Lightweight nodular cast iron crankshaft for heavy duty engines

Abstract

An automotive crankshaft includes a crankshaft casting made of nodular cast iron. The crankshaft casting includes a plurality of main journal coaxially aligned on a common crankshaft casting axis. A plurality of crankpin journal is fixedly connected to the main journal by a separate web. A plurality of lightening holes integrally form a separate lightening hole of the plurality of lightening holes within a separate crankpin journal of the plurality of crankpin journals during casting. A bubble space is positioned proximate to a middle portion of a selected lightening hole of the plurality of lightening holes of the crankpin journal. The bubble space locally increases a passage size of the selected lightening hole of the plurality of lightening holes and lightens a mass of the separate crankpin journal of the plurality of crankpin journals.

Description

Technical Field

[0001] This disclosure relates to systems and methods for balancing the crankshaft of an automobile engine. Background Technology

[0002] Cast iron crankshafts used in automobile engines typically include counterweights to balance the rotational forces acting on the crankshaft journals caused by piston loads. Known crankshaft designs generally add extra weight or mass at the counterweight location to avoid increasing the size of the cast counterweight, which must be done within predetermined physical space constraints. A common material used for adding counterweight mass is tungsten. This extra mass must be secured in place as inserts, which increases the cost of the crankshaft and the overall engine weight.

[0003] Therefore, while the current crankshaft counterweight mass achieves its intended purpose of balancing crankshaft loads, a new and improved crankshaft design is needed to eliminate the need for the added counterweight mass. Summary of the Invention

[0004] According to several aspects, an automotive crankshaft includes a casting made of ductile iron, comprising: a plurality of main journals coaxially aligned on a common crankshaft axis; a plurality of crank pin journals fixedly connected to the main journals by individual webs; and a plurality of weight-reducing holes, wherein, during casting, an individual weight-reducing hole is integrally formed within an individual crank pin journal. A bubble space is positioned approximately at the midpoint of a selected weight-reducing hole among the plurality of weight-reducing holes in the crank pin journal. The bubble space locally increases the channel size of the selected weight-reducing hole and reduces the mass of the individual crank pin journal.

[0005] In another aspect of this disclosure, the plurality of weight-reducing holes of the crank pin journal have a generally V-shaped geometry. A first opening end of a selected weight-reducing hole in the crank pin journal has a first diameter, and a second opening end of a selected weight-reducing hole in the weight-reducing hole has a second diameter.

[0006] In another aspect of this disclosure, the first diameter is smaller than the second diameter.

[0007] In another aspect of this disclosure, the surface of the bubble space is about 0.5 mm deep and reduces at least one material property of the crankshaft.

[0008] In another aspect of this disclosure, the Young's modulus of the skin surface of the bubble space is reduced by approximately 15% compared to the total Young's modulus of the casting.

[0009] In another aspect of this disclosure, the tensile strength of the skin surface of the bubble space is reduced by approximately 30% compared to the total tensile strength of the casting.

[0010] In another aspect of this disclosure, the fatigue strength of the skin surface of the bubble space is reduced by approximately 30% compared to the total fatigue strength of the casting.

[0011] In another aspect of this disclosure, ductile iron is defined as high-modulus iron.

[0012] In another aspect of this disclosure, the center of the first in the bubble space is laterally shifted relative to the center of the second in the bubble space.

[0013] In another aspect of this disclosure, the journal weight reduction hole is formed in a separate journal within the journal.

[0014] According to several aspects, an automotive casting includes a crankshaft casting made of ductile iron, comprising: a plurality of main journals coaxially aligned on a common crankshaft axis; a plurality of crank pin journals fixedly connected to the main journals by individual webs; and a plurality of counterweights fixedly connected to the casting. A plurality of counterweight holes are integrally formed during casting within the main journals and in the individual crank pin journals. The plurality of counterweight holes in the crank pin journals have a generally V-shaped geometry. Bubble spaces are positioned approximately at the middle portion of selected counterweight holes among the plurality of counterweight holes in the crank pin journals. The bubble spaces locally increase the channel size of the selected counterweight holes and reduce the mass of the individual crank pin journals in the crank pin journals.

[0015] In another aspect of this disclosure, the smooth curved region transitions between the weight-reducing pores and the bubble space.

