JP2002155791A - Control device of diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a smoke while preventing a deterioration of a fuel consumption by carrying out a divided injection of main fuel and appropriately controlling the divided injection depending on an operation state in a diesel engine. SOLUTION: A fuel injection valve 5 for injecting a fuel and a fuel injection control means 37 for controlling a fuel injection from this fuel injection valve are provided in a combustion chamber of the diesel engine. This fuel injection control means 37 divides and carries out a main fuel injection for producing a torque to a plurality of times at an operation area from a low load side to a high load side at at least low speed area of the engine for a period from near a compression top dead point to a former stage of an expansion stroke. A starting timing of the injection at a latter stage side of the main fuel injection is delayed at an operation area at a high load side as compared with an operation area at the low load side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control system for a diesel engine, and more particularly to a technique for reducing smoke by dividing fuel injection.

[0002]

2. Description of the Related Art Conventionally, as disclosed in Japanese Patent Application Laid-Open No. 3-160148, for example, in a diesel engine having a fuel injection valve for injecting fuel into a combustion chamber, fuel injection from the fuel injection valve is divided. To be performed, for example, by dividing into pilot injection and main injection, or further dividing main injection into a plurality of times, and by controlling the injection interval and each injection pulse width, smoke contained in exhaust gas, Techniques for reducing harmful substances such as hydrocarbons and nitrogen oxides are known.

[0003]

If the fuel injection from the fuel injection valve is divided as described above, and in particular, the main fuel injection for generating torque is performed in a divided manner, it is advantageous for reducing smoke. In such a case, the timing of the second-stage injection (the interval between the first-stage injection and the second-stage injection) affects not only the smoke reduction effect but also the fuel consumption performance and the output performance. That is, as will be described in detail later, if the timing of the injection at the later stage is delayed within the specific range of the first half of the expansion stroke, the smoke is reduced, but the fuel consumption performance is liable to deteriorate. In addition, the degree to which the timing of the injection at the subsequent stage affects the smoke reduction effect differs from the degree to which the fuel consumption performance is affected, depending on the operating state.

Conventionally, such points have not been sufficiently investigated, so that there is room for improvement in terms of reducing smoke and improving fuel efficiency.

In view of the foregoing, the present invention reduces the smoke while preventing the fuel consumption from deteriorating by dividing the main fuel injection and controlling the divided injection appropriately according to the operating condition. It is an object of the present invention to provide a diesel engine control device which can perform the control.

[0006]

SUMMARY OF THE INVENTION The present invention comprises a fuel injection valve for injecting fuel into a combustion chamber of a diesel engine, and fuel injection control means for controlling fuel injection from the fuel injection valve. The control means divides the main fuel injection for torque generation into a plurality of times during a period from near the compression top dead center to the first half of the expansion stroke at least in an operation range from a low load side to a high load side in a low speed range of the engine. At the same time, the start timing of the latter-stage injection of the main fuel injection is controlled to be delayed in the high-load operation region as compared with the low-load operation region.

[0007] It is particularly preferable that the main fuel injection continues to be performed in a low-load region of an operation region in which the main fuel injection is divided into a plurality of times, and the main fuel injection is interrupted in a region above a predetermined load. The start timing of the latter injection of the injection is changed according to the engine load.

According to this device, on the low load side of the engine, which originally has little smoke, deterioration of fuel efficiency can be avoided by making the start timing of the injection in the latter stage relatively early.
On the other hand, on the high-load side of the engine, the start timing of the second-stage injection is delayed, so that the carbon particles generated in the combustion of the first-stage injected fuel burn the second-stage injected fuel, as described later in detail. As a result, smoke is greatly reduced by burning.

[0009] In the device of the present invention, the low engine,
In the medium-load and high-load operation regions in the medium-speed region, the start timing of the latter-stage injection of the main fuel injection may be controlled so that the combustion by the main fuel injection is interrupted.

In the apparatus of the present invention, a turbocharger driven by exhaust energy to supercharge intake air, an exhaust gas recirculation device for recirculating a part of exhaust gas to an intake system, and exhaust gas by the exhaust gas recirculation device Exhaust gas recirculation control means for controlling the amount of gas recirculation, the latter part of the main fuel injection in the supercharging region in the low and medium speed regions of the engine so that the combustion by the main fuel injection is interrupted by the fuel injection control means. It is preferable to control the start timing of the side injection and to control the exhaust gas recirculation amount by the exhaust gas recirculation control means so that the excess air ratio in the combustion chamber becomes a target value corresponding to the operating state.

In this manner, in the supercharging region in the low and medium speed range of the engine, the start timing of the latter-stage injection is delayed so that the exhaust energy is increased, so that the supercharging of the turbocharger is performed. Action is enhanced. In addition, the delay in the start timing of the injection on the subsequent stage and the increase in the amount of intake air due to supercharging have an advantageous effect on reducing smoke, and
The exhaust gas recirculation amount increases in accordance with the increase in the intake air amount due to the supercharging, so that NOx is also reduced.

