U.S. patent number 3,777,722 [Application Number 05/068,698] was granted by the patent office on 1973-12-11 for free piston engine.
Invention is credited to Karl Werner Lenger.
United States Patent |
3,777,722 |
Lenger |
December 11, 1973 |
**Please see images for:
( Certificate of Correction ) ** |
FREE PISTON ENGINE
Abstract
A piston engine comprises a cylinder defining a combustion
chamber, a ringless piston reciprocally mounted within the
cylinder, the cylinder having means spaced from the combustion
chamber and defining a zone of reduced clearance around the piston.
This zone-defining means includes means for lubricating the zone to
reduce friction. The lubricating means may comprise a gas-flow
arrangement, or a bushing formed of self-lubricating material, or
both of these features. The cylinder and piston are fabricated from
materials having a maximum coefficient of thermal expansion of 30
.times. 10.sup..sup.-7 /.degree. C. The engine may include a
compressor piston reiprocal in a compressor cylinder which are
designed for minimal heat expansion.
Inventors: |
Lenger; Karl Werner (Hamburg,
DT) |
Family
ID: |
5745139 |
Appl.
No.: |
05/068,698 |
Filed: |
September 1, 1970 |
Foreign Application Priority Data
|
|
|
|
|
Sep 11, 1969 [DT] |
|
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P 19 45 924.6 |
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Current U.S.
Class: |
123/46R; 92/127;
123/193.2; 123/193.4; 184/6.8; 92/86.5; 92/153 |
Current CPC
Class: |
F04B
39/12 (20130101); F04B 31/00 (20130101); F04B
39/0005 (20130101); F05C 2201/0466 (20130101); F05C
2253/12 (20130101); F02B 2075/025 (20130101) |
Current International
Class: |
F04B
39/12 (20060101); F04B 31/00 (20060101); F04B
39/00 (20060101); F02B 75/02 (20060101); F02b
071/00 (); F02d 039/10 (); F02f 001/20 () |
Field of
Search: |
;123/46R,46SC,46A,46B,193CP,193R,193C ;92/127,153,86.5 ;308/5
;184/6.8 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Smith; Al Lawrence
Claims
What is claimed is:
1. A free piston engine comprising:
power cylinder means including internal wall means, a combustion
chamber and scavenging port means in said internal wall means;
a ringless power piston disposed for reciprocal movement in said
power cylinder means;
compressor cylinder means;
a compressor piston disposed for reciprocal movement in said
compressor cylinder means and being operably connected to said
ringless power piston;
said power cylinder means having guide means spaced axially from
the combustion chamber and extending radially inwardly of said wall
means to define a zone of reduced clearance around said ringless
power piston;
said guide means being rigidly mounted relative to said wall means
and arranged co-axially with said power piston;
said guide means having means including opening means communicating
with said zone, for supplying said zone with a flow of lubricating
gas around said power piston to inhibit the occurrence of friction
between said ringless power piston and said power cylinder
means.
2. An engine according to claim 1 wherein the power piston and the
power cylinder means are comprised of a material having a maximum
coefficient of thermal expansion of 30 .times. 10.sup.-.sup.7
/.degree. C..
3. An engine according to claim 2 wherein the compressor piston and
the compressor cylinder means are comprised of a material having a
maximum coefficient of thermal expansion of 30 .times.
10.sup.-.sup.7 /.degree. C..
4. An engine according to claim 1 wherein the power piston, the
power cylinder means, the compressor piston, and the compressor
cylinder means are comprised of a ceramic material having a
coefficient of thermal expansion of approximately 10 .times.
10.sup.-.sup.7 /.degree. C..
5. An engine according to claim 4 and further including a metal
shell disposed around an outer periphery of said power cylinder
means for reinforcing said power cylinder means.
6. An engine according to claim 1 wherein the power piston, the
power cylinder means, the compressor piston, and the compressor
cylinder means are comprised of Invar steel.
7. An engine according to claim 1 and further including a limiting
means at one end of said compressor cylinder means to limit
longitudinal travel of said power piston and said compressor
piston.
