US2178310A - Motor compressor - Google Patents

Description

Oct. 31, 1939. R. P. PEscARA MOTOR COMPRESSOR Filed Jan. 20, 1934 s Sheets-Sheet 1 Raul Pater os Pescaru Oct. 31, 1939. R. P. PESCARA MOTOR COMPRESSOR Filed Jan. 20, 19:54 5 Sheets-Sheet 2 Rom Pataras Pespa'ra Oct 1, 1939. R. P. PESCARA 2,178,310

' MOTOR COMPRESSOR Filed Jan. 20, 1934 3 Sheets-Sheet 3 I Patented o' r. 31, 1939.

UNITED STATES PATENT OFFICE Moron coMrnEsson Raul Pateras Pescara, Paris, France, assignor of one-tenth to Socie'te dEtudes et de Participations, Eau, Gar, Electricite, Energie, S. A,

Geneva, Switzerland Application January 20, 1934, Serial. No. 707,595

In Belgium January 20,1933 v 32 Claims. .(ci. arc-e) 5 being arranged to move freely in at least one compression cylinder in line with said motor cylinder,

. in such manner that the motor cylinder and the portion of the piston that cooperates therewith form an internal combustion englne, whilethe l0 compression cylinder (or cylinders in the case of a machine of the multiple stage type) forms the compressor proper. Preferably, compressors comprise .two pistons moving in op-v posite directions in said motor cylinder and two compression cylinders, or groups of staged compression cylinders, cooperating with said pistons respectively and disposed on either side of said,

motor cylinder.

In such motor-compressors,- the return stroke 2 of the pistons is ensured by the expansion. of both the air remaining in said compression cylinders at the end of the outstroke of the pistons, on the one hand, and the compressed gas cushions imprisoned in compensating chambers suitably provided between the pistons and parts rigidlycarried by the cylinders.

The object of the present invention is to provide a motor-compressor of the type above referred to that is capable of working in a satisfactory manner during the starting period, that is'to say for the time elapsing between the startnormal ing of the motor-compressor and its working.

It will be readily understood that, for this period, the compensating chambers must be filled' with gas at a relatively high pressure in order to ensure the return of the piston or pistons.

According to my invention, I provide an auxillary reservoir adapted to be filled with compressed gas (air) and means for connecting said reservoir with said-compensating chamber (or chambers) when the motor-compressor is to be started. I choose the volume of the reservoir and the gas pressure therein in such manner that, when said reservoir is connected with said chamber, the gas present in the reservoir expands down to a pressure that is 'sumcient for ensuring the correct return stroke of the piston.

Another object of myinvention is to provide '50 a motor-compressor of the type above referred to with means for throttling the passage of air from the compression cylinders (or from at least one of them when the-machine is of the multiple stage type) for certain values of the discharge pressurelowe'r than the d scharge pressljire cOlIethese motor sponding to normal conditions of working of the motor-compressor. 7

Still another object of my invention is to provlde motor-compressors of the type .above referred to with means for bringing their pistons 5 into fixed positions closeto the positions they occupy at the end of their outward strokes.

According to the present invention, the last mentioned means cause a gas under pressure to act on the back faces of the compression portions 10 of the pistons (or of at least one of them).

These and other features of my invention will appear from the following detailed description thereof.

Preferred embodiments of the present inven- 15 tion will be hereinafter described with reference to the accompanying drawings, given merely by way of example, and in which:

Fig. i is a partial diagrammatic axial sectional view of a motor compressor of the single-stage go type'according to the present invention; Fig. 1a is a detail cross section through valve M of Fig. 1. l

Fig. 2 is a view similar to Fig. l, of a motorcompressor of the double-stage type according to 25 the present invention;

Figs. 3 to 6 inclusive are four diagrams illustrating the working of the device according to the present invention;

Fig. 'i is an enlarged view of another form of 30 one of the elements of the motor compressor according to Fig 2; I

Figs. 8 and 9 are enlarged views of another-embodiment of another one of the elements of the motor-compressor according to Fig. 2, respec- 85 tively in cross section and in section on the line X-X of Fig. 8;

Fig. 10 is a view similar to Figs. 1 and 21showing another embodiment of a motor-compressor of the double-stage type according to the present so invention.

As shown in Figs. 1, 2 and 10 of the drawings, the motor compressor comprises a motor cylinder l, on either side of which are disposed the compression cylinders I with air inlets 6t and two 45 double pistons 6| adapted to cooperate each at one end with the motor cylinder and at the other -'end with the compression cylinder (Fig. 1) or such manner that, account being taken of the action of the amount of air remaining in the clearance spaces 62 of the compression cylinders, 65

the good working of the apparatus may be ensured for all normal conditions of working of the machine, once the delivery pressure has reached its normal value.

