WO2003098044A1

WO2003098044A1 - Crankshaft, in particular for compressor

Info

Publication number: WO2003098044A1
Application number: PCT/IT2002/000323
Authority: WO
Inventors: Vittorio Bianchi
Original assignee: Embraco Europe S.R.L.
Priority date: 2002-05-17
Filing date: 2002-05-17
Publication date: 2003-11-27
Also published as: DE10297740T5; AU2002304251A1; CN1625652A; BR0215715A

Abstract

The crankshaft, in particular for a compressor, comprises at least one substantially cylindrical main journal (10), one crank arm (12), and one substantially cylindrical crank pin (14). It also has, on its outer surface, at least one recess (16a, 16b) located on the main journal (10) in a first position axially in the vicinity of the crank arm (12) and conforming circumferentially to the position of the crank pin (14), or on the crank pin (14) in a second position, circumferentially opposite the first position.

Description

Crankshaft, in particular for compressor

The present invention relates to a crankshaft, in particular for a compressor.

In greater detail, the crankshaft comprises at least one substantially cylindrical main journal, one crank arm and one substantially cylindrical crank pin. Typically, in the operating condition, the main journal is supported rotatably by main bearings, the crank pin is connected to a connecting-rod big-end, . and a lubricating fluid is interposed between the mechanical parts which are in contact, to reduce the friction generated by. their relative rotation.

The object of the present invention is to provide a crankshaft the geometrical design of which permits a further reduction in the friction due to rotation.

According to the invention, this object is achieved by means of a crankshaft having the features indicated at the beginning of the present description and characterized in that it has, on its outer surface, at least one recess located on the main journal in a first position axially in the vicinity of the crank arm and conforming circumferentially to the position of the crank pin, or on the crank "pin in a second position circumferentially opposite the first position.

The recess or recesses of the crankshaft of the invention are formed within the circumferential arc which, in the most critical stage of rotation, is subject to the mechanical stress which, in principle, is the least of those acting on the various arcs of the respective circular section. They do not therefore have the adverse effect of reducing the pressure of the layer of lubricating fluid which is present in the critical regions that are subject to the greatest mechanical stresses. At the same time, however, they reduce the relative sliding surface between the crankshaft and the respective bearings and consequently the friction, which is substantially proportional to the extent of that surface.

Further advantages and characteristics of the present invention will become clear from the following detailed description, provided by way of non-limiting example, with reference to the appended drawings, in which:.

Figure 1 is a perspective view of a crankshaft of the invention, connected to a connecting rod,

Figure 2 is a perspective view of the elements shown in Figure 1 in the disconnected configuration,

Figure 3 is a section taken on the line III-III of Figure 1,.

Figure 4 is an enlarged view of a detail of Figure 3, and

Figure 5 is a section view taken on the line V-V of Figure 3.

A crankshaft, in particular for a compressor, comprises, at least one substantially cylindrical main journal 10, one crank arm 12, and one substantially cylindrical crank pin 14.

A first recess 16a is formed in the outer surface of the main journal 10 in a first position axially in the vicinity of the crank arm 12 and conforming circumferentially to the position of the crank pin 14, that is, on the same side of a plane perpendicular to the median plane of the crank pin 14 {and hence transverse the plane of the sheet with reference to Figure 5) and extending through the longitudinal axis 18 of the journal 10.

A second recess 16b is formed in the outer surface of the crank pin 14, in a second position circumferentially opposite the first position.

A third recess 16c is formed in the outer surface of the main journal 10 in a third position, axially offset relative to the crank arm 12 and circumferentially opposite the first position, that is, on the opposite side of a plane perpendicular to the median plane of the crank pin 14 (and hence transverse the plane of the sheet with reference to Figure 5) and extending through the longitudinal axis 18 of the journal 10.

The recesses 16a, 16b, 16c have a substantially rectangular shape with rounded corners and an angular extent, in the circumferential direction, of about 120°.

In variants of the invention, not shown, the recesses 16a, 16b, 16c may have, independently of one another, different angular extents in the circumferential direction, for example, within the range between 60° and 180° and preferably between 90° and 150°.

The recesses 16a, 16b, 16c preferably have a depth, which is optionally variable, of between 40 μm and 300 μm.

The crank arm 12 is shaped in conventional manner as a plate, counterweighted in order to balance the centrifugal forces of inertia. Also conventionally, the outer surfaces of the main journal 10 and of the crank pin 14 are grooved with helical grooves 20 used for the distribution of lubricating fluid supplied by a pump located inside the crankshaft and not visible in the drawings.

