Note: Descriptions are shown in the official language in which they were submitted.
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LlpUID PI~-TO~I E~lGIME
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Thls inveneion relates tG an internai comDustisn
liquid piston enqine for driving a hydraulic motor in order
to propel a vehicle.
Internal combustion engines commonly comprise a
combustion cylinder contalninq a fixed stroke metallic piston
connected bv means of a connecting rod to a crank shaft for
converting the linear motion of the piston to a rotary motior..
Such an engine suffers several drawbacks. For example,
because of the pressure usually necessary in the cylinder
to provide a suitable ,motive force and because of the fixed
stroke of the piston, the pressure in the cylinder at the end
of the power stroke is generally much greater than one
atmosphere. If the exhaust gases are exhausted at this high
pressure, their potential for useful work is lost. Further,
in order to lessen the noise of pressuri ed exhaust gases, a
muffler is often interposed between the exhaust port of the
cylinder and the environment. Another drawback is in the need
for a speed reduction device, generally in the form of a
t-ansmission, connected be~ween the crank sha-t and the driven
elements in order to make use of the rotary motion produced
bv the engine to propel a vehicle. A furthe; drawback result-
from the fact that an idling engine of this tvpe consumes
fuel.
Liquld piston internal combustion engines are also ';noJ..,
however, these also suffer drawbacks and have not gained
acceptance as an alternative to the metallic piston enqine. For
example, Canadian Patent !86,282 issued September 9, 1952 to
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Munguet c1iscloses a liquld piston engine adapted for propulsion
or marine vehicles. This engine comprlses a U-shaped cylin~e
partially filled with hydraulic fluid. A charge supplied above
the hydraulic fluid in one ley of the U is exploded causing the
hydraulic fluid to be thrown toward the top of the other leg of the
U. The resultant increasing pressure in this other leg slows and
reverses the motion of the hydraulic fluid so that the cycle may
repeat. The back and forth motion of the hydraulic fluid is con-
verted to rotary motion by a reversible impeller in the base of the
U-shaped cylinder. As with the metallic piston engine, this
engine would produce exhaust at a relatively high pressure, thus
lowering efficiency and creating noise. Further, the turbulence
created each time the hydraulic fluid passed the impeller would
further decrease efficiency. The necessity of reversing the
impeller to the end of each stroke would create difficult mechanical
and timing problems.
This invention seeks to overcome one or more of the
drawbacks present in a metallic piston engine while not suffering
some of the drawbacks of previously known liquid piston engines.
Accordingly, the present invention is a propulsion system for
a vehicle comprising: an internal combustion engine having: at least one
cylinder including a liauid piston, a combustion chamber and a hydraulic fluid
outlet; a liquid piston level,sensor for indicating at least the maximum and
minimum permissible levels of the liquid piston; a cylinder pressure sensor;
means for terminating a power stroke of the cylinder and for commencing an
exhaust stroke in response to at least the level sensor; means for completing
the exhaust stroke in response to at least the level sensor; at least
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a first hydraulic motor and a second Larger capacity, lG"er
pressure hydraulic motor; means to selectivel~ csupie el~her
of the motors to the hydraulic fluid outlet of the cylinder.
In the drawings which illustrate a preferred
embodiment of the invention,
Fiqure l is a schematic of a cylinder of a liquid
piston engine made in accordance with an embodiment of this
invention;
Figure 2 is a schematic of a liquid piston engine
o made in accordance with an embodiment of this invention.
Turning now to Figure l, it is seen that end 10 of
combustion cylinder 1 has a valved hydraulic fluid inlet
2 and a valved hydraulic fluid outlet 3. The other end 11
of the cylinder has a valved air inlet 4, a valved fuel
inlet 5, and a valved combustion products exhaust 6. The
cylinder also has a liquid piston level sensor 7 running along
a portion thereof and a combustion cylinder pressure sensor 8.
