WO2003046337A1

WO2003046337A1 - Power machine

Info

Publication number: WO2003046337A1
Application number: PCT/SE2002/002175
Authority: WO
Inventors: Gunnar Leijonberg
Original assignee: Gul & Co Development AB; Gul and Co Dev AB
Current assignee: Gul & Co Development AB; Gul and Co Dev AB
Priority date: 2001-11-30
Filing date: 2002-11-27
Publication date: 2003-06-05
Anticipated expiration: 2004-05-30
Also published as: AU2002354392A1; SE0104056D0; SE518608C2; SE0104056L

Abstract

The present invention relates to an arrangement in a prime mover having two pistons, which have a piston rod (5) fixed to each piston and are arranged in a common cylinder liner and work synchronously in opposition to one another, and means for translating power between the linear motion of the pistons and the rotary motion of the rotating part (14) of the arrangement. This comprises a cam /(4), which forms a closed curve, the axis of the rotating part being arranged perpendicular to the cylinder liner and each piston rod in its part remote from the piston carrying two wheels (8, 9), which are capable of rotating on shafts (6, 7) and are each designed to follow the rotating cam (4) on either side thereof. The cam (4) preferably has a thickness varying over its circumference. For guiding the short piston in the cylinder liner, the arrangement comprises linear bearings acting on the piston rod.

Description

The present invention relates to the type of prime movers, engines or compressors which have two or more pistons working in opposition to one another, especially ones sharing a common combustion space, in a fixed cylinder, the power being translated into a rotary motion without intermediate crankshaft.

The present invention relates to translation of the power into a rotary motion and to the support and guiding of pistons and piston rods.

In internal combustion engines the power derived from a reciprocating motion is generally translated into a rotary motion by some form of crankshaft or similar arrangement. In certain cases, however, crankshafts are less suitable and this is particularly so where reciprocating motions in different, frequently entirely opposing directions must together be translated into a rotary motion. This applies in particular to the type of prime movers, that is to say internal combustion engines, compressors and pumps in which two pistons work simultaneously in opposition to one another in a common cylinder liner. The use of crankshafts in such cases results in complicated mechanical constructions in order to combine the power derived from the two pistons into a common rotary motion. Power can instead be translated from a reciprocating motion into a rotary motion by means of a ball bearing which runs in various races and comprises a ball enclosed by a ball holder, which is fixed on a piston rod associated with each ball or corresponding arrangement for translating the linear motion, as described, for example, in the international patent application bearing the application number WO 97/37155.

The object of the present invention is an improved arrangement of the said type. The arrangement comprises a fixed part of the machine and a part rotating in relation thereto. In a cylinder centrally located in relation to the axis of rotation of the rotating part there are two pistons, which constitute working pistons in an internal combustion engine sharing a common combustion space. Fixed to each piston is a piston rod, which according to the invention at its end opposite the piston carries arrangements for interaction with a flange or cam projecting from the rotating part. The said arrangements are preferably wheels but they may also take the form of sliding means such as pins or slide surfaces. Linear bearings, which are arranged in the fixed part, act on the piston rod and together with the piston guide the said piston and piston rod in the right direction of movement.

In comparison to hitherto known embodiments of similar arrangements, the invention means that the rotating cam or its equivalent can be provided with a smaller diameter and hence a lower peripheral speed under otherwise given conditions, i.e. rotational speed of the output shaft. This also affords the further advantage that the overall dimensions of the arrangement can be reduced. Yet another advantage obtained by means of the arrangement according to the invention is that the friction losses are small, since only rolling friction occurs between the components of the arrangement.

The arrangement according to the invention has the characteristics specified in claim 1. Further embodiments of the invention have the characteristics specified in the other claims.

The invention will be described in more detail below with reference to the example of a preferred embodiment shown in the drawings attached.

Figure 1 shows the pistons forming part of the arrangement and the rotating disk with projecting cam,

Figure 2 A-C shows different views of a piston,

Figure 3 shows a section through arrangement in plan view,

Figure 4 shows a section through the arrangement in side view

Figure 5 shows parts of the arrangement in a position occurring during operation.

The arrangement shown in the figures comprises a part 13 that is fixed in relation to the base on which the arrangement is mounted, and a rotating part 14 moveable in relation thereto. The fixed part 13 comprises cylinder 15 with a centrally situated combustion space 16 and outer cooling flanges 17. In the fixed part there are also linear bearing arrangements in the form of races 12. Pistons 1, 2 are provided for reciprocating movement in the cylinder 15. The rotating part 14 comprises a flange or cam 4, which forms a closed curve of a type described below.

Fixed to each piston 1, 2 is a piston rod 5, which at its opposite end carries vanes 10, which interact with and run in the linear bearing races 12. Each piston rod 5 also carries two shafts or shaft journals 6, 7 on which wheels 8, 9 are fitted.

The wheels 8, 9 are rotatably supported on the shafts 6, 7 and bear, at least during parts of a working cycle, against each side of the cam respectively. The embodiment shown in the figures is intended for internal combustion engines, the inner wheel 8 advantageously having a larger diameter than the outer wheel 9, since the mechanical stresses are greater on the inner wheel. The shaft 6 of the inner wheel is therefore also fixed at both ends into a fork-like arrangement, whilst the shaft of the outer wheel projects like a journal from the piston rod.

The shafts 6, 7 are firmly mounted in the piston rod 5, the term firmly mounted also encompassing any sprung mounting with rubber bushings, for example. During the reciprocating movements of the piston, the inner wheel passes into and out of the cylinder liner, the space there accessible thus being utilized in order to allow the cam to be located as close as possible to the centre of rotation.

