CRANKSHAFT FOR RECIPROCATING ENGINE

Abstract

A crankshaft includes journals that define a central axis of rotation; crank pins that are eccentric with respect to the journals; crank arms connecting the journals to the crank pins; and counterweights integrated with the crank arms. Each of the crank arms has recesses in a surface adjacent to the crank pin. The recesses are disposed inward of peripheral regions in both sides along an edge of the surface, and are disposed along the peripheral regions. The crankshaft has a reduced weight, an increased torsional rigidity and an increased flexural rigidity.

Claims

1. A crankshaft for a reciprocating engine, the crankshaft comprising: journals that define a central axis of rotation; crank pins that are eccentric with respect to the journals; crank arms connecting the journals to the crank pins; and counterweights integrated with the crank arms, wherein the crankshaft is to be mounted in a reciprocating engine; and wherein each of the crank arms has recesses in a surface adjacent to the crank pin, the recesses disposed inward of peripheral regions in both sides along an edge of the surface, the recesses disposed along the peripheral regions, thereby making a central region inward of the recesses thick.

2. The crankshaft for a reciprocating engine according to claim 1, wherein the recesses are connected together at a center of rotation of the crankshaft.

3. The crankshaft for a reciprocating engine according to claim 1, wherein the recesses are connected together at a position shifted toward the crank pin from a center of rotation of the crankshaft.

4. The crankshaft for a reciprocating engine according to claim 1, wherein the recesses are extended along an edge of the journal and are connected together at a position shifted toward the counterweight from a center of rotation of the crankshaft.

5. The crankshaft for a reciprocating engine according to claim 1, wherein the recesses are symmetric with respect to a line connecting an axis of the journal to an axis of the crank pin.

6. The crankshaft for a reciprocating engine according to claim 2, wherein the recesses are symmetric with respect to a line connecting an axis of the journal to an axis of the crank pin.

7. The crankshaft for a reciprocating engine according to claim 3, wherein the recesses are symmetric with respect to a line connecting an axis of the journal to an axis of the crank pin.

8. The crankshaft for a reciprocating engine according to claim 4, wherein the recesses are symmetric with respect to a line connecting an axis of the journal to an axis of the crank pin.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0029] FIG. 1 is a schematic side view of an example of common crankshafts for multiple cylinder engines.

[0030] FIG. 2 is a schematic diagram illustrating a method for evaluating the flexural rigidity of a crank arm.

[0031] FIGS. 3(a) and 3(b) are schematic diagrams illustrating a method for evaluating the torsional rigidity of a crank arm, wherein FIG. 3(a) is a side view of a throw, and FIG. 3(b) is a front view thereof in the axial direction.

[0032] FIGS. 4(a) to 4(c) are diagrams showing typical examples in which the crank arm is assumed to be a simple circular plate from the standpoint of torsional rigidity in the sense of Strength of Materials, wherein FIG. 4(a) shows a circular plate having a rectangular cross section, FIG. 4(b) shows a circular plate having a projected cross section, and FIG. 4(c) shows a circular plate having a recessed cross section.

[0033] FIGS. 5(a) to 5(c) are diagrams showing typical examples in which the crank arm is assumed to be a simple beam from the standpoint of flexural rigidity in the sense of Strength of Materials, wherein FIG. 5(a) shows a beam having a rectangular cross section, FIG. 5(b) shows a beam having a projected cross section, and FIG. 5(c) shows a beam having a recessed cross section.

[0034] FIG. 6 is a graph summarizing the magnitude relationships between the beams having the respective cross-sectional shapes in the area moment of inertia and in the polar moment of inertia, which are directly related to flexural rigidity and torsional rigidity.

[0035] FIGS. 7(a) to 7(e) are schematic views showing an example of a crank arm shape in a crankshaft according to a first embodiment of the present invention, wherein FIG. 7(a) is a front view of the crank arm as seen from the crank pin in the axial direction, FIG. 7(b) is a cross-sectional view taken along the line A-A, FIG. 7(c) is a cross-sectional view taken along the line B-B, FIG. 7(d) is a cross-sectional view taken along the line C-C, and FIG. 7(e) is a cross-sectional view taken along the line D-D.