The combustion cylinder is of an inverted U configuration, the
leg of the U having the hydraulic fluid inlet and outlet being
~o the longer leg. ~ arail 3 is loc~ed at the bottom of ~he
U. The cylinder is partially filled with a chemical insulator
a,
The cylinder,a3 described,~may be ope_ated as a two-
stroke compression ignition engine in the following manner. Hydraulic fluid
15 under moderate pressure is supplied via hydraulic fluid inlet
2 to the end lO of cylinae; 1 so that the chemical insulator l
moves toward the olher end 11 of the cvlinder. As the
hydraulic f'uid begins to enter the cylinder, valve 12 of
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exhaust 6 is open. The level of the chemical insulator is
sensed by level sensor 7 and when this level reaches a pre-
determined level, as illustrated in Fiyure 1, check valve
13 opens and air under pressure is supplied to the cylinder
via air inlet 4. A short time is given for the air to purge
the volume intermediate the chemical insulator and end 11,
then exhaust valve 12 closes. The pressure of the air supply
is sufficient to permit spontaneous combustion of the fuel.
After exhaust valve 12 closes the pressure in the cylinder
rapidly rises to the pressure of the air supplied at inlet 4,
at which point valve 13 closes. This condition may be sensed
directly by pressure sensor 8. Fuel is then injected via
fuel inlet 5 into the cylinder. This initiates the power stroke.
Fuel spontaneously combusts increasing the pressure in the volume
between cylinder end 11 and the chemical insulator 14 thereby
driving the chemical insulator toward end 10 of the cylinder.
The chemical insulator in turn drives hydraulic fluid 15 past
check valve 18 through hydraulic fluid outlet 3. Hydraulic
fluid inlet 2 is closed by the back flow on check valve 16.
The exiting hydraulic fluid is used to drive hydraulic motors
as will be hereinafter described.
The air supply pressure may be higher than the
minimum necessary for ,spontaneous combustion. This will
increase the oxygen supply in the cylinder and assist in
obtaining complete combustion.
Efficiency of the cylinder would be enhanced if
each power stroke were as long as possible. The maximum
power stroke length is determined by the length of the cylinder
and by noting that the chemical insulator is not to be ejected
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from the cylinder. Further, it is desirable that the pre,sure
in the cylinder at the end of the power strcke be close ~o
one atmosphere in order to minimize exhaust noise and thus
avoid the necessity of a muffler. ~n the other hand, in order
for the exiting hydraulic fluid to impart a significant tor~ue
to the hydraulic motors, the terminal pressure in the cylinder
must be somewhat higher than one atmosphere. Twenty p.s.i.
has been found to be a suitable compromise terminal pressure.
In order to maximize the power stroke length and
minimize the exhaust pressure, fuel in~ection must be termin-
ated at a determinab~e moment which, assuming complete
combustion does not lag fuel injection appreciably, depends
upon the instantaneous pressure in the cylinder and the
level of the chemical insulator. By way of example, if the
rate of fuel injection was such that the cylinder pressure
reached and maintained 200 p.s.i., then fuel injection
would need to be terminated when the level of the chemical
insulator 14 was such that the volume in the cylinder above
the chemical insulator was one-tenth the volume above the
chemical insulator at the maximum power stroke length.
The appropriate time to terminate fuel injection
may be determined by a logic unit (not shown) whlch receives
the outputs of the noted level and pressure sensors. It will
be obvious to one skilled in the art that the same result
could be achieved by measuring other engine parameters than
those described.
Clearly, when the rate of fuel injection is greater,
the duration of fuel injection will be shorter in order that
the pressure in the cylinder drop to 20 p.s.i. when the
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maximum power stroke length i5 reached. The enyine may be
constructed so that this operation is overridden when emergenc-
~power is needed. That is, fuel may then be injected for a
longer time than would otherwise be permitted resulting in the
pressure in the c~linder at the end of the maximum power
stroke length being greater than 20 p.s.i..
When the level sensor 7 senses that the level of
the chemical insulator is such that the maximum power stroke
length has been achieved - and therefore the level of the
chemical insulator in the other leg of the cylinder has
neared end 10 - exhaust valve 12 is opened, outlet valve 18
closed and hydraulic fluid inlet valve 16 opened so that the
exhaust stroke commences and the cycle aforedescribed repeats.
