EP1446568A1

EP1446568A1 - Method for controlling an internal combustion engine

Info

Publication number: EP1446568A1
Application number: EP02791690A
Authority: EP
Inventors: Armin DÖLKER
Original assignee: MTU Friedrichshafen GmbH
Current assignee: Rolls Royce Solutions GmbH
Priority date: 2001-11-24
Filing date: 2002-11-20
Publication date: 2004-08-18
Anticipated expiration: 2022-11-20
Also published as: EP1446568B1; US20040249555A1; DE50205611D1; WO2003046357A8; US7010415B2; ES2254770T3; DE10157641A1; DE10157641C2; WO2003046357A1

Abstract

The invention relates to an internal combustion engine (1) having a common rail injection system, wherein once a defective rail pressure sensor (10) is detected, transition from normal to emergency operation is considerably determined by a transition function. Said transition function is previously determined in normal operation on the basis of the progression of a deviation. The deviation is calculated by comparing set and real rail pressure (pCR). The invention ensures troublefree and continuous transition from normal to emergency operation.

Description

Method for controlling an internal combustion engine

The invention relates to a method for controlling an internal combustion engine according to the preamble of the first claim.

In a common rail injection system, the rail pressure is regulated. The rail pressure actual value, ie the controlled variable, is recorded by an electronic control unit via a rail pressure sensor. This calculates the control deviation from a target / actual comparison of the rail pressure and uses a rail pressure controller to determine a control signal for an actuator, for example a suction throttle or a pressure control valve. Since the rail pressure is an essential parameter for the injection quality, a faulty rail pressure sensor must be reacted to with suitable measures. In the event of a defective rail pressure sensor, DE 199 16 100 A1 suggests switching from normal operation to start operation. The rail pressure is controlled in the start mode. Here, a high-pressure pump is set to maximum delivery capacity and a pressure control valve, which determines the outflow from the rail, is closed. The problem with this solution is the abrupt transition from normal to start-up operation, as well as the resulting high rail pressure.

An emergency operation (limp home) for an internal combustion engine with a defective rail pressure sensor is known from US Pat. No. 5,937,826. In emergency operation, the high-pressure pump is controlled via a map depending on the engine speed and a target injection quantity. The problem here is that a high rail pressure can occur immediately after the transition to emergency operation due to the previously large control deviation. This can increase the engine speed. This undefined operating state is maintained until the engine speed controller reduces the target injection quantity and indirectly controls the rail pressure via the map.

The invention is therefore based on the object of making the transition from normal operation to emergency operation more secure. The object is achieved by a method for controlling an internal combustion engine with the features of the first claim. The configurations for this are shown in the subclaims.

The invention provides that the transition from normal operation to emergency operation is largely determined by a transition function. This transition function is previously determined in normal operation from the time course of the control deviation of the rail pressure. For this purpose, the control deviations within a measurement period or a specifiable number of control deviations can be considered. As a measure, at the end of normal operation, the transition function specifies a negative control deviation for the rail pressure controller in accordance with the measurement period or number of control deviations recorded in normal operation. As an alternative measure, it is provided that a correction volume flow of the controlled system is specified by the transition function. The correction volume flow is calculated from the difference between two control deviations. Both measures offer the advantage that there is a defined, continuous transition from normal operation to emergency operation. The direct effect of the transition function on the rail pressure controller or the controlled system results in a short response time after the rail pressure sensor fails.

At the end of the transition function, a change is made to the map known from the prior art. As an accompanying measure, an evaluation map is provided, by means of which the values of the map are additionally evaluated. In addition, the map is corrected by limit lines, which supports the indirect determination of the rail pressure via the engine speed controller.

A preferred embodiment is shown in the drawings. Show it:

Figure 1 is a block diagram;

Figure 2 shows a control loop, first embodiment; Figure 3 shows a control loop, second embodiment;

FIGS. 4A, 4B show a time diagram;

Figure 5 shows a transition function;

Figure 6 is a map; to determine the leakage volume flow Figure 7 shows an evaluation map;

FIG. 8 shows a limit line;

Figure 9 is a map; to determine the leakage volume flow

Figure 10 shows a program flow chart.

