WO2010070446A1

WO2010070446A1 - Rough idle detecting apparatus and rough idle detecting method for internal combustion engine

Info

Publication number: WO2010070446A1
Application number: PCT/IB2009/007921
Authority: WO
Inventors: Ryusuke Yoshida; Jun Tahara
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2008-12-16
Filing date: 2009-12-08
Publication date: 2010-06-24
Also published as: JP2010144533A

Abstract

A rough idle detecting apparatus for an internal combustion engine includes: a crank angle sensor (23) detecting a crank rotational speed; a workload corresponding value calculating unit (32) extracting a fluctuation component of the crank rotational speed due to combustion in each cylinder (2) based on the crank rotational speed and calculating a workload corresponding value by integrating the fluctuation component; a torque corresponding value calculating unit (33) calculating a torque corresponding value from a difference in square between the low-speed crank rotational at a start of a cylinder expansion stroke and the high-speed crank rotational in that expansion stroke; and an abnormal cylinder detecting unit (36) comparing the workload and torque corresponding values with corresponding determination thresholds cylinder (2) by cylinder (2) and determining that combustion in the cylinder (2), of which the workload and torque corresponding values are smaller than the determination thresholds, causes a rough idle situation.

Description

ROUGH IDLE DETECTING APPARATUS AND ROUGH IDLE DETECTING

METHOD FOR INTERNAL COMBUSTION ENGINE

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The invention relates to a rough idle detecting apparatus and rough idle detecting method for an internal combustion engine and, more particularly, to a rough idle detecting apparatus and rough idle detecting method for an internal combustion engine, which detect a rough idle situation in which an engine rotational speed unstably fluctuates against a target rotational speed because of an insufficient fuel injection amount, or the like, while the internal combustion engine is idling.

2. Description of the Related Art

[0002] In an internal combustion engine, such as a vehicle engine, a fuel injection amount from an injector into a cylinder is controlled so that an engine rotational speed during idling (hereinafter, referred to as idle rotational speed) attains a target rotational speed of the idle rotational speed control executed by an electronic control unit (ECU) . However, there may occur a rough idle situation in which, as an actual fuel injection amount becomes insufficient or fluctuates with respect to an injection amount for which the ECU instructs the injector, the engine rotational speed unstably fluctuates against the target rotational speed and, therefore, uncomfortable vibrations occur during idling (for example, during a cold-start). Then, there has been suggested an apparatus that is able to detect a rough idle situation and then execute control for eliminating the rough idle situation. [0003] A rough idle detecting apparatus for an internal combustion engine of this type in a related art determines whether the engine is restarted at a high temperature on the basis of a coolant temperature while the engine is idling, and, when the count value of a misfire counter provided for an on-board diagnosis system of the engine exceeds a predetermined value at the time when the engine is restarted at a high temperature at which an actual injection amount tends to become insufficient or fluctuate because of occurrence of fuel vapor, determines that a rough idle situation has occurred. In this apparatus, when it is determined that the rough idle situation has occurred, the target rotational speed of the idle rotational speed control is increased to eliminate the rough idle situation (for example, see Japanese Patent Application Publication No. 2007-192081 (JP-A-2007-192081)).

[0004] In addition, for example, Japanese Patent Application Publication No. 2007-327341 (JP-A-2007-327341) describes another apparatus. The apparatus learns injection characteristics by equally dividing fuel injection into about multiple times of pilot injections during idle rotational speed control of a diesel engine. On the other hand, the apparatus acquires an engine rotation signal pulse into a filtering unit corresponding to a band-pass filter in accordance with the combustion interval of each cylinder in an operating state where an injection amount is larger than or equal to a predetermined amount, calculates an instantaneous torque corresponding value by extracting only a rotation fluctuation component at each time point by the filtering unit, and acquires the instantaneous torque corresponding value into an integration unit to perform integration in a range at a combustion interval of each cylinder to thereby calculate a cylinder-by-cylinder workload, which is a torque accumulated value of each cylinder, for each cylinder. Thus, relative variations of injection characteristics among the cylinders are learned.

[0005] However, in the rough idle detecting apparatus for an internal combustion engine according to the related art, the count value of the misfire counter is utilized, so diagnostic accuracy is higher than that of the configuration that it is determined whether a rough idle situation has occurred only on the basis of a deviation between the target rotational speed and the actual rotational speed. However, the above apparatus does not directly detect an actual rotation fluctuation due to combustion of each cylinder in a rough idle situation accompanied by uncomfortable vibrations, so the diagnostic accuracy is not sufficient. Therefore, there is a possibility that, although the rough idle situation accompanied by uncomfortable vibrations has not occurred, an unnecessary increase in fuel injection amount is carried out as a rough idle elimination control. Thus, there has been a problem in terms of idling stability and fuel economy.

[0006] In addition, in the apparatus that integrates an instantaneous torque corresponding value at a predetermined interval of each combustion interval of each cylinder, variations in injection characteristics among the cylinders may be acquired; however, the influence of torque generated in the same combustion tends to be exerted on the integral values of cylinders of which the expansion strokes take place successively.

Thus, there is a case where an actual rotation fluctuation due to combustion of each cylinder in the rough idle situation accompanied by uncomfortable vibrations cannot be accurately detected. Therefore, there is a need for improvement in order to obtain high diagnostic accuracy at which it is possible to accurately determine whether a rough idle situation has occurred.

SUMMARY OF THE INVENTION

[0007] The invention provides a rough idle detecting apparatus and rough idle detecting method for an internal combustion engine, which are able to accurately determine whether a rough idle situation has occurred with high diagnostic accuracy.

[0008] A first aspect of the invention provides a rough idle detecting apparatus for an internal combustion engine, which detects a rough idle situation in which a rotational speed of a crankshaft of the internal combustion engine fluctuates against a target rotational speed under an idle operating condition in which the rotational speed of the crankshaft is controlled to the target rotational speed. The rough idle detecting apparatus includes: rotational speed detecting means that detects the rotational speed of the crankshaft of the internal combustion engine; workload corresponding value calculating means that extracts a fluctuation component of the rotational speed of the crankshaft due to combustion in a cylinder of the internal combustion engine on the basis of the rotational speed of the crankshaft, detected by the rotational speed detecting means, and that calculates a workload corresponding value by integrating the extracted fluctuation component; torque corresponding value calculating means that calculates a torque corresponding value corresponding to a torque generated in the cylinder from a difference between the square of the rotational speed of the crankshaft in a relatively low-speed rotation angular range at a timing at which an expansion stroke of the cylinder starts and the square of the rotational speed of the crankshaft in a high-speed rotation angular range in which the rotational speed of the crankshaft in the expansion stroke of the cylinder reaches a maximum speed range; and abnormal cylinder determining means that respectively compares the workload corresponding value and the torque corresponding value with corresponding determination thresholds, and that determines that combustion in the cylinder causes the rough idle situation when the workload corresponding value and the torque corresponding value are respectively smaller than the corresponding determination thresholds.

[0009] With the above configuration, an actual rotation fluctuation due to combustion in each cylinder in a rough idle situation of the internal combustion engine may be accurately identified as a variation in workload at each predetermined interval corresponding to combustion interval and a variation in torque generated in each combustion of each cylinder on the basis of the workload corresponding value and the torque corresponding value. Thus, the rough idle detecting apparatus is able to accurately determine whether a rough idle situation has occurred and which cylinder causes the rough idle situation with high diagnostic accuracy. In addition, when the workload corresponding value and the torque corresponding value are calculated for another control in the internal combustion engine, it is possible to carry out highly accurate rough idle detection without increasing a calculation load.

