US2408089A - Internal-combustion engine - Google Patents

Description

sepr.j24, 194s.

F. A. MuNTz n INTERNAL-COMBUSTON ENGINE Filed'v Feb. 27, 1943 3 Sheets-Sheet 1 IIIA .TI l

lNvE Nirofi F. A. l. MUNTZ .l INTERNAL-CMBUSTION ENGINE Filedrebf 27, 1943 Sept. 24, 1946.

Fig. -10.

.3 Sheets-Sheet 5 rtion of this gas-generator.

Patented Sept. 24, 1946 assignor to Alan Muntz & Company Limited, a company of Great Hounslow, England,

Britain Application February 27, 194s, serial No. 477,395 In Great Britain February 12, 1942 13 Claims.

This invention relates to internal-combustion operated reciprocating machines of the kind in which a power piston and a compressor piston are connected together for operation in unison, the

movement of this piston assembly being so-cony trolled that the inner dead point of the power piston is not mechanically fixed. Such a machine may be of the completely free-piston type, in which neither the inner nor the outer dead point is so fixed, or of the semi-free-piston type as exemplied in British patent to Pescaral No. 557,206. The invention is especially, but not exlclusively, concerned with internal-combustionwith reference to some of the accompanying drawings, in which:

Fig. 1 is a diagrammatic sectionalside elevation of an opposed-piston type of internal-combustion-operated compression-ignition gas-generator generally of-known type, but modified in V accordance with this invention, the section being generally in a vertical plane, but the middle part being taken on the line I-I in Fig. 6.

Figs. 2 to 5 are graphs illustrating the opera- In .each of these graphs the abscissa shows working pressure P in lbs. per sq. in. absolute, while "the Yabsciss'a meets the ordinate scale at the zero point of the latter.

Fig. 6 is a cross section on the line 6-6 in Fig. 1 drawn to alarger scale in rather less diagrammatic form. i

Fig. 7 shows diagrammatically part of a control system of the same gas-generator.-

Fig. 8 is a diagrammatic sectional sideA elevation 2 let 'ports I2 and exhaust ports I3. The `power cylinder is mountedV co-aXially within a cylindrical casing I4 which forms the shell of a scavenge air receiver I communicating directly with the inlet ports I2. Theexhaust ,ports I3 are connected by a manifold I6 to a delivery connection I1 for the motive gas, which communicates with the inletconnection of va turbine (not shown). On the end wallsIBA and IBB of the scavenge air receiver are mounted, co-axially with the power cylinder I0, combined compressor and cushion cylinders ISA and ISB co-operating with pistons 20A and 20B which are rigidly couof the middle part of an alternative form of gasgenerator embodying this invention. Y Fig.'9 is a diagrammatic sectional end elevation ofV the cushion control gear of the gas-generator shown in Figs. 1 and 6, taken on the line 5 9 in Fig. 10, and

Fig. 10 is a section on the line I 0-I0 in Fig. 9. The gas-generator shown in Fig. 1 has a power cylinder I0 co-operating with opposed power pistons IIA and IIB which control respectively inpled by rods ZIA and ZIB to the power pistons IIA and IIB respectively. The inner portions'of the cylinders I9A and ISB act as scavenge air compressors, being provided with inlet valves, such as 22A and 22B, and delivery valves, 'such as 23A and 23B, the latter delivering directly to the scavenge air receiver I5. The outer portions of the cylinders IBA and IBB serve as pneumatic cushions which during each expansion stroke of the power pistons IIA and VI IB store the energy necessary to return the free-piston assemblies through the following stroke when the compressor portions perform 'their delivery stroke and the power pistons their compression stroke.

