JP4182770B2 - diesel engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a catalyst warm-up technology in a diesel engine.
[0002]
[Prior art]
In a diesel engine, a catalyst is usually used to purify exhaust gas. Such a catalyst cannot exhibit its purification function unless it reaches a certain temperature or higher. Therefore, normally, at the time of starting the diesel engine, a warm-up operation for increasing the bed temperature of the catalyst is performed.
[0003]
As a technology for warming up a catalyst in a diesel engine, for example, there is one described in Patent Document 1. In this technique, a second EGR passage for raising the temperature of the catalyst is provided separately from the normal first EGR passage. The first EGR passage recirculates the exhaust gas from the upstream side of the catalyst to the intake side, while the second EGR passage recirculates the exhaust gas from the downstream side of the catalyst to the intake side. . When the catalyst is at a low temperature, the exhaust gas is recirculated from the downstream side of the catalyst using the second EGR passage so that the entire amount of exhaust gas discharged from the engine flows through the catalyst. The rise has been accelerated.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-229973
[Patent Document 2]
Japanese Patent Laid-Open No. 5-4448
[Patent Document 3]
Japanese Patent Laid-Open No. 10-274086
[Patent Document 4]
Japanese Patent Laid-Open No. 10-274087
[Patent Document 5]
Japanese Patent No. 3092569
[Patent Document 6]
Japanese Patent No. 3331935
[0005]
[Problems to be solved by the invention]
However, if normal operation is performed immediately after the catalyst is warmed up, the catalyst may be cooled by a large amount of exhaust gas, and the activity of the catalyst may be reduced. Therefore, conventionally, there has been a demand for a technique that can promote warm-up of the catalyst and maintain its activity.
[0006]
The present invention has been made to solve the above-described conventional problems, and an object of the present invention is to provide a technique capable of promoting warm-up of a catalyst and maintaining its activity.
[0007]
[Means for solving the problems and their functions and effects]
In order to achieve the above object, the diesel engine of the present invention provides:
A combustion chamber;
A fuel injection device for injecting fuel into the combustion chamber;
A catalyst for purifying exhaust gas from the combustion chamber;
A control unit for controlling a plurality of devices of the diesel engine including the fuel injection device;
With
The controller is
In order to warm up and maintain the activity of the catalyst, the first warm-up operation mode is executed in the early warm-up period after the diesel engine is started, and the second warm-up period is performed in the late warm-up period after the early warm-up period. Execute machine operation mode,
The first warm-up operation mode is a mode in which the energy of the exhaust gas flowing through the catalyst is higher than the energy of the exhaust gas flowing through the catalyst in the normal operation mode of the diesel engine after the late warm-up period. ,
The second warm-up operation mode is an operation mode in which the temperature of the exhaust gas flowing through the catalyst is higher than the temperature of the exhaust gas flowing through the catalyst in the normal operation mode.
[0008]
In the early warm-up period, the energy of the exhaust gas flowing through the catalyst is higher than in the normal operation mode, so that the catalyst can be activated quickly. Further, in the latter warm-up period, the temperature of the exhaust gas flowing through the catalyst is higher than that in the normal operation mode, so that the activity can be maintained without excessively cooling the catalyst.
[0009]
The second warm-up operation mode may be a mode in which the flow rate of exhaust gas flowing through the catalyst is smaller than both the first warm-up operation mode and the normal operation mode.
[0010]
In the mode in which the flow rate of the exhaust gas flowing through the catalyst is small, the effect of cooling the catalyst is small even when the exhaust gas temperature is somewhat low, so that the catalyst activity can be maintained.
[0011]
The second warm-up operation mode may be an operation mode in which the excess air ratio in the combustion chamber is smaller than both the first warm-up operation mode and the normal operation mode.
[0012]
In the operation mode in which the excess air ratio is small, the exhaust gas temperature is high, so that the activity of the catalyst can be maintained efficiently.
[0013]
The second warm-up operation mode may be a mode having higher fuel efficiency than the first warm-up operation mode and lower fuel efficiency than the normal operation mode.
[0014]
According to this configuration, the activity of the catalyst can be maintained without significantly deteriorating the fuel efficiency.
[0015]
The early warm-up period may be a period until the cooling water temperature of the diesel engine reaches a predetermined temperature.
[0016]
Alternatively, the early warm-up period may be a period until the temperature of the catalyst reaches a predetermined temperature.
[0017]
According to these configurations, the catalyst can be sufficiently activated during the early warm-up period.
[0018]
The second warm-up operation mode may be executed when a predetermined operation condition including that a required load on the diesel engine is lower than a predetermined value is satisfied.
[0019]
In this configuration, since the second warm-up operation mode is executed only at a relatively low load during the late warm-up period, the activity of the catalyst can be reduced without excessively sacrificing the engine performance and fuel efficiency. Can be maintained.
[0020]
Note that the second warm-up operation mode may be a low-temperature combustion mode.
[0021]
In the low temperature combustion mode, the combustion exhaust gas is less and the combustion exhaust gas temperature tends to be higher than in the normal operation mode. Therefore, if the low temperature combustion mode is adopted as the second warm-up operation mode, the activity of the catalyst can be maintained.
[0022]
In the first warm-up operation mode, the control unit controls the fuel injection device to perform (i) fuel injection divided into pilot injection and main injection, and (ii) injection of the pilot injection. The volume ratio is set to a value higher than the injection volume ratio of the pilot injection executed in the normal operation mode, and (iii) the main injection timing is set to the main injection executed in the normal operation mode. It is preferable to set the time point later than the injection amount time.
[0023]
In this configuration, since the injection amount ratio of the pilot injection is set to a high value in the first warm-up operation mode during the early warm-up period, the temperature and pressure of the combustion chamber can be sufficiently increased before the main injection. . As a result, the fuel injected in the main injection can be sufficiently burned to suppress the HC concentration, and even if the injection timing of the main injection is delayed to increase the exhaust energy, no misfire occurs. The engine can be operated. As a result, warming up of the catalyst can be promoted while suppressing the HC concentration in the exhaust gas.
[0024]
In addition, the injection amount ratio of the pilot injection in the first warm-up operation mode is a value in a range of about 2 to about 5 times the injection amount ratio of the pilot injection executed in the normal operation mode. Is preferred.
[0025]
If the injection ratio of pilot injection is set to a value within this range, it is possible to set the injection timing of the main injection sufficiently late so that the exhaust energy becomes sufficiently high.
[0026]
It is preferable that the injection timing of the pilot injection in the first warm-up operation mode is set before the compression top dead center, and the injection timing of the main injection is set after the compression top dead center.
[0027]
According to this configuration, by setting the pilot injection before the compression top dead center, the temperature and pressure in the combustion chamber can be sufficiently increased before the main injection, and the main injection is set after the compression top dead center. By doing so, the exhaust energy can be increased.
[0028]
The diesel engine further includes a temperature detection unit for detecting a temperature that substantially indicates the bed temperature of the catalyst, and the control unit is configured to perform the first warming according to the bed temperature of the catalyst. The injection ratio of the pilot injection and the timing of the main injection in the machine operation mode may be adjusted.
