JP4802142B2 - diesel engine - Google Patents

Description

  The present invention relates to a diesel engine, and more particularly, to a diesel engine provided with a variable displacement turbocharger with variable intake capacity.

  Conventionally, in order to purify exhaust gas of a diesel engine, an exhaust aftertreatment device such as an oxidation catalyst, a selective reduction catalyst (SCR), a DPF with catalyst, etc. has been provided, and in order to operate the exhaust aftertreatment device efficiently, the exhaust temperature There is a technique for maintaining the exhaust gas temperature high even in an operation region where the temperature drops (see, for example, Patent Document 1).

  In this technique, when the exhaust gas temperature is lower than a predetermined value, the exhaust gas is guided to the EGR bypass passage that bypasses the EGR cooler installed in the EGR passage through which the EGR gas flows.

  However, when the engine is in a no-load operation state while the vehicle is operating, the fuel injection is stopped, the exhaust gas temperature is lowered, and the low temperature exhaust gas flows into the exhaust aftertreatment device. The temperature of the will decrease.

In such a case, it is effective to limit the flow rate of the exhaust gas in order to suppress a decrease in the exhaust gas temperature. In particular, when the engine is equipped with a variable displacement turbocharger, it is possible to open the nozzle vane. It is effective to reduce the exhaust pressure by lowering the supercharging pressure.
Japanese Patent Laying-Open No. 2005-2975

  However, if the nozzle vane is opened too much with a variable capacity turbocharger when the engine is not loaded, the pressure in the intake manifold becomes negative, for example, oil leaks from the seal part of the valve stem to the intake port, or a rubber hose The opening of the nozzle vane is set so that the inside of the hose may be blocked due to a negative pressure and the intake manifold is maintained at a positive pressure. In other words, by setting the opening degree of the nozzle vane so as to maintain the positive pressure, a further improvement margin remains from the viewpoint of reducing the exhaust gas flow rate.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a diesel engine that achieves both a positive pressure maintenance in an intake manifold and a suppression of a temperature drop in an exhaust aftertreatment device. To do.

  According to a first aspect of the present invention, there is provided a load detection means for detecting a load state of an engine, a variable capacity turbocharger that supercharges intake air using exhaust energy, and an overcharge state that detects a supercharging state of the variable capacity turbocharger. In a diesel engine comprising a supply state detection means and a control means for controlling an opening degree of a nozzle vane of the variable capacity turbocharger, the control means detects the detection when the engine changes from a load state to a no-load state. In accordance with the supercharged state, the opening degree of the nozzle vane is set so that the pressure in the intake manifold of the engine becomes substantially atmospheric pressure while maintaining a positive pressure, and the first opening degree When the engine is in an unloaded state and the detected supercharging state becomes the first supercharging state. The opening degree of the ruby vane is controlled to the second opening degree, and the opening degree of the nozzle vane is changed to the second supercharging state when the supercharging state becomes a second supercharging state lower than the first supercharging state. The diesel engine is characterized in that the control is performed so that the pressure in the intake manifold is maintained at a positive pressure by switching from the second opening to the first opening.

  In a second aspect based on the first aspect, the supercharging state detecting means detects the boost pressure of the variable capacity turbocharger as the supercharging state, and the control means is that the engine is in a no-load state, When the detected boost pressure becomes a first predetermined value, the opening degree of the nozzle vane is controlled to the second opening degree, and when the boost pressure becomes a second predetermined value lower than the first predetermined value. The diesel engine is characterized in that the opening of the nozzle vane is switched from the second opening to the first opening, and the pressure in the intake manifold is controlled to maintain a positive pressure.

  In a third aspect based on the first aspect, the supercharging state detecting means detects the rotational speed of the capacity variable turbocharger as the supercharging state, and the control means is configured such that the engine is in a no-load state, When the detected rotational speed reaches a third predetermined value, the opening degree of the nozzle vane is controlled to the second opening degree, and when the rotational speed reaches a fourth predetermined value lower than the third predetermined value. The diesel engine is characterized in that the opening of the nozzle vane is switched from the second opening to the first opening, and the pressure in the intake manifold is controlled to maintain a positive pressure.

