engine

Abstract

To stabilize decompression to inhibit occurrences of compression loss and abnormal noise during operation.SOLUTION: An exhaust camshaft (31) is supported by a cylinder head, and a decompression device (40B) is attached to the exhaust camshaft. The decompression device includes: a decompression camshaft formed with a decompression cam (46B) that can protrude and be immersed with respect to a base circle of an exhaust cam (33B) of the exhaust camshaft, a decompression arm (51B) that moves in an opening direction due to centrifugal force accompanying rotation of the exhaust camshaft to protrude the decompression cam, and a spring (56B) that moves the decompression arm in a closing direction by spring force resisting the centrifugal force to immerse the decompression cam. In the decompression device, the opening direction of the decompression arm can be changed to the same direction or an opposite direction to a rotation direction of the exhaust camshaft for each cylinder.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention ,workman relates to an engine.

Background Art

[0002] A decompression (decompression) device that evacuates the pressure in the cylinder at engine startup to smoothly start the engine is known (see, for example, Patent Document 1). The decompression device switches the operation and release of decompression by projecting and retracting the decompression cam from the cam base surface of the exhaust cam. A C-shaped decompression arm is provided around the camshaft. The base end of the decompression arm on the leading side in the rotation direction of the camshaft is swingably connected to the camshaft side, and the tip of the decompression arm on the trailing side in the rotation direction of the camshaft is connected to the decompression cam.

[0003] At engine startup, the decompression arm is attracted to the operating position by a spring and is not moved from the operating position. At this time, the decompression cam protrudes from the cam base surface, the decompression cam hits the valve tappet, the exhaust valve opens slightly, and the starting performance of the engine is improved. On the other hand, when the rotational speed of the camshaft increases after engine startup, the decompression arm is moved from the operating position to the release position by centrifugal force. At this time, the decompression cam is immersed under the cam base surface and does not hit the valve tappet, so the exhaust valve remains closed.

Prior Art Documents

Patent Documents

[0004] [[ID=2⑧]]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Normally, to prevent the decompressor from disengaging when the engine starts, the decompressor arm is connected to the camshaft on the leading side in the direction of the camshaft's rotation, and the opening direction of the decompressor arm is the same as the direction of the camshaft's rotation. However, during operation after the engine starts, the decompressor arm may move from the disengaged position to the activated position when the rotational fluctuations become larger on the acceleration side. In multi-cylinder engines, there are cylinders that are affected by rotational fluctuations at the timing when the decompressor moves over the valve tappet, which can cause the decompressor to malfunction during operation, resulting in compression loss or abnormal noise.

[0006] This invention has been made in view of the above, and it is possible to stabilize the decompression and suppress compression loss and the occurrence of abnormal noises during operation. ru e The purpose is to provide vegans. [Means for solving the problem]

[0007] One aspect of the present invention engine teeth, A cylinder in which multiple cylinders are formed, The exhaust camshaft is supported by the cylinder head. Each cylinder Decompression device attached to the exhaust camshaft and an engine equipped with And, The decompression device, A decompression camshaft is formed on which a decompression cam that can move in and out relative to the base circle of the exhaust cam of the exhaust camshaft is formed, and the decompression cam moves in the opening direction due to the centrifugal force accompanying the rotation of the exhaust camshaft. Immersion A decompression arm is used to move the decompression arm in the closing direction by a spring force that resists centrifugal force, and the decompression cam is moved by the spring force that resists centrifugal force. protrusion It is equipped with a spring that causes, The decompression device is installed such that the opening direction of the decompression arm for each cylinder is selected to be either in the same direction as or opposite to the rotation direction of the exhaust camshaft, and the combustion intervals of the plurality of cylinders are unequal, with two cylinders at 270 degrees and 450 degrees, the opening direction of the decompression arm of the first cylinder to burn is in the same direction as the rotation direction of the exhaust camshaft, and the opening direction of the decompression arm of the other cylinder to burn later is in the opposite direction to the rotation direction of the exhaust camshaft. This solves the above problem. [Effects of the Invention]

