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Claims  |
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What is claimed is:
1. A free piston combustion engine comprising:
body means defining a pair of opposed combustion cylinders;
a combustion piston reciprocably disposed in each said combustion cylinder
for reciprocal motion therein;
piston rod means connecting said combustion pistons one to another whereby
said combustion pistons may reciprocate in unison in their respective
combustion cylinders;
hydraulic power output means including at least one pair of hydraulic
cylinder spaces having an associated hydraulic piston reciprocably
disposed therein, said hydraulic piston being operatively linked to said
piston rod so as to reciprocate in unison therewith;
hydraulic accumulator means for storage of hydraulic fluid under elevated
pressure for use in starting said engine;
hydraulic inlet check valves for controlling inlet of hydraulic fluid to
each said hydraulic cylinder space, said hydraulic inlet check valves each
including a first check valve member movable between a first position in
which it permits inlet of hydraulic fluid to its respective hydraulic
cylinder and a second position in which it prevents inlet of hydraulic
fluid thereto;
first hydraulic control means connected between said hydraulic accumulator
means and said hydraulic cylinder spaces for controlling flow of hydraulic
fluid from said hydraulic accumulator means to said hydraulic cylinder
spaces during starting of said engine, said first hydraulic control means
including a directional valve means permitting, in one condition thereof,
inlet of hydraulic fluid from said hydraulic accumulator means to one of a
respective pair of hydraulic cylinder spaces and outlet of hydraulic fluid
from the other one thereof and permitting, in another condition of said
directional valve means, inlet of hydraulic fluid from said hydraulic
accumulator means to said other hydraulic cylinder space of said pair and
outlet of hydraulic fluid from said one hydraulic cylinder space of said
pair;
hydraulic outlet check valves for controlling outlet of hydraulic fluid
from each said hydraulic cylinder space, said hydraulic outlet check
valves each including a second check valve member movable between a first
position in which it permits outlet of hydraulic fluid from its respective
hydraulic cylinder space to an output supply line and a second position in
which it prevents outlet of hydraulic fluid from its respective hydraulic
cylinder space; and
second hydraulic control means connected between said hydraulic accumulator
means and said hydraulic outlet check valves arranged to permit
application of an elevated control pressure to said second check valve
members so as to move them each to its respective said second position to
prevent outlet of hydraulic fluid from its associated hydraulic cylinder
space during starting of said engine so long as the pressure within said
associated hydraulic cylinder space does not exceed said elevated control
pressure;
said first hydraulic control means being arranged to permit, during
starting of said engine, by repeated switching of said directional valve
means between said first and second conditions thereof, hydraulic fluid to
enter each of said pair of hydraulic cylinder spaces in turn from said
hydraulic accumulator means thereby to impart reciprocal motion to said
piston rod and to said combustion pistons so as to produce in said
combustion cylinders in turn a desired compression pressure at which
combustion can be initiated therein; and
said second hydraulic control means being arranged so that, at a
predetermined moment after said piston rod together with said pistons
begins to reciprocate, said control pressure is removed from said second
check valve members to permit outlet of hydraulic fluid from said
hydraulic cylinder spaces.
2. A free piston combustion engine according to claim 1, wherein said
hydraulic power output means comprises a double-acting piston and cylinder
arrangement including a single piston slidable within a common cylinder
and dividing said common cylinder into said pair of opposed said hydraulic
cylinder spaces.
3. A free piston combustion engine according to claim 1, wherein said
hydraulic power output means comprises a pair of single-acting
piston/cylinder pumps in a boxer arrangement.
4. A free piston combustion engine according to claim 1, wherein said
second hydraulic control means includes a control valve having a first
inlet connected to said hydraulic accumulator means, a second inlet
connected to said output supply line, and an outlet connected to said
hydraulic outlet check valves, said control valve including a check valve
member movable between a first end position in which it permits
communication between said first inlet and said outlet to permit
application of hydraulic pressure from the hydraulic accumulator means to
said second check valve members to bias them towards their respective
second positions and a second end position in which it permits
communication between said second inlet and said outlet to permit the
pressure on the two sides of the said second check valve members
substantially to equalise to permit free movement thereof between their
respective said first and second positions.
5. A free piston combustion engine according to claim 4, wherein each said
hydraulic outlet check valve further comprises spring means resiliently
biasing said second check valve member towards its second position whereby
said control pressure is provided by a combination of hydraulic pressure
from said hydraulic accumulator means and spring pressure provided by said
spring means.
6. A free piston combustion engine according to claim 1, wherein said
output supply line is provided with a hydraulic motor arranged to drive an
electric generator and a flushing pump.
