JP4722676B2 - Fuel injection control device for multi-cylinder engine - Google Patents

Description

  The present invention relates to a fuel injection control device for a multi-cylinder engine that appropriately controls a fuel injection amount at the time of starting an engine to reduce exhaust emission and improve fuel efficiency.

  Conventionally, the required fuel injection amount at start-up is affected by the external environment of the engine (outside air temperature, cooling water temperature as engine temperature, fuel temperature, etc.), but is generally set based only on the cooling water temperature. ing.

  In the case of cold start or the like where the coolant temperature is low, the fuel adhering to the wall surface such as the intake port is difficult to vaporize, so the fuel injection amount at start is set to an increased value. On the other hand, since the fuel adhering to the wall surface of the intake port or the like is easily vaporized when restarting at a relatively high coolant temperature, the starting fuel injection amount is set to a reduced value. Then, after starting, the fuel injection amount at start-up is shifted to normal operation as the cooling water temperature increases or gradually decreased.

  As a technique for controlling the fuel injection amount at the start, for example, in Patent Document 1 (Japanese Patent Laid-Open No. 2002-213280), the fuel increase is not initially performed at the start, and the fuel increase is corrected after a predetermined time has elapsed after the start operation. By performing the above, a technology is disclosed in which the engine is started with a minimum amount of fuel, exhaust gas emission during starting is reduced, and fuel consumption is improved.

  Further, in Patent Document 2 (Japanese Patent Application Laid-Open No. 2004-183502), in one combustion cycle (hereinafter referred to as “first combustion cycle”) performed after the engine is started, the amount of fuel adhering to the wall surface is added based on the cooling water temperature. In the second combustion cycle, the primary fuel injection amount is set, and the secondary fuel injection amount in which the amount of fuel adhering to the wall surface during the first combustion cycle is subtracted based on the coolant temperature is determined in the second combustion cycle that is continuous with the first fuel cycle. It is disclosed.

According to the technique disclosed in Patent Document 2, since the amount of fuel adhering to the wall surface is added to the fuel injection amount during the initial combustion cycle, leaning of the air-fuel ratio is prevented. Further, since the fuel adhering to the wall surface at the first combustion cycle is subtracted from the fuel injection amount at the second combustion cycle, enrichment of the air-fuel ratio can be prevented.
JP 2002-213280 A JP 2004-183502 A

  In the technology disclosed in each of the above-described patent documents, the initial combustion cycle at the time of starting performs fuel injection control uniformly with the primary fuel injection amount set based on the coolant temperature.

  However, when the fuel injection amount of the initial combustion cycle is uniformly controlled, for example, in the case of an engine in which the fuel injection timing is set while the intake valve is closed in a port injection type injector, When the fuel injection target cylinder in the eye is in the intake stroke, the first fuel injection target cylinder reaches the expansion stroke and the first explosion (first combustion) is performed. Therefore, during the intake stroke of the third fuel injection target cylinder, work by combustion is performed for the first time, engine torque is generated, and the engine speed increases.

  When the engine speed increases, the closing timing of the exhaust valve is advanced, and accordingly, the backflow of the intake air to the intake port side is reduced. Therefore, the volume efficiency of the third injection target cylinder is increased.

  FIG. 10 shows the relationship between the stroke of each cylinder of the 4-cylinder engine and the engine speed. As shown in FIG. 4C, when the combustion order of the four-cylinder engine is # 3 → # 2 → # 4 → # 1, and the first injection cylinder (exhaust stroke) after the start is cylinder # 3, Fuel injection is performed in order from the cylinder # 3. Thereafter, as shown in FIG. 5B, when the cylinder # 3 is in the intake stroke and the intake valve is opened, the fuel injected into the exhaust port is supplied into the cylinder together with the intake air to become an air-fuel mixture. . The air-fuel mixture in the cylinder burns during the expansion stroke, as shown in FIG. Therefore, when the engine is started, work by combustion is not performed and the engine torque does not increase until the fuel injected into the first injection cylinder (exhaust stroke) reaches the expansion stroke after the third stroke.

  On the other hand, as shown by the solid line in FIG. 5A, when the cylinder # 3, which has initially injected fuel, reaches the expansion stroke and performs work by combustion, engine torque is generated by this initial explosion and engine rotation occurs. The number Ne increases. Therefore, the volumetric efficiency of cylinder # 4 in the intake stroke at that time increases. However, since the fuel supplied to the cylinder # 4 is already injected in the exhaust stroke, the air-fuel ratio of the cylinder # 4 becomes lean.

