WO2008085932A2

WO2008085932A2 - Magnetic spline drive system and method

Info

Publication number: WO2008085932A2
Application number: PCT/US2008/000182
Authority: WO
Inventors: Richard J. Wise
Original assignee: Magnetic Torque International, Ltd.
Priority date: 2007-01-09
Filing date: 2008-01-07
Publication date: 2008-07-17
Also published as: WO2008085932A3

Abstract

A system is provided for transferring rotational motion. The system includes an outer housing; a plurality of first magnets disposed within the outer housing along an inner region of the outer housing; an inner rotor disposed within the outer housing; a plurality of second magnets disposed along an outer region of the inner rotor; a first shaft connected to the outer housing and extending in a first axial direction; and a second shaft connected to the inner rotor and extending in a second axial direction. The outer housing and the inner rotor are connected to each other such that the inner rotor can move relative to the outer housing along either the first axial direction or the second axial direction, the outer housing can rotate about the inner rotor, and a gap exists between an inner face of the outer housing and an outer face of the inner rotor.

Description

TITLE OF THE INVENTION MAGNETIC SPLINE DRIVE SYSTEM AND METHOD

[0001] BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

[0002] The invention relates to a magnetic drive system, and more particularly to a magnetic spline drive system.

DISCUSSION OF THE RELATED ART

[0003] Drive systems for vehicles commonly use a system of drive shafts connected together using a spline geometry machined into the drive shafts. This allows for the transfer of rotational motion and torque from a driver body/shaft to a driven body/shaft, as well as axial movement along a direction of the driver and driven bodies/shafts. FIG. 1 is a perspective schematic view of a spline drive coupling according to the prior art. In FIG. 1 , a shaft 16 includes a plurality of external splines 16a that are engaged with internal splines

14a of the body/housing 14. Accordingly, rotational motion and torque of the shaft 16 may be transferred to the body/housing 14 using the internal and external splines 14a and 16a.

In addition, a certain amount of axial displacement may occur between the shaft 16 and the body/housing 14 and still provide for transmission of the rotational motion and torque between the shaft 16 and the body/housing 14.

[0004] As an exemplary application of the spline drive of FIG. 1, FIG. 2 is a side view of a spline drive according to the prior art. In FIG. 2, a driveshaft 10 includes universal couplings 12 and first and second shafts 14 and 16. Here, the shaft 16 is engaged with an internal portion of the shaft 14. Specifically, the shaft 16 has a plurality of external splines

16a that engage a corresponding plurality of internal splines (not shown) of the shaft 14.

Accordingly, rotational motion and torque of the shaft 16 may be transferred to the shaft

14 using the internal and external splines 14a and 16a.

[0005] However, the conventional modes for transferring rotational motion using a spline drive system fail to provide for the possibility of an over-torque situation.

Specifically, as shown in FIG. 2, when the driven shaft (either shaft 14 or 16) becomes unable to rotate, i.e., locked-up, and the driver shaft (either 16 or 14) continues to rotate, the internal and external splines of the driver/drive shafts 14 and 16 will shear. As a result, the shafts 14 and 16 will begin to rotate without the transferring of rotational motion and torque. In other words, once the torque transmitted along the driver shaft exceeds the shear strength of either the internal or external splines, then the transmission of rotational motion between the shafts ceases. Accordingly, the shafts must be replaced, resulting in significant amounts of lost production time and costs.

[0006] An alternative drive system is required to accommodate the over-torque condition without destroying the drive system. Moreover, an alternative drive system is required that can automatically and quickly return to a normal mode of rotational motion and torque transmission once the over-torque condition is resolved.

SUMMARY OF THE INVENTION

[0007] Particular embodiments of the invention provide a system for transferring rotational motion. The system includes an outer housing; a plurality of first magnets disposed within the outer housing along an inner region of the outer housing; an inner rotor disposed within the outer housing; a plurality of second magnets disposed along an outer region of the inner rotor; a first shaft connected to the outer housing and extending in a first axial direction; and a second shaft connected to the inner rotor and extending in a second axial direction. The outer housing and the inner rotor are connected to each other such that the inner rotor can move relative to the outer housing along either the first axial direction or the second axial direction, the outer housing can rotate about the inner rotor, and a gap exists between an inner face of the outer housing and an outer face of the inner rotor.

[0008] Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. Objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description as well as the appended drawings.

