JP6069697B2 - Diesel engine control device and control method - Google Patents

Description

  The present invention relates to a control device and control method for a diesel engine, and more particularly to control during energization of a glow plug.

  When the engine is cold started, the inside of the cylinder is heated by a glow plug, and early pilot injection in a relatively low compression state and proximity pilot injection within 15 ° CA immediately before the main injection are performed prior to the main injection. (See Patent Document 1). In this case, when the coolant temperature is equal to or lower than the predetermined value Twc, the glow plug temperature is equal to or higher than the predetermined value Tgc, and the engine speed is lower than the predetermined value Nec, it is determined that the initial explosion has not yet occurred, Proximity pilot injection is performed to improve ignitability. Here, the predetermined value Twc is, for example, −20 ° C., and the predetermined value Nec is, for example, 200 rpm.

  On the other hand, when the cooling water temperature is equal to or lower than the predetermined value Twc, the glow plug temperature is equal to or higher than the predetermined value Tgc, and the engine speed is equal to or higher than the predetermined value Nec, it is determined that the ignition is relatively easy, and the proximity pilot injection is stopped or The proximity pilot injection amount is reduced.

JP 2007-262897 A

  By the way, in the said patent document 1, in order to improve ignition, only a proximity pilot injection is performed, and the combustion state in the cylinder which arises after ignition is not considered at all. If the proximity pilot injection is stopped or the proximity pilot injection amount is reduced at the timing when ignition can be performed, improvement in combustion at the time of cold start under energization of the glow plug and a low outside air temperature condition cannot be expected.

  Accordingly, an object of the present invention is to provide an apparatus that can improve combustion at the time of cold start under energization of a glow plug and under a low outside air temperature condition.

A control device for a diesel engine according to the present invention includes a glow plug that heats a gas in a cylinder at a cold start, and a direct injection fuel injection valve in which one of a plurality of injection holes is directed to the glow plug. And a common rail fuel injection device capable of performing at least two pilot injections prior to injection. Further, in the diesel engine control device of the present invention, when the glow plug is energized and at a cold start under a low outside air temperature condition, a rotational fluctuation that increases in response to an increase in the engine temperature from the cold start, The injection amount of the pilot injection executed between the first pilot injection and the main injection is reduced in accordance with the temperature rise of the engine from the cold start so as to suppress the rotational fluctuation .

  According to the present invention, the injection amount of the pilot injection executed between the initial pilot injection and the main injection is reduced in accordance with the temperature rise of the engine since the cold start. Appropriate pilot injection can be executed based on the temperature change. As a result, combustion in the cylinder is improved not only in the initial start period but also in the late start period, so that the operability after the cold start is improved and white smoke can be reduced.

It is a schematic block diagram of the control apparatus of the diesel engine of 1st Embodiment of this invention. It is the schematic block diagram which looked at one cylinder from the top. 4 shows four different multistage pilot injection patterns examined by the inventor of the basic invention. FIG. 5 is a characteristic diagram showing the relationship between a value obtained by differentiating the amount of heat generated by the entire multistage pilot injection with a crank angle and the indicated mean effective pressure. FIG. 5 is a characteristic diagram summarizing the indicated mean effective pressure and the rate of change for the four cases studied by the inventor of the basic invention. It is the bar graph which put together the average glow plug vicinity temperature and the average glow plug vicinity equivalent ratio about four cases which the inventor of the basic invention examined. It is a characteristic view of the heat release rate at the time of one combustion in a combustion chamber. It is a characteristic view with respect to the cooling water temperature of the initial pilot injection amount ratio. It is a model figure which shows the change of an engine speed when performing multistage pilot injection at the time of cold start. It is a timing chart of the heat release rate of cases 1 and 2 in the initial startup period. It is a timing chart of the heat release rate of cases 1 and 2 in the starting late period. It is a flowchart for demonstrating calculation of the main injection quantity of 1st Embodiment of this invention, and each pilot injection quantity of 3 times. It is a characteristic view of the initial pilot injection amount of the first embodiment. It is a characteristic view of the 2nd pilot injection quantity of a 1st embodiment. It is a characteristic view of the third pilot injection amount of the first embodiment. It is a flowchart for demonstrating calculation of the main injection amount of 2nd Embodiment, and each pilot injection amount of 3 times. It is a characteristic view of the initial pilot injection amount of the second embodiment. It is a characteristic view of the second pilot injection amount of the second embodiment. It is a characteristic view of the third pilot injection amount of the second embodiment. It is a flowchart for demonstrating calculation of the main injection quantity of 3rd Embodiment, and each pilot injection quantity of 3 times. It is a characteristic view of the initial pilot injection amount of the third embodiment. It is a characteristic view of the second pilot injection amount of the third embodiment. It is a characteristic view of the third pilot injection amount of the third embodiment.

  Embodiments of the present invention will be described below with reference to the drawings.

(First embodiment)
FIG. 1 is a schematic configuration diagram of a control device for a diesel engine according to a first embodiment of the present invention. In FIG. 1, intake air is supercharged by an intake compressor 10 </ b> A provided in an intake passage 2 of a diesel engine 1, cooled by an intercooler 3, passes through an intake throttle valve 4, passes through a collector 5, and is combusted in a combustion chamber of each cylinder. Flow into.

  The engine 1 includes a common rail fuel injection device 6. The common rail fuel injection device 6 mainly includes a high pressure fuel pump 7, a common rail 8, and a fuel injection valve 9. The fuel is increased in pressure by the common rail fuel injection device 6, that is, by the high pressure fuel pump 7, sent to the common rail 8, and directly injected into the combustion chamber from the fuel injection valve 9 (direct injection fuel injection valve) of each cylinder. . The air flowing into the combustion chamber and the fuel injected from the fuel injection valve 9 are combusted by compression ignition in the combustion chamber, and the exhaust flows out to the exhaust passage 11.

  A part of the exhaust gas flowing into the exhaust passage 11 is recirculated to the intake side through the EGR passage 12 as EGR gas. An EGR valve 13 is provided in the EGR passage 12 in order to control the flow rate flowing through the EGR passage 12.

  The remainder of the exhaust gas that is not recirculated passes through the exhaust turbine 10B and drives the exhaust turbine 10B. A variable nozzle 10D is provided at the scroll inlet of the exhaust turbine 10B. When the variable nozzle 10D is throttled (the variable nozzle opening is decreased), the exhaust flow velocity increases and the rotational speed of the exhaust turbine 10B increases. Then, the rotational speed of the intake compressor 10A coaxial with the exhaust turbine 10B increases, and the intake compressor 10A supercharges intake air. On the other hand, when the variable nozzle 10D is opened (the variable nozzle opening is increased), the exhaust flow velocity decreases, and the rotational speed of the exhaust turbine 10B decreases. Then, the rotational speed of the intake compressor 10A coaxial with the exhaust turbine 10B decreases, and the intake compressor 10A does not supercharge the intake air. A hydraulically driven or electrically driven actuator 10E is attached to drive the variable nozzle 10D.

