FASTENING SUCH A BUSHING.

TECHNICAL FIELD

[0001] The invention relates to a bushing, a first part of two mutually rotating parts comprising such a bushing, and a method of attaching a bushing to a first part of two mutually rotating parts, such as a rotor or a stator.

BACKGROUND

[0002] A bushing is conventionally used to provide a sliding contact between two mutually rotating parts, i.e. two parts that rotate with respect to each other, such as e.g. a rotor and a stator of an electric or hydraulic motor. A bushing is arranged to provide a low frictional support surface between two mutually rotating parts. Especially, the bushing is arranged to cope with radial forces acting between such rotating parts.

[0003] In the application of a motor comprising a rotor inside a stator, a bushing may be attached at either end of the rotor on the inside of the stator and/or on the outside of the rotor. Conventionally, the bushing is attached to either the rotor or the stator by means of an adhesive and/or by press fitting.

[0004] Bushings are generally exposed to heavy forces, especially forces acting radially and sideways on the bushings. Long term exposure of the bushing may lead to loosening and degradation of the bushing. Therefore, in order to guarantee correct running of the apparatus in which the bushing is used, the bushings need to be replaced at regular intervals.

[0005] Hence, there is a need of a bushing that provides a more reliable long-term use.

SUMMARY OF THE INVENTION

[0006] It is an object of the present invention to provide a bushing that provides a close and reliable fit in the interaction between two mutually rotating parts.

[0007] According to a first aspect the invention relates to a bushing to be arranged between two mutually rotating parts, one part being arranged inside the other, which bushing has the shape of a hollow cylinder and comprises a first cylindrical surface arranged to engagingly attach to a first part of the two mutually rotating parts and a second cylindrical surface for sliding contact with a second part of the two mutually rotating parts, the first and second cylindrical surfaces being arranged on opposite sides of the bushing, one facing radially inwards and the other facing radially outwards, wherein the first cylindrical surface comprises a threaded portion arranged to engage with a complementary threaded portion on said first part and a first cylindrical portion arranged to be press fitted to a corresponding first cylindrical portion of said first part.

[0008] According to a second aspect the invention relates to a first part of two mutually rotating parts comprising a bushing for sliding contact with a second part of the two mutually rotating part, the bushing having the shape of a hollow cylinder and comprises a first cylindrical surface arranged to engagingly attach to said first part of the two mutually rotating parts and a second cylindrical surface for sliding contact with a second part of the two mutually rotating part, the first and second cylindrical surfaces being arranged on opposite sides of the bushing, one facing radially inwards and the other facing radially outwards, wherein the first cylindrical surface comprises a threaded portion arranged in engagement with a corresponding threaded portion on the first part of the two mutually rotating parts and a first cylindrical portion arranged in a press fit with a corresponding first cylindrical portion on said first part.

[0009] The first cylindrical surface of the bushing further comprises a second cylindrical portion arranged to be press fitted to corresponding first cylindrical portion on said first part, wherein the first cylindrical portion and the second cylindrical portion of the bushing are arranged on opposite sides of the threaded portion.

[0010] The two cylindrical portions on opposite sides of the threaded portion is advantageous as it relieves the thread from shear forces. Instead, such forces will be handled at respective sides of the thread, in the cylindrical portions.

[001 1] Further, the press fitting of the first and second cylindrical portions will provide fluid tight sealings at both ends of the bushing, such that no other sealings are needed.

[0012] In a specific embodiment the bushing comprises an axial abutment surface arranged to abut a shoulder on said first part.

[0013] In a specific embodiment the first cylindrical surface of the bushing constitutes the outer surface of the bushing arranged to engagingly attach to an inner surface of the first part of the two mutually rotating parts. Alternatively, the first cylindrical surface of the bushing constitutes the inner surface of the bushing arranged to engagingly attach to the outer surface of the first part of the two mutually rotating parts. [0014] In a specific embodiment the first cylindrical portion of the bushing is arranged axially outside of the threaded portion, the first cylindrical portion having a greater diameter than the threaded portion.

[0015] According to a third aspect the invention relates to a method of attaching a bushing to a first part of two mutually rotating part, the bushing having the shape of a hollow cylinder and comprising a first cylindrical surface arranged to engagingly attach to a first part of the two mutually rotating parts and a second cylindrical surface for sliding contact with a second part of the two mutually rotating part, the first and second cylindrical surfaces being arranged on opposite sides of the bushing, one of the first and second cylindrical surfaces facing radially inwards and the other facing radially outwards, wherein the first cylindrical surface comprises a threaded portion arranged to engage with a corresponding threaded portion on the first part of the two mutually rotating part and a first cylindrical portion arranged to be press fitted to the corresponding first cylindrical portion on said first part. The method comprises the steps of clamping the bushing to a state of reduced or enhanced

circumference, and threading the bushing, in said state of reduced or enhanced

circumference, into threaded engagement with said first part, releasing said clamping so as to engage the first cylindrical portion of the first cylindrical surface in a press fit with the corresponding first cylindrical portion of said first part.

