EP0078561A2 - Free piston internal-combustion engine with an independently driven cam - Google Patents

Abstract

The engine comprises one or more units having a pair of pistons on a common shaft connecting two opposed cylinders and driving the permanent-magnet moving part of a linear alternator. The shaft carries two robust pegs engaging the rim of a cam driven by an independent eccentric motor. The cam rotates substantially in synchronism with the engine so that the pegs are in virtual contact with it and no energy loss is implied. The contact becomes positive if the piston rod overruns or if one cylinder misfiring fails to initiate compression in the other. The engine can be started by means of the independent motor without recourse to compressed air or use of the linear alternator as a starter motor.

Description

The present invention relates to an internal combustion engine with free pistons, especially for the actuation of a linear alternator, comprising at least one pair of opposite cylinders whose pistons are reciprocally connected by a rod connected in an intermediate point to the moving element of a linear alternator or other means of using the energy produced.

It is known that, particularly in the use for actuating electric generators, internal combustion engines of the connecting rod-crank type prove to be unsatisfactory both by their relatively low efficiency and by the production of harmful gases to which they give rise. Their replacement by gas turbines is only possible in the case of very large powers, because of the costs of these turbines and the technological problems which they cause. So-called free piston engines have been proposed for medium power applications. In these engines, given the absence of the constraints determined by the connecting rods, it is essentially the inertia of the moving parts which delays movement of the piston immediately after the start of combustion, thereby ensuring the availability of sufficient time for vaporization, mixing and combustion in the cylinder chamber, while the thrust corresponding to the high pressures which occur in this phase, instead of being thwarted by the linkage, is accumulated in the form of kinetic energy and it is used thereafter in the cycle. In these engines therefore, in addition to the simplifications of construction and the reduction of mechanical losses, inherent directly in the elimination of crankshafts, we also obtain more favorable conditions for the transformation of energy, with the consequence of an increase in efficiency. and a reduction in heat losses, in the temperature of the exhaust gases and in the content therein of polluting substances and in particular of nitrogen oxides.

However, free piston engines in turn cause serious problems which have not yet been fully resolved; among these problems, the most serious concern the supply of energy to effect the compression stroke, the synchronization of the movement of the different pistons and the limitation of the stroke of the latter, problems these which in traditional engines are solved by the presence of connecting rods connected to an engine shaft provided with a flywheel, while in free piston engines there are no corresponding parts.

For the execution of the compression stroke it has been proposed (Jarret) to oppose to the pistons hydraulic springs, which however cause difficulties constructive and yield losses and result in fluid losses; the particular problem is solved, during normal operation (Allais), by an arrangement with opposite cylinders, but this solution proves to be ineffective in the absence of combustion, if it is not integrated by other means, which until now have been constituted by gear systems or by connecting rods, which it seems appropriate to avoid. No effective solution not making use of connecting rods or gears has been proposed until now to ensure the limitation of the piston stroke to a predetermined value, or to ensure synchronism in the movement of the pistons in an engine comprising several units.

The present invention aims to achieve a free piston engine suitable for being coupled to a generator with linear alternator, which is completely devoid of linkages and gears intended to transmit the mechanical energy produced, and in which however are ensured the execution of the compression stroke even in the event of a lack of combustion, the execution by the pistons of a stroke extending between limits prefixed with precision, and the possibility, in the case of engines with several units, easy synchronization.

This object is achieved, according to the invention, by the fact that an engine of the type considered comprises at least one cam actuated by an independent engine, in a substantially synchronous manner with the displacements of the piston rod, and engaging with pusher means connected to the piston rod, so as not to give rise to a substantial transmission of energy during normal operation, but to limit the travel of the pistons and to transfer to them the energy necessary for compression in the event of abnormal operation of the free piston engine.

