GB2088017A

GB2088017A - Screw and Nut Mechanism

Info

Publication number: GB2088017A
Application number: GB8133550A
Authority: GB
Original assignee: Tecnomare SpA
Current assignee: Tecnomare SpA
Priority date: 1980-11-12
Filing date: 1981-11-06
Publication date: 1982-06-03
Also published as: IT1134214B; IT8025902A0; FR2493925B1; GB2088017B; NO813798L; FR2493925A1

Abstract

An electrical device for converting mechanical power deriving from reciprocal motion to mechanical power associated with rotary motion consists of screw-threaded bodies (14, 111) arranged in a screw-and-nut fashion, one body (14) being a rotor and the other body (111) being a slider. On the threads of the rotor, there are arranged, in hollow spaces, electrical conductors (20, 21, 22, 23) which carry currents giving rise to magnetic fields. These fields enable the drive to be transferred without mutual contact between the component parts. <IMAGE>

Description

SPECIFICATION Energy Conversion Device This invention relates to a device for converting mechanical power associated with reciprocation, for example the mechanical power associated with the low-speed reciprocation of a movable body, to mechanical energy associated with rotation.

A typical example of such bodies are floaters subjected to wave motion and particular reference will be made herein to such bodies, but without restricting the possible applications of the invention to that particular field.

Mechanical, hydraulic, oil-actuated or pneumatic devices for converting the reciprocation of bodies subjected to the motion of waves to rotary motion at a speed adapted to actuate a machine are known. The machine can be an AC or DC generator or a machine which directly employs such power, for example, a pump. The known devices generally speaking, have the defects that they include component parts prone to considerable wear and/or that they have low power efficiencies.

The device according to this invention broadly speaking, consists of a component subjected to reciprocal motion, this component being called hereinafter the "slider" and a component to which rotary motion is imparted, this component being called hereinafter the "rotor".

The conversion of the reciprocal motion of the slider into rotary motion of the rotor takes place by means of magnetized helical screw threads connected to the slider and to the rotor, respectively. The surfaces of the slider and of the rotor are confrontingly arranged but are kept spaced apart, as the slider is being moved, by the action of magnetic fields generated by electric coils arranged on the screw-threads, and currents, adjusted as a function of the distance between the confronting surfaces and of the magnitude of the power to be converted, are caused to flow through the coils.

According to the present invention, there is provided an electric device for converting mechanical power associated with rectilinear reciprocation to mechanical energy associated with rotary motion, comprising a cylindrical body the outer cylindrical surface of which supports one or more parallel threads having a helical outline along a substantial portion of its length; a body having a cylindrical hollow space which contains and supports in its interior a screwthread compiementary to that of the cylindrical body first named, the two bodies being arranged coaxially the one within the other as a screw and a nut but without any contact therebetween, a substantial distance, which is a magnetic gap, being maintained between the confronting threads; and one or more conductors arranged in hollow spaces formed through the surface which are not parallel to the axis of the cylindrical bodies of at least one of the threads, said hollow spaces having a helical trend coherent with the threads substantially along the entire length thereof, said conductors being laid in the interior of said hollow spaces and electrically insulated therefrom, said conductors having energization currents flowing therethrough to create magnetic fields.

In a preferred embodiment, the internal cylindrical body is secured to guideways which permit its rectilinear reciprocation along the axis of the cylinder while preventing rotation about the same axis and is the slider connected to the body having the rectilinear reciprocation and the energy of which is to be converted, and the hollow cylindrical body is connected to bearings so that it may be rotated about its central axis but it is not permitted to carry out translational motions along said axis and is the rotor connected to the working machine having a rotary motion.

In another preferred embodiment, the hollow cylindrical body placed internally is secured to bearings which permit its rotary motion about its axis but not any translation along said axis and is the rotor connected to the working machine, and the hollow cylindrical body is secured to guides which permit its rectilinear reciprocation along the axis of the cylinder but prevent rotation about said axis and is the slider connected to the body having a rectilinear reciprocal motion.

For a better understanding of the invention, reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 is a sectional view of a device o;F the invention; Figure 2 is a sectional view of a portion of the device shown in Figure 1; Figure 3 is a developed view, on a planar surface, of a portion of the device shown in Figure 1; Figure 4 is a sectional view along line A-A of Figure 1; and Figure 5 is a partly sectional view and a partly perspective view, of a portion of the device shown in Figure 1.

