JP2007332876A - Control device of diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce NOx, to reduce THC, to reduce combustion noise, and to avoid a misfire, at the highland, in a control device of a diesel engine. <P>SOLUTION: This supercharging diesel engine with an intercooler performs intercooler bypass control for bypassing the intercooler to the whole or partial suction air, when an engine load is in a predetermined low-medium load area or when supercharging pressure is a predetermined value or less, in a low atmospheric pressure environment (Step 106), and also performs swirl ratio reduction control for increasing fuel injection pressure, by reducing the swirl ratio, when the engine load is in a medium-high load area or when the supercharging pressure exceeds the predetermined value, in the low atmospheric pressure environment. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a control device for a diesel engine.

  In recent years, there has been a demand for further reduction of emissions for diesel engines (compression ignition internal combustion engines) mounted on automobiles and the like. In order to meet this requirement, for example, a NOx storage reduction or selective reduction type NOx catalyst or a catalyst such as DPNR (Diesel Particulate-NOx-Reduction system) that simultaneously reduces NOx and PM (Particulate Matter) can be used. Has been done. In order to effectively exert such an exhaust purification action of the catalyst, an intake throttle valve is also provided in the intake passage of the diesel engine. The exhaust temperature can be raised by reducing the amount of intake air with the intake throttle valve at a light load or the like where the catalyst is less likely to be effective due to the low exhaust temperature.

  Moreover, in the turbo diesel engine with an intercooler which is the mainstream of recent diesel engines, the compression ratio tends to be lower than that in the past in order to increase the output. That is, in order to increase the output, it is necessary to burn a lot of fuel in the cylinder. Increasing the amount of fuel burned in the cylinder increases the maximum in-cylinder pressure. However, for reasons of engine mechanical strength, there is a desire to avoid increasing the maximum in-cylinder pressure as much as possible. In view of this, a design has been made in which a large amount of fuel can be combusted in the cylinder without increasing the maximum in-cylinder pressure by lowering the compression ratio than before.

  By the way, in the highland where the atmospheric pressure is low, the amount of air in the cylinder is reduced as the air density is smaller than in the flatland (lowland). For this reason, the compression end pressure (compression pressure) decreases, and thus the compression end temperature also decreases. That is, the in-cylinder pressure and the in-cylinder temperature at the time when fuel is injected are reduced. As a result, in order to control the diesel engine, an operating condition different from that on the flat ground may be required. Japanese Patent Laid-Open No. 2003-155949 discloses a fuel injection device for an internal combustion engine intended to control a pilot injection amount as intended without being affected by changes in environmental conditions such as atmospheric pressure. .

JP 2003-155949 A JP 7-49074 A JP 2000-120457 A JP 2002-201949 A JP-A-6-17654

  As described above, in the highland area, the pressure and temperature at the compression end are lower than in the flatland area, so that the fuel tends to be difficult to burn. As a result, it becomes difficult to operate in the same manner as on flat grounds, and in particular, in a light load range, misfire is likely to occur, and THC (hydrocarbon) in the exhaust gas is likely to increase. In particular, in a recent diesel engine having a low compression ratio, the pressure and temperature at the compression end are further lowered, so that these problems are more likely to occur.

  In order to solve the problems of misfire and increase in THC in high altitudes, conventionally, the injection timing is advanced to facilitate fuel combustion, or the intake throttle valve is opened to increase the intake air amount. However, if the injection timing is advanced, the in-cylinder temperature becomes higher, which causes a problem that NOx in the exhaust gas increases and combustion noise increases. Further, when the intake throttle valve is opened to increase the intake air amount, the exhaust gas temperature is lowered, so that there is a problem that the temperature of the catalyst becomes low and the exhaust gas purification action cannot be exhibited.

  The present invention has been made in view of the above points, and an object thereof is to provide a control device for a diesel engine that can achieve NOx reduction, THC reduction, combustion noise reduction, and misfire avoidance at high altitudes. .

A first invention is a control device for a diesel engine,
A turbocharger that compresses the intake air of the diesel engine;
An intercooler for cooling the intake air compressed by the supercharger;
Bypass means for bypassing the intercooler and allowing air to be sucked;
Low atmospheric pressure environment determining means for determining whether or not the atmospheric pressure is in a low atmospheric pressure environment having a predetermined value or less;
Intercooler bypass control means for performing intercooler bypass control for bypassing the intercooler to all or part of the intake air when it is determined that the vehicle is in the low atmospheric pressure environment;
It is characterized by providing.

The second invention is the first invention, wherein
The intercooler bypass control means performs the intercooler bypass control when the engine load is in a predetermined low / medium load range or when the supercharging pressure is equal to or lower than a predetermined value.

