JP2014077387A - Internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an internal combustion engine capable of making EGR effective while suppressing an increase in an in-cylinder maximum pressure due to supercharging.SOLUTION: An internal combustion engine having a plurality of cylinders 2 includes: turbochargers 5 and 6 for supercharging suction air of the cylinder 2; an intake and exhaust valve control unit 8 for controlling a valve timing of an intake valve 3 of the cylinder 2; an EGR passage 7 for recirculating an exhaust gas of the cylinder 2 to an intake side; and an ECU 10 for controlling an exhaust pressure or a supercharging pressure. The intake and exhaust valve control unit 8 controls the valve timing of the intake valve 3 to suppress an increase in an in-cylinder maximum pressure of the cylinder 2 due to supercharging.

Description

  The present invention relates to an internal combustion engine capable of changing the valve timing of intake and exhaust valves.

  Conventionally, for example, the following Patent Document 1 is known as a technical document relating to such an internal combustion engine. Patent Document 1 discloses a diesel engine provided in a vehicle that controls the actual compression ratio in a cylinder by controlling the valve timing of intake and exhaust valves in accordance with the engine operating state.

JP 2002-54489 A

  By the way, a turbocharger is widely used to increase the output of an internal combustion engine. However, if a supercharger is simply adopted, the maximum cylinder pressure in the cylinder increases due to supercharging, which may adversely affect the mechanical strength of the internal combustion engine body. Further, when the supercharging pressure becomes higher than the exhaust pressure of the cylinder, there is a problem that EGR is not effective and fuel consumption is deteriorated.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an internal combustion engine capable of making EGR effective while suppressing an increase in the in-cylinder maximum pressure due to supercharging.

  In order to solve the above problems, the present invention is an internal combustion engine having a plurality of cylinders, a supercharger for supercharging the intake air of the cylinders, and an intake valve control means for controlling the valve timing of the intake valves of the cylinders And an EGR passage for recirculating the exhaust gas of the cylinder to the intake side, and a pressure control means for controlling the exhaust pressure of the cylinder or the supercharging pressure of the supercharger. The valve timing of the intake valve is controlled so as to suppress an increase in the cylinder maximum pressure due to supercharging of the machine.

  According to the internal combustion engine of the present invention, the increase in the in-cylinder maximum pressure of the cylinder is suppressed by controlling the valve timing of the intake valve while performing supercharging by the supercharger. The influence on the mechanical strength of the internal combustion engine main body due to the increase in the in-cylinder maximum pressure can be suppressed. Further, according to this internal combustion engine, when the differential pressure between the supercharging pressure and the exhaust pressure of the cylinder disappears, EGR becomes ineffective, and by controlling the exhaust pressure to exceed the supercharging pressure by the pressure control means, EGR can be enabled. Therefore, according to this internal combustion engine, while achieving high output by supercharging, the influence on the mechanical strength of the internal combustion engine main body due to the increase in the maximum cylinder pressure is suppressed, and a long life is achieved. Fuel efficiency can be improved by ensuring the effectiveness.

In the internal combustion engine according to the present invention, the supercharger is a variable nozzle turbocharger, and the pressure control means changes the nozzle of the supercharger so that the exhaust pressure of the cylinder becomes larger than the supercharge pressure of the supercharger. May be.
According to this internal combustion engine, by changing the nozzle of the variable nozzle turbocharger to make the exhaust pressure of the cylinder larger than the supercharging pressure of the supercharger, the EGR is made effective while achieving high output by supercharging. Can do.

The internal combustion engine according to the present invention further comprises an exhaust brake valve provided in the exhaust passage of the cylinder, and the pressure control means controls the exhaust brake valve so that the exhaust pressure of the cylinder becomes larger than the supercharging pressure of the supercharger. May be.
According to this internal combustion engine, by controlling the exhaust brake valve to increase the exhaust pressure of the cylinder (pressure in the exhaust passage), the exhaust pressure of the cylinder is made sufficiently larger than the supercharging pressure of the supercharger. The EGR can be made effective while increasing the output by supercharging.

