EP0061405B1 - Hydraulic pistion pump with a variable stroke, and pressure-fluid generator using such a pump - Google Patents

Abstract

The present invention relates to a double-acting hydraulic pump comprising a piston moving with a reciprocal rectilinear movement inside a cylinder of which each chamber is provided with a suction valve and a delivery valve, the rod of said piston being adapted to be driven by a variable-displacement driving member. The said piston rod extends beyond the piston and moves, outside the cylinder within a space of variable volume, provided in the body of the pump, which communicates, with a member controlling the by-pass device through which the two chambers of the cylinder communicate.

Description

Numerous types of double-acting hydraulic piston pumps are already known, essentially comprising a cylinder in which a piston moves, the rod of which is coupled to a motor member. The piston defines two chambers in the cylinder and each of them is provided with a suction valve disposed on a supply line connected to a hydraulic fluid reservoir and with a discharge valve opening onto a connected discharge line. to devices using pressurized fluid.

We also know by internal combustion engines, called free piston, whose useful power is regulated by the piston stroke. Such engines essentially comprise a combustion chamber into which are introduced a liquid or gaseous fuel and an oxidizer, according to suitable cycles.

In some of these engines, an appropriate zone of the piston evolves in a cylinder and defines there two chambers. The first, said pumping chamber, is capable of being placed in communication with the atmosphere with a view to filling it with air; the latter is then partially discharged into the combustion chamber to ensure the role of the oxidant there. The second chamber, called the mattress chamber, also capable of being supplied with atmospheric air, constitutes an elastic element repelling the piston of the engine and thus ensuring the compression of the fuel-oxidant mixture before it explodes. It is known that one of the main advantages of this type of engine is to avoid the need for a mechanical connection of the piston with the fixed casing while allowing high security with respect to the risks presented by the free piston.

It appeared interesting to seek to drive a hydraulic pump by a motor of the type briefly mentioned above, to constitute a generator of hydraulic fluid under pressure, capable of providing a fluid flow rate automatically adapted to the demand of the user devices. However, it was necessary to resolve the difficulties presented by the use of a pump, the working stroke of which, as a function of the power demanded, must be compatible with the stroke of the drive member, itself dependent on the power it provides.

The invention therefore firstly relates to a double-acting hydraulic pump, the piston of which can be provided by a variable-stroke motor member. In a pump of this type, the flow rate supplied is of course a function of the outward and return stroke of the piston, at least in the vicinity of the maximum load of the pump and more precisely up to approximately 60% of this maximum load. Below this load, it can be seen that it generally becomes impossible to adjust the stroke of the drive member. It has already been proposed in this regard to limit the delivery rate by the temporary introduction of pressure drops (rolling) but such a solution has the serious drawback of causing an energy loss resulting in practice in a significant reduction in the discharge pressure. It was therefore advisable to seek a pump allowing, without loss of energy, an automatic adjustment of the pumped flow, from the zero load to the maximum load of the pump.

According to the invention, the piston rod of the pump is extended beyond the piston and evolves, outside the cylinder, in a variable volume capacity formed in the body of the pump, communicating with the control member. a bypass device connecting the two chambers of the pump cylinder.

This bypass device can be produced in various ways, but, according to an advantageous characteristic of the invention, it is constituted by a drawer moving in front of two orifices communicating respectively with each of the chambers of the cylinder, this drawer being subjected, against the action of an adjustable spring (depending on the flow rate requested from the pump), the action of the pressure prevailing in the variable volume capacity.

Another difficulty encountered in this type of pump results from the pulsating shape of the pressure due to the reciprocating movement of the piston. In general, a pulsating pressure is not favorable for the proper functioning of the user devices and it was therefore advisable to dampen the pulsations as much as possible. To this end, the pump according to the invention may comprise, on the delivery pipe, a fluid accumulator situated downstream of the delivery valves of each of the chambers. @ (at the bottom of the page)

The corollary of the previous difficulty is that the flow aspirated by the pump is itself pulsating. Provision is therefore made to have, upstream of the suction valves of each of the chambers, a fluid accumulator @ and to supply the latter by a booster pump itself driven by an auxiliary motor. The delivery of the booster pump will also advantageously be linked to the variable volume capacity mentioned above so as to compensate for any leaks occurring during the operation of the bypass device controlled by said capacity.

