Method for recognizing a state of change of a fuel injector

Abstract

A method for recognizing a state change of a fuel injector of an internal combustion engine, in which fuel from a high-pressure accumulator is injected into a combustion chamber with the aid of the fuel injector. A value that is representative of a static flow rate of fuel through the fuel injector is ascertained. A state change of the fuel injector is deduced when the representative value differs from a comparative value by more than a first threshold value.

Claims

1. A method for recognizing a functional impairment of a fuel injector of an internal combustion engine in a motor vehicle, in which fuel from a high-pressure accumulator is injected into a combustion chamber using the fuel injector, the method comprising: measuring during a fuel injection by the fuel injector using a pressure sensor, a pressure drop in the high-pressure accumulator; ascertaining a value that is representative of a static flow rate of fuel through the fuel injector, the representative value being ascertained as a ratio of the measured pressure drop to a time period of the fuel injection; comparing the representative value to a comparative value, the comparative value being an average of representative values of: (i) all fuel injectors of the internal combustion engine, or (ii) all fuel injectors of the internal combustion engine except the fuel injector, wherein each of the representative values is a ratio of a measured pressure drop during a fuel injection of a respective one of the fuel injectors to a time period of the fuel injection of the respective one of the fuel injectors; determining functional impairment of the fuel injector when the representative value deviates from the comparative value by greater than a first threshold value; and based on determining the functional impairment, performing at least one of the following: (i) storing information about the functional impairment of the fuel injector in memory, (ii) sending a warning message to a driver of the motor vehicle about the functional impairment of the fuel injector, the sending of the warning message including activating a warning light in the motor vehicle or displaying a notification in the motor vehicle about the functional impairment, (iii) adapting a flow rate of the fuel injector, (iv) performing a cleaning operation of the fuel injector by changing combustion conditions in the internal combustion engine.

2. The method as recited in claim 1, wherein a defect that has been present since the fuel injector began operation is determined as the functional impairment when the representative value deviates from the comparative value without a preceding adaptation of the flow rate of the fuel injector.

3. The method as recited in claim 1, wherein a defect during operation of the fuel injector is determined as the functional impairment when the representative value deviates from the comparative value after a preceding adaptation of the flow rate of the fuel injector.

4. The method as recited in claim 1, wherein carbonization is determined as the functional impairment when the representative value deviates from the comparative value after multiple preceding adaptations of the flow rate of the fuel injector, in each case in the same direction.

5. The method as recited in claim 1, further comprising: detecting that the fuel injector has been replaced by comparing representative values of the fuel injector ascertained in successive driving cycles, and determining the representative values deviate from each other by more than a threshold value.

6. The method as recited in claim 1, wherein based on determining the functional impairment, the information about the functional impairment is stored in the memory.

7. The method as recited in claim 1, wherein based on determining the functional impairment, the warning message is sent to the driver.

8. The method as recited in claim 1, wherein the comparative value is repeatedly or continuously updated.

9. The method as recited in claim 1, wherein a curve of the deviation of the representative value from the comparative value is detected and stored over a service life of the internal combustion engine.

10. The method as recited in claim 1, wherein the first threshold is 10% of the comparative value.

11. The method as recited in claim 1, wherein the first threshold is 25% of the comparative value.

12. The method as recited in claim 1, wherein based on determining the functional impairment, the flow rate of the fuel injector is adapted.

13. The method as recited in claim 1, wherein based on determining the functional impairment, the cleaning operation of the fuel injector is performed by changing the combustion conditions in the internal combustion engine.

14. A processing unit configured for recognizing a functional impairment of a fuel injector of an internal combustion engine in a motor vehicle, in which fuel from a high-pressure accumulator is injected into a combustion chamber using the fuel injector, the processing unit configured to: measuring during a fuel injection by the fuel injector using a pressure sensor, a pressure drop in the high-pressure accumulator; ascertain a value that is representative of a static flow rate of fuel through the fuel injector, the representative value being ascertained as a ratio of the measured pressure drop to a time period of the fuel injection; compare the representative value to a comparative value, the comparative value is an average of representative values of: (i) all fuel injectors of the internal combustion engine, or (ii) all fuel injectors of the internal combustion engine except the fuel injector, wherein each of the representative values is a ratio of a measured pressure drop during a fuel injection of a respective one of the fuel injectors to a time period of the fuel injection of the respective one of the fuel injectors; determine a functional impairment of the fuel injector when the representative value deviates from the comparative value by greater than a first threshold value; and based on determining the functional impairment, perform at least one of the following: (i) store information about the functional impairment of the fuel injector in memory, (ii) send a warning message to a driver of the motor vehicle about the functional impairment of the fuel injector, the sending of the warning message including activation of a warning light in the motor vehicle or display of a notification in the motor vehicle about the functional impairment, (iii) adapt a flow rate of the fuel injector, (iv) perform a cleaning operation of the fuel injector by changing combustion conditions in the internal combustion engine.

