Exhaust Structure for Engine and Engine

The present disclosure relates to an exhaust structure for an engine and an engine.

As a type of exhaust structure for an engine having a catalyst, an engine described in WO 2022/180742 A1 is known. Such an engine is desirable to suppress progress of deterioration of the catalyst.

The present disclosure has been made in view of the above-described circumstance, and an object thereof is to provide an exhaust structure for an engine capable of suppressing the progress of deterioration of a catalyst.

In order to solve the above problem, an exhaust structure for an engine according to one aspect of the present disclosure includes: an exhaust pipe connected to an engine body, the exhaust pipe into which an exhaust gas is introduced from the engine body; a catalyst body that purifies an exhaust gas; and a housing case that houses the catalyst body, in which the housing case includes an inlet portion connected to a downstream end portion of the exhaust pipe, the inlet portion into which an exhaust gas is introduced from the exhaust pipe, an outlet portion that leads out an exhaust gas from the housing case to an outside, and an expansion chamber provided on a more upstream side than the catalyst body in a flow direction of an exhaust gas from the inlet portion toward the outlet portion and having a space defined inside, and a volume of the expansion chamber is larger than a volume of the catalyst body.

Hereinafter, an embodiment of an engine according to the present disclosure will be described with reference to the drawings.

is a schematic front view of an engineaccording to an embodiment of the present disclosure.is a schematic side view of the engine. An engineof the present disclosure includes an engine body, an exhaust system, and a cooling fan. The engineis mounted on a vehicle or the like. For example, the engineis mounted on a riding type mower and is used as a traveling source of the mower and a driving source of the cutting blade.is a schematic perspective view of the engine bodyand the exhaust system.is a schematic plan view of the engine bodyand the exhaust system.is a schematic bottom view of the engine bodyand the exhaust system.illustrates the engine bodywith a part thereof broken. In, a part of an internal structure of a catalyst built-in mufflerdescribed later of the exhaust systemis indicated by a broken line.

The engine bodyis a reciprocating engine. The engine bodyis a so-called V-twin engine including two cylindersA andB. An engine may be required to have a purification function for purifying harmful components contained in exhaust gas. For example, the harmful component is assumed to be hydrocarbon, carbon monoxide, and nitrogen oxide.

The engine bodyincludes a pair of cylinder blocksA andB, a pair of cylinder headsA andB, and a pair of head coversA andB. The cylinder headsA andB are fastened to the cylinder blocksA andB, respectively. The head coversA andB are attached to the cylinder headsA andB, respectively.

One cylinderA and one cylinderB are formed in the two cylinder blocksA andB, respectively. An inner peripheral surface of each of the cylindersA andB has a cylindrical surface shape. The engine bodyincludes a first pistonA. The first pistonA reciprocates in the first cylinderA, which is one cylinderA, along a first cylinder axis line X, which is an axis thereof. The engine bodyincludes a second pistonB. The second pistonB reciprocates in the second cylinderB, which is the other cylinderB, along a second cylinder axis line X, which is an axis thereof. The engine bodyincludes a crankshaft. The crankshaftis connected to both of the two pistonsA andB. The crankshaftis rotationally driven by the two pistonsA andB. The engine bodyincludes a crankcase. The crankcaseis connected to the cylinder blocksA andB. The crankshaftis housed inside the crankcase.

The crankshaftextends in an up-down direction, that is, a vertical direction. A crankshaft line X, which is a rotation center line of the crankshaft, extends in the up-down direction. The first cylinder axis line Xand the second cylinder axis line Xextend horizontally. As described above, the engine bodyis used in a posture in which the crankshaft line Xextends in the up-down direction and the cylinder axis lines Xand Xextend horizontally. In other words, the engine bodyis designed on the premise that the engine bodyis mounted on a work machine in a state where the crankshaft line Xextends up-down. The engineis provided with an oil pan that stores engine oil. The oil pan is disposed on one side in the direction along the crankshaft line Xwith respect to the engine body. In the present embodiment, the oil pan is disposed below the engine body.

