JP4858647B2 - Fuel injection pressure control device for internal combustion engine - Google Patents

Description

  The present invention relates to a fuel injection pressure control device for an internal combustion engine represented by a diesel engine. In particular, the present invention relates to a countermeasure for optimizing the combustion state of the air-fuel mixture.

  As is well known in the art, in a diesel engine used as an automobile engine or the like, a fuel injection valve (hereinafter referred to as an injector) may be used depending on the engine speed, accelerator operation amount, cooling water temperature, intake air temperature, and the like. The fuel injection control for adjusting the fuel injection timing and the fuel injection amount is performed (see, for example, Patent Document 1 below).

  By the way, the combustion of the diesel engine consists of premixed combustion and diffusion combustion. When fuel injection from the fuel injection valve is started, a combustible air-fuel mixture is first generated by fuel vaporization and diffusion (ignition delay period). Next, this combustible air-fuel mixture self-ignites almost simultaneously in several places in the combustion chamber, and the combustion proceeds rapidly (premixed combustion). Further, fuel injection into the combustion chamber is continued, and combustion is continuously performed (diffusion combustion). Thereafter, since unburned fuel exists even after the fuel injection is completed, heat generation is continued for a while (afterburn period).

  Further, in a diesel engine, the more the fuel is vaporized in the cylinder, the higher the flame propagation speed after ignition. When the flame propagation speed increases, the amount of fuel burned at a time increases too much, and the pressure in the cylinder increases rapidly, causing vibration and noise. Such a phenomenon is called diesel knocking and often occurs particularly during low-load operation. In such a situation, the generation amount of nitrogen oxides (hereinafter referred to as “NOx”) increases as the combustion temperature rapidly rises, and exhaust emission deteriorates.

As a technique for solving these problems, adjustment of fuel pressure (hereinafter also referred to as fuel injection pressure) is performed as disclosed in Patent Documents 2 to 4 below. In general, the fuel pressure is set high to increase the combustion speed in the cylinder, and conversely, the fuel pressure is set low to suppress the generation of vibration and noise. .
JP 2001-254645 A Japanese Patent Laid-Open No. 3-18647 JP-A-6-207548 JP 11-315730 A

  By the way, in the conventional diesel engine, as a method for setting the fuel pressure according to the operating state, the fuel pressure is adapted for each engine operating state such as the engine speed and the engine torque (corresponding to the engine load). It was. In other words, for each engine operating condition, experimentally, the appropriate value for the fuel pressure is experimentally determined individually, and the fuel pressure setting map is created by mapping the corresponding fuel pressure values for each of these many engine operating conditions. Was creating. Then, according to the fuel pressure setting map, a target fuel pressure suitable for the current engine operating state is set, and control of the high pressure fuel pump is performed.

  Hereinafter, an example of a procedure for creating a fuel pressure setting map so far will be described. In order to create this fuel pressure setting map, first, the fuel pressure setting map shown in FIG. 9 (a) is prepared, and on the other hand, the experimental value of the fuel pressure is experimentally obtained by trial and error. The fuel pressure setting map is changed in the order of 9 (b) and FIG. 9 (c).

  First, FIG. 9A is a fuel pressure setting map in which the fuel pressure is gradually set higher as the engine speed increases in the entire operation region. In this fuel pressure setting map, the equal fuel pressure line (straight line indicated by a broken line in the figure) is along the vertical axis (engine torque axis) in the figure so as to coincide with the equal rotation number line. This fuel pressure setting map realizes good drivability and can prevent fuel pressure delay by rapidly increasing the fuel pressure in response to the engine speed increase even in the low engine speed range. .

  However, in the fuel pressure setting map shown in FIG. 9A, a problem remains in the quietness of the engine. Therefore, compared to the fuel pressure setting map shown in FIG. 9A, the low fuel pressure region in the low torque region is expanded to the high rotation side, and the engine quietness in this operating region can be obtained well. Change to the fuel pressure setting map shown in 9 (b). The amount of change at this time is obtained by experimental trial and error.

  However, in the fuel pressure setting map shown in FIG. 9B, there remains a problem in the exhaust emission of the engine. Therefore, compared with the fuel pressure setting map shown in FIG. 9 (b), the high fuel pressure region in the middle torque region is expanded to the low rotation side, and this operation region (particularly, the one-dot chain line in FIG. 9 (c)). The operation is changed to a fuel pressure setting map shown in FIG. 9C, which can improve the exhaust emission by promoting atomization of the fuel in the operation region surrounded by. The amount of change at this time is also obtained by experimental trial and error. In addition, the fuel pressure setting map shown in FIG. 9C expands the low fuel pressure region around the maximum torque line to the high rotation side, thereby suppressing oil dilution.

  Because of the creation procedure as described above, the creation of the fuel pressure setting map required a great deal of labor. Not only that, but because the experimental value of the fuel pressure was determined individually by trial and error for each engine operating condition, there was no guarantee that the proper fuel pressure was set over the entire engine operating range. . In other words, under certain operating conditions, although combustion noise and NOx generation can be reduced, combustion efficiency may deteriorate and sufficient engine torque may not be obtained. Conversely, high engine torque is sufficient. In some cases, however, the combustion noise increases and the amount of NOx generated increases.

  As described above, conventionally, the fuel pressure conformity value is determined by trial and error, which leads to complication of conformance and it is impossible to construct a systematic fuel pressure setting method common to various engines. In addition, it cannot be said that the fuel pressure is optimized over the entire engine operation area, and there is still room for improvement.

  The present invention has been made in view of such points, and an object of the present invention is to systematically set the fuel injection pressure when setting an appropriate fuel injection pressure according to the operating state of the internal combustion engine. Another object of the present invention is to provide a fuel injection pressure control device capable of executing fuel injection with the fuel injection pressure set by the above.

-Principle of solving the problem-
The solution principle of the present invention taken to achieve the above object has a unique correlation between the required output (required power) of the internal combustion engine and the fuel injection pressure (for example, the target fuel pressure in the common rail). Make it. In addition, in a situation where the output of the internal combustion engine changes due to a change in at least one of the rotational speed and torque of the internal combustion engine, fuel injection can be performed at an appropriate fuel pressure according to the change. In a situation where the output of the internal combustion engine does not change even if the rotational speed or torque changes, the fuel pressure is not changed from the appropriate value set so far. This makes it possible to bring the change rate of heat generation rate during combustion of the air-fuel mixture closer to the ideal state.

-Solution-
Specifically, the present invention is based on a fuel injection pressure control device for an internal combustion engine that controls the pressure of fuel injected into the cylinder of the compression ignition type internal combustion engine. For this fuel injection pressure control device, by preallocating the equal fuel injection pressure region over substantially the entire operable region of the internal combustion engine with respect to the equal output region required for the internal combustion engine, The fuel injection pressure is adjusted in accordance with the output required for the internal combustion engine, and the ratio of the change amount of the fuel injection pressure to the change amount of the output required for the internal combustion engine is smaller in the lower rotation region of the internal combustion engine. It is set to be.

  Due to this specific matter, when the output required for the internal combustion engine changes during operation of the internal combustion engine, the fuel injection pressure (target) is set so that the fuel injection pressure assigned in advance corresponding to the required output of the internal combustion engine is obtained. Fuel injection pressure) is set. Since this fuel injection pressure is obtained by assigning an equal fuel injection pressure region to an equal output region, a systematic fuel pressure setting method common to various engines should be established. It is possible to simplify the creation of a fuel pressure setting map for setting an appropriate fuel injection pressure according to the operating state of the internal combustion engine.

