Fluid actuators

A fluid actuator (10) including a chamber (14) in which a piston assembly (17) reciprocates. The piston assembly (17) includes a pair of spaced pistons (18, 19) which divide the chamber (14) into three sections (20, 21, 22) and a passageway (29) which supports a valve member (30). Reciprocating movement of the slide valve member (30) causes fluid to be directed to the chamber sections (20) and (22) and thereby corresponding reciprocating movement of the piston assembly (17). The actuator (10) may be applied to the control of any device such as valves of internal combustion engines, fuel injectors or comprise actuating means for the piston of an internal combustion engine.

TECHNICAL FIELD 
This invention relates to fluid actuators which in one particular aspect 
are applicable to the control of various mechanisms in internal combustion 
engines, for example exhaust and inlet valves or fuel injectors and which 
in a further aspect are applicable to the extraction of power from 
reciprocating pistons of internal combustion engines. The actuators of the 
invention however may be applied to other situations for example as 
servomechanisms or for accurate control of movement. 
BACKGROUND ART 
Conventional internal combustion engines are provided with a number of 
different operating mechanisms for controlling inlet and outlet valves for 
the engine cylinders or in the case of fuel injected engines for 
controlling the injectors. Usually such mechanisms take the form of cam 
shafts, rockers, return springs or other mechanical actuating elements. 
Such mechanism suffer a number of disadvantages and limitations including 
in the case of valved engines poor valve cooling, poor lubrication, a lack 
of ability to maintain alignment of the valves with their seats, poor 
control over movement of the valve and an excessive amount of power which 
is required to overcome the valve seating springs. 
Particular disadvantages associated with fuel injectors include lack of 
flexibility of injection timing, excessive mechanical components in the 
injector drive train, an excessive amount of power wastage in operating 
the injectors and their drive train and a lack of ease of assembly and 
removability of the injectors and associated drive train from the engine 
during maintenance. 
Conventional internal combustion engines usually also include reciprocating 
pistons which are coupled to a crank shaft via piston rods, however, this 
form of mechanical connection has limitations resulting in limitation of 
transmission of usable energy from the piston to the crank shaft caused by 
changes of the lever arm at the crank shaft from zero at the start of the 
stroke through a maximum at approximately half stroke to zero at the end 
of the stroke. Further disadvantages arise because of side thrust friction 
losses causing cylinder and piston wear induced by thrust angles of the 
connecting rods relative to the cylinder bore centre line during rotation 
of the crank shaft. Lack of flexibility in the control of the rate of 
expansion of the gases of combustion also occurs due to utilization of a 
rotating crank shaft rigidly attached to the reciprocating pistons by 
connecting rods consequently leading to a considerable loss in the 
recovery of usable energy from the gases of combustion. 
SUMMARY OF THE INVENTION 
The present invention aims to provide a fluid actuator which may be applied 
to the many different applications where accurate control of movement is 
required. In one application, the fluid actuator of the invention may be 
used for the control of the inlet and exhaust valves of internal 
combustion engines so as to give increased control over movement of the 
valve and allowing for variable timing of the valve operating cycle. The 
present invention also aims to provide an arrangement which in the latter 
application reduces the reciprocating mass of the valve operating 
mechanism and reduces the rate of wear of the valve and its guides whilst 
increasing valve cooling and obtaining improved control over valve 
alignment with their seats. The present invention also aims to provide an 
actuator which when applied to the operation of fuel injectors enables 
simple control of injection timing, reduces the mass of injector drive 
train, which decreases the power required to operate the injectors and 
improves ease of assembly and disassembly of the injectors and their drive 
train to and from the engine. 
In its applicability to the extraction of usable energy from the 
reciprocating pistons of internal combustion engines the present invention 
provides an actuator which permits greater recovery of usable energy, 
reduces side thrust friction losses and consequent rates of cylinder tear 
and provides a degree of flexibility to control the rate of expansion of 
the gases of combustion. 