When viewed along the crankshaft line X, that is, when viewed along the up-down direction, the first cylinder axis line Xand the second cylinder axis line Xintersect so as to form a V shape. Specifically, as viewed along the up-down direction, the first cylinder axis line Xand the second cylinder axis line Xintersect each other. Of the first cylinder axis line X, a line segment extending toward the first cylinderA from an intersection Pwith the second cylinder axis line Xas a base point is a first reference line X. Of the second cylinder axis line X, a line segment extending toward the second cylinderB from the intersection Pas a base point is a second reference line X. The first reference line Xand the second reference line Xform an angle of less than 180 degrees, and form a V shape. When viewed along the up-down direction, the intersection Pis located at a point on the crankshaft line X.

In the present embodiment, as viewed along the up-down direction, a center line XC dividing the entire engine bodyinto halves divides the angle formed by the first reference line Xand the second reference line Xinto two equal parts. Hereinafter, a direction along this center line XC is called a front-rear direction. The cylindersA andB are separated from the crankshaftin the front-rear direction. Hereinafter, the crankshaftside with respect to each of the cylindersA andB is called a rear side, and the opposite side is called a front side. A direction orthogonal to the up-down direction and the front-back direction is called a left-right direction. Directions illustrated in each drawing represent the directions defined as described above. In each drawing, the cylinder located on the right side of the two cylindersA andB is illustrated as the first cylinderA, and the cylinder located on the left side is illustrated as the second cylinderB. Also in the following description, the cylinder located on the right side is treated as the first cylinderA, and the cylinder located on the left side is treated as the second cylinderB.

Intake portsA andB for introducing intake air into the cylindersA andB are formed in the cylinder headsA andB, respectively. The first intake portA corresponding to the first cylinderA opens on the left side surface of the first cylinder headA. The second intake portB corresponding to the second cylinderB opens on the right side surface of the second cylinder headB. Each of the intake portsA andB is connected to an intake system device such as an intake pipe, but illustration of the intake system device is omitted.

Exhaust portsA andB for leading out the exhaust gas generated in the cylindersA andB from the cylindersA andB are formed in the cylinder headsA andB, respectively. The downstream end portion of the first exhaust portA corresponding to the first cylinderA, that is, an outletA of the first exhaust portA is open to the lower surface of the first cylinder headA. The downstream end portion of the second exhaust portB corresponding to the second cylinderB, that is, an outletB of the second exhaust portB opens on the lower surface of the second cylinder headB. The first exhaust portA and the second exhaust portB are arranged in the left-right direction. When viewed along the up-down direction, the first exhaust portA and the second exhaust portB are formed at symmetrical positions about the center line XC. As described above, in the first embodiment, the port array direction, which is the arrangement direction of the first exhaust portA and the second exhaust portB, coincides with the left-right direction. In other words, in the description of the engineaccording to the first embodiment, the port array direction is called a left-right direction.

The engineincludes a first output shaftand a second output shaftthat are rotatable integrally with the crankshaft. The first output shaftprotrudes downward from the lower surface of the crankcase. The first output shaftis connected to a wheel, a cutting blade, or the like, and rotates the wheel, the cutting blade, or the like. The second output shaftprotrudes upward from the upper surface of the crankcase.

The exhaust systemis a system that discharges the exhaust gas generated in each of the cylindersA andB into the atmosphere. The exhaust systemis connected to the engine body. The exhaust systemis provided with an exhaust pipeand the catalyst built-in muffler. The exhaust pipeand the catalyst built-in mufflerare components that define an exhaust passage through which exhaust gas flows. The exhaust pipeand the catalyst built-in mufflerare provided in this order from the upstream side in the flow direction of the exhaust gas.

The engine bodyis an air-cooled engine. The outer surfaces of the cylinder blocksA andB and the cylinder headsA andB are provided with a plurality of cooling fins.

The fansends air to the engine bodyto cool the engine body. The fanis disposed above the crankcase. The crankcaseconstitutes a rear side part of the engine body, and the fanis disposed above the rear side part of the engine body.

