JP3678042B2 - Diesel engine combustion control system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a combustion control device for a diesel engine.
[0002]
[Prior art]
As a combustion method of a diesel engine, there is a low-temperature premixed combustion that reduces NOx and particulates discharged from the engine. This delays the fuel injection timing until after the compression top dead center, and also reduces the oxygen concentration by exhaust gas recirculation (EGR), thereby lengthening the fuel ignition delay period. During this ignition delay period, the fuel is sufficiently vaporized. An air-fuel mixture is formed, and low-temperature premixed combustion is performed with a low concentration of oxygen.
[0003]
In this case, there is a proposal that the low-temperature premixed combustion can be performed on the engine high load side by setting the engine compression ratio to a compression ratio lower than the normal compression ratio (see Japanese Patent Application Laid-Open No. 8-254134).
[0004]
When the compression ratio of the engine is high, the compression temperature rises relatively, so that the temperature at the start of combustion (cylinder atmosphere temperature at the start of combustion) increases. Since the combustion temperature further increases after the start of combustion, if this exceeds the range of the low temperature premixed combustion, the low temperature premixed combustion cannot be performed.
[0005]
In particular, when the engine load increases, the temperature of the exhaust gas that is recirculated during intake increases, so the intake gas temperature increases, and the actual compression ratio increases due to intake air supercharging by the turbocharger. The temperature rose beyond the temperature range of premix combustion, and therefore, low temperature premix combustion could only be performed on the low load side.
[0006]
On the other hand, by lowering the compression ratio by the proposed apparatus, the combustion start temperature is relatively lowered, and the low temperature premixed combustion can be performed on the higher load side.
[0007]
[Problems to be solved by the invention]
However, when the compression ratio is lowered, the combustion start temperature in the low load region is excessively lowered and the combustion becomes unstable on the low load side.
[0008]
Therefore, in the above-described conventional apparatus, on the low load side where low-temperature premixed combustion cannot be performed, the oxygen concentration is increased by reducing the EGR amount, and the fuel injection timing is advanced, so that the start of combustion is advanced and combustion is performed. To stabilize.
[0009]
However, in this case, the NOx emission amount increases due to the decrease in the EGR amount and the advance of the injection timing, and the low-temperature premixed combustion is not performed, so the combustion noise increases and the fuel consumption also deteriorates.
[0010]
Therefore, an object of the present invention is to enable low-temperature premixed combustion in a wide operating range of the engine even when the compression ratio is lower than the normal compression ratio.
[0011]
[Means for Solving the Problems]
  The first invention isThe fuel injection timing is delayed until after the compression top dead center, and the fuel ignition delay period is lengthened. During this ignition delay period, a premixed gas in which the fuel is sufficiently vaporized is formed, and under a low concentration of oxygen. BurnIn a diesel engine that performs low-temperature premixed combustion at a low compression ratio, as shown in FIG. 25, a fuel injection valve 81 in which the fuel injection timing is variable, and a temperature increase control device 82 that raises the working gas temperature in the combustion chamber. And a means 83 for predicting the atmospheric temperature in the cylinder at the start of combustion, and determining whether the atmospheric temperature in the cylinder at the start of combustion is in a region lower than the first target temperature T1 for maintaining the low-temperature premixed combustion. Means 84 and the temperature increase control device so that the atmospheric temperature in the cylinder at the start of combustion exceeds the first target temperature when it is determined that the atmospheric temperature in the cylinder at the start of combustion is lower than the first target temperature T1. 82 is operated to control the temperature rise, and a means 85 is provided for adjusting the fuel injection timing of the fuel injection valve 81 so that the rate of increase in the combustion temperature becomes a predetermined value or more.
[0012]
In the second invention, the in-cylinder atmosphere temperature t2 at the start of the combustion in the first invention is predicted based on the compression ratio ε and the engine load.
[0013]
In the third invention, in the first invention, the cylinder atmosphere temperature t2 at the start of the combustion is predicted based on the compression ratio ε and the intake gas temperature.
[0014]
In the fourth invention, in any one of the first to third inventions, in order to make the temperature increase rate of the main combustion equal to or higher than the predetermined value, the start of combustion is set to 5 ° to 20 ° after the compression top dead center. The fuel injection timing is controlled so as to be in the range.
[0015]
According to a fifth invention, in any one of the first to fourth inventions, an intake valve closing timing control mechanism is provided as the temperature raising control device, and the in-cylinder ambient temperature t2 at the start of combustion is the first target temperature. When the temperature is lower than T1 and higher than the second target temperature T2 lower than the first target temperature T1, the temperature increase control is performed by advancing the closing timing of the intake valve.
[0016]
According to a sixth aspect of the invention, the fifth aspect of the invention further includes a swirl control mechanism as the temperature increase control device, wherein the in-cylinder ambient temperature t2 at the start of combustion is equal to or lower than the second target temperature T2, and the second target temperature. When the temperature is higher than the third target temperature T3 lower than T2, the temperature rise control is performed by advancing the intake valve closing timing and lowering the swirl ratio.
[0017]
According to a seventh invention, in the fifth invention, a supercharging pressure control mechanism is further provided as the temperature increase control device, the cylinder atmosphere temperature t2 at the start of combustion is equal to or lower than the second target temperature T2, and the second When the temperature is higher than the third target temperature T3 that is lower than the target temperature T2, the temperature rise control is performed by advancing the intake valve closing timing, lowering the swirl ratio, and further increasing the supercharging pressure.
[0018]
According to an eighth aspect of the invention, the fuel injection control mechanism is further provided as the temperature increase control device in the sixth or seventh aspect of the invention, and the cylinder atmosphere temperature t2 at the start of combustion is equal to or lower than the third target temperature T3. When the temperature is higher than the fourth target temperature T4, which is lower than the third target temperature T3, the intake valve closing timing is advanced, the swirl ratio is lowered, and pilot injection is performed prior to the main fuel injection and pilot injection The temperature rise control is performed by setting the pilot injection timing so that the combustion due to is terminated before the main injection.
[0019]
  In the ninth inventionThe secondIn the seventh aspect of the present invention, a fuel injection control mechanism is further provided as the temperature increase control device, and a cylinder atmosphere temperature t2 at the start of combustion is a third target temperature T3 or lower and lower than the third target temperature T3. When the temperature is higher than the target temperature T4, the intake valve closing timing is advanced, the swirl ratio is lowered, the boost pressure is increased, pilot injection is performed before the main fuel injection, and combustion by the pilot injection is The temperature increase control is performed by setting the pilot injection timing to end before the main injection.
[0020]
In a tenth aspect of the invention, in the eighth or ninth aspect of the invention, the fuel main injection timing is controlled so that the main injection fuel is ignited after the end of the main injection of fuel.
