Claims:WE CLAIM:
1. A casting member (100) for a power unit (12) of a vehicle (10), comprising:
a first peripheral portion (110) having a first thickness, such that one or more gating members are formed on the first peripheral portion (110) during casting of the casting member (100);
a second peripheral portion (120) having a second thickness, wherein the second thickness is lower than the first thickness; and
a main member body (130) extending from the first peripheral portion (110) to the second peripheral portion (120) such that thickness of the main member body (130) gradually decreases from the first thickness at the first peripheral portion (110) to the second thickness at the second peripheral portion (120).

2. The casting member (100) as claimed in claim 1, wherein the power unit (12) comprises of an internal combustion engine and the casting member (100) is a transmission case of the internal combustion engine for a saddle type vehicle (10).

3. The casting member (100) as claimed in claim 2, wherein the main member body (130) comprises a kick starter shaft receiving portion (140) for receiving a kick starter shaft for the saddle type vehicle (10).

4. The casting member (100) as claimed in claim 3, wherein the kick starter shaft receiving portion (140) is positioned closer to the first peripheral portion (110) than the second peripheral portion (120).

5. The casting member (100) as claimed in claim 3, wherein the main member body (130) comprises a stopper portion (150) for limiting movement of a kick starter gear for the saddle type vehicle (10).

6. The casting member (100) as claimed in claim 5, wherein the stopper portion (150) is disposed adjoining the first peripheral portion (110).

7. The casting member (100) as claimed in claim 1, wherein the power unit (12) comprises of an internal combustion engine and the casting member is a cover clutch of the internal combustion engine for a saddle type vehicle (10).

8. The casting member (100) as claimed in claim 1, wherein the power unit (12) comprises of an electric drive source, and the casting member is a transmission case of the electric drive source for a saddle type vehicle (10).

9. A die for casting a casting member (100) of a power unit (12) of a vehicle (10), comprising:
a first portion for forming of a first peripheral portion (110) of the casting member (100) having a first thickness, such that the first portion has one or more gating slots through which molten metal is inserted in the die;
a second portion for forming a second peripheral portion (120) of the casting member (100) having a second thickness, wherein the second thickness is lower than the first thickness; and
a third portion for forming a main member body (130) of the casting member (100) extending from the first peripheral portion (110) to the second peripheral portion (120) such that thickness of the main member body (130) gradually decreases from the first thickness at the first peripheral portion (110) to the second thickness at the second peripheral portion (120).

10. A method for casting a casting member (100) of a power unit (12) of a vehicle (10), comprising the steps of:
inserting molten metal in one or more gating slots formed on a first portion of a die to form a first peripheral portion (110) of the casting member (100) having a first thickness;
allowing the molten metal to flow towards a second portion of the die via a third portion of the die, to form a second peripheral portion (120) of the casting member (100) having a second thickness, wherein the second thickness is lower than the first thickness, and a main member body (130) extending from the first peripheral portion (110) to the second peripheral portion (120) such that thickness of the main member body (130) gradually decreases from the first thickness at the first peripheral portion (110) to the second thickness at the second peripheral portion (120);
solidifying the molten metal inside the die;
ejecting the solidified metal from inside the die; and
degating one or more gating members formed on the first peripheral portion (110) of the casting member (100).
, Description:FIELD OF THE INVENTION
[001] The present invention relates to a casting member for a power unit of a vehicle.

BACKGROUND OF THE INVENTION
[002] In conventional saddle type vehicles, a power unit such as an internal combustion engine is usually encased in a transmission cover. The said transmission cover is usually made of metal and conventionally manufactured by a casting process.
[003] The wall thickness of a casting typically lies around 3 millimetres. A higher wall thickness of the casting would invariably result in an overall increase of the weight of the transmission cover which consequently results in increased emission of exhaust gases and also results in poorer fuel economy.
[004] However, reducing wall thickness of the casting below the conventional standard of around 3 millimetres would result in a multitude of problems. Firstly, to produce a uniform thickness of about 2.2 to 2.5 millimetres, a higher feeding velocity, typically, 4.5 m/sec of molten metal is necessary which can be effectuated only by high pressure die-casting machines having tonnage in excess of 800, which would result in increment the cost of manufacturing.
[005] Further, a major impediment towards manufacturing a thin-walled casting member arises due to improper filling of the cavity in a die, cold filling, warpage of component, porosity defects in the thin cross sections of the die. Further, due to reduced wall thickness, fill times of the casting is cut down significantly, which results in sudden solidification in the thin cross sections of the die.
[006] Furthermore, since a key function of the transmission cover is to provide structural support to parts (such as, bearings), at certain places, it is preferred to have a thick wall for the casting member. When the casting member is uniformly thin walled, it would be detrimental to the structural integrity of the vehicle itself. Moreover, when molten metal flows from thinner cross-section to a thicker cross-section, due to the reduction in flow speed, it solidifies in the thin cross-section resulting in creation of voids in the thicker cross-sections. A plurality of gating slots are usually employed in manufacturing thin-walled casting members which increases the cost to manufacture and results in other drawbacks like weld lines and flashes.
[007] Thus, there is a need in the art for a casting member for a power unit of a vehicle which addresses the aforementioned problems.

