JPH11101147A - Engine control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an engine control device in which a catalyst converter having NOx occlusion type catalyst which can purify NOx in exhaust gas even in a lean air-fuel ratio condition, and which enables the engine to operate in a uniformly burning condition in a high load range or a high speed range, and to operate in a stratified burning condition in a low load and low speed range in a steady-state condition. SOLUTION: An injection dividing control means 35a divides fuel injection into two parts, so as to carry out the fuel injection at first and second times during intake stroke in a high load and low speed range. Fuel injection is carried out during intake stroke and during compression stroke, once per stroke, in a transient operating range in which combustion is changed over between a stratified burning condition and a uniform burning condition in a steady-state operating condition. In association with the division of the fuel injection, a fuel pressure control means 35b lowers the injection pressure of an injector 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control apparatus for a direct injection gasoline engine capable of performing stratified combustion in an air-fuel ratio lean state, and more particularly, to a state in which a NOx storage type catalyst provided in an exhaust passage is saturated. Belongs to the technical field of control for preventing such situations.

[0002]

2. Description of the Related Art Conventionally, as a control device for this type of engine, for example, as disclosed in International Publication No. WO93 / 07363, an air-fuel ratio is provided in an exhaust passage of the engine on a leaner side than a stoichiometric air-fuel ratio. A catalytic converter having a NOx storage type catalyst that stores nitrogen oxides (NOx) in exhaust gas and releases and releases and reduces the stored NOx when the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio. The air-fuel ratio is controlled to the rich side in the acceleration operation state and the full load operation state of the engine, while the air-fuel ratio is controlled to the lean side in other operation states.

Further, in the above-described control device, for example, when the steady operation state of the engine at the air-fuel ratio lean continues for a long time, the NOx storage amount becomes a saturated state exceeding the NOx storage capacity of the catalyst. In order to prevent this, control is performed to switch the air-fuel ratio to a rich state at predetermined intervals to release the NOx stored in the catalyst and purify it by reduction.

[0004]

However, in the above-mentioned conventional control device, the air-fuel ratio is switched to the rich side only to prevent the saturation of the catalyst even when the operation can be performed with the air-fuel ratio lean. And the fuel is consumed excessively, which is not preferable from the viewpoint of reducing fuel consumption.

[0005] Further, since the switching of the air-fuel ratio is performed irrespective of the driver's driving operation, there is also a disadvantage that the driver tends to feel uncomfortable with a shock generated due to a change in the operating state of the engine accompanying this.

Further, as shown in FIG. 18, when the catalyst temperature becomes higher than a predetermined value (for example, 400 ° C. or more), the NOx storage capacity of the NOx storage type catalyst decreases, and the NOx storage capacity of the NOx storage type catalyst in the air-fuel ratio lean state is reduced. There is a temperature dependency that the NOx purification rate is considerably reduced. That is, when the catalyst temperature becomes higher than a predetermined value, the NOx storage type catalyst is likely to be saturated. Therefore, it is necessary to suppress the temperature rise of the catalyst in order to suppress this.

The present invention has been made in view of the above points, and a main object of the present invention is to release NOx from a NOx storage type catalyst in a carbon monoxide (CO) atmosphere having a reducing action. By focusing on the fact that the catalyst becomes easy and utilizing this fact to promote the refreshing of the catalyst, it is intended to reduce the fuel consumption while preventing the catalyst from becoming saturated.

[0008]

In order to achieve the above object, according to the present invention, the fuel injection in a predetermined operating state of the engine is performed by dividing the fuel injection into a plurality of times. The CO emission was increased to promote catalyst refresh.

Specifically, the invention according to claim 1 is provided with a fuel injection valve for directly injecting fuel into a combustion chamber of a cylinder and an exhaust passage of an engine, wherein an air-fuel ratio is leaner than a stoichiometric air-fuel ratio. A NOx storage catalyst that stores nitrogen oxides in the exhaust gas when the engine is in the high-speed or high-speed range. The present invention is directed to a control device for an engine that injects fuel so as to be in a stratified combustion state in a low-load and low-speed region of the state. When the engine is in a predetermined operating state, an injection division control means is provided for dividing the fuel injection by the fuel injection valve into a plurality of injections and executing at least the first fuel injection in the intake stroke.

According to this configuration, when the engine is in the predetermined operating state, the fuel injection is divided into a plurality of times by the operation control of the fuel injection valve by the injection split control means. Then, the number of times of opening the fuel injection valve per cycle increases, and accordingly, the proportion of coarse-grained fuel injected in the early stage of opening the fuel injection valve increases, and the state of vaporization and atomization of fuel deteriorates. . For this reason, although the air-fuel mixture distribution in the entire combustion chamber is substantially uniform, the amount of CO emissions increases due to local incomplete combustion in the fine part. Then, the catalyst provided in the exhaust passage is wrapped in CO in the exhaust gas and easily releases the stored NOx, thereby promoting the refresh of the catalyst. Therefore, the frequency of switching the air-fuel ratio for refreshing the catalyst can be reduced, and the richness of the air-fuel ratio at the time of switching can be reduced.Thus, although there is an increase in fuel efficiency due to the deterioration of the fuel vaporization and atomization state, It is possible to reduce fuel consumption as compared with the related art, and it is possible to reduce a shock caused by a change in the operating state of the engine.

According to the second aspect of the present invention, the injection split control means in the first aspect of the present invention executes the fuel injection by the fuel injection valve a plurality of times during the intake stroke. As a result, during the intake stroke of the cylinder,
The second and subsequent fuel injections are performed while the first injected fuel is diffused in the combustion chamber, and the uniformity of the air-fuel mixture in the combustion chamber is promoted. Thus, an increase in fuel efficiency due to local incomplete combustion associated with the split injection can be suppressed. Further, since the exhaust gas temperature is reduced by shortening the combustion time, a decrease in the NOx purification rate due to an increase in the temperature of the catalyst is suppressed.

According to the third aspect of the present invention, the first or second aspect is provided.
The injection split control means according to the invention described in (1) uses the last fuel injection of the splits before the bottom dead center in the intake stroke.
It is to be executed within the crank angle range after degrees. As a result, the last fuel injection is performed near the end of the intake stroke when the piston speed is low, and since the time from fuel injection to ignition is short, the fuel injected at this time is vaporized and atomized. The ignition is performed in an insufficient state, and accordingly, the amount of CO emission increases, and the refresh of the catalyst is further promoted.

According to a fourth aspect of the present invention, the injection split control means in the third aspect of the invention executes the last fuel injection of the split in the first half of the compression stroke of the cylinder. As a result, the time from the last fuel injection to the ignition becomes extremely short, and the fuel injected at this time is ignited in a state in which vaporization and atomization is extremely poor, and the amount of CO emission increases. The catalyst refreshing effect is extremely high.

Further, the time from the first fuel injection to the last fuel injection can be made relatively long as compared with the case where the last fuel injection is executed in the intake stroke of the cylinder, so that the cycle time is shortened. The fuel injection can be performed even in a high engine speed region where it is substantially difficult to execute a plurality of fuel injections during the intake stroke.

According to a fifth aspect of the present invention, when the engine is in a high-load low-speed range, the injection split control means in the first aspect of the present invention controls the fuel injection by the fuel injection valve a plurality of times during the intake stroke. The fuel injection is divided so that at least the first fuel injection is performed within the crank angle range from 40 degrees after top dead center to 40 degrees before bottom dead center.

That is, in general, the amount of heat generated by the engine is large in a high load range, so that the catalyst temperature tends to increase.
Therefore, in the present invention, the fuel injection division control in the intake stroke of the cylinder is executed in the high load region, so that
As in the described invention, the temperature rise of the catalyst is suppressed. At this time, at least the first fuel injection is performed from 40 degrees after the top dead center where the piston speed is high to 40 degrees before the bottom dead center.
Running within a crank angle range up to degrees or less can promote fuel and air mixing.

In addition, since the engine speed is longer in the low engine speed region than in the high engine speed region, the fuel injection is divided into a plurality of injections in order to make the mixing state of fuel and air uniform. Is extremely effective.

According to a sixth aspect of the present invention, the injection split control means according to the first aspect of the present invention is configured such that when the engine is in a middle load and low or medium rotation range, the fuel injection by the fuel injection valve is performed. Is divided into a plurality of times in the intake stroke so that at least the first fuel injection is performed within a crank angle range from 40 degrees after top dead center to 40 degrees before bottom dead center.

