A CONTACT RETENTION 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 cylinder head of 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 a valve train in the cylinder
head through a camshaft. A timing chain 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] The motion of the camshaft is carried to the respective valves
through at least one rocker arm for each valve. On transfer of the motion, the cam lobe lifts one end of rocker armthrough a cam follower and the other end of the rocker arm engages with a valve stem of the concerned valve. For efficient functioning of the valve train, valve lash is provided in the valve train. Valve lash is the gap or clearance .between a head portion of a valve stem and a tappet of the rocker arm. Valve lash is provided to allow mechanical (thermal) expansion and lengthening of the valve stem as the cylinder head is heated during operation. If the valve lash is not proper, the thermal expansion lifts the valve off its valve seat and interferes with the engine performance. Additionally, thermal expansion also
leads to an increase in the distance between a cam bore and a rocker bore which
i creates a clearance between the cam follower and the cam lobe.
[0005] However, if additional clearance is provided, some clearance will
remain even after engine warm up resulting in lost motion. This is because as the cam lobe tries to open the concerned valve, some motion is lost in overcoming the increased clearance between the cam follower and the cam lobe. Resultantly, the valve opens late and affects engine performance. The problem is aggravated in situations like sudden acceleration or very high engine rpm when the contact between the cam lobe and the cam follower is lost momentarily. Therefore, in the immediate next cycle of rotation, the cam lobe hits the cam follower with more force which causes increase in cylinder head noise and rattling.

SUMMARY OF THE INVENTION
[0006] It is therefore important that the cam follower of the rocker arm
remains in continuous contact with the cam lobe even during high temperature conditions in the cylinder head. An object of the present subject matter is to disclose a contact retention system in a cylinder head of an internal combustion engine which retains the contact between the cam follower and the cam lobe. Another object of the present invention is to reduce the cylinder head noise caused due to increase in impact.
[0007] To this end, the present invention discloses, an internal combustion
engine having a cylinder head provided with a . contact retention system.Thecontact retention system comprises at least one retractable member connected to at least one rocker arm, and a supporting member supporting the at least one retractable member. The supporting member protrudes from a surfacein the upper portion of the cylinder head in the direction of the long axis of the at least one rocker arm. The contact retention system keeps a follower of the at least one rocker arm in positive contact with a lobe of a cam. Thus even during high engine temperatures and at high engine rpm or sudden change in engine rpm, the motion of the at least one rocker arm towards the concerned valve is contained. This reduces the impact noise. The aforementioned system is very simple and easily implementable in an IC engine, preferably a small engine, without any significant changes to the cylinder head.
[0008] 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
[0009] 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:
[00010] FIG. 1 shows a sectional side view of a typical internal combustion
engine.
[00011] FIG. 2 shows a perspective view of a valve train system of the
internal combustion engine according to the present invention.
[00012] FIG. 3 shows a side illustrative view of a contact retention system
associated with a cylinder head of the IC engine.
[00013] FIG. 4 shows a side sectional view of the contact retention system
of FIG. 3.
[00014] FIG. 5 shows a top view of the cylinder head of the IC engine
according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[00015] 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. It is contemplated that the proposed invention is usable in internal combustion engines within the spirit and scope of this invention including horizontal engines, verticalengines 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.The brief description is to be understood as an exemplary embodiment and reading of the invention is not intended to be taken restrictively.
[00016] 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 2a coupled to the upper part of the cylinder block 3. The cylinder head 2a is covered from the top by a cylinder cover 2b.The cylinder head 2a 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 2a and the crankcase 4. A reciprocating piston 5slidably 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.
[00017] A first port 10 and a second port 9formed in the cylinder head 2a
communicate with a combustion chamber 6 formed by being surrounded by the cylinder bore, the cylinder head 2a and the piston 5. The second port 9(also called intake port) allows the air-fuel mixture to enter the combustion chamber 6whereas