7. A free piston combustion engine according to claim 1, wherein said first
hydraulic control means and said second hydraulic control means are under
the control of an electronic controller which is connected to sensors
arranged to sense the speed and position of said free piston unit.
8. A free piston combustion engine according to claim 7 wherein said
electronic controller is arranged to initiate fuel injection at a moment
which is selected from the moment at which said free piston unit has
completed a preset number of reciprocating movements and the moment at
which said free piston unit has attained a predetermined magnitude of
inertial energy and wherein said electronic controller is arranged to
disable said first hydraulic control means and stop switching of said
directional valve means between its first and second positions at a second
moment selected from said first moment, a moment immediately before said
first moment, and a moment immediately after said first moment, thereby to
permit said hydraulic cylinder spaces to receive hydraulic fluid via said
hydraulic inlet check valve means from a reservoir for hydraulic fluid.
9. A free piston combustion engine according to claim 1, wherein a further
pressure accumulator means is connected to said output supply means and
wherein said hydraulic accumulator means can be pressurized to a higher
pressure than the pressure in said further pressure accumulator means.
10. An internal combustion assisted hydraulic engine comprising:
body means defining a pair of opposed combustion chambers;
a combustion piston reciprocably disposed in each said combustion chamber
for reciprocal motion therein;
a piston rod rigidly connecting said combustion pistons to cause said
combustion pistons to reciprocate in their respective combustion chambers
in unison with said piston rod as a free piston unit;
at least one double-acting hydraulic pump comprising a pair of hydraulic
cylinder spaces with a hydraulic piston reciprocably disposed therein,
said hydraulic piston or pistons being operatively connected to said
piston rod to move in unison therewith;
a reservoir for hydraulic fluid;
an output pressure line for supply of hydraulic fluid under pressure to a
hydraulic actuator;
hydraulic accumulator means for storage of hydraulic fluid under pressure
for starting said engine;
hydraulic inlet check valves for controlling inlet of hydraulic fluid to
said hydraulic cylinder spaces, each said hydraulic inlet check valve
including a first check valve member movable between a first position in
which it permits inlet to its respective cylinder space of hydraulic fluid
from said reservoir and a second position in which it prevents inlet of
hydraulic fluid to its respective hydraulic cylinder space;
hydraulic outlet check valves for controlling outlet of hydraulic fluid
from said hydraulic cylinder spaces, each said hydraulic outlet check
valve including a second check valve member movable between a first
position in which it permits outlet of hydraulic fluid from its respective
hydraulic cylinder space to said output pressure line, and a second
position in which it prevents outlet of respective hydraulic fluid from
said hydraulic cylinder space to said output pressure line;
first hydraulic control means connected between said hydraulic accumulator
means and said hydraulic cylinder spaces and including a directional valve
means permitting, in one condition thereof, inlet of hydraulic fluid from
said hydraulic accumulator means to one hydraulic cylinder space of the or
a said pair of hydraulic cylinder spaces and outlet of hydraulic fluid
from the other hydraulic cylinder space of the respective pair of
hydraulic cylinder spaces to said reservoir and, in another condition
thereof, outlet of hydraulic fluid from said one hydraulic cylinder space
to said reservoir and inlet of hydraulic fluid to said other hydraulic
cylinder space from said hydraulic accumulator means; and
second hydraulic control means for applying, during starting of said
engine, a hydraulic control pressure to said second check valve members to
bias them each towards its respective second position to prevent outlet of
hydraulic fluid from its associated hydraulic cylinder space to said
output pressure line so long as the pressure biasing said second check
valve members towards their respective second positions exceeds the
pressure within said associated hydraulic cylinder space;
said first hydraulic control means being arranged so that, during starting
of said engine, said directional valve means is repeatedly switched
between its first and second positions to pressurize the hydraulic
cylinder spaces of the or each said pair of hydraulic cylinder spaces in
turn thereby to cause reciprocation of said free piston unit until a
desired compression pressure has been achieved in a respective said
combustion chamber sufficient to permit initiation of the combustion
process therein; and
said second hydraulic control means being arranged so that, at a desired
instant after said piston unit begins to reciprocate, said hydraulic
control pressure is released to permit hydraulic fluid to flow from said
hydraulic cylinder spaces to said output pressure line.
11. An internal combustion assisted hydraulic engine according to claim 10,
wherein said double-acting hydraulic pump means comprises a piston movable
within a common cylinder and dividing said common cylinder into a pair of
hydraulic cylinder spaces.
