EP3781788B1

EP3781788B1 - Free piston engine generator and method for producing electric power

Info

Publication number: EP3781788B1
Application number: EP18723416.6A
Authority: EP
Inventors: Sergio NIZZOLA; Pietro NIZZOLA
Original assignee: Suisse Technology Group Sa
Current assignee: Suisse Technology Group Sa
Priority date: 2018-04-19
Filing date: 2018-04-19
Publication date: 2022-07-13
Anticipated expiration: 2038-04-19
Also published as: WO2019201447A1; EP3781788A1

Description

Technical Field

The present invention relates to an apparatus and a method for producing electric power.
More particularly, the present invention relates to an apparatus and a method for producing electric power intended for a stand-alone power generator or for being installed in transport means (including road vehicles, boats, aircrafts), working means, lifting means, in order to increase the charge duration of the batteries, or, more generally, intended for being associated as a supporting unit with any equipment where the need to increase the charge duration of the accumulators is felt, or yet for being used in plants for electric power production by means of renewable sources, in order to increase the accumulation capacity of the batteries. Furthermore, the present invention relates to an apparatus and a method for producing electric power from gas, i.e. methane, BioGAS, hydrogen or CNG such that the present invention also can be applied with fuels being obtained by regenerative processes.

Prior Art

Electric power generating assemblies incorporating an internal combustion engine and exploiting therefore the high energy content of hydrocarbon fuels are known in the art.
US Patent No. 6 349 683 discloses a two-stroke or four-stroke internal combustion engine including a cylinder in which a combustion chamber is formed and a piston arranged to reciprocate within the cylinder. To this end, the piston is connected to a rod, and a helical spring has one end fastened to the cylinder and the opposite end fastened to the rod associated with the piston, whereby the piston moves (in the expansion step) against the spring resistance. The rod, at its distal end from the piston, carries an electrical induction coil that, by following the reciprocating motion of the piston, moves relative to a stationary permanent magnet, so as to generate electric power.
US Patent Application No. 2002/0139323 discloses an internal combustion engine including a pair of opposed pistons which are rigidly connected together by means of a common rod and are driven in an oscillatory movement. Said common rod carries a coil that, by following the oscillatory motion of the rod, moves relative to a stationary permanent magnet, so as to generate electric power.
WO 01/9475 A1 shows a free-piston internal combustion engine, where the pistons have inlet valves integrated in the pistons.
Even if such prior art solutions enable obtaining electric power generation, they have a number of drawbacks.
More particularly, using a spring in order to brake the piston movement entails a number of complications, related in particular to fatigue stresses that can lead to the breakage of the spring itself and consequently of the engine.
Moreover, also the extension of the piston stroke and the attainable compression level are limited because of the presence of the spring, and this consequently limits the engine efficiency.
It is the main object of the present invention to overcome the drawbacks of the prior art solutions, by providing an electric power production apparatus and a respective method applying said apparatus, which is reliable, durable and efficient.
Moreover, for example in every forth and back cycle of each piston of a specific embodiment of the invention, two ignitions occur instead of one, and this allows considerably increasing the performance of the apparatus according to an embodiment of the invention and the power supplied by it.

Brief Description of the Invention

The present invention provides an apparatus for producing electric power, according to claim 1.
The apparatus for producing electric power can be configured for transforming chemical energy for example of a fuel into electrical energy using electrical and/or magnetic means. Thus the apparatus more specifically can be understood as a transforming apparatus for transforming the type of energy. The magnetic means can be a one or more permanent magnets or an induction coil, which is provided with electrical current if the magnet is activated.
The present invention is based on the finding that an efficient operation of the apparatus can be realized, if air can be taken into the combustion chamber or if exhaust gas can be deducted out from the combustion chamber in a way with low resistance and a space-saving manner. This can be accomplished by providing the piston with a piston valve which blocks or unblocks an opening in the piston, such that a channel though the piston for air (to be taken into the combustion chamber) and/or for exhaust gas (to be conducted out of the combustion chamber) is controlled by the piston valve. Then air intake can then be accomplished in a state of the piston in which the piston is moving to enlarge the combustion chamber so as to put pressure on the air on the opposite of the piston (with respect to the combustion chamber) to pass though the opening in the piston (and an opened piston valve) into the combustion chamber. Through the movement of the piston, which in turn can result in the transfer of the air into the combustion chamber, the combustion chamber can be filled with air in a very low resistant way. On the other side, also exhaust gas can conducted out of the combustion chamber though the opening in the piston (which is controlled by the piston valve), if for example the piston reduces the size of the combustion chamber by a respective movement. This also facilitates a deduction of exhaust gas with low resistance. Furthermore, due to the piston opening, which is controllable by the piston valve, it is also possible to omit a separate duct for the intake of air to the combustion chamber or for deducing the exhaust gas from the combustion chamber.
The present invention provides the advantage that by a little modification of known components of an apparatus for producing electrical power a significant improvement can be realized. Especially by reducing the resistance of the air intake or the deduction of exhaust gas it is now possible to fill the combustion chamber faster or to deduct the exhaust gas from the combustion chamber faster so that a higher efficiency of the apparatus for producing electrical power can be achieved. Furthermore, the apparatus disclosed here can be built in a space-saving manner as due to the piston opening in combination with the piston valve a duct on the outer surface of the housing can be omitted. This feature is especially important in scenarios for use of the apparatus, in which just little space is available, as for example in
In a specific embodiment of the present invention the piston valve is configured for being actuated pneumatically and/or the piston valve being coupled with a spring in order to bring the piston valve into a position blocking the piston opening. The piston valve can therefore be reset by a spring to block the piston opening and/or to be opened by a pressure of fluid, being located opposite to the combustion chamber with respect to the piston. This embodiment of the present invention provides the advantage that the piston valve does not need an electrical contact or have an controllable means to be actuated which in turn would suffer a degradation while the lifetime of the apparatus due to the quick and strong movements of the piston carrying the piston valve. Alternatively or additionally the piston valve can also be activated by an electronical means like a electronical magnet.
Furthermore, another embodiment of the invention has a control chamber being fluidically coupled to the combustion chamber if the piston valve is opened. The combustion chamber can be understood as a chamber, which is located opposite the combustion chamber regarding the piston. The control chamber can be fluidically coupled with the combustion chamber if the piston valve is opened, such that a fluid like air or exhaust gases or fuel can pass from the control chamber though the piston opening to the combustion chamber or vice versa. Such an embodiment of the present invention provides the advantage of controlling the pressure in the control chamber such that for example the operation of the piston valve can in turn be indirectly controlled by the pressure in the control chamber. This facilitated the control of the piston valve due to the lack of active components being provided to the piston in order to open or close the piston valve.
In another specific embodiment of the present invention a control unit is provided, wherein the control unit is configured for controlling a pressure of a fluid in the control chamber. The control unit can be a unit which is capable to modify the pressure in the control chamber by controllable means, i.e. a valve, a heating element, an explosive pill etc.... Such an embodiment of the present invention provides the advantage of controlling the pressure in the control chamber with simple technical means in order to control the operation of the piston valve.
Additionally, in another embodiment of the invention the control unit is configured for controlling the pressure of the fluid in the control chamber by opening or closing a control valve, the control valve being arranged for blocking or unblocking a fluid passage form a fluid reservoir to the control chamber. This embodiment of the present invention provides the advantage of a technically very simple means in order to control the pressure of the fluid in the control chamber. Thus, the operation of the piston valve can be indirectly controlled in a very easy an effective way.
In a specific embodiment of the present invention that the control unit is configured for controlling the pressure in the control chamber by using an electrically activatable control means. For example the control unit is configured for electrically actuating a magnet to open or close the control valve. Such an embodiment of the present invention provides the advantage of a very fast activation of the control valve in order to indirectly control the piston very fine tuned or with a high granularity.
Furthermore, in another embodiment of the present invention the apparatus further comprises a housing valve being arranged in the housing of the apparatus, the housing valve being configured for blocking or unblocking an opening in the housing in order to provide air to the combustion chamber and/or in order to conduct exhaust gas from the combustion chamber, especially the housing valve being arranged in a wall segment of the housing opposite to the piston. Such an embodiment of the present invention provides the advantage that a unidirectional flow of air and/or exhaust gas can be arranged. Thus, the air and/or the exhaust gas does not need to turn its flow direction when being taking into the combustion chamber through the piston opening and conducted through the housing valve or when being taking into the combustion chamber through the housing opening and conducted through the piston valve. In this way, it is also possible to enlarge the efficiency due to a reduction of resistance of the air/exhaust gas when passing the combustion chamber.
According to a further embodiment of the present invention the movable magnetic means comprise at least one permanent magnet and/or the sets of stationary magnetic means comprise at least one induction coil. Such an embodiment of the present invention provides the advantage that no electrical contacts have to be provided on moving components of the apparatus, thus increasing the lifetime of the apparatus.
Furthermore, according to the present invention the apparatus comprises a second combustion chamber being formed at a second end of said housing at which a second substantially cylindrical portion is formed and wherein a second piston is housed within said second portion of said housing and delimits said second combustion chamber, said second piston being housed free within said second portion of said housing and being arranged to reciprocate therein, said second piston being connected to a first end of a second rod, the said second rod has fastened thereto one or more support means carrying second sets of movable magnetic means, facing second sets of stationary magnetic means for producing electric power when the second movable magnetic means are moved with respect to the second set of stationary magnetic means, where the second piston comprises a second piston valve being configured for blocking or unblocking a second piston opening in the second piston in order to provide air to the second combustion chamber and/or in order to conduct exhaust gas from the second combustion chamber.
According to the present invention the apparatus comprises a third piston being connected at the rod at an opposed end to said piston and said second rod carrying a fourth piston at the opposed end to the second piston, said third piston and said fourth piston defining, together with the walls of said housing, a third combustion chamber formed in an intermediate portion of said housing, and wherein said third piston comprises a third piston valve being configured for blocking or unblocking a third piston opening in the third piston in order to provide air to the third combustion chamber and/or in order to conduct exhaust gas from the third combustion chamber and/or the fourth piston comprises a fourth piston valve being configured for blocking or unblocking a fourth piston opening in the fourth piston in order to provide air to the third combustion chamber and/or in order to conduct exhaust gas from the third combustion chamber. Therefore the present invention provides the advantage of a further increased efficiency , with three combustion chambers respectively pistons each being provided with said piston valve, wherein the three combustion chambers are coupled together with the rod and the second rod, each having two pistons as defined. This enables the operation of a very efficient apparatus for producing electrical power.
Additionally, in another embodiment of the invention said rod and said second rod are coaxially arranged, so that said third combustion chamber has a substantially cylindrical shape and/or wherein said rod and said second rod have the same size and mass, wherein said piston and second piston have the same size and mass and wherein said third and fourth pistons have the same size and mass. Such an embodiment of the present invention provides the advantage that the apparatus can be arranged in a very efficient and small size and/or can be operated in a mode having little vibrations.
In another embodiment of the present invention a method for operating an apparatus as described herein is disclosed, wherein the method comprises the following step:
Controlling the piston valve such that air is provided to the combustion chamber and/or exhaust gas is conducted from the combustion chamber through the piston opening.
The above mentioned advantages can also be realized by way of this method.
Furthermore a control unit is also disclosed being configured for controlling and/or executing at least the step of the method disclosed in this description. The above mentioned advantages can also be realized by way of this control unit. Finally, according to another embodiment of the present invention, a computer program for controlling and/or executing the step of the method as disclosed in this description, when the computer program is executed on a control unit.
The apparatus for producing electric power can, for example, include a housing in which a first substantially cylindrical portion is formed, inside which a first combustion chamber is formed and a first piston is arranged to reciprocate. Moreover, a second substantially cylindrical portion is formed inside said housing, a second combustion chamber being formed inside the second portion and a second piston being arranged to reciprocate within the second portion. The first piston is connected to a first end of a first rod, which carries at its opposed second end a third piston. The second piston is connected to a first end of a second rod, which carries at its opposed second end a fourth piston. The third and fourth pistons define, together with the housing walls, a third combustion chamber, which is therefore located between said third and fourth pistons and within which said third and fourth pistons are arranged to reciprocate.
The combustion chamber(s) the movable magnetic means and/or the the stationary magnetic means can have any displacement and/or can be water-cooled or air cooled.
For example, the first and second rods are coaxial, so that the third combustion chamber has a substantially cylindrical shape and the housing of the apparatus according to the invention has a substantially cylindrical shape.
The first rod is for example rigidly connected, by means of one or more first supports, to a set of first coils / first permanent magnets that, by following the reciprocating motion of the first and third pistons, move relative to a set of stationary first permanent magnets / stationary first coils, so as to generate electric power. The second rod for example is rigidly connected, by means of one or more second supports, to a set of second coils / second permanent magnets that, by following the reciprocating motion of the second and fourth pistons, move relative to a set of stationary second permanent magnets / stationary second coils, so as to generate electric power.
Advantageously, in the apparatus for producing electric power for example the movement of each piston is braked not only by the electric power generation but also by the compression of the piston located at the opposed end of the respective rod.
Consequently, the embodiments described in this description allows overcoming the limitations of the prior art solutions, imposed by the provision of springs or other elastically resistant means.
Moreover, for example in every forth and back cycle of each piston, two ignitions occur instead of one, and this allows considerably increasing the performance of the apparatus according to the invention and the power supplied by it.
Moreover, for example with respect to a configuration including two opposed free pistons, the approach described herein for example allows significantly reducing vibrations, since it comprises equal oscillating masses moving in opposition.
At the same time, with respect to a configuration including two opposed free pistons, the approach described herein for example allows reducing the displacement of the individual pistons, and consequently the overall size, for a given amount of electric power produced.
For example, in every forth and back cycle, the provision of said third combustion chamber, common to the third and fourth pistons, allows synchronizing the system, i.e. the reciprocating movement of the first and second rods and of the elements connected thereto.
For example, the apparatus for producing electric power according to the invention can be manufactured by using standard, commercially available components, and this ensures reliability and limited prices.

