and if the desired mass flow is limited by the maximum mass flow. This ensures on the one hand that the desired mass flow can be controlled only delayed. On the other hand, it is possible that the desired mass flow can be suddenly reduced and thus deactivated.

Of particular importance is the realization of the method according to the invention in the form of a computer program which is provided for the control unit of the internal combustion engine. The computer program can run on a computer of the control unit and is suitable for carrying out the method according to the invention. In this case, therefore, the invention is realized by the computer program, so that this computer program in the same way represents the invention as the method to whose execution the computer program is suitable. The computer program can be stored on a flash memory. As a computer, a microprocessor may be provided.

Other possible applications and advantages of the invention will become apparent from the following description of embodiments of the invention, in the figures the drawing are shown.

Embodiments of the invention

FIG. 1

shows a schematic block diagram of an embodiment of an internal combustion engine according to the invention, and

FIG. 2

shows a schematic block diagram of an embodiment of a method according to the invention for operating the internal combustion engine of Figure 1.

1 shows an internal combustion engine 1 of a motor vehicle is shown, in which a piston 2 in a cylinder 3 back and forth. The cylinder 3 is provided with a combustion chamber 4 which is delimited inter alia by the piston 2, an inlet valve 5 and an outlet valve 6. With the intake valve 5, an intake pipe 7 and with the exhaust valve 6, an exhaust pipe 8 is coupled.

In the region of the inlet valve 5 and the outlet valve 6, an injection valve 9 and a spark plug 10 protrude into the combustion chamber 4. Via the injection valve 9, fuel can be injected into the combustion chamber 4. With the spark plug 10, the fuel in the combustion chamber 4 can be ignited.

In the intake pipe 7, a rotatable throttle valve 11 is housed, via which the intake pipe 7 air can be supplied. The amount of air supplied depends on the Angular position of the throttle valve 11. In the exhaust pipe 8, a catalyst 12 is housed, which serves to purify the exhaust gases resulting from the combustion of the fuel.

From a charcoal filter 14 of a fuel tank 15, a tank vent line 16 leads to the intake pipe 7. In the tank vent line 16, a tank vent valve 17 is housed, with which the amount of the intake pipe 7 supplied air / fuel mixture is adjustable. The activated carbon filter 14, the tank vent line 16 and the tank vent valve 17 form a so-called tank vent.

The piston 2 is set by the combustion of the fuel in the combustion chamber 4 in a reciprocating motion, which is transmitted to a non-illustrated crankshaft and exerts on this torque.

A control unit 18 is acted upon by input signals 19, which represent operating variables of the internal combustion engine 1 measured by means of sensors. For example, the controller 18 is connected to an air mass sensor, a lambda sensor, a speed sensor, and the like. Furthermore, the controller 18 is connected to an accelerator pedal sensor which generates a signal indicative of the position of a driver-operable accelerator pedal and thus the requested torque. The control unit 18 generates output signals 20 with which the behavior of the internal combustion engine 1 can be influenced via actuators or actuators. For example, the controller 18 is connected to the injection valve 9, the spark plug 10 and the throttle valve 11 and the like, and generates the signals required for driving them.

Among other things, the controller 18 is provided to the Operating variables of the internal combustion engine 1 to control and / or to regulate. For example, the fuel mass injected by the injection valve 9 into the combustion chamber 4 is controlled and / or regulated by the control unit 18, in particular with regard to low fuel consumption and / or low pollutant development. For this purpose, the control unit 18 is provided with a microprocessor which has stored in a storage medium, in particular in a flash memory, a program which is adapted to perform said control and / or regulation.

The internal combustion engine 1 of Figure 1 can be operated in a plurality of modes. Thus, it is possible to operate the internal combustion engine 1 in a homogeneous operation, a stratified operation, a homogeneous lean operation, a stratified operation with homogeneous basic charge and the like.

In homogeneous operation, the fuel is injected during the intake phase of the injection valve 9 directly into the combustion chamber 4 of the internal combustion engine 1. The fuel is thereby largely swirled until ignition, so that a substantially homogeneous fuel / air mixture is formed in the combustion chamber 4. The torque to be generated is set essentially by the position of the throttle valve 11 by the control unit 18. In homogeneous operation, the operating variables of the internal combustion engine 1 are controlled and / or regulated such that lambda is equal to one. Homogenous operation is used in particular at full load.

The homogeneous lean operation largely corresponds to the homogeneous operation, but the lambda is set to a value greater than one.

In stratified operation, the fuel is injected during the compression phase of the injection valve 9 directly into the combustion chamber 4 of the internal combustion engine 1. Thus, in the ignition by the spark plug 10 no homogeneous mixture in the combustion chamber 4 is present, but a fuel stratification. The throttle valve 11 may, except for requirements e.g. the tank ventilation, fully open and the internal combustion engine 1 are operated so that throttled. The torque to be generated is largely set in shift operation via the fuel mass. With the shift operation, the internal combustion engine 1 can be operated in particular at idle and at partial load.