[0029]
Or the said diesel engine is further provided with the temperature detection part for detecting the temperature which shows the cooling water temperature of the said combustion chamber substantially, The said control part is a said 1st according to the said cooling water temperature. The pilot injection ratio and the main injection timing in the warm-up operation mode may be adjusted.
[0030]
According to these configurations, it is possible to set an appropriate fuel injection state corresponding to the warm-up state, and thereby it is possible to further promote the warm-up of the catalyst more efficiently.
[0031]
In addition, the injection amount ratio of the pilot injection and the injection timing of the main injection in the first warm-up operation mode may be set so that the main injection corresponds to a timing immediately before the misfire limit.
[0032]
If the main injection timing is set immediately before the misfire limit, exhaust energy can be increased as much as possible without causing misfire. Therefore, it is possible to further promote the warm-up of the catalyst.
[0033]
The time immediately before the misfire limit is preferably a crank angle range from the misfire limit to about 2 ° before the misfire limit.
[0034]
In this range, the exhaust energy can be sufficiently increased.
[0035]
The diesel engine further includes an EGR device for returning exhaust gas from the combustion chamber to an intake passage to the combustion chamber, and a glow plug provided at an intake port of the combustion chamber. The control unit, in the first warm-up operation mode, (a) EGR cut operation to stop the exhaust gas recirculation by the EGR device, (b) continuous intake air heating operation by the glow plug, (C) At least one of the idling engine speed increasing operation for increasing the idling engine speed of the diesel engine to be higher than the idling engine speed in the normal operation mode may be executed.
[0036]
Since these three types of operations all contribute to an increase in exhaust energy, the warm-up of the catalyst can be further promoted.
[0037]
The diesel engine further includes a supercharger that compresses intake air supplied to the combustion chamber using energy of exhaust gas from the combustion chamber, and the supercharger is supplied to the supercharger. A variable supercharger capable of adjusting the supercharging pressure of the intake air by adjusting the exhaust working pressure may be used. At this time, in the first warm-up operation mode, the control unit may increase the operating pressure of the exhaust of the variable turbocharger more than the operating pressure in the normal operation mode.
[0038]
When the operating pressure of the exhaust of the variable turbocharger is increased, the pump loss increases and the exhaust energy increases. As a result, it is possible to promote warming up of the catalyst without increasing the HC concentration.
[0039]
The diesel engine further includes an intake throttle valve for restricting an intake passage to the combustion chamber, and the control unit further controls a throttle amount of the intake throttle valve in the first warm-up operation mode. You may make it increase more than the aperture amount in the said normal driving | operation mode.
[0040]
When the intake throttle amount is increased, the pump loss increases, so that the exhaust energy increases. Further, when the intake air is throttled, the intake air amount decreases, so that the exhaust temperature rises. As a result, it is possible to further promote the warm-up of the catalyst without increasing the HC concentration.
[0041]
The diesel engine further includes an intake throttle valve for restricting an intake passage to the combustion chamber, and the control unit continuously opens and closes the intake throttle valve in the first warm-up operation mode. You may do it.
[0042]
In this diesel engine, since the intake throttle valve is continuously opened and closed, the exhaust energy can be increased by the mechanical energy. As a result, it is possible to promote warming up of the catalyst without increasing the HC concentration.
[0043]
The present invention can be realized in various modes, for example, a diesel engine (compression ignition internal combustion engine), a diesel engine catalyst warm-up control apparatus or method, a vehicle using a diesel engine, It can be realized in a mode such as a moving body.
[0044]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described in the following order based on examples.
A. Overview of device configuration and operation:
B. How to promote catalyst warm-up and maintain activity when starting the engine:
C. First example of warm-up control:
D. Second embodiment of warm-up control:
E. Third example of warm-up control:
F. Fourth example of warm-up control:
G. Modified example
[0045]
A. Overview of device configuration and operation:
FIG. 1 is an explanatory diagram showing a schematic configuration of a diesel engine 10 according to an embodiment of the present invention. The diesel engine 10 is a so-called four-cylinder engine and has four combustion chambers # 1 to # 4. Air is supplied to each combustion chamber via an intake pipe 12. The fuel injection device includes a fuel pump 18, a common rail 19, and a fuel injection valve 14. The fuel is boosted by the fuel pump 18 and distributed to the fuel injection valves 14 of the respective combustion chambers via the common rail 19. The fuel injection valve 14 is controlled by the control unit 30 to inject fuel into each combustion chamber at an appropriate injection timing and injection amount. The exhaust gas generated by the combustion is discharged to the exhaust pipe 16. In addition, the diesel engine 10 of a present Example is used as a motor | power_engine for generating the driving force of a vehicle.
[0046]
The engine 10 is provided with a supercharger 20. The supercharger 20 adjusts the opening area of the turbine 21 provided in the exhaust pipe 16, the compressor 22 provided in the intake pipe 12, the shaft 23 that connects both, and the inlet nozzle 25 of the turbine 21. The actuator 26 is provided. When the combustion exhaust gas discharged from the combustion chamber rotates the turbine 21 of the supercharger 20, the compressor 22 rotates through the shaft 23, compresses the air, and supplies the compressed combustion chamber to each combustion chamber. The supercharger 20 is a variable supercharger that can change the driving pressure of exhaust gas by an actuator 26, and is generally called a variable nozzle turbo (VNT) or a variable capacity turbo.
[0047]
An air cleaner (not shown) is provided on the upstream side of the compressor 22. The compressor 22 compresses the air taken in via the air cleaner and supplies it to each combustion chamber. An intercooler 24 is provided on the downstream side of the compressor 22. The air compressed by the compressor 22 is cooled by the intercooler 24 and then supplied to each combustion chamber. A throttle valve 28 (intake throttle valve) is provided on the downstream side of the intercooler 24.
[0048]
A main catalyst 40 is provided in the exhaust pipe 16 on the downstream side of the turbine 21. As the main catalyst 40, for example, a NOx occlusion reduction type catalyst which is a catalyst capable of removing both particulate matter such as soot and SOF (Soluble Organic Fraction) contained in combustion exhaust gas and NOx is used.
[0049]
The NOx occlusion reduction type catalyst accumulates NOx when the air-fuel ratio when the combustion reaction proceeds in the combustion chamber is thinner than the stoichiometric air-fuel ratio (so-called lean case). When the air-fuel ratio is higher than the stoichiometric air-fuel ratio (so-called rich) or stoichiometric air-fuel ratio (so-called stoichiometry), the accumulated NOx is released. By such an operation, NOx in the combustion exhaust gas is purified. Further, the NOx occlusion reduction type catalyst also has an activity as an oxidation catalyst. The combustion exhaust gas is purified by oxidizing soot and SOF in the combustion exhaust gas on the catalyst.
[0050]
The exhaust pipe 16 and the intake pipe 12 are connected by an EGR flow path 60, and a part of the combustion exhaust gas can be recirculated to the intake pipe 12 through the EGR flow path 60. The amount of exhaust gas recirculated to the intake pipe 12 is controlled by adjusting the opening degree of the EGR valve 62 and the throttle valve 28. An EGR cooler 64 is further provided in the EGR flow path 60, and the combustion exhaust gas is cooled by the EGR cooler 64 before being introduced into the intake pipe 12. Further, an EGR catalyst 66 is provided on the upstream side of the EGR cooler 64. The EGR catalyst 66 includes an oxidation catalyst, and oxidizes and removes particulate matter such as SOF in the combustion exhaust gas introduced into the intake pipe 12. The EGR catalyst 66 may be omitted.
