GB2478999A

GB2478999A - An interlocking assembly comprising a pinless piston and connecting rod

Info

Publication number: GB2478999A
Application number: GB201005153A
Authority: GB
Inventors: Daniel James Chidley
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-03-26
Filing date: 2010-03-26
Publication date: 2011-09-28
Anticipated expiration: 2030-03-26
Also published as: GB2478999B; GB201005153D0

Abstract

A piston 2 extends along a central axis with a crown and a skirt 11 depending from the crown. The piston 2 has retaining bosses 6 diametrically opposed about the central axis the bosses 6 being attached to and extending radially inward from the skirt 11. The underside of the crown includes a pocket 4. An assembly including the piston 2 further includes a connecting rod 1 terminating at a small end configured to engage in the aforementioned pocket 4 and retaining bosses 6. At no point in the operational cycle is disengagement of the assembled components possible; this being by virtue of the design and the natural limitation of connecting rod angle measured relative to the central axis. The piston 2 and connecting rod 1 are free to be mutually disengaged once the connecting rod 1 has been disassembled from the drive shaft and the relative angle between these components increased to a greater value than that attained during normal operation.

Description

An interlocking assembly comprising a pinless piston and connecting rod

BACKGROUND OF THE INVENTION

This invention relates generally to reciprocating machines and particularly to piston and connecting rod assemblies in internal combustion engines.

Piston constructions in common usage are known to include a pair of diametrically opposed pin bosses connected to a crown. The crown transmits the gas pressure load through to a connecting rod via the pair of pin bosses and an intermediate gudgeon pin.

Two skirts are known to join onto the two pin bosses. The piston has a thrust side skirt which bears the lateral load reaction from the gas pressure and a non-thrust side skirt which functions principally as a guide for the crown. To transform the linear motion of the piston into a rotary motion the large end of the connecting rod is attached to a crankshaft in an engine and the small end of this connecting rod is received between the pin bosses for operable attachment to the piston via a gudgeon pin. A typical connecting rod length in common usage is three to four times greater than the crank eccentric throw of the respective machine this yielding a maximum angular excursion of the connecting rod either side of the cylinder axis being between 145° to 19.50 the precise value of this latter angle depending upon the exact geometry of the crank throw and the connecting rod length.

To comply with modern emission regulations. to reduce fuel consumption, and to increase specific power output, it is increasingly necessary to build robust components able to support higher cylinder pressures and heat flux than previous designs allowed.

The underlying motives for this invention seek to combine such robust components with the possibility of easier and cheaper manufacture and assembly.

Designs exist where the conventional gudgeon pin is omitted in favour of an alternative means of linking the connecting rod directly to the piston. In such cases of direct attachment the connecting rod is typically assembled via a keyway in the side of the piston body.

SUMMARY OF THE INVENTION

This invention is an alternative means of directly linking a connecting rod to a piston hereinafter referred to as the two components. The value of the relative angle [beta] described between the longitudinal axis of the connecting rod and the piston central axis necessary for assembly and disengagement of these components is designed to be sufficiently great that this condition is unattainable during normal engine operation. The maximum value of angle beta under normal operation of engines in common usage is in the range of 14.5° to 19.5°.

Assembly is achieved by two consecutive manipulations: -Firstly by translation the piston and connecting rod are assembled together whilst maintaining a fixed relative angle between the two components. The latter angle is greater than that which occurs during normal engine operation.

-Secondly the angle between the piston axis and connecting rod is reduced by a relative rotation of the two components such that they adopt a normal operating position. The latter action serves to engage the small end of the connecting rod with the piston body.

A main pocket hereinafter referred to as a swivel shell is found directly under the piston crown and serves to transmit the thrust load exerted by the gas pressure existing above the piston, The piston has two retention bosses protruding inwards from the skirt which serve to prevent the two components from separating under inertial loads. The extremity of the connecting rod at its small end hereinafter referred to as a swivel head is in contact with and is free to slide against the surface of the swivel shell as the two components enjoy relative rotational motion under normal engine operation. The swivel head has two lugs one each side whose lower surfaces are machined to mate with the bosses on the piston skirt. The bearing surfaces between the two components share a common concentric axis which is parallel with the engin&s rotational axis such that they form a hinged joint between the piston body and connecting rod small end. In a variation on this design non-cylindrical mating surfaces are envisaged to cater for inhomogeneous thermal expansions and deformations. Other types of joint are also envisaged allowing for extra rotational degrees of freedom.

