EP2449241B1 - Method for controlling the rail pressure in a common-rail injection system of a combustion engine - Google Patents

Description

The invention relates to a method for controlling and regulating an internal combustion engine according to claim 1.

In an internal combustion engine with a common rail system, the quality of the combustion is largely determined by the pressure level in the rail. The rail pressure is therefore regulated to comply with the legal emission limit values. Typically, a rail pressure control circuit comprises a comparison point for determining a control deviation, a pressure regulator for calculating an actuating signal, the controlled system and a software filter in the feedback branch for calculating the actual rail pressure. The control deviation is calculated from a target rail pressure to the actual rail pressure. The controlled system includes the pressure actuator, the rail and the injectors for injecting the fuel into the combustion chambers of the internal combustion engine.

From the DE 197 31 995 A1 a common rail system with pressure control is known, in which the pressure regulator is equipped with different regulator parameters. The pressure control should be more stable due to the different controller parameters. The controller parameters in turn are calculated depending on operating parameters, here: the engine speed and the target injection quantity. Using the controller parameters, the pressure controller then calculates the control signal for a pressure control valve, via which the fuel outflow from the rail into the fuel tank is determined. The pressure control valve is consequently arranged on the high-pressure side of the common rail system. An electrical pre-feed pump or a controllable high-pressure pump are shown in this reference as alternative measures for pressure regulation.

Also the DE 103 30 466 B3 describes a common rail system with pressure control, in which the pressure regulator accesses a suction throttle via the control signal. About the Suction throttle in turn determines the inlet cross-section to the high-pressure pump. The suction throttle is consequently arranged on the low pressure side of the common rail system. In addition, a passive pressure relief valve can be provided as a protective measure against excessive rail pressure in this common rail system. The fuel is then drained from the rail into the fuel tank via the open pressure relief valve. A corresponding common rail system with a passive pressure relief valve is out of the DE 10 2006 040 441 B3 known.

From the DE 198 02 583 A1 is a memory injection system with a pressure actuator, which has a shut-off body operated by an electromagnetic drive. The pressure control takes place by means of a cascade connection of two control devices, the first control device determining a control signal with a target current value for the electromagnetic drive and a second control device adapting the current value detected in the electromagnetic drive to the predetermined target current value.

From the WO 2006/136414 A1 is a control and regulation procedure for an internal combustion engine with common rail system, in which a rail pressure is regulated in normal operation. A second actual rail pressure is determined via a second filter, and a load shedding is recognized when the second actual rail pressure exceeds a first limit value. When a load shedding is detected, the rail pressure is controlled by setting a PWM signal to a PWM value that is higher than in normal operation by means of a PWM specification.

From the DE 10 2005 008 039 A1 are a device and a method for controlling an internal combustion engine. In the event of an aborted starting process, an actuating element for influencing the fuel pressure in the sense of maintaining and / or increasing the pressure is activated until a further condition is met.

Due to the design, a control and constant leakage occur in a common rail system. The control leakage is effective when the injector is controlled electrically, that is, during the duration of the injection. As the injection duration decreases, the control leakage also decreases. Constant leakage is always effective, that is, even if the injector is not activated. This is also caused by the component tolerances. Since the constant leakage increases with Rail pressure increases and decreases with falling rail pressure, the pressure vibrations in the rail are damped. The opposite is true with tax leakage. If the rail pressure increases, the injection duration is shortened to display a constant injection quantity, which results in a decreasing control leakage. If the rail pressure drops, the injection duration is increased accordingly, which results in increasing control leakage. The control leakage means that the pressure vibrations in the rail are amplified. The control and constant leakage represent a loss volume flow, which is pumped and compressed by the high pressure pump. However, this loss volume flow means that the high pressure pump must be designed larger than necessary. In addition, part of the drive energy of the high-pressure pump is converted into heat, which in turn heats up the fuel and reduces the efficiency of the internal combustion engine.

In practice, the components are cast together to reduce the constant leakage. However, reducing the constant leakage has the disadvantage that the stability behavior of the common rail system deteriorates and pressure control becomes more difficult. This becomes clear in the low-load range, because here the injection quantity, i.e. the volume of fuel withdrawn, is very small. This becomes just as clear with a load shedding from 100% to 0% load, since the injection quantity is reduced to zero here and the rail pressure therefore only slowly decreases again. This in turn causes a long settling time.

Starting from a common rail system with rail pressure control via a low-pressure suction throttle and with reduced constant leakage, the invention is based on the object of optimizing the stability behavior and the settling time.

This object is achieved by a method for controlling and regulating an internal combustion engine having the features of claim 1. The configurations are shown in the subclaims.

