DE102011075108A1 - A method of determining a control amount of an injector - Google Patents

Abstract

A method and an arrangement for determining a control quantity of an injector (10) are presented. The method is used in particular in an injector (10) in an internal combustion engine of a motor vehicle. The injector (10) is actuated over a period of time that is short enough so that fuel (38) is not yet injected into a combustion chamber (40) and that system behavior follows that causes a drop in pressure due to a backflow of the fuel Tax amount causes, the tax amount is determined on the basis of the drop in pressure.

Description

The invention relates to a method for determining a control quantity of an injector in a common-rail injection and to an arrangement for carrying out the method. The method is used in particular in an internal combustion engine of a motor vehicle.

State of the art

In a common-rail injection in an internal combustion engine, which is also referred to as accumulator injection, fuel is brought to a high pressure level with a high-pressure pump. This pressurized fuel is conveyed into a fuel rail (common rail), to which in turn at least one injection valve or an injector is connected. This injector injects the fuel directly into the combustion chamber of the internal combustion engine, for example the internal combustion engine of a motor vehicle.

From the publication DE 10 2005 006 361 A1 For example, a method for operating an internal combustion engine is known in which fuel is conveyed, at least temporarily, under pressure into a rail, which is referred to here as a fuel manifold. At least one injector is connected to the rail, which injects the fuel directly into an associated combustion chamber. A pressure difference that occurs in the rail at least one injection is detected. The rail is considered as a substantially closed system. In this way, the amount of fuel can be accurately determined.

In diesel common rail systems, the compressible volume of the fuel is on the order of the amount of fuel of a single injection. Therefore, the high-pressure pump must continuously provide for the maintenance of the pressure.

The currently used injectors of diesel common rail systems are usually switched indirectly via a so-called servo valve. In this case, the servo valve is actuated during electrical actuation, which thus lowers the fuel pressure applied in the control chamber by discharging fuel, the so-called control quantity, through defined throttles into the injector return. By thus formed pressure difference between promoted high pressure and lowered pressure by driving the servo valve in the injector hydraulic opens the injector and fuel, namely the injection quantity is injected into the combustion chamber. So that the hydraulic pressure in the rail or accumulator does not drop by the injections in the time average, fuel must be nachgefördert in the rail. This additional funding is done via the rail pressure regulator, which measures the present rail pressure by means of the rail pressure sensor and regulates the fuel delivery in the rail via a metering device or via a control unit that regulates the outflow of fuel from the rail.

About the position of the metering device or rail pressure regulator application in the rail supplied total amount is known. Analogously, the position of the pressure regulating valve or a comparable control unit on the rail can also be used for the measuring method. The amount delivered to the rail at constant rail pressure thus corresponds to the sum of injection quantity, injector leakage and control quantity. A differentiated measurement of these quantities is currently only possible to a limited extent when driving.

The copy DE 10 2005 028 137 A1 describes a method for measuring the control amount of injectors of a high-pressure injection system. In this case, the control amount is determined by comparing the injectors in the installed state with each other and / or by a comparison with absolute limits. The described procedure is repeated for each injection valve until each injection valve was switched off once. In this way, a check of the control amount of the injectors in the installed state is possible.

The object of the invention is to provide a method by means of which the activation of, in particular, servo-assisted injectors can be supported to such an extent that the amount of steric occurring can be measured separately from other influences or quantities in an injector-specific manner. Furthermore, it should be identified from which activation period the injector emits only a control quantity and / or actual injections of fuel into the combustion chamber.

Disclosure of the invention

Against this background, a method according to claim 1 and an arrangement with the features of claim 10 are presented. Embodiments result from the dependent claims and the description.

The present method is thus based on the drop in pressure, whereby the pressure in the rail or in the injector can be measured. This pressure drop is shown, for example, in the rail pressure signal. In this case, the injector is driven over a period of time that is sufficiently short that injection of fuel in a combustion chamber is not yet carried out, and that system behavior follows that causes the control quantity to flow back.

In one embodiment, the pressure drop in the supply line and / or the injector or the rail caused by the injection process, namely the injection quantity and the control quantity, is detected by a pressure measurement in the fuel supply line or in the rail. This can be recognized, for example, in the rail pressure signal. When measuring the Raildruckeinbruchs now a differentiation is made in actual control amount and injection quantity. This separation is possible if the injector is only electrically energized so short that the servo valve opens briefly, but there is no fuel injection of the injector. The detectable pressure drop in the rail or in the injector itself or in the supply line can thus be directly related to the control quantity. A direct resolution to cylinder or even after a single injection event is possible.

In an alternative embodiment, it is determined what amount of fuel is required to compensate for a pressure drop caused by the control amount in the time average. In this way, the tax amount is determined. It is advantageous that it is known what quantity must be nachgefördert to compensate for the pressure drop in the time average.

