Method and control unit for controlling an injection valve

Abstract

Method for controlling an injection valve (14) with which fuel is metered directly into a combustion chamber (12) of an internal combustion engine (10), wherein the injection valve (14) is controlled with a current (I) when the internal combustion engine (12) is running, which has a first current profile (58) with a booster phase (60) and a holding phase (62), wherein the current (1) in the booster phase (60) is dominated by a contribution from a first charge storage device (36) and in the holding phase (62) is supplied by a second charge storage device (28) without contributions from the first charge storage device (36), characterized in that the injection valve (14) is controlled with a current (I) when the internal combustion engine (10) is started, which has a second current profile (64) without a holding phase (62), and that the fuel for a combustion chamber fill at start-up is supplied by repeatedly controlling the injection valve (14) with the second current profile (64). is injected.

Description

Prior ArtThe invention relates to a method and a control device for controlling an injection valve according to the preambles of the independent claims.Such a method and such a control device are known in each case from the Kraftbuntechnische Taschenbuch, 25th Edition, Friedrich Vieweg & Sohn Verlag, GWV Fachverlage GmbH, Wiesbaden, 2003, ISBN 3-528-23876-3, there pages 616 and 617. According to this reference, the fuel pressures required in direct gasoline injection require special high pressure injection valves to meter and atomize the fuel. The high-pressure injection valve has, inter alia, a coil and a magnet armature which is movable relative to the coil and is connected to a nozzle needle. A current flow in the coil generates a magnetic field that lifts the nozzle needle from a seat and releases an injection cross section via which fuel is metered. When the coil current is switched off, the nozzle needle is pressed onto its seat by a spring force and interrupts the injection process. In the case of inwardly opening needle valves, the fuel pressure assists the closing process. In the opening, the fuel pressure acts against the opening direction, so that the magnetic field strength required for opening the injection cross section and thus the required coil current are also dependent on the fuel pressure.From DE 198 33 830 A1 and EP 1 396 630 A2 a method and a device for controlling at least one solenoid valve, which serves for controlling the injection of fuel into an internal combustion engine, are known. The injection valves are controlled with a current curve which initially contains a tightening or booster phase and later a holding phase. Furthermore, these references show that the current profile is changed depending on operating variables of the internal combustion engine, such as the fuel pressure.EP 1 286 034 A1 likewise describes a method and a device for actuating a solenoid valve. In this device, the duration of the tightening phase is selected in such a way that the solenoid valve reliably reaches its working position.DE 100 14 228 A1 likewise discloses a method and a device for actuating a fuel injection valve. During the activation phase of the solenoid valve, several booster pulses are activated one after the other, the positions of which in time within the activation phase can be freely selected.DE 10 2004 063 079 A1, which is not prepublished, describes a method for operating an internal combustion engine. In this device, in specific operating states in which a high fuel pressure prevails, the system is switched from a standard value to an increased value or a longer duration of the booster current.For opening and maintaining open an internally opening high pressure injection valve in a direct gasoline injection system, a complex first flow profile is used in the prior art. The first current profile has a boost phase in which the high-pressure injection valve is connected to a boost capacitor as the first charge storage device. The booster capacitor has typically been charged to a voltage of 50-90 V before the connection to the coil of the injection valve and supplies a correspondingly high booster current in the booster phase, with which the nozzle needle is quickly raised. When the nozzle needle is raised, a small coil current is sufficient to keep the injection valve open. The lower coil current is generated in the hold phase by connecting the coil to a second charge storage device, which provides a lower voltage. A vehicle battery is an example of a second charge storage. Control of the holding current is effected by clocking the connection to the second charge store.In direct gasoline injection systems, the highest system pressure is limited upward in normal operation by a pressure limiting valve. The limit value of the fuel pressure defined by the pressure limiting valve is typically reached, for example, at a start of a hot internal combustion engine. When the internal combustion engine is shut down, it is at a standstill that the fuel heats up and thus leads to an increase in the fuel pressure in the fuel pressure accumulator as far as the opening of the pressure limiting valve. During the hot start, this leads to an increased current requirement in the boost and hold phase. When the starter is actuated, the vehicle electrical system voltage decreases on account of the high current requirement of the starter in conjunction with the internal resistance of the vehicle battery, which limits the maximum possible holding current in the holding phase.The unfavourable combination of the high fuel pressure, against which the injection valve with an increased holding current demand must be kept open, with the maximum value of the holding current which is reduced by the load on the vehicle battery, can lead to the available maximum value falling below the holding current demand. Then, the injection valve may close too early, which may result in insufficient fuel metering at start-up. As a result, misfire may occur. In extreme cases, it may happen that the internal combustion engine cannot be started.Disclosure of the InventionTechnical TaskAgainst this background, the object of the invention