JP4978525B2 - Exhaust system for turbocharged engine - Google Patents

Description

  The present invention relates to a supercharged engine equipped with an exhaust turbocharger.

  Conventionally, as a means for increasing the engine output torque, a supercharging device for increasing the intake pressure is known. A typical example is an exhaust turbocharger. This exhaust turbocharger is a turbine that is connected to a turbine provided in an exhaust passage and a compressor provided in an intake passage by a shaft. The compressor is driven by rotating the turbine with exhaust gas, and intake pressure is reduced. It is configured to raise.

  Further, in this exhaust turbocharger, it has been considered to enhance the supercharging effect using the dynamic pressure of the exhaust in an operation region where the exhaust gas flow rate is small.

For example, in the exhaust system disclosed in Patent Document 1, a primary exhaust port and a “secondary exhaust port” are provided for each cylinder of an engine having a plurality of cylinders, and exhaust passages connected to the primary exhaust port of each cylinder are assembled. Then, the assembled primary side exhaust passage is connected to the primary side turbine scroll of the exhaust turbocharger, and the exhaust passage connected to the secondary exhaust port of each cylinder is gathered to collect the secondary side exhaust gas. In a predetermined supercharging operation region where the passage is connected to the secondary turbine scroll of the exhaust turbocharger and the exhaust passage on the secondary side is provided and the exhaust gas flow rate is low, the exhaust on the secondary side is controlled by the control valve. Close the passage so that the exhaust gas is guided only from the exhaust passage on the primary side to the exhaust turbocharger. To have.
JP-A-2-91422

  According to the exhaust device disclosed in Patent Document 1, in a predetermined supercharging operation region where the flow rate of exhaust gas is small, the dynamic pressure energy due to the exhaust gas blowdown (exhaust blowing) from the primary exhaust port is excessive. A flow rate of the exhaust gas is increased by supplying the exhaust gas to the exhaust turbocharger only from the primary side exhaust passage.

  However, since the exhaust passage leading to the primary exhaust port is gathered in the middle and then connected to the turbocharger, the dynamic pressure is reduced due to exhaust interference at the gathering part, etc. There was a point left to do.

  In view of the above circumstances, the present invention can further increase the dynamic pressure energy given to the exhaust turbocharger in a predetermined supercharging operation region where the flow rate of exhaust gas is small, and can effectively enhance the supercharging performance. An object is to provide an exhaust device for an engine with a supercharger.

  In order to solve the above problems, the present invention provides an exhaust system for a supercharged engine comprising an engine having a plurality of cylinders and an exhaust turbocharger. A primary exhaust port that exhausts exhaust gas in the operation region and provided in each of the cylinders described above, restricts the exhaust gas discharge amount in a predetermined supercharging operation region, and exhaust gas discharge amount in other high-speed operation regions A secondary exhaust port for releasing the restriction, a primary exhaust passage for connecting the primary exhaust port of each cylinder and the exhaust turbocharger, and a secondary exhaust passage for connecting the secondary exhaust port of each cylinder and the exhaust turbocharger The primary exhaust passage corresponds to the primary exhaust port of each cylinder and is configured to be connected to the exhaust turbocharger in an independent state. Is the secondary exhaust passage, is set in the middle the exhaust passage, in which are configured to be connected to the exhaust turbocharger downstream from the set section.

  According to this configuration, in the predetermined supercharging operation region, the outflow amount of the exhaust gas from the secondary exhaust port is limited, and the exhaust gas mainly passes from the primary exhaust port through the primary exhaust passage to the exhaust turbocharger. By being guided, the flow rate of the exhaust gas is increased, and dynamic pressure energy by blowdown when the primary exhaust port is opened is given to the turbocharger.