According to the present invention, I provide an auxiliary reservoir 3, adapted to be filled with a compressed gas (for instance air) and to be subsequently placed into communication with the compensating cushions 2 through passage 2|. The volume of the reservoir and the pressure of the gas therein are such that,.when it is connected with said cushions for the starting of the motor-compressor, the gas present therein expands down to a pressure that remains sufficient for ensuring the correct return of the pistons during the starting period.

According to a preferred embodiment of my invention, I provide a three way cock 4! adapted to connect a pipe 5, through which compressed air is fed from any suitable source, either with reservoir 3, through a conduit 6, or with a device adapted to work under control of this compressed air, for connecting reservoir 3 with cushion 2, the compressed airfrom pipe 5 being then conveyed to this device through a conduit 7.

According to the present embodiment shown in the drawings, the device in question comprises a small cylinder 8' in which is mounted a piston 8 operatively connected with a-valve 9 adapted to open or cut oil the connection between reservoir 3 and chamber 2. A spring I tends to maintain said valve 9 in its.closed position. The above mentioned conduit 7 opens into said small cylinder at a point thereof such that, when air under pressure is fed through said conduit, piston 8 compresses spring [0 and valve 9 opens the passage 2| between reservoir 3 and the compensating air chamber 2.

It will be readily understood that a mere displacement of cock 4 suflices for charging reservoir 3, while another displacement of said cock causes said reservoir to be connected with chamher 2 and consequently the piston to be suddenly moved. inwardly.

Due to the relatively great volume of reservoir 3 as compared with that of chamber 2, the pressure in said chamber will vary but relatively little duringthe displacements of the piston, and this pressure will always remain sufiicient for insuring, by itself, the correct return of the pistons. This condition is necessary because, when the machine is starting, the air remaining in the clearance spaces of the compression cylinders does not supply any appreciable energy.

ments of the pistons, the delivery pressure (that is to say the pressure of the compressed air fed to the reservoir ll through outlet 64) increases. The energy supplied by the air remaining in the clearance spaces of the compression cylinders at the end of the outward stroke of the pistons is then added to the energy of air cushions 2 and it becomes necessary to reduce the pressure in said compensating chambers 2.

According to my invention, the volume oi. these chambers 2 is so chosen as to ensure a good working of the machine, as above explained, when said machine is working under normal conditions. Thepressure in reservoir. 3 and the volume of said reservoir are so chosen that the initial pressure in chambers 2, when the pistons are pushed inwardly, is considerably higher (for instance by 15 kilogrammes) than the normal delivery pressure of the compressor. Furthermore, I provide automatic means for reducing, prefer- However, after some reciprocating displaceably in a progressive manner, the pressure existing in said air chambers 2 from said initial pressure down to the normal pressure as the delivery pressure is increasing up to its normal value.

With such an arrangement, the total energy serving to return the pistons always correctly ensures said return, especially during the period elapsing between the first reciprocating displacement of the pistons and the establishing of stable conditions of running.

As shown in the drawings, the means for re ducing the pressure inthe compensating chambers consist of a stopping device inserted between a conduit l2 connected to said auxiliary reservoir 3 and a conduit [3 connected through conduit 64 to reservoir II. This stopping device is controlled in an automatic manner by the pressures existing in these two reservoirs, and eventually, in the case of multiple-stage compressors, by the pressure (or the pressures) existing in the lower stage (or in the lower stages) of said compressor.

In the case of a compressor discharging compressed air directly into reservoir ii, the stopping device above referred to may be made as shown in Fig. 1, which corresponds to the case of a single-stage compressor.

This device comprises a valve piston l4 having seats l4 and 14" inserted between conduits I2 and 13, said piston 14 being kept in its closed position for instance by a spring l5, preferably adjustable. Valve piston i4 is operatively connected witha stepped piston iii-ll subjected to the action of fluids under pressure tending to open valve piston l4.

The small piston l6 moves in a cylindrical chamber connected through tube l8 with compensating chamber 2, while the annular "piston i'l moves in a chamber connected through tube IS with the outlet of the compressor, so that the pressure in said chamber is equal to the delivery pressure.

The whole is devised in such manner that the pressure exerted initially on piston 16, when the motor-compressor is started, is not sufficient for overcoming the action of spring l5. But when the delivery pressure increases, the action on piston l1, added to that on piston l6, causes piston valve H to open against the action of spring I5, in a progressive manner, so as to permit air to flow through pipe l3 to reservoir II and thus gradually reduce the pressure in compensating chamber 2.

In the more complicated case of a compressor that normally discharges the compressed air through chamber 2, said chamber being then connected through tube l2 with the stopping device above referred to, this device may be made as shownin Figs. 2 and 10,. which show, byway of example, two-stage compressors.