[0009] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings:

[0011] FIG. 1 is a perspective schematic view of a spline drive coupling according to the prior art;

[0012] FIG. 2 is a side view of a spline drive according to the prior art; [0013] FIG. 3 shows a perspective schematic view of an exemplary magnetic spline drive system according to the invention;

[0014] FIG. 4 shows a cross-sectional view of the exemplary embodiment of FIG. 3 according to the invention;

[0015] FIG. 5 is a perspective schematic view of an exemplary internal rotor according to the invention.

[0016] FIG. 6 is a perspective schematic view of another exemplary magnetic spline drive system according to the invention;

[0017] FIG. 7 is a perspective schematic view of another exemplary magnetic spline drive system according to the invention;

[0018] FIG. 8 is a perspective schematic view of an exemplary magnetic interaction of the exemplary spline drive system of FIG. 7;

[0019] FIG. 9 is an end view of an exemplary cylindrical magnet of the exemplary spline drive system of FIG. 7;

[0020] FIG. 10 is an end view of another exemplary cylindrical magnet of the exemplary spline drive system of FIG. 7;

[0021] FIG. 11 is an end view of another exemplary cylindrical magnet of the exemplary spline drive system of FIG. 7;

[0022] FIG. 12 is a schematic view of an exemplary magnet configuration according to the invention; and

[0023] FIG. 13 is a perspective schematic view of another exemplary magnetic spline drive system according to the invention. DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION [0024] Reference will now be made in detail to embodiments of the invention, examples of which are illustrated in the accompanying drawings.

[0025] FIG. 3 shows a perspective view of an exemplary spline drive system according to the invention. In FIG. 3, a spline drive system 100 includes a housing end plate 110, an external housing 120, an internal rotor 130, and a rotor end plate 140. A first shaft 115 is connected to the housing end plate 110 and a second shaft 136 is connected to the internal rotor 130. A plurality of first magnets 121, 122, 123 are placed along an axial direction of the external housing 120, and a plurality of second magnets 131, 132, 133 are disposed along an axial direction of the internal rotor 130. The first magnet 121 has (in this example) its North magnetic polar orientation 121n facing inward toward the internal rotor 130, and its South magnetic polar orientation 121s facing outward away from the external housing 120. The first magnets 122 and 123 are similarly oriented. The second magnet 131 has its North magnetic polar orientation 13 In facing outward toward the external housing 120 facing the North magnetic polar orientations of the first magnets 121, 122, 123, and its South magnetic polar orientation 131s facing inward toward the second shaft 136. The second magnets 132 and 133 are similarly oriented.

[0026] Accordingly, the North magnetic polar orientations of the first magnets 121, 122, 123 are disposed between adjacent North magnetic polar orientations of the second magnets 131, 132, 133. Thus, rotation of the external housing 120 causes the first magnets 121, 122, 123 to impart rotation of the internal rotor 130 due to the combined magnet repulsion of the first and second magnets 121, 122, 123 and 131, 132, 133. Similarly, torque transmitted by the rotation of the external housing 120 is imparted to the internal rotor 130 due to the magnet repulsion of the first and second magnets 121, 122, 123 and 131, 132, 133.

[0027] FIG. 4 shows a cross-sectional view of the exemplary embodiment of FIG. 3. hi FIG. 4, the internal rotor 130 is concentrically disposed inside the external housing 120 using bearings 110a mounted within the housing end plate 110 and bearings 140a mounted within the rotor end plate 140. The housing end plate 110 is connected to the external housing 120 using a plurality of fasteners 110b positioned within holes 110c of the housing end plate 110 and the holes 120a of the external housing 120. As shown in FIGs. 1 and 4, each of the holes 120a of the external housing 120 are positioned in groups between each of the first magnets 121, 122, 123, and the grouping of the holes 110c of the housing end plate 110 align with the group of holes 120a of the external housing 120. Similarly, the rotor end plate 140 is connected to the external housing 120 using a plurality of fasteners 140b positioned within holes 140a of the rotor end plate 140 and holes 120b of the external housing 120.

[0028] In FIG. 4, the internal rotor 130 is shown having a body portion 135 integrally formed with the second shaft 136. As shown, a forward portion 135a of the body portion 135 extends through the bearings 110a and a rear portion 135b of the body portion 135 extends through the bearings 140a. As a result, the forward and rear portions 135a and 135b are allowed to rotate. Alternatively, the body portion 135 and the second shaft 136 may be formed as plural elements such that the second shaft 136 may be affixed to the body portion 135 using known shaft coupling methods. Accordingly, a forward portion of the second shaft 136 may extend through the bearings 140a and the rear portion 135b of the second shaft 136 may extend through the bearings 140a.

