JP2018119482A - Engine and saddle riding type vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an engine that can supply an appropriate amount of secondary air to an exhaust passage at appropriate timing.SOLUTION: An engine includes a combustion chamber, an exhaust passage, a secondary air passage, an air control device, and a throttle. The exhaust passage is connected to the combustion chamber. The secondary air passage is connected to the exhaust passage, and secondary air to be supplied to the exhaust passage passes therethrough. The air control device includes a valve element for opening/closing the secondary air passage, and is provided in the secondary air passage. The throttle is provided in the secondary air passage. The valve element is a one-way valve for opening/closing the secondary air passage depending on exhaust pressure in the exhaust passage. In the secondary air passage, a flow passage capacity downstream from the throttle is larger than a flow passage capacity from the valve element to the exhaust passage.SELECTED DRAWING: Figure 6

Description

  The present invention relates to an engine and a saddle riding type vehicle.

  Some engines include an exhaust purification device that burns unburned components contained in exhaust gas by introducing secondary air into the exhaust passage. The exhaust purification device includes a secondary air passage connected to the exhaust passage and an air control device that controls the secondary air supplied to the exhaust passage.

  The air control device includes, for example, a valve body that opens and closes a secondary air passage, and the valve body opens the secondary air passage when the exhaust passage side becomes negative pressure. Thereby, secondary air is supplied to the exhaust passage and mixed with the exhaust in the exhaust passage. As a result, unburned components in the exhaust are burned in the exhaust passage, and the exhaust is purified.

Japanese Patent Laid-Open No. 2002-227641

  In order to effectively purify the exhaust, it is important to supply an appropriate amount of secondary air to the exhaust passage at an appropriate timing. For example, if the amount of secondary air is too small, unburned components will not be burned sufficiently, and the CO purification effect will be low. Conversely, if the amount of secondary air is too large, the oxygen component becomes excessive, and the NOx purification effect becomes low.

  In addition, since the valve body of the air control device is opened and closed according to the exhaust pressure pulsation in the exhaust path, the exhaust purification effect is affected by the exhaust pressure pulsation.

  The flow rate of the air passing through the secondary air passage can be set by the inner diameter of the pipe constituting the secondary air passage. However, it is not easy to select a tube so as to obtain a desired purification effect in consideration of various factors as described above.

  Even if the flow rate of the air passing through the secondary air passage is appropriately adjusted, if the valve body is closed before the appropriate amount of secondary air reaches the exhaust passage, the air is supplied to the exhaust passage. Secondary air becomes insufficient. Even in this case, a desired purification effect cannot be obtained.

  An object of the present invention is to provide an engine that can supply an appropriate amount of secondary air to an exhaust passage at an appropriate timing.

  The engine according to the first aspect includes a combustion chamber, an exhaust passage, a secondary air passage, an air control device, and a throttle. The exhaust passage is connected to the combustion chamber. The secondary air passage is connected to the exhaust passage. The secondary air supplied to the exhaust passage passes through the secondary air passage. The air control device includes a valve body that opens and closes the secondary air passage, and is provided in the secondary air passage. The restriction is provided in the secondary air passage. The valve body is a one-way valve that opens and closes the secondary air passage according to the pressure of the exhaust gas in the exhaust passage. In the secondary air passage, the passage volume downstream from the throttle is larger than the passage volume from the valve body to the exhaust passage.

  In the engine according to this aspect, a throttle is provided in the secondary air passage. Therefore, by adjusting the inner diameter of the flow path of the throttle and the arrangement of the throttle in the secondary air passage, an appropriate amount of secondary air can be easily adjusted to obtain a desired purification effect. Further, in the secondary air passage, the passage volume downstream from the throttle is larger than the passage volume from the valve body to the exhaust passage. Therefore, a large amount of secondary air can be secured upstream of the valve body and between the throttle and the valve body. When the secondary air is supplied to the exhaust passage, the pressure of the secondary air upstream of the valve body is higher than the pressure of the secondary air downstream of the valve body. Therefore, when the valve body is opened, an appropriate amount of secondary air can be quickly supplied to the exhaust passage.

  The secondary air passage may include a first passage and a second passage. The first passage may be provided upstream of the air control device in the secondary air passage. The second passage may be provided downstream of the air control device in the secondary air passage. The restriction may be provided in the first passage. In this case, it is possible to avoid the influence on the function of the valve body that occurs when the throttle is provided in the second passage.

