NO132546B - - Google Patents

Description

Electric generator driven by a piston engine.

The present invention relates to a device for converting potential

energy in fuel into electrical energy in the form of alternating voltage in an alternating current source (dynamo-electrical output power), and more particularly for the production of electrical power by utilizing the kinetic energy and potential energy developed in an internal combustion engine of the free-piston type built together with an alternating current generator working with longitudinal vibrations.

An object of the invention is to produce a motor with only two main moving parts. Another object of the invention is to enable regulation of the combustion in the engine in such a way that its thermal efficiency within a large load range is kept at an essentially constant, high level. In connection with this, according to the invention, there is a continuous change in the energy distribution between kinetic energy and potential energy, but in such a way that the transition from one form of energy to the other takes place continuously and without energy loss. This is achieved by adapting the mass of the moving • parts as well as their vibration amplitude and frequency in such a way that both the accumulated kinetic energy in the moving parts at maximum speed and the stored potential energy in the gas at maximum displacement of the moving parts amount to approx. twenty times the sum of the internal energy loss and the energy extracted from the electricity generator per radian period at full load.

A distinct advantage of such an engine

is that with the help of the movable de-

ler's inertia has the ability to equalize the disturbances resulting from the individual explosions, so the timing of the explosion and the combustion rate do not have to be exact functions of the position of the pistons in relation to the dead centers, as is the case with a normal piston and crankshaft engine. As a result, large compression and/or expansion ratios can be used, with high thermal efficiency, but without energy loss as a result of ignition.

In order to realize this inventive idea with regard to an exchange between kinetic energy and potential energy carried out with less loss, supplemented at arbitrary times by the supply of heat energy, the intention is to use an energy conversion procedure comprising the following measures: 1) The degree of compression (which entails an adiabatic temperature increase) of the working medium is allowed to determine the point of the compression stroke where ignition of the fuel will take place (the ignition point). 2) The working parts of the engine are allowed to reverse their direction of movement at any time under the influence of the sum of the pressures due to the transformed kinetic energy of the moving pistons, which acts as potential energy of the compressed gas, as well as the pressure due to the heat of combustion, without regard to the real position of the pistons, so that the working parts seek to maintain their periodic oscillating movement with constant maximum sla<g>len<g>de Csvinenin<g>samrjlitude) oe speed and thereby produce a constant maximum pressure. 3) The electrical output voltage is brought to be proportional to said constant rate of oscillation. 4) The amount of fuel supplied for each working period is regulated by means of the aforementioned electrical output voltage and/or load current, whereby it is ensured that the mechanical oscillation amplitude and frequency and the electrical output voltage and frequency will remain essentially constant with varying load.

Using the above-mentioned method, according to the invention, a power plant of the type with free-piston motor and axially movable inductor generator and with compression ignition of a fuel/air mixture is obtained, according to the invention, which is fed into an annular space between opposite ends of two free-pistons before compression begins. These pistons have a mass that is just large enough that at maximum piston speed they have an accumulated kinetic energy that amounts to approximately twenty times the sum of the internal energy loss and the energy taken from the electric generator per radian period at full load. The pistons are ring-shaped and made of electrically conductive material, so that they can fulfill the additional task of serving as movable single-winding inductors in the vibrating inductor generator that forms the plant's electrical power source.

It is known that an internal combustion engine's thermal efficiency depends on the engine's compression ratio (and on its expansion ratio, when these two quantities are not equal), and that as a rule, higher efficiencies are obtained with a higher compression-expansion ratio . It is also known that in most effective thermodynamic processes the ratio between effective maximum pressure and mean pressure is large, and that very large compression ratios and/or expansion ratios beyond certain limit values are not desirable. An excessively large compression ratio results in the working medium reaching such a high temperature only as a result of the adiabatic compression effects that it is not possible to supply sufficient heat to the gas at constant volume without extreme maximum pressures and temperatures. This can best be done at constant pressure. The supply of heat at constant pressure, however, means that the expansion ratio becomes smaller than the compression ratio, and therefore lowers the thermodynamic efficiency. There is thus for a given engine an optimal compression and expansion ratio and an optimal ratio between effective mean pressure and maximum pressure, which gives the engine the greatest possible output power combined with the greatest possible thermodynamic and total efficiency at full load, and which allows maintenance of this efficiency at both higher and lower load values.

In what follows, it will be shown that the optimal ratio between effective mean pressure and maximum pressure in a free-piston engine at full load is 2 . K QL, where QL is the ratio between the individual moving pistons' mass reactance (slow mass, living force) and the mechanical loss resistance (motion resistance) against which they work, and further that the modulus value for Q, for an engine at full load should be :

where r is the compression ratio, i.e. the ratio between the uncompressed and the compressed gas volume in the combustion chamber before combustion, and B is the so-called boundary temperature ratio. Furthermore, it must be shown that the ratio between the maximum temperature in the combustion chamber and the temperature that originates exclusively from adiabatic compression should be B, where

at full load, which results in an outlet pressure that is equal to the critical throat pressure (throat pressure) at the moment when the outlet opening is opened, so that the exhaust gases receive a maximum speed impulse with a minimum of unused heat energy to obtain optimal excitation of the resonant outlet and inlet channels which form the flushing device in the proposed engine. K is the ratio between specific heat of combustion at constant pressure and at constant volume for the working fluid used.

