POWER SHAPED MULTIPAD HYDRODYNAMIC JOURNAL BEARING

Abstract: A fixed shape hydrodynamic journal bearing (l0) is provided having a plurality of pads(18),each pad having a peak(22) ,a trough(20) ,and a curve(24) connecting the peak and the trough, the curve being defined by the equation: h = r + s (1-ϑ₁/ϑ₂) α .

Description: This invention relates to a hydrodynamic fixed shape journal bearing disposed about an axis and having an outer surface, and an inner surface having a plurality of pads, each pad having a peak, a trough and a curved surface connecting said peak and trough. High speed turbomachines require special journal bearings to support their rotating parts. Hydrodynamic bearings operate under the principle of hydrodynamic generation, wherein pressure is generated in the clearance between the bearing surface and the rotating part, such pressure producing a net load capacity and film stiffness. Hydrodynamic bearings are ideal for high speed applications because friction and lubrication requirements are minimized. Variably shaped hydrodynamic bearings, such as foil bearings and tilting or pivoting pad bearings, have superior environmental, load, and stability characteristics yet are expensive and relatively difficult to manufacture. Known fixed shape bearings, such as axial groove, step, and multipocket bearings, while easier to construct lose stability at relatively low revolutions per minute and have relatively lower load capabilities. A fixed shape hydrodynamic bearing according to the precharacterizing portion of claim 1 is disclosed in FR-A-1275662. Accordingly, new forms of fixed shape hydrodynamic journal bearings are sought providing improved stability and load carrying capacity. Thus, the object of the invention is to provide a hydrodynamic fixed shape journal bearing that has good stability and relatively high load capacity. According to the invention, to achieve this, the hydrodynamic fixed shape journal bearing is characterized in that the points of the curved surface are defined by the equation h = r + s (1 - ϑ₁/ϑ₂) α where h = distance of a point on the curve from the axis of the bearing r = length of a radius r₁ emanating from the axis of the bearing and intersecting a peak of a pad s = difference between the length of the radius r₁ and the length of a radius r₂ emanating from the axis and intersecting a through of the pad ϑ₁ = angular distance from the first radius to the point of the curve ϑ₂ = angular distance from the first radius to the second radius α = power of the curve. According to a preferred feature of the bearing the power of the curve is a number from four to six. The foregoing, and other features and advantages of the bearing will become more apparent in light of the following detailed description and accompanying drawing, wherein: The figure is a side view of the bearing of the invention. The curves portrayed have been exaggerated for ease of illustration. Referring to the drawing, an embodiment of a hydrodynamic journal bearing 10 for use in turbo-machinery operating at 40,000 rpms or more, is shown. A rotor 12 which rotates in a counterclockwise direction is supported within the bearing. The bearing and the rotor have a common axis 14. The bearing has a cylindrical outer surface 16 and a fixed shape inner surface 17. The inner surface is defined by a plurality of pads 18. Each pad has a trough 20, a peak 22 and a curve 24 connecting the trough and the peak. For a two inch bearing (that is, a circle (not shown), which intersects the peaks of the bearing, has a diameter of two inches) the clearance between the rotor and the peaks should approximate one-half of a millimeter. A step 26, which may lie along a radius r₂ connects the peak of a pad to the trough of an adjacent pad. The points of each curve are defined by the equation: h = r + s (1 - ϑ₁/ϑ₂) α where h = distance of a point on the curve from the axis of the bearing r = length of a radius r₁ emanating from the axis of the bearing and intersecting a peak of a pad s = difference between the length of the radius r₁ and the length of the radius r₂ emanating from the axis and intersecting a trough of the pad ϑ₁ = angular distance from the first radius to the point of the curve ϑ₂ = angular distance from the first radius to the second radius α = power of the curve. It has been found that a power of the curve is a number from four to six. Such a power provides an ideal natural shape for developing pressure to support the rotating rotor 12. Similarly, a bearing having from 4-6 pads is ideal. The bearing may be molded of a composite such as Vespel manufactured by Dupont or another suitable plastic. The bearing may also be machined from steel (or other suitable metal) and then polymer coated. The polymer coating prevents metal to metal contact when the bearing is not in use. Such a bearing provides up to 2008 more load capacity and up to eight times higher stability threshold speed than some fixed shape bearings and is far easier and less expensive to construct than a variable shaped bearing.

Claims: 1. Hydrodynamic fixed shape journal bearing disposed about an axis (14) and having an outer surface (16), and an inner surface (17) having a plurality of pads (18), each pad (18) having a peak (22), a trough (20) and a curved surface (24) connecting said peak (22) and trough (20), characterized in that the points of the curved surface (24) are defined by the equation: h = r + s (1 - ϑ₁/ϑ₂) α where h = distance of a point on the curve from the axis (14) of the bearing r = length of a radius r₁ emanating from the axis (14) of the bearing and intersecting a peak (22) of a pad (18) s = difference between the length of the radius r₁ and the length of a radius r₂ emanating from the axis (14) and intersecting a through (20) of the pad (18) ϑ₁ = angular distance from the first radius to the point of the curve ϑ₂ = angular distance from the first radius to the second radius α = power of the curve. 2. Bearing according to claim 1, characterized in that α = a number from 4 to 6 3. Bearing according to claim 1, characterized in that a peak (22) of each pad (18) and a trough (20) of an adjacent pad (18) intersect said radius r₂ emanating from said axis (14). 4. Bearing according to claim 1, characterized in that said bearing has from 4 to 6 pads (18).

Inventors: GIRIDHARI, AGRAWAL LAL
Applicants: UNITED TECHNOLOGIES CORPORATION
Application year: 1988
Main classification: F16C33
IPC codes: F16C17, F16C33