WO2022118341A2

WO2022118341A2 - A power unit

Info

Publication number: WO2022118341A2
Application number: PCT/IN2021/051129
Authority: WO
Inventors: Lakshmi Narasimhan VARADHA IYENGAR; Balasubramanian THIRUVALLUR LOGANATHAN; Vythilingam KARUNAHARAN
Original assignee: Tvs Motor Company Limited
Priority date: 2020-12-03
Filing date: 2021-11-30
Publication date: 2022-06-09
Also published as: WO2022118341A3

Abstract

The present subject matter relates to a power unit with a variable valve timing system. The power unit (100) comprises a cylinder head assembly (102). A variable valve timing system (200) comprises a first cam (211) for actuating one or more first valves (218) through a first rocker arm (205). The first rocker arm (205) pivotable about a first axis (S-S') of a first rocker shaft (225). The second cam (212) for selectively actuating the one or more first valves (218) through a second rocker arm (230). The second rocker arm (230) pivotable about the first axis (S-S'). An engaging unit (240) configured to engage the first rocker arm (220) with the second rocker arm (230) through a first engagement (265).

Description

A POWER UNIT

TECHNICAL FIELD

[0001] The present subject matter, in general, relates to a power unit, and, in particular relates to variable valve timing system for the power unit.

BACKGROUND

[0002] Generally, a power unit like an internal combustion (IC) engine converts chemical energy into mechanical energy by combustion of air-fuel mixture within a combustion chamber of the IC engine. The IC engine, among other components, has a cylinder head assembly atop a cylinder block. The cylinder block defines the combustion chamber that accommodates a reciprocating piston. Combustion of airfuel mixture causes the piston to undergo reciprocating motion transferring the energy generated during combustion to a crankshaft through a connecting rod thereby driving the crankshaft in a rotational manner.

[0003] Combustion of air-fuel mixture generates exhaust gases that needs to be scavenged from the combustion chamber through an exhaust system. Thus, the cylinder head assembly disposed atop the cylinder block is provided with plurality of valves that open and close at intervals for intake of air-fuel mixture into a combustion chamber and for scavenging of exhaust gases from the combustion chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] The detailed description is described with reference to the accompanying figures. In the figures, similar numbers are used throughout to reference like features and components.

[0005] Fig. 1 illustrates a front perspective view of a power unit, in accordance with an embodiment of the present subject matter.

[0006] Fig. 2 (a) depicts a schematic side view of a cylinder head assembly in accordance with an embodiment of the present subject matter.

[0007] Fig. 2 (ba) depicts a schematic perspective view of the variable valve timing system, in accordance with an embodiment of the present subject matter. [0008] Fig. 2 (bb) illustrates an exploded view of various components of a variable valve timing system, in accordance with an embodiment of the present subject matter.

[0009] Fig. 2 (c) illustrates an enlarged perspective view of the first rocker arm, in accordance with an embodiment of the present subject matter.

[00010] Fig. 2 (d) illustrates an enlarged perspective view of the second rocker arm, in accordance with an embodiment of the present subject matter.

[00011] Fig. 2 (e) illustrates an enlarged perspective view of the first rocker shaft, in accordance with an embodiment of the present subject matter.

[00012] Fig. 2 (f) illustrates a schematic axial view of the variable valve timing system, in accordance with an embodiment of the present subject matter.

[00013] Fig 2 (g) illustrates a sectional view of the variable valve timing system, with section taken along axis A-A’, in accordance with an embodiment of the present subject matter.

[00014] Fig. 2 (h) illustrates another sectional view of the variable valve timing system, with section taken along axis B-B’, in accordance with an embodiment of the present subject matter.

[00015] Fig. 3 depicts an exemplary graph of valve timing system in an engaged and a disengaged condition, in accordance with an embodiment of the present subject matter.

[00016] Fig. 4 (a) a schematic view of a system 400 for operation of the variable valve timing system 200 for a power unit 100, in accordance with an embodiment of the present subject matter.

[00017] Fig. 4 (b) depicts a method of operation of the system, which is shown in Fig. 4 (a), in accordance with an embodiment of the present subject matter.

DETAILED DESCRIPTION

[00018] Generally, the power unit is provided with plurality of valves. The plurality of valves corresponds to an intake and an exhaust of the power unit. For example, a basic configuration of valves may have a single intake valve and a single exhaust valve for intake of air-fuel mixture and for scavenging of exhaust gases, respectively. Depending upon the intake and the exhaust requirements, typically more than one valve is provided for intake and more than one valve is provided for exhaust. Generally, the plurality of valves is in normally closed condition and a valve timing mechanism is used to open each valve for a defined time interval. The valve timing mechanism comprises a camshaft for opening and closing the valves, wherein the camshaft can be driven by a chain driven.

[00019] Generally, a fixed valve timing is provided in smaller commuter vehicles like two-wheeler, three-wheelers or in small cars that incorporate power unit with lOOOcc or less. The term ‘valve timing’, typically refers to an opening time and a closing time of a valve. The fixed valve timing has fixed opening time and closing time of the valves with respect to a given combustion cycle of the IC engine. Since, the valve timing is dependent on the rotation of the crankshaft and the camshaft, a duration for which a valve is kept open keeps on reducing with increasing engine speed (due to increase in rotation per minute). The fixed valve timing of intake and exhaust system, significantly affects volumetric efficiency of the power unit. For example, during higher speeds of IC engine operation, breathability of the power unit may be affected due to a valve timing that is tuned for lower engine speeds. Similar problems may arise due to inadequate combustion time or inadequate scavenging time. As a consequence, the conventional IC engines perform efficiently only in a certain range of engine speed and the performance gets affected either at low speed or high speed.

