Free-piston motor with hydraulic or pneumatic energy transmission

A free-piston motor with hydraulic or pneumatic energy transmission comprising at least one free-piston unit designed for intermittent operation using always the same optimal cycle comprising a compression and an expansion stroke and consisting of a cylinder (88) with at least one free piston (89) which is slidable to-and-fro therein, said piston (89) being connected to a member (90) of general plunger-like shape which is adapted to slide to-and-fro inside at least one stationarily mounted chamber member (95) and which delimits within said chamber member a first or plunger chamber (93) which is in communication with a source of pressurized fluid (103) through an operable valve member (82,83), a second or displacement chamber (96) which is in communication via a nonreturn valve (99) with a reservoir (100) and is connected via a second nonreturn valve (102) to an accumulator (103), and a third or buffer chamber (97) which is in open communication with said accumulator (103). Preferably the cylinder (88) contains two free pistons (89, 89 ') and both plunger chambers (93, 93') are in communication with said source of pressurized fluid (103) through one common operable valve member, the displacement chambers being each in communication with the accumulator via a pipe incorporating an operable valve member, or each plunger chamber (93, 93') is in communication with said source of pressurized fluid (103) through its own separate operable valve member (82, 83), so that during the waiting time after each cycle the piston positions can be corrected if necessary.

The invention relates to an apparatus for driving a member, such as a 
wheel, pulley, rod or similar member, comprising at least one rotary or 
linear motor which is coupled to said member and is driven by a 
pressurized fluid, particularly a hydraulic motor or similar hydraulic 
apparatus, which on one side is in communication via a pipe with at least 
one accumulator for a pressurized fluid, particularly a liquid, and on the 
other side with an outlet leading to a reservoir for said liquid, and 
further comprising at least one free-piston unit consisting of a cylinder 
with at least one free piston which is slidable to-and-fro therein and 
which delimits a space within the cylinder in such a manner that on the 
expansion stroke of the piston, during which the latter is moved in the 
one direction, the volume of the space is increased, while on the 
compression stroke of the piston, during which the latter is displaced in 
the other direction, the volume of the space is reduced, while means are 
provided for the admission and discharge of a gas into and out of said 
space respectively, together with means for heating the gas compressed in 
said space by the compression stroke of the piston, the latter being 
connected to a member of general plunger-like shape which is adapted to 
slide to-and-fro inside at least one stationarily mounted chamber member, 
at least two parts of different diameters of the periphery of the 
plunger-shaped member making sliding fits with parts of the inside wall of 
the chamber member, while the plunger-shaped member has three 
substantially radial surfaces each of which delimits within the chamber 
member a substantially closed chamber whose capacity gradually varies as 
the piston makes its expansion and compression strokes, of which surfaces 
a first radial surface delimits a first or plunger chamber which is in 
communication with a source of pressurized fluid, and a second radial 
surface delimits a second or displacement chamber which is in 
communication via a nonreturn valve with the reservoir and is connected 
via a second nonreturn valve to the accumulator, so that during the stroke 
of the piston whereby the capacity of the second chamber is increased 
liquid is drawn out of the reservoir into this chamber and during the 
other, opposite stroke of the piston whereby the capacity of the second 
chamber is reduced this liquid is forced out of said chamber in order to 
load the accumulator, and the third radial surface has a smaller operative 
area than the first radial surface and delimits substantially inside the 
chamber member a third chamber, while its capacity increases and decreases 
respectively during the expansion and compression strokes of the piston. 
Such apparatus is known from U.S. Pat. No. 4,382,748. 
In an apparatus of this type the accumulator is filled during operation 
with a fluid, particularly a liquid, such as oil, under high pressure. 
Through an adjustment of a regulatable control slide valve connected to a 
fixed linear or rotary hydraulic motor, oil is caused to flow out of the 
accumulator to the hydraulic motor and from the latter to the liquid 
reservoir, while mechanical power is delivered to the output shaft of the 
hydraulic motor, and the pressure in the accumulator will decrease. 
