Machine part with several integrated ball bearings

Abstract

The present invention relates to a machine part with a housing 1 with an inner surface with a circular cross-section forming a first integral part of a machine element, and an inner rotary element 3 with an outer surface with a circular cross- section forming a second integral part of the machine element. The machine element includes at least three ball bearings with three or more of outer ball bearing races 9 in the inner surface with a circular cross-section 23, three or more inner ball bearing races 8 in the outer surface with a circular cross-section 24, aligned with the outer ball bearing races 9, a plurality of ball bearing balls 2 between the outer ball bearing races 9 and the inner ball bearing races 8 and at least one slot 10 with a slot-lid 11 in the housing 1, forming a gap in the outer ball bearing races 9 and forming at least point of access for the ball bearing balls, wherein the slot-lid 11 including at least one ball bearing race portion. The invention also concerns a machine part as described above forming a part of a linear actuator.

Description

Machine part with several integrated ball bearingsTechnical Field

[0001] The present invention relates a machine part with several integrated ball bearings and in particular to a machine part with roller bearings for cylinders exposed to axial and radial forces. The present invention is developed to enable compact designs with high performance, high speed, low weight and high load ratings. Furthermore, the present invention is developed to provide higher flexibility and low parts count when designing rotating parts, compared to traditional machine parts with ball bearings. The invention is applicable in linear actuators for converting rotational motion to linear motion, and vice versa. The invention was developed for electric linear actuators substituting hydraulic cylinders on land, submerged and subsea, but may be suitable for many other applications.Background Art

[0002] Ball bearings typically include an inner bearing ring with an inner bearing race, an outer bearing ring with an outer bearing race, bearing balls and a cage providing spacings between the bearing balls. The bearing balls are typically in a number that fills half or less of the space between the inner and outer bearing rings to allow assembly. The bearings balls are fed axially in between the inner and outer bearing rings during assembly before installation of the cage holding the bearing balls apart.

[0003] Other ball bearings have removable bearing races or bearing cones, allowing the ball bearing balls to be in a number to completely fill the bearing with bearing balls before the removable bearing race is installed. Again, the bearing balls are fed axially into the bearing during assembly and a space between the parts must be present to allow assembly.

[0004] A mechanical component with a bearing of the above type must be designed to allow installation of the bearing, and a space between the cylindrical component / shaft / and a housing surrounding the cylindrical component must be sufficient to allow room for the bearing balls.

[0005] Specialty bearings, such as some bicycle wheel bearings, include two bearing races in a wheel hub and two removable cones on a shaft. The bearing races in the wheel hub are accessible axially until the shaft and cones are installed.

[0006] In either case, the inner and outer diameter of the bearings dictate the space between the shaft and the housing the shaft is supported in. A bearing with more than two rows of bearing balls with the same diameter is impossible to assemble.

[0007] The contact faces of a bearing are typically of hardened and highly wear resistant materials to allow high surface stresses and to increase the lifespan of the bearing. Such materials are, however, expensive and not necessarily suitable for other applications.

[0008] It is an object of the invention to provide a machine part including bearings that overcome the above disadvantages of existing machine pars.

[0009] In particular, it is an object of the invention to provide a machine part that allows a small clearance between an element with a circular cross-section and a housing.

[0010] Furthermore, it is an object of the invention to provide a machine part that is easy to design with a high number of ball bearing ball and thus low surface stresses, allowing the use of a greater range of materials.

[0011] Furthermore, it is an object of the invention to provide a machine part where the outer housing of the bearing is allowed to be loaded in tension.

[0012] Furthermore, it is an object of the invention to provide a machine part with a bearing that does not require axial access to the bearing.

[0013] Furthermore, it is an object of the invention to provide an improved and more compact machine part for supporting and transferring loads with very low friction and losses.

[0014] Furthermore, it is an object of the invention to provide solutions that allow improved efficiency and reduced environmental impact when performing operations at land, at sea and subsea.

[0015] The invention is particularly applicable for bearings for well-known cylinders and devices providing a reciprocating motion.