The main journal 10 is mounted rotatably (Figure 5) in a support 22 having a main bearing 24 and a secondary bearing 26 facing the axial portions of the journal 10 having the first and third recesses 16a, 16c on their outer surfaces, respectively.

The crank pin 14 is mounted rotatably in an annular big end 28 of a connecting .rod 30, which big end 28 acts as a bearing. In known manner, a shaft 32 extends from the big end 28 of the connecting rod 30 and is articulated at its opposite end to a piston 34 which is mounted for sliding in a cylinder 36 of the compressor (Figure 1) .

In operation, the crankshaft is subjected to mechanical stresses which are variable in dependence on the angle of rotation about the longitudinal axis 18. In particular, these stresses are greatest when the piston 34 is in the to -dead-centre position (Figure 1) which corresponds to the maximum compression of gas in the cylinder 36 and which thus constitutes the most critical stage for the development of frictional forces on the crankshaft. At this stage, the crank pin 14 has the greatest eccentricity relative to the hole 38 in the big end 28 of the connecting rod 30 (see Figure 4, in which the phenomenon is accentuated in comparison with reality for greater clarity of illustration) and is displaced towards the arc of the big end 28 to which the shaft 32 is fixed. The layer 40 of lubricating fluid interposed between this arc and the crank pin 14 is therefore subject to the greatest pressure and can exert its supporting action on the crankshaft. In contrast, the diametrally opposed portion of the crank pin 14 (that is, that facing away from the shaft 32) and the layer of lubricating fluid 42 adjacent thereto are less stressed. This diametrally opposed portion of the crank pin 14 is that portion in which the second recess 16b is formed. This recess 16b thus brings about a reduction in the relative sliding surface between the crank pin 14 and the big end 28 of the connecting rod 30 and consequently in the relative friction, whereas it does not have the adverse effect of reducing the pressure of the layer 40 of lubricating fluid which is present in the regions that are subject to greater stress.

Substantially similar phenomena occur in the portions of the main journal 10 having the first recess 16a and the third recess 16c which face the main bearing 24 and the secondary bearing 26, respectively. It should, however, be noted that, whereas the first recess 16a is turned through 180° relative to the second recess 16b, the third recess 16c is arranged in a similar angular position to the second recess. In any case, the first and third recess 16a and 16c are also adjacent the least stressed portions of lubricating fluid of the respective circular sections. They therefore also have the effect of reducing friction without adversely affecting the lubricating fluid which is present in the regions that are subject to greater stress.

Naturally, the principle of the invention remaining the same, the details of construction and forms of embodiment may be varied widely with respect to those described purely by way of example, without thereby departing from its scope. In particular, the various recesses may, independently of one another, be of substantially any shape, including asymmetric shapes. Moreover, the edges of the recesses may be chamfered or rounded.

Claims

1. A crankshaft, in particular for a compressor, comprising at least one substantially cylindrical main journal (10) , one crank arm (12) , and one substantially cylindrical crank pin (14) , the crankshaft being characterized in that it has, on its outer surface, at least one recess (16a, 16b) located on the main journal (10) in a first position axially in the vicinity of the crank arm (12) and conforming circumferentially to the position of the crank pin (14) , or on the crank pin (14) in a. second position circumferentially opposite the first position.

2. A crankshaft according to Claim 1, characterized in that it has a first recess (16a) located on the main journal (10) in the first position axially in the vicinity of the crank arm (12) and conforming circumferentially to the position of the crank pin (14) , and a second recess (16b) located on the crank pin (14) in the second position circumferentially opposite the first position.

3. A crankshaft according to any one of the preceding claims, characterized in that the at least one recess (16a, 16b) has a substantially rectangular shape with rounded corners .

4. A crankshaft according to any one of the preceding claims, characterized in that the at least one recess (16a, 16b) has an angular extent, in the circumferential direction, of between 60° and 180° and preferably between 90° and 150°.

5. A crankshaft according to any one of the preceding claims, characterized in that the at least one recess (16a, 16b) has a depth of between 40 μm and 300 μm.

6. A crankshaft according to any one of the preceding claims, characterized in that it also has a third recess (16c) located on the main journal (10) in a third position axially offset relative to the crank arm (12) and circumferentially opposite the first position.

7. A crankshaft according to Claim 6, characterized in that the third recess (16c) has a depth of between 40 μm and 300 μm.