DE102015203984B4 - Method for carrying out a charge exchange in an internal combustion engine - Google Patents

Abstract

A method for carrying out a charge exchange in an internal combustion engine with - at least one cylinder head with at least one cylinder, each cylinder having at least one inlet opening for supplying fresh air via the intake system and at least one outlet opening for discharging the exhaust gases via Abgasabführsystem and has a piston which along a Piston longitudinal axis between a bottom dead center and a top dead center is movable, and - at least two valve trains having at least two valves, which are movable along its longitudinal axis between a valve closed position and a valve open position under full control of a maximum valve lift to the at least one inlet opening and the at least one outlet opening of the at least one cylinder as part of a charge exchange and to block and with at least two actuators to open the valves against a biasing force, in which - the exhaust valve of the at least one exhaust port is actuated in such a manner that this exhaust valve performs an additional valve lift before the piston reaches bottom dead center during the charge cycle and after the exhaust valve has made the maximum valve lift as part of the charge cycle, the exhaust valve being at least one exhaust valve Outlet opening for the purpose of completing the additional valve lift is only actuated if there is a pressure gradient of the type that the pressure in the intake system is greater than the pressure in the Abgasabführsystem.

Description

• – mindestens einem Zylinderkopf mit mindestens einem Zylinder, wobei jeder Zylinder mindestens eine Einlassöffnung zum Zuführen von Frischluft via Ansaugsystem und mindestens eine Auslassöffnung zum Abführen der Abgase via Abgasabführsystem aufweist und über einen Kolben verfügt, der entlang einer Kolbenlängsachse zwischen einem unteren Totpunkt und einem oberen Totpunkt bewegbar ist, und
• – mindestens zwei Ventiltrieben mit mindestens zwei Ventilen, die entlang ihrer Längsachse zwischen einer Ventilschließstellung und einer Ventiloffenstellung unter Vollführung eines maximalen Ventilhubs bewegbar sind, um die mindestens eine Einlassöffnung und die mindestens eine Auslassöffnung des mindestens einen Zylinders im Rahmen eines Ladungswechsels freizugeben und zu versperren, und mit mindestens zwei Betätigungseinrichtungen, um die Ventile entgegen einer Vorspannkraft zu öffnen.

The invention relates to a method for carrying out a charge exchange in an internal combustion engine with

• - At least one cylinder head with at least one cylinder, each cylinder having at least one inlet opening for supplying fresh air via the intake system and at least one outlet opening for discharging the exhaust gases via Abgasabführsystem and has a piston along a piston longitudinal axis between a bottom dead center and top dead center is movable, and
• At least two valve trains having at least two valves, which are movable along their longitudinal axis between a valve closed position and a valve open position with full control of a maximum valve lift in order to release and obstruct the at least one inlet opening and the at least one outlet opening of the at least one cylinder in the context of a charge exchange, and at least two actuators to open the valves against a biasing force.

An internal combustion engine of the type mentioned is used as a drive for motor vehicles. In the context of the present invention, the term internal combustion engine comprises gasoline engines, diesel engines, but also hybrid internal combustion engines, which use a hybrid combustion process, and hybrid drives, which in addition to the internal combustion engine comprise an electric motor which can be electrically connected to the internal combustion engine, which receives power from the internal combustion engine or as switchable auxiliary drive additionally delivers power.

Internal combustion engines have a cylinder block and at least one cylinder head, which are connected to form at least one cylinder. The cylinder block has a corresponding number of cylinder bores for receiving the pistons or the cylinder tubes. The cylinder head is usually used to hold the valve train. To control the charge cycle, an internal combustion engine requires controls and actuators to operate the controls. As part of the change of charge of a cylinder, the expulsion of the combustion gases via at least one outlet opening and the filling of the combustion chamber, d. H. the intake of fresh air via at least one inlet opening. For controlling the charge cycle, four-stroke engines use almost exclusively globe valves as control members which, during operation of the internal combustion engine, perform an oscillating stroke movement along their longitudinal axis and in this way release and close the inlet and outlet openings. The required for the movement of a valve actuator including the valve itself is referred to as a valve train.

It is the task of the valve drive to release or close at least one inlet and / or outlet opening of a cylinder in good time, with the aim of rapidly releasing flow cross sections which are as large as possible in order to keep the throttling losses in the incoming and outflowing gas flows low and one To ensure the best possible filling of the cylinder or a complete discharge of the exhaust gases. In the prior art, therefore, a cylinder is also frequently and increasingly equipped with two or more inlet and outlet ports.

