TECHNICAL FIELD
The present invention, in general, relates to a cylinder head assembly of an internal combustion engine and in particular relates to a multi valve cylinder head assembly for a small capacity spark ignition engine.
BACKGROUND
Typically, a cylinder head is a detachable plate that covers the closed end of a cylinder chamber of a reciprocating engine or pump. The cylinder head assembly design plays an important role in determining fuel economy, quality of exhaust emissions, and torque output of an internal combustion engine. The shape of the combustion chamber beneath the cylinder head, inlet/outlet passages and ports through the cylinder head determine a major portion of the volumetric efficiency and the compression ratio of the engine.
Conventionally, an engine used cylinder heads with one intake and one exhaust valve. It is generally known that getting fresh air/fuel mixture into and exhaust gases out of the engine quickly, enables the engine to deliver more power and hence become more efficient. One of the ways to get more power is to make the engine bigger in size.. But, the use of bigger engines, especially for small vehicles, is not desirable as bigger means more fuel used, more emissions and a higher cost of operation.
The need for improved engine breathing and increased power output, typically at higher speeds, led to the implementation of multi-valve cylinder heads . So by increasing the number of valves, the engine could breathe better, increasing its efficiency and still be economical The additional valves allow more air-fuel mixture to enter the combustion

chamber and let the exhaust gases to escape more easily. This improves the volumetric efficiency of the engine. Multiple valves are advantageous especially at high speeds, since the valve area can be increased to improve the inlet and outlet efficiency.
Such an arrangement of the cylinder head is usually not incorporated in small capacity engines due to design constraints. In addition, fast engine breathing due to additional valves increases the air induction, thereby deteriorating engine performance at lower speeds and lower loads. As a result, in conventional multi-valve engines, the engine tends to run inefficiently at low speeds.
To increase fuel economy various intake systems are also employed. One such intake system involves stratified charge combustion engines. Here, ignition begins in a layer made up of pockets of a rich mixture surrounded by a leaner mixture. A leaner average air-fuel ratio provides greater fuel economy and less exhaust emissions. To obtain the desired air-fuel ratio, fuel injectors are used. The arrangement as described above works well in slow constant speed applications, but has proven difficult to manage across a higher range of engine speeds and loads incurred in automotive uses.
Another reason for poor performance of engines at higher speeds is the higher inertia of valve train parts, especially with single intake and single exhaust valves.
Therefore, there is a need of a cylinder head assembly, which overcomes the aforementioned problems, thereby providing a more economical and a more efficient internal combustion engine.

SUMMARY
The subject matter described herein is directed to a multivalve cylinder head assembly of an internal combustion engine.
The multivalve cylinder head assembly as described herein includes a cylinder head, a combustion chamber, a carburetor for supplying air fuel mixture to a combustion chamber, and an intake pipe. Further, the cylinder head includes a plurality of intake ports, a plurality of exhaust ports, and an opening for a spark plug. The air fuel mixture from the plurality of intake ports entering into the combustion chamber is burnt therein. The intake ports further include a charging port and a volumetric port. The intake pipe, which includes a plurality of intake passages, connects the carburetor with the intake ports. The intake passages align with the corresponding intake ports for supplying the air-fuel mixture from the carburetor to the combustion chamber via the intake ports. Depending on the throttle input, the carburetor supplies the air-fuel mixture to the charging port and thereafter to the volumetric port.
In another embodiment, an exhaust gas return conduit opens into at least one of the two intake ports. Such an arrangement reduces the NOx emissions and also help improve the fuel economy.
The cylinder head assembly of the present subject matter is configured to maintain the regular features of the engine while providing benefits in terms of enhanced fuel economy, higher engine output, and lower exhaust emissions.
These and other features, aspects, and advantages of the present subject matter will be better understood with reference to the following description and appended claims. This summary is provided to introduce a selection of concepts in a simplified

form. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
The novel features of the invention are set forth in the appended claims hereto. The invention itself, however, as well as a preferred mode of use, further objectives, and advantages thereof, will best be understood by reference to the following detailed description of illustrative embodiments when read in conjunction with the accompanying drawings, wherein the same numbers are used throughout the drawings to reference like features, and wherein:
Fig. 1 illustrates a cross sectional view of a cylinder head assembly of an internal combustion engine with respect to one embodiment of the present invention.
Fig. 2 illustrates a sectional view of a cylinder head in the cylinder head assembly with respect to one embodiment of the present invention
Fig. 3 illustrates a perspective view of a bottom side of a cylinder head with respect to one embodiment of the present invention,
Fig.4 illustrates a perspective view of a top side of the cylinder head when viewed in the direction of x, with respect to Fig.3, according to one embodiment of the present invention.
Fig. 5 illustrates a perspective view of a front side of the cylinder head when viewed in the direction of y, with respect to Fig. 4, according to one embodiment of the present invention.