[0051]
The control unit 30 receives measurement values from sensors for detecting the engine speed Ne, the accelerator depression amount L, and the engine cooling water temperature Ten, and in accordance with these measurement values, the fuel pump 18 and the fuel The injection valve 14, EGR valve 62, throttle valve 28 and the like are controlled. In addition to these, various sensors are provided as sensors. For example, the common rail 19 is provided with a pressure sensor 50 for detecting the fuel pressure. An air flow meter 52 for detecting the intake air amount is provided on the upstream side of the compressor 22 in the intake pipe 12. The exhaust pipe 16 is provided with an air-fuel ratio sensor 72 for detecting the air-fuel ratio. Further, the main catalyst 40 is provided with a temperature sensor 42 for detecting the catalyst bed temperature.
[0052]
FIG. 2 shows that when the EGR rate ([EGR gas amount] / [EGR gas amount + intake air amount]) is gradually increased, NOx concentration, smoke, CO (carbon monoxide) concentration in the combustion exhaust gas, It is explanatory drawing which showed notably the mode that HC (unburned hydrocarbon type compound) density | concentration changes. In the example of FIG. 2, the combustion injection timing is fixed. Here, the smoke is an index representing the concentration of carbon-containing suspended fine particles such as soot in the exhaust gas, and is measured by a dedicated measuring device called a smoke meter. When the exhaust gas contains no carbon-containing suspended fine particles such as soot, the smoke value is 0, and the smoke value increases as the concentration of the fine particles increases. In the example of FIG. 2, the smoke value starts to increase when the EGR rate exceeds 40%. However, when the EGR rate is further increased to exceed about 60%, smoke hardly occurs. Further, the NOx concentration decreases as the EGR rate increases. That is, if the EGR rate is sufficiently increased, the NOx emission amount can be reduced to almost 0 (about 10 ppm at most) and the smoke can also be reduced to almost 0. In the present specification, a combustion mode in which the EGR rate is set to a value of 60% or more to reduce smoke and NOx concentration is referred to as “low temperature combustion”. Further, a normal combustion mode performed at an EGR rate lower than that of low-temperature combustion is referred to as “normal combustion”. In normal combustion, the EGR rate is suppressed to 50% or less. The name “low temperature combustion” is derived from the fact that in this combustion mode, the local combustion temperature in the combustion chamber is suppressed to a considerably lower temperature than usual by the action of EGR gas. It is known that when the local combustion temperature is low, the amount of smoke and NOx generated tends to be reduced. The low temperature combustion is described in detail in, for example, Japanese Patent No. 3092569 disclosed by the present applicant.
[0053]
As shown in the uppermost part of FIG. 2, the air-fuel ratio decreases as the EGR rate increases. If the intake air amount (the sum of the intake air amount and the EGR gas amount) supplied into the combustion chamber in one intake step is constant, the air intake amount decreases as the EGR gas amount increases. Since the oxygen concentration in the EGR gas is lower than the oxygen concentration of normal air, the air-fuel ratio approaches the rich side as the EGR gas amount increases, that is, as the EGR rate increases. As shown in FIG. 2, since the EGR rate is higher in the low temperature combustion than in the normal combustion, the air-fuel ratio is shifted to the rich side as compared with the normal combustion.
[0054]
Diesel engine combustion is usually performed under a lean air-fuel ratio. Even when performing EGR, the air-fuel ratio is kept lean in normal combustion. When the EGR gas amount is further increased, combustion can be performed under the condition that the air-fuel ratio becomes the stoichiometric air-fuel ratio (stoichiometry). Strictly speaking, the air-fuel ratio depends on the composition of the fuel, but the stoichiometric air-fuel ratio takes a value in the vicinity of 14.7 to 14.8 for most fuels. If the EGR gas amount is further increased from the stoichiometric air-fuel ratio, the air-fuel ratio becomes rich.
[0055]
FIG. 3 shows various combustion-related characteristics when the EGR rate is changed and the air-fuel ratio (A / F) is changed (the amount of smoke in the combustion exhaust gas, the fuel consumption of the diesel engine, the catalyst bed temperature, and the gas temperature containing the catalyst). It is explanatory drawing which showed notably that a mode changes. Here, the catalyst bed temperature and the catalyst-containing gas temperature represent the catalyst bed temperature in the main catalyst 40 of FIG. 1 and the combustion exhaust gas temperature flowing into this catalyst, respectively. As shown in FIG. 3, low-temperature combustion is classified into lean low-temperature combustion that is performed leaner than the stoichiometric air-fuel ratio and rich low-temperature combustion that is performed richer than the stoichiometric air-fuel ratio.
[0056]
Lean low-temperature combustion can sufficiently suppress smoke, and exhibits excellent fuel efficiency to an extent that is sufficiently acceptable as compared with normal combustion. When performing lean low-temperature combustion, as shown in FIG. 2, the HC concentration and the CO concentration in the combustion exhaust gas are higher than in the normal combustion. However, in the low temperature combustion, the combustion exhaust gas is less and the combustion exhaust gas temperature tends to be higher than in the normal combustion. Therefore, when performing low temperature combustion, the catalyst bed temperature can be kept higher (FIG. 3). By keeping the catalyst bed temperature high in this way, the HC concentration and CO concentration in the exhaust gas discharged to the outside can be easily reduced. Thus, lean low-temperature combustion is an excellent combustion mode that can discharge extremely clean exhaust gas when combined with the main catalyst 40.
[0057]
As described above, low-temperature combustion is a combustion mode in which a large amount of EGR gas is circulated to lower the combustion temperature. Therefore, it is practically possible to employ low-temperature combustion only when the load is low. That is, in order to operate the engine at a higher load, it is necessary to increase the fuel injection amount and the intake air amount. Here, the total value of the amount of air sucked into the combustion chamber by one intake and the amount of exhaust gas recirculated to the intake side does not change in principle. Therefore, if the amount of air increases, the amount of exhaust gas recirculation increases. Decrease accordingly. For this reason, when the load is high, the EGR rate cannot be kept high enough to achieve low-temperature combustion. Therefore, normal combustion is performed during medium and high loads. NOx generated by performing normal combustion at medium and high loads is stored in the main catalyst, which is a NOx storage reduction catalyst. The NOx occluded in this way is reduced by HC and CO discharged when low-temperature combustion is performed under a low load.
[0058]
FIG. 4 is a graph showing a low temperature combustion operation region and a normal combustion operation region. As shown in FIG. 4, low-temperature combustion can be performed when the engine operating condition is in the relatively low output region R1, and normal combustion is performed when the engine operating condition is in the relatively high output region R2. However, it is also possible to perform normal combustion in the low temperature combustion operation region. Therefore, in the low temperature combustion operation region, either low temperature combustion or normal combustion is selected as necessary. More specifically, a map in which the exhaust gas air-fuel ratio targeted for control is set using the engine speed and the required torque of the engine as parameters is stored as a map for low-temperature combustion and a map for normal combustion, respectively. In the selected combustion mode, control is performed so that the air-fuel ratio detected by the air-fuel ratio sensor 72 attached to the exhaust pipe 16 becomes the target air-fuel ratio. Such a map is stored in a ROM (not shown) of the control unit 30.