[0021]
In the eleventh aspect of the invention, in any one of the eighth to tenth aspects, the opening / closing timing of one of the plurality of exhaust valves provided for one cylinder as the temperature rise control device can be arbitrarily controlled. And an EGR valve that controls the amount of exhaust gas recirculated during intake, and the intake valve closing timing is advanced when the in-cylinder atmosphere temperature t2 at the start of combustion is equal to or lower than the fourth target temperature T4. The pilot injection is performed so that the main injection is performed after the combustion of the pilot injection is completed, and the one exhaust valve is opened in the intake stroke and the EGR is performed. The temperature increase control is performed by closing the valve.
[0022]
In the twelfth invention, in any one of the eighth to tenth inventions, it is possible to arbitrarily control the opening / closing timing of one of the plurality of exhaust valves provided for one cylinder as the temperature rise control device. An exhaust valve opening / closing mechanism, an intake valve control mechanism that can arbitrarily adjust the opening / closing timing of the intake valve, and an EGR valve that controls the amount of exhaust gas recirculated during intake, and the atmospheric temperature in the cylinder at the start of combustion When t2 is equal to or lower than the fourth target temperature T4, the pilot valve is advanced so that the intake valve closing timing is advanced, the swirl ratio is lowered, the boost pressure is increased, and the main injection is performed after the pilot injection combustion is completed. Each amount of EGR gas and intake air that is injected and flows into the combustion chamber via the EGR valve is reduced as the cooling water temperature is lowered, and the exhaust valve is opened back during the intake stroke to flow back into the combustion chamber. By increasing the amount of EGR gas as the cooling water temperature is low, performing the Atsushi Nobori control.
[0023]
In a thirteenth aspect, the exhaust port on the one exhaust valve side that opens in the intake stroke in the eleventh or twelfth aspect is formed in a helical port.
[0024]
  In the fourteenth invention, from the first to the first4In any one of the inventions up toFirstTarget temperature T1It sets according to load so that temperature may become low, so that engine load becomes low.
In a fifteenth aspect, in the fifth aspect, at least one of the first target temperature T1 and the second target temperature T2 is set according to the load so that the temperature decreases as the engine load decreases.
According to a sixteenth aspect, in the sixth or seventh aspect, at least one of the second target temperature T2 and the third target temperature T3 is set according to the load so that the temperature decreases as the engine load decreases.
According to a seventeenth aspect, in any one of the eighth to tenth aspects, at least one of the third target temperature T3 and the fourth target temperature T4 is set according to a load so that the temperature decreases as the engine load decreases. To set.
In an eighteenth aspect of the invention, in any one of the eleventh to thirteenth aspects, the fourth target temperature T4 is set according to the load so that the temperature decreases as the engine load decreases.
[0025]
  First19As shown in FIG. 26, in the diesel engine that performs low-temperature premixed combustion at a low compression ratio, the fuel injection valve 81 in which the fuel injection timing is variable and the working gas temperature in the combustion chamber are increased. The temperature control device 82, the means 91 for detecting the engine load that affects the atmospheric temperature in the cylinder at the start of combustion, the engine load is equal to or lower than the first target load for maintaining the low temperature premixed combustion, and the first target Means 92 for determining whether the load is higher than the second target load (C region) lower than the load, and the engine load is equal to or lower than the first target load and higher than the second target load. Means 93 for operating the temperature increase control device 82 to control the temperature increase and adjusting the fuel injection timing of the fuel injection valve 81 so that the rate of increase in the combustion temperature is equal to or greater than a predetermined value. The provided.
[0026]
  First20In the invention of the19In the invention, the temperature raising control device further includes a swirl control mechanism, and when the load range (D region) is lower than the second target load and higher than the third target load lower than the second target load, The temperature increase control is performed by advancing the intake valve closing timing and lowering the swirl ratio.
[0027]
  First21In the invention of the19According to the invention, when the temperature rise control device is further provided with a supercharging pressure control mechanism and is in a load range (D region) that is lower than the second target load and higher than the third target load that is lower than the second target load. The temperature increase control is performed by advancing the intake valve closing timing, lowering the swirl ratio, and further increasing the supercharging pressure.
[0028]
  First22In the invention of the19Or second20In the present invention, the temperature raising control device further includes a fuel injection control mechanism, and when the load range (E region) is lower than the third target load and higher than the fourth target load lower than the third target load. Advance the intake valve closing timing, lower the swirl ratio, and set the pilot injection timing so that pilot injection is performed prior to the main injection of fuel and combustion by pilot injection ends before the main injection Thus, the temperature increase control is performed.
[0029]
  First23In the invention of the19Or second20In the present invention, the temperature raising control device further includes a fuel injection control mechanism, and when the load range (E region) is lower than the third target load and higher than the fourth target load lower than the third target load. The intake valve closing timing is advanced, the swirl ratio is lowered, the boost pressure is increased, pilot injection is performed prior to the main injection of fuel, and combustion by pilot injection is terminated before the main injection The temperature rise control is performed by setting the pilot injection timing at.
[0030]
  First24In the invention of the22Or second23In this invention, the fuel main injection timing is controlled so that the main injected fuel is ignited after the main injection of the fuel is completed.
[0031]
【The invention's effect】
In the first, second, third, fourth, and fourteenth inventions, the low temperature premixed combustion as it is because the in-cylinder atmosphere temperature at the start of combustion becomes lower than the first target temperature for maintaining the low temperature premixed combustion. When the temperature range is reached, the temperature rise control device is operated so that the temperature inside the cylinder at the start of combustion exceeds the first target temperature, and the temperature rise control is performed. Since the fuel injection timing of the fuel injection valve is adjusted so that the low temperature premixed combustion can be performed at a low temperature or a low load region where the low temperature premixed combustion could not be performed according to the conventional device ( The expansion of the low temperature premixed combustion zone), and thus, combustion noise, fuel consumption, HC, PM, and NOx were all improved from the conventional apparatus.
[0032]
In addition, according to the conventional device, it is possible to realize low temperature premixed combustion at a low temperature or to a low load side where it was difficult to perform low temperature premixed combustion. Perhaps the low temperature premixed combustion zone can be shifted to the high load side.
[0033]
  5th and 1st19In this invention, the actual compression ratio increases with the advance of the intake valve closing timing, and according to the fifth invention, the cylinder ambient temperature at the start of combustion is lower than the first target temperature and higher than the second target temperature. Even when it is high,19According to this invention, it is possible to prevent a decrease in the combustion start temperature even in a load range (C region) that is equal to or lower than the first target load and higher than the second target load.
[0034]
  6th, 7th, 7th20The second21In each of the inventions, since the swirl is weakened, the cooling loss during the compression stroke is reduced, and according to the sixth and seventh inventions, the atmospheric temperature in the cylinder at the start of combustion is equal to or lower than the second target temperature, and When the temperature is higher than the third target temperature,20The second21According to this invention, it is possible to prevent a decrease in the combustion start temperature even in a load range (D region) that is equal to or lower than the second target load and higher than the third target load.
[0035]
  However, the combustion worsens due to the reduction of the swirl ratio in this state.21According to the invention, the boost pressure is increased to increase the amount of intake air, and thus the swirl ratio is decreased, so that the working gas is increased to maintain the angular kinetic energy at the compression top dead center. Deterioration can be prevented, and this supercharging increases the intake air temperature, which contributes to an increase in the combustion start temperature.
