JP2012127267A - Egr device of multicylinder engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an EGR device of a multicylinder engine for smoothly guiding EGR gas.SOLUTION: This EGR device 60 of the multicylinder engine 1 includes first and second EGR tributary passages 61 and 62 for recirculating the EGR gas to an intake passage 20 by using exhaust pulsation pressure. The passage lengths La and LB of the first and second EGR tributary passages 61 and 62 are different, and a passage length difference (La-Lb) of the first and second EGR tributary passages 61 and 62 is set so that mutual exhaust pressure waves propagating from the first and second EGR tributary passages 61 and 62 are mutually weakened by an EGR junction 63.

Description

  The present invention relates to an EGR device for a multi-cylinder engine that recirculates EGR gas using exhaust pulsation pressure.

  The EGR device for a multi-cylinder engine disclosed in Patent Document 1 includes two exhaust manifolds that collect exhaust from cylinder groups whose ignition orders are not continuous with each other, and takes out EGR gas from each exhaust manifold and guides it to an intake passage. There are two EGR passages and two check valves (reed valves) that stop the backflow of EGR gas guided by each EGR passage, and the intake pressure is higher than the exhaust pressure due to the operation of the supercharger. The check valve is opened using exhaust pulsation pressure propagating to the two EGR passages even in the load operation state, and the EGR gas is recirculated to each cylinder.

  The EGR device includes a merging portion that collects two EGR passages, and a check valve (reed valve) that stops the backflow of EGR gas guided by each EGR passage is interposed in the merging portion.

  In the EGR device for a multi-cylinder engine disclosed in Patent Document 2, check valves are provided in two EGR passages, respectively, so that the EGR gas guided by the EGR passages is prevented from flowing backward.

JP 2009-215983 A JP 2004-308487 A

  However, in an EGR device for a multi-cylinder engine that recirculates EGR gas to the intake passage using the exhaust pulsation pressure, if there is a difference in the passage length between the two EGR passages due to the mounting layout, the joining portion of each EGR passage As a result, the exhaust pulsation pressure increases (see FIG. 12), the detection and control of the EGR gas flow rate become inaccurate, and the variation between cylinders increases.

  In order to avoid the above problems, if the path lengths of the two EGR paths are set to be approximately equal, there is a problem that the mounting layout becomes difficult.

  The present invention has been made in view of the above problems, and an object thereof is to provide an EGR device for a multi-cylinder engine in which EGR gas is smoothly guided.

  The present invention relates to an EGR device for a multi-cylinder engine that recirculates EGR gas to an intake passage using exhaust pulsation pressure, and collects exhaust from cylinder groups whose ignition orders are not continuous with each other. First and second EGR branch passages for extracting EGR gas from the manifold, and first and second check valves for stopping the backflow of EGR gas respectively guided by the first and second EGR branch passages; , EGR junctions for joining the EGR gas respectively guided by the first and second EGR branch passages, and EGR junction passages for guiding the EGR gas joined by the EGR junction to the intake passage. The passage lengths of the EGR tributary passages of the first and second EGR tributary passages are different to such an extent that the mounting layout is facilitated, and the first and second EGR tributary passages have different passage lengths. Exhaust pressure waves each other propagating from GR tributaries passage is characterized in that it is set destructively at EGR junction.

  According to the present invention, the exhaust pressure waves propagating to the first and second EGR tributaries are weakened at the EGR junction, so that the EGR gas is smoothly guided from the EGR junction through the EGR merging passage. The flow rate control accuracy and the variation between cylinders are improved, and the charging efficiency for intake air can be increased.

  When the first and second EGR tributary passages are arranged around the engine body, the length of the pipe can be reduced as compared with the structure in which the passage lengths of the first and second EGR tributary passages are made equal. It becomes possible, and the freedom degree which installs an EGR cooler is raised.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram of the EGR apparatus of the multicylinder engine which shows embodiment of this invention. FIG. 3 is a side view of the first and second exhaust manifolds. Sectional drawing which shows the site | part connected to the turbine of a central block similarly. The block diagram of an EGR cooler similarly. Sectional drawing of an EGR cooler. Similarly, a sectional view and a side view of an EGR junction. Similarly, a sectional view and a side view of an EGR gas flow rate detector. The perspective view of an EGR gas flow control valve similarly. The front view of an EGR gas flow control valve similarly. Similarly, the diagram which calculated | required the exhaust pressure waveform which propagates from the 1st, 2nd EGR branch passage by simulation. The diagram which calculated | required the exhaust pressure waveform which propagates from the 1st, 2nd EGR branch passage by simulation. The diagram which calculated | required the exhaust pressure waveform which propagates from the 1st, 2nd EGR branch passage by simulation.

