Determining the size of a leak in a fuel tank system

Abstract

The present invention relates to a method for determining the size of a leak in a fuel tank system of a vehicle having an internal combustion engine, the method comprising: starting (102) the internal combustion engine; determining (104) the parking time of the vehicle and / or the temperature difference between the fuel in the fuel tank system and the vehicle environment; checking (106) whether at least one of a plurality of diagnostic conditions is met, wherein if the parking time is longer than a predetermined minimum parking time, a first diagnostic condition of the plurality of diagnostic conditions is met, and wherein if the temperature difference is less than a predetermined maximum temperature difference, a second diagnostic condition of the plurality of diagnostic conditions is met, and (d) if at least one of the plurality of diagnostic conditions is met, performing the following steps: (d1) shutting off (108) the fuel tank system; (d2) waiting (110) until a predetermined waiting time has elapsed; (d3) evacuating (112) the fuel tank system; (d4) recording (114) the time-varying process of pressure in the fuel tank system; and (d5) determining (116) the size of a leak in the fuel tank system based on the recorded time-varying process of pressure. The present invention also relates to engine control devices and computer programs.

Description

Technical Field

[0001] This invention relates to the technical field of vehicle diagnostics. More particularly, it relates to methods and apparatus for determining the size of leaks in the fuel tank system of a vehicle with an internal combustion engine. The invention also relates to engine control devices and computer programs. Background Technology

[0002] Many different methods are known for detecting leaks in fuel tanks, such as the NVLD method (NVLD = Natural Vacuum Leakage Detection) and the LDV method (LDV = Leakage Detection by Vacuum).

[0003] In the NVLD method, the entire system is shut off on the fresh air supply side by means of a spring-loaded check valve. The check valve is designed by means of a diaphragm to open autonomously at a minimum overpressure within the chamber (>1-2 hPa relative to ambient pressure), while under negative pressure it only opens when the pressure difference exceeds 10 hPa. Furthermore, not only the diaphragm but also the electrical contacts are located in a so-called NVLD module, which closes under a certain negative pressure. Diagnostics using the NVLD are performed during engine shutdown and over a period of several hours. This takes full advantage of the fact that the chamber cools down in most cases after the engine is turned off (e.g., due to cold nighttime temperatures). This causes a pressure drop within the chamber, resulting in a natural vacuum. If the system is sealed and the temperature drop is large enough, a sufficient negative pressure is created to close the switching contacts in the NVLD. Small electronic devices that continuously monitor the temperature and switching contacts then report to the engine control unit upon the next engine start whether the temperature change is sufficient and whether the switching contacts have closed. If the system is not sealed enough, the switch will not close even if the temperature drop would be sufficient. In this case, the system is evaluated as unsealed.

[0004] In the LDV method, negative pressure in the tank system is generated externally, for example by the vehicle engine or, in the case of an active air venting system, by a blower pump. For this, the fresh air supply to the system must be shut off via a shut-off valve. To identify the current level of fuel evaporation, pressure is measured in the closed system. Subsequently, the vehicle engine or blower pump draws gas out of the system through the tank vent valve (TEV), and if sufficient negative pressure is built up, the TEV is also shut off. The system is now sealed, and if there are no leaks, the negative pressure should remain constant, and thus fuel evaporation will not occur. The pressure change process in the system is measured, and the size of the leak (Leck) can be inferred from the measured pressure increase. To generate negative pressure, a small amount of gas must therefore be drawn from the tank system. Since these gases from the system inherently contain fuel vapor, they cannot be blown into the environment. For this reason, the gas is supplied to the vehicle engine for combustion there. Therefore, the vehicle engine must be running. A running engine means the vehicle is in a driving cycle and, for example, is moving. This movement, in turn, causes the fuel to slosh around in the tank. Exhaust systems often extend close to the tank, causing the tank to have varying temperatures at different points. Fluctuations in the tank contents due to fuel evaporation can lead to pressure changes. For this reason, accurately diagnosing small orifices (e.g., 0.5 mm or less) while driving is very difficult. Therefore, this type of diagnostic is mostly performed during idling. However, in modern vehicles, sufficiently long idling periods are rare due to stop / start operations, so diagnostics cannot be performed frequently. To perform diagnostics, stop / start operations must be prohibited, which naturally increases fuel consumption. Summary of the Invention

[0005] The objective of this invention is to enable reliable diagnosis of small tank leaks on a regular basis without increasing fuel consumption.

