Abnormality detection device, abnormality detection method, and program

Abstract

Provided is a method for detecting an abnormality of the combustion state in an engine combustion chamber, without additionally providing a sensor in a cylinder. This abnormality detection device comprises a determination unit that, when the temperature of exhaust gas discharged from an engine increases at a rate greater than a prescribed rate of increase within a prescribed first time after the air-fuel ratio of the engine changes to be on the lean side, determines that the combustion state in the combustion chamber of the engine is abnormal.

Description

Anomaly detection device, anomaly detection method, and program

[0001] This disclosure claims priority to Japanese Patent Application No. 2024-066053, filed on April 16, 2024, the contents of which are incorporated herein by reference.

[0002] When a solenoid valve installed in the system supplying fuel gas to a gas engine cylinder becomes clogged with debris, fuel gas can flow into the cylinder even when the solenoid valve is closed. The inflow of fuel gas affects the combustion state. Conventionally, a pressure sensor is installed in the cylinder and the combustion state is monitored by detecting changes in pressure inside the cylinder. However, installing a pressure sensor in each of the multiple cylinders in a gas engine increases costs. Although a temperature sensor is installed in the exhaust system of a gas engine, detecting the inflow of fuel gas into the cylinder from the solenoid valve using this exhaust-side temperature sensor is delayed because it takes time for the exhaust temperature to reach a specified failure value. Therefore, in gas engines without a pressure sensor installed in the cylinder, the inflow of fuel gas causes the exhaust temperature to rise, and protection cannot be activated until knocking occurs, which may result in damage to the engine.

[0003] As a related technique, Patent Document 1 discloses a method for detecting abnormal combustion in a combustion chamber by using the air-fuel ratio of exhaust gas detected by an air-fuel ratio sensor and the temperature of the exhaust gas detected by a temperature sensor. However, even if the components of the exhaust gas are monitored by an air-fuel ratio sensor instead of installing a pressure sensor in the cylinder, the installation of the air-fuel ratio sensor is costly. Patent Document 2 discloses a method for controlling the amount of fuel gas supplied to a gas engine.

[0004] Japanese Patent Publication No. 2000-291485 Japanese Patent Publication No. 7457663

[0005] There is a need for a technology that can detect abnormalities in the combustion state in an engine combustion chamber without providing a pressure sensor, etc., in each cylinder. Patent Documents 1 and 2 do not disclose a method for detecting abnormalities in the combustion state without providing a pressure sensor, etc., in each cylinder.

[0006] The present disclosure provides an anomaly detection device, an anomaly detection method, and a program that can solve the above-mentioned problems.

[0007] According to one aspect of the present disclosure, an abnormality detection device includes a determination unit that determines that the combustion state in the combustion chamber of the engine is abnormal if the temperature of the exhaust gas emitted from the engine increases at a rate exceeding a predetermined rate of increase within a predetermined first time period after the air-fuel ratio of the engine changes to the lean side.

[0008] According to one aspect of the present disclosure, an abnormality detection device determines that the combustion state in the combustion chamber of the engine is abnormal if the temperature of the exhaust gas emitted from the engine increases at a rate greater than a predetermined rate of increase within a predetermined first time period after the air-fuel ratio of the engine changes to the lean side.

[0009] According to one aspect of the present disclosure, a computer is caused to execute a process of determining that the combustion state in the combustion chamber of the engine is abnormal when the temperature of the exhaust gas emitted from the engine increases at a rate exceeding a predetermined rate of increase within a predetermined first time period after the air-fuel ratio of the engine changes to the lean side.

[0010] According to the above-described abnormality detection device, abnormality detection method, and program, abnormalities in the combustion state in the combustion chamber of the engine can be detected early without the need for additional sensors.

[0011] It is a schematic configuration diagram of an engine according to an embodiment. It is a first diagram showing an example of an abnormality detection logic according to an embodiment. It is a second diagram showing an example of an abnormality detection logic according to an embodiment. It is a flowchart showing an example of an abnormality detection process according to an embodiment. It is a schematic diagram showing an example of a hardware configuration of an abnormality detection device according to an embodiment.

