EP2358988B1 - Control and regulation method for an internal combustion engine having a common rail system - Google Patents

Description

The invention relates to a control and regulating method for an internal combustion engine having a common rail system, in which the rail pressure is controlled in normal operation and is changed with detection of a load shedding from the control to the control mode, wherein in the control mode, the PWM signal for acting on the controlled system is temporarily set to a higher than normal operation PWM value.

In a common rail system, a high pressure pump delivers fuel from a fuel tank into a rail. The inlet cross section to the high pressure pump is determined by a variable suction throttle. On the rail are injectors via which the fuel is injected into the combustion chambers of the internal combustion engine. Since the quality of the combustion depends crucially on the pressure level in the rail, this is regulated. The high pressure control circuit includes a pressure regulator, the suction throttle with high pressure pump and the rail as a controlled system and a filter in the feedback branch. In this high-pressure control circuit, the pressure level in the rail corresponds to the controlled variable. The measured pressure values of the rail are converted via the filter into an actual rail pressure and compared with a desired rail pressure. The resulting deviation is then converted via the pressure regulator into a control signal for the suction throttle. The actuating signal corresponds to z. B. a volume flow with the unit liters / minute. Typically, the control signal is implemented electrically as a PWM signal (pulse width modulated) with a constant frequency, for example 50 Hz. The high-pressure control circuit described above is from the DE 103 30 466 B3 known.

Due to the high dynamics of a load shedding control technology is a difficult to control process, so after a load shedding the rail pressure with a Pressure gradients of up to 4000 bar / second increase. If, for example, the internal combustion engine is operated at a stationary rail pressure of 1800 bar and the PWM frequency is 50 Hz, corresponding to 20 ms period duration, then the rail pressure can rise by up to 80 bar before reacting to the load shedding via the change of the PWM signal. To make matters worse, that pressure signal detection, manipulated variable calculation and outputting of the PWM signal at different times, so asynchronous done. In the worst case, the resulting dead time can be up to two PWM periods. This dead time is critical because the maximum rail pressure is limited by a passive pressure relief valve, which opens at 1950 bar, for example.

To improve the safety of the pressure control during a load shedding beats the DE 10 2005 029 138 B3 before switching from control to control mode. In control mode, the PWM signal for controlling the suction throttle is temporarily set via a staircase function to an increased PWM value, whereby the closing process of the suction throttle is accelerated.

To improve the dynamics of large setpoint jumps beats the DE 40 20 654 A1 that the pulse end of the PWM signal or the frequency of the PWM signal of the current development of the setpoints and actual values is tracked. The basic prerequisite for this method, however, is the time-synchronous start of the PWM signal and the acquisition of the setpoint actual values. For the pressure control in the common rail system, this method is out of the question, since an asynchronism of pressure control and PWM signal is the rule here. In addition, in a load shedding due to the high pressure gradient, a frequency tracking, in the sense of a frequency increase with subsequent frequency reduction, technically unrepresentable.

To reduce pressure oscillations in the rail, which are excited by the suction throttle, sees the DE 103 30 466 B3 a frequency switching of the PWM signal before. For this purpose, a critical engine speed is calculated from the angular distance between two injections and the frequency of the PWM signal, in which the frequencies of the PWM signal and the injection are almost the same size and from this defines a speed range. If the engine speed passes through this speed range, then the PWM signal from a first frequency, for example, 100 Hz, to a second Frequency, for example, 120 Hz, switched. Frequency switching stabilizes the high-pressure control loop in the range around the critical speeds.

Starting from the in the DE 10 2005 029 138 B3 described temporary PWM specification in a load shedding, the invention is based on the object to further optimize the pressure control in a load shedding.

This object is achieved by the features listed in claim 1. In the dependent claims, the embodiments are shown.

Like in the DE 10 2005 029 138 B3 represented, is calculated by a first filter, the first actual rail pressure and from this the control deviation. At the same time, a second, faster filter calculates a second actual rail pressure. A load shedding is now recognized that the second actual rail pressure exceeds a first limit. Upon detection of the load shedding, the PWM signal is then switched from a first frequency, for example 50 Hz, to a second, much higher frequency, for example 500 Hz. Thereafter, if the second actual rail pressure exceeds a second threshold, the control mode is changed to the temporary PWM default. Due to the much higher PWM frequency, the temporary PWM specification starts earlier. The optimization is thus that the dead time between detection of the load shedding and outputting the PWM signal is shortened, with the advantage of a significant reduction of the rail pressure overshoot after load shedding.