  Therefore, as indicated by the solid line in FIG. 5A, even if the cylinder # 4 performs work due to combustion in the expansion stroke, the generated engine torque is insufficient because the air-fuel ratio is lean, and the engine speed Ne Increase rate (N3-N2) becomes lower than the increase rate (N2-N1) of the engine speed Ne due to combustion of the previous cylinder # 2. In addition, this causes an increase in the engine speed Ne (N4-N3) due to the combustion of the next cylinder # 1, resulting in instability of starting up of the engine speed at start-up. . The characteristic indicated by the broken line in FIG. 10A indicates the engine speed Ne that can be obtained by this embodiment, and this characteristic will be described later.

  As a countermeasure, it is conceivable to detect changes in the engine speed Ne or the intake pipe pressure downstream of the throttle valve, and to correct the fuel injection amount in response to these changes, but the control response is not sufficient and the initial combustion is It is difficult to properly correct the fuel injection amount in the cycle.

  Although it is conceivable to increase the fuel injection amount set during the first combustion cycle in anticipation of an increase in volumetric efficiency, the first and second injection cylinders ((# 3, # 2 in FIG. 10 (c)). The fuel injection amount to be supplied to () is wasted by the increased amount, and there is a problem that fuel consumption and exhaust emission deteriorate.

  On the other hand, even if the fuel injection at the start is performed in the intake stroke, such as a lean burn engine, the first explosion is performed in the expansion stroke after the second stroke, so the intake stroke occurs in the first explosion. The air-fuel ratio of the cylinder becomes lean, causing the same problem as described above.

  Such a tendency is not limited to a four-cylinder engine, and similarly appears in a six-cylinder engine. Since the first injection cylinder is subjected to the initial explosion and engine torque is generated, the cylinder in the intake stroke at that time. Since the volumetric efficiency of the cylinder increases, the air-fuel ratio of the cylinder temporarily becomes lean.

  In view of the above circumstances, the present invention can appropriately control the air-fuel ratios of all the cylinders in the initial combustion cycle to realize a smooth start-up of the engine speed, as well as improve fuel efficiency and reduce exhaust emissions. An object of the present invention is to provide a fuel injection control device for a multi-cylinder engine capable of performing the same.

In order to achieve the above object, the present invention comprises initial fuel injection amount setting means for setting the fuel injection amount at the start of each cylinder during the initial combustion cycle based on the engine temperature, and the start time set during the initial fuel cycle. In a fuel injection control device for a multi-cylinder engine that performs work by combustion in the expansion stroke of each cylinder at the fuel injection amount, the start-up fuel injection amount set by the initial fuel injection amount setting means is the first fuel injection. A primary fuel injection amount for the remaining cylinders excluding the other cylinders in the intake stroke when the cylinder is in the expansion stroke, and a secondary fuel injection amount for the other cylinders, the primary fuel injection amount being the engine is set based on the engine temperature at the start, increased by increasing the engine speed at the time of the expansion stroke of the cylinder in which the secondary fuel injection amount is fuel is injected the first Is the fact characterized.

  According to the present invention, since the fuel injection amount of the cylinder in the intake stroke at the time of the first explosion is increased by an amount corresponding to the increase in volumetric efficiency, the air-fuel ratios of all the cylinders in the initial combustion cycle are appropriately controlled, and the engine rotation Not only can the number of smooth rises be realized, but also fuel efficiency can be improved and exhaust emissions can be reduced.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of an engine, and FIG. 2 is a circuit configuration diagram of an electronic control system.

  Reference numeral 1 in FIG. 1 denotes a multi-cylinder engine (hereinafter simply referred to as “engine”), and in the figure, a horizontally opposed four-cylinder engine is shown. Cylinder heads 2 are provided in both the left and right banks of the cylinder block 1a of the engine 1, and an intake port 2a and an exhaust port 2b are formed in each cylinder head 2 for each cylinder.

  Further, the downstream end of the intake manifold 3 communicates with each intake port 2 a, and the upstream side of the intake manifold 3 is gathered in the air chamber 4. Further, a throttle chamber 5 communicates with the upstream side of the air chamber 4, an intake pipe 6 communicates with the upstream side of the throttle chamber 5, and an air cleaner 7 is attached to the upstream end of the intake pipe 6, and is connected to the air cleaner 7. The chamber 8 communicates with the air intake passage.