[0010] In addition, the workload corresponding value calculating means may extract a fluctuation component of the rotational speed of the crankshaft due to combustion in each of a plurality of the cylinders of the internal combustion engine cylinder by cylinder, may integrate the extracted fluctuation component in a predetermined rotation range at each combustion interval of each cylinder to repeatedly calculate the workload corresponding value of each cylinder a predetermined repetition number of times, and may calculate an averaged workload corresponding value by averaging the calculated workload corresponding values, and the torque corresponding value calculating means may repeatedly calculate the torque corresponding value corresponding to the torque generated in each cylinder from a difference between the square of the rotational speed of the crankshaft in the relatively low-speed rotation angular range at a timing at which the expansion stroke of each cylinder starts and the square of the rotational speed of the crankshaft in the high-speed rotation angular range in which the rotational speed of the crankshaft reaches a maximum speed range in the expansion stroke of each cylinder at each combustion interval of each cylinder the predetermined repetition number of times, and may calculate an averaged torque corresponding value by averaging the calculated torque corresponding values for each cylinder.

[0011] With the above configuration, an actual rotation fluctuation in a rough idle situation of the internal combustion engine may be accurately identified on the basis of the averaged workload corresponding value and the averaged torque corresponding value. Thus, the rough idle detecting apparatus is able to accurately determine whether a rough idle situation has occurred with high diagnostic accuracy. Here, the averaging may be, for example, so-called smoothing that calculates an average value between a currently calculated value and a previously averaged value (hereinafter, referred to as previous value).

[0012] In addition, for the cylinder of which the averaged workload corresponding value and the averaged torque corresponding value are respectively smaller than the corresponding determination thresholds, the abnormal cylinder determining means may set an abnormality detection flag that indicates that combustion in that cylinder causes the rough idle situation.

[0013] With the above configuration, an abnormality detection flag is set for a cylinder that is likely to cause a rough idle situation. Thus, by referring to the abnormality detection flag, it is possible to quickly identify the cause at the time of inspection on rough idle vibrations, or the like, so serviceability improves. Note that the flag setting status of the abnormality detection flag may be allowed to be easily referred to at the time of maintenance at a dealer, or the like, as diagnostic information, or may be stored in a nonvolatile memory or a backup memory as history information.

[0014] In addition, the first aspect of the invention may further include precondition determining means that determines whether a predetermined precondition for executing a process of detecting a rough idle situation of the internal combustion engine is satisfied, and, when the precondition is satisfied, the workload corresponding value calculating means and the abnormal cylinder determining means may execute respective processes. [0015] With the above configuration, only when the precondition for executing a process of detecting a rough idle situation is satisfied, the detecting process is executed. Thus, the calculation resources that execute a process of detecting a rough idle situation may be allocated to another necessary calculation process during normal operation, so calculation resources may be efficiently used. [0016] In addition, the precondition may include a condition in which a condition for executing learning process for learning injection characteristics of a fuel injection valve provided for each cylinder of the internal combustion engine is satisfied, a condition in which an accelerator operation amount is minimum, a condition in which a vehicle speed of a vehicle that uses the internal combustion engine as a power source is zero, and a condition in which idle up control, in which an idle rotational speed at the time of cold-start of the internal combustion engine is set at a rotational speed higher than an idle rotational speed at the time of completion of warm-up of the internal combustion engine, is not executed.

[0017] With the above configuration, it is possible to accurately detect fluctuations in idle rotational speed under substantially a fixed condition in which disturbance factors are suppressed.

[0018] In addition, the precondition may further include at least one of a condition in which an auxiliary machine load of the internal combustion engine is not being switched or a condition in which a transmission mounted on the vehicle and drivably coupled to the internal combustion engine is in neutral.

[0019] With the above configuration, it is possible to accurately calculate fluctuations in idle rotational speed under a substantially fixed condition in which disturbance factors are further suppressed. [0020] In addition, the internal combustion engine may be a common rail multi-cylinder diesel engine, and the precondition may further include a condition in which switching of a fuel injection condition carried out by the fuel injection valve of the diesel engine is prohibited.

[0021] With the above configuration, it is possible to accurately detect fluctuations in idle rotational speed under substantially a fixed condition in which disturbance factors are further reliably suppressed.

[0022] In addition, the workload corresponding value calculating means and the torque corresponding value calculating means may acquire the rotational speed of the crankshaft, detected by the rotational speed detecting means, at a predetermined interval corresponding to the number of cylinders of the internal combustion engine at mutually different rotation phases.

[0023] With the above configuration, it is possible to accurately calculate the workload corresponding value and the torque corresponding value at respective optimal timings for calculation, and, in addition, it is possible to avoid concentration of processing load on calculation resources used in both calculating means.

[0024] In addition, the abnormal cylinder determining means may be able to switch between a first determination mode in which the workload corresponding value and the torque corresponding value are respectively compared with corresponding determination thresholds to make determination as to whether the rough idle situation has occurred and a second determination mode in which only one of the workload corresponding value and the torque corresponding value is compared with a corresponding one of the determination thresholds to make determination as to whether the rough idle situation has occurred.

[0025] With the above configuration, the apparatus is compatible with both cases where both the workload corresponding value and the torque corresponding value are calculated and where only any one of the workload corresponding value and the torque corresponding value is calculated. Thus, the apparatus may be employed as a rough idle detecting apparatus for internal combustion engines of various specifications. [0026] A second aspect of the invention provides a rough idle detecting method for an internal combustion engine, which detects a rough idle situation in which a rotational speed of a crankshaft of the internal combustion engine fluctuates against a target rotational speed under an idle operating condition in which the rotational speed of the crankshaft is controlled to the target rotational speed. The rough idle detecting method includes: detecting the rotational speed of the crankshaft of the internal combustion engine; extracting a fluctuation component of the rotational speed of the crankshaft due to combustion in a cylinder of the internal combustion engine on the basis of the detected rotational speed, and calculating a workload corresponding value by integrating the extracted fluctuation component; calculating a torque corresponding value corresponding to a torque generated in the cylinder from a difference between the square of the rotational speed of the crankshaft in a relatively low-speed rotation angular range at a timing at which an expansion stroke of the cylinder starts and the square of the rotational speed of the crankshaft in a high-speed rotation angular range in which the rotational speed of the crankshaft in the expansion stroke of the cylinder reaches a maximum speed range; and respectively comparing the calculated workload corresponding value and the calculated torque corresponding value with corresponding determination thresholds, and determining that combustion in the cylinder causes the rough idle situation when the calculated workload corresponding value and the calculated torque corresponding value are respectively smaller than the corresponding determination thresholds.

[0027] With the second aspect of the invention, an actual rotation fluctuation due to combustion in each cylinder in a rough idle situation of the internal combustion engine may be accurately identified as a variation in workload at each predetermined interval corresponding to combustion interval and a variation in torque generated in each combustion of each cylinder on the basis of the workload corresponding value and the torque corresponding value. Thus, the rough idle detecting method is able to accurately determine whether a rough idle situation has occurred and which cylinder causes the rough idle situation with high diagnostic accuracy. In addition, when the workload corresponding value and the torque corresponding value are calculated for another control in the internal combustion engine, it is possible to carry out highly accurate rough idle detection without increasing a calculation load.

