EP1446568B1 - Method for controlling an internal combustion engine - Google Patents

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

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. Via a rail pressure sensor, the rail pressure actual value, ie the controlled variable, is detected by an electronic control unit. This calculates the control deviation from a nominal-actual comparison of the rail pressure and determines via a rail pressure regulator a drive signal for an actuator, such as a suction throttle or a pressure control valve. Since the rail pressure represents an essential parameter for the injection quality, it is necessary to respond to a faulty rail pressure sensor by taking appropriate measures. DE 199 16 100 A1 proposes, in the case of a defective rail pressure sensor, to switch from normal operation to a starting operation. In start mode, the rail pressure is controlled. Here, a high-pressure pump is set to maximum capacity and a pressure control valve, which determines the outflow from the rail, closed. The problem with this solution is the abrupt transition from normal to start operation, as well as the resulting high rail pressure.

From US 5,937,826 an emergency operation (limp home) for an internal combustion engine with a defective rail pressure sensor is known. In emergency mode, the high-pressure pump is controlled via a map depending on the engine speed and a target injection quantity. The problem here is that immediately after the transition to emergency operation due to the previously large control deviation can set a high rail pressure. This can increase the engine speed. This undefined operating state is maintained until the engine speed controller reduces the desired injection quantity and controls the rail pressure indirectly via the characteristic map.

The invention is therefore based on the task of making the transition from normal operation to emergency operation safer.

The object is achieved by a method for controlling an internal combustion engine having the features of the first claim. The embodiments for this purpose 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 predeterminable number of control deviations can be considered. As a measure, at the end of normal operation by the transition function, a negative control deviation for the rail pressure regulator is specified according to the measured period or number of control deviations detected during normal operation. As an alternative measure, it is provided that a correction volume flow of the controlled system is predetermined by the transition function. The correction volume flow is calculated from the difference between two control deviations. Both measures have the advantage that a defined, continuous transition from normal operation to emergency operation takes place. The immediate effect of the transition function on the rail pressure controller or the controlled system results in a short reaction time after failure of the rail pressure sensor.

With the end of the transition function is changed to the known from the prior art map. As a flanking 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.

Figur 1

ein Blockschaltbild;

Figur 2

einen Regelkreis, erste Ausführung;

Figur 3

einen Regelkreis, zweite Ausführung;

Figur 4A, 4B

ein Zeitdiagramm;

Figur 5

eine Übergangsfunktion;

Figur 6

ein Kennfeld; zur Bestimmung des Leckage-Volumenstroms

Figur 7

ein Bewertungs-Kennfeld;

Figur 8

eine Grenzwertlinie;

Figur 9

ein Kennfeld; zur Bestimmung des Leckage-Volumenstroms

Figur 10

einen Programmablaufplan.

In the drawings, a preferred embodiment is shown. Show it:

FIG. 1

a block diagram;

FIG. 2

a control loop, first embodiment;

FIG. 3

a control loop, second embodiment;

Figure 4A, 4B

a timing diagram;

FIG. 5

a transitional function;

FIG. 6

a map; for determining the leakage volume flow

FIG. 7

an evaluation map;

FIG. 8

a limit line;

FIG. 9

a map; for determining the leakage volume flow

FIG. 10

a program schedule.

1 shows a block diagram of an internal combustion engine 1 with 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 text which follows, 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. About the suction throttle 5, the volume flow to the first pump 6 is set. The first pump 6 in turn delivers the fuel under high pressure in the rail 7. The pressure level in the rail 7 is more than 1200 bar in diesel engines. With the rail 7, the injectors 8 are connected. Through the injectors 8, the fuel is injected into the combustion chambers of the internal combustion engine 1.

