GB2023740A - Rotary positive-displacement fluid-machine - Google Patents

Abstract

A machine which may be a compressor or an I.C. engine has a part-spherical chamber (1), a rotor (2) with an inclined surface (32) and a rotor (5), which in shape resembles a wedge cut from a sphere, the rotational axis of the rotor (5) being inclined to that of the rotor (2) at the same angle ( alpha ) as the surface (32) is inclined to a plane normal to its axis, the wedge surfaces of the rotor (5) intersecting one another at or adjacent the centre of the chamber (1) and being in sealing engagement with the inclined surface. Two chambers (7, 8) which vary in volume as the rotors rotate are thus provided, the rotor (5) running at half the speed of the rotor (2). There may be no transmission means between the two rotors. <IMAGE>

Description

SPECIFICATION Positive displacement rotary device having a spherical work chamber The invention relates to a positive displacement rotary device having a spherical work chamber and two displacement elements arranged for rotation therein.

In a known device of this kind the first displacement element takes the form of a hemispherical member whose diametric surface is formed with teeth extending like a spiral from the centre portion towards the periphery. The tooth depth increases towards the periphery, all the tooth tips lying on a conical surface whose apex forms an obtuse angle. The second displacement element is in the form of a sector of a sphere and its conical surface has teeth matching the teeth of the first displacement element. When the machine operates the two sets of teeth so cooperate with one another as to bound between them spaces which alternately decrease and increase in size, so that the machine can be operated either as a prime mover, e.g. a motor; or as a work machine, e.g. a pump or compressor.The known device is very expensive, for if the machine is to operate at all the teeth, which include curved tooth flanks, must be produced to very high standards of accuracy. If the tooth flank surfaces are produced inaccurately, the sealing gaps between the cooperating tooth surfaces, and therefore the leakage losses of the machine, become excessive.

It is an object of the invention so to improve a machine of the kind described that its production is simplified considerably.

Accordingly the present invention provides a positive displacement rotary device having a part-spherical work chamber and two displacement elements arranged for rotation therein, in which one of the displacement elements is in the form of a swash-plate having a plane circular surface inclined at an angle a to a plane perpendicular to its axis of rotation in the chamber; and the other displacement element is generally in the form of a wedgeshaped part of a sphere and its axis of rotation axis is inclined at the same angle a to the axis of rotation of the said one displacement element; the wedge surfaces of said other element intersecting one another at or adjacent the centre of the chamber and said other element being in continuous sealing engagement near the line of intersection of its wedge surfaces with the plane circular surface of the first displacement element.

In such a machine both the displacement elements have shapes which are geometrically simple and which can be manufactured readily. The geometric simplicity of the shapes obviates the difficulties in sealing the work chamber, since sealing between the two displacement elements is operative only along straight lies or plain surfaces. It is a simple matter to reduce very considerably the leakage losses arising from gaps between the components with such shapes. Consequently, both the initial cost and operating reliability of the device can be improved over known such devices.

In order to promote a fuller understanding of the above and other aspects of the present invention, some embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a view in cross-section in diagrammatic form, and greatly simplified, showing the basic construction of a device embodying the invention; Figures 2 and 3 are each a cross-section through the device of Fig. 1 but with the two displacement elements in different positions; Figure 4 is a cross-section through a more detailed arrangement of the device of Fig. 1, and Figures 5 to 9 are views, each in crosssection, of other arrangements of the device shown in Fig. 4.

Referring to Figs. 1 to 3, a first displacement element 2 is disposed in a spherical chamber 1 formed in a casing, and is rigidly connected to a shaft 3 for rotation in casing 1. In shape the element 2 resembles a swashplate, having a plane circular surface 32 inclined at an angle a to a plane 33 which is perpendicular to the aixs of rotation of the element 2. The plane surface 32 passes through the centre of the spherical chamber 1. That surface of the element 2 which is remote from the plane surface 32 is partspherical and adapted to the spherical shape of casing 1.

Also disposed in casing 1 is a second displacement element 5 having a shaft 4 mounted for rotation in the casing. The axis of rotation of the second element 5 is inclined at an angle a to the axis of the first element 2, the latter angle a being equal to the angle of inclination a of the surface 32. In shape the second displacement element 5 is a wedgeshaped part of a sphere, the two wedge surfaces intersecting at the centre of the spherical casing 1. The wedge surfaces intersect along a line 6-6 in Figs. 1 to 3, the second element being in continuous sealingtight engagement along that line with the plane surface 32.

Two work chambers 7, 8 are thus formed between, on the one hand, the surface 32 and, on the other hand, the two wedge surfaces and alternately increase and decrease in size as the two elements 2, 5 rotate.

In Fig. 1 the elements 2, 5 are shown in a position in which the work chamber 7 is at its maximum size corresponding to an opening angle 4a while the work chamber 8 is at its minimum size corresponding to a zero opening angle between the element faces defining that work chamber.

