ROTARY SEAL ROTARY ENGINE

Abstract: A rotary seal rotary engine has a lobed or vaned rotor which co-operates with a rotary seal member in the manner of a Root's blower. The rotor (60) has a cylindrical hub portion (62) and at least one lobe or vane (63) which extends radially outwardly from the cylindrical surface of the hub. The lobe or vane (63) has a part-cylindrical shape with the axis thereof displaced from the axis of rotation (68) of the rotor (60). A method of manufacturing the rotor (60), rotary seal member (70) and housing (3) by extruding each in a predetermined profile of indefinite length and slicing into lengths according to the required axial dimension is also disclosed.

Description: ROTARY SEAL ROTARY ENGINE TECHNICAL FIELD THIS INVENTION relates to apparatus for use as a pump, compressor or fluid motor. The apparatus will herein be described with particular reference to its operation as a pump but it will be under¬ stood that the apparatus may equally be used as a comp¬ ressor, a vacuum pump or as a hydraulic motor to be driven by a medium under pressure. BACKGROUND ART A well known class of rotary engines comprises a housing having an inlet spaced apart from an outlet, a rotor mounted for axial rotation within the housing about a first axis and a rotary seal member mounted for axial rotation within the housing about a second axis parallel to the first. The rotor typically comprises a generally cylindrical hub portion and at least one vane member or lobe which extends radially outwardly from the hub cylindrical surface. During rotation of the rotor the vane member periphery sweeps the housing wall from the inlet to the outlet positively displacing a medium admitted at the inlet towards the outlet. The rotary seal member typically comprises a cylindrical hub portion adapted during rotation of the rotor to form a seal at a line of rolling contact therebetween the seal line being situated between the outlet and the inlet in the direction of rotation of the rotor and preventing ( OMPI displacement of the medium from the outlet to the inlet thereby forcing medium displaced by rotation of the rotor from the outlet. The rotary seal is provided with a profile which during rotation of the rotary seal permits the passage of the at least one vane or lobe between the plane extending through the first and second axis while maintaining a seal between the rotor and rotary seal . Pumps of the type described above will hereinafter be referred to as "rotary seal rotary engines" of which a typical example is that known as a Root's blower. Rotary seal rotary engines in which the rotary seal ele¬ ment and the rotor are each driven in synchronization with the other by timing gears, instead of being driven one by the other, present particular problems in sealing and require complex profiles for the rotor and the rotary seal element. Those profiles in turn require that the housing interior wall be of a generally straight sided profile having circular end walls centered on the respective rotor and seal axes and typically define a considerable volume between the rotor lobe, the housing and the rotary seal element at the maximum compression point of the rotor cycle. Such pumps are not well adapted to deliver a medium being pumped at a high pressure or velocity and in fact are usually used to maintain a fairly constant flow of medium with little variation in pressure. The present invention provides a rotary seal rotary engine which in preferred embodiments is of relatively simple construction and has a higher performance to cost ratio than rotary seal rotary engines hitherto available. According to one aspect the invention consists in a rotary seal rotary engine comprising : a rotor having a cylindrical hub portion and a lobe extending to a radius greater than that of the hub; a rotary seal element having a cylindrical hub por¬ tion and adapted to co-operate with the rotor during rotation of the rotor and the rotary seal element to form a seal with said rotor, said engine being cha¬ racterised in that said lobe has a part-cylindrical shape of which the lobe cylindrical axis is displaced from the axis of rotation of the rotor. According to another aspect the invention consists in a rotary seal rotary engine as defined above wherein the rotor hub and the rotary seal hub are of equal radius and an outlet port is located on or adjacent a cusp formed in the housing profile on the chord shared by said intersect¬ ing circles. According to a further aspect the invention consists in a rotary seal rotary