JP5446919B2 - 4 cycle engine decompression device - Google Patents

Description

  The present invention relates to a 4-cycle engine decompression device (decompression; hereinafter simply referred to as decompression) provided in a valve operating device for a 4-cycle engine.

  2. Description of the Related Art Conventionally, a four-cycle engine (internal combustion engine) including a double overhead camshaft (DOHC: Double Over Camshaft) valve operating device is known. Further, a four-cycle engine including a decompression device that improves the startability by reducing the pressure in the combustion chamber (close to atmospheric pressure) is known (see, for example, Patent Document 1).

  FIG. 9 is a partial cross-sectional view showing an example of a cylinder head and a valve operating mechanism of a 4-cycle DOHC type engine. FIG. 9 is a view showing a valve operating mechanism on the exhaust valve side. FIG. 9 is a view showing the decompression device in a state where the exhaust camshaft is rotating during normal operation of the engine, and shows a non-operating state of the decompression device.

  The cylinder head 102 of the engine 101 includes a DOHC type valve gear 103, an intake valve (not shown) and an exhaust valve 104 that are opened and closed by the valve gear 103.

  The valve gear 103 is integrated with an intake side camshaft (not shown) and an exhaust side camshaft 105 to which rotation of a crankshaft (not shown) is transmitted via a timing chain (not shown) and the like. Are provided with two intake side cams (not shown) and two exhaust side cams 108 formed integrally with the exhaust side camshaft 105.

  The intake valve and the exhaust valve 104 are opened and closed according to the respective cam profiles of the intake side cam rotated integrally with the intake side camshaft or the exhaust side cam 108 rotated integrally with the exhaust side camshaft 105.

  The exhaust side camshaft 105 includes a decompression cam shaft storage portion 109 and a centrifugal weight type decompression device 111. The decompression cam shaft storage portion 109 is formed to be recessed in the peripheral surface of the exhaust camshaft 105.

  The decompression device 111 includes a decompression cam 112 formed in a half-moon shape as viewed in the axial direction of the exhaust-side camshaft 105, a decompression cam shaft 113 in which the decompression cam 112 is integrally formed at one end, and the other of the decompression cam shaft 113. And a return spring 115 that urges the decompression arm 114 in a direction against the centrifugal force generated by the rotation of the exhaust camshaft 105.

  The decompression cam shaft 113 is disposed in the decompression cam shaft housing portion 109 and is rotatably supported. The decompression cam 112 has a half-moon shaped arc portion and a chord portion as the decompression cam shaft 113 rotates, and the arc portion protrudes from the decompression cam shaft housing portion 109 or is housed in the decompression cam shaft housing portion 109. The

As shown in FIGS. 9 and 11, the decompression arm 114 has a center of gravity located on the radially outer side with respect to the axial center O0 of the exhaust-side camshaft 105 and the axial center of the decompression camshaft 113. The decompression arm 114 is moved in the opening operation direction Y0 in which the center of gravity of the decompression arm 114 is separated from the axis O0 of the exhaust side camshaft 105 while being centered on the axis of the decompression camshaft 113 due to the centrifugal force caused by the rotation of the exhaust side camshaft 105. It is swung. The decompression device 111 rotates the decompression cam shaft 113 by the swinging of the decompression arm 114 so that the arc portion of the decompression cam 112 is accommodated in the decompression cam shaft accommodating portion 109.

  The return spring 115 restricts the swinging of the decompression arm 114 in the opening operation direction Y0 until the rotational speed of the exhaust camshaft 105 (the rotational speed per unit time) exceeds a predetermined magnitude. Further, the return spring 115 causes the decompression arm 114 to swing in the closing operation direction X0 so that the center of gravity of the decompression arm 114 approaches the axis O0 of the exhaust camshaft 105.

  10 and 11 are diagrams showing the relationship between the exhaust cam 108 and the decompression device 111 when the exhaust camshaft 105 is stopped or rotating at an extremely low speed, and shows the operating state of the decompression device 111. ing.

  As shown in FIGS. 10 and 11, in a state where the engine 101 is stopped, the decompression device 111 positions the center of gravity of the decompression arm 114 close to the axis O <b> 0 of the exhaust camshaft 105. At this time, the decompression device 111 causes the arc portion of the decompression cam 112 to protrude from the decompression cam shaft storage portion 109. In this state, the arc portion of the decompression cam 112 protrudes radially outward from the base circle of the cam profile of the exhaust cam 108. The protruding arc portion of the decompression cam 112 lifts the exhaust valve 104 by a small amount to open the exhaust valve 104 to reduce (decompress) compression in the combustion chamber when the engine 101 is started. In this way, the decompression device 111 facilitates starting of the engine 101.

  Here, the rotation direction of the exhaust side camshaft 105 is indicated by an arrow Z0. Further, the rotation direction of the decompression cam shaft 113 for projecting the arc portion of the decompression cam 112 is indicated by α0, and the rotation direction of the decompression cam shaft 113 for accommodating the arc portion of the decompression cam 112 is indicated by β0.