Fig. 6 illustrates a perspective view of a back side of the cylinder head when viewed in the direction of y with respect to Fig.4, according to one embodiment of the present invention.
Fig. 7 illustrates a perspective view of a right side of the cylinder head when viewed in the direction of y with respect to Fig.4, according to one embodiment of the present invention.
Fig. 8 illustrates a perspective view of a left side of the cylinder head when viewed in the direction of y with respect to Fig.4, according to one embodiment of the present invention.
Fig. 9(a), 9(b) and 9(c) provide perspective views of a front side, a cross section, and a bottom side of an intake pipe in the cylinder head assembly, according to one embodiment of the present invention.
DESCRIPTION
In order to address the aforesaid challenges, according to at least one embodiment of the present subject matter, a multivalve cylinder head assembly for a small capacity spark ignition engine is provided.
The cylinder head assembly of the present subject matter achieves enhanced fuel economy under various load requirements. The multivalve cylinder head assembly also yields higher engine output with lower exhaust emissions. Further, the multi valve cylinder head assembly described herein employs a more efficient fuel intake system, provides lower valve train inertia, and gives enhanced performance both at low and high

speeds. Moreover, the construction of the intake pipe is such that the transfer of vibrations from the cylinder head to the carburetor is reduced.
Fig. 1 illustrates a cross sectional view of a cylinder head assembly 100 of an internal combustion engine with respect to one embodiment of the present invention. As shown in Fig.l, the cylinder head assembly 100 of the present invention broadly includes a carburetor 102 connected to an intake pipe 104, which in turn opens into a cylinder head 106.
The carburetor 102 blends air and fuel entering therein. The operation of the exemplary system of the present invention uses a round piston type or slide valve type carburetor 102. In this kind of carburetor, a piston moves up and down in its chamber forming a throttle device to control the air-fuel mixture, or a throttle device can additionally be provided with a throttle valve in one or both of the intake ports. The intake pipe 104 connects the carburetor 102 to the cylinder head 106 in order to supply the air-fuel mixture to a combustion chamber through the cylinder head 106.
In another embodiment, throttle valves are provided separately. As the vacuum between a throttle valve and the piston changes, the piston inside the carburetor 102 moves up and down in its chamber, which causes an attached tapered needle to move in or out of the jet controlling the fuel
Fig. 2 shows a sectional view of a cylinder head of the cylinder head assembly as described in Fig. 1 with respect to one embodiment of the present invention. The cylinder head 106 includes two intake valves 202a and 202b, collectively referred as 202, that control the flow of the air-fuel mixture into a combustion chamber 204 defined on one of the sides of the cylinder head 106. A tip end of a spark plug 206 is disposed substantially

at the centre of the combustion chamber 204 while a terminal end of the spark plug 206 extends outside the cylinder head 106. The spark plug 206 provides a spark nearly at the end of a compression stroke that consequently results in flame propagation and a power stroke.
The cylinder head further includes two exhaust valves (not shown in the figure), a cam shaft sprocket assembly (not shown in the figure) connected to a crankshaft sprocket assembly (not shown in the figure) through an endless chain. The camshaft sprocket, the chain, and the crankshaft sprocket are disposed inside a cam chain chamber 208 and together constitute a sprocket chain assembly. When the crankshaft rotates, it provides rotation to the chain through the crankshaft sprocket disposed on one end of the crankshaft. The rotational movement of the chain is transferred to the camshaft sprocket, which consequently drives the camshaft. The movement of the cam shaft finally controls the timing of opening and closing of the intake and exhaust valves.
Fig. 3 shows a perspective bottom (first side) view of the cylinder head with respect to one embodiment of the present invention. The bottom side of the cylinder head is adapted for directly mounting the cylinder head 106 to a cylinder block. The bottom side also defines a section of the combustion chamber 204 having a pent roof shape.. The section of the combustion chamber 204 defines a major arc of a circle at the boundary where the combustion chamber 204 adjoins with the surface of the bottom side of the cylinder head 106. The pent roof design facilitates in having a multi-valve or, more particularly, a four-valve cylinder head fitted thereto. Further, fig,3 illustrates two intake ports 302a and 302b, collectively referred as 302, which open inside the combustion chamber 204. During a suction stroke, the air-fuel mixture enters the combustion