  In a fourth aspect based on the first aspect, the supercharging state detecting means detects the boost pressure of the variable capacity turbocharger as the supercharging state, and the control means is that the engine is in a no-load state, When the detected boost pressure reaches a first predetermined value, the opening degree of the nozzle vane is controlled to the second opening degree, and when a predetermined time has elapsed after reaching the first predetermined value, the nozzle vane The diesel engine is characterized in that the opening in the intake manifold is switched from the second opening to the first opening, and the pressure in the intake manifold is controlled to maintain a positive pressure.

  In a fifth aspect based on any one of the first to fourth aspects, the second opening is set so that the pressure in the intake manifold is changed from a positive pressure to a negative pressure when the engine is unloaded. It is a diesel engine characterized by being made.

  In the first to fifth inventions, when the engine is in a no-load state, the second opening having a large opening is used to weaken the supercharging state, reduce the exhaust flow rate, and suppress the temperature drop of the exhaust aftertreatment device. it can. In addition, the pressure in the intake manifold reaches a negative pressure by maintaining the second opening, but the pressure in the intake manifold is switched to the first opening before the negative pressure is reached. Can be maintained at a positive pressure. Thereby, problems such as oil leaking from the seal portion of the valve stem to the intake port can be solved.

  As described above, in the present invention, it is possible to achieve a high level of both maintaining the positive pressure in the intake manifold and suppressing the temperature decrease of the exhaust aftertreatment device when the engine is not loaded.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows the configuration of a diesel engine equipped with a variable displacement turbocharger, wherein 1 is a diesel engine, 6 is an intake passage, 7 is an exhaust passage, 8 is an air cleaner, and 11 is a nozzle vane 14 having a variable angle. A variable capacity turbocharger (hereinafter simply referred to as a turbocharger) 31 is an exhaust aftertreatment device.

  The turbocharger 11 includes a turbine 12 that is rotated by pressure energy of exhaust gas, and a compressor 13 that is coaxially connected to the turbine 12 and that pumps intake air to the intake passage 6. As shown in FIG. 2, the turbine 12 is introduced with exhaust gas that has passed through a plurality of nozzle vanes 14 whose angles can be varied, and the nozzle vanes 14 are controlled to a predetermined opening degree by the operation of an actuator (not shown). The opening, which is the opening area defined between the inner wall surface of the case that houses the turbine 12 and the tip of the nozzle vane 14, is appropriately set to a predetermined opening area according to the operating state of the engine.

  An intercooler 14 is interposed on the downstream side of the compressor 13 in the intake passage 6 to cool the intake air. The intercooler 14 is an air-cooled heat exchanger, and urges heat radiation from the intake air compressed by the compressor 13 to rise in temperature to the outside air. The intercooler 14 is not limited to this, and a water-cooled heat exchanger in which cooling water circulates may be used as a cooling medium. A pressure sensor 35 for detecting the boost pressure by the turbocharger 11 is installed in the intake manifold 17, and an output signal of the pressure sensor 35 is output to the control unit 34.

  As an exhaust gas recirculation device, an EGR passage 32 connecting the exhaust passage 7 and the intake passage 6 is disposed. The EGR passage 32 communicates the passage 7 a upstream of the turbine 12 in the exhaust passage 7 and the passage 6 a downstream of the compressor 13 in the intake passage 6. In the present embodiment, the EGR passage 32 communicates the exhaust manifold 16 and the intake manifold 17 attached to the main body of the engine 1.

  An electromagnetic EGR valve 33 is interposed in the middle of the EGR passage 32. The recirculation amount of the exhaust gas recirculation gas flowing through the EGR passage 32 is adjusted by the opening degree of the EGR valve 33. The control unit 34 controls the opening degree of the EGR valve 33 in accordance with the operating state such as the rotational speed and load of the engine 1, and exhaust gas recirculation suitable for the operating state is performed.