Further, the present invention includes a fuel injection valve for injecting fuel into a combustion chamber of a diesel engine, and fuel injection control means for controlling fuel injection from the fuel injection valve.
This fuel injection control means divides the main fuel injection for torque generation into a plurality of times in a period from near the compression top dead center to the first half of the expansion stroke at least in an operation range from a low load side to a high load side in a low speed range of the engine. The main fuel injection is performed such that the main fuel injection continues to be performed during a steady operation in a low load region of the operation region in which the main fuel injection is divided into a plurality of times, and the combustion is interrupted during an accelerated operation. This is configured to control the start timing of the injection at the latter stage of the injection.

According to the present invention, the fuel consumption is prevented from deteriorating by controlling the combustion by the main fuel injection to be continued during the steady operation, while the post-injection is started so that the combustion by the main fuel injection is interrupted during the acceleration. By delaying the timing, generation of smoke is sufficiently suppressed.

[0014] The device of the invention preferably comprises a turbocharger. Further, the fuel injection control means causes the pilot injection to be performed prior to the main fuel injection from the fuel injection valve, and at the early stage of the acceleration, the pilot injection start timing is advanced, and the increase rate of the pilot injection is increased. It is preferable that the ratio be larger than the ratio.

In this manner, in the initial stage of the acceleration, the smoke is reduced by delaying the start timing of the subsequent injection, and the ratio of the premixed combustion by the pilot injection is increased, thereby increasing the torque. In addition, since the exhaust energy is increased by delaying the injection at the subsequent stage, the supercharging action of the turbocharger is promoted, and the acceleration performance is improved.

Further, it is preferable that the fuel injection control means accelerates the start timing of the latter-stage injection of the main fuel injection and reduces or cuts the pilot injection amount after the initial stage of acceleration.

In this manner, if the supercharging is sufficiently performed by the turbocharger after the initial stage of acceleration, the timing of the second-stage injection is advanced so as to be advantageous for improving output and reducing fuel consumption. The pilot injection amount is reduced or cut.

Further, in the above-described apparatus, in the operation region in which the main fuel injection is divided into a plurality of times, the injection amount of the latter stage of the main fuel injection is made smaller than the injection amount of the former stage, and It is preferable that the higher the load side, the smaller the ratio of the injection amount in the latter stage.

[0019] In this case, deterioration of fuel efficiency is suppressed as much as possible.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

FIG. 1 shows the overall structure of a diesel engine to which the present invention is applied. The engine body 1 of the diesel engine has a plurality of cylinders (only one is shown in the figure) 2, and a piston 3 is inserted into each cylinder 2 in a reciprocating manner. A combustion chamber 4 is defined in 2. A fuel injection valve 5 is provided at substantially the center of the upper surface of the combustion chamber 4, and fuel is injected from the fuel injection valve 5 into the combustion chamber 4.

Each of the fuel injection valves 5 is connected to a common rail 6 for storing high-pressure fuel. The common rail 6 is provided with a pressure sensor 6a for detecting an internal fuel pressure (common rail pressure) and a crankshaft. A high-pressure supply pump 8 driven by 7 is connected. Then, the fuel supply pressure by the high-pressure supply pump 8 is controlled by an ECU described later, so that the fuel pressure in the common rail 6 detected by the pressure sensor 6a is controlled to be a target value corresponding to the operation state. The fuel pressure is maintained at about 20 MPa during the idle operation of the engine, and the fuel pressure increases as the engine load increases (the fuel injection amount increases).

The crankshaft 7 is provided with a crank angle sensor 9 for detecting the rotation angle. The crank angle sensor 9 includes a plate to be detected provided at the end of the crankshaft 7 and an electromagnetic pickup disposed to face the outer periphery of the plate. And outputs a pulse signal by detecting the passage of the projection formed on the substrate.

The intake passage 10 is connected to the engine body 1.
And the exhaust passage 20 are connected.

The intake passage 10 has a downstream portion branched for each of the cylinders 2 via a surge tank (not shown), and the branch portion is connected to each of the cylinders 2 via an intake port.
Are connected to the combustion chamber 4. In addition, the surge tank is provided with an intake pressure sensor 10a that detects the pressure of intake air supplied into each cylinder 2.

The intake passage 10 has, in order from the upstream side, an air flow sensor 11 for detecting a flow rate of intake air taken into the engine body 1 and a blower 1 of a turbocharger 12.
3, an intercooler 15 for cooling the air compressed by the blower 13, and an intake throttle valve 16 for changing the flow area of the intake air.