  The flow passage cross-sectional area of the throttle may be ½ or less of the flow passage cross-sectional area of the first passage. In this case, the flow rate of the secondary air can be limited to be small by the restriction.

  The flow passage cross-sectional area of the throttle may be ½ or less of the flow passage cross-sectional area of the second passage. In this case, the flow rate of the secondary air can be limited to be small by the restriction.

  The throttle is separate from the secondary air passage and may be attached to the secondary air passage. In this case, the flow rate of the secondary air can be easily adjusted by selecting a throttle having an appropriate flow path cross-sectional area and attaching it to the secondary air passage. As a result, it is possible to easily cope with a desired difference in purification effect or a difference in engine characteristics.

  The secondary air passage may include an air cleaner and a first supply pipe. The first supply pipe may connect an air cleaner and an air control device. The throttle may be provided at a connection portion between the air cleaner and the first supply pipe.

  The air cleaner may include a connection port connected to the first supply pipe. The aperture is separate from the air cleaner and may be attached to the connection port. In this case, the throttle can be easily attached to the secondary air passage.

  The throttle may include a protrusion that protrudes from the first supply pipe toward the inside of the air cleaner. In this case, even if the throttle is removed from the air cleaner together with the first supply pipe, the protrusion is visible from the outside because it protrudes from the first supply pipe. Therefore, the user can notice that the throttle has come out of the air cleaner together with the first supply pipe.

  The engine may further include an intake passage and a pressure transmission pipe. The intake passage may be connected to the combustion chamber. The pressure transmission pipe may transmit the pressure of the intake air in the intake passage to the air control device. The air control device may further include an air cut valve that opens and closes the secondary air passage according to the pressure of the intake air in the intake passage. In the secondary air passage, the passage volume downstream from the throttle may be larger than the passage volume from the air cut valve to the exhaust passage. In this case, a large amount of secondary air can be secured upstream of the air cut valve and between the throttle and the air cut valve.

  In the secondary air passage, the flow volume from the throttle to the valve body may be larger than the flow volume from the valve body to the exhaust passage. In this case, a large amount of secondary air can be secured between the throttle and the valve body. The pressure of the secondary air between the throttle and the valve body is higher than the pressure of the secondary air downstream of the valve body. Therefore, when the valve body is opened, an appropriate amount of secondary air can be quickly supplied to the exhaust passage.

  A straddle-type vehicle according to a second aspect includes the engine described above.

  According to the present invention, in the engine, an appropriate amount of secondary air can be supplied to the exhaust passage at an appropriate timing.

1 is a side view of a saddle riding type vehicle according to an embodiment. It is a side view which shows an engine and an intake system. It is a top view which shows an engine and an intake system. It is a schematic diagram which shows the structure of an engine and an intake system. It is an expanded sectional view of a throttle and a connection port of an air cleaner. It is a schematic diagram which shows the structure of the engine and intake system which concern on other embodiment.

  Hereinafter, a straddle-type vehicle according to an embodiment will be described with reference to the drawings. FIG. 1 is a side view of a saddle riding type vehicle 1 according to the embodiment.

  The saddle riding type vehicle 1 according to the present embodiment is a motorcycle. As shown in FIGS. 1 and 2, the saddle riding type vehicle 1 includes a body frame 2, a fuel tank 3, a seat 4, an engine 5, a steering device 6, a front wheel 7, and a rear wheel 8. Including.

  The vehicle body frame 2 includes a head pipe 11. The head pipe 11 is disposed at the vehicle center in the vehicle width direction and extends forward and downward. A headlight 15 is disposed in front of the head pipe 11. The fuel tank 3 is disposed behind the head pipe 11. The seat 4 is disposed behind the fuel tank 3. In the present embodiment, the front, rear, left, and right directions are directions when viewed from the driver seated on the seat 4.

  The steering device 6 is rotatably supported by the head pipe 11. The steering device 6 includes a steering shaft 12, left and right suspensions 13, and a handle member 14. The steering shaft 12 is inserted into the head pipe 11 and is supported so as to be rotatable with respect to the head pipe 11. The handle member 14 is connected to the steering shaft 12.

