JP2002364313A - Rocker arm - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rocker arm which can be easily manufactured, has high durability and reliability, and can achieve a compact valve operating structure. SOLUTION: In an OHC engine in which an intake valve and an exhaust valve are driven by a single valve cam 29, an intake side rocker arm formed by casting or forging between the valve cam 29 and both intake and exhaust valves. 34a and an exhaust-side rocker arm 34b are interposed. One of the rocker arms 34a and 34b is disposed so as to straddle the other rocker arm, and the two rocker arms 34a and 34b are disposed with good layout efficiency to realize a compact valve operating structure. In addition, non-contact portions extending beyond the cam surface 29a along the axial direction of the valve cam 29 are provided on the slippers 35a and 35b which are in sliding contact with the cam surface 29a of the valve cam 29 to prevent the slipper edge from hitting one side. I do.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rocker arm of an OHC engine, and more particularly to a technique effective when applied to an engine in which a single valve cam opens and closes an intake valve and an exhaust valve.

[0002]

2. Description of the Related Art Conventionally, in an OHC (overhead camshaft) type general-purpose engine, a valve cam is disposed on a cylinder head side, and is driven by a chain, a cog belt, or the like in synchronization with a crankshaft. A slipper of a rocker arm provided so as to be swingable about a rocker shaft is in sliding contact with the valve operating cam, and the rocker arm swings with the rotation of the valve operating cam to open and close the intake valve and the exhaust valve. Is performed.

For example, Japanese Patent Application Laid-Open No. 8-177416 discloses an engine employing such a valve operating mechanism. There, a single camshaft drives the intake and exhaust valves, and between the camshaft and both valves,
The cam followers are arranged symmetrically with respect to the camshaft.

On the other hand, a general-purpose engine having a rocker arm made of sheet metal has been studied in order to reduce the weight of the device. Also in the engine of the above-mentioned publication, the cam follower is considered to be made of sheet metal from the illustrated shape. Therefore,
The present inventors also conducted various studies on a sheet metal rocker arm, and were able to achieve certain results in terms of engine weight reduction. Also, by using a sheet metal rocker arm, a compact valve train with a short axial length is realized in engines where the cam surface of the valve cam and the intake and exhaust valves are offset in the axial direction of the cam. We were able to.

[0005]

However, when a rocker arm made of sheet metal is employed, the rocker arm has a three-dimensional shape when the cam surface and the valve position are apart from each other. A process is required. In this case, if the rocker arm made of sheet metal is made to have a simple shape, as described in the above-mentioned publication, a device such as individually supporting the rocker arms for each valve using two shafts is required. And disadvantages in terms of size.

[0006] Comparing a sheet metal product with a conventional forged or cast product, the latter is superior in terms of durability. It is desirable that the product be manufactured or cast. However, when trying to apply a forged or cast rocker arm to improve durability reliability, an engine with cams and valves offset as described above requires a compact valve train as in the case of sheet metal. There is a problem that it is difficult to put together.

As described above, according to the study of the present inventors,
Although there are certain restrictions on the use of sheet metal rocker arms in terms of cost and durability reliability, it was found that simply replacing them with forged or cast products would make it difficult to make them as compact as sheet metal. . Therefore, it has been desired to develop a valve train structure that can satisfy both the requirements for cost and durability reliability and the requirement for compactness.

It is an object of the present invention to provide a rocker arm which is easy to manufacture, has high durability and reliability, and can achieve a compact valve operating structure.

[0009]

According to the present invention, there is provided a rocker arm for an engine, comprising: a valve cam for an OHC engine which drives an intake valve and an exhaust valve by a single valve cam; A rocker arm interposed therebetween, wherein the intake-side and exhaust-side rocker arms are three-dimensionally crossed with each other.

According to the present invention, since the rocker arms are three-dimensionally crossed and one straddles the other, two rocker arms on the intake side and the exhaust side can be arranged with good layout efficiency, and the camshaft can be arranged. It is possible to realize a compact valve operating structure having a short axial length. Therefore, for example, even in an engine in which the valve operating cam and the intake and exhaust valves are offset, it is possible to use a forged or cast rocker arm instead, while maintaining the compactness of the sheet metal rocker arm. Become.