The function is ended when the second actual rail pressure falls below the first limit value reduced by a hysteresis value. At the end of the function, the PWM signal from the second frequency is then switched back to the first, lower frequency. Since the higher PWM frequency is set only for a short period of time, the power dissipation and heat generation of the switching transistors in the electronic engine control unit remain within the specification specified by the semiconductor manufacturer.

Figur 1

ein Systemschaubild,

Figur 2

einen Hockdruck-Regelkreis als Blockschaltbild,

Figur 3

einen Lastabwurf als Zeitdiagramm,

Figur 4

ein Zustandsdiagramm und

Figur 5

einen Programm-Ablaufplan.

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

FIG. 1

a system diagram,

FIG. 2

a high-pressure control loop as a block diagram,

FIG. 3

a load shedding as a time diagram,

FIG. 4

a state diagram and

FIG. 5

a program schedule.

The FIG. 1 shows a system diagram of an electronically controlled internal combustion engine 1 with a common rail system. The common rail system comprises as mechanical components a low pressure pump 3 for conveying fuel from a tank 2, a suction throttle 4 for influencing the volume flow, a high pressure pump 5, a rail 6 and injectors 8 for injecting fuel into the combustion chambers of the internal combustion engine 1.

The internal combustion engine 1 is controlled via an electronic engine control unit 9 (ECU). In the FIG. 1 are the input variables of the electronic engine control unit 9 exemplified by the rail pressure pCR, which is detected by a pressure sensor 7, the engine speed nMOT and a size ON. The size ON is representative of the other input signals, for example for the oil or the fuel temperature. The illustrated outputs of the electronic engine control unit 9 are a PWM signal PWM for controlling the intake throttle 4, a power-determining signal ve for driving the injectors 8 and a size OFF. The power-determining signal ve characterizes a start of injection and an injection duration. The size OFF is representative of the other control signals for controlling the internal combustion engine 1, for example, a control signal for controlling an EGR valve. The illustrated common rail system can of course also be designed as a common rail system with individual memories. In this case, the individual memory is integrated in the injector 8, in which case the individual accumulator pressure pE is another input signal of the electronic engine control unit 9.

The FIG. 2 shows the high-pressure control loop for regulating the rail pressure as a block diagram. The input quantity corresponds to a nominal rail pressure pCR (SL). The output quantity corresponds to the raw value of the rail pressure pCR. From the raw value of the rail pressure pCR, a first actual rail pressure pCR1 (IST) is determined by means of a first filter 15. This is compared with the set point pCR (SL) at a summation point A, resulting in a control deviation ep. From the control deviation ep, a manipulated variable is calculated by means of a pressure regulator 10. The manipulated variable corresponds to a volume flow qV1. The physical unit of the volume flow is liters / minute. Optionally, it is provided that the calculated nominal consumption is added to the volume flow qV1. The volume flow qV1 corresponds to the input variable for a limit 11. The limit 11 can be speed-dependent, input variable nMOT. The output qV2 of the limit 11 is then converted in a calculation 12 into a PWM signal PWM1. The PWM signal PWM1 represents the duty cycle and the frequency fPWM corresponds to the frequency, for example 50 Hz (period: 20 ms). In the conversion, the fluctuations of the operating voltage and the pilot fuel pressure are taken into account. The PWM signal PWM1 is the input of a first switch 13. A second input of the first switch 13 is a PWM signal PWM2. Depending on the position, the output signal PWM of the first switch 13 corresponds either to the signal PWM1 or PWM2. With the PWM signal PWM then the solenoid of the suction throttle is applied. As a result, the path of the magnetic core is changed, whereby the flow rate of the high-pressure pump is influenced freely. The high-pressure pump, the suction throttle and the rail correspond to a controlled system 14. From the rail 6, a consumption volume flow qV3 is discharged via the injectors 8. This closes the control loop.

This control loop is supplemented by the temporary PWM specification, as this one from the DE 10 2005 029 138 B3 is known. The elements of the temporary PWM specification are a second filter 17 for calculating a second actual rail pressure pCR2 (IST), a function block 18 for determining a signal SZ1 for driving the first switch 13 and a PWM default 16. In the control mode is the first switch 13 in the position a, ie the calculated by the pressure regulator 10 manipulated variable qV1 is limited, converted into a PWM signal PWM1 and thus the controlled system 14 is applied. If the second actual rail pressure pCR2 (IST) exceeds a limit value, here: the second limit value GW2, the function block 18 changes the signal level of the signal SZ1, whereby the first switch 13 is reversed to the position b. In the position b, a PWM value PWM2, which is increased in comparison to the normal mode, is temporarily output via the PWM preset 16. In other words, it is changed from the control mode to the control mode. The temporary PWM specification can - as shown - be designed staircase. After expiry of a predefinable period then the first switch 13 changes back to position a. Thus, the control mode is set again.

