The disclosure of Japanese Patent Application No. 2022-177553 filed on Nov. 4, 2022, including specification, drawings and claims is incorporated herein by reference in its entirety.
The present invention relates to a decompression device and an engine.
There is known a decompression device that relieves a pressure in a cylinder body when starting an engine to start the engine smoothly (see, for example, JP6934905B). The decompression device switches decompression operation and release by making a decompression cam protrude from and be immersed under a cam base surface of an exhaust cam. A C-plate-shaped decompression arm is provided around a camshaft, a base end of the decompression arm on a leading side in a rotation direction of the camshaft is swingably connected to a camshaft side, and a tip end of the decompression arm on a trailing side in the rotation direction of the camshaft is connected to the decompression cam.
When the engine is started, the decompression arm is pulled to an operating position by a spring and the decompression arm is not moved from the operating position. Here, the decompression cam protrudes from the cam base surface and hits a valve tappet, opening an exhaust valve slightly and improving engine startability. On the other hand, when a rotation speed of the camshaft increases after the engine is started, centrifugal force moves the decompression arm from the operating position to a releasing position. Here, the decompression cam is immersed under the cam base surface, and the exhaust valve is kept closed because the decompression cam does not hit the valve tappet.
Normally, the decompression arm is connected to the camshaft side on the leading side in the rotation direction of the camshaft and the opening direction of the decompression arm is set to the same as the rotation direction of the camshaft so that the decompression is not released when the engine is started. However, during operation after the engine is started, the decompression arm may move from the releasing position to the operating position when a rotational fluctuation increases toward an acceleration side. In a multi-cylinder engine, when the decompression passes over the valve tappet, there is a cylinder that is affected by the rotational fluctuation, and there is a problem that the decompression malfunctions during operation and causes compression loss and abnormal noise.
A decompression device and an engine of a present embodiment can stabilize decompression and preventing compression loss and abnormal noise during operation.
An aspect of the present embodiment is a decompression device that is attached to an exhaust camshaft while the exhaust camshaft is supported by a cylinder head, the decompression device including a decompression camshaft formed with a decompression cam that can protrude and be immersed with respect to a base circle of an exhaust cam of the exhaust camshaft, a decompression arm that moves in an opening direction due to centrifugal force accompanying rotation of the exhaust camshaft to protrude the decompression cam, and a spring 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 in a same direction or in an opposite direction to a rotation direction of the exhaust camshaft for each cylinder.
According to the decompression device of the aspect of the present embodiment, 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 in the same direction to the rotation direction of the exhaust camshaft so that the decompression is not easily released when the engine is started. In a cylinder which is affected by a rotational fluctuation when the decompression cam passes over the valve tappet during operation, the opening direction of the decompression arm is set in the opposite direction to the rotation direction of the exhaust camshaft. The decompression does not operate by an influence of the rotational fluctuation and the occurrence of compression loss and abnormal noise is prevented. Since there is no need to adjust a weight of the decompression arm or a load of the spring, an increase in working hours and design changes can be prevented.
An exhaust camshaft is supported by a cylinder head of an aspect of the present embodiment, 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 is formed with a decompression cam that can protrude and be immersed with respect to a base circle of an exhaust cam of the exhaust camshaft. Centrifugal force accompanying rotation of the exhaust camshaft moves the decompression arm in an opening direction to protrude the decompression cam, and spring force of the spring that resists the centrifugal force moves the decompression arm in a closing direction to immerse the decompression cam. The opening direction of the decompression arm can be changed in a same direction or in an opposite direction to a rotation direction of the exhaust camshaft for each cylinder. In a normal cylinder, an opening direction of the decompression arm is set in the same direction to the rotation direction of the exhaust camshaft so that the decompression is not easily released when the engine is started. In a cylinder which is affected by a rotational fluctuation when the decompression cam passes over a valve tappet during operation, the opening direction of the decompression arm is set in an opposite direction to the rotation direction of the exhaust camshaft. The decompression does not operate by an influence of the rotational fluctuation and occurrence of compression loss and abnormal noise is prevented. Since there is no need to adjust a weight of the decompression arm or a load of the spring, an increase in working hours and design changes can be prevented.
An engine of a present example will be described below with reference to the accompanying drawings.
As illustrated in
As illustrated in
An intake camshaft 26 is supported on a rear side of the cylinder head 13, and an exhaust camshaft 31 is supported on a front side of the cylinder head 13. The intake camshaft 26 and the exhaust camshaft 31 extend in a left-right direction, and an intake cam sprocket 27 and an exhaust cam sprocket 32 are respectively provided at left end portions of the intake camshaft 26 and the exhaust camshaft 31. The intake camshaft 26 is formed with four intake cams 28A and 28B that are in contact with the valve tappets 25A and 25B of the intake valves. The exhaust camshaft 31 is formed with four exhaust cams 33A and 33B that are in contact with the valve tappets 25A and 25B of the exhaust valves.
