MONITORING THE FUNCTION OF SOLENOID VALVES FOR FUEL INJECTION SYSTEMS

Abstract

The invention relates to a method (100) for operating a solenoid valve (1) for metering a fuel (2) in a fuel injection system (3). The solenoid valve can be actuated against a restoring force (12) by an electromagnet (11), wherein the time curve l(t) of the current I flowing through the electromagnet (11) and/or the time curve U(t) of the voltage U applied to the electromagnet (11) are detected during at least one opening process of the solenoid valve (1). The opening time t.sub.ON and the closing time t.sub.OFF of the solenoid valve (1) are evaluated (110) from the time curve I(t) and/or U(t), and the actual opening duration T.sub.T=t.sub.OFFt.sub.ON of the solenoid valve (1) is compared (140) with a reference value T.sub.R and/or the mass flow dm/dt flowing through the solenoid valve (1) is detected (120) and compared (142) with a reference value M.sub.R during at least one opening process of the solenoid valve (1); and/or a leakage dm/dt of fuel (2) through the solenoid valve (1) is detected (130) in the closed state of the solenoid valve (1). The invention also relates to a corresponding controller (5), a fuel injection system (3), and a computer program product.

Claims

1. A method (100) for operating a solenoid valve (1) for metering a fuel (2) in a fuel injection system (3), wherein the solenoid valve is configured to be actuated counter to a return force (12) by an electromagnet (11), characterized in that the method comprising: detecting, at at least one opening of the solenoid valve (1), either or both of a temporal profile I(t) of a current I flowing through the electromagnet (11) and a temporal profile U(t) of a voltage U applied to the electromagnet (11); evaluating, from either or both of the temporal profile I(t) and the temporal profile U(t), an opening time tON and a closure time tOFF of the solenoid valve (1); comparing an actual opening duration TT=tOFFtON of the solenoid valve (1).

2. The method (100) as claimed in claim 1, the method further comprising evaluating a degree of wear W of the solenoid valve (1), which influences a mass flow dm/dt through the solenoid valve (1), from either or both of the temporal profile I(t) and the temporal profile U(t).

3. The method (100) as claimed in claim 2, wherein the degree of wear W is retrieved from a calibration database (4).

4. The method (100) as claimed in claim 1, the method further comprising compensating or correcting a difference in the actual opening duration TT with respect to the reference value TR by changing the voltage temporal profile u(t) applied to the electromagnet (11) or the current temporal profile i(t) applied to the electromagnet (11).

5. The method (100) as claimed in claim 1, wherein the solenoid valve (1) meters fuel (2) into an intake manifold (31) of the fuel injection system (3) and a leakage dm/dt of fuel (2) passing through the solenoid valve (1) is detected by measuring a gas composition (32) in the intake manifold (31).

6. The method (100) as claimed in claim 5, wherein the gas composition (32) is measured by measuring a speed of sound c in the intake manifold (31).

7. The method (100) as claimed in claim 1, the method further comprising evaluating an estimation of the remaining lifetime of the solenoid valve (1) from archived detected values of the opening duration TT.

8. A controller (5) for operating a solenoid valve (1) that is configured to be actuated counter to a return force (12) by an electromagnet (11), the controller comprising a calibration database (4) configured to assign a degree of wear W of the solenoid valve (1) to either or both of a temporal profile I(t) of a current I flowing through the electromagnet (11) and to a temporal profile U(t) of a voltage U applied to the electromagnet (11).

9. A fuel injection system (3) comprising at least one intake manifold (31); and at least one solenoid valve (1) for metering fuel (2) into the intake manifold (31), wherein a measurement apparatus (33) for measuring a speed of sound c in the intake manifold (31) is arranged in or on the intake manifold (31), downstream of the solenoid valve (1).

10. The fuel injection system (3) as claimed in claim 9, wherein the measurement apparatus (33) comprises at least one oscillation generator (34).

11. A non-transitory computer-readable medium storing instructions that, when executed by a processor of a computer, cause the computer to perform the method as claimed in claim 1.

12. The method (100) as claimed in claim 1 further comprising detecting, at at least one opening of the solenoid valve (1), a mass flow dm/dt through the solenoid valve (1) and comparing the mass flow dm/dt with a reference value MR.

13. The method (100) as claimed in claim 12, the method further comprising compensating or correcting a difference in the mass flow dm/dt with respect to the reference value MR by changing the voltage temporal profile u(t) applied to the electromagnet (11) or the current temporal profile i(t) applied to the electromagnet (11).

14. The method (100) as claimed in claim 12, the method further comprising evaluating an estimation of the remaining lifetime of the solenoid valve (1) from archived detected values of the mass flow dm/dt.

15. The method (100) as claimed in claim 1 further comprising detecting, in a closed state of the solenoid valve (1), a leakage dm/dt of fuel (2) passing through the solenoid valve (1).

16. The method (100) as claimed in claim 15, the method further comprising evaluating an estimation of the remaining lifetime of the solenoid valve (1) from archived detected values of the leakage dm/dt.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Further measures that improve the invention are illustrated in more detail below, with reference to figures, together with the description of the preferred exemplary embodiments of the invention.

[0028] FIG. 1 shows an exemplary embodiment of the method 100 according to the invention;

[0029] FIG. 2 shows an exemplary embodiment of the fuel injection system 3 according to the invention;

[0030] FIG. 3 shows exemplary temporal profiles u(t) of the voltage at the electromagnet 11, I(t) of the current response of the electromagnet 11 and h(t) of the stroke of the solenoid valve 1.

