JP4501107B2 - Fuel injection control method for internal combustion engine - Google Patents

Description

  The present invention relates to a fuel injection control method for an internal combustion engine, and more specifically, includes an in-cylinder injector that injects fuel into a cylinder and an intake port injector that injects fuel into an intake port. The present invention relates to a fuel injection control method for a so-called dual injection type internal combustion engine.

  Generally, an in-cylinder injector for injecting fuel into a cylinder and an intake port injector for injecting fuel into an intake port are provided, and these injectors are selected according to the operating region of the engine. There is known a so-called dual injection type internal combustion engine that is used by switching to only one of these, or that both injectors are used in a predetermined operating region.

  As an example of such a dual injection type internal combustion engine, Patent Document 1 includes an intake port injection injector and an in-cylinder injector, and adheres to the inner wall surface of the intake port when port injection is started. Estimates the fuel amount, estimates the inflow amount of attached fuel that flows into the engine combustion chamber when port injection is stopped, and increases the in-cylinder injection amount by the attached fuel amount when port injection is started A fuel injection type internal combustion engine that corrects and corrects the in-cylinder injection amount by an inflow amount when port injection is stopped is disclosed.

JP-A-5-2321221

  However, in the fuel injection type internal combustion engine described in Patent Document 1, the purpose is to solve the problem caused by the attached fuel when the port injection is started or stopped, and the in-cylinder injection is started. There is no mention about.

  By the way, in a dual-injection internal combustion engine, an engine that is used by switching to only one of the injectors depending on the operation region, or only an intake port injection injector is used in some operation regions, and intake port injection is used in other operation regions. In an engine that uses both the in-cylinder and in-cylinder injectors, there is an operating region in which the in-cylinder injector is not used. In such an engine, for example, when the in-cylinder injector is stopped and the operation is performed by injecting only from the intake port injector, the in-cylinder injector is exposed to high-temperature combustion gas. However, since the cooling effect by the injection of itself disappears, the injection characteristic changes due to the heat load. As a result, when the fuel injection from the in-cylinder injector is started, if the fuel is injected from the in-cylinder injector as it is in accordance with a predetermined fuel injection amount as a function of the engine load or the like, a desired fuel injection amount is obtained. Thus, there is a problem in that the air-fuel ratio shifts and the emission is deteriorated and the catalyst temperature is excessively increased.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a fuel injection control method for an internal combustion engine that does not cause a deviation of the air-fuel ratio and can suppress the deterioration of emissions and the excessive increase in catalyst temperature. .

A fuel injection control method for an internal combustion engine according to an aspect of the present invention that achieves the above object includes an in-cylinder injector that injects fuel into a cylinder and an intake port injection that injects fuel into an intake port. In an internal combustion engine provided with an injector, when fuel injection from the in-cylinder injector is stopped and fuel injection from the in- cylinder injector is started after fuel injection from only the intake port injector The fuel injection amount is corrected in accordance with the temperature at the fuel injection start time of the in-cylinder injector that rises during the fuel injection stop period .

  Here, the correction of the fuel injection amount is preferably performed by gradually decreasing the correction amount in accordance with the elapsed time from the start of fuel injection from the in-cylinder injector or the fuel injection amount.

  Further, it is preferable that the fuel injection from the intake port injection injector is set to the intake-synchronized injection before the start of fuel injection from the in-cylinder injector.

  According to a fuel injection control method for an internal combustion engine according to an aspect of the present invention, it is provided with an in-cylinder injector that injects fuel into a cylinder and an intake port injector that injects fuel into an intake port. In the internal combustion engine, when fuel injection from the in-cylinder injector is started, the fuel injection amount is corrected according to the temperature of the in-cylinder injector, so that a desired fuel injection amount is secured. Therefore, the deviation of the air-fuel ratio does not occur, and it is possible to suppress the deterioration of the emission and the excessive increase of the catalyst temperature.

  Here, according to the mode in which the correction of the fuel injection amount is performed by gradually decreasing the correction amount corresponding to the elapsed time from the start of fuel injection from the in-cylinder injector or the fuel injection amount, The injector is cooled by its own injection and returns to a normal injection characteristic state corresponding to the elapsed time from the start of fuel injection or the fuel injection amount, so that a desired fuel injection amount is secured even after a predetermined time has elapsed.

