JP4578560B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine mounted on a vehicle or the like, and more particularly to a control device for an internal combustion engine that controls the intake air amount to a multi-cylinder internal combustion engine having three or more cylinders.

  2. Description of the Related Art Conventionally, there is known a control device for an internal combustion engine in which a throttle valve is provided in an intake passage of each cylinder of a multi-cylinder internal combustion engine, and the intake amount to each cylinder is controlled by opening and closing the throttle valve.

  In this internal combustion engine, since the throttle valve provided in the intake passage of each cylinder can be controlled independently, the intake amount to each cylinder can be individually controlled.

  However, in general, in an internal combustion engine, there are individual differences in the intake passages and throttle valves of each cylinder, so even if the throttle valve of each cylinder is set to the same opening degree, the intake amount to each cylinder may be uneven. . When the intake air amount to each cylinder becomes non-uniform, it is considered that air-fuel ratio variation and torque variation between cylinders occur.

  When the torque variation between the cylinders becomes large, the in-cycle fluctuation of the engine torque becomes large, and there is a risk that vibrations unpleasant to the driver may occur. In addition, when the air-fuel ratio variation between cylinders increases, the in-cycle fluctuation of the air-fuel ratio of the exhaust gas flowing into the catalyst increases, so the fluctuation range of the exhaust gas air-fuel ratio protrudes from the catalyst purification window and the exhaust gas purification rate May decrease.

  In order to avoid such a state, it is necessary to make the intake air amount to each cylinder uniform. In order to make the intake air amount to each cylinder uniform, it is necessary to first estimate the cylinders having different intake air amounts, and in particular, the cylinders having the most different intake air amounts compared to other cylinders (hereinafter referred to as the maximum intake air amount variation cylinder). It becomes.

  As a technique for estimating the cylinder with the largest variation in intake air amount, the crank speed (engine speed) is constantly calculated, and the crank speed (engine speed) of each cylinder is obtained by comparing it with the output of the cylinder discrimination sensor. In addition, a technique for estimating the cylinder with the maximum intake air amount variation has been proposed (see, for example, Patent Document 1).

  Further, there has been proposed a technique for calculating the area of the output waveform of the air flow sensor in a predetermined period for each intake stroke of each cylinder, and calculating the variation rate of the intake amount between the cylinders or the intake amount for each cylinder (for example, , See Patent Document 2).

  Further, a technique for estimating the intake air amount of each cylinder from a pressure sensor attached to the intake manifold and an air flow sensor has been proposed (see, for example, Patent Document 3).

JP 2003-193889 A (paragraph 0019, FIGS. 1 and 4) JP 2004-176644 A (summary column, FIG. 1) Japanese Patent Laying-Open No. 2006-70728 (paragraphs 0025 to 0032, FIGS. 2 and 3)

  However, the technique disclosed in Patent Document 1, that is, the estimation technique of the maximum intake air amount variation cylinder due to the variation in crank speed, is not only the variation in the intake air amount but also the fuel amount variation, so the crank speed varies. Even if the number of cylinders is estimated, there is a problem that it is difficult to estimate whether or not the intake amount of the target cylinder varies compared to other cylinders.

  The technique disclosed in Patent Document 2 calculates the intake air amount variation between cylinders from the area in a predetermined period of the output waveform of the airflow sensor for each intake stroke of each cylinder. The operation state in which the condition for the predetermined period is satisfied is limited, and an engine in which the predetermined period cannot be set may be considered depending on the engine. There is a problem that it is difficult to calculate the variation in intake air amount between cylinders.

  In addition, the technique disclosed in Patent Document 3 estimates the intake air amount of each cylinder using a pressure sensor and an air flow sensor. Therefore, it is possible to estimate a cylinder having a different intake air amount. In addition, there is a problem that complicated calculation is required when estimating the intake air amount.

  The present invention has been made to solve the above-described problems. In an internal combustion engine provided with intake air amount control means for each cylinder, it is not affected by variations in fuel amount, and can be calculated with one pressure detection means and simple calculation. The present invention provides a control device for an internal combustion engine that estimates a cylinder with a maximum intake air amount variation.

  An internal combustion engine control apparatus according to the present invention is an internal combustion engine control apparatus that controls an intake amount to a multi-cylinder internal combustion engine having three or more cylinders, and is provided in an intake passage of each cylinder of the multi-cylinder internal combustion engine. Intake amount control means, a communication pipe connecting the intake passages downstream of the intake air quantity control means in each cylinder, and a detection period setting means for setting a period for detecting the pressure in the communication pipe for each cylinder And a pressure detection means for detecting the pressure in the communication pipe during the detection period, and a first cylinder for estimating the largest intake amount variation cylinder that has the most intake amount compared to other cylinders when the load of the internal combustion engine is low. And a second intake air amount variation maximum cylinder estimating unit for estimating an intake air amount variation maximum cylinder that is the most different in intake air amount compared to other cylinders when the load of the internal combustion engine is high. And switching the first intake air amount variation maximum cylinder estimating means and the second intake air amount variation maximum cylinder estimating means according to the load of the internal combustion engine to estimate a cylinder having the maximum intake air amount variation. To do.