  The engine controller 21 is input with signals of the accelerator opening (accelerator pedal depression amount) from the accelerator sensor 22 and the engine rotational speed signal from the crank angle sensor 23. The controller 21 calculates the fuel injection timing and the fuel injection amount of the main injection based on the engine load (accelerator opening degree and the like) and the engine rotation speed, and outputs a valve opening command signal corresponding to these to the fuel injection valve 9. To do. Further, the engine controller 21 performs EGR control and supercharging pressure control in a coordinated manner so that the target EGR rate and the target intake air amount can be obtained. The engine controller 21 is constituted by a microcomputer having a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and an input / output interface (I / O interface).

  A filter 14 that collects particulates in the exhaust is disposed in the exhaust passage 11 downstream of the exhaust turbine 10B. When the particulate accumulation amount of the filter 14 reaches a predetermined value (threshold), the engine controller 21 performs the regeneration process of the filter 14 by performing the post injection in the expansion stroke or the exhaust stroke immediately after the main injection. That is, the post-injection amount and post-injection timing are determined in advance according to the engine load and rotational speed so as to obtain the target regeneration temperature, and the post-injection according to the engine load and rotational speed at that time is determined. Post injection is performed so that the injection amount and the post injection timing can be obtained. As a result, the particulates accumulated on the filter 14 are removed by combustion, and the filter 14 is regenerated.

  In order to perform complete regeneration in which all the particulates accumulated in the filter 14 are burned and removed, it is necessary to raise the particulate combustion temperature as much as possible within a range not exceeding the allowable temperature of the filter 14 during the regeneration process. It becomes. For this reason, an oxidation catalyst (noble metal) 15 is disposed upstream of the filter 14. The catalyst 15 burns exhaust components (HC, CO) flowing in by post-injection for regeneration processing of the filter 14 to raise the temperature of the filter 14 and promote combustion of particulates in the filter 14. The catalyst 15 may be coated with an oxidation catalyst on the carrier constituting the filter 14 instead of separately providing the catalyst 15 before the filter 14. At this time, the oxidation reaction at the time of burning the particulates is promoted and the temperature of the filter 14 is substantially increased accordingly, and the burning of the particulates in the filter 14 is promoted. The catalyst 15 is not limited to the oxidation catalyst. Any catalyst having an oxidation function (for example, a three-way catalyst) can be replaced with an oxidation catalyst.

  Since the diesel engine 1 is somewhat difficult to start when cold, a cold start glow plug 31 is provided facing each cylinder (combustion chamber) to control the temperature of the gas (air mixture) in the cylinder. The engine 1 is raised to help ignition and start the engine 1.

  FIG. 2 is a schematic configuration diagram of one cylinder 41 as viewed from above. A fuel injection valve 9 (direct injection fuel injection valve) is placed in the combustion chamber 43 at a substantially central position on the ceiling of the combustion chamber 43 formed in the upper part of the cylinder 42. Two intake valves 44, 45 and two exhaust valves 46, 47 are arranged around the fuel injection valve 9. The tip of the fuel injection valve 9 has, for example, eight injection holes, and fuel is injected from each injection hole in eight directions at equal intervals toward the cylinder 42 wall. One of the plurality of nozzle holes is directed to the glow plug 31. In the combustion chamber 43, a swirl in the direction of the arrow shown in the figure is generated, whereby the sprayed fuel F is bent in the clockwise direction in FIG. The glow plug 31 is provided, for example, facing the combustion chamber 43 from a position between the two intake valves 44 and 45, and heats the gas in the cylinder. When the atomized fuel F from the fuel injection valve 9 is supplied to the periphery of the glow plug 31 heated by energization when the engine is cold, the air-fuel mixture in the vicinity of the glow plug 31 is ignited and becomes a seed flame and spreads. It will be. The position where the glow plug 31 is provided is not limited to this, and may be between the intake valve and the exhaust valve or between the two exhaust valves 46 and 47. The number of intake / exhaust valves and the number of injection holes of the fuel injection valve 9 are not limited to those shown in FIG.

  Recently, there is a tendency to reduce the compression ratio of the engine to around 15. The merit of the low compression ratio is that the output of the engine 1 can be improved, NOx in the exhaust can be reduced, and the pumping loss can be reduced. Specifically, as the maximum value of the in-cylinder pressure decreases due to the low compression ratio, more fuel can be injected from the fuel injection valve 9 into the combustion chamber 43, thereby improving the output of the engine. By reducing the compression ratio, the combustion temperature in the combustion chamber can be lowered, and the generation of NOx can be suppressed. Pumping loss is also reduced by the low compression ratio.

  However, on the other hand, due to the low compression ratio, the combustion stability deteriorates due to misfire at the time of cold start under conditions of low outside air temperature, for example, −25 ° C. below zero.

  Therefore, the inventor of the basic invention preceding the present invention effectively uses the function of the glow plug 31 as a fuel ignition source in order to suppress misfire during cold start at low outside air temperature conditions. We focused on the point that is important. That is, combustion stability is improved by introducing fuel from pilot injection prior to main injection (hereinafter, also simply referred to as “pilot injection”) to the vicinity of the glow plug 31 to form a kind of fire that becomes the core of combustion. . However, when there is too much fuel that does not vaporize in the vicinity of the glow plug 31, the fuel takes the heat from the glow plug 31 and vaporizes. The glow plug 31 is cooled, and a fire type cannot be formed.

  In order to avoid such cooling of the glow plug 31 due to excessive pilot injection fuel, the pilot injection fuel amount per one time (hereinafter referred to as “pilot injection amount”) is obtained by multi-stage pilot injection. It is to reduce. If the amount of fuel sprayed at one time is reduced, the amount of heat taken from the glow plug 31 per predetermined time is reduced, and the temperature drop of the glow plug 31 can be suppressed.

  Here, when the engine is cold started, the inside of the cylinder is heated by a glow plug, and early pilot injection in a relatively low compression state and proximity pilot injection within 15 ° CA immediately before the main injection are performed prior to the main injection. There is a conventional apparatus for performing the above. However, in the conventional apparatus, only the proximity pilot injection is executed in order to improve the ignition, and no consideration is given to the combustion state in the cylinder that occurs after the ignition. If the proximity pilot injection is stopped or the proximity pilot injection amount is reduced at a timing when ignition can be performed, combustion improvement at the time of cold start under a low outside air temperature condition when energizing the glow plug cannot be expected.

  Therefore, in the basic invention, the value obtained by differentiating the amount of heat generated by the entire multistage pilot injection with the crank angle is equal to or greater than a predetermined value when the glow plug 31 is energized and cold start is performed under a low outside air temperature condition. The number of pilot injections and the amount of each pilot injection when performing multistage pilot injection were determined. As a result, the temperature drop of the glow plug 31 at the time of ignition can be suppressed, and the equivalent ratio in the vicinity of the glow plug 31 can be kept high. It is possible to stabilize the combustion in the cylinder at the start.