engine as defined above wherein the rotor and rotary seal element are housed in a housing having an inner wall which in profile closely envelope the intersecting circles swept respectively by the periphery of the lobe and the periphery of the rotary seal element. By way of example only the invention will now be described with reference to the accompanying drawings in which:- Fig. 1 is a cross section showing the general arran¬ gement of parts of an embodiment of the invention when assembled together; Fig. 2 shows shaft 61 and rotor 60 of Fig. 1 in more detail in a side elevation; . IPO Fig. 3 shows the rotor of Fig. 2 in an end elevation; Fig. 4 shows shaft 71 and rotary seal element 70 of Fig. 1 in more detail in a side elevation; Fig. 5 shows the rotary seal element 70 of Fig. 4 in more detail in an end elevation; Fig. 6 shows an end elevation of peripheral housing 3 of Fig. 1; Fig. 7 is a schematic diagram useful for describing the operation of the apparatus of Fig. 1; Figs. 8A to 8E illustrate the effects of pressure on an oncoming lobe for varying ratios of rotor radius to lobe radius; and Fig. 9 is a diagrammatic representation of two rotors of equal radius R having centres E and F. With reference to Fig. 1 there is shown a casing assembly comprising five elements; a drive-end wall 1, a bearing support element 2, a pump peripheral housing 3, a timing gear case 4, and a cover plate 5 which are fastened toge¬ ther by means not shown in Fig. 1. Timing gear case 4 has a wall 40 which together with parallel opposing wall 20 of support element 2 and with internal wall 30 of peripheral housing 3 defines a pump chamber. Situated within the pump chamber is a rotor 60 mounted for axial rotation on shaft 61 which is supported by bearings 21 from bearing support element 2 and is supported by bearings 41 from timing gear case 4. Also situated within the pump chamber is a rotary seal element 70 mounted for axial rotation on shaft 71 which is supported by bearings 22 from bearing support element 2 and is supported by bearings 48 from timing gear case 4. Shafts 61 and 71 are driven in synchronous rotation by means of intermeshing timing gears 42 and 43 keyed res¬ pectively on shafts 61 and 71 by key means 44 and held in place each by a washer 45 and a lock nut 46 threaded to the stub of the respective shaft. A similar washer 45 and lock nut 46 is provided at the other end of shaft 71. Shaft 61 extends to outside the casing assembly. A mech¬ anical seal assembly indicated generally at 10 is mounted to shaft 61 so as to provide a seal therewith and has a rotating seal interface with a seal face 11 of drive end wall 1. A drive gear 12 is keyed to shaft 61 by key means 44 external of the casing assembly whereby shaft 61 is adap¬ ted to be driven in rotation. Rotor 60 is shown in further detail in Figs. 2 and 3 com¬ prises a hub portion 62 of radius R and two lobes 63 extending from the rotor axis 68 to a radius greater than that of hub 62. Lobes 63 are centered on diametrically opposite sides of hub portion 62 and each has a part-cy¬ lindrical shape whereof the cylinder axis 64 is preferably situated at distance R from the rotor axis 68. The radius of the part-cylindrical shape is indicated as r. The rotor has a central mounting bush provided with a key way 65 whereby the rotor is secured to shaft 61 as shown in Fig. 3. Shaft 61 is stepped and threaded at 66 to accommodate mechanical seal 10 and at 67 to accommodate lock nut 14 (Fig. 1). Rotary seal element 70 is shown in further detail in Figs. 5 and 6 and comprises a generally cylindrical hub portion 72 of radius R equal to that of hub portion 62 of the rotor and has two depressions of part-cylindrical surface 73. Depressions 73 are centered on diametrically opposite sides of hub 72 and the cylinder axis 74 of cylindrical depression surface 73 is situated at radius R from the axis 78 of the rotary seal element. The radius of the depression cylindrical surface, r, corresponds to the radius of the lobe part-cylindrical surface. Rotary seal element 70 has a central bush provided with keyway 75 whereby it is secured to shaft 71. Each end portions 79 of shaft 71 and one end portion 69 of shaft 61 are threaded to receive a lock nut 46. Rotor 60 and rotary seal element 70 each extend in the axial direction for a distance which corresponds to 7 or is smaller by a small tolerance than the distance separating walls 20 and 40 defining opposite sides of the pump cham¬ ber. With reference to Fig. 6 there is shown the cross section of the pumping chamber in