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Title:
TILTING PAD BEARINGS FOR VOLUME PRODUCTION
Document Type and Number:
WIPO Patent Application WO/2015/130490
Kind Code:
A1
Abstract:
A method of producing cast tilting pad journal and thrust bearings is provided. The cast tilting pad bearing (1, 20, 30) includes a bearing housing (3, 11, 33) and tilting pads (2, 12, 32), and each pad (2, 12, 32) cast-in-place with the bearing housing (3, 11, 33) via a web (5, 13, 35).

Inventors:
DIEMER PAUL DANIEL (US)
Application Number:
US2015/015824
Publication Date:
September 03, 2015
Filing Date:
February 13, 2015
Export Citation:
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Assignee:
BORGWARNER INC (US)
International Classes:
B22D15/02; F16C17/03; F16C17/06; F16C33/14
Foreign References:
US5603574A1997-02-18
US5927379A1999-07-27
JP2004084038A2004-03-18
JPH08320016A1996-12-03
US20110188789A12011-08-04
Attorney, Agent or Firm:
ASHER, Robin W. et al. (Canfield Paddock and Stone, P.L.C.,150 West Jefferson, Suite 250, Detroit Michigan, US)
Download PDF:
Claims:
What is claimed:

1. A method of producing a cast tilting pad bearing (1 , 20, 30) comprising a bearing housing (3, 11, 33), and tilting pads (2, 12, 32), each pad (2, 12, 32) cast-in-place with the bearing housing (3, 11, 33) via a web (5, 13, 35), the method steps including

forming a mold (50) having the shape of a bearing precursor (60);

introducing molten metal into the mold (50);

cooling the mold (50) and its contents;

removing the bearing precursor (60) from the mold (50); and

cutting the bearing precursor (60) to separate portions of the bearing precursor (60) into individual pads (2, 12, 32).

2. The method of claim 1, wherein the mold (50) comprises

a hollow, cylindrical outer form (52);

a solid, cylindrical inner form (54) positioned coaxially within the outer form (52); and arcuate inner forms (56) that are aligned on a circumference of a circle disposed between the cylindrical inner form (54) and the outer form (52).

3. The method of claim 1 wherein the tilting pad bearing (1, 20, 30) comprises a journal bearing (1, 20).

4. The method of claim 1 wherein the tilting pad bearing (1, 20, 30) comprises a thrust bearing (30).

5. A method of producing an investment cast tilting pad bearing (1, 20, 30) comprising a bearing housing (3, 11, 33) and tilting pads (2, 12, 32), each pad (2, 12, 32) cast-in-place with the bearing housing (3, 11, 33) via a web (5, 13, 35), the method steps including

making a pattern of the tilting pad bearing (1, 20, 30);

dipping the pattern into a slurry of fine refractory material containing a binder;

coating the dipped pattern with coarse ceramic particles;

allowing the coated, dipped pattern to harden into a mold (50);

introducing molten metal into the mold (50); and

destroying the mold (50) allowing the tilting pad bearing (1, 20, 30) to be removed.

6. The method of claim 5, wherein the mold (50) has the shape of a bearing precursor (60), and the method further includes the step of cutting the bearing precursor (60) to separate portions of the bearing precursor (60) into individual pads (2, 12, 32).

7. The method of claim 5, wherein the mold (50) has the shape of a finished bearing.

8. The method of claim 5, wherein the mold (50) comprises

a hollow, cylindrical outer form (52);

a solid, cylindrical inner form (54) positioned coaxially within the outer form (52); and arcuate inner forms (56) that are aligned on a circumference of a circle disposed between the cylindrical inner form (54) and the outer form (52).

9. The method of claim 5 in which the pattern comprises wax.

10. The method of claim 5 in which the pattern comprises foam.

11. A method of producing a metal powder cast tilting pad bearing (1, 20, 30) comprising a bearing housing (3, 11, 33) and tilting pads (2, 12, 32), each pad (2, 12, 32) cast-in-place with the bearing housing (3, 11, 33) via a web (5, 13, 35), the method steps including

forming a mold (50) having the shape of the tilting pad bearing (1, 20, 30);

placing metal powder in the mold (50);

compacting the metal powder in the mold (50);

sintering the compacted metal powder;

cooling the mold (50); and

removing the tilting pad bearing (1, 20, 30) from the mold (50).

