A VARIABLE VALVE TIMING SYSTEM
FIELD OF THE INVENTION
[0001] The subject matter as described herein, relates generally to an
internal combustion engine and more particularly, but not exclusively, to a.cam switching based variable valve timing system for an internal combustion engine.
BACKGROUND OF THE INVENTION
[0002] A conventional internal combustion engine converts chemical
energy into mechanical energy by combustion of air-fuel mixture within a combustion chamber of the engine. The said engine, among other components, has a cylinder comprising a cylinder head atop the cylinder and receiving a reciprocating piston from the bottom. On combustion of the air-fuel mixture, the piston transfers the energy generated during combustion to a crankshaft through a connecting rod thereby driving the crankshaft. In this way, the reciprocatory motion of the piston is converted to rotatory motion of the crankshaft. The crankshaft rotation then powers the vehicle.
[0003] The crankshaft transmits its drive to valve train through a
camshaft. A timing chain provided therebetween synchronizes the rotation of crankshaft and camshaft so that the valves in the valve train open and close at the proper times during the intake and exhaust strokes. It causes the valves to open and close at very specific intervals for optimum operation of engine.

[0004] Despite being far more powerful and fuel efficient than their
predecessors, present generation engines have several inherent compromises in their operation. One of the biggest drawbacks with them is the fixed valve timing regardless of engine speed. Hence, though these engines have optimal valve timing for a specific engine speed, they run sub optimally at all other speeds. Valve timing significantly affects volumetric efficiency which has great influence on engine torque, emissions and drivability. Thus, the timing of the valves has to be continuously changed with engine speed for obtaining the highest volumetric efficiency.
[0005] Therefore, such cam-driven engines use variable valve timing
systems to adjust valve lift or duration or both in associated valves in the engine cylinder. With variable valve timing, optimal valve opening and closing times can be achieved at every engine speed and engine performance is improved. In one of the ways to achieve variable valve timing, the engine may incorporate cam profile switching mechanism which allows for independently changing valve timing and valve lift by switching between independent cam profiles. Generally, one cam profile is used for low engine speed/load conditions and one other profile is used for high engine speed/load conditions to achieve fuel economy benefits. Such a . change in valve lift with engine speed can lead to torque increase over the entire operating range of the engine. Presently, the mechanisms available for cam profile switching are very complex and involve a lot of components. These are difficult to incorporate in a small engine which has space and layout constraints. Further, they

also require a lot of force and hydraulic pressure for actuation of the cam profile switching mechanism.
SUMMARY OF THE INVENTION
[0006] An object of the present subject matter is to disclose a cam profile
switching based variable valve timing system to switch between different cam lobe profiles. Another object of this subject matter is to selectively engage at least two different cam profiles based on engine speed in a three valve internal combustion engine for opening and closing of gas exchange valves. Yet another object of the present subject matter is to actuate the cam profile switching mechanism by using minimal energy and minimal components.
[0007] To this end, the present invention discloses an internal combustion
engine having a cylinder head with a plurality of valves. A first cam operates a first valve through a first rocker arm. A second cam jointly operates a second valve and a third valve through a second rocker arm. A third cam selectively operates the second rocker arm through a cam profile switching mechanism comprising a third rocker shaft supporting a third rocker arm, an axially slidable engaging member and a locking member. The engaging member and the third rocker shaft are connected to each other so that their relative radial movement is locked.
[0008] When the engaging member engages and locks with the locking
member, the third cam having bigger lobe height and duration drives the second rocker arm and the second cam is functionally deactivated. In an embodiment, the

cam profile switching mechanism is actuated during high engine speed operation and deactivated during low engine speed operation. The present invention, achieves two different valve lift modes through aforementioned cam profile switching mechanism which thus leads to variable valve timing at different engine speeds and optimises the engine efficiency. The aforementioned mechanism is a very simple and easily implementable in a small engine without any significant changes to the cylinder head.
[0009] The foregoing objectives and summary is provided to introduce a
selection of concepts in a simplified form, and is not limiting. To fully appreciate these and other objects of the present subject matter as well as the subject matter itself, all of which will become apparent to those skilled in the art, the ensuing detailed description of the subject matter and the claims should be read in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
[00010] The above and other features, aspects and advantages of the subject
matter will be better understood with regard to the following description, appended claims and accompanying drawings where:
[00011] FIG. 1 shows a side view of an internal combustion engine
according to the present invention.
[00012] FIG. 2 shows a perspective view of the valve train system of the
internal combustion engine according to the present invention.

