JP6191279B2 - Engine decompression device - Google Patents

Description

  The present invention relates to an engine decompression device for opening an exhaust valve and decompressing a combustion chamber by a decompression operation when the engine is started.

  Conventionally, a decompression device is known as a device for facilitating engine start. When the engine is started using, for example, a driving force of a starter motor, the decompression device operates so as to slightly open the exhaust valve and slightly release the air-fuel mixture in the combustion chamber during the compression stroke (decompression operation). . Thereby, the compression overcoming torque (engine friction) is reduced, and the engine can be easily started.

  For example, a conventional decompression device described in Patent Document 1 includes a decompression shaft rotatably provided on a camshaft having an exhaust cam that controls opening and closing of an exhaust valve, and a cam surface of the exhaust cam at one end of the decompression shaft. And a mass weight that rotates the decompression cam by the action of a centrifugal force associated with the rotation of the camshaft.

  When the engine is started, the decompression cam protrudes from the cam surface of the exhaust cam that controls the opening and closing of the exhaust valve, so that the lifter is lifted slightly in the compression stroke to slightly open the exhaust valve and decompress the combustion chamber. On the other hand, when the engine starts and the rotational speed of the camshaft increases, the decompression cam rotates due to the centrifugal force generated by the rotation of the camshaft, and the decompression cam is immersed in the cam surface of the exhaust cam, so that the exhaust valve in the compression stroke Will remain closed.

JP 2003-254025 A

  The decompression device described in Patent Document 1 described above has a structure in which the mass weight is attached to the outside of the cam sprocket, and includes a bolt for fixing the mass weight, a stopper plate for restricting the rotation of the mass weight, and the like. It is necessary to provide. Therefore, there are problems that the number of parts increases and the structure becomes complicated.

  Also, the decompression shaft is inserted into the notch groove of the camshaft from the outside of the cam sprocket, and it is necessary to select a bearing with a large inner diameter to rotatably support the decompression shaft and the camshaft. Therefore, there is a problem that the decompression device becomes large.

  In addition, since the cam surface on the base circle side of the decompression cam is cut out to accommodate the decompression cam, the lifter is pushed at the edge portion where the cam surface is cut off depending on the engine speed, which may cause instability. There is a problem that the decompression cam may operate under circumstances.

  The present invention has been made in view of the above-described problems, and is an engine that can reduce the number of parts, simplify the structure, reduce the size and weight, and perform the decompression operation and the release operation smoothly and reliably. An object is to provide a decompression device.

  In order to achieve the above-described object, the present invention provides a decompression device for an engine for decompressing a combustion chamber by opening an exhaust valve by a decompression operation at the time of starting the engine, and at the position adjacent to the exhaust cam on the camshaft. An eccentric portion formed eccentrically on the camshaft, an eccentric groove recessed in the eccentric portion side of the base circle of the exhaust cam, an eccentric weight provided rotatably on the eccentric portion, and the camshaft And a decompression shaft that protrudes from the eccentric weight toward the eccentric groove along the axial direction of the eccentric weight, and is formed to engage with the eccentric groove. A decompression operation position projecting in a radial direction from a cam surface on the base circle side of the exhaust cam, and the decompression shaft in the cam surface on the base circle side of the exhaust cam. Characterized in that it is configured such that the decompression operation releasing position where the immersion is regulated between.

  According to this feature, the mass spout (or decompression arm) is not provided on the outside of the cam sprocket, but a bolt for fixing the mass weight (or decompression arm), a stopper plate for restricting its rotation, etc. Since it is not necessary to provide, the number of parts can be reduced and the structure can be simplified. In addition, there is no need to insert the decompression shaft into the notch groove of the camshaft from the outside of the cam sprocket, and it is not necessary to select a bearing with a large inner diameter in order to support the decompression shaft and the camshaft rotatably. Thus, the decompression device can be reduced in size and weight. In addition, since it is not necessary to cut out the cam surface on the base circle side of the exhaust cam to accommodate the decompression cam, the decompression cam may operate under unstable conditions, such as pushing the lifter at the edge where the cam surface is notched. And no abnormal noise is generated or breakage occurs. Therefore, durability can be improved, the quietness of the decompression operation can be ensured, and the decompression operation and the release operation thereof can be performed smoothly and reliably.

