JP4403641B2 - Fuel injection system for diesel engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a fuel injection device for a diesel engine provided with a fuel injection valve that directly injects fuel into a combustion chamber in a cylinder.
[0002]
[Prior art]
  In this type of diesel engine, fuel required for one combustion cycle is collectively injected (hereinafter referred to as collective injection) near the top dead center of the compression stroke, and this collective injection is performed as necessary. Pilot injection for injecting a small amount of fuel is performed before this. On the other hand, there is also known split injection in which fuel is not injected in a lump but is divided into a plurality of times near the top dead center of the compression stroke.
[0003]
  For example, Japanese Patent Application Laid-Open No. 9-209866 describes that split injection is started from the top dead center of the compression stroke, and that the amount of each injection is increased as the number of subsequent injections increases. It is intended to control the heat generation rate in the combustion chamber extensively and appropriately. In Japanese Patent Laid-Open No. 10-128204, pre-injection for injecting a small amount of fuel causes ignition in the combustion chamber, and subsequent main injection is divided into a plurality of times, soot and NOx (nitrogen). It is described that the generation amount of (oxide) is suppressed.
[0004]
  Japanese Patent Laid-Open No. 10-141124 discloses preliminary injection for injecting fuel at the beginning of the intake stroke, main injection for injecting fuel near the compression stroke top dead center, and pilot injection before main injection. , Partial lean premixed compression ignition combustion to suppress NOx generation, reduce black smoke emissions, improve fuel economy, startability only as main injection when engine starts in cold weather And suppressing excessive generation of white smoke.
[0005]
[Problems to be solved by the invention]
  As described above, in the diesel engine, when appropriate divided injection is performed, it is advantageous for controlling the heat generation rate in the combustion chamber and reducing smoke emission and NOx. However, if split injection is performed when the in-cylinder temperature is low, for example, when the engine is started, combustion becomes unstable, leading to deterioration in startability and emission. This is because when fuel is divided and injected, it is necessary to provide a predetermined injection stop time (a period from when the fuel injection valve is closed to when it is opened next). This is because the in-cylinder temperature is considerably lowered.
[0006]
  In addition, pilot injection for the purpose of reducing combustion noise during low-speed / low-load operation such as idle operation or pre-injection for injecting fuel from the intake stroke to the first half of the compression stroke as premixed compression ignition combustion may be performed. is there. At that time, in order to improve the exhaust gas purification efficiency by the catalyst, the injection start timing may be retarded in order to increase the exhaust gas temperature. Even in this case, if the fuel split injection is executed, the fuel injection end time is considerable. The flammability deteriorates.
[0007]
  The present invention is intended to solve such problems.
[0008]
[Means for Solving the Problems]
  For this purpose, the present invention appropriately suppresses or prohibits split fuel injection.
[0009]
  That is, the present invention includes a fuel injection valve disposed so as to face an in-cylinder combustion chamber of an engine,
  Requested output detecting means for detecting the requested output of the engine;
  An injection amount determining means for determining a fuel injection amount according to a detection result by the request output detecting means;,
Injection timing setting means for setting the fuel injection start timing based on the engine speed and the target torque;With
  A diesel engine that injects fuel of an injection amount determined by the injection amount determination means into a plurality of times by the fuel injection valve in the vicinity of the top dead center of the compression stroke of the cylinder and so as to continue combustion by fuel injection. In the fuel injection device of
  It is estimated that the in-cylinder temperature of the engine is in a low temperature state before the engine complete explosion and before a predetermined time elapses after the complete explosion, and after a predetermined time has elapsed since the complete explosion. Is a temperature state estimating means for estimating that the in-cylinder temperature is in a high temperature state,
  When the temperature state estimating means estimates that the engine is in the low temperature state with respect to the in-cylinder temperature, it is estimated that the engine is in the high temperature state (provided that the engine water temperature is higher than a predetermined value and the engine is So that the fuel injection end time is earlier than (except when the engine is running at high speed or high speed)Without changing the fuel injection amount determined by the injection amount determining means and the fuel injection start time set by the injection timing setting means,It is characterized by comprising an injection form changing means for changing the form of the split fuel injection or injecting the fuel all at once without dividing the fuel.