Fig. 2 shows the position reached by the first element 2 after it has rotated through 90 ; the second element 5 has rotated through 45 , line 6-6 of the second element being in continuous engagement with the plane surface 32 of the first element 2 and sealing the chambers 7, 8 off from one another. In this position the work chamber 7 has decreased in size and the work chamber 8 is increased.

A further position is shown in Fig. 3 where the first element 2 has rotated through 180 and the second element 5 through 90 . The line 6-6 of the second element still remains in engagement with the surface 32 and separates the two chambers 7, 8 from one another, the chambers 7, 8 being of the same size in this position.

After one complete revolution of the shaft 3 the system returns to the position shown in Fig 1-i.e. in each revolution of the element 2 one work chamber decreases in size from the full opening angle to zero while the opposite work chamber increases in size from zero to the full opening angle.

The second element 5 makes half a revolution for each single complete revolution of the first element 2-i.e. the shaft 4 runs at half the speed of the shaft 3.

The shaft 4 need not be driven independently since the first element 2 so drives the second element 5 positively that the line 6-6 of the second element is always in engagement with the surface 32 of the element 2.

However, no torque must be transmitted, since the forces acting on the second element 5 are always in equilibrium because of the symmetrical arrangement of the shaft 4.

The linear contact along the line 6-6 can be obviated as in the embodiment of Fig. 4 by the line 6-6 being replaced by a sealing surface in the form of a sealing bar or rod 9 placed between the first displacement element 22 and the second displacement element 25.

The bar 9 has a plane surface in sealing engagement with the plane surface 32' of the first element 22 and its surface 34 facing the second element 25 is in the form of a part circular cylindrical surface in sealing engagement with a correspondingly concave surface in the second element 25. This feature provides the further advantage that the plane surface 32' of the first element 32 and the wedge surfaces of the second element 25 do not need to pass through the centre of the sphere. As shown in Fig. 4, equidistant surfaces displaced by an amount indicated at 10 from the theoretical surfaces shown in chain lines may be provided without disturbing the theoretically correct system of motions. Bar 9 is rotatably mounted on the surface 32' by means of a pin 11 in the element 22.Also, the theoretically correct spherical shape of the surface of the chamber 1 and of the two displacement elements 22, 25 has been left only where necessary because of the motional relationships, and so the bearings for the shafts 3, 4 can be moved closer to the displacement elements 22, 25.

This device relies on fineness of the gaps between the elements for sealing the gaps being bounded only by parallel surfaces.

If greater sealing tightness is required than can be provided by such gaps, simple additional sealing elements can be provided in the manner shown in Fig. 5, where a normal resilient piston ring 1 2 is provided on the periphery of the first displacement element 42. The second displacement element 45 receives in its spherical surface two half piston rings 1 3 which extend generally parallel to the respective adjacent wedge surfaces and are pressed against casing 1 by springs 1 (not shown).

The use of the piston rings 1 2, 1 3 with contact along circles provides sealing tightness of the same high quality as in reciprocating piston machines and better than the sealing tightness of other rotary piston machines where the conventional form of sealing contact along the sides of a rectangle which is needed is always dubious.

As Fig. 5 also shows, a spring 14 may be provided around the shaft 4 and to press the second element 45 against the sealing bar 9 and press the latter against the first displacement element 42. It is immaterial if this leads to a gap arising between the outer periphery of the second element 45 and the inside surface of the chamber 1 since the half rings 1 3 are responsive for sealing in this region.

This kind of seal is particularly suitable for machines used as vacuum pumps since the negative pressure in the work chamber concerned tends to pull the two elements 45, 42 together, thus enhancing the effect of the spring 14.

Fig. 6 shows another form of sealing associated with the bar 9 and of use more particularly in cases where the work chambers operate at a positive pressure tending to force the two displacement elements 52, 55 apart from one another. A gap may arise between the second element 55 and the bar 9 and this gap is sealed in the region by means of a spring-biassed sealing strip 1 5 or the like.

Also, the two end faces of the bar 9 can be sealed by resiliently biassed mernbers (not shown).

Another feature shown in Fig. 6 is an orifice 1 6 in the wall of the spherical chamber 1; the orifice 1 6 is cyclically closed by the first element 52 as it rotates, then opened when the work chamber 7 has almost reached its maximum volume. This control of the orifice 1 6 is of use in cases when the machine is used as a "two-stroke" engine. Two orifices 1 6 can be provided close together, one serving as an inlet port and the other as an exhaust port; because of the inclination of the plane surface 32' of the first displacement element 52 the exhaust port opens and closes earlier than the inlet port, in a manner which is advantageous for mixture changing.

Referring to Fig. 7, the wall of chamber 1 is formed with an orifice 1 7 which the second displacement element 55 closes cyclically as it rotates but which is open when the work chamber 8 has almost reached minimum volume. This control of the orifice 1 7 is of use for an oil-immersed compressor. Oil immersion has three purposes-lubrication, improving the efficiency of the gap seal and cooling the gas, so that high compression ratios can be achieved at reasonable final temperatures.