[0016] Traditional hydraulic actuators typically provide high linear forces in compact configurations, normally in cylinder / piston arrangements. Hydraulic systems however, leak fluid and causes pollution issues no matter how well they are maintained.

[0017] Electric systems without hydraulics eliminate problems with oil leaks, simplifies digitalization, and have potential for lower overall power requirements. Many systems have been developed to compete with hydraulic actuators, but high complexity, low mechanical efficiency and large building size have offset the advantages of utilizing electric energy.

[0018] Compactness is essential in making compact actuators to replace hydraulic actuators within the space limitations.

[0019] The present invention offered by allowing three or more ball bearings of the present invention, offsets the traditional disadvantages of non-hydraulic systems and facilitates robust designs and long service life.

[0020] The present invention also relates to an improved and more compact system for converting rotational torque to axial force or vice versa. The present invention can contribute to very low losses while reducing the disadvantages of linear actuators discussed above. Compactness is essential when replacing hydraulic actuators in confined areas.

[0021] The machine part of the invention includes an integral, multirow, ball bearing between two elements, forming a part of a larger, load bearing structure.Summary of invention

[0022] The present invention concerns a machine part with a housing with an inner surface with a circular cross-section forming a first integral part of a machine element and an inner rotary element with an outer surface with a circular cross-section forming a second integral part of the machine element. The machine part includes at least three ball bearings. The at least three ball bearings include three or more of outer ball bearing races in the inner surface with a circular cross-section, three or more inner ball bearing races in the outer surface with a circular cross-section,aligned with the outer ball bearing races, and a plurality of ball bearing balls between the outer ball bearing races and the inner ball bearing races. At least one slot with a slot-lid in the housing is configured to provide at least one point of access for the ball bearing balls.

[0023] The at least one slot in the housing may extend between an outside of the housing and at least one of the at least three outer ball bearing races.

[0024] The at least one ball bearing race portion may be included in the slot-lid.

[0025] The machine part may include at least one slot and one slot-lid for each ball bearing.

[0026] The slots in the housing may be shifted a distance in a circumferential direction in relation to each other along the inner surface with a circular crosssection.

[0027] The slots may be located at equal distances from each other along the circumference of the inner surface with a circular cross-section.

[0028] The one or more slot-lids covering said slots may include a plurality of ball bearing races.

[0029] The housing may form an integral part of one of a motor housing, a pump housing, a linear actuator housing, a transmission and a gear box.

[0030] The inner rotary element may form one of a motor shaft, a pump shaft, a part of a linear actuator, a transmission shaft and a shaft in a gear box.

[0031] A difference between an inner diameter of the housing and an outer diameter of the inner rotary element may be equal to or less than a diameter of a ball bearing ball in the ball bearing between the housing and the inner rotary element.

[0032] The ball bearing balls may fill the bearing races such that a sum of the diameters of the number of ball bearing balls in one ball bearing equals the length of the circumference of the bearing at the location of the center of the ball bearing balls.

[0033] The inner surface of the housing and the outer surface of the inner rotary element may be cylindrical.

[0034] The inner surface of the housing and the outer surface of the inner rotary element may be conical.

[0035] The at least three ball bearings may have equal diameters.

[0036] Each slot-lid may be formed as a bolt with a threaded portion and an end facing one of the outer ball bearing races.

[0037] Said end of said slot-lid forms a concave hemispherical surface.

[0038] Furthermore, the invention concerns a machine part as described above forming a powered linear actuator configured to provide a transition between a rotational motion and a linear motion. The outer housing includes a cavity, and the inner rotary element includes an outer drive element surrounding the inner rotary element. A leadscrew with a leadscrew helical ball race is located inside the inner rotary element and connected to a linear motion drive rod extending through the outer housing. Bearing balls are located in a helical ball race formed by the leadscrew helical ball race and the inner rotary element inner helical ball race. The plurality of housing inner ball bearing races surrounds the housing cavity.

