DESC:FIELD OF INVENTION
[0001] The present invention relates to an internal combustion engine and more particularly to a camshaft assembly for the internal combustion engine.
BACKGROUND OF INVENTION
[0002] Generally, an internal combustion engine acts as the power unit of a vehicle. After receiving of an air-fuel mixture, a combustion process is carried out in the internal combustion engine through which power is generated. The internal combustion engine receives a substantial amount of air-fuel mixture which is burnt to generate power for transmission of the vehicle. The internal combustion engine mostly comprises of a cylinder block, cylinder head, piston, connecting rod, crankshaft, crankcase and many other operational parts as such associated to it.
[0003] Typically, the internal combustion engine comprises of an exhaust and inlet port. The air-fuel mixture enters the internal combustion engine through the inlet port, whereas after proper combustion the exhaust produced leaves the internal combustion engine through the exhaust port. An exhaust and inlet valve is provided which controls the opening and closing of the exhaust and inlet port. In addition to it, a camshaft assembly is provided in the cylinder head of the internal combustion engine which controls the opening and closing of the exhaust and inlet valve. In addition to it, a sparkplug is also provided in the cylinder head of the internal combustion engine which generates the required spark for combustion of the air-fuel mixture.
[0004] The sparkplug is disposed at an inclined angle in the cylinder head of the internal combustion engine. However, the degree of freedom provided to the sparkplug is very less. Spark plug orientation is one of the critical aspects for the operation of the internal combustion engine. In furtherance to it, orienting sparkplug in a conventional internal combustion engine is not possible beyond a point due to possibility of low wall thickness between spark plug and camshaft assembly.
[0005] Hence, it is an objective of the present subject matter to provide an improved camshaft assembly which allows a better orientation and degree of freedom for the sparkplug. Furthermore, it also desired to have a higher wall thickness for the cylinder head which helps in improving the orientation angle of the sparkplug.
BRIEF DESCRIPTION OF DRAWINGS
[0006] Figure 1 illustrates a side view of an exemplary two-wheeled vehicle in accordance with an embodiment of the present subject matter.
[0007] Figure 2 illustrates a cross-sectional view of an internal combustion engine in accordance with an embodiment of the present subject matter.
[0008] Figure 3 illustrates a cross-sectional view of a cylinder head of the internal combustion engine in accordance with an embodiment of the present subject matter.
[0009] Figure 4 illustrates a cross sectional view of a ball bearing supported camshaft assembly disposed inside the cylinder head for of a known system
[00010] Figure 5 illustrates a cross-sectional view of the cylinder head of the internal combustion engine in accordance with an embodiment of the present subject matter.
[00011] Figure 6 illustrates a cross-sectional view of a camshaft assembly disposed within the cylinder head in accordance with an embodiment of the present subject matter.
DETAILED DESCRIPTION
[00012] Typically, an internal combustion engine is coupled to the drive wheel, which is generally the rear wheel. Mostly, the internal combustion engine comprises of a cylinder bore where the combustion occurs to provide the needed power for the forward motion of the vehicle. The internal combustion (IC) engine, among other components, comprises of a cylinder on top of which a cylinder head is mounted. The cylinder head is mounted to accommodate and receive the to-and-fro motion of the piston reciprocating from the bottom in an upward direction. On combustion of an air-fuel mixture, the piston transfers the energy generated during combustion to a crankshaft through a connecting rod thereby driving the crankshaft. In this way, the reciprocatory motion of the piston is converted to rotary motion of the crankshaft which in turn powers the vehicle.