The method consists in that, in addition to the rail pressure control via the low-pressure suction throttle as the first pressure control element, a rail pressure disturbance variable for influencing the rail pressure is generated via a pressure control valve on the high pressure side as the second pressure control element. Fuel is diverted from the rail into a fuel tank via the pressure control valve on the high-pressure side, the position of which is determined via a PWM signal. Furthermore, the method consists in that when the normal function is set, the PWM signal is calculated as a function of a resulting desired volume flow and when the protective function is set, the PWM signal is temporarily set to a maximum value. The protective function temporarily shuts off a higher fuel volume flow from the rail, reducing the increase in rail pressure and protecting the rail from pressure peaks. An unwanted response of the passive pressure relief valve is also prevented and limited to the actual emergencies.

The protective function is set when a dynamic rail pressure exceeds a maximum pressure value and the protective function is enabled. The maximum pressure value is chosen so that the rail pressure does not reach this pressure value in stationary operation. The dynamic rail pressure is calculated from the raw values of the rail pressure using a fast filter. The protective function is reset and the normal function is set when a specified time period has expired. An oscillation between the functions is prevented by the fact that after the change from the protective function back to the normal function, the protective function remains locked. This is only released again when the dynamic rail pressure falls below the maximum pressure value by a hysteresis value.

It is proposed according to the invention that if the normal function is set, it is reset and a standstill function is set if an engine standstill is detected, a PWM signal of zero being output when the standstill function is set. The change from the standstill function to the normal function takes place when the actual rail pressure exceeds a start value and a verified engine speed is recognized, that is, when the internal combustion engine is recognized as rotating at the same time. The advantage is that the rail pressure builds up reliably when the engine is started.

The resulting target volume flow is calculated from a static and a dynamic target volume flow. The static target volume flow is in turn calculated as a function of a target injection quantity and the engine speed using a target volume flow map. In the case of a torque-oriented structure, a target torque is used instead of the target injection quantity. A constant leak is simulated via the static target volume flow, in that the fuel is only shunted in the low-load range and in a small amount. It is advantageous that there is no significant increase in the fuel temperature and also no significant reduction in the efficiency of the internal combustion engine. The increased stability of the rail pressure control circuit in the low-load range can be recognized, for example, by the rail pressure remaining approximately constant in overrun mode. The dynamic target volume flow is calculated via a dynamic correction depending on a target rail pressure and the actual rail pressure or the control deviation derived therefrom. If the control deviation is negative, for example in the event of a load shedding, the static target volume flow is corrected via the dynamic target volume flow. Otherwise there is no change in the static target volume flow. The increase in the rail pressure is counteracted via the dynamic set volume flow, with the advantage that the settling time of the system can be improved again.

Figur 1

ein Systemschaubild,

Figur 2

einen Raildruck-Regelkreis,

Figur 3

ein Blockschaltbild des Raildruck-Regelkreises mit Steuerung,

Figur 4

ein Blockschaltbild einer Berechnung,

Figur 5

einen Stromregler,

Figur 6

ein Soll-Volumenstrom-Kennfeld,

Figur 7

ein Diagramm der Funktionszustände,

Figur 8

ein erstes Unterprogramm,

Figur 9

ein zweites Unterprogramm,

Figur 10

ein drittes Unterprogramm,

Figur 11

ein erstes Zeitdiagramm und

Figur 12

ein zweites Zeitdiagramm.

A preferred exemplary embodiment is shown in the figures. Show it:

Figure 1

a system diagram,

Figure 2

a rail pressure control loop,

Figure 3

a block diagram of the rail pressure control circuit with control,

Figure 4

a block diagram of a calculation,

Figure 5

a current regulator,

Figure 6

a target volume flow map,

Figure 7

a diagram of the functional states,

Figure 8

a first subroutine,

Figure 9

a second subroutine,

Figure 10

a third subroutine,

Figure 11

a first timing diagram and

Figure 12

a second timing diagram.

The Figure 1 shows a system diagram of an electronically controlled internal combustion engine 1 with a common rail system. The common rail system comprises the following mechanical components: a low-pressure pump 3 for delivering fuel from a fuel tank 2, a variable, low-pressure suction throttle 4 for influencing the fuel volume flow flowing through it, a high-pressure pump 5 for delivering fuel while increasing the pressure, a rail 6 for storing of fuel and injectors 7 for injecting the fuel into the combustion chambers of the internal combustion engine 1. Optionally, the common rail system can also be designed with individual stores, in which case, for example, an individual store 8 is integrated in the injector 7 as an additional buffer volume. To protect against an impermissibly high pressure level in the rail 6, a passive pressure relief valve 11 is provided which, in the open state, controls the fuel from the rail 6. An electrically controllable pressure control valve 12 also connects the rail 6 to the fuel tank 2. A fuel volume flow is defined via the position of the pressure control valve 12 and is derived from the rail 6 into the fuel tank 2. In the further text, this fuel volume flow is referred to as rail pressure disturbance variable VDRV.

