Patent Application
20190178179
The invention relates to a method for operating a combustion machine having a fuel tank system that comprises a fuel tank vent valve. The invention also relates to a combustion machine that is suitable for carrying out such a method as well as to a motor vehicle having such a combustion machine.
As a rule, a fuel tank system for a combustion machine of a motor vehicle has a vent line so that a rising pressure in the fuel tank of the tank system caused, for instance, by fuel that is evaporating at high ambient temperatures can be relieved to the atmosphere. In this process, also in view of the emissions standards, only the smallest possible amounts of fuel vapors are allowed to escape into the environment. This is prevented in that a fuel vapor filter, which is usually configured in the form of an activated carbon filter that absorbs the fuel vapors, is integrated into the vent line.
In order to regenerate such a fuel vapor filter, such a tank system is additionally provided with a purge gas line which is connected, on the one hand, to the fuel vapor filter and, on the other hand, to the fresh gas line of the combustion machine. During operation of the combustion machine, ambient air can at times be drawn in via an atmospheric port of the fuel vapor filter by means of the negative pressure that prevails in the area of the opening of the purge gas line, and this ambient air flows through the fuel vapor filter in the direction opposite to the direction in which the fuel vapors are flowing out of the fuel tank and into the fuel vapor filter, thus purging the filter. In this manner, the fuel vapors from the fuel vapor filter are fed via the fresh gas line to the combustion chambers of the internal combustion engine of the combustion machine.
U.S. Pat. Appln. No. 2003/0047161 A1 discloses a fuel tank system of a combustion machine having a direct-injection gas engine in which the type of combustion process and the amount of fuel injected during the purging of the fuel tank system are set as a function of a target value deviation for the fuel-to-air ratio, said deviation being determined on the basis of the measured value of a lambda sensor.
U.S. Pat. Appln. No. 2002/0162457 A1 describes a method for venting a fuel tank system of a combustion machine, whereby, on the basis of the hydrocarbon (HC) content in the purge gas, a decision is made as to when the fuel vapor filter has to be purged and when this purging can be ended again. In this context, the hydrocarbon content in the purge gas is determined by means of an appropriate HC sensor.
The invention was based on the objective of putting forward an advantageous method for determining the hydrocarbon content in the purge gas of a fuel tank system of a combustion machine.
This objective is achieved by means of a method according to patent claims. A combustion machine that is suitable for carrying out such a method is the subject matter of patent claims. Advantageous embodiments of the method according to the invention and preferred embodiments of the combustion machine according to the invention are the subject matters of the other patent claims and/or they ensue from the description of the invention below.
According to the invention, a method to determine the hydrocarbon content in the purge gas of a fuel tank system of a combustion machine is being provided, whereby the fuel tank system comprises at least
In this context, the expression determining the “qualitative” loading refers to the fact that at least one statement is made about the concrete composition of some of the hydrocarbons in the mixture of hydrocarbons contained in the purge gas.
The term “fuel vapor filter” does not mean according to the invention that it has to filter the volatile fuel in gaseous form. Rather, the fuel can already have (partially) condensed out again during the filtering procedure.
Aside from the determination of the quantitative loading, which is preferably carried out parallel to the determination of the qualitative loading, the determination according to the invention of the qualitative loading allows a very precise assessment of the influence that the purge gas—which is fed to the fresh gas line of the combustion machine and from there to the internal combustion engine—exerts on the combustion processes during operation of the internal combustion engine. As a result, countermeasures can thus be carried out very precisely such as, for instance, adjusting the amount of fuel that is injected into the combustion chambers of the internal combustion engine for the individual work cycles, and this adjustment serves to compensate for the hydrocarbons that are introduced into the combustion chambers along with the purge gas. In this manner, the fuel-fresh gas mixtures that are thermally converted in the combustion chambers during the individual work cycles can be kept very exactly within the range of a prescribed target value or within a target value range, and this has a positive impact on the operating behavior of the internal combustion engine or of the entire combustion machine, and especially on the volumetric efficiency and/or on the emission behavior.
Accordingly, the invention also relates to a method for operating a combustion machine, said method encompassing the determination according to the invention of the hydrocarbon content in the purge gas of a fuel tank system of the combustion machine and, based on the result of this determination, encompassing the adjustment of parameters that influence combustion processes that take place in an internal combustion engine during operation of the combustion machine.
The preferably quantitative determination of the loading of the purge gas with hydrocarbons—a procedure in which preferably the amount of the hydrocarbons in relation to the total amount of purge gas, that is to say, the relative hydrocarbon content (in percent by volume or in percent by weight) is determined—preferably takes place only or one time (for the period of time) at the end of the period of time, as a result of which, based on pressure measurements, very precise results can be obtained pertaining to the quantitative loading of the purge gas with hydrocarbons.
