EP1556603B1 - Method for charging a piezoelectric actuator on an injection valve and controller - Google Patents

Description

The invention relates to a method for charging a piezoelectric actuator of an injection valve according to the preamble of patent claim 1 and a control device according to claim 1. In modern injection systems for internal combustion engines piezoelectric actuators are used. The piezoelectric actuator has the advantage that it quickly changes its length by charging or discharging. The piezoelectric actuator is used at the injection valve to control the injection process. For example, it is known to control a servo valve with the piezoelectric actuator, which closes a drain of a pressure chamber. The pressure chamber is in operative connection with an injection needle, wherein, depending on the pressure in the pressure chamber, the injection needle closes or releases injection holes. Depending on the open or closed position of the servo valve, the pressure in the pressure chamber is adjusted.

Furthermore, it is known to move an injection needle directly with the piezoelectric actuator. The position of the needle is determined depending on the length of the piezoelectric actuator.

In addition, different fuel pressures are used in modern injection systems, especially in diesel injection systems when injecting the fuel. To inject a certain amount of fuel, the piezoelectric actuator is held for a certain activation time in an active position. The fuel quantity to be injected is determined via the activation time. Characteristics for the fuel quantity to be injected differ depending on the activation time for different fuel pressures. Especially for high fuel pressures occurs in the range of small amounts of fuel, a steep increase in the amount of fuel to be dispensed with increase in the activation time. A steep characteristic curve has the disadvantage that the amount of fuel to be dispensed can be precisely determined only with a very precise adherence to the activation time. However, this injection behavior means that either the drive time must be precisely met, which requires a technically complex and expensive solution. On the other hand, this injection behavior, however, leads to relatively large inaccuracies in the injected fuel quantity in a less technically complex solution.

Out DE 100 17 367 A1 For example, a method and a device for driving at least one capacitive actuator are known. The capacitive actuator is formed in a fuel injection valve of an internal combustion engine. The described method charges a capacitive actuator by means of resonant output stages. The resonant output stages have charging capacitors whose capacitances form a resonant circuit with the capacity of the actuator and with the inductance of the charge-reversing coils. From a combustion point of view and to achieve the lowest fuel injection quantities, the shortest possible charging times should be sought, which, however, lead to high noise emissions. Therefore, the charging times are regulated and short charging times predominantly used in those areas where the noise emissions are not bothersome, such as at high engine speeds. The described method and apparatus allow for both shortening and lengthening the charging time of the capacitive actuator of the fuel injector.

Out DE 199 44 733 A1 a further device for driving at least one capacitive actuator of a fuel injection valve is known, with which the charging time of the capacitive actuator can be adjusted by means of a clocked transformer.

Out DE 101 58 553 A1 is a driving circuit for a piezoelectric actuator and a fuel injection system is known, wherein the piezoelectric actuator of an injector for discharging fuel is charged, the actuator depending on the state of charge changes its length, depending on the length of the actuator, the fuel delivery is controlled, wherein for Fuel delivery of the charge state of the actuator is changed during a charge time, wherein after a fixed drive time, the charge state of the actuator is brought back to an initial state, wherein the charging time is changed depending on the pressure of the injected fuel, wherein at a higher fuel pressure, a shorter charging time is set.

Out EP 1 138 904 A1 a method and a device for charging a piezoelectric actuator for an injection valve is known, wherein the piezoelectric actuator to be supplied energy to achieve a desired stroke in dependence on the pressure of the fuel to be injected is determined. The energy to be supplied is determined by a corresponding charging voltage of the actuator, in particular by a charging time. At a high fuel pressure, the charging time is set shorter than at a low fuel pressure.

The object of the invention is to provide an improved method for injecting fuel with a piezoelectrically operated injection valve.

The object of the invention is achieved by the method according to claim 1 and by the control device according to claim 9. Further advantageous embodiments of the invention are specified in the dependent claims.