The internal combustion engine 1 is controlled and regulated by an electronic control unit 11 (EDC). The electronic control unit 11 includes the usual components of a microcomputer system, such as a microprocessor, I / O devices, buffers and memory devices (EEPROM, RAM). In the memory modules relevant for the operation of the internal combustion engine 1 operating data in maps / curves are applied. About this calculates the electronic control unit 11 from the input variables, the output variables. The following input variables are shown by way of example in FIG. 1: a rail pressure actual value pCR (IST) which is measured by means of a rail pressure sensor 10, the rotational speed nMOT of the internal combustion engine 1, a desired power FW, a cylinder internal pressure pIN which is measured by means of pressure sensors 9 and an input quantity E. The input variable E subsumes, for example, the charge air pressure pLL of the turbocharger 2 and the temperatures of the coolants and lubricants. In FIG. 1, a signal ADV for controlling the suction throttle 5 and an output variable A are shown as output variables of the electronic control unit 11. The output variable A is representative of the further 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 drive 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, i. the funded by the first pump 4 flow freely passes to the second pump. 6

FIG. 2 shows a control circuit in a first embodiment. This includes as basic elements a first summation point 16, a rail pressure controller 13, a conversion 17 and the rail 7. The conversion 17 includes the conversion of the desired volume flow V (SOLL) in the drive signal ADV, the suction throttle 5 and the second pump. 6 The conversion 17 is supplied with input quantities E, for example the fuel 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 corresponding to the normal operation of the internal combustion engine (solid line). In normal operation, the actual rail pressure actual value pCR (IST) at the first summation point 16 is compared with the reference variable, ie the rail pressure setpoint pCR (SW), and supplied to the rail pressure controller 13 as a control deviation dR. Depending on the control deviation dR, the rail pressure regulator 13 determines a regulator volume flow VR. At the second summation point 18, a consumption volume flow V (VER) is added to this regulator volume flow. The consumption volume flow V (VER) is calculated as a function of the engine speed nMOT and a desired injection quantity Q (SW). From these two volumetric flows results as a manipulated variable of the setpoint flow V (SOLL), which represents the input to the conversion 17. By means of the conversion 17, the drive signal ADV is generated for the suction throttle 5, from which then via the second pump 6, an actual volume flow V (IST) results.

Upon detection of a defective rail pressure sensor, the first switch 12 changes to the dashed switching position. In this switching 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 control 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 regulator 13 in accordance with the measurement period detected in normal operation. After this time step has elapsed, the transition function ÜF is ended and the second switch 15 changes to the position shown in dashed lines. The nominal volume flow V (SOLL) 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).

FIG. 3 shows the control circuit in a second embodiment. Compared to Figure 2, the control circuit of Figure 3 differs 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. With the detection of a defective rail pressure sensor, the second switch 15 and the third switch 20 change to the dashed position. The rail pressure regulator 13 is immediately deactivated. The nominal volume flow V (SOLL) 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 (KORR) 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 given to the DT1 element 19 as a negated step function. The transition function ÜF will be explained in more detail in connection with FIG. 4B. If the output of the DT1 element 19 falls below a threshold value or a time step has expired, the transition function is deactivated. The third switch 20 then returns to its home position (normal operation). The nominal volume flow V (SOLL) is then specified only by the map 14 and the consumption flow rate V (VER).

FIG. 4 consists of the partial figures 4A and 4B. FIG. 4A shows a pressure curve of the rail pressure actual value pCR (IST) and of the rail pressure setpoint pCR (SW), and FIG. 4B shows the resulting system deviation dR. At time t1, the rail pressure actual value pCR (IST) corresponds to the rail pressure setpoint 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 of FIG. 4B. After time t1, the rail pressure actual value pCR (IST) begins to decrease. The cause is a defective rail pressure sensor 10. At time t3, a control deviation dR3 is already present at point B. At time t5, the defect is detected at point C. From the two curves of FIG. 4A, a control deviation dR corresponding to the curve with the points D, B and E results for the measurement period dt in FIG. 4B.

The further course of the method according to the control circuit of Figure 2 is as follows: With detection of the defective rail pressure sensor at time t5, the transition function ÜF is activated. This is shown in FIG. The transition function ÜF corresponds to the negated control deviations dR. From the time t6, the same time duration as the measurement period dt this set the rail pressure controller 13, curve F and G. For example, the time measured at point t3 control point dR3 at time t8 as -dR3. From the time t10, the transition function ÜF is deactivated by the second switch 15 changes its switching position. Instead of the measurement period dt, a predeterminable number of control deviations can also be used.

