US3194007A - Free piston gas generators - Google Patents

Description

July 13, 1 M. BOUVIER ETAL 3,194,007

FREE PISTON GAS GENERATORS Filed July 7, 1964 5? I37 I 36 Z1 Z0 3 31 E9 26' ]9;O J6 J4 in; J3

I77 I II 11.,

INVENTOR United States Patent Office 3,1943%? Patented July 13, 1955 3,194,007 FREE PISTON GAS GENERATORS Maurice Bouvier, Villeurbanne, and Auguste Moiroux,

Lyons, France, assignors to Societe dEtudes et de Participations, Eau, Gaz, Eleetricite, Energize S.A., Geneva, Switzerland Filed July 7, 1964, Ser. No. 380,833 Claims priority, application France, July 25, 1%3, 942,695 3 Claims. (Cl. 60-13) The present invention relates to free piston gas generators, or auto-generators, comprising a stabilizer serving to adapt the mass of air present in the return energy pneumatic accumulators (hereinafter called cushions) to the variations of the load under which the gas generator is working.

For this purpose, it is known to have the stabiliser controlled, on the one hand, by a factor depending upon the load of the gas generator, this factor generally being the pressure existing in the air reservoir, or casing, disposed between the compressor unit of the gas generator and the motor unit thereof, and, on the other hand, by a pressure characteristic of the cushion, or cushions, this characteristic pressure being for instance either the mean value of the instantaneous pressures existing in said cushion, or cushions, or a pressure collected from the cushion, or cushions, when the free piston, or pistons, is, or are, in a predetermined position with respect to the fixed unit of the gas generator.

It is also known to arrange the stabiliser in such manner, that, when the load of the gas generator increases, the mass of air in the cushion, or cushions increases so as to produce an increase of the final compression pres sure in the motor unit of the gas generator and inversely, which has for its effect to increase the number of reciprocations per unit of time of the generator pistons when the load of the generator increases and to reduce this number when this load decreases. Such a variation of the number of strokes of the pistons per unit of time permits of reducing the variations of length of said strokes which are necessary to take into account variations of the load under which the gas generator is working.

It is also known further to increase the variation of the final compression in the motor unit and, consequently, the variation of the number of strokes per unit of time, by connecting with that of the chambers of the stabiliser where the pressure is determined by the characteristic pressure of the cushion, or cushions, a leak the influence of which increases when the load of the gas generator increases and inversely. The object of this leak is to weaken the influence of the characteristic pressure of the cushion upon the stabiliser and to delay the resetting of said stabiliser into neutral position, where it closes the cushion or cushions. Up to the present time, this leak was controlled in response to variations of the length of the strokes of the free piston or pistons, and this in such manner that the leak, between two consecutive strokes of said piston or pistons, remained open the longer as .the stroke was longer. However this manner of controlling the leak involved some drawbacks. First it required maintaining a relatively important difference between the lengths of the strokes of the free piston or pistons. Furthermore it did not permit of compensating for the influence of some defects in fluidtightness capable 'of varying the control pressure acting in the stabiliser in response to variations of the characteristic pressure of the cushion.

The chief object of the present invention is to obviate this drawback.

The invention consists chiefly in having the diiference between, on the one hand, the characteristic pressure of the cushion, such as it exists in said cushion or just at the outlet thereof, and, on the other hand, the pressure depending upon this. characteristic pressure and acting upon the stabiliser, controlled by the member the position of which determines the amount of fuel injected into the motor unit of the gas generator.

Preferably the chamber of the stabiliser subjected to the effect of the pressure varying as a function of the characteristic pressure of the cushion is provided with a leak opening adapted to be opened or closed by an element moving together with the fuel regulating member, this opening being provided on a movable support which is subjected, on the one hand, to the characteristic pressure of the cushion at the outlet thereof, that is to say when it is not yet reduced by a disengagement of said leak opening and on the other hand to the pressure reduced by said disengagement or of the leak opening, a spring being further provided to add its action to that of said reduced pressure.

A preferred embodiment of the present invention will be hereinafter described with reference to the appended drawing, given merely by way of example, and which diagrammatically shows, in longitudinal section, a gas generator according to the invention.

