WO2015079916A1 - Single-cylinder sohc engine and rocker arm for single-cylinder sohc engine - Google Patents

Abstract

The objective of the present invention is to provide a smaller-sized single-cylinder SOHC engine by increasing the degree of freedom in the design of the engine while preventing an increase in mechanical loss. An intake rocker arm (32) and an exhaust rocker arm (33) respectively have sliding surfaces (46, 56), which have a width in the direction of the axis of rotation (C2) of a cam shaft (31) that is less than the width (D2) of the end parts (44a, 54a) of cam arm parts (44, 54) close to boss parts (43, 53), with these sliding surfaces respectively sliding with respect to an intake cam (40) and an exhaust cam (41) via a coating having a lower coefficient of friction and higher hardness than that of the base material of the sliding surfaces. The sliding surfaces (46, 56) are arranged in a row in the direction of the axis of rotation (C2) of the cam shaft (31).

Description

Single cylinder SOHC engine and rocker arm for single cylinder SOHC engine

The present invention relates to a single cylinder SOHC engine having a rocker arm and a rocker arm for a single cylinder SOHC engine.

The engine includes a cylinder body having a cylinder hole, a cylinder head fixed to the cylinder body, and a piston slidably fitted in the cylinder hole and connected to the crankshaft. The cylinder head is formed with an intake passage and an exhaust passage that allow a combustion chamber formed between the cylinder head and the piston to communicate with the outside. An intake valve and an exhaust valve are disposed at the open ends of the intake passage and the exhaust passage on the combustion chamber side, respectively. The intake valve and the exhaust valve are opened and closed by a valve operating device. This valve operating device is arranged in the cylinder head.

A single cylinder engine is an engine having only one cylinder hole. A single-cylinder engine is provided with a so-called SOHC (Single OverHead Camshaft) type valve gear that drives an intake valve and an exhaust valve with a single camshaft in order to reduce the size of the engine (for example, Patent Document 1). reference).

The SOHC type valve gear includes a camshaft provided with an intake cam and an exhaust cam, an intake rocker arm that is pressed and rocked by the intake cam and presses the intake valve in a direction to open, and an exhaust And an exhaust rocker arm that is oscillated by being pressed by the cam, and that presses the exhaust valve in the opening direction. The intake and exhaust rocker arms are rotatably supported by intake and exhaust rocker shafts arranged in parallel across the camshaft.

A single-cylinder SOHC engine often uses a roller rocker arm in which a roller is provided at a contact portion with a cam (see, for example, Patent Document 1).

Also, some valve gears are provided with a decompression mechanism for releasing the compression pressure at the start of the engine and improving the startability (see, for example, Patent Document 1). The decompression mechanism is disposed on the camshaft. The decompression mechanism of Patent Document 1 includes a decompression weight that swings due to centrifugal force generated by rotation of a camshaft, and a decompression cam that swings in conjunction with the decompression weight.

Further, some valve gears include a variable valve timing mechanism for changing the opening / closing timing of an intake valve or an exhaust valve (see, for example, Patent Document 1). The variable valve timing mechanism has an actuator attached to the wall of the cylinder head. The actuator has a rod that can advance and retract in the axial direction of the camshaft. The engine of Patent Document 1 has two intake rocker arms and two intake cams, and the two intake rocker arms are formed with holes penetrating in the axial direction of the camshaft. In Patent Document 1, the actuator rod presses the connecting pin accommodated in the hole of one intake rocker arm and pushes it into the hole of the other intake rocker arm by the operation of the actuator. . The actuator of such a variable valve timing mechanism is disposed on the rocker shaft when viewed from the cylinder axial direction.

JP 2011-202625 A

¡The roller of the roller rocker arm rolls against the cam. Therefore, in order to ensure the rolling fatigue strength on the cam side, it is necessary to increase the axial width of the cam shaft of the roller and the cam to some extent. Further, since the roller is supported by both ends, the tip of the roller rocker arm on the cam side is longer than the roller alone in the axial direction of the camshaft. Therefore, in a single-cylinder SOHC engine provided with a roller rocker arm, the cylinder head is likely to increase in size in the axial direction of the camshaft.

In addition, when a single cylinder SOHC engine equipped with a roller rocker arm is equipped with a decompression mechanism or a variable valve timing mechanism as described above, the cylinder head tends to be larger in the axial direction of the camshaft.

Accordingly, an object of the present invention is to provide a single-cylinder SOHC engine that can reduce the size of the engine by increasing the degree of freedom in engine design while suppressing an increase in mechanical loss.

Means for Solving the Problems and Effects of the Invention

The single cylinder SOHC engine of the present invention includes a cylinder body portion having a single cylinder hole, a cylinder head portion that covers one end opening of the cylinder hole and forms at least a part of a combustion chamber, and the cylinder head portion. A camshaft provided and rotatable, wherein at least one intake cam and at least one exhaust cam are provided side by side in the rotation axis direction, and each is arranged in parallel with the camshaft; A rocker shaft and an exhaust rocker shaft; at least one intake valve capable of opening and closing an intake port provided in the combustion chamber; and at least one exhaust valve capable of opening and closing an exhaust port provided in the combustion chamber; An intake boss portion supported by the intake rocker shaft; and an intake cam projecting from the intake boss portion; An intake cam arm portion that touches and is pressed by the intake cam, and an intake valve arm that protrudes from the intake boss portion and has an end portion that contacts the intake valve and presses the intake valve in the opening direction. And at least one intake rocker arm swingable about a central axis of the intake rocker shaft, an exhaust boss supported by the exhaust rocker shaft, and protruding from the exhaust boss The exhaust cam arm portion that contacts the exhaust cam and is pressed by the exhaust cam, protrudes from the exhaust boss portion, the end portion contacts the exhaust valve, and opens the exhaust valve An exhaust valve arm for pressing, and at least one exhaust rocker arm swingable around a central axis of the exhaust rocker shaft, The intake rocker arm is integrally formed with the intake cam arm portion, and the width thereof is smaller than the width of the end portion of the intake cam arm portion close to the intake boss portion in the rotation axis direction. And an intake sliding surface that slides on the intake cam through a coating having a lower coefficient of friction and higher hardness than the base material, and the exhaust rocker arm is integrally formed with the exhaust cam arm portion. In the rotational axis direction of the camshaft, the width is formed smaller than the width of the end portion of the exhaust cam arm portion close to the exhaust boss portion, and the friction coefficient is lower than that of the base material and the coating has a high hardness. And an exhaust sliding surface provided so as to be aligned with the intake sliding surface of the intake rocker arm and the rotational axis of the camshaft. And features.

The intake rocker arm includes an intake boss portion supported by the intake rocker shaft, an intake cam arm portion that protrudes from the intake boss portion, contacts the intake cam, and is pressed by the intake cam, and an intake boss And an intake valve arm portion that protrudes from the portion and has an end portion that contacts the intake valve and presses the intake valve in the opening direction. The intake rocker arm is integrally formed with the intake cam arm portion, and has an intake sliding surface that slides on the intake cam through a coating having a lower coefficient of friction and higher hardness than the base material.
The exhaust rocker arm includes an exhaust boss supported by the exhaust rocker shaft, an exhaust cam arm that protrudes from the exhaust boss, contacts the exhaust cam, and is pressed by the exhaust cam; And an exhaust valve arm portion that protrudes from the boss portion and has an end portion that contacts the exhaust valve and presses the exhaust valve in the opening direction. The exhaust rocker arm is integrally formed with the exhaust cam arm portion, and has an exhaust sliding surface that slides on the exhaust cam through a coating having a lower friction coefficient and higher hardness than the base material.
Hereinafter, the intake rocker arm and the exhaust rocker arm may be collectively referred to as a rocker arm. Other names with “for intake” and “for exhaust” may also be collectively referred to.
According to the above-described configuration, the sliding surface of the cam arm portion and the cam slide through the film. This coating has a lower coefficient of friction than the substrate of the sliding surface. Therefore, the coefficient of friction between the coating and the surface sliding with the coating is small.
When the width of the sliding surface of the cam shaft in the rotation axis direction is reduced, the rocker arm can be reduced in weight, and as a result, mechanical loss can be reduced. On the other hand, the contact surface pressure between the sliding surface and the cam increases. An increase in contact surface pressure leads to an increase in frictional force. However, in the present invention, as described above, the friction coefficient between the contact surfaces is reduced by the coating. Therefore, even if the width of the sliding shaft in the rotational axis direction of the camshaft is reduced, the mechanical force due to the increase in the frictional force is increased. Increase in loss can be suppressed.
The width of the cam shaft at the end of the cam arm near the boss in the rotational axis direction is determined by the magnitude of the force applied to the rocker arm, and does not become extremely large. Therefore, in the rotation axis direction of the cam shaft, the width of the sliding surface of the cam arm portion is made smaller than the width of the end portion close to the boss portion of the cam arm portion, so that the width of the sliding surface can be reduced. It can be made smaller than the width of the end portion on the side.
Therefore, in the present invention, while suppressing an increase in mechanical loss, the width of the intake sliding surface and the exhaust sliding surface in the rotational axis direction of the camshaft is set to the width of the cam-side end portion of the conventional rocker arm. Can be smaller.