[0039] Brief description of the drawings:

[0040] Fig. 1 is a cross-section of a first machine part of the invention with an integral, multi-row ball bearing;

[0041] Fig. 2 is a cross-section of a second machine part of the invention with an integral, multi-row ball bearing;

[0042] Fig. 3 is a cross-section of a ball screw actuator of the invention with an integral, multi-row ball bearing;

[0043] Fig. 4 is a perspective view, partly cut through, of a detail of the ball screw actuator of the invention;

[0044] Fig. 5 is a schematic representation of an embodiment of a machine part suggesting the location of several slots, allowing insertion of ball bearing balls;

[0045] Fig. 6 is a perspective view, partly cut through, according to a further aspect of the present invention;

[0046] Fig. 7 shows a portion of fig. 6 in greater detail; and

[0047] Fig. 8 is a cross section of a bolt design of the slot lid shown in figs. 6, 7.Detailed description of the invention

[0048] Fig. 1 is a cross-section of a first machine part of the invention with an integral, multi-row ball bearing. The machine part includes a housing 1 forming an integral part of a machine element such as a motor housing, a pump housing, a part of a linear actuator, a transmission housing or a gear box.

[0049] Furthermore, the machine part includes an inner rotary element 3 also forming an integral part of the machine element. The inner rotary element 3 forms a mechanical element such as a motor shaft, a pump shaft, a part of a linear actuator, a transmission shaft or a shaft in a gear box. The inner rotary element 3 may be hollow or solid.

[0050] Multiple ball bearing races and ball bearing balls 2 of the multi-row ball bearing, allow rotation of the inner rotary element 3 in relation to the housing 1 while taking up forces in axial and radial directions. The ball bearing races are annular. Fig. 1 shows six annular ball bearing races, and the number of ball bearings should be at least three to provide a load carrying capacity in a very slim configuration.

[0051] A removable slot-lid 11 is located in a slot 10 forming a gap / opening in the housing 1 and is secured to the housing 1 with machine screws. The removable slotlid 11 includes multiple, outer ball bearing races and the combination of the ball bearing races of the housing 1 and the bearing races of the slot-lid, form the complete outer bearing races for the ball bearing balls 2. A transition between each individual bearing race of the lid and the housing may be offset in relation to an adjacent transition to place the transitions at different locations along the circumference of the outer ball race to distribute the wear and forces on the bearing races. The slot-lid 11 may include integrated or separate ball bearing races allowing exchange of the ball bearing races without exchanging the entire lid. A slot-lid including a separate ball bearing race may also simplify use of dissimilar materials.

[0052] The inner rotary element 3 and the housing 1 include multiple, aligned ball bearing races. Ball bearing balls 2 are located in the ball bearing races.

[0053] The configuration of the present invention eliminates any risk of bearing rings becoming dislodged from their seats.

[0054] Using one or several removable slot-lids 11 allows assembly of the bearing without having to insert the bearing balls in the gap between the housing 1 and the inner rotary element 3, allowing this gap to be almost negligible. The determining design parameter for the gap may then be other considerations such as lubrication and thermal expansion issues. Consequently, this enables a compact design.

[0055] Omitting the limitation in the number of ball races also allows the use of small bearing balls, thus reducing the overall diameter of the design.

[0056] Omitting the limitation in the number of ball races may also reduce the surface load in the bearing races, thus increasing the freedom when selecting the materials for the components.

[0057] Omitting a cage holding the bearing balls allows the bearing races to be completely filled with bearing balls, and this also contributes to reduce the surface load between the bearing balls and the bearing races.

[0058] Fig. 2 is a cross-section of a second machine part of the invention with an integral, multi-row ball bearing as disclosed in fig. 1 . An inner rotary element 3 is rotationally supported in housing 1 and bearing balls 2 are located in six ball bearing races on the inside of the housing 1 and on the outside of the inner rotary element 3. The housing 1 includes a cylinder clevis attachment 14 allowing the housing to be secured to a component and to form a part of a cylinder arrangement. Again, a removable slot-lid 11 with multiple ball bearing races is located in a slot 10 in the housing 1 such that bearing races of the slot-lid and of the housing form complete outer bearing races for the ball bearing balls 2.