One of the main applications of the hydraulic pump which has just been briefly described is, as already indicated, its use with a free piston motor to constitute an autonomous generator of hydraulic power.

• @ Un tel accumulateur a déjà été proposé par le brevet DE-A-2 648 958 GB-A-1 332 799 et US-A-4097 198, et on en connait les avantages.
• @tel que ceux décrits par les brevets antérieurs précités,

tion particulière et vise notamment un générateur de fluide hydraulique sous pression comportant un moteur à piston libre, connu en soi, cependant que le piston de la pompe hydraulique, du type précédemment décrit, est attelé au piston du moteur et disposé coaxialement à celui-ci pour constituer avec lui un équipage mobile monobloc n'ayant aucune liaison mécanique avec l'extérieur. On conserve ainsi les avantages du moteur à piston libre évoqués plus haut.The invention also extends to this applica-

• @ Such an accumulator has already been proposed by patent DE-A-2 648 958 GB-A-1 332 799 and US-A-4097 198, and the advantages are known.
• @ such as those described by the aforementioned prior patents,

tion particular and aims in particular a pressurized hydraulic fluid generator comprising a free piston engine, known per se, however that the piston of the hydraulic pump, of the type described above, is coupled to the piston of the engine and arranged coaxially thereto to constitute with it a one-piece mobile assembly having no mechanical connection with the outside. This keeps the advantages of the free piston engine mentioned above.

The invention however provides, in the case of such a generator, to advantageously produce the auxiliary motor of the booster pump of the hydraulic pump. Such an auxiliary engine is driven by the pressurized air existing in the mattress chamber of the free piston engine. For reference, the auxiliary engine will itself be a single-acting piston engine whose piston is subjected, against the action of a return spring, to the action of the pressure prevailing in the mattress chamber.

The invention will be better understood and its advantages, as well as various other characteristics will appear during the description which follows, with reference to the accompanying drawings of an advantageous embodiment, given solely by way of example.

• - la figure 1 est une coupe longitudinale d'un générateur de fluide hydraulique sous pression conforme à l'invention;
• - la figure 1a est un vue analogue à la fig. 1 d'une variante de réalisation, limitée à la région du piston du moteur à combustion interne;
• - la figure 2 est une coupe suivant II-II de la figure 1;
• - la figure 3 est une coupe suivant III-III de la figure 1;
• -la figure 4 est une coupe suivant IV-IV de la figure 1;
• - la figure 5 est une coupe suivant V-V de la figure 3;
• - la figure 6 est un diagramme représentant le débit instantané Q de la pompe hydraulique, en fonction du temps T dans le cas.d'une débit moyen A voisin du débit maximal;
• la figure 7 est un diagramme analogue à celui de la figure 6, dans le cas d'un débit moyen partiel B;
• - la figure 8 est une vue analogue à la figure 1 d'un mode avantageux de réalisation, avec arrachement partiel dans la région du moteur à combustion interne; et
• les figures 9a et 9b sont des demi-coupes suivant IXa-IXa et IXb-IXb de la figure ^-8.

In the drawings:

• - Figure 1 is a longitudinal section of a pressurized hydraulic fluid generator according to the invention;
• - Figure 1a is a view similar to FIG. 1 of an alternative embodiment, limited to the region of the piston of the internal combustion engine;
• - Figure 2 is a section along II-II of Figure 1;
• - Figure 3 is a section along III-III of Figure 1;
• FIG 4 is a section on IV-IV of Figure 1;
• - Figure 5 is a section along VV of Figure 3;
• - Figure 6 is a diagram representing the instantaneous flow Q of the hydraulic pump, as a function of time T in the case of an average flow A close to the maximum flow;
• Figure 7 is a diagram similar to that of Figure 6, in the case of a partial average flow B;
• - Figure 8 is a view similar to Figure 1 of an advantageous embodiment, partially cut away in the region of the internal combustion engine; and
• Figures 9a and 9b are half-sections along IXa-IXa and IXb-IXb of Figure ^- 8.

