JP5464079B2 - diesel engine - Google Patents

Description

  The present invention relates to a diesel engine provided with a catalyst having an oxidation function and a diesel particulate filter in an exhaust passage.

  Conventionally, a diesel engine in which a diesel particulate filter (hereinafter also referred to as “DPF”) is provided in an exhaust passage is well known. The DPF captures particulate matter (PM) in the exhaust gas, and needs to be regenerated as the amount of particulate matter deposited increases. A catalyst having an oxidation function, for example, an oxidation catalyst is usually provided on the upstream side of the DPF, and this catalyst is used for regeneration of the DPF. For example, in a diesel engine according to Patent Document 1, after performing main injection that injects fuel for generating torque into a cylinder, post-injection is performed to introduce unburned fuel into the exhaust passage. When the unburned fuel reaches the catalyst, it undergoes an oxidation reaction to raise the exhaust temperature. As a result, PM deposited on the DPF is incinerated and removed by high-temperature exhaust. In this way, DPF regeneration is performed.

JP 2009-293383 A

  However, in the regeneration of the DPF as described above, the oxidation reaction of the unburned fuel in the catalyst is essential. However, when the exhaust temperature is low, the reaction of the unburned fuel in the catalyst may be insufficient. As a result, the exhaust temperature does not rise sufficiently, and it becomes difficult to regenerate the DPF.

  The technology disclosed herein has been made in view of such a point, and an object thereof is to enable regeneration of the DPF even under a situation where the exhaust gas temperature is low.

The technology disclosed herein includes an engine body that is supplied with fuel mainly composed of light oil, a fuel injection valve that is disposed facing a cylinder of the engine body and directly injects fuel into the cylinder, A variable valve mechanism capable of changing an opening / closing timing of at least one of an intake valve and an exhaust valve of the engine body, a catalyst having an oxidation function disposed in an exhaust passage connected to the engine body, and the exhaust passage A diesel engine equipped with a DPF disposed downstream of the catalyst is an object. The diesel engine performs the filter regeneration of the DPF by causing the fuel injection valve to perform main injection for injecting fuel for generating main combustion and second post-injection for injecting fuel after the main combustion. And a regeneration control unit that executes the regeneration control unit before the second subsequent injection in addition to the main injection and the second subsequent injection when the engine body is in a relatively low load region. A low load mode for causing the fuel injection valve to perform a first post-injection for injecting fuel during a main combustion period, and the fuel injection valve when the engine body is in a relatively high load region. And a high load mode in which the main injection and the second post injection are performed without causing the first post injection, and in the low load mode, the engine body is in a relatively low rotation region. One day , An EGR mode for the internal EGR via the variable valve mechanism, when the engine body is in the region of relatively high rotation, is intended to include a non-EGR mode is not performed the internal EGR.

  According to the above configuration, when the engine body is in a predetermined operation region, for example, an operation region in which the exhaust temperature does not easily rise, the filter regeneration is performed by performing the second second-stage injection while performing internal EGR. That is, by performing the internal EGR, the exhaust temperature in the cylinder rises, which is advantageous for activating or maintaining the catalyst. By performing the second post-stage injection in this state, the unburned fuel discharged to the exhaust passage is efficiently oxidized in the catalyst, and the DPF can be heated by the oxidation reaction heat generated accordingly. Thereby, PM collected by DPF can be burned and removed. Thus, filter regeneration is performed.

  That is, when the exhaust gas temperature is low, the unburned fuel cannot be sufficiently oxidized in the catalyst only by the second post-injection, and the filter regeneration becomes difficult. Therefore, by performing internal EGR in addition to the second post-stage injection, it is possible to increase the exhaust gas temperature and promote the oxidation of unburned fuel in the catalyst, and thus it is possible to perform filter regeneration.

  The predetermined operation region in which the EGR mode is performed can be set to an operation region in which the exhaust temperature is assumed to be a temperature at which the unburned fuel cannot be sufficiently oxidized in the catalyst only by the second post-injection.

  However, depending on the operation region, the exhaust temperature may not be sufficiently increased only by the internal EGR. That is, the fuel injection amount is relatively small and the exhaust temperature is not high in the relatively low load region in the predetermined operation region in which the EGR mode is performed. Therefore, there is a possibility that the exhaust temperature cannot be raised to the extent that the unburned fuel is sufficiently oxidized in the catalyst only by the internal EGR.