[0036] FIGS. 8(a) to 8(e) are schematic views showing an example of a crank arm shape in a crankshaft according to a second embodiment of the present invention, wherein FIG. 8(a) is a front view of the crank arm as seen from the crank pin in the axial direction, FIG. 8(b) is a cross-sectional view taken along the line E-E, FIG. 8(c) is a cross-sectional view taken along the line F-F, FIG. 8(d) is a cross-sectional view taken along the line G-G, and FIG. 8(e) is a cross-sectional view taken along the line H-H.

[0037] FIGS. 9(a) to 9(e) are schematic views showing an example of a crank arm shape in a crankshaft according to a third embodiment of the present invention, wherein FIG. 9(a) is a front view of the crank arm as seen from the crank pin in the axial direction, FIG. 9(b) is a cross-sectional view taken along the line I-I, FIG. 9(c) is a cross-sectional view taken along the line J-J, FIG. 9(d) is a cross-sectional view taken along the line K-K, and FIG. 9(e) is a cross-sectional view taken along the line L-L.

[0038] FIGS. 10(a) to 10(e) are schematic views showing an example of a crank arm shape in a crankshaft according to a fourth embodiment of the present invention, wherein FIG. 10(a) is a front view of the crank arm as seen from the crank pin in the axial direction, FIG. 10(b) is a cross-sectional view taken along the line M-M, FIG. 10(c) is a cross-sectional view taken along the line N-N, FIG. 10(d) is a cross-sectional view taken along the line O-O, and FIG. 10(e) is a cross-sectional view taken along the line P-P.

DESCRIPTION OF EMBODIMENTS

[0039] Embodiments of the crankshaft for a reciprocating engine according to the present invention will now be described.

1. Basic Techniques to Consider in Designing Crankshaft

1-1. Flexural Rigidity of Crank Arm

[0040] FIG. 2 is a schematic diagram illustrating a method for evaluating the flexural rigidity of a crank arm. As shown in FIG. 2, in each throw of the crankshaft, a load F of combustion pressure generated by the explosion in the cylinder is applied to the crank pin P via a conrod. Since the journals J at the both ends of each throw are supported by bearings, the load F is transmitted to the journal bearings from the crank pin P via the crank arms A. Thus, each of the crank arms A becomes subjected to a load of three-point bending, and a bending moment M acts on the crank arm A. Accordingly, in each crank arm A, compressive stress occurs at the outside in the thickness direction (the side adjacent to the journal J), and tensile stress occurs at the inside in the thickness direction (the side adjacent to the pin P).

[0041] In the case where the diameters of the crank pin P and the journal J have been determined as design specifications, the flexural rigidity of the crank arm A depends on the crank arm shape of each throw. The counterweight W seldom contributes to the flexural rigidity. The displacement u of the axial center of the crank pin P the direction in which the load of combustion pressure is applied is proportional to the load F of combustion pressure applied to the crank pin P and is inversely proportional to the flexural rigidity as shown in the following formula (1).

u proportional to F/(Flexural Rigidity)   (1)

1-2. Torsional Rigidity of Crank Arm

[0042] FIGS. 3(a) and 3(b) are schematic diagrams illustrating a method for evaluating the torsional rigidity of a crank arm. FIG. 3(a) is a side view of a throw, and FIG. 3(b) is a front view thereof in the axial direction. The crankshaft rotates about the journal J, which causes a torsional torque T as shown in FIGS. 3(a) and 3(b). Thus, it is necessary to enhance the torsional rigidity of the crank arm A in order to ensure smooth rotation against the torsional vibrations of the crankshaft without causing resonance.

[0043] In the case where the diameters of the crank pin P and the journal J have been determined as design specifications, the torsional rigidity of the crank arm A depends on the crank arm shape of each throw. The counterweight W seldom contributes to the torsional rigidity. The torsion angle y of the journal J is proportional to the torsional torque T and inversely proportional to the torsional rigidity as shown in the following formula (2).

y proportional to T/(Torsional Rigidity)   (2)

2. Crankshaft According to Present Invention

2-1. Approach for Increasing Stiffness of Crank Arm

[0044] As stated above, the counterweight seldom contributes to the flexural rigidity and torsional rigidity. Accordingly, the present embodiment provides a crank arm shape that can achieve a reduction in weight and an increase in flexural rigidity in combination with an increase in torsional rigidity.

