Fluid-operated miniature engine

Miniature engine operated by an expanding gaseous fluid, which comprises a cylinder (18), piston (20) and inlet valve (29), the upper part of the piston (20) cooperating with a radially expansible resilient diaphragm (28), which is secured to the piston (20) and performs momentarily a pneumatic seal-engagement function along the periphery of said cylinder (18) during the gaseous expansion phase.

This invention concerns a fluid-operated miniature engine; more precisely 
it concerns a miniature engine suitable to be actuated by the energy of a 
gaseous fluid under pressure such as air, carbon dioxide, Freon or another 
gas which can be employed for the purpose. 
A miniature engine of this type is properly employed with models for the 
movement of toys, dynamic models, small mechanisms, small tools, fans, 
etc. 
For the movement of models, toys, etc. of the above type it is the normal 
practice to use small internal-combustion engines, small electric motors, 
small motors operated by spring or elastic band and also small or 
miniature fluid-operated engines. 
Document EP-A-No. 0,151,314 discloses a device provided with a piston which 
is movable within a cylinder. Said piston operates on a connecting 
rod-crank assembly. The axis of the crank is connected, for instance, to 
the propeller of a model-airplane. The device is further provided with a 
gas inlet valve, which may be closed by means of a ball, on which a 
protuberance of the piston acts. 
GB-A-No. 2,029,908 discloses a fluid-operated miniature motor which uses a 
complex structure so as to be able to perform all the functions needed for 
its operation with an acceptable efficiency at an acceptable cost. 
U.S. Pat. Nos. 2,588,478 and 3,703,848 disclose very simplified 
fluid-operated miniature engines the efficiency of which is inadequate for 
their employment. These engines have to be fed with high pressure fluids 
which are hard to transport and handle and besides are dangerous. 
DE-A-No. 2.912.556 discloses substantially a miniature engine of the same 
type as those of the above two U.S. patents. This patent is the same as 
GB-A-No. 2,018,366 and provides for the exhaust valve to be actuated by a 
prong jutting out from the crown of the piston. 
The known engines have their feeder valve operated by a prong on the 
piston. Moreover, they do not provide for an exhaust valve apart from 
lateral holes at the end of the stroke of the piston. 
All the known fluid-operated miniature engines entail inadequate efficiency 
and high production costs since, in view of the measurements involved, 
which are very small and amount only to millimeters, the working 
tolerances have to be very small, and this is hard to accomplish, above 
all in mass production. 
Furthermore, if the fluid-operated miniature engines of a known type are to 
maintain their efficiency on the assumption that the production tolerances 
are the right ones, they have to comprise a plurality of parts made of 
hard and costly materials, which require lubrication to prevent such 
tolerances being affected by wear and the efficiency being speedily lost. 
Otherwise the known miniature engines require resilient seal-engagement 
packings which cause great wear between piston and cylinder to the 
detriment of the efficiency. 
BE-C-355.350 discloses an engine operated by a fluid under pressure, the 
engine comprising an exhaust valve actuated by the piston itself by means 
of a plunger lodged in the piston, thus entailing great complications in 
fabrication and operation. 
U.S. Pat. No. 3,910,160 too employs exhaust valves actuated by plungers 
governed by the head of the connecting rod; this embodiment involves not 
only great constructional complications but also dimensions such as make 
necessary a piston displacement of a considerable value. 
U.S. Pat. No. 4,190,024 discloses a Diesel engine with an exhaust slit of 
the type traditional in two-stroke engines. 
This invention therefore provides a fluid-operated miniature engine of the 
same type as that of U.S. Pat. No. 2,588,478 but suitable to work mainly 
at medium-low pressures without particular lubrication problems and to be 
realised with inexpensive materials such as plastics, for instance. 
The invention also provides a miniature engine the components of which can 
be made by moulding or other systems compatible with mass production 
without problems of accurate, limited tolerances. 
The invention therefore has the purpose also of obtaining components having 
relatively wide working and fit tolerances. 
This is achieved by a miniature engine having the features disclosed in 
claim 1. 
According to the invention a resilient diaphragm solidly fixed to the upper 
crown of the piston is made to cooperate with the upper part of the 
expansion cylinder. This diaphragm performs a pneumatic seal-engagement 
function in relation to the expanding fluid during at least part of the 
fluid expansion phase, thus reducing consumption considerably. 
According to a form of embodiment the chamber to store the fluid under 
pressure can cooperate with a valve actuated, for instance, by the piston 
itself so as to maximize the effect of the fluid under pressure. 
According to a further form of embodiment the crankshaft cooperates with an 
eccentric support able to obtain required timing in relation to the top 
dead centre point of the piston. 
