Method for calculating a residual gas mass in a cylinder of an internal combustion engine and controller

Abstract

A method of calculating a residual gas mass in a cylinder of an internal combustion engine, wherein the cylinder has at least one intake valve and one exhaust valve, comprising: obtaining a cylinder residual gas mass base value that is based on a predefined model; determining a first cylinder residual gas mass value that indicates a cylinder residual gas mass remaining in the cylinder clearance volume after an expulsion of exhaust gas; determining a second cylinder residual gas mass value that indicates a cylinder residual gas mass flowing into the cylinder due to a valve overlap of the intake valve and the exhaust valve, wherein the second cylinder residual gas mass value is determined based on the cylinder residual gas mass base value and the first cylinder residual gas mass value; and calculating the residual gas mass in the cylinder, based on the first and second cylinder residual gas mass values.

Claims

1. A method for calculating an instantaneous residual gas mass m.sub.RG1 in a cylinder of an internal combustion engine, wherein the cylinder has at least one intake valve and one exhaust valve, comprising: obtaining a cylinder residual gas mass base value m.sub.RG0 for a stationary operating state of the internal combustion engine at an exhaust gas temperature T.sub.0, wherein the cylinder residual gas mass base value m.sub.RG0 is based on a predefined model; determining a first cylinder residual gas mass value m.sub.tot0 that indicates a cylinder residual gas mass remaining in the cylinder clearance volume after an expulsion of exhaust gas; determining a second cylinder residual gas mass value m.sub.res0 that indicates a cylinder residual gas mass flowing into the cylinder due to a valve overlap of the intake valve and the exhaust valve, wherein m.sub.RG0=m.sub.tot0+m.sub.res0, and wherein the second cylinder residual gas mass value m.sub.res0 is determined by subtracting the first cylinder residual gas mass value m.sub.tot0 from the cylinder residual gas mass base value m.sub.RG0; determining an instantaneous exhaust gas temperature T.sub.1; and calculating the instantaneous residual gas mass m.sub.RG1 in the cylinder, based on a first instantaneous cylinder residual gas mass value m.sub.tot1 and a second instantaneous cylinder residual gas mass value m.sub.res1, wherein m.sub.RG1=m.sub.tot1+m.sub.res1, wherein the first instantaneous cylinder residual gas mass value m.sub.tot1 is calculated according to m.sub.tot1=m.sub.tot0(T.sub.0/T.sub.1), and the second instantaneous cylinder residual gas mass value m.sub.res1 is calculated according to m.sub.res1=m.sub.res0{square root over (T.sub.0/T.sub.1)}.

2. The method according to claim 1, wherein the first cylinder residual gas mass value is determined based on a predefined model.

3. A controller for an internal combustion engine of motor vehicle, including a processor and a memory, wherein the controller is configured for carrying out the method according to one of the preceding claims.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the invention are now described by way of example, with reference to the appended drawings, in which:

(2) FIG. 1 schematically shows an exemplary embodiment of a cylinder during a valve overlap;

(3) FIG. 2 schematically shows an engine control unit; and

(4) FIG. 3 shows a flow chart of a method for calculating a residual gas quantity.

DETAILED DESCRIPTION OF THE INVENTION

(5) An exemplary embodiment of a cylinder 1 of an internal combustion engine is schematically illustrated in FIG. 1. The cylinder 1 has a combustion chamber 2 in which fuel that is injected via an injector 5 is combusted. The cylinder 1 has an intake valve 3 that is coupled to an intake manifold 6, from which combustion air passes into the cylinder 1 through the intake valve 3 and into the combustion chamber 2. In addition, the cylinder 1 has an exhaust valve 4 that is coupled to an exhaust manifold 7, through which exhaust gas is conducted from the combustion chamber 2 into the exhaust manifold 7. In addition, a cylinder piston 8 is present which is driven by a crankshaft 9, as is basically known to those skilled in the art.

(6) In FIG. 1 the cylinder 1 is illustrated in a valve overlap position in which the intake valve 3 and the exhaust valve 4 are both open, so that exhaust gas may pass from the exhaust manifold 7, through the combustion chamber 2, and into the intake manifold 6, and from there in a subsequent work cycle may flow back out of the intake manifold 6 into the combustion chamber 2.