  This will be specifically described. FIG. 3 shows four different multi-stage pilot injection patterns studied by the inventors of the basic invention, together with the main injection following the multi-stage pilot injection. In FIG. 3, IT1 to IT4 are the injection timings of each of the multistage pilot injections. IT5 is the injection timing of the main injection, and is provided before the compression top dead center TDC. The fuel amounts Q1 to Q6 of each of the multistage pilot injections and main injections are represented by the difference in height, and the higher the height, the larger the injection amount (fuel amount).

  Here, the fuel amount obtained by combining the fuel amount of the main injection (hereinafter referred to as “main injection amount”) Q1, Q2 and the total of all pilot injection amounts (hereinafter referred to as “total pilot injection amount”) Qpital is case 1. It is the same with ~ 4. Moreover, in all cases 1 to 4, the total pilot injection amount Qpitot is larger than the main injection amounts Q1 and Q2.

  Case 4 serves as a basic invention, and cases 1 to 3 serve as reference examples 1 to 3 for the basic invention. First, in Case 1 as Reference Example 1, the second pilot injection amount Q4 is set larger than the first pilot injection amount Q3. Then, the first pilot injection amount Q3 is injected by IT1, and the second pilot injection amount Q4 is injected by IT3.

  Next, Cases 2 and 3 as Reference Examples 2 and 3 will be described mainly with respect to differences from Case 1. In case 2, the first pilot injection in case 1 is divided into two and the injection timings are IT1 and TI2 (each divided pilot injection amount Q5 is half of Q3), and the injection timing of the third pilot injection Is IT4. In case 3, the main injection amount is reduced from Q1 to Q2, and the fuel (Q1-Q2) for the shaved portion is added to the initial pilot injection amount to obtain Q6 (= Q3 + (Q1-Q2)). It is. The injection timing of each pilot injection is the same as in case 1.

  In case 4 as the basic invention, the pilot injection is divided into the initial pilot and the remaining two times, and the ratio of the initial pilot injection amount Q4 to the total pilot injection amount Qpitot is determined as the total pilot of each of the remaining two pilot injection amounts Q5. It is set to be larger than the ratio of the injection amount. Specifically, since the total pilot injection amount Qpital is Q3 + Q4, the first pilot injection amount is Q4, the second pilot injection amount and the third pilot injection amount are Q5 (= half Q3). The first pilot injection amount Q4 is injected by IT1, the second pilot injection amount Q5 is injected by IT2, and the third pilot injection amount Q5 is injected by IT4. Hereinafter, the ratio of the initial pilot injection amount to the total pilot injection amount is simply “initial pilot injection amount ratio”, and the ratio of the remaining two pilot injection amounts to the total pilot injection amount is simply “remaining pilot injection amount ratio”. "

  For each of the four cases where the pilot injection pattern is set as described above, the characteristics shown in FIGS. 4 and 5 are simulated by conducting an actual machine experiment when the glow plug 31 is energized and during cold start under a low outside air temperature condition. The characteristics shown in FIG. 6 were obtained. First, FIG. 4 shows the characteristics found for the first time by the inventors of the basic invention. In FIG. 4, the vertical axis is the indicated mean effective pressure Pi [MPa] obtained by one-cycle combustion by multistage pilot injection and main injection, and the horizontal axis is a value obtained by differentiating the amount of heat generated by the entire multistage pilot injection by the crank angle. The characteristic indicated by the broken line is obtained for the first time with dQpilot / dθ [J / deg]. The “one cycle” described above is, for example, a single cylinder engine, and one cycle includes four strokes of an intake stroke, a compression stroke, an explosion stroke, and an exhaust stroke.

  Here, the above-mentioned “amount of heat generated by the entire pilot injection” Qpilot was calculated as follows. That is, FIG. 7 is a graph showing the characteristics of the heat generation rate [J / deg] of combustion generated in one cycle in the combustion chamber with the crank angle [deg] as the horizontal axis. Even if pilot injection is made multistage, a small mountain (first mountain) is generated first due to heat generation by the entire multistage pilot injection, followed by a large mountain (second mountain) due to heat generation by main injection. Become. In the fuel injection in which the pilot injection is added prior to the main injection, the heat generation of the two-level mountain occurs. Therefore, if the area of the first-level mountain (the hatched portion in FIG. 7) is calculated, it is expressed as “the whole pilot injection” The amount of heat generated by Qpilot [J]. Then, dQpilot / dθ [J / deg] can be obtained by dividing the “heat generation amount by the entire pilot injection” Qpilot by the crank angle section [deg] in which the heat generation by the entire multistage pilot injection has occurred.

  In FIG. 7, the peak of heat generation at the first mountain occurs at the compression top dead center TDC. This is because the peak of the heat generation at the first mountain occurs at the compression top dead center TDC by chance. It is because it was an engine which produced. The basic invention is not limited to the engine. The basic invention can also be applied to a diesel engine in which the first peak of heat generation occurs before or after the compression top dead center TDC.

  Returning to FIG. 4, according to an actual machine experiment, the indicated mean effective pressure Pi increases from A to B as dQpilot / dθ increases from the smaller side, and the indicated mean effective pressure Pi in a region where dQpilot / dθ is equal to or greater than a predetermined value D. Has settled to an equilibrium value from B to C. In the cases 1 to 3 shown in FIG. 3, dQpilot / dθ is included in the region less than D, and in the case 4 shown in FIG. 3, dQpilot / dθ is included in the region greater than D. It was.

  In FIG. 4, the dQpilot / dθ on the horizontal axis is larger in the region where dQpilot / dθ is less than the predetermined value D, and the greater the value, the greater the amount of heat generated by the multistage pilot injection. This represents an increase in Pi. In the region where dQpilot / dθ is equal to or greater than the predetermined value D, the indicated mean effective pressure Pi does not become larger than the value at D but shows an equilibrium value. From this, if dQpilot / dθ is in the region of D or more, it can be interpreted that the fire type formed in the vicinity of the glow plug 31 grows smoothly and stabilizes combustion. On the other hand, when dQpilot / dθ is in the region below the predetermined value D, the degree of heat generation is small even in the multistage pilot injection, that is, no fire is formed in the vicinity of the glow plug 31 or the fire is formed. However, it is interpreted that the fire type cannot grow smoothly and misfire can occur. Therefore, it is only necessary to determine the number of pilot injections and the amount of each pilot injection when performing multi-stage pilot injection so that dQpilot / dθ is equal to or greater than a predetermined value D determined in advance.

  The tendency of the broken line characteristic shown in FIG. 4 does not change depending on the engine specification, but the specific value of Pi in B and C and the specific value of D differ depending on the engine specification. And the predetermined value D may be determined.

  Next, FIG. 5 is a characteristic diagram in which the illustrated mean effective pressure Pi is represented by a bar graph and the variation rate of Pi is represented by a line graph for cases 1 to 4 shown in FIG. As shown in FIG. 5, the indicated mean effective pressure Pi is higher in the case 2 than in the case 1. However, in the case 3, the indicated mean effective pressure Pi is lower than in the case 2. In the case 4, the indicated mean effective pressure Pi is higher than in any of the cases 1 to 3. On the other hand, the variation rate of Pi increases in the order of Case 1, Case 2, and Case 3, and is the smallest in Case 4.

