AU2013386647B2

AU2013386647B2 - Cylinder head, method for manufacturing same, and engine

Info

Publication number: AU2013386647B2
Application number: AU2013386647A
Authority: AU
Inventors: Zhisheng Hu; Jian LAN; Ming Lu; Duode QIAN; Derun Tang; Tao Xu; Jiulin ZHENG
Original assignee: Anhui Jianghuai Automobile Group Corp
Current assignee: Anhui Jianghuai Automobile Group Corp
Priority date: 2013-04-18
Filing date: 2013-09-05
Publication date: 2016-10-20
Anticipated expiration: 2033-09-05
Also published as: AU2013386647A1; RU2015149110A; CL2015003051A1; RU2629848C2; WO2014169553A1; BR112015026313A2

Abstract

A cylinder head and an overhead camshaft engine using the cylinder head. The cylinder head has a top surface (1), an inlet side surface (2), an exhaust side surface (3), a front end surface (4), and a rear end surface (5), a camshaft mounting base (6) and a rocker arm support mounting boss (7) being distributed on the top surface, and a through return passage (8) being provided between the front end surface and the rear end surface. The cylinder head has a first fuel straight channel (10) vertically extending downwards from the rocker arm support mounting boss and a second fuel straight channel (11) horizontally extending from the inlet side surface, the first fuel straight channel communicating with the second fuel straight channel and the second fuel straight channel communicating with the return passage. An L-shaped pipe (200) or an arc pipe (300) can be used to replace the first fuel straight channel and the second fuel straight channel. The cylinder head can make the structure of the engine more compact, thereby further implementing miniaturization.

Description

Cylinder head, method for manufacturing same, and engine Technical Field

The present invention relates to an engine, particularly to a cylinder head, an engine using the cylinder head and a method for manufacturing the cylinder head.

Background Art

Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.

In the development processes used in the automobile industry, it is a common pursuit for designers to seek to realize a more compact engine.

In the Chinese invention patent with the application number of CN 96192117X an application date of October 16, 1996 and the title “Rocker arm assembly of internal combustion engine”, an internal combustion engine is disclosed. This engine includes valve rocker arm that is mounted to a cylinder head through a rocker arm bearing. When the rocker arm bearing is fixed onto the cylinder head, a rocker arm bearing mounting boss should be cast on the cylinder head. In addition, to lubricate the valve rocker arm, a lubricating oil passage is provided to the rocker arm bearing and the rocker arm bearing gasket. In this disclosure, the valve rocker arm needs to be supported by a push rod, which restricts the ability to reduce the height of the engine.

In the Chinese utility model patent with the application number of CN 2012204012771, an application date of August 14, 2012 and the title “Overhead camshaft cylinder head”, an oil return passage of a cylinder head is disclosed to supply oil to an oil passage of a rocker arm bearing mounting boss. Since the structure of the engine is already very compact, the oil return passage can be only provided below the camshaft mounting base to leave space for a surrounding water jacket and other members. With a viewing of facilitating machining, the rocker arm bearing mounting boss is provided with an inclined oil channel to communicate with the oil return passage. However, the inclined oil channel restricts further downsizing of the engine, and therefore improvement is needed.

Summary of the Invention

It is an object of the preferred embodiments of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

According to a first aspect of the invention there is provided a cylinder head comprising a top surface, an air inlet side surface, an air exhaust side surface, a front end surface and a rear end surface, a camshaft mounting base, a rocker arm bearing mounting boss being provided on the top surface, and an oil return passage extending through the front end surface and the rear end surface, wherein the cylinder head further comprises a first substantially straight oil channel extending vertically downwards from the rocker arm bearing mounting boss and a second substantially straight oil channel extending horizontally from the air inlet side surface, the first straight oil channel and the second straight oil channel being in fluidic communication with each other, and the second straight oil channel being in fluidic communication with the oil returning passage.

According to a second aspect of the invention there is provided an overhead camshaft engine comprising: a cylinder head as herein disclosed; a camshaft mounted in the camshaft mounting base; a rocker arm bearing mounted on the rocker arm bearing mounting boss, and comprising an air inlet rocker arm supporting gasket and an air exhaust rocker arm supporting gasket, the air inlet rocker arm supporting gasket and the air exhaust rocker arm supporting gasket being connected with each other through a bridging portion and being respectively mounted with an air inlet rocker arm bearing and an air exhaust rocker arm bearing; an air inlet rocker arm having a cam follower driven by the camshaft at one end thereof and a pair of air inlet valves connected at the other end thereof, with a rotation shaft at an intermediate portion of the air inlet rocker arm mounted on the air inlet rocker arm bearing; and an air exhaust rocker arm, having a cam follower driven by the camshaft at one end thereof and a pair of air exhaust valves connected at the other end thereof, with a rotation shaft at an intermediate portion of the air exhaust rocker arm mounted on the air exhaust rocker arm bearing, wherein the rotation shafts of the air inlet rocker arm and the exhaust rocker arm are substantially parallel and displaced from each other.

According to a third aspect of the invention there is provided a cylinder head comprising a top surface, a bottom surface, an air inlet side surface, an air exhaust side surface, a front end surface and a rear end surface, a camshaft mounting base, a rocker arm bearing mounting boss being provided on the top surface, and an oil returning passage extending through the front end surface and the rear end surface, wherein the cylinder head further comprises an L-shaped pipe cast therein and having: a vertical portion with an end that defines an opening at the rocker arm bearing mounting boss; a horizontal portion that is in fluidic communication with the oil returning passage; and a spacing being provided between one end of the horizontal portion and the air inlet side surface.

According to a fourth aspect of the invention there is provided a method for manufacturing a cylinder head comprising the steps of: pre-embedding an L-shaped pipe in a casting mold; pouring a casting material and cooling the same such that the L-shaped pipe is cast into a cylinder head to provide, in use, a substantially vertical portion and a substantially horizontal portion, and providing an opening at an end of the vertical portion at a rocker arm bearing mounting boss of the cylinder head, wherein a spacing is provided between an end of the horizontal portion and an air inlet side surface of the cylinder head; and machining an oil return passage such that the oil return passage is in fluidic communication with the horizontal portion of the L-shaped pipe.

According to a fifth aspect of the invention there is provided a cylinder head comprising a top surface, a bottom surface, an air inlet side surface, an air exhaust side surface, a front end surface and a rear end surface, a camshaft mounting base having a shaft hole, a rocker arm bearing mounting boss on the top surface, and an oil returning passage extending through the front end surface and the rear end surface, wherein the cylinder head further comprises an arcuate pipe cast therein that follows an arcuate path having a centre point, the arcuate pipe being in fluidic communication with the oil returning passage and having an opening in one end thereof, the opening being provided at or adjacent to the rocker arm bearing mounting boss, and the centre point substantially coinciding with a centre of the shaft hole.