Also, by reducing the width of the intake sliding surface and the exhaust sliding surface in the direction of the rotation axis of the camshaft, space can be secured accordingly. The intake sliding surface and the exhaust sliding surface are provided side by side in the rotational axis direction of the camshaft. Therefore, secure a wide space between the intake sliding surface and the exhaust sliding surface, or widen the space outside the camshaft rotation axis direction of the intake sliding surface and the exhaust sliding surface. Can do. Thereby, the design freedom of an engine can be raised. By increasing the degree of design freedom, it becomes easier to devise for downsizing the engine. For example, the engine can be downsized by reducing the width of the camshaft in the rotational axis direction and reducing the length of the camshaft.

A cylinder body portion having a single cylinder hole, a cylinder head portion that covers one end opening of the cylinder hole and that constitutes at least a part of the combustion chamber, is provided in the cylinder head portion, is rotatable, and is at least 1 One intake cam and at least one exhaust cam arranged side by side in the rotational axis direction, an intake rocker shaft and an exhaust rocker shaft respectively disposed in parallel with the camshaft, and a combustion chamber At least one intake valve capable of opening and closing the provided intake port, at least one exhaust valve capable of opening and closing the exhaust port provided in the combustion chamber, and an intake boss portion supported by the intake rocker shaft; A single-cylinder engine comprising at least one intake rocker arm and at least one exhaust rocker arm is A small margin of interior space compared to a multi-cylinder engine. Therefore, in the single cylinder engine, it is effective to reduce the size of the engine to secure the internal space and improve the design freedom. Also, many devices equipped with a single cylinder engine have a small space outside the engine. Therefore, this space can be effectively utilized by reducing the size of the single cylinder engine and increasing the space outside the engine.

In addition, a film having a lower coefficient of friction and higher hardness than the base material of the sliding surface is interposed between the sliding surface of the rocker arm and the cam, so that there is a gap between the sliding surface of the rocker arm and the cam. Can prevent seizing.

In the single-cylinder SOHC engine of the present invention, the sliding surface for intake and the sliding surface for exhaust are in the direction of the central axis of the cylinder hole with respect to the camshaft when viewed from the rotational axis of the camshaft. It is preferable to be provided in one direction.

According to this configuration, the intake sliding surface and the exhaust sliding surface have a small width in the rotational axis direction of the camshaft and are aligned in the rotational axis direction of the camshaft. In addition, the sliding surface for intake and the sliding surface for exhaust are provided in one direction in the direction of the central axis of the cylinder hole with respect to the camshaft as viewed from the rotational axis direction of the camshaft. Therefore, the intake sliding surface and the exhaust sliding surface can be arranged in a small space. This facilitates securing a large space in the engine. Therefore, the degree of freedom in engine design can be further improved, and the engine can be further downsized.

In the single cylinder SOHC engine of the present invention, when the rotational axis direction of the camshaft is a left-right direction, one of the intake rocker shaft and the exhaust rocker shaft is provided above the camshaft, and the other is The intake sliding surface and the exhaust sliding surface are provided below the camshaft, and are provided between the intake rocker shaft and the exhaust rocker shaft when viewed from the central axis direction of the cylinder hole. In addition, both are preferably provided in front of or behind the camshaft.

According to this configuration, the intake sliding surface and the exhaust sliding surface have a small width in the rotation axis direction (left-right direction) of the camshaft and are aligned in the rotation axis direction of the camshaft. In addition, the intake sliding surface and the exhaust sliding surface are provided between the intake rocker shaft and the exhaust rocker shaft when viewed from the direction of the center axis of the cylinder hole, both of which are in front of or behind the camshaft. Placed in. Therefore, the intake sliding surface and the exhaust sliding surface can be arranged in a small space. Furthermore, one of the intake rocker shaft and the exhaust rocker shaft is provided above the camshaft, and the other is provided below the camshaft. Therefore, it is easy to narrow the distance between the intake sliding surface and the exhaust sliding surface in the left-right direction.
These make it easy to secure a large space in the engine. Therefore, the engine design freedom can be further improved, and the engine can be further downsized.

In the single-cylinder SOHC engine of the present invention, when the rotation axis direction of the camshaft is a left-right direction, the intake cam arm portion is vertically moved from the intake boss portion when viewed from the center axis direction of the cylinder hole. Preferably, the exhaust cam arm portion protrudes vertically from the exhaust boss portion, and the intake sliding surface and the exhaust sliding surface are provided so as to be aligned in the left-right direction.

According to this configuration, the intake cam arm portion and the exhaust cam arm portion protrude from the intake boss portion and the exhaust boss portion in the vertical direction perpendicular to the rotation axis direction (left-right direction) of the camshaft. Therefore, when the intake sliding surface and the exhaust sliding surface are both arranged in front or rear of the camshaft, one is arranged above the camshaft, and the other is arranged below the camshaft, It is easy to narrow the distance between the intake sliding surface and the exhaust sliding surface in the left-right direction. This facilitates securing a large space in the engine. Therefore, the degree of freedom in engine design can be further improved, and the engine can be further downsized.

In the single-cylinder SOHC engine of the present invention, it is preferable that the intake cam arm portion and the exhaust cam arm portion have a hole penetrating in the rotation axis direction of the cam shaft.

According to this configuration, the intake cam arm portion and the exhaust cam arm portion have holes penetrating in the rotation axis direction of the cam shaft. Accordingly, the intake rocker arm and the exhaust rocker arm can be reduced in weight. The mechanical loss can be reduced by reducing the weight, while maintaining the strength of the intake cam arm and exhaust cam arm, while increasing the width of the intake sliding surface and exhaust sliding surface in the rotation axis direction of the camshaft. Can be small. As a result, the degree of freedom in engine design can be further improved, and the engine can be further downsized.

In the single-cylinder SOHC engine of the present invention, the intake cam arm portion is formed such that a width of an end portion close to the intake boss portion is maximized in a width in a rotation axis direction of the cam shaft. The cam arm portion is preferably formed so that the width of the end portion close to the exhaust boss portion is maximized in the width of the cam shaft in the rotation axis direction.

In the single cylinder SOHC engine of the present invention, the intake cam has a width smaller than a width of an end portion of the intake cam arm portion close to the intake boss portion in the rotation axis direction of the camshaft, and the exhaust cam. The cam preferably has a width smaller than a width of an end portion of the exhaust cam arm portion close to the exhaust boss portion in a rotation axis direction of the cam shaft.

According to this configuration, since the intake cam and the exhaust cam have a small width in the rotation axis direction of the camshaft, a space can be secured in the vicinity of the camshaft without increasing the size of the engine. Further, by arranging the cams close to each other, a large space can be secured in the outer peripheral portion of the camshaft without increasing the size of the engine. By securing such a space, the degree of freedom in designing the engine can be further improved, so that the engine can be further downsized.
Further, since the width of the cam shaft of the intake cam and the exhaust cam in the rotation axis direction is small, the engine can be downsized by shortening the length of the cam shaft.

The single-cylinder SOHC engine of the present invention further includes a spark plug provided in the cylinder head portion so that a tip portion faces the combustion chamber, and a part of the spark plug is disposed on the rotation axis of the camshaft. It is preferable that

According to this configuration, the spark plug is provided in the cylinder head portion so that a part of the spark plug is located on the rotation axis of the camshaft. Since the intake cam and the exhaust cam have a small width in the rotation axis direction of the camshaft, the length of the camshaft can be shortened. By shortening the length of the camshaft, the wall on which the ignition plug of the cylinder head portion is provided can be shifted to the inside of the cylinder head portion. Thereby, the space used when maintaining a spark plug is securable.

In the single-cylinder SOHC engine of the present invention, the intake valve and the exhaust valve each have a valve shaft portion and a valve umbrella portion connected to a tip end of the valve shaft, and the intake sliding surface and It is preferable that the exhaust sliding surface has a width in the rotation axis direction of the camshaft that is smaller than a minimum diameter of the valve shaft portion of the intake valve and the exhaust valve.

The diameters of the valve shafts of the intake and exhaust valves are determined by the magnitude of the force that the intake and exhaust valves receive from the camshaft and do not become extremely large. According to the above configuration, the width of the intake sliding surface and the exhaust sliding surface in the rotation axis direction of the camshaft is only smaller than the width of the end portions near the boss portions of the intake cam arm portion and the exhaust cam arm portion. It is smaller than the minimum diameter of the valve shaft. Therefore, when the diameter of the valve shaft portion is smaller than the width of the end portions close to the boss portions of the intake cam arm portion and the exhaust cam arm portion, the design freedom of the engine is further improved and the engine can be further downsized. .

In the single-cylinder SOHC engine of the present invention, it is preferable to include a decompression mechanism mounted on the camshaft. According to this configuration, the decompression mechanism can be arranged while suppressing the enlargement of the engine.

The single-cylinder SOHC engine of the present invention includes a variable valve timing mechanism that includes a plurality of at least one of the intake rocker arm and the exhaust rocker arm, and includes an actuator having a rod arranged in parallel with the camshaft. It is preferable. According to this configuration, the variable valve timing mechanism can be arranged while suppressing an increase in size of the engine.

In the single cylinder SOHC engine of the present invention, the intake boss portion and the exhaust boss portion are rotatably supported by the intake rocker shaft and the exhaust rocker shaft, respectively, A coating having a lower coefficient of friction and a higher hardness than the base material is formed on at least a portion of the outer peripheral surface of the exhaust rocker shaft that contacts the intake boss and the exhaust boss. preferable.

