GB2352664A

GB2352664A - Engine shaft casting process including preformed slug member

Info

Publication number: GB2352664A
Application number: GB0016395A
Authority: GB
Inventors: Michael Leon Briggs; Nathaniel David Hansen
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 1999-07-06
Filing date: 2000-07-05
Publication date: 2001-02-07
Also published as: GB0016395D0; DE10033974A1

Abstract

A casting process for a cast iron engine shaft (10) comprises positioning a balance-weight slug member (14) into a casting sand mold cavity portion (18) prior to the pouring of molten metal, obviating the need to drill slug bores into the casting counterweight (12). The slug member, in one form, has a mushroom-like shape with its base (26) retained by an adhesive to the cavity portion radial outer end wall (30), juxtaposed the counterweight exterior surface upon the shaft being removed from the mold. The slug member shape allows the' molten metal to flow around the slug member which, upon cooling, solidifies to retain the slug in cast-in-place manner.

Description

2352664 ENGINE SHAFT CASTING PROCESS The present invention relates

generally to cast iron shafts for internal combustion engines and, more specifically, to a process for casting balance-weight slug members within the shaft counterweight portions.

In the casting of engine crankshafts or the like, balancing problems arise because their offset integral segments cause vibrations, which must be dampened by integral counterweight portions. As each counterweight radius is limited, because it must clear the piston and engine block during operation, a costly solution is to design engines larger than would otherwise be necessary to minimize out-of-balance problems. In limited production cases, crankshafts are approximately balanced during casting. The shafts are then tuned to a favorable balance by drilling one or more bores in their counterweight portions and inserting therein a heavy-metal slug member such as 20 tungsten. As this process also requires the expense of securing each slug member in its bore, as by screw fasteners, welds, etc., mass production of crankshaft castings has yet to be achieved. One known balancing procedure is found in U.S. Pat. No. 4,779,316 issued Oct. 25 25, 1988 to Cherry et al., entitled "Crankshaft and a Process for balancing the same." Descriptions of casting processes may be found in publications on the subject, such as Iron Casting Handbook, published by the Iron Casting Society, Inc. in 1981. 30 According to the present invention, there is provided a process for casting an engine shaft of a first metal, about its axis or rotation, by means of one or more balance-weight slug members of a second metal, wherein the second metal is selected from a group of heavy-metals having a predetermined melting point temperature relative to the pouring temperature of the first metal, comprising the steps of:

forming a sand mold of two mating parts containing a cavity conforming to the shaft which includes at least one counterweight cavity portion defined by tapered, inwardly converging, opposed side walls; securing a slug member at predetermined location in the cavity portion of one mold part adjacent a radial outer end wall of the cavity portion relative to the shaft axis; joining the mold parts and filling the cavity with a molten flow of the first metal such that it encircles a portion of the slug member; and upon the molten metal cooling it solidifies, such that the slug member is permanently cast-in-place within the counterweight portion.

The present invention provides an improved casting is process for manufacturing iron crankshafts, balance shafts, and the like for use on internal combustion engines. While the process is designed for use in combination with "green sand" casting technology, it will be noted that other casting processes, such as shell mold casting, may be employed with the invention.

one advantage of the present invention is to provide crankshaft castings or the like for internal combustion engines whereby one or more balanceweight slug members are cast-in-place with the shaft during the casting process.

Another feature involves locating a slug member, having a mushroom-like shape that includes a head section, an intermediate neck section, and a base section, in a counterweight cavity portion of a casting mold. The slug member base is secured to the cavity portion outer end wall by means of a suitable adhesive. Upon pouring the molten casting metal into the mold, the flow of the metal surrounds the slug member. After the metal has solidified the slug member is cast in the counterweight portion, with its base juxtaposed the shaft free surface, thus reducing the overall rotating counterweight mass required for engine static and dynamic balancing.

The instant casting process may also be used in the casting of engine balance shafts, whereby a slug member is cast adjacent the free end of each of its coaxial, halfround, eccentric counterweight portions. In another form of the casting process a slug member, having a spherical shape, includes a pair of oppositely extending, diametrically aligned, projections. Each projection is received in an associated slot formed in an opposed, tapered sand wall of the counterweight portion cavity. The slots position the slug member a predetermined dimension from the cavity portion end wall, thereby defining a passage for the molten metal to flow around and cast the slug member in the counterweight. A spherical slug member may be provided with a pair of oppositely extending spikes to position the slug member adjacent the cavity portion closed end.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a perspective view, with parts broken away, of an iron crankshaft casting for an engine having balance weight slug members cast with its counterweight portions as disclosed in the invention; Figure 2 is a fragmentary, perspective view of a half- part of a green sand mold, adapted to mate with a similar half-part (not shown), to form a mold cavity for the crankshaft of Figure 1; Figure 3 is an enlarged fragmentary cross sectional view taken on the line 3-3 of Figure 2; 30 Figure 4 is a fragmentary cross sectional view, partly in elevation, taken on the line 4-4 of Figure 3; Figure 5 is a cross sectional view, similar to Figure 4, showing a spherical slug member having a pair of oppositely extending projections received in opposed slots of a sand mold cavity portion; Figure 6 is a fragmentary cross sectional view taken on the line 6-6 of figure 5; Figure 7 is a cross sectional view, similar to Figure 4, showing a modified spherical slug member; Figure 8 is a side elevation view, with parts broken away, of a balancing shaft, showing a balance-weight slug member adjacent each free end of its eccentric counterweight portions; and Figure 9 is a cross sectional view, partly in elevation, taken along the line 9-9 of Figure 8.