[0016] Specifically, the bushing includes a grip portion at which the bushing is clamped, wherein the method includes a further step of machining said grip portion after said bushing has been attached to said first part.

[0017] Other embodiments and advantages will be apparent from the detailed description and the appended drawings.

BRIEF DESCRIPTION OF DRAWINGS

[0018] An exemplary embodiment related to the invention will now be described with reference to the appended drawings, in which;

Fig. 1 shows a schematic embodiment of a hydraulic motor, in which two bushings are arranged in the space between the stator and the rotor,

Fig. 2 shows a first embodiment of a bushing being arranged inside an upper stator part,

Fig. 3 shows a first embodiment of a bushing arranged inside an upper stator part, Fig. 4 is a detailed view of the bushing in fig. 3, and

Fig. 5 is a detailed view of a second embodiment of a bushing arranged inside a

stator.

DETAILED DESCRIPTION OF EMBODIMENTS

[0019] In Fig. 1 a hydraulic motor is shown in a sectional view. The hydraulic motor comprises two mutually rotating parts 1 and 2, whereof the second part 2 is arranged inside the first part 1 . In the exemplary embodiment shown in fig. 1 the two mutually rotating parts 1 and 2 are a stator and a rotor of a hydraulic motor. The invention is however not limited to a motor of any kind, but is useful in any application comprises two mutually rotating parts, one being arranged to rotate inside the other.

[0020] In the shown embodiment the first part 1 , in the form of a stator, is comprised of an upper stator part 3 and a lower stator part 4 that encloses a stator ring 1 a between them. Bolts 5 are arranged to keep the package constituted by the upper stator part 3, the lower stator part 4 and the stator ring 1 a together. For the understanding of this application, each part of the package comprised of the upper stator part 3, the lower stator part 4 and the stator ring 1 a is to be viewed as parts of an integral unit constituting the first part 1.

[0021] In the shown embodiment the upper stator part 3 of the first part 1 is firmly connected to a first attachment device 7, which is adapted for hanging attachment to a crane arm or the like, the first attachment device 7 comprising two loops for receiving a carrying bar of e.g. a crane arm. The second part 2 is firmly connected to a second attachment device 8 at which a tool, such as grip arm, an excavator or the like may be attached. The second part 2 of the shown embodiment is hence arranged to carry a tool, such that the major forces acting on the second part 2 are caused by gravitation and acts axially downwards on said second part 2.

[0022] An axial bearing 6 is arranged at a lower first end between the first and second parts 1 and 2 to handle the axial forces acting downwards on the second part 2. At each end of the second part 2, inside the first part 1 and between mutually rotating surfaces of said first and second part 1 and 2 a bushing 10 is arranged to provide a low frictional support between the first and second part 1 and 2.

[0023] The bushings 10 are arranged to handle radial forces and forces acting sideways between the first and second part, which forces may arise during operation when the second part 2 is tilted with respect to first part 1 . In the shown embodiment no axial bearing is arranged at the upper interface between the first and second part 1 and 2. Such forces, e.g. axial forces, pushing the second part 2 axially upwards with respect to the first part, may however be produced during normal operation, e.g. when a tool carried by the second attachment device 8 of the second part is pushed such that it touches base with the ground. Therefore, the upper bushing 10 should be arranged to cope with axial forces, which is more closely described below. A gap 9 is arranged between the upper end of the second part 2 and the upper stator part 3 of the first part 1 , such that no interaction may occur between said second part 2 and said first part 1 at this interface.

[0024] In the following a method of attaching the bushing 10 to the first part 1 of two mutually rotating parts will be described with reference to figs. 2 and 3.

[0025] In a first step the bushing 10 is clamped to a reduced or enhanced

circumference (not shown in the figures). For the embodiments shown in appended drawings the bushing 10 is clamped to a reduced circumference in order fit inside the space inside the first part 1. The bushing 10 may however just as well be provided with an internal threaded portion to be threaded onto a part carrying an external thread, in which case the bushing would need to be expanded so as to allow the press-fit portion of the bushing to be received outside said part.

[0026] In said reduced or enhanced circumference, the bushing 10 is threaded into engagement with said first part 1. Specifically, in the shown embodiment, one bushing 10 is inserted into engagement with the upper stator part 3 of the first part 1 , and one bushing 10 is inserted into engagement with the lower stator part 4 of the first part 1. The bushings 10 are inserted prior to joining of the upper stator part 3, the lower stator part 4, and the stator ring 1 a to the first part 1 .

[0027] Each bushing 10 is threaded inwards until an axial abutment surface 15 has reached a corresponding shoulder on the first part 1 . When said abutment is achieved the clamping of the bushing 10 is released so as to engage the first cylindrical portion 14 of the first cylindrical surface 1 1 in a press fit with the corresponding first cylindrical portion 4 of said first part 1.