[0036]
  8th, 9th, 10th, 10th22The second23According to the invention, pilot injection is performed. Therefore, according to the eighth, ninth, and tenth inventions, when the atmospheric temperature in the cylinder at the start of main combustion combustion is equal to or lower than the third target temperature and higher than the fourth target temperature. And again22The second23In this invention, it is possible to increase the atmospheric temperature in the cylinder at the start of the combustion of the main combustion even in a load range (E region) which is equal to or lower than the third target load and higher than the fourth target load.
[0037]
According to the eleventh and twelfth inventions, low-temperature premixed combustion can be realized even when the atmospheric temperature in the cylinder at the start of combustion is equal to or lower than the fourth target temperature, thereby further improving exhaust performance at low water temperature. To do.
[0038]
In the thirteenth invention, it is possible to prevent the swirl ratio in the combustion chamber from being lowered due to the opening of one of the exhaust valves in the intake stroke.
[0039]
When the region determination is performed based on the engine load, the accuracy of the region determination is lowered when the intake air temperature is different from the matching temperature. However, in the fifth to fourteenth inventions, based on the combustion start temperature itself. Since the region determination is performed, the region determination can be performed accurately regardless of the intake air temperature such as the difference between summer and winter.
[0040]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic configuration diagram of a diesel engine.
[0041]
In the combustion of a diesel engine, the amount of NOx produced greatly depends on the combustion temperature, and it is effective to lower the combustion temperature relatively for the reduction. In the low temperature premixed combustion system, the oxygen concentration is reduced by an exhaust gas recirculation system (EGR), thereby realizing low temperature combustion. For this reason, the exhaust passage 2 and the intake passage 3 are connected by an EGR passage 4, and a diaphragm type EGR valve 6 that operates according to the control negative pressure from the negative pressure control valve 5 is provided in the middle of the EGR passage 4. A part of the exhaust is recirculated into the intake air.
[0042]
The negative pressure control valve 5 is driven by a duty control signal from the control unit 41 so as to obtain an appropriate EGR rate according to the operating conditions of the engine. For example, the EGR rate is set to a maximum of 100 percent (the intake air flow rate and the EGR gas flow rate are the same amount) in a low rotation and low load range, and the EGR rate is decreased as the rotation speed and load increase. Since the exhaust gas temperature rises on the high load side, when a large amount of EGR gas is recirculated, the intake air temperature rises, which in turn causes the combustion temperature to rise relatively, reducing the effect of reducing NOx, and igniting the injected fuel. The delay period is shortened and premixed combustion cannot be realized. For this reason, the EGR rate is decreased as the load becomes higher.
[0043]
An EGR gas cooling device 7 is provided in the middle of the EGR passage 4. This is formed around the EGR passage 4 and has a water jacket 8 in which a part of the engine cooling water is circulated, and the circulation amount of this cooling water is a flow rate provided at the cooling water inlet 7a. It can be adjusted by the control valve 9. The degree of cooling of the EGR gas increases as the opening degree of the control valve 9 increases according to a command from the control unit 41.
[0044]
The intake passage near the intake port of the engine is provided with a swirl control valve (not shown). When the opening degree of the swirl control valve is controlled by the control unit 41 and is closed in the low engine speed and low load range (the opening degree is decreased), the flow rate of the intake air sucked into the combustion chamber is increased and the swirl strong against the combustion chamber Is generated. However, when the swirl becomes strong, the heat exchange rate of the working gas in the cylinder increases, and the working gas temperature relatively decreases.
[0045]
A hollow combustion chamber (not shown) formed in the piston is a large-diameter toroidal combustion chamber. In this, the piston cavity is formed in a cylindrical shape from the crown to the bottom of the piston without restricting the inlet, and a conical part is formed in the center of the bottom, and this conical part enters the piston cavity later in the compression stroke. In order not to give resistance to the swirl that flows while swirling, the mixing of air and fuel is further improved.
[0046]
Thus, the swirl generated by the swirl control valve is diffused from the inside of the piston cavity to the outside of the cavity as the piston descends during the combustion process, due to the cylindrical piston cavity that does not restrict the inlet. The swirl is maintained outside the cavity.
[0047]
The exhaust passage 2 is provided with a turbocharger downstream of the branch point of the EGR passage 4. This turbocharger is provided with a variable vane 53 driven by a step motor 54 at the scroll inlet of the exhaust turbine 52. The variable vane 53 is controlled by the control unit 41, and is controlled to a vane angle that increases the flow rate of the exhaust gas introduced into the exhaust turbine 52 on the low rotation side so that a predetermined supercharging pressure is obtained from the low engine rotation range. On the high rotation side, the vane angle (full open state) that allows exhaust to be introduced into the exhaust turbine 52 without resistance is controlled. Further, the variable vane 53 is controlled to a vane angle at which a desired supercharging pressure is obtained depending on the operating conditions.
[0048]
The engine includes a common rail fuel injection device 10.
[0049]
This is mainly composed of a fuel tank (not shown), a supply pump 14, a common rail (accumulation chamber) 16, and a fuel injection nozzle 17 provided for each cylinder, and the high-pressure fuel generated in the high-pressure supply pump 14 is stored in the common rail 16. The start and end of the injection can be freely controlled by opening and closing the nozzle needle by the three-way valve 25 in the fuel injection nozzle 17. The fuel pressure in the common rail 16 is always controlled to an optimum value required by the engine by a pressure sensor (not shown) and a discharge amount control mechanism (not shown) of the supply pump 14.
[0050]
The control of the fuel injection amount, the injection timing, the fuel pressure, and the like is performed by a control unit 41 constituted by a microprocessor. For this reason, the control unit 41 receives signals from the accelerator opening sensor 33, the sensor 34 for detecting the engine speed and the crank angle, the sensor 35 for cylinder discrimination, and the water temperature sensor 36. The control unit 41 calculates the target fuel injection amount and the fuel injection timing according to the engine speed and the accelerator opening, and controls the on-time of the three-way valve 25 in the nozzle corresponding to the target fuel injection amount. Further, the ON timing of the three-way valve 25 is controlled corresponding to the target injection timing. Further, the fuel pressure of the common rail 16 is feedback-controlled through the discharge amount control mechanism of the supply pump 14 so that the common rail pressure detected by a pressure sensor (not shown) matches the target pressure.
[0051]
The fuel injection timing is delayed from the normal injection timing in order to realize low temperature premixed combustion. As will be described later, the fuel injection is set to start within a predetermined range after the compression top dead center at the crank angle. As a result, the ignition delay period of the injected fuel is lengthened, during which the fuel vaporization is promoted, and it is possible to ignite in a state sufficiently mixed with air. As a result, low-temperature premixed combustion is performed under a low oxygen concentration due to exhaust gas recirculation, and NOx can be reduced without increasing particulates.