The intake throttle valve 16 is a butterfly valve provided with a notch so that intake air can flow even in a fully closed state. Like the EGR valve 24 described later, a solenoid valve 18 for negative pressure control is provided. As the magnitude of the negative pressure acting on the diaphragm actuator 17 is adjusted by
The valve opening is configured to be changed. The installation portion of the intake throttle valve 16 is provided with a sensor for detecting the valve opening.

On the other hand, the exhaust passage 20 has an upstream portion branched for each cylinder 2, and the branch portion is connected to the combustion chamber 4 of each cylinder 2 via an exhaust port. In the exhaust passage 20, a turbine 14 of the turbocharger 12 and a catalyst 21 for purifying exhaust gas are arranged in this order from the upstream side.

The turbine 14 and the blower 13 of the turbocharger 12 are connected via a shaft (not shown). The turbine 14 is driven by the exhaust gas flow, and the blower 13 rotates in conjunction with the drive. It is designed to supercharge the intake air. The illustrated turbocharger 12 is composed of a variable geometry turbo (VGT) configured so that the nozzle cross-sectional area of the exhaust passage 20 changes. A diaphragm actuator 22 for changing the pressure and an electromagnetic valve 23 for controlling a negative pressure of the diaphragm actuator 22 are provided.

An exhaust gas recirculation passage (hereinafter referred to as EGR) for recirculating a part of the exhaust gas to the intake
A passage 25 is connected to the upstream side of the turbine 14. A downstream end of the EGR passage 25 is connected to the intake passage 10 on the downstream side of the intake throttle valve 16, and a negative pressure operation in which the valve opening is adjustable in the middle of the EGR passage 25. An exhaust gas recirculation amount control valve (hereinafter, referred to as an EGR valve) 26 is provided, and the EGR valve 26 and the EGR passage 25 constitute an exhaust gas recirculation device 24.

In the EGR valve 26, a valve body (not shown) is urged in a closing direction by a spring.
The opening degree of the EGR passage 25 is linearly adjusted by being driven in the opening direction by the diaphragm type actuator 26a. That is, a negative pressure passage 27 is connected to the diaphragm type actuator 26a, and the negative pressure passage 27 is connected to a vacuum pump (negative pressure source) 29 via a negative pressure control electromagnetic valve 28. . The solenoid valve 28 is connected to the negative pressure passage 2.
By communicating or shutting off 7, the negative pressure for driving the EGR valve is adjusted, and the EGR valve 26 is driven to open and close. Further, a lift sensor 30 for detecting the position of the valve body is provided at the installation portion of the EGR valve 26.

The fuel injection valve 5, the high-pressure supply pump 8, the intake throttle valve 16, the EGR valve 26, the turbocharger 12, etc. are provided with an engine control unit (hereinafter referred to as EC).
The operating state is controlled in accordance with a control signal output from the U) 35. In addition, the EC
U35 includes an output signal of the pressure sensor 6a, an output signal of the crank angle sensor 9, an output signal of the air flow sensor 11, and an output signal of an accelerator sensor 32 for detecting an operation amount of an accelerator pedal operated by a driver. Etc. are input.

The ECU 35 determines the operating state of the engine, determines the operating state of the engine, controls the fuel injection from the fuel injection valve 5, controls the fuel injection, and determines the amount of exhaust gas recirculated by the exhaust gas recirculation device 24. And exhaust gas recirculation control means 38 for controlling.

The operating state discriminating means 36 is based on the engine speed obtained by measuring the cycle of the output signal of the crank angle sensor 9, the accelerator opening (accelerator pedal operation amount) detected by the accelerator sensor 32, and the like. The operating state of the engine is checked to determine which operating area the operating state belongs to in the control map as shown in FIG. 2, and whether or not the vehicle is in an accelerating operating state based on the rate of change of the accelerator opening. It is supposed to.

The fuel injection control means 37 controls the main fuel injection for generating torque during a period from the vicinity of the compression top dead center to the first half of the expansion stroke at least in the operation range from the low load side to the high load side in the low speed range of the engine. The fuel injection valve 5 is controlled so that the fuel injection valve 5 is divided into a plurality of injections and the start timing of the latter-stage injection of the main fuel injection is delayed in the high-load operation region compared to the low-load operation region. I do.

In particular, in the low load region of the operating region in which the main fuel injection is performed in a plurality of divided times, the start timing of the latter-stage injection is made relatively early so that the combustion by the main fuel injection is continued ( However, the start timing of the subsequent-stage injection is delayed so that the combustion by the main fuel injection is interrupted in a region where the load is equal to or more than a predetermined load. In addition, the start timing of the latter-stage injection is delayed so that the combustion by the main fuel injection is interrupted even during the acceleration operation.

Further, prior to the main injection, the pilot injection is performed at an appropriate timing before the top dead center of the piston, and the injection amount and the injection timing of the pilot injection are controlled in accordance with the operation state.