[00013] The cylinder head also comprises of an inlet valve and exhaust valve which allows the air-fuel mixture to enter and exhaust to leave the internal combustion engine. A camshaft assembly is also provided in the cylinder head of the internal combustion which helps in opening and closing of the inlet valve and exhaust valve. Furthermore, a sparkplug is disposed within the cylinder head of the internal combustion engine which generates the required spark for combustion of the air-fuel mixture. The spark plug is generally oriented to aim in between the two valves namely inlet valve and an exhaust valve. A two valve system of the internal combustion engine has a larger space available on both the sides of the camshaft assembly along which a sparkplug can be disposed and oriented according to the requirements. A four valve arrangement for the internal combustion engine provides a larger opening for charge entry & exhaust exit during their respective strokes. Since, a plurality of smaller holes are more efficient than a single bigger hole, a four valve system is comparatively more efficient relative to a two valve system because the venturi effect fills the cylinder faster with the small valves. Also, the smaller valves weigh less and can withstand higher rpm. Hence, for the same rpm with greater number of smaller valves, the shape of the combustion chamber can be more efficient.
[00014] Combustion development is an important phase of the internal combustion engine. Combustion chamber design, sparkplug location, air-fuel mixing and charge motion play significant role in engine performance, fuel economy and in reducing knocking tendency etc. To achieve this, sparkplug orientation for three valve and four valve air cooled/liquid cooled internal combustion engines is generally targeted near center of combustion chamber to reduce burn duration.
[00015] The internal combustion engine comprises of a plurality of valves disposed on each side of the camshaft assembly. The camshaft assembly for an engine is normally supported on the cylinder head using two ball bearings at the ends of the shaft, which help the camshaft to rotate on a camshaft axis. A ball bearing is a type of rolling-element bearing that uses balls to maintain the separation between the bearing races. The purpose of a ball bearing is to reduce rotational friction and support radial and axial loads by using at least two races to contain the balls and transmit the loads through the balls. In most applications, one race is stationary and the other is attached to the rotating assembly (e.g., a hub or shaft). Due to presence of the ball bearings at ends of the camshaft, the cylinder head will have a limited space in surrounding space of the camshaft for disposing and orienting a spark plug. Furthermore, the degree of freedom with which the spark plug can be oriented is limited as the available space on both the sides of the camshaft is reduced due to the presence of ball bearings at both the ends of the camshaft.
[00016] Sparkplug orientation and location of sparkplug tip is critical for operation of the internal combustion engine. Ideally sparkplug needs to be located vertically and in center of combustion chamber to achieve higher efficiency and reduced emissions. In air/oil cooled engines sparkplug is assembled from sides. Orienting the spark plug in conventional engines is not possible beyond a point due to possibility of low wall thickness between spark plug and camshaft bearing. In cases where no bearings are used, friction may be higher and may lead to functional loss and lowered performance. For a sparkplug, with higher inclination angle from vertical, it is difficult to achieve uniform wall thickness between spark plug, intake and exhaust valve seats which may lead to cylinder head failures. Hence, it is desired to reduce the angle of inclination of the sparkplug with the vertical as much as possible.
[00017] Therefore, an objective of the present subject matter is to provide a camshaft assembly which provides ample space for the spark plug orientation and increased degree of freedom. In addition to it, the present subject enables a reduced angle of inclination for the spark plug and improves the uniformity of cylinder wall thickness between the sparkplug and camshaft assembly.
[00018] In an embodiment, a camshaft assembly is provided in a cylinder head of an internal combustion engine comprising of four valves which provides an advantageous space formation inside cylinder head to dispose and orient a spark plug with greater degree of freedom. In order to solve problem of disposing and orienting a spark plug, a new camshaft bearing arrangement is proposed without compromising with the structural, dynamic and performance issues. Furthermore, as per the present subject matter, the camshaft assembly comprises of a camshaft inner and a camshaft outer. Camshaft inner is non-rotating portion of the camshaft assembly located in cylinder head, which at a first end is bolted using a bolt to the cylinder head and rests inside a slot in cylinder head at a second end. In furtherance to it, camshaft outer is the rotating element which is disposed over the camshaft inner.