  ADVANTAGE OF THE INVENTION According to this invention, the internal combustion engine which can make EGR effective, suppressing the increase in the cylinder maximum pressure by supercharging can be provided.

It is the schematic which shows the structure of the engine which concerns on this embodiment. It is a logP-logV diagram explaining the mirror cycle of this embodiment. It is a flowchart which shows the flow of control by ECU.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

  An engine (internal combustion engine) 1 according to this embodiment shown in FIG. 1 is a diesel engine that is used as a power source of a vehicle and has a plurality of cylinders 2. The cylinder 2 is provided with an intake valve 3 and an exhaust valve 4. The engine 1 is a so-called Miller cycle engine, and the intake valve 3 is closed earlier or later than the bottom dead center, thereby maintaining the compression ratio in the cylinder 2 smaller than the expansion ratio and suppressing the occurrence of knocking and high thermal efficiency. Can be obtained.

  The engine 1 includes a low-pressure stage turbocharger (supercharger) 5 and a high-pressure stage turbocharger (supercharger) 6, an EGR passage 7, and an intake / exhaust valve control unit (intake valve control means) constituting a two-stage supercharging system. ) 8, an exhaust brake valve 9, and an ECU (pressure control means) [Engine Control Unit] 10.

  The low-pressure stage turbocharger 5 includes a low-pressure stage compressor 5 </ b> A disposed on the inlet side of the intake passage 11 and a low-pressure stage turbine 5 </ b> B disposed on the outlet side of the exhaust passage 12. In the low-pressure stage turbocharger 5, the low-pressure stage turbine 5 </ b> B is rotated by the exhaust energy of the exhaust gas, so that the low-pressure stage compressor 5 </ b> A is driven to compress the air in the intake passage 11, that is, supercharge.

  The high-pressure turbocharger 6 includes a high-pressure compressor 6A and a high-pressure turbine 6B. The high pressure compressor 6A is disposed downstream of the low pressure compressor 5A in the intake passage 11, and the high pressure turbine 6B is disposed upstream of the low pressure turbine 5B in the exhaust passage 12.

  Also in the high-pressure stage turbocharger 6, the high-pressure stage turbine 6 </ b> B is rotated by the exhaust energy of the exhaust gas, so that the high-pressure stage compressor 6 </ b> A is driven and supercharging in the intake passage 11 is performed.

  The high-pressure stage turbocharger 6 has a smaller capacity than the low-pressure stage turbocharger 5. In other words, the low-pressure stage turbocharger 5 having a larger capacity than the high-pressure stage turbocharger 6 is used. This is because exhaust energy is once recovered in the high-pressure stage turbocharger 6 and the expanded exhaust gas is handled by the low-pressure stage turbocharger 5.

  The air flowing through the intake passage 11 is compressed in the order of the low-pressure compressor 5A and the high-pressure compressor 6A and is supplied into the cylinder 2 of the engine 1 body. The intake passage 11 is provided with an intercooler 13 for cooling the air whose temperature has increased due to compression by the low-pressure compressor 5A, and an after-cooler 14 for cooling the air whose temperature has increased by compression by the high-pressure compressor 6A. ing. The intercooler 13 is not necessarily provided.

  The low-pressure stage turbocharger 5 and the high-pressure stage turbocharger 6 are variable nozzle turbochargers, and have a plurality of variable vanes on the turbine side. The low-pressure stage turbocharger 5 and the high-pressure stage turbocharger 6 change the supercharging efficiency by controlling the flow rate of the exhaust gas by changing the opening degree of the variable nozzle composed of a plurality of variable vanes.

  The EGR passage 7 is a passage for recirculation by returning a part of the exhaust gas in the exhaust passage 12 to the intake passage 11. In the middle of the EGR passage 7, an EGR valve 15 for controlling the flow rate of the exhaust gas passing therethrough and an EGR cooler 16 for cooling the exhaust gas are provided.