When starting the engine 10, it is necessary to rotate the crankshaft 17 (see
As illustrated in
On the other hand, as illustrated in
For example, as illustrated in
As illustrated in
As such, the decompression arm 62 does not move when passing over the valve tappet in one cylinder in which combustion occurs first, but the decompression arm 62 moves when passing over the valve tappet in the other cylinder in which combustion occurs later. In particular, after the rotation speed drops below idling, abnormal noise is likely to occur when the rotation speed suddenly fluctuates to the acceleration side due to combustion in one cylinder. Therefore, in the engine 10 of the present example, the decompression devices 40A and 40B that can change opening directions of decompression arms 51A and 51B (see
The decompression device will be described with reference to
As illustrated in
As illustrated in
The decompression camshaft 45 is accommodated in the accommodation groove 36 of the exhaust camshaft 31 and the accommodation groove 43 of the decompression holder 41 to be swingable. One end side of the decompression camshaft 45 protrudes from a back surface of the decompression holder 41, and an outer peripheral surface of the protruding portion is flatly notched to form a decompression cam 46 having a D-shaped cross section. By swinging the decompression cam 46, an orientation of a flat surface 47 is changed, so that the decompression cam 46 is formed to protrude and be immersed with respect to the base circle of an exhaust cam 33. A decompression pin 48 is fixed to the other end side of the decompression camshaft 45, and the decompression cam 46 swings when the decompression pin 48 is operated.
The decompression arm 51 is formed in a C-plate shape, and a base end of the decompression arm 51 is connected to a surface of the decompression holder 41 through a pivot 52 to be swingable. A pair of holding claws 53 are formed on a tip end side of the decompression arm 51, and a decompression pin 48 of the decompression camshaft 45 is inserted between the pair of holding claws 53 to connect the decompression arm 51 and the decompression camshaft 45. The decompression arm 51 swings under 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 (see
One end of the spring 56 is hooked in the hanging groove 44 of the decompression holder 41 and the other end of the spring 56 is hooked in the hanging hole 54 of the decompression arm 51. The decompression arm 51 is pulled in a closing direction by the spring force of the spring 56. In such a decompression device 40, the decompression arm 51 is moved in an opening direction by the centrifugal force accompanying the rotation of the exhaust camshaft 31, and the decompression cam 46 protrudes from the base circle of the exhaust cam 33. In the decompression device 40, the decompression arm 51 is moved in a closing direction by the spring force of the spring 56 that resists the centrifugal force, and the decompression cam 46 is immersed in the base circle of the exhaust cam 33.
The opening direction of the decompression arm 51 can be changed to the same direction as or opposite direction to the rotation direction of the exhaust camshaft 31 depending on an attachment orientation of the decompression holder 41 with respect to the exhaust camshaft 31. The engine 10 of the present example is a two-cylinder engine with unequal combustion intervals of 270 degrees and 450 degrees, and the decompression operation time of the cylinder 21B comes immediately after the combustion of the cylinder 21A. Therefore, similar decompression devices 40 are used on the cylinder 21A side in which combustion occurs first and the cylinder 21B side in which combustion occurs later, but the decompression devices 40 of the cylinder 21A and the cylinder 21B are attached to the exhaust camshaft 31 in an opposite direction to each other.
The decompression operation will be described with reference to
As illustrated in
When the engine is started, the centrifugal force F1 does not strongly act on the decompression arm 51A. The decompression arm 51A is pulled in the closing direction by the spring force F2 of the spring 56A, and the decompression arm 51A is positioned at the decompression operating position P1. The decompression cam 46A is connected to the tip end of the decompression arm 51A via the decompression pin 48A, and the flat surface 47A of the decompression cam 46A faces the side surface of the accommodation groove 36A. Therefore, the decompression cam 46A partially protrudes from the base circle of the exhaust cam 33A and comes into contact with the valve tappet 25A (see
As illustrated in
In the cylinder 21A (one cylinder) in which combustion occurs first, the decompression operation time is not immediately after the combustion of the cylinder 21B (the other cylinder) (see
As illustrated in
When the engine is started, the centrifugal force F1 does not strongly act on the decompression arm 51B. The decompression arm 51B is pulled in the closing direction by the spring force F2 of the spring 56B, and the decompression arm 51B is positioned at the decompression operating position P1. The decompression cam 46B is connected to the tip end of the decompression arm 51B via the decompression pin 48B, and the flat surface 47B of the decompression cam 46B faces a side surface of the accommodation groove 36B. Therefore, the decompression cam 46B partially protrudes from the base circle of the exhaust cam 33B and comes into contact with the valve tappet 25B (see
As illustrated in
In the cylinder 21B (the other cylinder) in which combustion occurs later, the decompression operation time is immediately after the combustion of the cylinder 21A (one cylinder) (see
More specifically, as illustrated in
As described above, according to the decompression device 40 of the present example, the opening directions of the decompression arms 51A and 51B can be changed for each of the cylinders 21A and 21B of the engine 10. In the cylinder 21A, the opening direction of the decompression arm 51A is set in the same direction to the rotation direction of the exhaust camshaft 31 so that the decompression is not easily released when the engine is started. In the cylinder 21B, which is affected by a rotational fluctuation when the decompression cam 46B passes over the valve tappet 25B during operation, the opening direction of the decompression arm 51B is set in the opposite direction to the rotation direction of the exhaust camshaft 31. The decompression does not malfunction by an influence of the rotational fluctuation, and the occurrence of compression loss and abnormal noise is prevented. Since weight adjustment of the decompression arms 51A and 51B and load adjustment of the springs 56A and 56B are not required, an increase in working hours and design changes can be prevented.