A method for carrying out a charge exchange according to the aforementioned type describes, for example, the DE 602 23 846 T2 , The exhaust valve performs in the intake stroke of the charge change an additional valve lift, whereby in cooperation with the then existing pressure gradient between Abgasabführsystem and cylinder internal exhaust gas recirculation is realized.

The US 2009 / 0194080A1 describes a method in which the intake valve during the discharge of the exhaust gas performs an additional valve lift to rinse the cylinder and remove residual gas. The DE 10 2013 004 800 A1 also relates to such a method.

The intake pipes leading to the intake ports and the exhaust pipes connecting to the exhaust ports are at least partially integrated in the cylinder head in the prior art.

In the development of internal combustion engines, it is a fundamental goal to minimize fuel consumption. In this context, the charging of internal combustion engines is becoming increasingly important. The charge is a suitable means to increase the capacity of an internal combustion engine with unchanged displacement or to reduce the displacement at the same power. At the same vehicle boundary conditions, the load collective can thus be shifted to higher loads in which the specific fuel consumption is lower. The charging of an internal combustion engine thus supports the efforts to minimize fuel consumption, d. H. to improve the efficiency of the internal combustion engine.

The design of the exhaust turbocharger often causes difficulties, in principle, a noticeable increase in performance in all speed ranges is sought. According to the prior art, however, a drop in torque is at Below a certain speed observed. This torque drop becomes understandable if it is taken into account that the boost pressure ratio depends on the turbine pressure ratio.

For example, if the engine speed is reduced, this leads to a smaller exhaust gas mass flow and thus to a smaller turbine pressure ratio. As a result, the boost pressure ratio and the charge pressure also decrease at lower speeds, which is equivalent to a torque drop.

Basically, the drop in charge pressure can be counteracted by a small exhaust gas turbocharger, d. H. an exhaust gas turbocharger with a small turbine cross section is used in order to generate a sufficient charge pressure even with small exhaust gas streams. Ultimately, the torque drop is thus shifted only to lower speeds. In addition, this approach, d. H. The reduction of the turbine cross-section limits, since the desired charging and performance should be possible even at high speeds without restriction and to the extent desired.

The torque characteristic of a supercharged internal combustion engine is attempted to be improved by different measures according to the prior art, for example by a small design of the turbine cross-section in combination with a Abgasabblasung or the use of multiple turbochargers.

The torque characteristic can be advantageously influenced by means of several exhaust gas turbochargers connected in series. By switching in series of two exhaust gas turbochargers, one of which is an exhaust gas turbocharger as a high-pressure stage and an exhaust gas turbocharger as a low-pressure stage, the engine map can be widened in an advantageous manner, both towards smaller compressor streams and towards larger compressor streams.

In particular, in the case of the exhaust gas turbocharger serving as a high-pressure stage, the pumping limit can be shifted towards smaller compressor flows, which means that high boost pressure ratios can be achieved even with small compressor flows, which significantly improves the torque characteristic in the lower rpm range. This is achieved by designing the high-pressure turbine for small exhaust gas mass flows and providing a bypass line, with which increasing exhaust gas mass flow increasingly exhaust gas is passed to the high-pressure turbine. For this purpose, the bypass line branches off from the exhaust-gas removal system upstream of the high-pressure turbine and flows back into the exhaust-gas removal system upstream of the low-pressure turbine, wherein a shut-off element is arranged in the bypass line in order to control the exhaust gas flow conducted past the high-pressure turbine.

The response of such a supercharged internal combustion engine is significantly improved over a comparable internal combustion engine with single-stage supercharging, since the smaller high-pressure stage is less sluggish, d. H. the speed of a smaller sized exhaust gas turbocharger accelerate faster.

The torque characteristic of a supercharged internal combustion engine may be further characterized by a plurality of turbochargers arranged in parallel, i. H. be improved by a plurality of parallel turbines with a smaller turbine cross-section, with turbines are switched successively with increasing exhaust gas.

The torque characteristic of a supercharged internal combustion engine can also be improved by the fact that the at least one exhaust gas turbocharger by a mechanical supercharger, d. H. a compressor, is added.

In addition to a conceptual improvement of the exhaust gas turbocharging, as described above, found in the prior art, methods for improving the torque characteristics of a charged by turbocharging internal combustion engine with which increases the torque, in particular the torque weakness at low speeds to be overcome. As a cause of the torque weakness at low speeds while the amount of exhaust gas is considered low at low speeds in principle.

