Two-stroke or four-stroke Otto-cycle engines or diesel engines provided with an electric generator are commonly used as power units for converting the energy obtained from combustion of petrol, fuel oil, natural gas or a similar fuel into electric energy. In the above-mentioned combustion engines the energy produced by fuel combustion makes the piston move to and fro. By means of a crank shaft, this motion is converted into a rotating motion, which rotates the generator when electricity is produced. However, the efficiency of the combustion engines in question as well as the amount of electric energy obtained per fuel unit is rather low. Furthermore, such engines are large and heavy and consist of several wearing parts, for which reason various substitutive solutions have been disclosed for converting fuel energy into electric energy.

In the apparatus disclosed in RU 2 046 966 one part of the electric generator consists of a permanent magnet piston which, when moving to and fro either in a straight cylinder or in a cylinder with the shape of a partial toroid between two combustion spaces, induces voltage in the coils outside the cylinder. It should be noted that the embodiment with the shape of a partial toroid disclosed in the publication is regarded as prior art with respect to the present invention. In practice the structure of the apparatus causes several problems because it is. impossible to meet all the requirements set for the piston material at the same time. On the one hand, the piston must be a permanent magnet which has a high-density magnetic flux and which does not become demagnetized. On the other hand, the piston has to withstand the high temperatures and loads prevailing in the combustion engine. In addition, the structure of the piston should be light so that moments of inertia can be

minimized. Also, as regards electromagnetic function of the generator, it is disadvantageous to mount the magnetic part in the piston because the density of the magnet flux and the voltage induced in the generator decrease rapidly as the distance between the magnet and the coil increases, i. e. the-electric power output by the generator decreases as the wall thickness of the cylinder increases. Because of the structure of the device it is thus necessary to make a compromise between the mechanical durability of the cylinder and the function of the generator. The cylinder matera ! should also be selected so that it does not interfere with the magnetic flux. In practice the function and durability of the power unit do not meet the requirements set for a power source intended for continuous use.

DE 4 209 040 discloses a power unit and its combustion engine driven application where a magnetic piston is moved in the cylinder by combustion gases, thus inducing voltage in a coil outside the cylinder. The apparatus also comprises closing valves which control the gas movement and are controlled by sensors provided in the cylinder. The solution of the publication has the same drawbacks as that disclosed in the Russian publication.

The object of the present invention is to provide a power unit to eliminate the above-mentioned drawbacks.

The power unit of the invention is characterized in that the pistons and the first generator section are mounted substantially rigidly with respect to each other and move together as a power transmission part, and the first and the second generator section are totally outside the cylinders.

The basic idea of the invention is that the pistons of the cylinder block in the power unit are mounted directly in the first generator section outside the cylinders without energy-wasting transmission means. For the sake of clarity it should be noted that the first section of the generator refers to the part comprising the magnets or coils and the second section of the generator to the part comprising the stator coils. The idea of a preferred embodiment is that electric energy is supplied to the second generator section and the power unit is used as an electric pump, in which case a liquid or gaseous pressure fluid is supplied to the cylinders. The idea of another preferred embodiment is that the power unit comprises two or more cylinder blocks mounted rigidly on a common shaft, and at least one of the cylinder blocks of the power unit functions as a combustion engine and at least one as

a pressure fluid pump. The idea of a third preferred embodiment is that two or more cylinder blocks are mounted rigidly on a common shaft, and at least one of the cylinder blocks is a combustion engine driven electric generator and at least one cylinder block is arranged to pump air or a mixture of air needed for fuel combustion into the cylinders of the cylinder blocks functioning as the combustion engine.

An advantage of the invention is that the pistons of the power unit and the first section of the e) ecthc fenerator are connected with each other directly, and thus the chemical energy of the fuel is converted into electric energy or the electric energy into energy of the pressure fluid with minimal energy losses. Consequently the efficiency of the power unit is very high. In addition, the first and the second section of the power unit generator are preferably placed close to each other, and thus the generator's capacity of producing electricity is optimal. The power unit is simple in structure, inexpensive to produce as well as small and light with respect to its output.

Furthermore, the structure of the power unit is durable and long-lasting since the first and the second section of the generator are completely outside the combustion engine part, and they are not subjected to thermal stress from the cylinder block to any significant extent. The power unit can also be modified in various ways for use as a four-stroke or two-stroke combustion engine driven generator, electric or combustion engine driven pump of a liquid or gaseous pressure fluid, electric generator driven by compressed air or another pressure fluid, or a combination of the above-mentioned embodiments.

