EP2705236B1 - Method for monitoring a passive pressure regulator valve - Google Patents

Description

The invention relates to a method for monitoring a passive pressure relief valve, via which fuel is derived from the rail of a common rail system in the fuel tank, is changed in recognizing a defective rail pressure sensor from rail pressure control mode in an emergency operation, wherein in emergency mode Rail pressure is gradually increased until the response of the pressure relief valve.

In the from the DE 10 2006 049 266 B3 known methods, the passive pressure relief valve is monitored for opening. An open pressure relief valve is detected after a load shedding because the rail pressure exceeds a limit value, subsequently again a stationary state of the internal combustion engine is detected and, in addition, a characteristic variable of the rail pressure control loop deviates significantly from a reference value. The characteristic variable of the rail pressure control loop is understood to mean the I component of the rail pressure regulator or, for example, a PWM signal for controlling the suction throttle. For the illustrated method, a functional rail pressure sensor is absolutely necessary.

Also the DE 10 2006 040 441 B3 describes a method for monitoring a passive pressure relief valve after a load shedding. In a first step, it is checked whether the rail pressure, starting from a stationary rail pressure, for example 1800 bar, has exceeded a first, higher limit value, for example 1850 bar. In a second step, it is then checked whether the rail pressure, despite a temporary loading of the suction throttle in the closing direction, a second, even higher limit, for example, 1920 bar, exceeds. If both limits have been exceeded, the pressure limiting valve is set as open. Due to the dispersion of the pressure relief valves, however, the case may occur in practice that the Pressure relief valve is recognized by the evaluation program as open, but in fact this is still closed. The consequence is an operator error alarm and an erroneous follow-up action. A functional rail pressure sensor is also essential in this process.

The invention is based on the object to recognize an open pressure relief valve in a generic common rail system even in case of failure of the rail pressure sensor.

The object is solved by the claim 1. In the dependent claims, the embodiments are shown.

The method consists in switching from control to emergency operation upon detection of a defective rail pressure sensor, wherein in the emergency mode the rail pressure is increased successively until the response of the pressure limiting valve. Since there is no information about the rail pressure in the event of a defective rail pressure sensor, the pressure limiting valve is then set as open if, in addition, the starting phase of the internal combustion engine is recognized to have ended after the change to emergency operation. After the pressure relief valve has been set open, its opening duration is monitored. The invention is therefore based on the finding that the operating time with the pressure relief valve open is decisive for the assessment of whether the pressure relief valve is still tight after a restart or already tends to leak. As is known, a pressure-limiting valve with leakage causes a decreasing overall efficiency, since the fuel flows out of the rail unused into the fuel tank. In the invention, it is advantageous that, in addition to a stable operating state in emergency operation, a secure limitation of the fault with regard to undesired leakage is also possible. Overall, the simple parameterization and implementation of the method is advantageous.

The opening duration of the pressure relief valve set as open is monitored by setting a first time limit and a second time limit for further operation. After expiration of the first time limit, a yellow alarm is initiated to alert the operator. After expiration of the second time limit then a red alarm is initiated as a recommendation to replace the pressure relief valve. If the operator stops the engine, the current opening time is saved. Becomes Thereafter, after starting the internal combustion engine an open pressure relief valve again detected, the stored opening time is counted and monitored for exceeding the first and second time limit.

In addition to the duration of monitoring, the frequency of opening operations is also recorded in addition. Thus, a yellow alarm is initiated at a first number of opening operations and a red alarm is initiated at a second number of opening operations. This solution is therefore based on the knowledge that the number of opening operations is crucial for the assessment of whether the pressure relief valve is still tight after a restart or already tends to leak.

Figur 1

ein Systemschaubild,

Figur 2

einen Raildruck-Regelkreis,

Figur 3

ein erstes Zeitdiagramm,

Figur 4

ein zweites Zeitdiagramm mit mehreren Öffnungsvorgängen,

Figur 5

einen Programmablaufplan und

Figur 6

ein Unterprogramm.