  A throttle valve 5a is interposed in the throttle chamber 5 described above. The throttle valve 5a is an electronically controlled throttle valve that is driven to open and close by a throttle actuator 5b serving as a driving means constituted by, for example, a stepping motor.

  In addition, at the downstream end of the intake manifold 3, an injector 11 whose injection direction is directed to the intake valve is disposed in each of the cylinders # 1 to # 4. In addition, the cylinder head 2 is provided with spark plugs 12 in the cylinders # 1 to # 4 that expose the discharge electrode at the tip to the combustion chamber of each cylinder.

  In this embodiment, the cylinder rows are arranged in two rows (RH, LH), and the pistons of each cylinder row are alternately connected to the crankshaft 30 via connecting rods (not shown). Yes. Cylinders # 1 and # 3 are arranged on the RH side, and cylinders # 2 and # 4 are arranged on the LH side, and the injection order (ignition order) is # 1 → # 3 → It is set from # 2 to # 4.

  Further, the upstream end of the exhaust manifold 14 is communicated with each exhaust port 2 b of the cylinder head 2, and the downstream side of the exhaust manifold 14 is gathered and communicated with the exhaust pipe 15. A catalyst 16 is interposed on the upstream side of the exhaust pipe 15, and a muffler 17 is communicated with the downstream side.

  Next, sensors and switches for detecting the operating state of the engine 1 will be described. An intake air amount sensor 20 for detecting the amount of intake air taken in via the air cleaner 7 is provided immediately downstream of the air cleaner 7 of the intake pipe 6. A throttle valve 5 a disposed in the throttle chamber 5 has a throttle opening degree. A throttle opening sensor 21 for detecting is continuously provided. Further, a cooling water temperature sensor 24 for detecting a cooling water temperature that is representative of the engine temperature is provided in the cooling water passage 23 that communicates between the left and right banks of the cylinder block 1 a of the engine 1. On the other hand, an air-fuel ratio sensor 25 that detects the air-fuel ratio from the oxygen concentration in the exhaust gas is disposed upstream of the catalyst 16. Further, a crank angle sensor 32 is provided on the outer periphery of the crank rotor 31 that is attached to the crankshaft 30 of the engine 1, and a cylinder discrimination sensor 34 is provided on the back surface of the intake cam pulley 33 that rotates 1/2 with respect to the crankshaft 30. It is opposite.

  In FIG. 2, reference numeral 50 denotes an engine control unit (E / G_ECU), which is mainly configured by a computer such as a microcomputer to which a CPU 51, ROM 52, RAM 53, backup RAM 54, and I / O interface 56 are connected via a bus line. Peripheral circuits such as a constant voltage circuit 57 for supplying a stabilized power supply to each unit, a drive circuit 58 connected to the I / O interface 56, and an A / D converter 59 are incorporated.

  The constant voltage circuit 57 is connected to the battery 61 via one relay contact of the power relay 60, one end of the relay coil is grounded, and the other end of the relay coil is connected to the drive circuit 58. Note that one end of an ignition switch 62 is connected to the battery 61, and the other end of the ignition switch 62 is connected to an input port of the I / O interface 56.

  Further, the constant voltage circuit 57 is directly connected to the battery 61. When the ignition switch 62 is detected to be turned on and the contact of the power relay 60 is closed, the constant voltage circuit 57 supplies power to each part in the E / G_ECU 50. Regardless of whether the ignition switch 62 is ON or OFF, the backup RAM 54 is always supplied with backup power.

  A starter motor 64 is connected to the battery 61 via a relay contact of the starter relay 63. Furthermore, one end of the relay coil of the starter relay 63 is grounded, and the other end is connected to the drive circuit 58. The relay coil of the starter relay 63 is energized when a starter switch 35 described later is turned on, and the relay contact is turned on.

  The input port of the I / O interface 56 is connected to an accelerator position sensor 65, a crank angle sensor 32, a cylinder discrimination sensor 34, a starter switch 35, and the like that detect the amount of depression of an accelerator pedal (not shown). Further, the intake air amount sensor 20, the throttle opening sensor 21, the cooling water temperature sensor 24, and the air-fuel ratio sensor 25 are connected via the A / D converter 59, and the battery voltage VB is input and monitored. .

