JP2010223077A - Internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To select optimal EGR in response to an engine operation condition. <P>SOLUTION: An intake passage 3 of an engine 1 includes a low pressure stage compressor 5C of a low pressure stage turbocharger 5 and a high pressure stage compressor 6C of a high pressure stage turbocharger 6 from the upstream side. An exhaust passage 4 includes a high pressure stage turbine 6T of the high pressure stage turbocharger 6 and a low pressure stage turbine 5T of the low pressure stage turbocharger 5 from the upstream side. An EGR device includes a first EGR passage 11 for taking out and recirculating exhaust gas from the upstream side of the low pressure stage turbine 5T to the upstream side of the low pressure stage compressor 5C of the intake passage 3 on the downstream side of the high pressure stage turbine 6T of the exhaust passage 4, a second EGR passage 12 for taking out and recirculating the exhaust gas from the downstream side of the low pressure stage turbine 5T of the exhaust passage 4 to the upstream side of the low pressure stage compressor 5C of the intake passage 3, and these opening-closing vales 21 and 22. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an internal combustion engine, and more particularly, to an EGR device that recirculates part of exhaust from an exhaust passage to an intake passage in an internal combustion engine that includes a low-pressure turbocharger and a high-pressure turbocharger.

  Patent Document 1 discloses a so-called two-stage turbo system. In this configuration, a low-pressure stage compressor and a high-pressure stage compressor are arranged in the intake passage sequentially from the upstream side, and a high-pressure turbine and a low-pressure stage turbine are arranged in the exhaust passage sequentially from the upstream side. A low-pressure stage turbine and a low-pressure stage compressor are coaxially connected to constitute a low-pressure stage turbocharger, and a high-pressure stage turbine and a high-pressure stage compressor are coaxially connected to constitute a high-pressure stage turbocharger. To do. In this way, by supercharging the intake air in two stages with the low-pressure stage compressor and the high-pressure stage compressor, the supercharging pressure can be increased efficiently from the low speed range, and the engine output is improved and the fuel consumption is reduced. Can do.

  In Patent Document 1, as an EGR device that recirculates a part of exhaust gas from an exhaust passage to an intake passage in a two-stage turbo system, exhaust is taken out from the upstream of a low-pressure turbine downstream of the high-pressure turbine in the exhaust passage. There is disclosed an EGR passage that is recirculated upstream of a low-pressure turbine in the passage. According to this, even in a low speed and high load region where the supercharging pressure exceeds the exhaust pressure, it is possible to secure the differential pressure between the inlet side and the outlet side of the EGR passage, and to secure the required EGR rate.

JP 2007-224801 A

  However, in the prior art described in Patent Document 1, a large amount of EGR with a large differential pressure is possible by securing a differential pressure between the inlet side and the outlet side of the EGR passage. In some cases, there were inconveniences depending on the operating conditions. For example, if the exhaust gas temperature becomes high at a high load, the temperature of the recirculated EGR gas is too high, and the original EGR effect (combustion temperature suppression for reducing NOx) may not be sufficiently exhibited.

  In view of such a situation, an object of the present invention is to make it possible to select an optimal EGR according to engine operating conditions.

  Therefore, the present invention is an EGR device for an internal combustion engine having a so-called two-stage turbo system, in which the exhaust is taken out from the upstream of the low-pressure stage turbine downstream of the high-pressure turbine in the exhaust passage and recirculated to the upstream of the low-pressure compressor of the intake passage. 1 EGR passage, a second EGR passage that takes the exhaust gas downstream of the low-pressure stage turbine of the exhaust passage and recirculates it upstream of the low-pressure stage compressor of the intake passage, and an EGR passage that selects the first and second EGR passages according to engine operating conditions And selecting means.

  According to the present invention, by selecting the first EGR passage, for example, EGR with a large differential pressure can be selected by removing the exhaust gas from a relatively high temperature and high pressure position. Further, by selecting the second EGR passage, the exhaust gas is taken out from a relatively low temperature and low pressure position, so that, for example, low temperature EGR is possible. Thus, for example, EGR with a large differential pressure and low-temperature EGR can be selected according to operating conditions.

