JP2024076086A - Engine misfire detection device - Google Patents

Abstract

[Problem] With regard to an engine misfire detection device, the accuracy of judging a misfire state is improved with a simple configuration. [Solution] The disclosed misfire detection device 10 for an engine 1 includes a calculation unit 11, a correction unit 12, and a judgment unit 13. The calculation unit 11 calculates a deviation D by subtracting a first angular velocity Ne1, which is the crank angular velocity Ne when the crank angle θ is a first angle θ1 in the first half of the combustion stroke of the engine 1, from a second angular velocity Ne2, which is the crank angular velocity Ne when the crank angle θ is a second angle θ2 in the second half of the combustion stroke. The correction unit 12 calculates a corrected deviation C by correcting the deviation D based on an average engine angular velocity deviation A corresponding to the trend of change in the crank angular velocity Ne in a predetermined crank angle range P2. The judgment unit 13 judges a misfire state of the engine 1 based on the corrected deviation C. [Selected Figure] Figure 1

Description

This case relates to a misfire detection device that detects misfires and partial misfires in an engine.

Conventionally, there are techniques for determining misfire conditions such as misfire and semi-misfire based on changes in the engine crank angular velocity (engine rotation speed). For example, a technique is known that calculates the amount of fluctuation from the crank angular velocity before combustion to the crank angular velocity after combustion in the combustion cycle of each cylinder of the engine, and determines whether or not a misfire has occurred by comparing this amount of fluctuation with a predetermined misfire determination value. It has also been proposed to set a lenient misfire determination value during sudden acceleration and deceleration in order to avoid erroneous misfire determination (see Patent Documents 1 and 2).

Patent No. 4490721 Japanese Patent Application Laid-Open No. 05-018311

On the other hand, simply relaxing the conditions for determining misfires during rapid acceleration and deceleration, as in conventional technology, makes it difficult to accurately grasp poor combustion that is close to a misfire (for example, slow combustion or a misfire during combustion), and there is a risk that the accuracy of determining the misfire state will decrease. For example, as a result of relaxing the conditions for determining misfires, it may not be possible to detect a misfire even if a slight misfire (poor combustion) is actually occurring.

One of the objectives of this invention was devised in light of the above problems, and is to provide an engine misfire detection device that can improve the accuracy of determining a misfire state with a simple configuration. However, this objective is not the only objective. Another objective of this invention is to achieve effects that cannot be obtained with conventional technology, which are derived from the configurations shown in the "Mode for carrying out the invention" described below.

The disclosed engine misfire detection device can be realized as the following disclosed aspects or application examples, and solves at least some of the above problems.
The disclosed engine misfire detection device includes a calculation unit that calculates a deviation by subtracting a first angular velocity, which is the crank angular velocity when the crank angle is a first angle in the first half of the engine combustion stroke, from a second angular velocity, which is the crank angular velocity when the crank angle is a second angle in the second half of the combustion stroke; a correction unit that calculates a corrected deviation by correcting the deviation based on an average engine angular velocity deviation corresponding to a change trend of the crank angular velocity within a specified crank angle range; and a judgment unit that judges a misfire state of the engine based on the corrected deviation.

The disclosed engine misfire detection device uses a correction deviation corrected based on the average engine angular velocity deviation, making it possible to improve the accuracy of determining a misfire state with a simple configuration.

1 is a block diagram for explaining the configuration of an engine and a misfire detection device; 4 is a graph for explaining an average engine angular velocity deviation A, a gradient influence value B, a correction deviation C, and a deviation D calculated by the misfire detection device, the graph showing a change in crank angular velocity Ne with respect to a crank angle θ. FIG. 4 is a diagram for explaining the relationship between the correction deviation C and a misfire state.

The disclosed engine misfire detection device can be applied to various engines, such as automobile engines, marine engines, industrial engines, and general-purpose engines. In the following embodiment, a misfire detection device applied to an engine mounted on a vehicle is illustrated. In addition, types of engines to which the misfire detection device can be applied include gasoline engines and diesel engines, and there are no restrictions on the number of cylinders or cylinder arrangement.

[1. Configuration]
A misfire detection device 10 as an embodiment is applied to an on-vehicle engine 1 shown in Fig. 1. The engine 1 is a four-cylinder, four-stroke gasoline engine. Fig. 1 shows one of the four cylinders provided in the engine 1. The engine 1 is provided with a fuel injection valve 2 and a spark plug 3. The fuel injection valve 2 is provided, for example, in an intake port for introducing intake air into the cylinder, and the spark plug 3 is provided at an upper part of the combustion chamber. If the engine 1 is a direct injection engine, the fuel injection valve 2 is provided in the combustion chamber. It is also possible to provide the fuel injection valve 2 in both the intake port and the combustion chamber.

