JP6131936B2 - Exhaust system for multi-cylinder engine - Google Patents

Description

  The present invention relates to an exhaust device for a multi-cylinder engine.

  2. Description of the Related Art Conventionally, a horizontal engine rear exhaust layout is known in which an engine is arranged so that a cylinder row direction faces a vehicle width direction in an engine room at the front of the vehicle, and an exhaust device is arranged at the rear of the engine. .

  As described in Patent Document 1, the exhaust device in this layout is provided for each cylinder in order from the upstream side in the exhaust gas flow direction, and the upstream end is connected to the exhaust port of the cylinder, and the downstream end. Are connected to the downstream end of the independent exhaust pipe, and is connected to the downstream end of the single exhaust pipe. And a catalyst device for purifying exhaust gas led out from the single exhaust pipe, and the catalyst device is disposed as close to the engine as possible for early activation and maintenance of the active state.

  The single exhaust pipe described in Patent Document 1 is configured to allow exhaust gas to flow from an independent exhaust pipe at a high speed, and to suck out (scavenge) exhaust gas from other independent exhaust pipes by the negative pressure generated thereby. This is a so-called dynamic pressure exhaust system that uses the ejector effect to promote exhaust. By promoting exhaust using the ejector effect, the driving torque of the engine can be improved.

  The layout of the horizontal engine rear exhaust is often applied to FF (front engine / front drive) vehicles. FF vehicles do not have the propeller shafts that FR (front engine / rear drive) vehicles and 4WD (four wheel drive) vehicles have, so there is no need to consider interference between the propeller shaft and the exhaust system. The tube can be configured straight (straight).

JP 2013-57255 A (particularly FIGS. 1 and 2)

  By the way, the layout of a horizontally placed engine rear exhaust may be applied to an FR vehicle or a 4WD vehicle. In this case, if the single exhaust pipe is configured in a straight line (straight), the propeller shaft that transmits the driving force of the engine to the rear wheels easily interferes with the exhaust device, and the mountability of the exhaust device on the vehicle is reduced. There is a problem. Further, the exhaust gas immediately after being discharged from the engine has high directivity, and after flowing into the single exhaust pipe, a high flow rate is maintained and a state with high directivity is maintained. For this reason, if the single exhaust pipe is configured linearly, the position where the exhaust gas is introduced into the catalyst device is different for each cylinder. As a result, there is a possibility that the detection result of the oxygen concentration sensor downstream of the catalyst device varies, or that unburned fuel discharged from the misfired cylinder remains attached to the support of the catalyst device for a long time.

  In order to solve these problems, a single exhaust pipe is composed of a merging portion that constitutes a dynamic pressure exhaust system and a loop portion that is connected to the downstream end of the merging portion and is bent in a loop shape. Can be considered. By providing the loop portion on the downstream side of the merging portion, the exhaust device can be arranged at a position where it does not interfere with the propeller shaft in the FR vehicle or 4WD vehicle. In addition, since the directivity of the exhaust gas can be weakened by providing the loop portion, it is possible to suppress that the position where the exhaust gas is introduced into the catalyst device differs (varies) between the cylinders.

  However, when the loop portion is provided, there is a problem that the scavenging effect by the dynamic pressure exhaust system is reduced and the driving torque generated in the engine is reduced. In other words, the position of the part where the exhaust gas flow velocity is large in the loop part is greatly biased to the outside of the loop part, and the pressure of exhaust gas (back pressure as viewed from the joining part) in the loop part increases and the pressure loss of the exhaust gas As a result, a reverse flow of the exhaust gas toward the independent exhaust pipe occurs in a part of the merging section, and the flow rate and flow rate of the exhaust gas flowing to the loop pipe side in the merging section are reduced, thereby reducing the scavenging effect. To do.

  The present invention has been made in view of such circumstances, and the exhaust of a multi-cylinder engine that can suppress a decrease in the scavenging effect in the dynamic pressure exhaust system while ensuring good vehicle mountability of the exhaust device. An object is to provide an apparatus.

In order to solve the above-described problems, the present invention is an exhaust system that is connected to a multi-cylinder engine disposed in an engine room at the front of a vehicle and is disposed to extend rearward from the multi-cylinder engine. In order from the upstream side in the flow direction, a plurality of independent exhaust pipes that are provided for each cylinder and whose upstream end is connected to the exhaust port of the cylinder and whose downstream ends are bundled are connected to the downstream end of the independent exhaust pipe A single exhaust pipe, and a catalyst device connected to the downstream end of the single exhaust pipe and purifying exhaust gas led out from the single exhaust pipe, the single exhaust pipe having a downstream side A collecting pipe having a straight section extending linearly while being connected to a throttle section and a downstream end section of the throttle section, the flow path area of which becomes smaller, and a downstream end section of the collecting pipe Connected to the And a loop tube bent in looped, the inner diameter of the upstream end of the loop tube along with being enlarged relative to the inner diameter of the straight portion, stage with respect to the inner diameter of the downstream end of the collecting pipe The diameter has been expanded.

  According to the present invention, since the inner diameter of the upstream end portion of the loop pipe is larger than the inner diameter of the straight section, the exhaust gas easily flows in the loop pipe from the upstream side to the downstream side. Pressure (back pressure) is reduced, and pressure loss is also reduced. As a result, the portion where the exhaust gas flow velocity is large is stably positioned near the central axis of the straight portion, so that the exhaust gas flows to the loop tube side without stagnation in the straight portion, and the exhaust gas flows from the loop tube side to the straight portion. Backflow to the independent exhaust pipe side is suppressed. As a result, the flow velocity and flow rate of the exhaust gas flowing from the independent exhaust pipe side to the loop pipe side in the collecting pipe are suppressed, and the scavenging effect (ejector effect) that sucks exhaust gas from other independent exhaust pipes is suppressed. Can do.

Further, by providing the loop pipe, it is possible to prevent the exhaust device from interfering with the propeller shaft of the FR vehicle or the 4WD vehicle, and to suppress the introduction position of the exhaust gas to the catalyst device from being different among the cylinders. .
In the present invention, the inner diameter of the upstream end of the loop pipe is increased stepwise relative to the inner diameter of the downstream end of the collecting pipe, so that the positive pressure wave of the exhaust gas discharged from the cylinder When the pressure reaches the upstream end of the loop tube, the positive pressure wave is reflected at the upstream end of the loop tube to generate a negative pressure wave. Since the negative pressure wave reaches the exhaust port of the other cylinder, the exhaust gas in the other cylinder is sucked out from the exhaust port by the negative pressure wave, and scavenging of the other cylinder is further promoted.
That is, the negative pressure generated by the ejector effect when the exhaust gas discharged from the cylinder is ejected to the collecting pipe and the positive pressure wave of the exhaust gas discharged from the cylinder are reflected by the upstream end portion of the loop pipe. A scavenging effect exceeding the scavenging effect obtained by the ejector effect alone is obtained in cooperation with the negative pressure wave.

  Therefore, according to the present invention, it is possible to suppress a decrease in the scavenging effect in the dynamic pressure exhaust system while ensuring good vehicle mountability of the exhaust device.

  In the present invention, the ratio of the inner diameter of the upstream end portion of the loop pipe to the inner diameter of the straight section is a predetermined ratio that suppresses the backflow of exhaust gas from the loop pipe side to the independent exhaust pipe side in the straight section. It is preferable that the value is set.