8. An engine according to claim 1 wherein a section of said power
piston disposed between said zone of reduced clearance and said
combustion chamber is of larger diameter than the section disposed
in such zone.
9. A free piston engine comprising:
power cylinder means including a combustion chamber and scavenging
port means;
a ringless power piston disposed for reciprocal movement in said
power cylinder means;
compressor cylinder means;
a compressor piston disposed for reciprocal movement in said
compressor cylinder means and being operably connected to said
power piston;
said power cylinder means having means spaced from the combustion
chamber and defining a zone of reduced clearance around said power
piston; said zone-defining means including;
a plurality of longitudinally spaced, circumferential ribs for
defining a plurality of sections;
inlet and outlet passage means communicating with said sections to
conduct a flow of gas along said sections; and
means for supplying a flow of gas to said zone at a pressure higher
than the pressure of scavenging air in the combustion zone to
inhibit the occurrence of friction between said power piston and
said power cylinder means.
10. An engine according to claim 9 wherein said inlet passage means
are smaller in size than said outlet passage means.
11. A piston engine comprising:
a cylinder defining a combustion chamber and including internal
wall means;
a ringless piston disposed for reciprocal movement in said
cylinder;
said cylinder having guide means spaced axially from the combustion
chamber and extending radially inwardly of said wall means to
define a zone of reduced clearance around said ringless piston;
said guide means being rigidly mounted relative to said wall means
and arranged co-axially with said piston;
said guide means having means, including opening means
communicating with said zone, for supplying said zone with a flow
of lubricating gas around said piston to inhibit the occurrence of
friction between said ringless piston and said cylinder.
12. An engine according to claim 11 wherein said zone-defining
means is comprised of a self-lubricating carbon material having a
maximum coefficient of thermal expansion on the order of 40 .times.
10.sup.-.sup.7 /.degree. C..
13. An engine according to claim 11 wherein said cylinder and said
piston are comprised of material having a maximum coefficient
thermal expansion of 30 .times. 10.sup.-.sup.7 /.degree. C.
14. A free piston engine comprising:
power cylinder including internal wall means, a combustion chamber
and scavenging port means, in said internal wall means;
a ringless power piston disposed for reciprocal movement in said
power cylinder means;
compressor cylinder means;
a compressor piston disposed for reciprocal movement in said
compressor cylinder means and being operably connected to said
ringless power piston;
said power cylinder means having guide means spaced axially from
the combustion chamber and extending radially inwardly of said wall
means to define a zone of reduced clearance around said ringless
power piston;
said guide means being rigidly mounted relative to said wall means
and arranged co-axially with said power piston;
said guide means including means for lubricating said zone to
inhibit the occurrence of friction between said power piston and
said power cylinder; and the power piston and the power cylinder
means being comprised of material having a maximum coefficient of
thermal expansion of 30 .times. 10.sup.-.sup.7 /.degree. C.
15. An engine according to claim 14 wherein said guide means is
comprised of a self-lubricating material having a maximum
coefficient of thermal expansion of 40 .times. 10.sup.-.sup.7
/.degree. C.; said guide means being disposed on the cold end of
the power cylinder means beyond the scavenging ports.
16. An engine according to claim 15 wherein said self-lubricating
material comprises carbon having ceramic particles added thereto
for resisting wear.
17. An engine according to claim 15 wherein said self-lubricating
material comprises a flame-sprayed coating on an innerwall of the
power cylinder means.
18. A free piston engine comprising:
power cylinder means including a combustion chamber and scavenging
port means;
a ringless power piston disposed for reciprocal movement in said
power cylinder means;
compressor cylinder means;
a compressor cylinder piston disposed for reciprocal movement in
said compressor cylinder means and being operably connected to said
power piston;
said power cylinder means having means spaced from the combustion
chamber and defining a zone of reduced clearance around said power
piston;
said zone-defining means including means for lubricating said zone
to inhibit the occurrence of friction between said power piston and
said power cylinder means;
said compressor cylinder means includes a pin extending
substantially co-axially with said power piston; said compressor
piston being provided with a cylindrical bushing mounting said
compressor piston for reciprocal movement on said pin; said
last-named bushing being comprised of self-lubricating
material;
said power piston including a hollow portion; and
a spring being fastened at one end to the power piston and at the
other end being fastened to the compressor cylinder means to
maintain the power piston and the compressor piston in contact
during starting of the engine.
