Patent Description:
An internal combustion (IC) engine is used to convert chemical energy into mechanical energy by combustion of air-fuel mixture. Thermal energy generated due to combustion of air-fuel mixture is used to provide motion for one or more reciprocating pistons inside a cylinder. The one or more reciprocating pistons transfers this reciprocating motion causing a rotary motion of one or more crankshaft(s) connected thereto through a connecting rod utilizing a slider-crank mechanism. The cylinder head comprises typically at least one intake port and at least one outlet port which allow the entry of air-fuel mixture and exit of burnt gases from the combustion chamber, respectively. In this operation, the precise movement and timing of the opening and closing of inlet aperture(s) and outlet aperture(s) to the combustion chamber is essential for accurate performance of the IC engine.

Generally, this opening and closing of the inlet/outlet apertures is controlled by various components present on the cylinder head and cylinder bore, and the opening & closing of the valves is actuated by one or more camshafts, which are driven by one or more crankshaft(s) through a camshaft transmission system. The cam shaft(s) include cam-lobes that control aperture opening and duration of aperture opening. One of the biggest drawbacks with many of commuter motor vehicle engines is the use of fixed timing for closing and opening of the apertures (through valves) because of which these engines are operated sub optimally. For example, the fixed timing of the valves at higher speeds causes the opening time to be set to the optimal setting, whereas a higher valve opening is desired. The intake valve might be closed late to use inertia of incoming air. However, such late opening of valve in lower engine speeds affects the volumetric efficiency of the engine. Thus, a fixed timing of the valve opening, even though set to optimum settings, affects the engine performance at a certain speed range. In the art, various, electrical, electromechanical, mechanical, and hydraulic means of achieving the cam phasing are known. For example, cam phasing, cam changing etc. are some of the techniques used in the art. For example, cam-phasing is one of the techniques that provides phase difference of one cam-lobe with another cam-lobe thereby achieving varied valve opening.

<CIT> discloses about a valve operating device for internal combustion engine. The cam phase changing mechanism includes a centrifugal weight (<NUM>) adjacent to an outer surface of the input rotation member (<NUM>) opposite to a bearing and supported by the input rotation member (<NUM>) with a pivot shaft (<NUM>). <CIT> further discloses a return spring (<NUM>) for biasing the weight in diameter reducing direction. Further, a driven flange (<NUM>) adjacent to the inner surface of the input rotation member (<NUM>) and fixed to a second cam shaft (<NUM>), a driving pin (<NUM>) connected to the centrifugal weight (<NUM>) and slidably fitted to the driven hole (<NUM>) through an open hole (<NUM>) of the input rotation member (<NUM>). Further, in <CIT> bolt (<NUM>) has been put in order to have axial stability of the cam phase changing mechanism.

<CIT> discloses a camshaft adjuster (<NUM>) for adjusting the angle of rotation of at least one camshaft (<NUM>) relative to a crankshaft of an internal combustion engine, having a drive element (<NUM>) for transmitting a rotational movement of the crankshaft to the camshaft (<NUM>). In an embodiment, between the drive element (<NUM>) and the camshaft (<NUM>) is arranged a unidirectional clutch (<NUM>) connecting the input member (<NUM>) to an intake camshaft (<NUM>) or connecting the input member (<NUM>) to an exhaust camshaft (<NUM>).

<CIT> discloses a method and apparatus for operating a four-cycle internal combustion engine, used for driving a vehicle, in which the beginning of the opening of the exhaust valve is advanced, from a middle rotational or load range of the engine, with a decreasing rotational speed and/or decreasing load of the engine.

Generally, cam phasing/changing enables engine to operate above its sub-optimal performance. For example, an intake valve if advanced during lower rotations per minute (RPM), then the intake valve undergoes early closure thereby minimizing backflow during the compression stroke by which volumetric efficiency and torque are improved in lower RPM. Further, at higher RPM, phasing can be performed on the intake valve which results in retarding/late closure of the intake valve thereby utilizing the momentum of the air entering the intake manifold at high speeds for scavenging. Similarly, the exhaust valve opening and closure can be either advanced or retarded by cam phasing. Also, cam phasing can be done both on the intake valve and exhaust valve.

