GB1571360A

GB1571360A - Diaphragm pumps and compressors

Info

Publication number: GB1571360A
Application number: GB13331/78A
Authority: GB
Original assignee: Gen & Country Lab Ltd
Current assignee: Gen & Country Lab Ltd
Priority date: 1978-04-05
Filing date: 1978-04-05
Publication date: 1980-07-16

Description

(54) IMPROVEMENTS TO DIAPHRAGM PUMPS AND COMPRESSORS (71) We, GENERAL AND COUNTRY LABORATORIES LIMITED, a British company, of Third Floor, 70/71 New Bond Street, London, W1Y 9DE, England, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to diaphragm pumps.

A particular interesting, but nonlimitative, field of application of these pumps is that of vehicle engines in which such pumps are particularly used for creating vacuums or for propelling a liquid (water, petrol, oil).

In these pumps, which are frequently driven at high rotational speeds capable of attaining and even exceeding 5,000 rpm., the connection of the push or connecting rod to the diaphragm and the lubrication of the said push rod pose a certain number of problems.

In accordance with the invention there is provided a diaphragm pump in which the diaphragm is driven from a drive member which is mounted rotatably and eccentrically on a rotary drive shaft, the drive member being coupled to the diaphragm by means comprising a length of flexible material; and resilient means arranged to tension the length of flexible material.

The invention comprises, apart from the said principal arrangements, certain other arrangements which are used preferably at the same time and will be described more explicitly below.

Two preferred embodiments of the invention will be described below in an obviously non-limitative way, with reference to the accompanying drawings.

Figure 1 of this drawing shows, schematically and in axial section, a diaphragm pump according to the invention.

Figure 2 shows part of this pump in a section along the line II-II in Figure 1.

Figure 3 is an explanatory diagram using again certain elements of Figure 1 according to a modification.

In each case the illustrated pump, intended for propelling a fluid (air, with the particular object of creating a partial vacuum or depression, or even water, oil or petrol), preferably on a motor vehicle, comprises a housing 1 consisting of two partial shell-shaped sections 2 and 3 clamped together with the aid of screws 4 along two flanges 5 and 6, with the generally circular edge of a flexible diaphragm 7 being interposed.

It is the theory of such a circular edge which will be adopted iI1 the following description in order to simplify same since it allows definition of an axis for the diaphragm, but this theory should obviously not be considered limitative, the diaphragm in question being able to assume a shape other than circular, for example, rectangular or elliptic.

The diaphragm 7 divides the interior of the housing 1 into two chambers 8 and 9.

Leading into one 8, of the said chambers, or pumping chamber, are an inlet 10 for admitting the fluid to be pumped and an outlet 11 for evacuating the pumped fluid, the said two pipes being equipped with appropriate valves knownper se.

Leading into the second chamber 9 is a rotary driving shaft with axis 12 rigidly locked with an eccentric crank pin 13 by way of a disc or arm 14 forming a crank.

The said connecting rod is replaced in accordance with the invention by a belt or band 15 comprising two free driving sides 16, parallel or substantially parallel to one another, between a metal disc 17 fixed to the centre of the diaphragm 7 and a pulley 18 rotatably mounted on the crank pin 13, each of the said two members (metal disc and pulley) comprising cylindrical convex areas (19, 20 in Figure 3) capable of receiving the ends of the free sides 16 with a creep-free rolling effect, and the tension of the said belt sides being ensured with the aid of a spring 21 which tends to constantly push the metal disc away from the pulley parallel to the axis of the diaphragm.

The band 15 comprises a strip, preferably a metal strip, of which the nature, the section and the degree of preforming are selected with regard to function of the tensile and bending stresses applied thereto.

In advantageous embodiments the band is a spring steel strip having a thickness of between 0.2 and 0.5 mm and a width of between 10 and 20 mm.

The central area of the diaphragm is clamped between a pair of coaxial rigid discs 22 and 23 and the clamping of the metal disc 17 on the said central area is ensured by a screw 24 which passes through the centres of the said two discs and of the diaphragm and is screwed axially into the said metal disc, the two ends of the band which are bent towards one another parallel to the central area in question on the diaphragm thus being clamped firmly between the metal disc 17 and the disc 23 opposite.

The positioning of the said bent ends can be aided and maintained by previous deformation of the belt or band, the result of which is to cause the latter to close up elastically over the metal disc 17.

The cylindrical (it should be understood that this term is used in its broader sense, not being restricted to exactly part-circular surfaces) convex areas 19 which define the metal disc 17 on its two sides covered by the band each have ideally an axis parallel to the axis 12; they are symmetrical with one another relative to the said axis and are connected by rounded beads C (Figure 3) to the planar parallel surfaces of the said metal disc which extend transversely to the axis of the diaphragm.

The radius R and the height H of the said cylindrical areas 19 in the direction of the diaphragm axis are selected in such a way that during operation of the pump the tangential point P of each side 16 of the belt with one of the said areas is displaced along the latter, without reaching its ends, while bringing into play the reciprocating effects of creep-free winding and unwinding motion.