19. An engine according to claim 18 wherein said bushing on said
compressor piston is comprised of an oil-impregnated sintered
metal.
20. An engine according to claim 18 wherein said bushing on said
compressor piston is comprised of an oil-impregnated ceramic
material.
21. An engine according to claim 18 wherein said bushing on said
compressor piston is comprised of an artificial graphite
material.
22. An engine according to claim 18 wherein said pin is hollow; and
said spring comprises a helical spring passing through the pin.
23. An engine according to claim 22 wherein said power piston is
provided with a bore; said compressor piston being provided with a
boss disposable with clearance within said bore such that said
compressor piston is radially movable relative to said power piston
to radially independent positions.
Description
BRIEF SUMMARY OF THE INVENTION
At the present time the maximum pressures developed in a free
piston engine are in the range of 1,700 to 2,100 pounds per square
inch. Obviously such high combustion pressures result in high
temperatures. For this reason some cooling is applied to cylinders
and pistons, which usually are provided with appropriate piston
rings, the cylinders being cooled from outside and the pistons
internally. This in effect makes the construction of such a free
piston engine compartively heavy and complicated with a consequent
lowering of the cyclic piston frequency and a decrease in developed
engine power, as these are interrelated. Any effort to increase the
engine power by increase of cylinder pressure leads to higher
stresses, particularly in the piston rings.
The piston rings, being relatively frail engine parts, are usually
the first to be affected by high thermal and mechanical stress. An
increased wear of pistons and cylinders is another immediate
result. There were efforts made to use pistons with no piston rings
in internal combustion engines. The pistons and cylinders were made
of the usual standard materials and the pistons were guided by a
special guide on the piston rods. As the piston and cylinder
materials had relatively high and dissimilar thermal expansion
coefficients it is obvious that during design this must have been
taken into account, creating at least in the cold condiiton, some
considerable clearance between pistons and cylinders. An
undesirable high loss from the slipping-by of gases was a result.
Another problem is a possible high burn-out rate of pistons and
cylinders caused by a large amount of hot gas slipping with high
speed past the gap between pistons and cylinders.
Even with the use of like, or similar, materials for the piston and
the cylinder the big clearence can not be avoided because in
operation the pistons are much hotter than the cylinders.
The aim of this invention is to create a free piston engine, of the
type mentioned above, but without the above problems.
DETAILED DESCRIPTION
The subject of this invention is a free piston engine of the type
described above, in which at least the power piston and the power
cylinder are made from material with a low thermal expansion
coefficient, and the clearence beyond the combustion chamber and
the gas ports is smaller than in the combustion chamber itself. The
pistons have no piston ring.
According to another preferred design, the compressor cylinder and
the cylinder guided compressor piston are also made from material
with low thermal expansion characteristics.
Preferably the material used for the construction of the pistons
and cylinders should have, at maximum, a small thermal expansion
coefficient of 30 .times. 10.sup.-.sup.7 /.degree. C. Such material
can be quarzite glass or some ceramic material or a nickel or
chromium nickel steel such as Invar Steel or Elinvar Steel.
The coefficient of thermal expansion of those steels is somewhat
higher than of the ceramics. Generally ceramic materials are
preferable, as the use of ceramics results in a lighter
construction and this allows a higher piston stroke frequency with
a related increase in engine power output. The ceramic materials
have a lower heat transfer coefficient with the advantage of lower
heat losses to the outside of the engine.
A useful ceramic material is represented by Pyroceram with a
thermal expansion coefficient of 10 .times. 10.sup.-.sup.7 /
.degree. C., which can be operated up to 1,200.degree. C.
The application of materials with very low thermal heat expansion,
as proposed above, makes it possible to keep the clearance between
the piston and cylinder very small and thus largely avoiding the
gas blow-by and virtually eliminating the afore-mentioned burn-out
damage.
When the power is made from a ceramic material it will be of
advantage to build around it a shrunk-un metal shell, which will
take the high pressure force and prevent damage or destruction of
the ceramic.