  The EGR passage 7 connects the exhaust passage 12 upstream of the exhaust brake valve 9 on the downstream side of the cylinder 2 and the intake passage 11 downstream of the aftercooler 14 on the upstream side of the cylinder 2. It constitutes the pressure EGR system. The connection place of the EGR passage 7 is not limited to the place described above.

  The intake / exhaust valve control unit 8 controls the valve timing and the lift amount of the intake valve 3 and the exhaust valve 4. The intake / exhaust valve control unit 8 drives the variable valve mechanism of the engine 1 to change the valve timing and the lift amount of the intake valve 3 and the exhaust valve 4. The configuration of the variable valve mechanism is not particularly limited as long as the valve timing and the lift amount can be changed. The variable valve mechanism changes the valve timing or the like by changing the rotation angle phase of the camshaft by, for example, hydraulic pressure or an electric motor.

  The exhaust brake valve 9 is provided in the exhaust passage 12 and is a valve for generating a braking force by increasing the exhaust pressure. The exhaust brake valve 9 is disposed in front (upstream side) of the high-pressure turbine 6B. The exhaust brake valve 9 increases the pressure in the exhaust passage 12 by reducing the opening and restricting the flow rate of the exhaust passage 12, and generates a braking force by increasing the pumping loss of the engine 1.

  The ECU 10 is an electronic control unit including a CPU [Central Processing Unit], a ROM [Read Only Memory], a RAM [Random Access Memory], and the like. In the ECU 10, a program stored in the ROM is loaded into the RAM and executed by the CPU to perform processing related to engine control.

  The ECU 10 is connected to the low-pressure stage turbocharger 5, the high-pressure stage turbocharger 6, the intake / exhaust valve control unit 8, the exhaust brake valve 9, and the EGR valve 15. The ECU 10 is connected to a supercharging pressure sensor 17 and an exhaust pressure sensor 18.

  The supercharging pressure sensor 17 is a pressure sensor provided in the intake passage 11 immediately after the high-pressure compressor 6A (downstream side). The supercharging pressure sensor 17 detects the pressure (supercharging pressure) Pt of the suction air after the two-stage supercharging. The exhaust pressure sensor 18 is a pressure sensor provided in the exhaust passage 12 between the cylinder 2 and the exhaust brake valve 9. The exhaust pressure sensor 18 detects the pressure (exhaust pressure) Pe of the exhaust gas in the exhaust passage 12.

  Based on the supercharging pressure Pt detected by the supercharging pressure sensor 17 and the exhaust pressure Pe detected by the exhaust pressure sensor 18, the ECU 10 performs low pressure stage turbocharger 5, high pressure stage turbocharger 6, intake / exhaust valve control unit 8, exhaust gas. The brake valve 9 and the EGR valve 15 are controlled.

  The ECU 10 controls the valve timing and pressure control (supercharging) of the intake valve 3 so as to suppress the increase in the in-cylinder maximum pressure Pmax of the cylinder 2 and to enable the EGR while achieving high output by supercharging. Control of pressure and exhaust pressure). The ECU 10 functions as pressure control means described in the claims.

  Here, FIG. 2 is a logP-logV diagram for explaining the mirror cycle of the present embodiment. 2 indicates the logarithm logP of the pressure P in the cylinder 2, and the horizontal axis indicates the logarithm logV of the gas volume V in the cylinder 2. FIG. 2 shows a logP-logV diagram (broken line) when supercharging is not performed and a logP-logV diagram (solid line) when supercharging and valve timing control are performed.

  First, the case where supercharging is not performed (broken line) will be described. As shown in FIG. 2, in the cylinder 2, the pressure P in the cylinder becomes the in-cylinder maximum pressure Pmax through an intake stroke (m1) for sucking air and then a compression stroke (m2) for compressing air by the piston. . Thereafter, the expansion stroke (m3) is performed by the combustion of the injected fuel, and after returning to the intake stroke (m1) through the exhaust stroke (m4) for exhausting the exhaust gas.