12. An internal combustion assisted hydraulic engine according to claim 10,
wherein said at least one double-acting hydraulic pump means comprises a
twin set of single-acting piston/cylinder pumps in a boxer arrangement.
13. An internal combustion assisted hydraulic engine according to claim 10,
wherein said output pressure line is provided with a low power hydraulic
motor arranged to drive an electric generator and a flushing pump.
14. An internal combustion assisted hydraulic engine according to claim 10,
wherein said first hydraulic control means and said second hydraulic
control means are arranged to be controllable by an electronic controller
which is connected to sensors sensing the speed and position of free
piston unit.
15. An internal combustion assisted hydraulic engine according to claim 10,
wherein said electronic controller is arranged to initiate fuel injection
at a first instant which is selected from the instant at which said free
piston unit has completed a preset number of reciprocating movements and
the instant at which said free piston unit has attained a predetermined
magnitude of an inertial energy, said electronic controller further being
arranged to disable said first hydraulic control means at a second instant
which is selected from said first instant, an instant immediately before
said first instant, and an instant immediately after said first instant,
thereby to permit hydraulic fluid to be drawn from said reservoir into
said hydraulic cylinder spaces via said hydraulic inlet check valves.
16. An internal combustion assisted hydraulic engine according to claim 10,
wherein a pressure accumulator means is connected to said output pressure
line, said hydraulic accumulator means being arranged to be pressurized to
a higher pressure than said pressure accumulator means.
17. An internal combustion assisted hydraulic engine according to claim 10,
wherein said second hydraulic control means includes a control valve
having a first inlet which can be placed in fluid communication with said
hydraulic accumulator means, a second inlet in fluid communication with
said output supply line, and an outlet in fluid communication with said
hydraulic outlet check valves, said control valve including a check valve
member movable between a first control position in which it permits fluid
communication between said first inlet and said outlet to permit
application of hydraulic pressure from said hydraulic accumulator means to
said second check valve members to bias them towards their respective
second positions and a second control position in which it permits
communication between said second inlet and said outlet to permit the
pressure on the two sides of said second check valve members to equalise
to permit free movement thereof between their respective first and second
positions and wherein said hydraulic control means further includes means
for interrupting communication between said hydraulic accumulator means
and said first inlet.
18. An internal combustion assisted hydraulic engine according to claim 17,
wherein each said hydraulic outlet check valve further comprises spring
means resiliently biasing said second check valve member towards its
second position whereby said pressure biasing said second check valve
member towards its second position during starting of said engine
comprises the sum of said hydraulic control pressure and spring pressure
provided by said spring means.
19. A method of starting an internal combustion assisted hydraulic engine
having a pair of opposed combustion chambers, a combustion piston
reciprocably disposed in each said combustion chamber and linked one to
another by a piston rod to form a free piston unit, at least one
double-acting hydraulic pump comprising a pair of hydraulic cylinder
spaces with a hydraulic piston reciprocably disposed therein, said
hydraulic piston or pistons being operatively connected to said piston rod
to move in unison therewith, one way inlet check valves for controlling
inlet of hydraulic fluid from a reservoir to said hydraulic cylinder
spaces, one way outlet check valves for controlling outlet of hydraulic
fluid from said hydraulic cylinder spaces, each said one way valve
including a check valve member movable under the influence of a control
pressure applied thereto between a first end position permitting flow of
hydraulic fluid through said check valve and a second position preventing
flow of hydraulic fluid through said check valve, said method comprising
the steps of:
providing a hydraulic accumulator means pressurized to an elevated pressure
for starting said engine;
connecting said hydraulic accumulator means to said one way outlet check
valves so as to apply the pressure prevailing in said hydraulic
accumulator means as an elevated hydraulic control pressure to said check
valve members thereof to close said one way outlet control valves;
supplying hydraulic fluid from said hydraulic accumulator means to each of
said hydraulic cylinder spaces of the or a said respective pair of said
hydraulic cylinder spaces in turn thereby to pressurize said hydraulic
cylinder spaces in turn and to impart a reciprocating motion to said free
piston unit; and
disconnecting said hydraulic accumulator means from said one-way outlet
check valves so as to remove the elevated hydraulic control pressure from
said check valve members thereof thereby to permit opening of said one way
outlet check valves at a moment selected from a first moment at which the
combustion process is initiated, a second moment immediately preceding
said first moment, and a third moment immediately following said first
moment.
20. A method according to claim 19, wherein closure of said one-way outlet
check valves is assisted by application of spring pressure from spring
means arranged to bias said respective check valve members towards their
closed positions.