  An EGR cooler 36 is interposed in the middle of the EGR passage 32 so as to cool the exhaust gas recirculation gas flowing through the EGR passage 32. The EGR cooler 36 is a water-cooled heat exchanger in which cooling water circulates as a cooling medium, and promotes heat radiation from the exhaust gas recirculation gas to the cooling water. The EGR cooler 36 is not limited to this, and an air-cooled heat exchanger may be used. An exhaust throttle valve 39 is provided in the middle of the exhaust passage 7, and the control unit 34 is configured to restrict the flow of exhaust gas by restricting the exhaust throttle valve 39 according to the operating state of the engine 1.

  The exhaust aftertreatment device 31 installed in the exhaust passage 7 downstream of the turbine 12 of the turbocharger 11 includes an oxidation catalyst, a selective reduction catalyst (SCR), a DPF with a catalyst, and the like in order to purify the exhaust gas.

  In the diesel engine configured as described above, when the operation state of the engine 1 is changed from the load state to the no-load state, the fuel injection is stopped and the temperature of the exhaust gas discharged is lowered. In this case, the low temperature exhaust gas flows into the exhaust aftertreatment device 31 located downstream, the temperature of the exhaust aftertreatment device 31 decreases, and the exhaust gas cannot be sufficiently purified when the operating state shifts to the load state. There is a fear. Therefore, the present invention controls the opening and closing of the nozzle vanes 14 according to the boost pressure in order to suppress the temperature drop of the exhaust aftertreatment device 31 and maintain the exhaust gas purification performance in the no-load operation state of the engine. By adopting such control, the exhaust flow rate is reduced while preventing the generation of negative pressure in the intake manifold, and the temperature drop of the exhaust aftertreatment device 31 is suppressed.

  Hereinafter, the opening / closing control of the nozzle vane 14 performed by the control unit 34 will be described with reference to the flowchart shown in FIG.

  The opening / closing control of the nozzle vane 14 according to the present invention is performed every time the control unit 34 detects a no-load state of the engine.

  First, in step S1, it is determined whether the engine 1 is in a no-load state. As a determination method, for example, an accelerator opening is detected using a sensor (not shown), and when the accelerator opening is zero, that is, the accelerator pedal is not depressed, it is determined that there is no load. When it is determined that there is no load, the process proceeds to step S2, and when it is loaded, the process proceeds to step S3, and normal output control is performed. Here, the normal output control in the load state means control in which the engine 1 outputs an output corresponding to the accelerator opening.

  In step S2, the boost pressure is read based on the detection value of the pressure sensor 35, and the boost pressure is compared with the first predetermined value. Here, the first predetermined value is a positive pressure higher than the atmospheric pressure, for example, a pressure set based on the maximum boost pressure of the turbocharger 11.

  If the detected boost pressure is greater than or equal to the first predetermined value, the intake air is supercharged and the exhaust gas flow rate continues to be high even after the engine 1 enters a no-load state, and the exhaust gas having a low temperature is exhausted. The temperature of the exhaust aftertreatment device 31 is promoted by flowing into the aftertreatment device 31.

  In this case, the process proceeds from step S2 to step S4, and the opening of the nozzle vane 14 is controlled to be a second opening larger than the first opening. Here, the first opening, which is the opening of the nozzle vane 14, is set so that the pressure in the intake manifold does not become a negative pressure in the intake manifold, that is, approximately the atmospheric pressure while maintaining the positive pressure. The second opening is an opening at which the pressure in the intake manifold is changed from a positive pressure to a negative pressure by maintaining the opening.

  In step S4, by the opening / closing control of the nozzle vane 14 that sets a second opening larger than the first opening when the engine is not loaded, the boost pressure by the turbocharger 11 decreases and the exhaust flow rate flowing into the exhaust aftertreatment device 31 is reduced. Thus, the temperature drop of the exhaust aftertreatment device 31 can be suppressed.

  If the boost pressure detected in step S2 is less than the first predetermined value, the process proceeds to step S5, and the read boost pressure is compared with the second predetermined value. Here, the second predetermined value is a positive pressure value close to the atmospheric pressure smaller than the first predetermined value.