Referring to the drawings and in particular to FIG. 1, a cast iron crankshaft, indicated generally at 10, includes a plurality of lobes or counterweight portions 12 aligned co-axially on its longitudinal rotational axis 13-13. Balance-weight slug members 14 are cast integral with one or more counterweight portions 12 in accordance with the present invention. The cast-in-place slug member is shown at 14 in a broken-away portion of Fig. 1.

Cast iron shafts for internal combustion engines are usually manufactured by a green sand casting process, which includes a mold comprising two mating half-parts, with moist sand compressed about a shaft pattern defining the mold cavity. The mold parts, which mate at a parting line separation between the parts, contain the shaft cavity into which the molten metal is poured to produce the casting.

In Fig. 2 there is shown portion of a casting mold half-part 16, with the pattern removed, defining a cavity portion 17 that matches the remaining mold half-part (not shown), to define the external shape of the crankshaft 10.

The mold half-part counterweight cavity portions 18 are configured, with the remaining mold half-part cavity portions, to cast the counterweight portions 12. With reference to Fig. 3, there is shown an enlarged portion of the mold half-part 16, including a slug member 14, with the part 16 having co-planar sand surfaces 19 defining the mold parting line separation.

As best seen in Fig. 4, the slug member 14 has the general shape of a mushroom; comprising a semi-spherical head section 20, an intermediate neck or stem section 22, and a ring-like radial collar or ring section 24 having a diameter substantially equal to the head section 22. The collar section 44 terminates in a disc-shaped foot or base section 26 of slightly reduced diameter than the ring section 24. Cavity portion 18 is defined by outwardly diverging side walls 28-28, and a curved bottom end wall 30.

The slug member 14 has its foot portion 26 supported on the end wall 30 and is glued thereto by an adhesive for retention during the casting process. An example of an adhesive for use in the disclosed process is made by "Foseco International Ltd", London, England and is sold under the Trademark CORFIX.

It will be noted that the slug member 14 is formed of a suitable heavy-metal with a melting point temperature greater than the pouring temperature of the casting metal.

The slug members in the disclosed process are made of tungsten while the casting metal is iron. The slug member 14 shape provides a recessed circular area 31, formed by the slug neck section 22, and an undercut surface area 32 defined by the base section 26. These areas define passageways for the flow of the pored molten iron around the slug member which, when cooled, retains it in the counterweight portion 12 in a cast-in-place manner juxtaposed the counterweight outer surface.

It will be understood that the invention contemplates slug members formed of a suitable heavy-metal, such as a lead alloy, with a melting point temperature that is less than the pouring temperature of the casting metal by a predetermined temperature differential. Upon the casting metal cooling, it solidifies to cast-in-place a lead alloy slug member by thermally bonding, i.e. fusing Integrally with its surface. It will be noted that in this form of the invention the slug member could have a cylindrical shape.

In Figs. 5 and 6 there is shown an arrangement for securing a second embodiment slug member 34 in the counterweight cavity portion 18. The slug member 34, which is spherical, has a pair of co-axially aligned, oppositely extending pin- like projections 36-36 which are adapted for sliding reception in an opposed pair of co planar slots 3838 formed in associated cavity walls 28- 28. The slots 38-38 terminate in closed end stops 40 located a predetermined dimension from the cavity end wall 30, forming a passageway 42 for the flow of poured molten iron during casting. Upon the iron solidifying, slug member 34 is cast-in-place in its associated counterweight portion, closely adjacent the casting outer surface. Next, the mold parts are broken apart, separating the casting from the sand. The exposed portions of the pins 38-38 are removed flush with the counterweight by finishing means, such as a trimmer die.

A third arrangement for securing a slug member is depicted in Fig. 7. A spherical balance-weight slug member 44, formed with two or more pair of oppositely extending spikes 46. The slug member 44 has a predetermined diameter, such that upon each spike penetrating into its associated cavity portion side wall the slug is wedged in place. Thus, the slug member is anchored in the cavity portion a predetermined dimension from its end wall 30, thereby defining a flow passage for the molten metal between the slug member and the end wall.

