WO2001002759A1

WO2001002759A1 - Articulated arrangement for piston and connecting rod assemblies with partially spherical contact surfaces

Info

Publication number: WO2001002759A1
Application number: PCT/GB2000/000230
Authority: WO
Inventors: Jean-Pierre Pirault; Alireza Veshagh
Original assignee: APPLIED ENGINE TECHNOLOGY Ltd
Current assignee: APPLIED ENGINE TECHNOLOGY Ltd
Priority date: 1999-01-29
Filing date: 2000-01-27
Publication date: 2001-01-11
Anticipated expiration: 2001-07-29

Abstract

An articulated piston and connecting rod assembly comprising a piston, the lower surface of the crown (82) of which is provided with a concave load bearing area (86), a connecting rod, having a part spherical small end (81) providing upper (85) and lower (187) convex load bearing areas, and a cradle (83) carried by the piston which retains the spherical or part spherical small end of the connecting rod loosely in the piston with the complementary load bearing areas in opposition. The piston assembly has a separate skirt (91) which is retained by a gudgeon pin (92) engaging with a clearance (191) in a bore (93) in the small end of the connecting rod. The major axis of the gudgeon pin and its retaining bore in the small end are coincident with an axis through the centre of the small end sphere and parallel to the crankshaft crankpin. The cradle and connecting rod small-end are dimensioned to allow assembly by inserting the small-end through an aperture in the cradle and rotating the small-end through 90°.

Description

ARTICULATED ARRANGEMENT for PISTON & CONNECTING ROD ASSEMBLIES with PARTIALLY SPHERICAL CONTACT SURFACES

Spherical ended, or part spherical, connecting rods, which engage with complementary surfaces in the piston, allow a direct load path transmission from the piston crown to the connecting rod, and this "ball-ended" arrangement also increases the hydrodynamic load carrying area between the piston and the connecting rod, in comparison to a conventional gudgeon pin/connecting rod/piston assembly. However, these ball-ended assemblies, cannot normally incorporate articulated pistons, which have a separate crown and skirt, as there is no means for connecting the skirt to the connecting rod.

Various embodiments of a piston and connecting rod assembly according to the invention are proposed that allow a partly spherical ended connecting rod/piston assembly to have an articulated skirt which is retained by a gudgeon pin engaging with a bore in the small end.

In the broadest aspect as set out in Claim 1 , the invention is an articulated piston and connecting rod assembly comprising a piston, the lower surface of the crown of which is provided with a concave load bearing area, a connecting rod, having a part spherical small end providing upper and lower convex load bearing areas, and a cradle carried by the piston which retains the part spherical small end of the connecting rod loosely in the piston, with a clearance between the load bearing area of the crown and the upper load bearing area of the small end, and a clearance between a load bearing area on the cradle and the lower load bearing area of the small end, and having a separate skirt which is retained by a gudgeon pin engaging with a bore in the small end of the connecting rod. Preferably the major axis of the gudgeon pin and its retaining bore in the small end are coincident with an axis through the centre of the small end sphere. Preferably, there is a clearance between the gudgeon pin and its retaining bore.

Other aspects of the invention are outlined in the further subordinate claims.

Background explanations and specific embodiments of the invention are now described by way of example with reference to the accompanying drawings in which:

Figure 1 shows (in part section) a prior art piston and connecting rod assembly with a spherical joint.

Figure 2a shows an embodiment of an articulated piston and connecting rod assembly according to the invention.

Figure 2b shows a view at right angles to that assembly shown in Figure 2a.

Figure 2c shows a perspective exploded assembly view corresponding to the views of Figure 2a & 2b, with a truncated conrod shank. Figure 2d shows a perspective quarter section through the assembly corresponding to the views of Figure 2a & 2b, with a truncated conrod shank.

Figure 2e shows an underside plan view of the piston crown which is part of the assembly shown in Fig.2a.

Figure 2f shows an underside plan view of the piston skirt with the cradle bolted in position.

Figure 2g shows an underside plan view of the piston skirt which is part of the assembly shown in Fig.2a.