  In the decompression device for an engine according to the present invention, a spring for biasing the eccentric weight is provided so that the eccentric weight moves to the decompression operation position when the engine is stopped.

  According to this feature, the decompression operation can be performed smoothly and reliably, and the performance of the decompression device can be improved.

  In the engine decompression device according to the present invention, the spring may be provided between the decompression shaft and the eccentric portion.

  According to this feature, the decompression releasing operation can be smoothly and reliably performed with a simple structure.

  In the decompression device for an engine according to the present invention, the outer peripheral surface of the decompression shaft is formed in a curved shape so that the decompression shaft rotates along the eccentric groove as the eccentric weight rotates. It is good also as being characterized by being comprised.

  According to this feature, the lifter will not be pushed at the edge part where the cam surface is cut off, and the decompression cam will not operate under unstable conditions, and abnormal noise will occur or damage will occur There is nothing. Therefore, durability can be improved, the quietness of the decompression operation can be ensured, and the decompression operation and the release operation thereof can be performed smoothly and reliably.

  In the engine decompression device according to the present invention, the decompression shaft may be provided integrally with the eccentric weight.

  According to this feature, it is not necessary to insert the decompression shaft into the notch groove of the camshaft from the outside of the cam sprocket, so that the decompression device can be reduced in size and weight.

  In the decompression device for an engine according to the present invention, the eccentric weight may be interposed between a bearing that rotatably supports the camshaft and the exhaust cam.

  According to this feature, since the axial movement of the eccentric weight is restricted by the bearing and the exhaust cam, the member for fixing the eccentric weight can be omitted, and the number of parts can be further reduced and the structure can be further simplified. Can do.

  According to the present invention, it is possible to obtain various excellent effects such as simplification of the structure, weight reduction of the decompression arm and cost reduction, and smooth and reliable operation of decompression operation and release operation thereof. Can do.

1 is a left side view showing a scooter type motorcycle to which an embodiment of an engine decompression device according to the present invention is applied. It is sectional drawing which shows the decompression apparatus of the engine which concerns on embodiment of this invention. It is a side view which shows the decompression apparatus of the engine which concerns on embodiment of this invention. It is a disassembled perspective view which shows the decompression apparatus of the engine which concerns on embodiment of this invention. It is a perspective view which shows the eccentric weight and decompression shaft of the decompression apparatus of the engine which concerns on embodiment of this invention. It is a perspective view which shows the state at the time of decompression operation | movement in the decompression apparatus of the engine which concerns on embodiment of this invention. It is a perspective view which shows the state at the time of decompression operation cancellation | release in the decompression apparatus of the engine which concerns on embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  First, a scooter type motorcycle 10 to which an embodiment of an engine decompression device according to the present invention is applied will be described with reference to FIG. FIG. 1 is a left side view showing a scooter type motorcycle 10 to which an embodiment of an engine decompression device according to the present invention is applied. In the following description, the front-rear and left-right directions are based on the driver when the vehicle is boarded.

  The scooter type motorcycle 10 includes an underbone body frame 11. The vehicle body frame 11 is configured such that an under frame 13 extends downward from a rear portion of a steering pipe 12 at the frontal portion, and a seat rail 14 extends obliquely upward and rearward from a lower portion of the under frame 13. Yes.

  A front fork 15 is supported on the steering pipe 12 together with a handle bar 16 formed at the upper end thereof so as to be rotatable left and right. A front wheel 17 is pivotally supported at the lower end of the front fork 15. A power unit 19 is pivotally supported at the lower center of the underframe 13 via a swing bracket 18 so as to be swingable in a vertical direction around a pivot shaft 20 as a support shaft.

  The power unit 19 is generally used for a scooter. An engine 21 and a transmission device 22 are integrally formed, and a rear wheel 23 is directly supported on the rear portion of the transmission device 22. A rear cushion unit 24 is stretched between the rear portion of the transmission device 22 and the seat rail 14, and the power unit 19 and the rear wheel 23 are buffered and suspended by the rear cushion unit 24.