The third invention is the first or second invention, wherein
An actual compression ratio increasing means for increasing a substantial compression ratio when the intercooler bypass control is executed is further provided.

Moreover, 4th invention is set in 3rd invention,
The actual compression ratio increasing means is an intake valve early closing means for bringing the intake valve closing timing closer to bottom dead center by advancing the intake valve closing timing.

According to a fifth invention, in any one of the first to fourth inventions,
The intercooler bypass control means is a bypass amount control means for controlling the amount of air that bypasses the intercooler so that the intake air temperature on the downstream side of the intercooler becomes a target temperature when the intercooler bypass control is executed. It is characterized by including.

The sixth invention is a control device for a diesel engine,
Variable swirl means for varying the swirl ratio of the diesel engine;
An injection pressure variable means for making the fuel injection pressure variable;
Low atmospheric pressure environment determining means for determining whether or not the atmospheric pressure is in a low atmospheric pressure environment having a predetermined value or less;
Swirl ratio lowering control means for performing swirl ratio lowering control for lowering the swirl ratio and increasing the fuel injection pressure when determined to be in the low atmospheric pressure environment;
It is characterized by providing.

The seventh invention is the sixth invention, wherein
The swirl ratio decrease control means executes the swirl ratio decrease control when the engine load is in a predetermined medium to high load range or when the supercharging pressure exceeds a predetermined value.

The eighth invention is the sixth or seventh invention, wherein
The diesel engine includes a plurality of intake valves per cylinder,
The variable swirl means makes the swirl ratio variable by making at least one of valve timing, working angle, and lift amount of some intake valves different from other intake valves in the same cylinder. Features.

The ninth invention is a control device for a diesel engine,
A turbocharger that compresses the intake air of the diesel engine;
An intercooler for cooling the intake air compressed by the supercharger;
Bypass means for bypassing the intercooler and allowing air to be sucked;
Variable swirl means for varying the swirl ratio;
An injection pressure variable means for making the fuel injection pressure variable;
Low atmospheric pressure environment determining means for determining whether or not the atmospheric pressure is in a low atmospheric pressure environment having a predetermined value or less;
When it is determined that the engine is in the low atmospheric pressure environment and the engine load is in a predetermined low / medium load range or the supercharging pressure is equal to or lower than a predetermined value, all or part of the intake air is Intercooler bypass control means for performing intercooler bypass control for bypassing the intercooler;
When it is determined that the engine is in the low atmospheric pressure environment and the engine load exceeds the low / medium load range or the supercharging pressure exceeds the predetermined value, the swirl ratio is reduced and fuel injection is performed. Swirl ratio lowering control means for performing swirl ratio lowering control for increasing the pressure;
It is characterized by providing.

  According to the first invention, it is possible to determine whether or not the supercharged diesel engine with an intercooler is in a low atmospheric pressure environment (high altitude). And when it exists in a low atmospheric pressure environment, an intercooler can be bypassed by all or one part intake air. By bypassing the intercooler, the intake air temperature can be increased, so that the compression end temperature can be increased. Further, the pressure loss generated in the intercooler is reduced and the intake pipe pressure is increased, so that the compression end pressure can be increased. Therefore, the pressure and temperature at the compression end can be secured sufficiently high even in a low atmospheric pressure environment. For this reason, it is possible to effectively suppress the increase in THC emission and the occurrence of misfire. In addition, according to the first aspect, the above-described effect can be obtained without excessively advancing the fuel injection timing. For this reason, there is no adverse effect associated with the advance of the fuel injection timing, that is, NOx emission amount and combustion noise increase. Furthermore, according to the first invention, the above-described effect can be obtained without excessively increasing the intake air amount. For this reason, it is possible to avoid the adverse effect of excessively increasing the amount of intake air, that is, inactivation of the catalyst due to a decrease in exhaust temperature.

  According to the second aspect of the invention, the intercooler bypass control can be executed when the engine load is in a predetermined low / medium load range or when the supercharging pressure is equal to or lower than a predetermined value. For this reason, the pressure and temperature at the compression end can be sufficiently increased even under a low atmospheric pressure environment even when the load or the supercharging pressure is small. Therefore, it is possible to effectively suppress the increase in THC emission and the occurrence of misfire.

  According to the third aspect, the substantial compression ratio can be increased when the intercooler bypass control is executed. For this reason, the pressure and temperature at the compression end can be further increased, and the increase in the THC discharge amount and the occurrence of misfire can be more reliably suppressed.

