CN107208765B

CN107208765B - Nut for a linear actuator, actuator and method of manufacture

Info

Publication number: CN107208765B
Application number: CN201580069230.6A
Authority: CN
Inventors: B·莫里兹
Original assignee: Hm Power Holding AG
Current assignee: Hm Power Guangdong Co ltd
Priority date: 2014-12-19
Filing date: 2015-12-17
Publication date: 2020-07-31
Anticipated expiration: 2035-12-17
Also published as: WO2016097849A1; SE542076C2; CN107208765A; SE1400604A1

Abstract

An operating nut (1) of a linear actuator comprises a threaded hole (2) for receiving a screw. The nut (1) comprises a plurality of elongated graphite elements (3) which are partially exposed in the threaded area, whereby the graphite elements (3) become part of the thread.

Description

Nut for a linear actuator, actuator and method of manufacture

Technical Field

The present invention relates to a linear actuator. More particularly, the present invention relates to a linear actuator including a screw and a nut that cooperate to provide linear motion. The present invention relates to a method of providing lubrication of an actuator. In particular, the present invention relates to an operating nut configured to receive a screw in a maintenance-free operation.

Background

A linear actuator is a mechanical device that generates linear motion from rotational motion. There are two main types of such linear actuators. The first type includes a rotating screw and a linear motion nut. The second type includes a rotating nut and a linear motion screw. The screw or nut may be operated by a conventional electric motor. Linear actuators are used in machine tools and industrial machinery, jacks, computer peripherals such as hard disk drives and printers, valves and buffers, high voltage switching devices, and many other areas where linear motion is required.

The term screw or spindle shall be understood as a threaded rod, pin, shaft or tube which serves as an axis of rotation or about which other objects rotate, thereby effecting linear motion. The threads of the screw and nut, respectively, are in meshing engagement with one another. The spindle converts the power generated by the motor into a linear feed rate and a feed force.

It is known that many linear actuators are capable of transferring large forces. However, these actuators involve grease or coatings such as teflon to reduce friction. These coatings are troublesome in harsh environments where small particles such as sand or metal chips can adhere to the coating. If these particles occupy the space between the screw and the nut, rapid wear or damage will occur. In addition, greases and coatings require maintenance over time to maintain low friction properties. In dealing with high pressures, maintenance-free operation and low friction between the screw and the nut is of paramount importance.

Teflon coated screws cannot handle large forces and in particular high contact pressures. Plastic nuts typically have high friction, resulting in high temperatures. The result of the high temperature can be severe wear or degradation of the material properties. Encapsulated screws comprising flexible bellows for anti-fouling have limited applications due to the increased space requirements. The encapsulated system is also difficult to inspect for functionality and wear.

Graphite is a good solid lubricant, which is known to be added to bearings made of brass or copper alloys. A solid plug of graphite is radially inserted into the bore of the base material. The manufacture of a screw or nut of such material is cumbersome. Since the screw thread can be axially processed, the thread can be interrupted by the radially aligned graphite plugs. Thus, the threaded portion will contain the base material, but the other portions of the thread contain pure graphite. Pure graphite cannot handle large forces.

In CN202612517, an automatic lubricating device for nut and screw drive mechanism is previously known. The aim of the mechanism is to overcome the drawbacks of the prior art mechanisms and to provide a nut-and-screw drive mechanism with simple maintenance with a lubricating effect.

The known mechanism consists of a graphite nut, a baffle, a drive nut and a lead screw. The graphite nut, the flapper, and the drive nut are rigidly connected such that the graphite nut is sandwiched between the flapper and the drive nut. The graphite nut and the driving nut move synchronously.

The automatic lubricating device also comprises a torsion spring arranged on the graphite nut. The device achieves lubrication action by relying on the self-movement of a nut-screw drive mechanism. The device is said to be maintenance-free and to be constructed of a simple structure with few mechanical parts. The device is also said to be convenient for maintenance and likewise said to be capable of being maintenance free.