With the above and other objects in view the present invention provides a 
fluid actuator including a chamber, a piston assembly arranged for 
reciprocating movement within said chamber, said piston assembly including 
first and second spaced apart pistons dividing said chamber into at least 
a first chamber section between said first piston and said chamber and a 
second chamber section between said first and second pistons, passageway 
means in said piston assembly, fluid inlet means communicating with said 
second chamber section and valve means for controlling the flow of fluid 
through said passageway means, said valve means be operable to communicate 
through said passageway means said first and second chamber sections so as 
to cause movement of said piston assembly in a first direction, said valve 
means being further operable to vent fluid from said first chamber section 
whereby to permit said piston assembly to move in a direction opposite 
said first direction. 
Preferably, said piston assembly defines between said second piston and 
said chamber a third chamber section, and said valve means is operable to 
communicate through said passageway means said second and third chamber 
sections so as to cause said piston assembly to move in said direction 
opposite said first direction. 
Most preferably, said piston assembly includes first, second and third port 
means communicating with said first, second and third chamber sections 
respectively and said valve means controls communication between said port 
means and said passageway means. The piston assembly suitably includes 
opposite portions extending beyond opposite ends of said chamber, and vent 
port means in said opposite portions and adapted for communication with 
said passageway means, said valve means being adapted to control 
communication of said vent port means with said first and third port means 
whereby to control venting of said first and third chamber sections. 
Preferably, said passageway extends longitudinally of said piston assembly 
and said valve means is slidable in said passageway. Suitably, said valve 
means includes a plurality of lands, said lands being adapted to open and 
close said port means to control communication thereof with said 
passageway. Preferably, said lands are separated by annular grooves 
defining fluid paths in said passageway. 
Means are suitably provided for reciprocating said valve means such that 
movement of said valve means in said first direction opens communication 
between said first and second port means and said passageway, and opens 
communication between said third port means and vent port means through 
said passageway, to cause said movement of said piston assembly in said 
first direction. 
Preferably, movement of said valve means in said opposite direction opens 
communication between said second and third port means and said passageway 
and opens communication between said first port means and vent port means 
through said passageway to cause movement of said piston assembly in said 
opposite direction. 
The actuator may also include further chamber sections communicating with 
the respective said vent port means and isolating vented fluid. 
In a further form, the actuator includes biasing means for opposing 
movement of said piston assembly in said first direction. Suitably, said 
biasing means acts on said second piston and comprises spring means 
disposed between said second piston and wall means at the other end of 
said chamber. 
The present invention also provides the combination of a fluid actuator as 
described above and a valve of an internal combustion engine, said piston 
assembly of said actuator being coupled to said engine valve and wherein 
movement of said operation of said valve means is adapted to cause opening 
and closing movement of said valve. Suitably, said engine valve includes a 
valve stem, said piston assembly being secured to or formed integrally 
with said stem and said passageway being disposed within said stem. 
The present invention further provides the combination of a fluid actuator 
as described above and a fuel injector having a reciprocatory plunger, 
said piston assembly of said actuator being coupled to said plunger and 
being adapted to reciprocate said plunger upon operation of said valve 
means. 
In a further form the present invention provides an internal combustion 
engine comprising a piston arranged for reciprocation in a cylinder and a 
fluid actuator as described above, said piston assembly of said actuator 
being coupled to said engine piston and wherein operation of said valve 
means causes reciprocation of said piston assembly and said engine piston. 
Preferably, said valve means is operated by cam means, rotation of said cam 
means causing reciprocation of said valve means and said piston assembly. 
Means may also be provide for varying the stroke of said engine piston or 
compression ratio of said engine by selectively repositioning the cam 
means.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring to the drawings and firstly to FIG. 1 there is illustrated a 
fluid actuator 10 according to the present invention adapted for the 
control of a valve 11 of an internal combustion engine, for example an 
inlet or exhaust valve. The actuator 10 includes a housing 12 of generally 
cylindrical form which is mounted to the head 13 of an engine and which 
includes a cylindrical chamber 14 defined between an end wall 15 of the 
housing 12 and intermediate annular wall 16. 
Arranged for reciprocation within the chamber 14 is a piston assembly 17 
which includes a pair of spaced apart annular pistons 18 and 19 which 
separate the chamber 14 into three chamber sections 20, 21 and 22. The 
valve 11 includes a valve stem 23 which is secured to the piston assembly 
17 for movement therewith. Alternatively the piston assembly 17 may be 
formed integrally with the valve stem 23. An inlet port 24 is provided in 
the wall of the housing 12 for the supply of hydraulic fluid to the 
chamber section 21. 
