Method for operating an internal combustion engine with partial shutdown

Abstract

Method for operating an internal combustion engine (10) with at least two cylinders (1, 2, 3, 4), wherein - each cylinder (1, 2, 3, 4) has at least one exhaust port to which an exhaust pipe (7a, 7b) is connected for the removal of exhaust gases via exhaust system (8), - each cylinder (1, 2, 3, 4) has at least one inlet opening to which an intake line (5a, 5b) is connected for supplying charge air via intake system (6), - at least two cylinders (1, 2, 3, 4) are configured in such a way that they form at least two groups, each with at least one cylinder (1, 2, 3, 4), wherein the at least one cylinder (1, 4) of a first group is a cylinder (1, 4) that is in operation even when the internal combustion engine (10) is partially shut down, and the at least one cylinder (2, 3) of a second group is designed as a load-dependent switchable cylinder (2, 3), - in the at least one intake line (5b) of the at least one load-dependent switchable cylinder (2, 3) an intake-side throttle element (9) is provided, with which the size of the flow cross-section of the intake line (5b) can be changed, whereby the amount of charge air supplied to the (10) at least one deactivated cylinder (2, 3) when the internal combustion engine is partially deactivated can be adjusted, and - in which at least one exhaust pipe (7b) of the at least one load-dependent switchable cylinder (2, 3) has an exhaust-side throttle element (11) with which the size of the flow cross-section of the exhaust pipe (7b) can be changed and with which the discharge of the exhaust gas from the at least one deactivated cylinder (2, 3) of the second group when the internal combustion engine (10) is partially deactivated can be controlled, characterized in that the at least one switchable cylinder (2, 3) of the second group is switched depending on the load T of the internal combustion engine (10), in such a way that this at least one switchable cylinder (2, 3) is deactivated when a predefinable load T is undershot down is switched off and when a predefined load T is exceeded upis switched on, whereby the amount of charge air supplied to the at least one deactivated cylinder (2, 3) during the partial deactivation is reduced, but not completely prevented, by actuating the at least one intake-side throttle element (9).

Description

[0001] The invention relates to a method for operating an internal combustion engine with at least two cylinders, in which - each cylinder has at least one exhaust port to which an exhaust pipe is connected for the removal of exhaust gases via an exhaust system, - each cylinder has at least one inlet opening to which an intake line for supplying charge air via the intake system is connected, - at least two cylinders are configured in such a way that they form at least two groups, each with at least one cylinder, wherein the at least one cylinder of a first group is a cylinder that is in operation even when the internal combustion engine is partially shut down, and the at least one cylinder of a second group is designed as a load-dependent switchable cylinder, - in the at least one intake line of the at least one load-dependent switchable cylinder, an intake-side throttle element is provided with which the size of the flow cross-section of the intake line can be changed, thereby making the amount of charge air supplied to the at least one deactivated cylinder during partial deactivation of the internal combustion engine adjustable, and - in which at least one exhaust pipe of at least one load-dependent switchable cylinder has an exhaust-side throttle element with which the size of the flow cross-section of the exhaust pipe can be changed and with which the discharge of the exhaust gas from the at least one deactivated cylinder of the second group can be controlled when the internal combustion engine is partially deactivated.

[0002] An internal combustion engine of the type mentioned is used as a motor vehicle drive and is described, for example, in JP S59-170 440 A. Within the scope of the present invention, the term internal combustion engine includes diesel engines, but also gasoline engines and hybrid internal combustion engines, i.e., internal combustion engines that are operated with a hybrid combustion process.

[0003] German patent application DE 10 2009 060 211 A1 describes a method of the type mentioned above with switching hysteresis, in which the switchable cylinders are switched off when a lower load limit is undershot and switched on when a further upper load limit is exceeded.

[0004] In the development of internal combustion engines, a fundamental goal is to minimize fuel consumption, with improved overall efficiency being the primary focus of efforts.

[0005] Fuel consumption and, consequently, efficiency are particularly problematic in spark-ignition engines (Otto engines). This is due to the fundamental operating principle of the Otto engine. Load control is generally achieved via a throttle valve located in the intake system. By adjusting the throttle valve, the pressure of the intake air downstream of it can be reduced to a greater or lesser extent. The more the throttle valve is closed, i.e., the more it restricts the intake system, the greater the pressure drop of the intake air across the throttle valve and the lower the pressure of the intake air downstream of the throttle valve and before it enters the at least two cylinders (i.e., combustion chambers). With a constant combustion chamber volume, the air mass (i.e., the quantity) can be adjusted in this way by controlling the pressure of the intake air.This also explains why quantity control proves to be disadvantageous, especially in partial load operation, because low loads require high throttling and pressure reduction in the intake system, which increases charge exchange losses with decreasing load and increasing throttling.

