DE102013202196A1 - Method of operating internal combustion engine involves closing outlet side of engine and adjusting opening of inlet side as compared with regular operation in operating mode in which engine is not supplied with fuel - Google Patents

Abstract

The outlet side of the internal combustion engine is closed and the opening of the inlet side as compared with a regular operation after is adjusted in an operating mode in which the engine is not supplied with fuel. The opening of the inlet side as compared with a regular operation is adjusted by the sucking in phase toward the shoving out phase of combustion engine operation. An independent claim is included for computer program for operating internal combustion engine.

Description

The present invention relates to a method for operating an internal combustion engine with an exhaust system downstream of the internal combustion engine, which has at least one catalyst device, and a computer program and a computer program product with program code for carrying out this method.

State of the art

For the aftertreatment of the exhaust gases of internal combustion engines, it is generally known, in particular in motor vehicles, that one or more catalysts are used in the exhaust gas system of the internal combustion engine, which reduce the concentration of the pollutants contained in the exhaust gas. For example, so-called three-way catalysts are used. In different modes of operation of the internal combustion engine, however, it may cause problems with the or the catalyst device (s). One such mode of operation is overrun operation. In order to reduce fuel consumption, the fuel supply to the engine is switched off in this mode, so there is no fuel injection and no combustion in the internal combustion engine, if this is compatible with any negative effects on emissions. However, when the fuel supply is switched off, the internal combustion engine nevertheless flows through air, that is to say in particular also with oxygen. The oxygen enters the downstream catalytic converter and is partially stored or enriched here. This means that in a subsequent normal combustion nitrogen oxides can not be reduced. To avoid this, a short-term fat operation of the internal combustion engine is usually performed after the overrun operation. In this case, a mixture is burned with excess fuel to achieve a so-called catalyst clearance. However, this is associated with a short-term increase in fuel consumption. Another problem with a coasting operation of the internal combustion engine is that due to the flow of the catalyst device with fresh air, a cooling of the catalyst occurs, which under certain circumstances falls below the temperature required for the operation of the catalyst, so that subsequently no optimal exhaust aftertreatment in the period after the resumption of regular operation is possible.

Similar problems occur in start / stop systems, in which the engine is switched off when the vehicle is stationary in order to achieve fuel savings. A renewed activation of the engine can be done in a comfortable manner, for example, by an actuation of the clutch by the driver. Corresponding problems also occur in vehicles with hybrid drives, in which internal combustion engines are combined with other drives, such as an electric motor. If the other drive, so for example the electric motor, is switched, the engine is turned off.

In all of these cases, after stopping the fuel supply to the internal combustion engine with a view to avoiding additional emissions after this phase, the internal combustion engine must be briefly operated with a rich fuel mixture to clear the oxygen enriched in the catalyst (s) during this phase , The present invention has for its object to avoid the conventionally required catalyst clearance and thus to reduce fuel consumption. In particular, a method is to be provided in which it is possible to dispense with enriching after a restart of the internal combustion engine, in particular in hybrid vehicles and / or in vehicles with start / stop systems and / or after overrun phases. Furthermore, with the present invention, a method is to be provided which can avoid cooling of the catalyst, in particular in overrun phases or during shutdown of the internal combustion engine in start / stop systems.

This object is achieved by a method for operating an internal combustion engine, as is apparent from the claim 1. Preferred embodiments of this method as well as a corresponding computer program and a computer program product result from the further claims.

Disclosure of the invention

Advantages of the invention

The inventive method is provided for operating an internal combustion engine, wherein the internal combustion engine has a downstream exhaust system. This exhaust system comprises at least one catalyst device, for example a conventional three-way catalyst. The internal combustion engine is equipped with at least one gas exchange device, via which the inlet side and the outlet side of the internal combustion engine is controlled. The internal combustion engine is, for example, a reciprocating internal combustion engine having one or more cylinders. On the inlet side of the cylinders, the gas supply is controlled by inlet valves, for example camshaft operated valves or electrohydraulic or electromagnetic valves. Similarly, the exhaust side of the cylinders is operated with exhaust valves. The gas exchange in the cylinders of the reciprocating internal combustion engine finds regular operation in a conventional manner instead. In this case, in a four-stroke cycle, there is an intake phase, a compression phase, an expansion phase and an extension phase. In the suction phase, the inlet side is opened and in the Ausschiebephase the outlet side is opened, which can lead to a short overlap of the valve opening times. The method according to the invention described below can also be carried out analogously in a two-stroke cycle. The prerequisite for carrying out the method according to the invention is that the valve control times are variable and that the exhaust valve or valves (e) are to be closed over a complete operating cycle. This is realized, for example, in engines with cylinder deactivation, wherein the cam is disengaged so that it can no longer come to a valve lift. The method thus requires a valve train variability. According to the invention, in an operating mode in which the internal combustion engine is not supplied with fuel (for example engine outlet), the exhaust side of the internal combustion engine is closed. Advantageously, at the same time the opening of the inlet side is adjusted in comparison with the regular operation to early.

