JP5447294B2 - diesel engine - Google Patents

Description

  The present invention relates to a diesel engine to which a fuel mainly composed of light oil is supplied.

  2. Description of the Related Art Conventionally, diesel engines that improve emission performance by performing exhaust gas recirculation (hereinafter referred to as EGR) are known (see Patent Document 1). By performing this EGR, the combustion temperature can be lowered and the amount of NOx generated can be reduced. The amount of EGR gas introduced into the cylinder is controlled by adjusting the opening of the EGR valve.

JP 2009-293383 A

  As described above, it is preferable to introduce the EGR gas into the cylinder from the viewpoint of improving the emission performance, but the EGR gas amount cannot be increased so much in the operation region where the engine load (that is, the required torque) is high. In other words, in the operating region where the engine load is high, the amount of fuel injection is large, so the oxygen concentration in the cylinder must be increased accordingly. Therefore, in the high load operation region, the EGR valve is controlled so as to lower the EGR rate in the cylinder, and the oxygen concentration is adjusted to be higher.

  In the configuration in which the EGR valve is controlled in this way, the following problems occur when the engine is accelerated. That is, when the engine is accelerated, the operating state of the engine shifts to the high load side. In order to increase the engine load, it is necessary to increase the fuel supply amount. However, in order to increase the fuel supply amount, the inside of the cylinder needs to have an oxygen concentration corresponding to the supply amount. That is, in order to quickly respond to the acceleration request, it is necessary to quickly adjust the oxygen concentration in the cylinder. However, even if the EGR valve is adjusted to close in order to increase the oxygen concentration, the EGR rate in the cylinder does not change suddenly, and a response is delayed. That is, since the responsiveness of the oxygen concentration in the cylinder to the adjustment of the EGR valve is poor, it is difficult to supply an appropriate amount of fuel according to the acceleration request at an appropriate timing. As a result, there is a problem that it cannot be accelerated appropriately.

  The technology disclosed herein has been made in view of such a point, and an object thereof is to improve acceleration performance in a diesel engine that adjusts an EGR rate in accordance with an engine load.

  The technology disclosed herein is directed to a diesel engine including an engine body to which fuel mainly composed of light oil is supplied. The diesel engine further includes an EGR valve for adjusting the amount of EGR gas introduced into the cylinder of the engine body, and an EGR valve control unit for adjusting the oxygen concentration in the cylinder by controlling the EGR valve. The EGR valve control unit controls the opening degree of the EGR valve according to the required load so that the oxygen concentration in the cylinder once increases and then increases as the required load of the engine body increases. When the engine body is accelerated from a load lower than the load corresponding to the minimum value of the oxygen concentration beyond the load corresponding to the minimum value, the increase rate of the required load is The control amount of the EGR valve is adjusted so that the oxygen concentration increases as the value increases.

  The diesel engine adjusts the oxygen concentration in the cylinder (hereinafter also simply referred to as “in-cylinder oxygen concentration”) in accordance with the required load of the engine body. Specifically, the in-cylinder oxygen concentration is adjusted to be high when the required load on the engine body is low. When the required load is low, the fuel supply amount is small and combustion becomes unstable. However, the fuel stability can be improved by increasing the in-cylinder oxygen concentration. When the required load on the engine body is larger than that, the EGR valve is opened and the in-cylinder oxygen concentration is adjusted low. By reducing the in-cylinder oxygen concentration, the combustion temperature can be suppressed and the emission performance can be improved. When the required load on the engine main body is larger, the in-cylinder oxygen concentration is adjusted to be high by controlling the EGR valve to close. When the required load is large, it is necessary to increase the fuel supply amount. In order to increase the fuel supply amount, it is necessary to increase the in-cylinder oxygen concentration. That is, by increasing the in-cylinder oxygen concentration when the required load is high, the fuel supply amount can be increased as desired, and the desired required load can be output.

  Assuming that the in-cylinder oxygen concentration is controlled in this manner, the control amount of the EGR valve is adjusted to a higher in-cylinder oxygen concentration as the increase rate of the required load of the engine body is larger. The That is, when the engine body is accelerated from the low load side beyond the load corresponding to the minimum value of the oxygen concentration and exceeding the load corresponding to the minimum value, the in-cylinder oxygen concentration increases as the required load increases. Thus, the EGR valve is controlled. When the in-cylinder oxygen concentration is adjusted in such a manner of change, it is necessary to quickly increase the in-cylinder oxygen concentration when the increase rate of the required load is large, that is, during rapid acceleration. On the other hand, the control amount of the EGR valve is adjusted so that the in-cylinder oxygen concentration increases as the increase rate of the required load increases. That is, when the increase rate of the required load is large, the in-cylinder oxygen concentration is set to be high in advance. As a result, even if the required load increases rapidly, the in-cylinder oxygen concentration is set to be high in advance, so that it is possible to respond to a rapid increase in the fuel supply amount accompanying the rapid increase in required load. Thereby, quick acceleration can be realized.

  Further, the EGR valve control unit adjusts the opening degree of the EGR valve to the required load of the engine body so that the oxygen concentration in the cylinder once increases as the required load of the engine body increases. The engine body is controlled to increase once and then decrease with increase, and the engine body is accelerated from the lower load side than the load corresponding to the minimum value of the oxygen concentration over the load corresponding to the minimum value. In this case, the control amount of the EGR valve may be adjusted so that the maximum value of the opening degree of the EGR valve decreases as the increase rate of the required load increases.

  That is, when the opening degree of the EGR valve is increased, the in-cylinder oxygen concentration is decreased, and when the opening degree of the EGR valve is decreased, the in-cylinder oxygen concentration is increased. And change in the opposite manner. The opening degree of the EGR valve controlled in this way has a maximum value in the same manner as the in-cylinder oxygen concentration has a minimum value. Therefore, by adjusting the control amount so that the maximum value of the opening degree of the EGR valve becomes smaller as the increase rate of the required load of the engine body becomes larger, the in-cylinder oxygen concentration becomes smaller as the increase rate of the required load of the engine body becomes larger. Adjustment can be made in the direction of increasing overall.

  Further, the EGR valve control unit is configured to increase the required load when the engine body is accelerated from a lower load side than the load corresponding to the minimum value of the oxygen concentration and exceeding the load corresponding to the minimum value. It is preferable to adjust the control amount of the EGR valve by slowing the valve opening operation speed of the EGR valve as the value increases.

