WO2007084014A1

WO2007084014A1 - Enhancements for swash plate pumps

Info

Publication number: WO2007084014A1
Application number: PCT/NZ2007/000013
Authority: WO
Inventors: Lindsay Dalziel; Ben Frank Smit; Lan Le Noc
Original assignee: Swashpump Technologies Limited
Priority date: 2006-01-18
Filing date: 2007-01-18
Publication date: 2007-07-26

Abstract

A swash-plate pump for fluids uses counterbalancing means within the rotating drive shaft to minimise vibration caused by the couple of the nutating swash plate. Resilient internal seals include radial vanes extending from the cone plate to contact the adjacent side of the swash plate, and a peripheral ring seal between the swash plate and the inner spherical part of the outer housing, to raise efficiency by reducing backflow. Resilient seals reduce the need for precision, so many plastics parts may be used. Carbon fibre leaf valves aid efficiency.

Description

TITLE ENHANCEMENTS FOR SWASH PLATE PUMPS

FIELD

This invention relates to slant axis rotary machines having swash plates - also called wobble plates or nutating disks - that interact with fluids, and to optimisation of such machines when used in particular as a pump for fluids.

BACKGROUND

The concept of a swash-plate machine has been described previously by Parker in US 3942384, (referring to a swash plate machine for use as an engine as well as a pump), Parker US 5735172 (referring in particular to lubrication), and by others. Parker's intellectual property serves as a basis for the present application. More recently, McMaster et al (US 6390052) describes a lubricated "wobble plate engine", with passing reference to use of the invention also as a pump, and briefly describes a radial sealing means similar to one of the sealing means to be described in the present patent.

Other known forms of pump having similar applications include the eccentric rotor pump used for example in refrigeration and heat-pump compressors, pumps with shaped chambers and rotors such as the Wankel type of rotary internal combustion engine, and the Rootes brand of air blower which is a version of gear pump with a small number of large intermesbing teeth on two cogs both turning within a closely fitting figure-8 shaped chamber. All of these include precisely made, often complex sliding surfaces and lubrication is usually considered necessary. For some pumping applications, the contaminating mist of lubricant that would result is considered undesirable.

PROBLEM TO BE SOLVED

Prototype pumps of this type built by the inventors and their predecessor have been quite inefficient (at up to around 40%), part of which is caused by leakage or backwards flow between closely opposed surfaces which are required to slide over each other yet confine and control the fluid to be pumped. Previous pumps built by the inventors and their predecessor have also exhibited significant dynamic imbalance resulting from motion of the oscillating swash plate when operated at a typical rate of 900 - 1500 rpm. Problems of these types have so far prevented commercial exploitation. OBJECT

It is an object of this invention to provide an improved swash-plate pump, having better efficiency and reduced vibration, or at least to provide the public with a useful choice.

STATEMENT OF INVENTION

In a first broad aspect this invention provides a pump in which a rigid swash plate is forced to oscillate from side to side in a rolling, non-rotatory motion termed nutation, within a housing providing a closely fitting internal space interrupted by at least one divider plate, about an intersection between an axis of rotation of a rotatable drive shaft and an axis of rotation of a slanted swash plate support means joined to the rotatable drive shaft, so that nutation of the swash plate forces any fluid within the space to be moved from an inlet port mounted through the housing towards an outlet port also mounted through the housing, wherein the pump is dynamically balanced by provision of counterbalancing means having a couple that opposes the couple of the nutating plate; the counterbalancing means comprising symmetrical pairs of counterweights and/or symmetrically removed material from selected positions along the drive shaft so that, when in use, vibration of the pump caused by nutation of the swash plate is reduced.

Preferably the masses and positions of the symmetrical pairs of counterweights and/or the symmetrically removed material to be used are calculated by a process of first calculating the characteristics of the couple created by the nutating swash plate, and then calculating the requirements for creating a counter-acting couple, as described in the accompanying text, given limitations imposed by the materials to be added or removed; their centres of mass in relation to the counter-acting couple, and dimensions of the pump that is to be made dynamically balanced.

In a second broad aspect this invention provides a pump in which the closely fitting internal space includes a pair of frustro-conical cones about the drive shaft facing and in close, sealing opposition to the nutating, rigid swash plate, wherein the close sealing opposition of at least one cone to an adjacent side of the swash plate is enhanced by providing a plurality of radially oriented, spaced- apart resilient sealing means covering substantially the full radial extent of the cone; each sealing means protruding lengthwise by a sufficient distance outward above the cone surface from a corresponding, closely fitting radial slot included in the surface of the cone to make contact from time to time with the nearest portion of the swash plate, so that any opportunity for flow in reverse of the fluid being pumped is reduced. Preferably each resilient sealing means includes an elongate seal having a lengthwise base that is wider than an upper part of the corresponding radial slot; the elongate seal being resiliently mounted by being supported above an elongate resilient material held within a lower, wider part of the corresponding radial slot, so that the projecting sealing means may be reversibly depressed into the cone during contact with the swash plate.

Preferably a cross-section through any elongate seal reveals a "T" profile; the base being the crossbar of the "T".

Preferably each side of the or each cone has from 10 to 50 radially extended seals so that, when in use, at least one protruding sealing means is in contact with the swash plate.

More preferably, each side of the or each cone has 30 radially extended seals separated by an included angle of 10 degrees so that, when in use, at least one protruding sealing means is in contact with the swash plate except at the position of the divider plate so that fluid is restricted from passing backwards between the swash plate and the adjacent cone plate, and so that changes in opposition distance may be taken up during use.

Preferably sufficient vanes are used, with regard to the amount of projection of any one vane, to provide that at least two vanes are in contact with the opposed swash plate at any time, so that the seal is mor effective.

In a related aspect, at least some of the radially extended seals are held in substantially radial slots cut into the swash plate and are extended toward the adjacent cone plate, so that the swash plate carries most of the sealing apparatus.