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

  As shown schematically in FIG. 1, the multi-cylinder engine 1 includes an intake passage 20 that guides intake air to each cylinder, an exhaust passage 30 that discharges exhaust from each cylinder, and a portion of the exhaust (hereinafter referred to as EGR gas). An EGR device 60 that recirculates to each cylinder through the passage 20 and a turbocharger 10 that supercharges intake air by exhaust energy are provided.

  The intake passage 20 includes, in order from the upstream side, an air cleaner 21 that removes foreign matters such as dust from the outside air, a compressor 11 that constitutes the turbocharger 10, an intercooler 22 that cools intake air, an intake manifold 19 that distributes intake air to each cylinder, An intake port (not shown) that opens to the combustion chamber wall of the cylinder is provided.

  The exhaust passage 30 is arranged in order from the upstream side, an exhaust port (not shown) that opens to the combustion chamber wall of each cylinder, first and second exhaust manifolds 31 and 32 that collect exhaust from each exhaust port, and the turbocharger 10. And a muffler 39 with a catalyst for purifying exhaust gas through the catalyst and silencing the exhaust sound.

  The diesel engine 1 includes an intake stroke in which intake air is sucked into a cylinder, a combustion stroke in which fuel injected and supplied to the cylinder is compressed and ignited, and an expansion in which an output shaft is driven to rotate by lowering a piston in the cylinder. In the stroke, the exhaust stroke in which the exhaust in the cylinder is discharged from the exhaust port is sequentially performed for each cylinder.

  The present invention can be applied not only to the diesel engine 1 but also to a spark ignition engine.

  The engine 1 includes six cylinders # 1 to # 6, and, for example, reaches an exhaust stroke with an interval of 120 degrees in the order of # 1, # 4, # 2, # 6, # 3, and # 5 cylinder.

  The first exhaust manifold 31 collects exhaust from the # 1, # 2, and # 3 cylinders whose ignition order is not continuous with each other (exhaust valve opening periods do not overlap). Similarly, the second exhaust manifold 32 collects exhaust from the # 4, # 6, and # 5 cylinders whose firing order is not continuous with each other. As a result, the exhaust flows discharged from the cylinders alternately flow into the first and second exhaust manifolds 31 and 32, and exhaust pressure pulsations occur according to the engine speed range.

  The present invention is not limited to the 6-cylinder engine 1 and can be applied to other multi-cylinder engines having 8 cylinders and 10 cylinders, for example. The exhaust passage 30 is not limited to the first and second exhaust manifolds 31 and 32, and may be configured to include third, fourth, and more exhaust manifolds. Correspondingly, the number of first and second EGR branch passages 61 and 62, first and second check valves 51 and 52, which will be described later, is also increased.

  FIG. 2 is a side view of the first and second exhaust manifolds 31 and 32. The first and second exhaust manifolds 31 and 32 are formed by assembling a central block 41 and front and rear blocks 42 and 43.

  The front block 42 has an opening (exhaust inlet) for the exhaust ports of the # 1 and # 2 cylinders, an opening (exhaust outlet) for the central block 41, and an opening (EGR gas outlet) for the EGR tributary passage 61.

  The rear block 43 has an opening (exhaust inlet) for the exhaust ports of the # 5 and # 6 cylinders, an opening (exhaust outlet) for the central block 41, and an opening (EGR gas outlet) for the EGR tributary passage 62.

  FIG. 3 is a cross-sectional view showing a portion of the central block 41 that is connected to the turbine 12. The central block 41 has openings (exhaust inlets) 47 and 48 for the exhaust ports of the # 5 and # 6 cylinders, openings (exhaust inlets) 45 and 46 for the front and rear blocks 42 and 43, and an opening for the turbine 12 of the turbocharger 10. The first and second ejectors 49 and 50 are included.

  The exhaust passage 30 includes an exhaust junction 33 that joins exhaust gas guided by the first and second exhaust manifolds 31 and 32 and guides the exhaust gas to the turbine 12 of the turbocharger 10. In the exhaust junction 33, the first and second ejectors 49 and 50 are formed so that the flow passage cross-sectional areas are smaller than the flow passage cross-sectional area on the upstream side, and are connected in parallel to the housing inlet 13 of the turbine 12. Is done. As indicated by arrows in FIG. 4, the exhaust blowdown flow at the initial stage of the exhaust stroke in each cylinder flows out from the first and second ejectors 49 and 50 alternately to the housing inlet 13, thereby Exhaust gas from the ejectors 49 and 50 is alternately sucked into the housing inlet 13 to improve exhaust efficiency.