  On the other hand, an actuator such as the throttle actuator 5 b and the injector 11 is connected to the output port of the I / O interface 56 via a drive circuit 58.

  The E / G_ECU 50 processes the detection signals from the sensors and switches, the battery voltage, and the like input via the I / O interface 56 by the CPU 51 according to the control program stored in the ROM 52 and is stored in the RAM 53. On the basis of various data stored in the backup RAM 54, fixed data stored in the ROM 52, etc., the fuel injection amount, throttle opening, etc. are calculated, and various operations such as air-fuel ratio control and idle speed control are performed. Take control.

  In accordance with the control program stored in the ROM 52, the CPU 51 calculates the engine speed Ne from the crank pulse from the crank angle sensor 32, calculates the fuel injection start timing based on the specific crank pulse, Based on the cam pulse from the cylinder discrimination sensor 34 that is interrupted between the pulse and the next crank pulse, cylinder discrimination of the fuel injection target cylinder is performed.

  Further, during normal operation, the fuel injection amount TAUGn is obtained based on the engine load Gn, and this fuel injection amount TAUGn is corrected with various correction values set based on various operation state parameters detected by the sensors and switches. Then, the final fuel injection amount TAU is calculated.

  Further, when starting the engine, the starting fuel injection amount is set based on the coolant temperature Tw detected by the coolant temperature sensor 24 at this time. The fuel injection amount at start-up includes the fuel injection amount (hereinafter referred to as “primary fuel injection amount”) TSTAF for the first, second and fourth fuel injection target cylinders in the first combustion cycle, and the third injection. There are a secondary fuel injection amount TSTAS for the second cylinder, and a third fuel injection amount TSTAN that is set for the second combustion cycle, that is, the fifth to eighth cylinders.

  Specifically, the primary fuel injection amount TSTAF, the secondary fuel injection amount TSTAS, and the tertiary fuel injection amount TSTAN described above are set according to the flowcharts shown in FIGS.

  When the ignition switch 62 is turned on, the drive power is turned on to the E / G_ECU 50, and the system is initialized.

  Then, the start-up injection control routine shown in FIG. 3 is started. First, in step S1, based on the crank pulse output from the crank angle sensor 32 and the cam pulse output from the cylinder discrimination sensor 34, the crank pulse and the next The cylinder of the fuel injection target cylinder is discriminated from the cam pulse interrupted between the crank pulse.

  Therefore, after the ignition switch 62 is turned on and the starter switch 35 is turned on to start cranking, the program is in a standby state until the crank pulse and the cam pulse are input.

  Then, when the crank pulse and the cam pulse are input to the E / G_ECU 50 and cylinder discrimination is performed, the process proceeds to step S2, and the primary fuel injection amount (TSTAF) table is interpolated based on the coolant temperature Tw that is representative of the engine temperature. With reference, the primary fuel injection amount TSTAF is set.

  The TSTAF table is composed of a series of addresses in the ROM 52, and in each area, the fuel injection amount for ensuring the starting performance in the cold state is preliminarily obtained from experiments and stored, and includes the fuel adhering to the wall surface. It is set as the total required injection amount.

  As shown in FIG. 5, the primary fuel injection amount TSTAF is set to a higher value as the cooling water temperature Tw is lower. That is, not all of the fuel injected from each injector 11 is vaporized and supplied to the combustion chamber, and a part of the fuel remains attached to the intake port 2a and the surrounding wall surface. In particular, at the time of cold start, since the wall surface temperature of the intake port or the like leading to the combustion chamber is low, the wall surface adhesion coefficient of the fuel becomes high, and the primary fuel injection amount TSTAF is increased correspondingly.

  Since the fuel wall adhesion amount has a causal relationship with the engine temperature, the primary fuel injection amount TSTAF is set based on the cooling water temperature Tw, which is representative of the engine temperature, so that proper fuel injection with the fuel wall adhesion amount taken into account. The amount can be set.

  In step S3, the fuel injection amount TAU for the injector 11 is set as the primary fuel injection amount TSTAF (TAU ← TSFAF). Then, a drive signal corresponding to the fuel injection amount TAU is output to the injector 11 of the first injection cylinder via the drive circuit 58 at a predetermined timing, and a predetermined amount of fuel is injected from the injector 11. The The fuel injection timing for the injector 11 is normal exhaust stroke injection in which fuel is injected in synchronism with the exhaust stroke and uniform mixed combustion is performed, and fuel is injected in synchronism with the intake stroke as in a lean burn engine, and stratified combustion is performed. There is inhalation stroke injection.