[0059]
Rich low temperature combustion is not usually used because it is a combustion mode in which the fuel consumption deteriorates as shown in FIG. 3, but the catalyst bed temperature can be raised as shown in FIG. This is usually done for a short time. That is, when normal combustion is continued, since the combustion exhaust gas temperature is low, the catalyst bed temperature gradually decreases and the catalytic activity may decrease. The catalyst activity can be recovered by raising the catalyst bed temperature.
[0060]
B. How to promote catalyst warm-up and maintain activity when starting the engine:
The warming up of the catalyst 40 is performed by the heat of exhaust gas passing through the catalyst 40. Here, if a turbulent flow model in a circular pipe is adopted as the flow of exhaust gas in the catalyst 40, the heat transfer amount Q from the exhaust gas to the catalyst 40 is given by the following equation (1).
[0061]
Q = C1 · Re ^0.8 ・ Pr ^1/3 ・ (Tg-Tc)
= C2 ・ V ^0.8 (Tg-Tc) (1)
Here, C1 and C2 are constants, Re is the number of lay nozzles, Pr is the Prandtl number, Tg is the temperature of the exhaust gas, Tc is the temperature of the catalyst, and V is the flow rate of the exhaust gas. Since the Prandtl number is determined only by the physical property value of the fluid, it is represented by a constant C2. The Reynolds number Re is proportional to the flow rate V of the exhaust gas.
[0062]
The warming up of the catalyst 40 is promoted as the heat transfer amount Q increases. Therefore, in order to promote the warming up of the catalyst 40, the following two means can be employed.
(A) Increase the temperature Tg of the exhaust gas.
(B) Increase the flow rate V of the exhaust gas.
[0063]
Various embodiments described below promote warming up of the catalyst 40 using at least one of these two means. Further, even after the catalyst 40 reaches the activation temperature, an operation for maintaining the activity for a while is performed. In the operation for maintaining the catalytic activity, means for increasing the temperature Tg of the exhaust gas is used.
[0064]
FIG. 5 shows an outline of catalyst warm-up in the embodiment of the present invention. The horizontal axis is the elapsed time from the start (cold start), and the vertical axis is the vehicle speed and the catalyst bed temperature. As shown in the upper part of the graph, the warm-up period is divided into an early warm-up period (early warm-up phase) and a late warm-up period (late warm-up phase). The change in vehicle speed in this example conforms to a predetermined vehicle performance test pattern.
[0065]
The early warm-up period t0 to t1 is a period for raising the catalyst bed temperature from the normal temperature to the activation temperature (for example, about 250 ° C.). In this early warm-up period, the catalyst warm-up promotion operation mode (described later) is executed, and thereby the catalyst bed temperature reaches the activation temperature at the end of the early warm-up period. The latter warm-up period t1 to t2 is a period for maintaining the catalyst bed temperature at the activation temperature or higher. In the latter warm-up period, the catalyst activity maintaining operation mode (described later) is executed when a predetermined operation condition including that the required load on the engine is lower than a predetermined value is satisfied. In the example of FIG. 5, as shown in the upper part of the figure, the catalyst activity maintaining operation mode is an operation condition in which the required load of the engine is low and the rotational speed is substantially constant (specifically, at constant speed running and idling). The catalyst activity maintaining operation mode is executed.
[0066]
After the late warm-up period (after time t2), normal operation is performed. At the end of the late warm-up period, the catalyst bed temperature has risen sufficiently, and the engine cooling water, the exhaust path, etc. have also risen sufficiently. Therefore, it is possible to maintain the catalyst bed temperature at the activation temperature or higher even if normal operation is performed without performing the catalyst warm-up promotion operation mode or the catalyst activation time operation mode. In the present specification, an operation mode normally performed after the late warm-up period is referred to as a “normal operation mode”. Further, the early warm-up period and the late warm-up period may be collectively referred to simply as “warm-up period”.
[0067]
As the catalyst warm-up promotion operation mode during the early warm-up period, an operation mode in which the energy of the exhaust gas flowing through the catalyst is higher than that in the normal operation mode after the warm-up period can be adopted. Here, the phrase “compared to the normal operation mode” means “compared to the case of the engine load and the rotational speed substantially the same as those in the normal operation mode”. Specific examples of the catalyst warm-up promotion operation mode will be described in detail later. As the catalyst activity maintaining operation mode during the late warm-up period, an operation mode in which the temperature of the exhaust gas flowing through the catalyst is higher than that in the normal operation mode after the warm-up period can be adopted. For example, the low-temperature combustion described with reference to FIGS. 2 and 3 can be employed as the catalyst activity maintaining operation mode.
[0068]
In order to raise the exhaust gas temperature in the catalyst activity maintaining operation mode, it is generally sufficient to lower the excess air ratio (that is, lower the air-fuel ratio) than in the normal operation mode. In particular, as the catalyst activity maintaining operation mode, it is preferable to lower the excess air ratio than both the normal operation mode and the catalyst warm-up promotion operation mode. This is because if the excess air ratio is high, the exhaust temperature is lowered by a large amount of air. Conversely, if the excess air ratio is lowered, the exhaust temperature can be increased. As shown in FIG. 3, low-temperature combustion has a considerably low air-fuel ratio, and the exhaust gas temperature is higher than that in the normal operation mode. Therefore, it can be adopted as the catalyst activity maintaining operation mode. Further, it is possible to raise the exhaust gas temperature by adopting a combustion mode other than the low temperature combustion as the catalyst activity maintaining operation mode, and lowering the excess air ratio compared to the normal operation mode after the warm-up period. Means for reducing the excess air ratio include a decrease in the opening degree of the throttle valve 28 (FIG. 1) and an increase in the EGR ratio. These two can be employed simultaneously.
[0069]
Further, as the catalyst activity maintaining operation mode, a mode in which the amount of exhaust gas flowing through the catalyst is reduced as compared with the normal operation mode can be adopted. In particular, as the catalyst activity maintaining operation mode, it is preferable to reduce the amount of exhaust gas flowing through the catalyst as compared with both the normal operation mode and the catalyst warm-up promotion operation mode. By doing so, it is possible to prevent the catalyst from being cooled by a large amount of exhaust gas, so that the activity of the catalyst can be maintained. As a means for reducing the amount of exhaust gas, a decrease in the opening of the throttle valve 28 or an increase in the EGR rate can be used.
[0070]
In addition, since the catalyst activity maintaining operation mode is intended to maintain the activation temperature of the catalyst 40, less energy may be given to the catalyst 40 than in the catalyst warm-up promotion operation mode. Therefore, it is preferable that the catalyst activity maintaining operation mode is an operation mode in which the fuel consumption is somewhat worse than the normal operation mode, but the fuel consumption is better (fuel efficiency) than the catalyst warm-up promotion operation mode.