  As described above, when the valve opening operation speed of the EGR valve is slowed down, the responsiveness is lowered only when the EGR valve is opened. Therefore, when the EGR valve is opened, the opening degree does not easily reach the target value, and consequently, the in-cylinder oxygen concentration also does not easily reach the target value. That is, since the EGR valve is opened when the in-cylinder oxygen concentration is decreased, the speed at which the in-cylinder oxygen concentration reaches the target value is decreased when the in-cylinder oxygen concentration is decreased. Here, in the configuration in which the in-cylinder oxygen concentration is adjusted so as to increase after decreasing once as the required load of the engine body increases, the in-cylinder oxygen concentration is reduced when the in-cylinder oxygen concentration starts to increase from the decrease. It will begin to rise before the target minimum is reached. The operation speed of the EGR valve is slow only in the valve opening operation, and the operation speed is not slow in the valve closing operation. Therefore, when the in-cylinder oxygen concentration is increased, the EGR valve is quickly closed.

  As a result, as the increase rate of the required load increases, the in-cylinder oxygen concentration is less likely to decrease to the target minimum value, and the in-cylinder oxygen concentration that rises after decreasing once increases in the vicinity of the minimum value as the increase rate of the required load increases. The density is adjusted to increase in the center.

Here, as a method of increasing the in-cylinder oxygen concentration, it is conceivable to change the target value of the opening degree of the EGR valve. However, it is only necessary to adjust the in-cylinder oxygen concentration to be higher when the required load increases. If the target value is changed, the opening degree of the EGR valve only reaches the changed target value even when the required load is in a steady state. On the other hand, when the operating speed of the EGR valve is changed, the responsiveness decreases, but the opening degree of the EGR valve eventually reaches the target value. That is, in the steady state of the required load, the cylinder oxygen concentration is as intended. That is, Ru can be prevented from being unnecessarily changed to in-cylinder oxygen concentration in the steady state.

  According to the present invention, in the configuration in which the EGR valve is controlled so that the oxygen concentration in the cylinder once increases and then increases as the required load of the engine body increases, the oxygen in the cylinder increases as the increase rate of the required load increases. By adjusting the control amount of the EGR valve so that the concentration becomes high, even if the increase rate of the required load is large, it is possible to respond quickly to the increase in the fuel supply amount accompanying the increase in the required load. Can be executed.

It is the schematic which shows the structure of a diesel engine. It is a block diagram concerning control of a diesel engine. It is a map which shows the combustion mode according to the state of the engine. It is a figure which shows an example of the fuel injection form in the diffusion combustion mode in a low load side spreading | diffusion area | region, and an example of the log | history of the heat release rate accompanying it. It is a figure which shows an example of the fuel injection form in a premix combustion mode, and an example of the log | history of the heat release rate in connection with it. It is a figure which shows an example of the fuel injection form in the diffusion combustion mode in a high load side diffusion area | region, and an example of the log | history of the heat release rate in connection with it. It is an example of the change characteristic figure of cylinder oxygen concentration with respect to engine load and rotation speed. It is a flowchart at the time of adjusting the control amount of an exhaust gas recirculation valve according to the increase rate of a request | requirement load. It is an example of the change characteristic of the in-cylinder oxygen concentration with respect to the engine load, which is adjusted according to the increase rate of the required load. It is an example of a change characteristic figure of engine load, number of rotations, and in-cylinder oxygen concentration according to the increase rate of demand load.

  Hereinafter, the diesel engine which concerns on embodiment is demonstrated based on drawing. The following description of the preferred embodiment is merely exemplary in nature. 1 and 2 show a schematic configuration of an engine (engine body) 1 according to the embodiment. The engine 1 is a diesel engine that is mounted on a vehicle and is supplied with fuel mainly composed of light oil. The cylinder block 11 is provided with a plurality of cylinders 11a (only one is shown), and the cylinder A cylinder head 12 disposed on the block 11 and an oil pan 13 disposed on the lower side of the cylinder block 11 and storing lubricating oil are provided. In each cylinder 11a of the engine 1, a piston 14 is fitted and removably fitted. A top surface of the piston 14 is formed with a cavity defining a reentrant combustion chamber 14a. The piston 14 is connected to the crankshaft 15 via a connecting rod 14b.

  Thus, the engine 1 is configured to have a relatively low compression ratio with a geometric compression ratio of 12 or more and 15 or less (for example, 14), thereby improving exhaust emission performance and thermal efficiency. It is trying to improve.

  In the cylinder head 12, an intake port 16 and an exhaust port 17 are formed for each cylinder 11a, and an intake valve 21 and an exhaust valve that open and close the opening of the intake port 16 and the exhaust port 17 on the combustion chamber 14a side. 22 are arranged respectively.

  In the valve systems that drive these intake and exhaust valves 21 and 22, respectively, a hydraulically operated variable mechanism that switches the operation mode of the exhaust valve 22 between a normal mode and a special mode on the exhaust valve side (see FIG. 2 below). VVM (Variable Valve Motion). Although detailed illustration of the configuration of the VVM 71 is omitted, two types of cams having different cam profiles, a first cam having one cam peak and a second cam having two cam peaks, and the first cam When a lost motion mechanism that selectively transmits the operating state of one of the first and second cams to the exhaust valve is included, and the operating state of the first cam is transmitted to the exhaust valve 22 The exhaust valve 22 operates in a normal mode in which the valve is opened only once during the exhaust stroke, whereas when the operating state of the second cam is transmitted to the exhaust valve 22, the exhaust valve 22 is in the exhaust stroke. In addition, the valve operates in a special mode in which the exhaust is opened twice so that the valve is opened during the intake stroke.

  Switching between the normal mode and the special mode of the VVM 71 is performed by hydraulic pressure supplied from an engine-driven hydraulic pump (not shown), and the special mode can be used in the control related to the internal EGR. In order to enable switching between the normal mode and the special mode, an electromagnetically driven valve system that drives the exhaust valve 22 by an electromagnetic actuator may be employed. The execution of the internal EGR is not limited to the double opening of the exhaust. For example, the internal EGR control may be performed by opening the intake valve 21 twice, or by opening the intake twice. An internal EGR control may be performed in which the burned gas remains by providing a negative overlap period in which both the intake valve 21 and the exhaust valve 22 are closed in the intake stroke. The internal EGR control by the VVM 71 is performed mainly when the engine 1 with low fuel ignitability is cold.

  The cylinder head 12 is provided with an injector 18 for injecting fuel, and a glow plug 19 for warming the intake air in each cylinder 11a and improving the ignitability of the fuel when the engine 1 is cold. The injector 18 is disposed such that its fuel injection port faces the combustion chamber 14a from the ceiling surface of the combustion chamber 14a. Basically, fuel is directly supplied to the combustion chamber 14a near the top dead center of the compression stroke. The injection is supplied.

