EP3938629A1

EP3938629A1 - An internal combustion engine

Info

Publication number: EP3938629A1
Application number: EP20769545.3A
Authority: EP
Inventors: Varadha Iyengar LAKSHMI NARASIMHAN; Thiruvallur Loganathan BALASUBRAMANIAN; Karunaharan VYTHILINGAM
Original assignee: TVS Motor Co Ltd
Current assignee: TVS Motor Co Ltd
Priority date: 2019-03-13
Filing date: 2020-02-14
Publication date: 2022-01-19
Also published as: EP3938629A4; WO2020183486A1; JP2022520881A; BR112021018176A2; CN113518853B; CN113518853A

Abstract

The present subject matter relates to a camshaft assembly for an internal combustion engine for providing a mechanical type variable valve timing. The camshaft assembly (200) includes a mechanical phasing assembly (230) disposed adjacent to one of at least one intake flange (220) and at least one exhaust flange (225). At least one radially preloaded mass member (235) is capable of performing phase shift of at least one of intake flange (220) and exhaust flange (225) with respect to the driven sprocket (205) depending on speed of rotation of camshaft assembly (200). An axial-load member (245) preloaded in axial direction is disposed adjacent to the mass member (235) exerting axial load thereon. The present subject matter improves the 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.

Description

AN INTERNAL COMBUSTION ENGINE

TECHNICAL FIELD

[0001] The present subject matter relates generally to an internal combustion (IC) engine for a motor vehicle. More particularly, the present subject matter relates to a camshaft assembly for the internal combustion engine providing a mechanical type variable valve timing.

BACKGROUND

[0002] 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.

[0003] 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.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] The detailed description is described with reference to the accompanying figures.

[0005] Fig. 1 illustrates a side view of an exemplary internal combustion (IC) engine according to an embodiment of the present subject matter.

[0006] Fig. 2 illustrates the exemplary sectional view of the IC engine, the cross-sectional taken along axis W-W’.

[0007] Fig. 3 (a) illustrates a perspective view of a camshaft assembly, in accordance with an embodiment of the present subject matter.

[0008] Fig. 3 (b) illustrates another isometric view of the camshaft assembly with selected parts thereon, in accordance with the embodiment of Fig. 3 (a).

[0009] Fig. 3 (c) shows a radial sectional view of the camshaft assembly 200 taken along axis UTT

[00010] Fig. 4 depicts a mass member in a first state and in a second state, in accordance with the embodiment of Fig. 3.

[00011] Fig. 5 (a) illustrates a sectional-view of the camshaft assembly, according to an embodiment of the present subject matter.

[00012] Fig. 5 (b) illustrates another sectional-view of the camshaft assembly, according to an embodiment of the present subject matter.

[00013] Fig. 6 illustrates an exploded view of the camshaft assembly, according to an embodiment of the present subject matter.

[00014] Fig. 7 illustrates a detailed sectional view of the camshaft assembly, according to an embodiment of the present subject matter. DETAILED DESCRIPTION

[00015] 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.

[00016] 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.

[00017] 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.

[00018] 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. [00019] 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.

[00020] 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.

[00021] 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.

[00022] 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.

[00023] 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.

[00024] 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. [00025] 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.

[00026] 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.

[00027] 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.

[00028] 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.

[00029] 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.

[00030] 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).

[00031] 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.

[00032] 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.

[00033] Thus, even when the phasing angle is increased to around 20 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 5-25 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.

[00034] 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.

[00035] 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. [00036] 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.

[00037] 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.

[00038] 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.

[00039] 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.