  FIG. 7 shows the fuel injection timing (pulse width) of each cylinder in the exhaust stroke injection, and FIG. 8 shows the fuel injection timing (pulse width) of each cylinder in the intake stroke injection.

  As shown in FIGS. 7 and 8, in the exhaust stroke injection and the intake stroke injection, when the first injection (first) injection cylinder is the cylinder # 3, the cylinder # 3 is in the first expansion stroke (initial explosion stroke). ), The third injection cylinder # 4 is in the intake stroke, an unillustrated intake valve is opened, and intake air is supplied to the cylinder # 4.

  When the first cylinder # 3 performs work by combustion (first explosion) during the expansion stroke, engine torque is generated and the engine speed Ne increases. Then, the closing timing of the exhaust valve is advanced, and the backflow of the intake air to the intake port side is reduced correspondingly, and therefore the volumetric efficiency of the cylinder # 4 in the intake stroke at the first explosion is increased.

  In step S4, the number of fuel injections is compared with the initial number of injections kCINJCJD in order to determine the cylinder whose volumetric efficiency increases. The initial value of the number of fuel injections is 0, and is counted up every time the fuel injection amount TAU is output.

  As described above, the cylinder whose volumetric efficiency increases is the cylinder that is in the intake stroke at the time of the first explosion, and in the case of a four-cylinder engine, it is the third injection cylinder (see FIGS. 7 and 8).

  Therefore, in the case of a four-cylinder engine, the initial injection number kCINJCJD = 2 is set. In this case, the number of ignitions may be counted instead of counting the number of fuel injections.

  When the number of fuel injections has not reached kCINJCJD (twice), the routine jumps to step S7, and when it has reached, the routine proceeds to step S5. Therefore, for example, when the first injection cylinder is # 3, the cylinder for which the fuel increase is to be performed is the third injection cylinder # 4.

  In step S5, the secondary fuel injection amount TSTAS is set by referring to the secondary fuel injection amount (TSTAS) table with interpolation calculation based on the coolant temperature Tw.

  Similar to the TSTAF table, the TSTAS table is composed of a series of addresses in the ROM 52. In each area, the secondary fuel injection amount TSTAS corresponding to the volumetric efficiency increased by the first explosion is obtained in advance for each cooling water temperature Tw by experiments or the like. Stored. Therefore, as shown in FIG. 5, the secondary fuel injection amount TSTAS is set to a value increased by an amount corresponding to the increase in volumetric efficiency relative to the primary fuel injection amount TSTAF.

  Next, the process proceeds to step S6, where the injector 11 of the third fuel injection cylinder, that is, when the first fuel injection target cylinder is the cylinder # 3, the fuel injection amount TAU for the injector 11 of the cylinder # 4 is set to The secondary fuel injection amount TSTAS is set (TAU ← TSTAS). Then, a drive signal corresponding to this fuel injection amount TAU is output to the injector 11 of the third fuel injection cylinder via the drive circuit 58 at a predetermined timing, and a predetermined amount of fuel is injected from the injector 11. The

  Thereafter, the process proceeds to step S7, where the number of times of fuel injection and the number of times of completion of the initial fuel cycle kCINJCJD2 are compared to determine whether or not the initial fuel cycle has ended. Since the secondary fuel injection amount TSTAS is set for the third injection cylinder in the initial combustion cycle, kCINJCJD2 = 4 is set in this embodiment employing a four-cylinder engine (see FIGS. 7 and 8). ).

  If the number of fuel injections is different from kCINJCJD2, that is, if the number of fuel injections is 1, 2, or 4, the process returns to step S2, and the primary fuel for the injector 11 of the next fuel injection target cylinder. An injection amount TSTAF is set. Therefore, the fuel injection amount TAU for the fourth injection cylinder, that is, the final cylinder in the initial combustion cycle, is set again by the primary fuel injection amount TSTAF. In this embodiment, the fuel injection amount TAU for the fourth injection cylinder is set as the primary fuel injection amount TSTAF in order to save fuel and improve fuel efficiency. However, there is no problem even if the fuel is increased. The fuel injection amount TAU for the fourth injection cylinder may be set as the secondary fuel injection amount TSTAS.