According to this configuration, a sufficient scavenging effect can be obtained by suppressing the backflow of exhaust gas in the straight portion.
Further, in order to solve the above problems, the present invention is an exhaust system that is connected to a multi-cylinder engine disposed in an engine room in a front portion of a vehicle and is disposed so as to extend rearward from the multi-cylinder engine. A plurality of independent exhaust pipes that are provided for each cylinder in order from the upstream side in the exhaust gas flow direction and whose upstream end is connected to the exhaust port of the cylinder and the downstream ends are bundled, and the downstream end of the independent exhaust pipe And a single exhaust pipe connected to the downstream end of the single exhaust pipe and a catalytic device for purifying exhaust gas led out from the single exhaust pipe, the single exhaust pipe comprising: A collecting pipe having a flow path area that decreases toward the downstream side, a collecting pipe that is connected to the downstream end of the throttling section and that extends straight while maintaining the inner diameter of the throttling section, and downstream of the collecting pipe Connected to the end A loop pipe bent in a loop shape, and an inner diameter of the upstream end portion of the loop pipe is expanded with respect to an inner diameter of the straight portion, and an inner diameter of the upstream end portion of the loop pipe and the straight tube The ratio of the inner diameter of the portion is set to a predetermined value that suppresses the backflow of the exhaust gas from the loop pipe side to the independent exhaust pipe side in the straight portion.
According to the present invention, since the inner diameter of the upstream end portion of the loop pipe is larger than the inner diameter of the straight section, the exhaust gas easily flows in the loop pipe from the upstream side to the downstream side. Pressure (back pressure) is reduced, and pressure loss is also reduced. As a result, the portion where the exhaust gas flow velocity is large is stably positioned near the central axis of the straight portion, so that the exhaust gas flows to the loop tube side without stagnation in the straight portion, and the exhaust gas flows from the loop tube side to the straight portion. Backflow to the independent exhaust pipe side is suppressed. As a result, the flow velocity and flow rate of the exhaust gas flowing from the independent exhaust pipe side to the loop pipe side in the collecting pipe are suppressed, and the scavenging effect (ejector effect) that sucks exhaust gas from other independent exhaust pipes is suppressed. Can do.
Further, by providing the loop pipe, it is possible to prevent the exhaust device from interfering with the propeller shaft of the FR vehicle or the 4WD vehicle, and to suppress the introduction position of the exhaust gas to the catalyst device from being different among the cylinders. .
In the present invention, the ratio of the inner diameter of the upstream end of the loop pipe to the inner diameter of the straight section suppresses the backflow of exhaust gas from the loop pipe side to the independent exhaust pipe side within the straight section. Since the predetermined value is set, it is possible to obtain a sufficient scavenging effect by suppressing the back flow of the exhaust gas in the straight portion.
Therefore, according to the present invention, it is possible to suppress a decrease in the scavenging effect in the dynamic pressure exhaust system while ensuring good vehicle mountability of the exhaust device.

  In the present invention, the engine includes an intake valve capable of opening and closing an intake port for introducing intake air into a cylinder, an exhaust valve capable of opening and closing an exhaust port for deriving exhaust gas from the cylinder, and at least a reference rotation at a predetermined engine speed. In an engine low speed range of less than a few, the opening period of the intake valve and the opening period of the exhaust valve of each cylinder overlap for a predetermined period, and the overlap period of the preceding cylinder between two cylinders in which the exhaust sequence is continuous A valve drive means for driving the intake valve and the exhaust valve so that the exhaust valve of the succeeding cylinder starts to open, and the length from the exhaust port to the upstream end of the loop pipe is: At least in the engine low speed region, the negative pressure wave generated by the reflection of the positive pressure wave of the exhaust gas discharged from the subsequent cylinder at the upstream end of the loop pipe is It may preferably be set to a length to reach the exhaust port of the preceding cylinder during the cylinder of the overlap period.

  According to this configuration, at least in the engine low speed range, the opening of the exhaust valve of the succeeding cylinder is started during the overlap period of the preceding cylinder between two cylinders in which the exhaust order is continuous, and the exhaust gas of the succeeding cylinder is A negative pressure wave generated by reflecting the positive pressure wave at the upstream end of the loop pipe reaches the exhaust port during the overlap period of the preceding cylinder. Therefore, at least in the engine low speed range, the exhaust gas in the preceding cylinder is sucked out to the exhaust port side by the negative pressure wave, and scavenging of the preceding cylinder is further promoted.

  In this invention, it is preferable that the ratio of the internal diameter of the upstream end part of the said loop pipe and the internal diameter of the said straight part is set to the range of 1.4-1.7.

  According to this configuration, a sufficient scavenging effect can be obtained by maximizing the effect of diameter expansion.

  In this invention, it is preferable that the said collecting pipe further has a diffuser part connected to the downstream end part of the said straight part, and a diameter becoming large downstream.

  According to this configuration, the pressure and temperature of the exhaust gas decreased in the throttle portion can be recovered in the diffuser portion. As a result, the positive pressure amount of the positive pressure wave of the exhaust gas reaching the upstream end portion of the loop pipe, and hence the negative pressure amount of the negative pressure wave generated by reflecting the positive pressure wave at the upstream end portion of the loop pipe can be increased. In addition, the effect of improving the scavenging performance of the cylinder by this negative pressure wave can be further enhanced. It is also advantageous in terms of catalyst activation.

Further, in order to solve the above problems, the present invention is an exhaust system that is connected to a multi-cylinder engine disposed in an engine room in a front portion of a vehicle and is disposed so as to extend rearward from the multi-cylinder engine. A plurality of independent exhaust pipes that are provided for each cylinder in order from the upstream side in the exhaust gas flow direction and whose upstream end is connected to the exhaust port of the cylinder and the downstream ends are bundled, and the downstream end of the independent exhaust pipe And a single exhaust pipe connected to the downstream end of the single exhaust pipe and a catalytic device for purifying exhaust gas led out from the single exhaust pipe, the single exhaust pipe comprising: A collecting pipe having a flow path area that decreases toward the downstream side, a collecting pipe that is connected to the downstream end of the throttling section and that extends straight while maintaining the inner diameter of the throttling section, and downstream of the collecting pipe Connected to the end Te and a loop tube bent into a loop shape, said collecting pipe further includes a diffuser portion diameter toward the downstream side increases is connected to the downstream end of the straight portion, the upstream end of the loop pipe The inner diameter is increased with respect to the inner diameter of the straight portion, and is increased stepwise with respect to the inner diameter of the downstream end portion of the diffuser portion .

According to the present invention, since the inner diameter of the upstream end portion of the loop pipe is larger than the inner diameter of the straight section, the exhaust gas easily flows in the loop pipe from the upstream side to the downstream side. Pressure (back pressure) is reduced, and pressure loss is also reduced. As a result, the portion where the exhaust gas flow velocity is large is stably positioned near the central axis of the straight portion, so that the exhaust gas flows to the loop tube side without stagnation in the straight portion, and the exhaust gas flows from the loop tube side to the straight portion. Backflow to the independent exhaust pipe side is suppressed. As a result, the flow velocity and flow rate of the exhaust gas flowing from the independent exhaust pipe side to the loop pipe side in the collecting pipe are suppressed, and the scavenging effect (ejector effect) that sucks exhaust gas from other independent exhaust pipes is suppressed. Can do.
Further, by providing the loop pipe, it is possible to prevent the exhaust device from interfering with the propeller shaft of the FR vehicle or the 4WD vehicle, and to suppress the introduction position of the exhaust gas to the catalyst device from being different among the cylinders. .
Further, in the present invention, the collecting pipe further includes a diffuser portion that is connected to the downstream end portion of the straight portion and has a diameter that increases toward the downstream side. It can be recovered in the diffuser section. As a result, the positive pressure amount of the positive pressure wave of the exhaust gas reaching the upstream end portion of the loop pipe, and hence the negative pressure amount of the negative pressure wave generated by reflecting the positive pressure wave at the upstream end portion of the loop pipe can be increased. In addition, the effect of improving the scavenging performance of the cylinder by this negative pressure wave can be further enhanced. It is also advantageous in terms of catalyst activation.
In the present invention, the inner diameter of the upstream end portion of the loop pipe is increased stepwise with respect to the inner diameter of the downstream end portion of the diffuser portion, so that the diffuser portion is gradually increased from the upstream side to the downstream side. Even if the diameter of the diffuser portion is increased, the downstream end portion of the diffuser portion and the upstream end portion of the loop pipe can be connected without making the diffuser portion longer than necessary . Also, the negative pressure generated by the ejector effect when the exhaust gas discharged from the cylinder is ejected to the collecting pipe and the positive pressure wave of the exhaust gas discharged from the cylinder are reflected at the upstream end of the loop pipe. A scavenging effect exceeding the scavenging effect obtained by the ejector effect alone is obtained in cooperation with the negative pressure wave.
Therefore, according to the present invention, it is possible to suppress a decrease in the scavenging effect in the dynamic pressure exhaust system while ensuring good vehicle mountability of the exhaust device.

