JP2007224867A - Control device for diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve exhaust emission characteristics by appropriately introducing exhaust emission recirculation gas even in heavy load operation in a control device for a diesel engine. <P>SOLUTION: A variable capacity supercharger 24 composed of a compressor 25 in an intake pipe 20 and a turbine 26 in an exhaust pipe 22 and a large number of nozzle vanes 28 is provided, and an EGR passage connecting the upstream side of the turbine 26 of the exhaust pipe 22 and the downstream side of the compressor 25 in the intake pipe 20 and including an EGR valve 32 is provided. A control device 33 can control an opening of the EGR valve 32 according to the operation state of the diesel engine and can control an opening of the nozzle vanes 28. The opening of the nozzle vane 28 is controlled to keep exhaust pressure in the exhaust pipe 22 higher than intake pressure in the intake pipe 20 during low-rotation speed heavy load operation. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a control device for a diesel engine having an exhaust gas recirculation function for circulating exhaust gas discharged from an exhaust system of the diesel engine to an intake system.

  In a diesel engine, an exhaust gas recirculation (EGR) device that circulates a part of exhaust gas to an intake system is applied to suppress generation of NOx. This EGR device is configured by connecting an exhaust passage and an intake passage of a diesel engine by an EGR passage, and providing an EGR valve in the EGR passage. Therefore, a predetermined amount of exhaust gas (EGR gas) is returned to the intake passage through the EGR passage by opening and closing the EGR valve in accordance with the operating state of the diesel engine. That is, when the diesel engine is in a high load state, the combustion temperature becomes high, and thus high concentration NOx is likely to be generated. At this time, the EGR valve is opened to return the EGR gas to the intake passage. Since this EGR gas has a relatively high specific heat and can absorb a large amount of heat, the combustion temperature in the combustion chamber decreases as the circulation amount of the EGR gas increases. The generation amount can be reduced.

  A turbocharger is applied as a method for improving the output of a diesel engine. This supercharger is configured by connecting a turbine provided in an exhaust passage and a compressor provided in an intake passage by a drive shaft. Therefore, by driving the turbine with the energy of the exhaust gas, the compressor integrated with the turbine is driven, and the intake air is compressed by this compressor to increase the charging efficiency, thereby improving the engine output.

  In addition, there exists what was described in the following patent document 1 as a diesel engine to which such an EGR apparatus and a supercharger were applied.

JP 2004-100508 A JP 2001-152879 A

  In the above-described conventional diesel engine, during high load operation, the EGR valve is opened to return the EGR gas to the intake passage, thereby lowering the combustion temperature and reducing the amount of NOx generated. The compressor is integrated with this turbine, and the intake air is compressed by the compressor integrated with the turbine to increase the charging efficiency and improve the engine output. However, when the EGR valve is opened in a state in which the charging efficiency of the intake air is increased by the supercharger during the low rotation and high load operation of the diesel engine, it becomes difficult to return the EGR gas in the exhaust passage to the intake passage. That is, when the supercharging ratio is increased by the supercharger, the pressure of the intake passage increases, and the pressure of the intake passage may become higher than the pressure of the exhaust passage. In this case, the EGR passage is opened by the EGR valve. Even if it is opened, the EGR gas in the exhaust passage cannot be introduced into the intake passage through the EGR passage. Therefore, there is a problem that the combustion temperature cannot be lowered by EGR gas during the high load operation of the diesel engine, and the amount of NOx generated cannot be reduced.

  In Patent Document 2 described above, the variable pressure nozzle and the exhaust throttle valve of the turbocharger are throttled to increase the exhaust pressure and the EGR amount, which not only complicates the structure but also increases the exhaust pressure. There is a problem that engine performance deteriorates too much.