According to a sixth aspect of the invention there is provided a method for manufacturing a cylinder head comprising the steps of: pre-embedding an arcuate pipe in a casting mold, the pipe following an arcuate path having a centre point; pouring a casting material and cooling the same such that the arcuate pipe is cast into a cylinder head and an opening of one end of the arcuate pipe is provided at a rocker arm bearing mounting boss of the cylinder head, wherein the centre point substantially coincides with a centre of a shaft hole of a camshaft mounting base; and machining an oil return passage such that the oil returning passage is in fluidic communication with the arcuate pipe.

According to a further aspect of the invention there is provided an overhead camshaft engine comprising: a cylinder head comprising a top surface, an air inlet side surface, an air exhaust side surface, a front end surface and a rear end surface, a camshaft mounting base, a rocker arm bearing mounting boss being provided on the top surface, and an oil return passage extending through the front end surface and the rear end surface, wherein the cylinder head further comprises a first substantially straight oil channel extending vertically downwards from the rocker arm bearing mounting boss and a second substantially straight oil channel extending horizontally from the air inlet side surface, the first straight oil channel and the second straight oil channel being in fluidic communication with each other, and the second straight oil channel being in fluidic communication with the oil returning passage; a camshaft mounted in the camshaft mounting base; a rocker arm bearing mounted on the rocker arm bearing mounting boss, and comprising an air inlet rocker arm supporting gasket and an air exhaust rocker arm supporting gasket, the air inlet rocker arm supporting gasket and the air exhaust rocker arm supporting gasket being connected with each other through a bridging portion and being respectively mounted with an air inlet rocker arm bearing and an air exhaust rocker arm bearing; an air inlet rocker arm having a cam follower driven by the camshaft at one end thereof and a pair of air inlet valves connected at the other end thereof, with a rotation shaft at an intermediate portion of the air inlet rocker arm mounted on the air inlet rocker arm bearing; and an air exhaust rocker arm, having a cam follower driven by the camshaft at one end thereof and a pair of air exhaust valves connected at the other end thereof, with a rotation shaft at an intermediate portion of the air exhaust rocker arm mounted on the air exhaust rocker arm bearing, wherein the rotation shafts of the air inlet rocker arm and the exhaust rocker arm are substantially parallel and displaced from each other; wherein each rocker arm bearing has two pairs of the air inlet supporting gasket and the exhaust rocker arm supporting gasket.

According to a further aspect of the invention there is provided a cylinder head comprising a top surface, a bottom surface, an air inlet side surface, an air exhaust side surface, a front end surface and a rear end surface, a camshaft mounting base, a rocker arm bearing mounting boss being provided on the top surface, and an oil returning passage extending through the front end surface and the rear end surface, wherein the cylinder head further comprises an L-shaped pipe cast therein and having: a vertical portion with an end that defines an opening at the rocker arm bearing mounting boss; a horizontal portion that is in fluidic communication with the oil returning passage; and a spacing being provided between one end of the horizontal portion and the air inlet side surface, a water jacket chamber is provided at the spacing between the end of the horizontal portion and the air inlet side surface.

According to a further aspect of the invention there is provided a method for manufacturing a cylinder head comprising the steps of: pre-embedding an L-shaped pipe in a casting mold; pouring a casting material and cooling the same such that the L-shaped pipe is cast into a cylinder head to provide, in use, a substantially vertical portion and a substantially horizontal portion, and providing an opening at an end of the vertical portion at a rocker arm bearing mounting boss of the cylinder head, wherein a spacing is provided between an end of the horizontal portion and an air inlet side surface of the cylinder head, a water jacket chamber is provided at the spacing between the end of the horizontal portion and the air inlet side surface; and machining an oil return passage such that the oil return passage is in fluidic communication with the horizontal portion of the L-shaped pipe.

According to a further aspect of the invention there is provided an overhead camshaft engine as herein disclosed, wherein the cylinder head further comprises an L-shaped pipe cast therein and having: a vertical portion with an end that defines an opening at the rocker arm bearing mounting boss; a horizontal portion that is in fluidic communication with the oil returning passage; and a spacing being provided between one end of the horizontal portion and the air inlet side surface, a water jacket chamber is provided at the spacing between the end of the horizontal portion and the air inlet side surface.

According to a further aspect of the invention there is provided an overhead camshaft engine as herein disclosed, wherein the camshaft mounting base includes a shaft hole and the cylinder head further comprises an arcuate pipe cast therein that follows an arcuate path having a centre point, the arcuate pipe being in fluidic communication with the oil returning passage and having an opening in one end thereof, the opening being provided at or adjacent to the rocker arm bearing mounting boss, and the centre point substantially coinciding with a centre of the shaft hole. A further object of the preferred embodiments of this invention is to overcome the above defects by providing a cylinder head compact in structure, thereby allowing further downsizing of an engine.

To realize this further object, the preferred embodiments of this invention provide the following technical solution: A cylinder head, which comprises: a top surface, an air inlet side surface, an air exhaust side surface, a front end surface and a rear end surface, a camshaft mounting base and a rocker arm bearing mounting boss being provided on the top surface, an oil returning passage extending through the front end surface and the rear end surface, the cylinder head further comprises a first straight oil channel extending vertically downwards from the rocker arm bearing mounting boss and a second straight oil channel extending horizontally from the air inlet side surface, the first straight oil channel and the second straight oil channel being in communication with each other, and the second straight oil channel being in communication with the oil returning passage.

Preferably, an opening of the second straight oil channel at the air inlet side surface is blocked.

Preferably, the opening of the second straight oil channel at the air inlet side surface is blocked by a blocking cap.

An overhead camshaft engine comprises: the above cylinder head; a camshaft mounted in the camshaft mounting base; a rocker arm bearing mounted on the rocker arm bearing mounting boss, which comprising an air inlet rocker arm supporting gasket and an air exhaust rocker arm supporting gasket, the air inlet rocker arm supporting gasket and the air exhaust rocker arm supporting gasket being connected with each other through a bridging portion and being respectively mounted with an air inlet rocker arm bearing and an air exhaust rocker arm bearing; an air inlet rocker arm, having a cam follower driven by the camshaft at one end thereof and a pair of air inlet valves connected at the other end thereof, with a rotation shaft at an intermediate portion of the air inlet rocker arm mounted on the air inlet rocker arm bearing; and an air exhaust rocker arm, having a cam follower driven by the camshaft at one end thereof and a pair of air exhaust valves connected at the other end thereof, with a rotation shaft at an intermediate portion of the air exhaust rocker arm mounted on the air exhaust rocker arm bearing, wherein the rotation shafts of the air inlet and exhaust rocker arms are parallelly displaced from each other.

