ITTO930646A1 - METHOD OF DIAGNOSIS OF MALFUNCTIONS OF THE HIGH PRESSURE CIRCUIT OF HIGH PRESSURE INJECTION SYSTEMS FOR INTERNAL COMBUSTION ENGINES - Google Patents

Description

DESCRIPTION

The present invention relates to a method of diagnosing malfunctions of the high pressure circuit of high pressure injection systems for internal combustion engines.

A high-pressure injection system is known comprising, broadly speaking, a fuel tank and a high-pressure injector feed circuit comprising in turn a pump for feeding high-pressure fuel to a fuel manifold. accumulation feeding a plurality? of injectors. The pump ? equipped with a pressure regulating solenoid valve, so as to supply fuel at a predetermined pressure.

In such an injection system? It is essential to continuously check the high pressure circuit, to avoid that the out of calibration of the pressure sensor, the blocking or malfunction of the adjustment organs or of the injectors and leaks in the circuit compromise the functionality? injection system.

The object of the present invention is to provide a method of diagnosing malfunctions capable of highlighting any malfunctions immediately after they have occurred.

According to the present invention, a method of diagnosing malfunctions of the high pressure circuit of high pressure injection systems for internal combustion engines is provided, said circuit including a high pressure pump suitable for supplying fuel at a pressure of a controlled value through cycles. regulation, characterized in that it comprises the steps of monitoring quantities related to the pressure generated by said pump in successive regulation cycles, comparing the trend of said quantities in said successive regulation cycles with reference values and generating fault signals in the event that said trend does not have a predetermined relationship with said reference values.

For a better understanding of the present invention, a preferred embodiment is now described, purely by way of non-limiting example, with reference to the attached drawings, in which:

- figure 1 shows a general diagram of the hydraulic system of an injection system which? applied the diagnosis system according to the invention;

Figure 2 illustrates a detail of the pressure regulator provided in the system of Figure 1;

Figure 3 presents a block diagram relating to the method of the invention;

- figure 4 shows the trend of the maximum and minimum reference pressures as a function of the number of revolutions;

- Figures 5A, 5B and 5C show the pressure and duty-cycle trends following the blocking in the open position of an injector in three different operating conditions; And

- figure 6 presents a diagram relating to the pressure / duty-cycle relationship used in the consistency check.

With reference to figure 1, it will come? now broadly described a high pressure injection system for internal combustion engines. The system, indicated with 1, comprises a tank 2 at atmospheric pressure connected, through a delivery line 5, to a radial piston pump 6. To pump 6? associated with a pressure regulating solenoid valve (or pressure regulator) 7 connected, via a discharge line 8, to the tank 2.

The pump 6 feeds the high pressure fuel to an accumulation manifold 10, through a line 11. The accumulation manifold 10, having the purpose of distributing the fuel to the injectors and damping the pressure oscillations due to the pumping and opening of the injectors,? consisting of a steel body preferably in the shape of a parallelepiped in which? was a cavity obtained? cylindrical extending along the entire length of the manifold itself and connected to the line 11 through a central hole 12. The manifold 10 also has four holes 13 distributed along the entire manifold and connected to four high pressure supply pipes 14 (up to 1500 bar ) for four injectors 15 of an engine 16. Each injector? moreover connected to a recirculation duct 17 for the fuel (used for the operation of the injector) which is discharged into the tank 2.

At one end? of the storage manifold 10? finally, a pressure sensor 18 of a known type is provided.

Conveniently, the pressure regulator 7? realized as shown in Figure 2, and comprises a body 20 defining a conical seat 21 for a spherical shutter 22. The combined force of a spring 24 and a solenoid 25 acts on the latter, through a tip 23, which cooperates with a core 26 integral with a rod 27 which in turn is integral with the tip 23. The shutter 22 separates an inlet duct 28, connected to the pump body 6, to a discharge duct 29, connected to the line 8. Varying the current fed to solenoid 25? It is possible to modulate the force exerted on the spherical obturator 22 in the closing direction and therefore the pressure on the pump outlet 6.

