DE102010008289A1 - Method for operating an internal combustion engine with two different fuels - Google Patents

Abstract

The invention relates to a method for switching a fuel supply of an internal combustion engine (2), which can be operated with different fuels, from a first fuel to a second fuel, wherein the internal combustion engine (2) has an exhaust gas treatment device (23) with a catalytic converter (24) that has an exhaust gas flow direction (25) is flowed through and in the exhaust gas flow direction (25) behind the catalyst (24) a lambda probe (26) is arranged. The lambda probe (26) is connected via at least one electrically conductive connection (27) to a first control unit (5) of the internal combustion engine (2). When switching the fuel supply, the electrical resistance of the connection (27) is changed.

Description

The invention relates to a method for reducing pollutants in motor vehicles, which are normally for use with gasoline and (subsequently) z. B. for the operation with liquefied petroleum gas (LPG: Liquefied Petroleum Gas) are set up. For this purpose, systems are offered with which for the operation of petrol or diesel equipped vehicles are retrofitted so that they can be operated in addition with LPG.

Such retrofit systems usually comprise a separate tank system and injection system for liquefied gas, which is installed in the motor vehicle in addition to the gasoline injection system. This injection system has its own control unit which controls the injection of liquid gas. This LPG injection control unit is normally connected to the regular operation engine control unit to process and convert its injection signals into appropriate LPG injection signals. For the LPG separate injectors are normally provided, which are arranged next to the injectors for normal operation with gasoline on the intake manifold of the internal combustion engine and supply the liquefied gas to the combustion chambers.

It has been found that the pollutant emission of the internal combustion engine is increased in operation with LPG under certain operating conditions compared to the pollutant emission in gasoline operation. This applies in particular to the emissions of nitrogen oxide compounds during load changes or at high load.

Based on this prior art, it is an object of the present invention at least partially solve the problems described. In particular, a method for switching over a fuel supply and a method for operating a fuel supply of an internal combustion engine are to be specified, by means of which, in particular, the pollutant emissions of an internal combustion engine retrofitted for operation with liquefied petroleum gas can be reduced.

These objects are achieved by a method according to the features of patent claim 1 and a method according to the features of patent claim 6. Further advantageous embodiments of the method are given in the dependent formulated claims. The features listed individually in the claims are combinable with each other in any technologically meaningful manner and can be supplemented by explanatory facts from the description, wherein further embodiments of the invention are shown.

The method according to the invention is a method for switching over a fuel supply of an internal combustion engine that can be operated with different fuels from a first fuel to a second fuel. In this case, the internal combustion engine has an exhaust gas treatment device with a catalyst, which is flowed through by exhaust gas with an exhaust gas flow direction and in the exhaust gas flow direction behind the catalyst, a lambda probe is arranged, which is connected via at least one electrically conductive connection with a first control unit of the internal combustion engine, wherein the electrical resistance of the connection is changed during the switching of the fuel supply.

The first control device is preferably the regular engine control of the motor vehicle. Normally two lambda probes are connected to this control unit. The first lambda probe is arranged regularly in the exhaust gas flow direction starting from the internal combustion engine of the motor vehicle in front of the catalytic converter and is called a control probe. With their help, the fuel mixture is roughly adjusted to the intended lambda. There is also a second lambda probe. This second lambda probe is arranged regularly in the exhaust gas flow direction starting from the internal combustion engine behind the catalytic converter and is referred to as the post-cat probe. The first controller regularly uses this so-called post-catalyst probe to monitor and fine tune the catalyst to a predetermined lambda. With this lambda fine trim is to be achieved that the catalyst to be converted the pollutant components are supplied in the ratio that this reaches as complete as possible implementation. For this purpose, the lambda probe permanently determines the residual oxygen content in the exhaust gas and transmits this value as an analog electrical signal to the first control unit, which together with other parameters produces a control signal for mixture formation, which generally results in an adaptation of the injection quantity in the internal combustion engine (lambda -Trimm control). Especially in internal combustion engines that are not (originally) prepared for operation with alternative fuels, this lambda control follows a fixed schedule.

It has been found that in retrofitted internal combustion engines to a (partial and / or temporary) deterioration of this tailored to the implementation of the exhaust pollutants situation on the catalyst can come because the optimal conversion window at different fuels, especially in gaseous and liquid fuel, from each other. In order to achieve the desired good conversion results here again, a manipulated or adapted signal of the lambda probe is supplied to the first control unit, such that (without reprogramming the first control unit) an adaptation of the lambda control with respect to the alternative fuel is reached. For this purpose, it has been found to be particularly simple and expedient that by changing the electrical resistance of the electrically conductive connection between the lambda probe and the first control unit, the desired adaptation of the injection signals to operation with liquid gas can be achieved. For example, an increase in the electrical resistance causes a damping of the signal. The resulting lower voltage values are interpreted as higher lambda (leaner mixture). The response of the controller is to increase the injection amount to reach the originally planned level again. The true lambda is a bit richer after the manipulation. Such an adaptation is particularly useful when an adaptation to a gaseous fuel is to take place, because here the conversion window is slightly shifted towards a richer fuel mixture. The thus adapted injection signals of the first control unit are regularly further processed by a second control unit and converted into injection signals for operation with the second fuel.