[0010]
  Therefore, when the in-cylinder temperature of the engine is high and combustibility is good, split injection is executed to improve emissions, improve fuel consumption, increase exhaust pressure (improve supercharging), and increase exhaust gas temperature. When the engine in-cylinder temperature is low while obtaining the desired effect, the fuel injection end timing is advanced by changing the split injection mode or by prohibiting split injection, which is advantageous for ensuring combustion stability. It is possible to avoid the deterioration of the emission property such as the occurrence of. The injection end time should not exceed, for example, 35 ° CA after the compression stroke top dead center during low engine load operation, and should not exceed 45 ° CA after the compression stroke top dead center during high engine load operation.Yes.
[0011]
the aboveThe change of the split injection mode can be performed by reducing the number of splits or by shortening the injection pause time from when the fuel injection valve is closed to when it is next opened.
[0012]
【The invention's effect】
  As described above, according to the present invention, when the in-cylinder temperature of the engine is lowWithout changing the fuel injection amount determined by the injection amount determining means and the fuel injection start time set by the injection timing setting means,By changing the fuel split injection mode or prohibiting split injection, the fuel injection end time is not delayed.In normal times, split injection is performed to improve emissions, improve fuel consumption, and reduce exhaust pressure. When priority should be given to ensuring combustion stability while obtaining the desired effects of split injection, such as an increase (increase in supercharging) and an increase in exhaust gas temperature, the end of fuel injection should be advanced to deteriorate combustibility. This is advantageous for improving the emission performance such as reducing the generation of soot.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0014]
  FIG. 1 shows an overall configuration of a fuel injection device A for a water-cooled diesel engine according to an embodiment of the present invention. Reference numeral 1 denotes an engine body of a multi-cylinder diesel engine mounted on a vehicle. The engine body 1 has a plurality of cylinders 2 (only one is shown), and a piston 3 is fitted in each cylinder 2 so as to be reciprocally movable. A combustion chamber 4 is formed. In addition, an injector (fuel injection valve) 5 is disposed at a substantially central portion of the upper surface of the combustion chamber 4 with the injection hole at the tip facing the combustion chamber 4, and the injection hole is provided at a predetermined injection timing for each cylinder. Is opened and closed to inject fuel directly into the combustion chamber 4.
[0015]
  Each injector 5 is connected to a common common rail (pressure accumulating chamber) 6 for storing high-pressure fuel, and a high-pressure supply pump 8 driven by a crankshaft 7 is connected to the common rail 6. The high-pressure supply pump 8 operates so that the fuel pressure in the common rail 6 detected by the pressure sensor 6a is maintained at a predetermined value or more. Further, a crank angle sensor 9 for detecting the rotation angle of the crankshaft 7 is provided. The crank angle sensor 9 is provided with a plate to be detected (not shown) provided at the end of the crankshaft 7 and an outer periphery thereof. The electromagnetic pickup is arranged so as to be opposed to each other, and the electromagnetic pickup outputs a pulse signal corresponding to the passage of protrusions formed at predetermined angles on the entire outer periphery of the plate to be detected. ing.
[0016]
  Reference numeral 10 denotes an intake passage for supplying intake air (air) filtered by an air cleaner (not shown) to the combustion chamber 4 of the engine body 1. A surge tank (not shown) is provided at the downstream end of the intake passage 10. Each passage branched from the surge tank is connected to the combustion chamber 4 of each cylinder 2 by an intake port. Further, the surge tank is provided with an intake pressure sensor 10a for detecting a supercharging pressure supplied to each cylinder 2. In the intake passage 10, in order from the upstream side to the downstream side, a hot film type air flow sensor 11 that detects an intake air flow rate sucked into the engine body 1 and a blower 12 that is driven by a turbine 21 to be described later and compresses the intake air. An intercooler 13 that cools the intake air compressed by the blower 12 and an intake throttle valve (intake air amount adjusting means) 14 that restricts the cross-sectional area of the intake passage 10 are provided. The intake throttle valve 14 is a butterfly valve provided with a notch so that intake air can flow even in a fully closed state. Like the EGR valve 24 described later, the magnitude of the negative pressure acting on the diaphragm 15 is negative. The opening degree of the valve is controlled by being adjusted by the control electromagnetic valve 16. The intake throttle valve 14 is provided with a sensor (not shown) for detecting the opening degree.