Since the oscillation amplitude and speed of the piston are essentially constant and independent of the load, it is clear that when the value of QL is high, the maximum pressure achieved during each working stroke can be kept essentially constant regardless of the load. This is the case because the total maximum force exerted on each of the pistons as a result of its movement and without taking into account the explosion force, can be shown to be F = yco2 . M, where co = 2jrf and M is the mass of one piston, while f is the frequency and y is the piston's range of motion. This force is great in comparison with the explosive force. To obtain the force value F, the mass of each piston must be:

where R is the mechanical load resistance to which the piston is subjected, and B is the limit temperature ratio, f is the frequency, M is the mass, r is the compression ratio and K is the ratio between the specific heat values.

During combustion at constant pressure, the effective mean pressure varies with the load, while the maximum pressure is always the same, regardless of the load. The effective mean pressure is regulated by the quantity of fuel supplied per work rate is regulated by the voltage-regulated fuel supply valve, so that it is just sufficient to cover the extracted load energy consumption as well as the internal losses. For full load, the desired design values for Q and the compression ratio r are thus achieved by dimensioning the mass of the pistons and their speed at an essentially constant amplitude to overcome the mechanical resistance to the piston movement represented by the load. The value of the expansion ratio is set using the limit temperature ratio B, which in turn is determined by regulating it per rate of work added hazardous quantity. During operation at full load, the effective mean pressure reaches its maximum value, which is therefore greater than the effective mean pressure for any load value that is less than full load, i.e. without overloading.

When the electrical load on the generator decreases, the system's mechanical Q-value increases, and the effective mean pressure decreases, while the supplied amount of fuel per rate is reduced. These design parameters ensure maximum efficiency of the system at full load, if the mechanical system's so-called idle Q-value, Qu, is high, i.e. the friction loss resistance in the no-load condition is small. It is determined that the no-load value Qu should be as high as possible and at least ten times the full-load value Qr, and that the full-load value Q should be numerically equal to:

in order to fulfill this desire.

Since the potential energy of the compressed gases as a result of the uptake of kinetic energy which is only due to the pistons' oscillation speed, under these conditions is at least twenty times the energy extracted from the electric generator plus the internal energy losses per radian period at full load, it is clear that, according to the law of the invariance of momentum, the pistons will reach their maximum range of motion when the calculated maximum pressure is reached, practically regardless of the point at which the explosion occurs.

Thus, if the explosion occurs before the pistons have reached the intended swing amplitude (stroke length), the inertial force will move them forward despite the explosion, until the entire amount of kinetic energy in the pistons has been transformed into potential energy in the gas. This energy is not lost, but is transferred back to the pistons in the form of kinetic energy during the return stroke. With a high mechanical Q-value for the engine's moving parts and with pistons that have no other elastic braking than the reversible forces from the compressed gas, a free and non-lossy exchange between kinetic energy and potential energy is thus obtained, which enables high compression ratios and high thermal efficiency without -there of a possibly occurring ignition. This leveling effect is a direct result of the described choice of the right values for the mass and speed of the pistons to ensure optimal full-load value Q, and optimal ratio between maximum pressure and effective mean pressure for the selected mechanical load resistance.

As the engine's load decreases as less electrical power is taken from the generator, the oscillation amplitude, maximum pressure, piston speed, output voltage and frequency remain constant, while the effective mean pressure, the amount of injected fuel per tact and the produced amperage are reduced and the mechanical Q-value increases.

In the limit position, the effective mean pressure is reduced to a value that is just sufficient to offset the friction losses and heat losses at zero load, represented by the idle value Qu, where there is no useful output and the amount of supplied fuel per strokes are minimal. Under these conditions, the engine works back and forth following essentially the same adiabat during the compression and expansion strokes, analogous to a pendulum that swings freely with minimal losses and no useful output power.

The engine's indicator diagram thus consists approximately of a single adiabat for the idle position and of two adiabats at a distance from each other along the volume axis for the full-load condition, i.e. combustion takes place at constant pressure with the effective mean pressure adapted to the load, constant stroke length and constant maximum pressure.

A free-piston engine that is designed in accordance with these data will achieve the highest efficiency at full load for a given compression ratio, will retain this efficiency for loads that are higher and lower than full load within a maximum possible load range, and will have an outlet pressure equal to the critical inlet pressure (throat pressure) at full load to induce as effective thermodynamic excitation as possible of the resonance-tuned inlet and outlet systems, which are proposed to be used for flushing.

The aforementioned data are the following:

Effective mean pressure = P0rK K ;

Qu^

Where:

f = the frequency

R = the mechanical load resistance

Qu = the no-load value for Q, i.e. the ratio between the mass reactance and the movement resistance at no-load.

