EP1896712B1 - Control and regulation method for an internal combustion engine provided with a common-railsystem - Google Patents

Abstract

The invention relates to a control and regulation method for an internal combustion engine (1) provided with a Common-Railsystem, wherein rail pressure (pCR) is regulated in normal operation. The invention is characterised in that a second actual rail pressure is determined by a second filter, load shedding is recognised when the second actual rail pressure exceeds a first threshold value and is controlled by recognising a load shedding of the rail pressure (pCR), wherein the PWM-signal (PWM) is set by a PWM-specification to a PWM value which is higher than in normal operation.

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 regulated in normal operation.

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. Typically, the pressure regulator is designed as a PID controller or PIDT1 controller, ie this comprises at least one proportional component (P component), one integral component (I component) and one differential component (D component). 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 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 electrically designed as a PWM signal (pulse width modulated). The high-pressure control circuit described above is from the DE 103 30 466 B3 known.
In DE 19 731 995 the transmission behavior of the pressure regulator is dependent on the operating parameters of the internal combustion engine.
To protect against too high a pressure level, a passive pressure limiting valve is arranged on the rail. If the pressure level is too high, the pressure-limiting valve opens, causing the fuel to drain from the rail into the fuel tank.

In practice, the following problem can occur: When a load shedding directly increases the engine speed. An increasing engine speed causes a magnitude-increasing speed control deviation at a constant setpoint speed. A speed controller reacts to this by reducing the injection quantity as a manipulated variable. A smaller injection quantity, in turn, causes less fuel to be taken from the rail and therefore the pressure level in the rail increases rapidly. To make matters worse, that the delivery rate of the high-pressure pump is speed-dependent. An increasing engine speed means a higher capacity and thus causes an additional pressure increase in the rail. Since the high-pressure control has a comparatively long reaction time, the rail pressure can rise so far that the pressure-limiting valve opens, z. At 1950 bar. As a result, the rail pressure drops z. B. from a value of 800 bar. At this pressure level, an equilibrium state of delivered fuel to derived fuel sets. This means that the rail pressure does not drop any further despite the open pressure-limiting valve. The pressure limiting valve only closes again when the speed of the internal combustion engine is reduced. The problem is therefore the unexpected opening of the pressure-limiting valve in a load shedding.

The not previously published German patent application with the official file number DE 10 2004 023 365.9 also describes a pressure control loop for a common rail system. In this pressure control loop, a second filter is arranged in addition to the first filter in the feedback branch. The second filter has a smaller time constant and a lower phase delay than the first filter. For the calculation of the controller components, the actual rail pressure determined by the second filter is used, which results in an improved dynamics of the high-pressure control circuit during load shedding.

However, it remains critical that the control signal calculated by the pressure regulator or the PWM signal is limited by the electrical characteristics of the electronic control unit, eg. B. maximum continuous current and power loss of the output transistor is severely limited. This means that in the case of a large control deviation, the pressure regulator calculates a maximum manipulated variable, but this ultimately results in a PWM signal with only approx. B. 22% pulse-pause ratio can be implemented. A permanently applied higher PWM value would cause deactivation of the final stage of the electronic control unit.

The object of the invention is to improve the safety of the pressure control in a load shedding.

The object is solved by the features of claim 1. The embodiments are shown in the subclaims.

The invention provides that a second actual rail pressure is determined via a second filter from the rail pressure and a Load shedding is detected when the second actual rail pressure exceeds a limit. Upon detection of a load shedding the rail pressure is then controlled by the PWM signal is set via a PWM default to a compared to the normal operation increased PWM value. This increased PWM value is set during a time period, e.g. B. as a staircase function.