The sequence of the method when using the control circuit according to the figure 3 is as follows: With detection of the defective rail pressure sensor at time t5, the control deviation at time t5, corresponding to the value of point E, of the control deviation at time t1, corresponding to the value of Point D, subtracted. This difference DIFF is shown in FIG. 4B. The transition function ÜF corresponds to the negated difference DIFF. This is performed as a jump function on the DT1 member 19. The correction volume flow V (KORR) is calculated via the DT1 element. After a predetermined period of time or falls below a threshold DT1 element 19 is turned off by the switch 20 is returned from the dashed to the switch position shown in solid.

Both methods offer the advantage that impermissible changes in the rail pressure due to a defective rail pressure sensor can be significantly reduced. The changes in the rail pressure in the sensor defect case arise because the high-pressure control loop continues to process the faulty sensor signal until the sensor defect is detected and calculates therefrom the actuating signal for the suction throttle.

FIG. 6 shows a map 14 for determining the leakage volume flow V (LKG). The abscissa shows the engine speed nMOT. On the ordinate, a desired injection quantity Q (SW) is plotted as the second input variable. The Z-axis corresponds to the leakage volume flow V (LKG). Each support point in this characteristic field is assigned a predefinable operating range. The operating areas are shown hatched in FIG. Such an operating range is defined by the quantities dn and dQ. Typical values are z. B. 100 revolutions and 50 cubic millimeters per stroke. In Figure 6, a support point A is shown as an example. 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 interpolation point A is assigned a leakage volume flow V (LKG) of, for example, 7.2 liters per minute as the Z value. The determined by means of the map 14 leakage volume flow V (LKG) is then weighted via a rating map, this is shown in Figure 7. For the example above, for example, the evaluation point A results in a weighting factor of 0.95. The leakage volume flow V (LKG) is thus finally calculated at 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 point n (A) and Q (A). Here, 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. To calculate the Z values of the characteristic map 14, the integrating portion of the rail pressure regulator 13 can be used instead of the regulator volume flow VR. Of course, the Z values can already be applied firmly even when the internal combustion engine is delivered. By means of the evaluation map of Figure 7, these Z-values can be corrected. As a result, an unacceptably high increase or decrease in the rail pressure after failure of the rail pressure sensor, caused by too large or too small stored values of the map 14, effectively prevented.

The map shown in Figure 6 14 has 5 times 4 interpolation points. The advantage here is the lower space requirement and the good clarity. The problem is the fact that smaller values of the desired injection quantity Q (SW) below Q (A) can not be displayed. For example, the target injection quantity Q (A) corresponds to a value of 40 cubic millimeters per stroke. Now, if the speed controller calculates a smaller value of the target injection quantity Q (SW), for example 18 cubic millimeters per stroke, then in the map 14 the interpolation point Q (A) is used. This too great value of the map 14 leads to an increase of 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 nodes by the introduction of a limit line. As a result of the limit value line, the leakage volume flow V (LKG) of the characteristic map 14 is linearly reduced in the range of desired injection quantity values which are smaller than the smallest stationarily driven nominal injection quantity values. Such a limit line GW is shown in FIG.

The abscissa represents the nominal injection quantity Q (SW). On the ordinate the output volume of the leakage volume flow V (LKG) is plotted. The limit value line GW is valid for a stationary engine speed, for example for the support point A from FIG. 6 with n (A) equal to 3000 revolutions per minute. A value Q (A) of 40 cubic millimeters per stroke corresponds to a leakage volume flow of 7.2 liters per minute. For a nominal 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. Consequently, the leakage volume flow V (LKG) calculated by means of the characteristic map 14 can be corrected to smaller values via the limit value line GW when the nominal injection quantity Q (SW) decreases. As a result, the rail pressure is limited in case of failure of the rail pressure sensor in the increase, it thus sets faster a stable operating point.