[0052]
Now, the combustion region of the low temperature premixed combustion will be described. In FIG. 2, the shaded region is a region where low temperature premixed combustion is possible (the lower limit is about 600 ° C., the upper limit is about 700 ° C., for example). Even if the temperature is higher or lower than this region, low temperature premix combustion is not possible.
[0053]
When the compression ratio of the engine is high, the combustion start temperature (atmosphere temperature at the start of combustion) becomes relatively high. Therefore, the combustion temperature becomes too high at a high load, and low temperature premixed combustion can be performed only at a low load. Can not.
[0054]
At a high load, the temperature of the exhaust gas recirculated during intake air increases, the intake gas temperature rises, and the actual compression ratio increases due to supercharging of the intake air. As a result, even if the compression ratio is the same, the in-cylinder gas temperature at the time of maximum compression increases, and the combustion start temperature increases.
[0055]
By the way, in the conventional apparatus disclosed in the above-mentioned JP-A-8-254134, it is possible to shift the low temperature premixed combustion region to the high load side by lowering the combustion start temperature by lowering the compression ratio. Become.
[0056]
However, on the other hand, the combustion start temperature in the low load region is too low, and the low temperature premixed combustion becomes very unstable on the low load side.
[0057]
In order to enable low-temperature premixed combustion at the low load side, in the present invention, the compression ratio of the engine is set to be lower than the compression ratio of 16 or less than that of a normal engine. The temperature increase control device described later is operated so that the temperature increases relatively, and the temperature increase control is performed. At the same time, the fuel injection timing is set, for example, between 5 ° and 20 ° after top dead center, and combustion starts. The rate of temperature rise later is increased.
[0058]
This will be further explained with reference to FIG. 3. The combustion start temperature t2 is in the illustrated premixed combustion possible zone (the temperature range from the target temperature T0 to the target temperature T1 (where T1 <T0)), and the start of main combustion. Is the crank angle and is 5 ° to 20 ° (experimental value) after compression top dead center, the target attainment temperature T ′ is always reached after the start of combustion. It has been confirmed.
[0059]
The target temperatures T0 and T1 and the target temperature T ′ that define the upper and lower limits of the premixed combustion possible zone are values that are uniquely determined from the fuel amount of the main injection and the main injection timing.
[0060]
On the other hand, when the combustion start temperature t2 is equal to or lower than the target temperature T1 necessary for the premix combustion, the target attainment temperature T ′ cannot be reached, and the low temperature premix combustion is not performed.
[0061]
Therefore, in the present invention, when the combustion start temperature t2 is equal to or lower than the target temperature T1, target temperatures T2, T3, and T4 (where T1> T2> T3> T4) are determined as will be described later with reference to FIG. In addition, the temperature rise control is performed in accordance with these temperature ranges, so that the combustion start temperature is increased to the premixed combustion possible zone.
[0062]
Next, the start of main combustion must be 5 ° to 20 ° after compression top dead center for the following reason.
[0063]
When the start of main combustion is immediately after compression top dead center, the temperature in the combustion chamber due to combustion tends to rise rapidly as shown by the solid line in FIG. However, since the compression temperature actually decreases as the compression top dead center progresses, the temperature rise when the main combustion starts after the top dead center is slightly higher as shown by the one-dot chain line. It will be a gentle rise curve. Therefore, premixed combustion is possible when the temperature reaches the target temperature T ′ by increasing the temperature including the decrease in the compression temperature, but when the main combustion is started after 20 ° after the compression top dead center, the compression temperature At this time, the temperature cannot reach the target temperature T ′ as indicated by the dotted line. Therefore, the limit on the slow start side of main combustion is set to 20 ° after compression top dead center.
[0064]
FIG. 5 shows the difference in heat generation rate depending on the combustion start timing. From this figure, when the start of combustion is 20 ° or more after compression top dead center, the heat generation rate pattern becomes as shown by a broken line, and the specific heat generation rate pattern at the time of low temperature premixed combustion shown by a one-dot chain line is It turns out that it cannot be obtained.
[0065]
Thus, the condition for causing low-temperature premixed combustion is that the rate of temperature increase from the start of combustion is a predetermined value or more and that the combustion start temperature t2 exceeds the target temperature T1 as described above. These have been confirmed by experiments.
[0066]
Next, the combustion control region will be described with reference to FIG.
[0067]
This figure shows the combustion control region with respect to the engine load (engine torque) and the rotational speed. The combustion start temperature t2 is related to the engine load and the rotational speed.
[0068]
In the present invention, as described above, the compression ratio is further reduced as compared with the conventional device (the conventional device has a compression ratio of 18 or less, whereas the compression ratio is 16 or less in the present invention). Thus, the low-temperature premixed combustion region is further expanded to the high load side.
[0069]
For this reason, on the low load side, the combustion start temperature becomes too low and the low temperature premixed combustion zone is deviated. In order to increase the combustion temperature, the intake valve closing timing is first advanced to the vicinity of the intake bottom dead center to increase the actual compression ratio. If it is not enough to advance the closing timing of the intake valve, in order to further increase the temperature, in addition to this, a low swirl ratio and a high boost pressure are further increased to further increase the actual compression ratio, which is still insufficient. At the load, pilot injection is further applied and preliminary combustion is performed to raise the combustion start temperature to enable low temperature premixed combustion.
[0070]
The control in each area shown in FIG. 6 will be further described in detail with reference to FIG.
[0071]
<1> A area
Since EGR is not performed at the maximum load point, the oxygen concentration is high and the boost pressure is high, so the combustion start temperature is also high, and so-called normal diesel combustion is performed.
[0072]
<2> B area
This region is a low temperature premixed combustion region where the load is smaller than the maximum load region, the oxygen concentration is reduced by a large amount of EGR, the temperature of the EGR gas is lowered by the cooling device 7, and the intake air temperature is controlled. The combustion start temperature decreases due to a delay in the main injection timing and a decrease in the supercharging pressure. This prolongs the ignition delay period, spreads the fuel sufficiently evaporated by the start of combustion, and realizes premixed combustion.
[0073]
<3> C region
The combustion start temperature is lower than the combustion start temperature of the premixed combustion due to the decrease in the EGR gas temperature accompanying the decrease in the load. Therefore, in order to maintain the premixed combustion, the intake valve closing which is later than the intake bottom dead center The combustion start temperature is raised by advancing the timing to approach the intake bottom dead center and increasing the actual compression ratio.
[0074]
<4> D region
Further, in the D and E regions where the load is reduced, if the oxygen concentration is kept at the same low level as that in the C region, the combustion rate is reduced, causing the problem of misfire and rapid increase in white smoke. For this reason, in the above conventional apparatus, the oxygen concentration is increased by decreasing the EGR amount, and the injection timing is advanced, so that the start of combustion is advanced to suppress misfire and unburned residue.