That is, the engine is in a stratified combustion state by the fuel injection immediately before ignition in the compression stroke in the low-load low-rotation region, while the engine is in the high-load or high-rotation region in the low-load low-rotation region.
A uniform combustion state is achieved by fuel injection at least in the first half of the intake stroke. Therefore, in the region of medium load and low rotation or medium rotation where the combustion state changes by switching, the fuel injection division control in the intake stroke is executed to change the combustion state of the engine to the uniform combustion state. And a stratified combustion state, and the connection of the engine output is improved. In addition, similarly to the invention described in claim 5, it is possible to suppress the temperature rise of the catalyst.

According to a seventh aspect of the present invention, the injection split control means in the first aspect of the present invention, when the engine is in the middle rotation range, performs the fuel injection at least a plurality of times including the fuel injection in the first half of the compression stroke. And executed. This allows the combustion state of the engine to be set to an intermediate combustion state when switching between the uniform combustion state and the stratified combustion state, similarly to the invention of claim 6. And the output of CO becomes extremely large, and the amount of CO emission becomes extremely large, similarly to the invention described in claim 4, so that the catalyst refreshing effect is extremely large.

According to an eighth aspect of the present invention, the injection split control means according to the first aspect of the present invention is arranged such that the engine has a first region in which the engine has a medium load and a low rotation speed or a medium rotation speed; And in a region including at least the first region of the second region of medium rotation, the fuel injection by the fuel injection valve is divided and executed at least a plurality of times including the fuel injection in the first half of the compression stroke. And

[0022] This improves the connection between the output of the engine when the combustion state of the engine is switched and the invention according to the above-described claim 7, similarly to the invention according to the sixth or seventh aspect. Similarly, the amount of CO emission becomes extremely large, so that the refreshing effect of the catalyst is extremely large.

According to a ninth aspect of the present invention, in the invention according to any one of the sixth, seventh and eighth aspects, when the division control of the fuel injection is executed by the injection division control means, the air-fuel ratio is increased. Air-fuel ratio control means for controlling the air-fuel ratio to the rich side below the stoichiometric air-fuel ratio is provided. As a result, the air-fuel ratio is controlled to the rich side by the air-fuel ratio control means, so that the engine output is improved. Therefore, it is possible to compensate for the decrease in the engine output due to local incomplete combustion accompanying the split injection. .

Further, by controlling the air-fuel ratio to the rich side, the CO emission concentration in the exhaust gas can be increased, which is also preferable for refreshing the catalyst.

According to a tenth aspect of the present invention, the injection split control means in the first aspect of the present invention performs fuel injection at least in the first half of the compression stroke when the engine is in a low-load high-speed region. When the engine is in the high-load, high-speed range,
The fuel injection is performed at a time near the top dead center from the exhaust stroke to the intake stroke.

Thus, in the low-load high-speed range, the catalyst is refreshed by increasing the amount of CO emission, as in the fourth aspect of the invention, whereas in the high-load high-speed range, the required output to the engine is increased. Is extremely high, and the injection time is prolonged in response to the increase in the fuel injection amount.Thus, by executing the fuel injection collectively as soon as possible, the vaporization and atomization state can be sufficiently improved even if the fuel injection amount is large. And thereby the engine output can be improved.

According to the eleventh aspect of the present invention, in the catalyst according to the fifth or sixth aspect, the purification rate decreases by a predetermined amount or more when the temperature condition becomes higher than a predetermined value. In addition to providing catalyst temperature determining means for determining that the temperature state of the catalyst has risen above the predetermined level, the injection split control means determines that the temperature state of the catalyst is higher than the predetermined level by the catalyst temperature determining means. Is determined,
From 40 degrees after top dead center to 40 before bottom dead center in the intake stroke
The fuel injection split control is performed so that the crank angle is within the crank angle range up to and before and the intermediate point between the first fuel injection and the last fuel injection is later than 90 degrees after the top dead center. If the catalyst temperature determining means determines that the temperature state of the catalyst is lower than the predetermined temperature state, the crank angle range is from 40 degrees after top dead center to 40 degrees before bottom dead center in the intake stroke. The fuel injection division control is performed so that the intermediate point between the first fuel injection and the last fuel injection is earlier than 90 degrees after the top dead center.

According to this configuration, when the catalyst temperature determining means determines that the temperature of the catalyst is equal to or higher than the predetermined temperature (for example, 400 ° C.), the injection timing of the fuel injection is retarded and the intake stroke is reduced. As shown in FIG. 10, the CO emission amount can be significantly increased as compared with the case where the injection timing is shifted toward the first half of the intake stroke, as shown in FIG. That is, when the temperature state of the catalyst is equal to or higher than a predetermined value and the NOx purification rate is reduced, the refreshing effect of the catalyst can be enhanced by increasing the amount of CO emission.

On the other hand, when it is determined by the catalyst temperature determining means that the temperature state of the catalyst is not equal to or higher than the predetermined value, the injection timing of the fuel injection is advanced to make it closer to the first half of the intake stroke, as shown in FIG. As described above, although the CO emission amount is slightly reduced as compared with the case where the injection timing is set in the latter half of the intake stroke, the fuel consumption is significantly reduced. In addition,
Even in this case, the CO emission amount is sufficiently increased as compared with the case where the fuel injection is performed collectively, and the catalyst is refreshed.

According to the twelfth aspect of the present invention, the third and eighth aspects are provided.
Alternatively, in the invention described in 10, the first fuel injection amount is set to be larger than the total fuel injection amount after the second fuel injection. As a result, more than half of the whole fuel is injected at the time of the first fuel injection, so that the vaporized and atomized state of the injected fuel as a whole is improved, resulting from local incomplete combustion accompanying the split injection. Increase in fuel efficiency is suppressed.

According to a thirteenth aspect of the present invention, in the first aspect of the invention, there is provided a purification rate determining means for determining that the purification rate of the catalyst has decreased by a predetermined amount or more, and the injection split control means has the purification rate determination means. When it is determined by the means that the purification rate has decreased by a predetermined amount or more, the fuel injection by the fuel injection valve is divided into a plurality of times and executed. With this,
When the purification rate of the catalyst actually decreases, the catalyst is refreshed by increasing the amount of CO emissions, thereby preventing the catalyst from becoming saturated and suppressing an increase in fuel efficiency due to split injection. can do.

According to a fourteenth aspect of the present invention, the purification rate determining means in the thirteenth aspect of the present invention determines that the purification rate decreases by a predetermined amount or more when the engine is continuously stratified for a set time or longer. The configuration was determined. With this,
When the engine is continuously in the stratified combustion state, the air-fuel ratio lean state continues during the period, and the NOx storage amount of the catalyst is increasing. Therefore, the purification rate accompanying the decrease in the NOx storage capacity of the catalyst is Can be determined.

According to a fifteenth aspect of the present invention, the purification rate determining means in the thirteenth aspect determines that the purification rate decreases by a predetermined amount or more when the catalyst temperature becomes higher than a set temperature. Thus, it is possible to determine a decrease in the purification rate due to a rise in the temperature of the catalyst.

According to a sixteenth aspect of the present invention, the purification rate determining means in the thirteenth aspect of the present invention is configured such that the longer the duration of the stratified combustion state of the engine and the higher the temperature state of the catalyst during that period. The lower the purification rate of the catalyst, the greater the determination. As a result, the purification rate of the catalyst decreases as the air-fuel ratio lean state continues and the NOx storage capacity of the catalyst decreases, and decreases as the temperature rises. The reduction in the purification rate can be accurately determined.

According to a seventeenth aspect of the present invention, in the first aspect of the invention, when the engine is in a steady operation state with a predetermined load or more or a predetermined number of revolutions or more, or in an acceleration operation state, the air-fuel ratio is theoretically adjusted. Air-fuel ratio control means for controlling near the air-fuel ratio or on the rich side than the stoichiometric air-fuel ratio is provided, and the injection division control means divides the fuel injection into a plurality of times when the engine is in one of the above operating states. It was configured to be executed.

Thus, when the engine is in a steady operation state at a predetermined load or higher or a predetermined rotation speed or higher, or in an accelerating operation state, the air-fuel ratio shifts to the rich side in response to an increase in the required output to the engine. Controlled, the NOx stored in the catalyst is released and reduced and purified, and at that time, the amount of CO emission in the exhaust gas is increased, so that the refresh of the catalyst can be effectively promoted. .

[0037] In the invention described in claim 18, the injection split control means in the invention described in claim 17 is characterized in that:
Steady-state operation state with a predetermined load or more or a predetermined number of rotations or more,
Or, when in the acceleration operation state, to include at least the fuel injection in the intake stroke and the fuel injection in the first half of the compression stroke,
The fuel injection is divided and executed several times, and subsequently, the fuel injection is divided and executed plural times in the intake stroke.