  In particular, since the primary exhaust passages corresponding to the primary exhaust ports of the cylinders are connected to the exhaust turbocharger in a state of being independent from each other, exhaust interference that occurs when collecting in the middle of the passage is caused. There is no. Further, by not gathering in the middle of the passage, the volume of each primary exhaust passage can be made as small as possible. As a result, it is possible to prevent a decrease in dynamic pressure and a decrease in exhaust flow velocity. Further, at locations where each primary exhaust passage is connected to the exhaust turbocharger, exhaust gas at a high flow rate is exhausted from one primary exhaust passage corresponding to the cylinder at the blowdown time immediately after the primary exhaust port is opened. As a result, an ejector effect that flows into the turbocharger and sucks the exhaust gas from the other primary exhaust passage is generated, thereby increasing the amount of exhaust gas flowing into the exhaust turbocharger.

  By these actions, the exhaust energy supplied to the exhaust turbocharger increases and the supercharging performance is improved.

  On the other hand, in the high-speed operation region where the exhaust gas flow rate is high, the restriction on the exhaust gas flow rate from the secondary exhaust port is released, and the exhaust gas is turbocharged from both the primary and secondary exhaust ports through the primary exhaust passage and the secondary exhaust passage. Guided to the supercharger, exhaust flow resistance is reduced. In addition, although the exhaust temperature becomes high in the high-speed operation region, the secondary exhaust passages are gathered in the middle, so that a cooling effect is obtained at this gathered portion, and the temperature rise can be suppressed.

  In the exhaust system for an engine with a supercharger according to the present invention, the exhaust turbocharger is a type in which a turbine wheel is disposed so as to protrude on an extension line of an exhaust path upstream of a turbine scroll, and each primary exhaust passage includes the above-described primary exhaust passage. It is preferable to be connected to the turbine scroll inner peripheral side of the turbocharger.

  If it does in this way, the flow of the exhaust gas which flows in into an exhaust turbo supercharger from a primary exhaust passage will act on a turbine wheel effectively in a predetermined supercharging operation field, and supercharging efficiency will be raised.

  The secondary exhaust port can limit the exhaust gas discharge amount using either a valve stop mechanism that can stop the operation of the exhaust valve or a valve lift amount variable mechanism that makes the lift amount of the exhaust valve variable. It is preferable.

  In this way, there is no need to provide a valve device or the like for restricting the flow in the exhaust passage, and the exhaust system can be made compact.

  As described above, according to the exhaust system for an engine with a turbocharger of the present invention, in a predetermined supercharging operation region where the flow rate of exhaust gas is small, the exhaust gas is mainly discharged from the primary exhaust port through the primary exhaust passage. In particular, since the primary exhaust passages corresponding to the primary exhaust ports of the cylinders are connected to the exhaust turbocharger in an independent state, the operation given to the exhaust turbocharger The pressure energy can be increased, and the supercharging performance can be effectively enhanced.

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

  FIG. 1 is a schematic configuration diagram of a supercharged engine according to an embodiment of the present invention. FIG. 2 is a partial side sectional view of the engine with a supercharger.

  The engine with a supercharger shown in these drawings is an in-line four-cylinder four-cycle engine, and the cylinder block 2 of the engine 1 includes first to fourth cylinders 3a, 3b, 3c, 3d (in order from one end side). The cylinders 3 are collectively referred to as one horizontal line. The configuration of each cylinder 3 is common, a combustion chamber 5 is formed above the piston 4 in the cylinder 3, and an intake port 6 for inhaling intake air and an exhaust port for exhausting exhaust are formed above the combustion chamber 5. In this embodiment, two intake ports 6 and two exhaust ports 8 are provided. Both intake ports 6 are provided with intake valves 7 for opening and closing the intake ports 6, and both exhaust ports 8 are provided with exhaust valves 9 for opening and closing them. Further, the cylinder head 10 is provided with a spark plug 11 that generates a spark at the top of the combustion chamber 5. In addition, an unillustrated fuel supply means including the fuel injection valve 12 is provided at an appropriate position.

