Method and control device for determining a desired intake manifold pressure of an internal combustion engine

Abstract

A method for determining a desired intake manifold pressure of an internal combustion engine by means of an iterative method, wherein a cylinder charge is determined for an intake manifold pressure iterated during the iterative method, and the desired intake manifold pressure is determined as a function of the cylinder air charge that has been determined. In addition, a control device for carrying out the method is provided.

Claims

1. A method for determining a desired intake manifold pressure of an internal combustion engine via an iterative method, the method comprising: determining a cylinder charge for an intake manifold pressure iterated during the iterative method; and determining the desired intake manifold pressure as a function of the cylinder charge that has been determined, wherein the desired intake manifold pressure is an iterated value representing an improved initial value for a subsequent iteration.

2. A method for determining a desired intake manifold pressure of an internal combustion engine via an iterative method, the method comprising: determining a cylinder charge for an intake manifold pressure iterated during the iterative method; and determining the desired intake manifold pressure as a function of the cylinder charge that has been determined, wherein the iterative method is a secant method.

3. The method according to claim 2, wherein a cylinder charge is determined for a first initial intake manifold pressure, and a second initial intake manifold pressure is determined in that the cylinder charge for the first initial intake manifold pressure is compared with a desired cylinder charge of the internal combustion engine, and wherein the second initial intake manifold pressure is determined as a function of the result of the comparison between the cylinder charge for the first initial intake manifold pressure and the desired cylinder charge.

4. The method according to claim 3, wherein the first initial intake manifold pressure is an actual intake manifold pressure.

5. The method according to claim 3, wherein the iterated intake manifold pressure is determined based on the first initial intake manifold pressure and the second initial intake manifold pressure is determined via the secant method.

6. The method according to claim 5, wherein the iterated intake manifold pressure is additionally determined as a function of the cylinder charge for the first initial intake manifold pressure and of the cylinder charge for the second initial intake manifold pressure.

7. A method for determining a desired intake manifold pressure of an internal combustion engine via an iterative method, the method comprising: determining a cylinder charge for an intake manifold pressure iterated during the iterative method; and determining the desired intake manifold pressure as a function of the cylinder charge that has been determined, wherein the cylinder charge for the iterated intake manifold pressure is determined as a function of a desired exhaust gas back pressure, and wherein the desired exhaust gas back pressure is determined as a function of the iterated intake manifold pressure.

8. The method according to claim 7, wherein the desired exhaust gas back pressure is determined from a quadratic approximation of the equation: ${\stackrel{.}{m}}_{\mathrm{Abg}}=A_{\mathrm{eff}}{p}_3\sqrt{\frac{2}{R_s{T}_3}}\psi \left(c_d;\frac{p_4}{p_3}\right),$ wherein {dot over (m)}.sub.Abg is a desired exhaust gas mass flow, A.sub.eff is an effective opening area of a throttle, p.sub.3 is a desired exhaust gas back pressure, p.sub.4 is a desired pressure after a turbine, R.sub.s is the specific gas constant of the exhaust gas, T.sub.3 is an exhaust gas temperature before the turbine, c.sub.d is a turbine flow factor and ψ(.Math.) is a flow function.

9. The method according to claim 7, wherein the desired exhaust gas back pressure is determined by an iterative method.

10. The method according to claim 9, wherein an initial exhaust gas back pressure is the iterated intake manifold pressure.

11. The method according to claim 10, wherein a reduced exhaust gas mass flow and a VTG drive duty cycle are determined as a function of the initial exhaust gas back pressure, and the iterated exhaust gas back pressure is determined as a function thereof.

12. The method according to claim 7, wherein the desired intake manifold pressure is determined from a desired pressure after a turbine and from a power balance of the turbine and of a compressor.

13. A method comprising: determining a desired exhaust gas back pressure of an internal combustion engine via a fixed-point method; and determining an iterated exhaust gas back pressure from a quadratic approximation of the equation: ${\stackrel{.}{m}}_{\mathrm{Abg}}=A_{\mathrm{eff}}{p}_3\sqrt{\frac{2}{R_s{T}_3}}\psi \left(c_d;\frac{p_4}{p_3}\right),$ wherein {dot over (m)}.sub.Abg is a desired exhaust gas mass flow, A.sub.eff is an effective opening area of a throttle, p.sub.3 is the desired exhaust gas back pressure, p.sub.4 is a desired pressure after a turbine, R.sub.s is the specific gas constant of the exhaust gas, T.sub.3 is an exhaust gas temperature before the turbine, c.sub.d is a turbine flow factor and ψ(.Math.) is a flow function, wherein the desired exhaust gas mass flow is a function of a previously iterated exhaust gas back pressure.