For example, by adjusting the fuel injection pressure, it is possible to bring the heat generation rate change state at the time of combustion of the air-fuel mixture closer to the ideal state. Specifically, if the fuel injection pressure is set high, the amount of increase in heat generation rate per unit time at the beginning of combustion can be increased (the inclination angle of the heat generation rate waveform can be increased), and the same injection amount can be obtained. Therefore, the combustion period can be shortened (the reduction in the heat generation rate can be set at an early timing). That is, the phase of the heat release rate waveform can be shortened with respect to the degree of advance of the crank angle (the heat release rate lowering timing can be shifted to the advance side). In addition, the peak value of the heat generation rate (the maximum value of the heat generation rate waveform) can be obtained high. Conversely, if the fuel injection pressure is set low, the inclination angle of the heat generation rate waveform at the beginning of combustion can be reduced, the phase of the heat generation rate waveform can be lengthened with respect to the degree of advance of the crank angle, The maximum value (peak value) of the heat release rate waveform can be lowered. As described above, the heat generation rate waveform can be changed by adjusting the fuel injection pressure, and the heat generation rate waveform can be brought close to an ideal waveform. Along with this, it becomes possible to simultaneously satisfy various requirements such as improvement of exhaust emission by reducing the amount of NOx generated, reduction of combustion noise during the combustion stroke, and sufficient securing of engine torque. And it becomes possible to simplify preparation of the fuel pressure setting map for obtaining such an ideal combustion form.
In addition, since the ratio of the change amount of the fuel injection pressure to the change amount of the output required for the internal combustion engine is set to be smaller in the low rotation region of the internal combustion engine, the fuel injection is reduced in the low rotation region of the internal combustion engine. The change in pressure is gradual, and a sudden increase in the combustion pressure in the cylinder in this operating state is avoided to suppress the generation of vibration and noise associated with combustion. On the other hand, in the high speed region of the internal combustion engine, for example, the fuel injection pressure is greatly changed as the torque increases, so that the required output can be obtained quickly and the response of the internal combustion engine is improved. ing.

  Specifically, as an allocation form of the equal fuel injection pressure region to the equal output region of the internal combustion engine, even if the rotational speed and torque of the internal combustion engine change, the output obtained from the changed rotational speed and torque changes. If not, the equal fuel injection pressure region is assigned to the equal output region of the internal combustion engine so as not to change the fuel injection pressure.

  Thus, the fuel injection pressure can be changed only when the required output of the internal combustion engine changes, and an appropriate fuel injection pressure can be uniquely set according to the required output of the internal combustion engine. For example, even if the rotational speed of the internal combustion engine increases, the required output does not change because the torque decreases, and conversely, the required output does not change because the rotational speed decreases even if the torque of the internal combustion engine increases. If it has not changed, the fuel injection pressure is not changed, and the appropriate value set up to that point is maintained.

  Further, as the allocation form of the fuel injection pressure region, a higher fuel injection pressure region is allocated to a region where the output required for the internal combustion engine is higher. That is, in the high torque operation state and the high rotation operation state of the internal combustion engine, the required output can be obtained by increasing the heat generation rate in the cylinder.

  More specifically, as the allocation form of the fuel injection pressure region, more specifically, when the rotational speed and torque of the internal combustion engine both increase, when the rotational speed of the internal combustion engine is constant and the torque increases, and The fuel injection pressure region is set so as to increase the fuel injection pressure in any case where the torque of the internal combustion engine is constant and the rotational speed increases. That is, the fuel injection pressure is adjusted so as to increase the fuel injection pressure only in a situation where the required output of the internal combustion engine increases.

  Further, a fuel pressure setting map referred to for adjusting the fuel injection pressure is as follows. In other words, the equal output line and the equal fuel injection pressure line drawn in the map with the horizontal axis representing the rotational speed of the internal combustion engine and the vertical axis representing the torque of the internal combustion engine substantially coincide with each other over substantially the entire operable range of the internal combustion engine. It has been made to.

  Specific methods for determining the fuel injection pressure corresponding to the output required for the internal combustion engine include the following. In other words, the fuel injection pressure has a proportional relationship with the output required for the internal combustion engine and a predetermined proportionality constant, and is predetermined with respect to the temporary fuel injection pressure obtained by multiplying the required output by the proportionality constant. The fuel injection pressure is obtained as a pressure added by the pressure offset amount.

  The pressure offset amount in this case is the crank after the compression top dead center when the main injection fuel injected from the fuel injection valve starts combustion when the piston of the internal combustion engine reaches the compression top dead center. When the angle reaches about 10 degrees, the heat generation rate is set to reach the maximum value.

  This makes it possible to specifically determine the fuel injection pressure according to the output required for the internal combustion engine. Further, if fuel injection is executed at the fuel injection pressure determined in this way, 50% of the air-fuel mixture in the cylinder has completed combustion at the time of 10 degrees after compression top dead center (ATDC 10 °). Situation. That is, about 50% of the total heat generation amount in the expansion stroke is generated by ATDC 10 °, and the internal combustion engine can be operated with high thermal efficiency.

  Specific methods for determining the fuel injection pressure in the combustion noise countermeasure output region, which is a relatively low output region as the output region required for the internal combustion engine, include the following. That is, the fuel injection pressure in the combustion noise countermeasure output region is added by a predetermined basic pressure offset amount to the temporary fuel injection pressure obtained by multiplying the output required for the internal combustion engine by a predetermined proportional constant. After obtaining the reference pressure, the reference pressure is obtained by correcting the decrease.

  In this case, the reduction correction amount with respect to the reference pressure in the combustion noise countermeasure output region is set to be larger as the output required for the internal combustion engine is smaller, so as to obtain the fuel injection pressure.

  If the pressure offset amount is set in this manner, the combustion noise in the combustion chamber when the output of the internal combustion engine is relatively low can be suppressed low, and the quietness of the internal combustion engine can be improved.

  Specific methods for determining the fuel injection pressure in the NOx countermeasure output region, which is a relatively high output region as the region of output required for the internal combustion engine, include the following. That is, the fuel injection pressure in the NOx countermeasure output region is a reference obtained by adding a predetermined basic pressure offset amount to the temporary fuel injection pressure obtained by multiplying the output required for the internal combustion engine by a predetermined proportional constant. After obtaining the pressure, the reference pressure is obtained by correcting the decrease.

  In this case, the reduction correction amount with respect to the reference pressure in the NOx countermeasure output region is set to be larger as the output required for the internal combustion engine is larger, so as to obtain the fuel injection pressure.

  By setting the pressure offset amount in this way, the combustion speed in the combustion chamber when the output of the internal combustion engine is relatively high can be kept low, and the amount of NOx generated due to combustion in the cylinder is greatly increased. Can be reduced.

  Further, as a specific method for determining the fuel injection pressure in the smoke countermeasure output region which is a substantially intermediate output region as an output region required for the internal combustion engine, the following may be mentioned. That is, the fuel injection pressure in the smoke countermeasure output region is a reference obtained by adding a predetermined basic pressure offset amount to the temporary fuel injection pressure obtained by multiplying the output required for the internal combustion engine by a predetermined proportionality constant. After obtaining the pressure, the reference pressure is obtained by correcting the increase.

