Method for monitoring a fuel supply system of an internal combustion engine and internal combustion engine for carrying out such a method

Abstract

Method for monitoring a fuel supply system (3) of an internal combustion engine (1), wherein - a first pressure quantity in the fuel supply system (3) in the area of ​​a pre-filter (9) and upstream of a low-pressure pump (11,11') is detected, wherein - a second pressure parameter is detected in the fuel supply system (3) downstream of the low-pressure pump (11,11') in the area of ​​a main filter (13), wherein - the first pressure quantity and the second pressure quantity are monitored for a fault condition of the fuel supply system (3), and wherein - is only detected as an error state if the error state is plausible based on both pressure variables, characterized in that, - if one of the pressure quantities selected from the first pressure quantity and the second pressure quantity indicates a fault condition of the fuel supply system (3), the fault condition is checked using the other pressure quantity selected from the second pressure quantity and the first pressure quantity, whereby the fault condition is only accepted if the check returns a positive result.

Description

[0001] The invention relates to a method for monitoring a fuel supply system of an internal combustion engine and to an internal combustion engine having a fuel supply system for carrying out such a method.

[0002] Such a fuel supply system comprises several components, in particular a pre-filter upstream of a low-pressure pump and a main filter, which is fluidically arranged between the low-pressure pump and a high-pressure pump. In general, fault conditions in such a fuel supply system are difficult to detect. Therefore, rigid maintenance intervals, especially replacement intervals, are often specified – especially for the low-pressure filter and the high-pressure filter. However, for safety reasons, these intervals are then systematically chosen to be shorter than necessary, so that functional filters are generally replaced. Relying on sensor-based fault detection, on the other hand, leads to the problem of false-positive fault diagnoses, for example, because a change in fuel viscosity – whether due to a change in fuel or a change in temperature – is interpreted in sensor feedback as equivalent to a filter breakthrough.Furthermore, it is difficult to reliably and accurately detect both slow-onset aging phenomena and rapidly occurring failures.

[0003] JP 2006-316 771 A discloses a device for testing a fuel supply device, wherein the fuel supply device has a low-pressure pump and a high-pressure pump, wherein a first fuel filter is arranged in a fuel path from a fuel tank to the low-pressure pump, wherein a second fuel filter is arranged in a second fuel path from the low-pressure pump to the high-pressure pump, wherein a first pressure sensor is arranged downstream of the first fuel filter in the first fuel path, wherein a second pressure sensor is arranged downstream of the second fuel filter in the second fuel path. A state of the fuel supply device is monitored using pressure measurement values ​​from the first pressure sensor and the second pressure sensor, wherein a specific fault state is detected using a decision tree based on the pressure measurement values.Only one of the two pressure measurements is considered in each branch of the decision tree. Even with this approach, the risk of false-positive error diagnoses is high.

[0004] The invention is based on the object of providing a method for monitoring a fuel supply system of an internal combustion engine and an internal combustion engine with a fuel supply system for carrying out such a method, wherein the aforementioned disadvantages do not occur.

[0005] The object is achieved by providing the present technical teaching, in particular the teaching of the independent claims as well as the embodiments disclosed in the dependent claims and the description.

[0006] The object is achieved in particular by providing a method for monitoring a fuel supply system of an internal combustion engine, in which a first pressure variable is detected in the fuel supply system in the region of a pre-filter, in particular downstream of the pre-filter, and upstream of a low-pressure pump. A second pressure variable is detected in the fuel supply system downstream of the low-pressure pump in the region of a main filter. The first pressure variable and the second pressure variable are monitored for a fault condition in the fuel supply system. Within the scope of the method, a fault condition is only detected if the fault condition is plausible based on both pressure variables.The intention is that if one of the pressure variables selected from the first pressure variable and the second pressure variable indicates a fault condition in the fuel supply system, the fault condition is checked using the other pressure variable selected from the second pressure variable and the first pressure variable. The fault condition is only accepted if the check returns a positive result. Incorporating both pressure variables into the assessment of the fault condition significantly reduces the problem of false-positive fault detections. In particular, the plausibility check using the two pressure variables makes it possible to distinguish between filter faults, such as filter perforations, on the one hand, and changes in fuel viscosity on the other. This, in turn, enables improved automated monitoring of the fuel supply system, eliminating the need for rigid, systematically too short maintenance intervals.In particular, due to the inclusion of both pressure variables in the detection of the fault condition, both slow aging phenomena can be monitored and rapidly occurring failures can be detected in a timely manner.

[0007] A fuel supply system is understood in particular to mean a system which is designed to supply fuel - in particular from a storage container, preferably a fuel tank - to an internal combustion engine for combustion, wherein the fuel supply system is designed in particular to bring the fuel from a low pressure level in the storage container, in particular ambient pressure, to a high pressure for introduction into a combustion chamber of the internal combustion engine, in particular for direct injection.

[0008] A pressure quantity is understood here, in particular, to be a measurable physical quantity that has the unit of pressure. The pressure quantity can be a single value or a temporal value profile. In particular, the pressure quantity can be based on a—particularly local—measurement, or it can be a differential quantity, in particular a difference between two measurements recorded at different locations. The pressure quantity can be specified as absolute pressure or as relative pressure, in particular as overpressure. Particularly preferably, the pressure quantity is specified as relative pressure, in particular as overpressure.