Preferably, the rocker arm bearing has an oil passage in communication with the first straight oil channel so as to provide lubricating oil to the air inlet rocker and the air exhaust rocker arm.

Preferably, a rotation shaft of the cam follower is made of brass.

Preferably, the rotation shaft of the cam follower is provided with a lubricating oil groove.

Preferably, each rocker arm bearing has two pairs of the air inlet rocker arm supporting gasket and the air exhaust rocker arm supporting gasket.

Since two straight oil channels perpendicular to each other are adopted in this invention instead of traditional inclined oil channels, a rotation trajectory of a cam of a camshaft can be substantially tangent with the two straight oil channels. Compared with a case in which a rotation trajectory of a cam of a camshaft is substantially tangent with inclined oil channels, the camshaft is closer to the rocker arm bearing mounting boss in a width direction between the air inlet side surface and the air exhaust side surface, and the height of the camshaft can be reduced. Accordingly, the whole size of an engine can be reduced, realizing a more compact engine.

Further, since the second straight oil channel is blocked by a blocking cap after being machined, which does not affect the performance of the engine while realizing blocking using the original blocking process, additional devices or processes are not needed.

Further, in preferred embodiments of this invention, since the camshaft directly contacts the cam follower of the valve rocker arm to drive the air inlet and exhaust rocker arms, and a push rod is saved, the structure is simpler and the height of the engine can be further reduced; since the rotation shafts of the air inlet and exhaust rocker arms are parallelly displaced from each other, the width of the engine can be further reduced, and air inlet and exhaust timing can be facilitated.

Further, since the rocker arm bearing has an oil passage in communication with the first straight oil channel, lubricating oil can be provided to the valve rocker arm and its assemblies, thereby prolonging the service life of the engine.

Further, since a rotation shaft of the cam follower is made of brass and provided with a lubricating oil groove, the anti-abrasion capability between the rotation shaft and the cam follower is enhanced, thereby prolonging their service lives.

Further, since each rocker arm bearing has two pairs of the air inlet rocker arm supporting gasket and the air exhaust rocker arm supporting gasket, the mounting accuracy can be improved, thereby ensuring the synchronization of air inlet and exhaust among adjacent cylinders. A further object of the preferred embodiments of this invention is to provide a cylinder head compact in structure for an engine, simple in manufacturing and high in accuracy.

To realize this further object, the preferred embodiments of this invention provide the following technical solution: A cylinder head comprises: a top surface, a bottom surface, an air inlet side surface, an air exhaust side surface, a front end surface and a rear end surface, a camshaft mounting base and a rocker arm bearing mounting boss being provided on the top surface, an oil returning passage extending through the front end surface and the rear end surface, the cylinder head further comprises an L-shaped pipe cast therein, an opening of an end of a vertical portion of the L-shaped pipe being provided at the rocker arm bearing mounting boss, a horizontal portion of the L-shaped pipe being in communication with the oil returning passage, and a spacing being provided between an end of the horizontal portion and the air inlet side surface.

Preferably, a smooth transition is provided between the vertical portion and the horizontal portion of the L-shaped pipe.

Preferably, an outer wall of the L-shaped pipe is provided with a protruding edge or point.

Preferably, a water jacket chamber is provided at the spacing between the end of the horizontal portion and the air inlet side surface. A method for manufacturing a cylinder head, comprises the steps of: pre-embedding an L-shaped pipe in a casting mold; pouring a casting material and cooling the same such that the L-shaped pipe is cast into a cylinder head, and an opening of an end of a vertical portion of the L-shaped pipe is provided at a rocker arm bearing mounting boss of the cylinder head, with a spacing provided between an end of a horizontal portion of the L-shaped pipe and an air inlet side surface of the cylinder head; and machining an oil returning passage such that the oil returning passage is in communication with the horizontal portion of the L-shaped pipe.

Preferably, after the casting is completed, machining is performed at the opening of the end of the vertical portion of the L-shaped pipe.

Preferably, after the casting is completed, machining is performed at the opening of the end of the vertical portion of the L-shaped pipe by cutting a portion of the L-shaped pipe and the casting material simultaneously such that the opening has a tapered shape.

Preferred embodiments of this invention include pre-embedding an L-shaped pipe in a casting mold during a casting process of a cylinder head, so that the L-shaped pipe is cast in the cylinder head, and an oil path from the rocker arm bearing mounting boss to the oil returning passage is formed therefore. As a result, horizontal and vertical drilling is saved, thereby simplifying the machining by saving some processes. In addition, the oil path is guaranteed to be through without considering the machining accuracy of the drilled holes. Further, since a spacing is provided between the end of the horizontal portion of the L-shaped pipe and the air inlet side surface, a process of blocking at the air inlet side surface is saved, while space is offered for a water jacket of the cylinder head.

Further, since a smooth transition is provided between the vertical portion and the horizontal portion of the L-shaped pipe, oil flow will become more smooth, and a risk that cracking of the cylinder head caused at the connection between the vertical portion and the horizontal portion due to stress concentration during the casting process can be eliminated or reduced.

Further, since an outer wall of the L-shaped pipe is provided with a protruding edge or point, connection between the L-shaped pipe and the casting material will be tighter.

Further, since a water jacket chamber is provided at the spacing between the end of the horizontal portion and the air inlet side surface, the distribution range of the cooling water jacket is greater, thereby facilitating the cooling of the cylinder.

Further, after the casting is completed, machining is performed at the opening of the end of the vertical portion of the L-shaped pipe, so that sarcoma, bumt-on sand and other excessive materials near the opening can be removed. As a result, the lubricating oil passage is prevented from being blocked, smooth oil supply is ensured, and the surface of the rocker arm bearing mounting boss will be smoother, thereby ensuring the mounting accuracy of the rocker arm bearing.

Further, after the casting is completed, machining is performed at the opening of the end of the vertical portion of the L-shaped pipe by cutting a portion of the L-shaped pipe and the casting material simultaneously such that the opening has a tapered shape. By doing so, sarcoma, bumt-on sand and other excessive materials near the opening can be removed, the lubricating oil passage is prevented from being blocked, smooth oil supply is ensured, and the surface of the rocker arm bearing mounting boss will be smoother, thereby ensuring the mounting accuracy of the rocker arm bearing. In addition, stress concentration at the casting material and the opening of the end of the L-shaped pipe during the casting process can be eliminated, thereby improving the stress-carrying capability. A further object of the preferred embodiments of this invention is to provide a compact engine having a cylinder head of simple machining processes, and capable of providing greater space for a cooling water jacket to sure better cooling effect.