As the bearing area and contact radius of the two components are greater than those possible with a conventional gudgeon pin assembly a substantially higher gas pressure can be applied for a given assembly mass. Furthermore the larger bearing area directly under the centre of the piston crown provides increased heat dissipation from the hottest part of the piston into the connecting rod thus allowing higher engine heat inputs. Despite the piston employing a standard compression height and skirt length its unique design results in a reduced piston height as measured at half distance between the two skirts when compared with that in current manufacture. This offers the potential to reduce the overall height of the engine. The absence of a floating gudgeon pin rotating on its axis and the corresponding absence of a 360° superfluous bearing surface also offers the potential to reduce friction losses in comparison with those experienced in engines in common usage.

The main bearing surface under the crown can be computer numerically controlled (CNC) milled using either a three dimensional complex surface machining process or employing a specially shaped milling wheel on a right-angle machining head if a shorter machining time is desired. The surfaces of the piston retention bosses responsible for bearing the inertia loading can be CNC milled with access provided through an aperture from the exterior of the piston or machined from the interior of the piston using a shaped milling wheel on a right-angle machining head.

DESCRIPTION OF DRAWINGS

The following drawings explain the invention in detail showing a preferred embodiment of a machined prototype and other advantageous embodiments, showing schematically: Fig. 1 a prototype assembly of connecting rod and piston for a crankshaft drive, Fig. 2 the connecting rod of the arrangement shown in Fig. 1.

Fig. 3 the piston of the arrangement shown in Fig. 1, Fig. 4 a bottom view of the two-component assembly from Fig. 1 shown in assembling and dismantling position, Fig. 5 a front sectional view through Fig. 4, Fig. 6 a bottom view of the two-component assembly from Fig. 1 shown with the connecting rod centrally disposed, Fig. 7 a front sectional view through Fig. 6, Fig. 8 a side sectional view through Fig. 6, Fig. 9. a particular embodiment that would be machined with a shaped milling wheel, Fig. 10 a particular embodiment with bolted retention bosses, Fig. ii a side sectional view through Fig. 10.

Fig. 1 shows a connecting rod 1 and a piston 2 of a crankshaft drive designed for but not limited to internal combustion engines and compressors. The connecting rod 1 shown in Fig. 2 is linked with the piston 2 shown in Fig. 3 by means of interlocking without the need for a gudgeon pin. The connecting rod 1 has a swivel head 3 and the piston 2 has a swivel shell 4 both having corresponding mating bearing areas. The swivel head of connecting rod 1 terminates in a lateral lug 5 at each side. Retention bosses 6 formed in both side walls 7 and mutually diametrically opposed interlock with lugs 5. The interlocking mechanism guarantees that the two components 1 and 2 whilst undergoing opposed vertical motion remain fastened together during engine operation. The interlocking elements 5 with mating surfaces 8 are formed as an integral part of the connecting rod 1. The interlocking elements 6 with mating surfaces 9 are formed as an integral part of piston 2. The connection between elements 5 and 6 is referred to as "interlocking". In this particular embodiment, the bearing surfaces 3, 4, 8 and 9 foim effectively a hinged joint with concentric surfaces. The concentric axis of the latter surfaces forms the rotational axis of the hinged joint.

The main bearing areas of the swivel head 3 and the swivel shell 4, are designed as segmental cylindrical surfaces which extend over an angle [alpha] of less than 180 degrees.

It can be seen from Fig. 4 and 5 that the interlocking elements 5 and 6 disengage when the connecting rod is tilted to its limiting position. In such position the two components can be assembled and dismantled. A cut-out 10 can be added to the skirt 11 to permit a greater tilt angle so effectively increasing the bearing arc length 12 and 13 of the bearing surfaces 8 and 9.

In the piston embodiment 2 where the retention surfaces 9 are machined from the exterior of side wall 7 a locally larger radius 14 is intrinsically used at the ends of the machined apertures 15 in order to lower the stress concentration. This larger machined radius 14 additionally provides increased clearance 16 so facilitating insertion of the connecting rod retention lugs 5 in the piston 2.

The piston design proposed here is of preference non-symmetrical being provided with a larger main bearing area towards the thrust side. The cut-out 10 is preferably positioned on the anti-thrust side implying that the connecting rod engagement is on the thrust side of the retention boss 6. The anti-thrust side 32 of boss 6 is deliberately extended to prevent excessive deflection of the retention bosses 6 due to inertial forces, The aperture 15 is sufficiently long to allow assembly of the connecting rod on the thrust side without its fouling on the non-thrust side during normal engine operation.