In this embodiment, the air outlet pipe 65 of the second stage cylinder 48 of the compressor is connected with the compensating a'ir chamber 2 through a check valve 20 permitting air .to flow only in the direction of said chamber duits l2 and 13, a valve piston 14 maintained in its closed position by suitable means, for instance a spring I preferably adjustable. This piston II is opratively connected with a triple piston 23, 2i, and The smaller piston element 23 is adapted to slide in a cylindrical chamber connected througha tube I8 and tube l2 with air chamber 2. Piston element 23 is adapted to slide in a cylindrical chamber connected through a tube IS with the outlet of the high pressure compression cylinder. Finally, piston element 25 is adapted to slide in a cylindrical chamber connected through a tube 26 with the outlet of the low pressure compression cylinders.

The whole is so arranged as to work in the same manner-as above explained with reference to the embodiment of Fig. 1. Besides, it should be well-understood that, in a general manner, if there are 1!. stages to the compressor (for instance 2), the stepped piston controlling valve 14 can include n+1 elements (for instance 3).

In Fig. 7, I have shown another embodiment of the stopping device adapted to be used in connection with a two-stage compressor. 7 In this embodiment the piston comprises three elements 23, 24 and 25, as in the case illustrated by Figs.

2 and 10. The cylinder elements in which move piston elements 24 and 25 are similarly connected, through tubes' l9 and 28 respectively, with the outlets of the high pressure compression .cylinders and of the low pressure compression cylinders respectively. A spring i5, the effect of which can be adjusted by means of a screw having a milled knob 21, pushes the composite piston in a downward direction.

Conduit i2 opens under the small piston 23 into a chamber-26'. Therefore, in this case, condult l8 can be dispensed with.

- Piston 23 is soarranged with respect 'to its cylinder that, when the combined piston is moved upwardly a suflicient distance, it causes chamber 28 to be connected with a chamber 29 itself connected with conduit l3, thus establishing the desired communication between conduits i2 and i3.

There is further provided a valve-piston 33 adapted to connect chamber 28 directly with conduit 3. closed position by a spring 3! and by an external pressure (atmosphericiacting on one of the faces of,a piston' 32 operatively connected with valve-piston 30, the other face of said piston 32 being subjected to the pressure existing in conduit l3. This device works in the following manner: When the motor compressor is still cold, which corresponds to a considerable increase of the passive resistances, it is advantageous to increase the energy ensuring the return of the pistons and ,to maintain a relatively high pressure in the compensating chambers 2, even when reservoir H is no longer empty. For this purpose I turn head 2'! which, by compressing spring l5, retards the time at which composite piston 232425 is lifted. when, on thecontrary, the motor-compressor is working under normal conditions, it is advantageous to reduce the loss of pressure of the compressed air through pipes I2 and i3. In order to obtain this result, the external pressure acting on piston 32 is'reduced and valve-piston moves upwardly under the action of the inner pressure acting on piston 32. Compressed air then passes directly from chamber 28 into conduit l3 through the aperture uncovered by the upward displacement of valvepiston 30.

r Advantageously, according to my invention, I

This valve piston 30 is kept in the;

for producing, in the discharge of at least one of the stages of the compressor, a throttling of the air flow, which is the more important as the pressure existing in the reservoir fed by said stage is higher. Preferably these means, which are automatically brought into play by the pressure above referred to, can be controlled manually..

Such an arrangement is shown in Figs. 2 and 10, as applied to the first stage of a two-stage compressor. It comprises a valve 34 inserted in the delivery conduit 64 of the low pressure compression cylinder I between said cylinder and intermediate reservoir 33. This valve 34 is operatively connected with a piston 36 and 'is subjected to the action of a spring 35 tending to maintain it in the closed position. The cylinder in which piston 36 is mounted is connected with reservoir 33 so that the pressure of the air present in said reservoir tends to open valve 34. Reservoir 33 is connected by conduit 66 containing a check valve to compression chamber 4 of the second stage.

I can also utilize the arrangement shown in Figs. 8 and 9.

In this case the outlet valves- 0f the compression cylinder and a chamber 31 connected with said intermediate reservoir 33 I can be placed into or out of communication by a piston valve 38 the lateral walls of' which are subjected to the delivery pressure and are provided with calibrated orifices'39. This valve 38 is pushed against its seat 40 by a spring 45. The inner part of said seat'is connected with said chamber 31. This arrangement works in the following manner:

When the machine is being started, the pressure in chamber 37 is relatively low and valve 33 remains in the closed position. But when the compression cylinder delivers air underpressu're through its outlet valves, a portion of said air passes through orifices 39 and the pressure in chamber 31 increases until it becomes sufiicient for progressively lifting piston valve 38 against the action of spring ti Whatever be the enrbodiment of the invention that is chosen, the working of the motor-compressor takes place as follows, with reference to the diagrams of Figs. 3 to 6 inclusive:

In these diagrams, the curves in solid lines correspond to the first strokes respectively in chamber 2 (Fig. 3) ,in the high pressure cylinders combine with the devices above described means (Fig. 4) and in the low pressure cylinders (Figs. 5 and 6).