It can preferably be provided that the defined period of time begins with the start-up of the compressor, and thus with the beginning of a purging procedure, and/or that it ends with the determination of several pressure values that are within the same value range. In this context, this value range is relatively small in comparison to the maximum difference among the measured pressure values, so that it is thus provided that the defined period of time ends when pressure values that are the same or approximately the same occur multiple times. As an alternative or in addition, however, it can also be provided that the defined period of time extends precisely to, or at least over, the defined number of pressure measurements.
In accordance with a preferred embodiment of a method according to the invention, it can be provided that, for the pressure measurements, in each case, a pressure gradient, a pressure differential relative to one of the other pressure measurements and/or a pressure gradient differential is determined, which are then analyzed with respect to at least one of these descriptive values that is characteristic of certain types of hydrocarbons in order to qualitatively determine the loading of the purge gas with hydrocarbons. In this manner, it can be provided, for example, that, in the case of a relatively large pressure gradient, the presence of a relatively high content of ethanol in the purge gas can be assumed.
It can likewise be preferably provided that the positions of at least some of the pressure measurements taken within the defined period of time and/or the time interval of at least some of the pressure measurements taken during a preceding start-up of the compressor are used in order to determine the qualitative loading of the purge gas with the hydrocarbons. This yields a very precise determination of the qualitative loading. For example, it can be provided that a relatively high content of ethanol in the purge gas is only assumed if a relatively large pressure gradient has been determined within a relatively early segment of the defined period of time and especially after the compressor has been started up.
In order to enhance the precision of the determination of the quantitative and/or qualitative loading of the purge gas with hydrocarbons, it can preferably be provided that the time interval between the pressure measurements is varied, at least at times. In particular, it can be provided that, within defined limits and relative to reference values, the larger a pressure gradient determined on the basis of the first pressure measurement is, the shorter the time interval selected between a first pressure measurement and a second pressure measurement. Consequently, it can preferably be provided that a first pressure gradient is determined on the basis of a first pressure measurement and a second pressure gradient is determined on the basis of a subsequent second pressure measurement, and, on the basis of the magnitude of the difference between these pressure gradients, the time interval between the second and a subsequent third pressure measurement is varied in such a way that a relatively small time interval is selected in the case of a relatively large difference between the pressure gradients.
It can preferably be provided that a method according to the invention is carried out at least once for each start-up of the compressor, so that, for each purging procedure, a determination according to the invention is made of the hydrocarbon content in the purge gas that is then being conveyed, so that, for each purging procedure, it is accordingly possible to carry out the most exact compensation possible of the influence exerted by the hydrocarbons that have been introduced via the purge gas into the combustion chambers of the internal combustion engine.
A combustion machine according to the invention comprises, on the one hand, at least
The method according to the invention can especially be employed in a fuel tank system of a combustion machine (according to the invention) whose internal combustion engine can be operated in an externally ignited manner, especially in accordance with the Otto principle, since the fuel used to operate such an internal combustion engine is usually relatively highly volatile (especially in comparison to diesel fuel), as a result of which the special need for a fuel tank vent system can be warranted.
A combustion machine according to the invention can especially be part of a motor vehicle. In this context, the internal combustion engine of the combustion machine can especially be designed to directly or indirectly provide the drive power for the motor vehicle. Therefore, the invention also relates to a motor vehicle, particularly to a motor vehicle on wheels (preferably a passenger car or a truck) having a combustion machine according to the invention.
The indefinite articles (“a”, “an”), especially in the patent claims and in the description that generally explains the patent claims, are to be understood as such and not as numbers. Therefore, components described in a concrete manner should be understood in such a way that they are present at least once and can also be present several times.
The invention will be explained in greater detail below, making reference to an embodiment shown in the drawings. The drawings show the following:
During operation of the combustion machine, in a known manner, gas mixtures consisting of fresh gas that is made up completely or primarily of ambient air and of fuel that is injected, for example, directly into the combustion chambers 28 by means of injection valves (not shown here) are burned in a defined sequence in the combustion chambers 28 of the internal combustion engine 20, said chambers being partially delimited by cylinders 30 of the internal combustion engine 20, whereby the pressure rises thus generated in the combustion chambers 28 are used to move pistons 32 that can be moved along the longitudinal axis in the cylinders 30. Through the interaction of connecting rods (not shown here), these movements of the pistons 32 can be converted into a rotational motion of a crankshaft (not shown here), whereby the movement of the pistons 32 via the connecting rods by means of the crankshaft simultaneously brings about a cyclical back-and-forth movement of the pistons 32. The exhaust gas generated in the combustion chambers 28 during the combustion of the fuel-fresh gas mixtures is discharged via the exhaust gas line 26, thereby flowing through the exhaust gas turbine 24, which causes a turbine impeller (not shown here) to rotate. This rotation of the turbine impeller is transferred by means of a shaft 34 to a compressor impeller (not shown here) of the charge air compressor 22, as a result of which the charge air compressor 22 compresses the fresh gas that is fed to the internal combustion engine 20 via the fresh gas line 18.