is to improve the starting behavior of an internal combustion engine.Technical SolutionThis object is achieved in a method and a control device of the type mentioned in the introduction in each case by the characterizing features of the associated independent claim in each case.Advantageous EffectsBy omitting the holding phase, that is to say by omitting contributions of the second charge storage device, the current is provided through the first charge storage device during starting and therefore largely independently of the voltage in the on-board power supply system. In one implementation of the first charge storage device as a booster capacitor, the latter provides its current contribution independently of the vehicle electrical system voltage, provided it is only sufficiently charged. In this case, the injection takes place by a booster phase of the second current profile which is longer than the first current profile. If the charge of the booster capacitor is not sufficient for injecting the fuel quantity required for a combustion chamber charge at the start with a single, coherent injection, the fuel can also be injected by multiple actuation of the injection valve with the second current profile. In the pauses between such individual partial injections, the booster capacitor can be recharged again by a charging circuit.Further advantages are evident from the description and the attached figures.It is understood that the features mentioned above and those still to be explained below can be used in each case not only in the specified combination, but also in other combinations or alone, without departing from the scope of the present invention.Brief Description of the DrawingsExemplary embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description. They show, in each case in schematic form: FIG. 1 shows an internal combustion engine as a technical environment of the invention; FIG. 2 shows a circuit diagram of an embodiment of an output stage of a control device together with a vehicle battery and an injection valve from FIG. 1.Embodiment(s) of the InventionFIG. 1 shows an internal combustion engine 10 having a combustion chamber 12 into which fuel is injected by means of an injection valve 14. The injection valve 14 is hydraulically connected to a fuel pressure accumulator 16 and is actuated by a control unit 18 with a control current I. When the control current I is sufficiently high, the injection valve 14 opens an injection cross section via which fuel is injected into the combustion chamber 12 on the fuel pressure accumulator 16. For generating the control current I, the control device 18 processes signals from various sensors, of which a temperature sensor 20, a fuel pressure sensor 22 and a rotational speed sensor 24 are shown in FIG. 1. The temperature sensor 20 detects a temperature T of the internal combustion engine 10, for example, the temperature of a coolant. Fuel pressure sensor 22 detects fuel pressure p in fuel pressure accumulator 16, and rotational speed sensor 24 detects a rotational speed n of a crankshaft or other shaft of internal combustion engine 10.The engine 10 has a starter 26 which is electrically driven. In this case, the electrical energy is taken from a vehicle battery 28, which maintains an on-board power supply voltage even when the internal combustion engine 10 is shut down and therefore when the generator of the internal combustion engine 10 is at a standstill. The starter 26 is switched on by an ignition lock 30, which for this purpose closes a starter switch 32. The vehicle battery 28 also supplies the control device 18 and the output stages accommodated therein with electrical energy.FIG. 2 illustrates the formation of the control current I within the control unit 18. the control unit 18 has, in the embodiment of FIG. 2, an output stage 34 with a booster capacitor 36, a high-side switch 38, a low-side switch 40, a booster switch 42, a first diode 44, a second diode 46 and a charging circuit 48 which has a third diode 50, a charging inductance 52 and a charging switch 54. The boost capacitor 36 represents an embodiment of a first charge storage. The first charge storage device is therefore also denoted by the reference sign 36 below. The output stage 34 is connected to the vehicle battery 28 in the manner shown, which represents a configuration of a second charge storage device. The second charge storage device is therefore also denoted by the reference numeral 28 below. The injection valve 14 is shown in FIG. 2 in simplified form as an inductance.The output stage 34 is controlled by the block 56, which represents the remaining control device functions, such as signal processing and signal processing. In this case, the control of the output stage 34 and thus the shaping of the control current 1 takes place by coordinated actuation of the switches 38, 40, 42 and 54. In a preferred embodiment, the block 56 processes in particular at least one of the signals p, D, n from FIG. 1.In the following, it is briefly explained how the block 56 generates a current profile with a booster phase and / or a holding phase in cooperation with the output stage 34. With switches 38 and 40 closed, a current flows through inductor 14 to the ground of second charge storage 28, the current flow through inductor 14 generating a magnetic field. Opening the low-side switch 40 interrupts the current flow. As a result, the magnetic field collapses, which induces a current in the inductance 14, which current charges the booster capacitor 36 via the diode 46. The boost capacitor 36 is further charged when the switch 54 is opened to interrupt current flow through the charging inductor 52 and through the switch 54 to the ground of the vehicle battery 28. In this case, the current generated by the magnetic field change in the charging inductance 52 charges the booster capacitor 36 via the diode 50.Since voltage peaks occur when the magnetic fields in the inductance 14 or the charging inductance 52 break down, which are greater than the vehicle electrical system voltage provided by the vehicle battery 28, the booster capacitor 36 can be charged to voltages which are substantially greater than the vehicle electrical system voltage. As mentioned at the beginning, typical