To realize this further object, preferred embodiments of this invention provide the following technical solution: A cylinder head comprises: a top surface, a bottom surface, an air inlet side surface, an air exhaust side surface, a front end surface and a rear end surface, a camshaft mounting base and a rocker arm bearing mounting boss being provided on the top surface, an oil returning passage extending through the front end surface and the rear end surface, the cylinder head further comprises an arcuate pipe cast therein, the arcuate pipe being in communication with the oil returning passage, an opening of one end of the arcuate pipe being provided at the rocker arm bearing mounting boss, and a circle center of the arcuate pipe coinciding with that of a shaft hole of the camshaft mounting base.

Preferably, a spacing is provided between the other end of the arcuate pipe and the air inlet side surface.

Preferably, a water jacket chamber is provided at the spacing.

Preferably, an outer wall of the arcuate pipe is provided with a protruding edge or point. A method for manufacturing a cylinder head, comprises the steps of: pre-embedding an arcuate pipe in a casting mold; pouring a casting material and cooling the same such that the arcuate pipe is cast into a cylinder head, and an opening of one end of the arcuate pipe is provided at a rocker arm bearing mounting boss of the cylinder head, with a circle center of the arcuate pipe coinciding with that of a shaft hole of the camshaft mounting base; and machining an oil returning passage such that the oil returning passage is in communication with the arcuate pipe.

Preferably, after the casting is completed, machining is performed at the opening of the arcuate pipe.

Preferably, after the casting is completed, machining is performed at the opening of the arcuate pipe by cutting a portion of the arcuate pipe and the casting material simultaneously at the opening such that the opening has a tapered shape.

Preferred embodiments of this invention include pre-embedding an arcuate pipe in a casting mold during a casting process of a cylinder head, so that the arcuate pipe is cast in the cylinder head, and an oil path from the rocker arm bearing mounting boss to the oil returning passage is formed. As a result, horizontal and vertical drilling is saved, thereby simplifying the machining by saving some processes. In addition, the oil path is guaranteed to be through without considering the machining accuracy of the drilled holes. Further, since a circle center of the arcuate pipe coincides with that of a shaft hole of the camshaft mounting base, a profile of the whole arcuate pipe can be substantially tangent with a rotation trajectory of a cam of a cam shaft, so that greater space can be provided for the water jacket chamber and the cooling effect improved while making an engine more compact. In addition, stress concentration can be prevented, since the arcuate shape of the pipe can improve the stress distribution between the casting material of the cylinder and the pipe.

Further, since a spacing is provided between one end of the arcuate pipe and the air inlet side surface, a process of blocking at the air inlet side surface is saved, while greater space is offered for a water jacket of the cylinder head.

Further, since a water jacket chamber is provided at the spacing, the cooling effect of the cooling water jacket can be improved.

Further, since an outer wall of the arcuate pipe is provided with a protruding edge or point, connection between the arcuate pipe and the casting material will be tighter.

Further, after the casting is completed, machining is performed at the opening of the arcuate pipe, so that sarcoma, burnt-on sand and other excessive materials near the opening can be removed. As a result, the lubricating oil passage is prevented from being blocked, smooth oil supply is ensured, and the surface of the rocker arm bearing mounting boss will be smoother, thereby ensuring the mounting accuracy of the rocker arm bearing.

Further, after the casting is completed, machining is performed at the opening of the arcuate pipe by cutting a portion of the arcuate pipe and the casting material simultaneously at the opening such that the opening has a tapered shape. By doing so, sarcoma, bumt-on sand and other excessive materials near the opening can be removed, the lubricating oil passage is prevented from being blocked, smooth oil supply is ensured, and the surface of the rocker arm bearing mounting boss will be smoother, thereby ensuring the mounting accuracy of the rocker arm. In addition, stress concentration at the casting material and the opening of the end of the arcuate pipe during the casting process can be eliminated, thereby improving the stress-carrying capability.

Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”.

Brief Description of the Drawings

The embodiments of this invention will be described in detail, and by way of example only, with reference to the drawings, in which:

Figure 1 is a top view of a cylinder head of an overhead camshaft engine;

Figure 2 is a perspective view of an engine according to an embodiment of this invention, with some parts of the engine omitted;

Figure 3 is a sectional view cut along the line A-A in Figure 1, showing the structure of a traditional lubricating oil passage;

Figure 4 is a sectional view cut along the line A-A in Figure 1 similar to Figure 3, showing the structure of a lubricating oil passage of a first embodiment of this invention;

Figure 5 is a schematic view in which the structures and principles of the lubricating oil passage of the first embodiment of this invention and a traditional lubricating oil passage are compared;

Figure 6 is a perspective view of a rocker arm bearing of the first embodiment of this invention;

Figure 7 is an exploded view of a valve rocker arm of the first embodiment of this invention;

Figure 8 is a local top view of Figure 2;

Figure 9 schematically shows a case in which the first and second straight oil channels of the first embodiment of this invention are displaced and only a part of them are connected;

Figure 10 is a front view of an L-shaped pipe of a second embodiment of this invention;

Figure 11 is a sectional view cut along the line A-A in Figure 1 similar to Figure 3, showing the structure of the lubricating oil passage of the second embodiment of this invention;

Figure 12 is a sectional view cut along the line A-A in Figure 1 similar to Figure 3, showing the structure of the lubricating oil passage of a third embodiment of this invention;

Figure 13 is a sectional view cut along the line A-A in Figure 1 similar to Figure 3, showing the structure of the lubricating oil passage of a fourth embodiment of this invention;

Figure 14 is a front view of an arcuate pipe of a fifth embodiment of this invention;

Figure 15 is a sectional view cut along the line A-A in Figure 1 similar to Figure 3, showing the structure of the lubricating oil passage of the fifth embodiment of this invention; and

Figure 16 schematically shows a case in which the first and fifth embodiments of this invention are compared.

Reference signs in the drawings: top surface 1, air inlet side surface 2, air exhaust side surface 3, front end surface 4, rear end surface 5, camshaft mounting base 6, rocker arm bearing mounting boss 7, oil returning passage 8, inclined oil channel 9, first straight oil channel 10, second straight oil channel 11, water jacket 12, camshaft 13, rocker arm bearing 14, air inlet rocker arm supporting gasket 15, air exhaust rocker arm supporting gasket 16, bridging portion 17, air inlet rocker arm bearing 18, air exhaust rocker arm bearing 19, air inlet rocker arm 20, air exhaust rocker arm 21, cam follower 22, air inlet valve 23, rotation shaft 24, air exhaust valve 25, oil passage 26, rotation shaft 27, lubricating oil groove 28, bolt 29, valve adjusting bolt 30, fastening nut 31, ball head bearing 32, valve bridge 33, L-shaped pipe 200, vertical portion 201, horizontal portion 202, protruding edge 203, first end 204, second end 205, bottom surface 215, arcuate pipe 300, first end 301, second end 302, protruding edge 303, shaft hole 61.

