DE102004026180A1 - Method for operating an internal combustion engine - Google Patents

Abstract

A method is proposed for operating an internal combustion engine (1), which enables a simple increase of the exhaust gas enthalpy. In this case, fuel in a suction pipe (5) of the internal combustion engine (1) upstream with a closed inlet valve (10). A valve overlap between an exhaust valve (20) and an intake valve (10) of at least one cylinder (15) is adjusted such that in an intake stroke with opening of the intake valve (10) of the at least one cylinder (15) of the internal combustion engine (1) the exhaust valve (15) 20) of the at least one cylinder (15) is still open, so that the upstream fuel enters an exhaust tract (25) of the internal combustion engine (1) and is ignited there together with a scavenging air mass also in the exhaust tract (25).

Description

State of technology

The The invention relates to a method for operating an internal combustion engine according to the preamble of the main claim.

It are already known methods for operating an internal combustion engine, in which fuel in a suction pipe of the internal combustion engine at upstream inlet valve is closed.

It It is also known that turbocharged engines, in particular those without variable geometry of the turbine of the exhaust gas turbocharger, at Start a torque weakness demonstrate. The comparatively low exhaust gas mass flow of the internal combustion engine at the starting speed leads To very bad efficiencies of both the turbine and the Compressor of the exhaust gas turbocharger. The consequence is a comparatively Low boost pressure build-up with comparatively low torque range in the lower speed range of the internal combustion engine. This can in the case, that the combustion engine drives a vehicle under extreme conditions Situations such as a steep pass at high altitude with switched on Ancillaries are hampered a startup.

From the DE 101 40 120 A1 a method for operating an internal combustion engine is known, which comprises an exhaust gas turbocharger, wherein in addition to a primary injection into one or more cylinders of the internal combustion engine, a post-injection is caused and wherein the post-injection generates a combustible air / fuel mixture, which by controlling an ignition means, which in Exhaust tract of the internal combustion engine is arranged, is ignited. In this case, the post-injection is carried out when the opening angles of the outlet valve and inlet valve of the corresponding cylinder overlap.

By a suitable big one Valve overlap, as for example by appropriate adjustment of the intake camshaft or the exhaust camshaft can be achieved, as well as at a sufficiently positive pressure gradient between the intake manifold and the exhaust tract upstream of the turbine of the exhaust gas turbocharger the possibility arises one not in the internal combustion process, ie the combustion process in a cylinder of the internal combustion engine participating air mass, a so-called scavenging air mass, which came together with the through the post-injection into the exhaust tract Fuel with the help of the ignition ignited in the exhaust system becomes. In this way, the exhaust enthalpy and thus the efficiency of the exhaust gas turbocharger increased. In addition, this way can be an optional heat existing catalyst faster in the exhaust tract.

Advantages of the invention

The inventive method for operating an internal combustion engine with the features of the main claim has in contrast the advantage that a valve overlap between an exhaust valve and an intake valve at least of a cylinder is adjusted such that in an intake stroke with open the intake valve of the at least one cylinder of the internal combustion engine the outlet valve of the at least one cylinder is still open, so that the upstream fuel enters an exhaust tract of the internal combustion engine and there along with one also in the exhaust tract arrived scavenging air ignited becomes. That way themselves to increase the exhaust enthalpy required combustion of an air / fuel mixture in the exhaust tract of the internal combustion engine also in the case of an internal combustion engine realize with intake manifold injection.

By in the subclaims listed activities are advantageous developments and improvements of the main claim specified method possible.

Especially it is advantageous if in dependence a predetermined first air / fuel ratio for the in the exhaust tract to be burned air / fuel mixture a target value for a vorzulagernde Fuel quantity is formed. This way also works for the combustion comply with the air / fuel mixture in the exhaust system a predetermined air / fuel mixture ratio or a desired one Air / fuel mixture ratio to adjust.

there can easily get the scavenging air mass into the exhaust tract dependent from the operating state of the internal combustion engine, in particular of operating variables such as the valve overlap, the Engine speed and engine load, are determined and dependent on the determined scavenging air mass and the predetermined first air / fuel mixture ratio of Setpoint for the vorzulagernde amount of fuel are formed.