[0017]
  An exhaust passage 20 discharges exhaust gas from the combustion chamber 4 of each cylinder 2, and is connected to the combustion chamber 4 of each cylinder 2 via an exhaust manifold. In this exhaust passage 20, in order from the upstream side to the downstream side, a linear O 2 sensor 17 that detects the oxygen concentration in the exhaust gas, a turbine 21 that is rotated by the exhaust flow, HC, CO in the exhaust gas, and A catalytic converter 22 capable of purifying NOx is provided.
[0018]
  An exhaust gas recirculation passage (hereinafter referred to as an EGR passage) 23 for recirculating a part of the exhaust gas to the intake side branches from a portion of the exhaust passage 20 upstream of the turbine 21, and the downstream end of the EGR passage 23 is an intake air. The intake passage 10 is connected to the downstream side of the throttle valve 14. An exhaust gas recirculation amount adjusting valve (intake air amount adjusting means: hereinafter referred to as an EGR valve) 24 whose opening degree can be adjusted is disposed near the downstream end in the middle of the EGR passage 23, and a part of the exhaust gas in the exhaust passage 20. Is recirculated to the intake passage 10 while the flow rate is adjusted by the EGR valve 24.
[0019]
  The EGR valve 24 is of a negative pressure responsive type, and a negative pressure passage 27 is connected to a negative pressure chamber of the valve box. The negative pressure passage 27 is connected to a vacuum pump (negative pressure source) 29 via a negative pressure control electromagnetic valve 28. The electromagnetic valve 28 is connected to a negative pressure passage by a control signal (current) from an ECU 35 described later. The EGR valve drive negative pressure in the negative pressure chamber is adjusted by communicating / blocking 27, whereby the opening degree of the EGR passage 23 is adjusted linearly.
[0020]
  The turbocharger 25 is a VGT (variable geometry turbo), to which a diaphragm 30 is attached, and a negative pressure acting on the diaphragm 30 is adjusted by an electromagnetic valve 31 for negative pressure control. Thus, the cross-sectional area of the exhaust gas passage is adjusted.
[0021]
  Each of the injectors 5, the high pressure supply pump 8, the intake throttle valve 14, the EGR valve 24, the turbocharger 25, and the like are configured to operate according to a control signal from a control unit (Engine Control Unit: hereinafter referred to as ECU) 35. Yes. On the other hand, the ECU 35 receives an output signal from the pressure sensor 6a, an output signal from the crank angle sensor 9, an output signal from the pressure sensor 10a, an output signal from the air flow sensor 11, and an output from the O2 sensor 17. An output signal, an output signal from the temperature sensor 18, an output signal from the lift sensor 26 of the EGR valve 24, and an accelerator opening sensor that detects an operation amount (accelerator opening) of an accelerator pedal (not shown) by the driver of the vehicle. At least an output signal from 32 and an output signal from a sensor (not shown) for detecting the engine water temperature are input.
[0022]
  The fuel injection amount (fuel supply amount) and fuel injection timing (ignition timing) by the injector 5 are controlled in accordance with the operating state of the engine body 1, and the common rail pressure, that is, fuel injection by the operation of the high-pressure supply pump 8 is controlled. In addition to this, the control of the exhaust gas recirculation amount (intake air amount) by the operation of the EGR valve 24 and the operation control (VGT control) of the turbocharger 25 are performed. Yes.
[0023]
  (Fuel injection control)
  In the ECU 35, a target torque map experimentally determined and recorded for the optimum value of the target torque with respect to changes in the accelerator opening (engine load) and the engine speed, and in response to changes in the target torque and the speed. A fuel injection amount map in which the optimum fuel injection amount Q determined experimentally is recorded electronically in a memory. Normally, a target torque is obtained based on the accelerator opening based on the output signal from the accelerator opening sensor 32 and the engine speed based on the output signal from the crank angle sensor 9, and the fuel is calculated based on the target torque and the engine speed. The injection amount Q is obtained, and the excitation time (valve opening time) of each injector 5 is determined based on the fuel injection amount Q and the common rail pressure detected by the pressure sensor 6a. The fuel injection amount obtained as described above may be corrected in accordance with the engine water temperature, the atmospheric pressure, etc., and the corrected fuel injection amount may be used as the fuel injection amount Q.