  According to the fourth aspect of the invention, when the intercooler bypass control is executed, the actual compression ratio can be increased by increasing the intake valve closing timing and bringing the intake valve closing timing closer to the bottom dead center. Thereby, an actual compression ratio can be increased easily.

  According to the fifth aspect, when the intercooler bypass control is executed, the amount of air that bypasses the intercooler can be controlled so that the intake air temperature on the downstream side of the intercooler becomes the target temperature. Thereby, increase of THC discharge | emission amount and generation | occurrence | production of misfire can be suppressed more reliably.

  According to the sixth aspect, it is possible to determine whether or not the diesel engine is in a low atmospheric pressure environment (high altitude). And when it exists in a low atmospheric pressure environment, a swirl ratio can be reduced and a fuel-injection pressure can be raised. By reducing the swirl ratio, the flow coefficient of the intake system is increased, so that the intake air amount can be increased. Therefore, the pressure and temperature at the compression end can be secured sufficiently high even in a low atmospheric pressure environment. For this reason, it is possible to effectively suppress the increase in THC emission and the occurrence of misfire. According to the sixth aspect of the invention, the fuel can be further atomized and injected by increasing the fuel injection pressure. Therefore, it is possible to reliably avoid an increase in smoke due to a reduction in the swirl ratio. According to the sixth aspect of the invention, the above effect can be obtained without excessively advancing the fuel injection timing. For this reason, there is no adverse effect associated with the advance of the fuel injection timing, that is, NOx emission amount and combustion noise increase.

  According to the seventh aspect, the swirl ratio reduction control can be executed when the engine load is in a predetermined middle / high load range or when the supercharging pressure exceeds a predetermined value. As a result, when the load and the supercharging pressure are large in a low atmospheric pressure environment, a sufficient intake air amount corresponding to the load and the supercharging pressure can be secured. Therefore, it is possible to effectively suppress the increase in THC emission and the occurrence of misfire.

  According to the eighth invention, the swirl ratio can be made variable by making at least one of the valve timing, the working angle, and the lift amount of some of the intake valves different from those of the other intake valves in the same cylinder. . As a result, the swirl ratio can be accurately changed with a high degree of freedom.

  According to the ninth aspect, it is possible to determine whether or not the supercharged diesel engine with an intercooler is in a low atmospheric pressure environment (high altitude). When the engine load is in a predetermined low / medium load range or when the supercharging pressure is equal to or lower than a predetermined value when the engine load is in a low atmospheric pressure environment, the intercooler is connected to all or part of the intake air. Can be bypassed. By bypassing the intercooler, the intake air temperature can be increased, so that the compression end temperature can be increased. Further, the pressure loss generated in the intercooler is reduced and the intake pipe pressure is increased, so that the compression end pressure can be increased. Therefore, the pressure and temperature at the compression end can be secured sufficiently high even in a low atmospheric pressure environment. For this reason, it is possible to effectively suppress the increase in THC emission and the occurrence of misfire. According to the ninth invention, when the engine load is in a low atmospheric pressure environment and the engine load exceeds the low / medium load range or the supercharging pressure exceeds the predetermined value, the swirl ratio is set. The fuel injection pressure can be increased and the fuel injection pressure can be increased. By reducing the swirl ratio, the flow coefficient of the intake system is increased, so that the intake air amount can be increased. Therefore, the pressure and temperature at the compression end can be secured sufficiently high even in a low atmospheric pressure environment. For this reason, it is possible to effectively suppress the increase in THC emission and the occurrence of misfire. Further, in this case, by increasing the fuel injection pressure, the fuel can be further atomized and injected. Therefore, it is possible to reliably avoid an increase in smoke due to a reduction in the swirl ratio. And according to 9th invention, the said effect can be acquired, without advancing fuel injection timing too much. For this reason, there is no adverse effect associated with the advance of the fuel injection timing, that is, NOx emission amount and combustion noise increase.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted.

Embodiment 1 FIG.
[Description of system configuration]
FIG. 1 is a diagram for explaining a system configuration according to the first embodiment of the present invention. The system shown in FIG. 1 includes a four-cycle diesel engine (compression ignition internal combustion engine) 10. It is assumed that the diesel engine 10 is mounted on a vehicle and used as a power source. Although the illustrated diesel engine 10 is an in-line four-cylinder type, in the present invention, the number of cylinders and the cylinder arrangement are not limited thereto.

  Each cylinder of the diesel engine 10 is provided with an injector 12 that injects fuel directly into the cylinder. The injectors 12 of each cylinder are connected to a common common rail 14. Fuel in a fuel tank (not shown) is pressurized to a predetermined fuel pressure by a supply pump 16, stored in the common rail 14, and supplied from the common rail 14 to each injector 12.