A further advantage results if the main fuel for combustion in the at least one cylinder of the internal combustion engine is injected at the earliest when the exhaust valve of the at least one cylinder is closed in the intake stroke is sen. In this way, the injection of fuel into the intake manifold of the internal combustion engine can be separated into a first amount of fuel provided for combustion in the exhaust tract and a second or main amount of fuel provided for combustion in the at least one cylinder of the internal combustion engine.

For this Separation can be a time interval between the injection of the Main fuel and the injection of the upstream fuel, so that the first fuel quantity and the second fuel quantity independent from each other be injected.

It However, it can also be provided in an advantageous manner that the Main fuel and the upstream fuel directly to each other be injected following. In this case, only one Injection for the main fuel and the upstream fuel required.

One Another advantage arises when the whole in the at least a cylinder to be injected fuel quantity depending on a predetermined second air / fuel mixture ratio both of the exhaust tract and the at least one cylinder to be burned Air / fuel mixture is specified. This way, despite two different injections during an intake stroke adjust the entire predetermined air / fuel mixture ratio.

One Another advantage arises when the air / fuel mixture in Exhaust tract through an ignition means ignited becomes. In this way it is ensured that in the exhaust tract actually get burned and air thus the exhaust enthalpy increases can be.

drawing

An embodiment of the invention is illustrated in the drawing and explained in more detail in the following description. Show it 1 a schematic view of an internal combustion engine and 2 a flowchart for an exemplary sequence of the method according to the invention.

description of the embodiment

In 1 features 1 an internal combustion engine, which may be designed, for example, as a gasoline engine or as a diesel engine and can drive a vehicle. The internal combustion engine 1 includes at least one cylinder 15 whose combustion chamber has an air supply 35 Fresh air can be supplied. Usually but not absolutely necessary in the air supply 35 an air mass meter 40 , For example, a hot-film air mass meter, which arranged the at least one cylinder 15 supplied fresh air mass flow measures and the measurement result to a motor control 85 forwards. The flow direction of the fresh air in the air supply 35 is in 1 indicated by an arrow. In the flow direction of the fresh air to the air mass meter 40 Below is in the air supply 35 a compressor 45 arranged, which is the at least one cylinder 15 supplied fresh air compressed and to do so from a turbine 75 an exhaust gas turbocharger via a shaft 90 is driven. The turbine 75 In turn, it is an exhaust gas mass flow in an exhaust tract 25 of the internal combustion engine 1 driven. The compressor 45 in the flow direction of the fresh air is below in the air supply 35 especially in the case of the training of the internal combustion engine 1 as gasoline engine a throttle 50 arranged. The opening degree of the throttle valve 50 is from the engine control 85 set in the manner known in the art, for example, to implement a driver's desired torque. In addition, it may be provided that the position of the throttle valve by a in 1 Throttle sensor, not shown, for example in the form of a potentiometer, detects and thus detected throttle position of the engine control 85 is reported as a signal for the engine load. The section of the air supply 35 between the throttle 50 and an inlet valve 10 of the at least one cylinder 15 is also called suction tube and is in 1 with the reference number 5 characterized. Into the suction pipe 5 is via an injection valve 55 Fuel injectable. The injection valve 55 is also from the engine control 85 controlled, for example, the way that sets a predetermined air / fuel ratio for the combustion. About the inlet valve 10 the fresh air and the fuel come out of the intake manifold 5 into the combustion chamber of the cylinder 15 when the inlet valve is open 10 , In the case of the training of the internal combustion engine 1 as gasoline engine is like in 1 dashed lines show a spark plug 60 provided in the combustion chamber of the at least one cylinder 15 ignited air / fuel mixture ignites. The spark plug 60 is also from the engine control 85 controlled in the conventional manner for setting a suitable ignition timing. The combustion of the air / fuel mixture in the combustion chamber of the at least one cylinder 15 formed exhaust gas is via an exhaust valve 20 from the combustion chamber of the at least one cylinder 15 in the exhaust tract 25 pushed out. In the area of at least one cylinder 15 is a speed sensor 65 arranged, which detects the engine speed in the manner known in the art and the measured value to the engine control 85 forwards. In the exhaust tract 25 can be optional as in 1 dashed illustrated an ignition means 30 , For example, in the form of a glow plug, arranged to be in the exhaust tract 25 ignite the resulting air / fuel mixture and thus increase the exhaust enthalpy. The ignition 30 is also from the engine control 85 controlled to provide the appropriate ignition temperature at the appropriate time. The flow direction of the exhaust gas is in 1 also marked by an arrow. The ignition 30 in the flow direction of the exhaust gas is below in the exhaust system 25 according to the example 1 a lambda probe 70 arranged. This measures the oxygen content in the exhaust gas in a manner known to those skilled in the art and passes this value to the engine control 85 Next, which determines an actual value for the entire air / fuel mixture ratio. The lambda probe 70 is in the flow direction of the exhaust gas below in the exhaust tract 25 the turbine 75 arranged. The order of lambda probe 70 and turbine 75 in the exhaust tract 25 can also be reversed. The turbine 75 is in the flow direction of the exhaust gas below in the exhaust tract 25 optionally, ie optionally a catalyst 80 arranged.