a plane perpendicular to the rotor axis defined by peripheral housing 3. In pro¬ file, internal wall 30 lies on the circumference of two overlapping circles. The larger circle has a radius equal to, or a tolerance greater than the envelope swept by the outer periphery of lobes 63 of rotor 60 during rotation and the smaller circle has a radius R equal to or a tole¬ rance greater than the radius of the rotary seal hub portion. The profile defines a cusp at each end of the common chord of the overlapping circles. Inlet port 32 and outlet port 31 communicate from outside of the pump chamber to inside of the pump chamber at or adjacent the plane of the common chord and for preference extend in the axial direction. Operation of the apparatus as a pump is best described with reference to Fig. 7. A fluid medium for example an oil is admitted at 32. Rotor 60 is driven in the direction indicated by arrow and, during a rotor half cycle, lobe 63A displaces a volume of fluid defined between rotor hub 62 pump housing wall 30, and rotor lobes 63A and 63B towards outlet 31. Rotary seal 70 is driven in synchronization with the rotor 60 and forms a rolling line seal between the surface of rotary seal hub portion 72 and the rotor hub 62 or between sur¬ face depressions 73 and lobes 63. Meanwhile the volume defined between lobe 63B, the outlet 31, and rotary seal element 70 is reduced and medium in that volume is forced from outlet 31. Some fluid admitted at 32 is also carried in the volume defined between rotary seal depression surface 73 and housing wall 30 towards outlet 31 where it is discharged into a small volume defined between the rotary seal ele¬ ment and an approaching rotor lobe to be forced from outlet 31 at high velocity and, when outlet 31 is of restricted cross section, under high pressure. While in a preferred embodiment of the pump the radius of the rotor hub is equal to the radius of the rotary seal hub, the radius of one may be made different from the other. Also while two lobes are preferred and give balan¬ ced rotation, the rotor essentially comprises at least one lobe and may comprise more than two lobes, the profile and/or speed of rotation of the rotary seal being modified accordingly. While it is preferred that the part-cylindrical shape of the rotor lobe has cylinder axis displaced from the rotor axis by a distance equal to the radius of the rotor hub portion, the cylinder axis of the lobe may be displaced from the rotor axis by a lesser distance. OMPI i A IPO The cylinder radius of the lobe part-cylindrical portion may be varied according to application. For preference it is the maximum radius permitted by the shaft radius of the rotary seal element when the apparatus is used for pump¬ ing, but is of a smaller radius when the apparatus is used as a fluid motor. The relative values of the rotor radius R and the lobe radius L can best be understood by the following consider¬ ation of the effect of fluid pressure on an oncoming lobe on the embodiment shown diagrammatically in Figs. 8A to 8E of the drawings. In general, the configuration can act either as a fluid motor due to the force exerted on the lobe by the fluid pressure P in the chamber (u) or as a pump due to the displacement of fluid caused by the -movement of the lobe around the chamber as a result of a torque being applied to rotor F. When fluid at pressure (P) is present in the chamber (u), a clockwise torque ( c) is produced about the centre (F) due to the force exerted on the face S-T, acting at right angles to the torque arm of length (R + -). If the width of the chamber is (W) then; At rotor angle ( C-N ) such that " ^^*^ β> there is a torque produced in the anti-clockwise direction {'T'ac) due to the exposure of part of the oncoming lobe to the fluid pressure. During the period 5< cc -^ ° this part is the face M-A. If (V) is the radial distance from M to A the torque prod¬ uced by this face is; T ac = P x W x V x (R + ) During the periodO^ * this part is the face M-N. However, as the force on face M-N is partially balanced by the force on the face N-Q, the net force is that produced by the unbalanced portion of the lobe equivalent to Q-X. As M-A equals Q-X for each corresponding value of be¬ fore and after T.D.C. { <=> =0), then T ac for the period < C Thus the magnitude of -IT ac varies from 0 to max to 0 as the rotor angle varies from - β to 0 to + β > , maximum value occuring simultaneously with the max value of V (when •=- * < =0) . The effect of this is to reduce the average clockwise torque applied to the rotor