15. The processing unit as recited in claim 14, wherein the first threshold is 10% of the comparative value.

16. The processing unit as recited in claim 14, wherein the first threshold is 25% of the comparative value.

17. A non-transitory machine-readable memory medium on which is stored a computer program for recognizing a functional impairment of a fuel injector of an internal combustion engine in a motor vehicle, in which fuel from a high-pressure accumulator is injected into a combustion chamber using the fuel injector, the computer program, when executed by a processor, causing the processor to perform: measuring during a fuel injection by the fuel injector using a pressure sensor, a pressure drop in the high-pressure accumulator; ascertaining a value that is representative of a static flow rate of fuel through the fuel injector, the representative value being ascertained as a ratio of the measured pressure drop to a time period of the fuel injection; comparing the representative value to a comparative value, the comparative value being an average of representative values of: (i) all fuel injectors of the internal combustion engine, or (ii) all fuel injectors of the internal combustion engine except the fuel injector, wherein each of the representative values is a ratio of a measured pressure drop during a fuel injection of a respective one of the fuel injectors to a time period of the fuel injection of the respective one of the fuel injectors; determining functional impairment of the fuel injector when the representative value deviates from the comparative value by greater than a first threshold value; and based on determining the functional impairment, performing at least one of the following: (i) storing information about the functional impairment of the fuel injector in memory, (ii) sending a warning message to a driver of the motor vehicle about the functional impairment of the fuel injector, the sending of the warning message including activating a warning light in the motor vehicle or displaying a notification in the motor vehicle about the functional impairment, (iii) adapting a flow rate of the fuel injector, (iv) performing a cleaning operation of the fuel injector by changing combustion conditions in the internal combustion engine.

18. The non-transitory machine-readable memory medium 17, wherein the first threshold is 10% of the comparative value.

19. The non-transitory machine-readable memory medium 17, wherein the first threshold is 25% of the comparative value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 schematically shows an internal combustion engine including a common rail system, which is suitable for carrying out a method according to the present invention.

(2) FIG. 2 shows a diagram of a flow volume for a fuel injector as a function of time.

(3) FIG. 3 shows a diagram of a pressure curve in a high-pressure accumulator during an injection operation.

(4) FIG. 4 shows a representative value of a static flow rate and a comparative value in a method according to the present invention in one preferred specific embodiment.

(5) FIG. 5 shows a curve of a representative value of a static flow rate in a method according to the present invention in another preferred specific embodiment.

(6) FIG. 6 shows a curve of a representative value of a static flow rate in a method according to the present invention in another preferred specific embodiment.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

(7) FIG. 1 schematically shows an internal combustion engine 100 that is suitable for carrying out a method according to the present invention. As an example, internal combustion engine 100 includes three combustion chambers or associated cylinders 105. Associated with each combustion chamber 105 is a fuel injector 130 which in turn is connected in each case to a high-pressure accumulator 120, a so-called rail, via which the fuel injector is supplied with fuel. It is understood that a method according to the present invention may also be carried out for an internal combustion engine that includes any other given number of cylinders, for example four, six, eight, or twelve cylinders.

(8) In addition, high-pressure accumulator 120 is fed with fuel from a fuel tank 140 via a high-pressure pump 110. High-pressure pump 110 is coupled to internal combustion engine 100, in particular in such a way that the high-pressure pump is driven via a crankshaft of the internal combustion engine or via a camshaft that is in turn coupled to the crankshaft.

(9) Control of fuel injectors 130 for metering fuel into the particular combustion chambers 105 takes place via a processing unit designed as an engine control unit 180. For the sake of clarity, only the connection from engine control unit 180 to one fuel injector 130 is illustrated, although it is understood that each fuel injector 130 is similarly connected to the engine control unit. Each fuel injector 130 may be specifically controlled. In addition, engine control unit 130 is configured for detecting the fuel pressure in high-pressure accumulator 120 with the aid of a pressure sensor 190.

(10) FIG. 2 illustrates a diagram of cumulative flow volume V through a fuel injector as a function of time t for a prolonged control of the fuel injector. A control period begins at point in time t.sub.0, and the valve needle begins to lift at point in time t.sub.1. An open period of the fuel injector thus also begins at point in time t.sub.1. It is apparent that cumulative flow volume V and the quantity of fuel that has flowed through the fuel injector constantly increase over a wide range after a brief period during the lifting of the valve needle. In this range, the valve needle is in so-called full lift; i.e., the valve needle is lifted completely or up to a setpoint height.

(11) During this time, a constant fuel quantity per unit time flows through the valve opening in the fuel injector; i.e., static flow rate Q.sub.stat, which indicates the slope of cumulative flow volume V, is constant. The magnitude of the static flow rate is an important factor which, as mentioned at the outset, determines the overall fuel quantity that is injected during an injection operation. Deviations or tolerances in the static flow rate therefore affect the injected fuel quantity per injection operation.

(12) The control period ends at point in time t.sub.3 and the closing time begins, during which the valve needle begins to drop. The closing time and the open period end at point in time t.sub.4, when the valve needle once again completely closes the valve.

(13) FIG. 3 illustrates a diagram of a pressure curve in a high-pressure accumulator during an injection operation, as a function of time t. It is apparent that pressure p in the high-pressure accumulator, except for certain fluctuations due to pump conveyance and fuel withdrawals due to injections, is essentially constant. During the injection operation, which lasts for a period t, pressure p in the high-pressure accumulator drops by a value p.

