The invention concerns a procedure for heating a catalyst in the exhaust gas system of a supercharged combustion engine with a direct fuel injection and variable gas exchange valve control by producing a reactive exhaust gas fuel/air mixture in the exhaust gas system, whereby an air percentage of the reactive fuel/air mixture is thereby produced that air is rinsed from a suction system of the combustion engine over its combustion chambers into the exhaust gas system. The invention furthermore concerns a control unit, which is customized to implement the procedure. Thereby the implementation means a control of the course of the procedure.
Such a procedure and such a control unit are already known from DE 100 63 750 A1. In this script one of several cylinders is used for pumping air out of the suction system into the exhaust gas system while fuel supply is disabled. The amount of the pumped air is controlled by interventions in a variable valve control of this cylinder. The turbo charger can be waived at the known subject and is therefore not significant for the pumping of air. Variable valve controls are furthermore known for example from the pocket book on motor vehicle technology, 25th edition, ISBN 3-528-23873-3, Robert Bosch GmbH, 2003, p. 474 and 475.
The heating of a catalyst by producing a reactive exhaust gas fuel/air mixture in the exhaust gas system is also already known from the publication of DE 100 63 750 A1 as injecting secondary air in a rich exhaust gas atmosphere. The secondary air is usually injected behind the outlet valves of the combustion engine and reacts there exothermically with a rich exhaust gas atmosphere, which results from combustions of combustion chamber fillings of the combustion engine. For injecting secondary air usually a separate secondary air pump is used, which is electronically driven.
The subject known from DE 100 63 750 A1 temporarily uses a cylinder of the combustion engine as a secondary air pump, so that a separate secondary air pump that is driven electrically or mechanically can be waived. But then the concerned cylinder is not available for a torque generation, which causes an increased uneven running.
It is for example known to produce a maximum heat quantity in the exhaust gas during an after-start phase of the combustion engine, without changing the power that has been raised in idle mode and the idle toque of ca. 1.200 min-1 that has been increased in the after-start phase. This is achieved at a combustion engine with a direct fuel injection thereby that a first percentage of the fuel amount is injected into the suction stroke and a second percentage of the fuel amount into the compression stroke. This results in a layered fuel apportionment in the combustion chamber with a zone of comparably rich and therefore well ignitable fuel/air mixture around the ignition plug that results from the injection of the second percentage. This operation of the combustion engine is also called homogeneous split mode, whereby split refers to the apportionment of the injection.
A charging concept with an exhaust gas turbo charger is known from DE 100 62 377 A1, whereby its shaft is driven by an electromotor. This drive shall reduce the so-called ‘turbo lag’ at operating point changes. The turbo lag originates as it is well known thereby that the turbine has to be initially accelerated at a sudden torque demand from an operating point with a low exhaust gas mass flow, in order to produce the required boost pressure on the compressor side. The supporting electronic drive reduces the resulting delay.
This charging concept, which has basically nothing to do with a catalyst heating procedure, is used in DE 100 62 377 A1, in order to replace the separate secondary air pump. Thereby the turbo charger is electronically driven when the catalyst has to be heated. Thereby it already produces a certain boost pressure even in operating points with low exhaust gas enthalpy, which is sufficient to let air flow out of the suction system over a pipe connection past the combustion chambers of the combustion engine into the exhaust gas system. Thereby a separate secondary air pump can be waived at turbo chargers that are supported by an electrical drive. But the secondary air injection requires even at these charging concepts an electric drive.
With this background the task of the invention is to provide a procedure and a control unit, which allows a heating of a catalyst in the exhaust gas of a combustion engine that is charged with an exhaust gas turbo charger, but which works in the concerned cylinder without a separate secondary air pump, without an electrical drive of the turbo charger or a compressor that is arranged in the suction pipe and without an alienated usage of individual cylinders as a secondary pump when the ignition or the fuel supply is disabled.
This task is solved each time with the features of the independent claims.
As a result of the combustion engine being operated at a procedure of the above mentioned type in idle mode after a cold start with a greater valve overlap and/or a greater valve overlap profile than in a normal operation, unburnt air flows from the suction system over the participating combustion chamber into the exhaust gas system when there is a sufficient pressure drop between the suction system and the exhaust gas system. But the pressure drop is not sufficient under normal circumstances or even has a negative sign, so that exhaust gas flows back into the combustion chamber or is only incompletely ejected. This is also known as internal exhaust gas recirculation.