The central idea of the invention is to substantially accelerate the closing process of the suction throttle by setting a high PWM value. Used is a suction throttle, which works against a spring when closing, d. H. which is normally open. If the PWM signal is increased, the path of the suction throttle slide is increased and the opening cross section of the suction throttle is reduced. In practice, it is sufficient to use this PWM specification for a very short time, e.g. B. 20 milliseconds, to act. The short-term introduction of higher energy in the suction throttle a higher dynamics of the actuator is achieved. Unintentional opening of the pressure-limiting valve is thus suppressed.

Another advantage of the invention is that in a stuck suction throttle slide this is common again by the increased energy input.

• Fig. 1 ein Systemschaubild;
• Fig. 2 einen Druck-Regelkreis;
• Fig. 3 ein Zeitdiagramm;
• Fig. 4 ein Zustandübergangsdiagramm;
• Fig. 5 einen Programmablaufplan;
• Fig. 6 einen Programmablaufplan;
• Fig. 7 einen Programmablaufplan.

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

• Fig. 1 a system diagram;
• Fig. 2 a pressure control loop;
• Fig. 3 a timing diagram;
• Fig. 4 a state transition diagram;
• Fig. 5 a program schedule;
• Fig. 6 a program schedule;
• Fig. 7 a program schedule.

The FIG. 1 shows a system diagram of an internal combustion engine 1 with common rail system. The common rail system comprises the following components: a low-pressure pump 3 for conveying fuel from a fuel tank 2, a variable suction throttle 4 for influencing the fuel flow rate flowing through, a high-pressure pump 5 for conveying the fuel with pressure increase, a rail 6 and Single memory 7 for storing the fuel and injectors 8 for injecting the fuel into the combustion chambers of the internal combustion engine. 1

This common rail system is at a maximum stationary rail pressure of z. B. operated 1800 bar. To protect against an inadmissibly high pressure level in the rail 6, a passive pressure-limiting valve 10 is provided. This opens at a pressure level of z. B. 1950 bar. In the open state, the fuel is removed from the rail 6 via the pressure-limiting valve 10 in the fuel tank 2. As a result, the pressure level in the rail 6 drops to a value of z. B. 800 bar.

The operation of the internal combustion engine 1 is determined by an electronic control unit (ADEC) 11. 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. In FIG. 1 For example, the following input variables are shown: the rail pressure pCR, which is measured by means of a rail pressure sensor 9, a motor speed nMOT, a signal FP for power input by the operator and an input value ON. For example, the input variable ON subsumes the charge air pressure of the exhaust gas turbocharger and the temperatures of the coolant / lubricant and of the fuel.

In FIG. 1 are shown as output variables of the electronic control unit 11, a signal PWM for controlling the suction throttle 4, a signal ve for controlling the injectors 8 and an output variable OFF. The output variable OFF is representative of the further control signals for controlling and regulating the internal combustion engine 1, for example a control signal for activating a second exhaust gas turbocharger in a register charging.

In FIG. 2 a pressure control loop is shown. 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 17. This is compared with the set point pCR (SL) at a summation point, resulting in a control deviation ep. From the control deviation ep, a manipulated variable is calculated by means of a pressure regulator 12. 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 13. The limit 13 can be speed-dependent, input variable nMOT. The output qV2 of the limit 13 is then converted in a calculation 14 into a PWM signal PWM1. The PWM signal PWM1 represents the duty cycle and the frequency fPWM corresponds to the fundamental frequency. When converting, fluctuations in the operating voltage and the pilot fuel pressure are taken into account. With the PWM signal PWM1 then the solenoid of the suction throttle is applied. As a result, the path of the magnetic core is changed, whereby the flow of the high-pressure pump is freely influenced. The high-pressure pump, the suction throttle, the rail and the individual memory correspond to a controlled system 16. From the rail 6, a desired consumption volume flow qV3 is discharged via the injectors 8. This closes the control loop.