Preferably each vane comprises an elongated, approximately "T"-shaped (wider below the slot) bearing grade PEEK plastics protrusion or similar, biased outwardly by an underlying resilient cord or tube of rubber, or alternatively biased by a metal spring.

In a third broad aspect this invention provides a pump wherein the close opposition of the housing to the peripheral edge of the swash plate is enhanced by providing at least one peripherally extendable sealing means about the periphery of the solid material of the swash plate, interrupted around the circumference of the swash plate by a space in the swash plate to accommodate the divider plate, and extending a sufficient distance from the periphery of the swash plate to make a sliding contact with the inside wall of the housing. Preferably the peripherally extendable sealing means comprises a curved strip of a sealing material held within a slot cut into the periphery of the solid material of the swash plate; the sealing material lying in contact with a circumferential length of an underlying resilient material so that the resilient 90 material maintains an outward pressure on the outer edge of the sealing material against the housing of the pump, so that fluid is restricted from passing over the top of the swash plate from one compartment to another, and so that changes in opposition distance may be taken up during use.

Preferably the material of the ring seal is a bearing grade PEEK plastics material, or similar.

Preferably the outward bias is enhanced by means of an underlying cord or tube of a resilient rubber 95 material.

In a fourth broad aspect this invention provides a pump for which the inlet port and the outlet port are mounted on the housing, on each side of the divider plate and facing the corresponding swash plate side, rather than on the peripheral edge of the housing, so that the flow of fluid is enhanced.

Optionally, at least one of the inlet port and the outlet port are provided with a one-way valve 100 included within the port.

Preferably the one-way valve is a non-return leaf valve, preferably using carbon fibre valve leaves.

In a fifth broad aspect this invention provides a swash-plate pump, for which at least a substantial part of the pump is comprised of at least one moulded plastics material.

PREFERRED EMBODIMENT

105 The description of the invention to be provided herein is given purely by way of example and is not to be taken in any way as limiting the scope or extent of the invention. Throughout this specification unless the text requires otherwise, the word "comprise" and variations such as "comprising" or "comprises" will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

no DRAWINGS

Fig 1 : is a cross-sectional diagram in a vertical plane, showing parts of the pump

Fig 2: is a perspective diagram showing the assembled pump obliquely and from the rear. Fig 3 : is a perspective diagram showing the assembled pump obliquely and from the front.

Fig 4: is a perspective diagram of a counterbalanced drive shaft and swash plate.

115 Fig 5 : is a cross-sectional diagram of a partially hollowed-out drive shaft.

Fig 6: is a plan view from the exterior of the divider cap.

Fig 7: is a perspective diagram of the divider cap.

Fig 8 : is a cross-section of a divider cap.

Fig 9: is a perspective diagram showing some parts accessible by removal of the divider cap.

120 Fig 10: is a section through a trunnion, divider plate, and associated shell bearings.

Fig 11: is a perspective diagram of radial sealing vanes within a cone plate.

Fig 12: is a section through three radial seals when in use.

Fig 13: as 13A, B, C, and D: shows aspects of the peripheral seal around the swash plate.

Fig 14: as 14A, B, and C: shows aspects of the radial seal around the cone plate, and the side

125 positioned ports with reed valves .

Fig 15: as 15 A and 15B graphically illustrates some results obtained from a prototype.

We shall first review the entire pump, so that novel aspects of the invention can be placed in context 130 with parts already in the public domain. See the cross-section in Fig 1. The external appearance of current prototypes is of a thick discoidal machine 100, with cooling fins 101 on the exterior, having a base 102 with mounting holes, ports 103, and a drive shaft 106 extending axially from one side. These are evident in Figs 2 and 3.

Unless seals that can adapt to variations in dimensions are used (see later), all co-operating parts

135 should be precisely made of materials sharing a preferably minimised coefficient of thermal expansion so that small clearances can be maintained between sliding parts despite temperature changes, even local changes such as are found during use near or at the exhaust port, and in the preferred absence of lubricating materials in the working chambers. Further, all parts should be made of materials which are hard-wearing, rigid, and which do not corrode during use. There are many

140 food-related, biotechnology, and medical fluid pumping operations where a pump that does not mix lubricating materials with the fluid is desirable.

As shown in a vertical cross-section in Fig 1, the housing contains an annular chamber defined in part by a radially outward spherical wall 105, a rotatable inner spherical driving portion 106A and facing, radially extending frustro-conical side walls 107 and 108 interconnecting the inner and outer 145 spherical walls. The annular chamber is cut across by a divider plate 140 which is fixed to the housing and which is sealed by a fluid-tight divider seal 141 (preferably made of a composite plastics: "Duralon"™ NlO (injection mouldable 70% bronze, PTFE, nylon 12, distributed by Duromer Pty Ltd, New South Wales), against the moving swash plate (see below). The two compression chambers work out of step with each other and could be connected in series or in

150 parallel. The invention may be scaled to any convenient size. The latest prototypes work with about 3.5 kW input power, operate at about 1000-1400 rpm (compatible with a 50 Hz induction motor), and are capable of moving about 1750 normal litres of air per minute at a 500 millibar pressure differential. At least about a 6000 hour duty cycle between services is desirable.

Rotatable drive shaft

155 The rotatable drive shaft 106, drawn with left-downward slanting hatching, extends through the central axis of the machine 100 and is journalled at bearings 110, 111, and 112 so that it may be rotated by an external motive force with low friction and while maintaining precise positioning. Back-to-back ball or tapered roller bearings 110 and 111 at one side of the housing locate the shaft axially to within about 0.1 mm. There is a keyway 113 or splines or the like on the drive shaft,

160 suitable for receiving a driving pulley or other power coupling. The non-driven end has a protective cover.