[00013] FIG. 3 shows a top sectional view of the valve train system of FIG.
2.
[00014] FIG. 4 shows a side sectional view illustrating a cam profile
switching mechanism according to the present invention.
[00015] . FIG. 5 shows an exploded view of the cam profile switching mechanism connected to the valve trainA
DETAILED DESCRIPTION OF THE INVENTION
[00016] The subject matter disclosed herein is now explained with the help
of rendered FIGs. 1-5. Various other features and embodiments of the present subject matter here will be discernible from the following further description thereof, set out hereunder. The detailed explanation of the constitution of parts other than the subject matter which constitutes an essential part has been omitted at suitable places. Furthermore, a longitudinal axis, except otherwise mentioned, refers to a front to rear axis relative to a shaft, while a lateral axis, except otherwise mentioned, refers generally to a side to side, or left to right axis relative to the shaft.. It is contemplated that the proposed invention is usable in internal combustion engines within the spirit and scope of this invention including horizontal engines, vertical engines and overhead cam supporting engines. The invention is explained with the help of a single cylinder internal combustion engine but the concepts introduced herein are applicable to multi-cylinder engines with adequate modifications.

[00017] FIG. 1 shows a side view of a four cycle internal combustion
engine 1. The four cycle engine 1 includes a crankcase 4, a cylinder block 3 coupled to the crankcase 4 and a cylinder head 2 coupled to the upper part of the cylinder block 3. The cylinder head 2 is located above the cylinder block 3 and the crankcase 4 is located below the cylinder block 3, with the cylinder block 3 located between the cylinder head 2 and the crankcase 4. A reciprocating piston 5 slidably fitted in the cylinder block 3 is connected via a connecting rod 7 to a crankshaft 8. The crankshaft 8 is rotatably supported by the crankcase 4.
[00018] A first port 10 and a second port 9 formed in the cylinder head 2
communicate with a combustion chamber 6 formed by being surrounded by the cylinder bore, the cylinder head 2 and the piston 5. The second port 9 allows the air-fuel mixture to enter the combustion chamber 6 whereas after the mixture is combusted, the exhaust gases are taken out of the combustion chamber 6 through . the first port 10. To facilitate this gas exchange, a plurality of valves is provided in the cylinder head 2. The exemplified engine is a three valve internal combustion engine. In an embodiment, a first valve 11 is provided at the combustion chamber side opening of the first port 10 whereas at least two other valves, namely a second valve 12 and a third valve 13, are provided at the combustion chamber side opening of the second port 9. According to another embodiment, the first valve 11 supports in the outlet of exhaust gases whereas the second valve 12 and third valve 13 support in the inlet of air-fuel mixture into the combustion chamber 6. The second valve 12 and the third valve 13 function jointly and both of them are jointly operational at any point of time for the inlet