[0075]
In contrast, in the present invention, in the region D, the swirl is first weakened to reduce the cooling loss during the compression stroke. However, combustion deterioration occurs due to a decrease in the swirl ratio. Therefore, the turbocharger increases the supercharging pressure to increase the intake air amount, thereby increasing the working gas amount corresponding to the decrease in the swirl ratio, and maintaining high angular kinetic energy even at the compression top dead center. . In addition, this high supercharging increases the intake air temperature and increases the actual compression ratio, which contributes to an increase in the combustion start temperature.
[0076]
<5> E region
In an extremely low load range (for example, at idling), it is necessary to further increase the combustion start temperature. Therefore, a small amount of pilot injection is performed prior to the main injection of fuel, and this fuel is burned to start main combustion. Increase the combustion chamber gas temperature. The main injection is performed after the combustion by the pilot injection is finished, and the pilot injection timing, the pilot injection amount, and the main injection timing are set so that the main combustion is started between 5 ° and 20 ° after the compression top dead center. To control. For example, in the vicinity of idle, the pilot injection timing is 35 ° before compression top dead center, and the pilot injection amount is 1 mm.^Three/ St, the main injection timing is 3 ° before compression top dead center.
[0077]
Here, the reason why the main injection is performed after the combustion for the pilot injection is completed is that the pilot injection in the present invention is intended to raise the combustion start temperature (and therefore does not promote the ignition of the main injection). ), And the main injection is to be burned after the ignition delay period.
[0078]
The effect when the control is performed as shown in FIG. 7 is shown in FIG.
[0079]
In the above-described conventional apparatus, NOx increases due to the decrease in the EGR amount in each of the regions D and E and the advance angle of the injection timing, and since low-temperature premixed combustion is not performed, combustion noise increases, fuel consumption, HC, PM (especially SOF) is also increasing.
[0080]
In contrast, in the present invention, low temperature premixed combustion is possible in each of the D and E regions, so NOx, combustion noise, fuel consumption, HC and PM (especially SOF) are all reduced to the same level as in the B region. (HC is slightly increased from the B region, and fuel consumption is better than the B region).
[0081]
FIG. 9 shows a comparison of NOx emission amounts at equal PM emission amounts when the vehicle is in the test mode. During low temperature premixed combustion with a high compression ratio, the NOx emission ratio on the high load side was large, but the NOx emission ratio on the high load side decreased due to the low compression ratio by the conventional device. However, since the EGR rate is decreased in order to prevent misfires in the low load region, NOx on the low load side is greatly increased.
[0082]
On the other hand, according to the present invention, NOx can be reduced even on the low load side. Therefore, compared with low-temperature premixed combustion at a high compression ratio, the total amount of NOx emission is 1/3 or less. It is the level of.
[0083]
Next, the flowchart of FIG. 10 shows the control contents of the temperature increase control performed by operating the temperature increase control device in order to enable premixed combustion in a low load region or the like, and is executed at regular intervals.
[0084]
In step 1, the engine speed Ne, the target engine torque Torq as the engine load, and the intake manifold temperature t1 (not shown but detected by a temperature sensor) are read. In step 2, the actual oxygen concentration and set value (for example, oxygen concentration 18%) are read. Compare
[0085]
Here, the oxygen concentration 18% of the set value is an upper limit value of the oxygen concentration when the low temperature premixed combustion is performed. Therefore, if the actual oxygen concentration is 18% or less, it can be determined that the low-temperature premixed combustion region is in the low-temperature premixed combustion region, and if it exceeds 18%. The oxygen concentration changes by adjusting the exhaust gas recirculation rate.
[0086]
As shown in FIG. 1, the actual oxygen concentration can be obtained by providing an air-fuel ratio sensor 38 in the exhaust passage 2 and an air flow meter 39 in the intake passage 3 and using the detected values of both. Needless to say, the set value (corresponding to an oxygen concentration of 18%) differs depending on the engine.
[0087]
When it is in the low temperature premixed combustion region, the process proceeds to steps 3, 4, 5, and 6 by comparing the combustion start temperature t2 with the target temperatures T1, T2, T3, and T4 (where T1> T2> T3> T4). Perform area determination.
[0088]
These target temperatures T1, T2, T3, and T4 are set according to the engine load and the number of revolutions. For example, maps such as those shown in FIGS. This may be obtained by searching based on the rotation speed Ne. For example, if the operating point determined by the load and the rotational speed is at U, then T1 is approximately 855K, T2 is approximately 845K, T3 is approximately 835K, and T4 is approximately 825K.
[0089]
Here, the correspondence relationship between the temperature region and the region shown in FIG. 7 is as follows.
[0090]
B region: t2> T1
C region: T1 ≧ t2> T2
D region: T2 ≧ t2> T3
E region: T3 ≧ t2> T4
It is conceivable that the region determination is performed by searching a map as shown in FIG. 6 based on the rotation speed and load. In this case, the accuracy of the region determination is lowered when the intake air temperature is different from the matching temperature. For example, since the combustion start temperature in winter is lower than in summer due to changes in intake air temperature, what was in the temperature range from T1 to T2 in summer will fall to the temperature range from T2 to T3 in winter. For example, in the winter, unlike the summer, the turbocharger control and swirl control valve control must be added.
[0091]
However, since the change in the intake air temperature does not appear in the map characteristic of FIG. 6, if the map characteristic of FIG. 6 is matched for summer, only the same control as summer is performed even in winter (in this case) The turbocharger and the swirl valve are not controlled), and the combustion temperature does not reach the target temperature.
[0092]
On the other hand, when determining the region based on the combustion temperature, it is possible to perform control according to changes in the intake air temperature (in the winter, control of the turbocharger and control of the swirl control valve can be added). .
[0093]
The combustion start temperature t2 [K] is between the intake manifold temperature (intake gas temperature) t1 [K].
t2 = t1 · εκ^-1
Where ε: compression ratio
κ: Specific heat ratio (≒ 1.3)
Therefore, it can be obtained from the intake manifold temperature t1. For example, if the intake manifold temperature is 50 ° C., then t2 = (273 + 50) · 16^1.3-1= 323.16^0.3≈850K. Of course, from the intake air temperature Ta [K] and the intake negative pressure Boost [mmHg]
t1 = Ta · (760 + Boost) / 760
The intake manifold temperature t1 may be estimated by the following equation.
[0094]
Thus, the combustion start temperature t2 can be predicted based on the compression ratio and the intake gas temperature t1 (or the engine load that affects the intake gas temperature).
[0095]
(1) When t2> T1, the process proceeds to steps 7 and 8, and a map having the contents shown in FIGS. 11 and 12 is searched from the rotational speed Ne and the target engine torque Torq to search the target EGR rate and the target main injection timing (target main injection timing (target main injection time). Determine the injection start time).
[0096]
{Circle over (2)} When T1 ≧ t2> T2, the process proceeds to Step 9, and after searching the map having the contents shown in FIG. 13 from the rotational speed Ne and the target engine torque Torq to obtain the target intake valve closing timing, Execute the operation.
[0097]
Normally, the actual compression ratio is increased and the combustion start temperature can be increased by advancing the intake valve closing timing set after the intake bottom dead center to near the bottom dead center.
