JP2001280191A - Fuel controller for diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce exhaust harmful components such as NOx, smoke, or the like by improving fuel consumption and output when a direct injection type diesel engine 1 is on the high load side in a high rotational range. SOLUTION: When the engine 1 is in a specified range A on the high load side in a high rotational range, an injector 5 is injection-operated so that a specified time interval (injection stop interval Tp) may be formed between the time when the sub injection operation is finished to make the full closed state to the time when the injector is opened for main injection. The sub injection amount Qp at the time when the engine 1 is on the low load side B in a middle rotational range is set so as to be larger than that in a specified range. When the engine 1 is fin the low load side C in a low rotational range, the sub injection amount is set so as to be further larger. When the engine is in a specified range A, the injection stop interval Tp is set so as to be longer than a case where the engine is in a middle rotational middle load range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel control system for a direct injection diesel engine, and particularly to a technical field of fuel injection control when the engine is in an operation region on a relatively high load side.

[0002]

2. Description of the Related Art Conventionally, when a direct-injection diesel engine is operating at a low speed and a low load, a main injection of fuel near a compression top dead center of a cylinder is mainly performed to reduce combustion noise. It is known that it is effective to perform so-called pilot injection in advance. That is, when the diesel engine is in a low-speed and low-load state, the temperature state of the combustion chamber is relatively low, and the ignition delay time of the fuel is long. Increases, the amount of generated NOx tends to increase.

Therefore, a small amount of fuel is injected prior to the main injection of the fuel, and the main fuel is injected toward a flame nucleus (fire type) formed by combustion of the fuel. The ignition delay can be greatly reduced, the initial premixed combustion can be reduced, and the combustion noise and the like can be reduced.

Meanwhile, there has been a proposal to execute such a pilot injection over a wider operating range of a diesel engine.
In the fuel injection control device disclosed in Japanese Unexamined Patent Publication, when the direct-injection diesel engine is in almost all operating regions except for a high-rotation and high-load specific region, while performing the pilot injection as described above, The pilot injection technique is applied even in a specific region to reduce the initial combustion.

That is, in the above conventional example,
Even if a normal pilot injection is performed in a specific region where the temperature of the combustion chamber is high, the fuel injected by the pilot is immediately burned out, and attention is paid to the fact that it does not become a fire. By doing so, the initial combustion is alleviated.

[0006]

However, the fuel injection control device of the prior art described above merely reduces the initial fuel injection rate by setting the injection operation of the fuel injection valve to a two-stage operation. Specifically, since the pilot injection is not performed when the engine is in a high load and high rotation state, it is not possible to obtain the effect of the pilot injection as described above. That is, in the conventional example, it can be said that the temperature of the combustion chamber is high because the engine is at a high rotation speed and a high load, but the ignition delay time is longer than when the ignition is formed by the pilot injection. However, in consideration of the fact that the fuel injection amount is large under a high load condition, it is actually impossible to sufficiently suppress the initial intense premixed combustion.

Further, in the prior art, since the initial injection rate of the fuel is merely reduced to reduce the premixed combustion, the output torque of the engine is reduced by an amount corresponding to the weakening of the premixed combustion. In addition, there is a disadvantage that the speed of diffusion combustion following the premix combustion also decreases, and the generation of smoke increases.

The present invention has been made in view of the above points, and an object of the present invention is to devise a fuel injection control procedure when a direct-injection diesel engine is on the high load side, particularly in a high rotation speed range. An object of the present invention is to achieve further reduction of harmful exhaust components such as NOx and smoke while improving fuel efficiency and output of an engine by improving stiffness and flammability.

[0009]

In order to achieve the above object, according to a first aspect of the present invention, when the engine is in a specific region where the engine speed is high and the load is high, the auxiliary injection of fuel by the fuel injection valve is performed. The injection is performed at intervals between the end of the sub-injection and the start of the main injection.

More specifically, the invention of claim 1 includes a fuel injection valve 5 for directly injecting fuel into a combustion chamber 4 in a cylinder 2 of the engine 1 as shown in FIG. The fuel injection valve 5 injects fuel into the main injection operation near the compression top dead center of the cylinder 2 and the sub-injection operation preceding it when the engine is on the low load side in the low rotation range. It is assumed that the diesel engine fuel control device A is used. The interval between the sub-injection and the main injection operation by the fuel injection valve 5 is defined as a period from the time when the sub-injection operation is completed and the fuel injection valve 5 is fully closed to the time when the fuel injection valve 5 starts to open for the main injection operation. An injection interval setting means 40e for setting a time interval between the fuel injection valve 5 and the fuel injection valve 5 when the engine 1 is in a specific area on the high load side in a high speed range.
And a fuel injection control means 40f for separately injecting the fuel into the sub-injection operation and the main injection operation such that the time interval set by the injection interval setting means 40e is provided.

With the above configuration, when the engine 1 is on the low load side in the low rotation range, the fuel injection valve 5 performs the sub-injection of the fuel in the compression stroke of the cylinder 2 as in the conventional pilot injection. The combustion of the sub-injected fuel raises the temperature and pressure state of the combustion chamber 4 and the formation of a flame nucleus serving as a kind of fire enhances the ignitability and combustibility of the subsequently injected fuel. As a result, the ignition delay time is shortened and the initial premixed combustion is reduced,
The generation of NOx in the early stage of combustion is suppressed, and the generation of smoke is also reduced by improving the combustibility.

On the other hand, when the engine 1 is in a specific region of high rotation and high load, the fuel injection valve 5 is controlled by the fuel injection control means 40f so that a predetermined time interval is provided between the sub-injection and the main injection operation. Is activated. At least a part of the sub-injected fuel is diffused in the combustion chamber 4 to form a lean premixed gas, and is thermally decomposed and reacts with the surrounding air in the latter half of the compression stroke of the cylinder as the temperature of the combustion chamber rises. Then, the temperature and pressure state of the combustion chamber 4 are further increased. When the main injection is performed by the fuel injection valve 5 in this state, the main injection fuel is immediately vaporized at the outer edge of the spray in the combustion chamber 4 in which the temperature and the pressure are increased as described above, and the surrounding lean fuel is diluted. An air-fuel mixture having a concentration suitable for combustion is formed together with the pre-mixed air, and combustion is started with almost no ignition delay. Then, the surrounding air-fuel mixture is continuously supplied toward the thus-formed flame kernel, and extremely excellent diffusion combustion is continuously performed.

Therefore, even when the engine 1 is in a high-speed and high-load state, the sub-injection can enhance the flammability of the main injection fuel to improve the fuel efficiency or the output, and to reduce the main injection fuel. Diffusion combustion can be performed satisfactorily from the beginning to suppress generation of NOx in the early stage of combustion, and also reduce generation of smoke in the latter period of combustion.

According to a second aspect of the present invention, the fuel injection control means causes the fuel to be injected into the sub-injection and the main injection by the fuel injection valve even when the engine is on the low load side in the middle rotation range. The sub-injection ratio, which is the ratio of the fuel injection amount by the sub-injection operation of the fuel injection valve to the main injection operation, is set to be larger than a specific region when the engine is on the low load side of the middle rotation range. The injection ratio setting means is provided.