Further, the rocker arm may be formed by casting or forging, whereby the durability reliability is improved, and the working process can be simplified as compared with the sheet metal rocker arm, and the manufacturing cost can be reduced. It becomes possible to plan.

Further, in the rocker arm, a non-contact portion extending beyond the end of the cam surface along the axial direction of the valve cam is provided on a slipper slidably in contact with the cam surface of the valve cam. Is also good. Thereby, even when the rocker arm is tilted, only one end of the slipper hits one side,
A situation in which the cam surface in that portion is worn can be prevented, and the durability and reliability of the device can be improved.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is an explanatory diagram showing a configuration of an OHC engine using a rocker arm according to an embodiment of the present invention, and FIG. 2 is a sectional view of the engine of FIG.

The engine shown in FIG. 1 is a single-cylinder four-cycle gasoline engine, and is a so-called inclined OHC engine in which the cylinder axis CL is inclined by an angle θ with respect to the vertical direction. In this engine, the engine body 1 is
The crankcase 3 is integrally formed on the lower side of the cylinder block 2 and is formed of iron or a light alloy such as an aluminum alloy. A cylinder head 4 made of an aluminum alloy or the like is mounted on the upper side of the cylinder block 2. Also, on the upper side of the cylinder head 4,
A rocker cover 5 made of sheet metal or synthetic resin is placed.

The right side surface of the crankcase 3 in FIG. 1 is largely open and forms a main bearing case mounting surface 6. A main bearing case 7 made of aluminum alloy or the like is mounted on the main bearing case mounting surface 6. Thereby, a crank chamber 8 is formed in the crankcase 3 and an oil pan 10 in which lubricating oil (hereinafter, abbreviated as oil) 9 is stored is formed below the crank chamber 8.

A main bearing 11a is press-fitted and fixed in the bearing case 7, and one end of the crankshaft 12 is supported there. Also, the main bearing 11a
An oil seal 13a is press-fitted and fixed to the outside.

A main bearing 11b is press-fitted and fixed to a wall surface 14 of the crankcase 3 opposite to the main bearing case mounting surface 6. The other end of the crankshaft 12 is supported by the main bearing 11b. An oil seal 13b is also provided outside the main bearing 11b.
The oil 9 stored in the oil pan 10 is removed from the crankshaft 12 by the 3a and 13b.
It does not leak outside.

A flywheel 15 and a cooling fan 16 are attached to an end of the crankshaft 12 extending from the wall surface 14 to the outside of the crankcase 3. The cooling fan 16 is provided outside the crankcase 3 and the housing 5.
7 and rotates with the crankshaft 12 to introduce cooling air from outside the housing 57. Then, the engine body 1, the cylinder head 4, and the like are cooled by the introduced cooling air. Further, a recoil device 17 is provided outside the housing 57. The crankshaft 12 is rotated by manually pulling a recoil lever, and the engine is started.

A cylinder bore 18 is formed inside the cylinder block 2. A piston 19 is slidably fitted in the cylinder bore 18. The upper end side of the cylinder bore 18 is closed by the cylinder head 4, and the top surface of the piston 19 and the bottom wall surface 2 of the cylinder head 4 are closed.
0 forms a combustion chamber 21. Note that an intake valve 22, an exhaust valve 23, a spark plug, and the like are exposed above the combustion chamber 21.

A small end 25 of a connecting rod 24 is rotatably connected to the piston 19 via a piston pin. A crank pin 27 of the crankshaft 12 is rotatably connected to the large end 26 of the connecting rod 24. Thus, the crankshaft 12 rotates with the vertical movement of the piston 19.

On the other hand, a camshaft 28 is arranged in the cylinder head 4 on the cylinder axis CL in parallel with the crankshaft 12. The camshaft 28 has a structure in which the valve cam 29 and the sprocket 31 are integrally formed. The valve operating cam 29 is driven by the timing valve operating system 30 in synchronization with the crankshaft 12.

On the other hand, a sprocket 32 is fixed to the crankshaft 12. Further, the chain chambers 50 and 51 are provided in the cylinder block 2 and the cylinder head 4.
Is formed, and between the two sprockets 31, 32,
They are connected by a chain 33 provided in the chain chambers 50 and 51. The sprockets 31 and 32 and the chain 33 form a timing valve operating system 30.
Is formed. The number of teeth of the sprocket 31 is twice the number of teeth of the sprocket 32, and the valve gear 29 rotates once when the crankshaft 12 rotates twice. The chain 33 is appropriately tensioned by a chain tensioner 55.