An advantage of the method according to the invention is that the amount of fuel to be delivered does not increase so much with an increase in the activation time of the piezoelectric actuator. This offers the advantage that the injected fuel quantities change less with the activation time. Thus, fluctuations in the driving time, which occur due to system inaccuracies have less influence on the amount of fuel to be injected. This makes the process more robust overall. This advantage is achieved in that the charging time, in which the piezoelectric actuator is brought from a rest load to a working charge, is selected depending on the fuel pressure.

Experiments have shown that at different pressures the charging time has different effects on the actual injected fuel quantity. Thus, it was recognized that the variation of the charging time depending on the fuel pressure allows an advantageous influence on the amount of fuel to be injected. In particular, the actual amount of fuel injected is less dependent on fuel pressure fluctuations.

In the embodiment of the present invention, the charge time is made longer at higher fuel pressure than at lower fuel pressure. By this measure, a large increase in the amount of fuel to be injected is reduced depending on the drive time at high fuel pressure. The Activation time at high fuel pressure reduced. The result is that, in contrast to previous methods, the amount of fuel to be delivered no longer increases so much when the activation time of the piezoelectric actuator is increased. Thus, the change of the injected fuel amount is kept at a variation of the driving time in limits. Consequently, system-related inaccuracies in the activation time have less effect on the quantity of fuel to be injected.

The method according to the invention is preferably used for charging times which lie between 100 and 300 μsec. With this bandwidth of the charging time sufficient for many applications influencing the change in the fuel quantity is achieved depending on the change of the driving time.

The inventive method is particularly suitable for use in injection systems having a fuel storage. The fuel accumulator supplies fuel to the injector with a definable fuel pressure. The fuel pressure is measured and the charging time of the piezoelectric actuator is adjusted depending on the measured fuel pressure.

Preferably, the inventive method is used in the delivery of very small amounts. Under very small amounts are understood amounts, for example, less than 20% of the maximum amount of fuel delivered. Experiments have shown that, especially for very small quantities, a large increase in the fuel quantity with an increase in the activation time and the same charging time occur. The large increase in the amount of fuel to be injected at the same drive time can be inventively reduced by extending the charging time at the same drive time.

Preferably, only the charging time of the piezoelectric actuator is changed and the charge to be applied to the piezoelectric actuator during the charging time is maintained unchanged.

In the injectors used are very small amounts in the range of less than 5 mm ³ , preferably in the range less than 2.5 mm ³ .

A simple realization of the method according to the invention is achieved in that the charging time is read from a map, and that in the map, the charging times are stored depending on the amount of fuel to be injected and the fuel pressure.

Preferably, the inventive method is used in a piezoelectric actuator which drives a servo valve. In particular, in the execution of a piezoelectric actuator with the use of a servo valve experiments have shown that an advantageous effect on the amount of fuel to be injected via a change in the charging time is achieved at preferably constant driving time of the piezoelectric actuator.

The invention will be explained in more detail below with reference to FIGS.

• Figur 1 eine schematische Darstellung eines piezoelektrischen Einspritzventils mit einer Ansteuerschaltung,
• Figur 2 eine schematische Darstellung der Ladungszustände bei einem Einspritzvorgang,
• Figur 3 einen schematischen Programmablauf zur Ansteuerung des Einspritzventils,
• Figur 4 ein erstes Injektorkennfeld, das Kennlinien für die eingespritzte Kraftstoffmenge in Abhängigkeit der Ansteuerzeit und verschiedener Kraftstoffdrücke zeigt,
• Figur 5 ein zweites Kennlinienfeld, das Kennlinien für die eingespritzte Kraftstoffmenge in Abhängigkeit von der Ansteuerzeit für verschiedene Ladezeiten zeigt, und
• Figur 6 ein drittes Kennlinienfeld, das Kennlinien für verschiedene Drücke für die eingespritzte Kraftstoffmenge in Abhängigkeit von der Ansteuerzeit zeigt, wobei bei den verschiedenen Drücken verschiedene Ladezeiten verwendet werden.