The curves in dotted lines correspond to the following strokes and in Figs. 3, 4 and 5 respectively. I

The dot anddash line curves correspond to the normal strokes in the same elements and in Figs. 3, 4 and 5 respectively.

If it be supposed that the first combustion takes place during the first outward stroke, as

the pressure in reservoirs 22 and-33 1s equal to the atmospheric pressure, valve 3 3' is nearly wholly closed and creates an important loss of ,pressure in the flow of compressed air from the first stage of compression. Valve piston M, which is merely subjected to the pressure of the air from chamber 2 acting on'smallpiston 23 remains in the closed position, thus cutting oifthe'.

connection between conduits l2 and 13, due to the action'of spring l5. At the end of the first outward stroke, the whole of the energy of the combustion has served to overcome the resistance of the air at substantially constant pressure in chamber 2, to' compress air in the first stage of the compressor (a portion of this Work being absorbed by the loss of pressure due to the closed position of valve 34) and to overcome the frictional resistances. As the variation of volume in cushion chambers 2 is small as compared with the total volume of the pipes and chambers that communicate with said cushions, the pressure therein has but little varied and the work absorbed by them is shown in Fig. 3 by surface m, n, p, q. The work in the first stage of compression is shown in Fig. 6 by surface h, i, a and the work in the second stage of compression is substantially equal to zero. The work for the return stroke is substantially the same as for the outward stroke because the cushion of air in the clearance space of the first stage compression cylinder supplies but very little energy.

During the following strokes of the pistons, as the pressure gradually'increases in reservoirs-22 and 33, valves 34 and it open, the pressure in the constant pressure air cushions 2 decreases (m n while the diagrams of the compression cylinders become 12 i, 7' for the first stage and Z 9 h 7 for the second stage. The energy in the compensating air cushions has therefore decreased while the energy in the air cushions of the clearance spaces of the compression cylinders has increased. Finally, when the machine is working under its normal conditions, valves 34 and I4 are fully opened due to the action of the pressure in the reservoirs. Thediagrams are now m 11 p, q, for the compensating air cushions, 1 9 W, 7 for the second stage of compression, and h i 7' for the first stage of com-: pression. Furthermore, check valve 20 opens for the passage of air toward the compensating air cushions, conduits l2, I3, and finally reservoir ll, Reservoir 3 then plays the part of a damper, so that the pulsations in the flow resulting from the reciprocating movements of the pistons are damped at the outlet from said reservoir 3 and at the inlet of the compensating air cushions 2.

In the preceding description it has been assumed that, when the motor-compressor is being started,-the positions of the pistons are close to those they occupy at the end of their outward strokes,

In order to ensure that this condition is always fulfilled, I advantageously arrange the motorcompressor in such manner that, in order to permit of subsequently starting it, the pistons are automatically, brought into fixed positions close to said outer positions through the action of a compressed gas acting on the rear faces of the compression portions of the pistons.

Although I may make use, for the displacement in question, of compressed air from any suitable source, I have found that it is particularly advantageous to make use:

(it) Either of the air that is present, after the stopping of the motor-compressor, in intermediate reservoirs 33, and in the high pressure compression cylinders, or in cushions 2 and the conduits l2 that are connected with said cushions;

' (b) Or the air that is present, for instance after failing to start the compressor, in chambers 2 and auxiliary reservoir 3, this air being, as above explained at a pressure higher than the normal delivery pressure.

For this purpose it will suffice, as shownin Fig.

(and therefore with chambers 2) and, on the other hand, through an automatic check valve 41 and conduits 61 preventing the outflow of air from chamber 45, with the chamber 48 of'the high pressure compression cylinder.

It will be readily understood that when valve 42 is opened, thus connecting chamber 45 with chambers 44, if for instance the motor-compressor has just been stopped and if it is desired to prepare it immediately for its subsequent starting, the compressed air present in chambers 48 and also in chambers 2 and in conduits l2 and 46 will expand into these chambers 44, thus tending to push the pistons away from each other. Then, when the pressure of this air becomes equal to the pressure in intermediate reservoir 33, the air present in this reservoir will pass through chambers 48 and will in turn expand into chambers 44.

If now, for instance due to a missed starting of the compressor, the intermediate reservoir 33 is empty, the air present in chambers 2 will be at a pressure sufiicient for bringing the pistons into their desired positions by expanding into chambers 44 through conduit 43, due to the opening of valve 42.

Of course, if no suitable device were provided, the air under pressure present in the low pressure compression cylinders would tend to oppose the desired displacement of the pistons.

It is therefore advantageous to provide valves 49, or the equivalent, in the walls of the low pressure compression cylinders and to have said valves opened at the proper time.