Thus, the gas-generator illustrated in the drawing comprises at least one compressor cylinder 1 and one motor cylinder 2, and a piston assembly formed by a compressor piston 3 and a motor piston 4, which pistons operate in cylinders 1 and 2, respectively.

The part of cylinder 1 adjoining motor cylinder 2 is provided with inlet valves 5 and delivery valves 6, the latter being fitted in a partition 7 which forms the internal head plate of compressor cylinder 1 and which separates the same from a scavenge air reservoir 8 forming a casing surrounding motor cylinder 2. The compressor cylinder proper is formed by a chamber or located between piston 3 and partition 7. On the other hand, the pneumatic return energy accumulator or cushion is formed by a chamber b located between the head 9 of compressor cylinder 1 and compressor piston 3.

Intake ports 10 and exhaust ports 11, controlled by motor piston 4, are provided in the wall of motor cylinder 2. Connected to the exhaust ports 11 is an exhaust pipe 12 through which the power gas constituted by the excess of scavenging air and the combustion gas of the motor cylinder is conveyed to a receiving machine such as a turbine (not shown).

Motor cylinder 2 is fitted with a fuel injector 13 supplied from an injection pump 14 through a pipe 15. The compression which is produced in motor cylinder 2 when the piston assembly 3, 4 has terminated its inward stroke (to the right in the drawing) is high enough for the fuel injected by injector 13 to be ignited by the heat of compression alone without the use of any special ignition device. The motor unit is a two-stroke engine operating on the diesel principle.

In the gas-generator illustrated in the drawing, injection pump 14 is driven by means of a rocking lever 16 oscillating about an axis 17 and which is driven by the piston assembly 3, 4 through the agency of rod 18 and link 19.

For the sake of simplicity in the description and drawing, a gas-generator having only one piston assembly 3,

4 has been described and illustrated but, as is usual .in

practice, the gas-generator will generally comprise two such assemblies which move in opposed directions in a single motor cylinder, the compressor pistons operating in compressor cylinders disposed on either side of the motor cylinder. Of course, the invention is applicable to the latter kind of gas-generator.

The means for controlling the quantity of fuel injected into motor cylinder 2 comprise a regulating member 20 which determines the quantity of fuel delivered per cycle by pump 14 and injected through injector 13'. In known 'manner, said member 20 consists of a toothed rack which operates the piston (not shown) of the piston pump. Rack 20is' controlled, in known manner, to increase or decrease'the fuel delivery by means, of a regulator (not shown) driven by the receiving machine (turbine) and acting on ,said rack 20 through a linkage, or, through hydraulic, electrical, or other means, in dependence upon the speed of the' receiving rtnach'ine. However, this control in dependence upon the speed of the receiving machine must remain within limits whose values. are dependent upon the, operating pressure, or a similar operating factor, of the gas-generator, such limits being defined by a lever 21 adapted to rotate around a spindle 22 and having one of its ends articulated to the control linkage of member I .20, the other end of the lever 21. comprising two cam surfaces 23, 24 and a stop 25 being provided between said cam surfaces 23and 24, the position of thestop 25 beingcontrolled by means tobe described hereinafter. The amount of air in cushion b is controlled by a device, known as a stabiliser and comprising a hollow slide valve 26 adapted to move in.a cylinder 27 disposed inside casing 8., Slide valve 26 is divided by a partition into two chambers, one of which is provided with check valves 28 which only open in such a Way as to allow the passage of air from the casing 8' into slide valve 26 while the check valves '29; of the other chamber open only in the opposeddirection so that air can flow out of slide valve 26 into the casing 8. The lateral wall of each of the two chambers is formed with an aperture 30, 31, these apertures serving, according to the axial position of slide valve 26, to connect one or the other of the last mentioned chambers to a pipe 32 connecting cylinder 27 with a cushion b. Slide valve 26, inits central position (that shown in the figure), cuts off its two chambers completely from pipe 32. Thus, according to its axial position, slide valve 26 either allows air to escape from cushion b into casing "8 through check valves 29 or permits-air to I return from casing 8 into cushion b through check valves 28 or it causes the quantity of air in accumulator b to be maintained constant. 7 V s The stabiliser just described is controlledon the one hand by. the action of the pressure existingin casing and on the other-hand by'the action of a pressure depending upon a characteristic pressure of cushion b and lower than it. The above mentioned characteristic pressure may be for instance either the mean pressure of the cushion or the pressure existing therein when piston occupies a given position. These pressures act upon ,a stepped differential piston-33 rigidly secured to slide valve 25 and one '5 of the surfaces .9; of which is subjected to the pressure depending upon the characteristic pressure of cushion b whereas its other surface s issubjected to the pressure existing in casing 8. Piston 33 is disposed in a cylinder 34 to which are connected, on the'one hand, a pipe 35 for placing the top of cylinder 34 in communication with casing 8 and, on the other hand a pipe 36 through which the pressure existing in casing 8, increases, and vice .versa,