during one complete revolution (and the starting torque when used as motor). It can be seen that as the ratio R/L increases, the values of -T ac (max) and 3 both decrease, with a corresponding improvement in average clockwise torque. As the volume of fluid passing through the chambers per unit of work remains relatively constant with varying values of R/L, it follows that the efficiency of the con¬ figuration as a fluid motor would improve with increasing R/L, while that as a pump would improve as R/L decreased. f . OMP In operation of the pump when shaft 61 and 71 are each driven synchronously at constant angular velocity, it is highly preferred to increase the radius of the lobe bet¬ ween the line at which the lobe surface intersects the rotor hub surface and the line at which the lobe surface intersects the rotary seal hub circumference when the lobe and the depression of the rotary seal are at maximum interpenetration. The lobe radius is increased on both the leading and trailing face of the lobe in the region defined between those two lines of intersection in a curve which ensures that a continuous seal is maintained at all times. The degree of increase in the lobe radius will now be explained by reference to Fig. 9 of the drawings which is a diagrammatic representation of two rotors of equal radius R having centres E and F, forming a centreline EF such that the circumferences of the ratios contact each other at a common tangent IJ. A circular lobe of radius L whose centre D lies on the circumference of one rotor mates with a circular aperture, also of radius L whose centre B lies on the circumference of the other rotor. Point A is the point at which the arc defining the aper¬ ture intersects the circumference of the rotor. Point C is the point at which the line AD intersects the circum¬ ference of the lobe. Lines AB and CD are by definition of equal length (radius L). The angle formed by the arms EF and EB (or FD) is the angle of rotation while the angle > is the value of =*- when the point A lies on line EF. g is the distance from point A to point C i.e. the gap between the lobe and the aperture and is the amount by which the radius of the lobe requires to be increased to maintain a continuous seal. When σ-*- =0 the points D and B coincide and points A and C lies on the same arc. Therefore g = 0 When o\ = β> the points A and C coincide. Therefore g = 0 When JS^--^ o, g is greater than zero due to the fol¬ lowing factors:- (i) the line DB is bisected by the line IJ (ii) the line DB is normal to the line IJ (iii) point A lines on the same side of line IJ as point B hence line AD is longer than line AB by the amount of AD-AC = g since AC=AB=L. The magnitude of g for any angle of rotation within the range ~ ~β> to + β for any value of R and L such that R ^ L is given by the formula L sin [180 - ( + arcos -2R) , ] J L sin [180 -. (< + arcos )] sin artan 2 (R-R cosc )- cos [180-(cs.+ arcos s„)] - Thus in a preferred form the invention resides in a rotary seal rotary engine as defined above wherein the radius of the lobe on both the leading and trailing face is increa¬ sed by an amount determined by the foregoing formula. The increase in radius may be effected by suitable prof¬ iling of the lobe or by providing an insert the outer face of which is profiled in accordance with the foregoing formula. -gJREΛ QMPI ^ IP _. It will be evident that as the ratio R/L increases the value of g becomes relatively small and the value of J3> decreases. When the radii of rotor and lobe are approximately the same the need to add material to the lobes to effect a seal throughout the complete revolution is greatest. At ratios around 3:1 (R : L) the values of (g) became very small and could possibly be ignored except in the high pressure stage of a compressor. Low ratios of R : L would be favourable in the pump con¬ figuration due to the reverse torque effect resulting in lower power input per unit of fluid output. As a fluid motor the reverse torque effect tends to reduce the power output due to the reduced net torque while the lobe is in mesh with the aperture. This effect diminishes as R : L increases. Small values of R : L have a size advantage: the circum¬ scribing circle becomes larger per unit of swept area as R : L increases. In other embodiments the cylindrical depression surface of the rotary seal extends in an arc of constant radius over most of the depression surface but increases in radial distance from the cylinder axis over a portion of the depression surface close to the circumfer¬ ence