JP2005133576A - Diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diesel engine in which the preliminary injection is made in an exhaust stroke range without the immediate ignition by obtaining a sufficient premixed time so that premixed combustion is promoted, and main injection fuel is quickly vaporized and burned in a combustion chamber raised in temperature so as to enable both the reductions in a formation amount of NOx and discharge of a smoke (PM). <P>SOLUTION: The diesel engine 1 is provided with a fuel injection device M to conduct main injection Js of high-pressure fuel into the combustion chamber 7 near a compression top dead center, and conduct the preliminary injection Js before the main injection, and a controller 27 to control the fuel injection device M corresponding to the operation condition. The controller 27 controls the injection so as to conduct the preliminary injection before the opening position tintop of a suction valve in a latter part of the exhaust stroke. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a diesel engine that performs preliminary injection prior to main injection, and more particularly to a diesel engine that can reduce the amount of black smoke emission while suppressing the generation of NOx.

  Diesel engines have been designed to delay fuel injection for the purpose of reducing NOx contained in the exhaust gas and reducing noise during combustion. Will increase. Therefore, the discharge of black smoke is improved by improving the atomization of fuel by implementing high-pressure injection. However, in this case, the combustion temperature rises and the amount of NOx emissions increases.

  Thus, in a diesel engine, suppressing the generation of NOx and reducing the emission amount of black smoke are in a trade-off relationship, and it has been difficult to improve both. Therefore, by separately performing pilot injection (preliminary injection) at a timing of 20 to 60 ° CA before compression top dead center prior to main injection, a lean air-fuel mixture is formed, NOx reduction, and smoke (PM) emissions are reduced. Reductions are being made.

For example, when the fuel injection system is a common rail, the engine controller controls the drive timing (injection timing) of the high-pressure injector and the energization time (fuel injection amount) to the solenoid valve coil, respectively. Realized.
Further, when the fuel injection system is a distributed pump, an open / close solenoid valve is provided on the injection pipe path between the plunger and the nozzle, and the energization time (fuel injection amount) to the coil of this open / close solenoid valve is pilot-injected. Opening and closing control is performed at each timing of (preliminary injection) and main injection to realize main injection and pilot injection prior to that.

  In JP-A-10-141124 (Patent Document 1), the fuel injection device uses a common rail, and as shown in FIG. 8, the first preliminary injection Js in the initial stage of the intake stroke and the middle stage of the compression stroke or A fuel injection device that performs pilot injection Jp, which is the second preliminary injection in the latter period, and main injection Jm near the compression top dead center is disclosed.

  Here, as the compression stroke progresses, a lean air-fuel mixture (not ignited due to a large heat capacity) is formed by the first preliminary injection Js, and the pilot injection Jp is formed in this state so that the pilot injected fuel is quickly gasified. Partly self-ignited. In the subsequent main injection Jm, the main injection fuel quickly vaporizes and burns in the combustion chamber whose temperature has been increased by both preliminary injections, and the lean air-fuel mixture by both preliminary injections also burns at once. In this case, by adjusting the first preliminary injection amount Js, the pilot injection amount Jp, and the main injection amount Jm, the generation of NOx can be suppressed and the smoke (PM) emission amount can be reduced.

JP-A-10-141124

  By the way, in the diesel engine of the premixed compression ignition system that performs the main injection and the preliminary injection preceding it to form a lean mixture in the compression stroke, the inventors have increased or decreased the NOx generation amount and the smoke (PM) emission amount. In order to clarify the characteristics, the preliminary injection timing was advanced and retarded, and the characteristics in each operating state were investigated.

  Here, in order to advance and retard the preliminary injection timing, the multi-cylinder diesel engine is set to 2000 rpm, the average effective pressure is set to 0.6 MPa, the main injection timing is set to 0.6 ° before top dead center, and EGR is turned on. Drove. Here, the NOx generation amount and the smoke (PM) discharge amount were measured according to the change in the preliminary injection timing, and the characteristics of the measured values are shown as an example in FIGS. 5 and 6.

