JP7491187B2 - Control device for internal combustion engine - Google Patents

Description

The present invention relates to a control device for an internal combustion engine.

Patent Document 1 describes a method of obtaining in advance a specific relationship between the methane number and basic calorific value for multiple types of reference gases with different methane number values, measuring the basic calorific value of the natural gas that is the gas to be measured, and calculating the methane number of the gas to be measured from the measured basic calorific value of the gas to be measured and the specific relationship.

Patent Document 1 also describes measuring a physical property value that has a specific correspondence with the calorific value, and determining the calorific value (converted calorific value) based on the measured value.

Furthermore, Patent Document 1 states that the basic calorific value of the gas to be measured is obtained based on the refractive index converted calorific value obtained from the refractive index of the gas to be measured and the sound speed converted calorific value obtained from the sound speed of the gas to be measured.

As described above, the methane number measuring device described in Patent Document 1 is equipped with a refractive index measuring means for measuring the refractive index of the measurement target gas and a sound speed measuring means for measuring the sound speed of the measurement target gas.

International Publication No. WO 2016/104270

However, refractive index measuring means and sound speed measuring means are not generally provided in vehicles. For this reason, providing these measuring means increases costs, which is an issue. In addition, space and labor are required to install these measuring means.

The present invention aims to provide an internal combustion engine control device that can estimate the composition of natural gas fuel using an inexpensive system.

In order to solve the above problems, the present invention is a control device for an internal combustion engine that uses one of a plurality of natural gases having different compositions as fuel and has an injector that injects the natural gas, and includes a reference fuel recording unit that calculates and records a reference fuel learning value that is a learning value of the reference fuel, based on the drive time of the injector when a reference fuel, the natural gas whose methane number is known, is used as fuel, a methane number estimation unit that calculates a current fuel learning value that is a learning value of the fuel currently being used, based on the drive time of the injector, calculates a fuel learning value difference that is the difference between the reference fuel learning value and the current fuel learning value, and estimates the methane number of the fuel currently being used based on the fuel learning value difference and the methane number of the reference fuel, and a throttle opening control unit that changes an offset value of the throttle opening when the internal combustion engine is under high load, in accordance with the methane number estimated by the methane number estimation unit .

In this way, the present invention makes it possible to estimate the composition of natural gas fuel using an inexpensive system.

FIG. 1 is a block diagram showing a schematic overall configuration of an internal combustion engine according to an embodiment of the present invention. FIG. 2 is a functional block diagram showing the configuration of a control device for an internal combustion engine according to one embodiment of the present invention. FIG. 3 is a graph showing the relationship between the methane number of natural gas and the calorific value per unit volume. FIG. 4 is a diagram showing an example of a table for estimating the methane number in the control device for an internal combustion engine according to one embodiment of the present invention. FIG. 5 is a diagram showing an example of a table for determining the throttle reduction amount or angle during high load from the estimated methane number in the control device for an internal combustion engine according to one embodiment of the present invention. FIG. 6 is a diagram showing an example of a table for determining a variable compression ratio mode from an estimated methane number in an internal combustion engine control device according to an embodiment of the present invention. FIG. 7 is a diagram showing an example of a table for determining an ignition retard angle from an estimated methane number in the control device for an internal combustion engine according to one embodiment of the present invention. FIG. 8 is a flowchart showing a procedure for recording a reference fuel learning value in the control device for an internal combustion engine according to one embodiment of the present invention. FIG. 9 is a flowchart showing a procedure of a methane number estimation process in the control device for an internal combustion engine according to one embodiment of the present invention.

The control device for an internal combustion engine according to one embodiment of the present invention is a control device for an internal combustion engine that uses one of a number of natural gases having different compositions as fuel and has an injector that injects natural gas, and is configured to include a reference fuel recording unit that calculates and records a reference fuel learning value, which is the learning value of the reference fuel, based on the drive time of the injector when a reference fuel, which is natural gas with a known methane number, is used as fuel, and a methane number estimation unit that calculates a current fuel learning value, which is the learning value of the fuel currently being used, based on the drive time of the injector, calculates a fuel learning value difference, which is the difference between the reference fuel learning value and the current fuel learning value, and estimates the methane number of the fuel currently being used based on the fuel learning value difference and the methane number of the reference fuel.

