DE102009053423A1 - Method and device for injecting an alternative fuel - Google Patents

Abstract

The invention relates to a method for injecting an alternative fuel to an internal combustion engine (2) of a motor vehicle (1) during operation, wherein the fuel supply of the internal combustion engine (2) is switchable between an alternative fuel and a regular fuel. It is first established that a balanced operating state is present in the operation of the internal combustion engine with alternative fuel. Then, a second injection period for the alternative fuel is determined. Subsequently, the fuel supply is switched from alternative fuel to regular fuel. Thereupon a first duration of injection is determined for the regular fuel. As a next step, the fuel supply is reset from regular fuel to alternative fuel, and then a correction of the second injection duration is determined taking into account the ratio of the regular and alternative fuel injection durations.

Description

The invention relates to a method for injection of an alternative fuel to an internal combustion engine of a motor vehicle during operation. The internal combustion engine is operable with an alternative fuel or a regular fuel. As a regular fuel in particular gasoline or diesel fuel and as an alternative fuel LPG (Liquified Petroleum Gas) referred to.

Such a method for injecting an alternative fuel is particularly advantageous in motor vehicles, which are operable with a regular fuel and an alternative fuel and have separate tank or supply systems for both types of fuel. Motor vehicles are normally designed by motor vehicle manufacturers solely for use with regular fuels such as gasoline or diesel. Due to the attractive price and the increasing availability of alternative fuels, in particular of LPG, it is increasingly desired to equip motor vehicles in addition in such a way that they can be operated in addition to operation with gasoline or diesel with LPG. Such equipped vehicles are either directly equipped for operation with two types of fuel by the motor vehicle manufacturer themselves, or they are later equipped with a retrofit system for operation with an additional fuel type, typically LPG.

The supply of alternative fuel can be done in different ways. For example, a mixing of the different types of fuel is possible even before the injection to the internal combustion engine, so that a common injector for the different types of fuel can be used. In addition, however, systems are also known in which the different types of fuel are supplied with separate injectors of an internal combustion engine. For injecting the fuel, the intended injectors are opened for a predetermined injection time. The injected amount of fuel thus results from the shape of the injector, the physical or chemical properties of the injected fuel, the pressure in the supply system to the injector and the opening time of the injector.

Different fuels usually have different physical and / or chemical properties. Regular fuels and alternative fuels differ in particular in their calorific value or their ignition behavior. Compared to regular fuels, such as gasoline or diesel, the density of LPG is lower. The stoichiometric air-fuel ratio, which has a lambda value of 1, is larger. The calorific value per volume LPG is lower than for gasoline or diesel and the octane number is higher. Overall, due to these characteristics in an internal combustion engine at a certain operating point, the required volume of LPG is greater than the volume of gas or diesel required at that operating point.

Available LPG is regularly composed of certain mass proportions of propane and butane, which may vary. Propane and butane regularly have different properties and the exact magnitude of the properties of LPG described above is significantly influenced by the respective mass proportions of propane and butane. Therefore, the above-mentioned properties of LPG are not always the same.

In motor vehicles that are operable with different types of fuel, an adjustment of the injection signals and in particular of the injection signal periods to the different types of fuel is required due to the described differences in the fuels. The required amount of alternative fuel often deviates from the required amount of regular fuel. In order to compensate for this, customized opening times for the alternative fuel and regular fuel injectors are required. This adaptation can be done by adjusting the injection signal duration. At least partially compensation is also possible by a suitable design of the injectors for LPG. However, such an adaptation by the physical design of the LPG injectors is concretely specified and therefore not adjustable. The adjustment of the opening times can be very complex and z. B. depending on the engine temperature, the pressure in the supply system to the injectors and / or the lambda value of the exhaust gases of the internal combustion engine fail differently.

Frequently, injection signals for controlling the injectors for injecting the alternative fuel from the injection signals for controlling the injectors for injecting the regular fuel are determined or calculated. This z. As engine temperature, the pressure in the supply system, the lambda value and / or other factors taken into account. For this purpose, corresponding maps can be stored in a control unit.

Such maps for calculating injection signals for the alternative fuel are typically determined for different types of vehicles and stored in the control unit for controlling the injection of the alternative fuel.

