Diagnostic method for a vehicular liquefied natural methane fuel system of an internal combustion engine

Abstract

Diagnostic method of a liquefied natural methane vehicle fuel system of an internal combustion engine operated by computer, the method comprising the following steps: (Step 1) first acquisition of a first methane level value and related timestamp, (Step 2) second acquisition of a second methane level and related timestamp and of the methane consumption between the first and second acquisition; (Step 3) Calculate a resulting level variation value net of the engine's methane consumption. (Step 4) Acquire at least one temperature value indicative of a cold engine condition. (Step 5) Verify a first condition: if said resulting variation value exceeds a first threshold (Cond1 = yes). Also verify a second condition: if the engine is in cold engine conditions based on at least one temperature value (Cond2 = yes). If both the first and second conditions are met, then (Step 6) Verify whether said time interval (Dt) is greater than a predetermined time threshold (Th). If so, (Step 6 = yes). Then (Step 7) Report that the vehicle has been left stationary for an excessive period with a full tank.

Description

Field of the invention

[0001] The present invention relates to the field of diagnostic methods and devices for vehicular methane fuel systems powered by internal combustion engines.

[0002] In this context, "vehicular" means that the fuel system is on board the vehicle.State of the art

[0003] The automotive field, focusing on natural gas (CNG), compressed natural gas (CNG), and liquefied natural gas (LNG), also known as automotive methane, is a growing industry that aims at providing more environmentally friendly and sustainable vehicles to address environmental challenges and greenhouse gas emissions.

[0004] The growing importance of natural gas vehicles in the automotive sector is due to several factors, including: reduction of emissions, diversification of energy sources, the pursuit of lower operating costs.

[0005] In fact, natural gas vehicles offer significant advantages in terms of pollutant emissions compared to gasoline or diesel vehicles. Combustion of natural gas produces fewer CO2 and particulate emissions, thus helping to reduce air pollution and greenhouse gas emissions. Furthermore, natural gas can be produced from a variety of sources, including organic waste, natural gas, and biogas, reducing dependence on petroleum-based fuels.

[0006] Overall, natural gas-powered vehicles offer lower operating costs than conventional gasoline or diesel vehicles, as the cost of natural gas is often lower than that of other fuels. The automotive industry therefore continues to invest in natural gas propulsion technologies, seeking to offer more efficient engines and advanced fuel systems, with the aim of improving the performance and reliability of natural gas vehicles.

[0007] The phenomenon of natural gas "venting" from liquefied natural gas (LNG) tanks represents a significant challenge. "Venting" involves the deliberate release of liquefied natural gas (LNG) into the atmosphere under controlled conditions during specific operating phases of LNG vehicles. This venting is designed to prevent dangerous overpressure in the LNG tank. Indeed, the liquefied gas is contained in the tank at temperatures of approximately 125° below zero. Clearly, this temperature cannot be maintained indefinitely, and therefore, controlled venting serves to keep the pressure within safe limits, thus preventing potentially dangerous overpressures.

[0008] Safety remains paramount in this context, due to the pronounced flammability of methane. Controlled venting effectively prevents the incidence of explosions or other dangerous events resulting from pressure fluctuations within LNG tanks, thus ensuring a safe driving experience.

[0009] Since methane is a greenhouse gas, measures must be taken to reduce venting.

[0010] These measures, on the one hand, reduce the environmental impact and, on the other, improve the energy efficiency of LNG vehicles.

[0011] In other words, reduced venting translates into reduced methane consumption to cover the prescribed distances, with a consequent reduction in carbon dioxide (CO2) emissions. Gas leaks, however, can also be unintentional, due to leaks in the vehicle's engine fuel system.

[0012] It is therefore difficult to assess the impact of venting on the vehicle's overall efficiency.

[0013] Unless specifically excluded in the detailed description that follows, the contents of this chapter are to be considered as an integral part of the detailed description.Summary of the invention

[0014] The purpose of this invention is to propose a method for assessing the wear of a natural gas supply circuit and determining whether any leaks are detected. Furthermore, the purpose is to determine whether such leaks occur during regular use of the vehicle or after a long period of inactivity.

[0015] The basic idea of this invention is to cyclically acquire the methane level value and calculate a value for the methane level variation between two consecutive values, subtracting the value of methane consumption by the internal combustion engine in the interval defined between two consecutive acquisitions of the methane level in the tank.

[0016] Obviously, the level variation between two consecutive acquisitions and the engine fuel consumption can be expressed in weight or as a percentage of the tank weight capacity. Therefore, those skilled in the art understand that a comparison between level variation and fuel consumption must be made meaningfully, that is, between homogeneous quantities.

