Claims:We Claim:
1. A camshaft assembly of a four stroke internal combustion engine (101) comprising:
at least one intake cam lobe (201), said at least one intake cam lobe (201) comprises of first centrifugal cam actuation system (105), said first centrifugal cam actuation system (105) is configured to reduce the amount of charge inducted by an intake cam lobe (201) during starting of the IC engine (101); and
at least one exhaust cam lobe (202), said at least one exhaust cam lobe (202) comprises a second cam actuation centrifugal system (106), said second centrifugal cam actuation system (106) is configured to induct the exhaust gases into said engine (101).

2. The camshaft assembly of a four stroke internal combustion engine (101) as claimed in claim 1, wherein said first centrifugal cam actuation system (105) comprises of
at least one decompression cam (105d); and
at least one decompression arm (105a) for activation and deactivation of said decompression cam (105d), wherein said decompression cam (105d) is activated for a predetermined duration (D).

3. The camshaft assembly of a four stroke internal combustion engine (101) as claimed in claim 2, wherein said predetermined duration (D) ranges from 20 degree to 100 degree of the crank angle during compression stroke.

4. The camshaft assembly of a four stroke internal combustion engine (101) as claimed in claim 1, wherein said second centrifugal cam actuation system (106) comprising of
at least one Exhaust Gas Recirculation (EGR) cam (106c), and
at least one Exhaust Gas Recirculation (EGR) arm (106a) for activation and deactivation of said EGR cam (106c), wherein said EGR cam (106c) is activated for a predetermined duration (D’).

5. The camshaft assembly of a four stroke internal combustion engine (101) as claimed in claim 4, wherein said predetermined duration (D’) ranges from 20 degree to 100 degree of the crank angle during suction stroke.

6. A method of operating a camshaft assembly of a single cylinder four-stroke internal combustion engine (101), said method comprising:
at step (S101), activating a decompression cam during starting of the engine for a predetermined duration (D’) based on camshaft centrifugal force;
at step (S102), reducing the charge inducted by an intake cam lobe of the camshaft assembly, owing to said activation of the decompression cam;
at step (S103), deactivating said decompression cam above predetermined engine operating state parameter values; and
at step (S104), recovering the reduced charge inducted by the intake cam lobe of the camshaft assembly, by said deactivation of the decompression cam.

7. The method of operating a camshaft assembly for a single cylinder four stroke internal combustion engine (101) as claimed in claim 6, wherein said engine state operating parameters includes engine speed above 1500 revolutions per minute.

8. A method of operating a camshaft assembly of a single cylinder four-stroke internal combustion engine (101), said method comprising:
at step (S105), activating an Exhaust Gas Recirculation (EGR) cam based on camshaft centrifugal force for a predetermined duration (D’) and above predetermined engine state operating parameter values during running of the engine; and
at step (S106), inducting exhaust gases into the charge inducted by an intake cam lobe of the camshaft assembly during suction stroke of said engine.

9. The method of operating a camshaft assembly of a single cylinder four stroke internal combustion engine (101) as claimed in claim 8, wherein said predetermined engine state operating parameter values includes engine speed above 2000 revolutions per minute.

10. A single cylinder four-stroke engine (101) mounted in a two wheeled saddle type vehicle, said engine comprising of single overhead camshaft assembly as claimed in any of the preceding claims. , Description:TECHNICAL FIELD
[0001] The present subject matter relates to an internal combustion (IC) engine. More particularly, to a four stroke Single Overhead Camshaft type (SOHC) IC engine.

BACKGROUND
[0002] Technological advancements are being made to make efficient and eco-friendly internal combustion (IC) engines. To this end, much attention has also been paid to development of valve trains to precisely control the combustion inside a combustion chamber of the IC engine.
[0003] The above information disclosed in this background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.