  SUMMARY OF THE INVENTION The present invention solves the above-described problems, and an object of the present invention is to provide a control device for a diesel engine that improves exhaust gas characteristics by properly introducing exhaust recirculation gas even in high-load operation. And

  In order to achieve the above object, a control apparatus for a diesel engine according to claim 1 of the present invention includes an exhaust gas recirculation passage for circulating exhaust gas in an exhaust passage to an intake passage, and an exhaust flow rate adjustment provided in the exhaust gas recirculation passage. A variable capacity supercharger capable of changing the supercharging pressure by adjusting the opening of the exhaust movable vane by connecting a valve, a turbine provided in the exhaust passage, and a compressor provided in the intake passage coaxially. And a control device for controlling the opening degree of the exhaust flow rate adjusting valve and the opening degree of the exhaust movable vane according to the operating state of the diesel engine. The opening of the exhaust movable vane is controlled such that the exhaust pressure in the exhaust passage is higher than the intake pressure in the intake passage.

  In the diesel engine control apparatus according to the second aspect of the invention, the control means increases the opening of the exhaust flow rate adjustment valve and decreases the opening of the exhaust movable vane when the diesel engine has a low rotation and a high load. It is characterized by.

  In the control apparatus for a diesel engine according to a third aspect of the invention, the control means controls the opening of the exhaust movable vane so that the compressor efficiency of the variable capacity supercharger is higher than 60% and lower than 70%. It is characterized by.

  In the control device for a diesel engine according to a fourth aspect of the invention, the control means sets an optimum opening degree of the exhaust movable vane at which the supercharging rate is optimum in accordance with the engine speed and the engine load, and the optimum opening degree. The opening degree of the exhaust movable vane is controlled to an angle smaller by a predetermined ratio.

  The control device for a diesel engine according to claim 5 is provided with an exhaust pressure sensor for detecting the exhaust pressure in the exhaust passage and an intake pressure sensor for detecting the intake pressure in the intake passage. The opening degree of the exhaust movable vane is controlled based on detection results of the atmospheric pressure sensor and the intake pressure sensor.

  According to the control apparatus for a diesel engine of the first aspect of the present invention, the exhaust recirculation passage having the exhaust flow adjustment valve, the variable capacity supercharger, and the opening of the exhaust flow adjustment valve according to the operating state of the diesel engine. And a control means for controlling the opening of the exhaust movable vane, and the control means controls the opening of the exhaust movable vane so that the exhaust pressure in the exhaust passage is higher than the intake pressure in the intake passage. In addition, the output can be improved by appropriately compressing the intake air by the variable capacity supercharger to increase the charging efficiency, and returning the exhaust gas to the intake passage through the exhaust recirculation passage when the exhaust pressure is higher than the intake pressure. The amount of NOx generated can be suppressed and the exhaust gas characteristics can be improved.

  According to the control apparatus for a diesel engine of the second aspect of the present invention, the control means increases the opening of the exhaust flow rate adjustment valve and decreases the opening of the exhaust movable vane when the diesel engine is under low rotation and high load. By reducing the opening of the movable vane, the exhaust pressure increases. At this time, increasing the opening of the exhaust flow rate adjustment valve makes it easier to return the exhaust to the intake passage through the exhaust recirculation passage, improving exhaust gas characteristics. can do.

  According to the control device for a diesel engine of the invention of claim 3, the control means controls the opening degree of the exhaust movable vane so that the compressor efficiency of the variable capacity supercharger is higher than 60% and lower than 70%. By appropriately controlling the variable capacity supercharger, the exhaust pressure becomes higher than the intake pressure, and the exhaust can be reliably returned to the intake passage through the exhaust recirculation passage.

  According to the control apparatus for the diesel engine of the fourth aspect of the invention, the control means sets the optimum opening degree of the exhaust movable vane at which the supercharging ratio is optimum in accordance with the engine speed and the engine load, and this optimum opening. Since the opening of the movable exhaust vane is controlled to an angle smaller than the specified angle, the supercharging efficiency is reduced, but the exhaust pressure can be made higher than the intake pressure and the exhaust can be reliably returned to the intake passage. Can be improved.

  According to the control apparatus for a diesel engine of the fifth aspect of the present invention, the exhaust pressure sensor and the intake pressure sensor are provided, and the control means determines the opening of the exhaust movable vane based on the detection results of the exhaust pressure sensor and the intake pressure sensor. Therefore, the exhaust pressure can be controlled to be higher than the intake pressure at all times, and the exhaust gas can be reliably returned to the intake passage through the exhaust recirculation passage, so that the amount of NOx generated can be suppressed and the exhaust gas characteristics can be improved.

