Method for open-loop and/or closed-loop control of an exhaust-gas turbocharger of an internal combustion engine motor vehicle

Abstract

A method for controlling and/or regulating an exhaust gas turbocharger of an internal combustion engine, the exhaust gas turbocharger being protected against an exceeding of a maximum rotational speed, an actual boost pressure being compared with a setpoint boost pressure. The risk of a maximum rotational speed of the exhaust gas turbocharger being exceeded is prevented in that a manipulated variable assigned to the exhaust gas turbocharger is compared with a manipulated variable limit characteristic and is limited, if necessary, the manipulated variable limit characteristic having a time-limited, first portion and a chronologically subsequent, second portion following a change in the setpoint boost pressure, the first portion ending after a predetermined target time, the second portion of the manipulated variable limit characteristic being reduced with respect to the first portion in such a way that the maximum rotational speed of the exhaust gas turbocharger is not reached.

Claims

1. A method for controlling and/or regulating an exhaust gas turbocharger of an internal combustion engine, the exhaust gas turbocharger being protected against an exceeding of a maximum rotational speed, the method comprising: comparing an actual boost pressure with a setpoint boost pressure in that a manipulated variable assigned to the exhaust gas turbocharger is compared with a manipulated variable limit characteristic and if a value of the manipulated variable is to exceed a value of the manipulated variable limit characteristic, the manipulated variable is limited to the value of the manipulated variable limit characteristic, the manipulated variable limit characteristic having a time-limited first portion and a chronologically subsequent second portion, the first portion and the second portion following a change in the setpoint boost pressure, the first portion ending after a predetermined target time; and reducing the second portion of the manipulated variable limit characteristic with respect to the first portion so that the maximum rotational speed of the exhaust gas turbocharger is not reached.

2. The method according to claim 1, wherein the predetermined target time is predetermined in that the actual boost pressure should presumably have reached the setpoint boost pressure within the predetermined target time during a fault-free operation.

3. The method according to claim 1, wherein a full modulation of the manipulated variable is described by the first portion, the first portion being a constant function up to the end of the predetermined target time.

4. The method according to claim 1, wherein the second portion of the manipulated variable limit characteristic is a monotonously decreasing function.

5. The method according to claim 1, wherein a position of a waste gate is described by the manipulated variable, the waste gate being closed in a case of a full modulation of the manipulated variable.

6. The method according to claim 1, wherein a guide vane position of the exhaust gas turbocharger having a variable turbine geometry is described by the manipulated variable.

7. The method according to claim 1, wherein a particulate filter is used in an exhaust tract of the internal combustion engine.

8. The method according to claim 7, wherein the particulate filter is a gasoline engine particulate filter.

9. The method according to claim 1, wherein the predetermined target time is predetermined as a function of a size of a setpoint boost pressure change, a presently engaged gear, an atmospheric pressure and a rotational speed of the internal combustion engine.

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 shows a setpoint boost pressure, an actual boost pressure of a manipulated variable of the exhaust gas turbocharger as well as a manipulated variable limit characteristic having a first, dynamic portion and a second, stationary portion, no leaks and no increased exhaust gas back pressure occurring; and

(3) FIG. 2 shows a diagram of a setpoint boost pressure, a delayed built-up actual boost pressure, a theoretically necessary control variable for reaching the setpoint boost pressure, thus again the manipulated variable limit characteristic, a leak and/or an increased exhaust gas back pressure occurring.

DETAILED DESCRIPTION

(4) FIGS. 1 and 2 show a setpoint boost pressure 1, 2, the setpoint boost pressure first being at a low level up to a point in time t0 and being at a higher level, namely setpoint boost pressure 2, starting at point in time t0. Such a change in setpoint boost pressure 1, 2 and point in time t0 may occur, for example, if the driver speeds up.

(5) During a regulation of the exhaust gas turbocharger, actual boost pressure 3 is compared with setpoint boost pressure 1, 2. In particular, a closed-loop controller is used to regulate the boost pressure. Actual boost pressure 3 corresponds to setpoint boost pressure 1 at point in time t0. Actual boost pressure 3 increases to the value of setpoint boost pressure 2 at later point in time t1. The time period between point in time t0 and point in time t1 is designated by Δx. A manipulated variable 4, 5, 6 of the exhaust gas turbocharger is changed to now increase actual boost pressure 3 starting from point in time t0. Manipulated variable 4 is less than 100% up to point in time t0. Between points in time t0 and t1, manipulated variable 5 is 100%, and starting at point in time t1, manipulated variable 6 is continuously reduced from the previous 100% full modulation of the exhaust gas turbocharger. Manipulated variable 4, 5, 6 describes, for example, the guide vane position of a VTG exhaust gas turbocharger or the position of a waste gate valve. During the full modulation between points in time t0 and t1, the waste gate valve is completely closed, and it is gradually opened starting at point in time t1 and is opened even farther prior to point in time t0. In the case of a VTG exhaust gas turbocharger, the guide vane position is closed in time period Δx, so that the turbine of the exhaust gas turbocharger undergoes maximum acceleration. Starting at point in time t1, the guide vane position is increasingly opened.

