WO2000034637A1

WO2000034637A1 - Crankshaft and connecting rod bearing

Info

Publication number: WO2000034637A1
Application number: PCT/CA1999/000232
Authority: WO
Inventors: Sam S. Shock
Original assignee: Shock Sam S
Priority date: 1998-12-04
Filing date: 1999-03-18
Publication date: 2000-06-15
Also published as: AU2822699A; CA2255007A1

Abstract

A crankshaft (10) for a reciprocating piston engine has a circular main shaft (12) supported by conventional bearings so as to rotate about the centroidal axis of the main shaft, plus a circular connecting rod journal (14) formed monolithically with or fixedly attached to the main shaft. The connecting rod journal (14) is larger in diameter than the main shaft (12), and the centroidal axes (B, C) of the connecting rod journal and the main shaft are separated but parallel such that the connecting rod journal (14) will rotate eccentrically around the centroidal axis (C) of the main shaft (12). The connecting rods (30) from the pistons (20) are rotatably mounted to a connecting rod bearing journal (14) which rotatably encircles the connecting rod bearing journal. When a piston (20) is in its power stroke, the resultant force in the corresponding connecting rod (30) imparts eccentric rotation of the connecting rod journal about the centroidal axis of the main shaft (12).

Description

CRANKSHAFT AND CONNECTING ROD BEARING

FIELD OF THE INVENTION

The present invention relates to a crankshaft for use in internal combustion engines with reciprocating pistons.

BACKGROUND OF THE INVENTION

Crankshafts convert linear motion of reciprocating pistons into rotational motion. An illustration of a conventional crankshaft (1) is shown in Figure 1 as prior art. With such a conventional crankshaft, the proximal end of a connecting rod has a bearing bore which engages a connecting rod journal (2). The proximal end of such a connecting rod travels in a circular orbit (3) about the central axis (4) of the crankshaft as the piston reciprocates in the cylinder bore. As the piston reciprocates from top dead center (TDC, or 12 o'clock) to bottom dead center (BDC, or 6 o'clock), the connecting rod journal moves from side to side from the 3 o'clock position to the 9 o'clock position. The stroke of the piston is also equal to the diameter of the circular motion of the connecting rod journal as well as the lateral side-to-side distance travelled.

Radial engine designs are commonly used in aircraft engines with a conventional crankshaft using well-known master rod and articulating link connecting rods. The master rod connects with the connecting rod bearing of the crankshaft while the link rods attach to the master rod. However, because the cylinders in such radial designs are typically in a vertical orientation, they are inherently prone to lubrication problems which entail special and inconvenient precautionary procedures in order to prevent engine damage which can be caused by inadequate cylinder lubrication.

In all engine designs with conventional crankshafts, the side-to-side movement of the connecting rod causes wear in the piston and the cylinder bore by imposing lateral forces on the piston within the cylinder bore. It would be beneficial if such side-to-side movement could be minimized while retaining the full stroke of piston travel. In other words, it would be beneficial to limit the angle by which the connecting rod deviates from the longitudinal axis of the cylinder bore during the crankshaft rotation cycle while maintaining the same stroke distance. This may be accomplished by providing a crankshaft and connecting rod journal/bearing assembly wherein the proximal end of the connecting rod travels in an elliptical orbit, rather than a circular one.

Therefore, there is a need in the art for a crankshaft which minimizes the side-to-side displacement of the proximal end of a connecting rod relative to the stroke of the piston.

SUMMARY OF THE INVENTION

In one aspect of the invention and in general terms, the invention comprises a crankshaft for use in an internal combustion engine having reciprocating pistons and connecting rods, said crankshaft comprising:

a) a circular main shaft having a centroidal axis of rotation;

b) a circular connecting rod journal fixedly associated with the main shaft, said connecting rod journal being of larger diameter than the main shaft, and having a centroidal axis which is parallel to centroidal axis of the main shaft; and

c) a connecting rod bearing collar having an inner bearing surface encircling the connecting rod journal, and having at least one exterior transverse pin in rotating connection with the proximal end of a connecting rod; wherein linear motion of the pistons causes the connecting rod journal to rotate eccentrically about the centroidal axis of the main shaft, and wherein each exterior transverse pin travels in an elliptical orbit.