The operating mode of the internal combustion engine 1 is determined by an electronic control unit (ECU) 10. The electronic control unit 10 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 10 uses these to calculate the output variables from the input variables. In the Figure 1 The following input variables are shown as examples: the rail pressure pCR, which is measured by means of a rail pressure sensor 9, an engine speed nMOT, a signal FP for power specification by the operator and an input variable IN. Under the The other sensor signals are summarized in input variable IN, for example the charge air pressure of an exhaust gas turbocharger. In a common rail system with individual stores 8, the individual store pressure pE is an additional input variable of the electronic control unit 10.

In Figure 1 The output variables of the electronic control unit 10 are a signal PWMSD for controlling the suction throttle 4 as the first pressure control element, a signal ve for controlling the injectors 7 (start / end of injection), a signal PWMDV for controlling the pressure control valve 12 as the second pressure control element and an output variable OFF. The position of the pressure control valve 12 and thus the rail pressure disturbance variable VDRV is defined via the signal PWMDV. The output variable AUS represents the other actuating signals for controlling and regulating the internal combustion engine 1, for example an actuating signal for activating a second exhaust gas turbocharger when register is being charged.

In the Figure 2 a rail pressure control circuit 13 for regulating the rail pressure pCR is shown. The input variables of the rail pressure control circuit 13 are: a target rail pressure pCR (SL), a volume flow which characterizes the target consumption Wb, the engine speed nMOT, the PWM basic frequency fPWM and a variable E1. Size E1 includes, for example, the battery voltage and the ohmic resistance of the induction choke coil with supply line, which are included in the calculation of the PWM signal. The output variables of the rail pressure control circuit 13 are the raw value of the rail pressure pCR, an actual rail pressure pCR (IST) and a dynamic rail pressure pCR (DYN). The actual rail pressure pCR (IST) and the dynamic rail pressure pCR (DYN) are in the in Figure 3 controller shown processed.

The actual rail pressure pCR (IST) is calculated from the raw value of the rail pressure pCR using a first filter 19. This is then compared with the setpoint pCR (SL) at a summation point A, which results in a control deviation ep. From the control deviation ep, a pressure controller 14 calculates its manipulated variable, which corresponds to a volume flow VR with the physical unit liter / minute. The calculated target consumption VVb is added to the volume flow VR at a summation point B. The target consumption VVb is calculated using a calculation 22 which is carried out in the Figure 3 is shown and explained in connection with this. The result of the addition at summation point B corresponds to an unlimited target volume flow VSDu (SL) of the suction throttle. The unlimited target volume flow VSDu (SL) is then limited as a function of the engine speed nMOT via a limitation 15. The output variable of the limitation 15 corresponds to a target volume flow VSD (SL) of the suction throttle. An electrical target current iSD (SL) of the suction throttle is then assigned to the target volume flow VSD (SL) via the pump characteristic curve 16. The target current iSD (SL) is converted into the PWM signal PWMSD in a calculation 17. The PWM signal PWMSD represents the duty cycle and the frequency fPWM corresponds to the basic frequency. The PWM signal PWMSD is then applied to the solenoid of the suction throttle. This changes the path of the magnetic core, which freely influences the flow rate of the high pressure pump. For safety reasons, the suction throttle is open when de-energized and is acted upon by the PWM control in the direction of the closed position. The calculation of the PWM signal 17 can be subordinated to a current control loop, such as this from the DE 10 2004 061 474 A1 is known. The high-pressure pump, the suction throttle, the rail and, if applicable, the individual accumulators correspond to a controlled system 18. The control loop is thus closed. From the raw value of the rail pressure pCR, the dynamic rail pressure pCR (DYN) is calculated via a second filter 20, which is one of the input variables of the block diagram of the Figure 3 is. The second filter 20 has a smaller time constant and a smaller phase delay than the first filter 19 in the feedback branch.