[0009] The fact that the first pressure variable is detected in the region of the pre-filter means, in particular, that the first pressure variable is detected immediately upstream and / or immediately downstream of the pre-filter, wherein, in particular, no further hydraulic element is arranged between the position of a pressure sensor for detecting the first pressure variable and the pre-filter. Preferably, the first pressure variable is detected immediately downstream of the pre-filter.

[0010] The fact that the second pressure variable is detected in the region of the main filter means in particular that the second pressure variable is detected immediately upstream and / or immediately downstream of the main filter, wherein in particular no further hydraulic element is arranged between the position of a pressure sensor for detecting the second pressure variable and the main filter.

[0011] The second pressure variable is preferably detected downstream of the low-pressure pump and upstream of a high-pressure pump. In particular, the main filter is preferably arranged fluidically between the low-pressure pump and the high-pressure pump, in particular upstream of a suction throttle associated with the high-pressure pump.

[0012] The fact that the error state is plausible based on both pressure variables means in particular that the error state exists with a certain probability, which is preferably higher than a predetermined limit probability, based on an evaluation or consideration of both pressure variables, i.e. the first pressure variable and the second pressure variable, and / or that no other, in particular no other more probable, cause for the observed behavior of the two pressure variables can be identified based on the two pressure variables.

[0013] According to the invention, if one of the pressure variables selected from the first pressure variable and the second pressure variable indicates a fault condition in the fuel supply system, the fault condition is checked using the other pressure variable selected from the second pressure variable and the first pressure variable. The fault condition is only accepted if the check returns a positive result, i.e., if the check using the other pressure variable confirms the fault condition or at least does not rule it out or makes it appear unlikely. The fact that the fault condition is only accepted in this case means, in particular, that the fault condition is only detected then.The fact that the test returns a positive result also means, in particular, that the test confirms the fault condition based on the other pressure variable, in particular in the sense that it does not suggest any other, more plausible, i.e. in particular more probable, cause or explanation for the behaviour of one pressure variable.

[0014] In particular, this way, false-positive detections of error conditions can be avoided.

[0015] According to a further development of the invention, a fault condition is only detected if the fault condition can be clearly assigned to one of the pressure variables selected from the first pressure variable and the second pressure variable. This is based on the consideration that if the fault condition can be assigned to both pressure variables, it is more likely that there is no fault in an individual component, for example the pre-filter or the main filter, but rather a common, in particular non-faulty, cause for the behavior of the two pressure variables, for example a change in the viscosity of the fuel, whether due to a fuel change or a temperature change.This is ultimately more likely than two independent components of the fuel supply system experiencing a fault condition simultaneously, for example, both the pre-filter and the main filter experiencing a filter failure at the same time. This also reliably prevents false-positive fault detections.

[0016] According to a further development of the invention, a temporal pressure value curve is recorded as the first pressure variable and as the second pressure variable. The temporal pressure value curve is preferably monitored for changes. This proves to be particularly advantageous with regard to monitoring the fuel supply system, since fault conditions are expressed in particular by changes in the temporal behavior of pressure values. For example, the pressure dropping across a filter changes slowly and steadily due to unavoidable contamination of the filter, which causes it to become increasingly clogged. A filter breakthrough or sudden blockage of the filter caused by a fault is expressed in an abrupt change in the temporal pressure value curve. In particular, the temporal pressure value curve is preferably monitored for a change in a temporal derivative, in particular a gradient, curvature, or a higher derivative.

[0017] Preferably, the pressure value curve is also monitored with regard to pressure limit values, in particular an upper pressure limit and a lower pressure limit, which should not be exceeded or undershot. If such a limit is exceeded or undershot, a warning message is preferably issued. Preferably, additional safety limit values ​​are defined, for example, an upper error limit that is higher than the upper pressure limit and / or a lower error limit that is lower than the lower pressure limit, with an error message being issued if the pressure value curve or the pressure variable exceeds such an error limit. In this case, it is assumed, in particular, that the fuel supply system is not functioning properly.

[0018] Furthermore, a tolerance band is preferably provided around an expected or simulated, in particular pre-calculated, temporal development of the pressure value curve, wherein a warning is issued when the pressure value curve leaves this tolerance band.

[0019] According to a further development of the invention, a local pressure, in particular a local pressure profile, is detected for the first pressure variable, in particular by a single pressure sensor. In particular, a single pressure sensor is preferably arranged downstream of the pre-filter and upstream of the low-pressure pump, which detects the first pressure variable. For the pre-filter, a single, local pressure detection is preferably sufficient, whereby the corresponding design with only one pressure sensor is cost-effective.

[0020] The second pressure variable is preferably recorded as a differential pressure, in particular a differential pressure value curve, in particular as a differential pressure falling across the main filter. For this purpose, two pressure sensors are preferably provided, with a first pressure sensor located upstream of the main filter and a second pressure sensor located downstream of the main filter, so that by calculating the difference between the measured values ​​of the first pressure sensor and the second pressure sensor, a differential pressure falling across the main filter can be determined. This allows the main filter to be monitored in a particularly precise and meaningful manner.

[0021] According to a further development of the invention, a fuel temperature variable is detected, preferably as a temperature profile over time, whereby the fault condition is only detected if the fault condition is also plausible based on the fuel temperature variable. In particular, temperature changes can be excluded as causes of false-positive fault detections.