In the prior art apparatus a pair of free piston moves in line 
reciprocation in a cylinder each of said pistons being connected with a 
pump piston slidably movable in a pump cylinder and with a compression 
piston slidably movable with said pump piston in a compression cylinder so 
that the first, second and third chambers mentioned herein above are 
formed. 
The first plunger chamber is in open communication with a source of 
pressurized fluid. Both second and third chambers are in communication 
with a low pressure inlet or reservoir through a nonreturn valve and with 
the accumulator also through a nonreturn valve. However the nonreturn 
valves in the communication between the second chamber and the accumulator 
and between the third chamber and the reservoir can be by-passed by 
opening first and second operable valves respectively whereas the 
nonreturn valve through which the third chamber is in communication with 
the accumulator can be made inoperative by closing a third operative 
valve. 
In a primary mode of operation the first and third operable valves are 
closed and the second operable valve is open so that the third chamber is 
solely in open communication with the reservoir and serves only as a means 
for interrupting the normal cycling motion with s pause period, the second 
operable valve then being closed so that said third chamber forms a 
pressure lock at the end of an expansion stroke, and as a means for 
resetting the free piston in starting the free piston engine, a high 
pressure fluid from an external source then being introduced into the 
third chamber whereas the second chamber is vented to inlet pressure by 
means of a reset spool valve and a reset actuator. 
In a secondary mode of operation the second operable valve is closed and 
the first and third operable valves are open so that then the third 
chamber forms the pump chamber instead of the second chamber as in the 
first mode of operation. 
The prior art apparatus is designed for a continuous reciprocating motion 
of the free pistons at a predetermined cycle rate what makes it necessary 
that the free pistons are mechanically interconnected since for a smooth 
operation of a free piston engine having two pistons the starting 
positions of said pistons at each cycle must lie within determined 
tolerance limits. However, such mechanical interconnection of the free 
pistons makes the engine complicated. 
The invention seeks to provide an apparatus of the kind defined which does 
not have said disadvantage, in that the free-piston unit according to the 
invention can work most effectively in intermittent operation, using 
always the same optimal cycle, that is to say the unit is stopped after 
each cycle comprising a compression and an expansion stroke, so that 
during the waiting time after each expansion stroke, the piston positions 
can be corrected, if necessary. 
This aim is achieved in that in the apparatus according to the invention 
the first or plunger chamber is in communication with said source of 
pressurized fluid through an operable valve member so that by opening said 
valve member the piston makes it compression stroke and the third chamber 
is solely in open communication with said accumulator so that at the end 
of the expansion stroke the third chamber forms a buffer chamber filled 
with liquid and in communication with the accumulator. In this arrangement 
the buffer chamber is preferably also in communication, via a pipe 
provided with a nonreturn valve, with the displacement chamber. 
In an apparatus constructed in this manner, when the pressure in the 
accumulator has reached a specific minimum value, the operable valve 
member is brought to the open position, so that the pressurized fluid 
flows from the source, preferably oil from the accumulator, into the 
plunger chamber, and through the resulting pressure applied to the first 
radial surface the piston will be caused to make the compression stroke, 
while oil is also drawn into the displacement or liquid chamber. The gas 
pressure in the cylinder chamber thus rises, and after the piston has 
reached a determined position a fuel, for example, is injected into the 
chamber and is burned, the burning preferably being initiated by 
self-ignition combustion, so that the pressure in the chamber rises 
sharply with the consequence that the piston is moved in the opposite 
direction to make the expansion stroke. During this expansion stroke the 
oil drawn into the displacement chamber is displaced to the accumulator 
and the fluid in the plunger chamber is forced back to the source. During 
the expansion stroke the valve member is brought back to the closed 
position, so that the movement of the free piston stops close to the end 
of the expansion stroke. 
During the expansion stroke of the free piston the fluid in the 
displacement and plunger chambers is thus under pressure, so that at the 
end of this stroke as a result of the compressibility of the fluid, said 
fluid will have the tendency to move the free piston a considerable 
distance in the opposite direction, when the piston would encounter 
practically no resistance in that direction as in the prior art apparatus. 