function. The first valve 11, second valve 12 and third valve 13 are driven by a camshaft 14 rotatably supported in the cylinder head 2 so as to open and close them. Rotational power is transmitted from the crankshaft 8 to the camshaft 14 by a timing transmission mechanism (not shown). In an embodiment, the timing transmission mechanism includes a drive sprocket supported on the crankshaft, a driven sprocket supported on the camshaft and an endless cam chain connecting the drive sprocket with the driven sprocket.
[00019] In an embodiment, the cylinder block 3 is vertically oriented with
respect to the ground plane and disposed in such a way that the long axis of the cylinder block 3 is approximately perpendicular to the longitudinal axis of the crankshaft 8.
[00020] FIG. 2 shows a perspective view of the valve train disposed in the
cylinder head 2 of the engine 1. The camshaft 14 driven by the crankshaft 8 comprises of a plurality of cams to drive the first valve 11, second valve 12 and the third valve 13. On rotation of camshaft 14, a first cam 15 drives the first valve 11 through a first rocker arm 19. The first rocker arm 19 oscillates around a first rocker shaft 18 placed adjacent to and above the camshaft 14 in the cylinder head 2. A cam end of the first rocker arm 19 comprises of a first cam follower 20. A valve end of the first rocker arm 19 moves in a direction opposite to the direction of the movement of the cam end through which it contacts the first valve 11. On rotation, the cam lobe of the first cam 15 lifts the first cam follower which passes the drive to the first rocker arm 19. The first rocker arm 19 oscillates around the first rocker shaft 18. Thus, the first cam 15 drives the first valve 11.

[00021] Similarly, the second valve 12 and the third valve 13 are driven
jointly by a second cam 16 through a second rocker arm 22. The second rocker arm 22 oscillates around a second rocker shaft 21 placed adjacently to and above camshaft 14. The second cam 16 is axially spaced from the first cam 15 on the camshaft 14 and drives a second cam follower 23 which is mounted to a cam end of the second rocker arm 22. A valve end of the second rocker.arm 22 is a V-type structure to jointly operate the second valve 12 and the third valve 13. The second rocker arm 22 is secured to the second rocker shaft 21. As shown in FIG. 5, the second rocker arm 22 has a first vertical opening 27. The second rocker shaft 21 has a second vertical opening 28. A fastening member 26 passes through the first opening 27 and the second opening 28 and fastens the second rocker arm 22 against the second rocker shaft 21. In an embodiment, the fastening member 26 is a threaded bolt. The valve end of the second rocker arm 22 moves in a direction opposite to the direction of the movement of the cam end.
[00022] The cylinder head further includes a third cam 17 configured to
selectively operate the second rocker arm 22 through a cam profile switching mechanism 30. The first cam 15, the second cam 16 and the third cam 17 are spaced apart, co-axial and are jointly supported on the camshaft 14 and rotate with it. However, they maintain a phase difference between them so as to maintain timing between the inlet of air-fuel mixture and outlet of exhaust gases. The phase difference is achieved by the cam lobes of the respective cams which are oriented at different angles to the camshaft 14.

[00023] The cam profile switching mechanism 30 is provided in the
cylinder head 2 so that, upon its actuation, the third cam 17 is able to jointly operate the second valve 12 and the third valve 13. The cam profile switching mechanism is actuated during high engine speed operation and deactivated during low engine speed operation. In an embodiment, the second cam 16 is configured to operate during low engine speed conditions whereas the third cam 17 is configured to operate during high engine speed conditions. The second cam 16 thus has a smaller lobe height and less duration than the third cam 17. Further, at any given point of time, only one of the second cam 16 or the third cam 17 operates the second rocker arm 22. The cam profile switching mechanism is now described in detail with the help of FIGs. 3-5.
[00024] The cam profile switching system 30 comprises of a third rocker
shaft 31 supporting and driven by a third rocker arm 24, an axially slidable engaging member 34 supported on said third rocker shaft 31 and a locking member 38 configured to lock with the engaging member. The third cam 17 drives the third rocker arm 24 through a third cam follower 25 provided at a cam end of the third rocker.arm 24.
[00025] The third rocker shaft 31 is supported on second rocker shaft 21.
The third rocker shaft 31 receives the second rocker shaft 21 along its longitudinal axis. In an embodiment, the third rocker shaft 31 has a bigger diameter than the second rocker shaft 21. The third rocker shaft 31 comprises of a one end portion 32 to support the engaging member 34 and a one other end portion 37 supporting the third rocker arm 24. In one embodiment, the third rocker arm 24 is press fitted