QL = the load value for Q, i.e. the ratio between the mass reactance and the resistance to movement when loaded.

ro =2jtf, and a radian period =

2 jt f

r = compression ratio,

M = mass of the moving pistons,

B = the so-called transition or boundary temperature ratio, i.e. the ratio between the volume of the gas after combustion but before expansion and the volume of the gas before combustion but after compression; it is also the ratio between the absolute temperature of the gas after combustion but before expansion and its absolute temperature after compression but before combustion.

P0 = the absolute ambient pressure.

K = ratio between specific heat at constant pressure and at constant volume; for air this ratio is 1.4.

The engine's working process is determined thermodynamically by the following parameters (the process is visualized by the indicator diagram in fig. 3). If

r = compression ratio = volume of wood

a divided by the volume at b,

B = the transition or boundary temperature ratio = the volume at c divided by the volume at b,

Q] = the load value for Q = the ratio between the mass reactance and the movement resistance, as

where:

R i is the mechanical resistance at full cargo,

M is the mass

f is the frequency and co is the angular frequency 2jtf,

Qu = the idle value for Q, in that

where R is the mechanical resistance

at idle,

M is the mass and

f is the frequency,

P() = ambient absolute pressure,

T(1 = the absolute temperature of the environment, and K == cv/ cv = the ratio between specific heat at constant pressure and at constant volume = 1.4 for air, then the following relations apply: 1) P. = P„

2) P„ = P0r<K>

3) Pc = P0r<K>

4) P(1 = P,BK

5) Take = T0

6) Tb = T()rK-,

7) Tc = Tor<K->L

8) Td = TBK

Thermal efficiency =

K(B-l)

Q - Q,

Mechanical efficiency = ——

Generator efficiency = G

Total efficiency =

i-( i)k-i b "- 1 1 QjllQ.. g L1 ( f) -K(B=TrJ q„~-g Effective mean pressure (mean working pressure) = P(irK . —^-— 2 QL

2 - K

BK = ( —) icty = 1.895 for air at normal pressure and K + 1

temperature.

B = 1.58 for air at normal pressure and temperature.

R, i.e. the mechanical load resistance against which the pistons work, is determined as follows:

The mechanical output power is similar

where y is the piston's amplitude (a quarter of the total distance between the ring-shaped pistons when they are furthest from each other), co = 2jtf (f is the frequency) and yco is the piston's maximum speed.

The value of the maximum force developed at the amplitude y and the mass M for a piston is: F1M.1X = yco2M, and this force is set equal to P()A . r<K> where:

Pn is the absolute pressure of the environment,

A is the effective end surface of the piston,

r is the compression ratio, and K is the ratio of specific heat at constant volume.

The value of the force that does work while overcoming the resistance R is: Feff = ycoR where y is the amplitude of a piston and R is the resistance to movement. This force value multiplied by n/ 2 and divided by the piston's effective end surface gives the mean working pressure:

If the effective mean pressure is used for calculating the developed work, the total stroke length of both pistons, i.e. 4y, shall be used as the stroke length.

The value of Q is:

For optimal performance, QL should also satisfy the equation:

These criteria can be met by appropriate selection of the mass and end surface of the pistons, of their oscillation amplitude and frequency, and of the load resistance R against which they work, while maintaining the transition or limit temperature ratio by regulating the amount of supplied fuel per work rate.

A typical design can show the following characteristic values: Q, = 22.75

r = 20.8

BK = 1.895

B = 1.58

P., = P„ = 1.03 kp/cm2

p'h = 72.42 kp/cm-'

P,.' = 72.42 kp/cm2

Pa = 1.958 kp/cm2

T., = T„ = 278° K

Th = 970° K

T,.' = 1550° K

T(i = 540° K

Qu = 10 QL = 227.5

Effective mean pressure or mean working pressure = 4.26 kp/cm2.

Heating efficiency = 67.2 per cent Mechanical efficiency = 90 per cent Generator efficiency = 86 per cent Total efficiency = 52 per cent

Occupied amount of heat per kg of air = 136 kcal.

Recovered amount of heat per kg of air = 91.5 kcal.

Amount of heat lost per kg of air = 44.5

kcal.

Resulting energy ratio 1626 kcal/ kilowatt hour.

The engine's flushing takes place in the following way: The outlet pressure is adjusted so that it becomes as large as the critical throat pressure (thorat pressure) at the outlet openings just as these are opened, by The amount of fuel supplied to the working funnel for full load is regulated so that the previously defined transition or boundary temperature conditions become B, where

The heat removed with the exhaust gases is used to blow out the combustion products through the exhaust pipe at a speed roughly equal to the speed of sound at the prevailing temperature and pressure conditions.

In order to facilitate the blowing out, the outlet or exhaust gas channel, counted from the openings 71 in fig. 1, made with a length L2 (77 in fig. 2), which is so adjusted that the pressure wave that advances to the left through the tube 45 in fig. 1, at the time of the opening of the outlet opening is met by a dilution or negative pressure wave, which moves to the right at the outlet openings, and which constituted a pressure wave in the previous beat. In the meantime, the wave has moved a suitable distance along the exhaust pipe, as it has changed phase by reflection at the outer end of the exhaust pipe 77 and then returns to the starting point as a dilution wave in the time interval between the first time the outlet openings are opened, and until these are opened the next time.