[0022] Furthermore, a temperature change detected based on the fuel temperature variable is preferably used to determine the tolerance band for the pressure value curve, whereby a tolerance adjustment to the respective fuel temperature is useful here, since the pressure value curve depends significantly on the current fuel temperature.

[0023] Alternatively or additionally, a current load point of the internal combustion engine is preferably recorded, whereby the fault condition is only detected if the fault condition is also plausible based on the current load point of the internal combustion engine. In this respect, it has been found that the pressure variables are particularly dependent on the load point, so that the corresponding inclusion of the current load point of the internal combustion engine is again advantageous in order to avoid false-positive fault detections.

[0024] According to a further development of the invention, if at least one of the pressure variables selected from the first pressure variable and the second pressure variable indicates a fault condition in the fuel supply system, the fault condition is checked for plausibility based on a further temporal development of the at least one pressure variable - in particular the pressure variable that indicates the fault condition. In this way, the further temporal development of the pressure variable can be used to determine whether a fault condition actually exists. If, for example, a change in the viscosity of the fuel occurs, which initially manifests itself as a filter breakthrough, the temporal development of the pressure variable returns to a normal development after a settling time due to aging / contamination effects. This, in turn, allows the determination that no filter breakthrough has occurred.It can therefore be used in particular to demonstrate plausibility that a certain temporal development will be reversed in the future because the viscosity has settled at a certain value and the mechanisms of contamination or aging will now take effect again.

[0025] According to a further development of the invention, the prefilter and the main filter are monitored for fault conditions based on the first pressure variable and the second pressure variable. The aforementioned advantages of the method arise particularly in connection with fault monitoring for these filters.

[0026] According to a further development of the invention, a filter breakthrough is detected on a specific filter, selected from the pre-filter and the main filter, if only the pressure variable assigned to the specific filter, selected from the first pressure variable and the second pressure variable, indicates filter breakthrough. However, a filter breakthrough is not detected if both pressure variables, i.e., the first pressure variable and the second pressure variable, each indicate a filter breakthrough. This is based on the idea that it is unlikely that both filters, namely the pre-filter and the main filter, experience a filter breakthrough at the same time.Therefore, if both pressure variables simultaneously indicate that there has been a filter breakthrough in the filters assigned to them, this is more likely than simultaneous breakthrough of both filters to indicate that there is a common, different cause for the corresponding values, in particular changes in the pressure variables. This can in particular be a change in the viscosity of the fuel used, whereby a reduction in viscosity in particular means that the fuel can pass through the filters more easily and with less flow resistance, which leads to a change in the pressure variables that can be misinterpreted as a filter breakthrough. Such a change in viscosity can result, for example, from a change in the fuel used and / or from a change in temperature, in particular an increase in temperature.

[0027] If, for example, the first pressure variable is a pressure value curve measured downstream of the pre-filter, the first pressure variable usually shows a negative gradient within a certain tolerance range if no fault condition exists. This is because the pre-filter becomes clogged over time, i.e. ages due to contamination. With a constant flow rate of the low-pressure pump, a decreasing fuel volume flow can be pumped through the pre-filter. The pressure downstream of the pre-filter therefore drops over time. If the pre-filter breaks through the filter, the gradient of the first pressure variable suddenly changes and takes on a positive sign because more fuel can now be pumped through the pre-filter. The same behavior can also result from a reduction in the viscosity of the fuel.

[0028] If, for example, the second pressure variable is recorded as a differential pressure value curve of the differential pressure falling across the main filter, this will exhibit a positive gradient during normal operation, as the differential pressure increases due to continuous, age-related contamination of the main filter. A filter breakthrough at the main filter leads to a sudden change in the gradient, which then takes on a negative sign, as the differential pressure across the main filter drops due to the breakthrough. However, the second pressure variable exhibits the same behavior when the viscosity of the fuel decreases. If the sign of the gradient of the respective assigned pressure variable changes at both the pre-filter and the main filter at the same time, this indicates a change in the viscosity of the fuel, since - as already explained - a simultaneous breakthrough at both filters is unlikely.Likewise, the signs will return to their original state in the future once the fuels with different viscosities have mixed and the pressures rise again due to filter contamination. This can be advantageously used to verify the plausibility of the data. However, if only one of the pressure variables changes the sign of its gradient, while the sign of the gradient remains constant for the other pressure variable, this suggests that a filter breakthrough has occurred at the affected filter whose associated pressure variable exhibits the change in the sign of the gradient.

[0029] In general, it can be said that a situation in which only one of the pressure variables indicates a fault condition, while the other does not, virtually rules out a common cause for the corresponding behavior of the pressure variables. It can then be logically concluded that a local cause lies in the area where the respective pressure variable is recorded, which in turn indicates the fault condition.

[0030] The fact that only the pressure value assigned to a specific filter indicates filter breakthrough means in particular that the pressure value assigned to the other filter does not indicate filter breakthrough.

[0031] A pressure quantity assigned to a specific filter is understood to be a pressure quantity that is recorded locally in the immediate vicinity of the corresponding filter, so that it is directly influenced by the behavior of the corresponding filter and thus allows a direct statement about the corresponding filter.

