Method for operating an internal combustion engine

The invention relates to a method for operating an internal combustion engine with at least one working cylinder in which a piston is moved up and down, so that an intake stroke, a compression stroke, a working stroke and a discharge stroke are successively performed within a working cycle of 720 degrees crankshaft At least three gas exchange valves, with an exhaust gas line, with at least one inlet duct which opens into a gas exchange valve in the form of an inlet valve and supplies at least combustion air to the working cylinder via this inlet valve with at least one outlet duct which opens into a gas exchange valve in the form of an outlet valve and which, Wherein at least one of the gas exchange valves of at least one of the working cylinders is used as an EGR valve and is supplied to this exhaust gas from an exhaust gas return line. 2. The exhaust gas recirculation line as claimed in claim 1, wherein the exhaust gas recirculation line comprises at least one exhaust gas recirculation line which is connected to the exhaust gas line of the internal combustion engine , According to the preamble of claim 1.

The exhaust gas recirculation is one of the essential elements of the internal engine NO_xReduction in a diesel engine. One differentiates the "external" exhaust gas recirculation (EGR), as for example from the<patcit id="pcit0001" dnum="DE19961292C2"><text>DE 199 61 292 C2</text></patcit> Known, with cooled and uncooled variants from the "internal" EGR, as for example from the <patcit id="pcit0002" dnum="DE102005053940A1"><text>DE 10 2005 053 940 A1</text></patcit> known. In the internal exhaust gas recirculation, the remaining or recirculated residual gas is usually realized by influencing the gas exchange valve control times by means of an additional opening of inlet or outlet valves or a negative valve overlap via a variable valve drive. The advantage of the internal EGRs compared to the external EGRs is the short paths and the fast reaction times as well as the direct dosage capability. However, the lack of the possibility of an effective cooling of the residual gas, as in the case of the external EGR, is disadvantageous.

In the known Miller / Atkinson cycle, the timing "intake valve closes" (ES) is shifted late. In this way, fresh gas or combustion air already present in the cylinder, which is also referred to herein as a cylinder charge, is partially pushed back into an intake channel for combustion air. This means a filling disadvantage which, however, is compensated by a charge with a suitable charge pressure. The charge pressure in the volume between the charge output and the engine inlet is to be regulated in such a way that the charge pressure closes the theoretical compression end pressure in the working cylinders of the internal combustion engine at the point in time at each Miller operating point, ie each operating point at which the Miller / Atkinson cycle is applied Respectively.

The positive effect of the Miller / Atkinson cycle by early or late timing for closing the intake valve on the NO_xEmission and homogeneity of the diesel mixture is known. Furthermore, in the case of ottomotor applications, the tilt tendency during high-loading can be significantly reduced. In contrast to the ottomotor, which can work with a positive valve overlap because of a lack of geometric constraints, a simple implementation of the method using a phase detector is generally not possible with the diesel engine. The reason for this is a mechanical collision of the valve with the piston in the case of early adjustment and increased pumping work during late adjustment.

In addition, as a rule, only one intake valve is available for the "Miller phase" before compression start, which can be adjusted up to crank angles far after charge change UT (lower dead point of the reciprocating piston after the charge change, ie between a discharge stroke and an intake stroke) May remain open before the start of compaction. Thus, for the outflow of fresh gas from the working cylinder during the "mill phase", only the volume of an intake duct is available, even if two or more intake ducts are provided for the respective working cylinder.

The <patcit id="pcit0003" dnum="US20070235011A1"><text>US 2007/0235011 A1</text></patcit> Shows a method for operating an internal combustion engine with an exhaust gas recirculation suitable for achieving NO x reduction. For this purpose, a working cylinder has a gas exchange valve, embodied as an EGR valve, to which exhaust gas is fed from an exhaust gas return line.

The <patcit id="pcit0004" dnum="DE10324988A1"><text>DE 103 24 988 A1</text></patcit> Discloses an internal combustion engine with an exhaust gas recirculation, on the cylinder of which an exhaust collecting container is arranged via a line. The line can be opened or closed via a valve.

The object of the invention is to improve a method of the above-mentioned type with respect to the metering of exhaust gas recirculation and the realization of a Miller-Atkinson cycle.