  If the pressure offset amount is set in this way, for example, even when the main injection is performed by multiple divided injections, the injection amount per unit time can be increased, and the injection period can be shortened. This can reduce the deterioration in efficiency associated with the longer injection period.

  In the present invention, with respect to the setting of the fuel injection pressure of the compression self-ignition internal combustion engine, the equal fuel injection pressure region is assigned in advance to substantially the entire operable region of the internal combustion engine with respect to the equal output region. I have to. Therefore, it is possible to construct a systematic fuel pressure setting method common to various engines.

FIG. 1 is a schematic configuration diagram of an engine and its control system according to the embodiment. FIG. 2 is a cross-sectional view showing a combustion chamber of a diesel engine and its peripheral portion. FIG. 3 is a block diagram showing a configuration of a control system such as an ECU. FIG. 4 is a waveform diagram showing a change state of the heat generation rate during the expansion stroke. FIG. 5 is a diagram showing the relationship between the engine required output in the reference example and the target fuel pressure set according to the required output. FIG. 6 is a diagram showing a fuel pressure setting map referred to when determining the target fuel pressure according to the reference example . FIG. 7 is a diagram showing a fuel pressure setting map referred to when determining the target fuel pressure according to the first embodiment . FIG. 8 is a diagram showing the relationship between the engine required output and the target fuel pressure set according to the required output in the second embodiment . FIG. 9 is a diagram for explaining an example of a procedure for creating a conventional fuel pressure setting map.

Explanation of symbols

1 engine (internal combustion engine)
3 Combustion chamber 13 Piston 23 Injector (fuel injection valve)

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present embodiment, a case where the present invention is applied to a common rail in-cylinder direct injection multi-cylinder (for example, in-line 4-cylinder) diesel engine (compression self-ignition internal combustion engine) mounted on an automobile will be described.

-Engine configuration-
First, a schematic configuration of a diesel engine (hereinafter simply referred to as an engine) according to the present embodiment will be described. FIG. 1 is a schematic configuration diagram of an engine 1 and its control system according to the present embodiment. FIG. 2 is a cross-sectional view showing the combustion chamber 3 of the diesel engine and its periphery.

  As shown in FIG. 1, the engine 1 according to the present embodiment is configured as a diesel engine system having a fuel supply system 2, a combustion chamber 3, an intake system 6, an exhaust system 7 and the like as main parts.

  The fuel supply system 2 includes a supply pump 21, a common rail 22, an injector (fuel injection valve) 23, a shutoff valve 24, a fuel addition valve 26, an engine fuel passage 27, an addition fuel passage 28, and the like.

  The supply pump 21 pumps fuel from the fuel tank, makes the pumped fuel high pressure, and supplies it to the common rail 22 via the engine fuel passage 27. The common rail 22 has a function as a pressure accumulation chamber that holds (accumulates) the high-pressure fuel supplied from the supply pump 21 at a predetermined pressure, and distributes the accumulated fuel to the injectors 23. The injector 23 includes a piezoelectric element (piezo element) therein, and is configured by a piezo injector that is appropriately opened to supply fuel into the combustion chamber 3. Details of the fuel injection control from the injector 23 will be described later.

  The supply pump 21 supplies a part of the fuel pumped from the fuel tank to the fuel addition valve 26 via the addition fuel passage 28. The added fuel passage 28 is provided with the shutoff valve 24 for shutting off the added fuel passage 28 and stopping fuel addition in an emergency.

  The fuel addition valve 26 is configured so that the fuel addition amount to the exhaust system 7 becomes a target addition amount (addition amount that makes the exhaust A / F become the target A / F) by an addition control operation by the ECU 100 described later. In addition, it is constituted by an electronically controlled on-off valve whose valve opening timing is controlled so that the fuel addition timing becomes a predetermined timing. That is, a desired fuel is injected and supplied from the fuel addition valve 26 to the exhaust system 7 (from the exhaust port 71 to the exhaust manifold 72) at an appropriate timing.

  The intake system 6 includes an intake manifold 63 connected to an intake port 15a formed in the cylinder head 15 (see FIG. 2), and an intake pipe 64 constituting an intake passage is connected to the intake manifold 63. Further, an air cleaner 65, an air flow meter 43, and a throttle valve 62 are arranged in this intake passage in order from the upstream side. The air flow meter 43 outputs an electrical signal corresponding to the amount of air flowing into the intake passage via the air cleaner 65.

  The exhaust system 7 includes an exhaust manifold 72 connected to an exhaust port 71 formed in the cylinder head 15, and exhaust pipes 73 and 74 constituting an exhaust passage are connected to the exhaust manifold 72. In addition, a maniverter (exhaust gas purification device) 77 including a NOx storage catalyst (NSR catalyst: NOx Storage Reduction catalyst) 75 and a DPNR catalyst (Diesel Particle-NOx Reduction catalyst) 76, which will be described later, is disposed in the exhaust passage. Yes. Hereinafter, the NSR catalyst 75 and the DPNR catalyst 76 will be described.

The NSR catalyst 75 is an NOx storage reduction catalyst. For example, alumina (Al ₂ O ₃ ) is used as a support, and potassium (K), sodium (Na), lithium (Li), cesium (Cs), for example, is supported on this support. Alkali metal such as barium (Ba), alkaline earth such as calcium (Ca), rare earth such as lanthanum (La) and yttrium (Y), and noble metal such as platinum (Pt) were supported. It has a configuration.

The NSR catalyst 75 occludes NOx in a state where a large amount of oxygen is present in the exhaust gas, has a low oxygen concentration in the exhaust gas, and a large amount of reducing component (for example, an unburned component (HC) of the fuel). In the existing state, NOx is reduced to NO ₂ or NO and released. NO NOx released as NO ₂ or NO, the N ₂ is further reduced due to quickly reacting with HC or CO in the exhaust. Further, HC and CO are oxidized to H ₂ O and CO ₂ by reducing NO ₂ and NO. That is, by appropriately adjusting the oxygen concentration and HC component in the exhaust gas introduced into the NSR catalyst 75, HC, CO, and NOx in the exhaust gas can be purified. In the present embodiment, the oxygen concentration and HC component in the exhaust gas can be adjusted by the fuel addition operation from the fuel addition valve 26.

  On the other hand, the DPNR catalyst 76 is, for example, a porous ceramic structure carrying a NOx storage reduction catalyst, and PM in the exhaust gas is collected when passing through the porous wall. Further, when the air-fuel ratio of the exhaust gas is lean, NOx in the exhaust gas is stored in the NOx storage reduction catalyst, and when the air-fuel ratio becomes rich, the stored NOx is reduced and released. Further, the DPNR catalyst 76 carries a catalyst that oxidizes and burns the collected PM (for example, an oxidation catalyst mainly composed of a noble metal such as platinum).

  Here, about the structure of the combustion chamber 3 of a diesel engine, and its peripheral part. This will be described with reference to FIG. As shown in FIG. 2, a cylinder block 11 constituting a part of the engine body is formed with a cylindrical cylinder bore 12 for each cylinder (four cylinders), and a piston 13 is formed inside each cylinder bore 12. Is accommodated so as to be slidable in the vertical direction.

  The combustion chamber 3 is formed above the top surface 13 a of the piston 13. That is, the combustion chamber 3 is defined by the lower surface of the cylinder head 15 attached to the upper part of the cylinder block 11 via the gasket 14, the inner wall surface of the cylinder bore 12, and the top surface 13 a of the piston 13. A cavity 13 b is formed in a substantially central portion of the top surface 13 a of the piston 13, and this cavity 13 b also constitutes a part of the combustion chamber 3.