The fanincludes a fan bodyincluding a plurality of blades, and a fan casesurrounding an outer periphery of the fan body. The fan bodyis connected to the second output shaft. The fan bodyis rotationally driven by the second output shaft. The fanis a centrifugal fan. When the fan bodyrotates, air is taken in from above the fan bodyand discharged to the outer peripheral side of the fan body.

The fan caseextends to the front side relative to the fan body. The front of the fan caseis generally covered with a deviceof an intake system or the like. The engineis provided with coversand. Each of the coversandextends downward from the vicinity of both left and right edges of the front part of the fan case. The coversandare disposed so as to cover both left and right sides of the engine body. With this configuration, the air released to the outer peripheral side of the fan bodyis mainly guided obliquely forward and downward from the front portion of the fan bodyas indicated by arrow Yin. As illustrated in, the front part of the engine bodyincluding the cylinder blocksA andB and the cylinder headsA andB is disposed at a position obliquely forward and downward of the fan body. As a result, the cylinder blocksA andB and the cylinder headsA andB are cooled by the air released by the fan.

Hereinafter, a detailed configuration of the exhaust systemthat is an exhaust structure for the engine according to the embodiment of the present disclosure will be described.is a cross-sectional view taken along line VI-VI of. Hereinafter, the upstream side and the downstream side in the flow direction of the exhaust gas are simply called upstream side and downstream side as appropriate.

The exhaust pipeis connected to the engine body. The exhaust gas discharged from the engine bodyflows inside the exhaust pipe. The exhaust pipeincludes a first exhaust pipeA and a second exhaust pipeB each connected to the engine body. The first exhaust pipeA is fixed to the lower surface of the first cylinder headA. The second exhaust pipeB is fixed to the lower surface of the second cylinder headB.

The first exhaust pipeA is connected to the outletA of the first exhaust portA. Exhaust gas generated in the first cylinderA is introduced into the first exhaust pipeA through the first exhaust portA.

The first exhaust pipeA extends from the outletA of the first exhaust portA toward a position obliquely forward and downward with respect to the outletA. When viewed along the up-down direction, the first exhaust pipeA extends straight in the front-rear direction. The second exhaust pipeB extends from the outletB of the second exhaust portB toward a position obliquely forward and downward with respect to the outletB. When viewed along the up-down direction, the second exhaust pipeB extends straight in the front-rear direction. In the present embodiment, both the first exhaust pipeA and the second exhaust pipeB are circular pipes. The inner diameter of the first exhaust pipeA and the inner diameter of the second exhaust pipeB are set to the same value.

The catalyst built-in mufflerincorporates a catalystas described later, and has a function of purifying exhaust gas. The catalyst built-in muffleralso has a function of reducing exhaust noise.

The catalyst built-in muffleris disposed between the first reference line Xand the second reference line X. In the present embodiment, the catalyst built-in muffleris disposed such that the substantially center in the left-right direction is located on the center line XC as viewed along the up-down direction. A dimension Lin the left-right direction of the catalyst built-in muffleris equal to or less than a dimension Lin the left-right direction of the engine body. The catalyst built-in muffleris disposed in a region between a right end and a left end of the engine bodyin the left-right direction.

The catalyst built-in muffleris disposed on a flow path of air sent from the fan. Specifically, the catalyst built-in muffleris disposed at a front position of a lower portion of the engine bodythat is a position obliquely forward and downward from a front portion of the fan body. As a result, the catalyst built-in mufflerreceives the air sent from the fanand is cooled by the air.

The catalyst built-in mufflerincludes a housing caseconstituting an outer shape thereof and a catalyst body. The catalyst bodyis housed inside the housing case.

The catalyst bodyhas a tubular shape. Exhaust gas is introduced into the inside of the catalyst bodyfrom an open end on one side in the axial direction thereof. The introduced exhaust gas is led out to the outside from the open end on the other side of the catalyst body. In the present embodiment, the catalyst bodyhas a cylindrical shape. The catalyst bodyhas an outer cylinderhaving a cylindrical shape constituting the outer shape thereof. The catalystis supported on a carrier provided inside the outer cylinder. The catalystis, for example, a three-way catalyst. For example, the catalyst bodyis formed in a honeycomb structure in which both axial ends are opened.