Non-rotating but oscillating swash plate

Inherent in the design of swash plate pumps is the existence of at least two chambers; one on each side of the swash plate, that are swept in unison though always 180 degrees out of phase. Pumps of

165 this type may use more than one compression chamber on each side by including two divider plates. For simplicity we shall assume just one divider plate and two chambers. The swash plate 130 is a rigid annular plate having two sides and a peripheral edge, and a radial slot (see below) to receive the divider 140. The inner edge, which may be thickened, is mounted by bearings 131, 13 IA inside a slanted groove on the truncated spherical drive shaft 106. The angle of the slant defines the amount

170 of nutation. Fig 1 includes the maximum slant of this prototype. Both sides of the swash plate are active (130 specifically indicates one side and 108 is the other side, in contact with the cone plate. It is important that the swash plate sides are parallel and in close opposition to the adjacent cone plate in order to confine the fluid being pumped within the moving virtual chamber. The swash plate drives fluid through the machine by nutating (oscillating from side to side with a rolling motion (but 175 not actually rotating with the rotation of the drive shaft) inside the annular chamber 104 and rolling with a little side movement against the conical sides 107, 108 of the chamber within the housing 107A, 108 A once for each revolution of the drive shaft. The nutation imposed by the rotational power applied to the drive shaft 106 and through the slanted mount (see Fig 5) to the swash plate can be likened to the protracted wobbling without actual rotation of a coin on a table top (or a car

180 tyre on the ground) if dropped obliquely. The swash plate is preferably rigid but of low mass and in the prototype a series of radial holes 132 are drilled into a thick plate to remove material. All surfaces of the swash plate are exposed from time to time to pressure differences and/or form sliding seals. Interestingly, the same limited zone of the pump and swash plate - leading to the outlet port - is preferentially exposed to heated gases The outer perimeter 137 of the swash plate is machined or

185 otherwise shaped to almost touch the interior profile of the radially outward spherical wall 105 in order to provide an outer seal that confines the fluid being pumped within a portion of the pumping zone. The gap between the two items should be minimised; just enough gap to allow for thermal expansion, so that the gap serves as a first-level functional seal. Extra clearance puts additional load on the seals.

190 The central bearings 131 and 13 IA (see fig 1) are sealed for life. Their oil seals are pressure balanced through passageway 109A and also preferably two "Nilos" or equivalent seals are used (as at 13 IS, on both sides) to help to keep the lubricant out of the chamber. Labyrinth passageways / seals (134, 135 in Figs 1 and 5) assist in reducing the cross-pressure that these central bearings are exposed to, hence helping keep the lubricant within the bearings from the fluid being pumped. All

195 other bearings may be also provided as "sealed for life" bearings.

As shown in Fig 4, one wide radially directed cut is made through the swash plate disk to allow the placement of a non-rotating vane or divider plate 140 (and 401 in Fig 4) that is fixed to the housing, crosses the annular chamber 104 and provides a stop to the circular movement of spaces containing fluid - so that the fluid has to pass through one or more ports to be used. The lower edge of the

200 divider plate is provided (see above) with a rubbing seal. Since the swash plate oscillates from side to side, a trunnion or sliding bearing 141 (part only shown in Fig 1 - better shown in Fig 4, Fig 9 or Fig 10) is employed inside the cut, which has a part-circular profile, to slide against the divider plate. This bearing is also required to act as a seal even though it is at a site of greatest pressure difference and sweeps to and fro across the divider plate during use. The plane of the cross-section of Fig 1

205 passes centrally through the thickness of the divider plate at the upper part of the drawing.

Part-spherical swash plate drive shaft Operation of the invention requires that the swash plate 130 be forced to wobble or nutate within the annular chamber 104 inside the housing 100 so that a space 104 available for the fluid to be pumped is continually moved around the axis of the drive shaft 106. This nutation is centered on the drive

210 axis (Fig 5: 106ax) even though the swash plate is mounted on a slanted axis Fig 5: 130ax), at the intersection of the two axis lines. The central section of the drive shaft 106 is dilated into a truncated spherical profile 106A, centered on that intersection. This is comprised of two mating parts (106, 106A) that are bolted together (by bolt 109) at a sloping surface and there define a deep, angularly offset, detailed groove 133. Bearings 131, 13 IA are installed within the groove so that the swash

215 plate can be mounted on the bearings within the angularly offset groove. Hence the drive shaft is free to rotate and will force the mounted swash plate to nutate on the slanted axis when the drive shaft is rotated. The swash plate cannot rotate because of the presence of the divider plate 140. Note that the diameter of the part of the drive shaft supporting the swash plate and contained the slanted axis is significantly larger than that of the distal parts of the drive shaft which are about 50 mm in diameter.

220 Part of the drive shaft is also shown in Fig 5, showing more clearly how assembly proceeds. Circular groove sets 134 and 135 comprise labyrinths that assist in sealing the drive shaft against the relatively rotating swash plate. 131 and 131 A indicate the position for the central bearings. 13 IS is one of a pair of "Nilos" seals that is required at both sides of this bearing pair. 106A is a portion of the inner, part-spherical surface of the chamber 104 of Fig 1.

225 Truncated cone member (x 2)

Although the truncated cone (107,108) against which the swash plate rolls could be a separate insert, in some at least of the prototypes it forms an integral part of the housing generally indicated as 107A and 108 A. The surface is at an angle such that it is parallel to the surface of the swash plate at maximum obliquity. The selected amount of excursion of the swash plate depends on evaluation of

230 the intended compression ratio as against suitable rate of rotation, pressure differential required, and other factors, in relation to optimisation of efficiency. A continually changing part of the swash plate 130 almost presses, in a rolling type of motion (with only minor rubbing action at about the 90 and 270 degree locations) against an adjacent part of the conical surface during operation. In Fig 1 the conical surface 108 is shown in closest proximity to the swash plate 130. The conical surface is

235 centered upon the rotational axis of the plate drive shaft. There is preferably a small amount of clearance - well under 1 mm - between the closest part of the plate and the cone. Any such clearance permits leakage causing a reduction of efficiency, while too much clearance would also put additional load on the radial seals, described later.