  FIG. 6 is a bar graph in which the average glow plug vicinity temperature [K] and the average glow plug vicinity equivalent ratio [nameless number] are summarized for the four cases 1 to 4 shown in FIG. Here, the “temperature near the glow plug” is a value of numerical calculation by simulation. The “equivalent ratio” is a value obtained by dividing the fuel-air ratio by the theoretical fuel-air ratio, where the reciprocal of the air-fuel ratio is the fuel-air ratio, the inverse of the stoichiometric air-fuel ratio is the theoretical fuel-air ratio, and the equivalent ratio is 1.0. Is equivalent to the stoichiometric air-fuel ratio. The “equivalent ratio in the vicinity of the glow plug” is a local equivalent ratio in the vicinity of the glow plug 31 and is not an average equivalent ratio in the entire combustion chamber. It is a value of numerical calculation by simulation in the vicinity of the glow plug 31. When the glow plug vicinity equivalence ratio is greater than 1.0, the mixture near the glow plug is on the rich side, and when the glow plug vicinity equivalence ratio is less than 1.0, the mixture near the glow plug is on the lean side.

  As shown in FIG. 6, in the case 2, the average temperature near the average glow plug is higher than in the case 1, and the equivalent ratio near the average glow plug is higher in the case 2 than in the case 1. Yes. However, in the case 3, the average glow plug vicinity equivalence ratio is larger than that in the case 2, but the average glow plug vicinity temperature is lower than that in the case 2. This means that when the initial pilot injection amount is increased to reduce the main injection amount as shown in the third stage of FIG. 3, the fuel that has reached the vicinity of the glow plug at one time takes heat away from the glow plug 31. This means that misfire is likely to occur. On the other hand, in case 4, the average glow plug vicinity temperature is higher than in any of cases 1 to 3, and the average glow plug vicinity equivalent ratio is higher than in any of cases 1 to 3.

  Next, FIG. 8 is a characteristic diagram of the initial pilot injection amount ratio with respect to the cooling water temperature. As shown in FIG. 8, the initial pilot injection amount ratio increases from 35% as the cooling water temperature Tw [° C.] decreases in the sub-zero region, and reaches approximately 80% at −30 ° C. Thus, the reason why the initial pilot injection amount ratio is increased as the cooling water temperature Tw is lowered is to improve the probability that the injected fuel contacts the glow plug 31 even in an extremely low temperature range of −30 ° C. . The characteristic diagram of FIG. The engine used in the actual machine experiment was in the range of 35% to 80%, but the characteristics shown in FIG. 8 are considered to be within the same range even if the engine specifications are different.

  Although the cooling water temperature Tw is taken on the horizontal axis in FIG. 8, it is not limited to this, and it may be the temperature (oil temperature) of the oil used for engine lubrication or the outside air temperature Ta. This is because the basic invention is intended for the cold start when the glow plug 31 is energized under the low outside air temperature condition, so that the cooling water temperature, the oil temperature, and the outside air temperature can be identified in this short time.

  In the case of the case 4 as the basic invention shown in the lowermost stage of FIG. 3, the pilot injection is performed in three stages, but it may be performed in multiple stages of two or more times. In case 4 as the basic invention shown at the bottom of FIG. 3, the second pilot injection amount and the third pilot injection amount are the same, but each pilot of the second and third pilots from the initial pilot injection amount. It is sufficient if the injection amount is small, and it is not always necessary to make the same amount. This completes the description of the basic invention.

  Next, the present invention improves the basic invention. This will be described with reference to FIG. FIG. 9 shows the multistage so that the value obtained by differentiating the amount of heat generated by the entire multistage pilot injection with the crank angle is equal to or greater than a predetermined value when the glow plug 31 is energized and during cold start under conditions of low outside air temperature. The model shows the change in engine speed when pilot injection is performed. Here, when the case 1 is a basic invention, the case 2 is a reference example for the basic invention, and the case 3 is a timing chart in the case of the first embodiment of the present invention.

  In FIG. 9, paying attention to the change in the combustion state in the cylinder from the cold start, a predetermined period immediately after the cold start (referred to as “starting initial period”) and a predetermined period thereafter (“starting late period”). This is roughly divided into two periods. In FIG. 9, it is assumed that t1 is a start start timing, a period from t2 to t3 is an initial start period, and a period from t3 to t4 is a late start period. In addition, in each frame on the right side of FIG. 9, patterns of multistage pilot injection and main injection are shown. Here, as in FIG. 3, the fuel amounts Q1, Q4, Q5, and Q7 of each of the multistage pilot injections and main injections are represented by different heights, and the higher the height, the larger the injection amount (fuel amount). I mean.

  The ratio of the first pilot injection amount to the total pilot injection amount is set to be larger than the ratio of the second and third pilot injection amounts to the total pilot injection amount, which is common to the three cases. .

  First, Case 1 is the basic invention itself. As shown in the uppermost frame on the right side of FIG. 9, the first, second, and third pilot injection amounts at this time are Q4, Q5, Q5, and the main injection amount is Q1 (the lowermost stage in FIG. 3). See also). In case 1, a favorable result is obtained because the fluctuation of the engine speed becomes small in the initial start period from t2 to t3. However, if you look closely, the inventor found for the first time that in the late start period from t3 immediately after the start initial period to t4, the engine speed fluctuates more than the start initial period from t2 to t3. It is.

  Next, in the case 2, as shown in the second frame on the right side of FIG. 9, the second and third pilot injection amounts are set as the second and third pilot injection amounts Q5 in the case 1, respectively. This is considered as less Q7 (Q7 <Q5). In case 2, the fluctuation of the engine speed is certainly smaller than that in case 1 in the late start period from t3 to t4, but this time the fluctuation of the engine speed is in case 1 in the initial start period from t2 to t3. On the contrary, it is getting bigger.

  Next, in case 3, as shown in the third frame on the right side of FIG. 9, the second and third pilot injection amounts are Q5 in the initial startup period from t2 to t3, from t3. Q7 is given in the late period of starting up to t4. In case 3, the engine speed fluctuation is smaller than that in case 2 in the initial start period from t2 to t3, and the engine speed fluctuation is smaller than in case 1 in the late start period from t3 to t4. That is, in the initial startup period from t2 to t3, the fluctuation of the engine rotation speed is the same as in case 1, and in the late startup period from t3 to t4, the fluctuation of the engine rotation speed is the same as in case 2. It has become a good point of.

  Next, when the inventor analyzed the three cases of FIG. 9, the following was inferred regarding combustion at extremely low temperatures. That is, in the initial startup period from t2 to t3 (immediately after startup), the temperature in the cylinder is low and fuel evaporation is poor. Therefore, by adopting the basic invention of case 1, the contact probability between the glow plug and the evaporated fuel is increased. It is preferable to increase the equivalent ratio in the vicinity of the glow plug. FIG. 10 is a timing chart (experimental result) for measuring the heat generation rate in the initial startup period when the engine is started under extremely low temperature conditions for Case 1 and Case 2. From FIG. 10, in the initial startup period, the heat generation rate is higher in case 1 in which the second and third pilot injection amounts are relatively large. As a result, it was confirmed that the engine speed was more stable in case 1 than in case 2 in which the pilot injection amounts for the second and third pilot injections were relatively small in the initial startup period.