As the motor works at a constant frequency, the adaptation of said channel's length can easily take place in accordance with what is stated in American patent document No. 2,102,559 (Kadenacy).

During the flushing process, air is admitted into the combustion chamber by opening the inlet ports 61 just after the outlet openings have been opened. An inlet pressure is automatically achieved at the inlet openings by resonance in the inlet pipe in the same way as at the outlet pipe, but so that a pressure wave in this case begins to propagate to the left at 61, fig. 1, after the flowing combustion products. This wave is followed by a dilution wave, which moves to the right along the inlet pipe 46, fig. 2, which has such a length L, that this wave, when it reaches the outer end of the pipe, undergoes a phase reversal, i.e. is transformed into a pressure wave and returns as such to the inlet openings 61 just as these are opened for the second time. Thus, an effective flushing of the combustion chamber is obtained by means of a pressure drop below the atmospheric pressure at the outlet openings at the same time as the respective openings are opened in turn.

In this way, it is achieved that the combustion products are effectively replaced with a new, cool filling of air and fuel without special auxiliary devices, e.g. flush pump. The energy that goes into obtaining this result is the heat energy that goes away with the exhaust gases and that would have been lost in any case. As this waste heat energy is utilized for flushing the engine through acoustic resonance in the inlet and outlet pipes, power loss, which is otherwise associated with driving the flushing pump, is eliminated.

Thus, the reversible adiabatic expansion rate describes the entire "toe part" of the thermodynamic circular process, shown with slanted lines in fig. 3, until the ambient pressure and temperature and the heat energy in this part are brought to perform the useful work for carrying out the flushing. This energy would otherwise have to be taken from the other part of the thermodynamic process. In this way, the process of combustion at constant pressure is utilized in the most advantageous way possible, and the total efficiency is kept at a value, which is determined exclusively by the thermodynamic conditions of the working process, without loss of

withdrawal of flushing power from the useful

output power. By adapting transitional or

the limit temperature ratio B at full load in such a way that

ensure that the result specified above is achieved

with the least possible sacrifice of heat energy from the "toe" of the indicator diagram.

By placing a jet pump nozzle 52 (fig. 2) at a suitable place with low pressure in the inlet pipe, a suitable mixture of liquid fuel and air can be obtained in accordance with the known gasification principle.

For the engine to work correctly, a certain phase coordination between the mutual movements of the pistons is required. In the case of the usual free-piston engine, this phase coordination is usually achieved by means of a system of racks, racks and connecting rods, which mechanically connect both pistons to each other. With the present engine, no such mechanical motion transmission or synchronization system is required. Automatic phase compensation is thereby achieved partly by means of air holes 80 and 81 in the annular damping or buffer cylinders 78 and 79 and partly by the electrical connection between the coils 13 - 16, which seeks to keep the stroke length and speed of the pistons 11 and 12 the same. Since these pistons are elastically connected through the common "stiffness" of the compressed gas in the combustion chamber 40, each change in the speed of one piston will be compensated by a similar change in the speed of the other piston thanks to the coupling effect through this gas column and the electric generators 13, 14, 21 and 15, 16, 22, which are connected in parallel or in series with the load network. This connection through the electric generators is thanks to the reversible nature of these generators, as they work as well as motors, if they are fed with electricity at the right frequency. Thus, if one piston's speed tends to exceed that of the other, the first piston, acting as a generator, will drive the second piston, acting as a motor, with the first's higher speed, and vice versa.

An exemplary embodiment of the invention shall be described in more detail below in connection with the attached drawings. On these, fig. 1 in an axial section, a free-piston engine, which is suitable for carrying out the invention. Fig. 2 shows an electrical circuit diagram and certain auxiliary devices, intended to be used in connection with the engine in accordance with fig. 1. Fig. 3 shows the progress of the thermodynamic work process in the present engine. Fig. 4 shows in axial section a modified embodiment of it, in fig. 1 showed a free piston engine, and fig. 5 shows this engine in cross-section along the line 5-5 in fig. 4.

The one in fig. 1 clarified engine has two

thin-walled, electrically conductive cylindrical-annular pistons 11, 12, which are located coaxially 1 line with each other and perform rectilinear vibration at high frequency in the permanent radial electromagnetic fields in the air gaps 91, 92, 93, 94, which are produced by the coils 21 . which is surrounded by magnetically conductive end rings 18, 19, provided with recesses for receiving said coils 13, 14, 15 and 16, as well as the auxiliary coils 21 and 22, which produce the polarizing flux in the gaps 91, 92, 93, 94 The coils 13-16 together with the rapidly vibrating piston and inductor elements 11 and 12 form the device for producing alternating current, but as the magnetic flux passes through the conducting pistons in the radial direction, is cut by the pistons, as these move first to one and then to the other side, whereby an alternating current is thus formed in the annular pistons, which is transferred by induction to the output circuit, which is formed by the wires 26 and 27, which is connected to the ends of the coils 13, 14 resp. 15, 16.