[0028] In the embodiment shown in figs. 2-3 the bushing 10 includes a grip portion 17 at which the bushing is clamped, wherein the method includes a further step of machining said grip portion 17 after the bushing has been attached to said first part 1 . Preferably, the grip portion is machined away, such that no part of the bushing 10 extends axially outside of the first part 1 . In figs.2 and 3 the bushing 10 is shown after being engagingly attached to upper stator part 3, but before the grip portion 17 have been machined away. As described above, a similar bushing 10 may be attached in a similar manner to the lower stator part 4 of the first part 1 .

[0029] In fig. 4, a detailed view of a first embodiment of a bushing 10 is shown, arranged inside a first part 1 of two mutually rotating parts 1 and 2. The bushing 10 has the shape of a hollow cylinder and comprises a first cylindrical surface 1 1 arranged to engagingly attach to the first part 1 of the two mutually rotating parts, and a second cylindrical surface 12 for sliding contact with a second part 2 of the two mutually rotating parts.

[0030] The first and second cylindrical surfaces 1 1 and 12 are arranged on opposite sides of the bushing 10, one of said surfaces facing radially inwards and the other facing radially outwards. In the shown embodiment the first cylindrical surface 1 1 is the outer circumferential surface of the bushing 10, arranged to engagingly attach to the inner surface of the first part 1 . In this embodiment, the first part 1 could typically be a stator of a motor. In an alternative embodiment the bushing could instead be arranged to be attached to the inner part of the mutually rotating parts 1 and 2, wherein the first cylindrical surface 1 1 is instead the inner circumferential surface of the bushing 10, arranged to engagingly attach to an outer circumferential surface of the first part 1 . In this alternative embodiment, the first part 1 could typically be a rotor of a motor, arranged inside a stator.

[0031] The first cylindrical surface 1 1 comprises a threaded portion 13 arranged to engage with a corresponding threaded portion on the first part 1 of the two mutually rotating parts 1 and 2, as well as a first cylindrical portion 14 arranged to be press fitted into engagement with a corresponding complementary first cylindrical portion of said first part 1 .

[0032] Further, the bushing 10 comprises an axial abutment surface 15 arranged to abut a shoulder on said first part 1 . The abutment offers a fluid tight barrier between the bushing and the first part 1. Further, the engagement between the first cylindrical portion 14 of the bushing 10 and the corresponding complementary first cylindrical portion on said first part 1 also offers a fluid tight barrier. The interaction between the axial abutment surface 15 and the shoulder on said first part 1 offers support, which support the bushing 10 such that it may handle axial forces acting on it.

[0033] In the shown embodiment, the axial abutment surface 15 and the first cylindrical portion 14 of the bushing 10 are arranged on opposite sides of the threaded portion 13. This is advantageous, inter alia, because it will make sure that the threaded portion 13 is protected by fluid tight barriers on each side, wherein the thread will be protected from fluids entering and potentially degrading the treads of the threaded portion. [0034] For an application where the bushing 10 is arranged in a hydraulic motor as illustrated in fig. 1 , it is important that the interface between the bushing and the first part 1 that faces the high-pressure part of the motor is made fluid tight, in order to avoid efficiency losses in the motor. In the embodiment shown in fig. 4 the high-pressure side is the interface between the first cylindrical portion 14 of the bushing 10 and the corresponding

complementary first cylindrical portion on said first part 1. In the other end of the bushing, i.e. at the interface between the axial abutment surface 15 and the corresponding shoulder on the first part, the pressure is lower, and the risk of potential losses is therefore negligible.

[0035] In addition to the first cylindrical portion 14, the first cylindrical surface 1 1 of the bushing 10 may comprise a second cylindrical portion 16 arranged to be press fitted into engagement with a corresponding second complementary cylindrical portion 6 on said first part 1 . With a tight fit on both sides of the threaded portion the forces acting on the threaded portion will be kept at a relatively low level, such that the threaded engagement will not be negatively affected by the forces acting between the first and second part 1 and 2 of the mutually rotating parts. In fact, already at one press fit engagement between the first part 1 and the bushing 10 a beneficial stress release at the interface of the threaded portion 13 is achieved.

[0036] In fig. 5 an alternative embodiment of a bushing is shown. A main difference with respect to the embodiment shown in fig. 4 is the location of the abutment surface 15 on the bushing 10. In this alternative embodiment the abutment surface is located axially outside of the threaded portion 13, wherein, in the embodiment of fig. 2, the abutment surface 15 is formed by the inner end of the bushing 10.

[0037] As is visible in the figures, for a bushing that is clamped inside the interior of a first part 1 , the circumference of the bushing increases along its axis from the inside, such that the first cylindrical portion 14 arranged axially outside of the threaded portion has a greater diameter than that of both the threaded portion 13 and the second cylindrical portion 16 inside of the threaded portion 13.

[0038] Above, the invention has been described with reference to specific

embodiments. The invention is however not limited to these embodiments. It is obvious to a person skilled in the art that other embodiments are possible within the scope of the following claims.