FIELD OF INVENTION:

This invention relates to crankshaft with hollow sections and method of making the same. Crankshaft is one of the basic components of IC engine which is subjected to severe thrust from piston and connecting rod and in combination converts reciprocating motion of piston into rotary motion.

Conventionally, crankshafts are manufactured by either forging or casting route which is followed by machining. Yield of both these processes, forging and machining or casting and machining is 60 to 80% and 40 to 60% respectively. This results in huge machining cost and waste of valuable material in the form of chips. Secondly, such constructions are to be made with solid sections which results in addition of mass to the vehicle.

Current invention describes assembled crankshaft with hollow construction of Main Bearing hereinafter referred to as MB journals and Crank Pin hereinafter referred to as CP journals. This results in improved metallic yield between 85 to 95% during manufacturing and reduced weight of crankshaft. Conceptually current invention is applicable to all crankshafts.

BACKGROUND OF INVENTION:

Crankshaft is one of the critical components of IC engine which is continuously subjected to thrust from piston and connecting rod once the engine starts. Crankshaft should have structural load carrying capabilities, because, it is subjected to shear, torsion and bending stresses throughout its length. Higher frequency of rotation makes the load cycle further critical.

Conventionally, two routes are followed to manufacture a crankshaft i.e. casting and forging followed by machining. Metallic yield of Crankshaft castings is between 40 to 60% and rest of the material is machined off. Secondly, castings are prone to typical casting defects like porosity, blow holes, etc because of which during designing safety factor for crankshafts is maintained on higher side. This results in bigger cross sections ultimately increasing weight of crankshaft. Although, casting route is economical, demerits associated with it like casting defects paves way for alternate manufacturing routes.

Second popular manufacturing route is forging the billet to the shape and then machining this forging for finished dimensions. Mechanically forged crankshafts are superior in strength due to grain flow in desired direction. Metallurgical defects are absent which improves reliability of different sections of crankshaft. This route is also economical competitive due to higher production rates. But, major disadvantage with this manufacturing route is extensive machining similar to cast crankshafts. Extensive machining not only increase cost but generates metallic waste in the form of chips. Metallic yield of forged crankshafts is between 60 to 80%.

There have been successful demonstrations of assembled crankshafts, but with hollow solid crank pins and main bearing journals. Hollow construction of crankshaft is more popular by casting method. There are some demonstrations of assembled crankshafts with hollow crank pin and hollow main bearing, but, it was possible in combination with some type of welding.

Current invention describes assembled crankshaft with hollow sections for MB journals and CP journals. Use of hollow sections results in reduced weight of crankshaft and saves lot of metallic waste which would otherwise be generated during machining. Metallic yield of crankshaft manufactured by assembly of hollow sections is between 90 to 95%. In current invention MB journals and CP journals chilled and are shrunk fitted into moderately heated lobe resulting into a interference fit.

OBJECT OF THIS INVENTION:

1 ) The main object of the invention is to reduce weight of crankshaft by adopting hollow construction. 2) Another invention is to redesign the crankshaft to reduce criticality of fillets and suggest alternate design without any fillet.

3) Yet another objective is to reduce metallic waste generated during machining and improve metallic yield of the process.

SUMMARY OF INVENTION:

As a concept, assembled crankshaft with hollow construction is applicable for all crankshafts of IC engines. As a case, this concept is demonstrated for crankshaft for two cylindered IC engine. Two cylinder IC has engine has two CP journals and three MB journals. Both the CP journals are located on one side and not on opposite sides. Main bearing journal and crankpin journals are proposed in hollow construction. Stress analysis is done with the help of Finite Element Analysis and accordingly materials for different sections are selected. Wall thickness of crank pin & main bearing journals is maintained between 4 to 8 mm. MB journals are found to be stressed to 175 to 350 MPa and stress on crank pins is between 250 to 380 MPa. Considering stress levels CP and MB journals can be manufactured in EN8 steel in hardened and tempered condition.