[0024]
  By the basic fuel injection control as described above, an amount of fuel corresponding to the target torque of the engine 1 (required output to the engine 1) is supplied, and the engine 1 has a relatively lean average air-fuel ratio in the combustion chamber 4 ( It is operated in a state of A / F ≧ 18). The accelerator opening sensor 32 and the crank angle sensor 9 correspond to request output detection means for detecting a request output to the engine 1.
[0025]
  A feature of the present invention is that the fuel injection amount Q determined based on the detection result by the required output detection means is set to the vicinity of the top dead center of the compression stroke of the cylinder by the injector 5 and combustion by fuel injection is continued. The injection is divided into a plurality of times, and the combustion stability is ensured so that the end timing of the main injection is not delayed by changing the divided injection mode according to the engine operating state or prohibiting the divided injection. This is to improve emissions.
[0026]
  -About split injection-
  That is, depending on the operating state of the engine, as shown in FIG. 2 (a), the main injection fuel is injected in the vicinity of the compression top dead center (hereinafter referred to as collective injection), or in FIG. As shown in the figure, either divided into two injections (referred to as two-split injection) or divided into three injections (referred to as three-split injection) as shown in FIG. . Further, when the fuel is injected in two or three times in such a manner, the fuel injection performance, the exhaust characteristics, etc. of the engine 1 are optimized by changing the injection stop time Δt during that time. The combustion state is changed. In addition, pilot injection (early injection) is performed during idle operation or low-speed operation of the engine, and a retard (retard) of the main injection start timing is performed.
[0027]
  2A to 2C, the actual excitation time (valve opening time) of the injector 5 is not only the fuel injection amount but also the common rail detected by the pressure sensor 6a. Determined by taking pressure into account.
[0028]
  Here, the combustion state when the main injection is divided will be described. When fuel is injected by the injector 5 in the vicinity of the compression top dead center of the cylinder 2, the fuel injected from the injection hole of the injector 5 is conical as a whole. While spreading into the combustion chamber 4 while forming a spray of shape, it splits by friction with air into fine oil droplets (fuel atomization), fuel evaporates from the surface of these oil droplets, and fuel vapor (Fuel vaporization atomization). At this time, since the air in the combustion chamber 4 is in a very high pressure and high viscosity state, as shown in FIG. Of these, the fuel oil droplets ejected earlier catch up with the subsequent fuel oil droplets and recombine, which may hinder atomization of the fuel and thus vaporization and atomization.
[0029]
  On the other hand, as shown in FIGS. 2 (b) and 2 (c), if the fuel is divided and injected several times, the fuel oil droplets ejected by opening the injector 5 will The fuel oil droplets ejected by opening the valve are less likely to catch up, and it can be generally avoided that fuel atomization is hindered due to recombination of the oil droplets. It is also possible to further increase the fuel injection pressure to further promote atomization of the fuel, and in this way, the distribution of fuel spray in the combustion chamber can be made more uniform and the air utilization rate can be further improved. Can be increased. The change in the mixed state of the fuel spray and air due to such divided injection is caused by various parameters such as fuel injection amount, injection timing, injection rate, fuel pressure, number of divided injections, injection pause time, and their interrelationships. It is also considered that the fuel consumption performance and exhaust temperature of the engine 1 or the concentration of gas components such as CO, HC and NOx in the exhaust gas change due to the change in the combustion state.
[0030]
  A four-cylinder diesel engine (displacement of about 2000 cc) equipped with a turbocharger similar to that of this embodiment is operated at a relatively low load and a low rotation state (about 1500 rpm). For each of the three divided injections, the injection pause time Δt of the injector 5 is appropriately changed in the range of 350 to 900 microseconds (μs), and the crank angle at the end of injection, the exhaust gas temperature, and the exhaust pressure that change accordingly. FIGS. 3 to 10 show examples of the experimental results obtained by measuring the relationship between the fuel efficiency, the smoke amount, and the like.
[0031]
  FIG. 3 shows the test results for the exhaust gas temperature. According to the figure, the exhaust gas temperature is higher in the 2-split injection than in the batch injection, and the exhaust gas temperature is higher in the 3-split injection than in the 2-split injection. In the figure, the two-split injection and the three-split injection measure the exhaust gas temperature while appropriately changing the injection pause time Δt of the injector 5 in the range of 350 to 900 microseconds (μs). If so, it can be seen that the exhaust gas temperature becomes higher when the injection pause time Δt is extended. In the two-split injection, the exhaust gas temperature is plotted when Δt = 350, 400, 700, and 900 μs. In the three-split injection, the exhaust gas temperature when Δt = 400, 550, 700, and 900 μs is plotted. Each is plotted.