[0012] <Embodiment> A combustion state abnormality detection method according to this embodiment will be described below with reference to the drawings. FIG. 1 is a schematic diagram of an engine 1 according to this embodiment. The engine 1 is a gas engine that uses fuel gas as fuel and outputs power by burning an air-fuel mixture produced by mixing the fuel gas with intake air (air). The engine 1 has multiple cylinders 10. FIG. 1 shows only one cylinder 10 as a representative example. The cylinder 10 includes a cylinder 3 and a piston 2 that reciprocates within the cylinder 3. The cylinder 3 is provided with an intake port 5 that is opened and closed by an intake valve 4 and an exhaust port 7 that is opened and closed by an exhaust valve 6. A combustion chamber 8 is defined between the cylinder 3 and the piston 2, and an ignition plug 9 is provided in the combustion chamber 8. An intake manifold 11 is connected to the intake port 5. An intake pipe 15 that supplies air and a fuel gas supply pipe 12 that supplies gas fuel are connected to the intake manifold 11. A gas supply electromagnetic valve 20 is attached to the fuel gas supply pipe 12, and the amount of fuel gas supplied to the intake manifold 11 is controlled by opening and closing the gas supply electromagnetic valve 20. A throttle valve 14 is provided in the intake pipe 15, and the flow rate of air supplied to the intake port 5 is adjusted by controlling the opening degree of the throttle valve 14. A compressor 13c of the turbocharger 13 is connected to the upper end of the intake pipe 15. An air cleaner 17 is connected to the upstream end of an intake pipe 16 connected to the compressor 13c, and external air is taken in. Air taken in from the outside is sent to the intake manifold 11 via the air cleaner 17, the intake pipe 16, the compressor 13c, and the intake pipe 15, and in the intake manifold 11, the fuel gas supplied from the fuel gas supply pipe 12 is mixed with the intake air taken in from the outside to generate an air-fuel mixture. The air-fuel mixture is supplied to the combustion chamber 8 via the intake port 5, and combustion takes place in the combustion chamber 8. On the other hand, an exhaust pipe 18 is connected to the exhaust port 7, and exhaust gas after combustion is discharged into the exhaust pipe 18 via the exhaust port 7. A turbine 13t of the turbocharger 13 is connected to the downstream end of the exhaust pipe 18. The compressor 13c of the turbocharger 13 and the turbine 13t rotate integrally via a rotary shaft 13s. An exhaust pipe 19 is connected to the turbine 13t.A temperature sensor 21 is installed in the exhaust pipe 18 to measure the temperature of the exhaust gas flowing through the exhaust pipe 18. The detected value (exhaust temperature Tex) of the temperature sensor 21 is sent to a control device 22 that controls the engine 1 and an abnormality detection device 30 that detects abnormal combustion in the combustion chamber 8. A temperature sensor 21 is provided for each cylinder 10.

[0013] In addition to the exhaust temperature Tex detected by the temperature sensor 21, the control device 22 acquires detected pressure and temperature values ​​from a pressure sensor (not shown) that measures the pressure within the intake manifold 11 and a temperature sensor (not shown) that measures the temperature within the intake manifold 11, respectively. The control device 22 acquires the engine speed from a rotation speed sensor (not shown) connected to a crankshaft (not shown) that is connected to the piston 2. The control device 22 calculates the mixture flow rate (Qmix) using the temperature and pressure within the intake manifold 11. A method for calculating the mixture flow rate (Qmix) is disclosed, for example, in Patent Document 2. The control device 22 performs feedback control (PID control) so that the engine speed detected by the rotation speed sensor becomes a target rotation speed. Specifically, the control device 22 calculates a command gas amount (Qgas), which is the amount of fuel gas supplied so that the engine speed becomes the target rotation speed, and controls the opening and closing of the gas supply solenoid valve 20 so that the calculated command gas amount (Qgas) can be supplied. Any known method can be used to calculate the command gas amount (Qgas). The control device 22 calculates the air-fuel ratio λ at a predetermined control cycle using the following equation (1), and adjusts the opening of the throttle valve 14 so that the air-fuel ratio λ becomes a target value. Lamba_st in equation (1) is a stoichiometric value, and is a parameter whose value is set in advance. Qmix and Qgas are the mixture flow rate and command gas amount (both calculated values) described above, respectively. The control device 22 outputs the calculated air-fuel ratio λ to the abnormality detection device 30. Air-fuel ratio λ = (Qmix - Qgas) / (Qgas × Lamba_st) ... (1)

[0014] The abnormality detection device 30 detects an abnormality in the combustion state of the combustion chamber 8 using the air-fuel ratio λ acquired from the control device 22 and the exhaust temperature Tex detected by the temperature sensor 21. As shown in the figure, the abnormality detection device 30 includes a signal acquisition unit 31, a determination unit 32, and an alarm output unit 33. While FIG. 1 illustrates a configuration example in which the control device 22 and the abnormality detection device 30 are configured as separate entities, the abnormality detection device 30 may be incorporated into the control device 22.

