Crankshaft for an alternative cooling compressor

Abstract

The present invention refers to a crankshaft (1) for an alternative compressor comprising a main shaft (21) connected to an eccentric pin (2) by means of a peripheral flange (3) containing a lubricating hole (24) extending through said eccentric pin (2) and through at least part of the body of main shaft (21), one of the edges of said hole (24) being on the cylindrical surface (2a) of said eccentric pin (2). With this type of hole, the present invention allows for the use of shafts having extremely low diameters (and, as result, with low viscous loss), even with high eccentricities, whereby an excellent capacity of oil pumping and mechanical strength is maintained.

Claims

1. A reciprocating compressor having a centrifugal oil pump, the reciprocating compressor comprising: a crankshaft comprising a main shaft connected to an eccentric pin and a lubricating hole extending linearly from a cylindrical surface of the eccentric pin to a cylindrical surface of a body of the main shaft, wherein the lubricating hole comprises a centerline contained on a plane (B-B), the plane (B-B) being parallel to, but not containing, a geometrical axis coincident with a center-line of the main shaft and the plane (B-B) being angularly displaced by an angle (B) relative to another plane (P) defined by the center-line of the main shaft and a centerline of the eccentric pin ensuring a radial depth (E) at or below 4.0 mm, wherein the radial depth (E) is measured from an inner surface of the lubricating hole relative to the cylindrical surface of the body of the main shaft, and wherein the main shaft is directly connected to the eccentric pin by a peripheral flange.

2. The reciprocating compressor, in accordance with claim 1, wherein the lubricating hole further comprises minimum wall thicknesses (esp.1 and esp.2) of 1.00 mm.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 illustrates a schematic view showing main parts of the mechanical kit assembly of a reciprocating cooling compressor, in accordance with the prior-art;

(2) FIG. 2 illustrates a cut view of the end portion of a conventional compressor crankshaft at which an eccentric pin is disposed, in accordance with the prior-art;

(3) FIG. 3 illustrates a cut view of the end portion of another type of a conventional compressor crankshaft at which an eccentric pin is disposed, in accordance with the prior-art.

(4) FIG. 4 illustrates a top view of a compressor crankshaft in accordance with a preferred embodiment of the present invention;

(5) FIG. 5 illustrates a cut view, indicated in FIG. 4, of the end portion of a compressor shaft at which the eccentric pin in accordance with the preferred embodiment of the present invention is disposed;

(6) FIG. 6 illustrates a cut view of the end portion of a compressor shaft at which an eccentric pin in accordance with an alternative embodiment of the present invention is disposed;

(7) FIG. 7 illustrates a top view of a compressor crankshaft in accordance with an alternative embodiment of the present invention.

(8) FIG. 8 illustrates a cut view, indicated in FIG. 7, of the end portion of a compressor crankshaft at which an eccentric pin in accordance with the alternative embodiment of the present invention is disposed;

(9) FIG. 9 illustrates a graph showing experimental results of oil flow rate measurements (pumping capacity) of a shaft, wherein the maximum radial depth (E) of lubricating hole 24 in relation to the shaft body surface has been varied;

(10) FIG. 10 illustrates a graph showing the result of a technical study for four different eccentricities of an eccentric pin, in which lubricating hole 24 was maintained fixed in relation to the body of the main shaft.

DETAILED DESCRIPTION OF THE INVENTION

(11) Next, the present invention will be described in more details based on execution examples represented in the drawings. It is to be construed that the principles of the present invention can be applied to any type, size or configuration of a reciprocating compressor.

(12) FIGS. 4 and 5 shows a preferred embodiment of the crankshaft of the present invention, wherein FIG. 4 is a top view and FIG. 5 is a partial cut view of end portion of the crankshaft at which an eccentric pin is disposed.

(13) As can be seen from these figures, crankshaft 1 of the present invention comprises a main shaft 21 connected to an eccentric pin 2 by means of a peripheral flange 3.

(14) Nevertheless, it should be observed that the presence of this flange is not necessary, wherein in other embodiments of the present invention the main shaft can be directly connected to the eccentric pin. A construction of these types of shafts is well known from the state of the art, and the function thereof has been formerly commented.

(15) To avoid problems and drawbacks associated with the solutions for holes of the state of the art, the crankshaft 1 of the present invention comprises a lubricating hole 24 whose end begins (or terminates, depending on the used machining technique) on the cylindrical surface 2b of pin 2, and terminates (or begins, depending on the used machining technique) on the cylindrical surface 21a of the body of main shaft 21, as can be seen from FIGS. 4 and 5.

(16) A helical lubricating channel (not shown) is provided on the cylindrical surface 21a of main shaft 21. Said helical lubricating channel is known from those skilled in the art and, therefore, it will not be described in detail herein.

(17) In the preferred embodiment shown in FIGS. 4 and 5, lubricating hole 24 comprises a centerline which is contained on a plane B-B, this latter being parallel to, but does not containing, a geometric axis coincident to the centerline of main shaft 21 and said plane (B-B) being angularly displaced an angle (B) relative to plane (P) defined by the centerlines of main shaft 21 and of eccentric pin 2 to minimize the maximum depth (E) of the inner surface of lubricating hole 24 relative to the cylindrical surface 21a of main shaft 21.