Divider plate

240 At least one divider plate 140 that traverses the annular compartment inside the housing is in functionally sealed contact with the cut made through the swash plate at the trunnion type bearing 141, shown in isolation in Fig 9. Both cone-shaped surfaces include a slot 142 (Fig 9) into which the edge of the divider plate is located. The (or each) divider plate 140 serves as a barrier to limit the otherwise free movement of fluid around the pump during operation. During use, fluid will be

245 pushed up against the barrier while the space occupied by the fluid is made smaller as the point of (almost) contact between the driven, nutating swash plate and the adjacent cone approaches the barrier. The fluid so forced can be pushed through a port into a pipe or the like. The (or each) divider plate is fixed at one place around the annular compartment of the machine, and transects the corresponding cut made through the swash plate. The divider plate is preferably made from (for

250 example) D2 tool steel. Its bearing faces are first surface ground, polished, and then heat treated to achieve about 58 Rockwell hardness before being titanium nitride coated to approximately 3 microns thick.

A trunnion 141 (see Figs 1, 9 (part of which is "exploded") and in particular the cross-section Fig 10, part of which is drawn as separated) is used to provide an improved seal plus bearing between the

255 divider plate 140 and the swash plate 130 regardless of instantaneous relative position. The trunnion bearing is an important component for dynamic sealing within the pump. It has a cylindrical base that is inserted into an aperture in the inclined groove of the drive shaft 106 and a pair of upraised arms 141 having a circular outside profile that clasp the divider plate as it passes through a slot between the arms. The part-circular outside profile of each arm matches the circular hole cut into the swash

260 plate so that the swash plate can swivel about the trunnion bearing. We prefer to use an intermediate part-cylindrical shell bearing 402 - see Fig 10 - which is placed between the part-cylindrical hole 401 drilled into each side of the swash plate 130, to which it is fixed, and the outer part of the arm 141 of the trunnion, against which it slides. The shell bearing may be made of, or coated with, a low-friction ceramic or other material. It is easier to replace than the swash plate. This invention provides that all

265 rubbing surfaces of the swash plate may be provided with replaceable seals. The (or each) trunnion bearing is a critical component for dynamic sealing within the pump. During use the bearing experiences a significant pressure difference from one side of the swash plate to the other and must seal against an unwanted flow of fluid, and it experiences a significant amount of rubbing friction against the swash plate because the interior of one arm of the bearing is pushed against the divider

270 plate by the tendency of the swash plate to rotate. Frictional losses within the swash plate drive, when under load, or back pressures exerted against the swash plate when the pump is working will cause one edge or the other of the swash plate to rub against this barrier. The trunnion may be made of a strong plastics material frictionally compatible (that is, having a low mutual coefficient of dynamic friction) with the surface of the divider plate. Bearing grade PEEK

275 (polyaryletheretherketone) is an example of a suitable plastics material with which to make the arms

141 of the trunnion. The divider plate and trunnion are located beneath an inspection port that allows replacement.

Inlet and Outlet Ports

These ports (130 and 130A) serve as coupling devices between external pipes and the internal 280 annular pumping space and are placed close to the (or each) divider. The ports may be associated with one-way valves although the inlet ports of the pump usually need no one-way valve mechanism. Valves become useful in some instances such as if two sides of the annular chamber are joined together in parallel, or if the pump is operated intermittently yet a pressure or vacuum is maintained continuously.

285 Thus far, a complete swash-plate pump has been described, including a few of the enhancements. Major enhancements according to the invention that will now be described may be applied to pumps and some may also be applied to other kinds of swash-plate machines such as internal-combustion engines and motors that are driven by fluid under pressure.

EXAMPLE 1 : Dynamic Balance.

290 The problem is that dynamic imbalance, owing to the swash plate being forced to move from side to side (nutate) at the rotational frequency of the drive shaft (such as at about 24 Hz for a 1200 rpm drive) leads to significant vibration and other deleterious effects.

For purposes of calculation, a pump was assumed to have: a drive shaft with tapered roller bearings located at 134 mm from the centre of the swash plate, and a supporting or end shaft with a cylindrical 295 roller bearing at 124 mm from the centre of the swash plate. The non-rotating swash plate was assumed to be 20 mm thick, and have an inclination angle of 15 degrees. It was supported by two tapered roller bearings at 30 mm centre-to-centre distance. Materials: shafts were austenitic (Ni- resist) SG cast iron, and the swash plate was austenitic (Ni-resist) flake cast iron.

The rotating parts (excluding the swash plate) were assumed to be dynamically balanced and the

300 swash plate, being not rotating, can exert no significant centrifugal forces. Any point on or in the swash plate experiences an oscillatory motion at the frequency of rotation in the axial direction of the shaft, because of the oblique mount of the plate on the shaft. There is a phase shift of 360 degrees in the oscillatory motion around the circumference of the swash plate (the nutation). As a first approximation the swash plate was divided into four point masses; one for each quadrant. Each point

305 mass experiences an oscillatory motion at the frequency of rotation in the axial direction of the shaft that is 90 degrees out of phase with a neighbouring point mass. This is equivalent to a couple rotating at the shaft speed.

To calculate the amplitude of this rotating couple, we calculated the mass m (kg) of each quadrant (from a Solidworks T representation of the pump), obtained the distance r (m) of the centre of 310 gravity of each quadrant from the axis (again from the model), obtained the centre-to-peak oscillation amplitude of each point mass d (m) assuming d = r sin θ where θ = 15 degrees, and assumed a rotation speed of ω (rad/s) where ω = 2.π /60 revolutions per minute. Figures were: m = 3.4 kg, r — 0.107 m, d = 0.028 m, and ω = 150 rad/s at 24 Hz / 1440 rpm.

