FUNCTIONAL MONITORING OF SOLENOID VALVES FOR FUEL INJECTION SYSTEMS

Description

[0001] The present invention relates to the operation of solenoid valves for fuels in fuel injection systems, especially in the field of large engines. State of the art

[0002] In injection systems for engines powered by gaseous fuel, the fuel is typically metered using electromagnetically actuated gas valves. When the electromagnet is energized, a valve disc assembly is moved against a restoring force exerted by one or more springs, opening one or more flow ports. To close the valve, the current is switched off. The valve disc assembly is then pressed back onto the stationary valve seat, thus closing the valve. This is therefore a so-called "normally closed" valve, which is closed in the de-energized state and ideally completely leak-tight. Such valves are known, for example, from DE 10 2013 212 191 A1.

[0003] The service life of such a valve is typically several hundred million load cycles. The main reason for its failure is an undesirable and uncontrolled increase in the amount of fuel injected due to wear, caused by two effects: Firstly, wear reduces the residual air gap, thus extending the shut-off time. Secondly, wear increases the valve lift, thereby reducing the flow resistance of the valve. Another reason for the end of a valve's service life can be leakage to the intake manifold of the fuel injection system, caused by wear in the area of ​​the sealing surfaces between the valve seat and the valve head.

[0004] DE 10 2014 220 795 A1 discloses a method for operating a solenoid valve injector, in which premature closing due to wear is detected from the voltage signal of the electromagnet and compensated for by increasing the control current for the electromagnet. GB 2 534 201 A discloses a method for determining the service life of valve assemblies, in which a time parameter of the valves is determined and compared with a limit value. EP 2 915 985 A1 discloses a method for the electrical monitoring of gas valves, with which functionality can be assessed and, if necessary, corrective action can be taken. DE 10 2008 041 528 A1 discloses a method for controlling a fuel injection device, in which electrical operating parameters are evaluated to detect a possible malfunction.DE 10 2013 211 464 A1 further discloses a method for operating an injection valve, in which it is checked whether a malfunction exists. DE 10 2015 104011 A1 discloses another method for determining the opening duration of a solenoid valve and compensating for a deviation from a desired opening duration. Disclosure of the invention

[0005] Within the scope of the invention, a method for operating a solenoid valve for metering fuel in a fuel injection system has been developed. The solenoid valve can be actuated by an electromagnet against a restoring force. The individual method steps according to the invention are carried out in accordance with the attached claims.

[0006] By maintaining complete control over the valve opening duration (TT), and in particular by recording the opening time (t ON), it is possible to prevent the injection of an excessive amount of fuel. This could lead to engine knocking. While in passenger car engines it is sufficient to detect an exceedance of the knock limit with a knock sensor and immediately counteract it, in large engines, such as those used for power generation or as main or auxiliary power units on ships, any exceedance of the knock limit must be strictly avoided. The large engine "remembers" the mechanical stress caused by each knocking event, and due to its significantly longer lifespan compared to passenger car engines, there is a high probability that this "record" will eventually be reached, leading to the engine failing without warning.Since the use of large engines is generally a profitable business, such failures are very costly and can also be dangerous, for example, if a ship becomes unmaneuverable. According to the invention, a difference between the actual opening time TT and the respective reference value TR is compensated and / or regulated by changing the current-time profile u(t) and / or the voltage-time profile i(t) applied to the electromagnet. Furthermore, recorded values ​​of the opening time TT are archived. An estimate of the remaining service life of the solenoid valve is then calculated from the archived values. In this way, the user can, for example, obtain information as to whether the solenoid valve needs to be replaced at the current service appointment or whether it can remain on the engine until the next service.

[0007] The measures implemented according to the invention thus make the operation of large gas-powered engines particularly safer. By closely monitoring the condition of the solenoid valves, it is no longer necessary to replace them preventively after fixed operating hour intervals. Instead, maintenance can be condition-based, thereby reducing the costs of both maintenance and downtime.

[0008] Alternatively, or in combination with measurements via I(t) and / or U(t), the opening time TT of the solenoid valve can also be measured, for example, with an accelerometer or structure-borne sound sensor that registers the impact of the armature in its end position. The existing sensors in the engine control unit can be used to measure I(t) and U(t). However, additional sensors can also be used, such as a Hall sensor, which can monitor the magnetic field of the electromagnet and thus I(t). In general, all sensors and measurement principles that allow direct or indirect conclusions to be drawn about the valve state and / or valve behavior can be used.

[0009] Once a wear-related change in the actual opening time TT is detected, it can be compensated for within certain limits by modifying the control of the solenoid valve. The valve then behaves almost like a new valve and can be used for a correspondingly longer period.