Generally, to perform cam phasing/changing, various electrical, electromechanical, and hydraulic means are used, which are complex and are not cost effective. For example, a solenoid, or a slider pin or the like are required, which is to be accommodated near the cam shaft portion that requires major space on the already compact cylinder head region. Additionally, for a saddle type two or three wheeled vehicle, it is an important requirement for the powertrain to be compact as possible to be enable packaging within small space & also allow ease of access to various parts of the powertrain for timey service & repair with simple tools & without having need to dismantle the powertrain from the vehicle. Further, such electro/electromechanical or hydraulic systems include an electrical or hydraulic driving means, which are powered by on board battery, and being controlled by a control unit. Moreover, addition of a control module like a controller adds up to the cost of the system and a motor, say stepper motor, for causing phasing makes the engine bulkier, especially the cylinder head portion. In some other solutions known in the art, a sliding mechanism for engaging and disengaging various rocker arms depending on speed is suggested. Even in such, systems, an externally controlled slider is required and a motor or the like is to be used to control the slider movement making the system expensive and bulkier. Thus, there is a need for an additional system and also those systems consume battery power. Moreover, the functional properties of the electrical and the mechanical systems are affected due to temperature variation in the engine, say during cold start or at high temperatures.

Moreover, in the art, mechanical phasing systems are known that are capable of performing cam phasing according to change in speed/RPM of the engines. Generally, mechanical phasing system may be used in compact vehicles like two-wheelers or three-wheelers that have compact engine layout. Also, such mechanical phasing system offer cost benefit due their capability of functioning without any electrical/ hydraulic controls. However, such systems are not foolproof and tend to malfunction when the phasing angle is increased. For example, in a mechanical system that uses centrifugal force for cam phasing, the cam phasing occurs abruptly even before the desired speed due to force component, say centrifugal force component/ inertia component, acting on the phasing means. Such problem is prominent in vehicles that use a single camshaft for controlling both the intake and exhaust valves as the torque of the camshaft is higher and also the operational speed of the camshaft is higher. Considering the case of sudden acceleration by the user, a sudden increase in velocity/speed of rotation of the camshaft is occurred, which results in sudden increase in centrifugal force causing increase in the centrifugal component thereby causing slip. Moreover, such premature may occur even in systems that used ball bearings, working due to centrifugal force. Thus, in such system cam phasing occurs at undesired speeds affecting performance of the system due to opening/closing of the valves at undesired conditions and also this could lead to poor emissions. For example, occurrence of the cam-phasing during mid-range affects the engine-performance as either intake time or undesired scavenging occurs affecting engine performance. Moreover, the systems known in the art may cause vibration due to presence of movable parts even though a preloading is done in radial direction, which may cause unnecessary noise.

Hence, there is need for a mechanical cam phasing system that can be implemented even in a compact IC engine and the cam phasing system should be capable of performing its function only at desired engine speed and should be capable of overcoming the aforementioned and other problems of the prior art.

Thus, the present subject matter provides an internal combustion engine provided with a mechanical phasing system/assembly using mechanical means and depending on the speed/RPM of the engine without the need for an external control.

The present subject matter provides a camshaft assembly that includes a mechanical phasing assembly that is capable of performing phase shifting of one of the intake lobe or the exhaust lobe with respect to other thereby advancing/retarding valve opening/closing.

The camshaft assembly of the present subject matter is capable of opening/closing of intake and exhaust valve(s) through an integrated member offering phase shifting.

The camshaft assembly, in one embodiment, includes a first-cam portion and a second-cam portion, wherein one or more bearings rotatably support the first-cam portion and the second-cam portion. Further, in one embodiment, another bearing, for example a roller bearing, is provided between the first-cam portion and the second portion to enable relative rotation thereof.

The intake flange is connected to one of the first-cam portion and the second-cam portion, and the exhaust flange is connected to other of the first-cam portion and the second-cam portion. The terms 'intake flange' and 'exhaust flange' are not limited to singular members and may include more than one flange. The camshaft assembly includes one or more cam lobes corresponding to each of the flanges, wherein the cam lobes are selected to perform valve lift as per the engine requirement. Similarly, the word cam lobe refers to any geometry of the profile of a member which performs the valve actuation.

The camshaft assembly includes a driven sprocket supported on one of the cam portions. In other words, the driven sprocket is secured to one of the cam portions. The mechanical phasing assembly includes a mass member that is capable of changing a position in a radial direction depending on speed of rotation of the camshaft assembly. The mass member is disposed adjacent to one of the intake flange or the exhaust flange.

