GB2269336A

GB2269336A - Manufacture of pistons.

Info

Publication number: GB2269336A
Application number: GB9216605A
Authority: GB
Inventors: David Alec Parker
Original assignee: T&N Technology Ltd
Current assignee: Federal Mogul Technology Ltd
Priority date: 1992-08-05
Filing date: 1992-08-05
Publication date: 1994-02-09
Anticipated expiration: 2012-08-05
Also published as: GB2269336B; GB9216605D0

Abstract

A piston is manufactured by forming a crown part (12) terminating at a circular surface (20), and a central part (14) which is axi-symmetrical and may define piston ring grooves (28). The central part (14) terminates at circular surfaces (22, 30) at each end. A skirt part (16) is also formed which terminates at a circular surface (32). The respective circular surfaces (20, 22, 30, 32) of the crown part (12), central part (14) and skirt part (16) are friction welded together to form the completed piston. The crown part and skirt part are initially held stationary while the central part is rotated frictionally against them. Subsequently the crown and skirt parts are released to rotate with the central part during fusion while their relative angular positioning is maintained. <IMAGE>

Description

MANUFACTURE OF PISTONS This invention is concerned with the manufacture of pistons, e.g. for internal combustion engines.

A typical piston for an internal combustion engine comprises a crown portion whose upper surface bounds a combustion chamber of the engine. The crown portion may be of elliptical shape (when viewed transversely to an axis of the piston) and may define a combustion bowl communicating with the combustion chamber. The crown portion is rarely axi-symmetrical. Such a typical piston also comprises a skirt portion which acts to guide the piston in its movement. The skirt portion may also be of an elliptical shape and provides thrust surfaces arranged to engage the wall of a cylinder in which the piston reciprocates. The skirt portion also provides bosses which support a gudgeon pin by which the piston is connected to the small end of a connecting rod. The skirt portion is not axi-symmetrical.

Between the crown portion of such a typical piston and the skirt portion thereof, a central or ring band portion is provided which defines a number of grooves, usually 3, extending parallel to one another around the piston. These grooves receive sealing and oil control rings arranged to project beyond the grooves towards the wall of the cylinder to reduce gas flow past the piston and to control lubrication.

The aforementioned typical piston is manufactured at present by casting the whole piston as a unit from metal, e.g. aluminium alloy, and machining the casting. This results in a complex manufacturing process.

It is an object of the present invention to provide a simpler method of manufacturing a piston.

The invention provides a method of manufacturing a piston comprising forming a crown part having a circular surface at one end thereof, forming a central part which is axi-symmetrical and has a circular surface at each end thereof, forming a skirt part having a circular surface at one end thereof, and friction welding the circular surfaces of the crown part and the skirt part to respective circular surfaces of the central part.

A method according to the invention enables a piston to be made-up from three parts each of which can be cast and machined separately thereby simplifying the casting and machining operations.

The axi-symmetric central part may have one or more ring grooves formed in a cylindrical surface thereof.

Preferably, to carry out said friction welding, the crown part, the central part, and the skirt part are assembled with said circular surfaces in contact with one another, and the central part is rotated while the crown part and the skirt part are pressed against the central part. This enables both friction welds to be carried out simultaneously. In order to ensure correct orientation between the crown part and the skirt part, preferably said crown part and said skirt part are held against rotation with the central part during a heat generation portion of the welding process, and are subsequently released for rotation with the central part, during a weld-forming portion of the welding process, with the crown part and the skirt part being held in a fixed orientation relative to one another.

The invention also provides an apparatus for use in manufacturing a piston, the apparatus comprising means for supporting a crown part of a piston for rotation about an axis and for movement in the direction of said axis, means for supporting a skirt part of a piston for rotation about said axis and for movement along said axis, means for supporting a central part of a piston for rotation about said axis between the crown part and the skirt part, means for rotating the central part about said axis, means for pressing the crown part and the skirt part against the central part, releasable means for holding the crown part and the skirt part against rotation about said axis, and means for maintaining the crown part and the skirt part in the same orientation relative to one another about said axis.

The invention also provides a piston constructed from three parts friction welded together, the parts comprising a crown part, an axi-symmetrical central part, and a skirt part.

There now follow detailed descriptions, to be read with reference to the accompanying drawings, of an illustrative apparatus for use in manufacturing a piston and of an illustrative method of manufacturing a piston using the illustrative apparatus.

In the drawings: Figure 1 is a diagrammatic side elevational view, partly in section, of the illustrative apparatus; and Figure 2 is an elevational view of a piston manufactured by the illustrative method using the illustrative apparatus.

The illustrative apparatus shown in Figure 1 is for use in manufacturing the piston 10 shown in Figure 2. The piston 10 is constructed from three parts which are manufactured separately and friction welded together by the illustrative apparatus. The three parts of the piston 10 are a crown part 12, a central 14, and a skirt part 16.

The crown part 12 has an upper surface 18 which, when the piston 10 is in use, bounds a combustion chamber and receives the force of the explosions in the combustion chamber. The crown part 12 has a lower surface 20 which abuts an upper surface 22 of the central part 14, the surfaces 20 and 22 being circular, of the same diameter, and centred on a central axis 24 of the piston 10. The position of the surfaces 20 and 22 is indicated by the broken line 26 in Figure 2.