[0006] To reduce the described losses, various strategies for derating a spark-ignited internal combustion engine were developed.

[0007] One approach to reducing throttling in the gasoline engine is, for example, a gasoline engine operating principle with direct injection. Direct fuel injection is a suitable means of achieving stratified combustion chamber charge. Direct fuel injection into the combustion chamber thus allows for quality control in the gasoline engine to a certain extent. Mixture formation occurs through the direct injection of fuel into the cylinders or into the air within the cylinders, and not through external mixture formation, where fuel is introduced into the intake air in the intake system.

[0008] Another way to optimize the combustion process of a gasoline engine is to use at least a partially variable valve train. Unlike conventional valve trains, where both the valve lift and timing are fixed, these parameters, which influence the combustion process and thus fuel consumption, can be varied to a greater or lesser extent using variable valve trains. Throttle-free, and therefore loss-free, load control is already possible if the intake valve closing time and lift can be varied. The air-fuel mixture flowing into the combustion chamber during the intake stroke is then controlled not by a throttle valve, but by the intake valve lift and opening duration. However, variable valve trains are very expensive and therefore often unsuitable for series production.

[0009] Another approach to reducing throttling in a gasoline engine is cylinder deactivation, i.e., the deactivation of individual cylinders in specific load ranges. The efficiency of the gasoline engine under partial load can be improved, i.e., increased, by partial deactivation. This is because deactivating one cylinder in a multi-cylinder internal combustion engine, at constant engine power, increases the load on the remaining cylinders still in operation. This allows the throttle valve to be opened further to introduce a larger mass of air into these cylinders, thus achieving an overall reduction in throttling of the internal combustion engine. During partial deactivation, the cylinders that remain in operation work in the higher load range, where specific fuel consumption is lower. The load spectrum is shifted towards higher loads.

[0010] Furthermore, the cylinders that continue to operate during the partial shutdown exhibit improved mixture formation due to the larger mass of air or mixture supplied.

[0011] Further efficiency advantages result from the fact that a deactivated cylinder, due to the lack of combustion, does not generate any wall heat losses as a result of heat transfer from the combustion gases to the combustion chamber walls.

[0012] Although diesel engines, i.e., self-igniting internal combustion engines, have a higher efficiency, i.e., lower fuel consumption, than gasoline engines, where the load is adjusted by means of throttling or quantity control via the cylinder filling, as described above, there is still potential and need for improvement in diesel engines with regard to fuel consumption and efficiency.

[0013] One concept for reducing fuel consumption in diesel engines is cylinder deactivation, i.e., the deactivation of individual cylinders in certain load ranges. The efficiency of the diesel engine under partial load can be improved, i.e., increased, by partial deactivation. This is because deactivating at least one cylinder in a multi-cylinder internal combustion engine, even in a diesel engine, increases the load on the remaining cylinders while maintaining constant engine power. This allows these cylinders to operate in higher load ranges, where specific fuel consumption is lower. The load spectrum in partial load operation of the diesel engine is thus shifted towards higher loads.

[0014] With regard to wall heat losses, the same advantages apply as with the Otto engine, which is why reference is made to the corresponding explanations.

[0015] Partial shutdown in diesel engines is also intended to prevent the fuel-air mixture from becoming too lean as part of quality control when the load decreases due to a reduction in the amount of fuel used.

[0016] The multi-cylinder internal combustion engines with partial shutdown described in the prior art and the associated methods for operating these internal combustion engines nevertheless exhibit significant potential for improvement, as will be briefly and exemplarily explained below using the diesel engine as an example.

[0017] In a direct-injection diesel engine, if the fuel supply to the deactivatable cylinders is interrupted (i.e., stopped) for the purpose of partial deactivation, the deactivated cylinders continue to participate in the charge exchange if the corresponding valve train of these cylinders is not deactivated or cannot be deactivated. The resulting charge exchange losses reduce and counteract the improvements in fuel consumption and efficiency achieved through partial deactivation, so that the benefit of partial deactivation is at least partially lost, meaning that, overall, partial deactivation actually results in a less significant improvement.

[0018] In practice, it is not effective to remedy the adverse effects described above by providing switchable valve trains, since switchable valve trains, like variable valve trains, are very expensive and are not suitable for series production.

[0019] Furthermore, switchable valve trains in turbocharged internal combustion engines can lead to additional problems, as the turbine of an exhaust gas turbocharger must be designed for a specific volume of exhaust gas and thus also for a specific number of cylinders. If the valve train of a deactivated cylinder is shut down, the total mass flow through the cylinders of the internal combustion engine decreases due to the lack of mass flow through the deactivated cylinders. The exhaust gas mass flow through the turbine decreases, and with it, often the turbine pressure ratio. This would result in a decrease in the boost pressure ratio, i.e., the boost pressure drops, and only a small amount of fresh air or charge air is supplied to the cylinders that remain in operation. The low charge air flow can also cause the compressor to operate beyond its surge line.Within the scope of the present invention, the term charge air is also used when the internal combustion engine is not turbocharged, but rather a naturally aspirated engine.