A crank angle sensor 4 for detecting a crank angle θ is provided near the crankshaft of the engine 1. The crank angle sensor 4 calculates a crank angular velocity (amount of change in crank angle θ per unit time) based on the time it takes for the crankshaft to rotate a predetermined angle (e.g., 10°). The crank angular velocity corresponds to an engine rotation speed Ne [rpm] (number of engine revolutions per unit time (one minute)). Therefore, in this embodiment, the crank angular velocity is denoted by the symbol Ne. In this embodiment, the crank angular velocity is calculated for every 10° of crank angle.
A catalytic device 5 for purifying exhaust gas is installed in the exhaust passage of the engine 1. Specific examples of the catalytic device 5 include a three-way catalyst, an oxidation catalyst, a DPF catalyst, an SCR catalyst, a storage reduction catalyst, etc. A catalyst temperature sensor 6 for detecting the catalyst temperature is provided near or inside the catalytic device 5.

At any position on the vehicle, an accelerator opening sensor 8 that detects the amount of depression of the accelerator pedal (accelerator opening) and a vehicle speed sensor 9 that detects a parameter corresponding to the vehicle speed (vehicle running speed) are provided. The accelerator opening is a parameter that corresponds to the driver's request for acceleration/deceleration, intention to start, intention to brake, etc. In addition, the vehicle speed sensor 9 detects, for example, the wheel speed, the angular velocity of the wheel axle, or the engine speed. The vehicle speed is calculated based on these values.

This vehicle is equipped with a catalyst control device 7 for raising the temperature of the catalyst device 5 and a misfire detection device 10 for judging the misfire state of the engine 1. Both of these are electronic control devices (ECU, Electronic Control Unit). Each electronic control device has a built-in processor (central processing unit), memory (main memory), storage device, interface device, etc. (not shown), which are connected to each other so that they can communicate with each other. The contents of the control executed by each electronic control device are recorded and saved in the memory or storage device as firmware or application programs. When a program is executed, the contents of the program are expanded in memory space and arithmetic processing is performed by the processor.

The catalyst control device 7 performs temperature rise control to adjust the operating state of the engine 1 so that the catalyst temperature is in a predetermined active temperature range or so that the catalyst temperature is in a temperature range suitable for exhaust gas purification. For example, when the engine 1 is started in a cold state, in order to quickly raise the catalyst temperature to the active temperature range, air-fuel ratio control is performed to adjust the air-fuel ratio to be leaner than the theoretical air-fuel ratio, fuel injection control is performed to retard the fuel injection timing, and ignition timing control is performed to retard the ignition timing. These temperature rise controls raise the exhaust gas temperature, and the catalyst temperature quickly rises to the active temperature range.

Furthermore, when the amount of exhaust particulate matter accumulated in the catalytic converter 5 increases, the above-mentioned air-fuel ratio control, fuel injection control, and ignition timing control are carried out in order to burn the exhaust particulate matter. These temperature rise controls allow the exhaust particulate matter to be burned quickly.
Alternatively, when the amount of the substances to be stored (such as nitrogen oxides, hydrocarbons, etc.) in the catalyst device 5 increases and exceeds a predetermined amount, the above-mentioned air-fuel ratio control, fuel injection control, and ignition timing control are performed to purify the substances to be stored while desorbing them. By these temperature rise controls, the substances to be stored are efficiently purified.

The misfire detection device 10 judges the misfire state of the engine 1. Here, it is judged at least whether the combustion state in the cylinder is normal or an abnormal misfire state. The misfire detection device 10 of this embodiment has a function to distinguish between "misfire (complete misfire)" and "semi-misfire" which are included in the misfire state. Misfire means that the mixture in the cylinder did not burn (there was no combustion reaction). Semi-misfire means that only a part of the mixture in the cylinder burned, the mixture burned incompletely due to slow combustion, or the combustion reaction stopped midway.