  In the present invention, the catalyst device includes a cylindrical casing and a catalyst main body accommodated in the casing, and the downstream end of the loop pipe has a direction in which exhaust gas flows out from the downstream end. It is preferable to be connected to the catalyst device so as to be inclined with respect to the axial center of the casing.

  According to this configuration, since the exhaust gas is introduced into the catalyst device so that the direction in which the exhaust gas flows out from the loop pipe is oblique to the axial center of the casing, the exhaust gas is diffused in the catalyst device. Can be promoted. Therefore, it is possible to more reliably suppress the position where the exhaust gas is introduced into the catalyst device from being different among the cylinders.

  In the present invention, it is preferable that at least a part of the independent exhaust pipe and the single exhaust pipe have a double pipe structure.

  According to this structure, the fall of the temperature of the exhaust gas introduce | transduced into a catalyst apparatus is suppressed, and the early activation and active state maintenance of a catalyst apparatus are ensured.

  In the present invention, it is preferable that a heat insulating material is applied to at least a part of the independent exhaust pipe and the single exhaust pipe.

  According to this structure, the fall of the temperature of the exhaust gas introduce | transduced into a catalyst apparatus is suppressed, and the early activation and active state maintenance of a catalyst apparatus are ensured.

  In the present invention, the engine is preferably a multi-cylinder engine arranged horizontally so that the cylinder row direction faces the vehicle width direction.

  According to this configuration, it is possible to suppress a reduction in the scavenging effect in the dynamic pressure exhaust system while ensuring a good vehicle mountability of the exhaust device in the layout of the horizontally placed engine rear exhaust.

  In this invention, it is preferable that the said catalyst apparatus and the said collecting pipe are connected via the said loop pipe | tube so that the said catalyst apparatus may be arrange | positioned and extended in the vehicle width direction under the said collecting pipe.

  According to this configuration, the exhaust device can be accommodated compactly in the tunnel portion of the floor panel. Moreover, it can avoid more reliably that an exhaust apparatus interferes with the propeller shaft of FR vehicle or 4WD vehicle.

  ADVANTAGE OF THE INVENTION According to this invention, the fall of the scavenging effect in a dynamic pressure exhaust system can be suppressed, ensuring the favorable vehicle mounting property of an exhaust apparatus.

1 is a plan view of an exhaust device for a multi-cylinder engine according to an embodiment of the present invention. It is a schematic plan view of the main-body part of the said engine. It is sectional drawing which shows the flow direction of the exhaust gas from the collection pipe | tube in the said exhaust apparatus to the upstream edge part vicinity of a loop pipe | tube. FIG. 4 is a cross-sectional view taken along line II in FIG. 3. It is the perspective view which looked at the exhaust apparatus of the said multi-cylinder engine from the upper left back. It is a right view of the exhaust device of the multi-cylinder engine. It is the figure which looked at the exhaust apparatus of the said multi-cylinder engine from the back. It is the elements on larger scale of FIG. 1 for demonstrating the bending angle of a loop pipe | tube. It is a top view which shows the exhaust apparatus which concerns on 1st Example of this embodiment. It is a top view which shows the exhaust apparatus which concerns on 2nd Example of this embodiment. It is a top view which shows the exhaust apparatus which concerns on a 1st comparative example. It is a top view which shows the exhaust apparatus which concerns on a 2nd comparative example. It is a graph which shows the relationship between the ratio (D1 / D0) of the internal diameter (D1) of the upstream end part of a loop pipe | tube, and the internal diameter (D0) of a straight part, and the exhaust_gas | exhaustion_gas | exhaustion amount from a preceding cylinder. (A) is a figure which shows the pressure distribution in the exhaust apparatus which concerns on 1st Example, (b) is a figure which shows the flow velocity distribution of the exhaust gas in the straight part of 1st Example. (A) is a figure which shows the pressure distribution in the exhaust apparatus which concerns on 2nd Example, (b) is a figure which shows the flow velocity distribution of the exhaust gas in the straight part of 2nd Example. (A) is a figure which shows the pressure distribution in the exhaust apparatus which concerns on a 1st comparative example, (b) is a figure which shows the flow velocity distribution of the exhaust gas in the straight part of a 1st comparative example. (A) is a figure which shows the pressure distribution in the exhaust apparatus which concerns on a 2nd comparative example, (b) is a figure which shows the flow velocity distribution of the exhaust gas in the straight part of a 2nd comparative example.

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

  In the following description, “front” means the vehicle front side, “rear” means the vehicle rear side, “left” means the left side in the vehicle width direction, and “right” means the vehicle width direction. Means the right side.

  As shown in FIG. 1, an exhaust device 1 for a multi-cylinder engine according to the present embodiment includes a cylinder head 11 and a cylinder block 12 (see FIGS. 5 to 7) in order from the upstream side in the exhaust gas flow direction. 10, an exhaust manifold 40 assembled to the rear portion of the engine 10, a collecting pipe 50 connected to the downstream end of the exhaust manifold 40, a loop pipe 60 connected to the downstream end of the collecting pipe 50, and a loop pipe 60 , A connecting pipe 80 connected to the downstream end of the catalytic apparatus 70, a flexible exhaust pipe 90 connected to the downstream end of the connecting pipe 80, and a flexible exhaust pipe 90 And a rear exhaust pipe 100 connected to the downstream end portion.

  The collecting pipe 50 and the loop pipe 60 constitute a “single exhaust pipe” in the claims.

  The engine 10 is an in-line four-cylinder four-cycle gasoline engine having first to fourth cylinders 13a to 13d. The engine 10 is a horizontally mounted engine that is disposed horizontally so that the direction of the cylinders 13a to 13d is directed in the vehicle width direction (left-right direction in FIG. 1) in the engine room 2 at the front of the vehicle. The exhaust device 1 is disposed so as to extend rearward (downward in FIG. 1) from the rear portion of the engine 10 (layout of a horizontally placed engine rear exhaust).

  As shown in FIG. 2, the cylinder head 11 includes an ignition plug 14 that faces the combustion chambers of the cylinders 13 a to 13 d, an intake port 15 and an exhaust port 16 that open to the combustion chamber, and an intake port 15 and an exhaust port 16. An intake valve 17 and an exhaust valve 18 that are opened and closed, and an intake valve drive mechanism 20 and an exhaust valve drive mechanism 30 are provided. The intake port 15 is for introducing intake air into the cylinders 13a to 13d, the exhaust port 16 is for discharging exhaust gas from the cylinders 13a to 13d, and the intake valve 17 and the exhaust valve 18 are the cylinders 13a to 13d and the intake air described above. This is for communicating or blocking the port 15 and the exhaust port 16. The intake valve drive mechanism 20 opens and closes the intake valve 17 at a predetermined timing, and the exhaust valve drive mechanism 30 opens and closes the exhaust valve 18 at a predetermined timing.