[0017] It is worth noting that the methane level acquisitions in the tank are performed cyclically when the vehicle is operating, according to a fixed period. However, when the vehicle is off, the methane level acquisition is inhibited to avoid consuming electricity.

[0018] Therefore, the time interval between two consecutive acquisitions is generally constant, unless the first acquisition was performed immediately before turning off the vehicle. Obviously, the time interval between the first and second acquisitions can vary depending on the length of time the vehicle is left off. Conversely, while the vehicle is operating, the time interval between the first and second acquisitions is substantially fixed, and since the method is performed cyclically, a second level acquisition can be used as the "first" acquisition compared to a subsequent acquisition, which is used as the "second" acquisition.

[0019] The dependent claims describe preferred variants of the invention and form an integral part of this specification.Brief description of the figures

[0020] Further objects and advantages of the present invention will be apparent from the following detailed description of an embodiment thereof (and variations thereof) and the accompanying drawings, which are provided for illustrative and non-limiting purposes only. Figure 1 shows a flowchart representing a preferred embodiment of the present diagnostic method.

[0021] The same reference numbers and letters in the figures identify the same elements, components, or functions.

[0022] It should also be noted that the terms "first," "second," "third," "upper," "lower," and the like may be used herein to distinguish various elements. These terms do not imply a spatial, sequential, or hierarchical order for the modified elements unless specifically indicated or inferred from the text.

[0023] The elements and features illustrated in the various preferred embodiments, including the drawings, may be combined with each other without departing from the scope of this application as described below.Detailed description of preferred embodiments

[0024] The present invention is described with the aid of Figure 1, which shows a flowchart of a diagnostic method related to methane leaks into the atmosphere from a methane-powered vehicle tank.

[0025] Start: The key is turned to ON on the dashboard, activating the analysis functions of the on-board ECU. Obviously, the processing unit can be activated in any way, rather than with a physical key. The processing unit performs the following steps cyclically at a predetermined time interval: Step 1: acquisition of the last methane level value in the tank TK and its corresponding timestamp, previously stored in a persistent memory DB; Step 2: acquisition of the current methane level in the tank TK and its corresponding timestamp stored in the persistent memory DB.

[0026] Two consecutive measurements are preferably spaced apart by a minimum time interval Dt of approximately 10 to 60 minutes. It should be considered that if the engine is turned off after step 1, the next ignition interval does not necessarily range from 10 to 60 minutes, as the measurement system is not operating when the internal combustion engine is turned off. Therefore, this interval is compared with a time threshold Th to distinguish between uninterrupted data acquisition and one in which the vehicle was turned off for a prolonged period.

[0027] Within the time interval between two consecutive acquisitions, each signal is sampled at a predetermined sampling frequency, and several metrics are calculated, including the minimum, maximum, and average values for each signal measured in the same interval Dt. This includes the fuel consumption of the internal combustion engine used in step 3 to assess whether the actual change in level is related to fuel consumption alone or is caused by a fuel system leak. Step 3: Calculation of a resulting level change value given by subtracting a first value from a second value, where the first value is given by a variation between said first and second tank levels, calculated in steps 1 and 2, and said second level value due to said methane consumption burned in the engine, in the same interval Dt. Step 4: Acquisition of at least one temperature value indicative of a cold engine condition, including a methane temperature value, an engine coolant temperature value, and an engine exhaust gas temperature value. Step 5: Checking two conditions evaluated using the resulting value calculated in step 3 and the at least one temperature value acquired in step 4: + Checking a first condition: if the resulting level variation value (calculated in step 3) exceeds a first threshold (Cond1 = yes) + Checking a second condition: if the engine is in cold condition based on the at least one temperature value (acquired in step 4) (Cond2 = yes); If both the first and second conditions are met, then: Step 6: Checking whether the time interval Dt between the said timestamps is greater than a predetermined time threshold (Th), If so (Step 6 = yes), then (Step 7) Reporting that the vehicle has been left off for an excessive period with a full tank; If, however, the time interval Dt is less than the predetermined threshold Th or the first condition is positive and the second condition is negative (Cond1 = yes, Cond2 = no), then Step 8: Reporting incorrect refuelling parameters or a leak in the engine fuel system. This is because the leak evidently occurs while the vehicle is operating or inactive for limited periods of time.