(7) FIG. 2 illustrates an engine control unit 10 that is configured for carrying out the method described herein for calculating a residual gas mass in a cylinder of an internal combustion engine, as also described in greater detail below in conjunction with FIG. 3.

(8) The engine control unit 10 has a processor 11, a memory 12, and an interface 13 for communicating with a bus system 14. By way of example, the interface 13 here is a CAN bus interface and the bus system 14 is a CAN bus system, without the present invention being limited in this regard.

(9) The engine control unit 10 carries out a method 20 (FIG. 3) for calculating a residual gas mass in a cylinder, such as the cylinder 1 in FIG. 1. The engine control unit 10 is configured in such a way that the processor 11 carries out the method described herein.

(10) At 21, the engine control unit 10 obtains a cylinder residual gas mass base value that is based on a predefined model, as discussed above. The predefined model is complex, and the cylinder residual gas mass base value is determined by stationarily operating the internal combustion engine on a test stand under standard conditions. Parameters thus obtained, for example also the stationary exhaust gas temperature (T.sub.0), are used for the model in order to determine the cylinder residual gas mass base value (m.sub.RG0) for stationary operation as precisely as possible. The cylinder residual gas mass base value is stored in the memory 12, and the processor 11 may obtain this value by retrieving it from the memory 12.

(11) At 22, the engine control unit 10 determines a first cylinder residual gas mass value (m.sub.tot0), which indicates a cylinder residual gas mass remaining in the cylinder clearance volume after an expulsion of exhaust gas, as already described above. In the present case, the first cylinder residual gas mass value is determined for the exhaust gas temperature (T.sub.0) determined during stationary operation. This value may, for example, also be stored in advance in the memory 12 or dynamically determined based on a predefined model.

(12) At 23, the engine control unit 10 determines a second cylinder residual gas mass value (m.sub.res0), which indicates a cylinder residual gas mass flowing into the cylinder 1 due to a valve overlap of the intake valve 3 and the exhaust valve 4, wherein the second cylinder residual gas mass value is determined based on the cylinder residual gas mass base value and the first cylinder residual gas mass value, in that the second cylinder residual gas mass value is determined by subtracting the first cylinder residual gas mass value from the cylinder residual gas mass base value.

(13) At 24, the engine control unit 10 calculates an instantaneous exhaust gas temperature (T.sub.1) during dynamic operation by retrieving this temperature either via the bus system 14 (from a corresponding temperature sensor, for example) and/or by calculating it using a model provided in the engine control unit 10.

(14) At 25, the engine control unit 10 calculates an instantaneous first cylinder residual gas mass value (m.sub.tot1), based on the first cylinder residual gas mass value (m.sub.tot0) and the instantaneous exhaust gas temperature (T.sub.1), as also described above.

(15) At 26, the engine control unit 10, calculates an instantaneous second cylinder residual gas mass value (m.sub.res1), based on the second cylinder residual gas mass value (m.sub.res0) and the instantaneous exhaust gas temperature (T.sub.1), as also described above.

(16) At 27, the engine control unit 10 calculates the instantaneous residual gas mass (m.sub.RG1) in the cylinder 1, based on the first instantaneous cylinder residual gas mass value (m.sub.tot1) and the second instantaneous cylinder residual gas mass value (m.sub.res1), as also described above.

(17) The method 20 may also be carried out for each cylinder of an internal combustion engine.

LIST OF REFERENCE NUMERALS

(18) 1 cylinder 2 combustion chamber 3 intake valve 4 exhaust valve 5 injector 6 intake manifold 7 exhaust manifold 8 cylinder piston 9 crankshaft 10 engine control unit 11 processor 12 memory 13 interface 14 bus 20 method for calculating a residual gas mass in a cylinder of an internal combustion engine 21 obtaining a cylinder residual gas mass base value 22 determining a first cylinder residual gas mass value 23 determining a second cylinder residual gas mass value 24 determining an instantaneous exhaust gas temperature 25 calculating a first instantaneous cylinder residual gas mass value 26 calculating a second instantaneous cylinder residual gas mass value 27 calculating the residual gas mass in the cylinder