of the seal hub rejoining the hub surface as a curve rather than at an angle of intersection with the hub circ¬ umference. Pressures in excess of 2000 psi have been produced in oil pumped by apparatus according to the invention. It is believed that this is achieved by virtue that at the point in the cycle of maximum compression, the volume defined between the casing surrounding the outlet, a rotor lobe and the rotary seal is very small, and by virtue that fluid is simultaneously being delivered to a contracting volume by the lobe and from the seal depression. Furthermore the volume between the seal line of the rotor lobe, cylindrical shape and the depression of the rotary seal contacts very rapidly squeezing any fluid there¬ between towards the outlet port at a very high velocity. At the point of maximum interengagement between the rotor lobe and the rotary seal depression the rotor and the rotary seal are in contact over an extended arc rather than merely in rolling line contact. In preferred embodiments, the part-cylindrical portion of the lobe and the part-cylindrical depression of the rotor extend parallel to one another over an arc of at least 90° centered on the cylinder radius of the lobe portion, at maximum interpenetration of the lobe in the depression. Similarly the peripheral housing 3 may be formed in inde¬ finite length and sliced to produce peripheral housings of desired length. If extruded, the peripheral housing extrusion may be formed with holes to be threaded after slicing to receive studs or bolts for mounting the housing slice in assembly with other parts, and inlet and outlet ports may be formed by machining. Other parts, such as drive end wall 1, bearing support element 2, timing gear case 4, cover plate 5, timing gears and the like, may be of the same dimensions for pump having widely differing axial dimensions of the pump chamber. Thus pumps of a variety of capacities may be made from a relatively small inventory of parts, the capacity of the pump or engine being varied substantially by selection of axial length of rotor, rotary seal and the peripheral housing element. Apparatus according to the invention may of course be manufactured by any other method. Apparatus according to the invention may be constructed from a wide range of materials which should be selected having regard to the end use intended for the apparatus. A preferred embodiment has been made predominantly from cast iron and from steel parts. Details of shape, configuration and assembly of parts can be varied to an extent which will be apparent to those skilled in the art from the description contained herein without departure from the inventive concept disclosed. OMPI ^

Claims: The Claims defining the invention are as follows:- 1. A rotary seal rotary engine comprising: a rotor having a cylindrical hub portion and a lobe extending to a radius greater than that of the hub; a rotary seal element having a cylindrical hub portion and adapted to co-operate with the rotor during rotation of the rotor and the rotary seal element to form a seal with said rotor, said engine being cha¬ racterised in that said lobe has a part-cylindrical shape of which the lobe cylindrical axis is displaced from the axis of rotation of the rotor. 2. A rotary seal rotary engine as claimed in claim 1 wherein the rotor hub and the rotary seal hub are of equal radius and an outlet port is located on or adjacent a cusp formed in the housing profile on the chord shared by said intersecting circles. 3. A rotary seal rotary engine as claimed in claim 2 wherein the rotary and rotary seal element are housed in a housing having an inner wall which in profile closely envelope the intersecting circles swept respectively by the periphery of the lobe and the periphery of the rotary seal element. 4. A rotary seal rotary engine as claimed in claim 1 wherein the radius of the lobe on both the leading and trailing face is increased by an amount g. determined by the following formula:- 91 sin artan ■ Ε E Ai - OMPI ^ WIPO < - wherein R is the radius of the rotor L is the radius of the lobe is the angle of rotation J2 is the value of -=**. when the point at which the arc defining the circumference of the rotor lies on the line joining the centres of rotation of the rotors. 5. A rotary seal rotary engine substantially as herein described with reference to the accompanying drawings.

Inventors: MARSH MERVYN ROY, MARSH, MERVYN, ROY
Applicants: MARSH MERVYN ROY, MARSH, MERVYN, ROY
Application year: 1982
Main classification: F01C1
IPC codes: F01C1