  Here, while the preliminary injection timing is in the exhaust stroke, NOx decreases before and after the intake valve opening timing, and in the intake stroke after the intake top dead center TDC, the preliminary injection timing reaches the vicinity of the exhaust valve closing position after the top dead center. NOx slightly increases in this region and then decreases, but when the preliminary injection timing is changed in the region around the intake top dead center TDC, the change in the NOx generation amount is relatively small.

On the other hand, the amount of smoke (PM) generated according to the change in the preliminary injection timing changes greatly before and after the intake valve opening timing when the preliminary injection timing is in the exhaust stroke, and the preliminary injection timing is the intake air after the top dead center TDC. In the stroke, it increases rapidly in the region after the vicinity of the exhaust valve closing position.
As described above, when the preliminary injection timing is changed around the intake top dead center TDC, the amount of smoke (PM) increases rapidly in the region after the exhaust valve close position in the intake stroke, and the intake valve opens in the exhaust stroke. It turned out to be greatly reduced before the time.

Therefore, in a premixed compression ignition type diesel engine that performs main injection and preliminary injection, in order to reduce both the amount of NOx generated and the amount of smoke (PM) discharged, preliminary injection is performed in the exhaust stroke, and the intake valve It is estimated that it is effective to perform in the intake TOP region Ein, which is the region before the opening timing.
Note that in the premixed compression ignition type diesel engine disclosed in Patent Document 1, the first preliminary injection Ts, the pilot injection Tp, and the main injection Tm are respectively performed at predetermined injection amounts, so that NOx and smoke (PM) can be obtained. Although the discharge amount is reduced, the first preliminary injection Ts is performed immediately after the exhaust valve is closed at the initial stage of the intake stroke (position p1 in FIG. 8). Considering the characteristics of FIG. ) Emissions are not expected to be sufficiently reduced.

  The present invention has been made in accordance with the above-described circumstances. By performing preliminary injection in the exhaust stroke region, premix combustion is promoted by obtaining sufficient premix time without immediately igniting. Another object of the present invention is to provide a diesel engine capable of reducing both NOx production and smoke (PM) emission by quickly evaporating and burning main injection fuel in a combustion chamber whose temperature has been raised.

  According to a first aspect of the present invention, a diesel engine mainly injects high-pressure fuel into a combustion chamber in the vicinity of the compression top dead center and performs preliminary injection prior to the main injection, and the injection according to the operating state. And a controller for controlling the apparatus, wherein the controller performs injection control so that the preliminary injection is performed at a later stage of the exhaust stroke and before the intake valve is opened.

  According to a second aspect of the present invention, there is provided a diesel engine that mainly injects high-pressure fuel into the cavity at the top of the piston in the vicinity of the compression top dead center and performs preliminary injection prior to the main injection, and the injection according to the operating state. And a controller for controlling the device, wherein the controller performs injection control so that the preliminary injection is performed at a time when all of the fuel reaches the cavity inner wall in the late stage of the exhaust stroke and before the intake valve is opened. And

  According to the first aspect of the present invention, by performing preliminary injection at such injection start timing, the pre-injected fuel is injected into the cavity inner wall and the top wall surface of the piston top, and at this time, the in-cylinder temperature is relatively low. Since the fuel is supplied in a low state, ignition does not occur immediately and sufficient premixing time is obtained, premixed combustion is promoted, and the main injection fuel is quickly vaporized in the combustion chamber whose temperature has been raised. The amount of NOx and smoke (PM) generated decreases. In addition, since the pre-injected fuel provides sufficient pre-mixing and pre-mix combustion is promoted, the pre-mix combustion area in the main injection period is reduced to reach diffusion combustion, so NOx is reduced and PM is also reduced. That is, the PM-NOx trade-off is improved.

  According to the second aspect of the present invention, the preliminary injection is performed at such an injection start timing, so that the preliminary injection fuel is injected so that all of the fuel reaches the cavity inner wall of the top of the piston. Because the fuel is supplied at a low temperature in the target cylinder, it will not ignite immediately, and sufficient premixing time will be obtained, premixed combustion (uniform combustion) will be promoted, and the temperature of the combustion chamber will rise Because the main injected fuel vaporizes and burns quickly, smoke (PM) decreases, and all the pre-injected fuel reaches the inner wall of the cavity, so that it is possible to reliably prevent the injected fuel from adhering to the inner wall of the cylinder, Oil dilution can be suppressed.

