FR3098551A1 - diagnostic process for a high pressure injection system - Google Patents

Abstract

Method for diagnosing an injection system comprising: - an injection rail fitted with a pressure sensor, and - a high pressure pump said method comprising the following three steps after detection of an operating fault in the fuel system. injection: - a) insulation of the injection rail and determination of any pressure variation in the injection rail, - b) fuel outlet from the injection rail but without supplying the injection rail with fuel and determination of a possible pressure variation in the injection rail, - c) entry of fuel into the injection rail but without letting fuel out of the injection rail and determination of a possible pressure variation in the injection rail. the injection rail, and - d) a fourth step of determining a diagnosis as a function of the pressure variations observed during the three preceding steps according to predetermined patterns. Abstract figure: Figure 2

Description

diagnostic method for a high pressure injection system

The present invention relates to a diagnostic method for a high pressure injection system in an internal combustion engine as well as a device implementing such a method.

This disclosure relates in particular to the field of the automotive industry. Thus, for example, in injection engines, it is known to have high pressure injectors supplied with fuel from an injection rail common to several (generally all) injectors. Fuel is pressurized in the injection rail and is introduced under pressure by the injectors into corresponding combustion chambers.

The fuel arrives in the injection rail from a tank. A pump, called the low-pressure pump, brings the fuel out of the tank and sends it through a filter to a pump, called the high-pressure pump, which supplies the common injection rail at the output. In general, the fuel temperature and pressure are measured at the tank outlet (downstream of the low pressure pump) and the pressure inside the common rail is also measured using a pressure sensor. The pressure in the injection rail is controlled in a closed loop from the information given by the pressure sensor associated with the injection rail. Fuel is delivered by a high-pressure pump generally equipped with an electrically controlled valve (on-off valve) to precisely measure the quantity of fuel delivered.

The system is normally expected to be leak free. However, to lower the pressure in the injection rail, it is most often planned to connect the injection rail to the tank by a decompression valve.

The entire injection system is associated with an electronic engine control unit that incorporates sophisticated software. This control unit is able to detect abnormal operation of the injection system.

The aim of the present invention is to provide a method which makes it possible to determine the cause of a malfunction of the injection system when such a malfunction is detected.

Summary

To this end, the present invention proposes a method for diagnosing an injection system associated with an electronic engine control unit comprising:

- an injection rail supplying at least one injector and equipped with a pressure sensor,

- a pump called a high-pressure pump for supplying the injection rail with fuel, and

– possibly a decompression valve allowing the pressure in the injection rail to be lowered.

According to the present invention, this method comprises the following three steps in any order after detection of an operating fault of the injection system:

- a) insulation of the injection rail, i.e. without any fuel inlet or outlet, and determination of any pressure variation in the injection rail by means in particular of its pressure sensor,

- b) fuel exit from the injection rail but without supplying the injection rail with fuel and determination of any variation in pressure in the injection rail by means in particular of its pressure sensor,

- c) entry of fuel into the injection rail but without letting fuel out of the injection rail and determination of any variation in pressure in the injection rail by means in particular of its pressure sensor, and

- d) a fourth step of determining a diagnosis according to the pressure variations observed during the three previous steps according to predetermined patterns.

An intrusive process is thus proposed which acts on components of the injection system in order to carry out a diagnosis according to the response received following each action (intrusion) carried out. This makes it possible to have a diagnosis with great reliability.

In the diagnostic method proposed, provision is made, for example, for each of the steps to be carried out over an engine time. In this way, it is possible to obtain a significant measurement without however having a significant impact on the level of vehicle driving.

According to a preferred method, steps a), b) and c) are carried out in this order since it is an order corresponding to the progress of an engine cycle.

In this diagnostic method described here, the three steps a), b) and c) are advantageously carried out one after the other, preferably in this order. A test cycle is then carried out which is not disturbed by the operation of the engine.