[0028] According to the aspects of the invention, an actual rotation fluctuation in an rough idle situation of the internal combustion engine may be accurately identified as a variation in workload at each predetermined interval corresponding to combustion interval and a variation in torque generated in each combustion of each cylinder on the basis of both the workload corresponding value and the torque corresponding value. Thus, it is possible to provide a rough idle detecting apparatus and rough idle detecting method for an internal combustion engine, which are able to accurately determine whether a rough idle situation has occurred.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The foregoing and further objects, features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

FIG. 1 is a schematic configuration diagram of a fuel injection system that includes a rough idle detecting apparatus for an internal combustion engine according to an embodiment of the invention; FIG. 2A and FIG. 2B are views that illustrate two types of rotational speed detecting periods used in the rough idle detecting apparatus for an internal combustion engine according to the embodiment of the invention; and

FIG. 3 is a flowchart of a detecting process executed in the rough idle detecting apparatus for an internal combustion engine according to the embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0030] Hereinafter, an embodiment of the invention will be described with reference to the accompanying drawings.

[0031] FIG. 1 is a schematic configuration diagram of a fuel injection system that includes a rough idle detecting apparatus for an internal combustion engine according to an embodiment of the invention. FIG. 2A and FIG. 2B are views that illustrate two types of rotational speed detecting periods used in the rough idle detecting apparatus for an internal combustion engine according to the embodiment of the invention.

[0032] First, the configuration will be described.

[0033] As shown in FIG 1, the rough idle detecting apparatus for an internal combustion engine according to the present embodiment is equipped for a fuel injection system that injects fuel to a plurality of cylinders 2 (only one cylinder is shown in FIG. 1) of an engine 1, which is a multi-cylinder internal combustion engine, for example, four-cylinder diesel engine.

[0034] The fuel injection system includes a fuel tank 11, a feed pump 12, a pressure pump 15, a metering valve 13, a common rail 17 and a plurality of, for example, four, electromagnetically driven or piezoelectrically driven injectors 18. The fuel tank 11 stores fuel, such as light oil, used in the engine 1. The feed pump 12 pumps and discharges fuel in the fuel tank 11 by the power from the engine 11. The pressure pump 15 is able to pressurize fuel, discharged from the feed pump 12 by the power from the engine 11, to a further high pressure. The metering valve 13 is configured as a known variable throttle element that varies its opening degree on the basis of an input metering instruction signal. The metering valve 13 is provided between the feed pump 12 and the pressure pump 15, and varies the amount of fuel drawn into the pressure pump 15 on the basis of the input metering instruction signal. The common rail 17 is able to accumulate and store fuel, pressurized by and discharged from the pressure pump 15, at a high pressure. The plurality of injectors 18 are provided in correspondence with a plurality of cylinders 2 of the engine 1.

[0035] The feed pump 12 is, for example, a known low-pressure fuel pump formed of a gear pump. [0036] In addition, the metering valve 13 is, for example, configured so that a fuel supply pressure from the feed pump 12 acts in a direction in which a metering valve element opens. The metering valve 13 is a variable throttle element that is open at a maximum opening degree when an internal coil is not energized and that is able to reduce the opening degree on the basis of an input metering instruction signal, which is the magnitude of electric current supplied to the internal coil when the internal coil is energized.

[0037] Note that a relief valve (not shown) is provided between the feed pump 12 and the metering valve 13. The relief valve is able to return redundant fuel discharged from the feed pump 12 to the fuel tank 11. [0038] Although a detailed structure is not shown in the drawing, the pressure pump 15 has a known structure that includes, in its pump housing, a reciprocally movable plunger, a camshaft 15a and a cam ring. The camshaft 15a serves as an input shaft that drives the plunger. The cam ring is rotatably fitted around an eccentric cam portion provided at an inner end of the camshaft 15a. The pressure pump 15 defines at least one pressure chamber between the pump housing and the plunger. The pressure chamber is used to draw, pressurize and discharge fuel by reciprocal movement of the plunger. The pressure pump 15 has an inlet port side check valve (not shown) and a discharge port side check valve (not shown). Back flow of fuel from the pressure pump 15 to the feed pump 12 is blocked by the inlet port side check valve, and backflow of fuel from the common rail 17 to the pressure pump 15 is blocked by the discharge port side check valve. Note that the pressure pump 15 may be integrated with the feed pump 12 to constitute a fuel supply pump.

[0039] The common rail 17 is accumulating means that is able to accumulate and store fuel, pressurized by and discharged from the pressure pump 15, at a high pressure without depending on a load or an engine rotational speed, and supply fuel to the injectors 18 at a stable pressure. A relief valve (not shown) is, for example, provided for the common rail 17. The relief valve limits an actual common rail pressure, which is a pressure of fuel inside the common rail 17, to a predetermined upper limit. [0040] Each of the plurality of injectors 18 includes an electromagnetic valve portion 18a and a fuel injecting portion 18b. The electromagnetic valve portion 18a is electrically connected to an electronic distribution unit (EDU) 20, which is a. drive unit for these injectors 18. The fuel injecting portion 18b has an injection hole (no reference numeral is assigned) at its distal end. The injection hole is exposed to a combustion chamber 3 of each cylinder 2. The fuel injecting portion 18b is connected to the common rail 17 via a high-pressure line 19. When the electromagnetic valve portion 18a is energized, the fuel injecting portion 18b is opened to inject fuel through the injection hole into the cylinder 2.

[0041] The EDU 20 is, for example, a known one that carries out electronic distribution for driving capacitive discharge injection to the electromagnetic valve portions 18a of the plurality of injectors 18. The EDU 20 independently opens the plurality of injectors 18 at the injection timings of the corresponding cylinders 2 in accordance with an injection instruction signal input from an electronic control unit, that is, an electronic control unit (ECU) 30, that electronically controls the engine 1. [0042] Although a specific hardware configuration is not shown in the drawing, the ECU 30 includes a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM) and a backup memory, such as a nonvolatile memory. The ECU 30 further includes an input interface circuit, an output interface circuit, and a communication interface. The input interface circuit includes an A/D converter, and the like. The output interface circuit includes a driver circuit, a relay switch, and the like. The communication interface is used to establish communication with another in-vehicle ECU, for example, a transmission control ECU (hereinafter, referred to as T-ECU) that controls an automatic transmission.

[0043] The ECU 30 includes a ROM that stores a control program for calculating an optimal injection timing and injection amount based on the rotational speed and load of the engine 1 and a control program for adjusting the opening degree of the metering valve 13 to cause the pressure of fuel in the common rail 17 to track the target fuel pressure suitable for the operating state of the engine 1 (hereinafter, these control programs are collectively referred to as a fuel injection control program). The ECU 30 is configured to generate an injection instruction signal so as to inject fuel into an injection timing cylinder 2, in which the compression stroke has been substantially completed, from among the plurality of cylinders 2 of the engine 1, in an injection mode selected from among a first injection mode, a second injection mode and a third injection mode. The first injection mode includes main injection and at least one pilot injection prior to the main injection. The second injection mode only includes main injection with no pilot injection. The third injection mode carries out post injection after main injection.

