FIELD OF THE DISCLOSURE

The present disclosure relates to crankshafts of reciprocating internal combustion piston engines, and more particularly to such crankshafts equipped with a vibration dampening counterweight. The present disclosure further concerns internal combustion piston engines equipped with such crankshafts.

BACKGROUND OF THE DISCLOSURE

In reciprocating internal combustion engines, the main purpose of a crankshaft counterweight is to balance the weight distribution of the rotating masses, and thereby reduce vibration. Typically, this is carried out by providing portions of increased mass on the crankshaft axially adjacent to the crank pin. Alternatively, also separate counterweight attached to the crankshaft have been provided. In general terms, it is desirable to have achieve a density of the counterweight as high as possible, so as to minimize the space occupied by said counterweights. For example, tungsten inserts have been used in conventional counterweight due to the high density of tungsten. The use of tungsten, however, is restricted by the associated material costs

Additionally, the reciprocating nature of piston engines causes rotational vibration of the counterweight itself, as the rotational forces exerted on the crankshaft by the piston are not constant. For example, US patent 6026776 discloses a counterweight, in which high- density inserts surrounded by an energy absorbing medium are provided in in openings. This kind of an arrangement is intended to absorb and dampen such rotational vibrations, but results in a relatively complex structure of the counterweight.

Another material known to be used in the inserts of counterweights is lead, which has a relatively high density (although less than that of tungsten), exhibits better vibration dampening characteristics, and is regarded as a more cost-efficient material as compared to tungsten. However, the use of lead is discouraged by the toxicity thereof.

For example, document EP 0345424 A1 discloses the use of lead inserts. BRIEF DESCRIPTION OF THE DISCLOSURE

An object of the present disclosure is to provide a counterweight for a crankshaft of a reciprocating internal combustion piston engine with a high density insert having vibration dampening characteristics, while minimizing the risk of contamination from the insert or the loss thereof. It is a further object of the present disclosure to provide a crankshaft equipped with such a counterweight, a reciprocating internal combustion piston engine provided with such crankshaft and a method for manufacturing such a counterweight.

The object of the disclosure is achieved by the counterweight, crankshaft, engine and methods which are characterized by what is stated in the respective independent claims. The preferred embodiments of the disclosure are disclosed in the dependent claims.

The disclosure is based on the idea of providing the body of the counterweight as a one- piece, monolithic structure defining a cavity, in which the insert is housed. Particularly, the cavity has a single opening towards a side at which the counterweight is attachable to a crankshaft, through which the insert is cast into the cavity.

An advantage of the disclosure is that that the monolithic body structure reduces the risk contamination from the insert due to of breakage of the body, while the positioning of the opening results in that centrifugal forces acting on the insert during operation of an associated engine ensure that the insert maintains its position within the cavity and does not strive to drift away from the cavity. Consequently, the use of vibration dampening insert materials, such as lead, is enabled, while contamination risk from the insert is reduced. Also, other materials, such as silver, bismuth, copper, tin or depleted uranium may be with less risk of contamination and/or loss of said insert material.

According to a first aspect of the present disclosure, a counterweight for a crankshaft of a reciprocating internal combustion piston engine is provided.

The counterweight has a body with a proximal side at which the counterweight is attachable to a crankshaft, and a freely extending distal side opposite to the proximal side. The body further comprises a cavity housing a solid insert. Most suitably, the insert is of a high-density material, such as the materials listed above. Furthermore, the body is of a monolithic structure defining the cavity, i.e. the body is of a single piece -structure, in which the cavity is formed. The cavity, in turn, has a single opening towards the proximal side, through which opening the solid insert has been introduced into the cavity by casting. The opening of the cavity towards the proximal side faces against a mating surface of the crankshaft, when the counterweight is attached thereto. In an embodiment of the first aspect according to the present disclosure, the opening of the cavity is closed by a lid. Most suitably, the lid is welded onto the body, thereby hermetically sealing the cavity.

In an embodiment of the first aspect according to the present disclosure, the body is formed of a single piece. Preferably, but not necessarily, the cavity is then subsequently machined onto the body.

For example, the body may be formed of a cast material, i.e., by casting. Particularly, the body may be formed e.g. from cast iron, although the use of other materials is foreseeable. The cavity may then be formed on to the body either in connection with casting or by subsequently machining.

Alternatively, the body may be formed of a suitable blank by machining a desired form onto the blank. The cavity may then be machined either in connection of with the machining the form of the body, or as a separate machining step.-

In an embodiment of the first aspect according to the present disclosure, the body comprises a through-hole extending between the proximal side and a distal side of the body. Such a through-hole is configured for receiving a fixing element therethrough so as to enable fixing the counterweight to a crankshaft.

Moreover, such a through-hole is most suitable spaced apart from the cavity. Particularly, the through-hole may be spaced apart from the cavity in a direction transverse to the radial direction (i.e., the direction running between the proximal side and the distal side). That is, the through-hole resides on a portion of the body at which a cavity is not exhibited.