  According to the present invention, in an internal combustion engine provided with intake air amount control means for each cylinder, the maximum intake air amount variation cylinder is estimated by one pressure detection means and simple calculation without being affected by the fuel amount fluctuation. Thus, there is an effect that it is possible to carry out control to make the intake air amount of each cylinder uniform.

1 is a schematic configuration diagram of an internal combustion engine according to Embodiment 1 of the present invention. It is a figure which shows the change of the pressure sensor output in the communicating pipe | tube of the internal combustion engine which estimates the air intake amount variation largest cylinder which concerns on Embodiment 1 of this invention. It is a flowchart showing the process which generate | occur | produces for every predetermined crank angle, when implementing the estimation of the load of the internal combustion engine which concerns on Embodiment 1 of this invention. It is a flowchart showing the high and low load determination processing which concerns on Embodiment 1 of this invention. It is a figure which shows the frequency | count of implementation after the process which detects the pressure maximum value which concerns on Embodiment 1 of this invention, the pressure in the present communicating pipe, and a pressure maximum value. It is a flowchart showing the high load determination flag process which concerns on Embodiment 1 of this invention. It is a figure which shows the relationship between the intake order and cylinder which concern on Embodiment 1 of this invention. It is a figure which shows the pressure change in a communicating pipe | tube when the pressure in the communicating pipe | tube corresponding to one cylinder which concerns on Embodiment 1 of this invention is substantially atmospheric pressure. It is a figure which shows the pressure change in a communicating pipe when the pressure in the communicating pipe corresponding to the two cylinders concerning Embodiment 1 of this invention is substantially atmospheric pressure. It is a flowchart showing the process which estimates the intake air amount variation largest cylinder corresponding to the high load which concerns on Embodiment 1 of this invention. It is a flowchart showing the process which detects the pressure minimum value which concerns on Embodiment 1 of this invention. It is a flowchart showing the process which estimates the variation largest cylinder using the pressure minimum value which concerns on Embodiment 1 of this invention. The number of executions of the processing for detecting the maximum value of the pressure in the processing after the EVC timing of the third cylinder in FIG. 9, the current pressure in the communication pipe, and the intake order indicate the minimum value of the pressure in the communication pipe for the first cylinder. FIG. It is a figure which shows the pressure minimum value after the process which detects the pressure minimum value in the communicating pipe with respect to four cylinders which concern on Embodiment 1 of this invention. It is a flowchart showing the process which estimates the intake amount variation largest cylinder at the time of low load which concerns on Embodiment 1 of this invention. It is a figure which shows the change of the pressure sensor output in the communicating pipe | tube of the internal combustion engine which estimates the air intake amount variation largest cylinder which concerns on Embodiment 1 of this invention. It is a flowchart showing the process which estimates the variation largest cylinder using the pressure maximum value which concerns on Embodiment 1 of this invention. It is a figure which shows the pressure maximum value after the process which detects the pressure maximum value in the communicating pipe with respect to four cylinders which concern on Embodiment 1 of this invention. 3 is a map prepared in advance showing information on a cylinder with the largest variation in intake air amount according to Embodiment 1 of the present invention. It is a figure which shows the relationship between the cylinder from which the pressure in the communicating pipe which concerns on Embodiment 1 of this invention becomes the maximum value, and the cylinder from which the minimum value is dispersion | variation. It is a figure which shows the timing which determines the high load which concerns on Embodiment 1 of this invention, and the timing which starts estimation of the largest intake-air-variation maximum cylinder. It is a figure which shows the timing which determines the high load which concerns on Embodiment 2 of this invention, and the timing which starts estimation of the largest intake-air-variation maximum cylinder. It is a flowchart showing the high and low load determination processing which concerns on Embodiment 2 of this invention. It is a flowchart showing the process which estimates the intake amount variation largest cylinder at the time of low load which concerns on Embodiment 2 of this invention. It is a flowchart showing the process which detects the pressure maximum value which concerns on Embodiment 2 of this invention.

  Exemplary embodiments of a control apparatus for an internal combustion engine according to the present invention will be described below with reference to the accompanying drawings. Note that the present invention is not limited to these embodiments.

Embodiment 1 FIG.
FIG. 1 shows an embodiment in which the present invention is applied to an internal combustion engine having four cylinders, the first cylinder to the fourth cylinder, and shows a schematic configuration of the internal combustion engine.
The engine 1 is provided with a throttle valve 3 as an intake air amount control means for restricting the intake air amount for each intake pipe 2 of each cylinder. A throttle actuator 4 for opening and closing the throttle valve 3 and a throttle valve are provided. A throttle opening degree detection sensor 5 for detecting the opening degree is provided. Further, a communication pipe 6 that connects the downstream sides of the throttle valve 3 of each cylinder to each other, and a pressure sensor 7 that is a means for detecting the pressure in the communication pipe 6 are disposed. Further, a crankshaft 8 is connected to an output shaft (not shown) of the internal combustion engine, and a crank angle detection sensor 9 for detecting the rotation speed of the crankshaft 8 and a cam angle detection sensor 10 as cylinder identification means are provided. Has been.