The central part 14 is located between the crown part 12 and the skirt part 16. The central part 14 is axisymmetrical about the axis 24 being cylindrical apart from three circumferential parallel ring grooves 28 formed in the cylindrical surface thereof. The central part 14 extends axially between the aforementioned surface 22 and a lower surface 30 which abuts an upper surface 32 of the skirt part 16. The surfaces 30 and 32 are both circular, of the same diameter, and centred on the axis 24. The position of the surfaces 30 and 32 is indicated by the broken line 34 in Figure 2.

The skirt part 16 is generally elliptical when viewed transversely of the axis 24 but its upper part tapers to the circular surface 32. The skirt part 16 provides thrust surfaces for transmitting lateral forces against the wall of a cylinder, in which the piston 10 reciprocates, and also provides supporting bosses (not shown) for a gudgeon pin.

The illustrative apparatus comprises a fixed bed 40 having two horizontal slideways 42 and 44 formed on an upper surface thereof. The slideways 42 and 44 are aligned longitudinally with one another and extend longitudinally of the bed 40. Between the slideways 42 and 44, a block 46 is fixed to the bed 40 and projects upwardly therefrom.

The illustrative apparatus also comprises crown part support means for supporting the crown part 12 for rotation about the axis 24 and for movement in the direction of the axis 24. This support means comprises a carriage 48 which is slidable on the slideway 42, a piston and cylinder assembly 50 fixedly mounted on the bed 40, and a chuck 52.

The chuck 52 is supported on bearings 54 mounted in a horizontal cylindrical passage through a block 55 which projects upwardly from the carriage 48. The chuck 52 defines a recess 56 in which the crown part 12 is received and is clamped by clamp screws (not shown). The recess 56 is shaped so that it can only receive the crown part 12 in a particular orientation relative to the axis 24. The chuck 52 can rotate about the axis 24 unless restrained by brake means mounted on the carriage 48. This brake means comprises pads 58 operable to engage opposite sides of an external flange 60 of the chuck 52, and a piston and cylinder assembly 62 operable to move the pads 58 into or out of engagement with said flange 60. The piston and cylinder assembly 50 is operable to move the carriage 48 and is connected thereto by a piston rod 64. Thus, when the crown part 12 is clamped in the recess 56, it can be pressed in the direction of the axis 24 by operation of the assembly 50 and whether it can rotate about the axis 24 can be controlled by operation of the assembly 62.

The illustrative apparatus also comprises skirt part support means for supporting the skirt part 16 for rotation about the axis 24 and for movement in the direction of the axis 24. This support means is generally similar to the crown part support means and comprises a carriage 66 which is slidable along the slideway 44 by the operation of a piston and cylinder assembly 68 mounted on the bed 40 and connected to the carriage 66 by a piston rod 70. The carriage 66 carries a block 72 having a horizontal cylindrical passage therethrough in which bearings 74 support a chuck 76 for rotation about the axis 24. The chuck 76 defines a recess 78 in which the skirt part 16 is received and is clamped by clamp screws (not shown). The recess 78 is shaped so that it can only receive the skirt part 14 in a particular orientation relative to the axis 24.This orientation is arranged to be such that the skirt part 16 is held in its correct orientation relative to the crown part 12. The chuck 76 also has an external flange 80 on which brake means, mounted on the carriage 66, can act to restrain rotation of the chuck 76 about the axis 24.

This brake means comprises a piston and cylinder assembly 82 operable to move pads 84 into or out of engagement with the flange 80. Thus, when the skirt part 16 is clamped in the recess 78, it can be pressed in the direction of the axis 24 by operation of the assembly 68 and it can rotate about the axis 24 unless braked by operation of the assembly 82.

The assemblies 50 and 68 provide means for pressing the crown part 12 and the skirt part 16 against the central part 14 while the assemblies 62 and 82 provide releasable means for holding the crown part and the skirt part against rotation about the axis 24.

The aforementioned block 46 which projects from the bed 40 between the recesses 56 and 78 has a horizontal passage 86 therethrough. The passage 86 contains bearings 88 on which a support 90 is rotatable about the axis 24.

The support 90 defines a passage 92 in which the central part 14 can be received and clamped by clamp screws (not shown). The orientation of the central part 14 about the axis 24 is immaterial as it is axi-symmetrical. The support 90 provides central part supporting means for supporting the central part 14 for rotation about the axis 24 between the parts 12 and 16.

The illustrative apparatus also comprises rotating means for rotating the central part 14 about the axis 24.

This means comprises a motor 94 (mounted on the bed 40 but shown above the rest of the apparatus in Figure 1). The motor 94 drives a gear 96 meshed with a toothed drive belt 98 also meshed with an externally-toothed axial flange 100 of the support 90. When clamped in the recess 56, the passage 92 and the recess 78 respectively, the crown part 12, the central part 14, and the skirt part 16 are in alignment with one another with the surfaces 20 and 22 facing one another and the surfaces 30 and 32 also facing one another.