[0032] In particular, the first pressure variable is assigned to the pre-filter because it is detected in its area, particularly immediately downstream of the pre-filter, particularly fluidically between the pre-filter and the low-pressure pump. Accordingly, the second pressure variable is assigned to the main filter because it is detected in the area of ​​the main filter.

[0033] According to a further development of the invention, the fuel supply system is used to supply a plurality of internal combustion engines, wherein the fault condition is checked for plausibility via at least two internal combustion engines of the plurality of internal combustion engines. This enables additional reliability in fault detection, in particular in avoiding false-positive detections of fault conditions. In particular, each internal combustion engine is preferably assigned a sub-fuel supply system, in particular with its own pre-filter and its own main filter, wherein a first pressure variable and a second pressure variable are recorded accordingly for each internal combustion engine. The various internal combustion engines are supplied with fuel by the various sub-fuel supply systems, preferably from a same reservoir.In particular, this results in a high degree of probability—analogous to the considerations explained above—that a fault condition, in particular a filter breakdown, actually only exists if the same fault condition is not detected simultaneously in multiple internal combustion engines. However, if the same fault condition, for example a filter breakdown, is detected simultaneously in multiple internal combustion engines, in particular for both filters, namely the respective main filter and the respective pre-filter, this again makes it more likely that another common cause, beyond the suspected fault condition, can be inferred than that a plurality of components are actually faulty at the same time.In particular, a change in fuel viscosity, whether due to a change in fuel or a change in temperature, affects a majority of internal combustion engines, particularly all internal combustion engines. In contrast, an actually occurring fault condition, in particular a filter perforation, at least with a high degree of probability only has a local effect on the respective filter and thus on the pressure variable directly associated with the filter.

[0034] Such a fuel supply system for supplying a plurality of internal combustion engines is particularly used in a so-called multi-engine system. Such multi-engine systems, in turn, are preferably used to drive rail vehicles, particularly as railway engines, or in watercraft, particularly as ship or boat engines, especially yacht or ferry engines. However, such a multi-engine system can also be designed for the parallel operation of a plurality of generators to generate electrical power. The use of multi-engine systems is by no means limited to the applications mentioned here.

[0035] According to a further development of the invention, it is provided that based on the first pressure variable and the second pressure variable - in particular in addition to the previously explained monitoring of the main filter and the pre-filter - at least one further component is monitored for a fault condition, wherein the further component is selected from a group consisting of: a low-pressure pump, preferably including a pre-throttle for the low-pressure pump; a shut-off valve; a suction throttle, in particular a suction throttle assigned to a high-pressure pump for flow control; and a high-pressure pump, in particular a lubricant supply for a high-pressure pump. Advantageously, at least one of these components can additionally be monitored for a fault condition based on the two pressure variables.

[0036] Preferably, at least the low-pressure pump, in particular including the pre-throttle, the suction throttle and the high-pressure pump are designed as a pump unit, in particular arranged integrally with one another and can be handled together, in particular removed from and installed in the fuel supply system.

[0037] The pre-throttle is preferably configured to limit the flow rate to the low-pressure pump. This limitation depends in particular on the first pressure variable and is designed for suction operation.

[0038] The shut-off valve preferably has a volume flow-dependent pressure characteristic. In particular, the second pressure variable is characteristic of the function of the shut-off valve, wherein the shut-off valve is preferably arranged in a fluidic shut-off line that branches off from a fluidic connection from the main filter to the suction throttle and leads back to a point upstream of the low-pressure pump, wherein it opens in particular into a fluidic connection between the pre-filter and the low-pressure pump. In particular, if the pressure detected downstream of the main filter exceeds a certain limit, a defect in the shut-off valve can be concluded, since, if functioning correctly, it should trigger and prevent the pressure from rising above the limit.If, on the other hand, the pressure measured downstream of the main filter is too low, this indicates wear, particularly due to leaks or loss of spring force, of the shut-off valve, causing an excessive flow rate to escape through the shut-off valve. However, a pressure that is too low downstream of the main filter can also indicate a defect in the low-pressure pump, which would then no longer be able to deliver the intended flow rate.

[0039] Lubrication of the high-pressure pump is preferably achieved via a lubrication path as a bypass flow path, which branches off upstream of the suction throttle and leads to the lubrication points of the high-pressure pump. If this bypass flow path becomes contaminated, lubrication is not provided. This can be determined, in particular, by monitoring the pressure downstream of the main filter. In particular, the pressure gradient here must not exceed a predetermined maximum gradient, otherwise too little fuel will flow to the lubrication points via the bypass flow path.

[0040] The object is also achieved by providing an internal combustion engine having a fuel supply system for supplying fuel to at least one combustion chamber of the internal combustion engine. The fuel supply system has a reservoir, in particular a fuel tank, which is fluidly connected to a low-pressure pump via a pre-filter. The low-pressure pump is fluidly connected to a high-pressure pump via a main filter. The internal combustion engine has a first pressure measuring device configured to detect a first pressure variable in the fuel supply system in the region of the pre-filter, in particular downstream of the pre-filter, and upstream of the low-pressure pump. The internal combustion engine also has a second pressure measuring device configured to detect a second pressure variable in the fuel supply system downstream of the low-pressure pump in the region of the main filter.The internal combustion engine further comprises a control unit which is operatively connected to the first pressure measuring device on the one hand and to the second pressure measuring device on the other hand and is configured to monitor the first pressure variable and the second pressure variable for a fault condition in the fuel supply system, but to only detect a fault condition if the fault condition is plausible based on both pressure variables, i.e. the first pressure variable and the second pressure variable. The control unit is therefore configured in particular to check the plausibility of the fault condition on the basis of both pressure variables. The control unit is configured in particular to carry out a method according to the invention or a method according to one of the previously described embodiments. In connection with the internal combustion engine, the advantages which have already been explained in connection with the method arise in particular.