In a preferred embodiment, the distance between the centroidal axis of the main shaft and the centroidal axis of the connection rod journal will be equal to the difference between the radius of the connecting rod journal and the radius of the main shaft, such that outer surface of the main shaft and the outer surface of the connecting rod journal are coincident at one point. The diameter of the connecting rod journal preferably will be at least 2.0 times, and most preferably about 2 times, the diameter of the main shaft.

The preferred embodiment is particularly suited to use with multi- cylinder radial internal combustion engines. The number of cylinders is not essential to the invention as claimed, although between 3 and 9 cylinders will be preferred.

Although the preferred embodiment illustrated and described herein is for specific use with a radial engine, it may be understood by one skilled in the art that the invention may be adapted for use with in-line and vee configurations of reciprocating engines without undue experimentation.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of an exemplary embodiment with reference to the accompanying simplified and schematic drawings.

In the drawings:

Figure 1 is a view of a prior art crankshaft with a connecting rod journal. Figure 2 is an isometric view of a preferred embodiment crankshaft of the present invention.

Figure 3 is a side view of the preferred embodiment.

Figure 4 is a transverse cross-sectional view of the preferred embodiment.

Figure 5 is a longitudinal cross-sectional view of the preferred embodiment.

Figure 5A is a transverse cross-sectional view showing the preferred connecting rod bearing collar.

Figure 6 is a schematic depiction of the preferred embodiment in use with a three-cylinder radial engine.

Figure 7 is a schematic depiction of the preferred embodiment of Figure 6 where the crankshaft has rotated slightly clockwise.

Figure 8 is a schematic depiction of the preferred embodiment of Figure 6 where the crankshaft has further rotated clockwise.

DETAILED DESCRIPTION OF THE INVENTION

The crankshaft (10) according to the Figures comprises a main shaft (12) on either side of, and formed integrally with, a connecting rod journal (14) having centroidal axis (B). The main shaft (12) will be supported by main bearings (not shown) as is well known in the art, such that the crankshaft may rotate along the centroidal axis (C) of the main shaft. The crankshaft converts the linear motion of reciprocating pistons (20) into rotational motion as a result of the connecting rods (30) acting on the eccentric connecting rod journal (14).

As illustrated in Figure 4, the diameter of the connecting rod journal (14) is larger than that of the main shaft (12). In the preferred embodiment, the ratio of the connecting rod journal (14) diameter to the main shaft (12) diameter is about 2.5:1. As shown in Figure 4, the main shaft (12) surface is internally tangential to the connecting rod journal (14) surface. In other words, the connecting rod journal (14) and the main shaft (12) are coincident at a point (A) on their respective circumferences. This condition is acheived by making the distances between axis (B) and axis (C) equal to the difference between the radius of the connecting rod journey (14) and the radius of the main shaft (12). In such a preferred embodiment, and as is apparent from Figures 6, 7, and 8, the stroke of the pistons (20) connected to such a crankshaft (10) is the difference between the diameter of the connecting rod journal (14) and the diameter of the main shaft (12).

It is not essential that the connecting rod journal (14) and the main shaft (12) be internally tangential, but it is preferred. As may be apparent to one skilled in the art, in every configuration where axis (B) is offset from axis (C), the necessary eccentricity will be present such that linear force exerted by the connecting rods (30) will cause the crankshaft (10) to rotate around axis (C). As long as the diameter of the connecting rod journal (14) is greater than that of the main shaft (12), such embodiment falls within the scope of the invention contemplated herein.