The invention will be described in greater detail in the accompanying drawings, in which Figure 1 is a schematic and partia ! cross-sectional view of an embodiment of the power unit according to the invention, Figure 2 schematically illustrates a power transmission part of an embodiment of the power unit according to the invention, and Figure 3 is a schematic cross-sectional view of an embodiment of the power unit according to the invention in the direction of the axis of the apparatus.

Figure 1 is a schematic and partial cross-sectional view of an embodiment of the power unit according to the invention. The power unit 1 comprises a frame 2 provided with four cylinders 3a, 3b, 3c, 3d which have the shape of a partial toroid and are on the same circumference, the midpoint of

which is on an imaginary axis 9. Each cylinder 3a to 3d is provided with a piston 4a, 4b, 4c, 4d which substantially has the size and the shape of the cross-section of the cylinder. The pistons may comprise gaskets for sealing the gap between the piston and the cylinder. All four pistons 4a to 4d are connected to one another firmly and substantially rigidly by means of piston rods 5a, 5b, 5c, 5d, bars 6a, 6b and a shaft 7. In the figure the shaft 7 is hollow and coaxial with the axis 9 of the toroid. Inside the shaft 7 there is an exhaust pipe 26 arranged coax. ially at a distance. The shaft 7 may also be of a different kind, or it may be totally omitted from the power unit in some embodiments. The cylinders 3a to 3d and the pistons 4a to 4d are made of materials commonly used in combustion engines and will not be described more closely here. The ends of the bars 6a, 6b towards the outer circumference which extend past the cylinders are provided with a substantially rigid member 8, preferably a discoid member, which comprises fixing members for the magnets 11 of the first section of the electric generator.

The disc 8 is preferably made of carbon fibre composite or a similar light and strong material, in which case the moment of inertia of the disc is preferably small. The frame 2 of the power unit can be opened and closed by the fixing members 12 on the plane of the figure. Thanks to the openable frame 2, it is easy to remove and install the cylinders 3a to 3d, which facilitates service of the engine and other similar measures significantly. The figure does not show coolant channels of the frame 2. Considering the function of the power unit, the temperature of the cylinder block can be maintained suitable by means of a cooling agent flowing in the coolant channels. Cooling of the power unit can naturally be arranged otherwise, e. g. using air cooling. The power unit illustrated in the figure functions as a two-stroke spark-ignited direct injection combustion engine. The apparatus comprises channels 13, which are obvious to a person skilled in the art, for supplying air or a mixture of air to the cylinders 3a to 3d and for leading exhaust gas out of the cylinders. In the position of the pistons 4a to 4d shown in the figure air/mixture of air has been compressed in cylinders 3a and 3c, and fuel has been injected into the combustion space 14a and 14c of the cylinders by injection means not shown in the figure. The flammable mixture is ignited with a spark generated in the ignition means in a manner known per se, and the power stroke of cylinders 3a and 3c starts. The combustion pressure of the mixture pushes pistons 4a and 4c forwards, and the substantially rigid power transmission part formed by

the pistons 4, piston rods 5, bars 6 and shaft 7 turns clockwise with the pistons. At the same time a compression stroke takes place in cylinders 3b and 3d during which air/mixture of air supplied to the cylinders 3b, 3d via a suction duct is compressed. The power transmission part continues to move clockwise until it reaches a position in which the mixture in cylinders 3b and 3d is ignited, and the power transmission part starts turning in the opposite direction, i. e. anti-clockwise, and the compression stroke takes place in cylinders 3a and 3c. In fact, the power transmission part moves to and fro, the swing centre being on the axis 9 of the toroid and the angle of deflection approximately 45°. The pendulous motion of the power transmission part is transmitted directly and without any loss to the first section 8,11 of the electric generator, and the motion of the magnet flux of the magnets 11 in this section with respect to the coils of the second generator section 18, shown with a broken line in the figure, induces voltage in said coils according to the known principles of electromagnetism.

Figure z schematically illustrates a power transmission part of an embodiment of the power unit according to the invention. The four pistons 4a to 4d of the power transmission part 15 are mounted rigidly on the piston rods 5a to 5d, which are fixed to the bars 6a, 6b, whose inner end is in turn mounted rigidly on the hollow shaft 7. Thus the pistons 4a to 4d, rods 5a to 5d, bars 6a, 6b and shaft 7 form a substantially rigid entity. In a preferred embodiment the pistons 4a to 4d, rods 5a to 5d, bars 6a, 6b and shaft 7 are made of the one and the same piece. There is a disc 8 mounted at the ends of the bars 6a, 6b towards the outer circumference, and the magnets 11 of the first section of the electric generator are attached to the disc. Alternatively, at least some magnets 11 may be replaced by coils, and the electric current fed into the coils generates a magnetic flux in a manner known per se. The pistons are provided with gaskets 16, preferably with piston rings, which seal the gap between the piston and the cylinder. For the sake of clarity the heads 17 of the pistons 4a to 4d shown in the figure are even, but naturally the piston head 17 can be shaped otherwise e. g. to optimize combustion. Furthermore, the piston head can be tilted to minimize the torque acting on the piston rod 5a to 5d.