By means of variable valve timing, the valve overlap, i. H. the crank angle range, in which the outlet is not yet closed when the inlet is open, can be varied. During valve overlap, purge losses may occur, with some of the intake fresh air flowing through the cylinder without participating in the subsequent combustion. A variable valve control allows a variation of the valve overlap among other things as a function of the speed.

In spark-ignition turbocharged spark-ignition internal combustion engines, a large valve overlap is suitable at low rotational speeds in order to significantly increase the maximum torque and to improve the unsteady operating behavior. A pressure differential between the inlet side and the outlet side at low speeds supports effective flushing of the cylinders with fresh air and ensures a larger cylinder filling and thus for a higher performance.

In gasoline engines with a relatively low compression ratio of, for example, ε ≈ 10 for naturally aspirated engines and ε ≈ 8 ... 9 for supercharged engines, the torque weakness at low speeds can be counteracted with a large valve overlap. In high-compression internal combustion engines, such as a diesel engine, a large valve overlap is often not feasible, since the piston when passing through the top dead center comes very close to the inlet valves and the exhaust valves and opening of the valves in the context of valve overlap can not be unrestricted.

A further problem with internal combustion engines charged by means of turbocharging is that the operation of the internal combustion engine is frequently limited, especially at full load, by the maximum permissible temperature at the turbine inlet. During operation, it must be ensured that the maximum permissible turbine inlet temperature is not exceeded, which is why it is not always possible to optimize operation with regard to fuel consumption or pollutant emissions. Under certain circumstances, an enrichment of the fuel-air mixture may be required to cool the exhaust gas.

In view of the above, it is the object of the present invention to provide a method according to the preamble of claim 1, with which the exhaust gas temperature can be reduced and the torque weakness of supercharged by turbocharging internal combustion engines can be counteracted at low speeds.

• – mindestens einem Zylinderkopf mit mindestens einem Zylinder, wobei jeder Zylinder mindestens eine Einlassöffnung zum Zuführen von Frischluft via Ansaugsystem und mindestens eine Auslassöffnung zum Abführen der Abgase via Abgasabführsystem aufweist und über einen Kolben verfügt, der entlang
• – einer Kolbenlängsachse zwischen einem unteren Totpunkt und einem oberen Totpunkt bewegbar ist, und
• – mindestens zwei Ventiltrieben mit mindestens zwei Ventilen, die entlang ihrer Längsachse zwischen einer Ventilschließstellung und einer Ventiloffenstellung unter Vollführung eines maximalen Ventilhubs bewegbar sind, um die mindestens eine Einlassöffnung und die mindestens eine Auslassöffnung des mindestens einen Zylinders im Rahmen eines Ladungswechsels freizugeben und zu versperren, und mit mindestens zwei Betätigungseinrichtungen, um die Ventile entgegen einer Vorspannkraft zu öffnen, bei dem
• – das Auslassventil der mindestens einen Auslassöffnung in der Weise betätigt wird, dass dieses Auslassventil einen zusätzlichen Ventilhub vollführt bevor der Kolben im Rahmen des Ladungswechsels den unteren Totpunkt erreicht und nachdem das Auslassventil im Rahmen des Ladungswechsels den maximalen Ventilhub vollführt hat, wobei das Auslassventil der mindestens einen Auslassöffnung zwecks Vollführung des zusätzlichen Ventilhubs nur dann betätigt wird, falls ein Druckgefälle der Art vorliegt, dass der Druck im Ansaugsystem größer ist als der Druck im Abgasabführsystem.

This object is achieved by a method for carrying out a charge exchange in an internal combustion engine with

• At least one cylinder head having at least one cylinder, each cylinder having at least one inlet opening for supplying fresh air via the intake system and at least one outlet opening for discharging the exhaust gases via the exhaust gas removal system and having a piston which runs along
• - A piston longitudinal axis between a bottom dead center and a top dead center is movable, and
• At least two valve trains having at least two valves, which are movable along their longitudinal axis between a valve closed position and a valve open position with full control of a maximum valve lift in order to release and obstruct the at least one inlet opening and the at least one outlet opening of the at least one cylinder in the context of a charge exchange, and at least two actuators to open the valves against a biasing force, wherein
• - The exhaust valve of the at least one outlet opening is actuated in such a manner that this exhaust valve performs an additional valve lift before the piston reaches the bottom dead center in the context of the charge cycle and after the exhaust valve has performed the maximum valve lift in the context of the charge cycle, wherein the exhaust valve of at least an outlet opening for the purpose of carrying out the additional valve lift is only actuated if there is a pressure gradient of the type that the pressure in the intake system is greater than the pressure in the Abgasabführsystem.