The pressure modulation is obtained by supplying the solenoid 25 with a current whose duty-cycle is modulated at a fixed oscillation frequency (PWM-Pulse Width Modulation technique) and by using a closed regulation loop which takes into account the actual pressure, measured through the pressure sensor 18 and the desired pressure value.

The method according to the invention has the purpose of periodically checking the functionality? of the elements of the plant 1, and precisely to verify: capacity? of the pump 6 to generate the required pressure; correct tightness of regulator 7; absence of leaks on the circuit; presence of injectors blocked open; correct operation of the electric control circuit of the regulator 7; sensitivity and functionality? pressure sensor 18.

According to a preferred embodiment example, schematically represented in Figure 3, four tests are periodically carried out: test on the maximum pressure measured (block 30); test on minimum measured pressure (block 31); pressure regulator command duty-cycle test (block 32); and test on congruence between measured pressure and duty-cycle (block 33).

In detail, the maximum measured pressure test (block 30) consists in verifying that the pressure measured by the sensor 18 in the manifold 10 does not exceed a maximum admissible value, for example of 1600 bar, which can be calibrated from the outside, in a predetermined number of checks. consecutive (for example five). Exceeding the maximum admissible value (represented by line A in figure 4)? index of the following types of faults: sensor 18 out of order (measurement error) p regulator 7 blocked closed (fault in the regulator which prevents or excessively reduces the flow of fuel under pressure from duct 28 to duct 29 of regulator 7).

The minimum measured pressure test (block 31) consists in checking that the measured pressure is not lower than a minimum admissible value in a predetermined number of consecutive checks, for example five. The minimum admissible value varies according to the engine speed, as shown by curve B in figure 4. The measurement of a pressure value lower than the admissible value? index of the following types of faults: an injector blocked open; faulty pump (does not guarantee the necessary flow rate); losses in the circuit due to leaks; sensor out of order. In particular, it is emphasized that the growth of the minimum permissible value with the engine speed? important to recognize the presence of an open blocked injector; in fact, at high revs, even when an injector? locked open, the pressure can? do not go below values that are acceptable and correspond to a condition of good operation in the case of low engine speed.

The pressure regulator command duty-cycle test (block 32) consists in verifying that the dutycycle (measured as a percentage) does not exceed a predetermined maximum value K2 (for example 97%) or is not less than a minimum predetermined value K1 (e.g. 2%) in a predetermined number of consecutive checks (e.g. five for the maximum value and 25 for the minimum value). In fact, the repeated exceeding of the maximum duty-cycle value? linked to the fact that the pressure measured during this period? always lower than the reference value foreseen by the regulator control system and? index of the same type of faults indicated for the test on the minimum value, as well as, possibly, the malfunctioning of the duty-cycle regulation electrical circuit. Conversely, should the duty-cycle remain at a very low value? linked to the fact that the measured pressure is maintained for a long time at a value higher than the reference value foreseen by the regulator control system and? index of sensor out of calibration 18 or excessive tightness of regulator 7.

Three examples of faults due to the locking in the open position of an injector are shown in figures 5A, 5B and 5C, relating to the pressure trend (with dashed line) and to the duty-cycle (with solid line) in three different conditions, following the blocking of an injector in correspondence with cycle 2 of the engine. Specifically, Figure 5A? relating to high pressure operation; in this case the fault is detected due to the permanence of the duty-cycle over the pre-established limit for pi? times. Figure 5B? relating to a condition of average pressure; also in this case the fault is detected based on the excessive value of the duty-cycle, even if pi? slowly of the case of figure 5A. Figure 5C? relating to a low pressure condition; in this case the fault is detected due to the detection of a too low pressure value for a certain number of times.

The test on congruence between measured pressure and dutycycle (block 33) exploits the link between the duty-cycle (or, more precisely, the effective current fed to the regulator 7) and the pressure measured in the manifold 10. This link? which can be represented by the curve C of figure 6 expressed as reference pressure PR as a function of the effective current. Curve C? variable within certain limits depending on the regulator used. To take this variability into account, an upper and lower tolerance value T is associated with the reference value PR (eg 300 bar), so that two curves DI and D2 are obtained which delimit an admissibility band.