14. The method according to claim 13, wherein the desired exhaust gas back pressure corresponds to the iterated exhaust gas back pressure after two iteration steps.

15. A control device for an internal combustion engine, the control device comprising a processor designed to carry out the method according to claim 1.

16. The method according to claim 1, wherein said iterative method comprises multiple iteration steps.

17. The method according to claim 1, wherein said determining the desired intake manifold pressure comprises an iterative calculation.

18. The method according to claim 1, further comprising: determining a first initial intake manifold pressure; determining a cylinder charge for the first initial intake manifold pressure; determining a second initial intake manifold pressure as a function of the cylinder charge for the first initial intake manifold pressure; determining a cylinder charge for the second initial intake manifold pressure; determining a first iterated intake manifold pressure; determining a cylinder charge for the first iterated intake manifold pressure; and determining whether the iteration can be terminated.

19. The method according to claim 18, further comprising repeating the iteration.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

(2) FIG. 1 schematically shows an internal combustion engine;

(3) FIG. 2 schematically shows a control device for carrying out a method for determining a desired intake manifold pressure;

(4) FIG. 3 schematically shows a flowchart of an exemplary embodiment of a method for determining a desired intake manifold pressure;

(5) FIG. 4 schematically shows a flowchart of a method for determining the cylinder charge;

(6) FIG. 5 schematically shows the basic principle of a secant method; and

(7) FIG. 6 schematically shows a flowchart of an iterative method for determining a desired exhaust back pressure.

DETAILED DESCRIPTION

(8) An internal combustion engine is shown schematically in FIG. 1. A cylinder 1 has a combustion chamber 10, in which the combustion of fuel that is injected through an injection valve 11 takes place. The cylinder 1 is coupled by an intake valve 12 to an intake manifold 13, from which fresh air arrives in the combustion chamber 10 through the intake valve 12. In addition, the cylinder 1 is coupled by an exhaust valve 14 to an exhaust manifold 15, through which the exhaust gas or residual gas is directed out of the combustion chamber 10 into the exhaust manifold 15. Furthermore, a cylinder piston 16 is present that is driven by a crankshaft. Located in the intake manifold 13 directly ahead of the intake valve 12 is an intake manifold pressure sensor 2, which is designed to detect an intake manifold pressure. Located in the exhaust manifold 15 directly behind the exhaust valve 14 is an exhaust back pressure sensor 3, which is designed to detect an exhaust gas back pressure. In FIG. 1, the cylinder 1 is represented at a point in time when the intake valve 12 and the exhaust valve 14 are open and a valve overlap is present.

(9) FIG. 2 shows a schematic representation of a control device 4 for carrying out a method for determining a desired intake manifold pressure. The control device 4 has a processor 40 that is connected to a signal input 41 for receiving data and a signal output 42 for issuing control commands to the internal combustion engine. The control device 4 also has a data memory 43 that is provided for storage of characteristic maps, algorithms, iteration instructions, defined parameters, and the like. The processor 40 is designed to carry out a method for determining a desired intake manifold pressure, as is described below with reference to FIG. 3 to FIG. 6.

(10) FIG. 3 shows a flowchart of a method 5 for determining a desired intake manifold pressure.

(11) Firstly, at 50 a first initial intake manifold pressure is determined. To this end, an actual intake manifold pressure, which serves as the first initial intake manifold pressure, is measured by means of the intake manifold pressure sensor.

(12) Next, at 51 a cylinder charge is determined for the first initial intake manifold pressure.

(13) To this end, as is shown in the diagram in FIG. 4, a desired turbocharger speed is determined at 60 as a function of the first initial intake manifold pressure. A desired exhaust gas back pressure is determined at 61 as a function of the first initial intake manifold pressure and the desired turbocharger speed that has been determined. The calculation of the desired exhaust gas back pressure is described below in detail with reference to FIG. 6. Next, at 62 the cylinder charge is determined as a function of the first initial intake manifold pressure and the desired exhaust gas back pressure.

(14) At 52 in FIG. 3, a second initial intake manifold pressure is determined as a function of the cylinder charge for the first initial intake manifold pressure. To this end, the cylinder charge for the first initial intake manifold pressure is compared with a desired cylinder charge of the internal combustion engine, and as a function of the result of the comparison an upper limit value p.sub.S2,max or a lower limit value p.sub.S2,min is defined as the second initial intake manifold pressure according to Equation (2) above from a characteristic map that defines a search region.

(15) At 53 a cylinder charge for the second initial intake manifold pressure is determined. The determination of the cylinder charge for the second initial intake manifold pressure takes place analogously to the determination of the cylinder charge for the first initial intake manifold pressure.