Fig.3 shows an oil feed arrangement which can be used with the assembly of this invention.

With reference to Figures 2a to 2g, these show a partially spherical articulated piston. The small end 81 of the connecting rod is located within the crown 82 and retained therein by a cradle 83. The small end is loose within the piston so that a first clearance 84 is defined between the load bearing areas 85, 86 of the small end and the crown, and a second clearance 87 is defined between the load bearing area 187 of the small end and the load bearing area 188 of the cradle. The force on the piston during the induction stroke is taken by contact between the cradle and the load bearing area 187 of the small end and the force during the combustion/expansion stroke, the compression stroke and the first half of the exhaust stroke is taken by contact of the two load bearing areas 85 & 86. Retaining set screws 88 clamp the cradle to the crown .The cradle is provided with legs 190 which receive the set screws and which pass with clearance through apertures 89 in the top wall 90 of the skirt 91. The top wall of the skirt forms a closure plate. An aperture 189, in the top wall of the skirt, for the connecting rod small end provides adequate clearance to allow for connecting rod angular movement during piston travel. The skirt is connected to the crown by means of a gudgeon pin 92, the ends of which engage in the bores 98 and 99 of the skirt and which passes with clearance 191 through a bore 93 in the small end.

There are various embodiments of the skirt closure plate. The closure plate may be separate from the skirt and held in place within the skirt by support means.

The closure plate may be flexible, the support means comprising a retaining groove on the inside of the skirt, which groove receives the outer edge of the closure plate and the plate is held in place by flexure of the plate.

In another embodiment, the skirt is provided with a threaded groove which receives the threaded outer edge of the closure plate.

In another embodiment, the inside of the piston skirt is provided with a groove and the outer edge of the closure plate is retained within the groove by a circlip.

In the embodiment shown in Figs. 2a and 2b, oil is fed to the load bearing area 85 of the small end via an oil feed passage 94 and lateral feed passages 95. The oil flows from the load bearing area via radial passages 96 in the crown to an oil receiving cavity 97, defined above the top wall 90 of the skirt. Oil distribution grooves (not shown) may be provided on the upper convex load bearing area of the small-end and/or on the load bearing area of the crown. The clearance between the aperture 189 in the skirt top wall and the small-end form a drain path from the cavity 97. The top wall may have additional apertures to form more drain paths.

In the embodiment shown in Figure 3, the bore in the small end is lined with a pair of axially spaced bushes 23 & 24. An oil feeder passage is defined within the connecting rod and intersects the gap 25 between the bushes, and an oil feed passage 26 in the small end opening to the small end load bearing area, via lateral oil feed passages 27, connects with the gap so that oil can flow from the feeder passage to the small end upper load bearing area.

In another embodiment for the oil feed, the bore in the small end is lined with a bush having a central section of reduced thickness defining a groove, a first passage in the connecting rod connects with the groove, a second passage in the small end also connects with the groove and exits the small end at the load bearing area, and third passages in the small end connect with the second passage and exit at the lateral surfaces of the small end, whereby oil from the first passage is fed to the load bearing area and the lateral surfaces of the small end.

Figs.2a & 2b also show that the connecting rod small end may have a major axis A (400) and a minor axis B (401).

Fig.2c also shows an optional assembly feature in which the cradle has a substantially rectangular aperture 200 that has essentially major (201) and minor (202) lengths or axes , the proportions of this aperture enabling the major axis of the small end to be inserted through the major axis of the cradle, the major axis of the small end/connecting rod being then rotated through 90° relative to the major axis of the aperture so that the lower load bearing area 187 of the smallend can engage with the complementary surface 188 of the cradle along the minor axis 202 with a clearance 87.

It should be noted, for the assemblies shown in Figs. 2a - 2g, that the clearances 84 and 87 are independent of the clearance, if there is a clearance, between the gudgeon pin 92 and the small-end bore 93. This is because in such assemblies the gudgeon pin only retains the skirt and is independent of the piston crown and cradle.

It is possible for the piston and connecting rod assemblies or parts of the assemblies, previously described, to be made in fibrous materials such as carbon-carbon. Other possible materials for the piston and or connecting rod are described in the following sections.