The piston assembly 17 includes a series of ports 25, 26 and 27 provided in 
its annular shaft 28 to communicate with the respective chamber sections 
20, 21 and 22 and through the stem 23 with a longitudinally extending 
internal bore 29 formed within the shaft 28 or stem 23 of the valve 11. 
Supported for reciprocation within the bore 29 is a slide valve member 30 
which includes spaced lands 31, 32 and 33 separated by annular grooves 34 
and 35 which define passageways for hydraulic fluid. Discharge ports 36 
are provided at the upper end of the piston assembly 17 to communicate 
with the bore 29 whilst at the lower end of the bore 29 a spring 37 is 
provided to urge the valve 33 to an upper position. Further discharge 
ports 38 are also provided in the shaft 28 at the lower end of the piston 
assembly 17 to communicate through the stem 23 with the bore 29. The ports 
38 preferably extend in a non-radial direction outwardly from the bore 29 
so that liquid discharging therefrom causes an off centre force to be 
applied to the valve stem 23 and rotation of the valve 11 so as to ensure 
even wearing on the valve seat. 
The lower part of the housing 12 beneath the wall 16 forms a drainage 
chamber 39 which vents through drainage ports 40. Further drainage ports 
41 communicate with the bore 29 in the region of the spring 37 to vent 
this portion of the bore 29. 
Optionally, a return spring 42 acting between a flange 43 secured to the 
valve stem 23 and the end wall 15 of the housing 12 may be provided to 
normally hold the valve 11 in a closed position. Operation of the slide 
valve member 30 may be controlled by a solenoid 44 which has its armature 
connected to, or integral with the valve member 30, or alternatively a 
conventional rotational cam and cam shaft acting directly or indirectly on 
the valve member 30. 
In use and as shown in FIGS. 2 to 6 the piston assembly 17 when the valve 
11 is seated is moved to a raised position under the influence of 
hydraulic fluid supplied through the port 24 passing into the port 26 
through the annular groove 34 to the chamber section 22 to act between the 
piston 19 and wall 16. In this position also the slide valve member 30 is 
held in a raised position. Fluid in the chamber section 20 communicates 
through the ports 25, annular groove 35 and ports 36 to drain. So as to 
open the valve 11, the slide valve member 30 is advanced by the solenoid 
44 (or a cam) as shown initially in FIG. 3 so that the land 32 blocks the 
passage of fluid from the inlet 24 to the chamber section 22. At the same 
time, fluid communication from the port 24 is opened through the ports 26, 
groove 35 and port 25 to the upper section 20 of the chamber 14, with the 
land 33 blocking its passage to the vent ports 36, whilst the lower 
chamber section 22 is vented through the ports 27, groove 34 and port 38 
to the drainage chamber 39 and through port 40 to drain. The fluid in the 
chamber section 20 acting between the piston 18 and housing end wall 15 
causes downward movement of the piston assembly 17 and thus opening 
movement of the valve 11. At the same time the slide valve member 30 is 
moved downwardly at the same rate by the solenoid 44 as shown in FIG. 4. 
It will be seen that during this motion the return spring 37 for the valve 
member 30 and return spring 42 for the valve 11 (if used) will be 
compressed. 
When the valve 11 approaches a fully opened position, the valve member 30 
is stopped in its movement as shown in FIG. 5 so that the land 32 blocks 
communication of the port 26 with the chamber section 20 and at the same 
time the land 31 blocks communication of the chamber section 22 with the 
drainage chamber 39. The chamber section 20, however, is opened to vent 
through the ports 25, passage 35 and ports 36, whilst the chamber 21 
communicates through the ports 26, and passage 34 to the chamber section 
22. 
As fluid is supplied to the chamber section 22 through ports 26, passageway 
34 and ports 27 whilst being vented from the chamber 20 through ports 25, 
passageway 35 and ports 36, the piston assembly 17 raises upwardly thereby 
moving the valve 11 again towards a closed position. At the same time, the 
slide valve member 30 is also retracted as shown in FIG. 6 so that the 
valve 11 and slide valve member 30 move upwards at the same rate until the 
valve 11 is closed and the slide valve member 30 moved to the position of 
FIG. 2. The piston assembly 12 is thus slaved to reciprocating movement of 
the slide valve member 30. 