The piston has a small height in relation to its stroke and is therefore not self-guiding in the cylinder liner. The height of the piston is suitably no greater than is required for the fitting of piston rings and for linear contact across the cylinder liner. For guiding the piston and the piston rod there is a linear bearing arrangement, which is arranged outside the cylinder liner and which in the embodiment shown consists of two vanes 10, 11, which run in linear bearings in the form of races 12 in the fixed part of the arrangement. The vanes 10, 11, as shown in the drawings, are preferably located between the wheel shafts 6, 7, viewed in the longitudinal direction of the piston rod. In addition to guiding the piston in the cylinder liner, this bearing guides the piston rod linearly in the direction of movement and prevents the piston rod running obliquely in relation to the cylinder axis.

The thickness of the cam 4 varies so that in any position the two wheels 8, 9 each bear against their side of the cam with a degree of play that is constant and as small as technically feasible and appropriate. This is shown in more detail in Figure 5, which shows a diagram of the two wheels 8, 9, belonging to a piston and the cam 4. The rotating part is assumed to have rotated approximately 30 degrees from the position shown in Figure 3. The play is measured along the perpendicular from the surface of the cam to the through the centre of the wheel. In the example shown in the figure, the play between the cam 4 and the outer wheel 9 is the distance "a", whilst the play between the cam 4 and the inner wheel 8 is zero. For the purposes of this description and the patent claims, the term constant play signifies that the sum of the two modes of play is constant regardless of which position the rotating part is turned to. Theoretically, it may be desirable for the play to be zero, but owing to the variations in dimensions and distance that can occur due to varying thermal conditions, it is in practice not possible to design for zero play. The term constant play also includes the variations that normally occur for technical manufacturing and operating reasons.

In order to entirely avoid any play between wheel and cam, the fixing of the wheel shaft may be made somewhat flexible, by means of a rubber bushing, for example, so that the wheel or wheels bear against the cam at all times. This can also be achieved by spring loading the shaft or by an elastic covering on the surface of the wheels that bears against the cam or in some other way. This affords the advantage that the wheel at all times rotates at a speed which matches the rotational speed of the cam, so that powerful acceleration can be avoided in the event of sudden contact between wheel and cam.

The cam is preferably designed with circular cylindrical section 18, 19 closest to the positions corresponding to the top and/or bottom dead centre of the pistons. The two lateral surfaces of the cam are then parallel with one another and this position means that the pistons are at a standstill. The embodiment can be modified in various ways without departing from the scope of the idea of the invention. Examples of such modifications are the shape of the cam, which can be modified in many different ways in order to obtain various types of working cycles. In the embodiment shown in the drawings, the curve is symmetrical in two planes and the two parts are mirror images of one another in these planes. In other embodiments the curve may be shifted so that the top or bottom dead centre of the pistons is offset and the curve may then have only one plane of symmetry, for example. Embodiments are also possible in which more than one top and bottom dead centres are obtained for each revolution of the rotating part. Other modifications may relate to the linear bearing, which may be designed, for example, so that a races in the vanes 10, 11 interact with projecting sections of the fixed part. Further modifications may relate to the wheel size ratio and the fixing of the shaft journals for the wheels. The wheels may also be arranged at a greater distance from the piston than that described above, in order to thereby prevent the inner wheel entering the cylinder liner during parts of each working cycle. This may be particularly relevant when wishing to provide some form of seal in the cylinder liner under the piston at its bottom dead centre.

Claims

1. Arrangement in a prime mover having two pistons, which have a piston rod (5) fixed to each piston and are arranged in a common cylinder liner and work synchronously in opposition to one another, and means for translating power between the linear motion of the pistons and the rotary motion of the rotating part (14) of the arrangement, comprising a cam (4) which forms a closed curve, characterised in that the axis of the rotating part is arranged perpendicular to the cylinder liner and that each piston rod in its part remote from the piston carries two drivers, which are each designed to follow the rotating cam (4) on either side thereof.

2. Arrangement according to claim 1, characterised in that the drivers comprise two wheels (8, 9), which are capable of rotating on shafts (6, 7).

3. Arrangement according to claim 1 or 2, characterised in that the cam (4) forms an elliptical or similar curve.

4. Arrangement according to claim 1, 2 or 3, characterised in that the cam 4 has a thickness varying over its circumference.

5. Arrangement according to claim 4, characterised in that the thickness of the cam varies so that the play between the wheels (8, 9) and the cam (4) is the same in any position.

6. Arrangement according to any of the preceding claims, characterised in that it comprises linear bearings acting on the piston rod.

7. Arrangement according to claim 6, characterised by vanes (10, 11) which are arranged on the piston rod and run in linear bearing races (12), which are arranged along the fixed part outside the cylinder liner.

8. Arrangement according to claim 7, characterised in that the vanes (10, 11) are located between the shafts 6, 7) viewed in the longitudinal direction of the piston rod. Arrangement in a prime mover having two pistons, which have a piston rod (5) fixed to each piston and are arranged in a fixed part of the machine in a common cylinder liner and work synchronously in opposition to one another, and means for translating power between the linear motion of the pistons and the rotary motion of the rotating part (14) of the arrangement, comprising a cam (4) which forms a closed curve, the axis of the rotating part being arranged perpendicular to the cylinder liner, characterised in that each piston rod in its part remote from the piston carries two wheels (8, 9), which are capable of rotating on shafts (6, 7) and are each designed to follow the rotating cam (4) on either side thereof, together with linear bearings in the fixed part of the arrangement acting on the piston rod.