  In the engine 1 of the present embodiment, as with a general four-cylinder engine, the cylinders 3 are shifted from each other so that the respective ignition timings sequentially reach every crank angle of 180 degrees (hereinafter referred to as 180 ° CA). It is driving. The ignition order is the first cylinder 3a → the third cylinder 3c → the fourth cylinder 3d → the second cylinder 3b. Therefore, for example, when the first cylinder 3a is in the expansion stroke, the second cylinder 3b is in the exhaust stroke, the third cylinder 3c is in the compression stroke, and the fourth cylinder 3d is in the intake stroke.

  In the engine 1, when one of the exhaust ports 8 is called a primary exhaust port 8a and the other is called a secondary exhaust port 8b, the primary exhaust port 8a discharges exhaust gas in the entire operating range of the engine, and the secondary exhaust port 8a. 8b is configured to limit the exhaust gas discharge amount in a predetermined supercharging operation region, and to release the exhaust gas discharge amount restriction in other high-speed operation regions.

  Such restriction of the exhaust gas discharge amount of the secondary exhaust port 8 b and release of the restriction are performed using the valve lift amount variable mechanism 15. That is, the intake valve 7 and the exhaust valve 9 are opened and closed by the valve mechanisms 13 and 14 each composed of a camshaft or the like, but the exhaust valve 9 for opening and closing the secondary exhaust port 8b is provided in the valve mechanism 14 on the exhaust side. On the other hand, a variable valve lift amount mechanism 15 that allows the lift amount and the valve opening period to be changed is incorporated.

  This variable valve lift amount mechanism 15 shows the lift characteristic of the exhaust valve 9 that opens and closes the secondary exhaust port 8b by making it possible to switch the valve cam, etc., and the broken line in the figure shows the maximum lift state EV2max shown by the solid line in FIG. It can be changed between the minimum lift state EV2min indicated by. In the maximum lift state EV2max, the exhaust valve 9 is opened at a predetermined time before the bottom dead center and closed at a predetermined time after the top dead center. In the minimum lift state EV2min, the lift amount and the valve opening are compared with those in the maximum lift state. The period is getting smaller.

  In FIG. 3, the characteristic indicated by symbol EV1 is the lift characteristic of the exhaust valve 9 that opens and closes the primary exhaust port 8a, and the characteristic indicated by symbol IV is the lift characteristic of the intake valve 7. In the embodiment, these are constant, and an overlap period OL in which both the intake valve 7 and the exhaust valve 9 are open is set near the top dead center.

  As shown in FIGS. 1 and 2, an intake passage 30 and an exhaust passage 40 are provided for the engine 1, and an exhaust turbocharger 20 is provided. The exhaust turbocharger 20 includes a turbine wheel 22 accommodated in a turbine housing 21, a compressor impeller 24 accommodated in a compressor housing 23, and a connecting portion 25 that connects them. The turbine housing 21 is connected to the exhaust passage 40, while the compressor housing 23 is connected to the intake passage 30. An intake air passage 30 downstream of the compressor is provided with an intercooler 31 for cooling intake air, and further, a throttle valve 32 for adjusting the intake air flow rate is provided downstream of the intercooler 31, and the intake air passing through the throttle valve 32 is supplied to the intake manifold 33. After that, it is supplied to each cylinder 3.

  The exhaust passage 40 is connected to a primary exhaust passage 41 connecting the primary exhaust port 8a of each cylinder 3 and the exhaust turbocharger 20, and to the secondary exhaust port 8b of each cylinder and the exhaust turbocharger 20. A secondary exhaust passage 42 is provided.

  As shown in FIG. 1, the primary exhaust passage 41 is connected to the turbine housing 21 of the exhaust turbocharger 20 in an independent state corresponding to the primary exhaust port 8a of each cylinder. On the other hand, the secondary exhaust passage 42 is gathered in the middle of the exhaust passage, and is connected to the turbine housing 21 of the exhaust turbocharger 20 downstream of the gathered portion.