During the course of operating the engine, the
chemical insulator acts as a motion damper isolating hydraulic
fluid 15 from any turbulence caused by combustion. It further
acts to trap any sediment resulting from combustion. Such
sediment may be removed by means of drain 9. Although the
chemical insulator is advantageous for these reasons, it may
be omitted in which case the hydraulic fluid itself acts as
the liquid piston.
Although some increase in efficiency is obtained if
the maximum power stro'ke length is achieved during each
- cycle, the engine will nevertheless function, and may exhaust
at 20 p.s.i., if operated with a variable stroke.
The engine of this invention may also operate as a
spark ignition engine. With such operation, the engine will
operate with a variable stroke. To operate as a spark ignition
engine, the schematic of Figure 1 is altered to include a means
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to ignite a charye of fuel and air in the cylinder. Further,
fuel and air line sensors are required in order to measure
the amount of fuel and air admitted to the cylinder. However,
level sensor 7 need only sense the maximum power stroke
length and the level wherl the exhaust stroke is to end.
Considering the spark ignition operation of the
engine, as before, hydraulic fluid 15 under moderate pressure
is supplied to the cylinder until level sensor 7 senses a
predetermined level at which the exhaust stroke is to end.
Valve 13 then opens admitting air under pressure to the
cylinder. Next, exhaust valve 12 closes and fuel valve 16
opens thereby mixing fuel with the air. Valve 16 then
closes and a spark ignites the charge beginning the power
stroke.
It will be reali~ed that the charge admitted to
the cylinder may not exceed a determinable maximum if the
pressure in the cylinder is to drop to 20 p.s.i. at the
maximum power stroke length. The amount of the charge is
measured by the fuel and air line sensors. ~s before, this
could be overrid~en when emergency power was required. If
the charge was less than the determinable maximum, then the
pressure in the cylinder would drop to 20 p.s.i. before
the maximum power stroke length was reached. The pressure
in the cylinder is monitored by the pressure sensor 8
and the power stroke is terminated and the exhaust stroke
commenced in response thereto. If the pressure has not
dropped to 20 p.s.i. by the time level sensor 7 senses that
the level of the chemical insulator is such that the maximum
power stroke length has been achieved, then the power stroke
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is terminated Ln response to a signal from level sensor 7
Thus, it will be seen that a variable stroke cylinder results.
A micro-processor may monitor the noted sensors and control
the cylinder valving accordinyly.
In order to utilize the hydraulic power produced
by the afore-described cylinders to propel a vehicle, a
cylinder is co-ordinated with others to propel hydraulic
motors.
In Figure 2, four cylinders, la, lb, lc, and ld
operated as a compression ignition engine are each connected
to a source of hydraulic fluid intank 19, fuel from injector
20 and pressuri~ed air from compressor 21. The exhaust of
each cylinder is connected to a common line 22. The valves
in the system are represented by triangles and, where appropriate,
have like reference numbers to the valves of Figure 1. The
hydraulic fluid outlet of each cylinder bifurcates and the
two branches are connected respectively into common lines
23a and 23b. The branches for each hydraulic fluid outlet
include valves (28a and 28b) to selectively communicate a
common line to a cylinder. Line 23a is connected to hydraulic mo.or
2~ and line 23b to hydraulic motor 25. The hydraulic motors
convert the linear motion of the hydraulic fluid to rotary
motion in order to drive axle 26 and wheel 27.
~ydraulic motor 2~ is a small capacity, high
pressure motor and hydraulic motor 25 is a larger capacity,
lower pressure motor.
A logic unit (not shown) has electrical connections
to the valves and sensors in the system. This unit is used
to time the occurrence of the opening and closing of each valve
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Eor each cylinder in resporlse to sicJnals from the level and
pressure sensors of each cylinder so that each cylinder
operates in the manner hereinbefore described and so that the
power strokes of the cylinders are co-ordinated. The unit
is also electrically connected to the valves in the branches
of the bifurcated hydraulic fluid outlets in order to select-
ively couple a cylinder to either motor 24 or motor 25.
More specifically, when the cylinders are operated
as a fixed stroke liquid piston compression ignition engine,
the logic unit functions to couple a cylinder to high pressure
hydraulic motor 24 whe,n the power stroke of the cylinder com-
mences, and maintains this connection until combustion in
the cylinder ceases and the pressure in the cylinder begins
tc decrease. Upon the pressure beginning to decrease,
the unit switches the hydraulic fluid outlet of the cylinder
into line 23b to drive lower pressure motor 25.
