Lead screw and lead screw nut assembly

Abstract

The present disclosure provides a lead screw and a lead screw nut assembly, the lead screw comprising: a lead screw body comprising a threaded segment, an outer surface of the threaded segment sequentially provided from inside to outside with: a metal chromium base bonding layer, and a tungsten carbide hardness support layer; wherein a thickness ratio of the metal chromium base bonding layer and the tungsten carbide hardness support layer is 1:3±0.1. The lead screw nut assembly comprises the above-mentioned lead screw and a nut threadedly connected to the threaded segment.

Description

Technical Field

[0001] This disclosure relates to a lead screw and lead screw nut assembly, belonging to the field of transmission component technology. Background Technology

[0002] As a core transmission component for precision linear motion, the surface properties of the threaded section of the lead screw directly determine the positioning accuracy, service life, and operational reliability of the equipment. Currently, traditional lead screws widely used in industry, such as uncoated carbon steel / alloy steel lead screws and hard chrome plated lead screws, have the following problems in practical applications:

[0003] First, traditional lead screws have a high coefficient of friction and are highly dependent on lubrication. The contact interface between the threaded section of a traditional lead screw and the balls or nuts is a direct metal-to-metal contact, resulting in a high coefficient of friction. To maintain normal operation, continuous grease or oil mist lubrication is necessary.

[0004] Secondly, the insufficient wear resistance of traditional lead screws leads to rapid accuracy degradation. The thread flank is prone to wear under alternating loads, resulting in accumulated lead errors that exceed tolerances and significantly increasing the total life cycle cost. Utility Model Content

[0005] This disclosure provides a lead screw and a lead screw nut assembly.

[0006] According to one aspect of this disclosure, a lead screw is provided, including a lead screw body, the lead screw body including a threaded section, and the outer surface of the threaded section being provided with a chromium base bonding layer and a tungsten carbide hardness support layer from the inside to the outside; wherein the thickness ratio of the chromium base bonding layer to the tungsten carbide hardness support layer is 1:3±0.1.

[0007] According to one aspect of the technical solution of this disclosure, a lead screw solves the defects of traditional lead screws by constructing a coating structure on the surface of the thread section with a thickness ratio of 1:3±0.1 for a double-layer chromium base bonding layer and a tungsten carbide hardness support layer. The chromium base bonding layer acts as a transition layer, forming a metallurgical bond with the lead screw body, improving the bonding strength between the coating and the substrate. The tungsten carbide hardness support layer enhances the wear resistance of the coating through tungsten carbide particles, slowing down the wear of the thread flank under alternating loads, delaying the accumulation of lead error, and thus extending the lead screw's accuracy retention period. Simultaneously, the tungsten carbide hardness support layer has a low coefficient of friction, reducing reliance on continuous grease / oil mist lubrication.

[0008] According to at least one embodiment of the lead screw of this disclosure, the thickness ratio of the chromium base bonding layer to the tungsten carbide hardness support layer is 1:3.

[0009] In the technical solution of this embodiment, the thickness ratio is an optimized ratio verified by experiments: the chromium base bonding layer provides sufficient interfacial bonding force, while the tungsten carbide hardness support layer achieves the best balance between wear resistance and flexibility.

[0010] According to at least one embodiment of the lead screw of the present disclosure, the thickness of the chromium base bonding layer is 0.5 micrometers, and the thickness of the tungsten carbide hardness support layer is 1.5 micrometers.

[0011] In the technical solution of this embodiment, this thickness combination is suitable for light load and high precision scenarios. The 0.5-micron chromium base bonding layer can effectively match the thermal expansion coefficient of the substrate and avoid interface stress concentration; the 1.5-micron tungsten carbide hardness support layer ensures wear resistance while maintaining the flexibility of the coating.

[0012] According to at least one embodiment of the lead screw of the present disclosure, the thickness of the chromium base bonding layer is 1 micrometer, and the thickness of the tungsten carbide hardness support layer is 3 micrometers.

[0013] In the technical solution of this embodiment, the thickness combination is designed for heavy-load conditions. The 1-micron chromium base bonding layer can enhance the interfacial bonding strength, while the 3-micron tungsten carbide hardness support layer provides a longer wear tolerance, slows down the wear rate of the thread profile height, extends the accuracy retention time of the lead screw under heavy alternating loads, and reduces the maintenance frequency caused by wear.

[0014] According to at least one embodiment of the lead screw of this disclosure, the total thickness of the chromium base bonding layer and the tungsten carbide hardness support layer is 2 to 4 micrometers.

[0015] In the technical solution of this embodiment, the functionality and reliability of the coating are balanced by thickness control. If it is too thin, the wear resistance will be insufficient, and if it is too thick, the internal stress will increase and it will be easy to peel off. This range ensures that the coating maintains structural integrity in various applications.

