LIGHTWEIGHT NODULAR IRON CRANKSHAFT FOR HEAVY DUTY ENGINE

Abstract

An automobile vehicle crankshaft including a crankshaft casting of a nodular iron. The crankshaft casting includes multiple main journals coaxially aligned on a common crankshaft casting axis. Multiple crankpin journals are fixedly connected to the main journals by individual webs. Multiple lightening holes have individual ones of the multiple lightening holes integrally formed within individual ones of the crankpin journals during casting. A bubble space is located proximate to a mid-portion of selected ones of the multiple lightening holes of the crankpin journals. The bubble space locally increases a passage size of the selected ones of the multiple lightening holes and reduces a mass of the individual ones of the crankpin journals.

Claims

1. An automobile vehicle crankshaft, comprising: a crankshaft casting of a nodular iron including: multiple main journals coaxially aligned on a common crankshaft casting axis; and multiple crankpin journals fixedly connected to the main journals by individual webs; multiple lightening holes, wherein individual ones of the multiple lightening holes are integrally formed within individual ones of the crankpin journals during casting; and a bubble space located proximate to a mid-portion of selected ones of the multiple lightening holes of the crankpin journals, the bubble space locally increasing a passage size of the selected ones of the multiple lightening holes and reducing a mass of the individual ones of the crankpin journals, wherein a skin surface of the bubble space is approximately 0.5 mm deep and reduces at least one of a Young's modulus, a tensile strength and a fatigue strength at the skin surface.

2. The automobile vehicle crankshaft of claim 1, wherein: the multiple lightening holes have a V-shaped geometry; and a first opening end of the selected ones of the multiple lightening holes of the multiple crankpin journals have a first diameter and a second opening end of the selected ones of the multiple lightening holes have a second diameter.

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

4. (canceled)

5. The automobile vehicle crankshaft of claim 1, wherein a Young's modulus of the skin surface of the bubble space is reduced by approximately 15% compared to an overall Young's modulus of the crankshaft casting.

6. The automobile vehicle crankshaft of claim 1, wherein a tensile strength of the skin surface of the bubble space is reduced by approximately 30% compared to an overall tensile strength of the crankshaft casting.

7. The automobile vehicle crankshaft of claim 1, wherein a fatigue strength of the skin surface of the bubble space is reduced by approximately 30% compared to an overall fatigue strength of the crankshaft casting.

8. The automobile vehicle crankshaft of claim 1, wherein the nodular iron has a Young's modulus in a range of 175 to 195 GPa.

9. (canceled)

10. The automobile vehicle crankshaft of claim 1, further including a first main journal oilway formed in at least one of the multiple main journals.

11. A casting, comprising: an automobile vehicle crankshaft casting of a nodular iron including: multiple main journals coaxially aligned on a common crankshaft axis; multiple crankpin journals fixedly connected to the main journals by individual webs; and multiple counterweights fixedly connected to the casting; multiple lightening holes, wherein the multiple main journals each include one of the multiple lightening holes integrally formed therein during casting and individual ones of the multiple crankpin journals each include one of the multiple lightening holes integrally formed therein during casting; the multiple lightening holes of the multiple crankpin journals having a V-shaped geometry; and a bubble space located proximate to a mid-portion of selected ones of the multiple lightening holes of the multiple crankpin journals, the bubble space locally increasing a passage size of the selected ones of the multiple lightening holes and reducing a mass of the individual ones of the multiple crankpin journals, wherein a skin surface of the bubble space is approximately 0.5 mm deep and reduces at least one material property of the crankshaft casting.

12. The casting of claim 11, further including a concave-shaped transition surface transitioning between the multiple lightening holes and the bubble space of selected ones of the multiple lightening holes of the multiple crankpin journals.

13. (canceled)

14. The casting of claim 11, wherein a bottom portion of the V-shaped geometry of the multiple lightening holes of the crankpin journals is directed toward the common crankshaft axis.

15. The casting of claim 11, wherein an oil passage extending into individual ones of the multiple crankpin journals passes outside of the multiple lightening holes.

