JP2016011609A - Internal combustion engine control unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the degradation of emission resulting from a failure in an intake VVT mechanism.SOLUTION: If an air-fuel ratio feedback control is to be executed to correct a fuel injection quantity by comparing an air-fuel ratio of gas flowing in an exhaust passage with a target air-fuel ratio, a variation range of a correction quantity of the fuel injection quantity in the feedback control is restricted by a guard value. Furthermore, if a VVT mechanism capable of varying intake valve timing falls into a state of being unable to return the intake valve timing to most retarded timing, the guard value is changed so as to expand the variation range of the correction quantity of the fuel injection quantity in the feedback control.

Description

  The present invention relates to a control device for controlling an internal combustion engine attached with a variable valve timing (Variable Valve Timing) mechanism.

  2. Description of the Related Art An internal combustion engine mounted on a vehicle is known that includes an intake VVT mechanism that can variably control the opening / closing timing of an intake valve (see, for example, the following patent document). This type of VVT mechanism changes the opening / closing timing of the intake valve by changing the rotational phase of the intake camshaft that drives the intake valve to open / close with respect to the crankshaft that is the output shaft of the internal combustion engine.

JP 2014-0666227 A

  The advance angle of the intake valve timing means the expansion of the valve overlap period in which both the intake valve and the exhaust valve are open. When the advance amount of the intake valve timing is large, the amount of internal exhaust gas recirculation (EGR) gas that is exhaust gas remaining in the cylinder increases, and the amount of fresh air charged in the cylinder decreases accordingly.

  If the VVT mechanism is stuck and the intake valve timing is advanced from the most retarded timing and the VVT mechanism is stuck, the amount of internal EGR will increase from the original assumption. The fuel injection amount must be reduced.

  In general, an ECU (Electronic Control Unit) that controls operation of an internal combustion engine detects an air-fuel ratio of a gas flowing through an exhaust passage via an air-fuel ratio sensor installed in the exhaust passage, and determines the air-fuel ratio and the target air-fuel ratio. Air-fuel ratio feedback control for correcting the fuel injection amount based on the deviation is performed. However, if the increase in the internal EGR amount, that is, the decrease in the fresh air amount due to the fixation of the VVT mechanism exceeds the range that can be corrected by the air-fuel ratio feedback control, the air-fuel ratio remains excessively rich and the harmful substances Increases emissions.

  The present invention, which has been made paying attention to the above problems, is intended to suppress the deterioration of the emission due to the failure of the intake VVT mechanism.

  In the present invention, a control device for controlling an internal combustion engine provided with a variable valve timing mechanism capable of changing an intake valve timing, refers to an output signal of an air-fuel ratio sensor provided on the exhaust passage, and flows through the exhaust passage. The air-fuel ratio feedback control for correcting the fuel injection amount by comparing the air-fuel ratio of the fuel and the target air-fuel ratio is performed, and the fluctuation range of the correction amount of the fuel injection amount in the air-fuel ratio feedback control is regulated by the guard value. When it is detected that the variable valve timing mechanism is fixed and the intake valve timing cannot be returned to the most retarded timing, the fluctuation range of the correction amount of the fuel injection amount in the air-fuel ratio feedback control is set. A control device for an internal combustion engine that changes the guard value so as to be expanded is configured.

  According to the present invention, it is possible to suppress the deterioration of the emission due to the failure of the intake VVT mechanism.

The figure which shows schematic structure of the internal combustion engine and control apparatus of one Embodiment of this invention. The figure which shows the structure of the variable valve timing mechanism accompanying the internal combustion engine of the embodiment. Timing diagram illustrating the pattern of the air-fuel ratio feedback control with reference to the output signal of the rear O ₂ sensor. The graph which illustrates the relationship between control center correction amount FACF and delay time TDR, TDL. Timing diagram illustrating the pattern of the air-fuel ratio feedback control with reference to the output signal of the rear O ₂ sensor. The figure which shows typically the structure of the crank angle sensor accompanying the internal combustion engine of the embodiment. The figure which shows typically the structure of the cam angle sensor accompanying the internal combustion engine of the embodiment. FIG. 3 is a timing diagram showing the interrelationship between strokes, crank angle signals, and cam angle signals of each cylinder of the internal combustion engine. The timing diagram which expands and shows a part of FIG. The flowchart which shows the example of the procedure of the control which the control apparatus of the embodiment implements. The timing diagram which shows the pattern in which the fluctuation | variation of the correction amount FAF of the fuel injection amount in air-fuel ratio feedback control is regulated by the guard value. FIG. 6 is a timing chart showing a pattern in which a variation in a fuel injection amount correction amount FACF in the air-fuel ratio feedback control is regulated by a guard value.

  An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an outline of an internal combustion engine for a vehicle in the present embodiment. The internal combustion engine in the present embodiment is a spark ignition type four-stroke engine and includes a plurality of cylinders 1 (one of which is shown in FIG. 1). In the vicinity of the intake port of each cylinder 1, an injector 11 for injecting fuel is provided. A spark plug 12 is attached to the ceiling of the combustion chamber of each cylinder 1. The spark plug 12 receives spark voltage generated by the ignition coil and causes spark discharge between the center electrode and the ground electrode.