[00020] Various attempts have been made in the past to address the above-stated problems relating to the fixed valve timing of the power unit by providing variable valve timing systems. However, such variable timing system are implemented in racing applications, or it is offered as a premium feature in vehicles owing to its cost and complexity. One such attempt was to achieve variable valve timing through cam profile switching. Such known systems suffer from the drawback of making the overall engine assembly bulkier. Thus, there has been a challenge to design the variable valve timing in compact power units like IC engines with single cylinder as the available space in cylinder head assembly region of such engines is small. The cylinder head typically has an additional requirement of adequate working space around its vicinity to enable operating space to service the system as well as its peripheral parts. Additionally, there is often need to install powertrain peripheral systems around the vicinity of cylinder head e.g. cooling system, sensors etc. which make the design more complex and difficult to achieve a compact engine layout. [00021] Further, the hydraulic based/ pressure-based systems that require provision of axial path inside the parts, makes the parts bulkier and the system requires maintenance at regular intervals due to use of hydraulics or pressure systems. Other setups such as a mechanical engaging unit between shafts for cam switching are also known in the art. However, the mechanical engaging units have higher weight to inertia thereby have the limitation of operating at higher engine speeds. Such engines with higher inertia require larger actuation system, which is a challenge in order to accommodate the same in compact power units. Further, such known systems are bulkier as camshaft is either axially extended to incorporate the switching system(s) or is radially extended to incorporate the hydraulic or mechanical actuation system making the camshaft and the valve timing assembly bulkier.

[00022] Thus, there is a need for providing a compact power unit with an improved variable valve timing system comprising a compact camshaft which overcomes all problems cited above and other problems of known art. The power unit needs to have a compact valve timing assembly in order to be packaged even in a small and compact power unit layout with an otherwise crowded cylinder head assembly portion.

[00023] Further, components used for variable valve timing system should have lower inertia in order to enable use of smaller actuation system that can be accommodated in even small sized engine and the lower inertia enables easy & reliable operation at higher speeds.

[00024] The present subject matter provides a power unit with a cylinder head assembly. The cylinder head assembly involves variable valve timing system with a camshaft comprising a first cam and a second cam for actuating one or more first valves. A first rocker arm corresponding to the first cam actuates the one or more first valves. A second rocker arm corresponding to the second cam enables actuation of the one or more first valve selectively. An engaging unit is configured to engage the first rocker arm with the second rocker arm through a first engagement whereby the system offers only minimal or negligible inertia. The present subject mater is capable of functioning effectively without any limitation even at higher speeds of operation of the power unit (analogous to speed of cam shaft and crankshaft). In a preferred embodiment, the engagement is a radial engagement. However, the first engagement can be atained by axial engagement along axis of the first rocker shaft.

[00025] In one embodiment, the first cam and the second cam are part of a cam shaft and are preferably disposed adjacent to each other thereby providing compact camshaft assembly. In one implementation, the first cam is low-lift cam and the second cam is a high-lift cam. The cam shaft is supported on a cylinder head assembly of the power unit.

[00026] In one embodiment, the first rocker arm comprises a valve end for engaging with the one or more first valves and a cam end, which is provided with a cam follower. The first rocker arm comprises a first aperture for mounting the first rocker arm to the first rocker shaft. The first rocker arm being provided with a first guide portion defining a first receiving portion for the first engagement. The first engagement is defined with respect to the first rocker shaft or with respect to an axis of the first rocker shaft.

[00027] In one embodiment, the first rocker arm comprises a first receiving portion extending from one side (peripheral side) of the first rocker arm towards other side (peripheral side). The first receiving portion is formed about a first engaging axis and the first engaging axis is configured to intersect with a shaft axis of the first rocker shaft in an orthogonal manner. The first receiving portion being provided for the first engagement through the engaging unit. The receiving portion is configured to pass through the aperture portion whereby the material addition done for creating the first receiving portion is compensated by material reduction done to create the same (as the receiving portion is a through hole, as per one implementation).

[00028] In one embodiment, the second rocker arm comprises a second aperture at one end and a roller member at other end. The second rocker arm being mounted to the first rocker shaft through the second aperture. The second rocker arm comprises a body portion forming a structural portion and at ends of the body portion, the second aperture and the roller end (cam end) are provided. The second arm does not have a valve end and hence, is smaller in length and lesser in weight when compared to the first rocker arm.

[00029] In one embodiment, the second rocker arm comprises a locking arm extending from the body portion along a direction of the shaft axis, which is analogous to an axis of the second aperture. The locking arm extends outward from the body portion. The locking arm is provided with a second receiving portion for the first engagement through the engagement unit.

[00030] In one embodiment, the second rocker arm is compactly disposed adjacent to the first rocker arm thereby creating a compact layout. Further, the locking arm is configured to be at least partially overlapping with the first rocker arm. Owing to the overlapping design of the locking arm with the first rocker arm, there is no requirement to provide any space between the first rocker and the second rocker arm thereby providing compactness.

[00031] In one embodiment, the second receiving portion is formed in a direction orthogonal to the direction of shaft axis of a first rocker shaft which is supporting the second rocker arm. Thus, the first engagement between the first rocker arm and the second rocker arm occurs through locking arm of the second rocker arm and the first receiving portion of the first rocker arm.

[00032] In one embodiment, the second receiving portion comprises a second engaging axis, which is configured to align with a first engaging axis of a first rocker arm thereby enabling first engagement therebetween. In one embodiment, the first engagement occurs through a linear motion, which is easier to perform.

[00033] In one embodiment, the first rocker shaft comprises a shaft receiving portion formed diametrically to extend from one circumferential side towards another circumferential side. The shaft receiving portion comprises a shaft engaging axis, which is orthogonal to a shaft axis. Further, the shaft axis is configured to intersect the shaft axis.

[00034] In one embodiment, the shaft engaging axis is configured to align with a first engaging axis of the fist rocker arm and a second engaging axis of the second rocker arm for first engagement.

[00035] In one embodiment, the engaging unit, being in a first condition of variable valve timing system, forms the first engagement between the first rocker arm and the first rocker shaft only. The first rocker arm and the first rocker shaft, in the first condition, pivot together during lift by the first cam (about the rocker shaft axis).

[00036] In one embodiment, the engaging unit in a second condition forms the first engagement between the first rocker arm, the first rocker shaft, and the second rocker arm, wherein the first rocker arm, the first rocker shaft, and the second rocker arm pivot together during lift by the second cam. Thus, in the actuated condition of the variable valve timing system, due to the first engagement, the first and second rocker arm pivot together, thereby creating variable timing.

[00037] In one embodiment, the engaging unit comprises a timing member capable of engaging with the first rocker arm, the first rocker shaft, and the second rocker arm, wherein the timing member being disposed in locking condition with the first rocker arm and the first rocker shaft.