As a result, the control device for an internal combustion engine according to one embodiment of the present invention can estimate the composition of natural gas fuel using an inexpensive system.

The following describes in detail an internal combustion engine control device according to an embodiment of the present invention with reference to the drawings.

(Configuration of the internal combustion engine)
In FIG. 1, an internal combustion engine 10 according to an embodiment of the present invention includes a mechanism for connecting a piston 11 to a piston rod 12 and accommodating the piston 11 in a cylinder bore 15 so as to be freely reciprocating, and is mounted on a vehicle or the like as a driving source. In the internal combustion engine 10, a combustion chamber 17 is formed between the inner surface of a lower part of a cylinder head 16 above the cylinder bore 15 and the upper surface of the piston 11. The internal combustion engine 10 is configured to reciprocate the piston 11 in the vertical direction in the figure by repeating combustion expansion and exhaust caused by igniting a mixture of intake combustion air and injected fuel introduced into the combustion chamber 17. As a result, the internal combustion engine 10 transmits the driving force of the reciprocating piston 11 via the piston rod 12, a transmission, etc., thereby rotating an axle, for example, to realize the running of the vehicle. Here, the internal combustion engine 10 ignites the mixture in the combustion chamber 17 by applying a high voltage boosted by an ignition coil 19 to an ignition plug (not shown) to generate a spark.

This internal combustion engine 10 has an intake valve 13 and an exhaust valve 14 arranged in a cylinder head 16. The intake valve 13 and the exhaust valve 14 are moved (lifted) in the downward direction in the figure by a drive cam (intake cam and exhaust cam) 28a that rotates integrally with a camshaft 28, and open and close by forming a gap between the intake port 21 and the opening edge of the exhaust port 22 that communicate with the combustion chamber 17.

An air cleaner 25 is connected to the intake port 21 via a surge tank 26 to form an intake manifold 23 that takes in clean outside air. A catalytic converter 27 containing a catalyst 27a is connected to the exhaust port 22 to form an exhaust manifold 24 that exhausts purified combustion gas. A throttle valve 29 that is linked to the accelerator pedal of the vehicle is located upstream of the surge tank 26. This internal combustion engine 10 is designed to optimize the air-fuel ratio of the mixture supplied to the combustion chamber 17 by adjusting the opening of the throttle valve 29 to control the amount of intake of combustion air (outside air) that is mixed with fuel.

The internal combustion engine 10 is also provided with a gasoline injector 31 and a CNG injector 32 as an injector near the intake port 21 of the intake manifold 23 so that it can selectively supply two types of fuel, liquid gasoline and gaseous CNG (Compressed Natural Gas) (which may also be LPG (Liquefied Petroleum Gas)), as the fuel to be injected into the combustion chamber 17.

The gasoline injector 31 is connected to the liquid fuel tank 33 via a liquid fuel supply pipe 34. The gasoline injector 31 injects gasoline stored in the liquid fuel tank 33 at normal pressure and supplies it into the combustion chamber 17 via the intake port 21. The liquid fuel tank 33 is equipped with a remaining amount sensor 33a that detects when the stored gasoline has been used up to a certain amount, and the remaining amount sensor 33a is connected to a control device 41, which will be described later.

The CNG injector 32 is connected to the gas fuel tank 36 via a gas fuel supply pipe 37. The CNG injector 32 adjusts the pressure of the CNG stored under high pressure in the gas fuel tank 36, injects it, and supplies it into the combustion chamber 17 via the intake port 21. Here, a stop valve 39 is provided in addition to a pressure reducing valve 38 in the gas fuel supply pipe 37, because it is difficult to block the supply of gaseous CNG (gaseous fuel) into the combustion chamber 17 using only the CNG injector 32.

(Configuration of the control device)
The internal combustion engine 10 includes a control device 41 that is constructed with a CPU, a memory, etc. The control device 41 executes a control program that is stored in advance based on various parameters, sensor information, etc., and performs overall control of the entire vehicle, including control of the air-fuel ratio of the fuel supplied to the internal combustion engine 10.