  The left and right suspensions 13 extend forward and downward. In FIG. 1, only the left suspension 13 is shown, and the right suspension is omitted. The front wheel 7 is rotatably supported by the left and right suspensions 13. The steering device 6 and the front wheel 7 rotate with respect to the head pipe 11 in accordance with the rotation of the handle member 14 in the left-right direction.

  The rear wheel 8 is supported by the vehicle body frame 2 via the swing arm 16. The rear wheel 8 is rotatably supported with respect to the swing arm 16. The swing arm 16 is swingably attached to the vehicle body frame 2.

  The engine 5 is disposed below the fuel tank 3. The engine 5 is supported by the body frame 2. The engine 5 includes a crankcase 21, a cylinder block 22, a cylinder head 23, and a head cover 24. The cylinder block 22 is connected to the crankcase 21. The cylinder head 23 is connected to the cylinder block 22. The head cover 24 is connected to the cylinder head 23. The cylinder block 22 and the cylinder head 23 are disposed to be inclined upward and forward.

  The “connection” is not limited to direct connection but includes indirect connection. Further, “connection” is not limited to the case where separate members are fixed to each other, but also includes that a plurality of portions are continuous in an integrated member.

  The saddle riding type vehicle 1 includes an exhaust pipe 25 and an intake pipe 26. The exhaust pipe 25 is connected to the cylinder head 23 of the engine 5. The exhaust pipe 25 is bent rearward from the front portion of the cylinder head 23 and is connected to a muffler (not shown). A catalyst 27 is disposed in the exhaust pipe 25. The intake pipe 26 is connected to the cylinder head 23. The intake pipe 26 extends rearward from the rear portion of the cylinder head 23.

  FIG. 2 is a side view showing the engine 5 and the intake system of the engine 5. FIG. 3 is a side view showing the engine 5 and the intake system of the engine 5. FIG. 4 is a schematic diagram showing the configuration of the engine 5 and the intake system of the engine 5. As shown in FIG. 4, the engine 5 includes a combustion chamber 31, an exhaust passage 32, and an intake passage 33. The combustion chamber 31 is disposed in the cylinder head 23. The exhaust passage 32 is connected to the combustion chamber 31. The intake passage 33 is connected to the combustion chamber 31.

  The exhaust passage 32 includes an exhaust port 34 and the exhaust pipe 25 described above. The exhaust port 34 is disposed in the cylinder head 23. The exhaust port 34 is opened and closed by an exhaust valve 35. The exhaust pipe 25 is connected to the exhaust port 34.

  The intake passage 33 includes an intake port 36 and the intake pipe 26 described above. The intake port 36 is disposed in the cylinder head 23. The intake port 36 is opened and closed by an intake valve 37. The intake pipe 26 is connected to the intake port 36. As shown in FIGS. 2 and 3, the intake pipe 26 is connected to an air cleaner 39 via a carburetor 38. The air cleaner 39 is disposed behind the engine 5. The air cleaner 39 is connected to the vaporizer 38 via the duct 40.

  The engine 5 includes an exhaust purification device 41. The exhaust purification device 41 burns unburned components contained in the exhaust by introducing secondary air into the exhaust passage 32. The exhaust purification device 41 includes a secondary air passage 42, an air control device 43, and a pressure transmission pipe 44. The secondary air passage 42 is connected to the exhaust passage 32. The secondary air supplied to the exhaust passage 32 passes through the secondary air passage 42. The secondary air passage 42 includes a first passage 45 and a second passage 46. The first passage 45 is located upstream of the air control device 43 in the secondary air passage 42. The second passage 46 is located downstream of the air control device 43 in the secondary air passage 42.

  The first passage 45 includes an air cleaner 39 and a first supply pipe 47. The first supply pipe 47 is a flexible pipe such as a rubber hose, for example. The first supply pipe 47 connects the air cleaner 39 and the air control device 43. Specifically, the air cleaner 39 includes a main body 391 and a connection port 392. The main body 391 houses a filter (not shown). The connection port 392 protrudes from the main body 391. The first supply pipe 47 is connected to the connection port 392 of the air cleaner 39.

  The second passage 46 includes a second supply pipe 48. The second supply pipe 48 is a flexible pipe such as a rubber hose, for example. The second supply pipe 48 connects the air control device 43 and the exhaust passage 32. Specifically, the engine 5 includes a secondary air inlet 51. The secondary air inlet 51 communicates with the exhaust port 34. As shown in FIG. 2, the secondary air inlet 51 is provided in the cylinder head 23. The second supply pipe 48 is connected to the secondary air inlet 51.