Maps that take into account all environmental and / or operational influences can not be determined in advance. There are influences that can not be determined beforehand. These include, for example, differences between the same motor vehicles. Due to the manufacturing process, identical internal combustion engines frequently have different characteristics in different temperature and rpm ranges which can not be determined in advance on a test vehicle. In addition, old motor vehicles in operation, which also affects the characteristics.

In particular, the composition of available LPG is different from propane and butane between summer and winter or depending on the region. These different compositions require different duration injections to achieve the same lambda value.

These influences can disturb the calculation of the injection signals for the alternative fuel, so that the internal combustion engine can be supplied with unsuitable fuel quantities and thus errors in the driving behavior of the motor vehicle, changes in the lambda value of the exhaust gases, faults in the exhaust aftertreatment system and / or consumption disadvantages of the internal combustion engine can occur.

On this basis, it is an object of the present invention to alleviate the technical problems described in connection with the prior art. In particular, an advantageous method for injecting an alternative fuel to an internal combustion engine of a motor vehicle and a particularly suitable for carrying out the method injection system or motor vehicle are presented.

These objects are achieved by a method according to the features of claim 1 and an injection system according to the features of claim 9 and a motor vehicle according to the features of claim 10. Further advantageous embodiments and fields of application of the invention are specified in the respective dependent formulated claims. The features listed individually in the claims can be combined with one another in any technologically meaningful manner and can be supplemented by explanatory facts from the description, in particular in conjunction with the figures, wherein further embodiments of the invention are shown.

• a) Feststellen, dass ein ausgeglichener Betriebszustand im Betrieb der Verbrennungskraftmaschine mit alternativem Kraftstoff vorliegt;
• b) Bestimmen einer zweiten Einspritzdauer fix den alternativen Kraftstoff;
• c) Umschalten der Kraftstoffversorgung von alternativem Kraftstoff auf regulären Kraftstoff;
• d) Feststellen einer ersten Einspritzdauer für den regulären Kraftstoff;
• e) Umschalten der Kraftstoffversorgung von regulärem Kraftstoff auf alternativen Kraftstoff;
• f) Korrigieren der zweiten Einspritzdauer unter Berücksichtigung des Verhältnisses der ersten Einspritzdauer zur zweiten Einspritzdauer.

The method according to the invention for injecting an alternative fuel to an internal combustion engine of a motor vehicle during operation, wherein the fuel supply of the internal combustion engine is switchable between an alternative fuel and a regular fuel, comprises at least the following steps:

• a) determining that a balanced operating condition exists in the operation of the alternative fuel internal combustion engine;
• b) determining a second injection duration fix the alternative fuel;
• c) switching the fuel supply of alternative fuel to regular fuel;
• d) determining a first duration of injection of the regular fuel;
• e) switching the fuel supply from regular fuel to alternative fuel;
• f) correcting the second injection duration taking into account the ratio of the first injection duration to the second injection duration.

The sequence of the steps of the method according to the invention can be varied in a technically meaningful manner. In particular, step a) can also take place during or after carrying out method steps b) to f). In particular, step a) can also be carried out or repeated between steps e) and f) so that, if necessary, a check can be made as to whether (still) a balanced operating state exists. Then can be used to determine a balanced operating condition on in steps b) to f) determined parameters.

In particular, the method according to the invention is a method for adapting the injection period for an alternative fuel to the injection period for a regular fuel. A prerequisite for the proper execution of the adaptation is a functioning lambda control by the first control unit.

The internal combustion engine of a motor vehicle suitable for the method according to the invention is normally equipped with first injectors for the regular fuel and with second injectors for the alternative fuel. The regulation of the second injectors for the alternative fuel takes place with the aid of a second control unit. This receives the injection signals which are output from a first controller, typically the engine control of the motor vehicle, to control the injection of the regular fuel with the first injectors. The second controller adjusts the alternative fuel injection durations such that the engine controller does not register that an alternative fuel is being used via its sensors located in, for example, the exhaust, intake, and / or internal combustion engine cooling circuits.