This object is achieved according to the invention by a method of the above type having the features characterized in claim 1. Advantageous embodiments of the invention are described in the further claims.

For this purpose, it is provided in accordance with the invention that, in a predetermined operating state of the internal combustion engine, the EGR valve is opened at least twice during a working cycle of 720 degrees crankshaft, an opening duration of the first opening of the EGR valve being timed with an opening of the EGR valve Exhaust valve during the ejection stroke and at least overlaps an opening duration of the second opening of the EGR valve with an opening period of the intake valve during the intake stroke, the EGR valve being closed between the first and second openings.

This has the advantage that, without the need for additional valves or actuators, an internal and external exhaust gas recirculation with a high degree of accuracy for the recirculated exhaust gas is simultaneously realized within a working cycle of the internal combustion engine.

A simultaneous representation of exhaust gas recirculation and the Miller Atkinson cycle by means of the EGR valve without additional valves or actuators, whereby an additional volume for the temporary storage of extended cylinder charge in the form of the exhaust gas return line is available, is thereby made available in a predetermined operating state of the internal combustion engine Within a working cycle of 720 degrees crankshaft, the EGR valve is timed after a lower dead point between an intake stroke and a compression stroke so late after the start of the compression stroke and time after the intake valve is closed that part of the cylinder charge is expelled into the exhaust gas return line before A compression stroke begins so that the internal combustion engine is operated with a Miller Atkinson cycle.

Internal exhaust gas recirculation is realized by selecting the opening duration of the first opening of the EGR valve such that an opening timing of the EGR valve for the first opening is timed at or after an opening timing of the exhaust valve for the discharge stroke and a closing timing of the EGR valve For the first opening is temporally at or before a closing time of the discharge valve for the discharge stroke. ,

An external exhaust gas recirculation is realized in that the opening duration of the second opening of the EGR valve is selected such that an opening timing of the EGR valve for the second opening is timed at or after an opening timing of the intake valve for the intake stroke and a closing timing of the EGR valve For the second opening is at or before a closing time of the intake valve for the intake stroke.

An optimum setting of an operating point of the internal combustion engine with minimized pollutant emissions is achieved by supplying exclusively fresh air or a basic quantity EGR to the intake valve, that pure or fresh air mixed exhaust gas is supplied to the EGR valve from a cooled or uncooled low-pressure EGR circuit and / Or that exhaust gas mixed with fresh air is fed to the EGR valve from a cooled or unchilled high-pressure EGR circuit.

The invention is explained in more detail below with reference to the drawing. This shows in<dl id="dl0001"><dt>FIG</dt><dd>A schematic block diagram of a preferred embodiment of an internal combustion engine for carrying out the method according to the invention,</dd><dt>FIG</dt><dd>A graphical representation of the piston movement as well as the valve movement of inlet, outlet valves and a gas exchange valve used as an EGR valve, wherein a Miller Atkinson cycle is implemented with little EGR,</dd><dt>FIG</dt><dd>A graphical representation of the piston movement and the valve movement of intake, exhaust valves and a gas exchange valve used as an EGR valve, wherein a Miller-Atkinson cycle is realized with a large amount of EGR and FIG</dd><dt>FIG.</dt><dd>A graphical representation of the piston movement as well as the valve movement of intake, exhaust valves and a gas exchange valve used as an EGR valve, wherein an internal and an external EGR with a two-way opening of the EGR valve is simultaneously implemented.</dd></dl>

In the <figref idrefs="f0001">FIG</figref> Is an operating cylinder 12, each working cylinder 12 being assigned intake valves 14 and an exhaust valve 16. Furthermore, a further gas exchange valve 18 is associated with each working cylinder 12. A fresh air supply duct 20 is supplied to the working cylinders 12 via the inlet valves 14 and corresponding inlet ducts 22 opening into the inlet valves 14 as combustion air and via an exhaust gas line 26 from the operating cylinders 12 via the outlet valves 16 and corresponding outlet ducts opening into the outlet valves 16 28 exhaust gas 30. A piston (not shown) is arranged movably up and down in each working cylinder 12 so that an intake stroke, a compression stroke, a working stroke and a discharge stroke are successively performed in each working cylinder within a working cycle of 720 degrees crankshaft.