  An intake passage 30 is connected to one side of the engine 1 so as to communicate with the intake port 16 of each cylinder 11a. On the other hand, an exhaust passage 40 for discharging burned gas (exhaust gas) from the combustion chamber 14a of each cylinder 11a is connected to the other side of the engine 1. In the intake passage 30 and the exhaust passage 40, as will be described in detail later, a large turbocharger 61 and a small turbocharger 62 for supercharging intake air are disposed.

  An air cleaner 31 that filters intake air is disposed at the upstream end of the intake passage 30. On the other hand, a surge tank 33 is disposed near the downstream end of the intake passage 30. The intake passage 30 downstream of the surge tank 33 is an independent passage branched for each cylinder 11a, and the downstream end of each independent passage is connected to the intake port 16 of each cylinder 11a.

  Between the air cleaner 31 and the surge tank 33 in the intake passage 30, compressors 61a and 62a of the large and small turbochargers 61 and 62, and an intercooler 35 for cooling the air compressed by the compressors 61a and 62a, A throttle valve 36 for adjusting the amount of intake air into the combustion chamber 14a of each cylinder 11a is provided. The throttle valve 36 is basically fully opened, but is fully closed when the engine 1 is stopped so that no shock is generated.

  The upstream portion of the exhaust passage 40 is constituted by an exhaust manifold having an independent passage branched for each cylinder 11a and connected to the outer end of the exhaust port 17 and a collecting portion where the independent passages gather. Yes.

  On the downstream side of the exhaust manifold in the exhaust passage 40, the turbine 62b of the small turbocharger 62, the turbine 61b of the large turbocharger 61, and exhaust for purifying harmful components in the exhaust gas in order from the upstream side. A purification device 41 and a silencer 42 are provided.

The exhaust purification device 41 includes an oxidation catalyst 41a and a diesel particulate filter (hereinafter referred to as a filter) 41b, which are arranged in this order from the upstream side. The oxidation catalyst 41a and the filter 41b are accommodated in one case. The oxidation catalyst 41a has an oxidation catalyst supporting platinum or platinum added with palladium or the like, and promotes a reaction in which CO and HC in the exhaust gas are oxidized to produce CO ₂ and H ₂ O. Is. The filter 41b collects particulates such as soot contained in the exhaust gas of the engine 1. The filter 41b may be coated with an oxidation catalyst.

  A portion of the intake passage 30 between the surge tank 33 and the throttle valve 36 (that is, a portion downstream of the small compressor 62a of the small turbocharger 62), the exhaust manifold and the small turbocharger in the exhaust passage 40. The portion between the turbocharger 62 and the small turbine 62 b (that is, the upstream portion of the small turbocharger 62 from the small turbine 62 b) is an exhaust gas recirculation for recirculating a part of the exhaust gas to the intake passage 30. They are connected by a passage 51 (high pressure EGR means). The exhaust gas recirculation passage 51 is provided with an exhaust gas recirculation valve 51a for adjusting the recirculation amount of the exhaust gas to the intake passage 30, and an EGR cooler 52 for cooling the exhaust gas with engine cooling water. ing. This exhaust gas recirculation valve 51a constitutes an EGR valve.

  The large turbocharger 61 has a large compressor 61 a disposed in the intake passage 30 and a large turbine 61 b disposed in the exhaust passage 40. The large compressor 61 a is disposed between the air cleaner 31 and the intercooler 35 in the intake passage 30. On the other hand, the large turbine 61b is disposed between the exhaust manifold and the oxidation catalyst 41a in the exhaust passage 40.

  The small turbocharger 62 has a small compressor 62 a disposed in the intake passage 30 and a small turbine 62 b disposed in the exhaust passage 40. The small compressor 62 a is disposed on the downstream side of the large compressor 61 a in the intake passage 30. On the other hand, the small turbine 62 b is disposed on the upstream side of the large turbine 61 b in the exhaust passage 40.

  That is, in the intake passage 30, a large compressor 61a and a small compressor 62a are arranged in series from the upstream side, and in the exhaust passage 40, a small turbine 62b and a large turbine 61b are arranged in series from the upstream side. Has been. The large and small turbines 61b and 62b are rotated by the exhaust gas flow, and the large and small compressors 61a and 62a connected to the large and small turbines 61b and 62b are rotated by the rotation of the large and small turbines 61b and 62b, respectively. Each operates.

  The small turbocharger 62 is relatively small, and the large turbocharger 61 is relatively large. That is, the large turbine 61 b of the large turbocharger 61 has a larger inertia than the small turbine 62 b of the small turbocharger 62.

  A small intake bypass passage 63 that bypasses the small compressor 62 a is connected to the intake passage 30. The small intake bypass passage 63 is provided with a small intake bypass valve 63 a for adjusting the amount of air flowing to the small intake bypass passage 63. The small intake bypass valve 63a is configured to be in a fully closed state (normally closed) when no power is supplied.

  On the other hand, the exhaust passage 40 is connected to a small exhaust bypass passage 64 that bypasses the small turbine 62b and a large exhaust bypass passage 65 that bypasses the large turbine 61b. The small exhaust bypass passage 64 is provided with a regulating valve 64a for adjusting the exhaust amount flowing to the small exhaust bypass passage 64, and the large exhaust bypass passage 65 has an exhaust amount flowing to the large exhaust bypass passage 65. A wastegate valve 65a for adjusting the pressure is provided. Both the regulating valve 64a and the waste gate valve 65a are configured to be in a fully open state (normally open) when no power is supplied.

  The large turbocharger 61 and the small turbocharger 62 are integrated into a single unit including the intake passage 30 and the exhaust passage 40 in which the large turbocharger 61 and the small turbocharger 62 are arranged, thereby forming a supercharger unit 60. doing. The supercharger unit 60 is attached to the engine 1.