[0008] One aspect of the present invention engineAccording to the specifications, the opening direction of the decompression arm can be changed for each cylinder of the engine. In a normal cylinder, the opening direction of the decompression arm is set to be the same as the rotation direction of the exhaust camshaft so that the decompression is not easily disengaged when the engine starts. In a cylinder where rotational fluctuations affect the timing at which the decompression cam crosses the valve tappet during operation, the opening direction of the decompression arm is set to be the opposite of the rotation direction of the exhaust camshaft. This prevents the decompression from operating due to the effects of rotational fluctuations, suppressing compression loss and the occurrence of abnormal noises. In addition, since weight adjustment of the decompression arm and load adjustment of the spring are not required, the increase in man-hours and design changes can be suppressed. [Brief explanation of the drawing]

[0009] [Figure 1] This is a right side view of the engine in this embodiment. [Figure 2] This is a top view of the cylinder head in this embodiment. [Figure 3] This is a diagram illustrating the decompression operation of the comparative decompression device. [Figure 4] This diagram shows the piston movement and the timing of the decompression device's operation. [Figure 5] This is a perspective view of the exhaust camshaft in this embodiment. [Figure 6] This is a perspective view of the decompression device of this embodiment. [Figure 7] This is an explanatory diagram of the decompression operation of the decompression device for one cylinder in this embodiment. [Figure 8] This is an explanatory diagram of the decompression operation of the decompression device for the other cylinder in this embodiment. [Modes for carrying out the invention]

[0010] In one embodiment of the present invention, an exhaust camshaft is supported in a cylinder head, and a decompression device is attached to the exhaust camshaft for each cylinder of the cylinder head. The decompression device includes a decompression camshaft, a decompression arm, and a spring. The decompression camshaft has a decompression cam formed on it that can move in and out relative to the base circle of the exhaust cam of the exhaust camshaft. Due to the centrifugal force accompanying the rotation of the exhaust camshaft, the decompression arm moves in the opening direction, and the decompression cam moves Immersion Then, the spring force of the spring, which resists the centrifugal force, moves the decompression arm in the closing direction, and the decompression cam Outstanding The opening direction of the decompression arm can be changed for each cylinder to be in the same direction as or opposite to the rotation direction of the exhaust camshaft. In normal cylinders, the opening direction of the decompression arm is set to be in the same direction as the rotation direction of the exhaust camshaft to prevent the decompression from being easily disengaged when the engine is started. In cylinders where rotational fluctuations affect the timing at which the decompression cam crosses the valve tappet during operation, the opening direction of the decompression arm is set to be in the opposite direction to the rotation direction of the exhaust camshaft. This prevents the decompression from operating due to the effects of rotational fluctuations, suppressing compression loss and the occurrence of abnormal noises. In addition, since weight adjustment of the decompression arm and load adjustment of the spring are not required, the increase in man-hours and design changes can be suppressed. [Examples]

[0011] The engine of this embodiment will be described below with reference to the attached drawings. Figure 1 is a right side view of the engine of this embodiment. Figure 2 is a top view of the cylinder head of this embodiment. Figure 3 is an explanatory diagram of the decompression operation of the decompression device of a comparative example. Figure 4 is a diagram showing the movement of the piston and the operating timing of the decompression device. In the following figures, arrow FR indicates the front of the vehicle, arrow RE indicates the rear of the vehicle, arrow L indicates the left side of the vehicle, and arrow R indicates the right side of the vehicle.

[0012] As shown in FIG. 1, the engine 10 is a two-cylinder four-stroke engine and is mounted on a saddle-type vehicle such as a motorcycle. A crankshaft 17 is accommodated in a crankcase 11 of the engine 10, and a cylinder assembly in which a cylinder 12, a cylinder head 13, and a cylinder head cover (not shown) are laminated is attached to the upper part of the crankcase 11. An oil pan 14 for storing oil for lubrication and cooling is attached to the lower part of the crankcase 11. A clutch cover 15 that covers the clutch chamber in the case is attached to the right side surface of the crankcase 11.

[0013] As shown in FIG. 2, cylinders 21A and 21B are formed in the cylinder 12 (see FIG. 1), and plug holes 22A and 22B connected to the cylinders 21A and 21B are formed in the cylinder head 13. Intake ports 23A and 23B for the cylinders 21A and 21B are formed on the back surface of the cylinder head 13, and exhaust ports 24A and 24B for the cylinders 21A and 21B are formed on the front surface of the cylinder head 13. Two intake valves (not shown) and two exhaust valves (not shown) are installed in the cylinder head 13 for the cylinder 21A, and two intake valves and two exhaust valves are installed in the cylinder head 13 for the cylinder 21B. Valve tappets 25A and 25B of each valve are exposed from the bottom surface of the cylinder head 13.