  As shown in FIG. 12, when the engine 101 is started and the exhaust camshaft 105 reaches a predetermined rotational speed, for example, an idling rotational speed, the decompression device 111 swings the decompression arm 114 in the opening operation direction Y0. Accordingly, the decompression device 111 accommodates the arc portion of the decompression cam 112 in the decompression cam shaft accommodation portion 109. In this state, the arc portion of the decompression cam 112 is accommodated radially inward from the base circle of the cam profile of the exhaust cam 108. As a result, the decompression device 111 does not hinder normal operation of the engine 101.

  As shown in FIG. 13, in the decompression device 111, the centrifugal force acting on the decompression arm 114 decreases as the rotational speed of the exhaust camshaft 105 decreases, and the decompression arm 114 is closed by the urging force of the return spring 115. Swing to X0. As a result, the arc portion of the decompression cam 112 projects from the decompression cam shaft housing 109 and projects radially outward from the base circle of the cam profile of the exhaust side cam 108. For this reason, the protruding arc portion of the decompression cam 112 opens the exhaust valve 104 slightly in the compression process when the engine 101 is started to reduce the compression in the combustion chamber (decompression), thereby facilitating the start of the engine 101. .

JP 2003-254025 A

  In the decompression device 111 as described above, as shown in FIG. 11, in the decompression operation state in which the arc portion of the decompression cam 112 protrudes, the frictional force F0 when the arc portion of the decompression cam 112 comes into contact with the tappet 117 is The rotational direction α0 of the decompression cam shaft 113 for projecting the arc portion of the decompression cam 112 is set to be opposite to the rotational direction Z0 of the exhaust camshaft 105 so as to act in the direction in which the exhaust camshaft 112 projects.

  Further, since the decompression arm 114 is integrally formed with the decompression cam shaft 113, the swinging direction of the decompression arm 114 inevitably follows the rotation direction of the decompression cam shaft 113 for projecting or storing the arc portion of the decompression cam 112. Direction. That is, the closing operation direction X0 of the decompression arm 114 for projecting the arc portion of the decompression cam 112 is set in a direction opposite to the rotation direction Z0 of the exhaust camshaft 105, and the opening of the decompression arm 114 for accommodating the arc portion of the decompression cam 112 is performed. The operation direction Y0 is set in the same direction as the rotation direction Z0 of the exhaust side camshaft 105.

  Further, when the engine 101 is stopped from the operating state (see FIG. 12), the engine 101 decelerates. At this time, the inertial force acting on the decompression arm 114 acts in the rotation direction Z0 of the exhaust camshaft 105, and the decompression arm 114 acts in the opening operation direction Y0. Therefore, even when the rotational speed of the engine 101 is reduced to a speed at which the centrifugal force acting on the decompression arm 114 falls below the biasing force of the return spring 115, the inertial force works in a direction to cancel the biasing force of the return spring 115. Therefore, the closing operation of the decompression arm 114 is inhibited, and a response delay occurs in the projecting operation (decompression operation) of the arc portion of the decompression cam 112 when the engine 101 stops.

  For this reason, as shown in FIG. 14, when the engine 101 stops with the arc portion of the decompression cam 112 in contact with the tappet 117, the inertial force disappears, and the arc portion of the decompression cam 112 is moved by the biasing force of the return spring 115. Even when trying to project, the urging force of the valve spring 116 is larger than the urging force of the return spring 115, so that the arc portion of the decompression cam 112 may not be projected. In this case, the compression in the combustion chamber is not reduced at the subsequent startup of the engine 101, and the engine 101 becomes difficult to start.

  The object of the present invention has been made in consideration of the above-described circumstances, and is a four-cycle engine capable of improving the responsiveness of the decompression operation to execute the decompression operation quickly and reliably and improving the startability of the engine. It is to provide a decompression device.