[0016] In another aspect of this disclosure, the skin surface of the bubble space is about 0.5 mm deep and reduces at least one of Young's modulus, tensile strength and fatigue strength at the skin surface.

[0017] In another aspect of this disclosure, the bottom portion of the V-shaped geometry of the plurality of weight-reducing holes of the crankpin journal points toward a common crankshaft axis.

[0018] In another aspect of this disclosure, an oil passage in a separate crank pin journal extending into the crank pin journal passes outside the weight reduction hole.

[0019] In another aspect of this disclosure, the V-shaped geometry of the plurality of weight-reducing holes in the crank pin journal and the length of the bubble space across the crankshaft normalize the stress.

[0020] In another aspect of this disclosure, the V-shaped geometry of the multiple weight-reducing holes and the bubble space balance the crankshaft and eliminate the need for heavy metal balancing inserts to be added to the counterweight.

[0021] According to several aspects, a method for producing a weight-reduced automotive crankshaft includes: forming a casting made of ductile iron, including: coaxially aligning a plurality of main journals on a common crankshaft axis; and fixing a plurality of crank pin journals between successive main journals of the plurality of main journals by separate webs; forming a plurality of weight-reducing holes during casting, such that a single weight-reducing hole of the plurality of weight-reducing holes is located within a single crank pin journal of the crank pin journal; and positioning a bubble space near the middle portion of a selected weight-reducing hole of the plurality of weight-reducing holes, the bubble space locally increasing the channel size of the selected weight-reducing hole of the weight-reducing hole and thereby reducing the mass of the single crank pin journal of the crank pin journal.

[0022] In another aspect of this disclosure, the method further includes forming a plurality of weight-reducing holes having a generally V-shaped geometry.

[0023] In another aspect of this disclosure, the method further includes filling the space along the crankshaft with a plurality of counterweights, the counterweights also being cast from ductile iron.

[0024] Other applicable areas will become apparent from the description provided herein. It should be understood that the descriptions and specific examples are intended for illustrative purposes only and are not intended to limit the scope of this disclosure.

[0025] The present invention also includes the following technical solutions.

[0026] Technical Solution 1. An automobile crankshaft, comprising:

[0027] A crankshaft casting made of ductile iron, the crankshaft casting comprising:

[0028] Multiple main journals coaxially aligned on the axis of a common crankshaft casting;

[0029] Multiple crank pin journals are fixedly connected to the main journal via individual webs;

[0030] Multiple weight-reducing holes, during casting, are integrally formed within individual crank pin journals in the crank pin journals; and

[0031] A bubble space is positioned in the middle of a selected weight reduction hole among a plurality of weight reduction holes near the crank pin journal. The bubble space locally increases the channel size of the selected weight reduction hole among the plurality of weight reduction holes and reduces the mass of the individual crank pin journal in the crank pin journal.

[0032] Technical Solution 2. The automobile crankshaft according to Technical Solution 1, wherein:

[0033] The multiple weight-reducing holes have a roughly V-shaped geometry; and

[0034] The first opening end of a selected weight reduction hole among a plurality of weight reduction holes of a plurality of crank pin journals has a first diameter, and the second opening end of a selected weight reduction hole among a plurality of weight reduction holes has a second diameter.

[0035] Technical Solution 3. The automobile crankshaft according to Technical Solution 2, wherein the first diameter is smaller than the second diameter.

[0036] Technical Solution 4. The automobile crankshaft according to Technical Solution 1, wherein the surface of the bubble space is approximately 0.5 mm deep and reduces at least one material property of the crankshaft casting.

[0037] Technical Solution 5. The automobile crankshaft according to Technical Solution 4, wherein the Young's modulus of the skin surface of the bubble space is reduced by approximately 15% compared to the total Young's modulus of the crankshaft casting.

[0038] Technical Solution 6. The automobile crankshaft according to Technical Solution 4, wherein the tensile strength of the skin surface of the bubble space is reduced by approximately 30% compared with the total tensile strength of the crankshaft casting.

[0039] Technical Solution 7. The automobile crankshaft according to Technical Solution 4, wherein the fatigue strength of the skin surface of the bubble space is reduced by approximately 30% compared to the total fatigue strength of the crankshaft casting.

[0040] Technical Solution 8. The automobile crankshaft according to Technical Solution 1, wherein the ductile iron is defined as high-modulus iron.