[0029] As shown in FIG. 4, a clearance C is formed between the North magnetic polar orientation faces of the first magnets 121, 122, 123 and the North magnetic polar orientation faces of the second magnets 131, 132, 133 (in FIG. 3). The clearance C may be about 0.040 inches, although clearances of less than 0.040 inches, as well as greater than 0.040 inches may be used. However, reducing the clearance C will increase the interaction between the repulsive magnetic fields of the first and second magnets 121, 122, 123 and 131, 132, 133, thereby increasing the magnetic repulsive coupling between the magnets. Increasing the magnetic repulsive coupling (MRC), will allow for the transmission of higher amounts of torque Tl and T2 between the first and second shafts 115 and 136. [0030] In FIGs. 3 and 4, either of the external housing 120 or the internal rotor 130 may be considered a driving member, wherein rotation of the external housing 120 or the internal rotor 130 will impart the rotational motion to the other of the external housing 120 and the internal rotor 130. hi either event, the MRC may be "broken" due to an over- torque condition. Specifically, the over-torque condition will occur when the torque seen by the spline drive system exceeds the maximum combined repulsive magnetic forces of the magnets. The maximum combined repulsive magnetic forces are related to a coupling length L, the width, the shape and the strength of the magnets as well as the clearance C between the magnets. For this reason, increasing either the MRC area, i.e., increasing the coupling length L or magnet width, or reducing the clearance C will increase the over- torque threshold value.

[0031] With regard to FIG. 3 and 4, when the over-torque condition occurs, each of the magnets 121, 122, 123 of the external housing 120 will slip past the magnets 131, 132, 133 of the internal rotor 130, regardless of which of the external housing 120 and the internal rotor 130 is the driver source. This slip-clutch mode of operation will allow for the safe disengagement of the external housing 120 and the internal rotor 130. Moreover, once the over-torque condition subsides, i.e., the driver torque Tl is reduced below the combined repulsive magnetic forces of the magnets then the magnets of the external housing 120 and the magnets of the internal rotor 130 will become mutually realigned to re-establish synchronous rotation of the first and second shafts 115 and 136. Thus, the delivered torque T2 will be transmitted along the second shaft 136.

[0032] As with most spline drive systems, some relative axial movement must be provided when the spline drive system is implemented into a drive train system of a vehicle. According to the invention, the arrangement of the external housing 120 and the internal rotor 130 will accommodate relative axial movement when used in a drive system for a vehicle. The axial movement allowed by the system can be, for example, more than 5%, more than 10%, or more than 25% of the length of one of the second magnets along its axial direction or along the direction of axial movement.

[0033] FIG. 5 is a perspective schematic view of an exemplary internal rotor according to the invention. In FIG. 5, an internal rotor 130 may include a body portion 130a having a plurality of troughs 130b that each receive a magnet 133a. Here, the magnets 133a may be bonded within each of the troughs 130b using an adhesive, or may be mechanically coupled to the troughs 130b using a fastener system. Accordingly, an outer surface 133b of each of the magnets 133a and the outer surface 130c of the body portion 130a may be continuous. [0034] Similarly, as shown in FIG. 3, each of the magnets 121, 122, 123 may be inserted into the external housing 120 such that a portion of the external housing 120 is provided between the North magnetic polar orientations of the magnets 121, 122, 123. Accordingly, in this example, the North magnetic polar orientations may not be exposed to the outer surfaces 133b of each of the magnets 133a (in FIG. 5).

[0035] According to the invention, increasing the coupling length L of the interacting magnets can be used to vary the over-torque condition. However, increasing the coupling length L of the interacting magnets may result in increasing the overall length of the magnetic spline drive system. Accordingly, different geometries may be used to vary the over-torque condition without increasing an overall length of the magnetic spline drive system.

[0036] FIG. 6 is a perspective schematic view of another exemplary magnetic spline drive system according to the invention. In FIG. 6, each of the magnets 162 of the external housing 120 may be formed having a helical geometry, and each of the magnets 163 of the internal rotor 130 may be formed having a helical geometry. Accordingly, the coupling length of the interaction of the magnets 122 and 133 may be increased without increasing the overall length of the magnetic spline drive system. Although the magnets 162 and 163 are shown having a limited amount of helical "twist," each of the magnets 162 and 163 may have increased or decreased amount of helical "twist" to accommodate the over- torque condition desired. For example, as shown in FIG. 6, the helical "twist" of the magnets 162 and 163 may be about 120 degrees along the lengthwise direction of the external housing 120 and the internal rotor 130, respectively.