[0014] An intake camshaft 26 is supported on the back side of the cylinder head 13, and an exhaust camshaft 31 is supported on the front side of the cylinder head 13. The intake camshaft 26 and the exhaust camshaft 31 extend in the left-right direction, and intake cam sprockets 27 and exhaust cam sprockets 32 are provided at the left end portions of the intake camshaft 26 and the exhaust camshaft 31. Four intake cams 28A and 28B that contact the valve tappets 25A and 25B of the intake valves are formed on the intake camshaft 26. Four exhaust cams 33A and 33B that contact the valve tappets 25A and 25B of the exhaust valves are formed on the exhaust camshaft 31.

[0015] When starting the engine 10, it is necessary to use a starter motor or the like to give the crankshaft 17 (see Figure 1) a running start. However, if the torque required to overcome the piston's compression top dead center is high, it is difficult to rotate the crankshaft 17 smoothly. For this reason, decompression devices 40A and 40B are attached to the exhaust camshaft 31 for each cylinder 21A and 21B. When starting the engine, the decompression devices are activated and the exhaust valves of cylinders 21A and 21B are slightly opened. Pressure is released from cylinders 21A and 21B, reducing the torque required to overcome the piston's compression top dead center, and allowing the engine 10 to start smoothly.

[0016] As shown in Figure 3(A), in the comparative example decompression device 60, the base end of the decompression arm 62 is connected to the decompression holder 61 on the leading side in the rotational direction of the camshaft, and the tip of the decompression arm 62 is connected to the decompression cam 63 on the following side in the rotational direction of the camshaft. That is, the opening direction of the decompression arm 62 is the same as the rotational direction of the camshaft. When the engine is started, the centrifugal force F1 acting on the decompression arm 62 is weak, and the decompression arm 62 is pulled in by the spring force F2 of the spring 64. When the decompression arm 62 is closed, the decompression cam 63 protrudes from the base circle of the exhaust cam during the compression stroke, and the decompression is activated.

[0017] On the other hand, as shown in Figure 3(B), during operation after engine start-up, the centrifugal force F1 acting on the decompression arm 62 increases, causing the decompression arm 62 to open against the spring force F2 of the spring 64. When the decompression arm 62 is open, the decompression cam 63 retracts into the base circle of the exhaust cam during the compression stroke, releasing the decompression. However, in the case of a multi-cylinder engine, the acceleration and deceleration characteristics of the engine become irregular depending on the combination of each cylinder cycle. Due to this characteristic, the opening and closing of the decompression arm 62 may become unstable in some cylinders due to the effects of irregular acceleration and deceleration.

[0018] For example, as shown in Figure 3(C), when the rotational speed drops below idling and then the rotational fluctuation increases significantly towards acceleration, the decompression arm 62 is strongly acted upon not only by centrifugal force F1 and the spring force F2 of the spring 64, but also by an inertial force F3. Since the rotational direction of the camshaft and the opening direction of the decompression arm 62 are the same, the inertial force F3 acts on the decompression arm 62 in the closing direction, and the decompression arm 62 is moved in the closing direction by the spring force F2 and the inertial force F3. In this way, if a sudden change in rotational fluctuation occurs during engine operation, the decompression may activate, causing compression loss or abnormal noise.

[0019] As shown in Figure 4, in an engine with two cylinders having unequal combustion intervals (for example, 270 degrees and 450 degrees), the decompression timing for the other cylinder occurs immediately after the combustion of one cylinder. When the rotational speed changes rapidly towards acceleration due to the combustion of one cylinder, the decompression of the other cylinder is pushed over the valve tappet, making the decompression of the other cylinder highly susceptible to the effects of rotational fluctuations. In the modified decompression device 60, the decompression arm 62 is moved in the closing direction and positioned between the operating position and the release position, causing the decompression cam 63 to be flicked by the valve tappet and generate an abnormal noise.

[0020] Thus, in the cylinder that burns first, the decompression arm 62 does not move at the timing of the valve tappet overcoming, but in the other cylinder that burns later, the decompression arm 62 moves at the timing of the valve tappet overcoming. In particular, abnormal noise is likely to occur when the rotational speed drops below idling speed and then the rotational speed changes abruptly towards acceleration due to the combustion of one cylinder. Therefore, in the engine 10 of this embodiment, decompression devices 40A and 40B are used in which the opening direction of the decompression arms 51A and 51B (see Figure 5) can be changed, and the opening direction of the decompression arms 51A and 51B is changed to be in an orientation suitable for cylinders 21A and 21B.