During use, the peak amplitude of acceleration α = dω² = 630 m/s²

315 The force required to generate this acceleration on the mass is F = m a = 2142 N.

A force of equal magnitude but opposite direction is applied to the diametrically opposite (180 deg apart) mass, while the masses at 90 degrees apart are assumed to have zero force applied (at that instant), being at zero velocity at that time. Hence the unbalanced dynamic couple, C (in Nm) caused by the two opposite masses is C = 2rF = 458 Nm. This inertial effect of the wobbling swash plate 320 imposed an equal and opposite couple on the shaft.

The calculation was repeated with a different method that avoided lumping the masses. The swash plate was assumed to be a solid annular disk with an inner radius r,- (0.045m), an outer radius r_o(0.17m), a density p (7100 kg/m³), and a thickness A(0.02 m). Then, the maximum couple C at any instant is calculated to be:

325 C = π/4 . p/z ω² cos θ. sin θ(r₀ ⁴ - r_; ⁴) The maximum couple is estimated as 521 Nm; 12% higher than the previous estimate.

We also calculate that other forces such as the pressure on the disk due to the pumping action and the friction between the trunnion and the divider plate are negligible in comparison with the inertial force of the moving swash plate. It seems unlikely that the mass of the swash plate can be reduced to 330 a sufficient extent yet retaining stiffness, either by removing more material or by changing the material from iron to aluminium or other lighter substances. Hence the optimal solution to the dynamic imbalance problem is to provide off-centre weight distribution that provides an equal and opposite couple.

Solution 1 : Because at the time we assumed there was no possibility to remove weight from within

335 the pump, we provide off-centre counterbalancing weights at the correct phase angle, on both ends of the rotating two-part shaft. Clearly, such a solution will impose bending moments on the shaft, calculated as 240 Nm for the example under consideration, at the bearings supporting the swash plate. A maximum shear force of 15,349 N also occurs in this region, though not simultaneously. The torsional moment is only about 15 Nm. We calculate that for a shaft made of cast iron and including

340 a safety factor of 10, the minimum recommended shaft diameter is 39 mm. Since the actual diameter is 50 mm, the shaft is safe from a deflection point of view.

External eccentric counterweights would be an inconvenient solution. We have identified a third and presently preferred solution, in which "negative counterweights" are created by boring out portions of the rotatable drive shaft in the area where the drive shaft diameter has been enlarged in order to

345 accommodate the slanted bearings that support the swash plate. In Fig 1, bored-out sections are shown as 150 and 151. In Fig 4, further bored-out portions not included in the cross section of Fig 1 are shown as 150A and 150B. These bored out portions must follow the movement of the swash plate exactly. The amount to be removed can be calculated in the same manner as above, or by using a series of sections through the rotating mass for a graphical analysis, or by trial and error, and may be

350 finally checked on a test-bed in a manner analogous to balancing a vehicle tyre. As a variation, or for trimming any remaining imbalance, a suitable mass of a heavy metal such as lead or even gold or depleted uranium may be embedded into the side opposite a bored-out portion. This enhancement alone assists substantially in commercial adoption of this type of pump.

EXAMPLE 2: Radial Finger seals

355 Problem: Ineffective sealing between the virtual compartment leading the moving point of contact or near-contact between the swash plate and the adjacent portion of the cone, and the trailing compartment leads to poor efficiency especially when the pressure difference across the pump rises. Leakage of this type gives rise to back-flow that detracts from the efficiency of the pump.

Figs 11 and 12 show the principle of providing a plurality of radially oriented sealing vanes that are 360 embedded within, the cone plates. Fig 11 is a view of a portion of a modified cone plate 108 with sealing vanes fitted, protruding toward lower left. Conveniently each slot 1200 extends from the outer edge almost to the inner edge of the cone plate and in the example each slot is 70 mm long and about 5 mm of cone plate is left intact at the inner border. An example preferred number is about 30 vanes separated by angles of 10 degrees although this can be varied. Sealing vanes may be omitted 365 close to the divider plate - see Fig 14A, showing that ports may be present at that site. Preferably sufficient vanes are used, with regard to the amount of projection of any one vane (in part a matter of vane dimensions and clearance, and in part related to the properties of the underlying resilient member (see below), to provide that at least two vanes are in contact with the opposed swash plate at any time. Having more than one vane in contact at a time enhances the effectiveness of the seal.

370 Fig 12 is a diagrammatic cross-section through a cone plate 108 with vanes when in use, in contact with a swash plate 130. A series of radially extending "T" shaped slots 1200 which are narrow at the open side facing the swash plate have been cut or milled into the cone plate. In this example (and without giving or implying any limitation as to dimensions) the open width is 5.5 mm and a shaped plastic sealing member 1201 is placed so as to extend outwardly by up to about 1 mm from the

375 surface of the cone plate along the full length of the T slot 1200. Preferred plastics for this member include PEEK (polyaryletheretherketone), PPS (polyphenylene sulphide), and the composite "Duralon"™ NlO (Rexnord Corp) or similar material. PPS or bearing grade PEEK (reinforced with carbon and including graphite and PTFE lubricants) may be the most preferred type, for longer life, but may also be the most costly option. The projecting surface that extends above the surface of the

380 cone plate is preferably slightly chamfered (as shown in Fig 12) leaving a 2 mm flat top (1204) along the centre line of the seal. The plastic member is assumed to be substantially stiff and is supported so as to be pushed outward from the cone plate surface from pressure applied below an "inverted T" - shaped base. The "T" base also limits the maximum extension of the seal so that the plastic member cannot fall out.

385 The pressure arises from a pair of resilient members 1203, shown as circular profiles, that comprise lengths of "O" ring (for example) rubber cord (or tube) that are retained in place to either side by the projection extending a short distance below the sealing member. Alternatives for the resilient members include nitrile rubber, "Viton" high temperature rubber (although a solid cord is quite hard and a tube version would be preferable) or a steel spring which allows more design flexibility and a 390 longer period of performance at a specified resilience. In Fig 12, contact area 1204' is shown experiencing some compression, as are the rather flattened resilient members 1203', while the seals at each side are in contact but only just, and their resilient supports 1203 are substantially uncompressed and circular. Plate 108B is a convenient removable backing for the cone plate that allows easy assembly of the seals in the prototypes, and replacement during maintenance.