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

FIG. 1

a system diagram,

FIG. 2

a rail pressure control loop,

FIG. 3

a first timing diagram,

FIG. 4

a second time diagram with several opening operations,

FIG. 5

a program schedule and

FIG. 6

a subroutine.

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 the following mechanical components: a low-pressure pump 3 for conveying fuel from a fuel tank 2, a variable intake throttle 4 for influencing the fuel volume flow flowing through it, a high-pressure pump 5 for conveying the fuel with pressure increase, a rail 6 for storing the 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 memories, in which case for example in the injector 7, a single memory 8 is integrated as an additional buffer volume. As a protection against an inadmissibly high pressure level in the rail 6, a passive pressure relief valve 11 is provided which opens, for example, at a rail pressure of 2400 bar and absteuert the fuel from the rail 6 into the fuel tank 2 in the open state.

The operation of the internal combustion engine 1 is determined by an electronic control unit (ECU) 10. The electronic control unit 10 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 10 from the input variables, the output variables. In the FIG. 1 the following input variables are shown by way of example: the rail pressure pCR, which is measured by means of a rail pressure sensor 9, an engine speed nMOT, a signal FP for output specification by the operator, optionally the individual accumulator pressure pE and an input variable ON. Under the input quantity ON, the further sensor signals are combined, for example the charge air pressure of an exhaust gas turbocharger. In FIG. 1 are shown as output variables of the electronic control unit 10 is a signal PWM for controlling the suction throttle 4, a signal ve for controlling the injectors 7 (start of injection / injection end) 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 for a control signal for activating a second exhaust gas turbocharger in a register charging.

The FIG. 2 shows a rail pressure control circuit 12 for regulating the rail pressure pCR. The input variables of the rail pressure control circuit 12 are: a desired rail pressure pCR (SL), a target consumption VVb, the engine speed nMOT, a signal SD as a marking of a defective rail pressure sensor and a quantity E1. The size E1 includes, for example, the basic PWM frequency, the battery voltage and the ohmic resistance of the intake throttle coil with supply line, which are included in the calculation of the PWM signal. The output of the rail pressure control circuit 12 is the raw value of the rail pressure pCR. From the raw value of the rail pressure pCR, the actual rail pressure pCR (IST) is calculated by means of a filter 13. This is then compared with the desired rail pressure pCR (SL) at a summation point A, resulting in a control deviation ep. From the control deviation ep, a pressure regulator 14 calculates its control variable, which corresponds to a regulator volume flow VR with the physical unit liters / minute. For the regulator volume flow VR, the calculated nominal consumption VVb is added to a summation point B. The target consumption VVb is calculated as a function of a desired injection quantity and the engine speed. The result of the addition at the summation point B corresponds to an unlimited volumetric flow Vu, which has a Limit 15 is limited depending on the engine speed nMOT. The output of the limit 15 corresponds to a desired volume flow V (SL), which is the input variable of a pump characteristic 16. Via the pump characteristic curve 16, the setpoint volume flow V (SL) is assigned a desired electric current i (SL). The desired current i (SL) is an input variable of a function block 17. The function block 17 contains the calculation of the PWM signal. The output of the function block 17 corresponds to the actual volume flow V (IST), which is conveyed by the high-pressure pump in the rail 6. The pressure level pCR in the rail is detected by the rail pressure sensor. Thus, the control loop 12 is closed.

If a defective rail pressure sensor is now detected (SD = 1), the control mode switches to emergency mode. In emergency mode, the rail pressure is increased successively until the response of the pressure relief valve. For this purpose, the suction throttle is acted upon in the opening direction, whereby then the high-pressure pump can promote more fuel. This is achieved by setting the setpoint current i (SL) as the drive signal of the suction throttle to an emergency stop value, for example zero ampere. Alternatively, the PWM signal can be set as the drive signal of the suction throttle to a Notlaufwert, for example, zero percent. Likewise, it is possible to switch over from a pump characteristic curve in normal operation to a limit curve during emergency operation. When the pressure relief valve is open, the rail pressure is between the pressure value at idle, z. B. 900 bar, and the pressure value at full load, z. B. 700 bar. Since the rail pressure in emergency mode is always within this pressure range, a stable operating condition with a uniform engine performance is guaranteed.