[00038] In one embodiment, the timing member gets in a locking condition with the second rocker arm thereby getting into a second condition upon actuation by the engaging unit.

[00039] In one embodiment, the engaging unit comprises a timing member configured to slide about a first receiving portion of the first rocker arm, and about a shaft receiving portion of the first rocker shaft. Further, the timing member is configured to slide selectively about the second rocker arm depending on the condition of the engaging unit.

[00040] In one embodiment, the second rocker arm being angular is preloaded by an elastic member. The rocker arm is connected to an attachment portion of the second rocker arm and its other end being connected to a structural member of the power unit.

[00041] In one embodiment, the engaging unit being provided with a contact member that abuts a timing member. The timing member is an outward curve with reference to the timing member. The timing member slides with the first rocker shaft and is in constant connection with the contact member and thereby with an actuator of the engaging unit.

[00042] In one embodiment, the engaging unit comprises an actuator unit being disposed on a cylinder head-cover of the power unit , and the actuator unit being disposed at a first angle a with reference to an imaginary plane passing through an upper periphery of a cylinder head of the power unit , wherein the first angle being in a range of 20 to 160 degrees.

[00043] The inertia of the system as disclosed in the present invention is low. This is achieved by eliminating an additional shaft parallel to the first rocker shaft. As a result, the effort or force required for actuation of the rocker arms is lower. Further, the rocker arms can be operated with ease even at higher speeds of engine operation without any performance or inertia lag.

[00044] The first rocker arm and the second rocker arm are selectively engaged when the engaging unit is in an actuated condition whereby the engaging unit couples the first rocker arm and the second rocker along with the first rocker shaft. The assembly is supported by rollers of the first rocker shaft where it oscillates along with the rocker arms.

[00045] The coupling/ engagement is not restricted to mechanical means and includes other coupling means say magnetic coupling etc. Further, the rocker arm (say, second rocker arm) with a corresponding cam having a higher lift gets actuated first and due to the engagement or coupling between the rocker arms, other rocker arm (first rocker arm) is also actuated due to the engagement or coupling whereby a longer lift is achieved. The engagement is done for a pre-determined range of speed of the power unit/ engine speed. Thus, the rocker arms are selectively engaged.

[00046] It is a feature that the present invention with first cam comprising smaller lift enables provision of a decompression system coupled with the first cam and it is disposed adjacent to the first cam. Thus, the decompression system is not sandwiched between the cams, which would affect the compact layout of the rocker arms as additional space between the cams is to be provided for packaging the decompression system. Packaging the decompression system between the cams will also result in rocker arms being moved away from each other (as rocker arms work in conjunction with cams) thereby requiring a longer rocker shaft, which would add weight, occupy more space and add to the cost.

[00047] It is a feature that the power unit comprises an actuator and the actuator is functionally connected to the interlocking member through a pivot arm. The pivot arm is pivoted about a pivot point and the actuator is configured to actuate the pivot arm, which cause the pivot arm to pivot thereby causing movement of the engaging unit, especially the interlocking member.

[00048] It is a feature that the actuator includes a solenoid or an electric motor or the like. It is an aspect that a solenoid that requires power only to change condition from actuated to -non-actuated condition & vice-versa may be used, which consumes less power. As the effort required is less due to lower inertia, a small size actuator can be used. Further, the actuator can be mounted on the cylinder head assembly or cylinder head-cover while still achieving a compact cylinder head layout design which his easy to assemble as well as service.

[00049] According to another aspect, the present subject matter is capable of being incorporated in a three valve or a four-valve engine. Power unit with variable valve timing system as explained above can be installed on the intake side and the exhaust side, both in single overhead cam systems (SOHC) and double overhead cam systems (DOHC).

[00050] Thus, the present invention offers improved drive characteristics as the compact power unit so designed is capable of being implemented on a two-wheeler, a three-wheeler or a multi-wheeler, which is aimed at providing best low speed drivability with one low speed cam - for city condition; best high speed drivability with high speed cam lobe - for racing condition; and best low speed & high speed condition - combination of city & highway conditions.

[00051] It is a feature that the system is operated or the switching is performed at higher gears, where the power unit is operated at higher engine speed thereby providing improved acceleration.

[00052] In an embodiment, as the variable valve timing system is actuated using an actuator, the cutoff speed can be varied for different applications, and the actuation can be done using controller/ ECU or a manually operated switch.

[00053] In one embodiment, when using an electronic actuator for the variable valve timing system, an electronic throttle can be synchronized to close in order to reduce speed for synchronization and engagement between cams.

[00054] These and other advantages of the present subject matter would be described in greater detail in conjunction with an embodiment of a power unit with the figures in the following description. Various other features and embodiments of the present subject matter here will be discernible from the following further description thereof, set out hereunder.

[00055] The detailed explanation of the present invention is explained with the help of a single cylinder type IC engine but the concepts introduced herein are applicable to multi-cylinder engines with single overhead cam (SOHC) or dual overhead cams (DOHC).

[00056] 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.

[00057] Arrows wherever provided on top right comer of the figure represent direction with respect to vehicle. Arrow F represents forward direction, arrow R represents rearward direction, arrow UW represents upward direction and arrow DW represents downward direction.

[00058] Fig. 1 illustrates a front perspective view of a power unit, in accordance with an embodiment of the present subject matter. The power unit 100 is an internal combustion engine with or without an electrically assisting motor. Hereinafter, the terms ‘power unit’ and ‘internal combustion (IC) engine’ are interchangeably used. The power unit 100 includes a crankcase assembly 104, 105, a cylinder block 103 coupled to the crankcase assembly 104, 105 and a cylinder head assembly 102 coupled to the upper part of the cylinder block 103, as per the depicted embodiment. A cylinder head-cover 101 is mounted to the cylinder head assembly 102 for covering a valve train system and other components mounted thereon. In the present embodiment, the cylinder block 103 defines a cylinder portion (not shown), which when assembled in a vehicle is a forwardly inclined type cylinder axis inclined with respect to a vertical direction of the vehicle so as to enable minimizing the overall size of the power unit. A reciprocating piston (not shown) is slidably fitted in the cylinder block 103 and the reciprocating piston is connected via a connecting rod (not shown) to a crankshaft (not shown). The crankshaft (not shown) is rotatably supported by the crankcase assembly 104, 105. The crankcase assembly 104, 105 is mounted with one or more covers 125 for covering components supported by the crankcase assembly 104, 105 from lateral direction(s) RH-LH.