  In addition, according to the mode in which the fuel injection from the intake port injector is changed to the intake-synchronized injection before the start of the fuel injection from the in-cylinder injector, the intake air is filled with the latent heat due to the vaporization of the intake-synchronized fuel. At the same time as efficiency increases, mixing is improved and combustion is improved.

  Embodiments of the present invention will be described below with reference to the drawings. First, an overall configuration of a dual injection internal combustion engine with a supercharger to which the present invention is applied will be described with reference to FIG. In the figure, reference numeral 10 denotes an engine with a variable valve timing mechanism and a supercharger (hereinafter simply referred to as “engine”). In the figure, an intake port injection injector and an in-cylinder injection injector are provided. Shows a gasoline engine. The cylinder block 11 of the engine 10 is provided with a cylinder head 12, and an intake port 13 and an exhaust port 14 are formed in the cylinder head 12 for each cylinder.

  As an intake system of the engine 10, an intake manifold 15 communicates with each intake port 13, and a throttle chamber 18 in which a throttle valve 17 is interposed via a surge tank 16 in which intake passages of the respective cylinders gather in the intake manifold 15. It is communicated. The throttle valve 17 is driven by a throttle motor 19. An intercooler 20 is interposed upstream of the throttle chamber 18, and the intercooler 20 communicates with a compressor 22 </ b> C of a turbocharger 22 as an example of a supercharger via an intake pipe 21, and further communicates with an air cleaner 23. Has been.

  An intake port injection injector 31 is disposed immediately upstream of the intake port 13 of each cylinder of the intake manifold 15, and fuel is directly injected into the cylinder head 12 into the combustion chamber of each cylinder in the cylinder block 11. An in-cylinder injector 33 is disposed. Each of the in-cylinder injectors 33 is connected to a fuel delivery pipe 35 to which high-pressure fuel is supplied from a high-pressure fuel pump 34. Further, a spark plug 36 is provided for each cylinder of the cylinder head 12.

  On the other hand, as an exhaust system of the engine 10, exhaust is joined by an exhaust manifold 25 communicating with each exhaust port 14 of the cylinder head 12, and an exhaust pipe 26 is connected to the exhaust manifold 25. Then, a turbine 22T of the turbocharger 22 is interposed in the exhaust pipe 26, and a catalyst, a muffler, and the like are disposed downstream thereof and released to the atmosphere. In the turbocharger 22, the compressor 22 </ b> C is rotationally driven by the energy of the exhaust gas flowing into the turbine 22 </ b> T, and sucks and pressurizes air to supercharge the turbocharger 22. In order to adjust the pressure, a variable nozzle 28 having a variable nozzle actuating actuator 27 composed of an electric actuator is provided. The variable nozzle actuation actuator 27 controls the supercharging pressure by adjusting the opening of the variable nozzle 28 in accordance with a control signal output from an electronic control unit (hereinafter referred to as ECU) 100 described later.

  Here, the variable valve timing mechanism of the engine 10 will be described. As is well known, the crankshaft 51 of the engine 10 is rotated by an intake camshaft and an exhaust camshaft respectively disposed in the cylinder head 12, a crank pulley fixed to the crankshaft 51, a timing belt, an intake cam pulley, It is transmitted through an exhaust cam pulley or the like, and the crankshaft 51 and the camshaft are set to have a 2-to-1 rotation angle. The intake cam provided on the intake camshaft and the exhaust cam provided on the exhaust camshaft (both not shown) are rotated at a rotation angle of 2: 1 with the crankshaft 51, respectively. Based on this, the intake valve 40 and the exhaust valve 41 are opened and closed.

  Between the intake camshaft and the intake cam pulley, the intake cam pulley and the intake camshaft are relatively rotated to continuously change the rotation phase (displacement angle) of the intake camshaft with respect to the crankshaft 51. A valve timing mechanism InVVT is provided. As is well known, this variable valve timing mechanism InVVT is hydraulically switched by an oil control valve 42 such as a linear solenoid valve or a duty solenoid valve, and operates according to a drive signal from an ECU 100 for engine control described later. .