The control loop described above is supplemented by a second filter 18, a function block 19, a PWM preset 20 and a switch 15. The switch 15 is arranged in the signal path between the calculation 14 and the controlled system 16. The switching state of the switch 15 is determined via a signal SZ, which is determined via the function block 19 as a function of a first limit value GW1, a second limit value GW2 and a second actual rail pressure pCR2 (IST). The second actual rail pressure pCR2 (IST) in turn is calculated via the second filter 18 from the raw value of the rail pressure pCR.

In FIG. 2 the switch 15 is shown in position 1, ie the signal PWM1 determined by the calculation 14 is the input variable of the controlled system 16. In a position 2 of the switch 15, a signal PWM2 is the input signal for the controlled system 16. The signal PWM2 is output by the PWM default 20 provided.

• Im Normalbetrieb ist der Schalter 15 in Stellung 1, d. h. die vom Druckregler 12 berechnete Stellgröße qV1 wird begrenzt, in ein PWM-Signal PWM1 umgesetzt und damit die Regelstrecke 16 beaufschlagt. Übersteigt der zweite Ist-Raildruck pCR2(IST) den ersten Grenzwert GW1, so ändert der Funktionsblock 19 den Signalpegel des Signals SZ, wodurch der Schalter 15 in die Stellung 2 wechselt. In dieser Stellung wird über die PWM-Vorgabe 20 temporär ein gegenüber dem Normalbetrieb erhöhter PWM-Wert PWM2 ausgegeben. Mit anderen Worten: Es wird vom Regelungsbetrieb in den Steuerungsbetrieb gewechselt. Nach Ablauf eines vorgebbaren Zeitraums wechselt dann der Schalter 15 wieder zurück in Stellung 1.

The block diagram of FIG. 2 has the following functionality:

• In normal operation, the switch 15 is in position 1, that is, the manipulated variable qV1 calculated by the pressure regulator 12 is limited, converted into a PWM signal PWM1 and thus applied to the controlled system 16. If the second actual rail pressure pCR2 (IST) exceeds the first limit value GW1, the function block 19 changes the signal level of the signal SZ, whereby the switch 15 changes to position 2. In this position, a PWM value PWM2 which is increased over normal operation is temporarily output via the PWM preset 20. In other words, it is changed from the control mode to the control mode. After a predeterminable period, the switch 15 then switches back to position 1.

The FIG. 3 consists of the FIGS. 3A to 3D , These show each over time: the logical switching state of a flag in FIG. 3A , a status in FIG. 3B , a course of the second actual rail pressure pCR2 (IST) in FIG. 3C and the course of the PWM signal as an input variable of the controlled system 16 in FIG. 3D. As values, percentages are plotted on the PWM ordinate, e.g. For example, 40% PWM signal means a corresponding duty cycle of 0.4 at constant PWM fundamental frequency fPWM. At time t1, the system is in normal operation, ie the rail pressure pCR is regulated by the pressure regulator 12. The flag and the status have the value 0. In the rail there is a pressure level of 1800 bar. The PWM signal in Figure 3D has the exemplary value of 4%. After the time t1, the rail pressure pCR and thus also the second actual rail pressure pCR2 (IST) begins to increase due to a load shedding. In practice, a load shedding corresponds to shutting down a consumer during generator operation or the replacement of a marine propulsion system. An increasing rail pressure pCR causes at a constant specification of the target rail pressure a likewise increasing in terms of absolute deviation ep. This control deviation ep is converted by the pressure regulator 12 in an increasing PWM signal, whereby the cross section of the suction throttle is reduced. In Figure 3D Therefore, the value of the PWM signal increases from the initial value 4%. In practice, the PWM signal in control mode, a maximum value of z. B. assume 22%. This maximum value is determined by the supply voltage and the maximum continuous suction throttle continuous current, eg. B. 24 volts and 2 amperes.