[00019] In an embodiment, the camshaft assembly according to the invention includes a plurality of cam and bearing elements. The cam is either attached or integrally formed on the camshaft outer at pre-determined locations. The camshaft inner and the cam shaft outer are separated through a needle roller bearing at plurality of locations along the camshaft axis. The camshaft inner is rigidly fixed to the cylinder head.
[00020] In an embodiment, the needle roller bearing comprises of an inner race and an outer race. In accordance to an embodiment of the present subject matter, the camshaft inner is rigidly attached to an inner race of a needle roller bearing, whereas the outer race of the needle roller bearing is coupled to the camshaft outer. Such a needle roller bearing mechanism allows the camshaft outer to rotate on the camshaft axis on the needle roller bearing. The use of a needle roller bearing in between a camshaft inner and camshaft outer avoids the usage of ball bearings at the two ends of the camshaft assembly. In an embodiment, the camshaft outer consists of an intake lobe and an exhaust lobe, a sprocket (either integral or assembled) which rotates along camshaft outer over the camshaft inner with one or more needle roller bearings. Due to presence of needle roller bearings along the lateral direction of the camshaft assembly, the ball bearings at the ends of the camshaft assembly can be avoided. Hence, due to absence of the ball bearings at the ends of the camshaft assembly, its effective required length is reduced and a space is created within the cylinder head. The sparkplug can be disposed in such a fashion so that extra space can be created, wherein said sparkplug can be oriented with an increased degree of freedom as compared to when ball bearings were present at the ends of the camshaft assembly.
[00021] Hence, the present invention does not require any ball bearings for the camshaft assembly. The invention described herein describes a camshaft assembly comprising of a camshaft inner and camshaft outer. The camshaft inner is a fixed element, whereas the camshaft outer is a rotating member disposed over camshaft inner through needle roller bearing. The needle roller bearing acts as the connecting link between camshaft inner and camshaft outer. Hence, the present invention decreases the length of the camshaft assembly by eliminating the ball bearing. Such a reduction creates an extra space which helps in improving the degree of freedom of the sparkplug and increases the cylinder wall thickness.
[00022] The aforesaid and other advantages of the present subject matter would be described in greater detail in conjunction with the figures in the following description.
[00023] Arrows provided in the top right corner of each figure depicts direction with respect to the vehicle, wherein an arrow F denotes front direction, an arrow R indicated R direction, an arrow Up denotes upward direction, an arrow Dw denoted downward direction, an arrow Rh denotes right side, an arrow Lh denoted left side, as and where applicable.
[00024] Fig. 1 illustrates a side view of an exemplary two-wheeled vehicle (10) in accordance with an embodiment of the present subject matter. The vehicle comprises of a main frame assembly (1) made of carbon fiber and resin material and is conventionally an underbone chassis frame which provides a generally open central area to permit “step-through” mounting by a rider. Typically, the frame assembly (1) comprises of a head tube (2), a main tube (3), and a pair of side tube LH (4) and side tube RH (5) (only one shown). The head tube (2) is disposed towards the front portion, wherein the main tube (3) extends downwardly and rearwardly from the head tube (2) forming a flat horizontal step-through portion (3S). The other end of the main tube (3) is connected with the pair of side-tubes (4, 5) through a bracket (not shown).
[00025] The head tube (2) is configured to rotatably support a steering tube (not shown) and further connected to the front suspension system (6) at the lower end. A handlebar support member (not shown) is connected to an upper end of the steering tube (not shown) and supports a handlebar assembly (9). The upper portion of a front wheel (7) is covered by a front fender (8). The pair of side-tubes (4, 5) extend from the other end of the main tube (3) being disposed parallel on either side of the vehicle (10) width direction. Each of the said side tube (4, 5) extends from the main tube (3) in an upward inclined fashion and gradually after a certain length extends rearward in a substantially horizontal and parallel fashion being placed in the vehicle widthwise direction. A plurality of cross pipes (not shown) is secured in between the pair of side-tubes (4, 5) at selected intervals to support vehicular attachments including a utility box (12), a seat assembly (11) and a fuel tank assembly (not shown). The vehicle furthermore, comprises of a side panel LH (23) and side panel RH (not shown) which covers the side tubes (4, 5) and covers the vehicle (10) structure from the sides.