  Next, a case where supercharging and valve timing control are performed (solid line) will be described. In this case, in the intake stroke (M1), the suction air is supplied into the cylinder 2 at the supercharging pressure Pt by the turbochargers 5 and 6, and subsequently enters the compression stroke (M2). Here, the ECU 10 controls the intake / exhaust valve control unit 8 so that the in-cylinder maximum pressure Pmax of the cylinder 2 is equivalent to that when the supercharging is not performed (broken line). The intake / exhaust valve control unit 8 performs control to advance or delay the closing timing of the intake valve 3 so as to suppress an increase in the in-cylinder maximum pressure Pmax due to supercharging.

  Thereafter, the exhaust stroke (M4) is performed through the expansion stroke (M3). Here, the ECU 10 determines whether or not the exhaust gas pressure Pe of the exhaust gas in the exhaust stroke (M4) is larger than the supercharging pressure Pt based on the detection results of the supercharging pressure sensor 17 and the exhaust pressure sensor 18. In addition, in order for EGR to work properly, the difference obtained by subtracting the supercharging pressure Pt from the exhaust pressure Pe in consideration of the necessity of a certain amount of differential pressure is not less than a predetermined value (positive predetermined value). May be used as the determination condition.

  When the ECU 10 determines that the exhaust pressure Pe is not larger than the supercharging pressure Pt (when Pe ≦ Pt), the ECU 10 controls the supercharging pressure Pt or the exhaust pressure Pe so that the exhaust pressure Pe becomes larger than the supercharging pressure Pt. Perform pressure control. Thereafter, the process returns to the intake stroke (M1) again.

  Next, the flow of control by the ECU 10 of the engine 1 will be described with reference to FIG. FIG. 3 is a flowchart showing a flow of control by the ECU 10.

  As shown in FIG. 3, in step S <b> 1, the ECU 10 detects the supercharging pressure Pt by the supercharging pressure sensor 17 and the exhaust pressure Pe by the exhaust pressure sensor 18.

  Next, as step S <b> 2, the ECU 10 transmits a control signal to the intake / exhaust valve control unit 8 based on the detected supercharging pressure Pt. The intake / exhaust valve control unit 8 performs valve timing control of the intake valve 3 in accordance with a control signal from the ECU 10. In the valve timing control, the valve closing timing of the intake valve 3 is changed so as to suppress an increase in the in-cylinder maximum pressure Pmax caused by supercharging.

  Subsequently, as step S3, the ECU 10 determines whether or not the exhaust pressure Pe is higher than the supercharging pressure Pt. If the ECU 10 determines that the exhaust pressure Pe is greater than the supercharging pressure Pt (when Pe> Pt), the ECU 10 determines that EGR is valid and ends the process. On the other hand, when the ECU 10 determines that the exhaust pressure Pe is not larger than the supercharging pressure Pt (when Pe ≦ Pt), the ECU 10 proceeds to step S4.

  In step S4, the ECU 10 performs pressure control for enabling EGR. As pressure control, the ECU 10 controls the turbochargers 5 and 6 and the exhaust brake valve 9 to make the exhaust pressure Pe larger than the supercharging pressure Pt.

  Specifically, the ECU 10 changes the exhaust pressure Pe by the flow control of the exhaust gas and the change of the supercharging pressure Pt by changing the supercharging efficiency by changing the opening degree of the variable nozzles of the turbochargers 5 and 6. And the exhaust pressure Pe is made larger than the supercharging pressure Pt. Further, the ECU 10 increases the exhaust pressure Pe in the exhaust passage 12 by decreasing the opening degree of the exhaust brake valve 9. In this way, the ECU 10 controls the pressure so that the exhaust pressure Pe becomes larger than the supercharging pressure Pt.

  Note that the ECU 10 does not always need to control all of the turbochargers 5 and 6 and the exhaust brake valve 9 as pressure control. The ECU 10 may perform pressure control using only the turbochargers 5 and 6 or may perform pressure control using only the exhaust brake valve 9. Further, the ECU 10 may perform pressure control using only one of the low-pressure stage turbocharger 5 and the high-pressure stage turbocharger 6. Further, the ECU 10 may change the control target in the pressure control and the number of control targets based on conditions such as the operating state of the engine 1 and the traveling state of the vehicle.