In the proposed method, it is possible to provide independently or in combination that:

- a failure of the injection rail pressure sensor is diagnosed if no pressure variation is detected during each of steps a), b) and c);

- a fuel leak at the injection rail is diagnosed if both:

1. a pressure drop is measured in step a),

2. a pressure drop is measured in step b), and

3. a pressure rise is measured in step c).

- a missed injection is diagnosed if both:

1. no pressure variation is measured in step a),

2. no pressure change is measured in step b), and

3. a pressure rise is measured in step c).

- a malfunction of the high pressure pump is diagnosed if both:

1. no pressure variation is measured in step a),

2. a pressure drop is measured in step b), and

3. No pressure change is measured in step c).

The present invention also relates to:

- A computer program product comprising instructions for implementing the diagnostic method as described above when this program is executed by a processor, and

– A non-transitory recording medium readable by a computer on which is recorded a program for the implementation of the diagnostic method as described above when this program is executed by a processor.

Other characteristics, details and advantages will appear on reading the detailed description below, and on analyzing the appended drawings, in which:

Fig. 1

schematically shows an example of a common rail injection system for an internal combustion engine.

Fig. 2

is an example of a flowchart for carrying out a diagnosis of the injection system of figure 1.

Fig. 3

shows a pressure curve corresponding to an injection system in working order.

Fig. 4

shows a pressure curve corresponding to an injection system with a fuel leak.

Fig. 5

shows a pressure curve corresponding to an injection system with an injection problem.

Fig. 6

shows a pressure curve corresponding to an injection system with a high pressure pump problem.

Fig. 7

shows a pressure curve corresponding to an injection system with a pressure sensor problem.

Fig. 8

shows a summary table for a diagnosis of the main faults that can be diagnosed.

The figures and the description below contain, for the most part, certain elements. They may therefore not only serve to better understand this disclosure but also contribute to its definition, if necessary.

Reference is now made to FIG. 1. The latter represents an injection system intended for a diesel-type engine, but the invention can also be applied to other types of common rail injection systems. .

There is shown in Figure 1 a fuel tank 2 inside which there is a pump, called low pressure pump 4, to allow the fuel located in the tank 2 to be brought to another pump, called high pressure pump 6. On leaving tank 2, the fuel passes through a first filter 8. Before reaching the high pressure pump 6, a temperature sensor 10 and a pressure sensor 12 are provided respectively for measuring the temperature and the pressure of the fuel before it enters the high pressure pump 6. The measurement signals emitted by these sensors are transmitted to an electronic engine control unit 14 (Engine Control Unit or even commonly ECU).

The high pressure pump includes a chamber 60, a second fuel filter 62 placed upstream of an inlet valve 64, a piston/cylinder assembly 66 and an outlet valve 68. The fuel that has passed through the first filter 8 enters chamber 60 and second filter 62 before joining piston/cylinder assembly 66 through inlet valve 64. This piston/cylinder assembly 66 increases the fuel pressure to the desired pressure before exiting the pump high pressure through the outlet valve 68 to join an injection rail 16 (called "rail" in English). At the entrance to the injection rail 16, we note the presence of a calibrated orifice 18. The fuel under high pressure located in the injection rail 16 is used to supply several (four in the illustrated embodiment) injectors 20 for injecting this fuel into a combustion chamber (one injector 20 per combustion chamber). Thus, this injection rail 16 is often called common injection rail (or common rail in English) because it supplies fuel to all the injectors (or at least to several of them). A high pressure sensor 22 constantly measures the pressure prevailing in the injection rail 16. The engine control unit 14 manages the low pressure pump 4, the high pressure pump 6 and in particular its inlet valve 64 as well as the injectors 20. To ensure this management, the engine control unit 14 comprises a processor programmed using advanced software and signals provided by multiple sensors including the temperature sensor 10, the pressure sensor 12 and the sensor high pressure 22. It is further noted that the injection rail 16 comprises a decompression valve 24 (or discharge valve) which makes it possible to reduce the pressure in the injection rail 16 and to return fuel to the tank 2.