  Next, in the late start period from t3 to t4, the periphery of the cylinder is warmed, so that the atomization of the fuel spray is relatively accelerated, and ignition continues and the environment in the cylinder is improved. For this reason, even in the late start period, if the same amount as the initial pilot period is supplied as the second and third pilot injection amounts as in Case 1, the second and third pilot injection amounts are started. It becomes excessive in the latter period, and the temperature of the glow plug 31 is decreased instead. This is considered to cause unstable combustion in the cylinder.

  On the other hand, in the case 2 in which the second and third pilot injection amounts are smaller than those in the case 1, the second and third pilot injection amounts are not excessive in the late start period, and the temperature of the glow plug 31 is reduced. It is considered that the equivalent ratio in the vicinity of the glow plug is secured while being suppressed. FIG. 11 is a timing chart (experimental result) for measuring the heat generation rate in the late start period when the engine is started under the same conditions as in FIG. 10 for case 1 and case 2. From FIG. 11, the heat generation rate is higher in case 2 in which the pilot injection amounts for the second and third times are relatively small in the late start period. As a result, it was confirmed that the engine rotation speed of case 2 was more stable than case 1 in which the pilot injection amounts of the second and third times were relatively large in the late start period.

  In this way, the basic invention is exclusively intended for the initial start period, so that it has not taken into account that the combustion state in the cylinder changes and is different from the initial start period in the late start period.

  Case 3 is the case of the first embodiment of the present invention. In case 3, in order to increase the contact probability between the evaporated fuel and the glow plug in the initial startup period in which the fuel is difficult to evaporate, the second and third pilot injection amounts are set to Q5 which is relatively large as in the basic invention. Then, in the late start period in which the fuel evaporates to some extent, the second and third pilot injection amounts are set to a relatively small Q7 so that the glow plug is not cooled by the fuel. That is, the second and third pilot injection amounts are decreased from Q5 to Q7 in accordance with the state change in the cylinder from the start. As a result, fluctuations in the idle rotation speed can be suppressed not only in the initial start period but also in the late start period.

  In FIG. 9, in order to clarify that the combustion state in the cylinder is different at different timings from the start, the description is divided into two parts, an initial start period and a late start period. Actually, the combustion state in the cylinder does not change stepwise from the initial start period to the late start period as shown in FIG. 9, but continuously changes with the elapsed time from the start. The combustion state in the cylinder continuously changing from this cold start can be known by the temperature rise of the engine cooling water. This is because when the engine cooling water is at the same temperature as the outside air when it is cold, the temperature of the engine cooling water rises due to a change in the combustion state in the cylinder from the start.

  Therefore, in the first embodiment of the present invention, when the glow plug 31 is energized and during cold start under a low outside air temperature condition, the second and third pilot injection amounts (the initial pilot injection and the main injection (Injection amount of pilot injection executed in the meantime) is reduced according to the temperature rise of the cooling water from the cold start (engine temperature rise).

  This control executed by the engine controller 21 will be described with reference to the flowchart of FIG.

  The flow of FIG. 12 is for calculating the main injection amount and each of the three pilot injection amounts, and is executed only once at a timing before a predetermined crank angle from the initial pilot injection timing at the time of the current fuel injection. That is, the flow before the first pilot injection timing at the time of the current fuel injection is set as the injection amount calculation timing, and the flow of FIG. 12 is performed every time the injection amount calculation timing of each cylinder is reached without distinguishing each cylinder. Execute.

  In step 1, the accelerator opening APO detected by the accelerator sensor 22, the engine rotational speed Ne [rpm] detected by the crank angle sensor 23, the cooling water temperature Tw [° C.] detected by the water temperature sensor 33, and the outside air temperature sensor 32. The detected outside air temperature Ta [° C.] is read.

In Step 2, based on the accelerator opening APO, the engine speed Ne, and the coolant temperature Tw, the total fuel injection amount Qtotal [mm ³ / st. ] Is calculated. For example, in the idle state, the target idle rotation speed is determined in advance, and the total fuel injection amount Qtotal is determined in advance so as to obtain this target idle rotation speed. Even if the target idle rotation speed cannot be obtained with the total fuel injection amount Qtotal, the target idle rotation speed can be obtained by employing feedback control of the idle rotation speed.

  In steps 3 to 6, it is determined whether or not all of the following conditions [1] to [4] are satisfied. If all of the conditions are satisfied, the process proceeds to steps 7 and 8 and if not, the process proceeds to steps 9 and 10. .

  [1] The glow plug 31 is being energized.

  [2] The outside temperature Ta is 0 ° C. or lower.

  [3] It is in an idle state (the accelerator opening is zero).

  [4] The cooling water temperature Tw is lower than the warm-up completion determination temperature Twth [° C.].

  The period during which the glow plug 31 is energized in [1] is only a short time such as several tens of seconds from the cold start of the engine. Only when the glow plug 31 is energized, the process proceeds to step 4 and subsequent steps. The condition [1] is that the fuel possessed by the glow plug 31 at a very low temperature in a low-compressed diesel engine (that is, when the glow plug 31 is energized and during a cold start under a low outside air temperature condition). This is to effectively use the function as an ignition source.

  The reason for the condition [2] is that combustion instability occurs under conditions of low outside air temperature where the outside air temperature Ta is 0 ° C. or lower. The reason for the above [3] is that combustion is most unstable in the idle state. The condition [4] is that the combustion in the cylinder becomes unstable when the engine is cold when the coolant temperature Tw is lower than the warm-up completion determination temperature Twth.

In Step 7 which is proceeded when the above conditions [1] to [4] are all satisfied, the first, second and third times are searched by searching the tables having the contents shown in FIGS. 13, 14 and 15 from the cooling water temperature. Pilot injection amounts Qpi1, Qpi2, Qpi3 [mm ³ / st. ] Is calculated. First, the second and third pilot injection amounts Qpi2 and Qpi3 are values that increase as the coolant temperature Tw decreases, as shown in FIGS. This is because the fuel spray becomes harder to vaporize as the temperature becomes extremely low, so that it is necessary to inject more fuel and increase the probability that the fuel spray contacts the glow plug 31. 14 and 15, the second and third pilot injection amounts Qpi2 and Qpi3 are set to constant values in the temperature region from the predetermined temperature Tw1 to the warm-up completion determination temperature Twth.

  Here, the operation of Step 7 in FIG. 12 is repeated until the cooling water temperature Tw becomes equal to or higher than the warm-up completion determination temperature Twth. The cooling water temperature Tw coincides with the outside air temperature before the cold start, and after the start, the change in the combustion state in the cylinder from the start is received, and gradually increases toward the warm-up completion determination temperature Twth. For this reason, in FIGS. 14 and 15, since the coolant temperature Tw shifts in the direction of the arrow after the start, the second and third pilot injection amounts Qpi2 and Qpi3 decrease accordingly. .

