Claims:WE CLAIM:
1. A piston (100) for an internal combustion engine (12), comprising;
a piston crown (120) having an upper surface (120A) exposed to a combustion chamber of the internal combustion engine (12); and a lower surface (120B) exposed to oil for cooling of the internal combustion engine (12), the lower surface (120B) having a variable profile varying from a centre (122) of the piston crown (120) to a first radially outward end (124) of the piston crown (120); and
a piston skirt (140) extending from the piston crown (120).

2. The piston (100) as claimed in claim 1, wherein the piston crown (120) has a variable thickness varying from the centre (122) of the piston crown (120) to the first radially outward end (124) of the piston crown (120).

3. The piston (100) as claimed in claim 2, wherein the piston crown (120) has a first thickness (t1) at the first radially outward end (124) of the piston crown (120) and a second thickness (t2) at the centre (122) of the piston crown (120) wherein the first thickness (t1) is lower than the second thickness (t2).

4. The piston (100) as claimed in claim 1, wherein the first radially outward end (124) of the piston crown (120) is at a radial distance of 0.15-0.35 times a diameter of the piston crown (120).

5. The piston (100) as claimed in claim 3, wherein the first thickness (t1) of the piston crown (120) at the first radially outward end (124) of the piston crown (120) ranges between 1.5mm - 3.5mm.

6. The piston (100) as claimed in claim 3, wherein the second thickness (t2) of the piston crown (120) at the centre (122) of the piston crown (120) ranges between 2mm – 4mm.

7. The piston (100) as claimed in claim 3, wherein the ratio of the second thickness (t2) to the first thickness (t1) ranges between 1.5 – 2.5.

8. The piston (100) as claimed in claim 3, wherein the lower surface (120B) of the piston crown (120) has a linearly tapered profile, tapering from the centre (122) of the piston crown (120) to the first radially outward end (124) of the piston crown (120), at a predetermined taper angle (?).

9. The piston (100) as claimed in claim 3, wherein the lower surface (120B) of the piston crown (120) has a curvedly tapered profile, tapering from the centre (122) of the piston crown (120) to the first radially outward end (124) of the piston crown (120).

10. The piston (100) as claimed in claim 3, wherein the lower surface (120B) of the piston crown (120) has a linearly tapered profile, tapering from a second radially outward end (126) of the piston crown (120) to the first radially outward end (124) of the piston crown (120) at a predetermined taper angle (?), wherein the second radially outward end (126) of the piston crown (120) is radially closer to the centre (122) of the piston crown (120) than the first radially outward end (124) of the piston crown (120).

11. The piston (100) as claimed in claim 10, wherein the lower surface (120B) of the piston crown (120) has a linearly uniform profile from the centre (122) of the piston crown (120) to the second radially outward end (126) of the piston crown (120).

12. The piston (100) as claimed in claim 8 or 10, wherein the predetermined angle (?) ranges between 65 degrees to 85 degrees.

13. The piston (100) as claimed in claim 3, wherein the lower surface (120B) of the piston crown (120) has a curvedly tapered profile, tapering from a second radially outward end (126) of the piston crown (120) to the first radially outward end (124) of the piston crown (120), wherein the second radially outward end (126) of the piston crown (120) is closer to the centre (122) of the piston crown (120) than the first radially outward end (124) of the piston crown (120).

14. The piston (100) as claimed in claim 13, wherein the lower surface (120B) of the piston crown (120) has a linearly uniform profile from the centre (122) of the piston crown (120) to the second radially outward end (126) of the piston crown (120).

15. The piston (100) as claimed in claim 1, wherein the upper surface (120A) of the piston crown (120) comprises a plurality of depressions (130) for accommodating a valve-head during a compression and an exhaust stroke of the piston (100).

16. The piston (100) as claimed in claim 15, wherein the plurality of depressions (130) are radially outwards from the centre (122) of the piston crown (120) as compared to the first radially outward end (124) of the piston crown (120).

17. The piston (100) as claimed in claim 15, wherein the lower surface (120B) of the piston crown (120) has a linearly uniform profile along the plurality of depressions (130).

18. The piston (100) as claimed in claim 17, wherein the piston crown (120) has a constant thickness (t3) along the plurality of depressions (130).

19. The piston (100) as claimed in claim 18, wherein the constant thickness (t3) of the piston crown (120) is equal to the first thickness (t1) of the piston crown (120).