Concerning the direct injection means

Additionally to the above description an apparatus for producing electric power is disclosed herein, including a housing at an end of which a portion is formed, wherein a piston is housed within said portion of said housing and delimits said combustion chamber, said piston being housed free within said portion of said housing and being arranged to reciprocate therein, said piston being connected to a end of a rod, the said rod has fastened thereto one or more support means carrying sets of movable magnetic means, facing sets of stationary magnetic means for producing electric power when the movable magnetic means are moved with respect to the stationary magnetic means characterized by
an fuel injection means, having a outlet to the combustion chamber, the outlet being arranged such that the outlet is fluidically disconnected to the combustion chamber in the state of the apparatus when fuel in the combustion chamber is exploded.
This embodiment provides the advantage that the injection means can be effectively sheltered from high pressures which occur in the instance of the explosion of the fuel in the combustion chamber.
In a further advantageous embodiment of the present invention the outlet of the fuel injection means is arranged such that it is covered by the piston in the state of the apparatus hen fuel in the combustion chamber is burnt. This embodiment of the invention provides the advantage that an easy positioning of the injection means can effectively shelter the components inside the injection means in the state the fuel explodes in the combustion chamber.
Furthermore, in another embodiment the fuel injection means comprises a one way valve at an outlet nozzle, the one way valve being configured for fluidically coupling the fuel injection means with the combustion chamber for providing fuel into the combustion chamber and for fluidically disconnecting the fuel injection means from the combustion chamber in the state of the apparatus when fuel is burnt or exploded in the combustion chamber. This embodiment requires very little modifications in order to provide the above mentioned advantages in the shelter of the injection means.
In a specific embodiment of the invention, the one way valve comprises a ball, being arranged to open said outlet nozzle for providing fuel into the combustion chamber and for closing said outlet nozzle in said state of the apparatus when fuel in the combustion chamber is burnt or exploded. This embodiment can be implemented in a very easy way.
Additionally or alternatively the movable magnetic means comprise at least one permanent magnet and/or the set of stationary magnetic means comprise at least one induction coil. This arrangement rises the lifetime of the apparatus due to the lack of electrical connections to moving parts.
Furthermore, according to the invention, a second combustion chamber is provided being formed at a second end of said housing at which a second substantially cylindrical portion is formed and wherein a second piston is housed within said second portion of said housing and delimits said second combustion chamber, said second piston being housed free within said second portion of said housing and being arranged to reciprocate therein, said second piston being connected to a end of a second rod, the said second rod has fastened thereto one or more support means carrying second sets of movable magnetic means, facing second sets of stationary magnetic means for producing electric power when the second movable magnetic means are moved with respect to the second set of stationary magnetic means, having a second fuel injection means, having a second outlet to the second combustion chamber, the second outlet being arranged such that the second outlet is fluidically disconnected to the second combustion chamber in the state of the apparatus when fuel in the second combustion chamber is burnt or exploded.
Furthermore, according to the invention, a third piston is connected at the rod at an opposed end to said piston and said second rod carrying a fourth piston at the opposed end to the second piston, said third piston and said fourth piston defining, together with the walls of said housing, a third combustion chamber formed in an intermediate portion of said housing, and an third fuel injection means, having a third outlet to the third combustion chamber, the third outlet being arranged such that the third outlet is fluidically disconnected to the third combustion chamber in the state of the apparatus when fuel in the third combustion chamber is burnt or exploded.
Furthermore, according to another embodiment of the invention, said rod and said second rod are coaxially arranged, so that said third combustion chamber has a substantially cylindrical shape and/or wherein said rod and said second rod have the same size and mass, wherein said piston and second piston have the same size and mass and wherein said third and fourth pistons have the same size and mass.
Furthermore, according to another embodiment of the invention, a method for operating an apparatus according to the preceding description is provided, wherein the method comprises the following step:
Controlling the injection means such that the outlet is fluidically disconnected to the combustion chamber in the state of the apparatus when fuel in the combustion chamber is burnt or exploded.
Furthermore, according to another embodiment of the invention, a control unit is disclosed being configured for controlling and/or executing at least the step of the above mentioned method.

Concerning the Magnetic cluth

Furthermore, according to another embodiment of the invention, an apparatus for producing electric power is disclosed, including a housing at an end of which a portion is formed, wherein a piston is housed within said portion of said housing and delimits said combustion chamber, said piston being housed free within said portion of said housing and being arranged to reciprocate therein, said piston being connected to a end of a rod, the said rod has fastened thereto one or more support means carrying sets of movable magnetic means, facing sets of stationary magnetic means for producing electric power when the movable magnetic means are moved with respect to the stationary magnetic means,

characterized by
an clutch unit for providing the stationary magnetic means or the movable magnetic means with electrical energy.