The housing casehas a bottomed cylindrical shape extending in the left-right direction. A space is defined inside the housing case. The housing caseincludes a case body, a right bottom wall, and a left bottom wall. The case bodyhas a cylindrical shape extending in the left-right direction. A central axis Xof the case bodyextends in the left-right direction. The axial direction of the case bodyand the housing casecoincides with the left-right direction. The right bottom wallis attached to the right end portion of the case body. The left bottom wallis attached to the left end portion of the case body. Each of the bottom wallsandhas a substantially disk shape. The bottom wallsandare attached to the case bodyso as to close the left and right openings of the case body.

In the case body, a first inlet portionA and a second inlet portionB for introducing exhaust gas into the housing caseare formed. These inlet portionsA andB are through holes penetrating the outer peripheral surface of the case body. The first inlet portionA is formed in a rear part of the outer peripheral surface of the case body. The first inlet portionA is provided near the right end portion of the outer peripheral surface of the case body. The second inlet portionB is formed in a rear part of the outer peripheral surface of the case body. The second inlet portionB is provided near the left end portion of the outer peripheral surface of the case body.

A downstream end portionA of the first exhaust pipeA is inserted into the first inlet portionA, and these are connected. A downstream end portionB of the second exhaust pipeB is inserted into the second inlet portionB, and these are connected. In the present embodiment, the exhaust pipesA andB and the case bodyare connected via a pair of left and right bracketsandfixed to the outer peripheral surface of the case body. Hereinafter, the downstream end portionA of the first exhaust pipeA is appropriately called a first exhaust pipe end portionA. The downstream end portionB of the second exhaust pipeB is called a second exhaust pipe end portionB.

In the present embodiment, the first exhaust pipe end portionA is attached to the first inlet portionA in a state of protruding inward in the radial direction of the case bodyfrom the inner peripheral surface of the case body. Similarly, the second exhaust pipe end portionB is attached to the second inlet portionB in a state of protruding inward in the radial direction of the case bodyfrom the inner peripheral surface of the case body. Protrusion amounts Lof the first exhaust pipe end portionA and the second exhaust pipe end portionB from the inner peripheral surface of the case bodyis the same as each other.

A central axis Xof the first exhaust pipe end portionA extends along the radial direction of the case body. The central axis Xof the first exhaust pipe end portionA intersects the central axis Xof the case body. Specifically, these central axes Xand Xare orthogonal to each other. Although not illustrated in detail, the central axis of the second exhaust pipe end portionB also extends along the radial direction of the case body. The central axis of the second exhaust pipe end portionB and the central axis Xof the case bodyare also orthogonal to each other.

The housing caseincludes a first partition portionand a second partition portionprovided inside thereof, and a communication pipe. The first partition portionand the second partition portionare separated from each other in the left-right direction. The first partition portionand the second partition portionare fixed to the case body.

The first partition portionincludes a first partition wallA orthogonal to the central axis Xof the housing case. The second partition portionincludes a second partition wallA orthogonal to the central axis Xof the housing case.

The first partition wallA and the second partition wallA have the same area as that of a cross-section orthogonal to the axial direction of the housing case. The first partition wallA and the second partition wallA define the inner space of the housing caseinto three spaces of a first expansion chamber S, a catalyst chamber S, and a second expansion chamber Sin the left-right direction. The first expansion chamber Sis a space between the first partition portionand the right bottom wall. The catalyst chamber Sis a space between the first partition portionand the second partition portion. The second expansion chamber Sis a space between the second partition portionand the left bottom wall. Note that the first expansion chamber Sis located on the right side of the housing case, and the second expansion chamber Sis located on the left side of the housing case. The catalyst chamber Sis located between the first expansion chamber Sand the second expansion chamber S. In the present embodiment, the separation distance between the first partition wallA and the right bottom walland the separation distance between the second partition wallA and the left bottom wallare the same in the left-right direction. The catalyst chamber Sis provided at the center in the left-right direction of the housing case.