  In this embodiment, ignition is performed at a timing shifted by 180 ° CA (crank angle) in the order of the first cylinder 13a → the third cylinder 13c → the fourth cylinder 13d → the second cylinder 13b. In this order, intake → compression → Each step of expansion → exhaust is performed at a timing shifted by 180 ° CA.

  The intake valve drive mechanism 20 has an intake camshaft 21 connected to the intake valve 17 and an intake VVT (Variable Valve Timing) 22. The intake camshaft 21 is connected to a crankshaft (not shown) and rotates with the rotation of the crankshaft to open and close the intake valve 17. The intake VVT 22 changes the phase difference between the crankshaft and the intake camshaft 21 to keep the intake valve 17 open period and lift amount constant, while keeping the intake valve 17 open and closed. Change the time.

The exhaust valve drive mechanism 30 has an exhaust camshaft 31 and an exhaust VVT 32 connected to the exhaust valve 18. The exhaust camshaft 31 is connected to the crankshaft and rotates as the crankshaft rotates to drive the exhaust valve 18 to open and close. The exhaust VVT 32 changes the phase difference between the crankshaft and the exhaust camshaft 31 to keep the exhaust valve 18 open period and lift amount constant while keeping the exhaust valve 18 open and closed. Change the time.

  The exhaust manifold 40 includes an assembly flange 40a (see FIGS. 5 to 7) on the rear surface of the cylinder head 11 and four independent exhaust pipes 41... 41 corresponding to the cylinders 13a to 13d. The independent exhaust pipes 41... 41 are connected at their upstream ends to the exhaust ports 16... 16 of the cylinders 13 a to 13 d and extend rearward of the vehicle while curving from the rear surface of the engine 10.

  As shown in FIG. 3, the collecting pipe 50 includes a collecting pipe main body 50A and a cylindrical outer pipe 50B that covers the peripheral surface of the collecting pipe main body 50A. That is, the collecting pipe 50 has a double pipe structure. By making the collecting pipe 50 have a double pipe structure, it is possible to suppress a temperature drop of the exhaust gas (in other words, keep the exhaust gas warm).

  Further, a heat insulating material is applied to the collecting pipe main body 50A and the outer pipe 50B. By applying the heat insulating material, it is possible to suppress the temperature drop of the exhaust gas.

  The collecting pipe main body 50A includes, in order from the upstream side, a throttle portion 50a whose flow area decreases toward the downstream side, a straight portion 50b that extends downstream while maintaining a flow passage area at the downstream end of the throttle portion 50a, and a downstream side And a diffuser portion 50c having a larger channel area toward the side.

  As shown in FIG. 3, downstream ends 41a... 41a of independent exhaust pipes 41... 41 are connected to the upstream end of the throttle 50a, and the upstream end of the loop pipe 60 is connected to the downstream end of the diffuser 50c. Connected. As shown in FIGS. 1 and 5 to 7, the collecting pipe 50 is disposed so as to extend obliquely leftward and obliquely downward from the upstream portion to the downstream portion behind the engine 10.

  As shown in FIG. 3, the inner diameter D <b> 1 of the upstream end 60 c of the loop pipe 60 is increased in a stepped manner relative to the inner diameter D <b> 2 of the downstream end of the collecting pipe 50. That is, in the example shown in FIG. 3, the inner diameter D1 of the upstream end portion 60c of the loop pipe 60 is expanded stepwise with respect to the inner diameter D2 of the downstream end portion of the diffuser portion 50c.

  “Expanding the diameter in a step shape” means expanding the diameter so that a step is generated between the downstream end 50c of the diffuser portion 50c and the upstream end 60c of the loop pipe 60. Does not mean expanding diameter).

  In the example shown in FIG. 3, the downstream end portion of the diffuser portion 50 c and the upstream end portion 60 c of the loop pipe 60 are connected via a flange portion 60 d. The bowl-shaped portion 60d has an opening through which exhaust gas passes. The inner peripheral portion of the bowl-shaped portion 60 d is connected to the downstream end portion of the diffuser portion 50 c, and the outer peripheral portion is connected to the upstream end portion 60 c of the loop pipe 60.

  The ratio (D1 / D0) of the inner diameter D1 of the upstream end portion 60c of the loop pipe 60 and the inner diameter D0 of the straight section 50b is the reverse flow of the exhaust gas from the loop pipe 60 side to the independent exhaust pipe 41 side in the straight section 50b. The predetermined value to be suppressed is set.

  Here, a mechanism for generating the backflow will be described. By providing the loop pipe 60, the position of the portion where the exhaust gas flow velocity is large in the loop pipe 60 is biased to the outside of the loop pipe 60, and the pressure of the exhaust gas in the loop pipe 60 (the back as viewed from the collecting pipe 50). Pressure) increases and the pressure loss of the exhaust gas increases, and as a result, a reverse flow of the exhaust gas toward the independent exhaust pipe 41 side occurs in a part of the collecting pipe 50.

  In order to suppress the occurrence of such a backflow, specifically, the value of D1 / D0 is preferably set in the range of 1.4 to 1.7. Within this range, the pressure (back pressure) in the loop pipe 60 can be reduced to suppress the backflow of exhaust gas from the loop pipe 60 side to the independent exhaust pipe 41 side in the straight portion 50b. When the value of D1 / D0 is less than 1.4, there is a possibility that the flow path area in the loop pipe 60 is not sufficient and the pressure in the loop pipe 60 cannot be suppressed. When the value of D1 / D0 exceeds 1.7, exhaust gas vortices are generated in the loop pipe 60, so that the exhaust gas does not flow smoothly downstream, and the pressure in the loop pipe 60 cannot be suppressed. there is a possibility.

  As shown in FIG. 4, the downstream ends 41a ... 41a of the independent exhaust pipes 41 ... 41 have a sector shape with a central angle of 90 °. The downstream end portions 41a... 41a are bundled to form a circle and connected to the upstream end portion of the throttle portion 50a. As shown in FIG. 4, a coupling plate 42 for bundling the downstream ends 41a of the independent exhaust pipes 41a to 41a is interposed between the downstream ends 41a to 41a.

  As shown in FIG. 1, the independent exhaust pipes 41... 41 extend from the exhaust ports 16. Exhaust gas discharged from the cylinders 13a to 13d flows into the throttle portion 50a of the collecting pipe 50 through the independent exhaust pipes 41. The independent exhaust pipes 41 ... 41 have a shape in which the flow path area becomes smaller toward the downstream side. Therefore, the exhaust gas flows from the downstream end portions 41a... 41a of the independent exhaust pipes 41. Since the throttle portion 50a has a shape in which the flow path area becomes smaller toward the downstream side, the exhaust gas flowing into the throttle portion 50a flows downstream while maintaining a high speed.

  The high-speed blowdown gas discharged from the cylinders 13 a to 13 d to the independent exhaust pipes 41... 41 by opening the exhaust valve 18 is increased in flow rate and flows into the throttle portion 50 a of the collecting pipe 50. Thereby, a negative pressure is generated in the throttle portion 50a, and the exhaust gas is sucked out from the other independent exhaust pipe 41 by this negative pressure (ejector effect).

  In the present embodiment, at least in the low speed and high load range (the engine speed is less than a predetermined reference speed), the opening period of the exhaust valve 18 and the opening period of the intake valve 17 of the cylinders 13a to 13d are the intake top dead center. So that the exhaust valves 18 of the subsequent cylinders 13a to 13d start to open during the overlap period of the preceding cylinders 13a to 13d between two cylinders that overlap with each other and the exhaust order continues. The intake valve drive mechanism 20 and the exhaust valve drive mechanism 30 are controlled by an ECU (Electronic Control Unit) (not shown).