In practical operation, the PWM signal is provided with a low PWM frequency fPWM, for example 50 Hz, from the corresponding driver software. The PWM value can therefore be updated in a 20 ms time frame. The low PWM frequency ensures that, first, the slider of the suction throttle moves, so only the sliding friction is overcome, and second, the power loss of the switching transistors in the electronic engine control unit remains within the specification. The pressure regulator 10 is calculated by the motor software with a constant sampling time. If the pressure regulator 10 recognizes a control deviation ep that increases in magnitude, it may be that a PWM period has started shortly before. The new, increased PWM duty cycle can therefore only be set at the beginning of the next PWM period, that is, at the earliest after the expiration of the 20 ms time interval. This in turn means that the rail pressure pCR continues to rise during the current and also at the beginning of the next PWM period. Due to the asynchronicity of the PWM signal and pressure controller sampling, this results in a corresponding dead time.

This is where the invention begins by the block diagram of FIG. 2 is supplemented by a function block 19 and a second switch 20. In control mode, the second switch 20 is in the position a, in which the first frequency f1 (50 Hz) determines the frequency fPWM. If the second actual rail pressure pCR2 (IST) exceeds a first limit value GW1, this is the case with a load shedding, then the function block 19 sets the activation signal SZ2 for activating the second switch 20 to a second value, whereby it is reversed to the position b , Now, the frequency fPWM corresponds to the second frequency f2 of, for example, 500 Hz. The PWM signal PWM1 is now updated every 2 ms. If the second actual rail pressure pCR2 (IST) exceeds the second limit value GW2, then the temporary PWM specification is activated. If the second actual rail pressure pCR2 (IST) falls below the difference between the first limit value and a hysteresis value, the switch 20 changes back to the position a, with which the PWM frequency fPWM is again identical to the first frequency f1.

The FIG. 3 shows a load shedding as a time diagram. The FIG. 3 consists of the subfigures 3A to 3D. These show each over time: in FIG. 3A the course of the second actual rail pressure pCR2 (IST), in FIG. 3B the value of the PWM signal PWM, in FIG. 3C the PWM signal in the pulse-pause display according to the prior art and in Figure 3D the PWM signal in the pulse-pause display according to the invention. To the PWM signal the FIG. 3C corresponds to the pressure curve shown as a solid line in the FIG. 3A , To the PWM signal the Figure 3D corresponds to the pressure curve shown as a dashed line in the FIG. 3A , The illustrated example was based on a first PWM frequency of 50 Hz, which corresponds to a time interval of 20 ms, and a second PWM frequency of 500 Hz, which corresponds to a time interval of 2 ms. The nominal rail pressure was maintained constant.

• Vor dem Zeitpunkt t1 wird die Brennkraftmaschine im stationären Zustand bei einem Raildruck von 1800 bar betrieben. Im stationären Zustand wird der Raildruck geregelt. Zum Zeitpunkt t1 erfolgt ein Abwerfen der Last, was ein Ansteigen des Raildrucks zur Folge hat. Der aus dem Raildruck über das erste Filter (Fig. 2: 15) berechnete erste Ist-Raildruck pCR1(IST) und der über das zweite Filter (Fig. 2: 17) berechnete zweite Ist-Raildruck pCR2(IST) steigen jeweils an. Der zunehmende erste Ist-Raildruck pCR1(IST) verursacht eine betragsmäßig zunehmende Regelabweichung, welche der Druckregler in ein zunehmendes PWM-Signal (Fig. 3B) umsetzt, wodurch die Saugdrossel in Schließrichtung bewegt wird. Übersteigt nun der zweite Ist-Raildruck pCR2(IST) zum Zeitpunkt t3 den zweiten Grenzwert GW2, hier: 1900 bar, Punkt B in Fig. 3A, so wird die temporäre PWM-Vorgabe aktiviert, es wird also vom Regelungsbetrieb in den Steuerungsbetrieb gewechselt. Ab dem Zeitpunkt t3 wird daher das PWM-Signal 20 ms lang auf 100% erhöht (Fig. 3B). Die eingestellte Frequenz des PWM-Signals bleibt unverändert bei 50 Hz. Zum Zeitpunkt t3 hat gerade eine neue PWM-Periode begonnen, so dass die PWM-Erhöhung nicht unmittelbar wirksam wird. Siehe in der Fig. 3C der vergrößert dargestellte Ausschnitt. Die PWM-Erhöhung wird erst 20 ms, also eine Periodendauer, später zum Zeitpunkt t5 wirksam. Dem PWM-Wert von 100 % in der Fig. 3B entspricht der Impuls D in der Fig. 3C. Auf Grund dieser Totzeit steigt der zweite Ist-Raildruck pCR2(IST) weiter an und erreicht mit dem Wert 2030 bar seinen Höchstwert.