At time t2, the second actual rail pressure pCR2 (IST) exceeds the first limit value GW1 of 1930 bar. When this limit value is exceeded, the flag is set to the value 1 ( FIG. 3A ) and the status changed from 0 to 1. This deactivates the control of the rail pressure and the PWM signal in Figure 3D controlled via the PWM default 20 during a period dt. In FIG. 3B is exemplified as a predetermined function a staircase function. Other mathematical functions, eg. As a parabola are possible.
At time t2, therefore, the PWM signal is set to an increased PWM value. In FIG. 3 this corresponds to the point W1 with the associated ordinate value 80%. At time t3, a first time step dt1 has elapsed, ie the status changes from 1 to 2, whereby the PWM signal in Figure 3D from the value 80%, point W1, to the value 40%, point W2. During a second period dt2, the PWM signal remains unchanged. With expiration of the second time step dt2 and end of the period dt, the I-part of the pressure regulator is initialized. As initialization values, either zero or a value corresponding to the negative nominal consumption volume flow qV3 are specified. In practice, the period dt is set to 20 msec. Due to the relatively short period of time, the maximum power loss of the output stage is not exceeded.

After initialization of the pressure regulator, the control process is completed and the rail pressure is regulated again. There to When the rail pressure pCR or the second actual rail pressure pCR2 (IST) has increased at an elevated level compared to normal operation, the pressure controller calculates the maximum possible PWM signal for the control operation, corresponding to 22% (FIG. Figure 3D ). At time t5, the second actual rail pressure pCR2 (IST) falls below a second limit value GW2 of 1900 bar. When the second limit value GW2 is undershot, the flag is set to the value 0. As a result, the control method is enabled again, ie the function could be activated again. As in FIG. 3C shown, the second actual rail pressure pCR2 (IST) decreases due to the closed suction throttle. At time t6, it is assumed that the second actual rail pressure pCR2 (IST) falls below the original pressure level of 1800 bar. As a consequence, the pressure regulator reduces the PWM signal back to the original value of 4%, time t7.

In FIG. 4 is a state transition diagram for the transitions from control mode in the control mode and shown vice versa. Also included are optional transitions if the user has activated only the first time step dt1 (dt1> 0) and / or the second time step dt2 (dt2> 0). The reference numeral 21 characterizes an activated control of the rail pressure. In control mode, the status has the value 0 and the PWM signal as the input variable of the controlled system has the value PWM1, which is specified by the pressure controller. If the second actual rail pressure pCR2 (IST) exceeds the first limit value GW1, a load shedding is detected. Upon detection of the load shedding and activated first time step dt1 (dt1> 0), the control 1 state, reference 22, is changed. In this state, the status has the value 1 and the PWM signal for acting on the controlled system is controlled via the PWM specification, output signal PWM2. The PWM signal is temporarily set to the value of the PWM signal via the PWM specification

Point W1 set. With expiration of the first time step dt1 and activated second time step dt2 (dt2> 0), the control 2 state, reference numeral 23, is changed. In this state, the status has the value 2 and the PWM signal is set to the value of the point W2 via the PWM default. With expiration of the second time step dt2 and thus expiration of the period dt is the state control 2 in the state control, reference numeral 21, changed. The control of the rail pressure is thus deactivated and the control reactivated.

If a first time step dt1 is activated by the user in control mode, state control, load shedding (dt1 = 0), then control 2 is switched directly. The return from the state control 2 in the control mode takes place with the expiration of the period dt.

In the state control 1, reference numeral 22, the transition to the control or to the state control 2 takes place as a function of the second time step dt2. If no second time step dt2 has been activated by the user (dt2 = 0), then the first time step dt1 is immediately returned to the control mode. If the user has activated a second time step dt2, the system changes to the state control 2, as described above.

In FIG. 5 is a program flow chart for the state control shown. At S1 it is checked whether the flag has the value 0. If the test result is positive, the program part is run through with steps S2 to S14. If the result of the test is negative, the program part is run through with steps S7 to S9.