  The turbocharged engine 1 is provided with a turbocharger 10 as a supercharger. In the turbocharger 10, an impeller (not shown) of the turbine 12 and an impeller (not shown) of the compressor 11 are coaxially connected. The impeller of the turbine 12 rotates at high speed by the energy of the exhaust, and the impeller of the compressor 11 sucks intake air from the rotation axis direction by the rotation, and discharges the compressed intake air in the rotation radius direction.

  The variable capacity turbocharger 10 is provided with a variable nozzle (not shown) at an inlet for introducing exhaust to the impeller of the turbine 12, and the nozzle area is changed by rotating the variable nozzle.

  The opening degree of the variable nozzle is controlled by the controller 9 according to the operating state of the engine 1. Thereby, the rotational speed of the turbocharger 10 is adjusted according to the opening degree of the variable nozzle, and the target supercharging pressure corresponding to the operating state of the engine 1 is obtained.

  The EGR device 60 takes out part of the exhaust gas as EGR gas from the upstream side of the turbine 12 in the exhaust passage 30, guides it to the downstream side from the compressor 11 in the intake passage 20, and returns it to each cylinder.

  The EGR device 60 passes through the first and second EGR tributary passages 61 and 62 and the first and second EGR tributary passages 61 and 62 that take out EGR gas from the first and second exhaust manifolds 31 and 32, respectively. A cooler inlet junction 93 that introduces the EGR gas to the EGR cooler 70, an EGR junction 63 that merges the EGR gas that has passed through the EGR cooler 70, and an EGR merge that guides the EGR gas merged in the EGR junction 63 to the intake passage 20 And a passage 64.

  4 is a configuration diagram of the EGR cooler 70, and FIG. 5 is a cross-sectional view of the EGR cooler 70.

  The EGR cooler 70 includes a cylindrical cooler housing 74, and a large number of cooling pipes (pipes) 73 extend linearly in the cooler housing 74, and are arranged in parallel to each other and spaced apart from each other. The cooling pipe 73 defines first and second EGR cooling flow paths 71 and 72 through which EGR gas flows.

  The EGR cooler 70 includes a refrigerant flow path 97 through which engine coolant flows as a refrigerant. The refrigerant flow path 97 is provided around the cooling pipe 73 inside the cooler housing 74. The cooler housing 74 is provided with a refrigerant inlet pipe 75 and a refrigerant outlet pipe 76. The refrigerant inlet pipe 75 and the refrigerant outlet pipe 76 are connected to a cooling water circulation circuit (not shown) of the engine 1 through a pipe (not shown). The engine coolant that circulates in the coolant circulation circuit of the engine 1 flows from the coolant inlet pipe 75 into the coolant channel 97 in the cooler housing 74 and flows through the coolant channel 97 in the course of the first and second EGR cooling channels. The heat of the EGR gas flowing through 71 and 72 is absorbed and returned to the coolant circulation circuit of the engine 1 from the refrigerant outlet pipe 76. The EGR gas passing through the EGR cooler 70 is cooled by exchanging heat with the engine coolant in the course of flowing through the first and second EGR cooling flow paths 71 and 72.

  The cooler housing 74 has flanges 77 and 78 on the inlet side and the outlet side, respectively. Pipes 65 and 66 of the first and second EGR branch passages 61 and 62 are connected to the flange 77 on the inlet side via a cooler inlet junction 93, respectively.

  The cooler inlet junction 93 includes a cylindrical cooler inlet housing 98. The cooler inlet housing 98 has flanges 101, 102, 103 on the inlet side and the outlet side, respectively, and a partition wall 96 on the inner side. Pipes 65 and 66 of the first and second EGR branch passages 61 and 62 are connected to the flanges 102 and 103 on the inlet side, respectively.

  The flange 103 on the outlet side of the cooler inlet housing 98 is connected to the flange 77 on the inlet side of the cooler housing 74.