  Specifically, the exhaust valve 18 of the third cylinder 13c starts to open during the overlap period of the exhaust valve 18 and the intake valve 17 of the first cylinder 13a, and the exhaust valve 18 and the intake valve of the third cylinder 13c start. The exhaust valve 18 of the fourth cylinder 13d starts to open during the overlap period with the 17 and the exhaust valve 18 of the second cylinder 13b starts during the overlap period of the exhaust valve 18 and the intake valve 17 of the fourth cylinder 13d. Starts opening, and the exhaust valve 18 of the first cylinder 13a starts to open during the overlap period of the exhaust valve 18 and the intake valve 17 of the second cylinder 13b.

  Therefore, during the overlap period of the exhaust valve 18 and the intake valve 17 of the first cylinder 13a, high-speed blowdown gas flows from the exhaust valve 18 of the third cylinder 13c into the throttle portion 50a, thereby causing the throttle portion 50a. A negative pressure is generated inside, and exhaust gas is sucked out from the independent exhaust pipe 41 connected to the first cylinder 13a by this negative pressure (ejector effect). The same applies to the other two cylinders adjacent to each other in the exhaust order, and an ejector effect is generated in which the exhaust gas is sucked from the independent exhaust pipe 41 connected to the preceding cylinders 13b to 13d. By these ejector effects, scavenging of the cylinders 13a to 13d during the overlap period is promoted.

  The length from the exhaust port 16 of the cylinders 13a to 13d to the upstream end 60c of the loop pipe 60 is such that the positive pressure wave of the exhaust gas discharged from the subsequent cylinders 13a to 13d is generated in the loop pipe 60 at least in the low speed and high load region. The negative pressure wave generated by reflection at the upstream end 60c is set to a length that reaches the exhaust port 16 of the preceding cylinders 13a to 13d during the overlap period of the preceding cylinders 13a to 13d.

  As shown in FIGS. 1 and 5 to 8, the loop pipe 60 communicates the downstream end portion of the collecting pipe 50 and the upstream end portion of the catalyst device 70. The loop tube 60 has a first bent portion 60a and a second bent portion 60b in order from the upstream side. The upstream portion of the first bent portion 60a, the portion between the first bent portion 60a and the second bent portion 60b, and the downstream portion of the second bent portion 60b are configured straight without being bent. Has been. As shown in FIG. 8, the axial center A of the portion upstream of the first bent portion 60 a extends diagonally to the left and tilts diagonally downward from the upstream side to the downstream side. The axis B of the portion between the first bent portion 60a and the second bent portion 60b extends obliquely leftward from the upstream side to the downstream side in a substantially horizontal plane. The axial center C of the downstream portion of the second bent portion 60b extends diagonally right forward from the upstream side to the downstream side in a substantially horizontal plane. In FIG. 8, the symbol D is the intersection of the axis A and the axis B, and the symbol E is the intersection of the axis B and the axis C.

  The sum (total) of the bending angle α of the bending portion 60a and the bending angle β of the bending portion 60b is, for example, 180 ° or more. In the present embodiment, the bending angles of the bent portions 60a and 60b are bending angles when viewed from the central axis direction of the cylinders 13a to 13d (vertical direction in the present embodiment), in other words, a plane orthogonal to the cylinder central axis. It refers to the bending angle that appears when projected onto the horizontal plane (in this embodiment) from the central axis direction.

  In the present embodiment, the bending angle α of the first bent portion 60a is 125 °, and the bending angle β of the second bent portion 60b is 75 °. That is, the sum of bending angles (α + β) is 200 °.

  The upper limit of the sum of the bending angles is not particularly limited, but is preferably about 360 °, for example. If the sum of the bending angles is excessively large, the manufacturing cost of the loop tube 60 is high. In addition, the exhaust gas flow rate may be excessively reduced.

  In the present embodiment, the bent portions 60a and 60b include bending components toward the same side. That is, the bending direction of the first bent portion 60a viewed from the upstream side is clockwise (clockwise), and the bent direction of the second bent portion 60b viewed from the upstream side is also clockwise (clockwise).

  As shown in FIG. 5, the catalyst device 70 includes a substantially cylindrical casing 71 provided with a dome-shaped end surface member 71 a at the upstream end, and a catalyst outside the figure having a three-way catalyst function accommodated in the casing 71. A main body (monolith carrier). A predetermined space is formed inside the end face member 71a. The downstream end portion 60 x of the loop pipe 60 is connected to the catalyst device 70 so that the direction in which the exhaust gas flows out from the downstream end portion 60 x is oblique to the axis of the casing 71.

  The catalyst device 70 and the collecting pipe 50 are connected via a loop pipe 60 so that the catalytic device 70 is arranged extending in the vehicle width direction below the collecting pipe 50 (see FIG. 5).

  As shown in FIG. 1, the connecting pipe 80 has a central portion in the flow direction bent in a clockwise direction (clockwise) and a downstream portion bent in a counterclockwise direction (counterclockwise). The downstream end portion of the connecting pipe 80 faces rearward.

  An oxygen concentration sensor (not shown) is disposed in the connecting pipe 80. The oxygen concentration sensor detects the oxygen concentration of the exhaust gas that has passed through the catalyst device 70.

  The flexible exhaust pipe 90 is for suppressing vibration transmitted from the vehicle body side and being transmitted to the exhaust system. The flexible exhaust pipe 90 extends diagonally to the left and obliquely downward from the upstream portion to the downstream portion. As shown in FIG. 1, the flexible exhaust pipe 90 is accommodated in the tunnel portion 5 of the floor panel 4.

  As shown in FIG. 1, the rear exhaust pipe 100 extends rearward while meandering slightly to the left and right within the tunnel portion 5 of the floor panel 4. 1, reference numeral 3 denotes a dash panel interposed between the engine room 2 and the passenger compartment. In FIGS. 1 and 5 to 7, reference numeral 101 denotes a downstream exhaust system component (not shown) in the rear exhaust pipe 100. ).

  Next, in order to prove that the exhaust device 1 according to the present embodiment exhibits an excellent effect, a model of an example according to the present embodiment and a model of a comparative example are produced, and using these models, the following The test was conducted.

<Example 1>
As shown in FIG. 9, the exhaust device 1 including the four independent exhaust pipes 41, the collecting pipe body 50 </ b> A, and the loop pipe 60 was configured. The exhaust device 1 also includes the catalyst device 70, the connecting pipe 80, the flexible exhaust pipe 90, and the rear exhaust pipe 100 shown in FIG. 1, but the illustration thereof is omitted in FIG. Further, although the loop pipe 60 of the exhaust device 1 shown in FIG. 9 is bent counterclockwise as a test model, there is no difference in the test results compared to the case of bending clockwise.

  One of the four independent exhaust pipes 41 (first independent exhaust pipe 41 from the left in FIG. 9) is connected to the first cylinder 13a in FIG. 1, and the upstream end of the second independent exhaust pipe 41 from the left is connected. The part was opened to the atmosphere, the third independent exhaust pipe 41 from the left was connected to the third cylinder 13c, the fourth independent exhaust pipe 41 from the left was connected to the fourth cylinder 13d, and the model of Example 1 was produced. .

  As shown in Table 1, in Example 1, the inner diameter of the upstream end portion of the loop pipe 60 (hereinafter referred to as “loop pipe diameter D1”) is 52 mm, and the inner diameter of the straight portion 50b (hereinafter referred to as “straight diameter D0”). 37) and the ratio of D1 to D0 (D1 / D0) was 1.4. The loop tube diameter D1 was increased stepwise with respect to the inner diameter (hereinafter referred to as “diffuser diameter D2”) of the downstream end of the diffuser portion 50c.

  The first cylinder 13a and the second cylinder 13b are cylinders in which the exhaust order is continuous. During the overlap period of the exhaust valve 18 and the intake valve 17 in the second cylinder 13b, the exhaust valve 18 of the first cylinder 13a starts to open. That is, the second cylinder 13b is a preceding cylinder, and the first cylinder 13a is a succeeding cylinder.