Here, in addition to the remaining amount sensor 33a, the control device 41 is connected to an intake temperature sensor 42, an upstream oxygen sensor 43, a downstream oxygen sensor 44, an engine water temperature sensor 45, a crank angle sensor 46, a cam angle sensor 47, a fuel changeover switch 48, an outside air temperature sensor 49, an intake pressure sensor 51, and a vehicle speed sensor 52.

The intake temperature sensor 42 is installed downstream of the air cleaner 25 and detects the intake temperature of the combustion air supplied to the combustion chamber 17. The upstream oxygen sensor 43 is installed upstream of the catalytic converter 27 and detects the oxygen concentration in the exhaust gas after combustion discharged from the combustion chamber 17 to detect the combustion status. The downstream oxygen sensor 44 is installed downstream of the catalytic converter 27 and detects the purification status by detecting the oxygen concentration in the exhaust gas after purification processing by the catalyst 27a.

The engine water temperature sensor 45 detects the engine water temperature, which is the temperature of the cooling water for the internal combustion engine 10. The crank angle sensor 46 detects the crank angle of a crankshaft (not shown) for the purpose of detecting the driving speed (driving speed) and synchronizing the fuel injection timing. The cam angle sensor 47 detects the cam angle of the intake camshaft 28 (intake cam 28a).

The fuel selector switch 48 allows the driver to manually select the fuel to be used depending on the driving conditions, such as when warming up or accelerating. The outside air temperature sensor 49 detects the temperature of the outside air used as the combustion air through the space in which the internal combustion engine 10 is housed, that is, the engine compartment. The intake pressure sensor 51 detects the intake pressure (negative pressure) when the mixture of intake combustion air and injected fuel in the intake manifold 23 is introduced into the combustion chamber 17. The vehicle speed sensor 52 detects the rotational speed of the axle (vehicle speed).

The control device 41 is adapted to selectively switch between liquid fuel and gaseous fuel, which have different properties, and supply them to the internal combustion engine 10 (combustion chamber 17), appropriately switching the fuel supplied to the combustion chamber 17 from gasoline to CNG, or from CNG to gasoline.

For example, the control device 41 switches the fuel to be used when a manual switching operation is performed using the fuel selector switch 48, when fuel shortage is detected in the liquid fuel tank 33 or the gas fuel tank 36, or depending on the operating mode of the internal combustion engine 10, such as warm-up operation, steady-state operation, or acceleration.

The operating mode of the internal combustion engine 10 can be set to select inexpensive CNG during warm-up or steady operation, and gasoline when accelerating or climbing hills, when torque is required.

However, there are many types of CNG fuel with different ratios of hydrocarbons such as methane and ethane, and it has a wider range of characteristics than gasoline. Therefore, in conventional control of the internal combustion engine 10, the control width is quite large and the feedback amount is too large, making it difficult to achieve optimal control and to bring out the best performance from the internal combustion engine 10.

The control device 41 of this embodiment estimates the methane number of the filled fuel and controls the internal combustion engine 10 based on the estimated methane number.

For this reason, as shown in FIG. 2, the control device 41 includes a reference fuel recording unit 61, a methane number estimation unit 62, a throttle opening control unit 63, and a compression ratio control unit 64.

The reference fuel recording unit 61 calculates and records the learning value of the reference fuel based on the operating time of the CNG injector 32 when a reference fuel with a known methane number is used as fuel.

The reference fuel recording unit 61 acquires the methane number of the reference fuel, for example, by an input signal from an external tool 101 configured to be able to communicate with the control device 41. As the external tool 101, for example, a service tool that is connected to a connector provided on the control device 41 to acquire information recorded by the control device 41 or set values in the memory unit of the control device 41 can be used.

The methane number estimation unit 62 calculates the fuel learning value of the fuel currently being used based on the operating time of the CNG injector 32, and estimates the methane number of the fuel currently being used based on the difference between the reference fuel learning value and the fuel learning value and the methane number of the reference fuel.