[00026] Generally, the utility box (12) is supported between the side tube LH (4) and side tube RH (5) so as to be disposed below the seat (11). A fuel tank assembly (not shown) may be disposed on between the rear portions of the pair of the side-tubes (4, 5). The vehicle (10) further comprises of a rear wheel (13) covered by a rear fender (14) with a tail light (15) disposed above it and a support bar (16) placed above the tail light (15) at the end of the seat assembly (11). The rear wheel (13) is supported towards the rear side of the main frame (1) by an internal combustion (IC) engine (19) which is horizontally coupled swingably to the rear of the frame assembly (1) of the two-wheeled vehicle (10) through a rear suspension system (17). The IC engine (19) transfers the drive directly to the rear wheel (13) as it is coupled directly to it through a continuously variable transmission (CVT) system (18). The vehicle further comprises of an air cleaner assembly to provide filtered air to the IC engine (shown in Fig. 4) for combustion.
[00027] Figure 2 illustrates a cross sectional view of the internal combustion engine (19) in accordance with an embodiment of the present subject matter. In an embodiment, the internal combustion engine (19) comprises of a cylinder block (20) to accommodate a piston (21) with its reciprocatory motion, such that the motion of the piston (21) is converted into rotational motion of crankshaft (22). In an embodiment, a cylinder head (23) is disposed above the cylinder block (20) to allow the combustion to happen. As explained above, the cylinder block (20) also comprises of exhaust port and inlet port through which the exhaust leaves and the air-fuel mixture enters into the internal combustion engine (19). The cylinder head (23) is provided with an exhaust valve (24) and inlet valve (25) which controls the opening and closing of the exhaust port and inlet port. In furtherance to it, the cylinder head (23) also comprises of a camshaft assembly (26), wherein the crankshaft (22) and camshaft assembly (26) extend parallel to each other, and the axis of rotation for the camshaft assembly (26) and that of the crankshaft (22) is similar to each other. The camshaft assembly (26) comprises of an exhaust lobe and inlet lobe disposed on it, which help in the opening and closing of the exhaust valve (24) and the inlet valve (25). A rocker arm and roller arrangement is provided for the opening and closing of the exhaust valve (24) and inlet valve (25), wherein the rocker and roller arm is in connection with the exhaust lobe and the inlet lobe, such that the rotation of the lobes helps in rotation of the roller and movement of the rocker arm resulting in opening and closing of the valves (24, 25).
[00028] Figure 3 illustrates a cross sectional view of the cylinder head (23) of the internal combustion engine (19) in accordance with an embodiment of the present subject matter. The camshaft (26) can be seen to be comprising of the exhaust lobe (31) and the inlet lobe (32). An exhaust side roller (33) is in connection with the exhaust lobe (31) and an inlet side roller (34) is in connection with the inlet lobe (32). The exhaust lobe (31) and inlet lobe (32) rotate and move along the axis of the rotation of the camshaft (26). This in turn results into the rotation of the exhaust side roller (33) and inlet side roller (34), which in turn is connected to an exhaust side arm (35) and an inlet side arm (36). The exhaust side arm (35) and inlet side arm (36) are connected to the exhaust valve (24) and the inlet valve (25), such that with the rotation of the exhaust side roller (33) and inlet side roller (34) the exhaust side arm (35) and inlet side arm (36) also move resulting in movement of the exhaust valve (24) and inlet valve (25). Thus, the movement of the exhaust valve (24) and inlet valve (25) result in opening and closing of the exhaust port (37) and inlet port (38) depending upon the type of stroke the internal combustion engine is going through.