Valve operating cam 29 and both intake and exhaust valves 2
An intake side rocker arm 34a and an exhaust side rocker arm 34b are disposed between the first and second rocker arms 2 and 23, respectively.
3 to 5 are explanatory views showing the arrangement of the rocker arms 34a and 34b. FIG. 3 shows the rocker arms 34a and 34b viewed from above the cylinder head 4, and FIG.
5 shows a case when viewed from the direction indicated by arrow A in FIG. 3, and FIG. 5 shows a case when viewed from the direction indicated by arrow B in FIG. FIG. 6 is a perspective view showing the configuration of the rocker arms 34a and 34b.

As shown in FIGS. 3 to 6, the rocker arm 3
The reference numerals 4a and 34b are attached so as to be swingable about the rocker shaft 36 supported by the rocker support 59. In the present embodiment, the rocker arms 34a,
An iron member formed by forging is used for 34b, and a rocker arm 34a is provided so as to straddle the rocker arm 34b, as shown in FIG.

Slippers 35a and 35b are formed at one ends of the rocker arms 34a and 34b so as to slide on the cam surface 29a of the valve cam 29, respectively. Further, screw holes 64a and 64b to which adjustment screws 56 for contacting the intake valve 22 and the exhaust valve 23 are formed are formed on the end opposite to the slippers 35a and 35b.

Further, the rocker arms 34a and 34b are provided at the center with rotation supporting portions 61a and 61b, in which shaft holes 62a and 62b through which the rocker shaft 36 is inserted are formed. In the present embodiment, the rocker arm 34a is provided with two rotation support portions 61a, each of which has a shaft hole 62a. This is to cause the rocker arm 34a that drives the valve located far from the valve operating cam 29 to perform a stable swinging operation. Therefore, the rotation supporting portion 61a ₁ is provided near the slipper 35a, and the rotation supporting portion 61a ₁ is provided near the intake valve 22. rotating support 61a ₂ is provided. And, the rocker arm 34a, connecting portion 63 so as to connect both rotating support 61a _1, 61a ₂ is provided, the rocker arm of the forked by the connecting portion 63 is formed.

As shown in FIG. 3, the rocker arm 34b
Of the two rocker supports 59
Attached so that it is sandwiched inside. The rotation support 61 a of the rocker arm 34 a is attached to the outside of the rocker support 59 so as to sandwich the rocker support 59. Then, the shaft holes 62a, 62
b, as shown in FIGS.
Is inserted. Thereby, both rocker arms 34a,
34b is mounted on the upper part of the cylinder head 4 while being supported by the rocker shaft 36 so as to be swingable and without play.

Here, in the engine, as described above, the rocker arm 34a is disposed so as to straddle the rocker arm 34b. In this case, as shown in FIG. 3, one end of the rocker arm 34b is in contact with the exhaust valve 23 on the right side of the rotation support portion 61b in the drawing. On the other hand, the other end side extends in the depth direction of the left side of the paper of the rotation support portion 61b, and comes into contact with the valve operating cam 29 with the slipper 35a ahead of it. In contrast,
Rocker arm 34a is brought into contact with the intake valve 22 in the drawing of the rotation supporting portion 61a ₂ of the lower side at the left side. Further, one end extends to the right rearward on the rotating support 61a _1, in contact with the valve operating cam 29 at its previous slippers 35b. A connecting portion 63 connecting the two rotation supporting portions 61a ₁ and 61a ₂ is provided so as to straddle the rocker arm 34b.

As described above, according to the present invention, since the rocker arms 34a and 34b are three-dimensionally crossed and one of the rocker arms 34a and 34b is arranged so as to straddle the other, a compact valve operating structure having a short camshaft axial length can be realized. Can be. In particular, even in an engine in which the valve operating cam 29 and the intake and exhaust valves 22 and 23 are offset, the valve operating system is downsized in the same manner as the sheet metal rocker arm while using a forged or cast rocker arm. It becomes possible. Also, the shape of both rocker arms 34a, 34b is also forged,
Since it does not have a complicated shape that hinders casting, it is possible to reduce the manufacturing cost as compared with a sheet metal product. Therefore, the layout of the valve train can be made compact while using a forged or cast rocker arm, and the durability and reliability can be improved, and the cylinder head can be downsized.