[0041] Technical Solution 9. The automobile crankshaft according to Technical Solution 1, wherein a first center of a bubble space located at the middle portion of a first of a plurality of weight reduction holes near a plurality of crank pin journals is laterally displaced relative to a second center of a bubble space located at the middle portion of a second of a plurality of weight reduction holes near a plurality of crank pin journals.

[0042] Technical Solution 10. The automobile crankshaft according to Technical Solution 1, further comprising a main journal weight reduction hole formed in a single main journal among a plurality of main journals.

[0043] Technical Solution 11. A casting comprising:

[0044] Automobile crankshaft castings made of ductile iron, the automobile crankshaft castings comprising:

[0045] Multiple main journals coaxially aligned on a common crankshaft axis;

[0046] Multiple crank pin journals fixedly connected to the main journal via individual webs; and

[0047] Multiple counterweights are fixedly connected to the casting;

[0048] Multiple weight-reducing holes are integrally formed in multiple main journals and individual crank pin journals in multiple crank pin journals during casting.

[0049] The multiple weight-reducing holes of the multiple crank pin journals have a generally V-shaped geometry; and

[0050] A bubble space is positioned near the middle portion of a selected weight reduction hole among multiple weight reduction holes of multiple crank pin journals. The bubble space locally increases the channel size of the selected weight reduction hole among multiple weight reduction holes and reduces the mass of the individual crank pin journal among multiple crank pin journals.

[0051] Technical Solution 12. The casting according to Technical Solution 11 further includes a smoothly curved region transitioning between the bubble space of a selected weight-reducing hole in a plurality of weight-reducing holes and a plurality of weight-reducing holes in a plurality of crank pin journals.

[0052] Technical Solution 13. The casting according to Technical Solution 11, wherein the surface of the bubble space is approximately 0.5 mm deep and at least one of Young's modulus, tensile strength and fatigue strength at the surface is reduced.

[0053] Technical Solution 14. The casting according to Technical Solution 11, wherein the bottom portion of the V-shaped geometry of the plurality of weight-reducing holes of the crank pin journal points to the common crankshaft axis.

[0054] Technical Solution 15. The casting according to Technical Solution 11, wherein the oil passages in the individual crank pin journals extending into the plurality of crank pin journals pass outside the plurality of weight reduction holes.

[0055] Technical Solution 16. The casting according to Technical Solution 11, wherein the V-shaped geometry of the multiple weight-reducing holes of the multiple crank pin journals and the bubble space spanning the length of the automobile crankshaft casting normalize the stress.

[0056] Technical Solution 17. The casting according to Technical Solution 11, wherein the V-shaped geometry of the plurality of weight-reducing holes and the bubble space balance the automotive crankshaft casting and eliminate the need for heavy metal balancing inserts added to the counterweight.

[0057] Technical Solution 18. A method for producing a weight-reduced automobile crankshaft, comprising:

[0058] Forming castings made of ductile iron includes:

[0059] Multiple main journals are coaxially aligned on a common crankshaft axis; and

[0060] Multiple crank pin journals are fixedly connected between consecutive main journals in multiple main journals by means of a separate web;

[0061] Multiple weight-reducing holes are formed during casting, such that each individual weight-reducing hole is located within a single crank pin journal among multiple crank pin journals; and

[0062] A bubble space is positioned close to the middle portion of a selected weight reduction hole among multiple weight reduction holes. The bubble space locally increases the channel size of the selected weight reduction hole among multiple weight reduction holes and thereby reduces the mass of an individual crank pin journal among multiple crank pin journals.

[0063] Technical Solution 19. The method according to Technical Solution 18 further includes forming a plurality of weight-reducing holes having a generally V-shaped geometry.

[0064] Technical Solution 20. The method according to Technical Solution 18 further includes filling the space along the casting with a plurality of counterweights, the plurality of counterweights also being cast from ductile iron. Attached Figure Description

[0065] The accompanying drawings described herein are for illustrative purposes only and are not intended to limit the scope of this disclosure in any way.