SUMMARY OF THE INVENTION
[008] In an aspect, the present invention is directed towards a casting member for a power unit of a vehicle that has a first peripheral portion having a first thickness such that one or more gating members are formed on the first peripheral portion during casting process of the casting member, a second peripheral portion having a second thickness and the second thickness is lower than the first thickness of the first peripheral portion, and a main member body that extends from the first peripheral portion to the second peripheral portion and the thickness of the main member body gradually decreases from the first thickness at the first peripheral portion to the second thickness at the second peripheral portion.
[009] In an embodiment of the invention, the power unit is an internal combustion engine, and the casting member is a transmission case of the said internal combustion engine.
[010] In a further embodiment of the invention, the main member body of the casting member has a kick starter receiving portion that receives a kick starter shaft for the saddle type vehicle.
[011] In a further embodiment of the invention, the kick starter shaft receiving portion is positioned closer to the first peripheral portion than the second peripheral portion.
[012] In a further embodiment of the invention, the main member of the casting member has a stopper portion that limits the movement of a kick starter gear for the vehicle.
[013] In a further embodiment of the invention, the stopper portion is disposed adjoining the first peripheral portion of the casting member.
[014] In a further embodiment of the invention, the power unit is an internal combustion engine, and the casting member is a cover clutch of the internal combustion engine for a saddle type vehicle.
[015] In a further embodiment of the invention, the power unit is an electric drive source, and the casting member is a transmission case of the electric drive source for a saddle type vehicle.
[016] In another aspect, the present invention is directed towards a die for casting a casting member of a power unit that has a first portion for forming of a first peripheral portion of the casting member having a first thickness, such that the first portion has one or more gating slots through which molten metal is inserted in the die, a second portion for forming a second peripheral portion of the casting member having a second thickness, wherein the second thickness is lower than the first thickness, and a third portion for forming a main member body of the casting member extending from the first peripheral portion to the second peripheral portion such that thickness of the main member body gradually decreases from the first thickness at the first peripheral portion to the second thickness at the second peripheral portion.
[017] In another aspect, the present invention is directed towards a method for casting a casting member of a power unit of a vehicle and the step involved are the following: inserting molten metal in one or more gating slots formed on a first portion of a die to form a first peripheral portion of the casting member having first thickness. Thereafter, allowing the metal to flow towards a second portion of the die via a third portion of the die, to form a second peripheral portion of the casting member having a second thickness, wherein the second thickness is lower than the first thickness, and a main member body extending from the first peripheral portion to the second peripheral portion such that thickness of the main member body gradually decreases from the first thickness at the first peripheral portion to the second thickness at the second peripheral portion. Thereafter, solidifying the molten metal inside the die. Thereafter, ejecting the solidified metal from inside the die. And finally, degating one or more gating members formed on first peripheral portion of the casting member.