20. The piston (100) as claimed in claim 18, wherein the constant thickness (t3) of the piston crown (120) along the plurality of depressions (130) ranges between 2mm – 3.5 mm.
, Description:FIELD OF THE INVENTION
[001] The present invention relates to a piston for an internal combustion engine.

BACKGROUND OF THE INVENTION
[002] In conventional motor vehicles, especially saddle-type vehicles, engine weight reduction is one of most challenging issues in engine design. High reciprocating and rotating masses in the engine cause higher inertial forces in the engine, which leads to higher vibrations and lower fuel efficiency. Therefore, mass reduction in these domains is vital for better performance of the saddle-type vehicle in terms of vibration, fuel consumption, pick up and durability.
[003] With regards to the reciprocating masses, there are two major reciprocating components in the engine, namely, a piston and a portion of connecting rod, while the other portion of the connecting rod rotates with crankshaft. Since, mass of the portion of the connecting rod rotating with the crankshaft is much higher than the mass of the portion of the connecting rod that is reciprocating, the piston is the highest contributor to the inertial forces being generated from reciprocating masses. Further, the piston having a high mass, in its movement from the top dead centre position to the bottom dead centre position will transfer greater amount of force to the crankshaft. This results in greater inertial forces, thereby leading to greater vibrations in the engine. A heavier piston would also require more fuel to cause its reciprocation, thereby hampering the fuel efficiency.
[004] Therefore, mass reduction of the piston is necessary to ensure that the reciprocating inertial forces generated in the engine are kept at a minimum. The mass reduction thereby reduces the vibration in the engine and ensures better fuel efficiency and performance of the engine.
[005] Attempts have been made to optimise the mass of the piston in an engine assembly by way of maintaining a complex empirical relationship between piston parameters such as compression height, piston pin boss axial and radial thickness etc., or by way of manufacturing the piston by precision cast net methodology. The piston mass optimisation in both aforementioned attempts is associated with high manufacturing cost and difficulty, performance drawbacks especially in terms of obtaining adequate piston thickness for higher CC engines, and increased lead time.
[006] Thus, there is a need in the art for a piston for an internal combustion engine which addresses at least the aforementioned problems.

SUMMARY OF THE INVENTION
[007] In one aspect, the present invention is directed at a piston for an internal combustion engine. Herein, the piston for the internal combustion engine has a piston crown having an upper surface that is exposed to a combustion chamber of the internal combustion engine, and a lower surface that is exposed to oil for cooling of the internal combustion engine. Further, the lower surface of the piston crown has a variable profile varying from a centre of the piston crown to a first radially outward end of the piston crown. Further, the piston has a piston skirt extending from the piston crown.
[008] In an embodiment of the invention, the piston crown has a variable thickness varying from the centre of the piston crown to the first radially outward end of the piston crown.
[009] In another embodiment of the invention, the piston crown has a first thickness (t1) at the first radially outward end of the piston crown and a second thickness (t2) at the centre of the piston crown wherein the first thickness (t1) is lower than the second thickness (t2). In an embodiment, the first radially outward end of the piston crown is at a radial distance of 0.15-0.35 times a diameter of the piston crown. In another embodiment, the first thickness (t1) of the piston crown at the first radially outward end of the piston crown ranges between 1.5mm - 3.5mm. In a further embodiment, the second thickness (t2) of the piston crown at the centre of the piston crown ranges between 2mm – 4mm. In yet another embodiment, the ratio of the second thickness (t2) to the first thickness (t1) ranges between 1.5 – 2.5.
[010] In a further embodiment of the invention, the lower surface of the piston crown has a linearly tapered profile, tapering from the centre of the piston crown to the first radially outward end of the piston crown at a predetermined taper angle (?). In an embodiment, the lower surface of the piston crown has a curvedly tapered profile, tapering from the centre of the piston crown to the first radially outward end of the piston crown. In another embodiment, the lower surface of the piston crown has a linearly tapered profile, tapering from a second radially outward end of the piston crown to the first radially outward end of the piston crown at a predetermined taper angle (?). In an embodiment, the predetermined angle (?) ranges between 65 degrees to 85 degrees. Herein, the second radially outward end of the piston crown is radially closer to the centre of the piston crown than the first radially outward end of the piston crown. In a further embodiment, the lower surface of the piston crown has a linearly uniform profile from the centre of the piston crown to the second radially outward end of the piston crown.
[011] In another embodiment of the invention, the lower surface of the piston crown has a curvedly tapered profile, tapering from a second radially outward end of the piston crown to the first radially outward end of the piston crown, wherein the second radially outward end of the piston crown is closer to the centre of the piston crown than the first radially outward end of the piston crown. In another embodiment, the lower surface of the piston crown has a linearly uniform profile from the centre of the piston crown to the second radially outward end of the piston crown.
[012] In a further embodiment of the invention, the upper surface of the piston crown has a plurality of depressions for accommodating a valve-head during a compression and an exhaust stroke of the piston. In an embodiment, the plurality of depressions are radially outwards from the centre of the piston crown as compared to the first radially outward end of the piston crown. In another embodiment, the lower surface of the piston crown has a linearly uniform profile along the plurality of depressions whereby the piston crown has a constant thickness (t3) along the plurality of depressions.
[013] In another embodiment of the invention, the constant thickness (t3) of the piston crown is equal to the first thickness (t1) of the piston crown. In another embodiment, the constant thickness (t3) of the piston crown along the plurality of depressions ranges between 2mm – 3.5 mm.