  Next, the characteristics of the initial pilot injection amount Qpi1 may be the same as in the basic invention. For example, the first pilot injection amount Qpi1 is the same as the characteristics of the second and third pilot injection amounts Qpi2 and Qpi3 as shown in FIG. Note that the initial pilot injection amount Qpi1 may be a constant value regardless of the cooling water temperature Tw, as indicated by a one-dot chain line.

  Further, at the same cooling water temperature Tw, the first pilot injection amount Qpi1 is set to be larger than the second and third pilot injection amounts Qpi2 and Qpi3. In other words, the ratio of the initial pilot injection amount Qpi1 to the total pilot injection amount is set larger than the ratio of the remaining pilot injection amounts Qpi2 and Qpi3 to the total pilot injection amount. This is also the same as the basic invention. In the present embodiment, the second pilot injection amount Qpi2 is made equal to the third pilot injection amount Qpi3. At this time, the calculated second pilot injection amount Qpi2 may be used as it is as the third pilot injection amount Qpi3, so that the characteristics of FIG. 15 can be omitted.

  Each of the three pilot injection amounts determined in this way has a value obtained by differentiating the amount of heat generated by the entire multistage pilot injection by the crank angle when the glow plug 31 is energized and during cold start under a low outside air temperature condition. It adapts so that it may become more than predetermined fixed value D (refer to Drawing 4). This is also the same as the basic invention.

In step 8, by subtracting the total pilot injection amount (Qpi1 + Qpi2 + Qpi3) from the total fuel injection amount Qtotal, that is, the main injection amount Qmain [mm ³ / st. ] Is calculated.

Qmain = Qtotal− (Qpi1 + Qpi2 + Qpi3) (1)
The total pilot injection amount (Qpi1 + Qpi2 + Qpi3) in the second term on the right side of the equation (1) may be larger than the main injection amount Qmain when the glow plug 31 is energized and during cold start under a low outside air temperature condition.

On the other hand, in step 9 which proceeds when all of the above conditions [1] to [4] are not satisfied, the pilot injection amounts Qpi1, Qpi2, and Qpi3 for the first time, the second time, and the third time are set to zero [mm ³ / st. ] Is set. In step 10, the total fuel injection amount Qtotal is directly used as the main injection amount Qmain [mm ³ / st. ].

  In the present embodiment, the second and third pilot injection amounts Qpi1 and Qpi2 are decreased in step 7 in accordance with the temperature rise of the cooling water from the start, but the present invention is not limited to this. For example, the second and third pilot injection amounts Qpi1, Qpi2 may be reduced in accordance with the temperature rise of engine lubricating oil (oil) from the start.

  In step 11, the calculated main injection amount Qmain and the first, second, and third pilot injection amounts Qpi1, Qpi2, and Qpi3 are output to a register. Alternatively, Qmain, Qpi1, Qpi2, and Qpi3 are stored in the memory.

  Each injection timing (IT1, IT2, IT4, TI5 in FIG. 3) of the first pilot injection, the second pilot injection, the third pilot injection, and the main injection is predetermined. In the flow (not shown), the injection amounts of Qpi1, Qpi2, Qpi3, and Qmain are intermittently supplied into the cylinder at the first pilot injection, the second pilot injection, the third pilot injection, and the main injection. Thus, the fuel injection valve 9 is opened in multiple stages.

  Here, the effect of this embodiment is demonstrated.

  According to the present embodiment, the glow plug 31 that heats the gas in the cylinder at the time of cold start and the fuel injection valve 9 (direct injection fuel injection valve) in which one of the plurality of injection holes faces the glow plug 31 are provided. And a common rail fuel injection device 6 capable of performing at least two pilot injections prior to the main injection, and the second, third, when the glow plug 31 is energized and during a cold start under a low outside air temperature condition. Each pilot injection amount Qpi2, Qpi3 (injection amount of pilot injection executed between the first pilot injection and main injection) is set to the temperature rise of the cooling water from the cold start or the temperature of the engine lubricating oil from the start. Since the amount is reduced according to the rise (engine temperature rise from the cold start) (see steps 3 to 7, FIG. 14 and FIG. 15 in FIG. 12), it is based on the temperature change in the cylinder immediately after the cold start. There were able to execute the appropriate pilot injection. As a result, combustion in the cylinder is improved not only in the initial start period but also in the late start period, so that the operability after the cold start is improved and white smoke can be reduced.

  According to the present embodiment, when the engine controller 21 is energized to the glow plug 31 and is cold-started under a low outside air temperature condition, the value (dQpilot / Since the number of pilot injections and the amount of each pilot injection are determined so that dθ) is equal to or greater than a predetermined value D determined in advance (see steps 3 to 6, 7, and 8 in FIG. 12). It is possible to maintain a high equivalence ratio in the vicinity of the glow plug 31 while preventing a decrease in the temperature of the glow plug 31 at the time of ignition, and during a cold start under a low outside air temperature condition in which combustion in the cylinder becomes unstable Combustion in the cylinder can be stabilized.

  According to the present embodiment, the pilot injection is performed twice or more, which is composed of the initial pilot injection and the remaining pilot injection following this, and the initial pilot injection amount ratio (occupies the total pilot injection amount of the initial pilot injection amount) Ratio) is set to be larger than the remaining pilot injection amount ratio (ratio of the remaining pilot injection amount to the total pilot injection amount), so that fuel vaporization is promoted by the multi-stage pilot injection twice or more, so that the glow plug 31 By increasing the equivalence ratio in the vicinity and increasing the initial pilot injection amount ratio and decreasing the remaining pilot injection amount ratio, it is possible to reduce the heat absorption from the glow plug 31 immediately before the main injection and suppress the decrease in the temperature of the glow plug 31. The equivalence ratio in the vicinity of the glow plug 31 and the glow plug 31 temperature can be kept high, and the ignition can be stabilized.

(Second Embodiment)
The flow of FIG. 16 is for calculating the main injection amount and the three pilot injection amounts of the second embodiment, and once at a timing before a predetermined crank angle from the initial pilot injection timing at the time of the current fuel injection. Just run. In other words, the timing of the predetermined crank angle before the initial pilot injection timing at the time of the current fuel injection is set as the injection amount calculation timing, and each time the injection amount calculation timing of each cylinder is reached without distinguishing each cylinder, the flow of FIG. Execute. The same parts as those in the flow of FIG.

  In the first embodiment, the second and third pilot injection amounts Qpi2 and Qpi3 are reduced in accordance with the temperature rise of the cooling water from the cold start and the temperature rise of the engine lubricating oil from the cold start. Here, the temperature rise of the cooling water and the lubricating oil since the cold start is representative of the temperature rise of the engine since the cold start. On the other hand, in the second embodiment, the pilot injection amounts Qpi2, Qpi3 for the second time and the third time are reduced according to the number of combustion cycles after starting the engine COUNT. This post-starting combustion cycle number COUNT is also representative of the temperature rise of the engine since the cold start.