As shown in Figure 3, the methane number determines the calorific value per unit volume, and the relationship between the methane number and the calorific value per unit volume is roughly linear, with the slope being determined by the physical properties.

In FIG. 3, if the calorific value of the reference fuel is Q _ini and the calorific value of the fuel currently being used is Q _c , the estimated MN, which is the methane number of the fuel currently being used, can be estimated from the difference and slope between Q _ini and Q _c .

Based on such characteristics, the methane number estimation unit 62 creates a table, for example as shown in FIG. 4 , for calculating an estimated MN, which is a methane number estimated from the difference between a reference fuel learned value FL _ini , which is the learned value of a reference fuel, and a current fuel learned value FL _c , which is the learned value of the fuel currently being used.

In FIG. 4, the estimated MN at which the difference between the reference fuel learning value FL _ini and the current fuel learning value FL _c becomes zero is the methane number of the reference fuel, and a table is created based on this methane number and the slope.

In other words, the learning values are values in which the difference between the learning values is equivalent to the difference in the amount of heat generated per unit volume. These "learning values" are "learning values related to the drive time of the CNG injector 32."

The throttle opening control unit 63 changes the offset value of the throttle opening when the internal combustion engine 10 is under high load, depending on the estimated methane number of the fuel currently being used.

The throttle opening control unit 63 determines an offset value for the throttle opening at high load, for example, from an estimated MN, which is the estimated methane number of the fuel currently being used, using a table that determines the amount of throttle reduction at high load, or the angle, as shown in FIG. 5.

The compression ratio control unit 64 changes the compression ratio of the internal combustion engine 10 according to the estimated methane number of the fuel currently being used. The compression ratio control unit 64 adjusts the compression ratio, for example, by adjusting the opening and closing timing of the intake valve 13.

The compression ratio control unit 64 determines the compression ratio mode of the internal combustion engine 10, for example, from a table for determining the variable compression ratio mode based on the estimated MN, which is the estimated methane number of the fuel currently being used, as shown in FIG. 6.

The control device 41 may adjust the ignition timing of the internal combustion engine 10, for example, using a table that determines the ignition retard angle from an estimated MN, which is the estimated methane number of the fuel currently being used, as shown in FIG. 7.

The reference fuel learning value recording process performed by the control device for an internal combustion engine according to this embodiment, which is configured as described above, will be described with reference to FIG. 8. The reference fuel learning value recording process described below is started, for example, when the reference fuel learning value recording mode is selected by a command from the external tool 101.

In step S1, the reference fuel recording unit 61 determines whether or not reference fuel learning is completed based on whether F _ini is 1. If it is determined that reference fuel learning is completed, the reference fuel recording unit 61 executes the process of step S2.

If it is determined that the reference fuel learning has not been completed, the reference fuel recording unit 61 executes the process of step S3.

In step S2, the reference fuel recording unit 61 erases the reference fuel learning value FL _ini and sets F _ini to 0. After executing the process of step S2, the reference fuel recording unit 61 executes the process of step S3.

In step S3, the reference fuel recording unit 61 determines whether or not the CNG filling amount P _tank of the gas fuel tank 36 is greater than a predetermined value. If it is determined that the filling amount P _tank is greater than the predetermined value, the reference fuel recording unit 61 executes the process of step S5.

When it is determined that the filled amount P _tank is not greater than the predetermined value, the reference fuel recording section 61 executes the process of step S4.

In step S4, the reference fuel recording unit 61 transmits a fuel refill command to, for example, the external tool 101, and causes fuel to be refilled. After executing the process of step S4, the reference fuel recording unit 61 executes the process of step S3.

In step S5, the reference fuel recording unit 61 acquires the methane number of the filled fuel, which is input from, for example, the external tool 101. After executing the process of step S5, the reference fuel recording unit 61 executes the process of step S6.

In step S6, the reference fuel recording unit 61 determines whether the internal combustion engine 10 is operating. If it is determined that the internal combustion engine 10 is operating, the reference fuel recording unit 61 executes the process of step S8.