  A seating seat 25 is placed on the body frame 11 above the seat rail 14 so as to be openable and closable, and an article storage chamber (not shown) in which a helmet and the like can be stored is provided below the seating seat 25. Therefore, by opening the seating sheet 25, it is possible to put in and out the article in the article storage chamber.

  The front and rear portions of the vehicle body frame 11 are covered with a front vehicle body cover 26 and a rear vehicle body cover 27 made of synthetic resin, respectively, so that the vehicle body appearance is adjusted. The front body cover 26 forms a leg shield 28, and the rear body cover 27 covers the surroundings of the article storage chamber and the front portion of the engine 21 below the seating seat 25.

  A low floor type step board 29 is provided between the handle bar 16 and the seat 25. The step board 29 is made of synthetic resin and is designed so that the front body cover 26 and the rear body cover 27 are made continuous.

  Next, an engine decompression device according to an embodiment of the present invention will be described in detail with reference mainly to FIGS. Here, FIG. 2 is a sectional view showing the decompression device for the engine according to the present embodiment, FIG. 3 is a side view showing the decompression device for the engine according to the present embodiment, and FIG. 4 shows the decompression device for the engine according to the present embodiment. FIG. 5 is a perspective view showing an eccentric weight and a decompression shaft of an engine decompression device according to the present embodiment, and FIG. 6 is a perspective view showing a state during decompression operation in the engine decompression device according to the present embodiment. FIG. 7 is a perspective view showing a state when the decompression operation is released in the decompression device for an engine according to the present embodiment.

  An engine 21 in FIG. 1 is a four-cycle engine having a single overhead camshaft (SOHC) type valve operating mechanism, and includes a single camshaft 30 inside a cylinder head (not shown). The camshaft 30 is rotatably supported by the cylinder head by ball bearings 31 and 32 provided at both ends. An intake cam 33 for opening and closing an intake valve and an exhaust cam 34 for opening and closing an exhaust valve are adjacent to one end portion on the camshaft 30 in order toward the other end portion, inside the one ball bearing 31. Are arranged.

  A cam sprocket 36 is fixed to the other end of the camshaft 30 by a sprocket knock pin 35 attached to the center of the camshaft 30 outside the other ball bearing 32. The cam sprocket 36 is connected to a cam drive gear (not shown) via a cam chain (not shown), and the rotation of a crankshaft (not shown) is transmitted to the cam sprocket 36 via the cam chain. As a result, the camshaft 30 is rotated, and the valve mechanism is operated.

  The camshaft 30 is provided with a decompression device 40. The decompression device 40 includes a columnar eccentric part 41 formed between the other ball bearing 32 on the camshaft 30 and the exhaust cam 34, an eccentric weight 42 provided rotatably on the eccentric part 41, It has.

  The eccentric portion 41 is formed eccentrically on the opposite side of the lift portion 34a of the exhaust cam 34, that is, on the base circle 34b (portion where the exhaust valve is not lifted) side of the exhaust cam 34, with the shaft center of the camshaft 30 interposed therebetween. Has been. Further, an eccentric groove 44 is provided in a fan shape in the axial direction on the side of the eccentric portion 41 of the base circle 34b of the exhaust cam 34 so as to follow the cam surface.

  As best shown in FIG. 5, the eccentric weight 42 includes a flat cylindrical base portion 45, a weight portion 46 formed on the outer peripheral surface of the base portion 45 by being curved over a substantially half circumference, It is comprised by. The thickness of the weight portion 46 in the radial direction is formed so that the other end portion 46b is thicker than the one end portion 46a. On the exhaust cam 34 side of the eccentric weight 42, a step portion 47 is formed in an arc shape between the base portion 45 and the weight portion 46.

  On the eccentric weight 42, a decompression shaft 48 projects toward the exhaust cam 34 so as to be parallel to the axial center of the camshaft 30 on the one end 46 a side of the weight portion 46 and engages with the eccentric groove 44. It is formed as follows. The decompression shaft 48 has a cylindrical shape and is integrally provided with the eccentric weight 42 by being press-fitted into the eccentric weight 42. The decompression shaft 48 may have a shape other than the columnar shape, such as a cylindrical shape, as long as the outer peripheral surface 48a has a curved shape.