  The first supply pipe 47 may be formed of a flexible material other than rubber. Alternatively, the first supply pipe 47 may be a non-flexible pipe such as a metal pipe. The second supply pipe 48 may be formed of a flexible material other than rubber. Alternatively, the second supply pipe 48 may be a non-flexible pipe such as a metal pipe.

  The air control device 43 is provided in the secondary air passage 42. The air control device 43 opens and closes the secondary air passage 42 in accordance with the exhaust pressure in the exhaust passage 32. The air control device 43 opens and closes the secondary air passage 42 according to the pressure of the intake air in the intake passage 33. As shown in FIG. 2, the air control device 43 is disposed above the engine 5. As shown in FIG. 3, at least a part of the air control device 43 overlaps the engine 5 in plan view. The air control device 43 is disposed behind the front end of the head cover 24. At least a part of the air control device 43 is disposed in front of the rear end of the head cover 24. Although not shown, the air control device 43 is attached to the vehicle body frame 2 via a bracket 49.

  The pressure transmission pipe 44 transmits the pressure of the intake air in the intake passage 33 to the air control device 43. The pressure transmission pipe 44 connects the intake passage 33 and the air control device 43. As shown in FIG. 2, the pressure transmission pipe 44 is connected to the intake pipe 26. The pressure transmission pipe 44 extends upward from the intake pipe 26.

  As shown in FIG. 4, the air control device 43 includes a main body case 61. The main body case 61 includes an inlet pipe 62, an outlet pipe 63, and a first air chamber 64. The inlet pipe 62 and the outlet pipe 63 communicate with the first air chamber 64. A first supply pipe 47 is connected to the inlet pipe 62. A second supply pipe 48 is connected to the outlet pipe 63.

  The air control device 43 includes a reed valve 65. The reed valve 65 is disposed in the first air chamber 64. The reed valve 65 opens and closes the secondary air passage 42 in accordance with the exhaust pressure in the exhaust passage 32. The reed valve 65 is a one-way valve, and allows the flow of air from the inlet pipe 62 to the outlet pipe 63 but restricts the flow of air from the outlet pipe 63 to the inlet pipe 62.

  The reed valve 65 opens and closes the first opening 66 in the first air chamber 64. The reed valve 65 is a leaf spring that functions as a valve body that opens and closes the first opening 66. The first opening 66 is located between the inlet pipe 62 and the outlet pipe 63 in the secondary air passage 42. When negative pressure in the exhaust passage 32 acts on the first air chamber 64 via the second supply pipe 48, the reed valve 65 opens the first opening 66. Thereby, the inlet pipe 62 and the outlet pipe 63 communicate with each other. When positive pressure in the exhaust passage 32 acts on the first air chamber 64 via the second supply pipe 48, the reed valve 65 closes the first opening 66. Thereby, the communication between the inlet pipe 62 and the outlet pipe 63 is blocked.

  The air control device 43 includes an air cut valve 67 and an actuator 68. The air cut valve 67 opens and closes the secondary air passage 42 according to the pressure of the intake air in the intake passage 33. The air cut valve 67 includes a valve body 71 and a valve shaft 72. The valve body 71 opens and closes the second opening 69 of the first air chamber 64. The second opening 69 is located between the inlet pipe 62 and the outlet pipe 63 in the secondary air passage 42. The valve shaft 72 is connected to the valve body 71.

  The actuator 68 includes a diaphragm 73 and a biasing member 74. The main body case 61 includes a second air chamber 75. The diaphragm 73 divides the second air chamber 75 into a first chamber 76 and a second chamber 77. The first chamber 76 communicates with the intake passage 33 via the pressure transmission pipe 44. The pressure of the intake air in the intake passage 33 is introduced into the first chamber 76 during the operation of the engine 5.

  The diaphragm 73 is connected to the valve shaft 72. The urging member 74 urges the diaphragm 73 in the direction in which the valve body 71 opens the second opening 69. The biasing member 74 is, for example, a coil spring.