[0006] This task is accomplished by a method for determining the size of a leak in the fuel tank system of a vehicle with an internal combustion engine, an engine control device for a vehicle with an internal combustion engine, and a computer program product. Advantageous embodiments of the invention are described in other examples.

[0007] According to a first aspect of the invention, a method for determining the size of a leak in a fuel tank system of a vehicle having an internal combustion engine is described. The described method includes the following: (a) starting the internal combustion engine; (b) determining the parking time of the vehicle and / or the temperature difference between the fuel in the fuel tank system and the vehicle environment; (c) checking whether at least one of a plurality of diagnostic conditions is met, wherein a first diagnostic condition of the plurality of diagnostic conditions is met if the parking time is longer than a predetermined minimum parking time, and a second diagnostic condition of the plurality of diagnostic conditions is met if the temperature difference is less than a predetermined maximum temperature difference; and (d) if at least one of the plurality of diagnostic conditions is met, performing the following steps: (d1) shutting off the fuel tank system; (d2) waiting until a predetermined waiting time has elapsed; (d3) evacuating the fuel tank system; (d4) recording the time-varying process of pressure in the fuel tank system; and (d5) determining the size of the leak in the fuel tank system based on the recorded time-varying process of pressure.

[0008] The described method is based on the understanding that the LDV method described at the beginning can be used particularly reliably, environmentally friendly, and accurately if the fuel in the fuel tank system is stable and stationary, that is, especially if it is not moved and has a temperature as close as possible to ambient temperature. According to the invention, this is determined by checking whether one or more diagnostic conditions are met. The actual LDV method is performed only if at least one of these diagnostic conditions is met, that is, the fresh air supply to the fuel tank system (e.g., by means of a shut-off valve or self-locking valve) is shut off, and then, after a short waiting period (during which fuel may evaporate), the fuel tank system is evacuated to create a vacuum, and thereafter (in the case of a closed fuel tank system), the time-varying process of pressure changes in the fuel tank system is recorded. If the fuel tank system is completely sealed, the pressure will remain substantially constant. However, if a leak is present, the recorded pressure change process will have a corresponding pressure increase.

[0009] According to one embodiment of the present invention, determining the size of the leak includes determining the gradient of the time-varying process of the pressure.

[0010] The gradient, or the rate of increase in pressure over time, is directly related to the size of the leak.

[0011] According to another embodiment of the present invention, if the pressure in the fuel tank system has been reduced by a predetermined value, then the fuel tank system is evacuated.

[0012] In other words, the vacuum continues until the pressure in the fuel tank system has been reduced to a predetermined value.

[0013] According to another embodiment of the invention, the predetermined value is between 5 mbar and 15 mbar, particularly between 8 mbar and 12 mbar, and particularly around 10 mbar.

[0014] According to another embodiment of the invention, vacuuming is performed by means of an internal combustion engine or a blower pump.

[0015] Therefore, no additional components are needed to create a vacuum.

[0016] According to another embodiment of the invention, if the idling phase is performed for a predetermined duration, then the third diagnostic condition among the plurality of diagnostic conditions is satisfied.

[0017] For example, for legal reasons, this idling phase can be automatically executed by the engine control unit immediately after a cold start in order to reduce emissions.

[0018] According to another embodiment of the present invention, if the internal combustion engine is running in idling and there is a stop / start prohibition, then the fourth diagnostic condition among the plurality of diagnostic conditions is satisfied.

[0019] In this state, there is sufficient time to execute the method according to the invention.

[0020] According to a second aspect of the present invention, an engine control device for a vehicle having an internal combustion engine is described. The described engine control device is configured to perform a method according to the first aspect and / or one of the above embodiments.

[0021] The described engine control device is basically based on the same idea as the method described above according to the first aspect.