BRIEF DESCRIPTION OF THE DRAWINGS
[0004] The present invention is described with reference to an exemplary embodiment of a single overhead camshaft type (SOHC) single cylinder IC engine with the accompanying figures. The same numbers are used throughout the drawings to reference like features and components. Further, the inventive features of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:
[0005] Figure 1(a) illustrates a top view of a cylinder head (102) along with internal parts of an IC engine (101) and a localized enlarged view, as per embodiment, in accordance with one example of the present subject matter.
[0006] Figure 1(b) illustrates a top view of a cylinder head (102) of an engine (101) as per embodiment, in accordance with one example of the present subject matter.
[0007] Figure 2(a) illustrates a perspective view of a single overhead type camshaft (SOHC) assembly of the engine (101), as per embodiment, in accordance with one example of the present subject matter.
[0008] Figure 2(b) illustrates a side view of the single overhead camshaft (SOHC) assembly of the engine (101) as per embodiment, in accordance with one example of the present subject matter.
[0009] Figure 3(a) illustrates a graph that shows relationship between lift of an intake and exhaust valves versus crank angle while starting of the four stroke (SOHC) type engine (101) as per embodiment, in accordance with one example of the present subject matter.
[00010] Figure 3(b) illustrates a graph that shows relationship between lift of an intake and exhaust valves versus crank angle after starting of the four stroke (SOHC) type engine (101) as per embodiment, in accordance with one example of the present subject matter.
[00011] Figure 3(c) illustrates a flow chart depicting method of activation-deactivation of first and second centrifugal cam actuation system as per embodiment, in accordance with one example of the present subject matter.