Thus, when the engine is on the low load side in the middle rotation range, the fuel injection valve performs the sub-injection of the fuel during the compression stroke of the cylinder, and the combustion of the sub-injected fuel causes the injection of the main injected fuel. By improving ignitability and flammability,
NOx and smoke are reduced, and fuel efficiency or output is improved. At this time, even if the temperature and the pressure state are lower than the specific area, the sub-injection ratio of the fuel is increased correspondingly, so that the combustion of the sub-injection fuel makes the temperature and the pressure state of the combustion chamber moderate. The sub-injection is performed before the flame kernel formed by the combustion of the sub-injection fuel is extinguished, and the combustion is appropriately continued. Can be obtained sufficiently.

According to a third aspect of the present invention, the sub-injection ratio setting means sets the sub-injection ratio of the fuel to be larger than the specific region when the engine is on the low load side in the low rotation range. Shall be.

[0017] Thus, a sufficient amount of fuel is sub-injected on the low load side in the low rotation range where the temperature and pressure are relatively low, and the combustion and combustion of the sub-injected fuel reduce the temperature and pressure of the combustion chamber. Can be enhanced. Further, the combustion of the sub-injection fuel can be appropriately continued to the combustion of the main injection fuel, and the effect of improving the combustibility by the sub-injection can be sufficiently obtained. Furthermore, when the engine gradually shifts from the low rotation range to the middle rotation range, and further to the high rotation range, the sub-injection ratio decreases accordingly, preventing a sudden change in the combustion state,
A good driving feel can be obtained.

A fuel control apparatus for a diesel engine according to a fourth aspect of the present invention provides a fuel injection valve for directly injecting fuel into an in-cylinder combustion chamber of an engine, and specifying a high load side in a high engine speed range of the engine. When in the region and the medium rotation medium load region adjacent to the low rotation or low load side of this region,
Fuel injection control means for injecting fuel by the fuel injection valve into a main injection operation near the compression top dead center of the cylinder and a sub-injection operation preceding the main injection operation, and sub-injection and main injection by the fuel injection valve Injection interval setting means for setting an operation interval such that a time interval is provided between the time when the sub-injection operation is completed and the fuel injection valve is fully closed and the time when the fuel injection valve is started to open for the main injection operation. Wherein the injection interval setting means sets the time interval to be longer when the engine is in the specific region than when the engine is in the medium rotation load region.

In this configuration, the sub-injection of the fuel is performed when the engine is in the high-rotation high-load specific region and the medium rotation medium load region adjacent thereto. Similarly to the above, it is possible to further reduce the harmful exhaust components such as NOx and smoke while improving the fuel efficiency and output of the engine by improving the combustibility of the main injection fuel. At this time, the time interval between the sub-injection and the main injection is made longer when the engine is in the specific region than in the medium rotation load region, so that the combustion of the main injection fuel is performed. Therefore, the effect of improving the combustibility by the sub-injection can be sufficiently obtained by appropriately continuing the combustion.

According to a fifth aspect of the present invention, the fuel injection control means according to the fourth aspect is arranged so as to determine whether the engine is in a first region on a low load side in a low rotation speed or a middle rotation speed region excluding a fuel cut region at the time of deceleration. Alternatively, when the fuel injection valve is at least in the second region on the high load side in the middle rotation speed region or the high rotation speed region, the fuel is injected into the sub-injection and the main injection operation separately by the fuel injection valve. Is set to be longer when the engine is in the second region than when it is in the first region.

Thus, when the engine is in a wide operating range including the first and second ranges, the effect of improving the combustion performance by the sub-injection can be obtained. In this case, the effect of improving fuel efficiency can be greatly improved. At this time, the time interval between the sub-injection and the main injection is made longer when the engine is in the second region than in the first region, so that the combustion of the main injection fuel is By appropriately continuing the combustion, it is possible to sufficiently obtain the effect of improving the combustibility by the sub-injection.

Next, a fuel control system for a diesel engine according to a sixth aspect of the present invention provides a fuel injection valve for directly injecting fuel into an in-cylinder combustion chamber of an engine; A fuel injection control means for injecting separately into a main injection operation near the top dead center and a sub injection operation preceding the main injection operation, and an interval between the sub injection and the main injection operation by the fuel injection valve; Injection interval setting means for setting a time interval between the time when the fuel injection valve is fully closed and the time when the fuel injection valve starts to open for the main injection operation. When the fuel injection amount by the sub-injection operation is Qp and the time interval is Tp, Qp
It is assumed that the value of / Tp is larger when the engine is on the high load side in the low speed range than when it is on the high load side in the high speed range.

As a result, when the engine is on the high load side in the low rotation range, the ratio of the sub injection amount Qp to the time interval Tp is larger than that in the high rotation range. That is, in a state in which a large amount of fuel corresponding to a high load is injected, the sub-injection amount Qp is increased even though the temperature state of the combustion chamber is lower than that in the high rotation region, so that the main injection The flammability of the injected fuel can be sufficiently improved. On the other hand, by reducing the sub-injection amount Qp on the high load side in the high rotation region where the combustion chamber 4 is rather overheated, the generation of NOx accompanying the premixed combustion of the sub-injected fuel is reduced and the reverse torque is reduced. be able to. Alternatively, if the time interval Tp is extended on the high load side in the high rotation range, the proportion of the sub-injected fuel that is diffused into the combustion chamber and becomes a lean premix is increased,
The same operation and effect as described above can be obtained while increasing the output torque of the engine.

According to the invention of claim 7, in claim 6,
The value of Qp / Tp is larger when the engine is on the high load side of the low speed range than when it is on the high load side of the middle speed range, and when the engine is on the high load side of the middle speed range, the value of the high speed range is high. It shall be larger than when it is on the load side. As a result, when the engine gradually shifts from the low rotation range to the middle rotation range to the high rotation range while the engine is operating at a relatively high load, the combustion state gradually changes accordingly. Therefore, a good driving feeling can be obtained.

[0025]

Embodiments of the present invention will be described below with reference to the drawings.

(Overall Configuration) FIG. 1 shows an overall configuration of a diesel engine fuel control device A according to an embodiment of the present invention, and 1 is a diesel engine mounted on a vehicle (not shown). This engine 1 has four cylinders 2, 2, 2, 2
Are arranged in series, and a piston (not shown) is fitted in each cylinder 2 so as to be able to reciprocate, and the piston causes a combustion chamber 4 in each cylinder 2. It is partitioned. In addition, an injector (fuel injection valve) 5 is disposed substantially at the center of the ceiling of each combustion chamber 4 so as to extend along the center line of the cylinder 2, which is exaggerated in the figure.

An injection nozzle is integrally provided at the distal end of each of the injectors 5, while the base end is connected to a common rail 6 for storing fuel in a predetermined high pressure state by branch pipes 6a, 6a,. The high-pressure fuel supplied from the common rail 6 is directly injected into the combustion chamber 4 by opening and closing the needle valve of the injection nozzle by an actuator (not shown). The common rail 6 is provided with a fuel pressure sensor 6b for detecting an internal fuel pressure (common rail pressure).