  Similarly, between the exhaust camshaft and the exhaust cam pulley, a hydraulic drive that continuously changes the rotational phase (displacement angle) of the exhaust camshaft with respect to the crankshaft 51 by relatively rotating the exhaust cam pulley and the exhaust camshaft. A variable valve timing mechanism ExVVT of the type is provided. The variable valve timing mechanism ExVVT, as with the intake side variable valve timing mechanism InVVT, is switched in oil pressure by an oil control valve 43 and is operated by a drive signal from an ECU 100 for engine control described later.

  Next, various sensors for detecting the engine operating state will be described. An air flow meter 101 and a temperature sensor 102 are interposed immediately downstream of the air cleaner 23 and the intercooler 20 in the intake pipe 21. In addition, a throttle position sensor 103 that is disposed in the throttle chamber 18 and detects the opening degree of the throttle valve 17 for adjusting the amount of air is connected, and the surge tank 16 is provided with an intake pipe pressure sensor 104. ing. Further, a fuel pressure sensor 105 for detecting fuel pressure is provided in the fuel delivery pipe 35, a knocking sensor 106 is attached to the cylinder block 11 of the engine 10, and a cooling water temperature sensor 107 is provided in the cylinder block 11. Further, a back pressure sensor 108 is disposed downstream of the joining portion where the exhaust manifold 25 joins.

  The intake-side variable valve timing mechanism InVVT and the exhaust-side variable valve timing mechanism ExInVVT are arranged on the outer periphery of a cam rotor that is fixed to the intake camshaft and the exhaust camshaft and rotates synchronously as a sensor for detecting the operation position. An intake-side cam position sensor 109 and an exhaust-side cam position sensor 110 that detect a plurality of formed protrusions at equal angles and output a cam position pulse representing the cam position are provided. In addition, a crank position sensor 111 is provided that detects protrusions at predetermined crank angles formed on the outer periphery of the crank rotor 52 that is attached to the crankshaft 51 and rotates synchronously, and outputs a crank pulse representing the crank angle. . Further, an air-fuel ratio sensor 112 is disposed downstream of the turbine 22T of the turbocharger 22. Reference numeral 113 denotes an accelerator opening sensor that generates an output voltage proportional to the amount of depression of the accelerator pedal.

  In FIG. 1, reference numeral 100 denotes an electronic control unit (hereinafter referred to as “ECU”), which processes signals from the various sensors described above to calculate control amounts for the various actuators, and performs fuel injection control, ignition It performs timing control, idle speed control, supercharging pressure control, valve timing control for intake valves and exhaust valves, and the like. The ECU 100 is composed mainly of a microcomputer to which a CPU, a ROM, a RAM, a backup RAM, a counter / timer group, an I / O interface, and the like are connected via a bus line, and supplies a stabilized power source to each part. Peripheral circuits such as a drive circuit connected to the I / O interface and an A / D converter are incorporated. The input port of the I / O interface includes an air flow meter 101, a temperature sensor 102, a throttle position sensor 103, an intake pipe pressure sensor 104, a fuel pressure sensor 105, a knocking sensor 106, a cooling water temperature sensor 107, a back pressure sensor 108, a cam. Position sensors 109 and 110, a crank position sensor 111, an air-fuel ratio sensor 112, an accelerator opening sensor 113, a vehicle speed sensor for detecting the vehicle speed, and the like are connected.

  On the other hand, the output port of the I / O interface includes a throttle motor 19, a variable nozzle actuating actuator 27, an intake port injector 31, a cylinder injector 33, a high pressure fuel pump 34, an ignition coil 36, and an oil control valve 42. And 43 are connected via a drive circuit.

  The ECU 100 processes detection signals from sensors input via the I / O interface according to a control program stored in the ROM, and stores various data stored in the RAM and the backup RAM. Engine operation control such as fuel injection amount and timing control, ignition timing control, supercharging pressure control, and valve timing control is performed based on various learning value data and fixed data such as a control map stored in the ROM.

  Here, one form of the control routine of the fuel injection control method in the engine configured as described above will be described with reference to the flowchart of FIG. In this control routine, the fuel injection amount and timing are determined on the basis of the engine load and the engine speed determined in correspondence with the control object from any one of the air flow meter 101, the intake pipe pressure sensor 104, and the accelerator opening sensor 113. Fuel injection control, a valve timing control through variable valve timing mechanisms InVVT and ExVVT, valve overlap amount control in which both the intake valve and the exhaust valve are opened, and supercharging through the turbocharger 22 This is executed every 180 degrees of rotation of the crankshaft 51 as a part of a normal control routine for controlling the engine to an optimum state such as pressure control.