In one embodiment, the mass member may be formed by two or more arc member that are split in circumferential direction and are held close to the axis through tensional-elastic member(s). The two or more arc members are capable of moving in a radial direction due to centrifugal force.

In one embodiment, the two or more arc members are provided with one or more apertures and one or more pins are configured to pass through the apertures, wherein the one or more pins are movable along with the arc members.

The intake flange, the exhaust flange, and the driven sprocket are provided with elongated slots, according to one implementation. According to one implementation, one of the flange of the intake flange and the exhaust flange is secured to the driven sprocket. That one of the flange and the driven sprocket are provided with elongated slot(s) on each thereof with a phasing angle or arc. Other flange of the intake flange and the exhaust flange with an elongated slot which is substantially extending in a radial direction. Thus, when the pin moves along the angular elongated slot of the driven sprocket and the one flange connected to driven sprocket, the pins tend to phase shift the other flange due to the angular movement of the pins.

For example, to phase shift the intake flange (to alter intake valve opening/closing depending on speed), the driven sprocket and the exhaust flange are provided with arc shaped elongated slots and the intake flange is provided with substantially radially extending elongated slots. Thus, when the mass member expands in radial direction, the pins moving along with the mass members move along the arc shaped elongated slots that phase shifts the intake flange.

The phase shifting assembly includes an axial-load member disposed substantially adjacent to one of the flanges. The axial-load member is preloaded in an axial direction to exert frictional force on the mass member.

In one embodiment, the driven sprocket, which is driven by the crankshaft, is connected to one of the flanges and the other flange is adapted to perform phase shifting with respect to the orientation of the driven sprocket. In another embodiment, both the flanges are adapted to undergo phase shifting with the respect to the driven sprocket either one at a time or both at a time (advancing or retarding).

In one embodiment, the axial-load member is disposed on one axial side of the driven sprocket and the axial-load member is provided with a preload in axial direction to exert force on the mass member. In one implementation, a retainer member is provided on other side of the driven sprocket and the retainer plate supports one end of a preload member, which is other side abutting the axial-load member.

The axial-load member exerting force in axial direction results in frictional force acting on the mass member from either sides. The frictional force balances a force component acting on the mass member, in a direction of movement of the pin along the elongated slot. This force component, otherwise, tends to move the pin in the radially outward direction, is balanced by the frictional force exerted by the axial-load member.

Thus, even when the phasing angle is increased to around <NUM> degrees, the pin does not tend to slip (even if the tangential velocity components is acting on the pin(s)) due to the frictional force. It is a feature of the present subject matter that the camshaft assembly can be adapted to be used for phasing in around the range of <NUM>-<NUM> degrees just by adjusting the preload on the axial-load member. For example, the assembly can be kept same and just the preload member like a spring can be replaced.

Preferably, at least two apertures on the mass member, at least two elongated slots on the flanges and the driven sprocket are provided, and correspondingly two pins are used to uniformly transfer rotation force from one component to another. Further, use of elongated slots reduce weight of the system and the structural integrity of the component is retained.

Further, the present subject matter is compactly accommodated in the axial direction. For example, in one embodiment, the driven sprocket is provided with a disc shaped groove and the axial-load member is compactly accommodated at the groove. Thus, no modifications of the layout are required, especially with reference to the cam lobes and the driven sprocket.

Further, the axial-load member suppresses any vibrations that may have occurred due to the mass member being formed by sub-members that are connected through tension spring.

In another embodiment, the mass member may be a collection of ball bearings annularly disposed and the ball bearings movable in a radial direction due to application of centrifugal force thereon. The movement of ball bearings in the radial direction (along a path angularly provided on one of the contact portions) enables phase shifting. The axial-load member is disposed to exert axial-load introducing frictional force on the mass member.

Various features and embodiments of the present subject matter here will be discernible from the following further description thereof, set out hereunder. According to an embodiment, an internal combustion engine (IC) described here is either one of the prime movers or the sole prime mover for a motor vehicle. The IC engine may be a forward inclined type or substantially horizontal type that is either fixedly mounted or swingably connected to the motor vehicle. The IC engine includes at least two valves per cylinder head viz. one intake & one exhaust valve.

The present subject matter along with all the accompanying embodiments and their other advantages would be described in greater detail with an embodiment of a single cylinder IC engine in conjunction with the figures in the following paragraphs.