FIG. 1 shows a block diagram of an internal combustion engine 1 with a common rail injection system. The common rail injection system comprises a first pump 4, a suction throttle 5, a second pump 6, a high-pressure accumulator and injectors 8. In the further text, the high-pressure accumulator is referred to as rail 7. The first pump 4 delivers the fuel from a fuel tank 3 to the suction throttle 5. The pressure level after the first pump 4 is, for example, 3 bar. The volume flow to the first pump 6 is determined via the suction throttle 5. The first pump 6 in turn conveys the fuel under high pressure into the rail 7. The pressure level in the rail 7 in diesel engines is more than 1200 bar. The injectors 8 are connected to the rail 7. The fuel is injected into the combustion chambers of the internal combustion engine 1 through the injectors 8.

The internal combustion engine 1 is controlled and regulated by an electronic control unit 1 1 (EDC). The electronic control unit 11 contains the usual components of a microcomputer system, for example a microprocessor, I / O modules, buffers and memory modules (EEPROM, RAM). The operating data relevant to the operation of the internal combustion engine 1 are applied in characteristic diagrams / characteristic curves in the memory modules. The electronic control unit 11 uses this to calculate the output variables from the input variables. The following input variables are shown by way of example in FIG. 1: an actual rail pressure pCR (IST), which is measured by means of a rail pressure sensor 10, the rotational speed nMOT of the internal combustion engine 1, a power request FW, an internal cylinder pressure pIN, which is measured by means of pressure sensors 9 and an input variable E. The input variable E includes, for example, the charge air pressure pLL of the turbocharger 2 and the temperatures of the coolants and lubricants. In Figure 1, a signal ADV for the output variables of the electronic control unit 1 1

Control of the suction throttle 5 and an output variable A shown. The output variable A represents the other control signals for controlling and regulating the internal combustion engine 1, for example the start of injection BOI and the injection quantity ve. In practice, the control signal ADV is designed as a PWM signal (pulse width modulated), via which a corresponding current value for the suction throttle 5 is set. At a current value of zero (i = 0), the suction throttle 5 is fully open, ie the volume flow delivered by the first pump 4 reaches the second pump 6 unhindered.

A control circuit is shown in a first embodiment in FIG. The basic elements include a first summation point 16, a rail pressure regulator 13, a conversion 17 and the rail 7. The conversion 17 includes the conversion of the desired volume flow V (TARGET) into the control signal ADV, the suction throttle 5 and the second pump 6 Input variables E are supplied to the conversion 17, for example the fuel pre-pressure, the operating voltage and the engine speed. The conversion 17 and the rail 7 correspond to the controlled system. This basic control loop is supplemented by a first switch 12, a second switch 15 and a second summation point 18. In Figure 2, the first switch 12 and second switch 15 are shown in their switching position according to the normal operation of the internal combustion engine (solid line). In normal operation, the rail pressure actual value pCR (IST) at the first summation point 16 is compared with the reference variable, that is to say the rail pressure setpoint pCR (SW), and fed to the rail pressure controller 13 as a control deviation dR. Depending on the control deviation dR, the rail pressure controller 13 determines a controller volume flow VR. At the second summation point 18, a consumption volume flow V (VER) is added to this controller volume flow. The consumption volume flow V (VER) is calculated as a function of the engine speed nMOT and a target injection quantity Q (SW). From these two volume flows, the desired volume flow V (TARGET), which represents the input variable for the conversion 17, results as a manipulated variable. The control signal ADV for the suction throttle 5 is generated by means of the conversion 17, which then results in an actual volume flow V (IST) via the second pump 6.