[0021] The decompression device will be described with reference to Figures 5 and 6. Figure 5 is a perspective view of the exhaust camshaft in this embodiment. Figure 6 is a perspective view of the decompression device in this embodiment. The decompression devices are denoted by symbols A and B, but A and B may be omitted when a specific decompression device is not being identified.

[0022] As shown in Figure 5, the left half of the exhaust camshaft 31 is provided with two exhaust cams 33A for cylinder 21A, and the right half of the exhaust camshaft 31 is provided with two exhaust cams 33B for cylinder 21B. The exhaust cams 33A and 33B are installed with a phase difference of 270 degrees. Decompression devices 40A and 40B are provided on the exhaust camshaft 31, flanking these four exhaust cams 33A and 33B. The decompression devices 40A and 40B are secured to the exhaust camshaft 31 with circlips 35A and 35B. The outer circumferential surface of the exhaust camshaft 31 is formed with housing grooves 36A and 36B for the decompression camshafts 45A and 45B.

[0023] As shown in Figures 5 and 6, the decompression device 40 is attached to the outer circumferential surface of the exhaust camshaft 31 via a decompression holder 41. The decompression holder 41 holds the decompression camshaft 45, the decompression arm 51, and the spring 56. The decompression holder 41 is formed in the shape of a ring plate with an open center, and the inner edge of the decompression holder 41 protrudes cylindrically towards the surface. A keyway 42 for the exhaust camshaft 31 and a housing groove 43 for the decompression camshaft 45 are formed on the inner edge of the decompression holder 41, and a hook groove 44 for the spring 56 is formed on the outer edge of the decompression holder 41.

[0024] The decompression camshaft 45 is pivotably housed in the housing groove 36 of the exhaust camshaft 31 and the housing groove 43 of the decompression holder 41. One end of the decompression camshaft 45 protrudes from the back surface of the decompression holder 41, and the outer circumferential surface of this protruding portion is cut flat to form a D-shaped decompression cam 46 in cross-section. The orientation of the flat surface 47 changes as the decompression cam 46 swings, allowing the decompression cam 46 to move in and out relative to the base circle of the exhaust cam 33. A decompression pin 48 is fixed to the other end of the decompression camshaft 45, and the decompression cam 46 swings when the decompression pin 48 is operated.

[0025] The decompression arm 51 is formed in a C-shape, and its base end is pivotably connected to the surface of the decompression holder 41 via a pivot 52. A pair of retaining claws 53 are formed on the tip side of the decompression arm 51, and the decompression pin 48 of the decompression camshaft 45 is inserted between the pair of retaining claws 53, connecting the decompression arm 51 and the decompression camshaft 45. The decompression arm 51 swings in response to the centrifugal force accompanying the rotation of the exhaust camshaft 31, and the swinging of the decompression arm 51 operates the decompression pin 48. A hanging hole 54 for a spring 56 (see Figure 7) is formed on the base end side of the decompression arm 51.

[0026] One end of the spring 56 is hooked into the hook groove 44 of the decompression holder 41, and the other end of the spring 56 is hooked into the hook hole 54 of the decompression arm 51. The spring force of the spring 56 pulls the decompression arm 51 in the closing direction. In this type of decompression device 40, the centrifugal force accompanying the rotation of the exhaust camshaft 31 moves the decompression arm 51 in the opening direction, causing the decompression cam 46 to move in the base circle of the exhaust cam 33. Immerse yourself in In addition, in the decompression device 40, the decompression arm 51 is moved in the closing direction by the spring force of the spring 56 that resists the centrifugal force, and the decompression cam 46 moves the base circle of the exhaust cam 33. protruding from It will be done.

[0027] Furthermore, the opening direction of the decompression arm 51 can be changed to the same direction as or opposite to the rotation direction of the exhaust camshaft 31 depending on the mounting orientation of the decompression holder 41 to the exhaust camshaft 31. The engine 10 in this embodiment is a two-cylinder engine with unequal combustion intervals of 270 degrees and 450 degrees, and the decompression timing for cylinder 21B occurs immediately after combustion of cylinder 21A. For this reason, the same decompression device 40 is used for both cylinder 21A, which burns first, and cylinder 21B, which burns later, but the decompression device 40 is mounted in opposite directions relative to the exhaust camshaft 31 for cylinder 21A and cylinder 21B.

