LENGTH-ADJUSTABLE CONNECTING ROD HAVING STOP SURFACES

Abstract

The invention relates to a length-adjustable connecting rod for a reciprocating piston engine, to a reciprocating piston engine, and to a vehicle having a reciprocating piston engine, wherein the connecting rod has a second connecting rod part with a guide cylinder, and a first connecting rod part with a guide shank, wherein the guide shank is accommodated by the guide cylinder and is movable relative thereto for adjustment of an effective connecting rod length, wherein the first connecting rod part has a first stop surface and the second connecting rod part has a second stop surface, wherein lying of the first stop surface against the second stop surface restricts a relative movement between the first connecting rod part and the second connecting rod part in a first direction, and wherein, when the first stop surface lies against the second stop surface, at least a portion of a compressive force acting on the connecting rod along the longitudinal axis of the connecting rod is transferred past the guide shank via the first stop surface and the second stop surface from the first connecting rod part into the second connecting rod part and/or vice versa.

Claims

1. A length-adjustable connecting rod for a reciprocating piston engine, the connecting rod comprising: a first connecting rod part; a second connecting rod part, wherein the second connecting rod part has a section with a guide cylinder on its end facing the first connecting rod part, wherein the first connecting rod part has a guide shank corresponding in form to the guide cylinder on its end facing the second connecting rod part, wherein the guide shank of the first connecting rod part is at least partly accommodated by the guide cylinder in a functional state of use of the connecting rod and is movable relative to the guide cylinder for adjusting an effective length of the connecting rod, wherein the first connecting rod part comprises a first stop surface and the second connecting rod part comprises a second stop surface, wherein the first stop surface lying against the second stop surface restricts a relative movement between the first connecting rod part and the second connecting rod part in a first direction, and wherein the connecting rod is designed such that when the first stop surface lies against the second stop surface, at least a portion of a compressive force acting on the connecting rod along a longitudinal axis of the connecting rod is transferred past the guide shank via the first stop surface and the second stop surface from the first connecting rod part into the second connecting rod part and/or from the connecting rod part into the first connecting rod part.

2. The connecting rod according to claim 1, wherein the connecting rod is configured such that the first stop surface lying against the second stop surface restricts a relative motion between the first connecting rod part and the second connecting rod part thereby shortening the effective length of the connecting rod.

3. The connecting rod according to claim 1, wherein the first connecting rod part and/or the second connecting rod part comprises at least one element of a connecting rod bearing, wherein the first connecting rod part is constructed to connect to a reciprocating piston of the reciprocating piston engine, and wherein the second connecting rod part is constructed to connect to a crankshaft of the reciprocating piston engine.

4. The connecting rod according to claim 1, wherein the connecting rod comprises a hydraulic length-adjusting device for adjusting the effective length of the connecting rod, wherein the hydraulic length-adjusting device comprises at least one hydraulic cylinder having a first hydraulic working chamber, a second hydraulic working chamber, and a piston, and wherein the piston of the hydraulic length-adjusting device is part of the first connecting rod part and the hydraulic cylinder is part of the second connecting rod part.

5. The connecting rod according to claim 4, wherein the guide cylinder forms the hydraulic cylinder of the hydraulic length-adjusting device and the guide shank forms the piston of the length-adjusting device, and wherein the piston of the hydraulic length-adjusting device divides the hydraulic cylinder of the hydraulic length-adjusting device into the first hydraulic working chamber and the second hydraulic working chamber.

6. The connecting rod according to claim 5, wherein the guide shank is a double-acting piston, and comprises a first effective hydraulic surface and a second effective hydraulic surface, wherein the first effective hydraulic surface is associated with the first hydraulic working chamber of the hydraulic length-adjusting device and the second effective hydraulic surface is associated with the second hydraulic working chamber, and wherein the size of the second effective hydraulic surface is at least 0.3 times that of the first effective hydraulic surface.

7. The connecting rod according to claim 1, wherein the second stop surface is a surface extending outwardly from the guide cylinder.

8. The connecting rod according to claim 1, wherein the second stop surface is at least partly formed by an edge surface of the end of the guide cylinder facing the first connecting rod part.