Referring to the drawings, the available mechanical power to be converted is a function of the movement, at a velocity V, of the slider 11 subjected to a pulse of magnitude F. The available power is thus equal to the product "Vx F".

The slider 1 above is to reciprocate along its axis 12. Thus, guideways 13 and corresponding projections 10 allow the slider 11 to move along the direction of its axis 12 and prevent rotary motion thereof. The slider 11 consists of a tube 111, preferably made of a non-magnetic steel, provided with a pair of threads 112 and 113 of a ferromagnetic material such as, for example, silicon alloyed iron. The threads 112 and 113 are arranged helically around a portion of the tube 111 and are integral with the latter. Externally of the slider 11 there is a rotor 14 which consists of a tube 141, preferably of a non-ferromagnetic material, provided with a pair of threads 142 and 143 of a ferromagnetic material, integral with the tube 141. The tube 141 has its axis coinciding with the axis 12 of the slider 11.The threads 142 and 143 are arranged helically and internally of the tube 141, and have the same pitch as the threads 1 12 and 113 of the slider 11, but are spaced apart therefrom by gaps 15, 16, 17 and 18.

The threads 142 and 143 of the rotor have a cross-section shaped so as to receive electric conductors 20, 21,22 and 23, which are electrically insulated and are secured to the threads by an appropriate insulating and adhesive material. The rotor 14 bears on thrust-bearings 144 and 146 which, in turn, bear on bearings 145. The rotor can thus rotate about the axis 12 but cannot move along the axis. In operation of the device, the movement of the slider 11, caused by the force F, tends to reduce the widths of the gaps 16 and 18 between the threads of the slider and the rotor, or to reduce the widths of the gaps 1 5 and 17 between the slider and the rotor, depending upon the direction of the movement.

The conductors 20, 21,22 and 23 have electric currents flowing therethrough, thereby generating magnetic fields which counteract the reduction of the width of the gaps while balancing the force F and acting upon the rotor with a driving torque M. When, due to the action of the force F, the threads 112 and 113 move upwards and tend to widen the gaps 15 and 17, the magnetic forces generated by the currents in conductors 20 and 22 attract the threads 142 and 112 towards one another and the threads 113 and 143 towards one another so as to keep the gaps between the slider and the rotor threads unaltered.

Inasmuch as the rotor can have only a rotary motion, the magnetic attraction is converted into a rotary motion, just as if the slider and the rotor were a screw and a nut. A condition which is vital for a satisfactory operation is the adjustment of current flowing in the conductors, and thus of the attraction forces, so as to maintain the gaps within a preselected range. Current is passed through the conductors 20 and 22 when the slider 11 moves in one direction, whereas no current is passed through the conductors 21 and 23. As the direction of movement of the slider 11 is reversed, that is at top dead centre or bottom dead centre, current is passed through conductors 21 and 23 whereas no current is passed through conductors 20 and 22.

In more detail, when the movement of the slider tends to reduce the gaps 16 and 18, an electric current I is passed through the conductor 20 in one direction and through the conductor 22 in the opposite direction. The current in conductors 20 and 22 generates magnetic fields shown as dotted lines 30, 31 and 32 in Figure 2, the arrows indicating the direction, either clockwise or anticlockwise, of the fields.

The magnetic fields in the gaps cause the confronting faces of the gaps to attract one another. The force of attraction between the faces is a function of the intensity of the current I and of the width of the gap if the gap is small as compared with the surface area. The attractive force FA acting upon each element of the faces is perpendicular to the surface of the element concerned, as shown in Figure 3. Each of the superficial elements is inclined relative to the axis 12 and is spaced apart therefrom.

The force FA acting upon a superficial element of the rotor 14 has a component force FR acting along the direction of the axis 12 and a component force FN perpendicular to the axis 12.

The torques generated by the forces FN of all of the superficial elements are combined into a driving torque M which acts upon the rotor 14, the latter thus being rotated at an angular speed o. The forces FR of all of the superficial elements are combined into a force equalling the thrust F acting upon the slider 11. The power vF associated with the motion of the slider 11 is converted into a power M.w associated with the rotation of the rotor 14. The transfer of motion from the slider 11 to the rotor 14 takes place by the action of the magnetic fields.