[00059] The cylinder head assembly 102 comprises an intake port 114 (shown in Fig. 2 (a)) and an exhaust port (not shown) formed thereon. The intake port 114 allows air-fuel mixture to enter the combustion chamber, whereas after combustion of the air-fuel mixture, the exhaust gases are scavenged out of the combustion chamber through the exhaust port. A plurality of valves is provided in the cylinder head assembly 102, and the plurality of valves are closed and opened at perdetermined timing to facilitate intake and exhaust process. In the depicted embodiment, the power unit 100 comprises two valves viz. a first valve 218 (shown in Fig. 2 (a)) and a second valve 217 (shown in Fig. 2 (a)).

[00060] Fig. 2 (a) depicts a schematic side view of a cylinder head assembly in accordance with an embodiment of the present subject matter. The cylinder head assembly 102 supports plurality of valves that cater to the intake side and exhaust side. Plurality of valves are driven by a camshaft 210 rotatably supported in the cylinder head assembly 102 so as to open and close the plurality of valves. Rotational power is transmitted from the crankshaft (not shown) to the camshaft 210 by a timing transmission mechanism (not shown). In an embodiment, the timing transmission mechanism includes a drive sprocket (not shown) supported on the crankshaft, a driven sprocket supported on the camshaft and an endless cam chain (not shown) connecting the drive sprocket with the driven sprocket (not shown).

[00061] The cylinder head assembly 102 defines a peripheral wall portion 110 with plurality of fins 290 defined on the periphery. Further, the camshaft 210 is rotatably supported on the cylinder head assembly 102. As per one embodiment, the mounting-schema of an engaging unit 240 forming part of a variable valve timing system 200 is depicted. In one embodiment, the engaging unit 240 comprises an actuator unit 205, which is disposed on the cylinder head-cover 101 of the power unit 100. The actuator unit 205 is disposed with its actuator axis A-A’ configured along a first angle a with reference to an imaginary plane P-P’ passing through or being parallel to an upper periphery UPP of the cylinder head assembly 102. In a preferred implementation, the first angle a is in a range of 20 to 160 degrees with reference to the plane P-P’. A variable valve timing system 200 is configured to vary a lift time of one or more valves of the plurality valves of the power unit. As per another embodiment, the axis A-A’ of the actuator 205 is configured substantially parallel to at least one of a valve axis V-V’ of a valve (preferably the second valve 217) of the cylinder head assembly 102.

[00062] Fig. 2 (ba) depicts a schematic perspective view of the variable valve timing system, in accordance with an embodiment of the present subject matter. Fig. 2 (bb) illustrates an exploded view of various components of a variable valve timing system 200, in accordance with an embodiment of the present subject matter. The cam shaft 210 comprises of one or more bearings 210A, 210B for rotatably supporting the camshaft 210 on to the cylinder head assembly 102. In the depicted embodiment, the camshaft 210 is rotatably supported by a first bearing 210A and 210B provided on either ends thereof. Further, camshaft 210 comprises a sprocket (not shown) for being driven by the crankshaft through a cam chain or any actuator. The camshaft 210 comprises plurality of cams with cam lobes to drive the first valve 218, and the second valve 217 (shown in Fig. 2 (a)) through corresponding rocker arms.

[00063] In the present embodiment, the camshaft 210 comprises a first cam 211, and a third cam 213. The third cam 213 comprises a third cam lobe (not labelled) for driving the second valve 217. The third cam 213 enables oscillation of a third rocker arm (not shown) thereby causing opening/ closing of the second valve 217. Further, the present invention provides the variable valve timing system for altering of opening/ closing time of the first valve 218. The variable valve timing system 200 (hereinafter ‘variable valve timing system’ may be briefly referred to as ‘system’) comprises an actuator 205 for enabling change of valve timing.

[00064] Further, the camshaft 210 comprises a first cam 211 with a first cam lobe (not labelled) that drives the first valve 218 through a first rocker arm 220. The first rocker arm 220 oscillates about a first rocker shaft 225 placed substantially parallel to a cam axis C-C’ of the camshaft 210. The first rocker shaft 225 is rotatably supported by plurality of rollers 229. The rollers 229 enable in reducing the friction. A valve end 221 of the first rocker arm 220 is disposed to be in contact with the first valve 218. Thus, upon rotation of the first cam lobe of the first cam 211, a cam follower 222 of the first rocker arm 220 is lifted thereby causing the first rocker arm 220 to pivot about the rocker shaft axis S-S’ of the first rocker shaft 225 causing the first valve 218 to move down thereby creating opening of the port.

[00065] The camshaft 210 includes a second cam 212 with a second cam lobe (not labelled), which is disposed adjacent to the first cam 211. Further, the system 200 comprises a second rocker arm 230 corresponding to the second cam 212. The second cam 212 is capable of driving/operating the second rocker arm 230. In one embodiment, the second rocker arm 230 is also supported about first rocker shaft 225 and it oscillates about the first axis S-S’. The second rocker arm 230 comprises a cam follower 232 that engages with the second cam 212. In one embodiment, the first cam 211 is a low-lift cam and the second cam 212 is a high-lift cam. The low- lift and high-lift is with reference to the timing of lift of valve.

[00066] The first rocker arm 220, the second rocker arm 230 are supported on the first rocker shaft 225. The second rocker arm 230 is provided with an elastic member 235 to exert angular preload on the second rocker arm 230. In one implementation, the elastic member 235 is a torsion spring, which has one end 236 connected to the second rocker arm 230 (at an attachment portion 230T) and other end 237 thereof locked with a structural member (not shown). The structural member can be a portion of the cylinder head assembly 102 or cylinder head-cover 101 or the like. Further, the variable valve timing system 200 comprises an engaging unit 240. The engaging unit 240 is configured to engage radially with first rocker arm 220 or both the first rocker arm 220 and the second rocker arm 230 based on radial depth of first engagement by the engaging unit 240. In other words, an actuator unit 205 is configured to engage the first rocker arm 220 with the second rocker arm 230 through a first engagement configured through a radial engaging timing member 245 and an engaging means 233 provided on the second rocker arm 230. The engaging unit 240 comprises a timing member 245, which is actuated by the actuator unit 205. A timing member 245 is configured to selectively engage with either the first rocker arm 230 or with both the first rocker arm 220 and the second rocker arm 235. The engaging unit 240, which is radially disposed to the rocking axis S-S’ of the rocker arms 220, 230 is configured to perform first engagement 265 therebetween through radial movement of the engaging timing member 245. In one implementation, the first engagement 265 comprises enabling elements including the timing member 245, the first guide portion 223 and the locking arm 233. In a preferred embodiment, the engagement is a radial engagement occurring in a radial direction. However, the first engagement can be attained by axial engagement along axis of the first rocker shaft.