As a result, it is expected that the catalyst temperature will not be so high immediately after the engine enters a steady operation state at a predetermined load or a predetermined rotation speed or more, or an acceleration operation state. By executing a plurality of fuel injections including the fuel injection in the first half, it is possible to give priority to the refresh of the catalyst due to an increase in the amount of CO emission.
On the other hand, if the engine is in one of the above operating states for a while, a rise in the catalyst temperature is expected, and therefore, in order to suppress the rise in the catalyst temperature, the fuel injection is divided in the intake stroke. Thus, the exhaust gas temperature can be reduced.

According to the nineteenth aspect of the present invention, the first to first aspects are provided.
8. In the invention according to any one of 8, the fuel pressure adjusting means for changing and adjusting the fuel injection pressure in the fuel injection valve,
A fuel pressure reduction control means for reducing the fuel injection pressure by the fuel pressure adjusting means when the fuel injection division control is executed by the injection division control means. As a result, by lowering the fuel injection pressure, the particle diameter of the fuel injected from the fuel injection valve becomes large, and the state of vaporization and atomization of the fuel is deteriorated. Refresh is further promoted.

According to a twentieth aspect of the present invention, the fuel pressure adjusting means according to the nineteenth aspect of the present invention provides a fuel pressure adjusting valve for reducing the hydraulic pressure of the high pressure injection path connecting the fuel pump and the fuel injection valve when the engine is started. And Thus, the cost of the system can be reduced by using the hydraulic pressure regulating valve originally provided for reducing the load on the fuel pump at the time of starting the engine.

According to a twenty-first aspect of the present invention, the fuel pressure adjusting means according to the nineteenth aspect sets the fuel injection pressure at the fuel injection valve to a first pressure set value of the lowest pressure, which is lower than the first pressure set value. The high pressure second pressure set value and the third pressure set value higher than the second pressure set value can be changed and adjusted in at least three stages, and the fuel pressure control means controls the fuel injection by the injection split control means. When the split control is executed, the fuel injection pressure in the fuel injection valve is controlled to a high pressure equal to or higher than the second pressure set value. In the invention according to claim 21, the fuel pressure adjusting means according to claim 19 is , The fuel injection pressure in the fuel injection valve is set to the first pressure of the lowest pressure.
A pressure setting value, a second pressure setting value higher than the first pressure setting value, and a third pressure setting value higher than the second pressure setting value. The control means is configured to control the fuel injection pressure at the fuel injection valve to a high pressure equal to or higher than the second pressure set value when the fuel injection split control is executed by the injection split control means.

Thus, the fuel injection pressure at the fuel injection valve when executing the fuel injection split control is different from the first pressure set value set to reduce the load on the fuel pump when the engine is started. Since the control can be performed to the second pressure set value, it is possible to adjust to the optimum value for increasing the amount of CO emission and reducing fuel consumption.

According to a twenty-second aspect of the present invention, in the fuel pressure control means according to the twenty-first aspect of the present invention, the last fuel injection divided by the injection division control means includes a crankshaft that is at least 40 degrees before bottom dead center in the intake stroke. When executed within the angular range, the fuel injection pressure at the fuel injector is controlled to a second pressure set value, while when the last fuel injection is not executed within the crank angle range, the fuel injection pressure is increased to the second The configuration is such that the pressure is controlled to a high pressure value equal to or higher than three pressure setting values.

That is, when the last divided fuel injection is performed in the crank angle range of 40 degrees or more before the bottom dead center in the intake stroke, the injection timing is set to give priority to the refresh of the catalyst due to an increase in the amount of CO emission. Since the fuel vaporization and atomization state is intended to be deteriorated by retarding the fuel as a whole, the fuel injection pressure is also reduced to the second set pressure value, so that the particle size of the fuel injected from the fuel injection valve is reduced. By making the diameter rough, the state of vaporization and atomization can be further deteriorated.

On the other hand, when the last fuel injection is not performed within the crank angle range, the fuel injection timing is advanced as a whole in order to suppress the deterioration of the vaporized and atomized state of the fuel in order to reduce the fuel consumption. Therefore, by increasing the fuel injection pressure to the third set pressure value or more, atomization of the fuel injected from the fuel injection valve can be prevented from being impaired.

[0046]

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

(Embodiment 1) FIG. 1 shows an engine control device E according to Embodiment 1 of the present invention, wherein 1 is an in-line 4-cylinder 4-cycle gasoline engine. The engine 1 has a cylinder block 3 having four cylinders 2, 2,... (Only one is shown), a cylinder head 4 mounted on the upper surface of the cylinder block 3, and can reciprocate in each cylinder 2. And a combustion chamber 6 surrounded by the piston 5 and the cylinder head 3 is formed in each of the cylinders 2. This combustion chamber 6
An ignition plug 7 is provided at the upper part of the ignition plug, and the ignition plug 7 is connected to an ignition circuit 8 including an igniter and the like. A fuel injection valve 9 is provided on a side wall of the combustion chamber 6, and fuel injected from the fuel injection valve 9 is trapped in a cavity (not shown) provided at the top of the piston 5, and a spark plug is provided. 7, a relatively dense mixture field is formed.

Reference numeral 10 denotes an intake passage for supplying intake air to the combustion chamber 6 of each of the cylinders 2. The upstream end of the intake passage 10 is connected to an air cleaner 11, while the downstream end is
It is connected to the combustion chamber 6 via the intake valve 12. A heat-sensitive airflow sensor 13 for detecting the amount of intake air taken into the engine 1 is provided in the intake passage 10.
The throttle valve 14 and the surge tank 15 are arranged in order from the upstream side. The throttle valve 14 is
The mechanical connection with the accelerator pedal has been disconnected,
The throttle opening is controlled by an actuator 14a that operates in response to a signal from an ECU 35 (Electronic Control Unit) described later.

On the other hand, reference numeral 20 denotes an exhaust passage for discharging exhaust gas from the combustion chamber 6, the upstream end of which is connected to the combustion chamber 6 via an exhaust valve 21. An O2 sensor 22 for detecting an air-fuel ratio and a catalytic converter 23 for purifying exhaust gas are arranged in the exhaust passage 20 in order from the upstream side. The O2 sensor 22 detects the air-fuel ratio based on the oxygen concentration in the exhaust gas, and the output changes abruptly at the stoichiometric air-fuel ratio.

The catalytic converter 23 operates in a lean state where the air-fuel ratio is larger than the stoichiometric air-fuel ratio.
While storing Ox, when the air-fuel ratio becomes rich below the stoichiometric air-fuel ratio, the stored NOx is released for reduction and purification.

That is, as shown in FIG. 2, the catalytic converter 23 has a NOx storage layer 23b on a carrier 23a.
And the catalyst material layer 23c are formed in layers with the former inside (the lower side in the figure) and the latter outside (the upper side in the figure). The carrier 23a is a cordierite honeycomb structure. The NOx storage layer 23b is mainly composed of a NOx storage type catalyst material in which a Pt component as a catalyst component and a Ba component as a NOx storage material are supported on activated alumina having a large specific surface area. The catalyst material layer 23c is mainly composed of a NOx reduction type catalyst material in which zeolite is supported as a support base and Pt components and Rh components are supported thereon.

The intake passage 10 and the exhaust passage 20
Is an EGR for recirculating a part of the exhaust gas to the intake side.
The EGR passage 24
Is provided with an EGR valve 25 for adjusting the exhaust gas recirculation amount.

The engine 1 is provided with a water temperature sensor 26 which is provided adjacent to the water jacket and detects a cooling water temperature. In addition, a crank angle sensor such as an electromagnetic pickup (not shown) is provided. The engine speed is detected based on a pulse signal output from the crank angle sensor.

Reference numeral 27 denotes a high-pressure fuel pump for increasing the pressure of the fuel sent from the fuel tank 28 and supplying it to the injector 9. Reference numeral 29 denotes a fuel-pressure adjusting means for changing and adjusting the discharge pressure of the high-pressure fuel pump. Pressure controller. The pressure controller 29 is composed of a pressure regulating valve that is duty-controlled by a control signal from the ECU 35 described later, and returns fuel from a fuel distributor (not shown) to the upstream side of the high-pressure fuel pump 27 to supply the fuel to the injector 9. Change and adjust the fuel pressure. Reference numeral 30 denotes a low-pressure fuel pump for pumping the fuel in the fuel tank 28 to the high-pressure fuel pump 27. The pressure of the fuel discharged from the low-pressure fuel pump 30 is adjusted by a low-pressure pressure regulator 31, and a fuel filter 32 is provided. Is sent to the high-pressure fuel pump 27.