  The decompression shaft 48 rotates along the eccentric groove 44 with the rotation of the eccentric weight 42 and moves to the one end 44a of the eccentric groove 44 in the radial direction from the cam surface on the base circle 34b side of the exhaust cam 34. The exhaust cam 34 is formed so as to be immersed in the cam surface on the base circle 34 b side when it moves to the other end 44 b of the eccentric groove 44. That is, the rotation range of the eccentric weight 42 is such that the decompression shaft 48 projects radially from the cam surface on the base circle 34b side of the exhaust cam 34 and the decompression shaft 48 on the base circle 34b side of the exhaust cam 34. It is regulated between the decompression operation release position that is immersed in the cam surface.

  A coiled return spring 49 is provided between the eccentric portion 41 and the decompression shaft 48. One end 49a of the return spring 49 is locked to the decompression shaft 48, and the other end is locked to a groove (not shown) formed in the eccentric portion 41. The return spring 49 is connected to the exhaust cam 34 and the base. The eccentric part 41 is provided around the step part 47 so as to follow the step part 47 with the part 45. Accordingly, the return spring 49 biases the decompression shaft 48 in a direction against the centrifugal force generated by the rotation of the eccentric weight 42.

  Next, the operation of the decompression device 40 having the above-described configuration will be described.

  2, 3 and 6, when the engine 21 is started, the decompression shaft 48 is brought into contact with and held by the one end 44a of the eccentric groove 44 by the urging force of the return spring 49, so that the eccentric portion of the eccentric weight 42 is held. Rotation in one direction on 41 (clockwise direction in FIG. 6) is restricted. At this time, the curved outer peripheral surface 48 a of the decompression shaft 48 is in a state of projecting in the radial direction with respect to the cam surface of the base circle 34 b of the exhaust cam 34.

  Therefore, when the engine 21 is started, the kick starter is operated or the cell motor is activated and the camshaft 30 is rotated, and in the compression process of the engine 21, the outer peripheral surface 48a of the decompression shaft 48 pushes up the lifter (not shown). The exhaust valve is slightly lifted to operate (decompression operation) so that the air-fuel mixture in the combustion chamber is slightly released. Thereby, in the compression process of the engine 21, the combustion chamber is depressurized, and the engine 21 can be started easily.

  Thereafter, when the rotational speed of the camshaft 30 reaches a predetermined rotational speed, for example, the idle rotational speed, the eccentric weight 42 is eccentric against the urging force of the return spring 49 by the action of centrifugal force as shown in FIG. The part 41 is rotated in the other direction (counterclockwise direction in FIG. 7), and this rotation is restricted by the decompression shaft 48 coming into contact with the other end 44 b of the eccentric groove 44. By the rotation of the decompression shaft 48, the decompression shaft 48 is immersed and accommodated in the cam surface of the base circle 34b of the exhaust cam 34, and the decompression operation is released. Thereby, in the compression process of the engine 21, the exhaust valve remains closed, and the engine 21 can perform normal operation.

  Thereafter, when the engine 21 is decelerated to stop, the centrifugal force acting on the eccentric weight 42 decreases. For this reason, the eccentric weight 42 swings in the one direction by the action of the urging force of the return spring 49. As a result, the outer peripheral surface 48a of the decompression shaft 48 projects from the cam surface of the base circle 34b of the exhaust cam 34, and the engine 21 is stopped in this state.

  According to the decompression device 40 having the above-described configuration, by providing the decompression shaft 48 on the eccentric weight 42, it is not necessary to attach a mass weight (or decompression arm) to the outside of the cam sprocket 36, and the mass weight (or decompression arm). ) And a stopper plate for restricting the rotation of the bolt are not required, so that the number of parts can be reduced and the structure can be simplified.

  Further, it is not necessary to insert the decompression shaft 48 into the notch groove of the camshaft from the outside of the cam sprocket 36, and it is necessary to select a bearing 32 having a large inner diameter in order to rotatably support the decompression shaft and the camshaft. Therefore, the decompression device 40 can be reduced in size and weight.