The common rail 6 has a high-pressure fuel supply pipe 7
Is connected to a high-pressure supply pump 8, and this high-pressure supply pump 8 is connected to a fuel tank 10 by a fuel supply pipe 9. The high-pressure supply pump 8 includes an engine 1
Is driven by receiving the rotation input from the crankshaft of the fuel tank 10 and sucks up the fuel in the fuel tank 10 through the fuel supply pipe 9 while filtering the fuel with the fuel filter 11, and sends the fuel to the common rail 6 by the jerk type pumping system. . Further, the high-pressure supply pump 8 is provided with an electromagnetic valve for adjusting a discharge amount of the pump by releasing a part of the fuel sent out by the pumping system to the fuel return pipe 12. By controlling in accordance with the value detected by the fuel pressure sensor 6b, the pressure state of the fuel in the common rail 6 is maintained at a predetermined state corresponding to the operating state of the engine 1.

Reference numeral 13 in the figure denotes a pressure limiter for discharging fuel from the common rail 6 when the common rail pressure becomes equal to or higher than a predetermined value. The fuel discharged from the pressure limiter passes through a fuel return pipe 14. It circulates and is returned to the fuel tank 10. Reference numeral 15 denotes a fuel return pipe for returning a part of the fuel from the injector 5 to the fuel tank 10.

Although not shown in detail, the engine 1 includes a crank angle sensor 16 for detecting a rotation angle of a crankshaft, a cam angle sensor 17 for detecting a rotation angle of a valve system camshaft, and a coolant temperature ( An engine water temperature sensor 18 for detecting an engine water temperature is provided. The crank angle sensor 16 is composed of a plate to be detected provided at the end of the crankshaft and an electromagnetic pickup arranged so as to face the outer periphery thereof, at equal intervals around the entire outer periphery of the plate to be detected. A pulse signal is output in response to the passage of the formed protrusion. The cam angle sensor 17 also includes a plurality of protrusions similarly provided at predetermined positions on the peripheral surface of the cam shaft, and an electromagnetic pickup that outputs a pulse signal when each of the protrusions passes. Reference numeral 19 denotes a vacuum pump driven by the cam shaft.

An intake passage 20 for supplying air filtered by an air cleaner (not shown) to the combustion chamber 4 is connected to one side surface (upper side in the figure) of the engine 1. A surge tank 21 is provided at a downstream end of the intake passage 20,
Each passage branched from the surge tank 21 communicates with the combustion chamber 4 of each cylinder 2 through an intake port (not shown). Further, the surge tank 21 is provided with a supercharging pressure sensor 22 for detecting a pressure state of intake air pressure-fed by a turbocharger 31 described later.

Further, a hot film type air flow sensor 23 for detecting a flow rate of intake air taken into the engine 1 is arranged in the intake passage 20 in order from the upstream side to the downstream side.
And a blower 24 that is driven by a turbine 29 to be described later to compress the intake air, an intercooler 25 that cools the intake air compressed by the blower 24, and an intake throttle valve 26 that is a butterfly valve. Although not shown in detail, the intake throttle valve 26 is configured such that the valve shaft is rotated by a stepping motor to be positioned in an arbitrary state from a fully closed state to a fully opened state. A notch is provided so as to flow in.

On the other hand, an exhaust manifold 27 for discharging combustion gas (exhaust gas) from the combustion chamber 4 of each cylinder 2 is connected to a side surface on the opposite side (lower side in the figure) of the engine 1. An exhaust passage 28 is connected to the downstream end gathering part. In the exhaust passage 28, the turbine 2 rotated by the exhaust gas flows in order from the upstream side to the downstream side.
9 and a catalytic converter 30 for removing harmful components (unburned HC, CO, NOx, smoke, etc.) in the exhaust gas.

Although not shown in detail, the turbocharger 31 composed of the turbine 29 and the blower 24 in the intake passage 20 has a movable flap to reduce the sectional area (nozzle sectional area) of the exhaust flow path to the turbine 29. VG to change
T (variable geometry turbo), and the flap is rotated by a negative pressure driven actuator 35 using negative pressure from a vacuum pump 19.

Although not shown in detail, the catalytic converter 30 has a cordierite carrier having a honeycomb structure having a large number of through holes extending in parallel with each other in the exhaust gas flowing direction. A catalyst layer of a so-called lean NOx catalyst is formed on each through hole wall surface. This lean NOx catalyst can reduce and purify NOx in exhaust gas even when the oxygen concentration in the exhaust gas is high, that is, in a lean state in which the average excess air ratio λ of the combustion chamber 4 is larger than 1. In the vicinity of the air-fuel ratio, it also functions as a three-way catalyst.

Further, the exhaust passage 28 is provided in the turbine 2
9 and is branched upstream of an exhaust gas recirculation passage (hereinafter referred to as an EGR passage) 33 that recirculates part of the exhaust gas to the intake side at a position upstream of the exhaust gas, and a downstream end of the EGR passage 33 is an intake throttle. It is connected to the intake passage 20 in the middle of the valve 26 and the surge tank 21 so that a part of the exhaust gas taken out from the exhaust passage 28 is returned to the intake passage 20. An exhaust gas recirculation amount control valve (hereinafter, referred to as an EGR valve) 34 whose opening can be adjusted is disposed near the downstream end of the EGR passage 33. The EGR valve 34 is connected to a flap of the turbocharger 31. Similarly, the opening / closing operation by the negative pressure drive type actuator 35 linearly changes the passage cross-sectional area of the EGR passage 33, and regulates the flow rate of the exhaust gas recirculated to the intake passage 20.

The injectors 5, the high-pressure supply pump 8, the intake throttle valve 26, the VGT 31, the EGR valve 34, etc.
All control units (Electronic Control
The unit is operated by a control signal from a unit (hereinafter referred to as an ECU) 40. On the other hand, the ECU 40 receives an output signal from the fuel pressure sensor 6b, an output signal from the crank angle sensor 16 and the cam angle sensor 17, an output signal from the engine coolant temperature sensor 18, and a signal from the supercharging pressure sensor 22. At least an output signal, an output signal from the air flow sensor 23, and an output signal from an accelerator opening sensor 36 that detects an operation amount (accelerator opening) of an accelerator pedal (not shown) by a driver of the vehicle are input. Has become.

As the basic control by the ECU 40, the target fuel injection amount is determined mainly based on the accelerator opening, the fuel injection amount and the injection timing are controlled by controlling the operation of the injector 5, and the high pressure The operation of the supply pump 8 controls the common rail pressure, that is, the fuel injection pressure. Further, by adjusting the intake air amount by controlling the operation of the intake throttle valve 26 and the EGR valve 34, the combustion chamber 4
Control the average excess air ratio. In addition, VGT31
By controlling the flap operation (VGT control), the supercharging efficiency of the intake air is increased.