The system diagram of the internal combustion engine with a supercharger which shows one Embodiment of this invention The figure which shows the operation area of EGR passage selection

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  An internal combustion engine 1 shown in FIG. 1 is, for example, a diesel engine, and a combustion chamber of each cylinder includes an intake valve and an exhaust valve (not shown) and a direct injection type fuel injection valve (not shown). Yes.

  Thereby, the intake air taken in from the air cleaner 2 is drawn into the combustion chamber of each cylinder through the intake passage 3 when the intake valve is opened. Then, fuel is injected from the fuel injection valve in the compression stroke, and the intake air and the fuel are combusted by compression ignition in the combustion chamber. The exhaust gas after combustion is discharged into the exhaust passage 4 by opening the exhaust valve.

  The internal combustion engine 1 also includes two turbochargers constituting a so-called two-stage turbo system, that is, a low-pressure stage turbocharger 5 and a high-pressure stage turbocharger 6.

  The low-pressure turbocharger 5 is disposed on the relatively upstream side of the intake passage 3 to supercharge intake air, and is disposed on the relatively downstream side of the exhaust passage 4 and is rotated by the pressure energy of the exhaust. And a drive shaft 5S that coaxially couples the low-pressure stage turbine 5T to drive the low-pressure stage compressor 5C by the low-pressure stage turbine 5T.

  The high-pressure turbocharger 6 is disposed on the relatively downstream side of the intake passage 3 (downstream side from the low-pressure compressor 5C) and supercharges intake air, and the upstream side of the exhaust passage 4 is relatively upstream. A high-pressure stage turbine 6T that is disposed (upstream from the low-pressure stage turbine 5T) and rotates by the pressure energy of the exhaust, and a drive shaft 6S that coaxially connects the high-pressure stage turbine 6T to drive the high-pressure stage compressor 6C. And comprising.

  In other words, the low-pressure stage compressor 5C and the high-pressure stage compressor 6C are arranged in the intake passage 3 sequentially from the upstream side, and the high-pressure stage turbine 6T and the low-pressure stage turbine 5T are arranged in the exhaust passage 4 sequentially from the upstream side. ing. Then, the low-pressure stage turbine 5T and the low-pressure stage compressor 5C are connected coaxially to constitute the low-pressure stage turbocharger 5, and the high-pressure stage turbine 6T and the high-pressure stage compressor 6C are connected coaxially to form the high-pressure stage turbo. A supercharger 6 is configured.

  Therefore, in the intake passage 3, the intake air taken in from the air cleaner 2 is supercharged by the low-pressure stage compressor 5C, further supercharged by the high-pressure stage compressor 6C, and cooled by the intercooler (not shown), and then the intake manifold. It flows into the combustion chamber of each cylinder via (not shown).

  In this way, by supercharging the intake air in two stages with the low-pressure compressor 5C and the high-pressure compressor 6C, the supercharging pressure can be increased efficiently from the low rotation range, and the engine output and fuel consumption can be reduced. You can plan.

  Further, in the exhaust passage 4, when the exhaust of each cylinder joins at an exhaust manifold (not shown) and first passes through the high-pressure turbine 6T, the high-pressure turbine 6T is driven with the pressure energy of the exhaust, and then When passing through the low pressure turbine 5T, the low pressure turbine 5T is driven by the pressure energy of the exhaust. Thereafter, the exhaust gas is exhausted through an exhaust gas aftertreatment device 7 including an exhaust gas purification catalyst and a DPF.

  If necessary, the exhaust passage 4 is provided with a bypass passage that bypasses the high-pressure turbine 6T and the low-pressure turbine 5T, and a control valve for bypass control of each bypass passage, but the illustration is omitted. If necessary, the intake passage 3 is provided with a bypass passage that bypasses the high-pressure compressor 6C and a control valve for bypass control of the bypass passage, but the illustration is omitted.

  Next, the EGR device in the above-described two-stage turbo system will be described.

  The EGR device includes a first EGR passage 11 that extracts exhaust from the high-pressure stage turbine 6T downstream of the exhaust passage 4 and upstream of the low-pressure stage turbine 5T and recirculates the intake passage 3 upstream of the low-pressure stage compressor 5C, and the low-pressure stage of the exhaust passage 4 There is provided a second EGR passage 12 that takes out the exhaust from the downstream of the turbine 5T and recirculates the intake passage 3 upstream of the low-pressure stage compressor 5C.