2-1-1. Shape for Increasing Torsional Rigidity

[0045] Here, an exemplary shape for increasing the torsional rigidity is studied based on the theory of Strength of Materials. For the crank arm A shown in FIGS. 3(a) and 3(b), an effective way to increase its torsional rigidity while maintaining a reduced weight is to increase its polar area moment of inertia.

[0046] FIGS. 4(a) to 4(c) are diagrams showing typical examples in which the crank arm is assumed to be a simple circular plate from the standpoint of torsional rigidity in the sense of Strength of Materials, wherein FIG. 4(a) shows a circular plate having a rectangular cross section, FIG. 4(b) shows a circular plate having a projected cross section, and FIG. 4(c) shows a circular plate having a recessed cross section. The rectangular cross section type circular plate shown in. FIG. 4(a), the projected cross section type circular plate shown in FIG. 4(b), and the recessed cross section type circular plate shown in FIG. 4(c) are assumed to be of equal weight for the sake of maintenance of a reduced weight. In other words, these circular plates are of equal volume in spite of the varied cross sections in rectangular, projected, and recessed shapes.

[0047] Specifically, the rectangular cross section type circular plate shown in FIG. 4(a) has a rectangular cross-sectional shape, and has a thickness of H.sub.0 and a diameter of B.sub.0. The projected cross section type circular plate shown in FIG. 4(b) has a projected cross-sectional shape in which the central portion projects with respect to the outer peripheral portion, and the diameter of the outermost circumference of the circular plate is B.sub.0. The projection in the central portion has a thickness of H.sub.2 and a diameter of B.sub.2, and the outer peripheral portion has a thickness of H.sub.1. The recessed cross section type circular plate shown in FIG. 4(c) has a recessed cross-sectional shape in which the central portion is recessed with respect to the outer peripheral portion, and the diameter of the outermost circumference of the circular plate is B.sub.0. The central portion has a thickness of H.sub.1 with the recession having a depth of H.sub.3 and having a diameter of B.sub.3.

[0048] The magnitude relationship between the torsional rigidities of the respective circular plates is investigated under the condition that they are of equal weight. In general, according to the theory of Strength of Materials, there is a relationship between the torsional rigidity, the polar area moment of inertia, and the torsion angle as shown in the following formulae (3) to (5). The relationship shown in the formulae indicates that increasing the polar area moment of inertia is effective at increasing the torsional rigidity.

Torsional rigidity: G×J/L   (3)

Polar area moment of inertia: J=(n/32)×d.sup.4   (4)

Torsion angle: γ=T×L/(G×J)   (5)

[0049] where L represents the axial length, G represents the modulus of rigidity, d represents the radius of the round bar, and T represents the torsional torque.

[0050] The condition that the three types of circular plates shown in FIGS. 4(a) to 4(c) are of equal weight means the condition that they are of equal volume. Accordingly, the relationship indicated by the following formula (6) is established among the dimensional parameters of the three types of circular plates.

(π/4)×B.sub.0×B.sub.0×H.sub.0=(π/4)×(B.sub.0×B.sub.0×H.sub.1+B.sub.2×B.sub.2×H.sub.2)=(π/4)×{B.sub.0×B.sub.0×(H.sub.1+B.sub.3)−B.sub.3×B.sub.3×H.sub.3)}  (6)

[0051] The polar area moments of inertia of the three types of circular plates are expressed by the following formulae (7) to (9), respectively, taking into account the thicknesses.