  The throttle actuator 4 is connected to an electronic control unit (ECU) 11 and is driven by an instruction from the ECU 11 to control the throttle valve 3. The ECU 11 receives signals from a throttle opening detection sensor 5, a pressure sensor 7, a crank angle detection sensor 9, a cam angle detection sensor 10, and an accelerator position sensor (not shown). Further, the engine 1 is provided with a fuel injection valve 12, a spark plug 13, an intake valve 14, an exhaust valve 15, and a piston 16. The ECU 11 is mainly composed of a microcomputer, and controls the throttle valve 3 as described above by executing various engine control programs stored in a built-in ROM (storage medium). The fuel injection amount of the fuel injection valve 12 and the ignition timing of the spark plug 13 are controlled according to the operating state.

  In FIG. 1, in order to simplify the drawing, the throttle valve 3, the throttle actuator 4, and the throttle opening degree detection sensor 5 are shown only for the first cylinder. Arranged in each of the cylinder and the fourth cylinder.

  The crankshaft 8 is connected to the piston 16, and the crankshaft 8 is rotated when the piston 16 moves up and down. A crank plate (not shown) is attached to the crankshaft 8. The crank plate has a protrusion, and the crank angle detection sensor 9 is configured to detect the rotation speed of the crankshaft 8 by detecting the protrusion. In this embodiment, the protrusions of the crank plate are installed every 10 degrees with reference to the time when the piston 16 is at the top dead center position.

  The control apparatus for an internal combustion engine according to the first embodiment is configured as described above. Next, a method for estimating the maximum intake amount variation cylinder will be described.

  FIG. 2 shows a change in pressure in the communication pipe 6 of the internal combustion engine for estimating the cylinder with the largest intake amount variation. In FIG. 2, the pressure in the communication pipe 6 is indicated by a solid line, and the fully closed timing (hereinafter referred to as EVC timing) of the exhaust valve 15 of each cylinder is indicated by a one-dot chain line. The intake stroke of each cylinder is also described at the same time. The vertical axis represents the pressure sensor output voltage, and the horizontal axis represents the crank angle.

  The processing of this embodiment will be described along the flowchart of FIG. FIG. 3 is a flowchart showing a process executed for each predetermined crank angle. In this embodiment, it is executed every 10 degrees of crank angle.

  First, in step S901, a process for determining whether the current load of the internal combustion engine is a high load or a low load (hereinafter, a high / low load determination process) is performed. The details of the high / low load determination process will be described later. If it is determined that the load is high, the high load determination flag FB is set (FB = 1). Conversely, if the load is determined to be low, the high load determination flag is set. FB is reset (FB = 0).

  Next, the process proceeds to the determination unit S902 to determine whether or not the high load determination flag FB = 1. If FB = 1, it is determined that the load is high, and the process proceeds to step S903. If FB = 1, the load is low, and the process proceeds to step S904.

  In step S903, an intake amount variation maximum cylinder estimation process corresponding to a high load is performed, and the process ends. The intake air amount variation maximum cylinder estimation process corresponding to a high load will be described later.

  In step S904, the intake amount variation maximum cylinder estimation process corresponding to the low load is performed, and the process ends. The intake air amount variation maximum cylinder estimation process corresponding to a low load will be described later.

  Next, the high / low load determination process shown in step S901 of FIG. 3 will be described using the flowchart of FIG.

  In FIG. 4, first, in the determination unit S1001, it is determined whether FEX = 1. FEX is a determination flag for processing for detecting the maximum pressure value used for determining the load of the internal combustion engine. FEX = 0 indicates that the process for detecting the maximum pressure value has been completed, and FEX = 1 indicates that the process for detecting the maximum pressure value is being performed. The initial value is FEX = 0. If FEX = 1, the process proceeds to determination unit S1002, and if not, the process proceeds to determination unit S1008. Processing after determination unit S1008 will be described later.

  It progresses to judgment part S1002, and it is judged whether the pressure PNOW in the present communication pipe 6 is larger than MAX. If the current pressure PNOW in the communication pipe 6 is large, the process proceeds to step S1003, and if not, the process proceeds to step S1004. In step S1003, the current pressure PNOW in communication pipe 6 is substituted for MAX, and the flow proceeds to step S1004. In step S1004, assuming that the process of detecting the maximum value of pressure is completed once, the process proceeds to determination unit S1005 as FCHK = FCHK + 1. FCHK is the number of executions of the process for detecting the maximum pressure value.

  Next, in determination unit S1005, it is determined whether or not FCHK = 5 in order to determine whether or not the detection period of the maximum value of pressure has ended. If FCHK = 5, the process proceeds to step S1006; otherwise, the process ends.