In order further to increase this eifect, the area a, of

piston'33 is subjected, not directly, to said characteristic pressure of the cushion but. to apressure depending upon said characteristic pressure and lower thancit, the difference between the characteristic pressure and the pressure deduced therefrom increasing when the load of the pressure generator increases and decreasing in the reverse case.--'-'- In the embodiment illustrated by the drawing, the characteristic pressure of cushion bis equal to the meanvalue passage 33. through conduit 36 to the surface s pf piston 33 to a of the instantaneous pressures existing in said cushion. For this purpose, there, is connected with cushion b a conduit 37 communicating with conduit -36 through a throttled In order to reduce the pressure transmitted value below the mean pressure in cushion b, a shunt conduit 39 is connected to conduit 36'downstream of throttled passage38. This shunt conduit 39 leads to a leak opening 40 itself controlled by a sleeve 41 operatively cono nected with therack 20 serving to control the amount of fuel injected into the power, cylinder 2 of thepressure generator. The'means forcontrolling leak orifice 40 are arrangedin such manner as to produce between, on the one, hand, the pressure acting upon the surface s of piston '33 and, on the other hand,'the mean value of the. in-

stantaneous pressures of cushion b a difference which is the more important as the position of rack corresponds to a more important amount of fuel injected into motor cylinder 2 at the end of every inward stroke of 20 pistons 3- 4.

v For this purpose, leak orifice 401is provided at the end of a conduit142 formed 'in'a rod 43 and the end 1 of which opposed to leak orifice 40 opens into a chamber A 45 which is connected, through conduit 39, with conduit 36. Rod 43 is controlled bya piston46 movable in a cylinder 47 the lower portions of whichforms said chamber '45. Piston 46' has one ofits sides subjected to the action of the pressure existing in chamber 45 and its other side subjected to the action of the characteristic pressure of cushion b. In the embodiment illustrated by the drawing, this characteristic pressure is transmitted to space 48, disposed inside cylinder 47 above piston 46, through a'conduit 49 br anching ofi' from conduit 37 at a point up- 'stream of throttled passage 38 so that the pressure in space 48 is substantially equal to the mean pressure of cushion b. V

Rod 43 is further subjected to the action of a spring 51. One. of the ends of this spring 51, bears against the under face of the head 52 of rod 43, whereas the other end of spring 51 bears against the fixed bottom 53 of cylinder 47. This spring 51, by keeping the head 52 of rod 43 constantly applied against piston 46, acts on the latter in the same direction as the pressure existing in chamber 45. a a

As already stated, the amplitude of the movements of ,rack 20v is limited by abutment 25 whichfis located between cam surfaces 23 and 24. However, this limitation 'must vary with the pressure existing in casing 8. For this. purpose 'abutment'25is supportedby one end of O a rod 54, the other end of which is secured to a piston 56 movable in acylinder 57'. This cylinder isconnected through a conduitl58; to conduit 35, so that the pressure in casing 8 acts on one of the sides of piston 56 the other side of which is subjected to the action of a r eturn spring 59.