The opposite movements of the free-piston assemblies are synchronised by a known system including two levers 24 and 24' capable oi oscillating equally. and oppositely about a common transverse axis. Thev ends of the lever 214 are rcoupled by connecting rods 25Avr and 25B to crossheads 26A and 26B fixed respectively on the piston rods 2IA and ZIB. The ends of the lever 24 are similarly coupled to the cross-heads 26A and' 26B by connecting rods 25'A and 25B. IThe piston assemblies are prevented from. rocking about the axis of the cylinders by arms 21A and 21B co-operating with slide bars 28A and 28B on the casing I4. A fuel-injection nozzle is denoted; by 29.

This gas-generator, as vso far described, is of known type and is adapted to operate in known. manner as follows. Starting fromthe coni-lguration shown in Fig. 1, the combustion products Y will have been swept from the power cylinder by air entering the inlet ports I2; some oi this air will follow the combustion products through Ythe exhaust ports I3; and the working pressures inr the receiver I5 and in the power 'cylinder I0, will be substantially equal to the pressure at which the motive gas is delivered by the gas-generator at the connection I'I. Thev two piston assemblies are rnow driven towards each other 3 by expansion of the cushion air compressed in the outer ends of the cylinders ISA and I9B and during this in-stroke the pistons 20A and 23B deliver compressed air through the valves 23A and 23B to the scavenge air receiver I5 while the power pistons i IA and I IB compress a charge of air in the power cylinder. As the piston assemblies approach their inner dead point, a charge of fuel is introduced through the injector 23. Combustion of the fuel is eiected by compression ignition, and the expansion of the combustion products in the power cylinder assisted by expansion of the air compressed in the clearance spaces at the inner ends of the cylinders ISA and IQB, drives the piston assemblies apart, the major part of the energy thus imparted to these assemblies being stored in the air cushions. Finally the piston I IB uncovers the exhaust ports I3, and a little later the piston I IA uncovers the inlet ports I2 ,the cycle thereafter being repeated. It will thus be apparent that compression of the working charge of air takes place in two stages: rst from atmospheric pressure to receiver pressure in the compressor cylinders IgA and I3B; and second from receiver pressure to nal comn pression pressure in the power cylinder I0.

1n such a gas-generator the working pressure, namely the delivery pressure of the motive gas at the connection I'l, and with it the charging pressure existing in the receiver I5, vary, with the load imposed on the generator by the varying demand of the turbine, over a substantial pressure range, for example up to '70 lbs. per sq. in. As a substantially constant iinal compression pressure in the combustion space of the power cylinder II) is desirableover the working range, it follows that the compression ratio of that part of the compression which takes place in the power cylinder I varies. As the working pressure increases, so does this compression ratio decrease, and consequently the pistons at the inner dead point are farther apart, or farther away from the middle of the cylinder. Fig. 2 shows by the full line how the distance (plotted as ordinate) of the inner dead point (IDP) of the heads of the pistons IIA and IIB from the middleY of the power cylinder Varies with working pressure P. The clearance volume of the inner end of the compressor cylinders ISA and ISB at the inner dead point must also increase as the working pressure increases, and assuming the outer dead point of the pistons to be constant, the result will be that the volume V of air delivered by the compressor pistons per stroke will fall as the working pressure increases, as is indicated by the full line in Fig. 3. Fig. 4 shows by the 'full line how the total volume VT of air delivered per unit time varies with the working pressure, while the full line in Fig. 5 is a curve plotted in terms of horse-power in the motive gas (G. H. P.) over the same range.

An object of this invention is to provide an improved internal-combustion machine of the kind specied and adapted to work with a varying charging pressure, in which means are provided for reducing variations in the inner dead point of the free pistons, or alternatively in the final compression pressure in the power cylinder, due to variations in charging pressure, whereby the output can be increased, as compared with known machines, over the higher range of charging pressures.

A further object is to provide a free-piston gas-generator in which the compressor part performs its delivery strokes simultaneously with the compression strokes in the motor part, under the influence of energy taken from the free pistons during each expansion stroke inthe motor part and stored in a pneumatic energy accumulator for return to the free pistons during the immediately succeeding stroke, and in which nevertheless the clearance volume in the compressor cylinder at the inner dead point is not undesirably increased as the working pressure rises.