When a defective rail pressure sensor is detected, the first switch 12 changes to the switch position shown in dashed lines. In this switch position, the control deviation is specified by the transition function ÜF. The transition function was previously determined in normal operation from the time course of the control deviations dR. In practice, the system deviations within a measurement period are considered. Alternatively, of course, only a predeterminable number of control deviations can be used. At the end of normal operation, the transition function ÜF defines the control deviation for the rail pressure controller 13 in accordance with the measurement period recorded in normal operation. After this time stage, the transition function ÜF is ended and the second switch 15 changes to the position shown in dashed lines. The target volume flow V (TARGET) is now calculated from the consumption volume flow V (VER) and a leakage volume flow V (LKG). This in turn is largely determined by the map 14 as a function of the engine speed nMOT and the target injection quantity Q (SW).

In Figure 3, the control loop is shown in a second embodiment. The control circuit of FIG. 3 differs from FIG. 2 by a DT1 element 19, a third switch 20 and the omission of the first switch 12. The second switch 15 and the third switch 20 are shown for normal operation (solid line). The function of the control loop in normal operation corresponds to the description in FIG. 2. When a defective rail pressure sensor is detected, the second switch 15 and the third switch 20 change to the dashed position. The rail pressure regulator 13 is deactivated immediately. The target volume flow V (TARGET) is now calculated additively from the leakage volume flow V (LKG), the consumption volume flow V (VER) and the correction volume flow V (KORR). The correction volume flow V (CORR) is determined via the DT1 element 19 from the transition function ÜF. This is calculated from a difference between two control deviations in normal operation and is given to the DT1 element 19 as a negated step function. The transition function ÜF is explained in more detail in connection with FIG. 4B. If the output variable of the DT1 element 19 falls below a threshold value or a timer has expired, the transition function is deactivated. The third switch 20 then returns to its starting position (normal operation). The target volume flow V (TARGET) is then only specified by the map 14 and the consumption volume flow V (VER).

Figure 4 consists of the sub-figures 4A and 4B. 4A shows a pressure curve of the rail pressure actual value pCR (IST) and the rail pressure setpoint pCR (SW) and FIG. 4B shows the resulting control deviation dR. At time t1, the actual rail pressure pCR (IST) corresponds to the desired rail pressure pCR (SW), corresponding to point A. In the following consideration it is assumed that the rail pressure setpoint pCR (SW) remains unchanged for the observation period. At time t1, the control deviation is zero, corresponding to point D in FIG. 4B. After the time t1, the rail pressure actual value pCR (IST) begins to decrease. The cause is a defective rail pressure sensor 10. At time t3, there is already a control deviation dR3 in point B. At time t5, the defect is recognized in point C. From the two curves in FIG. 4A, a control deviation dR results for the measurement period dt in FIG. 4B corresponding to the curve with points D, B and E.

The further sequence of the method according to the control circuit of FIG. 2 is as follows: When the defective rail pressure sensor is detected at time t5, the transition function ÜF is activated. This is shown in Figure 5. The transition function ÜF corresponds to the negated control deviations dR. From time tό, the rail pressure controller 13 is given the same time as the measurement period dt, curve F and G. For example, the control deviation dR3 measured at time t3 in point B is specified as -dR3 at time t8. From time t10, the transition function ÜF is deactivated by the second switch 15 changing its switching position. Instead of the measurement period dt, a predeterminable number of control deviations can also be used.

The course of the method when using the control circuit according to FIG. 3 is as follows: upon detection of the defective rail pressure sensor at time t5, the control deviation at time t5, corresponding to the value of point E, becomes from the control deviation at time t1, corresponding to the value of Point D, subtracted. This difference DIFF is shown in Figure 4B. The transition function ÜF corresponds to the negated difference DIFF. This is performed as a step function on the DT1 element 19. The correction volume flow V (KORR) is calculated via the DT1 element. After a predeterminable period of time has elapsed or if a threshold value is undershot, the DT1 element 19 is switched off in that the switch 20 is returned from the switch position shown in dashed lines to the solid position. Both methods offer the advantage that inadmissible changes in rail pressure due to a defective rail pressure sensor can be significantly reduced. The changes in the rail pressure in the event of a sensor defect occur because the high-pressure control circuit continues to process the faulty sensor signal until the sensor defect is recognized, and the actuating signal for the suction throttle is calculated from this.