According to the example 1 also the valve timing of the intake valve 10 and the exhaust valve 20 from the engine control 85 specified. This can be done, for example, according to a fully variable valve control in a manner known to those skilled in the art. Alternatively, the opening and closing times of the intake valve 10 and the exhaust valve 20 be set in a manner known in the art by appropriate adjustment of an intake camshaft and / or egg ner exhaust camshaft. In this case, a variable camshaft adjustment can be provided. The following is an example of a fully variable valve control can be assumed.

According to the invention, it is now provided that via the injection valve 55 Fuel in the intake manifold 5 with closed inlet valve 10 is stored upstream. Furthermore, a valve overlap between the opening time of the exhaust valve 20 and the opening time of the intake valve 10 set such that in an intake stroke of the at least one cylinder 15 with the opening of the inlet valve 10 the outlet valve 20 is still open, so that the upstream fuel in the exhaust tract 25 arrives and there together with a likewise in the exhaust tract 25 reached scavenging air mass is ignited.

It can be z. B. for the in the exhaust system 25 be set to be ignited air / fuel mixture, a first air / fuel mixture ratio. Furthermore, in the exhaust tract 25 reached purge air mass depending on the operating condition of the engine 1 be determined. In particular, the scavenging air mass in known manner from operating variables of the internal combustion engine 1 as the valve overlap, the engine speed and the engine load are determined. The valve overlap is in the engine control 85 due to the activation of the inlet valve 10 and the exhaust valve 20 According to the fully variable valve timing, and characterizes the time or angle at which in the intake stroke, both the intake valve 10 as well as the exhaust valve 20 are open. In the case of using intake camshaft and / or exhaust camshaft, the valve overlap is known due to the known adjustment of the intake camshaft with respect to the exhaust camshaft. The engine speed is determined by the speed sensor 65 made available. The engine load can be determined from the throttle position in a manner known to those skilled in the art. From the mentioned operating variables, the scavenging air mass can be modeled in a manner known to the person skilled in the art. Alternatively, the scavenging air mass can be determined via one or more characteristic maps as a function of the aforementioned operating variables of valve overlap, engine speed and engine load. The maps can be suitably applied in a manner known to those skilled in the art, for example on a test bed. Depending on the thus determined scavenging air mass and the predetermined first air / fuel mixture ratio can then determine a target value for the amount of fuel to be pre-stored. For this purpose, for example, by means of another map depending on the purge air mass and the predetermined first air / fuel mixture ratio of the required Vorlagerungswinkel or the required storage time for the injection of the fuel in the intake manifold 5 be determined. This further characteristic field can likewise be suitably applied to a test stand in a manner known to the person skilled in the art. The required advance angle or the required storage time represents that angle or the time in or in which the fuel is closed when the intake valve is closed 10 in the suction pipe 5 must be injected. If then subsequently in an intake stroke of the at least one cylinder 15 the inlet valve 