Method for limiting an air charge of an internal combustion engine

Abstract

A method for limiting an air charge of an internal combustion engine. A maximum permissible pre-controlled charge and an exhaust-gas temperature-dependent delta charge are determined by means of a PI controller. A total permissible charge is determined on the basis of the maximum permissible pre-controlled charge and the exhaust-gas temperature-dependent delta-charge, and the air charge of the internal combustion engine is limited by the total permissible charge.

Claims

1. A method for limiting an air charge of an internal combustion engine, the method comprising the following steps: determining, using a PI controller, a maximum permissible pre-controlled charge and an exhaust-gas temperature-dependent delta charge; determining a total permissible charge based on the maximum permissible pre-controlled charge and the exhaust-gas temperature-dependent delta-charge; and limiting the air charge of the internal combustion engine by the total permissible charge.

2. The method according to claim 1, wherein the air charge is an air charge of cylinders of the internal combustion engine.

3. The method according to claim 1, wherein the maximum permissible pre-controlled charge is determined using a characteristic curve approach or an inverted exhaust gas temperature model.

4. The method according to claim 1, wherein the exhaust-gas temperature-dependent delta charge determined using the PI controller based on a difference between an actual manifold temperature and a predeterminable limit value of a component to be protected in an exhaust tract.

5. The method according to claim 1, wherein an exhaust gas temperature model is determined based on a speed of the internal combustion engine and a target temperature at an exhaust valve, in an application phase.

6. The method according to claim 1, wherein a release condition for the method is issued when one of predeterminable actual temperatures of components installed in an exhaust tract exceeds its respective temperature threshold value.

7. A non-transitory machine-readable storage medium on which is stored a computer program for limiting an air charge of an internal combustion engine, the computer program, when executed by a computer, causing the computer to perform the following steps: determining, using a PI controller, a maximum permissible pre-controlled charge and an exhaust-gas temperature-dependent delta charge; determining a total permissible charge based on the maximum permissible pre-controlled charge and the exhaust-gas temperature-dependent delta-charge; and limiting the air charge of the internal combustion engine by the total permissible charge.

8. An electronic control device configured to limit an air charge of an internal combustion engine, the control device configured to: determine, using a PI controller, a maximum permissible pre-controlled charge and an exhaust-gas temperature-dependent delta charge; determine a total permissible charge based on the maximum permissible pre-controlled charge and the exhaust-gas temperature-dependent delta-charge; and limit the air charge of the internal combustion engine by the total permissible charge.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a schematic illustration of an exemplary embodiment of a catalytic converter system that is suitable for carrying out the method according to the present invention.

(2) FIG. 2 shows a schematic flow diagram of an exemplary embodiment of the method according to the present invention for limiting an air charge.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

(3) FIG. 1 shows a schematic illustration of an exemplary structure of an exhaust tract with two catalytic converters 20, 30 connected in series. The exhaust tract of an internal combustion engine 10 is shown, wherein the internal combustion engine 10 emits combustion exhaust gases in the direction of the arrow. For example, the exhaust gas aftertreatment system comprises a first catalytic converter 20. This is followed by a second catalytic converter 30. A compressor 17 of a turbocharger 16 can be arranged upstream of the internal combustion engine 10. A first temperature sensor 61 is arranged downstream of the internal combustion engine 10 and upstream of the exhaust turbine 15 of the turbocharger 16. The first catalytic converter 20 then follows downstream of the exhaust turbine 15 of the turbocharger 16. A second temperature sensor 62 can be arranged downstream of the first catalytic converter 20 and upstream of the second catalytic converter 30.

(4) A third temperature sensor 63 can be arranged downstream of the second catalytic converter.

(5) The sensors are connected to a control device 100, for example by cable, and the control device 100 receives the signals from the sensors and subsequently stores them.

(6) The system further comprises an air-mass sensor not further shown, e.g., a hot-film air-mass sensor (HFM) in an air intake tract not further shown, which determines the exhaust gas mass flow dm.sub.exh. Furthermore, conventional engine variables, such as the injection quantity q.sub.inj, charge values, such as the cylinder charges ratairchrg.sub.cyl, an air-fuel ratio , a driver's desired torque, a speed n.sub.eng are available to the control device 100.

(7) Furthermore, the control device 100 comprises a model for determining the ignition angle ZW.sub.actual along with an exhaust gas temperature model.

(8) The first temperature sensor 61 can preferably be used to determine a manifold temperature T.sub.Exh,Mnf. Furthermore, a turbine temperature T.sub.Turb,out downstream of the exhaust turbine 15 and upstream of the first catalytic converter 20 can also be determined on the basis of the first temperature sensor using a temperature model.