The rotation of the two displacement elements hurls surplus oil onto the outer wall of the work chamber, the oil then being scraped off the wall by the edge of the first displacement element 52 and conveyed to the exhaust port or orifice 1 7. The risk of "water-hammer" is therefore avoided.

Referring to Fig. 8, the first displacement element 62 has two ducts 63, 64 co-operating for control puposes with ducts 18, 28 in the chamber 1. In other words, the displacement element 62 of Fig. 8 is in the form of a valve rotor. Since the same rotates at the speed of the shaft 3, it can be used to control all the circuits which start again after one revolution, as is usually the case with pumps and compressors; timings can be chosen to suit the circumstances of individual cases.

When the machine shown in Fig. 8 is required to operate as a vacuum pump, the rotor can also have the so called "Weiss duct" which obviates the effect of the unavoidable dead space by briefly interconnecting the work chambers 7 and 8 when one is at its maximum volume and the other at its minimum.

As Fig. 9 shows, another possibility is for the second displacement element 75 to take the form of a valve rotor co-operating with ducts 19, 29. This rotor can control all the cylic processes which start again after one revolution of the shaft 3. However, all the control ports must be provided in duplicate an arranged diammetrically opposite one another since the valve rotor of Fig. 9 runs at half the speed of the shaft 3.

The second displacement element 75 in the form of a valve rotor can be used to control a cyclic process which begins again after two revolutions of the shaft 3, since it runs at half the speed thereof. This feature makes it possible to device a "four-stroke" engine of very simple construction. In this case the contours of the two wedge surfaces of the second displacement element are, with advantage, different from one another. As Fig. 9 shows, the wedge surface which is in contact with the surface 32' of the first displacement element 72 at the end of the exhaust period is plane.

The burnt gases are therefore completely expelled and the weight of the fresh charge increases correspondingly. The opposite wedge surface is formed with a recess 20.

Since the latter wedge surface contacts the surface 32' of the first displacement element one revolution later-i.e. upon the termination of compression-the magnitude of the required compression is determined by the size of the recess 20.

Figs. 6 to 9 shows various possible control features on their own. In practice, however, combination of two or more control features will be chosen, depending on what is best for the immediate problem. For the sake of simplicity the two valve rotors shown in Figs. 8 and 9 are portrayed as flat rotors, but the control surfaces of these rotors can be conical or spherical or cylindrical instead of flat. Similarly, the shaft mountings and the casing of chamber 1, which latter must be divided, have been shown in simplified form.

Where the machines described operate with unlubricated work chambers, all the sealing elements 9, 12, 13, 1 5 can be made of a self-lubricating material such as carbon or Teflon. The inside of the chamber 1 is devoid of any parts needing lubrication; the external lubricated shaft bearings can have conventional forms of protection on the inside against oil loss.

Claims (10)

1. A positive displacement rotary device having a part spherical work chamber and two displacement elements arranged for rotation therein, in which one of the displacement elements is in the form of a swash-plate having a plane circular surface inclined at an angle a to a plane perpendicular to its axis of rotation in the chamber; and the other displacement element is generally in the form of a wedge-shaped part of a sphere, and its axis of rotation axis is inclined at the same angle a to the axis of rotation of said one displacement element; the wedge surfaces of said other element intersecting one another at or adjacent the centre of the chamber and said other element being in continuous sealing engagement near the line of intersection of its wedge surfaces with the plane circular surface of the first displacement element.

2. A device as claimed in Claim 1, in which a sealing bar or rod is disposed between the displacement elements and arranged to slide on the plane surface of the first displacement element.

3. A device a claimed in Claim 2, in which the sealing bar engages the second displacement element with a part circular cylindrical surface.

4. A device as calimed in Claim 2 or 3, in which the sealing bar is rotatably located in a central bore in the first displacement element by means of a pin.

5. A device as claimed in any of Claims 1 to 4, in which the periphery of the first displacement element and the part spherical surface of the second displacement element are sealed to the wall of the spherical work chamber by means of resiliently biassed sealing strips.

6. A device as claimed in Claim 3, 4 or 5 in which a sealing strip is provided to be operative between the sealing bar and the second displacement element.

7. A device as claimed in any of Claims 1 to 6, in which a spring is disposed between a casing bounding the spherical work chamber and the second displacement element to press the second displacement element against the first displacement element.

8. A device as claimed in any one of Claims 1 to 7, in which the work chamber is formed with at least one orifice which cooperates with at least one of the two displacement elements to control flow of charge to and from work chambers formed between the displacement elements within the chamber.

9. A device as claimed in any one of Claims 1 to 7, in which the first displacement element comprises a valve rotor which cooperates with one or more orifices in the chamber around the first displacement element to control flow of charge to or from work chambers formed between the displacement elements within the chamber.

10. A positive displacement rotary device substantially as herein described with reference to the accompanying drawings.