The connecting rods (30) engage the connecting rod journal (14) by a connecting rod bearing collar (40), which rotatably encircles the connecting rod journal (14). In the preferred enbodiment, the inner bore of the connecting rod bearing collar (40) is bored to a close tolerance to fit the connecting rod journal (14), and may include lubrication means (not shown) as is well known in the art. As shown in Figures 5 and 5 A, the outer periphery of the connecting rod bearing collar (40) defines a circumferential channel (41) through which a plurality of connecting rod pins (42) are transversely located. The proximal end (30a) of each connecting rod (30) rotationally attaches to one of the connecting rod pins (42) in a conventional fashion.

Figure 6 illustrates a three-cylinder application of the preferred embodiment. This configuration has been chosen to exemplify the operation of a preferred embodiment; however, it will be appreciated by one skilled in the art that the preferred embodiment may be easily adapted to any number of cylinders which can be fit into a radial array. In the position shown in Figure 6, a first piston (20A) in a first cylinder (61) is shown in the top dead center position. The second piston (20B) in the second cylinder (62) has just passed bottom dead center as the crankshaft rotates in a clockwise direction, and is in the compression stroke. The third piston (20C) in the third cylinder (63) is close to reaching bottom dead center position.

In Figure 7, the crankshaft has rotated clockwise approximately 30° from the position shown in Figure 6. The connecting rod (30) attached to the second piston (20B) is now near its largest crank angle, shown in Figure 7 as angle θ. The elliptical orbit (D) of the proximal end (30a) of each connecting rod (30) is shown in this illustration, from which it may be readily seen that the side-to-side travel of proximal end (30a) of the connecting rod (30) is less than the stroke of the corresponding piston (20). The short diameter (Dl) of the ellipse (D) is approximately 35% shorter than the long diameter (D2), which is equal to the stroke of the piston (20). Thus, in the embodiment shown in Figures 6, 7, and 8, the side-to-side travel is approximately 35% less than if the motion were circular, as it is in prior art crankshafts. The ratio of Dl to D2 will vary depending on the ratio of the diameters of the main shaft (12) and the connecting rod journal (14).

In Figure 8, the crankshaft (10) has rotated 120° from the position shown in Figure 6. As a result, the second piston (20B) is now at top dead center, the third piston (20C) has just passed bottom dead center, and the first piston (20A) is nearing bottom dead center. As is obvious from the Figures, when a line (F) passing through axis (B) and axis (C) bisects a cylinder, the corresponding piston (20) will be at either top dead center or bottom dead center depending upon whether the proximal end (30a) of the corresponding connecting rod (30) is adjacent to the coincident point (A) of the main shaft (12) and the connecting rod journal (14), or opposite that point.

The crankshaft (10) of the present invention may be fabricated using conventional casting or forging techniques which are well known in the art. The connecting rod journal (14) may be formed monohthically with the main shaft (12) or may be fixedly attached to it.

As will be apparent to those skilled in the art, various modifications, adaptations and variations of the foregoing specific disclosure can be made without departing from the teachings of the present invention.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A crankshaft for use in an internal combustion engine having reciprocating pistons and connecting rods, said crankshaft comprising:

a) a circular main shaft having a centroidal axis of rotation;

c) a connecting rod bearing collar having an inner bearing surface encircling the connecting rod journal, and having at least one exterior transverse pin in rotating connection with the proximal end of a connecting rod;

wherein linear motion of the pistons causes the connecting rod journal to rotate eccentrically about the centroidal axis of the main shaft, and wherein each exterior transverse pin travels in an elliptical orbit.

2. The crankshaft of claim 1 wherein the outer surface of the main shaft and the outer surface of the connecting rod journal are coincident at one point.

3. The crankshaft of claim 1 or 2 wherein the diameter of the connecting rod journal is at least twice the diameter of the main shaft.

4. The crankshaft of claim 3 wherein the diameter of the connecting rod journal is approximately 2.5 times larger than the diameter of the main shaft.

5. The crankshaft of claim 1, 2, 3 or 4 having two or more pins for use with a multi-cylinder radial internal combustion engine.

6. The crankshaft of claim 5 adapted for use with a radial internal combustion engine having 9 or fewer cylinders.