This embodiment of the present invention provides the advantage to bring the rod in a defined position for example in the start up of the apparatus by implementing a defined magnetic force on the movable or stationary magnetic means which in turn brings the rod in the desired position. This can be done in order to facilitate the startup procedure of the apparatus as in this state the linear electromagnetic motor can be used for moving the pistons back and forth so as to regularize the movement of the pistons respectively the moveable magnetic means with respect to the stationary magnetic means. If the apparatus is in normal operation mode, the clutch unit can be configured to stop providing electrical energy to the stationary or movable magnetic means and switch to a state in which electrical energy is collected from the linear motor respectively the moveable magnetic means with respect to the stationary magnetic means.
Furthermore, according to another embodiment of the invention, the clutch unit is configured to provide induction coils of the stationary or movable magnetic means with a different current at different time intervals.
Furthermore, according to another embodiment of the invention, the clutch unit is configured to provide the different coils of the stationary or movable magnetic means with a current at different time intervals, wherein the sum of the current is constant over a sum of several time intervals.
Additionally, according to another embodiment of the invention, the clutch unit can be configured to disconnect a provision of electrical energy to the moveable or stationary magnetic means and start a collection of electrical energy from the moveable or stationary magnetic means. This configuration of the clutch unit provides that advantage that the clutch unit facilitated the startup procedure of the apparatus, such that the normal operation mode of the apparatus can be reached in a shorter time after the startup of the apparatus.

Concerning the Sound reduction

Furthermore, according to another embodiment of the invention, an apparatus for producing electric power is disclosed, including a housing at an end of which a portion is formed, wherein a piston is housed within said portion of said housing and delimits said combustion chamber , said piston being housed free within said portion of said housing and being arranged to reciprocate therein, said piston being connected to a end of a rod, the said rod has fastened thereto one or more support means carrying sets of movable magnetic means, facing sets of stationary magnetic means for producing electric power when the movable magnetic means are moved with respect to the stationary magnetic means,

characterized by
an exhaust pipe system for deducting exhaust gas from the combustion chamber and/or a second combustion chamber, wherein said exhaust pipe system has a first pipe and a second pipe, the first pipe element and the second pipe element each having a input for exhaust gas from the combustion chamber and/or a second combustion chamber, wherein the first pipe and the second pipe have a common output for said exhaust gas, wherein a length of the first pipe is longer than a length of the second pipe.

Such an embodiment of the present invention provides the advantage that the noise originating from the combustion chambers can be extinguished by destructive overlap of the sound in the first and second pipes.
Furthermore, according to another embodiment of the invention, the difference of the length of the first pipe and the length of the second pipe is dependent on at least one frequency in the spectrum of the noise of the exhaust gases and/or in that the difference of the first pipe and the length of the second pipe corresponds to a phase shift of 180 degrees at the common output at least one frequency of the spectrum of the noise of the exhaust gases. Specifically the difference of the length of the first and second pipe is in the range between 8.5m and 8.5mm, corresponding to a frequency range between 20 Hz and 20'000 Hz to be extinguished.
Furthermore, according to the invention, the second combustion chamber being formed at a second end of said housing at which a second substantially cylindrical portion is formed and wherein a second piston is housed within said second portion of said housing and delimits said second combustion chamber, said second piston being housed free within said second portion of said housing and being arranged to reciprocate therein, said second piston being connected to a (first) end of a second rod, the said second rod has fastened thereto one or more support means carrying second sets of movable magnetic means, facing second sets of stationary magnetic means for producing electric power when the second movable magnetic means are moved with respect to the second set of stationary magnetic means, characterized in that the first pipe is connected to the combustion chamber and the second pipe is connected to the second combustion chamber.
Furthermore, according to the invention, wherein a third piston being connected at the rod at an opposed end to said piston and said second rod carrying a fourth piston at the opposed end to the second piston, said third piston and said fourth piston defining, together with the walls of said housing, a third combustion chamber formed in an intermediate portion of said housing, and wherein said third piston comprises a third piston valve being configured for blocking or unblocking a third piston opening in the third piston in order to provide air to the third combustion chamber and/or in order to conduct exhaust gas from the third combustion chamber and/or the fourth piston comprises a fourth piston valve being configured for blocking or unblocking a fourth piston opening in the fourth piston in order to provide air to the third combustion chamber and/or in order to conduct exhaust gas from the third combustion chamber, characterized in that the exhaust pipe system has a third pipe being connected to the third combustion wherein the third pipe has a first portion and a second portion, the first and second portions being arranged in order to guide exhaust gas in parallel from a common third pipe inlet to a common third pipe junction, and the first portion being longer than the second portion.

Concerning the flat linear motor pairs

characterized in that
the set of movable magnetic means are mounted on a flat ferromagnetic support means and by a further set of movable magnetic means, the further set of movable magnetic means being mounted on a further flat ferromagnetic support means at an opposite side of the rod with respect to the set of movable magnetic means.

This embodiment of the present invention provides the advantage that a symmetric balance of the forces on the rod can be obtained such that the resulting torque can be minimized. Also it is possible to store a large about of kinetic energy in such an embodiment of the apparatus.
Furthermore, according to another embodiment of the invention, comprising at least four sets of movable magnetic means each mounted on a flat ferromagnetic support means, each of the sets of movable magnetic means being arranged opposite of another of the set of movable magnetic means with respect to the rod.
Furthermore, according to another embodiment of the invention, in which the faces of adjacent magnets of the movable or stationary magnetic means have the different polarity. This enables a high magnetic flux in the vicinity of the induction coils of the respective stationary or movable magnetic means.

Brief Description of the Figures

Further features and advantages of the present invention will become more apparent from the following detailed description of an exemplary apparatus for producing electric power shown in Fig. 1a to 1d, which is to be modified for advantageous embodiments of the present invention. The exemplary apparatus shown in Fig. 1a to 1d thus forms a basis which can be modified according to embodiments of the present invention, the respective embodiments given by way of non-limiting example with reference to the accompanying drawings, in which:

Fig. 1a schematically shows a longitudinal sectional view of an apparatus for producing electric power in a first operating position, forming a basis for the explanation of specific embodiments of the present invention with respect to the figures 2 to 7;
Fig. 1b schematically shows a longitudinal sectional view of the apparatus for producing electric power shown in Fig. 1a, in a second operating position;
Fig. 1c schematically shows a longitudinal sectional view of the apparatus for producing electric power shown in Fig. 1a, in a third operating position;
Fig. 1d schematically shows a longitudinal sectional view of the apparatus for producing electric power shown in Fig. 1a, in a fourth operating position;
Fig. 2A and 2B show each cross-sectional views of the portion of the left hand side of the apparatus as depicted in the Figures 1a to 1d having the piston;
Fig. 3A shows a cross-sectional view of the ignition means for use in the apparatus as for example shown in Figure 2A or 2B;
Fig. 4A and 4B each show a longitudinal sectional view of an embodiment of an apparatus for producing electric power;
Fig. 5 shows a longitudinal sectional view of another embodiment of an apparatus for producing electric power;
Fig. 6A schematically show each a longitudinal sectional view of another embodiment of an apparatus for producing electric power;
Fig. 6B shows a details section of the left side movable magnetic mean;
Fig. 6C shows a cross-sectional view of a detail of another embodiment of the moveable magnetic means;
Fig. 6D shows a cross-sectional view of a detail of another embodiment of the moveable magnetic means;
Figure 6E shows a cross-sectional view of a detail of another embodiment of the moveable magnetic means;
Fig 7 schematically shows a longitudinal sectional view of an embodiment of the apparatus for producing electric power;
Fig. 8 shows a flow chart of an embodiment of the present invention implemented as a method for operating an apparatus; and
Fig. 9 shows a block diagram of an embodiment of the present invention implemented as a control unit for operating an apparatus.

For the sake of clarity, in Figs. 1a to 1d the portion of the apparatus for producing electric power at the right hand side of the drawings, i.e. the portion included between the third combustion chamber and the second combustion chamber is fictitiously rotated by 90° relative to its actual arrangement.