The inlet port 24 is preferably fitted with a non-return valve so as to 
preclude the possibility of valve bounce in the event of engine overspeed 
or the operation of an engine with excessively low hydraulic pressure 
supply. In most cases, hydraulic fluid to the inlet port 24 is supplied as 
the existing lubrication oil in an engine pressurised by a conventional 
oil pump. To increase pressure in the hydraulic supply however, the normal 
oil pump may be replaced by a pump with increased capacity or an auxiliary 
pump may be provided for direct supply of fluid sometimes other than 
lubrication oil to the inlet port 24. The housing 12 for assembly and 
disassembly purposes is preferably formed into at least two parts 
separable or joinable at the position 12' by an connection arrangement 
known in the art. 
FIG. 7 illustrates in sectional view the preferred form of piston assembly 
17 which comprises a component separate from the valve stem 23. The piston 
assembly 17 however may have the alternative form shown in FIG. 8 where 
the respective pistons 18 and 19 have frustoconical opposing faces 45 to 
facilitate the transfer of hydraulic fluid into the port 26. 
FIG. 9 illustrates in sectional view, a valve stem 23 having the piston 
assembly 17 and thus pistons 18 and 19 formed integrally therewith. 
FIG. 10 illustrates the modified engine valve 11 formed in accordance with 
the present invention for use in association with the piston assembly 17 
of FIG. 7 whilst the slide valve member 30 is suitably of the cross 
sectional form shown in FIG. 11. In the embodiment of FIG. 12 however, the 
valve member 30 includes a longitudinally extending bore 46 which extends 
through the end of the valve 30 or communicates with a radially extending 
port 47 to vent the portion of the bore 35 containing the spring 37. In 
this arrangement, of course, the vent port 41 may be eliminated. 
The housing 12 as shown in FIG. 1 may also be constructed in any of the 
forms shown in FIGS. 13 to 15. In FIG. 13, the housing 12 includes a top 
part 12a and a bottom part 12b defining the annular wall 16, the part 12a 
having an internal shoulder 48 against which the part 12b abuts. 
Preferably the parts 12a and 12b are pressed and held together by any 
suitable mounting means or clamp securing the housing to the engine head 
13. In FIG. 14, the housing 12 is in one part however the annular wall 16 
is of washer-shaped form and held against the shoulder 48 by a circlip 49 
or like connector. In FIG. 15, the housing 12 is again in two parts 12a 
and 12b with the annular wall 16 in this embodiment being a separate 
washer like part held against the shoulder 48 by the housing part 12b. 
In the embodiment of FIGS. 16A and 16B, the actuator is arranged within the 
head 13 of a engine and like parts of the actuator of FIG. 1 have been 
given like numerals in FIGS. 16 and 17. The housing 12 in both instance 
may be split longitudinally to facilitate assembly and disassembly of the 
unit and its placement within the head 13. In FIG. 16A, the housing 12 is 
placed into the head 13 from the lower side being located within a stepped 
bore 13' within the head 13 to mate therewith and be held in place by a 
circlip 13". In the arrangement of FIG. 16B, the housing 12 is inserted 
into the bore 13' from the top side of the head 13 to be again held in 
position by the circlip 13". In either case the housing 12 may be split as 
at 12' and 12" to facilitate assembly. 
The timing of the opening and closing of the valve 11 may be simply 
controlled by varying the timing of operation of the solenoid 44 which can 
be microprocessor controlled. The above described arrangement also 
eliminates mechanical valve drive trains and permits infinitely variable 
valve timing and duration of lift. The arrangement also provides the 
possibility of decompressing individual cylinders or groups of cylinders 
so as to give lighter cranking loads during engine start up procedures. 
Simplified alteration of the valve timing also permits the starting of 
engines by direct air injection into a cylinder and the facilitating of an 
engine braking capacity. Overall, a simplified lighter engine with fewer 
wearing parts results. 
Referring now to FIGS. 17 and 18 there is illustrated a fuel injector 50 
which is arranged to be driven by a fluid actuator 51 according to the 
present invention which in this aspect is a single acting actuator. The 
actuator 51 includes a cylindrical chamber 52 which is mounted to the 
injector 50 through a connection 53 which may comprise a threaded or any 
other connection and which supports a reciprocating piston assembly 54. 