voltages of a charged booster capacitor 36 in the described application are between 50 and 90 volts with an on-board power supply voltage of typically 12 volts.If the charged booster capacitor 36 is discharged via the diode 44, the inductance 14 and the switch 40 when the switches 42 and 40 are closed, a correspondingly large discharge current I flows, which generates a high magnetic field strength and a high injection valve opening force. The position of the switch 38 is not essential. Due to the high voltage of the booster capacitor 36, the current I through the injection valve inductance 14 in this booster phase is dominated by the contribution of the booster capacitor 36 as the first charge storage. The switch 38 can thus be open or closed.In order to realize a holding phase, in the prior art the booster capacitor 36 is disconnected from the inductance 14 by opening the switch 42 and the switch 38 is closed when the switch 40 is closed. In this case, a lower holding current I flows via the switch 38, the inductance 14 and the switch 40, wherein the current I is driven by the voltage of the vehicle battery 28 as the second charge storage. If the resulting current I is greater than is required for keeping the injection valve 14 open, the temporal mean value of the current intensity of the current I can be reduced by clocked opening and closing of the low-side switch 40. This has the additional advantage that the booster capacitor 36 is recharged via the diode 46 when the switch 40 is open.The result is then a first current profile 58, as is shown in FIG. 3 in qualitative form as a curve of current I over time t. In this case, the time segment 60 corresponds to a boost phase, and the time segment 62 corresponds to a holding phase. This first current profile 58 corresponds to the current profile known from the prior art. Such a holding phase is distinguished in that the current through the inductance 14 is supplied during this holding phase by the second charge storage device 28, i.e. in the embodiment of FIG. 2 by the vehicle battery 28, without contributions from the first charge storage device 36, that is to say from the booster capacitor 36.FIG. 4, on the other hand, shows an embodiment 64 of a second current profile, as is produced in an embodiment of the invention. The configuration 64 of a second current profile differs from the first current profile 58 in that the second current profile 64 does not have a holding phase 62, in which a current is supplied from the vehicle battery as a second charge storage device without contributions from the first charge storage device. Instead, the second current profile 64 has a longer booster phase 66, wherein the extension is produced by a stringing together of individual booster phases 60.1, 60.2, 60.3. In the embodiment 64 of a second current profile, four charging and discharging phases of the booster capacitor 36 have been arranged in series. The sequence is carried out in such a way that the booster switch 42 is opened when an upper current intensity I_o is reached and is closed when a lower current intensity I_u is reached or after a pause time 61.1, 61.2, 61.3 has elapsed, which begins when the booster switch 42 is opened. The value of the lower current intensity I_u and / or the pause time 61.1, 61.2, 61.3 is predetermined in such a way that the magnetic force generated in this case is sufficient to keep the injection valve 14 open.The low-side switch 40 is opened and closed in synchronization with the booster switch 42. When the booster switch 42 is open and the low-side switch 40 is open, the booster capacitor is charged as a first charge storage 36 via the diode 46, the electrical energy originating from the collapsing magnetic field of the injection valve inductance 14. To supplement ohmic losses, the booster capacitor 36 can be charged in parallel in time by the charging circuit 48. In comparison with the first current profile 58 from FIG. 3, the current profile 64 from FIG. 4 is distinguished by the absence of a holding phase in which the current I is dependent on the voltage of the vehicle battery as the second charge storage 28. Instead, the second current profile 64 of FIG. 4 is independent of the vehicle electrical system voltage and the voltage of the vehicle battery 28.If the longer booster phase 66 of the second flow profile 64 is not sufficient to reduce the required fuel quantity, a plurality of second flow profiles 64, 68,... and thus a plurality of injections for a combustion chamber charge can be controlled until the required fuel quantity is reached. Since the current in the booster phase 66 is independent of the battery voltage, the undesirable leaning of the combustion chamber charge does not occur during the hot start. During normal operation with the engine running, the use of multiple boost pulses of the boost phases 60.1, 60.2,... for individual injections is limited in that the time required for recharging the boost capacitor 36 is no longer available at higher rotational speeds because the distance between the injections for different combustion chamber charges decreases with increasing rotational speed. Due to the low rotational speeds at the start, however, this limitation is of no importance in the invention.After the end of the start, which is detected by the control device 18, for example, by evaluating the rotational speed signal n, if n exceeds a threshold value, the second current profile 64 switches over again to the known first current profile 58. This threshold value is also referred to as the end-of-start rotational speed and is a few hundred min -1. Accordingly, alternatively or additionally, the battery voltage or on-board power supply voltage can be evaluated and, upon the rise of the battery voltage or on-board power supply voltage, after the starter / starter 26 has been switched off, the system can be reversed from the second current profile 64 to the first current profile 58. As a further alternative or in addition, the changeover from the second current profile 64 to the first current profile 58 can take place when the injection pressure p falls below a pressure threshold value at the start of a pressure threshold value after it has been reduced by the first injections.