9. The connecting rod according to claim 1, wherein the first stop surface is a surface extending outwardly from the guide shank.

10. The connecting rod according to claim 1, wherein the first connecting rod part is at least a two-part design, wherein the first connecting rod part is comprised of a first section and the guide shank, wherein the guide shank is connected to the first section in an area of its end opposite the second connecting rod part.

11. The connecting rod according to claim 10, wherein the guide shank is screwed to the first section in the area of its end opposite the second connecting rod part.

12. The connecting rod according to claim 10, wherein the first stop surface of the first connecting rod part is formed by an edge surface of a wall of a drill hole of the first section of the first connecting rod part facing the second connecting rod part.

13. The connecting rod according to claim 1, wherein an effective length of the guide shank relative to a depth of the guide cylinder is dimensioned such that when the effective length of the connecting rod is being shortened, an end of the guide shank facing the second connecting rod part first bottoms with the guide cylinder before the first stop surface rests against the second stop surface.

14. The connecting rod according to claim 1, wherein the connecting rod is configured such that the first stop surface does not bottom with the second stop surface until a defined compressive force acting on the connecting rod along the longitudinal axis is reached.

15. The connecting rod according to claim 1, wherein the compressive force acting on the connecting rod is completely transferred past the guide shank via the first stop surface and the second stop surface from the first connecting rod part into the second connecting rod part and/or from the second connecting rod part into the first connecting rod part upon the first stop surface lying against the second stop surface.

16. The connecting rod according to claim 13, wherein the effective length of the guide shank is of smaller dimension than the depth of the guide cylinder such that before the end of the guide shank facing the second connecting rod part contacts a base of the guide cylinder during the shortening of the effective length of the connecting rod, the first stop surface rests against the second stop surface.

17. A reciprocating piston engine having at least one connecting rod, wherein the connecting rod is designed in accordance with claim 1.

18. A vehicle with a reciprocating piston engine wherein the reciprocating piston engine is designed in accordance with claim 17.

Description

[0060] FIG. 1a shows a first exemplary embodiment of an inventive length-adjustable connecting rod 10 having a first connecting rod part 11 as well as a second connecting rod part 12, wherein the first connecting rod part 11 comprises a small connecting rod eye 13 on a first piston-side end for connecting the connecting rod 10 to a reciprocating piston of a reciprocating piston internal combustion engine. At the other crankshaft-side end of the connecting rod 10, the connecting rod 10 has a large connecting rod eye 23 for connecting the connecting rod 10 to a crankshaft of the reciprocating piston engine.

[0061] As can be seen from FIG. 1b, the second connecting rod part 12 comprises a section with a guide cylinder 17 on its end facing the first connecting rod part 11. The first connecting rod part 11 has a guide shank 15 of corresponding design to the guide cylinder 17 at its end facing the second connecting rod part 12.

[0062] The guide shank 15 is thereby at least partially accommodated by the guide cylinder 17 and can be displaced relative to the guide cylinder 17, or second connecting rod part 12 respectively, along a longitudinal axis L of the connecting rod 10 for adjusting an effective connecting rod length LP relative to said guide cylinder 17, which is indicated in FIG. 1b by the not further specified double arrow. In particular, the guide shank 15 can be pushed into the guide cylinder 17 or respectively pulled out of same. A telescoping of the guide shank 15 and guide cylinder 17 together thereby effects a shortening of an effective connecting rod length LP while a pulling apart or respectively withdrawing of the guide shank 15 from the guide cylinder 17 leads to a lengthening of the effective connecting rod length LP.

[0063] The effective connecting rod length LP can thereby be adjusted between a minimum effective connecting rod length LP1 and a maximum effective connecting rod length LP2, which differs by magnitude LP (see e.g. FIG. 2). The effective connecting rod length LP is thereby defined by the distance between the two rotational axes of the connecting rod 10 about which the connecting rod 10 can rotate on the piston side and crankshaft side in a functional state of use.

[0064] FIG. 2 shows an enlarged detail of the inventive connecting rod 10 from FIG. 1a and 1b, by means of which it is particularly easy to see how the guide cylinder 17 of the second connecting rod part 12 receives the guide shank 15 of the first connecting rod part 11.