The misfire detection device 10 is connected to a crank angle sensor 4, a catalyst control device 7, an accelerator opening sensor 8, and a vehicle speed sensor 9. In this embodiment, the misfire detection device 10 judges the misfire state of the engine 1 based on the crank angle θ detected by the crank angle sensor 4 and the crank angular velocity Ne, which is its time derivative, when judging the misfire state. In addition, the misfire state of the engine 1 is judged taking into account information related to the operating state of the engine 1 (accelerator opening, vehicle speed, implementation status of temperature rise control of the catalyst device 5). The judgment result here is reflected in the notification device 14.

The notification device 14 is an output device for notifying the occupant of the misfire state determined by the misfire detection device 10, and is, for example, a warning light or a display device. For example, if it is determined that the engine 1 is in a misfire state, an indicator or a telltale mark indicating the misfire state is lit on the notification device 14. Also, if it is determined that the combustion state of the engine 1 is normal, the indicator or the telltale mark indicating the misfire state is turned off.

As shown in FIG. 1, the misfire detection device 10 is provided with a calculation unit 11, a correction unit 12, and a judgment unit 13. These elements are shown by conveniently classifying the functions of the misfire detection device 10 for judging the misfire state of the engine 1. These elements may be written as independent programs, or as a composite program combining all of these functions.

The calculation unit 11 calculates a deviation D between the crank angular velocity Ne in the first half of a combustion stroke and the crank angular velocity Ne in the second half of the combustion stroke in the combustion cycle of the engine 1. Here, the crank angular velocity Ne when the crank angle θ is a first angle _θ1 in the first half of the combustion stroke of the engine 1 is defined as a first angular velocity _Ne1 . Also, the crank angular velocity Ne when the crank angle θ is a second angle _θ2 in the second half of the combustion stroke is defined as a second angular velocity _Ne2 . The calculation unit 11 subtracts the first angular velocity _Ne1 from the second angular velocity _Ne2 to calculate the deviation D (D= _Ne2 - _Ne1 ).

The first angle _θ1 is set in the first half of the combustion stroke of the engine 1, and the second angle _θ2 is set in the second half of the combustion stroke of the engine 1. The range between the first angle _θ1 and the second angle _θ2 is called a judgment angle width _P1 . In this embodiment, the values of the first angle _θ1 and the second angle _θ2 are set so that the judgment angle width _P1 is 130° ( _θ2 = _θ1 + 130°).

There are two possible definitions for the first half and second half of the combustion stroke. The first definition is based on the crank angle θ, and defines the first half of the entire combustion stroke, i.e., in this embodiment (a four-cylinder, four-stroke gasoline engine), as the range θ<90 [° ATDC], and the second half, i.e., the range 90≦θ [° ATDC], as the second half of the combustion stroke. The boundary value between the first and second half (90 [° ATDC]) may be changed depending on the type and operating state of the engine 1, etc.

The second definition is based on the crank angular velocity Ne, and defines the range before the time (or crank angle θ) when the crank angular velocity Ne is maximum in the combustion stroke as the first half of the combustion stroke, and the range after that time (or crank angle θ) as the second half of the combustion stroke. In this embodiment, in either case, the angle corresponding to the start point of the combustion stroke is around 0° ATDC, and the angle corresponding to the end point is around 180° ATDC. Note that the time (or crank angle θ) that is the boundary between the first and second halves may be shifted forward or backward based on the time (or crank angle θ) when the crank angular velocity Ne is maximum.

In this application, the "combustion stroke" refers to the combustion stroke of the entire engine 1. That is, in a four-cylinder, four-stroke gasoline engine, the strokes of each cylinder are shifted by 180° with respect to the crank angle θ, so the combustion strokes occur every 180° and start and end within a range of 180°.

The correction unit 12 corrects the deviation D in consideration of the influence of the overall change tendency obtained by smoothing out the periodic fluctuation of the crank angular velocity Ne. The correction unit 12 calculates an average engine angular velocity deviation A corresponding to the overall change tendency (degree of increase or decrease, gradient, trend) of the crank angular velocity Ne in a predetermined crank angle range _P2 , and calculates a corrected deviation C by correcting the deviation D based on the average engine angular velocity deviation A.

The predetermined crank angle range _P2 is preferably short enough to reflect the overall change tendency of the crank angular velocity Ne, and long enough to ensure a sufficient number of samples. For example, the predetermined crank angle range _P2 is preferably wider than the judgment angle width _P1 ( _P1 < _P2 ), and is preferably set so as to completely include the judgment angle width _P1 (the start point of the predetermined crank angle range _P2 is before the start point of the judgment angle width _P1 , and the end point of the predetermined crank angle range _P2 is after the end point of the judgment angle width _P1 ). In this embodiment, the misfire judgment is calculated every 180° with respect to the crank angle θ, so that the end point of the predetermined crank angle range _P2 may be set within the calculation range of the misfire judgment that includes the judgment angle width _P1 .