To carry out the method according to the invention, it is first established in step a) that there is a balanced operating state during operation of the internal combustion engine. In particular, it is checked whether a balanced operating state exists. By "balanced operating state" is meant an operating state in which the internal combustion engine is operated relatively constant. A "balanced operating state" may also be referred to as a "stationary operating state". Such an operating state is characterized for example by a constant temperature of the internal combustion engine (engine temperature). Also, a sufficient constancy of speed and load can be a prerequisite for a "balanced operating state". In particular, operating sections of the motor vehicle with constant speed at constant track conditions (after warm-up) are meant. Within the framework of a balanced operating state, certain fluctuations of various parameters, such as, for example, the speed of the internal combustion engine, the duration of injection or the temperature within defined limits may also be permitted. For example, fluctuations in the relevant operating parameters of a maximum of 10%, a maximum of 5% or a maximum of 3% in a review period of, for example, a maximum of 60 sec., A maximum of 30 sec. or maximum 15 sec. be allowed in the context of a balanced operating state. For a particularly accurate, arithmetically not very complex and reliable adaptation is particularly important to ensure that the injection duration and / or engine load from the beginning of the adaptation (alternative fuel) until the end of the adaptation (again alternative fuel) only (negligible) little changes.

After a balanced operating state of the internal combustion engine has been determined in step a), a second injection period for the alternative fuel is determined in step b). The lambda control of the first control unit must regularly ensure that the correct lambda value (usually 1.0) is maintained.

It is preferable to measure directly the time output by the first control unit and not the time modified by the second control unit on the basis of the nozzle size, map point, gas pressure, etc. A second injection duration is thus to be understood as meaning the output of the first control unit occurring during the injection of the alternative fuel.

Subsequently, in step c), the fuel supply of the internal combustion engine is converted from alternative fuel to regular fuel. Now, instead of alternative fuel with the help of the second injectors, regular fuel is injected by means of first injectors. The second control unit for controlling the second injectors for injecting the alternative fuel is thus deactivated or suspends the injection of the alternative fuel. It is a period of time until the conditions have equalized in the motor vehicle after the switch and the injection of the second fuel takes place, as they would take place if previously no alternative fuel injection would have taken place. It is also waited until the lambda value is corrected, so there are essentially no fluctuations in the lambda value caused by the changeover. After this state has occurred, a first injection period for the regular fuel is determined in step d). This, too, is optionally stored in a memory.

Then, in step e), the alternative fuel is switched back. If appropriate, it is also possible to wait here until the conditions have become uniform after the changeover and a new measurement of the second injection duration for the second fuel is carried out.

The two injection durations for the alternative fuel, one of which has been determined before switching to the first fuel and one after switching back to the second fuel, can be compared during a check of the operating state (step a)). If both values are equal, it can be diagnosed with great certainty that the load has changed during the adaptation only within the permitted limits (tolerance). If this is the case, the adaptation is valid, otherwise it must be repeated. In such a procedure, step a) is at least partially carried out during the process according to the invention.

Subsequently, in step f), a correction of the calculation of the second injection duration in the second control device takes place taking into account the two determined injection durations (first injection duration and second injection duration). If a further second injection duration has been determined in step e), a mean value of the second injection duration determined in step b) and the second injection duration determined in step e) can be used for the correction of the calculation in step f) as the second injection duration.

The correction can be carried out in such a way that a correction factor for the second injection duration is determined on the basis of information stored in the second control unit. However, it is also possible to modify the map used for the calculation of the injection signals. With repeated implementation of the invention Method with different balanced operating conditions of the internal combustion engine, a corrected map can be constructed.

The method according to the invention is particularly suitable when the regular fuel is gasoline or diesel and the alternative fuel is LPG (Liquefied Petroleum Gas). The engine control of a motor vehicle equipped for operation with gasoline or diesel is normally set up in such a way that it can compensate for age-related or due to production fluctuations in the motor vehicle manufacturing deviations between motor vehicles. It is not suitable for compensating such deviations for an alternative fuel. This adaptation can be carried out particularly advantageously with the aid of the method according to the invention.

The method according to the invention is also advantageous if the alternative fuel is CNG (compressed natural gas) or natural gas. The differences between petrol and / or diesel and CNG are more pronounced than the differences between petrol and / or diesel and LPG. CNG typically contains methane as the largest mass fraction and only a lower proportion by mass of propane and butane. Propane and butane are, as stated above, the main components of LPG.