According to another embodiment the outlets for the expanded fluid at the 
end of the piston stroke can be obtained with appropriate radial slits 
machined along the length of the piston, these slits becoming uncovered at 
a suitable moment by the return of the resilient diaphragm to its relaxed 
position. 
According to another form of embodiment a device is provided which can 
govern the opening and closure of the fluid inlet valve in relation to the 
top dead centre point of the piston.

A miniature engine 10 according to the above figures comprises components 
made of a moulded plastic except a shaft 11 and spring 24 consisting of a 
metal in this case and a diaphragm 28 made of soft rubber, in this 
instance a silicone rubber, rubber latex or natural rubber or another 
material possessing great resilience. 
To indicate the dimensions involved and the resulting constructional and 
operational problems which led to the embodiments of the invention, it may 
be noted that a piston 20 of the miniature engine can have a bore ranging 
from 4 up to 12-20 mm. 
A base 30 supports a crankshaft 11 and contains in a casing 14 a flywheel 
12 solidly fixed to the crankshaft 11 and performing the function of a 
crank. 
The flywheel 12 comprises a pivot 13 to which a connecting rod 15 is 
rotatably fitted. The casing 14 is closed with a cover 16 which may 
include an exhaust hole 17. The piston 20 slides in a cylinder 18. 
The piston 20 comprises radially arranged lengthwise grooves 19, which 
connect the crown of the piston 20 to the casing 14 and exhaust hole 17. 
A cylinder head 26 cooperates with the base 30 in the upper part of the 
engine. Mechanical fixture connection of the base 30 to the cylinder head 
26 can be obtained in any known manner. 
In the example shown a diaphragm 28 is secured in cooperation with the 
upper part of the cylinder 18. The diaphragm 28 can normally have a 
cup-shaped conformation (FIGS. 1 and 4) or the conformation of a toric 
omega (FIGS. 2, 3 and 5) or a toric "V" (FIGS. 6 to 10). 
All the conformations of the diaphragm 28 posses a feature arising from the 
soft, resilient material of which the diaphragm consists, namely a feature 
according to which, when there is pressure in an expansion chamber 27, the 
diaphragm 28 expands radially and fits against the inner circumferential 
wall of the cylinder 18 and rests on a crown 120 of the piston 20. 
In FIGS. 1 to 5 the diaphragm is squashed against the circumferential wall 
of the cylinder 18 by the pressure of the liquid, whereas in FIGS. 6 to 10 
the diaphragm is squashed first of all against the circumferential wall of 
the cylinder 18 and against the upper crown 120 of the piston 20 by the 
conformation of the upper crown 126 of the cylinder 18, while thereafter 
it is the pressure of the fluid which keeps it in that position until the 
expanding pressure in the expansion chamber 27 becomes equal to the thrust 
of the diaphragm, which then takes up again its original shape. As the 
piston 20 descends inside the cylinder 18, the pressure in the expansion 
chamber 27 is reduced. 
While the piston 20 continues its downstroke and the expansion chamber 27 
is lengthened, there is a moment when the resilient force of return to its 
original position possessed by the diaphragm 28 becomes greater than the 
pressure of the fluid then held in the expansion chamber 27 as then 
constituted. 
In such a situation the diaphragm 28 takes up its original conformation 
once again and opens a toric ring of communication between the expansion 
chamber 27 and the casing 14 through grooves 19. 
When the toric ring of communication is obtained about the diaphragm 28, 
which has again taken up its original conformation, the pressure in the 
expansion chamber 27 quickly becomes equal to the atmospheric pressure and 
thus enables the piston 20 to rise without encountering opposed pressures. 
The diaphragm 28 is made of a resilient material such as a soft rubber, for 
instance silicone rubber, rubber latex or natural sheet rubber or any 
other material possessing a great capacity of expansion in a substantially 
or wholly resilient field. 
The expansion chamber 27 and, in the case of FIGS. 4 and 5, the storage 
chamber 127 are positioned above the diaphragm 28. 
The cylinder head 26 includes an inlet valve 29, which in this case is 
actuated by a push rod 21 located on the piston 20 at about the top dead 
centre point of the piston. This valve 29 can also be positioned elsewhere 
and be actuated otherwise. 
In the example shown the inlet valve 29 is opened by the push rod 21 when 
the latter overcomes the thrust of a spring 24 and displaces a small disk 
22 or ball or other suitable means from a seating 23. 
The variants of FIGS. 8 to 10 provide a device suitable to govern the 
opening and closure of the inlet valve 29 in a required manner and at the 
desired times in relation to the top dead centre point of the piston 20. 
The operation of the device is based on the following principle. 
Since there is pressure in the chamber above the small disk 22, the latter 
22 opens at once when the push rod 21 acts on the small disk 22 or ball or 
other suitable element. 