  An exhaust passage 18 of the diesel engine 10 is branched by an exhaust manifold 20 and connected to an exhaust port 22 (see FIG. 2) of each cylinder. The diesel engine 10 according to this embodiment includes a turbocharger 24. The exhaust passage 18 is connected to the exhaust turbine of the turbocharger 24.

  A catalyst 26 for purifying exhaust gas is provided in the exhaust passage 18 downstream of the turbocharger 24. As the catalyst 26, for example, an occlusion reduction type or selective reduction type NOx catalyst, a DPNR (Diesel Particulate-NOx-Reduction system), an oxidation catalyst, or a combination thereof can be used.

  An air cleaner 30 is provided near the inlet of the intake passage 28 of the diesel engine 10. The air drawn through the air cleaner 30 is compressed by the intake compressor of the turbocharger 24 and then cooled by the intercooler 32. The intake air that has passed through the intercooler 32 is distributed by the intake manifold 34 to the intake ports 35 (see FIG. 2) of the respective cylinders.

  An intake throttle valve 36 is installed between the intercooler 32 and the intake manifold 34 in the intake passage 28. In a light load range or the like, the exhaust temperature can be raised by limiting the intake air amount by reducing the opening of the intake throttle valve 36. Further, an air flow meter 38 for detecting the amount of intake air is installed in the vicinity of the intake passage 28 downstream of the air cleaner 30.

  One end of an external EGR passage 40 is connected to the intake passage 28 in the vicinity of the intake manifold 34. The other end of the external EGR passage 40 is connected to the vicinity of the exhaust manifold 20 of the exhaust passage 18. In this system, a part of the exhaust gas (burned gas) can be recirculated to the intake passage 28 through the external EGR passage 40, that is, external EGR (Exhaust Gas Recirculation) can be performed.

  In the middle of the external EGR passage 40, an EGR cooler 42 for cooling the external EGR gas is provided. An EGR valve 44 is provided downstream of the EGR cooler 42 in the external EGR passage 40. As the opening degree of the EGR valve 44 is increased, the amount of exhaust gas passing through the external EGR passage 40, that is, the amount of external EGR can be increased.

  Between the intercooler 32 and the intake throttle valve 36 in the intake passage 28, a supercharging pressure sensor 46 that detects the supercharging pressure and an intake air temperature sensor 47 that detects the intake air temperature are installed. The system also includes an accelerator opening sensor 48 that detects the amount of depression of the accelerator pedal (accelerator opening) of a vehicle on which the diesel engine 10 is mounted, and an atmospheric pressure sensor 70 that detects atmospheric pressure.

  In this system, a bypass passage 66 that bypasses the intercooler 32 is provided. That is, the bypass passage 66 connects (short-circuits) the upstream side and the downstream side of the intercooler 32. In the present system, by providing the bypass passage 66, all or part of the intake air can be sucked into the diesel engine 10 without passing through the intercooler 32.

  A bypass control valve 68 is provided at a branch portion where the intake passage 28 branches into the intercooler 32 side and the bypass passage 66 side. By adjusting the state (posture) of the bypass control valve 68, the ratio between the amount of air sucked through the intercooler 32 and the amount of air sucked without passing through the intercooler 32 can be freely controlled. .

  In addition, this system includes an ECU (Electronic Control Unit) 50. The ECU 50 is connected to the various sensors and actuators described above. The ECU 50 controls the operating state of the diesel engine 10 by driving each actuator according to a predetermined program based on those signals and information.

  FIG. 2 is a view showing a cross section of one cylinder of the diesel engine 10 in the system shown in FIG. Hereinafter, the diesel engine 10 will be further described. As shown in FIG. 2, a crank angle sensor 62 that detects the rotation angle (crank angle) of the crankshaft 60 is attached in the vicinity of the crankshaft 60 of the diesel engine 10. The crank angle sensor 62 is connected to the ECU 50. According to the signal from the crank angle sensor 62, the engine speed and the like can be detected.

  In the present embodiment, it is assumed that the diesel engine 10 is provided with two intake valves 52 and two exhaust valves 56 per cylinder. The diesel engine 10 further includes an intake variable valve mechanism 54 that drives the intake valve 52 and an exhaust variable valve mechanism 58 that drives the exhaust valve 56. The intake variable valve mechanism 54 can continuously change the valve timing, the operating angle, and the lift amount of the intake valve 52. The intake variable valve mechanism 54 can vary the valve timing, the operating angle, and the lift amount between one intake valve 52 and the other intake valve 52 of the same cylinder. The exhaust variable valve mechanism 58 can continuously change at least one of the valve timing, the operating angle, and the lift amount of the exhaust valve 56. These intake variable valve mechanism 54 and exhaust variable valve mechanism 58 are connected to the ECU 50. Specific configurations of the intake variable valve mechanism 54 and the exhaust variable valve mechanism 58 are not particularly limited, and may be a mechanical mechanism, an electromagnetically driven valve, a hydraulically driven valve, or the like.