According to a development of the method, after step f), the injections take place taking into account the correction determined in step f), wherein these corrections are stored in a memory, so that they are available again during the next engine run. Since the calculation and application of the adaptation factor takes place directly after the end of the method steps a) to f), the advantages of the method according to the invention are utilized directly; at the same time, the influence of the method according to the invention on the consumption of regular fuel and on the driving behavior of the motor vehicle remains minimal.

The method according to the invention is also advantageous if the method steps a) to f) are carried out several times, for example with each new drive of the motor vehicle.

Furthermore, it is also proposed that the method be repeated several times in the manner of a loop immediately after one another. By "immediately after one another" is meant here that the method is carried out during operation at a time interval of less than 10 minutes and in particular less than 5 minutes. By repeatedly repeating the method steps, an improved adaptation of the second injection duration can take place, because a stepwise correction of the second injection duration can be achieved.

Furthermore, the method is advantageous if, after each execution of the method steps a) to e) in step e), a correction of the calculation is taken into account only to a maximum of 20%, preferably a maximum of 15% and in particular a maximum of 10%. The proportions given here indicate in each case a maximum permissible change in the injection durations in relation to one another. In the unlikely event of a false adaptation, there is thus no excessive impairment of the operation of the internal combustion engine. Now, if the method according to the invention is carried out repeatedly in succession several times, the error which has occurred due to a wrong adaptation can be corrected quickly.

Also advantageous is the inventive method, if the implementation of the method takes a maximum of 40 seconds. By this is meant that all steps that are implemented in carrying out the method according to the invention, take place within 40 seconds. Over such periods of time are in driving operation of a motor vehicle before regularly balanced operating conditions. The longer the time required for the entire implementation of the method according to the invention, the less likely it is that a balanced operating state is present throughout. A maximum duration of 40 seconds has proven to be beneficial.

The method according to the invention is also advantageous if the method is only carried out if the internal combustion engine has already been operated with alternative fuel for at least 60 seconds. In particular, it is meant here that the internal combustion engine has already been operated continuously with alternative fuel for 60 seconds immediately before carrying out the method according to the invention. Next should also be active during this period, the lambda control of the motor vehicle. This is to ensure that the operating conditions of the internal combustion engine with alternative fuel are already independent of the switching phase from regular to alternative fuel and independent of the starting phase of the internal combustion engine.

Also advantageous is the inventive method, if in step a) a balanced operating state during operation of the internal combustion engine is recognized that an injection duration over the period of operation of the internal combustion engine within a tolerance is constant. Alternatively or cumulatively, the speed of the internal combustion engine, the Temperature of the cooling water of the internal combustion engine or other parameters, such as the pressure in the exhaust system of the internal combustion engine to determine whether a balanced operating condition exists, are used. It is also possible to use the pressure in the intake of the internal combustion engine. As part of the control of the alternative fuel injection method, the injection durations are processed. These signals are thus available and are also suitable for sufficiently accurately diagnosing a balanced operating state of the internal combustion engine. Deviations in the duration of injection within a maximum of 5% or even a maximum of 3% can still be tolerated in the context of a balanced operating state of the internal combustion engine. If the deviations of the parameters which characterize the balanced operating state exceed the specified threshold values, a balanced operating state is no longer diagnosed.

Also according to the invention is an injection system, comprising a second control device and at least one second injectors, wherein the second control device for operating the second injectors is set up according to a method according to the invention. This can be achieved in particular by an appropriate control software. A second control unit of such an injection system has connection lines to the second injectors. At the same time it has connections to which connection lines from the first control unit of the motor vehicle or from the engine control of the motor vehicle can be connected. Through these connection lines, first injection signals are received, which are normally provided for controlling the first injectors for the regular fuel. Also, a connection may be provided on the second control unit, via which an external input signal for switching the fuel supply from regular fuel to alternative fuel or vice versa can get into the second control unit. The switching from regular fuel to alternative fuel and vice versa can also be done in the second controller. Particularly preferably, the second control unit also has output lines, via which the second control unit can be connected to the first injectors for supplying the internal combustion engine with regular fuel. When regular fuel injection is to occur, signals for the first injectors are simply switched through the second controller without being affected by the second controller.