  Exemplary embodiments of a control apparatus for a diesel engine according to the present invention will be described below in detail with reference to the accompanying drawings. Note that the present invention is not limited to the embodiments.

  FIG. 1 is a schematic configuration diagram illustrating a control device for a diesel engine according to an embodiment of the present invention.

  In the diesel engine control apparatus of the present embodiment, as shown in FIG. 1, a plurality of cylinder bores 12 are formed in the engine body 11, and pistons 13 are supported on the cylinder bores 12 so as to be vertically movable. A combustion chamber 14 is formed in a region defined by 11 and the top surface of the piston 13. An intake port 15 and an exhaust port 16 communicate with the upper portion of the combustion chamber 14, and lower ends of the intake valve 17 and the exhaust valve 18 are located. The intake valve 17 and the exhaust valve 18 are urged and supported in a direction to close the intake port 15 and the exhaust port 16, and intake cams and exhaust cams of an intake camshaft and an exhaust camshaft (not shown) are connected to the intake valve 17 and the exhaust camshaft. By acting on the exhaust valve 18, the intake port 17 and the exhaust port 18 can be opened and closed. The engine body 11 is equipped with a high-pressure injector 19 that injects high-pressure fuel into the combustion chamber 14.

  An intake pipe (intake passage) 20 is connected to the intake port 15 via an intake manifold, and an air cleaner 21 is attached to an air intake port of the intake pipe 20. On the other hand, an exhaust pipe (exhaust passage) 22 is connected to the exhaust port 16 via an exhaust manifold. The exhaust pipe 22 purifies harmful substances such as HC, CO, and NOx contained in the exhaust gas. The catalyst device 23 is mounted.

  Further, the diesel engine of this embodiment is provided with a variable capacity supercharger (variable capacity supercharger) 24. In the variable capacity supercharger 24, a compressor 25 provided in an intake pipe 20 and a turbine 26 provided in an exhaust pipe 22 are connected together by a support shaft 27 so as to be integrally rotatable. In addition, a large number of nozzle vanes 28 are arranged at equal intervals in the circumferential direction. The opening degree of the nozzle vane 28 can be adjusted by the actuator 29. By reducing (squeezing) the opening degree of the nozzle vane 28, the flow velocity of the exhaust gas flowing in the turbine 26 can be increased.

  Further, between the upstream side of the supercharger 24 (turbine 26) in the exhaust pipe 22 and the downstream side of the supercharger 24 (compressor 25) in the intake pipe 20, EGR is recirculated as EGR gas. A passage (exhaust gas recirculation passage) 30 is provided. The EGR passage 30 is provided with an EGR cooler 31 that cools the EGR gas with engine cooling water, and an EGR valve (exhaust flow rate adjustment valve) 32 that adjusts the amount of EGR gas to be recirculated.

  The vehicle is provided with a control device 33 that comprehensively controls the diesel engine. That is, detection results from the engine speed sensor 34, the accelerator opening sensor 35, and the like are input to the control device 33. The control device 33 can control the high-pressure injector 19 by calculating optimum values such as the fuel injection amount and the injection timing based on the engine operating state such as the input engine speed and accelerator opening. . The control device 33 can control the variable capacity supercharger 24 and can adjust the opening degree of the nozzle vane 28 based on the engine operating state. Further, the control device 33 can control the EGR valve 32 and can adjust the opening degree of the EGR valve 32 based on the engine operating state.

  In the control device for the diesel engine according to the present embodiment configured as described above, the control device 33 is configured so that the exhaust pressure in the exhaust pipe 22 is higher than the intake pressure in the intake pipe 20. The opening is adjusted.

  That is, as described above, the EGR passage 30 having the EGR valve 32 is provided, and the control device 33 operates the diesel engine, that is, a high load operation in which combustion temperature is high and high concentration NOx is likely to be generated. Occasionally, by opening the EGR valve 32 and increasing a large amount of EGR gas from the EGR passage 30 to the intake pipe 20, the combustion temperature of the combustion chamber 14 is lowered by the EGR gas, and the combustion temperature decreases. Thus, the amount of NOx generated can be reduced. Further, a variable capacity supercharger 24 is provided, and the control device 33 reduces the opening of the nozzle vane 28 in the operation state of the diesel engine, that is, at a low speed when the output is insufficient, to reduce the turbine 26. By increasing the speed of the exhaust gas flowing into the turbine, the turbine 26 and the compressor 25 are rotated at a high speed by the restrained exhaust gas flow, and the intake air is compressed by the compressor 25 to increase the charging efficiency and improve the engine output. .