DETAILED DESCRIPTION
[00012] Various features and embodiments of the present subject matter here will be discernible from the following further description thereof, set out hereunder.
[00013] Typically, an internal combustion (IC) engine comprises of a crankcase, a cylinder block coupled to the crankcase. A cylinder head is coupled to an upper part of the cylinder block and a head cover is coupled to an upper part of the cylinder head. A piston is slidably fitted in the cylinder block and is connected via a connecting rod with a crankshaft. The crankshaft is rotatably supported by the crankcase.
[00014] The induction and exhaust processes in above described IC engine are controlled by a mechanical system known as a valve train responsible for operation of the valves. Typically such valve train has at least two valves, an intake valve and an exhaust valve generally inclined relative to the cylinder axis. An intake port and an exhaust port formed in the cylinder head communicate with a combustion chamber formed by being surrounded by a cylinder bore, the cylinder head and the piston. The intake valve is provided at the combustion chamber side opening of the intake port and the exhaust valve is provided at the combustion chamber side opening of the exhaust port. A camshaft is rotatably supported by the cylinder head so as to open/close the intake valve and the exhaust valve. The rotational power is transmitted from the crankshaft to the camshaft by the valve train. The intake and exhaust valves are operated via rocker arms connected to the camshaft.
[00015] Conventionally during cranking, the piston in the cylinder moves towards top end of the combustion chamber and has to overcome the gaseous pressure in the cylinder as the intake and exhaust valves are closed. Therefore, manual cranking through a starter lever or kick lever requires more effort by a user and is often burdensome. More specifically, the compression pressure is higher during starting of the IC engine which leads to higher human effort to start the IC engine. One of the commonly known solutions to address the above problem with respect to startability is decompression. Typically, known auto decompression techniques momentarily release the compression pressure during cranking by letting some charge to leave the combustion chamber by opening exhaust valve, which relive the compression for starting an engine. The opening of exhaust valve is done by decompression system which is fitted in an exhaust lobe. Thus, the charge that leaves the cylinder during the auto decompression process is left unburnt, which add to overall starting emissions. This is because, the decompression occurs before a compression stroke, which makes the charge leaving the exhaust valve, post decompression to remain unburnt.
[00016] Further, when the IC engine starting temperature is lower, the unburnt charge cannot get converted to less harmful gases in emission control devices like catalytic converter. Additionally, the problem of emissions is compounded when the IC engine starting temperature is low and the auto decompression occurs prior to the compression stroke.
[00017] Therefore, there is a need to provide an IC engine to overcome the above-stated problems, which avoid the unburnt gases from leaving the exhaust leading to increase in emissions and other problems of known art.
[00018] To this end, it is an object of the present invention is to provide a compact, cost effective and reliable engine which ensures ease of startability as well as reduces the emissions by eliminating the emission of unburnt gases.
[00019] According to the present subject matter to attain the above-mentioned objectives, a first characteristic of the present invention a camshaft assembly of a four stroke internal combustion engine comprises of : at least one intake cam lobe, said at least one intake cam lobe comprises of first centrifugal system, said first centrifugal cam actuation system is configured to reduce the amount of charge inducted by an intake cam lobe during starting of the IC engine; and at least one exhaust cam lobe, said at least one exhaust cam lobe comprises a second centrifugal system, said second centrifugal cam actuation system is configured to induct the exhaust gases into said engine.
[00020] In addition to the first characteristic, a second characteristic of the present invention comprises of a camshaft assembly of a four stroke internal combustion engine , wherein said first centrifugal cam actuation system comprises of at least one decompression cam; and at least one decompression arm for activation and deactivation of said decompression cam, wherein said decompression cam is activated for a predetermined duration at a predetermined point of time post completing the intake of the charge from the intake port.
[00021] In addition to the first characteristic and a second characteristic, a third characteristic of the present invention comprises of camshaft assembly of a four stroke internal combustion engine, wherein said predetermined duration ranges from 20 degree to 100 degree of the crank angle during compression stroke.
[00022] In addition to the first characteristic, a fourth characteristic of the present invention comprises of the camshaft assembly of a four stroke internal combustion engine, wherein said second centrifugal cam actuation system comprising of at least one Exhaust Gas Recirculation (EGR) cam, and at least one Exhaust Gas Recirculation (EGR) arm for activation and deactivation of said EGR cam, wherein said EGR cam is activated for a predetermined duration.
[00023] In addition to the first characteristic and a fourth characteristic, a fifth characteristic of the present invention comprises of the camshaft assembly of a four stroke internal combustion engine, wherein said EGR cam predetermined duration ranges from 20 degree to 100 degree of the crank angle during suction stroke.