16. The casting of claim 11, wherein the V-shaped geometry and the bubble space of the multiple lightening holes of the multiple crankpin journals normalize a stress across a length of the automobile vehicle crankshaft casting.

17. The casting of claim 11, wherein the V-shaped geometry and the bubble space of the multiple lightening holes balance the automobile vehicle crankshaft casting.

18. A method to produce a automobile vehicle crankshaft, comprising: creating a casting of a nodular iron including: coaxially aligning multiple main journals on a common crankshaft axis; and fixedly connecting multiple crankpin journals between successive ones of the multiple main journals by individual webs; forming multiple lightening holes, wherein individual ones of the multiple lightening holes are formed within individual ones of the multiple crankpin journals during casting; and locating a bubble space proximate to a mid-portion of selected ones of the multiple lightening holes, the bubble space locally increasing a passage size of the selected ones of the multiple lightening holes and thereby reducing a mass of the individual ones of the multiple crankpin journals, wherein a skin surface of the bubble space is approximately 0.5 mm deep and reduces at least one of a Young's modulus, a tensile strength and a fatigue strength at the skin surface.

19. The method of claim 18, wherein the multiple lightening holes have a V-shaped geometry.

20. The method of claim 18, further including interspacing multiple counterweights along the casting, the multiple counterweights also cast of the nodular iron.

21. The method of claim 18, wherein a tensile strength of the skin surface of the bubble space is reduced by approximately 30% compared to an overall tensile strength of the crankshaft casting.

22. The method of claim 18, wherein a fatigue strength of the skin surface of the bubble space is reduced by approximately 30% compared to an overall fatigue strength of the crankshaft casting.

23. The method of claim 18, wherein the nodular iron has a Young's modulus in a range of 175 to 195 GPa.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

[0027] FIG. 1 is a front elevational perspective view of a nodular iron crankshaft according to an exemplary aspect;

[0028] FIG. 2 is a cross sectional elevational view taken at section 2 of FIG. 1;

[0029] FIG. 3 is a cross sectional elevational view taken at section 3 of FIG. 1;

[0030] FIG. 4 is a cross sectional elevational view of area 4 of FIG. 2;

[0031] FIG. 5 is a side elevational view of a lightening hole according to an exemplary aspect;

[0032] FIG. 6 is a cross sectional view of a lightening hole according to an exemplary aspect; and

[0033] FIG. 7 is a cross sectional view of area 7 of FIG. 6.

DETAILED DESCRIPTION

[0034] The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses.

[0035] Referring to FIG. 1, a reduced weight nodular iron crankshaft and a method to produce a reduced weight nodular iron crankshaft 10 of the present disclosure includes a cast nodular iron crankshaft 12 having components formed about and axially rotatable with respect to a longitudinal rotational axis 14. The cast nodular iron crankshaft 12 in an exemplary aspect shown supports a 4-cylinder engine, however a nodular iron crankshaft modified from FIG. 1 may be provided to support any number of engine cylinders using the design features of the cast nodular iron crankshaft 12. The nodular iron crankshaft 12 includes components directly aligned along the longitudinal rotational axis 14 including a crank nose 16 and a flywheel mounting flange 18. Additional components directly aligned along the longitudinal rotational axis 14 include a first main journal 20, a second main journal 22, a third main journal 24 and a fourth main journal 26. A fifth main journal, not visible in this view, is shown and described in reference to FIG. 2.

[0036] Components of the cast nodular iron crankshaft 12 which are offset from the longitudinal rotational axis 14 include a first pin journal 28, a second pin journal 30, a third pin journal 32 and a fourth pin journal 34. Rotational load balancing of the cast nodular iron crankshaft 12 is achieved in part using paired counterweights connected to the individual pin journals and to successive ones of the main journals. The paired counterweights have common components including counterweight portions connected by crankpin journal webs to the individual pin journals. For example, to balance a load of the first pin journal 28 a first paired counterweight 36 includes a first counterweight portion 36a connected to the first main journal 20 and to the first pin journal 28 by a first crankpin journal web 37, and a second counterweight portion 36b connected to the second main journal 22 and also to the first pin journal 28 by a second crankpin journal web 37b. Individual ones of the pin journals including the first pin journal 28 also include at least one crankpin oil hole such as a first crankpin journal oil hole 39a and a second crankpin journal oil hole 39b to deliver lubrication oil to the first pin journal 28. The paired counterweights further include a second paired counterweight 38 connected to and balancing a load of the second pin journal 30, a third paired counterweight 40 connected to and balancing a load of the third pin journal 32, and a fourth paired counterweight 42 connected to and balancing a load of the fourth pin journal 34.