If we refer to FIG. 1, we see that a generator according to the invention essentially comprises a free piston engine designated by the general reference 1 and a hydraulic pump designated by the general reference 2.

The engine 1 is constituted, as is known, by a combustion chamber 3 in which a piston 4 operates. In the example shown, the engine is of the two-stroke Diesel type. The piston 4 has at its end opposite to the combustion chamber an annular portion 5 evolving in a cylinder 6 and delimiting on the one hand, a chamber 7, called pumping, and, on the other hand, a chamber 8, called chamber -mattress. Valves 9 allow the chamber 7 to communicate with the atmosphere, while valves 10 open onto conduits 11 communicating with the combustion chamber, when the piston 4 releases the corresponding lights. A duct 13 schematically shown and provided with a valve 13 allows the filling of the metelas chamber 8 from the air contained in the pumping chamber 7, in particular to compensate for the air leaks occurring in this mattress chamber at during operation.

Without describing in detail the known operation of such an engine, it will simply be recalled that after the explosion of the fuel-oxidant mixture in the combustion chamber 3, the piston 4 is pushed back until the scanning lights of the conduits 11 are released. At the same time its annular portion 5 compresses the air contained in the mattress chamber 8. The elastic energy thus stored will serve to return the piston 4 inside the combustion chamber to compress the mixture previously introduced therein. for a new explosion.

The hydraulic pump 2, which is driven by the motor 1, is constituted by a body 14, fixed to the body of the motor, in which a cylinder 15 is preferably provided. coaxial with the cylinder 6 of the engine and its combustion chamber 3. Preferably also, the cylinder 15 is constituted by an attached jacket, mounted in the bore 14a of the body 14.

The piston 16 and the pump is coupled to the piston 4 of the engine by means of a piston rod 17, coaxial with the latter and constituting with it a one-piece assembly. The piston 16 thus defines in the cylinder 15 two chambers 18 and 19, each of them being provided with at least one suction valve 20 and one discharge valve 21.

Two sealing rings 25set 25a close the chambers 18 and 19 and also ensure the immobilization of the cylinder 15 in the axial direction, while allowing the passage of the piston rod 17 under conditions which will be specified even further .

In Figure 2, we see the suction valves 20 opening into the chamber 18 and supplied by conduits 22. The suction valves corresponding to the chamber 19 are arranged similarly in the vicinity of the discharge valve 21 corresponding to this bedroom.

Although FIG. 1 represents an engine 1 whose piston 4 receives the rod 17 of the piston 16 of the pump on its face opposite to the combustion chamber, FIG. 1a shows an alternative embodiment which makes it possible to reduce the longitudinal dimensions of the generator.

To this end, the face of the piston 4 opposite the combustion chamber is open and allows the latter to cover, at least in part, the body 14 of the pump, when the movable assembly is in the position shown in FIG. 1. The mattress chamber 8 then partially extends inside the piston 4 , however that the rod 17 of the piston 16 of the hydraulic pump is coupled to the piston 4 on its face limiting the combustion chamber.

On the side opposite the piston 16, the piston rod 17 is extended by a coaxial rod 23 which moves outside the chamber 19 in a capacity 24 formed in a part 14b fixed to the body 14 of the pump. The sealing ring 25 traversed by the rod 23 avoids any communication between the chamber 19 and the capacity 24. For reasons which will appear later, the capacity 24 must have a variable volume. To this end, an accumulator 26 communicates by a conduit 27 with the capacity 24. It is constituted by a piston 28 evolving in a cylindrical chamber and subjected to the action of a spring 29.