The invention creates the pressure drop, which is necessary for an air overflow that takes place through the combustion chamber, from a comparably high pressure in the suction system to a comparably low pressure in the exhaust gas system by a significant increase of the exhaust gas enthalpy, which results in an increased energy transfer on the turbine of the turbo charger and therefore in a quick increase and sufficient high boost pressure level of the combustion engine in idle mode. Thereby a normal operation means an operation, in which no secondary air supply should be created, which is the case for example at a combustion engine at operating temperature and sufficiently heated exhaust gas systems.
The operation of the combustion engine with a direct injection of fuel into its combustion chambers and with an apportionment that takes place after a cold start of a fuel amount, which has to injected before the beginning of a combustion, into at least two partial injections per ignition and combustion engine, creates very stabile combustions, which allow very late ignition angles. At combustion procedures that are air- and wall-formed late ignition angles up to ca. 25 degrees after OT can be adjusted and at jet-formed combustion procedures even later ignition angles up to ca. 30-35 degrees crankshaft angle after OT at a stabile torque behavior and controllable raw emissions can be adjusted.
The ignition angle efficiency, which means the quotient of the torque at a delayed ignition angle in the numerator and the torque at an ignition angle that is optimal for a maximum torque development, decreases more and more with an increasing late time displacement of the ignition.
The efficiency loss causes an increased exhaust gas temperature and therefore an increased exhaust gas enthalpy due to thermodynamic regularities. Furthermore the combustion engine has to be operated at a delayed ignition with increased combustion chamber fillings, in order to compensate the torque loss that comes along with the efficiency decline. The given ignition angle values result from increasing the combustion chamber fillings up to values of over 75% of the maximum filling that is possible under normal circumstances. An operation with such values of the combustion chamber filling means here also an almost de-throttled operation.
This causes an increased exhaust gas mass flow, which also increases the exhaust gas enthalpy. With an increasing exhaust gas enthalpy the driver input that is transferred to the turbine of the exhaust gas turbo charger increases. Altogether this results therefore in a comparably high exhaust gas amount, whose temperature is comparably high due to the bad ignition angle efficiency, so that a maximum heat flow (enthalpy current) adjusts in the exhaust gas system.
The resulting increase of the exhaust gas enthalpy alone already causes an accelerated heating of the exhaust gas system. Furthermore it causes that the turbo charger without a supporting electrical driver establishes within a few seconds after a cold start a comparably high boost pressure and therefore a pressure drop or a scavenging loss to the exhaust gas. It turned out, that this scavenging loss is already sufficient big also at a low engine speed in the range of the idle engine speed of the combustion engine, in order to let air flow from the suction system over the combustion chamber into the exhaust gas system during a valve overlap or a valve overlap profile that has been purposefully increased at a load alternation-ot and therefore simultaneously opened inlet valve and outlet valve.
Therefore a separate secondary air pump can be waived even at one-staged charging concepts, which work without an electrically supported turbo charger and without an additional compressor (for example root-injector, compressor) that is electrically or mechanically driven by the combustion engine. Therefore the invention uses the basically known homogeneous split mode at a supercharged combustion engine for a boost pressure increase, in order to create a sufficient scavenging loss (pressure drop) for a secondary air injection between the suction system and the exhaust gas system. The invention furthermore uses the chance that arises from a variable valve control to control the amount of secondary air that flows over the participating combustion chambers.
Thereby all cylinders can be participating regularly at the secondary air overflow, whereby unbalances at the operation of individual cylinders among each other can be avoided. As a desired result a negative influence on the running smoothness of the combustion engine is avoided. A further advantage is that the valve overlap and/or the valve overlap profile can be adjusted equally for all cylinders, for example by twisting the cam shaft. A more expensive, cylinder-individual controlling of the gas exchange valves is therefore not necessary.
Further advantages of the invention accrue form the dependent claims, the description and the attached figures.
It shall be understood that the previously mentioned and the following features that still have to be explainer further can not only be used in the given combination, but also in other combinations or alone, without leaving the scope of the present invention.
Embodiments of the invention are illustrated in the drawings and further explained in the following description. It is schematically shown in:
In particular
An exchange of the filling of the combustion chamber 12 is controlled with inlet valves 18 and outlet valves 20, which are opened and closed phase-synchronically to the movement of the piston 14. The actuation of the gas exchange valves 18 and 20 takes place over actuators 19 and 21, whereby an actuator 19 always actuates one or several inlet valves 18 and whereby actuator 21 always actuates one or several outlet valves 20.
The actuators 19, 21 are preferably realized as electro-mechanical, electromagnetic, electro-hydraulic, electro-pneumatic actuators or a combination of such actuators. Familiar cam shafts for example are such, whose phase position that is relative to a crank shaft is influenced by an actuator that is actuated with oil pressure and electrically controlled. Changing the phase position, which causes an earlier opening of the inlet valves (and/or a later closing of the outlet valves), also results in an increase of the valve overlap.