As already stated, it is not provided in the second control unit of the LPG injection system that it influences the engine control (first control unit) of the motor vehicle. Therefore, no adjustments can be made directly by means of the second control unit, which adapt the specifications of the first control unit on the specifics of the operation with LPG. About the (timely targeted) change in the electrical resistance of the signal line between the engine control unit (first control unit) and the lambda probe (for the lambda control), an adaptation of these signals can be achieved. Thus, a change in the functionality of the engine control unit is possible without direct intervention in the engine control unit is required.

Thus, the stored in the engine control unit control strategy remains unchanged, due to the changed input signal but also correspondingly changed output signals are generated, which are then suitable for the low-emission operation with LPG. Thus, it can also be prevented that run in the engine control unit during operation with LPG unwanted, based on incorrect assumptions about the pollutant emissions adaptation processes, even after the end of the operation with LPG or second fuel still on the (regular) operation with the first fuel impact.

The first fuel and the second fuel can be chosen arbitrarily. The method according to the invention can always be used if the fuel supply of an internal combustion engine is to be switched between different types of fuel. The method is not limited to internal combustion engines retrofitted for operation with LPG.

However, the method is particularly advantageous if the first fuel is gasoline or diesel and the second fuel is liquefied petroleum gas (LPG) or compressed natural gas (CNG). In particular, in a combination of these different fuels as the first fuel and second fuel can be achieved by changing the resistance, an advantageous adaptation.

Also advantageous is the method for switching a fuel supply according to one of the preceding claims, when the electrical resistance is increased or decreased by at least 1000 Ω [ohm] and by a maximum of 10,000 Ω [ohm]. This range of values has proved to be successful, in particular for the gasoline / LPG application, with regard to the desired exhaust gas values. If a resistance smaller than 1000 Ω is used, there is a risk that the enrichment will be too low and lean components (NOx) will still be emitted. In the case that the resistance is set larger than 10,000 Ω, there is the problem that it is over-enriched and fat components (CO, HC) are emitted to an increased degree. The adjusted resistance depends on the internal resistance and the voltage / lambda characteristic of the lambda probe used and should be re-determined from case to case.

In an advantageous embodiment of the method according to the invention, the operation of the internal combustion engine with the first fuel from the first control unit and the operation of the internal combustion engine with the second fuel from the second control unit are controlled, wherein the second control unit processes output signals of the first control unit. In particular, the second control unit does not provide any direct feedback to the first control unit with regard to the control operations which take place for the control of the operation with the second fuel in the second control unit.

In addition, an embodiment of the method according to the invention is preferred in which the lambda probe is a jump probe (two-point probe). By the aforementioned lambda probe is meant the post-cat probe. Preferably, the Lambda probe a Nernst probe. With this type of probe, the output voltage depends on the lambda value. A series connection with the electrical resistance thus causes a shift of the measured lambda value in the direction of lean (higher air content).

The invention also relates to a method for operating a fuel supply of an internal combustion engine, wherein the internal combustion engine with a first fuel and a second fuel is operable and each switching of the fuel supply between the two fuels according to the method for switching the fuel supply according to the invention, wherein the The first fuel is gasoline and the second fuel is liquefied petroleum gas (LPG) and with each switch from gasoline to liquefied gas the electrical resistance of the connection is increased by one value and the resistance is lowered by the same value every time the liquefied petroleum gas is changed over.

The method of operating the fuel supply is particularly advantageous if the value is between 4,000 Ω (ohms) and 6,000 Ω (ohms). Most preferably, the value is 4,900 ohms (ohms).

The illustrated advantages and particular embodiments of the method for switching a fuel supply of an internal combustion engine and the method for operating a fuel supply of an internal combustion engine are transferable to each other. For the method described advantages and special embodiments may also apply to the other method.

Further claimed within the scope of the invention is a motor vehicle having an internal combustion engine with a first control unit and with an exhaust treatment device, which can be traversed by exhaust gas of the internal combustion engine with an exhaust gas flow direction and a catalyst and arranged in the exhaust gas flow direction downstream of the catalyst lambda probe, wherein an electric Connection exists between the lambda probe and the first control device having at least a first current path and a second current path, wherein in the second current path, an electrical resistance component is provided and can be switched between the first current path and the second current path with a switch, wherein the switch is connected to the second control device.