DETAILED DESCRIPTION

[0031] In FIG. 1, the actual opening duration T.sub.T, the mass flow dm/dt and/or the leakage dm/dt of the solenoid valve 1 are determined in parallel steps 110, 120 and/or 130. In steps 140, 142 and 144, it is respectively checked whether T.sub.T corresponds to the reference value T.sub.R, whether dm/dt corresponds to the reference value M.sub.R, and whether the leakage dm/dt=0. If this is the case (truth value 1), there is branching back to the respective measurement 110, 120 or 130.

[0032] By contrast, if there is a deviation (truth value 0), then it is initially checked in step 150, which is identical for all three variables T.sub.T, dm/dt and dm/dt, whether there is a severe malfunction.

[0033] In the event of a severe malfunction (truth value 1), an emergency stop of the engine is prompted in step 160. Otherwise (truth value 0), it is checked in steps 170 and 180 whether the opening time T.sub.T, respectively the mass flow dm/dt, is able to be compensated or corrected by changing the driving of the solenoid valve 1. If this is possible (truth value 1), the appropriate measures are taken in steps 200 and 210; the solenoid valve 1 is driven by way of the appropriate voltage signal u(t) and/or the appropriate current signal i(t). A significant decisive factor is in this case the energization duration of the electromagnet 11. If compensation or correction is not possible (truth value 0), the user is informed in step 190 that maintenance is necessary.

[0034] A leakage dm/dt is fundamentally not able to be compensated by changed driving of the solenoid valve 1. Therefore, a possible leakage that does not constitute a severe malfunction is merely investigated so as to determine whether it is greater than a predefined threshold value THR. If this is the case (truth value 1), the user is informed that maintenance is due in step 190. By contrast, if the threshold value THR is not exceeded (truth value 0), there is branching back to the determination of the leakage in step 130.

[0035] Instead of the variables T.sub.T, dm/dt and dm/dt, the respective raw data from which these variables were determined, that is to say for example characteristic variables of the temporal profiles I(t) and U(t), may also be compared directly with corresponding reference values.

[0036] FIG. 2 schematically shows one exemplary embodiment of an injection system 3 for fuel 2 according to the invention. Air 30 is taken in through the intake manifold 31. To mix the air 30 thoroughly with fuel 2, the fuel 2 is metered in through the solenoid valve 1. The solenoid valve 1 is able to be actuated counter to a return force, which is exerted by a valve spring 12, by an electromagnet 11.

[0037] The controller 5 applies, to the electromagnet 11, a voltage that follows a temporal program u(t), and/or a current that follows a temporal program i(t). At the same time, the controller measures the temporal profile U(t) of the voltage U actually applied to the electromagnet 11 and/or the temporal profile I(t) of the current I actually flowing through the electromagnet 11. The controller 5 contains a calibration database 4 from which it retrieves the degree of wear W of the solenoid valve 1 that corresponds to the temporal profile I(t) and/or U(t).

[0038] To measure the leakage dm/dt of the solenoid valve 1 in the closed state, the gas composition 32 in the intake manifold 31 is measured downstream of the site at which the solenoid valve 1 meters the fuel 2 into the intake manifold 31. To this end, a transmitter 34 and a receiver 35 for ultrasound are arranged in the intake manifold 31. The speed of sound c in the intake manifold 31 is able to be determined from the phase difference between the emitted and the received ultrasonic wave. The evaluation unit 36, which, together with the transmitter 34 and the receiver 35, forms the measurement apparatus 33, determines the sought gas composition 32 from the speed of sound c. The controller 5 in turn determines the sought leakage dm/dt from this.

[0039] FIG. 3 shows, by way of example, the temporal profiles u(t) of the voltage applied to the electromagnet 11, I(t) of the current driven through the electromagnet 11 thereby and h(t) of the stroke of the solenoid valve 1 during an injection cycle.

[0040] To open the solenoid valve 1, a high boost voltage U.sub.B is initially applied in a boost phase B, such that the current I quickly increases to the boost current I.sub.B. Next, in a pull-in phase P, the voltage is modulated in the form of a rectangular-wave signal between zero and U.sub.B, such that the current I fluctuates around a temporal average value I.sub.P. The solenoid valve 1 opens in the pull-in phase P; the stroke h(t) increases quickly and ultimately reaches its maximum level.

[0041] At a time at which the solenoid valve 1 is completely open, the electromagnet 11 is briefly switched into a freewheeling phase F in which no voltage is applied thereto. The current I subsides in this phase to a holding current level I.sub.H.

[0042] To keep the solenoid valve 1 open, the voltage u(t) applied to the electromagnet 11 is again modulated between zero and U.sub.B in the holding phase H, but with a reduced ratio between switch-on duration and switch-off duration. The current I(t) accordingly now fluctuates around the lower temporal average value I.sub.H.

[0043] To close the solenoid valve 1 at the end of the injection cycle, an extinguishing voltage pulse with reverse polarity is applied to the electromagnet 11 in the extinguishing phase L. As a result, the energy in the magnetic circuit of the solenoid valve 1 quickly subsides. This in turn means that the return force of the valve spring 12 prevails and the stroke h(t) of the solenoid valve 1 reduces until the solenoid valve 1 is ultimately completely closed.