  The intake passage 3 for supplying intake air takes in air from the outside and guides it to the intake port of each cylinder 1. On the intake passage 3, an air cleaner 31, an electronic throttle valve 32, a surge tank 33, and an intake manifold 34 are arranged in this order from the upstream.

  The exhaust passage 4 for discharging the exhaust guides the exhaust generated as a result of burning the fuel in the cylinder 1 from the exhaust port of each cylinder 1 to the outside. An exhaust manifold 42 and an exhaust purification three-way catalyst 41 are disposed on the exhaust passage 4.

Air-fuel ratio sensors 43 and 44 for detecting the air-fuel ratio of the exhaust gas flowing through the exhaust passage are installed upstream and downstream of the catalyst 41 in the exhaust passage 4. Each of the air-fuel ratio sensors 43 and 44 may be an O ₂ sensor having a non-linear output characteristic with respect to the air-fuel ratio of the exhaust gas, or a linear A / F sensor having an output characteristic proportional to the air-fuel ratio of the exhaust gas. There may be. In the present embodiment, an O ₂ sensor that outputs a voltage signal corresponding to the oxygen concentration in the exhaust gas is assumed for each of the upstream and downstream air-fuel ratio sensors 43 and 44 of the catalyst 41. The output characteristics of the O ₂ sensors 43 and 44 show that the output change rate with respect to the air-fuel ratio shows a large and steep slope in a certain range (window) near the stoichiometric air-fuel ratio, and the low saturation value in the lean region where the air-fuel ratio is larger than that. In the rich region where the air-fuel ratio is small, a so-called Z characteristic curve is drawn which gradually approaches the high saturation value.

  The external EGR device 2 realizes a so-called high-pressure loop EGR. The EGR device 21 communicates the upstream side of the catalyst 41 in the exhaust passage 4 and the downstream side of the throttle valve 32 in the intake passage 3, and the EGR passage 21. The EGR cooler 22 provided in the EGR passage and the EGR valve 23 that opens and closes the EGR passage 21 and controls the flow rate of the EGR gas flowing through the EGR passage 21 are used as elements. The inlet of the EGR passage 21 is connected to the exhaust manifold 42 in the exhaust passage 4 or a predetermined location downstream thereof. The outlet of the EGR passage 21 is connected to a predetermined location downstream of the throttle valve 32 in the intake passage 3, specifically to a surge tank 33.

  As shown in FIG. 2, in the internal combustion engine in the present embodiment, a timing chain 74 is wound around a crank sprocket 71, an intake side sprocket 72 and an exhaust side sprocket 73, and the rotational driving force provided from the crankshaft by this timing chain 74. Is transmitted to the intake camshaft via the intake side sprocket 72 and to the exhaust camshaft via the exhaust side sprocket 73.

  In addition, a VVT mechanism 6 is interposed between the intake side sprocket 72 and the intake camshaft. The VVT mechanism 6 in the present embodiment changes the opening / closing timing of the intake valve by changing the rotational phase of the intake camshaft with respect to the crankshaft.

  The housing 61 of the VVT mechanism 6 is fixed to the intake side sprocket 72, and the intake side sprocket 72 and the housing 61 rotate integrally with the crankshaft. On the other hand, the rotor 62 fixed to one end portion of the intake camshaft is housed in the housing 61 and can rotate relative to the intake-side sprocket 72 and the housing 61. A plurality of fluid chambers into which hydraulic fluid flows in and out are formed inside the housing 61, and each fluid chamber is partitioned into an advance chamber 612 and a retard chamber 611 by a vane 621 formed on the outer peripheral portion of the rotor 62. Has been.

  The hydraulic fluid stored in the oil pan 81 is supplied from the hydraulic pump 82 to the hydraulic (hydraulic) circuit of the VVT mechanism 6. The hydraulic pump 82 is driven by power from the internal combustion engine. An OCV (Oil Control Valve) 9 that is a switching control valve is provided between the hydraulic pump 82 and the VVT mechanism 6. By operating the flow rate and direction of the hydraulic fluid via the OCV 9, the hydraulic fluid pumped from the oil pan 81 can be selectively supplied to the advance chamber 612 or the retard chamber 611. Then, the housing 61 rotates relative to the rotor 62, and the opening / closing timing of the intake valve can be advanced or retarded.

  The OCV 9 is a so-called electromagnetic four-way spool valve. As shown in FIG. 2, the OCV 9 has a supply port 91 connected to the discharge port of the hydraulic pump 82, an A port 92 connected to the advance chamber 612 of the housing 61, and a B port connected to the retard chamber 611 of the housing 61. 93 and drain ports 94 and 95 connected to the oil pan 81. The spool of the OCV 9 switches the internal particle path by an advancing and retreating operation, and connects the A port 92 and the B port 93 to one of the supply port 91 and the drain ports 94 and 95, respectively. Further, when the spool 96 is in the neutral position, the internal fluid path is interrupted, and the A port 92 and the B port 93 are not communicated with the supply port 91 and the drain ports 94 and 95. FIG. 2 shows a state where the spool 96 is in the neutral position.

  The spool 96 is driven by a solenoid 97. That is, the advance / retreat distance of the spool 96 changes according to the duty ratio of the pulse current (or voltage) input to the solenoid 97 as the control signal m.