The present invention is provided on a camshaft supported by a cylinder head and provided with an exhaust side cam, a decompression camshaft extending in the axial direction and housed rotatably, and one end of the decompression camshaft, A decompression cam integrally provided with a circular arc portion and a chord portion that can project or be accommodated with respect to the base circle of the exhaust side cam, and the decompression cam shaft rotates by the action of centrifugal force caused by the rotation of the cam shaft. A decompression arm that houses the decompression cam, and a return arm that biases the decompression arm in a direction against the centrifugal force to close the decompression arm, and rotates the decompression cam shaft to project the decompression cam. A four-cycle engine having a spring and opening the exhaust valve by a decompression operation for projecting the decompression cam to decompress the combustion chamber. In Comp device, decompressing arm to the opening and closing operation is formed in a front view C-shape, is swingably supported attachment of the end of the exhaust camshaft as a swing center, the axis of the exhaust camshaft The center of gravity of the decompression arm is separated from the axis of the exhaust camshaft, with the center of gravity being located radially outward relative to the center, and the center of the rocking center as a result of the centrifugal force associated with the rotation of the exhaust camshaft. The decompression arm swings in the direction to store the arc portion and the string portion of the decompression cam inside the base circle of the exhaust side cam, while the decompression arm and the decompression cam shaft are connected to the decompression arm. The pin and the engaging groove are connected to each other through an engaging member including an engaging groove formed on the decompression cam shaft. It is arranged between the axis of the decompression cam shaft, and the swing direction of the decompression arm and the rotation direction of the decompression cam shaft are set in opposite directions and the arc portion of the decompression cam protrudes during the closing operation of the decompression arm Inertia that acts on the decompression arm in addition to the urging force of the return spring when the engine is decelerated to stop the engine by setting the direction of rotation of the decompression cam shaft to the direction opposite to the direction of rotation of the exhaust camshaft. Friction force received from the exhaust side tappet by force is applied in a direction in which the arc portion and the string portion of the decompression cam protrude .

  According to the present invention, the opening operation direction of the decompression arm is set in the opposite direction to the rotation direction of the camshaft, that is, the closing operation direction of the decompression arm is set in the same direction as the rotation direction of the camshaft, so the engine stops. Inertia force acting on the decompression arm in the rotational direction of the camshaft acts in the closing operation direction of the decompression arm. For this reason, the decompression arm is quickly closed by the inertia force and the urging force of the return spring to cause the decompression cam to protrude early, so that the responsiveness of the decompression operation can be improved. As a result, the decompression operation can be executed quickly and reliably, and the startability of the engine can be improved.

1 is a left side view showing a motorcycle equipped with an engine to which an embodiment of a decompression device for a four-cycle engine according to the present invention is applied. Sectional drawing which shows the valve operating apparatus in the engine of FIG. 1 with a cylinder head. Sectional drawing which shows the cam sprocket and decompression apparatus of the valve operating apparatus in the engine of FIG. 1 with a cylinder head. Sectional drawing which follows the IV-IV line of FIG. The decompression operation state of the decompression device of Drawing 4 is shown, (A) and (B) are sectional views in alignment with a VA-VA line in Drawing 4, and a VB arrow line view, respectively. FIG. 5 shows an intermediate state (decompression intermediate state) between a decompression operation state and a decompression non-operation state in the decompression device of FIG. 4, and FIGS. 5A and 5B correspond to FIGS. 5A and 5B, respectively. The decompression non-operation state in the decompression device of Drawing 4 is shown, and (A) and (B) are figures corresponding to Drawing 5 (A) and (B), respectively. The disassembled perspective view of the decompression apparatus of FIG. Sectional drawing which shows the decompression | non-operation state in the decompression apparatus of the conventional 4 cycle engine. Sectional drawing which shows the decompression operation state of the decompression apparatus of FIG. XI arrow line view of FIG. Explanatory drawing which shows the decompression | non-operation state in the decompression apparatus of FIG.9 and FIG.10. Explanatory drawing which shows the decompression operation state of the decompression apparatus in FIG.9 and FIG.10. Explanatory drawing in order to demonstrate the malfunction which arose in the decompression apparatus of FIG.9 and FIG.10.

  The best mode for carrying out the present invention will be described below with reference to the drawings. However, the present invention is not limited to these embodiments.

  As shown in FIG. 1, the motorcycle 1 includes a body frame 2 constituting a framework. The vehicle body frame 2 includes a head pipe 3 installed on the front side, a pair of left and right main frames 4 extending from the head pipe 3 obliquely downward to the rear side, and extending downward from the head pipe 3. Down tube 5, a pair of left and right lower tubes 7 connected to the lower end of the down tube 5 and extending rearward, and connected to the rear end of the main frame 4 and connected to the rear end of the lower tube 7 The pivot frame 8 is provided.

  The head pipe 3 pivotally supports a steering mechanism 11 disposed on the front side of the vehicle body frame 2. The steering mechanism 11 is pivotally supported with respect to the vehicle body frame 2 so as to be rotatable in the left-right direction. The steering mechanism 11 includes a steering head 12 pivotally supported on the head pipe 3, a pair of left and right front forks 13 provided on the steering head 12, and a shaft supported rotatably on the lower portion of the front fork 13. A front fender 15 that is provided on the front fork 13 and covers the top of the front wheel 14, and a handlebar 17 that is provided above the steering head 12. The steering mechanism 11 rotates the front wheel 14 left and right by a steering force applied to the handlebar 17.

  The pair of left and right pivot frames 8 pivotally support a rear wheel suspension device 18 disposed on the rear side of the vehicle body frame 2 so as to be swingable in the vertical direction of the vehicle body frame 2. The rear wheel suspension device 18 is pivotally attached to a pivot shaft 19 installed on the lower end portion of the pivot frame 8. The rear wheel suspension device 18 includes a swing arm 21 having a front end pivotally attached to a pivot shaft 19 and a suspension 23 that elastically supports the swing arm 21 on the vehicle body frame 2. A rear wheel 22 is rotatably supported at the rear end of the swing arm 21.