Claims

Method for controlling an injection valve (14), with which fuel is metered directly into a combustion chamber (12) of an internal combustion engine (10), wherein the injection valve (14) is controlled with a current (I) when the internal combustion engine (12) is running, which current profile has a first current profile (58) with a booster phase (60) and a holding phase (62), wherein the current (1) is dominated by a contribution of a first charge store (36) in the booster phase (60) and is supplied by a second charge store (28) without contributions of the first charge store (36) in the holding phase (62), characterized in that the injection valve (14) is controlled with a current (I) when the internal combustion engine (10) is started, which has a second current profile (64) without a holding phase (62) and that the fuel for a combustion chamber charge is injected at the start by the second current profile (64) being activated several times by the injection valve (14).Method according to Claim 1, characterized in that the second current profile (64) has a booster phase (66) which is longer than the first current profile (58).Method according to Claim 2, characterized in that the longer booster phase (66) is generated by a coherent sequence of booster pulses (60.1, 60.2, 60.3).Method according to one of the preceding claims, characterized in that a rotational speed (n) of the internal combustion engine (10) is detected and in that the second current profile (64) is replaced by the first current profile (58) if a starting end rotational speed of the internal combustion engine (10) is exceeded.Method according to one of Claims 1 to 4, characterized in that an injection pressure is detected in a fuel pressure accumulator (16) of the internal combustion engine (10), and in that the second current profile (64) is replaced by the first current profile (58) if an injection pressure (p) falls below a pressure threshold value at the start.Method according to one of Claims 1 to 4, characterized in that a battery voltage of the internal combustion engine (10) is detected at the start, and in that the second current profile (64) is replaced by the first current profile (58) if the battery voltage exceeds a voltage threshold value.Method according to one of the preceding claims, characterized in that, at a start, a battery voltage of the internal combustion engine (10) is detected and / or a temperature (T) of the internal combustion engine (10) is detected and / or an injection pressure (p) in a fuel pressure accumulator (16) of the internal combustion engine (10) is detected, and in that the injection valve (14) is actuated with the second current profile (64) only if the battery voltage is less than a voltage threshold value, and / or the temperature (T) is greater than a temperature threshold value and / or the injection pressure (p) is greater than a pressure threshold value.Control device (18) for controlling an electromagnetic high-pressure injection valve (14), with which fuel is metered directly into a combustion chamber (12) of an internal combustion engine (10), wherein the control device (18) is configured to control the injection valve (14) with a current (I) when the internal combustion engine (10) is running, which current has a first current profile (58) with a booster phase (60) and a holding phase (62), wherein the current (I) is dominated by a contribution of a first charge store (36) in the booster phase (60) and is supplied by a second charge store (28) without contributions of the first charge store (36) in the holding phase (62), characterized in that the control device (18) is further configured to control the injection valve (14) with a second current profile (64) when the internal combustion engine (10) is started, which has no holding phase (62) and that the fuel for a combustion chamber charge is injected at the start by the second current profile (64) being controlled several times by the injection valve (14).Control device (18) according to Claim 8, characterized in that it is designed to control the sequence of a method according to one of Claims 2 to 7.

Images