As can best be understood from the known devices, the drive nut is responsive to forces, while the graphite nut is responsive to lubrication. The entire length of the assembly nut may become significant as they are axially attached to each other. The assembly length of the nut reduces the length of action of the device. It will also be understood from the drawings that the screw has two threads, but the graphite nut can only lubricate one of them. For lubrication of multi-threaded screw-nut applications, the overall length of the nut is increased since both the drive nut and the graphite nut must have a length equal to all of the multiple threads of the screw. The application of the spring indicates that the graphite is pushed against the screw. The wear of the graphite nut is thus greater than the wear of the drive nut. This does not form a maintenance free solution. When the graphite nut has worn, it must be replaced, regardless of whether the drive nut is worn.

A vehicle brake with a spindle/nut arrangement accommodated in a container filled with hydraulic oil is previously known from DE 102011121765. The purpose of the brake is to provide a mechanical efficiency that does not significantly degrade during the possible lifetime of the brake.

Various solutions are disclosed with solid lubricated components in the threaded area. Some of these solid parts are rigid and bear radially against the thread by spring force. The others are positioned in axially aligned grooves that open into the threaded region. In one embodiment, the solid state device is comprised of a solid state lubricant such as graphite. The lubrication of the solid parts, although in contact with the threaded counterpart, can be maintained until the solid parts are completely worn away, i.e. no longer present. In another embodiment, the solid component is composed of a carrier material that does not itself provide lubrication, but has the ability to take one or more desired lubricants and allow them to be released again over an extended period of time. Such a resilient solid component may operate like a sponge saturated with the desired lubricant.

In one embodiment, there are five grooves formed on the inside of the nut. As is clearly understood, the actual location and form of the solid state components are not known, as they are not shown in the drawings. However, the multiple grooves around the inside of the threaded hole will cause portions of the threads to be cut away. Thus, the continuous thread will be cut into a plurality of segments. The length of the thread itself will therefore be reduced and the load-bearing capacity will be reduced. In said document, there is neither description nor illustration of the formation of a solid component with a threaded surface.

In the case of elastic materials, the solid parts are made oversized and are therefore compressed by the screw. But firstly the pressure against the threads will provide frictional resistance and secondly the resilient pressure will also wipe off any lubricating coating. In the case of a rigid material, the solid part is made to a missing dimension and is thus positioned outside the thread of the screw and will not be positioned in the threaded area. The lubricating effect is in this case achieved by a relative pivoting movement of the solid parts in the grooves.

Self-lubricating and maintenance free actuators require lubrication as an integral element of the original screw or nut material. At any time in the future, no additional lubrication is necessary, regardless of the life of the actuator. To achieve true self-lubrication, lubrication cannot be added. The actuator cannot be damaged until its design life. Thus, the lubrication must remain part of the actuator throughout its life without requiring external maintenance.

Disclosure of Invention

This and other objects of the present invention are to seek ways to improve self-lubricating linear actuators.

According to the present invention, these objects are achieved by a method for operating a nut for a linear actuator characterized by the features of independent claim 1 or characterized by the steps of independent claim 8. Preferred embodiments are described in the dependent claims.

According to the invention, the nut of the screw-nut actuator comprises at least one elongated graphite member partially exposed in the threaded region of the nut. The elongated graphite elements are axially oriented with respect to the threaded bore of the nut. In one embodiment, the nut comprises a plurality of elongate graphite elements.

In one embodiment of the invention, the graphite element comprises solid graphite. In one embodiment, the nut includes a plurality of apertures into which the solid graphite rods are inserted and secured. In one embodiment, the orifice is filled with a composite comprising graphite. In one embodiment, the positioning and securing of the elongate graphite elements is performed prior to one or more thread operations. This causes the graphite to be exposed within the thread so that portions of the graphite element will become part of the thread itself.

Self-lubricating actuators are provided due to the continuous transfer of lubricating material to the engaging surfaces of the threads. This transfer process forms a graphite film onto the thread according to the invention. The graphite film provides lubrication of the screw threads and reduces friction over the length of the screw.

According to the invention, the exposed portion of the graphite element in the threaded region of the nut will provide lubrication of the meshing screw by a thin coating of graphite dust. The surface of the threaded wing of the screw will contact the threaded wing surface of the nut. While the screw is rotating, the surface of the screw thread will experience a contact path along the nut thread that partially contains the graphite regions. As a result of the rotation, small particles of graphite will flake off the exposed graphite areas and smear on the threads. Thus, the material of the nut and graphite rod will wear together during the life of the actuator.