The propulsion system operates without a transmission
or differential so that hydraulic motors 24 and 25 are directly
coupled to axle 26. Motor 24 is not leveraged as greatly as
motor 25 so that it requires a higher operating pressure under
a given load condition. On the other hand, being less leveraged,
a given throughput in motor 24 will produce a greater angular
rotation of axle 26 than a corresponding throughput in motor 25.
The constant or increasing pressure obtained in a
cylinder during combustion in thus applied to motor 24 so
that motor 24 is used as the main driving force. When the
pressure in the cylinder begins to decrease and the cylinder's
output is switched to motor 25, the pressure, being at first only
slightly less than the pressure applied to motor 24, will
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result in a grea~er torque being app]ied to axle 26 than that
applied by motor 24 before the cylinder's output was switched.
This condition will only last momentarily as motor 25 is a
high capacity motor so that the pressure in the cylinder w.ill
soon drop to a point where the torque produced by motor 25
is not sufficiently great to maintain the instantaneous
angular velocity of axle 26. Nevertheless, the rotation of axle
26 will continue to be assisted by the diminishing driving
pressure in the cylinder.
When the pressure in the cylinder drops to 20 p.s.i.,
or the maximum power s~roke length is reached, the logic unit
interrupts fluid communication between line 23b and the
hydraulic fluid outlet 3 and opens exhaust valve 13.
The utilization of a second larger capacity, lower
pressure hydraulic motor considerably shortens the time
needed to drop the pressure in a combustion cylinder as compared
with the time which would be required should no second motor
be employed. Thus, the second hydraulic motor permits the
cylinders to fire more rapidly and, therefore, increases the
achievable power output of the engine.
As will be apparent, spark ignition cylinders
may also be connected in a manner similar to that illustrated
in Figure 2. However, as the cylinder pressure begins to drop
immediately after the explosi.on caused by ignition, hydraulic
fluid exiting from a given cylinder will be switched from
hydraulic motor 24 to hydraulic motor 25 at a pressure determined
by the logic unit rather than at the moment cylinder pressure
begins to decrease.
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As noted, the logic unit co-ordinates the po-"er
strokes of the cylinders. To do so, the unit will commence
combustion in, for example, cylinder lb and connect this
cylinder with motor 24 only after the pressure in the previousl
fired cylinder la has begun to decrease and cylinder la has
been switched to motor 25. Since motor 25 rapidly throughputs
the remaining hydraulic fluid in a cylinder, fluid communication
between cylinder la and motor 25 will have been cut off prior
to the time when the pressure in cylinder lb begins to decrease
and the cylinder is switched to motor 25. In this way, the
unit will fire each cylinder in turn.
When the vehicle is standing, unit 28 will not fire
any cylinder until it is desired to move the vehicle. Thus,
unlike a metallic piston engine, the fluid piston engine
of this invention does not idle.
The hydraulic fluid tank 19 is located above the
combustion cylinders so that gravity will provide a sufficient
- force to drive the hydraulic fluid into the combustion
cylinders. For some applications, however, it may be desired
to pressurize the tank 19 in order to minimize the time
necessary to fill the cylinders.
The hydraulic motors 24 and 25 may comprise cylinders
containing metallic pistons connected to a crankshaft which
forms part of axle 26. Alternatively, they maybe screw type
hydraulic motors. Selection of the particular hydraulic motor
will depend on the requirements for the particular power house.
The hydraulic fluid output of these motors is normally channelled
directly to a hydraulic fluid reservoir for reuse in the
combustion cylinders. However, when a modest braking force
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is required, the output of the hydraulic motor may be first
coupled to a com~ressor in order to pressurize the air supply
for the combustion cylinders - the torque on the axle resulting
from the momentum of the vehicle driving the hydraulic motors
for this purpose and hence slowing the vehicle.
A set of hydraulic motors 24 and 25 may be connected
to each wheel it is desired to drive. In a vehicle with a
trailer, the wheels of the trailer may also be driven by
hydraulic motors supplied by a supply line from the engine.
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