Specifically, for example, as fuel injection control,
As will be described in detail later, the injector 5 is operated to perform an injection operation near the compression top dead center (TDC) of the cylinder (main injection operation), and a fuel injection amount of about 6 times to the combustion chamber 4 of the cylinder 2.
While injecting and supplying 0 to 90% or more of the fuel (hereinafter, also simply referred to as main injection), the injector 5 is operated to inject during the compression stroke of the cylinder 2 prior to the main injection (sub-injection operation),
The fuel of about 40 to 10% or less of the target fuel injection amount is injected and supplied to the combustion chamber 4 (hereinafter, also simply referred to as sub-injection). At this time, as will be described in detail later, the ratio of the sub-injection amount of the fuel to the main injection amount (sub-injection ratio) and the time interval between the sub-injection and the main injection are changed according to the load condition of the engine 1 and the change in the rotation speed. By making detailed changes, an optimal combustion state can always be obtained with respect to changes in the load state and temperature state of the engine 1.

The operation control of the EGR valve 34 (EG
As the R control, for example, a target excess air ratio common to all the cylinders 2 is determined according to the operating state of the engine 1, and the actual intake air amount into the combustion chamber 4 of each cylinder 2 based on the output of the airflow sensor. Is detected, and the exhaust gas recirculation amount is controlled based on the detected value and the fuel injection amount for each cylinder 2 so as to achieve the target excess air ratio. That is, by adjusting the exhaust gas recirculation amount for each cylinder 2, the intake amount of fresh air (outside air) into the combustion chamber 4 is changed, and the excess air ratio of the combustion chamber 4 in each cylinder 2 is changed to the target excess air ratio. Control so that

Further, as for the operation control of the intake throttle valve 26, in order to recirculate a required amount of exhaust gas by the EGR control as described above, the intake throttle valve 26 is mainly closed at the time of idling operation of the engine 1, While a negative pressure is generated in the passage 20, the intake throttle valve 26 is set to be almost fully opened in other operation states.

(Fuel Injection Control) Next, details of the fuel injection control will be described with reference to FIGS.

FIG. 2 is a functional block diagram showing the configuration of the fuel injection control unit in the ECU 40. In FIG. 2, reference numeral 40a denotes the accelerator opening Acc detected by the accelerator opening sensor 36 and the output of the crank angle sensor 16. A target torque calculator 40a that calculates a target torque Trq corresponding to the required output of the engine 1 based on the engine speed ne obtained from the signal. This target torque calculation unit 40a
Is realized by executing a control program stored in the memory of the ECU 40.

Based on the target torque Trq calculated by the target torque calculating section 40a, the fresh air amount Air measured by the air flow sensor 23, and the engine speed ne, the target injection amount calculating section 40b stores a tertiary data stored in the memory. The basic target fuel injection amount Qb is calculated with reference to the original control map (fuel injection amount map). Although not shown, this fuel injection amount map records an optimum fuel injection amount Qb experimentally determined according to changes in the target torque Trq of the engine 1 and the engine speed ne, and the value of Qb is The higher the target torque Trq and the higher the engine speed ne, the higher the setting and the higher the recording.
In the target injection amount calculating section 40b, the basic target fuel injection amount Qb obtained as described above is further corrected according to the engine water temperature, the intake pressure, and the like, and is set as the target fuel injection amount Qb.

Further, based on the accelerator opening Acc and the engine speed ne, the basic injection timing setting section 40c refers to the control map (basic injection timing map) on the memory and refers to the basic injection timing ITb of the injector 5. Is calculated. The basic injection timing ITb is a timing at which the main injection operation of the injector 5 ends and the needle valve closes (crank angle position).
Is set. Although not shown, the injection timing map is obtained by experimentally obtaining and recording basic injection timing corresponding to engine water temperature, common rail pressure, engine speed, and the like. The advance is set and recorded as the water temperature is lower, the common rail pressure is lower, and the engine speed ne is higher.

Subsequently, based on the target fuel injection amount Qb obtained by the target injection amount calculating section 40b and the engine speed ne, the sub-injection ratio calculating section 40d stores a control map (injection ratio map) on a memory. With reference to the above, a sub-injection ratio Rp, which is a ratio of the sub-injection amount of fuel by the injector 5 to the main injection amount, is calculated. In this injection ratio map, as shown in FIG. 3, the sub-injection ratio Rp is set so as to correspond to the target fuel injection amount Qb and the engine speed ne. Except for the deceleration fuel cut region where the fuel injection supply is sometimes stopped, the lower the fuel injection amount is on the low load side, the higher the sub injection ratio Rp (for example, Rp = about 70%), while the higher the fuel injection amount is On the load side and the high rotation side, as the load state and the rotation speed increase, the sub-injection ratio Rp gradually decreases, and in the high rotation and high load specific region (a) shown by hatching in the figure, for example, Rp = 5% or less.

In other words, the sub-injection ratio Rp is greater when the engine 1 is in the low load side (the range (b) shown by the phantom line in the figure) of the middle rotation range than when it is in the specific region (b). It is set to increase, and the sub-injection ratio
Rp is set to be larger when the engine 1 is on the low load side of the low rotation range (range (c) shown by a virtual line in the figure) than when it is in the specific region (a).

The total fuel injection amount including the sub-injection and the main injection increases as the load state of the engine 1 increases. Further, in this embodiment, when the engine 1 is on the high load side in the low rotation range, the sub-injection amount is increased in order to promptly increase the exhaust flow rate to the turbocharger 31, so that as a result, As shown in FIG. 4, the sub injection amount Qp of the fuel varies slightly in accordance with the load state and the rotational speed state of the engine 1. That is, when the engine 1 is on the high load side at a low rotation speed, the sub injection amount Qp of the fuel is relatively large (large), for example, 3 to 4 mm ³ . On the other hand, the sub injection amount Qp is, for example, 1.
It is relatively small (small amount) of 5 to ² mm ^3, and on the low load side in the low speed range to the middle speed range, it is an intermediate amount (medium amount: for example, 2 to 2.5 mm ³ ).

Here, the low, middle, and high rotation ranges of the engine 1 refer to those obtained by roughly dividing the operating range of the engine into three equal parts with respect to the engine speed.
For example, in this embodiment, the low rotation range is a range where the engine speed ne is lower than about 1500 rpm, and the middle rotation range is ne = about 1500 rpm to about 25 rpm.
The engine speed ne may be a range where the engine speed ne is higher than about 2500 rpm.

The target fuel injection amount Qb and the engine speed ne
Based on the above, the injection stop interval calculation unit 40e (see FIG. 2) calculates the injection stop interval Tp with reference to the control map (injection interval map) in the memory. This injection stop interval
Tp is a time interval from the time when the sub-injection operation of the injector 5 ends and the needle valve is fully closed to the time when the injector 5 starts to open for the main injection operation. In the sub-injection interval map, as shown in FIG. 5, an injection stop interval Tp is set so as to correspond to the target fuel injection amount Qb and the engine speed ne. When the engine 1 is on the low-load side of the low-speed range except for the fuel cut-off region, the injection stop interval Tp is the shortest (for example, Tp = about 1.5 milliseconds). Side, the injection stop interval Tp gradually increases, and in a high-rotation and high-load area (a) (specific area) as shown by hatching in the figure, for example, Tp = about 2.5 ~ 3 ms or more.