[00040] Fig. 1 illustrates a side view of the IC engine 100, according to an embodiment of the present subject matter. The IC engine 100 includes a cylinder block 102 supported by a crankcase 101 of the IC engine. The cylinder block 102 defines a cylinder portion at which a piston can perform reciprocating motion. A cylinder head 103 is mounted to the cylinder block 102 and the cylinder head 103 acts as one end of said cylinder portion. The cylinder block 102 is provided with cooling fins 106 and the cylinder head 103 may be provided with the cooling fins. The IC engine 100 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 110 through a connecting rod (not shown). Further, a cylinder head-cover 104 is mounted to the cylinder head 103. The crankcase 101 is made up of left-side crankcase and right-side crankcase. The crankcase 101 rotatably supports the crankshaft 110. Further, an electric machine like a magneto assembly 111 or an integrated starter generator is mounted to the crankshaft 110. The magneto assembly 111 during operation is used to charge a battery (not shown). The cylinder head 103 includes an intake port 105 and an exhaust port (not shown) that are provided on a first face and a second face of the cylinder head 103. 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 103 supports a camshaft assembly 200 (partially shown in Fig. 2) that is capable of operating intake valve(s) and exhaust valve(s) of the IC engine 100. Fig. 2 illustrates a sectional view of the IC engine 100 taken along the line W-W’ according to an embodiment of the present subject matter.

[00041] The IC engine 100 includes a driving gear 113 connected to the crankshaft 110 and rotates integrally with it. The driving gear 113 acts a primary drive and is capable of transferring rotational force to a primary driven 112. A primary driven gear 112 is thus operably connected to the crankshaft 110. The cylinder head 103 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 200 (partially shown) is rotatably mounted to the cylinder head 103. A cam chain 114 operably connects the crankshaft 110 and camshaft assembly 200. A driven sprocket 205 of the camshaft assembly 200 is configured to be meshed with the driving gear 113 and the driven sprocket 205 transfers rotary motion of the crankshaft 110 to the camshaft assembly 200. In one embodiment, a ratio of the driven sprocket 205 to the driving gear 113 is 2, by which for every two rotations of crankshaft 110 the camshaft assembly 200 will undergo one rotation. The IC engine 100 is provided with one or more chain-tensioner(s) 115 that enable in adjusting the tension of the cam chain 114 through an adjustment member 116. [00042] Fig. 3 (a) illustrates an isometric view of the camshaft assembly, in accordance with an embodiment of the present subject matter. Fig. 3 (b) illustrates another isometric view of the camshaft assembly with selected parts thereon, in accordance with the embodiment of Fig. 3 (a). Fig. 3 (c) shows a radial sectional view of the camshaft assembly 200 taken along axis U-U’. The camshaft assembly 200 includes at least one intake lobe 210 and at least one exhaust lobe 211. The cam chain 114 is loaded around the driving gear 113, and driven sprocket 205. The camshaft assembly 200 is rotatably supported by one or more bearings 215, 216. the present embodiment, the camshaft assembly 200 includes a first-cam portion 201 and a second-cam portion 202. Further, the driven sprocket 205 is disposed about the axis of rotation of the aforementioned components. The camshaft assembly 200 includes a mechanical phasing assembly 230. The camshaft assembly 200 includes at least one intake flange 220 corresponding to at least one intake lobe 210 and at least one exhaust flange 225 corresponding to at least one exhaust lobe 211. In the present embodiment, the intake flange 220 is disposed between the mass member 235 and the exhaust flange 225.

[00043] In one embodiment, the camshaft assembly 200 is also provided with a decompression system 280. The decompression system 280 includes a decompression arm pivoted at one end and having a movable end. The decompression arm is supported on the exhaust flange 225 by a preloaded elastic member. The decompression system 280 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.