In one embodiment of the invention, the bore containing graphite is made prior to machining the threaded bore. In one embodiment, the plurality of elongated graphite elements are arranged in a circular pattern, with a threaded hole machined in the center of the circular pattern. By sizing and exposing the graphite rod in the threaded area, many variations of the lubrication area can be constructed. The nut material may be any type of solid material, such as plastic or metal. Preferably, brass composite and stainless steel are used in order to achieve sufficient strength. Any type of thread profile may be used, such as trapezoidal and square profiles.

According to the invention, the elongated graphite element is positioned so that it becomes part of the nut thread to be machined. In one embodiment, the cross-section of the elongate graphite elements is greater than the depth of the thread. In this embodiment, the longitudinal portion of the graphite element will extend as a backstay through the entire nut. The other part will become part of the thread. In one embodiment, the elongate graphite elements are fixed by glue. However, if the graphite element becomes loose, it may also be held in place by the dorsal bone. In one embodiment of the invention, the diameter of the innermost portion of the contact graphite element is larger than the innermost diameter of the thread. This results in the innermost portion of the thread being continuously formed from the base material. The balance of lubrication and strength properties is therefore designed by selecting the location and cross-section of the elongate graphite elements.

The nut according to the invention can be used for both types of linear actuators. Thus, the nut of the present invention can be used in linear actuators having a rotary screw and linear actuators having a rotary nut.

In a first aspect of the invention, this object is achieved by an operating nut for a linear actuator, the operating nut comprising a threaded hole for receiving a screw, wherein the nut comprises at least one elongated graphite element partially exposed in a threaded area and constituting part of the thread. In one embodiment, the graphite elements are axially aligned in a circle around the threaded hole. In one embodiment, the graphite element comprises an impregnating oil. In one embodiment, the graphite element comprises a solid graphite rod. In one embodiment, the graphite element comprises a composite of graphite. In one embodiment, the threads of the nut comprise a trapezoidal form.

In a second aspect of the invention, the object is achieved by a method of manufacturing an operating nut for a linear actuator, wherein a nut body of a solid material is provided, a plurality of apertures are arranged in a circle around a predetermined threaded hole in the nut body such that the apertures will be partially exposed within the threaded hole of the predetermined hole, the apertures are filled with graphite, and the threaded hole is machined in the circle. Additionally, the method includes impregnating graphite with the oil.

Drawings

Other features and advantages of the present invention will become more readily apparent to those of ordinary skill in the art from the following detailed description, taken in conjunction with the accompanying drawings, in which:

figure 1 is a three-dimensional view of an operating nut according to the invention,

FIG. 2 is a body of the operating nut to be processed, an

Fig. 3 is a linear actuator comprising a nut according to the invention.

Detailed Description

An operating nut 1 for receiving a not shown screw of a linear actuator according to the invention is shown in fig. 1. In the embodiment shown, the nut comprises nine elongate graphite elements in the form of rods 3 surrounding the threaded holes 2. The nut further comprises a first actuator shoulder 4 and a second actuator shoulder 5 for translating movement. The graphite rod is disposed parallel to the threaded bore and such that a portion of the rod acts as a portion of the threads of the nut. Thus, portions of the graphite shank are exposed on either side of the thread ridge.

In one embodiment of the invention, the holes 7 are treated first. The hole has an inner diameter 2a, which inner diameter 2a will then become the inner diameter of the thread to be machined. The thread to be machined will include an outer diameter 2b, which in the embodiment shown is positioned midway into the graphite rod. The area between the inner diameter and the outer diameter will thus become the threaded area 9. When the thread is subsequently machined, the portion of the shank will thus become part of the thread itself. By making the graphite rod a threaded part, not only can adequate lubrication be achieved, but the other parts of the rod are used as the dorsal bone. Thus, the rod being processed will look like a toothed rack with teeth being part of the thread. All threaded portions of the rod will be held together by the dorsal bone.

Any position of the rod is possible according to the invention, as long as part of the rod is contained within the thread. In one embodiment of the invention, the imaginary circle 8 of the innermost part of the contact rod will be positioned between the internal thread diameter 2a and the external thread diameter 2 b.