In other words, when the engine 1 is in the area (A), the injection stop interval Tp is set to the medium rotation medium load area adjacent to the low rotation and low load side of the area (A) (the virtual line in the figure). Is set to be longer than when it is in the range (d) shown by. Further, as shown in FIG. 6, for example, a region on the low load side in the low rotation speed to the middle rotation speed region excluding the deceleration fuel cut region is defined as a first region (e), and the region on the high load side in the middle rotation speed or the high rotation speed region. If the region is a second region (f), the injection stop interval Tp is set to be longer when the engine 1 is in the second region (f) than when it is in the first region (e). It can be said that.

As described above, since the basic fuel injection timing ITb by the injector 5 is changed according to the operating state of the engine 1, the start timing of the sub-injection is eventually determined by the timing shown in FIG.
As shown in the figure, the angle changes in accordance with the load state and the rotational speed state of the engine 1, and the angle is advanced toward the high rotation side or the high load side. For example, before the compression top dead center (BTDC) 90 ° CA-5 ° CA
In the range.

Then, the target fuel injection amount Qb, the basic injection timing ITb, the sub-injection ratio Rp, the injection stop interval Tp, the common rail pressure CRp detected by the fuel pressure sensor 6b, and the like are sent to the injection control unit 40f. The injection control unit 40f determines the start timing of the sub-injection and the main injection operation of the injector 5 and the excitation time in each injection operation based on these input values. That is, first, the target fuel injection amount Qb is distributed based on the sub injection ratio Rp, and the sub injection amount Qp and the main injection amount Qm of the fuel are obtained.

Qp = {Rp / (1 + Rp)} × Qb, Qm = ｛(1
−Rp) / (1 + Rp)｝ × Qb Further, based on the sub-injection amount Qp, the main injection amount Qm, and the common rail pressure CRp, the excitation time in the sub-injection and the main injection operation of the injector 5 is obtained, respectively. Based on the excitation time during injection operation and the basic injection timing ITb,
The start timing of the main injection operation (main injection timing ITm) is set, and based on the main injection timing ITm, the injection stop interval Tp, and the excitation time of the sub injection operation, the start timing of the sub main injection operation ( The sub injection timing ITp) is set. When it is determined based on the signal from the crank angle sensor 16 that the sub-injection timing ITp or the main injection timing ITm has been reached for each cylinder 2, the injection control unit 40f determines the injector for each cylinder 2 5, a control signal (ejection pulse signal) is output,
Thereby, the operation control of the injector 5 is performed.

The target torque Trq obtained by the target torque calculation section 40a is output to an EGR control section (not shown) to be used for calculating a target excess air ratio. Further, the target fuel injection amount Qb obtained by the target injection amount calculation unit 40b is also output to the EGR control unit, and is used for calculating the target fresh air amount together with the target excess air ratio. Then, the opening of the EGR valve 34 is controlled using the target fresh air amount as a control target value.

In the block diagram shown in FIG. 2, the injection ratio calculation unit 40d determines the sub injection ratio Rp of the fuel by the injector 5 when the engine 1 is on the low load side (b) of the middle rotation range. This corresponds to the injection ratio setting means for setting the number to be larger than that in the case (a), and to be larger when the load is on the low load side (c) in the low rotation range.

Further, the injection stop interval setting section 40e includes:
The interval between the sub-injection and the main injection operation by the injector 5 is
Injection interval setting for setting an injection stop interval Tp (time interval) between the time when the sub-injection operation is completed and the injector 5 is fully closed and the time when the injector 5 starts to open for the main injection operation. It corresponds to the means. The injection stop interval setting section 40e sets the injection stop interval Tp so that the injection stop interval Tp is longer when the engine 1 is in the specific region (a) than in the middle rotation load region (d). When the engine 1 is in the second region (f) on the high load side, the injection stop interval Tp is set to the first region (e) on the low load side.
Is set to be longer than that in

Further, when the engine 1 is in the specific region (a), the injection control section 40f supplies fuel by the injector 5 so that the injection stop interval Tp set by the injection stop interval setting section 40e becomes vacant. It corresponds to the fuel injection control means for performing the injection separately for the sub-injection and the main injection operation. The injection ratio calculation unit 40d, the injection stop interval setting unit 40e, and the injection control unit 40f are all provided by the ECU 4
This is realized by executing a control program stored in the memory of the memory No. 0.

(Improvement of Combustion by Sub-Injection) Here, the improvement of the combustion state by performing the above-described sub-injection will be described by taking as an example a case where the engine 1 is on the low load side in a low rotation range. .

FIG. 8 shows changes in the lift state of the needle valve of the injector 5, the heat release rate, and the cylinder pressure when the engine 1 is on the low load side in the low rotation range. In the case where the fuel is injected collectively near the compression top dead center (TDC) of the cylinder 2 without performing the sub-injection of the fuel as shown by the broken line in FIG. While the liquid droplets are broken up and vaporized, the heat generation rate temporarily becomes negative due to the latent heat of vaporization. Then, when the vaporization or thermal decomposition of the fuel proceeds and the fuel and the air are partially mixed to form a combustible mixture mainly at the outer edge of the fuel spray, that is, when the ignition delay period has elapsed, The air-fuel mixture self-ignites and burns violently (premixed combustion).

At this time, as shown in the figure, the heat generation rate shows a steep peak, the temperature state of the combustion chamber 4 also rises a little later, and the pressure (in-cylinder pressure) of the combustion chamber 4 rises sharply. As a result, combustion noise increases,
The generation amount of NOx increases. The surrounding fuel vapor and air are continuously supplied to the flame kernel formed by such intense premixed combustion, so that so-called diffusion combustion is continuously performed. When the temperature state of the chamber 6 decreases, the combustion is rapidly terminated.

In the case where the sub-injection of fuel is performed in such a normal combustion state as shown by a solid line in FIG.
By the sub-injection operation of the injector 5, about 10% of the whole fuel is injected during the compression stroke of the cylinder 2 (for example, BTDC 50 ° CA). After the fuel is vaporized and partially mixed with the air as described above, when the temperature state of the combustion chamber 4 exceeds the self-ignition temperature of the fuel (for example, BTDC 30 ° CA), the fuel ignites and burns. When the main injection operation of the injector 5 is performed where the temperature and pressure state of the combustion chamber 4 is increased and a flame nucleus serving as a fire is formed by this combustion, atomization characteristics of fuel spray are performed by high pressure injection of a common rail type. Is extremely good, the ignition delay of newly injected fuel is extremely short, and most of this fuel is in a very good diffusion combustion state from the beginning.