[0044] In addition, an accelerator operation amount sensor 21, a fuel pressure sensor 22, and a crank angle sensor 23 (rotational speed detecting means) are connected to the ECU 30. The accelerator operation amount sensor 21 detects an accelerator operation amount on a vehicle (not shown) equipped with the engine 1. The fuel pressure sensor 22 is attached to the common rail 17. The crank angle sensor 23 detects the rotational speed of a crankshaft 5 of the engine 1, for example, using a magnetic gear pulser 23b attached to the camshaft 15a. Then, the ECU 30 acquires a signal Pc detected by the fuel pressure sensor 22 to detect the pressure of fuel in the common rail 17, that is, an actual common rail pressure, and compares the actual common rail pressure with a target common rail pressure set in accordance with the operating state of the engine 1, such as signals detected by the accelerator operation amount sensor 21 and the crank angle sensor 23, and then adjust the opening degree of the metering valve 13 so that the actual common rail pressure in the common rail 17 coincides with the target common rail pressure.

[0045] Furthermore, a group of sensors and switches are connected to the ECU 30. The group of sensors include a vehicle speed sensor 24 that detects a vehicle speed, a coolant temperature sensor 25 that detects a coolant temperature, and the like. The switches include a neutral switch 26 that lights up a neutral position indicator for a transmission (not shown), an air conditioner switch 27 that turns on the power of a vehicle air-conditioning system, and the like. [0046] In accordance with the control program prestored in the ROM, the ECU

30 sets a target rail pressure of the common rail 17 during operation of the engine 1, calculates injection timings and fuel injection amounts based on the operating state of the engine 1, and then outputs an opening degree adjustment signal Iv (see FIG. 1) to the metering Valve 13 and an injection instruction signal Iq to the electromagnetic valve portions 18a of the injectors 18 at appropriate timings, on the basis of information detected by the group of sensors and set value information of the switches, prestored in the backup memory, for example, on the basis of information of a pulse signal detected by the crank angle sensor 23 as the rotational speed of the engine 1 and a cylinder determination signal (which may be, for example, a chipped-tooth signal corresponding to a chipped-tooth position of the pulser 23b or a detection signal of a cylinder determining protrusion attached to the crankshaft 5) by which it is possible to determine the cylinder that shifts from the compression stroke into the expansion stroke, and on the basis of information of the detected accelerator operation amount signal. [0047]

In addition, the ECU 30 has programs, maps, set value information, and the like, to not only carry out the function of the rotational speed detecting means that detects the rotational speed of the crankshaft 5 of the engine 1 in a predetermined detection unit angle, for example, in ten degrees, in cooperation with the crank angle sensor 23 but also carry out the functions of a condition determining unit 31, a workload corresponding value calculating unit 32, a torque corresponding value calculating unit 33, an average value calculating unit 34, a precondition satisfaction time counter 35 and an abnormal cylinder detecting unit 36, which will be described later.

[0048] Specifically, the condition determining unit 31 is precondition determining means that determines whether a precondition for rough idle abnormality detecting process is satisfied at the time of calculating the fuel injection amount of each cylinder 2. Here, the precondition for rough idle abnormality detecting process is a stable idle condition in which a certain period of time has elapsed from start of the engine 1, for example, a condition in which the accelerator operation amount is 0 (%), the neutral switch 26 is turned on, which indicates that the automatic transmission located downstream of the engine 1 is in neutral, and the coolant temperature has reached a coolant temperature level at which injection amount learning process is possible, that is, so-called the engine 1 is not in idle up operation, switching of the air conditioner switch 27, which is switching of an auxiliary machine load, is not being switched, the vehicle speed is 0 (km/h) and the group of sensors related to detection of these conditions are not abnormal. In the present embodiment, furthermore, it is a stable idle operating condition that a process that causes combustion fluctuations, such as switching the number of pilot injections of the engine 1 (for example, switching to an injection pattern selected from among a plurality of injection patterns, such as pilot injection twice, pilot injection once, no pilot injection, and post injection), is not carried out. [0049] For example, as described in JP-A-2007-327341, the workload corresponding value calculating unit 32 is workload corresponding value calculating means that acquires a rotational speed signal (hereinafter rotational speed Ne) from the crank angle sensor 23 into a built-in filtering unit corresponding to a band-pass filter on the basis of a combustion interval of each cylinder 2 in an operating condition having a predetermined injection amount or above, that calculates an instantaneous torque corresponding value by extracting only a rotation fluctuation component at each time point in the filtering unit and that acquires the instantaneous torque corresponding value into an integration unit to perform integration in a range at a combustion interval of each cylinder to thereby calculate a workload corresponding value, which is a torque accumulated value of each cylinder, for each cylinder 2. The integration interval in the integration unit is set, for example, within a range of 180⁰CA from BTDC 90° to ATDC 90° on the basis of the combustion interval of each cylinder 2. Note that the BTDC is before top dead center, the ATDC is after top dead center and CA is a crank rotation angle

C⁾. [0050] Specifically, in the workload corresponding value calculating unit 32, the rotational speed Ne is sampled at an interval of output pulse of the crank angle sensor 23, for example, at an interval of 10⁰CA, and filtering expressed by the following mathematical expression (1) is performed in the built-in filtering unit having a transfer function discretized from the following mathematical expression (2). Thus, an instantaneous torque corresponding value Neflt, which is a rotation fluctuation component at each time point and from which a high-frequency component and a low-frequency component outside a rotation fluctuation frequency range of the crank rotational speed are removed, may be calculated.

Neflt (i) =k1 x Ne (i) + k2 x Ne (i -2) + k3 x Neflt (i - 1 ) +k4 x Neflt (i -2) - - -(D

2 ξ ωs

G (s) = ^{■ • ■} (2) s² + 2ξ ωs + ω ²

[0051] Note that, in the mathematical expression (1), Ne(i) is a current sampling value of the rotational speed Ne, Ne(i-2) is a second previous sampling value of the rotational speed Ne, Neflt(i-l) is a previous value calculated for the instantaneous torque corresponding value Neflt, and Neflt(i-2) is a second previous value calculated for the instantaneous torque corresponding value Neflt, and these values will be stored in a specific work memory area in the RAM of the ECU 30, which is part of the workload corresponding value calculating unit 32. kl to k4 are constants, and are stored in the ROM or nonvolatile memory of the ECU 30. In addition, in the mathematical expression (2), ζ is an attenuation coefficient, ω is a response frequency corresponding to a combustion frequency of the engine 1, s is a Laplace operator, and the constants kl to k4 in the mathematical expression (1) are respectively set at certain values on the basis of ω = combustion frequency. In addition, the combustion frequency is set from the inverse of the combustion interval of the four-stroke engine 1 (period of time corresponding to a combustion angular interval 720⁰CA divided by the number of cylinders n). In the following description, the engine 1 has four cylinders, and the combustion angular interval is 180⁰CA. [0052] The integration unit of the workload corresponding value calculating unit 32 acquires an instantaneous torque corresponding value Neflt at an interval of 10⁰CA, at twice the interval or at three times the interval, and then integrates the acquired instantaneous torque corresponding value Neflt in a range of 180⁰CA at a predetermined interval corresponding to the combustion interval of each cylinder 2 to calculate substantially cylinder-by-cylinder workload corresponding values Sneflt#l to Sneflt#4, which are the accumulated instantaneous torque corresponding values of the respective cylinders 2. Note that #1 to #4 indicate cylinder numbers, and combustion of the engine 1 repeatedly take place in the order of #1, #3, #4 and #2. [0053] The torque corresponding value calculating unit 33 is torque corresponding value calculating means that, when the precondition for rough idle abnormality detecting process is satisfied, calculates a torque corresponding value, corresponding to a torque generated in each cylinder 2, from a difference between the square of the rotational speed of the crankshaft 5 in a low-speed rotation angular range Ra of the crankshaft 5 and the square of the rotational speed of the crankshaft 5 in a high-speed rotation angular range Rb of the crankshaft 5. The low-speed rotation angular range Ra comes at the time when the compression stroke of each cylinder 2 has been substantially completed and reaches the timing at which the expansion stroke starts. The high-speed rotation angular range Rb comes in the expansion (combustion) stroke of each cylinder 2.