The predetermined crank angle range _P2 may be set based on the fluctuation period of the crank angular velocity Ne. For example, in a four-cylinder four-stroke engine, the combustion stroke is repeated at a crank angle period of 180°. Therefore, it is conceivable to set the predetermined crank angle range _P2 to 180°. Note that if the predetermined crank angle range _P2 is around 180° (e.g., 160 to 200°), the overall change tendency of the crank angular velocity Ne can be grasped, so the predetermined crank angle range _P2 does not need to be set to 180° strictly. In addition, the predetermined crank angle range _P2 may be set to a range around an integer multiple of 180° (e.g., 160 to 200°, 340 to 380°, 520 to 560°, 700 to 740°, etc.). Similarly, in a three-cylinder four-stroke engine, the combustion stroke of the cylinder is repeated at a crank angle period of 240°. Therefore, the predetermined crank angle range _P2 may be set to about 240° (for example, 220 to 260°) or may be set to a range of about an integer multiple of 240° (for example, 220 to 260°, 460 to 500°, 700 to 740°, etc.).

However, since the purpose of the predetermined crank angle range _P2 is to observe the overall change tendency of the crank angular velocity Ne in the vicinity of the judgment angle width _P1 , it is preferable that the width of the predetermined crank angle range _P2 is not too large. If the width of the predetermined crank angle range _P2 is too large, it will reflect the change tendency of the crank angular velocity Ne at timing unrelated to the judgment angle width _P1 . Therefore, it is preferable that the predetermined crank angle range _P2 is set to the crank angle period of the combustion stroke (180° in a four-cylinder four-stroke engine).

In this embodiment, the crank angle θ at the end of the predetermined crank angle range _P2 is set to coincide with the second angle _θ2 , and the width of the predetermined crank angle range _P2 is set to 180°. Here, the crank angle θ at the start of the predetermined crank angle range _P2 is set to a third angle _θ3 , and the crank angular velocity Ne when the crank angle θ is the third angle _θ3 is set to a third angular velocity _Ne3 . The third angle _θ3 is the crank angle 180° before the second angle _θ2 ( _θ3 = _θ2 - 180°).

The correction unit 12 calculates the average engine angular velocity deviation A by subtracting the third angular velocity _Ne3 from the second angular velocity _Ne2 (A= _Ne2 - _Ne3 ). The value of the average engine angular velocity deviation A represents the degree to which the crank angular velocity Ne has increased or decreased between the start point and the end point of the specified crank angle range _P2 . To reflect this value in the deviation D, the correction unit 12 calculates a gradient influence value B which is the product of the average engine angular velocity deviation A and the ratio of the judgment angle width _P1 between the first angle _θ1 and the second angle _θ2 with respect to the specified crank angle range _P2 [B=A×( _P1 / _P2 )].

The gradient influence value B indicates the degree to which the global change tendency of the crank angular velocity Ne affects the deviation D. The correction unit 12 then subtracts the gradient influence value B from the deviation D to calculate a corrected deviation C (C=D-B). The corrected deviation C corresponds to the deviation D obtained by removing the influence of the global change tendency of the crank angular velocity Ne. In other words, the corrected deviation C indicates the degree to which the crank angular velocity Ne has changed during the determination angle width _P1 when the global change tendency is removed from the fluctuation of the crank angular velocity Ne and the resulting fluctuation is standardized to a constant periodic fluctuation.

The determination unit 13 determines whether the engine 1 is in a misfire state based on the correction deviation C. Here, the misfire state is determined using the relationship between the correction deviation C and the misfire state as shown in FIG. 3, for example. In this embodiment, the determination unit 13 determines that the combustion state is normal when the correction deviation C exceeds a first determination value _C1 . In this case, an indicator or a _telltale mark indicating the misfire state is not displayed on the notification device 14. The first determination value _C1 may be a positive value or a negative value. The value of the first determination value _C1 may be set based on experiments, analysis, etc., as a value that can determine whether the combustion state is normal or not, based on the set values of the first angle θ1 and the second angle _θ2 .