According to this configuration, a coating film having a lower coefficient of friction and higher hardness than the base material is formed on at least a portion of the outer peripheral surface of the rocker shaft that contacts the boss portion. Thereby, the frictional force between the rocker shaft and the boss portion of the rocker arm can be reduced, and seizure between the rocker shaft and the boss portion of the rocker arm can be prevented. Therefore, an increase in engine mechanical loss can be further suppressed.

In the single-cylinder SOHC engine of the present invention, a coating having a lower coefficient of friction and higher hardness than the base material is formed on the surface of the end of the intake valve arm that presses the intake valve. It is preferable that a coating film having a lower friction coefficient and higher hardness than the base material is formed on the surface of the end portion of the exhaust valve arm portion that presses the exhaust valve.

According to this configuration, a film having a lower friction coefficient and higher hardness than the base material is formed on the surface of the end portion of the valve arm portion of the rocker arm that presses the valve. Thereby, it arises between the edge part which presses the valve | bulb of a valve arm part, and a valve, or the edge part which presses the valve | bulb of a valve arm part, and the components which are provided in a valve and are pressed by the said edge part. The frictional force can be reduced and seizure between the two can be prevented. Therefore, an increase in engine mechanical loss can be further suppressed.

In the single-cylinder SOHC engine of the present invention, the intake shim disposed between the intake valve arm portion and the intake valve, and the exhaust valve arm portion and the exhaust valve are disposed. It is preferable that an exhaust shim is provided, and a film having a lower friction coefficient and higher hardness than the base material is formed on the surfaces of the intake shim and the exhaust shim.

According to this configuration, a film having a lower friction coefficient and higher hardness than the base material is formed on the surface of the shim disposed between the valve arm portion and the valve. Thereby, the frictional force between the valve arm portion and the shim can be reduced, and seizure between the valve arm portion and the shim can be prevented. Therefore, an increase in engine mechanical loss can be further suppressed.

In the single-cylinder SOHC engine of the present invention, the coating having a lower coefficient of friction and higher hardness than the base material of the intake sliding surface is formed on at least one of the intake sliding surface and the intake cam. It is preferable that at least one of the exhaust sliding surface and the intake cam is formed with the coating film having a lower friction coefficient and higher hardness than the base material of the exhaust sliding surface.

The rocker arm for a single cylinder SOHC engine of the present invention is the intake rocker arm or the exhaust rocker arm used in the single cylinder SOHC engine of the present invention, wherein the intake sliding surface or the exhaust sliding surface. Furthermore, the coating film having a lower friction coefficient and higher hardness than the base material is formed.

1 is a side view showing a partial cross section of an engine unit to which a single cylinder SOHC engine according to an embodiment of the present invention is applied. It is the elements on larger scale of Drawing 1, and is a sectional view of a single cylinder SOHC engine. It is sectional drawing of the single cylinder SOHC engine in FIG. FIG. 2 is a view of the single-cylinder SOHC engine shown in FIG. 1 as viewed from the cylinder cover side with the cylinder cover and a reinforcing plate removed. It is sectional drawing of the single cylinder engine which concerns on other embodiment of this invention. It is sectional drawing of the single cylinder engine which concerns on other embodiment of this invention. FIG. 7 is a view of the single cylinder SOHC engine shown in FIG. 6 viewed from the cylinder cover side with the cylinder cover and the reinforcing plate removed. It is the figure which looked at the rocker arm which concerns on other embodiment of this invention from the center axis line direction of the cylinder hole.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 discloses a swing type engine unit 1 used in, for example, a scooter type motorcycle. The engine unit 1 includes a single-cylinder SOHC engine 2 and a transmission case 3 that also serves as a swing arm. The single cylinder SOHC engine 2 is a water-cooled four-cycle engine. In the following description, the front-rear direction is the vehicle front-rear direction viewed from the rider seated on the motorcycle seat, and the left-right direction is the vehicle left-right direction viewed from the rider seated on the seat ( (Width direction of the vehicle). Moreover, the arrow F direction and the arrow B direction of each drawing represent the front and the rear, the arrow L direction and the arrow R direction represent the left side and the right side, and the arrow U direction and the arrow D direction are Represents the top and bottom.

The transmission case 3 extends rearward from the single cylinder SOHC engine 2. The transmission case 3 incorporates a V-belt type automatic transmission 4, and a rear wheel (not shown) driven by the V-belt type automatic transmission 4 is supported at the rear end portion of the transmission case 3. .

The single-cylinder SOHC engine 2 has a crankcase 5, a cylinder body portion 6, and a cylinder head portion 7 that are integrated with the transmission case 3. The crankcase 5 accommodates the crankshaft 8. The crankshaft 8 is horizontally disposed along the width direction (left-right direction) of the motorcycle body, and one end of the crankshaft 8 is connected to the input end of the V-belt type automatic transmission 4 via an automatic centrifugal clutch. It is connected to.

A cylinder hole 9 is formed in the cylinder body 6. A piston 10 is accommodated in the cylinder hole 9. A central axis C1 of the cylinder hole 9 extends in the front-rear direction. The piston 10 is connected to the crankshaft 8 via a connecting rod 11. The cylinder body 6 protrudes substantially horizontally from the crankcase 5 toward the front.

As shown in FIG. 2, the cylinder head portion 7 covers the front opening of the cylinder hole 9. The cylinder head portion 7 has a recess 12 on the surface facing the cylinder hole 9. A combustion chamber 13 is formed between the recess 12 and the piston 10. The cylinder head portion 7 includes two intake passages 14 (only one is shown in FIG. 2) that opens to the combustion chamber 13 and a single exhaust passage 15 that opens to the combustion chamber 13. The two intake passages 14 are formed to extend forward and upward from two intake ports 14a (only one is shown in FIG. 2) formed in the recess 12. The two air inlets 14a are formed side by side in the left-right direction. The exhaust passage 15 is formed to extend forward and downward from an exhaust port 15 a formed in the recess 12.

The two intake ports 14a are opened and closed by two intake valves 16 (only one is shown in FIG. 2). The intake valve 16 includes a valve umbrella portion 16a that opens and closes the intake port 14a, and a valve shaft portion 16b that extends forward and upward from the valve umbrella portion 16a. The valve shaft portion 16 b is supported by the cylinder head portion 7 via the valve guide 17. The two valve shaft portions 16b are arranged in parallel in the left-right direction.

The ignition plug 68 is attached to the cylinder head portion 7. The tip of the spark plug 68 is disposed facing the combustion chamber 13. The spark plug 68 is inserted into the combustion chamber 13 from the outer surface of the single cylinder SOHC engine 2.

A spring retainer 21 is attached to the front end of the valve shaft 16b. The front end portion of the valve shaft portion 16b is fitted into the hole in the center portion of the spring retainer 21. An intake spring 22 is interposed between the outer peripheral portion of the spring retainer 21 and the cylinder head portion 7. The intake valve 16 is urged by an intake spring 22 in a direction to close the intake port 14a.

The exhaust port 15 a is opened and closed by an exhaust valve 18. The exhaust valve 18 includes a valve umbrella portion 18a that opens and closes the exhaust port 15a, and a valve shaft portion 18b that extends forward and downward from the valve umbrella portion 18a. The valve shaft portion 18 b is supported by the cylinder head portion 7 via the valve guide 19.

A spring retainer 23 is attached to the front end portion of the valve shaft portion 18b. The front end portion of the valve shaft portion 18 b is fitted in the hole in the center portion of the spring retainer 23. An exhaust spring 24 is interposed between the outer peripheral portion of the spring retainer 23 and the cylinder head portion 7. The exhaust valve 18 is biased by the exhaust spring 24 in a direction to close the exhaust port 15a.

The minimum diameter of the valve shaft portion 16b of the intake valve 16 and the minimum diameter of the valve shaft portion 18b of the exhaust valve 18 are substantially the same.

The cylinder head portion 7 has outer walls 25a, 25b, 25c, and 25d. As shown in FIGS. 3 and 4, the first outer wall 25 a forms the right surface of the cylinder head portion 7, and the second outer wall 25 b forms the left surface of the cylinder head portion 7. The first outer wall 25a and the second outer wall 25b face each other in the left-right direction. As shown in FIGS. 2 and 4, the third outer wall 25 c forms the upper surface of the cylinder head portion 7, and the fourth outer wall 25 d forms the lower surface of the cylinder head portion 7. The third outer wall 25c and the fourth outer wall 25d face each other in the vertical direction.

</ RTI> Inside the cylinder head part 7, a valve operating chamber 26 is formed with the front opened. A detachable head cover 27 is attached to the front end portion of the cylinder head portion 7. The head cover 27 covers the open end of the valve operating chamber 26.

The spark plug 68 described above is attached to the first outer wall 25a. The first outer wall 25 a is formed in a concave shape protruding toward the inside of the valve operating chamber 26. In the vertical direction, the spark plug 68 is disposed at the same position as the concave portion of the first outer wall 25a. When viewed from the direction of the central axis C1 of the cylinder hole 9, the spark plug 68 is connected to a boss portion 43 of the cam arm portion 44 of the intake rocker arm 32 described later and a cam arm portion 54 of the exhaust rocker arm 33 described later. Between the boss portion 53 and the connecting portion. The spark plug 68 is positioned between a center axis C3 of an intake rocker shaft 34, which will be described later, and a center axis C4 of an exhaust rocker shaft 35, which will be described later, when viewed from the direction of the center axis C1 of the cylinder hole 9. ing. In other words, the spark plug 68 is located between the central axes C3 and C4 in the vertical direction. Further, a part of the spark plug 68 is disposed on a rotation axis C2 of the cam shaft 31 described later.

