EP0657648A1

EP0657648A1 - Multi-cylinder reciprocating pump with axial pistons

Info

Publication number: EP0657648A1
Application number: EP94202158A
Authority: EP
Inventors: Ivano Montanari
Original assignee: Annovi Reverberi SpA
Current assignee: Annovi Reverberi SpA
Priority date: 1993-12-10
Filing date: 1994-07-25
Publication date: 1995-06-14
Also published as: IT1262843B; ITRE930085A0; ITRE930085A1

Abstract

The pump comprises, for operating the pistons (10), a linkage of the type provided with a surface (12) rigid with the motion input shaft and inclined to the plane perpendicular to the axis of the shaft (11), said inclined surface (12) acting with unilateral bearing constraints on the rear end of the pistons (10) to implement their outward stroke; a plate (20) constrained to the rear end of each piston (10) by a bearing constraint which subjects the piston (10) to a reaction with a component parallel to the piston axis and in the same direction as the return stroke of the piston (10); the central portion of the plate (20) rests on a fulcrum element (30) coaxial to the shaft (11) and arranged to subject the plate (20) to a reaction with a component parallel to the axes of the pistons and having the same direction as the return stroke of the pistons (10).

Description

This invention relates to a multi-cylinder reciprocating pump with axial pistons of the type in which the piston movement is produced by a linkage with a frontal cam defined by a surface rigid with the motion input shaft and inclined to the plane perpendicular to the shaft axis. This inclined surface acts on the rear ends of the pistons via unilateral bearing constraints, so urging the pistons to effect their outward stroke.
In known pumps of the aforesaid type, the piston return stroke, for implementing the suction stage, is produced by the action of cylindrical elastic springs associated with the pistons and acting by compression.
These return springs give rise to various drawbacks which up to the present time it has not been possible to overcome.
A first drawback is that part of the energy provided by the motor is used to compress the springs, with consequent energy wastage.
In addition, particularly for pumps of relatively small power, the resistance offered by these springs is particularly negative towards initial movement, to the extent that it is difficult to start the pump if conditions are not completely favourable.
Moreover, for pumps operating at high rpm (in excess of 3000 rpm) special springs are required capable of very effectively responding to the high piston oscillation frequency, such springs being of relatively costly manufacture and in addition requiring a high pre-compression load, resulting in particularly high energy loss (as stated). In addition, with prolonged use and time, the return springs lose their elasticity to the extent that in the long term they no longer operate satisfactorily.
An object of the present invention is to provide a pump of the aforesaid type which obviates said drawbacks connected with the presence of the piston return springs.
A further object of the present invention is to improve and simplify the means which secure the inclined surface to the rear ends of the pistons.
A general object of the present invention is to improve the piston mechanical efficiency.
These and further objects are attained by the present invention as characterised in the claims.
The invention is shown in detail in the figures, which illustrate one embodiment thereof.

Figure 1 is a side view of the pump with certain parts removed in order to show the members relative to the present invention.
Figure 2 is a section on the plane II-II of Figure 1.
Figure 3 is an enlarged detail of the plate 20 sectioned on the plane III-III of Figure 2.
Figure 4 shows a part of the pump sectioned on the plane IV-IV of Figure 2.
Figure 5 shows an alternative embodiment of the plate 20.
Figure 6 is a detail shown sectioned on the plane VI-VI of Figure 5.