In order to keep the rings 18 and 19 in a fixed position in relation to the core 17 and at the same time obtain a device for retaining the vibrating inductor pistons 11 and 12, there are three holding elements 31, 32, 33, of which the elements 31 and 32 have opposing flanges 34 respectively 35 which join each side of the ring 18 and are attached to this by means of bolts not shown. The elements 32 and 33 have similar, opposite flanges 36 or 37, which is attached to the ring 19 in a similar manner. The middle holder element 32 is, as shown, provided with cooling fins 39 to facilitate temperature regulation, and its inside forms an outer cylindrical boundary wall for the annular combustion chamber 40, whose inner boundary wall is formed by the mantle surface of the core 17.

The ends of the core 17 are extended to form stubs with inlet and outlet channels 44 and 45 for a mixture of fuel and air. This mixture is formed in the inlet line 46 (fig. 2), by suction of fuel, which is supplied to the line 46 from a storage tank 47 under the control of a valve 48, which is influenced in the opening direction by a spring 49 but is closed through the force of attraction from a solenoid 50, which is supplied with magnetizing current from the generator circuits 26 and 27. As long as the voltage across the wires 26 and 27 remains constant, which is the case as long as the vibration speed of the pistons 11 and 12 is constant, the attraction force of the solenoid 50 becomes constant and sufficient for to keep the valve set in the necessary intermediate position against the action of the spring 49, which strives to open the valve completely. Since the solenoid 50 is operated with alternating current, it must of course be equipped with a suitable short-circuit circuit on part of its movable armature 51, so that this is affected by a non-pole-changing attraction force, for alternating current-operated solenoids with a movable armature or movable core usual way. If so desired, a load current can be used in a known but not shown way to adjust the fuel valve, with or without voltage regulation of the type described.

The inlet pipe 46, with a length L adapted to resonance, ensures through the longitudinal, i.e. acoustic resonance oscillations, that an overpressure is obtained outside the combustion chamber 40 in fig. 1, periodically with its beginning just as the inlet ports 61 are opened, so that a sufficient inflow of fuel-air mixture into the chamber 40 is thereby established. The fuel-air mixture is thus fed in intermittently, i.e. every time the inlet openings 61 are exposed by the fact that the piston 12 is displaced to its right end position. The fuel is introduced into the inlet pipe 46 through the valve 48 by being sucked into a low-pressure anode in the pipe 46. It can be seen that such periodic reciprocating movements of the piston 12, "inlet stroke", are made possible through the explosions of the fuel mixture in the chamber 40. These periodic explosions occur when the opposing pistons 11 and 12 compress the introduced fuel-air mixture between them, until self-ignition temperature is reached. By appropriate regulation of the introduced fuel quantity per inlet stroke, oscillation resonance with prescribed amplitude and frequency is obtained. The pistons 11 and 12 form the swing masses, and the gas cushions in the chambers 78 and 79 as well as in the combustion chamber 40 the non-linear elastic damping notand, which gives the necessary output frequency, which e.g. can go up to sixty periods per second. It is realized that the vibration frequency of an oscillating system of this type, where the damping resistance is non-linear, i.e. the return force is not proportional to the displacement, depends, among other things, on a. of the oscillation amplitude.

In the present engine, this parameter, i.e. the amplitude, is fixed by the fact that damping cylinder openings 80 and 81 are opened at one end of the piston stroke and by the above-mentioned trade-off of the maximum pressure in the chamber 40 between the pistons 11 and 12 taking place with the help of their kinetic energy , and at the other end of the piston stroke by opening the outlet opening 71 and the inlet opening 61 as well as a corresponding balancing of the peak or maximum pressure in the damping cylinders 78, 79.

As indicated above, the ignition points can vary from stroke to stroke, while temperature and pressure fluctuate somewhat around their mean values, but the energy accumulation capacity of the moving parts (equivalent to the energy developed by at least 20 explosions) ensures a constant energy exchange from stroke to stroke , regardless of such variations with regard to ignition point position.

When the inlet opening 61 is exposed (of which, if desired, more than two can be present, so that the total inlet area is at least as large as the cross-sectional area of the combustion chamber 40), the outlet openings 71 are also exposed to enable flushing out of the combustion products, thereby the new fuel air charge flows more into the combustion chamber. The total area of the outlet openings 71 can likewise be at least as large as the annular cross-sectional area of the combustion chamber 40 in order to obtain optimal flushing conditions. If desired, the openings 71 can be opened immediately before the openings 61, so that there is a small time shift between outlet and inlet in accordance with the formula developed in the Kadenacy patents, of which US patent document 2,144,065 can be cited as an example. In order to facilitate the blow-out process, a resonant outlet or exhaust pipe 77 of suitable length L2 can be used (Fig. 2), so that the pressure in the exhaust system is periodically lowered below atmospheric pressure every time the outlet opening 71 is opened. The length L2 of this pipe includes the length of the outlet channel 45 right up to the openings 71.

As the pistons 11 and 12 move axially outward, they compress air in the annular damping cylinders or pockets 78, 79, and the pressure in this air serves as a return force to return the pistons to their inner position, the ignition position. In order for this to take place without loss, the entire course is made to take place adiabatically and reversibly by providing the annular chambers 31 and 33 with suitable thermal insulation to prevent the loss of the adiabatic pressure heat.