  When the duty ratio of the control signal m is relatively large, the hydraulic fluid pressure discharged from the hydraulic pump 82 is supplied to the advance chamber 612 through the A port 92, while already stored in the retard chamber 611. The hydraulic fluid flows down toward the oil pan 81 through the B port 93, and the vane 621 and the rotor 62 are rotated so that the volume of the advance chamber 612 is enlarged and the volume of the retard chamber 611 is reduced. As a result, the rotational phase of the intake camshaft, in other words, the displacement angle of the intake camshaft with respect to the crankshaft is advanced, and the intake valve timing is advanced.

  On the contrary, when the duty ratio of the control signal m is relatively small, the hydraulic fluid pressure discharged from the hydraulic pump 82 is supplied to the retard chamber 611 through the B port 93, while already stored in the advance chamber 612. The working fluid that has flown down flows toward the oil pan 81 through the A port 92, and the vane 621 and the rotor 62 rotate so that the volume of the retard chamber 611 is expanded and the volume of the advance chamber 612 is decreased. . As a result, the displacement angle of the intake camshaft relative to the crankshaft is retarded, and the intake valve timing is retarded.

  Generally speaking, the valve timing of the intake valve is advanced faster as the duty ratio of the control signal m is larger than neutral, and the valve timing of the intake valve is retarded faster as the duty ratio is smaller than neutral.

  The ECU 0 as the control device for the internal combustion engine of the present embodiment is a microcomputer system having a processor, a memory, an input interface, an output interface, and the like.

  The input interface includes a vehicle speed signal a output from a vehicle speed sensor that detects the actual vehicle speed of the vehicle, a crank angle signal b output from an engine rotation sensor that detects the rotation angle and engine speed of the crankshaft, and depression of an accelerator pedal. Accelerator opening signal c output from a sensor that detects the amount as an accelerator opening (engine output required by the driver, so-called required load), intake air temperature and intake air pressure in intake passage 3 (especially surge tank 33). The intake air temperature / intake pressure signal d output from the temperature / pressure sensor to be detected, the coolant temperature signal e output from the water temperature sensor that detects the coolant temperature indicating the temperature of the internal combustion engine, and the exhaust gas upstream of the catalyst 41 An air-fuel ratio signal f output from an air-fuel ratio sensor 43 that detects the air-fuel ratio, and an air-fuel ratio that detects the air-fuel ratio of exhaust gas downstream of the catalyst 41. The air-fuel ratio signal g outputted from the ratio sensor 44, the intake timing signal serving as a cam angle signal h or the like to be output from the cam angle sensor at a plurality of cam angle of the intake camshaft is input.

  From the output interface, an ignition signal i for the igniter 13 of the spark plug 12, a fuel injection signal j for the injector 11, an opening operation signal k for the throttle valve 32, and an opening operation signal for the EGR valve 23. l, a control signal m or the like is output to the OCV 9.

  The processor of the ECU 0 interprets and executes a program stored in the memory in advance, calculates operation parameters, and controls the operation of the internal combustion engine. The ECU 0 acquires various information a, b, c, d, e, f, g, and h necessary for operation control of the internal combustion engine via the input interface, knows the engine speed, and is charged in the cylinder 1 Estimate the amount of intake (fresh air). Based on the engine speed and intake air amount, etc., the required fuel injection amount, fuel injection timing (including the number of times of fuel injection for one combustion), fuel injection pressure, required EGR rate (or EGR amount), Various operating parameters such as ignition timing and intake valve timing are determined. The ECU 0 applies various control signals i, j, k, l and m corresponding to the operation parameters via the output interface.

  Further, the ECU 0 inputs a control signal o to an electric motor (starter motor or motor generator, not shown) when the internal combustion engine is started (it may be a cold start or a return from an idling stop). Then, cranking is performed by rotating the crankshaft with an electric motor. Cranking ends when the internal combustion engine starts from the first explosion to a continuous explosion and the engine speed, that is, the rotation speed of the crankshaft, exceeds a judgment value determined according to the coolant temperature, etc. (assuming that the explosion has been completed) To do.

The ECU 0 performs feedback control of the air-fuel ratio of the air-fuel mixture filled in the cylinder 1 and, consequently, the air-fuel ratio of the exhaust gas discharged from the cylinder 1 and guided to the catalyst 41. The ECU 0 first determines a basic injection amount TP that is commensurate with the amount of fresh air charged into the cylinder 1. Next, the basic injection amount TP is corrected with a feedback correction coefficient FAF determined according to the air-fuel ratio on the upstream side of the catalyst 41. Further, various correction coefficients K determined according to the state of the internal combustion engine and the invalid injection time of the injector 36 The final fuel injection time (energization time for the injector 11) T is calculated in consideration of TAUV. The fuel injection time T is
T = TP × FAF × K + TAUV
It becomes. Then, the signal j is input to the injector 11 for the fuel injection time T, and the injector 11 is opened to inject fuel.

The feedback control with reference to the air-fuel ratio signal f on the upstream side of the catalyst 41 is performed, for example, when the cooling water temperature of the internal combustion engine is equal to or higher than a predetermined temperature, the fuel is not cut, the power is not increased, and the predetermined time has elapsed from the start of the internal combustion engine. Is performed when all conditions such as the front O ₂ sensor 43 is active and the intake pressure is normal are satisfied.