However, in the apparatus of the invention such resistance is present in 
that at the end of the expansion stroke the third chamber forms a buffer 
chamber filled with liquid and in communication with the accumulator 
whereas during the expansion stroke a part of the oil displaced from the 
displacement chamber to the accumulator is delivered to the buffer 
chamber, so that when the movement of the piston is reversed at the end of 
the expansion stroke, this movement will be braked by the pressure acting 
on the third radial surface. In addition, a part of the compression energy 
of the oil in the plunger and liquid chambers is recovered, in that oil is 
displaced by the third radial surface to the accumulator. 
Preferably two free pistons are disposed in the cylinder, which move 
towards one another in the compression stroke and away from one another in 
the expansion stroke. 
According to the invention in that case either both plunger chamber are in 
communication with the source of pressurized fluid through one common 
operable valve member or each plunger chamber is in communication with 
said source through its own separate operable valve member. 
In the latter case, by opening one of said valve members slightly before 
the other valve member, a divergence from the symmetrical position of the 
pistons in their outermost positions inside the cylinder can be corrected 
in that then the compression stroke of the piston situated most to the 
outside is initiated in advance of the compression stroke of the other 
piston. For a smooth operation of the free-piston unit comprising two 
pistons it is necessary for the starting positions of the free pistons to 
lie within determined tolerance limits. An other advantage of this 
configuration is a reduced average waiting time between cycles, resulting 
in a higher maximum power output. 
In order to have also in the former case the possibility to correct a 
divergence from the symmetrical position of the pistons, in that case the 
liquid chambers are each in communication, via a pipe incorporating an 
operable valve member, with the accumulator. During the waiting time after 
each expansion stroke it is then possible, if necessary, for one or both 
of the two valve members, to be operated in order to correct the piston 
positions. 
The plunger chamber and the displacement chamber may preferably each be 
brought into communication with the reservoir via an operable valve. By 
opening these valves the free piston can be brought into the correct 
starting position for the purpose of starting up the unit after a lengthy 
stoppage, since because of the oil pressure still acting on the third 
surface the piston will be moved outwards. 
Advantageously a preferably adjustable constriction is then preferably 
provided downstream of the operable valve in the connection between the 
displacement chamber and the reservoir, whereby the speed of the free 
piston can be controlled in its movement to the starting position. 
In view of the fact that in an apparatus according to the invention a 
substantially constant pressure prevails in the hydraulic system, the 
ratio between the amount of heat given out by the aforesaid space inside 
the cylinder and the amount of delivered oil is nearly constant. The 
cylinder of the unit can therefore be provided in an advantageous manner 
with jacketing for the purpose of cooling the cylinder by means of the 
liquid, this jacketing being at one end in communication with the 
hydromotor outlet leading to the reservoir and at the other end in 
communication with the reservoir via a cooler. 
The cooler preferably contains a hydraulically driven fan, the drive of 
which is connected at one end to the accumulator and at the other end via 
the cooler to the reservoir, so that this fan can be switched on if the 
temperature exceeds an acceptable maximum level. 
In view of the fact that it is of great importance that in the apparatus 
according to the invention the operable valve members, particularly the 
regulating valve members, should be valves which open and close rapidly, 
these valve members are according to the invention so constructed that 
they comprise a body which is provided with respective connections to the 
high and low pressure parts of the pip concerned and which has at least 
one through passage in which a valve element is received, with its bottom 
face resting on a seat, an is adapted to be moved away from and towards 
said seat, this passage being in communication at one end with the high 
pressure connection and at the other end with the low pressure connection, 
so that the high pressure acts on the top face and the low pressure on the 
bottom face of the valve element, and beneath the latter a pin-like member 
is disposed which is slidable inside a bore away from and towards the 
valve element and has at least one substantially radial surface delimiting 
inside the bore a substantially closed space which is in communication, 
via preloaded nonreturn valves with the high pressure connection, so that 
this space is always filled with the liquid under high pressure, while 
means are provided for raising the pressure and supplying liquid, so that 
the pin-like member is thereby displaced an the valve element is lifted 
off its seat. In this arrangement the aforesaid surface of the pin-like 
member is preferably formed by a shoulder surface provided on the pin-like 
member and directed away from the valve member, while the bore in which 
said pin-like member is received is in communication at the bottom end 
with the high pressure connection, so that the high pressure acts on that 
end surface of the pin-like member which is situated at a distance from 
the shoulder surface. The means for raising the pressure advantageously 
consist of at least one piezoelectric element by which an electric signal 
with a short time delay and short switching time is converted into a 
mechanical signal of great power and short stroke. 