[0066] Figure 1 This is a front perspective view of a ductile iron crankshaft according to an exemplary aspect;

[0067] Figure 2 Is Figure 1 A front view of the cross-section taken at point 2 of the section;

[0068] Figure 3 Is Figure 1 A front view of the cross-section taken at point 3 of the section;

[0069] Figure 4 yes Figure 2 A front view of the cross-section of section 4;

[0070] Figure 5 This is a side front view of the weight reduction hole according to an exemplary aspect;

[0071] Figure 6 It is a cross-sectional view of the weight reduction hole according to an exemplary aspect; and

[0072] Figure 7 yes Figure 6 A cross-sectional view of section 7. Detailed Implementation

[0073] The following description is exemplary in nature and is not intended to limit this disclosure, application, or use.

[0074] refer to Figure 1The weight-reduced ductile iron crankshaft disclosed herein and the method for producing the weight-reduced ductile iron crankshaft 10 include casting a ductile iron crankshaft 12 having components formed about a longitudinal axis of rotation 14 and axially rotatable relative to the longitudinal axis of rotation 14. In the illustrated exemplary aspect, the cast ductile iron crankshaft 12 supports a 4-cylinder engine; however, it may be provided that... Figure 1 The modified ductile iron crankshaft utilizes the design features of a cast ductile iron crankshaft 12 to support any number of engine cylinders. The ductile iron crankshaft 12 includes components directly aligned along the longitudinal axis of rotation 14, including a crank nose 16 and a flywheel mounting flange 18. Additional components directly aligned along the longitudinal axis of rotation 14 include a first main journal 20, a second main journal 22, a third main journal 24, and a fourth main journal 26. (Reference) Figure 2 The fifth spindle journal, which is not visible in this view, is shown and described.

[0075] The components of the cast ductile iron crankshaft 12 offset from the longitudinal axis of rotation 14 include a first journal 28, a second journal 30, a third journal 32, and a fourth journal 34. The rotational load balancing portion of the cast ductile iron crankshaft 12 is achieved using paired counterweights connected to individual journals and consecutive main journals. The paired counterweights have common components, including counterweight portions connected to individual journals via crankshaft journal webs. For example, to balance the load on the first journal 28, the first paired counterweight 36 includes a first counterweight portion 36a connected to the first main journal 20 and the first journal 28 via the first crankshaft journal web 37, and a second counterweight portion 36b connected to the second main journal 22 and the first journal 28 via the second crankshaft journal web 37b. The individual journal including the first journal 28 also includes at least one crank pin oil hole (such as the first crank pin oil hole 39a and the second crank pin oil hole 39b) to deliver lubricating oil to the first journal 28. The paired counterweights further include a second paired counterweight 38 connected to the second journal 30 and balancing its load, a third paired counterweight 40 connected to the third journal 32 and balancing its load, and a fourth paired counterweight 42 connected to the fourth journal 34 and balancing its load.

[0076] refer to Figure 2 And refer again Figure 1To eliminate the need for further load balancing of the cast ductile iron crankshaft 12 by fixing additional weight to the distal end of the counterweight (such as by adding heavy metals, including tungsten), crankshaft load balancing is achieved by forming shaped weight-reducing holes in individual pin journals within the pin journals during the casting of the cast ductile iron crankshaft 12. The size, shape, and position of the weight-reducing holes are "adjusted" during crankshaft design to reduce crankshaft weight and achieve crankshaft load balancing, while eliminating the need to add additional weight to the end of the counterweight as is common in known crankshaft designs.

[0077] Continue to refer to Figure 2 The crankshaft journals, which are located at opposite ends of the cast ductile iron crankshaft 12, defining the first and fourth journals 28 and 34, achieve maximum crankshaft load balance by adding V-shaped weight-reducing holes. Each V-shaped weight-reducing hole has a bubble space defining a bubble-shaped portion, which is positioned to provide maximum journal mass reduction. The bubble space or bubble-shaped portion is positioned near the middle portion of a selected weight-reducing hole among the plurality of weight-reducing holes on the crankshaft journal, and can be referenced as described below. Figure 4 Such an offset. The first V-shaped weight-reducing hole 46 is located in the first pivot journal 28. The first V-shaped weight-reducing hole 46 is formed within the first pivot journal 28 during the casting of the cast ductile iron crankshaft 12 and includes a first bubble-shaped portion 48 pointing outward relative to the longitudinal axis of rotation 14. A first opening 50 entering the first V-shaped weight-reducing hole 46 points towards the crank nose 16, and a corresponding second opening 52 points towards the flywheel mounting flange 18. A second V-shaped weight-reducing hole 54, including a second bubble-shaped portion 55 pointing outward relative to the longitudinal axis of rotation 14, is formed within the fourth pivot journal 34 during casting and can be configured as a mirror image of the first V-shaped weight-reducing hole 46 and the first bubble-shaped portion 48. According to several aspects, the first bubble-shaped portion 48 can be laterally displaced during the design phase of 14 to maximize the mass offset away from the first main journal 20, and thus maximize the load balance of the cast ductile iron crankshaft 12. Lateral displacement can be along a first displacement direction 56 away from the first main journal 20 or along a second displacement direction 58 toward the first main journal 20. The second bubble-shaped portion 55 can be laterally displaced during the design phase of the cast ductile iron crankshaft 12 to maximize the mass offset away from the flywheel mounting flange 18, and thus maximize the load balance of the cast ductile iron crankshaft 12.