  In the pressure control, the exhaust pressure Pe may be controlled to be larger than the supercharging pressure Pt by a predetermined pressure or more in order to make the EGR function sufficiently. An appropriate value is set as the predetermined pressure in order to obtain a sufficient differential pressure that allows the EGR to function.

  After executing the pressure control to ensure the effectiveness of EGR, the ECU 10 ends the process and repeats from step S1 again. In FIG. 3, the valve timing control and the pressure control are described as one flow, but these controls may be executed as separate and independent flows.

  According to the engine 1 according to this embodiment described above, the in-cylinder maximum pressure Pmax of the cylinder 2 is controlled by controlling the valve timing of the intake valve 3 while supercharging the intake air to the cylinder 2 by the turbochargers 5 and 6. Since the increase is suppressed, it is possible to suppress the influence on the mechanical strength of the engine body due to the increase in the in-cylinder maximum pressure Pmax while achieving high output by supercharging.

  Further, according to this engine 1, EGR becomes ineffective when the differential pressure between the supercharging pressure Pt and the exhaust pressure Pe disappears. Therefore, by controlling the exhaust pressure Pe to sufficiently exceed the supercharging pressure Pt, EGR is achieved. Can be activated. Therefore, according to the engine 1, while achieving high output by supercharging, the influence on the mechanical strength of the engine body due to the increase in the in-cylinder maximum pressure Pmax is suppressed, and a longer life is achieved. Fuel efficiency can be improved by ensuring the effectiveness.

  Further, according to the engine 1, variable nozzle turbochargers are employed as the turbochargers 5 and 6, and the exhaust pressure Pe is made larger than the supercharging pressure Pt by changing the opening degree of these nozzles. EGR can be validated while achieving output.

  Further, according to the engine 1, the exhaust pressure Pe of the cylinder 2 is increased by controlling the exhaust brake valve 9 so that the exhaust pressure Pe is sufficiently larger than the supercharging pressure Pt. EGR can be made effective while achieving the above.

  The present invention is not limited to the embodiment described above. For example, the engine 1 is not necessarily provided with a two-stage supercharging system, and may be a one-stage supercharging system. Further, the pressure control method is not limited to the above.

  DESCRIPTION OF SYMBOLS 1 ... Engine 2 ... Cylinder 3 ... Intake valve 4 ... Exhaust valve 5 ... Low pressure stage turbocharger (supercharger) 5A ... Low pressure stage compressor 5B ... Low pressure stage turbine 6 ... High pressure stage turbocharger (supercharger) 6A ... High pressure stage Compressor 6B ... High-pressure turbine 7 ... EGR passage 8 ... Intake / exhaust valve control unit (intake valve control means) 9 ... Exhaust brake valve 11 ... Intake passage 12 ... Exhaust passage 13 ... Intercooler 14 ... After cooler 15 ... EGR valve 16 ... EGR cooler 17 ... Supercharging pressure sensor 18 ... Exhaust pressure sensor

Claims (3)

An internal combustion engine having a plurality of cylinders,
A supercharger for supercharging the suction air of the cylinder;
Intake valve control means for controlling the valve timing of the intake valve of the cylinder;
An EGR passage for recirculating the exhaust gas of the cylinder to the intake side;
Pressure control means for controlling the exhaust pressure of the cylinder or the supercharging pressure of the supercharger,
The internal combustion engine, wherein the intake valve control means controls the valve timing of the intake valve so as to suppress an increase in the in-cylinder maximum pressure of the cylinder due to supercharging of the supercharger. The supercharger is a variable nozzle turbocharger;
2. The internal combustion engine according to claim 1, wherein the pressure control unit changes a nozzle of the supercharger so that an exhaust pressure of the cylinder is larger than the supercharging pressure of the supercharger. An exhaust brake valve provided in the exhaust passage of the cylinder;
3. The internal combustion engine according to claim 1, wherein the pressure control unit controls the exhaust brake valve so that an exhaust pressure of the cylinder becomes larger than the supercharging pressure of the supercharger.

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