  Here, the setting of the detection period will be described. It is known that the maximum value of the pressure in the communication pipe 6 appears during the intake stroke after the EVC timing. In this embodiment, the detection range of the maximum value of the pressure during the detection period is a crank angle of 50 degrees. Set. That is, in this embodiment, since the process is performed every 10 degrees of crank angle, FCHK = 5. The detection range in this case is as shown in FIG.

  In step S1006, high load determination flag processing is performed, and the flow proceeds to step S1007. The high load determination flag process is a process for determining whether or not the load of the internal combustion engine is a high load, and performing the flag process. The details will be described later according to the flowchart of FIG. In step S1007, FEX = 0 and the process ends.

  Here, a case where FEX = 1 is not satisfied in the determination unit S1001 will be described. If FEX = 1, the process proceeds to determination unit S1008 to determine whether the current crank angle is the EVC timing. The determination is made, for example, by storing the EVC timing in the ECU 11 in advance and comparing it with the current crank angle. If it is the EVC timing, the process advances to step S1009 to initialize each value by assuming that the detection of the maximum value of the pressure is started, and the process ends. The initial values are FEX = 1, FCHK = 0, and MAX = PNOW.

  When the EVC timing does not match the step size of the pressure detection timing, for example, when the step size of the pressure detection timing is every 10 degrees, and the EVC timing is 25 degrees after the # 1 cylinder intake top dead center, the crank angle is 20 degrees The EVC timing may be set, or the EVC timing may be set at 30 degrees. In this embodiment, the EVC timing is 30 degrees after the # 1 cylinder intake top dead center. The EVC timing of each cylinder is set every 180 degrees from the # 1 cylinder EVC timing.

  When the process shown in FIG. 4 is performed, for example, the values of FCHK, PNOW, and MAX in the process after the # 1 cylinder EVC timing of FIG. 2 are as shown in FIG. In this case, PNOW when FCHK = 1 is MAX, and MAX = 3.89.

  Next, the high load determination flag process shown in step S1006 in FIG. 4 will be described using the flowchart in FIG.

  In FIG. 6, first, it is determined whether or not MAX is larger than PL1 in the determination unit S1101. If MAX is large, the process proceeds to step S1102, and if not, the process proceeds to step S1103. PL1 is a value for determining whether the load of the internal combustion engine is high. When the load of the internal combustion engine becomes high, a period in which the pressure in the communication pipe 6 is saturated appears. Since the pressure is saturated at about atmospheric pressure, PL1 is set to about atmospheric pressure. Since the sensor used here has a sensor value of 4 indicating atmospheric pressure, PL1 is set to about 3.8.

  In step S1102, it is determined that the load is high, the high load determination flag FB = 1, the number of times FTR = 0 continuously detected that the load is not high, the low load pressure maximum value processing flag FEX2 = 0, the intake order n The processing ends when = 1. Here, n is the intake sequence. For example, when step S1102 is performed after the EVC timing of the # 1 cylinder, the relationship between the intake sequence and the actual cylinder is as shown in FIG. The relationship of FIG. 7 is set when n = 1. The low load pressure maximum value processing flag FEX2 is initialized so that low load processing is not started in a state where FEX2 = 1 when the next low load is reached.

  If MAX is smaller than PL1 in determination unit S1101, the process proceeds to step S1103, and FTR = FTR + 1 is set. Proceeding to determination unit S1104, it is determined whether FTR ≧ 4 as confirmation of whether all the cylinders (four cylinders in this embodiment) are under low load. If FTR ≧ 4, the process proceeds to step S1105. In step S1105, it is determined that the load is low, and the processing ends with FB = 0, the high load pressure minimum value processing flag FEX1 = 0, and n = 1. The high load pressure minimum value processing flag FEX1 is initialized so that high load processing is not started in a state where FEX = 1 when the next high load is reached. If FTR ≧ 4 in the determination unit S1104, the process ends as it is.

  As described above, it is possible to determine that the load of the internal combustion engine is high by detecting that MAX for one cylinder is greater than or equal to PL1. Also, by determining the load of the internal combustion engine from MAX for one cylinder, it is possible to quickly determine the load when it changes to the high load side, and to switch the estimation means when the pressure in the communication pipe 6 exceeds PL1. When the load becomes high, the intake air amount variation maximum cylinder estimating means corresponding to the high load can be selected.

In addition, a method of performing the process of FIG. 4 on a plurality of cylinders and determining that the load of the internal combustion engine is a high load when MAX of the plurality of cylinders is greater than or equal to PL1 is conceivable.
FIG. 8 shows a case where the MAX of one cylinder is greater than or equal to PL1. As shown in FIG. 8, when the MAX of one cylinder is greater than or equal to PL1, it is possible to carry out an estimation method that uses, for example, the maximum pressure value as the maximum value of the communication pipe pressure for that cylinder. is there.

