DE102016124835A1 - Method for heating an injection valve - Google Patents

Abstract

The invention relates to a method for heating an injection valve on a fuel system of an internal combustion engine in order to improve the heating of at least the injection valve and to ensure trouble-free operation of the internal combustion engine and to minimize an unequal distribution of a combustion air ratio and a rough running of the internal combustion engine.

Description

The present invention relates to a method for heating an injection valve on a fuel system of an internal combustion engine.

Furthermore, the present invention relates to an engine controller of an internal combustion engine, which is adapted to carry out a method for heating an injection valve on a fuel system of the internal combustion engine.

Also, the present invention relates to an internal combustion engine having an engine controller configured to perform a method of heating an injector on a fuel system of the internal combustion engine.

Like in the EP 1 455 077 A2 disclosed, an internal combustion engine can be operated with a primary fuel or with an alternative fuel. The primary fuel is usually used for a start of the internal combustion engine and there is a fuel changeover to the alternative fuel during operation. There is a need to heat an alternative fuel injection valve from fuel switching to bring it to operating temperature. However, when the injector opens during heating, both accidental entry of air into a fuel line located upstream of the injector and unwanted leakage of fuel from the fuel line may result. Air in the fuel system causes a short-term fuel shortage immediately after switching. On the other hand, leakage of fuel during heating causes a disturbance of the combustion air ratio and an unequal distribution of fuel to the respective cylinders.

Further, in the fuel switching from the primary fuel to the alternative fuel, there may arise the problem that the injectors that introduce the alternative fuel into the internal combustion engine are sticky or do not open properly for other reasons such as soiling, tolerance deviations, or aging.

The object of the invention is therefore to improve a method for heating at least one injection valve on a fuel system of an internal combustion engine. In particular, it is an object of the present invention to ensure a trouble-free operation of the internal combustion engine and to minimize the unequal distribution of the combustion air ratio and a rough running of the internal combustion engine.

To achieve this object, a method is proposed for heating at least one injection valve on a fuel system of an internal combustion engine which is operable with a primary fuel and with at least one alternative fuel, wherein the injection valve is heated in time before a fuel switch from the primary fuel to the alternative fuel and wherein Heating of the injection valve in response to a valve pressure difference of the injection valve takes place.

The term "valve pressure difference" is understood to mean the difference between the pressures downstream and upstream of the injection valve. A positive valve pressure difference exists when the pressure upstream of the injector is greater than the pressure downstream of the injector.

The primary fuel here is the fuel that is used to start the internal combustion engine. If there are conditions for trouble-free operation with alternative fuel, the fuel is switched to alternative fuel operation.

The use of the valve pressure difference of the injector for heating has the advantage that the amount of alternative fuel supplied during heating of the internal combustion engine can be controlled. As can be seen immediately, the amount of fuel can also be controlled in such a way that either only a small amount of alternative fuel is supplied to the internal combustion engine or the supply of alternative fuel is completely prevented. This can also be configured such that the amount of air that enters the fuel system via the injection valve at a negative valve pressure difference is minimized.

An injection valve includes a magnetizable coil, by means of which by applying an electric current, a valve needle can be opened. Since such injectors have a static flow and the coils themselves can be used for heating, it is advantageous for the present invention, when for heating the injection valve is energized during a drive time with an electric current. The drive duration is the parameter with which the heating power can be controlled if the voltage and the current for driving the injection valve is not variable. This is advantageous since a signal already present in an engine control can be used to control the heat output and the activation duration is in a known relationship to the injection quantity. Thus, the driving time can be selected so that only a small amount of fuel or no amount of fuel escapes, if the injection valve a Grenzansteuerdauer has from which still no fuel is injected.

Since the activation duration for heating the injection valve is in relation to the heating power, it is advantageous for the invention, when the fuel switching takes place, if a time integral of the activation duration is greater than a heating threshold.

Unequal distribution is when one of several cylinders of the internal combustion engine relative to the other cylinders, a different mixture is supplied. This can occur by cyclically and alternately driving the injection valves. In this respect, it is understood that heating by energizing the injectors can not be done in each cycle but also intermittently. So it is possible, for example, to heat only in every eighth cycle to control the desired heating power.

It is understood that the primary fuel may also be a gaseous fuel. Furthermore, it should be understood that the problem underlying the object may also occur on a fuel system using a liquid alternative fuel.

Advantageous developments of the invention are specified in the dependent claims.

Further, the invention improving measures will be explained in more detail below together with the description of a preferred embodiment of the invention with reference to the single figure. It show the

1 a schematic representation of the internal combustion engine,

2 a diagram for determining the heating parameter,

3 schematically the formation of the switching condition and

4 schematically the formation of the further heating parameter.

The 1 represents an internal combustion engine 1 with a cylinder 25 , a liftable in the cylinder 25 included piston 26 and with an exhaust valve 27 and with an inlet valve 30 in the cylinder 25 there is a spark plug on the top side 29 , and opens the inlet valve 30 , can be a fuel-air mixture in the cylinder 25 arrive, and the burned fuel-air mixture can when opening the exhaust valve 27 in the exhaust duct 28 escape. In front of the inlet valve 30 is a suction tube 14 formed upstream through a throttle 23 in an air filter 22 empties. During operation of the internal combustion engine 1 will air over the air filter 22 through the suction pipe 14 sucked.