Show it

• FIG. 1 a schematic representation of a piezoelectric injector with a drive circuit,
• FIG. 2 a schematic representation of the charge states in an injection process,
• FIG. 3 a schematic program sequence for controlling the injection valve,
• FIG. 4 a first injector map showing fuel injected quantity characteristics as a function of drive time and various fuel pressures;
• FIG. 5 a second characteristic field, which shows characteristics for the injected fuel quantity as a function of the activation time for different charging times, and
• FIG. 6 a third characteristic curve showing characteristic curves for different pressures for the injected fuel quantity as a function of the activation time, wherein different charging times are used at the different pressures.

FIG. 1 shows in a schematic representation, an injection valve 1 with a piezoelectric actuator 2. The piezoelectric actuator 2 is in operative connection with an injection needle 3, the injection ports 4 opens or closes depending on the length of the piezoelectric actuator 2.

In the illustrated embodiment, a transmission module 5, a servo valve 6, a pressure chamber 7 and a control piston 8 is arranged as an operative connection between the injection needle 3 and the actuator 2. The servo valve 6 is in the illustrated embodiment, an outwardly opening valve which controls an outflow of the pressure chamber 7. In a further embodiment, the servo valve can also be designed to open inwardly. The piezoelectric actuator 2 is biased by a Bourdon tube pressure and connected in the upper part fixed to the housing of the injector. When the piezoelectric actuator is charged with an electric charge, the piezoelectric actuator expands and presses on the transfer module 5 from above. As a result, the transfer module 5 pulls a closing member of the servo valve 6 upward away from the outflow of the pressure chamber 7. The transmission module 5 is designed as an inverse transmission module, which in the case of a change in length of the actuator 2 in the direction of the transmission module 5, a closing member of the Servo valve 6 lifts up in the direction of the piezoelectric actuator 2. In this way, the outflow of the pressure chamber 7 is released.

The pressure chamber 7 is supplied via a feed line 9 with a throttle with a fluid at a predetermined pressure. The pressure chamber 7 is also via the movable control piston 8 in operative connection with the injection needle 3. If a high pressure prevails in the pressure chamber 7, the injection needle 3 is pressed onto a sealing seat and thus closes the injection holes 4. Between the injection needle 3 and the housing of the injection valve an injection chamber 15 is formed, which is hydraulically connected depending on the position of the injection needle with the injection quenchers 4 or not.

The injection needle 3 is biased by spring elements, not shown, in such a way that the injection needle 3 wants to lift off from the injection holes 4. If the pressure in the pressure chamber 7 drops due to an opening of the servo valve 6, the injection needle 3 lifts off from the injection holes 4 and releases the injection holes 4. The injection begins.

The injection chamber 15 and the supply line 9 are hydraulically connected to a fuel reservoir 10. The fuel accumulator 10 is supplied by a pump 11, preferably a high pressure pump, with fuel at a predetermined pressure. The fuel accumulator 10 in turn supplies the pressure chamber 7 and the injection chamber 15 with the fuel.

At the fuel reservoir 10, a pressure sensor 16 is arranged, which detects the pressure in the fuel reservoir 10 and forwards via a measuring line to a control unit 12. The control unit 12 is connected via measurement signals S with sensors of the internal combustion engine in connection, the operating conditions of the internal combustion engine such. B. the speed and the driver's request, ie the accelerator pedal position, capture and forward to the controller 12. The control unit 12 is also via a control line with the pump 11, connected via a data line to a data memory 14 and via a further control line to an output stage 13. The output stage 13 is connected via electrical lines to the piezoelectric actuator in combination. The actuator 2 is charged with the desired electrical charge via the electrical lines. The control unit 12 determines due to the operating conditions of the internal combustion engine such. As the speed and the accelerator pedal position depending on maps stored in the memory 14, times for charging and discharging the piezoelectric actuator 2. In addition, the controller 12 determines a charging time within which the output stage 13 charges the piezoelectric actuator to a desired charge , The charging process is performed by the output stage 13, which is controlled in the corresponding manner by the control unit 12.