Further objects of the invention will be apparent from the following description of two specific embodiments thereof.

Some of the novel features, provided in accor-:lM ance with this invention, of the generally known gas-generator shown in Fig. l will now be described with reference to Figs. 1 and 6. riwo auxn iliary chambers 36 and 3S are adapted to co1nmunicate with the middle part of the power cylinder It), which forms the main combustion chamber, by ports 3l and 3l. These two chambers are diametrically opposed in the medial transverse plane of the power cylinder, and their axis is inclined to the axis of the synchronising levers 24 and 2A in such a manner as to ac commodate also in the same plane two diametrically opposed fuel-injection nozzles 2S and 29', one of said chambers and one of said nozzles being on one side of the lever axis, and the other of each on the other side. As these chambers are identical, only chamber 3!) will be described in detail.

The port 3| is formed in a cup 32 of heatresisting metal iitted with clearance in a socket 33 in the power cylinder Ill, which is tted within a cylinder housing 34. A domed cover 35, secured to the housing 34 by screw studs 36, cooperates with the cup 32 to. form the auxiliary chamber 30. A poppet valve 3l has a face 33 adapted to engage a seating 39 surrounding the port 3! at its side within the cup. The stem of the valve 31 passes through a gland Mi in the cover 35. At the inner end of the gland is a seating 4I, adapted to be engaged by a face 42 on the head'of the valve 37. The valve stem is fixed to a piston 43 operating in a double-acting servo-motorv cylinder 44 and urged towards the axis of the power cylinder lil by a helical cornpression spring 45. Oil transfer pipes 43 and 41 communicate with the 'cylinder Irl on the outer and inner sides respectively of the piston 43.

When the working pressure of the gas-generator is low, oil pressure is released (in a manner hereinafter described) in the pipes 47 and may be applied to the pipes |45 from a source 139 (Fig. 7) of oil at constant pressure, which provides the energy for operating the servo-motors, in order to supplement the action of the springs 45, with the result that the valves 37 are held on the seatings 39, and so isolate the auxiliary chambers 30 and 30 from the main combustion chamber. The gas-generator now operates in the normal way. When the working pressure rises to a predetermined value, oil pressure is released in the pipes 46 and applied to the pipes 4l, so that the valves 31 are disengaged `from the seatings 39 and held on the seatings "il adjacent to the glands 4I). As a result the auxiliary chambers are put into communication with the main combustion chamber. Now the total volume of the combustion chamber at the inner dead point, namely the volume to which the air charge is compressed, will remain the same as in engine not having the auxiliary chambers but otherwise '5 equivalent,V but that portion of vit .contained in the main combustion chamberv will be reduced by the volume of the auxiliary chambers. The result is that the pistons will come closer together at the inner dead point than they would have done in the absence of the auxiliary chambers,. and consequently the clearance volumes at the inner ends of the cylinders 9A and |9B will also be kept small, instead of increasing with increasing working pressure so that the volume of free air delivered by the compressor portion will be largely maintained as the working pressure rises. The dotted lines in Figs. 2 to 5 show the periormance when the auxiliary chambers are operative and indicate how the output is increased over the range of higher working pressures.