As shown in FIG. 3, the ECU 0 corresponds to the output voltage f of the front O ₂ sensor 43, which is a sensor for detecting the air-fuel ratio of the gas upstream of the catalyst 41, with the target air-fuel ratio of the gas upstream of the catalyst 41. Compared to a target value (target voltage value; indicated by a one-dot chain line) to be rich, if it is higher than its upstream target value, it is determined to be lean, and if it is lower than its upstream target value, it is determined to be lean. Usually, the target value is a value corresponding to the theoretical air-fuel ratio or the vicinity thereof.

  Then, the ECU 0 adjusts the feedback correction coefficient FAF to increase or decrease based on the determination result of the air / fuel ratio of the gas upstream of the catalyst 41. Specifically, while it is determined that the air-fuel ratio is rich, the feedback correction coefficient FAF is gradually decreased by the lean integral value KIM per unit time (or control cycle, calculation cycle), while the air-fuel ratio is lean. During the determination, the feedback correction coefficient FAF is increased by the rich integral value KIP per unit time.

  When the feedback correction amount FAF decreases, the fuel injection amount by the injector 11 is reduced, and the air-fuel ratio of the air-fuel mixture moves toward lean. On the contrary, when the feedback correction amount FAF increases, the fuel injection amount by the injector 11 is increased, and the air-fuel ratio of the air-fuel mixture becomes richer.

However, when the output voltage f of the front O ₂ sensor 43 fluctuates so as to cross the target voltage value, the determination result of the air-fuel ratio of the gas upstream of the catalyst 41 is not immediately reversed, but the delay times TDL, TDR The judgment result is inverted after waiting for elapse of time. That is, when the output voltage f of the front O ₂ sensor 43 is switched from rich to lean (below the target voltage value), it is determined that the air-fuel ratio has been reversed from rich to lean after the lean determination delay time TDL has elapsed. . In addition, when the output voltage f of the front O ₂ sensor 43 is switched from lean to rich (exceeding the target voltage value), it is determined that the air-fuel ratio has been reversed from lean to rich after the elapse of the rich determination delay time TDR. .

The lean determination delay time TDL and the rich determination delay time TDR are provided because the air / fuel ratio lean / rich determination result is inverted several times in a short time when noise is mixed in the output signal of the O ₂ sensor 43. It is intended to prevent chattering that increases or decreases so that the fuel injection amount vibrates.

  The delay times TDL and TDR increase or decrease according to the control center correction amount FACF. FIG. 4 illustrates the relationship between the correction amount FACF and the delay times TDL and TDR. As the correction amount FACF increases, the lean determination delay time TDL (represented by a broken line) is shortened, and the rich determination delay time TDR (represented by a solid line) is extended. In this case, the time when the feedback correction coefficient FAF starts to decrease is delayed, and the time when the feedback correction coefficient FAF starts to increase increases. As a result, the fuel injection amount increases on average, and the control center of the air-fuel ratio feedback control is displaced to the rich side.

  In turn, the smaller the correction amount FACF, the longer the lean determination delay time TDL and the shorter the rich determination delay time TDR. Then, the time when the feedback correction coefficient FAF starts to decrease from the increase is advanced, and the time when the feedback correction coefficient FAF starts to increase is delayed. As a result, the fuel injection amount decreases on average, and the control center of the air-fuel ratio feedback control is displaced to the lean side.

The ECU 0 also calculates the control center correction amount FACF during the air-fuel ratio feedback control. This correction amount FACF is determined according to the air-fuel ratio on the downstream side of the catalyst 41. Referenced feedback control of the air-fuel ratio signal g on the downstream side of the catalyst 41 is, for example, the cooling water temperature is equal to or higher than a predetermined temperature, and a predetermined time elapses after the start of the air-fuel ratio feedback control, the front O ₂ sensor 43 and / or rear A predetermined time elapses after the O ₂ sensor 44 is activated, the fuel correction amount in the transition period is less than a predetermined value, and the vehicle speed is 0 or less than a predetermined value close to 0 in the idle state or predetermined in the non-idle state. Performed when all conditions such as in the operating range are satisfied.

As shown in FIG. 5, the ECU 0 corresponds to the output voltage g of the rear O ₂ sensor 44, which is a sensor for detecting the air-fuel ratio of the gas downstream of the catalyst 41, with the target air-fuel ratio of the gas downstream of the catalyst 41. Compared to a target value (target voltage value; indicated by a chain line), it is determined to be rich if it is higher than the downstream target value and lean if it is lower than the downstream target value. This downstream target value may not match the upstream target value that is compared with the output signal f of the front O ₂ sensor 43.

  Then, the ECU 0 increases or decreases the control center correction amount FACF based on the determination result of the air-fuel ratio of the gas downstream of the catalyst 41. Specifically, while it is determined that the air-fuel ratio is rich, the control center correction amount FACF is decreased by the lean integrated value FACFKIM per unit time (or control cycle, calculation cycle), while the air-fuel ratio is lean. While it is determined that there is, the control center correction amount FACF is increased by the rich integral value FACFKIP per unit time.

  As already described, when the control center correction amount FACF decreases, the air-fuel ratio control center moves toward lean. Conversely, when the control center correction amount FACF increases, the air-fuel ratio control center moves toward rich.

