METHOD FOR ACTIVATING A BOOST PRESSURE CONTROL

Abstract

A method for activating a boost pressure control for an internal combustion engine, which contains, in a through-flow direction, a compressor, a charge air line, a throttle valve, an intake manifold, at least one combustion chamber and a turbine speed-coupled to the compressor, an aperture of the throttle valve being controllable, a driving of the turbine being controllable by an exhaust gas flow, and the method including: predefining a setpoint intake manifold pressure; calculating a simplified inverse flow characteristic of the throttle valve; calculating a pseudo setpoint aperture of the throttle valve, based on the simplified inverse flow characteristic and the setpoint intake manifold pressure; and controlling the driving of the turbine, based on an exceeding of a maximum aperture of the throttle valve by the pseudo setpoint aperture of the throttle valve.

Claims

1. A method for activating a boost pressure control for an internal combustion engine, which comprises, in a through-flow direction, a compressor, a charge air line, a throttle valve, an intake manifold, at least one combustion chamber, and a turbine speed-coupled to the compressor, an aperture of the throttle valve being controllable, a driving of the turbine being controllable by an exhaust gas flow, the method comprising: predefining a setpoint intake manifold pressure; calculating a simplified inverse flow characteristic of the throttle valve; calculating a pseudo setpoint aperture of the throttle valve based on the simplified inverse flow characteristic and the setpoint intake manifold pressure; and controlling the driving of the turbine based on an exceeding of a maximum aperture of the throttle valve by the pseudo setpoint aperture of the throttle valve.

2. The method according to claim 1, wherein the calculation of the simplified inverse flow characteristic includes: linearizing an inverse flow characteristic in a working point.

3. The method according to claim 2, wherein the working point is selected such that a quotient of the intake manifold pressure in relation to the boost pressure is in a range from 0.90 to 0.995.

4. The method according to claim 1, wherein the control of the driving is based on a difference from the maximum aperture and the pseudo setpoint aperture and includes limiting a control variable for the case that the pseudo setpoint aperture is smaller than the maximum aperture.

5. A method for controlling a throttle valve comprising: activating a boost pressure control according to claim 1; controlling an aperture of the throttle valve based on a setpoint intake manifold pressure; and limiting a control response to the maximum aperture.

6. A computer program product adapted to perform the method according to claim 1.

7. A storage medium comprising the computer program product according to claim 6.

8. A control unit communicatively connectable to a turbocharger drive unit or additionally to a throttle valve drive unit, the control unit being adapted to perform the method according to claim 1.

9. A rechargeable internal combustion engine comprising a compressor; a charge air line; a throttle valve; an intake manifold; a combustion chamber; a turbine speed-coupled to the compressor; and a control unit according to claim 8, wherein, in a through-flow direction, an aperture of the throttle valve is controllable via the control unit, and wherein a driving of the turbine is controllable by an exhaust gas flow.

10. A vehicle, comprising the internal combustion engine (1) according to claim 9.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] 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:

[0046] FIG. 1 schematically shows an internal combustion engine according to a first example;

[0047] FIG. 2 shows a sequence of a method according to the invention according to the first example;

[0048] FIG. 3 shows a simplification during the method according to the first example;

[0049] FIG. 4a shows multiple diagrams of a behavior of an internal combustion engine according to the conventional art;

[0050] FIG. 4b shows multiple diagrams, which correspond to the ones in FIG. 4a, of a behavior of the internal combustion engine according to the invention; and

[0051] FIG. 5 schematically shows an internal combustion engine according to a second example.

DETAILED DESCRIPTION

[0052] One exemplary embodiment of an internal combustion engine 1 according to the first example is described on the basis of FIG. 1. Internal combustion engine 1 contains an air intake line 2, which opens into a compressor 3. A charge air line 4 leads from compressor 3 to a throttle valve 5. An intake manifold 6 leads from throttle valve 5 to multiple cylinders. Each cylinder forms a combustion chamber 7 together with a cylinder head, which is not illustrated, valves, which are not illustrated, and a piston, which is not illustrated. A shared manifold 8 leads from combustion chambers 7 to a turbine 9. Turbine 9 is rotatably fixedly coupled with compressor 3 via a shaft 10 to form a turbocharger 11. An exhaust gas line 12 abuts turbine 9.

[0053] A control unit 13 is coupled with a throttle valve drive unit, which is not illustrated, of throttle valve 5 via a control line 14 for the purpose of transferring signals. Throttle valve 5 is adjustable, and it is pivoted by throttle valve drive unit according to the signals from control unit 13. An aperture of throttle valve 5 may thus be predefined by control unit 13.

[0054] Control unit 13 is coupled with a turbine drive unit, which is not illustrated, of turbine 9 via a control line 15 for the purpose of transferring signals. According to the first specific embodiment, turbine 9 in internal combustion engine 1 is a turbine having a variable turbine geometry, as is often used in spark-ignition engines. A signal from control unit 13 may thus set the turbine drive unit to the flow resistance of turbine 9. The flow resistance corresponds to the driving of turbine 9.