In view of the fact that the apparatus according to the invention offers 
many possible forms of regulation for the piston movements and positions, 
it is preferable to use two free pistons which during the compression 
stroke move towards one another and during the expansion stroke move away 
from one another, while in the cylinder inlet and outlet ports are 
provided which are disposed symmetrically in relation to the centre of the 
cylinder, and according to the invention one free piston has a lower mass 
than the other free piston. In an apparatus constructed in this manner the 
lighter piston will thus be the first, during the expansion stroke, to 
open the outlet ports situated on the side where this piston is disposed, 
and during the compression stroke will be the first to close them, which 
will have an advantageous effect on the scavenging of the chamber. In 
addition, this difference in mass will have a favourable influence on the 
combustion process. By adaptation of the various plunger surface areas it 
is possible to influence still further the strokes and the movement cycles 
of the free pistons in order to optimize the effect described above. Thus 
in the previous described construction the movement of the pistons is 
typically asymmetrical.

As shown in FIG. 1, the apparatus comprises in this case a variable 
hydraulic motor 1, which is connected via the pipe 2 to an accumulator 3 
for pressurized liquid and which has an outlet 4 for this liquid, leading 
to a reservoir 5 which may optionally be under a low superatmospheric 
pressure. 
In addition, a free-piston unit is provided which consists of a cylinder 6 
containing two free pistons 7 and 7' which are reciprocatingly slidable 
therein and which during the compression stroke move towards one another 
and during the expansion stroke move away from one another, said free 
pistons together delimiting a space 8 inside the cylinder 6. This space is 
for example in the form of a combustion chamber, the wall of the cylinder 
6 being in that case provided with inlet and outlet ports (not shown), 
while means (not shown) for injecting a fuel into the combustion chamber 8 
are provided, so that the combustion of said fuel takes place in 
accordance with the two-stroke diesel principle. 
The pistons 7 and 7' are substantially identical, so that only the piston 7 
will be further described, the same reference numerals with the addition 
of a prime being used to designate corresponding parts of the piston 7'. 
The piston 7 is connected to a plunger-shaped member 9, which comprises a 
first part 10 adapted to slide reciprocatingly inside a chamber member 11, 
the outer peripheral surface of said part 10 making a sliding fit with the 
inside wall of the chamber member 11, so that the end surface 12 of said 
part 10 delimits inside the member 11 a plunger space 13 which is in 
communication with the accumulator 3 via a pipe 14 and a valve system 26. 
The plunger-shaped member 9 has a second part 15, the outer peripheral 
surface of which makes a sliding fit with the inside surface of a second 
chamber member 16 and which has a first annular end face 17 which delimits 
a displacement chamber 18 inside the chamber member 16. This displacement 
chamber 18 is in communication via a pipe 19, provided with a nonreturn 
valve 20, with the liquid reservoir 5, and via a pipe 21, provided with a 
nonreturn valve 22, with the accumulator 3. The second part 15 of the 
plunger-shaped member 9 also has a second annular end face 23, which is 
directed oppositely to the end face 17 and which delimits a buffer chamber 
24 inside the second chamber member 16. This buffer chamber 24 is in 
communication via a line 25 not only with the accumulator but also via the 
valve 22 or 29 with the displacement chamber 18. 