  The piston 13 has a small end portion 18a of a connecting rod 18 connected by a piston pin 13c, and a large end portion of the connecting rod 18 is connected to a crankshaft that is an engine output shaft. As a result, the reciprocating movement of the piston 13 in the cylinder bore 12 is transmitted to the crankshaft via the connecting rod 18, and the engine output is obtained by rotating the crankshaft. Further, a glow plug 19 is disposed toward the combustion chamber 3. The glow plug 19 functions as a start-up assisting device that is heated red when an electric current is applied immediately before the engine 1 is started and a part of the fuel spray is blown onto the glow plug 19 to promote ignition and combustion.

  The cylinder head 15 is formed with an intake port 15a for introducing air into the combustion chamber 3 and an exhaust port 71 for discharging exhaust gas from the combustion chamber 3, and an intake valve for opening and closing the intake port 15a. 16 and an exhaust valve 17 for opening and closing the exhaust port 71 are provided. The intake valve 16 and the exhaust valve 17 are disposed to face each other with the cylinder center line P interposed therebetween. That is, the engine 1 is configured as a cross flow type. The cylinder head 15 is provided with the injector 23 that directly injects fuel into the combustion chamber 3. The injector 23 is disposed at a substantially upper center of the combustion chamber 3 in a standing posture along the cylinder center line P, and injects fuel introduced from the common rail 22 toward the combustion chamber 3 at a predetermined timing. It has become.

  Furthermore, as shown in FIG. 1, the engine 1 is provided with a supercharger (turbocharger) 5. The turbocharger 5 includes a turbine wheel 5B and a compressor wheel 5C that are connected via a turbine shaft 5A. The compressor wheel 5C is disposed facing the inside of the intake pipe 64, and the turbine wheel 5B is disposed facing the inside of the exhaust pipe 73. Therefore, the turbocharger 5 performs a so-called supercharging operation in which the compressor wheel 5C is rotated using the exhaust flow (exhaust pressure) received by the turbine wheel 5B to increase the intake pressure. The turbocharger 5 in the present embodiment is a variable nozzle type turbocharger, and a variable nozzle vane mechanism (not shown) is provided on the turbine wheel 5B side. By adjusting the opening of the variable nozzle vane mechanism, the engine 1 supercharging pressure can be adjusted.

  An intake pipe 64 of the intake system 6 is provided with an intercooler 61 for forcibly cooling the intake air whose temperature has been raised by supercharging in the turbocharger 5. The throttle valve 62 provided further downstream than the intercooler 61 is an electronically controlled on-off valve whose opening degree can be adjusted steplessly. It has a function of narrowing down the area and adjusting (reducing) the supply amount of the intake air.

  Further, the engine 1 is provided with an exhaust gas recirculation passage (EGR passage) 8 that connects the intake system 6 and the exhaust system 7. The EGR passage 8 is configured to reduce the combustion temperature by recirculating a part of the exhaust gas to the intake system 6 and supplying it again to the combustion chamber 3, thereby reducing the amount of NOx generated. In addition, the EGR passage 8 is opened and closed steplessly by electronic control, and the exhaust gas passing through the EGR passage 8 (recirculating) is cooled by an EGR valve 81 that can freely adjust the exhaust flow rate flowing through the passage. An EGR cooler 82 is provided.

-Sensors-
Various sensors are attached to each part of the engine 1, and signals related to the environmental conditions of each part and the operating state of the engine 1 are output.

  For example, the air flow meter 43 outputs a detection signal corresponding to the flow rate of intake air (intake air amount) upstream of the throttle valve 62 in the intake system 6. The intake air temperature sensor 49 is disposed in the intake manifold 63 and outputs a detection signal corresponding to the temperature of the intake air. The intake pressure sensor 48 is disposed in the intake manifold 63 and outputs a detection signal corresponding to the intake air pressure. The A / F (air-fuel ratio) sensor 44 outputs a detection signal that continuously changes in accordance with the oxygen concentration in the exhaust gas downstream of the manipulator 77 of the exhaust system 7. Similarly, the exhaust temperature sensor 45 outputs a detection signal corresponding to the temperature of the exhaust gas (exhaust temperature) downstream of the manipulator 77 of the exhaust system 7. The rail pressure sensor 41 outputs a detection signal corresponding to the fuel pressure stored in the common rail 22. The throttle opening sensor 42 detects the opening of the throttle valve 62.

-ECU-
As shown in FIG. 3, the ECU 100 includes a CPU 101, a ROM 102, a RAM 103, a backup RAM 104, and the like. The ROM 102 stores various control programs, maps that are referred to when the various control programs are executed, and the like. The CPU 101 executes various arithmetic processes based on various control programs and maps stored in the ROM 102. The RAM 103 is a memory that temporarily stores calculation results of the CPU 101, data input from each sensor, and the like. The backup RAM 104 is a nonvolatile memory that stores data to be saved when the engine 1 is stopped, for example. Memory.

  The CPU 101, the ROM 102, the RAM 103, and the backup RAM 104 are connected to each other via the bus 107, and are connected to the input interface 105 and the output interface 106.

  The input interface 105 is connected to the rail pressure sensor 41, the throttle opening sensor 42, the air flow meter 43, the A / F sensor 44, the exhaust temperature sensor 45, the intake pressure sensor 48, and the intake temperature sensor 49. Further, the input interface 105 includes a water temperature sensor 46 that outputs a detection signal corresponding to the cooling water temperature of the engine 1, an accelerator opening sensor 47 that outputs a detection signal corresponding to the depression amount of the accelerator pedal, and the engine 1. A crank position sensor 40 that outputs a detection signal (pulse) each time the output shaft (crankshaft) rotates by a certain angle is connected. On the other hand, the injector 23, the fuel addition valve 26, the throttle valve 62, the EGR valve 81, and the like are connected to the output interface 106.

  The ECU 100 executes various controls of the engine 1 based on the outputs of the various sensors described above. Furthermore, the ECU 100 executes pilot injection, pre-injection, main injection, after-injection, and post-injection as fuel injection control of the injector 23.

  The fuel injection pressure for executing these fuel injections is determined by the internal pressure of the common rail 22. As the common rail internal pressure, generally, the target value of the fuel pressure supplied from the common rail 22 to the injector 23, that is, the target rail pressure, increases as the engine load (engine load) increases and the engine speed (engine speed) increases. It will be expensive. That is, when the engine load is high, the amount of air sucked into the combustion chamber 3 is large. Therefore, a large amount of fuel must be injected from the injector 23 into the combustion chamber 3, and therefore the injection from the injector 23 is performed. The pressure needs to be high. Further, when the engine speed is high, the injection period is short, so the amount of fuel injected per unit time must be increased, and therefore the injection pressure from the injector 23 needs to be increased. . Thus, the target rail pressure is generally set based on the engine load and the engine speed. As a feature of the present embodiment, a specific method for setting the target value of the fuel pressure will be described later.

  As for the fuel injection parameters in the fuel injection such as the pilot injection and the main injection, the optimum values vary depending on the temperature conditions such as the engine and the intake air.