The first inlet portionA is provided in the first expansion chamber S. The first inlet portionA is formed on the outer peripheral surface of the case bodythat defines the first expansion chamber S. The second inlet portionB is provided in the second expansion chamber S. The second inlet portionB is formed on the outer peripheral surface of the case bodythat defines the second expansion chamber S.

The volume of the first expansion chamber Sis larger than the volume of the catalyst body. The volume of the catalyst bodyis a volume of a space formed inside the catalyst bodythrough which the exhaust gas can pass. The volume of the catalyst bodyin the present embodiment approximates the volume of the catalyst body, and therefore the volume of the catalyst bodyis specified as the volume of the catalyst body.

In the present embodiment, the volume of the first expansion chamber Sis set to betimes or more and 10 times or less the volume of the catalyst body. Specifically, a volume Vof the catalyst bodycan be expressed as V˜d×d×π/4×Lusing outer diameters dof the catalyst bodyand the outer cylinderand axial dimensions Lof the catalyst bodyand the outer cylinder. A volume Vof the first expansion chamber Scan be expressed as V˜d×d×π/4×Lusing an inner diameter dof the case bodyand a separation distance Lin the left-right direction between the right bottom walland the first partition wallA. In the present embodiment, the volume Vof the first expansion chamber Sis set to be 2 times or more and 10 times or less the volume Vof the catalyst body. Note that in the above and the following expressions, π is a circular constant.

The volume of the second expansion chamber Sis larger than the volume of the catalyst body. In the present embodiment, the volume of the second expansion chamber Sis set to be 2 times or more and 10 times or less the volume of the catalyst body. Specifically, a volume Vof the second expansion chamber Scan be expressed as V˜(d{circumflex over ( )}2−d{circumflex over ( )}2)×π/4×Lusing the inner diameter dof the case body, a separation distance Lin the left-right direction between the left bottom walland the second partition wallA, and an outer diameter dof the communication pipedescribed later. In the present embodiment, the volume Vof the second expansion chamber Sis set to be 2 times or more and 10 times or less the volume Vof the catalyst body.

In the present embodiment, the volume Vof the first expansion chamber Sand the volume Vof the second expansion chamber Sare set to the same volume. In other words, the first partition portionand the second partition portionare disposed such that the volume relationship is achieved in a state where the communication pipeis disposed in the second expansion chamber S. Here, the volume Vof the first expansion chamber Sand the volume Vof the second expansion chamber Sare preferably set to be 2.5 times or more, more preferably 3 times or more and 5 times or less the volume of the catalyst body. Accordingly, in the present embodiment, the volume Vof the first expansion chamber Sand the volume Vof the second expansion chamber Sare set to about 4 times the volume Vof the catalyst body.

The flow path area of the exhaust gas at the upstream end portion of the first expansion chamber Sis set to be 2 times or more the flow path area of the exhaust gas at the downstream end portion of the first exhaust pipeA. Similarly, the flow path area of the exhaust gas at the upstream end portion of the second expansion chamber Sis set to be 2 times or more the flow path area of the exhaust gas at the downstream end portion of the second exhaust pipeB. Hereinafter, the flow path area of the exhaust gas at the downstream end portion of the first exhaust pipeA is appropriately called a downstream end area of the first exhaust pipeA. Similarly, the flow path area of the exhaust gas at the downstream end portion of the second exhaust pipeB is appropriately called a downstream end area of the second exhaust pipeB. The flow path area of the exhaust gas at the downstream end portion of the first exhaust pipeA is the same as the opening area of the downstream open end of the first exhaust pipeA. The flow path area of the exhaust gas at the downstream end portion of the second exhaust pipeB is the same as the opening area of the downstream open end of the second exhaust pipeB.