[00029] Figure 4 illustrates a cross sectional view of a ball bearing supported camshaft assembly (40) disposed inside the cylinder head for of a known system. The camshaft assembly (40) comprises of a camshaft inner (42) which is rigidly attached to the inner race of the bearing (41, 46). The outer race of the bearings (41, 46) is fixed with an interference fit or rigidly fixed to the cylinder head portion thereby allowing the camshaft assembly along with lobes (43, 44) to rotate on a camshaft axis. In a typical camshaft assembly (40) and sparkplug (45) arrangement in the cylinder head, the angle of inclination of the sparkplug (45) is defined by O which is the angle made by the axis SS’ (passing through the sparkplug) with the horizontal. In such a prior art, the angle of inclination O of the spark plug (45) cannot be increased beyond a certain angle due to a possible fouling with the cylinder head portion accommodating ball bearing (46). Hence, the degree of freedom for orientation and disposing of sparkplug (45) is limited and many a times it becomes difficult for the angle of inclination to meet requirements of an engine. Also, since the angle of inclination O of the spark plug (45) is less in such a cylinder head, the sparkplug body is closer to the cylinder head wall due to which it is further difficult to maintain a desired cylinder wall thickness.
[00030] Figure 5 shows a cross sectional view of cylinder head (23) according to one embodiment of the present invention. As per the present subject matter, the camshaft assembly (26) comprises of a camshaft inner (51) and a camshaft outer (54) having a same cylindrical profile, wherein said camshaft outer (54) is disposed over camshaft inner (51). The camshaft outer (54) is attached over camshaft inner (51) through a plurality of needle roller bearings (52, 53), wherein said camshaft inner (51) is fixed and camshaft outer (54) rotates over said camshaft inner (51). The plurality of needle roller bearing (52, 53) comprises of a first needle roller bearing (52) and a second needle roller bearing (53). The plurality of needle roller bearing (52, 53) comprises of an inner race (shown in n Fig. 6) which is its bottom profile attached to camshaft inner (51), and an outer race (shown in n Fig. 6) which is its top profile attached to camshaft outer (54). In an embodiment, the inlet lobe (32) operates the inlet valve (25) and the exhaust lobe (31) operates the exhaust valve (24). The exhaust lobe (31) and inlet lobe (32) are joined to the camshaft outer (54). The camshaft inner (51) is rigidly attached to the cylinder head (23) with its first end bolted to the cylinder head (23) using bolt (55) and the second end is rested inside a slot (57) made within the cylinder head (23). The camshaft inner (51) is further attached to inner race of first needle roller bearing (52) and second needle roller bearing (53) and the camshaft outer (54) is rigidly attached to the outer race of the first needle roller bearing (52) and second needle roller bearing (53). Thus, a rotation of the outer race of the first needle roller bearing (52) and second needle roller bearing (53) results into the rotation of exhaust lobe (31) and inlet lobe (32) to operate the intake valve (25) and exhaust valve (24). In an embodiment, a sparkplug (58) with a vertical axis (SS’) passing through its center is provided within the cylinder head (23) of the internal combustion engine (19). As illustrated in Figure 5, due to elimination of ball bearing from the two ends of the camshaft assembly (26) its effective length is significantly reduced and angle O’ which determines the degree of freedom for orientation of the sparkplug (58) is increased significantly. The angle for achieving best layout & performance can now be substantially more than 60°. Hence, the camshaft assembly (26) as described herein in the present invention helps in disposing the sparkplug (58) with increased degree of freedom for orientation with respect to the cylinder axis CC’ passing vertically through its center. Another advantage of such an arrangement is that in such an arrangement of sparkplug (58), a greater cylinder wall thickness can be achieved.