A guiding device for the power piston, made preferably from a
self-lubricating material with maximum thermal expansion
coefficient of 40 .times. 10.sup.-.sup.7 /.degree. C., is provided
outside of the combustion chamber area. Graphite or artificial
carbon preferably may be used, with embedded ceramic grains to
enhance the wear properties, if necessary. The guiding device can
be designed as a cylindrical bearing and located on the "cold" end
of the power cylinders. It can also be, according to the invention,
built-up on the inner wall of the cylinder by the flame spraying
process.
According to one preferred design of the invention, some gas under
pressure is introduced into the power piston guiding device, which
acts as a gas lubricating bearing. If such a gas bearing is used it
is desirable that the bearing area of the power piston guiding
device be subdivided into smaller sections by an arrangement of
longitudinal and circumferential ribs. Each of the sections is
provided by one or more pressure gas inlet openings and one or more
pressure gas vent openings. To maintain the uniform gas pressure
around the guide, which tends to hold the power piston in a
radially central position, it is important that the gas vent
openings are large enough to vent the gas quickly. In the case of
some momentary displacement of the piston towards the cylinder
wall, the gas with inadequate venting may cause a local build-up of
pressure, which would result in an unbalance of the pressure in the
guide area and prevent the reestablishment of the power piston into
the central position. In other words, if owing to sideward
displacement of the piston, the gas is allowed to penetrate behind
the sections and ribs on one side of the guide area, due to the
lack of proper venting it will act on a bigger area than on the
other side where it acts within sections only, thus creating an
unbalance of the force, pressing the piston against the cylinder
wall and preventing a frictionless operation. To prevent this from
happening, the gas which crept behind the ribs must be removed as
fast as possible.
According to another preferred design of this invention, the
compressor piston can also be made without piston rings, guided
centrally by a bearing bush, fabricated from a self-lubricating or
a lubricant impregnated material, running on a central pin. The
power piston and the compressor piston should preferably be made as
separate parts and the power piston mounted on a boss of the
compressor piston with proper clearance.
The design of a free piston engine, according to this invention,
allows us to use comparatively high pressures without a danger of
damage to the principal parts. Also a higher stroke frequency of
the piston can be used with consequent higher power output.
Application of ceramic materials to the construction of pistons and
cylinders results in weight reduction with a further possibility of
higher piston frequency and subsequent higher power output.
The invention will be further explained by the following
drawings:
Fig. 1 is a partial section, showing the part of the free piston
Engine, which is important for the explanation of the
invention.
FIG. 2 is a partial section showing the piston guide device,
according to the invention.
FIG. 3 is an alternative design of the piston guide device, as
described in the invention.
FIG. 4 is a partial section of another alternative design of the
piston guide device, as described in the invention.
FIG. 5 is a partial section of another variation in design of the
piston guide device as claimed in the invention.
FIG. 6 & 7 are two partial sections in which the use of the gas
bearing, as described in the invention, is explained.
FIG. 1 shows, in a schematic way, all the parts of a free piston
engine, working on the two cycle uniflow principle, which are
required to explain the invention. Free piston engines of this type
are well known.
According to the drawing, power 1 is shown in a power cylinder 2 in
which it can move in longitudinal direction. The power cylinder 2
is provided with the usual scavenging ports 3, through which the
exhaust gases and the scavenging air leave the cylinder. These
exhaust gases, by way of an exhaust duct 4, enter the gas storage
tank (not shown). The back or "cold" end of the power piston 1, is
mechanically connected to the compressor piston 5, which can move
back and forth in the cylinder 6. The movement of the compressor
piston 5, towards the left, as in FIG. 1, expels air from the
cylinder. This air had entered the cylinder in the previous piston
5 stroke, i.e., toward the right, through the generally circular
inlet valves 7. By the way of an air outlet valve, 8, this air is
exhausted into an air storage tank, 9, from which, with appropriate
timing it enters the cylinder, 2. The compressor piston, 5,
operates the compression stroke in a known way under the force of
an air cushion. As may be viewed in FIG. 1, this air cushion is
formed by the air, trapped on the right side of the piston, 5, in
cylinder, 6.