According to the invention, the outlet valve of the at least one outlet opening carries out at least two valve lifts, with the actual, larger valve lift, which primarily serves to change the charge, being followed by an additional, smaller valve lift.

If an exhaust valve is opened again during the suction process of the charge cycle, in which the piston moves down, before the piston reaches the bottom dead center, the at least one inlet valve is still open. The fresh air introduced via the inlet opening can then flow through the cylinder due to the valve lift, which the outlet valve additionally performs, and leave again via the outlet.

A rinsing of residual gas does not take place in the present case or at most to an insignificant extent. When supercharged by turbocharging internal combustion engines of the purge but has the effect that a arranged in Abgasabführsystem turbine of an exhaust gas turbocharger, a larger mass flow is provided. The larger mass flow through the turbine causes a higher turbine pressure ratio, a higher boost pressure ratio and thus a higher boost pressure on the intake side, which contributes to a better filling of the cylinder, d. H. to the largest possible fresh cylinder charge in the next work cycle. This leads to an increase in performance and an increase in torque at a constant speed.

However, the larger mass flow has a lower temperature, since the guided through the cylinder fresh air is heated neither by purged residual gas nor by a piston located adjacent to the bottom dead center. The lack of heating of the fresh air can be used in an advantageous manner to specifically cool the mass flow supplied to the turbine, d. H. to lower the turbine inlet temperature.

In this respect, with the method according to the invention, in which the exhaust valve of the at least one exhaust port performs an additional valve lift, not only the boost pressure and thus the torque are raised on the intake side, but in particular the exhaust gas temperature is lowered on the exhaust side, ie the exhaust gas mass flow is cooled.

While with a larger valve overlap, in which the inlet valve must be opened earlier or the exhaust valve closed later, there is a risk that the top dead center piston comes into contact with an open inlet valve or an open exhaust valve, the additional invention can be Stroke before reaching the bottom dead center and thus spaced to perform top dead center, so that the piston can not touch or damage the open valves.

According to the invention, the outlet valve of the at least one outlet opening is actuated for the purpose of carrying out the additional valve lift only if there is a pressure gradient such that the pressure in the intake system is greater than the pressure in the exhaust gas removal system. Decisive here is the pressure gradient between the cylinder inlet and the cylinder outlet, i. between the at least one inlet opening and the at least one outlet opening of a cylinder.

A pressure gradient between the intake system and the exhaust system supports a flow of fresh air through the cylinder. In this context, it should be taken into account that gas-dynamic wave processes take place in the intake system and in the exhaust-gas removal system, in particular due to the intermittent gas exchange, which is why the pressure on the inlet side and outlet side usually changes over time.

The inventive method thus solves the problem underlying the invention, namely to provide a method by which the exhaust gas temperature lowered and the torque weakness of supercharged by turbocharging internal combustion engine can be counteracted at low speeds.

Further advantageous embodiments of the method according to the invention are discussed in connection with the subclaims.

Embodiments of the method in which the outlet valve of the at least one outlet opening is actuated for the purpose of carrying out the additional valve lift are advantageous, while at least one inlet opening of the at least one cylinder is at least temporarily open. The fresh air introduced via the inlet opening can in the present flow unhindered through the cylinder and leave the cylinder in the context of the additional valve lift via the outlet opening, whereby a flow through the cylinder is advantageously supported and thus an introduction of the fresh air into the exhaust gas removal system.

Advantageous embodiments of the method, in which the additional valve lift of the exhaust valve is performed up to 50 ° CA before bottom dead center.

Advantageous embodiments of the method in which the additional valve lift of the exhaust valve is performed up to 30 ° CA before bottom dead center.

The closer the additional valve lift is performed at bottom dead center, the lower the heating or the temperature increase of the fresh air when passing over the combustion chamber inner walls, in particular of the piston head, drops out. The crank angle mark at which the additional valve lift is performed is to be matched with the amount of additional valve lift.

Embodiments of the method are advantageous in which the outlet valve of the at least one outlet opening is returned to the closed position during the charge cycle after the maximum valve lift has been completed, before this outlet valve is opened again for the purpose of carrying out the additional valve lift.