  Therefore, the regeneration control unit performs the first second-stage injection and the second second-stage injection while performing the internal EGR in the relatively low load region of the predetermined operation region in which the EGR mode is performed. Perform filter regeneration. As described above, the first second-stage injection is a fuel injection that is performed before the second second-stage injection and during the main combustion period. That is, the first second-stage injection is a second-stage injection for continuing main combustion, and has a function of suppressing a temperature drop in the cylinder during the expansion stroke. Therefore, even if the exhaust temperature cannot be sufficiently increased only by the internal EGR, the exhaust temperature can be increased to such an extent that the unburned fuel is sufficiently oxidized in the catalyst by performing the first post-injection. . As a result, filter regeneration can be performed.

  On the other hand, in the relatively high load region of the predetermined operation region in which the EGR mode is performed, the exhaust temperature can be raised to the extent that the unburned fuel is sufficiently oxidized in the catalyst only by the internal EGR. The filter regeneration is performed by the internal EGR and the second second-stage injection without performing the first second-stage injection.

  It is preferable that the main combustion during the regeneration of the filter is combustion mainly composed of diffusion combustion.

  Diffusion combustion has a longer combustion period than premixed combustion. That is, in the diffusion combustion, by combining the first post-stage injection, the combustion period can be prolonged more effectively, and the temperature drop in the cylinder during the expansion stroke can be suppressed.

  In addition, the regeneration control unit preferably causes the fuel injection valve to perform pre-stage injection for injecting fuel so that pre-stage combustion that leads to diffusion combustion occurs at the start or before the start of main combustion during the regeneration of the filter. .

  This pre-stage injection can suppress the ignition delay of the fuel due to the main injection and can lead to stable diffusion combustion. That is, when the main combustion is unstable, even if the first second-stage injection is performed at a predetermined timing, the main combustion period may be lost. In particular, when the gas temperature is low and the load is low, the ignitability is poor and the main combustion can be unstable. On the other hand, by performing the pre-injection, for example, the main combustion can be stabilized even when the gas temperature is low and the load range is low. When the main combustion is stabilized, the first post-stage injection can be reliably performed within the main combustion period.

  Furthermore, it is preferable that the number of times of the second latter-stage injection is greater than the number of times of the first latter-stage injection.

  The total injection amount by the second second-stage injection is determined as an amount required for filter regeneration. Therefore, an increase in the number of second second-stage injections means that the amount of injection per second second-stage injection is reduced. The injection amount per time affects the fuel reach distance. That is, the fuel reach distance becomes longer as the injection amount per time increases. Since the fuel injected by the second post-stage injection does not burn in the cylinder, when the injection amount per one increases, the fuel easily reaches the inner wall of the cylinder and adheres to the inner wall. The fuel adhering to the inner wall of the cylinder wall can be mixed with oil by the reciprocating motion of the piston. That is, when the injection amount per one time is too large, the sprayed fuel can cause oil dilution. That is, by relatively increasing the number of times of the second second-stage injection, the injection amount per second second-stage injection can be reduced, and as a result, oil dilution can be suppressed.

  On the other hand, the first post-injection causes the combustion that continues to the main combustion, and thus affects the torque. Therefore, it is preferable that the injection amount of the first second-stage injection is small. That is, by relatively reducing the number of first post-stage injections, the total amount of fuel injected by the first post-stage injection can be reduced, and the influence on torque can be reduced.

  The diesel engine may further include a turbocharger having a turbine disposed on the upstream side of the DPF in the exhaust passage.

  According to said structure, since the heat quantity of exhaust gas is absorbed by the turbine, it exists in the tendency for the exhaust temperature in the said catalyst and DPF to become low. That is, the presence of the turbine in the exhaust passage is disadvantageous from the viewpoint of promoting oxidation of the unburned fuel in the catalyst. Therefore, in a diesel engine equipped with a turbocharger, it is particularly effective to provide the EGR mode or the low load mode.

  Further, the geometric compression ratio of the engine body may be 15 or less.