[0022] According to a third aspect of the invention, a computer program having computer-executable instructions is described, wherein, when executed by a processor, the computer-executable instructions are configured to perform a method according to the first aspect and / or one of the above embodiments.

[0023] In the sense of this document, the naming of such a computer program has the same meaning as the terminology of a program element, computer program product, and / or computer-readable medium that contains instructions for controlling a computer system in order to coordinate the operation of the system or method in a suitable manner to achieve the effects associated with the method according to the invention.

[0024] Computer programs can be implemented as computer-readable instruction code in any suitable programming language, such as JAVA, C++, etc. Computer programs can be stored on computer-readable storage media (CD-ROM, DVD, Blu-ray disc, removable drive, volatile or non-volatile memory, internal memory / processor, etc.). The instruction code can program a computer or other programmable device, such as, in particular, control equipment for the engine of a motor vehicle, to perform the desired function. Furthermore, computer programs can be provided on networks, such as the Internet, and can be downloaded by users from said network when needed.

[0025] This invention can be implemented by means of a computer program, i.e., software, or by means of one or more specialized circuits, i.e., hardware, or in any hybrid form, i.e., by software components and hardware components.

[0026] It should be noted that embodiments of the invention have been described with respect to different inventive subjects. In particular, some embodiments of the invention are described using method claims, while other embodiments are described using device claims. However, it will immediately become apparent to those skilled in the art upon reading this application that, unless explicitly stated otherwise, any combination of features from different types of the inventive subject matter is possible, in addition to combinations of features belonging to one type of inventive subject matter. Summary of the Invention

[0028] Other advantages and features of the present invention will become apparent from the following exemplary description of preferred embodiments.

[0029] Figure 1 A flowchart of the method according to the present invention is shown.

[0030] Figure 2 Showing during execution Figure 1 The method shown is the time-varying process of pressure and control signals.

[0031] It should be noted that the embodiments described below represent only a limited selection of possible variations of the present invention. Detailed Implementation

[0032] Figure 1A flowchart of a method 100 according to the invention for determining the size of a leak in a fuel tank system of a vehicle with an internal combustion engine is shown. At 102, the vehicle's internal combustion engine is started, and at 104, one or more parameter values ​​are determined, which are crucial for further process flow. These parameter values ​​may, in particular, be the vehicle's parking time, i.e., how long the vehicle has been shut down before starting at 102, and / or the difference between the fuel temperature in the tank system and the ambient temperature. Importantly, statements regarding the stillness and stability of the fuel in the tank can be derived from one or more parameter values. Then at 106 (using the determined parameter values), it is checked whether at least one of a plurality of diagnostic conditions is met. If the parking time is longer than a predetermined minimum parking time, then, for example, a first diagnostic condition among the plurality of diagnostic conditions is met. If the temperature difference is less than a predetermined maximum temperature difference, then, for example, a second diagnostic condition among the plurality of diagnostic conditions is met. If an idling phase of the internal combustion engine is performed for a predetermined duration, then, for example, a third diagnostic condition among the plurality of diagnostic conditions is met. If the internal combustion engine is running while idling and a stop / start prohibition condition exists, then, for example, the fourth diagnostic condition out of several diagnostic conditions is met. If one or more of these diagnostic conditions are met, it can be assumed that the fuel will remain stationary for a period of time, and an LDV analysis can be performed.

[0033] If one of the diagnostic conditions is not met (N = No at 106), the method terminates (at least temporarily) at 107, whereby it can, of course, be restarted at a later time. If at least one of the multiple diagnostic conditions is met (J = Yes at 106), the LDV method is performed using the steps described below. At 108, the fresh air supply to the fuel tank system is shut off by closing the electrically operated shut-off valve. After the fresh air supply is shut off, a wait is taken at 110 until a predetermined waiting time has elapsed, allowing for possible fuel evaporation. The evaporation rate can be determined by pressure measurement. The fuel tank system is then evacuated at 112 by drawing gas from the system via the fuel tank vent valve (TEV) using the internal combustion engine or by means of a blower pump. Preferably, this evacuation continues until the pressure is reduced by a predetermined value, for example, 10 mbar. Subsequently, the pressure change over time in the fuel tank system is recorded at 114, and at 116, the size of any leaks in the fuel tank system is determined based on the recorded pressure change over time, particularly the gradient of the pressure change over time. The larger the gradient, the larger the leak. However, if the gradient corresponds only to a previously determined evaporation rate, there is no leak.