By means of these measures according to the invention, it is achieved that in a mode of operation without fuel supply, that is to say in particular after switching off the internal combustion engine or in coasting mode, no fresh air mass flow is passed through the catalyst. The outflow of the exhaust gas from the combustion chamber into the exhaust tract is avoided. The fresh air mass flow introduced into the internal combustion engine or into the cylinders does not reach the exhaust gas side of the internal combustion engine and consequently also not the catalyst. As a result, an oxygen storage in the catalyst is avoided, so that subsequently no catalyst removal by operation with a rich fuel mixture is required. This is achieved by shutting off the exhaust valves during the fuel delivery mode. The entire charge change takes place solely by the advance adjustment with the intake valves, in particular by an extreme advance adjustment.

The adjustment of the opening of the inlet side to early takes place in particular from the intake phase in the direction of the Ausschiebephase the engine operation. For this purpose, for example, timing for the intake valves can be used as they are used in so-called scavenging. The scavenging refers to an operating mode of an internal combustion engine in which the opening times of intake and exhaust valves overlap greatly. This operation is conventionally performed at low speeds and high loads of a supercharged engine. As a result, an overflow of the fresh air is achieved in areas in which the instantaneous charge pressure is greater than the exhaust gas back pressure. Part of the sucked cold fresh air thus flushes the hot exhaust gas located in the cylinder into the exhaust manifold, whereby an internal cooling of the combustion chamber is achieved and the knocking behavior of the engine can be improved. According to the invention, therefore, similar timing for the intake valves as in scavenging can be used. However, according to the invention, unlike the scavenging, the exhaust valves are kept closed. The opening of the intake valves may, for example, at about 30 ° CA (crank angle) before the charge cycle OT (top dead center) take place. The adjustment to early can also be intensified. For example, the early adjustment can already take place at an opening time of 60-70 ° CA before change of charge TDC. Particularly preferred for the advance adjustment is a range between 30 ° CA, in particular 40 ° CA, and 70 ° CA before charge cycle TDC, these opening times each refer to a valve lift of 0.5 mm. Depending on the engine geometry, problems with the distance between the piston in the cylinder and the intake valves may occur when opening the inlet side very early. This should be taken into account in the interpretation of the method according to the invention.

In a particularly preferred manner, the adjustment of the opening of the inlet side takes place early such that it comes at the end of the Ausschiebephase the engine operation and at the beginning of the intake phase of the internal combustion engine operation to an overflow of gases from the internal combustion engine via the inlet side. The gases can thus escape in these phases through the intake valves in the intake manifold. The throttle action of the intake valves is very low in the air mass flows that are usually present in overrun mode or when stopping and starting the internal combustion engine in a hybrid drive or in a start / stop system.

In a preferred variant of the method according to the invention, the inlet side of the internal combustion engine is briefly opened during the discharge phase and reopened in the subsequent intake phase. However, this embodiment requires the possibility of multiple opening of the inlet valve (s). This mode of operation is carried out in particular during the run-out and / or the start-up of the internal combustion engine. Here, the charge cycle losses can be kept very low or completely avoided, without the risk that the intake valves and the pistons collide in the cylinders.

Preferably, the internal combustion engine during operation, in which the internal combustion engine is not supplied with fuel is up to an increased speed, such as an idle speed, dragged up. The increased speed is, in particular, a minimum speed at which the internal combustion engine can run. In extreme cases, this can also be the speed "0". The lugging can be done for example by means of an electric motor or by a clutch start. The particular advantage of this is that no residual gas is stored in the intake manifold of the internal combustion engine. The cylinder is completely decoupled from the exhaust system and a suckback of exhaust gas, which can lead to misfiring in extreme cases, is avoided. The electric machine required for this embodiment can be realized in a conventional vehicle, for example, by the starter, which can tow the engine to starting speed, for example, about 300 rpm. For example, in hybrid vehicles can be used for the towing the powerful electric motor of the hybrid drive.