[0059] Fig. 3 is an illustration of an inverted ball screw actuator forming a machine part with an inner rotary element 3 with an internal helical ball race supported inside a cavity 21 of a housing 1. In the context of this specification is “inverted” intended to describe that is the leadscrew 5, is located inside the inner rotary element 3. This is opposed to a traditional helical ball raced linear actuator where a driven glide nut surrounds a helically, ball raced, rotational screw.

[0060] The inner rotary element 3 is supported in the housing by six ball bearings including bearing races for ball bearing balls 2 formed by inner ball bearing races 8 in the inner rotary element 3 and outer ball bearing races 9 in the housing 1 .

[0061] The inner rotary element 3 is driven in rotation by a motor 20 through a transmission 18, and a gear meshing with a gear rim 19 forms a drive element surrounding the inner rotary element 3. A radial bearing 4, typically a plain bearing or a needle bearing, supports the inner rotary element 3 in the housing 1 , and takes up forces from the meshing gears. The drive element provides a drive for the inner rotary element 3. Alternative drive elements include a chain driven sprocket and a rim driven electric motor driving the inner rotary element 3 directly without a transmission.

[0062] The gear rim 19 is located close to the centre of the inner rotary element 3 to provide increased torsional stiffness and thus reduced flexibility at the end positions of the drive rod 17. The gear rim 19 may however be located at both the inner and outer end of the housing 1 , and increased flexibility at the outer extreme positions of the drive rod can sometimes be advantageous. The ability to locate the gear rim 19 at different locations along the inner rotary element 3 increases the design flexibility and allows flexibility in actuator and motor configurations to suit different needs and space requirements.

[0063] The transmission 18 typically includes planetary gears.

[0064] The motor is typically an electric motor, but the invention is applicable to other types of motive elements. The linear actuator may be used to convert linear motion to rotating motion and the motor may then for instance be substituted with a generator generating electric power.

[0065] The leadscrew 5 is fixed to the drive rod 17 with the rod clevis attachment 13 to transfer the force and to prevent rotation of the leadscrew 5. Rod seals 15 prevent ingress of dirt and fluids into the housing 1 . The housing 1 , may be filled with fluid for lubrication and to prevent ingress of fluids, typically in submerged applications.

[0066] In ball screw and nut designs the balls are recirculated as they roll along the race or course by the relative motion of the screw and nut. A structure to recirculate the balls is thus required. In the present invention, the leadscrew 5 includes a leadscrew body having outer helical ball rolling grooves I races and a deflector circuit for re-circulation of the lead screw balls. The cylinder clevis attachment 14, the end stop sensor 12 and the slot-lid 11 are shown attached to the housing 1

[0067] Fig. 4 shows a detail of fig. 3, with the inner ball bearing races 8 of the inner rotary element 3 and outer ball bearing races 9 inside the housing and a slot 10 in the housing 1 for loading balls into the ball bearing races. The slot 10 allows the balls to be installed or removed during assembly and maintenance. The slot-lid 11 covers the slot 10 and includes lid ball races to provide ball races across the slot 10.

[0068] The inner rotary element helical ball race 7 and the leadscrew 5 helical ball race 6 provide the ball race transferring motion between linear motion and rotating motion. The pathway for recirculation of balls inside the leadscrew 5 is not shown. The cylinder clevis attachment 14 is secured to the housing 2.

[0069] The annular ball bearings allow rotary motion while preventing linear motion between the inner rotary element 3 and the housing 1.

[0070] An end stop sensor 12 sensing the piston position at the end, is located at the end of the housing 1 and provides a signal to stop or change direction of the rotation of the motor. The drive rod 17 is fixed to the leadscrew 5.