[0052] Polar area moment of inertia of a rectangular cross section type circular plate:

J.sub.(A)=(π/32)×H.sub.1×B.sub.0.sup.4   (7)

[0053] Polar area moment of inertia of a projected cross section type circular plate:

J.sub.(B)=(π/32)×(H.sub.1×B.sub.0.sup.4+H.sub.2×B.sub.2.sup.4)   (8)

[0054] Polar area moment of inertia of a recessed cross section type circular plate:

J.sub.(C)=(π/32)×{(H.sub.1+H.sub.3)×B.sub.0.sup.4−H.sub.3×B.sub.3.sup.4}  (9)

[0055] Based on the formulae (7) to (9), the magnitude relationship between the polar area moment of inertia J.sub.(A) of a rectangular cross section type circular plate, the polar area moment of inertia J.sub.(B) of a projected cross section type circular plate, and the polar area moment of inertia J.sub.(C) of a recessed cross section type circular plate is expressed by the following formula (10).

J.sub.(B)<J.sub.(A)<J.sub.(C)   (10)

[0056] This formula (10) is the conclusion drawn theoretically from Strength of Materials. This conclusion can be understood from the observation in the sense of Strength of Materials that, qualitatively speaking, a cross-sectional shape in which materials are placed in greater proportion in locations farther from the torsion center provides a higher polar area moment of inertia.

[0057] For example, a case is considered as an illustrative example in which the dimensional parameters are set as follows so that the condition of equal weight, i.e., the condition of the above formula (6) can be satisfied: B.sub.0=100 mm, H.sub.0=20 mm, H.sub.1=10 mm, H.sub.2=H.sub.3=20 mm, and B.sub.2=B.sub.3=100/√{square root over ( )}2=70.71 mm.

[0058] In the case of this illustrative example, the polar area moment of inertia J.sub.(A) of a rectangular cross section type circular plate is determined as shown in the following formula (11) according to the above formula (7).

J.sub.(A)=1.96×10.sup.8   (11)

[0059] The polar area moment of inertia J.sub.(B) of a projected cross section type circular plate is determined as shown in the following formula (12) according to the above formula (8).

J.sub.(B)=1.47×10.sup.8   (12)

[0060] The polar area moment of inertia J.sub.(C) of a recessed cross section type circular plate is determined as shown in the following formula (13) according to the above formula (9).

J.sub.(C)=2.45×10.sup.8   (13)

[0061] The formulae (11) to (13) numerically confirm that the relationship expressed by the above formula (10) holds.

[0062] Thus, projected cross section type circular plates, rectangular cross section type circular plates, and recessed cross section type circular plates are in ascending order in magnitude of torsional rigidity against torsional loads, and therefore the shape of recessed cross section type circular plates is the most desirable.

2-1-2. Shape for Increasing Flexural Rigidity

[0063] Here, an exemplary shape for increasing the flexural rigidity is studied based on the theory of Strength of Materials. For the crank arm A shown in FIG. 2, an efficient way to increase its flexural rigidity while maintaining a reduced weight is to increase its area moment of inertia against bending.

[0064] FIGS. 5(a) to 5(c) are diagrams showing typical examples in which the cross-sectional shape of the crank arm is simplified and the crank arm is assumed to be a simple beam from the standpoint of flexural rigidity in the sense of Strength of Materials, wherein FIG. 5(a) shows a beam having a rectangular cross section, FIG. 5(b) shows a beam having a projected cross section, and FIG. 5(c) shows a beam having a recessed cross section. The rectangular cross section type beam shown in FIG. 5(a), the projected cross section type beam shown in FIG. 5(b), and the recessed cross section type beam shown in FIG. 5(c) are assumed to be of equal weight for the sake of maintenance of a reduced weight. In other words, these beams are of equal cross-sectional area in spite of the varied cross sections in rectangular, projected, and recessed shapes.

[0065] Specifically, the rectangular cross section type beam shown in FIG. 5(a) has a rectangular cross-sectional shape, and has a thickness of Ho and a width of B.sub.3. The projected cross section type beam shown in FIG. 5(b) has a projected cross-sectional shape in which the central portion projects with respect to the opposite side portions, and the maximum width of the beam is B.sub.3. The central portion has a thickness of H.sub.2 and a width of B.sub.2, and the opposite side portions each have a thickness of H.sub.1 and a width of B.sub.1/2. The recessed cross section type beam shown in FIG. 5(c) has a recessed cross-sectional shape in which the central portion is recessed with respect to the opposite side portions, and the maximum width of the beam is B.sub.3. The central portion has a thickness of H.sub.1 and a width of B.sub.1, and the opposite side portions each have a thickness of H.sub.2 and a width of B.sub.2/2.