[00067] The actuator 205, as per one embodiment, is mounted to the cylinder headcover 101. The actuator 205 comprises a flange portion 206 and one or more mounting points 207. Through the mounting points 207 of the flange portion, the actuator 205 is secured. The timing member 245 extends from the actuator 205 into the cylinder head-cover 101 to engage with the first rocker arm 220 and the second rocker arm 230. As per an aspect of the present invention, the rocker arm 220 is configured with an engaging guide portion 223 (shown in Fig 2(c)) in form of a boss in a radial direction configured with a receiving portion 224 (shown in Fig 2(c)), to receive the timing member 245 thereat wherein the timing member 245 passes through an opening in the receiving portion 224. As per an aspect of the present invention, the timing member 245 is configured to move in an oscillatory manner through the said opening in the rocker arm 220 wherein the timing member after slidably passing through an opening of the first rocker shaft 225 is further being capable of sliding through a co-axial opening 234 (shown in Fig 2(d) of the second rocker arm 230 thereby resulting in a synchronized engagement of the first rocker arm as well as the second rocker arm 230.

[00068] Fig. 2 (c) illustrates an enlarged perspective view of the first rocker arm 220, in accordance with an embodiment of the present subject matter. The first rocker arm 220 comprises the valve end 221 and a cam end with a cam follower 222. A first aperture 220A is provided for mounting the first rocker arm 220 to the first rocker shaft 225. Further, the first rocker arm 220 comprises a first guide portion 223. About the first guide portion 223, a first receiving portion 224 is formed. The first receiving portion 224 extends from one side of the first rocker arm 220 towards other side (diametrically). The first receiving portion 224 passes through the first aperture 220A. Further, a first engaging axis E-E’ is defined about the first receiving portion 224. In one embodiment, the first engaging axis E-E’ intersects with the rocker shaft axis S-S . The timing member 245 (shown in Fig. 2 (b)) is slidable through the first receiving portion 224.

[00069] Fig. 2 (d) illustrates an enlarged perspective view of the second rocker arm, in accordance with an embodiment of the present subject matter. The second rocker arm 230 comprises a second aperture 230A, which is provided at one end thereof. At other end of the second rocker arm 230, the roller member 232 is provided. The second aperture 230A extends in a direction orthogonal to direction of extension of second rocker arm 230. Through the second aperture 230A, the second rocker arm 230 is mounted to the first rocker shaft 225.

[00070] Further, the second rocker arm 230 comprises a body portion 230B, which forms the structural portion that forms the cam end and the aperture portion 230A and a portion between them. The second rocker arm 230 comprises a locking arm

233, which extends from the body portion 230B along the direction of the rocker shaft axis S-S’, which is co-axially aligned to an axis of the second aperture (not marked, as it overlaps with S-S’). The locking arm 233 is provided such that it does not interfere with the aperture portion 230A when axially outwards of the body portion 230B. In an assembled condition, the body portion 230B would be disposed adjacent to the first rocker arm 220 (shown in Fig. 2 (b)). The locking arm 233 is configured to be at least partially below the first rocker arm 220 (in assembled condition). Further, the locking arm 233 is provided with a second receiving portion

234, which extends in a direction orthogonal to the direction of rocker shaft axis S- S’. An axis of second receiving portion is referred to as a second engaging axis El- El’. In an assembled condition, the second receiving portion 234 aligns with the first receiving portion 224 of the first rocker arm 220. Depending on radial and linear depth of movement of the timing member 245, the timing member 245 engages with only the first rocker arm 220 or with both the first rocker arm 220 and the second rocker arm 230 (first engagement 265).

[00071] Fig. 2 (e) illustrates an enlarged perspective view of the first rocker shaft, in accordance with an embodiment of the present subject matter. The first rocker shaft 225 in accordance with one embodiment, is a cylindrical member. The rocker shaft 225 has a first end 226 and a second end 227. The first rocker shaft 225 comprises the shaft axis S-S’, which coincides with a long axis thereof. The first rocker shaft 225 comprises a timing member receiving portion 228, which is formed in a direction orthogonal to the shaft axis S-S’. In other words, the timing member receiving portion 228 is formed diametrically to extend from a circumferential portion towards a circumferential portion on opposite side. In an assembled condition, the timing member receiving portion 228, which comprises a shaft engaging axis E2-E2’, aligning with the first engaging axis E-E’ of the fist rocker arm 220 and the second engaging axis El -El’.

[00072] Fig. 2 (f) illustrates a schematic axial view of the variable valve timing system, in accordance with an embodiment of the present subject matter. The first rocker arm 220 and the second rocker arm 230 are supported on the first rocker shaft 225. In the variable valve timing system 200, the second rocker arm 230 at least partially overlaps with the first rocker arm 220. In one embodiment, the second rocker arm 230 is shorter in length (length between the shaft axis S-S’ and the roller rolling member axis (not labelled)) when compared to the first rocker arm 220 thereby making the system 200 further compact. In the depicted view, the locking arm 233 that along the rocker shaft axis S-S’ (shown in Fig. 2 (c)) extends below the first rocker arm 220, without interfering with any structural or functional features of the first rocker arm 220. The cam ends of both the rocker arms 220, 230 rest on the respective cam lobes. The timing member 245, which in one embodiment is a cylindrical timing pin (not by limitation), shown in dotted line, is capable of engaging with the first rocker arm 220, the first rocker shaft 225, and the second rocker arm 230. The timing member 245 is radially and linearly slidable through the first receiving portion 224, the timing member receiving portion 228, and into the second engaging portion 234 (all three shown in respective part level figures). In a first condition, the timing member 245 engages with the first rocker arm 220 and the first rocker shaft 225 only. In a second condition, the timing member 245 engages with the first rocker shaft 225, the first rocker 220 and the second rocker arm 230 thereby forming a combined first engagement 265. The timing member 245 radially extends into the receiving portions of the rocker arms 220, 230 and the rocker shaft 225 to establish an engagement therebetween. In other words, the timing member 245 enables engagement of the first rocker arm 220 with the second rocker arm 230 through the first engagement. [00073] In one embodiment, the engaging unit 240 is provided with a contact member 250. As shown in Fig. 2 (f), the contact member contacts the timing member 245. Specially, contact member 250 abuts with an end of the timing member 245 and other end of timing member 245 slides inside the rocker arms and rocker shaft. In one embodiment, the contact member 250 is an outward curve with reference to the timing member 245. The timing member 245, which is pivoting with the first rocker shaft 225 is configured to be in constant connection/ preloaded physical contact with the contact member 250 in order to maintain the timing member 245 to be in an engaged condition with the second contact member 250. In one embodiment, the timing member 245 is spring loaded. Thus, when the actuator unit 205 is disengaged, the timing member 245 returns to the non-actuated condition (from the second rocker arm 230).