BRIEF DESCRIPTION OF THE DRAWINGS
[014] Reference will be made to embodiments of the invention, examples of which may be illustrated in accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.
Figure 1 illustrates a right-side view of an exemplary motor vehicle, in accordance with an embodiment of the invention.
Figure 2 illustrates a sectional view of a piston for an internal combustion engine, in accordance with an embodiment of the invention.
Figure 3 illustrates a magnified sectional view of the piston, in accordance with an embodiment of the invention.
Figure 4 illustrates the magnified sectional view of the piston, in accordance with an embodiment of the invention.
Figure 5 illustrates the magnified sectional view of the piston, in accordance with an embodiment of the invention.
Figure 6 illustrates the sectional view of the piston, in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION
[015] The present invention relates to a piston for an internal combustion engine.
[016] Figure 1 illustrates an exemplary motor vehicle 10, in accordance with an embodiment of the invention. The motor vehicle 10 has an internal combustion engine 12 that is vertically disposed. Preferably, the internal combustion engine 12 is a single-cylinder type internal combustion engine. The motor vehicle 10 has a front wheel 14, a rear wheel 16, a frame member, a seat assembly 18 and a fuel tank 20. The frame member includes a head pipe 22, a main tube 24, a down tube (not shown), and seat rails (not shown). The head pipe 22 supports a steering shaft (not shown) and two telescopic front suspensions 26 (only one shown) attached to the steering shaft through a lower bracket (not shown). The two telescopic front suspensions 26 support the front wheel 14. The upper portion of the front wheel 14 is covered by a front fender 28 mounted to the lower portion of the telescopic front suspension 26 at the end of the steering shaft. A handlebar 30 is fixed to upper bracket not shown and can rotate to both sides. A head light 32, a visor guard (not shown) and instrument cluster (not shown) is arranged on an upper portion of the head pipe 22. The frame member has a down tube (not shown) that may be located in front of the internal combustion engine 12 and extends slantingly downward from head pipe 22. The main tube 24 of the frame member is located above the internal combustion engine 12 and extends rearward from head pipe 22. The internal combustion engine 12 is mounted at the front to the down tube and a rear of the internal combustion engine 12 is mounted at the rear portion of the main tube 24. In an embodiment, the internal combustion engine 12 is mounted vertically, with a cylinder block extending vertically above a crankcase. In an alternative embodiment, the internal combustion engine 12 is mounted horizontally (not shown) with the cylinder block extending horizontally forwardly from the crankcase. In an embodiment, the cylinder block is disposed rearwardly of the down tube.
[017] The fuel tank 20 is mounted on the horizontal portion of the main tube 24. Seat rails are joined to main tube 24 and extend rearward to support a seat assembly 18. A rear swing arm 34 is connected to the frame member to swing vertically, and the rear wheel 16 is connected to rear end of the rear swing arm 34. Generally, the rear swing arm 34 is supported by a mono rear suspension 36 (as illustrated in the present embodiment) or through two suspensions on either side of the motor vehicle 10. A taillight unit 33 is disposed at the end of the motor vehicle 10 and at the rear of the seat assembly 18. A grab rail 35 is also provided on the rear of the seat rails. The rear wheel 16 arranged below seat 18 rotates by the driving force of the Internal combustion engine 12 transmitted through a chain drive (not shown) from the Internal combustion engine 12. A rear fender 38 is disposed above the rear wheel 16.
[018] Further, an exhaust pipe 40 of the vehicle extends vertically downward from the internal combustion engine 12 up to a point and then extends below the internal combustion engine 12, longitudinally along the vehicle length before terminating in a muffler 42. The muffler 42 is typically disposed adjoining the rear wheel 16.