The connecting rod swivel head 3 is also preferably non-symmetrical. Fig. 2 shows stiffening ribs 17 down the sides of swivel head 3 and connecting rod shank 18 minimising the swivel head deflection under load. To improve stiffness the thrust side has a larger support 19 down the side of the retention lugs 5. The non-thrust side 20 of the lug engages with the retention boss 6 on the piston and is shaped accordingly. The swivel head form 3 has a similar corresponding shape to the swivel shell 4 in the piston. To achieve an increased bearing area. the arc length 21 defined at the centre may be typically longer than that at the lug extremities 22 as shown on the cross section in Fig. 5 and 7.

As shown in Fig. 7, the piston has a standard compression height and skirt length but a reduced piston height as measured half way between the skirts. This offers the potential of reducing the overall height of the engine and results from cutting a radius 23 in the body of the piston the magnitude of which is equal to the outer crankshaft radius. In Fig. 6 this particular embodiment has four pockets 24 machined out from underneath the crown these serving to reduce weight and provide efficient oil cooling. Ribs 25 between the swivel shell 4 and the skirt 11 provide support to the piston crown.

Frictional forces can be minimized by designing the lateral guidance of the connecting rod to be provided between lateral surface 30 on the connecting rod 1 and 31 on the retention boss 6 as seen in Fig. 8. An oil relief channel 26 may be machined between the oil scraper groove 27 and the internal bearing areas. As the piston reciprocates in normal motion oil is forced from the oil scraper-ring groove down this channel directly onto the main bearing areas 3,4,8 and 9.

In an alternative embodiment shown in Fig. 9 it is foreseen to omit the aperture 15 in the side wall 7 such that machining of the retention bearing surfaces 9 is no longer accomplished via an aperture. The piston could be manufactured employing a milling cutter specially shaped to directly form in one machining operation the main pocket 4 and bearing surface 9 on the retention bosses 6. In this variation it would not be feasible to form the retention boss extension 32 to one side. In this case a drilled oil relief hole would be required in lieu of the oil relief channel 26.

Fig. 10 shows yet another embodiment where weight reduction is achieved by machining apertures proposed at 28 in the side wall 7 To increase stiffness between the skirt and main bearing area a bridge of material 29 is envisaged.

The possibility is foreseen to manufacture the retention boss 6 as a separate component from the piston body so allowing the boss to be machined prior to assembly. The retention bosses could be attached to the side wall 7 by means such as welding or a bolted joint 33. In this particular case shown in Fig. 11 there is no longer a design requirement for the connecting rod to be preset at any particular tilt angle to allow its disengagement from the piston as assembly and dismantling are assured by virtue of the retention boss.

There is an optimum combination of contact radiuses, bearing arc lengths, retention boss width, skirt cut-out and overall dimensions of piston and connecting rod that yield best performance without compromising assembly operations.