The pump to which the present invention is applied is of the type comprising a number of pistons 10 with their axes parallel to each other and parallel to the motion input shaft 11, which is driven by an electric motor (not shown in the figures) or by any other type of motor.
To move the pistons 10 with reciprocating movement a linkage is provided comprising a surface 12 rigid with the shaft 11 and inclined to the plane perpendicular to the shaft axis.
By means of unilateral bearing constraints, described in detail hereinafter, the surface 12 acts on the rear end of the pistons 10 to effect their outward stroke.
In detail, the pump shown in the figures comprises a casing 13 which encloses the motor, and to which there is fixed an intermediate structure 14 in which the cylinders 15 within which the pistons 10 slide are inserted.
To the structure 14 there is fixed a front body 16 internally comprising usual distribution valves and suction and delivery ducts (not shown in the figures because they are of known type); the inlet 17 to the suction ducts can be seen in Figure 1.
The figures show a pump with three pistons 10 uniformly spaced equidistantly apart, however the invention is applicable equally to multi-cylinder pumps with a different number of pistons 10.
According to the present invention, a plate 20 is provided, secured to the rear end of each piston 10 with a bearing constraint which subjects the piston 10 to a reaction having a component parallel to the axis of the pistons 10 and in the same direction as the return stroke of the pistons.
According to the preferred but not exclusive embodiment shown in the figures, this bearing constraint between the plate 20 and each piston comprises, for each piston 10, a spherical cap 21' fixed to the rear end of the relative piston 10 and with its convexity facing the piston. In detail, to the rear end of each piston 10 there is connected, via a stem 22, a ball 21 the centre of which lies on the axis of the piston 10 (in particular, the ball 21 and stem 22 are formed integrally with the piston 10); that surface part of the ball 21 facing the piston 10 defines said spherical cap 21'.
The plate 20 makes contact with the caps 21' via respective profiled apertures 24, the width of which is less than the diameter of the ball 21, and which define seats providing contact with the caps 21'. In detail, the apertures 24 are in the form of a slot having an initial rectilinear part 24' extending from the periphery of the plate 20 and terminating with a circular arc portion 24''. In the plate shown in Figures 2 and 3, the width of the initial portion 24' is constant and the terminal portion 24'' has a semi-circumferential profile (Figure 2). As can be seen from the section taken on the plane III-III, the edge of the aperture 24 is straight but inclined so that contact with the cap 21' takes place at an intermediate point thereof (Figure 3). Using this particular plate 20, the inclination of the surface 12 can be varied in that the apertures 24 equally provide contact with the caps 21' if the distance between the regions of contact between the plate 20 and two of the caps 21' varies.
Figures 5 and 6 show a plate 20 usable for constant inclination of the surface 12. With this embodiment, the terminal portion 24'' extends through an angle greater than 180°C and has a diameter greater than the width of the initial portion 24', which is just a little greater than the diameter of the stem 22. As can be seen from the section taken on the plane VII-VII, the edge of the aperture 24 has an arched profile and mates with the profile of the cap 21'.
According to the invention there is also provided a fulcrum element 30 coaxial with the shaft 11 and having a convex surface 31 on which the central portion of the plate 20 rests, to subject the plate 20 to a reaction with a component parallel to the axis of the pistons 10 and in the same direction as the return stroke of the pistons.
In the preferred but not exclusive embodiment shown in the figures, the fulcrum element 30 is inserted, in a manner slidable in an axial direction, into a cavity 32 provided in the structure 14. By means of an elastic spring 33 precompressed between the end of the cavity 32 and the element 30, this latter is thrust constantly against the plate 20; the intensity of this thrust is such as to maintain the plate 20 constantly in contact with the rear ends of the pistons 10 and these latter constrained to and in contact with the inclined surface 12.
According to the preferred but not exclusive embodiment shown in the figures, there is provided a plate 41 of antifriction material rigid with the shaft 11 and fixed onto an inclined flat face of a block 18 keyed onto the end of the shaft 11. The plate 41 has a flat face facing the pistons 10 and defining said inclined surface 12. The surface 12 is secured to the ends of the pistons by slide shoes 42.
Each shoe 42 has a flat face 42' which slides in contact with the inclined surface 12 (ie with the antifriction plate 41) and comprises in its opposite face a concave surface 42'' which mates with that surface portion (spherical cap 21'') of the ball 21 facing the surface 12. The contact between the surfaces 42'' and 21'' forms a ball joint.
In operation, on rotating the shaft 11, this rotates the inclined surface 12 which, by sliding against the slide shoes 42 which remain constrained to the balls 21, axially thrusts the pistons 10 with thrust cycles mutually offset by 120°C, in the direction of the delivery stroke (towards the left in Figure 1).
The fulcrum element 30 and the plate 20, together with their contact constraints with the spherical caps 21', form a positive drive system which enables the pistons 10 to undergo axial movement while causing them to constantly rest, via the slide shoes 42, against the inclined surface 12, to follow the axial movements of the points of this latter.
In this respect, the plate 20 acts acts as a (three-dimensional) lever the fulcrum of which is defined by the point of bearing against the convex surface 31 of the element 30 which, while one or two of the pistons are urged by the inclined surface 12 to effect the delivery stroke, produces the return stroke of the other two pistons or of the other piston respectively. The movement which the plate 20 undergoes relative to the element 30 is a rolling movement on the surface 31 of this latter, hence there is no energy loss by friction.
The thrust of the spring 33 is such as to overcome the opposing thrusts developed by the operation of the pump, hence the element 30 is practically at rest. The spring 33 serves mainly to achieve precise contact between the elements of the positive drive system by taking-up inevitable machining tolerances.
Basically, the present invention achieves return of tie pistons 10 without the use of springs, and instead by a balanced system which neither consumes energy uselessly nor requires the overcoming of opposing (spring) forces or other means to return the pistons.
Moreover, the particular constraint between the rear ends of the pistons 10 and the surface 12 is extremely simple, effective and of low constructional cost.

Claims

A multi-cylinder reciprocating pump with axial pistons, comprising, for operating the pistons (10), a linkage of the type provided with a surface (12) rigid with the motion input shaft and inclined to the plane perpendicular to the axis of the shaft (11), said inclined surface (12) acting with unilateral bearing constraints on the rear end of the pistons (10) to implement their outward stroke, characterised by comprising a plate (20) constrained to the rear end of each piston (10) by a bearing constraint which subjects the piston (10) to a reaction with a component parallel to the piston axis and in the same direction as the return stroke of the piston (10), the central portion of the plate (20) resting on the convex surface (31) of a fulcrum element (30) coaxial to the shaft (11) and arranged to subject the plate (20) to a reaction with a component parallel to the axes of the pistons and having the same direction as the return stroke of the pistons (10).
A pump as claimed in claim 1, characterised in that said bearing constraint between the plate (20) and each piston (10) comprises a spherical cap (21') fixed to the rear end of the piston (10) and having its convexity facing the piston, and an aperture (24) provided in the plate (24) to define a seat of contact with the spherical cap (21').
A pump as claimed in claim 1, characterised in that said fulcrum element (30) is urged against said plate (20) by elastic means (33) the thrust of which is such as to maintain the plate (20) in contact with the rear ends of the pistons (10) and to maintain these ends in contact with the inclined surface (12).
A pump as claimed in claim 1, characterised by comprising: a plate (41) of antifriction material rigid with the motion input shaft (11) and having a flat face facing the pistons (10) which defines said inclined surface (12); and slide shoes (42) each with a flat face (42') slidable in contact with the inclined surface (12), said shoes (42) being each constrained to the rear end of a relative piston (10) by a ball joint.
A pump as claimed in claim 4, characterised in that to the rear end of each piston (10) there is fixed a second spherical cap (21'') with its convexity facing the inclined surface (12), each slide shoe (42) having a concavity (42'') facing the pistons (10) and mating with the second spherical cap (21'') of the respective piston (10).