The pipes 14, 14' contain an operable valve member 26, so that on the 
opening of this valve, which takes place after the pressure in the 
accumulator 3 has fallen below a specific minimum level, the plunger 
chambers 13, 13' are brought into open communication with the accumulator 
3, whereby because of the liquid pressure acting on the faces 12, 12' the 
pistons 7, 7' are driven towards one another for the performance of the 
compression stroke, the gas pressure in the chamber 8 thus rising. At the 
same time liquid is also drawn out of the reservoir 5, via the pipes 19, 
19' and valves 20, 20', into the displacement chambers 18, 18'. After the 
pistons 7, 7' have reached a determined position, fuel is injected into 
the chamber 8, the burning of which is initiated by self-ignition 
combustion, so that the gas pressure in the chamber 48 rises sharply, with 
the consequence that the pistons are moved away from on another for the 
performance of the expansion stroke. During this expansion stroke, liquid 
present in the plunger chambers 13, 13' and liquid from the chambers 18, 
18' are displaced via respective pipes 14, 14' and 21, 21' to the 
accumulator 3, while a part of these last-mentioned liquid flows is also 
passed via the pipes 25, 25' to the buffer chambers 24, 24'. As the end of 
the expansion stroke approaches, the valve 26 is closed again. At the end 
of the expansion stroke the movements of the pistons are reversed because 
of the compressibility of the liquid still present in the chambers 13, 13' 
and 18, 18', while however the pistons 7, 7' are braked by the liquid 
pressure acting on the surfaces 23, 23' of the buffer chambers 24, 24'. In 
order then to prevent the occurence of cavitation in the chambers 13, 13', 
the pipes 14, 14' are connected via the pipe 27, containing the nonreturn 
valve 28, to the liquid reservoir 3, so that liquid can be drawn via the 
pipes 27, 14, 14' into the plunger chambers 13, 13'. 
In order to ensure good operation of the free-piston motor it is of great 
importance that after each expansion stroke the starting positions of the 
pistons 7, 7' should lie within close tolerance limits. To enable these 
starting positions to be corrected during the waiting time after an 
expansion stroke, the operable valve members 29, 29' are provided. By 
opening one or both of these valve members, the respective piston 7, 7' 
can be slightly displaced in the direction of the other piston in view of 
the fact that the displacement chamber 18, 18' is thereby brought into 
open communication with the accumulator 3, so that the liquid pressure 
prevailing in the accumulator 3 acts on the surface 17, 17' which has a 
larger working area than the surface 23, 23 of the buffer chamber 24, 24'. 
In addition, the displacement chambers 18, 18' can be brought into open 
communication with the liquid reservoir 5 via the pipes 30, 30' through 
the opening of the valve members 31, while the plunger chambers 13, 13' 
can be similarly brought into open communication with the liquid reservoir 
5 via the pipes 14, 14', 27 through the opening of the valve member 32, so 
that because of the liquid pressure acting on the surfaces 23, 23' of the 
buffer chambers 24, 24' both the pistons 7, 7' can be brought into the 
correct outer starting position, which is of particular importance when 
the free-piston motor is started up after a long stoppage. 
Furthermore, an adjustable constriction 33 is provided, by means of which 
the speed at which the pistons 7, 7' are brought to the outer starting 
positions can be adjusted. Moreover, when a cold motor has to be started, 
this constriction can be used to control the pressure in the displacement 
chambers 18, 18', in which case only the valve member 31 is operated. This 
is necessary in order to maintain a constant stroke of the free piston 7, 
7' despite higher viscosity and lower combustion efficiency. 
In addition, a pump 34 is provided, with the aid of which the hydraulic 
system can be pressurized after a long stoppage. 
For the cooling of the combustion chamber 8 a cooling coil 71 is disposed 
around the cylinder 6 and is covered by a jacket 72 of insulating 
material. The coil 71 is in communication at one end, via the pipe 73, 
with the outlet 4 of the hydraulic motor 1, and at the other end, via the 
pipe 74, with a cooler 75, and also, via the pipe 76, with the reservoir 
5. In this way the combustion chamber 8 can thus be cooled with the aid of 
return oil from the hydraulic system. 
In order to increase the cooling capacity of the cooler 75 under extreme 
conditions a fan 77 is provided, which is driven by the hydraulic motor 
78, the latter being in communication with the accumulator 3 via the pipe 
79 and the valve 80 contained in it. 
In order to be able to cool the chamber 8 when the hydraulic motor 1 is at 
rest, so that there is no return oil flow, the valve 81 can be operated to 
enable cooled oil to be pumped from the reservoir 5 through the coil 71 by 
means of the pump 34. 