  Specific structures of the primary exhaust passage 41 and the secondary exhaust passage 42 will be described with reference to FIGS.

  FIG. 4 shows a structure in which the primary exhaust passage 41 and the secondary exhaust passage 42 are combined and connected to the exhaust turbocharger 20. FIGS. 5A and 5B show the primary exhaust passage 41 and the secondary exhaust passage 42. And are shown separately.

  As shown in these figures, each primary exhaust passage 41 has an upstream end connected to the primary exhaust port 8a of each cylinder and approaches each other on the downstream side, but does not merge and is partitioned by a passage wall. They are gathering together. On the other hand, the secondary exhaust passage 42 is divided into cylinders on the upstream side and connected to the secondary exhaust port 8b of each cylinder 3, and gathers in the middle of the passage, and forms a single passage on the downstream side. And as shown in FIG. 6, the downstream end part of each primary exhaust passage 41 is formed in a cross-sectional substantially fan shape, and the downstream end part of the path | pass where the secondary exhaust passage 42 gathered is formed in a cross-sectional substantially semicircle, The downstream end portion of the primary exhaust passage 41 and the downstream end portion of the secondary exhaust passage 42 are gathered together to form a substantially circular cross section as a whole.

  FIG. 7 shows a specific structure of the inside of the exhaust turbocharger 20 and the connection portion of the exhaust passage 40 to the exhaust turbocharger 20 of the present embodiment. In this figure, the exhaust turbocharger 20 is shown in a cross section in a direction orthogonal to the axis of the turbine wheel 22, and the exhaust passages 41 and 42 are schematically shown in a cross section in a direction orthogonal to the exhaust gas flow direction. .

  As shown in this figure, the turbine housing 21 of the exhaust turbocharger 20 includes a turbine scroll 21a formed of a cochlear-shaped casing surrounding the turbine wheel 22, and an exhaust introduction portion 21b connected to the upstream side of the turbine scroll 21a. A flange 21c is formed at the upstream end of the exhaust introduction portion 21b, and the downstream ends of the primary exhaust passage 41 and the secondary exhaust passage 42 are connected to this portion.

  Further, the turbine wheel 22 located in the turbine scroll 21a has a large number of blades, and the tip of the blades is disposed so as to protrude on an extension line of the exhaust introduction portion 21b (exhaust passage upstream of the turbine scroll). Has been.

  With respect to the exhaust turbocharger 20 of this type, the downstream end portion of each primary exhaust passage 41 is connected to the inner peripheral side of the turbine scroll 21a via the exhaust introduction portion 21b, and downstream of the secondary exhaust port 42. The end portion is connected to the outer peripheral side of the turbine scroll 21a via the exhaust introduction portion 21b.

  The operation of the engine 1 is electrically controlled by an engine control unit (ECU) 50 shown in FIG. The engine control unit 50 is constituted by a microprocessor having a CPU, a memory, a counter timer group, an interface, a bus connecting these units, and the like.

  Various detection means such as a crank angle sensor SN1, an airflow sensor SN2, a rotation speed sensor SN3, an accelerator opening sensor SN4, and a vehicle speed sensor SN5 are connected to the engine control unit 50 as input elements. The engine control unit 50 controls the fuel supply means including the fuel injection valve 12, the ignition device including the spark plug 11, the actuator (not shown) of the throttle valve 32, the variable valve lift amount mechanism 15, and the like. It has become.

  FIG. 8 is a characteristic diagram illustrating a setting example of an operation region for performing control according to the operation state by the engine control unit. In this figure, the horizontal axis indicates the engine speed Ne (rpm), and the vertical axis indicates the required load (required torque) τ (N · m).

  In the operation characteristics shown in the figure, a low-speed dynamic pressure supercharging operation region (predetermined supercharging operation region) R1 and a high-speed operation region R2 are set with a line from a predetermined low speed and high load to a high speed and low load as a boundary. Has been.