(9) The second temperature sensor 62 can be used to determine a first catalytic converter temperature T.sub.Cat1,out downstream of the first catalytic converter 20. Furthermore, a temperature model stored on the control device 100 can be used to determine a first modeled catalytic converter temperature T.sub.Cat1,mod for the first catalytic converter 20 on the basis of the first catalytic converter temperature T.sub.Cat1,out.

(10) The third temperature sensor 63 can be used to determine a second catalytic converter temperature T.sub.Cat1,out downstream of the second catalytic converter 30. Furthermore, a temperature model stored on the control device 100 can be used to determine a second modeled catalytic converter temperature T.sub.Cat2,mod for the second catalytic converter 30 on the basis of the second catalytic converter temperature T.sub.Cat2,out. Alternatively, the first catalytic converter temperature T.sub.Cat1,out can also be used as an input variable.

(11) The temperature model that is used here, which is stored on the control device 100, can determine different temperature values within the exhaust tract on the basis of a plurality of input variables, such as the engine load and/or engine speed n.sub.eng and/or the ignition angle efficiency and/or the air-fuel ratio and/or the vehicle speed and/or ambient temperature T.sub.Env and/or exhaust gas temperature T.sub.exh.

(12) Furthermore, in an application phase, temperature limit values for components installed in the exhaust tract are stored in the control device 100, wherein such temperature limit values must not be exceeded or permanently exceeded. Temperatures may also be determined or modeled at desired locations in the exhaust tract, such as the location near the exhaust valves of the internal combustion engine 10.

(13) FIG. 2 shows a first exemplary sequence of the method for limiting the charge control for an internal combustion engine.

(14) In a first step 200, a release condition for the method is checked by means of the control device 100.

(15) For this purpose, a plurality of actual temperatures within the exhaust tract is continuously determined by the control device 100.

(16) In the following example, this is limited to the manifold temperature T.sub.Exh,Mnf, the first catalytic converter temperature T.sub.Cat1,out and the second catalytic converter temperature T.sub.Cat2,out.

(17) However, the method can be applied without limitation to any temperature that can be measured or modeled in the exhaust tract. For example, temperatures from sensors, such as the temperature signals or temperatures of the first, second and third temperature sensors 61, 62, 63 may be used. Alternatively, however, temperatures in the exhaust tract modeled via temperature models can also be used.

(18) For each temperature determined, a temperature limit value is stored in the control device 100, which was preferably determined in an application phase for the monitored temperatures.

(19) In the present example, these temperature limit values are referred to as a first limit value S.sub.Exh,Mnf for the manifold temperature T.sub.Exh,Mnf, a second limit value S.sub.Cat1,mod for the first catalytic converter 20, and a third limit value S.sub.Cat2,mod for the second catalytic converter 30.

(20) The control device 100 now continuously determines the manifold temperature T.sub.Exh,Mnf, the first catalytic converter temperature T.sub.Cat1,out and the second catalytic converter temperature T.sub.Cat2,out.

(21) If one of the monitored temperatures T.sub.Exh,Mnf, T.sub.Cat1,out, T.sub.Cat2,out exceeds its relevant limit value S.sub.Exh,Mnf, S.sub.Cat1,mod, S.sub.Cat2,mod, the release is issued and the method can be continued in a step 210.

(22) In an alternative embodiment, a predeterminable time period as to how long a monitored temperature T.sub.Exh,Mnf, T.sub.Cat1,out, T.sub.Cat2,out must exceed the relevant limit value S.sub.Exh,Mnf, S.sub.Cat1,mod, S.sub.Cat2,mod before the method is continued in a step 210 can also be stored in the control device 100.

(23) In a further advantageous embodiment, it can also be determined by means of a predictive function calculated on the control device 100 whether one of the monitored temperatures T.sub.Exh,Mnf, T.sub.Cat1,out, T.sub.Cat2,out will exceed the relevant limit value S.sub.Exh,Mnf, S.sub.Cat1,mod, S.sub.Cat2,mod, and if exceeding is detected the release is issued and the method can be continued in step 210.

(24) In the following example, it is assumed that the manifold temperature T.sub.Exh,Mnf exceeds or will exceed the first limit value S.sub.Exh,Mnf.

(25) In a step 210, a maximum permissible pre-controlled charge ratairchrg.sub.pre is determined by means of a pre-control.