21. A method according to claim 19, wherein the step of alternatively
pressurizing said hydraulic cylinder spaces includes the step of switching
a directional valve between end positions permitting flow of hydraulic
fluid into one said cylinder hydraulic space and out from the other said
hydraulic cylinder space of the or a said pair of hydraulic cylinder
spaces while said piston unit is moving in one direction and allowing
inlet of hydraulic fluid to said other hydraulic cylinder space and outlet
of hydraulic fluid from said one hydraulic cylinder space when said piston
unit is moving in the other direction, switching of said directional valve
being under control of an electronic controller in dependence upon
information about the position and speed of said free piston unit derived
by said controller from signals from sensors mounted in the engine.
22. A method according to claim 19, wherein initiation of the combustion
process in said combustion chambers is effected after a first
predetermined time from initiating starting of said engine, said
predetermined time being selected from a time period required for said
free piston unit to complete a preset number of reciprocating movements
and a time period sufficient for the free piston to attain a predetermined
magnitude of inertial energy, and wherein, after a second predetermined
time from initiation of the starting procedure, said second time being
selected from said first predetermined time, a time interval slightly
shorter than said first predetermined time, and a time period slightly
longer than said first predetermined time, the step of alternately
pressurizing said hydraulic cylinder spaces from said hydraulic
accumulator means is terminated, thereby allowing hydraulic fluid to be
drawn from said reservoir into said hydraulic cylinder spaces via said
one-way inlet check valves. |
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Claims |
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Description |
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FIELD OF THE INVENTION
The present invention relates to a method for starting hydraulically a
combustion engine having a freely movable piston. The invention further
concerns an apparatus including a freely reciprocating piston unit to
which is connected a double-acting hydraulic piston/cylinder device, whose
cylinders are connected via one-way pressure-driven check valves, that is,
the check valves of the pressure side, to a hydraulic actuator and via
one-way suction valves to a hydraulic storage reservoir.
BACKGROUND OF THE INVENTION
The construction and principle of the free piston combustion engine is
disclosed in FI-A-80760 and in U.S. Pat. No.-A-4,992,301. Worth mentioning
as further references to the conventional technique are U.S. Pat.
No.-A-3,089,305, U.S. Pat. No.-A-3,995,974 and U.S. Pat. No.-A-4,097,198.
One of the problems associated with the development of free piston
combustion engines has arisen from starting of the engine. According to
the method described in U.S. Pat. No.-A-3,995,974, starting is performed
using the same hydraulic cylinder-operated apparatus that after starting
is used for power output from the engine, and the valve elements, which
are included in the hydraulic circuit between the hydraulic accumulator
for the starting pressure and the cylinders of the hydraulic
piston/cylinder device, are controlled to switch their position so as to
cause the opposite sides of the hydraulic piston/cylinder device to be
alternately pressurized, while simultaneously allowing the cylinder space
opposite to that being pressurized to be connected via a return line to
the hydraulic reservoir. Such an arrangement achieves a reciprocating
motion in a simple and useful manner without a dedicated hydraulic power
source, whereby the engine construction is simplified, the weight is
simultaneously reduced and the price minimized.
There remains, however, the need for starting the reciprocating motion of
the free piston unit with the help of sufficient inertial energy before
the combustion process can be initiated.
Therefore, in many appliances it would be advantageous to be able to use an
essentially high pressure as the starting pressure than the pressure
available in the pressure accumulator provided between the hydraulic
piston/cylinder device and the actuator itself. This is not possible,
however, if the pressure of the hydraulic cylinders is allowed also during
starting to be imposed over the pressure-driven check valves to the
pressure accumulator of the load and the pressure-regulating valve; and
further, to the flywheel engine, which is driven by the pressure of the
hydraulic cylinders during the normal running of the engine as described
in U.S. Pat. No.-A-3,995,974.
A special problem with the last mentioned prior art proposal is that the
hydraulic circuit to the load is arranged to be cut off during the
starting phase by a separate clutch valve. The clutch valves presently
available are, however, too slow to make the necessary ON and OFF
switching with the high flow rates and pressures in question.
SUMMARY OF THE INVENTION
The invention seeks to provide a method of starting a free piston
combustion engine with such an improvement over prior art techniques that
makes it possible to boost and quicken the starting of the engine. It
further seeks to provide an improved free piston combustion engine which
is easy and quick to start.