' The operation of said means for controlling the leak is asfollows: v I

When, due to an increase of the load of the plant to which the pressure generator belongs, rack 26 is moved,

, 6 for instance, by the. regulating device of the turbine to which the gases from the generator are fed, in the direction of the arrow this displacement produces, on the one hand, an increase of the'amount of fuel injected into the power cylinder and, on the other hand, a displacement of sleeve 41 so. that the free section of leak opening v40 is increased. a r

' This increase of the amountof fuel that is injected produces an increase of the pressure in the casing, whereby the stabilizer is displaced in a direction which permits compressed air to flow through conduit 32 into cushion b.

w On-the other hand the increase of the cross section of leak orifice 40 causes the pressure to drop in chamber 45, so that piston 46,under'the effect of'the characteristic'pressure in cushion b which has not decreased, transmitted to space'48, moves in the downward direction together with rod 43, thus compressing spring 51. This displacement again reduces the cross section of leak 40. Of course the inflow of air into cushion b increases the characteristic pressure therein (in this case the mean pressure therein), which causes a rise of the pressure both in chamber 45 and in space 48. However the difference between the respective pressures in said chamber and said space increases more and more as rack 20 is moved in direction in view of the fact that when a new state of equilibrium is reached the compression of spring 51 has increased. This results from the fact that in order to have piston 46 once more in the balanced state it is necessary to have P being the pressure force exerted by the characteristic pressure of cushion b in space 48 upon piston 46, P being the pressure force exerted in chamber 45 upon said piston 46 by the pressure therein, which is reduced by the existence of the leak orifice 40 and R being the force exerted by the spring upon orifice 40 and R being the force exerted by the spring upon piston 46. Consequently the greater the value of R the higher the difference between P and P In view of the fact that P (pressure derived from the mean pressure) is at the same time the pressure acting upon the surface s of piston 33 it follows that this pressure P is the smaller with respect to the mean pressure of the cushion as rack 20 has been moved to a greater distance in the direction corresponding to an increase of the amount of fuel that is injected.

It should be reminded here that, in the case of an increase of the mass of air into cushion b, the increase of the pressure derived from the characteristic pressure in said cushion b and acting upon the surface .9 of piston 33 is intended to bring the movable element 26 of the stabiliser into the neutral position, where it closes conduit 32 after a given mass of air has flown into cushion b. Owing to the present invention, this closing is delayed and the mass of air that is admitted into cushion b is increased with respect to what would take place if the characteristic pressure acted directly upon the surface s of piston 33 instead of making use of the pressure reduced by leak orifice 40. This increase of the mass of air is the more important as the displacement of rack 2% in direction is greater.

In case of a decrease of the load of the pressure generator, the result is reversed. This means that the difference between the characteristic pressure of the cushion and the pressure derived from said characteristic pressure decreases when the load decreases.

The invention has many advantages.

First it permits of reducing the variations of length of stroke of the free pistons as much as it may be desired. Furthermore, there is obtained an automatic compensation of the uncontrollable leaks which might have an influence upon the pressure acting upon the surface s of piston 33. These leaks may take place for instance between the two chambers limited in cylinder 34 by surfaces s and s either at the place where the rod that connects piston 33 with sliding member 26 passes through the end wall of cylinder 34, or at the place where rod 43 extends through the end wall 53 of chamber 45', or again between spaces 45 and 48 which are separated from each other by piston 46 in cylinder 47.

In view of the fact that, in the balanced state of the system, leak orifice 40 is always slightly open, the existence of uncontrollable leaks merely has for its effect slightlyto reduce the free cross section of opening 40, this reduction being the more important as the noncontrollable leaks are also important.

Finally, another advantage consists in the fact that the mass of air of the cushion cannot undergo too quick variations since the amplitude of the movement of sleeve 41 which controls leak orifice 4G is limited in the same manner as the amplitude of the movements of rock 20 6 itself by the cooperation of abutment 25 with cam surfaces 23-24.

According to a modification, the part which controls the free section of leak orifice 40 is actuated through the means, generally consisting of a variable pressure liquid for transmitting the control pulses of the regulating device of the turbine fed by the pressure generator to the part (generally rack 20) which determines, by its position, the amount of fuel injected to the motor unit of the gas generator.

In a general manner, While the above description discloses what is deemed to be a practical and eflicient embodiment of the present invention, said invention is not limited thereto as there might be changes made in the arrangement, disposition and form of the parts without departing from the principle of the invention as comprehended within the scope of the appended claims.

