METHOD FOR OPERATING AN INTERNAL COMBUSTION POWER ENGINE

Description

[0001] The invention relates to a method for operating an internal combustion engine according to the preamble of claim 1.

[0002] DE 102 42 226 A1 discloses a method for forming an ignitable fuel-air mixture in a combustion chamber of a spark-ignition internal combustion engine with direct injection, in which combustion air is supplied to a combustion chamber via at least one intake port. Fuel is injected into the combustion chamber by means of a fuel injector arranged in the combustion chamber. A fuel-air mixture formed is ignited by means of at least one spark plug arranged in the combustion chamber, the fuel injection occurring in several partial quantities. It is provided that, in homogeneous operation of the internal combustion engine, the fuel injection is designed such that a first and a second partial quantity are introduced during the intake stroke and a third partial quantity during the compression stroke, the ignition of the fuel-air mixture formed occurring at a time between 0° and 100° of crankshaft angle after the end of the injection of the third partial quantity.

[0003] Furthermore, in a stratified charge operation of the internal combustion engine, it is provided that the fuel injection is designed such that a first, a second and a third partial quantity are introduced into the combustion chamber in a compression stroke of the internal combustion engine, wherein the fuel injection of the second partial quantity is terminated at a crank angle that lies in a range between 15° crank angle before the ignition of the formed fuel-air mixture and 4° crank angle after the ignition of the formed fuel-air mixture.

[0004] German patent DE 10 2004 061 142 A1 discloses a known method for controlling an internal combustion engine. The internal combustion engine comprises a device for switching the effective valve lift curves of charge-swapping valves, a throttle valve controllable by a control unit, and at least one controllable injection element. Prior to switching the valve lift curves, the switching request is detected, and the throttle valve position is predictively changed before the switching occurs. It is provided that, at least after the predictive correction of the throttle valve position triggered by the switching request, the desired target and actual torque are continuously determined, and the switching of the effective valve lift curve occurs with a time delay relative to the switching request. The switching point is determined from the deviation of the actual torque from the target torque.

[0005] Furthermore, US Patent 2011 / 0108001 A1 discloses a self-igniting gasoline engine comprising a combustion control device with an injector that injects fuel directly into a combustion chamber, a variable valve timing device that modifies valve timing, at least two intake valves, at least two exhaust valves, a spark plug positioned in a central section of the combustion chamber, and an injector positioned adjacent to the spark plug towards a central section of the combustion chamber. The exhaust valve has a symmetrical valve lift, where the lift and opening section of the at least two exhaust valves are equal at low lift, and the intake valve has an asymmetrical valve lift, where the lift and opening section of the at least two intake valves are different at low lift.Furthermore, US Patent 2008 / 0271436 A1 discloses a method for operating a four-stroke internal combustion engine with a variable-volume combustion chamber defined by a piston moving back and forth within a cylinder between top dead center and bottom dead center. The engine features intake and exhaust ports, intake and exhaust valves controlled during repeated, sequential exhaust, intake, compression, and expansion strokes of the piston, a direct fuel injection system, and a spark ignition system. The method includes selectively implementing one of several operating modes in response to predetermined catalyst and engine temperature conditions.

[0006] Furthermore, EP 1 484 494 A2 discloses a combustion control device and a method for a direct-injection engine, wherein, when the engine is operating in the partial load range, the valve opening / closing mode of an intake valve and / or an exhaust valve is controlled such that exhaust gases remain in a combustion chamber. The control is effected by injecting fuel into the remaining exhaust gases at least once during a combustion cycle via a fuel injector, and by igniting an air-fuel mixture in the second half of a compression stroke thereafter.

[0007] Furthermore, a spark-ignition gasoline engine comprising a control device is known from EP 1 840 357 A2. The control device is operable when an engine operating zone is a high-load operating zone in order to set the closing time of an intake valve such that an effective compression ratio of 13 or more is maintained, and to retard the ignition timing to a point within a predetermined stroke range immediately after top dead center of a compression stroke.

[0008] Finally, WO 2006 / 063372 A1 discloses a method for operating an internal combustion engine, wherein at least in a first engine operating range both external and internal exhaust gas recirculation are carried out. To increase the residual gas tolerance in the full-load range and to reduce the tendency to knock, particularly during or before a knocking event, it is provided that the kinetic turbulent energy in the cylinder is increased – compared to a reference operating point, preferably at high load – at least briefly, wherein the residual gas content in the cylinder is adjusted, at least during the increase in turbulent kinetic energy, by varying the opening time of the intake valve, the closing time of the intake valve and / or the closing time of the exhaust valve.