[0055] Among other things, steps of a method for activating a turbocharger controller and steps of a method for controlling a throttle valve, including the method for activating a turbocharger controller, run in control unit 13.

[0056] In a first step S1, a torque demand M.sub.soll is detected. For example, control unit 13 reads out an accelerator pedal travel sensor, or a driver assistance system reports a torque demand to control unit 13.

[0057] Requested torque M.sub.soll is converted into a requested intake manifold pressure p.sub.sr,soll in a step S2. An engine characteristic map, for example, is used for this purpose.

[0058] Requested intake manifold pressure p.sub.sr,soll is converted into a pseudo setpoint aperture Ã.sub.DK,soll. A throttle equation is simplified for this purpose in step S3.

[0059] The background will be briefly discussed for a better understanding. The throttle equation may be solved for the throttle valve area and is then as follows:

[00002]$A_{\mathrm{DK}}=\frac{\frac{V}{\kappa {\mathrm{RT}}_2}{\stackrel{.}{p}}_{\mathrm{sr}}+w_{\mathrm{vlv}}-w_{\mathrm{TEV}}}{\sqrt{\frac{2}{{\mathrm{RT}}_1}}{p}_{\mathrm{vd}}\Psi \left(p_{\mathrm{sr}}/p_{\mathrm{vd}}\right)}-A_{\mathrm{DK},\mathrm{Leak}}$

[0060] Where the following mean:

A.sub.DK throttle valve area;
V intake manifold volume;
κ specific heat of the air;
R gas constant of the air;
T.sub.2 temperature in intake manifold 4;
pressure change in intake manifold 4;
w.sub.vtv mass flow in combustion chambers 7 (in technical terms: “over the valves”);
p.sub.sr pressure in intake manifold 4;
w.sub.TEV tank venting mass flow;
T.sub.1 temperature upstream from throttle 5;
p.sub.vd pressure upstream from throttle 5;
ψ throttle flow characteristic;
a coefficient; and
b coefficient.

[0061] To be able to reliably calculate inverse flow characteristic 1/Ψ(p.sub.sr/p.sub.vd), the latter is simplified according to FIG. 3. In FIG. 3, hyperbolic function 1/Ψ is plotted over pressure ratio Π=p.sub.sr/p.sub.vd. In FIG. 3, a working point is indicated by a dashed line at Π=0.98. In this working point, inverse flow characteristic 1/Ψ is linearized to a straight line L. In the working point, straight line L abuts inverse flow characteristic 1/Ψ as a tangent. Straight line L has the following form:

L=a+b*Π.

[0062] Straight line L is now inserted into the throttle equation. In addition, the following effects are intentionally disregarded, due to their limited influence during the transition from the throttle control to the boost pressure control, and the corresponding terms have been removed from the throttle equation:

[00003]$\frac{V}{\kappa {\mathrm{RT}}_2}{\stackrel{.}{p}}_{\mathrm{sr}}$

container dynamic in the intake manifold and

[0063] w.sub.TEV throttle valve leak due to manufacturing tolerance and/or wear.

[0064] The mass flow over the valves in the transition region from the throttle control to the boost pressure control is also assumed as a constant w.sub.vtv,soll.

[0065] The throttle equation may this be simplified as follows in order to calculate pseudo setpoint aperture Ã.sub.DK,soll in step S3:

[00004]${\tilde{A}}_{\mathrm{DK},\mathrm{soil}}=\frac{w_{\mathrm{vlv},\mathrm{soil}}}{\sqrt{\frac{2}{{\mathrm{RT}}_1}}{p}_{\mathrm{vd}}}\left(a+b\frac{p_{\mathrm{sr},\mathrm{soil}}}{p_{\mathrm{vd}}}\right)$

[0066] Value Ã.sub.DK,soll is then subtracted from maximum aperture A.sub.DK,max in step S4.

[0067] The difference from maximum aperture A.sub.DK,max and pseudo setpoint aperture Ã.sub.DK,soll is then entered into a controller as the input variable in step S5 In this specific embodiment, a control variable is determined with the aid of a PI controller in step S5. The output of the I element is limited to a maximum value in such a way that a constantly positive input variable does not result in a constantly increasing controller response. In other words: As long as pseudo setpoint aperture Ã.sub.DK,soll is smaller than maximum aperture A.sub.DK,max, an accumulation of the controller output is prevented. This anti-windup function prevents an overflowing control variable as well as a long response time at the moment of the transition from the throttle control to the boost pressure control. In the first specific embodiment, a stop, which is not illustrated, limits the mechanism for adjusting the turbine geometry as a securing function. Turbine 9 may therefore be controlled below a minimal drive. An accumulation of the I element would thus not result in a readjustment of turbine 9.

[0068] After step S5, control variable r.sub.Gov is continuously output to the drive unit of turbine 9. The drive unit sets turbine 9 according to transmitted variable r.sub.Gov in step S6. A corresponding boost pressure p.sub.vd,ist is obtained as the result of step S6.