  The motorcycle 1 includes an engine 26 in a space surrounded by the main frame 4, the down tube 5, the lower tube 7, and the pivot frame 8. The engine 26 is a four-cycle engine provided with a cylinder head 27 having a DOHC valve gear 50 (FIG. 2). An exhaust pipe 28 is connected to the engine 26. The exhaust pipe 28 extends around the right side of the engine 26 and extends behind the vehicle body frame 2. The rear end of the exhaust pipe 28 is connected to an exhaust muffler 29. The power of the engine 26 is transmitted to the rear wheel 22 via a drive sprocket (not shown), a chain 31, and a driven sprocket 32 in order.

  The motorcycle 1 further includes a fuel tank 33 disposed above the engine 26, a rider's seat 35 disposed behind the fuel tank 33, and a rear portion covering the lower and rear portions of the seat 35. A frame cover 36 and a rear fender 37 extending from the rear portion of the seating seat 35 toward the rear of the vehicle body frame 2 and covering the upper portion of the rear wheel 22 are provided.

  As shown in FIG. 2, the cylinder head 27 of the engine 26 communicates with a combustion chamber 39 formed between the cylinder block 38, two intake ports 40 communicated with the combustion chamber 39, and the combustion chamber 39. Two exhaust ports 41. The intake port 40 and the exhaust port 41 are provided with valve seats 42 and 43 at the connection portions with the combustion chamber 39, respectively.

  Further, the cylinder head 27 is a DOHC type that opens and closes two intake valves 44 provided in the intake port 40, two exhaust valves 47 provided in the exhaust port 41, and each of the intake valve 44 and the exhaust valve 47. A valve gear 50 is provided.

  The intake valve 44 opens and closes the intake port 40. The intake valve 44 includes an umbrella-shaped valve body 45 and a valve stem 46 extending substantially upward from the valve body 45. On the other hand, the cylinder head 27 includes a stem guide 51 into which the valve stem 46 is slidably inserted. The exhaust valve 47 opens and closes the exhaust port 41. The exhaust valve 47 includes an umbrella-shaped valve body 48 and a valve stem 49 extending substantially upward from the valve body 48. On the other hand, the cylinder head 27 includes a stem guide 52 into which the valve stem 49 is slidably inserted. When the cylinder head 27 is viewed from the side, the intake valve 44 and the exhaust valve 47 are disposed such that the valve stems 46 and 49 are substantially V-shaped.

  The valve gear 50 includes an intake side camshaft 54 rotatably supported by the cylinder head 27, two intake side cams 55 provided on the intake side camshaft 54, and a cam profile of the intake side cam 55. Accordingly, an intake side tappet 56 that lifts the intake valve 44 and an intake side valve spring 57 that biases the intake valve 44 in the closing direction are provided. Further, as shown in FIGS. 2 and 4, the valve operating apparatus 50 includes an exhaust side camshaft 61 rotatably supported by the cylinder head 27 and two exhaust side cams provided on the exhaust side camshaft 61. The cam 62 includes an exhaust side tappet 63 that lifts the exhaust valve 47 according to the cam profile of the exhaust side cam 62, and an exhaust side valve spring 64 that biases the exhaust valve 47 in the closing direction.

  The intake side camshaft 54 shown in FIG. 2 is positioned above the intake valve 44 and is rotatably supported by the cylinder head 27 and the head cover 66. The axis of the intake camshaft 54 is disposed on a substantially extended line of the valve stem 46 of the intake valve 44. The intake side cam 55 is formed integrally with the intake side camshaft 54. The intake side cam 55 is provided at an appropriate position where each intake valve 44 can be lifted. The intake side tappet 56 is sandwiched between the intake valve 44 and the intake side cam 55, and converts the rotational motion of the intake side cam 55 into the reciprocating motion of the intake valve 44.

  The intake side valve spring 57 is provided between a spring retainer 68 provided at the upper end of the valve stem 46 and a spring seat 71 loosely fitted to the stem guide 51. The intake side valve spring 57 urges the intake valve 44 in a closing direction via a spring retainer 68. The valve body 45 of the intake valve 44 is pressed against the valve seat 42 by the urging force of the intake side valve spring 57 to close the intake port 40.

  As shown in FIGS. 2 and 4, the exhaust camshaft 61 is positioned above the exhaust valve 47 and is rotatably supported by the cylinder head 27 and the head cover 66. The axial center of the exhaust camshaft 61 is disposed on a substantially extended line of the valve stem 49 of the exhaust valve 47. The intake-side camshaft 54 and the exhaust-side camshaft 61 are arranged so that their axial centers are substantially parallel.