If the machine were run withthe auxiliary chambers operative when the working pressure was low, there would be a risk of the power pistons touchingeach other at the innerd'ead point. Consequently it is desirable to provide control pressure is applied from the scavenge air receiver through an orifice 58 to a pressure-responsive bellows |00. A spiral cam 53 fixed on the shaft 60 of the synchronising lever 24 actuates a tappet 6|, the displacement of which is directly proportional to the displacements ofthe free-piston assemblies; therefore variation in the inner dead point of the tappet stroke is also diy rectly proportional to variation in the inner dead mechanism which ensures that the auxiliary point of the free-piston assemblies. The tappet actuates a device |0| having an output member |02 .which is adapted to follow variations in the inner dead pointof the tappet. The inner-deadpoint follower |0| and the bellows |00 are arranged to control the cushion air content through a differential mechanism consisting of a lever |03 having its ends operatively connected by rollers |04 and |05 to cross-heads |06 and |07 on the Y output members of the follower |0| and the bellows |00. The lever |03 is pivoted to a slide bar |08 which is connected by a multiplying lever |09 to a hydraulic relay. This relay consists of a double-acting piston Ill]l operating in a cylinder under control of a valve4 I2. This valve is actuated by a floating levei1 H3 which is connected by a link l |4 to the multiplying lever. |00

and which derives a return motion from the piston ||0'by means of a pin-and-slot connectial opening of the valves-31 during the period Y of peak pressure. The control mechanism shown to the source 49 of oil Yunder pressure-,and ,the

pipes 41 to a sump, and in an alternative position to connect the pipes 41 to the sourcer49 andthe pipes 46 .to the sump. The valve 48 is controlled by a piston 50 operating in acylinder 5|. The

piston 50 is biased by a spring 52 towards the position shown and is urged in the opposite direction by the scavenge air pressure applied to the cylinder 5| by a pipe 53 opening through the scavenge air receiver casing |4. A springloaded ball 54 co-operates .withV two .notches in the stem of the valve 48. When the scavenge air pressure acting on the piston 50 rises to a predetermined value, it overcomesthe restraint of the spring 52 and the ball 54 and moves the pilot valve y48 to the left. The servo-motor pistons 43 thereupon open thevalves 31 so that the auxiliary chambers 3|) and 30 become operative. When the scavenge air pressure falls to a predetermined value, the pilot valve is restored bythe spring 52 to the position shown, and the valves 31 are accordingly shut. f

The gas-generator shown in Figs. 1 and 6 is provided with automatic control gear for varying the quantity of air in the cushions in accordance with variation in the working pressure. This control gear may be of any suitable type; but it will be assumed that it is the one described in patent application No. 492,865 of E. S; L. Beale filed June 30, 1943, and the control gear will therefore be described only in so far as it concerns the present invention. Referring to Fig. 6, the control gear is contained within a casing 55, and it is capable of delivering air to, or withdrawing air from, a pipe 56 branching to pipes 51A and 51B' which lead to the cushions. The quantities of air so delivered and withdrawn are determined automatically by variation both in the scavenge air pressure and also in the inner dead point of the free pistons. The scavenge air tion ||5 Vto the piston rod |6. A transfer valve actuated by the rod H0 has two piston lands ||1 and ||8 which normally close ports ||9 and 'l 20 communicating respectively through oppositely acting non-return valves |2| and |22 with the Vchamber |23 to which the scavenge air pressure is admitted through the oriiice 58. The transfervalve'also has a port `|24 opening between the lands and connected to the cushion pipe 55. Inoperation, the vcushion air pressure oscillates, in synchronism with the reciprocation ofthe free pistons, between a maximum value which exceeds,

and a minimum value which is less than, the

Y scavenge air pressure.l-Variation of the inner the transfer valve to move appropriately. If

this valve rises, it connects port il@ to port |24. Consequently, during the part of the cycle when the scavenge air pressure :exceeds the cushion pressure, air is transferred through the nonreturn Valve |2| to the cushions until the transfer valve is again closed by the cushion air contents rising to a suitable value. Similarly, if the transfer valve falls, air is discharged from the cushion through the port |20 and the non-return valve |22 during( the part of the cycle when the cushion pressure is higher than the scavenge air pressure.