As a result, as shown by the solid line in the figure, the peak of the heat generation rate due to the premixed combustion in the initial stage of combustion is significantly lower than that in the normal combustion state, while the speed of diffusion combustion is significantly higher. Therefore, the heat generation rate in the latter half of the combustion is maintained at a high state similar to the peak. Thus, when all the fuel has been burned well and the combustion is completed in a relatively short combustion period, the heat release rate also rapidly decreases.

The change in the cylinder internal pressure is determined by
The pressure rise due to the combustion of the sub-injection overlaps with the pressure rise due to the rise of the pressure, and a first peak appears near the compression top dead center (TDC) of the cylinder 2. A second peak with a longer duration appears. As described above, the average pressure in the cylinder 2 is increased by increasing the in-cylinder pressure quickly near the TDC and maintaining the high-pressure state near the peak for a relatively long time.

As described above, by performing the sub-injection prior to the main injection in the compression stroke of the cylinder 2, the rise of the main injection fuel in the early stage of combustion is stepwise gentler than in the case where the sub-injection is not performed. This makes it possible to
The generation of NOx due to combustion is suppressed, and the combustion noise is also reduced. Also, by increasing the diffusion combustion rate,
Since the combustion period is shortened as a whole, generation of smoke at the end of the combustion period can be reduced.

In order to improve the combustion state by the sub-injection as described above, it is extremely important that the process from the combustion of the sub-injected fuel to the start of the main injection fuel is appropriately continued. The amount of fuel to be sub-injected and the time interval to the main injection must be appropriately set according to the temperature state of the combustion chamber 4 and the like. That is, for example, if the sub-injection combustion is too small or too early in relation to the start timing of the main injection, the main injection is performed after the combustion of the sub-injected fuel ends and the flame kernel disappears. However, the ignitability of the main injection fuel cannot be sufficiently increased. On the other hand, if the timing of the sub-injection is too late, the main injection will be performed in a state where the combustion of the fuel is insufficient, and the ignitability cannot be improved much in this case as well.

If the amount of the sub-injected fuel is too large, not only is the fuel wasted, but also the combustion produces a so-called reverse torque, which may cause a significant deterioration in fuel efficiency. Further, depending on the operating state of the engine 1, particularly in a high-speed and high-load state where the temperature state of the combustion chamber 4 is high, a large amount of NOx is generated during the combustion of the sub-injected fuel, or the burned gas resulting from the combustion is generated. May significantly reduce the combustion rate of the main injected fuel, increasing the generation of smoke.

Therefore, in the fuel control apparatus A of this embodiment, as described above, the sub-injection ratio Rp and the injection stop interval Tp are finely changed based on a preset control map, so that Fuel efficiency,
Various conflicting demands such as output improvement, reliability improvement, reduction of harmful exhaust components, noise suppression, etc. can be satisfied at a high level. Further, even when the engine 1 is in a high-speed and high-load operating state, The combustion is improved by sub-injection.

That is, as shown in the flow chart of FIG. 9, first, in step S1 after the start, data such as the engine speed ne and the accelerator opening Acc are input. In the following step S2, the data from the fuel injection amount map is obtained. The target fuel injection amount Qb is calculated based on the read value.
Subsequently, in step S3, the basic injection timing ITb is calculated from the basic injection timing map, and in the following step S4, the sub-injection ratio Rp is read from the injection ratio map and set.

Thus, when the engine 1 is on the low load side in the low rotation range and the temperature state of the combustion chamber 4 is low, the sub-injection ratio Rp is set relatively high, and the total of the sub-injection and the main injection is combined. Even if the fuel injection amount is small, a sufficient amount of sub-injection is performed so as to be appropriately continued to the main injection. As the load state of the engine 1 increases, the set value of the sub-injection ratio Rp gradually decreases, but the total fuel injection amount increases in accordance with the increase in the engine load. Rather increase gradually (see FIG. 4). On the other hand, when the engine speed increases from the low-speed low-load region, the total fuel injection amount does not change much, so as the set value of the sub-injection ratio Rp decreases, the sub-injection amount Qp also gradually decreases, As a result, the sub-injection ratio Rp becomes the smallest in the high-rotation and high-load region.

Subsequently, in step S5, the sub-injection amount Qp and the main injection amount Qm are obtained based on the target fuel injection amount Qb and the sub-injection ratio Rp. In the following step S6, the injection stop interval Tp is obtained from the injection interval map. Read. That is, when the temperature of the combustion chamber 4 is low when the engine 1 is on the low load side in the low rotation range, the injection stop interval Tp is set relatively short. And the main injection is performed while the pressure condition is increased and the fire remains. Further, the injection stop interval Tp gradually increases as the load state or the rotation speed of the engine 1 increases (see FIG. 5). In the high-rotation and high-load specific region, the injection stop interval Tp is set to be the longest, whereby most of the sub-injected fuel diffuses to a lean state in which self-ignition is not performed. A lean premix is formed.

Referring to the relationship between the sub-injection amount Qp and the injection stop interval Tp shown in FIGS. 4 and 5, for example, FIG.
As schematically shown at 0, the value represented as Qp / Tp is
It can be seen that when the engine 1 is in the low speed range over the entire region on the high load side, the engine 1 is smaller than in the middle speed range, and when it is in the middle speed range, it is smaller than in the high speed range. This is because when the engine 1 is in a high load state, the injection stop interval Tp does not change much even if the engine speed ne changes as shown in FIG.
The fact that the engine 1 is in a high load state while having a low rotation speed means that the output torque should be increased as much as possible in a low temperature state as compared with a high rotation speed range.
As shown in FIG. 4, the sub-injection amount Qp is increased,
On the other hand, in the state of high rotation and high load, the temperature state of the combustion chamber 4 is sufficiently high, so that the auxiliary injection amount Qp may be rather small.

Then, according to the sub-injection ratio Rp and the injection stop interval Tp, which have been finely set as described above, step S
At 7, the start timings ITp and ITm of the sub-injection and the main injection by the injector 5 are set for each cylinder 2. Subsequently, in step S8, it is determined whether or not the sub-injection timing ITp has been reached based on the crank angle signal, and it is waited until the injection timing has come (determination is NO), and if it becomes the injection timing (determination is YES), step S9 is performed. To output an injection pulse signal corresponding to the sub-injection amount Qp to the injector 5,
The sub injection operation is performed. Subsequently, in step S10, it is determined whether or not the main injection timing ITm has been reached based on the crank angle signal, and it is waited until the injection timing has been reached (determination is NO). Proceeding to S11, an injection pulse signal corresponding to the main injection amount Qm is output to the injector 5 to perform the main injection operation, and thereafter, the routine returns.

(Effects of Embodiment) Therefore, according to the fuel control system A for the engine according to this embodiment, first, the cylinder 2
Each injector 5 injects fuel separately into sub-injection and main injection, and the combustion of the sub-injected fuel enhances the ignitability and combustion speed of the main injection. As a result, it is possible to shorten the diffusion combustion period while suppressing the rapid rise in temperature and pressure in the initial stage of combustion, and to reduce harmful exhaust components and suppress noise while improving the output of the engine 1 or reducing fuel consumption. can do.