More specifically, the fuel injection from the fuel injection valve 5 is performed as follows in each of the operation regions a to e in the low and medium speed regions below a predetermined rotation speed Na (for example, 2500 rpm) as shown in FIG. Is controlled.

As shown in FIG.
In the low-load region b, the medium-load region c, the high-load region d, and the full-load region e excluding the idling operation region a in the medium-speed region, the main fuel injection is performed after the pilot injection PI in the former-stage injection M.
The injection is divided into two, that is, the first injection and the second injection M2. In the idling operation range a, since the amount of fuel injection is small (the excess air ratio is large), the smoke is small and there is no need to reduce the smoke by dividing the main fuel injection. Done only once.

In the low load region b of the operation region in which the main fuel injection is divided, the pre-injection M1 is started near the top dead center after the pilot injection PI is performed, and after the pre-injection M1, the pre-injection M1 is started. The latter-stage injection M2 is started relatively early before the diffusion combustion by the injection M1 is completed. For example, the start timing of the latter-stage injection M2 is about ATDC20 ° CA
(ATDC means after top dead center, CA means crank angle).

In the middle load range c and the high load range d, after the pilot injection PI is performed, after the pre-injection M1, the post-injection M2 is started at the end of diffusion combustion by the pre-injection M1 or at a later time, For example, the latter injection M2
Is set after about 30 ° CA of ATDC.
Then, as the fuel injection amount increases, the end timing of the diffusion combustion by the first-stage injection is delayed, so that the start timing of the second-stage injection M2 is further delayed in the high-load region d than in the middle-load region c. The start timing of the second-stage injection M2 is set to about ATDC60 in order to avoid an extreme deterioration in fuel efficiency and a drop in torque.
It is preferable to set within a range up to ° CA.

In the full load region e, in order to prioritize the output improvement, the timing of the latter injection M2 of the main fuel injection is advanced, and the interval between the former injection M1 and the latter injection M2 is shortened. Since the exhaust energy is high in the full load region e, the main fuel injection M may be performed once (collective injection).

When the main fuel injection is divided, the post-stage injection amount is made smaller than the pre-stage injection amount, and the ratio of the post-stage injection amount to the main fuel injection amount is reduced as the load increases.

Further, when the acceleration operation state f (operation state change indicated by the arrow in FIG. 2) is reached, the fuel is actually injected into each cylinder 2 at or near the end time of the diffusion combustion by the preceding injection. Thus, the start timing of the second-stage injection is set. In particular, as a preferable control when a turbocharger is provided, in the initial stage of acceleration, the start timing of the second-stage injection M2 of the main fuel injection is delayed, as indicated by the solid line in FIG. The pilot injection amount and the main fuel injection amount are increased, of which the increase ratio of the pilot injection amount is greater than the increase ratio of the main fuel injection amount, and the start timing of the pilot injection PI is advanced, so that the pilot interval (pilot interval) is increased. The interval between the injection and the main fuel injection) is increased. When the initial stage of acceleration has passed, the start timing of the second-stage injection M2 of the main fuel injection is advanced, and the pilot injection amount and the pilot interval are reduced, as indicated by the broken line in FIG. Is cut.

The exhaust gas recirculation control means 38 controls the amount of exhaust gas recirculation so that the excess air ratio in the combustion chamber becomes a target value corresponding to the operating state. Specifically, the target excess air ratio is set according to the operating state (for example, the target torque and the engine speed set based on the accelerator opening and the like), and the target fuel injection amount is set. The target fresh air amount is obtained from the target fresh air amount and the target fuel injection amount. Based on a comparison between the target fresh air amount and the actual fresh air amount detected by the airflow sensor 11, the actual fresh air amount is calculated with respect to the target fresh air amount. If it is too large, EGR tends to increase the exhaust gas recirculation amount.
The EGR valve 26 is controlled such that the valve 26 is controlled, and if the actual fresh air amount is small, the exhaust gas recirculation amount is reduced.

The operation of the apparatus of the present embodiment as described above is as follows.
Next, description will be made with reference to FIGS.

FIG. 5 shows that the operating state is low, medium speed and low load (FIG. 2).
(In the region b in the middle), low-medium-speed / medium load (in the region c in FIG. 2), and case where the vehicle is in a medium-speed / medium-high load (in the region d in FIG. 2). 7 is a graph showing experimental results obtained by examining changes in the amount of smoke generated when the main fuel injection is divided and the injection start timing of the subsequent injection is variously changed. In this figure, the horizontal axis represents the crank angle at the start of the second-stage injection, the vertical axis represents the amount of smoke generated, and the one-dot chain line in the figure represents low medium speed / low load, low medium speed / medium load, medium speed / medium high load. In each case, the smoke generation amounts S _L0 , S _M0 , and S _H0 when the main fuel injection is the batch injection are shown. Also, Δ
S _L , ΔS _M , and ΔS _H indicate the smoke reduction allowance in each of the above cases as compared with the one at the time of the batch injection when the later injection start timing of the main fuel injection is delayed.