<FIG> illustrates a side view of the IC engine <NUM>, according to an embodiment of the present subject matter. The IC engine <NUM> includes a cylinder block <NUM> supported by a crankcase <NUM> of the IC engine. The cylinder block <NUM> defines a cylinder portion at which a piston can perform reciprocating motion. A cylinder head <NUM> is mounted to the cylinder block <NUM> and the cylinder head <NUM> acts as one end of said cylinder portion. The cylinder block <NUM> is provided with cooling fins <NUM> and the cylinder head <NUM> may be provided with the cooling fins. The IC engine <NUM> comprises a piston (not shown) performing a reciprocating motion in the cylinder portion due to force imparted to it by the combustion of air-fuel mixture. This reciprocating motion is converted and transferred to a rotary motion of a crankshaft <NUM> through a connecting rod (not shown). Further, a cylinder head-cover <NUM> is mounted to the cylinder head <NUM>. The crankcase <NUM> is made up of left-side crankcase and right-side crankcase. The crankcase <NUM> rotatably supports the crankshaft <NUM>. Further, an electric machine like a magneto assembly <NUM> or an integrated starter generator is mounted to the crankshaft <NUM>. The magneto assembly <NUM> during operation is used to charge a battery (not shown). The cylinder head <NUM> includes an intake port <NUM> and an exhaust port (not shown) that are provided on a first face and a second face of the cylinder head <NUM>. In the present embodiment, the first face is an upward facing side and the second face is a downward facing side thereof. Further, the cylinder head <NUM> supports a camshaft assembly <NUM> (partially shown in <FIG>) that is capable of operating intake valve(s) and exhaust valve(s) of the IC engine <NUM>. <FIG> illustrates a sectional view of the IC engine <NUM> taken along the line W-W' according to an embodiment of the present subject matter.

The IC engine <NUM> includes a driving gear <NUM> connected to the crankshaft <NUM> and rotates integrally with it. The driving gear <NUM> acts a primary drive and is capable of transferring rotational force to a primary driven <NUM>. A primary driven gear <NUM> is thus operably connected to the crankshaft <NUM>. The cylinder head <NUM> comprises a valve train arrangement to control opening and closing of intake and exhaust valves thereby controlling intake of air-fuel mixture and outlet of exhaust gases. A camshaft assembly <NUM> (partially shown) is rotatably mounted to the cylinder head <NUM>. A cam chain <NUM> operably connects the crankshaft <NUM> and camshaft assembly <NUM>. A driven sprocket <NUM> of the camshaft assembly <NUM> is configured to be meshed with the driving gear <NUM> and the driven sprocket <NUM> transfers rotary motion of the crankshaft <NUM> to the camshaft assembly <NUM>. In one embodiment, a ratio of the driven sprocket <NUM> to the driving gear <NUM> is <NUM>, by which for every two rotations of crankshaft <NUM> the camshaft assembly <NUM> will undergo one rotation. The IC engine <NUM> is provided with one or more chain-tensioner(s) <NUM> that enable in adjusting the tension of the cam chain <NUM> through an adjustment member <NUM>.

<FIG> illustrates an isometric view of the camshaft assembly, in accordance with an embodiment of the present subject matter. <FIG> illustrates another isometric view of the camshaft assembly with selected parts thereon, in accordance with the embodiment of <FIG>. <FIG> shows a radial sectional view of the camshaft assembly <NUM> taken along axis U-U'. The camshaft assembly <NUM> includes at least one intake lobe <NUM> and at least one exhaust lobe <NUM>. The cam chain <NUM> is loaded around the driving gear <NUM>, and driven sprocket <NUM>. The camshaft assembly <NUM> is rotatably supported by one or more bearings <NUM>, <NUM>. the present embodiment, the camshaft assembly <NUM> includes a first-cam portion <NUM> and a second-cam portion <NUM>. Further, the driven sprocket <NUM> is disposed about the axis of rotation of the aforementioned components. The camshaft assembly <NUM> includes a mechanical phasing assembly <NUM>. The camshaft assembly <NUM> includes at least one intake flange <NUM> corresponding to at least one intake lobe <NUM> and at least one exhaust flange <NUM> corresponding to at least one exhaust lobe <NUM>. In the present embodiment, the intake flange <NUM> is disposed between the mass member <NUM> and the exhaust flange <NUM>.