The diesel engine 1 configured as described above is controlled by a powertrain control module (hereinafter referred to as PCM) 10. The PCM 10 includes a microprocessor having a CPU, a memory, a counter timer group, an interface, and a path connecting these units. The PCM 10 constitutes an EGR valve control unit and a combustion control unit. As shown in FIG. 2, the PCM 10 includes a water temperature sensor SW1 that detects the temperature of the engine cooling water, a supercharging pressure sensor SW2 that is attached to the surge tank 33 and detects the pressure of the air supplied to the combustion chamber 14a, An intake air temperature sensor SW3 that detects the temperature of the intake air, a crank angle sensor SW4 that detects the rotation angle of the crankshaft 15, and an accelerator opening sensor that detects an accelerator opening corresponding to an operation amount of an accelerator pedal (not shown) of the vehicle. Detection signals of SW5, an intake CO ₂ sensor SW6 for detecting the carbon dioxide concentration in the intake air, and an exhaust CO ₂ sensor SW7 for detecting the carbon dioxide concentration in the exhaust gas are input, and various calculations are performed based on these detection signals. To determine the state of the engine 1 and the vehicle, and according to this, the injector 18, the glow plug 19, and the valve train VVM71, various valves 36,51a, 53a, and outputs 63a, 64a, the actuator to control signals 65a.

(Outline of engine combustion control)
The basic control of the engine 1 by the PCM 10 mainly determines the required load (that is, the target torque) based on the accelerator opening, and controls the operation of the injector 18 based on the fuel injection amount and the injection timing corresponding thereto. It is realized by. The required load is set to increase as the accelerator opening increases and the engine speed increases, and the fuel injection amount is set based on the required load and the engine speed. The injection amount is set to increase as the required load increases and as the engine speed increases. Further, the recirculation ratio (EGR rate) of the exhaust gas into the cylinder 11a is controlled by controlling the opening degree of the throttle valve 36 and the exhaust gas recirculation valve 51a (external EGR control) and by controlling the VVM 71 (internal EGR control).

  FIG. 3 is a map showing the combustion mode according to the state of the engine when the engine 1 is half warmed up and warm. As shown in FIG. 3, when the engine 1 is semi-warm and warm, a plurality of operation areas are set according to the engine speed and the engine load (actual total fuel injection amount). Is set to combustion mode. The operation region A is an operation region in which EGR is executed in a steady state and the combustion mode is switched between the premixed combustion mode and the diffusion combustion mode. The operation area A is an operation area with a relatively low rotation and a low load. Specifically, the operation region A is a low rotation side when the engine speed is divided into a low rotation side and a high rotation side, and the engine load is 2 between the low load side and the high load side. This is the area on the low load side when divided into two.

  Hereinafter, the fuel injection mode in each operation region will be described with reference to FIGS. The fuel injection amount and heat generation rate shown in FIGS. 4 to 6 do not necessarily indicate the relative fuel injection amount or the heat generation rate when these figures are compared with each other. .

  FIG. 4 shows an example (lower diagram) of the history of fuel injection in the operating region a1 (upper diagram) and the associated heat release rate in the cylinder 11a. The operation region a1 is a region in the operation region A, and is a relatively low load operation region including an idle region. Specifically, the operation area a1 is an area of low load when the operation area A is divided into three, low load, medium load, and high load of the engine. In this operation region a1, the PCM 10 is in the diffusion combustion mode and causes the engine 1 to perform diffusion combustion. Diffusion combustion is combustion in which combustion proceeds while fuel and air are diffused and mixed, in other words, fuel injection and combustion partially overlap in time. Since this diffusion combustion has a shorter ignition delay than premixed combustion, it is easy to control the start timing of combustion. In addition, since diffusion combustion is slower than premixed combustion, combustion pressure is low and combustion noise is reduced.

  In the fuel injection mode in the operation region a1, during the compression stroke before the compression top dead center, fuel injection with a relatively large injection amount (pre-injection) is executed twice with a predetermined time interval, and compression top dead In the vicinity of the point, main injection with a relatively short pulse width is executed, and then one fuel injection (after injection) is executed. Accordingly, a total of four fuel injections are executed in this operation region a1. The pre-injection causes pre-combustion having a sufficient heat generation rate so that the peak of the heat generation rate occurs at a predetermined time before compression top dead center. In other words, pre-combustion occurs before the start of main combustion, thereby increasing the temperature and pressure in the cylinder 11a at the time of starting main injection. This shortens the ignition delay time of the fuel injected by the main injection. Main injection starts injection at a predetermined timing before compression top dead center or at compression top dead center as shown in the figure, but the main combustion associated with the main injection is compressed because the ignition delay time is short. Starts near top dead center. This can be advantageous for improving thermal efficiency and thus fuel economy. Moreover, said combustion makes the rise in the heat release rate of the subsequent main combustion slow. This can be advantageous in reducing combustion noise and improving NVH (Noise Vibration Harshness) performance. That is, the pre-injection and the accompanying pre-combustion can increase the controllability of the main combustion to generate the main combustion at a desired timing, which can be advantageous for improving fuel efficiency and NVH performance. After-injection is fuel injection that is performed during main combustion, in other words, during heat generation by main combustion, and at least part of the fuel spray injected by after-injection is after compression top dead center. It reaches in the cavity of the piston 14 descending. Preferably, most of the fuel spray injected by after injection reaches the cavity. This after injection accelerates the main combustion and shortens the afterburn period. That is, the execution of the after injection makes it possible to shorten the combustion period without affecting the rising of the main combustion. This is advantageous for improving the torque and can contribute to improving the fuel efficiency.

  FIG. 5 shows an example (lower diagram) of the history of fuel injection in the operating region a2 (upper diagram) and the associated heat release rate in the cylinder 11a. The operation region a2 is a region in the operation region A, and is a relatively medium load operation region. Specifically, the operation region a2 is a medium load region in the case where the operation region A is divided into three of a low load, a medium load, and a high load of the engine. In this operation region a2, the PCM 10 enters the premixed combustion mode and causes the engine 1 to perform premixed combustion. The premixed combustion is combustion that is ignited after mixing fuel and air, in other words, combustion in which combustion starts after fuel injection. Since this premixed combustion is combustion after fuel and air are mixed to some extent, oxygen in the cylinder 11a can be used effectively, and even when the in-cylinder oxygen concentration is low, the generation of smoke is suppressed. be able to.

  The fuel injection mode in the operation region a2 is that during the compression stroke (before compression top dead center), fuel injection is performed three times with a predetermined time interval, and the fuel injection amount to be injected at a relatively early timing is set. The amount of fuel injection injected at relatively late timing is relatively small. This is because fuel premixability is improved by injecting as much fuel as possible as early as possible. Further, the three fuel injections are executed at the timing when all of the fuel injected by each injection reaches the cavity. The fuel injected in this way is burned by self-ignition near the compression top dead center while being sufficiently mixed with air. Such a premixed combustion mode is advantageous in terms of fuel consumption and exhaust emission. That is, since the premixed combustion (solid line in the figure) has a shorter combustion period than the diffusion combustion shown by the broken line, it is possible to generate a torque that is gathered at a desired time and improve fuel efficiency.