Embodiments for carrying out the invention

Referring to Figures 1-2, a cylinder head comprises: a top surface 1, an air inlet side surface 2 having an air inlet, an air exhaust side surface 3 having an air outlet, a front end surface 4 facing a timing wheel system and a rear end surface 5 opposing the front end surface 4. A person skilled in the art should understand that the top surface 1 is defined relative to a bottom surface 215 of the cylinder head contacting a cylinder body (not shown), while the front and rear end surfaces 4, 5 are defined relative to the position of the timing wheel system. Of course, other definitions may be used as well. A camshaft mounting base 6 and a neighboring rocker arm bearing mounting boss 7 are provided on the top surface 1. A camshaft 13 is installed in a shaft hole 61 of a camshaft mounting base 6. The camshaft 13 drives an air inlet rocker arm 20 through rotation to drive a pair of air inlet valves 23, and drives an air exhaust rocker arm 21 to drive a pair of air exhaust valves 25. An oil returning passage 8 extends from the front end surface 4 to the rear end surface 5, and extends through the whole cylinder head between the front and rear end surfaces 4, 5 as a part of a cylinder lubricating oil path.

Referring to Figure 3, since space needs to be reserved for avoiding a water jacket 12 and surrounding members, there is little space to select the machining position of the oil returning passage 8, which will be substantially positioned obliquely below the rocker arm bearing mounting boss 7 and neighboring the air inlet side surface 2. In the prior arts, usually an inclined oil channel 9 is drilled on the rocker arm bearing mounting boss 7 to communicate with the oil returning passage 8 to lubricate an air valve rocker arm assembly (including air inlet and exhaust rocker arms). In this way, drilling for once is enough, thereby facilitating machining.

Referring to Figure 4, which is different from Figure 3, a first straight oil channel 10 is drilled vertically downwards from the rocker arm bearing mounting boss 7 in this invention, and a second straight oil channel 11 is drilled horizontally from the air inlet side surface 2 to communicate with the first straight oil channel 10 and the oil returning passage 8, so that oil in the oil returning passage 8 can reach the rocker arm bearing mounting boss 7 and the air valve rocker arms via the second straight oil channel 11 and the first straight oil channel 10. Of course, an opening of the machined second straight oil channel 11 at the air inlet side surface 2 should be blocked by welding, for example, to ensure oil supply effect and engine performance. However, blocking is preferably performed by pressing a blocking cap. Since after machining of a cylinder head is finished, water holes and oil holes usually need to be blocked, such a blocking method can be carried out by existing devices and processes without adding welding devices and processes to the production line.

Figure 5 schematically illustrates the advantages of straight oil channels over inclined ones. In Figure 5, a circle represents the rotation trajectory of the cam on the camshaft 13, which is depicted by a dotted line when an inclined oil channel is adopted, while depicted by a solid line when straight oil channels are adopted. When an inclined oil channel 9 is adopted, the cam rotation trajectory represented by the dotted circle at most can reach a position tangent to the inclined oil channel 9 represented by a dotted line (of course, the dotted circle cannot be actually tangent to the inclined oil channel due to an channel wall of the inclined oil channel 9). In this case, the width from the dotted circle to the opening of the inclined oil channel 9 on the rocker arm bearing mounting boss 7 is Wl, that is, the minimum width from the air inlet side surface 2 of the cylinder head to this opening is Wl (when not considering the thickness of the camshaft mounting base 6). A height from the dotted circle to the oil returning passage 8 is HI. When the first straight oil channel 10 and the second straight oil channel 11 are adopted, the circle center C of the dotted circle reaches the circle center C of the solid circle. The cam rotation trajectory represented by the solid circle is estimated to at most reach a position tangent to the first straight oil channel 10 and the second straight oil channel 11 represented by the solid lines (similar to the above case, tangency is impossible). As a result, a width W2 from the air inlet side surface 2 of the cylinder head to the opening of the first straight oil channel 10 can be obviously smaller than Wl, and a height H2 from the solid circle to the oil returning passage 8 can be obviously smaller than HI. In other words, compared with the case of adopting an inclined oil channel 9 while maintaining other conditions, when first straight oil channel 10 and second straight oil channel 11 are adopted, the height and width of the cylinder head can be reduced. Of course, a person skilled in the art should understand that the other reason why the solid circle cannot be tangent to the first straight oil channel 10 is that, if tangency exists, the camshaft will directly press the rotational shaft of the air valve rocker arm, thereby failing to drive the air valve rocker arm; but this does not prevent the reduction of the cylinder head in its width direction compared with the case of adopting an inclined oil channel 9; even if the circle center C of the cam rotation trajectory moves vertically downwards, which cannot reduce the width of the cylinder, the height of the cylinder can be reduced. In other words, when the first straight oil channel 10 and the second straight oil channel 11 replace the inclined oil channel 9, at least the height of the cylinder head can be reduced, or both the height and width thereof can be reduced. Therefore, the above structure downsizes an engine. Although drilling needs to be performed twice in this embodiment, this can reduce an engine weight and offer greater advantages for arranging the space of a whole vehicle, so the structure of present embodiment is more cost-effective.

Figure 6 illustrates the structure of a rocker arm bearing 14 used in an engine of this invention. The rocker arm bearing 14 includes an air inlet rocker arm supporting gasket 15 and an air exhaust rocker arm supporting gasket 16, the air inlet rocker arm supporting gasket and the air exhaust rocker arm supporting gasket are connected with each other through a bridging portion 17 and are respectively mounted with an air inlet rocker arm bearing 18 and an air exhaust rocker arm bearing 19. An oil passage is provided on a bottom surface of the rocker arm bearing 14 and communicates with the first straight oil channel 10, so that oil from the oil returning passage 8 can enter the air inlet rocker arm 20 and the exhaust rocker arm 21 for lubricating the same. Lubricating oil passages inside valve rocker arms are already recorded in multiple patent documents and the prior arts, so they will not be detailed in this application. One air inlet rocker arm supporting gasket 15 and one air exhaust rocker arm supporting gasket 16 are grouped into a pair to support the air inlet rocker arm 20 and the exhaust rocker arm 21 of the same combustion chamber. In this invention, each rocker arm bearing 14 has two pairs of air inlet and exhaust rocker arm supporting gaskets 15, 16, so each rocker arm bearing 14 can support the air inlet and exhaust rocker arms 20, 21 of two adjacent combustion chambers. This facilitates not only installation but also control of installation accuracy, while guaranteeing the timing synchronization of the air inlet and exhaust rocker arms 20, 21 of adjacent combustion chambers.