The software for carrying out a method according to the invention, which is implemented in the second control unit of the injection system, may also include maps. Here, on the one hand maps are possible, which are firmly stored, on the other hand can also be changed with the method according to the invention variable maps, which adapt to changing properties of the motor vehicle.

Also according to the invention is a motor vehicle with an internal combustion engine, which is operable with a regular fuel and an alternative fuel, the motor vehicle having a first controller and first injectors for supplying the internal combustion engine with regular fuel and an inventive injection system, wherein the first control device and the second Control unit of the Einspitzsystems are arranged together for carrying out the method according to the invention. Such a motor vehicle may in particular be a retrofitted motor vehicle, which has been equipped by the motor vehicle manufacturer only for operation with regular fuel, and was later provided with a retrofit system, the retrofit system having an inventive injection system and an associated fuel supply system and a tank system for an alternative fuel.

The particular advantages and refinements which are described for the method according to the invention are valid and applicable analogously for the injection system according to the invention as well as for the motor vehicle according to the invention. The same applies to the advantages and properties described with particular reference to the injection system according to the invention and the motor vehicle according to the invention, which are analogously applicable and transferable to the method according to the invention.

The invention and the technical environment will be explained in more detail with reference to FIGS. The figures show particularly preferred embodiments, to which the invention is not limited. In particular, it should be noted that the figures and in particular the illustrated proportions are only schematic. They show schematically:

1 a motor vehicle, which is set up to carry out the method according to the invention, and

2 a block diagram which describes the implementation of a variant of the method according to the invention.

1 shows a motor vehicle 1 with an internal combustion engine 2 , which is adapted for operation with either a regular fuel or an alternative fuel. As regular Fuel is in the motor vehicle 1 preferably gasoline or diesel and used as an alternative fuel preferred LPG. In 1 is just a cylinder 11 the internal combustion engine 2 shown. The cylinder 11 is via the intake pipe 8th with air and fueled. Exhaust gases escape from the cylinder 11 over the exhaust manifold 9 out. In addition, there is a cylinder 11 a spark plug 18 for ignition of the operation of the internal combustion engine 2 in the cylinder 11 present ignitable mixture. The suction line 8th can over the cylinder 11 with a valve 10 be closed. Exactly the exhaust manifold 9 opposite the cylinder 11 with a valve 10 be closed.

In operation with regular fuel, the internal combustion engine 2 from the first controller 5 controlled. The first controller 5 is in particular the engine control of the motor vehicle. A regular fuel then passes through the first injector 3 in the intake pipe 8th the internal combustion engine 2 ,

Should the motor vehicle 1 operated with LPG, via the switch 7 a change to LPG operation. The switch 7 is in the 1 set such that a fuel supply with LPG takes place and the fuel supply of the internal combustion engine 2 is interrupted with regular fuel. The fuel supply with LPG is thus according to 1 from the second controller 6 regulated, which in turn from the first controller 5 is controlled. For the second control unit 6 and the switch 7 Here a simplified representation was chosen. The control unit 6 and the switch 7 can also be integrated with one another in one component. In particular, it is also possible that signals from the first control unit 5 to the first injector 3 also the second control unit 6 (optionally) happen.

The second control unit 6 may receive different signals to control the injection of the LPG. For example, a lambda input 13 provided, via which a lambda value of the exhaust system, not shown, of the internal combustion engine 2 in the second control unit 6 can get. The temperature sensor 21 determines the cooling water temperature of the internal combustion engine 2 in the cooling circuit 12 the internal combustion engine 2 , Also the signal of this temperature sensor 21 can from the second controller 6 be recycled. The second control unit 6 calculated from the signal it receives from the first controller 5 receives and which actually to control the first injector 3 is thought, in combination with the other the second controller 6 available signals, a signal for the second injector 4 , which LPG in the intake pipe 8th the internal combustion engine 2 injects.