  FIG. 6 shows an example (lower diagram) of the history of fuel injection in the operating region a3 (upper diagram) and the associated heat release rate in the cylinder 11a. The operation region a3 is a region within the operation region A and is a relatively high load operation region. Specifically, the operation area a3 is a high-load area when the operation area A is divided into three engine loads, a low load, an intermediate load, and a high load. In this operation region a3, the PCM 10 enters the diffusion combustion mode, and causes the engine 1 to perform diffusion combustion. In the fuel injection mode in the operation region a3, fuel injection (pre-injection) with a relatively large injection amount is performed once during the compression stroke before the compression top dead center, and the pulse width is relatively close to the compression top dead center. The short main injection is executed, and thereafter, one fuel injection (after injection) is executed. Accordingly, in this operation region a3, a total of three fuel injections are executed. Even in the diffusion combustion mode of the operation region a3, the pre-injection and the accompanying pre-combustion increase the controllability of the main combustion to generate the main combustion at a desired timing, thereby improving the fuel consumption and the NVH performance. Can do. That is, in diffusion combustion (solid line in the figure), since the increase in the heat generation rate is slower than in the premixed combustion indicated by the broken line, the maximum value of the heat generation rate can be suppressed and combustion noise is suppressed. be able to. Since the fuel injection amount is larger in the operation region a3 than in the operation region a1 on the low load side, this suppression of combustion noise is particularly effective.

  In the operation region B, the PCM 10 does not enter the premixed combustion mode, always enters the diffusion combustion mode, and causes the engine 1 to perform diffusion combustion. As for the fuel injection mode in the operation region B, the presence / absence, number and timing of pre-injection, the number and timing of main injection, and the presence / absence, number and timing of after-injection are set according to the load and rotation speed of the engine 1. The

  Further, the PCM 10 adjusts the oxygen concentration in the cylinder 11a by controlling the exhaust gas recirculation valve 51a in accordance with the operation state of the engine 1 in order to execute desired combustion in each operation region. FIG. 7 shows an example of a change characteristic chart of the in-cylinder oxygen concentration with respect to the engine load and the rotational speed. As shown in FIG. 7, the PCM 10 increases the opening degree of the exhaust gas recirculation valve 51 a so that the in-cylinder oxygen concentration once decreases and becomes minimum as the required load of the engine 1 increases and then increases. Control.

  More specifically, in the low load side diffusion region a1, the PCM 10 causes the exhaust gas recirculation valve 51a to decrease the in-cylinder oxygen concentration, that is, to increase the opening as the required load of the engine 1 increases. To control. The PCM 10 is in the diffusion combustion mode until the in-cylinder oxygen concentration reaches a predetermined value. This predetermined value is the in-cylinder oxygen concentration capable of premixed combustion.

  When the in-cylinder oxygen concentration becomes a predetermined value or more, the PCM 10 enters the premixed combustion mode. In other words, when the operating state of the engine 1 is in the premixing region a2, the PCM 10 controls the exhaust gas recirculation valve 51a so that the in-cylinder oxygen concentration becomes equal to or higher than a predetermined value. In addition, the hatching part in a figure has shown the premixing area | region a2. In the premixing region, the PCM 1 causes the exhaust gas recirculation valve 51a to turn upward after the in-cylinder oxygen concentration once decreases as the required load of the engine 1 increases, that is, the opening degree increases on the low load side. However, the maximum value is eventually reached and the opening degree is controlled to be smaller on the high load side.

  In the high load side diffusion region a3, which is a region on the higher load side than the premixing region a2, the PCM 10 causes the exhaust gas recirculation valve 51a to increase the in-cylinder oxygen concentration as the required load of the engine 1 increases. That is, control is performed so that the opening degree becomes small. That is, as the load on the engine 1 increases, the EGR gas decreases from the cylinder 11a.

  As described above, in the premixing region a2, the in-cylinder oxygen concentration is adjusted to be lower than that in the low load side and high load side diffusion regions a1 and a3. That is, in order to perform the premixed combustion, it is necessary to sufficiently mix the fuel and the air before the ignition is performed after the fuel is injected into the cylinder 11a. Therefore, a certain ignition delay is required. Therefore, in the premix region a2, the opening degree of the exhaust gas recirculation valve 51a is increased to reduce the in-cylinder oxygen concentration. Thus, in the premixing region a2, an ignition delay is ensured by suppressing the in-cylinder oxygen concentration, thereby creating an environment in which premixed combustion can be realized.

  On the other hand, in a region where the required load of the engine 1 is low, the amount of fuel supplied into the cylinder 11a is small, so that combustion tends to become unstable. For this reason, it is not preferable to introduce a large amount of EGR gas into the cylinder 11a, and it is necessary to increase the in-cylinder oxygen concentration as much as possible to create an environment in which combustion is stable. Therefore, in the low load side diffusion region a1, the in-cylinder oxygen concentration is increased by reducing the opening degree of the exhaust gas recirculation valve 51a. When the in-cylinder oxygen concentration is high, the ignition delay cannot be sufficiently secured. Therefore, when the combustion is injected into the cylinder 11a, the combustion starts before the fuel and air are mixed, and the premixed combustion is performed. Difficult to do. Therefore, the combustion mode in this region a1 is diffusion combustion. In the first place, diffusion combustion is easier to control the start timing of combustion than premixed combustion, and therefore diffusion combustion is preferable from the viewpoint of stabilization of combustion in an environment where such combustion is unstable. .

  Further, in a region where the required load of the engine 1 is high, the fuel supply amount (that is, the fuel injection amount) increases. When the fuel supply amount increases, it is necessary to increase the in-cylinder oxygen concentration in order to meet the supply amount. Therefore, in the high load side diffusion region a3, the in-cylinder oxygen concentration is increased by reducing the opening degree of the exhaust gas recirculation valve 51a. When the in-cylinder oxygen concentration becomes high, it becomes impossible to ensure a sufficient ignition delay, and it becomes difficult to perform premixed combustion. Therefore, the combustion mode in this region a3 is diffusion combustion. Moreover, in the high load side diffusion region a3, the amount of fuel supply is large, so that combustion noise increases. On the other hand, in the high load side diffusion region a3, the combustion noise is reduced and the NVH performance is improved by setting the combustion form to diffusion combustion. That is, diffusion combustion is advantageous in that the combustion noise is low because the combustion pressure is lower than that of premixed combustion.