[0020] The effects described above lead to a limitation of the applicability of partial engine shutdown, namely a restriction of the load range in which partial shutdown can be used. A reduced amount of charge air supplied to the cylinders operating during partial shutdown reduces the efficiency or quality of combustion and has a detrimental effect on fuel consumption and pollutant emissions.

[0021] The boost pressure during partial engine shutdown, and thus the amount of charge air supplied to the cylinders still in operation, could be increased, for example, by using a smaller turbine cross-section and simultaneously venting exhaust gases. This would also expand the load range relevant for partial engine shutdown. However, this approach has the disadvantage that the boost pressure is insufficient when all cylinders are operating.

[0022] The boost pressure during partial shutdown, and thus the amount of charge air supplied to the cylinders still in operation, could also be increased by equipping the turbine with a variable turbine geometry that allows the effective turbine cross-section to be adjusted to the current exhaust mass flow. However, this would simultaneously increase the exhaust back pressure in the exhaust system upstream of the turbine, which in turn leads to higher charge exchange losses in the cylinders still in operation.

[0023] To address the problem described above regarding the low amount of charge air supplied to the cylinders still operating during partial shutdown, the prior art involves providing a throttle element in at least one intake manifold of each load-dependent switchable cylinder. This element allows the size of the intake manifold's flow cross-section to be varied, thereby adjusting the amount of charge air supplied to the deactivated cylinder during partial engine shutdown. In this way, the charge air supply to the deactivated cylinders—i.e., the amount of charge air supplied during partial shutdown—can be reduced and controlled, and if necessary, even completely eliminated, without requiring the switchable cylinders to be equipped with switchable valve trains, which would incur high costs.

[0024] By actuating the throttle element provided in the intake line of a deactivated cylinder, the flow cross-section of the intake line is changed, in particular reduced, thereby allowing the amount of charge air supplied to the deactivated cylinder during partial deactivation to be adjusted, metered and controlled.

[0025] As already described in connection with the prior art, the deactivated cylinders continue to participate in the charge exchange because the associated – non-switchable – valve train of these cylinders continues to be actuated, i.e., it remains operational, and is not deactivated along with the cylinders. However, the charge air supply can be reduced by means of a throttle element, as described above. Less or no charge air is supplied to reduce the charge exchange losses of the deactivated cylinders.

[0026] The reduced charge air flow through the deactivated cylinder (at least one) leads – compared to an unchanged charge air flow with a fully open intake manifold – to reduced heat transfer due to convection. This means the deactivated cylinders do not cool down, or cool down less, during partial deactivation. This is particularly advantageous with regard to pollutant emissions, especially unburned hydrocarbon emissions, as the deactivated cylinders reach their operating temperature again immediately after the partial deactivation ends.

[0027] Reducing the charge air flow by means of a throttle element has further advantages over internal combustion engines in which the charge air supply is completely prevented by means of switchable valve trains, which essentially result from the fact that the mass flow through the internal combustion engine is higher when the charge air supply is reduced than when the supply of charge air is completely prevented.

[0028] This offers advantages for internal combustion engines with exhaust gas turbocharging. The higher mass flow leads to a higher turbine pressure ratio and thus to a higher boost pressure, allowing a larger quantity of charge air to be supplied to the cylinders operating during partial deactivation. This also expands the applicability of partial deactivation, namely the load range in which it can be used, and improves combustion efficiency and thus the fuel consumption and emissions performance of the internal combustion engine.

[0029] In light of the foregoing, the object of the present invention is to demonstrate a method for operating an internal combustion engine according to the preamble of claim 1, which further optimizes partial shutdown.