[0066] The magnitude relationship between the stiffnesses of the respective beams against bending loads is investigated under the condition that they are of equal weight. In general, the relationship between the flexural rigidity of a rectangular beam and the area moment of inertia thereof is expressed by the following formulae (14) to (16) based on the theory of Strength of Materials. The relationship shown in the formulae indicates that increasing the area moment of inertia results in increasing the flexural rigidity.

Flexural Rigidity: E×I   (14)

Area moment of inertia: I=(1/12)×b×h.sup.3   (15)

Flexural displacement: u=k(M/(E×I))   (16)

[0067] where b represents the width, h represents the thickness, E represents the Young's modulus, M represents the bending moment, and k represents the shape factor.

[0068] The condition that the three types of beams shown in FIGS. 5(a) to 5(c) are of equal weight means the condition that they are of equal volume, i.e., they are of equal cross-sectional area. Accordingly, the relationship indicated by the following formula (17) is established among the dimensional parameters of the three types of beams.

B.sub.3×H.sub.0=(H.sub.2×B.sub.2+B.sub.1×H.sub.1)=(H.sub.2×B.sub.2+B.sub.1×H.sub.1)   (17)

[0069] The area moments of inertia of the three types of beams are expressed by the following formulae (18) to (20), respectively.

[0070] Area moment of inertia of a rectangular cross section type beam:

I.sub.(D)=(1/12)×B.sub.3×H.sub.0.sup.3   (18)

[0071] Area moment of inertia of a projected cross section type beam:

I.sub.(E)=1/3×(B.sub.3×E.sub.2.sup.3−B.sub.1×H.sub.3.sup.3+B.sub.2×E.sub.1.sup.3)   (19)

[0072] where E.sub.2 is determined by “(B.sub.2×H.sub.2.sup.2+B.sub.1×H.sub.1.sup.2)/{2×(B.sub.2×H.sub.2+B.sub.1×H.sub.1)}”, E.sub.1 is determined by “H.sub.2−E.sub.2”, and H.sub.3 is determined by “E.sub.2−H.sub.1”.

[0073] Area moment of inertia of a recessed cross section type beam:

I.sub.(F)=1/3×(B.sub.3×E.sub.2.sup.3−B.sub.1×H.sub.3.sup.3+B.sub.2×E.sub.1.sup.3)   (20)

[0074] where E.sub.2 is determined by “(B.sub.2×H.sub.2.sup.2+B.sub.1×H.sub.1.sup.2)/{2×(B.sub.2×H.sub.2+B.sub.1×H.sub.1)}”, E.sub.1 is determined by “H.sub.2−E.sub.2”, and H.sub.3 is determined by “E.sub.2−H.sub.1”.

[0075] The above formulae (19) and (20) are in the same form. This indicates that the area moment of inertia I.sub.(E) of a projected cross section type beam equals the area moment of inertia I.sub.(F) of a recessed cross section type beam under the condition that they are of equal weight.

[0076] In short, the magnitude relationship between the area moment of inertia I.sub.(D) of a rectangular cross section type beam, the area moment of inertia I.sub.(E) of a projected cross section type beam, and the area moment of inertia I.sub.(F) of a recessed cross section type beam is expressed by the following formula (21).

I.sub.(D)<I.sub.(E)=I.sub.(F)   (21)

[0077] This formula (21) is the conclusion drawn theoretically from Strength of Materials. This conclusion can be understood from the observation in the sense of Strength of Materials that, qualitatively speaking, a cross-sectional shape such that materials are placed in greater proportion in locations farther from the neutral plane of bending provides a higher area moment of inertia.

[0078] For example, a case is considered as an illustrative example in which the dimensional parameters are set as follows so that the condition of the equal weight, i.e., the condition of the above formula (17) can be satisfied: B.sub.1=B.sub.2=50 mm, B.sub.3=100 mm, H.sub.0=20 mm, H.sub.1=10 mm, and H.sub.2=30 mm, by which E.sub.1=12.5 mm, E.sub.2=17.5 mm, and H.sub.3=7.5 mm.