Description of a Preferred Embodiment

Referring to Figs. 1a to 1d, there is shown the exemplary apparatus for producing electric power, which serves as a basis for modifications to implement embodiments of the present invention, wherein the apparatus being denoted in the whole document by reference numeral 1.
Apparatus 1 includes a housing 3 at a (first) end of which a (first) substantially cylindrical portion 3a is formed, housing a (first) combustion chamber 5a.
In a manner known per se, the (first) combustion chamber 5a has for example a substantially cylindrical shape and is equipped with fuel injection means (not shown in the Figures 1a to 1d) and with ignition means 7a for fuel ignition. Moreover, the (first) combustion chamber 5a is equipped with an inlet port 8a in communication with an inlet duct 9a for introducing air into the (first) combustion chamber. Said inlet duct 9a is in communication with an intake duct 11a equipped with an intake valve 10a, and opens into the (first) combustion chamber or, preferably, into a pre-compression chamber connected thereto, as it will be described in detail hereinafter. The (first) combustion chamber 5a is also equipped with an outlet port 12a in communication with an exhaust duct 13a for the outflow of exhaust gases from the (first) combustion chamber.
A (first) piston 15a is mounted free inside the (first) portion 3a of housing 3 and delimits the (first) combustion chamber 5a. The (first) piston 15a is housed in said (first) portion 3a of housing 3 so as to be able to reciprocate within it.
At a second end, opposed to the (first) end, housing 3 has a second (for example substantially cylindrical) portion 3b, housing a second combustion chamber 5b.
In a manner known per se, the second combustion chamber 5b has a (for example substantially cylindrical) shape and is equipped with fuel injection means (not shown in the Figures 1a to 1d) and with ignition means 7b for fuel ignition. Moreover, the second combustion chamber 5b is equipped with an inlet port 8b in communication with an inlet duct 9b for introducing air into the second combustion chamber. Said inlet duct 9b is in communication with an intake duct 11b equipped with an intake valve 10b, and opens into the second combustion chamber or, preferably, into a pre-compression chamber connected thereto, as it will be described in detail hereinafter. The second combustion chamber 5b is also equipped with an outlet port 12b in communication with an exhaust duct 13b for the outflow of exhaust gases from the second combustion chamber.
A second piston 15b is mounted free inside the second portion 3b of housing 3 and delimits the second combustion chamber 5b. The second piston 15b is housed in said second portion 3b of housing 3 so as to be able to reciprocate within it.
The (first) piston 15a is connected to a (first) end of a (first) rod 17a, which carries at its opposed end a third piston 15c, and the second piston 15b is connected to a (first) end of a second rod 17b, which carries at its opposed end a fourth piston 15d.
The third piston 15c and the fourth piston 15d define, together with the walls of housing 3, a third combustion chamber 5c, which is formed in an intermediate, substantially central portion 3c of said housing 3.
Also the third combustion chamber 5c is equipped with fuel injection means (not shown in the Figures 1a to 1d) and with ignition means 7c for fuel ignition. Moreover, the third combustion chamber 5c is equipped with two inlet ports 8c, 8d in communication with respective inlet ducts 9c, 9d for introducing air into the third combustion chamber. A (first) inlet duct 9c is in communication with intake duct 11a of the (first) combustion chamber 5a through an intake valve 10c and opens into the second combustion chamber or, preferably, into a pre-compression chamber connected thereto, as it will be described in detail hereinafter. A second inlet duct 9d is in communication with intake duct 11b of the second combustion chamber 5b through an intake valve 10d and opens into the third combustion chamber or, preferably, into a pre-compression chamber connected thereto, as it will be described in detail hereinafter. The third combustion chamber 5c is also equipped with two outlet ports 12c, 12d in communication with exhaust duct 13a of the (first) combustion chamber and exhaust duct 13b of the second combustion chamber, respectively, for the outflow of exhaust gases from the third combustion chamber.
Preferably, as shown in the drawings 1a to 1d, rods 17a, 17b are coaxially arranged, so that also the third combustion chamber 5c has for example a substantially cylindrical shape and housing 3 of apparatus 1 has in the whole for example a substantially cylindrical shape.
Preferably, in order to obtain a proper operation in steady state condition and to minimize vibrations, the (first) and second rods 17a, 17b have the same mass and the same size, the (first) and second pistons 15a, 15b have the same mass and the same size, and the third and fourth pistons 15c, 15d have the same mass and the same size. More preferably, all pistons 15a - 15d have the same mass and the same size.
Advantageously, in the illustrated embodiment, the (first) rod 17a is mounted on longitudinal bearings 19a, 19c (or similar components) suitably arranged so as to define a (first) space 21a which is located between the (first) piston 15a and one of said bearings (bearing 19a) and is in communication with supply duct 11a and inlet duct 9a of the (first) combustion chamber, and a second space 21 which is located between the (first) piston 15a and the other one 19c of said bearings and is in communication with supply duct 11a and inlet duct 9c of the third combustion chamber. As stated before, said spaces 21a, 21c can be advantageously exploited as pre-compression chambers for a first compression of air coming from supply duct 11a before such air enters inlet duct 9a of the (first) combustion chamber or inlet duct 9c of the third combustion chamber, as it will be disclosed hereinafter.
Similarly, in the illustrated embodiment of the apparatus 1, the second rod 17b is mounted on longitudinal bearings 19b, 19d (or similar components) suitably arranged so as to define a first space 21b which is located between the second piston 15b and one of said bearings (bearing 19b) and is in communication with supply duct 11b and inlet duct 9b of the second combustion chamber, and a second space 21d which is located between the fourth piston 15d and the other one 19d of said bearings and is in communication with supply duct 11b and inlet duct 9d of the third combustion chamber. As stated before, said spaces 21b, 21d can be advantageously exploited as pre-compression chambers for a (first) compression of air coming from supply duct 11b before such air enters inlet duct 9b of the second combustion chamber or inlet duct 9d of the third combustion chamber, as it will be disclosed hereinafter.
According to the invention, one or more (first) supports 23a are fastened to the (first) rod 17a, preferably in an intermediate position between the (first) piston 15a and the third piston 15c. Those supports carry sets of (first) magnets 25a facing sets of (first) induction coils 27a, so that, when the (first) piston 15a reciprocates within the (first) portion 3a of housing 3, the (first) magnets 25a reciprocate relative to the (first) coils 27a.
Preferably, two (first) supports 23a (only one of which is shown in Figs. 1a to 1d) are fastened to the (first) rod 17a. Said supports are arranged at 180° relative to each other and each of them carries a respective set of (first) magnets 25a, facing a respective set of (first) induction coils 27a.
It will be apparent to the skilled in the art that, in an alternative embodiment of the invention, the (first) supports 23a could carry the induction coils and the magnets could be stationary and arranged so as to face the paths of said coils.
However, a configuration in which the (first) coils 27a are stationary and the (first) magnets 26a are fixedly connected to the (first) rod 17a is deemed preferable, especially taking into account the reduced weight of the magnets with respect to the coils. Furthermore the electrical connection of moving coils having stationary magnets would be much more complicated than the electrical connection of stationary induction coils with moving magnets.
Additionally, one or more second supports 23b are fastened to the second rod 17b, preferably in an intermediate position between the second piston 15b and the fourth piston 15d. Those supports carry sets of second magnets 25b facing sets of second induction coils 27b, so that, when the second piston 15b reciprocates within the second portion 3b of housing 3, the second magnets 25b reciprocate relative to the second coils 27b.
Preferably, two second supports 23b (only one of which is shown in Figs. 1a to 1d) are fastened to the second rod 17b. Said supports are arranged at 180° relative to each other and each of them carries a respective set of second magnets 25b, facing a respective set of second induction coils 27b.
Preferably, the second supports 23b are offset by 90° relative to the (first) supports 23a.
It will be apparent to the skilled in the art that, in an alternative embodiment of the invention, the second supports 23b could carry the induction coils and the magnets could be stationary and arranged so as to face the path of said coils.
However, a configuration in which the second coils 27b are stationary and the second magnets 26b are fixedly connected to the second rod 17b is deemed preferable, especially taking into account the reduced weight of the magnets with respect to the coils and/or possible problems in the electrical connection of induction coils if these were fastened to the second rod 17b.
Therefore, in the illustrated embodiment, apparatus 1 for producing electric power according to the invention comprises for example in the whole four sets of magnets (two sets of (first) magnets 25a and two sets of second magnets 25b) and four sets of respective coils (two sets of (first) coils 27 a and two sets of second coils 27b) arranged in a cross-shaped pattern.
Respective pumps for fuel injection and small pumps for lubricating oil can moreover be fastened to the (first) rod 17a as well as to the second rod 17b.
Preferably, supports 23a, 23b, as well as the elements associated therewith and further components, if any, mounted on rods 17a, 17b, have the same mass and the same size, so as to maintain the overall symmetry of apparatus 1 for producing electric power.
The operation of apparatus 1 for producing electric power as shown in Figures 1a to 1d can be summarized as follows.
All pistons 15a to 15d operate according to the principle of a two-stroke engine.
In a (first) step, shown in Fig 1a, the third and fourth pistons 15c, 15d are at their minimum relative distance and compress the air-fuel mixture present in the third combustion chamber 5c. Conversely, the (first) and second combustion chambers 5a, 5b are in communication with the respective inlet ducts 9a, 9b and exhaust ducts 13a, 13b through the respective inlet ports 8a, 8b and outlet ports 12a, 12b.
The air-fuel mixture present in the third combustion chamber 5c is therefore ignited and ignition occurs, as a consequence of which the third and fourth pistons 15c, 15d are moved away from each other. Consequently, the (first) piston 15a moves towards the end of the (first) portion 3a of housing 3 and covers inlet port 8a and outlet port 12a. At this point, fuel is injected into the (first) combustion chamber and the (first) piston 15a starts compressing the air-fuel mixture present in said (first) combustion chamber 5a. At the same time, the second piston 15b moves towards the end of the second portion 3b of housing 3 and covers inlet port 8b and outlet port 12b. At this point, fuel is injected into the second combustion chamber and the second piston 15b starts compressing the air-fuel mixture present in the second combustion chamber 5b. In the meanwhile, the third and fourth pistons 15c, 15d, during their movement away from each other, cause a first compression of air present in pre-compression chambers 21c, 21d. This step is shown in Fig. 1b.
Fig. 1c shows the step in which the distance between the (first) piston 15a and the end of the (first) portion 3a of housing 3 is minimum, as is the distance between the second piston 15b and the end of the second portion 3b of housing 3. In the meanwhile, the third piston 15c and the fourth piston 15d, continuing their movement away from each other, have left respective outlet ports 12c, 12d of the third combustion chamber uncovered, thereby allowing outflow of exhaust gases into respective exhaust ducts 13c, 13d. At the same time, the third piston 15c and the fourth piston 15d have left respective inlet ports 8c, 8d of the third combustion chamber uncovered, thereby allowing substitution of the exhaust gases discharged with pre-compressed fresh air coming from respective inlet ducts 9c, 9d.