If the test at S1 indicates that the flag has the value 0, then S2 checks whether there is load shedding. If the second actual rail pressure pCR2 (IST) is below the first limit value GW1, the control of the rail pressure is maintained at S10, ie the PWM signal represents a function of the control deviation ep. Thereafter, this program part is ended. If a load shedding is detected at S2, the flag is set to the value 1 at S3 and tested at S4 whether the user has activated the first time step dt1. If the timer is activated (result of the query: yes), the PWM signal is controlled via the PWM specification at S5, here the value PWM2 (W1). Afterwards, the status is set to the value 1 at S6 and this program part is ended.

If no first time step dt1 was activated, ie. H. If the query at S4 is negative, it is checked at S11 whether the user has activated the second time step dt2. If no second time step dt2 is activated (result of query S11: no), control of the rail pressure remains activated in S13. The program flow path S4, S11 and S13 thus takes into account the case that the function was not activated by the user. If the check at S11 indicates that the second time step dt2 has been activated, the PWM signal is set to the value PWM2 (W2) at S12. Then the status is set to the value 2 at S14 and this program path is ended.

If it was detected at S1 that the flag does not correspond to the value 0, then it is checked at S7 whether the second actual rail pressure pCR2 (IST) is less than or equal to the second limit value GW2. If this is the case, the flag is set to the value 0 at S8 and the program sequence continues at S9. If the test at S7 shows that the second actual rail pressure is above the second limit value, the program sequence continues at S9 and the regulation of the rail pressure pCR remains activated. Afterwards this program part is finished.

In FIG. 6 a program flow chart for the temporary PWM specification is displayed when the first time step dt1 is activated, state: control 1. At S1, a time t is set to the value t plus sampling time. At S2 it is checked whether this time is greater than / equal to the first time step dt1, ie whether the first time step has already expired. If the first time step dt1 has not yet elapsed (result of the query: no), the PWM signal is set to the value PWM2 (W1), for example, at S10. B. 80%, set and then leave this program part. If the check at S2 reveals that the first time step dt1 has elapsed, the time is set to the value 0 at S3 and checked at S4 whether the user has activated the second time step dt2. If no second time step dt2 has been activated, the program part is run through with steps S5 to S9. When the second time step dt2 is activated, the program part is run through with the steps S11 and S12.

If second time step dt2 is not activated (result of query S4: no), the I-part of the pressure controller is initialized at S5. The value 0 or a value corresponding to the negative nominal consumption volume flow can be used as initialization values. At S6, the control of the rail pressure is then activated, ie the PWM signal is calculated via the pressure regulator as a function of the control deviation ep. Then the status is set to 0 at S7. At S8, it is checked whether the second actual rail pressure pCR2 (IST) is less than or equal to the second limit value GW2. If this is the case, the flag is set to the value 0 in S9 and the program part is left. If the test at S8 reveals that the second actual rail pressure pCR2 (IST) is above the second limit value GW2, then this program part is immediately left.

If the test at S4 indicates that the second time step dt2 has been set, the PWM signal is set to the value of the point W2 via the PWM specification, output signal PWM2, at S11. Then the status is set to the value 2 at S12 and the program part is exited.

In FIG. 7 a program flow chart for the state control 2 is shown. At S1, a sampling time is added at a time t. After that, it is checked at S2 whether the second time step dt2 has expired. If this is not the case (result of query S2: no), the PWM signal is set to the value PWM2 (W2) and the program part is left at S9 via the PWM specification. If the test at S2 shows that the second time step dt2 has elapsed, the time t is set to the value 0 at S3 and the I-part of the pressure regulator is initialized at S4 as described above. Thereafter, the control is activated at S5, ie the PWM signal is determined as a function of the control deviation ep. At S6, the status is set to the value 0. At S7 it is checked whether the second actual rail pressure pCR2 (IST) is less than or equal to the second limit value GW2. If this is the case, the flag is set to the value 0 in S8 and the program part is left. If the test at S7 shows that the second actual rail pressure pCR2 (IST) is above the second limit value GW2, the program part is immediately left.