Assembly of loose parts is done with the help of fixtures.

STATEMENT OF INVENTION:

Accordingly the present invention discloses a hollow crankshaft for IC engines comprising

plurality of Main Bearing (MB) Journals (5) and Crank Pin (CP) Journals (3) both constituted from hollow section;

plurality of flanges (1 ) configured with a blind counter bore (10) for accommodating said Main Bearing (MB) Journal (5) and a counter hole (9) for accommodating Crank Pin (CP) Journal (3), one through hole (8) in counter hole for Crank Pin (CP) Journals (3) and one through hole (4) connecting said Main Bearing (MB) Journals (5) and Crank Pin (CP) Journals (3); at least one hole provided on each of said (MB) Journals (5) and Crank Pin (CP) Journals (3) for providing oil through it for lubrication;

at least one arrangement provided on crankshaft for restraining oil drain from the crankshaft when not in operation; and

at least one lid (2) provided on through hole (8) drilled from counter bore for CP journal.

Accordingly the present invention also discloses a hollow crankshaft for IC engines comprising

plurality of Main Bearing (MB) Journals (5) and Crank Pin (CP) Journals (3) both constituted from hollow section are provided with chamfer at the ends of said CP journal and said MB journal such that when assembled in crankshaft ensures an opening (4') to connect them for oil lubrication;

plurality of flanges (1 ) configured with a blind counter bore (10) for accommodating said Main Bearing (MB) Journal (5) and a counter hole (9) for accommodating Crank Pin (CP) Journal (3);

at least one hole provided on each of said (MB) Journals (5) and Crank Pin (CP) Journals (3) for providing oil through it for lubrication;

at least one arrangement provided on crankshaft for restraining oil drain from the crankshaft when not in operation.

BRIEF DESCRIPTION OF DRAWING:

According to the present invention

Figure 1 shows a hollow crankshaft.

Figure 2 shows Unit of a first main bearing journal, first crankpin journal & a flange. Figure 3 shows an alternate design construction.

Figure 4 shows First main bearing, first crank pin and flange of alternate construction. Figure 5 shows Construction of flange. DETAILED DESCRIPTION OF INVENTION:

To demonstrate the hollow construction of a crankshaft, crankshaft for IC engine is selected. Current invention illustrates the hollow construction and method of making the same. The exemplary IC engine is a two cylinder engine with both the pins on one side. Weight of a two cylinder engine crankshaft is 6.37 kg in solid construction, which reduces to 5.2 kg in hollow construction. This leads reduction in weight by 18.3 %. Similarly the weight crank shaft of three cylinder, four cylinder or any multiple cylinder IC engine can be saved providing such hollow construction.

Conventionally, crankshafts are manufactured by casting or forging route. This route entails heavy machining operations and leads to metallic waste. Almost 20 to 40% of material is machined off from a forged crankshaft. Cast crankshaft involves wastages to the similar level and total waste is close to 40 to 60 %. Although, metallic waste can be recycled, involves cost and energy for conversion. Hence, such designs are not environment friendly and neither economical. Metallic yield for hollow crankshaft is 90 to 95% which means there is at least 30 to 55% improvement in metallic yield. This improvement in metallic yield would save energy and cost for conversion of scrap to metal.

As compared to these routes hollow construction is a very cost effective and economical method of producing a crankshaft. MB (main bearing) journals and CP (crank pin) journals can be converted to hollow construction, and in case of IC engine it is demonstrated that assembled-hollow construction of crankshaft survives similar load conditions as crankshaft in solid construction.