Half of a form of construction of the free-piston unit according to the 
invention, of the type shown in FIG. 1, is shown in longitudinal section 
in FIG. 2. A free piston 36 is reciprocatingly slidable in the cylinder 
35. The free piston 36 is connected to a tube 37 which is closed at the 
piston end and at the other end is provided with a radial thickening 38. A 
second tube 39 mounted in a fixed block 44 extends inside the tube 37, the 
inner periphery of the thickening 38 on the tube 37 making a sliding fit 
with the outer periphery of the tube 39, so that the tubes 37 and 39 form 
together a plunger chamber 40 which at 41 is in communication, via the 
pipe 14" an the operable valve member 32', with the accumulator 3', and 
which at the other end is bounded by the surface 42, of which the part 
delimited by the outside diameter of the tube 39 coincides with the 
surface 12 in FIG. 1. A bush-shaped member 43 is mounted at its one end in 
the fixed block 44 and at the other end in a body 45 connected to the wall 
of the cylinder 35. The bush-shaped member 43 is disposed coaxially around 
the tubes 37 and 39 in such a manner that the outer peripheral surface of 
the radial thickening 38 makes a sliding fit with the inside wall of the 
bush-shaped member 43, so that on one side of the thickening 38 an annular 
displacement chamber 46 having an operative surface 47 is formed, while on 
the other side of the thickening 38 a buffer chamber 48 having an 
operative surface 49 is formed. The displacement chamber 46 is in 
communication via the connection 50 with the pipe 19" leading to the 
liquid reservoir 5' and containing the nonreturn valve 20', and via the 
connection 51 to the pipe 21" leading to the accumulator 3' and containing 
the nonreturn valve 22". The buffer chamber 48 is in communication with 
the pipe 25" via the connection 52. 
The embodiment shown in FIG. 2 has a compact construction and high 
efficiency. This high efficiency is achieved, inter alia, through the 
elastic deformation of the wall of the tube 39 during the compression 
stroke, whereby the clearance and consequently the leakage between the 
members 38 and 39 will be reduced. 
During the expansion stroke there is no pressure differential over the tube 
39, so that there is a greater clearance between 38 and 39 and therefore 
lower losses due to friction. Moreover, in this embodiment the surfaces 
which are difficult to machine are relatively small, so that production 
costs are lower. 
FIG. 3 shows schematically a second form of construction of the apparatus 
according to the invention in which only the free-piston unit is shown. 
This second form of construction differs from the first form substantially 
only in that the valve 26 in FIG. 1 is replaced by two valves 82, 83. 
Moreover also the single valves 31 and 28, 32 in FIG. 1 are replaced by 
two valves 84, 85 and two valves 86, 87 respectively. 
The free-piston unit comprises a cylinder 88 containing two free-pistons 89 
and 89' which are reciprocatingly slidable therein. Each piston 89, 89' is 
connected to a plunger-shaped member 90, 90' which comprises a first part 
91, 91' which with its end surface delimits inside a chamber member 92, 
92' a plunger-space 93, 93'. Said plunger-shaped member 90, 90' has a 
second part 94, 94' which delimits inside the chamber element 95, 95' at 
the one side a displacement chamber 96, 96' and at the other side a buffer 
chamber 97, 97'. Said displacement chamber 96, 96' is in communication via 
a pipe 98, 98' provided with a nonreturn valve 99, 99', with the liquid 
reservoir 100, and via a pipe 101, 101', provided with a nonreturn valve 
102, 102' with the accumulator 103, whereas the buffer chamber 97, 97' is 
in communication via a line 104, 104' not only with the accumulator 103 
but also via the valve 102 with the displacement chamber 96, 96'. 
Each plunger-chamber 93, 93' is in communication with the accumulator 103 
via an own separate operable valve member 82, 83 respectively so that a 
diversion from the symmetrical position of the pistons 89, 89' in their 
outermost positions inside the cylinder 88 can be corrected by opening one 
of the valve members 82, 83 slightly before the other valve member so that 
the compression stroke of the piston 89, 89' situated most to the outside 
inside cylinder 88 is initiated in advance of the compression stroke of 
the other piston. Thus the valve members 29, 29' which are provided for 
this correction purpose in FIG. 1 are disposed off in the second 
embodiment. 