  However, when the turbocharger 24 increases the intake air supercharging rate during low-speed high-load operation of the diesel engine, the intake pressure of the intake pipe 20 increases, and this intake pressure becomes higher than the exhaust pressure of the exhaust pipe 22. In this case, even if the EGR passage 30 is opened by the EGR valve 32, the exhaust gas (EGR gas) of the exhaust pipe 2 cannot be introduced from the EGR passage 30 into the intake pipe 20, and the EGR gas Therefore, the combustion temperature cannot be reduced to suppress the generation of NOx.

  Therefore, in this embodiment, when the EGR valve 32 is opened and EGR gas is introduced into the intake pipe 20 from the EGR passage 30, the exhaust pressure of the exhaust pipe 22 is excessively higher than the intake pressure of the intake pipe 20. The opening degree of the nozzle vane 28 in the feeder 24 is adjusted. In this case, the control device 33 increases the opening degree of the EGR valve 32 and reduces the opening degree of the nozzle vane 28 when the diesel engine is under a low rotation and high load.

  More specifically, the control device 33 uses the engine speed detected by the engine speed sensor 34 and the nozzle vane with the optimum supercharging rate based on the accelerator opening (engine load) detected by the accelerator opening sensor 35. The optimum opening degree is set to 28, and the opening degree of the nozzle vane 28 is predetermined from the optimum opening degree when the diesel engine is likely to have an intake pressure higher than the exhaust pressure of the exhaust pipe 22 at a low rotation and high load. The angle is set to a small angle. That is, the control device 33 adjusts the opening degree of the nozzle vane 28 so that the compressor efficiency of the supercharger 24 is higher than 60% and lower than 70%.

  In this case, the intake pipe 20 (or intake manifold) connected to the intake port 15 is provided with an intake pressure sensor 36 for detecting intake pressure, and the exhaust pipe 22 (or exhaust manifold) connected to the exhaust port 16. An exhaust pressure sensor 37 for detecting the exhaust pressure is provided, and the control device 33 can adjust the opening degree of the nozzle vane 28 based on the detection results of the intake pressure sensor 36 and the exhaust pressure sensor 37.

  Therefore, by setting the opening degree of the nozzle vane 28 in the supercharger 24 at a low rotation and high load of the diesel engine at an angle smaller than the optimum opening degree set based on the engine speed and the accelerator opening degree, If the exhaust pressure upstream of the supercharger 24 in the exhaust pipe 22 is increased, and the EGR valve 32 is opened at this time, the exhaust gas in the exhaust pipe 22 is introduced into the intake pipe 20 as EGR gas through the EGR passage 30. The combustion temperature of the combustion chamber 14 can be lowered by the large amount of EGR gas, and the amount of NOx generated can be reduced as the combustion temperature decreases. In this case, detection results of the intake pressure sensor 36 and the exhaust pressure sensor 37 are input to the control device 33, and the exhaust pressure of the exhaust pipe 22 is higher than the intake pressure of the intake pipe 20. Thus, the opening degree of the nozzle vane 28 is adjusted.

  As described above, in the control device for the diesel engine according to the present embodiment, the variable displacement supercharger 24 including the compressor 25 of the intake pipe 20, the turbine 26 of the exhaust pipe 22, and a number of nozzle vanes 28 is provided. An EGR passage having an EGR valve 32 is provided by connecting the upstream side of the turbine 26 in the pipe 22 and the downstream side of the compressor 25 in the intake pipe 20, and the controller 33 controls the EGR valve 32 according to the operating state of the diesel engine. The opening of the nozzle vane 28 is controlled so that the exhaust pressure of the exhaust pipe 22 becomes higher than the intake pressure of the intake pipe 20 at low load and high load. Control the degree.