As it is well known the valve overlap thereby means the angle range of a rotary movement of the crank shaft (or cam shaft) of the combustion engine 10, in which at least one inlet valve and at least one outlet valve of a cylinder are opened together. Also known are variable valve controls, at which the valve stroke can be switched or continuously changed alternatively or additionally to a change of the phase position of at least one cam shaft, which influences the valve overlap profile among others. The valve overlap profile means here the effective opening profile between the suction system and the exhaust gas system. When both the inlet valve and the outlet valve of a cylinder are opened simultaneously this is the smaller opening profile of the mutually opened valves 18, 20.
Besides the different possibilities for a variable actuation of the gas exchange valves 18 and 20 are known to the expert for example from the previously mentioned pocket book on motor vehicle technology and are not illustrated in detail in
At an opened inlet valve 18 and a downstream moving piston 14, thus in the suction stroke, air flows from a suction system 22 into the combustion chamber 12. Fuel 26 is dosed to the air in the combustion chamber 12 over an injector 24. At an opened outlet valve 20 exhaust gas that results from a combustion of the combustion chamber fillings is ejected into an exhaust gas system 28, which provides at least one three-way catalyst 30. Generally the exhaust gas system 28 contains several catalysts, for example a pre-catalyst 30 that is built in close to the engine and a main catalyst 32 that is built in further away from the engine, which can be a three-way catalyst or a NOx-storage catalyst.
The combustion engine 10 features a turbo charger 34 with a turbine 36 and a compressor 38. The compressor 38 is arranged between a manifold 40 and the pre-catalyst 30 in the streaming direction of the exhaust gases. The pressure drop over the turbine 36 can be limited by a waste gate valve 42. But the invention is also usable if associated with turbo chargers without waste gate valves, for example if associated with turbo chargers with variable turbine geometry. A secondary air introduction into the exhaust gas system 28 takes place as the subject of
In the embodiment of
The control unit 48 creates corrective signals from the signals of this and if necessary further sensors in order to control actuators for controlling the combustion engine 10. In the embodiment of
Analogously to the illustration of the sensors it also applies to the depicted actuators, that the illustration of
Besides the control unit 48 is customized especially programmed to implement the suggested procedure and/or one of its embodiments and/or to control a corresponding course of procedure.
In a preferred embodiment the control unit 48 converts performance requirements of the combustion engine 10 into a nominal value for the torque that has to be produced altogether by the combustion engine 10, and apportions these torques into torque rates, which are influenced by the corrective signals S_L for the filling control, S_K for the fuel metering, S_Z for the ignition control and S_WG for the boost pressure control. The filling rate is adjusted with the corrective signal S_L by a corresponding setting of the throttle valve 62 or a variable controlling of inlet valves 18. The fuel rate is adjusted with the corrective signal S_K basically by the injected fuel mass and the way of the apportionment of the fuel mass that has to be injected into one or several partial injections as well as the relative status of the partial injections to each other and to the movement of the piston 14, thus by an injection timing. The maximal torque that is possible at the present air filling results from optimal air ratio lambda, optimal injection timing and optimal ignition angle.
In particular
Instead of an apportionment into two partial injections the fuel amount that is injected with the first injection model M_1 can also be apportioned into more than two partial injections. The possibility of apportioning is limited by the dosing ability of small quantities of the injector 24. The apportionment into at least two partial injections, of which the earlier preferably takes place in the suction stroke stroke_1 and the latter definitely in the same working stroke for the ignition, is significant for the model M_1, whereby the air ratio lambda in the combustion chamber (thus without secondary air) is smaller than 1 and an air ratio lambda in the exhaust gas (thus with secondary air) is higher than 1.
Simultaneously or quickly afterwards in step 72 at a sufficient boost pressure the valve overlap or the valve overlap profile is adjusted from a value that is normal for the present operating conditions, thus especially for the idle mode, to an increased value, in order to enable an overflow of secondary air from the suction system 22 through the combustion chamber 12 into the exhaust gas system 28. The increase can for example take place with a stable time delay in the dimension of a few seconds towards the activating of the homogeneous split mode or depending on the exceeding of a boost pressure threshold.