[00044] Fig. 4 shows a mass member, in accordance with the embodiment of Fig. 3. Fig. 5 (a) shows a sectional view of the exhaust cam assembly 200 taken along axis X-X’, in accordance with an embodiment as depicted in Fig. 3 (a). Fig. 5 (b) shows another sectional view of the exhaust cam assembly 200 taken along axis V-V’, in accordance with an embodiment as depicted in Fig. 3 (b). Fig. 6 depicts an exploded view of the of the camshaft assembly, according to an embodiment of the present subject matter. The first-cam portion 201 is rotatably supported by first bearing 215 and has the intake lobe 210 integrally formed. The first-cam portion 201 extends substantially along axis of the cam shaft assembly

200 and is connected to the intake flange 220 Similarly, the second-cam portion 202 has the exhaust lobe 211 integrally formed and is rotatably supported by the second bearing 216. The second-cam portion 202 is at least partially coaxially disposed about the first cam portion 201. In one embodiment, a roller bearing 214 is disposed between the first-cam portion 201 and the second-cam portion 202. The exhaust flange 225 is supported by the second-cam portion 202. The camshaft assembly 200 is rotatably supported on the cylinder head 103 (shown in Fig. 1).

[00045] The driven sprocket 205 is supported on the first-cam portion 201 in the present embodiment. The driven sprocket 205 is secured to the first-cam portion

201 through a fastener 243. Also, locking fasteners 241 (shown in Fig. 6) are provided to secure the retainer plate 240, the driven sprocket 205 and a flange 225 together. The mechanical phasing assembly 230 includes an axial-load member 245. The mass member 235 is supported on the intake flange 220. Further, the axial-load member 245 is disposed adjacent to the intake flange 220, in accordance with the present embodiment. The mass member 235 may be disposed adjacent to at least one of the flanges. Furthermore, the camshaft assembly 200 includes an axial-load member 245, wherein the mass member 235 is sandwiched between the axial-load member 245 and the intake flange 220.

[00046] The axial-load member 245 is disposed substantially on one side of the driven sprocket 205 and a retainer plate 240 is provided on other side of the driven sprocket 205. The driven sprocket 205 includes one or more through holes 206 and one or more axial force-elastic member 242 are provided between the axial-load member 245 and the retainer plate 240 through the through holes 206 thereby providing a preload on the axial-load member 245.

[00047] The driven sprocket 205 provides rotational force received from the crankshaft 110 through one or more pins 255 (shown in Fig. 3 (b)). The one or more pins form part of the mechanical phasing assembly 230. Each of the driven sprocket 205, the intake flange 220, the exhaust flange 225 are provided with elongated slots 260, 261, 262 and the one or more pins 255 are disposed about the elongated slots 260, 261, 262 whereby the rotational force from the driven sprocket 205 is transferred to the flanges 220, 225 thereby enabling rotation of the lobes 210, 211. Further, the axial-load member 245 is also provided with the elongated slot 263.

[00048] The mass member 235 is formed by a first-arc member 236 and a second-arc member 237 that are connected to each other through a tensional- elastic member(s) 238 (shown in Fig. 4). The mass member 235 during rotation of the camshaft assembly 200, due to the centrifugal force tends to expand in the radially outward direction, when the centrifugal force exceeds the stiffness (k). The elastic members 238 are selected such that the stiffness (k) will be exceeded by the centrifugal force after a predetermined RPM of the camshaft assembly 200. One of the flanges 220, 225 is provided with an angular elongated portion 261, which is arc shaped portion.

[00049] The first-arc member 236 and the second-arc member 237 are provided with one or more apertures 270 through which the pins 255 are passing. The motion of the arc member 236, 237 is guided by the elongated slots 260 provided on the driven sprocket 205. The motion of the arc member 236, 337 in radial direction due to the centrifugal force enables the pins 255 to movement along with arc member 236, 237 and the pins 255 slide through the elongated slots 260, 262, 263. However, a first elongated slot 261 is arc shaped elongated slot(s) provided on at least one flange 225 causes the flange 225 to shift phase due to the movement of the pins 255 thereby causing a phase shift at a desired speed/RPM with respect to a second elongated slot 262 provided on other of the flange 220 that is substantially linearly extending in the radial direction.