Claims

CLAIMS1. A crankshaft drive, in particular for but not limited to internal combustion engines and compressors, with connecting rod and piston, characterized by a connecting rod (1) linked to a piston (2) by means of interlocking without need for a gudgeon pin.
2. The crankshaft drive asserted in claim 1, characterized by the connecting rod (1) having a swivel head (3) and the piston (2) a receiving swivel shell (4) or vice-versa, the elements (3) and (4) mutually engaging.
3. The crankshaft drive asserted in claim 1, characterized by the connecting rod (1) and the piston (2) having interlocking elements respectively (5) and (6) that preclude disengagement of these components during normal operation.
4. The crankshaft drive asserted in claim 3, characterized by the interlocking elements (5, 6) being formed as one piece with the connecting rod (1) and the piston (2) respectively.
5. The crankshaft drive asserted in claim 3, characterized by the interlocking element (6) being a separate component manufactured from either a similar or a different material and affixed to the piston body by means of a secure joint (33), such as but not limited to a bolted joint or weld.
6. The crankshaft drive asserted in claims 4 and 5, characterized by the interlocking elements (5,6) being continuously engaged during normal engine operation when the magnitude of the relative angle between the connecting rod and piston axes is less than a certain value and becoming disengaged when this value is exceeded the latter condition being uniquely possible when the engine is dismantled.
7. The crankshaft drive asserted in claim 5, characterized by the fixture of the interlocking element (6) being the principal means of assembly and disassembly such that there is no requirement for any prescribed relative angle to be set between components for these operations to be performed.
8. The crankshaft drive asserted in claim 2, characterized by the contact region of the swivel head surface (3) and swivel shell surface (4) being designed as concentric surfaces and extending over an angle ([alpha]) of less than 180 degrees. These surfaces form a hinged joint with at least one rotational degree of freedom.
9. The crankshaft drive asserted in claim 3, characterized by the contact region of the lugs (5) and retention bosses (6) being designed as concentric surfaces effectively rotating in an oscillatory manner about a point coincidental with the common axis of the concentric surfaces mentioned in claim 8.
10. The crankshaft drive asserted in claim 3, characterized by the interlocking element (5) having an asymmetrical shape. The side (20) that engages into the retention bosses (6), has a relieved form to facilitate assembly. Material is added to the opposite side (19) to increase the stiffness of the lugs (5).
11. The crankshaft drive asserted in claim 2, characterized by the bearing contact arc length (21) between the swivel shell (4) and head (3) being longer as measured at the centre-line of the latter component than towards the lug ends (5).
12. The crankshaft drive asserted in claim 6, characterized in that the shape of one or more skirts can as an option be relieved by a cut-out recess (10) to allow a greater relative angle between the components when disassembled from the engine.
13. To facilitate manufacture of the piston retention bosses (6) employed in the crankshaft drive mentioned in claim 4, it is foreseen as an option to form an aperture (15) in the piston from the outer surface of the wall (7).
14. The ends of the aperture (15) asserted in claim 13 terminate at a locally larger radius (14) to relieve stress concentrations and provide increased clearance (16) to facilitate insertion of the lugs (5).
15. The crankshaft drive asserted in claim 13, characterized by the retention boss (6) being abbreviated towards the side of piston (2) where access (16) for the lugs (5) is provided and extended on the opposite side (32).
16. The piston asserted in claim 4, characterized by the machining of swivel shell (4) and retention boss (6) being performed in one operation by virtue of a suitably shaped milling cutter.
17. The crankshaft drive according to any one of the claims 8 to 9, characterized in that the concentricity of bearing surfaces 3,4,8 and 9 can be modified in order to compensate for thermal and load induced deformations.
18. The crankshaft drive according to any one of the claims 8 to 9, characterized in that the bearing surfaces 3,4,8 and 9 enjoy one extra or two extra rotational degrees of freedom.
19. The crankshaft drive asserted in claims 1 to 3, characterized by the piston (2) having one or more oil relief channels or holes (26), formed in the side wall (7) and extending through the oil scraper ring groove (27) into the internal bearing regions (3),(4),(8) and (9).
20. The crankshaft drive asserted in claims 1 to 3, characterized by the piston body terminating at its lower extremity in a machined recess (23) the radius of such being equal to that of the crankshaft outer radius.
21. The crankshaft drive asserted in claims ito 3, characterized by the swivel head (3) and the shank (18) being mutually linked together by stiffening ribs (17) the height of which increases towards the aforesaid swivel head.
22. The crankshaft drive asserted in claims 1 to 3, characterized by the swivel shell area (4) and the skirt (11) being mutually linked together by ribs (25) providing support to the crown and (29) effectively stiffening the central region of the skirt.
23. The crankshaft drive asserted in claims 1 to 3, characterized by the presence of one or more pockets (24) under the piston crown to minimise piston weight and optimise cooling.
24. The crankshaft drive asserted in claims 1 to 3, characterized in that material may be removed to foim apertures (28) in the side walls (7) of the piston skirt thus serving to lighten the piston.
25. The crankshaft drive asserted in claims 1 to 3, characterized in that the connecting rod lateral guidance can be accommodated between a face on the connecting rod swivel head (30) and piston retention boss (31).
