JP2014173516A - Diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diesel engine capable of curbing a problem with an excessive PM (particulate matter) accumulation amount on a DPF (a diesel particulate filter).SOLUTION: In a diesel engine, when the same is in a DPF regeneration mode and a DOC (a diesel oxidation catalyst) inlet exhaust temperature T is not less than a post injection lower limit temperature TN, unburnt fuel mixed in exhaust is burnt through catalyst combustion of a DOC and PMs accumulated on a DPF is burnt and removed with temperature increased by exhaust in a manner that allows a common rail type fuel injection device to execute a post injection following a main injection in accordance with an instruction of a fuel injection control device (S6). When an estimated value E of an exhaust flow rate is equal to a predetermined reference flow rate E1, the post injection lower limit temperature TN is set at a predetermined reference lower limit temperature T1 (S4). When the estimated value E of the exhaust flow rate is a small flow rate E0 less than the predetermined reference flow rate E1, the post injection lower limit temperature TN is set at a lower limit temperature T0 less than the reference lower limit temperature T1 (S10).

Description

The present invention relates to a diesel engine, and more particularly, to a diesel engine that can prevent a problem that an amount of PM accumulated in a DPF is excessive.
Among terms used in this specification, claims, and drawings, DPF is an abbreviation for diesel particulate filter, PM is an abbreviation for particulate matter contained in exhaust, and DOC is an abbreviation for diesel oxidation catalyst. .

Conventionally, there are the following diesel engines (for example, see Patent Document 1).
DPF disposed in the exhaust path, DPF PM accumulation amount estimation device, common rail fuel injection device, fuel injection control device for controlling fuel injection of the common rail fuel injection device, and upstream of the DPF DOC is provided,
When the estimated value of the PM accumulation amount of the DPF reaches a predetermined DPF regeneration mode start value, the DPF regeneration mode is started. In the DPF regeneration mode, when the DOC inlet exhaust temperature is equal to or higher than the predetermined post injection lower limit temperature. The post-injection after the main injection by the common rail fuel injection device is carried out by the command of the fuel injection control device,
A diesel engine in which unburned fuel mixed in exhaust is catalytically combusted in DOC, and PM accumulated in the DPF is incinerated and removed by raising the temperature of the exhaust.
According to this type of diesel engine, there is an advantage that the DPF can be regenerated and used by incineration removal of PM deposited on the DPF.

  However, this type of diesel engine has a problem because the post injection lower limit temperature is set to a constant value equal to or higher than the DOC activation temperature.

Japanese Patent Laying-Open No. 2010-151058 (see FIG. 1)

<< Problem >> There is a possibility that the amount of PM accumulated in the DPF becomes excessive.
Since the post-injection lower limit temperature is set to a constant value equal to or higher than the DOC activation temperature, the frequency at which the DOC inlet exhaust temperature reaches the post-injection lower limit temperature when the light load operation is continued in the DPF regeneration mode. Therefore, there is a risk that the post-injection opportunity is lost and the amount of PM accumulated in the DPF becomes excessive.

  The subject of this invention is providing the diesel engine which can prevent the malfunction which the PM deposit amount of DPF becomes excessive.

The post-injection lower limit temperature is set to a constant value higher than the DOC activation temperature because the DOC inlet exhaust temperature at the time of post-injection is made as high as possible, the DOC oxidation function is fully activated, and the unburned through the DOC This is because it is considered to reduce the fuel slip ratio.
However, the inventors of the present invention have found that, as a result of research, when the exhaust gas flow rate is small, the oxidation efficiency of DOC increases even when the DOC inlet exhaust temperature is relatively low, and the unburned fuel that passes through the DOC increases. It was discovered that the slip ratio was reduced, and the present invention was achieved.