[00074] The first condition and the second condition are achieved by actuation of the actuator unit 205, which further linearly actuates the timing member 245. The first condition and the second condition are explained through the following description in conjunction with Figs. 2 (g) & 2 (h). The actuator 205 can be a small sized solenoid (actuator 205 shown in Fig. 2 (a) is enlarged of explanation purposes and is not to be considered in relative size terms with other components). Further, the actuator can be a solenoid or the like that requires power only to change from one state/ condition to another state/ condition thereby requiring low power. The system may include an electronic control unit (ECU) (not shown) or an integrated controller or a manual switch to enable the actuation of the system 200. For engagement, when there is misalignment between the receiving portion, the control unit/controller waits for synchronization moment and then performs the first engagement 265 by linear movement of the timing member 245.

[00075] Figs. 2 (g) illustrates a sectional view of the variable valve timing system, with section taken along axis A-A’, in accordance with an embodiment of the present subject matter when only first rocker arm is engaged. Fig. 2 (h) illustrates another sectional view of the variable valve timing system, with section taken along axis B-B’ when both first and second rocker arm are engaged, in accordance with an embodiment of the present subject matter. Fig. 2 (g) illustrates the first conditions, and Fig. 2 (h) illustrates the second condition. The first condition is denoted by reference sign 260 and the second condition is denoted by reference sign ‘270’

[00076] In the first condition 260, the actuator unit 205 is in a non-actuated condition. The timing member 245 is in engagement with the first receiving portion 224 and the timing member receiving portion 228 only. Therefore, the first rocker arm 220 and the first rocker shaft 225 are in an engaged condition. When the first cam 211 lifts the first rocker arm 220 and the first rocker shaft 225 also pivots with the first rocker arm 220, as they are in engagement with the timing member 245. As can be seen in Fig. 2 (g), the timing member 245 stops within the first rocker arm 220 and does not extend into the second rocker arm 230. Even though the second cam 212 causes a lift of the second rocker arm 230, its does not get transferred to the first rocker arm 220 and consequently to the first valve 218. The timing member 245 also pivots along with the first rocker shaft 225 and the first rocker arm 220. Moreover, the second rocker arm 230 is restricted from free movement by the elastic member 235. In one embodiment, the system 200 comprises a decompression unit 280 (shown in Fig. 2 (g)) disposed adjacent to the third cam 213.

[00077] In the second condition as depicted in Fig. 2 (h), the timing member 245 extends into the second receiving portion 234. The timing member 245 is radially actuated causing the timing member 245 to move further into the second receiving portion 234 in a linear manner. Thus, the timing member 245 engages with the first rocker arm 220, the first rocker shaft 225 and the second rocker arm 230. In such a condition, all the aforementioned three elements move/pivot as a single unit. Further, the second cam 212, which is high-lift cam, engages with the second rocker arm 230 causing it to lift thereby causing the first rocker arm 220 also to be pivot with a high lift. The valve end 221 of the rocker arm 220 causes the first valve 218 to be actuated. Further, the timing member 245, which is critical part for first engagement is substantially (80% or more) enclosed inside the rocker arms 220, 230 and the rocker arm shaft 225, whereby only the actuator is disposed radially outward.

[00078] Fig. 3 depicts an exemplary graph of valve timing system in an engaged and a disengaged condition, in accordance with an embodiment of the present subject matter. In the present embodiment, the variable valve timing system is configured on the intake valves. The curve E represents a lift of exhaust valve/ second valve 217. The curves IC and I represent a valve lift of the intake valve(s)/ first valve(s) 218 according to an engaged or disengaged (actuated or unactuated) condition of the variable valve timing system 200, respectively. In an unactuated condition, the first valve 218 has smaller valve lift, represented by curve I, due to a first cam and corresponding first rocker arm actuating the valves. In an actuated condition or the second condition 270, the first valves 218 undergoes a larger lift, represented by curve IC, due to the second cam and corresponding second rocker arm actuating the first valves 218. Further, in the actuated condition, the second rocker arm and the first rocker arm are in an engaged condition and the second cam drives the second rocker arm. The present invention enables variable valve timing even at higher speeds without settling to a fixed valve lift that would be between curve I and curve IC.

[00079] Fig. 4 (a) a schematic view of a system 400 for operation of the variable valve timing system 200 for a power unit 100, in accordance with an embodiment of the present subject matter. The system 400 comprises of a first rocker shaft 225. A first rocker arm 220 is mounted to the first rocker shaft 225. A second rocker arm 230 is mounted to the first rocker shaft 225. In the depicted schematic view, the first rocker arm 220, the first rocker shaft 225, and the second rocker arm 230 are shown as concentric circles for ease of depiction (not to be considered as a limitation). Further, the system 200 comprises an electronic control unit 430 configured to actuate an engaging unit 240 to connect the first rocker arm 220 with the second rocker arm 230 through a first engagement 265 based on one or more inputs 405, 410, 420. The one or more inputs includes, but not limited to, a rider input 405 like a switch, which the user can manually control. Further, one or more inputs includes a rider mode input 410, which includes a ride mode tuning of the power unit, which may a terrain change mode, a rain mode, an ABS modification mode etc. Further, the one or more inputs includes a power unit-speed sensor 420, which is used by the electronic control unit 430 to actuate the second rocker arm 230 thereby creating a higher lift of a corresponding valve. [00080] Further, the system 400 includes an engaging unit 240 that comprises an actuator 205 for causing a linear movement of the timing member 245 thereby creating the first engagement 265.