A malfunction of a component of this injection system can lead to acute symptoms such as, for example, a loss of power, stalling or even polluting emissions beyond the standards in force. Such a malfunction generally has repercussions on the pressure within the injection rail 16 and the signal supplied by the high pressure sensor 22 is important for carrying out a diagnosis on board the vehicle. However, determining the cause of the malfunction is much more difficult than simply noting the malfunction. Furthermore, the diagnosis cannot be based solely on the signal provided by the high pressure sensor 22 because this sensor may also be defective. There is thus proposed in the remainder of the description a method making it possible to carry out on board the vehicle a diagnosis following the detection of a malfunction.

Figure 2 offers a flowchart for establishing a diagnosis when a malfunction has been observed.

In this figure 2, step 100 corresponds to the finding of a fault in the injection system described above.

Once this observation has been made, it is proposed to carry out three distinct tests, in three phases PH 1, PH 2 and PH 3. These three phases can be carried out in the order which will be described below (preferred embodiment) or in a different order. They can be performed one directly after the other (preferred embodiment) but they can also be performed by allowing time to pass (or a few engine cycles) between two phases.

During a first phase, PH 1, it is proposed to isolate the injection rail 16, that is to say not to allow fuel to enter or leave it. To prevent fuel from entering, the outlet valve 68 of the high pressure pump 6 is cut off (closed). controlled and all the injectors 20 remain in the closed position and, on the other hand, the decompression valve 24 is in the closed position.

Thus, it is expected that the pressure in the injection rail 16 will not vary during this phase. If a variation is observed, it should only be a decrease in pressure. It can then be assumed that this pressure drop (or negative pressure gradient) is due to a leak at the level of the injection rail 16. It could also be another cause.

During a second phase, PH 2, it is proposed to open an injector 20 without allowing fuel to enter the injection rail 16. The outlet valve 68 of the high pressure pump 6 remains closed, as does the decompression valve 24. During this phase, it is therefore expected to have a drop in pressure in the injection rail 16, that is to say to observe at the level of the high pressure sensor 22 a gradient of negative pressure.

In this injection phase, the pressure variation to be measured can be estimated beforehand. Indeed, the quantity of fuel to be injected, dV, is known. It is determined, for example by the engine control unit 14 or else by another on-board computer. The withdrawal of this volume of fuel dV from the injection rail 16 causes a drop in pressure dP within the injection rail 16. This pressure variation, dP, as a first approximation, is given by the following formula:

dP=(K/V)*dV

in which :
K is a modulus (known as the bulk modulus) which is notably dependent on the temperature and the pressure prevailing in the injection rail 16. This temperature is known and the pressure is measured by the high pressure sensor 22. usually knows the variations of K as a function of this temperature and pressure and the values of K are generally stored in the control unit determining the quantity of fuel to be injected,
V is the overall volume of the injection rail 16.

Thus, if the injectors 20 and the high pressure sensor 22 are operating normally (and in the absence of a leak at the level of the injection rail 16), it is possible to predict the pressure variation in the injection rail 16 during of the PH 2 phase.

This phase PH 2 can be carried out once with opening of an injector 20 or as often as there are injectors 20 (or another number of times).

During the third phase, PH 3, it is proposed to bring fuel into the injection rail 16 without letting it out. Therefore, it is therefore planned to open the outlet valve 68 of the high pressure pump 6 and to keep the decompression valve 24 closed as well as to close all the injectors 20.

During this third phase, an increase in the pressure in the injection rail 16 is expected. The high pressure sensor 22 is therefore supposed to record a positive pressure gradient in the injection rail 16.

As already mentioned, the different phases above can each be carried out one or more times. They can be alternated, once a phase then another and yet another, and we start again. You can also perform the same phase several times in a row (possibly leaving time between two test phases). Any variant can be considered here.

It is also possible to envisage a variant of phase PH 2 in which the injection rail 16 is tested by letting fuel out of it without letting any in. In this variant, instead of activating an injector 20 to inject fuel into an associated combustion chamber, one could open the decompression valve 24. Here too, a pressure drop (negative pressure gradient) is expected but it is more difficult to quantify this pressure drop.