  For example, the ECU 100 adjusts the fuel discharge amount of the supply pump 21 so that the common rail pressure becomes equal to the target rail pressure set based on the engine operating state, that is, the fuel injection pressure matches the target injection pressure. To measure. Further, the ECU 100 determines the fuel injection amount and the fuel injection form based on the engine operating state. Specifically, the ECU 100 calculates the engine rotation speed based on the detection value of the crank position sensor 40 and obtains the depression amount (accelerator opening) to the accelerator pedal based on the detection value of the accelerator opening sensor 47. The total fuel injection amount (the sum of the injection amount in the pre-injection and the injection amount in the main injection) is determined based on the engine speed and the accelerator opening.

-Setting of target fuel pressure-
Next, a target fuel pressure setting method and a fuel pressure setting map, which are features of the present embodiment, will be described. First, a technical idea when setting the target fuel pressure in the present embodiment will be described.

  In the diesel engine 1, it is important to simultaneously satisfy various requirements such as improvement of exhaust emission by reducing the amount of NOx generated, reduction of combustion noise during the combustion stroke, and sufficient securing of engine torque. The inventor of the present invention can appropriately control the change state of the heat generation rate in the cylinder during the combustion stroke (change state represented by the heat generation rate waveform) as a method for simultaneously satisfying these requirements. Focusing on the effectiveness, we found a target fuel pressure setting method as described below as a method for controlling the change state of the heat generation rate.

  The solid line in FIG. 4 shows an ideal heat generation rate waveform related to combustion of fuel injected by main injection, with the horizontal axis representing the crank angle and the vertical axis representing the heat generation rate. TDC in the figure indicates the crank angle position corresponding to the compression top dead center of the piston 13. As this heat generation rate waveform, for example, combustion of fuel injected by main injection is started from the compression top dead center (TDC) of the piston 13, and a predetermined piston position after the compression top dead center (for example, compression top dead center). The heat generation rate reaches a maximum value (peak value) at the time 10 degrees after (ATDC 10 °), and further, a predetermined piston position after compression top dead center (for example, 25 degrees after compression top dead center (ATDC 25 °)). The combustion of the fuel injected in the main injection ends at the time). If combustion of the air-fuel mixture is performed in such a state where the heat generation rate changes, for example, 50% of the air-fuel mixture in the cylinder burns at 10 degrees after compression top dead center (ATDC 10 °). Completed status. That is, about 50% of the total heat generation amount in the expansion stroke is generated by ATDC 10 °, and the engine 1 can be operated with high thermal efficiency.

  In addition, the waveform shown with a dashed-dotted line in FIG. 4 has shown the heat release rate waveform which concerns on combustion of the fuel injected by the said pre-injection. Thereby, stable diffusion combustion of the fuel injected by the main injection is realized. For example, the amount of heat of 10 [J] is generated by the combustion of the fuel injected by the pre-injection. This value is not limited to this. For example, it is appropriately set according to the total fuel injection amount. Although not shown, pilot injection is also performed prior to the pre-injection, thereby sufficiently increasing the in-cylinder temperature and ensuring good ignitability of the fuel injected in the main injection.

  As described above, in this embodiment, the cylinder is sufficiently preheated by the pilot injection and the pre-injection. When main injection, which will be described later, is started by this preheating, the fuel injected by the main injection is immediately exposed to a temperature environment equal to or higher than the self-ignition temperature, and thermal decomposition proceeds. After the injection, combustion starts immediately. Will be.

  Specifically, the fuel ignition delay in a diesel engine includes a physical delay and a chemical delay. The physical delay is the time required for evaporation / mixing of the fuel droplets and depends on the gas temperature of the combustion field. On the other hand, the chemical delay is the time required for chemical bond decomposition and oxidation heat generation of fuel vapor. As described above, in the situation where the cylinder is sufficiently preheated, the physical delay can be minimized, and as a result, the ignition delay can be minimized.

  Therefore, the premixed combustion is hardly performed as the combustion mode of the fuel injected by the main injection. As a result, controlling the fuel injection timing is substantially equivalent to controlling the combustion timing as it is, and the controllability of combustion can be greatly improved. That is, until now, the premixed combustion has occupied a considerable proportion of the combustion of the diesel engine. In the present embodiment, the fuel injection timing and the fuel injection are reduced by minimizing the premixed combustion rate. Control of the heat generation rate waveform (ignition timing and heat generation amount) by controlling the amount (controlling the injection rate waveform) can greatly improve the controllability of combustion. In the present embodiment, this new mode of combustion is referred to as “sequential combustion (combustion started immediately after fuel is injected)” or “controlled combustion (combustion actively controlled by fuel injection timing and fuel injection amount)”. ".

  Further, the waveform indicated by a two-dot chain line α in FIG. 4 is a heat generation rate waveform when the fuel injection pressure is set higher than an appropriate value, and both the combustion speed and the peak value are too high, and the combustion This is a state in which there is a concern about an increase in sound and an increase in the amount of NOx generated. On the other hand, the waveform indicated by the two-dot chain line β in FIG. 4 is a heat release rate waveform when the fuel injection pressure is set lower than the appropriate value, and the timing at which the combustion speed is low and the peak appears is greatly retarded. There is a concern that sufficient engine torque cannot be ensured by shifting to.

  As described above, the target fuel pressure setting method according to the present embodiment is a technical idea that the combustion efficiency is improved by optimizing the change state of the heat generation rate (optimization of the heat generation rate waveform). It is based on. In order to realize this, the target fuel pressure is set as described later. Hereinafter, a plurality of embodiments of the target fuel pressure setting method will be described.

(Reference example)
First, a reference example will be described.

The solid line in FIG. 5 shows the relationship between the required output (required power) in the engine 1 according to this reference example and the target fuel pressure set according to the required output. Thus, the required output and the target fuel pressure are in a proportional relationship, and the target fuel pressure is uniquely determined with respect to the required output. In other words, the target fuel pressure is assigned in advance to each required output.

  Hereinafter, a method for setting the target fuel pressure with respect to the required output will be specifically described with reference to FIG.

  First, a temporary fuel pressure line indicated by a broken line in FIG. 5 is set. This temporary fuel pressure line is set so that the target fuel pressure is also “0” when the required output is “0”, and is given as a straight line passing through the origin of the graph shown in FIG. 5 and having a predetermined inclination. It has been.

  The inclination of the temporary fuel pressure line is determined by the displacement of the engine 1 or the like. That is, for example, the inclination of the temporary fuel pressure line is set smaller for the engine 1 having a larger displacement. The target fuel pressure on the temporary fuel pressure line corresponds to the temporary fuel injection pressure in the present invention, and this temporary fuel injection pressure has a predetermined proportionality constant (corresponding to the inclination of the temporary fuel pressure line) with respect to the required output. It is calculated as a proportional relationship. In other words, the temporary fuel injection pressure is obtained by multiplying the required output by a predetermined proportional constant, and the set of the temporary fuel injection pressure is the temporary fuel pressure line.

  Then, the temporary fuel pressure line is moved parallel to the high fuel pressure side (upper side in FIG. 5) by a predetermined pressure offset amount with respect to the power center of gravity point (the point of the required output of 40 kW in the case shown in FIG. 5) on the temporary fuel pressure line. Thus, a fuel pressure line indicated by a solid line in the figure is set. The power centroid point is not limited to the above value.

  Here, the power center-of-gravity point is set as a value corresponding to the most frequently used output in the output range of the engine 1.