[Features of Embodiment 1]
(Variable swirl)
In the diesel engine 10, the intake variable valve mechanism 54 can make the operating angle and lift amount of one of the two intake valves 52 provided in the same cylinder smaller than the other operating angle and lift amount. By doing so, the swirl ratio can be made larger than when the operating angle and the lift amount of the two intake valves 52 are equal. In this case, the swirl ratio can be increased as the operating angle and the lift amount of the one intake valve 52 are reduced. Further, the operating angle and the lift amount of the one intake valve 52 may be zero. When the swirl ratio is increased, the speed of the rotational motion of the air generated in the cylinder (combustion chamber) is increased and the mixing of the fuel and air during combustion is promoted, so that smoke can be reduced. In the system of the present embodiment, the swirl ratio can be changed as described above according to the operating state of the diesel engine 10.

  As described above, since the atmospheric pressure is lower in the highland than in the flatland, the compression end pressure (compression pressure) decreases, and as a result, the compression end temperature also decreases. Here, the compression end means a state in the cylinder when the air sucked into the cylinder is compressed by the piston 64 and fuel is injected from the injector 12 (main injection). When the pressure and temperature at the compression end are low, the fuel is difficult to burn. For this reason, in the highland area, it becomes difficult to operate in the same manner as in the flatland area, and there is a problem that misfire is likely to occur and THC (hydrocarbon) in the exhaust gas is likely to increase (particularly in a light load region). In order to solve such a problem, in the present embodiment, intercooler bypass control and swirl ratio reduction control described below are performed.

(Intercooler bypass control)
In this system, based on the atmospheric pressure detected by the atmospheric pressure sensor 70, it can be determined whether or not the vehicle is in a high altitude (under a low atmospheric pressure environment). When it is determined that the vehicle is in a high altitude, the intake air compressed by the turbocharger 24 is sucked into the diesel engine 10 through the bypass passage 66 without passing through the intercooler 32. As a result, the intake air temperature can be increased by the amount that the intake air is not cooled by the intercooler 32. Therefore, the compression end temperature can be increased. Further, since the pressure loss generated in the intercooler 32 is eliminated, the intake pipe pressure can be increased. Therefore, the compression end pressure can be increased. Thus, the pressure and temperature at the compression end can be increased by bypassing the intercooler 32. For this reason, it is possible to effectively suppress the increase in THC emission and the occurrence of misfire.

  In this embodiment, the substantial compression ratio (hereinafter referred to as “actual compression ratio”) is increased by advancing the closing timing of the intake valve 52 together with the bypass of the intercooler 32. FIG. 3 is a diagram showing the lift characteristics of the intake valve 52. In FIG. 3, the alternate long and short dash line is a lift curve during normal operation, that is, on a flat ground. As shown in the lift curve, during normal operation, the intake valve closing timing is set after the bottom dead center (BDC) in order to effectively use the intake inertia in the high rotation range. On the other hand, the broken line in FIG. 3 is a lift curve when the intercooler bypass control is executed. As shown in this lift curve, when the intercooler bypass control is executed, the intake valve closing timing is advanced to approach the bottom dead center. The time when the compression of the air in the cylinder is substantially started is the time when the intake valve is closed. Therefore, by increasing the intake valve closing timing, the compression start timing of the in-cylinder air can be advanced, so that the actual compression ratio can be increased. When the actual compression ratio is increased, the pressure and temperature at the compression end can be further increased. Therefore, an increase in the THC emission amount and the occurrence of misfire can be more reliably suppressed.

  The intercooler bypass control is executed when the engine load is equal to or less than a predetermined value (hereinafter referred to as “low / medium load range”). When the engine load exceeds the predetermined value (hereinafter referred to as “medium / high load range”), the swirl ratio reduction control described below is executed instead of the intercooler bypass control.

(Swirl ratio reduction control)
In the present embodiment, when it is determined that the vehicle is in a high altitude region, and when the vehicle is in a medium to high load region, the operation of the intake variable valve mechanism 54 is controlled so that the swirl ratio is reduced as compared to when traveling on a flat ground. In addition, the fuel injection pressure from the injector 12 is increased. In the middle and high load range, a large amount of fuel is burned in the cylinder, so it is necessary to secure a large amount of air sucked into the cylinder. When the swirl ratio is reduced, the flow coefficient of the intake system is increased. Therefore, the amount of air sucked into the cylinder can be increased by reducing the swirl ratio.