(18) Therefore, by minimizing the maximum depth (E) (or maximizing the minimum radius (R1)), a lower restriction to the oil flowing from said main shaft 21 to eccentric pin 2 is obtained.

(19) Hence, using a configuration such as the one of the present invention, a high degree of flexibility for the position of lubricating hole 24 is achieved, where a maximum radial depth (E)values below 4.0 mmcan be obtained by correctly combining angles (B) and (D)wherein (D) is the angle of the drilling starting position of lubricating hole 24 on the surface 2b of eccentric pin 2), when the dimensions given by eccentricity (A), diameter (F) of lubricating hole 24 and diameters of main shaft 21 and eccentric pin 2 of the crankshaft 1 are considered.

(20) The benefit attained by increasing the minimum radius (R1) (or reducing the maximum radial depth (E) to the oil flow rate can be seen from FIG. 9, which shows inversely proportional ratio between reduction in the maximum radial depth (E) and increase in the oil flow rate.

(21) In order to achieve a correct machining of the lubricating hole 24, in accordance with the preferred embodiment of the invention, the drilling tool must be introduced from with an angle (D) in relation to the center of the eccentric pin, and, in relation to the plane (B-B), the lubricating hole 24 has an inclination at angle (I) in relation to the centerline of the main shaft 21, wherein such angles (D and I) are defined by: the eccentricity (A) of the eccentric pin 2; the diameters of main shaft 21 and eccentric pin 2; and the axial distance between the beginning and end (H and C heights) of the hole on the surfaces of main shaft 21 and eccentric pin 2.

(22) The beginning of the hole on the cylindrical surface 2b of eccentric pin 2 permits using angles (I) of about 45, which, in combination with the angle (B), allows for said hole to be disposed in a region which ensures satisfactory wall thicknesses (esp1 and esp2 in FIG. 5, above 1.0 mm) even with the use of shafts having: diameter of main shaft and eccentric pin less than 14.0 mm; diameters (F) of hole of 2.5 mm or greater; eccentricities of 12.0 mm or greater; reduced thicknesses of the peripheral flange defining axial seat.

(23) Upon analyzing the manufacture process required for machining said lubricating hole 24, taking into account that shafts having different eccentricities are produced in the same equipment, it is possible to simplify this process (time reduction in the preparation of machines or setup) by maintaining a fixed position of lubricating hole 24 in relation to the body of the main shaft 21 for a determined range of eccentricities (A).

(24) As depicted in FIG. 4, by maintaining the angle (B) and minimum radius (R0) fixed, the starting position of lubricating hole 24 on the surface of eccentric pin 2b defined by angle (D), turns out to be variable with eccentricity (A). FIG. 8 shows this situation for different eccentricities (eccentricities 6, 8, 10 and 12 mm).

(25) FIG. 6 shows an alternative embodiment of the present invention, where lubricating hole 24 is not a hole that entirely passes through main shaft 21 of crankshaft 1. In this sense, FIG. 6 illustrates crankshaft in a cut view corresponding to cut B-B shown in the embodiment of FIG. 4.

(26) In this case, it is used a complementary hole 25 interconnecting lubricating hole 24 with a helical channel on the surface of main shaft 21.

(27) Said complementary hole 25 can be perpendicular to the surface of main shaft 21, as shown in FIG. 6, or can have any other type of suitable direction.

(28) Additionally, in another alternative embodiment, as illustrated in FIGS. 7 and 8, lubricating hole 24 can totally or partially terminate on the axial surface 3a of peripheral flange 3 similarly to the termination of the lubricating hole 24 depicted in FIG. 3. Maximum depth (E) becomes zero because minimum radius (R1) is greater than radius (Rc) of the body of main shaft 21, and, consequently, there will be no more need to ensure a minimum thickness (esp.2).

(29) For this particular configuration in which lubricating hole 24 partially reaches the main shaft body, said lubricating hole 24 is no longer completely formed in this region and then it passes to form a (semi-cylindrical) channel over the cylindrical surface 21a of the body of main shaft 21, which can be directly connected to a helical lubricating channel normally disposed at said shafts.

(30) Additionally, the present invention is not only applicable to crankshafts with eccentric pin axially disposed at one of the ends of the main body, wherein it can also be used in crankshafts at which an eccentric pin is disposed between two main bearings of a crankshaft.

(31) The present invention allows for a high degree of flexibility on the design of a hole of a compressor crankshaft, the present invention permitting: to increase the thicknesses (esp.1 and esp.2) of the shaft wall thus ensuring a maximum radial depth (E) suitable for the oil pumping process; and to dispose the beginning and the end of the hole in a region outside the bearing load region (region where are produced the higher pressures of the lubricating film during hydrodynamic regime); to simplify the machining process (reduction in the time of machining preparation or setup), whereby a fixed position of lubricating hole 24 in relation to the body of shaft 21 for a determined range of eccentricities (A) is maintained.

(32) In fact, the present invention provides for the use of crankshafts having extremely low diameters (and, consequently, having low viscous loss) even with high eccentricities (12.0 mm or above) thereby maintaining an excellent capacity of oil pumping, mechanical strength and being easy to fabricate.

(33) It should be understood that the description provided based on the figures above only refers to possible embodiments for the crankshaft of the present invention, where the true scope of the object of the present invention is defined by the appended claims.