The cylinder head portion 7 has a support wall 28 inside the valve operating chamber 26. The support wall 28 is connected to the third outer wall 25c, and is disposed between the first outer wall 25a and the second outer wall 25b. The valve shaft portion 16 b of the intake valve 16 and the valve shaft portion 18 b of the exhaust valve 18 are located between the first outer wall 25 a and the support wall 28.

The valve operating chamber 26 houses a valve operating device 30 that opens and closes the intake valve 16 and the exhaust valve 18. The valve gear 30 includes a camshaft 31, an intake rocker arm 32, an exhaust rocker arm 33, an intake rocker shaft 34, and an exhaust rocker shaft 35. In FIG. 3, the exhaust rocker arm 33 shows only the cut end face, and the exhaust rocker shaft 35 is not shown.

The camshaft 31 is rotatably supported by the cylinder head portion 7. As shown in FIG. 3, one end portion (right end portion) of the camshaft 31 is rotatably supported with respect to the first outer wall 25 a via a bearing 36. The other end portion (left end portion) of the camshaft 31 is rotatably supported with respect to the support wall 28 via a bearing 37. The camshaft 31 is disposed horizontally along the width direction (left-right direction) of the vehicle body.

The other end portion (left end portion) of the camshaft 31 is disposed to the left of the support wall 28, and a sprocket (or pulley) 38 is fixed thereto. A chain (or belt) 39 is bridged between the sprocket 38 and a sprocket (not shown) provided on the crankshaft 8. As a result, the camshaft 31 rotates in the forward direction in the direction indicated by the arrow in FIG. 2 (the direction of rotation of the rear wheel when the motorcycle moves forward).

The camshaft 31 is provided with an intake cam 40 and an exhaust cam 41 side by side in the left-right direction (the direction of the rotation axis C2 of the camshaft 31). A coating (not shown) similar to the coating 62 described later is formed on the outer peripheral surfaces of the intake cam 40 and the exhaust cam 41. The coating may be formed not only on the outer peripheral surfaces of the intake cam 40 and the exhaust cam 41 but also on the axial end surfaces.

Although not shown, the camshaft 31 is formed with an oil passage that opens to the outer peripheral surfaces of the intake cam 40 and the exhaust cam 41.

As shown in FIG. 2, the intake rocker shaft 34 is provided on the front upper side of the camshaft 31. The intake rocker shaft 34 is in parallel with the camshaft 31. The intake rocker shaft 34 is supported by the cylinder head portion 7 so as not to rotate. As shown in FIG. 4, one end portion (right end portion) of the intake rocker shaft 34 is supported by a bearing portion 42 that protrudes from the first outer wall 25 a to the valve operating chamber 26. The other end (left end) of the intake rocker shaft 34 is supported by the support wall 28. A film (not shown) similar to the film 62 described later is formed on the outer peripheral surface of the intake rocker shaft 34.

The intake rocker arm 32 is swingably supported by the intake rocker shaft 34. As shown in FIG. 2, the intake rocker arm 32 includes a cylindrical boss portion 43 (intake boss portion of the present invention), a cam arm portion 44 (intake cam arm portion of the present invention), and two valve arm portions. 45A and 45B (see FIG. 4 for 45A). Each of the two valve arm portions 45A and 45B corresponds to an intake valve arm portion of the present invention. The intake rocker shaft 34 passes through the boss portion 43. The boss portion 43 is supported so as to be swingable with respect to the intake rocker shaft 34 and to be slidable in the axial direction (left-right direction).

The intake rocker arm 32 is formed by integral molding. The cam arm portion 44 projects downward from the outer peripheral surface of the boss portion 43. The cam arm portion 44 is formed with a hole 47 penetrating in the left-right direction (the direction of the rotational axis C2 of the camshaft 31). The cam arm portion 44 is connected to two locations separated in the circumferential direction of the outer peripheral portion of the boss portion 43.

A sliding surface 46 (sliding surface for intake of the present invention) is formed at the rear lower end of the cam arm portion 44. The sliding surface 46 slides with the outer peripheral surface of the intake cam 40. The intake rocker arm 32 is pressed by the intake cam 40 and swings around the central axis C <b> 3 of the intake rocker shaft 34. A coating 62 is formed on the sliding surface 46. Therefore, strictly speaking, the sliding surface 46 has an outer periphery of the intake cam 40 via a coating 62 formed on the sliding surface 46 and a coating (not shown) formed on the outer peripheral surface of the intake cam 40. Sliding with the surface. In the present embodiment, the coating 62 is formed not only on the sliding surface 46 but also on the surface of the intake rocker arm 32 other than the inner peripheral surface of the boss portion 43. In the partial enlarged view shown in FIG. 3, the thickness of the film 62 is exaggerated.

The coating 62 has a lower coefficient of friction and higher hardness than the base material of the intake rocker arm 32 (also the base material of the sliding surface 46). In other words, the coating 62 is formed by subjecting the sliding surface 46 to a surface treatment that lowers the coefficient of friction and increases the hardness as compared with the base material. The friction coefficient of the film 62 is lower than the friction coefficient of the surface subjected to the surface treatment with the chromium nitride coating or the sintered material. In other words, the coating film 62 has high seizure resistance. Specifically, the coating 62 is preferably, for example, a carbon-based hard coating, and more specifically DLC (Diamond Like Carbon). DLC has a self-lubricating property that is a characteristic of a graphite structure, and therefore has a low friction coefficient and high seizure resistance. Compared to this DLC, for example, a film made of a chromium nitride coating does not have self-lubricating properties and has a relatively high friction coefficient. Further, since DLC has a diamond structure, it has a higher maximum hardness and higher wear resistance than a film formed by chromium nitride coating.

As shown in FIG. 4, the width D1 of the sliding surface 46 of the cam arm 44 in the left-right direction (the direction of the rotation axis C2 of the camshaft 31) is smaller than the width W of the outer peripheral surface of the intake cam 40 in the left-right direction. Further, the width D1 in the left-right direction of the sliding surface 46 of the cam arm portion 44 is smaller than the minimum diameter of the valve shaft portion 16b of the intake valve 16. The lateral width of the portion other than the sliding surface 46 at the end (the end provided with the sliding surface 46) opposite to the boss 43 of the cam arm 44 is the lateral width D1 of the sliding surface 46. Is almost the same.

In the vicinity of the boss portion 43, the cam arm portion 44 has a width in the left-right direction that is closer to the boss portion 43. The lateral width D2 of the connecting portion 44a of the cam arm portion 44 with the boss portion 43 (the end portion of the cam arm portion 44 close to the boss portion 43) is larger than the lateral width D1 of the sliding surface 46 of the cam arm portion 44. . The cam arm portion 44 has the maximum width in the left-right direction at the connecting portion 44 a with the boss portion 43.

Note that the width in the left-right direction (the direction of the rotational axis C2 of the camshaft 31) of the connecting portion 44a of the cam arm 44 with the boss 43 is the direction of the central axis C1 of the cylinder hole 9 and This is the length of a straight line connecting inflection points between the curvature of the outer surface (left surface and right surface) in the left-right direction and the curvature of the outer peripheral surface of the boss portion 43 in the left-right direction. In the present embodiment, the outer peripheral surface of the boss portion 43 extends in the left-right direction. Therefore, when viewed from the direction of the central axis C1 of the cylinder hole 9, the length of the straight line connecting the boundary positions of the straight line corresponding to the outer peripheral surface of the boss portion 43 and the two curves corresponding to the left and right both surfaces of the cam arm portion 44 Is the width in the left-right direction of the connecting portion 44 a with the boss portion 43 of the cam arm portion 44.

The lateral width D2 of the connecting portion 44a of the cam arm portion 44 with the boss portion 43 is larger than the lateral width W of the outer peripheral surface of the intake cam 40 and the minimum diameter of the valve shaft portions 16b and 18b.

The valve arm portions 45 </ b> A and 45 </ b> B protrude upward from the outer peripheral surface of the boss portion 43. When the intake rocker arm 32 is viewed from the head cover 27 side, the valve arm portions 45A and 45B are formed in a V shape that is separated from each other toward the top (see FIG. 4).

As shown in FIG. 2, each of the valve arm portions 45A and 45B is formed with a hole 48 penetrating in the left-right direction (the direction of the rotation axis C2 of the camshaft 31). The valve arm portions 45 </ b> A and 45 </ b> B are connected to two locations separated from each other in the circumferential direction of the outer peripheral portion of the boss portion 43. In one of the two places, the valve arm portions 45 </ b> A and 45 </ b> B are connected to the cam arm portion 44.

A pressing portion 49 is formed at each end of the valve arm portions 45A and 45B opposite to the boss portion 43. The pressing portion 49 faces the tip of the valve shaft portion 16 b of the intake valve 16. When the intake rocker arm 32 is pressed by the intake cam 40 and swings, the intake rocker arm 32 presses the two intake valves 16 in the direction to open the two intake valves 16.

A disk-shaped shim 50 (the intake shim of the present invention) is disposed between each pressing portion 49 of the intake rocker arm 32 and the tip of the valve shaft portion 16b. The shim 50 is for adjusting the tappet clearance. The shim 50 is detachably mounted in the central hole of the spring retainer 21 and is in contact with the pressing portion 49 of the intake rocker arm 32. A film (not shown) similar to the film 62 is formed on the surface of the shim 50. Therefore, the pressing portion 49 contacts the surface of the shim 50 via the coating 62 formed on the pressing portion 49 and the coating formed on the surface of the shim 50.