If it is determined that the internal combustion engine 10 is not operating, the reference fuel recording unit 61 executes the process of step S7.

In step S7, the reference fuel recording unit 61 issues an engine operation command to operate the internal combustion engine 10 using CNG. After executing the process of step S7, the reference fuel recording unit 61 executes the process of step S6.

In step S8, the reference fuel recording unit 61 determines whether the engine water temperature is higher than a predetermined temperature. If it is determined that the engine water temperature is higher than the predetermined temperature, the reference fuel recording unit 61 executes the process of step S10.

If it is determined that the engine water temperature is not higher than the predetermined temperature, the reference fuel recording unit 61 executes the process of step S9.

In step S9, the reference fuel recording unit 61 transmits a complete warm-up command to, for example, the external tool 101, and warms up the internal combustion engine 10. After executing the process of step S9, the reference fuel recording unit 61 executes the process of step S8.

In step S10, the reference fuel recording unit 61 performs reference fuel learning to calculate a learning value using the filled CNG as the reference fuel, and calculates a reference fuel learning value FL _ini . After executing the process of step S10, the reference fuel recording unit 61 executes the process of step S11.

The learning to calculate the learning value is performed, for example, by setting the operating state of the internal combustion engine 10 to a target state when the internal combustion engine 10 is idling or in a steady running state. At this time, the drive time of the CNG injector 32 is changed by feedback control. The learning value is calculated based on this changed drive time of the CNG injector 32.

In step S11, the reference fuel recording unit 61 records the calculated reference fuel learning value FL _ini in the storage unit of the control device 41. After executing the process of step S11, the reference fuel recording unit 61 executes the process of step S12.

In step S12, the reference fuel recording unit 61 sets F _ini to 1, thereby indicating that reference fuel learning has been completed.

Next, the methane number estimation process performed by the control device for the internal combustion engine according to this embodiment will be described with reference to FIG. 9. Note that the methane number estimation process described below is started, for example, when the internal combustion engine 10 is idling or in a steady running state.

In step S21, the methane number estimation unit 62 determines whether or not reference fuel learning is completed based on whether F _ini is 1. If it is determined that reference fuel learning is completed, the methane number estimation unit 62 executes the process of step S22.

If it is determined that the reference fuel learning has not been completed, the methane number estimation unit 62 ends the methane number estimation process.

In step S22, the methane number estimation unit 62 determines whether the engine water temperature is higher than a predetermined temperature. If it is determined that the engine water temperature is higher than the predetermined temperature, the methane number estimation unit 62 executes the process of step S23.

If it is determined that the engine water temperature is not higher than the predetermined temperature, the methane number estimation unit 62 ends the methane number estimation process.

In step S23, the methane number estimation unit 62 performs learning using the filled CNG to calculate and update a current fuel learning value _FLc , which is a learning value of the CNG currently being used. After executing the process of step S23, the methane number estimation unit 62 executes the process of step S24.

In step S24, the methane number estimation unit 62 calculates a fuel learning value difference by subtracting the current fuel learning value FL _c from the reference fuel learning value FL _ini . After executing the process of step S24, the methane number estimation unit 62 executes the process of step S25.

In step S25, the methane number estimation unit 62 calculates the estimated methane number MN of the CNG currently being used from the fuel learning value difference. After executing the process of step S25, the methane number estimation unit 62 executes the process of step S26.

In step S26, the methane number estimation unit 62 notifies each control unit, such as the throttle opening control unit 63 and the compression ratio control unit 64, of the estimated MN to activate each control. After executing the process of step S26, the methane number estimation unit 62 ends the methane number estimation process.

As described above, this embodiment includes a reference fuel recording unit 61 that calculates and records the learning value of the reference fuel based on the driving time of the CNG injector 32 when a reference fuel with a known methane number is used as fuel, and a methane number estimation unit 62 that calculates the fuel learning value of the fuel currently being used based on the driving time of the CNG injector 32 and estimates the methane number of the fuel currently being used based on the difference between the reference fuel learning value and the fuel learning value.