Further, as the pressure offset amount, when the fuel of the main injection injected from the injector 23 starts combustion at the compression top dead center (TDC) of the piston 13, a predetermined piston position (after the compression top dead center) It is set so that the heat generation rate in the cylinder reaches a maximum value (peak value) at 10 degrees after compression top dead center (ATDC 10 °). That is, the pressure offset amount is set so that an ideal heat generation rate waveform indicated by a solid line in FIG. 4 can be obtained at the power barycentric point. The pressure offset amount is individually set for each type of engine 1 through experiments and simulations in advance according to the displacement of the engine 1 and the number of cylinders. Further, in the fuel supply system 2 of the engine 1 according to this reference example , the upper limit value (upper limit rail pressure) of the target fuel pressure is set to 200 MPa.

  FIG. 6 is a fuel pressure setting map that is referred to when the target fuel pressure is determined. This fuel pressure setting map is created according to the fuel pressure line shown by the solid line in FIG. 5 and is stored in the ROM 102, for example. In this fuel pressure setting map, the horizontal axis is the engine speed, and the vertical axis is the engine torque. Further, Tmax in FIG. 6 indicates a maximum torque line.

  As a feature of this fuel pressure setting map, an equal fuel injection pressure line (equal fuel injection pressure region) indicated by A to I in the figure is a required output (required power) to the engine 1 that is obtained based on the depression amount of the accelerator pedal. Are allocated to the equal power line (equal output region). That is, in this fuel pressure setting map, the equal power line and the equal fuel injection pressure line are set to substantially coincide.

  Specifically, a curve A in FIG. 6 is a line having a required engine output of 10 kW, and a line of 66 MPa is allocated as the fuel injection pressure. Hereinafter, similarly, the curve B is a line with a required engine output of 20 kW, and a line with 83 MPa is allocated as the fuel injection pressure. A curve C is a line having a required engine output of 30 kW, and a line of 100 MPa is allocated to this as a fuel injection pressure. A curve D is a line having a required engine output of 40 kW, and a line of 116 MPa is allocated to the line as a fuel injection pressure. Curve E is a line with a required engine output of 50 kW, and a line with 133 MPa is allocated as the fuel injection pressure. A curve F is a line having a required engine output of 60 kW, and a line of 150 MPa is allocated as the fuel injection pressure. Curve G is a line with a required engine output of 70 kW, and a line of 166 MPa is allocated to this as the fuel injection pressure. A curve H is a line having an engine output demand of 80 kW, and a line of 183 MPa is allocated as the fuel injection pressure. Curve I is a line with a required engine output of 90 kW, and a line with 200 MPa is allocated as the fuel injection pressure. These values are not limited to this, and are set as appropriate according to the performance characteristics of the engine 1 and the like.

  Further, in each of the lines A to I, the ratio of the change amount of the fuel injection pressure to the change amount of the engine required output is set to be approximately equal.

  From the above, the fuel injection pressure control device according to the present invention is constituted by the ROM 102, the supply pump 21, and the CPU 101 that store the fuel pressure setting map.

  In accordance with the fuel pressure setting map created in this way, a target fuel pressure suitable for a required output to the engine 1 is set, and the supply pump 21 is controlled.

  Also, when both the engine speed and the engine torque increase (see arrow I in FIG. 6), when the engine speed is constant and the engine torque increases (see arrow II in FIG. 6), and In any case where the engine torque is constant and the engine speed increases (see arrow III in FIG. 6), the fuel injection pressure is increased. This ensures a fuel injection amount suitable for the intake air amount when the engine torque (engine load) is high, and increases the fuel injection amount per unit time when the engine speed is high, which is required in a short period of time. A fuel injection amount can be secured. For this reason, regardless of the engine output and the engine speed, it is possible to always realize the combustion mode with an ideal heat generation rate waveform as shown by the solid line in FIG. 4 and to reduce the NOx generation amount. Various requirements such as improvement of exhaust emission, reduction of combustion noise during combustion stroke, and sufficient securing of engine torque can be combined.

  On the other hand, even if the engine speed and the engine torque change, if the engine output after the change does not change (see arrow IV in FIG. 6), the fuel injection pressure is not changed so far. Maintain the appropriate value of the set fuel injection pressure. In other words, the fuel injection pressure is not changed when the engine operating state changes along the equal fuel injection pressure line (corresponding to the equal power line), and the combustion mode with the ideal heat release rate waveform described above is used. To continue. In this case, it is possible to continuously satisfy various requirements such as improvement of exhaust emission by reducing the amount of NOx generated, reduction of combustion noise during the combustion stroke, and sufficient securing of engine torque.

As described above, in this reference example, there is a unique correlation between the required output (required power) for the engine 1 and the fuel injection pressure (common rail pressure), and at least one of the engine speed and the engine torque. When the engine output changes as a result of the change, fuel injection can be performed at an appropriate fuel pressure accordingly, and conversely, the engine output does not change even if the engine speed or engine torque changes. The fuel pressure is not changed from the appropriate value that has been set. This makes it possible to bring the heat generation rate change state closer to the ideal state over substantially the entire engine operation region. In addition, since this reference example constructs a systematic fuel pressure setting method common to various engines, a fuel pressure setting map for setting an appropriate fuel injection pressure according to the operating state of the engine 1 is shown. It is possible to simplify the creation.

(First embodiment)
Next, the first embodiment will be described. The present embodiment is a modification of the fuel pressure setting map, and other configurations and control methods are the same as those of the reference example described above. Therefore, only the fuel pressure setting map will be described here.

  FIG. 7 is a fuel pressure setting map that is referred to when the target fuel pressure is determined in the present embodiment. This fuel pressure setting map is stored in the ROM 102, for example.

As a feature of this fuel pressure setting map, the equal fuel injection pressure line (equal fuel injection pressure region) indicated by A to L in the figure is obtained based on the depression amount of the accelerator pedal, as in the reference example described above. Assigned to an equal power line (equal output region) of a required output (required power) for the engine 1 to be operated. That is, also in this fuel pressure setting map, the equal power line and the equal fuel injection pressure line are set to substantially coincide.

  Specifically, a curve A in FIG. 7 is a line having a required engine output of 10 kW, and a line of 30 MPa is allocated to the fuel injection pressure. Hereinafter, similarly, the curve B is a line having a required engine output of 20 kW, and a line of 45 MPa is allocated to the fuel injection pressure. A curve C is a line having a required engine output of 30 kW, and a line of 60 MPa is allocated as the fuel injection pressure. Curve D is a line with a required engine output of 40 kW, and a line of 75 MPa is allocated to this as fuel injection pressure. A curve E is a line having a required engine output of 50 kW, and a line of 90 MPa is allocated to the fuel injection pressure. Curve F is a line with a required engine output of 60 kW, and a line of 105 MPa is allocated to this as the fuel injection pressure. A curve G is a line having a required engine output of 70 kW, and a line of 120 MPa is allocated as the fuel injection pressure. A curve H is a line with an engine output demand of 80 kW, and a line with 135 MPa is allocated as the fuel injection pressure. Curve I is a line with a required engine output of 90 kW, and a line with 150 MPa is allocated as the fuel injection pressure. A curve J is a line having a required engine output of 100 kW, and a line of 165 MPa is allocated to the line as a fuel injection pressure. A curve K is a line having a required engine output of 110 kW, and a line of 180 MPa is allocated as the fuel injection pressure. A curve L is a line having a required engine output of 120 kW, and a line of 200 MPa is allocated as the fuel injection pressure. These values are not limited to this, and are set as appropriate according to the performance characteristics of the engine 1 and the like.