chamber 204 through the intake ports 302. Each opening of the intake ports 302 inside the combustion chamber 204 also houses a seat for the intake valves 202.
Openings for two-exhaust ports 304a and 304b, collectively referred as 304, are disposed diametrically opposite to the intake ports 302. During the exhaust stroke, the exhaust ports 304 provide a path for exhaust gases from the combustion chamber 204 to an exhaust manifold. The bottom side also houses a pair of seats for both the exhaust valves. The combustion chamber 204 also houses an opening 306, substantially at the center of the combustion chamber 204, for the spark plug 206 as shown in Fig 3. By arranging the spark plug 206 between the four valves, i.e., two intake and exhaust valves, a position is achieved which is beneficial from the point of view of achieving increased combustion efficiency and fuel economy. An opening for the cam chain chamber 208 is also disposed adjacent to the combustion chamber 204. Engines having such a four valve arrangement with a centrally placed spark plug achieve better combustion over a wide range of engine speeds and thus are suitable for lean burn designs.
Fig.4 illustrates a perspective view of a top (second side) of the cylinder head according to an embodiment of the present invention. When viewed in the direction of x, with respect to Fig.3, the bottom side and the top side of the cylinder head 106 are the two opposite sides of the cylinder head 106. The top side is inclined at an acute angle to a plane defined by the bottom side, which helps in easy access to and assembling of different components of the cylinder head 106. The top side provides a housing for the cam shaft assembly (not shown in figure), and a valve train. A cover (not shown in the figure), is fastened on top of the cylinder head 106 for safety and protection.

As shown in Fig.4, the two intake valves 202a and 202b are disposed within valve guides 402a and 402b, respectively. Also, two exhaust valves 404a and 404b are disposed within valve guides 406a and 406b, respectively. The valve guides are sealed by valve stem oil seals (not shown in the figure). The valve stem oil seals keep excess oil out of the combustion chamber 204. The stem end of valves is disposed in the valve guides on the top side. Further, the other end or face end of the valves is disposed inside the combustion chamber 204 towards the bottom side. Fig.4 further illustrates an opening for the cam chain chamber 208 that extends to the combustion chamber 204.
In order to allow a maximum amount of the air-fuel mixture to enter into the cylinder and a maximum amount of exhaust gases to escape out it is desirable that inlet and exhaust valve open and close as efficiently as possible. To achieve these aims the components of the valve train are subjected to high accelerations as the inertia of the components has to be overcome.. Therefore, as the mass of the valve train components increases, the components would need to be subjected to greater accelerations.
So, in order to reduce the effect of inertia, the diameter of a valve head is made smaller and the valves are made lighter than the conventional valves. As small and light weight valves reduce the effects of inertia and also the valve-spring force needed to close the valve at a high engine speed is reduced. Such a design of the valves as described herein reduces the effect of inertia as the valve-spring force needed to close the valve at a high engine speed is reduced. Consequently, the performance, both at low speed and high speed, is enhanced.

Fig. 5 provides a perspective view of a third side of the cylinder head according to one embodiment of the present invention The third side is a front side of the cylinder head 106 when viewed in the direction of y, with respect to Fig. 4. As shown in the Fig.5, the third side defines a wall 502 of the cam chain chamber 208,
Fig. 6 illustrates a fourth side of the cylinder head according to an embodiment of the present invention. The fourth side is also the back side of the cylinder head 106, when viewed in the direction of y with respect to Fig.4. An opening 306 is provided that extends to the combustion chamber 204 and provides a housing for the spark plug 206.
Fig. 7 illustrates a fifth side of the cylinder head 106 according to an embodiment of the present invention. The fifth side is also the right side of cylinder head 106 when viewed in the direction of y, with respect to Fig. 4.
With respect to Fig. 7, the two intake ports 302a and 302b are divided into a charging port and a volumetric port respectively. Both the volumetric and the charging ports are disposed side by side in such a way that the volumetric port 302b is disposed above the charging port 302a. Also, the volumetric port 302b runs parallel to the charging port 302a separately up to the combustion chamber 204. The volumetric port 302b is designed to have a stronger curvature as compared with the charging port 302a, but shows a lower inclination towards the valve axis. Such an arrangement of the volumetric port 302b produces a charge stream directed approximately against the centre of the cylinder head 106, which helps in filling of the combusfion chamber with the air-fuel mixture.
The charging port 302a is strongly inclined towards the valve axis and is designed as a tangential or swirl port to incorporate only a low curvature. The tangential port is