[0078] refer to Figure 3 And refer to again Figure 2According to several aspects, the third V-shaped weight-reducing hole 60 is formed within the second pin journal 30 during casting, and the fourth V-shaped weight-reducing hole 62 is formed within the third pin journal 32. According to several aspects, the third V-shaped weight-reducing hole 60 and the fourth V-shaped weight-reducing hole 62 lack the characteristic of bubble-shaped portions, as shown in the figure, unless it is determined during analysis that the balanced cast ductile iron crankshaft 12 requires the use of bubble-shaped portions in the third V-shaped weight-reducing hole 60 and the fourth V-shaped weight-reducing hole 62. It should be noted that the first V-shaped weight-reducing hole 46, the second V-shaped weight-reducing hole 54, the third V-shaped weight-reducing hole 60, and the fourth V-shaped weight-reducing hole 62 are provided individually in the cast state and do not require post-cast machining or deburring to achieve the crankshaft balance requirements.

[0079] refer to Figure 4 And refer to again Figures 1 to 3 In this document, further details of the first V-shaped weight-reducing hole 46 and the common details of the four pin journals are discussed with reference to the first V-shaped weight-reducing hole 46 and the first pin journal 28. Therefore, further discussion to describe the remaining pin journals is not provided here. A transition region is provided between the main journal and the pin journals to improve crankshaft fatigue performance. The first transition region 64 of the first pin journal 28 is defined between a first reference plane 66 defined at the first surface 68 of the first pin journal 28 and a second reference plane 70 defined by the second surface 71 of the first raised shoulder 72, thereby defining the outer extent of the machined contact surface 74 of the first pin journal 28.

[0080] The second transition region 76 of the first pin journal 28 points opposite to the first transition region 64 and is defined between a third reference plane 78 defined at the third surface 80 of the first pin journal 28 and a fourth reference plane 82 defined by the fourth surface 83 of the second raised shoulder 84, thereby defining the outer extent of the machined contact surface 74 of the first pin journal 28. The transition region has a significant impact on the frequency response function (FRF) at the fillets provided together with the cast ductile iron crankshaft 1. An exemplary configuration of the first pin fillet 86 is provided between the intersection of the mass defining the first pin journal 28 and the fourth reference plane 82 of the second transition region 76. Similarly, an exemplary configuration of the first master fillet 88 is provided between the intersection of the mass defining the second master journal 22 and the third reference plane 78.

[0081] Journal oil passages (including at least a first main journal oil passage 90) are provided in individual journals in the pin journal and the main journal. A first opening 50 defines the curvature that aligns the first opening 50 entering the first V-shaped weight reduction hole 46 with the first concave surface 92 of the first pin journal 28. Similarly, a second opening 52 defines the curvature that aligns the second opening 52 entering the first V-shaped weight reduction hole 46 with the second concave surface 94 of the first pin journal 28.

[0082] The first bubble-shaped portion 48 includes multiple transition and bubble surfaces, including a first concave transition surface 96 positioned close to and facing the first opening 50. The first concave transition surface 96 transitions into a first convex surface 98, which further transitions into a straight segment 100 close to the center of the first bubble-shaped portion 48. The straight segment 100 then transitions into a second convex surface 102. The second convex surface 102 then transitions into a second concave transition surface 104 positioned close to and facing the second opening 52. The first bubble-shaped portion 48 faces outward relative to the longitudinal axis of rotation 14 and is positioned relative to the bottom V-shaped segment 106 of the first bubble-shaped portion 48.