The ventilation openings 80 and 81 contribute to the function of the damping pockets 78 and 79 by letting in new air during each compression stroke to thereby replace the air that may have leaked out during the inlet or expansion stroke. They also serve as a phase compensating device and as an amplitude limiting device to keep the pistons 11 and 12 in phase with each other and at the intended vibration or oscillation frequency, as described above.

The pistons 11 and 12 are provided with suitable (not shown) piston rings at suitable locations along both the outside and the inside to enable efficient pressure production in the combustion chamber 40 and in the damper cylinders 78, 79 in the usual manner.

The peripheral expansion of the annular pistons 11 and 12 due to the heat of combustion (which heat expansion due to the engine's low maximum temperature and high thermal efficiency is small compared to a conventional piston engine) is partially compensated by the movement in the radial direction, as mentioned piston rings has in its tracks, and partly by choosing suitable construction material for the outer cylinder wall or jacket 32, the inner core 17 and the damping chamber walls 31 and 33, so that these obtain the same thermal expansion coefficient as the pistons 11 and 12. The gaps or between the spaces 91-94 must be sufficiently large to allow for thermal expansion to occur without causing a change in the relative position of the coils 13-16. For reasons of thermal expansion, the damping or buffer chambers or rings 31 and 33 are attached to the magnet rings or coil holders 18 and 19 in such a way that they are maintained centered with respect to the longitudinal axis of the motor, and longitudinal movement in both directions is prevented while radial expansion and contraction are permitted to the same extent as for pistons 11 and 12. By using equally heavy pistons working in counterphase, the machine is statically and dynamically balanced and thus works without vibration, as a unit considered.

It is immediately realized that all of the previously outlined construction and work

principles can equally well be applied for a free-piston engine with direct fuel injection or air diffuser injection of fuel during the later part of the inlet stroke, so that only air is compressed in the chamber 40 during the earlier part of the stroke in the same way as with diesel engines. Even if thus compression and ignition of a fuel-air mixture is considered to be preferable, the inventive concept also includes all forms of fuel injection and their advantages with regard to the possibility of arbitrary selection of the ignition point.

The invention can also be carried out in a different way than as described. The stated principles can be utilized individually just as well in the one indicated here as in any equivalent combination; likewise, the constructive and functional connections between the engine's various parts can be varied within the framework of the subsequent patent claims.

As is known, the annular fields can be obtained with permanent magnets. When such magnets are used, it is important that the radial dimension of the gap is kept small in order to be able to use the smallest possible amount of permanent magnetic material. The single-layer inductor coils with their windings, according to the preceding description, can be replaced by a multi-layer piston winding, as shown in fig. 4.1 accordance with this modified embodiment, the currents are induced directly in these moving winding layers, instead of in the one, short-circuited winding layer, and are transferred from there through induction to the output windings. With this measure, the eddy current or copper losses are reduced, while at the same time the device becomes cheaper by the fact that the necessary permanent magnet is smaller, as you get a construction in which the radial dimension of the gap or slot can be made shorter, while still getting the same output power. As no short-circuited winding layer is thus used, the electrical Q value of the winding can be made larger, which is an important factor, especially at lower frequencies.

In order to use a multi-layer winding, it is necessary to wind one half of the piston winding, e.g. clockwise and the other half counter-clockwise, as the piston winding's respective halves vibrate in the magnetic field, which in the radial direction is oppositely directed. Power is extracted from the multi-layer windings of the pistons through the fact that the buffer or damping chambers at both ends of the motor are isolated and the piston rings are used as slip rings to guide the current produced in the moving coils to the damping chambers. A suitable electrical cable can be connected to the chambers for extracting power from them. The piston rings on the inner ends of the pistons also serve as slip rings and close a return connection from the coils through the machine body, as the inner piston rings are "grounded" directly to the machine body and fixed structure.

Both the oppositely wound halves of each piston coil are connected in series with each other, and both complete piston coils, each consisting of two oppositely wound halves in series with each other, may be connected in parallel with each other to enable phase regulation between both pistons mutually , as described above.