  In the so-called low compression ratio diesel engine as described above, the exhaust temperature is low. That is, the low compression ratio of the engine body is disadvantageous from the viewpoint of promoting oxidation of unburned fuel in the catalyst. Therefore, in a diesel engine with a low compression ratio, it is particularly effective to provide the EGR mode or the low load mode.

  According to the diesel engine, even if the exhaust gas temperature is low, by performing the first rear injection in addition to the internal EGR, it is possible to increase the temperature in the cylinder, and thus the exhaust temperature, and the second rear engine. Unburned fuel by injection can be sufficiently oxidized in the catalyst. As a result, even if the exhaust gas temperature is low, the filter regeneration can be performed by raising the exhaust gas temperature early.

It is the schematic which shows the structure of the diesel engine with a turbocharger. It is a block diagram concerning control of a diesel engine. It is an example of the map of the regeneration mode of DPF according to the state of a diesel engine. It is a figure which shows an example of the fuel injection form in the area | region a1, 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 the area | region a2, 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 area | region B, 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 the area | region C, and an example of the log | history of the heat release rate accompanying it.

  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.

  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) 71). 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. This VVM 71 constitutes a variable valve mechanism.

  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 cylinder head 12 is provided with an injector 18 for injecting fuel and a glow plug 19 for warming intake air to improve 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. This injector 18 constitutes a combustion injection valve.

  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 DPF 41b, which are arranged in this order from the upstream side. The oxidation catalyst 41a and the DPF 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 oxidation catalyst 41a constitutes a catalyst having an oxidation function. The DPF 41b collects PM such as soot contained in the exhaust gas of the engine 1 and is formed of a heat-resistant ceramic material such as silicon carbide (SiC) or cordierite. It is a three-dimensional mesh filter formed of a flow type filter or a heat resistant ceramic fiber. The DPF 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. 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. Yes.

  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.

  The intake passage 30 is connected to a small intake bypass passage 63 that bypasses the small compressor 62a. 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 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 a control device. 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. SW5, upstream exhaust pressure sensor SW6 for detecting the exhaust pressure upstream of DPF 41b, and downstream exhaust pressure sensor SW7 for detecting the exhaust pressure downstream of DPF 41b are input, and based on these detection signals The state of the engine 1 and the vehicle is determined by performing various calculations, and the injector 18 and the glow plug are accordingly determined. 19, VVM71 of the valve operating system, various valves 36,51a, 63a, 64a, and outputs a control signal to 65a actuator.

  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, thereby improving exhaust emission performance and thermal efficiency. I am doing so. On the other hand, in the engine 1, torque is increased by the large and small turbochargers 61 and 62 described above to compensate for a low compression ratio of the geometric compression ratio.

(Outline of engine combustion control)
The PCM 10 determines the target torque (target load) mainly based on the engine speed and the accelerator opening as the basic control of the engine 1, and determines the fuel injection amount, the injection timing, and the like corresponding thereto. This is realized by operation control of the injector 18. The target torque is set so as to increase as the accelerator opening increases and as the engine speed increases. A fuel injection amount is set based on the target torque and the engine speed. The injection amount is set to increase as the target torque increases and as the engine speed increases.

  Further, the PCM 10 controls the recirculation ratio of the exhaust gas into the cylinder 11a by controlling the opening degree of the throttle valve 36 and the exhaust gas recirculation valve 51a (external EGR control) and controlling the VVM 71 (internal EGR control).

  Further, the PCM 10 performs filter regeneration of the DPF 41b by controlling the operation of the injector 18 and the VVM 71 when the regeneration condition of the DPF 41b is satisfied. Here, the regeneration condition of the DPF 41b is a predetermined condition that can be determined to require the regeneration of the DPF 41b. As an example, in the present embodiment, the differential pressure ΔP between the upstream exhaust pressure and the downstream exhaust pressure of the DPF 41b detected by the upstream and downstream exhaust pressure sensors SW6 and SW7 is equal to or greater than a predetermined value. The regeneration condition of the DPF 41b is established. That is, as the amount of PM collected by the DPF 41b increases, the flow of exhaust gas in the DPF 41b becomes worse and the differential pressure ΔP increases. The filter regeneration ends when the differential pressure ΔP falls below a predetermined lower limit value that is smaller than a predetermined value as a regeneration condition.