But if the push rod 21 comprises a resilient element 221 which enables the 
piston 20 to continue rising without the small disk 22 having to move at 
once, then the opening of the valve 29 is retarded and its closure is also 
retarded since the resilient yielding of the resilient element 221 has to 
be taken up. 
The delay in such opening depends on the correlation between the properties 
of the resilient element 221 and the feed pressure of the fluid; the less 
the resilient element 221 is pre-loaded before opening the inlet valve 29, 
the sooner that valve is opened. 
FIG. 8 provides for the resilient element 221 to act directly on the disk 
or other element 22 that closes the inlet valve. 
FIG. 9 provides for the resilient element 221 to act through a pin 121, 
whereas in FIG. 10 the pin 121 is anchored to an extension of the 
diaphragm 28, such extension thus constituting the resilient element 221. 
The method of working is the following. When the inlet valve 29 is open, 
the fluid under pressure expands in the storage chamber 27, which is 
sealed since the diaphragm 28 rests in seal-engagement on the inner 
circumferential wall of the cylinder 18. 
As the crankshaft 11 continues its rotation, the piston 20 descends, and 
this downstroke is assisted by expansion of the fluid under pressure in 
the expansion chamber 27 forming in the cylinder 18. 
The piston 20 descends; when equilibrium is reached between the pressure of 
the fluid and the resilience of the material of which the diaphragm 28 
consists, the diaphragm detaches itself from the circumferential wall of 
the cylinder 18 and frees a toric space that communicates with exhaust 
passages consisting of the grooves 19 in the piston. 
As the gas pours out through the grooves 19 in the piston 20, the pressure 
in the expansion chamber 27 drops substantially to zero. 
As a result, the ipstroke of the piston 20 is facilitated since the 
expansion chamber 27 is now at the environmental pressure. 
According to the invention a support 31 is provided in cooperation with the 
base 30 and comprises a hole with which an eccentric bearing 32 
cooperates. 
A splined coupling may be provided between the front part of the eccentric 
bearing 32 and the front part of the support 31 so as to maintain the 
required, reciprocal, radial positioning of the support 31 and eccentric 
bearing 32. A clamping plug 34 may be included. 
By means of this system it is possible to determine accurately the top dead 
centre point of the piston 20 and thus to obtain correct timing. 
The diaphragms 28 are shown in the figures. The diaphragm 28 of FIGS. 1 and 
4 cooperates at the top dead centre point with a tapered wall 39 of the 
cylinder 18, thus enabling the expansion chamber 27 to be pressurized. 
Instead of the tapered wall 39, FIGS. 6 to 10 show the diaphragm 28 thrust 
until it touches the crown 126 of the expansion chamber 27, thus creating 
a required hermetic seal and a mechanical deformation of the diaphragm 28 
that causes a pneumatic seal. 
The embodiment of FIGS. 2, 3 and 5 forms a variant of such second 
embodiment and comprises a diaphragm 28 conformed as a toric omega and 
rested against the crown of the expansion chamber 27 to create a 
seal-engagement therewith. The omega-shaped conformation of its ears 33 
enables the diaphragm to be easily deformed radially. 
The upper head 120 of the piston 20 can be conformed as a support cradle, 
and the upper crown of the expansion chamber 27 may be suitably rounded to 
facilitate the sliding of the ears 33 in maintaining a seal-engagement. 
According to the form of embodiment of FIG. 3 and enlargement 41 in the 
cylinder in correspondence with the bottom dead centre point of the piston 
20 facilitates the return of the diaphragm 28 to its normal position. 
According to another form of embodiment (FIGS. 4 and 5) an intermediate 
valve 35 may be provided and serves to keep the fluid under pressure in 
the storage chamber 127 for a period long enough for the piston 20 to pass 
its top dead centre point and for the expansion of the fluid to take place 
only during the downstroke of the piston and therefore when such expansion 
is of assistance. 
Such valve 35 can be arranged in various ways. FIG. 4 provides a support 
disk 36 with a sealing ring 38. The support disk 36 comprises at its 
centre in cooperation with the push rod 21 a hollow cone 37, which closes 
or substantially reduces the passage of fluid around the push rod 21 while 
the push rod is cooperating with the top end of the hollow cone 37. 
In FIG. 5 the support disk 36 cooperates with a ring 40 made of a soft, 
resilient material and positioned on the push rod 21. While the ring 40 is 
acting on the central hole of the support disk 36, a seal-engagement is 
obtained. 
It can be seen from the above that, in contrast to the known art of 
miniature engines, the miniature engine of this invention has an exhaust 
valve open throughout the whole period of the upstroke of the piston 20, 
and therefore owing to the elimination of compression during the upstroke 
the efficiency of this engine is better than that of the types known in 
the art.