In the configuration shown in Fig. 1c, the air-fuel mixture present in the (first) combustion chamber 5a is ignited, as is the air-fuel mixture present in the second combustion chamber 5b. Consequently ignition occurs in both said combustion chambers, as a consequence of which the (first) piston 15a is moved away from the end of the (first) portion 3a of housing 3 and the second piston 15b is moved away from the end of the second portion 3b of housing 3. In this manner, they cause a (first) compression of air contained in pre-compression chambers 21a, 21b, respectively. Moreover, the third piston 15c and the fourth piston 15d start moving towards each other, so as to cover again inlet ports 8c, 8d and outlet ports 12c, 12d of the third combustion chamber 5c. At this point, fuel can be introduced into the third combustion chamber 5c and the third piston 15c and the fourth piston 15d, continuing their movement towards each other, compress the air-fuel mixture present in said third combustion chamber 5c. This step is shown in Fig. 1d.
By continuing the movement of the third and fourth pistons 15c, 15d towards each other until attaining the maximum compression, the configuration shown in Fig. 1a is resumed and the cycle is over. It will be appreciated that, in Fig. 1a, the (first) piston 15a has moved away from the end of the (first) portion 3a of housing 3 sufficiently to uncover inlet port 8a and outlet port 12a, thereby allowing the outflow of exhaust gases into exhaust duct 13a and the substitution of said exhaust gases with pre-compressed fresh air coming from inlet duct 9a. In a wholly similar manner, the second piston 15b has moved away from the end of the second portion 3b of housing 3 sufficiently to uncover inlet port 8b and outlet port 12b, thereby allowing the outflow of exhaust gases into exhaust duct 13b and the substitution of said exhaust gases with pre-compressed fresh air coming from inlet duct 9b.
As it is clearly apparent from Figs. 1a - 1d, the cycle described above results in a reciprocating linear motion of the (first) rod 17a and the second rod 17b.
Consequently, the sets of first and second magnets 25a, 25b move of reciprocating linear motion relative to the sets of stationary (first) coils 27a and second coils 27b, respectively, thereby generating an electric current.
Advantageously, during the reciprocating linear motion, in every forth and back cycle of the (first) rod 17a, two ignitions occur instead of one, namely, one ignition in the (first) combustion chamber 5a and the other in the third combustion chamber 5c. Similarly, in every forth and back cycle of the second rod 17b, two ignitions occur instead of one, namely, one ignition in the second combustion chamber 5b and the other in the third combustion chamber 5c. Consequently, the efficiency of apparatus 1 according to the invention and the amount of electric power generated by it are particularly high.
Moreover, advantageously, the compressions in combustion chambers 5a, 5c located at the opposed sides of the (first) rod 17a determine, jointly with the production of electric power by the (first) magnets 25a and the (first) coils 27a, the braking effect on said (first) rod 17a, and the compressions in combustion chambers 5b, 5c located at the opposed sides of the second rod 17b determine, jointly with the production of electric power by the second magnets 25b and the second coils 27b, the braking effect on said second rod 17b: it is the compressions in the combustion chambers located at the opposed sides of each rod that oppose the inertia of each rod, which is free.
It is to be appreciated that, at the start, electric generation units consisting of the sets of magnets 25a, 25b and the sets of coils 27a, 27b can be advantageously exploited to start the cycle of compressions and expansions in the various combustion chambers 5a - 5c. More particularly, coils 27a, 27b can be excited so as to bring the third and fourth pistons 15c, 15d to the position of maximum mutual distance, so as to allow filling the third combustion chamber 5c. Subsequently, always thanks to the coil excitation, the third and fourth pistons 15c, 15d can be moved towards each other so as to compress the air-fuel mixture present in said third combustion chamber. At this point, the mixture is ignited by ignition means 7c and the start takes place.
In steady state condition, the frequency of the reciprocating linear motion of rods 17a, 17b and of the pistons associated therewith can be adjusted so as to minimize fuel consumption.
Said steady state condition should be constant, without accelerations or decelerations and without modifications in the load of the electric generation units consisting of the sets of magnets 25a, 25b and the sets of coils 27a, 27b.
Thanks to the fact that the ignition in the third combustion chamber 5c acts in the same way on the third and fourth pistons 15c, 15d, the system is continuously calibrated and the movements of both rods 17a, 17b are identical (in opposed directions) and synchronous.
This not only ensures a stationary regime, but also allows avoiding vibrations, since equal oscillating masses moving in opposition are obtained.
Apparatus 1 disclosed above may use, as fuel, any liquid or gaseous fuel available in the market (including gasoline, naphtha, kerosene, liquefied petroleum gas, methane and natural gas).
Even if the Figures schematically show a direct injection system, it will be apparent for the skilled in the art that an indirect injection system or a system with conventional suction of a liquid or gaseous fuel can be used.
The individual components can be cooled either with air (by means of natural or forced circulation), or with water or other cooling liquids.
The above description clearly makes it apparent that the apparatus for producing electric power is reliable, robust and efficient, and thus it allows wholly achieving the objects set forth above.
Moreover, the apparatus advantageously comprises a reduced number of components.
The previous description of the apparatus 1 should be modified because it refers mainly to applications with batteries, automotive in particular. In the following description of embodiments of the invention, applications as generators, micro cogenerators and generators for mini BioGAS power station can be also considered.
As often free piston generators with two pistons and two combustion chambers are disclosed, synchronizing the movement of the pistons in such a way to reduce vibrations, the same configuration of two pistons but with four combustion chambers in order to increase the power density of the generator can also be implemented. However there no hint is given in the state of the art on how to reduce the environment impact of the two stroke engine, on how to improve the reliability of the injectors, on how to reduce the acoustic noise and on how to detach the linear motors during the start-up step. Moreover in the prior art the generator is build based on cylindrical linear motors, having the disadvantage of the limited magnetic force, of the reduced power generation and of the limited modularity.
The goal of the embodiments of this invention is to improve the generator by proposing the use of an intake valve on the top of the piston fueling fresh air into the combustion chamber. Additionally an optional exhaust valve on the top of the cylinder is also disclosed to evacuate the exhaust gases. This configuration allows a much better replacement of the exhaust with the intake during the scavenging phase and, at the same time, avoid the direct evacuation of intake gases - typical on simple conventional two stroke engines. By placing an injector directly into the combustion chamber according to another embodiment of the invention, it is possible to improve the reliability of the injector itself because during the explosion it is protected by the piston again high pressures.
A further improvement respectively embodiment of the invention is related to the exhaust system. By using matched pipes it is possible to reduce acoustic noise.
It is also proposed according to another embodiment of the invention to use a magnetic clutch to detach the sled from the electrical motor once the two stroke motor starts. This is particularly important during the start-up of generators having four independent combustion chambers because at the beginning the linear (electromagnetic) motors used are much more powerful compared to the combustion engines and using a close loop control can block the ramp up phase of the generator.
The last improvement proposed according to an embodiment of the invention is the use of flat linear motors (having for example an iron core) in order to increase the magnetic force and the power generation. This kind of motors have much better performances but have the disadvantage of the strong attraction forces. To avoid this it is proposed to mount always two of them back-to-back in a symmetrical way around a rod so to cancel the effect of the attraction forces. Therefore the back-to-back positioning of the linear motors reduces the requirements of the bears.
In order to further improve the previously described apparatus 1 for producing electric power different modifications can be accomplished, which are to be considered independent from each other such that it is not necessary to have all modifications implemented, which are here described in one single embodiment.
A first significant improvement can be obtained by a first embodiment of the present invention, if one of the ducts, specifically inlet duct 9a is modified such as to be integrated into the piston 15a for example.
Figure 2A shows a cross-sectional view of the portion of the left hand side of the apparatus 1 as depicted in the Figures 1a to 1d having the piston 15a.
In order to reduce the constructed space of the apparatus 1, as mentioned above, the inlet duct (or a respective outlet duct 13a) can be implemented into the piston 15a. Therefore the piston 15a can be provides with a piston opening 200a, which can be blocked (i.e. closed) or unblocked (i.e. opened) by a piston valve 205a. The piston valve 205a being can for example be reset by a spring 210a to a closed position, in which the piston opening 200a is blocked. This arrangement of the piston 15a with the piston opening 200a and the piston valve 205a now provides the advantage that the inlet duct 9a can be omitted, thus reducing the constructed space of the apparatus 1. Furthermore, by a movement of the piston 15a in the housing 3 also a intake of air into the combustion chamber 5a can be accomplished with less resistance as the guidance of the air through the outside inlet duct 9a as shown in Figure 1a to 1d is not necessary any more.
In order to actuate the piston valve 205a in an easy manner, a control chamber 215a is for example arranged below the piston 15a, i.e. which is at the opposite of the piston 15a with respect to the combustion chamber 5a. The control chamber 215a substitutes the pre-compression chamber 21a. In addition the control chamber 215a is fluidically sealed against the environment outside the housing 3 in order to include a fluid like air with a specific adjustable pressure. The pressure in the control unit 125 a can be adjusted for example by a control unit 220a, which in turn is capable to control an actuator 225a of a control valve 230a, for example by electrical means like an electrically magnet to open the control valve 230a; the closure of the control valve 230a can be performed by a control valve spring 240a. The control valve 230a is arranged to open or close a control chamber opening 235a, wherein in the open state of the control valve 230a air can be taken into the control chamber 215a by, for example, a compressor which is not shown in Figure 2A. If the air is taken into the control chamber 215a and the control valve 230a is closed again and in a downward movement of the piston 15a as shown in Figure 2A, the pressure in the control chamber 215a will rise and lead to a pneumatic opening of the piston valve 205a such that the air in the control chamber 215a is transferred into the combustion chamber 5a.
Now, if the air is in the combustion chamber 5a and the piston 15a is moving upwards again, fuel can be injected by the fuel injection means 245a into the combustion chamber 5a which then can be ignited by the ignition means 7a such that the fuel is burnt and the piston 15a is moving downward again. By controlling a housing valve 250a, which is located in a wall 155a of the housing 3 opposite to the piston 15a, the exhaust gas in the combustion chamber 5a can be conducted outside the combustion chamber 5a in order to prepare the combustion chamber 5a for a new air intake though the piston opening 200a. Due to the preferred arrangement of the housing valve 250a opposite to the piston opening 200a in the piston 15a the intake and the outlet of the combustion chamber 5a are located as far away as possible and also in a direct line so that a constant flow of the air into the combustion chamber 5a and an outlet of exhaust gas out of the combustion chamber 5a can be implemented, such that a flow resistance of the fluid is minimized.