FIG. 2 shows a schematic representation of the charge states of the piezoelectric actuator 2 for an injection process. In the diagram of FIG. 2 the charge Q of the actuator 2 is plotted over the time t. Before a first time T1, the actuator 2 has a rest load. At a first time T1, the output stage 13 begins to charge the piezoelectric actuator. At a second time T2, the charge of the piezoelectric actuator with a maximum value M reaches a working charge. The time between the first and second times T1, T2 is referred to as the charging time. In the period between the second time T2 and a third time T3, the charge of the piezoelectric actuator remains unchanged. At the third time T3, the output stage 13 begins to discharge the piezoelectric actuator. Within a discharge time, the piezoelectric actuator is discharged back to the initial state until a subsequent fourth time T4.

The drive time is the time duration between the first time T1 and the third time T3. Analogous to the characteristic of the FIG. 2 Time-delayed the opening behavior of the injection valve. A short time after the first time T1, the injection needle is lifted from the injection holes, so that a discharge of fuel begins. Shortly after the second time T2, the injection needle reaches a maximum opening stroke, so that a maximum fuel flow is discharged via the injection holes. A short time after the third time T3, the injection needle moves in the direction of the injection holes and closes the injection holes short time after the fourth time T4.

FIG. 3 shows in a schematic program sequence, the sequence of the method according to the invention. At program point 100, the controller 12 detects the data required to control the injector 1. In this case, the pressure in the fuel storage 10 is detected. Subsequently, the control unit 12 determines depending on operating parameters such. As the speed and the driver's request and depending on Kaftstoffdruck the beginning of the control of the piezoelectric actuator, the charging time and the driving time. The charging time is part of the driving time. According to the charging time is determined depending on the pressure of the fuel. The charging time can be calculated depending on stored functions depending on the pressure or read from a map that is stored in the data memory 14. In a further embodiment, the fuel pressure is not measured directly, but calculated using the available operating parameters. For example, as an operating parameter, the delivery line of the pump 11, the speed of the internal combustion engine and the amount of fuel to be dispensed from the injection valve can be used to calculate the fuel pressure.

At the following program item 110, the control unit 12 calculates the amount of fuel to be injected.

At the following program point 120, the control unit 12 calculates the activation time for the injection valve from the fuel pressure and the quantity of fuel to be injected. In addition, will according to the invention set the charging time depending on the fuel pressure. The charging time is preferably read from a map which is stored in the data memory 14. The map has a data field which determines the charging time as a function of the fuel quantity to be injected, as a function of the fuel pressure and as a function of the activation time.

In the following program item 130, the control unit 12 controls the output stage 13 in such a way that the injection valve 1 is driven according to the determined charging time and the determined activation time.

FIG. 4 shows a schematic representation of a characteristic field which shows the amount of fuel to be injected as a function of the driving time for different fuel pressures according to previously known driving method for an injection valve with a piezoelectric actuator. The uppermost characteristic corresponds to a fuel pressure of 1600 bar, a mean characteristic to a fuel pressure of 800 bar and the lowest characteristic to a fuel pressure of 200 bar. It can be seen that, especially at higher pressures, the fuel quantity to be injected increases strongly with the activation time. The large increase in the amount of fuel injected relates to an area where smaller amounts of fuel are injected.

FIG. 5 shows a characteristic field, which shows the injected amount of fuel in dependence on the driving time of the piezoelectric actuator of the injection valve. Different characteristics are shown, which were recorded for the same fuel pressure but for different charging times. Three characteristics are shown, which were recorded for the same fuel pressure, but the top characteristic with a charging time of 120 m / sec, the average characteristic with a charging time of 200 m / sec and the lower characteristic with a charging time of 300 m / sec was recorded. Out of the FIG. 5 It can be seen that the slope of the characteristic is flattened by an extension of the charging time. A flatter characteristic means that a change of the driving time leads to a smaller increase of the injected fuel quantity. Thus is off FIG. 5 It can be seen that the variation of the charging time represents a means for influencing the injection characteristic of the injection valve.