As shown in this figure, when the main fuel injection is divided, the smoke tends to be reduced as compared with the collective injection. Particularly, in the case of a low / medium speed / medium load or a medium / medium / high load, the details will be described later. combustion end of the fuel of the preceding injection point S (Fig. 7, see FIG. 8) by starting the succeeding injection on or after, smoke reduction allowance [Delta] S _M, [Delta] S _H increases. This seems to be due to the following reasons.

That is, if the injected fuel is heated in a state where mixing is insufficient and air is locally insufficient, soot (smoke) is generated due to carbonization of the fuel. However, if the main fuel injection is divided, mixing is performed. Being better reduces soot. Furthermore, even if soot is generated in the combustion of the fuel of the first stage injection, at the time when the combustion is completed, carbon particles and oxygen, which are components of soot, are sufficiently mixed by the in-cylinder flow, and the in-cylinder temperature is high. When the fuel is supplied, the fuel is in a state of being easily ignited. When the latter-stage injection is started in this state, the carbon particles are sufficiently burned together with the fuel. Thus, smoke is further reduced.

However, at low to medium speeds and low loads, the amount of smoke is inherently relatively small due to the large excess air ratio, and the start of the second stage injection can be delayed after the end of combustion S of the first stage fuel. The smoke reduction allowance ΔS _L does not increase so much.

FIG. 6 is a graph showing the results of an experiment for examining the change in fuel efficiency when the main fuel injection is divided and the injection start timing of the subsequent injection is variously changed in each of the above cases. In this figure, the horizontal axis represents the crank angle at the start of succeeding injection, and the vertical axis is the fuel consumption rate, fuel consumption F _L 0 when the dashed line is obtained by a batch injection and main fuel injection when the above in the figure, F _M 0 and F _H 0 are shown. ΔF _L , Δ
F _M and ΔF _H indicate the fuel consumption rate increase in the above-described cases compared with the one at the time of the batch injection when the later-stage injection start timing of the main fuel injection is delayed.

As shown in this figure, as the main fuel injection is divided and the subsequent injection is delayed, the heat generation efficiency is reduced and the fuel efficiency is increased (deteriorated). In particular, at low to medium speeds and low loads, the fuel consumption rate increase ΔF _L increases when the start of the second-stage injection is delayed so much as to become after the combustion end point S of the fuel of the first-stage injection. On the other hand, at low / medium speed / medium load or medium / medium / high load, the heat generation efficiency is originally high, the fuel efficiency is low, and the post-injection start timing at which the fuel is actually injected into each cylinder 2 is set to the pre-injection. Even if it is delayed until after the end of combustion S of the fuel, the fuel consumption rate increase ΔF _M and ΔF _H are relatively small within the range of ATDC 50 ° to 60 °.

From the data shown in FIGS. 5 and 6, in the low-medium-speed and low-load region (low injection amount region) where the amount of smoke generation is originally small, the post-injection start timing is set to the end of the combustion of the fuel in the pre-injection. On the other hand, in the middle to high load range, the later injection start timing is delayed as the load becomes higher so as to be after the end of the combustion of the fuel in the former injection (but within a range of up to less than 60 ° ATDC). Thus, it can be understood that the smoke can be sufficiently reduced while suppressing the deterioration of the fuel economy as much as possible.

Here, the end point of the combustion of the fuel in the first stage injection is the time point S at which the heat generation rate becomes 0 as shown in FIGS. 7A to 7C, and FIGS. 8A to 8C. The rate of increase becomes zero when viewed in terms of the mass combustion ratio (the increase in the mass combustion ratio is interrupted, and the graph extends substantially horizontally).
Time point S. FIG. 7 shows the temporal change of the heat release rate during the period from near the compression top dead center to the first half of the expansion stroke, and FIG. 8 shows the temporal change of the mass combustion ratio during the above period. (A) at low / medium speed / low load, (b) at low / medium speed / medium load, and (c) at medium speed / high load. In these figures, in the curves showing the changes in the heat release rate and the mass combustion rate, the solid line indicates the case where the main fuel injection is performed as a single injection, and the broken line indicates that the main fuel injection is divided and the subsequent injection is started. The timing is set to the end point S of the combustion of the preceding injection.
In this case, the main fuel injection is divided and the start timing of the subsequent injection is set near the end point S of the preceding injection.