  However, as shown in FIG. 9, when the MAX of a plurality of cylinders is greater than or equal to PL1, the cylinder having the maximum pressure among all the cylinders cannot be determined, so that the estimation means using the maximum pressure value cannot be used. Therefore, by detecting that the MAX of a plurality of cylinders is greater than or equal to PL1 and switching the estimation means, it is possible to select the intake quantity variation maximum cylinder estimation means corresponding to the high load when the load becomes high.

  When detecting that the MAX of one cylinder is greater than or equal to PL1 and switching the estimation means, the load has changed compared to when detecting that the MAX of multiple cylinders is greater than or equal to PL1 and switching the estimation means. Sometimes the estimation means can be switched quickly.

Next, details of the process of estimating the maximum intake air amount variation cylinder corresponding to the high load shown in step S903 in FIG. 3 will be described with reference to the flowchart of FIG.
Assume that the flowchart of FIG. 3 is performed in a state where the pressure in the communication pipe 6 changes as shown in FIG.

  First, determination unit S1201 determines whether FEX1 = 1. FEX1 is a determination flag for processing for detecting the minimum pressure value used for estimating the maximum intake air amount variation cylinder. FEX1 = 0 indicates that the process for detecting the minimum pressure value has been completed, and FEX1 = 1 indicates that the process for detecting the minimum pressure value is being performed. The initial value is FEX1 = 0.

  In determination unit S1201, if FEX1 = 1, the process proceeds to step S1202, and if not, the process proceeds to determination unit S1205. Processing after determination unit S1205 will be described later.

  Proceeding to step S1202, processing for detecting the minimum pressure value is performed. The process for detecting the minimum pressure value will be described later with reference to the flowchart of FIG.

  Next, the process proceeds to determination unit S1203, where it is determined whether n = 5 in order to confirm whether the minimum pressure values of all cylinders have been detected. If n = 5, the process proceeds to step S1204, the process of estimating the maximum variation cylinder is performed using the minimum pressure value, and the process ends. Otherwise, the process ends. Details of the process of estimating the maximum variation cylinder using the minimum pressure value will be described later according to the flowchart of FIG.

  Next, a description will be given of the determination unit S1205 and subsequent steps that are performed when FEX = 1 is not satisfied in the determination unit S1201. In judgment part S1205, it is judged whether the present crank angle is an EVC timing. If it is determined in step S1205 that the EVC timing is reached, the process proceeds to step S1206. If it is not the EVC timing, the process ends.

  In step S1206, FEX1 = 1, FCHK1 = 1, MIN (n) = PNOW, and the process ends. FCHK1 is the number of executions of the process for detecting the minimum pressure value. In this embodiment, the number of processes for detecting the minimum pressure value is 10 times. MIN (n) is a pressure minimum value corresponding to the nth cylinder in the intake order. The initial value of n is 1.

  Next, a process representing a process for detecting the minimum pressure value, which is the process in step S1202 in FIG. 10, will be described with reference to the flowchart in FIG.

  First, PNOW and MIN (n) are compared in determination unit S1301, and if PNOW is small, the process proceeds to step S1302, and PNOW is substituted into MIN (n), and the process proceeds to step S1303. Otherwise, the process proceeds to step S1303 as it is.

  In step S1303, this process is performed once, and FCHK1 is incremented, and the process proceeds to determination unit S1304.

  In determination unit S1304, it is determined whether FCHK1 is 10. If FCHK1 is 10, the process proceeds to step S1305, n is incremented assuming that the process of detecting the minimum pressure value is completed, and the process ends with FEX1 = 0. If FCHK1 is other than 10, the process ends.

  In this embodiment, for example, when a result as shown in FIG. 13 is obtained, the PNOW when FCHK1 = 6 is MIN (1).

  Next, the process of estimating the maximum variation cylinder using the minimum pressure value, which is the process of step S1204 of FIG. 10, will be described with reference to the flowchart of FIG. Assume that the processing of FIG. 11 is performed and the result shown in FIG. 14 is obtained. The relationship between the intake order n and the cylinder is as shown in FIG.

  First, in step S1401, an average value AVE of MIN (n) is calculated. For example, in the result of FIG. 14, AVE = 3.6. In step S1402, MIN (n) is compared with AVE, and n when the absolute value of the difference is the largest is specified and is set as K. In the result of FIG. 14, the absolute value of the difference becomes the largest when n = 1. Therefore, K = 1.

  Proceeding to determination unit S1403, AVE-MIN (K) is calculated. If greater than 0, the process proceeds to step S1404; otherwise, the process proceeds to step S1405. In the case of the result of FIG. 14, AVE-MIN (1) = 0.1, which is larger than 0, and thus the process proceeds to step S1404.

  In step S1404, it is estimated that the cylinder immediately before the intake order K is the cylinder with the largest intake amount variation, and the intake amount is smaller than that of the other cylinders. Since K = 1 in the result of FIG. 14, the cylinder immediately before the intake order is the # 1 cylinder from the relationship of FIG.

  In step S1405, it is estimated that the cylinder immediately before the intake order K is the cylinder with the largest intake amount variation, and the intake amount is larger than that of the other cylinders. In step S1404 and step S1405, the process proceeds to step S1406. In step S1406, n = 1 and the process ends.