[0071] Fig. 5 is a schematic representation of an embodiment of a machine part suggesting the location of several slots 10 for ball bearing balls in the housing 1 . Fig.5 suggests six ball bearings and one slot 10 for each bearing. Clearly the six ball bearings and the six slots are not located in the same plane, and the drawing is thus not an actual drawing through a cross-section of the machine part. The six slots 10 are located 60° apart along the circumference of an inner surface 22 of the housing 1 with a circular cross-section to distribute the loads and wear. The distance between the slots may ensure that no ball bearing balls pass a transition between a slot and an outer ball race in the housing 1 simultaneously to ensure smooth operation and even wear. Fig. 5 could also illustrate three ball bearings with two slots 10 for each bearing. Using two slots 10 for each ball bearing will facilitate removal of ball bearing balls for maintenance. The inner rotary element 3 includes an outer surface 23 also with a circular cross section. The outer surface 23 and the inner surface 22 are typically cylindrical with a uniform diameter along the length but may in some situations have a stepped diameter.

[0072] Ball bearing diameter in the present disclosure describes the diameter of the ball bearing at the center of the ball bearing balls.

[0073] Fig. 6 is a perspective view, partly cut through, according to a further aspect of the present invention. Access for the ball bearing balls to the annular bearings with the inner ball bearing race 8 and the outer ball bearing race 9, is through the slots 10 in the housing 1. There is one slot 10 for each annular bearing. Each slot 10 is shaped as a bore and is threaded to allow a threaded slot lid 11 to be screwed into the slot 10. The threaded slot lid includes a threaded portion and a bolt head and includes the ball bearing race portion at the end to provide a complete outer ball bearing race 9 for the bearing balls when the slot lid 11 is installed. Fig. 6 shows six separate annular ball bearings, each located in a plane perpendicular to a central axis of the inner rotary element 3. Accordingly, the embodiment of fig. 6 discloses six slots 10 and six slot lids 11 .

[0074] Fig. 6 is a general solution not showing a lead screw inside the inner rotary element 3.

[0075] Fig. 7 is a perspective view, partly cut through, of the solution of Fig. 6 in greater detail. Each threaded slot lid 11 to be screwed into a slot 10 in the housing 1 , is shaped as a bolt with a threaded portion 24 and a bolt head 25 and includes a concave hemispherical ball bearing race portion 16 at the end to provide a portion of the outer ball bearing race for the bearing balls when the slot lid 11 is installed. Fig. 7 shows six separate annular ball bearings, each located in a plane perpendicular to a central axis of the inner rotary element 3. The inner ball bearing races 8 are uninterrupted.

[0076] The slots 10 are staggered to distribute the forces due to the imperfections that inevitably are introduced by the slots and the ball bearing race portions.

[0077] Fig. 8 shows a cross section of the slot lid 11 of fig. 6, 7 with a threaded portion 24, a bolt head 25 and a concave hemispherical ball bearing race portion 16 at the end to provide the portion of the outer ball bearing races for the bearing balls when the slot lid 11 is installed. A hex key opening 26 in the bolt head 25 allows the slot lid 11 to be screwed in please. The concave hemispherical ball bearing race portion 16 allows the slot lid 11 to be installed without considering a specific rotation of the slot lid.

[0078] The concave hemispherical ball bearing race portion 16 thus allows the slot lid 11 to be installed by screwing the slot lid 11 into the housing and by tightening theslot lid to a specific torque, but without considering the position (in rotation) of the bolt head in relation to the housing.

[0079] Clearly the solution with individual slot lids 11 and slots 10 is applicable to the embodiments shown in figures 3,4 and vice versa. Clearly also, the individual slots 10 can be distributed around the circumference of the housing as shown in fig, 5.

[0080] Again, may each annular ball bearing include several slots and slot lids to facilitate removal of the ball bearing balls for maintenance.