In FIG. 1, reference numeral 35 denotes an engine control unit (ECU) constituted by a microcomputer or the like. Output signals from the air flow sensor 13, the O2 sensor 22, the crank angle sensor, the water temperature sensor 26, the accelerator opening sensor 34, and the like are input to the ECU 35. On the other hand, a signal (pulse signal) for controlling fuel injection to the fuel injection valve 9 is output from the ECU 35, and a control signal is output to the ignition circuit 8, the actuator 14a of the throttle valve 14, the pressure controller 29, and the like. You.

That is, the ECU 35 mainly comprises
Determination of warm-up of the engine 1, determination of the operating state of the engine 1,
The operating range of the engine 1 is determined, and based on the results of these determinations, referring to an electronically stored map, controlling the injection timing and injection pulse width of the fuel injection valve 9, controlling the fuel pressure, and controlling the throttle valve 14 An injection division control means 35a for performing fuel injection divided into a plurality of times and executing the fuel injection control, and a fuel pressure control means for lowering the fuel injection pressure at the time of the normal batch fuel injection 35b and an air-fuel ratio for controlling the air-fuel ratio to near the stoichiometric air-fuel ratio or to a richer side than the stoichiometric air-fuel ratio when the engine 1 is in a steady operation state at a predetermined load or a predetermined rotation speed or more, or in an acceleration operation state. Control means 35c (known).

Specifically, the operating region of the engine 1 is divided into four operating regions based on the engine speed and the engine load in each of the steady operation state shown in FIG. 3 and the accelerated operation state shown in FIG. Have been. In the steady operation state of the engine 1 shown in FIG.
The fuel injection immediately before ignition in the compression stroke causes the engine 1
To a stratified combustion state, and the air-fuel ratio lean (for example, A / F
≧ 22), and in each of the other operating regions II, III, and IV, at least the first fuel injection is executed in the intake stroke to bring the engine 1 into a uniform combustion state. , Air-fuel ratio rich (for example, A / F = 12 to
This is the area where operation is performed in 14). Similarly, each of the operation regions XI, XII, XIII, XIV in the acceleration operation state shown in FIG.
This is a region where the engine 1 is made to be in a uniform combustion state and operated at an air-fuel ratio rich (for example, A / F = 12 to 14).

A feature of the present invention is that when the engine 1 is in a predetermined operation state, the fuel injection is divided into a plurality of times and executed by the injection split control means 35a, so that the CO emission in the exhaust gas is reduced. The amount was increased to promote catalyst refresh.

(Division Control of Fuel Injection) The division control of fuel injection by the injection division control means 35a will be specifically described with reference to flowcharts shown in FIGS.

In step S1 in FIG. 5, the engine speed, accelerator opening, measured values of the air flow sensor, engine water temperature, starter output, etc. are read.
At 2, it is determined whether the engine 1 is starting. That is, if the starter motor is off or the engine speed is higher than the predetermined speed, it is determined that the engine is not starting, and the process proceeds to step S5 described later, while the starter motor is on and the engine speed is lower. If the rotation speed is equal to or less than the predetermined rotation speed, it is determined that the engine is being started, and the process proceeds to step S3.

In step S3, the injection pulse width TaK and the injection timing corresponding to the start of the engine are read out from a map stored electronically. The injection pulse width TaK is set to a large value so that the air-fuel ratio is made rich to ensure good startability. Subsequent step S
In No. 4, the injection pulse width TaK at the time of the start is set to the first injection pulse width TaK1 in the intake stroke, the second fuel injection pulse width TaK2 in the intake stroke, and the fuel injection pulse width TaK3, in the compression stroke. TaD is set to 0. Here, the injection pulse widths TaK1, TaK2, TaK3, and TaD are set to injection timings as shown in FIG. 8, respectively.

That is, at the time of starting the engine, FIG.
As shown in FIG. 5, the fuel injection is performed as a batch injection in the first half of the intake stroke, and the process proceeds to step S29 in FIG. 5, and the fuel injection is executed in steps S29 to S39 as described later. As a result, the engine 1 blows up in a uniform combustion state.

On the other hand, if it is determined in step S2 that the engine is not being started, the process proceeds to step S5, in which the engine water temperature in the operating state is adjusted to a predetermined temperature (for example, 70 ° C. to 80 ° C.) corresponding to the warm-up state of the engine 1. C) It is determined whether or not it is the above. And, if the temperature is lower than the predetermined temperature,
Since the engine is in a cold state, the process proceeds to step S8 described later. On the other hand, if the engine temperature is equal to or higher than the predetermined temperature, the engine is in a warm-up state. . That is, when the engine speed, the engine load, or the accelerator opening increases by a predetermined amount or more, it is determined that the engine 1 is in the acceleration operation state. If it is determined that the vehicle is not in the accelerating operation state, the process proceeds to step S23 (see FIG. 6), which will be described later. If it is determined that the vehicle is in the accelerating operation state, the process proceeds to step S7, based on the engine speed and the engine load. It is determined whether or not the operation state 1 is in the operation region XI or the operation region XIV (see FIG. 4).

That is, when the engine speed is, for example, 3000 rpm or less and the engine load is, for example, 1/2 or less of the full load (operating region XI in FIG. 4) in the acceleration operation state of the engine 1, the step Proceed to S8. The engine speed is, for example, 4000 rpm or more, or the engine load is, for example, 3/4 of the full load.
And the engine speed is, for example, 3000
If it is not less than rpm (operation region XIV in FIG. 4), the process proceeds to step S8. The engine load may be obtained, for example, from the intake charging efficiency, and the intake charging efficiency is calculated from the output of the airflow sensor and the engine speed.

In step S8, the injection pulse width TaK is calculated. Here, if the engine 1 is in a semi-warmed state (for example, a state where the engine water temperature is 40 ° C. to 70 ° C.),
From the viewpoint of ensuring combustion stability and purifying exhaust gas, the injection pulse width TaK is calculated so that the air-fuel ratio becomes substantially the stoichiometric air-fuel ratio. If the engine 1 is in a warm-up state, the injection pulse width TaK is calculated based on the accelerator operation amount and the engine load so as to be rich in the air-fuel ratio. Is obtained.

In the subsequent step S9, the calculated injection pulse width TaK is set to the first injection pulse width TaK1 in the intake stroke, as in step S4, and the other injection pulse widths TaK2, TaK3, TaD are set. Is set to 0, and the fuel injection is performed as a batch injection in the first half of the intake stroke as shown in FIG. Then, the process proceeds to step S10 to calculate the injection timing of the above-described batch injection.
In steps S29 to S39, fuel injection is performed.

On the other hand, if it is determined in step S7 that neither the operating region XI nor the operating region XIV is present, the process proceeds to step S11 in FIG. 6 and, as in step S7, based on the engine speed and the engine load. It is determined whether or not the operating state of the engine 1 is in the operating region XIII. That is, when it is determined that the engine 1 is in the high-load and low-speed operation region (the operation region XIII in FIG. 4) in the accelerated operation state, the process proceeds to step S20 described below,
Not in that operating area (ie, in operating area XII in the figure)
If determined, the process proceeds to step S12.

In this step S12, it is determined whether or not the value of the flag FlagAck is 1. If it is not 1, the process proceeds to step S13 to set the value of the flag FlagAck to 1,
After setting the timer in the subsequent step S14, the process proceeds to step S16. On the other hand, if the flag FlagAck = 1 in the step S12, it is determined in a step S15 whether or not the timer is being set. If the timer is not being set, the process proceeds to a step S19, while if the timer is being set, the process proceeds to a step S16.

In step S16, similarly to step S8, the injection pulse width TaK is calculated based on the accelerator operation amount and the engine load so that the air-fuel ratio becomes rich, and a high output corresponding to the acceleration operation state of the engine 1 is obtained. Will be obtained. In the following step S17, based on the injection pulse width TaK calculated in the above step S16,
The injection pulse widths TaK1 to TaK3 are obtained. That is, TaK1 = (1−a) × TaK TaK2 = 0 TaK3 = a × TaK where a is a division coefficient for changing the division ratio of the fuel injection amount and is set based on various test results. However, in order to reduce fuel consumption, it is preferable that a ≦ 0.5. In addition, the injection pulse width TaD = 0.