  On the other hand, if the swirl ratio is reduced, the effect of the swirl, that is, the effect of promoting the mixing of the fuel and the air is reduced, so that smoke tends to increase. Therefore, when the swirl ratio reduction control is executed, the increase of the fuel injection pressure is also performed to prevent the increase in smoke. When the fuel injection pressure is increased, fuel can be atomized and injected, so that mixing with air can be promoted. For this reason, smoke can be reduced.

  In addition, when the swirl ratio reduction control is executed, the intake air is passed through the intercooler 32 without bypassing the intercooler 32. In the medium and high load range, the turbocharger 24 operates more effectively than in the low and medium load range, so that the supercharging pressure becomes high. For this reason, the intake air temperature at the outlet of the turbocharger 24 increases. In such a case, it is more effective in reducing THC to increase the charging efficiency by cooling the intake air with the intercooler 32 and to increase the amount of air sucked into the cylinder. Therefore, the intake air is passed through the intercooler 32 as usual without bypassing the intercooler 32.

[Specific Processing in Embodiment 1]
FIG. 4 is a flowchart of a routine executed by the ECU 50 in the present embodiment in order to realize the above function. This routine is repeatedly executed every predetermined time. According to the routine shown in FIG. 4, it is first determined whether or not the vehicle is in a high altitude (under a low atmospheric pressure environment) that requires intercooler bypass control or swirl ratio reduction control (step 100). Specifically, first, the current atmospheric pressure P ₀ detected by the atmospheric pressure sensor 70 is read. Next, the success or failure of the following inequality is determined.
Standard atmospheric pressure −P ₀ ≧ 10 kPa (1)

  The value of the standard atmospheric pressure in the above equation (1) is assumed to be stored in advance in the ECU 50. If the above equation (1) is not established in step 100, it can be determined that the atmospheric pressure is not low enough to require intercooler bypass control or swirl ratio reduction control. Therefore, in this case, predetermined base control (normal control) is performed (step 102), and the current processing cycle of this routine is terminated.

  On the other hand, if the above equation (1) is established in step 100, it can be determined that the vehicle is at a high altitude where the atmospheric pressure is low enough to require intercooler bypass control and swirl ratio reduction control. In this case, next, the current engine speed and accelerator opening are read, and based on these values, it is determined whether or not the engine is in a low / medium load range (step 104).

If it is determined in step 104 that the vehicle is in the low / medium load range, the above-described intercooler bypass control is executed (step 106). That is, the state of the bypass control valve 68 is controlled so that the intake air does not pass through the intercooler 32 but passes through the bypass passage 66. Further, the operation of the intake variable valve mechanism 54 is controlled so that the closing timing of the intake valve 52 is advanced. In this case, a map that defines the relationship between the atmospheric pressure P ₀ and the closing timing of the intake valve 52 is stored in the ECU 50 in advance, and control is performed so that the closing timing of the intake valve 52 is earlier as the atmospheric pressure P ₀ is lower. May be.

On the other hand, if it is determined in step 104 that the vehicle is in the low / medium load range, the aforementioned swirl ratio reduction control is executed (step 108). In this swirl ratio reduction control, for example, the swirl ratio is controlled to be smaller than that during base control (when traveling on flat ground) by one of the following methods.
(1) In the case where the intake single valve closing for holding one of the two intake valves 52 of the same cylinder in the closed state is performed in the region on the light load side, the region in which the intake single valve closes is performed during base control. Move to the lighter load side. Alternatively, the intake single valve is not closed over the entire operation range.
(2) When the working angle and lift amount of one of the two intake valves 52 of the same cylinder are made smaller than the other working angle and lift amount, the working angle and lift of the one intake valve 52 Make the amount larger than the base control to reduce the difference between the two. Alternatively, the operating angle and lift amount of both intake valves 52 are made equal.

  Further, in the swirl ratio reduction control in step 108, the state of the bypass control valve 68 is controlled so that the intake air passes through the intercooler 32 without bypassing the intercooler 32 to the intake air. Further, the operation of the supply pump 16 is controlled so that the pressure in the common rail 14 (rail pressure) becomes larger than that during base control. As a result, the fuel injection pressure from the injector 12 is increased.