[0083] According to several aspects, the lateral centerline 108 of the first bubble-shaped portion 48 is oriented transversely to the machined contact surface 74 of the first pin journal 28. (See previous reference...) Figure 2 As indicated, the lateral centerline 108, and therefore the lateral position of the first bubble-shaped portion 48, can be shifted along a first shifting direction 56 away from the first main journal 20 or along a second shifting direction 58.

[0084] refer to Figure 5 And refer to again Figure 2 and Figure 4 The exemplary first bubble-shaped portion 48 may have the same size as 50 and 52, or 50 may have a different opening size than 52. The inner skin surface 112 of the cast pin journal weight-reducing hole may be retained as desired after casting without further deburring or surface smoothing.

[0085] refer to Figure 6 And refer to again Figure 5 During durability analysis, it was determined that the inner skin surface 112 of the pin journal weight-reducing hole, with a depth of approximately 0.5 mm at the first outer portion 114 of the bubble portion and the second outer portion 116 opposite the bubble portion, exhibits reduced material properties compared to other areas of the cast ductile iron crankshaft 12. Therefore, it has been assumed that the Young's modulus (E) is reduced by approximately 15%, and the tensile strength (TS) and fatigue strength (FS) in the inner skin surface 112 of the pin journal weight-reducing hole are reduced by approximately 30%.

[0086] Based on several factors, a special reference is set only in the journal pin. Figure 2 and Figure 4 The weight-reducing holes described herein. It should also be noted that cast weight-reducing holes or broaching holes, similar in configuration to those described herein and used in pin journals, can also be provided in the main journal.

[0087] refer to Figure 7 And refer to again Figure 6In the cast state of the inner skin surface 112 of the pin journal weight reduction hole, a deteriorated skin layer 118 may exist. The possibility of the presence of a deteriorated skin layer 118 supports a reduction of approximately 15% in Young's modulus (E) and a reduction of approximately 30% in tensile strength (TS) and fatigue strength (FS) in the inner skin surface 112 of the pin journal weight reduction hole.

[0088] The ductile iron alloys for crankshafts (including cast ductile iron crankshaft 12) as defined herein are described in more detail with reference to U.S. Patent Application Publication No. US2021 / 0115540, published April 22, 2021, the subject matter of which is incorporated herein by reference. Ductile iron alloys may include iron, about 2.2 to about 3.2 wt% (or exactly 2.2-3.2 wt%) of carbon, about 1.7 to about 2.3 wt% (or exactly 1.7-2.3 wt%) of silicon, about 0.2 to about 0.6 wt% (or exactly 0.2-0.6 wt%) of manganese, about 0.2 to about 0.6 wt% (or exactly 0.2-0.6 wt%) of copper, about 0.1 to about 0.4 wt% (or exactly 0.1-0.4 wt%) of chromium, about 0.4 to about 0.8 wt% (or exactly 0.4-0.8 wt%) of nickel, about 0.15 to about 0.45 wt% (or exactly 0.15-0.45 wt%) of molybdenum, and about 0.2 to about 1.0 wt% (or exactly 0.2-1.0 wt%) of carbon. The alloy contains cobalt (approximately 0.02 to 0.06 wt%) and magnesium (approximately 0.02-0.06 wt%). A carbon equivalent of approximately 2.8 to 4.0 wt% is maintained. Iron may be provided in an amount of at least 90 wt%. Iron may be present in an amount greater than 90% pearlitic microstructure. Iron surrounds multiple graphite spheres, most of which have a diameter in the range of 1 to 5 micrometers, thus defining the ductile iron alloy. The ductile iron alloy may have a spheroidization rate greater than 85%, and the graphite spheres may have a number density greater than 200 graphite spheres per square millimeter. Iron is present in an amount greater than 90% pearlitic microstructure, wherein iron surrounds multiple graphite spheres.

[0089] Ductile iron alloys may also include one or more of the following: phosphorus, in an amount not exceeding 0.03% by weight; sulfur, in an amount not exceeding 0.02% by weight; and one or more rare earth elements, in a total amount not exceeding 0.002% by weight. For example, ductile iron alloys may contain iron, carbon, silicon, manganese, copper, chromium, nickel, molybdenum, cobalt, and magnesium, and may also contain phosphorus, sulfur, and rare earth elements. The included rare earth elements may be cerium alone or in combination with other rare earth elements. Ductile iron alloys have a Young's modulus in the range of 175 to 195 GPa and a casting ultimate tensile strength in the range of 750 to 950 MPa.