Figures 2 and 7 illustrate the configuration of a valve rocker arm (including an air inlet rocker arm 20 and an air exhaust rocker arm 21) of this invention. One end of the valve rocker arm is provided with a cam follower 22 whose rotation shaft 27 is preferably made of brass to provide better abrasion resistance. Meanwhile, the rotation shaft 27 is provided with a lubricating oil groove 28 into which oil from oil returning passage 8 can enter to provide lubrication between the rotation shaft 27 and the cam follower 22. The other end of the valve rocker arm is provided with a valve adjusting bolt 30 whose end forms a ball head-ball socket engagement relation with a ball head bearing 32. The ball head bearing 32 presses a valve bridge 33 along with swing of the valve rocker arm to drive a pair of air inlet valves 23 or a pair of air exhaust valves 25, realizing the drive link between the valve rocker arm and the air inlet valves or air exhaust valves. The installation height of the air inlet valves 23 and air exhaust valves 25 is adjusted by the valve adjusting bolt 30. After adjustment is completed, the valve adjusting bolt 30 is locked by a fastening nut 31. A rotation shaft 24 is installed at a middle portion of two ends of the valve rocker arm. When assembling an engine, the camshaft 13 is installed in the camshaft mounting base 6, the each rocker arm bearing 14 is mounted on the rocker arm bearing mounting boss 7, and a bolt 29 passes through the rotation shaft 24 to respectively fix the air inlet rocker arm 20 and the air exhaust rocker arm 21 onto the air inlet rocker arm bearing 18 and the air exhaust rocker arm bearing 19, so that the air inlet rocker arm 20 and the air exhaust rocker arm 21 can swing about the rotation shaft 24. As a result, the cam on the camshaft 13 directly contacts the cam follower 22 to drive the valve rocker arm.

Referring to Figure 8, to adapt to different opening time of the air inlet valves 23 and air exhaust valves 25, axis a of the rotation shaft of the air inlet rocker arm 20 and axis b of the rotation shaft of the air exhaust rocker arm 21 are parallelly displaced from each other and are not overlapped.

In a first embodiment of this invention, a first straight oil channel 10 is drilled vertically downwards from the rocker arm bearing mounting boss 7, and a second straight oil channel 11 is drilled horizontally from the air inlet side surface 2 to communicate with the first straight oil channel 10 and the oil returning passage 8, so that oil in the oil returning passage 8 can reach the rocker arm bearing mounting boss 7 and the air valve rocker arms via the second straight oil channel 11 and the first straight oil channel 10. By replacing an inclined oil channel with two straight oil channels, the rotation trajectory of the cam on the camshaft 13 can be made tangent to the two straight oil channels, realizing a compact and downsized engine. However, to ensure oil supply effect and engine performance, an opening of the machined second straight oil channel 11 at the air inlet side surface 2 should be blocked by welding or press-fitting a blocking cap, for example. If the machining accuracy cannot be guaranteed, the first and second straight oil channels 10, 11 may be misaligned and may not be able to communicate with each other, causing the produced cylinder head to become a waste product, or only a portion of them is in communication (as shown in Figure 9). In addition, since the second straight oil channel 11 needs to be drilled from the air inlet side surface 2, the water jacket chamber 12 cannot be cast at a portion between the oil returning passage 8 and the air inlet side surface 2. In other words, the water jacket chamber 12 can only be positioned below the second straight oil channel 11 at this position, affecting the heat diffussion effect of the cylinder head. Further, even if the cam rotation trajectory is tangent to the two straight oil channels, a water jacket chamber still cannot be cast at a position B shown in Figure 4. If a water jacket chamber is provided here, space must be reserved to avoid the oil returning passage 8 and the first and second straight oil channels 10, 11, causing design of the water jacket too complex. Even if the water jacket chamber is provided at the position B, since the water jacket chamber is made by casting while the oil returning passage 8 and the first and second straight oil channels 10, 11 are machined after casting, a portion of the chamber at the position B can be easily penetrated when machining such that oil and cooling liquid are mixed. This is quite hard to realize and will produce excessive waste products easily.

Referring to Figure 10, in a second embodiment of this invention, an L-shaped pipe 200 has a vertical portion 201 and a horizontal portion 202. The end of the vertical portion 201 is marked as a first end 204, and the end of the horizontal portion 202 as a second end 205, with the first end 204 being the opening end. When casting the cylinder head, the L-shaped pipe 200 is placed in a casting mold as a pre-embedded member. Then, a casting material such as an aluminum alloy or cast iron is poured into the casting mold. After the casting material is cooled, the L-shaped pipe 200 is cast in the casting material as a part of the cylinder head. To increase the connection tightness with the casting material, an outer wall of the L-shaped pipe 200 is preferably provided with multiple protruding edges 203. The protruding edges 203 shown in the figures has a linear shape, but as can be easily conceived by those skilled in the art, it may be in other shapes such as a circle or a curve. Or the outer wall of the L-shaped pipe 200 is formed with protruding points like pits to ensure good connection.

Referring to Figure 11, after casting the L-shaped pipe 200 in the cylinder head, an opening of the first end 204 is provided at the rocker arm bearing mounting boss 7 to provide lubrication to the rocker arm bearing 14, the air inlet rocker arm 20 and the air exhaust rocker arm 21. The oil returning passage 8 is formed by machining after casting the cylinder head such that the oil returning passage 8 is in communication with the horizontal portion 202. A spacing S is provided between the second end 205 and the air inlet side surface 2, that is, the horizontal portion 202 has no opening at the air inlet side surface 2, and blocking is unnecessary there. In this way, while maintaining the advantage of a downsized cylinder head by replacing an inclined oil channel with straight oil channels, this invention saves two drilling processes and a blocking process. In addition, the vertical portion 201 and the horizontal portion 202 of the L-shaped pipe 200 are ensured to be through completely, preventing displacement between the straight oil channels. Further, a weight-reducing hollow can be machined at the spacing S, or the water jacket chamber 12 can be arranged here when casting. To obtain better cooling effect of the water jacket, a water jacket chamber 12 is preferably provided at the spacing S. In this embodiment, the second end 205 terminates at the oil returning passage 8. Those skilled in the art can easily assume that the second end 205 may extend further towards the air inlet side surface 2 due to the machining accuracy but not reach the air inlet side surface 2. Accordingly, the spacing S will be reduced. If casting defects such as bumt-on sand and sarcoma appear during the casting process, the installation accuracy of the air inlet rocker arm 20 and the air exhaust rocker arm 21 as well the air inlet and exhaust phase accuracy will be affected. Further, the opening may be partially or completely blocked by such casting defects, so that oil and other liquids cannot flow smoothly. Therefore, machining, such as drilling and counter boring, is preferably performed at the opening of the first end 204 to remove excessive materials near the opening like sarcoma and burnt-on sand. In a third embodiment of this invention, only excessive materials near the opening of the first end 204 is removed by drilling.