What we claim is:

1. A free piston auto-generator which comprises, in combination, a motor unit and a compressor unit, said motor unit including two motor elements, a motor piston and a motor cylinder, one movable in the other to form between them a variable volume fuel combustion chamber, fuel feed means opening into said fuel combustion chamber, means for controlling said fuel feed means, said compressor unit including two compressor elements, a compressor piston and a compressor cylinder, one movable in the other, each of said compressor elements being fixed with respect to one of said motor elements, respectively, a casing fixed with respect to said motor cylinder, for feeding compressed air thereto, said compressor elements forming between them an air compression chamber, check valve means for admitting air from the atmosphere into said air compression chamber on every increase of volume of said air compression chamber, check valve means for delivering compressed air from said air compression chamber to said casing on every reduction of volume of said air compression chamber, said compressor elements forming between them an air cushion chamber the volume of which is reduced on every increase of volume of said fuel combustion chamber, whereby expansion of said air cushion produces every return stroke of said motor piston, a conduit having one end thereof in communication with said air cushion chamber, a stabiliser valve mounted to control the communication between the other end of said conduit and said casing, said stabiliser valve including a cylindrical housing, a hollow slide valve slidable in said casing and having a neutral position therein and check valve means carried by said slide valve arranged to open a unidirectional communication from said casing to said conduit when said slide valve is moved in one direction from said neutral position thereof and a undirectional communication from sad conduit to said casing when said slide valve is moved in the other direction from said neutral position thereof, means operative by a pressure at least substantially proportional to the pressure in said casing for urging said slide valve in said first mentioned direction, means forming a space containing air under pressure supplied from said air cushion chamber, means operative by the pressure in said space for urging said slide valve in said second mentioned direction, variable air leak means in communication with said space and means for controlling said air leak means operative by said means for controlling said fuel feed means, said means for controlling said air leak means being arranged to tend to increase the free cross section of said air leak means when said means for controlling said fuel means is caused to increase the feed of fuel and to tend to reduce said free cross section when the feed of fuel is decreased.

2. A free piston auto-generator which comprises, in combination, a motor unit and a compressor unit, said motor unit including two motor elements, a motor piston and a motor cylinder, one movable in the other to form between them a variable volume fuel combustion chamber, fuel feed means opening into said fuel combustion chamume of said air compression chamber, check valve means for'delivering compressed air from said air compression chamber to said casing on every reduction of volume of said air compression chamber, said compressor elements forming between them an air cushion chamber the volume of which is reduced on every increase of volume of said fuel combustion chamber, whereby expansion of said air cushion produces every return stroke of said motor piston, a conduit having one end thereof in communication with said air cushion chamber, a stabiliser, valve mounted to control the communication between'the other end of said conduit and said casing, said'stabiliser'valve including a cylindrical housing, a hollow slide valve slid.-

able in said casing and having a neutral position therein and check valve means carried by said slide valve arranged to open a unidirectionl communication from said casing to said conduit when said slide valve is moved in one direction from said neutral position thereof anda unidirectional communication from said conduit to said casing when said slide valve is movedrinrthe other direction from said neutral position thereof, means operative by a pressure at'least substantially proportional to therpressure in said casing for urging said slide valve in said first men- 8 said compressor unit including two compressor elements, a compressor piston and a compressor cylinder, one movable-in the other, each of said compressor elements being fixed with respect toone of said motor elements, respectively, a casing fixed with respect to said motor cylinder for feeding compressed air thereto,said compressor elements forming between them an air compression chamberycheck valve means for admitting air from the atmosphere into said air compression chamber on every intioned direction, means forming a space; means for feed- 7 ing said space with air under a pressure variable in the same way as the mass of air insaid cushion chamber,

means operative by the pressure in said space for urging said slide valve in said second mentioned direction, a cylinder fixed with respect to said casing, a piston fitting slidably in said last mentioned cylinder and dividing itinto two chambers, a first one ,and a second one, conduit means for connecting said first chamber with said air cushion, conduit means for connecting said second chamber with said space, a rod slidable axially in said last mentioned cylinder, said rod bearing against said last men'- limiting'said second chamber, one end-of said rod bearing against said piston, a spring interposed between said end of said rodand said end wall of said last mentioned cylinder for urging said last mentioned piston in the same direction as the air pressure in said second chamber, a