BRIEF DESCRIPTION OF THE DRAWINGS
[018] 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 left side view of an exemplary saddle type vehicle, in accordance with an embodiment of the invention.
Figure 2 illustrates a perspective view of a casting member for a power unit of a vehicle, in accordance with an embodiment of the invention.
Figure 3 illustrates a top perspective view of a casting member for a power unit of a vehicle, in accordance with an embodiment of the invention.
Figure 4 illustrates a side view of a casting member for a power unit of a vehicle, in accordance with an embodiment of the invention.
Figure 5 illustrates a perspective view of a casting member for a power unit of a vehicle, in accordance with an embodiment of the invention.
Figure 6 illustrates a method for casting a casting member of a power unit of a vehicle, in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION
[019] The present invention relates to a casting member for a power unit of a vehicle. More particularly, the present invention relates to a casting member for a power unit of a saddle type vehicle and a method of casting thereof.
[020] Figure 1 illustrates a left-side view of an exemplary motor vehicle 10, in accordance with an embodiment of the present subject matter. The vehicle 10 comprises a frame (not shown). The frame comprises a head tube (not shown), and a portion of a main tube (not shown) extending rearwardly downward from the head tube to a floorboard 18. One or more front suspensions 44 connect a front wheel 14 to a handlebar 20, which forms a steering assembly of the vehicle 10. The steering assembly is rotatably disposed about the head tube. The main tube further includes a portion extending horizontally and rearwardly from the frame. Further, the frame includes one or more rear tubes extending inclinedly rearward from a rear portion of the main tube towards a rear portion of the vehicle 10.
[021] The vehicle 10 includes a power unit 12 that may comprise at least an internal combustion (IC) engine or an electric drive source. The power unit 12 is coupled to a rear wheel 16. In one embodiment, the engine or the electric drive source is swingably connected to the frame. In one embodiment, the engine or the electric drive source is mounted to a swing arm (not shown) and the swing arm is swingably connected to the frame. Further, the vehicle 10 includes a transmission means (not shown) coupling the rear wheel 16 to the power unit 12. The transmission means includes a continuously variable transmission, an automatic transmission, or a fixed ratio transmission. A seat assembly 22 is disposed above the power unit 12 and is supported by the rear tubes (not shown) of the frame. The seat assembly 22 is hingedly openable. The frame defines a step-through portion ahead of the seat assembly 22. The floorboard 18 is disposed at the step-through portion, wherein a rider can operate the vehicle 10 in a seated position by resting feet on the floorboard 18. Further, the floorboard 18 is capable of carrying loads.
[022] Further, the frame is covered by plurality of body panels including a front panel 30 having a front face 30A and a rear face 30B, an under-seat cover 32, and a left and a right-side panel 33 disposed on the frame and covering the frame and parts mounted thereof.
[023] In addition, a front fender 24 is covering at least a portion of the front wheel 14. A utility box (not shown) is disposed below the seat assembly 22 and is supported by the frame. A rear fender 26 is covering at least a portion of the rear wheel 16 and is positioned upwardly of the rear wheel 16. One or more suspension(s) 46 are provided in the rear portion of the vehicle 10 for connecting the swing arm and the rear wheel 16 to the frame for damping the forces from the rear wheel 16 and the engine (not shown) from reaching the frame.
[024] Furthermore, the vehicle 10 comprises of plurality of electrical and electronic components including a headlight 36, a taillight 38, an alternator (not shown), and a starter motor (not shown).
[025] Figure 2 illustrates a perspective view of a casting member 100 for the power unit 12 of the vehicle 10. As referenced in Figure 2 and Figure 3, the casting member 100 comprises of a first peripheral portion 110 having a first thickness, a second peripheral portion 120 having a second thickness and a main body member 130 extending from the first peripheral portion 110 to the second peripheral portion 120. The main member body 130 extends between the first peripheral portion 110 and the second peripheral portion 120 in a substantially arched profile, thereby defining a space to accommodate vehicle components as required.
[026] The second thickness of the second peripheral portion 120 is lower than the first thickness of the first peripheral portion 110. Further, a thickness of the main member body 130 decreases gradually from the first thickness at the first peripheral portion 110 to the second thickness at the second peripheral portion 120.
[027] The casting member 100 is configured such that during casting of the casting member in an appropriate die or mould, one or more gating member are formed on the first peripheral portion 110 of the casting member 100. This means that when molten metal is inserted in a die to cast the casting member, it is inserted such that the first peripheral portion 110 is formed first, and then the molten metal flows through the second peripheral portion 120 through the main member body 130, as illustrated by arrows in Figure 2. Thus, the one or more gating members being formed on the first peripheral portion 110, which has a higher thickness than the second peripheral portion 120, enables molten metal to encounter reducing wall thickness throughout its path, from the first peripheral portion 110 through the main member body 130 to the second peripheral portion 120. This consequently enables proper casting across varying thickness of the casting member 100.