These valves 49 are preferably so positioned that they allow the air present in the low pressure compression cylinders to escape into the atmosphere until the pistons come close to their extreme outer positions but that, from this time on, the air present in these cylinders can no longer escape, thus forming a. cushion which stops without shock the pistons in the desired positions,

If, for this position of the pistons, valves 49 are now in communication with chambers 44, the air which will have expanded into these chambers 44 will be allowed to escape into the atmosphere.

It should be noted that, in some types of motor-compressors according to the present invention, these chambers 44 serve to compress at least a portion of the air utilized for the scavenging of the motor-cylinder. Accordingly, as shown in Fig. 10, these chambers 44 are provided with inlet valves 68 and connected through check valves 50 with a chamber 5| into which open the air inlet ports 52 of the motor cylinder, which has an exhaust outlet 59.

In the case of motor-compressors of that type it will be necessary, if it is desired to introduce compressed air into chambers 44 in order to push the pistons outwardly, to provide means for cutting off the communication between chamber 5| and the inside of the motor cylinder I (for instance a valve 53), while said compressed air is being introduced into chamber 44.

Finally, when auxiliary reservoir 3 communicated with the outlet of the compressor (for instance with reservoir 22) through a check valve' 20, it will be advantageous to provide means for keeping this valve closed while said reservoir 3 is being filled with air under pressure. As, under normal conditions of working, the pressure in this reservoir is equal to the delivery pressure of the compressor, valve 20 has no tendency to each of these valves. But I have found that it is more advantageous to operate the whole of them by means of a single control device since they must all be brought into play simultaneously.

According to the embodiment shown in the drawings (Fig, 10) I provide for each of these valves a piston (ll, l2, l3 and 1.4 respectively) operatively connected with it, a cylinder for said piston, means (conduits i5, 16, 54 and 1! respectively) for causing compressed air to act on one of the faces of said piston and elastic means (a spring) tending to maintain the valve in one of its positions (either closed or open). In the case of valve'20, the spring tends to maintain the valve in the closed position and the pressure acting on the piston also tends to maintain the valve in the closed position. In the case of valve 53, the spring tends to 'keep the valve in the open position while the pressure acting onthe piston serves to close the valve.- In the case of both valve" 82 and valve 49, the spring tends to keep the valve in the closed position, while the pressure actuated piston acts to open the valve.

It will then suffice to connect each of these cylinders through suitable conduits with a common compressed air pipe 54 (which may consist of pipe 5 itself) and to provide on said pipe a control cock 55. By moving this cook, the four valves above referred to will be simultaneously actuated in the desired manner.

While I have described what I deem to be preferred embodiments of my invention, it should be well understood that I do not wish to be limited thereto as there might be changes made in the, arrangement, disposition and form of the parts without departing from the principle of my invention as comprehended within the=scope of the appended claims.

What I claim is:

1. A motor compressor comprising in combination, a motor cylinder, at least one compression cylinder disposed adjacent to said motor cylinder and in line therewith, a piston member I adapted to slide freely at one end in said motor cylinder and at the other end in said compression cylinder, means rigidly connected with said cylinders and arranged to cooperate with said piston member for forming therewith a chamber containing a compensating cushion of gas. for bringing back said piston member to its initial position after each outstroke thereof, 'an auxiliary compressed gas reservoir, and means forconnecting said reservoir with said chamber so as to eifect startingof the motor-compressor, the volume of said reservoir and the gas pressure therein being so chosen that wh'nsaid reservoir is connected with said chamber the gas present in the reservoir'expandsdown to a pressure that issuflicient for ensuring the correct return stroke of the piston member.

2. A motor-compressor comprising in combination, a motor cylinder, at least one compression cylinder disposed adjacent to said motor cylinder and in line therewith, a piston member adapted to slide freely at one end in 'said motor cylinder. and at the other end in said compression cylinder, means rigidly connected with said cylinders and arranged to cooperate with said piston member for forming therewith a chamber containing a compensating cushion of gas for bringing back said piston member -to its initial position after each outstroke thereof, an

auxiliary gas reservoir, a device operative by a gas under pressure for connecting said reservoir with said chamber so as to effect starting of the motor-compressor, a conduit of compressed gas and means for connecting said conduit either with said reservoir or with said device, the volume of said reservoir and the gas pressure therein being so chosen that when 'sa'idreservoir is connected with said chamber the gas present in the reservoir expands down to a pressure that is sufiicient for ensuring the correct return stroke of the piston member.