  If the boost pressure is less than or equal to the second predetermined value, if the current opening degree of the nozzle vane 14 is the second opening degree, the pressure in the intake manifold may become negative pressure. The opening is returned to the first opening. That is, control is performed so that the opening degree of the nozzle vane 14 is reduced. As described above, in the case of the second predetermined value or less, the opening of the nozzle vane 14 is returned to the first opening smaller than the second opening, thereby suppressing the pressure in the intake manifold from becoming negative. In other words, the second predetermined value is set so that the pressure in the intake manifold maintains a positive pressure or becomes substantially atmospheric pressure after returning to the first opening.

  On the other hand, when the boost pressure exceeds the second predetermined value, the process proceeds to step S7, and the current opening degree of the nozzle vane 14 is maintained.

  Next, the effect of the opening / closing control of the nozzle vane 14 of the present invention will be described below with reference to FIG.

FIG. 4 shows a change in the flow rate of the exhaust gas flowing into the exhaust aftertreatment device 31 in a time series, similarly a change in the intake manifold pressure, and a change in the opening degree of the nozzle vane 14. In the figure, the characteristic indicated by A indicates the characteristic according to the present invention, the characteristic indicated by B indicates the opening / closing characteristic of the conventional nozzle vane 14, that is, the characteristic at the first opening (O _{1 in the} figure), and the characteristic indicated by C. Indicates the characteristics when the opening degree of the nozzle vane 14 is not returned from the second opening degree (O _{2 in the} figure) to the first opening degree at time T2, that is, when the second opening degree is maintained.

Engine 1 is changed from the load state to the no-load state at the time T1, keep the boost pressure is determined to be the first predetermined value P ₁ or more, the pressure of opening the intake manifold of the nozzle vane 14 is a positive pressure The second opening degree O ₂ is set to be larger than the first opening degree O ₁ that is set to be atmospheric pressure. Thus, by setting the opening degree of the nozzle vane 14 to the second opening degree O ₂ having a larger opening degree, the boost pressure of the turbocharger 11 is lowered, and the exhaust flow rate is compared with the case of the first opening degree O _1. Can be reduced rapidly. However, if the second opening degree O ₂ is maintained, as shown in the characteristic C, the pressure in the intake manifold becomes negative, so that oil leaks from the seal portion of the valve stem as described above to the intake port. A failure will occur. Therefore, in the present invention, when the boost pressure reaches the second predetermined value P ₂ lower than the first predetermined value P ₁ at time T2, the opening degree of the nozzle vane 14 is changed from the second opening degree O ₂ to the first opening degree O ₁ . And switch. By switching to the first opening O _{1 having} a small opening, the pressure in the intake manifold is suppressed from becoming negative.

As described above, in the present invention, the opening degree of the nozzle vane 14 is set to the second opening degree O ₂ at which a negative pressure can be generated in the intake manifold when the engine 1 changes from a loaded state to a no-load state. By switching from the second opening O ₂ to the first opening O ₁ where no negative pressure is generated at the second predetermined value P ₂ , the pressure in the intake manifold is maintained at a positive pressure while the hatched portion in FIG. The exhaust flow rate shown can be reduced, and the temperature drop of the exhaust aftertreatment device 31 can be suppressed.

  In the present embodiment, the opening / closing control of the nozzle vane 14 for switching the opening of the two types of nozzle vanes 14 has been described. However, for example, the opening in such a manner that the pressure in the intake manifold becomes a negative pressure is increased in more stages. The exhaust flow rate may be further reduced by switching to a stage.

  FIG. 5 is a flowchart for explaining the second embodiment of the present invention. In the first embodiment, the opening degree of the nozzle vane 14 is switched based on the boost pressure, but in this embodiment, the opening degree of the nozzle vane 14 is switched based on the rotational speed of the turbocharger 11. Is provided. Hereinafter, a description will be given based on the flowchart.

  The opening / closing control of the nozzle vane 14 of the present embodiment is performed every time the control unit 34 detects an unloaded state of the engine.