Thanks to this arrangement, the rod of the unit, and consequently the relative pistons, are forced to move within the limits and according to the law of movement preset by the cam actuated by its own independent motor. With an appropriate design of the cam profile and by adjusting its actuation speed adequately, there is the possibility of ensuring that, during normal operation, the law of movement imposed by the cam coincides with the movement spontaneous of the free piston unit, so that no transfer of energy takes place between the cam (and therefore its independent motor) and the pusher (and therefore the free piston motor). However, the presence of the cam positively prevents that, due to any malfunction of the functioning, the free pistons can exceed the stroke limits which have been assigned to it, and, in the event of an accidental omission of one or more combustions, the cam intervenes by driving, by the pusher, the rod of the unit and thus making accomplish the compression stroke which otherwise could not have taken place. In addition, in the case of engines having several units, it suffices to establish synchronization between the respective cams, to obtain complete synchronization of the different units.

Thanks to the realization of a favorable law of piston movement and the elimination of any connecting rods or power gears, as well as other organs, such as hydraulic springs, a free piston engine according to the invention gives a handsome overall yield blow larger than that of traditional piston engines and even somewhat higher than that of turbines of the same power; a strong economy is also achievable in the consumption of lubricating oil, while the reduced pollution characteristics of free piston engines can be exploited in the most favorable way. Finally, the cam with independent engine can be used for starting the engine, if it is considered appropriate, as an alternative to compressed air systems or for the temporary use, as engine, of the linear alternator, systems known to present for free piston engines.

The invention also relates to special arrangements for an engine of the indicated type, and in particular a magnetic support for the elimination of the load applied to the walls of the cylinders, in large engines, because of the weight of the moving parts; and provisions for correct operation in engines with coal dust or other solid fuel feed.

• Fig. 1 montre, en vue de dessous, le schéma d'une unité de moteur à pistons libres avec came a commande indépendante, selon l'invention;
• Fig. 2 montre une vue latérale de l'unité de moteur selon la figure 1;
• Figs. 3 et 4 montrent, d'une façon similaire aux figures 1 et 2, un moteur comprenant deux unités opposées avec une came unique à commande indépendante;
• Figs. 5 et 6 montrent, d'une façon similiaire aux figures 3 et 4, un moteur avec support magnétique des tiges des unités;
• Figs. 7 et 8 montrent en section des détails des cylindres d'un moteur selon les figures 3 et 4, ou 5 et 6, destiné à fonctionner à poussier de charbon ou autre combustible solide;
• Fig. 9 montre la composition d'un ensemble la production d'énergie électrique, utilisant le moteur selon l'invention.

The characteristics and advantages indicated and others of the object of the invention will result more clearly from the following description of some embodiments, indicated by way of nonlimiting examples, represented very schematically in the appended drawings, in which:

• Fig. 1 shows, in bottom view, the diagram of a free piston engine unit with independently controlled cam, according to the invention;
• Fig. 2 shows a side view of the engine unit according to Figure 1;
• Figs. 3 and 4 show, in a similar way to Figures 1 and 2, an engine comprising two opposite units with a single cam with independent control;
• Figs. 5 and 6 show, in a manner similar to FIGS. 3 and 4, a motor with magnetic support for the rods of the units;
• Figs. 7 and 8 show in section details of the cylinders of an engine according to FIGS. 3 and 4, or 5 and 6, intended to operate with coal dust or other solid fuel;
• Fig. 9 shows the composition of an assembly producing electrical energy, using the motor according to the invention.

For simplicity and clarity of representation, in all the figures we have omitted the auxiliary service parts, such as the lights, the valves, the injectors, the washing, cooling and lubrication means, and so on, parts thereof which belong to the known technique and do not need to be modified for the application of the invention.