10 is opened, so is due to the valve overlap the exhaust valve 20 still open. Thus, when the inlet valve is closed 10 upstream fuel together with the purge air mass in the case of a positive pressure gradient between the intake manifold 5 and the exhaust tract 25 over the opened inlet valve 10 , the combustion chamber of the at least one cylinder 15 and the exhaust valve 20 in the exhaust tract 25 flow and there by means of the ignition means 30 ignited. The positive pressure gradient between the intake manifold 5 and the exhaust tract 25 is z. B. in the art known manner by a suitable configuration of the geometry of the exhaust system 25 and the geometry of the turbine 75 realized. For setting the positive pressure gradient between the suction pipe 5 and the exhaust tract 25 It is additionally conducive if a suitable number of cylinders for the internal combustion engine 1 is selected, in particular when a few cylinders are used on a cylinder bank, for example in the case of a three-cylinder engine or a six-cylinder engine, the exhaust side two cylinder banks and thus includes two exhaust lines, each according to the exhaust tract 25 to 1 are formed. The positive pressure gradient exists between the intake manifold 5 and the exhaust tract 25 in the flow direction of the exhaust gas in front of the turbine 75 , By burning the air / fuel mixture in the exhaust system 25 in the flow direction of the exhaust gas in front of the turbine 75 the exhaust gas enthalpy is increased, thereby improving the efficiency of the exhaust gas turbocharger. This leads to an increased supply of torque in the lower speed range of the internal combustion engine, so that, for example, the so-called turbo lag can be compensated for when starting up. By increasing the exhaust gas enthalpy also faster heating of the catalyst 80 especially during the cold start of the internal combustion engine 1 allows.

The purge air mass flow is the air mass flow that occurs during the valve overlap, ie during the state of simultaneous opening of the intake valve 10 and the exhaust valve 20 due to the positive pressure gradient between intake manifold 5 and exhaust tract 25 from the air supply 35 or the suction tube 5 over the combustion chamber of the at least one cylinder 15 in the exhaust tract 25 passes or as residual gas from the combustion chamber of the at least one cylinder 15 from the scavenging air into the exhaust tract 25 is displaced. The setpoint for the quantity of fuel to be stored is determined by appropriate control of the injection valve 55 from the engine control 85 implemented. The upstream fuel is also referred to as flushing fuel and also due to the positive pressure gradient between the intake manifold 5 and exhaust tract 25 after opening the inlet valve 10 during the valve overlap from the intake manifold 5 over the combustion chamber of the at least one cylinder 15 in the exhaust tract 25 rinsed and ignited there together with the scavenging air. The setpoint for the quantity of fuel to be stored was chosen as described so that, starting from the determined scavenging air mass, a desired air / fuel mixture ratio, which was designated as the first predetermined air / fuel mixture ratio, is established. This desired air / fuel mixture ratio can be used to optimize the ignition process in the exhaust system 25 smaller at the beginning 1 and thus be given in bold. Subsequently, and ideally, then the desired value for the pre-stored fuel mass can be selected so that a stoichiometric air / fuel mixture ratio in the exhaust system 25 established.