The second injector 4 gets the LPG from the tank 16 , The LPG gets out of the tank 16 out with the pump 17 promoted and passes through the supply line 14 to the second injector 4 , In addition to the supply line 14 exists from the second injector 4 back to the tank 16 a return line 15 through which excess LPG from the injector 4 back to the tank 16 is encouraged. In the return line 15 is a pressure sensor 20 intended. The signal of the pressure sensor 20 also gets to the second control unit 6 and is used in this to calculate the injection signal for the second injector 4 with recycled. In particular, the return line 15 also provided by heating and insufficient pressure in the supply line 14 gaseous LPG from the second injector 4 back to the tank 16 namely, it is to be achieved that (only) liquid LPG via the second injectors 4 is delivered. Gaseous LPG is in the area of the second injector 4 undesirable because the injection of the LPG by the second injector 4 in the intake pipe 8th should be liquid.

This has many advantages in the supply of the internal combustion engine 2 with LPG on.

In the return line 15 There is also a pressure regulator 19 with which the pressure of the LPG in the supply line 14 and in particular in front of the injector 4 can be adjusted. The second injector 4 and the second controller 6 together with their connecting lines form a retrofittable injection system 22 ,

2 shows schematically as a block diagram the implementation of the inventive method for adaptation. At any time during operation of the alternative fuel internal combustion engine, the process start takes place 23 instead of. If necessary, then finds an initialization 24 various parameters for the inventive method instead. Here is an example of the initialization of a counter for a loop 41 for the multiple implementation of the method steps a) to f) of the method according to the invention. After initialization 24 finds an operating condition test 25 instead, in which it is checked whether a balanced operating state is present in the operation of the internal combustion engine. If such an operating state in the operating condition test 25 was not registered, the verification loop begins 39 to run. The operating condition test 25 is performed until a balanced operating condition is diagnosed. Alternative to the verification loop 39 If appropriate, the method according to the invention can also be aborted if no balanced operating state has been diagnosed in step a). The start of the process 23 is then re-triggered at a later time and a new operating condition test 25 he follows.

When in the operating condition test 25 a balanced operating condition has been diagnosed, takes place in a step b) a first measurement 26 , In this case, a second injection duration t _{2a is} determined. The second injection duration t _2a characterizes the operation with alternative fuel during the balanced operating state. The second injection duration t _2a is stored in a memory 38 filed for the second injection duration t _2a . The lambda value λ ₂ is regulated by the lambda control of the first control device and is constant. Advantageously, the time output by the first control unit is measured directly and not the time modified by the second control unit on the basis of the nozzle size, map point, gas pressure or other possible parameters.

After the first measurement 26 in step c), a first switchover takes place 27 from alternative fuel to regular fuel. Subsequently, in step d), a second measurement is carried out 28 , In this measurement, a first injection duration t _{1 is} determined. The lambda control here ensures a constant first lambda value λ ₁ , which is typically equal to the second lambda value λ ₂ . The first injection duration t ₁ is in a memory 36 deposited for the first injection duration t ₁ . Subsequently, in step e), a second switching 48 carried back to the alternative fuel. Optionally, a new measurement of the injection duration t _2b , which takes place in the memory 43 is deposited. If this is the case, step a) can at least partially make a comparison 44 of t _2a and t _2b , by which it can be determined whether the operating point has changed inadmissibly during the adaptation. If this is the case, the adaptation must be repeated. This is done with the help of the correction loop 47 , If the operating points are close to each other, it can be assumed that the same load condition prevailed even in the intermediate phase with the regular fuel. In this case, for example, the average of the two alternative fuel injection periods t _2a and t _{2b may be} stored in memory 45 deposited and used for further calculation. Subsequently, in step f), the calculation of a correction factor takes place based on the ratio of the injection durations t ₁ and t ₂ .

Alternatively, a new second injection duration or a parameter of a characteristic field can also be determined. After the calculation 30 is the determined correction by the limitation 31 modified so that adaptation takes place only to a limited extent. The calculated and limited correction factors (K) and the new second injection durations t ₂ can be stored in a map memory 40 be deposited. In this way, they are available for further injections of alternative fuel to the internal combustion engine. After the limit 31 is completed, the correction factor is applied 32 or a regular execution of second injections taking into account the calculated correction. This ensures that the operation of the motor vehicle with alternative fuel continues undisturbed even after completion of the process.