[0037] FIG. 7 is a perspective schematic view of another exemplary magnetic spline drive system according to the invention. In FIG. 7, each of the magnets 172 of the external housing 120 may be formed having cylindrical geometries, and each of the magnets 173 of the internal rotor 130 may be cylindrical. Accordingly, as shown in FIG. 8, the magnetic field orientations of the magnets 172 and 173 may be such that the North and South magnetic fields extend along lengths of the magnets 172 and 173. Thus, upon rotation of the external housing 120, the North magnetic fields of the magnets 172 and 173 oppose each other to impart rotation of the internal rotor 130 due to the combined magnet repulsion of the magnets 172 and 173. Similarly, torque transmitted by the rotation of the external housing 120 is imparted to the internal rotor 130 due to the magnet repulsion of the magnets 172 and 173. However, due to the direction of the opposing magnetic forces and the geometries of the magnets 172 and 173, a system is required to prevent the cylindrical magnets 172 and 173 from rotating within their respective bores in the external housing 120 and the internal rotor 130.

[0038] FIG. 9 is an end view of an example of a cylindrical magnet that can be used in the spline drive system of FIG. 7. In FIG. 9, the cylindrical magnets 172', 173' may include a pair of opposing extensions 172a, 173a. The opposing extensions 172a, 173a may be positioned at regions where the North and South magnetic fields interface 172b, 173b. In addition, each of the opposing extensions 172a, 173a may extend along an entire length of the cylindrical magnets 172', 173', or may be provided only at end portions of the cylindrical magnets 172', 173'. The external housing and the body portion of the internal rotor may include corresponding channels disposed along their lengths to receive the extensions.. Thus, the relative magnetic orientations of the magnets 172', 173' may be maintained to supply the repulsive magnetic forces to impart the rotational motion. [0039] FIG. 10 is an end view of another example of a cylindrical magnet that can be used in the spline drive system of FIG. 7. In FIG. 10, the cylindrical magnets 172", 173" may include a flat region 172c, 173 c disposed at one or both end portions of the cylindrical magnets 172", 173". The flat regions 172c, 173c may be positioned at regions where the North and South magnetic fields interface, or may be provided more toward the North or South end regions of the magnets. The external housing and the body portion of the internal rotor may include corresponding flat portions to receive the flat regions 172c, 173c. Thus, the relative magnetic orientations of the magnets 172", 173" may be maintained to supply the repulsive magnetic forces to impart the rotational motion. [0040] FIG. 11 is an end view of another example of a cylindrical magnet that can be used with the spline drive system of FIG. 7. In FIG. 10, the cylindrical magnets 172'", 173'" may include opposing flat sides 172d, 173d extending along lengths of the cylindrical magnets 172'", 173"'. The opposing flat sides 172d, 173d may extend along an entire length of the cylindrical magnets 172'", 173'", as shown, or may only be provided at one or both end portions of the magnets 172'", 173'". The external housing and the body portion of the internal rotor may include corresponding flat portions. Thus, the relative magnetic orientations of the magnets 172'", 173'" may be maintained to supply the repulsive magnetic forces to impart the rotational motion. [0041] FIG. 12 is a schematic view of an exemplary magnet configuration according to the invention, hi FIG. 12, some or all of the magnets 182 of the external housing 120 may be provided with a backing plate 185 that is disposed along the South magnetic surface. In this example, the backing plate 185 is shown to completely cover the South magnetic surface of the magnet 182. However, some or all of the magnets 182 of the external housing 120 may be provided with a backing plate 186 that is disposed along the South magnetic surface. In this example, the backing plate 186 is shown to cover only a portion of the South magnetic surface of the magnet 182. Each of the magnets of the internal rotor may also be provided with any of the backing plates 185 or 186. [0042] In FIG. 12, each of the exemplary backing plates 185, 186 displaces the North magnetic field of each of the magnets 182. Accordingly, with reference to FIGs. 1 and 12, the backing plates 185, 186 force the North magnetic field to be displaced along a direction toward the internal rotor 130. Similarly, with regard to use of the backing plates 185, 186 in the internal rotor 130, the North magnetic fields of the magnets of the internal rotor will be displaced along a direction toward the external housing 120. As a result, the repulsive magnetic forces between each of the magnets may be increased due to the displaced North magnetic fields. Thus, the combined repulsive magnetic fields may more effectively impart the rotational motion from the external housing 120 to the internal rotor 130, or impart the rotational motion from the internal rotor 130 to the external housing 120, depending upon which of the external housing 120 or the internal rotor 130 is used as the driving source. The backing plates 185, 186 may, for example, be made of magnetically conductive materials, such as mild steel.