FIG. 1 shows an overall configuration of a diesel engine 1 as an embodiment of the present invention and a fuel injection device M mounted on a main body 2 of the diesel engine (hereinafter simply referred to as an engine) 1.
The main body 2 of the engine 1 includes a cylinder block 3 at an upper portion thereof, a cylinder head 4 integrally coupled to the upper side thereof, and a head cover (not shown). Although the engine 1 is a multi-cylinder engine having a plurality of cylinders having the same configuration, here, only one cylinder will be mainly described in order to avoid redundant description. Here, the cylinder block 3 has a piston 6 slidably disposed in an internal cylinder 5, and a combustion chamber 7 is formed between the lower walls of the cylinder 5, the piston 6, and the cylinder head 4 in a variable volume.

  A fuel injection valve 8 is attached to the lower wall of the cylinder head 4 so as to face the combustion chamber 7, and an intake port 11 that is opened and closed by the intake valve 9 at a position that does not interfere with the fuel injection valve 8 and an exhaust valve 12. An exhaust port 13 that is opened and closed is formed. The intake / exhaust valves 9 and 12 are driven to open and close by receiving rotation of the engine crankshaft through a valve system (not shown).

  The intake port 11 introduces air from the intake passage IN side into the combustion chamber 7 when the intake valve 9 is opened. A throttle valve 17 for adjusting the intake air amount Qa may be disposed. The exhaust port 13 is formed so that when the exhaust valve 12 is opened, the exhaust from the combustion chamber 7 is exhausted to the exhaust passage EX side having an exhaust gas purification device (not shown). As the exhaust gas purification device, a known continuous regeneration exhaust gas purification device in which an oxidation catalyst and a particulate filter are arranged in series can be used.

Between the intake port 11 and the exhaust port 13, an EGR passage 21 having an EGR control valve 19 is provided in the middle, and thereby, exhaust gas in the exhaust port 13 is recirculated to the intake port 11 to suppress the NOx emission amount. An exhaust gas recirculation device (EGR device) 16 is formed.
The piston 6 has a cavity 22 recessed in the top wall, and when the piston reaches near the top dead center, fuel particles from a plurality of nozzles of the fuel injection valve 8 can be sprayed toward the inner peripheral wall 221 of the cavity. Is formed.

  Here, in relation to the injection angle β of the fuel particles from the plurality of injection holes of the fuel injection valve 8 and the opening shape of the cavity 22, as shown in FIGS. Can reach all the inner wall of the cavity 22, and in the top dead center separation region Eout outside the region, the injection fuel is set to partially or entirely reach the outside of the cavity 22.

  As shown in FIG. 1, the fuel injection valve 8, the common rail 24, and the fuel pump 25 constitute a main part of the fuel injection device M. Here, the fuel in the fuel tank 38 is supplied to the common rail 24 via the fuel supply pipe 18 and the fuel pump 25. The fuel supplied to the common rail 24 is supplied to the fuel injection valve 8 through each injection pipe 23. A fuel pressure sensor 26 for detecting an internal fuel pressure is attached to the common rail 24, and an output signal (rail pressure) Pr of the fuel pressure sensor 26 is output to an engine controller (hereinafter simply referred to as an ECU) 27. . The rail pressure control circuit of the ECU 27 controls the discharge amount of the fuel pump 25 so that the rail pressure Pr in the common rail 24 becomes the target fuel pressure.

Although FIG. 1 shows the fuel injection valve 8 of the first cylinder and its fuel supply system, the other cylinders also have a fuel injection valve and its fuel supply system having the same configuration, and each of these electromagnetic actuators is also connected to the ECU 27. Connected to.
The ECU 27 is a digital computer, and includes a ROM (read only memory) 29, a RAM (random access memory) 31, a CPU (microprocessor) 32, an input port 33 and an output port 34 connected to each other by a bidirectional bus 28. Here, in particular, a function as a fuel supply control means is provided.