That is, in the operating region XII, as shown in FIG. 8C, the fuel injection is divided into two parts before and after the predetermined time elapses after the engine 1 enters the acceleration operation state. , Once each in the intake stroke and the compression stroke. As a result, the number of injections of the injector 9 per cycle increases, and the proportion of coarse-grained fuel injected in the early stage of valve opening increases accordingly, and the state of vaporization and atomization of fuel deteriorates. For this reason, the amount of CO emission increases due to local incomplete combustion in the fine portion of the air-fuel mixture, and the catalytic converter 23 provided in the exhaust passage 20 is wrapped in CO in the exhaust gas to occlude the occlusion. Since the released NOx is easily released, the catalyst is refreshed. In particular, 2
Since the second fuel injection is performed in the compression stroke, the time from this fuel injection to ignition becomes extremely short, and the injected fuel is ignited in a state of extremely poor vaporization and atomization, so that the CO emission amount is reduced. Is extremely large.

On the other hand, if it is determined in step S15 that the timer is not being set, the flow advances to step S19 to clear the flag FlagAck, and then to step S20.
If it is determined in step S11 that the engine 1 is in the operating region XIII, the process proceeds to step S20. In this step S20, steps S8, S16
Similarly to the above, the injection pulse width TaK is calculated based on the accelerator operation amount and the engine load, the air-fuel ratio becomes rich, and a high output corresponding to the acceleration operation state of the engine 1 can be obtained. In the following step S21, based on the injection pulse width TaK calculated in the above step S20,
The respective injection pulse widths TaK1 to TaK3 are obtained. That is, TaK1 = b × TaKTaK2 = (1−b) × TaKTaK3 = 0 where b is a division coefficient for changing the division ratio of the fuel injection amount, and is set based on various test results. However, in order to reduce fuel consumption, it is preferable that b> 0.5. In addition, the injection pulse width TaD = 0.

That is, in the operating region XII, when a predetermined time has elapsed after the engine 1 enters the accelerating operation state, and in the operating region XIII, as shown in FIG. And is executed in the intake stroke. As a result, the number of injections of the injector 9 per cycle increases, so that the amount of CO emission increases as described above, the refresh of the catalyst is promoted, and the initially injected fuel diffuses in the combustion chamber 6. Since the second fuel injection is performed during the period, and the uniformity of the air-fuel mixture in the combustion chamber 6 is promoted, it is possible to reduce the exhaust gas temperature by suppressing the combustion time, thereby suppressing the catalyst temperature rise. it can. In addition, the operating efficiency of the engine 1 can be improved by shortening the combustion time, and an increase in fuel efficiency due to local incomplete combustion accompanying split injection can be suppressed.

On the other hand, if it is determined in step S6 that the engine 1 is not in the accelerating operation state, that is, in the steady operation state, the process proceeds to step S23, where the engine 1 is controlled based on the engine speed and the engine load. In the operating region where the operating state of the engine 1 is high load and low speed (FIG. 3)
Is determined to be in the operating region II).

That is, in the steady operation state of the engine 1, the engine speed is increased to a predetermined speed (for example, 3000 rpm).
pm), and when the engine load is in a high load region of a predetermined value or more (for example, 2/3 or more of the full load), the operation state of the engine 1 is a high load and low speed operation. It is determined that it is in the area II,
Proceeding to S22, the fuel injection is divided into two before and after the intake stroke and executed as described above.

That is, in the operating region II, a high load is applied to the engine 1, so that the generated heat becomes large and the catalyst temperature easily rises. However, the temperature increase of the catalyst is suppressed by the split control of the fuel injection in the intake stroke. be able to. In the operation region II, the engine speed is low and the cycle time of the engine 1 is longer than in the high rotation operation region. Therefore, in order to make the mixing state of fuel and air uniform, the fuel injection is divided into a plurality of times. It is extremely effective to do so.

At this time, the injection timing of the two fuel injections before and after is set within a crank angle range from 40 degrees after the top dead center to 40 degrees before the bottom dead center in the intake stroke. In this crank angle range, the piston speed is extremely high as shown in FIG. 9, so that the mixing of the injected fuel and the intake air can be promoted.

The injection timing is changed according to the temperature state of the catalyst. That is, when the temperature state of the catalyst becomes equal to or higher than the predetermined temperature (for example, 400 ° C.) and the NOx purification rate decreases, the injection timings of the front and rear two fuel injections are delayed as a whole toward the latter half of the intake stroke. By squaring, as shown in FIG. 10, the amount of CO emission can be significantly increased, so that the refresh effect of the catalyst can be enhanced. On the other hand, if the temperature state of the catalyst is not equal to or higher than the predetermined temperature, the injection timing is shifted toward the first half of the intake stroke as a whole, as compared to the case where the injection timing is shifted toward the latter half of the intake stroke as shown in FIG. Fuel economy can be reduced. Even in this case, compared with the case where the fuel injection is performed at once, the CO emission amount is sufficiently increased, and there is a catalyst refreshing effect.

In order to determine the temperature state of the catalyst, a gas temperature sensor is provided, for example, inside the catalytic converter 23 or in the exhaust passage 20 immediately before the converter, and the catalyst temperature is estimated from the detected temperature of the gas temperature sensor. In this case, the determination may be made.

If it is determined in step S23 in FIG. 6 that the operating state of the engine 1 is not in the operating region II, the process proceeds to step S24, and the process proceeds to step S23.
Based on the engine speed and engine load,
When the operating state of the engine 1 is low load (for example, の of full load)
It is determined whether or not the operation range is low (for example, 3000 rotations or less) (operation region I in FIG. 3). If the operation region is not this operation region, the process proceeds to step S28 to be described later. If there is, the process proceeds to step S25.

In step S25, the injection pulse width T
aD is calculated based on the accelerator operation amount and the engine load. Here, the operation region I is a region in which the engine 1 is operated in a stratified combustion state, and has an injection pulse width TaD.
Is set to a small value so that the air-fuel ratio becomes lean. In the following step S26, the values of the injection pulse widths TaK1, TaK2 and Ta3 other than the injection pulse width TaD are set to 0, and the fuel injection is performed as a batch injection in the compression stroke. Then, after proceeding to step S27 to calculate the injection timing, in steps S29 to S39 in FIG. 7, FIG.
As shown in (2), the fuel injection is performed immediately before the ignition timing of the compression stroke. As a result, the engine 1 is brought into the stratified combustion state at the lean air-fuel ratio.

On the other hand, in step S24, the engine 1
If it is determined that the operation state of the engine 1 is not in the operation region I, the process proceeds to step S28, and the operation state of the engine 1 is changed to the stratified combustion state and the uniform combustion state based on the engine speed and the engine load as in step S24. It is determined whether or not the vehicle is in a transitional operation region (operation region IV in FIG. 3).
This operation region IV is a combination of the first operation region and the second operation region, and the first operation region is a medium load (for example, 以上 or more of full load and ２ or less of full load), In addition, low rotation (for example, 3000 rotations or less) or medium rotation (for example, 300 rotations or less)
(0 to 4000 revolutions). In addition, the second
Is an operation region in which the rotation is medium and the load is low (for example, a load smaller than 1/2 of the full load) or the load is medium.

If it is determined that the operating state of the engine 1 is in the operating region IV, the above-described steps S16 to S16 are performed.
Then, as shown in FIG. 8 (c), the fuel injection is divided into two parts before and after, and is executed once each in the intake stroke and the compression stroke. Thus, in a transitional operation region (operation region IV) in which the combustion state changes between a stratified combustion state (operation region I) and a uniform combustion state (operation regions II and III), the combustion state of the engine 1 is changed. A combustion state intermediate between stratified combustion and uniform combustion can be achieved, and the connection of the engine output is improved. Note that, in the above-described operation region IV, the fuel injection may be divided and executed twice before and after the intake stroke.

On the other hand, in step S28, the engine 1
If it is determined that the operating state is not in the operating region IV, that is,
It is determined that the vehicle is in the operating region III, and the above steps S8 to S8
Proceeding to 10, the fuel injection is performed as a batch injection in the first half of the intake stroke, as shown in FIG. As a result, the required output to the engine 1 is extremely high, and a high load (for example, 2/3 of the full load) in which the injection time is increased in accordance with the increase in the fuel injection amount
As described above, in the operation range of middle and high rotations (for example, 3000 rotations or more), the engine output is improved by executing the fuel injection collectively. At that time, the injection timing
If it is near the top dead center from the exhaust stroke to the intake stroke,
Even if the fuel injection amount is large, the state of vaporization and atomization can be sufficiently improved, and the engine output can be further improved.

In the low load operation range (for example, a load lower than 1/2 of the full load) in the above operation range III, FIG.
As shown in (c), the fuel injection may be performed once in each of the intake stroke and the compression stroke, so that the refresh of the catalyst may be promoted by increasing the amount of CO emissions.