The radius R in question is preferably greater than half the distance between the centres of the two opposite cylindrical areas.

If for example this distance is 35 mm where the height H is 7 mm, the radius R advantageously selected is equal to 30 mm or 60 mm: in this numerical example the width of each planar transverse face of the metal disc 17 can be of the order of 25 mm.

The pulley 18 is mounted on the crank pin 13 by means of a self-lubricating bearing 25.

In the example illustrated in Figures 1 and 2, the pulley hays an outer cylindrical contour of revolution about the axis of the crank pin 13 and is provided with a shallow groove 26 (Figure 2) which facilitates axial positioning of the belt.

However, in order to benefit from the vertical position and particularly from greater radii of curvature for the cylindrical convex areas 20 of the said pulley 18, it is possible to give the generating line of the cylinder which externally defines the said pulley a form similar to that of the corresponding generating line of the metal disc, but slightly thicker in the axial direction so as to allow the crank pin 13 and the bearing 25 to be accommodated inside the said pulley: the shape in question is therefore defined by two identical and diametrically opposite circular arcs which are interconnected with one another by two rectilinear transverse sections.

In this latter theory, the radius of the cylindrical areas 20 in question may be the same.as that adopted for the cylindrical areas 19 of the metal disc 17.

The spring 21 must be, at the same time: - sufficiently strong to ensure that the belt 15 remains in a constant driving or tensioned state during the operation of the pump, despite the different stresses exerted thereon by its own inertia and by that of the movable equipment so that in relation to the diaphragm 7 the spring/belt assembly serves well in its function as a rigid push and pull rod, - and not too strong so as not to overload or overstrain the said belt 15 unnecessarily.

The force of such a spring will possibly be, for example, between 5 and 25 kg for the above-mentioned applications to vehicles.

In the illustrated embodiment, the said spring 21 comprises a helical compression spring situated between the two sides 16 of the band and interposed between the metal disc 17 and a bracket or support 27 inside the chamber 9 and forming part of the housing 1.

In this particularly advantageous embodiment the metal disc 17 is extended by a cylindrical stem 28 coaxial with the axis of the diaphragm and the said stem is slidably mounted in a fixed cylindrical seating.

The said seating preferably comprises two self-lubricating rings 29 which are in turn mounted in a sleeve 30 extending the support 27 in the direction of the diaphragm and being encircled by the spring 21.

Owing to the guiding ensured by axial sliding of the stem 28 in its seating, the central area of the diaphragm remains absolutely parallel to itself and centred on its own axis during operation of the pump.

To ensure this axial guiding, a cylindrical projection coaxial with the diaphragm could also be fitted on the face of the diaphragm furtherst away from the metal disc 17, or to be more precise, on the disc 22, the said projection co-operating with a complementary cylindrical seating provided in the cas ing 2.

In such a theory the spring 21 could be a helical tension spring enclosing this tip and set between the diaphragm and the casing 2.

According to another modification the two above-mentioned methods of axial guiding could be employed simultaneously, in which case the elastic pull exerted axially on the metal disc can therefore be created by either of the two described springs or with the aid of the said two springs simultaneously.

Figure 3 shows the positions occupied by the metal disc 17, the pulley 18 and the band 15 which is tensioned between these two elements in the case of, respectively, the bottom dead-centre of the pump (position indicated by dot-and-dash lines) and the central point of this travel between this bottom dead-centre and the top dead-centre (position shown by continuous lines).

Between these two positions, the centre 0 of the pulley 18 has described a quarter circle about the axis 12, but the said pulley has remained parallel to itself.

A fastening means (screw, rivet, welding point or, more simply, a catch or stop) for fixing the belt on the pulley is diagrammatically represented at 31 in Figure 3, in the centre of the planar surface of the said pulley furthest away from the diaphragm.

Such a fastening prevents any creeping of the belt on the pulley, but it is not essential to ensure such prevention, particularly in a case where the pulley is not revolving, since the interconnecting areas between the extreme planar surface and the lateral cylindrical areas of the said pulley are covered by preformed sections of the belt, which sections are not prone to creeping on account of the tension exerted on the said belt.

To increase the performance of the pump, it may be advantageous to give the belt a permanent previous curvature which provides the two belt sides 16 with a slightly outwardly curved appearance.

As a result, and irrespective of which embodiment is adopted, there is finally obtained a pump, whose composition, functioning and advantages (particularly the advantage of removing any necessity for a lubricant for the part connecting the crank to the diaphragm, a part which in this case is formed by a "dry transmission" member) are sufficiently established in the preceding description.

It goes without saying and, moreover, follows from the preceding description that the invention is by no means limited to those methods of application and embodiments which have been more particularly envisaged; on the contrary, it includes all its modifications.

WHAT WE CLAIM IS: 1. A diaphragm pump in which the diaphragm is driven from a drive member which is mounted rotatably and eccentrically on a rotary drive shaft, the drive member being coupled to the diaphragm by means comprising a length of flexible material; and resilient means arranged to tension the length of flexible material.