  The exhaust purification device 41 includes a throttle 78 disposed in the secondary air passage 42. In the secondary air passage 42, the passage volume downstream from the throttle 78 is larger than the passage volume from the reed valve 65 to the exhaust passage 32. In the secondary air passage 42, the passage volume from the throttle 78 to the reed valve 65 is larger than the passage volume from the reed valve 65 to the exhaust passage 32. In the secondary air passage 42, the passage volume downstream from the throttle 78 is larger than the passage volume from the air cut valve 67 to the exhaust passage 32. In the secondary air passage 42, the passage volume from the throttle 78 to the air cut valve 67 is larger than the passage volume from the air cut valve 67 to the exhaust passage 32.

  In the secondary air passage 42, the path length from the throttle 78 to the reed valve 65 is longer than the path length from the reed valve 65 to the exhaust passage 32. In the secondary air passage 42, the path length from the throttle 78 to the air cut valve 67 is longer than the path length from the air cut valve 67 to the exhaust passage 32.

  The diaphragm 78 is disposed in the first passage 45. The throttle 78 is separate from the secondary air passage 42 and is attached to the secondary air passage 42. Specifically, the diaphragm 78 is separate from the air cleaner 39 and is attached to the connection port 392. FIG. 5 is an enlarged cross-sectional view of the aperture 78 and the connection port 392 of the air cleaner 39.

  As shown in FIG. 5, the diaphragm 78 includes a head portion 81, a shaft portion 82, and a protruding portion 83. The outer diameter of the head portion 81 is larger than the inner diameter of the connection port 392. The outer diameter of the head portion 81 is equal to or smaller than the outer diameter of the connection port 392. The head part 81 is in contact with the tip of the connection port 392.

  The shaft portion 82 is inserted into the hole of the connection port 392. The diaphragm 78 includes a hole 84 that passes through the shaft portion 82 and the head portion 81. Preferably, the cross-sectional area of the hole 84 in a plane perpendicular to the axis of the restrictor 78, that is, the cross-sectional area of the flow path of the restrictor 78 is ½ or less of the cross-sectional area of the first passage 45. The channel cross-sectional area of the restriction 78 may be 1/3 or less of the channel cross-sectional area of the first passage 45. The channel cross-sectional area of the restriction 78 may be 1/10 or less of the channel cross-sectional area of the first passage 45.

  Preferably, the flow passage cross-sectional area of the restriction 78 is not more than ½ of the flow passage cross-sectional area of the second passage 46. The channel cross-sectional area of the restriction 78 may be 1/3 or less of the channel cross-sectional area of the second passage 46. The channel cross-sectional area of the restriction 78 may be 1/10 or less of the channel cross-sectional area of the second passage 46.

  The channel cross-sectional area of the restriction 78 may be ½ or less of the channel cross-sectional area of the connection port 392. The channel cross-sectional area of the restriction 78 may be 1/3 or less of the channel cross-sectional area of the connection port 392. The channel cross-sectional area of the restriction 78 may be 1/10 or less of the channel cross-sectional area of the connection port 392.

  In the axial direction of the diaphragm 78, the shaft portion 82 and the protruding portion 83 are longer than the connection port 392. Accordingly, the protruding portion 83 protrudes from the first supply pipe 47 toward the inside of the air cleaner 39. The outer diameter of the protrusion 83 is larger than the inner diameter of the connection port 392.

  Next, the operation of the exhaust purification device 41 according to this embodiment will be described. During the operation of the engine 5, pulsation occurs in the exhaust pressure in the exhaust passage 32. When the negative pressure in the exhaust passage 32 is transmitted to the reed valve 65 of the air control device 43 via the second supply pipe 48, the reed valve 65 is opened. Thus, outside air is introduced into the exhaust passage 32 via the air cleaner 39, the first supply pipe 47, the air control device 43, and the second supply pipe 48. As a result, combustion of unburned components in the exhaust is promoted in the exhaust passage 32, and the exhaust is purified. When the absolute value of the negative pressure in the exhaust passage 32 falls below a predetermined value, the reed valve 65 is closed. Thereby, the backflow of the exhaust gas in the secondary air passage 42 is prevented.

  Further, when the throttle valve of the carburetor 38 is rapidly throttled during sudden deceleration, negative pressure is generated in the intake passage 33. In this case, the diaphragm 73 is deformed toward the first chamber 76 against the urging force of the urging member 74, whereby the air cut valve 67 is closed.