[00050] In the present embodiment, the exhaust flange 225 is secured to the driven sprocket 205 and a spacer 275 is provided therebetween. The spacer 275 enables to maintain a pre-determined spacing between the driven sprocket 205 and the flanges thereby causing the axial-load member 245 and the mass member 235 to function without any additional axial-load from other elements. The rotation of the driven sprocket 205 rotates the exhaust flange 261 thereby maintaining same phase. Further, the exhaust flange 225 is provided with the angular elongated slot 261, which is having certain degree of movement (angular rotation) causing the intake flange 220 to undergo phase shift when the pins 255 are sliding in a radially outward direction. Thus, the intake lobe 210 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 5-25 degrees. The axial-load plate 245 exerts an axial force on the mass member 235 because of which slipping of the arc members 236, 237 in radial direction is reduced.

[00051] Fig. 7 shows an enlarged/detailed view of the section of the camshaft assembly 200, in accordance with an embodiment of the present subject matter. The camshaft assembly 200 when is subjected to rotation, the arc members 236, 237 of the mass member 235 are subjected to centrifugal force CF that tends to pull the arc members in a radially outward direction. The arc member 236, 237 are connected to each other through elastic members 238 having stiffness k that tends to pull the arc members 236, 237 in a radially inward direction with a force KF. Further, the axial-load member 245, due to the preload acting thereon, exerts an axial force on the arc member 236, 237. Thus, the arc members 236, 237; that are sandwiched between the flange 220 and the axial-load member 245, receives frictional force FF on the mass member 235 and due to the stiffness/tension of the elastic member(s) 238 the premature phasing is controlled.

[00052] The pin 255, which is one of the essential component of the mechanical phasing assembly 230 that is passing through the apertures 270 is also subjected to the forces acting on the mass member 235. Due to the torque experienced by the camshaft assembly 200, which is the valve train torque, it has one force component acting in a direction of the movement of the pin 255 along the elongated slot in the radial direction. This force component, otherwise, tends to move the pin 255 in the radially outward direction is balanced by the frictional force exerted by the axial-load member 245. Only when the speed/RPM of the engine 100, which is analogous to the speed of the camshaft assembly 200, is higher, the centrifugal force CF supersedes the force KF exerted by the elastic members 238 and the frictional force FF acting on the arc members 236, 237 by which the arc members 236, 237 move in radially outward direction. Thus, the movement of the pins 255 changes the orientation of the flange 220 causing phase shifting. Further, the roller bearing 214 provided between an inner periphery of the second-cam portion 202 and an outer periphery of the first-cam portion 201 enables ease of relative rotation between the cam portions 201, 202 during phase shifting. Thus, the mechanical phasing assembly 230 according to the present subject matter occurs according to a method defined by the following equation (1). The method of causing mechanical phasing, as detailed in Fig. 8, according to the present subject matter is detailed below:

CF = KF+ m (FF) . (1)

[00053] The axial-load member 245 preloaded in axial direction disposed for exerting axial load in the camshaft assembly 200 exerts resistance/frictional force FF on lateral surfaces of mass member 235, according to one embodiment. The axial-load member 245 offers a frictional force FF dependent on the frictional co efficient m of the axial-load member 245, which is inherent surface friction of the material or a frictional coefficient due to a surface coating provided on the axial- load member 245 to counter any excessive centrifugal forces acting on the mass member 235 during certain operating conditions like sudden acceleration or the like.

[00054] 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 100 to be in operational condition whereby the crankshaft rotates the camshaft assembly 200. Due to the rotation of the camshaft assembly 200, a centrifugal force acts on the mass member 235, which is preloaded in radial direction. Further, at step S302, the centrifugal force CF acting on the mass member 235 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 230 occurs automatically. Further, the centrifugal force CF acting on the mass member 235 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. m 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 m 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.