[0009] It has been shown that when operating an internal combustion engine, in particular a gasoline engine, with relatively small valve lifts of at least one gas exchange valve assigned to a combustion chamber of the internal combustion engine, in particular an intake valve, disadvantages can arise with regard to the charge movement of the fuel-air mixture in the combustion chamber compared to larger valve lifts.

[0010] It is therefore an object of the present invention to provide a method for operating an internal combustion engine in which the disadvantages of charge movement are at least very minor or avoided.

[0011] This problem is solved by a method for operating an internal combustion engine with the features of claim 1. Advantageous embodiments with expedient and non-trivial further developments of the invention are specified in the remaining claims.

[0012] In such a method for operating an internal combustion engine designed as a spark-ignition engine in a motor vehicle, at least one injection device is used to inject fuel directly into at least one combustion chamber of the internal combustion engine. Furthermore, an ignition device is used to ignite a mixture of fuel and air in the combustion chamber.

[0013] The internal combustion engine is operated either in at least one first operating mode with at least one first valve lift of at least one gas exchange valve associated with the combustion chamber, or in at least one second operating mode with at least one second valve lift, which is smaller than the first valve lift. In other words, injection and ignition are carried out in both operating modes, with the gas exchange valve performing the first valve lift in the first operating mode and the second valve lift in the second operating mode when the gas exchange valve opens and closes. The second valve lift is smaller than the first valve lift.

[0014] To compensate for the disadvantages of reduced charge motion of the mixture in the second operating mode with the second valve lift compared to the first operating mode with the first, larger valve lift, at least one additional injection of fuel directly into the combustion chamber is performed prior to ignition to support charge motion in the second operating mode. By supporting charge motion through this additional injection, slower combustion in the second operating mode compared to the first can also be avoided, resulting in efficient operation of the internal combustion engine with low fuel consumption and low CO₂ emissions. The method according to the invention thus enables the representation of the valve timing of the gas exchange valve.of at least one camshaft of the internal combustion engine that actuates the gas exchange valve in the second operating mode, which results in very low fuel consumption due to very low charge exchange work.

[0015] Furthermore, in the second operating mode, the internal combustion engine is operated, at least to a large extent, in homogeneous mode. In homogeneous mode, the mixture is particularly homogeneous compared to a possible stratified charge operation of the internal combustion engine, thus enabling particularly efficient operation of the engine.

[0016] Furthermore, it is provided that the load of the internal combustion engine is adjusted in a first load range of the second operating mode by means of a throttle valve, in a second load range of the second operating mode via a camshaft which is assigned to at least one intake valve associated with the combustion chamber, and in a third load range of the second operating mode via a wastegate control in the charging range.

[0017] Preferably, the further injection is carried out close to the ignition point. This leads to a particularly advantageous support of the charge motion and thus to a particularly advantageous turbulence of the mixture, especially at the time of ignition, resulting in very high combustion stability. This benefits the efficient operation of the internal combustion engine.

[0018] To achieve very good charge motion and thus very good turbulence that has a positive effect on combustion stability, it is preferably provided that the further injection is carried out after the at least one first injection.

[0019] In a further advantageous embodiment of the invention, it is provided that, at least in the second operating mode, a multi-spark ignition is carried out. This achieves a particularly high combustion stability, resulting in very efficient operation of the internal combustion engine, for example, a reciprocating piston engine.

[0020] The internal combustion engine can also be operated, at least to a large extent, in homogeneous operation in the first operating mode.

[0021] Fuel consumption and thus CO2 emissions of the internal combustion engine can be kept particularly low if the load setting of the internal combustion engine in the second operating mode is carried out by means of at least one throttle valve arranged in an intake tract of the internal combustion engine and / or by means of a charging level of at least one exhaust gas turbocharger assigned to the internal combustion engine and / or by means of a phase adjustment of the camshaft, i.e. by means of a change in the timing of the gas exchange valve, which is designed in particular as an intake valve.

[0022] In a further advantageous embodiment, the internal combustion engine is operated in the second operating mode when at least one value characterizing the temperature of the internal combustion engine exceeds a predefinable threshold. The threshold is, for example, 50°C. This ensures efficient and fuel-efficient operation of the internal combustion engine.

[0023] The gas exchange valve is preferably an inlet valve in which, at least in one open position, air from an intake tract of the internal combustion engine can flow into the combustion chamber.