Figure 2B shows a cross-sectional view of the combustion chamber 5a with the piston 15a and the control chamber 215a in a moment of the piston 15a in which fuel is ignited by the ignition means 7a. In this Figure 2B another embodiment of the present invention can be shown. In this embodiment, the outlet 260a of the injection means, is covered by the piston 15a such that the explosion of fuel, which can be gas, gasoline, biogas (i.e. gas from renewable sources) or the like. If the outlet 260a of the injection means 245a is covered, stress on the output 245a can be significantly reduced such that the lifetime of the ignition means 245a can be prolonged in order to provide a better apparatus 1 for producing electric power.
Summarizing the above description with other words, in order to reduce as much as possible the environment impact of the two stroke engine, it is often helpful to have an optimized scavenging phase where all the exhaust gas is replaced by the new intake (fresh air). It is also very important to avoid the evacuation together with the exhaust of the intake before the explosion. The solution proposed is shown in Fig 2A. The intake, which is marked in Figure 1A in a dark grey shadow in the lower part of the piston 15a is fed from the intake valve respectively the piston valve 205a placed in the piston 15a and pushes (in the direction of the big arrow shown in Figure 2A) the exhaust (which is marked in Figure 2A with a light grey shadow) out through the exhaust valve (which is also named housing valve 250a) located on the opposite side of the cylinder wall with respect to the piston 15a. Therefore the uniformity of the air/gas flux is given by the central intake valve respectively the piston valve 15a. By controlling electronically the opening time of the valves like the piston valve 205a or the control valve 230a, it is possible to avoid the evacuation of the intake before the explosion and it could also be interesting to keep some hot exhaust in the cylinder in order to increase the temperature just before the next explosion. The main aspect of the embodiment of the invention can be seen in the introduction of a said piston valve 205a in the middle of the piston 15a which allows a very precise opening window thanks to the realization of this scavenging process is only possible by using valves.
Figure 3 shows a cross-sectional view of the ignition means 245a for use in the apparatus 1 as for example shown in Figure 2A or 2B. Herein, according to a further embodiment of the invention, a one way valve 300 at the outlet 260a or nozzle 310 of the ignition means 245a is provided in order to avoid a high pressure, caused by the explosion of the fuel in the combustion chamber 5a, to enter the output 260a or nozzle 310 of the injection means 245a. This way, damage of components of the injection means 245a can mainly be reduced or avoided, which in turn again enlarges the lifetime of the apparatus 1.
In a specific embodiment of the present invention, the one way valve 300 can comprise a ball 320, especially a metal ball, which covers a channel 330 for the fuel during the injection of the fuel into the combustion chamber 5a. In this moment, the ball 320 is pressed on the opening of the channel 330 such that the interior components of the injection means 245a are protected when the explosion of the fuel occurs. Thus it is suggested using a moving metallic ball 320 to protect the injector means 245a. Another solution is to use a metallic cylinder or of similar shape in metal to block the high temperature air coming into the injector means 245a.
In other word summarized, in can be noted that in order to have gas (for example methane, BioGAS, hydrogen, CNG) as fuel it is helpful to use injectors to provide the combustion chamber with the fuel. Because the pressures caused by the explosions of the free piston engine can be set on a wide range, care should be taken to avoid damaging the injector respectively injection means 245a during the explosion. For this reason an embodiment of the new invention has been introduced by positioning the injector or injection means 245a in the save zone as shown in Figure 2B. Indeed, inside this save zone the injector or injection means 245a is protected during the explosions from the high pressure by the piston 15a respectively the rings of the piston 15a. Moreover, by injecting the fuel at the beginning of the compression phase (up movement of the piston 15a), the efficiency of the engine or apparatus 1 is improved because of the increased gas compression. This is possible by exploiting the energy of the explosion itself during the up movement of the piston 15a. The result is a much more efficient and strong explosion.
In other words, in the presently disclosed embodiments of the invention 2 protections are drawn: from the explosion pressure - at the explosion time- and from the explosion temperature - shortly after the explosion when the piston is moving and opening the injector means 245 window.
Referring back to the arrangement of the piston 15a having the piston valve 205a and the piston opening 200a, it can be noted that this arrangement not necessarily must be implemented in combination with just one single combustion chamber 5a as shown in the Figures 2A and 2B. The arrangement of the piston 15a with the piston valve 205a and the piston opening 200a can also be realized for the second combustion chamber 15b with the second piston 15b and the third combustion chamber 5c, having the third piston 15c and the fourth piston 15d.
Figure 4A shows a longitudinal sectional view of an embodiment of an apparatus 1 for producing electric power in which the piston 15a, the second piston 15b, the third piston 15c as well as the fourth piston 15d are provided with respective piston openings 200a, 200b, 200c, 200d and corresponding piston valves 205a, 205b, 205c, 205d. The piston valves 205 and the piston openings 200 can be denoted with respect the arrangement in the second piston 15b as second piston opening 200b and second piston valve 205b, in the third piston 15c as third piston opening 200c and third piston valve 205c or in the fourth piston 15d as fourth piston opening 200d and fourth piston valve 205d. Analogously a second control chamber 215b, a second control unit 220b, a second control valve 225b, a second ignition means 245b and a second housing valve 250b are provided in order to control the fluid, especially air, through the second piston opening 200b.
Additionally a third control chamber 215c, a third control unit 220c, a third control valve 225c, a third injection means 245c and a third housing valve 250c are provided in order to control the fluid, especially air, through the third piston opening 200c. Finally a fourth control chamber 215d, a fourth control unit 220d, a fourth control valve 225d and a fourth injection means 245d are provided in order to control the fluid, especially air, through the fourth piston opening 200d.
The function of the above mentioned elements with respect to the second piston 15b, the third piston 15c and the fourth piston 15d correspond to the function of the corresponding elements described with respect to the piston 15a shown in Figures 2A and 2B.
Furthermore, Figure 4A shows a mechanical means 400a for opening and closing the housing valve 250a with respect to the movement of the rod 17a. Additionally a second mechanical means 400b is provided in order to open and close the second housing valve 250b with respect to the movement of the second rod 17b. Finally a third mechanical means 400c is provided in order to open and close the third housing valve 250c with respect to the movement of the rod 17a and the second rod 17b.
Figure 4B schematically shows a longitudinal sectional view of another embodiment of an apparatus 1 for producing electric power. In contrast to the apparatus 1 shown in Figure 4A now the control unit 220a is arranged to have a compressor (not shown) and a reservoir 410a in order to provide the desired pressure in the control chamber 215a. In order to pre-heat the air or the fluid to be let into the control chamber 215a a part of the exhaust gas, conducted out of the combustion chamber 5a by through the housing valve 250a is fed back to the inlet of the control chamber 215a, such that fluid or air to be taken into the control chamber 215a can be heated. Furthermore, the control unit 220a can be configured to (for example pneumatically or hydraulically) control also the housing valve 250a to open or to close in order to control the timing of the stated of the piston 15a in the operation of apparatus 1.
The second piston 15b, the third piston 15c as well as the fourth piston 15d are also provided with the elements arranged as the previously described element with respect to the piston 15a, as shown in Figure 4B on the right hand side. The reference numerals are chosen accordingly to clarify the corresponding elements in the combination with the second piston 15b, the third piston 15c and the fourth piston 15d.
Thus the valves 250a, 230a 205a and the corresponding valves with respect of the second piston 15b, the third piston 15c and the fourth piston 15d can be controlled mechanically (as can be seen from Figure 4A, with rods and levers as mechanical means 400) or electronically (as can be seen in Figure 4B, pneumatic and hydraulic). The electronic control can be preferred in order to be flexible in the opening and closing time. By using this scavenging solution and an external compressor for the intake, it is further possible to avoid to burn the piston lubrication, thus reducing the environment impact, by keeping the piston lubrication completely separated from the intake air.
Possible alternatives are related to the position of the valves 205 themselves. If the exhaust valve or housing valve 250 being defined on the cylinder head respectively the piston 15, as an alternative one could place the valve for the air intake on the on the side near to the head respectively to the wall of the housing at a position, in which the housing valve 150 is located in the figures 2A and 2B for example.
Possible alternative could also be the gas flow. It is suggestes to have the intake valve or piston valve 105 on the piston 15 and the exhaust valve or housing valve 250 on the cylinder head in the housing 3. As alternative the flow of fluid or gas could be defined flow from the head (then intake valve) to the valve in the piston 15 for the exhaust gas.
However, the use of the valve in the wall of the housing is not necessary for the functionality of the embodiment described herein. The use of valves on the head of the cylinder is thus not the main focus, it would be also advantageous to have only the valve in the piston and not the combination of both valves.
Figure 5 schematically shows a longitudinal sectional view of another embodiment of an apparatus 1 for producing electric power. The apparatus 1 as shown in Figure 5 is based on the embodiment of the pistons 15a to 15d having the piston openings 200a to 200d as well as the piston valves 205a to 205d. In addition to the embodiment of the pistons 15a to 15d an exhaust pipe system 500 is provided, having a first pipe 505 and a second pipe 510. The first pipe 505 is configured for conducting exhaust gas from the housing valve 250a to a junction 515 wherein the second pipe 510 is configured for conducting exhaust gas from the second housing valve 250b to the junction 515. The first pipe 505 has a first length L₁ and the second pipe 510 has a second length L₂. The second length L₂ is by a length difference ΔP longer than the first length L₁. This length difference ΔP is chosen such that noise originating from the combustion chamber 5a extinguishes with noise, originating from the second combustion chamber 5b. For example the length difference ΔP can be chosen to be between 8.5m and 8.5mm. Thus, according to Equation (1) a noise in a frequency range between signal frequencies Frequency_signal = 20Hz and 20'000Hz can be extinguished, especially if the noise in the combustion chamber 5a and the second combustion chamber 5b is generated at nearly the same time instant, which is true for the operation of the apparatus according Figure 5. $Δ P = \frac{{Velocity}_{sound}}{2 \times {Frequency}_{signal}}$
Nevertheless, it should be noted, that also the exhaust gas conducted away from the third combustion chamber 5c can be separated in analog first and second pipes (not shown in Figure 5), now from a common junction at the beginning of the third housing valve 250c to an ending junction of such a exhaust gas system 500. This again results in a extinction of noise due to a phase shift of said noise by 180°, which results in a destructive overlapping of the sound waves of this noise.