  The exhaust side cam 62 is formed integrally with the exhaust side cam shaft 61. Further, the exhaust side cams 62 are provided at appropriate positions where the respective exhaust valves 47 can be lifted. The exhaust side tappet 63 is sandwiched between the exhaust valve 47 and the exhaust side cam 62, and converts the rotational motion of the exhaust side cam 62 into the reciprocating motion of the exhaust valve 47.

  The exhaust side valve spring 64 is provided between a spring retainer 72 provided at the upper end portion of the valve stem 49 and a spring seat 73 loosely fitted to the stem guide 52. The exhaust side valve spring 64 biases the exhaust valve 47 in the closing direction via the spring retainer 72. The valve body 48 of the exhaust valve 47 is pressed against the valve seat 43 by the urging force of the exhaust side valve spring 64 to close the exhaust port 41.

  The valve operating device 50 rotates the intake side camshaft 54 and the intake side cam 55 together to open and close the intake valve 44 via the intake side tappet 56. Further, the valve gear 50 rotates the exhaust side camshaft 61 and the exhaust side cam 62 integrally to open and close the exhaust valve 47 via the exhaust side tappet 63.

  The valve operating apparatus 50 according to the present embodiment is a so-called direct hitting type in which the intake valve 44 and the exhaust valve 47 are directly driven via the intake side tappet 56 and the exhaust side tappet 63, but is not limited thereto. A rocker arm type may be used.

  As shown in FIGS. 3 and 4, the intake side camshaft 54 and the exhaust side camshaft 61 of the engine 26 include cam sprockets 74 and 75 at one end. These cam sprockets 74 and 75 are connected via a cam chain 76 to a cam drive sprocket (not shown) provided on a crankshaft (not shown). The rotation of the crankshaft accompanying the operation of the engine 26 is transmitted to the valve operating device 50, specifically, the intake side camshaft 54 and the exhaust side camshaft 61 via a cam chain or the like, and the intake valve 44 and the exhaust valve 47 are passed through. Open and close.

  Here, the rotation direction of the exhaust camshaft 61 is the direction in which the cam sprocket 75 is rotated from the crankshaft of the engine 26 in the steady operation state via the cam chain 76 (solid arrow R in FIG. 3).

  As shown in FIGS. 3, 4, and 8, the valve gear 50 as described above includes a centrifugal decompression device 80 at the end of the exhaust camshaft 61 on the cam sprocket 75 side. The decompression device 80 includes a decompression cam shaft 81, a decompression cam 82, a decompression arm 83, a return spring 84, and an engagement member 85, and opens the exhaust valve 47 by a decompression operation that causes the decompression cam 82 to project when the engine 26 is started. It is made to valve and the combustion chamber 39 is pressure-reduced.

  Here, the exhaust camshaft 61 is pivotally supported by the cylinder head 27 via a ball bearing 77 on the cam sprocket 75 side and between the two exhaust cams 62 via a slide bearing 78. In addition, the exhaust camshaft 61 is partially recessed to form a decompression camshaft storage portion 79. The decompression camshaft storage portion 79 extends along the axial direction of the exhaust camshaft 61 in a region from the vicinity of the exhaust cam 62 on the cam sprocket 75 side to the end of the exhaust camshaft 61 where the cam sprocket 75 is provided. It is formed.

  The decompression camshaft 81 passes through the cam sprocket 75 and reaches the decompression camshaft housing portion 79 of the exhaust camshaft 61, and the exhaust camshaft 81 is located in the region where the tip of the decompression camshaft 81 approaches the exhaust cam 62 on the cam sprocket 75 side. 61 extends in the axial direction and is accommodated in the decompression cam shaft accommodating portion 79. Further, the decompression cam shaft 81 is rotatably supported in the decompression cam shaft housing portion 79 by the exhaust side cam shaft 61 and the ball bearing 77.

  The decompression cam 82 is provided integrally with the distal end portion of the decompression cam shaft 81, and is composed of a half-moon arc portion 82A and a chord portion 82B as viewed in the axial direction. As shown in FIGS. 5 to 7, the arc portion 82 </ b> A of the decompression cam 82 is provided so as to protrude or be accommodated in the radial direction with respect to the base circle 86 of the exhaust camshaft 62. The arc portion 82A of the decompression cam 82 protrudes from the base circle 86 of the exhaust side camshaft 62, so that the exhaust valve 47 is slightly lifted in a section where the valve lift amount in the cam profile of the exhaust side cam 62 becomes zero. 39 can be decompressed.

  The decompression arm 83 is configured separately from the decompression cam shaft 81 and swings to the end of the exhaust camshaft 61 and the cam sprocket 75 by a bolt 88 through a spacer 87 as shown in FIGS. It is pivotally supported. The decompression arm 83 is formed in a U-shape when viewed from the front, and has a center of gravity located radially outward with respect to the axis O of the exhaust side camshaft 61 as shown in FIGS. Therefore, the decompression arm 83 swings in the direction in which the center of gravity of the decompression arm 83 separates from the axis O of the exhaust side camshaft 61 as a center of the spacer 87 by the action of centrifugal force accompanying the rotation of the exhaust side camshaft 61. Perform opening operation.