[0065] In this exemplary embodiment of an inventive connecting rod 10, the first connecting rod part 11 is of multi-part design and is in particular comprised of a first section 14 comprising the small connecting rod eye 13 as well as the guide shank 15, whereby the first section 14 of the first connecting rod part 11 exhibits a drill hole 16 with an inner threading (not further specified here) into which is screwed a first end 15A of the guide shank 15, wherein the guide shank 15 also comprises a correspondingly designed external threading (not further specified) in this area 15A. In an alternative configuration of an inventive connecting rod, the guide shank 15 can be connected to the first connecting rod part 11 by means of transverse shrink fit; i.e. by means of an interference fit, whereby the guide shank 15 and/or the first section 14 of the first connecting rod part 11, in particular the drill hole 16 in the first connecting rod part 11, is in particular correspondingly larger to that end.

[0066] For adjusting the effective connecting rod length, the inventive connecting rod 10 comprises a not further specified hydraulic length-adjusting device having a hydraulic cylinder and a piston able to move relative to each another along a displacement axis to adjust the effective connecting rod length, whereby the displacement axis in this exemplary embodiment of an inventive connecting rod 10 coincides with the longitudinal axis L of the connecting rod and the guide cylinder 17 forms the hydraulic cylinder of the length-adjusting device and the guide shank 15 the piston of the length-adjusting device. The length-adjusting device thereby functions according to the same principle as described in WO 2015/055582 A2 as already mentioned several times above.

[0067] The guide cylinder 17 thereby forms the hydraulic cylinder 17 of the length-adjusting device and the guide shank 15 the piston 15, whereby the guide shank 15 is designed as a double-acting or respectively two-stage stepped piston 15 and divides a hydraulic working chamber in the guide cylinder 17 into a first, in this case lower, hydraulic chamber H1 as well as a second, in this case upper, hydraulic chamber H2, wherein appropriate seals 19 are provided for sealing the two hydraulic chambers H1 and H2 from one another and from the guide cylinder 17 at the guide shank 15.

[0068] The guide shank 15 designed as a double-acting stepped piston comprises a first effective hydraulic surface A1 and a second effective hydraulic surface A2, whereby the first effective hydraulic surface A1 is allocated to the first hydraulic working chamber H1 of the length-adjusting device and the second effective hydraulic surface A2 to the second hydraulic working chamber H2 and in particular arranged on the side of the guide shank 15 opposite from the free end of said guide shank 15. The size of the second effective hydraulic surface A2 is thereby 0.5 times that of the first effective hydraulic surface A1.

[0069] According to the invention, the first connecting rod part 11 comprises a stop surface 20 and the second connecting rod part 12 a second stop surface 21, wherein a lying of the first stop surface 20 against the second stop surface 21 restricts a telescoping of the first connecting rod part 11 and second connecting rod part 12, or guide shank 15 and guide cylinder 17 respectively, and thus a (further) shortening of the effective connecting rod length, whereby this exemplary embodiment of an inventive connecting rod 10 is designed such that the first stop surface 20 lies against/bears on the second stop surface 21 when the minimum effective connecting rod length LP1 has been reached.

[0070] According to the invention, upon the first stop surface 20 resting against the second stop surface 21 in this connecting rod 10, a compressive force F acting on the connecting rod 10 along the longitudinal axis L of the connecting rod 10, symbolically represented here by the F arrow, is completely transferred past the guide shank 15 via the first stop surface 20 and the second stop surface 21 from the first connecting rod part 11 into the second connecting rod part 12 or vice versa.

[0071] In addition, a length LF of the guide shank 15 is dimensioned in relation to a depth T of the guide cylinder 17 such that before the end of the guide shank 15B facing the second connecting rod part 12 reaches a base 17B of the guide cylinder 17 during the shortening of the effective connecting rod length LP (by the telescoping of guide shank 15 and guide cylinder 17), the first stop surface 20 rests against the second stop surface 21.