12. The method of claim 11, wherein the mold (50) has the shape of a bearing precursor (60), and the method further includes the step of cutting the bearing precursor (60) to separate portions of the bearing precursor (60) into individual pads (2, 12, 32).

13 The method of claim 11, wherein the mold (50) has the shape of a finished bearing.

14. The method of claim 11 , wherein the mold (50) comprises

a hollow, cylindrical outer form (52);

a solid, cylindrical inner form (54) positioned coaxially within the outer form (52); and arcuate inner forms (56) that are aligned on a circumference of a circle disposed between the cylindrical inner form (54) and the outer form (52).

Description:
TILTING PAD BEARINGS FOR VOLUME PRODUCTION

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and all the benefits of U.S. Provisional Application No. 61/944,602, filed on February 26, 2014 and entitled "Tilting Pad Bearings For Volume Production," which is incorporated herein by reference.

BACKGROUND

Field of the Invention

This invention relates to tilting pad bearings in which the bearing pads of the tilting pad bearing are cast-in-place with the bearing housing, and methods of manufacturing the tilting pad bearings.

Description of Related Art

A tilting pad bearing is a type of bearing in which individual tilting bearing elements (e.g., pads) are arranged around the circumference of a rotating shaft. Tilting pad bearings can also be configured to serve as thrust bearings by placement of the pads along a thrust surface. In tilting pad bearings, either rotation of the shaft or pressure created by an external pump causes the fluid in the bearing to press upon the tilting pads. The pressure causes the pad to tilt and creates a wedge of fluid between the bearing and the shaft or runner. The wedge is thickest at the leading edge of the bearing pad and thinnest at the trailing edge.

An advantage of tilting pad bearing is that the pads can move independently of each other and thus, a tilting pad bearing is able to damp vibrations caused by rotation of the device. The pads of the tilt pad bearing can individually shift to accommodate various loading conditions, thus the bearing geometry is always optimized for load capacity and efficiency. The tilting pad bearing is inherently more stable than many other journal or thrust bearings and thus the tilting pad bearing allows greater flexibility in the design, application, and manufacturing.

However, some tilting pad bearings are assemblies of many individual parts such as a housing or shell, pads, pad pivots, and springs. Each of these parts must be machined to a very tight tolerance to overcome stacked tolerance of the finished assembly and yield an acceptable shaft clearance. In addition, small bearings require tighter tolerances than large bearings. As a result, it can be very expensive to manufacture each of the components of the conventional tilting pad bearing and then assemble the same. There is a need for a method of manufacturing tilting pad bearing which is uncomplicated, easy and economical.

SUMMARY

In some aspects, a method of producing a cast tilting pad bearing is described. The tilting pad bearing includes a bearing housing and tilting pads, each pad cast-in-place with the bearing housing via a web. The method includes forming a mold having the shape of a bearing precursor; introducing molten metal into the mold; cooling the mold and its contents; removing the bearing precursor from the mold; and cutting the bearing precursor to separate portions of the bearing precursor into individual pads.

The method may include one or more of the following features: The mold comprises a hollow, cylindrical outer form; a solid, cylindrical inner form positioned coaxially within the outer form; and arcuate inner forms that are aligned on a circumference of a circle disposed between the cylindrical inner form and the outer form. The tilting pad bearing comprises a journal bearing. The tilting pad bearing comprises a thrust bearing.

In some aspects a method of producing an investment cast tilting pad bearing is described. The tilting pad bearing includes a bearing housing and tilting pads, each pad cast-in- place with the bearing housing via a web. The method includes making a pattern of the tilting pad bearing; dipping the pattern into a slurry of fine refractory material containing a binder; coating the dipped pattern with coarse ceramic particles; allowing the coated, dipped pattern to harden into a mold; introducing molten metal into the mold; and destroying the mold allowing the tilting pad bearing to be removed.