  On the other hand, when the number of fuel injections is kCINJCJD2 (number of fuel injections = kCINJCJD2), the initial fuel cycle is completed, and the process proceeds to step S8. In step S8, the tertiary fuel injection amount TSTAN is set with reference to the tertiary fuel injection amount (TSTAN) table with interpolation calculation based on the coolant temperature Tw.

  Similar to the TSTAF table, the TSTAN table is composed of a series of addresses in the ROM 52, and in each area, the tertiary fuel injection is performed mainly for the purpose of ensuring the starting performance in the cold state and reducing exhaust emissions and improving fuel efficiency. The amount of fuel adhering to the wall surface remaining during the first combustion cycle is subtracted from the required fuel injection amount set based on the coolant temperature Tw at the time, and the total amount of the value obtained by adding the fuel adhering to the wall surface this time is the tertiary fuel injection amount Stored as TSTAN.

  As shown in FIG. 5, the tertiary fuel injection amount TSTAN stored in the TSTAN table is set to a higher value as the cooling water temperature Tw is lower, and compared to the primary fuel injection amount TSTAF, during the first combustion cycle. Since the fuel adhering to the wall surface is subtracted, the value is low.

  In step S9, the fuel injection amount TAU for the injector 11 of the fuel injection target cylinder is set as the tertiary fuel injection amount TSTAN (TAU ← TSTAN). Then, a drive signal corresponding to the fuel injection amount TAU is output to the injector 11 of the fuel injection target cylinder via the drive circuit 58 at a predetermined timing, and a predetermined amount of fuel is injected from the injector 11.

  Thereafter, the process proceeds to step S10, in which it is determined whether or not the engine has completely exploded by comparing the engine speed Ne with a complete explosion determination speed TSTJDG (for example, 500 rpm), and at the same time whether or not the tertiary fuel injection has ended. Whether or not the number of fuel injections counted from the beginning of the start has reached the number of times the second combustion cycle ends kCINJCJD3.

  If the complete explosion determination rotation speed TSTJDG is not engine explosion of TSTJDG> Ne, or if the number of fuel injections has not reached the second combustion cycle end number kCINJCJD3 (fuel injection number <kCINJCJD3), the process returns to step S8. Returning to step S8, the tertiary fuel injection amount TSTAN for the injector 11 of the next fuel injection target cylinder is set. In this case as well, the number of ignitions may be counted instead of counting the number of fuel injections. Further, since the engine employed in this embodiment is a four-cylinder engine, the number of times the second combustion cycle ends kCINJCJD3 is set to kCINJCJD3 = 8 (see FIGS. 7 and 8).

  On the other hand, when it is determined that the complete explosion determination rotational speed TSTJDG is the engine complete explosion of TSTJDG ≦ Ne and the number of fuel injections has reached the second combustion cycle end number kCINJCJD3 (injection number ≧ kCINJCJD3), routine Exit.

  As described above, in this embodiment, the primary fuel injection amount TSTAF at the time of the first combustion cycle having the highest fuel wall adhesion coefficient is set to a value obtained by adding the wall adhesion fuel amount between the start of the engine and the complete explosion. Further, for the cylinder (cylinder # 4 in FIGS. 7 and 8) in the intake stroke when the cylinder that reaches the first expansion stroke in the initial combustion cycle (cylinder # 3 in FIGS. 7 and 8) performs work by combustion. Since the fuel injection amount is set at a value (secondary fuel injection amount TSTAS) increased in consideration of the increase in volumetric efficiency due to the increase in the engine speed Ne, the air-fuel ratio of the cylinder does not become lean. Further, since the shortage of torque has been eliminated and the factor that adversely affects the next cylinder (cylinder # 1 in FIGS. 7 and 8) has been eliminated, the engine speed Ne as shown by the broken line in FIG. Smooth It can be increased.

  Further, the tertiary fuel injection amount TSTAN supplied in the second round combustion cycle is set to a value obtained by subtracting the wall surface fuel adhering during the initial combustion cycle and adding the current wall surface fuel adhering amount. The fuel ratio can be obtained, good startability can be obtained, exhaust emission can be reduced, and fuel consumption can be improved at the start.

  Furthermore, since the primary fuel injection amount TSTAF and the secondary fuel injection amount TSTAS and the tertiary fuel injection amount TSTAN at the first combustion cycle and the tertiary fuel injection amount TSTAN are stored in separate tables with the cooling water temperature as a parameter representing the engine temperature as a parameter, Since the fuel injection amounts TSTAF, TSTAS, and TSTAN can be set relatively freely for each cooling water temperature region, the fuel injection amounts TSTAF, TSTAS, and TSTAN can be set more appropriately.