The piston assembly 54 includes a pair of spaced apart pistons 55 and 56 
mounted on or formed integrally with a hollow sleeve 57 which defines a 
bore 58 for receiving a slide valve member 59. Ports 60 communicate the 
region between the pistons 55 and 56 which comprises a supply chamber 61 
with the bore 58 whilst further ports 62 communicate the region above the 
piston 55 which comprises a working chamber 63 with the bore 58, the 
chamber 63 being defined between the piston 55 and an annular wall 64 
extending transversely of the chamber 52. A vent chamber 65 is formed 
above the wall 64 being defined by an annular spacer 66 and further ports 
67 formed in the sleeve 57 communicate the chamber 65 with the bore 58. A 
return spring 68 extends between the piston 56 and injector 50 to normally 
bias the piston assembly 54 to the raised attitude shown. The piston 
assembly 54 is also positively coupled at 69 to the plunger 70 of the 
injector 50. 
The slide valve member 59 includes a pair of spaced lands 71 and 72 
separated by an annular groove 73 and a return spring 74 located in the 
lower end of the bore 58 normally biases the slide valve member 59 
upwardly to the position shown in FIG. 18. A bore 75 opening to the top of 
the assembly or optionally a vent 75' communicating with the bore 75 vents 
the lower end of the bore 58 (containing the spring 74) in the latter case 
to a lower chamber section 76 which contains the return spring 68 with 
that chamber itself being vented through ports 77. The upper vent chamber 
65 is also vented through a port or ports 78 and the lower edges of each 
port 77 and 78 act as weirs so that operating fluid is always maintained 
in the respective chambers 65 and 76 for lubrication purposes. The slide 
valve member 59 is coupled to a double acting solenoid 79 which includes 
an armature 80 whose upward movement is restricted by a cap 81. Hydraulic 
fluid is supplied to the chamber section 61 through a supply port 82 which 
is connected to any suitable supply of hydraulic fluid. 
In use and as shown in FIGS. 19 to 23 the return springs 74 and 68 
initially maintain the slide valve member 59 and piston assembly 54 in a 
raised attitude and the injector plunger 70 retracted. Hydraulic fluid 
supplied through the supply port 82 of the chamber 61 is blocked from 
passage through ports 60 by the land 71, whilst the working chamber 63 is 
vented via the ports 62, groove 73 and ports 67. 
Initial actuation of the solenoid 79 causes the slide valve member 59 to be 
advanced as shown in FIG. 20 so that the land 72 blocks the ports 67 
whilst the land 71 opens the ports 60 so that fluid may pass from the 
supply chamber 61 through the groove 73, and ports 62 into the working 
chamber 63. This fluid working between the piston 55 and wall 64 causes 
the piston assembly 54 to be advanced against the force of the spring 68 
as shown in FIG. 21 causing the injector plunger 70 to operate and apply a 
charge of fuel into an engine cylinder. 
Reversing of the solenoid 79 will cause retraction of the slide valve 59 as 
shown in FIG. 22 so that the ports 60 are blocked thereby preventing 
further fluid passing into the working chamber 63 whilst chamber 63 is 
vented via the ports 62, groove 73 and ports 67. The compressed spring 68 
will thus cause the piston assembly 54 to retract as shown in FIG. 23. 
The stroke of the plunger 70 is thus governed by the extent of movement of 
the armature 80 of the solenoid 79 so that the amount of fuel supplied by 
the injector on each stroke can be selectively varied and its rate of 
injection controlled by varying the power supplied to the solenoid. 
Alternatively, the plunger 70 of the injector may be operated at its full 
stroke at all times and the fuel metered by a spill port under the control 
of a solenoid operated valve ducted from the injector high pressure fuel 
chamber. 