The procedure of the prior art method is as follows:

• Before the time t1, the internal combustion engine is operated in the steady state at a rail pressure of 1800 bar. In steady state, the rail pressure is regulated. At time t1, the load is dropped, resulting in an increase in the rail pressure. The from the rail pressure on the first filter ( Fig. 2 : 15) calculated first actual rail pressure pCR1 (IST) and via the second filter ( Fig. 2 : 17) calculated second actual rail pressure pCR2 (IST) increase respectively. The increasing first actual rail pressure pCR1 (IST) causes a magnitude-increasing control deviation, which the pressure regulator converts into an increasing PWM signal ( Fig. 3B ), whereby the suction throttle is moved in the closing direction. Now exceeds the second actual rail pressure pCR2 (IST) at time t3, the second threshold GW2, here: 1900 bar, point B in Fig. 3A , the temporary PWM specification is activated, so it is changed from the control mode to the control mode. From time t3, therefore, the PWM signal is increased to 100% for 20 ms ( Fig. 3B ). The set frequency of the PWM signal remains unchanged at 50 Hz. At time t3, a new PWM period has just started, so that the PWM increase does not take effect immediately. See in the Fig. 3C the enlarged detail shown. The PWM increase only takes effect 20 ms, ie one period duration, later at time t5. The PWM value of 100% in the Fig. 3B corresponds to the pulse D in the Fig. 3C , Due to this dead time of rising second actual rail pressure pCR2 (IST) continues, reaching its maximum value of 2030 bar.

• Der zweite Ist-Raildruck pCR2(IST) überschreitet zum Zeitpunkt t2 den ersten Grenzwert GW1, hier: 1850 bar, Punkt A in Fig. 3A. Mit Überschreiten des ersten Grenzwerts GW1 wird auf die zweite PWM-Frequenz 500 Hz umgeschaltet (Fig. 3D). Zum Zeitpunkt t3 überschreitet der zweite Ist-Raildruck pCR2(IST) dann den zweiten Grenzwert GW2, hier: 1900 bar, Punkt B in Fig. 3A. Mit Überschreiten des zweiten Grenzwerts GW2 wird die temporäre PWM-Vorgabe aktiviert, also vom Regelungsbetrieb in den Steuerungsbetrieb gewechselt. Dem PWM-Wert von 100 % in der Fig. 3B entspricht der Impuls E in der Fig. 3D, ab dem Zeitpunkt t4. Die Totzeit bis zur Wirksamkeit der PWM-Erhöhung beträgt diesmal ebenfalls wiederum eine volle Periodendauer, nur beträgt diese jetzt 2 ms. Insgesamt wird die PWM-Erhöhung also 18 ms früher wirksam. Als Folge steigt der zweite Ist-Raildruck pCR2(IST) diesmal nur auf 1940 bar an. Die Umschaltung der PWM-Frequenz reduziert daher den Hochdruck-Überschwinger um 90 bar. In der Fig. 3A ist dies mit dem Bezugszeichen dp dargestellt.

The procedure of the method according to the invention is as follows:

• The second actual rail pressure pCR2 (IST) exceeds the first limit value GW1 at the time t2, here: 1850 bar, point A in Fig. 3A , When the first limit GW1 is exceeded, the second PWM frequency is switched to 500 Hz ( Fig. 3D ). At time t3, the second actual rail pressure pCR2 (IST) then exceeds the second limit value GW2, here: 1900 bar, point B in Fig. 3A , When the second limit value GW2 is exceeded, the temporary PWM specification is activated, that is, it is changed over from the control mode to the control mode. The PWM value of 100% in the Fig. 3B corresponds to the momentum E in the Fig. 3D , from the time t4. The dead time to the effectiveness of the PWM increase this time again also a full period, only this is now 2 ms. Overall, the PWM increase thus takes effect 18 ms earlier. As a result, the second actual rail pressure pCR2 (IST) only increases to 1940 bar this time. Switching the PWM frequency therefore reduces the high pressure overshoot by 90 bar. In the Fig. 3A this is represented by the reference numeral dp.