The increase in the clearance volume of the power cylinder l0 caused by rendering the auxiliary chambers 30 and 30 operative, has the effect of reducing the distance of the inner dead point from the middle of the power cylinder I0 required fora given compression ratio. If no steps were taken to alter the-adjustment of the inner-dead-point control gear, the inner-deadpoint follower tappet 6I would attain an inner dead point such as to indicate to the control gear that the inner dead point of the free pistons was to-o small (i. e. the inner dead point was too near the middle of the power cylinder) when in fact it was correct, and would operate -on the control gear to cause air to be withdrawn from the cushions, so that the compression ratio would be automatically reduced. Consequently according to a further feature o'f the invention, means are provided which alter the adjustment of the innerdead-point control gear simultaneously with the rendering of the auxiliary chambers operative, in such a way as to maintain the same compression ratio as existed before the auxiliary chambers were operative. Fig. 7 shows such means. The tappet 6l is provided with a. cam follower Ei?. the head of which is formed as a piston 63 operating in a cylindrical cavity in the tappet between stops 64 and S5. A relatively strong compression spring 65 is adapted to hold the cam-follower 52 continuously in the extended position shown. The lower end of the cylindrical cavity communicates by a por|J S1 with a channel SS in the tappet guide 59, and the channel 68 is connected by a pipe 'lll to the oil-transfer pipes el' of the servo-motor cylinders 44. Consequently, when the pilot valve 48 operates to allow oil under pressure to iiow to the pipes 41, and thus open the valves 31 of the auxiliary chambers, o-il under pressure is also admitted beneath the piston E3 of the cam-follower 62 which is thereby retracted into the tappet through the distance that will correct the relationship between the free-piston position and the tappet position, so as to take account of the change in inner dead point made necessary by the bringing into operation of the auxiliary chamber. W'hen the oil pressure is released from the pipe l@ on closing of the valves 3l of the i auxiliary chambers, the cam-follower Si is again extended with respect to the tappet 6I by the spring 5F., which is strong enough to prevent movement of the cam follower into the tappet throughout their working stroke.

In accordance with the invention, the eiective volume of the auxiliary combustion space may be progressively increased. This result may be attained by putting two or more auxiliary chambers successively into operation. Alternatively, the auxiliary chamber may be constituted by a cylinder communicating with the main combustion chamber, if desired through a valve-con trolled port, and containing a piston which is capable of being moved between various positions of adjustment for the purpose of varying the effective volume of the auxiliary chamber, whereby the inner dead point of the combustion pistons can be maintained approximately constant over the whole range of working pressure. Such an arrangement is shown in Fig. 8, where the auxiliary chamber 30A is formed by a piston H in a cylinder l2, the lower end of which communicates with the main combustion chamber by a port SIA in the power cylinder I0. The

inner face of the piston 'H is provided with a l valve facing 38A adapted to seal the port 3|A when the piston Il is in its lowest position. The effective volume of the auxiliary chamber 30A is adjusted by a shaft i3 operated either by hand or by automatic means hereafter described and .carrying a bevel wheel 'i4 which meshes with a bevel wheel 75 having internal splines mating with a splined portion I6 of the rod of the piston 7l. A screwed portion 'll of this rod is engaged in a screw-threaded bo-ss T8 on the cap of the cylinder 12.