[0071]
C. First example of warm-up control:
FIG. 6 is an explanatory diagram showing an operating state of the diesel engine 10 in the first embodiment of the warm-up control. The horizontal axis in FIG. 5 is the time from the start (cold start), and the vertical axis is the engine coolant temperature, the fuel injection timing, and the EGR rate in order from the top. When the engine is started at time t0, the catalyst warm-up promotion operation (catalyst warm-up combustion) for warming up the catalyst 40 is performed during the early warm-up period until time t1 when the engine coolant temperature reaches the predetermined temperature CATo. Done. The early warm-up period is set as a period until the engine coolant temperature reaches a predetermined temperature CATon. Alternatively, it may be a period until the catalyst bed temperature reaches a predetermined temperature. In the late warm-up period from time t1 to time t2, the catalyst activity maintaining operation mode and the normal operation mode are performed. In this embodiment, the low-temperature combustion described with reference to FIGS. 2 and 3 is performed in the catalyst activity maintaining operation mode, and the normal combustion is performed in the normal operation mode. After time t2, the normal operation mode (normal combustion) after warm-up is performed. In FIG. 6, the low-temperature combustion and normal combustion periods in the late warm-up periods t1 to t2 are illustrated in a simplified manner for convenience of illustration.
[0072]
During the early warm-up period t0 to t1, fuel injection is divided into pilot injection and main injection. The injection amount of pilot injection is set to about 30% of the total injection amount of one combustion cycle, and the injection amount of main injection is set to about 70%. The injection timing of pilot injection is about 10 ° before compression top dead center TDC (ie, TDC−about 10 °), and the injection timing of main injection is about 10 ° behind compression top dead center TDC (ie, TDC + about). 10 °). In the present specification, “injection timing” means the injection start timing. The meaning of the set value of the injection amount and the injection timing during the warm-up period will be described later.
[0073]
The EGR rate is set to 0 during the early warm-up period. That is, the EGR valve 62 is closed, and the recirculation of the combustion exhaust gas is cut off. This is because if the EGR is performed during the early warm-up period, the exhaust gas temperature is lowered by the EGR cooler 64 (FIG. 1), so that the warm-up may be suppressed. As can be understood from this, the EGR cut operation during the warm-up period can be used as means for increasing the temperature Tg of the exhaust gas in the above-described equation (1). However, a certain amount of EGR may be performed during the warm-up period. For example, the EGR rate may be set to 10 to 20% during acceleration. By setting the EGR rate to such a low value, warming up of the catalyst 40 can be promoted, and an excessive increase in NOx due to EGR cut can be prevented.
[0074]
In the late warm-up period t1 to t2, low temperature combustion is performed under relatively low load operating conditions, and normal combustion is performed under relatively high load operating conditions. As described with reference to FIG. 3, the low temperature combustion has a higher catalyst input gas temperature than the normal combustion, so that the activity of the catalyst 40 can be maintained. Further, since the catalyst 40 has reached the activation temperature during the early warm-up period, it is not necessary to continuously perform low-temperature combustion (catalyst activity maintaining operation) during the later warm-up period, and intermittent low-temperature combustion is sufficient. It is. In contrast, in the early warm-up period t0 to t1, it is preferable to continuously perform the catalyst warm-up promotion operation regardless of the engine load. The end timing of the late warm-up period can be determined by simply measuring the time of the late warm-up period. Alternatively, the late warm-up period may be terminated when the catalyst bed temperature or the engine cooling water temperature reaches a predetermined value.
[0075]
During normal combustion during the late warm-up period, pilot injection and main injection are performed as in the case of catalyst warm-up combustion during the early warm-up period. However, during normal combustion, the injection amount of pilot injection is set to about 10% of the total injection amount of one combustion cycle, and the injection amount of main injection is set to about 90%. Further, the injection timing of pilot injection is (TDC−about 15 °), and the injection timing of main injection is (TDC + about 5 °). In the normal operation mode after time t2, normal combustion is performed as in the latter warm-up period.
[0076]
FIG. 7A shows a change in pressure in the combustion chamber during the early warm-up period, and FIG. 7B shows a change in heat generation amount. The horizontal axis in FIGS. 7A and 7B is the crank angle θ. During the early warm-up period, since the pilot injection and the main injection are performed at a time away from the compression top dead center TDC, the rate of pressure increase near the compression top dead center TDC is low. For this reason, the so-called isovolume is reduced. In a diesel engine, it is generally known that when the isovolume decreases, the thermal efficiency decreases and the exhaust energy increases. More specifically, the pilot-injected fuel burns before compression top dead center TDC to generate heat, but this heat does not work to the outside and increases the temperature and pressure in the combustion chamber. Used. Since the main injection is also performed at a time far from the compression top dead center TDC, a considerable part of the heat generation amount is used for increasing the temperature of the exhaust gas.
[0077]
The injection timing and injection amount of pilot injection and main injection during the early warm-up period are determined in consideration of the following matters. In order to increase the exhaust energy, it is desirable that the main injection be performed at the latest possible time after the compression top dead center TDC (that is, by delaying as much as possible). However, if the main injection is retarded too much, misfire may occur. Therefore, if the injection amount of pilot injection is increased, the temperature of the combustion chamber rises, so that the possibility of misfire when the main injection is retarded can be reduced. Further, there is a certain preferable value (for example, 20 ° in crank angle) between the injection timings of the pilot injection and the main injection. Accordingly, the injection timings of the pilot injection and the main injection are determined so that the possibility of misfire is low and the injection timing of the main injection is as late as possible. Further, the injection timing and the injection amount of the pilot injection and the main injection are determined so as to include the increase in exhaust energy and satisfy the required load. As a result, during the early warm-up period, the amount of pilot injection is larger than that of normal combustion, and the injection timing of main injection is set later.
[0078]
Note that, under equal load operating conditions, the total amount of injection is larger in the catalyst warm-up combustion during the early warm-up period than in the normal combustion. The injection ratio (pilot injection amount / total injection quantity) of pilot injection during the early warm-up period is preferably about 2 to about 5 times the injection ratio of pilot injection in normal combustion.
[0079]
As can be understood from the above description, the fuel injection during the early warm-up period of the first embodiment has the following characteristics.
(1) The injection amount ratio of pilot injection during the early warm-up period is higher than the injection amount ratio of pilot injection executed in normal combustion after the early warm-up period.
(2) The injection timing of main injection during the early warm-up period is later than the injection amount timing of main injection executed in normal combustion after the warm-up period.
[0080]
By performing such control, it is possible to retard the main injection considerably, increase the exhaust energy, and warm up the catalyst 40 more efficiently. Further, since the amount of pilot injection is large, the temperature and pressure in the combustion chamber are considerably increased during main injection. For this reason, since the fuel injected by the main injection burns sufficiently, the HC concentration in the combustion exhaust gas can be reduced. That is, in the first embodiment, it is possible to efficiently warm up the catalyst while suppressing the HC concentration.
[0081]
Although there is some flexibility in the timing of pilot injection and main injection, pilot warm-up is performed before compression top dead center and main injection is performed after compression top dead center for warming up the catalyst. It is preferable. By doing so, it is possible to warm up the catalyst more efficiently while suppressing the HC concentration.
[0082]
FIG. 8 shows an execution example of the warm-up operation (catalyst warm-up promotion operation and catalyst activity maintenance operation) according to the first embodiment. The change in vehicle speed is the same as that shown in FIG. When the warm-up operation is performed, the catalyst bed temperature reaches the activation temperature at the end t1 of the early warm-up period after about 70 seconds from the start, and is maintained above the activation temperature thereafter. On the other hand, when the warm-up operation is not performed, the activation temperature is reached after about 1000 seconds have elapsed since the start. As can be understood from this, it is possible to activate the catalyst 40 in a short time by performing the catalyst warm-up operation of the first embodiment, and it is possible to maintain the activity thereafter.