  If the throttle valve of the carburetor 38 is rapidly throttled, the flow rate of intake air increases, and the amount of fuel sucked out increases. In that case, the air-fuel mixture may be temporarily excessively rich, misfiring may occur in the combustion chamber 3135, and a large amount of unburned air-fuel mixture may be discharged into the exhaust passage 32. At this time, when secondary air is injected into the exhaust passage 32, so-called afterburn occurs in which the unburned air-fuel mixture becomes an appropriate air-fuel ratio by mixing with the secondary air and burns explosively.

  However, in the engine 5 according to the present embodiment, the supply of secondary air into the exhaust passage 32 is stopped by closing the air cut valve 67 during sudden deceleration. Thereby, the occurrence of afterburning can be prevented.

  In the engine 5 according to this aspect described above, the throttle 78 is provided in the secondary air passage 42. Therefore, by adjusting the inner diameter of the flow path of the throttle 78 and the arrangement of the throttle 78 in the secondary air passage 42, it is possible to easily adjust the amount of secondary air suitable for obtaining a desired purification effect. it can.

  Further, noise may occur due to pressure pulsation in the exhaust passage 32 and the natural frequencies of the first supply pipe 47, the air control device 43, and the second supply pipe 48. In the engine 5 according to this aspect, the noise characteristics can be improved by adjusting the inner diameter of the flow path of the throttle 78 and the arrangement of the throttle 78 in the secondary air passage 42 according to the natural frequency.

  In the secondary air passage 42, the passage volume downstream from the throttle 78 is larger than the passage volume from the reed valve 65 to the exhaust passage 32. Therefore, a large amount of secondary air can be secured upstream of the reed valve 65 and between the throttle 78 and the reed valve 65. When secondary air is supplied to the exhaust passage 32, the pressure of secondary air upstream of the reed valve 65 is higher than the pressure of secondary air downstream of the reed valve 65. Therefore, when the reed valve 65 is opened, an appropriate amount of secondary air can be quickly supplied to the exhaust passage 32.

  The diaphragm 78 is disposed in the first passage 45. Therefore, it is possible to avoid the influence on the function of the reed valve 65 that occurs when the throttle 78 is disposed in the second passage 46. For example, if the throttle 78 is disposed downstream of the reed valve 65, the opening / closing operation of the reed valve 65 due to pressure pulsation in the exhaust passage 32 may be affected. However, by arranging the throttle 78 in the first passage 45, it is possible to suppress such an influence on the opening / closing operation of the reed valve 65.

  The throttle 78 is separate from the secondary air passage 42 and is attached to the secondary air passage 42. Therefore, the flow rate of the secondary air can be easily adjusted by selecting the throttle 78 having an appropriate flow path cross-sectional area and attaching it to the secondary air passage 42. Thereby, it is possible to easily cope with a desired difference in purification effect or a difference in characteristics of the engine 5.

  As described above, in order to appropriately adjust the amount of secondary air in order to obtain a desired purification effect, high-precision processing is required when forming a hole in the throttle 78. Therefore, when the hole of the connection port 392 of the air cleaner 39 is narrowed and used as an aperture, it is necessary to process the connection port 392 of the air cleaner 39 with high accuracy, which is not easy.

  In contrast, in the present embodiment, the diaphragm 78 is a separate body from the air cleaner 39 and is attached to the connection port 392 of the air cleaner 39. Therefore, by attaching the pre-processed throttle 78 to the connection port 392 of the air cleaner 39, it is possible to easily provide the secondary air passage 42 with a hole having an arbitrary flow path cross-sectional area.

  The restrictor 78 includes a protrusion 83 that protrudes from the first supply pipe 47 toward the inside of the air cleaner 39. Therefore, even if the restrictor 78 comes out of the air cleaner 39 together with the first supply pipe 47, it can be visually recognized from the outside because the protruding portion 83 comes out of the first supply pipe 47. Accordingly, the user can notice that the throttle 78 has been removed from the air cleaner 39 together with the first supply pipe 47.

  As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the summary of invention.

  The straddle-type vehicle is not limited to a motorcycle, and may be other types of vehicles such as a rough terrain vehicle (ALL-TERRAIN VEHICLE) or a snowmobile. The motorcycle is not limited to a sports type vehicle as in the above embodiment, but may be a scooter or a moped. The number of front wheels may be two or more. Alternatively, the number of rear wheels may be two or more.