[028] Reference is made to Figure 4 which illustrates a side view of the casting member 100 for the power unit 12 of the vehicle 10. In an embodiment, the power unit 12 comprises the internal combustion engine and the casting member 100 is a transmission case of the internal combustion engine for the saddle type vehicle 10. In this embodiment, as referenced in Figure 4 and Figure 5, the main member body 130 of the casting member 100 comprises a kick starter shaft receiving portion 140 for receiving a kick starter shaft for the saddle type vehicle 10. Herein, the kick starter shaft receiving portion 140 is positioned closer to the first peripheral portion 110 than the second peripheral portion 120. In other words, the disposition of the kick starter shaft receiving portion 140 is in greater proximity to the first peripheral portion 110 than the second peripheral portion 120. The kick starter shaft, being a relatively bulky component and receiving heavy loads during a kickstart operation, demands that the portion of the transmission case, in this case, the kick starter shaft receiving portion 140, provides greater structural support. Since the main member body 130 has a greater thickness near the first peripheral portion 110 than the second peripheral portion, position of the kick starter shaft receiving portion 140 closer to the first peripheral portion 110, which has greater thickness, will provide greater support to the kick starter shaft
[029] In another embodiment of the present invention, the main member body 130 of the casting member 100 comprises a stopper portion 150 for limiting movement of a kick starter gear for the saddle type vehicle 10. The stopper portion 150 is positioned is adjoining to the first peripheral portion 110 of the casting member 100, as the greater thickness of the casting member 100 near the first peripheral portion 110 is capable of withstanding greater load.
[030] In an alternate embodiment, the casting member 100 is a cover clutch for the saddle type vehicle 10. In another alternate embodiment, the power unit 12 comprises of an electric drive source and the casting member 100 is a transmission case of the electric drive source for the saddle type vehicle 10.
[031] In another aspect, the present invention is directed towards a a die for casting the casting the casting member 100 of the power unit 12 of the vehicle 10. The die comprises a first portion for forming of the first peripheral portion 110 of the casting member 100 having a first thickness, such that the first portion has one or more gating slots through which molten metal is inserted in the die. Further, the die comprises a second portion for forming the second peripheral portion 120 of the casting member 100 having a second thickness, wherein the second thickness is lower than the first thickness of the first peripheral portion 110. Furthermore, the die comprises a third portion for forming the main member body 130 of the casting member 100 extending from the first peripheral portion 110 to the second peripheral portion 120 such that thickness of the main member body 130 gradually decreases from the first thickness at the first peripheral portion 110 to the second thickness at the second peripheral portion 120.
[032] Figure 6 illustrates a method 200 for casting the casting member 100 of the power unit 12 of the vehicle 10. At step 2A, molten metal is inserted in one or more gating slots formed on the first portion of the die to form a first peripheral portion 110 of the casting member 100 having a first thickness. At step 2B, molten metal is allowed to flow towards a second portion of the die via a third portion of the die to form the second peripheral portion 120 of the casting member 100 having a second thickness, and a main member body 130 extending from the first peripheral portion 110 to the second peripheral portion 120. The second thickness so formed, is lower than the first thickness. Herein, the thickness of the main member body 130 gradually decreases from the first thickness at the first peripheral portion 110 to the second thickness at the second peripheral portion 120. At step 2C, the molten metal is solidified inside the die. At step 2D, the molten metal so solidified assumes the required structural configuration of the casting member 100 and is ejected from inside the die. At step 2E, the one or more gating members formed on the first peripheral portion 110 of the casting member 100 are degated, to obtain the casting member 100 as required.
[033] Advantageously, the present invention provides a casting member for a power unit of a vehicle and a method of casting thereof having non-uniform thickness of walls of the casting member. The casting member of the present invention has a reduced overall thickness by around 10 percentage meanwhile increase thickness up to 3 percentage in certain localized areas such as the first peripheral portion. Resultantly, the overall weight of the casting member is lowered which consequently results in a decrease in emission of exhaust gases and also results in better fuel economy.
[034] Further, in the casting of the casting member of the present invention, issues such as improper filling of the die, or warpage or cold filling, that arise in uniformly thin-walled cavity cross-sections or in cavities with cross-section increasing from thin to thicker, do not arise. Resultantly, the present invention resolves issues such as porosity of the casting member, improper filling of the cavity, sudden solidification and voids in thicker cross-sections.
[035] Furthermore, one or more gating slots are employed in a first peripheral portion having a first thickness wherein the first thickness is the maximum thickness of the casting member. Due to this, there are no weld lines or flashes during degating. In addition, the present invention does not require specialized high pressure die casting machines and thus cost of manufacture is not affected.
[036] 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.