is a cross-sectional view taken along line VII-VII of. A surface taken along line VII-VII inis a surface along the downstream open ends of the first exhaust pipeA and the second exhaust pipeB. This surface is a surface orthogonal to the flow direction of the exhaust gas at the downstream end portionsA andB of the first exhaust pipeA and the second exhaust pipeB. This surface is a surface orthogonal to the flow direction of the exhaust gas at the upstream end portions of the first expansion chamber Sand the second expansion chamber S. The flow path area of the exhaust gas at the upstream end portion of the first expansion chamber Sis a cross-sectional area of the first expansion chamber Sin the surface according to. Hereinafter, this area is appropriately called an upstream end area of the first expansion chamber S. The flow path area of the exhaust gas at the upstream end portion of the second expansion chamber Sis the cross-sectional area of the second expansion chamber Sin the surface according to. Hereinafter, this area is appropriately called an upstream end area of the second expansion chamber S.

A downstream end area Wof the first exhaust pipeA is expressed as W˜d×d×π/4 using an inner diameter dof the downstream end portionA of the first exhaust pipeA. A downstream end area Wof the second exhaust pipeB is expressed as W˜d×d×π/4 using an inner diameter dof the downstream end portionB of the second exhaust pipeB. As described above, the inner diameter dof the first exhaust pipeA and the inner diameter dof the second exhaust pipeB are the same. The downstream end area Wof the first exhaust pipeA and the downstream end area Wof the second exhaust pipeB are the same. An upstream end area Wof the first expansion chamber Sis expressed as W˜L×Lusing a dimension Lin the radial direction of the case bodyin the cross-section illustrated in. An upstream end area Wof the second expansion chamber Sis expressed as W˜L×L. As described above, in the present embodiment, the relationship between the downstream end area Wof the first exhaust pipeA and the upstream end area Wof the first expansion chamber Sis W≥2×W. The relationship between the downstream end area Wof the second exhaust pipeB and the upstream end area Wof the second expansion chamber Sis W≥2×W.

The first partition portionhas a first outer peripheral wallB. The first outer peripheral wallB extends leftward from the outer peripheral edge of the first partition wallA. The first outer peripheral wallB is joined to the inner peripheral surface of the case bodyby welding or the like. The second partition portionhas a second outer peripheral wallB. The second outer peripheral wallB extends leftward from the outer peripheral edge of the second partition wallA. The second outer peripheral wallB is joined to the inner peripheral surface of the case bodyby welding or the like.

The first partition portionhas a first surrounding wallC. The first surrounding wallC has a cylindrical shape extending along the left-right direction. The first surrounding wallC protrudes leftward from the left side surface of the first partition wallA. The central axis of the first surrounding wallC and the central axis of the case bodysubstantially coincide with each other. The first surrounding wallC is disposed at a position separated from the inner peripheral surface of the case bodytoward the inner peripheral side. The first partition wallA, the first outer peripheral wallB, and the first surrounding wallC are integrally formed with one another.

The second partition portionhas a second surrounding wallC. The second surrounding wallC has a cylindrical shape extending along the left-right direction. The second surrounding wallC protrudes rightward from the right side surface of the second partition wallA. The central axis of the second surrounding wallC and the central axis of the case bodysubstantially coincide with each other. The second surrounding wallC is disposed at a position separated from the inner peripheral surface of the case bodytoward the inner peripheral side. The second partition wallA, the second outer peripheral wallB, and the second surrounding wallC are integrally formed with one another. The second surrounding wallC and the first surrounding wallC are separated from each other in the left-right direction. The first surrounding wallC and the second surrounding wallC correspond to the “surrounding wall” in the present disclosure.

The catalyst bodyis housed in the catalyst chamber S. The catalyst bodyis disposed at the center of the catalyst chamber Sand the housing casein the left-right direction. As illustrated inand the like, the catalyst chamber Sand the catalyst bodyare positioned on the center line XC as viewed along the up-down direction.

The catalyst bodyis supported by the first surrounding wallC and the second surrounding wallC in a posture extending across the first surrounding wallC and the second surrounding wallC.