The unit shown in Figure 1 comprises two opposite cylinders and 2, in which are arranged the pistons, 3 and 4 respectively, rigidly connected to each other by a rod 5 which, in an intermediate point, supports the means d 'use, in this case inductor 6; for example with permanent magnet, of a linear alternator 7. These parts form a free piston engine with electric generator, of a type which by itself has already been proposed by the same applicant, in which the compression stroke of each cylinder is activated by the trigger in the opposite cylinder, so that in normal operation it is not necessary to use auxiliary means to activate compression, while the stroke limits are imposed (but not rigidly) by the compressive strength of the mixture intended to give rise to successive combustion. However, these two effects are lacking in certain cases of irregularity of operation, and to remedy this drawback, according to the invention, a cam 11 is provided, carried and actuated by an independent eccentric motor 9, and engaging with a pusher secured to rod 5 of the unit. This pusher may be constituted by a pair of robust pins 8, possibly with rollers, or by a groove in the rod 5 or other equivalent means; the cam is illustrated as having a circular profile, but it is understood that its profile can be preset in an appropriate manner for the best operation of the free piston engine. The independent motor 9 is controlled in such a way that the rotation of the cam 11 is substantially synchronous with the operation of the free piston engine, so that in normal operation the engagement between the cam 11 and the pusher 8 is only virtual and does not involve any resistance or transmission of energy. However, if the rod 5 tends not to stop at the preset stroke limit, the contact between the pusher and the cam becomes active and the stroke of the rod 5, with the pistons 3 and 4, is positively limited. Similarly, if one of the cylinders omits combustion and consequently is not able to activate the compression in the opposite cylinder, the pusher 8 enters into active cooperation with the cam 11, and the independent motor 9 of the latter provides the energy necessary to effect the compression, thus avoiding the stopping of the free piston engine. Likewise, starting the free piston engine can be carried out by the independent engine 9 when it is not desired to use compressed air systems or to use the linear alternator as a starting engine, as is customary for free piston engines.

Preferably, the independent motor 9 is controlled so that the cam 11 tends to slightly advance relative to the movement of the pusher 8, thereby avoiding any obstacle, under normal conditions, to the movement of the rod 5 and, by therefore, the operation of the free piston engine. Appropriate means, not shown, prevent the rotation of the rod 5 on itself in order to maintain the pusher 8 in the correct position of cooperation with the cam 11.

The cam 11 is provided with a balancing mass 10. This mass can be modified with respect to what is necessary for the balancing of the cam itself, with the aim of achieving partial balancing of the free piston engine, which by itself is not balanced.

The independent motor 9 must be of a type capable of providing greater torque if necessary, without appreciably changing its own speed. It may therefore be a bypass excitation motor, a metasearch engine or an electric motor provided with an appropriate electronic control device. Appropriate means can be used to disconnect the linear alternator during the periods in which the independent engine 9 must face the functional shortcomings of the free piston engine, so as to limit the load applied to the independent engine.

Figures 3 and 4 show an arrangement of two units similar to that shown in Figures 1 and 2, which in itself is balanced and requires a single cam for the service of the two units, further establishing a rigid synchronism between them. The two units, of which the one on the right is indicated by the same references of the unit described above, and the one on the left is indicated by corresponding references provided with an apex, are arranged symmetrically, with the pistons 3 and 3 ' opposite one another in a single central cylinder 1 '; the cam 12 (which in this case cannot be circular but must be substantially elliptical or oval) has at least one axis of symmetry and cooperates with the two pushers 8 and 8 ⁸ of the rods 5 and 5 '. In this case, either the free piston engine or the cam are in themselves balanced both statically and dynamically and do not require any balancing weight. For symmetry of construction and actuation, a second cam 12 ′, having its own independent motor 9 ′ or kinematically connected to the first cam 12, can be arranged as shown in FIG. 4.

It is clear that, by appropriately choosing the profile of the cam 11 or 12, it is possible to pre-establish for the pistons the stroke most indicated for the various functional effects, and, if desired, we can also influence the law of piston movement in order to regulate some phases, especially those of combustion and expansion. For the same purpose, instead of or in addition to the appropriate choice of the profile of the cam, provision may be made for actuation of the latter at variable speed by the independent motor 9, subject to appropriate electronic control and / or to periodic interruptions of food. By using in circuits You can also carry out a control which can vary depending on the operating conditions, for example depending on the load imposed on the linear alternators.