The motor vehicle according to the invention is particularly suitable for carrying out the method according to the invention for switching over a fuel supply and / or for carrying out the method according to the invention for operating a fuel supply of an internal combustion engine. The switch is preferably controlled by the second controller. At the same time, the second control unit controls at least one changeover switch which can divert the injection signals from the first control unit to the second control unit or to the injectors for operation with liquid gas. Each time the fuel supply is switched, the switch ensures switching between the first current path and the second current path. Switch and switch are preferably always operated in parallel.

It should be noted that the advantages and preferred embodiments described for the inventive methods are transferable and applicable to the motor vehicle according to the invention. In the same way, the advantages and special configurations described for the motor vehicle according to the invention can be transferred to the methods 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. Show it:

1 a motor vehicle according to the invention; and

2 : The emissions of nitrogen oxides during an exhaust test at different operating conditions of a motor vehicle compared to each other.

1 shows a motor vehicle 1 with an internal combustion engine 2 , which is adapted for operation with either a first fuel or a second fuel. In 1 is just a combustion chamber 11 the internal combustion engine 2 shown. The combustion chamber 11 is via the intake pipe 8th with air and fueled. Exhaust gases escape from the combustion chamber 11 over the exhaust pipe 9 out. In addition, there is the combustion chamber 11 a spark plug 18 for ignition of the operation of the internal combustion engine 2 in the combustion chamber 11 present ignitable mixture. The suction line 8th can be compared to the combustion chamber 11 with a valve 10 be closed. The same applies to the exhaust pipe 9 opposite the combustion chamber 11 with a valve 10 be closed.

In operation with the first 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 1 , A first fuel (in particular gasoline) then passes through a first injector 3 in the intake pipe 8th the internal combustion engine 2 , It is in each case a first injector 3 for every combustion chamber 11 intended.

Should the motor vehicle 1 with second fuel (in particular LPG) are operated via the switch 7 a switchover to the second fuel. The switch 7 is in the 1 set such that a fuel supply with second fuel and the fuel supply of the internal combustion engine 2 is interrupted with the first fuel. The fuel supply with the second fuel is thus according to 1 from the second controller 6 controlled, 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 second control unit 6 and the switch 7 can also be integrated with one another in one component. The switch 7 is from the second controller 6 controlled. 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 (optional) pass, these signals from the second controller 6 then not be modified.

The second control unit 6 may receive different signals to control the injection of the second fuel. For example, a lambda input 13 provided, via which a lambda value, not shown here lambda sensor (before catalyst), 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 controller calculates from the signal which 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 control unit 6 available signals, a signal for the second injector 4 which introduces the second fuel into the intake line 8th the internal combustion engine 2 injects. The signal reaches the second injector 4 over the signal line 36 , In each case, a second injector is preferred 4 per combustion chamber 11 intended.

The second injector 4 receives the second fuel from the tank 16 , The second fuel 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 second fuel (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 the return line 15 There is also a pressure regulator 19 with which the pressure of the LPG in the supply line 14 and especially before the second injector 4 can be adjusted. In particular, the return line 15 in combination with the pressure regulator 19 also provided that by heating and insufficient pressure in the supply line 14 no gaseous LPG is produced - namely, it is to be achieved that (only) liquid LPG via the second injectors 4 is delivered.

The second injector 4 , the signal lines 36 and the second controller 6 together form a kit for a retrofittable injection system 22 ,

Through the exhaust pipe 9 get the exhaust gases of the internal combustion engine 2 in the exhaust treatment device 23 in which it is a catalyst 24 with an exhaust gas flow direction 25 flow through. In the exhaust gas flow direction 25 behind the catalyst 24 is a lambda probe 26 arranged, which via an electrical connection 27 with the first controller 5 connected is. The electrical connection 27 indicates a first current path 28 and a second current path 29 on. In the second rung 29 is an electrical resistance component 30 arranged. Between the first rung 28 and the second current path 29 can with the switch 31 be switched. The desk 31 will as well as the switch 7 for switching the fuel supply of the internal combustion engine 2 from first fuel to second fuel and vice versa controlled by the second controller. Switching of the switch 7 and the switch 31 usually occurs at the same time when switching over a fuel supply.

The 2 shows a diagram of the emission of nitrogen oxide compounds of a motor vehicle during an exhaust gas test. The diagram is divided into two parts. In the upper part of the pollutant emissions of a motor vehicle is shown. In the lower part is the speed 32 related to the upper part. The speed 32 is on the speed axis 39 in units of [km / h] (kilometers per hour). The upper part and the lower part both have the same time axis 37 which is scaled by the unit [s] (seconds). The various emissions of nitrogen oxide compounds are in the upper part of the pollutant axis 38 applied. The pollutant axis 38 is scaled by the unit [g / s] (grams per second). The amount of nitrogen oxide ejected per second is plotted.