[0054] Here, the low-speed rotation angular range Ra corresponds to a rotation angular range in which the rotational speed of the crankshaft 5 reaches a minimum speed range because of a work for compressing air in the cylinder 2 under the idle operating condition that satisfies the precondition, and is set at an angular range of multiple times of the detection unit angle, which is the unit of detecting the rotation of the crankshaft 5, for example, as shown in FIG. 2A and FIG. 2B, a 60 degree rotation angular range from BTDC20⁰ to ATDC40⁰. In addition, the high-speed rotation angular range Rb corresponds to a rotation angular range in which the rotational speed of the crankshaft 5 reaches a maximum speed range in the expansion stroke of each cylinder 2, and is set at an angular range of multiple times of the detection unit angle, which is the unit of detecting the rotation of the crankshaft 5, for example, a 60 degree rotation angular range from ATDC50⁰ to ATDCIlO⁰. Note that the engine 1 is in the stable idle condition, so the average value of the engine rotational speed Ne (rpm) is, for example, about 600 (rpm).

[0055] The torque corresponding value calculated by the torque corresponding value calculating unit 33 is, more specifically, a value ΔNe² = Nea² - Neb² obtained as a difference between the squares of the rotational speeds Nea and Neb (Nea - Neb ) on the basis of a low-speed crank rotational speed Nea (rpm) and a high-speed crank rotational speed Neb (rpm). The low-speed crank rotational speed Nea (rpm) is calculated by the following mathematical expression (3) from a relatively long rotation period of time Δta (μsec) required for the crankshaft 5 to pass the low-speed rotation angular range Ra at the timing at which the expansion stroke of each cylinder 2 starts. The high-speed crank rotational speed Neb (rpm) is calculated by the following mathematical expression (4) from a relatively short rotation period of time Δtb required for the crankshaft 5 to pass the high-speed rotation angular range Rb in the expansion stroke of each cylinder 2.

60 [° CA] /360 [° CA]

Nea = - - " O)

Δ ta x 1 O^~6 [ s ]

60 [° CA] /360 [° CA]

Neb = ^{■ ■ ■} (4)

Δ tb x 1 0^~6 [ s ]

[0056] That is, where the rotational moment of inertia of the kinetic system of the engine 1 is I, when the kinetic energy of the engine 1 is increased from a kinetic energy (l/2)I(2πNea)² in the low-speed rotation angular range Ra to a kinetic energy (l/2)I(2πNeb)² in the high-speed rotation angular range Rb by a torque generated by combustion in the cylinder 2 in the expansion (combustion) stroke, the torque generated by that cylinder 2 may be regarded as approximately (l/2)I(2π)²(Nea²-Neb²), which is proportional to (Nea - Neb²). Thus, the generated torque may be obtained from this ΔNe². Here, 2πNea and 2πNeb each are an angular velocity (rad/sec).

[0057] The torque corresponding values ΔNe², corresponding to the torques generated by the cylinders 2 and calculated by the torque corresponding value calculating unit 33, and the workload corresponding values Sneflt#l to Sneflt#4, calculated at a predetermined interval corresponding to the combustion interval by the workload corresponding value calculating unit 32, are acquired by the average value calculating unit 34. Note that, in the following description, an arbitrary cylinder number is denoted by #k. [0058] Each time the average value calculating unit 34 acquires the workload corresponding value Sneflt#l to Sneflt#4 that is currently calculated by the workload corresponding value calculating unit 32, the average value calculating unit 34 holds the current cylinder-by-cylinder workload corresponding value efic_eficout(#k(i)) in a corresponding work memory area, calculates an average value between the current cylinder-by-cylinder workload corresponding value efic_eficout(#k(i)) and a value einstab_eficoutav(#k(i-l)) stored in the memory as the previously averaged value, and then stores the calculated result in the work memory area as a workload corresponding average value einstab_eficoutav(#k(i)), which is a currently averaged workload corresponding value. Here, the variable i corresponds to the number of times the condition determining unit 31 determines that the condition is satisfied, and corresponds to the count value of the precondition satisfaction time counter 35.

[0059] In addition, each time the average value calculating unit 34 acquires the torque corresponding value ΔNe²(#l) to ΔNe²(#4) for each cylinder 2 calculated by the torque corresponding value calculating unit 33, the average value calculating unit 34 holds the current torque corresponding value edom2_edom2(#k(i)) in a corresponding work memory area, calculates an average value between the current torque corresponding value edom2_edom2(#k(i)) and a value einstab_edom2av(#k(i-l)) stored in the memory as the previously averaged value, and then stores the calculated result in the work memory area as a torque corresponding average value einstab_edom2av(#k(i)), which is a currently averaged torque corresponding value.

[0060] That is, the average value calculating unit 34 carries out so-called smoothing process by calculating the average value between the workload corresponding average value einstab_eficoutav(#k(i)) corresponding to value currently calculated by the workload corresponding value calculating unit 32 and the previously averaged workload corresponding average value einstab_eficoutav(#k(i-l)) and the average value between the torque corresponding average value einstab_edom2av(#k(i)) corresponding to value currently calculated by the torque corresponding value calculating unit 33 and the previously averaged torque corresponding average value einstab_edom2av(#k(i-l)). [0061] The precondition satisfaction time counter 35 is sequentially incremented

(+1) until the set value becomes, for example, 200 and the number of times the condition is satisfied in the condition determining unit 31 reaches 200. As the precondition satisfaction time counter 35 reaches the set value, the precondition satisfaction time counter 35 outputs the workload corresponding average value einstab_eficoutav(#k(i)) and torque corresponding average value einstab_edom2av(#k(i)) that are finally stored in the average value calculating unit 34 at that time point to the abnormal cylinder detecting unit 36 as the detected information to require the abnormal cylinder detecting unit 36 to carry out abnormal cylinder detecting process. Note that the count up state of the precondition satisfaction time counter 35 is, for example, cleared by a clear request signal from the abnormal cylinder detecting unit 36.

[0062] That is, the workload corresponding value calculating unit 32 and the average value calculating unit 34 cooperatively constitute workload corresponding value calculating means according to the aspect of the invention, and extracts a fluctuation component of the rotational speed Ne of the crankshaft 5 due to combustion in each of the plurality of cylinders 2 of the engine 1 cylinder 2 by cylinder 2 while integrating the fluctuation component at a predetermined rotation angular range (180⁰CA) of each combustion interval of each cylinder 2, repeatedly calculates the workload corresponding value efic_eficout(#k(i)) for each cylinder 2 a predetermined repetition number of times, for example, 200 times, and calculates the workload corresponding average value einstab_eficoutav(#k(i)) by averaging the calculated workload corresponding values efic_eficout(#k(l)) to efic_eficout(#k(200)).