  FIG. 3 is a map showing the regeneration mode of the DPF 41b according to the state of the engine 1 when the engine 1 is warm. That is, when the filter regeneration condition is satisfied when the engine 1 is warm, the PCM 10 performs filter regeneration based on the map shown in FIG. As shown in FIG. 3, when the engine 1 is warm, a plurality of operation regions are set according to the engine speed and the engine load (actual total fuel injection amount), and the regeneration mode is set for each operation region. Is set.

  Hereinafter, the regeneration mode of each operation region will be described with reference to FIGS. The fuel injection amount and the heat generation rate shown in FIGS. 4 to 7 do not necessarily indicate the relative fuel injection amount or the heat generation rate when these figures are compared with each other. .

  First, three operation areas A to C when the operation area of the engine 1 is divided into three according to the engine load will be described.

  4 shows an example of the fuel injection mode (upper diagram) in the operation region a1 in the operation region A and the history of the heat generation rate in the cylinder 11a (lower diagram), and FIG. 5 shows the operation region in the operation region A. An example (lower diagram) of the history of the heat generation rate in the cylinder 11a accompanying the fuel injection mode (upper diagram) at a2 is shown. The operation area A is an extremely high load operation area that is 90% or more of the maximum load among high loads, and includes operation areas a1 and a2. The operation region a2 is a relatively high rotation operation region in the operation region A. The operation area a1 is an area other than the operation area a2 in the operation area A.

  In the operation region a1, during the compression stroke, one fuel injection (pilot injection) is performed, and the main injection is performed once in the vicinity of the compression top dead center. Perform fuel injection. In the operation region a1, by performing pilot injection as pre-injection, the fuel premixability is improved to be advantageous in terms of soot generation, and the number of fuel injections is limited to only two times of pilot injection and main injection. As a result, a sufficient amount of fuel can be ensured during main injection to ensure high torque. On the other hand, in the operation region a2, the main injection is executed only once near the compression top dead center. That is, in this operation region a2, the output is increased and the maximum torque is ensured while improving the robustness.

  In the operation area A, the exhaust gas temperature is high, and the PM collected in the DPF 41b can be naturally incinerated and removed. Therefore, special control for filter regeneration such as post injection described later is not performed.

  FIG. 6 shows an example (lower diagram) of the history of fuel injection in the operating region B (upper diagram) and the associated heat release rate in the cylinder 11a. The operation area B is an operation area of partial load (medium load) and high load (excluding the area area A). In this operation region B, during the compression stroke before the compression top dead center, the pre-injection is executed once, the main injection is executed once near the compression top dead center, and the post injection is performed twice after the main injection. Run. Here, the pre-injection is a fuel injection for generating a pre-combustion at a predetermined time before the compression top dead center to suppress a fuel ignition delay due to the main injection. The main injection is fuel injection for generating main combustion that is combustion for generating torque of the engine 1. The post-injection is a fuel injection that is injected after the main combustion and introduces unburned fuel into the exhaust passage 40. In other words, the post injection is a fuel injection that does not cause combustion in the cylinder 11a.

  In the operation region B, pre-combustion having a sufficient heat generation rate before main combustion by main injection is generated at a predetermined time before compression top dead center. Thereby, the subsequent main combustion can be generated stably. The pre-combustion also has an effect of slowing the increase in the heat generation rate of the main combustion. Thus, avoiding the rapid increase in the heat generation rate can be advantageous in reducing combustion noise and improving NVH performance. And post injection is performed after the main combustion by main injection. As a result, unburned fuel is introduced into the exhaust passage 40 and reaches the oxidation catalyst 41a. In this operation region B, since the exhaust temperature is sufficient to activate the oxidation catalyst 41a, the unburned fuel is favorably oxidized in the oxidation catalyst 41a. Then, the PM trapped in the DPF 41b is burned and removed by the oxidation reaction heat generated along with this. That is, filter regeneration is performed.