[0015] The signal acquisition unit 31 acquires the air-fuel ratio λ from the control device 22 and acquires the exhaust temperature Tex from the temperature sensor 21. The determination unit 32 monitors the air-fuel ratio λ and the exhaust temperature Tex to determine whether or not there is an abnormality in the combustion state in the combustion chamber 8. A method for determining whether or not there is an abnormality in the combustion state will be described below with reference to FIGS. 2 and 3.

[0016] The alarm output unit 33 outputs an alarm when the determination unit 32 determines that there is an abnormality in the combustion state. For example, the alarm output unit 33 outputs the alarm to the control device 22, a monitoring device, a display device (not shown), or the like. The alarm includes, for example, the result of the abnormality determination by the determination unit 32, the time when the abnormality was determined to exist, the level of the abnormality, and the like. For example, the alarm output unit 33 may output an alarm indicating that a level 1 abnormality has been detected when an abnormality that does not require stopping the engine 1 has been detected, or may output a level 2 alarm and stop the engine 1 when a combustion abnormality that requires an emergency stop of the engine 1 has been detected. An emergency stop refers to quickly stopping the engine 1 due to an imminent danger.

[0017] (Abnormality Determination Logic 1) FIG. 2 shows an example of abnormality detection logic according to the embodiment. In a gas engine that uses a gas supply solenoid valve 20 to directly supply gas into the intake port 5, if debris or other foreign matter gets caught in the gas supply solenoid valve 20, fuel gas flows into the intake manifold 11 even when the gas supply solenoid valve 20 is closed, and excess fuel is supplied to the combustion chamber 8. This can result in abnormal combustion. During engine 1 operation, the air-fuel ratio λ calculated in the control device 22 becomes richer as the command gas amount Qgas increases (as can be seen from equation (1), when the air-fuel ratio λ becomes richer, the value of the air-fuel ratio λ decreases). If debris or other foreign matter gets caught in the gas supply solenoid valve 20, the engine 1 rotation speed increases excessively by the amount of fuel gas inflow, causing the exhaust temperature to rise. Then, the feedback control described above is activated, and the control device 22 reduces the command gas amount Qgas to reduce the engine 1 rotation speed. As a result, the air-fuel ratio λ becomes leaner (the value of the air-fuel ratio λ increases). Since the commanded gas amount Qgas is reduced, combustion in the combustion chamber 8 should be suppressed, and the exhaust gas temperature Tex should decrease. However, even if the commanded gas amount Qgas is reduced, if more fuel is supplied than the commanded gas amount Qgas due to the influence of debris or other factors, the exhaust gas temperature Tex will rise. The determination unit 32 monitors whether such a phenomenon occurs, and if the exhaust gas temperature Tex of the exhaust gas discharged from the cylinder 10 rises immediately (e.g., within 5 seconds) after the air-fuel ratio λ shifts to the lean side, it determines that fuel is leaking from the gas supply solenoid valve 20 due to debris or other factors in that cylinder 10. Excessive fuel supply from the gas supply solenoid valve 20 leads to abnormal combustion. Therefore, when the determination unit 32 detects an excessive fuel supply state, it determines that the combustion state is abnormal. More specifically, the determination unit 32 calculates the exhaust temperature change amount = dTex / dt from the exhaust temperature Tex acquired from the signal acquisition unit 31 at each moment. The judgment unit 32 then monitors the air-fuel ratio λ acquired by the signal acquisition unit 31 and the calculated dTex / dt, and judges that an abnormality has occurred if the exhaust gas temperature change amount dTex / dt rises above a predetermined value within a predetermined time (for example, within 5 seconds) after the air-fuel ratio λ becomes lean (the value of the air-fuel ratio λ increases).

[0018] Here, the determination unit 32 determines that a level 1 abnormality has been detected if the rate of increase in the amount of change in exhaust temperature immediately after the air-fuel ratio λ has changed to the lean side is an abnormal rate that does not require stopping the engine 1, and determines that a level 2 abnormality has been detected if the rate of increase is such that engine 1 must be stopped immediately, and outputs this determination result to the alarm output unit 33.

