EP1458954B1

EP1458954B1 - Coaxial energy converter

Info

Publication number: EP1458954B1
Application number: EP02778114A
Authority: EP
Inventors: Odd J. Edvardsen
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-11-08
Filing date: 2002-11-08
Publication date: 2008-05-07
Anticipated expiration: 2022-11-08
Also published as: ATE394582T1; WO2003056137A8; DE60226490D1; EP1458954A1; AU2002339765A1; WO2003056137A1; NO320961B1; NO20015468L; NO20015468D0

Abstract

An energy converter, particularly for use as a hydrodynamic pump, compressor, motor or turbine, comprising a stator (1) with a bore (4), where at least one helical groove (8) is formed in the wall of the bore (4), and a rotor (2) with an external surface (10), where at least one helical groove (18) is formed in the outer surface (10). The stator (1) and the rotor (2) are designed to rotate relative to each other, and at least the rotor (1) is designed to be coupled to a shaft (3) for transmission of torque. The bore (4) in the stator (1) and the external surface (10) of the rotor (2) are conical with a complementary taper.

Description

The present invention regards an energy converter, particularly for use as a hydrodynamic pump, compressor, motor or turbine, comprising a first part with a bore, where at least one helical groove is formed in the wall of the bore, and a second part with an external surface in which there is formed at least one helical groove, the first and second parts being designed to rotate relative to each other, and where at least one of the first and second parts is designed to be coupled to a shaft for transmission of torque.
A number of pumps for pumping fluid, and also motors, are known, which pumps and motors are based wholly or in part on utilisation of the energy in fluids. Often, one and the same unit will be able, with certain adaptations, to act as both pump, compressor, motor and turbine. This is also the case for the energy converter according to the present invention.
As an example of the state of the art, GB 2234557 describes a hydroelectric generator in which two rotatable cylinders are arranged one inside the other. The cylinders each have helical flow paths directed in opposite directions. Thus the cylinders will rotate in the opposite direction of each other. The rotation is transmitted via a system of cogwheels to en electric generator. The cross section of the cylinders is constant along their entire length.
GB 1573334 describes a cylindrical water wheel with wings that are twisted helically around the shaft. It is located inside a chamber with smooth walls. The cross sections of the water wheel and the chamber are constant along the entire active length.
US 4378195 describes a cylindrical rotor with a rough surface placed inside a chamber with smooth walls. Here, the chamber and the rotor also have the same cross section along the entire length.
US 4412417 describes a wave power station where a rotor is equipped with at least two helical wings slightly offset relative to each other. The rotor is not located in a housing, and has a constant cross section along its entire length.
US 5313103 describes a type of windmill with a rotor having a helical vane. This is not located in a housing either. The rotor has a constant cross section along its entire length.
DE 3802069 also describes a type of windmill. Here, the rotor is conical, with a set of helical vanes. However, there is no rotor chamber.
GB 1157273 describes a screw-type motor in which two oppositely twisted helical wings have been placed after each other on the same shaft inside a chamber with smooth walls. The cross section of both the rotor and the chamber is the same along the entire length.
WO 94/13957 describes an impeller. Here, the rotor is constructed from helical wings attached to a central conical body. The walls of the rotor chamber are smooth.
GB 987114 describes a mixer especially designed for mixing plastic materials, which shows the features of the preamble of claim 1. The mixer comprises a rotor and a stator, both of which are provided with helical grooves. The helical grooves on the rotor and the stator may be laid/twisted in opposite directions. Here, the grooves have an approximately rectangular cross section.
The present invention aims to provide an energy converter, particularly for use as a hydraulic pump, compressor, motor or turbine, for co-operation with one or more fluids, which is flexible in use, has low internal friction, is simple to manufacture, with low tolerance requirements, and which is highly applicable in several areas of use. This is achieved by the characteristics stated in the characterising part of the appended Claim 1.
The bore in the first part and the external surface of the second part are conical and exhibit complementary taper. In the following, the terms conical and cone denote all shapes where the diameter of one end is smaller than that of the other. This does not necessarily imply that the increase in diameter is constant. A machine according to the invention having "bottle shaped" parts may also be utilised.
The invention will now be explained in greater detail with reference to the accompanying figures, in which:

Figure 1a is a schematic diagram of an energy converter according to the present invention;
Figure 1b shows the energy converter according to Figure 1a seen in the direction of arrow A;
Figure 1c shows the energy converter according to Figure 1a seen in the direction of arrow B,
Figure 1d shows an alternative design of the stator;
Figure 1e shows an alternative design of the rotor;
Figure 1f shows an assembly of the rotor and the stator;
Figure 2 illustrates the operating principles of the present invention;
Figure 3 shows the stator according to Figure 1a;
Figure 4 shows the rotor according to Figure 1a; and
Figure 5 schematically illustrates a practical use of the energy converter according to the invention.

Figure 1a shows an example of an embodiment of an energy converter according to the present invention. In Figure 1a, one can imagine both the rotor and the stator to be shown as partially transparent. The energy converter consists of a stator 1 and a rotor 2. A shaft 3 is attached to the rotor.
Figure 3 schematically illustrates the stator 1. Here, one may also imagine the rotor and the stator to be shown as partially transparent. It defines an internal, conical bore 4 with its smallest diameter D1 to the left in Figure 3 and the largest diameter D2 to the right in the figure. It is expedient for a small section 5 by the smaller diameter D1 to be constructed with a uniform diameter, while the rest of the stator has an internal surface 6 that forms an angle α with the external cylindrical surface 7 of the stator. Advantageously, the angle α lies between 1° and 3°.
Helical grooves 8 are formed in the internal surface 6. Preferably, several helical grooves are formed and offset slightly relative to each other. In the embodiment shown, 12 helical grooves are laid/twisted at an angle of 45° or less to the longitudinal axis of the stator. The number of grooves may be higher or lower than this.
Preferably, the section 5 having a uniform diameter constitutes between 5% and 20% of the length of the stator. It is also expedient for the diameters D1 and D2 to measure approximately 1/3 to 1/5 of the overall length of the stator.
The grooves 8 are very shallow at the largest diameter D2 of the stator 1 (to the right in Figure 3), having a depth of approximately zero at this end of the stator 1. The depth of the grooves then increases gradually towards the opposite end of the stator at diameter D 1 (to the left in Figure 3). Here, the grooves 8 reach a depth approximately equal to the diameter D2, leaving the bottom of the grooves 8 lying along the surface of an imaginary cylinder corresponding to the diameter D2. This simplifies the production of the stator 1 considerably, as will be explained below. However, this is not critical to the operation, and for stators cast into a ready-made shape, the bottom of the grooves may also lie along an imaginary cone. The pitch of the grooves 8 may be uniform along the entire length of the stator, or it may vary.
Figure 4 shows the rotor 2. The rotor 2 has a conical outer surface 10 that forms an angle α with an imaginary cylinder circumscribing the rotor 2. The angle α is the same as for the stator 1. The largest diameter D3 of the rotor 2 is at the end where the shaft 3 is attached. Here is also a section 15 of uniform diameter. The diameter D3 may be approximately equal to the largest diameter of the stator, D2. The smallest diameter D4 of the rotor is equal to or smaller than the smallest diameter D1 of the stator 1.
Grooves 18 corresponding to the grooves 8 in the stator are formed in the surface 10 of the rotor. The number of grooves and their pitch angle may be the same as for the grooves 8 in the stator 1, but they may also deviate from this. However, the grooves 18 are laid/twisted in the opposite direction of the grooves 8 in the stator 1. In order to achieve the best possible efficiency, the grooves in the stator 1 and the rotor 2 must intersect at 90 °.
It is expedient for the section 15 of uniform diameter to constitute between 5% and 20% of the length of the rotor. Preferably, the diameters D3 and D4 measure approximately 1/3 to 1/5 of the overall length of the rotor.
The grooves 18 are very shallow at the smallest diameter D4 of the rotor 2 (to the left in Figure 4) and have a depth of approximately zero at this end of the rotor 2. The depth of the grooves increases gradually towards the opposite end of the rotor at diameter D3 (to the right in Figure 4). Here, the grooves 18 reach a depth approximately equal to the diameter D4, so as to leave the bottom of the grooves 18 lying along the surface of an imaginary cylinder equivalent to diameter D4. This simplifies the production of the rotor 2 considerably, as will be explained below. However, this is not of critical importance to the operation, and for rotors that are cast into a ready-made shape, the bottom of the grooves may also lie along an imaginary cone. The pitch of the grooves 18 may be the same along the entire length of the rotor, or it may vary.
Preferably, the stator 1 and the rotor 2 have approximately the same length.