The increase of the PWM frequency is deactivated when the second actual rail pressure pCR2 (IST) falls below the first limit value GW1 by a predetermined hysteresis value pHY, for example 30 bar, in the point C. As a result, 500 Hz is switched from the second frequency to the first frequency 50 Hz, see Fig. 3D at time t6. Since, in the context of the invention, switching to a high PWM frequency occurs only during the high-pressure overshoot (period t2 / t6), the heat generation of the power output stage remains within the permissible hardware specification despite the large number of transistor switching operations.

The switching logic of the invention is in the FIG. 4 shown. In stationary operation, the PWM frequency fPWM is set to the first frequency f1, for example 50 Hz. If the second actual rail pressure pCR2 (IST) is greater than or equal to the first limit value GW1, the PWM frequency fPWM is set to the second frequency f2, for example 500 Hz. The switching back to the first frequency f1 takes place when the first limit value GW1 is undershot by the hysteresis value pHY.

The FIG. 5 shows a program flowchart of the method. At S1, a flag 0 is initialized and the frequency fPWM of the PWM signal is set to the value f1, for example 50 Hz. When polling in S2, the value of the flag is checked. If the value is 1, the program part is run through with the steps S6 to S8. On the other hand, if the value of the flag is 0, then the program part is run through with steps S3 to S5. During the first program run (flag = 0), it is then checked at S3 whether the second actual rail pressure pCR2 (IST) reaches or exceeds the first limit value GW1. If this is not the case, query result S3: no, the internal combustion engine is stationary and the program sequence is continued at A. If, on the other hand, a load shedding is detected at S3, query result S3: yes, then at S4 the second frequency f2, for example 500 Hz, is switched over. The PWM value can now be changed within a 2 ms time frame. The flag is then set to the value 1 at S5 and the program sequence continues at A.

If the query at S2 indicates that the flag has the value 1, query result S2: yes, then it is checked at S6 whether the second actual rail pressure pCR2 (IST) is less than or equal to the switch-off threshold. The switch-off threshold is set to the difference between the first limit value GW1 and the hysteresis value pHY. If the switch-off threshold has not yet fallen below, the program sequence continues at A. If the switch-off threshold has been reached or undershot, query result S6: yes, the frequency fPWM of the PWM signal is switched from the second frequency f2 back to the first frequency f1 at S7. The flag is then set to its initialization value 0, S8, and the program sequence continues at A.

reference numeral

1

Internal combustion engine

2

tank

3

Low pressure pump

4

interphase

5

high pressure pump

6

Rail

7

Pressure sensor (rail)

8th

injector

9

electronic engine control unit (ECU)

10

pressure regulator

11

limit

12

Calculation PWM signal

13

first switch

14

controlled system

15

first filter

16

PWM assignment

17

second filter

18

function block

19

function block

20

second switch

Claims (3)

1. Control and regulating method for an internal combustion engine (1) having a common rail system, in which method, during normal operation, a rail pressure (pCR) is regulated by virtue of a first actual rail pressure (pCR1(IST)) being determined from the rail pressure (pCR) by means of a first filter (15), a regulating deviation (ep) is calculated from a setpoint rail pressure (pCR(SL)) and from the first actual rail pressure (pCR1(IST)), an actuating variable (qV1) is calculated from the regulating deviation (ep) by means of a pressure regulator (10), and a PWM signal (PWM1) with a first PWM frequency (f1) for the activation of a regulating path (14) is defined as a function of the actuating variable (qV1), in which method a second actual rail pressure (pCR2(IST)) is determined by means of a second filter (17), a load dump is identified if the second actual rail pressure (pCR2(IST)) exceeds a first threshold value (GW1), the PWM signal (PWM1) is switched from the first PWM frequency (f1) to a second, significantly higher PWM frequency (f2) upon the exceedance of the first threshold value (GW1), and in which method, upon the exceedance of a second threshold value (GW2), the rail pressure (pCR) is controlled by virtue of the PWM signal (PWM1) being set temporarily to a PWM value (PWM2) which is elevated in relation to normal operation.
2. Method according to Claim 1,
   characterized
   in that, after the expiry of a time interval, the control operation with elevated PWM value (PWM2) is deactivated and the regulating operation is activated.
3. Method according to Claim 2,
   characterized
   in that the PWM signal (PWM1) is switched from the second PWM frequency (f2) to the first PWM frequency (f1) when the second actual rail pressure (pCR2(IST)) falls below the first threshold value (GW1) again by a hysteresis value (pHY).

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