According to the present invention there is provided a method for starting
a free piston combustion engine hydraulically, in which method starting of
the engine is provided by means of the same double-acting hydraulic
piston/cylinder device that after the starting of the engine is used for
power output from the engine; and in which controlling valve elements are
placed in the hydraulic circuit between a hydraulic accumulator of the
starting pressure and the cylinders of the piston/cylinder device to
switch their position so that the opposite sides of the hydraulic piston
become alternately pressurized, while the cylinder space being opposite to
the pressurized cylinder space becomes simultaneously connected via a
return line to a reservoir, wherein for the duration of the starting the
one-way check valves of the hydraulic cylinders are controlled to a closed
state, whereby they prevent the flow of the hydraulic fluid away from the
cylinder spaces, and during initiation of the combustion process or
alternatively, immediately before or after initiation of the combustion
process, the check valves are released for normal operation, in which they
allow only a one-way flow of the hydraulic fluid, namely away from the
cylinders.
Thus, in the method in accordance with the invention, during starting the
one way pressure-driven check valves of the hydraulic cylinders are
controlled to a closed state, whereby they prevent the flow of the
hydraulic fluid from the cylinders, while during starting or immediately
before or after starting, the check valves are released for normal
operation, whereby they permit only a one-way flow of the hydraulic fluid
which is away from the cylinders.
Preferably the one-way check valves are controlled to be closed by the
pressure of the hydraulic accumulator of the starting pressure. In one
arrangement the position switching of the direction changing valve
elements is controlled on the basis of position and speed information
issued by position and speed sensors of the free piston unit.
The initiation of fuel injection may be controlled to occur only after the
free piston unit has been forced to make a preset number of reciprocating
movements, or alternatively, when the free piston unit has attained a
sufficient magnitude of inertial energy, and so that, simultaneously with
the initiation of fuel injection or alternatively, immediately before or
after it, said direction-changing valve elements are controlled to a
position in which the connection of one of the cylinder spaces to the
hydraulic accumulator of the starting pressure, and respectively, the
connection of the other cylinder space to the reservoir are both
simultaneously cut off.
The invention further provides an apparatus for starting a free piston
engine hydraulically, said apparatus comprising:
a free piston unit with which is associated a double-acting hydraulic
piston/cylinder device;
one-way pressure-driven check valves, or the check valves of the pressure
side, via which the cylinder spaces of said piston/cylinder device are
connected to a hydraulic actuator;
one-way suction valves, via which said cylinder spaces are connected to a
hydraulic storage reservoir;
a first set of valve elements in the pressure line between the hydraulic
accumulator of the starting pressure and the cylinder spaces of said
piston/cylinder device, the first set of valve elements being controllable
to change their position so that the opposite sides of the hydraulic
piston become alternately pressurized, while the cylinder space being
opposite to the pressurized cylinder space becomes simultaneously
connected via a return line to the reservoir; and
a second set of valve elements for cutting off the hydraulic fluid flow
between the cylinder spaces and the actuator for the duration of the
starting;
wherein the second set of valve elements include said one-way check valves
that are arranged to be controllable during starting by the pressure of
the hydraulic accumulator of the starting pressure to a closed state,
whereby they prevent the fluid flow from the cylinder spaces to the
actuator.
In such an apparatus the hydraulic accumulator of the starting pressure may
be connected to said one-way check valves via such valve elements of the
second set of valve elements that in their first position control the
check valves to a closed state and in their second position release the
check valves to allow a one-way fluid flow from the cylinder spaces to the
actuator. Moreover the pressure line leading to the actuator can be
provided with a low-power hydraulic motor rotating an electric generator
and a flushing pump.
Preferably said first and second sets of valve elements are arranged
controllable by a controller, which is connected to sensors sensing the
speed and position of the free piston unit. Such an electronic controller
can be arranged to initiate fuel injection only after the free piston unit
has been forced to make a preset number of reciprocating movements, or
alternatively, when the free piston unit has attained a sufficient
magnitude of inertial energy, and so that, simultaneously with the
initiation of fuel injection or alternatively, immediately before or after
it, said controller is arranged to control said first set of valve
elements to a position in which the connection of one of the cylinder
spaces to the hydraulic accumulator of the starting pressure, and
respectively, the connection of the other cylinder space to the reservoir
are both simultaneously cut off.
It is preferred that the pressure in the hydraulic accumulator of the
starting pressure is higher than the pressure in a pressure accumulator
connected to a pressure line between the double-acting piston/cylinder
device and the actuator.
