[0001] The present invention concerns an electromagnetically operated pump for the precise
and controlled feeding of oil to two-stroke internal-combustion engines.
[0002] There are known to be in technique many types of pumps allowing to feed two-stroke
internal-combustion engines with precise and controlled amounts of oil, in strict
correlation with the running of the actual engine. Amongst others, use is already
being made since quite some time of electrically operated pumps, in which an electromagnetic
coil controls the piston of a cylinder in axis therewith, against the action of a
spring, so as to empty at each working cycle a pumping chamber thereof in which the
oil to be fed is metered.
[0003] The present invention concerns a pump of this type, with the object to improve its
characteristics as far as structural simplicity, and metering precision and easiness,
all being very important in view of the special use for which said pump is intended.
[0004] To reach this object, the pump according to the invention - comprising in a casing:
a cylinder; a piston element with a through pipe, axially movable in said cylinder;
an electromagnetic coil external to the cylinder, to control the movements of the
piston element against the action of spring means; a pumping and metering chamber
for the oil to be fed, at one end of the cylinder; and valve means housed in said
casing, close to said end, one of said means cooperating with said piston element
- is characterized in that the stroke of the piston element is limited, on one side,
by the plane surface of the casing onto which abuts the cylinder in correspondence
of said chamber and, on the other side, by the inner surface of a cup bearing, with
a projecting peripheral edge thereof, onto the end of the cylinder opposite to that
of the chamber, stout spring means being interposed between said cup and the casing
to stop the cylinder therein.
[0005] The invention will now be described in further detail, with reference to the accompanying
drawing, the only figure of which represents an axial section view of the improved
pump according to the invention.
[0006] As clearly shown on the drawing, the pump according to the invention comprises a
casing 1, containing a cylinder 2 and a piston element 3, axially movable into the
cylinder 2 and crossed by a pipe 4 connected with branches 5 and 6 - for oil inlet
and outlet respectively - of the casing 1. At one end of the cylinder 2 there is a
chamber 7 for pumping the oil to be fed, delimited by the plane surface 8 of the casing
1, onto which bears the cylinder 2, and by the bottom end 9 of the piston element
3. Externally to the cylinder 2 there is an electromagnetic coil 10 fed with pulse
current in strict correlation with the running of the two-stroke engine to be equipped
with the pump. When energized, said coil 10 controls the movements of the piston element
3 towards the chamber 7, against the action of a spring 11 which acts in an opposite
sense when the coil 10 is de-energized. Two ball valves 12, 13, are provided in the
casing 1 close to the oil pumping chamber 7, the first of said valves cooperating
with the bottom end 9 of the piston element 3, in correspondence of the outlet of
the pipe 4. As better explained hereinafter, when the piston element 3 is moved by
the electromagnetic coil 10, the valve 12 is closed while the valve 13 opens; viceversa,
the valve 13 closes when the piston element 3 is moved by the spring 11 and while
the valve 12 opens.
[0007] According to the invention, an abutment 14 is formed on the piston element 3, close
to the end opposite to the bottom end 9, said abutment 14 being apt to cooperate with
the inner surface 15 of a cup 16, apt to stop the cylinder 2 into the casing 1. Said
cup 16 bears in fact with its projecting peripheral edge 17 onto said cylinder 2 and
is pressed against the same by a stout Belleville spring 18 engaging the plane surface
19 of the casing 1. The stroke of the piston element 3 into the cylinder 2 is thereby
limited by the cooperation, on one side, between the abutment 14 and the inner surface
15 of the cup 16, and on the other side, between the bottom end 9 of the piston element
3 and the plane surface 8 of the casing 1.
[0008] Said stroke determines the capacity (or volume) of the pumping chamber 7 and the
metering of the oil to be fed.
[0009] The figure of the accompanying drawing illustrates the pump according to the invention
with the chamber 7 full of oil, the piston element 3 having its bottom end 9 spaced
apart from the plane surface 8 of the casing 1 and the abutment 14 in contact with
the inner surface 15 of the cup 16. When, in operation, the coil 10 is energized,
the piston element 3 moves towards the plane surface 8 compressing the oil into the
chamber 7, while the valve 12 closes the pipe 4 into which flows the oil let in through
the branch 5. The oil pressure in the chamber 7 opens the valve 13 and the oil is
fed through the branch 6 into the engine. Thus, the pumping of the oil is carried
out by energizing the electromagnetic coil 10. The piston element 3 stops, with the
chamber 7 empty, when the bottom element 9 thereof cooperates with the plane surface
8 of the casing 1. When the coil 10 is de-energized and its action ceases, the spring
11 causes the piston element 3 to return into its initial rest position; the valve
13, no longer subject to pressure, closes while the valve 12 opens, due to the difference
between the pressure of the oil let in upstream of the branch 5 and the oil pressure
downstream thereof. The oil thus fills again the pumping chamber 7.
[0010] The pump described heretofore has a very simple structure and its working is very
reliable; but, above all, it can be very easily adapted, at extremely reduced costs,
to the most different requirements of capacity: the volume of the oil pumping and
metering chamber 7 (namely, the amount of oil being fed at each piston stroke C) can
in fact be easily adjusted, not only by acting on the axial position of the abutment
14 of the piston element 3, but also by simply replacing the existing cup 16 with
a similar cup in which the projection of its peripheral edge 17 differs from the inner
surface 15 thereof, or even by varying with a simple mechanical operation the projection
in the cup 16 being used. It can be easily seen that, by keeping unchanged all the
other components of the pump and by merely replacing the cup 16, a single pump - with
specific characteristics according to the invention - can feed even considerably different
oil capacities per piston stroke, and be thus immediately adapted to many different
requirements and applications. The same can be done, with a simple mechanical operation,
by reducing to different extents the starting projection of the edge 17 in respect
of the inner surface 15 of a cup 16 of given dimensions. Moreover, the simple mechanical
working of the cup allows to obtain - in case of special requirements, but, if wishing,
also in mass production - extremely precise meterings of the oil volumes being pumped
at each piston stroke. Finally, as already said, the structure of the pump according
to the invention allows to obtain all this at extremely reduced costs and without
having to carry out particularly elaborate mechanical operations.
[0011] It is anyhow understood that further embodiments of the pump can be provided, other
than that described heretofore, without thereby departing from the protection scope
of the present invention.
1. Electromagnetically operated pump to feed two-stroke internal-combustion engines with
precise and controlled amounts of oil - of the type comprising, in a casing (1): a
cylinder (2); a piston element (3) with a through pipe (4), axially movable in said
cylinder (2); an electromagnetic coil (10) external to the cylinder (2), to control
the movements of the piston element (3) against the action of spring means (11); a
pumping and metering chamber (7) for the oil to be fed, at one end (9) of the cylinder
(2); and valve means (12, 13) housed in said casing (1) close to said end (9), one
of said means (12) cooperating with said piston element (3) - is characterized in that the stroke of the piston element (3) is limited, on one side, by the plane surface
(8) of the casing (1) onto which abuts the cylinder (2) in correspondence of said
chamber (7) and, on the other side, by the inner surface (15) of a cup (16) bearing,
with a projecting peripheral edge (17) thereof, onto the end of the cylinder (2) opposite
to that of the chamber (7), stout spring means (18) being interposed between said
cup (16) and the casing (1) to stop the cylinder (2) therein.