[0063] In addition, the torque corresponding value calculating unit 33 and the average value calculating unit 34 cooperatively constitute torque corresponding value calculating means according to the aspect of the invention, and acquire the rotational speed Ne corresponding to a crank rotation signal from the crank angle sensor 23 at a combustion interval of each cylinder 2 at a crank rotation phase different from that of the workload corresponding value calculating means, repeatedly calculates the torque corresponding value edom2_edom2(#k(i)) corresponding to the torque generated in each cylinder 2 from a difference (Nea² - Neb²) between the square of the rotational speed Ne of the crankshaft 5 in the relatively low-speed rotation angular range Ra at a timing at which the expansion stroke of each cylinder 2 starts and the square of the rotational speed Ne of the crankshaft 5 in the high-speed rotation angular range Rb at which the rotational speed of the crankshaft 5 reaches a maximum speed range in the expansion stroke of each cylinder 2 the repetition number of times, for example, 200 times, and calculates the torque corresponding average value einstab_edom2av(#k(i)) by averaging the torque corresponding values edom2_edom2(#k(l)) to edom2_edom2(#k(200)) of each cylinder 2.

[0064] The abnormal cylinder detecting unit 36 executes abnormal cylinder determination process in which the averaged workload corresponding value and the torque corresponding value, that is, the workload corresponding average value einstab_eficoutav(#k(i)) and torque corresponding average value einstab_edom2av(#k(i)) of each cylinder 2 output from the average value calculating unit 34, are compared with respective determination thresholds hi and h2, and, when the workload corresponding value and the torque corresponding value are respectively smaller than the corresponding determination thresholds, it is determined that combustion in that cylinder 2 causes a rough idle situation.

[0065] In addition, for the cylinder 2 of which the workload corresponding average value einstab_eficoutav(#k(i)) and torque corresponding average value einstab_edom2av(#k(i)) of each cylinder output from the average value calculating unit 34 are respectively smaller than the corresponding determination thresholds hi and h2, the abnormal cylinder detecting unit 36 sets a rough idle abnormality detection flag einstab exdrough that indicates that combustion in that cylinder 2 causes a rough idle situation and a rough idle cylinder flag einstab exdcyl that indicates the cylinder number of that cylinder 2, and then stores them jn a diagnostic information storage area in the RAM and/or backup memory of the ECU 30. Note that the diagnostic information storage area in the memory may be read by an external diagnostic device 100 when the external diagnostic device 100 is connected to a known inspecting communication port of the ECU 30, and is referred to at the time of inspection or maintenance at a dealer, or the like.

[0066] Furthermore, the abnormal cylinder detecting unit 36 is able to switch between a first determination mode in which the averaged workload corresponding value and the averaged torque corresponding value, that is, the workload corresponding average value einstab_eficoutav(#k(i)) and the torque corresponding average value einstab_edom2av(#k(i)), are respectively compared with the corresponding determination thresholds hi and h2 to determine whether a rough idle situation has occurred and a second determination mode in which only one of the workload corresponding average value einstab_eficoutav(#k(i)) and the torque corresponding average value einstab_edom2av(#k(i)) is compared with a corresponding one of the determination thresholds hi and h2 to determine whether a rough idle situation has occurred. Set value information that sets which determination mode is used for operation is, for example, stored in the ROM or backup memory of the ECU 30. [0067] Next, the operation will be described. [0068] FIG. 3 is a flowchart of a detecting process executed by the rough idle detecting apparatus for an internal combustion engine according to the present embodiment. During operation of the engine 1, the process shown in FIG. 3 is repeatedly executed at a predetermined calculation interval in the ECU 30.

[0069] First, the condition determining unit 31 determines whether the precondition for the above described rough idle abnormality detecting process is satisfied (step SIl).

[0070] At this time, when it is determined that the precondition for the rough idle abnormality detecting process is satisfied, the engine 1 is operated in a stable idle condition with no load fluctuations.

[0071] As the precondition for the rough idle abnormality detecting process is satisfied (YES in step SIl), the precondition satisfaction time counter 35 is incremented (step S12), and then a fluctuation component of the rotational speed Ne of the crankshaft 5 due to combustion in each of the plurality of cylinders 2 of the engine 1 is extracted by the workload corresponding value calculating unit 32 for each cylinder 2, and is integrated in a predetermined rotation angular range (180⁰CA) at a combustion interval of each cylinder 2 to calculate each of the workload corresponding values Sneflt#l to Sneflt#4, the currently calculated value is acquired by the average value calculating unit 34 as the workload corresponding value efic_eficout(#k(i)), the average value between the currently calculated value and a value einstab_eficoutav(#k(i-l)) stored in the average value calculating unit 34 as a previously averaged value is calculated, and then the calculated result is stored as a currently averaged workload corresponding average value einstab_eficoutav(#k(i)) (step S 13).

[0072] In addition to this, the torque corresponding value calculating unit 33 acquires the rotational speed Ne at a combustion interval of each cylinder 2 at a crank rotation phase different from that of the workload corresponding value calculating unit 32, and calculates each of the torque corresponding values ΔNe²(#l) to ΔNe²(#4), corresponding to the torque generated in each cylinder 2 from a difference (Nea² - Neb²) between the square of the rotational speed Ne in the relatively low-speed rotation angular range Ra at a timing at which the expansion stroke of each cylinder 2 starts and the square of the rotational speed Ne in the high-speed rotation angular range Rb in which the rotational speed of the crankshaft 5 reaches a maximum speed range in the expansion stroke of each cylinder 2, and then, the currently calculated value is acquired by the average value calculating unit 34 as a current torque corresponding value edom2_edom2(#k(i)), the average value between the currently calculated value and a value einstab_edom2av(#k(i-l)) stored in the memory as a previously averaged value is stored in the memory as a currently averaged torque corresponding average values einstab_edom2av(#k(i)) (step S 13). [0073] Subsequently, it is determined whether the count value of the precondition satisfaction time counter 35 has reached 200 (step S 14). When the count value has not reached 200 (NO in step S 14), the current process ends.

[0074] In this case, as the precondition for rough idle abnormality detecting process is satisfied thereafter, the above described series of calculation and averaging processes will be repeated again.

[0075] That is, until the count value of the precondition satisfaction time counter 35 reaches 200, the workload corresponding value calculating unit 32 repeatedly calculates the workload corresponding value efic_eficout(#k(i)), and calculates the workload corresponding average value einstab_eficoutav(#k(i)) that is smoothed by sequentially calculating the average value from the workload corresponding values efic_eficout(#k(l)) to efic_eficout(#k(200)), while, on the other hand, the torque corresponding value calculating unit 33 repeatedly calculates the torque corresponding value edom2_edom2(#k(i)) of each cylinder 2, and calculates the torque corresponding average value einstab_edom2av(#k(i)) that is smoothed by sequentially calculating the average value from the torque corresponding value edom2_edom2(#k(l)) to the torque corresponding value edom2_edom2(#k(200)) for each cylinder 2.

[0076] On the other hand, as the count value of the precondition satisfaction time counter 35 reaches 200 (YES in step S 14), the abnormal cylinder detecting unit 36 compares the workload corresponding average value einstab_eficoutav(#k(i)) and torque corresponding average value einstab_edom2av(#k(i)) of each cylinder 2 with the corresponding determination thresholds hi and h2 on the basis of outputs from the average value calculating unit 34 (step S15).