Piston and connecting rod assemblies or parts of the assemblies, as previously described, can be made in fibrous reinforced materials such as carbon fibre reinforced plastics. Piston and connecting rod assemblies or parts of the assemblies, as previously described, can be made in metallic materials and alloys such as steel, cast-iron or aluminium alloys.

The piston crown portion of piston and connecting rod assemblies, as previously described, can be made in a particular metallic material or metallic alloys such as steel, cast-iron or aluminium alloys, whilst the piston skirt and/or cradle are made in a different one of the metallic or alloy materials.

The piston crown portion of piston and connecting rod assemblies, as previously described, can be made in a fibrous material such as carbon-carbon, whilst the piston skirt and/or cradle are made in a metal or metallic alloy material such as steel, aluminium alloy or cast-iron.

The piston crown portion of piston and connecting rod assemblies, as previously described, can be made in a fibrous material such as carbon-carbon, whilst the piston skirt and/or cradle are made in a fibre reinforced material such as carbon fibre or fibre reinforced plastics.

The connecting rods of the connecting rod/piston assemblies, as previously described, can be made from metallic alloys, carbon-carbon or fibre reinforced plastic composite materials.

Claims

1. An articulated piston and connecting rod assembly comprising a piston, the lower surface of the crown of which is provided with a concave load bearing area, a connecting rod, having a part spherical small end providing upper and lower convex load bearing areas, and a cradle carried by the piston which retains the spherical or part spherical small end of the connecting rod loosely in the piston with a clearance between the load bearing area of the crown and the upper load bearing area of the small end, and a clearance between a load bearing area on the cradle and the lower load bearing area of the small-end, and having a separate skirt which is retained by a gudgeon pin engaging with a bore in the small end of the connecting rod.

2. A piston and connecting rod assembly as claimed in claim 1 in which the skirt is provided with bosses having bores which receive the ends of the gudgeon pin and the gudgeon pin is received with clearance within a bore in the small end.

3. A piston and connecting rod assembly as claimed in any preceding claim in which the radius of the load bearing area of the crown is marginally larger than the radius of the upper load bearing area of the connecting rod small-end and the centres of curvature of the load bearing areas lie on the central axis of the gudgeon pin and small end bore.

4. A piston and connecting rod assembly as claimed in any of the previous claims in which the cradle is formed by arcuate members retained against the crown by set screws passing through legs carried by the cradle, the upper curved surfaces of the members forming a part spherical load bearing area in opposition to and spaced from the lower load bearing area of the small end.

5. A piston and connecting rod assembly as claimed in 4 in which the top wall of the skirt is provided with a single aperture, to receive with clearance the small-end of the connecting rod, and apertures to receive with clearance the legs of the cradle.

6 A piston and connecting rod assembly, as claimed in any preceding claim, in which means are provided to feed oil between the upper load bearing area of the crown and the upper load bearing of the small-end.

7. A piston and connecting rod assembly as claimed in claim 6 in which the means to feed oil comprises an oil feed passage in the small end of the connecting rod, around the gudgeon pin, which passage opens to the upper load bearing area of the small-end.

8. A piston and connecting rod assembly as claimed in claim 7 in which oil distribution grooves are provided on the load bearing area of the small end, which grooves connect with the oil feed passage.

. A piston and connecting rod assembly as claimed in claim 8 in which oil distribution grooves are provided on the load bearing area of the piston crown.

10. A piston and connecting rod assembly as claimed in any of claims 6-9 in which an oil receiving cavity is defined within the crown by the top wall of the skirt.

11. A piston and connecting rod assembly as claimed in claim 10 in which the clearance, between the small end and the aperture in the top wall of the skirt, forms a drain path for the oil in the oil receiving cavity.

12. A piston and connecting rod assembly as claimed in 10 and 11 in which the closure plate is provided with apertures to form a drain path for the oil in the oil receiving cavity.

13. A piston and connecting rod assembly as claimed in claim 10 in which the closure plate is integral with the skirt and forms the top wall of the skirt.