Thus, a unique property of our free piston engine is the synchronization of the explosions. This guarantees the simultaneous explosion of the external combustion chambers followed by the simultaneous explosion of the internal ones. The exhaust pipes have been designed in a specific embodiment of the invention in such a way to cancel the acoustic noise at the output junction 515. This is realized by making the travel length L₁ in the first pipe 505 and the travel length L₂ in the second pipe 510 of the sound waves to have a phase shift of 180° at the pipes junction 515 for some well-defined frequency. At the pipes junction 515 the difference of the travel length of the sound waves has to be equal to ΔP according to Equ (1) such that the sound waves destructively overlap and a noise extinction occurs.
Alternatives fo the pipes for the exhaust pipe system 500 could be in the shape of the exhaust pipe (round, rectangular, ...). Here only the length used by the sound waves is specified, because physically it only depends on this fact.
In the above description and especially in Figure 5, only an embodiment is disclosed in which the sound elimination of the external combustion chambers is provided. The same applies obviously also for the central chambers. However the internal chamber noise reduction is kept only as possible alternative because one possible realization is to have just one big combustion chamber in the center having just one exhaust pipe, in this case the noise cancellation is an option.
Figure 6A schematically shows a longitudinal sectional view of another embodiment of an apparatus 1 for producing electric power. In this embodiment the movable magnetic means 25a, which are implemented as permanent magnets are mounted on a flat ferromagnetic support 23a. This ferromagnetic support means 23a is configured to have at opposite sides of the rod 17a two flat support members 600 on which the magnets 610 each are fixed. Furthermore, also at the second rod 17b second movable magnetic means 25b are fixed, which are also implemented as permanent magnets and are mounted on a second flat ferromagnetic support 23b. This second ferromagnetic support means 23b is also configured to have at opposite sides of the rod 17a two flat support members 600 on which the magnets 610 each are fixed. As can be seen from Figure 6A, the movable magnetic means are located paired around the rod 17a or 17b, which in turn provides the advantage that in a fast movement of the rod 17a or the second rod 17b the forces on the moveable magnetic means 23a can be lowered due to a symmetrical arrangement around the rod 17a respectively the second rod 17b. On the other hand the symmetrical arrangement of the flat support means provides the advantage to store a high amount of kinetic energy in the operation of the apparatus 1.
Figure 6B shows a details section of the left side movable magnetic means 23a, in which the magnets 600 are positioned on the flat support means 600, which can be made of iron. The magnets 6110 are positioned such, that adjacent magnets 610 have different polarity at their faces 620
Figure 6C shows a cross-sectional view of a detail of another embodiment of the moveable magnetic means 23a, which can be applied in the apparatus 1 according to Figure 6A. In Figure 6C it can be seen that the flat support means 600 are on the one hand side located paired or pairwise opposite each other with respect to the rod 17a such that a balances operation of the moveable magnetic means 23a can be reaches. Furthermore, Figure 6C also shows that the flat support means 600 can be arranged in a distance to the rod 17a, which should be no larger than 100mm. This is a good tradeoff between an acceptable low torque (small distance = small torque) and the allowable mass (used to store the kinetic energy, large distance = large mass = high energy storage capability).
Figure 6D shows a cross-sectional view of a detail of another embodiment of the moveable magnetic means 23a, which can be applied in the apparatus 1 according to Figure 6A. In contrast to the embodiment of Figure 6C now four flat support members 600 are provided, each being arranged opposite to another flat support means 600 around the rod 17a. This arrangement further improves the torque and the energy storage capacity of the moveable magnetic means 23a.
Figure 6E shows a cross-sectional view of a detail of another embodiment of the moveable magnetic means 23a, which can be applied in the apparatus 1 according to Figure 6A. In contrast to the embodiment of Figure 6C now six flat support members 600 are provided, each being arranged opposite to another flat support means 600 around the rod 17a. This arrangement again further improves the torque and the energy storage capacity of the moveable magnetic means 25a.
It is thus possible increase the magnetic movement force by using iron core flat linear motors having a flat support member 600. The disadvantage of this solution is that the iron core generates a very strong attraction force between permanent magnet 25 and stator coils 27. These attraction forces can be so high to dramatically increase the friction forces and therefore reducing the advantages of the movement forces or even to damage the bears 19. To overcome to these issues it is proposed to mount always two flat linear motors having such flat ferromagnetic support members 600 symmetrically back-to-back for each piston 15 so that the attraction forces can be compensated by themselves. This arrangement can be seen form the Figures 6C to 6E. Furthermore, in this approach it is helpful to have the same magnet polarity face to face: NORD with NORD, SOUTH with SOUTH as depicted in Figure 6B.
Also it is possible to have different configurations. It is mentioned that only 2 motors back-to-back (just in one dimension x-y, defined as "2 b-2-b" in Figure 6C), but it is possible to have also a three dimension implementation with 4-6-8-... magnet planes back-to-back.
Figure 7 schematically shows a longitudinal sectional view of an embodiment of the apparatus 1 for producing electric power. In this embodiment at least one clutch unit 700 which is capable to provide the stationary magnetic means 27a or the second stationary magnetic means 27b with electrical energy. This provides the advantage that especially in the start up process the rod 17a and/or the second rod 17b can be moved in a desired manner by implementing a defined magnetic force on the magnets 610 due to the provision of electrical energy to the coils 710.
This clutch unit 700 is especially helpful in a startup situation of the apparatus 1, as this situation is one of the most critical issue of the free piston four combustion chambers engine, in particular the decoupling of the linear motors. During this step, the linear (electromagnetic) motors act as motor and control the movement of the pistons 15 to generate a synchronized movement allowing the explosions in all the four combustion engines. The startup process can only be successful if all four combustion chambers 5 have regular and synchronized explosions. But because during the startup step the power of the combustion motors can be much weaker than that of the linear motors -depends on the control algorithm- it is difficult to detect if the startup is successful or not and consequently it is very hard to find the right moment to switch off the linear motors. In the prior art the pistons are for example controlled by a close loop algorithm of the linear motors where the position and velocity follow a well-defined setting. This imply that during the first explosions, the pistons 15 tend to be faster than the electrical motors (respectively the movable and stationary magnetic means) and consequently the control algorithm increases the magnetic force to break the movement. Unfortunately breaking the pistons 15 also avoids the necessary speed increase to come out of the startup step. It is therefore obvious that the close loop algorithm is not the best choice at the startup. By using a magnetic clutch unit 700 as mentioned here the pistons 15 can be automatically decoupled from the linear motors and therefore the free piston engine automatically comes out of the startup step as soon as the combustion chambers are working correctly.
The magnetic clutch unit 700 works for example in such a way that as long as the forces of the combustion motors are lower than that of the linear motors, the pistons 15 follow the linear motors comprising the moveable and stationary magnetic means 23 and 27, but as soon the combustion motors start, the pistons 15 are free to follow the combustion motors. The realization of the magnetic clutch unit 700 is quite simple. The control algorithm is based on an open loop and set a constant current through the stator coils 710 of the linear motors. This current imposes a fix magnetic force, which can be calculated according to Equ. 2 moving the piston 15 and this is independent from its position. $\vec{F} = \vec{I} l \times \vec{B}$
Being an open loop the magnetic force of the linear motor is always the same, i.e. is not increased as a function of the position or velocity, and therefore the piston 15 is free to move as soon as the force of the combustion motor is higher than that of the linear motor. As soon as the electronic circuits detect an acceleration of the piston 15, the current in the stator coils 710 is switched off and the movement is only given by the combustion motors. As soon as the operation is stable, the linear motors are switched on again, but in this time as a current generators, thus converting the chemical energy of the combustion motors into electrical energy.
During the current generator mode, the electrical energy is extracted from the linear motor by "misusing" the output stage of the inverter. In this operating mode, the output transistors of the inverter are controlled as three independent step up converters. When the low side transistors are on (the high side transistors are off in this moment), the piston movement charges the coil inductance, when the high side transistor are switched on (the low side transistors are off in this moment) the coil inductance discharges the accumulated energy on the DC-bus of the inverter. Even if it is much more complex compared to the simple diodes solution, this method gives a much better control of the generator because it allows a fine setting of the output current and therefore it allows a fine tuning of the output power around its maximum (in a similar way as for the MPP tracking system of the solar panels).
In a specific embodiment of the invention it is also defined that the operating mode of the linear motor during start up uses a magnetic clutch unit 700 because the final effect is the same. If the forces of the combustion chambers are high enough, then the clutch detach the linear motor from the pistons. This advantage can be implemented with an open loop control, i.e. the control logic is not monitoring and maintaining the position of the piston by changing the current value of the linear motor accordingly.
Figure 8 shows a flow chart of an embodiment of the present invention implemented as a method 800 for operating an apparatus as disclosed herein. The method 800 comprises the step 810 of controlling the piston valve such that air is provided to the combustion chamber and/or exhaust gas is conducted from the combustion chamber through the piston opening.
Figure 9 shows a block diagram of an embodiment of the present invention implemented as a control unit 220 (220a to 220d) for operating an apparatus as disclosed herein. The control unit 220 respectively (220a to 220d) comprises a unit 910 for controlling the piston valve such that air is provided to the combustion chamber and/or exhaust gas is conducted from the combustion chamber through the piston opening.
Further, it will be understood that the embodiment described here in detail has been given only by way of example and that several changes and modifications in the reach of the skilled in the art are possible, without thereby departing from the scope of the invention as defined in the appended claims.
In particular, even if in the illustrated embodiment each rod carries two supports arranged at 180° relative to each other, it is also possible to provide rods carrying each a different number of supports: e.g., four supports arranged at 90° relative to one another could be associated with each rod.
Moreover, even if in the illustrated embodiment the pistons operate according to the principle of a two-stroke engine, it is also possible to provide that said pistons operate according to the principle of a four-stroke engine.