[0090] The weight-reduced ductile iron crankshaft disclosed herein and the method for producing the weight-reduced ductile iron crankshaft 10 include weight-reducing holes shaped such that the stress across the length of the crankshaft is normalized. The crankshaft can be balanced without the use of heavy metal inserts such as tungsten in the counterweight. Based on integrated computer-aided engineering (CAE) analysis, the ductile iron crankshaft exhibits similar durability performance to that of a forged steel crankshaft.

[0091] The weight-reduced ductile iron crankshaft disclosed herein and the method for producing the weight-reduced ductile iron crankshaft 10 offer several advantages. These include a lightweight ductile iron crankshaft for heavy-duty engines, featuring weight-reducing bores in all main journals and pin journals. There is no need to add heavy and expensive materials (such as tungsten) to the crankshaft counterweight to meet balance requirements. The ductile iron crankshaft 12 is approximately 800 grams lighter than a known forged steel crankshaft of equivalent size. Furthermore, a high-strength and high-modulus ductile iron alloy is used for the crankshaft.

[0092] The description in this disclosure is exemplary in nature only, and variations thereof that do not depart from the spirit and scope of this disclosure are intended to fall within its scope. Such variations should not be considered as departing from the spirit and scope of this disclosure.

Claims

1. An automobile crankshaft, comprising: A crankshaft casting made of ductile iron, the crankshaft casting comprising: Multiple main journals coaxially aligned on the axis of a common crankshaft casting; Multiple crank pin journals are fixedly connected to the main journal via individual webs; Multiple weight-reducing holes, wherein during casting, each individual weight-reducing hole is integrally formed within a separate crank pin journal, wherein each of the multiple weight-reducing holes is V-shaped, having a bottom V-shaped section arranged between a first open end and a second open end; and A bubble space is formed within a selected weight-reducing hole of a plurality of weight-reducing holes and positioned near the middle portion of the selected weight-reducing hole of a plurality of weight-reducing holes of a crankpin journal. The bubble space is oriented outward relative to the common crankshaft casting axis and is positioned away from the bottom V-shaped section. The bubble space includes a top surface and a bottom surface, the bottom surface being closer to the common crankshaft casting axis than the top surface. The top surface has a first concave transition surface positioned adjacent to and facing the first opening end, wherein the first concave transition surface transitions into a first convex surface, and the first convex surface further transitions into a flat section opposite to the bottom V-shaped section. The segment transitions to a second convex surface, which further transitions to a second concave transition surface positioned adjacent to and facing the second opening end; the bottom surface has a third concave transition surface positioned adjacent to and facing the first opening end, wherein the third concave transition surface transitions to a lower straight section near the bottom V-shaped section, wherein the lower straight section transitions to a fourth concave transition surface positioned adjacent to and facing the second opening end, wherein the bubble space locally increases the channel size of selected weight-reducing holes among a plurality of weight-reducing holes and reduces the mass of individual crank pin journals in crank pin journals, wherein the skin surface of the bubble space is 0.5 mm deep and reduces at least one of Young's modulus, tensile strength and fatigue strength at the skin surface.

2. The automobile crankshaft according to claim 1, wherein: The first opening end of a selected weight reduction hole among a plurality of weight reduction holes of a plurality of crank pin journals has a first diameter, and the second opening end of a selected weight reduction hole among a plurality of weight reduction holes has a second diameter.

3. The automobile crankshaft according to claim 2, wherein, The first diameter is smaller than the second diameter.

4. The automobile crankshaft according to claim 1, wherein, Compared to the overall Young's modulus of the crankshaft casting, the Young's modulus of the skin surface of the bubble space is reduced by 15%.

5. The automobile crankshaft according to claim 1, wherein, Compared to the total tensile strength of the crankshaft casting, the tensile strength of the skin surface of the bubble space is reduced by 30%.

6. The automobile crankshaft according to claim 1, wherein, Compared with the total fatigue strength of the crankshaft casting, the fatigue strength of the skin surface of the bubble space is reduced by 30%.