[0032]
  FIG. 4 shows the test results for the exhaust pressure. According to FIG. 4, it can be seen that the exhaust pressure increases as the exhaust gas temperature increases as the number of fuel injection divisions and the injection pause time Δt are increased. In other words, if the fuel is divided and injected, the end time of combustion will be delayed by that amount, so the exhaust energy will naturally increase, and even with the same amount of fuel, the combustion energy itself will be increased by improving the combustibility. Since it increases, both the exhaust gas temperature and the exhaust pressure increase as shown in the test results. And if the exhaust energy increases in this way, the supercharging capability of the turbocharger 25 also improves, so that the supercharging pressure (boost pressure) can be increased as shown in FIG.
[0033]
  Similarly, FIG. 6 shows a test result obtained by measuring the change in the fuel consumption rate. The fuel injection rate is improved in the two-part injection rather than the batch injection. In the case of the three-part injection, the injector It can be seen that when the injection stop time Δt of 5 is short, the fuel consumption rate is slightly improved, while the fuel consumption rate deteriorates as the injection stop time Δt becomes longer. This is because the combustibility is improved and the mechanical efficiency is improved by the divided injection, and at the same time, the thermal efficiency is lowered. From this, it can be said that it is preferable not to delay the end time of the injection.
[0034]
  Furthermore, similarly, the measurement results of the emission amounts of smoke, NOx, CO, and HC, which are harmful components in the exhaust gas, are shown in FIGS. That is, according to FIG. 7, in both the two-split and three-split injections, the smoke amount can be reduced when the injection pause time Δt of the injector 5 is short, while the smoke amount as the injection pause time Δt becomes longer. It can be seen that increases. Further, in the case of NOx shown in FIG. 8, it can be seen that, on the contrary, the generation of NOx can be reduced when the injection pause time Δt of the injector 5 is longer in both of the two-split and three-split injections. Furthermore, as shown in FIG. 9 and FIG. 10 respectively, the same tendency as smoke is observed in the CO and HC emissions.
[0035]
  Further, regarding the number of divisions, if the number of divisions is set to 3 as shown in the respective drawings, the exhaust gas temperature, the exhaust pressure, and the supercharging pressure increase, and the NOx amount decreases. On the other hand, if the injection pause time Δt of the injector 5 is shortened, the amount of smoke and CO emission does not increase greatly even if the number of divisions is increased, but may rather decrease. In addition, with regard to HC, the emission amount is reduced as compared with the collective injection by using the two-part or three-part injection.
[0036]
  A specific fuel injection control processing procedure will be described below.
[0037]
  -Control example 1-
  FIG. 11 is a flowchart relating to the control example 1. This control is executed in synchronization with the crank angle signal for each cylinder.
[0038]
  In Step A1 after the start, data such as a crank angle signal, an airflow sensor output, and an accelerator opening are read. In the subsequent step A2, a target torque is set by referring to the map based on the accelerator opening and the engine speed, and the fuel injection amount Q is referred to based on the engine speed, the target torque and the intake air amount. To decide. This step A2 constitutes an injection amount determining means.
[0039]
  In subsequent step A3, the basic injection timing It is set with reference to the map based on the engine speed and the target torque. The basic injection timing It corresponds to the start timing of main injection (first fuel injection in the case of split injection), and is set before the top dead center of the compression stroke. In addition, since the ignition delay time of fuel spray differs depending on the engine water temperature and the engine speed, the basic injection timing It is earlier as the engine water temperature is lower and the engine speed is higher. Is set to be.
[0040]
  In the next step A4, it is determined based on the crank angle signal whether or not the engine has been started, that is, whether or not the complete explosion has occurred. If the engine has been started (before the complete explosion), the in-cylinder temperature of the engine is lowered. When it is determined that there is a fuel injection, the process proceeds to step A5, and fuel injection is performed at the fuel injection amount Q determined in step A2 and the injection timing It set in step A3. That is, since the in-cylinder temperature of the engine is low, the split injection is prohibited, and the engine is reliably started by improving the combustion stability.