<Example 2>
As shown in Table 1, in Example 2, the loop tube diameter D1 was 62 mm, the straight diameter D0 was 37 mm, D1 / D0 was 1.7, and the other configurations were the same as in Example 1.

<Comparative Example 1>
As shown in Table 1, in Comparative Example 1, the loop tube diameter D1 was 45 mm, the straight diameter D0 was 37 mm, and D1 / D0 was 1.2. The loop pipe diameter D1 was set to be the same as the diffuser diameter D2. The rest of the configuration was the same as in Example 1.

<Comparative example 2>
As shown in Table 1, in Comparative Example 2, the loop tube diameter D1 was 77 mm, the straight diameter D0 was 37 mm, D1 / D0 was 2.1, and the other configurations were the same as in Example 1. Similar to Example 1, the loop tube diameter D1 was increased stepwise relative to the diffuser diameter D2.

<Test method 1>
In Examples 1 and 2 and Comparative Examples 1 and 2, a flow meter (not shown) was attached to the upstream end of the second independent exhaust pipe 41 from the left (hereinafter referred to as “second independent exhaust pipe 41”). . Then, the scavenging amount (g / s) at the upstream end of the second independent exhaust pipe 41 when the exhaust valve 18 of the first cylinder 13a started to open during the overlap period in the second cylinder 13b was measured. (See the scavenging amount column in Table 1 and FIG. 13).

<Test method 2>
In Examples 1 and 2 and Comparative Examples 1 and 2, the pressure distribution of the exhaust gas in the collecting pipe 50 connected to the second independent exhaust pipe 41 and the loop pipe 60 connected to the collecting pipe 50 was measured ( 14 to 17 (a)).

  In Examples 1 and 2 and Comparative Examples 1 and 2, the flow velocity distribution of the exhaust gas in the straight portion 50b was measured (see FIGS. 14 to 17 (b)).

<Test result of test method 1>
As shown in the column of scavenging amount in Table 1 and the broken line in FIG. 13, the scavenging amount in Examples 1 and 2 was larger than the scavenging amount in Comparative Examples 1 and 2. In particular, in the first comparative example in which the loop pipe diameter D1 is set to be the same as the diffuser diameter D2, the scavenging amount is remarkably small. In Comparative Example 2 in which the loop pipe diameter D1 was increased stepwise with respect to the diffuser diameter D2, the scavenging amount was smaller than in Examples 1 and 2, but the scavenging amount was considerably larger than that in Comparative Example 1.

<Test result of test method 2>
As shown to (a) of FIGS. 14-17, the pressure of the exhaust gas in the downstream end part vicinity (one-dot chain line part) of the diffuser part 50c in Examples 1 and 2 was smaller than the pressure in Comparative Examples 1 and 2. .

  Moreover, as shown to (b) of FIGS. 14-17, in Example 1 and 2, the position of the part with a large flow velocity was stable in the axial center vicinity of the straight part 50b. Further, no backflow occurred in Example 1, and backflow was almost suppressed in Example 2.

  On the other hand, in Comparative Examples 1 and 2, the position of the portion where the flow velocity is large is displaced outward from the axis of the straight portion 50b as compared with Examples 1 and 2. Further, in Comparative Examples 1 and 2, backflow occurred in a large region, and the area where this backflow occurred was particularly large in Comparative Example 1 in which the loop tube diameter D1 was set to be the same as the diffuser diameter D2.

<Discussion>
From the above test results, the pressure in the loop pipe 60 is suppressed by expanding the loop pipe diameter D1 with respect to the straight diameter D0 and setting the value of D1 / D0 in the range of 1.4 to 1.7. As a result, it was confirmed that the backflow in the straight portion 50b was suppressed and the scavenging amount in the independent exhaust pipe 41 was increased. The reason why the backflow is suppressed is that by increasing the loop pipe diameter D1 relative to the straight diameter D0, the exhaust gas easily flows in the loop pipe 60 from the upstream side to the downstream side. This is because the pressure is suppressed and the portion where the flow rate of the exhaust gas in the straight portion 50b is large is stably positioned near the central axis of the straight portion 50b. By suppressing the backflow, a decrease in the ejector effect is suppressed.

  Further, it was confirmed that the scavenging amount in the independent exhaust pipe 41 is further increased by expanding the loop pipe diameter D1 stepwise with respect to the diffuser diameter D2. This is because when the positive pressure wave of the exhaust gas discharged from the cylinder 13a reaches the upstream end 60c of the loop pipe 60 by expanding the loop pipe diameter D1 stepwise with respect to the diffuser diameter D2, This is because the negative pressure wave is generated by the reflection of the positive pressure wave at the upstream end 60c of the loop pipe 60, and the negative pressure wave reaches the upstream end of the second cylinder 13b. That is, the negative pressure generated by the ejector effect cooperates with the negative pressure wave generated by reflecting the positive pressure wave of the exhaust gas discharged from the cylinder 13a at 60c of the loop pipe 60, and scavenging obtained by the ejector effect alone. A scavenging effect exceeding the effect is obtained.

  As described above, according to the present embodiment, the inner diameter (loop pipe diameter) D1 of the upstream end portion 60c of the loop pipe 60 is larger than the inner diameter D0 of the straight section 50b. It becomes easy to flow in the loop pipe 60 from the upstream side toward the downstream side, the pressure (back pressure) in the loop pipe 60 is reduced, and the pressure loss is also reduced. As a result, the portion where the exhaust gas flow velocity is large is stably positioned near the central axis of the straight portion 50b, so that the exhaust gas flows toward the loop tube 60 without stagnating in the straight portion 50b, and the exhaust gas flows into the straight portion 50b. Back flow from the loop pipe 60 side to the independent exhaust pipe 41 side is suppressed. As a result, the flow velocity and flow rate of the exhaust gas flowing from the independent exhaust pipe 41 side to the loop pipe 60 side in the collecting pipe 50 are suppressed, and the scavenging effect (ejector effect) of sucking exhaust gas from the other independent exhaust pipe 41 is suppressed. The decrease can be suppressed.

  Further, the provision of the loop pipe 60 prevents the exhaust device 1 from interfering with the propeller shaft of the FR vehicle or the 4WD vehicle while maintaining the horizontal layout of the engine, and introduces the exhaust gas into the catalyst device 70. Can be suppressed between the cylinders.

  Therefore, according to the present embodiment, it is possible to suppress a decrease in the scavenging effect in the dynamic pressure exhaust system while ensuring good vehicle mountability of the exhaust device 1.

  Further, in the present embodiment, the inner diameter D1 of the upstream end portion 60c of the loop pipe 60 is expanded stepwise with respect to the inner diameter D2 of the downstream end portion (downstream end portion of the diffuser portion 50c) of the collecting pipe 50. Therefore, when the positive pressure wave of the exhaust gas discharged from the cylinders 13 a to 13 d reaches the upstream end 60 c of the loop pipe 60, the positive pressure wave is reflected by the upstream end 60 c of the loop pipe 60, thereby causing a negative pressure wave. Will occur. Since the negative pressure wave reaches the exhaust port 16 of the other cylinders 13a to 13d, the exhaust gas in the other cylinders 13a to 13d is sucked out from the exhaust port 16 by the negative pressure wave, and the other cylinders 13a to 13d. Scavenging is further promoted.

  That is, the negative pressure generated by the ejector effect when the exhaust gas discharged from the cylinders 13a to 13d is ejected to the collecting pipe 50 and the positive pressure wave of the exhaust gas discharged from the cylinders 13a to 13d are generated at 60c of the loop pipe 60. A scavenging effect exceeding the scavenging effect obtained by the ejector effect alone is obtained in cooperation with the negative pressure wave generated by reflection.