In order to prevent risk of the power pistons hitting each other through operating with a large auxiliary chamber volume when the working pressure is low, means are provided for automatically disabling the fuel-injection system under such circumstances. The injection nozzle 29 is supplied through a pipe 19 by an injection pump (such as Bil in Fig. 6 driven off the shaft of the synchronising lever 24') A hydraulically controlled spill valve 8| on the pipe 'is is normally kept closed by oil pressure in a pipe 82. A piston valve 83 normally opens the pipe G2 to a source 84 of oil under pressure. The piston valve 83 is controlled jointly by a compression spring 85 and a lever 86 one end of which bears on the end of the rod of the piston .'i and the other end of which is pivotally connected to the rod of a piston 81 working in a cylinder 8S. A spring 89 urges the piston 8'! upwards against the soavenge air pressure applied to its upper face by a duct 98. If the relationship between scavenge air pressure and effective volume of the chamber 38A departs from predetermined limits, the valve S3 closes and the oil pressure in the pipe 82 is released by a leak 9|, so that the spill valve 8| opens and the machine stops. The piston 81 may be operatively connected to the control shaft I3 by a repeater mechanism of any desired type, indicated schematically at 92, and deriving its return motion from the lever 35. This mechanism, on displacement of the valve 83 due to variation of the scavenge air pressure acting on the piston 81, rotates the shaft 'i3 in such a sense as to restore the valve 83 to the normal position shown, and, as the valve attains this position, the return connection operates to stop the repeater mechanism. In this manner the effective volume 0f the chamber 38A can be caused to vary automatically in response to variation of the scavenge air pressure, the spill valve 8| opening on failure of the repeater mechanism.

I claim:

1. An internal-combustion-operated motivegas generator having a power cylinder including a combustion chamber, an air-compressor cylinder co-axial with said power cylinder, a power piston and a compressor piston slidable in said cylinders respectively, said pistons being connected together for operation in unison in such a manner that said compressor piston performs its delivery strokes simultaneously with the compression strokes of said power piston, a pneumatic cushion associated with said pistons for storing energy imparted to them during the expansion strokes of said power piston and returning energy to said pistons during the compression strokes of said power cylinder, means for causing at least a part of the air compressed in said compressor cylinder to scavenge and charge said power cylinder, an auxiliary chamber capable of communicating with said combustion chamber, valve means for interrupting communication between said chambers, and control means operable for varying the volume of said auxiliary chamber.

2. An internal-combustion-operated reciprocating machine having a power cylinder open at each end, a pair of power pistons slidable in said power cylinder, synchronising means for constraining said pistons to move oppositely and including a pair of members oscillable about a common synchroniser axis normal to the axis of said cylinder, said members being disposed on opposite sides of said cylinder, an air compressor cylinder co-axial with said power cylinder, a compressor piston connected to one of said power pistons for movement in unison therewith and slidable in said compressor cylinder, said compressor piston being arranged to perform its delivery strokes simultaneously with the compression strokes of said power pistons, means for causing at least part of the air compressed in said compressor cylinder to scavenge and charge said power cylinder, a pneumatic cushion associated with one Aofsaid pistons for storing energy of combustion in said power cylinder and returning energy to said pistons during said com- ,Y

pression strokes, an auxiliary chamber capable of communicating with the middle portion of said power cylinder, the Yaxis of said auxiliary chamber being inclined withV respect to said common synchroniser axis, a valve for interruptingY communication between said chamber and said power cylinder, and a fuel-injection nozzle, communicating with the middle portion of said power cylinder and disposed on the same side of said common synchroniser axis as said chamber, the axis of said nozzle being inclined oppositely to said chamber axis with respect to saidV common synchroniser axis. f

3. An internal-combustion-operated reciprocating machine having apower cylinder` open at each end, a pair of power `pistons slidable in` said power cylinder, synchronising means for constraining said pistons to move oppositely and including a pair of members oscillable about a commonsynchroniser axis normal to the axis of said cylinder, said members being disposed on opposite sides of said cylinder, an air compressor cylinder co-axial ywith said power cylinder, a

compressor piston connected to one of said powerv pistons for movement in unison therewith and slidable in said compressor cylinder, said compressor piston being arranged to perform its delivery strokes simultaneously with the compression strokesY of said power pistons, means for causing at least part of the air compressed in said compressor cylinder to scavenge and charge said power cylinder, a pneumatic cushion associated with one of said pistons for storing energy y operatedfmeans for opening said valve, and-means of said nozzles and said common synchroniser axis lying substantially in a common planel normal to said power-cylinder axis in such a manner that one of said chambersand one of said nozzles lie on one side of said synchroniser axis and the other of said chambers and the other,