Furthermore, the internal combustion engine has 1 via a primary injection nozzle 13 to which primary fuel 10 from a primary fuel tank 12 via a primary fuel line 24 is introduced, and the injection valve 13 allows injection of the primary fuel 12 in the suction pipe 14 ,

Furthermore, the fuel supply of the internal combustion engine 1 an alternative fuel 11 up in an alternative fuel tank 15 is stored. The primary fuel 10 is for example gasoline or diesel, and the alternative fuel 11 is a gas, such as LPG, especially LPG (Liquified Petroleum Gas) or other gases that are suitable for an internal combustion engine 1 to operate such as natural gas (CNG / LNG: Compressed Natural Gas, Liquefied Natural Gas) or hydrogen or a mixture of the aforementioned fuels.

It is understood that between the suction pipe 14 and the air filter 22 Also, a compressor may be arranged, by means of which the sucked air is compressed. In this respect, in the intake manifold 14 Also pressures greater than 1bar (absolute) occur.

The feed tract for the alternative fuel 11 starts with the alternative fuel tank 15 to which a high pressure line 31 followed. The system pressure in the alternative fuel tank 15 and thus in the high pressure line 31 is typically 11 bar for LPG and 200 bar for natural gas. In the high pressure line 31 is a shut-off valve 19 attached to which is an evaporator 21 and in the case of natural gas, a pressure reducer (not shown) connects. In the evaporator 21 becomes the liquid alternative fuel 11 preferably completely evaporated, and during the evaporation, a pressure drop to a medium pressure, by means of the evaporator to a value of 1 bar above a pressure in the intake manifold 14 is set. This is followed by the evaporator 21 a medium pressure line 18 that the essentially evaporated alternative fuel 11 to an injection valve 17 leads. The injection valve 17 is via a control device 20 so controlled that the injection valve 17 synchronized with the intake stroke of the internal combustion engine 1 opens in a pulsed manner and a quantified amount of alternative fuel 11 to a to the injection valve 17 subsequent low pressure line 16 emits. About the low pressure line 16 becomes the alternative fuel 11 to the suction pipe 14 guided and mixed in this with over the air filter 22 sucked air. The in the medium pressure line 18 set fuel pressure is about 1 bar above a pressure of the low-pressure line 16 ,

The control device 20 forms with the injector 17 and not shown in detail pressure measuring devices at least in the low pressure line 16 and in the medium pressure line 18 a heating device which is designed such that the heating of the injection valve 17 has at least one heating parameter and wherein the heating parameter is determined based on a valve pressure difference of the injection valve. The heating parameter here is the activation duration of the injection valve 17 ,

The control device 20 , which includes a motor control, thereby serves in operative connection with the injection valve 17 to the ordinary operation of the injector 17 for the allocation of the alternative fuel 11 to the internal combustion engine 1 , wherein the control device 20 is additionally designed to the heating device according to the invention for fuel switching of a fuel supply to the internal combustion engine 1 from the primary fuel 10 on the alternative fuel 11 to control. The control is in this case carried out according to the inventive method. Thus, in the control device 20 at least one of the heating conditions are programmed.

During operation of the internal combustion engine 1 is next to the pressure in the low pressure line 16 and the medium pressure line 18 also a cooling water temperature of the internal combustion engine 1 measured and continuously in the control device 20 evaluated. From the pressures of the two pressure lines 16 . 18 the valve pressure difference is formed, which is used as a heating condition for the formation of the heating parameter.

How out 2 As can be seen, the relationship between the heating parameter designed as a driving duration and the heating condition formed from the valve pressure difference of the injection valve can be formed in a non-linear manner so that the injection valve is energized with a high activation duration near a valve pressure difference of 0 mbar. The activation duration is selected to be so high that opening of the injection valve 17 in any case occurs. The very small valve pressure difference, however, causes an escape of gas from the medium pressure line 18 in the low pressure line 16 is minimized. As soon as the valve pressure difference increases and the amount of gas entering the intake manifold 14 would also increase, the driving time is reduced. For higher valve pressure differences, the activation duration does not necessarily have to be reduced to 0 ms, because the injection valve 17 has a Mindestansteuerdauer, under which a physical opening is no longer possible. Furthermore, it is possible that a mechanism of the injection valve 17 is formed such that a high valve pressure difference opening the injector 17 counteracts and a higher drive time is required to effect an opening. This is the case, for example, when a needle or a differently pronounced closing element of the injection nozzle 17 against the fuel pressure in the medium pressure line 18 acts.

For negative valve pressure differences, it is necessary to greatly reduce the drive time to a negative mass flow at the injector 17 to prevent. The negative mass flow leads to an entry of air into the medium pressure line 18 whereby the engine operation during fuel switching from gasoline to LPG due to lack of gas due to the in the medium pressure line 18 resulting air cushion is disturbed. Therefore, drive durations in the range of negative valve pressure differences are in a range below the minimum drive duration in order to heat the coils of the injection valve 17 as well as the injection valve 17 not having to minimize yourself excessively.