after the mixture is combusted, the exhaust gases are taken out of the combustion
chamber 6 through the first port 10 (also called as exhaust port). To facilitate this
gas exchange, a plurality of valves is provided in the cylinder head 2a. The
exemplified engine is a three valve internal combustion engine. However, the
concepts disclosed herein are equally applicable in a two valve and a four valve
engine. Each port is provided with at least one valve for gas exchange. 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
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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 13function 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.
[00018] ( In apreferred 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.
[00019] FIG. 2 shows a perspective view of the valve train disposed in the
cylinder head 2a 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. At least one rocker arm drives at least one valve. 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.
[00020] 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 i5 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 approximately 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.

The valve end of the second rocker arm 22 moves in a direction opposite to the . direction of the movement of the cam end.
[00021] The first cam 15 and the second cam 16 are co-axially spaced apart
and 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 first cam 15 and the second cam 16 which are oriented at different angles to the camshaft 14.
[00022] During high temperatures in small engines, the constituents of.
valve train expand which results in a clearance being developed between the cam follower and the cam lobe of each rocker arm. For instance, a clearance is observed between the second cam follower 23 and the lobe of the second cam 16. Therefore, FIG. 3 shows the cylinder head 2a configured to have a contact retention system 50 to prevent the loss of contact between the respective cam lobe and cam follower, for example, between the second cam follower 23 and lobe of
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second cam 16. The cylinder head 2a comprises an upper portion having a surface 59 facing opposite to the crankcase.
[00023] The contact retention system 50 is operatively connected with at
least one rocker arm in the cylinder head. According to a feature of the present "invention, the cylinder head 2a comprises of a plurality of contact retention systems wherein at least one contact retention system is connected to at least one rocker arm in the cylinder head. In the embodiment as, shown in FIG. 3, the cylinder head 2acomprises of a one contact retention system connected to the

second rocker arm 22 and a one other contact retention system connected to the first rocker arm 19. For the purposes of brevity, only one contact retention system and its construction is explained below with the help of FIGs. 3-5.
[00024] The contact retention system 50 comprises of at least one
retractable member 51 connected to at least one rocker arm and a supporting member 52protruding from said surface59of the cylinder head in the direction of the long axis of the at least one rocker armand supporting the at least one retractable member51. For the purpose of illustration, the at least one rocker arm referred here is the second rocker arm 22. The retractable member 51 is connected to the second rocker arm 22 and supported by the supporting member 52. The supporting member 52 fixedly holds the retractable member 51 at one of its end.
[00025] A portion of the supporting member 52 protrudes horizontally from
said surface 59in the direction of the second rocker arm22. In an embodiment, the supporting member is integrally formed with the upper portion of the cylinder head2ahaving the surface 59. In another embodiment, supporting member 52is separately secured to said surface 59in such a way that the supporting member 52 is substantially seated on the surface 59of the cylinder head.A securing member 54 secures the supporting member 52 to the surface 59 of the cylinder head 2a. A mounting hole 55 is provided in the surface 59 to receive a portion of the securing member 54 through which the supporting member 52 is secured to the upper surface 59 of the cylinder head. In an embodiment, the mounting hole 55 is threaded.

[00026] FIG. 4 shows a side sectional view of the contact retention
system50.The retractable member 51comprises of two end portions, a head endportion 56a and an arm endportion 56b.The arm endportion 56b is movably connected to the at least one rocker arm, namely the second rocker arm 22 and the head endportion 56a is fixedly connected to the supporting member 52. The supporting member 52 comprises of a first recess 53 to accommodate the head endportion 56a of the retractable member 51. The second rocker arm 22 comprises of a second recess 24 to accommodate the arm endportion 56b of the retractable member 51. The second recess 24 is provided in the portion between the second rocker shaft 21and the valve end of the second rocker arm22.
[00027] In an embodiment, the retractable member Slincludes a spring.
More particularly, the retractable member includes a tension spring. In an embodiment, the supporting member 52 is a plate. The plate is made of any material including a metal, alloy or heat resistant plastic resin.
[00028] In the present invention, the spring force of retractable member 51
is used to retain contact of second cam follower 23 with the lobe of the second cam 16. Thus, even during base circle position, the second cam follower 23 is in positive contact with the lobe of the second cam 16. The retractable member 51 used to load the second rocker arm 22 against the lobe of the second cam 16 is weaker than the valve spring so that the first portion of the second cam rotation turns the second rocker arm to a position in which it merely acts as a rigid abutment^ transmitting force to the second valve 12.