The method was described with reference to a load shedding. In practice, the illustrated method can generally also always be used when a very rapid reduction of the injection quantity causes a pressure increase in the rail. This takes place during load shedding, an engine stop as well as a sudden reduction of the desired torque or the desired injection quantity with detection of a supercharger overspeed in an exhaust gas turbocharger.

• durch das temporär erhöhte PWM-Signal wird eine höhere Dynamik des Stellglieds erreicht, wodurch ein unbeabsichtigtes Öffnen des Druck-Begrenzungsventils bei einem Lastabwurf verhindert wird;
• durch die Deaktivierung der Regelung und das erhöhte PWM-Signal kann ein festsitzender Saugdrossel-Schieber wieder gängig gemacht werden;
• das zweite Filter, der Schalter und die PWM-Vorgabe können in der Software des elektronischen Steuergeräts abgebildet werden, wodurch das Steuerungsverfahren nachträglich applizierbar ist;
• die temporäre PWM-Vorgabe kann das in der DE 10 2004 023 365.9 dargestellte Verfahren ergänzen.

The invention offers the following advantages:

• by the temporarily increased PWM signal, a higher dynamics of the actuator is achieved, whereby unintentional opening of the pressure-limiting valve is prevented in a load shedding;
• by deactivating the control and the increased PWM signal, a stuck suction throttle slide can be made common again;
• the second filter, the switch and the PWM specification can be mapped in the software of the electronic control unit, whereby the control method can be subsequently applied;
• the temporary PWM default can do this in the DE 10 2004 023 365.9 complement the procedure described.

reference numeral

1

Internal combustion engine

2

Fuel tank

3

Low pressure pump

4

interphase

5

High pressure pump

6

Rail

7

Single memory

8th

injector

9

Rail pressure sensor

10

Pressure relief valve

11

electronic control unit (ADEC)

12

pressure regulator

13

limit

14

calculation

15

switch

16

controlled system

17

first filter

18

second filter

19

function block

20

PWM assignment

21

regulation

22

Control 1

23

Control 2

Claims (6)

1. Control and regulation method for an internal combustion engine (1) having a common rail system, in which method, in 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 (17), a regulating error (ep) being calculated from a setpoint rail pressure (pCR(SL)) and the first actual rail pressure (pCR1(IST)), an actuating variable (qV1) being calculated from the regulating error (ep) by means of a pressure regulator (12), and a PWM signal (PWM) for driving a regulating system (16) being defined as a function of the actuating variable (qV1), characterized
   in that a second actual rail pressure (pCR2(IST)) is determined by means of a second filter (18) with a smaller time constant and smaller phase lag than the first filter (17), load dumping is detected if the second actual rail pressure (pCR2(IST)) exceeds a first limit value (GW1), and upon the detection of load dumping, the rail pressure (pCR) is controlled by virtue of the PWM signal (PWM) being set by means of a PWM preset selection (20) to an increased PWM value (PWM2) in relation to normal operation, as a result of which the fuel volume flow fed into the rail (6) is reduced.
2. Control and regulation method according to Claim 1,
   characterized
   in that the increased PWM value (PWM2) is preset during a time period (dt).
3. Control and regulation method according to Claim 2,
   characterized
   in that, within the time period (dt), the increased PWM value (PWM2) is preset according to a step function.
4. Control and regulation method according to Claim 2 or 3,
   characterized
   in that, upon the expiry of the time period (dt), an I component of the pressure regulator (12) is initialized with the value zero or with a value corresponding to the negative setpoint consumption volume flow (qV3).
5. Control and regulation method according to Claim 4,
   characterized
   in that, after the initialization of the pressure regulator (12), the rail pressure (pCR) is regulated again corresponding to the normal mode.
6. Control and regulation method according to one of the preceding claims,
   characterized
   in that the control method is enabled to preset an increased PWM value again when the second actual rail pressure (pCR2(IST)) falls below a second limit value (GW2).

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