26. The crankshaft drive according to any one of the claims 1 to 3, characterized in that the load bearing areas (3) and (4) of the swivel joint and lugs (5) and retention bosses (6) have a wear-resistant and/or friction-reducing bearing surface or coating.Amendments to the claims have been filed as followsCLAIMS1. A crankshaft drive for a reciprocating machine, the crankshaft drive comprising a connecting rod (1) and a piston (2) linked by means of interlocking in which one of the connecting rod (l)and piston (2) has a swivel head (3) and the other of the connecting rod (I) and piston (2) has a receiving swivel shell (4), the swivel head (3) and swivel shell (4) being mutually engaging; wherein the connecting rod (1) and piston (2) further comprise interlocking elements (5,6) that preclude disengagement of the connecting rod (1) and piston (2) during normal machine operation when the magnitude of the relative angle between a longitudinal axis of the connecting rod (I) and a central axis of the piston (2) is less than a predetermined value and becoming disengaged when this value is exceeded, the latter condition being uniquely possible when the machine is dismantled.2. A crankshaft drive according to claim 1, in which the reciprocating machine is an internal combustion engine or a compressor.3. A crankshaft drive according to claim 1, characterized by the interlocking elements (5, 6) being formed as one piece with the connecting rod (I) and the piston (2) respectively.4. A crankshaft drive according to claim I, characterized by the interlocking element (6) being a separate component manufactured from either a similar or a different material and affixed to the piston body by means of a secure joint (33), such as but not limited to a bolted joint or weld.5. A crankshaft drive according to claim 1, characterized by the contact region of the swivel head surface (3) and swivel shell surface (4) being designed as concentric surfaces and extending over an angle ([alpha]) of less than 180 degrees, forming a hinged joint with at least one rotational degree of freedom.6. A crankshaft drive according to claim I, characterized by the contact region of the lugs (5) and retention bosses (6) being designed as concentric surfaces effectively rotating in an oscillatory manner about a point coincidental with the common axis of the concentric * surfaces mentioned in claim 5.7. A crankshaft drive according to claim 1, characterized by the interlocking element (5) : having an asymmetrical shape, the side (20) that engages into the retention bosses (6) having a relieved form to facilitate assembly.8. A crankshaft drive according to claim 1, characterized by the bearing contact arc length (21) between the swivel shell (4) and head (3) being longer as measured at the * * centre-line of the latter component than towards the lug ends (5).9. A crankshaft drive according to claim 1, characterized in that the shape of one or more skirts can as an option be relieved by a cut-out recess (10) to allow a greater relative angle between the connecting rod (1) and piston (2) when disassembled from the reciprocating machine.U10. A crankshaft drive according to claim 3, characterized by a machined aperture (15) in the piston outer wall (7) facilitating manufacture of the piston retention bosses (6).II. A crankshaft drive according to claim tO, characterized by the ends of the aperture (iS) terminating at a locally larger radius (14) to relieve stress concentrations and provide increased clearance (16) to facilitate insertion of the tugs (5).12. A crankshaft drive according to claim 10, characterized by the retention boss (6) being abbreviated towards the side of piston (2) where access (16) for the tugs (5) is provided and extended on the opposite side (32).13. A crankshaft drive according to claim 3,characterized by the machining of swivel shell (4) and retention boss (6) being performed in one operation by virtue of a suitably shaped milling cutter.14. A crankshaft drive according to any one of the claims 5 to 6. characterized in that the concentricity of bearing surfaces 3,4,8 and 9 can be modified in order to compensate for thermal and toad induced deformations.15. A crankshaft drive according to any one of the claims 5 to 6, characterized in that the bearing surfaces 3,4,8 and 9 enjoy one extra or two extra rotational degrees of freedom, 16. A crankshaft drive according to claims 1 and 2, characterized by the piston (2) having one or more oil relief channels or holes (26), formed in the side wall (7) and extending through the oil scraper ring groove (27) into the internal bearing regions (3),(4),(8) and (9).17. A crankshaft drive according to claims I and 2, characterized by the piston body terminating at its lower extremity in a machined recess (23) the radius of such being equal to that of the crankshaft outer radius.18. A crankshaft drive according to claims 1 and 2, characterized by the swivel head (3) and the shank (18) being mutually linkedtogetlier by stiffening ribs (17) the height of which increases towards the aforesaid swivel head.19. A crankshaft drive according to claims I and 2, characterized by the swivel shell area * (4) and the skirt (II) being mutually linked together by ribs (25) providing support to the, / crown and (29) effectively stiffening the central region of the skirt.20. A crankshaft drive according to claims I and 2, characierized by the presence of one or more pockets (24) under the piston crown to minimise piston weight and optimise cooling.21. A crankshaft drive according to claims I and 2, characterized in that material may be removed to form apertures (28) in the side walls (7) of the piston skirt thus serving to lighten the piston.22. A crankshaft drive according to claims I and 2, characterized in that the connecting rod lateral guidance being accommodated between a face on the connecting rod swivel head (30) and piston retention boss (31).23. A crankshaft drive according to claims I and 2, characterized in that the load bearing areas (3) and (4) of the swivel joint and lugs (5) and retention bosses (6) have a wear-resistant and/or friction-reducing bearing surface or coating. *.I. * I *I*SS* .SIS* * SS***.** * *S**.*.* * S S. * ***SS..... I 5