[0037] Referring to FIG. 2 and again to FIG. 1, to eliminate a need to further load balance the cast nodular iron crankshaft 12 by fixing additional weight to distal ends of the counterweights, such as by the addition of heavy metals including tungsten, crankshaft load balancing is accomplished by the formation of shaped lightening holes in individual ones of the pin journals during casting of the cast nodular iron crankshaft 12. The lightening holes are “tuned” during crankshaft design for size, shape and location to reduce crankshaft weight and achieve crankshaft load balancing while eliminating the need to add additional weight to the ends of the counterweights as is common in known crankshaft designs.

[0038] With continuing reference to FIG. 2, the pin journals positioned at opposed ends of the cast nodular iron crankshaft 12 defining the first pin journal 28 and the fourth pin journal 34 have been determined to achieve maximum crankshaft load balancing by the addition of V-shaped lightening holes individually having a bubble space defining a bubble-shaped portion located to provide maximum pin journal mass reduction. The bubble space or bubble-shaped portion is located proximate to a mid-portion of selected ones of the multiple lightening holes of the crankpin journals and may be shifted as noted below with respect to FIG. 4. A first V-shaped lightening hole 46 is located in the first pin journal 28. The first V-shaped lightening hole 46 is created within the first pin journal 28 during casting of the cast nodular iron crankshaft 12 and includes a first bubble-shaped portion 48 outwardly directed with respect to the longitudinal rotational axis 14. A first opening 50 into the first V-shaped lightening hole 46 is directed toward the crank nose 16 and an opposed second opening 52 is directed toward the flywheel mounting flange 18. A second V-shaped lightening hole 54 including a second bubble-shaped portion 55 outwardly directed with respect to the longitudinal rotational axis 14 is created within the fourth pin journal 34 during casting which may be configured as a mirror image of the first V-shaped lightening hole 46 and the first bubble-shaped portion 48. According to several aspects the first bubble-shaped portion 48 may be laterally displaced during a design phase of the 14 to maximize a mass shift away from the first main journal 20 and therefore to maximize load balance of the cast nodular iron crankshaft 12. Lateral displacement may be in a first displacement direction 56 away from the first main journal 20 or in a second displacement direction 58 which is toward the first main journal 20. The second bubble-shaped portion 55 may be laterally displaced during a design phase of the cast nodular iron crankshaft 12 to maximize a mass shift away from the flywheel mounting flange 18 and therefore to maximize load balance of the cast nodular iron crankshaft 12.

[0039] Referring to FIG. 3 and again to FIG. 2, according to several aspects, a third V-shaped lightening hole 60 is created within the second pin journal 30 during casting and a fourth V-shaped lightening hole 62 is created within the third pin journal 32. According to several aspects, the third V-shaped lightening hole 60 and the fourth V-shaped lightening hole 62 lack the feature of the bubble-shaped portion, as shown, unless during analysis it is determined that balancing the cast nodular iron crankshaft 12 also requires the use of the bubble-shaped portion in the third V-shaped lightening hole 60 and the fourth V-shaped lightening hole 62. It is noted that the first V-shaped lightening hole 46, the second V-shaped lightening hole 54, the third V-shaped lightening hole 60 and the fourth V-shaped lightening hole 62 are individually provided in an as-cast condition and do not require post casting machining or de-burring to achieve crankshaft balancing requirements.