  The difference from the first embodiment will be mainly described. In step 21, the engine rotational speed Ne is compared with zero. When the engine speed Ne is zero, it is determined that the engine has not been started, and the routine proceeds to step 22 where the number of combustion cycles after starting the engine is set to COUNT = 0 for initialization.

  If the engine speed Ne is not zero in step 21, it is determined that the engine has started, and the process proceeds to step 23, where the number of combustion cycles after starting the engine COUNT is incremented, that is, the number of combustion cycles after starting COUNT [-] according to the following equation. Is calculated.

COUNT = COUNTz + 1 (2)
However, COUNTz: the previous value of COUNT,
Since Ne ≠ 0 continues in step 21 after starting is started, the process proceeds to step 23 and the operation in step 23 is repeated. This gradually increases the number of combustion cycles COUNT after starting the engine.

When all the conditions [1] to [4] are satisfied, the process proceeds to step 24. In step 24, the first, second, and third pilot injection amounts Qpi1, Qpi2, Qpi3 [are searched by searching the tables having the contents shown in FIGS. 17, 18, and 19 from the number of combustion cycles after starting the engine COUNT. mm ³ / st. ] Is calculated. First, as shown in FIGS. 18 and 19, the second and third pilot injection amounts Qpi2 and Qpi3 are values that increase as the number of combustion cycles after starting the engine COUNT decreases. This means that the smaller the number of combustion cycles after starting the engine COUNT, the lower the coolant temperature Tw. The lower the temperature becomes, the less the fuel spray is vaporized, so that more fuel is injected. This is because it is necessary to increase the probability of touching. 14 and 15, the second and third times in the post-startup combustion cycle number region from the predetermined post-startup combustion cycle number COUNT1 to the post-startup warm-up completion determination combustion cycle number COUNTth corresponding to the warm-up completion determination temperature. Each pilot injection amount is a constant value.

  Here, the operation of step 24 in FIG. 16 is repeated until the cooling water temperature Tw becomes equal to or higher than the warm-up completion determination temperature Twth. The cooling water temperature Tw coincides with the outside air temperature before the cold start, and after the start, the change in the combustion state in the cylinder from the start is received, and gradually increases toward the warm-up completion determination temperature Twth. The number of combustion cycles COUNT after starting the engine increases as the temperature of the cooling water rises. For this reason, in FIGS. 18 and 19, the number of combustion cycles after engine startup COUNT shifts in the direction of the arrow after startup, and accordingly, the second and third pilot injection amounts Qpi 2 and Qpi 3 decrease accordingly. It will be followed.

  Next, the characteristics of the initial pilot injection amount Qpi1 may be the same as in the basic invention. For example, the first pilot injection amount Qpi1 is the same as the characteristics of the second and third pilot injection amounts Qpi2 and Qpi3 as shown in FIG. Note that the initial pilot injection amount Qpi1 may be a constant value regardless of the number of combustion cycles after starting the engine COUNT, as indicated by the one-dot chain line.

  Further, at the same post-startup combustion cycle number COUNT, the initial pilot injection amount Qpi1 is set to be larger than the second and third pilot injection amounts Qpi2 and Qpi3. In other words, the ratio of the initial pilot injection amount Qpi1 to the total pilot injection amount is set larger than the ratio of the remaining pilot injection amounts Qpi2 and Qpi3 to the total pilot injection amount. This is also the same as the basic invention. In the second embodiment, the second pilot injection amount Qpi2 is made equal to the third pilot injection amount Qpi3. At this time, since the calculated second pilot injection amount Qpi2 may be used as it is as the third pilot injection amount Qpi3, the characteristics of FIG. 19 can be omitted.

  Each of the three pilot injection amounts determined in this way has a value obtained by differentiating the amount of heat generated by the entire multistage pilot injection by the crank angle when the glow plug 31 is energized and during cold start under a low outside air temperature condition. It adapts so that it may become more than predetermined fixed value D (refer to Drawing 4). This is also the same as the basic invention.

  In the second embodiment, the number of combustion cycles COUNT after starting the engine is measured, but this is not a limitation. For example, the elapsed time after starting the engine is initially set to zero at step 22 in FIG. 16, and the elapsed time after starting the engine is calculated at step 23 by the following equation.

Time = Timez + ΔT (3)
However, Timez: the previous value of ime,
ΔT: execution time interval of the routine of FIG.
Then, by searching a table having the same contents as those in FIGS. 17, 18, and 19 from the post-start elapsed time Time in step 24 of FIG. 16, the first, second, and third pilot injection amounts Qpi1, Qpi2, Qpi3 may be calculated.

  According to the second embodiment, the glow plug 31 that heats the gas in the cylinder during cold start, and the fuel injection valve 9 (direct injection fuel injection valve) in which one of the plurality of injection holes faces the glow plug 31. And a common rail fuel injection device 6 capable of performing pilot injection at least twice prior to main injection, and the second time at the time of energizing the glow plug 31 and cold starting at low outside air temperature conditions, The third pilot injection amount Qpi2, Qpi3 (injection amount of pilot injection executed between the first pilot injection and the main injection) is set to the number of combustion cycles COUNT after engine startup and the elapsed time Time after engine startup (cold). (Corresponding to the engine temperature rise from the start) (see steps 3 to 6, 24, FIG. 18 and FIG. 19 in FIG. 16). Produce the effect. That is, appropriate pilot injection based on the temperature change in the cylinder immediately after the cold start can be executed, thereby improving the combustion in the cylinder not only in the initial start period but also in the late start period. The drivability after startup is good and white smoke can be reduced.

(Third embodiment)
The flow of FIG. 20 is for calculating the main injection amount and the three pilot injection amounts of the third embodiment, and is once at a timing before a predetermined crank angle from the initial pilot injection timing at the time of the current fuel injection. Just run. In other words, the timing of the predetermined crank angle before the initial pilot injection timing at the time of the current fuel injection is set as the injection amount calculation timing, and each time the injection amount calculation timing of each cylinder is reached without distinguishing each cylinder, the flow of FIG. Execute. The same parts as those in the flow of FIG. 16 of the second embodiment are denoted by the same reference numerals.

  In the second embodiment, the second and third pilot injection amounts Qpi2 and Qpi3 are reduced according to the number of combustion cycles after starting the engine COUNT and the time after starting the engine Time. On the other hand, in the third embodiment, the second and third pilot injection amounts Qpi2 and Qpi3 are reduced according to the integrated fuel injection amount IntQ after the engine is started. The integrated fuel amount IntQ after start-up is also representative of the engine temperature rise from the cold start.

  The difference from the second embodiment will be mainly described. In step 31, it is determined whether or not the first cylinder discrimination signal is input. When the first cylinder discrimination signal is inputted, it is judged that the engine has just started, and the routine proceeds to step 32, where the integrated fuel injection amount IntQ = 0 after the engine is started for initialization.

In step 31, it is determined that the first cylinder discrimination signal is not inputted, that is, the second and subsequent cylinder discrimination is started. At this time, the routine proceeds to step 33, where Qtotalz which is the previous value of the total fuel injection amount is added to IntQz which is the previous value of the accumulated fuel injection amount after starting, that is, the accumulated fuel injection amount IntQ [ mm ³ / st. ] Is calculated.