  In this embodiment, the ratio (D1 / D0) of the inner diameter D1 of the upstream end 60c of the loop pipe 60 to the inner diameter D0 of the straight section 50b is the independent exhaust pipe 41 from the loop pipe 60 side in the straight section 50b. Since it is set to a predetermined value that suppresses the backflow of the exhaust gas to the side, a sufficient scavenging effect can be obtained by suppressing the backflow of the exhaust gas within the straight portion 50b.

  In the present embodiment, at least in the engine low speed range, the opening of the exhaust valves of the succeeding cylinders 13a to 13d is started during the overlap period of the preceding cylinders 13a to 13d between two cylinders in which the exhaust order is continuous. At the same time, the negative pressure wave generated by reflecting the positive pressure wave of the exhaust gas of the succeeding cylinders 13a to 13d at the upstream end 60c of the loop pipe 60 reaches the exhaust port during the overlap period of the preceding cylinders 13a to 13d. Accordingly, at least in the engine low speed region, the exhaust gas in the preceding cylinders 13a to 13d is sucked out to the exhaust port side by the negative pressure wave, and the scavenging of the preceding cylinders 13a to 13d is further promoted.

  In the present embodiment, the ratio (D1 / D0) of the inner diameter D1 of the upstream end portion 60c of the loop pipe 60 and the inner diameter D0 of the straight portion 50b is set in the range of 1.4 to 1.7. Therefore, a sufficient scavenging effect can be obtained by maximizing the effect of diameter expansion.

  Further, in the present embodiment, the collecting pipe 50 includes the diffuser portion 50c that is connected to the downstream end portion of the straight portion 50b and has a diameter that increases toward the downstream side. Therefore, the pressure of the exhaust gas that has decreased in the throttle portion 50a and The temperature can be recovered in the diffuser portion 50c. Thereby, the positive pressure amount of the positive pressure wave of the exhaust gas reaching the upstream end portion 60 c of the loop pipe 60, and the negative pressure amount of the negative pressure wave generated by reflecting the positive pressure wave at the upstream end portion 60 c of the loop pipe 60. And the effect of improving the scavenging performance of the cylinders 13a to 13d by this negative pressure wave can be further enhanced. It is also advantageous in terms of activation of the catalyst body.

  Further, in the present embodiment, the inner diameter D1 of the upstream end portion 60c of the loop pipe 60 is expanded stepwise with respect to the inner diameter D2 of the downstream end portion of the diffuser portion 50c, so that the diffuser portion 50c is on the upstream side. Even if the diameter of the diffuser portion 50c gradually increases from the downstream side to the downstream side, the downstream end portion of the diffuser portion 50c and the upstream end portion 60c of the loop pipe 60 can be connected without making the diffuser portion 50c longer than necessary. .

  Further, in the present embodiment, since the catalyst device 70 and the collecting pipe 50 are connected via the loop pipe 60 so that the catalytic device 70 extends in the vehicle width direction below the collecting pipe 50, The exhaust device 1 can be accommodated in the tunnel portion 5 of the floor panel 4 in a compact manner. Further, it is possible to more reliably avoid the exhaust device 1 from interfering with the propeller shaft of the FR vehicle or the 4WD vehicle while maintaining the layout of the engine horizontally.

  Further, in the present embodiment, the catalyst device 1 includes a cylindrical casing 71 and a catalyst main body accommodated in the casing 71, and the downstream end of the loop pipe 60 is exhaust gas from the downstream end. Is connected to the catalyst device 70 so that the direction in which the gas flows out is oblique to the axis of the casing 71. For this reason, since the exhaust gas is introduced into the catalyst device 70 so that the direction in which the exhaust gas flows out of the loop pipe 60 is oblique to the axis of the casing 71, the diffusion of the exhaust gas in the catalyst device 70 Can be promoted. Accordingly, it is possible to more reliably suppress the position where the exhaust gas is introduced into the catalyst device 70 from different cylinders.

  Further, in the present embodiment, since the collecting pipe 50 has a double pipe structure, a decrease in the temperature of the exhaust gas introduced into the catalytic device 70 is suppressed, and early activation and maintenance of the active state of the catalytic device 70 are prevented. Secured.

  Further, in the present embodiment, since the heat insulating material is applied to the collecting pipe 50, a decrease in the temperature of the exhaust gas introduced into the catalyst device 70 is suppressed, and early activation and maintenance of the active state of the catalyst device 70 are prevented. Secured.

  Further, in the present embodiment, the engine 10 is a multi-cylinder engine that is disposed horizontally so that the cylinder row direction faces the vehicle width direction. It is possible to suppress a decrease in the scavenging effect in the dynamic pressure exhaust system while ensuring a good vehicle mountability.

  In the above-described embodiment, the collecting pipe 50 is configured by the throttle portion 50a, the straight portion 50b, and the diffuser portion 50c, but may be configured by the throttle portion 50a and the straight portion 50b by omitting the diffuser portion 50c. Good. In this case, the upstream end portion 60c of the loop pipe 60 is connected to the downstream end portion of the straight portion 50b. The inner diameter D1 of the upstream end portion 60c of the loop pipe 60 is increased stepwise with respect to the inner diameter D0 of the downstream end portion of the straight portion 50b. Further, the ratio (D1 / D0) of the inner diameter D1 of the upstream end 60c of the loop pipe 60 and the inner diameter D0 of the downstream end of the straight section 50b is the loop pipe 60 side in the straight section 50b as in the above embodiment. Is set to a predetermined value that suppresses the backflow of the exhaust gas to the independent exhaust pipe 41 side, and is preferably set to a range of 1.4 to 1.7.

  Moreover, in the said embodiment, although the loop pipe | tube 60 was bent twice, it is not restricted to this, You may bend 3 times or more. Although the upper limit of the number of bending is not particularly limited, for example, about 10 is preferable. If it is bent too many times, the manufacturing cost of the loop tube is high. In addition, the exhaust gas flow rate may be excessively reduced. Further, instead of intermittently bending the loop tube 60 at a plurality of locations, the loop tube 60 may be bent continuously over its entire length.

  Further, the total sum of the bending angles may be less than 180 °. The lower limit of the sum of the bending angles is not particularly limited, but is preferably about 90 °, for example. If the sum of the bending angles is excessively small, the exhaust gas flow rate may not decrease so much.

  Moreover, you may own one bending part whose angle is 180 degrees or more. In this case as well, the upper limit of the bending angle is not particularly limited, but is preferably about 360 °, for example. If the bending angle is excessively large, the manufacturing cost of the loop tube is high. In addition, the exhaust gas flow rate may be excessively reduced.

  Moreover, the bending parts 60a and 60b do not need to contain the bending component to the same side mutually. For example, the first bent portion 60a may be bent only in the horizontal plane, and the second bent portion 60b may be bent only in the vertical plane. Alternatively, the first bent portion 60a may be bent rightward when viewed from the upstream side in the horizontal plane, and the second bent portion 60b may be bent leftward when viewed from the upstream side in the horizontal plane.

  In the above embodiment, the loop pipe 60 is bent in the clockwise direction, but may be bent in the counterclockwise direction.

  In the above embodiment, the collecting pipe 50 has a double pipe structure in order to keep the exhaust gas warm, but in addition to the collecting pipe 50, the independent exhaust pipe 41 and the loop pipe 60 may have a double pipe structure.

  In the above embodiment, a heat insulating material is applied to the collecting pipe 50 to keep the exhaust gas warm, but in addition to the collecting pipe 50, a heat insulating material is also applied to the independent exhaust pipe 41 and the loop pipe 60. Also good.

  In addition, the intake valve drive mechanism 20 and the exhaust valve drive mechanism 30 are configured so that the opening period of the exhaust valve 18 and the opening period of the intake valve 17 of the cylinders 13a to 13d are increased during intake in the low speed and high load area. The exhaust valves 18 of the succeeding cylinders 13a to 13d start to open during the overlap period of the preceding cylinders 13a to 13d between two cylinders that overlap with each other with the dead point interposed therebetween and the exhaust order continues. May be controlled.