The piston head 17 may be provided e. g. with a ceramic thermal insulator which significantly decreases heat conduction to the rod 5a to 5d, bar 6a, 6b and first generator section 8,11. Heat conduction to the first section 8,11 of

the generator can also be reduced by placing thermal insulators between the contact surfaces of the disc 8 and the bar 6a, 6b.

Figure 3 is a schematic cross-sectional view of an embodiment of the power unit according to the invention in the direction of the shaft 7 of the apparatus. The power unit operates according to the two-stroke principle, fuel is injected directly into the combustion space 14 and the mixture of fuel and air is ignited by an electric spark. The power unit comprises three cylinder blocks 19a, 19b, 19c which are arranged one after the other so that each power transmission part of the cylinder blocks 19a, 19b, 19c has a common shaft 7 by means of which the power transmission parts of-each cylinder block 19a, 19b, 19c are arranged substantially rigidly with respect to one another. The first and the third cylinder block 19a, 19c function as the combustion engine and the second block 19b, which is placed between the above-mentioned blocks, functions as a pump which pumps air or a mixture of air needed for fuel combustion into the cylinders 3 of the first and the third cylinder block 19a, 19c via suction ducts 20 and suction inlets 21 of the combustion engine blocks 19a, 19c. The pump 19b receives its pumping energy through the shaft 7 from the first and the third cylinder block 19a, 19c. To achieve a sufficient pumping efficiency, the diameter of the cylinders 3'in the pump 19b is substantially larger than that of the cylinders 3 of the first or the third block 19a, 19c. Fuel is injected into the combustion space 14 in a manner known per se by injection means 22 and the mixture is ignited by a sparking pjug 23. Combustion gases produced in combustion are pushed out of the cylinders 3 into exhaust outlets 24 and exhaust ducts 25 by fresh air or a mixture of-air flowing into the cylinder 3 through the suction inlet 21. The exhaust ducts 25 of the cylinders 3 are connected to an exhaust pipe 26 inside the hollow shaft 7. The disc 8 and its magnets, which form the first section of the electric generator, are mounted in each of the three cylinder blocks 19a to 19c of the power unit. The second sections 18 of each three generators are mounted substantially rigidly to the frame 2a to 2c of the respective cylinder block 19a to 19c. In the figure the section of the second part 18 is shown only on the left side of the third cylinder group, but the second part 18 is naturally arranged around the first generator section 8 of each cylinder block 19a to 19c. As the pistons mounted in cylinders 3,3'and the first generator sections move to and fro with respect to the second generator section 18 mounted rigidly to the frame 2a to 2c, all three generators produce electricity. The shaft 7 of the power unit is provided

with bearings 27 by means of which the power unit is attached to its mounting.

Bearings 27 between the power unit and its mounting allow the frame 2a to 2c to turn during the power stroke in the opposite direction with respect to the power transmission part, which makes running of the power unit smoother.

Due to the higher moment of inertia of the frame 2a to 2c the turning angle of the frame is considerably smaller than that of the power transmission part.

The drawings and the related description are only intended to illustrate the inventive concept. The details of the invention may vary within the scope of the claims. Thus the number of cylinders in the cylinder blocks of the power unit may differ from four; however, there must be at least two cylinders to enable to-and-fro motion. The running of the power unit may also be based on the four-stroke principle in which case the apparatus is provided with appropriate, generally known suction and exhaust ducts and vaive gear.

Valves may be controlled mechanically or electrically or in another appropriate manner. So that a four-stroke power unit could function, its cylinder block must comprise at least four cylinders. The power unit may also be a two-stroke or a four-stroke compression ignition engine. A power unit consisting of two or more cylinder blocks may not only function as a combustion engine driven electric generator but also as a pressure fluid pump which pumps gaseous or liquid pressure fluid for use outside the apparatus. At the same time the generators of the apparatus can naturally be used for producing electricity.

The apparatus can also be used as an electric pressure fluid pump where the first and the second section of the generator function as an electric motor operated by electric energy which is supplied into the second section and obtained from a source outside the apparatus.