directed tangentially to the cylinder bore surface. The charging port 302a produces a flow which hits the cylinder wall of the combustion chamber 204 tangentially. This leads to the formation of a strong swirling movement in the cylinder head 106. Also, the charging port 302a defines an edge at the point where it joins with the combustion chamber 204 to provide a swirl action. Three threaded holes 704a, 704b, and 704c are provided on the fifth side of the cylinder head 106 for clamping the intake pipe 104.
Fig. 8 illustrates a sixth side of a cylinder head according to an embodiment of the present invention. The sixth side is also the left side of cylinder head 106, when viewed in the y direction with respect to Fig. 4.
An opening 802 is provided for the two exhaust ports 304 on the sixth or the left side. The opening 802 extends to the combustion chamber 204 on the first or the bottom side. After the combustion of the air-fuel mixture, i.e., exhaust stroke, the exhaust gases blow off outside the combustion chamber 204 through the opening 802 into the exhaust manifold (not shown in the figure).
In another embodiment of the present invention, an exhaust gas return conduit opens into at least one of the two intake ports. Such an arrangement recirculates exhaust gases into the intake stream. As, the exhaust gases have already gone under combustion , they do not burn again when they are recirculated and hence dilute the incoming air-fuel mixture. The recirculation of the exhaust gases into the combustion chamber chemically slows and cools the combustion process by several hundred degrees, thus reducing NOx emissions. Also, as few of the gases go under partial combustion, so when they are recirculated they undergo combustion again, thus providing a better fuel economy. The

fuel economy is further improved by exhaust gas recirculation due to the reduction in throttling losses during intake of air stream.
In yet another embodiment of the present invention, an exhaust gas return conduit opens into the charging port 302a.
Fig. 9(a), 9(b) and 9(c) provide different perspective views, namely front, cross sectional, and bottom views of the intake pipe, according to an embodiment of the present invention.
In Fig 9(a) a first end 902 is connected to the carburetor 102 (according to Fig.l) such that the carburetor 102 is disposed in the zone of branching off of the two separate intake passages. Further, a second end 904 of the intake pipe 104 is formed using a metal such as aluminum. The second end 904 is extended to the first end 902 of the intake pipe 104 by molding an elastomeric material over the metal. Elastomers are used here as they show a unique property of bouncing back to their original shape even after being stretched many times of their original dimensions, without any permanent deformation. Such a construction of the intake pipe 104 reduces the transfer of vibrations from the cylinder head 106 to the carburetor 102.
In Fig 9(b) the intake pipel04 includes two intake passages 906a and 906b, collectively referred as 906, and a wall 908. The intake passages 906a and 906b supply the air-fuel mixture to the charging port 302a and the volumetric port 302b, respectively. The wall 908 separates the two intake passages 906a and 906b. Further, the wall 908 keeps the separation between the two intake passages 906a and 906b till each of the intake passages joins the charging port 302a and the volumetric port 302b. The intake passages 906a and 906b run substantially parallel to each other. Further, the carburetor

102 is disposed at a zone at the beginning of the separating wall 908 of the intake pipe 104.
In Fig 9(c), the second end 904 of the intake pipe 104 is clamped to the fifth or the right side of the cylinder head 106 via the threaded holes 704a, 704b, and 704c. The intake pipe 104 is clamped such that the two ports 910a and 910b align themselves with the intake ports 302a and 302b, respectively, on the cylinder head 106.
In operation, on acceleration, the carburetor 102 supplies the air-fuel mixture first through the charging port 302a and, only when the charging port 302a is substantially open, then through the volumetric port 302b. The volumetric port 302b is mechanically opened after a particular percentage of total pull of a throttle cable is reached. Therefore, under full throttle conditions, both the ports, 302a and 302b, are fully uncovered. Similarly, on deceleration, if the power requirement decreases beyond the particular percentage of the total pull of the throttle cable, the volumetric port 302b is closed. Due to this, an optimum amount of air-fuel mixture is received in the combustion chamber 204 for different speeds of the vehicle, thereby resulting in enhanced fuel efficiency.
Under low load conditions, a comparatively leaner air-fuel mixture enters the combustion chamber 204 through the charging port 302a. As the air-fuel mixture received from the charging port 302a is lean, the mixture is burnt in a comparatively shorter duration, leading to an improved torque output, less fuel consumption, and low emissions. The lean air-fuel mixture also ensures that the fuel consumption and Nitrogen oxides (NOx) emissions of the engine are reduced.
On the other hand, when the torque requirement is high, i.e., during high load conditions, a comparatively rich air-fuel mixture enters through the volumetric port 302b