  On the other hand, when the rotational speed of the engine 1 is relatively high, the PCM 10 increases so that the in-cylinder oxygen concentration once decreases and becomes a minimum as the required load of the engine 1 increases. Although the opening degree of the exhaust gas recirculation valve 51a is controlled, even if the in-cylinder oxygen concentration is minimized, it does not decrease to a value at which premixed combustion can be realized. That is, when the rotational speed of the engine 1 is high, the piston 14 moves fast, so the injection period during which all of the injected fuel can reach the cavity is shortened. Therefore, it is difficult to execute combustion injection at a timing suitable for premixed combustion. Therefore, in a region where the rotational speed of the engine 1 is relatively high, the combustion of the engine 1 is diffused combustion, and accordingly, the in-cylinder oxygen concentration is not excessively lowered, and the diffusive combustion is executed with the minimum value. It is within the possible range. Thus, combustion can be stabilized by performing diffusion combustion in the high rotation region of the engine 1. In addition, the emission performance can be improved by reducing the in-cylinder oxygen concentration within a range where diffusion combustion can be performed.

  That is, the PCM 10 switches between the premixed combustion mode and the diffusion combustion mode by controlling the exhaust gas recirculation valve 51a in addition to the switching of the fuel injection mode. Specifically, the PCM 10 controls the exhaust gas recirculation valve 51a as described above, calculates the in-cylinder oxygen concentration from the output of each sensor, and the calculated in-cylinder oxygen concentration corresponds to the premixed combustion range. If it is within the hatched region (FIG. 7), the premixed combustion mode is set, and if the calculated in-cylinder oxygen concentration is within a range corresponding to diffusion combustion, the diffusion combustion mode is set. The in-cylinder oxygen concentration is calculated, for example, based on outputs from an air flow sensor (not shown), a supercharging pressure sensor SW2, an exhaust flow rate sensor (not shown), an exhaust oxygen concentration sensor (not shown), and the like. However, the method for calculating the in-cylinder oxygen concentration is not limited to this.

  In addition, before the engine 1 becomes semi-warm (for example, when the engine water temperature is 40 ° C.), that is, when it is cold, the in-cylinder temperature is increased by the internal EGR or the glow plug 19 to activate the exhaust purification device 41. Is in an ON state, and premixed combustion cannot be performed. Therefore, before the engine 1 is semi-warm up, switching between the premixed combustion mode and the diffusion combustion mode is not executed, and combustion control peculiar to cold time based on diffusion combustion is performed.

  Thus, in the engine 1, the in-cylinder oxygen concentration is adjusted according to the required load. Here, when the required load increases, the in-cylinder oxygen concentration follows the change characteristic diagram of the in-cylinder oxygen concentration with respect to the engine load and the rotational speed shown in FIG. 7 from the low load side to the high load side. Adjusted to When the required load increases rapidly, the in-cylinder oxygen concentration needs to be adjusted quickly. In particular, when the in-cylinder oxygen concentration is increased, the fuel supply amount is increased in accordance with an increase in the required load. If the in-cylinder oxygen concentration cannot be increased immediately, the fuel supply corresponding to the required load is performed. The quantity cannot be supplied, and as a result, the demand load cannot be increased quickly.

  Therefore, when the engine 1 is accelerated from a load lower than the load corresponding to the minimum value of the in-cylinder oxygen concentration beyond the load corresponding to the minimum value, the PCM 1 increases in the cylinder as the increase rate of the required load increases. The control amount of the exhaust gas recirculation valve 51a is adjusted so that the oxygen concentration becomes high. Hereinafter, the adjustment of the control amount of the exhaust gas recirculation valve 51a will be described in detail. FIG. 8 shows a flowchart for adjusting the control amount of the exhaust gas recirculation valve 51a in accordance with the increase rate of the required load. FIG. 9 shows a cylinder for the required load that is adjusted in accordance with the increase rate of the required load. An example of the change characteristic of the internal oxygen concentration is shown, and FIG. 10 shows an example of a change characteristic diagram of the engine load, the rotational speed, and the in-cylinder oxygen concentration according to the increase rate of the required load.

  First, in step S1, the PCM 1 calculates the in-cylinder oxygen concentration target value A from the target torque (that is, the required load) and the engine speed.

  Next, in step S2, the adjustment amount Δ of the in-cylinder oxygen concentration is calculated from the increase rate of the target torque. Specifically, the increase rate of the target torque is calculated from the increase rate of the accelerator pedal depression amount. The PCM 1 has a map, table or function of the adjustment amount Δ with respect to the target torque increase rate, and obtains the adjustment amount Δ from the calculated target torque increase rate. Here, the adjustment amount Δ is set to increase as the increase rate of the target torque increases.

  Subsequently, in step S3, it is determined whether or not the in-cylinder oxygen concentration target value A is equal to or greater than the current in-cylinder oxygen concentration command value B. That is, it is determined whether to reduce the in-cylinder oxygen concentration. The in-cylinder oxygen concentration command value B is a reference value when outputting the command value to the exhaust gas recirculation valve 51a. The opening degree of the exhaust gas recirculation valve 51a is controlled so that the actual in-cylinder oxygen concentration becomes the in-cylinder concentration command value B.

  When the in-cylinder oxygen concentration target value A is smaller than the in-cylinder oxygen concentration command value B (No), the process proceeds to step S5. The in-cylinder oxygen concentration target value A is smaller than the in-cylinder oxygen concentration command value B when reducing the in-cylinder oxygen concentration and increasing the opening of the exhaust gas recirculation valve 51a. In step S5, the adjustment amount Δ is added to the in-cylinder oxygen concentration target value A, and this value is used as the in-cylinder oxygen concentration command value B. Then, the PCM 1 controls the exhaust gas recirculation valve 51a so as to have an opening degree corresponding to the in-cylinder oxygen concentration command value B. That is, when reducing the in-cylinder oxygen concentration, the in-cylinder oxygen concentration target value A is not directly used as the in-cylinder oxygen concentration command value B, but the adjustment amount Δ is added to the in-cylinder oxygen concentration target value A to increase the in-cylinder oxygen concentration. The concentration command value B is assumed. As a result, when reducing the in-cylinder oxygen concentration, the in-cylinder oxygen concentration command value B is adjusted (corrected) to be higher than the target value A.