In one embodiment, the camshaft assembly <NUM> is also provided with a decompression system <NUM>. The decompression system <NUM> includes a decompression arm pivoted at one end and having a movable end. The decompression arm is supported on the exhaust flange <NUM> by a preloaded elastic member. The decompression system <NUM> enables the exhaust valve to have an additional lift during compression stroke during engine startup and the additional lift is curtailed once the engine speed crosses a predefined value.

<FIG> shows a mass member, in accordance with the embodiment of <FIG>. <FIG> shows a sectional view of the exhaust cam assembly <NUM> taken along axis X-X', in accordance with an embodiment as depicted in <FIG>. <FIG> shows another sectional view of the exhaust cam assembly <NUM> taken along axis V-V', in accordance with an embodiment as depicted in <FIG>. <FIG> depicts an exploded view of the of the camshaft assembly, according to an embodiment of the present subject matter. The first-cam portion <NUM> is rotatably supported by first bearing <NUM> and has the intake lobe <NUM> integrally formed. The first-cam portion <NUM> extends substantially along axis of the cam shaft assembly <NUM> and is connected to the intake flange <NUM> Similarly, the second-cam portion <NUM> has the exhaust lobe <NUM> integrally formed and is rotatably supported by the second bearing <NUM>. The second-cam portion <NUM> is at least partially coaxially disposed about the first cam portion <NUM>. In one embodiment, a roller bearing <NUM> is disposed between the first-cam portion <NUM> and the second-cam portion <NUM>. The exhaust flange <NUM> is supported by the second-cam portion <NUM>. The camshaft assembly <NUM> is rotatably supported on the cylinder head <NUM> (shown in <FIG>).

The driven sprocket <NUM> is supported on the first-cam portion <NUM> in the present embodiment. The driven sprocket <NUM> is secured to the first-cam portion <NUM> through a fastener <NUM>. Also, locking fasteners <NUM> (shown in <FIG>) are provided to secure the retainer plate <NUM>, the driven sprocket <NUM> and a flange <NUM> together. The mechanical phasing assembly <NUM> includes an axial-load member <NUM>. The mass member <NUM> is supported on the intake flange <NUM>. Further, the axial-load member <NUM> is disposed adjacent to the intake flange <NUM>, in accordance with the present embodiment. The mass member <NUM> may be disposed adjacent to at least one of the flanges. Furthermore, the camshaft assembly <NUM> includes an axial-load member <NUM>, wherein the mass member <NUM> is sandwiched between the axial-load member <NUM> and the intake flange <NUM>.

The axial-load member <NUM> is disposed substantially on one side of the driven sprocket <NUM> and a retainer plate <NUM> is provided on other side of the driven sprocket <NUM>. The driven sprocket <NUM> includes one or more through holes <NUM> and one or more axial force-elastic member <NUM> are provided between the axial-load member <NUM> and the retainer plate <NUM> through the through holes <NUM> thereby providing a preload on the axial-load member <NUM>.

The driven sprocket <NUM> provides rotational force received from the crankshaft <NUM> through one or more pins <NUM> (shown in <FIG>). The one or more pins form part of the mechanical phasing assembly <NUM>. Each of the driven sprocket <NUM>, the intake flange <NUM>, the exhaust flange <NUM> are provided with elongated slots <NUM>, <NUM>, <NUM> and the one or more pins <NUM> are disposed about the elongated slots <NUM>, <NUM>, <NUM> whereby the rotational force from the driven sprocket <NUM> is transferred to the flanges <NUM>, <NUM> thereby enabling rotation of the lobes <NUM>, <NUM>. Further, the axial-load member <NUM> is also provided with the elongated slot <NUM>.

The mass member <NUM> is formed by a first-arc member <NUM> and a second-arc member <NUM> that are connected to each other through a tensional-elastic member(s) <NUM> (shown in <FIG>). The mass member <NUM> during rotation of the camshaft assembly <NUM>, due to the centrifugal force tends to expand in the radially outward direction, when the centrifugal force exceeds the stiffness (k). The elastic members <NUM> are selected such that the stiffness (k) will be exceeded by the centrifugal force after a predetermined RPM of the camshaft assembly <NUM>. One of the flanges <NUM>, <NUM> is provided with an angular elongated portion <NUM>, which is arc shaped portion.