  First, when control is started, the electronic control unit 100 determines the engine load obtained by detection from the accelerator opening sensor 113 and the air flow meter 101 at every predetermined time and the engine speed obtained by calculation from the crank position sensor 111. To determine the operating state of the engine or the switching request region. That is, in step S21, the port injection (Pi) region “1” in which fuel is injected only from the intake port injection injector 31 or the direct injection from the in-cylinder injector 33 in addition to this port injection (Pi) ( It is determined whether the port injection (Pi) + direct injection (Di) region “2” in which Di) is also performed. In the present embodiment, these areas “1” and “2” are determined substantially corresponding to the engine load, as shown in FIG. 3 (A). “1” is the region “2” under the high load operation condition. In the region “2”, the fuel injection amount ratio from the intake port injector 31 and the in-cylinder injector 33 is generally set as shown in FIG.

  Therefore, if it is determined in step S21 that switching of the region is not necessary, that is, if “No”, the port injection (Pi) that is the fuel injection from only the intake port injection injector 31 is continued. Exit. On the other hand, when switching is necessary, in other words, when direct injection (Di) is performed in addition to port injection (Pi), that is, when it is necessary to start fuel injection from the in-cylinder injector 33, step In S22, the timer time t is set to 0 in order to obtain the start time. Further, in step S23, it is determined whether or not the set time t has passed the predetermined time B. When the predetermined time B has not elapsed, that is, in the case of “No”, the process proceeds to step S24, and the fuel injection amount from the in-cylinder injector 33 is corrected.

  Here, the correction of the fuel injection amount will be described. Now, let Qmin be the minimum fuel injection amount that is a controllable injection amount from the in-cylinder injector 33, and let Qmin0 be the minimum fuel injection amount in the steady state. Further, the minimum fuel injection amount at the temperature T when the in-cylinder injector 33 is exposed to the high-temperature combustion gas during the stop and rises to the temperature T as a result of the change in the injection characteristic is defined as QminT. Then, the minimum fuel injection amount when the fuel injection is started from the in-cylinder injector 33 (t = 0) and the time t has elapsed within the predetermined time B after the cooling operation starts is defined as QminT (t). On the other hand, when the correction coefficient for correcting the fuel injection amount is At, the correction coefficient at the temperature T is AtT, the correction coefficient when the time t has elapsed is AtT (t), and the predetermined time B has elapsed. After that, At = 1. The above relationship is illustrated in FIG.

Therefore, in step S24, the minimum fuel injection amount QminT at the temperature T of the in-cylinder injector 33 is obtained from the operating state using the engine load and the rotation speed as parameters as the parameters before starting the injection. This map value is obtained in advance by experiments or the like and stored in the ROM according to the type of the in-cylinder injector 33 used. At the same time, the correction coefficient AtT corresponding to this is obtained in the same manner. Therefore, the corrected fuel injection amount Q from the in-cylinder injector 33 is obtained using the following equation as the fuel injection amount Q (t) when the time t has elapsed.
Q (t) = QminT * AtT (t)

  The required fuel injection amount supplied for the entire engine is stored in a map according to the operating conditions, and is determined as shown in FIG. 3B and intake port injection injector 31 and in-cylinder injection. The fuel injection amount from the intake port injection injector 31 is based on the corrected fuel injection amount Q (t) from the in-cylinder injector 33 in accordance with the ratio of the fuel injection amount from the fuel injector 33. Desired. Thus, when the fuel injection from the in-cylinder injector 33 is started, the above-described corrected fuel injection amount is injected from the in-cylinder injector 33, so that it is possible to prevent an air-fuel ratio shift or the like from occurring. Is done.