[0077] At this time, when the workload corresponding average value einstab_eficoutav(#k(i)) and the torque corresponding average value einstab_edom2av(#k(i)) are respectively larger than or equal to the corresponding determination thresholds hi and h2 (NO in step S 15), an idle normal flag einstab exprough that indicates that the idle operation condition is normal is set (step S16). [0078] Conversely, when the workload corresponding average value einstab_eficoutav(#k(i)) and the torque corresponding average value einstab_edom2av(#k(i)) are respectively smaller than the corresponding determination thresholds hi and h2 (YES in step S 15), a rough idle abnormality detection flag einstab exdrough that indicates that a rough idle abnormal cylinder is detected and a rough idle abnormal cylinder flag einstab exdcl that indicates the cylinder number of the rough idle abnormal cylinder are respectively set (step S 17).

[0079] After that, the count value of the precondition satisfaction time counter 35 is cleared (step S18), and the current process ends.

[0080] Then, in the next detecting process, when the condition determining unit 31 determines that the precondition for rough idle abnormality detecting process is satisfied (YES in step SIl), the above series of processes (steps S12 to S18) are executed again. When the condition determining unit 31 does not determine that the precondition for rough idle abnormality detecting process is satisfied (NO in step SIl), the count value of the precondition satisfaction time counter 35 is immediately cleared (step S 18), and the next process ends.

[0081] In this way, in the present embodiment, on the basis of the workload corresponding average value einstab_eficoutav(#k(i)) and torque corresponding average value einstab_edom2av(#k(i)) calculated through different methods by measuring the actual rotational speed of the crankshaft 5 of the engine 1, a variation in workload at a predetermined angular interval (180⁰CA) corresponding to a combustion interval of each cylinder 2 and a variation in torque generated through combustion of each cylinder 2 are detected. Thus, the rough idle detecting apparatus is able to accurately determine whether actual fuel injection amounts from the injectors 18 become insufficient or fluctuate and, therefore, the actual rotational speed fluctuates against the target rotational speed set in the ECU 30 to cause a rough idle situation accompanied by uncomfortable vibrations with high diagnostic accuracy. In addition, when the workload corresponding value or the torque corresponding value is calculated in another control for the engine 1, it is possible to carry out highly accurate rough idle detection without increasing a calculation load on the ECU 30.

[0082] In addition, in the present embodiment, when the rough idle detecting condition is satisfied for a predetermined period of time or longer (for example, a period of time during which the precondition satisfaction time counter value reaches 200), rough idle detection is carried out on the basis of the workload corresponding average value einstab_eficoutav(#k(i)) and the torque corresponding average value einstab_edom2av(#k(i)) that are averaged during then. Thus, it is possible to accurately detect actual rotation fluctuations of combustion of each cylinder 2 and the cylinder 2 that causes rough idle vibrations under the rough idle situation of the engine 1.

[0083] Furthermore, in addition to setting of the rough idle abnormality detection flag einstab exdrough that indicates that the rough idle abnormal cylinder is detected, the rough idle abnormal cylinder flag einstab exdcl is set for the cylinder 2 of which the workload corresponding average value einstab_eficoutav(#k(i)) and the torque corresponding average value einstab_edom2av(#k(i)) are respectively smaller than the corresponding determination thresholds hi and h2 as the cylinder that is highly likely to cause a rough idle situation, and is then stored and held in a readable form when diagnosed by an external diagnostic device 100. Thus, at the time of inspection or maintenance at a dealer, or the like, for rough idle vibrations, by referring to the rough idle abnormality detection flag einstab exdrough and the rough idle abnormal cylinder flag einstab exdcl, it is possible to quickly and reliably identify occurrence of a rough idle situation and its cause. Hence, it is possible to improve serviceability.

[0084] In addition, in the present embodiment, only when the precondition for executing rough idle abnormality detecting process is satisfied, the above described detecting processes are executed. Thus, the throughput of the CPU in the ECU 30 that executes a process of detecting a rough idle situation may be allocated to another necessary calculation process during normal operation, so calculation resources may be efficiently used.

[0085] In addition, the precondition for carrying out rough idle abnormality detection includes the condition for executing learning process (for example, learning process for variations in fuel injection amount of each injector 18 under idle rotational speed control) in which the injection characteristics of the injector 18 provided for each cylinder 2 of the engine 1 are learned is satisfied, the condition that the accelerator operation amount is minimum (0%), the condition that the vehicle speed of the vehicle that uses the engine 1 as a power source is zero (km/h), and the condition that idle up control in which the idle rotational speed during cold-start of the engine 1 is set at a rotational speed higher than the idle rotational speed at the time of completion of warm-up of the engine 1 is not executed. Thus, it is possible to accurately detect fluctuations in idle rotational speed under a substantially fixed condition in which disturbance factors are suppressed. [0086] In addition, the precondition includes at least one of the condition that the auxiliary machine (air conditioner, or the like) load of the engine 1 is not being switched or the condition that the transmission is in neutral, and further includes the condition that switching of fuel injection condition (combustion mode) carried out by each injector 18 of the engine 1, which is the common rail multi-cylinder diesel engine, is prohibited. Thus, it is possible to accurately calculate fluctuations in idle rotational speed under a substantially fixed condition in which disturbance factors are further suppressed.

[0087] In addition, rough idle detection and rough idle abnormal cylinder detection are carried out on the basis of the workload corresponding average value einstab_eficoutav(#k(i)) and the torque corresponding average value einstab_edom2av(#k(i)) that are accurately calculated at optimal timings by measuring the actual rotational speed of the crankshaft 5 at predetermined intervals corresponding to the number of cylinders of the engine 1 at mutually different rotation phases. Thus, it is possible to avoid concentration of a processing load on the CPU (resources for calculation) of the ECU 30.

[0088] Furthermore, the abnormal cylinder detecting unit 36 may be switched between the first determination mode and the second determination mode. Thus, even in the control mode in which the ECU 30 of the engine 1 calculates both the workload corresponding value and the torque corresponding value or in the control mode in which the ECU 30 calculates only any one of the workload corresponding value and the torque corresponding value, both modes are compatible. Thus, it is possible to provide a rough idle detecting apparatus that is compatible with engines of various modes.

[0089] Note that in the above described embodiment, for the cylinder 2 of which both the workload corresponding average value einstab_eficoutav(#k(i)) and torque corresponding average value einstab_edom2av(#k(i)) of each cylinder 2 are respectively smaller than the corresponding determination thresholds hi and h2, the abnormality detection flag is set to indicate that combustion in that cylinder 2 causes a rough idle situation. Instead, for the cylinder 2 of which at least one of the workload corresponding average value einstab_eficoutav(#k(i)) and torque corresponding average value einstab_edom2av(#k(i)) of each cylinder 2 is smaller than a corresponding one of the determination thresholds hi and h2, a flag that indicates that combustion in that cylinder 2 causes a rough idle situation may be set. Depending on whether both average values are respectively smaller than the determination thresholds hi and h2 or only any one of the average values is smaller than a corresponding one of the determination thresholds hi and h2, a plurality of types of rough idle abnormality detection flags may be set to indicate different diagnostic levels such that the cylinder is an abnormal cylinder or a candidate for abnormal cylinder.

[0090] In addition, in the above embodiment, the rotation measurement period for calculating the workload corresponding value and the rotation measurement period for calculating the torque corresponding value are set to periods having different phases at each combustion interval. Instead, by setting the low-speed rotation angular range Ra and the high-speed rotation angular range Rb within the rotation measurement period for calculating the workload corresponding value, the rotation measurement period for calculating the torque corresponding value may be set at the same phase as that of the rotation measurement period for calculating the workload corresponding value.