The already mentioned advantages of the method according to the invention are particularly useful in motor vehicles, in which the overrun operation is carried out in the manner described. Furthermore, the method according to the invention can be used with particular advantage in motor vehicles with a start / stop system or in motor vehicles with hybrid drive. By using the method according to the invention during operation, in which the internal combustion engine is not supplied with fuel, the fuel consumption can be significantly reduced, since a subsequent catalyst clearing can be omitted by operation with a rich fuel mixture. Furthermore, a particular advantage of the method according to the invention is that a cooling of the catalyst or catalysts in coasting phases or otherwise shut off the fuel supply is reduced, since the exhaust line according to the invention is not flushed with cool fresh air. As a result, the required operating temperature of the catalyst or catalysts is maintained, so that in a subsequent regular operation of the internal combustion engine optimal exhaust gas aftertreatment is secured.

The invention further comprises a computer program which executes all the steps of the method described, when it is executed on a computing device or a control device, and a computer program product with program code, which is stored on a machine-readable carrier, for carrying out the described method. The implementation of the method according to the invention as a computer program has the advantage that this program can also be used without problems in existing motor vehicles in order to be able to use the advantages of the method in an operating mode of the internal combustion engine in which the fuel supply is switched off. Thus, a total of fuel savings can be achieved and optimal exhaust aftertreatment can be ensured.

Further features and advantages of the invention will become apparent from the following description of exemplary embodiments in conjunction with the drawings. In this case, the individual features can be implemented individually or in combination with each other.

Brief description of the drawings

In the drawings show:

1 graphical representation of the valve train characteristics in the context of the inventive method;

2 graphical representation of the fresh air mass flow in the exhaust system during shutdown and restart of an internal combustion engine;

3 graphical representation of the valve train and the cylinder pressure to illustrate the method according to the invention;

4 Graphical representation of the charge cycle losses in a restart of the engine and

5 graphical representation of the towing process of the internal combustion engine at different valve positions.

Description of exemplary embodiments

In 1 various valve characteristics are illustrated to illustrate the process of the invention. The illustrations in this and the following figures are based on a charge cycle simulation. On the X-axis in 1 is ° KW n. ZOT (ignition TDC, TDC = top dead center) plotted, which represents the time of the respective valve opening with respect to the phases or cycles of internal combustion engine operation. The dashed line 11 denotes the valve lift of the exhaust valve in a regular operation of the internal combustion engine. The opening of the exhaust valve takes place during normal operation during the exhaust phase. In the subsequent intake phase, the intake valve is opened and the exhaust valve is closed. Fresh air flows into the cylinder and the piston moves until bottom dead center (UT) is reached at maximum volume in the cylinder. When the inlet valve is closed, the volume in the cylinder is compressed during normal operation. The piston moves up until the top dead center (TDC) is reached and the mixture in the cylinder is maximally compressed. After ignition, the mixture expands in the cylinder. The piston moves until the bottom dead center (UT) is reached. When the exhaust valve is open, the discharge phase takes place, in which the gas mixture, as exhaust gas from the combustion, leaves the cylinder in the direction of the exhaust gas line. In this regular operation of the internal combustion engine, there is a minimum valve overlap of the opening of the exhaust valve and the inlet valve.

According to the exhaust valve is shut down in an operation in which no fuel supply takes place, for example, by disengaging the cam of the drive shaft. The decommissioning of the exhaust valve is in the 1 through an arrow 111 below the curve 11 shown. So there is no opening of the or the exhaust valves instead. The curves 12 . 13 and 14 indicate the valve lift of the intake valve. According to the invention, the regular opening of the intake valve is adjusted to early, indicated here by the arrow 112 , The opening characteristics 12 . 13 and 14 the intake valve are increasingly shifted to early, in particular the courses 13 and 14 represent an advance according to the invention. Even with regular operation, the valve timing is usually dependent on the engine operating point. The history 12 describes an already relatively early inlet opening that can occur operating point-dependent in this form even in a conventional operation.

2 illustrates the resulting fresh air mass flow through the catalyst in a hybrid vehicle. The X axis denotes the time, with the time 21 the beginning of the engine stop, the time 22 the restart and the time 23 reaching a speed of 300 rpm. The hatched area 24 represents the mass passing through in the exhaust system or in the catalytic converter in the case of a regular (conventional) engine run-off and start-up procedure, ie with a regular opening of the intake and exhaust valves. Until the engine is out 21 the engine is idling, with fuel being transferred. The mass flow 24 until the beginning of the engine spill is thus to be understood as exhaust gas mass flow. With the start of the engine shutdown 21 when switching off the injection and the ignition is the mass flow 24 through the catalyst from fresh air. This amount decreases over time as the engine runs out. After the restart 22 In the internal combustion engine, the internal combustion engine of the hybrid vehicle is towed up to the speed required for a fired operation (eg, 300 rpm) by means of a correspondingly powerful electric machine. In this phase, the catalyst is increasingly being flowed through with fresh air, so that then there is a saturation of the catalyst with oxygen. After reaching the required speed at the time 23 the combustion is started, so that the mass flow in the exhaust line then consists of exhaust gas. For the removal of the catalyst, a brief fat operation is required.