[00055] Further, the axial-load member 245, in accordance with the present embodiment, is a circular disc shaped member that is disposed adjacent to the driven sprocket 205. Further, an axial face of the driven sprocket 205 is provided with a disc shaped groove, which is capable of accommodating the axial-load member 245 at the groove. Thus, the axial-load member 245 is having a first inward axial face 246 and the driven sprocket 205 having a second inward axial face 207, and the first inward axial face 246 and the second inward axial face 207 are disposed along a plane P taken orthogonally to an axis A -A’ of the camshaft assembly 200. Thus, the axial-load member 245 is accommodated in the same amount space that is required to accommodate the driven sprocket 205. This eliminates the need for additional mounting space on the camshaft assembly 200, especially the space between the driven sprocket and the cam lobes 210, 211. As, the position of the cam chain 114 which gets connected to the crankshaft, the accommodation space of the cam chain 114, and the position of the valves, with which the cam lobes 210, 211 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.

[00056] In one implementation, an axial face of the axial-load member 245 and the axial face of the flange 220 that are facing the mass member 235 are machined or provided with surface coating to achieve a desired frictional coefficient.

[00057] 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.

List of reference numerals:

100 engine 240 retainer plate

101 crankcase 241 locking fasteners

102 cylinder block 242 axial force-elastic member 103 cylinder head 35 243 fastener

104 cylinder head-cover 245 axial-load member

105 intake port 246 first inward axial face

110 crankshaft 255 pin(s)

111 magneto assembly 260/

113 driving gear 40 261/

114 cam chain 262/

115 chain-tensioner 263 elongated slot

116 adjustment member 270 aperture(s)

200 camshaft assembly 275 spacer

201 first-cam portion 45 280 decompression system

202 second-cam portion

205 driven gear/cam sprocket

206 holes

207 second inward axial face

210 intake lobe

211 exhaust lobe

214

215/

216/ bearing

220 intake flange

225 exhaust flange

230 phasing assembly

235 mass member

236 first-arc member

237 second-arc member

238 tensional-elastic member

Claims

We claim:

1. An internal combustion engine (100) comprising:

a cylinder block (102);

at least one piston slidably movable within a cylinder portion defined by said cylinder block (102);

a cylinder head (103) forming one end of said cylinder portion, said cylinder head (103) supporting one or more intake valve(s) and one or more exhaust valve(s);

a crankshaft (110) connected to said piston through a connecting rod, said crankshaft (110) rotatably supported by a crankcase (101) of said engine (100); and

a camshaft assembly (200) rotatably supported by said cylinder head (103), said camshaft assembly (200) includes a driven sprocket (205) and said camshaft assembly (200) connected to said crankshaft (110) through said driven sprocket (205), said camshaft assembly (200) comprising: a first-cam portion (201) and a second-cam portion (202);

at least one intake flange (220) and at least one exhaust flange (225), said at least one intake flange (220) connected to one of said first-cam portion (201) and said second-cam portion (202), and said at least one exhaust flange (225) connected to other of said first-cam portion (201) and said second-cam portion (202);

a mechanical phasing assembly (230) disposed adjacent to one of said at least one intake flange (220) and said at least one exhaust flange (225), said mechanical phasing assembly (230) includes at least one radially preloaded mass member (235), said mass member (235) capable of performing phase shift of at least one of said at least one intake flange (220) and said at least one of said exhaust flange (225) with respect to said driven sprocket (205) depending on speed of rotation of said camshaft assembly (200), and an axial-load member (245) preloaded in axial direction is disposed for exerting axial load.

2. The internal combustion engine (100) as claimed in claim 1, wherein said axial-load member (245) preloaded in axial direction is disposed adjacent to said mass member (235) exerting axial load thereon.

3. The internal combustion engine (100) as claimed in claim 1, wherein said retainer plate (240) disposed at axial end of said camshaft assembly (200) and adjacent to said driven sprocket (205), and one or more axial force-elastic member(s) (242), capable of exerting force on said axial-load member (245), are disposed between the axial-load member (245) and the retainer plate (240) passing through one or more hole(s) (206) of said driven sprocket (205).

4. The internal combustion engine (100) as claimed in claim 1, wherein said driven sprocket (205) is secured to one of said at least one intake flange (220) and at least one exhaust flange (225).