The method may include one or more of the following features: The mold has the shape of a bearing precursor, and the method further includes the step of cutting the bearing precursor to separate portions of the bearing precursor into individual pads. The mold has the shape of a finished bearing. The mold comprises a hollow, cylindrical outer form; a solid, cylindrical inner form positioned coaxially within the outer form; and arcuate inner forms that are aligned on a circumference of a circle disposed between the cylindrical inner form and the outer form. The pattern comprises wax. The pattern comprises foam.

In some aspects a method of producing metal powder cast tilting pad bearing is described. The tilting pad bearing includes a bearing housing and tilting pads, each pad cast-in- place with the bearing housing via a web. The method includes forming a mold having the shape of the tilting pad bearing; placing metal powder in the mold; compacting the metal powder in the mold; sintering the compacted metal powder; cooling the mold; and removing the tilting pad bearing from the mold.

The method may include one or more of the following features: The mold has the shape of a bearing precursor, and the method further includes the step of cutting the bearing precursor to separate portions of the bearing precursor into individual pads. The mold has the shape of a finished bearing. The mold comprises a hollow, cylindrical outer form; a solid, cylindrical inner form positioned coaxially within the outer form; and arcuate inner forms that are aligned on a circumference of a circle disposed between the cylindrical inner form and the outer form.

Journal tilting pad bearings and/or thrust tilting pad bearings can be cast in as a single-piece unit. The bearing pad is part of the bearing housing. The pad is suspended from the bearing housing by a web of the bearing material. Behind the tilting pads there are cavities into which the tilting pads can tilt. The web acts as suspension for the pad and as a spring which allows each pad to tilt and move independently of the other pads.

By using a casting process, a journal tilting pad bearing and/or a thrust tilting pad bearing, which includes the bulk bearing material, the pad, the flexible web supporting the pad, and the cavities into which the pad can tilt, are formed as a single unit. The cast tilting pad bearing requires only minimal grinding, lapping, or honing to achieve the proper finish and functionality. Casting is a simple manufacturing process that produces tilting pad bearings at a lower cost than some conventional production methods. For example, some conventional tilting pad bearings can be complex devices having many parts that are expensive to manufacture and assemble. Using a casting process to form the tilting pad bearings at a lower cost than some conventional production methods will overcome the economic barrier to using tilting pad bearings in automotive applications such as turbocharger design.

In addition, because only minimal grinding, lapping, or honing is required to finish a cast tilting pad bearing, the cast tilting pad bearing can be produced at a lower cost than some conventional tilting pad bearings such as those made using a wire electric discharge machining (EDM) method, which is very accurate but very time consuming and expensive to perform.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 A is a side sectional view of a tilting pad journal bearing having cast-in-place tilting bearing pads at each end.

Figure IB is a cross-sectional view of the tilting pad journal bearing of Figure 1 as seen along the line 1 B— 1 B .

Figure 2 is a cross-sectional view of another embodiment tilting pad journal bearing.

Figure 3 is an end view of a tilting pad thrust bearing having cast in-place tilting pads.

Figure 4 is a cross sectional view of a tilting pad of the thrust bearing as seen along line 4— 4 of Figure 3.

Figure 5 is a cross-sectional view of a tilting pad journal bearing mold.

Figure 6 is a cross-sectional view of a bearing precursor.

Figure 7 is a cross-sectional view of the bearing precursor of Figure 6 after the inner annular portion is separated into individual bearing pads.

Figure 8 is a flow chart illustrating a method of casting a tilting pad bearing.

Figure 9 is a flow chart illustrating a method of investment casting a tilting pad bearing.

Figure 10 is a flow chart illustrating a method of powder metal casting a tilting pad bearing.

Advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings. DETAILED DESCRIPTION