[00029] The functioning of the contact retention system50 is now
explained. Due to the presence of the retractable memberSl, the second cam follower 23 of the second rocker arm 22 is biased towards the lobe of the second cam 16. The retractable memberSl retains positive contact between the second cam follower and the lobe of the second cam. Thus, even during very high temperatures in the cylinder head, the positive contact is maintained between the second cam follower 23 and the lobe of the second cam 16 during the base circle position. Hence, at very high engine rpm or during sudden change of engine rpm, the motion of the second rocker arm towards the second valve is contained by the retractable member. Since the cam lobe and the second cam follower are never out of contact, there is no possibility of impact and resultant impact noise..Further, in an embodiment, the spring force of the retractable member is significantly less than the spring force of a spring of the valve being operated by the second rocker arm 22.
[00030] 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. 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.
[00031] 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 (1) having a cylinder head (2a) and a
crankcase (4), the cylinder head (2a) comprising: an upper portion having
a surface (59) facing opposite to the crankcase and at least one rocker arm
(19, 22) supported on at least one rocker shaft (18, 21) and operating at
least one valve (11, 12, 13), characterised in that, the cylinder head (2a)
includes a contact retention system (50) comprising:
at least one retractable member (51) connected to the at least one rocker arm (19, 22), and
a supporting member (52) protruding from said surface (59) of the cylinder head in the direction of the long axis of the at least one rocker arm (19, 22) and supporting the at least one retractable member (51),
wherein the contact retention system (50) maintains positive contact between a lobe of a cam (15,16) and a follower (20, 23) of the at least one rocker arm (19, 22).
2. The internal combustion engine as claimed in claim 1, wherein the supporting member (52) is secured to said surface (59) of the cylinder head through a securing member (54).
3. The internal combustion engine as claimed in claim 2, wherein a portion of the securing member (54) is received in a mounting hole (55) provided in the upper portion having the surface (59).

4. The internal combustion engine as claimed in claim 1, wherein the supporting member (52) is integrally formed in the upper portion of the cylinder head (2a).
5. The internal combustion engine as claimed in claim 1, wherein the at least one retracting member (51) comprises of a head endportion (56a) fixedly connected to the supporting member (52) and an arm endportion (56b) movably connected to the at least one rocker arm (19, 22).
6. The internal combustion engine as claimed in claim 5, wherein the arm endportioji (56b)of the at least one retractable member (51) is accommodated in a second recess (24) provided in the at least one rocker arm (19, 22).
7. The internal combustion engine as claimed in claim 6, wherein the second recess (24) is provided in the portion between the at least one rocker shaft (18, 21) and a valve end of the at least one rocker arm (19, 22).
8. The internal combustion engine as claimed in claim 5, wherein the head endportion (56a) of the at least one retractable member (51) is accommodated in a first recess (23) provided in the supporting member . (52).
9. The internal combustion engine as claimed in claim 1, wherein the spring force of the retractable member (51) is less than the spring force of a springprovided in the least one valve (11, 12, 13) operated by the at least one rocker arm (19, 22).

10. The internal combustion engine as claimed in any of the preceding claims, wherein the at least one retractable member (51) includes a tension spring and wherein the supporting member (52) includes a plate made of a group consisting of metal, alloy or heat resistant plastic resin.