Flanges are subjected to the stress levels of 300 to 380MPa and CP journals are subjected to stresses of the order of 250 to 380 MPa. Low alloy medium carbon steel, such as EN8 steel in hardened and tempered condition can be used for CP journals, MB journals and flanges with required reliability. Loose pieces of CP journal, MB journal and flanges are held in position and assembled with the help of precision fixtures. Fixtures used for assembling are manufactured with precise dimensional controls. Assembly of said MB journal (5) and CP journal (3) to their respective counter bores (10) and (9) in said flanges increases the circumferential surface area of contact between said MB journal and CP journal and their respective counter bores in said flanges. This allows distribution of stress to said circumferential surface area of contact thereby avoiding conventional failure of crank shaft at fillet radius.

Use of hollow crank pins result in significant weight reduction because it also reduces counter weights on flanges. Fig 1 is a sketch of assembled hollow crankshaft. Fig 2 describes assembly features of first main MB journal (5), first CP journal (3) and a flange in-between (1 ). Weight of the crankshaft can be optimized by reducing thickness of flange at CP journal end. Flange is manufactured with one blind counter bore (10) for MB journal, one counter hole (9) for CP journal and one through hole (8) in counter hole (9) for CP journal. CP journal and MB journal are tubes with some specified predetermined thickness to suit the service loads. Dimensions of MB journal and CP journal and counter bores in flange are such that interference fit diametrical interference of 0.12 to 0.15 mm is achieved. Flange is held on fixture and CP & MB journals are shrunk fitted or has interference fit. Because assembly of loose parts is critical process, there is need to provide a through hole in flanges. During assembly, guide rod on fixture passes through this through hole and assists in maintaining relative dimensional tolerance of assembly of crankshaft. Similar hole through counter bore for MB journal should be provided for additional guide rods, if necessary to ensure further control on positional and dimensional tolerances. Flange is also provided with an oil hole (4), which connects cavities of CP journal & MB journal. During application, oil is supplied through engine block to oil hole (6) on MB journal. Cavity of MB journal is filled with oil, then through oil hole (4) in the flange, oil is supplied to cavity of crank pin. After this cavity is filled, oil is supplied for lubrication through oil hole (7) on CP journal. While not in operation there is threat of oil drain which can be addressed by providing a spring and a ball arrangement on engine block, just near oil hole (6), on MB journal. The through hole drilled from counter bore for CP journal needs to be sealed by a lid (2), to ensure continuous supply of oil for lubrication.

Another embodiment or Alternate construction for assembled crankshaft with hollow CP & MB journals is shown in fig 3. Fig 4 shows main difference with the construction shown in fig 2. Oil hole (4) shown in the fig 2, is eliminated in construction shown in fig 4. Chamfer provided at the end of CP journal & MB journal are so assembled to ensure an opening (4') with area more than the sectional area of oil hole (7) on CP journal. In Figure 4 the First main bearing, first crank pin and flange of alternate construction with main bearing (5) and crank pin (3) are shown. Number (1 ) is flange or web. Number (4') is opening to pass lubricating oil from MB to CP. Through holes may be drilled from counter bores for CP journal & MB journal to allow assembly guide rods to pass through, as discussed for fig 2.

After starting engine, oil pressure builds and through hole in MB (6) enters the cavity of MB journal. Once MB journal cavity is full, then through oil (4) hole in flange, oil enters cavity of crank pin. Through hole (7) in crank pin, oil is supplied for lubrication.

Flange is manufactured by powder metallurgy route or by forming or by machining rolled sections. Powder metallurgy route provides better control over weight. CP & MB journals are manufactured from tubes either seamless tubes or welded tubes.

Flange is held on fixture and CP & MB journals are shrunk fitted. Assembly starts with a flange and either a CP journal or a MB journal. Then, assembly is continued in sequence by assembling adjacent parts. Dimensional accuracies of crank shaft are controlled by dimensional accuracies of loose parts and tolerances of assembly fixture. The foregoing description is a specific embodiment of the present invention. It should be appreciated that this embodiment is described for purpose of illustration only, and that numerous alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the invention. It is intended that all such modifications and alterations be included insofar as they come within the scope of the invention as claimed or the equivalents thereof.