3. A motor-compressor comprising in combinat'.on, a motor cylinder, at least one compression to slide freely at one end in said motor cylinder and at the other end in said compression cylinder; means rigidly connected with said cylinder and .arranged to cooperate with said piston member for forming therewith a chamber containing a compensating cushion of gas for bringing back said piston member to its initial position after each outstroke thereof, an auxiliary reservoir constructed to be connected with said, chamber,

' voir expands down to a pressure that is suflicient for ensuring the correct return stroke of the piston member. v

4. A motor-compressor com rising in combination, a motor cylinder, at least one compression cylinder disposed adjacent to said motor cylinder and in line therewith, a 'piston' member adapted cylinder disposed adjacent to said motor cylinder and in line therewith, a piston member adapted to slide freely at one end in said compression cylinder and at the other end. in said motor cylinder, means rigidly connected with. said cylin ders and arranged to cooperate with said piston member for forming therewith a chamber containing a' compensating. cushion of gas for bringing back said piston member to its initial position after each outstroke thereof, an auxiliary compressed gas reservoir, means for connecting said reservoir with said chamber so as to permit of starting the motor-compressor, the volume of said reservoir and the gas pressuretherein being so chosen that when said reservoir is connected reservoir, to a pressure substantially equal to the delivery pressure of the comp'ressonas said delivery pressure increases, during the starting period of the compressor, up to its normal value.

5. A motor-compressor comprising in combination, a motor cylinder, at least one compression cylinder disposed adjacent to said motor cylinder and in line therewith, a piston member adapted to slide freely at one end in said motor cylinder and at the other .end in said compression cylinder, means rigidly connected with said cylinders and arranged to cooperate with said piston member for forming therewith a chamber containing a compensating cushion of gas for bringing back said piston member to its initial position after each outstroke thereof, an auxiliary compressed gas reservoir, means for connecting said reservoir with said chamber so as to effect starting of said compressor, the volume of said reservoir and the gas pressure therein being so chosen that when said reservoir is connected with said chamber the gas present in said reservoir expands down to a pressure that remains suflicient for ensuring the correct return stroke of the piston member, a conduit connected with said auxiliary reservoir, a reservoir for the compressed air delivered by the motor-compressor, a conduit connected with the last mentioned, reservoir, a

pressure equalizing valve for controlling the communication between said two conduits and means responsive to the variations of both the pressure in the auxiliary reservoir and the delivery pressure of the compressor for actuating said valve, so as to gradually connect said conduits together as said delivery pressure increases.

6. A motor-compressor of the single-stage type, according to claim 5, in which the last mentioned means comprise two pistons both rigidly connected with said valve, two cylinders for said two pistons respectively, means for connecting one of the two last mentioned cylinders with said compensating chamber, and means for feeding into the other one of these two last mentioned cylinders a gas at the pressure existing in the second mentioned reservoir.

7. A motor compressor of the multiple stage type according to claim 5, comprising a plurality of compression cylinders adapted to successively receive air at a certain pressure and to further compress it, further comprising valve means, inserted between the outlet of the last compression cylinder and said compensating chamber,

for permitting air to flow only in the direction of said chamber, the last mentioned means of claim 5 comprising a plurality of pistons all rigid,- ly connected with said pressure equalizing valve, a cylinder for each of the last mentioned pistons, means for connecting one of the last mentioned cylinders with said compensating chamber and means for connecting the other last mentioned cylinders with at least some of theoutlets of these compression cylinders respectively.

8. A motor-compressor comprising in combination, a motor cylinder, at least one compression cylinder, disposed adjacent to said motor cylinder and in line therewith, a reservoir, a passage connecting said reservoir with said compression cylinder, a piston member adapted to slide freely at one end in said motor cylinder and at the other end in said compression cylinder, means reservoir with said chamber so as to eflect starting of the motor-compressor, the volume of said auxiliary reservoir and the gas pressure therein being so chosen that when said auxiliary reservoir is connected with said chamber the gas present in said auxiliary reservoir expands down to a pressure that is sufficient for ensuring the correct return stroke of the piston member, and means operative by the air pressure in the first mentioned reservoir for temporarily throttling said passage between said compression cylinder and the first mentioned reservoir when the pressure in said first mentioned reservoir is lower than the normal working pressure therein.

9. A motor compressor comprising in combination, a motor cylinder, at least one compression cylinder disposed adjacent to said motor cylinder and in line therewith, a piston member adapted to slide freely at one end in said motor cylinder and at the other end in said compression cylinder, means rigidly connected with said cylinders and arranged to cooperate with said piston member for forming therewith a chamber containing a compensating cushion of gas for bringing back said piston member to its initial position after each outstroke thereof, an auxiliary compressed gas reservoir, means for connecting said reservoir with said chamber so as to effect starting of the motor-compressor, the volume of said reservoir and the gas pressure therein being so chosen that when the reservoir is connected with said chamber the gas present in said reservoir expands down to a pressure that remains sufficient for ensuring the correct return stroke of the piston, and means for causing a compressed gas to act on the rear face of the portion of the piston member that coacts with said compression cylinder, so as to move said piston member outwardly to a predetermined position close to its extreme outer position.

10. A motor compressor according to claim 25 in which the last mentioned means comprise at least one conduit for connecting said compensating chamber with the rear space of said compression cylinder, and a valve for controlling the flow of compressed air through said conduit.