  A load sensor 37 that generates an output voltage proportional to the depression amount (accelerator opening) θa of the accelerator pedal 36 is connected to the accelerator pedal 35 of the vehicle. The output voltage of the load sensor 37 is passed through an AD converter (not shown). Input to the input port 33. Further, a crank angle sensor 39 that generates an output pulse δθ (engine speed signal) every time a crankshaft (not shown) rotates, for example, by 30 ° is connected to the input port 33. In addition, the crank angle sensor 39 is provided with a cylinder discriminating device 42, which outputs a discrimination signal δc for each cylinder of the multi-cylinder engine. On the other hand, the output port 34 is connected to the fuel injection valve 8 via an injection valve drive circuit D2 (see FIG. 2), to the fuel pump 25 via a pump drive circuit D1 (see FIG. 2), and via a drive circuit (not shown). Each is connected to the EGR control valve 19.

The ECU 27 takes in the detection signals from the crank angle sensor 39, the load sensor 37, and the fuel pressure sensor 26, and controls the fuel injection valve 8, the fuel pump 25, the EGR control valve 19, and the like.
Here, the ECU 27 functions as a fuel supply control means, and has various functions as shown in FIG.
That is, the fuel supply control means takes in the engine speed Ne, the accelerator opening θa as the engine load, and the rail pressure Pr, and drives the injection amount calculation unit A1, the rail pressure calculation unit A2, and the injection timing calculation unit A3.

  The injection amount calculation unit A1 of the fuel supply control means calculates the main and preliminary injection amounts Qm, Qs using a map mp1, and this injection amount map mp1 is the entire engine operating range based on the engine speed Ne and the accelerator opening θa. Are divided into a predetermined number of regions eq, and optimum main and preliminary injection amounts Qm and Qs are set for each of the divided operation regions.

  The rail pressure calculation unit A2 of the fuel supply control means calculates the rail pressure Pr by the rail pressure map mp2, and this rail pressure map mp2 divides the injection amount Qf (= Qm + Qs) into three large, medium and small amounts. Is set as a parameter to set a rail pressure Pr corresponding to the engine speed Ne. The rail pressure Pr as the target fuel pressure is input to the pump drive circuit D1, and here, the discharge amount of the fuel pump 25 is controlled so that the rail pressure Pr in the common rail 24 becomes the target fuel pressure.

  Further, the injection amount calculation unit A1 divides the rail pressure Pr from the rail pressure calculation unit A2 into three large, medium, and small pressure regions, that is, Pra or less, Prb (> Pra) or less, Prc ( > Prb) Classification is made as follows. Here, maps mp3a to mp3c (refer to FIG. 2) for calculating main and preliminary injection amounts Qm and Qs and main and preliminary injection periods Tm and Ts (refer to FIG. 3) are provided for each corresponding region of the divided rail pressure Pr. . The injection amount calculation unit A1 calculates maps mp3a to mp3c corresponding to the corresponding areas of the divided rail pressure Pr, and calculates the optimum main and preliminary injection periods Tm and Ts along the map. The main and preliminary injection periods Tm and Ts are input to the injection period control unit of the injection valve drive circuit D2.

  The injection timing calculation unit A3 of the fuel supply control means calculates the main injection timing tm and the preliminary injection timing ts using the map mp4. Here, the injection timing map mp4 divides the entire operating range of the engine based on the engine speed Ne and the accelerator opening θa into a predetermined number of regions et and optimizes the main injection timing tm and the preliminary injection for each divided operating range. The time ts can be set.

Further, the injection timing calculation unit A3 inputs the obtained main injection timing tm and preliminary injection timing ts to the injection timing control unit of the injection valve drive circuit D2.
Here, the main injection timing tm is set to such a characteristic that the high rotation / high load region is relatively advanced and the middle rotation / middle load region and the low rotation / low load region are relatively retarded.
On the other hand, the preliminary injection timing ts is tintop (see FIG. 4) before the intake valve opening position in the late stage of the exhaust stroke (before intake top dead center), and is the time when all the fuel can reach the inner wall of the cavity 22. It is set to be performed in a certain crank angle region Ein (see FIGS. 3 and 4).