Different from the second embodiment shown in Figure 11, in a third embodiment of this invention shown in Figure 12, an arcuate smooth transition is provided between the vertical portion 201 and the horizontal portion 202 of the L-shaped pipe 200, such that oil in the oil returning passage 8 can flow out smoothly, and a risk of crack generation caused by stress concentration at the connection between the vertical portion 201 and the horizontal portion 202 when the casting material cools and contracts can be avoided or reduced . At the opening of the first end 204 on the rocker arm bearing mounting boss 7, during casting, since the physical properties of the material of the L-shaped pipe 200 are different from those of the casting material, stress concentration can easily occur at a drastic transition edge of the two materials.

Different from the third embodiment shown in Figure 12, in a fourth embodiment of this invention shown in Figure 13, the opening of the first end 204 on the rocker arm bearing mounting boss 7 is machined into a tapered shape, and a portion of materials of the L-shaped pipe 200 and the casting material near the opening of the first end 204 are cut simultaneously. In this way, by performing machining only once, stress concentration between the L-shaped pipe 200 and the casting material of the cylinder head can be eliminated, and casting defects such as bumt-on sand and sarcoma near the opening of the vertical portion of the L-shaped pipe can be prevented, so that the installation accuracy and force-bearing performance of the rocker arm bearing mounting boss 7 can be guaranteed while facilitating outflow of oil. Those skilled in the art can easily assume that a tapered opening can also be machined in the second embodiment of this invention.

Referring to Figure 14, an arcuate pipe 300 includes a first end 301 and a second end 302, with the first end 301 being an opening end. When casting the cylinder head, the arcuate pipe 300 is placed in a casting mold as a pre-embedded member. Then, a casting material such as an aluminum alloy or cast iron is poured into the casting mold. After the casting material is cooled, the arcuate pipe 300 is cast in the casting material as a part of the cylinder head. Since the arcuate pipe 300 is arcuate, cracks caused by stress concentration when the casting material around the arcuate pipe 300 is cooled can be avoided or reduced. To increase the connection tightness with the casting material, an outer wall of the arcuate pipe 300 is preferably provided with multiple protruding edges 303. As can be easily conceived by those skilled in the art, the protruding edge 303 may be in various shapes such as a circle or a curve. Or the protruding edge 303 may be replaced by protruding points like pits to ensure good connection.

Referring to Figure 15, the arcuate pipe 300 becomes a part of the cylinder head after being cast therein, and an opening of the first end 301 is provided on the rocker arm bearing mounting boss 7. The oil returning passage 8 is formed by machining such that the oil returning passage 8 is in communication with the arcuate pipe 300 to provide lubrication to the rocker arm bearing 14, the air inlet rocker arm 20 and the air exhaust rocker arm 21. The circle center of the arcuate pipe 300 coincides with that of the shaft hole 61 of the camshaft mounting base 6, namely, both being C, so that the part B in Figure 5 is radially away from the circle center C. In other words, the part B is at an outer side of the arcuate pipe 300 relative to the circle center. As a result, the water jacket chamber 12 can extend to the part B without leaving space for avoiding the arcuate pipe 300. The water jacket chamber can be integrally formed with the arcuate pipe 300 (or an arcuate lubricating oil passage) during casting, thereby reducing the design and machining complexity level. Since the circle center of the arcuate pipe 300 coincides with that of the shaft hole 61 of the camshaft mounting base 6, the water jacket chamber can be arranged by taking advantage of the existing space as much as possible, thereby producing better cooling effect. Since the arcuate pipe 300 is a through member itself, displacement between straight oil channels is avoided. In this embodiment, the second end 302 terminates at the oil returning passage 8, and is separated from the air inlet side surface 2 by a spacing S. In other words, the arcuate pipe 300 has no opening at the air inlet side surface 2, saving a blocking process. Further, a weight-reducing hollow can be machined at the spacing S, or the water jacket chamber 12 can be arranged here when casting. To obtain better cooling effect, the water jacket chamber 12 is preferably provided at the spacing S. Those skilled in the art can easily assume that the second end 302 may extend towards and even reach the air inlet side surface 2 due to machining accuracy. However, due to the above considerations, this is not advantageous, and is not a preferred solution of this invention. Since a roughcast usually has casting defects such as bumt-on sand and sarcoma, the opening at the first end 301 may be partially or completely blocked and oil cannot flow smoothly. At the same time, the surface smooth degree of the rocker arm bearing mounting boss may be affected, and the installation accuracy of the air inlet and exhaust rocker arms as well as the air allocation accuracy may be affected. Therefore, cutting machining, such as drilling, counter boring and milling, is preferably performed at the opening of the first end 301 after casting is finished to avoid casting defects. In that case, the opening will not be blocked, the surface of the rocker arm bearing mounting boss will be smoother, and the installation accuracy will be improved. When machining the opening, only excessive materials near the opening like sarcoma and burnt-on sand can be removed by drilling, or a portion of materials of the arcuate pipe 300 and a portion of casting material at the opening can be cut away simultaneously by counter boring the tapered hole. During casting, since the physical properties of the material of the arcuate pipe 300 are different from those of the casting material, stress concentration can easily occur at a drastic transition edge of the two materials. Therefore, an opening of the first end 301 of the arcuate pipe 300 provided at the rocker arm bearing mounting boss 7 is preferably cut into a tapered shape. In this way, by performing machining only once, stress concentration between the arcuate pipe 300 and the casting material of the cylinder head can be eliminated, and casting defects such as burnt-on sand and sarcoma near the opening can be eliminated, thereby facilitating outflow of oil and improving the installation accuracy.

Figure 16 schematically shows the advantages of a fifth embodiment of this invention over the first (or the second or the fourth) embodiment. To make it clearer, all the oil passages in Figure 8 are represented by lines or curves. To make a compact structure, a rotation trajectory (shown by the shaft hole 61 in this application instead) of the cam of the camshaft 13 is inclined to be tangent with the lubricating oil passages when designing the cylinder head. Under existing technical conditions, if the inclined oil channel 9 (shown by a dotted line) is used as a lubricating oil passage, the circle center of the shaft hole 61 (shown by a dotted line at this time) of the camshaft mounting base 6 is at the position C1. While in the first embodiment of this invention, when the first and second straight oil channels 10, 11 are adopted as lubricating oil passages, the circle center of the shaft hole 61 (shown by a solid line at this time) of the camshaft mounting base 6 is moved to the position C2, thereby reducing either or both of the width and height of the cylinder head. However, the part B is enclosed by the profiles of the first and second straight oil channels 10, 11, the oil returning passage 8 and the shaft hole 61, and filled by the casting material completely, so it is hard to arrange the water jacket chamber 12 at the part B. In the fifth embodiment of this invention, when the arcuate pipe 300 is used, since the lubricating oil passage has an arcuate shape and is concentric with the shaft hole 61, the arcuate pipe 300 will be substantially tangent to the shaft hole 61. In this case, an enclosed space is very small, so that more space is offered for the water jacket chamber 12, thereby improving the cooling effect of the cylinder head and realizing a downsized engine.