  When the startup injection control routine is completed, the post-startup injection control routine shown in FIG. 4 is started. First, in step S11, the TSTA table is referenced with interpolation calculation based on the coolant temperature Tw, and the tertiary fuel injection amount is determined. In step S12, TSTAN is set, and on the basis of the cooling water temperature Tw, the wall surface adhesion coefficient (TAUSTM) table is referenced with interpolation calculation to set the wall surface adhesion coefficient TAUSTM. The wall surface adhesion coefficient TAUSTM indicates the ratio of fuel injected from the injector 11 to the wall surface such as the intake port, and is set between 1.5 and 1, for example, according to the cooling water temperature Tw. When TAUSTM = 1, the wall surface attached fuel amount becomes zero. Therefore, the wall surface sticking coefficient TAUSTM gradually approaches a value from 1.5 to 1 as the elapsed time after the engine starts increases.

Next, the process proceeds to step S13, where the fuel injection amount TAUST is set from the tertiary fuel injection amount TSTAN and the wall surface adhesion coefficient TAUSTM based on the following equation.
TAUST = TSTAN / TAUSTM

  In step S14, the fuel injection amount TAUGn is set by referring to the fuel injection amount (TAUGn) table with interpolation calculation based on the engine load Gn or by calculation. In addition to directly measuring the engine load Gn, the engine load Gn may be set based on, for example, the engine speed Ne and the intake air amount Qa.

  Then, the process proceeds to step S15, and the fuel injection amounts TAUST and TAUGN set in steps S13 and S14 are compared. When TAUST ≧ TAUGn, the process proceeds to step S16, and the fuel injection amount TAUST is determined as the final fuel injection amount TAU of this time. (TAU ← TAUST) and exit the routine.

  On the other hand, when TAUST <TAUGn, the process proceeds to step S17, and the fuel injection amount TAUGn set in step S14 is corrected with various correction values set based on various operation state parameters detected by the sensors and switches. The final fuel injection amount TAU is calculated.

  Next, according to the time chart shown in FIG. 6, an example of the fuel injection control according to this embodiment will be described.

  After the ignition switch 62 is turned on (t1) and the starter switch 35 is turned on (t2), the fuel injection amount TAU is increased up to the second injection (t2 to t3) in the first combustion cycle (t2 to t5). The primary fuel injection amount TSTAF stored in the TSTAF table is set. Since the primary fuel injection amount TSTAF is added with the fuel adhering to the wall surface, the air-fuel ratio does not become lean and good startability can be obtained.

  When the cylinder for the third injection (t3 to t4) thereafter is in the intake stroke, the cylinder that is injected first becomes the first explosion and the engine speed Ne increases, so that the volumetric efficiency increases. Therefore, in order to prevent leaning of the air-fuel ratio, the fuel for the third injection is set with the secondary fuel injection amount TSTAS taking into account the increase in volumetric efficiency stored in the TSTAS table. As a result, leaning of the air-fuel ratio is suppressed, torque shortage does not occur, the engine speed Ne does not drop, and a smooth increase in engine speed can be obtained. Furthermore, since only the fuel injection amount of one cylinder is increased, compared with the case where the fuel injection amount of all cylinders in the first combustion cycle is increased, fuel is not wasted, and fuel consumption is improved and exhaust emission is reduced. be able to.

  Thereafter, in the second combustion cycle (t5 to t6), the fuel injection amount TAU is set at the tertiary fuel injection amount TSTAN stored in the TSTAN table. Since the tertiary fuel injection amount TSTAN is subtracted from the fuel adhering to the wall surface at the time of the first combustion cycle, the air-fuel ratio does not become rich and good startability can be obtained.

  When the second round combustion cycle (t5 to t6) is completed and the engine is completely detonated, the control proceeds to post-startup fuel injection control, and the fuel injection is performed with a value obtained by correcting the tertiary fuel injection amount TSTAN with the wall surface adhesion coefficient TAUSTM. Set the quantity TAUST. The tertiary fuel injection amount TSTAN becomes a low value as the cooling water temperature Tw increases, and the wall surface adhesion coefficient TAUSTM also approaches 1 as the cooling water temperature Tw rises. TAUST is a value that decreases for each fuel injection as the cooling water temperature Tw increases. At that time, the fuel injection amount TAUGn is set based on the engine load Gn, and the final fuel injection amount TAU is set as the fuel injection amount TAUST while TAUST ≧ TAUGn (t6 to t7). When TAUST <TAUGn, the final fuel injection amount TAU is set based on the fuel injection amount TAUGn thereafter.