[0041]
  When the complete explosion has occurred, the routine proceeds to step A6, where it is determined whether or not the engine is idling based on the accelerator opening. That is, the engine is determined to be in acceleration operation when the rate of increase in accelerator opening is greater than or equal to a predetermined value. If it is at the time of acceleration operation, it will progress to step A7 and will set injection into 3 division | segmentation injection (step A5). That is, the fuel injection amount Q is equally divided and given as the first injection amount Q1, the second injection amount Q2, and the third injection amount Q3, and the injection pause time Δt is optimal from a relatively long range of 500 to 1000 μs. Give value. The reason why the injection pause time Δt is increased is that this can increase the exhaust pressure (see FIG. 4), which is advantageous for acceleration.
[0042]
  When the engine is not in acceleration operation, the routine proceeds to step A8, where it is determined whether or not the engine has passed a predetermined time since the complete explosion. In other words, the engine determines whether or not the in-cylinder temperature is in an operating state. When the predetermined time has elapsed, it is determined that the in-cylinder temperature is high.
[0043]
  When it is determined in step A8 that the predetermined time has not passed (the in-cylinder temperature is in a low temperature state), the process proceeds to step A5, the fuel injection amount Q determined in step A2, and the injection timing set in step A3 A batch injection of fuel is executed at It. That is, when split injection is performed, fuel injection end timing is delayed and combustibility is deteriorated, so split injection is prohibited.
[0044]
  When it is determined in step A8 that the predetermined time has elapsed, the process proceeds to step A9, where it is determined whether or not the engine coolant temperature is low (when the coolant temperature is 70 ° C. or lower or 80 ° C. or lower). When the cooling water temperature is low, the process proceeds to step A10 to determine whether or not the idling operation is being performed. If the idling operation is being performed, the process proceeds to step A11 to set the injection amount and the injection timing to perform pilot injection. To do. Further, the routine proceeds to step A12, where the main injection start timing It is retarded by the crank angle Ic1, and then the routine proceeds to step A5 where pilot injection and main injection (collective injection) are executed. Even when it is not during idling, when it is determined in step A13 that the engine speed is low, similar pilot injection and collective injection are performed.
[0045]
  Pilot injection is performed to reduce engine combustion noise during idling or low speed operation. In addition, when pilot injection is performed, since the combustibility can be obtained even if the injection start timing is somewhat late, the injection start timing is retarded, thereby delaying the injection end timing and raising the exhaust gas temperature, thereby The activity of this is intended. However, when the cooling water temperature is low, when split injection is performed, the injection end timing becomes too late, the combustibility deteriorates and the generation amount of soot and HC increases. It is a jet.
[0046]
  When it is determined in step A13 that the engine is not operating at a low speed, that is, in an intermediate or high speed operation state, the process proceeds to step A14 where the three-part injection is set and the injection is executed (step A5). That is, the fuel injection amount Q is equally divided and given as the first, second, and third injection amounts Q1, Q2, and Q3, and the optimum value is given from the range of 50 to 700 μs as the injection pause time Δt. In this case, since the retard of the injection start timing is not performed, split injection is employed.
[0047]
  If it is determined in step A9 that the cooling water temperature is high, the process proceeds to step A15 to determine whether or not the idling operation is being performed. If the idling operation is being performed, the process proceeds to step A16 and pilot injection is performed. The injection amount and injection timing are set as much as possible. Further, the routine proceeds to step A17, where the start timing It of the main injection is retarded by the crank angle Ic2, and the routine proceeds to step A18, where each injection quantity Q1, Q2 and injection pause time Δt (from the range of 50 to 500 μs) is executed. An appropriate Δt) is set, and the routine proceeds to step A5 where pilot injection and two-part injection are executed. Further, even when it is not during idling, when it is determined in step A19 that the engine speed is low, similar pilot injection and two-split injection are executed.
[0048]
  The reason why the split injection is performed in step A18 while the split injection is performed in step A14 is that the main injection start timing It is retarded. That is, since the injection end timing is too late when the three-split injection is used, a two-split injection with a small number of splits is adopted from the viewpoint of ensuring combustion stability and improving the emission performance. Note that step A18 may shorten the injection pause time Δt as three-split injection.