crease ofyolume of said air compression chamber, check valve means for delivering compressed airfrom said air compression chamber to said casing on every reduction of volume of said air compression chamber, said compressor elements forming between them an air cushion chamber the volume of which is reduced on every increase of volume of said fuel combustion chamber, whereby expansion of said air cushion produces every return stroke 7 ofrsaid motor piston, a conduit having one end thereof in communication with said air cushion chamber, a stabiliser valve mounted to control the communication between the other end of said conduit and said casing, said stabiliser valve including a cylindrical housing, a hollow slide valve slidable in said casing and having a neutral position therein andcheck ,valve means carried by said slide valve arranged to open a unidirectionalcommunication from said casing ,to said conduit when said slide valve is moved in one direction from said neutral position thereof and a unidirectional communication from said conduit to said casing when said slide valve is moved inthe other direction from said neutral position thereof, means operative by a; pressure at least substantially proportional to the pressure in said casing for urging said slide valve in said first mentioned direction, means forming a variable volume space, conduit means between said space and said air cushion chamber including a throttled section, means operative by the pressure in said space for urging said slide valve in said second mentioned direction, a cylinder fixed with respect to said casing, a piston fitting slidably in said last mentioned cylinder and dividing it into two chambers, a first one and a second one, conduit means for connecting said first chamber with said air cushion chamber, said last vmentioned conduit means including a throttled section, conduit means for connecting said second chamber with said space, a rod slidable axially in said last mentioned tioned piston, said rod extending slidably with a fiuidtightfit through the end wall of said last mentioned cylinder:

cylinder, said rod bearing against said last mentioned piston, said rod extending slidably witha fiuidtight fit through the end Wall of said 'last mentioned cylinder limiting said second chamber, one end of said rodbearing against said piston,a spring interposed between said end of said rod and said end wall of said last mentioned cylinder for urging said last mentioned piston in the same direction as the air pressure in said second chamber, a sleeve slidably sleeve slidably fitting on said mama rod being provided with a longitudinal conduit having at one end thereof an opening in said second chamber and at the other end thereof an opening adjacent'to said sleeve so as to be controlled by it, and means for operatively connecting said sleeve with said means for controlling said fuel feed means arranged to tend to reduce the freecross section of said second mentioned opening when said means for controlling said fuel feed means is moved in the direction,

tending to reduce the feed of fuel and to tend to increase said free cross section when the feed of fuelfis caused to be'increased. i I

. 3. A free piston auto-generator which comprises, in combination, a motor unit and a compressor unit, said motor unit including two motor elements, a motor piston and a motorvcylinder, one movable in the other to form between them a variable volume fuel combustion chamber, fuel feed means opening into said fuel combustion chamber, means for controlling said fuel feed means,

fitting on said rod, said rod' being provided'witha longitudinal conduit having at one end thereof an opening in said, second'chamber' and at the other end thereof an opening adjacent to 'said sleeve so as to be controlled by it, and means for operatively connecting said sleeve with said .means for controliing'said fuel feed means arranged to tend to reduce the free cross section of said second mentioned opening when said means for controlling said fuel feed means is moved in the direction tending to reduce the feed of fuel and to tend to increase "said free cross section when the feed of fuel is caused to be increased.

References Cited by the Examiner UNITED STATES PATENTS i 3,038,298 6/62 Horgen 6()-13

Claims (1)