[0041] The first pressure measuring device is preferably designed as a single, first pressure sensor. The first pressure sensor is preferably arranged downstream of the pre-filter and upstream of the low-pressure pump in the fluidic connection between the pre-filter and the low-pressure pump, in particular in a fuel line that fluidically connects the pre-filter to the low-pressure pump.

[0042] The second pressure measuring device is preferably arranged upstream of the high-pressure pump. Particularly preferably, the second pressure measuring device is arranged in the fluid connection between the low-pressure pump and the high-pressure pump, in particular in a fuel line that fluidly connects the low-pressure pump to the high-pressure pump. In particular, the first pressure measuring device is preferably arranged directly upstream of the main filter and / or directly downstream of the main filter.

[0043] In a particularly preferred embodiment, the second pressure measuring device has two second pressure sensors, wherein a first second pressure sensor is arranged upstream of the main filter, in particular directly upstream of the main filter, and a second second pressure sensor is arranged downstream of the main filter, in particular directly downstream of the main filter. The control unit is preferably operatively connected to both second pressure sensors. In a preferred embodiment, it is configured to determine, in particular calculate, a differential pressure falling across the main filter as a second pressure variable from measured values ​​of the two second pressure sensors.

[0044] The internal combustion engine preferably has a temperature sensor arranged and configured to detect a fuel temperature variable, with the control unit being operatively connected to the temperature sensor. The control unit is further preferably configured to check the plausibility of the fault condition based on the detected fuel temperature variable. The temperature sensor is preferably arranged in the fluid connection between the pre-filter and the low-pressure pump, or in the region of the reservoir, in particular on the reservoir.

[0045] Preferably, the fuel supply system comprises two low-pressure pumps which are arranged fluidically parallel to each other in the fluid connection between the pre-filter and the main filter.

[0046] The high-pressure pump is preferably assigned a suction throttle which is arranged downstream of the high-pressure pump in the fluidic connection between the main filter and the high-pressure pump, wherein the control unit is operatively connected to the suction throttle and is configured to control the suction throttle to regulate a volume flow delivered by the high-pressure pump.

[0047] Preferably, the fuel supply system has a shut-off valve which is arranged in a shut-off line which branches off from the fluidic connection between the main filter and the high-pressure pump, in particular between the main filter and the suction throttle, and in a preferred embodiment opens upstream of the at least one low-pressure pump, in particular into the fluidic connection between the pre-filter and the at least one low-pressure pump.

[0048] The fuel supply system preferably has two high-pressure pumps arranged parallel to each other in terms of flow, with the flow connection between the main filter and the high-pressure pumps branching to the two high-pressure pumps. Each high-pressure pump is preferably assigned its own suction throttle, which is arranged upstream of the respective high-pressure pump.

[0049] The two high-pressure pumps preferably each serve to separately supply fuel to a respective, separate high-pressure accumulator. The respective high-pressure accumulator is preferably configured for a combustion chamber group, in particular a cylinder bank, of an internal combustion engine having two combustion chamber groups, in particular cylinder banks, as a common high-pressure accumulator, in particular as a so-called common rail, for the combustion chambers of the respective cylinder bank. Of course, with a larger number of combustion chamber groups, for example, with three cylinder banks in the case of a W engine, it is also possible to provide three high-pressure pumps—preferably each with an associated intake throttle.In particular, each high-pressure accumulator of the internal combustion engine is preferably separately assigned a high-pressure pump - in particular with an associated suction throttle - wherein all high-pressure pumps are connected - fluidically parallel to one another - to the same main filter.

[0050] Preferably, each high-pressure pump is assigned a shut-off valve in a corresponding shut-off line.

[0051] The fuel supply system preferably has a lubrication path for lubricating the at least one high-pressure pump. The lubrication path branches off from the fluid connection between the main filter and the high-pressure pump downstream of the main filter, preferably upstream of the intake throttle, and flows into the high-pressure pump, in particular at at least one lubrication point of the high-pressure pump. Preferably, each high-pressure pump is assigned such a lubrication path. The at least one high-pressure pump is thus lubricated, in particular, by fuel.

[0052] The fuel supply system preferably has a leakage path from the at least one high-pressure pump into the reservoir, which is particularly configured to guide fuel used as lubricant from the high-pressure pump back into the reservoir. In particular, each high-pressure pump is preferably assigned such a leakage path.

[0053] The description of the method, on the one hand, and of the internal combustion engine, on the other hand, are preferably to be understood as complementary to one another. Features of the internal combustion engine that were explained explicitly or implicitly in connection with the method are preferably, individually or in combination with one another, features of a preferred exemplary embodiment of the internal combustion engine. Method steps that were explained explicitly or implicitly in connection with the internal combustion engine are preferably, individually or in combination with one another, steps of a preferred embodiment of the method. This is preferably characterized by at least one method step that is determined by at least one feature of an internal combustion engine according to the invention or of an exemplary embodiment of the internal combustion engine.The internal combustion engine is preferably characterized by at least one feature which is determined by at least one step of the method according to the invention or an embodiment of the method.