If the pressure on the rail is measured, it is determined how an existing rail pressure regulator or a pressure regulating valve must react on the rail in order to keep the rail pressure constant over the time average. The rail pressure is, for example, in a car in the range of 2,000 bar. For a truck this value is usually higher.

Thus, a method is presented with which, at least in some of the embodiments, the control amount injector-individual, separate from other influences, can be measured. For this purpose, a pressure gauge can be used in the injector supply line or in the injector itself or in the rail. In the method, the injector to be measured is actuated only very briefly, so that the servo valve opens and there is a control amount, but the injector nozzle does not yet open and the injector does not release an injection quantity. The outflow of the control quantity leads to a pressure drop in the injector supply line or in the injector or the rail, which can be detected via the existing pressure sensor. By means of a corresponding calculation method, the elapsed control quantity can then be determined.

In one embodiment of the method, the known rail pressure regulator structure is used. For example, an injector to be measured is actuated only very briefly for the method, so that the servo valve opens and a control quantity is present, but the injector still does not release an injection quantity. For this purpose, the injector is only briefly, for example. About 120 ☐s, driven. This value varies depending on the injector design. The outflow of the control amount leads to a pressure drop in the injector supply / injector itself and the rail, which can be detected by the rail pressure regulator and compensated in the time average. Using a corresponding calculation method of the Raildruckstellergrößen then the flowed control amount can be calculated.

The knowledge of the injector-individual control quantity can be used to relatively measure and correct the production spread between individual injectors and to obtain information on the state, such as, for example, the aging, etc., of the individual injectors in the context of a monitoring method. This monitoring procedure can be carried out at regular intervals during operation of the vehicle or during a workshop visit.

Another advantage of the method lies in the increase of functional accuracies, such. As for a flow compensation control in common-rail systems based on the rail pressure drop during injection, in which only the total amount of control amount and injection quantity of the individual injectors can be equated.

With the knowledge of the control quantity, said method can make even more exact corrections, in particular for the injection quantity calculation.

A further embodiment in which it is possible to profit from the knowledge of the control quantity is the rail pressure reduction control via so-called blank shots. In the blank shot method, the injector is also driven so short that there is only one control quantity but no injection quantity. This is used to reduce the rail pressure during load changes of the engine, eg. B. in the thrust, reduce. The speed of this reduction in rail pressure depends on the size of the individual control quantities. If the control quantity is known or measured, this Raildruckabbaufunktion can be pre-controlled more accurately. In addition, in the blank-shot process, care must be taken to ensure that only one control quantity and no injection quantity is available, ie. H. that no injection takes place, which can also be monitored with the illustrated method.

Depending on the injector principle, it can also be detected by the method described here, starting from which adjacent actuation duration of the injector, in addition to the control amount, fuel is actually injected into the combustion chamber. This driving time, in which the injector actually opens and injects depending on the rail pressure, is an important parameter on the aging state of the injector or the nozzle and can be used to correct the injector map, namely the dependence of the injection amount of the driving time. In addition, the determined maximum actuation duration, at which no injection quantity is present, can be used for the blank-shot method, in order to enable the maximum reduction in rail pressure in a regulated manner.

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the respectively specified combination but also in other combinations or alone, without departing from the scope of the present invention.

Brief description of the drawings

1 shows an embodiment of the injector.

2 shows in a flow chart a possible sequence of the method described.

Embodiments of the invention

The invention is schematically illustrated by means of embodiments in the drawings and will be described in detail below with reference to the drawings.

In 1 is a schematic representation of an embodiment of an injector shown in total with the reference numeral 10 is provided. Furthermore, the illustration shows a rail 12 with a sensor 14 for detecting the rail pressure, with a pressure control valve 16 coupled to a tank 18 and a metering unit 20 with a high pressure valve 22 , By means of the metering device 20 will fuel under pressure from the tank 18 in the rail 12 promoted. The pressure in the rail 12 is with the sensor 14 captured and can with the pressure control valve 16 be managed.

The injector 10 includes a nozzle 30 , a nozzle needle 32 , a control or servo valve 34 in which a control room 36 is provided. For injecting (arrow 38 ) of fuel in a combustion chamber 40 becomes the servo valve 34 pressed, the tax amount from the control room 36 over a return 44 flowing back. Subsequently, the injection takes place 38 in the combustion chamber 40 , The required fuel is supplied via a supply line 42 the rail 12 taken. In addition to an injector leakage, both the injection quantity and the control quantity become the rail 12 taken.

The presented method now makes it possible to differentiate injection quantity and control quantity.