In another aspect of the invention there is provided a free piston
combustion engine comprising:
body means defining a pair of opposed combustion cylinders;
a combustion piston reciprocably disposed in each said combustion cylinder
for reciprocal motion therein;
piston rod means connecting said combustion pistons one to another whereby
said combustion pistons may reciprocate in unison in their respective
combustion cylinders;
hydraulic power output means including at least one pair of hydraulic
cylinder spaces having an associated hydraulic piston reciprocably
disposed therein, said hydraulic piston being operatively linked to said
piston rod so as to reciprocate in unison therewith;
hydraulic accumulator means for storage of hydraulic fluid under elevated
pressure for use in starting said engine;
hydraulic inlet check valves for controlling inlet of hydraulic fluid to
each said hydraulic cylinder space, said hydraulic inlet check valves each
including a first check valve member movable between a first position in
which it permits inlet of hydraulic fluid to its respective hydraulic
cylinder and a second position in which it prevents inlet of hydraulic
fluid thereto;
first hydraulic control means connected between said hydraulic accumulator
means and said hydraulic cylinder spaces for controlling flow of hydraulic
fluid from said hydraulic accumulator means to said hydraulic cylinder
spaces during starting of said engine, said first hydraulic control means
including a directional valve means permitting, in one condition thereof,
inlet of hydraulic fluid from said hydraulic accumulator means to one of a
respective pair of hydraulic cylinder spaces and outlet of hydraulic fluid
from the other one thereof and permitting, in another condition of said
directional valve means, inlet of hydraulic fluid from said hydraulic
accumulator means to said other hydraulic cylinder space of said pair and
outlet of hydraulic fluid from said one hydraulic cylinder space of said
pair;
hydraulic outlet check valves for controlling outlet of hydraulic fluid
from each said hydraulic cylinder space, said hydraulic outlet check
valves each including a second check valve member movable between a first
position in which it permits outlet of hydraulic fluid from its respective
hydraulic cylinder space to an output supply line and a second position in
which it prevents outlet of hydraulic fluid from its respective hydraulic
cylinder space; and
second hydraulic control means connected between said hydraulic accumulator
means and said hydraulic outlet check valves arranged to permit
application of an elevated control pressure to said second check valve
members so as to move them each to its respective said second position to
prevent outlet of hydraulic fluid from its associated hydraulic cylinder
space during starting of said engine so long as the pressure within said
associated hydraulic cylinder space does not exceed said elevated control
pressure;
said first hydraulic control means being arranged to permit, during
starting of said engine, by repeated switching of said directional valve
means between said first and second conditions thereof, hydraulic fluid to
enter each of said pair of hydraulic cylinder spaces in turn from said
hydraulic accumulator means thereby to impart reciprocal motion to said
piston rod and to said combustion pistons so as to produce in said
combustion cylinders in turn a desired compression pressure at which
combustion can be initiated therein; and
said second hydraulic control means being arranged so that, at a
predetermined moment after said piston rod together with said pistons
begins to reciprocate, said control pressure is removed from said second
check valve members to permit outlet of hydraulic fluid from said
hydraulic cylinder spaces.
In such a free piston combustion engine said hydraulic power output means
may comprise a double-acting piston and cylinder arrangement including a
single piston slidable within a common cylinder and dividing said common
cylinder into said pair of opposed said hydraulic cylinder spaces;
alternatively said hydraulic power output means may comprise a pair of
single-acting piston/cylinder pumps in a boxer arrangement.
Said second hydraulic control means can include a control valve having a
first inlet connected to said hydraulic accumulator means, a second inlet
connected to said output supply line, and an outlet connected to said
hydraulic outlet check valves, said control valve including a check valve
member movable between a first end position in which it permits
communication between said first inlet and said outlet to permit
application of hydraulic pressure from the hydraulic accumulator means to
said second check valve members to bias them towards their respective
second positions and a second end position in which it permits
communication between said second inlet and said outlet to permit the
pressure on the two sides of the said second check valve members
substantially to equalise to permit free movement thereof between their
respective said first and second positions.
It is preferred that each said hydraulic outlet check valve further
comprises spring means resiliently biasing said second check valve member
towards its second position whereby said control pressure is provided by a
combination of hydraulic pressure from said hydraulic accumulator means
and spring pressure provided by said spring means.
Conveniently said output supply line is provided with a hydraulic motor
arranged to drive an electric generator and a flushing pump.
In one form of engine according to the invention said first hydraulic
control means and said second hydraulic control means are under the
control of an electronic controller which is connected to sensors arranged
to sense the speed and position of said free piston unit. Preferably said
electronic controller is arranged to initiate fuel injection at a moment
which is selected from the moment at which said free piston unit has
completed a preset number of reciprocating movements and the moment at
which said free piston unit has attained a predetermined magnitude of
inertial energy and wherein said electronic controller is arranged to
disable said first hydraulic control means and stop switching of said
directional valve means between its first and second positions at a second
moment selected from said first moment, a moment immediately before said
first moment, and a moment immediately after said first moment, thereby to
permit said hydraulic cylinder spaces to receive hydraulic fluid via said
hydraulic inlet check valve means from a reservoir for hydraulic fluid.