A compressor 32 of an exhaust gas turbocharger 34 and a charge air cooler 36 are arranged in the fresh air supply duct 20. A turbine 38 of the exhaust gas turbocharger 34 and a particle filter 40, such as a diesel particle filter, are arranged in the exhaust gas line 26. Furthermore, an exhaust gas return line 42 is provided for returning exhaust gas 30 into the combustion process into the working cylinder 12. This exhaust gas return line 42 is connected downstream of the turbine 38 with the exhaust gas line 26 and has an EGR cooler 44 and a charge air cooler 46 for EGR, the latter possibly also being configured in a structural unit with the charge air cooler 36. Furthermore, a bypass line 48 is provided in the exhaust gas return line 42 which bridges the EGR cooler 44 and the charge air cooler 46 for EGR and has a bypass valve 50.

The fourth gas exchange valve 18 of each working cylinder 12 is neither connected to an inlet channel 22 nor to an outlet channel 28 but to the exhaust gas return line 42. In this way, one of the gas exchange valves of each working cylinder actuated by a corresponding camshaft serves directly as an EGR valve.

In the <figref idrefs="f0002">FIGS. 2 to 4</figref> A crank angle is plotted on a horizontal axis 52 and a lifting movement is applied to a vertical axis 54. A top dead center (OT) of the reciprocating piston during the charge change (between the discharge stroke and the intake stroke) at 58 is a lower dead center (UT) of the reciprocating piston before the charge change (between the working stroke and the discharge stroke) Dead center (UT) of the reciprocating piston after the charge change (between the intake stroke and the compression stroke). A first graph 62 illustrates the stroke movement 54 over the crank angle 52 for the piston, a second graph 64 illustrates the stroke movement 54 via the crank angle 52 for the exhaust valves 16, a third graph 66 illustrates the stroke movement 54 via the crank angle 52 for the intake valves 14 and A fourth graph 68 (dashed line) illustrates the lifting movement 54 via the crank angle 52 for those gas exchange valves 18 which are not connected either to an inlet channel 22 nor to an outlet channel 28 but to the exhaust gas return line 42 (EGR valves).

In the first alternative according to <figref idrefs="f0002">FIG</figref> An external exhaust gas recirculation occurs while the intake valves 14 are open and still thereafter. Although the inlet valve 14 according to the third graph 66 is regular, the EGR valve 18 remains longer open according to the fourth graph 68 and closes only after the intake valve 14 has been closed according to the third graph 66 as well as after the UT 60. In this way, The EGR valve 18 remains open in accordance with the fourth graph 68, so that part of the cylinder charge previously introduced via the inlet valve 14 is pushed out into the exhaust gas return line 42 before the actual compression is completed according to the control cycle Closing also of the EGR valve 18 according to the fourth graph 68 begins. By shifting the opening of the EGR valve 18 in the direction of the arrow 76, the Miller Atkinson cycle is more or less strongly pronounced. At the same time, the height of the fourth graph 68 and the opening duration control the amount of external exhaust gas recirculation. In the example according to FIG<figref idrefs="f0002">FIG</figref> A small amount of exhaust gas is recycled. Thus, the EGR valve 18 simultaneously represents the Atkinson cycle and the EGR so that no additional valve timing (VVT) is required for the intake valves 14 and exhaust valves 16. The actuation of the inlet valves 14 and outlet valves 16 can be effected with rigid cams and without camshaft adjustment or the like. Respectively.

In the second alternative according to <figref idrefs="f0002">FIG</figref> The external exhaust gas recirculation is performed during and after the intake valves 14 are opened. In contrast to the first alternative according to<figref idrefs="f0002">FIG</figref> The fourth graph 68 is significantly higher and the opening time of the EGR valves 18 is substantially longer so that a large amount of exhaust gas is returned. The Miller Atkinson cycle is performed as in the first alternative<figref idrefs="f0002">FIG</figref> By late closing the EGR valves 18 simultaneously with the EGR. The intake valves 14 are closed regularly, ie not for a Miller Atkinson cycle. Both in the embodiment according to FIG<figref idrefs="f0002">FIG</figref> As well as that according to <figref idrefs="f0002">FIG</figref> A pushing-out of a part of the cylinder charge into the intake channel 22, but instead into the EGR line 42, takes place despite the realization of a Miller Atkinson cycle.