[0010] In a particularly advantageous embodiment of the invention, a wear degree W of the solenoid valve is additionally evaluated from the time-dependent values ​​I(t) and / or U(t). The inventors have recognized that any wear that significantly affects the mass flow rate dm / dt also affects the armature movement of the solenoid valve. This influence on the armature movement, in turn, generates characteristic current and voltage signals in the magnetic circuit, which can be measured.

[0011] Particularly advantageous is the retrieval of the wear degree W, corresponding to the time-dependent values ​​I(t) and / or U(t), from a calibration database. Such a calibration database, which could be, for example, a table of values ​​or a characteristic curve, can be determined in advance using one or more test valves of the same type during a wear test on a test bench. This wear test can, in particular, be a compression test. During this test, the wear W can be measured periodically, and the extent to which I(t) and U(t) deviate from the valve's new state during opening and / or closing can be recorded.

[0012] In a particularly advantageous embodiment of the invention, the solenoid valve meters the fuel into a suction pipe of the fuel injection system.

[0013] The evaluation, compensation and regulation of wear-related deviations can be performed by the existing engine control unit, but also with additional electronics.

[0014] The invention also relates to a control unit for carrying out a method according to one of the appended claims 1 or 3. According to the invention, the control unit comprises a calibration database which assigns a wear degree W of the solenoid valve to a time profile I(t) of the current I flowing through the electromagnet, and / or to a time profile U(t) of the voltage U applied to the electromagnet.

[0015] Furthermore, the invention relates to a fuel injection system with at least one intake manifold and at least one solenoid valve for metering fuel into the intake manifold. According to the invention, a measuring device for the speed of sound c in the intake manifold is arranged in or on the intake manifold downstream of the solenoid valve. As previously stated, this measuring device comprises at least one vibration generator.

[0016] Since the method can utilize all sensors already present on the engine and / or in the control unit, it can be largely or even completely implemented by a software modification of the processes in the control unit. Such software is a marketable product in its own right. The invention therefore also relates to a computer program product with machine-readable instructions which, when executed on a computer and / or on a control unit, cause the computer and / or the control unit to execute a method according to the invention and / or upgrade to a control unit according to the invention.

[0017] Furthermore, the calibration database used to determine wear also constitutes a product that can be sold together with the software for carrying out the method or independently. The invention therefore also relates to a computer program product with a calibration database for a solenoid valve that can be actuated by an electromagnet against a restoring force. The calibration database assigns a wear degree W of the solenoid valve to a time profile I(t) of the current I flowing through the electromagnet, and / or to a time profile U(t) of the voltage U applied to the electromagnet.

[0018] Further measures improving the invention are described in more detail below, together with a description of preferred embodiments of the invention, with reference to figures. Examples of implementation

[0019] It shows: Figure 1 Exemplary embodiment of method 100 according to the invention; Figure 2 Exemplary embodiment of the fuel injection system 3 according to the invention; Figure 3 Exemplary time profiles u(t) of the voltage at electromagnet 11, I(t) of the current response of electromagnet 11 and h(t) of the stroke of solenoid valve 1.

[0020] After Figure 1 In parallel steps 110, 120, and / or 130, the actual opening time TT, the mass flow rate dm / dt, and / or the leakage dm' / dt of solenoid valve 1 are determined. In steps 140, 142, and 144, respectively, it is checked whether TT corresponds to the reference value TR, whether dm / dt corresponds to the reference value MR, and whether the leakage dm' / dt = 0. If this is the case (truth value 1), the process branches back to the respective measurement 110, 120, or 130.

[0021] If, however, a deviation is present (truth value 0), then in the same step 150 for all three quantities TT, dm / dt and dm' / dt, it is first checked whether a serious malfunction is present.

[0022] In the event of a serious malfunction (truth value 1), an emergency stop of the motor is initiated in step 160. Otherwise (truth value 0), steps 170 and 180 check whether the opening time TT can be compensated for or adjusted by changing the control signal of solenoid valve 1. If this is possible (truth value 1), the appropriate measures are taken in steps 200 and 210; solenoid valve 1 is controlled with the appropriate voltage signal u(t) and / or the appropriate current signal i(t). A key parameter here is the duration of current flow to the electromagnet 11. If compensation or adjustment is not possible (truth value 0), the user is informed in step 190 that maintenance is required.

[0023] A leakage dm' / dt cannot be compensated for by changing the control of solenoid valve 1. Therefore, any leakage that does not represent a serious malfunction is only checked to see if it exceeds a predefined threshold value T HR. If this is the case (truth value 1), the user is informed about the required maintenance in step 190. If, however, the threshold value T HR is not exceeded (truth value 0), the process returns to determining the leakage in step 130.