(6) The exhaust gas turbocharger is protected against an exceeding of a maximum rotational speed. For this purpose, manipulated variable 4, 5, 6 assigned to the exhaust gas turbocharger is compared with a manipulated variable limit characteristic 7, 8, and manipulated variable 4, 5, 6 is limited, if necessary, to the value of manipulated variable limit characteristic 7, 8 during the regulation. Manipulated variable 4, 5, 6 may maximally take on the value of manipulated value limit characteristic 7, 8.

(7) Manipulated variable limit characteristic 7, 8 has a time-limited first, dynamic portion 7 and a chronologically subsequent second, stationary portion 8, following a change in setpoint boost pressure 1, 2 at point in time t0. First, dynamic portion 7 ends at point in time t1 after a predetermined target time Δx. Target time Δx specifies the time period within which actual boost pressure 3 has presumably reached setpoint boost pressure 2. This time period or target time Δx is determined ahead of time by measurements or by a simulation or a calculation.

(8) FIG. 1 shows an operating state of the internal combustion engine and the motor vehicle, in which no leaks and no increased back pressure occur, and actual boost pressure 3 now reaches setpoint boost pressure 2 within target time Δx, i.e. up to point in time t1. First, dynamic portion 7 is preferably constant within time window Δx. Dynamic portion 7 corresponds to full modulation of manipulated variable 5, which is clarified in the drawing by the indication “100%.”

(9) The full modulation of manipulated variable 7 is canceled by manipulated variable 6 after time t1, since the rotational speed of the internal combustion engine increases simultaneously, and the position of the waste gate may be partially open, or the position of the guide vane may be partially open, due to the now increased mass flow through the exhaust gas turbocharger. Manipulated variable 5 and dynamic portion 7 coincide during time Δx. Afterwards, i.e. after time t1, manipulated variable 6 is below stationary portion 8 of manipulated variable limit characteristic 7, 8. The profile of stationary portion 8 is selected in such a way that the exhaust gas turbocharger is unable to reach the maximum rotational speed even with an increased mass flow. The method has the advantage that, without the presence of a leak and/or the presence of an increased exhaust gas back pressure—for example, due to a loaded gasoline engine particulate filter—manipulated variable 6, 7 is not limited, whereby no driving power impairments occur.

(10) FIG. 2 now shows a case, in which a leak and/or an increased exhaust has back pressure occur(s), due to a loaded particulate filter.

(11) Once again, the same change in setpoint boost pressure 1, 2 is illustrated at a point in time t0. A delayed buildup of actual boost pressure 9 now occurs, due to the leak. Actual boost pressure 9 has not yet reached setpoint boost pressure 2 at point in time t1. To now protect the exhaust gas turbocharger against an excess rotational speed, a full modulation of the exhaust gas turbocharger is canceled at point in time t1, since stationary portion 7 of manipulated variable limit characteristic 7, 8 takes effect starting at point in time t1. In other words, manipulated variable 10 runs along manipulated variable limit characteristic 8, namely stationary portion 8, starting at point in time t1. FIG. 2 also shows the embodiment if no excess rotational speed protection were present, in which case the manipulated variable would continue to be held in the full modulation during time period Δy between point in time t1 and point in time t2 (cf. reference numeral 11), and the full modulation of manipulated variable 11 is canceled in the form of decrease 12 only at point in time t2, when actual boost pressure 9 has, in fact, reached setpoint boost pressure 2. However, this case is prevented by the excess rotational speed protection, since the manipulated variable has already been limited by stationary portion 8 after previously stored time t1.

(12) The method has the advantage that manipulated variable limit characteristic 7, 8 is easy to input and also has a maximum effect. Turbocharger damage due to an excess rotational speed may be effectively and safely avoided thereby. With the aid of the method, the manipulated variable limit characteristic in stationary portion 8 as well as in dynamic portion 7 is determined in such a way that a maximum possible turbocharger actuator position is calculated. This manipulated variable limit characteristic is independent of the actual change in actual boost pressure 3, 9. Due to the fact that the manipulated variable limit characteristic is independent of the actual boost pressure, feedback is avoided if a fault occurs, for example due to an excessively high exhaust gas back pressure or due to a leak. With the aid of the method according to the invention, the turbocharger actuator may be limited in its position in the case of a fine leak or a high particulate filter load, so that no excess rotational speed occurs. The advantage is achieved with the aid of the method that the fault-free operation of the internal combustion engine is not affected by the limitation (cf. FIG. 1).

(13) If another dynamic change in the driving behavior is now expected after point in time t1 or t2, the method starts over again, and the time-limited actuator limiting takes effect again for the transient operation. The method prevents the disturbance variables from being compensated for by more turbine power when regulating the pressure of the engine and the exhaust gas turbine using a closed-loop controller, which could result in damage to the charger.

(14) 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