  Further, the ECU 0 learns the fuel injection amount correction amount FAF and / or FACF calculated through the air-fuel ratio feedback control and uses it for the subsequent control. The ECU 0 is a period in which the correction amount FAF and / or FACF is sufficiently adjusted and does not change under a certain operating region, that is, the amount of change per unit time of the correction amount FAF and / or FACF is 0 or less than a predetermined value. Is stored in the memory in association with a parameter indicating the operation region of the internal combustion engine at that time [engine speed, intake pressure in surge tank 33].

  Thereafter, when transitioning to the same operation region again, the learning value of the correction amount FAF and / or FACF previously stored in the memory (associated with the current operation region) is read out, and the learning value is used. To correct the fuel injection amount. As a result, the fuel injection amount T can be quickly controlled to a suitable value corresponding to the operation region, the time during which the gas air-fuel ratio deviates from the target air-fuel ratio is shortened, and the emission is further improved and the fuel consumption performance is improved. Effective for improvement.

  Note that a certain guard is applied to fluctuations in the correction amounts FAF and FACF calculated in the air-fuel ratio feedback control. That is, as shown in FIG. 11, if the upper limit guard value is exceeded by adding the integral value KIP to the most recent correction amount FAF, the correction amount FAF is clipped to the upper limit guard value, and from the most recent correction amount FAF. When the integral value KIM is subtracted from the lower limit guard value, the correction amount FAF is clipped to the lower limit guard value.

  Similarly, as shown in FIG. 12, when the integral value FACFKIP is added to the most recent correction amount FACF to exceed the upper limit guard value, the correction amount FACF is clipped to the upper limit guard value, and the latest correction amount FACF If the integrated value FACFKIM is subtracted from the lower limit guard value, the correction amount FACF is clipped to the lower limit guard value.

  When the correction amount FAF and / or FACF of the fuel injection amount is clipped to the guard value, the correction amount FAF and / or FACF is not stored in the memory as a learning value.

  The upper limit guard value and the lower limit guard value with respect to the correction amount FAF and / or FACF are the difference in the characteristics of each internal combustion engine due to variations in the components of the internal combustion engine and the like, the transition of the operating range of the internal combustion engine, temporary malfunction, etc. In view of this, the correction amounts FAF and / or FACF are provided in a preventive manner so as not to take an extreme value. If the correction amount FAF and / or FACF of the fuel injection amount is not guarded at all, and the fluctuation range of the correction amount FAF and / or FACF is not regulated, the air-fuel mixture is in a transition period where the operation region of the internal combustion engine changes. Combustion becomes unstable and there is a risk that a shock will occur and adversely affect drivability. In order to eliminate such a risk, the fluctuation range of the correction amount FAF and / or FACF is regulated by the guard value.

  The required value for the required EGR rate, that is, the EGR rate that is the ratio of the EGR gas in the air-fuel mixture filled in the cylinder 1, is highest in the medium load region where the load of the internal combustion engine is medium, and the load decreases as the load decreases. It decreases, and it decreases as the load increases. The required EGR rate is 0 and the opening degree of the EGR valve 23 is also 0 in an idle operation or a low load operation region close to this, or in a high load (or full load) operation region where the accelerator opening is fully open or close to full open. .

  The opening / closing timing of the intake valve takes the most retarded angle position, which is the most retarded timing when the internal combustion engine is started, idling, and in the low load operation region. At the most retarded position, the intake valve of each cylinder 1 opens at a timing near or near the exhaust top dead center of the cylinder 1, and a predetermined crank angle has elapsed after the intake bottom dead center (the crankshaft rotates at the crank angle). Closed at the timing.

  In the middle load or high load operation region, the intake valve timing is advanced from the most retarded position via the VVT mechanism 6. However, in the high-speed operation region, it is preferable to delay the closing timing of the intake valve as the engine speed increases.

  The advance angle of the intake valve timing means an expansion of a valve overlap period in which both the intake valve and the exhaust valve are opened. If the advance amount of the intake valve timing is large, the amount of internal EGR gas remaining in the cylinder 1 in the intake stroke increases, and the amount of fresh air charged in the cylinder 1 decreases. Therefore, the basic amount TP of the fuel injection amount needs to be determined in consideration of the advance amount of the intake valve timing. In the memory of the ECU 0, the relationship between the basic injection amount TP and the operation range of the internal combustion engine [engine speed, intake pressure in the surge tank 33], the opening degree of the EGR valve 23, the advance amount of the intake valve timing, and the like are previously stored. The specified map data is stored. The ECU 0 searches the map using the current operation region of the internal combustion engine, the opening degree of the EGR valve 23, the advance amount of the intake valve timing, and the like as keys, and obtains a basic injection amount TP to be set.

  The advance amount of the intake valve timing implemented by the VVT mechanism 6 is known with reference to the crank angle signal b output from the crank angle sensor and the cam angle signal h output from the cam angle sensor. As shown in FIG. 6, the crank angle sensor senses the rotation angle of the rotor 75 that is fixed to the crankshaft and rotates integrally with the crankshaft. The rotor 75 is formed with teeth or projections 76 at every predetermined angle along the rotation direction of the crankshaft. Typically, each time the crankshaft rotates 10 ° CA, teeth or protrusions 76 are arranged.