The side of the fuel vapor filter 14 of the fuel tank system facing away from the vent line 12 and the purge gas line 16 (with respect to its filtering effect for fuel vapors) is fluidically connected to the atmosphere via an ambient air line 38, for which purpose the ambient air line 38 forms an atmospheric port 44.
The fuel tank 10 is partially filled with fuel, whereby a part of this fuel, which is actually liquid, has usually evaporated, so that fuel in a gaseous state of aggregation is also present in the fuel tank 10. Such an evaporation of fuel in the fuel tank 10 is intensified by a relatively high temperature of the fuel, and this can occur especially at relatively high ambient temperatures as well as in the case of a change in the ambient pressure, for instance, if a motor vehicle comprising the combustion machine is being driven up a mountain. In order to prevent an impermissibly high excess pressure in the fuel tank 10 due to such evaporation, the possibility exists to equalize the pressure with the ambient pressure via the vent line 12 and the fuel vapor filter 14 as well as via the ambient air line 38, whereby the fuel vapor filter 14 prevents such a pressure equalization from allowing fuel vapors to escape into the environment.
Such a venting of the fuel tank 10 leads to an increasing saturation of the fuel vapor filter 14 which, in turn, requires the filter to be regenerated at regular intervals. For this purpose, it is provided for the fuel vapor filter 14 to be purged in that ambient air is drawn in via the atmospheric port 44 and via the ambient air line 38. This ambient air flows through the fuel vapor filter 14 in the opposite direction from that of the flow during the venting of the fuel tank 10, as a result of which fuel molecules absorbed in the fuel vapor filter 14 are carried along by the ambient air and introduced into the fresh gas line 18 via the purge gas line 16. Consequently, this fuel, which usually contains a mixture of different hydrocarbons, is conveyed to the combustion chambers 28 of the internal combustion engine 20 in order to be burned.
Such a purging of the fuel vapor filter 14 is only provided for at times and always during operation of the internal combustion engine 20 because only then can the fuel that has been introduced into the fresh gas line 18 by the purging of the fuel vapor filter 14 also be reliably fed into the combustion chambers 28 in order to be burned. In contrast, if fuel is introduced into the fresh gas line 18 when the internal combustion engine 20 is not being operated, this could cause the gaseous fuel to escape into the environment via leaks in the fresh gas line 18 and especially via an intake opening of the fresh gas line 18.
A fuel tank vent valve 42 that is integrated into the purge gas line 16 is arranged as close as possible to the purge gas line opening 40 leading into the fresh gas line 18, or else it is integrated into it.
In order to purge the fuel vapor filter 14, there is a need for a sufficient pressure gradient between, on the one hand, the ambient pressure and, on the other hand, the pressure in the fresh gas line 18 in the vicinity of the opening 40 of the purge gas line 16, whereby this pressure gradient is not always present due to greatly fluctuating pressures in the fresh gas line 18 during operation of the internal combustion engine 20. During operation of the internal combustion engine 20 and thus of the charge air compressor 22, the pressure of the fresh gas in the section of the fresh gas line 18 in the area of the opening 40 of the purge gas 16 is usually so low that there is a sufficient pressure gradient relative to the ambient pressure that is present at the atmospheric port 44. However, this is not always the case.
In order to allow purging of the fuel vapor filter 14 at any time so that its complete saturation can be reliably prevented, the fuel tank system of the combustion machine also comprises a compressor 46 that is integrated into the purge gas line 16, whereby said compressor 46 is also normally referred to as a “purge air pump” and it can be configured in the form of a piston compressor, especially as a rotary vane compressor or else as a radial fan. When this compressor 46 is being operated, ambient air can be actively drawn in via the atmospheric port 44, and this air then flows through the fuel vapor filter 14 in order to purge it, and is then conveyed via the compressor 46 all the way to the opening 40 of the purge gas line 16.
At least the compressor 46, the fuel tank vent valve 42, the throttle valve 36 and a pressure sensor 50 that is integrated into the purge gas line 16 can be actuated by means of a control device 48 (for example, the engine control unit of the combustion machine).
At the same time as the end of the defined period of time, an evaluation is made of the pressure curve or of each pressure curve, on the basis of which it is possible to derive, on the one hand, the quantitative and, on the one hand, the qualitative, loading of the purge gas that is being conveyed by the compressor during the appertaining period of time and that is subsequently flowing or already has flowed into the fresh gas line, together with hydrocarbons. This evaluation is especially based on the fact that the various hydrocarbons contained in the purge gas exhibit different densities, on the one hand, in comparison to each other and, on the other hand, in comparison to ambient air that is likewise contained in the purge gas. In this context, on the basis of the averaged rise in the pressure over the appertaining period of time, especially the quantitative loading of the purge gas with hydrocarbons can be determined, whereas on the basis of the characteristic curve of the pressure during the appertaining period of time, conclusions can be drawn about the qualitative loading and thus about the composition of the mixture containing various hydrocarbons in the purge gas. For instance, the upper pressure curve of the two curves depicted in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2017 129 769.3 | Dec 2017 | DE | national |