IntQ = IntQz + Qtotalz (4)
Where IntQz: the previous value of IntQ,
Qtotalz: the previous value of Qtotal,
After the input of the first cylinder determination signal, it is determined not to be immediately after the input of the first cylinder determination signal after step 31. Therefore, the process proceeds to step 33, and the operation of step 33 is repeated. As a result, the integrated fuel injection amount IntQ gradually increases after the engine is started.

When all the conditions [1] to [4] are satisfied, the process proceeds to step 34. In step 34, the first, second, and third pilot injection amounts Qpi1, Qpi2, Qpi3 are searched by searching a table having the contents shown in FIGS. 21, 22, and 23 from the accumulated fuel injection amount IntQ after starting the engine. [Mm ³ / st. ] Is calculated. First, as shown in FIGS. 22 and 23, the second and third pilot injection amounts Qpi2 and Qpi3 are values that increase as the integrated fuel injection amount IntQ after the engine starts decreases. This means that the smaller the integrated fuel injection amount IntQ after starting the engine, the lower the coolant temperature Tw, and the lower the temperature becomes, the more difficult the fuel spray is to vaporize. This is because the probability of touching 31 needs to be increased. 22 and 23, the second time in the post-startup integrated fuel injection amount region from the predetermined post-startup integrated fuel injection amount IntQ1 to the warmup completion determination post-startup integrated fuel injection amount IntQth corresponding to the warmup completion determination temperature. The third pilot injection amount Q is a constant value.

  Here, the operation of step 34 in FIG. 20 is repeated until the cooling water temperature Tw becomes equal to or higher than the warm-up completion determination temperature Twth. The cooling water temperature Tw coincides with the outside air temperature before the cold start, and after the start, the change in the combustion state in the cylinder from the start is received, and gradually increases toward the warm-up completion determination temperature Twth. The integrated fuel injection amount IntQ increases after the engine starts in accordance with the temperature rise of the cooling water. For this reason, in FIGS. 18 and 19, since the integrated fuel injection amount IntQ after the engine starts is shifted in the direction of the arrow after the start, the second and third pilot injection amounts Qpi2 and Qpi3 decrease accordingly. It will be done.

  Next, the characteristics of the initial pilot injection amount Qpi1 may be the same as in the basic invention. For example, the first pilot injection amount Qpi1 is the same as the characteristics of the second and third pilot injection amounts Qpi2 and Qpi3 as shown in FIG. Note that the initial pilot injection amount Qpi1 may be a constant value regardless of the integrated fuel injection amount IntQ after the engine is started, as indicated by a one-dot chain line.

  Further, at the same post-startup integrated fuel injection amount IntQ, the initial pilot injection amount Qpi1 is set to be larger than the second and third pilot injection amounts Qpi2 and Qpi3. In other words, the ratio of the initial pilot injection amount Qpi1 to the total pilot injection amount is set larger than the ratio of the remaining pilot injection amounts Qpi2 and Qpi3 to the total pilot injection amount. This is also the same as the basic invention. In the third embodiment, the second pilot injection amount Qpi2 is made equal to the third pilot injection amount Qpi3. At this time, the calculated second pilot injection amount Qpi2 may be used as it is as the third pilot injection amount Qpi3, so that the characteristics of FIG. 23 can be omitted.

  Each of the three pilot injection amounts determined in this way has a value obtained by differentiating the amount of heat generated by the entire multistage pilot injection by the crank angle when the glow plug 31 is energized and during cold start under a low outside air temperature condition. It adapts so that it may become more than predetermined fixed value D (refer to Drawing 4). This is also the same as the basic invention.

  According to the third embodiment, the glow plug 31 that heats the gas in the cylinder at the time of cold start, and the fuel injection valve 9 (direct injection fuel injection valve) in which one of the plurality of injection holes faces the glow plug 31. And a common rail fuel injection device 6 capable of performing pilot injection at least twice prior to main injection, and the second time at the time of energizing the glow plug 31 and cold starting at low outside air temperature conditions, The third pilot injection amount Qpi2, Qpi3 (the injection amount of the pilot injection executed between the first pilot injection and the main injection) is the integrated fuel injection amount IntQ (the engine temperature increase from the cold start) (Refer to steps 3 to 6, 34, FIG. 22 and FIG. 23 in FIG. 20), the same effect as in the second embodiment is produced. That is, appropriate pilot injection based on the temperature change in the cylinder immediately after the cold start can be executed, thereby improving the combustion in the cylinder not only in the initial start period but also in the late start period. The drivability after startup is good and white smoke can be reduced.

1 Engine 6 Common Rail Fuel Injection Device 9 Fuel Injection Valve (Direct Injection Fuel Injection Valve)
21 Engine controller 23 Crank angle sensor (angular velocity detection means)
31 Glow plug 33 Water temperature sensor

Claims (8)

A glow plug that heats the gas in the cylinder during cold start;
A common rail fuel injection device having one direct injection fuel injection valve directed to the glow plug and capable of performing at least two pilot injections prior to the main injection;
When the glow plug is energized and during a cold start under a low outside air temperature condition, between the first pilot injection and the main injection, the rotational fluctuation increases as the engine temperature rises from the cold start. A control device for a diesel engine, wherein an injection amount of pilot injection to be executed is reduced to a side to suppress the rotational fluctuation in accordance with an increase in engine temperature from the cold start.   The diesel engine control device according to claim 1, wherein the temperature increase of the engine is a temperature increase of cooling water of the engine.   The diesel engine control device according to claim 1, wherein the temperature increase of the engine is a temperature increase of lubricating oil of the engine.   The diesel engine control device according to claim 1, wherein the temperature rise of the engine is an elapsed time after starting of the engine.   The diesel engine control device according to claim 1, wherein the temperature increase of the engine is an accumulated fuel amount after the engine is started.   When the glow plug is energized and during cold start under a low outside air temperature condition, the plurality of pilots is set such that a value obtained by differentiating the heat generation amount of the plurality of pilot injections by a crank angle is equal to or greater than a predetermined value determined in advance. The diesel engine control device according to any one of claims 1 to 5, wherein the number of pilot injections and the respective injection amounts of the pilot injections when performing the injection are determined.   The pilot injection is performed at least twice including the initial pilot injection and the subsequent pilot injection, and the ratio of the initial pilot injection amount to the total pilot injection amount is the total of the remaining pilot injection amounts. 7. The diesel engine control device according to claim 6, wherein the control device is set to be larger than a ratio of the pilot injection amount. A glow plug that heats the gas in the cylinder during cold start;
A common rail fuel injection device having one direct injection fuel injection valve directed to the glow plug and capable of performing at least two pilot injections prior to the main injection;
When the glow plug is energized and during a cold start under a low outside air temperature condition, between the first pilot injection and the main injection, the rotational fluctuation increases as the engine temperature rises from the cold start. A control method for a diesel engine, characterized in that an injection amount of pilot injection to be executed is reduced to a side to suppress the rotation fluctuation in accordance with an increase in engine temperature since the cold start.