  According to the routine processing shown in FIG. 4 described above, the pressure and temperature at the compression end can be sufficiently increased even when traveling at a high altitude with a low atmospheric pressure, and the intake air amount can be reduced. It can be secured sufficiently. For this reason, the THC emission amount can be reduced. Furthermore, the occurrence of misfire can be reliably prevented.

  Further, according to the routine processing shown in FIG. 4, the above-described effects can be obtained without excessively increasing the fuel injection timing. For this reason, NOx emission amount does not increase and combustion noise does not increase. Furthermore, the above-described effect can be obtained without opening the intake throttle valve to increase the intake air amount, so that the exhaust temperature can be prevented from becoming too low. For this reason, the purification action of the catalyst 26 can be exhibited effectively.

  Moreover, in this embodiment, according to the magnitude | size of the load of the diesel engine 10, either intercooler bypass control or swirl ratio fall control is performed. Thereby, the said effect can be acquired irrespective of the magnitude of load.

  In the present embodiment, whether or not the vehicle is in a high altitude with a low atmospheric pressure is determined based on a signal from the atmospheric pressure sensor 70, but the determination method is not limited to this. For example, the altitude of the traveling point of the vehicle may be obtained by a car navigation system using GPS (Global Positioning System), and it may be determined whether the vehicle is in a low atmospheric pressure environment according to the altitude.

  In step 104 of the routine shown in FIG. 4, whether to perform intercooler bypass control or swirl ratio reduction control is determined according to the load (accelerator opening). This may be determined accordingly. That is, the supercharging pressure detected by the supercharging pressure sensor 46 is compared with a predetermined determination value in step 104, and when the supercharging pressure is equal to or lower than the determination value, intercooler bypass control is performed, and the supercharging pressure is determined. When the value exceeds the determination value, swirl ratio reduction control may be executed. In addition to the determination based on the load or the supercharging pressure, the intercooler bypass control or the swirl ratio lowering control is performed on the condition that the current engine speed is equal to or less than a predetermined value, that is, in the low speed region. You may make it perform.

  In the first embodiment described above, when the intercooler bypass control is executed, the entire amount of intake air is passed through the bypass passage 66, but a part of the intake air is passed through the bypass passage 66, and the rest is the intercooler. 32 may be allowed to pass. Further, the ratio of the amount of air passing through the intercooler 32 and the amount of bypassed air is adjusted by feedback control of the state of the bypass control valve 68 so that the intake air temperature detected by the intake air temperature sensor 47 becomes the target temperature. You may make it do.

  Further, in the first embodiment described above, the intake variable valve operating mechanism 54 so that the operating angle and lift amount of one intake valve 52 of the same cylinder and the operating angle and lift amount of the other intake valve 52 are different. Although the swirl ratio is made variable by operating the, the method for making the swirl ratio variable is not limited to this. For example, the swirl ratio may be made variable using a known swirl control valve. In that case, in the swirl ratio reduction control, the swirl ratio can be reduced by adjusting the opening of the swirl control valve.

Further, in the first embodiment described above, a sufficient intake air amount is ensured by reducing the swirl ratio in the middle and high load range at high altitudes. However, a technique other than reducing the swirl ratio, for example, The intake air amount may be secured by any of the following methods.
(1) As shown by the solid line in FIG. 3, at least one of the operating angle and the lift amount of the intake valve 52 is made larger than that when traveling on flat ground.
(2) The opening time of the exhaust valve 56 is made earlier than when traveling on flat ground. As a result, the exhaust energy increases and the rotational speed of the turbocharger 24 increases, so that the supercharging pressure can be increased. For this reason, a sufficient amount of intake air can be secured.

  In the first embodiment described above, the turbocharger 24 is the “supercharger” in the first and ninth inventions, and the bypass passage 66 and the bypass control valve 68 are the first and ninth inventions. Corresponds to “bypass means” in FIG. Further, when the ECU 50 executes the processing of step 100, the “low atmospheric pressure environment determination means” in the first, sixth and ninth inventions executes the processing of steps 104 and 106. The “intercooler bypass control means” in the first, second and ninth inventions makes the “actual compression ratio increasing means” in the third invention by advancing the closing timing of the intake valve 52 in the processing of step 106. And the "intake valve early closing means" in the fourth invention performs the processing of steps 104 and 108, so that the "swirl ratio reduction control means" in the sixth, seventh and ninth inventions respectively It has been realized.

  In the first embodiment described above, the ECU 50 feedback-controls the state of the bypass control valve 68 so that the intake air temperature detected by the intake air temperature sensor 47 at the time of execution of the intercooler bypass control becomes the target temperature. In the fifth aspect of the present invention, the “bypass amount control means” allows intake so that the operating angle and lift amount of one intake valve 52 of the same cylinder and the operating angle and lift amount of the other intake valve 52 are different. By operating the variable valve mechanism 54, the “variable swirl means” in the sixth, eighth and ninth inventions controls the operation of the supply pump 16 to change the rail pressure, thereby changing the sixth and ninth. Each of the “injection pressure varying means” in the present invention is realized.