[0030] This problem is solved by a method for operating an internal combustion engine with at least two cylinders, in which - each cylinder has at least one exhaust port to which an exhaust pipe is connected for the removal of exhaust gases via an exhaust system, - each cylinder has at least one inlet opening to which an intake line for supplying charge air via the intake system is connected, - at least two cylinders are configured in such a way that they form at least two groups, each with at least one cylinder, wherein the at least one cylinder of a first group is a cylinder that is also in operation when the internal combustion engine is partially shut down, and the at least one cylinder of a second group is designed as a load-dependent switchable cylinder, - in the at least one intake line of the at least one load-dependent switchable cylinder, an intake-side throttle element is provided with which the size of the flow cross-section of the intake line can be changed, thereby making the amount of charge air supplied to the at least one deactivated cylinder during partial deactivation of the internal combustion engine adjustable, and - in which at least one exhaust pipe of at least one load-dependent switchable cylinder has an exhaust-side throttle element with which the size of the flow cross-section of the exhaust pipe can be changed and with which the discharge of the exhaust gas from the at least one deactivated cylinder of the second group during partial shutdown of the internal combustion engine can be controlled. which is characterized in that - the at least one switchable cylinder of the second group is switched depending on the load T of the internal combustion engine, in such a way that this at least one switchable cylinder is deactivated when a predefinable load T is undershot down is switched off and when a predefined load T is exceeded upis switched on, whereby the amount of charge air supplied to the at least one deactivated cylinder during the partial deactivation is reduced, but not completely prevented, by actuating the at least one intake-side throttle element.

[0031] In the internal combustion engine, in addition to the at least one intake-side throttle element provided in the intake system of the at least one load-dependent switchable cylinder, at least one exhaust-side throttle element is arranged in the exhaust system of the at least one load-dependent switchable cylinder.

[0032] While an intake-side throttle element controls the charge air supply to a deactivated cylinder, i.e., reduces the amount of charge air supplied during partial deactivation, an exhaust-side throttle element serves to prevent or reduce unwanted backflow of exhaust gas into a deactivated cylinder of the second group. Furthermore, the charge exchange losses of a deactivated cylinder can be reduced by appropriately controlling the exhaust-side throttle element. Opening an exhaust-side throttle element should preferably be avoided when there is a vacuum in the corresponding deactivated cylinder or when the pressure is lower than in the exhaust system between the cylinder and the exhaust-side throttle element.

[0033] According to the wording, an exhaust-side throttle element is supposed to control the discharge of exhaust gas from at least one cylinder of the second group that is deactivated during partial shutdown of the internal combustion engine. Strictly speaking, however, no hot exhaust gas is discharged during partial shutdown, but rather charge air or fresh air. But at least during the first operating cycle of partial shutdown, the exhaust gas from the preceding, and thus the hot exhaust gas from the last firing cycle, is discharged via the exhaust system. During the subsequent operating cycles of partial shutdown, charge air or fresh air is then discharged. Nevertheless, the present invention refers to the discharge of hot exhaust gas.

[0034] Providing at least one exhaust-side throttle element offers significant cost advantages compared to variable or switchable valve trains.

[0035] The method according to the invention discloses a method according to the preamble of claim 1, which further optimizes the partial shutdown. This solves the problem underlying the invention.

[0036] The internal combustion engine has at least two cylinders or at least two groups, each with at least one cylinder. Therefore, internal combustion engines with three cylinders configured in three groups of one cylinder each, or internal combustion engines with six cylinders configured in three groups of two cylinders each, are also included. The three cylinder groups can be successively activated or deactivated as part of a partial shutdown, which also allows for a double switching operation. This further optimizes the partial shutdown. The cylinder groups can also contain a different number of cylinders.

[0037] The design of the internal combustion engine optimizes its efficiency in partial load operation, i.e., at low loads, where a low load T low preferably a load that is less than 50%, preferably less than 30% of the maximum load T max,n at the currently existing rotational speed n.

[0038] Different internal combustion engines sometimes require different process variants.

[0039] The specified limit loads T for falling below or exceeding down and T up They can be the same size, but also different sizes. When an internal combustion engine is running, the cylinders of the first cylinder group are constantly in operation. The second cylinder group is then switched on or off.

[0040] Further advantageous embodiments of the method are discussed in connection with the dependent claims.

[0041] Advantageous are process variants in which at least one cylinder of the second group is switched off as soon as the specified load T is reached. down is undershot and the instantaneous load for a predefined time period Δt l is lower than this specified load T down .

[0042] The introduction of an additional condition for switching off the cylinders of the second group, i.e., partial shutdown, is intended to prevent excessively frequent switching on and off, in particular partial shutdown when the load only briefly exceeds the specified load T. down falls below and then rises again, or by the specified value for the load T down fluctuates, without falling below a certain level justifying or requiring a partial shutdown.

[0043] For these reasons, process variants are also advantageous in which at least one cylinder of the second group is activated as soon as the specified load T is reached. up is exceeded and the instantaneous load for a predefined time period Δt2 is higher than this predefined load T up .

[0044] Advantageous are process variants in which the fuel supply to at least one switchable cylinder is deactivated during shutdown. This results in benefits regarding fuel consumption and pollutant emissions, thus supporting the objective pursued with partial shutdown, namely to reduce fuel consumption and improve efficiency. In compression-ignition internal combustion engines, it may even be necessary to deactivate the fuel supply to reliably prevent ignition of the mixture in the cylinder.