Heating of the injector 17 With low drive times may have the disadvantage that, although a heating of these can still take place, but the detachment of a possible present adhesion of the injection valve 17 is not sufficiently solved before switching from gasoline to gas operation. The switching, which is allowed from a defined cooling water temperature includes, in the present embodiment, a switching condition, which must be additionally met to allow switching.

How out 3 it can be seen that the driving time is used to form the switching condition. The integral of the control period is compared with the Heizschwellwert. If the integral of the activation duration exceeds the heating threshold value, the switchover condition is met and switching from gasoline to gas is performed, as long as the cooling water temperature is also sufficiently high.

The integral of the control period is representative of the over the energization of the injector 17 in this introduced heating power. Alternatively, the current and / or the heating power could also be used to form an injection valve 17 registered amount of heat are used.

In the 3 In addition, a calculation block can be connected upstream of the integrator, which drive times are only forwarded to the integrator from the minimum drive duration. Thus, the switching condition is actually met only when the injection valve 17 has opened for defined cycles.

Opening the injector 17 during heating causes, as already explained above, a supply of gas into the suction pipe 14 and therefore in the cylinder 25 the internal combustion engine 1 , The resulting inequality among the various cylinders of the internal combustion engine is dependent on the ratio of the mass of the gas to the mass of the injected gasoline. Consequently, the measure of the unequal distribution is not only dependent on the amount of the gas introduced but also on the injection quantity of the gasoline. At operating points with high injection quantities, the internal combustion engine is thus substantially less sensitive to the imbalance in the combustion air ratio of the individual cylinders caused by the additional gas.

The imbalance between the cylinders 25 the internal combustion engine 1 Stems, therefore, that the energizing of the injectors 17 takes place at a defined distance, on the one hand to control the amount of heating cycles on the one hand, the introduced heating energy and on the other hand to limit the mass of additionally introduced gas. For example, for energizing the injectors 25 be set a distance of nine cycles, which would have the consequence that only every ninth injection process of the primary injection valves 13 an energization of the injection valve 17 he follows. As can be seen immediately occurs here an unequal distribution of the fuel mass of the cylinder 25 because a heating cycle that allows a small amount of gas to escape can be followed by eight cycles without additional fuel.

4 shows the schematic relationship between further heating condition and the other heating parameters. Here, the further heating condition is an engine load of the internal combustion engine 1 , The further heating parameter determined therefrom by means of a non-linear relationship corresponds to a drive factor with which the activation duration in the control device 20 is factored. The weighting of the drive time with the drive factor means that at low engine loads, as they occur somewhat at slow constant speed or at idle, the drive time is reduced accordingly. By this measure, the proportion of gas relative to the proportion of gasoline is kept low, which in turn minimizes a disturbance of the combustion air ratio and minimizes the unequal distribution between the cylinders. As can be seen immediately instead of the engine load and an injection quantity or intake manifold pressure of the internal combustion engine 1 be used as another heating condition.

The invention is not limited in its execution to the above-mentioned preferred embodiment. Rather, a number of variants is conceivable, which makes use of the illustrated solution even with fundamentally different types of use.

Any features and / or advantages resulting from the claims, the description or the drawings, including constructive details or spatial arrangements, can be essential to the invention, both individually and in the most diverse combinations. In particular, it is possible to combine any of the heating conditions with each other and this for heating the injection valve 17 query.

LIST OF REFERENCE NUMBERS

1

 Internal combustion engine

10

 Primary fuel

11

 Alternative fuel

12

 Primary fuel tank

13

 Primäreinspritzdüse

14

 suction tube

15

 Alternative fuel tank

16

 Low-pressure line

17

 Injector

18

 Medium pressure line

19

 shut-off valve

20

 control device

21

 Evaporator

22

 air filter

23

 throttle

24

 Primary fuel line

25

 cylinder

26

 piston

27

 outlet valve

28

 exhaust duct

29

 spark plug

30

 intake valve

31

 High-pressure line

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

• EP 1455077 A2 [0004]

Claims (6)

Method for heating at least one injection valve ( 17 ) on a fuel system of an internal combustion engine ( 1 ) containing a primary fuel ( 10 ) and at least one alternative fuel ( 11 ) is operable, wherein the injection valve ( 17 ) prior to fuel switching from the primary fuel ( 10 ) on the alternative fuel ( 11 ) is heated and wherein the heating of the injection valve ( 17 ) as a function of a valve pressure difference of the injection valve ( 17 ) he follows. A method according to claim 1, characterized in that for heating the injection valve ( 17 ) is energized during a drive time with an electric current. A method according to claim 2, characterized in that the fuel switching takes place when a time integral of the control period is greater than a Heizschwellwert. Method according to claims 1 to 3, characterized in that a drive factor for correcting the actuation duration as a function of an engine load of the internal combustion engine ( 1 ) is formed. Motor controller, which is adapted to perform the method according to claims 1 to 4. Internal combustion engine having a motor controller according to claim 5.

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