In an embodiment of the first aspect according to the present disclosure, the body comprises a plurality of cavities and the counterweight comprises a plurality of inserts received in the plurality of cavities, respectively.

Preferably, but not necessarily, if a through-hole and multiple cavities are present, as discussed above, the through-hole resides between adjacent cavities.

In an embodiment of the first aspect according to the present disclosure, the body comprises a plurality of through-holes such that a cavity and a respective insert received in the cavity resides between adjacent trough-holes.

It should be noted that the first aspect of the present disclosure encompasses any combination of two or more embodiments, or variants thereof, as discussed above.

According to a second aspect of the present disclosure, a crankshaft for a reciprocating internal combustion piston engine is provided. Particularly, the crankshaft comprises the counterweight according the first aspect of the present disclosure. Moreover, the counterweight is attached to the crankshaft at the proximal end of the counterweight’s body.

In an embodiment according to the second aspect of the present disclosure, the counterweight is a counterweight having a body with a through-hole, as discussed above in connection with the first aspect of the present disclosure. Moreover, the counterweight is attached to the crankshaft with a fixing element extending through the through-hole.

In an embodiment of the first aspect according to the present disclosure, a mating surface of the crankshaft, at which the counterweight is attached, covers the opening.

It should be noted that the second aspect of the present disclosure encompasses any combination of two or more embodiments, or variants thereof, as discussed above.

According to a third aspect of the present disclosure, a reciprocating internal combustion piston engine is provided. Particularly, the engine comprises the crankshaft according to any of the second aspect of the disclosure.

According to a fourth aspect of the present disclosure a method for manufacturing a counterweight for a crankshaft of a reciprocating internal combustion piston engine is provided.

The method comprises the steps of:

- providing a body having a proximal side at which the counterweight is attachable to a crankshaft, and a freely extending distal side opposite to the proximal side,

- providing a cavity on the body, and

- providing a solid insert within the cavity.

Particularly, the body is provided as a monolithic structure defining the cavity, such that the cavity has an opening towards the proximal side. Moreover, the solid insert is introduced into the cavity through the opening by casting. Most suitably, the insert is of a high-density material, such as the materials listed above.

In an embodiment of the fourth aspect according to the present disclosure, the method further comprises a step of closing the opening with a lid, subsequent to casting the insert. Most suitably, the such a lid may be welded over the opening, so as to hermetically seal the cavity.

In an embodiment of the fourth aspect according to the present disclosure, the body is formed of a single piece. Preferably, but not necessarily, the cavity is then subsequently machined onto the body. For example, the body may be formed of a cast material, i.e., by casting. Particularly, the body may be formed e.g. from cast iron, although the use of other materials is foreseeable. The cavity may then be formed on to the body either in connection with casting or by subsequently machining.

Alternatively, the body may be formed of a suitable blank by machining a desired form onto the blank. The cavity may then be machined either in connection of with the machining the form of the body, or as a separate machining step.

It should be noted that the fourth aspect of the present disclosure encompasses any combination of two or more embodiments, or variants thereof, as discussed above.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the disclosure will be described in greater detail by means of preferred embodiments with reference to the accompanying drawings, in which

Fig. 1 schematically illustrates a cut view of a crankshaft equipped with a counterweight according to an embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

The cut view of Fig. 1 is illustrated along an axial direction of a crankshaft 1 to which the counterweight 2 is attachable. That is, the view of Fig. 1 is cut along a radial plane transverse to the axial direction of a crankshaft 1 .

Particularly, the counterweight 2 has a monolithic body 3. That is, the body 3 has a one- piece structure. Furthermore, the body 3 has a proximal side at which it is attached to the crankshaft 1 , and a distal side 3b facing away from the crankshaft.

In the embodiment of Fig. 1 , three cavities 4 are provided on the body, extending between the proximal side 3a and distal sides 3b. The cavities 4 have respective openings 4a towards the proximal side 3a. That is, the cavities open towards the crankshaft, when attached to it. Furthermore, it should be noted that the cavities 4 have no other openings

Each opening 4a is closed by a lid 6, thus sealing the inserts 5 in their respective cavities.

Moreover, in the embodiment of Fig. 1 , two through holes 7 are provided on the counterweight, extending through the body 3 between the proximal and distal sides 3a, 3b. Particularly, the through holes 7 are configured for receiving a fixing element 7 for attaching the counter weight to the crankshaft 1 .

Notably, the through holes 7 are space apart from the cavities 4, i.e., the through holes 7 reside at portion of the body 3 at which cavities 4 are not present. In the particular configuration of Fig. 1 the through holes 7 and cavities are arranged such that the through holes 7 reside between adjacent cavities 4, and one of the cavities 4 resides between adjacent through holes 7. However, it is apparent to the skilled person, that other configurations are possible also.