of said nozzles lie on the other side of said synchroniser axis. I

4. An internal-combustion-operated recipro-` cating machine having a` power cylinder including a combustion chamber, a compressor cylinderY co-axial with said power cylinder, a power piston i and a compressor piston slidable in said cylinders respectively, said pistons `being connected together for operation in unison as a piston asseml bly so controlled that vthe inner dead point of said power piston is unconstrained mechanically,

means for charging said power cylinder at a variable pressure, an auxiliary chamber having a port for communication with said combustion chamber, a poppet valve having a head disposed within saidauxiliary chamberfor sealing said port and a stem passing through a gland in the wall of said auxiliary chamber, a spring biasing said valve towards its closed position, power serving in response to reduction of' said charging pressure to below a given value to de-energize said power operated means. l

5. An internal-combustion-operated reciprocating machine having a power cylinder includinsa combustion chamber, a compressor cylinderi co-axial with said power cylinder, a power piston and a compressor piston slidable in. said cylinders respectively, said pistons being connectedV together for operation in unison as a piston assembly so controlled that the inner dead point of said power piston is unconstrained mechanically, means for charging said power cylinder at a variable pressure, an auxiliary chamber capable orcommunicating with said combustion chamber, valve means for interrupting communication between said chambers, and a devicel responsive to variation of. said vcharging pressure for opening said valve automatically when said charging pressure rises to apredetermined value. v

6. An internal-combustion-operated reciprocating machine having a power `cylinder including a combustion chamber, a compressor cylin-l der co-axial with said power cylinder, a power piston and a compressor piston slidable in said cylinders respectively, said pistons being connected together for operation in unison as a piston assembly so controlled that the inner dead point of said power piston is unconstrained rnechanicaHy, means for charging said power cylinpoint of said power piston is unconstrained mechanically,-means for charging said power cylinder at a variable pressure, an auxiliary chamber having a port for communication with said combustion chamber, a poppet valve having a head disposed within said auxiliary chamber for sealing said port and a stem passing through a gland in the wall of said auxiliary chamber, a spring biasing said valve towards its closed position, and

a double-acting hydraulic servo-motor opera-V tively connected with said valve and capable of serving as a hydraulic damper in the event of loss of pressure of its operating liquid.

8. An internal-combustion-operated vreciprocating machine having `a'power cylinder includ-il ing a combustion chamber, a compressor cylinder co-axial with said power cylinder, a power pis-` ton and a compressor piston slidable in said'cylinders respectively, said pistons being connected together for operation in unison as piston assembly so controlled that the inner dead point of said power piston is unconstrained mechanically, means for charging said power cylinder at a Variable pressure, an auxiliary chamber having a port for communication with said combustion chamber, a puppet valve having a head disposed within said auxiliary chamber for sealing said port and a stem passing through a gland in the wall of said auxiliary chamber, a

aziospee 11 spring biasing said valve towards its closed position, a double-acting servo-motor operatively connected with said valve, and a reversing controller for said servo-motor automatically responsive to variation in said charging pressure.

9. An internal-combustion-'operated motivegas generator having a power cylinder including a combustion chamber, an air-compressor cylinder co-axial with said power cylinder, a power piston and a compressor piston slidable in said cylinders respectively, said pistons being connected together for operation in unison in su'ch a manner that said compressor piston performs its delivery strokes simultaneously with the compression strokes of said power piston, a pneumatic cushion associated with said pistons for storing energy imparted to them during the expansion strokes of said power piston and returning energy to said pistons during the compression strokes of said power cylinder, means for causing at least a part of the air compressed in said compressor cylinder to scavenge and charge said power cylinder, an auxiliary chamber communicating with said power cylinder, and control means responsive to variation in the delivery pressure of said compressor cylinder for automatically rendering said auxiliary chamber inoperative in consequence of reduction of said delivery pressure below a predetermined value.

