GB2092235A

GB2092235A - Counterbalanced Crankshaft

Info

Publication number: GB2092235A
Application number: GB8137989A
Authority: GB
Original assignee: Komatsu Ltd
Current assignee: Komatsu Ltd
Priority date: 1980-12-23
Filing date: 1981-12-16
Publication date: 1982-08-11
Also published as: JPS57107453A; DE3151091A1

Abstract

In an arrangement of counterweights mounted on a crankshaft for a V type 12-cylinder reciprocating internal combustion engine each of the counterweights is mounted as shown on the crankshaft in a direction to minimize the inertia force exerted on each journal portion J1 to J7 so as to prevent the load imposed on the main journal bearings thereof from becoming excessive and to enable oil films of an adequate thickness to be kept readily on the bearings. <IMAGE>

Description

SPECIFICATION Counterbalanced Crankshaft This invention relates to an arrangement of counterweights mounted on a crankshaft, and more particularly to an arrangement of counterweights mounted on a crankshaft for V type 1 2-cylinder reciprocating internal combustion engines.

In the conventional arrangement of counterweights mounted on a crankshaft, the inertia forces of the counterweights exerted on the journals could not counterbalance satisfactorily the inertia forces of the rotary motion parts (i.e., crankpins and big end portions of connecting rods), and therefore there has been a tendency for the load applied on the main journal bearings to become excessive thereby making it difficult to keep oil films of an adequate thickness on the bearings.

This invention provides a counterbalanced crankshaft which comprises a succession of cranked portions and is rotatably supported at its end portions by end journals and between each pair of adjacent cranked portions by an intermediate journal, wherein the centrifugal forces at each journal are balanced by one or more counterweights of which a single counterweight at each end journal is offset 1 800 from the end cranked portions, one or more counterweights at an axially central intermediate journal are offset 1800 from coplanar cranked portions immediately adjacent thereto, and a single counterweight at each other intermediate journal is in or near an axial plane bisecting the angle between the cranked portions immediately adjacent thereto.Such an arrangement of counterweights mounted on a crankshaft of an internal combustion engine has the effect of preventing the load imposed on the main journal bearings from becoming excessive, and enables oil films of an adequate thickness to be maintained more easily on those bearings.

In accordance with one aspect of the invention, there is provided a counterbalanced crankshaft that comprises six cranked portions which (when numbered consecutively from one end of the crankshaft) comprise first and sixth cranked portions aligned in a first axial plane, second and fifth cranked portions aligned in a second axial plane, and third and fourth cranked portions aligned in a third axial plane at 1200 to the second plane, each cranked portions comprising a pair of crank arms holding a rotary motion part therebetween and the crank arms of the first third, fourth and sixth cranked portions having counterweights associated therewith, wherein the counterweights associated with the axially outermost crank arms of the first and sixth cranked portions lie in the first plane, the counterweights associated with the axially innermost crank arms of the third and fourth cranked portions lie in the third plane, the counterweights associated with the axially innermost crank arms of the first and sixth cranked portions lie approximately midway between the second and third planes, and the counterweight associated with the axially outermost crank arms of the third and fourth cranked portions lie approximately midway between the first and second planes.

Drawings:- Figure 1 is a diagrammatic representation of a prior art arrangement of counterweights mounted on a crankshaft; Figure 2 is an explanatory view of the phase angles of the prior art arrangement of counterweights; Figures 3(1) to 3(lV) are vector diagrams showing the relationship between the inertia force of the rotary motion parts exerted on each journal of a prior art crankshaft and the inertia force of the prior arrangement of counterweights; Figure 4 is a diagrammatic representation showing the construction of one embodiment relating to an arrangement of counterweights of the present invention; Figure 5 is an explanatory view of the phase angles of the arrangement of counterweights shown in Figure 4;; Figures 6(1) to 6(lV) are vector diagrams showing the relationship between the inertia force of rotary motion parts exerted on each journal of a crankshaft of the present invention and the inertia force of the counterweights in the arrangement of the present invention: and Figure 7 is a diagram showing the minimum thickness of oil film on each journal.