At this time, as described above, the sub-injection ratio Rp and the injection stop interval Tp are finely changed in accordance with the load condition and the number of revolutions of the engine 1, and the combustion of the sub-injection fuel is substantially performed in almost all operation regions. Since the combustion of the injected fuel is appropriately continued, the above-mentioned effects can be sufficiently obtained over the entire operation range of the engine 1.

Specifically, FIG. 11 shows the lift state of the needle valve of the injector 5, the heat release rate, and the cylinder pressure in the idle range, low-speed low-load range, medium-speed medium-load range and high-speed high-load range of the engine 1. Are shown in relation to each other. In the idle region shown by a thin solid line in FIG. 3, the sub-injection is performed on the most retarded side, and the injection amount is set to be larger than that in the middle load region. In this way, in the idle region where the temperature and pressure state of the firing chamber 4 are the lowest, a sufficient amount of heat generation is secured before the main injection while the misfire is reliably prevented, and the main injection Combustion of the injected fuel can be smoothly continued, and the combustion noise can be significantly reduced.

In the low-rotation, low-load region shown by the broken line in the same drawing, the sub-injection is performed on the retard side as compared with the medium-load or high-load state, which is earlier than the idle region. Is appropriately continued to the combustion of the main injected fuel, and the combustibility is greatly improved. Further, the premixed combustion speed of the main injection fuel in the initial stage of combustion is appropriately reduced by the burned gas generated by the combustion of the sub-injection fuel, so that the generation amount of NOx is further reduced. The internal EGR effect due to such burned gas is further enhanced by advancing the sub-injection and increasing the injection amount in a middle rotation and middle load region indicated by a virtual line in FIG. In addition, in the middle rotation and medium load region, a part of the injected fuel is diffused to a lean state due to the advance angle of the sub-injection, and the ignition does not occur until the main injection is performed as described later. , The engine output or the fuel efficiency is further improved.

As described above, in the normal operating range of the engine 1 in the low-speed and middle-speed ranges, the engine 1
The sub-injection ratio Rp and the injection stop interval Tp are gradually changed in accordance with changes in the load state and the rotation speed ne, so that the combustion state of the engine 1 also changes gradually and does not change suddenly. For this reason, for example, when the vehicle gradually increases the traveling speed on a flat road, the operating state of the engine 1 is set so as to be along the boundary on the high load side of the deceleration fuel cut region (see FIG. 3). When gradually shifting from a low rotation low load to a medium rotation medium load, and further to a high rotation high load, a good driving feeling with less shock is obtained stably.

On the other hand, as shown by the thick solid line in FIG. 11, when the engine 1 is in the high load range, the injection stop interval Tp is set sufficiently long, so that most of the sub-injected fuel is supplied to the cylinder. The fuel is not ignited before the compression top dead center of No. 2 and burns together with the main injected fuel. Hereinafter, such a combustion state will be described in detail.

As described above, as the operating range of the engine 1 shifts to the high rotation side or the high load side, the sub-injection timing of the fuel by the injector 5 is advanced. For example, in the specific region (a), the sub-injection This is performed in the middle of the compression stroke of the cylinder 2 (for example, BTDC 90 ° CA). Most of the fuel sub-injected early in this way is sufficiently mixed with the air in the combustion chamber 4 and sufficiently vaporized and atomized, and diffuses to a relatively wide area, and reaches a so-called auto-ignition temperature. However, the mixture becomes a lean mixture that does not start combustion. The lean premixture thus formed does not self-ignite even in the late stage of the compression stroke of the cylinder 2, and gradually reacts with the surrounding oxygen as the crank angle progresses (cool flame reaction), and the combustion proceeds. The temperature state and pressure state of the chamber 4 are increased.

In this state, when the main injection is performed in the vicinity of the compression top dead center of the cylinder 2, the engine 1 is in the high-speed and high-load region, and the temperature state is high. In the combustion chamber 4 in which the temperature and the pressure are further increased by the cool flame reaction of the sub-injected fuel, the main injection is performed by the common rail type high pressure injection, together with the extremely good atomization characteristics of the fuel spray. The fuel spray evaporates immediately at its outer edge, which forms a mixture having a concentration suitable for combustion with the surrounding lean premix, and starts combustion with almost no ignition delay. Then, the surrounding air-fuel mixture is continuously supplied toward the flame kernel formed at the outer edge of the spray in this way, and extremely excellent diffusion combustion is continuously performed.

That is, even when the engine 1 is in the high-speed and high-load state, the sub-injection is performed in the same manner as when the sub-injection of the fuel is performed in the low-speed low-load region or the medium-speed medium load region as described above. The diffusion combustion speed can be greatly increased while suppressing the momentum of the initial combustion as compared with the case where the combustion is not performed. In addition, the fuel sub-injected into the combustion chamber 4 at an early stage is sufficiently mixed in advance with the surrounding air, and then burns upon the combustion of the main injection fuel. improves.

As a result, as shown in FIG. 11, while the peak of the heat generation rate in the initial stage of combustion is lowered, favorable diffusion combustion showing a heat generation rate close to the peak is performed, and the combustion period is relatively short. Will be shorter. As a result, N
While suppressing the generation of Ox, the generation of smoke in the latter stage of combustion can also be reduced. Further, a sharp rise in the cylinder pressure in the initial stage of combustion is suppressed, and a high pressure state close to the peak is maintained for a relatively long time. A high output can be obtained without impairing the heat resistance under the full load condition, or the fuel injection amount can be reduced correspondingly to further improve the fuel efficiency.

As described above, in order to diffuse most of the sub-injected fuel and form the lean premix in the combustion chamber 4, the injection stop interval between the sub-injection and the main injection of the injector 5 is required. Tp needs to be longer than a predetermined time interval,
This predetermined time interval depends on the temperature state and pressure state of the combustion chamber 4,
Alternatively, although it depends on the amount of sub-injection of fuel, etc., in short, lean mixing in which, for example, 80% or more of the sub-injected fuel diffuses in the combustion chamber 4 and does not start combustion even when the so-called self-ignition temperature is reached. It can be said that the time interval is such as to form a mind.

[0085]

As described above, according to the fuel control system for a diesel engine according to the first aspect of the present invention,
Even when the engine is in a specific region where the engine speed is high and the load is high, the sub injection of the fuel by the fuel injection valve is performed such that a time interval is provided between the end of the sub injection and the start of the main injection. Thus, the sub-injection enhances the flammability of the main injection fuel to improve fuel efficiency or output, and at the same time, diffuses the main injection fuel satisfactorily from almost the beginning to produce NOx in the early stage of combustion. While suppressing, the generation of smoke in the latter stage of combustion can also be reduced.

According to the second aspect of the present invention, even when the engine is on the low load side in the middle rotation range, the ignitability and the combustibility of the main injection fuel are enhanced by the sub-injection of the fuel to reduce NOx and smoke. In addition, improvement in fuel efficiency or output can be achieved. At this time, by increasing the sub-injection ratio of the fuel as compared to the specific region, the process from combustion of the sub-injection fuel to combustion of the main injection fuel can be appropriately continued, and the above effect can be sufficiently obtained.