  Note that the preliminary injection is performed for the predetermined injection period Ts from the preliminary injection timing ts, but there is no operating region in which the predetermined injection period Ts is shifted to the retard side (right side in FIGS. 3 and 4) from tintop before the intake valve opening position. Thus, the preliminary injection timing tsb is sufficiently advanced in advance.

  In this case, the preliminary injection timing tsb is set to be performed in the crank angle region Ein, which is a timing at which all the fuel can reach the inner wall of the cavity 22, but basically, the fuel particles of the preliminary injection are cylinders. It suffices if the oil dilution (oil dilution) can be suppressed by reliably preventing scattering and adhesion to the inner wall side. For this reason, in the operation region where some fuel particles are scattered in the vicinity of the peripheral edge portion a (see FIG. 1) of the cavity 22 of the piston top wall, the fuel particles do not reach the cylinder inner wall side. It is not necessary for all the fuel to reach the inner wall of the tee 22. From this point, the allowable range for setting the advance injection timing ts can be increased.

When such an engine is driven, the fuel supply control means of the ECU 27 executes the fuel supply control routine of FIG.
The ECU 27 drives an exhaust gas recirculation device (EGR device) 16 that suppresses the NOx emission amount in a main routine (not shown), executes other well-known engine control, and steps in the fuel supply control routine of FIG. Reach s1. In step s1, the engine speed Ne, the accelerator opening θa that is the engine load, and other engine operation information (not shown) are captured. In step s2, an engine operating range eq (see mp1 in FIG. 2) corresponding to the engine speed Ne and the accelerator opening θa is obtained, and main and preliminary injection amounts Qm and Qs corresponding to the engine operating range eq are calculated. In step s3, an addition value of the main and preliminary injection amounts Qm and Qs is calculated as an injection amount Qf (= Qm + Qs). Next, the injection amount Qf is calculated as three large, medium, and small values in the rail pressure map mp2. It is calculated whether it corresponds to any one of the injection amount areas divided by the amount, and a characteristic line corresponding to the calculated injection amount area (added as large, medium and small in mp2) and a target value corresponding to the engine speed Ne. A certain rail pressure Pro is calculated.

  When step s4 is reached, whether the rail pressure Pro, which is the calculated target value, falls into one of the three large (Prc or higher), medium (Prc> Prb> Pra), or small (Pra or lower) pressure ranges. Calculate. Next, one of the rail pressure maps mp3a to mp3c2 (see FIG. 2) corresponding to the rail pressure range is selected, and the main and preliminary injection amounts Qm and Qs corresponding to the main and preliminary injection periods Tm are selected using the selected rail pressure map. , Ts, respectively.

When step s5 is reached, an engine operating range et corresponding to the engine speed Ne and the accelerator opening θa is obtained, and main and preliminary injection timings tm and ts corresponding to the engine operating range et are calculated.
Thereafter, in step s6, the main and preliminary injection periods Tm and Ts are input to the injection period control unit d2-1 of the injection valve drive circuit D2, and the main injection timing tm and the preliminary injection timing ts are input to the injection timing control unit d2-2. input. Thereby, the injection valve drive circuit D2 counts the discrimination signal δc and the output pulse δθ (unit crank angle signal), executes the preliminary injection Js of the preliminary injection period Ts from the preliminary injection timing ts, and performs the main injection from the main injection timing tm. The main injection Jm for the period Tm is executed.

Further, in step s7, the calculated rail pressure Pro of the target value is input to the pump drive circuit D1. As a result, the pump drive circuit D1 drives and controls the fuel pump 25 so that the current rail pressure Prn matches the target value Pro.
Thus, the preliminary injection is in the late stage of the exhaust stroke (before the intake top dead center), before the intake valve opening position tintop (see FIG. 4), and at the time when all the fuel can reach the inner wall of the cavity 22. Fuel injection can be controlled in the crank angle region Ein (see FIGS. 3 and 4).

  At this time, since the pre-injected fuel particles have a relatively low in-cylinder temperature, they do not ignite immediately, and a sufficient premixing time is obtained. The fuel that has been promoted and the temperature of the combustion chamber 7 that has been subjected to the main injection Jm is rapidly vaporized and burned in the combustion chamber 7, so that the amount of NOx and smoke (PM) generated is reduced.