[0079] In the case of this illustrative example, the area moment of inertia I.sub.(D) of a rectangular cross section type beam is determined as shown in the following formula (22) according to the above formula (18).

I.sub.(D)=6.67×10.sup.4   (22)

[0080] The area moment of inertia I.sub.(E) of a projected cross section type beam is determined as shown in the following formula (23) according to the above formula (19).

I.sub.(E)=2.04×10.sup.5   (23)

[0081] The area moment of inertia I.sub.(F) of a recessed cross section type beam is determined as shown in the following formula (24) according to the above formula (20).

I.sub.(F)=2.04×10.sup.5   (24)

[0082] The formulae (22) to (24) numerically confirm that the relationship expressed by the above formula (21) holds.

[0083] Thus, projected cross section type beams and recessed cross section type beams have comparable flexural rigidities against bending loads, and therefore partially thickened crank arm shapes such as those of a projected cross section type beam and a recessed cross section type beam are preferable to the shape of a rectangular cross section type beam because such thickened crank arm shapes provide a higher flexural rigidity.

2-1-3. Summarization of Shapes for Increasing Flexural Rigidity and Torsional Rigidity

[0084] FIG. 6 is a graph summarizing the magnitude relationships between the beams having the respective cross-sectional shapes in the area moment of inertia and in the polar moment of inertia, which are directly related to flexural rigidity and torsional rigidity. In FIG. 6, the polar moments of inertia and the area moments of inertia resulting from the cross sectional shapes shown in FIGS. 4(a) to 4(c) and FIGS. 5(a) to 5(c), i.e., the rectangular cross section, the projected cross section, and the recessed cross section, are presented as relative values assuming that the values of the rectangular cross section are the reference “1”.

[0085] The results shown in FIG. 6 indicate that thickening the crank arm is an efficient way to increase both the flexural rigidity and the torsional rigidity. FIG. 6 shows that the projected cross-sectional shape results in an increase in flexural rigidity while the recessed cross-sectional shape results in an increase in torsional rigidity. Therefore, a combination of a projected shape and a recessed shape will result in both an increase in flexural rigidity and an increase in torsional rigidity.

2-2. Overview of Crankshaft According to Present Invention

[0086] As mentioned above, an efficient way to increase both the flexural rigidity and the torsional rigidity is to design the crank arm to have a cross-sectional shape that is a combination of a projected shape and a recessed shape. Specifically, the peripheral regions in both sides along the edge of the crank arm are configured to be thick, the regions inward of the peripheral regions are configured to be thin, and the central region further inward thereof (a region through which the crank arm centerline passes and which is adjacent to the journal) is configured to be thick. By configuring the peripheral regions, which are farther from the torsion center of the crank arm, to be thick and configuring the regions inward thereof to be thin, it is possible to ensure a high torsional rigidity while achieving a reduction in weight. The large thickness of the peripheral regions of the crank arm contributes to ensuring of the flexural rigidity. In addition, the large thickness of the central region of the crank arm contributes to ensuring of the flexural rigidity.

[0087] In light of these things, in a crankshaft of the present embodiment, a crank arm has recesses in the surface adjacent to the crank pin, and the recesses are disposed in regions inward of periphery regions in both sides along the edge of the surface, and are disposed along the peripheral regions. Accordingly, the peripheral regions of the crank arm outward of the recesses are thickened, and the regions inward of the peripheral regions are thinned because of the recesses. Further, the region inward of the recesses is thickened. Thereby, the crankshaft of the present embodiment has a reduced weight, an increased torsional rigidity and an increased flexural rigidity.