The above steps S4, S10, S18, S
In steps S29 of FIG. 7 following S22 and S27, it is halved whether or not the injection pulse width TaK1 of fuel injection is equal to zero.
If it is not = 0, the routine proceeds to step 30, where it is determined that the injection timing of the injection pulse TaK1 has come. If the injection timing has reached the injection pulse width TaK1 calculated in step S3, S10, S18 or S22, respectively. ,
Proceeding to step S31, fuel injection is performed.

In step S29, TaK1
If = 0, the process proceeds to step S32. Thereafter, in steps S32 to S34, the same processing as in steps S29 to S31 is performed for the injection pulse width TaK2.
In the following steps S35 to S39, the upper injection pulse width TaK
The same processing is performed for 3, TaD, and the process returns.

Note that the opening of the throttle valve 14 is shown in FIG.
Is controlled in accordance with the accelerator operation amount by the driver according to the throttle opening characteristic shown in FIG. That is, in the acceleration operation state, the throttle opening characteristic of the TVA shown in the figure is selected, while in the steady operation state, the throttle opening characteristic of the TVB shown in the figure is selected.

(Control of Fuel Pressure) Next, the fuel pressure control means 35b
The control of the fuel injection pressure according to FIG.
This will be described with reference to FIG.

At step T1 in the flowchart of FIG. 12, it is determined whether or not the engine 1 is starting based on the starter signal. That is, if the starter motor is in the ON state and the engine speed is equal to or lower than the predetermined speed, it is determined that the engine is being started, and the process proceeds to step T2, and the set pressure of the pressure controller 29 is set to the first pressure set value of the lowest pressure. (See FIG. 13). As a result, the fuel injection pressure at the fuel injection valve 9 becomes extremely low, and the load on the fuel pumps 27 and 30 at the time of starting the engine can be reduced.

On the other hand, in step T1, the start
If the motor is off or the engine speed is higher than the predetermined speed, it is determined that the engine is not being started, and the process proceeds to step T3, where the operating state of the engine 1 executes the fuel injection split control as described above. It is determined whether or not it is in the operation area (split control area). That is, for example, in the case of the operation regions I, III, XI, and XIV (see FIGS. 3 and 4), since the region is not the divided control region, the process proceeds to step T6 described later, while, for example, the operation regions II, IV, XII, and XIII If so, it is determined that the area is the divided control area, and the process proceeds to step T4.

In step T4, it is determined whether or not the last divided fuel injection is performed in the crank angle range of 40 degrees before the bottom dead center in the intake stroke of the cylinder.
Then, if it is executed within the crank angle range, the process proceeds to step T5, where the set pressure of the pressure controller 29 is controlled to the second pressure set value of the intermediate pressure. This second
Since the pressure set value is lower than the third pressure set value which is a normal fuel injection pressure, the particle diameter of the fuel injected from the injector 9 becomes coarse, and the state of vaporization and atomization of the fuel deteriorates. As a result, the amount of CO emission increases, and the refresh of the catalyst is further promoted.

That is, when the last fuel injection is performed in the crank angle range of 40 degrees or more before the bottom dead center in the intake stroke, the entire injection timing is refreshed to refresh the catalyst due to an increase in the amount of CO emission. Therefore, by lowering the fuel pressure at the same time, CO
Emissions are to be further increased.

On the other hand, if it is determined in step T4 that the last divided fuel injection has not been executed in the crank angle range of 40 ° before the bottom dead center in the intake stroke of the cylinder, that is,
Since the injection timing is advanced as a whole in order to reduce fuel consumption, the process proceeds to step T6, where the set pressure of the pressure controller 29 is controlled to a third pressure set value which is a normal fuel injection pressure. . In this way, the fuel consumption can be reduced without impairing the atomization of the fuel injected from the injector 9.

Next, the function and effect of the first embodiment will be described.

In the first embodiment, the operating range (operating state) of the engine 1 is determined on the basis of the engine load and the engine speed, and the different fuel injection division control is performed in each operating range to thereby reduce the CO emission. , The fuel consumption can be reduced, the fuel consumption can be reduced, and the temperature rise of the catalyst can be suppressed.

That is, in the high-load and low-speed operation region (operation region II) in the steady operation state of the engine 1, the fuel injection is divided into two parts before and after the intake stroke and executed. The increase in the amount of CO emission can promote the refresh of the catalyst, thereby reducing the frequency of switching the air-fuel ratio for refreshing the catalyst and lowering the richness of the air-fuel ratio at that time. As a result, the fuel consumption is increased due to the deterioration of the vaporized and atomized state of the fuel, but the fuel consumption is reduced as compared with the conventional one, and the shock due to the change in the operating state of the engine 1 is reduced. Can be.

Further, in the above-mentioned operating region II, the calorific value of the engine 1 is increased due to the high load, and the catalyst temperature is likely to be increased. However, the combustion time is shortened by the two fuel injections before and after the intake stroke. Since the exhaust gas temperature can be reduced, the temperature rise of the catalyst can be suppressed. In the operating region II, the engine speed is low, and the cycle time of the engine is longer than in the high-speed operating region. Therefore, in order to make the mixing state of fuel and air uniform, the fuel injection is divided into a plurality of times. It is extremely effective.

Further, in a steady operation state of the engine 1, a transitional operation region (operation region IV) between an operation region in a stratified combustion state (operation region I) and an operation region in a uniform combustion state (operation regions II and III). )), The fuel injection is divided and executed twice before and after, so that the combustion state of the engine 1 when switching between the stratified combustion state and the uniform combustion state is changed to an intermediate combustion state between them. And the connection between the engine outputs can be improved.

Further, at this time, the fuel injection is performed once in each of the intake stroke and the compression stroke, so that the time from the second fuel injection to the ignition becomes extremely short. Since the ignition is performed in a state where vaporization and atomization are extremely poor, the refreshing effect of the catalyst due to an increase in the amount of CO emission is also extremely high.

Further, in the operating region XII in the acceleration operation state of the engine 1, the fuel injection is executed once in each of the intake stroke and the compression stroke until a predetermined time elapses after the acceleration operation state. As described above, the refresh effect of the catalyst due to the increase in the amount of CO emission can be extremely enhanced. On the other hand, when the predetermined period elapses and the catalyst temperature rise is predicted, the fuel injection is divided into the intake strokes. By doing so, the exhaust gas temperature can be reduced as described above, and the temperature rise of the catalyst can be suppressed.

In addition, when the CO emission is increased by dividing the fuel injection (operating regions II, IV, XII, XIII),
Since the fuel injection pressure is controlled to the second pressure set value lower than the third pressure set value which is the normal fuel injection pressure, the particle diameter of the fuel injected from the injector 9 due to the decrease in the fuel pressure is reduced. By degrading the state of vaporization and atomization of the fuel by roughening, the refreshing effect of the catalyst due to an increase in the amount of CO emission can be enhanced.

(Embodiment 2) FIGS. 14 and 15 show an engine control device E according to Embodiment 2 of the present invention (note that the same parts as those in FIGS. 1, 5, 6 and 7 are shown). , And the description thereof is omitted. This embodiment has the same configuration as that of the first embodiment, but further includes a purification rate determining unit 36 for determining a purification rate state of the catalyst.
When the purification rate determining means 36 determines that the purification rate of the catalyst has decreased by a predetermined amount or more, the fuel injection is divided into two parts before and after the fuel injection.

That is, in FIG. 14, step S1
Steps S5 to S5 are the same as steps S1 to S5 of the first embodiment, but in step S51 subsequent to step S5, it is determined whether the catalyst temperature is equal to or higher than the set temperature. If the temperature is not equal to or higher than the set temperature, step S6
Proceeding to the subsequent steps, while executing the same control as in the first embodiment, if the catalyst temperature is equal to or higher than the set temperature, it is determined that the purification rate has decreased by a predetermined amount or more, and step S20 in FIG.
In steps S20 to S22, two divided injection control operations before and after the intake stroke are performed.

To determine the temperature state of the catalyst, for example, a gas temperature sensor is provided inside the catalytic converter 23 or in the exhaust passage 20 immediately before the catalytic converter 23, and the catalyst temperature is estimated from the detected temperature of the gas temperature sensor. In this case, the determination may be made.

Further, in FIG.
S24 corresponds to steps S12 to S2 of the first embodiment, respectively.
Step S2 which is the same as Step 4 but follows Step S24
At 41, it is determined whether or not the operating state of the engine 1 is in the operating region I for a set time or more. If the time is not equal to or longer than the set time, the process proceeds to step S25 and thereafter to execute the same control as in the first embodiment. It is determined that the NOx storage amount of the catalyst has increased due to the continuation, and the purification rate has decreased by a predetermined amount or more with a decrease in the NOx storage capacity, and the process proceeds to step S16. And executes two divided injection controls before and after.