Referring to Figures 1A and IB, a tilting pad journal bearing 1 is cast as a single- piece entity that includes a cylindrical housing 3 that surrounds a rotating shaft 4. The bearing housing 3 includes a first end 3 a and a second end 3b that is opposed to the first end 3 a. Bearing pads 2 are cast-in-place adjacent each end 3a, 3b of the bearing housing 3, and are disposed along a circumference of the inner surface 3 c of the housing 3 so as to reside between the bearing housing inner surface 3 c and the shaft 4. The bearing pads 2 are formed integrally with the housing 3, and are connected to the bearing housing inner surface 3 c via a web 5 that is integral to both the respective pad 2 and the housing 3 whereby the bearing pad 2 is suspended from the bearing housing inner surface 3c. In the illustrated embodiment, four bearing pads 2 (e.g., pads 2a, 2b, 2c, 2d) are disposed at each end 3a, 3b of the bearing housing 3. The bearing pads 2 have a curvature which matches the curvature of the rotating shaft 4. Optional fluid inlets 6 allow lubricant flow from the bearing housing outer surface 3d to the bearing housing inner surface 3c. Although four fluid inlets 6 are shown, more or fewer fluid inlets can be provided. The space between the radially-outward surface of each bearing pad 2 and the bearing housing inner surface 3 c defines a cavity 7. The cavities 7 provide room for the pads 2 to tilt about the web 5 relative to the bearing housing 3. In addition, the web 5 acts as a spring, and a spring force of the web 5 is determined by the bearing material, and shape and dimensions of the web 5.

Referring to Figure 2, an alternative embodiment tilting pad journal bearing 20 is a cast entity that includes a cylindrical housing 11 that surrounds a rotating shaft 22. Bearing pads 12 are disposed along a circumference of the inner surface 11c of the housing 11 so as to reside between the bearing housing inner surface 11c and the shaft 22. The bearing pads 12 are cast separately from the housing 11, and are connected to the bearing housing inner surface 11c via a block 10 that is rigidly connected to the bearing housing 11. For example, in the illustrated embodiment, the block 10 has tapered side surfaces 10a, 10b, and is received in a groove 16 formed on the bearing housing inner surface 11c. The groove 16 includes correspondingly tapered sides 16a, 16b that cooperatively engage tapered sides surfaces 10a, 10b of the block 10. The block 10 is connected to the pad 12 via a web 13 that is integral to both the respective pad 12 and the block 10 whereby the bearing pad 12 is suspended from the block 10, and thus also the bearing housing inner surface 11c. Each block 10 is cast as a single entity with the associated web 13 and tilting bearing pad 12. In the illustrated embodiment, the journal tilting pad bearing 20 has four bearing pads 12 (e.g., pads 12a, 12b, 12c, 12d) at each respective end of the bearing 20. The bearing pads 12 have a curvature which matches the curvature of the rotating shaft 22. Optional fluid inlets 14 allow lubricant flow from the bearing outer surface 1 Id to the bearing housing inner surface 11c. Although four fluid inlets 14 are shown, more or fewer fluid inlets can be provided. The space between the radially outward surface of each bearing pad 12 and the bearing housing inner surface 11c defines a cavity 18. The cavities 18 provide room for the pads 12 to tilt about the web 13 relative to the bearing housing 11. In addition, the web 13 acts as a spring, and a spring force of the web 13 is determined by the bearing material, and shape and dimensions of the web 13.

Although the tilting pad journal bearings 1, 20 are illustrated as having four bearing pads 2, 12, the method of producing the bearing pads 2, 12 may be applied to any a journal tilting pad bearing design. The number, spacing, and the amount of support material of the pads 2, 12 may be varied for specific applications.

Although the tilting pad journal bearing 1 includes the bearing pads 2 that are cast-in-place adjacent each end 3a, 3b of the bearing housing 3, the tilting pad journal bearing 1 may alternatively have a single set of cast-in-place bearing pads positioned centrally between the ends 3 a, 3b.

Referring to Figure 3, a tilting pad thrust bearing 30 is cast as a single-piece entity that includes a disc-shaped bearing housing 33 having a central opening 36 that receives a rotating shaft 4 (not shown in Figure 3). The bearing housing 33 includes a first axially-facing surface 34a, and a second axially-facing surfacing surface 34b (not shown) that is opposed to the first axially-facing surface 34a. Bearing pads 32 are cast-in-place on the axially-facing surfaces 34a, 34b so as to lie generally parallel to the respective axially-facing surface 34a, 34b. The bearing pads 32 are formed integrally with the housing 33, and are connected to the respective axially-facing surface 34a, 34b via a web 35 that is integral to both the respective pad 32 and the housing 33 whereby the bearing pad 32 is suspended from the respective axially-facing surface 34a, 34b. In the illustrated embodiment, four bearing pads 32 (e.g., pads 32a, 32b, 32c, 32d) are disposed on each of the axially-facing surfaces 34a, 34b. Each of the bearing pads 32 has a radially inward-facing edge 38 that has a curvature that matches the curvature of the rotating shaft 4. Four optional fluid inlets 40 allow lubricant flow from the bearing housing outer surface 33d to the bearing housing inner surface 33c. The space between the axially inward-facing surface of each bearing pad 32 and the respective axially-facing surface 34a, 34b of the bearing housing 33 defines a cavity 37 (Figure 4). The cavities 37 provide room for the pads 32 to tilt about the web 35 relative to the bearing housing 33. In addition, the web 35 acts as a spring, and a spring force of the web 35 is determined by the bearing material, and shape and dimensions of the web 35.