Invention specific matters of the invention according to claim 1 are as follows.
As illustrated in FIG. 1, the DPF (2) disposed in the exhaust path (1), the PM deposition amount estimation device (3) of the DPF (2), the common rail fuel injection device (4), and the common rail A fuel injection control device (5) for controlling the fuel injection of the fuel injection device (4), and a DOC (6) disposed on the upstream side of the DPF (2),
As illustrated in FIG. 2A, when the estimated value (P) of the PM accumulation amount of the DPF (2) reaches a predetermined DPF regeneration mode start value (P1), the DPF regeneration mode is started (S2 In the DPF regeneration mode, when the DOC inlet exhaust temperature (T) is equal to or higher than a predetermined post-injection lower limit temperature (TN), the main rail by the common rail fuel injection device (4) is instructed by the fuel injection control device (5). Post-injection after injection is performed (S6),
As illustrated in FIG. 1, unburned fuel mixed in the exhaust (7) is catalytically combusted in the DOC (6), and PM accumulated in the DPF (2) is incinerated and removed by raising the temperature of the exhaust (7). In diesel engines,
As illustrated in FIG. 1, an exhaust gas flow rate estimating device (8) and a post injection lower limit temperature (TN) setting device (9) are provided,
2A and 2B, when the estimated value (E) of the exhaust flow rate is a predetermined reference flow rate (E1), the post injection lower limit temperature (TN) is set to the predetermined reference lower limit temperature (T1). ) Is set (S4), and the estimated value (E) of the exhaust flow rate is a low flow rate (E0) less than the reference flow rate (E1), the post injection lower limit temperature (TN) is set to the reference lower limit temperature (T1). A diesel engine characterized by being set (S10) to a lower lower limit temperature (T0) of less than.

(Invention of Claim 1)
The invention according to claim 1 has the following effects.
<Effect> It is possible to prevent a problem that the amount of PM accumulated in the DPF becomes excessive.
As illustrated in FIGS. 2 (A) and 2 (B), when the estimated value (E) of the exhaust flow rate is a low flow rate (E0) less than the reference flow rate (E1), the post injection lower limit temperature (TN) is the reference lower limit. Since the lower lower limit temperature (T0) lower than the temperature (T1) is set (S10), even when the light load operation continues in the DPF regeneration mode, the DOC inlet exhaust temperature (T) becomes the post injection lower limit temperature (TN). Can be increased, and a problem that the amount of PM accumulated in the DPF (2) becomes excessive can be prevented.

<Effect> Even when the post-injection lower limit temperature is set to a lower limit temperature lower than the reference lower limit temperature, the slip ratio of unburned fuel that passes through the DOC can be kept small.
As illustrated in FIGS. 2A and 2B, when the estimated value (E) of the exhaust flow rate is a low flow rate (E0) less than the reference flow rate (E1), the post-injection lower limit temperature (TN) is the above reference value. Even when the lower limit temperature (T0) lower than the lower limit temperature (T1) is set (S10), the slip ratio of unburned fuel that passes through the DOC (6) can be kept small.
The reason is that when the exhaust gas flow rate is small, the flow rate of the exhaust gas (7) is slow and the contact time between the DOC (6) and the unburned fuel in the exhaust gas (7) becomes long. Even if the post-injection lower limit temperature (TN) is set to a lower lower limit temperature (T0) lower than the reference lower limit temperature (T1) (S10), the oxidation efficiency of DOC (6) increases and DOC (6 It is estimated that the oxidation ability of 6) is maintained at a necessary height.

The invention according to claim 2 has the following effect in addition to the effect of the invention according to claim 1.
<Effect> The post injection lower limit temperature can be optimized according to the exhaust gas flow rate.
As illustrated in FIGS. 2A and 2B, when the estimated value (E) of the exhaust flow rate is a small flow rate (E0) less than the reference flow rate (E1), the estimated value (E) of the exhaust flow rate is small. As the lower limit temperature (T0) set (S10) to the post injection lower limit temperature (TN) becomes lower, the post injection lower limit temperature (TN) can be optimized according to the exhaust gas flow rate.