  FIG. 7 shows an example (lower diagram) of the history of fuel injection in the operating region C (upper diagram) and the associated heat release rate in the cylinder 11a. The operation region C is a relatively low load operation region. In this operation region C, during the compression stroke before the compression top dead center, the pre-injection is executed once, the main injection is executed once near the compression top dead center, and the after injection is performed once after the main injection. The post injection is executed twice after the after injection. Here, the after-injection is a fuel injection that is injected during the main combustion period and generates combustion following the main combustion. The main combustion period includes at least TDC and is a period from the start of heat generation by main combustion to the end. After-injection is executed at a relatively late timing of the main combustion period (a timing included in at least the second half when the main combustion period is divided into two). More specifically, after-injection is executed at a timing (maintenance limit) at which main combustion is continued and at a timing (advance limit) at which fuel spray reaches outside the cavity of the descending piston 14. The After-injection continues the main combustion and extends the combustion period. In addition, the broken line in FIG. 7 represents the heat generation rate by main combustion when not performing after injection. This suppresses a decrease in the temperature in the cylinder 11a (hereinafter also simply referred to as the in-cylinder temperature), and maintains the in-cylinder temperature during the expansion stroke at a high temperature. As a result, the exhaust temperature also increases.

  Since the operation region C is a low-load operation region, the fuel injection amount is small and the exhaust temperature is relatively low. That is, the operation region C is a disadvantageous region in which the unburned fuel obtained by post injection is oxidized by the oxidation catalyst 41a. Therefore, by performing after injection, the in-cylinder temperature and the exhaust temperature are raised. As a result, unburned fuel is satisfactorily oxidized in the oxidation catalyst 41a, and PM trapped in the DPF 41b can be appropriately burned and removed by the oxidation reaction heat. That is, filter regeneration can be performed satisfactorily.

  In addition, among the operation areas C, the operation area c1 having an extremely low rotation and a low load, including the idle area, is an operation area having an extremely low rotation and a low load, and therefore, the exhaust temperature is an extremely low area. In addition, the hydraulic pressure required to drive the VVM 71 cannot be ensured. That is, internal EGR cannot be performed. Therefore, in this operation region c1, since the exhaust temperature cannot be sufficiently increased, filter regeneration is not executed.

  Here, in the operation regions B and C, the operation state of the engine 1 is a relatively low rotation operation region (the low rotation side when the engine operation region is divided into a low rotation side and a high rotation side) (Operating area E) is provided with an operating area E in which post injection is performed while internal EGR is being performed. Since the operation region E is a low rotation operation region, the exhaust temperature is relatively low. That is, the operation region E is a disadvantageous region in which the unburned fuel obtained by the post injection is oxidized by the oxidation catalyst 41a. Therefore, in the operation region E, the in-cylinder temperature and the exhaust gas temperature are increased by performing internal EGR by opening the exhaust gas twice during filter regeneration. That is, when the internal EGR is performed, the exhaust gas once discharged into the exhaust passage 40 is recirculated into the cylinder 11a, and the in-cylinder temperature rises. In this state, when the next combustion is executed, the exhaust temperature also rises. As described above, in the operation region E, the in-cylinder temperature and the exhaust gas temperature are increased by the internal EGR, and the unburned combustion is efficiently oxidized by the oxidation catalyst 41a.

  Among the operation areas E, in the operation area on the relatively high load side (high load side area when the engine operation area is divided into the low load side and the high load side) e1, the above operation is performed. Similarly to the region B, during the compression stroke before the compression top dead center, the pre-injection is executed once, the main injection is executed once near the compression top dead center, and the post injection is performed twice after the main injection. Run. In this operation region e1, since the internal EGR is performed, the in-cylinder temperature is high and the exhaust temperature is also high. Therefore, the unburned fuel by post injection sufficiently oxidizes in the oxidation catalyst 41a and generates sufficient reaction heat. As a result, the DPF 41b is also regenerated well. Note that the operation region e1 is expanded to a high load and high rotation side. This is disadvantageous from the viewpoint of promoting the oxidation reaction because the increase in the flow rate of the exhaust gas shortens the residence time of the unburned fuel in the oxidation catalyst 41a. Therefore, the required temperature of the exhaust gas for promoting the oxidation reaction is also increased. Therefore, the operating range in which the exhaust temperature is increased by performing the internal EGR is expanded to the high load and high rotation side where the flow rate of the exhaust gas increases. The pre-injection corresponds to the front-stage injection, and the post-injection corresponds to the second rear-stage injection.