The power piston, 1, and the power cylinder, 2, in the proposed
design are made from a material with a very low thermal expansion,
the thermal expansion coeficient being of the maximum order of 30
.times. 10.sup.-.sup.7 /.degree. C., preferably from a ceramic
material with thermal expansion coeff. of the order of 10
.times.10.sup.-.sup.7 /.degree. C. and which can be operated in
temperatures up to 1,200.degree. C. The power piston, 1, and the
power cylinder, 2, can also be made of a nickel steel or
chrom-nickel steel such as Invar or Elinvar. Those steels have a
somewhat higher thermal expansion than quarzite glass or ceramic
material such as Pyroceram.
To prevent damage or destruction of the ceramic cylinder material
by the high cylinder pressures, a cylindrical reinforcement shell
made of metal or steel is shrunken over the ceramic. This shell,
20, takes the cylinder pressure stresses and prevents damage to the
ceramic material. The power piston, 1, is guided in the area beyond
the scavenging ports, 3, in a special piston guiding device, 10.
This guiding device, according to FIG. 1. is in the form of a
bearing bush made from a self-lubricating material with a maximum
thermal expansion coefficient of 40 .times. 10.sup.-.sup.7
/.degree. C., such as carbon, graphite or artificial carbon, which
may have some ceramic particles included to enhance the wear
resistance. To create better sliding conditions, and to diminish
friction, a device, 11, is added by which a gas under pressure is
delivered to the piston guiding device in the direction of the
power piston. This gas under pressure may come as air from a
seperate source or may be taken from the gas delivered by the
engine.
As is visible in FIG. 1 there is, on the wall of the power
cylinder, 2, at the point where the guide device, 10, starts, a
small step. This step is located in such a way that the clearence
between the power piston, 1, and the cylinder wall in the area, 12,
just in front of guiding device, 10, is slightly larger than in the
area, 13, inside the guiding device, 10. The clearance in the area,
13, of the guiding device, 10, is large enough so that any direct
contact between the power piston, 1, and the guiding device, 10, is
largely avoided. The clearance between the power piston, 1, and the
cylinder wall in the area 12, is somewhat larger than in the area
13. This clearance in the area 12 is large enough so that if the
power piston, 1, is deflected within limits the of its clearance in
the guiding device, it would not come in contact with the cylinder
wall of the combustion chamber, and yet small enough such that the
loss of pressure through this gap is still within permissible
limits. This step is also intended to assure the presence of
uniform gas pressure all around the circumference of the piston, so
that in case the piston is however slightly deflected into an askew
position, the pressure would not act on one side of the piston
only, which would result in a contact between the power piston and
the cylinder wall. In an absence of such a step it would be
impossible to avoid this contact.
The FIGS. 2 & 3 show two alternative designs of the piston
guide device namely 10a or 10b.
According to FIG. 2 the piston guide device 10a is in the form of a
bearing bush made from a self-lubricating material, such as
graphite, artificial carbon or similar material, and is located on
the "cold" end of the power cylinder, 2. The bearing face of the
bush, 10a, is as shown more distinctly in FIG. 6 & 7, is
subdivided into a number seperate sections by means of longitudinal
ribs, 14, and circumferential ribs, 15. Each section is provided
with a gas inlet opening, 16, and each section is also provided
with gas outlet openings, 17. The gas outlet openings are located
in the space between adjacent sections, for example, in circular
grooves. The flow of gas is schematically indicated by arrows in
FIG. 6. It is important that the gas supplied through the inlet
openings, 16, can be vented fast enough through the gas outlet
openings, 17. For this reason, and also to lower slightly the gas
pressure and increase the volume of outgoing gas, the gas vent
openings should be made larger than the gas inlet opeings, 16. It
is also important that no more gas is supplied than can be easily
removed.
An inadequate size of vent openings, 17, may result in some serious
trouble, in particular when the power piston, 1, under the
influence of some outside forces is deflected slightly from the
central position to an askew one. In such a case the clearence of
the longitudinal and circumferetial ribs on one part of the piston
will be greater, than on the other side. This in effect will cause
an inbalance of forces and if the gas cannot be vented fast enough,
the force deflecting the piston from the center will be permanently
greater than the force trying to reinstate the piston in the
central position.