Subsequently in step 74 a parameter A is established and determined, which shows the effect of the secondary air overflow. A time meter reading or a constant that characterizes the temperature of the turbo charger 34, the manifold 40 or of a catalyst 30, 32 are preferred as a parameter. Combinations of such constants are also possible. The parameter A is compared to a threshold value S_A as a termination criteria in step 76. When exceeding S_A the homogeneous split mode is terminated in step 78 and the valve overlap is reduced back to a value that is normal for the present operating conditions, which minimizes the overflow of secondary air through combustion chambers 12 or which causes, at a reduction of the boost pressure and a therefore resulting conversion of the direction of the scavenging loss, a recirculation of exhaust gas in the combustion chamber. The latter is also called an internal exhaust gas recirculation.
Step 80 branches into a normal operation of the combustion engine 10, in which no special measures for increasing the exhaust gas enthalpy are activated. The transfer can also take place step-by-step by reducing the valve overlap and/or the valve overlap profile first and then terminating the homogeneous split mode. The order can also be reversed.
The effect of the procedure according to the invention is illustrated by the time course of the engine speed n, the boost pressure p and a control bit SB that are shown in
A starter accelerates the combustion engine at the point of time t0 onto a starter engine speed of a little over 200 min-1. With constituting combustions in the combustion chambers 12 the engine speed n of the combustion engine 10 increases more and exceeds a starting engine speed threshold of about 400 min-1 at the point of time t1. Subsequently it quickly levels out at an increased idle engine speed of about 1.200 min-1. Due to the suction of the first combustion chamber fillings from the suction system 22 at a turbine 36 that is still not rotating or still not rotating fast the boost pressure p before the inlet valves 18 sinks initially. When exceeding the starting engine speed threshold at the point of time t1 the after-starting phase begins. The control bit SB from
In order to provide a high enthalpy flow in the exhaust gas during this after-starting phase, the control unit 48 provides suboptimal ignition angles over the corrective variable S_Z, which cause a torque loss over the therefore reduced ignition angle efficiency, which is compensated by an increased filling of the combustion chambers 12 that is produced by corrective signals S_L. The turbine 36 of the exhaust gas turbo charger 34 is quickly accelerated by the enthalpy flow in the exhaust gas that is high due to the almost complete de-throttling, so that the boost pressure p increases quickly up to values of over 1200 mbar. During such boost pressures the pressure difference between the boost pressure on the fresh air side of the secondary air duct 44 and the exhaust gas side of the secondary air duct 44 is big enough in order to let fresh air from the suction system 22 flow into the exhaust gas system 28 at an opened secondary air valve 46.
Therefore the control unit 48 controls the valve overlap and/or a valve overlap profile by releasing an opening corrective signal S_SLE. By an additional influence of the fuel corrective signals S_K an air ratio lambda is altogether adjusted in the exhaust gas in the over-stoichiometric operation, for example an air ratio lambda=1,1. Depending on the amount of the fresh air that has been injected into the exhaust gas, the air ratio lambda in the combustion chamber 12 is adjusted on to correspondingly lower values, which can also lie in the under-stoichiometric operation (lambda<1, fuel surplus).
Thereby a good ignition ability and a stabile combustion of the fuel/air mixture that is comprised in the combustion chambers are achieved. Simultaneously the over-stoichiometric air ratio in the exhaust gas is very important especially in the first phase after a start finish, because the still cold pre-catalyst 30 can not reduce hydrocarbons yet. Therefore the only possibility to limit the hydrocarbon emissions that are stored in the environment is to limit the raw emissions of the combustion engine 10. This limitation is a desired result of the operation with an air ratio lambda bigger than 1 in the exhaust gas.
A high exhaust gas amount is produced by the increased filling, which has furthermore a comparably high temperature due to the suboptimal ignition angle efficiency and which provides an oxygen surplus. Altogether a high heat flow or enthalpy flow is therefore produced. As soon as a termination criterion is fulfilled at the point of time t2, the increase of the exhaust gas enthalpy is terminated. The engine speed n of the combustion engine 10 falls then back on its normal idle engine speed, which lies typically between 500 and 100 min-1. The de-throttling that exceeds the necessary scope during normal operation is terminated. Thereby the pressure p between the throttle valve 62 that is than less opened and the inlet valves 18 drops a lot. In the drawing of
The low pressure is then not sufficient for a secondary air overflow, so that the valve overlap and/or the valve overlap profile are reduced on time. The pressure difference dp represents the extent of the pressure change, which is produced between the points of time t1 and t2 and which is used for a secondary air overflow. Without the idea for using the pressure change for a secondary air overflow the increased exhaust gas enthalpy, which results from the homogeneous split mode, would rather be terminated by opening the waste gate valve 42.
Number | Date | Country | Kind |
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10 2007 056 216.2 | Nov 2007 | DE | national |