Furthermore, it is provided that the fuel for combustion in at least one cylinder 15 , which is also referred to as the main fuel, at the earliest then via the injector 55 in the suction pipe 5 is injected when the exhaust valve 20 of the at least one cylinder 15 in the intake stroke of the at least one cylinder 15 closed is. The inlet valve 10 is still open. Thus, the actual combustion in at least one cylinder 15 necessary fuel mass with opened inlet valve 10 and closed exhaust valve 20 injected in the form of the main fuel. In this case, the injection of the main fuel can take place by a time interval separate from the injection of the upstream fuel. In this way, the injection of fuel for the intake stroke of the at least one cylinder 15 divided into two separate injections. Alternatively, it can also be provided, the injection of fuel for the intake stroke of the at least one cylinder 15 continuously, ie that the main fuel and the upstream fuel are injected directly consecutively. In this way, there is only a single injection of fuel for the intake stroke of the at least one cylinder 15 required. With the closing of the exhaust valve 20 is then injected fuel only in the combustion chamber of the at least one cylinder 15 burns and thus represents the main fuel. The before closing the exhaust valve 20 Injected fuel is then the upstream fuel, as far as it is in the exhaust tract 25 is burned, and thus represents the upstream fuel. The determined Vorlagerungswinkel or the determined storage time must be set in this case, starting from an angle or time to which the injection of fuel via the injection valve 55 in the suction pipe 5 no longer for the passage of this fuel into the exhaust tract 25 and thus the combustion of this fuel in the exhaust system 25 leads. This angle or time, for example, can be suitably applied to a test stand and thereby stored in dependence on operating variables of the internal combustion engine, such as engine speed and engine load in a map. In this case, in this case, the injection of the main fuel certainly still start at a time at which the exhaust valve 20 still open. In both cases, the inlet valve should be 10 be open at least as long until both the upstream fuel and the main fuel completely at least until the combustion chamber of the at least one cylinder 15 has arrived.

Finally, it may be provided that the entire for the intake stroke in the at least one cylinder 15 amount of fuel to be injected depending on a predetermined second air / fuel mixture ratio of both the exhaust tract 25 as well as in the combustion chamber of the mindes at least one cylinder 15 to be burned air / fuel mixture is specified. This can be realized, for example, with the aid of a so-called lambda control in a manner known to the person skilled in the art. This is done by the lambda probe 70 determined oxygen content in the exhaust gas from the engine control 85 in an actual value for the air / fuel mixture ratio of both the exhaust tract 25 as well as in the combustion chamber of the at least one cylinder 15 converted burned air / fuel mixture, compared with the predetermined second air / fuel mixture ratio and, depending on the comparison, the injection valve 55 from the engine control 85 controlled such that the amount of the main fuel to be injected is adapted to approximate the determined actual value to the predetermined second air / fuel mixture ratio. The amount of pre-stored fuel is already determined by the first predetermined air / fuel mixture ratio in the manner described above. The second predetermined air / fuel mixture ratio can also be selected, for example, as a stoichiometric air / fuel mixture ratio.

In 2 a flow chart for an exemplary sequence of the method according to the invention is shown. After the start of the program determines the engine control 85 at a program point 100 in the manner described the purge air mass depends on the operating variables of the internal combustion engine 1 , Subsequently, becomes a program point 105 branched.

At program point 105 calculates the engine control 85 in the manner described, the Vorlagerungswinkel or the Vorlagerungszeit for the injection of the upstream fuel from the opening time of the intake valve 10 in the intake stroke of the at least one cylinder 15 , Subsequently, becomes a program point 110 branched.

At program point 110 the actual value of the air / fuel ratio is based on the measurement signal of the lambda probe 70 from the engine control 85 determined in the manner described. Subsequently, becomes a program point 115 branched.

At program point 115 determines the engine control 85 by means of the lambda control in the manner described by comparing the actual value with the predetermined second air / fuel mixture ratio, the amount of the main fuel to be injected. Subsequently, becomes a program point 120 branched.

At program point 120 initiates the engine control 85 the injection of the upstream fuel from the determined Vorlagerungszeitpunkt on. Subsequently, becomes a program point 125 branched.

At program point 125 checks the engine control 85 by comparing the amount of already upstream fuel with the amount of pre-stored fuel, whether the amount of vorzulagernden fuel has already been achieved. If this is the case, then becomes a program point 130 branches, otherwise becomes program point 120 branches back and continues to store fuel upstream.

At program point 130 checks the engine control 85 whether the exhaust valve 20 already closed. If this is the case, then becomes a program point 135 otherwise it becomes a program point 140 branched.

At program point 135 initiates the engine control 85 the injection of the main fuel. Afterwards the program is left.