  First, in step S1, it is determined whether the engine 1 is in a no-load state. If it is determined that there is no load, the process proceeds to step S11. If it is a load, the process proceeds to step S3, and normal output control is performed.

  In step S11, the rotational speed of the turbocharger 11 is read, and this rotational speed is compared with a third predetermined value. Here, the third predetermined value is, for example, a pressure set based on the maximum rotation speed of the turbocharger 11.

  If the detected number of revolutions is equal to or greater than the third predetermined value, the intake air is supercharged and the exhaust gas flow rate continues to be high even after the engine 1 enters a no-load state, and the exhaust gas having a low temperature is exhausted. The temperature of the exhaust aftertreatment device 31 is promoted by flowing into the aftertreatment device 31.

  In this case, the process proceeds from step S11 to step S4, and the opening of the nozzle vane 14 is controlled to be a second opening larger than the first opening.

  In step S4, by the opening / closing control of the nozzle vane 14 that sets a second opening larger than the first opening when the engine is not loaded, the boost pressure by the turbocharger 11 decreases and the exhaust flow rate flowing into the exhaust aftertreatment device 31 is reduced. Thus, the temperature drop of the exhaust aftertreatment device 31 can be suppressed.

  If the boost pressure detected in step S11 is less than the first predetermined value, the process proceeds to step S12, and the read rotation speed is compared with the fourth predetermined value. Here, the fourth predetermined value is a rotational speed value smaller than the third predetermined value.

  If the rotational speed is equal to or smaller than the fourth predetermined value, the current pressure in the intake manifold may become negative if the current opening degree of the nozzle vane 14 is the second opening degree. The opening is returned to the first opening. That is, control is performed so that the opening degree of the nozzle vane 14 is reduced. Thus, when it is below the fourth predetermined value, the opening of the nozzle vane 14 is returned to the first opening smaller than the second opening, thereby suppressing the pressure in the intake manifold from becoming negative. In other words, the fourth predetermined value is set so that the pressure in the intake manifold maintains a positive pressure or becomes substantially atmospheric pressure after returning to the first opening.

  On the other hand, when the rotation speed exceeds the fourth predetermined value, the process proceeds to step S7, and the current opening degree of the nozzle vane 14 is maintained.

  Thus, by switching the opening degree of the nozzle vane 14 based on the change in the rotational speed of the turbocharger 11, the generation of negative pressure in the intake manifold can be suppressed with higher accuracy, and the exhaust flow rate can be reduced.

  FIG. 6 is a flowchart for explaining the third embodiment of the present invention. In the first embodiment, the opening degree of the nozzle vane 14 is switched from the second opening degree to the first opening degree based on the boost pressure. In this embodiment, a certain time has elapsed after switching to the second opening degree. In this case, the opening degree of the nozzle vane 14 is switched to the first opening degree. Hereinafter, a description will be given based on the flowchart.

  The opening / closing control of the nozzle vane 14 according to the present invention is performed every time the control unit 34 detects a no-load state of the engine.

  First, in step S21, it is determined whether or not the engine 1 is in a no-load state. If it is determined that there is no load, the process proceeds to step S22. If it is a load, the process proceeds to step S23, and normal output control is performed.

  In step S22, the boost pressure is read based on the detection value of the pressure sensor 35, and the boost pressure is compared with the first predetermined value.

  If the detected boost pressure is greater than or equal to the first predetermined value, the intake air is supercharged and the exhaust gas flow rate continues to be high even after the engine 1 enters a no-load state, and the exhaust gas having a low temperature is exhausted. The temperature of the exhaust aftertreatment device 31 is promoted by flowing into the aftertreatment device 31.

  In this case, the process proceeds from step S22 to step S24, and the opening of the nozzle vane 14 is controlled to be a second opening larger than the first opening.

  In step S24, the opening / closing control of the nozzle vane 14 that sets the second opening larger than the first opening when the engine is not loaded reduces the boost pressure by the turbocharger 11 and reduces the exhaust flow rate flowing into the exhaust aftertreatment device 31. Thus, the temperature drop of the exhaust aftertreatment device 31 can be suppressed.