FIG. 6 shows a map 14 for determining the leakage volume flow V (LKG). The engine speed nMOT is plotted on the abscissa. A target injection quantity Q (SW) is plotted on the ordinate as the second input variable. The Z axis corresponds to the leakage volume flow V (LKG). A presettable operating area is assigned to each support point in this map. The operating areas are shown hatched in FIG. 6. Such an operating range is defined by the quantities dn and dQ. Typical values are e.g. B. 100 revolutions and 50 cubic millimeters per stroke. A support point A is shown as an example in FIG. This interpolation point A results from the two input values n (A) equal to 3000 revolutions per minute and Q (A) equal to 40 cubic millimeters per stroke. The support point A is assigned a leakage volume flow V (LKG) of, for example, 7.2 liters per minute as the Z value. The leakage volume flow V (LKG) determined by means of the map 14 is then weighted via an evaluation map, which is shown in FIG. 7. For the example above, there is, for example, an evaluation factor of 0.95 for support point A. The leakage volume flow V (LKG) is ultimately 6.84 liters per minute.

The Z values of the characteristic map 14 are determined in normal operation whenever the common rail injection system is in a steady state, for example at the operating points n (A) and O (A). The controller volume flow VR or the filtered value is assigned to the corresponding operating range of the map 14 and stored as a Z value. The stored values represent a measure of the leakage of the common rail injection system. The integrating part of the rail pressure regulator 13 can be used instead of the regulator volume flow VR to calculate the Z values of the characteristic diagram 14. Of course, the Z values can already be permanently applied when the internal combustion engine is delivered. These Z values can be corrected using the evaluation map in FIG. This can result in an impermissibly high rise or fall in the rail pressure after the rail Pressure sensor, due to too large or too small stored values of the map 14, can be effectively prevented.

The map 14 shown in Figure 6 has 5 times 4 support points. The advantage of this is the lower storage space requirement and the good clarity. The problem is that smaller values of the target injection quantity Q (SW) below Q (A) cannot be represented. The target injection quantity (A) corresponds, for example, to a value of 40 cubic millimeters per stroke. If the speed controller now calculates a smaller value of the target injection quantity Q (SW), for example 18 cubic millimeters per stroke, the reference point Q (A) is used in the characteristic diagram 14. This too large value of the map 14 leads to an increase in the rail pressure in emergency operation and thus to greater stress on the crankshaft. This problem can be alleviated by using a map 14 with few support points by introducing a limit line. The leakage volume flow V (LKG) of the characteristic diagram 14 is linearly reduced by the limit value line in the range of target injection quantity values that are smaller than the smallest stationary target injection quantity values. Such a limit line GW is shown in FIG. 8.

The target injection quantity Q (SW) is plotted on the abscissa. The leakage volume flow V (LKG) is plotted on the ordinate as the output variable. The limit line GW applies to a stationary engine speed, for example for the support point A from FIG. 6 with n (A) equal to 3000 revolutions per minute. A leakage volume flow of 7.2 liters per minute corresponds to a value Q (A) of 40 cubic millimeters per stroke. With a target injection quantity Q (SW) of 18 cubic millimeters per stroke calculated by the speed controller, a corresponding leakage volume flow of 1.9 liters per minute is calculated. About the

The limit line GW can consequently be used to correct the leakage volume flow V (LKG) calculated by means of the characteristic diagram 14 with smaller values as the desired injection quantity (SW) falls. As a result, the rail pressure is limited in the event of an increase in the rail pressure sensor failure, which means that a stable operating point is established more quickly.

