GB2143615A - Crankshaft - Google Patents

Abstract

A crankshaft has a completely hollow interior 18. This results in a substantial reduction in weight. In order to ensure that proper lubrication is maintained, openings 22 formed in the crankshaft walls forming the journals 10 and the crank webs 12 are connected by passages 24 which extend across the hollow interior and are made of a material other than that of the crankshaft itself. The passages 24 may be formed by tubes or by tubular voids in a filling material which fills the hollow interior 18. In addition, the crankshaft webs 16 may be circular. <IMAGE>

Description

SPECIFICATION Crankshaft This invention relates to a crankshaft, for example of the type used in an internal combustion engine.

Hollow crankshafts are known in principle. They have the advantage of substantial weight savings compared with conventional solid crankshafts. Problems arise however in equipping a hollow crankshaft with the necessary passageways for lubricating oil between the crankshaft journals and the crank pins, According to the invention, there is provided a crankshaft having a hollow interior, lubrication openings through the walls of the crankshaft in the areas of the journals and of the crank pins, and lubrication conduits extending through the hollow interior, each conduit connecting a crank pin open ing to a journal opening and being formed of a material other than the material of the crankshaft.

Refeences here and elsewhere in this specification and claims to a hollow interior do not exclude the possibility that the interior may be filled with a material other than that of which the crankshaft wall is made.

The conduits may be formed by flexible tubes traversing the hollow interior of the crankshaft.

Alternatively the hollow interior may be filled, for example with a plastics material, the voids formed in the filling material and extending between lubrication openings may form the conduit.

With conventional solid crankshafts, the lubrication conduits have been formed by drilling the shaft, with each drilled hole extending between a crank pin and a journal. Since a drilled hole has to be straight, it is not always possible to arrange the lubrication openings at the optimum position around the crank pin or journal circumference. The use of a flexible tube means that the lubrication conduits no longer have to be straight, and the crankshaft designer is free to position the openings at the most advantageous place.

The invention also provides a crankshaft having a hollow interior, wherein the crank webs supporting the crank pins are circular when seen in a transverse cross section.

In a conventional crankshaft, the crank webs are associated with a degree of "windage" i.e. they have to displace air as the shaft rotates. It would be theoretically possible to make the webs circular, but the extra weight and material cost involved wouid outweigh any advantage gained from reduced win dage. However with a hollow crankshaft, circular webs can be used without any weight increase, since a circular cylindrical shell is inherently stronger than a shell of another shape, and the walls can then be made relatively thin.

The invention will now be further described, by way of example, with reference to the accompanying drawing, in which: Figure 1 is an elevation, partly in section, of a crankshaft in accordance with the invention: and Figure 2 is a transverse cross-section through the crankshaft of Figure 1 on the line ll-ll.

The crankshaft shown has three journals 10, four crankpins 12 and crank webs 16 supporting the pins 12. The shaft is made by casting, and a core is used to produce a hollow interior 18 in the shaft. This hollow is as large as is possible (i.e. the walls of the shaft are made as thin as possible) consistent with adequate strength for the crankshaft to fulfill its function. The core is removed after casting through apertures 20 in the walls of the webs.

After casting, the crankshaft is machined the conventional way.

In each journal 10 and in each crank pin 12 there is a lubrication opening 22. There is an optimum position around the journal or pin circumference for these openings which can be positioned accordingly. These openings extend through the crankshaft wall into the hollow interior 8.

The openings 22 are joined by lubrication conduits 24, which may be formed in a number of different ways.

The "core" may be inserted between the openings to be connected, traversing the hollow interior 18. A filling material can then be cast into the interior 18, and the "cores" removed leaving passages through the filling material. The filling material should be impervious to lubricating oil.

It is, however, preferred to leave the hollow interior 18 substantially empty, but just to connect the openings by flexible tubes, probably of a plastics material. These tubes, which must be impervious to lubricating oil, will be sealed to the openings 22.

Where a conduit has to lead from one opening to two other openings, a branched tube may be used as can be seen in the centre of Figure 1. It may for example be possible to thread a knitted tubular material (as used by surgeons in replacing human arteries) between the openings, and then to coat this material with plastics.

Figure 2 shows a section through a crank web 16 and illustrates how a circular cross-section is possible, with thin walls, to reduce windage and weight.

It is within the scope of this invention, as defined by the claims which follow, for the lubrication conduits to be straight.

1. A crankshaft having a hollow interior, lubrication openings through the wall of the crankshaft in the areas of the journals and of the crank pins, and lubrication conduits extending through the hollow interior, each conduit connecting a crank pin opening to a journal opening and being formed of a material other than the material of the crankshaft.

2. A crankshaft as claimed in Claim 1, wherein the conduits are formed by tubes.

3. A crankshaft as claimed in Claim 2, wherein the tubes are flexible.

4. A crankshaft as claimed in Claim 1, wherein the interior of the crankshaft is filled with filling material, and passages formed in the filling material form conduits.