In FIG. 14 and FIG. 15, steps 51 and 241 constitute the purification rate judging means 36.

Therefore, in the second embodiment, the same operation and effect as those of the first embodiment can be obtained, and the purification rate state of the catalyst can be determined based on the temperature state of the catalyst and the duration of the stratified combustion state. Therefore, when it is determined that the purification rate of the catalyst has decreased by a predetermined amount or more, the fuel injection division control is executed, and the catalyst can be refreshed due to an increase in the amount of CO emission. This can prevent fuel consumption from increasing due to split injection.

As shown in FIG. 16, for example, an O2 sensor 22 for air-fuel ratio feedback control, which is provided on the downstream side of the catalytic converter 23 in the exhaust passage 20 and is provided on the upstream side, as the purification rate determining means. The same O2 sensor 33 may be provided, and the purification rate determining means 37 may directly determine the purification rate state of the catalyst based on the output of the O2 sensors 33.

That is, for example, when the engine 1 is in a semi-warmed state (when the engine water temperature is between 40 ° C. and 70 ° C.), the ECU 35 controls the O 2 sensor 22 so that the air-fuel ratio becomes the stoichiometric air-fuel ratio. Feedback control based on the output is performed. At this time, the output of the O2 sensor 22 is as shown in FIG. 17A, while the output from the O2 sensor 33 downstream of the catalytic converter 23 is (B) or (c) of FIG.

More specifically, when the air-fuel ratio is approximately the stoichiometric air-fuel ratio and the purification rate of the catalyst is high, unburned hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas are converted into nitrogen oxides. By reacting with substances (NOx) and oxygen (O2), the oxygen concentration decreases in the exhaust gas downstream of the catalytic converter 23, so that the output of the downstream O2 sensor 33 is as shown in FIG.
As shown in (2), the number of inversions is extremely small as compared with the output of the O2 sensor 22 on the upstream side. On the other hand, as the purification rate of the catalyst decreases, the output of the downstream O2 sensor 33 becomes
The number of inversions increases as shown in FIG.
2 The output of the sensor 22 approaches. Accordingly, the purification rate determining means 37 can determine a reduction in the purification rate of the catalyst by a predetermined value or more based on the upstream O2 sensor 22 and the downstream O2 sensor 33.

[0111]

As described above, according to the engine control apparatus of the first aspect of the present invention, the fuel injection is divided into a plurality of times by the injection division control means, so that the CO emission amount is reduced. It can be increased to promote catalyst refresh. Therefore, the frequency of switching the air-fuel ratio for refreshing the catalyst can be reduced, and the richness of the air-fuel ratio at that time can be reduced. In addition, the fuel consumption can be reduced as compared with the related art, and the shock caused by the change in the operating state of the engine can be reduced.

According to the second aspect of the present invention, the fuel injection is divided into a plurality of times in the intake stroke and executed, thereby promoting the uniformity of the air-fuel mixture in the combustion chamber and suppressing an increase in fuel efficiency due to the divided injection. Further, since the exhaust gas temperature is reduced by shortening the combustion time, the decrease in the NOx purification rate due to the increase in the temperature of the catalyst is suppressed.

According to the third aspect of the present invention, the last divided fuel injection is executed within a crank angle range of 40 degrees or more before the bottom dead center in the intake stroke, so that the effect of refreshing the catalyst due to an increase in the amount of CO emission can be obtained. Can be enhanced.

According to the fourth aspect of the present invention, by executing the last divided fuel injection in the first half of the compression stroke, the effect of refreshing the catalyst due to an increase in the amount of CO emission can be extremely increased. Further, the present invention can be executed even in a high rotation region of an engine having a short cycle time.

According to the fifth aspect of the present invention, the fuel injection division control in the intake stroke is executed in the high-load low-speed region of the engine, so that the catalyst temperature rise can be suppressed even at a high load. it can. Further, by executing at least the first fuel injection within the crank angle range where the piston speed is high, the mixing of fuel and air can be promoted.

According to the sixth aspect of the invention, the combustion state of the engine when switching between the stratified combustion state and the uniform combustion state can be set to an intermediate combustion state between them, and the connection of the engine output can be achieved. Will be better. Further, similarly to the invention of the fifth aspect, it is possible to suppress the temperature rise of the catalyst.

According to the invention described in any one of the seventh and eighth aspects, the connection of the engine output is improved in the same manner as in the sixth aspect of the invention, and also in the same manner as in the fourth aspect of the invention. The refreshing effect of the catalyst is extremely large.

According to the ninth aspect of the present invention, by controlling the air-fuel ratio to the rich side during the split control of the fuel injection, the decrease in the engine output caused by the local incomplete combustion accompanying the split injection is compensated. Can be.

According to the tenth aspect of the invention, it is possible to promote the refreshing of the catalyst in the low-load high-speed range and to improve the engine output in the high-load high-speed range.

According to the eleventh aspect of the present invention, the refresh of the catalyst and the reduction of fuel consumption due to an increase in the amount of CO emissions can be achieved at a high level according to the temperature state of the catalyst.

According to the twelfth aspect of the invention, by setting the first fuel injection amount to be larger than the total fuel injection amount of the second and subsequent fuel injections, it is possible to suppress an increase in fuel consumption due to the split injection.

According to the thirteenth aspect of the invention, when the purification rate of the catalyst actually decreases, the catalyst is refreshed by increasing the amount of CO emission, thereby preventing the saturated state of the catalyst and performing the divided injection. The fuel consumption increase accompanying the above can be suppressed.

According to the fourteenth aspect, when the engine is continuously in the stratified combustion state, the catalyst NOx
A decrease in the purification rate due to a decrease in the storage capacity is determined, and a decrease in the purification rate of the catalyst as the temperature rises is determined. Further, according to the sixteenth aspect, it is possible to accurately determine a decrease in the purification rate of the catalyst based on the NOx storage capacity of the catalyst and the temperature state.

According to the seventeenth aspect, it is possible to cope with an increase in the required output to the engine and to effectively promote the refresh of the catalyst.

According to the eighteenth aspect of the invention, while the catalyst temperature is not so high, priority is given to the refreshing of the catalyst due to an increase in the amount of CO emission, while if the catalyst temperature is expected to rise, the exhaust gas temperature is reduced. It is possible to give priority to suppressing the temperature rise of the catalyst by lowering the temperature.

According to the nineteenth aspect of the present invention, in addition to the division control of the fuel injection, the particle size of the fuel to be injected is reduced by lowering the fuel injection pressure, so that the catalyst can be further refreshed due to an increase in the amount of CO emission. Can be promoted.

According to the twentieth aspect, the cost of the system can be reduced by using the conventional hydraulic pressure regulating valve.

According to the twenty-first aspect, the fuel injection pressure at the time of executing the fuel injection division control can be adjusted to an optimum value for increasing the amount of CO emission and reducing the fuel consumption.

According to the twenty-second aspect of the present invention, when priority is given to the refresh of the catalyst due to an increase in the amount of CO emission, the fuel injection pressure is reduced to the second pressure set value to further deteriorate the state of vaporization and atomization. On the other hand, when priority is given to the reduction of fuel consumption, the atomization of the fuel injected from the fuel injection valve can be prevented from being impaired by increasing the fuel injection pressure to the third pressure set value or more.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a sectional view showing a configuration of a catalytic converter.

FIG. 3 is an explanatory diagram showing an operating region of an engine set in accordance with an engine speed and an engine load in a steady operation state of the engine.

FIG. 4 is a diagram corresponding to FIG. 3 in an accelerating operation state of the engine.

FIG. 5 is a flowchart showing a specific procedure of split control of fuel injection at the time of engine start, at the time of engine cold air, and in the operation regions III, XI, and XIV.

FIG. 6 is a flowchart showing a specific procedure of fuel injection division control in operation regions I, II, IV, XII and XIII.

FIG. 7 is a flowchart illustrating a specific procedure of fuel injection control.

FIG. 8 is an explanatory diagram showing an outline of fuel injection timing for each operation region.

FIG. 9 is a graph showing a piston speed in an intake stroke and a compression stroke of a cylinder.

FIG. 10 shows the fuel injection timing in the intake stroke and C
It is a graph which shows the correlation data with O emission amount, fuel consumption, and exhaust gas temperature.

FIG. 11 is a characteristic diagram showing a throttle opening characteristic according to an accelerator opening.