Although this invention is described with reference to the above embodiments, this invention is not limited to these embodiments but to the claims. Modifications to the embodiments can be easily made by those skilled in the art without departing from the concept and scope of this invention.

Claims

Claims

1. An overhead camshaft engine comprising: a cylinder head comprising a top surface, an air inlet side surface, an air exhaust side surface, a front end surface and a rear end surface, a camshaft mounting base, a rocker arm bearing mounting boss being provided on the top surface, and an oil return passage extending through the front end surface and the rear end surface, wherein the cylinder head further comprises a first substantially straight oil channel extending vertically downwards from the rocker arm bearing mounting boss and a second substantially straight oil channel extending horizontally from the air inlet side surface, the first straight oil channel and the second straight oil channel being in fluidic communication with each other, and the second straight oil channel being in fluidic communication with the oil returning passage; a camshaft mounted in the camshaft mounting base; a rocker arm bearing mounted on the rocker arm bearing mounting boss, and comprising an air inlet rocker arm supporting gasket and an air exhaust rocker arm supporting gasket, the air inlet rocker arm supporting gasket and the air exhaust rocker arm supporting gasket being connected with each other through a bridging portion and being respectively mounted with an air inlet rocker arm bearing and an air exhaust rocker arm bearing; an air inlet rocker arm having a cam follower driven by the camshaft at one end thereof and a pair of air inlet valves connected at the other end thereof, with a rotation shaft at an intermediate portion of the air inlet rocker arm mounted on the air inlet rocker arm bearing; and an air exhaust rocker arm, having a cam follower driven by the camshaft at one end thereof and a pair of air exhaust valves connected at the other end thereof, with a rotation shaft at an intermediate portion of the air exhaust rocker arm mounted on the air exhaust rocker arm bearing, wherein the rotation shafts of the air inlet rocker arm and the exhaust rocker arm are substantially parallel and displaced from each other; wherein each rocker arm bearing has two pairs of the air inlet supporting gasket and the exhaust rocker arm supporting gasket.
2. The overhead camshaft engine according to claim 1, wherein the second straight oil channel includes an opening at the air inlet side surface, the opening being blocked.
3. The overhead camshaft engine according to claim 2, wherein the opening is blocked by a blocking cap.
4. The overhead camshaft engine according to claim 1, wherein the rocker arm bearing has an oil passage in fluidic communication with the first straight oil channel to provide lubricating oil to the air inlet rocker arm and the exhaust rocker arm.
5. The overhead camshaft engine according to any one of claims 1 to 4, wherein a rotation shaft of the cam follower is made of brass.
6. The overhead camshaft engine according to any one of claims 1 to 5, wherein the rotation shaft of the cam follower is provided with a lubricating oil groove.
7. The overhead camshaft engine according to claim 1, wherein the cylinder head further comprises an L-shaped pipe cast therein and having: a vertical portion with an end that defines an opening at the rocker arm bearing mounting boss; a horizontal portion that is in fluidic communication with the oil returning passage; and a spacing being provided between one end of the horizontal portion and the air inlet side surface, a water jacket chamber is provided at the spacing between the end of the horizontal portion and the air inlet side surface.
8. The overhead camshaft engine according to claim 7, wherein a smooth transition is provided between the vertical portion and the horizontal portion of the L-shaped pipe.
9. The overhead camshaft engine according to claim 7 or claim 8, wherein an outer wall of the L-shaped pipe is provided with a protruding edge or point.
10. A method for manufacturing a cylinder head according to claim 7, the method comprising the steps of: pre-embedding an L-shaped pipe in a casting mold; pouring a casting material and cooling the same such that the L-shaped pipe is cast into a cylinder head to provide, in use, a substantially vertical portion and a substantially horizontal portion, and providing an opening at an end of the vertical portion at a rocker arm bearing mounting boss of the cylinder head, wherein a spacing is provided between an end of the horizontal portion and an air inlet side surface of the cylinder head, a water jacket chamber is provided at the spacing between the end of the horizontal portion and the air inlet side surface; and machining an oil return passage such that the oil return passage is in fluidic communication with the horizontal portion of the L-shaped pipe.
11. The method for manufacturing a cylinder head according to claim 10, wherein after the casting is completed, machining is performed at the opening of the end of the vertical portion of the L-shaped pipe.
12. The method for manufacturing a cylinder head according to claim 10 or claim 11, wherein after the casting is completed, machining is performed at the opening of the end of the vertical portion of the L-shaped pipe by cutting a portion of materials of the L-shaped pipe and a portion of the casting material simultaneously such that the opening has a tapered shape.
13. The overhead camshaft engine according to claim 1, wherein the camshaft mounting base includes a shaft hole and the cylinder head further comprises an arcuate pipe cast therein that follows an arcuate path having a centre point, the arcuate pipe being in fluidic communication with the oil returning passage and having an opening in one end thereof, the opening being provided at or adjacent to the rocker arm bearing mounting boss, and the centre point substantially coinciding with a centre of the shaft hole.
14. The overhead camshaft engine according to claim 13, wherein a spacing is provided between the other end of the arcuate pipe and the air inlet side surface.
15. The overhead camshaft engine according to claim 14, wherein a water jacket chamber is provided at the spacing.
16. The overhead camshaft engine according to any one of claims 13 to 15, wherein an outer wall of the arcuate pipe is provided with a protruding edge or point.
17. A method for manufacturing a cylinder head according to claim 13, the method comprising the steps of: pre-embedding an arcuate pipe in a casting mold, the pipe following an arcuate path having a centre point; pouring a casting material and cooling the same such that the arcuate pipe is cast into a cylinder head and an opening of one end of the arcuate pipe is provided at a rocker arm bearing mounting boss of the cylinder head, wherein the centre point substantially coincides with a centre of a shaft hole of a camshaft mounting base; and machining an oil return passage such that the oil returning passage is in fluidic communication with the arcuate pipe.
18. The method for manufacturing a cylinder head according to claim 17, wherein after the casting is completed, machining is performed at the opening of the arcuate pipe.
19. The method for manufacturing a cylinder head according to claim 17 or claim 18, wherein after the casting is completed, machining is performed at the opening of the arcuate pipe by cutting a portion of material of the arcuate pipe and a portion of the casting material at the opening simultaneously such that the opening has a tapered shape.