Claims

An apparatus (1) for producing electric power, the apparatus being formed as a free-piston combustion engine, the apparatus (1) including a housing (3) at an end of which a portion (3a) is formed, housing a combustion chamber (5a), wherein a piston (15a) is housed within said portion (3a) of said housing (3) and delimits said combustion chamber (5a), said piston (15a) being housed free within said portion (3a) of said housing (3) and being arranged to reciprocate therein, said piston (15a) being connected to an end of a rod (17a), the said rod (17a) has fastened thereto one or more support means (23a) carrying sets of movable magnetic means (25a, 27a), facing sets of stationary magnetic means (27a, 25a) for producing electric power when the movable magnetic means (25a, 27a) are moved with respect to the stationary magnetic means (27a, 25a), wherein
the piston (15a) comprises a piston valve (205a) being configured for blocking or unblocking an piston opening (200a) in the piston (15a) in order to provide air to the combustion chamber (5a) and/or in order to conduct exhaust gas from the combustion chamber (5a), wherein the apparatus comprises

a second combustion chamber (5b) being formed at a second end of said housing (3) at which a second substantially cylindrical portion (3b) is formed and wherein a second piston (15b) is housed within said second portion (3b) of said housing (3) and delimits said second combustion chamber (5b), said second piston (15b) being housed free within said second portion of said housing (3) and being arranged to reciprocate therein, said second piston (15b) being connected to an end of a second rod (17b), the said second rod (17b) has fastened thereto one or more support means (23b) carrying second sets of movable magnetic means (25b, 27b), facing second sets of stationary magnetic means (27b, 25b) for producing electric power when the second movable magnetic means (25b, 27b) are moved with respect to the second set of stationary magnetic means (27b, 25b), the second piston (15b) comprising a second piston valve (205b) being configured for blocking or unblocking a second piston opening (200b) in the second piston (15b) in order to provide air to the second combustion chamber (5b) and/or in order to conduct exhaust gas from the second combustion chamber (5b) and

characterized by a third piston (15c) being connected at the rod (17a) at an opposed end to said piston (15a) and said second rod (17b) carrying a fourth piston (15d) at the opposed end to the second piston (15b), said third piston (15c) and said fourth piston (15d) defining, together with the walls of said housing (3), a third combustion chamber (5c) formed in an intermediate portion (3c) of said housing (3), and wherein said third piston (15c) comprises a third piston valve (205c) being configured for blocking or unblocking a third piston opening (200c) in the third piston (15c) in order to provide air to the third combustion chamber (5c) and/or in order to conduct exhaust gas from the third combustion chamber (5c) and/or the fourth piston (15d) comprises a fourth piston valve (205d) being configured for blocking or unblocking a fourth piston opening (200d) in the fourth piston (15c) in order to provide air to the third combustion chamber (5c) and/or in order to conduct exhaust gas from the third combustion chamber (5c).
The apparatus (1) according to claim 1, characterized in that the piston valve (205a) is configured for being actuated pneumatically and/or the piston valve (205a) being coupled with a spring (210a) in order to bring the piston valve (205a) into a position blocking the piston opening (200a).
The apparatus (1) according to one of the preceding claims, characterized by a control chamber (215a) being fluidically coupled to the combustion chamber (5a) if the piston valve (205a) is opened.
The apparatus (1) according to claim 3, characterized by a control unit (220a), wherein the control unit (220a) is configured for controlling a pressure of a fluid in the control chamber (215a).
The apparatus (1) according to claim 4, characterized in that the control unit (220a) is configured for controlling the pressure of the fluid in the control chamber (215a) by opening or closing a control valve (230a), especially the control valve (230a) or an actuator (225a) being arranged for blocking or unblocking a fluid passage from a fluid reservoir (410) to the control chamber (215a).
The apparatus (1) according to one of claims 4 or 5, characterized in that the control unit (220a) is configured for controlling the pressure in the control chamber (215a) by using an electrically activatable control means (225a).
The apparatus (1) according to one of the preceding claims, characterized in that the apparatus (1) further comprises a housing valve (250a) being arranged in the housing (3) of the apparatus (1), the housing valve (250a) being configured for blocking or unblocking an opening in the housing (3) in order to provide air to the combustion chamber (5a) and/or in order to conduct exhaust gas from the combustion chamber (5a), especially the housing valve (250a) being arranged in a wall segment of the housing (3) opposite to the piston (15a).
The apparatus (1) according to one of the preceding claims, characterized in that the movable magnetic means (25a, 27a) comprise at least one permanent magnet (610) and/or the sets of stationary magnetic means (27a, 25a) comprise at least one induction coil (710).
The apparatus (1) according to one of the preceding claims, characterized in that said rod (17a) and said second rod (17b) are coaxially arranged, so that said third combustion chamber (5c) has a substantially cylindrical shape and/or wherein said rod (17a) and said second rod (17b) have the same size and mass, wherein said piston (15a) and second piston (15b) have the same size and mass and wherein said third and fourth pistons (15c, 15d) have the same size and mass.
Method (800) for operating an apparatus according to one of the preceding claims, wherein the method (800) comprises the following step:
- Controlling (810) the piston valve (205a) such that air is provided to the combustion chamber (5a) and/or exhaust gas is conducted from the combustion chamber (5a) through the piston opening.
Control unit (220a) being configured to control and/or to execute at least the step of the method according to claim 10.
Computer program comprising instructions to cause the control unit (220a) of claim 11 to execute the step(s) of the method of claim 10.