  After step S24, the process proceeds to step S25, the timer time t is incremented by 1, and the process returns to step S23 again. In step S23, as described above, it is determined whether or not the time t has passed the predetermined time B. Unless the predetermined time B has elapsed, the process proceeds to step S24, and as described above, the in-cylinder injection is performed. The fuel injection amount from the injector 33 is corrected. However, in this case, as a result of the fuel injection from the in-cylinder injector 33, the temperature is lowered by the cooling action, so the correction coefficient AtT (t) is also reduced, and the correction amount itself is also reduced. . When the time t has passed the predetermined time B, the routine proceeds to step S26, where the steady fuel injection amount Q from the in-cylinder injector 33 is obtained as Q = Qmin0 * 1. Thus, a desired fuel injection amount from the in-cylinder injector 33 is ensured even after a predetermined time has elapsed.

  Instead of the elapsed time from the start of fuel injection described above, the amount of fuel injection from the start of fuel injection may be integrated to estimate the degree of nozzle cooling, and Qmin may be corrected.

  Next, the control of the second embodiment of the fuel injection control method for the internal combustion engine of the present invention will be described below. In the present embodiment, as shown in FIG. 5, in the middle / low load operation region “1” of the engine 10, port injection (Pi) is performed only from the intake port injector 31, and the intake port injection Port injection (Pi) + for injecting fuel from both the in-cylinder injector 33 and the intake port injector 31 from an operating state in which injection from the injector 31 is not performed in synchronism with the intake stroke and is performed by so-called asynchronous injection This is to be dealt with when shifting to the direct injection (Di) operation state.

  Therefore, when the control is started, the current engine load and rotation speed are acquired in step S61 in the flowchart shown in FIG. In step S62, it is determined whether or not the engine load is equal to or greater than a predetermined load. The predetermined load is a load just before the transition that is slightly below the boundary line between the middle / low load operation region “1” and the high load operation region “2” shown in FIG. If it is determined in step S62 that the load is equal to or greater than the predetermined load, the process proceeds to step S62, and the injection timing of the port injection (Pi) is changed from intake asynchronous injection to intake synchronous injection. On the other hand, if it is determined in step S62 that the load is less than the predetermined load, the process proceeds to step S64, and the port injection (Pi) injection timing is continued without being changed. Thus, if the fuel injection from the intake port injector 31 is changed to the intake-synchronized injection before the start of the fuel injection from the in-cylinder injector 33, the intake air is caused by the latent heat due to the vaporization of the intake-synchronized fuel. At the same time, the mixing efficiency is improved and mixing is improved, and combustion is improved.

  In the above-described embodiment, in order to obtain the corrected fuel injection amount Q, the minimum fuel injection amount and the correction coefficient are separately obtained and calculated from them, but this is the temperature of the in-cylinder injector. Or by estimating the temperature from the operating state before the start of fuel injection, a map of the corrected fuel injection amount may be created in advance so as to directly correspond to these temperatures. Good.

1 is a schematic diagram showing a schematic configuration of an internal combustion engine to which a fuel injection control method according to the present invention is applied. It is a flowchart which shows an example of control of the fuel-injection control method which concerns on this invention. In one Embodiment of this invention, it is a graph which shows (A) the injection form corresponding to the driving | operation area | region, and (B) injection ratio. In one embodiment of the present invention, it is a graph explaining a fuel injection amount correction method. In other embodiment of this invention, it is a time chart explaining a mode when it transfers to a fuel injection start. It is a flowchart which shows an example of the control in other embodiment of the fuel-injection control method of this invention.

Explanation of symbols

31 Injector for intake port injection 33 Injector for in-cylinder injection 100 Electronic control unit

Claims (3)

In an internal combustion engine comprising an in-cylinder injector that injects fuel into a cylinder and an intake port injector that injects fuel into the intake port,
When the fuel injection from the in-cylinder injector is stopped and the fuel injection from the in- cylinder injector is started after the fuel injection from only the intake port injector, the fuel injection is stopped during the fuel injection stop period. A fuel injection control method for an internal combustion engine, wherein the fuel injection amount is corrected in accordance with the temperature of the fuel injection start time of the rising in-cylinder injector. 2. The correction of the fuel injection amount is performed by gradually decreasing the correction amount corresponding to the elapsed time from the fuel injection start time from the in-cylinder injector or the fuel injection amount. A fuel injection control method for an internal combustion engine according to claim 1.   3. The fuel injection control for an internal combustion engine according to claim 1 or 2, wherein the fuel injection from the intake port injection injector is changed to intake synchronous injection before the start of fuel injection from the in-cylinder injector. Method.

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