  FIG. 9 shows a case where the idea of this embodiment is applied to a 4-cycle 6-cylinder engine. In the six-cylinder engine according to this embodiment, the injection order (ignition order) is set as # 1 → # 6 → # 3 → # 2 → # 5 → # 4, and the first injection cylinder in the exhaust stroke injection is # 1. In this case, when this injection cylinder is in the expansion stroke and engine torque is generated by combustion, the volumetric efficiency of cylinder # 2 in the intake stroke at that time increases. Therefore, the present embodiment can be applied by increasing the fuel injection amount for the fourth injection cylinder # 2.

  Specifically, the initial injection number kCINJCJD of the start-up injection control routine shown in FIG. 3 is set to 3, the initial fuel cycle end number kCINJCJD2 is set to 6, and the second combustion cycle end number kCINJCJD3 is set to 12.

  The present invention is not limited to the above-described embodiment. For example, the secondary fuel injection amount may be increased by adding or multiplying the primary fuel injection amount by an increase coefficient.

  In the above-described four-cylinder engine, the primary fuel injection amount is set to the first injection, the second injection, and the fourth injection, but the primary fuel injection amount is set to the first injection and the second injection, and the secondary fuel injection amount is set to 3. It is good also as a 4th injection. Further, in a 6-cylinder engine, the primary fuel injection amount may be changed from the first injection to the third injection, and the secondary fuel injection amount may be changed from the fourth injection to the sixth injection.

Schematic configuration diagram of the engine Circuit diagram of electronic control system Flow chart showing start-up injection control routine Flow chart showing post-startup injection control routine Explanatory drawing of a primary fuel injection amount table, a secondary fuel injection amount table, and a tertiary fuel injection amount table Time chart showing an example of fuel injection control Time chart showing fuel injection timing of each cylinder in exhaust stroke injection Time chart showing fuel injection timing of each cylinder in intake stroke injection Time chart showing fuel injection timing of each cylinder in exhaust stroke injection of 6 cylinder engine (A) is a time chart showing the increase in engine speed from the first explosion, (b) is an explanatory diagram showing the correspondence between the combustion cylinder of (a) and the cylinder in the intake stroke, and (c) is an illustration of (b). Explanatory drawing showing the correspondence between the cylinders in the intake stroke and the injection cylinders

Explanation of symbols

1 ... Engine,
11 ... Injector,
25 ... Air-fuel ratio sensor,
50. Engine control device,
TAU, TAUST, TAUGn ... Fuel injection amount,
TSTAF: Primary fuel injection amount,
TSTAS ... Secondary fuel injection amount,
Tw ... cooling water temperature,
kCINJCJD: Initial number of injections,
kCINJCJD2: Number of times the first fuel cycle ends kCINJCJD3: Number of times the second combustion cycle ends

Claims (3)

An initial fuel injection amount setting means for setting a starting fuel injection amount of each cylinder during the initial combustion cycle based on the engine temperature;
In a fuel injection control device for a multi-cylinder engine that performs work by combustion in an expansion stroke of each cylinder at the start-up fuel injection amount set during the initial fuel cycle,
The starting fuel injection amount set by the initial fuel injection amount setting means is the primary fuel injection amount for the remaining cylinders excluding the other cylinders in the intake stroke when the cylinder into which fuel was initially injected is in the expansion stroke. And a secondary fuel injection amount for the other cylinders,
The primary fuel injection amount is set based on the engine temperature at the time of starting the engine, that the secondary fuel injection amount is increased by the increase in the engine speed during the expansion stroke of the cylinder in which fuel is injected The first A fuel injection control device for a multi-cylinder engine. The multi-cylinder engine is a four-cylinder engine, and the other cylinder that supplies the secondary fuel injection amount is a third injection cylinder from the cylinder that first injected fuel. A fuel injection control device for a multi-cylinder engine according to claim 1. The multi-cylinder engine is a six-cylinder engine, and the other cylinder that supplies the secondary fuel injection amount is a fourth injection cylinder from the cylinder that first injected the fuel. A fuel injection control device for a multi-cylinder engine according to claim 1.

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