7. The automobile crankshaft according to claim 1, wherein, Ductile iron is a type of high-modulus iron.

8. The automobile crankshaft according to claim 1, wherein, The first center of the bubble space located at the middle portion of the first of a plurality of weight reduction holes close to the plurality of crank pin journals is laterally shifted relative to the second center of the bubble space located at the middle portion of the second of a plurality of weight reduction holes close to the plurality of crank pin journals.

9. The automobile crankshaft according to claim 1, further comprising a main journal weight reduction hole formed in a single main journal among a plurality of main journals.

10. A casting comprising: Automobile crankshaft castings made of ductile iron, the automobile crankshaft castings comprising: Multiple main journals coaxially aligned on a common crankshaft axis; Multiple crank pin journals fixedly connected to the main journal via individual webs; and Multiple counterweights are fixedly connected to the casting; Multiple weight-reducing holes are integrally formed in multiple main journals and individual crank pin journals in multiple crank pin journals during casting. Multiple weight-reducing holes in multiple crank pin journals have a generally V-shaped geometry, with a bottom V-shaped section arranged between a first open end and a second open end; and A bubble space is formed within a selected weight-reducing hole of a plurality of weight-reducing holes and positioned near the middle portion of the selected weight-reducing hole of a plurality of crankshaft journals. The bubble space is oriented outward relative to the common crankshaft casting axis and is positioned away from the bottom V-shaped section. The bubble space includes a top surface and a bottom surface, the bottom surface being closer to the common crankshaft casting axis than the top surface. The top surface has a first concave transition surface positioned adjacent to and facing a first opening end, wherein the first concave transition surface transitions into a first convex surface, and the first convex surface further transitions into a flat section opposite to the bottom V-shaped section. The segment transitions to a second convex surface, which further transitions to a second concave transition surface positioned adjacent to and facing the second opening end; the bottom surface has a third concave transition surface positioned adjacent to and facing the first opening end, wherein the third concave transition surface transitions to a lower straight section near the bottom V-shaped section, wherein the lower straight section transitions to a fourth concave transition surface positioned adjacent to and facing the second opening end, wherein the bubble space locally increases the channel size of selected weight-reducing holes among a plurality of weight-reducing holes and reduces the mass of individual crank pin journals among a plurality of crank pin journals, wherein the skin surface of the bubble space is 0.5 mm deep and reduces at least one of Young's modulus, tensile strength and fatigue strength at the skin surface.

11. The casting of claim 10, further comprising a smooth curved region transitioning between the bubble space of a selected weight-reducing hole among a plurality of weight-reducing holes and a plurality of weight-reducing holes of a plurality of crank pin journals.

12. The casting according to claim 10, wherein, The bottom portion of the V-shaped geometry of the multiple weight-reducing holes of the crankpin journal points towards the common crankshaft axis.

13. The casting according to claim 10, wherein, Oil passages in individual crankpin journals extending into multiple crankpin journals pass outside multiple weight reduction holes.

14. The casting according to claim 10, wherein, The V-shaped geometry of multiple weight-reducing holes and bubble spaces across the length of the automotive crankshaft casting normalizes stress.

15. The casting according to claim 10, wherein, The V-shaped geometry of multiple weight-reducing holes and the bubble space balance the automotive crankshaft casting and eliminate the need for heavy metal balancing inserts added to the counterweight.

16. A method for producing a lighter automotive crankshaft according to any one of claims 1-9, comprising: Forming castings made of ductile iron includes: Multiple main journals are coaxially aligned on a common crankshaft axis; and Multiple crank pin journals are fixedly connected between consecutive main journals in multiple main journals by means of a separate web; Multiple weight-reducing holes are formed during casting, such that each individual weight-reducing hole is located within a single crank pin journal among multiple crank pin journals; and A bubble space is positioned close to the middle portion of a selected weight reduction hole among multiple weight reduction holes. The bubble space locally increases the channel size of the selected weight reduction hole among multiple weight reduction holes and thereby reduces the mass of an individual crank pin journal among multiple crank pin journals.

17. The method of claim 16, further comprising forming a plurality of weight-reducing holes having a generally V-shaped geometry.

18. The method of claim 16, further comprising filling the space along the casting with a plurality of counterweights, the plurality of counterweights also being cast from ductile iron.

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