to the one other end portion 37 of the third rocker shaft 31. The engaging member
34 and the third rocker shaft 31 are connected to each other so that their relative
radial movement is locked. In an embodiment, the one end portion 32 of the third
rocker shaft 31 has external splines. Correspondingly, the engaging member 34
comprises a central mating surface 35 having radial internal splines. Due to the
splined connection, the engaging member and the third rocker shaft 31 are radially
locked with each other.
>
[00026] Therefore, the engaging member 34 is capable of only sliding
axially to actuate the cam profile switching mechanism. In an embodiment, the
engaging member 34 is disposed between the third rocker arm 24 and the locking
member 38. In an embodiment, an axial surface of the engaging member 34
facing the locking member comprises of at least one projection 36 protruding
along the long axis of the third rocker shaft 31. Correspondingly, the locking
member 38 comprises of at least one corresponding slot 39 configured to receive
the at least one projection 36. When the engaging member 34 slides axially and
locks (or engages) with the locking member 38, the cam profile switching
mechanism is actuated after which the drive obtained by the third rocker shaft 31
is passed to the second rocker shaft 21.
[00027] Further, the second rocker shaft 21 comprises of a non-rocker end
portion 29 rigidly connected to the locking member 38 through a securing member 40. The non-rocker end portion 29 passes through the hollow third rocker shaft 31. In an embodiment, the locking member 38 is a circular structure

supported on the non-rocker end portion 29. In an embodiment, the locking member is a flange.
[00028] The engaging member engages or disengages with the locking
member by an actuating means. In an embodiment, the actuating means can be electrically driven or mechanically driven. The actuating means acts on the engaging member to slide it axially so as to allow it to actuate or deactivate the cam profile switching mechanism. In an embodiment, the actuation of the cam profile switching mechanism occurs at high engine speed so that during high speed/load conditions, more air-fuel mixture is available to the combustion chamber 6.
[00029] The working of the cam profile switching mechanism is now
explained. When the cam profile switching mechanism is disengaged, the crankshaft 8 drives the camshaft 14. On rotation of the camshaft 14, the first cam 15, second cam 16 and the third cam 17 rotate. The second cam 16 operates the second cam follower 23 which drives the second rocker arm 22. As the second rocker arm 22 oscillates, the second rocker shaft 21 rotates and the locking member 38 rigidly connected to the second rocker shaft 21 also rotates. Meanwhile simultaneously, the third cam 17 drives the third rocker arm 24 due to which the third rocker shaft 31 rotates. However, since the engaging member 34 is not engaged with the locking member 38, the drive of the third rocker shaft 31 is not passed to the second rocker arm 22 and the third rocker shaft 31 freely rotates against the rotation of the second rocker shaft 21. In this manner, the second cam operates the second valve 12 and the third valve 13. The first cam drives the first

valve 11 and the exhaust gases after combustion exit from the. combustion chamber through the first port.
[00030] When the cam profile switching mechanism is actuated, the
actuating means causes the engaging member 34 to slide axially towards the locking member 38 and the at least one projection 36 is received by the at least one slot 39 of the locking member 38. This happens during the base circle valve event. The third rocker shaft 31 is now operatively engaged with the second rocker shaft 21 through the locking member 38 and no free rotation between the two shafts is possible. When the camshaft 14 drives the plurality of cams, the second cam 16 and the third cam 17 rotate. The third cam 17 rotates the third rocker shaft 31 which rotates the engaging member 34. The engaging member 34 rotates the locking member 38 which is rigidly connected to the second rocker shaft 21. Until this condition, both the second cam 16 and the third cam 17 drive the second rocker.arm 22. However, the second cam 16 has a smaller lobe height and less duration than the third cam 17. Therefore, the rotation of the locking member 38 due to the third cam 17 is more than the rotation of the locking member due to the second cam 16 and hence the oscillation of the third rocker arm 24 is transmitted to the second rocker shaft 21. The second rocker shaft 21 rotates and passes the drive from third cam 17 to the second rocker arm 22. The . second valve 12 and the third valve 13 are thus driven by the third cam 17 and the mechanism switches the drive from the second cam 16 to the third cam 17. The second cam is thus functionally deactivated. Thus, the valves 12, 13 are open for