[0028] If, however, Cond1 is not satisfied: Step 9: Storing, in the persistent DB memory with a corresponding timestamp, the optimal condition found: this represents an optimal condition both in terms of vehicle usage and fuel system integrity and refuelling quality. Note that the first condition Cond1 takes priority over the second condition; in fact, if it is negative Cond1 = no, step 9 is continued regardless of the condition Cond2. When the processing unit is activated, it does not know a priori how much time has passed since the last reading of the methane level and the other signals described below. Therefore, the comparison between two timestamps from two consecutive acquisitions defines the first time interval Dt, which can range from: A minimum of 10 to 60 minutes, A potentially unlimited maximum, if the vehicle is reactivated after many days, months, or years.

[0029] The first time interval Dt is "short," meaning between 10 and 60 minutes, while the engine is operating. "Operating" means the crankshaft rotation speed is greater than 300 rpm. The threshold Th is used to distinguish between a short stop, for example, of a few hours, and a long stop, for example, exceeding 10 days.

[0030] Therefore, the method involves cyclic acquisition of a methane level value, Step 1 and Step 2, and the calculation, Step 3, of a methane level variation value between two consecutive level values that identify a first time interval Dt, subtracting a second level (measured in Step 1) from a first level (measured in Step 2) and further subtracting the engine methane consumption in the same first time interval Dt.

[0031] In Step 4, at least one temperature value indicative of a cold engine condition is acquired.

[0032] In step 5, it is evaluated whether the level variation value calculated in step 3 is higher than a threshold (Cond1 = yes), and to report in Step 8 a leak in the fuel system or an incorrect refuelling, when the first time interval Dt exceeds the time threshold Th (Cond2 = no), for example by 10 days, and to report an incorrect use of the vehicle, in Step 7, when the said time interval is higher than the second time threshold Th (Cond2 = yes).

[0033] The warning of non-optimal vehicle use, step 7, indicates a situation in which the vehicle is not experiencing any problems, but is being misused, meaning the natural gas tank is left full and unused for extended periods, such as periods exceeding 10 days or even longer, which promotes venting and therefore the loss of some of the contained natural gas. When managing a fleet of vehicles, the recommendations in step 7 can be essential for significantly reducing fuel consumption and modifying refuelling and vehicle usage strategies.

[0034] The vehicle can advantageously be equipped with an instrument panel displaying a message recommending not leaving the vehicle with a full natural gas tank for extended periods.

[0035] The warning in step 8 indicates a leak in the vehicle's engine fuel system or a refuelling problem.

[0036] This is because the leak can be detected with a cold engine, but after a limited period of inactivity, or even with a warm engine while driving.

[0037] As with step 7, step 8 can include an alarm message displayed on the instrument panel, prompting the driver to change the fuelling station and, if the warning persists, to take the vehicle to a workshop to identify and repair the methane leak.

[0038] For example, the system can be programmed to store an error message in persistent memory, accompanied by a timestamp. The first time that step 8 is reached, a message is displayed prompting the driver to check the fuelling parameters of the fuelling station being used.

[0039] After refuelling, if the diagnostic method reaches Step 8 again, the message shown on the display may preferably change, prompting the vehicle to be taken to a workshop to check the fuel system for leaks.

[0040] It's worth noting that refuelling at incorrect temperatures and pressures can lead to more frequent bleeding. Therefore, to rule out a fuel system-related problem, the method initially attempts to prevent unnecessary service visits by ruling out a fuelling issue.

[0041] A significant change in the fuel tank level is detected using the following formula:

[0042] Where: Fuel_Level_last represents the last value, expressed as a percentage, of the tank level monitored by the processing equipment; Engine_Fuel_rate_avg represents the average consumption in the interval Dt, expressed in [l / h]; Dt is the time interval for analyzing the signals described in this description, expressed in hours [h]; Tank_Capacity indicates the maximum capacity of the methane tank, expressed in liters; [i] is the index of the analysis time interval Dt identified between two consecutive methane level acquisitions.

[0043] Advantageously, this formula takes into account not only the variation in the methane level in the tank between two time points, but also the average methane consumption within the period, thus avoiding identifying as gas released into the atmosphere gas that was actually used to power the engine. The second condition, i.e., whether the engine is cold, can be determined using the following conditions: Engine_Exhaust_Temperature_min [i] < 120 °C (Th1) Engine_Coolant_Temperature_min [i] >= 30 °C (Th3) Engine_Fuel_Temperature_avg [i] < 50 °C (Th2) Where Engine_Exhaust_Temperature_min indicates the minimum exhaust gas temperature recorded within each time interval Dt, Engine_Coolant_Temperature_min indicates the minimum coolant temperature recorded within each time interval Dt, Engine_Fuel_Temperature_avg indicates the average monitored methane temperature measured during the time interval Dt.

[0044] The present invention can advantageously be implemented using a computer program that includes coding means for implementing one or more steps of the method, when this program is executed. on a computer. It is therefore understood that the scope of protection extends to said computer program and also to computer-readable media comprising a recorded message, said computer-readable media comprising program coding means for implementing one or more steps of the method when said program is executed on a computer.