For obtaining a better understanding of the present invention, a conventional arrangement of counterweights will first be described below with reference to Figures 1 to 3.

A crankshaft "A" of a conventional V type 12cylinder reciprocating internal combustion engine comprises, as shown in Figure 1, four pairs or eight sets in total of counterweights, 1 F, 1 R, 3F, 3R, 4F, 4R, 6F and 6R mounted thereon. The respective two counterweights of the first pair 1 F and 1 R, the second pair 3F and 3R, the third pair 4F and 4R and the fourth pair 6F and 6R are located each in the same plane. Further, the counterweights of the first pair 1 F and 1 R and those of the fourth pair 6F and 6R are located in the same plane, whilst the counterweights of the second pair 3F and 3R and the third pair 4F and 4R are located in a plane out of phase at an angle of 1 800 relative to the plane of the first pair 1 F and 1 R and the fourth pair 6F and 6R.Therefore, the relationship between vectors V,', V2,, V3,, and V4' of the inertia forces of the respective rotary motion parts (crankpins and big ends of connecting rods) B1, B2, B3 and B4 and a vector V of the inertia force of the corresponding counterweight, as exerted on respective journals J1, J2, J3 and J4, will be as shown in Figures 3(1), 3(11), 3(111) and 3(IV).

It will be seen that the inertia forces of the counterweights do not completely counterbalance the inertia forces of the rotary motion parts, so that the load on the main journal bearings can become excessive rendering it difficult to keep oil films of an adequate thickness on the bearings.

The minimum thickness of oil films on each journal in the conventional arrangement is as shown by a dotted line in Figure 7.

An arrangement of counterweights according to the present invention will now be described with reference to Figures 4 to 6.

In Figure 4, reference numeral 1 denotes a crankshaft and 2 a flywheel. Reference characters J1,J2, J3 J4, J5 J6 and J7 denote first, second, third, fourth, fifth, sixth and seventh journals of the crankshaft, and reference numerals B,, B2, B3, B4, B5 and Be indicate first, second, third, fourth, fifth and sixth rotary motion parts carrying gyrating masses.

Mounted on crank arms C, and D, holding the first rotary motion part B, of the crankshaft 1 therebetween are counterweights 1 F and 1 R, and mounted on crank arms C3 and D3 holding the third rotary motion part B3 of the crankshaft 1 therebetween are counterweights 3F and 3R.

Mounted on crank arms C4 and D4 holding the fourth rotary motion part B4 of the crankshaft 1 therebetween are counterweights 4F and 4R, and mounted on crank arms C6 and D8 holding the sixth rotary motion part Be therebetween are counterweights 6F and 6R.

The axially outermost counterweight 1 F of the first pair of counterweights 1 F and 1 A, and the axially outermost counterweight 6R of the fourth pair of counterweights 6F and 6R are angularly displaced 1800 from the crank arms C, and D,, which themselves lie in the same plane and on the same side of the crankshaft 1. The respective innermost counterweights 1 R and 6F of the first and the fourth pairs of counterweights are located out of phase at an angle a=600+1 50 counterclockwise (as viewed axially towards the flywheel 2) relative to the counterweight 1 F of the first pair and the counterweight 6R of the fourth pair.

Moreover, the innermost counterweight 3R of the second pair of counterweights and the inner counterweight 4F of the third pair of counterweights, which are adjacent to each other, are each angularly displaced 1 800 from the crank arms D3 and C4 which are separated by the fourth journal J4 and which lie in the same plane and on the same side of the axis of the crankshaft 1. Thus the counterweights 3R and 4F are mounted out of phase at an angle of 1800+1 50 relative to the counterweight 1 R of the aforementioned first pair.

Further, the respective outermost counterweights 3F and 4R of the second and the third pair of counterweights are located out of phase at an angle a=60 +15 clockwise (as viewed axially towards the flywheel 2) relative to the counterweight 3R of the second pair and the counterweight 4F of the third pair, and also out of phase at an angle of 1800 relative to the counterweight 1 F of the first pair of counterweights.