FIG. 12 is a flowchart illustrating a control procedure of a fuel injection pressure.

FIG. 13 is an explanatory diagram showing first, second, and third pressure set values that have been set.

FIG. 14 is a diagram corresponding to FIG. 5 according to the second embodiment.

FIG. 15 is a diagram corresponding to FIG. 6 according to the second embodiment.

FIG. 16 is a diagram corresponding to FIG. 1 according to a modification of the second embodiment.

FIG. 17 is an explanatory diagram showing an output example of O2 sensors provided respectively on the upstream side and the downstream side of the catalyst.

FIG. 18 is a characteristic diagram showing the dependency of the NOx purification rate of the catalyst on the catalyst temperature.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Engine 2 Cylinder (cylinder) 6 Combustion chamber 9 Injector (fuel injection valve) 20 Exhaust passage 23 Catalytic converter (NOX storage type catalyst) 35a Injection split control means 35b Fuel pressure control means 35c Air-fuel ratio control means 36, 37 Purification rate determination means 27, 30 Fuel pump 29 Pressure controller (fuel pressure adjusting means)

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02D 41/04 335 F02D 41/04 335C

Claims (22)

[Claims] A fuel injection valve for directly injecting fuel into a combustion chamber of a cylinder, and a fuel injection valve provided in an exhaust passage of an engine for reducing nitrogen oxides in exhaust gas when an air-fuel ratio is leaner than a stoichiometric air-fuel ratio. A NOx storage type catalyst for storing the fuel, and injects fuel so as to be in a uniform combustion state in a high load range or a high rotation range of the engine, and stratified combustion in a low load and low rotation range in a steady operation state of the engine. An engine control device for injecting fuel so as to be in a state, wherein when the engine is in a predetermined operation state, fuel injection by a fuel injection valve is divided into a plurality of times, and at least a first fuel injection is performed. An engine control device provided with injection division control means for executing injection in an intake stroke. 2. The engine control device according to claim 1, wherein the injection split control means splits and executes the fuel injection by the fuel injection valve a plurality of times during the intake stroke. 3. The injection division control means according to claim 1, wherein the injection division control means executes the last fuel injection of the division within a crank angle range of 40 degrees before bottom dead center in an intake stroke. Characteristic engine control device. 4. The engine control device according to claim 1, wherein the injection split control means executes the last fuel injection of the split in the first half of the compression stroke. 5. The fuel injection control device according to claim 1, wherein the injection division control means divides the fuel injection by the fuel injection valve into a plurality of times in an intake stroke when the engine is in a high-load low-speed region, and performs at least a first fuel injection. An engine control device characterized in that injection is performed so as to be performed within a crank angle range from 40 degrees after top dead center to 40 degrees before bottom dead center. 6. The fuel injection control device according to claim 1, wherein the injection split control means splits the fuel injection by the fuel injection valve into a plurality of times during the intake stroke when the engine is in a middle load and low or medium speed region. , At least one
The first fuel injection is from 40 degrees after top dead center to 40 before bottom dead center.
An engine control device configured to be executed so as to be within a crank angle range up to a degree or less. 7. The fuel injection control device according to claim 1, wherein the injection split control means includes:
An engine control device configured to execute fuel injection in a plurality of times including at least fuel injection in the first half of a compression stroke. 8. The fuel injection control device according to claim 1, wherein the engine is divided into a first region in which the engine has a medium load and a low rotation speed or a medium rotation, and a second region in which the engine has a low load or a medium load and a medium rotation speed. Wherein at least a region including the first region is configured to execute the fuel injection by the fuel injection valve in a plurality of times including at least the fuel injection in the first half of the compression stroke. Engine control device. 9. One of claims 6, 7 or 8
An engine control device, further comprising: air-fuel ratio control means for controlling an air-fuel ratio to a rich side equal to or lower than a stoichiometric air-fuel ratio when fuel injection division control is performed by injection division control means. 10. The fuel injection control device according to claim 1, wherein when the engine is in a low-load and high-speed region, the fuel injection is divided into a plurality of fuel injections including fuel injection at least in the first half of the compression stroke. On the other hand, when the engine is in the region of high load and high revolution, the engine control device is configured to execute fuel injection collectively near the top dead center from the exhaust stroke to the intake stroke. . 11. The catalyst according to claim 5, wherein the purification rate of the catalyst is reduced by a predetermined value when the temperature condition is higher than a predetermined value, and it is determined that the temperature condition of the catalyst is higher than the predetermined value. When the catalyst temperature determining unit determines that the temperature of the catalyst is higher than the predetermined value, the injection split control unit starts from 40 degrees after the top dead center in the intake stroke. The split control of the fuel injection is performed so that the crank angle is within the crank angle range before 40 degrees before the bottom dead center and the intermediate point between the first fuel injection and the last fuel injection is later than 90 degrees after the top dead center. On the other hand, when the catalyst temperature determining means determines that the temperature state of the catalyst is lower than the predetermined temperature state, the catalyst temperature determining means determines whether the temperature of the catalyst is lower than 40 degrees after the top dead center in the intake stroke and before 40 degrees before the bottom dead center. Kula The fuel injection division control is performed so that the angle between the first fuel injection and the last fuel injection is earlier than 90 degrees after the top dead center within the angle range. An engine control device characterized by the above-mentioned. 12. The engine control device according to claim 3, wherein the first fuel injection amount is set to be larger than the total fuel injection amount after the second fuel injection. 13. The method according to claim 1, further comprising a purifying rate determining means for determining that the purifying rate of the catalyst has decreased by a predetermined value or more. An engine control device characterized in that when it is determined, the fuel injection by the fuel injection valve is divided into a plurality of times and executed. 14. The purification rate determination means according to claim 13, wherein the purification rate determination means is configured to determine a reduction of the purification rate by a predetermined amount or more when the engine is continuously in a stratified combustion state for a set time or more. An engine control device characterized by the above-mentioned. 15. The engine according to claim 13, wherein the purification rate determination means is configured to determine a reduction of the purification rate by a predetermined value or more when the catalyst temperature becomes equal to or higher than the set temperature. Control device. 16. The purifying rate determining means according to claim 13, wherein the purifying rate of the catalyst decreases as the duration of the stratified combustion state of the engine is longer and the temperature state of the catalyst during that time is higher. An engine control device configured to determine that the engine is large. 17. The air-fuel ratio according to claim 1, wherein the air-fuel ratio is near the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio when the engine is in a steady operation state at a predetermined load or higher or a predetermined rotation speed or higher, or in an acceleration operation state. The air-fuel ratio control means for controlling the fuel injection is provided on the side, and the injection split control means is configured to execute the fuel injection in a plurality of times when the engine is in one of the above operating states. Characteristic engine control device. 18. The fuel injection and compression system according to claim 17, wherein when the engine is in a steady operation state with a predetermined load or more or a predetermined number of revolutions or more, or in an acceleration operation state, at least during the intake stroke. In order to include the fuel injection in the first half of the stroke, the fuel injection is divided and executed multiple times,
Subsequently, an engine control device is configured to execute the fuel injection in a plurality of times in the intake stroke. 19. The fuel injection control device according to claim 1, wherein the fuel injection pressure control means for changing and adjusting the fuel injection pressure in the fuel injection valve and the fuel injection split control by the injection split control means are executed. An engine control device provided with fuel pressure control means for reducing fuel injection pressure by fuel pressure adjustment means. 20. The engine according to claim 19, wherein the fuel pressure adjusting means is a hydraulic pressure adjusting valve for reducing the hydraulic pressure of a high pressure injection path connecting the fuel pump and the fuel injection valve at the time of starting the engine. Control device. 21. The fuel pressure adjusting device according to claim 19, wherein the fuel pressure adjusting means adjusts a fuel injection pressure at the fuel injection valve.
The first pressure set value of the minimum pressure, the second pressure set value higher than the first pressure set value, and the third pressure set value higher than the second pressure set value can be changed and adjusted in at least three stages. The fuel pressure control means is configured to control the fuel injection pressure at the fuel injection valve to a high pressure equal to or higher than the second pressure set value when the fuel injection split control is executed by the injection split control means. A control device for an engine, comprising: 22. The fuel pressure control means according to claim 21, wherein the last fuel injection divided by the injection division control means is:
When executed within the crank angle range of 40 degrees before the bottom dead center in the intake stroke, the fuel injection pressure at the fuel injection valve is controlled to the second pressure set value, while the last fuel injection is performed in the crank angle range. The engine control device is configured to control the fuel injection pressure to a high pressure value equal to or higher than the third pressure set value when not executed in the engine.