[0049]
  The pilot injection setting in step A16 is to reduce engine combustion noise, but the retard amount Ic2 in step A17 is made smaller than the retard amount Ic1 in step A12 when cold. This is because the catalyst temperature is low during the idling operation and the low rotation operation, and therefore priority is given to the increase in exhaust gas temperature (see FIG. 3) due to the divided injection in step A18 in order to improve the activity of the catalyst. That is, if the retard amount Ic2 is increased, the injection end timing is further delayed by the split injection, leading to deterioration of combustibility and generation of soot. Therefore, the retard amount Ic2 here is suppressed to a small range.
[0050]
  When it is determined in step A19 that the engine is not operating at a low speed, that is, in an intermediate or high speed operation state, the process proceeds to step A14 where the three-part injection is set and the injection is executed (step A5).
[0051]
  In the above control example, the pilot injection is performed only during the idling operation and the low rotation operation. However, the pilot injection is continued even when it is determined at the middle rotation or the high rotation operation in step A13 or A19. Thus, the engine sound may not be changed suddenly.
[0052]
  -Control example 2-
  FIG. 12 is a flowchart of the control example 2. In the control example 1, the divided injection is prohibited when the in-cylinder temperature is low. However, in the control example 2, the divided injection is executed, but the injection end timing is not delayed. In other words, in other words, the divided injection mode is such that the time from the start to the end of the main injection does not become long.
[0053]
  Steps B1 to B8 after the start are the same as in Control Example 1. When it is determined in step B8 that the predetermined time has not elapsed since the complete explosion, the routine proceeds to step B9, where the two-split injection is set and the injection is executed (step B5). That is, the fuel injection amount Q is equally divided and given as the first injection amount Q1 and the second injection amount Q2, and the optimum value is given from the range of 700 to 1000 μs as the injection pause time Δt. Divided injection is performed, but the in-cylinder temperature is low, so that the injection end timing is delayed as two-split injection. However, the injection pause time Δt is made as long as possible in order to increase the temperature of the catalyst early (see FIG. 3).
[0054]
  When it is determined in step B8 that the predetermined time has elapsed, the process proceeds to step B10 to determine whether or not the engine coolant temperature is low (when the coolant temperature is 70 ° C. or lower or 80 ° C. or lower). When the cooling water temperature is low, the process proceeds to step B11 to determine whether or not the idling operation is being performed. If the idling operation is being performed, the process proceeds to step B12 to set the injection amount and the injection timing so as to perform pilot injection. To do. Further, the process proceeds to step B13, where the start timing It of the main injection is retarded by the crank angle Ic, the process proceeds to step B14, and the injection amounts Q1, Q2 and the injection pause time Δt are set so as to execute the 2-split injection. The pilot injection and the two-part injection are executed. Even when it is not during idling, when it is determined in step B15 that the engine speed is low, similar pilot injection and two-split injection are executed.
[0055]
  The setting of pilot injection in step B12 is for reducing engine combustion noise, the setting of the retard amount Ic in step B13 is for raising the exhaust gas temperature, and the two-split injection in step B14 is also for raising the exhaust gas temperature. (See FIG. 3). It is advantageous to set the injection pause time Δt shorter to suppress the generation of smoke, CO, and HC (see FIGS. 7, 9, and 10).
[0056]
  When it is determined in step B15 that the engine is not operating at a low speed, that is, in an operation state of medium to high speed, the process proceeds to step B16, in which three-part injection is set and injection is executed (step B5). That is, the fuel injection amount Q is equally divided and given as the first, second, and third injection amounts Q1, Q2, and Q3, and the optimum value is given from the range of 200 to 1000 μs as the injection pause time Δt. The injection pause time Δt is increased as the cooling water temperature is lowered to increase the temperature of the exhaust gas (see FIG. 3).
[0057]
  The reason why the step B16 is divided into three and the step B14 is divided into two is because the main injection start timing It is retarded. That is, since the injection end timing is too late when the three-split injection is used, a two-split injection with a small number of splits is adopted from the viewpoint of ensuring combustion stability and improving the emission performance. Note that step B14 may be performed by shortening the injection pause time Δt as three-split injection.
[0058]
  When it is determined in step B10 that the cooling water temperature is high, the process proceeds to step B17 to determine whether or not the idling operation is being performed. If the idling operation is being performed, the process proceeds to steps B12 to B14 and pilot injection is performed. The retard at the main injection start timing and the two-split injection are performed. Even if it is not during idling, when it is determined in step B18 that it is during low speed operation, the process similarly proceeds to steps B12 to B14.