Advantageously, when the rotor 2 is placed in the stator as shown in Figure 1a, a section of the rotor 2 protrudes from the stator 1, and correspondingly, a section of the stator 1 is not overlapped by the rotor 2. The significance of this will be explained below. However, the energy converter will function perfectly also when the rotor can be inserted fully into the stator.
Figure 1b shows the energy converter of Figure 1a seen in the direction of arrow A in Figure 1a. Here, the entrance to the 12 grooves 8 in the stator can be seen at the point of their greatest depth. The rotor 2 here appears with a smooth surface, as the grooves in the rotor have a depth of approximately zero at this end of the energy converter.
Figure 1c shows the energy converter of Figure 1a seen in the direction of arrow B in Figure 1a. Here, the entrance to the 12 grooves 18 in the rotor 2 can be seen at the point of their greatest depth. The stator 1 here appears with a smooth surface, as the grooves in the stator have a depth of approximately zero at this end of the energy converter.
Figure 1d shows an alternative embodiment of the stator. As with Figure 1b, the drawing shows a section through the energy converter at the end where the grooves 8' in the stator 1' have their greatest depth. The rotor 2' here appears with a smooth surface, as the grooves in the rotor have a depth of approximately zero at this end of the energy converter. What distinguishes this embodiment from the embodiment in Figure 1b is the fact that the width of the grooves 8' increases in the direction of depth, so as to allow optimal utilisation of the cross sectional area of the stator 1' as a flow area. Thus only a relatively thin wall 1a remains outside the grooves 8', in addition to a thin wall 1b between the individual grooves 8' in the stator 1'. The purpose of this wall is to keep fluids in and provide the stator with sufficient strength and rigidity, but apart from this, it should be as thin as possible.
Figure 1e shows an alternative embodiment of the rotor 2'. As with Figure 1c, the drawing shows a section through the energy converter at the end where the grooves 18' in the rotor 2' have their greatest depth. The stator 1' here appears with a smooth surface, as the grooves in the stator have a depth of approximately zero at this end of the energy converter. What distinguishes this embodiment from the embodiment in Figure 1c is the fact that the width of the grooves 18' decreases in the direction of depth, so as to allow optimal utilisation of the cross sectional area of the rotor 2' as a flow area. As a result, the cross section of the grooves assumes an approximate wedge-shape. This leaves only a small core area 2a in the rotor and a thin wall 2b between the individual grooves 18'. The function of this core area is primarily to provide the stator with sufficient rigidity and strength, and it should be as small as possible.
Figure 1f shows an assembly of the rotor 2' in Figure 1e and the stator 1' in Figure 1d, which gives a better impression of the area of the grooves 8' and 18' in the stator 1' and the rotor 2' respectively, in relation to each other. Preferably, the areas of the grooves 8' and the grooves 18' at the largest flow area for the two parts is the same, but may also be made dissimilar by increasing or decreasing the diameter of the two parts (external diameter for the rotor and internal diameter for the stator). Obviously, the location of the largest flow area for the rotor and the same for the stator will not coincide, but will preferably be at opposite ends of the energy converter. Consequently, Figure 1f is a section through the stator at one end and the rotor at the other end of the energy converter.
The operation of the energy converter will now be explained in greater detail with reference to Figure 2, where one groove 18 from the rotor and one groove 8 from the stator have been taken out in order to illustrate the principle. For the purposes of this example, the energy converter will be used as a hydraulic motor. Fluid flows in at the end of the stator 1 having the smallest diameterD1 (see arrow A in Fig. 1) but the greatest groove depth. As the grooves in the rotor 2 at this end of the energy converter have a depth of zero, the fluid will flow along the grooves 8 in the stator 1. However, the grooves 8 in the stator 1 become shallower as the fluid flows along groove 8. Coincident with this, the grooves 18 in the rotor 2 become deeper. The fluid will therefore be forced to flow across into the groove 18 in the rotor 2. Figure 2 shows a picture of the situation at a given moment in time for two grooves, one groove 8 in the stator 1 and one groove 18 in the rotor 2. Here, groove 8 and groove 18 can be seen to intersect at approximately right angles at point X at this given point in time. Therefore, some of the fluid will here flow across from groove 8, the cross section of which is steadily decreasing, to groove 18, the cross section of which is steadily increasing. At the same time, the fluid has to go through a 90° change in direction (here from flowing down to the right to flowing up to the right). This change in direction causes a force to be applied to the rotor 2, which is then forced to rotate.