To prevent an inadmissible increase in the rail pressure in emergency operation, the map 14 can also have more support points. If the rail pressure rises after the rail pressure sensor fails, the engine speed also rises. As a follow-up reaction, the Speed controller the target injection quantity O (SW). The leakage volume flow V (LKG) is consequently determined from the characteristic diagram 14 for the target injection quantity values O (SW) which become ever smaller. An increase in the rail pressure in emergency operation can be effectively prevented if the map 14 has small leakage volume flows (Z values), ideally the value zero liters, in the range of target injection quantity values that are smaller than the smallest stationary target injection quantity values per minute. An excessive increase in the rail pressure is prevented since the target volume flow V (TARGET) is reduced with increasing rail pressure. In particular in the low-load range of the internal combustion engine, the rail pressure rise is limited at an early stage. FIG. 9 shows a section of a characteristic map 14 designed in this way. During operation, smaller target injection quantity values Q (SW) are assigned correspondingly smaller leakage volume flows (Z values). The leakage volume flow V (LKG) calculated in this way is then weighted using the evaluation map in FIG. 7.

FIG. 10 shows a program flow chart of the method. This begins in step S1 after the electronic control unit has been initialized. The start process for the internal combustion engine is activated at S2. Then it is checked whether the starting process has ended. In practice, the starting process is ended when the rail pressure actual value pCR (ACTUAL) exceeds a limit value (controller enable pressure) and / or the engine speed nMOT exceeds a limit value (controller enable speed). If the start process has not yet ended, a waiting loop is run through with S4. After the starting process has ended, the control of the rail pressure pCR is activated at S5. The control deviation dR over time is then recorded and stored at S6. The control deviations dR of a measurement period dt or a predeterminable number of values can be selected. S7 checks whether the values supplied by the rail pressure sensor are correct. If the rail pressure sensor is free of errors, normal operation is maintained, step S8, and the program flow chart is continued at S5. If the check at S7 shows that the signals of the rail pressure sensor are faulty, emergency operation and the transition function ÜF are activated, steps S9 and S 10. The transition pressure ÜF inversely specifies the stored control deviation for the rail pressure controller or a correction is made - Volume flow determined from the difference between two control deviations. Then it is checked at S1 1 whether the measurement period dt has expired. Alternatively, the query can be carried out for a number (n) of control deviations instead of the time (dt). If the query at S1 1 is negative, a waiting loop is run through with step S12. If the test result in S11 is positive, the transition function is ended, step S 13. In emergency operation, the rail pressure is determined indirectly by the speed controller via the map 14. As a further measure, the operator of the internal combustion engine is informed about the emergency operation, e.g. B. via a corresponding warning lamp and a diagnostic entry.

LIST OF REFERENCE NUMBERS

Internal combustion engine

turbocharger

Fuel tank first pump

Second pump suction throttle

Rail (high pressure accumulator)

injector

Pressure sensor (internal cylinder pressure)

Rail pressure sensor

Electronic control unit (EDC) first switch

Rail-pressure regulator

Map of the second switch first summation point

Conversion of the second summation point

DT1 link third switch

Claims

1. A method for controlling an internal combustion engine in which a rail pressure is regulated in normal operation and a switch is made from normal operation to emergency operation when a defective rail pressure sensor is detected, the rail pressure being controlled in emergency operation, characterized in that the transition from normal operation to emergency operation is decisive is determined by a transition function (ÜF).

2. A method for controlling an internal combustion engine according to claim 1, characterized in that the transition function (ÜF) is determined from control deviations (dR) in normal operation, the control deviations (dR) from the target-actual comparison of the rail pressure actual value (pCR ( ACTUAL)) is calculated with the rail pressure setpoint (pCR (SW)).

3. The method for controlling an internal combustion engine according to claim 2, characterized in that the control deviations of a measurement period (dt) are considered to determine the transition function (ÜF) (dR (t), t = 1 ... dt).