Each test, or phase, is for example carried out during an engine time. For a four-cylinder, four-stroke engine, this corresponds to a 180° rotation of the engine crankshaft, ie 180°CRK. Such a duration makes it possible to carry out a test which, on the one hand, is long enough to allow a significant recording of the pressure variation in the injection rail 16 and, on the other hand, not to be felt when driving the vehicle. Given that an injection is planned, it is reasonable to carry out three phases PH 1, PH 2 and PH 3 one after the other without having any feeling when driving the vehicle.

Once the various tests have been carried out, a diagnosis must be made.

As an illustrative example, some pressure variations are shown in the figures. It has been assumed here each time that a first phase PH 1, a second phase PH 2 and a third phase PH 3 are carried out one after the other.

Figure 3 illustrates the pressure variation in the injection rail 16 when everything is in order. We thus notice that there is no pressure variation during the PH 1 phase (schematized by Ø), that the pressure decreases (negative gradient or Grad < 0) during the second phase (PH 2) and that the pressure increases (positive gradient or else Grad > 0) during the third phase (PH 3).

Figure 4 shows a pressure curve of an injection system that is no longer tight. This is visible in particular during the PH 1 phase where a pressure variation is clearly observed with a negative pressure gradient (Grad < 0) but also during the second PH 2 phase where the pressure gradient is more pronounced. In the third phase PH 3, we also notice that after a significant increase in pressure, a pressure drop begins.

Figure 5 illustrates a pressure variation when there is a fuel injection misfire. Here, during the second phase PH 2, no fuel comes out of the injection rail 16. The pressure inside the latter thus remains constant.

Figure 6 illustrates a malfunction of the high pressure pump 6. Here, the tests during the first phase PH 1 and the second phase PH 2 happen as explained in Figure 3 but during the last test, during the phase PH 3, the pressure in the injection rail 16 no longer increases and remains at its level at the end of the second phase PH 2.

Figure 7 illustrates the particular case of a pressure remaining constant during the three tests carried out. In such a case, either many components have failed or the pressure sensor itself is not working. It is this last hypothesis that is retained because it is more likely than a simultaneous failure of several components.

Figure 8 is a simplified table of the main diagnoses that can be made based on the pressure measurements made during the tests of three different types that are carried out during the first phase, the second phase and the third phase described above.

The diagnostic method (FIG. 2) provides for comparing the pressure results obtained with the table of FIG. 8 at step 200, once the measurements have been carried out during at least one phase PH 1, one phase PH 2 and a PH 3 phase.

The table in figure 8 shows the scenarios presented in figures 4 to 7. In this table, Ø means that there is no pressure variation measured during the phase concerned (or a pressure variation less at a predetermined threshold), grad < 0 means that a pressure variation is detected going in the direction of a decrease in pressure with a (derived) variation greater at least locally and/or globally during the test at a threshold predetermined while grad>0 means that a pressure variation is detected going in the direction of an increase in pressure with a variation (derivative) greater at least locally and/or globally during the test than a predetermined threshold.

In this table :
- PB1 corresponds to a leak at the level of the injection rail;
- PB2 corresponds to a failure at the level of the injection;
- PB3 corresponds to a malfunction of the high pressure pump and
- PB4 corresponds to a failure of the high pressure sensor (measuring the pressure in the injection rail).

The method of FIG. 2 provides for a final step 300 which is the action to be carried out according to the diagnosis carried out in step 200. It is possible, for example, to envisage operation in degraded mode in the event of failure of the high pressure pump.

This technical solution and its mentioned variants can be applied to carry out the diagnosis of a malfunction which has been observed in an injection system.

The solution proposed here has the advantage of being a software solution which makes it possible to pinpoint the cause of a malfunction, which may also be a failure of the injection rail pressure sensor.

Performing a diagnosis while the vehicle is running provides an immediate diagnosis that can be saved. Indeed, some breakdowns may not recur when the vehicle is checked on the test bench and/or in after-sales service.