Accordingly, the relationship between vectors V,', V2,, V3' and V4, of the inertia forces of the respective first, second, third and fourth rotary motion parts B,, B2, B3 and B4 and a vector V of the inertia force of the corresponding counterweight, as exerted on respective journals Jt, J2, J3 and4, are as shown in Figures 6(1), 6(11), 6(111) and 6(lV).

It will be understand from Figures 6(1) to 6(lV) that the pairs of counterweights 1 F, 1 R; 3F, 3R; 4F, 4R; and 6F, 6R are mounted in such a manner as to minimize the net inertia forces of the rotary motion parts exerted on the journals J1,J2, J3 and J4,respectively.

Further, the minimum thickness of oil films kept on the surfaces of the journals will be as shown by a solid line in Figure 7 and is thicker than that of the oil films available on the journals of the conventional system (shown by a dotted line) so that it becomes possible to ensure that oil films of an adequate thickness are maintained on the main journals.

As described in detail hereinabove, the present invention is characterised by that it comprises the first pair of counterweights 1 F and 1 R mounted on the pair of crank arms holding the first rotary motion part Br of the crankshaft 1 therebetween, the second pair of counterweights 3F and 3R mounted on the pair of crank arms holding the third rotary motion part B3 of the crankshaft therebetween, the third pair of counterweights 4F and 4R mounted on the pair of crank arms holding the fourth rotary motion part B4 therebetween and the fourth pair of counterweights 6F and 6R mounted on the pair of crank arms holding the sixth rotary motion part Be therebetween, a pair of counterweights 1 F and 6R being located out of phase at an angle of 1 800 relative to the rotary motion parts B, and B,, respectively, a pair of counterweights 3R and 4F being located out of phase at an angle of 1 800 relative to the rotary motion parts B3 and B4, respectively, respective two counterweights in each pair, that is, 1 F and 1 R, 3F and 3R, 4F and 4R and 6F and 6R being out of phase at an angle a=600+150 relative to each other. Advantageously, as shown in Figure 5, the counterweights 1 F, 6R, 3F and 4R are located in the same plane as the rotary motion parts BX and B and the counterweights 3F, 4F, 1 R and 6F are located in the same plane as the rotary motion parts B3 and B4.

Claims

1. A counterbalanced crankshaft which comprises a succession of cranked portions and is rotatably supported at its end portions by end journals and between each pair of adjacent cranked portions by an intermediate journal, wherein the centrifugal forces at each journal are balanced by one or more counterweights of which a single counterweight at each end journal is offset 1800 from the end cranked portions, one or more counterweights at an axially central intermediate journal are offset 1800 from coplanar cranked portions immediately adjacent thereto, and a single counterweight at each other intermediate journal is in or near an axial plane bisecting the angle between the cranked portions immediately adjacent thereto.

2. A counterbalanced crankshaft that comprises six cranked portions which (when numbered consecutively from one end of the crankshaft) comprise first and sixth cranked portions aligned in a first axial plane, second and fifth cranked portions aligned in a second axial plane, and third and fourth cranked portions aligned in a third axial plane at 1200 to the second plane, each cranked portion comprising a pair of crank arms holding a rotary motion part therebetween and the crank arms of the first, third, fourth and sixth cranked portions having counterweights associated therewith, wherein the counterweights associated with the axially outermost crank arms of the first and sixth cranked portions lie in the first plane, the counterweights associated with the axially innermost crank arms of the third and fourth cranked portions lie in the third plane, the counterweights associated with the axially innermost crank arms of the first and sixth cranked portions lie approximately midway between the second and third planes, and the counterweights associated with the axially outermost crank arms of the third and fourth cranked portions lie approximately midway between the first and second planes.

3. A counterbalanced crankshaft according to claim 2 wherein the second axial plane is at 1200 to the first plane and the third axial plane is at 1 200 to the first and second planes.

4. A counterbalanced crankshaft according to claim 2 or claim 3 wherein the counterweights on the crank arms of each cranked portion are displaced by an angle an600*1 50 one from the other.

5. A counterbalanced crankshaft substantially as described herein with reference to Figures 4 to 7 of the drawings.