EP1443209A2

EP1443209A2 - Water pump

Info

Publication number: EP1443209A2
Application number: EP03078651A
Authority: EP
Inventors: Fulvio Montipo'
Original assignee: Interpump Engineering SRL
Current assignee: Interpump Engineering SRL
Priority date: 2003-01-16
Filing date: 2003-11-20
Publication date: 2004-08-04
Also published as: ITRE20030001U1; ITRE20030001V0; EP1443209A3

Abstract

Water pump, comprising a casing (1) carrying a rotatable shaft (9) provided with at least one eccentric cam (7) for operating at least one automatically returning radial piston (13), the operative chamber of which is connected to intake and delivery conduits respectively by way of interposed automatic valve means, between the eccentric cam and the piston there being interposed an idle annular thrust member (6) which constantly contacts the piston head.

Description

The present invention relates to a hydraulic pump, a typical but non-exclusive use for which is in the hobby and do-it-yourself field and in the semi-professional field.
For example it can be applied in the field of jet washers or other small machines or plants, which need not be described in detail.
The purpose of the invention is to patent a water pump and the apparatus which incorporates it, such as the said jet washers or other similar implementations.
Domestic jet washers are known provided with a hydraulic service pump, well known to experts of the specific art, but which will not be described in detail.
It is sufficient to state that the pumps intended for such uses are generally small, their most significant characteristics being definable as follows: capacity about 3-10 I/min, pressure about 40-120 bar, and power about 1500 W, within which ranges the water pumps of the invention also generally fall.
Experience has demonstrated that such piston pumps have complex and costly piston operating linkages, often incompatible with the use for which they are intended.
The main object of the present invention is to provide a water pump able to overcome the aforedefined problem, i.e. able to operate with improved reliability, and which is of low cost, with consequent corresponding greater reliability and lower cost of the apparatus which incorporates it.
Another object of the invention is to achieve said objective within the context of a simple, compact and lightweight construction which is particularly reliable and of long life, as will be clarified hereinafter.
Said objects are attained by a water pump presenting the characteristics indicated in the claims.
In a totally general sense, the pump comprises a casing carrying a rotatable shaft to be connected to a suitable drive unit, and having at least one cylindrical eccentric cam for operating at least one radial piston combined with elastic return means, and of which the operative chamber is connected to two headers, namely for intake and delivery respectively, by way of interposed automatic non-return valves.
In general, at least two diametrically opposing pistons are provided, working in phase opposition.
Moreover, between said eccentric cam and the head of each piston there is interposed an idle annular thrust member against which said head constantly rests by the effect of said elastic return means.
According to the invention, the generally linear zone of mutual contact between said piston and said thrust member is misaligned with the longitudinal axis of the piston.
When the eccentric cam rotates, it also drags with it the thrust member, the piston acting against said thrust member with a relatively small force during intake, said force being substantially equal to the thrust of the piston elastic return means, and with a relatively large force during delivery, substantially equal to the thrust of the elastic means plus the resistance offered by the pumped water.
In short, during the intake stroke the thrust member is only lightly loaded and slides on the piston head, whereas during the delivery stroke it is highly loaded, hence rolls on the piston head instead of sliding.
By virtue of said misalignment, which constitutes a basic characteristic of the invention, wear on the coupling between the thrust member and piston is strongly retarded because during the intake stroke the friction forces in play present a component coplanar with the piston head and passing through the centre of the mutual contact zone between the piston and thrust member, to create a moment which causes the piston to rotate about itself.
Essentially, the thrust member presents only limited sliding on the piston head, because by virtue of the piston rotation, said thrust member acts on gradually differing peripheral regions of the piston.
All the objects of the invention are hence attained.
The characteristics and the constructional merits of the invention, together with its operation, will be apparent from the ensuing detailed description thereof, given with reference to the accompanying drawings, in which:
Figure 1 is the section I-I indicated in Figure 2.
Figure 2 is the section II-II indicated in Figure 1.
Figure 3 is the section III-III of Figure 1.
Figure 4 is the view in the direction IV of Figure 1.
Said figures show a body of regular shape, of square profile in the illustrated example (Figure 1), forming the pump casing 1.
In the base of said casing 1 there is provided a cylindrical recess 2 of differential cross-section, on the opposite side there being provided a rib 3 (see Figures 2 and 3).
Along the peripheral edge of the base of the casing 1, where the recess 2 opens, there is provided a holed circular flange 10 provided to connect the pump to a suitable drive unit, generally an electric motor (not shown), the output shaft of which is indicated by 9 in Figure 2.
Said shaft 9 is rotatably mounted within said recess 2 via a bearing 8, beyond which it presents an eccentric cam 7 on which an idle annular thrust member 6 is mounted, described hereinafter.
The longitudinal axes of said shaft and said eccentric cam 7 are indicated by 99 and 77 respectively, their misalignment being indicated by d (see Figures 1 and 2).
In the casing 1 there are provided, on one side and the other of said recess 2, two parallel through holes 5, 4 of differential cross-section, which are perpendicular to said shaft 9 (Figure 1) and to said rib 3 (Figure 3). The first 5 of said through holes constitutes the pump intake conduit, and the second 4 the delivery conduit.
The lesser-diameter central portion of the hole 5 communicates with an intake port 55 provided in the rib 3 (Figures 1 and 4), the two greater-diameter terminal portions each containing an automatic intake valve 50 (Figure 1).
Likewise, the hole 4 has a lesser-diameter central portion which communicates with a delivery port 44 provided in the rib 3 (Figures 1, 3 and 4), and two greater-diameter terminal portions which each contain an automatic delivery valve 40.