[0043] FIG. 13 is a perspective schematic view of another exemplary magnetic spline drive system according to the invention. In FIG. 13, different magnet geometries may be used in the external housing 120 and the internal rotor 130. For example, the magnets 192 of the external housing 120 may include a cylindrical geometry, and the magnets 193 of the internal rotor 130 may include a rectangular geometry. However, the different geometries of the magnets 192 and 193 used in the external housing 120 and the internal rotor 130 must be selected to efficiently impart the rotational motion due to the combined repulsive magnetic forces between the magnets 192 and 193.

[0044] According to the invention, a system may be provided that can transmit torque between input and output shafts, and accommodate the condition where the output shaft cannot be turned by the input torque.

[0045] It will be apparent to those skilled in the art that various modifications and variations can be made in the magnetic spline drive of the invention without departing from the spirit or scope of the invention.

Claims

I claim:

1. A system for transferring rotational motion, the system comprising: an outer housing; a plurality of first magnets disposed within the outer housing along an inner region of the outer housing; an inner rotor disposed within the outer housing; a plurality of second magnets disposed along an outer region of the inner rotor; a first shaft connected to the outer housing and extending in a first axial direction; and a second shaft connected to the inner rotor and extending in a second axial direction, wherein the outer housing and the inner rotor are connected to each other such that the inner rotor can move relative to the outer housing along either the first axial direction or the second axial direction, the outer housing can rotate about the inner rotor, and a gap exists between an inner face of the outer housing and an outer face of the inner rotor.

2. The system of claim 1 , wherein the inner rotor can move relative to the outer housing along either the first axial direction or the second axial direction a distance that is at least 5% of a length of one of the second magnets, the length of the second magnets being taken in the second axial direction.

3. The system of claim 2, wherein the inner rotor can move relative to the outer housing along either the first axial direction or the second axial direction a distance that is at least 10% of a length of one of the second magnets.

4. The system of claim 3, wherein the inner rotor can move relative to the outer housing along either the first axial direction or the second axial direction a distance that is at least 25% of a length of one of the second magnets.

5. The system of claim 1, wherein each of the first magnets is oriented such that one of its magnetic poles produces a repulsive magnetic force with at least one of the second magnets.

6. The system of claim 1 , further comprising a first bearing within the outer housing, the first bearing rotatably retaining an end portion of the inner rotor.

7. The system of claim 1 , further comprising a plurality of longitudinal grooves located in the outer housing, each of the grooves containing one of the first magnets.

8. The system of claim 1 , further comprising a plurality of troughs in the inner rotor, each of the troughs containing one of the second magnets.

9. The system of claim 1, wherein each of the first magnets has a cross- sectional shape that is cylindrical, rectangular or trapezoidal, and each of the second magnets has a cross-sectional shape that is cylindrical, rectangular, or trapezoidal.

10. The system of claim 1 , further comprising a plurality of backing plates, each backing plate being disposed between one of the first magnets and the outer housing.

11. The system of claim 1 , further comprising a plurality of backing plates, each backing plate being disposed between one of the second magnets and the inner rotor.

12. The system of claim 1, wherein one of the first and second magnets has a cylindrical cross-section and a magnetic orientation device.

13. The system of claim 12, wherein the magnetic orientation device includes at least one of opposing extensions, opposing flat sides, and a flat end region.

14. The system of claim 1, wherein the first magnets include a helical geometry along the first axial direction and the second magnets include a helical geometry along the second axial direction.

15. A method of transferring rotational motion, comprising: rotating a first housing having a first axial direction and a plurality of first magnets; rotating a second housing having a second axial direction and a plurality of second magnets, the rotation of the second housing resulting from repulsive magnetic forces between the first magnets and the second magnets; providing a gap between the first housing and the second housing such that the first housing can rotate relative to the second housing; and allowing the first housing to move relative to the second housing along the first axial direction.

16. The method of claim 15, wherein the first housing can move relative to the second housing along the first axial direction a distance that is at least 5% of a length of one of the second magnets, the length of the second magnet being taken in the second axial direction.

17. The method of claim 16, wherein the first housing can move relative to the second housing along the first axial direction a distance that is at least 10% of a length of one of the second magnets.

18. The method of claim 17, wherein the first housing can move relative to the second housing along the first axial direction a distance that is at least 25% of a length of one of the second magnets.

19. The method of claim 15, wherein the first housing is an external housing and the second housing is an internal rotor located inside the external housing.

20. The method of claim 15, wherein the second housing is an external housing and the first housing is an internal rotor located inside the external housing.