[019] Figure 2 illustrates a piston 100 for the internal combustion engine 12, in accordance with an embodiment of the invention. As illustrated in Figure 2, the piston 100 has a piston crown 120. In that, the piston crown 120 has an upper surface 120A that is exposed to a combustion chamber of the internal combustion engine 12. The upper surface 120A of the piston crown 120 is therefore exposed to hot gases in the combustion chamber, which on expansion, exert force on the upper surface 120A of the piston crown 120. This causes the piston 100 to reciprocate in a cylinder (not shown) of the internal combustion engine 12. Further, the piston crown 120 has a lower surface 120B. The lower surface 120B is exposed to oil for cooling and lubrication of the internal combustion engine 12. In operation, oil comes in contact with the lower surface 120B of the piston crown 120, and cools the piston crown 120, hence maintaining the temperature of the piston crown 120 under operable limits.
[020] The piston 100 further has a piston skirt 140 extending from the piston crown 120. The piston skirt 140 is disposed at a clearance from the walls of the cylinder of the internal combustion engine 12. The piston skirt 140 has a plurality of ring grooves machined thereon to hold piston rings that ensure gases from the combustion chamber do not leak into the gap between the cylinder and the piston 100.
[021] As further illustrated in Figure 2, the lower surface 120B of the piston crown 120 has a variable profile varying from a centre 122 of the piston crown 120 to a first radially outward end 124 of the piston crown 120. As a result, the piston crown 120 has a variable thickness varying from the centre 122 of the piston crown 120 to the first radially outward end 124 of the piston crown 120, as illustrated in Figure 3.
[022] Figure 4 illustrates a magnified sectional view of the piston 100, in accordance with an embodiment of the invention. As illustrated in Figure 4, the piston crown 120 has a first thickness (t1) at the first radially outward end 124 of the piston crown 120, and a second thickness (t2) at the centre 122 of the piston crown 120. Herein, the first thickness (t1) is lower than the second thickness (t2). The reduced thickness of the of the piston crown 120 at the first radially outward end 124 reduces the mass of the piston 100. Herein, in an embodiment of the invention, the first thickness (t1) of the piston crown 120 at the first radially outward end 124 of the piston crown 120 ranges between 1.5mm - 3.5mm. Further, the second thickness (t2) of the piston crown 120 at the centre 122 of the piston crown 120 ranges between 2mm – 4mm. Resultantly, the ratio of the second thickness (t2) to the first thickness (t1) ranges between 1.5 – 2.5.
[023] In an embodiment of the invention, the first radially outward end 124 of the piston crown 120 is at a radial distance of 0.15-0.35 times a diameter of the piston crown 120.
[024] In an embodiment of the invention as illustrated in Figure 4, to achieve the reduced thickness of the piston crown 120 at the first radially outward end 124, the lower surface 120B of the piston crown 120 has a tapered profile. Herein, in an embodiment of the invention, the lower surface 120B of the piston crown 120 has a linearly uniform profile from the centre 122 of the piston crown 120 to a second radially outward end 126 of the piston crown 120. Therefore, the thickness of the piston crown 120 at the second radially outward end 126 is equal to the second thickness (t2) of the piston crown 120 at the centre 122 of the piston crown 120. As can be seen in Figure 4, the second radially outward end 126 of the piston crown 120 is radially closer to the centre 122 of the piston crown 120 than the first radially outward end 124 of the piston crown 120.
[025] Thereafter, the lower surface 120B of the piston crown 120 has a linearly tapering profile, which tapers from the second radially outward end 126 of the piston crown 120 to the first radially outward end 124 of the piston crown 120. This results in the thickness of the piston crown 120 gradually reducing from the second thickness (t2) at the second radially outward end 126 of the piston crown 120 to the first thickness (t1) at the first radially outward end 124 of the piston crown 120, in a linear manner. The lower surface 120B of the piston crown 120 tapers from the second radially outward end 126 of the piston crown 120 to the first radially outward end 124 of the piston crown 120, at a predetermined taper angle (?). Herein, the predetermined taper angle (?) is calculated from a normal axis passing through the second radially outward end 126 of the piston crown 120. In an embodiment of the invention, the predetermined taper angle (?) ranges between 65 degrees and 85 degrees.
[026] In an alternative embodiment of the invention, the lower surface 120B of the piston crown 120 has a curvedly tapering profile, which tapers from the second radially outward end 126 of the piston crown 120 to the first radially outward end 124 of the piston crown 120. This results in the thickness of the piston crown 120 gradually reducing from the second thickness (t2) at the second radially outward end 126 to the first thickness (t1) at the first radially outward 124, in a curved manner.