As shown in FIG. 4, a spring 51 is disposed on the outer periphery of the intake rocker shaft 34 on the left side of the boss 43 of the intake rocker arm 32. The intake rocker arm 32 is biased by the spring 51 toward the first outer wall 25a (that is, to the right). More specifically, the boss portion 43 is pressed against the end surface of the bearing portion 42 of the first outer wall 25a by the spring 51.

When adjusting the tappet clearance, first, a thickness gauge is inserted between the pressing portion 49 of the intake rocker arm 32 and the shim 50 to measure the tappet clearance. By replacing the shim 50 with a different thickness based on the measurement result, the tappet clearance on the intake side can be adjusted to a specified value.

When replacing the shim 50, the operator rocks the intake rocker arm 32 toward the second outer wall 25b against the biasing force of the spring 51. As a result, the pressing portion 49 located at the tip of the valve arm portions 45 </ b> A and 45 </ b> B is shifted to the side of the shim 50. In this state, for example, the shim 50 is taken out using a magnet driver. Thereafter, a new shim 50 is mounted on the spring retainer 21, and then the intake rocker arm 32 is slid to the original position.

Although not shown, lubricating oil ejected from an oil passage (not shown) of the camshaft 31 is guided between the boss portion 43 and the intake rocker shaft 34 to the boss portion 43 of the intake rocker arm 32. The oil supply hole is formed.

The exhaust rocker shaft 35 is disposed in front of and below the camshaft 31. The exhaust rocker shaft 35 is in parallel with the camshaft 31 and the intake rocker shaft 34. The exhaust rocker shaft 35 is supported by the cylinder head portion 7 so as not to rotate. One end portion (right end portion) of the exhaust rocker shaft 35 is fitted into a bearing portion 52 that protrudes from the first outer wall 25a to the valve operating chamber 26. The other end (left end) of the exhaust rocker shaft 35 is supported by the support wall 28. A film (not shown) similar to the film 62 is formed on the outer peripheral surface of the exhaust rocker shaft 35.

The exhaust rocker arm 33 is swingably supported by the exhaust rocker shaft 35. The exhaust rocker arm 33 includes a cylindrical boss 53 (exhaust boss according to the present invention), a cam arm 54 (exhaust cam arm according to the present invention), and a single valve arm 55 (exhaust according to the present invention). Valve arm section). The exhaust rocker shaft 35 passes through the boss portion 53. The boss portion 53 is supported so as to be swingable with respect to the exhaust rocker shaft 35 and to be slidable in the axial direction (left-right direction).

The exhaust rocker arm 33 is formed by integral molding. The cam arm portion 54 protrudes upward from the outer peripheral surface of the boss portion 53. The cam arm portion 54 is formed with a hole 57 penetrating in the left-right direction (the direction of the rotation axis C2 of the camshaft 31). The cam arm portion 54 is connected to two locations separated in the circumferential direction of the outer peripheral portion of the boss portion 53.

A sliding surface 56 (exhaust sliding surface of the present invention) is formed at the rear upper end of the cam arm portion 54. The sliding surface 56 is aligned with the sliding surface 46 of the intake rocker arm 32 in the left-right direction. As shown in FIG. 4, the sliding surface 56 is located to the left of the sliding surface 46. The sliding surfaces 46 and 56 are provided between the intake rocker shaft 34 and the exhaust rocker shaft 35 when viewed from the front-rear direction (the direction of the central axis C1 of the cylinder hole 9). In other words, the sliding surfaces 46 and 56 are positioned between the intake rocker shaft 34 and the exhaust rocker shaft 35 in the vertical direction. Further, as shown in FIG. 2, when viewed from the left-right direction (the direction of the rotational axis C2 of the camshaft 31), the sliding surfaces 46 and 56 are forward of the camshaft 31 (one direction of the central axis C1 of the cylinder hole 9). ).

The sliding surface 56 slides with the outer peripheral surface of the exhaust cam 41. The exhaust rocker arm 33 is pressed by the exhaust cam 41 and swings around the central axis C <b> 4 of the exhaust rocker shaft 35. A film (not shown) similar to the film 62 is formed on the sliding surface 56. Therefore, strictly speaking, the sliding surface 56 slides with the outer peripheral surface of the exhaust cam 41 via the coating formed on the sliding surface 56 and the coating formed on the outer peripheral surface of the exhaust cam 41. In the present embodiment, the coating is formed not only on the sliding surface 56 but also on the surface of the exhaust rocker arm 33 other than the inner peripheral surface of the boss portion 53.

As shown in FIG. 4, the lateral width of the sliding surface 56 of the cam arm 54 is smaller than the lateral width of the outer peripheral surface of the exhaust cam 41. Further, the lateral width of the sliding surface 56 of the cam arm portion 54 is smaller than the minimum diameter of the valve shaft portion 18 b of the exhaust valve 18. The lateral width of the portion other than the sliding surface 56 at the end of the cam arm portion 54 opposite to the boss 53 (the end provided with the sliding surface 56) is equal to the lateral width of the sliding surface 56. It is almost the same.

In the vicinity of the boss portion 53, the cam arm portion 54 has a width in the left-right direction that is closer to the boss portion 53. The lateral width of the connecting portion 54a of the cam arm portion 54 with the boss portion 53 (the end portion of the cam arm portion 54 close to the boss portion 53) is greater than the lateral width of the sliding surface 56 of the cam arm portion 54. The cam arm portion 54 has the maximum width in the left-right direction at the connecting portion 54 a with the boss portion 53.

The lateral width of the connecting portion 54a of the cam arm portion 54 with the boss portion 53 is the curvature of the outer surface (left surface and right surface) of the cam arm portion 54 with respect to the lateral direction when viewed from the direction of the central axis C1 of the cylinder hole 9. And the length of a straight line connecting inflection points with the curvature of the outer peripheral surface of the boss portion 53 with respect to the left-right direction.

The lateral width of the connecting portion 54a of the cam arm portion 54 with the boss portion 53 is larger than the lateral width of the outer peripheral surface of the exhaust cam 41 and the minimum diameter of the valve shaft portions 16b and 18b.

The valve arm portion 55 projects downward from the outer peripheral surface of the boss portion 53. The valve arm 55 is formed with a hole 58 penetrating in the left-right direction. The valve arm portion 55 is connected to two locations separated in the circumferential direction of the outer peripheral portion of the boss portion 53. In one of the two places, the valve arm portion 55 is connected to the cam arm portion 54.

A pressing portion 59 is formed at the end of the valve arm portion 55 opposite to the boss portion 53. The pressing portion 59 faces the tip of the valve shaft portion 18b of the exhaust valve 18. When the exhaust rocker arm 33 is pressed by the exhaust cam 41 and swings, the exhaust rocker arm 33 presses the exhaust valve 18 in a direction to open the exhaust valve 18.

A disc-shaped shim 60 (exhaust shim of the present invention) is disposed between the pressing portion 59 of the exhaust rocker arm 33 and the tip of the valve shaft portion 18b. The shim 60 is for adjusting the tappet clearance. The shim 60 is detachably mounted in the central hole of the spring retainer 23 and is in contact with the pressing portion 59 of the exhaust rocker arm 33. A film (not shown) similar to the film 62 is formed on the surface of the shim 60. Therefore, the pressing portion 59 is in contact with the surface of the shim 60 via the coating formed on the pressing portion 59 and the coating formed on the surface of the shim 60.

As shown in FIG. 4, a spring 61 is disposed on the outer periphery of the exhaust rocker shaft 35 on the right side of the boss 53 of the exhaust rocker arm 33. The exhaust rocker arm 33 is urged toward the second outer wall 25b by the spring 61 (that is, to the left). More specifically, the boss portion 53 is pressed against the support wall 28 by the spring 61.

タ Tappet clearance adjustment is performed in the same way as the intake side.

Although not shown, lubricating oil ejected from an oil passage (not shown) of the camshaft 31 is guided between the boss portion 53 and the exhaust rocker shaft 35 to the boss portion 53 of the exhaust rocker arm 33. The oil supply hole is formed.

2 and 3, a reinforcing plate 65 is fixed to the cylinder head portion 7. The reinforcing plate 65 is disposed across the end surface of the first outer wall 25 a and the end surface of the support wall 28. The reinforcing plate 65 has a substantially square shape, and a substantially square hole is formed in the center of the reinforcing plate 65.

A pair of stud bolts 66 protrude from the front end surface of the support wall 28 and the front end surface of the first outer wall 25a (see FIG. 4). The stud bolt 66 passes through holes formed at the four corners of the reinforcing plate 65. A nut 67 is attached to the tip of the stud bolt 66.

The single cylinder SOHC engine 2 of the present embodiment has the following features.
In the present embodiment, a coating film (62) is formed on the sliding surfaces 46, 56 of the cam arm portions 44, 54, and a coating film (not shown) similar to the coating film 62 is formed on the outer peripheral surface of the cams 40, 41. Has been. Therefore, the sliding surfaces 46 and 56 of the cam arm portions 44 and 54 and the outer peripheral surface of the cams 40 and 41 slide through the two films. This coating has a lower coefficient of friction than the base material of the sliding surfaces 46 and 56. Therefore, the coefficient of friction between the coating and the surface sliding with the coating is small.