(Invention of Claim 3)
The invention according to claim 3 has the following effect in addition to the effect of the invention according to claim 1 or claim 2.
<Effect> Even when the exhaust gas flow rate is large, the slip ratio of unburned fuel passing through the DOC can be reduced.
Even when the exhaust gas flow rate is large, the slip ratio of unburned fuel passing through the DOC (6) can be reduced.
The reason is that when the exhaust gas flow rate is large, the flow rate of the exhaust gas (7) is high and the contact time between the DOC (6) and the unburned fuel in the exhaust gas (7) is shortened. However, as shown in FIGS. 2A and 2B, when the estimated value (E) of the exhaust flow rate is a large flow rate (E2) exceeding the reference flow rate (E1), post injection is performed. Since the lower limit temperature (TN) is set to the lower limit temperature (T2) higher than the reference lower limit temperature (T1) (S11), the activation of the oxidation function of the DOC (6) by the high temperature causes the DOC (6) to It is estimated that the oxidation capacity is maintained at a necessary height.

The invention according to claim 4 has the following effect in addition to the effect of the invention according to claim 3.
<Effect> The post injection lower limit temperature can be optimized according to the exhaust gas flow rate.
As illustrated in FIGS. 2 (A) and 2 (B), when the estimated value (E) of the exhaust flow rate is a large flow rate (E2) exceeding the reference flow rate (E1), the estimated value (E) of the exhaust flow rate is As the amount increases, the lower limit temperature (T2) set (S11) to the post-injection lower limit temperature (TN) becomes higher, so that the post-injection lower limit temperature (TN) can be optimized according to the exhaust gas flow rate.

It is a mimetic diagram of a diesel engine concerning an embodiment of the present invention. FIG. 2A is a flowchart of processing by the control means of the engine of FIG. 1, and FIG. 2B is a graph showing the relationship between the estimated value of the exhaust flow rate and the post injection lower limit temperature.

  1 to 2 are diagrams illustrating a diesel engine according to an embodiment of the present invention. In this embodiment, a vertical in-line multi-cylinder diesel engine will be described.

This diesel engine is configured as follows.
As shown in FIG. 1, the cylinder head (11) is assembled to the upper part of the cylinder block (10), the engine cooling fan (12) is arranged at the front part of the cylinder block (10), and the rear part of the cylinder block (10). A flywheel (13) is arranged on the side. An exhaust manifold (14) is assembled to one side of the cylinder head (11), a supercharger (15) is assembled to the exhaust manifold (14), and an exhaust path (1) downstream of the supercharger (15). An exhaust purification device (16) is disposed in the front. A common rail fuel injection device (4) is attached to the cylinder head (11).

The configuration of the common rail fuel injection device (4) is as follows.
As shown in FIG. 1, a common rail (19) is connected to a fuel tank (17) via a fuel supply pump (18), and a fuel injector (20) for each cylinder is connected to the common rail (19).
The pulsar rotor (21) is attached to the flywheel (13), the pickup coil (22) is opposed to the pulsar rotor (21), the camshaft rotor (23) is attached to the valve operating camshaft (34), and the camshaft rotor ( 23) is opposed to the cylinder discrimination sensor (24), the pickup engine (22) detects the actual engine speed and the crank angle, and the cylinder discrimination sensor (24) detects the top dead center of the predetermined cylinder as the compression top dead center. The combustion stroke of each cylinder is detected, such as whether it is exhaust top dead center. A target speed detection sensor (25) detects the speed control position of the speed control lever (26), that is, the engine target speed.

As shown in FIG. 1, a pickup coil (22), a cylinder discrimination sensor (24), and a target rotational speed detection sensor (25) are connected to a solenoid valve (20) of a fuel injector (20) via a fuel injection control device (5). 27).
The fuel injection control device (5) calculates a fuel injection amount (main injection amount) based on the deviation between the target engine speed and the actual engine speed, and at a predetermined timing based on the crank angle, the fuel injector (20). A predetermined amount of main injection is performed.
The fuel injection control device (5) is an arithmetic processing unit of the engine ECU (28). Engine ECU is an abbreviation for engine electronic control unit.