  On the other hand, in the operation region E, the operation region on the relatively low load side (the region on the low load side when the engine operation region is divided into the low load side and the high load side) e2, Similarly to the operation region C, during the compression stroke before the compression top dead center, the pre-injection is executed once, the main injection is executed once near the compression top dead center, and the after injection is performed after the main injection. The post-injection is executed twice after the after injection. That is, since the fuel injection amount is small in the operation region e2, the exhaust gas temperature is relatively difficult to rise even in the operation region E. Therefore, in the operation region e2, in-cylinder temperature and exhaust gas temperature are increased as much as possible by performing after injection in addition to internal EGR. That is, in the operation region e2, not only the exhaust gas temperature is simply raised by the after injection, but the temperature of the EGR gas recirculated into the cylinder 11a by the internal EGR is also increased. Thus, the exhaust gas temperature can be further increased by the synergistic effect of the after injection and the internal EGR. The after injection corresponds to the first second-stage injection.

  Here, the control mode in the operation region E corresponds to the EGR mode, the control mode in the operation region e1 corresponds to the high load mode, and the control mode in the operation region e2 corresponds to the low load mode.

  In the present embodiment, the engine load boundary between the operation region e1 and the operation region e2 matches the engine load boundary between the operation region B and the operation region C. However, the present invention is not limited to this. The boundary between the two may be different.

  Therefore, according to this embodiment, when the DPF 41b is regenerated, if the engine 1 is in an operation region of relatively low rotation and low load, filter regeneration is executed by performing post injection while performing internal EGR. . Thus, by performing the internal EGR in parallel with the post-injection, the activation of the oxidation catalyst 41a is promoted by increasing the in-cylinder temperature and the exhaust temperature, even in the operation region where the exhaust temperature does not easily rise, and the oxidation The unburned fuel in the catalyst 41a can be favorably oxidized.

  In addition, after-injection is added in the operation region e2 on the relatively low load side among the operation regions in which filter regeneration is performed in the EGR mode. That is, in this low load side operation region e2, the exhaust gas temperature is hardly increased because the fuel injection amount is small. Therefore, even if the internal EGR is performed, it is difficult to raise the exhaust temperature to a temperature that sufficiently activates the oxidation catalyst 41a. Therefore, the exhaust temperature is further increased by performing after injection. According to this after injection, the combustion in the cylinder 11a is prolonged, and the in-cylinder temperature rises and the exhaust temperature rises. When the internal EGR is combined with this, the exhaust gas recirculated as the EGR gas also has a high temperature, so that the effect of increasing the exhaust temperature by the internal EGR can be further improved. That is, in the operation region e2 on the low load side, activation of the oxidation catalyst 41a can be promoted and the regeneration of the DPF 41b can be favorably performed by further increasing the exhaust gas temperature by the synergistic effect of the after injection and the internal EGR. .

  In particular, the engine 1 of this embodiment has a geometric compression ratio set to a low compression ratio of 12 to 15. In the engine 1 with a low compression ratio, the exhaust temperature hardly rises, which is disadvantageous for filter regeneration. Thus, even in a disadvantageous condition for filter regeneration, filter regeneration can be achieved by combining internal EGR and after-injection.

  Furthermore, the engine 1 of the present embodiment is provided with a turbine 62b of the small turbocharger 62 and a turbine 61b of the large turbocharger 61 on the upstream side of the oxidation catalyst 41a in the exhaust passage 40. In such a configuration, a part of the heat quantity of the exhaust gas is taken away by the turbines 62b and 61b. That is, in the engine 1 provided with the turbocharger, it is particularly effective to raise the exhaust temperature by internal EGR and after injection.

Further, since the main combustion of the engine 1 is not premixed combustion but combustion mainly consisting of diffusion combustion, the combustion in the cylinder 11a can be satisfactorily prolonged by the after injection. That is, premixed combustion is inherently short in the combustion period and is not suitable for extending the combustion period. On the other hand, diffusion combustion is inherently long in combustion period, and thus is suitable for extending the combustion period. Furthermore, since diffusion combustion has a long combustion period, it is easy to execute after injection at an appropriate timing, and combustion that continues to main combustion can be appropriately generated.