In the present example, the opening direction of the decompression arm can be changed depending on the attachment orientation of the decompression holder with respect 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.
In the present example, an engine with two cylinders with unequal combustion intervals of 270 degrees and 450 degrees is exemplified, but the combustion interval and the number of cylinders can be changed as appropriate as long as the engine is a multi-cylinder engine.
The decompression device of the present example is not limited to the straddle-type vehicle described above, and may be employed in other vehicles such as a four-wheeled motor vehicle. The straddle-type vehicle is not limited to vehicles in general in which a driver rides while straddling a seat, but also includes scooter-type vehicles in which a driver rides without straddling a seat.
As described above, a first aspect is a decompression device (40) that is attached to an exhaust camshaft (31) while the exhaust camshaft is supported by a cylinder head (13), the decompression device including a decompression camshaft (45) formed with a decompression cam (46) that can protrude and be immersed with respect to a base circle of an exhaust cam (33) of the exhaust camshaft, a decompression arm (51) that moves in an opening direction due to centrifugal force accompanying rotation of the exhaust camshaft to protrude the decompression cam, and a spring (56) that moves the decompression arm in a closing direction by spring force resisting the centrifugal force to immerse the decompression cam, where the opening direction of the decompression arm can be changed in a same direction or in an opposite direction to a rotation direction of the exhaust camshaft for each cylinder. According to such 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 in the same direction to the rotation direction of the exhaust camshaft so that the decompression is not easily released when the engine is started. In the cylinder which is affected by a rotational fluctuation when the decompression cam passes over the valve tappet during operation, the opening direction of the decompression arm is set in the opposite direction to the rotation direction of the exhaust camshaft. The decompression does not operate by an influence of the rotational fluctuation and the occurrence of compression loss and abnormal noise is prevented. Since there is no need to adjust a weight of the decompression arm or a load of the spring, an increase in working hours and design changes can be prevented.
According to a second aspect, in the first aspect, the decompression device further includes a decompression holder (41) for holding the decompression camshaft, the decompression arm, and the spring on an outer surface of the exhaust camshaft, where the opening direction of the decompression arm can be changed in the same direction or in the opposite direction to the rotation direction of the exhaust camshaft, depending on an attachment orientation of the decompression holder with respect to the exhaust camshaft. According to such configuration, an orientation of the opening direction of the decompression arm can be easily changed depending on the attachment orientation of the decompression holder.
A third aspect is an engine (10) including the decompression device of the first and second aspects, and a cylinder body (12) in which a plurality of cylinders (21) are formed, where combustion intervals of the plurality of cylinders are unequal intervals. According to such configuration, the decompression operation time of the other cylinder is likely to come immediately after combustion of one cylinder. However, by setting the opening direction of the decompression arm of the other cylinder in the direction opposite to the rotation direction of the exhaust camshaft, the decompression operation due to a rotational fluctuation is prevented.
According to a fourth aspect, in the third aspect, two cylinders are provided with unequal intervals of 270 degrees and 450 degrees in the combustion intervals of the plurality of cylinders, and the opening direction of the decompression arm of one cylinder in which combustion occurs first is a same as the rotation direction of the exhaust camshaft, and the opening direction of the decompression arm of the other cylinder in which combustion occurs later is opposite to the rotation direction of the exhaust camshaft. According to such configuration, the decompression operation time of the other cylinder comes immediately after 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, decompression operation due to rotational fluctuation is prevented.
Although the present example is described, another example may be a combination of the above-described example and a modification example in whole or in part.
The technology of the present invention is not limited to the above-described example, and may be variously changed, replaced, and modified without departing from the spirit of the technical idea. When the technical idea can be realized in another way by advancement of technology or another derived technology, the method may be used for implementation. Therefore, the claims cover all implementations that may fall within the scope of the technical concept.
Number | Date | Country | Kind |
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2022-177553 | Nov 2022 | JP | national |