As illustrated in Fig. 8, a conventional balance shaft casting, generally indicated at 50, includes a pair of left and right, mirror image, eccentric counterweight portions 52 and 521, which are aligned co-axially on longitudinal pivot axis 53-53. Corresponding details of the counterweight portions are denoted by the same reference numerals, except that the right portion numerals are primed. In Fig. 9 the left counterweight portion 52 has a half-round crosssection, with its planar side 54 facing downward while the right counterweight portion 521 is revolved 18 0 degrees about axis 53-53, relative to the portion 52. Fig. 8 shows the portions 52 and 521 joined at their opposed, proximal ends by a central disc portion 58 while their distal ends are formed with associated disc portions 60 and 601.

The balance shaft 50 is cast in a manner similar to the crankshaft casting of Fig. 1. Each counterweight portion 52 and 521 is cast in a sand mold cavity (not shown), wherein left slug member 64 and right slug member 641 are each glued in their associated mirror image mold cavity in the manner as the slug member 14. Slug members 64 and 641 have the same shape as the member 14, and are identical in mass, to provide an overbalance. Upon the balance member 50 being cast, Fig. 9 shows the slug member 64 having base portion 66 juxtaposed its outer semi-circular surface 56, while the slug member 641 is positioned with its base portion 661 juxtaposed its outer semi-circular surface 56'.

8

Claims

1. A process for casting an engine shaft of a first metal, about its axis or rotation, by means of one or more balance-weight slug members of a second metal, wherein the second metal is selected from a group of heavy-metals having a predetermined melting point temperature relative to the pouring temperature of the first metal, comprising the steps of:

forming a sand mold of two mating parts containing a cavity conforming to the shaft which includes at least one counterweight cavity portion defined by tapered, inwardly converging, opposed side walls; securing a slug member at predetermined location in the cavity portion of one mold part adjacent a radial outer end wall of the cavity portion relative to the shaft axis; joining the mold parts and filling the cavity with a molten flow of the first metal such that it encircles a portion of the slug member; and 20 upon the molten metal cooling it solidifies, such that the slug member is permanently cast-in-place within the counterweight portion.

2. A process as claimed in Claim 1, wherein a section of the slug member is secured by adhesive means to the radial outer end wall, such that upon the molten metal solidifying, a section of the slug member is located juxtaposed an outer radial surface of the counterweight formed by the counterweight cavity portion outer end wall.

3. A process as claimed in Claim 1, wherein the second heavy-metal having melting point temperature that is greater than the pouring temperature of the first metal.

4. A process as claimed in claim 1, wherein a second heavy-metal has a melting point temperature that is a less than the pouring temperature of the first metal by a predetermined temperature differential, such that the surface of the slug member is fused integrally with the first metal upon its cooling and solidifying.

S. A process as claimed in claim 1, wherein the shaft is an iron crankshaft, and wherein the slug member is formed of tungsten having a predetermined mass, thereby creating an overbalance condition, enabling final balancing of the crankshaft casting by drilling holes in one or more of its counterweight portions.

6. A process as claimed in Claim 1, wherein the shaft is a balance shaft having a pair of coaxial eccentric, halfround, mirror image, counterweight portions, such that a slug member is cast-in-place in each eccentric counterweight portion adjacent its associated axial outer end.

7. A process as claimed in Claim 1, wherein the slug member formed of a one-piece a mushroom-like shape comprising a spherical head section, an intermediate neck section, and a radial extending collar section terminating in a base having a smaller diameter than the collar section.

8. A process as claimed in claim 1, wherein the slug member has a pair of co-axially aligned, oppositely extending, projections adapted for reception in opposed, coplanar slots formed in the cavity portion tapered, inwardly converging side walls, and wherein the pair of slots each terminate in a stop edge at a predetermined dimension from the cavity portion end wall, such that, upon each projection contacting its associated stop edge, the slug member is positioned at a determined dimension from the cavity portion end wall, thereby defining a flow passage for the molten metal between the slug member and the end wall.

9. A process as claimed in claim 1, wherein the slug member is spherical, and wherein the projections extend in diametrically opposed directions.

10. A process as claimed in claim 1, wherein the slug member is spherical and is formed with a pair of spikes extending in diametrically opposite directions, and wherein the slug member has a predetermined diameter such that upon each spike penetrating its associated side wall the slug is wedged against the cavity portion side walls, thereby anchoring the slug member in the cavity portion a predetermined dimension from the cavity portion end wall, thereby defining a flow passage for the molten metal between the slug member and the end wall.

11. A process for casting an engine shaft substantially as herein described with reference to and as illustrated in the accompanying drawings.