The configuration of the exhaust purification device (16) is as follows.
As shown in FIG. 1, the DPF (2) disposed in the exhaust path (1), the PM deposition amount estimation device (3) of the DPF (2), the common rail fuel injection device (4), and the common rail type A fuel injection control device (5) for controlling the fuel injection of the fuel injection device (4) and a DOC (6) disposed on the upstream side of the DPF (2) are provided.
The common rail fuel injection device (4) and the fuel injection control device (5) for controlling the fuel injection of the common rail fuel injection device (4) also function as components of the exhaust purification device (16).

The contents of the components of the exhaust emission control device (16) are as follows.
As shown in FIG. 1, the DPF (2) and the DOC (6) are accommodated in the exhaust purification case (29).
The DPF (2) is a cylindrical ceramic filter having a honeycomb structure inside and a plurality of cells (2a) (2a) extending in the axial length direction, and inlets and outlets of adjacent cells (2a) (2a). Is alternately sealed, and the exhaust (7) is passed through the porous wall (2b) between the cells (2a) and (2a), and the PM in the exhaust (7) is captured by the porous wall (2b). Of the type.
The DOC (6) is a cylindrical ceramic carrier on which an oxidation catalyst component is supported. The inside of the carrier has a honeycomb structure and includes a plurality of cells (6a) extending in the axial length direction. ) Is a through-flow type in which an oxidation catalyst component is supported and exhaust gas (7) is passed through the cell (6a).

As shown in FIG. 1, the PM accumulation amount estimation device (3) of the DPF (2) is an arithmetic processing unit of the engine ECU (28). The exhaust purification case (29) is provided with a DPF inlet exhaust temperature sensor (30), a DPF inlet exhaust pressure sensor (31), and a differential pressure sensor (32) for detecting a differential pressure between the DPF inlet and the outlet. Based on the correlation map between the detected values of the sensors (30), (31) and (32) and the PM deposition amount in the DPF, the PM deposition amount of the DPF (2) is estimated by the PM deposition amount estimation device (3) of the DPF (2). The quantity is estimated. In addition, based on the correlation map of the fuel injection amount, the DPF inlet exhaust temperature, and the PM accumulation amount at the DPF, and further, based on the correlation map of the engine operation time and the PM accumulation amount at the DPF, the DPF (2) The PM accumulation amount of the DPF (2) is estimated by the PM accumulation amount estimation device (3).
The exhaust purification case (29) is also provided with a DOC inlet exhaust temperature sensor (33). An intake throttle valve (not shown) is provided in the intake path (not shown), and when the DOC inlet exhaust temperature (T) is lower than a predetermined post-injection lower limit temperature (TN), the intake throttle opening is set. As a result, the DOC inlet exhaust temperature (T) is increased.

The outline of the DPF regeneration process is as follows.
As shown in FIG. 2A, when the estimated value (P) of the PM accumulation amount of the DPF (2) reaches a predetermined DPF regeneration mode start value (P1), the DPF regeneration mode is started (S2). In the DPF regeneration mode, when the DOC inlet exhaust temperature (T) is equal to or higher than a predetermined post-injection lower limit temperature (TN), the main injection by the common rail fuel injection device (4) is instructed by the command of the fuel injection control device (5). Subsequent post injection is performed (S6).
As shown in FIG. 1, unburned fuel mixed in the exhaust (7) is catalytically combusted in the DOC (6), and PM accumulated in the DPF (2) is incinerated and removed by raising the temperature of the exhaust (7). It is configured as follows.

The timing of main injection and post injection is as follows.
The main injection is started within the range of 0 ° ± 5 ° of compression top dead center of the cylinder at the crank angle.
Post injection is started within a range of 100 ° ± 40 ° after the compression top dead center of the cylinder at a crank angle.