  Inside the cooler inlet housing 98, the first and second cooler introduction paths 94 and 95 are partitioned by a partition wall 96. The first and second cooler introduction passages 94 and 95 communicate with the first and second EGR cooling passages 71 and 72, respectively, and constitute first and second EGR branch passages 61 and 62, respectively. In other words, in each cooling pipe 73 of the EGR cooler 70, the one that communicates with the first cooler introduction passage 94 defines the first EGR cooling passage 71 and the one that communicates with the second cooler introduction passage 95. Second EGR cooling channels 71 and 72 are defined. As a result, the EGR gas flowing through the first and second EGR tributary passages 61 and 62 goes to the first and second EGR cooling flow paths 71 and 72 via the first and second cooler introduction paths 94 and 95. It is guided.

  The EGR gas that has passed through the first and second EGR cooling channels 71 and 72 of the EGR cooler 70 joins at the EGR junction 63 and is guided to the intake passage 20 through the EGR junction passage 64.

  The first and second EGR cooling flow paths 71 and 72 are not limited to the structure provided in one EGR cooler 70, and the first and second EGR cooling flow paths 71 and 72 are provided in two EGR coolers, respectively. It is good also as a structure to be made.

  An EGR gas flow rate detector 3 and an EGR gas flow rate control valve 4 are interposed in the EGR merging passage 64.

  Exhaust pressure pulsations generated in the first and second exhaust manifolds 31 and 32 are propagated to the first and second EGR branch passages 61 and 62 in accordance with the engine speed range.

  The EGR junction 63 includes first and second check valves 51 and 52 that open and close the first and second EGR branch passages 61 and 62, respectively.

  6A is a cross-sectional view of the EGR junction 63 taken along the line AA in FIG. 6B, and FIG. 6B is a side view of the EGR junction 63. FIG.

  The EGR junction 63 includes a cylindrical junction housing 14. The junction housing 14 has flanges 15 and 16 on the inlet side and the outlet side, respectively, and a partition wall 17 on the inner side. An outlet side flange 78 of the cooler housing 74 is connected to the inlet side flange 15. A flange 35 (see FIG. 7) of the EGR gas flow rate detector 3 is connected to the outlet side flange 16 via a pipe (not shown).

  On the inner side of the junction housing 14, the first and second EGR branch passages 81 and 82 that are the downstream ends of the first and second EGR branch passages 61 and 62 and the EGR junction that is the upstream end of the EGR junction passage 64. An end 83 is provided.

  The upstream side in the junction housing 14 is partitioned into first and second EGR branch ends 81 and 82 by a partition wall 17. First and second check valves 51 and 52 are accommodated in the first and second EGR branch ends 81 and 82, respectively.

  The first and second check valves 51 and 52 include a valve seat 53 interposed in the junction housing 14 and two reed valves 54 seated on the valve seat 53.

  The valve seat 53 has a valve seat surface 55 that is V-shaped in cross section and has a hollow structure and is inclined with respect to each other. The valve seat surface 55 is formed in an annular shape so that the end of the reed valve 54 is seated. An opening (not shown) through which the EGR gas passes is formed inside the valve seat surface 55.

  The reed valve 54 is formed of a rectangular spring plate, and a base end portion thereof is fastened to the valve seat 53 by a plurality of screws 91.

  In the first and second check valves 51 and 52, when the differential pressure across the front and rear is not more than a predetermined value, the reed valve 54 is seated on the valve seat surface 55 by its elastic restoring force, The EGR branch ends 81 and 82 are respectively closed.

  When the differential pressure across the first and second check valves 51 and 52 exceeds a predetermined value, the reed valve 54 bends against its elastic restoring force and separates from the valve seat surface 55. Then, the first and second EGR branch ends 81 and 82 are opened. When the first and second check valves 51 and 52 are opened in this way, the EGR gas passes through the valve seat 53 and passes through the first and second EGR branch ends 81 and 82 as indicated by arrows in FIG. Flowing.

  As a result, the exhaust pulsation pressure generated in the first and second exhaust manifolds 31 and 32 propagates to the first and second EGR branch passages 61 and 62, and the peak value of the exhaust pulsation pressure becomes the intake pressure of the intake passage 20. In the operation state exceeding, the first and second check valves 51 and 52 are alternately opened, and the EGR gas guided to the first and second EGR branch passages 61 and 62 joins at the EGR junction 63. , The EGR merging passage 64 is led to the intake passage 20.

  The partition wall 17 is formed so as to protrude downstream from the leading ends of the reed valve 54 and the valve seat 53. In the high load operation state where the first and second check valves 51 and 52 are alternately opened, the EGR gas flowing through the first and second EGR branch ends 81 and 82 runs along the housing inner wall surface 18 and the partition wall 17. Thus, the exhaust pressure wave propagating to one of the first and second EGR branch ends 81 and 82 can be prevented from propagating beyond the partition wall 17 to the other.