[0072] The connecting rod 10 is in particular designed such that a small gap 18 always remains between the guide shank 15, in particular its lower end 15B, and the base 17B of the guide cylinder 17 so that compressive force F applied on the connecting rod 10 after the minimum effective connecting rod length LP1 has been reached can always be entirely transferred past the guide shank 15 via the first stop surface 20 and the second stop surface 21 from the first connecting rod part 11 into the second connecting rod part 12 and/or vice versa, which is symbolized in FIG. 2 by the F1 arrow. In other words, an inventive connecting rod designed according to the first exemplary embodiment 10 is preferably designed such that even upon possible elastic deformation of the guide cylinder 17 resulting from an extremely high compressive force F, the lower end of 15B of the guide shank 15 does not bottom with and/or abut against the base 17B of the guide cylinder 17. Albeit this is not absolutely imperative. Important is only that the load on the guide shank 15 is sufficiently relieved.

[0073] Since the compressive force F acting on the connecting rod 10, which results from the combustion pressure in the associated combustion chamber of the reciprocating piston engine, is at its greatest in the downstroke when a minimum effective connecting rod length LP1 is set and dissipated via the guide cylinder 17 and not via the guide shank 15 in the inventive connecting rod 10 at minimum set effective connecting rod length LP1, a maximum compressive force load acting on the guide shank 15 during the operation of the reciprocating piston engine, in particular maximum compressive force F acting on the guide shank 15 during the operation of the reciprocating piston engine, can be reduced.

[0074] Consequently the guide shank 15 itself can be dimensioned smaller, whereby the potential relieving of load on the guide shank 15 made possible by the invention in particular enables reducing the guide shank 15 cross section. A larger hydraulic working surface can thereby be provided above all in the upper hydraulic chamber H2 on the piston 15 formed by the guide shank 15, in particular on the side of the piston 15 facing the first connecting rod part 11. In particular, a second effective hydraulic surface A2 can be provided, its size amounting to at least 0.3 times the first effective hydraulic surface, preferably at least 0.4 times or, as in the present exemplary embodiment, 0.5 times or higher. The resulting hydraulic compression ratios on piston 15 in the hydraulic length-adjusting device during operation can thereby be improved. As a result, the risk of an unwanted change in the set effective connecting rod length LP, in particular an unwanted rebound, can in turn be reduced or even completely eliminated respectively.

[0075] There are however limitations set on the smaller dimensioning of the guide shank 15, particularly with regard to buckling and operational stability (HCF=high cycle fatigue), which are in particular defined by the pressure loads resulting at greater effective connecting rod lengths LP. Although the pressure loads occurring at greater effective connecting rod lengths LP are overall lower in the downstroke than at minimum effective connecting rod length LP1, the first stop surface 20 does not lie against the second stop surface 21 at greater effective connecting rod lengths LP such that compressive force F acting on the connecting rod 10 cannot be led off via the guide cylinder 17 but instead entirely via the guide shank 15 and the hydraulic medium is retained in the lower hydraulic chamber H1. Meaning that no relieving of guide shank 15 load is achieved in this case.

[0076] FIG. 3a shows a detail of a second exemplary embodiment of an inventive connecting rod 30, wherein the connecting rod 30 is in principle structured exactly the same as the inventive connecting rod 10 described on the basis of FIGS. 1a to 2. Functionally identical components are accordingly provided with identical reference numerals. In the inventive connecting rod 30 depicted in FIG. 3a, however, the length LF of the guide shank 15 relative to the depth T of the guide cylinder 17 is dimensioned differently thereto.

[0077] In the exemplary embodiment of an inventive connecting rod 30 depicted in FIG. 3a, the length LF of the guide shank 15 is thereby selected to be larger than the depth T of the guide cylinder 17 by tolerance amount S.

[0078] When the effective connecting rod length LP is being shortened by the telescoping of guide shank 15 and guide cylinder 17, the lower end 15B of the guide shank 15 thus first bottoms with the base 17B of the guide cylinder 17; i.e. abuts against same, before the first stop surface 20 rests against the second stop surface 21. In this state, the entire compressive force F applied on connecting rod 30 is transferred from the first connecting rod part 11 via the guide shank 15, in particular to the base 17B of the guide cylinder 17.