It is a figure for demonstrating the system configuration | structure of Embodiment 1 of this invention. It is a figure which shows the cross section of one cylinder of the diesel engine in the system shown in FIG. It is a figure which shows the lift characteristic of the intake valve in Embodiment 1 of this invention. It is a flowchart of the routine performed in Embodiment 1 of the present invention.

Explanation of symbols

10 diesel engine 12 injector 14 common rail 18 exhaust passage 20 exhaust manifold 22 exhaust port 24 turbocharger 26 catalyst 28 intake passage 34 intake manifold 36 intake throttle valve 38 air flow meter 40 external EGR passage 44 EGR valve 46 supercharging pressure sensor 47 suction Temperature sensor 50 ECU
52 Intake valve 54 Intake variable valve mechanism 56 Exhaust valve 58 Exhaust variable valve mechanism 62 Crank angle sensor 64 Piston 66 Bypass passage 68 Bypass control valve 70 Atmospheric pressure sensor

Claims (9)

A turbocharger that compresses the intake air of the diesel engine;
An intercooler for cooling the intake air compressed by the supercharger;
Bypass means for bypassing the intercooler and allowing air to be sucked;
Low atmospheric pressure environment determining means for determining whether or not the atmospheric pressure is in a low atmospheric pressure environment having a predetermined value or less;
Intercooler bypass control means for performing intercooler bypass control for bypassing the intercooler to all or part of the intake air when it is determined that the vehicle is in the low atmospheric pressure environment;
A control device for a diesel engine, comprising:   The intercooler bypass control means executes the intercooler bypass control when the engine load is in a predetermined low / medium load range or when the supercharging pressure is a predetermined value or less. The diesel engine control device described.   The diesel engine control device according to claim 1 or 2, further comprising an actual compression ratio increasing means for increasing a substantial compression ratio when the intercooler bypass control is executed.   4. The control device for a diesel engine according to claim 3, wherein the actual compression ratio increasing means is an intake valve early closing means for bringing the intake valve closing timing closer to bottom dead center by advancing the intake valve closing timing.   The intercooler bypass control means is a bypass amount control means for controlling the amount of air that bypasses the intercooler so that the intake air temperature on the downstream side of the intercooler becomes a target temperature when the intercooler bypass control is executed. The diesel engine control device according to claim 1, comprising: Variable swirl means for varying the swirl ratio of the diesel engine;
An injection pressure variable means for making the fuel injection pressure variable;
Low atmospheric pressure environment determining means for determining whether or not the atmospheric pressure is in a low atmospheric pressure environment having a predetermined value or less;
Swirl ratio lowering control means for performing swirl ratio lowering control for lowering the swirl ratio and increasing the fuel injection pressure when determined to be in the low atmospheric pressure environment;
A control device for a diesel engine, comprising:   7. The swirl ratio reduction control means executes the swirl ratio reduction control when the engine load is in a predetermined medium to high load range or when the supercharging pressure exceeds a predetermined value. Diesel engine control device. The diesel engine includes a plurality of intake valves per cylinder,
The variable swirl means makes the swirl ratio variable by making at least one of valve timing, working angle, and lift amount of some intake valves different from other intake valves in the same cylinder. 8. The diesel engine control device according to claim 6, wherein the control device is a diesel engine. A turbocharger that compresses the intake air of the diesel engine;
An intercooler for cooling the intake air compressed by the supercharger;
Bypass means for bypassing the intercooler and allowing air to be sucked;
Variable swirl means for varying the swirl ratio;
An injection pressure variable means for making the fuel injection pressure variable;
Low atmospheric pressure environment determining means for determining whether or not the atmospheric pressure is in a low atmospheric pressure environment having a predetermined value or less;
When it is determined that the engine is in the low atmospheric pressure environment and the engine load is in a predetermined low / medium load range or the supercharging pressure is equal to or lower than a predetermined value, all or part of the intake air is Intercooler bypass control means for performing intercooler bypass control for bypassing the intercooler;
When it is determined that the engine is in the low atmospheric pressure environment and the engine load exceeds the low / medium load range or the supercharging pressure exceeds the predetermined value, the swirl ratio is reduced and fuel injection is performed. Swirl ratio lowering control means for performing swirl ratio lowering control for increasing the pressure;
A control device for a diesel engine, comprising:

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