14. A piston and connecting rod assembly as claimed in claim 10 in which the closure plate is separate from the skirt and is held in place within the skirt by support means.

15. A piston and connecting rod assembly as claimed in claim 10 in which the closure plate is flexible and the support means comprises a retaining groove on the inside of the skirt, which groove receives the outer edge of the closure plate and the plate is held in place by flexure of the plate.

16. A piston and connnecting rod assembly as claimed in claim 10 in which the inside of the skirt is provide with a threaded groove which receives the threaded outer edge of the plate.

17. A piston and connecting rod assembly as claimed in claim 10 in which the inside of the piston skirt is provided with a groove and the outer edge of the closure plate is retained within the groove by a circlip.

18. A piston and connecting rod assembly as claimed in any of claims 10-17 in which the piston crown is provided with radial apertures connecting the load bearing area and adjacent areas of the crown to the oil receiving cavity.

19. A piston and connecting rod assembly as claimed in any of the claims 7-18 in which the small end of the connecting rod is provided with lateral oil feed passages which connect the oil feed passage to the small-end.

20. A piston and connecting rod assembly as claimed in claim 19 in which the parts of the laterally extending oil passages that exit at the surface of the small end are of larger diameter than the parts adjacent the oil feed passage.

21. A piston and connecting rod assembly as claimed in any of the claims 7-20 in which the bore in the small end is lined with a pair of axially spaced bushes, an oil feeder passage is defined within the connecting rod and intersects the gap between the bushes, and an oil feed passage in the small end opening to the small end load bearing area connects with the gap so that oil can flow from the feeder passage to the small end load bearing area.

22. A piston and connecting rod assembly as claimed in the previous claims 7-20 in which the bore in the small end is lined with a bush having a central section of reduced thickness defining a groove, a first passage in the connecting rod connects with the groove, a second passage in the small end also connects with the groove and exits the small end at the load bearing area, and third passages in the small end connect with the second passage and exit at the lateral surfaces of the small end, whereby oil from the first passage is fed to the load bearing area and the lateral surfaces of the small end.

23 A piston and connecting rod assembly, as claimed in any of the preceding claims, in which the small-end and an aperture in the cradle, have major and minor lengths or axes, the proportions of the aperture in the cradle enabling the major axis of the small end to be inserted through the major axis of the aperture, the major axis of the small end being then rotated through 90° relative to the major axis of the aperture so that the part spherical underside of the small-end can engage with the load bearing area of the cradle along the minor axis with a clearance

24 A piston and connecting rod assembly substantially as described with reference to Figures 2a to 2g and Fig.3.

25 Piston and connecting rod assemblies or parts of the assemblies, as in any of the aforementioned claims, made in fibrous materials such as carbon-carbon.

26 Piston and connecting rod assemblies or parts of the assemblies, as claimed in any of the claims 1-24, made in fibrous reinforced materials such as carbon fibre reinforced plastics.

27 Piston and connecting rod assemblies or parts of the assemblies, as claimed in any of the claims 1-24, made in metallic materials and alloys such as steel, cast-iron or aluminium alloys.

28 Piston and connecting rod assemblies, with the crown portion of the piston assemblies, as in any of the claims 1- 24, made in a particular metallic material/alloys such as steel, cast-iron or aluminium alloys, whilst the skirt and/or cradle are made in a different one of the metallic/alloy materials.

29 Piston and connecting rod assemblies, with the crown portion of the piston assemblies, as in any of the claims 1 - 24, made in a fibrous material such as carbon-carbon, whilst the skirt and/or cradle are made in a metallic/alloy material such as steel, aluminium alloy or cast-iron.

30 Piston and connecting rod assemblies, with the crown portion of the piston assemblies, as claimed in any of the claims 1 -24, made in a fibrous material such as carbon-carbon, whilst the skirt and/or cradle are made in a fibre reinforced material such as carbon fibre reinforced plastics. Piston and connecting rod assemblies, as claimed in claims 1-30, with connecting rods which are made from metallic alloys, carbon-carbon or fibre reinforced plastic composite materials.