Although the tilting pad thrust bearing 30 is illustrated as having four bearing pads 32 on each axially-facing surface 34a, 34b, the method of producing the bearing pads 32 may be applied to any a tilting pad thrust bearing design. The number, spacing, and the amount of support material of the pads 32 may be varied for specific applications.

In hydrostatic embodiments, lubricating fluid such as oil, water, coolant or air, may be provided to the cast tilting pad bearing 1, 20, 30 under pressure provided by an exterior fluid pump. The pressure of the lubricant is high enough that there is no contact between the tilting pad 2, 12, 32 and the shaft or runner, and the fluid acts as the actual bearing element supporting the radial or thrust loads. In other embodiments, the cast tilting pad bearing 1, 20, 30 is hydrodynamic and the fluid pressure is created by the rotation of the shaft. Like the hydrostatic embodiments, the lubricant fluid, rather than the tilting pad, 2, 12, 14, has contact with the shaft or runner. Accordingly, cast tilting pad bearings 1, 20, 30 show little wear and can have very long service lives. The lubricating characteristics of steel bearings may be improved by coating them with a lubricant material such as polyimides, graphite, polytetraflouroethylene (PTFE), molybdenum disulfide (M0S2), and dense nickel containing composite coatings such as PS304 or PS400. These materials can be beneficial when the shaft is just beginning to rotate. When the shaft is rotating, it is supported by a film of the working fluid. However, there can be shaft-to- bearing contact when the shaft is just beginning to rotate. These lubricant coatings provide a good lubrication until the shaft comes up to speed and is supported on the fluid film.

In use, the tilting pad bearing 1, 20, 30 absorbs vibrations of the rotating shaft 4. This absorption of vibration results from the fact that the pads 2, 12, 32 can tilt independently of each other and change their tilt angle in response to vibrations. Every such change in tilt angle is a stress on the web material 5, 13, 35 which is acting as a spring. To improve the service life of the bearing, it is important to select a bearing material having good fatigue resistance. Although spring steels have better fatigue resistance, the use of spring steel is not required to make a functional long lasting bearing. The bearings described herein may be formed of steel to take advantage of steel's fatigue resistance and temperature properties. Where large deflections are expected, cast steel bearings would be preferred.

Where the fatigue resistance of steel is not required, brass is a useful bearing material. Brass bearings have a self-lubricating property and are thus useful in applications with frequent starts and stops. The selection of the bearing pad material and the thickness of the web 5, 13, 35 connecting the pad 2, 12, 32 to the respective bearing housing 3, 11, 33 depends upon the application for which the bearing is intended. For light-load applications, the web 5, 13, 35 can have a small cross-sectional area. Heavier load applications would require providing the web 5, 13, 19 with a relatively larger cross-sectional area.

Referring to Figures 5-8, in some embodiments, the tilting pad journal bearings 1, 20 and the tilting pad thrust bearings 30 are formed by casting. The casting processes for producing a tilting pad journal bearing 1, 20 and a tilting pad thrust bearing 30 are substantially similar, and thus will only be described with respect to the tilting pad journal bearing 1 described above with respect to Figs. 1A and IB. The casting process begins with forming a mold 50 (Figure 5) having the general shape of the bearing 1 (step 100, Figure 8). More specifically, the mold 50 has the shape of a bearing precursor 60. For example, the mold 50 includes a hollow, cylindrical outer form 52 defining the outer surface of the housing 3. Inner forms are provided within the outer form 52 to define vacancies. In this embodiment, a solid, cylindrical inner form 54 that defines an inner surface of the pad 2 is positioned coaxially within the outer form 52. In addition, four arcuate inner forms 56a, 56b, 56c, 56d are aligned on a circumference of a circle C disposed between the cylindrical inner form 54 and the outer form 52. The arcuate inner forms 56a, 56b, 56c, 56d are equidistantly spaced along the circle C, and will define the cavities 7 between the pads 2 and the bearing housing 3.