As shown in FIGS. 7 and 8, the combustion end point S of the above-mentioned pre-injection is about 30 ° CA ATDC at low load in low and medium speed ranges, and ATDC 35 ° at medium load.
At about CA, ATDC is about 48 ° CA under high load. Various methods for specifically obtaining the combustion end point S of the pre-injection can be considered. For example, a temperature sensor for detecting the temperature in the combustion chamber and a combustion light sensor for detecting combustion light are provided. The time point S can be determined by examining whether the temperature in the combustion chamber after the pre-injection has dropped to a predetermined temperature or lower based on whether the emission of combustion light has ceased. Alternatively, a differential value of a value obtained by subtracting the adiabatic expansion temperature from the temperature in the combustion chamber detected by the temperature sensor may be obtained, and the time point S may be obtained when this value becomes 0 from minus.

Instead of obtaining the end point S of the combustion of the pre-injection based on the signal of the sensor as described above, the end of the combustion of the pre-injection in various operating states in the range of medium load to high load in the low and medium speed ranges. The time point S may be experimentally checked beforehand, stored in a memory as a map, and read out according to the actual operation state.

In any case, in the middle to high load operating range in the low and middle speed ranges, the combustion end point S of the first-stage injection is determined.
Alternatively, immediately after this time point, the latter-stage injection is started, and the higher the load (the greater the fuel injection amount), the later the combustion end time point S of the first-stage injection is delayed, so that the start timing of the second-stage injection is delayed.

FIG. 9 shows a case in which the main fuel injection is divided into a pre-injection and a post-injection and the ratio (P / T) of the post-injection amount (P) to the total main injection amount (T) is variously changed. This shows the change in fuel efficiency. FIG. 9A shows a state in which the start timing of the second-stage injection (the timing of starting the fuel injection into the cylinder 2) in the low-medium-speed / low-load operation state is determined by the AT before the combustion end point S of the first-stage injection
When DC is set to 8 ° CA (dashed line), the start timing of the second stage injection is set to ATDC which is near the combustion end time S of the first stage injection.
The case of 30 ° CA (solid line) is shown.
FIG. 9 (b) shows a state in which the start timing of the post-injection is set to the ATD before the combustion end point S of the pre-injection in the low-medium speed / medium load operation state.
When C20 ° CA is set (dashed line), the start timing of the second-stage injection is set to ATDC which is near the combustion end point S of the first-stage injection.
The case of 35 ° CA (solid line) is shown.
FIG. 9C shows the case where the start timing of the second stage injection is set to ATDC 20 ° CA before the combustion end time S of the first stage injection (dashed line) and the start timing of the second stage injection in the middle-speed / medium-high load operation state. In the vicinity of the combustion end time point S of the pre-stage injection.
The case where TDC is 48 ° CA (solid line) is shown.

As shown in these figures, if the start timing of the post-injection is set before the combustion end point S of the pre-injection, the fuel consumption rate does not change much even if the ratio (P / T) of the post-injection amount increases. However, if the start timing of the post-injection is near or after the end point S of the combustion of the pre-injection, the fuel consumption deteriorates in accordance with the increase of the ratio (P / T) of the post-injection amount. When the ratio (P / T) exceeds 25%, the fuel consumption deteriorates remarkably. At a medium load, the fuel consumption deteriorates remarkably when the ratio (P / T) of the post-injection amount exceeds 20%. The ratio (P / T) of the post injection amount is 15%
If it exceeds, the deterioration of fuel economy becomes remarkable.

Therefore, the post-injection amount is made smaller than the pre-injection amount, and especially in the middle load range or high load range where the start timing of the post-injection is after the combustion end time S of the pre-injection, the ratio (P / T) is preferably in the range of 10% to 20%, and is preferably reduced as the load increases, from the viewpoint of fuel efficiency.

As described above, the main fuel injection is divided in the operation range (regions b, c, and d in FIG. 2) from low to medium speed low load to high load, and the start timing of the subsequent injection and the injection The ratio of the amount is controlled in accordance with the operation state, and it is particularly preferable to set the start timing of the second-stage injection to ATDC3 in a low load range.
In the region of medium load to high load, the start timing of the second stage injection is set to 30 ° CA to
TDC 60 ° CA range, ratio of post injection amount (P / T)
Is controlled in the range of 10% to 20%, it is possible to sufficiently reduce smoke while minimizing deterioration of fuel efficiency.

In addition, if the start timing of the second stage injection is delayed as described above in the range of medium load to high load, the whole combustion period is prolonged, but the second stage combustion is performed in the expansion stroke and the first stage injection is performed. Combustion does not continue, the combustion temperature becomes relatively low, and therefore, an increase in NOx in a medium to high load region is also suppressed.

Further, in the supercharging region, in addition to the above-described fuel control, supercharging is performed by the turbocharger 12, and the excess air ratio in the combustion chamber is reduced by the exhaust gas recirculation control means 38. By controlling the exhaust gas recirculation amount so as to be a target value according to the operating state, it is more advantageous to reduce smoke and NOx. That is, when the main combustion is divided and the start timing of the subsequent injection is delayed, the exhaust energy is increased and the turbocharger 12 is increased.
The supercharging effect of the supercharger is increased, and the increase of the intake air amount due to the supercharging is advantageous in reducing the smoke. Will increase, thereby reducing NOx.