[0045] Advantageous are process variants in which - when switching off at least one load-dependent switchable cylinder, the fuel supply to that cylinder is deactivated before the at least one intake-side throttle element is actuated, and - when at least one deactivated cylinder is switched on, at least one intake-side throttle element is actuated before the fuel supply to the at least one deactivated cylinder is activated.

[0046] This approach ensures stable transient operating behavior of the turbocharger of a turbocharged internal combustion engine or of the internal combustion engine itself and takes into account the fact that the fuel supply to the internal combustion engine can be deactivated and reactivated immediately, i.e. with little time delay, whereas the turbocharger, during partial shutdown, i.e. when switching off the switchable cylinders and when switching the deactivated cylinders back on, only responds with a certain time delay, i.e. reacts to changes with a delay.

[0047] Advantageous are process variants in which the at least one cylinder in operation is ignited by means of self-ignition.

[0048] The above method variant refers to processes in which combustion is initiated by means of auto-ignition, and thus also to working processes such as those commonly used in diesel engines.

[0049] Method variants are also advantageous in which each cylinder is equipped with an ignition device to initiate a spark ignition, wherein the ignition device of the at least one switchable cylinder is preferably deactivated when switched off.

[0050] The above variant of the method relates to the application of the method to a spark-ignition internal combustion engine, for example a direct-injection gasoline engine, whose cylinders are each equipped with an ignition device to initiate spark ignition.

[0051] However, it is also possible to use a hybrid combustion process with auto-ignition to operate a gasoline engine, for example, the so-called HCCI process, also known as the space ignition process or CAI process. This process is based on controlled auto-ignition of the fuel supplied to the cylinder. The fuel is burned with excess air, i.e., superstoichiometrically, as in a diesel engine. Due to the low combustion temperatures, the lean-burn gasoline engine exhibits comparatively low nitrogen oxide emissions and, also as a result of the lean mixture, no soot emissions. Furthermore, the HCCI process leads to high thermal efficiency. The fuel can be injected directly into the cylinders or into the intake manifold.

[0052] Advantageous are embodiments of the method in which the predefinable load T down and / or T upThe system depends on the engine speed n. Therefore, there isn't just one specific load that triggers switching regardless of the engine speed n. Instead, the system operates based on engine speed, defining a range within the engine map where partial shutdown occurs.

[0053] In principle, other operating parameters of the internal combustion engine can be used as a criterion for a partial shutdown, for example the engine temperature or the coolant temperature after a cold start of the internal combustion engine.

[0054] Advantageous are process variants in which a predetermined minimum quantity of charge air is supplied to the at least one deactivated cylinder, and no less. In this case, a valve located in the intake manifold of a switchable cylinder is not completely closed during partial deactivation. If a flap is used as a throttling element, it is harmless that this flap exhibits a leakage flow in the closed position.

[0055] Advantageous are embodiments of the method in which the amount of charge air supplied to the at least one deactivated cylinder is also determined by the load T, the rotational speed n, the coolant temperature, the oil temperature, the engine temperature and / or the like.

[0056] Internal combustion engines are advantageous in which at least one intake-side throttle element and / or at least one exhaust-side throttle element is a valve.

[0057] Internal combustion engines are also advantageous in which at least one intake-side throttle element and / or at least one exhaust-side throttle element is a pivotable flap.

[0058] Internal combustion engines are advantageous if at least one intake-side throttle element and / or at least one exhaust-side throttle element is continuously adjustable.

[0059] The design of the throttle element as a continuously variable throttle allows for precise metering of the charge air volume introduced into the deactivated cylinders. The charge air volume can be determined based on the specific operating point, particularly with regard to minimizing charge exchange losses or achieving the required boost pressure. The throttle element's control can take into account the load T, the engine speed n, and, in the case of a liquid-cooled internal combustion engine, the coolant temperature, the oil temperature, and / or similar factors.

[0060] Nevertheless, internal combustion engines can be advantageous in which the throttle element can be switched in two stages or more stages.

[0061] The throttle element can be electrically, hydraulically, pneumatically, mechanically or magnetically controlled, preferably by means of motor control.

[0062] Internal combustion engines that are designed for turbocharging are advantageous.

[0063] Advantageous in this respect are internal combustion engines in which at least one exhaust gas turbocharger is provided, comprising a turbine arranged in the exhaust gas discharge system and a compressor arranged in the intake system.

[0064] The advantage of an exhaust gas turbocharger, for example, compared to a mechanical supercharger, is that no mechanical connection is required for power transmission between the turbocharger and the internal combustion engine. While a mechanical supercharger draws all the energy required for its operation from the internal combustion engine, thus reducing the available power and negatively impacting efficiency, the exhaust gas turbocharger utilizes the energy of the hot exhaust gases.