Advantageous embodiments of the method in which an additional valve lift is performed, which is less than a quarter of the maximum valve lift.

Advantageous embodiments of the method in which an additional valve lift is performed, which is less than one sixth of the maximum valve lift.

Advantageous embodiments of the method in which an additional valve lift is performed, which is less than one-eighth of the maximum valve lift.

The amount of the additional valve lift is always to be matched with the crank angle mark, to which the additional valve lift is performed. However, a large number of other parameters can be taken into consideration, for example the piston shape, the shape of the combustion chamber roof, but in particular the compression ratio ε of the cylinder or of the internal combustion engine.

Embodiments of the method in which an additional valve lift of less than 2 mm is performed are advantageous.

Embodiments of the method in which an additional valve lift of less than 1.5 mm is performed are advantageous.

The details of the above process variants for the additional valve lift are only examples and are intended to illustrate the ratio to the maximum valve lift, which can easily be 8mm to 12mm.

Embodiments of the method in which a diesel engine is used as the internal combustion engine are advantageous. As already stated, the method according to the invention is particularly advantageous in high-compression internal combustion engines, such as diesel engines, in which the valves for realizing a valve overlap can not be operated and opened in the desired manner and opened as the piston is very close when passing through top dead center comes up to the valves. The risk that the piston comes into contact with an open outlet valve does not exist in the method according to the invention.

Embodiments of the method in which a supercharged internal combustion engine is used as the internal combustion engine are advantageous.

A pressure gradient between the intake system and the exhaust system helps to flow through the cylinder, d. H. the introduction of fresh air into the Abgasabführsystem via cylinder, so that it is advantageous to provide a high pressure in the intake system. The latter can be achieved by charging the internal combustion engine. Then prevails in the intake system of the boost generated by boost, which is often higher at low speeds than the exhaust back pressure in Abgasabführsystem.

The pressures in the intake and exhaust systems continuously change due to the intermittent charge change. The evacuation of the combustion gases is based on the beginning of the charge cycle on the high pressure difference between the combustion chamber and Abgasabführsystem. This pressure-driven flow process is accompanied by a high pressure peak. In the course of the charge cycle, the pressures in the combustion chamber and in the Abgasabführsystem the same and the combustion gases are ejected due to the stroke of the piston. On the inlet side also occur larger pressure changes. Consequently, the pressure difference between the intake system and the Abgasabführsystem constantly changes, d. H. between the inlet opening and the outlet opening of the cylinder.

In this context, embodiments of the method in which an internal combustion engine charged by means of turbocharging is used as the internal combustion engine are advantageous.

When charged by turbocharging supercharged internal combustion engines, the introduction of fresh air has the special effect that the arranged in Abgasabführsystem turbine of the exhaust gas turbocharger gets a larger mass flow available. This larger mass flow through the turbine leads on the inlet side to a higher charge pressure and ultimately to an increase in the torque. In addition, the cooling effect achieved by means of fresh air proves to be particularly advantageous.

Advantageous embodiments of the method in which the inlet valve of the at least one inlet opening is actuated in such a manner that this inlet valve performs an additional valve lift before the piston reaches the top dead center in the context of the charge cycle and before the inlet valve in the context of the charge cycle the maximum valve performs.

The additional smaller valve lift of the intake valve is used to purge residual gas from the cylinder. The Restgasausspülung is assisted by the fact that the piston moves to the top dead center, passes through the top dead center or is near the top dead center just before top dead center, so that the instantaneous combustion chamber volume at full management of the additional valve lift of the intake valve comparatively is small or only slightly larger than the compression volume at which the piston is at top dead center.

The most extensive rinsing of the residual gas ensures the largest possible fresh cylinder charge in the next cycle and thus a higher energy yield in the subsequent combustion cycle, d. H. an increase in performance and thus a torque increase at the same, especially low speed.

When charged by turbocharging supercharged internal combustion engines of the purge has yet another advantageous effect, namely the effect that the arranged in Abgasabführsystem turbine of an exhaust gas turbocharger is a larger mass flow available or is provided. The larger mass flow through the turbine causes a higher turbine pressure ratio, a higher boost pressure ratio and thus a higher boost pressure on the inlet side, which also leads to a contributes better filling of the cylinder, ie the largest possible fresh cylinder charge in the next working cycle. Also, this effect leads to an increase in performance, ie an increase in torque at a constant speed.