The history 25 the mass flow on the catalyst represents the circumstances when carrying out the method according to the invention, in which the exhaust valves are closed in the manner described. First, the mass flow curve corresponds 25 to the engine outlet 21 the regular course and is to be understood as exhaust gas mass flow. With the start of the engine shutdown 21 the exhaust valves are switched off according to the invention, so that in the sequence the mass flow through the catalyst is equal to or near zero. A flow through the catalyst with fresh air is avoided. After restarting the engine, the exhaust valves initially remain closed until the required speed for a fired operation is reached. Until this time, the mass flow through the catalyst remains close to or equal to zero. When the internal combustion engine through the electric machine to the required speed (300 rpm) at the time 23 the fired operation is started and the exhaust valves are opened in a regular manner. From this point on, the mass flow through the catalyst increases abruptly, since the catalyst again flows through exhaust gas from the combustion process. In this application of the invention in a hybrid vehicle is achieved that the catalyst is not flowed through both during engine shutdown and during the entire startup process with fresh air. Only after reaching the required speed of the engine are fired again and opened the exhaust valves in a conventional manner to allow the change of charge. Since according to the invention it is achieved that no oxygen enrichment takes place in the catalytic converter during the phase of the parked engine or when switching off the fuel injection and during the subsequent starting process, a subsequent enrichment during recommissioning of the internal combustion engine, ie a short operation with a rich fuel mixture, can be dispensed with for catalyst removal become. According to the invention, therefore, a consumption advantage is achieved.

3 again illustrates in sketched way the control of the valves in the course of the method according to the invention. On the X-axis, ZOT denotes the top dead center of the piston in the cylinder at the ignition timing. UT indicates the bottom dead center of the piston in the cylinder and LOT indicates the charge cycle TDC of the piston in the cylinder. Between ZOT and UT takes place in a regular operation of the internal combustion engine, the expansion of the ignited mixture in the cylinder. Between UT and LOT takes place in the usual mode of operation of the output of the burned mixture from the Cylinder in the exhaust system instead. Between LOT and UT fresh air is sucked in via the open inlet valve. Between UT and a renewed ZOT the compression of the mixture takes place in the cylinder. The history 31 refers to the pressure in the cylinder. During the expansion phase, the pressure is high and drops as the piston in the cylinder moves toward bottom dead center. During the ejection phase, the pressure in the cylinder increases again slightly to drop again until the intake phase. During regular operation, usually the exhaust valve would be at the time 32 be opened. According to the invention, however, no opening of the exhaust valve takes place. The opening of the inlet valve is through the curve 33 indicated. In comparison with a usual control of the intake valve is the opening characteristic 33 to early, in this presentation so to the left, shifted in the direction of the (theoretical) Ausschiebephase. The maximum opening of the inlet valve is here shortly after top dead center at the end of the Ausschiebephase. So even during the ejection phase, the inlet valve is clearly open. The sooner the intake valve is opened, the lower the intermediate compression, ie the cylinder pressure increase shortly before LOT, and thus also the additional charge exchange losses, so that an extreme advance adjustment is very advantageous. However, with the degree of advance of the intake valve, a possible collision with the piston in the cylinder must be considered.

4 illustrates the charge cycle losses as a function of the position of the intake valve opening. The history 41 shows the charge cycle losses in a valve train characteristic according to a regular operation of the internal combustion engine, ie at regular opening of the exhaust valve and the intake valve. The courses 42 . 43 and 44 represent the opening characteristics of the intake valve according to the invention, in which the exhaust valve remains closed. This increases the early adjustment of 42 to 44 at. Point of time 45 indicates the beginning of the engine shutdown. Point of time 46 indicates the restart of the internal combustion engine. The illustration shows that the charge cycle losses, recognizable by the change in the mean pressure pmi _LW , at the restart and at the time of departure are dependent on the intake valve position and increase with increasing retarded position. The inlet valve position 44 with the maximum advance in this example, therefore, is the most favorable with regard to the charge cycle losses. The higher charge cycle losses, especially at the latest intake valve position 42 The result of this is that the piston is already in the compression phase when the intake valve opens and allows the gas to be changed. This leads to an intermediate compression in the gas exchange phase.