  Then, in the dynamic pressure supercharging operation region R1, the engine control unit 50 sets the variable valve lift amount mechanism 15 so that the exhaust valve 9 that opens and closes the secondary exhaust port 8b is in the minimum lift state EV2min indicated by a broken line in FIG. Control. On the other hand, in the high speed operation region R2, the valve lift variable mechanism 15 is controlled so that the exhaust valve 9 that opens and closes the secondary exhaust port 8b is set to the maximum lift state EV2max indicated by the solid line in FIG.

  According to the exhaust device of the present embodiment as described above, in the dynamic pressure supercharging operation region R1 where the flow rate of exhaust gas is relatively small, the exhaust valve 9 that opens and closes the secondary exhaust port 8b is in the minimum lift state EV2min (see FIG. 3). The variable valve lift amount mechanism 15 is controlled so that the exhaust amount from the secondary exhaust port 8b is limited. In this state, the exhaust gas is mainly led from the primary exhaust port 8a through the primary exhaust passage 41 to the exhaust turbocharger 20, thereby increasing the flow rate of the exhaust gas. Then, the dynamic pressure energy by blowdown when the primary exhaust port 8a is opened is given to the exhaust turbocharger 20.

  In this case, each primary exhaust passage 41 corresponding to the primary exhaust port 8a of each cylinder 3 is connected to the exhaust turbocharger 20 in an independent state. Therefore, it is possible to prevent a decrease in dynamic pressure and a decrease in exhaust flow velocity due to the exhaust interference. Further, by not gathering in the middle of the passage, the volume of each primary exhaust passage 41 can be made as small as possible. For this reason, the dynamic pressure and exhaust flow velocity by blowdown can be kept high.

  Further, at the place where each primary exhaust passage 8a is connected to the exhaust turbocharger 20, a high flow velocity is obtained from one primary exhaust passage 41 corresponding to the cylinder at the blow-down time immediately after the primary exhaust port 8a is opened. The exhaust gas flows into the exhaust turbocharger, and accordingly, an ejector effect in which the exhaust gas is sucked out from the other primary exhaust passage 41 is generated, thereby increasing the amount of exhaust gas flowing into the exhaust turbocharger 20. .

  Further, in the present embodiment, the exhaust turbocharger 20 is of a type in which the tip of the blade of the turbine wheel 22 is disposed so as to protrude on the extension line of the exhaust passage upstream of the turbine scroll 21a. On the other hand, since each primary exhaust passage 41 is connected to the inner peripheral side of the turbine scroll 21a, the exhaust flow velocity on the inner peripheral side of the turbine scroll 21a where the tip of the blade of the turbine wheel 22 is located is increased. Thus, the energy of the exhaust gas is given to the turbine wheel 22.

  By these actions, the exhaust energy supplied to the exhaust turbocharger 20 increases, and the supercharging performance is improved.

  Further, the lift characteristic EV1 of the exhaust valve 9 that opens and closes the primary exhaust port 8a and the lift characteristic IV of the intake valve 7 are set as shown in FIG. 3, and both the intake valve 7 and the exhaust valve 9 are near the top dead center. By setting the open overlap period OL, scavenging of the combustion chamber is performed during the overlap period OL, but the scavenging performance is further improved by exhausting the exhaust gas by the ejector effect. Therefore, the charging efficiency of the engine can be improved by improving the scavenging performance in addition to improving the supercharging performance.

  On the other hand, in the high speed operation region R2 where the exhaust gas flow rate is large, the valve lift variable mechanism 15 is controlled so that the exhaust valve 9 that opens and closes the secondary exhaust port 8b is in the maximum lift state EV2max (see FIG. 3). The restriction on the exhaust amount from the port 8b is released, and the exhaust gas is guided to the exhaust turbocharger 20 through the primary exhaust passage 41 and the secondary exhaust passage 42 from both the primary exhaust port 8a and the secondary exhaust port 8b. Thereby, the exhaust flow resistance is reduced. Further, although the exhaust temperature becomes high in the high-speed operation region, the secondary exhaust passage 42 is gathered in the middle, so that a cooling effect by adiabatic expansion is obtained at this gathered portion, thereby suppressing an increase in the exhaust temperature. it can.