On the other hand, the cam surface 29a of the valve cam 29 has
As described above, the slippers 35a and 35b are in sliding contact.
FIG. 7 is a cross-sectional view taken along line XX of FIG.
The positional relationship between the cams 29a and the cams 29a is shown.
I have. In the present embodiment, as shown in FIG.
The rippers 35a and 35b are axially moved with respect to the cam surface 29a.
It is located at an offset position, part of which is
Extending along the direction beyond the cam surface 29a.
You. That is, the slippers 35a and 35b have one point in FIG.
It extends together to the position shown by the chain line P, and the cam surface 29a
A portion (between P and Q) exceeding the end Q is in contact with the cam surface 29a.
A non-contact portion 65 that does not touch is formed. This paraphrases
Then, one of the slippers 35a and 35b is placed on the cam surface 29a.
End E of ₁Only the sliding contact, the end E on the non-contact portion 65 side_TwoHa
That is, it is not in contact with the memory surface 29a.

Conventionally, the sliding surfaces of the slippers 35a and 35b are in sliding contact with the cam surface 29a over the entire length thereof, and both ends thereof are in contact with the cam surface 29a. However, in this manner slipper end portions strikes the cam surface, the rocker arm 34a, the 34b tilts in the Y direction in FIG. 5, slippers 35a, only the valve-side end portion E ₂ of 35b are partial contact, the cam surface 29a is The problem of uneven wear occurs. On the other hand, the rocker arms 34a, 34b
In, since the end portion E ₂ is outside of the cam surfaces 29a, never cam surface 29a is damaged by contact edges even in such a case. Therefore, abrasion of the cam surface 29a is prevented, and the life of the device is prolonged, so that the durability reliability can be improved.

The other ends of the rocker arms 34a and 34b are in contact with the distal ends of the intake valve 22 and the exhaust valve 23 via adjustment screws 56. Rocker arm 3
Screw holes 64a, 64b are formed at the ends of 4a, 34b, and adjustment screw 56 is screwed into them, as shown in FIG. The adjusting screw 56 is adjusted so that the lower end thereof is in contact with the upper end of the intake valve 22 or the exhaust valve 23, and the rocker arms 34 a, 34 are fixed by the lock nut 66.
fixed to b. On the other hand, the intake valve 22 and the exhaust valve 2
3 is urged in the valve closing direction by the valve spring 37, and the adjusting screw 56 is also pressed upward. As a result, the rocker arms 34a and 34b receive a force in the rotational direction about the rocker shaft 36, and the slippers 35a and
5b is pressed against the valve cam 29.

Then, the valve cam 29 rotates and the cam surface 29
When the rocker arms 34a and 34b swing due to a,
The adjusting screw 56 pushes down the intake valve 22 and the exhaust valve 23, and the valves are opened. On the other hand, after passing through the cam surface 29a, the intake valve 22 and the exhaust valve 23 are closed by the valve spring 37. At the same time, the adjusting screw 56 is also pushed up, and the rocker arms 34a, 34
b swings. In other words, the rocker arms 34a and 34b swing with the rotation of the valve operating cam 29.
The opening and closing of the intake valve 22 and the exhaust valve 23 are performed.

On the other hand, the timing valve system 30 includes the connecting rod 24
Is lubricated by a scraper 38 provided at the large end 26 of the main body. As shown in FIG. 2, the scraper 38 extends downward from the lower member 39 of the large end portion 26, that is, extends in the radial direction of the crankshaft 12, and draws a trajectory as shown by a dashed line in FIG. Oscillate with the rotation of the crankshaft 12. Thus, the oil 9 accumulated in the oil pan 10 is scraped up, and when the scraper 38 comes out of the oil level 40, the oil 9 is splashed on the chain 33, and the timing valve system 30 is lubricated.