4. The method of control and regulation according to claim 2, characterized in that a predeterminable number (n) of control deviations (dR (i), i = 1 ... n) are considered to determine the transition function (ÜF).

5. A method for controlling an internal combustion engine according to claim 3 or 4, characterized in that the transition function (ÜF) corresponds to the negated control deviations (dR (t), dR (i)).

6. The method for controlling an internal combustion engine according to claim 5, characterized in that when the transition function (ÜF) is activated, a regulator volume flow (VR) is calculated via a rail pressure regulator (13) as a function of the transfer function (ÜF).

7. A method for controlling an internal combustion engine according to claim 6, characterized characterized that the transition function (ÜF) is ended after the measurement period (dt) or according to the number (n).

8. A method for controlling an internal combustion engine according to claim 3 or 4, characterized in that the transition function (ÜF) is calculated from a difference (DIFF) of a first and second control deviation (dR (t), dR (i)).

9. A method for controlling an internal combustion engine according to claim 8, characterized in that the transition function (ÜF) corresponds to the negated difference (DIFF).

10. The method for controlling an internal combustion engine according to claim 9, characterized in that a correction volume flow (V (KORR)) is calculated from the transfer function (ÜF) via a DT1 element (19).

11. The method for controlling an internal combustion engine according to claim 10, characterized in that the transition function (ÜF) is deactivated when the correction volume flow (V (KORR)) falls below a limit value (GW) (V (KORR) <GW) or one The timer has expired.

12. A method for controlling an internal combustion engine according to claims 5 to 7, characterized in that when the transition function (ÜF) is activated, a desired volume flow (V (TARGET)) from the controller volume flow (VR) and a consumption volume flow (V ( VER)) is calculated.

13. A method for controlling an internal combustion engine according to claims 8 to 11, characterized in that when the transition function (ÜF) is activated, the desired volume flow (V (SOLL)) from the consumption volume flow (V (VER)) and the correction volume flow (V (CORR)) is calculated.

14. A method for controlling an internal combustion engine according to claim 13, characterized in that the target volume flow (V (SOLL)) is additionally calculated from a leakage volume flow (V (LKG)) determined by means of a map (14).

15. A method for controlling an internal combustion engine according to one of the preceding claims, characterized in that when the transition function (ÜF) has ended, the desired volume flow (V (SOLL)) from the consumption volume flow (V (VER)) and the leakage volume flow ( V (LKG)) is calculated.

16. A method for controlling an internal combustion engine according to claim 12 or 13, characterized in that the consumption volume flow (V (VER)) is calculated as a function of an engine speed (nMOT) and a target injection quantity (Q (SW)) (V ( VER) = f (nMOT, Q (SW))).

17. A method for controlling an internal combustion engine according to claim 15, characterized in that the values of the leakage volume flow (V (LKG)) stored in the map (14) are determined in normal operation by the value of the controller volume flow (VR) in the steady state. is set as the corresponding value of the leakage volume flow (V (LKG)) and the value of the leakage volume flow (V (LKG)) is stored in the map (14).

18. A method for controlling an internal combustion engine according to claim 17, characterized in that the regulator volume flow (VR) is additionally filtered.

19. A method for controlling an internal combustion engine according to claim 15, characterized in that the values of the leakage volume flow (V (LKG)) stored in the characteristic diagram (14) are determined in normal operation by the integrating part (I part) of the in the stationary state Rail pressure controller (13) is set as the corresponding value of the leakage volume flow (V (LKG)) and the value of the leakage volume flow (V (LKG)) is stored in the map (14).

20. A method for controlling an internal combustion engine according to one of the preceding claims, characterized in that with a decreasing target injection quantity (Q (SW)) the leakage volume flow (V (LKG)) is corrected to small values via limit lines (GW).

21. A method for controlling an internal combustion engine according to claim 20, characterized characterized that the leakage volume flow (V (LKG)) is additionally evaluated via an evaluation map.