[0019] This allows early detection of a condition in which abnormal combustion may occur in the combustion chamber 8. Generally, a temperature sensor is provided on the exhaust side of an engine, and the air-fuel ratio is also calculated during control. The abnormality detection logic illustrated in FIG. 2 allows for detection of abnormalities in the combustion state or early detection of abnormalities and protection without the need for additional pressure sensors or the like for each cylinder 10. By using the exhaust temperature change dTex / dt, abnormalities can be detected earlier than with conventional abnormality detection methods that determine an abnormality when the exhaust temperature exceeds a threshold value. By dividing the abnormality level into two stages, operation can be continued as long as possible while ensuring safety when an abnormality occurs, and if operation must be stopped, operation of the engine 1 can be stopped promptly.

[0020] (Abnormality Determination Logic 2) Figure 3 shows a more detailed example of the abnormality detection logic according to this embodiment. The logic in the portion enclosed by 32b is logic for detecting an excessive supply of fuel gas when debris suddenly becomes caught in the gas supply solenoid valve 20. The logic compares the deviation between the current air-fuel ratio λ and the air-fuel ratio λ a certain time ago (for example, 4 to 6 seconds ago) with a predetermined deviation determination value to determine whether the air-fuel ratio λ has suddenly become leaner than the air-fuel ratio λ from the certain time ago. If the current air-fuel ratio λ has suddenly become leaner than the air-fuel ratio λ from the certain time ago, the logic 32b outputs an ON signal from the "ONE SHOT" circuit to the OR circuit 32f for a predetermined period of time; otherwise, it outputs an OFF signal.

[0021] The logic in the portion enclosed by 32a is used to detect an excessive supply of fuel gas when fuel gas slowly flows in from the gas supply solenoid valve 20, rather than when dust is suddenly trapped as described above. The air-fuel ratio λ obtained from the control device 22 is passed through a low-pass filter to remove sudden fluctuations and noise, and the air-fuel ratio λ after passing through the low-pass filter is compared with a predetermined threshold value. The predetermined threshold value is a value obtained by adding a predetermined judgment value to the target value of the air-fuel ratio λ. While the air-fuel ratio λ after passing through the low-pass filter exceeds this threshold value (while a lean state continues), the logic 32a outputs an ON signal to the OR circuit 32f; otherwise, an OFF signal is output. When an ON signal is output from either the logic 32a or the logic 32b, the OR circuit 32f outputs an ON signal to the AND circuit 32g. When an OFF signal is output from both the logic 32a and the logic 32b, the OR circuit 32f outputs an OFF signal to the AND circuit 32g.

[0022] The logic in the portion enclosed by 32c is logic for determining whether the rate of increase in the amount of change in the exhaust gas temperature for each cylinder 10 exceeds a threshold value. The determination unit 32 calculates the amount of change in the exhaust gas temperature Tex, dTex / dt. The amount of change in the exhaust gas temperature dTex / dt is passed through a low-pass filter to remove sudden fluctuations and noise, and the amount of change in the exhaust gas temperature dTex / dt after passing through the low-pass filter is compared with a predetermined threshold value (first threshold value). The predetermined threshold value is a determination value set for each cylinder 10. Because there are individual differences between cylinders 10, a determination value is set for each cylinder 10. While the amount of change in the exhaust gas temperature dTex / dt after passing through the low-pass filter exceeds the threshold value, the logic 32c outputs an ON signal to the AND circuit 32g; otherwise, an OFF signal is output.

[0023] The logic in the portion enclosed by 32d is logic for halting abnormality detection because an abnormality cannot be correctly determined during transient operation in which the load changes suddenly, such as when a load is applied or removed, or when an abnormality occurs in the temperature sensor 21 used for abnormality determination or in the sensors that detect the pressure and temperature inside the intake manifold 11. An ON signal is output from logic 32d to AND circuit 32g only when there is no sensor abnormality and the engine 1 is not in a transient state, and an OFF signal is output in all other cases.

[0024] The logic in the portion enclosed by 32e is logic that does not perform abnormality detection when starting or stopping the engine 1. When the output of the engine 1 exceeds a predetermined threshold, the logic 32e outputs an ON signal to the AND circuit 32g, and in other cases, an OFF signal is output.