[0040] Referring to FIG. 4 and again to FIGS. 1 through 3, further details of the first V-shaped lightening hole 46 and details common to the four pin journals are discussed herein in reference to the first V-shaped lightening hole 46 and the first pin journal 28, therefore no further discussion is provided herein to further describe the remaining pin journals and pin journals. Transition regions are provided between the main journals and the pin journals to improve crankshaft fatigue performance. A first transition region 64 of the first pin journal 28 is bounded between a first reference plane 66 defined at a first surface 68 of the first pin journal 28 and a second reference plane 70 defined by a second surface 71 of a first raised shoulder 72 defining an outer extent of a machined contact surface 74 of the first pin journal 28.

[0041] A second transition region 76 of the first pin journal 28 is oppositely directed with respect to the first transition region 64 and is bounded between a third reference plane 78 defined at a third surface 80 of the first pin journal 28 and a fourth reference plane 82 defined by a fourth surface 83 of a second raised shoulder 84 defining an outer extent of the machined contact surface 74 of the first pin journal 28. The transition regions have a large effect on a frequency response function (FRF) at the fillets provided with the cast nodular iron crankshaft 1. An exemplary configuration of a first pin fillet 86 is provided between an intersection of a mass defining the first pin journal 28 and the fourth reference plane 82 of the second transition region 76. Similarly, an exemplary configuration of a first main fillet 88 is provided between an intersection of a mass defining the second main journal 22 and the third reference plane 78.

[0042] Journal oilways including at least a first main journal oilway 90 are provided in individual ones of the pin journals and the main journals. The first opening 50 defines a curvature aligning the first opening 50 into the first V-shaped lightening hole 46 with a first concave-shaped surface 92 of the first pin journal 28. Similarly, the second opening 52 defines a curvature aligning the second opening 52 into the first V-shaped lightening hole 46 with a second concave-shaped surface 94 of the first pin journal 28.

[0043] The first bubble-shaped portion 48 includes multiple transition and bubble surfaces including a first concave-shaped transition surface 96 located proximate to and facing toward the first opening 50. The first concave-shaped transition surface 96 transitions into a first convex-shaped surface 98 which further transitions into a straight segment 100 proximate to a center of the first bubble-shaped portion 48. The straight segment 100 then transitions into a second convex-shaped surface 102. The second convex-shaped surface 102 then transitions into a second concave-shaped transition surface 104 located proximate to and facing toward the second opening 52. The first bubble-shaped portion 48 faces outwardly with respect to the longitudinal rotational axis 14 and is oppositely positioned with respect to a bottom V-section 106 of the first bubble-shaped portion 48.

[0044] According to several aspects, a lateral centerline 108 of the first bubble-shaped portion 48 is oriented transverse to the machined contact surface 74 of the first pin journal 28. As previously noted with respect to FIG. 2, the lateral centerline 108 and therefore a lateral position of the first bubble-shaped portion 48 may be shifted in either the first displacement direction 56 away from the first main journal 20 or in the second displacement direction 58.

[0045] Referring to FIG. 5 and again to FIGS. 2 and 4, the exemplary first bubble-shaped portion 48 may have a same size of the 50 and the 52, or the 50 may have a different opening size than the 52. An as-cast pin journal lightening hole inner skin surface 112 may be retained without further deburring or surface smoothing after casting as desired.

[0046] Referring to FIG. 6 and again to FIG. 5, during durability analysis is has been determined that the pin journal lightening hole inner skin surface 112 having a depth of approximately 0.5 mm at a first outer portion 114 of the bubble portion and at a second outer portion 116 opposed to the bubble portion exhibits reduced material properties compared to other regions of the cast nodular iron crankshaft 12. It has therefore been assumed that a Young's modulus (E) is reduced by approximately 15%, and a tensile strength (TS) and a fatigue strength (FS) in the pin journal lightening hole inner skin surface 112 are decreased by approximately 30%.

[0047] According to several aspects the lightening holes as described with particularity with respect to FIGS. 2 and 4 are provided only in the pin journals. It is also noted cast lightening holes or drawing holes similar in configuration to the lightening holes described herein and used in the pin journals may also be provided in the main journals.