In general the piston, 1, slides largely frictionless on a layer of
bearing gas in power cylinder, 2. In case of failure of the bearing
gas pressure or as a resu t of short acting factors only, piston 1
starts gliding on the self-lubricating surface of the guide device,
10. In this way the wear of the piston, 1, of cylinder 2, can be
almost entirely eliminated.
The pressure of the gas supplied through the inlet openings, 16,
should be kept slightly higher then the pressure of the scavenging
air. The pressure difference depends on the design of the piston
guide device. In general it was found that the higher the
scavenging air pressure the higher the difference of the gas
bearing pressure, is required.
The design as shown in FIG. 3 is operationally the same as in FIG.
2 and in FIG. 6 & 7. The arrangement in FIG. 3 is different in
that there the self-lubricating material, preferably with a maximum
thermal expansion coefficient of 40 .times. 10.sup.-.sup.7
/.degree. C. is deposited on the cylinder wall by the flame
spraying process. The arrangement in FIG. 4 differs from FIG. 2 in
that the step in front of the piston guide device, 10, as described
before, is replaced partially by a somewhat longer guide bearing
bush, 10c, extending to the inside, and in part by a shoulder
formed on the outside face of the piston, 1. The clearance between
the power piston, 1, and the wall of the cylinder, 2, is also
slightly larger in area 12, in front of the piston guide device,
10, than in area 13, within the piston guide.
FIG. 5 shows a simplified design of the piston guide device which
now consists of a simple cylindrical bearing bush made from a
self-lubricating material, as specified before. No bearing gas is
used with this design.
In some cases it is possible to build the piston guide device from
a material with no special self-lubricating characteristics. Such a
design would be similar to the one shown in FIG. 3, no
self-lubricating material is deposited on the cylinder wall,
however the gas bearing device should be incorporated. The
compressor piston, 5, moving in the cylinder, 6, is guided on a
centrally located guide pin, 18, with an interposed cylindrical
bush 19 made from some self-lubricating or lubricant impregnated
material. If a self-lubricating material is used it can be the same
material as the power piston guide bearing bushing, 10. If an oil
absorbant material is used, it may be a sintered metal with
graphite lubrication, or an oil impregnated metal, or an oil
impregnated ceramic. To keep the thermal expansion coefficient low,
nickel-graphite or chrome-nickel graphite with interspersed Invar
or Elinvar particles may be used. Special bearing bushes from
similar materials can be made.
The compressor piston, 5, on the side towards the power piston, 1,
is provided with a boss, 21, that matches a properly designed end
face, 22, of the power piston. As shown, the end, 22, of the power
piston fits over the boss, 21, on the compressor piston, 5, with a
radial clearance, so that the ringless compressor piston can find a
radially independent position. A mechanical connection of piston 1
and piston 5 is effected by an interlock of the piston end, 22,
with the face of compressor piston 5.
The coupling between the power piston, 1, and compressor piston 5,
is achieved by spring 23, (preferably of a helical type), connected
on one end to the power piston, 1, and on the other end to the
compressor cylinder, 6. The spring, 23, extends through the hollow
guide pin, 18, through compressor piston 5. The guide pin, 18, is
made in one solid piece with the compressor cylinder, 6, or it is
connected with it permanently, in some other way. For limiting the
travel of the compressor piston, 5, to the right, as per FIG. 1, a
limiting ring, 24, is provided in the compressor cylinder, 6, as
shown in FIG. 1.
If some additional cooling of the engine is required water can be
injected in the combustion chamber in the standard way, seperately
or combined with fuel. The equipment for such a water injection
system is well known so that further explanation is not necessary.
The free piston engine, built according to these plans can be
operated with twice the piston stroke frequency as other existing
free piston engines. Thus the use of this engine permits a much
higher power output to be obtained from an engine of the same size.
Through the use of this invention it is possible to build free
piston engines with a high specific power output, which makes them
applicable to motor traction purposes, as well as stationary and
ship propulsion engines.
* * * * *