When the width (D1) of the sliding surface 46, 56 in the direction of the rotation axis C2 of the camshaft 31 is reduced, the rocker arms 32, 33 can be reduced in weight, and as a result, mechanical loss can be reduced. On the other hand, the contact surface pressure between the sliding surfaces 46 and 56 and the cams 40 and 41 increases. An increase in contact surface pressure leads to an increase in frictional force. However, in this embodiment, since the friction coefficient between the contact surfaces is lowered by the coating, even if the width of the sliding surfaces 46 and 56 in the direction of the rotation axis C2 of the camshaft 31 is reduced, the frictional force is increased. The increase in mechanical loss due to can be suppressed.

The width (D2) of the cam shaft 31 in the direction of the rotation axis C2 of the end portions 44a and 54a of the cam arm portions 44 and 54 close to the boss portions 43 and 53 is determined by the magnitude of the force applied to the rocker arms 32 and 33. , Never become extremely large. Therefore, in the direction of the rotation axis C2 of the camshaft 31, the width (D1) of the sliding surfaces 46, 56 of the cam arm portions 44, 54 is set to the end portions 44a, 54a close to the boss portions 43, 53 of the cam arm portions 44, 54. By making it smaller than the width (D2), the width (D1) of the sliding surfaces 46, 56 can be made smaller than the width of the end portion on the cam side of the conventional rocker arm.
Therefore, in this embodiment, while suppressing an increase in mechanical loss, the width (D1) of the sliding surfaces 46 and 56 in the direction of the rotation axis C2 of the camshaft 31 is set to the cam-side end of the conventional rocker arm. Can be smaller than the width of.

Further, by reducing the width (D1) of the sliding surfaces 46 and 56 in the direction of the rotation axis C2 of the camshaft 31, space can be secured accordingly. The sliding surface 46 and the sliding surface 56 are provided side by side in the rotational axis direction of the camshaft 31. Therefore, it is possible to secure a wide space between the sliding surface 46 and the sliding surface 56, or to widen a space outside the sliding surface 46 and the sliding surface 56 in the direction of the rotation axis C2 of the camshaft 31. it can. Thereby, the design freedom of the engine 2 can be raised. By increasing the degree of design freedom, it becomes easier to devise for downsizing the engine 2. For example, the engine 2 can be downsized by reducing the width of the cams 40 and 41 in the direction of the rotation axis C2 of the camshaft 31 and shortening the length of the camshaft 31.

Since the engine 2 of the present embodiment is a single cylinder engine, the internal space is less than that of a multi-cylinder engine. Therefore, in the engine 2 of the present embodiment, it is effective to reduce the size of the engine 2 to secure the internal space and improve the design freedom. Also, many devices equipped with a single cylinder engine have a small space outside the engine. Therefore, the space can be effectively utilized by downsizing the engine 2 and increasing the space outside the engine 2.

Further, between the sliding surfaces 46 and 56 of the rocker arms 32 and 33 and the cams 40 and 41, a coating (62) having a lower coefficient of friction and higher hardness than the base material of the sliding surfaces 46 and 56 is interposed. Therefore, seizure can be prevented from occurring between the sliding surfaces 46, 56 of the rocker arms 32, 33 and the cams 40, 41.

Further, the sliding surface 46 and the sliding surface 56 have a small width in the direction of the rotation axis C2 of the camshaft 31 and are aligned in the direction of the rotation axis C2 of the camshaft 31. In addition, the sliding surface 46 and the sliding surface 56 are unidirectional (forward) in the direction of the central axis C1 of the cylinder hole 9 with respect to the camshaft 31 when viewed from the direction of the rotational axis C2 of the camshaft 31. Provided. Therefore, the sliding surface 46 and the sliding surface 56 can be concentrated and arranged in a small space. Thereby, it becomes easy to ensure a large space in the engine 2. Therefore, since the design freedom of the engine 2 can be further improved, the engine 2 can be further downsized.

The sliding surface 46 and the sliding surface 56 have a small width in the direction (left-right direction) of the rotation axis C2 of the camshaft 31, and are aligned in the direction of the rotation axis C2 of the camshaft 31. In addition, the sliding surface 46 and the sliding surface 56 are provided between the intake rocker shaft 34 and the exhaust rocker shaft 35 when viewed from the direction of the central axis C <b> 1 of the cylinder hole 9. Placed in front of. Therefore, the sliding surface 46 and the sliding surface 56 can be arranged in a smaller space. Further, an intake rocker shaft 34 is provided above the camshaft 31, and an exhaust rocker shaft 35 is provided below the camshaft 31. Therefore, it is easy to narrow the distance between the sliding surface 46 and the sliding surface 56 in the left-right direction.
Thus, it becomes easy to secure a large space in the engine 2. Therefore, since the design freedom of the engine 2 can be further improved, the engine 2 can be further downsized.

Further, the cam arm portions 44 and 54 protrude from the boss portions 43 and 53 in the vertical direction perpendicular to the direction of the rotation axis C2 (left and right direction) of the camshaft 31. Therefore, it is easy to narrow the distance between the sliding surface 46 and the sliding surface 56 in the left-right direction. Thereby, it becomes easy to ensure a large space in the engine 2. Therefore, since the design freedom of the engine 2 can be further improved, the engine 2 can be further downsized.

Further, the cam arm portions 44 and 54 have holes 47 and 57 penetrating in the direction of the rotation axis C2 of the camshaft 31. Thereby, the rocker arms 32 and 33 can be reduced in weight. Since the mechanical loss can be reduced by reducing the weight, the width of the sliding surface 46, 56 in the direction of the rotation axis C2 of the camshaft 31 can be made smaller while maintaining the strength of the cam arm portions 44, 54. Thereby, since the design freedom of the engine 2 can be further improved, the engine 2 can be further downsized.

Further, the valve arm portions 45A, 45B, 55 have holes 48, 58 penetrating in the direction of the rotation axis C2 of the camshaft 31. Thereby, the rocker arms 32 and 33 can be reduced in weight. Since the mechanical loss can be reduced by reducing the weight, the width of the sliding surfaces 46 and 56 in the direction of the rotation axis C2 of the camshaft 31 can be further reduced. Thereby, since the design freedom of the engine 2 can be further improved, the engine 2 can be further downsized.

The cams 40 and 41 are smaller in width in the direction of the rotation axis C2 of the cam shaft 31 than the end portions 44a and 54a of the cam arm portions 44 and 54 near the boss portions 43 and 53. Since the cams 40 and 41 have a small width in the direction of the rotation axis C2 of the camshaft 31, a space can be secured in the vicinity of the camshaft 31 without increasing the size of the engine 2. Further, by arranging the cams 40 and 41 close to each other, a large space can be secured in the outer peripheral portion of the cam shaft 31 without increasing the size of the engine 2. By securing such a space, the design freedom of the engine 2 can be further improved, and therefore the engine 2 can be further downsized.
Further, since the width of the cams 40 and 41 in the direction of the rotation axis C2 of the camshaft 31 is small, the engine 2 can be downsized by shortening the length of the camshaft 31.

The spark plug 68 is provided on the first outer wall 25a of the cylinder head portion 7 so that a part thereof is positioned on the rotation axis C2 of the camshaft 31. Since the cams 40 and 41 have a small width in the direction of the rotational axis C2 of the camshaft 31, the length of the camshaft 31 can be shortened. By shortening the length of the cam shaft 31, the first outer wall 25 a provided with the ignition plug 68 of the cylinder head portion 7 can be shifted to the inside of the cylinder head portion 7. Specifically, in the present embodiment, the depth of the concave portion of the first outer wall 25a can be increased. Thereby, the space used when maintaining the spark plug 68 can be secured.

The diameters of the valve shafts 16b and 18b of the valves 16 and 18 are determined by the magnitude of the force that the valves 16 and 18 receive from the camshaft 31, and do not become extremely large. The width of the sliding surfaces 46 and 56 in the direction of the rotation axis C2 of the camshaft 31 is not only smaller than the width of the end portions 44a and 54a close to the boss portions 43 and 53 of the cam arm portions 44 and 54, but also the valve shaft portion 16b. Smaller than the minimum diameter of 18b. In the present embodiment, the diameters of the valve shaft portions 16b and 18b are smaller than the widths of the end portions 44a and 54a close to the boss portions 43 and 53 of the cam arm portions 44 and 54. Therefore, since the width of the sliding surfaces 46 and 56 in the direction of the rotation axis C2 of the camshaft 31 can be made smaller, the design freedom of the engine 2 is further improved, and the engine 2 can be further downsized.

Further, a coating film (not shown) having a lower friction coefficient and higher hardness than the base material is formed on the outer peripheral surfaces of the rocker shafts 34 and 35. Thereby, the frictional force between the outer peripheral surface of the rocker shafts 34 and 35 and the inner peripheral surface of the boss portions 43 and 53 of the rocker arms 32 and 33 can be reduced, and the rocker shafts 34 and 35 and the rocker arms 32 and 33 can be reduced. Burn-in with the boss portions 43 and 53 can be prevented. Therefore, an increase in mechanical loss of the engine 2 can be further suppressed.