As the rotor is rotating and there is a large number of grooves in the rotor and the stator, a large number of constantly moving points of intersection will result. Therefore, there will be an uninterrupted flow of fluid from the grooves 8 to the grooves 18, which will promote an increase in the rotation of the rotor, thus increasing the energy conversion. The torque may then be drawn from the shaft 3 and used, e.g. for running a generator. The higher the number of grooves in the rotor and the stator, the higher the number of points of intersection, which in turn makes the energy converter operate more smoothly and gives a higher efficiency.
When used as a pump, the energy converter will work in the opposite way, with rotation of the rotor 2 creating a negative pressure in the grooves 8 in the stator 1 which sucks fluid into the grooves 8, while creating an overpressure in the grooves 18 which forces the fluid out at the opposite end of the pump.
The principles that apply when using the energy converter as a compressor will basically be the same as when using it as a pump. It is also possible to use the energy converter as a fuel turbine, with combustion of a fuel being initiated at the entrance to the turbine, and fuel and any expansion gas expanding through the turbine. However, this will require the energy converter to be constructed with a relatively small inlet area and a relatively large outlet area, due to the volumetric expansion.
For the embodiment in Figures 1b and 1c, the net orifice area (flow area) through the converter will typically be in the range 30 - 40% of the axial cross sectional area of the stator. For the embodiment in Figures 1d and 1f, it is substantially larger. When using the energy converter as a liquid turbine or a pump, it is important for the flow area to be approximately constant throughout the energy converter in order to avoid cavitation caused by local pressure drops or pressure increases.
It may also be important for the angle α of taper to be approximately the same for the bore of the stator and the external surface of the rotor, in order to avoid leakage and back flow which may reduce the efficiency and lead to overheating. In some cases however, it may be appropriate for the rotor or the stator to have a slightly convex or concave shape (e.g. a barrel shape) but still have a largest diameter at one end and a smallest diameter at the other end.
Preferably, there is contact between the surfaces of the rotor and the stator along their entire lengths, possibly with the exception of a thin fluid film between the parts. This gives a good sealing effect and avoids leakage, and will also enable the components to wear evenly in relation to each other.
One part (the rotor or the stator) may be made from a softer material than the other, allowing the running surface of this to adapt to the harder part after a period of operation. This may enhance the sealing effect between the parts.
Figure 5 schematically shows a practical example of a use of the energy converter. Here it is pumping oil, and this oil is also used to drive the device.
A hydraulic motor 20 and a hydraulic pump 21 are placed in a common housing 22. The motor 20 has a stator 20a that is fixed relative to the housing 22 through being attached to a partition 24, and a rotor 20b. The pump 21 has a stator 21a that is fixed relative to the housing 22 through being attached to a partition 25, and a rotor 21b. The rotors 20b and 21b are coupled to a common shaft 23.
The displacement volume of the pump 21 is greater than that of the motor 20. The pump 21 and the motor 20 are arranged in a manner such that the outlet end of the motor 20 faces the inlet end of the pump 21.
An inlet 26 for propellant fluid is disposed at the inlet end of the motor 20 to the left of the partition 24. An inlet 27 for pumping medium is disposed between the partitions 24 and 25, and an outlet 28 for both the propellant fluid and the pumping medium is disposed at the outlet end of the pump 21 to the right of the partition 25.
A propellant medium such as e.g. oil is supplied through inlet 26 under pressure and forced through the motor 20. This rotates the rotor 20b of the motor 20, in turn driving the rotor 21b of the pump 21 via the shaft 23. As the displacement volume of the pump 21 is greater than that of the motor 20, a negative pressure will be created in the chamber between the partitions 24 and 25. This causes pumping medium to be sucked in through the inlet 27, to be mixed with the propellant medium flowing out through the outlet of the motor 20, and to be pulled through the pump 21. The unified fluid flow is then forced out through outlet 28. The object of this solution is to convert the energy in high pressure fluid into mechanical rotational energy for driving a larger piece of low pressure equipment, which converts mechanical energy into fluid energy with a lower pressure but a significantly larger volume.