The nut may have any number of threads. The axial length of the nut is determined by the strength of the nut material and the number of turns of the thread. Preferably, the nut comprises a single thread, for example six turns. The nut may include any number of elongated graphite elements. The graphite element may comprise a rod or pellet which is bonded to the body of the nut. The graphite elements may be 2-3 mm in diameter. Preferably, the diameter of the shank is greater than the depth of the thread. After the threaded hole is made, the elongated graphite element becomes part of the thread. The orifice for the graphite rod is arranged in a circle around the threaded hole to be machined. Holes with trapezoidal threads can be machined on the circular inside of the graphite element when the rod is firmly bonded to the nut. The position of the graphite element is selected such that a portion of the element is exposed within the thread. Both the nut body and the graphite rod are then processed through the same thread machining tool. What remains about each thread is a plurality of exposed graphite pellets.

The graphite may be impregnated with oil to achieve a film that adheres better to the surface but is not easily washed off. Thus, a thin coating of impregnated graphite will remain on the surfaces as the sliding surfaces of the nut and screw move in relative rotation. If the nut wears, the surface of the graphite will also wear at the same rate, thus providing and maintaining a graphite coating.

A linear actuator comprising a nut 1 according to the invention is shown in fig. 3. The nuts comprise a common shoulder 4 and are rotatably arranged on an actuator screw 6.

Although advantageous, the scope of the present invention is not limited by the embodiments presented, but may also include embodiments apparent to those of ordinary skill in the art. For example, a plastic nut may be used. The elongated graphite elements may be of any size and cross-section. Any number of threads may be used in the nut. For faster operation, two or three threads may be used. The graphite rod will always be exposed in each thread and constitute part of the thread. With the same effect, the elongate graphite elements can be positioned in the screw. Also, the machining of the threads may be performed before the insertion of the graphite elements.

Claims

1. Operating nut (1) for a linear actuator, said operating nut being composed of a solid material and comprising a threaded hole (7) for receiving a screw (6) in meshing engagement and at least one elongated graphite element (3), characterized in that the at least one elongated graphite element (3) is an integral element of the operating nut and constitutes a part of the meshing engagement, and in that the thread of the operating nut and the part of the elongated graphite element (3) form a single thread, wherein the at least one elongated graphite element (3) comprises a solid graphite rod which is fixed within an aperture axially aligned with the threaded hole (7) of the nut (1) and which is partly arranged in a threaded region (9) of the nut (1).

2. Operating nut according to claim 1, wherein at least one elongated graphite element (3) is positioned such that an imaginary circle (8) contacting its innermost part is located between the internal thread diameter (2a) and the external thread diameter (2b) of the operating nut.

3. Operating nut according to claim 1 or 2, wherein at least one elongated graphite element (3) contains impregnating oil.

4. Operating nut according to claim 1 or 2, wherein at least one elongated graphite element (3) comprises a composite containing graphite.

5. Linear actuator comprising a screw (6) and an operating nut (1) for the linear actuator, said operating nut being composed of a solid material and comprising a threaded hole (7) for receiving the screw (6) in meshing engagement and at least one elongated graphite element (3), characterized in that the at least one elongated graphite element (3) is an integral element of the operating nut and constitutes a part of the meshing engagement, and in that the thread of the operating nut and said part of the elongated graphite element (3) form a single thread, wherein the at least one elongated graphite element (3) comprises a solid graphite rod which is fixed in an aperture axially aligned with the threaded hole (7) of the nut (1) and which is arranged partly in a threaded region (9) of the nut (1).

6. A method of manufacturing an operating nut (1) for a linear actuator, said operating nut comprising a plurality of elongated graphite elements (3), characterized by providing a nut body of solid material, machining a plurality of axially aligned apertures in a circle (8) around a predetermined threaded hole (7) in the nut body, such that the apertures position parts in a threaded zone (9) to be machined, inserting the elongated graphite elements (3) into the apertures, and simultaneously machining the threaded hole of the nut and the graphite elements, thereby forming a continuous single thread with the threads of the operating nut and the parts of the elongated graphite elements (3).

7. The method of claim 6, further comprising impregnating the elongate graphite elements with oil.

8. Use of an operating nut according to any of claims 1-4 or a method according to any of claims 6-7 for providing a linear actuator for the switchgear industry.