  Further, each of the lines A to L is set such that the ratio of the change amount of the fuel injection pressure to the change amount of the engine required output becomes smaller as the engine speed is in the low rotation region. That is, the interval between the lines is set wider in the low rotation region than in the high rotation region.

  In accordance with the fuel pressure setting map created in this way, a target fuel pressure suitable for a required output to the engine 1 is set, and the supply pump 21 is controlled.

  Also, when both the engine speed and the engine torque increase (see arrow I in FIG. 7), when the engine speed is constant and the engine torque increases (see arrow II in FIG. 7), and The fuel injection pressure is increased in any case where the engine torque is constant and the engine speed increases (see arrow III in FIG. 7). This ensures a fuel injection amount suitable for the intake air amount when the engine torque (engine load) is high, and increases the fuel injection amount per unit time when the engine speed is high, which is required in a short period of time. A fuel injection amount can be secured. For this reason, regardless of the engine output and the engine speed, it is possible to always realize the combustion mode with an ideal heat generation rate waveform as shown by the solid line in FIG. 4 and to reduce the NOx generation amount. Various requirements such as improvement of exhaust emission, reduction of combustion noise during combustion stroke, and sufficient securing of engine torque can be combined.

  On the other hand, even if the engine speed and the engine torque change, if the engine output after the change does not change (see arrow IV in FIG. 7), the fuel injection pressure is not changed so far. Maintain the appropriate value of the set fuel injection pressure. In other words, the fuel injection pressure is not changed when the engine operating state changes along the equal fuel injection pressure line (corresponding to the equal power line), and the combustion mode with the ideal heat release rate waveform described above is used. To continue. In this case, it is possible to continuously satisfy various requirements such as improvement of exhaust emission by reducing the amount of NOx generated, reduction of combustion noise during the combustion stroke, and sufficient securing of engine torque.

  As described above, also in this embodiment, there is a unique correlation between the required output (required power) for the engine 1 and the fuel injection pressure (common rail pressure). This makes it possible to bring the heat generation rate change state closer to the ideal state over substantially the entire engine operation region. In addition, since the present embodiment constructs a systematic fuel pressure setting method common to various engines, a fuel pressure setting map for setting an appropriate fuel injection pressure according to the operating state of the engine 1 is shown. It is possible to simplify the creation.

  Further, as described above, in the fuel pressure setting map according to the present embodiment, the ratio of the change amount of the fuel injection pressure to the change amount of the engine output is set so as to become smaller as the engine speed is in the low rotation region. For this reason, in the low rotation region of the engine 1, the change in the fuel injection pressure is gradual, and a sudden increase in the combustion pressure in the cylinder in this operating state can be avoided to suppress the generation of vibration and noise associated with combustion. . On the other hand, in the high rotation region of the engine 1, for example, the fuel injection pressure is greatly changed as the torque increases, so that the required output can be quickly obtained and the response of the engine 1 can be obtained satisfactorily. be able to.

(Second Embodiment)
Next, a second embodiment will be described. In the reference example described above, the fuel pressure line (see FIG. 5) is set so that the target fuel pressure is in a proportional relationship with the required output of the engine 1. In this embodiment, instead, the fuel pressure line shown in FIG. 5 (in this embodiment, this fuel pressure line becomes a second temporary fuel pressure line described later for obtaining the temporary fuel injection pressure in the present invention). On the other hand, the fuel pressure line is optimized by reducing or increasing the target fuel pressure. This will be specifically described below.

  The solid line in FIG. 8 shows the relationship between the required output (required power) in the engine 1 according to this embodiment and the target fuel pressure set according to the required output. Thus, although the required output and the target fuel pressure are not in a proportional relationship, the target fuel pressure is uniquely determined with respect to the required output. In other words, the target fuel pressure is assigned in advance to each required output.

  Hereinafter, a method for setting the target fuel pressure with respect to the required output will be specifically described with reference to FIG.

First, as in the case of the reference example described above, a first temporary fuel pressure line (a temporary fuel pressure line in the above reference example ) indicated by a one-dot chain line in FIG. The first temporary fuel pressure line is set so that the target fuel pressure is also “0” when the required output is “0”, and has a predetermined inclination through the origin of the graph shown in FIG. Is given as a straight line.

The inclination of the first temporary fuel pressure line is determined by the displacement of the engine 1 and the like as in the case of the reference example described above. The target fuel pressure on the first temporary fuel pressure line corresponds to the temporary fuel injection pressure referred to in the present invention, and this temporary fuel injection pressure is a predetermined proportional constant with respect to the required output (the first temporary fuel pressure line). It is calculated as a proportional relationship. In other words, the temporary fuel injection pressure is obtained by multiplying the required output by a predetermined proportionality constant, and the set of the temporary fuel injection pressure is the first temporary fuel pressure line.

  Then, with respect to the power centroid point on the first temporary fuel pressure line (the point of the required output of 40 kW in the case shown in FIG. 8), the first temporary offset amount (the basic pressure offset amount in the present invention) is the first temporary offset. The fuel pressure line is moved in parallel to the high fuel pressure side (upper side in FIG. 8), thereby setting a second temporary fuel pressure line indicated by a broken line in the figure. The power centroid point is not limited to the above value.

The power barycentric point and the pressure offset amount are obtained by the same method as in the above-described reference example , and thus description thereof is omitted here.

  The final fuel pressure line is set by performing the reduction correction and the increase correction of the target fuel pressure as described below with respect to the second temporary fuel pressure line set in this way.

  First, the fuel injection pressure in the combustion noise countermeasure output region, which is a relatively low output region as the region of output required for the engine 1, is the fuel pressure on the second temporary fuel pressure line (reference pressure in the present invention). It is obtained by correcting for weight loss. The amount of reduction correction with respect to the reference pressure on the second temporary fuel pressure line is set to be larger as the output required for the engine 1 is smaller. That is, the smaller the output required for the engine 1, the greater the amount is reduced with respect to the reference pressure on the second temporary fuel pressure line, and the lower the target fuel pressure is set.

  Further, the fuel injection pressure in the NOx countermeasure output region, which is a relatively high output region as the output region required for the engine 1, is obtained by reducing the reference pressure on the second temporary fuel pressure line. . The amount of reduction correction with respect to the reference pressure on the second temporary fuel pressure line is set to be larger as the output required for the engine 1 is larger. That is, as the output required for the engine 1 is larger, the amount is reduced with respect to the reference pressure on the second temporary fuel pressure line, and the target fuel pressure is set lower.

  Further, the fuel injection pressure in the smoke countermeasure output region, which is a substantially intermediate output region of the output possible region of the engine 1 as an output region required for the engine 1, increases the reference pressure on the second temporary fuel pressure line. It is calculated by correcting. The amount of increase correction with respect to the reference pressure on the second temporary fuel pressure line is the continuity of the fuel pressure line (continuity of the combustion noise countermeasure output area and smoke countermeasure output area, NOx countermeasure output area and smoke countermeasure output area). Is set to be small on the combustion noise countermeasure output region side and the NOx countermeasure output region side.

  Since the fuel pressure line is set as described above and the target fuel pressure is determined accordingly, the following effects can be obtained.