5. A crankshaft having a hollow interior, wherein the crank webs supporting the crank pins are circular

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Crankshaft This invention relates to a crankshaft, for example of the type used in an internal combustion engine. Hollow crankshafts are known in principle. They have the advantage of substantial weight savings compared with conventional solid crankshafts. Problems arise however in equipping a hollow crankshaft with the necessary passageways for lubricating oil between the crankshaft journals and the crank pins, According to the invention, there is provided a crankshaft having a hollow interior, lubrication openings through the walls of the crankshaft in the areas of the journals and of the crank pins, and lubrication conduits extending through the hollow interior, each conduit connecting a crank pin open ing to a journal opening and being formed of a material other than the material of the crankshaft. Refeences here and elsewhere in this specification and claims to a hollow interior do not exclude the possibility that the interior may be filled with a material other than that of which the crankshaft wall is made. The conduits may be formed by flexible tubes traversing the hollow interior of the crankshaft. Alternatively the hollow interior may be filled, for example with a plastics material, the voids formed in the filling material and extending between lubrication openings may form the conduit. With conventional solid crankshafts, the lubrication conduits have been formed by drilling the shaft, with each drilled hole extending between a crank pin and a journal. Since a drilled hole has to be straight, it is not always possible to arrange the lubrication openings at the optimum position around the crank pin or journal circumference. The use of a flexible tube means that the lubrication conduits no longer have to be straight, and the crankshaft designer is free to position the openings at the most advantageous place. The invention also provides a crankshaft having a hollow interior, wherein the crank webs supporting the crank pins are circular when seen in a transverse cross section. In a conventional crankshaft, the crank webs are associated with a degree of "windage" i.e. they have to displace air as the shaft rotates. It would be theoretically possible to make the webs circular, but the extra weight and material cost involved wouid outweigh any advantage gained from reduced win dage. However with a hollow crankshaft, circular webs can be used without any weight increase, since a circular cylindrical shell is inherently stronger than a shell of another shape, and the walls can then be made relatively thin. The invention will now be further described, by way of example, with reference to the accompanying drawing, in which: Figure 1 is an elevation, partly in section, of a crankshaft in accordance with the invention: and Figure 2 is a transverse cross-section through the crankshaft of Figure 1 on the line ll-ll. The crankshaft shown has three journals 10, four crankpins 12 and crank webs 16 supporting the pins 12. The shaft is made by casting, and a core is used to produce a hollow interior 18 in the shaft. This hollow is as large as is possible (i.e. the walls of the shaft are made as thin as possible) consistent with adequate strength for the crankshaft to fulfill its function. The core is removed after casting through apertures 20 in the walls of the webs. After casting, the crankshaft is machined the conventional way. In each journal 10 and in each crank pin 12 there is a lubrication opening 22. There is an optimum position around the journal or pin circumference for these openings which can be positioned accordingly. These openings extend through the crankshaft wall into the hollow interior 8. The openings 22 are joined by lubrication conduits 24, which may be formed in a number of different ways. The "core" may be inserted between the openings to be connected, traversing the hollow interior 18. A filling material can then be cast into the interior 18, and the "cores" removed leaving passages through the filling material. The filling material should be impervious to lubricating oil. It is, however, preferred to leave the hollow interior 18 substantially empty, but just to connect the openings by flexible tubes, probably of a plastics material. These tubes, which must be impervious to lubricating oil, will be sealed to the openings 22. Where a conduit has to lead from one opening to two other openings, a branched tube may be used as can be seen in the centre of Figure 1. It may for example be possible to thread a knitted tubular material (as used by surgeons in replacing human arteries) between the openings, and then to coat this material with plastics. Figure 2 shows a section through a crank web 16 and illustrates how a circular cross-section is possible, with thin walls, to reduce windage and weight. It is within the scope of this invention, as defined by the claims which follow, for the lubrication conduits to be straight. CLAIMS

1. A crankshaft having a hollow interior, lubrication openings through the wall of the crankshaft in the areas of the journals and of the crank pins, and lubrication conduits extending through the hollow interior, each conduit connecting a crank pin opening to a journal opening and being formed of a material other than the material of the crankshaft.

2. A crankshaft as claimed in Claim 1, wherein the conduits are formed by tubes.

3. A crankshaft as claimed in Claim 2, wherein the tubes are flexible.

4. A crankshaft as claimed in Claim 1, wherein the interior of the crankshaft is filled with filling material, and passages formed in the filling material form conduits.

5. A crankshaft having a hollow interior, wherein the crank webs supporting the crank pins are circular when seen in a transverse cross section.

6. A crankshaft substantially as herein described with reference to the accompanying drawing.