[00024] A sixth characteristic of the present invention is a method of operating a camshaft assembly of a single cylinder four-stroke internal combustion engine, said method comprising: activating a decompression cam during starting of the engine for a predetermined duration based on camshaft centrifugal force; reducing the charge inducted by an intake cam lobe of the camshaft assembly, owing to said activation of the decompression cam; deactivating said decompression cam above predetermined one or more engine operating state parameter value; and recovering the reduced charge inducted by the intake cam lobe of the camshaft assembly, by said deactivation of the decompression cam.
[00025] In addition to the sixth characteristic, a seventh characteristic of the present invention is the method of operating a camshaft assembly for a single cylinder four stroke internal combustion engine, wherein one or more said predetermined engine state operating parameter includes engine speed above 1500 revolutions per minute (r.p.m).
[00026] A eighth characteristic of the present invention is a method of operating a camshaft assembly of a single cylinder four-stroke internal combustion engine, said method comprising: activating the Exhaust Gas Recirculation (EGR) cam based on centrifugal force for a predetermined duration and above predetermined one or more engine state operating parameter value during running of the engine; and inducting exhaust gases into the charge inducted by an intake cam lobe of the camshaft assembly during suction stroke of said engine.
[00027] In addition to the eighth characteristic, a ninth characteristic of the present invention is the method of operating a camshaft assembly of a single cylinder four stroke internal combustion engine, wherein said predetermined engine state operating parameter values incudes engine speed above 2000 rev. per minute.
[00028] In addition to the first characteristic to ninth characteristic of the present invention is a single cylinder four-stroke engine mounted in a two wheeled saddle type vehicle, said engine comprising of single overhead camshaft assembly.
[00029] The present subject matter is further described with reference to accompanying figures. It should be noted that the description and figures merely illustrate principles of the present subject matter. Various arrangements may be devised that, although not explicitly described or shown herein, encompass the principles of the present subject matter. Moreover, all statements herein reciting principles, aspects, and examples of the present subject matter, as well as specific examples thereof, are intended to encompass equivalents thereof.
[00030] The foregoing disclosure is not intended to limit the present disclosure to the precise forms or particular fields of use disclosed. As such, it is contemplated that various alternate embodiments and/or modifications to the present disclosure, whether explicitly described or implied herein, are possible in light of the disclosure. Having thus described embodiments of the present disclosure, a person of ordinary skill in the art will recognize that changes may be made in form and detail without departing from the scope of the present disclosure. Thus, the present disclosure is limited only by the claims.
[00031] In the foregoing specification, the disclosure has been described with reference to specific embodiments. However, as one skilled in the art will appreciate, various embodiments disclosed herein can be modified or otherwise implemented in various other ways without departing from the spirit and scope of the disclosure. Accordingly, this description is to be considered as illustrative and is for the purpose of teaching those skilled in the art the manner of making and using various embodiments of the disclosure. It is to be understood that the forms of disclosure herein shown and described are to be taken as representative embodiments. Equivalent elements, materials, processes or steps may be substituted for those representatively illustrated and described herein. Moreover, certain features of the disclosure may be utilized independently of the use of other features, all as would be apparent to one skilled in the art after having the benefit of this description of the disclosure. Expressions such as “including”, “comprising”, “incorporating”, “consisting of”, “have”, “is” used to describe and claim the present disclosure are intended to be construed in a non-exclusive manner, namely allowing for items, components or elements not explicitly described also to be present. Reference to the singular is also to be construed to relate to the plural.
[00032] Further, various embodiments disclosed herein are to be taken in the illustrative and explanatory sense, and should in no way be construed as limiting of the present disclosure. All joinder references (e.g., attached, affixed, coupled, connected, etc.) are only used to aid the reader's understanding of the present disclosure, and may not create limitations, particularly as to the position, orientation, or use of the systems and/or methods disclosed herein. Therefore, joinder references, if any, are to be construed broadly. Moreover, such joinder references do not necessarily infer that two elements are directly connected to each other.
[00033] Additionally, all numerical terms, such as, but not limited to, “first”, “second”, “third”, “primary”, “secondary”, “main” or any other ordinary and/or numerical terms, should also be taken only as identifiers, to assist the reader's understanding of the various elements, embodiments, variations and/or modifications of the present disclosure, and may not create any limitations, particularly as to the order, or preference, of any element, embodiment, variation and/or modification relative to, or over, another element, embodiment, variation and/or modification.