  The first and second cooler introduction passages 94 and 95, the first and second EGR cooling passages 71 and 72, the first and second EGR branch ends 81 and 82 respectively extend in a straight line, and are center lines. O are formed symmetrically with respect to each other.

  The EGR gas passing through the first and second EGR tributary passages 61 and 62 passes through the first and second cooler introduction passages 94 and 95 as shown by arrows in the drawing, and is at the inlet side end of the cooler housing 74. From the first and second EGR cooling channels 71 and 72 without being merged with each other, and after being cooled through the first and second EGR cooling channels 71 and 72, the first and second The two EGR branch ends 81 and 82 are led to the EGR merging passage 64.

  Here, the first and second EGR tributary ends 81 and 82 in the EGR junction 63 from the upstream ends of the first and second EGR tributary ends 81 and 82 connected to the first and second exhaust manifolds 31 and 32 ( The distances to the tip of the partition wall 17 are the first and second EGR branch passages 61 and 62, and the passage lengths are La and Lb.

  In the present invention, the passage lengths La and Lb of the first and second EGR branch passages 61 and 62 are made different from each other, and the passage length difference (La−Lb) is determined by the first and second check valves 51 and 52. During rated operation of the engine 1 that opens and closes, the pulsation of the exhaust pressure wave propagating to the first and second EGR branch ends 81 and 82 is configured to weaken at the EGR junction end 83.

  Specifically, at the rated operation of the engine 1, when the wavelength of the exhaust pressure wave propagating from the first and second exhaust manifolds 31 and 32 to the first and second EGR branch ends 81 and 82 is λ, The passage lengths La and Lb of the first and second EGR branch passages 61 and 62 are made different from each other, and the passage length difference ΔL (= La−Lb) is set to approximately λ / 4.

Here, if c is the speed of sound and f is the frequency of the exhaust pressure wave, the wavelength λ of the exhaust pressure wave can be obtained by the following equation.
λ = c / f (m)
If Te is the temperature of the EGR gas and SQRT is the square root, the speed of sound c can be obtained by the following equation.
c≈20.05 * SQRT (273 + Te) (m / s)
When M (= 3) is the number of cylinders communicating with the first and second exhaust manifolds 31 and 32, and N is the rotational speed (rpm) of the engine 1, the frequency f of the exhaust pressure wave can be obtained by the following equation.
f = M * N / (360 / M) = 3 * N / (360/3) = N / 40 (Hz)
10 (a) and 12 (b) show the exhaust pressure waveform propagating from the first and second EGR tributary passages 61 and 62 to the EGR merging end 83 when the passage length difference ΔL is changed. It is the diagram calculated | required by simulation. The horizontal axis of this diagram is the crank angle (deg) of the engine 1, and the vertical axis is the exhaust pressure (pressure of EGR gas). In each figure, a one-dot chain line indicates an average exhaust pressure (average EGR gas pressure).

  The exhaust pressure waveform includes an initial peak P1 generated by an exhaust blowdown flow that flows from the cylinder to the exhaust port as the exhaust valve (not shown) opens in the initial stage of the exhaust stroke in each cylinder, and this peak. An early bottom B1 that occurs after P1, a late peak P2 that is caused by an exhaust flow that is pushed out from the cylinder to the exhaust port by raising the cylinder in the late stage of the exhaust stroke, and a late bottom B2 that occurs after this peak P2. Are in order.

  FIG. 10 shows characteristics when the passage lengths La and Lb of the first and second EGR branch passages 61 and 62 are made different and the passage length difference ΔL is set to approximately λ / 4. As shown in this figure, the exhaust pressure waveforms propagating from the first and second EGR tributary passages 61 and 62 are offset by the initial peak P1 and the late bottom B2 at the EGR merging end 83, The peak P2 and the initial bottom B1 cancel each other, and the exhaust pressure pulsation generated at the EGR merging end 83 is weakened. As a result, the EGR gas is smoothly guided from the EGR merging end 83 through the EGR merging passage 64.

  The same characteristics can be obtained not only when the path length difference ΔL is set to approximately λ / 4 but also when ΔL is set to 1 + λ / 4, 2 + λ / 4, and 3 + λ / 4, respectively.