  The crank angle sensor faces the outer periphery of the rotor 75, detects that each tooth or protrusion 76 passes near the sensor, and transmits a pulse signal as the crank angle signal b each time. The ECU 0 receives this pulse as the crank angle signal b. The crank angle signal b represents the crank angle, which is the current rotation angle of the crankshaft, and the current position of the piston of each cylinder 1.

  However, the crank angle sensor does not output 36 pulses during one rotation of the crankshaft. The teeth or protrusions 76 of the crankshaft rotor 75 are partially missing. In the example shown in FIG. 6, the seventeenth, eighteenth, twenty-second, and twenty-first cutout portions 761 and the thirty-fifth and thirty-sixth cutout portions 762 are roughly divided into two. There are two missing tooth portions 761, 762. The missing tooth portions 761 and 762 each correspond to a specific rotational phase angle of the crankshaft. That is, the continuous missing tooth portion 761 corresponds to 180 ° CA and 540 ° CA, and the single missing tooth portion 762 corresponds to 0 ° and 360 ° CA.

  Then, as shown in FIG. 8, due to the above-mentioned missing tooth portions 761 and 762, a part of the pulse train of the crank angle signal b is also lost. Based on this defect, it is possible to know the absolute angle of the crankshaft. If the timing of the first pulse after the missing thirty-sixth pulse is 0 ° CA (or 360 ° CA), the timing of the nineteenth pulse following the missing eighteenth pulse is 180 °. That is, CA (or 540 ° CA). The timing of the 0 ° CA pulse is substantially equal to the compression top dead center of a specific cylinder (second cylinder in the illustrated example) 1.

  As shown in FIG. 7, the cam angle sensor also senses the rotation angle of the rotor 77 that is fixed to the intake camshaft and rotates together with the camshaft. The rotor 77 is formed with teeth or projections 78 for each angle obtained by dividing at least one revolution of the intake camshaft by the number of cylinders. In the case of a three-cylinder engine, teeth or protrusions 78 are arranged every time the intake camshaft rotates 120 °.

  The rotational speed of the camshaft is one half of the rotational speed of the crankshaft. Therefore, the above-described teeth or protrusions 78 are arranged every 240 ° CA in terms of the crank angle.

  In addition, in the present embodiment, the rotor 77 is provided with one tooth or projection 79 for generating an additional cam angle signal h between the teeth or projections 78 every 240 ° CA.

  The cam angle sensor faces the outer periphery of the rotor 77, detects that each tooth or protrusion 78, 79 passes near the sensor, and transmits a pulse signal as the cam angle signal h each time. The ECU 0 receives this pulse as the cam angle signal h.

  The basic cam angle signal h generated due to the teeth or protrusions 78 indicates that any cylinder 1 has reached a predetermined stroke. As shown in FIG. 8, the basic cam angle signal h is deviated from the compression top dead center in each cylinder 1 to the advance side by a predetermined crank angle (a value within the range of 30 ° CA to 80 ° CA). It also indicates the timing of the intake valve which is located at the timing and is operated via the VVT mechanism 6.

  Further, the additional cam angle signal h generated due to the teeth or protrusions 79 is an aid for determining the stroke of each cylinder 1. In the example shown in FIGS. 7 and 8, the pulse of the additional cam angle signal h is at a timing advanced by 60 ° CA from the pulse of the basic cam angle signal h representing the vicinity of the compression top dead center of the first cylinder 1. Existing. When these two cam angle signal h pulses are continuously received at an interval of 60 ° CA, which is apparent from the pulse train of the crank angle signal b, the compression top dead center of the first cylinder 1 is immediately after the latter pulse. It turns out that it is.

  The output timing of the cam angle signal h is synchronized with the intake valve timing. That is, the phase difference between the pulse of the cam angle signal h and the opening / closing timing of the intake valve in each cylinder 1 is constant. Therefore, the value of the crank angle when the cam angle signal h is output represents the intake valve timing embodied by the VVT mechanism 6.

  However, there are individual differences in the components of the internal combustion engine (particularly, sprockets 71, 72, 73, timing chain 74, rotors 75, 77, etc.). Therefore, the phase difference between the generation timing of the cam angle signal h and the intake valve timing varies from one internal combustion engine to another, and the relationship between the generation timing of the cam angle signal h and the specific crank angle value also varies from one internal combustion engine to another. It varies.

  Therefore, in order to correctly grasp the advance amount of the intake valve timing, it is necessary to learn in advance the generation timing of the cam angle signal h when the intake valve timing is returned to the most delayed timing. As shown in FIG. 9, the ECU 0 operates the intake valve timing to the most retarded timing via the VVT mechanism 6 during the idling operation in which the accelerator pedal depression amount is 0 or almost 0, and the cam angle signal h Is obtained and stored in the memory as a reference crank angle α representing the most retarded angle position of the VVT mechanism 6.

  In the subsequent control, the crank angle at the timing at which the cam angle signal h is output and the reference crank angle α described above, while appropriately advancing the intake valve timing from the most retarded position according to the operating region of the internal combustion engine, etc. To obtain an advance amount from the most retarded position of the intake valve timing currently implemented by the VVT mechanism 6.