in the region of the spark plug 206 while a generally lean air-fuel mixture enters through the charging port 302a near the walls of the combustion chamber 204. Thus, during the power stroke, even though a lean air-fuel mixture is maintained in the combustion chamber 204, torque output is high and, at the same time, fuel consumption and emission levels are low. Further, during the exhaust stroke, due to the provision of two exhaust ports and two exhaust valves, exhaust gases escape more easily.
In yet another embodiment of the present invention, an opening (not shown) is provided in the intake passage separating wall 908, which is closed by a valve which opens only when there is a substantial pressure difference between the volumetric port side and the charging port side.
In yet another embodiment of the present invention, the throttle valves (not shown) open successively in a register like manner, so that first the charging port 302a opens and the volumetric port 302b opens thereafter.
In yet another embodiment of the present invention, the carburetor 102 is provided with a full load power jet, which is arranged in the direction of the volumetric port 302b.
The aforementioned versions of the subject matter and equivalent thereof have many advantages, including those, which are described below.
The cylinder head assembly described herein yields higher engine output and lower exhaust emissions. Further, the cylinder head assembly achieves an enhanced fuel economy under various load requirements. Moreover, the construction of the intake pipe reduces the transfer of vibrations from the cylinder head to the carburetor. Also, the

present subject matter provides a cylinder head assembly with lower inertia mass of the valve train to obtain enhanced performance both at low and high engine speeds.
Although the subject matter has been described in considerable detail with reference to certain preferred embodiments thereof, other embodiments are possible. As such, the spirit and scope of the invention should not be limited to the description of the preferred embodiment contained therein. Various other embodiments of the invention will be apparent to a person skilled in the art or follow from routine experimentation.

I/We claim:
1. A multivalve cylinder head assembly (100) for an internal combustion engine,
said multivalve cylinder head assembly (100) comprising:
a carburetor (102) for supplying an air-fuel mixture;
an intake pipe (104) connecting said carburetor (102) with a plurality of
intake ports (302); and
a cylinder head (106) comprising said plurality of intake ports (302), a
plurality of exhaust ports (304) and an opening (306) for at least one spark
plug (206);
characterized in that,
said intake pipe (104) includes a plurality of intake passages (906), and said intake passages (906) open into said plurality of intake ports (302), wherein based on input throttle said air-fuel mixture enters into a combustion chamber (204) through one or more of said plurality of intake ports (302).
2. The muhivalve cylinder head assembly (100) as claimed in claim 1, wherein said plurality of intake ports (302) comprise at least one intake port is designed as a charging port (302a) and at least one intake port designed as a volumetric port (302b).
3. The multivalve cylinder head assembly (100) as claimed in claim 2, wherein said charging port (302a) is provided as a tangential port.
4. The muhivalve cylinder head assembly (100) as claimed in claim 1, wherein said carburetor (102) supplies said air-fuel mixture to said charging port (302a), when power requirement corresponds to a value lesser than a particular

percentage of the total pull of a throttle cable, and to both said charging port (302a) and said volumetric port (302b), when power requirement corresponds to a value greater than said particular percentage of the total pull of the throttle cable.
5. The multivalve cylinder head assembly (100) as claimed in claim 2, wherein said charging port (302a) receives a lean air-fuel mixture and said volumetric port (302b) receives a rich air-fuel mixture from said carburetor (102).
6. The multivalve cylinder head assembly (100) as claimed in claim I, wherein said plurality of exhaust ports (304) comprise a first exhaust port (304a) and a second exhaust port (304b), which are disposed opposite to said plurality of intake ports (302).
7. The multivalve cylinder head assembly (100) as claimed in claim 1, wherein said carburetor (102) is a slide valve carburetor (102) having a slide valve disposed therein.
8. The multivalve cylinder head assembly (100) as claimed in claim 1, wherein an exhaust gas return conduit opens into at least one of said intake ports (302).
9. The multivalve cylinder head assembly (100) as claimed in claim 2, wherein an exhaust gas return conduit opens into said charging port (302a).
10. The multivalve cylinder head assembly (100) as claimed in claim 1, wherein said opening (306) for the at least one spark plug (206) is substantially at the center of said combustion chamber (204).

11. The multivalve cylinder head assembly (100) as claimed in claim 2, wherein
said carburetor (102) is provided with a full load power jet arranged in direction
of said volumetric port (302b).
12. The multivalve cylinder head assembly (100) as claimed in claim 1, wherein
said intake pipe (104) comprises:
a first end attached to said carburetor (102) and a second end attached to said cylinder head (106),
wherein said second end is formed using a metal and is extended to said first end by molding an elastomeric material over the metal.