To prevent an inadmissible increase in the rail pressure in emergency mode, the map 14 may also have more nodes. If the rail pressure increases after the rail pressure sensor has failed, the engine speed also increases. As a consequence, the reduced Speed controller the set injection quantity Q (SW). The leakage volume flow V (LKG) is thus determined from the map 14 for ever smaller target injection quantity values Q (SW). An increase in the rail pressure during emergency operation can be effectively prevented if the map 14 in the range of target injection amount values that are smaller than the smallest stationary driven target injection amount values, with small leakage volume flows (Z values), ideally the value zero liter per minute, is occupied. An excessive increase in the rail pressure is prevented because the setpoint flow V (DESIRED) is reduced with increasing rail pressure. Especially in the low load range of the internal combustion engine, limiting the increase in rail pressure occurs at an early stage. FIG. 9 shows a section of a characteristic map 14 executed in this way. During operation, smaller setpoint injection quantity values Q (SW) are assigned correspondingly smaller leakage volume flows (Z values). The thus calculated leakage volume flow V (LKG) is then weighted via the evaluation map of Figure 7.

FIG. 10 shows a program flowchart of the method. This begins at step S 1 after the initialization of the electronic control unit. At S2, the starting process for the internal combustion engine is activated. Thereafter, it is checked whether the starting process is completed. In practice, the starting process is terminated when the rail pressure actual value pCR (IST) exceeds a limit value (regulator release pressure) and / or the engine rotational speed nMOT exceeds a limit value (controller release rotational speed). If the boot process has not been completed yet, a wait loop will pass through with S4. After the starting process is finished, the control of the rail pressure pCR is activated at S5. Thereafter, at S6, the deviation dR is detected over time and stored. The control deviations dR of a measurement period dt or a predefinable number of values can be selected here. At S7 it is checked whether the values supplied by the rail pressure sensor are free from errors. If the rail pressure sensor is faultless, normal operation is maintained, step S8, and the program flow continues at S5. If the test at S7 shows that the signals of the rail pressure sensor are faulty, the emergency operation and the transition function ÜF are activated, steps S9 and S10. The transition function ÜF predefines the stored control deviation inversely to the rail pressure controller or it becomes a correction Volumetric flow determined from the difference between two control deviations. Thereafter, it is checked at S11 whether the measurement period dt has elapsed. Alternatively, the query may be executed instead of the time (dt) to a number (n) of deviations.

If the query at S11 is negative, a waiting loop is passed through with step S12. If the result of the test is positive in S11, the transfer function is completed, step S13. In emergency mode, 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 z. B. via a corresponding warning lamp and a diagnostic entry.

LIST OF REFERENCE NUMBERS

1

Internal combustion engine

2

turbocharger

3

Fuel tank

4

first pump

5

interphase

6

second pump

7

Rail (high-pressure accumulator)

8th

injector

9

Pressure sensor (cylinder internal pressure)

10

Rail pressure sensor

11

Electronic control unit (EDC)

12

first switch

13

Rail-pressure regulator

14

map

15

second switch

16

first summation point

17

conversion

18

second summation point

19

DT1

20

third switch

Claims (20)