Between the above operating modes of the internal combustion engine 1 can be switched back and forth depending on operating variables of the internal combustion engine 1 and. Such switches are performed by the controller 18. For this purpose, an operating mode map is present in the control unit 18, in which an associated operating mode is stored for each operating point of the internal combustion engine 1.

The tank ventilation described above must be included in the entire control and / or regulation of the internal combustion engine 1. In this case, a plurality of parameters of the tank ventilation are to be considered, such as the loading of the activated carbon filter 14 with hydrocarbons, the position of the tank vent valve 17, the current operating state of the internal combustion engine 1, in particular the current operating mode of the same, requested by the driver and the internal combustion engine 1 to be delivered torque, and the like. For this inclusion of the tank ventilation, it is necessary ftevflos a target flow factor via the tank vent valve 17 and a target mass flow mestsoll on the tank vent valve 17 to determine.

A method is explained below with reference to FIG. 2, with which the stated desired flow factor ftevflos and the stated desired mass flow mstesoll can be determined.

For this purpose, an integrator 20 is provided in the figure 2, the output signal represents a specific target fuel rate fkastes the tank ventilation. This specific target fuel rate fkastes is multiplicatively linked to the loading ftead of the activated carbon filter 14. The result of this multiplication is compared with a desired fuel fraction fkates the tank ventilation. This desired fuel fraction fkates is determined by a block 22 and represents that desired fuel fraction to be supplied by the tank vent.

The result of the aforementioned comparison may possibly still be linked to a factor supplied by a block 23 for correction or adaptation purposes. The resulting signal is then supplied to the integrator 21 as an input signal. Ultimately, therefore, the integrator 21, the aforementioned comparison result in possibly weighted form.

From a block 24, a maximum value fkastex for the specific fuel rate of the tank ventilation is generated and forwarded to the integrator 21. By this maximum value fkastex the output signal of the integrator 21, so the specific target fuel rate fkastes the tank ventilation is limited.

The integrator 21 with the associated feedback loop represents a control loop with which the specific target fuel rate fkastes on the target fuel content fkates the tank ventilation is regulated. The integrator 21 of this control loop is limited to the maximum value fkastex the specific fuel rate for the tank ventilation.

The output signal of the aforementioned control circuit, ie the specific target fuel rate fkastes, is converted into a maximum flow factor ftevflox via the tank venting valve 17. For this purpose, first the specific target fuel rate fkastes is divided by the lambda desired value lamsbg. The resulting desired purge rate ftefsoll is multiplied by the total mass flow mssgin in the intake pipe 7. The resulting mass flow is finally divided by the mass flow msteo present with the tank vent valve 17 open. The result of these steps is the already mentioned maximum value for the flow factor ftevflox via the tank-venting valve 17.

The maximum value ftevflox for the flow factor via the tank venting valve 17 is supplied to an integrator 25 and limits its output signal. This output signal of the integrator 25 is the desired flow factor ftevflos via the tank ventilation valve 17. This desired flow factor ftevflos is fed back to the input of the integrator 25. In this feedback loop, multiplication by a correction or other factor generated by block 26 may occur. Furthermore, it is possible that in the feedback loop a further link with operating variables of the internal combustion engine takes place in a block 27.

The desired flow factor generated by the integrator 25 ftevflos is multiply linked to the mass flow msteo that is present when the tank vent valve 17 is open. The result of this multiplication represents a maximum mass flow mstemx via the tank venting valve 17. This maximum mass flow mstemx is fed to a further integrator 28 as the maximum value.

The integrator 28 generates as an output signal the desired mass flow mstesoll over the tank vent valve 17. This target mass flow mstesoll is fed back to the input of the integrator 28. In this case, it is possible that the desired mass flow is mulitplikativ mstesoll with a factor, this factor is generated by a block 29. Furthermore, it is possible for further operating variables of the internal combustion engine 1 to be taken into account in the feedback loop by means of a block 30.

The output signal of the integrator 28, that is, the desired mass flow mstesoll is limited to the maximum value mstemx the mass flow through the tank vent valve 17.

The two integrators 25 and 28 are positively fed back via their respective feedback loops. This means that both integrators 25, 28 always have the tendency to increase their output signal. The slope of such an increase of the respective output signal depends on the feedback loop, and there in particular on influencing the feedback signal. The said slope can thus be adjusted to desired values via the blocks 26, 27 and via the blocks 29, 30.

At the same time, both integrators 25, 28 are each limited by a maximum value. This means that Output of the two integrators 25, 28 on the one hand always increases, on the other hand, however, is always limited by the respective applied maximum value.