11. A motor-compressor according to claim 25 in which the last mentioned means comprise at least "one conduit for connecting the outlet of the compressor with the rear space of said compression cylinder, and a valve for controlling the flow of compressed air through said conduit.

12. A motor-compressor of the multiple-stage type according to claim 25 comprising a plurality of compression cylinders connected in series, the first of which is the low pressure cylinder and the last of which is the high pressure cylinder, and at least an intermediate reservoir between two of them, the last mentioned means of claim 25 including means for connecting said intermediate reservoir with the rear space of said low pressure compression cylinder, and a valve for controlling the flow of compressed air through the last mentioned means.

13. A motor-compressor of the multiple-stage type according to claim 25 comprising a plurality of compression cylinders connected in series, the first of which is the low pressure cylinder and the last of which is the high pressure cylinder, in which the last mentioned means 01' claim 25 include a chamber directly connected with the outlet of the compressor, a conduit opening into the rear space of the low pressure compression cylinder, a valve for controlling the connection be tween the last mentioned chamber and said last mentioned conduit, and means for connecting the last mentioned chamber with the high pressure compression cylinder, the last mentioned means including a check valve adapted to prevent the outflow of air from the last mentioned chamber.

14. A motor compressor according to claim 25 further comprising means provided in said compression cylinder for allowing the air present in the compression chamber thereof to escape when the last mentioned means of claim 25 are brought into play. I

15. A motor compressor according to claim 25 further comprising, an outlet valve provided in the lateral wall of said compression cylinder adapted to permit the outflow of air from the compression chamber of said cylinder when the last mentioned means of claim 25 are brought into play, said outlet valve being so positioned as to be cut off from said compression chamber by the piston member when the latter is nearing said predetermined. position close to the end of its outward stroke, whereby a cushion of air is imprisoned in said compression chamber of the the compression chamber thereof to escape when the last mentioned means of claim 25 are brought into play, and means for causing said compressed gas to cease to act on the rear face of the portion of the piston member that coacts with said compression cylinder when the piston member has reached its predetermined position close to its extreme outer position.

17. A motor compressor according to claim 25 further comprising, an outlet valve provided in prisoned in said compression chamber of the compression cylinder, thus stopping the piston member without shock in the desired position,-

said piston memberbeing so devised as to uncover said last mentioned valve after cutting it ofi from said compression chamber when the piston member has reachedsaid predetermined position, so as to permit the compressed gas acting on the rear face of the piston member to escape into the atmosphere. L

18. A motor-compressor according to claim 25 of the type in which the rear chamber of the compression cylinder serves to supply air for the scavenging of the motor cylinder, further comprising means for preventing the compressed gas from said rear chamber from passing into said motor cylinder when the last mentioned means of claim 25 arebrought into play.

19. A motor-compressor according to claim 25 further comprising 'a check valve connecting the outlet of the compressor with said auxiliary reservoir, and means for keeping the lastmentioned valve in the closed position when said auxiliary reservoir is being filled with compressed air. 20. A motor compressor .of the multiple-stage type according to claim 25 comprising a plurality of compression cylinders connected in series, the

7 first of which is the low pressure cylinder and the last of which is the high pressure. cylinder, in

which the last mentioned means of claim 25 include a chamber directly connected with the outlet of the compressor, a conduit opening .into the rearspace of the low pressure compression cylinder, avalve for controlling the connection between the last mentioned chamber and the last mentioned conduit and means for connecting the last mentioned chamber with the high pressure compression cylinder, the last mentioned means including a check valve adapted to prevent the outflow of air from the last mentioned chamber, the compressor further comprising, an outlet valve provided in the lateral wall of the low pressure compression cylinder adapted to permit the outflow of air from the compression chamber of said cylinder when the last mentioned means of claim 25 are brought into play, said outlet valve being so positioned as to be cut off from-said compression chamber by the piston member when the latter is nearing said predetermined position close to the end of its outward stroke, whereby a cushion of air is imprisoned in said compression chamber of the compression cylinder, thus stopping the piston member without shock in the desired position, a valve for closing the connection between the rear chamber of said low pressure compression cylinder and the motor cylinder, a

check valve connecting the outlet of the compressor with said auxiliary reservoir, and pneumatic means for'simultaneously opening the first and third mentioned valves and closing the two last mentioned ones. 21.-A motor compressor comprising in combination, a motor cylinder; at least one compression cylinder disposed adjacent to said motor cyl-. ,inder and in line -therewith, a piston member adapted to slide freely at one end in said motor cylinder and at the other end in said compression cylinder, means rigidly connected with said cylinders and arranged to cooperate with said piston member for forming therewith a chamber containing a compensating cushion of gas forbringing back said piston member to its initial position after each outstroke thereof, an auxiliary compressed gas reservoir, and means for connecting said reservoir with said chamber so as to efiect starting of the motor compressor, the gas pressure in said reservoir being suificient for ensuring the correct return stroke of the piston,- whereas the volume of said reservoir is relatively great as compared with that of saidchamber,