[0081] Characteristics and advantages of the present disclosure and additional features and benefits will be readily apparent to those skilled in the art upon consideration of the following detailed description of exemplary embodiments of the present disclosure and referring to the accompanying figures. The description herein and appended drawings, being of example embodiments, are not intended to limit the claims of this patent application. On the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the claims. Many changes may be made to the embodiments and details disclosed herein without departing from such spirit and scope. The objects, advantages, and features of the invention will become more apparent by reference to the drawings which are appended hereto and wherein like numerals indicate like parts and wherein an illustrative embodiment of the invention is shown.

Claims

CLAIMS1 . A machine part comprising a housing (1 ) with an inner surface (22) with a circular cross-section forming a first integral part of a machine element, and an inner rotary element (3) with an outer surface (23) with a circular cross-section forming a second integral part of the machine element; at least three ball bearings including:-three or more of outer ball bearing races (9) in the inner surface with a circular cross-section (22);-three or more inner ball bearing races (8) in the outer surface with a circular crosssection (23), aligned with the outer ball bearing races (9);-a plurality of ball bearing balls (2) between the outer ball bearing races (9) and the inner ball bearing races (8); at least one slot (10) with a slot-lid (11 ) in the housing (1 ) wherein the at least one slot (10) in the housing (1) is configured to provide at least one point of access for the ball bearing balls (2)..

2. The machine part of claim 1 , wherein the at least one slot (10) in the housing (1 ) extends between an outside of the housing and at least one of the at least three outer ball bearing races (9).

3. The machine part of one of claims 1 , 2, wherein at least one ball bearing race portion is included in the slot-lid (11 ).

4. The machine part of one of claims 1-3, including at least one slot (10) and one slot-lid (11 ) for each ball bearing.

5. The machine part of claim 4, including a plurality of slots (11 ), and wherein the slots (10) in the housing (1 ) are shifted a distance in a circumferential direction in relation to each other along the inner surface (22) with a circular cross-section.

6. The machine part of claim 5, wherein the slots (1 ) are located at equal distances from each other along the circumference of the inner surface (22) with a circular cross-section.

7. The machine part of claim 1 , wherein the slot-lid (11) covering said at least one slot (10), includes at least three ball bearing races.

8. The machine part of one of the claims 1 -7, wherein the housing (1 ) forms an integral part of one of a motor housing, a pump housing, a linear actuator housing, a transmission and a gear box.

9. The machine part of one of the claims 1-6 wherein the inner rotary element (3) is one of a motor shaft, a pump shaft, a part of a linear actuator, a transmission shaft and a shaft in a gear box.

10. The machine part of one of the claims 1-9, wherein a difference between the inner diameter of the housing (1 ) and the outer diameter of the inner rotary element (3) is equal to or less than a diameter of a ball bearing ball (2) in the at least three ball bearings between the housing (1) and the inner rotary element (3).11 . The machine part of one of the claims 1 -10, wherein the ball bearing balls fill the bearing races such that a sum of the diameters of the number of ball bearing balls equals the length of the circumference of the bearing at a location of a center of the ball bearing balls.

12. The machine part of one of the claims 1-11 , wherein the inner surface (22) of the housing (1 ) and the outer surface (23) of the inner rotary element (3) are cylindrical.

13. The machine part of one of the claims 1-12, wherein the at least three ball bearings have equal diameters.

14. The machine part of one of the claims 4-6, wherein each slot-lid (11 ) is formed as a bolt with a threaded portion and an end facing one of the outer ball bearing races (9).

15. The machine part of claim 14, wherein said end of said slot-lid (11 ) forms a concave hemispherical surface (16).

16. A machine part of one of the preceding claims, forming a powered linear actuator configured to provide a transition between a rotational motion and a linear motion, wherein the outer housing (1 ) includes a cavity (21 ); the inner rotary element (3) includes an outer drive element surrounding the inner rotary element (3); a leadscrew (5) with a leadscrew helical ball race (6) inside the inner rotary element (3) and connected to a linear motion drive rod (17) extending through the outer housing (1 ); bearing balls in a helical ball race formed by the leadscrew helical ball race (6) and the inner rotary element helical ball race (7); and wherein the plurality of housing inner ball bearing races (9) surround the housing cavity (21).

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