  As described above, by performing the processes of FIGS. 10, 11, and 12, when the load of the internal combustion engine is high, it is possible to estimate the maximum intake amount variation cylinder with the output of the pressure sensor and simple calculation. .

  Next, the process of estimating the intake air amount variation maximum cylinder corresponding to the low load shown in step S904 in FIG. 3 will be described with reference to the flowchart of FIG. It is assumed that the flowchart of FIG. 15 is performed in a state where the pressure in the communication pipe 6 changes as shown in FIG. FIG. 16 shows the pressure in the communication pipe 6 by a solid line, and shows the EVC timing by a one-dot chain line. The intake stroke of each cylinder is also described at the same time. The vertical axis represents the pressure sensor output voltage, and the horizontal axis represents the crank angle.

First, determination unit S1501 determines whether FEX2 = 1. FEX2 is a processing flag for determining the maximum pressure value for each cylinder used for estimating the maximum variation cylinder. FEX2 = 0 indicates that the process for determining the maximum pressure value has been completed, and FEX2 = 1 indicates that the process for determining the maximum pressure value is being performed. The initial value is FEX2 = 0.
If FEX2 = 1, the process proceeds to step S1502, and if not, the process proceeds to determination unit S1507. Processing subsequent to the determination unit S1507 will be described later.

  Proceeding to step S1502, MAX calculated in the high / low load determination processing of FIG. 10 is substituted into MAX2 (n). MAX2 (n) is the maximum pressure value when the intake sequence is n. The initial value of n is 1.

  Next, the process proceeds to determination unit S1503 to determine whether or not FCHK = 5. If FCHK = 5, n = n + 1 and FEX2 = 0 are set in step S1504, and the process proceeds to determination unit S1505. Otherwise, the process proceeds to determination unit S1505.

The process proceeds to determination unit S1505 to determine whether n = 5. If n = 5, the process proceeds to step S1506. If n = 5, the process ends.
In step S1506, a process for estimating the maximum variation cylinder is performed using the maximum pressure value, and the process ends. The process of estimating the variation maximum cylinder using the maximum pressure value will be described later according to the flowchart of FIG.

  Next, a description will be given of the determination unit S1507 and subsequent steps that are performed when FEX2 = 1 is not satisfied in the determination unit S1501. In judgment part S1507, it is judged whether the present crank angle is an EVC timing.

  If it is determined in step S1507 that the EVC timing is reached, the flow advances to step S1508 to complete the processing with FEX2 = 1 and MAX2 (n) = 0. If the timing is not EVC timing, the processing ends.

  Next, the process of estimating the maximum variation cylinder using the maximum pressure value shown in step S1506 in FIG. 15 will be described with reference to the flowchart in FIG. It is assumed that the process of FIG. 15 is performed until immediately before step S706, and the result shown in FIG. 18 is obtained.

  First, in step S1601, MAX2 (n) are compared with each other, n that is the maximum value is specified, and is set as KMAX. In the result of FIG. 18, MAX2 (n) when n = 1 is maximized, so KMAX = 1.

  In step S1602, MAX2 (n) are respectively compared to identify the minimum value n, which is set to KMIN. In the case of the result of FIG. 18, MAX2 (n) when n = 2 is minimized, so that KMIN = 2.

  Proceeding to step S1603, KFIX is determined from KMAX and KMIN with reference to the map of FIG. In the result of FIG. 18, KFIX = 4. FIG. 19 is created from the relationship of FIG.

  The process proceeds to determination unit S1604 to determine whether KFIX = 0. If KFIX = 0, the process proceeds to step S1605; otherwise, the process proceeds to determination unit S1606. In the case of the result of FIG. 18, since KFIX = 4, the process proceeds to step S1606.

  If the process proceeds to step S1605, it is estimated that there is no cylinder with the largest intake amount variation, and the process proceeds to step S1610.

  When the process proceeds to determination unit S1606, it is determined whether KFIX <5. If KFIX <5, the process proceeds to step S1607; otherwise, the process proceeds to step S1608. In the case of the result of FIG. 18, since KFIX = 4 <5, the process proceeds to step S1607.

  Proceeding to step S1607, it is estimated that the KFIX-th cylinder with the intake order having the largest intake amount variation and that the intake amount is smaller than that of the other cylinders, and the process proceeds to step S1610. In the result of FIG. 18, since KFIX = 4, it is estimated from the relationship of FIG. 7 that the # 1 cylinder is the cylinder with the largest intake amount variation and the intake amount is smaller than the other cylinders.

  When the process proceeds to step S1608, KFIX = KFIX-4 is calculated, and the process proceeds to step S1609. In step S1609, it is estimated that the cylinder having the KFIX-th intake order is the cylinder having the largest intake amount variation and the intake amount is larger than that of the other cylinders, and the flow proceeds to step S1610.

  In step S1610, n = 1 and the process ends.