[0028] The decompression operation will be explained with reference to Figures 7 and 8. Figure 7 is an explanatory diagram of the decompression operation of the decompression device for one cylinder in this embodiment. Figure 8 is an explanatory diagram of the decompression operation of the decompression device for the other cylinder in this embodiment.

[0029] As shown in Figure 7(A), the decompression device 40A for cylinder 21A, which burns first, is mounted on the exhaust camshaft 31 in the same orientation as the decompression device 60 of the comparative example. The base end of the decompression arm 51A is connected to the decompression holder 41A on the leading side in the rotational direction of the exhaust camshaft 31, and the tip of the decompression arm 51A is connected to the decompression cam 46A on the following side in the rotational direction of the exhaust camshaft 31. That is, the opening direction of the decompression arm 51A of the decompression device 40A is in the same direction as the rotational direction of the exhaust camshaft 31. The decompression arm 51A is supported so as to be able to swing between the decompression operating position P1 and the release position P2.

[0030] When the engine is started, the centrifugal force F1 does not act strongly on the decompression arm 51A. The spring force F2 of the spring 56A pulls the decompression arm 51A in the closing direction, positioning the decompression arm 51A in the decompression operating position P1. The decompression cam 46A is connected to the tip of the decompression arm 51A via a decompression pin 48A, and the flat surface 47A of the decompression cam 46A is oriented toward the side of the housing groove 36A. As a result, the decompression cam 46A partially protrudes from the base circle of the exhaust cam 33A, and the decompression is activated when the decompression cam 46A contacts the valve tappet 25A (see Figure 2) from the circular surface side.

[0031] As shown in Figure 7(B), a strong centrifugal force F1 acts on the decompression arm 51A during operation after engine start. The centrifugal force F1 moves the decompression arm 51A in the opening direction against the spring force F2 of the spring 56A, positioning the decompression arm 51A in the decompression release position P2. The tip of the decompression arm 51A operates the decompression pin 48A, causing the flat surface 47A of the decompression cam 46A to face the opening side of the housing groove 36A. As a result, the decompression cam 46A retracts into the base circle of the exhaust cam 33A, avoiding contact between the valve tappet 25A and the decompression cam 46A, and thus releasing the decompression.

[0032] In cylinder 21A (one cylinder), which burns first, the decompression timing does not occur immediately after the combustion of cylinder 21B (the other cylinder) (see Figure 4). The decompression timing for cylinder 21A occurs during the exhaust stroke of cylinder 21B, and the timing of the decompression of cylinder 21A does not cause a sudden change in rotational speed towards acceleration due to the combustion of cylinder 21B. Therefore, the decompression of cylinder 21A does not malfunction when it passes over the valve tappet 25A during operation, contact between the valve tappet 25A and the decompression cam 46A is avoided, and compression loss and the generation of abnormal noise in cylinder 21A are prevented.

[0033] As shown in Figure 8(A), the decompression device 40B for cylinder 21B, which burns later, is mounted on the exhaust camshaft 31 in the opposite direction to the decompression device 60 of the comparative example. The base end of the decompression arm 51B is connected to the decompression holder 41B on the side that follows the rotation direction of the exhaust camshaft 31, and the tip of the decompression arm 51B is connected to the decompression cam 46B on the side that leads the rotation direction of the exhaust camshaft 31. In other words, the opening direction of the decompression arm 51B of the decompression device 40B is opposite to the rotation direction of the exhaust camshaft 31. The decompression arm 51B is supported so as to be able to swing between the decompression operating position P1 and the release position P2.

[0034] When the engine is started, the centrifugal force F1 does not act strongly on the decompression arm 51B. The spring force F2 of the spring 56B pulls the decompression arm 51B in the closing direction, positioning the decompression arm 51B in the decompression operating position P1. The decompression cam 46B is connected to the tip of the decompression arm 51B via a decompression pin 48B, and the flat surface 47B of the decompression cam 46B is oriented toward the side of the housing groove 36B. As a result, the decompression cam 46B partially protrudes from the base circle of the exhaust cam 33B, and the decompression is activated when the decompression cam 46B contacts the valve tappet 25B (see Figure 2) from the flat surface 47B side.