The FIG. 3 shows in a timing diagram an opening operation of the pressure relief valve with monitoring of the opening time. Over time, the following are shown: the rail pressure pCR, the process variable SD for marking a defective rail pressure sensor, a process variable SDL for marking the intake throttle flow, a signal START engine start, a process variable DBV as a state identifier of the pressure relief valve, a process variable D1 for the yellow alarm, a Process variable D2 for the red alarm, a process variable engine is Mst for the detection of a stationary internal combustion engine and a signal RS as a reset signal.

At time t0, the system and rail pressure sensor are error free. Thus, the process variable SD has the value SD = 0. The rail pressure is pCR = 1000 bar. The boot process is not finished yet, so the process variable START = 1. At the time t1, the failure of the rail pressure sensor is detected, the signal SD changes from the value 0 to the value 1. With detection of a defective rail pressure sensor is changed from the control to the emergency operation. In emergency operation, the pressure relief valve is selectively opened, for example, by setting the solistrom of the suction throttle to the value 0 amperes. The process variable SDL changes from the value 1 to the value SDL = 0. Due to the fully opened intake throttle, the high-pressure pump delivers a larger volume flow into the rail, so that the rail pressure now rises after time t1. At time t2, the engine speed, not shown, reaches the idle speed, d. H. the internal combustion engine leaves the starting phase. Accordingly, the signal START changes from the value 1 to the value 0.

Since the rail pressure can no longer be measured, therefore, can not be determined exactly when the pressure relief valve opens. For this reason, that time is assumed as the opening time, in which both a defective rail pressure sensor has been detected, here: time t1, as well as the start phase of the internal combustion engine is also completed. This is the time t2. Therefore, at time t2, the pressure relief valve is set to open. The signal DBV now changes from the value 0 to the value DBV = 1. From time t2, the opening time of the pressure limiting valve is monitored for exceeding a first time limit tLi1 and a second time limit tLi2. In practical operation, the first time limit tLi1 may be, for example, 3 operating hours and the second time limit tLi2 may be, for example, 5 operating hours. At time t3, the first time limit tLi1 is reached. The process variable D1 therefore changes at the time t3 to the value D1 = 1, whereby a yellow alarm is initiated to warn the operator. At time t4, the second time limit tLi2 is reached. The process variable D2 changes to the value D2 = 1 at this time, which triggers a red alarm.

At time t5, the engine is stopped by the operator, whereby the process variable engine is Mst set to the value Mst = 1. Since the pressure relief valve is closed when the engine is stationary, the Signal DBV is now reset to the value DBV = 0. The internal combustion engine is back in the starting phase, the signal START is reset to the value 1. At time t6, the rail pressure sensor is replaced, the sensor defect displayed disappears, ie the signal SD is reset to the value SD = 0. At time t7, the reset button is pressed (RS = 1), thus the two alarms disappear, ie the signals D1 and D2 are reset from the value 1 to the value 0. The alarms would also be reset if the defective rail pressure sensor had not been replaced at that time.

If the internal combustion engine is switched off before the opening time has exceeded the first time limit tLi1 or the second time limit tLi2, then the current opening time is stored when the engine standstill is detected. If, after a restart of the internal combustion engine, an open pressure limiting valve is detected again at a later time, the stored opening time is counted further and monitored for limit violation. By this measure, the safety is increased by a pressure relief valve is detected with unwanted leakage.

The FIG. 4 shows a method in which the number of opening operations is monitored in addition to the opening time of the pressure relief valve. For the sake of clarity are in the FIG. 4 the two time limits tLi1 and tLi2 omitted. Over time are shown: the rail pressure pCR, a counter Z, the process variable SD to identify a defective rail pressure sensor, a process variable SDL to identify the Saugdrosselstroms, a signal engine start START, a process variable DBV as a state identifier of the pressure relief valve, a process variable D1 for the yellow alarm, a process variable D2 for the red alarm, a process variable motor Mst stands for the detection of a stationary internal combustion engine and a signal RS as a reset signal.