395 It will be appreciated that a swash plate coming into contact with the seal during use exhibits some lateral movement particularly at the 90 and 270 degree sectors in relation to the divider plate. This form of seal (a) tolerates scuffing, and (b) accommodates small amounts of distortion such as may be caused by thermal expansion or wear or by the looser tolerances often inherent in plastics moulding..

EXAMPLE 3: Ports (A)

400 Problem: Maintenance of the divider plate and trunnion bearing without taking the entire pump apart; easy access to ports from either side.

In this version as shown in Fig 6, 7, 8 and 9, the ports are mounted centripetally upon a divider cap over the divider plate; (Fig 1 - 160) the cap also comprising an easily demountable window into the interior of the swash pump. Bolts or cap screws at 161 and 161 A fix the cap in place, optionally with

405 a gasket. This cap has been found to be a highly convenient inspection port that permits inspection (see Fig 9) of the divider plate 140, the trunnion 141, and part of the swash plate 130, or allows replacement of the trunnion assembly and/or divider plate without having to dismantle the remainder of the pump. The divider plate is placed beneath the cap inside a groove (142 in Fig 14A) and forms a seal against the underneath surface. In Fig 6, the cap 160 is shown from the outside in face view.

410 Apertures 162 and 163 admit fluid to be positively displaced, while apertures 162A and 163 A release fluid that has been positively displaced - or vice versa, if the drive shaft 106 turns in the other direction. Ports 103, 103A are mounted upon this cap; their manifolds are visible in Figs 2 and 3. (This drawing shows no mounting base. The oblique view of Fig 7 and the cross-section in Fig 8 (from A-A in Fig 6) show the part-circular profile of the underneath of the cap against which the

415 swash plate 130, and the divider plate 140 with the trunnion 141 form a sliding seal (Fig 4). Fig 9 is a view into the interior of the pump when the divider cap has been removed. The divider plate 140 and the trunnion 141 are visible and can be lifted out. Part of the swash plate 130 is visible. Inspection and some maintenance is possible without further dismantling the entire pump. EXAMPLE 4 Ports (B)

420 Problem: Ports which restrict flow or which open or close belatedly reduce the efficiency of the pump. Placement of ports, reduction of dead space, and the type of valve used have been improved in this Example. The cover (160) over the divider plate 140 and the trunnion 141 is retained.

With reference to Fig 14A and 14 B, the placement of ports is not on the outer edge but is on the outer side of each of the two chambers of the swash pump. The apertures (1401, 1402) are made

425 through the cone plate on each side (this example bearing radial seals 1200) and are separated by a groove 142 for the divider plate. Fig 14 A shows a cone plate 108 bearing radial seals (described elsewhere). The inlet (1402) and outlet (1401) are defined by the orientation of the preferred oneway valves. This position has several advantages. The exhaust gas in particular is pressed directly towards the port by the advancing swash plate 130 (not shown), assisting in efficiency. Valves are

430 less vulnerable to damage and the pump shape is more compact. Further, the valves and pipes need not be removed in this configuration if the divider cover (160) is removed for internal inspection since the plumbing is attached to the valves not the cover. Also, ports located at the sides do not interfere with the sealing ring (see below) used around the periphery of the swash plate.

A second enhancement is to the valves themselves. Assuming that the type of valve required on at 435 least the outlet port is an asynchronous non-return valve that is forced open by sufficient differential pressure, a kind of reed valve having petals made from carbon fibre sheet is presently preferred. Such valves are used in go-kart engines. They exhibit a very fast response time, since the petals are light and rigid. (One source is the company IAME Spa of Verdellino, Italy). The outside view of the two ports 1401 and 1402 is shown in Fig 14B. The preferred reed valve mounted upon port 1401 is 440 comprised of a frame bolted on to the pump housing. The frame 1403 is a type of "A" frame against which four petals (such as 1404) are bolted. Each petal normally presses against the frame, forming a barrier to the inflow of gas at this point, but can be forced open by a differential pressure arising from exhaust gases within. The reed valve may be enclosed (see housing 1405 in Fig 14 C) assisting in the leading away of exhaust gases or the containment of noise. A version of the valve in which a 445 pair of petals are mounted flat in a flat frame would have very little dead space. Containment as by housing 1405 is also useful for blower applications, since the product is the exhaust gas under pressure which must be sent to a pressure receiver via suitable plumbing (such as cap 1406) from the contained valve box.

EXAMPLE 5: Peripheral seal on the swash plate. 450 Problem: Insufficient sealing between the periphery of the oscillating swash plate and the fixed housing lets fluid leak from one side of the pump, around the swash plate and to the other side, again giving rise to back-flow that leads to poor efficiency. This is a long surface to be sealed. (The inner edge of the swash plate is invested with labyrinth seals and bearings,) Simply relying on a precise clearance between the swash plate periphery and the inner part-spherical housing is unreliable,

455 because some clearance must be provided, such as when the pump heats up when pumping a gas and its parts expand differentially around the pumping zone. Most heat is present where the gas is most compressed.

This Example (see Fig 13 A-D) provides extended peripheral sealing means placed within and extending slightly from the outer edge of the swash plate. This seal is rather like a piston ring in an

460 ordinary piston engine. Fig 13A is a section through the entire pump, with the sealing ring in the swash plate periphery at the label E. Fig 13B shows an isolated sealing ring 1301 (the gap would be placed around the divider plate 140). Fig 13C is a perspective view of a swash plate 130 including a slot 1302 for a ring, and at 13D a cross section (taken from the circular area marked E, adjacent the chamber 104 in fig 13A) is shown through the outer perimeter 137 of the swash plate, which as

465 described in previous examples is curved from side to side in order to match the profile of the radially outward spherical wall 105.