This allows the methane number of the fuel currently being used to be estimated based on the difference between the reference fuel learning value and the fuel learning value. This makes it possible to estimate the composition of CNG fuel using an inexpensive system.

In addition, the reference fuel recording unit 61 obtains the methane number of the reference fuel based on an input signal from the external tool 101.

As a result, the methane number of the reference fuel is set by an input signal from the external tool 101. This allows the methane number of the reference fuel to be easily changed, making it possible to estimate the composition of CNG fuel in various locations around the world using an inexpensive system.

The system also includes a throttle opening control unit 63 that changes the offset value of the throttle opening when the internal combustion engine 10 is under high load, depending on the estimated methane number of the fuel currently being used.

By shifting the center of control to an appropriate position during throttle control under high load, excessive use of feedback control can be avoided. This reduces the risk of impairing exhaust gas purification performance, fuel economy, and driving performance.

The catalyst window can be adjusted appropriately to accommodate changes in fuel composition. This improves exhaust gas purification performance and reduces the environmental impact.

The system also includes a compression ratio control unit 64 that changes the compression ratio of the internal combustion engine 10 according to the estimated methane number of the fuel currently being used.

In compression ratio control, by shifting the control center to an appropriate position, it is possible to avoid excessive use of feedback control. This reduces the risk of impairing exhaust gas purification performance, fuel efficiency, and driving performance.

The catalyst window can be adjusted appropriately to accommodate changes in fuel composition. This improves exhaust gas purification performance and reduces the environmental impact.

In this embodiment, the methane number of the reference fuel is input by the external tool 101, but it is also possible to determine the reference fuel in advance and record information such as the methane number of the reference fuel in the control device 41 before shipping from the production factory.

In this embodiment, an example has been described in which the control device 41 performs various determinations and calculations based on various sensor information, but the present invention is not limited to this. The control device 41 may have a communication unit capable of communicating with an external device such as an external server, and the external device may perform various determinations and calculations based on the detection information of the various sensors transmitted from the communication unit. The communication unit may receive the determination results and calculation results, and the received determination results and calculation results may be used to perform various controls.

Although an embodiment of the present invention has been disclosed, it is apparent that modifications may be made by one of ordinary skill in the art without departing from the scope of the present invention. All such modifications and equivalents are intended to be included in the following claims.

10 internal combustion engine 29 throttle valve 32 CNG injector (injector)
41 Control device 45 Engine water temperature sensor 61 Reference fuel recording unit 62 Methane number estimation unit 63 Throttle opening control unit 64 Compression ratio control unit 101 External tool

Claims (2)

A control device for an internal combustion engine using one of a plurality of natural gases having different compositions as fuel and having an injector that injects the natural gas, comprising:
a reference fuel recording unit that calculates and records a reference fuel learning value, which is a learning value of the reference fuel, based on a driving time of the injector when the reference fuel, which is the natural gas whose methane number is known, is used as fuel; and
a methane number estimation unit that calculates a current fuel learning value that is a learning value of a fuel currently being used based on a drive time of the injector, calculates a fuel learning value difference that is a difference between the reference fuel learning value and the current fuel learning value, and estimates the methane number of the fuel currently being used based on the fuel learning value difference and the methane number of the reference fuel;
a throttle opening control unit that changes an offset value of a throttle opening when the internal combustion engine is under high load, in accordance with the methane number estimated by the methane number estimation unit . A control device for an internal combustion engine using one of a plurality of natural gases having different compositions as fuel and having an injector that injects the natural gas, comprising:
a reference fuel recording unit that calculates and records a reference fuel learning value, which is a learning value of the reference fuel, based on a driving time of the injector when the reference fuel, which is the natural gas whose methane number is known, is used as fuel; and
a methane number estimation unit that calculates a current fuel learning value that is a learning value of a fuel currently being used based on a drive time of the injector, calculates a fuel learning value difference that is a difference between the reference fuel learning value and the current fuel learning value, and estimates the methane number of the fuel currently being used based on the fuel learning value difference and the methane number of the reference fuel;
a compression ratio control unit that changes a compression ratio of the internal combustion engine in accordance with the methane number estimated by the methane number estimation unit .

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