Once the mold 50 has been formed, molten metal is introduced into the mold 50 (step 102) to form the bearing precursor 60 (Figure 6). The metal may be poured into the mold 50 or it may be forced into the mold 50 under pressure. The metal used to produce the tilting pad bearing 1 may be selected from a variety of metals including brass, steel, iron, and specialty alloys. After the poured metal within the mold 50 is cooled (step 104), the bearing precursor 60 is removed from the mold 50 (step 106). The bearing precursor 60 includes an outer annular portion 62 that defines the bearing housing 3, an inner annular portion 64 that provides the basis for forming the pads 2, and radially-extending arms 66 that define the respective webs 5. Arcuate vacancies 68 are defined between the outer annular portion 62, the inner annular portion 64 and the respective arms 66, and a cylindrical center vacancy 70 is defined by an inner surface 64a of the inner annular portion 64.

The tilting pad journal bearing 1 (Figure 7) is obtained by separating the inner annular portion 64 into four individual parts (e.g., the pads 2)(step 108), for example by machining or laser cutting. In particular, four equidistant radial cuts are formed that extend between the inner surface 64a of the inner annular portion 64, and an outer surface 64b of the inner annular portion 64, such that the arcuate vacancies 68 are in fluid communication with the center vacancy 70. In addition, although casting methods produce parts having a good finish and tolerances, some grinding, lapping, or honing may be required to achieve the proper tolerances and surface finishes. Hard turning processes can also be used to produce good surface finishes.

Although the cast bearing 1 requires the post-casting finishing described in step 108, such grinding, lapping, or honing the bearings of the present invention are less expensive than bearings produced by a conventional process such as electrical discharge machining (EDM), which, when used to form tilting pad bearings, also require some grinding, lapping, or honing to achieve a proper surface finish.

In an alternative embodiment, the mold 50 can be formed having a shape corresponding to the tilting pad journal bearing 1. Accordingly, no bearing precursor is formed, and since the pads 2 are cast-in-place as individual elements, the separating step can be omitted. Referring to Fig. 9, the tilting pad bearings 1, 20, 30 can be formed using an investment casting process. The investment casting process uses a mold made around a form or pattern. The pattern need not be the same material as final object. For example, lost-wax casting employs a pattern formed of wax (i.e., beeswax), while lost-foam casting employs a pattern formed of foam (i.e., polystyrene foam). There are many types of waxes and foams which can be used, and any other readily removable material which can be fashioned into the desired shape may be used to produce the pattern, even low melting metals. When forming the pattern of the tilting pad bearing, it is advantageous to use foam as the pattern material, and to use the foam pattern in a lost foam casting process, since this process is suitable for making complex castings, and the end results are dimensionally accurate, have a good surface finish, and no parting lines are formed in the end product. The investment casting process may be either a direct process or an indirect process. The direct process uses the pattern itself as the basis for the formation of the investment. The indirect process uses the pattern to create multiple wax copies of the form.

The first step (200) of the process of investment casting the tilting pad journal bearing 1 includes making a pattern of the tilting pad journal bearing 1 including the pads 2 connected to the bearing housing via webs 5. For example, the pattern is made of polystryrene foam. Once the pattern is made, the pattern is used to create a ceramic mold. The ceramic mold is produced in steps 102-106, as follows:

In the second step (202), the pattern is dipped into a slurry of fine refractory material containing a binder. The excess slurry is allowed to drain off, producing a smooth, uniform surface on the exterior of the pattern.

In the third step (204), the dipped pattern is coated with coarse ceramic particles, for example by dipping. The coarse ceramic material also contains a binder. It is desirable to have a mold that is approximately 5 to 15 mm thick. If the mold is not sufficiently thick after the fine and course dipping, the dipping and coating steps may be repeated until the proper thickness is achieved.