[0024] Instead of the quantities TT, dm / dt and dm' / dt, the respective raw data from which these quantities were determined, i.e., parameters of the time profiles I(t) and U(t), can also be directly compared with corresponding reference values.

[0025] Figure 2Figure 1 schematically shows an embodiment of an injection system 3 for fuel 2 according to the invention. Air 30 is drawn in via the intake manifold 31. To mix the air 30 with the fuel 2, the fuel 2 is metered through the solenoid valve 1. The solenoid valve 1 can be actuated by an electromagnet 11 against a restoring force exerted by a valve spring 12.

[0026] The control unit 5 applies a voltage following a time program u(t) and / or a current following a time program i(t) to the electromagnet 11. Simultaneously, the control unit measures the time profile U(t) of the actual voltage U applied to the electromagnet 11 and / or the time profile I(t) of the actual current I flowing through the electromagnet 11. The control unit 5 contains a calibration database 4 from which it retrieves the wear degree W of the solenoid valve 1 corresponding to the time profile I(t) and / or U(t).

[0027] 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 point where the solenoid valve 1 meters the fuel 2 into the intake manifold 31. For this purpose, 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 can be determined from the phase shift between the emitted and the received ultrasound wave. The evaluation unit 36, which together with the transmitter 34 and the receiver 35 forms the measuring device 33, determines the desired gas composition 32 from the speed of sound c. The control unit 5 then uses this to determine the desired leakage dm' / dt.

[0028] Figure 3 Figure 1 shows, by way of example, the time courses u(t) of the voltage applied to the electromagnet 11, I(t) of the current driven by the electromagnet 11 and h(t) of the stroke of the solenoid valve 1 during an injection cycle.

[0029] To open solenoid valve 1, a high boost voltage UB is initially applied in a boost phase B, causing the current I to rise rapidly to the boost current IB. Subsequently, in a pull-in phase P, the voltage is modulated as a square wave between zero and UB, so that the current I fluctuates around a time-averaged value IP. During the pull-in phase P, solenoid valve 1 opens; the stroke h(t) increases rapidly and eventually reaches its maximum level.

[0030] At a point when the solenoid valve 1 is fully open, the electromagnet 11 is briefly switched to a free-running phase F, in which no voltage is applied to it. During this phase, the current I decays to a holding current level IH.

[0031] To keep the solenoid valve 1 open, the voltage u(t) applied to the electromagnet 11 is again modulated between zero and UB during the holding phase H, but with a reduced ratio between on-time and off-time. Accordingly, the current I(t) now fluctuates around the lower time-averaged value IH.

[0032] To close solenoid valve 1 at the end of the injection cycle, a quenching voltage pulse with reversed polarity is applied to electromagnet 11 during the quenching phase L. This rapidly dissipates the energy in the magnetic circuit of solenoid valve 1. As a result, the restoring force of the valve spring 12 becomes dominant, and the stroke h(t) of solenoid valve 1 decreases until the solenoid valve 1 is finally completely closed.

Claims

1. Method (100) for operating a solenoid valve (1) for metering a fuel (2) in a fuel injection system (3), wherein the solenoid valve is able to be actuated counter to a return force (12) by an electromagnet (11), characterized in that upon at least one opening of the solenoid valve (1), the temporal profile I(t) of the current I flowing through the electromagnet (11) and / or the temporal profile U(t) of the voltage U applied to the electromagnet (11) are / is recorded, and, from the temporal profile I(t) and / or U(t), the opening time tON and the closure time tOFF of the solenoid valve (1) are evaluated (110), and the actual opening duration TT=tOFF-tON of the solenoid valve (1) is compared (140) with a reference value TR, and a difference between the actual opening duration TT and the reference value TR is compensated for and / or corrected (200, 210) by changing the current temporal profile I(t) applied to the electromagnet (11) and / or the voltage temporal profile U(t) applied to the electromagnet (11), wherein recorded values of the opening duration TT are archived and an estimation of the remaining lifetime of the solenoid valve (1) is evaluated from the archived values.

2. Method (100) according to Claim 1, characterized in that a degree of wear W of the solenoid valve (1) is additionally evaluated from the temporal profile I(t) and / or U(t).

3. Method (100) according to Claim 2, characterized in that the degree of wear W corresponding to the temporal profile I(t) and / or U(t) is retrieved from a calibration database (4).

4. Controller (5) for carrying out a method according to Claim 1 or 3, characterized in that the controller comprises a calibration database (4) that assigns a degree of wear W of the solenoid valve (1) to a temporal profile I(t) of the current I flowing through the electromagnet (11) and / or to a temporal profile U(t) of the voltage U applied to the electromagnet (11).

5. Computer program product containing machine-readable instructions that, when they are executed on a controller (5) according to Claim 4, cause the controller (5) to execute a method according to one of Claims 1 to 3.