[0035] As shown in Figure 8(B), a strong centrifugal force F1 acts on the decompression arm 51B during operation after engine start. The centrifugal force F1 moves the decompression arm 51B in the opening direction against the spring force F2 of the spring 56B, positioning the decompression arm 51B in the decompression release position P2. The tip of the decompression arm 51B operates the decompression pin 48B, causing the flat surface 47B of the decompression cam 46B to face the opening side of the housing groove 36B. As a result, the decompression cam 46B retracts into the base circle of the exhaust cam 33B, avoiding contact between the valve tappet 25B and the decompression cam 46B, and thus releasing the decompression.

[0036] In cylinder 21B (the other cylinder), which burns later, the decompression timing is immediately after the combustion of cylinder 21A (the other cylinder) (see Figure 4). The decompression timing of cylinder 21B is during the combustion stroke of cylinder 21A, and at the timing of the decompression of cylinder 21B, the rotational speed changes sharply to the acceleration side due to the combustion of cylinder 21A. During operation, an inertial force acts on the decompression arm 51A at the timing when it passes over the valve tappet 25B, but since the decompression arm 51B does not move in the closing direction, the decompression does not malfunction. Contact between the valve tappet 25B and the decompression cam 46B is avoided, preventing compression loss and the generation of abnormal noise in cylinder 21A.

[0037] More specifically, as shown in Figure 8(C), when the rotational speed of the engine 10 changes rapidly towards acceleration, an inertial force F3 acts on the decompression arm 51B in addition to the centrifugal force F1 and spring force F2. As described above, since the opening direction of the decompression arm 51B is opposite to the rotational direction of the exhaust camshaft 31, the inertial force F3 acts on the decompression arm 51B in the opening direction, not the closing direction. Because the decompression arm 51B does not move in the closing direction at the timing of overcoming the valve tappet 25B, the decompression arm 51B is maintained in the released position P2, preventing malfunction of the decompression during operation.

[0038] As described above, with the decompression device 40 of this embodiment, the opening direction of the decompression arms 51A and 51B can be changed for each cylinder 21A and 21B of the engine 10. In cylinder 21A, the opening direction of the decompression arm 51A is set to be the same as the rotation direction of the exhaust camshaft 31 so that the decompression is not easily released when the engine starts. In cylinder 21B, which is affected by rotational fluctuations at the timing when the decompression cam 46B crosses the valve tappet 25B during operation, the opening direction of the decompression arm 51B is set to be the opposite direction to the rotation direction of the exhaust camshaft 31. This prevents the decompression from malfunctioning due to the effects of rotational fluctuations, suppressing compression loss and the occurrence of abnormal noises. In addition, since weight adjustment of the decompression arms 51A and 51B and load adjustment of the springs 56A and 56B are not required, the increase in man-hours and design changes can be suppressed.

[0039] In this embodiment, the opening direction of the decompression arm can be changed by the mounting orientation of the decompression holder to the exhaust camshaft, but the decompression device only needs to be configured so that the opening direction of the decompression arm can be changed.

[0040] Furthermore, although this embodiment uses a two-cylinder engine with unequal combustion intervals of 270 degrees and 450 degrees as an example, any multi-cylinder engine will suffice, and the combustion interval and number of cylinders can be changed as appropriate.

[0041] Furthermore, the decompression device of this embodiment may be used not only in the saddle-type vehicle described above, but also in other vehicles such as four-wheeled automobiles. It should be noted that the term "saddle-type vehicle" is not limited to all vehicles in which the driver sits straddling a seat, but also includes scooter-type vehicles in which the driver does not straddle a seat.

[0042] As described above, the first embodiment is a decompression device (40) attached to an exhaust camshaft (31) supported by a cylinder head (13), comprising a decompression camshaft (46) having a decompression cam (46) formed thereon that can move in and out relative to the base circle of the exhaust cam (33) of the exhaust camshaft, and a mechanism that moves in the opening direction due to the centrifugal force accompanying the rotation of the exhaust camshaft to release the decompression cam. Immersion A decompression arm (51) moves the decompression arm in the closing direction due to a spring force that resists centrifugal force, and the decompression cam moves in the closing direction. protrusionThe decompression arm is equipped with a spring (56) that causes it to open, and the opening direction of the decompression arm can be changed for each cylinder to be in the same direction as or opposite to the rotation direction of the exhaust camshaft. With this configuration, the opening direction of the decompression arm can be changed for each cylinder of the engine. In a normal cylinder, the opening direction of the decompression arm is set to be in the same direction as the rotation direction of the exhaust camshaft so that the decompression is not easily released when the engine starts. In a cylinder that is affected by rotational fluctuations at the timing when the decompression cam crosses the valve tappet during operation, the opening direction of the decompression arm is set to be in the opposite direction to the rotation direction of the exhaust camshaft. The decompression does not operate due to the effects of rotational fluctuations, and the occurrence of compression loss and abnormal noise is suppressed. In addition, since it is not necessary to adjust the weight of the decompression arm or the load of the spring, the increase in man-hours and design changes can be suppressed.