  Therefore, when the diesel engine has a low rotation speed and a high load, the output can be improved by appropriately compressing the intake air by the variable capacity supercharger 24 to increase the charging efficiency, and the exhaust pressure is higher than the intake pressure. Thus, the exhaust gas can be returned to the intake pipe 20 through the EGR passage 32, and the amount of NOx generated can be suppressed and the exhaust gas characteristics can be improved.

  Further, in the control device for the diesel engine of the present embodiment, the control device 33 increases the opening degree of the EGR valve 32 and reduces the opening degree of the nozzle vane 28 when the diesel engine has a low rotation and a high load. Therefore, the exhaust pressure increases by reducing the opening of the nozzle vane 28. At this time, the opening of the EGR valve 32 is increased to facilitate returning the exhaust gas to the intake pipe 20 through the EGR passage 30. Can be improved.

  Further, in the control device for the diesel engine according to the present embodiment, the control device 33 sets the optimum opening degree of the nozzle vane 28 at which the supercharging rate is optimum in accordance with the engine speed and the accelerator opening degree. The opening degree of the nozzle vane 28 is controlled to an angle smaller by a predetermined ratio. Accordingly, although the supercharging efficiency is lowered, the exhaust pressure can be made higher than the intake pressure and the exhaust can be reliably returned to the intake pipe 20, and the exhaust gas characteristics can be improved.

  In the above-described embodiment, the engine speed and the accelerator opening are applied as parameters for setting the opening of the nozzle vane 28 in the supercharger 24. However, the accelerator opening may be an engine load, and the fuel injection amount. Or volumetric efficiency.

  The diesel engine control device according to the present invention improves the engine output by the supercharger and improves the exhaust gas characteristics by exhaust gas recirculation regardless of the operating state of the engine. Can be applied.

It is a schematic block diagram showing the control apparatus of the diesel engine which concerns on one Example of this invention.

Explanation of symbols

11 Engine body 14 Combustion chamber 20 Intake pipe (intake passage)
22 Exhaust pipe (exhaust passage)
24 Supercharger (variable capacity supercharger)
25 Compressor 26 Turbine 28 Nozzle vane (exhaust movable vane)
29 Actuator 30 EGR passage (exhaust gas recirculation passage)
32 EGR valve (exhaust flow rate curing valve)
33 Control device (control means)
36 Intake pressure sensor 37 Exhaust pressure sensor

Claims (5)

  An exhaust gas recirculation passage that circulates exhaust gas in the exhaust passage to the intake passage, an exhaust flow rate adjustment valve provided in the exhaust gas recirculation passage, a turbine provided in the exhaust passage, and a compressor provided in the intake passage; Is connected on the same axis and adjusts the opening of the exhaust movable vane to control the opening of the exhaust flow adjustment valve according to the variable capacity supercharger that can change the supercharging pressure and the operating condition of the diesel engine And a control unit for controlling the opening degree of the exhaust movable vane, wherein the control unit is configured so that the exhaust pressure in the exhaust passage is higher than the intake pressure in the intake passage. A control device for a diesel engine, which controls an opening degree of an exhaust movable vane.   2. The diesel engine control device according to claim 1, wherein the control unit increases the opening of the exhaust flow rate adjustment valve and decreases the opening of the exhaust movable vane when the diesel engine is under low rotation and high load. Diesel engine control device.   3. The diesel engine control apparatus according to claim 1, wherein the control means controls the opening of the exhaust movable vane so that the compressor efficiency of the variable capacity supercharger is higher than 60% and lower than 70%. A diesel engine control device.   The diesel engine control apparatus according to any one of claims 1 to 3, wherein the control means determines an optimum opening degree of the exhaust movable vane at which a supercharging rate is optimum in accordance with an engine speed and an engine load. A control device for a diesel engine, characterized in that the opening of the exhaust movable vane is set and controlled at an angle smaller than the optimum opening by a predetermined percentage.   The diesel engine control device according to any one of claims 1 to 4, further comprising an exhaust pressure sensor that detects an exhaust pressure of the exhaust passage, and an intake pressure sensor that detects an intake pressure of the intake passage. The control device for a diesel engine, wherein the control means controls the opening of the exhaust movable vane based on detection results of the exhaust pressure sensor and the intake pressure sensor.

Images