  Further, in the EGR mode, by performing the pre-injection, it is possible to suppress the ignition delay of the fuel due to the main injection and to stably generate the main combustion. Even if after-injection is performed at a fixed timing, if the main combustion is unstable, the after-injection may be out of the main combustion period and combustion that continues to the main combustion may not be generated. That is, by stabilizing the main combustion, the subsequent combustion by the after injection can be stably generated, and the combustion can be prolonged for a long time.

  Here, the number of after injections and post injections is not limited to the above number. However, it is preferable that the number of post injections is larger than the number of after injections. That is, the total injection amount by post injection is determined as the amount required for filter regeneration, and as the number of post injections increases, the injection amount per post injection decreases. When the amount of post-injection decreases, the reach of injected fuel decreases. Here, since the fuel injected by the post injection does not burn in the cylinder 11a, it exists as unburned fuel in the cylinder 11a. The unburned fuel is easily discharged out of the cylinder 11a when drifting in the cylinder 11a. However, if the unburned fuel adheres to the inner wall of the cylinder 11a, it remains on the inner wall without being discharged into the cylinder 11a. In some cases. In this case, it can be mixed with oil by the reciprocating motion of the piston 14 and cause oil dilution. That is, by increasing the number of post injections, the fuel reaching the inner wall of the cylinder 11a can be reduced, and oil dilution can be suppressed.

  On the other hand, after-injection causes combustion that continues to main combustion, and thus affects torque. In controlling the torque, an increase in the amount of control is not preferable because it complicates the control. Therefore, it is preferable that the number of after injections is small. That is, by relatively reducing the number of after injections, the total amount of fuel injected by the after injection can be reduced, and the influence on the torque can be reduced.

  In addition, said fuel injection form is only an example, and is not restricted to these. In particular, in the operation areas e1 and e2, pre-injection may be omitted, and the number of main injections, after-injections, and post-injections is not limited to the above example.

1 Diesel engine (engine body)
10 PCM (Reproduction Control Unit)
11a Cylinder 18 injector (fuel injection valve)
21 Intake valve 22 Exhaust valve 40 Exhaust passage 41a Oxidation catalyst (catalyst)
41b DPF
61 Large turbocharger 61b Turbine 62 Small turbocharger 62b Turbine 71 VVM (Variable valve mechanism)

Claims (6)

An engine main body to which fuel mainly composed of light oil is supplied; a fuel injection valve that faces the cylinder of the engine main body and directly injects fuel into the cylinder; an intake valve and an exhaust of the engine main body A variable valve mechanism capable of changing an opening / closing timing of at least one of the valves, a catalyst having an oxidation function disposed in an exhaust passage connected to the engine body, and a downstream of the catalyst in the exhaust passage. A diesel engine equipped with a diesel particulate filter installed;
Regeneration control for performing filter regeneration of the diesel particulate filter by causing the fuel injection valve to perform main injection for injecting fuel for generating main combustion and second post-injection for injecting fuel after the main combustion. Further comprising
When the engine body is in a relatively low load region, the regeneration control unit is in addition to the main injection and the second post-stage injection, and before the second post-stage injection and during the main combustion period. When the fuel injection valve performs a first post-injection for injecting fuel, and when the engine body is in a relatively high load region, the fuel injection valve performs the first post-injection. Without having to perform the main injection and the second post-injection,
The low load mode includes an EGR mode in which internal EGR is performed via the variable valve mechanism when the engine body is in a relatively low rotation area, and an area in which the engine body is relatively high rotation. And a non-EGR mode in which the internal EGR is not performed . The diesel engine according to claim 1,
A diesel engine characterized in that main combustion during regeneration of the filter is combustion mainly consisting of diffusion combustion. The diesel engine according to claim 2,
The regeneration control unit causes the fuel injection valve to perform pre-injection to inject fuel so that pre-combustion that leads to diffusion combustion occurs at the start or before the start of main combustion during the filter regeneration. diesel engine. The diesel engine according to any one of claims 1 to 3,
The diesel engine characterized in that the number of times of the second second-stage injection is greater than the number of times of the first second-stage injection. The diesel engine according to any one of claims 1 to 4,
The diesel engine further comprising a turbocharger having a turbine disposed in the exhaust passage on the upstream side of the diesel particulate filter. The diesel engine according to any one of claims 1 to 5,
A diesel engine characterized in that the engine body has a geometric compression ratio of 15 or less.

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