The introduced as part of the Restgasausspülung in the cylinder or passed through the cylinder fresh air is also heated in the overflow of the piston crown and the hot combustion chamber inner walls due to convection, so that introduced into the Abgasabführsystem mass flow has a higher temperature and thus an increased enthalpy.

In addition, the hot flushed residual gas further contributes to increase the enthalpy of the mass flow, which is supplied to the turbine. In addition to increasing the mass flow and the increase in enthalpy - as described above - leads to a higher boost pressure and thus to an increase in torque.

While at a larger valve overlap there is a risk that the top dead center piston comes into contact with an open inlet valve or an open exhaust valve, the additional lift of the intake valve before reaching top dead center can be performed without the piston, the open inlet valve touched and damaged.

Although an additional intake-side valve lift is more sensitive to changes in exhaust back pressure than an additional exhaust-side valve lift, it is more effective in increasing exhaust mass flow and increasing exhaust enthalpy as an additional exhaust-side valve lift.

In this case, embodiments of the method may be advantageous in which the inlet valve of the at least one inlet opening is returned to the closed position after complete execution of the additional valve stroke, before this inlet valve is opened again for the purpose of carrying out the maximum valve lift as part of the charge cycle.

However, embodiments of the method may also be advantageous in which the inlet valve of the at least one inlet opening is not transferred to the closed position after completion of the additional valve lift, but is further opened for the purpose of carrying out the maximum valve lift as part of the charge exchange.

Optionally, there is not the time available to transfer the intake valve after completion of the additional valve lift in the closed position, since this intake valve for the purpose of the change of charge must be opened immediately wide and complete. This may for example be the case when the additional valve lift is performed very close to top dead center.

In this connection, however, embodiments of the method may advantageously be advantageous in which the inlet valve of the at least one inlet opening is initially moved in the direction of the closed position after the additional valve stroke has been completed, in order to reduce the valve lift.

In this context, embodiments of the method may advantageously be advantageous in which the inlet valve of the at least one inlet opening is moved in the direction of the closed position after completion of the additional valve stroke in order to reduce the valve lift by half or less.

Embodiments of the method may also be advantageous, in which the inlet valve of the at least one inlet opening is moved in the direction of the closed position after completion of the additional valve lift in order to reduce the valve lift by at least one third.

Embodiments of the method may also be advantageous in which the inlet valve of the at least one inlet opening is moved in the direction of the closed position after completion of the additional valve lift in order to reduce the valve lift by at least a quarter.

According to the above method variants, a valve lift curve is formed with at least two maxima. Ie. When the additional valve lift is reached, the inlet valve is not opened further directly in order to carry out the maximum valve lift for the purpose of changing the charge, but initially moves in the direction of the closed position. Ie. The valve lift is initially reduced before further opening is initiated.

This approach may be required, for example, if the additional valve lift is performed very close to top dead center to prevent contact of the piston with the intake valve. Then it is advantageous to reduce the valve lift before the intake valve is further opened or fully opened during the charge cycle.

Nevertheless, upon reaching the additional valve lift, the intake valve may also be further opened directly or retarded to perform the maximum valve lift for the purpose of a charge exchange.

In internal combustion engines, in which each cylinder has at least two inlet openings for Supplying fresh air via the intake system and having at least two outlet openings for discharging the exhaust gases via Abgasabführsystem, embodiments are advantageous, which are characterized in that the exhaust valves of at least two outlet openings are actuated in such a way that these exhaust valves perform an additional valve lift.

In internal combustion engines in which each cylinder has at least two inlet openings for supplying fresh air via the intake system and at least two outlet openings for discharging the exhaust gases via Abgasabführsystem, embodiments are advantageous, which are characterized in that the outlet valve is actuated by at least one outlet opening in the manner that this exhaust valve performs an additional valve lift.

In the following the invention with reference to two variants of the method and the 1a and 1b described in more detail. Hereby shows:

1a in a diagram, the valve lift curves h _intake , h _exhaust an intake valve and an exhaust valve according to a first embodiment of the method, and

1b in a diagram, the valve lift curves h _intake , h _{exhaust of} an intake valve and an exhaust valve according to a second embodiment of the method.

1a shows in a diagram the valve lift curves h _intake , h _{exhaust of} an intake valve and an exhaust valve according to a first embodiment of the method. In addition, the pressure difference .DELTA.p between the intake system and the Abgasabführsystem, ie between the inlet side and the outlet side.