[0024] Further advantages, features, and details of the invention will become apparent from the following description of a preferred embodiment and from the drawing. The features and combinations of features mentioned above in the description, as well as those mentioned below in the figure description and / or shown in the figures alone, can be used not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the invention.

[0025] The drawing shows in: Fig. 1 is a schematic representation of a characteristic map of a gasoline engine for a motor vehicle, which has a first operating range of the internal combustion engine with a large valve lift of the intake valves and a second operating range with a small valve lift of the intake valves, the representation serving to illustrate a valve lift strategy of the internal combustion engine; and Fig. 2 is a further schematic representation of the characteristic map according to Fig. 1 , where the representation serves to illustrate a load control strategy of the Otto engine.

[0026] The Fig. 1 Diagram 10 shows the rotational speed of a spark-ignition engine on its abscissa 12, increasing according to a directional arrow 14. The load of the spark-ignition engine is plotted on the ordinate 16 of Diagram 10, increasing according to a directional arrow 18. Diagram 10 also includes the engine's characteristic curve 20, which serves to illustrate a method for operating the spark-ignition engine.

[0027] Again Fig. 1 As can be seen, the characteristic map 20 has a first characteristic map area 22 and a second characteristic map area 24. The first characteristic map area 22 corresponds to a first operating mode of the gasoline engine, in which the gasoline engine is operated with at least one first valve lift curve. The first valve lift curve causes the respective first valve lifts of the intake valves of the gasoline engine.

[0028] The second characteristic map area 24 corresponds to a second operating mode of the gasoline engine, in which the engine is operated with at least one second valve lift curve. This second valve lift curve results in a second valve lift of the intake valves. These second valve lifts are smaller than the first valve lifts.

[0029] The intake valves of a gasoline engine, for example, are actuated by at least one camshaft. This means that the camshaft interacts with the intake valves so that the intake valves – depending on the operating mode – execute their respective valve lifts and open and close accordingly.

[0030] To represent the different valve lifts, the camshaft includes, for example, first cams assigned to the first valve lifts and second cams assigned to the second valve lifts. The camshaft interacts with the intake valves via its cams.

[0031] The gasoline engine can be operated in either the first operating mode (first map area 22) or the second operating mode (second map area 24). In so-called fired operation of the gasoline engine, fuel is injected directly into the combustion chambers, specifically the cylinders, in both operating modes. Each combustion chamber is assigned at least one injection valve, through which fuel is injected directly into the corresponding combustion chamber.

[0032] Furthermore, each combustion chamber is assigned at least one intake valve. When the intake valves are in an open position, air flowing through the intake manifold of the gasoline engine can enter the respective combustion chambers via intake ports and mix with the fuel injected directly into the combustion chambers. This creates a fuel-air mixture, which is ignited and then combusts.

[0033] To ignite the respective fuel-air mixture in the combustion chamber, each combustion chamber is equipped with at least one spark plug, which generates a spark. The moment at which the spark is generated and the fuel-air mixture is ignited is called the ignition point. The moment at which the fuel is injected directly into the respective combustion chambers is called the injection point.

[0034] When the gasoline engine is operated in the second operating mode, the intake valves open less wide than in the first operating mode because they perform the smaller, second valve lifts. In other words, the intake valves in the second operating mode provide smaller opening cross-sections through which air can flow into the respective combustion chambers than in the first operating mode. As the Fig. 1 As can be seen, the gasoline engine operates in the second operating mode at predefined loads and / or speeds, while the first operating mode is used at comparatively higher loads and / or speeds. This means that the gasoline engine operates in the second operating mode at relatively low speeds and / or loads, and in the first operating mode at comparatively higher speeds and / or loads. If the speed and / or load exceeds at least a predefined threshold, the engine switches from the second to the first operating mode and vice versa.

[0035] In the second operating mode, the Otto engine is largely operated in a homogeneous mode, whereby the second characteristic map area 24 has a hysteresis area 26 with respect to load and speed.

[0036] To compensate for or avoid the reduced charge motion of the fuel-air mixture in the second operating mode compared to the first, due to the shorter second valve lifts, at least one additional fuel injection into the combustion chambers is performed shortly after ignition to support the charge motion of the fuel-air mixture in the second operating mode. This results in highly advantageous charge motion and turbulence, leading to very high combustion stability of the fuel-air mixture. Consequently, valve timing of at least one camshaft can be implemented that results in very low fuel consumption and thus low CO₂ emissions from the gasoline engine due to minimal charge exchange work.