5. The internal combustion engine (100) as claimed in claim 1, wherein said camshaft assembly (200) includes at least one intake lobe (210) connected to corresponding at least one intake flange (220), and at least one exhaust lobe (211) connected to corresponding at least one exhaust flange (225), and said intake lobe (210) and said exhaust lobe (211) are adapted to control opening and closing of said valves, and said lobes (210, 215) are disposed on one side of the axial-load member (245) and said retainer plate (240) is disposed on other side of the axial- load member (245).

6. The internal combustion engine (100) as claimed in claim 1, wherein said axial-load member (245) is a circular disc shaped member disposed adjacent to the driven sprocket (205), and wherein said driven sprocket (205) is provided with a disc shaped groove capable of accommodating the axial-load member (245) thereat.

7. The internal combustion engine (100) as claimed in claim 1, wherein said axial-load member (245) is having a first inward axial face (246) and said driven sprocket (205) having a second inward axial face (207), and said first inward axial face (246) and said second inward axial face (207) are disposed along a plane (P) taken orthogonally to an axis (A- A’) of said camshaft assembly (200).

8. The internal combustion engine (1000 as claimed in claim 1, wherein said phasing assembly (230) includes one or more pins (255), said one or more pins (255), extending in axial direction, are disposed passing through one or more elongated slot(s) (260, 261, 262, 263) provided on said driven sprocket (205), on said intake flange (220), on said exhaust flange (225), and on said axial-load member (245), wherein said one or more elongated slot(s) (260, 261, 262, 263) includes an angular elongated slot (261).

9. The internal combustion engine (100) as claimed in claim 5, wherein said mass member (235) is formed by two or more arc members (236, 237) that are connected to each other through one or more tensional-elastic member(s) (238), and said arc members (236, 237) are in frictional contact with said axial-load member (245), and a spacer (275) is disposed between the driven sprocket (205) and at least one flange (261, 262) to maintain a pre-determined spacing.

10. The internal combustion engine as claimed in claim 1, wherein said mass member (235) is formed by a first-arc member (236) and a second-arc member (237) forming two or more arc members (236, 337), said arc members (236, 237) are provided with one or more apertures (270) for accommodating at least one pin (255) passing therethrough, said pin (255) passing through plurality of elongated slots (261, 262) provided on at least one intake flange (220) and at least one exhaust flange (225) causing a phase shift therebetween leading to variable valve timing control.

11. The internal combustion engine as claimed in claim 7, wherein said plurality of elongated slots (261, 262) includes a first elongated slot (261) provided on one of at least one intake flange (220) and at least one exhaust flange (225) extending in radial direction in arc shaped manner and a second elongated slot (262) provided on other of at least one intake flange (220) and at least one exhaust flange (225) extending substantially in a linear-radial direction.

12. A motor vehicle comprising said internal combustion engine (100) as claimed in any of the preceding claims.

13. A camshaft assembly (200) capable of being rotatably supported on a cylinder head (103) of an internal combustion engine (100), said camshaft assembly (200) comprising:

a driven sprocket (205);

two or more cam portion(s) (201, 202);

at least one intake flange (220) connected to at least one of said two or more cam portion(s) (201, 202); and

at least one exhaust flange (225) connected to at least one other of said two or more cam portion (202);

a mechanical phasing assembly (230) capable of performing phase shift of at least one flange (220, 225) with respect to said driven sprocket (205) depending on speed of rotation of said camshaft assembly (200); and an axial-load member (245) preloaded in axial direction for exerting axial load.

14. A method of operation of a mechanical phasing assembly (230) of a camshaft assembly (200) for an internal combustion engine (100), said method comprising steps of:

checking a centrifugal force (CF) acting on a mass member (235) of said camshaft assembly (200);

comparing said centrifugal force (CF) with a cumulative force of a stiffness force (FF) exerted by a tensional force elastic member () and a frictional force (p(FF)) exerted by an axial load member (245); and causing mechanical phasing by said mechanical phasing assembly (230) when sais centrifugal force (CF) exceed said cumulative force.