[00031] Figure 6 illustrates a cross-sectional view of the camshaft assembly (26) in accordance with an embodiment of the present subject matter. In an embodiment, the camshaft outer (54) is capable of rotating on the plurality of needle roller bearings (52, 53) placed in-between the camshaft outer (54) and camshaft inner (51). The camshaft inner (51) is rigidly attached to the cylinder head (23) using bolt (55). The other end of the camshaft inner (51) is rigidly joined to the cylinder head (23) by creating slot (57) within it. The plurality of needle roller bearings (52, 53) comprises of inner race (61) which is its bottom profile and is attached to camshaft inner (51), and outer race (62) which is its top profile attached to camshaft outer (54). Hence, the current assembly eliminates the need of extra ball bearings which was required for the assembly of camshaft in the cylinder head.
[00032] Thus, the present subject matter provides a camshaft assembly (26) disposed in a cylinder head (23) of an internal combustion engine (19). As per the present subject matter, the camshaft assembly (26) comprises of a camshaft outer (54) and a camshaft inner (51). The camshaft inner (51) is rigidly fixed in the cylinder head (23), whereas the camshaft outer (54) is a rotational member disposed over said camshaft inner (51). The camshaft outer (54) and camshaft inner (51) are attached to each through a plurality of needle ball bearings (52, 53). As per the present subject matter, the camshaft outer (54) rotates over said camshaft inner (51) through the provided plurality of ball bearings (52, 53). Thus, the present subject matter eliminates the need of extra ball bearings which was required previously. Hence, the present subject matter reduces the length of the camshaft assembly (26) and allows a greater degree of freedom for sparkplug (58) disposed in the cylinder head (23).
[00033] It is to be understood that the aspects of the embodiments are not necessarily limited to the features described herein. Many modifications and variations of the present subject matter are possible in the light of above disclosure. Therefore, within the scope of claims of the present subject matter, the present disclosure may be practiced other than as specifically described.
,CLAIMS:We Claim:
1. An internal combustion engine (19) for a vehicle (10), said internal combustion engine (19) comprising:
a cylinder head (23) disposed over said internal combustion engine (19) enabling a space for combustion of air-fuel mixture and comprising a horizontal axis CC’ passing substantially through center;
a sparkplug (58) disposed in said cylinder head (23) to provide a spark for combustion of air-fuel mixture; and
a camshaft assembly (26) disposed within said cylinder head (23), wherein said camshaft assembly (26) comprises a camshaft inner (51) rigidly fixed in said cylinder head (23) and a rotatable camshaft outer (54) disposed over said camshaft inner (51),
2. The internal combustion engine (19) as claimed in claim 1, wherein said camshaft inner (51) and said camshaft outer (54) are attached through a plurality of needle roller bearings (52, 53) enabling angle formed by said sparkplug (58) with respect to axis CC’ to be more than 60 degrees.
3. The internal combustion engine (19) as claimed in claim 1, wherein said camshaft inner (51) is rigidly fixed in said cylinder head (23) using a bolt (55) and a slot (57) formed in said cylinder head (23).
4. The internal combustion engine (19) as claimed in claim 1, wherein said camshaft outer (54) is enabled to rotate over said camshaft inner (51).
5. The internal combustion engine (19) as claimed in claim 1, wherein said camshaft outer (54) comprises of an exhaust lobe (31) and an inlet lobe (32) formed along its outer periphery.
6. The internal combustion engine (19) as claimed in claim 5, wherein said exhaust lobe (31) and said inlet lobe (32) rotate along said camshaft outer (54).
7. The internal combustion engine (19) as claimed in claim 1, wherein said plurality of needle roller bearings (52, 53) comprises of a first needle roller bearing (52) and a second needle roller bearing (53).
8. The internal combustion engine (19) as claimed in claim 1, wherein said camshaft outer (54) is attached to said camshaft inner (51) through said first needle roller bearing (52) and said second needle roller bearing (53).
9. The internal combustion engine (19) as claimed in claim 2, wherein said inner race (61) of said plurality of needle roller bearings (52, 53) being a bottom profile is attached to said camshaft inner (51).
10. The internal combustion engine (19) as claimed in claim 2, wherein said outer race (62) of said plurality of needle roller bearings (52, 53) being a top profile is attached to said camshaft outer (54).