At program point 140 goes through the engine control 85 a waiting loop of z. B. several milliseconds. Then becomes program point 130 Branched back.

Signaled the driver of the vehicle a start-up operation by appropriate operation of the accelerator pedal, so in the full load range and at relatively low engine speeds, for example. Up to 2200 revolutions per minute for the purpose of so-called degree of delivery optimization or for the purpose of achieving a sufficiently high spontaneous torque, the intake camshaft be adjusted to their earliest possible position or the inlet valve 10 for as early as possible closing of the engine control 85 be controlled. By early closing of the inlet valve 10 becomes the cylinder filling of the at least one cylinder 15 Significantly improved at the low engine speeds mentioned, as a retraction already sucked air mass is prevented. At the same time existing large valve overlap also results in a sufficiently large purging air mass flow, the residual gas from the at least one cylinder 15 in the exhaust tract 25 rinses.

By the method according to the invention, the exhaust gas enthalpy can be upstream of the turbine 75 increase the exhaust gas turbocharger even when using an internal combustion engine with intake manifold injection. As a result of this increased exhaust enthalpy, the turbine can 75 the exhaust gas turbocharger provide more mechanical power for the compression of charge air. The starting behavior of the vehicle can thus be significantly improved due to the increased boost pressure.

The inventive method can also be realized without the use of a catalyst and / or without the use of an ignition means. The in the exhaust tract 25 upstream of the turbine 75 achieved temperatures can ignite the air / fuel mixture in the exhaust system 25 suffice.

Claims (10)

Method for operating an internal combustion engine ( 1 ), with fuel in a suction pipe ( 5 ) of the internal combustion engine ( 1 ) with closed inlet valve ( 10 ), characterized in that a valve overlap between an outlet valve ( 20 ) and an inlet valve ( 10 ) at least one cylinder ( 15 ) is set such that in an intake stroke with opening of the intake valve ( 10 ) of the at least one cylinder ( 15 ) of the internal combustion engine ( 1 ) the outlet valve ( 20 ) of the at least one cylinder ( 15 ) is still open, so that the upstream fuel in an exhaust tract ( 25 ) of the internal combustion engine ( 1 ) and there together with a likewise in the exhaust tract ( 25 ) reached scavenging air mass is ignited. Method according to claim 1, characterized in that that the required valve overlap over a corresponding camshaft adjustment is set. Method according to claim 1 , characterized in that the required valve overlap by a corresponding, in particular fully variable, control of the intake valve ( 10 ) and the exhaust valve ( 20 ) is set. Method according to one of the preceding claims, characterized in that in dependence on a predetermined first air / fuel mixture ratio for the in the exhaust tract ( 25 ) to be burned air / fuel mixture is a setpoint for a vorzulagernde amount of fuel is formed. A method according to claim 4, characterized in that in the exhaust tract ( 25 ) scavenged air mass depending on the operating condition of the internal combustion engine ( 1 ), in particular of operating variables such as the valve overlap, the engine speed and the engine load, is determined and that depending on the determined purge air mass and the predetermined first air / fuel mixture ratio of the setpoint for the fuel quantity to be stored is formed. Method according to one of the preceding claims, characterized in that the main fuel for combustion in at least one cylinder ( 15 ) of the internal combustion engine ( 1 ) is injected at the earliest when the exhaust valve ( 20 ) of the at least one cylinder ( 15 ) is closed in the intake stroke. Method according to Claim 6, characterized that the main fuel and the upstream fuel through a Time interval to be injected separately. Method according to Claim 6, characterized that the main fuel and the upstream fuel immediately be injected consecutively. Method according to one of claims 6 to 8, characterized in that the entire in the at least one cylinder ( 15 ) fuel quantity to be injected as a function of a predetermined second air / fuel mixture ratio of both in the exhaust tract ( 25 ) as well as in at least one cylinder ( 15 ) to be burned air / fuel mixture is specified. Method according to one of the preceding claims, characterized in that the air-fuel mixture in the exhaust tract ( 25 ) by an ignition means ( 30 ) is ignited.