[0025] When ON signals are output from all of logic 32c, logic 32d, logic 32e, and OR circuit 32f, an ON signal is output from AND circuit 32g; otherwise, an OFF signal is output. The determination unit 32 determines that an abnormality exists when an ON signal is output from AND circuit 32g, and determines that no abnormality exists when an OFF signal is output from AND circuit 32g. At this time, the determination unit 32 determines whether the exhaust gas temperature change dTex / dt exceeds a predetermined threshold (second threshold) for determining whether operation should be stopped. If it does exceed the second threshold, it determines that a level 2 abnormality requiring an emergency shutdown has occurred. If it is equal to or less than the second threshold, it determines that a level 1 abnormality has occurred, allowing operation to continue.

[0026] 3 , the determination unit 32 determines that there is an abnormal combustion state if the exhaust gas temperature change rate dTex / dt increases above a predetermined first threshold value during a certain period of time after the air-fuel ratio λ suddenly becomes lean, or while the air-fuel ratio λ continues to exceed the predetermined threshold value, except when a sensor abnormality occurs, when the engine 1 is in a transient state, or when the engine output is equal to or lower than the threshold value. This prevents erroneous detection due to a sensor abnormality or a transient state, and enables early detection of abnormal combustion or its precursor (excessive fuel supply state). By setting threshold values ​​(first and second threshold values) for determining the rate of increase of the exhaust gas temperature change rate dTex / dt for each cylinder 10, it is possible to accurately detect an abnormal combustion state.

[0027] (Operation) Next, the flow of the abnormality detection process will be described with reference to FIG. 4 . FIG. 4 is a flowchart illustrating an example of the abnormality detection process according to the embodiment. The abnormality detection device 30 repeats the following process at a predetermined control period. First, the signal acquisition unit 31 acquires the air-fuel ratio λ and the exhaust temperature Tex (step S1). The signal acquisition unit 31 outputs the acquired air-fuel ratio λ and exhaust temperature Tex to the determination unit 32. The determination unit 32 receives the air-fuel ratio λ and the exhaust temperature Tex and stores this information for a certain period of time. Next, the determination unit 32 determines whether or not there is an abnormality in the combustion state (step S2). The determination unit 32 determines whether or not there is an abnormality in the combustion state for each of the multiple cylinders 10 using the abnormality determination logic illustrated in FIG. 2 or 3 . If there is an abnormality, the determination unit 32 compares the rate of increase of the exhaust temperature change amount dTex / dt with a second threshold value to determine the abnormality level. If the rate of increase exceeds the second threshold value, the determination unit 32 determines that there is a Level 2 abnormality that requires an emergency stop. If the rate of increase is equal to or less than the second threshold value, the determination unit 32 determines that there is a Level 1 abnormality. If the determination result indicates no abnormality (Step S3; No), the process proceeds to Step S7. If an abnormality is detected (Step S3; Yes), the determination unit 32 outputs the determination result indicating that an abnormality has been detected and the level of the abnormality to the alarm output unit 33. The alarm output unit 33, upon receiving the determination result, outputs an alarm according to the abnormality level. For example, if an emergency stop is required (Step S4; Yes), the alarm output unit 33 outputs an alarm to a display device or the like indicating that an abnormality requiring an emergency stop has been detected, and outputs a signal to the control device 22 instructing the control device 22 to stop the engine 1 (Step S6). Upon receiving this signal, the control device 22 stops the engine 1. If an emergency stop is not required (Step S4; No), the alarm output unit 33 outputs an alarm to a display device or the like indicating that an abnormality has been detected (Step S5). Next, the abnormality detection device 30 determines whether to end the abnormality detection process (Step S7). For example, when a command to stop the operation of the engine 1 is input by the user, the abnormality detection device 30 determines to end the abnormality detection process (step S7; Yes), and ends the process of the flowchart in Fig. 4. If the abnormality detection process is not to be ended (step S7; No), the process from step S1 is repeatedly executed.

[0028] (Effects) As described above, according to this embodiment, it is possible to detect an abnormal combustion state (for example, a level 2 abnormality) in the combustion chamber 8 or a sign thereof (fuel gas unintentionally flowing into the cylinder 10 from the gas supply solenoid valve 20) without additionally installing an expensive pressure sensor in each cylinder 10. Since the abnormality is detected based on a change in the air-fuel ratio λ and the rate of increase in exhaust temperature, it is possible to detect the abnormality earlier than with the conventional method of detecting abnormal combustion based on an increase in exhaust temperature.