As is understood from the above, the load applied to the cam by the pushers, in the event of serious disturbances, can become very high, and this in correspondence of the points of maximum and minimum distance of the cam from its center. In order to avoid a massive and heavy construction of the cam in order to provide for necessities which can arise only rarely, it is possible to install, as shown in FIG. 3, support means 30 to the inside the cam, and outside of it, arranged so as to be touched by the cam during its normal rotation; in the event of a heavy overload, the cam undergoes a slight elastic deformation and bears against said means 30 and 31, thus discharging the excess stress received. The support means 30 and 31 may be with rollers, or they may also be fixed, in this case accepting the braking effect which they exert on the cam when the latter touches them; which does not seem serious considering the very low frequency of this event.

As an alternative, it is also possible to install limit stops for the stroke acting on the pushers 8, 8 'of the rods 5 and 5'.

Thanks to these measures, the cams can be projected with a view to their moderate normal load and not to the maximum foreseeable load in exceptional cases, such as for example rupture of the piston rings or the like. So. the cams can be of light construction, for example in ribbed sheet metal.

The motor according to the invention already having by itself high efficiency and high specific power, it is possible to produce according to the invention motors of reduced overall weight and size compared to normal motors of the same power, which, as is known, is of particular importance for industry.

Since a free piston engine generally requires to be installed with the cylinders in an at least approximately horizontal position, the weight of the pistons, rod and inductor of the linear alternator rests on one side of the cylinder wall, which could produce drawbacks, especially in large motors. In order to avoid this phenomenon, the invention provides for magnetic support of the mobile parts, as shown in FIG. 6. The rods 5 and S 'are provided, in this case, with sliding slides 13, 14, 13', 14 ' above supports 15, 16, 15 ', ₁ 6'; both the slides and the supports are permanently magnetized so that the respective homonymous poles are arranged one opposite the other and repel each other. By an appropriate design of these parts one can compensate, exactly or at least approximately, for the weight of the moving parts, and support them without introducing friction. The arrangement turns out to be particularly suitable when linear generators having several inductors and armatures are used, as shown in FIGS. 5 and 6, with the aim of obtaining from the alternators a current having a behavior closer to the sinusoidal behavior.

The invention can be applied to free piston engines both for carburetion and for injection of liquid or gaseous fuel and with spark or compression ignition. However, the invention also lends itself advantageously ment to the production of adiabatic motors powered by coal dust or other solid fuel. In this case, special provisions must be used either to obtain the engine's adiabaticity, or to promote the elimination of ash from combustion. Figures 7 and 8 show such arrangements respectively for a cylinder 17 with opposite pistons (corresponding to cylinder 1 'of the previous figures) and for an end cylinder 18. By 19 are indicated the respective air inlet orifices and by 20 are indicated the exhaust orifices, which pass through the walls of the cylinders 17 and 18 and their internal coatings 21 and 22 of ceramic material; by 23 is indicated the coal dust injector and the broken dashed lines indicate the path of the air flow from the inlet orifice 19 to the exhaust orifice 20. Near the latter is arranged a electrode 24 which, as soon as combustion has taken place, is supplied with a high electric voltage, so as to exert a strong electrostatic attraction on the ashes produced by combustion, which are attracted towards the exhaust orifice and then are expelled by the washing air flow. Preferably, the electrode 24 is then grounded in order to avoid phenomena of electrostatic attraction on the injected fuel dust, which could compromise its uniform distribution in the cylinder for combustion.

If the current produced by the linear alternators, which as a rule does not have a satisfactory sinusoidal behavior cannot be used as it is, as shown in figure 9 it can be sent from the generator rectifier 25 actuated by the motor according to the invention to a rectifier group 26 and then to a DC motor 27 coupled to a flywheel 28, downstream of which the energy produced can be used in any direct or indirect way, by example by driving an alternator 29 capable of supplying a sinusoidal current, or a metagenerator intended to supply traction meta-motors, and so on. The flywheel 28 provides torque uniformity, even in the event of a lack of some combustion in the cylinders. In addition, the flywheel can carry suitable ventilation vanes for cooling the linear alternator or other parts.