On the other hand, when the correction deviation C is equal to or less than the first judgment value _C1 , the judgment unit 13 judges that the engine 1 is in a misfire state, and outputs a signal to cause the alarm device 14 to light and display an indicator or a telltale mark indicating the misfire state. When the correction deviation C is equal to or less than the first judgment value _C1 and exceeds the second judgment value _C2 (where _C2 < _C1 ), the judgment unit 13 judges that the engine 1 is in a semi-misfire state. On the other hand, when the correction deviation C is equal to or less than the second judgment value _C2 , the judgment unit 13 judges that the engine 1 is in a complete misfire state. When the alarm device 14 can distinguish between a semi-misfire and a misfire and display the indicator or the telltale mark corresponding to each state, the alarm device 14 may be caused to light and display the indicator or the telltale mark. When the judgment unit 13 judges that the engine 1 is in a semi-misfire state, control may be performed to eliminate the semi-misfire, such as by increasing the fuel injection amount.

Since a semi-misfire is not a complete misfire, when the determination unit 13 determines that the engine is a semi-misfire, it does not have to display this on the alarm device 14. Furthermore, a complete misfire may be determined when the determination unit 13 has determined that the engine is a misfire multiple times (when the correction deviation C is equal to or smaller than the second determination value _C2 multiple times).

In the above determination, only when a predetermined condition is satisfied, the determination unit 13 may determine that the engine 1 is in a misfire state. For example, the determination unit 13 may determine that the engine 1 is in a misfire state when any of the following conditions is satisfied:
Condition 1: The vehicle is decelerating for a predetermined period of time or longer. Condition 2: The temperature rise control of the catalytic converter 5 is being carried out.

Condition 1 can be determined based on the accelerator opening and the vehicle speed. For example, it may be determined that Condition 1 is satisfied when the accelerator opening decreases from a relatively large value and the state continues for a predetermined time or more (e.g., one second or more). Alternatively, it may be determined that Condition 1 is satisfied when the vehicle speed continues to decrease for a predetermined time or more (e.g., one second or more).
Condition 2 can be determined based on the operating state of the catalyst control device 7. For example, it may be determined that Condition 2 is satisfied when the catalyst control device 7 is performing air-fuel ratio control, fuel injection control, and ignition timing control for raising the temperature of the catalyst device 5.

If neither condition 1 nor 2 is met, the determination unit 13 may stop determining whether a misfire has occurred. In this case, misfire may be determined from a temporary drop in the average rotation speed, as in conventional misfire determination, for example, based on the deviation between the previous and previous angular acceleration (the rate of change in rotation speed deviation), the previous angular velocity value, and the deviation between the previous and current angular acceleration. Note that this conventional misfire determination has difficulty detecting a temporary drop in angular acceleration when combustion slows down.

2. Effects
(1) The misfire detection device 10 of this embodiment includes a calculation unit 11, a correction unit 12, and a judgment unit 13. The calculation unit 11 calculates a deviation D by subtracting a first angular velocity Ne1, which is the crank angular velocity Ne when the crank angle θ is a first angle _θ1 in the first half of the combustion stroke of the engine ₁ , from a second angular velocity _Ne2 , which is the crank angular velocity Ne when the crank angle θ is a second angle _θ2 in the second half of the combustion stroke. The correction unit 12 calculates a corrected deviation C by correcting the deviation D based on an average engine angular velocity deviation A corresponding to a general change tendency of the crank angular velocity Ne in a predetermined crank angle range _P2 . The judgment unit 13 judges a misfire state of the engine 1 based on the corrected deviation C.

In this way, by calculating the corrected deviation C by correcting the deviation D based on the average engine angular velocity deviation A, and judging the misfire state of the engine 1 based on the corrected deviation C, it is possible to evaluate the misfire state while eliminating the influence of the overall change trend of the crank angular velocity Ne. For example, as shown in FIG. 2, if the crank angular velocity Ne is decreasing overall over a crank angle width greater than the cycle in which the combustion stroke of the engine 1 is repeated due to deceleration of the vehicle or the like (crank angle cycle of 180° in FIG. 2), the value of the deviation D becomes small (a negative value in FIG. 2), which makes it easy to erroneously judge that the engine 1 is in a misfire state. Conversely, if the crank angular velocity Ne is increasing overall, it makes it easy to erroneously judge that the engine 1 is not in a misfire state.