In the fourth step (206), the dipped, coated pattern is allowed to harden into a mold. In particular, the dipped, coated pattern is allowed to dry, and is then heated to cause the ceramic particles and binder to bond together. In a lost-wax casting process in which the pattern is formed of wax, the heat is also used to remove the wax pattern from the mold. In the fifth step (208), molten metal is poured into the hardened mold and allowed to cool to form the tilting pad journal bearing 1.

In a lost-foam casting process, the foam pattern remains in place within the mold, and the molten metal is poured onto the foam, which evaporates as the molten metal enters the mold. In the sixth step (210), the tilting pad journal bearing 1 is removed from the mold, for example by destroying the mold.

Because the bearing housing 1 , the pads 2 and the webs 5 are cast together as a single piece, manufacturing costs are reduced due to both reduced cost and complexity of the components, and to the reduced cost of assembly of the components.

In the investment casting process, the individual pads 2 may be cast-in-place. Alternatively, the pads 2 may be cast as an annular member that is connected to the bearing housing via circumferentially-spaced arms, and then separated into individual pads in a subsequent processing step, as described above with respect to Figs. 6 and 7.

Referring to Figure 10, the tilting pad bearings 1, 20, 30 can be formed using a powder metal casting process.

The powder metal casting process begins with forming a mold having the shape of the tilting pad bearing 1 (step 300).

Once the mold has been formed, metal powder is placed in the mold (step 302).

Next, the metal powder within the mold is subjected to pressure to compact the powder until it conforms to the shape of the mold (step 304). Optionally, the metal powder may be pressed a second time. This increases the quality of the final product.

Once the powder within the mold has been compacted, it is sintered to cause coalescence of the powder into the final bearing material assembly (step 306).

The sintered bearing is cooled (step 308) and removed from the form (step 310). The powder metal process may be used to produce brass, iron, steel, or specialty alloy bearings.

Although the powder casting method produces parts having a good finish and tolerances, some grinding, lapping, or honing may be required to achieve the proper tolerances and surface finishes. Hard turning processes can also be used to produce good surface finishes.

In the powder casting process, the mold may correspond to the shape of the tilting pad bearing 1, whereby the individual pads 2 are cast-in-place. Alternatively, the pads 2 may be cast as an annular member that is connected to the bearing housing via circumferentially-spaced arms, and then separated into individual pads in a subsequent processing step, as described above with respect to Figs. 6 and 7.

The tilting pad bearings 1, 20, 30 can be used in heavy equipment such as industrial machines, large turbines, ship propeller shafts, and the like. When used in heavy equipment, the number of pads 2, 12, 32 in the tilting pad bearings 1, 20, 30 can be increased and/or the shape of the pad 2, 12, 32 may be changed to obtain increased load capacity.

The tilting pad bearings 1, 20, 30 are particularly useful in turbochargers for internal combustion engines. A turbocharger is a type of forced induction system used with internal combustion engines. Turbochargers deliver compressed air to an engine intake, allowing more fuel to be combusted, thus boosting an engine's horsepower without significantly increasing engine weight. Turbochargers typically include a turbine housing connected to the engine's exhaust manifold, a compressor housing connected to the engine's intake manifold, and a center bearing housing coupling the turbine and compressor housings together. Small turbine wheels used in conjunction with an internal combustion engine may rotate at speeds which may exceed 300,000 revolutions per minute. The turbocharger shaft is directly connected to the turbine wheel and thus is also rotating at speeds which may exceed 300,000 revolutions per minute in small turbines. A bearing in a turbocharger must provide very low friction in order to allow the rapid rotation of the turbocharger shaft. At high rotational speeds, rotodynamic instability must be controlled. An unstable bearing can allow the shaft to develop whirl, which produces subsynchronous vibrations. If not controlled, such whirl can lead to bearing destruction. The cast tilting pad bearings 1, 20, 30 described herein are sufficiently economical to permit use in a turbocharger, and will provide low friction, and prevent rotodynamic instability. Although particular preferred embodiments of the invention have been disclosed in detail for illustrative purposes, it will be recognized that variations or modifications of the disclosed apparatus, including the rearrangement of parts, lie within the scope of the present invention.