Further the liquid chambers 96, 96' can be brought into open communication 
with the reservoir 100 through pipe 105, 105' by opening the valve members 
84, 85 respectively, while the plunger chambers 93, 93' can be brought 
into open communication with the liquid reservoir 100 by opening the valve 
members 86, 87 respectively so that because of the liquid pressure acting 
on the surfaces of the plunger shaped element which delimits the buffer 
chambers 97, 97', both pistons 89, 89' can be brought into the correct 
outer starting position. 
Furthermore an adjustable constriction 84', 85' is provided, by means of 
which the speed at which the pistons are brought to the outer starting 
positions can be adjusted. 
The second embodiment offers the advantage with respect to the first 
embodiment that each side of the free-piston unit requires only one intake 
and one outlet conduit so that the reliability of the apparatus is 
increased and the risk of failures is decreased. Furthermore a reduction 
of waiting time after each cycle is obtained, resulting in an increased 
top power output. 
FIG. 4 shows an axial section of a form of construction of an operable 
valve member according to the invention, this form of construction being 
particularly suitable for the operable valves 29, 22; 29', 22'; 82 and 83. 
The valve member comprises a body 53 which is tightly enclosed in the 
partially shown jacket 53'. The body has connections 54 and 55 for 
connection to the high pressure part, that is to say in the case of the 
previously described systems the accumulator side, and tee low pressure 
part respectively of the pipe in question. The connections 54 merges into 
a passage 56, which in turn merges into a chamber 56'. A bore 57 and a 
plurality of bores 58 and a plurality of bores 59 open into the chamber 
56'. 
The bores 58 bring the chamber 56' into open communication with the annular 
chamber 60, so that the high pressure prevails in said chamber 60. 
The bores 59 also open into the annular chamber 60, while at this outlet 
point a valve seat is formed, onto which a preferably spherical valve body 
61 is pressed by means of the spring 62, the high pressure inside chamber 
60 acting on the top face of valve body 61 which faces away from said 
valve seat. 
In addition, each bore 59 is in communication with a passage 63 which is in 
communication with the connection 55 on the low pressure side so that the 
low pressure acts on the bottom face of valve body 61. A pin-shaped member 
64 is arranged to slide in each bore 59 and has a shoulder surface 65 
which is directed towards the connection 54 and which delimits inside the 
bore 59 a chamber which is in communication with the space 69 via the 
passage 66, the annular space 67, and the transverse passage 68. 
The bore 57, in which one or more (in the present case two) preloaded 
nonreturn valves are disposed, also leads out into the annular space 67, 
so that the space under the shoulder 65, the passage 66, the annular space 
67, the passage 68 and the space 69 will always be filled with liquid 
under high pressure. In the body 53 at least one actuator, in the 
embodiment shown specifically a piezoelectric element 70 is disposed which 
drives a membrane- or plunger-shaped body 70', so that when a voltage is 
applied to an element of this kind a displacement of great power but short 
stroke is produced, which is converted by means of the hydrostatic 
transmission into a larger displacement of the pin-shaped member 64, 
whereby the spherical valve member 61 is lifted off its seat. This results 
in the establishment of communication between the annular space 60 and the 
passage 63, which means that the liquid can flow from the connection 54 
through the passage 56, the chamber 56', the bores 58, the annular chamber 
60, and the passage 63 to the connection 55. If in the closed situation 
the pressure at the connection 55 rises above the pressure at the 
connection 54, the balls 61 will be lifted off because of the pressure 
differential over these balls, and the liquid will flow from the 
connection 55, via the space 60, the bores 58, the chamber 56', and the 
passage 56 to the connection 54. In addition to its on-off function for a 
flow of liquid from the connection 54 to the connection 55, the valve thus 
has also a non-return function for an oppositely directed flow, so that 
with a single valve it is possible to replace an on-off valve and a 
nonreturn valve mounted in a bypass, as shown in FIG. 1, for example, at 
29, 22; 26 and in FIG. 3 at 82, 83 and 86, 87.