It follows from the foregoing that there is an advantage in the apparatus according to the invention in that the transfer of motion takes place between moving parts which do not contact one another and are not separated by any lubricant fluid, so that frictional losses and wear are virtually eliminated so that a high efficiency can be achieved.

In Figure 3, which is a development on a planar surface of a convolution of the threads 112, 11 3, 142, and 143, shows that the arrangement of the threads permits mutual sliding when the slider 11 is moved in the direction of its axis 12 and the rotor 14 is rotated in a plane perpendicular thereto. The provision of a gap between each slider thread and each rotor thread makes it possible to achieve frictionless motion between the respective surfaces of the slider and the rotor, the above advantages being thereby obtained.

A preferred construction of the device of the invention will now be described with reference to the directions of the magnetic fields which act between the slider and the rotor.

The directions of the magnetic fields around the conductors 20 and 22 are opposite one another to prevent a significant amount of the magnetic flux generated by the current I from becoming linked and from flowing through the gaps 1 6 and 18, thereby causing an undesirable attraction between the faces which define the gaps 16 and 18.

It is apparent, therefore, that it is an advantage for the device according to the invention to have two, or other even number, of threads for each pitch of the siider and, correspondingly, to have two or other even number of threads for each rotor pitch. This particular preferred embodiment permits the currents in the conductors of adjoining threads of the rotor to flow in opposite directions. The magnetomotive force between the faces separated by the gaps 1 6 and 18 is substantially negligible so that any interlinking of the magnetic fields of the conductors of two or more adjoining threads is prevented and the occurrence of undesirable forces is offset.It is possible, within the scope of the invention, for the device to have a single slider thread and a single rotor thread, or to have an odd number of slider threads and, correspondingly, an odd number of rotor threads. This embodiment operates well but does not have the advantages of the preferred embodiment.

More particularly, one should take into account the undesirable forces due to the magnetic flux which flows through each gap which would tend to become reduced by the effect of the reciprocal motion imparted to the slider. These undesirable forces may be reduced by conventional means, and, more particularly, by passing currents having appropriate directions and intensities through the conductors arranged in the hollow spaces of the gaps which tend to reduce in width, and/or by controlling the gap widths so that a gap which tends to be reduced by the effect of the imparted motion has a width which is substantially greater than a gap which tends to become widened, so as to offer a substantially greater reluctance to the flow of the undesirable magnetic flux.The currents are delivered to the rotor conductors by conventional devices, and are adjusted as a function of the distance between the surfaces and the magnitude of the power to be converted. The currents are regulated such that the forces due to the magnetic fields are, at eve instant of time, such as to balance the force F acting upon the slider, i.e. by rotating the rotor by a torque M and at an angular speed o, such as to bring into effect the relationship Fv=Mw, which indicates an equilibrium between the instantaneous powers associated with the motions of the slider and the rotor.

Inasmuch as a comparatively high angular speed co can be obtained, the power associated with motion of the rotor can conveniently be converted into electric power by conventional machines driven by the rotor. What has been described hereinbefore with reference to the motion of the slider tending to reduce the gaps 16 and 1 8 and with reference to the conductor 20 and 22 also applies with reference to the motion of the slider in the opposite direction, tending to narrow the gaps 1 5 and 17, and with reference to the conductors 21 and 23.

Thus, transfer of the mechanical energy from the slider to the rotor takes place regardless of the direction of motion of the slider. Inasmuch as the magnetic fields must be variable in order that a balance of the forces may be obtained, a preferred condition is that the components which are most exposed to such variations be made of a material which is electrically nonconductive, or, if a conductive material must be used, it should be in laminar form or so shaped as to prevent Foucault or eddy currents. An exception, obviously, is represented by the electric coils intended to produce the magnetic fields.

Herein, reference has been made, for simplification purposes, to screw threads having a rectangular outline and to a single coil along the threads. The outline of the threads and the arrangement and the number of conductors can be varied in practice within a wide range.

Hereinbefore, reference has been made to the case in which the slider is a screw-like body which is disposed internally and which is capable of moving along its axis whereas it cannot rotate, whereas the rotor is a "nut" body which is disposed externally and which can rotate but cannot move along its axis. The invention can be embodied in the opposite way, i.e. the rotor being a screw-like body which can rotate but cannot move along its axis, and the slider being a "nut" body which can move along its axis but cannot rotate.