The scraper 38 has a substantially L-shaped cross section, and includes a bottom wall 41 and a side wall 42 erected integrally with the bottom wall 41 at one end of the bottom wall 41. In addition,
In the present embodiment, the angle α between the bottom wall 41 and the side wall 42 is
Is formed at 90 °, but the angle between them is not limited to a right angle, and may be appropriately selected from about 60 ° to 90 °.

With such a swinging movement of the scraper 38, the oil 9 is scraped up by the bottom wall 41, and the oil 9 scraped up by the bottom wall 41 is guided by the side wall 42 and is opposed to the side wall 42. Jumped to the side. That is, the droplets of the oil 9 are also splashed obliquely three-dimensionally on the sides of the scraper 38, and are splashed in the direction near the root of the chain tensioner 55. Further, a part thereof hits the inner wall of the crankcase 3 and rebounds in the direction of the chain 33. Therefore, the oil 9 can be sprayed on the chain 33 that is arranged offset to the main bearing case 7 side with respect to the scraper 38, and the oil 9 can be supplied to the chain 33 reliably.

The oil 9 splashed on the chain 33 in this way is carried to the cylinder head 4 side as the chain 33 moves, and the sprocket 31 is also lubricated. The sprocket 32 is also lubricated by the oil 9 attached to the chain 33.

A part of the oil 9 attached to the chain 33 is shaken off by the centrifugal force on the cylinder head 4 side. That is, when the chain 33 is wound around the sprocket 31, a part thereof is
And is separated from the chain 33 in the circumferential direction. In the engine, the rocker cover 5 is disposed above the sprocket 31, and the splash of the oil 9 hits the ceiling surface 53 of the rocker cover 5. Then, the oil 9 attached to the ceiling surface 53 flows downward along the ceiling surface 53 and returns to the oil pan 10 along the chain chambers 51 and 50.

Further, as shown in FIG. 1, a convex portion 54 is formed on a part of the ceiling surface 53 of the rocker cover 5, and the oil 9 attached to the ceiling surface 53 drops from the convex portion 54. It is like that. The convex portion 54 is located above a sliding contact portion between the valve cam 29 and the slippers 35a and 35b, and the sliding contact portion is lubricated by the oil 9 dripped from the sliding portion.

A gas-liquid separation chamber 43 is provided inside the cylinder head 4 separately from the chain chamber 51.
In the rocker cover 5, a gas-liquid separation chamber 45 communicating with the gas-liquid separation chamber 43 via a reed valve 44 is formed. Further, the gas-liquid separation chamber 45 is connected to an air cleaner 47 via a blow-by passage 46.
The air cleaner 47 is connected to an intake port 49 in the cylinder head 4 via a carburetor 48.

The gas-liquid separation chambers 43 and 45 supply blow-by gas stored in the crank chamber 8 to the air cleaner 4.
When the gas is refluxed to the mist 7, the mist of the oil 9 contained in the blow-by gas is separated. In the engine, the gas-liquid separation chamber 43 is open to a chain chamber 50 formed separately from the cylinder bore 18. That is, at the upper end of the chain chamber 50 of the cylinder block 2,
A gas inlet 52 is provided, and the blow-by gas flowing into the chain chamber 50 flows into the gas-liquid separation chamber 43 via the gas inlet 52. Then, by flowing through the gas-liquid separation chamber 43, the oil mist therein adheres to the wall surface of the gas-liquid separation chamber 43, and the blow-by gas and the oil mist are separated. At this time, the oil separated in the gas-liquid separation chamber 43 is returned to the oil pan 10 along the wall surfaces of the gas-liquid separation chamber 43 and the chain chamber 50.

The blow-by gas flowing into the rocker cover 5 via the reed valve 44 is further separated into oil mist in the gas-liquid separation chamber 45. That is, the oil mist in the blow-by gas that has entered the gas-liquid separation chamber 45 adheres to the wall surface of the gas-liquid separation chamber 45, and further performs gas-liquid separation. An oil return hole (not shown) is provided on the lower surface side of the rocker cover 5, and the oil adhering to the wall surface of the gas-liquid separation chamber 45 flows out of the oil return hole into the chain chambers 51 and 50, and the chain chamber 51 , 50 and returned to the oil pan 10.

