Note: Descriptions are shown in the official language in which they were submitted.
CA 02652914 2008-11-20
Printeti: 16/06/2008 ` DESCPAMD IT2007000368'
Description
Positive displacement piston pump, for lubrication
Technical Field
The device of the present invention relates to the lubrication of mechanical
components of reciprocating compressors and of small-sized internal combustion
engines. In order to supply the necessary amount of liquid lubricant in the
above
machines, lubrication systems are required that are capable of handling even
very
modest lubricant flow rates and to supply them to the required points;
moreover,
said systems should have a simple mechanics, be realizable at low cost, and be
able to utilise the motion provided by the machine on which they are mounted,
without resorting to unduly camplicated mechanisms (like additional small
shafts,
power takeoffs.. etc.).
Background Art
At present, lubrication in small-sized piston engines and in reciprocating
compressors is performed substantially either by splash lubrication, in case
this
, . ,
method is considered satisfactory, or by employing gear pumps, in case the
needs
of a good lubrication are more pressing. Recently, mechanically actuated
(usually
by a cam), small-sized, positive displacement pumps have also been developed,
as
well as electromagnetically controlled valves, specifically for small internal
combustion motors of motorcycles or scooters..
Splash lubrication, which relies on the splashing and agitation caused by the
very
components to be lubricated (which are wetted by the oil generally contained
inside
an oil sump), has the advantage to be extremely economical and simple,
provided it
is able to insure a'sufficient lubrication. Nevertheless, it has considerable
drawbacks,
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like the need to maintain a constant lubricant level inside the oil sump in
order to
avoid seizure, the fact that the lubricant is not accurately supplied only to
the points
were it is really needed, the fact that it is impossible to supply the
lubricant under
pressure, the impossibility of using this kind of system in two-stroke engines
with
dry sump oil pumps, since in these applications the sump oil pump must work
under
dry conditions. Lubrication under pressure has become the mostly used system
because of its undoubted advantages linked to its utilisation, these
advantages being,
among others, the increase of the performance of the kinematical couples
lubricated
under pressure as compared with that obtainable without the contribution of
the feed
pressure. In particular, the lubrication relying on gear pumps has the
advantage of
putting under pressure the lubrication circuit and of allowing to accurately
reach the
various points or areas to be lubricated, with the required oil flow rate and
the correct
(prescribed) pressure value.
In this case, the lubricant also has the not negligible task of cooling the
surfaces
which are in mutual contact. Also the use of cam-actuated positive
displacement
pumps has quickly become widespread, besides that of electromagnetic pumps, in
the
field of small-sized internal combustion engines and in the technical field of
compressors, due to the possibility of feeding the lubricant under pressure,
by
controlling the flow rates, and therefore, taking advantage of the possibility
of
cooling down the various lubricated kinematical couples. However, the
inconvenience of the utilisation of gear pumps lies in the increased costs
involved in
the production of high-quality mechanical components, like gearwheels for
instance,
and in the need to provide an adequate power takeoff (drive), so that the
machine to
be lubricated is more difficult to manufacture. On the other hand, the
drawbacks of
utilising cam-actuated pumps, in their commonly used version, are the
requirement
of their assembling in the vicinity of the driving shaft and the need of
having
available an adequate oil level in the oil sump in order to permit the priming
(pump
starting). Moreover, the disadvantages of using electromagnetically controlled
pumps
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are generally the increased production cost, the electric power absorption,
and the
necessity of providing a control unit.
Brief Description of Drawings
The invention will now be described for illustrative purposes only having
regard to
three of its possible embodiments, which are neither limitative nor binding,
and
which are depicted in the annexed drawings, in which:
FIGURE 1 shows the first embodiment of the needle-shaped positive displacement
pump according to the present invention;
FIGURES 2a and 2b are two orthogonal views of the second embodiment of the
needle-shaped positive displacement pump according to the present invention;
FIGURES 3a and 3b are two orthogonal views of the third embodiment of needle
shaped positive displacement pump according to the present invention.
Description of the Invention and of its Preferred Embodiments
The present invention suggests a valid alternative to conventionally used
arrangements in the field of lubrication systems for small-sized, internal
combustion
motors, and for positive displacement compressors. In substance, it consists
of a
piston pump whose structure, however, is such as to permit to put under
pressure the
lubricant taken from the oil sump, wherein, the free, upper surface of the oil
level
may also be located far away from the rotating members of the machine. This
holds
in particular in an application concerning air compressors of the
reciprocating kind,
which generally have an oil sump located somewhat distant from the driving
shaft
from which it is possible to draw the motion for the actuation of the pump.
Fig. 1
shows a schematic cross-section of a possible embodiment of the present
invention,
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formed by:
- a cylinder body 1;
- a piston (plunger) 2;
- a check valve 3;
- a suction duct 4;
- a link rod 5;
- a plug 6;
- a crank 7.
The operation of this system - called "A-version" -, shown in Fig. 1, is as
follows:
The crank 7, by rotating around its own axis, gives rise to a relative motion -
by
means of the link rod 5 - between the piston 2 (which is hinged at the
eccentric hole
of the crank) and the cylinder body 1. This motion is the classical
reciprocating
motion of a conventional crank mechanism, whose stroke equals twice the
distance
between the axis of the crank 7 and the axis X of the eccentric hole of the
crank 7.