  FIG. 11 shows the characteristics when the passage lengths La and Lb of the first and second EGR branch passages 61 and 62 are set equal (ΔL = 0). As shown in this figure, the exhaust pressure waveforms propagating from the first and second EGR tributary passages 61 and 62 interfere with each other at the EGR merging end 83 where a portion higher than the average pressure and a portion lower than the average pressure interfere with each other. The peak P1 and the late peak P2 overlap, and the initial bottom B1 and the late bottom B2 overlap, so the exhaust pressure pulsation generated at the EGR merging end 83 is not sufficiently weakened.

  FIG. 12 shows the characteristics when the passage lengths La and Lb of the first and second EGR branch passages 61 and 62 are made different and the passage length difference ΔL is set to approximately λ / 2. As shown in this figure, the exhaust pressure waveforms propagating from the first and second EGR branch passages 61 and 62 are such that the initial peak P1 overlaps and the later peak P2 overlaps at the EGR merging end 83. The exhaust pressure pulsation generated at the EGR merging end 83 is strengthened, and the most preferable state is obtained.

  The junction housing 14 has a cylindrical housing inner wall surface 18. The cross-sectional area of the flow path defined inside the housing inner wall surface 18 gradually decreases from the upstream side to the downstream side.

  The ratio of the flow path cross-sectional area decreasing with respect to the flow path distance is such that the EGR junction end 83 provided on the downstream side of the partition wall 17 from the first and second EGR branch ends 81 and 82 provided with the partition wall 17. Becomes smaller.

  In the housing inner wall surface 18, an inclination angle θ / 2 with respect to the center line O is larger at a portion that defines the EGR merging end 83 than a portion that defines the first and second EGR branch ends 81 and 82. Formed as follows.

  The throttle angle θ of the housing inner wall surface 18 at the portion that defines the EGR merging end 83 is set to, for example, about 30 ° within a range of 45 ° or less.

  Accordingly, the EGR gas smoothly flows from the first and second EGR branch passages 61 and 62 to the EGR merging end 83 and is guided to the EGR gas flow rate detector 3.

  7A is a cross-sectional view of the EGR gas flow rate detector 3 along the line AA in FIG. 7B, and FIG. 7B is a side view of the EGR gas flow rate detector 3. FIG.

  The EGR gas flow rate detector 3 includes a cylindrical sensor housing 34 interposed in the EGR merging passage 64, and detects the flow rate of EGR gas by the pressure in the sensor housing 34.

  The sensor housing 34 has flanges 35 and 36 on the inlet side and the outlet side, respectively. The inlet-side flange 35 is connected to the flange 16 of the junction housing 14. The EGR gas flow rate control valve 4 is connected to the flange 36 on the outlet side via a pipe.

  An inner wall surface 92 of the sensor housing 34 defines a throttle portion 37. The narrowed portion 37 has a cross-sectional area that gradually decreases from the upstream side to the central portion, and gradually increases from the central portion to the downstream side.

  A hole 38 is opened on the upstream side of the throttle portion 37, and a high pressure side pressure detector (not shown) for detecting the pressure is interposed in the hole 38.

  A hole 89 is opened at the center of the throttle portion 37, and a low-pressure side pressure detector (not shown) for detecting the pressure is interposed in the hole 89.

  A hole 44 is opened on the downstream side of the throttle portion 37, and a temperature detector (not shown) for detecting the temperature is interposed in the hole 44.

  The controller 9 inputs detection signals from the high pressure side pressure detector and the low pressure side pressure detector, and calculates the flow rate of EGR gas based on the pressure difference between the two. Further, the controller 9 receives a detection signal from the temperature detector and corrects the flow rate of the EGR gas based on the detected temperature of the EGR gas.

  FIG. 8 is a perspective view of the EGR gas flow rate control valve 4. FIG. 9 is a front view of the EGR gas flow rate control valve 4.

  The EGR gas flow rate control valve 4 includes a valve housing 23 that guides EGR gas flowing out from the EGR gas flow rate detector 3 to the intake manifold 19, a valve (not shown) accommodated in the valve housing 23, And an actuator 27 that opens and closes.

  The valve housing 23 has three flanges 24, 25 and 26. The two inlet side flanges 24 and 25 are connected to a flange 36 on the outlet side of the sensor housing 34 via a pipe. A flange 26 on the outlet side of the valve housing 23 is connected to the intake manifold 19.

  When the EGR gas flow rate control valve 4 is opened, EGR gas flows into the valve housing 23 from the openings of the two inlet side flanges 24 and 25 as shown by arrows in FIG. 8, and the opening of the flange 26 on the outlet side is opened. To the intake manifold 19. The EGR gas flow rate control valve 4 changes the flow rate of EGR gas according to the opening degree.