On the surfaces of the pressing portions 49 and 59 (end portions of the present invention) that press the valve 16 of the valve arm portions 45 and 55, a coating (62) having a lower coefficient of friction and higher hardness than the base material is formed. . Thereby, the friction which arises between the press parts 49 and 59 which press the valves 16 and 18 of the valve arm parts 45 and 55, and the shims 50 and 60 which are provided in the valves 16 and 18 and are pressed by the press parts 49 and 59. The force can be reduced and seizure between the two can be prevented. Therefore, an increase in mechanical loss of the engine 2 can be further suppressed.

In addition, a film (not shown) having a lower friction coefficient and higher hardness than the base material is formed on the surfaces of the shims 50 and 60 disposed between the valve arm portions 45 and 55 and the valves 16 and 18. Yes. Thereby, the frictional force between the valve arm portions 45 and 55 and the shims 50 and 60 can be reduced, and seizure between the valve arm portions 45 and 55 and the shims 50 and 60 can be prevented. Therefore, an increase in mechanical loss of the engine 2 can be further suppressed.

When the roller rocker arm is used, since the roller is heavy, the spring force of the spring that biases the valve in the closing direction is increased in order to cause the roller to follow the cam. The spring force increases as the rotation speed increases. For this reason, the camshaft drive torque is reduced because the frictional resistance between the roller and the cam is small, but the camshaft drive torque is increased due to the large spring force.
On the other hand, in this embodiment, since the rocker arms 32 and 33 and the cams 40 and 41 are slid, even if the surface treatment for reducing the coefficient of friction is applied to the sliding portions, the roller rocker arm is used. However, the frictional resistance is slightly increased. For this reason, the driving torque of the camshaft 31 is increased by the amount corresponding to the increased frictional resistance as compared with the case of using the roller rocker arm. However, since the rocker arms 32 and 33 can be reduced in weight, the spring force of the intake and exhaust springs 22 and 24 can be reduced, and the drive torque of the camshaft 31 can be reduced accordingly. As a result, an increase in driving torque of the camshaft 31 can be suppressed, and an increase in mechanical loss can be suppressed.

The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made as long as they are described in the claims. Moreover, the example of a change mentioned later can be implemented in combination as appropriate. In the present specification, the term “preferred” is non-exclusive, and means “preferably but not limited to”.

In the above embodiment, the coating is formed on both the sliding surface 46 of the cam arm portion 44 of the intake rocker arm 32 and the outer peripheral surface of the intake cam 40, but the coating is formed only on one of them. Also good. The same applies to the exhaust rocker arm 33 and the exhaust cam 41. In this case, the sliding surfaces 46 and 56 and the cams 40 and 41 slide through the film. Therefore, the same effect as the above embodiment can be obtained. However, it is preferable to form a coating on the sliding surfaces 46 and 56 and the outer peripheral surfaces of the cams 40 and 41 as in the above-described embodiment in that the frictional force can be further reduced and the mechanical loss can be further reduced.

In the above embodiment, the coating is formed on both the surface of the pressing portion 49 and the surface of the shim 50, but the coating may be formed on only one of them. Moreover, the coating film may not be formed on both the pressing portion 49 and the shim 50. Similarly, the pressing part 59 and the shim 60 may have a film formed on only one of them, or may not have a film formed on both.

In the above-described embodiment, the coating is formed on the entire outer peripheral surface of the rocker shafts 34 and 35, but at least the inner peripheral surface of the boss portions 43 and 53 when the engine is driven among the outer peripheral surfaces of the rocker shafts 34 and 35. As long as a film is formed in a region in contact with the film, the film may not be formed in other portions. Moreover, the coating film may not be formed on the outer peripheral surfaces of the rocker shafts 34 and 35.

In the above embodiment, the cam arm portions 44 and 54 of the rocker arms 32 and 33 have holes 47 and 57 that penetrate in the direction of the rotation axis C2 of the camshaft 31, but the rocker arms are closed by the holes 47 and 57. The shape may be different. Further, the valve arm portions 45A, 45B, and 55 have holes 48 and 58, but the holes 48 and 58 may be closed.

In the above embodiment, the tip portions (pressing portions 49, 59) of the valve arm portions 45A, 45B, 55 of the rocker shafts 34, 35 press the valves 16, 18 via the shims 50, 60. However, it is not limited to this configuration. An adjustment screw may be provided at the tip of the valve arm portion of the rocker shaft, and the valve may be pressed by the adjustment screw.

When the shims 50 and 60 are not provided, the springs 51 and 61 for replacing the shims 50 and 60 are not necessary. In this case, the separation distance between the intake cam 40 and the exhaust cam 41 and the separation distance between the sliding surface 46 of the intake rocker shaft 34 and the sliding surface 56 of the exhaust rocker shaft 35 are smaller than those in the above embodiment. can do. As a result, a larger space can be secured in the cylinder head portion 7. Alternatively, the cylinder head portion 7 can be further downsized.

The number of intake and exhaust cams, the number of intake and exhaust valves, and the number of intake and exhaust rocker arms may be different from the above embodiment. Further, the number of valve arm portions and the number of cam-side arms provided in one intake rocker arm may be different from those in the above embodiment. Similarly for the exhaust rocker arm, the number of valve arm portions and the number of cam side arms may be different from those in the above embodiment.

In the above embodiment, the single-cylinder SOHC engine 2 has one intake rocker shaft 34, but may have two or more intake rocker shafts. In this case, the number of intake rocker arms is equal to or greater than the number of intake rocker shafts. Further, the single cylinder SOHC engine 2 may have two or more exhaust rocker shafts.

In the above embodiment, the valve arm portions 45A, 45B, 55 of the intake and exhaust rocker arms 32, 33 intersect the direction perpendicular to the direction of the rotation axis C2 of the camshaft 31 from the boss portions 43, 53. Although extending in the direction, the shape of the valve arm portion is not limited to this. For example, as shown in FIG. 8, the valve arm portion 345 of the intake rocker arm 332 may extend from the boss portion 343 in a direction perpendicular to the direction of the rotation axis C <b> 2 of the camshaft 31. In this case, as shown in FIG. 8, it is preferable that the cam arm portion 344 and the valve arm portion 345 are arranged on one straight line when viewed from the front-rear direction (the direction of the central axis C1 of the cylinder hole 9).

For example, as shown in FIG. 5, the engine 202 may include a decompression mechanism 170 for releasing the compression pressure when the engine is started. The decompression mechanism 170 is attached to the outer periphery of the camshaft 31. The decompression mechanism 170 is disposed on the exhaust cam 41 opposite to the intake cam 40 (on the spark plug 68 side). A specific configuration of the decompression mechanism 170 is the same as that of a conventional decompression mechanism as described in, for example, Japanese Patent Application Laid-Open No. 2011-202625.

As in the above-described embodiment, since the lateral width of the sliding surfaces 46 and 56 of the rocker arms 32 and 33 and the lateral width of the cams 40 and 41 are small, a space can be secured on the outer periphery of the camshaft 31. Therefore, since the decompression mechanism 170 can be disposed in this space, the decompression mechanism 170 can be disposed while suppressing an increase in the size of the engine.

For example, as shown in FIGS. 6 and 7, the engine 202 may include a variable valve timing mechanism 280 for changing the opening / closing timing of the two intake valves 16 and 16 (or two exhaust valves). An exhaust cam 41 and two intake cams 240A and 240B are formed on the cam shaft 231 of the engine 202. The engine 202 has two intake rocker arms 232A and 232B. Specific configurations of the two intake rocker arms 232A and 232B and the variable valve timing mechanism 280 are the same as those of the conventional variable valve timing mechanism described in, for example, Japanese Patent Application Laid-Open No. 2011-202625.

The variable valve timing mechanism 280 has an actuator 281 attached to the first outer wall 225a of the cylinder head portion 207. The actuator 281 has a rod 281 a that can advance and retract in the axial direction of the camshaft 231. The actuator 281 is disposed on the central axis of the intake rocker shaft 34 when viewed from the central axis direction of the cylinder hole 9. The lateral width of the sliding surfaces of the intake rocker arms 232A and 232B is substantially the same as the lateral width of the sliding surface 46 of the above embodiment. In FIG. 6, only the cam arm portions of the intake rocker arms 232A and 232B are shown, and the boss portion and the valve arm portion are not shown. Further, in FIG. 6, the display of the intake rocker shaft 34 is omitted.

Due to the small width of the sliding surfaces of the rocker arms 232A, 232B, 33 in the left-right direction and the width of the cams 240A, 240B, 41 in the left-right direction, the first outer wall 225a of the cylinder head portion 207 is moved toward the valve operating chamber 26. The depth of the concave portion of the first outer wall 225a can be increased. Therefore, a space for arranging the actuator 281 outside the cylinder head portion 207 can be secured. Therefore, the actuator 281 of the variable valve timing mechanism 280 can be disposed while suppressing an increase in the size of the engine 202.

Note that the actuator of the variable valve timing mechanism may be arranged inside the cylinder head.

In the above embodiment, the rocker shafts 34 and 35 are supported by the cylinder head portion 7 so as not to move, and the rocker shafts 32 and 35 are supported by the rocker shafts 34 and 35 so as to be swingable. Not. The rocker shafts 34 and 35 are swingably supported by the cylinder head unit 7, and the rocker arms 32 and 33 may be fixed to the rocker shafts 34 and 35.

The single-cylinder SOHC engine 2 of the above embodiment is a water cooling type, but may be an air cooling type.

In the above embodiment, the cylinder body portion 6 and the cylinder head portion 7 are separate members, but may be a member in which the cylinder body portion and the cylinder head portion are integrated.

