The present invention is for the kind of power machines, en¬ gines, pumps or compressors which have two or more pistons which work against each other and preferably have a common com¬ bustion space within a stationary cylinder and where the power is transmitted to or from a rotating movement without an inter¬ mediate crankshaft.

Independent of wether the machine works as an engine compressor or pump there is a need to cool the cylinder bore. For certain applications such as engines for lawn-mowers and power saws these must be cooled by air as it in practice is very difficult or impossible to arrange a water cooling system.

At combustion engines the transmission of force from a to and from motion to a rotating motion generally is by means of some kind of crankshaft or the like. In certain cases however crank¬ shafts are less suitable, and this is especially the case when to and from motions with different, often directly opposite di¬ rections together shall be transmitted into a rotating motion. Especially this is the case by that kind of power machines e.g. combustion engines, compressors or pumps, where two pistons at the same time work against each other in a common cylinder bore . In these cases the use of crankshaft bring with them com¬ plicating mechanical designs to put together the power from the two pistons into one common rotating motion. The transmission of force between a to and from motion and a rotating motion may instead take place using a ball bearing which runs in several tracks and includes a ball which is surrounded by a ball holder which is attached to one piston rod or the like member for each ball for transmission of the linear motion into rotating mo¬ tion. It is also possible to exchange the balls for other means with corresponding functions, for example rolls or pins which

roll or slide in the tracks.

One such device has two parallel plane discs both a stationary disc and one relatively thereto rotating disc. In one relative to the disc centrally positioned cylinder there are two pistons which are working pistons of a combustion engine, and have a common combustion space. Fixed joined to each piston there is a piston rod which at its opposite end has a holder means for the ball by which the force from the to and fro motion is transmit¬ ted to the rotating disc. The balls also serve as bearing be¬ tween the stationary disc and the rotating disc. The rotating disc is mounted onto a holder which in turn is mounted onto an outgoing shaft from which the rotating force is taken for use for various driving purposes. The balls can move both in linear tracks in the fixed disc, and in a common elliptic or otherwise closed shaped track in the rotating disc. In other embodiments tracks may be substituted for by raised edges where roller or slide bearings contact the sides of the edges.

The present invention is for a machine as described above, where air-coolmg of the cylinder is arranged. There are spe¬ cial difficulties in arranging air-cooling at machines of the above mentioned kind, as at known designs the power transmis¬ sion mechanism has brought with it a design of the machine in its entirety such that it has not been possible to arrange a sufficient cooling air flow. The present invention offers a so¬ lution to this problem by a device with the characteristics which are mentioned in the characterising part of claim 1. Other embodiments of the device are described in the dependent claims.

The invention will below be described with reference to the em¬ bodiment which is shown in the enclosed figures.

Figure 1 shows a cross section of a machine according to the invention.

Figure 2 shows the machine of figure 1 in cross section at right angle to figure 1.

Figure 3 shows the machine of figure 1 in cross section at right angles to figures 1 and 2.

Figure 4 shows another embodiment of the invention in a cross section corresponding to figure 2.

Figure 5 is a perspective view of the invention with some parts removed and in partial cross section.

The device shown in the figures has two parallel plane discs, one which is named stationary disc 8 and one relatively thereto rotating disc 13. The stationary disc 8 is carried by a housing 9 and the disc 8 in turn carries one in its centre positioned cylinder 1 having end walls 2, 3. In the cylinder there are two pistons 4, 5 which are working pistons, and in a combustion en¬ gine preferably have a common combustion space.

Fixedly joined to each of the piston 4, 5 is a piston rod 6, 7 which at its opposite end has a holder means 17, 18 for the ball 15, 16 by which the force from the to and fro motion is transmitted to the rotating disc 13. The balls 15, 16 also serve as bearing between the stationary disc 8 and the rotating disc 13. The rotating disc 13 is mounted onto a holder 10 which m turn is mounted onto an outgoing shaft 23 from which the ro¬ tating force is taken to be used for various purposes . In the preferred embodiment of the invention the centre axes of the cylinder bore coincides with the line of movement of the balls.

The balls 15, 16 can move both in linear tracks 11, 24 in the fixed disc and in a common elliptic track 12 in the rotating

Valves may be arranged adjacent to the upper dead centre, UDC, of the pistons at opposite sides in the centre of the cylinder bore. In the cylinder there are corresponding valve seats and the shafts are designed in consideration of the through bores and stearings which are in stationary parts closed to the cyl¬ inder. Preferably the from the cylinder outer ends of the valve shafts directly contact a regulating curve or contact surface which is a part of the rotating disc.

Cooling of the cylinder is obtained by that holes or channels 30, 31 are arranged both in the rotating and the stationary discs and cooling air flows through these channels. In order to further improve the cooling the outside of the cylinder may have flanges 32, as shown in figure 1. In a preferred embodi¬ ment of the invention the conveyance of cooling air to or from the rotating disc is by means of a hollow shaft 33, which is connected to this disc. The flow of air may take place either directly inside the shaft or inside one in the shaft mounted stationary tubular means. This tubular means may be directly or indirectly joined to the stationary disc. Cooling air is di¬ rected to both sides of the cylinder and in those cases where the power machine is equipped with valves which are arranged mainly at right angle to the direction of movement of the pis¬ tons, four such cooling channels may be arranged. In other em¬ bodiments of the invention the means which connect the rotating disc and the outgoing shaft are so designed that they also function as fan blades 34, 35 and cause a desired air flow.

A preferred embodiment of the invention is shown m figure 5. Here the stationary disc is built together with, or forms a

part of the housing which fully surrounds the rotating disc. All lubricated parts of the device are within this housing which downwards (according to figure 5) is delimited by an oil sealed bearing. The outgoing shaft from the rotating disc is hollow and cooling air is directed through the shaft to the in¬ ner bowl shaped volume wherein the cylinder having cooling flanges is positioned.

The airflow may in some applications be used also for other purposes than cooling only. When the power machine is used as a engine for lawn-mowers the airflow may be directed to the cut grass and affect this either to be blown to a collector at the lawn-mower or flow back to the knives to be cut into smaller pieces.