[0034] The method 100 described above can be executed directly by the engine control unit using existing hardware (such as pressure sensors, shut-off valves, exhaust valves, and blower pumps).

[0035] Figure 2 Showing during execution Figure 1 The method shown is the time-varying process of the control signal 240 for the blower pump and the control signal 230 for the shut-off valve, and the pressure 220. The vehicle is driven with the shut-off valve open and the blower pump activated until time point T1, where the pressure 220 in the fuel system changes. At time point T1, the vehicle is parked (or stopped and switched to idling), that is, the tank exhaust valve is closed, the blower pump is deactivated, and thereafter the shut-off valve is closed. The waiting 110 described above begins at time point T2. Here, the pressure 220 increases by a value 222 until the waiting ends at T3. Now the vacuuming 112 of the fuel tank system described above begins, in which the blower pump is reactivated and the tank exhaust valve is opened. At time point T4, a desired negative pressure 224 of, for example, 10 mbar, is reached, and the blower pump and tank exhaust valve are closed again. Thereafter, due to evaporation and possible leaks, the pressure 220 in the still closed system increases more or less. Figure 2 Three possible pressure change processes 226, 227, and 228 from time point T5 are shown, each corresponding to a different scenario. The flat change process 226 has an increase or gradient comparable to the pressure increase measured between T2 and T3 due to evaporation. In this case, it can be inferred that there is no leak. The slightly steeper change process 227 exceeds the measured evaporation rate and corresponds, for example, to a leak size of 0.5 mm. The steepest change process 228 also exceeds the measured evaporation rate and corresponds, for example, to a leak size of 1 mm. At time point T6, the fresh air supply shut-off valve is reopened, and the blower pump and chamber exhaust valve are reactivated.

Claims

1. A method for determining the size of a leak in a fuel tank system of a vehicle having an internal combustion engine, the method comprising: Start the internal combustion engine. Determine the vehicle's parking time, i.e., how long the vehicle has been shut down before starting, and determine the temperature difference between the fuel in the fuel tank system and the vehicle's ambient environment. The test verifies whether at least two of a plurality of diagnostic conditions are met, wherein if the storage time is longer than a predetermined minimum storage time, then a first diagnostic condition is met, and if the temperature difference is less than a predetermined maximum temperature difference, then a second diagnostic condition is met. If at least two of the multiple diagnostic criteria are met, then perform the following steps: Shut down the fuel tank system. Wait until the scheduled waiting time has passed. Evacuate the fuel tank system. Record the time-varying pressure changes in the fuel tank system, and The size of the leak in the fuel tank system is determined based on the recorded time-varying pressure.

2. The method of claim 1, wherein determining the size of the leak includes determining the gradient of the time-varying process of the pressure.

3. The method according to claim 1 or 2, wherein if the pressure in the fuel tank system has been reduced by a predetermined value, then the fuel tank system is evacuated.

4. The method of claim 3, wherein the predetermined value is between 5 mbar and 15 mbar.

5. The method according to claim 1 or 2, wherein the vacuuming is performed by means of the internal combustion engine or a blower pump.

6. The method according to claim 1 or 2, wherein if the idling phase is performed for a predetermined duration, a third diagnostic condition among the plurality of diagnostic conditions is satisfied.

7. The method according to claim 1 or 2, wherein if the internal combustion engine is running in idling and a stop / start prohibition exists, then the fourth diagnostic condition among the plurality of diagnostic conditions is satisfied.

8. An engine control device for a vehicle having an internal combustion engine, said engine control device being configured to perform the method of any one of claims 1 to 7.

9. A computer program product having computer-executable instructions, wherein, when executed by a processor, the computer-executable instructions are configured to perform the method of any one of claims 1 to 7.

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