It is also possible, instead of using the pumping medium as a propellant, to place a partition between the motor and the pump and arrange an outlet for propellant to the left of this partition. This makes it possible to use a propellant other than the pumping medium. However, it is the feature of being able to make use of the same fluid that makes the converter particularly useful, as it eliminates sealing problems and mixing of different fluids.
Another highly relevant area of use for the energy converter according to the invention is hydroelectric power. The energy converter according to the invention is particularly well suited to drawing off energy at high pressure. As such it will be highly appropriate to use the energy converter as a turbine when exploiting small hydroelectric resources, i.e. hydroelectric resources with a relatively low water regime but a steep hydraulic gradient (pressure head). The energy converter in accordance with the invention is also suited for wave power stations. In this case, the pressure is relatively low, while the water regime is high. However, this will involve a change in the length/diameter ratio of the energy converter, through the diameter being increased in order to increase the flow area.
The energy converter may also be used as an expansion engine, e.g. as an internal combustion engine. Preferably, the flow area then increases in the direction of the flow of the combustion medium. This may be done e.g. by increasing the width of the grooves in the direction of flow.
The energy converter is particularly favourable in terms of manufacture, as it makes few demands w.r.t. tolerances. Both the rotor and the stator can be cast to the finished shape without requiring any significant finishing treatment. Generally, it is only necessary to remove burrs and polish those surfaces that come into contact with each other.
Alternatively, the bore of the stator may be milled out, and the grooves may be turned. The grooves of the rotor may also be turned through simple operations.
There is no requirement for seals between the rotor and the stator. The rotor is inserted into the stator until they just touch. In accordance with a special embodiment, there may even be a small clearance between the rotor and the stator. In operation, a small fluid cushion will form between the rotor and the stator, on which the rotor will float. Therefore, the rotor does not need to be supported at both ends. This embodiment may be relevant to special applications. However, the rotor should normally be supported at both ends, so as to achieve minimum - approximately zero - clearance between the stator and the rotor, which avoids cavitation and recirculation. Moreover, one of the parts should be made from a softer material, so that upon wearing down, the rotor may be pushed further into the stator.
This in turn means that the only place where a seal against rotating parts may be required, is around the shaft from the rotor. In certain cases, such as for the example of Figure 5, this is not required either.
As mentioned previously, the rotor and the stator are constructed so as not to allow them to be brought together fully. Although this is greatly exaggerated in the figure, the purpose of this is to allow the rotor to be pushed further into the stator as the contact surfaces of the rotor and the stator are worn down. In this way, the service life of the parts can be lengthened without maintenance. This insertion of the rotor may be carried out manually by readjusting a set screw at regular intervals; but it may also be automatic, for instance by the rotor being biased against the stator and being fed into this as the parts wear down.
Because it adapts to the degree of wear, the energy converter according to the invention is highly insensitive to particles and contamination in the medium flowing through it. Even with a highly abrasive medium such as drilling mud, the length of the service life of the energy converter will still be adequate.
The above is also one of the more important reasons why the demands w.r.t. tolerances during manufacture are small. Although deviations may occur for a brand new energy converter, causing leakage between the rotor and the stator, the rotor and the stator will adjust to each other with use, thus providing a better and better sealing effect.
The rotor and the stator may be made from different materials, depending on the area of use. Relevant materials may be steel, aluminium and various types of thermoset plastic or thermoplastic.
In the embodiment shown, the cross-sectional shape of the grooves 8 and 18 is quadrangular. However, it may also be rounded or triangular, or have another shape that is appropriate in terms of the manufacturing process or provides optimum efficiency for the application in question.
Clearly, the stator 1 does not necessarily have to be stationary, but may rotate in the opposite direction of the rotor, which in fact gives the energy converter two rotors. Likewise, the inner part may be stationary and act as a stator while the outer part rotates and functions as a rotor.