[0054] The invention is explained in more detail below with reference to the drawings, which show: Fig. 1 is a schematic representation of an embodiment of an internal combustion engine with a fuel supply system; Fig. 2 a first schematic representation of the operation of an embodiment of a method for monitoring a fuel supply system of an internal combustion engine, and Fig. 3 a second schematic representation of the embodiment of the method.

[0055] Fig. 1 shows a schematic representation of an embodiment of an internal combustion engine 1 having a fuel supply system 3 for supplying fuel to at least one combustion chamber 5 of the internal combustion engine 1. In Fig. 1 schematically illustrates eight combustion chambers 5, of which only one is identified with the corresponding reference numeral for the sake of clarity. The combustion chambers 5 are grouped in groups of four into two combustion chamber groups 4, 4', in particular cylinder banks. The internal combustion engine 1 is therefore preferably designed as a V-engine.

[0056] The fuel supply system 3 has a reservoir 6, here in particular a fuel tank 7, which is fluidically connected to a low-pressure pump 11 via a pre-filter 9. In the embodiment of the internal combustion engine 1 shown here, two low-pressure pumps 11, 11' are arranged fluidically parallel to one another downstream of the pre-filter 9. The low-pressure pump 11, here both low-pressure pumps 11, 11' arranged parallel to one another, is / are fluidly connected to a high-pressure pump 15, here to two high-pressure pumps 15, 15', via a main filter 13. The flow path for the fuel branches off downstream of the pre-filter 9 to the two low-pressure pumps 11, 11', and then rejoins downstream of the low-pressure pumps 11, 11', with the main filter 13 being assigned to the low-pressure pumps 11, 11' as a common main filter 13.Downstream of the main filter 13, the flow path then branches off again to the two high-pressure pumps 15, 15', which are arranged parallel to each other in terms of flow.

[0057] Each of the high-pressure pumps 15, 15' is assigned to a combustion chamber group 4, 4' of the two combustion chamber groups 4, 4'.

[0058] The internal combustion engine 1 has a first pressure measuring device 16, here a single first pressure sensor 17, which is configured to detect a first pressure variable in the fuel supply system 3 in the region, in particular downstream of the pre-filter 9, and upstream of the low-pressure pumps 11, 11'. The internal combustion engine 1 also has a second pressure measuring device 18, which is configured to detect a second pressure variable in the fuel supply system 3 downstream of the low-pressure pumps 11, 11' in the region of the main filter 13. In the embodiment shown here, the second pressure measuring device 18 has two second pressure sensors 19, namely a first second pressure sensor 19.1 upstream of the main filter 13, and a second second pressure sensor 19.2 downstream of the main filter 13, wherein the second pressure variable is detected as a differential pressure, formed from the difference between the pressures detected by the second pressure sensors 19.1, 19.2.The second pressure variable is therefore in particular a differential pressure falling across the main filter 13.

[0059] The internal combustion engine 1 also has a control unit 21, which is operatively connected, in a manner not explicitly shown here for the sake of clarity, to the first pressure sensor 17 on the one hand and to the second pressure sensors 19.1, 19.2 on the other hand, and is configured to monitor the first pressure variable and the second pressure variable for a fault condition in the fuel supply system 3, but only to detect a fault condition if the fault condition is plausible based on both pressure variables. This results in improved automated monitoring of the fuel supply system 3, wherein, in particular, slow-onset aging phenomena can be monitored and rapidly occurring failures can be detected in a timely manner. In particular, a distinction can be made between missing filters, for example filter perforations, on the one hand, and changes in fuel viscosity on the other.Last but not least, this reduces the problem of false-positive error detections in such a fuel supply system 3.

[0060] The control unit 21 is particularly configured to check the error state based on the other pressure variable selected from the second pressure variable and the first pressure variable when one of the pressure variables selected from the first pressure variable and the second pressure variable indicates a fault condition of the fuel supply system 3, and to accept the fault condition only if the check returns a positive result.

[0061] The control unit 21 is configured, in particular, to detect an error condition only if the error condition can be clearly assigned to one of the pressure variables selected from the first pressure variable and the second pressure variable. The control unit 21 is configured, in particular, to record a temporal pressure value curve as the first pressure variable and as the second pressure variable, wherein the pressure value curve is preferably monitored for changes.

[0062] The internal combustion engine 1 preferably also has a temperature sensor 23, which is arranged and configured to detect a fuel temperature variable. The control unit 21 is operatively connected to the temperature sensor 23 and configured to check the plausibility of the fault condition also on the basis of the detected fuel temperature variable. The temperature sensor 23 is Fig. 1, the temperature sensor is arranged on the fuel tank 7. Alternatively or additionally, it is also possible for a temperature sensor, in particular the temperature sensor 23, to be arranged in the fluidic connection between the pre-filter 9 and the low-pressure pumps 11, 11'.

[0063] The control unit 21 is preferably alternatively or additionally configured to detect a load point of the internal combustion engine 1, wherein it only detects a fault condition if the fault condition is also plausible based on the detected load point.