  As described above, by performing the processing of FIGS. 15 and 17, when the load of the internal combustion engine is low, it is possible to estimate the maximum intake amount variation cylinder by the output of the pressure sensor and simple calculation.

  As described above, according to the first embodiment, the high load determination shown in FIGS. 2, 3, and 4 is performed using the pressure in the communication pipe 6, and the low load is shown in FIGS. 15 and 17. By performing the processing shown in FIGS. 10, 11, and 12 at a high load, it is possible to select an intake air amount variation estimating means suitable for the load of the internal combustion engine. It is possible to estimate the cylinder with the largest variation in intake air amount.

Embodiment 2. FIG.
Next, a second embodiment will be described. In the first embodiment, as shown in FIG. 21, after performing the high load determination, the maximum intake amount variation cylinder is estimated from the next EVC timing. This is because the pressure in the communication pipe 6 is minimized when the high load determination is performed. This is because there is a possibility that the timing of the value has passed.

  Here, when the pressure in the communication pipe 6 becomes substantially atmospheric pressure after the EVC timing, it is considered that the pressure in the communication pipe 6 is almost atmospheric pressure immediately before the EVC timing. As shown in FIG. 22, a method is conceivable in which the maximum intake cylinder variation estimation can be quickly performed by detecting the pressure in the communication pipe 6 immediately before the EVC timing and performing a high load determination. As shown in FIG. 2, a specific process when the pressure in the communication pipe 6 changes will be described with reference to the flowchart of FIG.

  FIG. 23 shows a process corresponding to the high / low load determination process shown in step S901 of FIG.

  First, in the determination unit S1701, it is determined whether or not the current crank angle is a timing for determining a preset high load. If it is the set timing, the process proceeds to the determination unit S1702, and if not, the process ends. For example, in the present embodiment, since the EVC timing is 30 degrees after the intake top dead center, the crank angle for determining a high load is set to 20 degrees after the intake top dead center.

In step S1702, PNOW is compared with a predetermined value PL2 set in advance. If PNOW is larger than PL2, the process proceeds to step S1703. Otherwise, the process proceeds to step S1704. The predetermined value PL2 set in advance is, for example, set to approximately atmospheric pressure PL2 = 3.6 because the sensor used here indicates atmospheric pressure when the sensor value is 4. Since the maximum value of the pressure in the communication pipe 6 comes after the EVC timing, it is generally not the maximum value at this time, and the value PL1 = 3.8 for determining the high load used in the first embodiment. This is because a lower value is set.
In the pressure in the communication pipe 6 in FIG. 2, the PNOW at 20 degrees after the intake top dead center is PNOW 3.89, and thus becomes larger than PL2 = 3.6, and the process proceeds to step S1703.

  Proceeding to step S1703, it is determined that the load is high, and FB = 1, FTR = 0, FEX2 = 0, n = 1, and the process ends.

  Next, processing after step S1704 will be described. In step S1704, FTR = FTR + 1 is set, and the process proceeds to determination unit S1705. In determination unit S1705, it is determined whether FTR ≧ 4. If FTR ≧ 4, the process proceeds to step S1706, and if not, the process ends. Proceeding to step S1706, the processing ends with FB = 0, FEX1 = 0, and n = 1.

  In the above method, there is no processing for detecting the maximum pressure value after the EVC timing during the high / low load determination processing, and therefore the processing for estimating the maximum variation cylinder using the maximum pressure value shown in FIG. 17 cannot be performed. Therefore, the intake air amount variation maximum cylinder estimation process corresponding to the low load needs to be changed to the process shown in FIG. The flowchart shown in FIG. 24 will be described.

First, the determination unit S1801 determines whether FEX2 = 1. FEX2 is a determination flag for processing for detecting the maximum pressure value used for estimating the maximum intake air amount variation cylinder. FEX2 = 0 indicates that the process for detecting the maximum pressure value has been completed, and FEX2 = 1 indicates that the process for detecting the maximum pressure value is being performed. The initial value is FEX1 = 0.
In determination unit S1801, if FEX2 = 1, the process proceeds to step S1802, and if not, the process proceeds to determination unit S1805. Processing subsequent to the determination unit S1805 will be described later.

  Proceeding to step S1802, a process for detecting the maximum pressure value is performed. The process for detecting the maximum pressure value will be described later with reference to the flowchart of FIG.

Next, the process proceeds to determination unit S1803, where it is determined whether n = 5 in order to confirm whether the maximum pressure values of all cylinders have been detected. If n = 5, the process proceeds to step S1804; otherwise, the process ends.
In step S1804, processing for estimating the maximum variation cylinder is performed using the maximum pressure value, and the processing ends. The process for estimating the maximum variation cylinder using the maximum pressure value is the process shown in FIG.

  Next, processing after determination unit S1805 will be described. The process proceeds to determination unit S1805 to determine whether or not the current crank angle is the EVC timing. If it is determined in step S1805 that the EVC timing is reached, the process proceeds to step S1806, and if it is not the EVC timing, the process ends.