FIGS. 24 and 25 illustrate an alternative form of actuator 82 coupled to a 
fuel injector 83, the actuator 82 in this instance being of the same form 
as that shown in FIG. 1 operating in double acting mode and in the same 
fashion as described in FIGS. 2 to 6. In the arrangement of FIG. 24, the 
slide valve member 84 is controlled by a solenoid 79 as described 
previously however alternatively and as shown in FIG. 25, the slide valve 
member 84 may be reciprocated by a rotatable cam 85 to cause opposite 
reciprocating movement of the piston assembly 86 of the actuator 82. So as 
to enable assembly and disassembly of the actuator 82, the chamber housing 
87 is suitably split at 88 to enable the piston assembly 86 to be removed 
from the housing 87. The split 88 may be defined by a threaded connection 
or any other suitable sealed connection. 
In the embodiment of FIGS. 24 and 25, the fluid vented from the actuator at 
89 freely mixes with the lubrication fluid or oil of the engine. However, 
to isolate the actuator operating fluid, the actuator 82 may be modified 
as shown in FIG. 26 for use say in situations where the injector is 
located externally of the engine. In this instance two further chambers 90 
and 91 are provided within the housing 87 to act as vent chambers for the 
collection of vented operating fluid. These chambers 90 and 91 are 
provided with respective outlet ports 92 and 93 which may be 
interconnected with a manifold and isolate the fluid returning to drain 
from cross contamination or loss when recycling. Again the housing 87 is 
split, in this instance at three positions 88, 88a and 88b to facilitate 
assembly and disassembly of the actuator. 
The slide valve member 84 in the above embodiments and where a cam 85 is 
used to control its reciprocation may include an end cap or shim 94 which 
may be made of varying thickness for varying the clearance/stroke of the 
valve member 84. Alternatively, this of course can be achieved through 
variations of the profile of the cam 85. 
Application of the actuator of the invention to the control of fuel 
injectors has a number of advantages permitting individual control of the 
injectors during engine operation giving more even power development by 
the engine and also permitting variable injection pressures to suit 
different fuels and different environmental conditions. Individual 
injectors may be isolated for reduced power operations and infinitely 
variable injection timing is possible using microprocessor controls. 
Both valve and injector assemblies as described above may be combined in an 
engine giving a much simpler two or four stroke engine due to the 
elimination of many parts. Such an engine may be readily controlled for 
direct reversing to suit various situations. 
Referring now to FIG. 27 there is illustrated an application of the 
actuator of the invention to the extraction of energy from a reciprocating 
piston. As shown schematically a piston 95 reciprocates in a cylinder 96 
of an internal combustion engine which may comprise a spark ignition 
engine or a compression ignition engine and be operated either as a four 
cycle or two cycle engine and for this purpose incorporates means for the 
supply of fuel and the removal of exhaust products. 
Mounted in line with the cylinder 96 but separated therefrom by a partition 
97 is a housing 98 which defines a cylindrical operating chamber 99 and a 
vent chamber 100 separated by a wall 101. Mounted within the housing 98 is 
a piston assembly 102 which includes a hollow tubular piston rod or sleeve 
103 having mounted thereon or formed integrally therewith a pair of 
pistons 104 and 105 which are arranged for reciprocation within the 
chamber 99 and divide the chamber 99 into a supply section 106 between the 
pistons 104 and 105 and opposite end sections 107 and 108 between the 
piston 104 and wall 101, and piston 105 and a further end wall 109 of the 
housing 98. The sleeve 103 includes a series of ports 110, 111, 112, 113 
and 114 which communicate with the internal bore 115 thereof. The chamber 
106 includes a port 116 for the supply of hydraulic fluid whilst a further 
port 117 communicates with the chamber 100 for venting fluid therefrom. 
Located with in the bore 115 is a slide valve member 118 arranged for 
reciprocation within the bore 115 and including spaced lands 119, 120 and 
121 separated by annular grooves 122 and 123. A return spring 124 is 
located within the bore 115 to engage the slide valve 118, the latter 
being centrally bored at 125 to define a vent terminating in a port 126 
for venting the end of the bore 115 so as to permit spring operation. 
The end of the slide valve 118 may be fitted with an end cap 127 which 
serves for clearance adjustment as a cam follower for engagement with a 
rotatable cam 128 on a cam shaft 129. The piston assembly 102 is coupled 
to the piston 95 for movement therewith. 