  Since the fuel injection pressure in the combustion noise countermeasure output region is corrected to decrease, the combustion noise in the combustion chamber 3 when the output of the engine 1 is relatively low can be suppressed, and the quietness of the engine 1 can be reduced. Can improve.

  In addition, since the fuel injection pressure in the NOx countermeasure output region is corrected to decrease, the combustion speed in the combustion chamber 3 when the output of the engine 1 is relatively high can be suppressed, and combustion in the cylinder can be suppressed. The amount of NOx generated can be significantly reduced. Further, the required output that reaches the upper limit value (upper limit rail pressure) of the target fuel pressure can be shifted to the higher output side.

  Further, since the fuel injection pressure in the smoke countermeasure output region is corrected to increase, the fuel injection amount per unit time even when the main injection is performed by a plurality of divided injections along with the EGR increase, for example. Can be increased, the injection period can be shortened, and the deterioration in efficiency associated with the longer injection period can be eliminated.

-Other embodiments-
Each embodiment described above demonstrated the case where this invention was applied to the in-line 4 cylinder diesel engine mounted in a motor vehicle. The present invention is applicable not only to automobiles but also to engines used for other purposes. Further, the number of cylinders and the engine type (separate type engine, V-type engine, etc.) are not particularly limited.

  In each of the above embodiments, the manipulator 77 includes the NSR catalyst 75 and the DPNR catalyst 76, but may include an NSR catalyst 75 and a DPF (Diesel Particle Filter).

  In each of the above embodiments, the equal fuel injection pressure line is allocated to the equal power line over the entire engine operation region. The present invention is not limited to this, and a region where the equal fuel injection pressure line does not coincide with the equal power line may be provided in a part of the engine operation region (for example, in the vicinity of the maximum torque line Tmax).

  In each of the above-described embodiments, the temporary fuel pressure line (broken line in FIG. 5) and the first temporary fuel pressure line (one-dot chain line in FIG. 8) are straight lines, and the required output and the target fuel pressure are proportionally related on this line. However, as indicated by a two-dot chain line in FIGS. 5 and 8, the temporary fuel pressure line or the first temporary fuel pressure line may be set as a curve (secondary curve). In this case, however, the target fuel pressure must be uniquely determined with respect to the required output.

  The present invention can be applied to control of fuel injection pressure in a common rail in-cylinder direct injection multi-cylinder diesel engine mounted on an automobile.

Claims (12)

In a fuel injection pressure control device for an internal combustion engine that controls the pressure of fuel injected into a cylinder of a compression self-ignition internal combustion engine,
By assigning an equal fuel injection pressure region over substantially the entire operable region of the internal combustion engine to an equal output region of the output required for the internal combustion engine in advance, the output required for the internal combustion engine is obtained. The fuel injection pressure is adjusted accordingly, and the ratio of the change amount of the fuel injection pressure to the change amount of the output required for the internal combustion engine is set to become smaller in the low rotation region of the internal combustion engine. A fuel injection pressure control device for an internal combustion engine. In the internal combustion engine fuel injection pressure control apparatus according to claim 1,
Even if the rotation speed and torque of the internal combustion engine change, if the output obtained from the rotation speed and torque after the change does not change, the equal output region of the internal combustion engine does not change the fuel injection pressure. A fuel injection pressure control device for an internal combustion engine, wherein an equal fuel injection pressure region is assigned to the engine. In the internal combustion engine fuel injection pressure control apparatus according to claim 1 or 2,
A fuel injection pressure control device for an internal combustion engine, wherein a higher fuel injection pressure region is assigned to a region where the output required for the internal combustion engine is higher. In the fuel injection pressure control device for an internal combustion engine according to claim 1, 2, or 3,
Both when the rotational speed and torque of the internal combustion engine increase, when the rotational speed of the internal combustion engine is constant and the torque increases, and when the torque of the internal combustion engine is constant and the rotational speed increases A fuel injection pressure control device for an internal combustion engine, wherein a fuel injection pressure region is set so as to increase the fuel injection pressure. In the fuel injection pressure control device for an internal combustion engine according to any one of claims 1 to 4,
The equal output line and the equal fuel injection pressure line drawn in the map in which the horizontal axis represents the rotational speed of the internal combustion engine and the vertical axis represents the torque of the internal combustion engine are made to substantially coincide with each other over substantially the entire operable range of the internal combustion engine. A fuel injection pressure control device for an internal combustion engine, wherein the fuel injection pressure is adjusted according to a fuel pressure setting map. In the fuel injection pressure control device for an internal combustion engine according to any one of claims 1 to 5,
The fuel injection pressure has a proportional relationship with the output required for the internal combustion engine and a predetermined proportionality constant, and the predetermined fuel injection pressure is obtained by multiplying the required output by the proportionality constant. A fuel injection pressure control apparatus for an internal combustion engine, characterized in that it is obtained as a pressure added by an offset amount. In the internal combustion engine fuel injection pressure control device according to claim 6,
The pressure offset amount is about the crank angle after the compression top dead center when the fuel of the main injection injected from the fuel injection valve starts combustion when the piston of the internal combustion engine reaches the compression top dead center. A fuel injection pressure control device for an internal combustion engine, wherein the heat generation rate is set to reach a maximum value when the temperature reaches 10 degrees. In the fuel injection pressure control device for an internal combustion engine according to any one of claims 1 to 5,
The fuel injection pressure in the combustion noise countermeasure output region, which is a relatively low output region as the region of output required for the internal combustion engine, is obtained by multiplying the output required for the internal combustion engine by a predetermined proportionality constant and provisional fuel injection A fuel injection pressure control apparatus for an internal combustion engine, wherein a reference pressure obtained by adding a predetermined basic pressure offset amount to a pressure is obtained, and then the reference pressure is obtained by reducing the amount of the reference pressure. In the fuel injection pressure control device for an internal combustion engine according to claim 8,
The fuel injection pressure of the internal combustion engine is characterized in that the fuel injection pressure is obtained by setting the amount of reduction correction with respect to the reference pressure in the combustion noise countermeasure output region to be larger as the output required for the internal combustion engine is smaller. Pressure control device. In the fuel injection pressure control device for an internal combustion engine according to any one of claims 1 to 5,
The fuel injection pressure in the NOx countermeasure output region which is a relatively high output region as the region required for the internal combustion engine is a temporary fuel injection pressure obtained by multiplying the output required for the internal combustion engine by a predetermined proportional constant. On the other hand, a fuel injection pressure control apparatus for an internal combustion engine, wherein a reference pressure obtained by adding a predetermined basic pressure offset amount is obtained and then the reference pressure is obtained by reducing the amount of the reference pressure. In the internal combustion engine fuel injection pressure control apparatus according to claim 10,
The fuel injection pressure of the internal combustion engine is characterized in that the fuel injection pressure is obtained by setting the reduction correction amount with respect to the reference pressure in the NOx countermeasure output region to be larger as the output required for the internal combustion engine is larger. Control device. In the fuel injection pressure control device for an internal combustion engine according to any one of claims 1 to 5,
The fuel injection pressure in the anti-smoke output region, which is a substantially intermediate output region of the output possible region of the internal combustion engine as the output region required for the internal combustion engine, is multiplied by a predetermined proportionality constant to the output required for the internal combustion engine. The internal combustion engine is characterized in that it is obtained by calculating a reference pressure obtained by adding a predetermined basic pressure offset amount to the temporary fuel injection pressure obtained and then correcting the reference pressure to increase. Fuel injection pressure control device.

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