In the third alternative according to <figref idrefs="f0002">FIG</figref> The EGR valves 18 are each opened twice within a working cycle of 720 degrees of crankshaft, each work cycle for each working cylinder each comprising an intake stroke, a compression stroke, a working stroke, and a discharge stroke. The first opening of the EGR valves 18 according to the fourth graph 68 takes place between the UT 56 and the TDC 58, while the outlet valve 16 is opened according to the second graph 64. This results in an internal EGR via the EGR valve 18, since exhaust gas is partly expelled from the working cylinder into the EGR line 42 and is later sucked back into the working cylinder. The second opening of the EGR valves 18 according to the fourth graph 68 takes place between the TDC 58 and the TDC 60 while the intake valve 14 is opened according to the third graph 66. Here, on the one hand, the exhaust gas of the preceding working cycle previously expelled into the EGR line 42 is sucked back into the working cylinder and, at the same time, external exhaust gas is returned. As a result of a higher design of the fourth graph 68 for the second opening compared to the first opening of the EGR valve 18, the previously expelled exhaust gas is conveyed completely into the working cylinder and additionally external exhaust gas is fed. This is indicated by the arrow 78 for the first opening of the EGR valve 18 and the arrow 80 for the second opening of the EGR valve 18.

In the illustrated internal combustion engine, it is provided, in the case of a motor configuration with more than two valves per working cylinder 12, to use a gas exchange valve 18 alone for the metering of exhaust gas recirculation / residual gas. The charging of this EGR valve 18 with a separate inlet channel is effected, for example, by the following variants:<ul><li>Pure exhaust gas from cooled low-pressure EGR circuit (possibly with own compressor stage);</li><li>Pure exhaust gas from cooled high-pressure EGR circuit;</li><li>Pure exhaust gas from uncooled high-pressure EGR circuit;</li><li>Air exhaust gas mixture from the aforementioned variants.</li></ul>

In all variants, the actual intake valves are only supplied with fresh air or a basic EGR quantity.

The control of the gas exchange valve 18 and possibly also of the further gas exchange valves 14, 16 is implemented by means of a variable valve drive (mechanical, electrical or hydraulic) and can take place with regard to the time both parallel to the inlet and also offset in time. The metering of recirculated exhaust gas is thus adjusted to each individual working cylinder 12 via positioning, lifting height and control width of the control of the gas exchange valves 18 and 14, 16, respectively.

In addition to the cyclically accurate metering capability of the EGR, the advantage of this arrangement is, above all, the utilization of the entire exhaust gas energy on the turbine side, whereas, compared to a conventional low-pressure arrangement, only the fresh air mass flow must be compressed. The EGR mass flow is sucked directly through the EGR valve 18 through the engine. The optional coolers 44, 46 and bypasses 50 are used for an air- and exhaust-side temperature management. An optional additional changeover valve 70 in a connecting conduit 72 between the exhaust conduit 26 upstream of the turbine 38 and the exhaust gas return conduit 42 allows the use of high pressure (HD) EGR and / or low pressure (ND) EGR. Optionally, a cooler 74 is arranged in the connecting line 72.

The fully variable EGR valve 18 is used by skillful arrangement of the control times to represent a Miller Atkinson cycle with late intake port of the EGR valve 18. By multiple actuation of the EGR valve 18 within a working cycle, a combination of internal and external EGR is achieved via a single valve. The control times of all other inlet and outlet valves 14, 16 can remain fixed and can be actuated by means of a simple cam-controlled control drive. In contrast to the known Miller Atkinson cycle, the cylinder charge is not pushed back into the intake tract, but into the EGR tract or the EGR line 42. The same applies to the internal EGR by means of the two-way opening of the EGR valve 18, as shown in FIG<figref idrefs="f0002">FIG</figref> Respectively.