A further pressure accumulator means can be connected to said output supply
means and said hydraulic accumulator means can be pressurized to a higher
pressure than the pressure in said further pressure accumulator means.
The invention also provides an internal combustion assisted hydraulic
engine comprising:
body means defining a pair of opposed combustion chambers;
a combustion piston reciprocably disposed in each said combustion chamber
for reciprocal motion therein;
a piston rod rigidly connecting said combustion pistons to cause said
combustion pistons to reciprocate in their respective combustion chamber
in unison with said piston rod as a free piston unit;
at least one double-acting hydraulic pump comprising a pair of hydraulic
cylinder spaces with a hydraulic piston reciprocably disposed therein,
said hydraulic piston or pistons being operatively connected to said
piston rod to move in unison therewith;
a reservoir for hydraulic fluid;
an output pressure line for supply of hydraulic fluid under pressure to a
hydraulic actuator;
hydraulic accumulator means for storage of hydraulic fluid under pressure
for starting said engine;
hydraulic inlet check valves for controlling inlet of hydraulic fluid to
said hydraulic cylinder spaces, each said hydraulic inlet check valve
including a first check valve member movable between a first position in
which it permits inlet to its respective cylinder space of hydraulic fluid
from said reservoir and a second position in which it prevents inlet of
hydraulic fluid to its respective hydraulic cylinder space;
hydraulic outlet check valves for controlling outlet of hydraulic fluid
from said hydraulic cylinder spaces, each said hydraulic outlet check
valve including a second check valve member movable between a first
position in which it permits outlet of hydraulic fluid from its respective
hydraulic cylinder space to said output pressure line, and a second
position in which it prevents outlet of respective hydraulic fluid from
said respective hydraulic cylinder space to said output pressure line;
first hydraulic control means connected between said hydraulic accumulator
means and said hydraulic cylinder spaces and including a directional valve
means permitting, in one condition thereof, inlet of hydraulic fluid from
said hydraulic accumulator means to one hydraulic cylinder space of the or
a said pair of hydraulic cylinder spaces and outlet of hydraulic fluid
from the other hydraulic cylinder space of the respective pair of
hydraulic cylinder spaces to said reservoir and, in another condition
thereof, outlet of hydraulic fluid from said one hydraulic cylinder space
to said reservoir and inlet of hydraulic fluid to said other hydraulic
cylinder space from said hydraulic accumulator means; and
second hydraulic control means for applying, during starting of said
engine, a hydraulic control pressure to said second check valve members to
bias them each towards its respective second position to prevent outlet of
hydraulic fluid from its associated hydraulic cylinder space to said
output pressure line so long as the pressure biasing said second check
valve members towards their respective second positions exceeds the
pressure within said associated hydraulic cylinder space;
said first hydraulic control means being arranged so that, during starting
of said engine, said directional valve means is repeatedly switched
between its first and second positions to pressurize the hydraulic
cylinder spaces of the or each said pair of hydraulic cylinder spaces in
turn thereby to cause reciprocation of said free piston unit until a
desired compression pressure has been achieved in a respective said
combustion chamber sufficient to permit initiation of the combustion
process therein; and
said second hydraulic control means being arranged so that, at a desired
instant after said piston unit begins to reciprocate, said hydraulic
control pressure is released to permit hydraulic fluid to flow from said
hydraulic cylinder spaces to said output pressure line.
In such an internal combustion assisted hydraulic engine said double-acting
hydraulic pump means can comprise a piston movable within a common
cylinder and dividing said common cylinder into a pair of hydraulic
cylinder spaces; alternatively said at least one double-acting hydraulic
pump means can comprise a twin set of single-acting piston/cylinder pumps
in a boxer arrangement. Such an engine may have in its output pressure
line a low power hydraulic motor arranged to drive an electric generator
and a flushing pump.
In one preferred embodiment said first hydraulic control means and said
second hydraulic control means are arranged to be controllable by an
electronic controller which is connected to sensors sensing the speed and
position of free piston unit. Thus said electronic controller can be
arranged to initiate fuel injection at a first instant which is selected
from the instant at which said free piston unit has completed a preset
number of reciprocating movements and the instant at which said free
piston unit has attained a predetermined magnitude of an inertial energy,
said electronic controller further being arranged to disable said first
hydraulic control means at a second instant which is selected from said
first instant, an instant immediately before said first instant, and an
instant immediately after said first instant, thereby to permit hydraulic
fluid to be drawn from said reservoir into said hydraulic cylinder spaces
via said hydraulic inlet check valves.