The two chambers 18 and 19 of the pump can be put in communication by a bypass device which will now be described. The conduits 30 and 31 communicating respectively with the chambers 18 and 19 open into a drawer distributor 32. In its rest position, shown in FIG. 1, the groove 33 of the drawer 32 ensures the communication of the conduits 30 and 31. The drawer 32 is however coupled to a piston 34 subjected to the action of a spring 35 and coming to rest bearing on the body 14 of the pump by its shoulder 34a. A control rod 36, capable of being coupled to a member for use, is slidably mounted in the part 14b of the pump body and allows the setting of the setting force of the spring 35. Effin, a chamber 37, formed in the body of the pump and one of the walls of which is constituted by the piston 34, communicates with the capacity 24 by a conduit 38.

It is now appropriate to return to the devices provided both for supplying the pump 2 with hydraulic fluid and for discharging this fluid, with a view in particular to remedying the drawbacks, mentioned above, which may result from a supply and of a pulsating repression.

For this purpose, there is first of all provided, from the supply orifice 39 connected to a fluid reservoir, a pump, called a booster pump, designated by the general reference 40 and at least a accumulator 41 (FIGS. 3 and 5) regulating the discharge pressure of this booster pump.

The booster pump is constituted by a piston 42 operating in a cylindrical chamber 43, one of the walls of which, essentially constituted by a plate 43a, comprises a suction valve 44 connected to the supply orifice 39. On the other share, discharge valves 45 allowing the communication of the chamber 43 with a chamber 46, itself connected to the supply conduits 22 via a conduit 47 (Figure 3). Bypassed on the conduit 47 is disposed the accumulator 41 comprising a piston 48 evolving in a chamber 49 and subjected to the action of a spring 50.

The booster pump 40, or more precisely its delivery chamber 46, is on the other hand connected by a conduit 24a, equipped with a non-return valve 24b (shown diagrammatically by a dotted line in FIG. 3), to the variable volume capacity 24, so as to compensate for any fruits from the latter.

The piston 42 of the booster pump is driven by an auxiliary motor designated by the general reference 51. In the example shown in FIG. 1, this motor comprises a piston 52 coupled to the piston 42 by means of a rod 53 and moving in a chamber 54 against the action of a spring 55 which is supported on a ring 56 fixed to the body of the pump. In its rest position shown in FIG. 1, the piston 52 also bears on the body of the engine 1. The chamber 54, one of the walls of which is constituted by the piston 52 is in communication via a conduit 57 with the chamber- mattress 8 of engine 1.

As regards the discharge of the hydraulic pump 2, conduits 58 collect the fluid having passed through the valves 21 and are connected to a main discharge conduit 59 intended to be placed in communication with the user devices. On the conduit 59 is disposed bypass an accumulator 60, which, in the example shown, is of the membrane type.

Before explaining the operation of the pump which has just been described with reference to FIGS. 1 to 5, it is necessary to underline certain peculiarities of the advantageous embodiment represented in FIGS. 8 and 9. In these figures, the same references which those already used in FIGS. 1 to 7 to designate the same members. Some additional markers will however be used from the number 100.

The particular features of the embodiment of FIGS. 8 and 9 essentially concern the structure of the body of the hydraulic pump 2, as well as the constitution of the booster pump 40 and of its single accumulator 41, these last two members being arranged coaxially with the rod 17 This arrangement makes it possible to reduce the size of the generator.

Over most of its length, the cylinder 15 of the pump has an outside diameter smaller than that of the bore 14a of the body 14 of the pump. It has at its left end (motor side) orifices 115, so that the chamber 18 opens into the annular space 118 located between the bore 14a and the cylinder 15. However, at its end opposite to the orifices 115, the cylinder 15 comprises a portion 115a, the outside diameter of which is identical to the inside diameter of the bore 14a: the annular space 118 can thus be isolated in a sealed manner from the chamber 19. Thanks to this arrangement, the suction valves 20 and of delivery 21 corresponding to chamber 18 can be grouped in the vicinity of those corresponding to room 19.

This arrangement allows the left part (motor side) of the pump 2 to be released in order to place the booster pump 40 and the accumulator 41 under conditions which will be specified later.