During the charge exchange, the exhaust gas is evacuated from the cylinder by opening the exhaust valve and performing the maximum valve lift Δh _{max, exhaust} . The intake valve is subsequently opened to refill the cylinder with fresh air, the intake valve performing the maximum valve lift Δh _{max, intake} as part of the charge cycle.

The intake valve is actuated in such a way that this intake valve performs an additional valve lift .DELTA.h _{add, intake} before the intake valve in the context of the charge cycle _, the maximum valve lift .DELTA.h _{max, intake} performs and before the piston top dead center in the context of the charge cycle reached. Consequently, the intake valve performs two valve strokes Δh _{max, intake} , Δh _{add, intake} , with the actual, larger valve lift Δh _{max, intake} , which primarily serves to change the charge, preceded by an additional smaller valve lift Δh _{add, intake} . The additional smaller valve lift Δh _{add, intake} serves to purge residual gas from the cylinder. The Restgasausspülung is supported by the fact that the piston moves to the top dead center, whereby the combustion chamber volume is reduced. A positive pressure drop Δp between the intake system and the exhaust gas discharge system additionally supports the flushing process with fresh air. The largest possible cylinder fresh charge in the next cycle ensures an increase in performance and a torque increase at the same speed.

When charged by turbocharging supercharged internal combustion engines, the purge has the effect that the arranged in the Abgasabführsystem turbine a larger mass flow is provided, whereby the inlet side, a higher boost pressure can be generated. The higher boost pressure also leads to an increase in torque at a constant speed. The hot rinsed residual gas increases the enthalpy of the turbine flow mass flow, which is further increased by the fact that the fresh air passed through the cylinder as part of the residual gas purging heats up as it flows through the cylinder due to convection.

In the present case, the intake valve after completion of the additional valve lift .DELTA.h _{add, intake is} not returned to the closed position, but further opened in order to perform the maximum valve lift .DELTA.h _{max, intake} in the context of the charge cycle. After completion of the additional valve lift .DELTA.h _{add, intake} valve is initially moved in the direction of the closed position in order to reduce the valve lift by almost half before this intake valve is opened further in order to carry out the maximum valve lift .DELTA.h _{max, intake} . The trained valve lift curve has two maxima.

The exhaust valve is actuated in such a manner that this exhaust valve also performs an additional valve lift Δh _{add, exhaust} .

After the exhaust valve has carried out the maximum valve lift .DELTA.h _{max, exhaust} during the charge cycle and before the piston reaches bottom dead center during intake, the exhaust valve is opened again.

While the exhaust valve performs the additional valve lift Δh _{add, exhaust} , the intake valve is still open. The fresh air introduced into the cylinder via the inlet opening can leave the cylinder via the outlet. A positive pressure drop Δp between the intake system and the exhaust system supports the flow through the cylinder. The additional valve lift .DELTA.h _{add, exhaust of} the exhaust valve is less the Restgasausspülung, but rather the cooling of the turbine mass flow supplied, ie the lowering of the turbine inlet temperature. The guided through the cylinder fresh air is heated neither by rinsed residual gas nor by a piston adjacent to the bottom dead center. Due to this lack of heating of the fresh air as it flows through the cylinder, a cooling effect can be achieved.

However, the additional valve lift Δh _{add, exhaust of} the exhaust valve is also suitable, although not to the same extent, to increase the mass flow supplied to the turbine and thereby increase the torque at a constant speed although this increased mass flow has a lower temperature. In this respect, an exhaust-side additional valve lift Δh _{add, exhaust} supports the intake-side additional valve lift Δh _{add, intake} .

1b shows in a diagram the valve lift curves h _intake , h _{exhaust of} an intake valve and an exhaust valve according to a second embodiment of the method. The pressure difference Δp between the intake system and the Abgasabführsystem is also shown.

It should only the differences to the in 1a For the remainder, reference is made to 1a , The same reference numerals are used.

Unlike the in 1a illustrated method variant performs the inlet valve according to the in 1b process variant shown no additional valve lift Δh _{add, intake} .

Nonetheless, the additional valve lift Δh _{add, exhaust of} the exhaust valve may serve to increase the mass flow supplied to the turbine to increase the torque and to cool that mass flow to lower the turbine inlet temperature.