2-3. Specific Examples

First Embodiment

[0088] FIGS. 7(a) to 7(e) are schematic views showing an example of a crank arm shape in a crankshaft according to a first embodiment. FIG. 7(a) is a front view of the crank arm as seen from the crank pin in the axial direction, FIG. 7(b) is a cross-sectional view taken along the line A-A, FIG. 7(c) is a cross-sectional view taken along the line B-B, FIG. 7(d) is a cross-sectional view taken along the line C-C, and FIG. 7(e) is a cross-sectional view taken along the line D-D. The A-A cross section in FIG. 7(b) is a cross section along a crank arm centerline Ac. The B-B cross section in FIG. 7(c) is a cross section perpendicular to a crank arm centerline Ac and including the center of rotation of the crankshaft (the axis Jc of the journal). The C-C cross section in FIG. 7(d) is a cross section parallel to the B-B cross section and taken at a position shifted toward the crank pin from the center of rotation of the crankshaft. The D-D cross section in FIG. 7(e) is a cross section parallel to the B-B cross section taken at a position shifted toward the counterweight from the center of rotation of the crankshaft.

[0089] In the crank arm A of the first embodiment shown in FIG. 7(a) to 7(e), recesses 10 are made in the surface adjacent to the crank pin P and are symmetric with respect to the crank arm centerline Ac. Specifically, the crank arm A has peripheral regions 11 in both sides along the edge of the surface adjacent to the crank pin P. Inward of the peripheral regions 11, the recesses 10 are made along the respective peripheral regions 11. Thereby, the peripheral regions 11 in both sides of the crank arm A are thickened, and the regions inward of the peripheral regions 11 are thinned because of the recesses 10. Further, the central region inward of the recesses 10 is thickened. This configuration of the crank arm allows for a reduction in weight, an increase in torsional rigidity and an increase in flexural rigidity of the crankshaft.

Second Embodiment

[0090] FIGS. 8(a) to 8(e) are schematic views showing an example of a crank arm shape in a crankshaft according to a second embodiment. FIG. 8(a) is a front view of the crank arm as seen from the crank pin in the axial direction, FIG. 8(b) is a cross-sectional view taken along the line E-E, FIG. 8(c) is a cross-sectional view taken along the line F-F, FIG. 8(d) is a cross-sectional view taken along the line G-G, and FIG. 8(e) is a cross-sectional view taken along the line The E-E cross section, F-F cross section, G-G cross section and H-H cross section are cross sections of the crank arm shown by FIG. 8(a) taken at positions corresponding to the positions of the A-A cross section, B-B cross section, C-C cross section and D-D cross section of the crank arm shown by FIG. 7(a), respectively.

[0091] The crank arm A of the second embodiment shown in FIGS. 8(a) to 8(e) is based on the configuration of the crank arm A of the first embodiment shown in FIGS. 7(a) to 7(e), and is a variation thereof with a partially modified configuration. In the second embodiment, as shown in FIGS. 8(a) and 8(b), the recesses 10 formed in the surface of the crank arm A adjacent to the crank pin P are extended to the crank arm centerline Ac. Accordingly, the recesses 10 are connected together at the center of rotation of the crankshaft, that is, the axis Jc of the journal J.

[0092] In the crank arm A of the second embodiment, the peripheral regions 11 in both sides are thickened, and the regions inward of the peripheral regions 11 are thinned because of the recesses 10. Further, the central region inward of the recesses 10 is thickened. In the second embodiment, also, the recesses 10 disposed in both sides are connected together, and the area of the recesses 10 is large as compared with the first embodiment. Thus, the crank arm A of the second embodiment allows for a reduction in weight, an increase in torsional rigidity and an increase in flexural rigidity of the crankshaft as is the case with the first embodiment. The shape of the crank arm A of the second embodiment is effective especially for weight reduction of the whole crankshaft.

Third Embodiment

[0093] FIGS. 9(a) to 9(e) are schematic views showing an example of a crank arm shape in a crankshaft according to a third embodiment. FIG. 9(a) is a front view of the crank arm as seen from the crank pin in the axial direction, FIG. 9(b) is a cross-sectional view taken along the line FIG. 9(c) is a cross-sectional view taken along the line J-J, FIG. 9(d) is a cross-sectional view taken along the line K-K, and FIG. 9(e) is a cross-sectional view taken along the line L-L. The I-I cross section, J-J cross section, K-K cross section and L-L cross section are cross sections of the crank arm shown by FIG. 9(a) taken at positions corresponding to the positions of the A-A cross section, B-B cross section, C-C cross section and D-D cross section of the crank arm shown by FIG. 7(a), respectively.