[00034] It will also be appreciated that one or more of the elements depicted in the drawings/figures can also be implemented in a more separated or integrated manner, or even removed or rendered as inoperable in certain cases, as is useful in accordance with a particular application. Additionally, any signal hatches in the drawings/figures should be considered only as exemplary, and not limiting, unless otherwise specifically specified.
[00035] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.
[00036] Figure 1(a) illustrates a top view of a cylinder head (102) along with internal parts of an IC engine (101) and a localized enlarged view and figure 1(b) illustrates a top view of a camshaft assembly as per embodiment, in accordance with one example of the present subject matter. For sake of brevity, both figure 1(a) and 1(b) will be discussed together. The IC engine (101) is four stroke IC engine comprising of a cylinder head (102) coupled to an upper part of a cylinder block (not shown). A camshaft (103) is rotatably supported by the cylinder head (102). The camshaft (103) is configured to have at least two cams. The intake and exhaust valves (not shown) are operated via rocker arms (104a, 104b) connected to the camshaft (103). A first centrifugal cam actuation system (105) is installed on one end of the camshaft (103) and a second centrifugal cam actuation system (106) on opposite end of the camshaft (103). The first centrifugal cam actuation system (105) comprises of decompression arm (105a) held abutted with a decompression cam (105d) (as shown in figure 2a) via an elastic preload provided by a decompression spring member (105b), rotatable about a pivot pin (not shown). The decompression arm (105a) operates a decompression cam (105d) (as shown in figure 2a) through a decompression connecting member (105c). The one end of the decompression arm (105a) connected to decompression cam (105d) (as shown in figure 2a) is configured to lock the decompression connecting member (105c) and thereby operate the decompression cam (105d) (as shown in figure 2a) on its rotation.
[00037] Figure 2(a) illustrates a perspective view of a single overhead type camshaft (SOHC) assembly and Figure 2(b) illustrates a side view of the single overhead camshaft assembly as per embodiment, in accordance with one example of the present subject matter. The first centrifugal cam actuation system (105) comprises of the decompression cam (105d) wherein a portion of said decompression cam (105d) is located in a decompression cam slot (105e) provided on the radial surface of intake cam lobe (201). The one half of the radial surface of the decompression cam (105d) is spherical whereas the other half is flat. During starting operation, the radial surface of the decompression cam (105d) is angularly aligned such that it faces the intake cam follower (107a) (as shown in figure 1).The radial surface lifts the cam follower (107a) (as shown in figure 1) which in turn opens an intake valve (not shown) momentarily by a predetermined value based on engine operating conditions. This configuration of the system reduces the amount of charge in combustion chamber of the IC engine (101). Thereafter, when the rotational speed of the camshaft (103) has reached a predetermined value, the decompression cam (105d) is deactivated. The decompression cam (105d) is deactivated when the decompression arm (105a) moves in radially outward direction which in turn axially rotates the decompression cam (105d) such that the flat surface of decompression cam (105d) angularly aligned to face the cam follower (107a) (as shown in figure 1). Thereby no lift is offered by the decompression cam (105d) which releases the intake valve (not shown) from open condition.
[00038] Further, the second centrifugal cam actuation system (106) comprising of an exhaust gas recirculation (EGR) cam (106c), and an exhaust gas recirculation (EGR) arm (106a). The EGR arm (106a) is held abutted with the EGR cam (106c) via an elastic preload provided by an EGR spring member (106b) and rotatable about an EGR pivot pin (106d). The EGR cam (106c) is located in an EGR slot (106e) provided on the radial surface of exhaust cam lobe (202). The one half of the radial surface of the EGR cam (106c) is spherical whereas the other half is flat. The EGR arm (106a) operates the EGR cam (106c) through an EGR connecting member (106f). The one end of the EGR arm (106a) connected to EGR cam (106c) is configured to lock its motion against the EGR connecting member (106f) and thereby operate the EGR cam (106c) on its rotation. During starting or idle condition, the flat surface of EGR cam (106c) faces the cam follower (107b) (as shown in figure 1).However, above predetermined rpm the EGR arm (106a) moves in a radially outward direction and rotates the EGR cam (106c) such that the radial surface of the EGR cam (106c) is angularly aligned faces the cam follower (107b) (as shown in figure 1). This results into lifting of the cam follower (107b) which in turn opens an exhaust valve (not shown) by a predetermined value based on engine operating conditions to allow inflow of unburnt gases from exhaust port (not shown) into combustion chamber of engine.