The first-arc member <NUM> and the second-arc member <NUM> are provided with one or more apertures <NUM> through which the pins <NUM> are passing. The motion of the arc member <NUM>, <NUM> is guided by the elongated slots <NUM> provided on the driven sprocket <NUM>. The motion of the arc member <NUM>, <NUM> in radial direction due to the centrifugal force enables the pins <NUM> to movement along with arc member <NUM>, <NUM> and the pins <NUM> slide through the elongated slots <NUM>, <NUM>, <NUM>. However, a first elongated slot <NUM> is arc shaped elongated slot(s) provided on at least one flange <NUM> causes the flange <NUM> to shift phase due to the movement of the pins <NUM> thereby causing a phase shift at a desired speed/RPM with respect to a second elongated slot <NUM> provided on other of the flange <NUM> that is substantially linearly extending in the radial direction.

In the present embodiment, the exhaust flange <NUM> is secured to the driven sprocket <NUM> and a spacer <NUM> is provided therebetween. The spacer <NUM> enables to maintain a pre-determined spacing between the driven sprocket <NUM> and the flanges thereby causing the axial-load member <NUM> and the mass member <NUM> to function without any additional axial-load from other elements. The rotation of the driven sprocket <NUM> rotates the exhaust flange <NUM> thereby maintaining same phase. Further, the exhaust flange <NUM> is provided with the angular elongated slot <NUM>, which is having certain degree of movement (angular rotation) causing the intake flange <NUM> to undergo phase shift when the pins <NUM> are sliding in a radially outward direction. Thus, the intake lobe <NUM> also undergoes a phase shift causing a change in intake valve opening/closing timing. As per an embodiment, the angular elongated slot offers a phase shift in the range of <NUM>-<NUM> degrees. The axial-load plate <NUM> exerts an axial force on the mass member <NUM> because of which slipping of the arc members <NUM>, <NUM> in radial direction is reduced.

<FIG> shows an enlarged/detailed view of the section of the camshaft assembly <NUM>, in accordance with an embodiment of the present subject matter. The camshaft assembly <NUM> when is subjected to rotation, the arc members <NUM>, <NUM> of the mass member <NUM> are subjected to centrifugal force CF that tends to pull the arc members in a radially outward direction. The arc member <NUM>, <NUM> are connected to each other through elastic members <NUM> having stiffness k that tends to pull the arc members <NUM>, <NUM> in a radially inward direction with a force KF. Further, the axial-load member <NUM>, due to the preload acting thereon, exerts an axial force on the arc member <NUM>, <NUM>. Thus, the arc members <NUM>, <NUM>; that are sandwiched between the flange <NUM> and the axial-load member <NUM>, receives frictional force FF on the mass member <NUM> and due to the stiffness/tension of the elastic member(s) <NUM> the premature phasing is controlled.

The pin <NUM>, which is one of the essential component of the mechanical phasing assembly <NUM> that is passing through the apertures <NUM> is also subjected to the forces acting on the mass member <NUM>. Due to the torque experienced by the camshaft assembly <NUM>, which is the valve train torque, it has one force component acting in a direction of the movement of the pin <NUM> along the elongated slot in the radial direction. This force component, otherwise, tends to move the pin <NUM> in the radially outward direction is balanced by the frictional force exerted by the axial-load member <NUM>. Only when the speed/RPM of the engine <NUM>, which is analogous to the speed of the camshaft assembly <NUM>, is higher, the centrifugal force CF supersedes the force KF exerted by the elastic members <NUM> and the frictional force FF acting on the arc members <NUM>, <NUM> by which the arc members <NUM>, <NUM> move in radially outward direction. Thus, the movement of the pins <NUM> changes the orientation of the flange <NUM> causing phase shifting. Further, the roller bearing <NUM> provided between an inner periphery of the second-cam portion <NUM> and an outer periphery of the first-cam portion <NUM> enables ease of relative rotation between the cam portions <NUM>, <NUM> during phase shifting. Thus, the mechanical phasing assembly <NUM> according to the present subject matter occurs according to a method defined by the following equation (<NUM>). The method of causing mechanical phasing, as detailed in <FIG>, according to the present subject matter is detailed below: <MAT>.