(14) Pressure p, once again except for certain fluctuations, subsequently remains at the lower level until p once again rises to the starting level due to extra conveyance by the high-pressure pump.

(15) The detection and evaluation of these pressure drops during injection operations take place with components that are generally present anyway, such as pressure sensor 190 and engine control unit 180, including corresponding input circuitry. Additional components are therefore not necessary. This evaluation takes place individually for each combustion chamber 105.

(16) As mentioned above, static flow rate Q.sub.stat through the fuel injector is characterized by the injected fuel quantity or its volume per unit time. In a high-pressure accumulator or rail that is pumped to system pressure, the injected volume is proportional to the pressure drop in the rail. The associated period corresponds to the open period of the fuel injector, which, as mentioned above, may be determined mechatronically with the aid of a so-called controlled valve operation (see German Patent Application No. DE 10 2009 002 593 A1, for example).

(17) By forming the quotient of the pressure drop or pressure difference p and the open period, i.e., period of injection t, a pressure rate is obtained as a substitute value or representative value R.sub.stat=p/t for static flow rate Q.sub.stat; i.e., for a measuring operation, Q.sub.stat:

(18) $\frac{p}{t}$
applies. Extra conveyance by the high-pressure pump should not fall into the relevant time window, and therefore may possibly need to be suppressed.

(19) FIG. 4 shows a diagram by way of example of three representative values R.sub.stat,1, R.sub.stat,2, and R.sub.stat,3 which may be ascertained, for example, for the fuel injectors shown in FIG. 1 according to the method described above.

(20) Also shown is a comparative value R.sub.stat which may be obtained, for example, from the two representative values R.sub.stat,1 and R.sub.stat,3, for example, as the arithmetic mean. The comparative value is thus ascertained from all fuel injectors except for the fuel injector being examined. However, it is also conceivable to ascertain the threshold value from all three fuel injectors (or all fuel injectors present), i.e., including the examined fuel injector, in which case the threshold values may need to be defined differently. However, recognizing a deviation is generally easier in the variant shown.

(21) A first threshold value R.sub.1 and a second threshold value R.sub.2 are also shown. As is apparent in FIG. 4, representative value R.sub.stat,2 deviates from comparative value R.sub.stat by more than first threshold value R.sub.1, but by less than second threshold value R.sub.2. In this case a defect of the fuel injector in question may be deduced, and the information concerning the defect may be stored in an error memory, for example. The injector should be replaced at the earliest opportunity.

(22) If during a subsequent check, for example, representative value R.sub.stat,2 deviates from comparative value R.sub.stat by more than second threshold value R.sub.2, for example, a warning message may be sent to a driver. The injector should be immediately replaced, since the extent of the defect or the functional impairment has become too great for a reliable or low-emission operation.

(23) FIG. 5 illustrates a curve of a representative value of a static flow rate as a function of time t in a method according to the present invention, in another preferred specific embodiment. The representative value shown here may be, for example, representative value R.sub.stat,2 shown in FIG. 3, which may be ascertained at points in time t.sub.1 through t.sub.5 in the manner described above. Points in time t.sub.1 through t.sub.5 in particular come from different driving cycles.

(24) Also shown is comparative value R.sub.stat, which may also be ascertained as described above. It is understood that the comparative value does not necessarily have to remain constant over time, as shown here, and instead may also vary when it is formed as the average value of multiple representative values.

(25) In the curve of the representative value, the deviation from the comparative value becomes increasingly greater. In particular, for example after each ascertainment of a deviation, i.e., at each of points in time t.sub.1 through t.sub.4, a readaptation, i.e., an adaptation of the static flow rate, may take place.

(26) However, as shown at point in time t.sub.5, for example, if a deviation from comparative value R.sub.stat by more than first threshold value R.sub.1 is now determined, based on the increasing deviation despite readaptations, a carbonized fuel injector is to be assumed. As an error correction measure, an attempt may be made to clean the fuel injector by changing the combustion conditions. Alternatively, or if this is not successful, the information concerning the carbonization may be stored in the error memory. The injector should then be replaced at the earliest opportunity.

(27) FIG. 6 illustrates a curve of a representative value of a static flow rate as a function of time t in a method according to the present invention, in another preferred specific embodiment. The representative value shown here may be, for example, representative value R.sub.stat,2 shown in FIG. 3, which may be ascertained for each point in time t.sub.6 through t.sub.8 in the manner described above.

(28) Also shown is comparative value R.sub.stat, which here may correspond, for example, to the representative value at point in time t.sub.7 or to an average value of the representative values at points in time t.sub.6 and t.sub.7.

(29) A deviation from comparative value R.sub.stat by more than first threshold value R.sub.1 is now to be determined at point in time t.sub.8.

(30) Since the comparative value is the representative value of the fuel injector at the same position in the internal combustion engine as at point in time t.sub.8, it is to be assumed that a different fuel injector is now present. A replacement of a fuel injector may be ascertained in this way.