  Thereafter, the process proceeds to step S6, and it is determined whether or not the in-cylinder oxygen concentration command value B is equal to or less than the in-cylinder oxygen concentration target value A. When the in-cylinder oxygen concentration command value B is equal to or less than the in-cylinder oxygen concentration target value A (Yes), the process proceeds to step S7, and the in-cylinder oxygen concentration command value B is set as the in-cylinder oxygen concentration target value A. That is, the in-cylinder oxygen concentration target value A is set to the in-cylinder oxygen concentration command value B without adding the adjustment amount Δ. On the other hand, when the in-cylinder oxygen concentration command value B is larger than the in-cylinder oxygen concentration target value A (No), the process proceeds to END.

  On the other hand, when the in-cylinder oxygen concentration target value A is equal to or greater than the current in-cylinder oxygen concentration command value B (Yes) in step S3, the process proceeds to step S4. When the in-cylinder oxygen concentration target value A is equal to or greater than the current in-cylinder oxygen concentration command value B, it is time to increase the in-cylinder oxygen concentration and to reduce the opening of the exhaust gas recirculation valve 51a. In step S4, the in-cylinder oxygen concentration target value A is set as the in-cylinder oxygen concentration command value B. That is, the in-cylinder oxygen concentration target value A is directly used as the in-cylinder oxygen concentration command value B without adding the adjustment amount Δ. As a result, when increasing the in-cylinder oxygen concentration, the in-cylinder oxygen concentration command value B is set as the target value A.

  As a result of this control, the in-cylinder oxygen concentration changes as shown in FIG. In other words, when the required load increase rate indicated by the alternate long and short dash line in the figure is large (that is, during rapid acceleration), the in-cylinder oxygen concentration is adjusted to be higher than the target value when the in-cylinder oxygen concentration decreases. Is done. Therefore, the minimum value of the in-cylinder oxygen concentration becomes larger than the target value indicated by the solid line in the figure. In the example of FIG. 9, the adjustment amount Δ increases as the required load increases. That is, the in-cylinder oxygen concentration is adjusted to a higher concentration side as it is closer to the minimum value.

  Eventually, the in-cylinder oxygen concentration starts to rise, but at the time when the in-cylinder oxygen concentration starts to rise, the in-cylinder oxygen concentration (that is, the minimum value) at that time is higher than the target value. Therefore, even if the exhaust gas recirculation valve 51a is controlled to adjust the in-cylinder oxygen concentration according to the target value, the actual in-cylinder oxygen concentration is initially higher than the target value, Gradually converge to the target value. That is, during rapid acceleration, when the in-cylinder oxygen concentration is increased, the actual in-cylinder oxygen concentration is adjusted to be higher than the original value (target value) corresponding to the required load. In this way, by increasing the in-cylinder oxygen concentration early, the in-cylinder oxygen concentration has already become a value corresponding to the fuel supply amount when attempting to increase the fuel supply amount in response to an increase in the required load. Therefore, the increased amount of fuel can be supplied immediately. As a result, rapid acceleration can be realized.

  In such a configuration, the minimum value of the in-cylinder oxygen concentration increases as the increase rate of the required load increases. However, when the increase rate of the required load exceeds a predetermined value, the minimum value of the in-cylinder oxygen concentration becomes the premixed combustion. It becomes higher than the upper limit (for example, 15% by weight) of the corresponding density (hatched area in FIG. 7). In such a case, the combustion of the engine 1 increases the output torque while maintaining diffusion combustion. That is, when the required load increase rate is less than the predetermined value, the combustion of the engine 1 is switched in the order of diffusion combustion, premixed combustion, and diffusion combustion as the required load increases. When the value exceeds the predetermined value, the premixed combustion mode is not entered, so that the diffusion combustion remains even if the required load increases. The fact that the minimum value of the in-cylinder oxygen concentration is higher than the concentration corresponding to premixed combustion means that the in-cylinder oxygen concentration does not decrease to such an extent that premixed combustion can be performed. In such a case, combustion can be stabilized by performing diffusion combustion without performing premixed combustion.

  For example, as shown in FIG. 10, when accelerating from the operation region a1 on the solid coordinate axis, the in-cylinder oxygen concentration increases as the required load increases during slow acceleration where the increase rate of the required load is less than a predetermined value. Decreases and enters the operation area a2 from the operation area a1 (refer to the area between the coordinate line of the solid line and the coordinate axis of the one-dot chain line). In the operation region a1, diffusion combustion is performed, but in the operation region a2, premixed combustion is performed. When the required load increases, the in-cylinder oxygen concentration starts to increase, and the output torque is increased while increasing the in-cylinder oxygen concentration (see the region between the dashed-dotted coordinate axis and the broken-line coordinate axis). As the required load further increases, the in-cylinder oxygen concentration further increases, the operating state of the engine 1 enters the operating region a3, and the combustion becomes diffusion combustion (refer to the region between the dotted coordinate axis and the solid coordinate axis). ). From there, the required load further increases, and the output torque is increased while raising the in-cylinder oxygen concentration (see the region between the solid coordinate axis and the dotted coordinate axis).

  On the other hand, in the case of full acceleration (corresponding to the two-dot chain line in FIG. 9), which is an example of sudden acceleration in which the increase rate of the required load is a predetermined value or more, the in-cylinder oxygen concentration from the operation region a1 on the solid coordinate axis Is increased as much as possible, and the output torque is increased as the required load increases. In this case, rather than entering the area on the coordinate axis side of the broken line or the alternate long and short dash line from the coordinate axis of the solid line, the area enters the area on the coordinate axis side of the dotted line. That is, since the engine does not enter the operation region a2, the output torque is increased while maintaining diffusion combustion.

  Therefore, according to the present embodiment, when the required load increases in the engine 1 that controls the exhaust gas recirculation valve 51a so as to increase the in-cylinder oxygen concentration after being once reduced and then increased as the required load increases. By adjusting the control amount of the exhaust gas recirculation valve 51a in the direction in which the in-cylinder oxygen concentration increases as the increase rate increases, the acceleration delay at the time of rapid acceleration of the in-cylinder oxygen concentration can be suppressed. As a result, acceleration performance can be improved.

  At this time, by adjusting the maximum value of the opening degree of the exhaust gas recirculation valve 51a, the minimum value of the in-cylinder oxygen concentration can be increased, and the in-cylinder oxygen concentration is prevented from excessively decreasing. be able to. As a result, it is possible to quickly cope with an increase in the in-cylinder oxygen concentration.