[0094] The crank arm A of the third embodiment shown in FIGS. 9(a) to 9(e) is based on the configuration of the crank arm A of the first embodiment shown in FIGS. 7(a) to 7(e), and is a variation thereof with a partially modified configuration. In the third embodiment, as shown in FIGS. 9(a) and 9(b), the recesses 10 formed in the surface of the crank arm A adjacent to the crank pin P are connected together at a position shifted toward the crank pin P from the center of rotation of the crankshaft.

[0095] In the crank arm A of the third embodiment, the peripheral regions 11 in both sides are thickened, and the regions inward of the peripheral regions 11 are thinned because of the recesses 10. Further, the central region inward of the recesses 10 is thickened. In the third embodiment, also, the area of the recesses 10 is large as compared with the first embodiment. Thus, the crank arm A of the third embodiment has the same effects with the second embodiment.

Fourth Embodiment

[0096] FIGS. 10(a) to 10(e) are schematic views showing an example of a crank arm shape in a crankshaft according to a fourth embodiment. FIG. 10(a) is a front view of the crank arm as seen from the crank pin in the axial direction, FIG. 10(b) is a cross-sectional view taken along the line M-M, FIG. 10(c) is a cross-sectional view taken along the line N-N, FIG. 10(d) is a cross-sectional view taken along the line O-O, and FIG. 10(e) is a cross-sectional view taken along the line P-P. The M-M cross section, N-N cross section, O-O cross section and P-P cross section are cross sections of the crank arm shown by FIG. 10(a) taken at positions corresponding to the positions of the A-A cross section, B-B cross section, C-C cross section and D-D cross section of the crank arm shown by FIG. 7(a), respectively.

[0097] The crank arm A of the fourth embodiment shown in FIGS. 10(a) to 10(e) is based on the configuration of the crank arm A of the first embodiment shown in FIGS. 7(a) to 7(e), and is a variation thereof with a partially modified configuration. In the fourth embodiment, as shown in FIGS. 10(a) and 10(b), the recesses 10 formed in the surface of the crank arm A adjacent to the crank pin P are connected together at a position shifted toward the counterweight W from the center of rotation of the crankshaft. Especially in the case shown by FIGS. 10(a) to 10(e), the recesses 10 are extended along the edge of the journal J and are connected together.

[0098] In the crank arm A of the fourth embodiment, the peripheral regions 11 in both sides are thickened, and the regions inward of the peripheral regions 11 are thinned because of the recesses 10. Further, the central region inward of the recesses 10 is thickened. In the fourth embodiment, also, the area of the recesses 10 is large as compared with the first embodiment. Thus, the crank arm A of the third embodiment has the same effects with the second and third embodiments.

[0099] The present invention is applicable to crankshafts to be mounted in a variety of reciprocating engines. Specifically, the engine may have any number of cylinders, for example, two cylinders, three cylinders, four cylinders, six cylinders, eight cylinders or ten cylinders, and even more cylinders. The cylinder arrangement may be of any type, for example, in-line type, V-type, opposed type or the like. The fuel for the engine may be of any kind, for example, gasoline, diesel, biofuel or the like. Also, the engines include a hybrid engine consisting of an internal-combustion engine and an electric motor.

INDUSTRIAL APPLICABILITY

[0100] The present invention is capable of being effectively utilized in crankshafts to be mounted in a variety of reciprocating engines.

DESCRIPTION OF REFERENCE SYMBOLS

[0101] 1: crankshaft

[0102] J, J1 to J5: journal

[0103] Jc: axis of journal

[0104] P, P1 to P4: crank pin

[0105] Pc: axis of crank pin

[0106] Fr: front part

[0107] Fl: flange

[0108] A, A1 to AS: crank arm

[0109] Ac: crank arm centerline

[0110] W, W1 to W8: counterweight

[0111] 2: damper pulley

[0112] 3: flywheel

[0113] 10: recess

[0114] 11: peripheral region