[0064] In particular, the control unit 21 is configured to monitor the pre-filter 9 and the main filter 13 for an error condition based on the first pressure variable and the second pressure variable.

[0065] The fuel supply system 3 can also be used to supply a plurality of internal combustion engines 1, wherein the fault condition is then preferably verified for plausibility via at least two internal combustion engines 1 of the plurality of internal combustion engines 1.

[0066] Each of the high-pressure pumps 15, 15' is preferably assigned a suction throttle 25, 25', which is arranged upstream of the respective high-pressure pump 15, 15' in the fluidic connection between the main filter 13 and the respective high-pressure pump 15, 15'. The control unit 21 is preferably operatively connected to the suction throttles 25, 25' and configured to control the suction throttles 25, 25' to regulate a volume flow delivered by the high-pressure pumps 15, 15'.

[0067] The two high-pressure pumps 15, 15' each preferably serve to separately supply a respective, separate high-pressure accumulator 27, 27' with fuel. The high-pressure accumulators 27, 27' are each assigned to one of the combustion chamber groups 4, 4'. In particular, the high-pressure accumulators 27, 27' are each designed as a common high-pressure accumulator, in particular a common rail, for the combustion chambers 5 of the respective associated combustion chamber group 4, 4' or cylinder bank.

[0068] Each high-pressure pump 15, 15' is assigned a shut-off valve 29, 29', which is arranged in a respective shut-off line 31, 31'. The shut-off lines 31, 31' each branch off from fluid connections between the main filter 13 and the respective high-pressure pump 15, 15', in particular upstream of the suction throttles 25, 25', and preferably rejoin the flow path for the fuel upstream of the low-pressure pumps 11, 11', in particular into the fluid connection between the pre-filter 9 and the low-pressure pumps 11, 11'.

[0069] Each high-pressure pump 15, 15' is also assigned a lubrication path 33, 33', which serves to lubricate the respective high-pressure pump 15, 15' with fuel as the lubricant. The lubrication path 33, 33' branches off from the fluid connection between the main filter 13 and the high-pressure pumps 15, 15' downstream of the main filter 13, in particular upstream of the suction throttles 25, 25', and opens into at least one lubrication point of the associated high-pressure pump 15, 15'.

[0070] The high-pressure pumps 15, 15' are preferably also assigned a leakage path 35, or a plurality of such leakage paths 35, wherein the at least one leakage path 35 is configured to guide fuel used as lubricant from the high-pressure pumps 15, 15' back into the fuel tank 7. In particular, each high-pressure pump 15, 15' is preferably assigned such a leakage path 35, or a common leakage path 35.

[0071] The control unit 21 is preferably configured to monitor the low-pressure pumps 11, 11', the shut-off valves 29, 29', the suction throttles 25, 25' and / or the high-pressure pumps 15, 15', in particular their lubrication, for a fault condition based on the first pressure variable and the second pressure variable - in particular additionally.

[0072] Fig. 2 shows a first schematic representation of the operation of an embodiment of a method for monitoring the fuel supply system 3.

[0073] In a), a first pressure variable, in this case a pressure value curve p1 detected by the first pressure sensor 17, is plotted against time t. In b), a second pressure variable, as the differential pressure Δp2 falling across the main filter 13, which is detected by the second pressure sensors 19.1, 19.2, is plotted against time t.

[0074] The first pressure variable shows the normal pressure value curve p1 for aging of the pre-filter 9, whereby the pressure measured downstream of the pre-filter 9 decreases over time t because the pre-filter 9 becomes clogged. Accordingly, with increasing aging, less fuel can pass through the pre-filter 9 per unit of time. The diagram at b) shows a filter breakthrough at the main filter 13. The differential pressure Δp2 falling across the main filter 13 initially increases—as expected with normal aging of the main filter 13—but then suddenly drops—from the occurrence of the filter breakthrough—with increasing time t. Since this fault condition in the form of a filter breakthrough is only detected at one of the filters, here the main filter 13, and not at the other filter, namely the pre-filter 9, the control unit 21 correctly identifies a fault condition, namely a filter breakthrough of the main filter 13.

[0075] The control unit 21 is in particular configured to detect a filter breakthrough on a specific filter selected from the pre-filter 9 and the main filter 13 if only the pressure variable assigned to the specific filter 9, 13 allows the filter breakthrough to be inferred.

[0076] Fig. Figure 3 shows a second schematic representation of the embodiment of the method. The diagrams are identical to the diagrams of the Fig. 2, so reference is made to the previous description.