  This opening operation direction is indicated by an arrow Y in FIG. Further, the center of swing of the decompression arm 83, that is, the center of the spacer 87 is indicated by the symbol P. The decompression arm 83 and the decompression cam shaft 81 are interlocked and connected using an engaging member 85 described in detail later, and the decompression cam shaft 81 is rotated by the opening operation of the decompression arm 83, and the arc portion 82A of the decompression cam 82 is exhausted. The side cam 62 is positioned in the radially inner storage position with respect to the base circle 86.

  As shown in FIGS. 4 and 8, the return spring 84 urges the decompression arm 83 in a direction against the centrifugal force generated by the rotation of the decompression arm 83. Accordingly, the return spring 84 restricts the swing of the decompression arm 83 until the rotational speed of the exhaust camshaft 61 (the rotational speed per unit time) exceeds a predetermined magnitude. Further, the urging force of the return spring 84 causes the decompression arm 83 to perform a closing operation that swings the center of gravity of the decompression arm 83 in a direction to approach the axis O of the exhaust camshaft 61.

  The closing operation direction of the decompression arm 83 is opposite to the opening operation direction Y of the decompression arm 83 described above, and is indicated by an arrow X in FIG. By the closing operation of the decompression arm 83, the decompression cam shaft 81 rotates in conjunction with the engaging member 85, and the arc portion 82A of the decompression cam 82 protrudes radially outward from the base circle 86 of the exhaust side cam 62. Position.

  As shown in FIGS. 4 and 8, the engaging member 85 interlocks and connects the decompression cam shaft 81 and the decompression arm 83 configured separately, and is installed in the decompression arm 83 (for example, press fit). ) Pin 89 and an engaging groove 90 formed in the decompression cam shaft 81. The engaging groove 90 is formed along the radial direction of the decompression cam shaft 81 at the base end portion 91 of the decompression cam shaft 81 opposite to the decompression cam 82. The pin 89 has an axis parallel to the decompression cam shaft 81 and engages with the engagement groove 90.

  5 to 7, the pin 89 rotates the decompression cam shaft 81 while sliding in the engagement groove 90 when the decompression arm 83 swings. In particular, the pin 89 and the engagement groove 90 are disposed between the swing center P of the decompression arm 83 and the axis Q of the decompression cam shaft 81. As a result, the movement direction (swing direction) of the decompression arm 83 and the movement direction (rotation direction) of the decompression cam shaft 81 are set in opposite directions.

  That is, the closing operation direction X (FIG. 5) of the decompression arm 83 and the turning direction α of the decompression cam shaft 81 that is rotated by the closing operation of the decompression arm 83 and projects the arc portion 82A of the decompression cam 82 are provided. Set in the opposite direction. Further, there is an opening operation direction Y (FIG. 7) of the decompression arm 83 and a rotation direction β of the decompression cam shaft 81 that is rotated by the opening operation of the decompression arm 83 and accommodates the arc portion 82A of the decompression cam 82. Set in the opposite direction.

  When the pin 89 and the engaging groove 90 are located on the opposite side of the center axis Q of the decompression cam shaft 81 from the swing center P of the decompression arm 83, the movement direction (rotation direction) of the decompression cam shaft 81 is the decompression arm. The direction of motion (swing direction) 83 is the same.

  The rotation direction α with respect to the axis Q of the decompression cam shaft 81 during the decompression operation for projecting the arc portion 82A of the decompression cam 82 (FIG. 5) is set to be opposite to the rotational direction Z of the exhaust camshaft 61. This is because the frictional force F received by the decompression cam 82 from the exhaust side tappet 63 is applied in the direction in which the decompression cam 82 protrudes, not in the direction in which the arc portion 82A of the decompression cam 82 is accommodated.

  Therefore, during the decompression operation for projecting the arc portion 82A of the decompression cam 82 (FIG. 5), the closing operation direction X of the decompression arm 83 is set to the same direction as the rotation direction Z of the exhaust camshaft 61. Become. Further, when the decompression is not in operation (FIG. 7) in which the arc portion 82A of the decompression cam 82 is accommodated, the opening operation direction Y of the decompression arm 83 is set to be opposite to the rotational direction Z of the exhaust camshaft 61. Become.

  As shown in FIG. 5, the rotation direction Z of the exhaust camshaft 61 described above is the direction of the inertial force that acts on the decompression arm 83 when the engine 26 is decelerated to stop. For this reason, when the engine 26 is decelerated to stop, the inertial force swings the decompression arm 83 in the closing operation direction X in addition to the urging force of the return spring 84, and the decompression cam shaft 81 rotates. The decompression operation of rotating in the direction α to project the arc portion 82A of the decompression cam 82 is performed quickly and early. As a result, the responsiveness of the decompression operation for projecting the arc portion 82A of the decompression cam 82 can be improved.