Subsequently, a loop control 33 occur. At the loop control 33 Various parameters necessary for the method according to the invention can be adapted. By way of example, the counting up of a slider counter is shown here. After the loop control 33 becomes a termination criterion 34 tested for the inventive method. Here is an example of the termination criterion 34 a check of the number of executed loop passes is shown. There are also other termination criteria 34 possible for the inventive method. For example, the method according to the invention can be aborted if a complete adaptation of the second injection duration has taken place. If the termination criterion 34 is not satisfied, the inventive method over the loop 41 in process step a) again with the operating state test 25 kick off. If the termination criterion 34 is satisfied, the end of the procedure 35 be initiated.

The method according to the invention is particularly advantageous in order to improve the supply of an alternative fuel to an internal combustion engine, which is also operable with a regular fuel. The control of the injection of the alternative fuel can be adapted with the inventive method to changing properties of the internal combustion engine and the alternative fuel. At the same time manufacturing differences between the same motor vehicles can be compensated with the method according to the invention.

LIST OF REFERENCE NUMBERS

1

motor vehicle

2

Internal combustion engine

3

first injector

4

second injector

5

first control unit

6

second control unit

7

switch

8th

suction

9

exhaust manifold

10

Valve

11

cylinder

12

Cooling circuit

13

Lambda input

14

supply line

15

Return line

16

tank

17

pump

18

spark plug

19

pressure regulator

20

pressure sensor

21

temperature sensor

22

injection

23

process start

24

initialization

25

Operating condition test

26

first measurement

27

first changeover

28

second measurement

29

Memory for first lambda value

30

calculation

31

limit

32

Application of the correction factor

33

loop control

34

termination criterion

35

process end

36

Memory for first injection duration

37

first memory for second lambda value

38

first storage for second injection duration

39

Checking loop

40

Characteristics memory

41

loop

42

second memory for second lambda value

43

second memory for second injection duration

44

Checking the operating state

45

Memory for second injection duration

46

Memory for second lambda value

47

demolition loop

48

second changeover

Claims (10)

Method for injecting an alternative fuel to an internal combustion engine ( 2 ) of a motor vehicle ( 1 ) in operation, wherein the fuel supply of the internal combustion engine ( 2 ) is switchable between an alternative fuel and a regular fuel, comprising at least the following steps: a) determining that a balanced operating condition exists in the operation of the internal combustion engine with alternative fuel; b) determining a second injection period for the alternative fuel; c) switching the fuel supply of alternative fuel to regular fuel; d) determining a first duration of injection of the regular fuel; e) switching the fuel supply from regular fuel to alternative fuel and re-determining the second injection duration; f) determining a correction of the second injection duration taking into account the ratio of the injection times with regular or alternative fuel. The method of claim 1, wherein the regular fuel is gasoline or diesel and the alternative fuel is LPG (Liquefied Petroleum Gas) or CNG (Compressed Natural Gas). Method according to one of the preceding claims, wherein after step f) the injections taking into account the correction determined in step f) and these corrections are stored in a memory, so that they are available again at the next engine run. Method according to one of the preceding claims, wherein the method steps a) to f) are repeated several times. Method according to one of the preceding claims, wherein after each implementation of the method steps a) to e) in step e) a correction of the calculation is taken into account only to a maximum proportion of 20%. Method according to one of the preceding claims, wherein the implementation of the method takes a maximum of 40 seconds. Method according to one of the preceding claims, wherein the method is performed only when the internal combustion engine ( 2 ) has been operated with alternative fuel for more than 60 seconds. Method according to one of the preceding claims, wherein in step a) a balanced operating state during operation of the internal combustion engine ( 2 ) is recognized by the fact that at least one injection duration or the engine temperature over a period of operation of the internal combustion engine within a tolerance is constant. Injection system ( 22 ), comprising a second control device ( 6 ) and at least one second injector ( 4 ), wherein the second control device ( 6 ) for operating the second injector ( 4 ) is arranged according to a method according to one of the preceding claims. Motor vehicle ( 1 ) with an internal combustion engine ( 2 ) operable with a regular fuel and an alternative fuel, wherein the motor vehicle ( 1 ) a first control device ( 5 ) and first injectors ( 3 ) for supplying the internal combustion engine ( 2 ) with regular fuel and an injection system ( 22 ) according to claim 9, wherein the first control device ( 5 ) and the second control device ( 6 ) of the injection system ( 22 ) are arranged together for carrying out a method according to one of the claims 1 to 8.

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