CA1252637A

CA1252637A - Liquid piston engine

Info

Publication number: CA1252637A
Application number: CA000484527A
Authority: CA
Inventors: Michel Laflamme
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-06-19
Filing date: 1985-06-19
Publication date: 1989-04-18

Abstract

ABSTRACT

A liquid piston combustion engine is disclosed for driving hydraulic motors in order to propel a vehicle. The engine exhausts at near one atmosphere and its efficiency i, enhanced by reason of its operation in response to various engine parameter sensors and by virtue of the co-ordination of the power strokes of the cylinders and the selective coupling of each cylinder to a high pressure low capacity hydraulic motor and a lower pressure higher capacity hydraulic motor. In one embodiment the liquid pistons have fixed strokes and, in another, variable length strokes.

Description

'7 LlpUID PI~-TO~I E~lGIME
-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 , ~d~
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'7 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 pab/~c '7 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 dm: ~
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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 pab/~-~L~S~

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 pab/~

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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 pab/~

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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 pab~

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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 pab/~~~

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 pab/ ~

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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 pabJ~, 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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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A propulsion system for a vehicle comprising:
a) an internal combustion engine having:
(i) at least one cylinder including a liquid piston, a combustion chamber and a hydraulic fluid outlet;
(ii) a liquid piston level sensor for indicating at least the maximum and minimum permissible levels of said liquid piston;
(iii) a cylinder pressure sensor;
(iv) means for terminating a power stroke of said cylinder and for commencing an exhaust stroke in response to at least said level sensor;
(v) means for completing said exhaust stroke in response to said level sensor;
b) at least a first hydraulic motor and a second larger capacity, lower pressure hydraulic motor;
c) means to selectively couple either of said motors to said hydraulic fluid outlet of said cylinder.

2. The system of claim 1 wherein said engine is a spark ignition engine and wherein said means for terminating a power stroke terminates the power stroke upon the first of following events:
(a) said pressure sensor sensing a predetermined pressure, and (b) said level sensor indicating that the liquid piston is at said predetermined level representing the maximum length of a power stroke.

3. The system of claim 2 wherein said predetermined pressure is about 20 p.s.i..

4. The system of claim 1 wherein said engine is a compression ignition engine and wherein said power stroke is terminated only when said level sensor indicates the liquid piston is at a predetermined level representing the maximum length of a power stroke and including means to vary the duration of combustion in said combustion chamber in response to said pressure sensor and said level sensor so that the pressure in said cylinder when said level sensor indicates the liquid piston is at said predetermined level is about a predetermined pressure.

5. The system of claim 4 wherein said predetermined pressure is about 20 p.s.i..

6. The system of claim 4 or claim 5 including means to override said means to vary the duration of combustion and to extend the duration of combustion

7. The system of claim 1 wherein the means to selectively couple either of said motors to said hydraulic fluid outlet of said cylinder couples said first motor to said hydraulic fluid outlet at the beginning of the power stroke of said cylinder and until the pressure in said cylinder begins to decrease and couples the second motor to said hydraulic fluid outlet when the pressure in the cylinder begins to decrease and until the exhaust stroke begins.

8. The system of claim 1 wherein said cylinder is U-shaped and includes a drain at its base.

9. The system of claim 1 or claim 8 wherein said cylinder includes a chemical insulator which remains in said cylinder during normal operation of said engine for exposure to combustion products in said cylinder.

10. The system of claim 1 wherein said cylinder further comprises a hydraulic fluid inlet and a source of hydraulic fluid under pressure selectively coupled to said inlet.

11. The system of claim 1 wherein each said hydraulic motor includes an hydraulic fluid inlet and an hydraulic fluid outlet and wherein said hydraulic fluid outlet is selectively coupled to an hydraulic compressor to slow said motor and pressurize a fluid or gas usable by said system.

12. The system of claim 1 wherein said vehicle is wheeled and includes a plurality of first and second hydraulic motors, each set of first and a second hydraulic motor for driving a selected wheel.

13. The system of claim 12 wherein said vehicle includes a trailer and a plurality of first and second hydraulic motors each first and second hydraulic motor comprising a set for driving a selected wheel of said trailer.