Proceeding from the base of its housing, each delivery valve 50 comprises an annular body 51 which provides the seat for a cup-shaped valve 52, a thrust spring 53 arranged to constantly force the valve 52 towards its seat, and a generally cage-shaped guide element 54 which contains said valve 52 and said spring 53, and maintains said annular body 51 in position. In its turn the guide element 54 is maintained in position by an intake and delivery header 56 (Figures 1-4) which is fixed onto the respective side of the casing 1 by screws 57 (Figures 3 and 4) by way of a gasket 58 (Figure 3).
Two identical headers 56 are provided, with each of which an intake valve 50 and a delivery valve 40 are associated.
As is well shown in Figure 1, the delivery valve 40 is identical to the intake valve 50. The two differ by being mounted mutually inverted, and are hence interchangeable.
Specifically, each delivery valve comprises an annular body 41 similar to 51, a cup valve 42 similar to 52, a thrust spring 43 similar to 53, a guide element 44 similar to 54, and a gasket 48 similar to 58.
With regard to the headers 56, these are identical, each comprising an elongate flat profiled body having a through longitudinal conduit closed by two terminal plugs 60.
Said elongate body has, at its ends, two lateral ports communicating with the seats of the valves 50 and 40, and at its centre a cylindrical dome 59 which opens towards the eccentric cam 7 of the shaft 9.
Said dome 59 is coaxial with a hole of differential cross-section which is provided in the casing 1, to open within the recess 2, and has its longitudinal axis perpendicular to that of the shaft 9 (Figure 1).
A jacket 12 acting as a guide for a flat headed piston 13 is housed in said hole and is retained therein by the respective header 56 by way of an interposed gasket 11.
Between the jacket 12, casing 1 and piston 13 there is positioned a double lipped annular gasket 14, said lips being maintained in their correct sealing position by a series of longitudinal holes 15 provided in the wall of said jacket 12, and opening at one end into the groove between said lips, and at the opposite end into the longitudinal conduit of the header 56. That end of the jacket 12 distant from the gasket 14 is received within said dome 59, where it presents inlets (see Figures 1 and 2) to enable water to pass.
The piston 13 is shaped as a cup which opens towards the respective header, against its base there resting the idle annular thrust member 6. Inside the piston 13 there is positioned a return spring 17 located between the base of said cup and a guide and friction reduction element 18 contained in the centre of the dome 59 of the header 56.
The transverse dimensions of said guide element 18, which is of generally cylindrical shape, are less than the inner diameter of the cavity of the piston 13, so that said cavity can fill with water.
Finally, with regard to the idle thrust member 6, this consists of a ball bearing, well visible in Figure 1. In the illustrated example, as shown in Figure 2, the outer face of the outer ring of said bearing is cylindrical, but there is nothing to prevent it from being shaped differently, for example as an annular sector of a spherical surface, of castor type.
According to the teachings of the invention, as shown in Figure 2, the central or median point of the generally linear zone of mutual contact between the thrust member 6 and the head of the piston 13 is misaligned with respect to the longitudinal axis of said piston 13, namely towards the mouth of the recess 2 of the casing 1.
Specifically, said misalignment, indicated by e in Figure 2, is such that the outer side of the thrust member, or bearing, 6 is virtually tangential to the outer surface of the piston 13.
The described pump operates as follows.
During the rotation of the shaft 9 the bearing 6 moves in all directions within the plane in which it lies, following the movement of the eccentric cam 7.
When the eccentric cam 7 moves towards its bottom dead centre (with reference to Figure 1), the lower piston 13 is undergoing its delivery stroke, i.e. the valve 40 is open and the valve 50 is closed, and inversely the upper piston 13 is undergoing its intake stroke, with the valves 40 and 50 closed and open respectively.
The two pistons 13 then exchange roles when the eccentric cam 7 moves towards its top dead centre, upwards with reference to Figure 1.
During these strokes the intake piston 13 presses against the bearing 6 with a force generally equal to the load of the respective return spring 17, and the delivery piston 13 presses against it with as force generally equal to the sum of the load of the spring plus the thrust determined by the pressure of the pumped water.
Said two forces are considerably different, with the result that the outer ring of the bearing 6, which rotates on the eccentric cam 7 in the opposite direction to the shaft 9, tends to side and drag the head of the intake piston by friction and cause it to rotate, whereas there is a much stronger contact with the head of the delivery piston 13, on which it rotates.
This has been verified by specific tests conducted on samples of pumps constructed in accordance with the teachings of the invention, which have resulted in attainment of the objectives defined in the introduction. Express reference has been made previously to the use of the pump of the invention on equipment generally of hobby type, however it is evident that the pump can also be used in other sectors, within the context of portable or non-portable hydraulic devices.

Claims

A water pump, characterised by comprising a casing (1) carrying a rotatable shaft (9) provided with at least one eccentric cam (7) for operating at least one automatically returning radial piston (13), the operative chamber of which is connected to intake and delivery conduits respectively by way of interposed automatic valve means, between the eccentric cam and the piston there being interposed an idle annular thrust member (6) which constantly contacts the piston head.
A pump as claimed in claim 1, characterised in that said idle annular member consists of a bearing with a generally cylindrical outer face.
A pump as claimed in claim 2, characterised in that the outer face of said idle annular member is generally convex.
A pump as claimed in claim 1, characterised in that the zone of mutual contact between said head and said idle member is misaligned with the longitudinal axis of the piston.
A pump as claimed in claim 4, characterised in that said idle member has its surface of contact with the piston close to the periphery of the piston head.
A pump as claimed in claim 1, characterised in that said at least one piston is shaped as a cup in which elastic means for its return, such as at least one compression spring, are housed.
A hydraulic apparatus, characterised by incorporating at least one pump in accordance with claims from 1 to 6.