  As shown in FIGS. 6 and 8, the decompression arm 83 is formed with restriction surfaces 92 on both sides of the pin 89. When the decompression arm 83 swings in the closing operation direction X (FIG. 5) or swings in the opening operation direction Y (FIG. 7), these restricting surfaces 92 abut against the base end portion 91 of the decompression cam shaft 81. As a result, the swing of the opening / closing operation of the decompression arm 83 is restricted.

  Next, the operation of the decompression device 80 will be described.

  When the engine 26 is started, the arc portion 82A of the decompression cam 82 protrudes from the base circle 86 of the exhaust cam 62 as shown in FIG. For this reason, when the engine 26 is started, the cell motor is started or the kick starter is operated to rotate the crankshaft. When the exhaust camshaft 61 is rotated accordingly, the arc portion 82A of the decompression cam 82 is compressed by the engine 26. In the process, the exhaust valve 47 is slightly lifted and rotated. Thereby, the compression in the combustion chamber 39 in the compression process of the engine 26 is reduced, and the engine 26 can be easily started.

  When the engine 26 is started and the exhaust camshaft 61 reaches a predetermined rotational speed, for example, an idle rotational speed, the decompression arm 83 swings in the opening operation direction Y as shown in FIGS. To do. As the decompression arm 83 swings in the opening operation direction Y, the decompression cam shaft 81 pivots in the rotational direction β, and the arc portion 82A of the decompression cam 82 is accommodated radially inward with respect to the base circle 86 of the exhaust side cam 62. Is done. As a result, the exhaust valve 47 does not open during the compression process of the engine 26, and the engine 26 operates normally.

  When the engine 26 is decelerated to stop, an inertial force acts on the decompression arm 83 in the same direction as the rotational direction Z of the exhaust camshaft 61. When the centrifugal force acting on the decompression arm 83 decreases, the decompression arm 83 swings in the closing operation direction X by the action of the biasing force of the return spring 84 and the inertial force, as shown in FIG. As a result, the decompression operation for causing the decompression cam shaft 81 to pivot in the rotational direction α and projecting the arc portion 82A of the decompression cam 82 from the base circle 86 of the exhaust side camshaft 61 is performed quickly and early. For this reason, the arc portion 82A of the decompression cam 82 is projected before the engine 26 is stopped, and the engine 26 is stopped in this state.

  With the configuration as described above, the following effects (1) to (5) are achieved according to the present embodiment.

  (1) The opening operation direction Y of the decompression arm 83 is set opposite to the rotation direction Z of the exhaust camshaft 61 (see FIG. 7), that is, the closing operation direction X of the decompression arm 83 is the rotation direction of the exhaust camshaft 61. Since it is set in the same direction as Z (see FIG. 5), the inertia force in the camshaft rotation direction Z acting on the decompression arm 83 when the engine 26 is stopped acts on the closing operation direction X of the decompression arm 83. be able to. For this reason, the decompression arm 83 is quickly closed by the inertia force and the urging force of the return spring 84 to rotate the decompression cam shaft 81 in the rotational direction α, so that the arc portion 82A of the decompression cam 82 is connected to the exhaust side cam. Since it can project at an early stage with respect to the 62 base circle 86, the responsiveness of the decompression operation can be improved.

  As a result, the arc portion 82A of the decompression cam 82 already protrudes before the engine 26 is stopped. Therefore, even when the decompression cam 82 comes into contact with the exhaust side tappet 63 and the engine 26 stops, The arc portion 82A presses the exhaust side tappet 63 and the exhaust valve 47 is slightly opened. Therefore, when the engine 26 is subsequently started, the decompression operation by the decompression device 80 can be performed quickly and reliably, and the startability of the engine 26 can be improved.

  (2) The decompression cam shaft 81 and the decompression arm 83 are configured separately, and the engaging member 85 (that is, the pin 89 and the engaging groove 90 that are engaged with each other) interlockingly connects the decompression cam shaft 81 and the decompression arm 83. It is disposed between the moving center P and the axis Q of the decompression cam shaft 81. For this reason, the movement direction (swinging direction) of the decompression arm 83 and the interlocking direction (rotation direction) of the decompression cam shaft 81 can be set in opposite directions. Further, the decompression cam shaft 81 is rotated in a range from the position of the decompression cam shaft 81 for accommodating the arc portion 82A of the decompression cam 82 (FIG. 7) to the position of the decompression cam shaft 81 for projecting the arc portion 82A of the decompression cam 82 (FIG. 5). The swing angle of the decompression arm 83 for movement (the sum angle of the angle θ1 in FIG. 5 and the angle θ2 in FIG. 7) can be set small, and the response delay of the decompression operation of the decompression device 80 due to the swinging motion of the decompression arm 83 Can be eliminated.