[0065] Turbocharged internal combustion engines are preferably equipped with an intercooler, which cools the compressed combustion air before it enters the cylinders. This further increases the density of the supplied charge air. The cooling also contributes to increased compression and better filling of the combustion chambers, i.e., to an improved volumetric efficiency. It can be advantageous to equip the intercooler with a bypass line to allow the engine to bypass the intercooler when necessary, for example, after a cold start.

[0066] Turbocharging is a suitable means of increasing the power output of an internal combustion engine without changing its displacement, or of reducing the displacement while maintaining the same power output. In either case, turbocharging leads to increased power output per unit volume and a more favorable power-to-weight ratio. If the displacement is reduced, the load spectrum can be shifted towards higher loads, resulting in lower specific fuel consumption, under the same vehicle conditions.

[0067] Designing exhaust gas turbocharging systems presents challenges, as the goal is generally to achieve a noticeable increase in power across the entire engine speed range. Current technology often exhibits a significant drop in torque when engine speeds fall below a certain threshold. The torque characteristics of a turbocharged internal combustion engine can be improved through various measures, such as incorporating multiple turbochargers – exhaust gas turbochargers and / or mechanical superchargers – in parallel and / or in series within the exhaust system.

[0068] Internal combustion engines are advantageous if at least one exhaust aftertreatment system is provided in the exhaust system; for example, an oxidation catalyst, a three-way catalyst, a storage catalyst, a selective catalyst and / or a particulate filter.

[0069] In internal combustion engines with four cylinders arranged in a row, embodiments are advantageous which are characterized in that the two outer cylinders and the two inner cylinders each form a group.

[0070] Internal combustion engines are advantageous if they have at least one exhaust gas recirculation system that includes a recirculation line branching off from the exhaust gas removal system and leading into the intake system.

[0071] Exhaust gas recirculation, i.e., the recirculation of combustion gases, is a suitable means of reducing nitrogen oxide emissions, with nitrogen oxide emissions being significantly reduced by increasing the exhaust gas recirculation rate. The exhaust gas recirculation rate x AGR is determined to x AGR = m AGR / (m AGR + m Frischluft ), where m AGR the mass of recirculated exhaust gas and m FrishluftThis refers to the supplied fresh air, which may be compressed and passed through a compressor. To achieve a significant reduction in nitrogen oxide emissions, high exhaust gas recirculation rates are required, on the order of x. AGR The percentage can be approximately 60% to 70%.

[0072] Internal combustion engines are advantageous in which a valve for adjusting the amount of exhaust gas recirculated is arranged in the exhaust gas recirculation return line.

[0073] In internal combustion engines with at least one exhaust gas turbocharger and exhaust gas recirculation, advantageous designs are those in which the exhaust gas recirculation return line branches off from the exhaust gas discharge system upstream of the turbine of the at least one exhaust gas turbocharger and enters the intake system downstream of the compressor. In this so-called high-pressure EGR, the exhaust gas is extracted from the exhaust gas discharge system upstream of the turbine and fed into the intake system downstream of the compressor. Therefore, the exhaust gas does not require any exhaust aftertreatment before recirculation, in particular, it does not need to be fed into a particulate filter, as there is no risk of compressor fouling.

[0074] However, operating an internal combustion engine with exhaust gas turbocharging and simultaneously using high-pressure EGR can lead to a conflict, as the recirculated exhaust gas is no longer available to drive the turbine. Increasing the exhaust gas recirculation rate reduces the exhaust gas flow introduced into the turbine. The reduced exhaust gas mass flow through the turbine results in a lower turbine pressure ratio, which in turn reduces the boost pressure ratio, equating to a lower charge air flow.

[0075] One solution to this is the so-called low-pressure EGR. Unlike high-pressure EGR, low-pressure EGR introduces exhaust gas into the intake system, which has already passed through the turbine. For this purpose, low-pressure EGR has a recirculation line that branches off from the exhaust gas removal system downstream of the turbine and preferably leads into the intake system upstream of the compressor.

[0076] The exhaust gas, recirculated to the intake side via low-pressure EGR, is mixed with fresh air. This mixture of fresh air and recirculated exhaust gas forms the charge air, which is then fed to the compressor and compressed.

[0077] Since low-pressure EGR often involves passing exhaust gas through the compressor, this gas must first undergo aftertreatment, particularly in a particulate filter. Deposits in the compressor, which alter its geometry, especially the flow cross-sections, and thus reduce its efficiency, must be avoided.

[0078] For the reasons mentioned above, internal combustion engines are advantageous in which the exhaust gas recirculation return line branches off from the exhaust gas discharge system downstream of the turbine of the at least one exhaust gas turbocharger and enters the intake system upstream of the compressor.