[0083]
In addition, it is also possible to perform normal combustion (normal operation mode) after the catalyst reaches the activation temperature without performing the late warm-up period. However, as explained with reference to FIG. 3, in the normal combustion, the temperature of the gas containing the catalyst is lower than that in the low-temperature combustion, and the EGR rate is lower than that in the low-temperature combustion. Therefore, if the operation is performed only by normal combustion immediately after the early warm-up period, the catalyst 40 may be cooled by a large amount of exhaust gas and become below the activation temperature, as indicated by a one-dot chain line in FIG. In contrast, in the present embodiment, low temperature combustion is performed under relatively low load operating conditions during the late warm-up period, so that the activity of the catalyst 40 can be maintained.
[0084]
In the example of FIG. 6, it is assumed that the injection ratio and the injection timing of the pilot injection and the main injection are kept constant during the early warm-up period, but these are changed according to the degree of warm-up. May be. FIG. 9 is a graph showing an example in which the injection ratio and the injection timing are changed according to the engine coolant temperature. In this example, as the engine coolant temperature increases, the injection ratio of pilot injection decreases, while the injection timing of main injection advances. In other words, the adjustment is performed so as to approach the normal combustion injection state as the engine coolant temperature rises. By doing so, it is possible to warm up the catalyst with an appropriate injection according to the degree of warming up. Instead of the engine coolant temperature, the injection ratio and injection timing of pilot injection and main injection may be changed according to the catalyst bed temperature.
[0085]
D. Second embodiment of warm-up control:
FIG. 10 is an explanatory diagram showing an operation state of the diesel engine 10 in the second embodiment of the warm-up control. In the second embodiment, as described below, the injection timing and the injection amount of the pilot injection and the main injection in the early warm-up period are optimized as compared with the first embodiment.
[0086]
FIG. 11 is an explanatory diagram showing the relationship between the main injection timing, the main injection amount, and the misfire region. As can be seen from this figure, if the main injection timing is retarded at a certain main injection amount, the misfire range is entered beyond the misfire limit. However, the smaller the main injection amount, the more the misfire limit crank angle shifts to the retard side. The solid line in FIG. 11 shows the relationship between the main injection timing and the injection amount for generating the same torque when the pilot injection amount is constant. Generally, when the injection timing of the main injection is retarded, the thermal efficiency is lowered. Therefore, under the condition that the pilot injection amount is maintained at a constant value, the main injection amount necessary for generating the same torque increases as the injection timing of the main injection is retarded. Further, when the pilot injection amount is increased, the same torque can be generated even if the main injection timing is retarded by the same main injection amount.
[0087]
By the way, in the critical region near the misfire limit, the main injection is sufficiently retarded, so that the exhaust gas temperature is raised. The exhaust gas temperature in the critical region depends on various fuel injection conditions. FIG. 12 is an explanatory diagram showing a change in the exhaust gas temperature Tg depending on the fuel injection condition. The horizontal axis in FIG. 12 is the main injection timing, and the vertical axis is the temperature of the combustion exhaust gas. The solid line is a graph when the pilot injection ratio Qp (the ratio of the pilot injection amount to the total injection amount) is 0%, the one-dot chain line is a graph when this is 20% and the two-dot chain line is 40%. As can be understood from this figure, when the pilot injection amount ratio Qp is increased from 0% to 20%, the main injection timing that becomes the misfire limit is retarded, so that the exhaust gas temperature Tg in the critical region of the misfire limit also increases. . However, if the pilot injection amount ratio Qp is excessively increased (for example, to 40%), the ratio of the main injection amount is decreased, so that the exhaust gas temperature Tg is decreased. FIG. 13 is a rewrite of the relationship of FIG. 12 into the relationship between the pilot injection amount ratio and the exhaust gas temperature Tg. As can be understood from this figure, there is an optimum condition of the pilot injection amount ratio such that the exhaust gas temperature Tg becomes the highest when the main injection condition is set in the critical region of FIG. Such optimum injection conditions are experimentally determined for each engine. Moreover, since this optimal injection condition also depends on the engine temperature, it is preferable to change it according to the engine coolant temperature, for example.
[0088]
When the total of the main injection amount and the pilot injection amount is constant, it is possible to optimize the injection conditions in consideration of the following two cases. That is, when the pilot injection amount is large, the main injection amount is decreased, but the timing of the main injection can be delayed. On the other hand, when the pilot injection amount is small, the main injection amount increases, but it is necessary to advance the timing of the main injection. The optimum conditions for the pilot injection and the main injection at which the exhaust gas temperature Tg becomes the highest are determined in consideration of the balance between these two cases. That is, this optimum condition exists between the condition where the pilot injection amount becomes the maximum possible amount and the condition where the pilot injection amount becomes the minimum possible amount in a range where no misfire occurs. Therefore, it is possible to find an optimum condition by searching between these two extreme conditions.
[0089]
As described above, in the second embodiment, during the early warm-up period, the injection amount ratio of the pilot injection and the injection timing of the main injection are the critical region immediately before the misfire limit so that the exhaust gas temperature Tg becomes the highest. It is set to correspond to the period of As a result, the exhaust energy increases, and it is possible to efficiently promote the warm-up of the catalyst. The range of the critical region is preferably a range from the misfire limit to about 2 ° before the misfire limit at the crank angle, and more preferably a range from the misfire limit to about 1 ° before the misfire limit. .
[0090]
In the second embodiment, in addition to adjusting the injection conditions, there are three means for promoting the temperature rise of the exhaust gas, that is, EGR cut operation, idling speed increase, and continuous use of the glow plug. Is being used.
[0091]
As shown in FIG. 10, in the second embodiment, EGR is cut during the early warm-up period, as in the first embodiment. As a result, it is possible to prevent the exhaust temperature from being lowered due to heat loss in the EGR cooler 64 (FIG. 1), and to promote warming up of the catalyst. In the example of FIG. 10, the idle speed is set to 1200 rpm during the early warm-up period, and is set to 950 rpm after the early warm-up period. As described above, when the idling speed is increased during the early warm-up period, the exhaust gas flow rate V in the above-described equation (1) can be increased, and thus the warm-up of the catalyst 40 can be promoted. is there.
[0092]
As shown in the lowermost part of FIG. 10, the glow plug is continuously used during the early warm-up period. FIG. 14 shows a longitudinal section of the combustion chamber. The combustion chamber 110 is composed of a cylinder wall 112, a cylinder head 114, and a piston 116. The cylinder head 114 is provided with an intake port 122 and an exhaust port 124. The intake port 122 is provided with an intake valve 132, and the exhaust port 124 is provided with an exhaust valve 134. A fuel injection valve 14 is provided at a substantially central position of the combustion chamber of the cylinder head 114, and a glow plug 126 is provided at a position adjacent to the nozzle 15 of the fuel injection valve 14. Note that the glow plug 126 may be disposed at a position where the intake air can be heated, and may be provided at the intake port 122, for example.