Further, in the device of this embodiment, the main fuel injection is divided even during acceleration, and the start timing of the latter injection is delayed so that the combustion is interrupted at least at the initial stage of acceleration, and particularly preferably as shown in FIG. , The acceleration performance is secured while the smoke is reduced.

That is, in the initial stage of the acceleration, the start timing of the second-stage injection is delayed until near or immediately after the combustion end point S of the first-stage injection, thereby reducing the smoke and increasing the rate of increase in the pilot injection. By doing so, the ratio of premixed combustion by pilot injection is increased while increasing the noise, thereby increasing the torque. In this case, the pilot injection timing is advanced in response to the increase in the pilot injection amount, so that the time for vaporization and atomization is secured, and the premixed combustion is favorably performed. Further, by delaying the second-stage injection, the exhaust energy is increased, whereby the supercharging action of the turbocharger 12 is promoted.

As the supercharging action of the turbocharger 12 is promoted in this way, the amount of intake air sharply increases after the initial stage of acceleration, and the smoke is increased due to the increase in the amount of intake air and the promotion of mixing. Reduced. Therefore, if the supercharging by the turbocharger is sufficiently performed after the initial stage of acceleration, it is advantageous for improving the output and reducing the fuel consumption.
The timing of the second-stage injection is advanced, and the pilot injection amount is reduced or cut.

In the above embodiment, when the main fuel injection is divided, the main fuel injection is divided into the first stage injection and the second stage injection, but may be divided into three or more. For example, in a region on the higher load side than a specific load in an operation region (medium load region to high load region) in which the start timing of the latter injection is after the end of the former injection, the main fuel injection is indicated by a two-dot chain line in FIG. , The injection start timing M3 'at the last stage is divided into three (M1', M2 ', M3'), and the main fuel injection M1 ', M
If the time is after the end point S of the diffusion combustion by 2 ', the carbon can be burned while the combustion period is prolonged, and the effect of increasing the exhaust energy and reducing the smoke and NOx can be further enhanced. .

The control in the operating region on the higher side than the predetermined engine speed Na is not limited by the present invention, and the injection amount and injection timing may be appropriately controlled so as to satisfy the output performance and the like. If divisional injection is difficult, batch injection may be used.

[0069]

As described above, according to the diesel engine control apparatus of the first aspect of the present invention, the main fuel injection is performed a plurality of times at least in the operation range from the low load side to the high load side in the low speed range of the engine. Since the start timing of the injection on the subsequent stage is delayed in the operation range on the high load side as compared with the operation range on the low load side,
On the low-load side of the engine, which inherently has less smoke, it is sufficient to delay the start of the latter-stage injection on the high-load side of the engine, while keeping the start of the latter-stage injection relatively early to avoid fuel consumption deterioration. Smoke can be reduced. Therefore, both prevention of deterioration of fuel efficiency and reduction of smoke can be achieved.

In particular, the combustion by the main fuel injection continues in the low load region of the operation region in which the main fuel injection is divided into a plurality of times, and the combustion in the subsequent stage is interrupted in the region where the load exceeds a predetermined load. By controlling the start timing, the effects of preventing fuel consumption deterioration and reducing smoke can be enhanced.

According to the control apparatus for a diesel engine according to the fifth aspect of the present invention, during steady operation in a low load region of an operation region in which the main fuel injection is divided into a plurality of times, combustion by the main fuel injection is not performed. Continuously, the start timing of the second-stage injection is controlled so that combustion is interrupted during the acceleration operation.This prevents smoke from deteriorating and ensures output performance while generating smoke during acceleration. Can be sufficiently suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing one embodiment of a diesel engine having a control device of the present invention.

FIG. 2 is an explanatory diagram showing a map of an operation region of fuel injection control.

FIG. 3 is an explanatory diagram showing a fuel injection mode and an injection timing in each operation region.

FIG. 4 is an explanatory diagram showing the form and injection timing of fuel injection during acceleration.

FIG. 5 is a graph showing a change in the amount of smoke generated when the main fuel injection is divided and the start timing of the subsequent injection is variously changed.

FIG. 6 is a graph showing a change in fuel efficiency when the main fuel injection is divided and the start timing of the subsequent injection is variously changed.

FIG. 7 is a graph showing a heat generation rate when the operating state is low load, medium load, and high load.

FIG. 8 is a graph showing the mass combustion ratio in each of the low, middle, and high load operating states.