longer duration and/or are pressed lower into the combustion chamber so as to allow more intake of combustible mixture.
[00031] According to an aspect, the third rocker shaft 31 oscillates freely
against the second rocker shaft 21 when the engaging member is not engaged to the locking member and is coated with a friction reducing agent to reduce friction between the two.
[00032] According to another aspect, the present invention is usable in a
two valve or a three valve or a four valve engine. In a two valve engine having atleast three cams on the camshaft, one cam is able to drive the first valve whereas either of the two cams is able to drive the second valve depending upon the actuation of the cam profile switching mechanism. The third valve is not available in a two valve engine. Similarly, the invention is usable with a four valve engine having two intake and two exhaust valve with at least four cams to drive them. The second and third valve would function as intake valves and are driven accordingly depending upon the actuation of the cam profile switching mechanism. The additional cam provided would drive the additional exhaust valve.
[00033] From the foregoing description, it will be appreciated that the
present invention offers many advantages including those described above. The present invention achieves two different valve lift modes through cam profile switching mechanism. According to another aspect, the cam profile switching mechanism is operational only when projections 36 from the engaging member 34 are received in the slots 39 of the locking member 38 which happens during the

base circle valve event. Hence, the energy required for such engagement or disengagement would be lower. Also, the mechanism described here is a very simple mechanism and can be accommodated without any significant changes to the cylinder head of a small engine to be used to drive a two wheeled vehicle. Since the mechanism has very few components, minimal change in the cylinder head is required.
[00034] The present subject matter is thus described. The description is not
intended to be exhaustive nor is it intended to limit the invention to the precise form disclosed. It will be apparent to those skilled in the art.that the disclosed embodiments may be modified in light of the above description. The embodiments described are chosen to provide an illustration of principles of the invention and its practical application to enable thereby one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore the forgoing description is to be considered exemplary, rather than limiting, and the true scope of the invention is that described in the appended claims.

We claim:
1. An internal combustion engine (IC) having a cylinder head (2) comprising
a first cam (15) driving a first valve (11) through a first rocker shaft
mounted first rocker arm (19) and a second cam (16) jointly driving a
second valve (12) and a third valve (13) through a second rocker shaft
mounted second rocker arm (22), characterised in that, the cylinder head
(2) includes a third cam (17) configured to selectively operate said second
rocker arm (22) through a cam profile switching mechanism (30), the cam
profile switching mechanism comprising:
a third rocker shaft (31) supporting a third rocker arm (24) and configured to selectively engage with the second rocker shaft (21), an axially slidable engaging member (34) supported on said third rocker shaft (31), a locking member (38) configured to lock with the engaging member (34), wherein the cam profile switching mechanism is actuated during high engine speed operation and deactivated during low engine speed operation.
2. The IC engine as claimed in claim 1, wherein the second rocker shaft (21) comprises of a non-rocker end portion (29) rigidly connected to the locking member (38) through a securing member (40).
3. The IC engine as claimed in claim 1, wherein the engaging member (34) is radially locked to a one end portion (32) of the third rocker shaft (31).
4. The IC engine as claimed in claim 1, wherein an axial surface of the engaging member (34) comprises of at least one projection (36) protruding

along the long axis of the third rocker shaft (31) and received in at least one corresponding slot (39) provided in the locking member (38) when the cam profile switching mechanism is actuated.
5. The IC engine as claimed in claim 1, wherein the third rocker arm (24) is press fitted to a one other end portion (37) of the third rocker shaft (31).
6. The IC engine as claimed in claim 1, wherein the third rocker shaft (31) is supported on second rocker shaft (21).
7. The IC engine as claimed in claim 1, wherein the engaging member (34) engages or disengages with the locking member (38) through an electrical or mechanical means.
8. The IC engine as claimed in claim 1, wherein the second cam (16) has a smaller lobe height and duration than the third cam (17).
9. The IC engine as claimed in claim 1, wherein the engaging member (34) is disposed between the third rocker arm (24) and the locking member (38).