[0048] Referring to FIG. 7 and again to FIG. 6, in the as-cast condition of the pin journal lightening hole inner skin surface 112 a degradation skin layer 118 may be present. The possibility of the degradation skin layer 118 being present supports the Young's modulus (E) being reduced by approximately 15%, and the tensile strength (TS) and the fatigue strength (FS) in the pin journal lightening hole inner skin surface 112 being decreased by approximately 30%.

[0049] The nodular iron alloys used for the crankshafts including the cast nodular iron crankshaft 12 defined herein are described in greater detail in reference to United States Patent Application Publication US2021/0115540, issued on Apr. 22, 2021, the subject matter of which is incorporated herein by reference. The nodular iron alloys may include iron, about 2.2 to about 3.2 weight percent (or exactly 2.2-3.2 wt %) carbon, about 1.7 to about 2.3 weight percent (or exactly 1.7-2.3 wt %) silicon, about 0.2 to about 0.6 weight percent (or exactly 0.2-0.6 wt %) manganese, about 0.2 to about 0.6 weight percent (or exactly 0.2-0.6 wt %) copper, about 0.1 to about 0.4 weight percent (or exactly 0.1-0.4 wt %) chromium, about 0.4 to about 0.8 weight percent (or exactly 0.4-0.8 wt %) nickel, about 0.15 to about 0.45 weight percent (or exactly 0.15-0.45 wt %) molybdenum, about 0.2 to about 1.0 weight percent (or exactly 0.2-1.0 wt %) cobalt, and about 0.02 to about 0.06 weight percent (or exactly 0.02-0.06 wt %) magnesium. A carbon equivalent of about 2.8 to about 4.0 weight percent is maintained. The iron may be provided in an amount of at least 90 weight percent. The iron may be present in an amount of greater than 90% of a pearlite microstructure. The iron surrounds a plurality of graphite nodules, wherein a majority of the graphite nodules have a diameter in a range of 1 to 5 micrometers, thereby defining a nodular iron alloy. The nodular iron alloy may have a nodularity greater than 85%, and the graphite nodules may have a number density of greater than 200 graphite nodules per square millimeter. The iron is present in an amount greater than 90% of a pearlite microstructure, wherein the iron surrounds a plurality of the graphite nodules.

[0050] The nodular iron alloy may also include one or more of the following: phosphorus in an amount not exceeding 0.03 weight percent; sulfur in an amount not exceeding 0.02 weight percent; and one or more rare earth elements in an amount not exceeding 0.002 weight percent in total. For example, the nodular iron alloy may contain iron, carbon, silicon, manganese, copper, chromium, nickel, molybdenum, cobalt, and magnesium, and which may also contain phosphorus, sulfur, and rare earth element(s). The rare earth element(s) included may be cerium alone or in combination with other rare earth elements. The nodular iron alloy has a Young's modulus in a range of 175 to 195 GPa, and an as-cast ultimate tensile strength in a range of 750 to 950 megapascal pressure unit (MPa).

[0051] A reduced weight nodular iron crankshaft and method to produce a reduced weight nodular iron crankshaft 10 of the present disclosure includes lightening holes that are shaped so that stress is normalized across a length of the crankshaft. The crankshaft may be balanced without the use of heavy metal inserts such as tungsten in the counterweights. The nodular iron crankshaft shows similar durability performance as a forged steel crankshaft based on comprehensive computer aided engineering (CAE) analysis.

[0052] A reduced weight nodular iron crankshaft and method to produce a reduced weight nodular iron crankshaft 10 of the present disclosure offers several advantages. These include a lightweight nodular iron crankshaft for heavy duty engines having lightening holes in all main and pin journals. No heavy and expensive (e.g., tungsten) is needed to add onto the crankshaft counterweights for balance requirements. The nodular iron crankshaft 12 is approximately 800 grams lighter than a comparably sized known counterpart forged steel crankshaft. In addition, a high strength and a high modulus nodular iron alloy is used for the crankshaft.

[0053] The description of the present disclosure is merely exemplary in nature and variations that do not depart from the gist of the present disclosure are intended to be within the scope of the present disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the present disclosure.