The above embodiment is an example in which the single-cylinder SOHC engine of the present invention is applied to a scooter type motorcycle, but the application target of the single-cylinder SOHC engine of the present invention is not limited to a scooter type motorcycle. The single-cylinder SOHC engine of the present invention may be applied to a motorcycle other than a scooter type, or may be applied to a straddle-type vehicle other than a motorcycle. Note that the saddle riding type vehicle refers to all vehicles that ride in a state in which an occupant straddles a saddle. The saddle riding type vehicle includes a motorcycle, a tricycle, a four-wheel buggy (ATV: All Terrain Vehicle), a water bike, a snowmobile, and the like.

In the present invention and the present specification, the friction coefficient of the coating film is lower than the friction coefficient of the base material of the sliding surface, for example. That is, it is lower than the friction coefficient with an object of a certain material A. The material A is not particularly limited.
In the present invention, the intake sliding surface and the exhaust sliding surface are aligned in the rotational axis direction of the camshaft. The intake sliding surface and the exhaust sliding surface are close to each other in the rotational axis direction of the camshaft. Including both the case of being separated and the case of being separated. In the present invention, the fact that the intake sliding surface and the exhaust sliding surface are aligned in the rotational axis direction of the camshaft means that any member is disposed between the intake sliding surface and the exhaust sliding surface. And the case where nothing is arranged.

2, 102, 202 Single cylinder SOHC engine 6 Cylinder body part 7, 207 Cylinder head part 9 Cylinder hole 13 Combustion chamber 14 Intake passage 14a Intake port 15 Exhaust passage 15a Exhaust port 16 Intake valve 16a, 18a Valve umbrella part 16b, 18b Valve shaft portion 18 Exhaust valve 22 Intake spring 24 Exhaust spring 30 Valve operating devices 31, 231 Camshafts 32, 232A, 232B, 332 Intake rocker arm 33 Exhaust rocker arm 34 Intake rocker shaft 35 Exhaust rocker shaft 40, 240A, 240B Intake cam 41 Exhaust cam 43, 53, 343 Boss portion 44, 54, 344 Cam arm portion 44a, 54a End portion 45, 55, 345 Valve arm portion 46, 56 Sliding surfaces 47, 48, 57 , 58 Hole 49, 59 Pressing part End)
50, 60 Shim 62 Film 68 Spark plug 170 Decompression mechanism 280 Variable valve timing mechanism 281 Actuator 281a Rod C1 Cylinder hole center axis C2 Camshaft rotation axis C3 Intake rocker shaft center axis C4 Exhaust rocker shaft center axis

Claims (16)

1. A cylinder body portion having a single cylinder hole;
   A cylinder head portion covering one end opening of the cylinder hole and constituting at least a part of the combustion chamber;
   A camshaft provided in the cylinder head portion and rotatable, wherein at least one intake cam and at least one exhaust cam are provided side by side in the rotation axis direction;
   An intake rocker shaft and an exhaust rocker shaft, each disposed in parallel with the camshaft;
   At least one intake valve capable of opening and closing an intake port provided in the combustion chamber and at least one exhaust valve capable of opening and closing an exhaust port provided in the combustion chamber;
   An intake boss supported by the intake rocker shaft, an intake cam arm that protrudes from the intake boss, contacts the intake cam, and is pressed by the intake cam; and the intake boss And an intake valve arm portion whose end is in contact with the intake valve and presses in the opening direction of the intake valve, and is capable of swinging around a central axis of the intake rocker shaft An intake rocker arm;
   An exhaust boss supported by the exhaust rocker shaft, an exhaust cam arm that protrudes from the exhaust boss, contacts the exhaust cam, and is pressed by the exhaust cam; and the exhaust boss And an exhaust valve arm portion whose end is in contact with the exhaust valve and presses the exhaust valve in a direction to open the exhaust valve, and is capable of swinging around a central axis of the exhaust rocker shaft An exhaust rocker arm,
   The intake rocker arm is integrally formed with the intake cam arm portion, and the width thereof is smaller than the width of the end portion of the intake cam arm portion close to the intake boss portion in the rotation axis direction. , Having a sliding surface for intake that slides with the intake cam through a coating having a lower coefficient of friction than the base material and high hardness,
   The exhaust rocker arm is integrally formed with the exhaust cam arm, and the width of the exhaust rocker arm is smaller than the width of the end of the exhaust cam arm close to the exhaust boss in the rotation axis direction. And sliding with the exhaust cam through a coating having a lower friction coefficient and higher hardness than the base material, and aligned with the intake sliding surface of the intake rocker arm and the rotational axis of the camshaft. A single-cylinder SOHC engine having an exhaust sliding surface provided.
2. The intake sliding surface and the exhaust sliding surface are provided in one direction in the central axis direction of the cylinder hole with respect to the camshaft when viewed from the rotational axis direction of the camshaft. The single-cylinder SOHC engine according to claim 1, wherein
3. When the direction of the axis of rotation of the camshaft is the left-right direction,
   One of the intake rocker shaft and the exhaust rocker shaft is provided above the camshaft, and the other is provided below the camshaft.
   The intake sliding surface and the exhaust sliding surface are provided between the intake rocker shaft and the exhaust rocker shaft when viewed from the center axis direction of the cylinder hole, and both are provided on the camshaft. The single-cylinder SOHC engine according to claim 1 or 2, wherein the single-cylinder SOHC engine is provided in front or rear.
4. When the rotation axis direction of the camshaft is the left-right direction, viewed from the center axis direction of the cylinder hole,
   The intake cam arm portion projects vertically from the intake boss portion,
   The exhaust cam arm portion projects vertically from the exhaust boss portion,
   The single-cylinder SOHC engine according to any one of claims 1 to 3, wherein the intake sliding surface and the exhaust sliding surface are provided so as to be aligned in the left-right direction.
5. The single-cylinder SOHC engine according to any one of claims 1 to 4, wherein the intake cam arm portion and the exhaust cam arm portion have a hole penetrating in a rotation axis direction of the cam shaft.
6. The intake cam arm portion is formed such that the width of the end portion close to the intake boss portion is maximized in the width of the camshaft in the rotation axis direction.
   6. The exhaust cam arm portion is formed so that a width of an end portion close to the exhaust boss portion is maximized in a width in a rotation axis direction of the cam shaft. A single-cylinder SOHC engine according to any one of the above.
7. The intake cam has a width smaller than a width of an end portion of the intake cam arm portion near the intake boss portion in the rotation axis direction of the camshaft,
   7. The exhaust cam has a width smaller than a width of an end portion of the exhaust cam arm portion close to the exhaust boss portion in a rotation axis direction of the cam shaft. The single-cylinder SOHC engine described in 1.
8. A spark plug provided on the cylinder head portion such that a tip portion faces the combustion chamber;
   The single-cylinder SOHC engine according to claim 7, wherein a part of the spark plug is disposed on a rotation axis of the camshaft.
9. The intake valve and the exhaust valve each have a valve shaft portion and a valve umbrella portion connected to the tip of the valve shaft,
   The intake sliding surface and the exhaust sliding surface have a width in the rotational axis direction of the camshaft smaller than a minimum diameter of the valve shaft portion of the intake valve and the exhaust valve. The single-cylinder SOHC engine according to any one of claims 1 to 8.
10. The single-cylinder SOHC engine according to claim 7, further comprising a decompression mechanism mounted on the camshaft.
11. A plurality of at least one of the intake rocker arm and the exhaust rocker arm;
    The single-cylinder SOHC engine according to any one of claims 1 to 10, further comprising a variable valve timing mechanism including an actuator having a rod arranged in parallel with the camshaft.
12. The intake boss portion and the exhaust boss portion are rotatably supported by the intake rocker shaft and the exhaust rocker shaft, respectively.
    Of the outer peripheral surfaces of the intake rocker shaft and the exhaust rocker shaft, at least a portion in contact with the intake boss portion and the exhaust boss portion has a coating having a lower coefficient of friction and higher hardness than the base material. The single-cylinder SOHC engine according to any one of claims 1 to 11, wherein the single-cylinder SOHC engine is formed.
13. On the surface of the end of the intake valve arm that presses the intake valve, a coating having a lower coefficient of friction and higher hardness than the base material is formed,
    13. A film having a lower coefficient of friction and higher hardness than the base material is formed on a surface of an end of the exhaust valve arm that presses the exhaust valve. A single-cylinder SOHC engine according to any one of the above.
14. An intake shim disposed between the intake valve arm and the intake valve;
    An exhaust shim disposed between the exhaust valve arm and the exhaust valve;
    The single cylinder according to any one of claims 1 to 13, wherein a coating having a lower coefficient of friction and higher hardness than a base material is formed on surfaces of the intake shim and the exhaust shim. SOHC engine.
15. At least one of the intake sliding surface and the intake cam is formed with the coating having a lower coefficient of friction and higher hardness than the base material of the intake sliding surface,
    The coating having a lower coefficient of friction and higher hardness than a base material of the exhaust sliding surface is formed on at least one of the exhaust sliding surface and the intake cam. The single cylinder SOHC engine according to any one of 14.
16. The intake rocker arm or the exhaust rocker arm used in the single-cylinder SOHC engine according to any one of claims 1 to 15, wherein the intake slide surface or the exhaust slide surface has a base thereof. A rocker arm for a single-cylinder SOHC engine, wherein the coating film having a lower friction coefficient and higher hardness than the material is formed.

Images