  During operation of the engine 1, exhaust flows discharged from the cylinders alternately flow into the first and second exhaust manifolds 31 and 32, and exhaust pressure pulsations are generated according to the engine speed range. At the exhaust junction 33, the exhaust blowdown flow at the beginning of the exhaust stroke in each cylinder flows out from the first and second ejectors 49 and 50 alternately to the housing inlet 13, whereby the first and second ejectors 49 and 50 are discharged. Exhaust gas from the air is alternately sucked into the housing inlet 13 to increase the exhaust efficiency.

  The EGR device 60 takes out EGR gas from the upstream side of the turbine 12 in the exhaust passage 30 and introduces it to the downstream side of the compressor 11 in the intake passage 20. By recirculating EGR gas to each cylinder, the combustion temperature in the combustion chamber is lowered and the amount of nitrogen oxides generated is suppressed.

  When the EGR gas is cooled by the EGR cooler 70, the charging efficiency (EGR rate) for intake air can be increased, and the first and second check valves 51, 52 and the like can be prevented from being overheated.

  The turbocharger 10 supercharges intake air compressed by exhaust energy from the intake passage 20 to each cylinder. Thereby, the amount of oxygen in the intake air supplied to each cylinder is secured.

  An operation state in which the exhaust pulsation pressure generated in the first and second exhaust manifolds 31 and 32 propagates to the first and second EGR tributary passages 61 and 62 and the peak value of the exhaust pulsation pressure exceeds the intake pressure of the intake passage 20. , The first and second check valves 51 and 52 are alternately opened, and the EGR gas guided to the first and second EGR branch passages 61 and 62 is merged at the EGR junction 63 to join the EGR. The air is guided to the intake passage 20 through the passage 64. As a result, the EGR gas can be recirculated to each cylinder even in a high-load operation state in which the intake pressure of the intake manifold 19 is higher than the average exhaust pressure of the first and second exhaust manifolds 31 and 32.

  The controller 9 obtains a target value of the EGR gas flow rate according to the operating state of the engine 1 based on a preset map, and the EGR gas flow rate detected via the EGR gas flow rate detector 3 approaches the target value. Thus, the opening degree of the EGR gas flow rate control valve 4 is feedback controlled.

  Hereinafter, the gist, operation, and effect of the present embodiment will be described.

  In the present embodiment, the EGR device 60 of the multi-cylinder engine 1 recirculates EGR gas to the intake passage 20 using exhaust pulsation pressure, and first collects exhaust from cylinder groups whose ignition sequences are not continuous with each other. The first and second EGR tributary passages 61 and 62 for taking out EGR gas from the second exhaust manifolds 31 and 32, respectively, and the EGR gas guided by the first and second EGR tributary passages 61 and 62 respectively flow backward. The EGR junction 63 and the EGR junction 63 joined the EGR gas guided by the first and second check valves 51 and 52 and the first and second EGR branch passages 61 and 62, respectively. An EGR merging passage 64 for guiding EGR gas to the intake passage 20, and a passage length La of the first and second EGR branch passages 61 and 62 LGR is different, and the exhaust pressure wave propagating from the first and second EGR branch passages 61 and 62 is different from each other in the passage length difference (La−Lb) between the first and second EGR branch passages 61 and 62. The configuration is set so as to weaken each other.

  Based on the above configuration, the EGR gas guided by the first and second EGR branch passages 61 and 62 opens the first and second check valves 51 and 52 at the EGR junction 63 and joins. Even in a high-load operation state where the intake pressure is higher than the exhaust pressure, the first and second check valves 51, 52 are configured to utilize the exhaust pulsation pressure propagating to the first and second EGR branch passages 61, 62. It becomes possible to alternately open the valve and recirculate the EGR gas to each cylinder.

  The pulsation of the exhaust pressure wave propagating to the first and second EGR branch ends 81 and 82 is weakened at the EGR junction 63 by reducing the passage length difference (La−Lb) between the first and second EGR branch passages 61 and 62. By setting so as to match, the EGR gas is smoothly guided from the EGR junction 63 through the EGR merging passage 64, the control accuracy of the EGR gas flow rate and the variation between the cylinders are improved, and the charging efficiency for the intake air is increased. It is done.

  Further, when the first and second EGR tributary passages 61 and 62 are arranged around the engine body, the first and second EGR tributary passages 61 and 62 have the same passage lengths La and Lb. In comparison, the length of the pipe can be reduced, and the degree of freedom for installing the EGR cooler 70 can be increased.