The Figure 3 shows as a block diagram the highly simplified rail pressure control circuit 13 of the Figure 2 and a controller 21. The rail pressure disturbance variable VDRV is generated via the controller 21, that is to say the volume flow which the pressure control valve controls from the rail into the fuel tank. The input variables of the controller 21 are: the target rail pressure pCR (SL), the actual rail pressure pCR (IST), the dynamic rail pressure pCR (DYN), the engine speed nMOT and a target injection quantity QSL. The target injection quantity QSL is either calculated via a map depending on the desired performance or corresponds to the manipulated variable of a speed controller. The physical unit of the target injection quantity QSL is mm ³ / stroke. As an alternative to the target injection quantity QSL, a target torque MSL can be used. The output variables are the target consumption Wb, which is fed to the rail pressure control circuit 13, and the rail pressure disturbance variable VDRV. A resultant target volume flow Vres (SL) is determined from a static and a dynamic component via the calculation 22. The calculation 22 is in the Figure 4 shown as a block diagram and is explained in connection with this. The The resulting set volume flow Vres (SL) and the actual rail pressure pCR (IST) are the input variables of a pressure control valve map 23, via which a set current iDV (SL) of the pressure control valve is calculated. The target current iDV (SL) in turn is the reference variable for a current control circuit 24. The current control circuit 24 is formed from a current controller 25, a switch S1, the pressure control valve 12 as a control system and a filter 26 in the feedback branch. The current regulator 25 is in the Figure 5 shown and explained in connection with this. As a manipulated variable, the current controller 25 outputs a PWM signal PWMR, which is an input variable of the switch S1. The other two input signals of switch S1 are zero and a temporary PWM signal PWMt. The temporary PWM signal PWMt is designed in such a way that an increased PWM value, for example 80%, is output in a time-controlled manner. Various function states are displayed via switch S1. If the switch is in position S1 = 1, a standstill function is set. A normal function is set in position S1 = 2 and a protective function is set in position S1 = 3. The output signal of the switch S1 then corresponds to the PWM signal PWMDV, with which the pressure control valve 12 is controlled. The electrical current iDV which arises at the pressure control valve 12 is measured and the actual current iDV (ACTUAL) is calculated via the filter 26, which is then fed back to the current regulator 25. The current control circuit 24 is thus closed.

In the Figure 4 the calculation 22 is shown as a block diagram. The input variables are the target rail pressure pCR (SL), the actual rail pressure pCR (IST), the dynamic rail pressure pCR (DYN), the engine speed nMOT and the target injection quantity QSL, alternatively the target torque MSL. The output variables are the target consumption VVb and the resulting target volume flow Vres (SL). Using the engine speed nMOT and the target injection quantity QSL, the static target volume flow Vs (SL) for the pressure control valve is calculated via a target volume flow map 27 (3D map). The target volume flow map 27 is designed in such a way that a positive value of the static target volume flow Vs (SL) is calculated in the low load range, for example when idling, while in the normal operating range a static target volume flow Vs (SL) of Zero is calculated. The specific embodiment of the target volume flow map 27 is shown in FIG Figure 6 shown and explained in connection with this. Also based on the engine speed nMOT and the target injection quantity QSL, the target consumption Wb, which is an input variable of the rail pressure control circuit 13, is calculated via the calculation 28. The static target volume flow Vs (SL) is determined by Corrected addition of a dynamic target volume flow Vd (SL). The dynamic set volume flow Vd (SL) is calculated via a dynamic correction 29 as a function of the control deviation. The control deviation in turn is calculated from the difference between the target rail pressure pCR (SL) and the actual rail pressure pCR (IST). Alternatively, the control deviation can also be calculated from the difference between the target rail pressure pCR (SL) and the dynamic rail pressure pCR (DYN). If the control deviation is greater than or equal to zero, a dynamic set volume flow Vd (SL) of zero liters / minute is output. If, on the other hand, the control deviation is negative, for example in the event of a load shedding, an increasingly larger dynamic target volume flow Vd (SL) is calculated if the control deviation falls below a limit value. In short: the pressure control valve then controls an increasing fuel volume flow into the fuel tank.
The sum of the static desired volume flow Vs (SL) and the dynamic desired volume flow Vd (SL) corresponds to a corrected desired volume flow Vk (SL), which has a limit 30 upwards to a maximum volume flow VMAX and downwards to the value zero is limited. The maximum volume flow VMAX is calculated using a (2D) characteristic curve 31 as a function of the actual rail pressure pCR (IST). The output variable of the limitation 30 then corresponds to the resulting target volume flow Vres (SL).