[0029] 5 is a schematic block diagram showing the hardware configuration of a control device according to an embodiment. A computer 90 includes a processor 91, a main memory 92, a storage 93, and an interface 94. The control device 22 and the anomaly detection device 30 described above are implemented in the computer 90. The operations of the above-described processing units are stored in the storage 93 in the form of a program. The processor 91 reads the program from the storage 93, loads it into the main memory 92, and executes the above-described processing in accordance with the program. The processor 91 allocates storage areas in the main memory 92 corresponding to the above-described storage units in accordance with the program. Examples of the processor 91 include a CPU (Central Processing Unit), a GPU (Graphic Processing Unit), and a microprocessor.

[0030] The program may be for realizing some of the functions to be performed by the computer 90. For example, the program may be combined with other programs already stored in storage or implemented in other devices to perform the functions. In another embodiment, the computer 90 may include a custom LSI (Large Scale Integrated Circuit) such as a programmable logic device (PLD) in addition to or instead of the above configuration. Examples of PLDs include programmable array logic (PAL), generic array logic (GAL), complex programmable logic device (CPLD), and field programmable gate array (FPGA). In this case, some or all of the functions realized by the processor 91 may be realized by the integrated circuit. Such an integrated circuit is also an example of a processor.

[0031] Examples of storage 93 include hard disk drives (HDDs), solid state drives (SSDs), magnetic disks, magneto-optical disks, compact disc read-only memories (CD-ROMs), digital versatile disc read-only memories (DVD-ROMs), and semiconductor memories. Storage 93 may be internal media directly connected to the bus of computer 90, or external media connected to computer 90 via interface 94 or a communication line. When this program is distributed to computer 90 via a communication line, computer 90 receiving the program may deploy the program in main memory 92 and execute the above-described processing. In at least one embodiment, storage 93 is a non-transitory, tangible storage medium. The program may be for implementing some of the above-described functions. Furthermore, the program may be a so-called differential file (differential program) that realizes the above-described functions in combination with other programs already stored in storage 93.

[0032] As described above, several embodiments according to the present disclosure have been described, but all of these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents as defined in the claims, as well as in the scope and spirit of the invention.

[0033] <Additional Notes> The anomaly detection device, the anomaly detection method, and the program described in each embodiment can be understood, for example, as follows.

[0034] (1) A first aspect of the abnormality detection device includes a determination unit that determines that the combustion state in the combustion chamber of the engine is abnormal when the temperature of exhaust gas discharged from the engine rises at a rate exceeding a predetermined rate within a first predetermined time period after the air-fuel ratio of the engine has changed to the lean side. This allows for early detection of an abnormality without the need for additional sensors.

[0035] (2) A second aspect of the abnormality detection device is the abnormality detection device of (1), wherein the determination unit determines that an abnormality has occurred when the temperature of the exhaust gas increases at a rate exceeding the rate of increase while the air-fuel ratio continues to be greater than a target air-fuel ratio by a predetermined value. This allows for early detection of an abnormality without the need for an additional sensor.

[0036] (3) A third aspect of the abnormality detection device is the abnormality detection device of (1) to (2), wherein the determination unit determines that an abnormality has occurred if the exhaust gas temperature rises faster than the rate of increase during the first time period from the first time period when the air-fuel ratio at a first time point is greater by a predetermined value than the air-fuel ratio at a predetermined time period before the first time point. This allows for early detection of an abnormality without the need for an additional sensor.

[0037] (4) The abnormality detection device according to a fourth aspect is the abnormality detection device of any one of (1) to (3), further comprising an alarm output unit that notifies the user that an abnormality in the combustion state has been detected when the determination unit determines that an abnormality has occurred. This allows for prompt notification when an abnormality is detected.

[0038] (5) A fifth aspect of the abnormality detection device is the abnormality detection device of (4), wherein the determination unit determines that an abnormality in the combustion state has occurred when the rate of increase in the temperature of the exhaust gas exceeds a predetermined first threshold, determines that an abnormality requiring stopping of the engine has occurred when the rate of increase in the temperature of the exhaust gas exceeds a second threshold that is greater than the first threshold, and when the determination unit determines that an abnormality requiring stopping of the engine has occurred, the warning output unit outputs an instruction signal to stop the engine. Thus, if an abnormality in the combustion state that requires emergency stopping of the engine is detected, the engine can be stopped.