[0093]
The glow plug 126 is normally used only for a very short time at the start in order to improve the startability of the engine 10. On the other hand, in the second embodiment, the glow plug 126 is continuously kept on for a considerably long time during the early warm-up period. By doing so, it is possible to further increase the exhaust gas temperature and promote warm-up of the catalyst 40.
[0094]
It is not necessary to perform the three types of operations of the EGR cut operation, the continuous intake air heating operation by the glow plug, and the idling engine speed increasing operation at the same time, but at least one of these operations must be warmed up early. It is preferable to execute in at least a part of the period. The degree of these operations is preferably changed depending on the engine coolant temperature and the catalyst temperature rise, and these operations may be stopped when they are no longer needed during the early warm-up period.
[0095]
E. Third example of warm-up control:
FIG. 15 is an explanatory diagram showing an operating state of the diesel engine 10 in the third embodiment of the warm-up control. In the third embodiment, the fuel injection timing and injection amount are the same as in the first embodiment shown in FIG. 6, but the inlet nozzle 25 (FIG. 1) of the variable nozzle turbo (VNT) 20 and the intake throttle (throttle valve). 28) is characterized in that the opening degree is narrowed during the early warm-up period. In addition, after the early warm-up period, the opening degree of the VNT and the intake throttle is adjusted according to the load request, but in the example of FIG.
[0096]
FIG. 16 illustrates the warm-up effect of the catalyst by adjusting the VNT and the intake throttle. When the nozzle opening degree of the VNT is decreased, the engine back pressure (pressure in the exhaust pipe 16) increases (block B2). Further, when the opening of the intake throttle is decreased, the intake pressure is decreased. An increase in engine back pressure and a decrease in intake pressure cause an increase in engine pump loss (block B3) and an increase in fuel required to generate the necessary power (block B4). As a result, the exhaust energy increases (block B5), and the warm-up of the catalyst can be promoted (block B6). Note that the reduction in the intake throttle opening also has the effect of increasing the intake air temperature by reducing the intake air amount.
[0097]
On the other hand, the increase in engine back pressure also has the effect of increasing the turbine speed (block B7). As the turbine speed increases, the intake pressure increases accordingly (block B8). Further, since the intake throttle valve is throttled, the flow velocity in the intake pipe increases (block B9). This means that the entropy of intake air increases, so that the intake air temperature rises (blocks B10 and B11). As a result, the exhaust energy increases (block B5), and the warm-up of the catalyst can be promoted (block B6).
[0098]
In this way, it is possible to promote the warm-up of the catalyst during the early warm-up period by narrowing the VNT and the intake throttle more than after warm-up. These controls are also unlikely to increase HC concentration. Therefore, warming up of the catalyst can be promoted while suppressing the HC concentration.
[0099]
F. Fourth example of warm-up control:
FIG. 17 is an explanatory diagram showing an operating state of the diesel engine 10 in the fourth embodiment of the warm-up control. The fourth embodiment has the same fuel injection timing and injection amount as the first embodiment shown in FIG. 6, but the intake throttle (throttle valve 28) is opened and closed at high speed during the early warm-up period. There is a feature. When the intake throttle is opened and closed at high speed, the energy is given to the intake air, the entropy of the intake air increases, and the intake air temperature rises. Accordingly, the exhaust temperature also increases, and the warming up of the catalyst can be promoted. In addition, since this control is unlikely to increase the HC concentration, it is possible to promote the warm-up of the catalyst while suppressing the HC concentration.
[0100]
As can be understood from the description of the third and fourth embodiments, the exhaust temperature is increased and the HC concentration is not increased by adjusting the opening of the intake throttle or VNT during the early warm-up period. It is possible to promote warming up of the catalyst. Note that the control employed in the third and fourth embodiments has no direct relationship with the fuel injection timing and the injection amount, and is used in any combination with the control in the first and second embodiments. It is possible.
[0101]
G. Variation:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.
[0102]
G1. Modification 1:
Further, the present invention is not limited to automobiles but can be applied to engines other than automobiles and engines of various moving bodies such as airplanes and ships.
[0103]
G2. Modification 2:
In the above embodiment, the operation period is switched using the engine cooling water temperature or the catalyst bed temperature, but the operation period may be switched using other measured values. Further, when a certain operation period reaches a predetermined length, it may be switched to another operation period.
[0104]
G3. Modification 3:
In the above embodiment, the catalyst bed temperature and the engine coolant temperature are directly measured using the temperature sensor, but these temperatures may be indirectly measured. That is, the temperature other than the catalyst and the engine coolant may be measured, and the catalyst bed temperature and the engine coolant temperature may be estimated from this temperature. In other words, you may make it use the temperature detection part for detecting the temperature which shows the bed temperature of a catalyst, or engine cooling water temperature substantially.
[0105]
G4. Modification 4:
The various set values (for example, fuel injection amount and injection timing) employed in the above embodiment are merely examples, and various other values can be employed. Moreover, it is possible to warm up the catalyst by variously combining various operations employed in the various embodiments described above.
[0106]
G5. Modification 5:
The above-described various operations for warming up the catalyst (operation mode) do not need to be continuously performed during the warm-up period, and may be performed at least during a part of the period. That is, in this specification, the words “in the warm-up period” or “during the warm-up period” mean “in at least a part of the warm-up period” unless otherwise specified.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a schematic configuration of a diesel engine 10 according to an embodiment.
FIG. 2 is an explanatory diagram conceptually showing how the concentrations of various substances in combustion exhaust gas change when the EGR rate is gradually increased.
FIG. 3 is an explanatory diagram conceptually showing how smoke and fuel consumption in combustion exhaust gas change when the air-fuel ratio (A / F) is changed.
FIG. 4 is a graph showing a low temperature combustion operation region and a normal combustion operation region.
FIG. 5 is an explanatory diagram showing an overview of catalyst warm-up operation.
FIG. 6 is an explanatory diagram showing an operating state of the diesel engine 10 in the first embodiment of warm-up control.
FIG. 7 is an explanatory diagram showing the relationship between the pressure change in the combustion chamber during the warm-up period and the heat generation amount in the first embodiment.
FIG. 8 is a graph showing an example of an execution result of a catalyst warm-up operation.
FIG. 9 is a graph showing an example of changing the injection ratio and the injection timing according to the engine coolant temperature.
FIG. 10 is an explanatory diagram showing an operating state of the diesel engine 10 in a second embodiment of warm-up control.
FIG. 11 is an explanatory diagram showing the relationship between the main injection timing and the main injection amount and the misfire region.
FIG. 12 is an explanatory diagram showing a change in exhaust gas temperature Tg depending on fuel injection conditions.
FIG. 13 is an explanatory diagram showing a relationship between a pilot injection amount ratio and an exhaust gas temperature Tg.
FIG. 14 is an explanatory view showing a longitudinal section of a combustion chamber.
FIG. 15 is an explanatory diagram showing an operating state of the diesel engine in a third embodiment of warm-up control.
FIG. 16 is an explanatory view of the warm-up effect of the catalyst by adjusting the VNT and the intake throttle.
FIG. 17 is an explanatory diagram showing an operating state of the diesel engine 10 in a fourth embodiment of warm-up control.