[0098]
(3) When T2 ≧ t2> T3, the process proceeds to Steps 10 and 11, and a map having the contents shown in FIGS. 14 and 15 is searched from the rotational speed Ne and the target engine torque Torq to obtain the target swirl ratio and the target supercharging pressure. After the determination, the operations of steps 9, 7, and 8 are executed.
[0099]
By increasing the supercharging pressure, the actual compression ratio is also increased, and the combustion start temperature can be increased accordingly. Further, if the swirl ratio is reduced to weaken the swirl, the heat exchange rate of the working gas in the cylinder is lowered, the cooling loss is reduced, the temperature drop of the working gas is suppressed, and this leads to an increase in the combustion start temperature.
[0100]
(4) When T3 ≧ t2> T4, the routine proceeds to step 12, and after searching the map having the contents shown in FIG. 16 from the rotational speed Ne and the target engine torque Torq, the target pilot injection amount and the target pilot injection timing are obtained. Steps 10, 11, 9, 7, and 8 are executed.
[0101]
Pilot injection increases the temperature of the cylinder working gas to increase the combustion start temperature.
[0102]
In FIG. 16, a small area at the lower left is 1 mm for pilot fuel injection.^Three/ St is the target pilot injection amount, and data with 35 ° before compression top dead center as the target pilot injection timing is included.
[0103]
Then, by an unillustrated flow, EGR valve control using the target EGR rate and injection timing control using the target main injection timing are performed in a temperature range of t2> T1.
[0104]
On the other hand, in the temperature range of T1 ≧ t2> T2, in addition to the above control, intake valve closing timing control for advancing the closing timing of the intake valve using the target intake valve closing timing is performed.
[0105]
Further, in the temperature range of T2 ≧ t2> T3, in addition to the above-described controls, swirl valve control using a target swirl ratio and supercharging pressure control using a target supercharging pressure are performed.
[0106]
Furthermore, in the temperature range of T3 ≧ t2> T4, in addition to all the above control, pilot injection control using the target pilot injection amount and the target pilot injection timing is performed.
[0107]
As a mechanism that can adjust the intake valve closing timing (that is, a variable valve timing mechanism), for example, a mechanism as shown in FIG. 17 can be adopted.
[0108]
60 is an intake valve, 61 is a valve spring that urges the intake valve 60 in the valve closing direction, and a piston 63 is provided in contact with the upper end of each intake valve 60, and the piston 63 is valved by the hydraulic pressure guided to the hydraulic chamber 62. The intake valve 60 is opened against the spring 61 and the intake valve 60 is opened.
[0109]
The hydraulic oil discharged from the oil pump 64 is selectively supplied from the accumulator 65 to the oil passages 68 and 69 via the inlet-side electromagnetic switching valves 66 and 67. Further, each intake air is selectively supplied to the hydraulic chambers 62 of the # 1, # 4, # 2, and # 3 cylinders via rotary valves 70 and 71 that rotate in synchronization with the engine rotation. Valve 60 is opened in turn.
[0110]
The hydraulic oil in each hydraulic chamber 62 is selectively released from the oil passages 68 and 69 to the tank 75 via the outlet side electromagnetic switching valves 73 and 74, whereby the intake valves 60 are sequentially closed. By controlling the outlet side electromagnetic switching valves 73 and 74, the closing timing of each intake valve 60 is freely controlled.
[0111]
Therefore, the variable valve timing mechanism 59 shown in FIG. 17 may control the outlet side electromagnetic switching valves 73 and 74 in accordance with the value of the target intake valve closing timing obtained by executing the flow of FIG.
[0112]
Thus, in the present invention, the low-temperature premixed combustion region can be expanded to the high load side by lowering the compression ratio to 16 or less as compared with the conventional device. Further, when the combustion start temperature falls within the temperature range where the low temperature premixed combustion is possible, the main combustion is started at a predetermined time (for example, between 5 ° and 20 ° after top dead center). In addition, the main injection timing is controlled, and the temperature rise control according to the temperature region is performed so that the combustion start temperature exceeds the target temperature T1, so that low temperature premixed combustion can be performed up to a low load region (low temperature region). That is, the low temperature premixed combustion zone can be expanded. As a result, all of NOx, combustion noise, fuel consumption, HC, and PM can be improved from the conventional device (see FIG. 8).
[0113]
Next, another embodiment of the present invention will be described with reference to the flowchart of FIG.
[0114]
This flowchart is described corresponding to FIG. 10 which is the flowchart of the first embodiment, and the same step numbers are assigned to the same parts as those in FIG.
[0115]
This embodiment is intended for an engine having a plurality of, for example, two exhaust valves per cylinder. In order to raise the combustion start temperature t2 even at an extremely low temperature, one of the plurality of exhaust valves is opened during the intake stroke and the EGR valve is closed, so that the high-temperature exhaust gas directly flows back into the combustion chamber. The gas temperature in the combustion chamber is raised so that the low temperature premixed combustion can be realized even when the combustion start temperature t2 becomes lower than the target temperature T4.
[0116]
For example, as shown in FIG. 19, the target EGR rate is considered to be 100% (the intake air amount and the EGR gas amount are the same amount). In this case, in order to maintain the maximum compression temperature (= combustion start temperature t2) at a predetermined value even if the cooling water temperature decreases, the pre-compression temperature (= intake manifold temperature t1) decreases as the cooling water temperature decreases as shown in the figure. Need to be high.
[0117]
Here, the pre-compression temperature is low-temperature exhaust gas flowing through the EGR valve, low-temperature air flowing through the intake passage, and high-temperature gas flowing back into the combustion chamber by opening one of the exhaust valves during the intake stroke. It is determined by the balance. Therefore, in order to set the pre-compression temperature to the characteristic shown in the drawing, it is only necessary to increase the flow rate of one exhaust valve that is opened during the intake stroke and decrease the intake valve flow rate and the EGR valve flow rate as the coolant temperature decreases.
[0118]
Returning to the flowchart of FIG. 18, only step 21 is different from FIG. That is, when the combustion start temperature t2 is equal to or lower than the target temperature T4, the process proceeds from step 6 to step 21, and a table set in the same manner as in FIG. 19 is searched based on the cooling water temperature, and the target EGR valve flow rate, target exhaust valve The flow rate and the target intake valve flow rate are obtained. Thereafter, as in the first embodiment, the operations of steps 12, 10, 11, 9, 7, and 8 are executed.
[0119]
Then, in the flow (not shown), the EGR valve opening and the intake valve opening are controlled so that the obtained target flow rates flow through the EGR valve, the exhaust valve, and the intake valve, and the exhaust valve opening during the intake stroke is controlled. Control.
[0120]
Also, since the EGR gas flows back to the combustion chamber by opening one of the exhaust valves during the intake stroke, the swirl in the combustion chamber becomes weak. Therefore, in order to prevent the swirl ratio from decreasing, the exhaust valve side that opens in the intake stroke The exhaust port is formed as a helical port so that the exhaust that flows backward causes a swirling motion in the combustion chamber.