  However, since the first and second EGR passages 11 and 12 have different EGR gas inlet portions, but the outlet portions may be the same, in this embodiment, the first EGR passage 11 and the inlet portion 12a from the inlet portion 11a. The second EGR passage 12 is joined together to form a common EGR passage 13, and the common EGR passage 13 is connected to a single outlet portion 13a. An EGR cooler 14 is disposed in the common EGR passage 13.

  Further, as a means for selecting the first and second EGR passages 11 and 12, an opening / closing valve 21 is provided at the inlet portion 11 a of the first EGR passage 11, and an opening / closing valve 22 is provided at the inlet portion 12 a of the second EGR passage 12.

  Accordingly, the first EGR passage 11 can be selected by opening the first on-off valve 21 and closing the second on-off valve 22, and conversely, by closing the first on-off valve 21 and opening the second on-off valve 22, 2EGR passage 12 can be selected.

  If necessary, an intake control valve (intake throttle valve) 23 may be provided upstream of the EGR passage outlet portion 13a in the intake passage 3.

  The opening / closing control of the first and second opening / closing valves 21 and 22 is performed by an electronic control unit (ECU) 30 for engine control.

  The ECU 30 includes a microcomputer, and receives signals related to engine operating conditions from the accelerator opening sensor 31, the engine speed sensor 32, etc., and the engine operating conditions detected based on these signals. Based on the above, the fuel injection amount and injection timing of the fuel injection valve are controlled, and the opening and closing of the on-off valves 21 and 22 is controlled. If necessary, the opening degree of the intake control valve 23 is controlled.

  Next, control of the on-off valves 21 and 22 (EGR passage selection control) according to engine operating conditions will be described.

  FIG. 2 shows the operation region of EGR passage selection. When the horizontal axis is the engine speed Ne and the vertical axis is the engine torque Te, the low load region (low rotation low load region) shown in FIG. It is controlled separately from the area (high rotation and high load area). In the ECU 30, the engine speed Ne is detected by the engine speed sensor 32, but the engine torque Te is calculated based on the fuel injection amount controlled by the engine 30 based on the engine operating conditions.

  In the low load region shown in FIG. A, the first EGR passage 11 is selected by opening the first on-off valve 21 and closing the second on-off valve 22.

  Further, in the high load region shown in FIG. B, the second EGR passage 12 is selected by closing the first on-off valve 21 and opening the second on-off valve 22.

  Therefore, in the low load region shown in FIG. A, by selecting the first EGR passage 11, the exhaust is taken out from the high pressure stage turbine 6T downstream of the exhaust passage 4 and from the low pressure stage turbine 5T upstream (inlet portion 11a), and the intake passage 3 Recirculation is performed upstream of the low-pressure stage compressor 5C (outlet portion 13a). That is, EGR with a large differential pressure can be selected by taking exhaust gas from a relatively high temperature and high pressure position.

  Further, in the high load region shown in FIG. B, by selecting the second EGR passage 12, the exhaust gas is taken out from the low-pressure turbine 5T downstream (inlet portion 12a) of the exhaust passage 4 and upstream of the low-pressure compressor 5C of the intake passage 3 ( Recirculate to outlet 13a). That is, a low temperature EGR can be selected by taking out the exhaust from a relatively low temperature and low pressure position.

  More specifically, in the low load region of FIG. A, since the load is low, the exhaust temperature is lower and the exhaust pressure is lower than the high load. Accordingly, in the low load region shown in FIG. A, the first EGR passage 11 is selected and the exhaust gas is taken out from the position on the high pressure side to increase the differential pressure between the inlet side and the outlet side of the EGR passage. Therefore, a large amount of EGR with a large differential pressure becomes possible.

  In particular, in recent years, a large amount of EGR has been demanded in response to a demand for greatly reducing exhaust NOx, and this demand can be satisfied.

  Conventionally, because of the large amount of EGR, in order to increase the differential pressure between the inlet side and the outlet side of the EGR passage, the intake control valve 23 upstream of the EGR passage outlet portion of the intake passage 3 is essential, which is a factor of high cost. However, the intake control valve 23 can be abolished.