At time t0, the system and rail pressure sensor are error free. At time t1, two events are combined. On the one hand, a running internal combustion engine is recognized, ie the variable engine is stopped Mst is reset to the value Mst = 0. On the other hand, a defective rail pressure sensor is detected, ie the variable SD is set to the value 1. As a result, the suction throttle in the opening direction applied. The process variable SDL is therefore SDL = 0. This leads to an increase in the rail pressure pCR. If the rail pressure pCR reaches the value pLi1 at the time t2, the engine speed (not shown) is identical to the idling speed. The start phase is completed. The process variable START is reset. Since now both conditions are met, ie the rail pressure sensor is defective and the star phase is completed, the pressure relief valve is set as open. The variable DBV is set to the value DBV = 1. Since now the first opening operation of the pressure limiting valve is detected, the counter Z assumes the value Z = 1. At the time t3, a motor standstill is detected, the signal motor is Mst is set to the value Mst = 1. The pressure relief valve is now closed, the variable DBV is reset to the value DBV = 0. The starting phase of the internal combustion engine is displayed again by setting the variable START to the value 1. The internal combustion engine is now restarted, so that at the time t4 a running internal combustion engine is detected. This resets the signal motor stalled Mst to the value Mst = 0. At time t5, an open pressure relief valve is again detected, whereby the counter Z is incremented to the value Z = 2. In the following, the internal combustion engine is repeatedly started and stopped again in the event of a further defective rail pressure sensor. At time t8, the pressure relief valve has opened nGELB times. The counter Z now has the value Z = nD1, whereby the limit for the activation of the yellow alarm is reached. The variable D1 is consequently set to the value 1. At time t11, the pressure relief valve has opened nROT times. The counter Z now has the value Z = nD2, whereby a red alarm is triggered. This is displayed by setting the variable D2 to the value D2 = 1. At time t12, a stationary internal combustion engine is detected, the signal motor is Mst changes from the value Mst = 0 to the value Mst = 1. Since the internal combustion engine is now standing, the pressure relief valve can be replaced. After replacing the pressure relief valve, the rail pressure sensor defect remains active because the rail pressure sensor was not replaced at the same time. This is indicated by the signal SD, which is still 1 identical. At time t13, the reset signal is now activated, the signal RS assumes the value 1. As a result both alarms are reset, ie the variables D1 and D2 are reset to the value 0. At the same time, the variable Z is reset to the value 0, so that the counting process can start again from the beginning.

FIG. 5 shows a program flowchart for monitoring the pressure relief valve in case of a defect of the rail pressure sensor. At S1 it is checked whether a defective rail pressure sensor has been detected. If this is not the case, query result S1: no, the program branches to normal operation. Otherwise, the value of the flag 3 is queried in S2. The flag 3 is always set when the pressure relief valve is set as open. In this respect, the flag 3 of the process variable DBV corresponds to the FIG. 3 and the FIG. 4 , If the flag 3 = 1, the program part S7 to S13 is run through. If the flag 3 = 0, the program part S3 to S6 is run through.

If it was determined at S2 that the pressure limiting valve is still closed, it is checked at S3, whether the starting phase of the internal combustion engine is completed. For this purpose, the engine speed is compared with the idle speed. If the start phase is not yet completed, that is, the process variable START is 1, the process continues at S14. If the start phase is completed, query result S5: no, then the counter Z is incremented at S4 and then checked at S5 in a subroutine UP the count. The subroutine is in the FIG. 6 and will be explained in connection with this figure. Subsequently, the flag 3 = 1 is set at S6, that is, the pressure limiting valve is set as open. Thereafter, the program flow continues at S14.

If it was detected at S2 that the pressure limiting valve was already set as open, flag3 = 1, the time t1 is incremented at S7. Subsequently, it is checked at S8 whether the time t1 has already exceeded the first time limit tLi1, for example 3 operating hours. If this is not the case, query result S8: no, the program flow continues at S10. Otherwise, the yellow alarm is set as a warning to the operator at S9. At S10 it is then checked whether the time t1 has already exceeded the second time limit tLi2, for example 5 operating hours. If this is not the case, query result S10: no, then the program flow continues at S12. Otherwise, the red alarm is set at S11. At S12, it is checked if the internal combustion engine is stationary. If this is not the case, the program sequence is continued at S14. Otherwise, the flag 3 = 0 is set at S13, that is, the pressure relief valve is considered closed. At S14 the following is checked in a query 1: If the reset button was pressed (RS = 1) and a yellow or red alarm is present and the motor is stopped (Mst = 1). If the query is negative, query result S14: no, that is the end of the program. Otherwise, the time t1 and the counter Z is set to 0 at S15. Then the program is finished.