[0045] Embodiment variations to the non-limiting example described are possible, without departing from the scope of protection of the present invention, which includes all embodiments equivalent to the claims for a person skilled in the art. From the above description, a person skilled in the art is able to implement the object of the invention without introducing further construction details.

Claims

1. Computer-controlled diagnostic method for a vehicle liquefied natural gas fuel system for an internal combustion engine, comprising the following steps: - (Step 1) first acquisition of a first methane level value and its corresponding timestamp (Step 1); - (Step 2) second acquisition of a second methane level and its corresponding timestamp, and a methane consumption between the first and second acquisitions; - (Step 3) calculation of a level variation value resulting from the subtraction of a first value from a second value, where the first value is given by a variation between said first and second levels, and said second value is given by said methane consumption; calculation of a time interval (Dt) given by a difference between the timestamps of said first and second acquisitions; - (Step 4) Acquisition of at least one temperature value indicative of a cold engine condition, including a methane temperature value, an engine coolant temperature value, an engine exhaust gas temperature value, - (Step 5) Verification of + a first condition: if the resulting variation value exceeds a first threshold (Cond1 = yes) and + a second condition: if the engine is in a cold engine condition based on at least one temperature value, (Cond2 = yes), if the first condition and the second condition are both verified, then (Step 6) Verification whether the time interval (Dt) is greater than a predetermined time threshold (Th), if so (Step 6 = yes), then (Step 7) Reporting that the vehicle has been left stationary for an excessive period with a full tank; If, however, the time interval (Dt) is less than said predetermined threshold (Th) or the first condition is positive and the second condition is negative (Cond1 = yes, Cond2 = no), then (Step 8) reporting incorrect refuelling parameters or a leak in the engine fuel system.

2. Method according to claim 1, wherein when the first condition is negative, then reporting, and optionally storing, optimal vehicle usage and fuel system conditions.

3. Method according to claim 1 or 2, wherein said second time threshold (Th) is at least 10 days.

4. Method according to any of the preceding claims, wherein said first threshold (Dt) is between 10 minutes and 1 hour.

5. A method according to any preceding claim, wherein, in said time interval, a minimum value, a maximum value, and an average value of the following measurements are acquired and stored: - methane level in the tank, - average fuel consumption (Engine_Fuel_rate_avg), - at least one of - exhaust gas temperature (Engine_Exhaust_Temperature) measured at a point on an exhaust gas aftertreatment device; - methane temperature (Engine_Fuel_Temperature); - engine coolant temperature (Engine_Coolant_Temperature).

6. A method according to any preceding claim, wherein said cold and operational engine condition is identified when a minimum exhaust gas temperature is lower than a first temperature threshold (Th1) and / or an average methane temperature is lower than a second temperature threshold (Th2), and / or a minimum coolant temperature is higher than a third temperature threshold (Th3).

7. A method according to any preceding claim, wherein said fuel consumption value from the internal combustion engine is calculated with the following formula: Engin e Fue l rat e avg i ∗ Dt i Tan k Capacity It expresses a percentage change in the level compared to the total volume of the methane tank. Where - Engine_Fuel_rate_avg represents the average consumption in the Dt interval, expressed in [l / h]; - Dt is the time interval between the first and second acquisition; - Tank_Capacity indicates the maximum capacity of the tank expressed in Liters; - [i] is an index indicating consecutive Dt analysis intervals.

8. A computer processing unit (ECU) for a methane-powered vehicle, wherein the processing unit is operatively connected - to a level sensor of a liquefied natural gas tank supplying an internal combustion engine of the vehicle, - to at least one temperature sensor for obtaining a temperature value indicative of a cold engine condition of the internal combustion engine, - to a vehicle fuel system connected to said natural gas tank to supply said internal combustion engine, wherein the processing unit is configured to perform all the steps of the method of any of claims 1-7.

9. A computer program comprising instructions for causing the processing unit of claim 8 to implement the method according to claim 1.

10. A computer-readable medium having stored the program of claim 9.

11. A land vehicle comprising an internal combustion engine fuelled by liquefied natural gas via a vehicle fuel system comprising a corresponding storage tank. liquefied methane and comprising a processing unit according to claim 8.

12. A vehicle according to claim 11, further comprising a human / machine interface and wherein said processing unit is operably connected to said human / machine interface means to display, by means of a recorded message, a signal - said signal of having left the vehicle stationary for an excessive period with a full tank and - said signal of incorrect refuelling parameters or a leak in the engine fuel system.

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