Another advantage of carrying out a diagnosis while the vehicle is running is that it is possible to react immediately, without waiting for a visit to the after-sales service. Thus, for example, if a failure of a high pressure sensor is diagnosed, i.e. the pressure in the injection rail is no longer detected, if no action is taken, the high pressure pump is based on erroneous information and there is a strong risk of creating a significant overpressure in the injection rail which could cause the rupture of components in the high pressure system. Once the diagnosis is made, it is possible to act (software) to avoid damage due to overpressure in the injection rail.

We also note that the actions taken to carry out the tests do not endanger the injection system. During phases PH 1 and PH 2, the pressure cannot theoretically increase in the injection rail. There is therefore no risk of overpressure. During the PH 3 phase, a pressure increase is created but it is limited in time and preferably follows a phase during which the pressure in the injection rail has decreased. The risk of overpressure during this third phase PH 3 is therefore very limited.

This disclosure is not limited to the exemplary embodiments described and the variants mentioned above, solely by way of example, but it encompasses all the variants that those skilled in the art may consider within the framework of the protection sought. .

2 tank

4 low pressure pump

6 high pressure pump

60 room

62 second filter

64 inlet valve

66 piston/cylinder assembly

68 outlet valve

8 first filter

10 temperature sensor

12 pressure sensor

14 engine control unit

16 fuel rail

18 calibrated orifice

20 injector

22 high pressure sensor

24 decompression valve

100 step

200 step

300 final stage

Claims (10)

Method for diagnosing an injection system associated with an electronic engine control unit (14) comprising:
- an injection rail (16) supplying at least one injector (20) and equipped with a pressure sensor (22), and
- a so-called high-pressure pump (6) for supplying the injection rail (16) with fuel,
characterized in that it comprises the following three steps in any order after detection of an operating fault of the injection system:
- a) isolation of the injection rail (16), that is to say without any fuel inlet or outlet, and determination of any pressure variation in the injection rail (16) by means in particular its pressure sensor (22),
- b) fuel outlet from the injection rail (16) but without supplying the injection rail (16) with fuel and determination of any pressure variation in the injection rail (16) by means in particular of its pressure sensor (22),
- c) fuel entering the injection rail (16) but without letting fuel out of the injection rail (16) and determining any pressure variation in the injection rail (16) by means of in particular its pressure sensor (22), and
- d) a fourth step of determining a diagnosis according to the pressure variations observed during the three preceding steps according to predetermined diagrams. Diagnostic method according to Claim 1, characterized in that each of the three steps is carried out over one engine stroke. Diagnostic method according to one of Claims 1 or 2, characterized in that steps a), b) and c) are carried out in this order. Diagnostic method according to one of Claims 1 to 3, characterized in that the three steps a), b) and c) are carried out one after the other, preferably in this order. Diagnostic method according to one of Claims 1 to 4, characterized in that a failure of the pressure sensor (22) of the injection rail (16) is diagnosed if no pressure variation is detected during each of steps a), b) and c). Diagnostic method according to one of Claims 1 to 5, characterized in that a fuel leak at the level of the injection rail (16) is diagnosed if both:
- a pressure drop is measured in step a),
- a pressure drop is measured in step b), and
- a pressure increase is measured in step c). Diagnostic method according to one of Claims 1 to 6, characterized in that an injection misfire is diagnosed if both:
- no pressure variation is measured in step a),
- no pressure variation is measured in step b), and
- a pressure increase is measured in step c). Diagnostic method according to one of Claims 1 to 7, characterized in that a malfunction of the high-pressure pump (6) is diagnosed if both:
- no pressure variation is measured in step a),
- a pressure drop is measured in step b), and
- no pressure variation is measured in step c). Computer program product comprising instructions for implementing the diagnostic method according to one of Claims 1 to 8 when this program is executed by a processor. Non-transitory recording medium readable by a computer on which is recorded a program for implementing the diagnostic method according to one of Claims 1 to 8 when this program is executed by a processor.