  As an example, a pulse of the cam angle signal h is currently output at a timing of −75 ° CA (0 ° CA to 75 ° CA advance angle), and the reference crank angle α learned during idling of the internal combustion engine is When −35 ° CA (0 ° CA to 35 ° CA minute advance), the intake valve timing is advanced by 40 ° CA from the most retarded position.

  By the way, foreign matter may be caught between the housing 61 and the rotor 62, and the VVT mechanism 6 may be fixed while the intake valve timing is advanced from the most retarded position. If learning of the above-mentioned reference crank angle α is executed in this state, a result of underestimating the advance amount of the intake valve timing in the subsequent control is caused.

  Suppose that the VVT mechanism 6 is fixed in an advanced state in which the pulse of the cam angle signal h is output at a timing of −75 ° CA, and the rotation operation of the rotor 62 becomes impossible. The reference crank angle α learned at this time is −75 ° CA. However, a guard can be applied to the learning value of the reference crank angle α in order to mitigate the adverse effects of erroneous learning of the reference crank angle α. When the guard value of the reference crank angle α is set to −55 ° CA (0 ° CA to 55 ° CA advance angle), the learned value of the reference crank angle α is obtained because −75 ° CA exceeds this guard value. Is clipped to a guard value of −55 ° CA. The learning value −55 ° CA is different from the true value −35 ° CA of the original reference crank angle α, but is closer to the true value than −75 ° CA.

  In the subsequent control of the internal combustion engine, the difference between the crank angle of the timing at which the cam angle signal h is output and the reference crank angle α is calculated to obtain the advance amount from the most retarded position of the intake valve timing. There is no change. Accordingly, if the pulse of the cam angle signal h is currently output at the timing of −75 ° CA, the ECU 0 guards the advance value of the current intake valve timing on the learning value of the reference crank angle α. Otherwise, it will be estimated at 0 ° CA. However, if the reference crank angle α is guarded, the reference crank angle α is set to −55 ° CA, so that the current intake valve timing advance amount is estimated to be 20 ° CA. In other words, the error in the advance amount of the intake valve timing is reduced by the guard.

  However, since the actual intake valve timing is advanced by 40 ° CA from its original most retarded angle position, the advance value of 0 ° CA or 20 ° CA is not appropriate. is there. This underestimation of the advance amount of the intake valve timing leads to an underestimation of the internal EGR amount, and an excessive basic injection amount TP is set with respect to the fresh air amount actually charged in the cylinder 1. Comparing with If the excessive increase in the basic injection amount TP exceeds the range that can be corrected by the air-fuel ratio feedback control (correction amounts FAF, FACF), the emission amount of harmful substances increases, and there is a concern that combustion failure or misfire may occur. Is done.

  Therefore, in this embodiment, when it is detected that the VVT mechanism 6 is fixed and the intake valve timing cannot be returned to the most retarded timing, the fuel injection amount correction amount FAF in the air-fuel ratio feedback control is detected. And the guard value for the correction amount FAF and / or FACF is changed so as to expand the fluctuation range of the FACF.

  FIG. 10 shows a procedure example of processing executed by the ECU 0 according to the present embodiment in accordance with a program. When the ECU 0 detects the possibility that the VVT mechanism 6 is stuck while being advanced from the most retarded position (step S1), the timer counts up (step S2), and the timer reaches a predetermined value. If the VVT mechanism 6 is not fixed even after a lapse of a predetermined time (step S3), the fuel injection amount correction amount FAF and / or the guard value for the FACF is corrected by air-fuel ratio feedback control. Start (steps S4 to S6).

The conditions for determining that the VVT mechanism 6 may be fixed in step S1 are as follows.
The reference crank angle α (absolute value) obtained by performing learning during idling of the internal combustion engine is a predetermined value (for example, −55 ° CA) or a learning value of the reference crank angle α is clipped as a guard value. The advance amount of the intake valve timing obtained by calculating the difference between the crank angle of the timing at which the cam angle signal h is output and the reference crank angle α (in other words, actually measured) can be obtained in the operating range of the internal combustion engine. The crank angle of the timing at which the cam angle signal h is output and the reference crank are deviated from the advance amount of the intake valve timing required (so-called target) accordingly by a predetermined value (for example, 5 ° CA) or more. The advance amount of the intake valve timing obtained by calculating the difference with the angle α is unchanged. The voltage of the output signal f of the front O ₂ sensor 43 is a predetermined value or more and / or the rear O ₂ sensor 44 The voltage of the output signal g is a predetermined value or more. That is, the ECU 0 in which the air-fuel ratio exceeds the predetermined value and the rich / air-fuel ratio feedback correction amount FAF sticks to the lower limit guard value and / or the air-fuel ratio feedback correction amount FACF sticks to the lower limit guard value is When at least one of the conditions listed in the above is satisfied, it is determined that the VVT mechanism 6 may be stuck.

  The ECU 0 regards that the VVT mechanism 6 is fixed and the intake valve timing cannot be returned to the most retarded timing because the step S3 becomes true. Then, the correction of the guard value for the fuel injection amount correction amount FAF and / or FACF is tried.

  In correcting the fuel injection amount correction amount FAF and / or the guard value for the FACF, the guard value is changed by a predetermined amount at each correction opportunity (step S4). As shown in the period T in FIGS. 11 and 12, the ECU 0 of the present embodiment lowers the lower limit guard value related to the fuel injection amount reduction correction by a predetermined amount in step S4. The number of times that the guard value has been corrected is counted (step S5). Thus, these steps S4 and S5 are repeated until it is determined that further correction of the guard value is not necessary (step S6).