[0037] In the present case, the second characteristic map area 24 has a sub-area 28 in which the internal combustion engine is also operated depending on the load and / or speed, and in which at least one further injection of fuel directly into the respective combustion chambers is carried out before the ignition, in particular very close to the ignition (near ignition), of the fuel-air mixture. In other words, a so-called ignition injection is carried out. The sub-area 28 also has a hysteresis range 29 with respect to load and speed.

[0038] Other possible activation conditions for the second operating mode include, for example, that the temperature of the gasoline engine, particularly its lubricant and / or coolant, exceeds 50°C. Furthermore, the second operating mode is only activated, for instance, once a warm-up process for heating the gasoline engine's catalytic converter and the engine's warm-up phase are complete. Idle operation and start-stop operation are also performed with reduced valve lift in the second operating mode.

[0039] The gasoline engine is preferably equipped with at least one exhaust gas turbocharger, by means of which the gasoline engine can be supplied with compressed air, i.e., turbocharged. This leads to particularly efficient operation of the gasoline engine.

[0040] As particularly evident from the Fig. 2As can be seen, the gasoline engine is subject to load control, i.e., the load of the gasoline engine is adjusted in the first operating range 22, i.e., in the first operating mode, by means of a throttle valve located in the intake manifold of the gasoline engine or by means of turbocharging. The quantity or mass of air flowing into the respective combustion chambers is adjusted to regulate the load.

[0041] In the second map area 24, with the second, smaller valve lifts, load adjustment is achieved in sub-area 30 of the second map area 24 via the throttle valve. In sub-area 32 of the second map area 24, load adjustment is achieved via the camshaft assigned to the intake valves and designated as the intake camshaft. In sub-area 34 of the second map area 24, load adjustment (load control) is achieved via a wastegate control system in the turbocharging range. The wastegate control system refers to the opening and closing of a valve element, designated as a wastegate, in a bypass device of the exhaust gas turbocharger. The bypass device is assigned to a turbine of the exhaust gas turbocharger and comprises a bypass channel through which the exhaust gas flowing through the gasoline engine can bypass a turbine wheel of the turbine and thus not drive it.

[0042] The bypass channel can be fluidically closed and opened by means of the valve element (waste gate). If the bypass channel is fluidly closed in a closed position of the valve element, exhaust gas cannot flow through it. This means that at least substantially all of the exhaust gas drives the turbine wheel. In at least one open position of the valve element, the bypass channel is fluidly opened, so that the exhaust gas can at least partially bypass the turbine wheel, although the exhaust gas bypassing the turbine wheel does not drive it. By opening and closing the valve element (waste gate control), the turbine's power output can be adjusted, and consequently, the pressure of the compressed air supplied to the gasoline engine (boost pressure), and thus, in turn, the quantity or mass of air supplied to the gasoline engine.

Claims

1. Method for operating an internal combustion engine, designed as a gasoline engine, of a motor vehicle, in which at least one injection of fuel directly into at least one combustion chamber of the internal combustion engine is carried out by means of at least one injection device and an ignition of a mixture of the fuel and air in the combustion chamber is carried out by means of an ignition device, the internal combustion engine being operated optionally in at least one first operating mode (22) with at least one first valve lift of at least one gas exchange valve of the internal combustion engine assigned to the combustion chamber or in at least one second operating mode (24) with at least one second valve lift of the gas exchange valve, which is smaller than the first valve lift, and for supporting a charge motion of the mixture in the second operating mode, at least one further injection of fuel directly into the combustion chamber being carried out before ignition, characterized in that in the second operating mode, the internal combustion engine is operated at least largely in a homogeneous charge mode in which the mixture is particularly homogeneous compared with a possible stratified charge mode of the internal combustion engine, a load of the internal combustion engine being set in a first load range (30) of the second operating mode by means of a throttle valve, in a second load range (32) of the second operating mode via a camshaft which is assigned to at least one inlet valve assigned to the combustion chamber, and in a third load range (34) of the second operating mode via a waste gate control mechanism in the charging range.

2. Method according to claim 1, characterized in that the further injection is carried out after the at least one first injection.

3. Method according to either claim 1 or claim 2, characterized in that in the second operating mode, a multipoint ignition is carried out as the ignition.

4. Method according to any of the preceding claims, characterized in that the internal combustion engine is operated in the second operating mode if at least one value characterizing at least one temperature of the internal combustion engine exceeds a specifiable threshold value.