[00081] Fig. 4 (b) depicts a method of operation of the system 400, which is shown in Fig. 4 (a), in accordance with an embodiment of the present subject matter. The method comprises a first step S450, at which the electronic control unit 430 receives one or more inputs 405, 410, 420. The one or more inputs includes a rider input 405, a ride mode input 410 and a power unit-speed sensor 420. At step S455, the electronic control unit 430 identifies a synchronization moment between a first rocker arm 220 and a second rocker arm 230 of the variable valve timing system 200. The electronic control unit 430 then at step S460 actuates a timing member 245 of the variable valve timing system 200 causing the first rocker arm 220 to engage with the second rocker arm 230 through a first engagement 265.

[00082] It is to be understood that the aspects of the embodiments are not necessarily limited to the features described herein. Many modifications and variations of the present subject matter are possible in the light of above disclosure. Therefore, within the scope of claims of the present subject matter, the present disclosure may be practiced other than as specifically described.

List of reference signs:

100 power unit 230 second rocker arm

101 cylinder head-cover 230T attachment portion

102 cylinder head assembly 35 230A second aperture

103 cylinder block 230B body portion

104. 105 crankcase assembly 232 roller member

110 peripheral wall portion 233 locking arm

114 intake port 234 second receiving portion

200 variable valve timing 40 235 elastic member system 236 one end (elastic member)

205 actuator unit 237 other end

206 flange portion 240 engaging unit

207 mounting points 245 timing member

210 camshaft 45 250 contact member

210A, 210B bearings 260 first condition

211 first cam 265 first engagement

212 second cam 270 second condition

213 third cam 280 decompression unit

218 first valve 50 290 fins

219 second valve A-A’ actuator axis

220 first rocker arm V-V’ valve axis

220A first aperture C-C’ cam axis

221 valve end (first rocker arm) D 1 first diameter

222 cam follower (first rocker 55 D2 second diameter arm) E-E’ first engaging axis

223 first guide portion El -El’ second engaging axis

224 first receiving portion E2-E2’ shaft engaging axis

225 first rocker shaft S-S’ first axis

226 first end 60 UPP upper periphery

227 second end P-P’ plane

228 shaft receiving portion 400 system

229 rollers 405 rider input ride mode input 430 electronic control unit power unit-speed sensor

Claims

We claim:

1. A power unit ( 100) comprising: a variable valve timing system (200) comprising: a first cam (211) for actuating one or more first valves (218) through a first rocker arm (220 ), the first rocker arm (220 ) pivotable about a first axis (S-S’) of a first rocker shaft (225); a second cam (212) for selectively actuating the one or more first valves (218) through a second rocker arm (230), the second rocker arm (230) pivotable about the first axis (S-S’); and an engaging unit (240) configured to engage the first rocker arm (220) with the second rocker arm (230) through a first engagement (265).

2. The power unit (100) as claimed in claim 1, wherein the first cam (211) and the second cam (212) being part of a cam shaft (210), wherein the cam shaft (210) being supported on a cylinder head assembly (102) of the power unit (100).

3. The power unit (100) as claimed in claim 1, wherein the first engagement (265) being a radial engagement (265), an axial engagement along axis (S-S’).

4. The power unit (100) as claimed in claim 1, wherein the radial engagement (265) being achieved through a timing member (245) of the engaging unit (240), wherein the timing member (245) causes engagement of the first rocker arm (230) with the second rocker arm (230).

5. The power unit (100) as claimed in claim 1, wherein the first rocker arm (220) comprises a valve end (221) for engaging with the one or more first valve(s) (218) and a cam end being provided with a cam follower (222), wherein the first rocker arm (220) comprises a first aperture (220A) mounting the first rocker arm (220) to the first rocker shaft (225), and the first rocker arm (220) being provided with a first guide portion (223) defining a first receiving portion (224).

6. The power unit (100) as claimed in claim 5, wherein the first rocker arm (220) comprises the first receiving portion (224) extending from one side of the first rocker arm (220) towards other side, wherein the first receiving portion (224) being formed about a first engaging axis (E-E’).

7. The power unit (100) as claimed in claim 6, wherein the first engaging axis (E-E’) being form to intersect a shaft axis (S-S’) of the first rocker shaft (220) orthogonally, and the first receiving portion (224) being provided for the first engagement (265).

8. The power unit (100) as claimed in claim 1, wherein the second rocker arm (230 ) comprises a second aperture (230A) at one end and a roller member (232) at other end, the second rocker arm (230) being mounted to the first rocker shaft (225) through the second aperture (230A), wherein second rocker arm (230 ) comprises a body portion (230B) forming a structural portion.

9. The power unit (100) as claimed in claim 6, wherein the second rocker arm (230 ) comprises a locking arm (233) extending from the body portion (230B) along a direction of the shaft axis (S-S’) being co-axially aligned to an axis of the second aperture (S-S’), and wherein the locking arm (233) being provided with a second receiving portion (234) for the first engagement (265).

10. The power unit (100) as claimed in claim 7, wherein the second rocker arm (230) being disposed adjacent to a first rocker arm (220), and the locking arm (233) being configured to be at least partially overlapping with the first rocker arm (220).

11. The power unit (100) as claimed in claim 6, wherein the second receiving portion (234) being formed in a direction orthogonal to the direction of shaft axis (S-S’) of a first rocker shaft (225) supporting the second rocker arm (230).

12. The power unit (100) as claimed in claim 6, wherein the second receiving portion (234) comprises a second engaging axis (El -El’), the second engaging axis (El-E’) configured to align with a first engaging axis (E-E’) of a first rocker arm (220).

13. The power unit (100) as claimed in claim 1, wherein the first rocker shaft (225) comprises a timing member receiving portion (228) formed diametrically to extend from a circumferential side towards another circumferential side, wherein the timing member receiving portion (228) comprises a shaft engaging axis (E2- E2’), the shaft engaging axis (E2-E2’) being orthogonal to the shaft axis (S-S’) and intersecting the shaft axis (S-S’).