Although the invention made by the inventor has been specifically described based on the embodiment, the invention is not limited to the embodiment and can be variously modified without departing from the gist of the invention. Needless to say,

For example, in the above-described embodiment, an example is shown in which a forged rocker arm is used, but a caster rocker arm may be used. In that case, a wear-resistant tip may be attached to or embedded in the cam contact surface of the slipper, thereby improving the durability reliability of the device. Further, in the above-described example, the intake side rocker arm 34a is formed bifurcated, and the exhaust side rocker arm 34b is straddled, but conversely, the rocker arm 34b is formed bifurcated, and the rocker arm 34a is straddled. It is good.

On the other hand, in the above-described embodiment, the present invention is applied to the inclined type engine. However, the present invention is naturally applied to a normal engine in which the cylinder axis is arranged along the vertical direction. It is possible. Although the single-cylinder air-cooled engine has been described as an example, the present invention can be applied to a multi-cylinder air-cooled engine or a single-cylinder or multi-cylinder water-cooled engine.

Further, the timing valve system 30 is connected to the sprocket 3
Although an example is shown in which the gears are constituted by 1, 32 and a chain 33, other known timing valve systems such as cog pulleys and cog belts and timing pulleys and timing belts can be applied. In the present invention, “rotation” is a concept including circular motion in both forward and reverse directions, and does not mean only circular motion in one direction.

[0047]

According to the rocker arm for an engine of the present invention, in an OHC engine in which an intake valve and an exhaust valve are driven by a single valve cam, the rocker arms on the intake side and the exhaust side are three-dimensionally crossed with each other. The two rocker arms can be arranged with good layout efficiency, and a compact valve operating structure with a short camshaft axial length can be realized.
Therefore, for example, even in an engine in which the valve operating cam and the intake and exhaust valves are offset, it is possible to use a forged or cast rocker arm instead, while maintaining the compactness of the sheet metal rocker arm. Become.

Further, by forming the rocker arm by casting or forging, it is possible to improve the durability reliability and to simplify the working process as compared with the sheet metal rocker arm, thereby making it possible to reduce the manufacturing cost. Become.

Further, by providing a non-contact portion extending beyond the cam surface along the axial direction of the valve operating cam on the slipper of the rocker arm, it is possible to prevent the edge of the slipper from hitting one side. Therefore, even when the rocker arm is tilted, it is possible to prevent a situation in which the cam surface of the one-side contact portion is greatly worn, and it is possible to improve the durability reliability of the device.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a configuration of an OHC engine using a rocker arm according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the engine of FIG. 1 in the cylinder axis direction.

FIG. 3 is an explanatory view showing an arrangement state of a rocker arm in the engine of FIG. 1 and shows the rocker arm as viewed from above a cylinder head.

FIG. 4 is an explanatory view showing an arrangement state of a rocker arm in the engine of FIG. 1, and shows the rocker arm viewed from a direction indicated by an arrow A in FIG. 3;

FIG. 5 is an explanatory view showing an arrangement state of a rocker arm in the engine of FIG. 1, and shows the rocker arm viewed from the direction of arrow B in FIG. 3;

FIG. 6 is a perspective view showing a configuration of a rocker arm.

FIG. 7 is a sectional view taken along line XX of FIG. 5, showing a positional relationship between the slipper and the cam surface.

[Explanation of symbols]

 Reference Signs List 22 intake valve 23 exhaust valve 29 valve operating cam 29a cam surface 34a intake side rocker arm 34b exhaust side rocker arm 35a, 35b slipper 65 non-contact portion

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3G016 AA02 AA07 AA19 BA23 BA34 BA36 BA46 BA49 BB12 BB18 BB21 BB25 CA14 CA22 CA28 CA29 CA34 CA52 EA03 EA05 FA01 FA04 GA01 GA02

Claims (3)

[Claims] 1. A rocker arm interposed between an intake valve and an exhaust valve of an OHC engine that drives an intake valve and an exhaust valve by a single valve cam, The rocker arm on the intake side and the rocker arm on the exhaust side are disposed so as to cross each other three-dimensionally. 2. The rocker arm according to claim 1, wherein said rocker arm is formed by casting or forging. 3. The rocker arm according to claim 1, wherein the rocker arm has a slipper that slides on a cam surface of the valve cam, and the slipper extends along an axial direction of the valve cam. A rocker arm having a non-contact portion extending beyond a cam surface end.