In use and assuming the piston 95 is at the lower end of its stroke within 
the cylinder 96 as shown in FIG. 28 and that the engine of which the 
cylinder 96 is a part is a four cycle engine, the cam shaft 129 is rotated 
so that the cam 128 moves the slide valve member 118 within the bore 115 
so that hydraulic fluid is supplied through the port 116 to pass into the 
chamber 106, port 112, groove 122 and port 111 into the chamber 108. This 
will cause the piston assembly 102 to be driven upwardly because the fluid 
acts between the piston 105 and end wall 109. At the same time fluid in 
the chamber 107 is vented through port 113, groove 123, port 114 and 
chamber 100 into the vent port 117. The piston 95 will thus be driven 
upwardly compressing the charge which has been supplied into the cylinder 
96. 
Ignition of the charge within the cylinder 96 drives the piston 95 and the 
coupled piston assembly 102 downwardly from the top position as shown on 
the right hand side of FIG. 28, whilst at the same time the cam 128 has 
advanced the slide valve 118 thereby closing communication between the 
supply port 116 and chamber 108 and causing fluid in that chamber to be 
forced out upon downward movement of the piston 95 through the port 111, 
groove 122 and port 110 where it is directed to do useful work for example 
for driving an hydraulic motor and thence return to a reservoir to be 
stored for future use. At the same time communication is opened between 
the port 116 and chamber 107 so that hydraulic fluid is admitted thereto. 
Movement of the slide valve member 118 again by the cam 128 as shown on the 
left hand side of FIG. 29 again causes fluid to be admitted to the chamber 
108 so that the piston assembly 102 is displaced upwardly causing the 
piston 95 to rise in cylinder 96 thereby causing exhaust gases therein to 
be discharged through an exhaust valve of the cylinder 96 in conventional 
fashion. At the same time, the valve 118 opens communication between the 
chamber 107 and chamber 100 so that hydraulic fluid is forced from chamber 
107 and through the outlet port 117 where again it may be directed to do 
useful work. 
Movement of the cam 128 then causes movement of the slide valve 118 to be 
reversed so that again fluid is directed from the chamber 106 into the 
chamber 107 whilst chamber 108 is vented through the port 110. This causes 
the piston assembly 102 to retract as shown on the right hand side of FIG. 
29 carrying with it the piston 95 which serves to draw in through the 
inlet valve of the cylinder 96 a fresh cylinder charge. 
A plurality of cylinders 96 and associated actuators may be arranged as 
shown in FIG. 30 with the outlets ports 110 being connected via one way 
valves 130 to a high pressure gallery 131 for supplying hydraulic fluid 
for driving a pump or other load. The slide valve member 118 is provided 
with a bore 132 stepped at 133 and located within the bore 132 is a 
secondary slide valve member 134 which operates against a return spring 
135 interposed between one end of the valve 134 and the step 133. 
The slide valve member 134 normally reciprocates in unison with the slide 
valve member 118 under the influence of the cam 128. A port 137 is 
provided in the slide valve member 118 for communication with the bore 132 
with communication of the port 137 with the bore 132 being controlled by 
the slide valve member 134. The slide valve member 134 is also centrally 
bored at 138, this bore comprising a fluid passageway normally venting the 
main spring chamber of the slide valve member 118 and also comprising a 
passageway for venting fluid from the chamber 108. 
The slide valve member 134 as shown in FIGS. 32 may be provided with 
channels 139 for discharge of hydraulic fluid from the bore 138, these 
channels communicating with channels 140 formed in the lower end of the 
slide valve 118. Alternatively or additionally, the cam 128 may be formed 
with an annular groove 141 communicating with the bore 138 for discharge 
of hydraulic fluid. 
In the event of a misfire, the non-return valve 130 associated with the 
misfiring cylinder 96 isolates the misfiring cylinder from the high 
pressure gallery 131. Fluid pressure however is maintained in the chamber 
section 108 with this pressure being insufficient to overcome the pressure 
in the gallery 31 and cause the valve 130 to open, and thus the piston 95 
will be unable to return from its top position after having been moved to 
that position by the piston assembly 102. The cam 128 however will 
continue rotating so that the slide valve member 134 under the urging of 
the spring-135 opens the port 137 so that fluid may drain therefrom 
through the bore 138 and either through the groove 141 or ports 139 and 
140. This will permit the piston 95 to return to a lower position for the 
next upward stroke. 