14. The power unit (100) as claimed in claim 13, wherein the shaft engaging axis (E2-E2’) being configured to align with a first engaging axis (E-E’) of the fist rocker arm (220) and a second engaging axis (El -El ) of the second rocker arm (230) for first engagement (265).

15. The power unit ( 100) as claimed in claim 1 , wherein the engaging unit (240) in a first condition (260) forms the first engagement (265) between the first rocker arm (220) and the first rocker shaft (225), and wherein the first rocker arm (220) and the first rocker shaft (225) pivot together during lift by the first cam (211) about the rocker shaft axis (S-S’) to actuate at least one of an inlet valve and an exhaust valve of the IC engine.

16. The power unit ( 100) as claimed in claim 1 , wherein the engaging unit (240) in a second condition (270) forms the first engagement (265) between the first rocker arm (220), the first rocker shaft (225), and the second rocker arm (230), wherein the first rocker arm (220), the first rocker shaft (225), and the second rocker arm (230) pivot together during lift by the second cam (211) o actuate at least one of an inlet valve and an exhaust valve of the IC engine.

17. The power unit ( 100) as claimed in claim 1 , wherein the engaging unit (240) comprises a timing member (245) capable of engaging with the first rocker arm (220), the first rocker shaft (225), and the second rocker arm (230), wherein the timing member (245) being disposed in locking condition with the first rocker arm (220) and the first rocker shaft (225).

18. The power unit (100) as claimed in claim 15, wherein the timing member (245) getting in a locking condition with the second rocker arm (230) thereby getting into a second condition (270) upon actuation by the engaging unit (240).

19. The power unit ( 100) as claimed in claim 1 , wherein the engaging unit (240) comprises a timing member (245) configured to slide about a first receiving portion (223 ) of the first rocker arm (220), about a timing member receiving portion (228 ) of the first rocker shaft (225), and selectively about the second receiving portion (234) of the second rocker arm (230).

20. The power unit (100) as claimed in claim 1, wherein the second rocker arm (230) being angularly preloaded by an elastic member (235), wherein one end (236) of the second rocker arm (230) being connected to an attachment portion (230T) of the second rocker arm (230) and other end (237) being connected to a structural member of the power unit (100).

21. The power unit ( 100) as claimed in claim 1 , wherein the engaging unit (240) being provided with a contact member (250) that abuts a timing member (245), wherein the contact member (250) being an outward curve with reference to the timing member (245 ), and wherein the timing member (245) sliding with the first rocker shaft (225) being in physical abutting connection with the contact member (250) and thereby with an actuator (205) of the engaging unit (240).

22. The power unit ( 100) as claimed in claim 1 , wherein the engaging unit (240) comprises an actuator unit (205 ) being disposed on a cylinder head-cover (101) of the power unit (100), and an actuating axis (A-A’) of the actuator unit (205) being disposed at a first angle (a) with reference to an imaginary plane (P-P’) passing through an upper periphery (UPP) of a cylinder head assembly (102) of the power unit (100), wherein the first angle (a) being in a range of 20 to 160 degrees.

23. The power unit (100) as claimed in claim 23, wherein the actuator axis (A- A’) being disposed substantially parallel to a valve axis (V-V’) of a second valve (217) of the power unit (100).

24. The power unit ( 100) for a motor vehicle as claimed in any of the preceding claims, wherein the power unit (100) being fixedly mounted or swingably mounted to the vehicle

25. A second rocker arm (230) for a power unit (100), the second rocker arm (230) comprising: a body portion (230B), the body portion (230B) comprises a cam end at one end and an aperture portion (230A) at other end; a locking arm (233), the locking arm (233) extends from the body portion (230B) along a direction of a shaft axis (S-S’) of the aperture portion (230A); the locking arm (233) being provided with a second receiving portion (234), the second receiving portion (234) comprises a second engaging axis (El -El’), and the second engaging axis (El -El’) being orthogonal to the shaft axis (S-S’) and intersecting with the shaft axis (S- S’).

26. A rocker arm assembly the rocker arm assembly comprising: a first rocker arm (220), the first rocker arm (220) being supported by a first rocker shaft (225); a second rocker arm (230), the second rocker arm (230) being supported by the first rocker shaft (225); and a timing member (245), wherein the first rocker arm (220) being provided with a first receiving portion (224), the second rocker arm (230) being provided with a second receiving portion (234), the first rocket shaft (225) being provided with a shaft receiving portion (228) having a shaft engaging axis (E2-E2’), wherein the shaft engaging axis (E2-E2’) being configured to align with a first engaging axis (E-E’) of the first receiving portion (224) and a second engaging axis (El- E’) of the second receiving portion (234), and the timing member (245) configured to engage the first rocker arm (220) with the second rocker arm (230) along the shaft engaging axis (E2- E2’) through a first engagement (265).

27. A system (400) of operation of a variable valve timing system (200) for a power unit (400), the system comprising: a first rocker shaft (225); a first rocker arm (220), the first rocker arm (220) being mounted to the first rocker shaft (225); a second rocker arm (230), the second rocker arm (230) being mounted to the first rocker shaft (225); and an electronic control unit (430) configured to actuate an engaging unit (240) to connect the first rocker arm (225) and the second rocker arm (230) through an engagement (265) based one or more inputs (405, 410, 420).

28. The system (400) as claimed in claim 23, wherein the engaging unit (240) comprises an actuator (205) for causing a linear movement of the timing member (245) thereby creating the first engagement (265).

29. The system (400) as claimed in claim 23, wherein the one or more inputs includes a rider input (405), a ride mode (410), and a speed value from a power unit-speed sensor (420).

30. A method of operation of a variable valve timing system (200, 400) for a power unit (100), wherein the method comprising step of: receiving one or more inputs by an electronic control unit (430), the one or more inputs including a rider input (405), a ride mode input (410) and a power unit-speed sensor (420); identifying a synchronization moment between a first rocker arm (220) and a second rocker arm (230), of the variable valve timing system

(200), by the electronic control unit (430); and actuating a timing member (245), of the variable valve timing system (200, 400), to cause the first rocker arm (220) to engage with the second rocker arm (230) through a first engagement (265).