(16) At 54 a first iterated intake manifold pressure is determined by means of a secant method. to this end, as is shown in FIG. 5, the cylinder charge r.sub.ps2 for the first initial intake manifold pressure p.sub.s1 and the cylinder charge r.sub.ps2 for the second initial intake manifold pressure p.sub.s2 are plotted over the intake manifold pressure p (X axis), and a secant S1 is drawn between the cylinder charges r.sub.ps1, r.sub.ps2. A point of intersection of the secant S1 with the X axis represents the first iterated intake manifold pressure p.sub.l1.

(17) At 55 a cylinder charge is determined for the first iterated intake manifold pressure that has been determined. The determination of the cylinder charge for the first iterated intake manifold pressure takes place analogously to the determination of the cylinder charge for the first initial intake manifold pressure.

(18) At 56 it is determined whether or not the iteration can be terminated. This can be determined as a function of a number of iterations already carried out or as a function of the cylinder charge for the first iterated intake manifold pressure. For example, the charge for the first iterated intake manifold pressure can be compared with the charge for the second initial intake manifold pressure, and a decision as to whether or not the iteration can be terminated can be made as a function of the result of the comparison.

(19) If it is determined at 56 that the iteration can be terminated, at 57 the last iterated intake manifold pressure that has been determined is output as the desired intake manifold pressure.

(20) If it is determined at 56 that the iteration cannot be terminated, the steps 54 to 56 are repeated. In so doing, at 54 a second iterated intake manifold pressure is determined by the means that, as shown in FIG. 5, a secant S2 is drawn through the cylinder charge r.sub.ps2 for the second initial intake manifold pressure and the cylinder charge r.sub.pl1 for the first iterated intake manifold pressure, and a point of intersection with the X axis is defined as the second iterated intake manifold pressure p.sub.l2. At 55 the cylinder charge for the second iterated intake manifold pressure is then defined, and at 56 it is determined whether or not the iteration can be terminated. To this end, the charge for the second iterated intake manifold pressure can be compared with the charge for the first iterated intake manifold pressure, and a decision as to whether or not the iteration can be terminated can be made as a function of the result of the comparison. If the iteration cannot be terminated, the steps 54 to 56 are repeated analogously for additional iterated intake manifold pressures.

(21) The iteration is repeated, for example a maximum of two times, and is then terminated. However, the maximum number of iterations can be defined in advance.

(22) In the first exemplary embodiment, the desired exhaust gas back pressure for determining a charge is determined for each of the initial intake manifold pressures and iterated intake manifold pressures according to the method 7 for determining a desired exhaust gas back pressure.

(23) At 70 an initial exhaust gas back pressure is defined. The initial exhaust gas back pressure is the intake manifold pressure that was used as a starting point in the relevant step of the method 5 for determining the desired intake manifold pressure. In other words, in step 51 of the method 5 the initial exhaust gas back pressure is the first initial intake manifold pressure, in step 53 it is the second initial intake manifold pressure, and in step 55 it is the iterated exhaust gas back pressure that was iterated in step 54.

(24) At 71 a reduced mass flow is determined as a function of the initial exhaust gas back pressure.

(25) At 72 a VTG drive duty cycle or an adjustment of an actuator of a turbocharger having a wastegate is then determined as a function of the initial intake manifold pressure and the reduced mass flow.

(26) At 73 an iterated exhaust gas back pressure is determined by means of Equation (3) above. Steps 71 to 73 each represent an iteration step of a fixed-point iteration.

(27) At 74 it is determined whether or not the iteration can be terminated. This is determined as a function of a number of iterations already carried out. The maximum number of iterations is 2 here.

(28) If it is determined at 74 that the iteration can be terminated, at 75 the last iterated exhaust gas back pressure that has been determined is output as the desired exhaust gas back pressure.

(29) If it is determined at 74 that the iteration cannot be terminated, the steps 71 to 74 are repeated. In so doing, in each case a reduced exhaust gas mass flow, a VTG drive duty cycle or an adjustment of an actuator of a turbocharger having a wastegate, and an additional iterated exhaust gas back pressure are determined as a function of the iterated exhaust gas back pressure.

(30) In a second exemplary embodiment, the exhaust gas back pressure is calculated at each calculation step 51, 53, 54 of the method 5 by means of Equation (3) above, and a reduced mass flow is determined with Equation (4) above. Then, the VTG drive duty cycle or the adjustment of the actuator of the turbocharger having a wastegate are determined therefrom.

(31) In a third exemplary embodiment, the desired exhaust gas back pressure is determined at each calculation step 51, 53, 54 of the method 5 from a desired pressure after a turbine and a power balance of the turbine and of a compressor.

(32) The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.