  In the above configuration, when the increase rate of the required load is large, the in-cylinder oxygen concentration target value A when the in-cylinder oxygen concentration is decreased is corrected by the adjustment amount Δ, but the in-cylinder oxygen concentration is decreased. However, the method for adjusting the in-cylinder oxygen concentration to be higher than the target value is not limited to this. For example, when the increase rate of the required load is large, the in-cylinder oxygen concentration target value A when the in-cylinder oxygen concentration is decreased may be left as it is, and the valve opening operation speed of the exhaust gas recirculation valve 51a may be decreased. Specifically, in a configuration in which an output signal is output to the exhaust gas recirculation valve 51a at each control cycle to control the opening of the exhaust gas recirculation valve 51a, the maximum adjustment amount of the opening that can be adjusted with one output is reduced. As a result, the valve opening speed of the exhaust gas recirculation valve 51a can be reduced. That is, if the maximum adjustment amount is reduced, the time required for opening the exhaust gas recirculation valve 51a to a desired opening becomes longer. On the other hand, the valve closing operation speed of the exhaust gas recirculation valve 51a when raising the in-cylinder oxygen concentration is not slow. For details, return the maximum adjustment amount to the original value.

  As a result, when the required load increases and the in-cylinder oxygen concentration decreases, the opening degree of the exhaust gas recirculation valve 51a decreases as the required load increases. Since the value corresponding to the value A cannot be followed, the actual in-cylinder oxygen concentration does not reach the target value A. Eventually, the in-cylinder oxygen concentration is increased, but the actual in-cylinder oxygen concentration starts to increase without reaching the target value A. As a result, the minimum value of the in-cylinder oxygen concentration becomes higher. (That is, in the direction in which the maximum value of the opening degree of the exhaust gas recirculation valve 51a is reduced). In addition, since the operating speed of the exhaust gas recirculation valve 51a when the in-cylinder oxygen concentration increases, the opening speed of the exhaust gas recirculation valve 51a increases as the required load increases. The value corresponding to the oxygen concentration target value A is followed as much as possible. In such a configuration, the greater the increase rate of the required load, the greater the difference between the actual in-cylinder oxygen concentration and the target value A. As a result, the greater the increase rate of the required load, the smaller the in-cylinder oxygen concentration. The value is greatly adjusted toward the high concentration side (that is, in the direction in which the maximum value of the opening degree of the exhaust gas recirculation valve 51a decreases). The maximum adjustment amount may be reduced as the increase rate of the required load is increased.

  In addition, by adjusting the valve opening operation speed of the exhaust gas recirculation valve 51a as described above, the above-described control can be realized when the required load increases, while in the steady state, the exhaust gas recirculation valve The opening degree of 51a can be made to reach a target value. That is, the opening degree of the exhaust gas recirculation valve 51a needs to be adjusted only when the required load changes so that the initial target value is reached in the steady state. However, if the target value is adjusted as in the above configuration, the opening degree reaches only the changed target value even in the steady state. On the other hand, when adjusting the valve opening speed of the exhaust gas recirculation valve 51a, it takes time, but eventually the opening degree reaches the target value. That is, in a steady state, the opening degree can reach the target value.

  Further, when the increase rate of the required load is equal to or greater than a predetermined value, the combustion can be stabilized by executing the combustion in the diffusion combustion mode without entering the premixed combustion mode.

  Further, since the responsiveness of the in-cylinder oxygen concentration to the control of the exhaust gas recirculation valve 51a is poor, the in-cylinder oxygen concentration tends to overshoot as shown by the broken line in FIG. However, as described above, the above-described overshoot can also be suppressed by adjusting the control amount of the exhaust gas recirculation valve 51a in a direction in which the in-cylinder oxygen concentration increases as the increase rate of the required load increases.

<< Other Embodiments >>
The present invention may be configured as follows with respect to the above embodiment.
Note that the number of pre-injection, main injection, and post-injection in the diffusion combustion mode is not limited to the above-mentioned number, and may be set as appropriate. Further, the number of fuel injections in the premixed combustion mode is not limited to the above number and may be set as appropriate. Further, the supply amount in each fuel injection is not limited to the above-described mode, and may be set as appropriate. Furthermore, the timing of each fuel injection is not limited to the above aspect, and may be set as appropriate.

  Further, although the engine 1 is controlled to switch between the premixed combustion mode and the diffusion combustion mode when the engine 1 is warmed up and warm, the present invention is not limited to this. That is, if the activation of the exhaust purification device 41, particularly the oxidation catalyst 41a is completed and the glow plug 19 is in the OFF state, premixed combustion can be performed. That is, the switching control between the premixed combustion mode and the diffusion combustion mode may be performed when the activation of the oxidation catalyst 41a is completed and the glow plug 19 is in the OFF state.

  In addition, the above embodiment is an essentially preferable illustration, Comprising: It does not intend restrict | limiting the range of this invention, its application thing, or its use.

  As described above, the present invention is useful for a diesel engine including an engine body to which a fuel mainly composed of light oil is supplied.

1 Engine (Engine body)
10 PCM (EGR valve control unit, combustion control unit)
11a Cylinder 51a Exhaust gas recirculation valve (EGR valve)

Claims (3)

A diesel engine having an engine body that is supplied with fuel mainly composed of light oil,
An EGR valve for adjusting the amount of EGR gas introduced into the cylinder of the engine body;
An EGR valve control unit that adjusts the oxygen concentration in the cylinder by controlling the EGR valve;
The EGR valve control unit
The opening degree of the EGR valve is controlled according to the required load so that the oxygen concentration in the cylinder once decreases as the required load of the engine body increases, and then increases.
When the engine body is accelerated beyond the load corresponding to the minimum value from the load corresponding to the minimum value of the oxygen concentration and exceeding the load corresponding to the minimum value, the oxygen concentration increases as the increase rate of the required load increases. A diesel engine that adjusts the control amount of the EGR valve. The diesel engine according to claim 1,
The EGR valve control unit
After increasing the opening of the EGR valve once with an increase in the required load of the engine body so that the oxygen concentration in the cylinder once increases with an increase in the required load of the engine body Control to decrease,
When the engine body is accelerated from a lower load side than the load corresponding to the minimum value of the oxygen concentration and exceeding the load corresponding to the minimum value, the opening degree of the EGR valve increases as the increase rate of the required load increases. A diesel engine that adjusts the control amount of the EGR valve so as to reduce the local maximum value. The diesel engine according to claim 1,
The EGR valve control unit has a large increase rate of the required load when the engine body is accelerated beyond a load corresponding to the minimum value from a lower load side than a load corresponding to the minimum value of the oxygen concentration. A diesel engine that adjusts the control amount of the EGR valve by slowing the valve opening operation speed of the EGR valve.

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