According to this Example, a peripheral slot 1302 is cut around nearly the entire periphery of the swash plate, as close as possible to the full 360 degrees but in practice extending over 350 degrees. The slot is just wide enough to admit a ring seal 1301 and permit the ring seal to slide in a radial

470 direction within the slot at any reasonable temperature in the absence of lubrication. If the slot is too wide there will be undesired sideways motion of the ring seal within the slot, possible fluid leakage and/or undesirable wear. As for a conventional piston engine piston ring, the ring seal 1301 is under slight compression when installed so that it presses lightly against the spherical wall 105. If required, this contact pressure may be boosted by pressure from an underlying resilient member such as a tube

475 or rod of rubber or the like (1303) lying deep within the slot 1302. Although a metal ring may have sufficient spring, the preferred material for this sealing ring is bearing grade PEEK (polyaryletheretherketone) - a plastic, or the composite "Duralon"™ NlO (injection mouldable 70% bronze, PTFE, nylon 12, distributed by Duromer Pty Ltd, New South Wales), or an analogous material. For a prototype, dimensions are: thickness about 6 mm, outer circumference about 340.5

480 mm. Installation may be facilitated by heating the sealing ring to about 100 deg C. Note that the inwardly directed radial holes shown in the swash plate illustrated in Fig 13C (which were made for purposes of lightening the swash plate) are likely to be seen only in experimental prototypes. In the first trial, the ring extended over only about 300 degrees because the ring ends, if longer, would have tended to catch in the peripheral port apertures that were located on the divider cap (in the outer 485 spherical face). The disadvantage with a 300 degrees version was that peak pressure differentials are reached where the sealing ring was absent and in that case the modification did not greatly improve the efficiency of the machine. More than one circumferential seal, placed side by side, may be used.

EXAMPLE 6: PUMP BODY MATERIALS

Problem: Manufacture of the pump entirely from machined metal, such as cast iron with a high

490 nickel content, is inherently costly and manufacturing procedures do not easily allow for economy of scale. Prototypes have been made of a metal alloy: cast iron including about 20% nickel. For various applications, naturally dependent on the material to be pumped, a metal pump body may be selected from a list including: "Ni resist" cast iron; Stainless steel alloy 420- martensitic stainless steel; stainless steel alloy 2205 - duplex stainless steel; high chromium iron; aluminium (cast); Ni resist D-

495 5 Cast Iron; Grey cast iron; or Titanium-6AL-4Va.

The plastics option is of interest for commercial production and is facilitated by the use of adaptable seals. Some or most components of the pump, apart from items such as the divider plate, the drive shaft components and bearings may be moulded in plastic by thermoforming, such as injection moulding as is known to those skilled in the art. Low friction between sliding parts can be an

500 advantage. Little if any finishing required, apart from due allowance for shrinkage of some types of plastics material, removal of sprues, and the like. A pump body may be moulded from one (or an an alloy of several) of the plastics included in the following currently available list of preferred engineering plastics subject of course to application environments such as the material to be pumped. The list includes modified polyphenylene oxide ("Noryl" (TM)); good to 275 deg F (152 deg C),

505 polyarylethyerketone "PEEK" (TM); good to 260 deg C, resistant to hydrolysis and FDA compliant, polyphenylene sulphide (PPS) which is good to 220 deg C, polysulfone; also FDA compliant and good to 148 deg C, FEP; an example melt processible fluorocarbon resin, good up to 204 deg C and PTFE, another fluorocarbon resin; good for use up to 260 deg C, as well as PEI polyetherimide, SPS sindiotactic polystyrene, and PBT polybutylene terephthalate. No doubt further suitable materials

510 will be developed during the life of this invention.

Although many of the suitable plastics listed here cost in the order of US$30 - $50 per kg the improvements in total manufacturing costs, inertness in relation to material being pumped, and weight may easily justify this material cost. The low specific gravity of plastic compensates for the apparently high price which is of course per kg., not per pump.

515 TEST RESULTS

Developments over the recent period have raised the efficiency of the pump considerably. In summary, an early prototype had about 40% efficiency. This was raised in a later prototype by about 10% with a sealing ring, by another 10% by the use of reed valves, and by about 5% by inclusion of the sealing vanes.

520 Fig 15A is a bar graph showing the effect that vacuum pressure (horizontal axis, in absolute mbar pressure) has on the delivered flow (shown as vertical bars, refer to the scale in left vertical axis). The graph also shows exhaust temperature as square dots and a best-fit average trend line as an overlaid line; referred to the temperature scale on the right vertical axis. The test conditions were: ambient temperature 20 deg C, and speed 1170 revolutions per minute. Power input : not shown.

525 Fig 15B is a bar graph showing the efficiency of the swash pump under the same test conditions as for the previous graph: pressure (horizontal axis, in mbar absolute pressure) against volumetric efficiency, being the points and the best-fit trend line, referred to the left vertical axis and the adiabatic efficiency (the vertical bars, referred to the right vertical axis).

FURTHER VARIATIONS

530 Seals: The swash plate may bear the radially extended, resiliently mounted sealing strips on each side, either instead of placing said strips on the cone plate, or interdigitated with the cone strips. This alteration makes the swash plate the carrier of much of the total sealing devices and makes manufacture of the cone assembly simpler.

Materials: Ceramic materials may provide some advantages such as for the swash plate or the divider 535 plate, and have been used in a commercial rotary internal combustion engine. High-temperature plastics materials can withstand likely operating temperatures, can be accurately formed by injection moulding and/or machining, and are cheaper and lighter. Much of the entire pump could be made from appropriate plastics materials.

Cooling means may be concentrated near the output port. 540 An AC induction or brushless electric motor could be included within the housing of the pump so that it becomes a self-contained unit and the motor may use the drive shaft bearings.

Power economy: using a variable speed drive feedback loop that controls (for example) the outlet pressure) would raise the efficiency of the pump.