It should however be noted that, in the variant ic described, the action of the spring 35 on the drawer 32 is exerted from the left to the right of FIG. 8 thanks to the lever 135. Thus, in its rest position visible on the Figure 8, the drawer 32 not ensure its groove 33, the communication between the conduits 30 and 31, while the piston 34 disposed at its end opposite the lever 135 bears directly by its shoulder 34a on the shoulder 114b e the part 14b fixed to the body 14 of the pump. As in the embodiment described above, the fluid contained in the capacity 24 and the accumulator 26 can act on the piston 34 in the direction opposite to the action of the spring 35.

The booster pump 40 visible in FIG. 8 has a substantially different constitution from that described above, while comprising the same essential members.

Around the pump body 14 is provided a casing 114 fixed to the motor 1 and having a central bore 114a, coaxial with the rod 17. An annular plate 43a is fixed in the space between the body 14 and the casing 114. of the motor 1, the plate 43a defines an annular chamber 43 in which the piston 42 of the booster pump moves. The face 152 of the piston 42 located on the side of the motor 1 closes the mattress chamber 8 and will thus constitute the piston 52 of the motor 51 of the booster pump. It can also be said that the piston 42 of the booster pump and the piston 52 of the motor 51 constitute a one-piece assembly. A ring 101 limits the axial movement of the piston 42-52 under the action of the spring 55 bearing on the plate 43a.

On the side of the chamber 43, the plate 43a carries an annular suction valve 44 connected to the supply orifice 39. On the other side, the plate 43a carries an annular discharge valve 45 allowing the communication of the chamber 43 with a chamber 46, itself connected to the suction valves 20 of the pump 2 by the conduits 47 (formed in the casing 114) and 22 shown diagrammatically in FIG. 8.

The chamber 46 is closed by the annular piston 48 of the shock absorber 41, this piston 48 being subjected to the action of the spring 50 bearing on the body 14 of the pump 2.

As those skilled in the art have already realized, the annular arrangement of the booster pump 40 and its accumulator 41 makes it possible to remove many dead spaces, such as the conduit 57 and the chamber 54 of the engine. 51, as well as the chamber 49 of the damper 41 which is here merged with the chamber 46. In addition, the conduits 47 and 22 may be shorter and less numerous than in the embodiment according to FIGS. 1 to 5.

Finally, it is obvious that the conduit 24a and its valve 24b, the roles of which have been explained above, will be provided in the casing 114 and then in the body 14 of the pump, although they have been shown diagrammatically in punctuated line on the figure 8.

The operation of the pump 2 is then carried out in the following manner, whatever the embodiment.

In what follows, the "moving stroke" of the mobile assembly piston 4-rod 17-piston 16-rod 23 will denote its displacement under the effect of an explosion in the combustion chamber 3. In FIG. 1 and in FIG. 8, this displacement is carried out from left to right. The "return race" will designate the movement in the opposite direction of the moving equipment.

It will first be assumed that the pump 2 provides its maximum flow rate, that is to say that the control rod 36 is in the position shown in the drawings, corresponding to the minimum setting force of the spring 35. In these conditions, the minimum pressure in the capacity 24 is sufficient to push the piston 34 completely against the action of the spring 35, the shoulder 34a then coming to bear on the stop 14c. The drawer 32 is thus kept in its closed position of the communication between the conduits 30 and 31.

During the "outward stroke" of the moving part, the volume of the chamber 18 increases and fills with fluid coming in particular from the accumulator or accumulators 41 through the suction valve or valves 20. On the contrary, the volume of the chamber 19 decreases and the fluid which it contains is discharged, through the corresponding valve 21, towards the accumulator 60 and from there towards the evacuation duct 59.

From similar operations occur during the "return stroke" of the moving assembly, the respective roles of the chambers 18 and 19 being reversed.