[027] In a further alternative embodiment of the invention as illustrated in Figure 5, to achieve the reduced thickness of the piston crown 120 at the first radially outward end 124, the lower surface 120B of the piston crown 120 has a linearly tapered profile which tapers directly from the centre 122 of the piston crown 120 to the first radially outward end 124 of the piston crown 120. This results in the thickness of the piston crown 120 gradually reducing from the second thickness (t2) at the centre 122 of the piston crown 120 to the first thickness (t1) at the first radially outward end 124 of the piston crown 120, in a linear manner. The lower surface 120B of the piston crown 120 tapers from the centre 122 of the piston crown 120 to the first radially outward end 124 of the piston crown 124, at the predetermined taper angle (?). Herein, the predetermined taper angle (?) is calculated from a normal axis passing through the centre 122 of the piston crown 120. As mentioned hereinbefore, the predetermined taper angle (?) ranges between 65 degrees and 85 degrees.
[028] In an alternative embodiment of the invention, the lower surface 120B of the piston crown 120 has a curvedly tapered profile which tapers directly from the centre 122 of the piston crown 120 to the first radially outward end 124 of the piston crown 120. This results in the thickness of the piston crown 120 gradually reducing from the second thickness (t2) at the centre 122 of the piston crown 120 to the first thickness (t1) at the first radially outward 124 of the piston crown 120, in a curved manner.
[029] As illustrated in Figure 6, the upper surface 120A of the piston crown 120 has a plurality of depressions 130, that accommodate a valve-head (not shown) during a compression and an exhaust stroke of the piston 100. The plurality of depressions 130 ensure that when the piston 100 is at a top-dead centre position, the piston crown 120 does not knock an exhaust valve-head or an intake valve-head which are in an open position when the piston 100 is at the top-dead centre position.
[030] As illustrated in Figure 6, the plurality of depressions 130 are radially outwards from the centre 122 of the piston crown 120 as compared to the first radially outward end 124 of the piston crown 120. Herein, the lower surface 120B of the piston crown 120 has a linearly uniform profile along the plurality of depressions 130. Resultantly, the piston crown 120 has a constant thickness (t3) along the plurality of depressions 130. In an embodiment of the invention, the constant thickness (t3) of the piston crown 120 is equal to the first thickness (t1) of the piston crown 120 at the first radially outward end 124 of the piston crown 120. In an embodiment of the invention. the constant thickness (t3) of the piston crown 120 along the plurality of depressions 130 ranges between 2mm – 3.5 mm.
[031] Advantageously, the present invention provides a piston for an internal combustion that has a reduced mass as opposed to pistons with unform piston crown thickness, and are easier to manufacture, thereby bringing down manufacturing costs. The piston of the present invention, being light in weight requires less fuel to move the piston and hence provides better fuel efficiency. Further, the reduced mass of the piston also results in better and quicker throttle response in the engine and lower emissions.
[032] The reduced mass of the piston results in the reduction of reciprocating masses in the engine, and hence the inertial forces caused by the reciprocating masses is reduced, thereby substantially reducing the vibrations in the engine caused by reciprocating masses.
[033] Furthermore, the thickness of the piston crown of the piston in the present invention also corresponds to the thermal stress distribution of the piston crown. This means, that maximum thickness of the piston crown is provided at the centre of the piston crown, where thermal stress is maximum and the thickness of the piston crown gradually reduces towards the first radially outward end, similar to the reducing thermal stress radially from the centre of the piston crown.
[034] While the present invention has been described with respect to certain embodiments, it will be apparent to those skilled in the art that various changes and modification may be made without departing from the scope of the invention as defined in the following claims.