Claims

An energy converter, particularly for use as a hydrodynamic pump, compressor, motor or turbine, comprising a first part (1) with a bore (4), where at least one helical groove (8) is formed in the wall of the bore (4), and a second part (2) with an external surface (10) in which there is formed at least one helical groove (18), the first (1) and second (2) parts being designed to rotate relative to each other, and where at least one of the first (1) and second (2) parts is designed to be coupled to a shaft (3) for transmission of torque; the bore (4) in the first part and the external surface (10) of the second part (2) being conical with a complementary taper; the groove(s) (8) in the first part (1) being laid/twisted in the opposite direction of the groove(s) (18) in the second part (2); the at least one groove (8, 18) being laid/twisted with a pitch that is constant along the length of the first (1) and/or second (2) part; the depth of the at least one groove (8) in the first part (1) increasing from that part of the bore (4) which has the largest diameter (D2) to that part of the bore (4) which has the smallest diameter (D1); the depth of the at least one groove (18) in the second part (2) increasing from that part of the second part (2) which has the smallest diameter (D4) to that part of the second part (2) which has the largest diameter (D3); the total flow area for the grooves (8, 18) being essentially constant along the length of the first (1) and/or the second (2) part, wherein a wall (1b) is located between adjacent grooves (8') in the cross-section of the first part (1'), which wall exhibits an approximately uniform thickness significantly smaller than the width of the groove(s) (8'), that a wall (2b) is located between adjacent grooves (18') in the cross-section of the second part (2'), which wall exhibits an approximately uniform thickness significantly smaller than the width of the groove(s) (18'), characterised in that the grooves are laid/twisted at an angle of 45° or smaller than 45° to the longitudinal axis of the first part and the second part, respectively.
Energy converter according to claim 1, characterised in that an inlet (26) for propellant fluid is at the end having the smallest second part diameter (D4) if the converter is used as a motor or turbine, and an inlet (27) for pumping fluid is at the end having the largest second part diameter (D3) if the converter is used as a pump.
An energy converter according to Claim 1 or 2, characterised in that the width of the groove(s) (8') in the first part (1') increases in the direction of depth.
An energy converter according to Claim 1, 2 or 3, characterised in that the groove(s) (18') in the second part (2') has/have a cross-section with the approximate shape of a wedge.
An energy converter according to one of the preceding claims, characterised in that the bottom of the at least one groove (8, 18) lies on the surface of an imaginary cylinder.
An energy converter according to one of the preceding Claims 1-4, characterised in that the bottom of the at least one groove (8, 18) lies on the surface of an imaginary cone.
An energy converter according to one of the preceding claims, characterised in that several parallel helical grooves (8, 18) are formed in the first (1) and/or the second (2) part.
An energy converter according to one of the preceding claims, characterised in that the second part (2) is a rotor supported only at one end.
An energy converter according to one of the preceding Claims 1-7, characterised in that the second part (2) is an unsupported rotor that floats freely in the first part.
An energy converter according to one of the preceding claims, characterised in that the width of the at least one helical groove (8,18) in the first (1) and/or the second (2) part increases in the direction of propellant flow.