  The configuration of the air control device 43 may be changed. For example, in the air control device 43, a valve body different from the reed valve 65 may be used. The structure of the air cut valve 67 may be changed. Alternatively, the air cut valve 67 may be omitted.

  The position and structure of the diaphragm 78 may be changed. For example, the diaphragm 78 may be disposed in the first supply pipe 47. The restrictor 78 may be disposed in the second passage 46. The restrictor 78 may be disposed in the second supply pipe 48. The restrictor 78 may be disposed in the air control device 43.

  The restrictor 78 may be formed integrally with the secondary air passage 42. For example, the diaphragm 78 may be formed integrally with the air cleaner 39. The restrictor 78 may be formed integrally with the first supply pipe 47. The restrictor 78 may be formed integrally with the second supply pipe 48. The restrictor 78 may be formed integrally with the air control device 43.

  In the secondary air passage 42, the path length from the throttle 78 to the reed valve 65 may be shorter than the path length from the reed valve 65 to the exhaust passage 32. Alternatively, the path length from the throttle 78 to the air cut valve 67 in the secondary air passage 42 may be shorter than the path length from the air cut valve 67 to the exhaust passage 32. Even in such a case, the air chamber 85 is connected between the throttle 78 and the reed valve 65 in the secondary air passage 42 as shown in FIG. Can be made larger than the channel volume from the reed valve 65 to the exhaust passage 32. Alternatively, the flow volume from the throttle 78 to the air cut valve 67 can be made larger than the flow volume from the air cut valve 67 to the exhaust passage 32 by the air chamber 85.

  According to the present invention, in the engine, an appropriate amount of secondary air can be supplied to the exhaust passage at an appropriate timing.

31 Combustion chamber 32 Exhaust passage 42 Secondary air passage 65 Reed valve 43 Air control device 78 Restriction 45 First passage 46 Second passage 39 Air cleaner 47 First supply pipe 392 Connection port 83 Projection portion 33 Intake passage 44 Pressure transmission pipe 67 Air Cut valve

Claims (11)

A combustion chamber;
An exhaust passage connected to the combustion chamber;
A secondary air passage connected to the exhaust passage and through which secondary air supplied to the exhaust passage passes;
An air control device including a valve body for opening and closing the secondary air passage, and provided in the secondary air passage;
A throttle provided in the secondary air passage;
With
The valve body is a one-way valve that opens and closes the secondary air passage according to the pressure of exhaust gas in the exhaust passage,
In the secondary air passage, the flow passage volume downstream from the throttle is larger than the flow passage volume from the valve body to the exhaust passage,
engine. The secondary air passage is
A first passage provided upstream of the air control device in the secondary air passage;
A second passage provided downstream of the air control device in the secondary air passage;
Including
The throttle is provided in the first passage,
The engine according to claim 1. The flow passage cross-sectional area of the throttle is ½ or less of the flow passage cross-sectional area of the first passage.
The engine according to claim 2. The flow passage cross-sectional area of the throttle is ½ or less of the flow passage cross-sectional area of the second passage.
The engine according to claim 2 or 3. The throttle is separate from the secondary air passage, and is attached to the secondary air passage.
The engine according to any one of claims 1 to 4. The secondary air passage is
An air cleaner,
A first supply pipe connecting the air cleaner and the air control device;
Including
The throttle is provided at a connection portion between the air cleaner and the first supply pipe.
The engine according to any one of claims 1 to 5. The air cleaner includes a connection port connected to the first supply pipe,
The aperture is separate from the air cleaner and is attached to the connection port.
The engine according to claim 6. The throttle includes a protruding portion that protrudes from the first supply pipe toward the inside of the air cleaner.
The engine according to claim 7. An intake passage connected to the combustion chamber;
A pressure transmission pipe for transmitting the pressure of the intake air in the intake passage to the air control device;
Further comprising
The air control device further includes an air cut valve that opens and closes the secondary air passage according to the pressure of intake air in the intake passage,
In the secondary air passage, the flow passage volume downstream from the throttle is larger than the flow passage volume from the air cut valve to the exhaust passage,
The engine according to any one of claims 1 to 8. In the secondary air passage, a passage volume from the throttle to the valve body is larger than a passage volume from the valve body to the exhaust passage.
The engine according to any one of claims 1 to 9. A straddle-type vehicle comprising the engine according to any one of claims 1 to 10.

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