[0079] In internal combustion engines where each cylinder has at least two intake ports, internal combustion engines are advantageous which are characterized in that the intake lines of each cylinder of the second group merge to form a partial intake line and each partial intake line is equipped with an intake-side throttle element.

[0080] Accordingly, a single throttle element is sufficient to reduce the charge air supply to a deactivated cylinder, even if the switchable cylinder has more than one intake port, i.e., at least two intake ports and therefore at least two intake lines.

[0081] In internal combustion engines where the second cylinder group has at least two intake ports, it is also advantageous for internal combustion engines to be characterized in that the intake manifolds of the second cylinder group merge to form a single intake manifold, and this intake manifold is equipped with at least one intake-side throttle element. Preferably, one intake-side throttle element is arranged in the single intake manifold.

[0082] Accordingly, a single throttle element is sufficient to reduce the charge air supply to the deactivated cylinders.

[0083] In principle, a throttle element can also be provided in each intake manifold of a deactivatable cylinder, which increases the number of throttle elements required, especially if the cylinders have more than one intake port and / or the second group includes more than one deactivatable cylinder.

[0084] Internal combustion engines are therefore also advantageous if each intake manifold of each cylinder in the second group is equipped with an intake-side throttle element.

[0085] The above statements regarding the at least one intake-side throttle element also apply analogously to the at least one intake-side throttle element.

[0086] In internal combustion engines where each cylinder has at least two exhaust ports, internal combustion engines are therefore advantageous which are characterized in that the exhaust lines of each cylinder of the second group merge into a partial exhaust line and each partial exhaust line is equipped with an exhaust-side throttle element.

[0087] In internal combustion engines where the second cylinder group has at least two exhaust ports, it is also advantageous for internal combustion engines to be characterized in that the exhaust pipes of the second cylinder group merge into a single exhaust manifold, and this exhaust manifold is equipped with at least one exhaust-side throttle element. Preferably, one exhaust-side throttle element is arranged in the combined exhaust manifold.

[0088] However, internal combustion engines can also be advantageous if each exhaust pipe of each cylinder in the second group is equipped with an exhaust-side throttle element.

[0089] Internal combustion engines are advantageous if each intake-side throttle element and / or each exhaust-side throttle element is arranged as close as possible to its corresponding cylinder. The smaller the flow volume between a throttle element and the corresponding cylinder opening, the more advantageous this is for the operation of the internal combustion engine, particularly for the activation and deactivation of the cylinders of the second group.

[0090] Internal combustion engines are therefore also advantageous in which each intake-side throttle element and / or each exhaust-side throttle element is arranged in or on which at least one cylinder head is located.

[0091] Internal combustion engines are advantageous if each cylinder is equipped with direct injection for the introduction of fuel.

[0092] Internal combustion engines are advantageous in which each cylinder is equipped with an injection nozzle for the purpose of direct injection.

[0093] The fuel supply can be deactivated more quickly and reliably for the purpose of partial shutdown in direct-injection internal combustion engines than in internal combustion engines with port injection, where residual fuel in the intake manifold can lead to unwanted combustion in the deactivated cylinder.

[0094] Nevertheless, internal combustion engines can be advantageous if they incorporate port fuel injection for the purpose of fuel supply.

[0095] The invention is described below using a self-igniting internal combustion engine and according to Fig. 1 explained in more detail. This shows: Fig. 1 Schematic representation of a self-igniting internal combustion engine.

[0096] Fig. Figure 1 schematically shows a self-igniting internal combustion engine 10.

[0097] It is a four-cylinder in-line engine 10 with direct injection, in which the four cylinders 1, 2, 3, 4 are arranged along the longitudinal axis of the cylinder head, i.e. in a line, and each is equipped with an injector for injecting fuel, the amount of fuel injected being used to adjust the air-fuel ratio λ (not shown).

[0098] Each cylinder 1, 2, 3, 4 has an intake line 5a, 5b for supplying charge air via intake system 6 and an exhaust line 7a, 7b for removing exhaust gases via exhaust system 8.

[0099] The internal combustion engine 10 is equipped with an exhaust gas turbocharger 12 for turbocharging purposes. The turbine 12a is located in a combined exhaust gas line 18 of the exhaust gas discharge system 8, and the compressor 12b is located in a combined intake line 16 of the intake system 6. The fresh air supplied to the internal combustion engine 10 is compressed in the compressor 12b, utilizing the enthalpy of the exhaust gas flow in the turbine 12a. For exhaust gas aftertreatment, a particulate filter 14, serving as an exhaust gas aftertreatment system 13, is provided in the combined exhaust gas line 18 downstream of the turbine 12a.