FIG. 6 shows the graphical representation of instantaneous flow rate Q of pump 2 (that is to say of the quantity of liquid discharged per unit of time) as a function of time. Thanks to the presence of the accumulator 60, the average flow represented by the line A in dotted lines is almost constant despite the significant variations in instantaneous flow, on the one hand during a race of the moving assembly, on the other hand share between the "outward race" and the "return race".

It is known, in fact, that in an engine of the type described above, the "outward stroke" takes place at a higher speed than the "return stroke".

If it is now assumed that the operating devices only demand a flow rate lower than the maximum flow rate, the discharge pressure will increase, thus causing a reduction in the length of the "moving back and forth strokes" of the moving assembly, the power of the motor 1 being kept practically constant by its own regulation. However, as indicated above, automatic adjustment of the pump flow according to demand is not possible. only over a certain load range between the maximum load and approximately 60% of the latter.

If the flow required by the user devices continues to decrease, an appropriate command acts on the rod 36 to compress the spring 35. The minimum pressure of the capacity 24 is then no longer sufficient to permanently maintain the piston 34 against the stop 14c .

At the start of the "forward stroke", the pressure in capacity 24 is close to the minimum pressure. The spring 35 therefore maintains the piston 34 and the slide 32 in the position shown in FIG. 1 or in FIG. 8, thus allowing communication between the two chambers 18 and 19. The fluid discharged from the chamber 19 passes directly into the chamber 18 via the conduits 31 and 30. The installed flow rate delivered by the pump is then zero as seen in FIG. 7.

This situation will continue until the pressure increases in the capacity 24, as a result of the depression of the rod 23, to a value sufficient to push the piston 34 against the spring 35. The drawer 32 then closes the communication between chambers 18 and 19, so that normal operation of the pump resumes. The instantaneous flow regains the value it had during operation at maximum flow (Figure 6), and decreases until the end of the "outward stroke".

At the start of the "return stroke", the pressure in the tank 24 is still high enough thanks to the accumulator 26, to keep the slide 32 in its closed position of the conduits 30 and 31. The fluid contained in the chamber 18 is discharged towards the accumulator 60 and the general line 59. When the pressure in the capacity 24 has sufficiently decreased, as a result of the withdrawal of the rod 23, the spring 35 will return the drawer 32 to the position of FIG. 1 or of the Figure 8. The fluid discharged from the chamber 18 will pass directly into the chamber 19 and the instantaneous flow rate of the pump will again be zero. This situation will continue until the end of the "return race" and in a new cycle will start again.

It is easily understood that the average partial flow rate B (FIG. 7) of the pump can be adjusted to any desired value, by adjusting the compression of the spring 35 by the control rod 36. If the force of the spring 35 is sufficient to maintain permanently, whatever the pressure in the capacity 24, the slide 32 in the position shown in FIG. 1, the average flow rate of the pump will be zero. The proper regulation of the motor 1 then acts on the latter to maintain its power at a minimum value, no loss of energy being thus recorded.

It should also be emphasized that the accumulator 60 is dimensioned in such a way that its capacity makes it possible to absorb and then restore the fluid discharged from the chambers 18 and 19, whatever the variations in the installed flow rate, due to the operation as well at maximum average flow than at partial average flow.

We will now indicate the operating conditions of the booster pump 40 and the various members associated with it to ensure a suitable supply of the pump with hydraulic fluid.

At each "outward stroke" of the moving assembly, the air pressure in the mattress chamber 8 increases and acts on the piston 52 which it pushes against the action of the spring 55.

The fluid contained in the chamber 42 is then discharged through the valves 45 towards the chamber 46 and, from there, towards the accumulator or accumulators 41 and the supply valves 20 by the conduits 47 and 22. The valves 20 do not open that to the extent that the chambers 18 and 19 need to be filled, which will not be the case during the phases of bringing these two chambers into communication with the drawer 32.

If the accumulator or accumulators 41 are filled with fluid, the piston 42 cannot discharge towards them the fluid from the chamber 43 and the piston 52 remains stationary. No risk is however entailed by this situation since the control of the piston 52 is elastic and constituted by the air pressure in the mattress chamber 8.