  In this embodiment, the wavelength of the exhaust pressure wave is λ, and the passage length difference (La−Lb) between the first and second EGR branch passages 61 and 62 is set to be approximately λ / 4 or less.

  Based on the above configuration, as shown in FIG. 10, the exhaust pressure waveforms propagating from the first and second EGR tributary passages 61, 62 have an initial peak P 1 and a late bottom B 2 at the EGR junction 63. The latter peak P2 and the initial bottom B1 cancel each other, and the exhaust pressure pulsation generated at the EGR junction 63 is effectively weakened. Thereby, the EGR gas is smoothly guided from the EGR junction 63 through the EGR merging passage 64.

  In the present embodiment, the EGR gas flow rate detector 3 includes an EGR gas flow rate detector 3 that detects the flow rate of EGR gas flowing through the EGR merging passage 64, and an EGR gas flow rate control valve 4 that adjusts the flow rate of EGR gas. The opening degree of the EGR gas flow rate control valve 4 is controlled according to the detection signal.

  Based on the above configuration, the exhaust pulsation pressure propagating through the first and second EGR branch passages 61 and 62 interferes with each other at the EGR junction 63, and the EGR gas whose pulsation pressure is reduced is supplied to the EGR gas flow rate detector 3. Led. As a result, the EGR gas flow rate detector 3 is suppressed from being affected by the exhaust pulsation pressure, and the EGR gas flow rate is stably detected. Therefore, the flow rate of the EGR gas is controlled via the EGR gas flow rate control valve 4. Feedback control can be performed with high accuracy.

  In the present embodiment, the EGR junction 63 includes an EGR merging end 83 that is an upstream end of the EGR merging passage 64 on the downstream side of the partition wall 17, and the flow path cross-sectional area of the EGR merging end 83 gradually increases from the upstream side to the downstream side. The configuration is reduced.

  Based on the above configuration, the flow of EGR gas from the first and second EGR branch passages 61 and 62 toward the EGR merging end 83 is smoothly throttled, and the EGR gas flow rate detector 3 is affected by the exhaust pulsation pressure. It can be suppressed.

  In the present embodiment, the first and second EGR cooling channels 71 and 72 and the first and second EGR branch ends 81 and 82 extend linearly.

  Based on the above configuration, the EGR gas from the first and second EGR cooling flow paths 71 and 72 to the first and second EGR branch ends 81 and 82 flows in a straight line, and the EGR cooler 70 and the EGR junction 63. The loss resistance of the EGR gas passing through the engine can be suppressed, and the charging efficiency for intake air can be increased.

  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.

DESCRIPTION OF SYMBOLS 1 Engine 3 EGR gas flow rate detector 4 EGR gas flow rate control valve 10 Turbocharger 20 Intake passage 30 Exhaust passage 31 First exhaust manifold 32 Second exhaust manifold 51 First check valve 52 Second check valve 60 EGR device 61 First EGR branch passage 62 Second EGR branch passage 63 EGR junction 64 EGR junction passage 81 First EGR branch end 82 Second EGR branch end 83 EGR junction end

Claims (3)

An EGR device for a multi-cylinder engine that recirculates EGR gas to an intake passage using exhaust pulsation pressure,
First and second EGR tributary passages that respectively take out EGR gas from first and second exhaust manifolds that respectively collect exhaust from cylinder groups whose ignition order is not continuous with each other;
First and second check valves for stopping the backflow of EGR gas respectively guided by the first and second EGR branch passages;
An EGR junction that joins the EGR gases respectively guided by the first and second EGR branch passages;
An EGR merge passage that guides the EGR gas merged at the EGR junction to the intake passage,
The first and second EGR tributary passages have different path lengths,
The passage length difference between the first and second EGR branch passages is set so that exhaust pressure waves propagating from the first and second EGR branch passages are weakened at the EGR junction. Multi-cylinder engine EGR device.   2. The EGR of a multi-cylinder engine according to claim 1, wherein a wavelength of the exhaust pressure wave is λ, and a path length difference between the first and second EGR branch passages is set to approximately λ / 4 or less. apparatus. An EGR gas flow rate detector for detecting a flow rate of EGR gas flowing through the EGR merging passage;
An EGR gas flow control valve for adjusting the flow rate of EGR gas,
The EGR device for a multi-cylinder engine according to claim 2, wherein the opening degree of the EGR gas flow rate control valve is controlled in accordance with a detection signal of the EGR gas flow rate detector.

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