The conditions for determining in step S6 that no further correction of the guard value for the fuel injection amount correction amount FAF and / or FACF is necessary are as follows.
The reference crank angle α (absolute value) obtained by performing learning during idling of the internal combustion engine is less than a predetermined value (for example, −55 ° CA), or the learned value of the reference crank angle α is a guard. The value of the advance of the intake valve timing obtained by calculating the difference between the crank angle of the timing at which the cam angle signal h is output and the reference crank angle α is calculated. The deviation from the advance amount of the intake valve timing (so-called target) required in accordance with the operation region or the like is less than a predetermined value (for example, 5 ° CA). Timing when the cam angle signal h is output crank angle and the reference crank angle α and the voltage is less than the predetermined value of the output signal f of the front O ₂ sensor 43 so advance amount of the intake valve timing obtained by calculating the difference changes, and Or less than a predetermined value the voltage of the output signal g of the rear O ₂ sensor 44. That is, the air-fuel ratio exceeds a predetermined value and is no longer rich. The air-fuel ratio feedback correction amount FAF is greater than the lower limit guard value and / or the air-fuel ratio feedback correction amount FACF is greater than the lower limit guard value. The above-listed conditions are that the VVT mechanism 6 is not fixed due to the removal of foreign matter caught between the housing 61 and the rotor 62 or the air-fuel mixture is emptied through air-fuel ratio feedback control. This is established when the fuel ratio can be made to follow the target air-fuel ratio. The ECU 0 ends the correction of the guard value for the correction amount FAF and / or FACF when at least one of the above-listed conditions is satisfied.

  The number of corrections of the guard value counted in step S5 suggests the amount of change between the initial guard value to which the VVT mechanism 6 is fixed and the corrected guard value. Needless to say, the amount of change from the initial guard value, that is, the total amount of correction can be obtained by multiplying the amount of correction of the guard value in step S4 (the amount by which the lower limit guard value is lowered) by the number of corrections counted in step S5. The number of corrections or the total correction amount described above suggests how much the crank angle is advanced from the most retarded angle position.

  In the present embodiment, a control device (ECU) 0 for controlling an internal combustion engine attached with a VVT mechanism 6 capable of changing the intake valve timing, and output signals f of air-fuel ratio sensors 43 and 44 provided on the exhaust passage 4. , G, the air-fuel ratio feedback control for correcting the fuel injection amount by comparing the air-fuel ratio of the gas flowing through the exhaust passage 4 with the target air-fuel ratio is performed. When the variation range of the correction amount FAF and / or FACF is regulated by the guard value, and when it is detected that the VVT mechanism 6 is fixed and the intake valve timing cannot be returned to the most retarded timing, The guard value is changed so as to extend the fluctuation range of the fuel injection amount correction amount FAF and / or FACF in the air-fuel ratio feedback control. To constitute a control apparatus 0 of combustion engine.

  According to the present embodiment, even if the reference crank angle α representing the most retarded position of the intake VVT mechanism 6 is erroneously learned, the VVT mechanism 6 fixes the correction range of the fuel injection amount by the air-fuel ratio feedback control. By expanding it more than normal (especially, lowering the lower limit guard value), the fuel injection amount T can be sufficiently corrected to approach the amount corresponding to the amount of fresh air charged in the cylinder 1. Then, the excessive richness of the air-fuel ratio is eliminated, and an increase in the discharge amount of harmful substances is suppressed.

  The present invention is not limited to the embodiment described in detail above. For example, the intake VVT mechanism 6 in the above embodiment is a vane type that changes the rotational phase angle of the intake camshaft relative to the crankshaft by hydraulic pressure (hydraulic pressure). The motor drive VVT to be realized may be adopted as the intake VVT mechanism 6.

  In addition, the specific configuration of each unit, the processing procedure, and the like can be variously modified without departing from the spirit of the present invention.

  The present invention can be applied to control of an internal combustion engine mounted on a vehicle.

0 ... Control unit (ECU)
4 ... Exhaust passages 43, 44 ... Air-fuel ratio sensors (front O ₂ sensor, rear O ₂ sensor)
6 ... Variable valve timing (VVT) mechanism b ... Crank angle signal f, g ... Output signal of air-fuel ratio sensor (air-fuel ratio signal)
h ... Intake valve timing (cam angle) signal α ... Reference crank angle

Claims (1)

A control device for controlling an internal combustion engine with a variable valve timing mechanism capable of changing an intake valve timing,
Refers to the output signal of the air-fuel ratio sensor provided on the exhaust passage, performs air-fuel ratio feedback control for correcting the fuel injection amount by comparing the air-fuel ratio of the gas flowing through the exhaust passage with the target air-fuel ratio,
While regulating the fluctuation range of the correction amount of the fuel injection amount in the air-fuel ratio feedback control by the guard value,
When it is detected that the variable valve timing mechanism is stuck and the intake valve timing cannot be returned to the most retarded timing, the fluctuation range of the fuel injection amount correction amount in the air-fuel ratio feedback control is expanded. A control device for an internal combustion engine that changes a guard value so that

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