2. A pump as claimed in claim 1 comprising two said lengths of flexible material each extending between, on the one hand, a member secured at a central area of the diaphragm and, on the other, said drive member, the two ends of each length of material resting respectively on two cylindrical convex areas having axes parallel to that of the drive shaft and carried by, respectively, said member and said drive member so as to permit succcessive winding and unwinding movements of the said length of material on a small arc of each corresponding convex area during each revolution of the drive shaft, the tension of the said lengths of material being ensured by the action of a spring which constantly biases said member away from said drive member.

3. A pump as claimed in claim 2, in which said member is the enlarged head of a shaft mounted so as to be slidable in a fixed guide substantially perpendicular to the diaphram and the spring is a helical compression spring, the two ends of which bear respectively against said member and a bearing surface provided externally on the fixed guide.

4. A pump as claimed in either of claims 2 or 3, in which the two lengths of flexible material are rectilinear and parallel to one another.

5. A device as claimed in either of claims 2 and 3, in which the two lengths of flexible material are slightly preformed to adapt them to the cylindrical areas of said member and drive member.

6. A pump as claimed in any one of claims 2 to 5, in which said member is screwed on to the central area of the diaphragm, with two ends of the lengths of flexible material bent towards one another and interposed parallel to the said central area.

7. A pump as claimed in any one of claims 2 to 6, in which the two lengths of flexible material are parts of a belt.

8. A pump as claimed in claim 7, wherein the belt is fixed to said drive member at its central point situated as far away as possible from the diaphragm.

9. A pump as claimed in any one of

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. To ensure this axial guiding, a cylindrical projection coaxial with the diaphragm could also be fitted on the face of the diaphragm furtherst away from the metal disc 17, or to be more precise, on the disc 22, the said projection co-operating with a complementary cylindrical seating provided in the cas ing 2. In such a theory the spring 21 could be a helical tension spring enclosing this tip and set between the diaphragm and the casing 2. According to another modification the two above-mentioned methods of axial guiding could be employed simultaneously, in which case the elastic pull exerted axially on the metal disc can therefore be created by either of the two described springs or with the aid of the said two springs simultaneously. Figure 3 shows the positions occupied by the metal disc 17, the pulley 18 and the band 15 which is tensioned between these two elements in the case of, respectively, the bottom dead-centre of the pump (position indicated by dot-and-dash lines) and the central point of this travel between this bottom dead-centre and the top dead-centre (position shown by continuous lines). Between these two positions, the centre 0 of the pulley 18 has described a quarter circle about the axis 12, but the said pulley has remained parallel to itself. A fastening means (screw, rivet, welding point or, more simply, a catch or stop) for fixing the belt on the pulley is diagrammatically represented at 31 in Figure 3, in the centre of the planar surface of the said pulley furthest away from the diaphragm. Such a fastening prevents any creeping of the belt on the pulley, but it is not essential to ensure such prevention, particularly in a case where the pulley is not revolving, since the interconnecting areas between the extreme planar surface and the lateral cylindrical areas of the said pulley are covered by preformed sections of the belt, which sections are not prone to creeping on account of the tension exerted on the said belt. To increase the performance of the pump, it may be advantageous to give the belt a permanent previous curvature which provides the two belt sides 16 with a slightly outwardly curved appearance. As a result, and irrespective of which embodiment is adopted, there is finally obtained a pump, whose composition, functioning and advantages (particularly the advantage of removing any necessity for a lubricant for the part connecting the crank to the diaphragm, a part which in this case is formed by a "dry transmission" member) are sufficiently established in the preceding description. It goes without saying and, moreover, follows from the preceding description that the invention is by no means limited to those methods of application and embodiments which have been more particularly envisaged; on the contrary, it includes all its modifications. WHAT WE CLAIM IS:

1. A diaphragm pump in which the diaphragm is driven from a drive member which is mounted rotatably and eccentrically on a rotary drive shaft, the drive member being coupled to the diaphragm by means comprising a length of flexible material; and resilient means arranged to tension the length of flexible material.

9. A pump as claimed in any one of

claims 2 to 7, in which each convex cylindrical area of said member and drive member, capable of receiving the flexible lengths, has a radius of curvature greater than the distance between the centre of said member or drive member, respectively, and the centre of the said cylindrical area.

10. A pump as claimed in any one of claims 2 to 9, in which the two convex cylindrical areas of said member and drive member are interconnected by two parallel planar surfaces, which are connected tossaid areas by rounded beads.

11. A pump as claimed in any one of claims 2 to 10, in which the force of the spring is between 5 and 25 kg.

12. A pump as claimed in any one of t;e preceding claims, in which the or each flexible member comprises a spring steel band with a thickness of between 0.2 and 0.5 mm and a width of between 10 and 20 mm.

13. A diaphragm pump substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

14. A diaphragm pump substantially as hereinbefore described with reference to Figures 1, 2 and 3 of the accompanying drawings.