In addition, the specific structure of the exhaust apparatus of this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the summary of this invention. Hereinafter, modified examples will be described.
(1) In the above embodiment, the variable valve lift amount mechanism 15 is provided as a means for limiting the exhaust amount of the exhaust gas from the secondary exhaust port 8b in the dynamic pressure supercharging operation region R1. In addition, a valve stop mechanism that can stop the operation of the exhaust valve may be provided. In this case, the valve stop mechanism may be controlled so that the valve is stopped in the dynamic pressure supercharging operation region R1 and the valve is operated in the high speed operation region R2.

Although it is conceivable to provide a valve device for controlling the flow rate of exhaust gas in the middle of the secondary exhaust passage, if the valve lift amount variable mechanism 15 or the valve stop mechanism is used, the exhaust system can have a compact structure. it can.
(2) In the above embodiment, the exhaust valve that opens and closes the primary exhaust port and the intake valve that opens and closes the intake port have constant opening and closing timing. However, a variable valve timing mechanism is provided for both or one of these valves. It is also possible to change the overlap period OL between the primary exhaust port and the intake port. In this case, the overlap period OL may be increased in the dynamic pressure supercharging operation region R1, and the overlap period OL may be decreased in the high speed operation region R2.

1 is a schematic configuration diagram of an engine with a supercharger according to an embodiment of the present invention. It is a partial sectional side view of the engine of FIG. It is explanatory drawing which shows the valve lift characteristic of an exhaust valve. It is a perspective view showing an exhaust passage and an exhaust turbocharger. The primary exhaust passage and the secondary exhaust passage are shown separately, (a) is a perspective view of the primary exhaust passage, and (b) is a perspective view of the secondary exhaust passage. It is a perspective view which shows the cross-sectional shape of the downstream end part of an exhaust passage. It is sectional drawing of a turbocharger. It is a characteristic view which shows the setting of the driving | operation area | region for performing control according to a driving | running state.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 3 Cylinder 8a Primary exhaust port 8b Secondary exhaust port 15 Valve lift amount variable mechanism 20 Exhaust turbo supercharger 21a Turbine scroll 22 Turbine wheel 41 Primary exhaust passage 42 Secondary exhaust passage

Claims (3)

In an exhaust system for an engine with a supercharger comprising an engine having a plurality of cylinders and an exhaust turbocharger,
A primary exhaust port provided in each cylinder of the engine for discharging exhaust gas in the entire operation region of the engine;
A secondary exhaust port provided in each of the cylinders for restricting the exhaust gas emission amount in a predetermined supercharging operation region and releasing the exhaust gas restriction in the other high-speed operation region;
A primary exhaust passage connecting the primary exhaust port of each cylinder and the exhaust turbocharger;
A secondary exhaust passage connecting the secondary exhaust port of each cylinder and the exhaust turbocharger;
The primary exhaust passage is configured to correspond to the primary exhaust port of each cylinder and to be connected to the exhaust turbocharger in an independent state,
An exhaust system for an engine with a supercharger, characterized in that the secondary exhaust passage is assembled in the middle of the exhaust passage and connected to the exhaust turbocharger downstream from the collecting portion.   The exhaust turbocharger is a type in which a turbine wheel is disposed so as to protrude on an extension line of an exhaust passage upstream of a turbine scroll, and each primary exhaust passage is connected to the turbine scroll inner peripheral side of the turbocharger. The exhaust system for an engine with a supercharger according to claim 1.   The secondary exhaust port can limit the exhaust gas discharge amount using either a valve stop mechanism that can stop the operation of the exhaust valve or a valve lift amount variable mechanism that makes the lift amount of the exhaust valve variable. The exhaust system for an engine with a supercharger according to claim 1 or 2.

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