The chamber 43 is filled through the valve 44 as a result of the vacuum created by the return of the piston 42, to the position shown in FIG. 1 or in FIG. 8, under the action of the spring 55.

Claims (13)

1. Double-acting hydraulic pump comprising a piston (16) moving with a reciprocal rectilinear movement inside a cylinder (15) of which each chamber (18, 19) is provided with a suction valve (20) and a delivery valve (21), the rod (17) of said piston (16) being designed to be driven by a variable-displacement driving member, characterized in that said piston rod (17) extends (23) beyond the piston and moves, outside the cylinder (15), within a space of variable volume (24), provided in the body (14, 14a) of the pump, which communicates, with a member (34, 36) controlling a by-pass device (32) creating a communication between the two chambers (18, 19) of the cylinder (15).

2. Hydraulic pump according to claim 1, characterized in that said space (24) of variable volume communicates with a fluid accumulator (26).

3. Hydraulic pump according to claim 1, characterized in that said by-pass device is constituted by a slide valve (32) moving in front of two orifices .(30, 31) communicating respectively with each one of the chambers (18, 19) of the cylinder (15), said slide valve being subjected, against the action of an adjustable spring (35), to the action of the pressure prevailing in said space (24) of variable volume.

4. Hydraulic pump according to claim 3, characterized in that the control of the flow of the pump is coupled to the member (36) used for adjusting the spring (35) of the slide valve (32) and its action is directed towards increasing the force of said spring in order to cause a reduction of the pump output rate.

5. Hydraulic pump according to claim 1, characterized in that an accumulator (60) of the fluid delivered by the pump is placed on a delivery conduit (59) downstream of the delivery valves (21) of each of the chambers (18, 19).

6. Hydraulic pump according to claim 1, characterized in that at least one accumulator of fluid (41) is placed on the supply conduits (47, 22) of each chamber (18, 19), upstream of the suction valve (20) corresponding to said chambers.

7. Hydraulic pump according to any one of the preceding claims, characterized in that a booster pump (40) driven by an auxiliary motor (51) and sucking up fluid from a fluid reservoir, is connected, via its delivery chamber (46), on the one hand, with the supply pipe of each chamber (18, 19) upstream of its suction valve (20) and of the corresponding accumulator (41), and on the other hand, with the space (24) of variable volume.

8. Hydraulic pump according to claim 7, characterized in that said booster pump (40) essentially comprises a piston (42) moving inside a cylindrical chamber (43) of which the face opposite that of the piston (42) is equipped with a suction valve (44) communicating with the reservoir and with a delivery valve (45) communicating with its delivery pipe (47).

9. Hydraulic pump according to claim 8, characterized in that the piston (42) and chamber (43) of the booster pump (40) are constituted by annular members placed inside a housing (114) around a cylindrical portion of the pump body (14), preferably co-axially to said pump body.

10. Generator of pressurized hydraul.ic fluid, using a hydraulic pump according to any one of claims 1 to 9, comprising an internal combustion engine (1) of which the piston (4) is coupled to the piston (16) of the hydraulic pump (2), characterized in that said engine is a free piston type engine, known per se, and in that the piston (16) of the hydraulic pump (2) is placed co-axially to the piston (4) of the engine in order to constitute therewith a monobloc movable assembly with no mechanical link with the outside.

11. Generator according to claim 10, characterized in that the cylinder (15) of the hydraulic pump extends at least partly inside the hollow piston (4) of the engine, and in that the piston rod (17) of the hydraulic pump is coupled to the engine piston on the wall thereof which defines the combustion chamber.

12. Generator according to any one of claims 10 and 11, characterized in that the piston (42) of the booster pump (40) is coupled to an auxiliary engine (51) with single-acting piston, said piston (52) of said auxiliary engine being subjected to the action of the compressed air contained in the bounce-chamber (8) of the engine (1).

13. Generator according to claim 12, characterized in that the piston (52) of the auxiliary engine (51) is subjected to the action of a spring (55) which tends to return it to the rest position.

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