It follows that the two integrators 25, 28 together with their feedback loops act as attenuators. On the one hand, the output signals of the two integrators 25, 28 can change in the direction of larger values, wherein - as stated - the slope of this change can be adjusted, but on the other hand the output signals of these two integrators 25, 28 are limited by the respective maximum values, so that a reduction of the maximum values immediately and immediately also leads to a reduction of the respective output signal of the associated integrator 25, 28.

This means in other words that the output signals of the two integrators 25, 28 are provided with a limitation of the Aufsteuergeschwindigkeit in the control to larger values, in the Absteuerung towards smaller values, however, such a speed limit is not present, so that the Absteuerung undelayed be upheld.

As mentioned, the output signal of the integrator 25 is the desired flow factor ftevflos for the tank-venting valve 17. With this desired flow-rate factor ftevflox, the tank-venting valve 17 is ultimately activated. This means that the tank-venting valve 17 can not be opened abruptly, but that when the tank-venting valve 17 is opened towards a greater flow, the said speed limit is present. At the same time, however, it is possible to close the tank-venting valve 17 instantaneously and thus abruptly. As has been explained, attacks at one such closing of the tank vent valve 17 no speed limit.

As has already been explained, the output signal of the integrator 28 is the setpoint mass flow mstesoll via the tank venting valve 17. This setpoint mass flow mstesoll can not change so abruptly. Instead, the control of the desired mass flow mstesoll can only be done with the aforementioned speed limit. Conversely, it is possible, abzusteuern the desired mass flow mstesoll abruptly and thus without delay. Here no speed limit intervenes.

In summary, a regulation of the specific desired fuel rate is therefore performed by the first integrator 21. From the specific nominal fuel rate fkastes, a damped desired flow factor ftevflos is derived with the aid of the second integrator 25. From the desired flow factor ftevflos, a damped desired mass flow mtsoll is finally determined with the aid of the third integrator 28. This entire process is usable for any lambda. The air-fuel ratio is taken into account via the desired Lambda lamsbg in the described method.

Claims (11)

1. Method for operating an internal combustion engine (1), in particular of a motor vehicle, in which fuel is injected into a combustion chamber (4) in at least two operating modes, and in which an air/fuel mix flows via a tank venting valve (17) and is fed to the combustion chamber (4), characterized in that an integrator (21) generates an output signal which represents a specific set fuel rate (fkastes) of the air/fuel mix flowing via the tank venting valve (17), which set fuel rate takes account of the current lambda of the internal combustion engine (1), in that a set fuel content (fkates) of the air/fuel mix flowing via the tank venting valve (17) is determined, which set fuel content represents the desired fuel content which is to be delivered via the tank venting valve (17), in that the specific set fuel rate (fkastes) is compared with the set fuel content (fkates), in that the result of the comparison is fed to the integrator (21), and in that the specific set fuel rate (fkastes) is in this way adjusted to the set fuel content (fkates) of the air/fuel mix flowing via the tank venting valve (17).
2. Method according to Claim 1, characterized in that the specific set fuel rate (fkastes) is generated by an integrator (25), in that the specific set fuel rate (fkastes) is compared with the set fuel content (fkates), and in that the result of the comparison is fed back to the integrator (25).
3. Method according to one of the preceding claims, characterized in that the specific set fuel rate (fkastes) is limited to a maximum value (fkastex) for the specific fuel rate.
4. Method according to one of the preceding claims, characterized in that the specific set fuel rate (fkastes) is converted into a maximum through-flow factor (ftevflox) for the air/fuel mix flowing via the tank venting valve (17).
5. Method according to one of the preceding claims, characterized in that a set through-flow factor (ftevflos) for the air/fuel mix flowing via the tank venting valve (17) is generated and damped.
6. Method according to Claims 4 and 5, characterized in that the set through-flow factor (ftevflos) is generated by an integrator (25) with positive feedback, and in that the set through-flow factor (ftevflos) is limited by the maximum through-flow factor (ftevflox).
7. Method according to one of the preceding claims, characterized in that a set mass flow (mstesoll) across the tank venting valve (17) is generated and damped.
8. Method according to Claims 6 and 7, characterized in that the set through-flow factor (ftevflos) is converted into a maximum mass flow (mstemx) across the tank venting valve (17), in that the set mass flow (mstesoll) is generated by an integrator (28) with positive feedback, and in that the set mass flow (mstesoll) is limited by the maximum mass flow (mstemx).
9. Computer program, characterized in that it is programmed to apply the method according to one of Claims 1 to 8.
10. Computer program according to Claim 9, characterized in that it is stored on a memory, in particular on a flash memory.
11. Control unit (18) for an internal combustion engine (1), in particular of a motor vehicle, characterized in that it is designed to apply the method according to one of Claims 1 to 8.

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