As shown in FIG. 1, an exhaust flow rate estimating device (8) and a post injection lower limit temperature (TN) setting device (9) are provided.
As shown in FIGS. 2A and 2B, when the estimated value (E) of the exhaust flow rate is the predetermined reference flow rate (E1), the post injection lower limit temperature (TN) is the predetermined reference lower limit temperature (T1). Is set (S4), and when the estimated value (E) of the exhaust flow rate is a low flow rate (E0) less than the reference flow rate (E1), the post injection lower limit temperature (TN) is lower than the reference lower limit temperature (T1). Is set to a lower lower limit temperature (T0) (S10).

  As shown in FIG. 1, both the exhaust flow rate estimating device (8) and the post injection lower limit temperature (TN) setting device (9) are arithmetic processing units of the engine ECU (28). An intake flow rate sensor (not shown) is provided in the intake path (not shown), and a detected value of the intake flow rate sensor, a fuel injection amount, a DOC inlet exhaust temperature sensor (33), a DPF inlet exhaust temperature sensor (30), The exhaust flow rate is estimated based on the detected value of the DPF inlet exhaust pressure sensor (31), and the post injection lower limit temperature (TN) is set based on the estimated value (E) of the exhaust flow rate. The exhaust flow rate estimation device (8) estimates an estimated value (E) of the exhaust flow rate that passes through the DOC (6). The reference lower limit temperature (T1) is 250 ° C.

  As shown in FIG. 2 (B), when the estimated value (E) of the exhaust flow rate is a small flow rate (E0) less than the reference flow rate (E1), the smaller the estimated value (E) of the exhaust flow rate, The lower limit temperature (T0) set (S10) to the injection lower limit temperature (TN) is lowered.

  As shown in FIGS. 2A and 2B, when the estimated value (E) of the exhaust flow rate is a large flow rate (E2) exceeding the reference flow rate (E1), the post-injection lower limit temperature (TN) is the above reference flow rate. A lower limit temperature (T2) higher than the lower limit temperature (T1) is set (S11).

  As shown in FIG. 2 (B), in the case where the estimated value (E) of the exhaust flow rate is a large flow rate (E2) exceeding the reference flow rate (E1), the post value increases as the estimated value (E) of the exhaust flow rate increases. The lower limit temperature (T2) set (S11) to the injection lower limit temperature (TN) becomes higher.

The flow of processing by the fuel injection control device (5) is as shown in FIG.
In step (S1), it is determined whether or not the estimated value (P) of the PM accumulation amount in the DPF (2) has reached the DPF regeneration mode start value (P1). If the determination is affirmative, step (S2) Proceed to
In step (S2), the DPF regeneration mode is started. In step (S3), it is determined whether or not the estimated value (E) of the exhaust flow rate matches the predetermined reference flow rate (E1). The process proceeds to step (S4).
In step (S4), the post injection lower limit temperature (TN) is set to a predetermined reference lower limit temperature (T1), and the process proceeds to step (S5).

In step (S5), it is determined whether or not the DOC inlet exhaust temperature (T) is equal to or higher than the post injection lower limit temperature (TN). If the determination is affirmative, the process proceeds to step (S6).
In step (S6), post injection after the main injection is performed, and the process proceeds to step (S7).
In step (S7), it is determined whether or not the DPF regeneration mode end condition is satisfied. If the determination is affirmative, the process proceeds to step (S8). The condition for ending the DPF regeneration mode is that the DPF inlet exhaust temperature (T) equal to or higher than a predetermined temperature continues for a predetermined time after the DPF regeneration mode is started (S2). The termination condition of the DPF regeneration mode may be that the estimated value (P) of the PM accumulation amount of the DPF (2) reaches a value (P0) lower than the DPF regeneration mode start value (P1).
In step (S8), the DPF regeneration mode is terminated, and the process returns to step (S1).