  In step S1806, the processing ends with FEX2 = 1, FCHK2 = 1, MAX2 (n) = PNOW. FCHK2 is the number of executions of the process for detecting the minimum pressure value. In the present embodiment, the number of processes for detecting the maximum pressure value is five. MAX2 (n) is the minimum pressure value when the intake sequence is n. The initial value of n is 1.

  Next, the process shown in step S1802 of FIG. 24 will be described with reference to the flowchart of FIG.

  First, in determination unit S1901, PNOW is compared with MAX2 (n). If PNOW is large, the process proceeds to step S1902, and if not, the process proceeds to step S1903.

  In step S1902, PNOW is substituted into MAX2 (n), and the process proceeds to step S1903. In step S1903, it is assumed that this process has been performed once, and FCHK2 is incremented, and the process proceeds to determination unit S1904.

  In determination unit S1904, it is determined whether FCHK2 is 5, and if it is 5, the process proceeds to step S1905, and n is incremented assuming that the process of detecting the minimum pressure value is completed, and the process ends with FEX2 = 0. Otherwise, the process ends.

  As described above, by performing the processing of FIG. 23, FIG. 24, and FIG. 25, it is possible to determine the load before the EVC timing, and from the next crank angle, the intake amount variation maximum cylinder estimation processing according to the load Therefore, it is possible to respond to changes in load more quickly.

  In each of the above embodiments, the case where the present invention is applied to an in-line four-cylinder engine has been described. However, the present invention is not limited to an in-line four-cylinder engine, but can be applied to a multi-cylinder engine having three or more cylinders. It is. Also, the V-type engine can be applied by attaching a communication pipe that connects the throttle downstreams of each bank to each other, or by attaching a communication pipe that connects the throttle downstreams of all cylinders to each other.

DESCRIPTION OF SYMBOLS 1 Engine 2 Intake pipe 3 Throttle valve 4 Throttle actuator 5 Throttle opening detection sensor 6 Communication pipe 7 Pressure detection sensor 8 Crankshaft 9 Crank angle detection sensor 10 Cam angle detection sensor 11 ECU 12 Fuel injection valve 13 Spark plug 14 Intake Valve 15 Exhaust valve 16 Piston

Claims (7)

A control device for an internal combustion engine for controlling an intake air amount to a multi-cylinder internal combustion engine having three or more cylinders,
Intake air amount control means provided in the intake passage of each cylinder of the multi-cylinder internal combustion engine;
A communication pipe connecting the intake passages on the downstream side of the intake air amount control means in each cylinder;
Detection period setting means for setting a period for detecting the pressure in the communication pipe for each cylinder;
Pressure detecting means for detecting the pressure in the communication pipe during the detection period;
First intake air amount variation maximum cylinder estimation means for estimating an intake air amount variation maximum cylinder having the most different intake air amount compared to other cylinders when the load of the internal combustion engine is low;
A second intake air amount variation maximum cylinder estimating means for estimating an intake air amount variation maximum cylinder having the largest intake air amount compared to other cylinders when the load of the internal combustion engine is high;
Switching between the first intake air amount variation maximum cylinder estimating unit and the second intake air amount variation maximum cylinder estimating unit according to the load of the internal combustion engine to estimate a cylinder having the maximum intake air amount variation. A control device for an internal combustion engine. The first intake air amount variation maximum cylinder estimating means includes:
Pressure maximum value detecting means for detecting a pressure maximum value in each detection period for each cylinder;
Maximum value cylinder specifying means for specifying a cylinder corresponding to a maximum value among the maximum pressure values corresponding to the cylinders;
Minimum value cylinder specifying means for specifying a cylinder corresponding to a minimum value among the maximum pressure values corresponding to the cylinders, and
2. The control apparatus for an internal combustion engine according to claim 1, wherein the maximum cylinder for intake air amount variation is estimated from the relationship between the maximum value cylinder and the minimum value cylinder. The second intake air amount variation maximum cylinder estimating means includes:
Pressure minimum value detecting means for detecting a minimum value of pressure in each detection period for each cylinder;
The control apparatus for an internal combustion engine according to claim 1 or 2, wherein it is estimated that the cylinder with the largest intake amount variation is estimated from the relationship between the minimum pressure values for the respective cylinders.   The internal combustion engine control according to claim 1, wherein when the maximum pressure value for any one of the cylinders of the internal combustion engine becomes equal to or greater than a predetermined value, it is determined that the load of the internal combustion engine is high. apparatus.   The load of the internal combustion engine is determined to be a high load when the maximum pressure value for at least two of the cylinders of the internal combustion engine is equal to or greater than a predetermined value. Control device for internal combustion engine.   4. The internal combustion engine according to claim 1, wherein when the pressure immediately before the closing timing of the exhaust valve for each of the cylinders exceeds a predetermined value, it is determined that the load of the internal combustion engine is high. Control device.   The control device for an internal combustion engine according to claim 4, wherein the predetermined value is substantially atmospheric pressure.