On the other hand, in this embodiment, an average engine angular velocity deviation A (a negative value in FIG. 2) corresponding to the overall trend of the crank angular velocity Ne, which is decreasing overall, is calculated, and deviation D is corrected based on the average engine angular velocity deviation A to calculate a corrected deviation C. The corrected deviation C is a value slightly larger than deviation D (a negative value with an absolute value smaller than deviation D in FIG. 2), making it easier to avoid erroneous determination that engine 1 is in a misfire state. Similarly, when crank angular velocity Ne is increasing overall, corrected deviation C is a value slightly smaller than deviation D, making it easier to avoid erroneous determination that engine 1 is not in a misfire state. Therefore, the accuracy of determining a misfire state can be improved with a simple configuration.

(2) In this embodiment, the determination unit 13 determines that the engine 1 is in a misfire state when the correction deviation C is equal to or smaller than the first determination value _C1 . In this manner, the misfire state of the engine ₁ can be determined with high accuracy with a simple configuration of comparing the magnitude relationship between the correction deviation C and the first determination value C1. In addition, in this embodiment, the determination unit 13 determines that the engine ₁ is in a "semi-misfire state" when the correction deviation C is smaller than the first determination value _C1 and exceeds a second determination value _C2 that is smaller than the first determination value C1, and determines that the engine 1 is in a "misfire state" when the correction deviation C is equal to or smaller than the second determination value _C2 . In this manner, by preparing two determination values, the degree of the misfire state can be determined in stages.

(3) In this embodiment, the predetermined crank angle range _P2 is set to be at least wider than the determination angle width _P1 between the first angle _θ1 and the second angle _θ2 . This makes it possible to accurately grasp the overall change tendency of the crank angular velocity Ne, and to improve the calculation accuracy of the average engine angular velocity deviation A. Therefore, the accuracy of correcting the deviation D can be improved, and the accuracy of determining the misfire state of the engine 1 can be improved.

2, in this embodiment, the end point of the predetermined crank angle range _P2 is the second angle _θ2 , and the start point of the predetermined crank angle range _P2 is a third angle _θ3 that is the predetermined crank angle range _P2 before the second angle _θ2 . In addition, when the crank angle θ is the third angle _θ3 , the crank angular velocity Ne is a third angular velocity _Ne3 , and the average engine angular velocity deviation A is a value obtained by subtracting the third angular velocity _Ne3 from the second angular velocity _Ne2 .

That is, the end point of the predetermined crank angle range _P2 is set to coincide with the end point of the judgment angle width _P1 . With such a setting, it is possible to obtain the overall change tendency of the crank angular velocity Ne (average engine angular velocity deviation A) at the time when the deviation D in the judgment angle width _P1 is determined, and the calculation accuracy of the corrected deviation C can be improved. Therefore, the correction accuracy of the deviation D can be improved, and the accuracy of judging the misfire state of the engine 1 can be improved. Furthermore, with a simple configuration of calculating the difference between two crank angular velocities Ne, it is possible to grasp the overall change tendency of the crank angular velocity Ne. This reduces the load involved in calculating the average engine angular velocity deviation A and the load involved in judging the misfire state.

(5) The correction unit 12 of this embodiment calculates a gradient influence value B, which is the product of the ratio of the judgment angle width _P1 between the first angle _θ1 and the second angle _θ2 with respect to the predetermined crank angle range _P2 and the average engine angular velocity deviation A, and calculates a correction deviation C by subtracting the gradient influence value B from the deviation D. By performing such a calculation, it is possible to accurately determine the value of the correction deviation C from which the influence of the overall change tendency of the crank angular velocity Ne has been subtracted. Therefore, it is possible to increase the accuracy of correcting the deviation D and improve the accuracy of determining whether the engine 1 is in a misfire state.

(6) In general, when the vehicle decelerates, the crank angular velocity Ne (engine rotation speed) may gradually decrease, which may lead to an erroneous determination that the engine 1 is in a misfire state. On the other hand, the correction unit 12 of this embodiment can calculate the correction deviation C when the vehicle equipped with the engine 1 is decelerating for a predetermined period of time or more. In this way, by using the correction deviation C to determine the misfire state when deceleration continues for a predetermined period of time or more, erroneous determinations due to deceleration can be avoided and the accuracy of determining the misfire state of the engine 1 can be improved.