  (3) The pin 89 implanted in the decompression arm 83 has an axis parallel to the decompression cam shaft 81, and this pin 89 is engaged with the engagement groove 90 of the decompression cam shaft 81 so that the decompression arm 83 and the decompression cam shaft 81 are They are linked together. For this reason, compared with the case where the pin 89 is extended in the radial direction of the decompression cam shaft 81, the connection part of the decompression cam shaft 81 and the decompression arm 83 can be reduced in size.

  (4) The rotational direction α with respect to the axis Q of the decompression cam shaft 81 during the decompression operation in which the arc portion 82A of the decompression cam 82 projects from the base circle 86 of the exhaust side cam 62 is the rotational direction Z of the exhaust side cam shaft 61. And set in the opposite direction. Thus, the protruding state of the decompression cam 82 can be maintained by the frictional force F received by the arc portion 82A of the decompression cam 82 from the exhaust side tappet 63 during the decompression operation, and the decompression operation can be executed reliably.

  (5) When the restriction surfaces 92 provided on both sides of the pin 89 in the decompression arm 83 abut on the outer peripheral surface of the base end portion 91 of the decompression cam shaft 81, the swing range of the decompression arm 83 is defined. For this reason, as shown in FIGS. 9 to 12, when the protrusion 119 of the decompression arm 114 is brought into contact with the stopper 118 provided at the end of the exhaust camshaft 105, the swing of the decompression arm 114 is restricted. In comparison with the above, a stopper protruding at the end of the exhaust camshaft 61 is not required, and the exhaust camshaft 61 can be reduced in weight.

  Further, the restriction position of the decompression arm 83 is determined by the two parts of the decompression arm 83 and the decompression cam shaft 81, and other parts such as the exhaust side camshaft 61 are not interposed. Therefore, the precision of the restriction position of the decompression arm 83 can be improved.

26 Engine 27 Cylinder head 39 Combustion chamber 47 Exhaust valve 50 Valve operating device 61 Exhaust side cam shaft 62 Exhaust side cam 80 Decompression device 81 Decompression cam shaft 82 Decompression cam 82A Decompression cam arc 83 Decompression arm 84 Return spring 85 Engaging member 86 Exhaust side Cam base circle 91 Decompression cam shaft base end 92 Restriction surface O Exhaust side camshaft axis P Decompression arm swing center Q Decompression cam shaft axis X Decompression arm closing direction Y Decompression arm opening direction Z Exhaust side camshaft rotation direction α, β Decompression cam shaft rotation direction

Claims (2)

A camshaft that is pivotally supported by a cylinder head and has an exhaust cam, a decompression cam shaft that extends in the axial direction and is rotatably accommodated, and is provided at one end of the decompression cam shaft. A decompression cam integrally provided with a circular arc portion and a string portion that can project or be accommodated with respect to the base circle of the base , and the decompression cam shaft is rotated by the action of centrifugal force accompanying the rotation of the camshaft, A decompression arm that houses the decompression cam; and a return spring that urges the decompression arm in a direction against the centrifugal force to close the decompression arm and rotates the decompression cam shaft to project the decompression cam. Then, the decompression operation of the four-cycle engine is performed by opening the exhaust valve and decompressing the combustion chamber by the decompression operation for projecting the decompression cam. In,
The decompression arm that opens and closes is formed in a U-shape when viewed from the front, and is pivotally supported with the attachment portion at the end of the exhaust side camshaft as a swinging center. The center of gravity of the decompression arm swings away from the center of the exhaust camshaft, with the center of gravity located on the outside in the radial direction. While the decompression arm for storing the arc portion and the string portion of the decompression cam inside the base circle of the exhaust side cam is performed,
The decompression arm and the decompression cam shaft are connected to each other via an engagement member comprising a pin implanted in the decompression arm and an engagement groove formed in the decompression cam shaft. The pin and the engagement groove are connected to the decompression arm. Arranged between the swing center of the arm and the axis of the decompression cam shaft, the swing direction of the decompression arm and the rotation direction of the decompression cam shaft are set in opposite directions,
The rotation direction with respect to the axis of the decompression cam shaft during the closing operation of the decompression arm for projecting the arc portion of the decompression cam is set to be opposite to the rotational direction of the exhaust camshaft,
When the engine is decelerated to stop, the friction force received from the exhaust side tappet by the inertial force acting on the decompression arm in addition to the urging force of the return spring acts in the direction in which the arc portion and the string portion of the decompression cam protrude. A decompression device for a four-cycle engine characterized by the above. Said engaging member, and a engaging groove which is engaged with the pin with the pin having an axis parallel to the decompression cam shaft with attached to decompressing arm, are formed along the radial direction of the decompression cam shaft 2. The decompression device for a four-cycle engine according to claim 1 , wherein the engagement groove is formed along a radial direction of the decompression cam shaft at a base end portion of the decompression cam shaft opposite to the decompression cam .

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