[0079] If the lower end 15B of the guide shank 15 is resting against the base 17B of the guide cylinder 17, application of a high enough compressive force F leads to an elastic deformation of the guide shank 15, in particular to a compressing of the guide shank 15 along the longitudinal axis L of the connecting rod 30 and thus to an elastic shortening of the guide shank 15 (shortened length=LF minus elastic deformation due to compressive force). As a result, there is a further elastically induced shortening of the effective connecting rod length LP, wherein a gap 22 always remains between stop surfaces 20 and 21 upon elastically induced shortening of the effective connecting rod length LP so that the entire compressive force F continues to be conducted via the guide shank 15.

[0080] The inventive connecting rod 30 is thereby designed, in particular the guide shank 15, such that after the guide shank 15 bottoms with the guide cylinder 17, the first stop surface 20 comes into contact and/or bottoms with the second stop surface 21 upon the reaching of a defined compressive force F acting on the connecting rod 30 along the longitudinal axis, which is in particular achieved by a deformation of the guide shank 15 caused by the magnitude S of compressive force F applied along the longitudinal axis L. This state is depicted in FIG. 3b.

[0081] The appropriate design to the guide shank 15, in particular appropriately dimensioned length LF as well as appropriately dimensioned cross section and appropriately selected material, allows a regulating of the deformation effected by the application of the defined compressive force F such that a shortening of the guide shank by magnitude S results, in particular as a result of wholly elastic deformation, compare FIG. 3a to FIG. 3b.

[0082] At the moment at which a compressive force F acting on the connecting rod 30 reaches the defined compressive force and the first stop surface 20 abuts against the second stop surface 21, a compressive force F applied on the connecting rod 30 is inventively at least partly; i.e. at least a portion of the compressive force F acting on the connecting rod along the longitudinal axis of the connecting rod 30, transferred past the guide shank 15 from the first connecting rod part 11 into the second connecting rod part 12 via the first stop surface 20 and the second stop surface 21, see FIG. 3b.

[0083] The portion of compressive force F transferred via stop surfaces 20 and 21 is thereby symbolically depicted in FIG. 3b by the F2 arrows and the remaining potion of compressive force F transferred from the first connecting rod part 11 into the second connecting rod part 12 via guide shank 15 is symbolized by the F3 arrow.

[0084] The guide shank 15 being screwed into section 14 of the first connecting rod part 11 and of rotationally symmetric design enables a particularly simple regulating of the effective length LF of the guide shank 15 and it being adapted to the guide cylinder 17 and of regulating the defined compressive force F or respectively setting the deformation S of the guide shank required for bottoming with the stop surfaces 20 and 21.

[0085] With the appropriate design of an inventive connecting rod, in particular a correspondingly wide range of permissible guide shank screw engagement depths, an inventive connecting rod having the properties of connecting rod 10 as described on the basis of FIG. 1 or a connecting rod having the properties of connecting rod 30 as described on the basis of FIGS. 2a and 2b can thus be alternatively provided as needed.

[0086] Obviously, a plurality of modifications, in particular structural modifications, are possible without departing from the scope of the claims.

LIST OF REFERENCE NUMERALS

[0087] 10, 30 inventive length-adjustable connecting rod

[0088] 11 first connecting rod part

[0089] 12 second connecting rod part

[0090] 13 small connecting rod eye

[0091] 14 first section of first connecting rod part

[0092] 15 guide shank

[0093] 15A first end of guide shank

[0094] 15B second end of guide shank

[0095] 16 drill hole

[0096] 17 guide cylinder

[0097] 17B base of guide cylinder

[0098] 18 gap

[0099] 19 seals

[0100] 20 first stop surface

[0101] 21 second stop surface

[0102] 22 gap between first and second stop surface upon the guide shank contacting the guide cylinder

[0103] 23 large connecting rod eye

[0104] A1 first effective hydraulic surface

[0105] A2 second effective hydraulic surface

[0106] F compressive force

[0107] F1, F2, F3 portion of compressive force

[0108] H1 first hydraulic chamber

[0109] H2 second hydraulic chamber

[0110] L longitudinal axis of connecting rod

[0111] LF effective guide shank length

[0112] PL effective connecting rod length

[0113] LP1 minimum effective connecting rod length

[0114] LP2 maximum effective connecting rod length

[0115] S gap height of the gap between first and second stop surface upon the guide shank contacting the guide cylinder

[0116] T guide cylinder depth