Note that if a correction deviation C that reflects the degree of deceleration is used during momentary deceleration (less than a specified time), the decrease in crank angular velocity Ne due to misfire will be reflected. Therefore, it is preferable to use the correction deviation C to determine the misfire state when deceleration continues for a specified time or more, making it difficult for a decrease in crank angular velocity Ne due to misfire to be reflected. Also, since misfires are unlikely to occur during acceleration, misfire determination using the correction deviation C is performed only during deceleration, and misfire determination is performed as in the conventional method during acceleration.

(7) When temperature rise control of the catalytic converter 5 is being implemented, combustion becomes slow and misfires become more likely to occur, and it is difficult to determine whether a misfire has occurred using conventional misfire determination methods. On the other hand, the correction unit 12 of this embodiment can calculate the correction deviation C when temperature rise control of the catalytic converter 5 disposed in the exhaust passage of the engine 1 is being implemented. In this way, if the correction deviation C is used to determine whether a misfire has occurred when temperature rise control is being implemented, erroneous determinations can be avoided and the accuracy of determining whether a misfire has occurred in the engine 1 can be improved.

[3. Other]
The above embodiment is merely illustrative, and is not intended to exclude various modifications and applications of techniques not specified in the embodiment. Each configuration of the embodiment can be modified in various ways without departing from the spirit of the embodiment. Furthermore, each configuration of the embodiment can be selected as necessary, or can be appropriately combined. For example, the above embodiment illustrates a misfire detection device 10 applied to an engine 1 mounted on a vehicle, but the application of the misfire detection device 10 is not limited to automobile engines, and can also be applied to marine engines, industrial engines, general-purpose engines, and the like.

In the above embodiment, the condition for determining that the engine 1 is in a misfire state is that "the correction deviation C is equal to or less than the first determination value _C1 ," but the specific condition is not limited to this. For example, the misfire state of the engine 1 may be determined by comparing the correction deviation C to which a predetermined offset value or drift value has been added or subtracted with the first determination value _C1 . By determining at least the misfire state of the engine 1 based on the correction deviation C, erroneous determination of the misfire state can be suppressed, and the same actions and effects as those of the above embodiment can be obtained.

In the above embodiment, the average engine angular velocity deviation _A is calculated by subtracting the third angular velocity _Ne3 at the start point (third angle _θ3 ) of the predetermined crank angle range _P2 from the second angular velocity _Ne2 at the end point (second angle θ2) of the predetermined crank angle range P2, but the specific method of calculating the average engine angular velocity deviation A is not limited to this. For example, the moving average value of the crank angular velocity Ne may be constantly calculated, and the increase or decrease in the moving average value in the predetermined crank angle range _P2 may be calculated as the average engine angular velocity deviation A. By using at least a value that corresponds to the overall change tendency of the crank angular velocity Ne (for example, a value such as the average engine angular velocity deviation A), it is possible to obtain the same functions and effects as the above embodiment and improve the accuracy of determining the misfire state.

[4. Notes]
The following supplementary notes are disclosed regarding the above-mentioned embodiments and modifications.
[Appendix 1]
a calculation unit (11) that calculates a deviation (D) obtained by subtracting a first angular velocity (Ne ₁ ), which is a crank angular velocity (Ne) when a crank angle (θ) is a first angle (θ ₁ ) in a first half of a combustion stroke of an engine (1), from a second angular velocity (Ne ₂ ), which is the crank angular velocity (Ne) when the crank angle (θ) is a second angle (θ ₂ ) in a second half of the combustion stroke;
a correction unit ( ₁₂ ) that calculates a corrected deviation (C) by correcting the deviation (D) based on an average engine angular velocity deviation (A) corresponding to a change tendency of the crank angular velocity (Ne) within a predetermined crank angle range (P 2 );
a determination unit (13) for determining a misfire state of the engine (1) based on the correction deviation (C);
A misfire detection device (10) for an engine (1), comprising:

[Appendix 2]
The misfire detection device (10) for an engine ( ₁ ) as described in Appendix 1, characterized in that the judgment unit (13) judges that the engine (1) is in a misfire state when the corrected deviation (C) is equal to or smaller than a first judgment value (C 1 ).

[Appendix 3]
3. The misfire detection device ( _{10) for an engine (1 )} according to claim 1 or 2, wherein the predetermined crank angle range ( _P2 ) is a range wider than at least a judgment angle width ( _P1 ) between the first angle (θ1) and the second angle (θ2).