FIG. 9 is a graph showing the relationship between the ratio of the post-injection amount to the total fuel injection amount and the fuel efficiency.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine main body 4 Combustion chamber 5 Fuel injection valve 12 Turbocharger 24 Exhaust gas recirculation device 35 ECU 36 Operating state determination means 37 Fuel injection control means 38 Exhaust gas recirculation control means

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 41/02 380 F02D 41/02 380C 41/04 385 41/04 385C 385B 43/00 301 43/00 301J 301N 301R F02M 25/07 550 F02M 25/07 550F 570 570J 570P (72) Inventor Keiji Araki 3-1, Fuchu-cho Shinchi, Aki-gun, Hiroshima Pref. Mazda F-term (reference) 3G062 AA01 AA03 AA05 BA00 BA02 BA04 BA06 CA06 DA01 DA02 EA08 EB15 ED01 ED04 ED10 FA02 FA09 FA23 GA00 GA01 GA02 GA04 GA06 GA15 GA21 3G084 AA01 AA03 BA05 BA08 BA09 BA13 BA15 BA20 CA03 CA04 CA09 DA02 DA10 EA04 EA11 EB08 EC01 EC03 FA00 FA07 FA10 FA11 A11 FA33 AA18 BB01 BB06 DC03 DE01S DG06 EC09 FA18 FA24 GA04 GA05 GA06 GA12 GA17 HA01Z HA05Z HA06Z HB03X HB03Z HD07Z HE01Z HE03Z HF08Z 3G301 HA02 HA04 HA06 HA11 HA13 JA02 JA24 KA07 KA08 KA09 KA12 KA24 LA03 LB11 LC07 MA01 MA11 MA18 NC02 PA01Z PA07Z PA11Z PB08ZPBZZ

Claims (9)

[Claims] A fuel injection valve for injecting fuel into a combustion chamber of a diesel engine; and a fuel injection control means for controlling fuel injection from the fuel injection valve. In the operating range from the low load side to the high load side in the region, the main fuel injection for torque generation is divided into multiple times during the period from near the compression top dead center to the first half of the expansion stroke, and the main fuel injection A control apparatus for a diesel engine, characterized in that control is performed such that the start timing of the injection at the subsequent stage is delayed in an operation region on a high load side as compared with an operation region on a low load side. 2. An operation region in which the main fuel injection is divided into a plurality of times, in which the combustion by the main fuel injection continues in a low load region, and the combustion is interrupted in a region above a predetermined load.
2. The control system for a diesel engine according to claim 1, wherein the start timing of the latter-stage injection of the main fuel injection is changed according to the engine load. 3. Controlling the start timing of the latter stage of the main fuel injection so that the combustion by the main fuel injection is interrupted in the middle and high load operation ranges of the engine in a low and medium speed range. The control device for a diesel engine according to claim 2, wherein 4. A turbocharger driven by exhaust energy to supercharge intake air, an exhaust gas recirculation device for recirculating a part of exhaust gas to an intake system, and an exhaust gas recirculation amount by the exhaust gas recirculation device. Exhaust gas recirculation control means for controlling, and in the supercharging region in the low and medium speed regions of the engine, the fuel injection control means makes the injection of the latter stage side of the main fuel injection so that the combustion by the main fuel injection is interrupted. 2. The diesel engine according to claim 1, wherein the start timing is controlled, and the exhaust gas recirculation amount is controlled by the exhaust gas recirculation control means so that the excess air ratio in the combustion chamber becomes a target value according to the operation state. Control device. 5. A fuel injection valve for injecting fuel into a combustion chamber of a diesel engine, and fuel injection control means for controlling fuel injection from the fuel injection valve, wherein the fuel injection control means includes at least a low speed engine. In the operating range from the low load side to the high load side in the region, the main fuel injection for torque generation is divided into multiple times during the period from near the compression top dead center to the first half of the expansion stroke, and the main fuel injection Start timing of injection of the latter stage of main fuel injection so that combustion by main fuel injection continues during steady operation in the low load region of the operation region divided into multiple operations and combustion is interrupted during accelerated operation. Control device for a diesel engine, characterized in that the control of the engine is performed. 6. The diesel engine control device according to claim 5, further comprising a turbocharger. 7. The fuel injection control means causes a pilot injection to be performed from the fuel injection valve prior to the main fuel injection, and hastens the pilot injection start timing in the initial stage of the acceleration.
7. The control apparatus for a diesel engine according to claim 6, wherein an increase rate of the pilot injection is made larger than an increase rate of the main fuel injection. 8. The fuel injection control means, when the initial stage of the acceleration has passed, advances the start timing of the latter-stage injection of the main fuel injection, and reduces or cuts the pilot injection amount. The control device for a diesel engine according to claim 7. 9. In an operation region in which the main fuel injection is divided into a plurality of times, the injection amount of the latter stage of the main fuel injection is made smaller than the injection amount of the former stage, and the higher the load, the more the latter stage. The control device for a diesel engine according to any one of claims 1 to 8, wherein the ratio of the side injection amount is reduced.