Due to the resulting charge exchange losses as a function of the adjustment of the intake valve opening results in a different engine run-up behavior. The engine run-up behavior is in the 5 shown for the different opening valve adjustments. For the towing process, a sufficiently strong electric machine is required. For example, for this purpose, the electric motor can be used in a vehicle with a hybrid engine or the starter of a conventional vehicle. The history 51 represents the Hochschleppvorgang at a regular valve characteristic, ie at an opening of both the intake valve and the exhaust valve during normal operation of an internal combustion engine. The courses 52 . 53 and 54 show the high towing behavior in a valve control according to the invention, ie with the exhaust valve closed and of 52 in the direction 54 with increasing advance of the intake valve. For example, the history shows 54 (As far as possible early adjustment in this example) a high-tow behavior, which comes closest to the towing behavior in a regular operation of the internal combustion engine. In the simulation presented here, only a very small torque was impressed. This simulation is therefore only to be understood as an example. For example, in hybrid systems, the towing is much faster, so that the higher charge exchange losses in the inventive method only noticeable within a few revolutions and thus are of little importance.

Measurements on a hybrid vehicle, which is operated in a conventional manner, show that in real driving the internal combustion engine is switched off frequently in certain driving situations for fuel saving reasons. After each restart of the internal combustion engine here goes the lambda signal in the rich range, ie λ <1, over. This is because the three-way catalyst is exposed to clean air every time the engine is stopped and started. In order to prevent a breakthrough of nitrogen oxide emissions due to oxygen oversupply in the catalytic converter and to allow the engine to be regulated in stoichiometric operation, the engine must be operated for a short time in grease (clearing out the catalytic converter). This rich engine operation increases fuel consumption because the excess fuel is not burned in the combustion chamber and thus can not be converted into torque. This form of catalyst purging is necessary even after a fuel cut. Although this mode of operation is often not taken into account in standardized vehicle certification cycles, it plays a major role in practice and possibly in future, more dynamic certifications. By the method according to the invention described the required after a coasting phase or after stopping the engine rich engine operation is no longer necessary. The clearing of the catalyst can be omitted, since according to the invention no fresh air and thus no oxygen enters the exhaust system, and since the catalyst is therefore not enriched with oxygen. The method according to the invention thus offers considerable potential for saving fuel. Moreover, in the operation of an internal combustion engine in the manner according to the invention, a cooling of the catalyst can be avoided during shutdown of the engine or during overrun, so that a non-optimal exhaust aftertreatment in the subsequent regular operation of the internal combustion engine is avoided due to a suboptimal operating temperature of the catalyst.

Claims (8)

Method for operating an internal combustion engine with an exhaust gas system downstream of the internal combustion engine having at least one catalyst device, and with at least one gas exchange device for controlling the inlet side and the exhaust side of the internal combustion engine, characterized in that in an operating mode in which the internal combustion engine is not supplied with fuel , the exhaust side of the engine is closed ( 111 ) and the opening of the inlet side is advanced (compared to a regular mode of operation) ( 112 ) becomes. A method according to claim 1, characterized in that the adjustment of the opening of the inlet side to early ( 112 ) is made from the suction phase in the direction of the Ausschiebephase the engine operation. A method according to claim 1 or claim 2, characterized in that the adjustment of the opening of the inlet side to early ( 112 ) is performed such that at the end of the Ausschiebephase the engine operation and at the beginning of the intake phase of the internal combustion engine operation comes to an overflow of gases from the internal combustion engine via the inlet side. Method according to one of the preceding claims, characterized in that the inlet side of the internal combustion engine is briefly opened during the Ausschiebephase and reopened during the intake phase. Method according to one of the preceding claims, characterized in that the internal combustion engine in the mode of operation in which the internal combustion engine is not supplied with fuel, is hauled up to an increased speed. Method according to one of the preceding claims, characterized in that the operating mode in which the internal combustion engine is not supplied with fuel, a coasting operation and / or switching off the internal combustion engine in a start / stop system and / or switching off the internal combustion engine at a Motor vehicle with hybrid drive is. A computer program executing all steps of a method according to any one of claims 1 to 6 when executed on a computing device or a controller. Computer program product with program code, which is stored on a machine-readable carrier, for performing a method according to one of claims 1 to 6, when the program is executed on a computing device or a control device.

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