According to the third aspect of the invention, when the engine is on the low load side in the low rotation range, a sufficient amount of fuel is sub-injected, and the combustion from the fuel to the main injection fuel is appropriately continuously performed. Thus, the ignitability and combustibility of the main injection fuel can be improved. In addition, when the engine gradually shifts from a low rotation range to a high rotation range, a good driving feel can be obtained.

According to the fuel control system for a diesel engine according to the fourth aspect of the present invention, when the engine is located in a high-rotation high-load specific region and a medium-rotation medium load region adjacent thereto, The same effect as that of the second invention can be obtained.

According to the fifth aspect of the present invention, the combustibility is improved by sub-injection in a wide operating range of the engine, and the effect of improving fuel efficiency can be greatly improved when viewed over the entire operating range of the engine. .

Next, according to the fuel control system for a diesel engine according to the sixth aspect of the present invention, when the engine is on the high load side in the low engine speed range, the sub-injection amount is increased so that the temperature condition is relatively low and Even in a state where the fuel injection amount is large, the sub-injection can sufficiently enhance the combustibility of the main injection fuel. On the high load side in the high rotation range,
By reducing the sub-injection amount or extending the time interval between the sub-injection and the main injection, the generation of NOx and the reverse torque can be reduced.

According to the seventh aspect of the invention, when the engine shifts from a low rotation range to a high rotation range while the engine is in a high load state, a good driving feeling is obtained.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a fuel control device according to an embodiment of the present invention.

FIG. 2 is a functional block diagram illustrating a configuration of a fuel injection control unit of an ECU.

FIG. 3 is a diagram showing an example of an injection ratio map in which a sub-injection ratio is set so as to correspond to a target fuel injection amount and an engine speed.

FIG. 4 is a map showing an example of a change in a sub-injection amount corresponding to a change in an engine load and an engine speed.

FIG. 5 is a diagram showing an example of an injection interval map in which an injection stop interval is set so as to correspond to a target fuel injection amount and an engine speed.

FIG. 6 is a diagram corresponding to FIG. 5, showing an example of a first region on the low load side and a second region on the high load side.

FIG. 7 is a flowchart showing an overall procedure of fuel injection control.

FIG. 8 is an explanatory diagram showing a case where sub-injection is performed and a case where sub-injection is not performed;

FIG. 9 is a flowchart illustrating a procedure of fuel injection control.

FIG. 10 is an explanatory diagram showing a tendency of a change in the value of Qp / Tp corresponding to a change in the engine speed in a high-load region of the engine.

FIG. 11 is a graph showing changes in the heat release rate and the in-cylinder pressure accompanying combustion when the engine is in an idle range, a low-speed low-load range, a medium-speed medium-load range, and a high-speed high-load range. FIG.

[Explanation of symbols]

 A Fuel control device for engine 1 Diesel engine 2 Cylinder 4 Combustion chamber 5 Injector (fuel injection valve) 40 Control unit 40d Sub-injection ratio calculation unit (injection ratio setting unit) 40e Injection stop interval calculation unit (injection interval setting unit) 40f Injection Control unit (fuel injection control means)

Claims (7)

[Claims] A fuel is directly injected into a combustion chamber in a cylinder of an engine.
A fuel injection valve for injecting, and when the engine is at least on a low load side in a low rotation range, a fuel is injected by the fuel injection valve into a main injection operation near a compression top dead center of a cylinder and a sub-injection preceding the main injection operation. In the fuel control device for a diesel engine, which is configured to perform the injection separately from the operation, the interval between the sub-injection and the main injection operation by the fuel injection valve,
Injection interval setting means for setting a time interval between the time when the sub-injection operation is completed and the fuel injection valve is fully closed and the time when the fuel injection valve is started to open for the main injection operation; Fuel injection in which fuel is injected by the fuel injection valve in a sub-injection mode and a main injection operation such that a time interval set by the injection interval setting means is left when the engine is in a specific region on the high load side in a rotation range. A fuel control device for a diesel engine, comprising: a control unit. 2. The fuel injection control device according to claim 1, wherein the fuel injection valve separates the fuel into a sub-injection operation and a main injection operation even when the engine is on a low load side in a middle rotation range. The sub-injection ratio, which is a ratio of the fuel injection amount to the main injection operation by the sub-injection operation of the fuel injection valve, is set to be larger than a specific region when the engine is on the low load side of the middle rotation region. A fuel control device for a diesel engine, comprising: 3. The sub-injection ratio setting means according to claim 2, wherein the sub-injection ratio setting means sets the sub-injection ratio of the fuel to be larger than a specific region when the engine is on a low load side in a low rotation range. A fuel control device for a diesel engine, comprising: 4. The fuel is directly supplied to an in-cylinder combustion chamber of an engine.
A fuel injection valve for injecting, when the engine is in a specific region on a high load side in a high rotation region and a medium rotation medium load region adjacent to a low rotation or low load side of this region, fuel is injected by the fuel injection valve; Fuel injection control means for injecting separately into a main injection operation near the compression top dead center of the cylinder and a sub-injection operation preceding the main injection operation, and an interval between the sub-injection and the main injection operation by the fuel injection valve,
Injection interval setting means for setting a time interval between the time when the sub-injection operation is completed and the fuel injection valve is fully closed and the time when the fuel injection valve is started to open for the main injection operation, and The fuel injection control device for a diesel engine, wherein the injection interval setting means sets the time interval to be longer when the engine is in the specific region than when the engine is in the middle rotation load region. . 5. The fuel injection control means according to claim 4, wherein the engine is in a first region on a low load side in a low rotation to medium rotation region excluding a fuel cut region at the time of deceleration, or at least a medium rotation. The fuel injection valve separates the fuel into sub-injection and main injection operation when the fuel injection valve is in the second region on the high load side in the high rotation range. And a time interval of the main injection operation is set to be longer when the engine is in the second region than in the first region. 6. The fuel is directly supplied to an in-cylinder combustion chamber of an engine.
A fuel injection valve for injecting, fuel injection control means for injecting fuel by the fuel injection valve into a main injection operation near a compression top dead center of a cylinder and a sub-injection operation preceding the main injection operation, and the fuel injection The interval between the sub-injection and main injection operation by the valve is
Injection interval setting means for setting a time interval between the time when the sub-injection operation is completed and the fuel injection valve is fully closed and the time when the fuel injection valve is started to open for the main injection operation, and When the fuel injection amount by the sub-injection operation of the fuel injection valve is Qp, and the time interval is Tp, the value of Qp / Tp is higher when the engine is on the higher load side in the low rotation range. A fuel control device for a diesel engine, the fuel control device being larger than in the first embodiment. 7. The system according to claim 6, wherein the value of Qp / Tp is larger when the engine is on the high load side in the low rotation speed range than when the engine is on the high load side in the middle rotation speed range. A fuel control device for a diesel engine, which is larger at a load side than at a high load side in a high rotation range.