The conductors can be inserted in the screw threads or in the nut threads according to constructional criteria of a mechanical or electrical nature.

In the application of a device according to the invention for the exploitation of the power of waves, the slider can be connected to a floater to which the waves impart motion and pulses in the vertical direction, which pulses are sinusoidal with time at least as a first approximation. The journals for the rotor bearings can be connected to a fixed anchoring structure. The power available from wave motion varies continually with time. During ascending motion, the thrust on the floater is exerted by the wave itself. As the upper dead centre is reached, the assembly of the floater and the slider fall due to gravity to the bottom dead centre. The dynamics of the system follow the known laws of the bodies subjected to wave motion and secured to anchoring members.In addition, the power available for conversion varies as a function of the shape, the dimensions, the anchorage and positioning of the floater, and as a function of the conditions of the sea, as is known.

The device enables mechanical power to be converted into power associated with rotary motion, at a high efficiency. The power losses are mainly those due to the friction of the slider in its guideways, the rolling friction of the bearings of the rotor, and the currents passed through the conductors. These losses are usually less than 10% of the transferred power, whereas the corresponding conversion losses in a pneumatic, oil-actuated or hydraulic system exceed 20%. For the same produced power, the device shown in the drawings normally permits one to achieve a substantial improvement in the produced power relative to the overall cost of the system, when exploiting the power of wave motion.

With a force of 60 N/cm2 on the separate surfaces of the gaps, the peak power transferred can be more than 200 W per kg of weight of the device. A device for transferring 100 kW may have a weight of 500 kg.

Claims

1. A device for converting mechanical power associated with reciprocation to mechanical energy associated with rotation, which device comprises a cylindrical body having one or more than one helical thread disposed around its outer periphery and a tubular body having one or more than one helical thread disposed around its inner periphery, the bodies being disposed coaxially the cylindrical body within the tubular body so that the thread or threads of one body mate with the thread or threads of the other body but so that there is no contact between the bodies, one body being capable of reciprocating along its axis but incapable of rotating about its axis and the other body being incapable of reciprocating along its axis but capable of rotating about its axis, the device further comprising means for magnetizing the or at least one thread of the cylindrical body and/or the or at least one thread of the tubular body.

2. A device as claimed in claim 1, wherein the cylindrical body includes at least one axial guide member disposed within an axial guideway so that the cylindrical body is capable of reciprocating along its axis but is incapable of rotating about its axis, and wherein the tubular body is disposed within bearings so that the tubular body is capable of rotating about its axis but is incapable or reciprocating along its axis.

3. A device as claimed in claim 1, wherein the tubular body includes at least one axial guide member disposed within an axial guideway so that the tubular body is capable of reciprocating along its axis but is incapable of rotating about its axis, and wherein the cylindrical body is disposed within bearings so that the cylindrical body is capable of rotating about its axis but is incapable of reciprocating along its axis.

4. A device as claimed in any of claims 1 to 3, wherein the magnetizing means comprises an insulated electrical conductor disposed in a channel in the respective thread.

5. A device as claimed in claim 4, wherein the channel has an opening directed towards a gap the width of which tends to increase when the body capable of reciprocating moves.

6. A device as claimed in any of claims 1 to 5, wherein the cylindrical body and the tubular body each have an even number of threads.

7. A device as claimed in claim 6, including means for feeding currents of opposite directions to adjacent conductors.

8. A device as claimed in any of claims 1 to 7, including means for adjusting the intensity of the current(s) fed to the conductor(s).

9. A device as claimed in claim 8, wherein the means for adjusting the intensity of the current(s) is able to adjust the current as a function of the width of the gap between the threads of the bodies, which gap should be kept substantially constant.

10. A device as claimed in claim 8, wherein the means for adjusting the intensity of the current(s) is able to adjust the current as a function of the power to be converted.

11. A device as claimed in any of claims 1 to 10, wherein the threads are ferromagnetic.

12. A device as claimed in any of claims 1 to 11, wherein the bodies are non-ferromagnetic.

13. A device as claimed in any of claims 1 to 12, wherein component parts made of electrically conductive material and subjected to magnetic fields generated by the currents (other than the conductors) have a laminar structure or an equivalent structure preventing the occurrence of Foucalt currents.

14. A device as claimed in claim 1, substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.