[Appendix 4]
the end point of the predetermined crank angle range (P ₂ ) is the second angle (θ ₂ );
a start point of the predetermined crank angle range (P ₂ ) is a third angle (θ ₃ ) that is the predetermined crank angle range (P ₂ ) before the second angle (θ ₂ );
when the crank angle (θ) is the third angle (θ ₃ ), the crank angular velocity (Ne) is a third angular velocity (Ne ₃ );
The misfire detection device (10) for an engine ( ₁ ) according to any one of appendixes 1 to 3, characterized in that the average engine angular velocity deviation (A) is a value obtained by subtracting the third angular velocity (Ne ₃ ) from the second angular velocity (Ne 2 ).

[Appendix 5]
The misfire detection device (10) for an engine ( ₁ ) according to any one of Appendices 1 to 4, wherein the correction unit ( ₁₂ ) calculates a gradient influence value (B) which is a product of a ratio of a judgment angle width (P ₁ ) between the first angle (θ ₁ ) and the second angle (θ 2 ) with respect to the specified crank angle range (P 2 ) and the average engine angular velocity deviation (A), and calculates a corrected deviation (C) by subtracting the gradient influence value (B) from the deviation (D).

[Appendix 6]
The misfire detection device (10) for an engine (1) described in any one of Appendices 1 to 5, wherein the correction unit (12) calculates the correction deviation (C) when a vehicle equipped with the engine (1) is decelerating for a predetermined period of time or more.

[Appendix 7]
The misfire detection device (10) for an engine (1) described in any one of Appendices 1 to 6, characterized in that the correction unit (12) calculates the correction deviation (C) when temperature rise control of a catalytic converter (5) interposed in an exhaust passage of the engine (1) is being performed.

This invention can be used in the manufacturing industry of engine misfire detection devices, and can also be used in the manufacturing industry of vehicles, ships, industrial machinery, etc. that are equipped with engines to which misfire detection devices are applied.

REFERENCE SIGNS LIST 1 Engine 2 Fuel injector 3 Spark plug 4 Crank angle sensor 5 Catalyst device 6 Catalyst temperature sensor 7 Catalyst control device 8 Accelerator opening sensor 9 Vehicle speed sensor 10 Misfire detection device 11 Calculation unit 12 Correction unit 13 Judgment unit 14 Notification device A Average engine angular velocity deviation B Gradient influence value C Correction deviation D Deviation P ₁ Judgment angle width P ₂ Predetermined crank angle range θ Crank angle θ ₁ First angle θ ₂ Second angle θ ₃ Third angle Ne Crank angular velocity Ne ₁ First angular velocity Ne ₂ Second angular velocity Ne ₃ Third angular velocity C ₁ First judgment value C ₂ Second judgment value

Claims (7)

a calculation unit that calculates a deviation obtained by subtracting a first angular velocity, which is a crank angular velocity when a crank angle is a first angle in a first half of a combustion stroke of the engine, from a second angular velocity, which is the crank angular velocity when the crank angle is a second angle in a second half of the combustion stroke;
a correction unit that calculates a corrected deviation by correcting the deviation based on an average engine angular velocity deviation corresponding to a change tendency of the crank angular velocity within a predetermined crank angle range;
a determination unit for determining a misfire state of the engine based on the correction deviation;
An engine misfire detection device comprising: 2. The engine misfire detection device according to claim 1, wherein the determination unit determines that the engine is in a misfire state when the corrected deviation is equal to or smaller than a first determination value. 2. The engine misfire detection device according to claim 1, wherein the predetermined crank angle range is wider than at least a determination angle width between the first angle and the second angle. an end point of the predetermined crank angle range is the second angle,
a start point of the predetermined crank angle range is a third angle which is an angle corresponding to the predetermined crank angle range before the second angle,
the crank angular velocity when the crank angle is the third angle is a third angular velocity,
4. The engine misfire detection device according to claim 3, wherein the average engine angular velocity deviation is a value obtained by subtracting the third angular velocity from the second angular velocity. 2. The engine misfire detection device according to claim 1, wherein the correction unit calculates a gradient influence value which is a product of a ratio of a judgment angle width between the first angle and the second angle with respect to the specified crank angle range and the average engine angular velocity deviation, and calculates a corrected deviation by subtracting the gradient influence value from the deviation. 2. The engine misfire detection device according to claim 1, wherein the correction unit calculates the correction deviation when a vehicle equipped with the engine is decelerating for a predetermined period of time or longer. 2. The engine misfire detection device according to claim 1, wherein the correction unit calculates the correction deviation when a temperature increase control of a catalytic converter disposed in an exhaust passage of the engine is being performed.

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