In the arrangement described above, the piston 95 undergoes a conventional 
four stroke cycle however it may readily be adapted for undergoing a two 
stroke cycle by providing appropriate exhaust ports in the cylinder 96. 
Furthermore, rather than extracting the hydraulic discharge for performing 
work, the hydraulic discharge may be utilised for the supply of auxiliary 
power and operation of the pistons only whilst the power to do useful work 
is extracted from the discharge gases of combustion by their passage 
through for example a turbine. In this form, the engine will be working in 
a form equivalent to a free piston engine without the disadvantages 
associated therewith. 
Referring now to FIG. 34, there is illustrated an arrangement for varying 
the compression ratio in a cylinder In the embodiment illustrated, the cam 
shaft 129 carries cams 128 for operating slide valves members 118 through 
the extended stems 118', the cams 128 being rotatably supported via 
bearings 142 on the shaft 129 but which may be engaged for rotational 
movement with the shaft 129 by means of indexing clutch assemblies 143 
such as a dog clutch which may be selectively engaged or disengaged by 
means of any suitable actuator such as an hydraulic ram or other device 
actuated by hydraulic pressure. As shown the shaft 129 is supported in 
bearings 144 in a frame 145, the latter being supported for adjustable 
movement in a vertical direction by means of, for example, a ram 146. 
Extension of the ram 146 will cause elevation of the frame 145 so as to 
cause raising of the piston assembly 102 and piston 95 within the cylinder 
96 thereby resulting in a cylinder which has the same working stroke but a 
higher compression ratio when the piston 95 is reciprocated. 
Alternatively, retraction of the ram 146 will cause lowering of the 
compression ratio. 
In the arrangement of FIG. 35, the cam shaft 129 is offset from operating 
stems 118' for the slide valves members 118 and again the cams 128 may be 
selectively engaged by the clutches 143. Reciprocatory movement of the 
slide valves 118 occurs via bell cranks 146, the latter being pivotally 
mounted at 147 on eccentrics 148. Rotation of the eccentrics will cause 
displacement of the pivotal mounts 147 of the bell cranks altering the 
ratios of leverage and thus the amount of movement transmitted to the 
valve stems 118' upon rotation of the cams 128. This arrangement thus 
permits selective alteration of the stroke and compression ratio of the 
piston 95 within the cylinder 96. 
In FIG. 36, the shaft 129 is supported rotatably via bearings 149 and 
eccentrically on respective spaced eccentric members 150, the latter being 
mounted rotatably in the engine frame. Again indexing clutches 143 are 
employed to enable selective engagement of the cams 128 with the shaft 
129. The eccentric members 150 are externally threaded at 151 and engaged 
by respective screw threaded spindles 152, the latter of which may be 
coupled via gearboxes 153 to a single adjustment shaft 154. Rotation of 
the shaft 154 will be transferred into rotation of the spindles 152 and 
thus rotation of the members 150 thereby altering the position of the 
shaft 129 relative to the valve stems 118'. This thereby serves to vary 
the stroke of the piston 95 and the compression ratio. In each of the 
above arrangements, selected cylinders may be isolated in the case of 
damage by simply disengaging the indexing 143 whilst continuing to operate 
the engine. 
The cams 128 may alternatively be fixedly mounted to the shaft 129 or 
formed integrally with the shaft 129 so as to always rotate with the shaft 
and be carried in bearings about the shaft rigidly mounted to the engine 
frame. Alternatively, the shaft may be mounted as described in FIGS. 34, 
FIG. 35 or FIG. 36. 
The present invention thus provides a fluid actuator which has many 
applications and which is particularly suited to use in controlling 
various functions at motor vehicles. Movement of the slide valve member in 
opposite directions causes corresponding slaved movement of the piston 
assembly so that the actuator of the present invention is particularly 
suited to servomechanism type applications. 
Many modifications and variations to the invention as would be apparent to 
persons skilled in the art may be made thereto without departing from the 
broad scope and ambit thereof as herein set forth. For example, different 
valving configurations may be employed other than the slide valve 
arrangement illustrated. Furthermore, whilst the actuator of the invention 
is primarily suited to be driven by liquid such as hydraulic fluid, it may 
readily be adapted to be driven by gases or air.