The one in fig. The engine shown in 4 has an inner part 100 with an inlet channel 101 and a coaxially aligned outlet channel 102. Between the channels 101 and 102 there is a guide element 103 designed for directing the gas flow, designed with guide surfaces 104, 105 , which cooperate with opposite wall surfaces 106 and 107 in the channel 101 resp. 102 to appropriately direct the inlet and outlet gases to the resp. from the combustion chamber through the openings 109 and 110. A cover 112 is placed at each end of the part, which is held in place in an appropriate manner, e.g. by pin and sleeve connections 113, 114, 115 provided with corresponding annular projections. A sealing ring 116 can, if necessary, be inserted between the thus connected parts for proper sealing of the motor. A flow-directing guide member 118 is fitted into each end cap and suitably held in place by means of spokes 119. Each of these guide members is provided with a guide surface which can cooperate with the inside of the jacket 120 to guide the gas flow inwards respectively outwardly. The opening or channel 121, which is formed between the guide member 118 and the inside of the jacket 120, is annular. If desired, the opening 121, instead of being closed annular, can be formed by a series or wreath of tubular channels. What is an essential criterion in this case is that the channel's or the cross-sectional area of the channels 121 should preferably be equal to the inlet channel 101 or cross-sectional area of the outlet channel 102. Furthermore, the cross-sectional area of the channel 101 is preferably equal to half of the cross-sectional area of the combustion chamber 124. There is also another series of inlet and outlet channels 126 and 127. The inlet channels 126 run in the longitudinal direction of the engine and preferably parallel to the central inlet channel 101 and are preferably distributed in a ring around the body, radially outside the corresponding piston. The axially inner ends of the channels 126 open into the inlet openings 128 which lie parallel to and in the middle of the inlet openings 109. However, these openings 128 are located on the opposite side of the annular combustion chamber wall 130, 131. The axially outer ends of the channels 126 join an intake channel 132 shared with the channels 121. The combined cross-sectional area of the channels 126 should be equal to half the cross-sectional area of the combustion chamber 124. The openings 128 can in turn have a combined passage area which is equal to or slightly less than half of the cross-sectional area of the annular chamber 124. The passage area of the openings 109 should, as mentioned, be equal to or slightly less than half of the cross-sectional area of the chamber 124. In order to achieve the best possible operating conditions, the channels 126 should have the same length as the central channel 101 apart from channel 121. The construction of the outlet end of this machine is, with respect to channels 127-102, the same as described above for the inlet end. The annular combustion chamber 124 is formed by the inner wall 131 and the outer wall 130 and is limited in the axial direction by the axially inner ends of the pistons 140 and 141. The pistons 140 and 141 are formed by axially inner and outer end masses 142 and 143, which are annular and united through an intermediate annular or tubular part 144, which forms the induction winding of the piston. The end masses 142 and 143 are provided with piston rings, which partly serve to seal the combustion resp. the damping chamber, partly serves as a current-conducting organ, whereby the piston rings on the axially inner end mass 142 serve to conduct current from the winding 144 through, in the following, connection lines to the load. The winding 144 consists of tightly wound copper wire, which is suitably glued or stapled together and stably mounted in a ring using glass or plastic binder which can withstand the temperature and pressure encountered. In said coil 144, the copper wire is wound clockwise on half the coil and counter-clockwise on the other half, whereby both according to fig. 4, the piston coil 144 performs reciprocating oscillating movements in the axial direction with a certain amplitude around the center position of the piston, whereby the amplitude of each hold is approximately equal to half of one of the pole surfaces. Consequently, the distance between adjacent polar surfaces is equal to the width of the polar surfaces themselves. An aeration pipe 173 is provided to supply replacement air for the leakage from the damping chamber 158.

The description given above of the inlet end of the engine according to fig. 4 also applies, with respect to both construction and working method, to the engine's outlet end, as the engine is fully symmetrical in relation to its cross-sectional plane.

coil halves are joined at the center of the coil. The coil's outer ends are suitably mechanically and electrically conductively inserted into the end masses 142 and 143 of the piston.

The inner end mass or piston part 142 is slidably axially movable in the annular chamber 124. Up to and axially outside this chamber 124 is placed an annular permanent magnet or electromagnet 150. If an electromagnet is used, there are magnetizing coils 151 for this. An annular projection 152 is formed on the body and together with the annular magnet 150 forms a narrow space or an air gap. The piston coil 144 is situated in this slot 153, which is annular. It is to be noted that the flux from the permanent or electromagnet 150 is radial and directed outwards along half the magnet and inwards along the other half of the same. As indicated above, a unidirectional current flow is obtained by reversing the winding direction in the piston coil 144. Said magnet 150 can be attached to the part with suitable aids, e.g. screws 155, and, if it is an electromagnet, magnetizing current can be supplied through the line 156, which at 157 is led in through the goods. Axially outside the piston and magnet 150 is another annular chamber 158, which is limited by an annular inner wall 159 and a corresponding outer wall 160. This chamber 158, the damping or buffer chamber, contains the axial outer end mass 143 of the piston. The piston part 143 stands in electrical and mechanical contact with the walls 159 and 160, whereby a suitable electrical contact pressure is obtained by means of the piston rings arranged around the piston part 143. The chamber walls 159 and 160 are isolated from the body by insulating members 161 and 162 of packing material, which appropriately enclose the damping chamber and its walls and provide electrical insulation and thermal insulation to prevent earth-shortening or heat loss. A wire 165, which is brought in through the body at 157 and passed through the insulation to the outer wall 160, diverts current from the present damping chamber. Furthermore, the device can be provided with suitable cooling fins 170 with a surrounding annular mantle plate 171 as well as with an inlet part 172 for air or water supply, so that air or water can be made to circulate through parts of the engine to keep its temperature at a desired level.