The additional valve lift .DELTA.h _{add, exhaust} the exhaust valve and the cooling effect achieved, ie lowering the temperature of the exhaust gas located in the Abgasabführsystems can also be used to protect arranged in Abgasabführsystem exhaust after-treatment systems from overheating, ie to protect against thermal overload.

reference numeral

• h _exhaust

  Valve lift of an exhaust valve

  h _intake

  Valve lift of an intake valve

  .delta.h

  valve

  Δh _{max, exhaust}

  maximum valve lift of an exhaust valve

  Δh _{max, intake}

  maximum valve lift of an intake valve

  Δh _{add, exhaust}

  additional valve lift of an exhaust valve

  Δh _{add, intake}

  additional valve lift of an intake valve

  Ap

  Pressure difference between intake system and exhaust gas removal system

  ° CA

  Degree crank angle

Claims (17)

A method for carrying out a charge exchange in an internal combustion engine having - at least one cylinder head with at least one cylinder, each cylinder having at least one inlet opening for supplying fresh air via the intake system and at least one outlet opening for discharging the exhaust gases via Abgasabführsystem and has a piston which along a Piston longitudinal axis between a bottom dead center and a top dead center is movable, and - at least two valve trains having at least two valves, which are movable along its longitudinal axis between a valve closed position and a valve open position to perform a maximum valve lift to the at least one inlet opening and the at least one outlet opening of the at least one cylinder as part of a charge exchange and to block and with at least two actuators to open the valves against a biasing force, in which - the exhaust valve of the at least one exhaust port is actuated in such a way that this exhaust valve performs an additional valve lift before the piston reaches the bottom dead center in the context of the charge cycle and after the exhaust valve has performed the maximum valve lift in the context of the charge cycle, wherein the exhaust valve of at least an outlet opening for the purpose of carrying out the additional valve lift is only actuated if there is a pressure gradient of the type that the pressure in the intake system is greater than the pressure in the Abgasabführsystem. A method according to claim 1, characterized in that the outlet valve of the at least one outlet opening is actuated for the purpose of carrying out the additional valve lift, while at least one inlet opening of the at least one cylinder is at least temporarily open. A method according to claim 1 or 2, characterized in that the additional valve lift of the exhaust valve is performed up to 50 ° CA before bottom dead center. Method according to one of the preceding claims, characterized in that the additional valve lift of the exhaust valve is performed up to 30 ° CA before bottom dead center. Method according to one of the preceding claims, characterized in that the exhaust valve of the at least one outlet opening after completion of the maximum valve lift in the context of the charge exchange is returned to the closed position, before this exhaust valve is opened again for the purpose of carrying out the additional valve lift. Method according to one of the preceding claims, characterized in that an additional valve lift is performed, which is less than a quarter of the maximum valve lift. Method according to one of the preceding claims, characterized in that an additional valve lift is performed, which is less than one sixth of the maximum valve lift. Method according to one of the preceding claims, characterized in that an additional valve lift of less than 2 mm is performed. Method according to one of the preceding claims, characterized in that an additional valve lift of less than 1.5 mm is performed. Method according to one of the preceding claims, characterized in that a diesel engine is used as the internal combustion engine. Method according to one of the preceding claims, characterized in that a supercharged internal combustion engine is used as an internal combustion engine. A method according to claim 11, characterized in that a charged by turbocharging internal combustion engine is used as the internal combustion engine. Method according to one of the preceding claims, characterized in that the inlet valve of the at least one inlet opening is actuated in such a way that this inlet valve performs an additional valve lift before the piston reaches the top dead center during the charge cycle and before the intake valve in the context of the charge cycle performs the maximum valve lift. A method according to claim 13, characterized in that the inlet valve of the at least one inlet opening after completion of the additional valve lift is again transferred to the closed position, before this inlet valve is opened again in order to perform the maximum valve lift in the context of the charge exchange. A method according to claim 13, characterized in that the inlet valve of the at least one inlet opening is not transferred after completion of the additional valve lift in the closed position, but further opened in order to carry out the maximum valve lift in the context of the charge exchange. A method according to claim 15, characterized in that the inlet valve of the at least one inlet opening after completion of the additional valve stroke is first moved in the direction of the closed position to reduce the valve lift. Method according to one of the preceding claims for carrying out a charge exchange in an internal combustion engine, wherein each cylinder has at least two inlet openings for supplying fresh air via the intake system and at least two outlet openings for discharging the exhaust gases via Abgasabführsystem, characterized in that the exhaust valves of at least two outlet openings in operated the way that these exhaust valves perform an additional valve lift.

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