  If the boost pressure detected in step S22 is less than the first predetermined value, the process proceeds to step S25, and normal output control is performed.

  In step S26 following step S24, the second opening is continued for a predetermined time after switching to the second opening, and in step S27, the opening of the nozzle vane 14 is returned to the first opening.

  Thus, the calculation load of the control unit 34 can be reduced by switching the opening degree of the nozzle vane 14 from the second opening degree to the first opening degree after a predetermined time has elapsed.

  The present invention is not limited to the above-described embodiment, and it is obvious that various modifications can be made within the scope of the technical idea.

1 is a configuration diagram of an exhaust emission control device showing an embodiment of the present invention. Schematic which shows the shape of a nozzle vane. The flowchart which similarly shows the control content. The figure explaining the effect of this invention. The flowchart which shows the control content of other embodiment. The flowchart which similarly shows the control content of other embodiment.

Explanation of symbols

1 Engine 6 Intake Passage 6a Passage 7 Exhaust Passage 7a Passage 11 Turbocharger 12 Turbine 13 Compressor 14 Nozzle Vane 16 Exhaust Manifold 17 Intake Manifold 31 Exhaust Aftertreatment Device 33 EGR Valve 34 Control Unit 35 Pressure Sensor

Claims (5)

Load detection means for detecting the load state of the engine;
A variable capacity turbocharger that uses exhaust energy to supercharge intake air,
Supercharging state detecting means for detecting the supercharging state of the capacity variable turbocharger;
In a diesel engine comprising control means for controlling the opening degree of the nozzle vanes of the variable capacity turbocharger,
When the engine changes from a load state to a no-load state, the control means determines the opening degree of the nozzle vane while maintaining the positive pressure in the intake manifold of the engine according to the detected supercharging state. Controlling either the first opening set to be substantially atmospheric pressure or the second opening larger than the first opening;
When the engine is in a no-load state and the detected supercharging state becomes the first supercharging state, the opening degree of the nozzle vane is controlled to the second opening degree,
When the supercharging state becomes the second supercharging state, which is lower than the first supercharging state, the opening degree of the nozzle vane is switched from the second opening degree to the first opening degree, and the intake air A diesel engine characterized by controlling the pressure in the manifold to maintain a positive pressure. The supercharging state detection means detects the boost pressure of the variable capacity turbocharger as the supercharging state,
The control means controls the opening of the nozzle vane to the second opening when the detected boost pressure reaches a first predetermined value when the engine is in a no-load state,
When the second predetermined value lower than the first predetermined value is reached, the opening degree of the nozzle vane is switched from the second opening degree to the first opening degree, and the pressure in the intake manifold becomes positive. It controls so that it may maintain, The diesel engine of Claim 1 characterized by the above-mentioned. The supercharging state detecting means detects the rotation speed of the capacity variable turbocharger as the supercharging state,
The control means controls the opening degree of the nozzle vane to the second opening degree when the engine is in a no-load state and the detected rotational speed reaches a third predetermined value.
When the rotation speed reaches a fourth predetermined value that is lower than the third predetermined value, the nozzle vane opening is switched from the second opening to the first opening, and the pressure in the intake manifold is positive. It controls so that it may maintain, The diesel engine of Claim 1 characterized by the above-mentioned. The supercharging state detection means detects the boost pressure of the variable capacity turbocharger as the supercharging state,
The control means controls the opening of the nozzle vane to the second opening when the detected boost pressure reaches a first predetermined value when the engine is in a no-load state,
When a predetermined time has elapsed since reaching the first predetermined value, the opening degree of the nozzle vane is switched from the second opening degree to the first opening degree so that the pressure in the intake manifold maintains a positive pressure. The diesel engine according to claim 1, wherein   5. The second opening degree is set such that the pressure in the intake manifold is changed from a positive pressure to a negative pressure when the engine is in a no-load state. 6. diesel engine.

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