[0091] As described above, the rough idle detecting apparatus for an internal combustion engine according to the aspect of the invention advantageously provides a rough idle detecting apparatus for an internal combustion engine with high diagnostic accuracy, which is able to accurately identify actual rotation fluctuations in a rough idle situation on the basis of both the workload corresponding value and the torque corresponding value, and is able to accurately determine whether a rough idle situation has occurred. Thus, it is useful for overall rough idle detecting apparatuses for an internal combustion engine, which detect a rough idle situation in which the engine rotational speed during idle operation of the internal combustion engine unstably fluctuates against the target rotational speed because of an insufficient fuel injection amount, or the like.

[0092] While the invention has been described with reference to example embodiments thereof, it is to be understood that the invention is not limited to the described embodiments or constructions. To the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the example embodiments are shown in various combinations and configurations, other combinations and configurations, including more, less or only a single element, are also within the scope of the invention.

Claims

CLAIMS:

1. A rough idle detecting apparatus for an internal combustion engine, which detects a rough idle situation in which a rotational speed of a crankshaft of the internal combustion engine fluctuates against a target rotational speed under an idle operating condition in which the rotational speed of the crankshaft is controlled to the target rotational speed, the rough idle detecting apparatus characterized by comprising: rotational speed detecting means that detects the rotational speed of the crankshaft of the internal combustion engine; workload corresponding value calculating means that extracts a fluctuation component of the rotational speed of the crankshaft due to combustion in a cylinder of the internal combustion engine on the basis of the rotational speed of the crankshaft, detected by the rotational speed detecting means, and that calculates a workload corresponding value by integrating the extracted fluctuation component; torque corresponding value calculating means that calculates a torque corresponding value corresponding to a torque generated in the cylinder from a difference between the square of the rotational speed of the crankshaft in a relatively low-speed rotation angular range at a timing at which an expansion stroke of the cylinder starts and the square of the rotational speed of the crankshaft in a high-speed rotation angular range in which the rotational speed of the crankshaft in the expansion stroke of the cylinder reaches a maximum speed range; and abnormal cylinder determining means that respectively compares the workload corresponding value and the torque corresponding value with corresponding determination thresholds, and that determines that combustion in the cylinder causes the rough idle situation when the workload corresponding value and the torque corresponding value are respectively smaller than the corresponding determination thresholds.

2. The rough idle detecting apparatus for an internal combustion engine according to claim 1, wherein the workload corresponding value calculating means extracts a fluctuation component of the rotational speed of the crankshaft due to combustion in each of a plurality of the cylinders of the internal combustion engine cylinder by cylinder, integrates the extracted fluctuation component in a predetermined rotation range at each combustion interval of each cylinder to repeatedly calculate the workload corresponding value of each cylinder a predetermined repetition number of times, and calculates an averaged workload corresponding value by averaging the calculated workload corresponding values, and the torque corresponding value calculating means repeatedly calculates the torque corresponding value corresponding to the torque generated in each cylinder from a difference between the square of the rotational speed of the crankshaft in the relatively low-speed rotation angular range at a timing at which the expansion stroke of each cylinder starts and the square of the rotational speed of the crankshaft in the high-speed rotation angular range in which the rotational speed of the crankshaft reaches a maximum speed range in the expansion stroke of each cylinder at each combustion interval of each cylinder the predetermined repetition number of times, and calculates an averaged torque corresponding value by averaging the calculated torque corresponding values for each cylinder.

3. The rough idle detecting apparatus for an internal combustion engine according to claim 1 or 2, wherein, for the cylinder of which the averaged workload corresponding value and the averaged torque corresponding value are respectively smaller than the corresponding determination thresholds, the abnormal cylinder determining means sets an abnormality detection flag that indicates that combustion in that cylinder causes the rough idle situation.

4. The rough idle detecting apparatus for an internal combustion engine according to any one of claims 1 to 3, further comprising: precondition determining means that determines whether a predetermined precondition for executing a process of detecting a rough idle situation of the internal combustion engine is satisfied, wherein when the precondition is satisfied, the workload corresponding value calculating means and the abnormal cylinder determining means execute respective processes.

5. The rough idle detecting apparatus for an internal combustion engine according to claim 4, wherein the precondition includes a condition in which a condition for executing learning process for learning injection characteristics of a fuel injection valve provided for each cylinder of the internal combustion engine is satisfied, a condition in which an accelerator operation amount is minimum, a condition in which a vehicle speed of a vehicle that uses the internal combustion engine as a power source is zero, and a condition in which idle up control, in which an idle rotational speed at the time of cold-start of the internal combustion engine is set at a rotational speed higher than an idle rotational speed at the time of completion of warm-up of the internal combustion engine, is not executed.

6. The rough idle detecting apparatus for an internal combustion engine according to claim 5, wherein the precondition further includes at least one of a condition in which an auxiliary machine load of the internal combustion engine is not being switched or a condition in which a transmission mounted on the vehicle and drivably coupled to the internal combustion engine is in neutral.

7. The rough idle detecting apparatus for an internal combustion engine according to claim 4, wherein the internal combustion engine is a common rail multi-cylinder diesel engine, and the precondition further includes a condition in which switching of a fuel injection condition carried out by the fuel injection valve of the diesel engine is prohibited.

8. The rough idle detecting apparatus for an internal combustion engine according to claim 7, wherein the workload corresponding value calculating means and the torque corresponding value calculating means acquire the rotational speed of the crankshaft, detected by the rotational speed detecting means, at a predetermined interval corresponding to the number of cylinders of the internal combustion engine at mutually different rotation phases.

9. The rough idle detecting apparatus for an internal combustion engine according to claim 7 or 8, wherein the abnormal cylinder determining means is able to switch between a first determination mode in which the workload corresponding value and the torque corresponding value are respectively compared with corresponding determination thresholds to make determination as to whether the rough idle situation has occurred and a second determination mode in which only one of the workload corresponding value and the torque corresponding value is compared with a corresponding one of the determination thresholds to make determination as to whether the rough idle situation has occurred.

10. A rough idle detecting method for an internal combustion engine, which detects a rough idle situation in which a rotational speed of a crankshaft of the internal combustion engine fluctuates against a target rotational speed under an idle operating condition in which the rotational speed of the crankshaft is controlled to the target rotational speed, the rough idle detecting method characterized by comprising: detecting the rotational speed of the crankshaft of the internal combustion engine; extracting a fluctuation component of the rotational speed of the crankshaft due to combustion in a cylinder of the internal combustion engine on the basis of the detected rotational speed, and calculating a workload corresponding value by integrating the extracted fluctuation component; calculating a torque corresponding value corresponding to a torque generated in the cylinder from a difference between the square of the rotational speed of the crankshaft in a relatively low-speed rotation angular range at a timing at which an expansion stroke of the cylinder starts and the square of the rotational speed of the crankshaft in a high-speed rotation angular range in which the rotational speed of the crankshaft in the expansion stroke of the cylinder reaches a maximum speed range; and respectively comparing the calculated workload corresponding value and the calculated torque corresponding value with corresponding determination thresholds, and determining that combustion in the cylinder causes the rough idle situation when the calculated workload corresponding value and the calculated torque corresponding value are respectively smaller than the corresponding determination thresholds.