1. A FREE PISTON AUTO-GENERATOR WHICH COMPRISES, IN COMBINATION, A MOTOR UNIT AND A COMPRESSOR UNIT, SAID MOTOR UNIT INCLUDING TWO MOTOR ELEMENTS, A MOTOR PISTON AND A MOTOR CYLINDER, ONE MOVABLE IN THE OTHER TO FORM BETWEEN THEM A VARIABLE VOLUME FUEL COMBUSTION CHAMBER, FUEL FEED MEANS OPENING INTO SAID FUEL COMBUSTION CHAMBER, MEANS FOR CONTROLLING SAID FUEL FEED MEANS, SAID COMPRESSOR UNIT INCLUDING TWO COMPRESSOR ELEMENTS, A COMPRESSOR PISTON AND A COMPRESSOR CYLINDER, ONE MOVABLE IN THE OTHER, EACH OF SAID COMPRESSOR ELEMENTS BEING FIXED WITH RESPECT TO ONE OF SAID MOTOR ELEMENTS, RESPECTIVELY, A CASING FIXED WITH RESPECT TO SAID MOTOR CYLINDER, FOR FEEDING COMPRESSED AIR THERETO, SAID COMPRESSOR ELEMENTS FORMING BETWEEN THEM AN AIR COMPRESSION CHAMBER, CHECK VALVE MEANS FOR ADMITTING AIR FROM THE ATMOSPHERE INTO SAID AIR COMPRESSION CHAMBER ON EVERY INCREASE OF VOLUME OF SAID AIR COMPRESSION CHAMBER, CHECK VALVE MEANS FOR DELIVERING COMPRESSED AIR FROM SAID AIR COMPRESSION CHAMBER TO SAID CASING ON EVERY REDUCTION OF VOLUME OF SAID AIR COMPRESSION CHAMBER, SAID COMPRESSOR ELEMENTS FORMING BETWEEN THEM AN AIR CUSHION CHAMBER THE VOLUME OF WHICH IS REDUCED ON EVERY INCREASE OF VOLUME OF SAID FUEL COMBUSTION CHAMBER, WHEREBY EXPANSION OF SAID AIR CUSHION PRODUCES EVERY RETURN STROKE OF SAID MOTOR PISTON, A CONDUIT HAVING ONE END THEREOF IN COMMUNICATION WITH SAID AIR CUSHION CHAMBER, A STABILISER VALVE MOUNTED TO CONTROL THE COMMUNICATION BETWEEN THE OTHER END OF SAID CONDUIT AND SAID CASING, SAID STABILISER VALVE INCLUDING A CYLINDRICAL HOUSING, A HOLLOW SLIDE VALVE SLIDABLE IN SAID CASING AND HAVING A NEUTRAL POSITION THEREIN AND CHECK VALVE MEANS CARRIED BY SAID SLIDE VALVE ARRANGED TO OPEN A UNDIRECTIONAL COMMUNICATION FROM SAID CASING TO SAID CONDUIT WHEN SAID SLIDE VALVE IS MOVED IN ONE DIRECTION FROM SAID NEUTRAL POSITION THEREOF AND A UNDIRECTIONAL COMMUNICATION FROM SAID CONDUIT TO SAID CASING WHEN SAID SLIDE VALVE IS MOVED IN THE OTHER DIRECTION FROM SAID NEUTRAL POSITION THEREOF, MEANS OPERATIVE BY A PRESSURE AT LEAST SUBSTANTIALLY PROPORTIONAL TO THE PRESSURE IN SAID CASING FOR URGING SAID SLIDE VALVE IN SAID FIRST MENTIONED DIRECTION, MEANS FORMING A SPACE CONTAINING AIR UNDER PRESSURE SUPPLIED FROM SAID AIR CUSHION CHAMBER, MEANS OPERATIVE BY THE PRESSURE IN SAID SPACE FOR URGING SAID SLIDE VALVE IN SAID SECOND MENTIONED DIRECTION, VARIABLE AIR LEAK MEANS IN COMMUNICATION WITH SAID SPACE AND MEANS FOR CONTROLLING SAID AIR LEAK MEANS OPERATIVE BY SAID MEANS FOR CONTROLLING SAID FUEL FEED MEANS, SAID MEANS FOR CONTROLLING SAID AIR LEAK MEANS BEING ARRANGED TO TEND TO INCREASE THE FREE CROSS SECTION OF SAID AIR LEAK MEANS WHEN SAID MEANS FOR CONTROLLING SAID FUEL MEANS IS CAUSED TO INCREASE THE FEED OF FUEL AND TO TEND TO REDUCE SAID FREE CROSS SECTION WHEN THE FEED OF FUEL IS DECREASED.

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