The outer surfaces of the flanges 60 and 80 are toothed and are meshed with gears of synchronisation means operable to maintain the chucks 52 and 76 and hence the crown part 12 and the skirt part 16 in the same orientation relative to one another about the axis 24. Specifically, the synchronisation means comprises a shaft 102 extending parallel to the axis 24, bearings 104 which support the shaft 102 for rotation about an axis parallel to the axis 24, a gear 106 fixed on the shaft 102 and meshed with the teeth on the flange 60, and a gear 108 fixed on the shaft 102 and meshed with the teeth on the flange 80. The gears 106 and 108 are elongated in the direction of the shaft 102 to allow for the sliding movement of the carriages 48 and 66 and parts mounted thereon, i.e. the teeth of the flanges 60 and 80 can slide longitudinally between the teeth of the gears 106 and 108.The particular orientations at which the recesses 56 and 78 receive the parts 12 and 16 are arranged relative to one another to be as required in the piston 10 and the synchronisation means retains these orientations relative to one another during operation of the apparatus.

The illustrative apparatus is used in the illustrative method of manufacturing the illustrative piston 10. In the illustrative method, the crown part 12, the central part 14, and the skirt part 16 are formed separately by casting and machining. Next, the illustrative apparatus is used to carry out a friction welding process in which the circular surfaces 20 and 22, and 30 and 32 are friction welded to each other to assemble the piston 10. The piston and cylinder assemblies 50 and 68 are operated to move the carriages 48 and 66 as far apart as possible. This enables the parts 12, 16 and 14 to be mounted in the chucks 52 and 56 and in the passage 92 respectively. The parts are clamped against rotation relative to their chuck or support.Next the piston and cylinder assemblies 50 and 68 are operated to move the carriages 48 and 66 along the slideways 42 and 44, respectively, until the surface 20 of the crown part 12 comes into contact with the surface 22 of the central part 14 and the surface 32 of the skirt portion 16 comes into contact with the surface 30 of the central part 14. The parts 12, 14 and 16 are now assembled with the circular surfaces 20 and 22, and 30 and 32 in contact with each other ready to be welded together. The assemblies 50 and 68 continue to operate to create pressure between the surfaces 20 and 22, and 30 and 32.

Next, in the illustrative method, a heat generation portion of the welding process takes place. The motor 94 is operated to rotate the central part 14 about the axis 24, while the crown part 12 and the skirt part 16 are pressed against the central part 14 by operation of the assemblies 50 and 68. During this portion of the process, the parts 12 and 16 are held against rotation with the central part 14 by operation of the assemblies 62 and 82, which press the pads 58 and 84 against the flanges 60 and 80.

When sufficient heat has been generated, by friction between the rotating faces 22 and 30 and the stationary faces 20 and 32, to enable welds to be made, the assemblies 62 and 82 are operated to release the crown part 12 and the skirt part 16 for rotation with the central part 14 and the pressure applied by the assemblies 50 and 68 is increased.

During this weld-forming portion of the welding process, the crown part 12 and the skirt part 16 are held in a fixed orientation relative to one another by the shaft 102 and the gears 106 and 108, i.e. the parts 12 and 16 rotate as a unit. The surfaces 20 and 22, and 30 and 32 are welded together along the lines 26 and 34, respectively.

Claims

1 A method of manufacturing a piston comprising forming a crown part having a circular surface at one end thereof, forming a central part which is axi symmetrical and has a circular surface at each end thereof, forming a skirt part having a circular surface at one end thereof, and friction welding the circular surfaces of the crown part and the skirt part to respective circular surfaces of the central part.

2 A method according to Claim 1, wherein the central part has one or more ring grooves formed therein.

3 A method according to either one of Claims 1 and 2, wherein, to carry out said friction welding, the crown part, the central part, and the skirt part are assembled with said circular surfaces in contact with one another, and the central part is rotated while the crown part and the skirt part are pressed against the central part.

4 A method according to Claim 3, wherein said crown part and said skirt part are held against rotation with the central part during a heat generation portion of the welding process, and are subsequently released for rotation with the central part, during a weld-forming portion of the welding process, with the crown part and the skirt part being held in a fixed orientation relative to one another.

5 A method of manufacturing a piston substantially as hereinbefore described with reference to the accompanying drawings.

6 An apparatus for use in manufacturing a piston, the apparatus comprising means for supporting a crown part of a piston for rotation about an axis and for movement in the direction of said axis, means for supporting a skirt part of a piston for rotation about said axis and for movement along said axis, means for supporting a central part of a piston for rotation about said axis between the crown part and the skirt part, means for rotating the central part about said axis, means for pressing the crown part and the skirt part against the central part, releasable means of holding the crown part and the skirt part against rotation about said axis, and means for maintaining the crown part and the skirt part in the same orientation relative to one another about said axis.

7 An apparatus for use in manufacturing a piston substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

8 A piston constructed from three parts friction welded together, the parts comprising a crown part, an axi symmetrical central part, and a skirt part.