The axial-load member <NUM> preloaded in axial direction disposed for exerting axial load in the camshaft assembly <NUM> exerts resistance/frictional force FF on lateral surfaces of mass member <NUM>, according to one embodiment. The axial-load member <NUM> offers a frictional force FF dependent on the frictional coefficient µ of the axial-load member <NUM>, which is inherent surface friction of the material or a frictional coefficient due to a surface coating provided on the axial-load member <NUM> to counter any excessive centrifugal forces acting on the mass member <NUM> during certain operating conditions like sudden acceleration or the like.

The method provides that, at step S301, the system which is mechanical phasing system which is operational without the need for any external control, requires the IC engine <NUM> to be in operational condition whereby the crankshaft rotates the camshaft assembly <NUM>. Due to the rotation of the camshaft assembly <NUM>, a centrifugal force acts on the mass member <NUM>, which is preloaded in radial direction. Further, at step S302, the centrifugal force CF acting on the mass member <NUM> is checked. The term 'checked' used herein is merely representative to explain the method and does not require actual checking as the mechanical phasing assembly <NUM> occurs automatically. Further, the centrifugal force CF acting on the mass member <NUM> is compared against the force KF exerted by the elastic member and the frictional force FF dependent on the co-efficient of friction. If the centrifugal force CF is less than a cumulative force of the stiffness force KF and the frictional force (i.e. µ time FF), then the system continues to check the centrifugal force CF going back to step S302. At step S303, if the centrifugal force CF exceeds the sum of the force KF and the frictional force µ time FF, then at step S304, the system performs mechanical phasing, which is performed without the need for any external control. This, causes a change in opening and closing time of the valves thereby catering to the intake and exhaust requirements at all speeds of operation of the engine.

Further, the axial-load member <NUM>, in accordance with the present embodiment, is a circular disc shaped member that is disposed adjacent to the driven sprocket <NUM>. Further, an axial face of the driven sprocket <NUM> is provided with a disc shaped groove, which is capable of accommodating the axial-load member <NUM> at the groove. Thus, the axial-load member <NUM> is having a first inward axial face <NUM> and the driven sprocket <NUM> having a second inward axial face <NUM>, and the first inward axial face <NUM> and the second inward axial face <NUM> are disposed along a plane P taken orthogonally to an axis A-A' of the camshaft assembly <NUM>. Thus, the axial-load member <NUM> is accommodated in the same amount space that is required to accommodate the driven sprocket <NUM>. This eliminates the need for additional mounting space on the camshaft assembly <NUM>, especially the space between the driven sprocket and the cam lobes <NUM>, <NUM>. As, the position of the cam chain <NUM> which gets connected to the crankshaft, the accommodation space of the cam chain <NUM>, and the position of the valves, with which the cam lobes <NUM>, <NUM> interact, need not be altered as per the present subject matter thereby retaining the available layout of the IC engine, especially the cylinder head. Thus, the present subject matter offers improved valve timing assembly/ mechanical phasing assembly that does not require any layout modifications.

In one implementation, an axial face of the axial-load member <NUM> and the axial face of the flange <NUM> that are facing the mass member <NUM> are machined or provided with surface coating to achieve a desired frictional coefficient.

Claim 1:
A camshaft assembly (<NUM>) capable of being rotatably supported on a cylinder head (<NUM>) of an internal combustion engine (<NUM>), said camshaft assembly (<NUM>) comprising:
a driven sprocket (<NUM>) configured to connect said camshaft assembly (<NUM>) connected to a crankshaft (<NUM>);
two or more cam portion(s) (<NUM>, <NUM>);
at least one intake flange (<NUM>) connected to at least one of said two or more cam portion(s) (<NUM>, <NUM>); and
at least one exhaust flange (<NUM>) connected to at least one other of said two or more cam portion (<NUM>);
a mechanical phasing assembly (<NUM>) capable of performing phase shift of at least one flange (<NUM>, <NUM>) with respect to said driven sprocket (<NUM>) depending on a speed of rotation of said camshaft assembly (<NUM>); and
wherein said mechanical phasing assembly (<NUM>) includes at least one radially preloaded mass member (<NUM>), said mass member (<NUM>) capable of performing phase shift of at least one of said at least one intake flange (<NUM>) and said at least one of said exhaust flange (<NUM>) with respect to said driven sprocket (<NUM>) depending on said speed of rotation of said camshaft assembly (<NUM>) an axial-load member (<NUM>) preloaded in axial direction for exerting axial load on the mass member (<NUM>).