  Further, the exhaust device 1 according to the present embodiment may be applied to FF vehicles other than FR vehicles and 4WD vehicles.

  Moreover, in the said embodiment, although the exhaust apparatus 1 is applied to the horizontal installation type engine 10, it is not limited to this, You may apply to the vertical installation type engine in which a cylinder row direction extends in the vehicle front-back direction. .

DESCRIPTION OF SYMBOLS 1 Exhaust apparatus of multi-cylinder engine 10 Engine 13a-13d 1st-4th cylinder 15 Intake port 16 Exhaust port 17 Intake valve 18 Exhaust valve 40 Exhaust manifold 41 Independent exhaust pipe 41a Downstream end part of independent exhaust pipe 50 Collecting pipe (single pipe One exhaust pipe)
50A Collecting pipe body 50a Restriction part 50b Straight part 50c Diffuser part 50B Outer pipe 60 Loop pipe (single exhaust pipe)
60a, 60b First and second bent portions of loop pipe 60c Upstream end of loop pipe 70 Catalyst device 71 Casing 71a End face member of casing 72 Catalyst body D0 Inner diameter of straight section D1 Inner diameter of upstream end of loop pipe D2 Diffuser section Inner diameter of the downstream end (downstream end of the collecting pipe)

Claims (12)

An exhaust system that is connected to a multi-cylinder engine disposed in an engine room at the front of the vehicle and is arranged to extend rearward from the multi-cylinder engine,
A plurality of independent exhaust pipes that are provided for each cylinder in order from the upstream side in the exhaust gas flow direction and whose upstream end is connected to the exhaust port of the cylinder and the downstream ends are bundled, and the downstream end of the independent exhaust pipe A single exhaust pipe connected to the catalyst, and a catalyst device connected to the downstream end of the single exhaust pipe and purifying exhaust gas derived from the single exhaust pipe,
The single exhaust pipe is connected to a throttle portion whose flow area decreases toward the downstream side, and a straight pipe that is connected to the downstream end of the throttle portion and that extends straight while maintaining the inner diameter of the throttle portion. And a loop pipe that is connected to the downstream end of the collecting pipe and bent in a loop shape,
The inner diameter of the upstream end of the loop pipe is expanded with respect to the inner diameter of the straight section, and is expanded stepwise with respect to the inner diameter of the downstream end of the collecting pipe.
An exhaust system for a multi-cylinder engine. The ratio between the inner diameter of the upstream end of the loop pipe and the inner diameter of the straight section is set to a predetermined value that suppresses the backflow of exhaust gas from the loop pipe side to the independent exhaust pipe side in the straight section. Yes ,
The exhaust system for a multi-cylinder engine according to claim 1, wherein An exhaust system that is connected to a multi-cylinder engine disposed in an engine room at the front of the vehicle and is arranged to extend rearward from the multi-cylinder engine,
A plurality of independent exhaust pipes that are provided for each cylinder in order from the upstream side in the exhaust gas flow direction and whose upstream end is connected to the exhaust port of the cylinder and the downstream ends are bundled, and the downstream end of the independent exhaust pipe A single exhaust pipe connected to the catalyst, and a catalyst device connected to the downstream end of the single exhaust pipe and purifying exhaust gas derived from the single exhaust pipe,
The single exhaust pipe is connected to a throttle portion whose flow area decreases toward the downstream side, and a straight pipe that is connected to the downstream end of the throttle portion and that extends straight while maintaining the inner diameter of the throttle portion. And a loop pipe that is connected to the downstream end of the collecting pipe and bent in a loop shape,
The inner diameter of the upstream end portion of the loop pipe is expanded with respect to the inner diameter of the straight portion,
The ratio between the inner diameter of the upstream end of the loop pipe and the inner diameter of the straight section is set to a predetermined value that suppresses the backflow of exhaust gas from the loop pipe side to the independent exhaust pipe side in the straight section. Yes,
An exhaust system for a multi-cylinder engine. The engine includes an intake valve capable of opening and closing an intake port for introducing intake air into the cylinder, an exhaust valve capable of opening and closing an exhaust port for deriving exhaust gas from the cylinder, and an engine low speed at least with an engine speed less than a predetermined reference speed In the region, the opening period of the intake valve and the opening period of the exhaust valve of each cylinder overlap each other for a predetermined period. Valve drive means for driving the intake valve and the exhaust valve so that the exhaust valve starts to open,
The length from the exhaust port to the upstream end of the loop pipe is caused by reflection of the positive pressure wave of the exhaust gas discharged from the succeeding cylinder at the upstream end of the loop pipe at least in the engine low speed region. The negative pressure wave is set to a length that reaches the exhaust port of the preceding cylinder during the overlap period of the preceding cylinder .
The exhaust device for a multi-cylinder engine according to any one of claims 1 to 3, wherein The ratio of the inner diameter of the upstream end portion of the loop pipe and the inner diameter of the straight portion is set in the range of 1.4 to 1.7 ,
The exhaust device for a multi-cylinder engine according to any one of claims 1 to 4, wherein The collecting pipe further has a diffuser portion connected to the downstream end portion of the straight portion and having a diameter increasing toward the downstream side ,
The exhaust system for a multi-cylinder engine according to any one of claims 1 to 5, wherein An exhaust system that is connected to a multi-cylinder engine disposed in an engine room at the front of the vehicle and is arranged to extend rearward from the multi-cylinder engine,
A plurality of independent exhaust pipes that are provided for each cylinder in order from the upstream side in the exhaust gas flow direction and whose upstream end is connected to the exhaust port of the cylinder and the downstream ends are bundled, and the downstream end of the independent exhaust pipe A single exhaust pipe connected to the catalyst, and a catalyst device connected to the downstream end of the single exhaust pipe and purifying exhaust gas derived from the single exhaust pipe,
The single exhaust pipe is connected to a throttle portion whose flow area decreases toward the downstream side, and a straight pipe that is connected to the downstream end of the throttle portion and that extends straight while maintaining the inner diameter of the throttle portion. And a loop pipe that is connected to the downstream end of the collecting pipe and bent in a loop shape,
The collecting pipe further includes a diffuser portion connected to the downstream end portion of the straight portion and having a diameter that increases toward the downstream side,
The inner diameter of the upstream end portion of the loop pipe is expanded with respect to the inner diameter of the straight portion, and is increased stepwise with respect to the inner diameter of the downstream end portion of the diffuser portion .
An exhaust system for a multi-cylinder engine. The catalyst device has a cylindrical casing and a catalyst main body accommodated in the casing,
The downstream end portion of the loop pipe is connected to the catalyst device such that the direction in which the exhaust gas flows out from the downstream end portion is oblique with respect to the axial center of the casing .
The exhaust device for a multi-cylinder engine according to any one of claims 1 to 7, wherein At least a part of the independent exhaust pipe and the single exhaust pipe has a double pipe structure ,
The exhaust device for a multi-cylinder engine according to any one of claims 1 to 8, wherein the exhaust device is a multi-cylinder engine. A heat insulating material is applied to at least a part of the independent exhaust pipe and the single exhaust pipe ,
The exhaust device for a multi-cylinder engine according to any one of claims 1 to 9, wherein The engine is a multi-cylinder engine arranged horizontally so that the cylinder row direction faces the vehicle width direction .
The exhaust device for a multi-cylinder engine according to any one of claims 1 to 10, wherein the exhaust device is a multi-cylinder engine. The catalyst device and the collecting pipe are connected via the loop pipe so that the catalytic apparatus is arranged extending in the vehicle width direction below the collecting pipe .
The exhaust system for a multi-cylinder engine according to claim 11, wherein