  Further, the outer peripheral surface 48a of the decompression shaft 48 is formed in a curved shape, and it is not necessary to cut out the cam surface on the base circle 34b side of the exhaust cam 34 in order to accommodate the decompression cam. The lifter is not pushed at the part, and the decompression cam does not operate under an unstable condition, and no abnormal sound is generated or damage is caused. Therefore, durability can be improved, the quietness of the decompression operation can be ensured, and the decompression operation and the release operation thereof can be performed smoothly and reliably.

  Furthermore, by providing the decompression shaft 48 integrally with the eccentric weight 42, it is not necessary to insert the decompression shaft 48 into the notch groove of the camshaft from the outside of the cam sprocket 36, so that the decompression device can be reduced in size and weight. Can do.

  Further, since the eccentric weight 42 is interposed between the bearing 32 and the exhaust cam 34, the axial movement of the eccentric weight 42 is restricted by the bearing 32 and the exhaust cam 34, and thus the member that fixes the eccentric weight 42. Can be omitted, and the number of parts can be reduced and the structure can be further simplified.

  In the above-described embodiment of the present invention, the case where the present invention is applied to the engine 21 of the scooter type motorcycle 10 has been described. However, this is merely an example, and the present invention is not limited to the motorcycle other than the scooter type motorcycle 10. Needless to say, it can also be applied to engines such as motorcycles.

  In addition, since the above description of the embodiment of the present invention describes a preferred embodiment of the decompression device for an engine according to the present invention, there may be various technically preferable limitations. The technical scope of the present invention is not limited to these embodiments unless specifically described to limit the present invention. That is, the above-described components in the embodiment of the present invention can be appropriately replaced with existing components and the like, and various variations including combinations with other existing components are possible. The description of the embodiment of the present invention described above does not limit the contents of the invention described in the claims.

21 Engine 30 Camshaft 32 Bearing 34 Exhaust cam 34b Base circle 40 Decompression device 41 Eccentric part 42 Eccentric weight 44 Eccentric groove 48 Decompression shaft 49 Return spring

Claims (7)

An engine decompression device for decompressing a combustion chamber by opening an exhaust valve by decompression operation when starting the engine,
A cylindrical eccentric portion formed on the camshaft; an eccentric weight provided rotatably on the eccentric portion; and a decompression shaft that opens the exhaust valve in response to the rotation of the eccentric weight. ,
The eccentric weight is interposed between a bearing that rotatably supports the camshaft and an exhaust cam on the camshaft, and the axial movement of the eccentric weight is restricted by the bearing ,
The eccentric portion, the decompression device of the engine, characterized that you have been formed eccentrically on the base circle side of the exhaust cam. The bearing includes an inner peripheral portion, a ball, and an outer peripheral portion from the radially inner side,
The eccentric weight includes a base portion and a weight portion from the radially inner side,
The decompression device for an engine according to claim 1, wherein the base portion is disposed radially inward of the outer peripheral portion. An eccentric portion formed eccentric to the camshaft at a position adjacent to the exhaust cam;
An eccentric groove recessed in the eccentric portion side of the base circle of the exhaust cam;
The eccentric weight provided rotatably on the eccentric part;
The decompression shaft formed so as to protrude from the eccentric weight toward the eccentric groove along the axial direction of the camshaft, and to be engaged with the eccentric groove;
A rotation range of the eccentric weight includes: a decompression operation position in which the decompression shaft projects radially from a cam surface on the base circle side of the exhaust cam; and the decompression shaft is a cam on the base circle side of the exhaust cam. The decompression device for an engine according to claim 1, wherein the decompression device is configured to be regulated between a decompression operation release position that is immersed in a plane.   The engine decompression device according to claim 3, further comprising a spring that biases the eccentric weight so that the eccentric weight moves to the decompression operation position when the engine is stopped.   The engine decompression device according to claim 4, wherein the spring is provided between the decompression shaft and the eccentric portion.   The outer periphery of the decompression shaft is formed in a curved shape, and the decompression shaft is configured to rotate along the eccentric groove as the eccentric weight rotates. The decompression device for an engine according to any one of claims 3 to 5.   The decompression device for an engine according to any one of claims 1 to 6, wherein the decompression shaft is provided integrally with the eccentric weight.

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