[0121]
In this way, when the combustion start temperature t2 is equal to or lower than the target temperature T4, the low-temperature EGR gas and the low-temperature intake air flowing into the combustion chamber via the EGR valve are reduced, and one exhaust valve is turned on during the intake stroke. Opening increases the hot EGR gas that flows back into the combustion chamber. In addition, at this time, the exhaust port of the exhaust valve that opens in the intake stroke is formed as a helical port in order to prevent the swirl in the combustion chamber from being lowered due to the opening of the exhaust valve. As a result, low temperature premixed combustion can be realized even at an extremely low temperature when the combustion start temperature t2 is equal to or lower than the target temperature T4, thereby further improving the exhaust performance at a low water temperature.
[0122]
The flow rates of the EGR valve, one exhaust valve, and the intake valve are changed according to the cooling water temperature. As the simplest control, one exhaust valve is opened by a predetermined opening in the intake stroke, The EGR valve and the intake valve may be closed to the minimum opening degree (this corresponds to the leftmost characteristic in FIG. 19).
[0123]
In the embodiment, the region is determined based on the combustion temperature. However, as described above with reference to FIG. 6, the region may be determined based on the rotation speed and the load. The flowchart in this case is shown in FIGS. 24 and 25 are described in correspondence with FIGS. 10 and 18 which are the flowcharts of the first and second embodiments. In FIG. 24 and FIG. ing.
[0124]
To explain this, in FIG. 6, the load that defines the boundary between the B region and the C region is the first target load, the load that defines the boundary between the C region and the D region is the second target load, and the load that defines the boundary between the D region and the E region. As a third target load, the temperature rise control is performed as follows.
[0125]
(1) When the load range (C region) is lower than the first target load and higher than the second target load, which is lower than the first target load, the temperature rise control is performed by advancing the closing timing of the intake valve. Perform (steps 33, 9).
[0126]
(2) When the load range is lower than the second target load and higher than the third target load (D region) lower than the second target load, the intake valve closing timing is advanced, and the swirl ratio is lowered. Further, the temperature rise control is performed by increasing the supercharging pressure (steps 34, 10, 11, 9).
[0127]
(3) When the load range (E region) is lower than the third target load and higher than the fourth target load (E region) lower than the third target load, the intake valve closing timing is advanced, and the swirl ratio is lowered, While increasing the supercharging pressure, pilot injection is performed before the main injection of fuel, and the pilot injection timing is set so that combustion by pilot injection ends before the main injection, thereby performing temperature rise control (Steps 35, 12, 10, 11, 9), the fuel main injection timing is controlled so that the main injected fuel is ignited after the end of the main injection of fuel.
[0128]
In the above embodiment, the oxygen amount is changed by the EGR rate. However, the present invention is not limited to this case. For example, the oxygen amount can be changed using an oxygen permeable membrane.
[Brief description of the drawings]
FIG. 1 is a control system diagram of a first embodiment.
FIG. 2 is a characteristic diagram showing characteristics of combustion start temperature according to engine load.
FIG. 3 is a characteristic diagram for explaining a combustion start temperature region and a target reached temperature in low-temperature premixed combustion.
FIG. 4 is a characteristic diagram of temperature rise when combustion start times are different.
FIG. 5 is a characteristic diagram of a heat release rate pattern when combustion start timings are different.
FIG. 6 is a region diagram in which control regions for engine speed and engine load are divided.
FIG. 7 is a characteristic diagram for explaining control for each region in FIG. 6;
FIG. 8 is a characteristic diagram showing a discharge characteristic such as NOx when the control of FIG. 7 is performed.
FIG. 9 is a characteristic diagram comparing NOx emissions at equal PM during mode running.
FIG. 10 is a flowchart for explaining control contents;
FIG. 11 is a characteristic diagram of a target EGR rate.
FIG. 12 is a characteristic diagram of target main injection timing.
FIG. 13 is a characteristic diagram of target intake valve closing timing.
FIG. 14 is a characteristic diagram of a target swirl ratio.
FIG. 15 is a characteristic diagram of a target boost pressure.
FIG. 16 is a characteristic diagram of a target pilot injection amount and a target pilot injection timing.
FIG. 17 is a schematic configuration diagram of a variable valve timing mechanism.
FIG. 18 is a flowchart for explaining control contents of the second embodiment;
FIG. 19 is a characteristic diagram of a target EGR valve flow rate, a target exhaust valve flow rate, and a target intake valve flow rate.
FIG. 20 is a map in which a first target temperature is set.
FIG. 21 is a map in which a second target temperature is set.
FIG. 22 is a map in which a third target temperature is set.
FIG. 23 is a map in which a fourth target temperature is set.
FIG. 24 is a flowchart for explaining control contents of the third embodiment;
FIG. 25 is a diagram corresponding to claims of the first invention.
FIG. 2619FIG.