In addition, since all of the pre-injected fuel reaches the inner wall of the cavity 22, it is possible to reliably prevent the injected fuel from adhering to the inner wall on the cylinder 5 side and to reliably suppress oil dilution (oil dilution).
Furthermore, since sufficient premixing is performed by the pre-injected Js fuel and the premixed combustion is promoted, the premixed combustion region in the main injection period is relatively reduced to lead to diffusion combustion, so that NOx is also reduced. PM is also reduced, ie, the PM-NOx trade-off is improved.

  In the above description, only the preliminary injection Js is performed in the exhaust stroke prior to the main injection Jm. However, in some cases, the pilot injection Jp (see the two-dot chain line in FIG. 3) is performed after the preliminary injection Js and immediately before the main injection Jm. NOx reduction may be performed, and post-injection Ja (see the two-dot chain line in FIG. 3) may be performed at a predetermined crank angle position immediately after main injection Jm, and the amount of NOx and smoke (PM) generated by these May be further reduced.

  In the above description, the operation region main injection timing tm and the preliminary injection timing ts are set according to the engine operation region et. In addition, the main injection timing tm is set to be retarded according to the operation region et. Further, by combining this with the preliminary injection timing ts being set to tintop before the intake valve opening position in the late stage of the exhaust stroke, further NOx reduction can be achieved.

  In the above description, an exhaust gas purification device (not shown) is provided on the exhaust path EX side. However, this exhaust gas purification device may be a selective reduction type NOx catalyst. In addition, when performing the preliminary injection Js in the later stage of the exhaust stroke, by adjusting the preliminary injection timing ts and the preliminary injection period Ts, in particular, some unburned HC is discharged, and this unburned HC is selectively reduced. It can be used as a reducing agent for the type NOx catalyst, and the NOx of the filter can be reduced.

  In the above description, the diesel engine is a premixed compression ignition type diesel engine and the fuel injection valve has a plurality of injection holes. However, the present invention can be similarly applied to a diesel engine using a single injection fuel injection valve.

1 is an overall schematic configuration diagram of a diesel engine as an embodiment of the present invention. It is a functional block diagram of the fuel supply control means of the diesel engine of FIG. FIG. 2 is an operational characteristic diagram of preliminary injection and main injection of the fuel injection device for the diesel engine of FIG. 1. FIG. 2 is an operational characteristic diagram in a preliminary injection region of the fuel injection device of the diesel engine of FIG. 1. FIG. 6 is a characteristic diagram of NOx emission when preliminary injection prior to main injection of a diesel engine is performed and the injection timing is varied. It is a characteristic figure of the amount of smoke discharged when the preliminary injection prior to the main injection of the diesel engine is varied at the injection timing. FIG. 2 is a flowchart characteristic explanatory diagram of a fuel supply control routine performed by an ECU of the diesel engine of FIG. 1. It is an operation characteristic diagram of the preliminary injection area, pilot injection, and main injection Jm which ECU of a conventional diesel engine performs.

Explanation of symbols

1 Diesel Engine 7 Combustion Chamber 22 Cavity 221 Cavity Inner Wall 27 ECU (Controller)
tintop Before intake valve open position Jm Main injection Js Pre-injection M Fuel injection device

Claims (2)

A diesel engine comprising: a fuel injection device that mainly injects high-pressure fuel into the combustion chamber in the vicinity of compression top dead center and performs preliminary injection prior to the main injection; and a controller that controls the injection device in accordance with operating conditions. In
The diesel engine according to claim 1, wherein the controller performs injection control so that the preliminary injection is performed at a later stage of the exhaust stroke and before the intake valve is opened. A fuel injection device that mainly injects high-pressure fuel into the cavity at the top of the piston in the vicinity of the compression top dead center and performs preliminary injection prior to the main injection; and a controller that controls the injection device in accordance with operating conditions. In a diesel engine
The diesel engine according to claim 1, wherein the controller performs the injection control so that the preliminary injection is performed at a time when the fuel reaches the inner wall of the cavity before the intake valve is opened at a later stage of the exhaust stroke.

Images