In the special embodiment in

Claims (19)

1. Electric generator driven by a free piston motor, characterized by devices for producing a magnetic field, and by at least one ring-shaped piston which is arranged to carry out a reciprocating movement in relation to this field, and which at least partly consists of an electrically inductive conductor. 2. Generator as stated in claim 1, characterized in that the piston's electrical conductors are designed with mass bodies placed on both sides of the conductor. 3. Generator as stated in claim 1 or 2, characterized in that the piston is firmly connected to a coil in which current can be induced during the movement of the piston. 4. Generator as set forth in claim 2 or 3, characterized in that the devices for generating the field are designed to generate an annular magnetic field with radially drawn lines of force, in which the electrically conductive part of the piston is movable, while those connected to this part mass bodies as well as the electrically conductive part have a ring-shaped cross-section. 5. Generator as stated in one of claims 1-4, characterized by an annular combustion chamber, in which part of the piston is movable, radially directed openings in the walls of the chamber arranged to be opened and closed by the movement of the piston, as well as channels that connect these openings with a gas channel common to several openings, and which have essentially the same length and a combined cross-sectional area essentially equal to the cross-sectional area of the combustion chamber. 6. Generator as indicated in one of the preceding claims, characterized in that the piston is provided with one or more piston rings, which partly seal against the walls of the combustion chamber and partly serve as transmission means to lead the current induced in the piston's conductor to an external load device. 7. Generator as stated in one of the preceding claims, characterized in that it includes two pistons which are movable towards and away from each other in a common combustion chamber, and that each piston is provided with electrically conducting bodies which are movable in each of its magnetic fields . 8. Generator as stated in claim 7, characterized in that the pistons themselves form conductors with an annular cross-section and small mass and with a large diameter in relation to their wall thickness, and that the pistons are surrounded by fixed windings in which current is induced by the movement of the pistons. 9. Generator as stated in claim 7 or 8, characterized in that the pistons have such a mass and are movable at such maximum speed that their kinetic energy at maximum speed and the potential energy of the gases compressed between the pistons at maximum pressure each amount to approx. twenty times the sum of the internal energy loss and the energy taken per radian period of the load. 10. Generator as stated in claim 9, characterized in that the pistons are driven so that the ratio between their mass reactance and the mechanical resistance to their movement at full load is of the order of 20:1. 11. Generator as stated in claim 10, characterized in that the drive device for the pistons is designed so that the value QL, i.e. the ratio between the moving pistons' slow mass (mass reactance) and the mechanical resistance to their movement at full load is: where r is the compression ratio, K is the ratio between specific heat at constant pressure and at constant volume and B is the ratio between the absolute temperature of the gas after combustion but before expansion; and the absolute temperature of the gas after compression, but before combustion. 12. Generator as specified in claim 11, characterized in that the ratio between the volume of the working medium after combustion, but before expansion, and its volume lum after compression, but before combustion, is B at full load, ie where K is the ratio between specific heat at constant pressure and at constant volume of the exhaust gases at the time of opening the outlet openings. 13. Generator as stated in claim 12, where the ratio between the absolute temperature of the working fluid after combustion, but before expansion, and its absolute temperature before combustion, but after compression, is B at full load, as 14. Generator as stated in claim 11, characterized in that the mass of each piston in grams is M, as where R is the mechanical resistance in ohms that counteracts the movement of the piston, f is the oscillation or vibration frequency in Hertz, r is the compression ratio, B is the limit temperature ratio at full load, which can be changed by regulating the amount of fuel supplied per work rate, and K is the ratio between specific heat at constant pressure and at constant volume of the working medium used. 15. Generator as specified in claim 14, characterized in that the limit temperature ratio B at full load is determined according to the formula: 16. Generator as stated in claim 11, characterized in that the moving pistons' mass, effective piston area, speed and oscillation amplitude (stroke length) are adapted so that at maximum compression as a result of only inertial forces, the maximum pressure developed in the combustion chamber is numerically equal to the ambient absolute pressure multiplied by the factor r<K>, where r is the compression ratio and K is the ratio between specific heat at constant pressure and at constant volume of the working fluid used. 17. Generator as stated in claim 14, characterized in that the effective mean pressure at full load when regulating the amount of supplied fuel per working rate goes up to —~ 2 °-l times the maximum pressure. 18. Generator as stated in claims 11-17, characterized in that it is provided with inlet and outlet pipes adjusted for resonance for direct flushing as well as with a device for regulating the amount of supplied fuel per working rate in such a way that the outlet pressure is mainly maintained at the value which entails the maximum outlet velocity of the exhaust gases at full load, and that this device includes outlet parts which are placed so that they produce the desired vibration frequency when the limit temperature ratio B is set to the value: where K is the ratio between specific heat at constant pressure and at constant volume of the working medium used at the time of opening the outlet openings. 19. Generator as stated in claim 18, characterized in that the channels are combined with a device to bring them into resonant oscillation when the outlet pressure reaches the value corresponding to the maximum outlet velocity, while this device includes outlet openings arranged so that they cause same vibration frequency in the aforementioned channels as in the moving parts of the engine, and that at the time of opening the outlet openings they cause an outlet pressure approximately equivalent to where P0 is the absolute pressure of the surroundings and K is the ratio between specific heat at constant pressure and at constant volume of the working medium used.