[0039] (6) A sixth aspect of the abnormality detection device is the abnormality detection device of any one of (1) to (5), wherein the determination unit does not determine an abnormality in the combustion state when an abnormality exists in the sensor that detects the temperature of the exhaust gas, when an abnormality exists in a sensor required for calculating the air-fuel ratio, when the operating state of the engine is in a transient state, or when the output of the engine is less than a predetermined value, thereby preventing erroneous detection.

[0040] (7) In the seventh aspect of the abnormality detection method, an abnormality detection device determines that the combustion state in the combustion chamber of the engine is abnormal when the temperature of the exhaust gas discharged from the engine rises at a rate exceeding a predetermined rate of increase within a predetermined first time period after the air-fuel ratio of the engine changes to the lean side.

[0041] (8) A program according to an eighth aspect causes a computer to execute a process of determining that the combustion state in the combustion chamber of the engine is abnormal when the temperature of the exhaust gas discharged from the engine rises at a rate exceeding a predetermined rate of increase within a predetermined first time period after the air-fuel ratio of the engine changes to the lean side.

[0042] According to the above-described abnormality detection device, abnormality detection method, and program, abnormalities in the combustion state in the combustion chamber of the engine can be detected early without the need for additional sensors.

[0043] DESCRIPTION OF SYMBOLS 1: Engine 2: Piston 3: Cylinder 4: Intake valve 5: Intake port 6: Exhaust valve 7: Exhaust port 8: Combustion chamber 9: Spark plug 10: Cylinder 11: Intake manifold 12: Fuel gas supply pipe 13: Supercharger 13t: Turbine 13s: Rotating shaft 13c: Compressor 14: Throttle valve 15: Intake pipe 16: Intake pipe 17: Air cleaner 18: Exhaust pipe 19: Exhaust pipe 20: Gas supply solenoid valve 21: Temperature sensor 30: Abnormality detection device 31: Signal acquisition unit 32: Determination unit 33: Alarm output unit 90: Computer 91: Processor 92: Main memory 93: Storage 94: Interface

Claims

1. An abnormality detection device comprising a judgment unit that judges that the combustion state in the combustion chamber of the engine is abnormal if the temperature of exhaust gas emitted from the engine rises at a rate exceeding a predetermined rate of rise within a predetermined first time period after the air-fuel ratio of the engine has changed to the lean side.

2. The abnormality detection device according to claim 1, wherein the determination unit determines that an abnormality has occurred when the temperature of the exhaust gas increases at a rate exceeding the rate of increase while the air-fuel ratio continues to be greater than a target air-fuel ratio by a predetermined value.

3. The abnormality detection device according to claim 1 or claim 2, wherein the judgment unit judges that an abnormality has occurred if the exhaust gas temperature rises at a rate exceeding the rate of rise during the first time period from the first time period when the air-fuel ratio at a first time point is greater by a predetermined value than the air-fuel ratio at a predetermined time period before the first time point.

4. An abnormality detection device according to claim 1 or claim 2, further comprising an alarm output unit that notifies the user that an abnormality in the combustion state has been detected when the determination unit determines that an abnormality has occurred.

5. The abnormality detection device described in claim 4, wherein the judgment unit judges that an abnormality in the combustion state has occurred when the rate of increase in the temperature of the exhaust gas exceeds a predetermined first threshold, and judges that an abnormality requiring the engine to be stopped has occurred when the rate of increase in the temperature of the exhaust gas exceeds a second threshold that is greater than the first threshold, and when the judgment unit judges that an abnormality requiring the engine to be stopped has occurred, the alarm output unit outputs an instruction signal to instruct the engine to be stopped.

6. An abnormality detection device as described in claim 1 or claim 2, wherein the judgment unit does not make an abnormality judgment on the combustion state when there is an abnormality in the sensor that detects the temperature of the exhaust gas, when there is an abnormality in a sensor necessary for calculating the air-fuel ratio, when the operating state of the engine is in a transient state, or when the output of the engine is less than a predetermined value.

7. An abnormality detection method, in which an abnormality detection device determines that the combustion state in the combustion chamber of the engine is abnormal when the temperature of exhaust gas emitted from the engine rises at a rate exceeding a predetermined rate of rise within a predetermined first time period after the air-fuel ratio of the engine changes to the lean side.

8. A program that causes a computer to execute a process of determining that the combustion state in the combustion chamber of the engine is abnormal when the temperature of the exhaust gas emitted from the engine rises at a rate exceeding a predetermined rate of increase within a predetermined first time period after the air-fuel ratio of the engine has changed to the lean side.

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