We have yet to explore variations in speed in relation to size, including hydrodynamic effects, in 545 order to get a higher efficiency.

There may be further opportunities in relation to types or designs of valves.

INDUSTRIAL APPLICABILITY and ADVANTAGES

The swash plate type of pump can serve as an economical replacement for other types. A particular advantage is that, owing to the rolling contact that forms a moving seal and with suitable 550 optimisation of materials and tolerances of sliding surfaces, from less to zero lubrication is needed and the risk of the pump itself contaminating the material being transported is reduced. The unique pumping action reduces noise and pulsatile pressure variations in the downstream pipes.

The sealing vanes seal against the swash plate and offer a lower leakage (of backwards flowing fluid) and hence more efficiency or a higher pressure differential, that can also result in a lower speed.

555 The measures taken to reduce or remove vibration are as close to the seat of the problem as possible.

Inspection and maintenance is simplified with the removable cover, the divider cap.

Finally, it will be understood that the scope of this invention as described and/or illustrated herein is not limited to the specified embodiments. Those of skill will appreciate that various modifications, additions, known equivalents, and substitutions are possible without departing from the scope and 560 spirit of the invention as set forth in the following claims.

Claims

WE CLAIM:

1) A swash-plate pump in which a rigid swash plate is forced to oscillate from side to side in a rolling, non-rotatory motion termed nutation, within a housing providing a closely fitting internal space interrupted by at least one divider plate, about an intersection between an axis of rotation

565 of a rotatable drive shaft and an axis of rotation of a slanted swash plate support means joined to the rotatable drive shaft, so that nutation of the swash plate forces any fluid within the space to be moved from an inlet port mounted through the housing towards an outlet port also mounted through the housing, characterised in that the pump is dynamically balanced by provision of counterbalancing means having a couple that opposes the couple of the nutating swash plate; the

570 counterbalancing means comprising symmetrical pairs of added counterweights and/or symmetrically removed material from selected positions along the drive shaft so that, when in use, vibration of the pump caused by nutation of the swash plate is reduced.

2) A pump as claimed in claim 1, characterised in that the masses and positions of the symmetrical pairs of counterweights and/or the symmetrically removed material to be used are calculated by a

575 process of first calculating the characteristics of the couple created by the nutating swash plate, and then calculating the requirements of a counter-acting couple, as described in the accompanying text, given limitations imposed by the materials to be added or removed; then- positions in relation to the counter-acting couple, and the dimensions of the pump that is to be made dynamically balanced.

580 3) A pump as claimed in claim 1, in which the closely fitting internal space includes a pair of frustro-conical cones about the drive shaft facing and in close opposition to a side of the nutating, rigid swash plate, characterised in that an effect of sealing between the opposing surfaces is enhanced by including a plurality of radially oriented, spaced-apart resilient sealing means, each extending substantially from the inner edge, in a radial direction, to the outer edge

585 of the cone; each sealing means protruding lengthwise by a sufficient distance from the cone surface out of a closely fitting radial slot included in the surface of the cone to make contact from time to time with the nearest portion of the swash plate, so that the gap between the cone surface and the adjacent side of the swash plate becomes at least partially sealed.

4) A pump as claimed in claim 3, characterised in that each resilient sealing means includes an

590 elongate seal having a lengthwise oriented base that is wider than an upper part of the corresponding radial slot and is thereby retained within; the elongate seal being resiliently mounted by pressure from an elongate resilient material held in compression within a lower, wider part of the corresponding radial slot, so that the projecting sealing means may be reversibly depressed into the cone, further compressing the resilient material, during contact with 595 the swash plate.

5) A pump as claimed in claim 4, characterised in that each side of the or each cone has from 10 to 50 radially extended seals so that, when in use, at least one protruding sealing means is in contact with the swash plate.

6) A pump as claimed in claim 5, characterised in that each side of the or each cone includes about 600 30 radially extended seals each separated by an included angle of about 10 degrees so that, when in use, at least one protruding sealing means remains in contact with the swash plate except when closest opposition is at the position of the ports by the divider plate, so that fluid is restricted from passing backwards between the swash plate and the adjacent cone plate, and so that changes in spacing may be taken up by the seals during use.

605 7) A pump as claimed in any one of claims 3 to 6, characterised in that at least some of the radially extended seals are held in substantially radial slots cut into the swash plate and are extended toward the adjacent cone plate.

8) A pump as claimed in claim 1, characterised in that a sealing effect of the close opposition of the inside outer spherical wall of the housing to the peripheral edge of the swash plate is

610 enhanced by providing at least one peripherally extendable resiliently mounted sealing means about the periphery or circumference of the swash plate, and extending a sufficient distance from the periphery of the swash plate to make a sliding contact with the inside outer spherical wall of the housing.

9) A pump as claimed in claim 8, characterised in that the peripherally extendable sealing means 615 comprises a curved strip of a sealing material held within a slot cut into the periphery of the solid material of the swash plate; the sealing material lying in firm contact with a circumferential length of an underlying resilient material so that the resilient material maintains an outward pressure on the outer edge of the sealing material against the inside outer spherical wall of the housing of the pump, so that fluid is restricted from passing over the top of the swash plate from 620 one compartment to another, and so that changes in the spacing may be taken up during use. 10) A pump as claimed in claim 1, characterised in that the or each inlet port and outlet port are mounted on the housing, on each side of the divider plate and facing the corresponding swash plate side, rather than on the peripheral edge of the housing, so that the flow of fluid is enhanced.

625 11) A pump as claimed in claim 10, characterised in that at least one outlet port is provided with a one-way valve included within, or beside, the port.

12) A pump as claimed in claim 11, characterised in that the one-way valve is a non-return leaf valve.

13) A pump as claimed in claim 12, characterised in that the one-way valve uses carbon fibre valve 630 leaves.

14) A pump as claimed in claim 1, characterised in that at least a substantial part of the pump is comprised of a moulded plastics material.