so that the pressure in said chamber will vary but relatively little during the displacements of the piston. 22. A motor compressor comprising in combinaand in" line therewith, a piston member adapted to slide freely at one end in said compression cylinder 'tion, a motor cylinder, at least one compression cylinder disposed adjacent to said motor cylinder. .60

and at the. other ezfd in said motor cylinder,

reservoir being suflicient for ensuring the cor-- rect return stroke of the piston member and means for automatically reducing the pressure of the compensating gas cushion present in said chamber from its initial value to a pressure sufficient for ensuring the correct return stroke during normal working of the machine as the delivery pressure of the compressor increases during the working period of the compressor up to its normal value.

23. A motor compressor comprising in combination, a motor cylinder, at least one compression cylinder disposed adjacent to said motor cylinder and in line therewith, a reservoir, a passage connecting said reservoir with said compression cylinder, a piston member adapted to slide freely at one end in said motor cylinder and at the other end in said compression cylinder, means rigidly connected with said cylinders and arranged to cooperate with said piston member for forming therewith a chamber containing a compensating cushion of gas for bringing back said piston member to its initial position after each outstroke thereof, and means for temporarily throttling said passage between said compression cylinder and said reservoir when the pressure in said reservoir is lower than the normal working pressure therein.

24. A motor compressor comprising in combination, a motor cylinder, at least one compression cylinder disposed adjacent to said motor cylinder and in line therewith, a reservoir, a passage connecting said reservoir with said compression cylinder, 3, piston member adapted to slide freely at one end in said motor cylinder and at the other end in said compression cylinder, means rigidly connected with said cylinders and arranged to cooperate with said piston member for forming therewith a chamber containing a compensating cushion of gas for bringing back said piston member to its initial position after each outstroke thereof, and means operative by the air pressure in said reservoir for temporarily throttling said passage between said compression cylinder and said reservoir when the pressure in said reservoir is lower than the normal working pressure therein.

25. A motor compressor comprising in combination, a motor cylinder, at least one compression cylinder disposed adjacent to said motor cylinder and in line therewith, a piston member adapted to slide freely at one end in said motor cylinder and at the other end in said compression cylinder, means rigidly connected with said cylinders, and arranged to cooperate with said piston member for forming therewith a chamber containing a compensating cushion of gas for bringing back said piston member to its initial position after each outstroke thereof, an auxiliary compressed gas reservoir, means for connecting said reservoir with said chamber so as to efiect starting of the motor compressor, and means for causing a compressed gas to act on the rear face of the portion of the piston member that coacts with said compression cylinder, so as to move said piston member outwardly to a predetermined position close to its extreme outer position.

26. In a free piston motor compressor, the .combination of a free piston, an energy storing device, means for delivering to said piston the energy for maintaining the reciprocation of said piston during the initial strokes, and means for gradually unloading said storing device.

27. In a free piston motor compressor, the

combination of a free piston, an energy storing device, means for delivering to said piston the energy for maintaining the reciprocation of said piston during the initial strokes, and means for gradually unloading said storing device, said storing device comprising an element coupled to said free piston and arranged to be acted upon by a compressed fluid.

28. In a free piston motor compressor, the combination of a free piston, an energy storing device, means for delivering to said piston the energy for maintaining the reciprocation of said piston during the initial strokes, means for charging said storing device within a short time-interval, and means for gradually unloading said storing device.

29. In a free piston motor compressor, the combination of a driving portion, a driven portion, a free piston for driving said driven portion by means of said driving portion, an energy storing device, means for delivering/to said piston the energy for maintaining the reciprocation of said piston during the initial strokes, means for causing during the initial strokes, said storing device to run loaded and said driven portion to run idle,

and means for gradually unloading said storing device and for loading said driven portion.

30. In a free piston motor compressor, the combination of a driving portion, a driven portion, a free piston for driving said driven portion by means of said driving portion, an energy storing device, means for delivering to said piston the energy for maintaining the reciprocation of said piston during the initial strokes, means for causing, during the initial strokes, said storing device to run loaded and said driven portion to run idle, and means for gradually loading said driven portion and for unloading said storing device automatically in dependency upon the loading of said driven portion.

31. In a free piston motor-compressor, the combination of a motor portion, a compressor, a reciprocating mass for transferring energy from said motor portion to said compressor, a discharge valve controlling the discharge of compressed gas from said compressor, an energy storing device for delivering to said mass the energy for maintaining the reciprocation of said mass during the initial strokes, and means for causing, during the initial strokes, said storing device to run loaded and said valve to be closed, and means for gradually unloading said storing device and for opening said sor, a reciprocating mass for transferring energy RAUL PATERAS PESCARA.

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