The congruence test therefore consists in determining the duty-cycle value of the supply current of the solenoid valve 7 according to the algorithms provided, conveniently of the proportional-integral type, as a function of the actual pressure measured and the desired pressure (the latter calculated in the ways envisaged, for example on the basis of engine parameters, as described in another patent application in the name of the applicant). Then, by means of a map, the reference value PR corresponding to the determined duty-cycle (as per curve C) is determined and it is checked whether the pressure value measured by the sensor 18 corresponds to this reference value PR within the expected tolerance (i.e. ? if the measured pressure value falls within the expected tolerance band). The fault condition that causes the measurement of pressure values outside the range foreseen in a certain number of consecutive checks? essentially the unbalance of the sensor 18; in fact, other types of faults are generally previously detected by the other checks, since this type of test? slow type.

The negative outcome of any one of the four checks described (as exemplified in Figure 3 by the OR gate 35) leads to the generation of a fault signal and the stopping of the motor (block 36).

With the method described? therefore it is possible to highlight malfunctioning conditions of the hydraulic circuit, otherwise not detectable, such as the locking in the open position of one of the injectors, in a simple and reliable way, discriminating any extraneous factors not linked to faults that may involve a transient variation of the control values of the circuit itself.

Finally, it is clear that modifications and variations can be made to the method described and illustrated here without thereby departing from the protective scope of the present invention.

Claims (8)

CLAIMS 1. Method for diagnosing malfunctions of the high pressure circuit of high pressure injection systems for internal combustion engines, said circuit including a high pressure pump (6) suitable for supplying fuel at a pressure of a controlled value through regulation cycles , characterized in that it comprises the steps of monitoring quantities related to the pressure generated by said high pressure pump (6) in successive regulation cycles, comparing the trend of said quantities in said successive regulation cycles with reference values and generating signals failure in the event that said trend does not have a predetermined relationship with said reference values. 2. Method according to claim 1, characterized by measuring the pressure supplied by said high pressure pump (6) to a manifold (10), comparing said measured pressure with a maximum reference value and generating a fault signal if said measured pressure is greater than said maximum value for a predetermined number of consecutive regulation cycles. 3. Method according to claim 1 or 2, characterized by measuring the pressure supplied by said high pressure pump (6) to a manifold (10), comparing said measured pressure with a minimum reference value and generating a fault signal if said measured pressure is lower than said minimum value for a predetermined number of consecutive cycles. 4. Method according to claim 3, characterized in that said minimum reference value? variable according to the engine speed (16). Method according to any one of the preceding claims, wherein said adjustment cycles comprise the step of varying the duty-cycle of a supply current of a pressure adjustment solenoid valve (7) associated with said high-pressure pump characterized in that measure your blood pressure to im entat aa from de tt to pump stop to pressure calculate the uty-cycle of the supply current based on the error between a desired pressure value and said measured pressure, compare said calculated duty-cycle with a minimum value and a maximum reference value and generate a fault signal if said duty-cycle calculated is outside an admissibility band? delimited by said minimum and maximum values for a predetermined number of consecutive regulation cycles. Method according to any one of the preceding claims, wherein said adjustment cycles comprise the step of varying the duty-cycle of a supply current of a pressure adjustment solenoid valve (7) associated with said high-pressure pump (6), characterized by measuring the pressure supplied by said high-pressure pump, calculating the duty-cycle of the supply current based on the error between a desired pressure value and said measured pressure, determining a reference pressure value based on said calculated duty-cycle, comparing said measured pressure and said reference pressure value and generating a fault signal if said measured pressure differs from said reference pressure value beyond a predetermined tolerance for a predetermined number of consecutive regulation cycles. 7. Method according to claim 6, characterized in that said step of determining a reference pressure value comprises the reading of said reference pressure value in a map storing pressure values as a function of the duty-cycle. 8. Method for diagnosing malfunctions of the high pressure circuit of high pressure injection systems for internal combustion engines, as described with reference to the attached drawings.