(26) In a first embodiment, the maximum permissible pre-controlled charge ratairchrg.sub.pre can be determined by means of a characteristic curve approach.

(27) The air mass flow rate mf.sub.air,cyl or the intake air participating in the combustion, the basic ignition angle ZW.sub.Bas at the knock limit, the actual ignition angle ZW.sub.Gru and the speed n.sub.eng are used as input variables for the characteristic diagram.

(28) On the basis of the current speed n.sub.eng, a maximum permissible pre-controlled charge based on the actual ignition angle ZW.sub.Gru and a maximum permissible pre-controlled charge based on the latest permissible ignition angle are determined from two characteristic diagrams in each case.

(29) Furthermore, a weighting factor G is determined for interpolating the characteristic curve approach on the basis of the ignition angle retardation and the speed n.sub.eng. In this case, the ignition angle retardation results from the difference between the basic ignition angle ZW.sub.Bas at the knock limit and the actual ignition angle Z.sub.Gru.

(30) By means of a simple interpolation, the maximum permissible pre-controlled charge ratairchrg.sub.pre for component protection can subsequently be determined based on the characteristic approach for the pre-control.

(31) Subsequently, the method will be continued in a step 220.

(32) In a second embodiment, the maximum permissible pre-controlled charge ratairchrg.sub.pre on the basis of the component protection can also be determined by means of an inverse exhaust gas temperature (EGT) model. The maximum permissible exhaust gas temperature in the manifold is first determined for component protection and subsequently corrected for a heat loss between the quasi-stationary exhaust gas temperature in the manifold and the exhaust gas temperature downstream of the exhaust valve. The exhaust gas temperature downstream of the exhaust valves is determined by means of a model stored on the control device 100 on the basis of the speed n.sub.eng and/or a relative humidity in the cylinder and/or an ignition angle and/or lambda correction.

(33) In this case, a difference between the exhaust gas temperature at the manifold and the exhaust gas temperature downstream of the exhaust valves is determined and subsequently added to the maximum permissible exhaust gas temperature in the manifold, and a maximum permissible exhaust gas temperature at the exhaust valves is obtained.

(34) The maximum permissible exhaust gas temperature at the exhaust valve is subsequently corrected by a correction factor of the current ignition angle efficiency and the air-fuel ratio .

(35) The lambda correction factor is determined on the basis of a target lambda limitation and the ignition angle efficiency correction factor is determined on the basis of the actual ignition angle efficiency.

(36) This gives a target temperature at the exhaust valves for component protection.

(37) On the basis of the target temperature at the exhaust valves for component protection and the current speed n.sub.eng, the maximum permissible pre-controlled charge ratairchrg.sub.pre is then determined by means of the inverse exhaust gas temperature (EGT) model on the basis of the inverse characteristic diagram. The inverse basic characteristic diagram is determined during an application phase on the basis of the speed n.sub.eng and a target temperature at the exhaust valve for the inverse exhaust gas temperature approach for calculating the maximum permissible charge on the basis of component protection and stored in the control device 100.

(38) Subsequently, the method can be continued in a step 220.

(39) In a step 220, an exhaust-gas temperature-dependent delta charge ratairchrg.sub.PI is determined by means of a PI controller. For this purpose, a difference between the actual manifold temperature T.sub.Exh,Mnf, and the first limit value S.sub.Exh,Mnf is determined and used as an input variable for a PI controller. The output signal of the PI controller is the exhaust-gas temperature-dependent delta charge ratairchrg.sub.PI.

(40) This calculation runs simultaneously with the calculation of the maximum permissible pre-controlled charge ratairchrg.sub.pre. Subsequently, the method can be continued in a step 230.

(41) In a step 230, the maximum permissible pre-controlled charge ratairchrg.sub.pre is added to the exhaust-gas temperature-dependent delta charge ratairchrg.sub.PI and a total permissible charge ratairchrg.sub.ges is obtained.

(42) This total permissible charge ratairchrg.sub.ges is fed to a maximum selector, wherein the maximum is selected between the total permissible charge ratairchrg.sub.ges and a speed-dependent limit for charge reduction on the basis of component protection.

(43) The result of the maximum selection is subsequently given to the charge control in the control device 100 and the charge for the combustion is limited so that a maximum temperature can be maintained in the exhaust tract or at the component to be protected.

(44) Subsequently, the method can be continued or terminated again in step 200.

(45) The limitation of the charge can preferably be carried out over a time range, or until the manifold temperature T.sub.Exh,Mnf falls below a predeterminable temperature S.sub.Reset.