The basis for this diagram was the following vehicle: Type: VW Golf engine: 1.6 liters, 75 KW first fuel: petrol second fuel: LPG

The vehicle has undergone the following emissions test: ECE + EUDC cycle.

The test was carried out on an exhaust roller test bench with CVS system (CVS = Constant Volume Sampling). Only the last part of the test is shown, because the higher engine speeds result in the highest engine load, and thus the highest nitrogen oxide emission.

A first (dotted) curve 33 shows the emission of nitrogen oxide compounds (after catalyst) in gasoline operation. It can be seen that, in particular during load changes in the high load range, a short time interval with increased nitrogen oxide emissions occurs.

The second (dashed) curve 34 shows the emission of nitrogen oxides in the exhaust gas test during operation of the motor vehicle with LPG, wherein no correction according to the invention takes place. It can be clearly seen that the emission of nitrogen oxide compounds in the critical time interval, in which the output is already increased in gasoline operation, is even more increased.

The third (solid) curve 35 shows the emission of pollutants in the same exhaust gas test during operation with LPG (liquefied petroleum gas), wherein a correction of the signal of the lambda probe according to the invention by a change in the resistance of the electrical connecting line takes place. It can be clearly seen that the output of nitrogen oxide compounds is even reduced here compared to the emission of nitrogen oxide compounds in gasoline operation.

Overall, a particularly advantageous and easy to implement variant has been disclosed by the method according to the invention, as the operation of an original engine control can be adapted to operate with LPG.

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 pipe

10

Valve

11

combustion chamber

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

Exhaust treatment device

24

catalyst

25

Exhaust gas flow direction

26

Lambda probe

27

electrical connection

28

first rung

29

second current path

30

electrical resistance component

31

switch

32

speed

33

first turn

34

second bend

35

third turn

36

signal line

37

timeline

38

pollutant axis

39

speed axis

Claims (8)

Method for switching over a fuel supply of an internal combustion engine that can be operated with different fuels ( 2 ) from a first fuel to a second fuel, wherein the internal combustion engine ( 2 ) an exhaust treatment device ( 23 ) with a catalyst ( 24 ), which of exhaust gas with an exhaust gas flow direction ( 25 ) is flowed through and in the exhaust gas flow direction ( 25 ) behind the catalyst ( 24 ) a lambda probe ( 26 ) is arranged, which via at least one electrically conductive connection ( 27 ) with a first control device ( 5 ) of the internal combustion engine ( 2 ), the electrical resistance of the connection ( 27 ) is changed when switching the fuel supply. The method of claim 1, wherein the first fuel is gasoline or diesel and the second fuel is liquefied petroleum gas (LPG) or compressed natural gas (CNG). Method for switching over a fuel supply according to one of the preceding claims, wherein the electrical resistance is increased or decreased by at least 1000 Ω [ohm] and by a maximum of 10,000 Ω [ohm]. Method for switching over a fuel supply according to one of the preceding claims, wherein the operation of the internal combustion engine ( 2 ) with the first fuel from the first controller ( 5 ) and the operation of the internal combustion engine ( 2 ) with the second fuel from a second control device ( 6 ), wherein the second control device ( 6 ) while output signals of the first control unit ( 5 ) processed. Method for switching over a fuel supply according to one of the preceding claims, wherein the lambda probe ( 26 ) is a jump probe (two-point probe). Method for operating a fuel supply of an internal combustion engine ( 2 ), wherein the internal combustion engine ( 2 ) is operable with a first fuel and with a second fuel and each switching of the fuel supply between the two fuels according to one of the preceding claims, wherein the first fuel is gasoline and the second fuel is liquefied petroleum gas (LPG) and at each switching of gasoline on LPG the electrical resistance of the electrical connection ( 27 ) is increased by one value and the resistance is lowered by the same value every time a liquefied petroleum gas is changed over. A method of operating the fuel supply of an internal combustion engine according to claim 6, wherein the value is between 4,000 Ω [ohm] and 6,000 Ω [ohm]. Motor vehicle ( 1 ), comprising an internal combustion engine ( 2 ) with a first control device ( 5 ) and with an exhaust treatment device ( 23 ), the exhaust of the internal combustion engine ( 2 ) with an exhaust gas flow direction ( 25 ) is flowed through and a catalyst ( 24 ) and in the exhaust gas flow direction ( 25 ) behind the catalyst ( 24 ) arranged lambda probe ( 26 ), wherein an electrical connection ( 27 ) between the lambda probe ( 26 ) and the first control unit ( 5 ), the at least one first current path ( 28 ) and a second current path ( 29 ), wherein in the second current path ( 29 ) an electrical resistance component ( 30 ) and between the first current path ( 28 ) and the second current path ( 29 ) with a switch ( 31 ) can be switched, the switch ( 31 ) with the second control device ( 6 ) connected is.

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