[0059]
  If it is determined in step B18 that the engine is not operating at a low speed, that is, in an intermediate or high speed operating state, the routine proceeds to step B19, where the two-split injection is set and the injection is executed (step B5). Since the catalyst temperature is considerably high during medium to high speed operation of the engine, the exhaust gas temperature is not increased by the three-part injection, and the two-part injection is given in order to give priority to the improvement of fuel consumption.
[0060]
  In the above control example, the pilot injection is performed only during the idling operation and the low rotation operation. However, the pilot injection is continued even when it is determined in step B15 or B18 that the operation is the middle rotation operation or the high rotation operation. Thus, the engine sound may not be changed suddenly.
[0061]
  Moreover, the division | segmentation number of division | segmentation injection can be arbitrarily set along the main point of this invention in the range of about 2-7.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a fuel injection device for a diesel engine according to the present invention.
FIG. 2 is an explanatory diagram of batch injection, split injection, and pilot injection according to the present invention.
FIG. 3 is a graph showing a change characteristic of the exhaust gas temperature of the engine when the injection form of the main injection is changed.
FIG. 4 is a graph showing a change characteristic of engine exhaust pressure when the injection mode of main injection is changed.
FIG. 5 is a graph showing a change characteristic of an engine boost pressure when the injection form of main injection is changed.
FIG. 6 is a graph showing a change characteristic of the fuel consumption rate of the engine when the injection form of the main injection is changed.
FIG. 7 is a graph showing a change characteristic of smoke emission from the engine when the injection form of main injection is changed.
FIG. 8 is a graph showing a change characteristic of the NOx emission amount from the engine when the injection form of the main injection is changed.
FIG. 9 is a graph showing a change characteristic of the CO emission amount from the engine when the injection form of the main injection is changed.
FIG. 10 is a graph showing a change characteristic of the HC emission amount from the engine when the injection form of the main injection is changed.
FIG. 11 is a flowchart of fuel injection control example 1 according to the present invention.
FIG. 12 is a flowchart of fuel injection control example 2 according to the present invention.
[Explanation of symbols]
  B Fuel injector
  1 Diesel engine
  2-cylinder
  4 Combustion chamber
  5 Injector (fuel injection valve)
  9 Crank angle sensor (required output detection means)
  22 Catalyst
  23 Exhaust gas recirculation passage
  24 Exhaust gas recirculation control valve
  25 turbocharger
  32 Accelerator opening sensor (required output detection means)
  35 ECU (control unit)

Claims (2)

A fuel injection valve arranged to face the combustion chamber in the cylinder of the engine;
Requested output detecting means for detecting the requested output of the engine;
An injection amount determining means for determining a fuel injection amount according to a detection result by the request output detecting means ;
Injection timing setting means for setting the fuel injection start timing based on the engine speed and the target torque ,
A diesel engine that injects fuel of an injection amount determined by the injection amount determination means into a plurality of times by the fuel injection valve in the vicinity of the top dead center of the compression stroke of the cylinder and so as to continue combustion by fuel injection. In the fuel injection device of
It is estimated that the in-cylinder temperature of the engine is in a low temperature state before the engine complete explosion and before a predetermined time elapses after the complete explosion, and after a predetermined time has elapsed since the complete explosion. Is a temperature state estimating means for estimating that the in-cylinder temperature is in a high temperature state,
When the temperature state estimating means estimates that the engine is in the low temperature state with respect to the in-cylinder temperature, it is estimated that the engine is in the high temperature state (provided that the engine water temperature is higher than a predetermined value and the engine is The fuel injection amount determined by the injection amount determining means and the fuel injection start set by the injection timing setting means so that the fuel injection end timing is earlier than that in the rotation or high rotation operation state) A diesel engine characterized by comprising: an injection form changing means for changing the form of split injection of the fuel without changing the timing or injecting the fuel all at once without dividing the fuel. Fuel injection device. The fuel injection device for a diesel engine according to claim 1 ,
The fuel injection device for a diesel engine is characterized in that the change of the split injection mode is executed by reducing the number of splits or by shortening the injection pause time from when the fuel injection valve is closed to when it is next opened.

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