[Explanation of symbols]
10 ... Diesel engine
12 ... Intake pipe
14 ... Fuel injection valve
15 ... Nozzle
16 ... exhaust pipe
18 ... Fuel pump
19 ... Common rail
20 ... supercharger
21 ... Turbine
22 ... Compressor
23 ... Shaft
24 ... Intercooler
25 ... Inlet nozzle
26 ... Actuator
28 ... Throttle valve
30 ... Control unit
40 ... Main catalyst
42 ... Temperature sensor
50 ... Pressure sensor
52 ... Air flow meter
60 ... EGR flow path
62 ... EGR valve
64 ... EGR cooler
66 ... EGR catalyst
72 ... Air-fuel ratio sensor
110 ... Combustion chamber
112 ... Cylinder wall
114 ... Cylinder head
116 ... Piston
122 ... Intake port
124 ... Exhaust port
126 ... Glow plug
132 ... Intake valve
134. Exhaust valve

Claims (18)

A diesel engine,
A combustion chamber;
A fuel injection device for injecting fuel into the combustion chamber;
A catalyst for purifying exhaust gas from the combustion chamber;
A control unit for controlling the diesel engine comprising the fuel injector,
With
The controller is
In order to warm up and maintain the activity of the catalyst, the first warm-up operation mode is executed in the early warm-up period after the diesel engine is started, and the second warm-up period is performed in the late warm-up period after the early warm-up period. Execute machine operation mode,
The first warm-up operation mode, the thermal energy of the exhaust gas flowing in the catalyst is generally greater than the thermal energy of the exhaust gas flowing through the catalytic mode in the operation mode of the diesel engine after the late warm-up period And
The second warm-up operation mode, the temperature of the exhaust gas flowing in the catalyst, Oh I at high operating mode than the temperature of the exhaust gas flowing through the catalyst in the normal operating mode, and the first A diesel engine, which is a mode in which the flow rate of exhaust gas flowing through the catalyst is smaller than in both the warm-up operation mode and the normal operation mode . The diesel engine according to claim 1 ,
The diesel engine in which the second warm-up operation mode is a mode in which an excess air ratio in the combustion chamber is smaller than both the first warm-up operation mode and the normal operation mode. The diesel engine according to claim 1 or 2 ,
The diesel engine in which the second warm-up operation mode is a mode in which the fuel efficiency is higher than that in the first warm-up operation mode and the fuel efficiency is lower than that in the normal operation mode. The diesel engine according to any one of claims 1 to 3 ,
The early warm-up period is a diesel engine, which is a period until the cooling water temperature of the diesel engine reaches a predetermined temperature. The diesel engine according to any one of claims 1 to 3 ,
The early warm-up period is a diesel engine that is a period until the temperature of the catalyst reaches a predetermined temperature. The diesel engine according to any one of claims 1 to 5 ,
The second warm-up operation mode is a diesel engine that is executed when a predetermined operation condition including that a required load on the diesel engine is lower than a predetermined value is satisfied. The diesel engine according to claim 6, wherein
The diesel engine, wherein the second warm-up operation mode is a low-temperature combustion mode. A diesel engine,
A combustion chamber;
A fuel injection device for injecting fuel into the combustion chamber;
A catalyst for purifying exhaust gas from the combustion chamber;
A control unit for controlling the diesel engine including the fuel injection device;
With
The controller is
In order to warm up and maintain the activity of the catalyst, the first warm-up operation mode is executed in the early warm-up period after the diesel engine is started, and the second warm-up period is performed in the late warm-up period after the early warm-up period. Execute machine operation mode,
The first warm-up operation mode is a mode in which the thermal energy of the exhaust gas flowing through the catalyst is higher than the thermal energy of the exhaust gas flowing through the catalyst in the normal operation mode of the diesel engine after the late warm-up period. And
The second warm-up operation mode, the temperature of the exhaust gas flowing through the catalyst is a high operating mode than the temperature of the exhaust gas flowing through the catalyst in the normal operating mode,
The control unit, in the first warm-up operation mode,
(I) controlling the fuel injection device so that the fuel injection is divided into pilot injection and main injection;
(Ii) setting the injection amount ratio of the pilot injection to a value higher than the injection amount ratio of the pilot injection executed in the normal operation mode;
(Iii) The injection timing of the main injection is set to a time point later than the injection amount timing of the main injection executed in the normal operation state.
diesel engine. The diesel engine according to claim 8 , wherein
The diesel engine injection amount ratio in the first warm-up operation mode is a value in a range of about 2 to about 5 times the injection amount ratio of pilot injection executed in the normal operation mode. . The diesel engine according to claim 8 or 9 , wherein
The diesel engine, wherein the injection timing of the pilot injection in the first warm-up operation mode is set before the compression top dead center, and the injection timing of the main injection is set after the compression top dead center. The diesel engine according to any one of claims 8 to 10 , further comprising:
A temperature detector for detecting a temperature substantially indicating the bed temperature of the catalyst;
The control unit is a diesel engine that adjusts an injection ratio of the pilot injection and a timing of the main injection in the first warm-up operation mode according to a bed temperature of the catalyst. The diesel engine according to any one of claims 8 to 10 , further comprising:
A temperature detection unit for detecting a temperature substantially indicating the cooling water temperature of the combustion chamber;
The control unit is a diesel engine that adjusts an injection ratio of the pilot injection and a timing of the main injection in the first warm-up operation mode according to the cooling water temperature. The diesel engine according to claim 8 , wherein
The diesel engine in which the injection amount ratio of the pilot injection and the injection timing of the main injection in the first warm-up operation mode are set so that the main injection corresponds to a timing immediately before the misfire limit. The diesel engine according to claim 13 ,
The diesel engine, wherein the time immediately before the misfire limit is a crank angle range from the misfire limit to approximately 2 ° before the misfire limit. The diesel engine according to claim 13 or 14 , further comprising:
An EGR device for recirculating exhaust gas from the combustion chamber to an intake passage to the combustion chamber;
A glow plug provided in the intake port of the combustion chamber;
With
The control unit, in the first warm-up operation mode,
(A) an EGR cut operation for stopping recirculation of exhaust gas by the EGR device;
(B) continuous intake air heating operation by the glow plug;
(C) Idle speed increasing operation for increasing the idle speed of the diesel engine higher than the idle speed in the normal operation mode;
A diesel engine running at least one of the above. The diesel engine according to any one of claims 8 to 15 , further comprising:
A supercharger that compresses intake air supplied to the combustion chamber using thermal energy of exhaust gas from the combustion chamber;
The supercharger is a variable supercharger capable of adjusting a supercharging pressure of the intake air by adjusting a working pressure of exhaust gas supplied to the supercharger,
In the first warm-up operation mode, the control unit raises the operating pressure of the exhaust of the variable turbocharger higher than the operating pressure in the normal operation mode. The diesel engine according to claim 16 , further comprising:
An intake throttle valve for restricting an intake passage to the combustion chamber;
In the first warm-up operation mode, the control unit further increases the throttle amount of the intake throttle valve more than the throttle amount in the normal operation mode. The diesel engine according to claim 16 , further comprising:
An intake throttle valve for restricting an intake passage to the combustion chamber;
The diesel engine according to claim 1, wherein the controller continuously opens and closes the intake throttle valve in the first warm-up operation mode.

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