[0077] Here, however, an event can be seen in the temporal course of both pressure variables, which could basically indicate a filter breakthrough, namely a corresponding kink, as above in Fig. 2b). In the case of the pre-filter 9, the pressure p1 rises again after the supposed filter breakthrough, which would also be the case in the case of an actual filter breakthrough, since more fuel would then flow through the pre-filter 9 per unit of time. However, since the corresponding filter breakthrough is now detected - in particular at the same time t1, or only with a slight time delay within a predetermined tolerance time interval - it seems more likely that there is a common cause for the observed phenomenon, whereas it seems implausible that both filters, namely the pre-filter 9 and the main filter 13, suffer a filter breakthrough at at least almost the same time. A situation as shown in diagrams a) and b) of Fig. 3, can occur, for example, when the viscosity of the fuel changes, in particular when the viscosity of the fuel decreases. Analogously, such a situation can also occur when the temperature of the fuel increases. Fig.The situation depicted in Figure 3 therefore suggests a fuel change rather than a filter fault. Likewise, it can be used for plausibility purposes that at a later time t2 the gradient changes again, i.e., the bend is reversed, since the viscosity has now adjusted to a certain value, but the mechanisms of contamination or aging are now taking effect again. In particular, it can therefore be provided that if at least one of the pressure variables, selected from the first pressure variable and the second pressure variable, indicates a fault in the fuel supply system 3, the fault is verified based on a further temporal development of the at least one pressure variable.

[0078] The control unit 21 is therefore preferably configured not to detect a filter breakthrough if the first pressure variable and the second pressure variable both indicate a filter breakthrough.

[0079] It becomes clear that the plausibility check of an error condition based on both pressure variables proposed here enables, in particular, a reduction of the problem of false-positive error detections.

Claims

[1] Method for monitoring a fuel supply system (3) of an internal combustion engine (1), wherein - a first pressure variable is detected in the fuel supply system (3) in the region of a pre-filter (9) and upstream of a low-pressure pump (11, 11'), wherein - a second pressure variable is detected in the fuel supply system (3) downstream of the low-pressure pump (11, 11') in the region of a main filter (13), wherein - the first pressure variable and the second pressure variable are monitored for a fault condition of the fuel supply system (3), and wherein - an error condition is only detected if the error condition is plausible based on both pressure variables, characterized by , that, - if one of the pressure variables selected from the first pressure variable and the second pressure variable indicates a fault condition of the fuel supply system (3), the fault condition is checked using the other pressure variable selected from the second pressure variable and the first pressure variable, the fault condition only being accepted if the check returns a positive result. [2] Method according to claim 1, characterized by that an error condition is only detected if the error condition can be clearly assigned to one of the print sizes selected from the first print size and the second print size. [3] Method according to one of the preceding claims, characterized by that a temporal pressure value curve is recorded as the first pressure variable and as the second pressure variable, whereby the pressure value curve is preferably monitored for changes. [4] Method according to one of the preceding claims, characterized bythat a local pressure (p1) is recorded for the first pressure variable, whereby the second pressure variable is recorded as a differential pressure (Δp2). [5] Method according to one of the preceding claims, characterized by , that a) a fuel temperature variable is recorded, whereby a fault condition is only detected if the fault condition is also plausible based on the fuel temperature variable, and / or b) a load point of the internal combustion engine (1) is detected, wherein a fault condition is only detected if the fault condition is also plausible on the basis of the detected load point of the internal combustion engine (1). [6] Method according to one of the preceding claims, characterized bythat, if at least one of the pressure variables selected from the first pressure variable and the second pressure variable indicates a fault condition of the fuel supply system (3), the fault condition is checked for plausibility on the basis of a further temporal development of the at least one pressure variable. [7] Method according to one of the preceding claims, characterized by that the pre-filter (9) and the main filter (13) are monitored for an error condition based on the first pressure variable and the second pressure variable. [8] Method according to one of the preceding claims, characterized by that a filter breakthrough on a specific filter, selected from the pre-filter (9) and the main filter (13), is detected if only the pressure variable assigned to the specific filter indicates the filter breakthrough, wherein a filter breakthrough is not detected if the first pressure variable and the second pressure variable indicate a filter breakthrough. [9] Method according to one of the preceding claims, characterized by that the fuel supply system (3) is used to supply a plurality of internal combustion engines (1), wherein the fault condition is plausibilized via at least two internal combustion engines (1) of the plurality of internal combustion engines (1). [10] Method according to one of the preceding claims, characterized by that at least one further component is monitored for a fault condition based on the first pressure variable and the second pressure variable, wherein the further component is selected from a group consisting of: a low-pressure pump (11, 11'), a shut-off valve (29, 29'), a suction throttle (25, 25'), and a high-pressure pump (15, 15'). [11] Internal combustion engine (1), comprising a fuel supply system (3) for supplying fuel to at least one combustion chamber (5) of the internal combustion engine (1), wherein the fuel supply system (3) - a storage container (6) which is fluidically connected via a pre-filter (9) to a low-pressure pump (11, 11'), wherein the - low-pressure pump (11, 11') is fluidically connected to a high-pressure pump (15, 15') via a main filter (13), wherein - the fuel supply system (3) has a first pressure measuring device (16) which is designed to detect a first pressure variable in the fuel supply system (3) in the region of the pre-filter (9) and upstream of the low-pressure pump (11, 11'), wherein - the fuel supply system (3) has a second pressure measuring device (18) which is designed to detect a second pressure variable in the fuel supply system (3) downstream of the low-pressure pump (11, 11') in the region of the main filter (13), and wherein - the internal combustion engine (1) has a control unit (21) which is operatively connected to the first pressure measuring device (16) and to the second pressure measuring device (18) and is configured to monitor the first pressure variable and the second pressure variable for a fault condition of the fuel supply system (3) and to detect a fault condition only if the fault condition is plausible based on the first pressure variable and the second pressure variable, wherein the control unit is configured to carry out a method according to one of claims 1 to 10.

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