Although we have considered the typical case in which the free piston engine drives a linear alternator to produce electrical energy, it is clear that the engine according to the invention can also be used to directly produce mechanical energy , especially if this energy is used in alternative form, such as for compressors, pumps and the like.

Claims (10)

1.- Internal combustion engine with free pistons, specially for actuating a linear alternator, comprising at least one pair of opposite cylinders (1, 2) whose pistons (3, 4) are reciprocally connected by a rod ( 5) connected in an intermediate point to the movable element (6) of a linear alternator (7) or of another means of using the energy produced, characterized in that it comprises at least one cam ( 11, 12), actuated by an independent motor (9), in a substantially synchronous manner with the displacements of the rod (5) of the pistons (3, 4), and engaging with pusher means (8) connected to the rod (5) of the pistons (3, 4), so as not to give rise to a substantial transmission of energy during normal operation, but to limit the stroke of the pistons (3, 4) and to transfer to these last energy required for compression in case of abnormal operation of the free piston engine. 2.- Motor according to claim 1, characterized in that it comprises at least two units opposite one another each comprising two pistons (3, 4; 3 ', 4') opposite connected to each other by a common rod (5; 5 '), the cam (12) actuated by an independent motor (9) being arranged to engage with pusher means (8; 8 ') arranged on the rods (5; 5 ¹ ) of the two units so as to serve them all two and to establish a precise synchronization between them. 3.- Motor according to claim 1 and possibly 2, characterized in that it comprises several units each formed by two opposite pistons (3, 4; 3 ', 4'; ...), connected to each other by a common rod (5; 5 ¹ ; ...) and several cams (12; ...) with independent motor (9; ... which cooperate with pusher means (8; 8 '; ...) carried by these rods (5; 5 ¹ ; ...), the synchronization between the different units of the engine being carried out by means of the synchronization of the respective cams (12; ...) with independent engine (9; ...). 4.- Motor according to one or more of the preceding claims, characterized in that the cam (11, 12) with independent motor (9) is profiled so as to substantially follow the movement of the pushers (8, 8 ') during most of the cycle, entering into cooperation with them in specific periods in order to favorably modify the law of motion of the free piston engine. 5.- Motor according to one or more of the preceding claims, characterized in that the cam (11, 12) is set in non-uniform movement by its own independent motor (9), in order to favorably modify the law of movement of the piston engine free. 6.- Motor according to one or more of the preceding claims, characterized in that the system comprising the cam (11, 12), the respective pushers (8, 8 ') and the independent motor (9) is designed to also provide for the starting operation of the free piston engine. 7.- Motor according to one or more of the preceding claims, characterized in that it comprises support means (30, 31) arranged so as to be touched by the cam (12) during its normal rotation and to offer that -this support in case of excessive stress applied to the cam (12) by the pushers (8, 8 '). 8.- Motor according to one or more of the preceding claims, characterized in that the rods (5; 5 ') of the pistons (3, 4; 3', 4 '), arranged in a substantially horizontal position, are connected to slides. (13, 14; 13 ¹ , 14 ') sliding above supports (15, 16; 15 ¹ ; 16 ¹ ), said slides and said supports being magnetized with the homonymous poles arranged one opposite the other to support, by magnetic repulsion, all or part of the weight of the rods (5, 5 ¹ ), the respective pistons (3, 4, 3 ¹ , 4 ') and the inductors (6, 6') of the linear alternators (7, 7 ') or other means of using energy. 9.- Motor according to one or more of the preceding claims, characterized in that, when it constitutes an adiabatic motor with dust supply of a solid fuel, the cylinders (17, 18) are coated internally with a ceramic material (21, 22), with an electrode (24) installed near the exhaust port (20), said electrode (24) being arranged to be connected to a high electrical voltage after combustion in order to attract the ashes to the exhaust port (20), and to be grounded at least during the injection of solid fuel dust. 10.- Motor according to one or more of the preceding claims, characterized in that it comprises an electronic control device for regulating the action of the cam (s) (11, 12) with independent motor (9) in a differential manner depending on the momentary engine operating conditions.

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