[0100] The internal combustion engine 10 is further equipped with an exhaust gas recirculation system 15, specifically a high-pressure EGR system. For this purpose, a recirculation line 17 branches off from the exhaust gas discharge system 8 upstream of the turbine 12a and opens into the intake system 6 downstream of the compressor 12b. A valve 19 for adjusting the amount of recirculated exhaust gas is arranged in the recirculation line 17 of the exhaust gas recirculation system 15.

[0101] The four cylinders 1, 2, 3, 4 are configured to form two groups of two cylinders each 1, 2, 3, 4, wherein the two outer cylinders 1, 4 form a first group, whose cylinders 1, 4 are also in operation when the internal combustion engine 10 is partially shut down, and the two inner cylinders 2, 3 form a second group, whose cylinders are designed as load-dependent switchable cylinders 2, 3, which are shut down as part of a partial shutdown.

[0102] In the intake lines 5b of the two inner cylinders 2, 3, intake-side throttle elements 9 are provided, with which the charge air quantity supplied to the deactivated cylinders 2, 3 is adjusted by changing the size of the flow cross-section of the intake line 5b.

[0103] Cylinders 2 and 3 of the second group are designed as switchable cylinders 2 and 3, which are deactivated during partial load operation when a predefined load is undershot. This is achieved by reducing the flow cross-section of their intake lines 5b by means of a throttle element 9 and deactivating the fuel injection. This increases the load requirement for the remaining cylinders 1 and 4 of the first group, which then operate at higher loads with lower specific fuel consumption. An improvement in efficiency is the result.

[0104] Exhaust gas lines 7b of the inner cylinders 2, 3 are equipped with exhaust-side throttle elements 11, which can change the size of the flow cross-sections of the associated exhaust gas lines 7b and with which the discharge of the exhaust gas or charge air from the deactivated cylinders 2, 3 can be controlled.

[0105] The exhaust-side throttle elements 11 are intended to prevent the inflow of exhaust gas or charge air into the deactivated cylinders 2 and 3 of the second group. Furthermore, the charge exchange losses of the deactivated cylinders 2 and 3 can be reduced by appropriately controlling the exhaust-side throttle elements 11.

Claims

[1] Method for operating an internal combustion engine (10) having at least two cylinders (1, 2, 3, 4), wherein - each cylinder (1, 2, 3, 4) has at least one exhaust port to which an exhaust pipe (7a, 7b) is connected for the removal of exhaust gases via exhaust system (8), - each cylinder (1, 2, 3, 4) has at least one inlet opening to which an intake line (5a, 5b) is connected for supplying charge air via intake system (6), - at least two cylinders (1, 2, 3, 4) are configured in such a way that they form at least two groups, each with at least one cylinder (1, 2, 3, 4), wherein the at least one cylinder (1, 4) of a first group is a cylinder (1, 4) that is in operation even when the internal combustion engine (10) is partially shut down, and the at least one cylinder (2, 3) of a second group is designed as a load-dependent switchable cylinder (2, 3), - in the at least one intake line (5b) of the at least one load-dependent switchable cylinder (2, 3) an intake-side throttle element (9) is provided, with which the size of the flow cross-section of the intake line (5b) can be changed, whereby the amount of charge air supplied to the (10) at least one deactivated cylinder (2, 3) when the internal combustion engine is partially deactivated can be adjusted, and - in which at least one exhaust pipe (7b) of at least one load-dependent switchable cylinder (2, 3) has an exhaust-side throttle element (11) with which the size of the flow cross-section of the exhaust pipe (7b) can be changed and with which the discharge of the exhaust gas from at least one deactivated cylinder (2, 3) of the second group can be controlled when the internal combustion engine (10) is partially deactivated, characterized by, that the at least one switchable cylinder (2, 3) of the second group is switched depending on the load T of the internal combustion engine (10), in such a way that this at least one switchable cylinder (2, 3) is switched off when a predefinable load T is undershot down is switched off and when a predefined load T is exceeded up is switched on, whereby the amount of charge air supplied to the at least one deactivated cylinder (2, 3) during the partial deactivation is reduced, but not completely prevented, by actuating the at least one intake-side throttle element (9). [2] Method according to claim 1, characterized by , that - when the at least one load-dependent switchable cylinder (2, 3) is deactivated, the fuel supply to the at least one switchable cylinder (2, 3) is first deactivated before the at least one intake-side throttle element (9) is actuated, and - when at least one deactivated cylinder (2, 3) is activated, at least one intake-side throttle element (9) is actuated before the fuel supply to the at least one deactivated cylinder (2, 3) is activated. [3] Method according to claim 1 or 2, characterized by , that a predefinable minimum amount of charge air is supplied to at least one deactivated cylinder (2, 3).

Images