10. An internal-combustion-operated reciprocating machine having a power cylinder includ-- ing a combustion chamber, a compressor cylinder co-axial with said power cylinder, a power piston and a compressor piston slidable in said cylinders respectively, said pistons being` connected together for operation in unison as a piston assembly so controlled that the inner dead point f said power piston is unconstrained mechanically, means for charging said power cylinder at a variable pressure, control mechanism including an adjustable follower device for following variations in said inner dead point, an auxiliary chamber capable of communicating with said combustion chamber, control means for rendering said auxiliary chamber alternatively operative and inoperative, and compensating means associated with said follower device and with said control means for altering the ad'- justment of said follower device automatically and simultaneously with the rendering ofvsaid auxiliary chamber operative and inoperative in such a way as to maintain substantially the same compression ratio in said power cylinder.

l1. An internal-combustion-operated motivegas generator having a power cylinder including a combustion chamber, an air-compressor cylinder co-aXial with said power cylinder, a power piston and a compressor piston slidable in said cylinders respectively, said pistons being connected together for operation in unison in such a manner that said compressor piston performs its delivery strokes simultaneously with the compression strokes of said power piston, a pneumatic cushion associated with said pistons for storing energy imparted to them during the expansion strokes of said power piston and returning energy to said pistons during the compression strokes of said power cylinder, means for causing at least a part of the air compressed in said compressor cylinder to .scavenge and charge said power cylinder, control mechanism including an adjustable follower device for following variation in the inner dead point-of said power piston, an auxiliary chamber capable of communicating with said combustion chamber, servo mechanism for rendering said auxiliary chamber alternatively operative and inoperative, and compensating means associated with said follower device and said servo mechanism for altering the adjustment of 'said follower device automatically and simultaneously with the rendering of said auxiliary chamber operative and inoperative in such a way as to maintain substantially the same compression ratio in said 'power cylinder.

12. An internal-combustion-operated motivegas generator having a power cylinder including a combustion chamber, an air-compressor cylinder co-axial with said power cylinder, a power piston and a compressor piston slidable in said cylinders respectively, said pistons being connected together for operation in unison in such a manner that said compressor piston performs its delivery strokes simultaneously with the cornpression strokes of said power piston, a pneumatic cushion associated with said pistons for storing energy imparted to them during the expansion strokes of said power piston and returning energy to said pistons during the compression strokes of said power cylinder, means for causing at least a part of the air compressed in said compressor cylinder to scavenge and charge `said power cylinder, control mechanism including an oscillable element of variable effective length for following variation of the inner dead point of said power piston, a hydraulic control device for varying said effective length, an auxiliary chamber capable of communicating with said combustion chamber, hydraulic servo mechanism for rendering said auxiliary chamber alternatively operative and inoperative, and a compensating connection for liquid between said hydraulic control device and said hydraulic servo mechanism which causes the effective length of said oscillable follower element to be varied automatically and simultaneously with the rendering r of said auxiliary chamber operative and inoperative in such a way as to maintain substantially (the same compression ratio in said power cylinder.

13. An internal-combustion-operated reciproeating machine having a power cylinder including a combustion chamber, a compressor cylinder co-axial with said power cylinder, a power piston and a compressor piston slidable in said cylinders respectively, said pistons being connected together for operation in unison as a piston assembly so controlled that the inner dead point of said power piston is unconstrained mechanically, means for charging said power cylin- .der at a variable pressure, a control member operable for stopping the machine, an auxiliary chamber capable of communicating with said combustion chamber, controlmeans for rendering saidauxiliary chamber alternatively operative and inoperative, and protective mechanism operatively associated with said stop control member and said control means and responsive to-variation in said charging pressure for automatically stopping the machine in response to the occurrence of an undesired relationship between said charging pressure and the effective volume of said auxiliary chamber.

FREDERICK ALAN AIRVING MUN'IZ.l

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