The Figure 5 shows the current regulator 25 from the Figure 3 , The input variables are the target current iDV (SL) for the pressure control valve, the actual current iDV (IST) of the pressure control valve, the battery voltage UBAT and controller parameters (kp, Tn). The output variable is the PWM signal PWMR. The current control deviation ei is first calculated from the target current iDV (SL) and the actual current iDV (IST). The current control deviation ei is the input variable of the controller 32. The controller 32 can be designed as a PI or PI (DT1) algorithm. The controller parameters are processed in the algorithm. These are characterized, among other things, by the proportional coefficient kp and the reset time Tn. The output variable of the regulator 32 is a target voltage UDV (SL) of the pressure control valve. This is divided by the battery voltage UBAT and then multiplied by 100. The result corresponds to the duty cycle of the PWM signal PWMR in percent. Optionally, a pilot control can also be provided, which consists of the set current iDV (SL) and the ohmic resistance of the pressure control valve Voltage component calculated, which is then added to the target voltage UDV (SL).

In the Figure 6 The target volume flow map 27 is shown. This is used to determine the static target volume flow Vs (SL) for the pressure control valve. The input variables are the engine speed nMOT and the target injection quantity QSL. In the horizontal direction, engine speed values from 0 to 2000 1 / min are plotted. The target injection quantity values from 0 to 270 mm ³ / stroke are plotted in the vertical direction. The values within the map then correspond to the assigned static target volume flow Vs (SL) in liters / minute. Part of the fuel volume flow to be controlled is determined via the target volume flow map 27. The target volume flow map 27 is designed in such a way that a static target volume flow of Vs (SL) = 0 liters / minute is calculated in the normal operating range. The normal operating range is double-framed in the figure. The simply framed area corresponds to the low-load area. In the low-load range, a positive value of the static target volume flow Vs (SL) is calculated. For example, with nMOT = 1000 1 / min and QSL = 30 mm ³ / stroke, a static target volume flow of Vs (SL) = 1.5 liters / minute is specified.

The Figure 7 shows the various functional states in a diagram, which are activated via switch S1 ( Fig. 3 ) can be realized. The reference symbol 33 denotes the standstill function, the reference symbol 34 denotes the normal function and the reference symbol 35 denotes the protective function. The standstill function is set when an engine standstill is detected. When the standstill function is set, the pressure control valve is not activated because switch S1 is in position 1 and therefore a PWM value of zero is output. So PWMDV = 0 applies. If the actual rail pressure pCR (IST) exceeds a start value pSTART, for example pSTART = 800 bar, and there is a verified engine speed nMOT (BKM = 1), i.e. if the internal combustion engine is recognized as rotating, the standstill function is reset and the normal function 34 set. During the transition, switch S1 changes to position S1 = 2. When normal function 34 is set, the PWM signal PWMDV for controlling the pressure control valve is calculated as a function of the resulting desired volume flow Vres (SL). So PWMDV = f (Vres (SL)) applies. The change back to the standstill function 33 takes place when an engine standstill is detected (BKM = 0). Is at If normal function 34 is set and if the dynamic rail pressure pCR (DYN) exceeds a maximum pressure value pMAX, a check is carried out to determine whether protective function 35 is enabled. This is done using a flag, which is referred to as a flag in the further description. An oscillation between the normal and the protective function is prevented via the flag. If the protective function 35 is additionally enabled (MERKER = 0), the normal function 34 is reset and the protective function 35 is set. With the change of function, switch S1 is switched to position S1 = 3. In this position, the PWM signal PWMDV is temporarily set to a maximum value, for example PWMt = 80%. PWMDV = PWMt applies. This time function can also be implemented as a time-controlled staircase function with different values, for example value 1 PWMt = 80% and value 2 PWMt = 60%. If a time stage t1 has expired, the protective function 35 is reset and the normal function 34 is set. The switch S1 changes its position from S1 = 3 to S1 = 2. The protective function 35 is only released again when the dynamic rail pressure pCR (DYN) falls below the maximum pressure value pMAX by a hysteresis value pHY.

In the Figure 8 a first subroutine UP1 is shown, which shows the transition from the standstill to the normal function. At S1 it is checked whether the engine has stopped. An engine standstill is detected if the engine speed nMOT falls below a limit speed of, for example, 80 rpm for a specific period of time, for example 2.5 seconds. If this is the case, query result S1: yes, switch S1 is switched to position S1 = 1 in S7, a PWM signal with the value zero is output in S8 (PWMDV = 0) and the program is ended. The standstill function is thus set. If a verified engine speed nMOT was detected, query result S1: no, it is checked at S2 whether the actual rail pressure pCR (IST) is greater than or equal to a start value pSTART, for example pSTART = 800 bar. If this is the case, query result S2: yes, switch S1 is moved to position S1 = 2. This means that the normal function is set. In the normal function, the PWM signal PWMDV is calculated as a function of the resulting target volume flow Vres (SL), S4. If the check at S2 shows that the actual rail pressure pCR (IST) is lower than the start value pSTART, query result S2: no, then at S5 it is checked based on the position of the switch S1 which function is currently set. If the normal function is set, query result S5: yes, the program flow is continued at S4.