[00039] Figure 3(a) illustrates a graph that shows relationship between lift of an intake and exhaust valve versus crank angle while starting of the four stroke SOHC type engine as per embodiment, in accordance with one example of the present subject matter, Figure 3(b) illustrates a graph that shows relationship between lift of an intake and exhaust valve versus crank angle after starting of the four stroke SOHC type engines internal combustion engine as per embodiment, in accordance with one example of the present subject matter, and Figure 3(c) a flow chart depicting method of activation-deactivation of first and second centrifugal cam actuation system as per embodiment, in accordance with one example of the present subject matter. For sake of brevity figure 3(a), figure 3(b) and figure 3(c) will be discussed together. During starting of the engine, as shown in graph the lift after closing of intake valve is represented by curve Y and lift for exhaust valve is represented by curve X, at step (S101), the decompression cam is activated at any of the range (D) of crank angles varying between 20 degree to 100 degree but disposed after the completion of the intake action. More specifically, the decompression cam is activated for duration (D) of not more than 100 degree of the crank angle during compression stroke as shown by curve A wherein compression stroke ranges from 540 to 720 degree of the crank angle. Subsequent to that, at step (S102), the charge inducted by the intake cam lobe of the camshaft assembly into the combustion chamber is minimised by the actuation of the decompression cam as per present invention. As per preferred embodiment, the decompression cam is located on the intake side cam lobe and the activation of decompression cam reduces the amount of charge in the engine by allowing some of the charge to flow back into intake system during initial stage of compression stroke of the engine. Subsequent to step (S102), at step (S103) the decompression cam is deactivated after starting of the engine when the engine speed exceeds a predetermined value e.g. 1500 rpm by enabling the flat surface of the decompression cam to engage with the follower leading to no more decompression beyond predetermined speed. This is enabled by the centrifugal force acting on the decompression arm resulting in rotation of the decompression cam and a flat surface of the cam being coming into engagement. Thereafter, at step (S104), once the engine starts, the reduced charge in the combustion chamber is restored after deactivation of decompression cam within few cycles of operation. The decompression cam is deactivated by opening of the decompression arm associated with the decompression cam by means of the centrifugal forces that are acting against the decompression spring member or any other equivalent elastic member. Thus, the deactivation of the decompression cam causes no significant drop in the overall charge inducted, as the inducted charges are controlled by the intake cam lobe.
[00040] Further, with reference to figure 3(b) during starting and idling of the engine, the Exhaust gas recirculation (EGR) cam remains deactivated. As shown in graph after closing of exhaust valve represented by curve X, during open state of intake valve represented by curve Y and when engine attains predetermined speed, The predetermined speed as per an embodiment is substantial about 2000 revs. per minute (r.p.m.). At step (S105) the EGR cam of the second centrifugal cam actuation system gets activated by centrifugal forces acting on the EGR arm associated with the EGR cam by means of the centrifugal forces that are acting against the spring. Subsequent to step (S105), at step (S106), exhaust gases are inducted into the fresh charge being inducted by an intake cam lobe of the camshaft assembly during suction stroke of said engine. An EGR action is configured at any of the range (D’) of crank angles varying of 20 degree to 100 degree. More specifically, the EGR cam is activated for duration (D’) of not more than 100 degree of the crank angle during suction stroke as shown by curve B wherein suction stroke ranges from 360 to 540 degree of the crank angle. Thus, the activation of the EGR cam causes induction of predetermined amount of exhaust gases into the incoming intake charge, which effects in reducing NOx emissions and like.
[00041] In an embodiment, the size of the EGR cam or the lift determines the amount of charge inducted from the exhaust. For instance, bigger the size of the EGR cam, higher is the internal EGR inducted into the intake charge. However, the amount of charge inducted cannot increase beyond a predetermined quantity as it may lead to charge dilution and stalling.
[00042] According to above architecture, the primary efficacy of the present invention is the compact and efficient engine comprising of first centrifugal cam actuation system and second centrifugal cam actuation system on same camshaft assembly wherein first centrifugal cam actuation system ensures ease of startability by reducing the effort required to crank the engine. Further, second centrifugal cam actuation system reduces the exhaust gas emission by burning the unburnt gases or like.
[00043] The above-described embodiments, and particularly any “preferred” embodiments, are possible examples of implementations and merely set forth for a clear understanding of the principles of the invention. It will be apparent to those skilled in the art that changes in form, connection, and detail may be made therein without departing from the spirit and scope of the invention.

List of References:

101 – Internal combustion Engine
102 – Cylinder head
103 – Camshaft
104a – Intake side rocker arm
104b – Exhaust side rocker arm
105 – First centrifugal cam actuation system
105a – Decompression arm
105b – Decompression spring member
105c – Decompression connecting member
105d – Decompression cam
105e – Decompression cam slot
106 – Second centrifugal cam actuation system
106a – EGR arm
106b – EGR Spring member
106c – EGR cam
106d – EGR pivot pin
106e – EGR Slot
106f – EGR connecting member
107a – Intake side cam follower
107b – Exhaust side cam follower
201 – Intake cam lobe
202 – Exhaust cam lobe