If the determination in step (S5) or step (S7) is negative, the process returns to step (S3).
If the determination in step (S3) is negative, the process proceeds to step (S9).
In step (S9), it is determined whether the estimated value (E) of the exhaust flow rate is less than the reference flow rate (E1). If the determination is affirmed, the process proceeds to step (S10).
In step (S10), the post injection lower limit temperature (TN) is set to a lower lower limit temperature (T0) lower than the reference temperature (T1), and the process proceeds to step (S5).
If the determination in step (S9) is negative, the process proceeds to step (S11).
In step (S11), the post injection lower limit temperature (TN) is set to a higher lower limit temperature (T2) that exceeds the reference temperature (T1), and the process proceeds to step (S5).

If the determination in step (S1) is negative, the process proceeds to step (S12).
In step (S12), the normal operation mode is set, and the process returns to step (S1).
In the normal operation mode, unlike the DPF regeneration mode, post-injection after main injection is not performed.

(1) Exhaust route
(2) DPF
(3) PM deposition amount estimation device
(4) Common rail fuel injection system
(5) Fuel injection control device
(6) DOC
(7) Exhaust
(8) Exhaust flow rate estimation device
(9) Post injection lower limit temperature setting device
(P) Estimated amount of PM deposition
(P1) DPF regeneration mode start value
(T) DOC inlet exhaust temperature
(TN) Post injection lower limit temperature
(T1) Reference lower limit temperature
(T0) Lower minimum temperature less than T1
(T2) High minimum temperature exceeding T1
(E) Estimated exhaust flow rate
(E1) Standard flow rate
(E0) Small flow rate less than E1
(E2) High flow rate exceeding E1
(S2) DPF regeneration mode starts
(S4) TN is set to T1
(S7) Post injection
(S10) TN is set to T0
(S11) TN set to T2

Claims (4)

The DPF (2) disposed in the exhaust path (1), the PM accumulation amount estimation device (3) of the DPF (2), the common rail fuel injection device (4), and the common rail fuel injection device (4) A fuel injection control device (5) for controlling fuel injection, and a DOC (6) disposed upstream of the DPF (2);
When the estimated value (P) of the PM accumulation amount of the DPF (2) reaches a predetermined DPF regeneration mode start value (P1), the DPF regeneration mode is started (S2). In the DPF regeneration mode, the DOC inlet exhaust is performed. When the temperature (T) is equal to or higher than a predetermined post-injection lower limit temperature (TN), post-main injection is performed after the main injection by the common rail fuel injection device (4) in response to a command from the fuel injection control device (5) (S6). ,
In a diesel engine in which unburned fuel mixed in the exhaust (7) is catalytically combusted in the DOC (6), and PM accumulated in the DPF (2) is incinerated and removed by raising the temperature of the exhaust (7).
An exhaust flow rate estimating device (8) and a post injection lower limit temperature (TN) setting device (9) are provided,
When the estimated value (E) of the exhaust flow rate is the predetermined reference flow rate (E1), the post injection lower limit temperature (TN) is set to the predetermined reference lower limit temperature (T1) (S4), and the estimated value of the exhaust flow rate ( When E) is a low flow rate (E0) less than the reference flow rate (E1), the post injection lower limit temperature (TN) is set to a lower lower limit temperature (T0) lower than the reference lower limit temperature (T1) (S10). Diesel engine characterized by that. The diesel engine according to claim 1,
When the estimated value (E) of the exhaust flow rate is a small flow rate (E0) less than the reference flow rate (E1), the lower the estimated value (E) of the exhaust flow rate is set to the post injection lower limit temperature (TN) (S10 ) Diesel engine characterized by lowering the lower limit temperature (T0). In the diesel engine according to claim 1 or 2,
In the case of a large flow rate (E2) where the estimated value (E) of the exhaust flow rate exceeds the reference flow rate (E1), the lower limit temperature (T2) where the post injection lower limit temperature (TN) is higher than the reference lower limit temperature (T1). A diesel engine characterized by being set to (S11). The diesel engine according to claim 3,
When the estimated value (E) of the exhaust flow rate is a large flow rate (E2) exceeding the reference flow rate (E1), the post-injection lower limit temperature (TN) is set as the estimated value (E) of the exhaust flow rate increases (S11). Diesel engine characterized in that the lower limit temperature (T2) is increased.

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