Otherwise, a PWM signal PWMDV with the value zero is output at S6 and the program run is ended.

In the Figure 9 a second subroutine UP2 is shown, which shows the transition from the normal function to the protective function. The status of the flag is checked at S1. An oscillation between the normal and the protective function is prevented via the flag. If the flag is zero, the program part is run through with steps S2 to S6. Otherwise the program part is run through with steps S7 to S9. If it has been determined in S1 that the flag is equal to zero, then it is checked in S2 whether the dynamic rail pressure pCR (DYN) is greater than or equal to a maximum pressure value pMAX. If this is not the case, query result S2: no, at S6 the PWM signal PWMDV is still calculated as a function of the resulting set volume flow Vres (SL) and the program is ended. If the query at S2 shows that the dynamic rail pressure pCR (DYN) has exceeded the maximum pressure value pMAX, the flag is set to the value 1 at S3, which prevents the protective function from being set again. The protective function is then set in S4 by moving switch S1 to position S1 = 3 and by setting the PWM signal PWMDV to the value PWMt in S5. The temporary PWM signal PWMt can, for example, be set to a value of PWMt = 80%. The program sequence is then ended.

If it has been determined in S1 that the flag is not zero and the protective function is not enabled, query result S1: no, the pressure level of the dynamic rail pressure pCR (DYN) is checked in S7. If the dynamic rail pressure pCR (DYN) has fallen below the maximum pressure value pMAX by at least a certain hysteresis value pHY, query result S7: yes, the flag is set to zero at S8, as a result of which the protective function is released again. If the query result at S7 is negative, the program flow at S9 continues with the calculation of the PWM signal PWMDV depending on the resulting set volume flow Vres (SL) and then the program flow ends.

In the Figure 10 a third subroutine UP3 is shown, which shows the transition from the protective function to the normal function. At S1, the time t is increased by dt. It is then checked at S2 whether the time t is greater than / equal to the time stage t1. Is this not the case, the PWM signal PWMDV remains determined by the temporary PWM signal PWMt at S8. The program sequence is then ended. If it was found in S2 that the time t is greater than / equal to the time stage t1, query result S2: yes, the time t is reset to zero in S3. The PWM signal PWMDV is then calculated as a function of the resulting set volume flow Vres (SL) at S4 and the switch S1 is moved to the position S1 = 2 at S5, which means that the normal function is set. At S6 it is checked whether the dynamic rail pressure pCR (DYN) has fallen below the maximum pressure value pMAX by at least the hysteresis value pHY. If this is not the case, the program flow is ended. Otherwise, the flag is set to zero in S7, which releases the protective function. The program sequence is then ended.

The Figure 11 shows in a first time diagram the starting process of an internal combustion engine with subsequent stop. The Figure 11 consists of the partial diagrams 11A to 11E. These show over time: the engine speed nMOT in Figure 11A , the actual rail pressure pCR (IST) in Figure 11B , the PWM signal PWMDV, with which the pressure control valve is controlled, in Figure 11C who have favourited Rail Pressure Disturbance VDRV in Figure 11D and the position of switch S1 in Figure 11E , The rail pressure disturbance variable VDRV corresponds to the volume flow that the pressure control valve controls from the rail into the fuel tank.

The engine speed nMOT first increases to the idling speed nMOT = 600 1 / min ( Figure 11A ). As soon as a verified engine speed is recognized, that is, as soon as the crankshaft rotates, a condition for the transition from the standstill function to the normal function is fulfilled. The actual rail pressure pCR (IST) also increases after the engine is started. If the actual rail pressure pCR (IST) exceeds the start value of pSTART = 800 bar at time t1, the second necessary condition is fulfilled. Now the standstill function is reset and the normal function is set by also moving switch S1 from S1 = 1 to position S1 = 2 at time t1. The pressure control valve is now activated. In this example, the PWM signal assumes the value PWMDV = 5%, see Figure 11C , A volume flow of 1.5 liters / min is controlled via the pressure control valve as rail pressure disturbance variable VDRV. The actual rail pressure pCR (IST) then swings to the idle value of pCR (IST) = 700 bar. The switch S1 maintains its position S1 = 2 unchanged, even if the actual rail pressure pCR (IST) falls below the start value pSTART = 800 bar at time t2 ( Figure 11B ). The PWM signal still has the value PWMDV = 5% and a volume flow of 1.5 liters / min is still controlled. An engine stop is triggered at time t3. The engine speed nMOT and the actual rail pressure pCR (IST) both drop to the value zero. An engine standstill is then detected at time t4. As a result, the normal function is reset and the standstill function is set instead, that is, the switch S1 changes in the Figure 11E its position from S1 = 2 to S1 = 1. Now the PWM signal PWMDV is no longer calculated, but set to the value zero. Fuel volume flow is therefore no longer shut off, which means that VDRV then assumes the value 0 liters / min.