1. Method for open-loop control of an internal combustion engine, in which a rail pressure is closed-loop controlled in the normal operating mode, and there is a changeover from the normal operating mode to an emergency operating mode when a defective rail pressure sensor is detected, the rail pressure being open-loop controlled in the emergency operating mode, characterized in that the changeover from the normal operating mode to the emergency operating mode is decisively determined by a changeover function (ÜF), the changeover function (ÜF) being determined from control errors (dR) in the normal operating mode, and the control errors (dR) being calculated from the setpoint/actual comparison of the rail pressure actual value (pCR(IST)) with the rail pressure setpoint value (pCR(SW)).
2. Method for open-loop control of an internal combustion engine according to Claim 1, characterized in that in order to determine the changeover function (ÜF) the control errors of a measuring time period (dt) are considered (dR(t), t=1...dt).
3. Method for open-loop and closed-loop control according to Claim 1, characterized in that in order to determine the changeover function (ÜF) a predefinable number (n) of control errors (dR(i), i=1...n) are considered.
4. Method for open-loop control of an internal combustion engine according to Claim 2 or 3, characterized in that the changeover function (ÜF) corresponds to the negated control errors (dR(t), dR(i)).
5. Method for open-loop control of an internal combustion engine according to Claim 4, characterized in that when the changeover function (ÜF) is activated a closed-loop controller volume flow (VR) is calculated by means of a rail pressure closed-loop controller (13) according to the changeover function (ÜF).
6. Method for open-loop control of an internal combustion engine according to Claim 5, characterized in that the changeover function (ÜF) is ended after the measuring time period (dt) has elapsed or in accordance with the number (n).
7. Method for open-loop control of an internal combustion engine according to Claim 2 or 3, characterized in that the changeover function (ÜF) is calculated from a difference (DIFF) between a first and a second control error (dR(t), dR(i)).
8. Method for open-loop control of an internal combustion engine according to Claim 7, characterized in that the changeover function (ÜF) corresponds to the negated difference (DIFF).
9. Method for open-loop control of an internal combustion engine according to Claim 8, characterized in that a correction volume flow (V(KORR)) is calculated from the changeover function (ÜF) by means of a DT1 element (19).
10. Method for open-loop control of an internal combustion engine according to Claim 9, characterized in that the changeover function (ÜF) is deactivated if the correction volume flow (V(KORR)) drops below a limiting value (GW) - (V(KORR)<GW)-or a time period has elapsed.
11. Method for open-loop control of an internal combustion engine according to Claims 4 to 6, characterized in that when the changeover function (ÜF) is activated a setpoint volume flow (V(SOLL)) is calculated from the closed-loop controller volume flow (VR) and a consumption volume flow (V(VER)).
12. Method for open-loop control of an internal combustion engine according to Claims 7 to 10, characterized in that when the changeover function (ÜF) is activated the setpoint volume flow (V(SOLL)) is calculated from the consumption volume flow (V(VER)) and the correction volume flow (V(KORR)).
13. Method for open-loop control of an internal combustion engine according to Claim 12, characterized in that the setpoint volume flow (V(SOLL)) is additionally calculated from a leakage volume flow (V(LKG)) determined by means of a characteristic diagram (14).
14. Method for open-loop control of an internal combustion engine according to one of the preceding claims, characterized in that when the changeover function (ÜF) has ended the setpoint volume flow (V(SOLL)) is calculated from the consumption volume flow (V(VER)) and the leakage volume flow (V(LKG)).
15. Method for open-loop control of an internal combustion engine according to Claim 11 or 12, characterized in that the consumption volume flow (V(VER)) is calculated as a function of an engine speed (nMOT) and a setpoint injection quantity (Q(SW)) - (V(VER)=f(nMOT, Q(SW))).
16. Method for open-loop control of an internal combustion engine according to Claim 14, characterized in that the values of the leakage volume flow (V(LKG)) which are stored in the characteristic diagram (14) are determined in the normal operating mode by setting the value of the closed-loop controller volume flow (VR) in the steady-state state as a corresponding value of the leakage volume flow (V(LKG)) and storing the value of the leakage volume flow (V(LKG)) in the characteristic diagram (14).
17. Method for open-loop control of an internal combustion engine according to Claim 16, characterized in that the closed-loop controller volume flow (VR) is additionally filtered.
18. Method for open-loop control of an internal combustion engine according to Claim 14, characterized in that the values of the leakage volume flow (V(LKG)) which are stored in the characteristic diagram (14) are determined in the normal operating mode by setting the integrating component (I component) of the rail pressure closed-loop controller (13) as a corresponding value of the leakage volume flow (V(LKG)) in the steady-state state and storing the value of the leakage volume flow (V(LKG)) in the characteristic diagram (14).
19. Method for open-loop control of an internal combustion engine according to one of the preceding claims, characterized in that when there is a decreasing setpoint injection quantity (Q(SW)) the leakage volume flow (V(LKG)) is corrected to smaller values by means of limiting value lines (GW).
20. Method for open-loop control of an internal combustion engine according to Claim 19, characterized in that the leakage volume flow (V(LKG)) is additionally evaluated by means of an evaluation characteristic diagram.

Images