In the program schedule of FIG. 5 the case is also considered that the rail pressure sensor fails during operation. In this case, after passing through S1 and S2, it is then detected at S3 that the starting phase has been completed, query result S3: no. The counter Z is then incremented at S4, the count is checked at S5 and the flag 3 = 1 is set immediately at S6. Thus, the pressure relief valve is considered open.

In the FIG. 6 is the subroutine UP shown, over which the counter Z is checked. The counter Z is incremented whenever an open pressure relief valve is detected. At S1 it is checked whether the counter Z is greater than / equal to a predeterminable number nGELB, for example 30; is. If this is not the case, then continue with S3. Otherwise, query result S1: yes, at S2 the yellow alarm is initiated to warn the operator. Subsequently, it is checked at S3 whether the counter Z is greater than / equal to a predeterminable number nROT, for example 50. If this is not the case, then the subroutine is ended. On the other hand, if the counter is greater than or equal to nROT, a red alarm is initiated at S4. The red alarm indicates to the operator that the pressure relief valve should be replaced. After that, the subroutine is finished, it is in the main program of FIG. 5 returned and continued there at S5 the main program.

reference numeral

1

Internal combustion engine

2

Fuel tank

3

Low pressure pump

4

interphase

5

high pressure pump

6

Rail

7

injector

8th

Single memory (optional)

9

Rail pressure sensor

10

electronic control unit (ECU)

11

Pressure relief valve, passive

12

Rail pressure control circuit

13

filter

14

pressure regulator

15

limit

16

Pump curve

17

function block

Claims (7)

1. Method for monitoring a passive pressure-limiting valve (11) by means of which fuel from the rail (6) of a common rail system is diverted into the fuel tank (2), in which, when a defective rail pressure sensor (9) is detected, there is a changeover from the rail pressure regulating mode into an emergency mode, wherein in the emergency mode the rail pressure is successively increased until the pressure-limiting valve (11) is triggered, in which in the emergency mode the pressure-limiting valve (11) is set as opened if in addition the starting phase of the internal combustion engine is detected as ended, and in which the opening duration of the pressure-limiting valve (11) is additionally monitored.
2. Method according to Claim 1,
   characterized
   in that the opening duration is monitored in that with the setting of an opened pressure-limiting valve (11) a first time limit (tLi1) and a second time limit (tLi2) are defined for further operation, after expiry of the first time limit (tLi1) a yellow alarm for warning the operator is initiated, and after the expiry of the second time limit (tLi2) a red alarm is initiated as a recommendation to replace the pressure-limiting valve (11).
3. Method according to Claim 2,
   characterized
   in that the current opening duration is stored after the shutting down of the internal combustion engine (1) and counting is continued after a restart of the internal combustion engine (1).
4. Method according to Claim 3,
   characterized
   in that after a restart of the internal combustion engine (1) the stored opening duration is set as decisive for the initiation of the yellow alarm and of the red alarm if the pressure-limiting valve (11) is detected again as opened.
5. Method according to Claim 1,
   characterized
   in that in addition to the monitoring of the opening duration the frequency of the opening processes is also detected.
6. Method according to Claim 5,
   characterized
   in that in the case of a first number (nYELLOW) of opening processes the yellow alarm is initiated, and in the case of a second number (nRED) of opening processes the red alarm is initiated.
7. Method according to Claim 1,
   characterized
   in that in the normal mode the rail pressure is regulated by means of a low-pressure-side suction throttle (4) as a first pressure actuating element in a rail pressure regulating circuit, and in the emergency mode the suction throttle is placed in a completely opened state.

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