  Conventionally, because of a large amount of EGR, in order to increase the differential pressure between the inlet side and the outlet side of the EGR passage, the intake control valve 23 upstream of the EGR passage outlet portion of the intake passage 3 is greatly throttled to generate a large negative pressure. As a result, a large negative pressure is generated in the low-pressure compressor 5C, and there is a concern about leakage of turbo lubricating oil to the intake system. In addition, in the case of the two-stage turbo, the rotation speed of the low-pressure stage compressor 5C is low in the normal control, which is extremely disadvantageous in terms of leakage performance compared to the case of the single turbo. In this regard, in the present embodiment, the intake control valve 23 can be abolished, or even if the intake control valve 23 is provided, it is not necessary to greatly reduce the intake pressure. Therefore, generation of negative pressure can be suppressed, and leakage of turbo lubricating oil can be prevented. Can do.

  In the low load region shown in FIG. A, the first EGR passage 11 is selected to take out the exhaust from the position on the high temperature side. However, because of the low load, the temperature is low in the first place. There is no fear of.

  Considering the warm-up time, the exhaust temperature is taken out from the position on the high temperature side, so that the combustion temperature at the warm-up time can be increased and early warm-up can be promoted. Therefore, it can be used for early warm-up at low temperatures. It also leads to measures against freezing of EGR piping.

  On the other hand, in the high load region shown in FIG. B, the exhaust temperature is higher and the exhaust pressure is higher than the low load because of the high load. Therefore, in the high load region shown in FIG. B, by selecting the second EGR passage 12 and taking out the exhaust from the low temperature side position, low temperature EGR is possible despite the high load.

  Further, in the high load region shown in FIG. B, by selecting the second EGR passage 12, the exhaust gas is taken out from the low pressure side position. The differential pressure on the side can be secured, and a sufficiently large amount of EGR becomes possible.

  Therefore, by such EGR passage selection control, it is possible to perform EGR in a large amount of relatively low temperature exhaust in the entire engine operation region, and it is possible to sufficiently exhibit the NOx reduction effect and the fuel consumption reduction effect by EGR. Become.

  In the above description, as the EGR passage selection means, the open / close valves 21 and 22 are provided in the respective EGR passages 11 and 12, but a flow path switching valve is provided at the junction with the common EGR passage 13 on the outlet side. Alternatively, any type of passage may be selected.

  In the above description, the diesel engine has been described as an example, but it goes without saying that the present invention can be applied to general internal combustion engines including a gasoline engine.

1 Internal combustion engine (diesel engine)
DESCRIPTION OF SYMBOLS 2 Air cleaner 3 Intake passage 4 Exhaust passage 5 Low pressure stage turbocharger 5C Low pressure stage compressor 5T Low pressure stage turbine 5S Drive shaft 6 High pressure stage turbocharger 6C High pressure stage compressor 6T High pressure stage turbine 6S Drive shaft 7 Exhaust aftertreatment device 11 First EGR passage 11a Inlet portion 12 Second EGR passage 12a Inlet portion 13 Common EGR passage 13a Outlet portion 14 EGR cooler 21 First on-off valve 22 Second on-off valve 23 Intake control valve 30 ECU
31 Accelerator opening sensor 32 Engine speed sensor

Claims (1)

A low-pressure stage turbo that includes a low-pressure stage compressor that is disposed in the intake passage and supercharges intake air, and a low-pressure stage turbine that is disposed in the exhaust passage and rotates by the pressure energy of the exhaust to drive the low-pressure stage compressor. A turbocharger,
A high-pressure stage compressor that is disposed on the downstream side of the low-pressure stage compressor in the intake passage and supercharges intake air; and a high-pressure stage compressor that is disposed on the upstream side of the low-pressure turbine in the exhaust path and rotates by the pressure energy of the exhaust. A high-pressure stage turbocharger configured to include a high-pressure stage turbine to be driven,
An EGR device that recirculates part of the exhaust gas from the exhaust passage to the intake passage,
The EGR device includes a first EGR passage that extracts exhaust from the upstream of the low-pressure stage turbine downstream of the high-pressure stage turbine in the exhaust passage and recirculates to the upstream of the low-pressure stage compressor of the intake passage, and from the downstream of the low-pressure stage turbine of the exhaust passage. A second EGR passage that takes out exhaust gas and recirculates the intake passage upstream of the low-pressure stage compressor; and an EGR passage selection means that selects the first and second EGR passages according to engine operating conditions. Internal combustion engine.

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