Said second hydraulic control means, in one form of engine, includes a
control valve having a first inlet which can be placed in fluid
communication with said hydraulic accumulator means, a second inlet in
fluid communication with said output supply line, and an outlet in fluid
communication with said hydraulic outlet check valves, said control valves
including a check valve member movable between a first control position in
which it permits fluid communication between said first inlet and said
outlet to permit application of hydraulic pressure from said hydraulic
accumulator means to said second check valve members to bias them towards
their respective second positions and a second control position in which
it permits communication between said second inlet and said outlet to
permit the pressure on the two sides of said second check valve members to
equalise to permit free movement thereof between their respective first
and second positions and wherein said hydraulic control means further
includes means for interrupting communication between said hydraulic
accumulator means and said first inlet. In such an engine each said
hydraulic outlet check valve preferably further comprises spring means
resiliently biasing said second check valve member towards its second
position whereby said pressure biasing said second check valve member
towards its second position during starting of said engine comprises the
sum of said hydraulic control pressure and spring pressure provided by
said spring means.
A pressure accumulator means may be connected to said output pressure line,
said hydraulic accumulator means being arranged to be pressurized to a
higher pressure than said pressure accumulator means.
In accordance with another aspect of the invention there is provided a
method of starting an internal combustion assisted hydraulic engine having
a pair of opposed combustion chambers, a combustion piston reciprocably
disposed in each said combustion chamber and linked one to another by a
piston rod to form a free piston unit, at least one double-acting
hydraulic pump comprising a pair of hydraulic cylinder spaces with a
hydraulic piston reciprocably disposed therein, said hydraulic piston or
pistons being operatively connected to said piston rod to move in unison
therewith, one way inlet check valves for controlling inlet of hydraulic
fluid from a reservoir to said hydraulic cylinder spaces, one way outlet
check valves for controlling outlet of hydraulic fluid from said hydraulic
cylinder spaces, each said one way valve including a check valve member
movable under the influence of a control pressure applied thereto between
a first end position permitting flow of hydraulic fluid through said check
valve and a second position preventing flow of hydraulic fluid through
said check valve, said method comprising the steps of:
providing a hydraulic accumulator means pressurized to an elevated pressure
for starting said engine;
connecting said hydraulic accumulator means to said one way outlet check
valves so as to apply the pressure prevailing in said hydraulic
accumulator means as an elevated hydraulic control pressure to said check
valve members thereof to close said one way outlet control valves;
supplying hydraulic fluid from said hydraulic accumulator means to each of
said hydraulic cylinder spaces of the or a said respective pair of said
hydraulic cylinder spaces in turn thereby pressurize said hydraulic
cylinder spaces in turn and to impart a reciprocating motion to said free
piston unit; and
disconnecting said hydraulic accumulator means from said one-way outlet
check valves so as to remove the elevated hydraulic control pressure from
said check valve members thereof thereby to permit opening of said one way
outlet check valves at a moment selected from a first moment at which the
combustion process is initiated, a second moment immediately preceding
said first moment, and a third moment immediately following said first
moment.
In this method closure of said one-way outlet check valves can be assisted
by application of spring pressure from spring means arranged to bias said
respective check valve members towards their closed positions.
The step of alternately pressurizing said hydraulic cylinder spaces may
include the step of switching a directional valve between end positions
permitting flow of hydraulic fluid into one said cylinder hydraulic space
and out from the other said hydraulic cylinder space of the or a said pair
of hydraulic cylinder spaces while said piston unit is moving in one
direction and allowing inlet of hydraulic fluid to said other hydraulic
cylinder space and outlet of hydraulic fluid from said one hydraulic
cylinder space when said piston unit is moving in the other direction,
switching of said directional valve being under control of an electronic
controller in dependence upon information about the position and speed of
said free piston unit derived by said controller from signals from sensors
mounted in the engine.
Initiation of the combustion process in said combustion chambers can be
effected after a first predetermined time from initiating starting of said
engine, said predetermined time being selected from a time period required
for said free piston unit to complete a preset number of reciprocating
movements and a time period sufficient for the free piston to attain a
predetermined magnitude of inertial energy, and wherein, after a second
predetermined time from initiation of the starting procedure, said second
time being selected from said first | | |