[0043] The second embodiment includes a decompression holder (41) that holds a decompression camshaft, a decompression arm, and a spring on the outer surface of the exhaust camshaft, and the opening direction of the decompression arm can be changed to the same direction as or opposite to the rotation direction of the exhaust camshaft depending on the mounting orientation of the decompression holder to the exhaust camshaft. With this configuration, the opening direction of the decompression arm can be easily changed depending on the mounting orientation of the decompression holder.

[0044] The third embodiment includes the decompression device described above in the first and second embodiments, and a cylinder (12) having a plurality of cylinders (21) formed thereon, wherein the combustion intervals of the plurality of cylinders are unequal. With this configuration, the timing of the decompression of one cylinder is likely to occur immediately after the combustion of one cylinder, but by setting the opening direction of the decompression arm of the other cylinder in the opposite direction to the rotation direction of the exhaust camshaft, the operation of the decompression due to rotational fluctuations can be suppressed.

[0045] The fourth embodiment is a two-cylinder engine in the third embodiment, with unequal combustion intervals of 270 degrees and 450 degrees. The opening direction of the decompression arm of the cylinder that burns first is the same as the rotation direction of the exhaust camshaft, while the opening direction of the decompression arm of the other cylinder that burns later is the opposite of the rotation direction of the exhaust camshaft. With this configuration, the decompression of the other cylinder activates immediately after the combustion of the first cylinder, but by setting the opening direction of the decompression arm of the other cylinder to the opposite of the rotation direction of the exhaust camshaft, decompression due to rotational fluctuations is suppressed.

[0046] Although this embodiment has been described, other embodiments may include combinations of the above embodiment and its modifications, either entirely or partially.

[0047] Furthermore, the technology of the present invention is not limited to the embodiments described above, and may be modified, substituted, or transformed in various ways without departing from the spirit of the technical idea. Moreover, if the technical idea can be realized in a different way by advances in the technology or by other derived technologies, it may be implemented by that method. Accordingly, the claims cover all embodiments that may fall within the scope of the technical idea. [Explanation of Symbols]

[0048] 10: Engine 12: Cylinder 13: Cylinder head 21 cylinders 31: Exhaust camshaft 33: Exhaust Cam 40: Decompression device 41: Decompression Holder 45: Decompression camshaft 46: Decompression Cam 48: Decompression pin 51: Decompression Arm 56: Spring

Claims

1. An engine comprising a cylinder having a plurality of cylinders formed thereon, an exhaust camshaft supported on the cylinder head, and a decompression device attached to the exhaust camshaft for each cylinder, The decompression device, A decompression camshaft having a decompression cam formed on it that can extend and retract relative to the base circle of the exhaust cam of the exhaust cam, A decompression arm moves in the opening direction due to the centrifugal force generated by the rotation of the exhaust camshaft, causing the decompression cam to retract. The device comprises a spring that moves the decompression arm in the closing direction by a spring force that resists centrifugal force, thereby causing the decompression cam to protrude, For each cylinder, the decompression device is installed with the opening direction of the decompression arm selected to be either in the same direction as or opposite to the rotation direction of the exhaust camshaft. The aforementioned two cylinders have unequal combustion intervals of 270 degrees and 450 degrees. An engine characterized in that the opening direction of the decompression arm of one cylinder that burns first is the same as the rotation direction of the exhaust camshaft, and the opening direction of the decompression arm of the other cylinder that burns later is the opposite direction to the rotation direction of the exhaust camshaft.

2. The decompression device is The exhaust camshaft is provided with a decompression holder on its outer surface that holds the decompression camshaft, the decompression arm, and the spring, The engine according to claim 1, characterized in that the opening direction of the decompression arm can be changed to the same direction as or opposite to the rotation direction of the exhaust camshaft depending on the mounting orientation of the decompression holder to the exhaust camshaft.

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