For example, while maintaining the activation time by lengthening the charging time, the injection behavior of the injection valve can be influenced in such a way that with increasing activation time there is a smaller increase in the injected fuel quantity. The smaller increase in injected fuel quantity as the drive time increases provides the advantage that a deviation from a target injection time calculated by the controller 12 has less of an impact on the actual amount of fuel injected. Thus, the actual amount of fuel injected is less affected by fluctuations in the driving time. Fluctuations in the activation time can be caused, for example, by system-related inaccuracies or production-related fluctuations in the electrical properties of the output stage.

FIG. 6 shows a characteristic field in which the injected fuel quantity is shown depending on the driving time and which is obtained according to the inventive method. The characteristic field of the FIG. 6 clearly shows that the characteristics increase less steeply with the activation time than in FIG. 4 , In particular, at high pressures, a flatter increase in the injected fuel quantity is achieved with an increase in the activation time by extending the charging time. This in FIG. 6 illustrated injection behavior of an injection valve shows a minimum injection quantity of 0.5 mm ³ . In addition, a minimum driving time is shown. Furthermore, various characteristics are shown, the injection quantities over the Ansteuerzeit for different pressures demonstrate. An upper dotted line shows a characteristic curve for a fuel pressure of 1600 bar and a loading time of 300 m / sec. A lowermost dashed line shows the injection quantity dependence of the driving time for a fuel pressure of 200 bar and a charging time of 200 m / sec.

In addition, according to the method according to the invention, the injected fuel quantity is also less dependent on pressure fluctuations. From the comparison of the characteristic 11 of FIG. 4 with the characteristics of the FIG. 6 It can clearly be seen that, with the same activation time, a variation of the injected fuel quantity as a function of different pressures at FIG. 6 is lower. The characteristic curves for different pressures are in the method according to the invention, whose injection behavior in FIG. 6 is shown, much closer together. It is particularly advantageous that hardly any changes in the injection quantity occur in the region of the smallest quantities when the pressure changes.

Claims (9)

1. Method for charging a piezoelectric actuator (2) of an injection valve (1) for dispensing fuel,
   with the actuator (2) changing its length as a function of the charge state, with the dispensing of fuel being controlled as a function of the length of the actuator,
   with the charge state of the actuator being changed during a charging period for dispensing fuel,
   with the charge state of the actuator being put back into an initial state again after a defined activation time,
   with the charge time being changed as a function of operating states,
   with the charge time being defined as a function of the pressure of the fuel to be injected,
   characterised in that a longer charge time is selected for high pressure than is selected for lower pressure.
2. The method according to claim 1, characterised in that an amount of fuel to be dispensed is dispensed with different charge times for different fuel pressure.
3. The method according to one of claims 1 or 2, characterised in that the charge time is set to between 100 und 300 µs.
4. The method according to one of claims 1 to 3, characterised in that the fuel to be injected is provided by a fuel accumulator (10) which is connected hydraulically to the injection valve (1), that the pressure of the fuel is measured, that the charge time of the actuator is defined for the amount of fuel to be injected as a function of the measured pressure.
5. The method according to one of claims 1 to 4, characterised in that the charge time is changed when the value of the amount of fuel to be dispensed lies below a smallest value.
6. The method according to claim 5, characterised in that the value of the smallest amount is less than 5 mm³, preferably less than 2.5 mm³.
7. The method according to one of claims 1 to 6, characterised in that the charge time is read out from an engine map, that the charge times are stored in the engine map as a function of the fuel pressure.
8. The method according to one of claims 1 to 7, characterised in that a servo valve (6) is controlled by the actuator (2), that the servo valve controls a sequence of a pressure chamber (7), that the pressure chamber (7) is filled with a fluid that is actively connected to an injection needle (3), that the injection needle (3) moves from an open into a closed position as a function of the pressure of the fluid and that the dispensing of fuel is controlled by the injection valve.
9. A control device operating in accordance with one of the above methods.

Images