[Explanation of symbols]
6 EGR valve
17 nozzles
33 Accelerator position sensor
34 Crank angle sensor
41 Control unit
52 turbocharger

Claims (24)

The fuel injection timing is delayed until after the compression top dead center, and the fuel ignition delay period is lengthened. During this ignition delay period, a premixed gas in which the fuel is sufficiently vaporized is formed, and under a low concentration of oxygen. In a diesel engine that performs low temperature premixed combustion with a low compression ratio,
A fuel injection valve with variable fuel injection timing;
A temperature raising control device for raising the temperature of the working gas in the combustion chamber;
Means for predicting the atmospheric temperature in the cylinder at the start of combustion;
Means for determining whether the atmospheric temperature in the cylinder at the start of combustion is in a region lower than the first target temperature for maintaining the low temperature premixed combustion;
When it is determined that the atmospheric temperature in the cylinder at the start of combustion is lower than the first target temperature, the temperature increase control device is operated so that the atmospheric temperature in the cylinder at the start of combustion exceeds the first target temperature. A diesel engine combustion control apparatus comprising: means for performing temperature control and adjusting a fuel injection timing of the fuel injection valve so that a rate of increase in combustion temperature is equal to or greater than a predetermined value.   The diesel engine combustion control apparatus according to claim 1, wherein the cylinder atmosphere temperature at the start of combustion is predicted based on a compression ratio and an engine load.   The combustion control device for a diesel engine according to claim 1, wherein the temperature in the cylinder at the start of combustion is predicted based on the compression ratio and the intake gas temperature.   The fuel injection timing is controlled so that the start of combustion falls within a range of 5 ° to 20 ° after compression top dead center so that the temperature rise rate of main combustion becomes equal to or greater than the predetermined value. Item 4. The combustion control apparatus for a diesel engine according to any one of Items 1 to 3.   An intake valve closing timing control mechanism is provided as the temperature raising control device, and the atmospheric temperature in the cylinder at the start of combustion is equal to or lower than the first target temperature and higher than a second target temperature lower than the first target temperature. The diesel engine combustion control device according to any one of claims 1 to 4, wherein the temperature increase control is performed by advancing a closing timing of the intake valve.   A swirl control mechanism is further provided as the temperature increase control device, and when the atmospheric temperature in the cylinder at the start of combustion is lower than the second target temperature and higher than a third target temperature lower than the second target temperature, 6. The diesel engine combustion control apparatus according to claim 5, wherein the temperature increase control is performed by advancing the intake valve closing timing and lowering a swirl ratio.   When the temperature rise control device further includes a supercharging pressure control mechanism, and the atmospheric temperature in the cylinder at the start of combustion is lower than the second target temperature and higher than a third target temperature lower than the second target temperature 6. The combustion control apparatus for a diesel engine according to claim 5, wherein the temperature increase control is performed by advancing the intake valve closing timing, lowering a swirl ratio, and further increasing a supercharging pressure. .   When the temperature rise control device further includes a fuel injection control mechanism, and when the atmosphere temperature in the cylinder at the start of combustion is lower than the third target temperature and higher than a fourth target temperature lower than the third target temperature, Advance the intake valve closing timing, lower the swirl ratio, and set the pilot injection timing so that pilot injection is performed prior to the main injection of fuel and combustion by pilot injection ends before the main injection The diesel engine combustion control apparatus according to claim 6 or 7, wherein the temperature rise control is performed. When the temperature rise control device further includes a fuel injection control mechanism, and when the atmosphere temperature in the cylinder at the start of combustion is lower than the third target temperature and higher than a fourth target temperature lower than the third target temperature, The intake valve closing timing is advanced, the swirl ratio is lowered, the boost pressure is increased, pilot injection is performed prior to the main injection of fuel, and combustion by pilot injection is terminated before the main injection The diesel engine combustion control apparatus according to claim 7 , wherein the temperature increase control is performed by setting a pilot injection timing in the engine.   10. The combustion control apparatus for a diesel engine according to claim 8, wherein the fuel main injection timing is controlled such that the main injected fuel is ignited after the main injection of fuel is completed.   A valve opening / closing mechanism capable of arbitrarily controlling the opening / closing timing of one of the plurality of exhaust valves provided for one cylinder as the temperature rise control device, and an EGR valve for controlling the amount of exhaust gas recirculated during intake When the atmospheric temperature in the cylinder at the start of combustion is equal to or lower than the fourth target temperature, the intake valve closing timing is advanced, the swirl ratio is lowered, the boost pressure is increased, and the pilot injection combustion is performed. 9. The temperature increase control is performed by performing pilot injection so that main injection is performed after completion, and opening the one exhaust valve and closing the EGR valve during an intake stroke. The combustion control device for a diesel engine according to any one of 10 to 10.   Exhaust valve opening / closing mechanism capable of arbitrarily controlling the opening / closing timing of one of the plurality of exhaust valves provided as a temperature rise control device for one cylinder, and intake air capable of arbitrarily adjusting the opening / closing timing of the intake valve A valve control mechanism and an EGR valve that controls the amount of exhaust gas recirculated during intake, and when the atmospheric temperature in the cylinder at the start of combustion is equal to or lower than the fourth target temperature, the intake valve closing timing is advanced, EGR gas and intake air that lower the swirl ratio, increase the supercharging pressure, perform the pilot injection so that the main injection is performed after the completion of the pilot injection combustion, and flow into the combustion chamber via the EGR valve As the cooling water temperature decreases, the temperature is reduced as the cooling water temperature decreases, and by opening one exhaust valve during the intake stroke, the amount of EGR gas flowing back to the combustion chamber is increased as the cooling water temperature decreases, so that the temperature increase control is performed. It combustion control apparatus for a diesel engine according to any one of claims 8, wherein up to 10.   The diesel engine combustion control device according to claim 11 or 12, wherein an exhaust port on the side of the one exhaust valve that is opened in the intake stroke is formed as a helical port. The diesel engine combustion control device according to any one of claims 1 to 4, wherein the first target temperature is set according to a load such that the temperature becomes higher as the engine load becomes lower.   6. The diesel engine combustion control apparatus according to claim 5, wherein at least one of the first target temperature and the second target temperature is set according to the load such that the temperature decreases as the engine load increases.   8. The diesel engine combustion control according to claim 6, wherein at least one of the second target temperature and the third target temperature is set according to a load such that the temperature decreases as the engine load increases. apparatus.   11. The apparatus according to claim 8, wherein at least one of the third target temperature and the fourth target temperature is set according to a load such that the temperature decreases as the engine load increases. Diesel engine combustion control device.   The diesel engine combustion control apparatus according to any one of claims 11 to 13, wherein the fourth target temperature is set according to a load such that the temperature becomes higher as the engine load becomes lower. In a diesel engine that performs low-temperature premixed combustion at a low compression ratio,
A fuel injection valve with variable fuel injection timing;
A temperature raising control device for raising the temperature of the working gas in the combustion chamber;
Means for detecting an engine load affecting the atmospheric temperature in the cylinder at the start of combustion;
Means for determining whether or not the engine load is equal to or lower than a first target load for maintaining low-temperature premixed combustion and in a load range higher than a second target load lower than the first target load;
When it is determined that the engine load is equal to or lower than the first target load and is higher than the second target load, the temperature increase control device is operated to perform the temperature increase control, and the rate of increase in the combustion temperature is Means for adjusting the fuel injection timing of the fuel injection valve so as to be equal to or greater than a predetermined value. A swirl control mechanism is further provided as the temperature increase control device, and the intake valve closing timing is advanced when the load range is lower than the second target load and higher than the third target load lower than the second target load. The combustion control device for a diesel engine according to claim 19 , wherein the temperature increase control is performed by lowering a swirl ratio. A boost pressure control mechanism is further provided as the temperature raising control device, and the intake valve closing timing is set when the load range is lower than the second target load and higher than the third target load lower than the second target load. The diesel engine combustion control apparatus according to claim 19 , wherein the temperature increase control is performed by advancing, lowering a swirl ratio, and further increasing a supercharging pressure. A fuel injection control mechanism is further provided as the temperature increase control device, and the intake valve closing timing is advanced when the load range is lower than the third target load and higher than the fourth target load lower than the third target load. The temperature increase control is performed by setting the pilot injection timing so that the pilot injection is performed before the main injection of fuel and the pilot injection is completed before the main injection. The combustion control device for a diesel engine according to claim 19 or 20 , wherein: A fuel injection control mechanism is further provided as the temperature increase control device, and the intake valve closing timing is advanced when the load range is lower than the third target load and higher than the fourth target load lower than the third target load. The pilot injection timing is set so that the pilot injection is performed before the main injection of fuel and the combustion by the pilot injection ends before the main injection. it makes combustion control device for a diesel engine according to claim 19 or 20, characterized in that the temperature increase control. 24. The combustion control apparatus for a diesel engine according to claim 22 or 23 , wherein the fuel main injection timing is controlled so that the main injected fuel is ignited after completion of the main fuel injection.

Images