The Figure 12 shows the transition from the normal function to the protective function in a second time diagram. The Figure 12 consists of the partial diagrams 12A to 12E. These show over time: the dynamic rail pressure pCR (DYN) in Figure 12A , the PWM signal PWMDV, with which the pressure control valve is controlled, in the Figure 12B , the rail pressure disturbance variable VDRV corresponding to the volume flow in the Figure 12C , the position of the switch S1 in the Figure 12D and the value of the flag in the Figure 12E ,

At time t1 there is a load shedding, for example because the generator load is switched off, as a result of which the dynamic rail pressure pCR (DYN) increases from an initial value pCR (DYN) = 2200 bar. At time t2, the dynamic rail pressure pCR (DYN) reaches the maximum pressure value pMAX = 2320 bar. Since the flag previously had the value zero, the protective function was enabled, which is why the PWM signal PWMDV is now temporarily set to the value PWMDV = PMWt = 100% by switching switch S1 from position S1 = 2 to position S1 = 3 is reversed. In other words: the normal function is reset and the protective function is set. With the protective function set, a volume flow of 4 liters / min into the fuel tank is now controlled as a rail pressure disturbance variable VDRV via the pressure control valve. At the same time, if the protective function is set, the flag is set to the value 1 ( Figure 12E ), whereby the protective function is locked. At time t3, time stage t1 has expired. The protective function and the normal function are reset at the end of time stage t1 activated by switching switch S1 from position S1 = 3 to position S1 = 2. The controlled volume flow consequently assumes the value 0 liters / min. At time t4, the dynamic rail pressure pCR (DYN) falls below the maximum pressure value pMAX = 2320 bar by a hysteresis value pHY = 70 bar. The flag thus changes from the value 1 to the value 0, whereby the protective function is released again.

In the Figure 12A a dashed line is drawn as a comparison, which shows a course of the dynamic rail pressure pCR (DYN) without a protective function. As can be seen, the overshoot of the dynamic rail pressure pCR (DYN) is significantly reduced by the protective function. In the figure, this is identified by the reference symbol dp.

In the description of the figures, a PWM signal in positive logic was used to control the pressure control valve, that is to say that if the PWM signal PWMDV is positive, the pressure control valve is acted upon in the opening direction (increasing opening cross section). Of course, the control analog to the suction throttle can also be carried out in negative logic. In this case, the pressure control valve is fully open when the PWM value is PWMDV = 0.

• Ein Überschwingen des Raildrucks, hier: dynamischer Raildruck, bei Laständerung am Abtrieb der Brennkraftmaschine wird deutlich reduziert;
• Das verringerte Überschwingen bewirkt eine kürzere Ausregelzeit und damit eine kürzere Reaktionszeit;
• Das mechanische System, insbesondere das Rail, wird vor Druckspitzen wirkungsvoll geschützt;
• Ein Öffnen des passiven Druckbegrenzungsventils wird auf die wirklichen Notfälle begrenzt;
• Das erfindungsgemäße Verfahren kann ergänzend zum bekannten Verfahren der Schnellbestromung der Saugdrossel bei einem Lastabwurf verwendet werden ( DE 10 2005 029 138 B3 );
• Der Druckaufbau des Raildrucks beim Startvorgang erfolgt ungehindert.

Bezugszeichen 1 Brennkraftmaschine 33 Stillstandfunktion 2 Kraftstofftank 34 Normalfunktion 3 Niederdruckpumpe 35 Schutzfunktion 4 Saugdrossel 5 Hochdruckpumpe 6 Rail 7 Injektor 8 Einzelspeicher (optional) 9 Rail-Drucksensor 10 elektronisches Steuergerät (ECU) 11 Druckbegrenzungsventil, passiv 12 Druckregelventil, elektrisch ansteuerbar 13 Raildruck-Regelkreis 14 Druckregler 15 Begrenzung 16 Pumpen-Kennlinie 17 Berechnung PWM-Signal 18 Regelstrecke 19 erstes Filter 20 zweites Filter 21 Steuerung 22 Berechnung 23 Druckregelventil-Kennfeld 24 Stromregelkreis (Druckregelventil) 25 Stromregler 26 Filter 27 Soll-Volumenstrom-Kennfeld 28 Berechnung Soll-Verbrauch 29 dynamische Korrektur 30 Begrenzung 31 Kennlinie 32 Regler In summary, the following advantages result for the method according to the invention:

• An overshoot of the rail pressure, here: dynamic rail pressure, is significantly reduced when the load on the output of the internal combustion engine changes;
• The reduced overshoot results in a shorter settling time and thus a shorter reaction time;
• The mechanical system, especially the rail, is effectively protected against pressure peaks;
• Opening the passive pressure relief valve is limited to the real emergencies;
• The method according to the invention can be used in addition to the known method of quickly energizing the suction throttle in the event of a load shedding ( DE 10 2005 029 138 B3 );
• The pressure build-up of the rail pressure during the starting process is unimpeded.

reference numeral 1 Internal combustion engine 33 Standstill function 2 Fuel tank 34 normal function 3 Low pressure pump 35 protection 4 interphase 5 high pressure pump 6 Rail 7 injector 8th Individual storage (optional) 9 Rail pressure sensor 10 electronic control unit (ECU) 11 Pressure relief valve, passive 12 Pressure control valve, electrically controllable 13 Rail pressure control circuit 14 pressure regulator 15 limit 16 Pump curve 17 Calculation of PWM signal 18 controlled system 19 first filter 20 second filter 21 control 22 calculation 23 Pressure control valve map 24 Current control loop (pressure control valve) 25 current regulator 26 filter 27 Target volumetric flow-map 28 Calculation of target consumption 29 dynamic correction 30 limit 31 curve 32 regulator

Claims (7)

1. Method for performing open-loop and closed-loop control of an internal combustion engine (1) with a common rail system, in which method the rail pressure (pCR), which is measured by means of a rail pressure sensor (9), is closed-loop controlled by means of a low-pressure-side intake throttle (4) as first pressure adjusting element in a rail pressure closed-loop control circuit (13), in which method a rail pressure interference variable (VDRV) for influencing the rail pressure (pCR) is generated by means of a high-pressure-side pressure control valve (12) as a second pressure adjusting element, by means of which fuel is discharged from the rail (6) into the fuel tank (2), and the position of which is determined by means of a PWM signal (PWMDV),
   characterized
   in that an actual rail pressure (pCR(IST)) is calculated from the rail pressure (pCR) by means of a first filter (19), and a dynamic rail pressure (pCR(DYN)) is calculated from the rail pressure (pCR) by means of a second filter (20), wherein a stationary state function (33) is set if a stationary state of the engine is detected (BKM = 0), wherein when a stationary state function (33) is set the PWM signal (PWMDV) is output with a value of zero, wherein the stationary state function (33) is reset and a normal function (34) is set if the actual rail pressure (pCR(IST)) exceeds the start value (pSTART) and a verified engine rotational speed (nMOT) is detected (BKM = 1), wherein when a normal function (34) is set the PWM signal (PWMDV) is calculated in accordance with a resulting setpoint volume flow (Vres(SL)), a protective function (35) is set if the dynamic rail pressure (pCR(DYN)) exceeds a maximum pressure value (pMAX), and the protective function (35) is enabled (MERKER = 0), wherein when a protective function (35) is set the PWM signal (PWMDV) is temporally set to a maximum value (PWMt).
2. Method according to Claim 1,
   characterized
   in that after the expiry of a time stage (t1) the temporal PWM signal is ended, the protective function (35) is reset and the normal function (34) is set again.
3. Method according to Claim 2,
   characterized
   in that when a normal function (34) is set the protective function (35) is enabled again if the dynamic rail pressure (pCR(DYN)) falls below the maximum pressure value (pMAX) by at least one hysteresis value (pHY).
4. Method according to Claim 1,
   characterized
   in that when a normal function (34) is set, said function is reset and the stationary state function (33) is set again if a stationary state of the engine is detected.
5. Method according to Claim 1,
   characterized
   in that the resulting setpoint volume flow (Vres(SL)) is calculated from a static setpoint volume flow (Vs(SL)) and a dynamic setpoint volume flow (Vd(SL)).
6. Method according to Claim 5,
   characterized
   in that the static setpoint volume flow (Vs(SL)) of the pressure control valve (12) is calculated in accordance with a setpoint injection quantity (QSL) and an engine rotational speed (nMOT) by means of a setpoint volume flow characteristic diagram (27).
7. Method according to Claim 5,
   characterized
   in that the dynamic setpoint volume flow (Vd(SL)) of the pressure control valve (12) is calculated by means of a dynamic correction (29) in accordance with a setpoint rail pressure (pCR(SL)) and an actual rail pressure (pCR(IST)) or the dynamic rail pressure (pCR(DYN)).

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