For the measurement of the control amount is typically a suitable operating condition of the injector 10 selected. For 4-stroke engines this is, for example, the gas cycle of the cylinder, since during this time the injector 10 do not need to inject. During such an "injection break" of the injector 12 , the injector will 10 Software supported by a method, for example, so short driven that a control amount of the servo valve 34 flows back, but the nozzle 30 of the injector 10 not open.

The pressure drop caused by the control amount in the injector supply line 42 or in the rail 12 or injector 10 is in one embodiment of the method with the sensor 14 detected. The determined in this way pressure drop can be converted in a control unit in a fuel tax amount. By a multiple control, typically at a high frequency, one obtains an increased pressure drop, which can then be detected and converted to a single control amount. Thus, an increased accuracy of the method is achieved. In this case, the method is simplified if the measurement process is carried out within a delivery pause of the high-pressure pump.

In an alternative embodiment of the method, the pressure drop caused by the control quantity in the injector supply line 42 or in the rail 12 or in the injector 10 by means of the rail pressure regulator or a pressure regulating device, preferably with the aid of the metering unit 20 and / or the pressure regulating valve 16 , balanced.

About an exit 50 of the pressure control valve 16 or a position of the metering unit 20 can be determined the nachgeförderte amount. If the procedure is carried out once with and once without so-called blank-shot (no injection quantity), the control amount of a single injector 10 be determined. To increase the accuracy of the procedure, the injector 10 are also repeatedly controlled in quick succession and the fuel Nachförderbedarf this sum control amount to be detected, which can then be converted to a single tax amount.

The measuring method described can be carried out injector-individually and at different, previously defined rail pressures. The tax amount is u. a. a function of rail pressure.

The thus determined injector-individual control quantities can be stored in a control unit in a map. The functionalities described above can then refer to these learning values.

In a further embodiment of the method, the test drive duration of the injector 10 continue to be raised until the injector 10 releases a control amount and further increase the drive time of the injector 10 opens and an injection 38 is present. Indicates the associated detected fuel delivery demand of the pressure control valve 16 or metering unit 20 in the transition from zero quantity to tax amount and / or tax amount to tax amount + injection quantity on a significant feature in the Nachförderbedarf on, the associated drive time at which the injector 10 opens for the first time and is stored in maps. Thus, a correction of the drive duration map of the injector 10 possible.

The method described can be carried out with software. It is characterized by the fact that, for example, the injector 10 is electrically driven in an operating state in which no injection 38 is required, as z. B. is the case with a gas cycle change. Furthermore, it may be a plurality of very short drives.

The presented method is used in particular in servo-assisted injectors in which at least one pressure sensor in the rail or injector or in an injector supply line and a rail pressure regulating unit is present.

In 2 is shown in a flowchart a possible sequence of the described method. In a first step 100 there is a short activation of the injector. It is important to ensure that the control period is chosen so short that no injection into the combustion chamber takes place. Due to the control amount required for the short control, a pressure drop occurs in the rail (step 102 ), in a further step 104 is detected with the pressure measuring unit. It will be in a final step 106 Determines how much fuel needs to be supplied to the rail to compensate for this pressure drop. This fuel quantity corresponds to the control amount.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102005006361 A1 [0003]
• DE 102005028137 A1 [0007]

Claims (10)

Method for determining a control quantity of an injector ( 10 ), in particular an injector ( 10 ) in an internal combustion engine of a motor vehicle, in which the injector ( 10 ) is driven over a period of time that is sufficiently short so that no injection ( 38 ) of fuel in a combustion chamber ( 40 ), and that a system behavior follows, which causes a backflow of the control amount, based on the drop in the pressure, the control amount is determined. The method of claim 1, wherein the waste is measured and the control amount is calculated from the measured waste. Method according to Claim 1, in which the control quantity is determined by way of compensation for the drop in pressure. Method according to one of claims 1 to 3, wherein the control amount is determined by means of a pressure regulating device which is used to compensate for the drop in pressure. Method according to one of claims 1 to 4, wherein the pressure in the injector ( 10 ) is measured. Method according to one of claims 1 to 4, wherein the pressure in the rail ( 12 ) is measured. Method according to one of claims 1 to 4, wherein the pressure in the line ( 42 ) is measured. Method according to one of claims 1 to 7, wherein the value of the determined control amount is stored in a map. Method according to one of claims 1 to 8, which is performed during a gas cycle change of a cylinder or when no torque request is present. Arrangement for determining the control quantity of an injector ( 10 ), in particular an injector ( 10 ) in an internal combustion engine of a motor vehicle, which is designed to prevent the injector ( 10 ) for a period of time that is sufficiently short so that no injection ( 38 ) of fuel in a combustion chamber ( 40 ), and that a drop in pressure is caused by a backflow of the control amount, the arrangement being further adapted to determine the control amount based on the drop in the pressure.

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