[0069] Boost pressure p.sub.vd,ist upstream from the throttle valve and setpoint intake manifold pressure p.sub.sr,soll, together with charge air temperature T.sub.1 and the setpoint mass flow in combustion chambers 7 w.sub.vtv,soll are the variables for redetermining pseudo setpoint aperture Ã.sub.DK,soll according to the above formula in step S3.

[0070] Setpoint intake manifold pressure p.sub.sr,soll determined in step S2 is also used in a step S7. In step S7, a corresponding aperture ASK is calculated from setpoint intake manifold pressure p.sub.sr,soll. This value is limited in absolute terms to the maximum aperture of throttle valve 5, so that the possibly limited variable A.sub.DK,lim is output as a control signal. In a subsequent step S8, the throttle valve drive actuates throttle valve 5 according to value A.sub.DK,lim, and a corresponding intake manifold pressure p.sub.sr,ist sets in.

[0071] If internal combustion engine 1 is operated in the lower power range, an intake manifold pressure p.sub.sr in intake manifold 6 is sufficient, which does not exceed the basic boost pressure minus a throttling loss of throttle valve 5. Since the basic boost pressure in charge air line 4 is sufficient to generate the requested torque M.sub.soll in internal combustion chambers 7, a greater drive of turbine 9 is not necessary as the minimal drive. Step S7 thus regulates the power of internal combustion engine 1 with the aid of value A.sub.DK,lim. Pseudo setpoint aperture Ã.sub.DK,soll determined in step S3 is smaller than maximal aperture A.sub.DK,max. Step S5 therefore yields only control signal r.sub.Gov having a minimal absolute value. In other words, internal combustion engine 7 is operated with the aid of the throttle control.

[0072] If internal combustion engine 1 is to output more power, it will enter the overtravel range. The internal combustion engine thus enters the power range, in which the intake manifold pressure must reach the basic boost pressure. Step S7 therefore outputs control variable A.sub.DK,lim with the maximum absolute value, and throttle valve 5 is opened all the way. In addition, pseudo setpoint aperture Ã.sub.DK,soll ascertained in steps S3 corresponds to maximum aperture A.sub.DK,max. In step S5, the controller therefore outputs only control signal r.sub.Gov with a minimal absolute value. In other words, internal combustion engine 7 is still operated with the aid of the throttle control.

[0073] If the power demand on internal combustion engine 1 further increases, the calculation in step S7 continues to output control variable A.sub.DK,lim with a maximum absolute value. At the same time pseudo setpoint aperture Ã.sub.DK,soll exceeds maximum aperture A.sub.DK,max with an absolute value. In step S5, the controller therefore outputs control signal r.sub.Gov with an increasing absolute value. In other words, internal combustion engine 7 is operated with the aid of the boost control.

[0074] This avoids a situation, in which the boost control enters into competition with the throttle control, so that throttle valve 5 would have to decrease an elevated boost pressure. An increased fuel consumption therefore does not occur with the method according to the invention.

[0075] FIG. 4b again illustrates the difference, based on a variant of the first specific embodiment compared to FIG. 4a. Only differences from the first specific embodiment are described. In both cases, a setpoint intake manifold pressure p.sub.sr,soll is requested at point in time to, which exceeds the basic boost pressure. The profiles of setpoint intake manifold pressure p.sub.sr,soll, intake manifold pressure psi- and boost pressure p.sub.vd are shown in the top diagram in each case. In the diagram second from the top, the resulting profile of r.sub.Gov is illustrated as a change signal to the drive unit of turbine 9. The controller in step S5, i.e., in the method according to the invention, was a prototype with a highly variable behavior in this test; cf. FIG. 4b. In the third diagram from the top, the advantageous effect of the invention is apparent. In the case of the control according to the prior art, a boost pressure p.sub.vd above setpoint intake manifold pressure p.sub.sr,soll is generated; cf. FIG. 4a; the aperture of throttle valve 5 is therefore reduced, so that more fuel is consumed. In the case of the control according to the invention, throttle valve 5 may remain open; cf. FIG. 4b; no unnecessary increased consumption is therefore induced. Starting at t.sub.0, the fourth diagram shows a similar acceleration behavior of internal combustion engine 1; i.e., the method according to the invention does not come at the cost of vehicle dynamics.

[0076] A further variant of the first specific embodiment is not illustrated in the figures. In step S5, a PID controller is used instead of a PI controller to achieve a more rapid response.

[0077] A second example of the invention is shown in FIG. 5. It corresponds to the first specific embodiment, with the exception of turbine 9. Instead of a turbine 9 having a variable geometry, a turbine 9 having an invariable geometry is used, and a wastegate valve 16 is connected upstream from turbine 9. If necessary, turbine 9 may be short-circuited, for example, with the aid of wastegate valve 16. In the second specific embodiment, turbine 9 is therefore driven with the aid of wastegate valve 16. The illustrated method changes only in terms of absolute value.

[0078] 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.