Starting from the bottom dead centre (BDC), the piston 2, while moving
upwards,
generates a negative pressure inside the cylinder 1, which is due to the fact
that there
is no fluid communication to the outside environment, because the suction
inlet 10
remains closed (obstructed) by the piston 2 itself, while the delivery is
controlled by
the check valve 3. When the piston 2 opens the suction inlet (suction opening)
10
obtained in the cylinder 1, lubricant is sucked through the suction inlet 4
immersed in
the lubricant (this system is self-starting or "self-priming" provided the
negative
pressure obtained inside the cylinder 1 insures the lifting of the liquid from
the free,
upper surface level, up to the suction opening 10). Upon reaching the top dead
centre
(TDC), the piston 2 inverts its direction of motion; there will be a first
phase of
backflow of lubricant through the suction inlet, but then, after the piston 2
has closed
this inlet 10, the delivery phase starts, after the opening of the check valve
3 under
the pressure force exerted by the compressed lubricant - on this check valve 3-
,
which overcomes the closure force of the spring 11 of the valve 3. Thus, the
lubricant
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first flows past the check valve 3 and then through a cavity obtained in the
piston 2,
until it reaches a delivery region. The plug 6 exerts a backing function
(abutment) on
the closure spring 11 of the check valve 3. The flow rate (delivery or
capacity) of the
pump of the invention can be modified by selecting an adequate cylinder bore
or a
5 suitable stroke (eccentricity of the hole on the crank).
In Fig. 2 there is shown a further version (embodiment) of the small pump
according
to the present invention, that will be named "B-version". This system
comprises:
- a cylinder body 1';
- a piston or plunger 2';
- a check valve 3';
- a small, flexible delivery tube (small delivery hose) 4';
- a crank 7';
- a pressure-relief valve 8' (optional).
In Fig. 1, and in the following figures, "X" always denotes the axis of the
eccentric
bore of the crank 7' and "Y" the axis of the driving shaft 13.
The operation of the system illustrated in Fig 2 (a and b) is basically the
same as that
of the device named "A-version", with the only difference that the lubricant
is now
compressed inside a cylinder body 1', which is substantially completely dipped
(immersed) in the lubricant, while it is supplied to the delivery region
through an
additional element forming essentially a small hose 4'. The operation is
detailed in
the following paragraph:
The crank 7', while rotating around its axis, brings about a relative motion
between
the piston 2' (hinged on the eccentric bore 9' of the crank; X-axis) and the
cylinder
body 1', the latter being hinged (at 15') to the oil sump (not shown). The
resulting
motion is a classical reciprocating motion of a conventional crank mechanism
whose
stroke is twice the distance existing between the axis of the crank 7' and the
axis X
of the eccentric bore 9' of the crank 7'. Starting from the BDC, the piston
2', in the
course of its upward motion, generates a negative pressure inside the cylinder
1'
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which is due to the fact that there is no fluid communication to the outside
because
the suction inlet (analogous to 10 of Fig. 1 but not shown in Figs. 2a, 2b) is
closed by
the piston itself and the delivery is controlled by the check valve 3'. When
the piston
2' opens said suction inlet obtained in the cylinder 1', lubricant is sucked
through
this suction inlet, which is immersed in the lubricant (this system,
obviously, is
always self-starting or "self priming"). Upon arriving at the TDC (top dead
centre)
the piston 2' inverts its direction of motion; there will be a first phase of
backflow
through the suction inlet, and then the delivery phase will start after the
piston 2' has
closed said inlet and the check valve 3' has opened under the pressure force
exerted -
on this check valve 3' - by the compressed lubricant, this pressure force
overcoming
the closing force of the spring (not shown in Fig. 2) of the valve 3'. The
lubricant,
after flowing beyond the check valve 3', will flow through the small hose 4'
and will
finally reach the delivery zone after having passed through a plurality of
passages 9'
and 12', thereby effecting eventually an accurate lubrication at the desired
points (the
components that need to be lubricated are not shown in the drawings). In this
version, the problem of connecting the pumping zone with the delivery zone,
which
are in relative motion, is solved by using a flexible tube 4'.
This system may be equipped with a pressure-relief valve 8'.
In the "C-version" corresponding to the third embodiment according to Fig. 3,
the
system includes:
- a cylinder body 1 ";
- a piston or plunger 2";
- a check valve 3";
- a rigid, delivery duct 4";
- a crank 7";
- an element 14";
- a pressure-relief valve 8".
The operation of the system named "C-version" (third embodiment) is identical
with
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the device named "B-version" (second embodiment) except that the lubricant
arrives
at the delivery zone by passing through an additional, rigid duct 4". In this
version,
the problem of connecting together the pumping zone with the delivery zone,
which
are in relative motion to each other, is solved by using a cylindrical rigid
element 4"
(rigid duct) that slides within the piston-bearing body 14". In this case too,
the
system may be equipped with a pressure-relief valve 8".
Obviously, also in the third embodiment of Fig. 3 (a and b), the pivoting
point (pivot
pin) 15" is hinged to the oil sump (not shown).