[0016] According to at least one embodiment of the lead screw of the present disclosure, the threaded section is located in the middle of the lead screw body, and cylindrical journals are provided at both ends of the lead screw. A transition section is provided between the journals and the threaded section, and the outer diameter of the transition section gradually increases in the direction toward the threaded section. The outer surface of the transition section is provided with a chromium base bonding layer and a tungsten carbide hardness support layer from the inside to the outside.

[0017] In the technical solution of this embodiment, the tapered structure of the transition section smoothly connects the journal and the threaded section, reducing stress concentration. At the same time, the transition section is simultaneously coated with a composite coating to avoid coating peeling caused by stress abrupt changes in the thread initiation area of ​​traditional lead screws.

[0018] According to at least one embodiment of the lead screw of the present disclosure, the journal end face is provided with a positioning stop perpendicular to the lead screw axis, and the transition section is located between the positioning stop and the threaded section.

[0019] In the technical solution of this embodiment, the positioning stop ensures the coaxiality of the assembly, the cylindrical journal provides the bearing mounting reference, and by extending the coating to the transition section, continuous protection is formed from the adjacent area of ​​the positioning stop to the threaded section.

[0020] According to at least one embodiment of the lead screw of the present disclosure, the chromium base bonding layer and the tungsten carbide hardness support layer are sequentially disposed on the outer surface of the thread section by magnetron sputtering.

[0021] In the technical solution of this embodiment, the magnetron sputtering process uniformly embeds chromium atoms and tungsten carbide particles into the diamond-like carbon network during the deposition process, ensuring that a functional layer with uniform thickness is obtained on the threaded curved surface, avoiding the problem of uneven thickness of traditional coatings on complex curved surfaces.

[0022] A lead screw according to at least one embodiment of the present disclosure is used for a steering mechanism of the rear wheels of a vehicle.

[0023] In the technical solution of this embodiment, by applying this coating, the frictional resistance during the steering process is reduced and the steering feel is improved; at the same time, the wear of the threaded section under dry friction conditions is reduced, and the maintenance-free cycle of the steering mechanism is extended, which is suitable for vehicle scenarios that require frequent steering.

[0024] According to at least one embodiment of the lead screw of the present disclosure, the threaded section is a trapezoidal threaded section.

[0025] In the technical solution of this embodiment, for the easily worn side area of ​​the trapezoidal thread, the composite coating can alleviate the problem of increased mating clearance caused by side wear of the traditional trapezoidal screw, thereby maintaining the long-term positioning accuracy of the steering mechanism.

[0026] According to another aspect of this disclosure, a lead screw and nut assembly is provided, including the lead screw described above, and a nut threadedly connected to the threaded section. The nut has a helical through hole at its center that is adapted to the threaded section. One end of the nut is provided with a flange, and the other end of the nut is provided with a cylindrical shaft section. A boss is provided on the side of the cylindrical shaft section near the flange.

[0027] According to one aspect of the technical solution of this disclosure, the lead screw and nut assembly converts rotational force into linear thrust by engaging the screw with the thread of the internal helical through hole of the nut through the rotational motion of the lead screw; the flange at one end of the nut connects to the load, drives the load to move and prevents the nut from rotating, and the boss at the other end can be used to constrain the movement of the nut, thereby realizing precise and reliable linear reciprocating motion. Attached Figure Description

[0028] The accompanying drawings illustrate exemplary embodiments of the present disclosure and, together with the description thereof, are used to explain the principles of the present disclosure. The drawings are included to provide a further understanding of the present disclosure and are incorporated in this specification and form a part of this specification.

[0029] Figure 1 It is a schematic structural view of a lead screw according to an embodiment of the present disclosure.

[0030] Figure 2 is Figure 1 a cross-sectional view of section A in

[0031] Figure 3 It is a schematic view of a coating area according to an embodiment of the present disclosure.

[0032] Figure 4 It is a schematic view of the layer structure of a coating according to an embodiment of the present disclosure.

[0033] Figure 5 It is a schematic view of the layer structure of a lead screw according to an embodiment of the present disclosure.

[0034] In the figure, the specific reference numerals are as follows:

[0035] 100 Lead screw body

[0036] 110 Thread section

[0037] 120 Journal

[0038] 130 Positioning stop

[0039] 140 Transition section

[0040] 200 Lead screw nut

[0041] 210 Helical through-hole

[0042] 220 Flange

[0043] 230 Cylindrical shaft section

[0044] 240 Boss

[0045] 300 Metal chromium primer bonding layer

[0046] 400 Tungsten carbide hardness support layer Detailed embodiments

[0047] The present disclosure will be further described in detail below in conjunction with the accompanying drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the relevant content and do not limit the present disclosure. Additionally, it should be noted that for the sake of convenience of description, only the parts related to the present disclosure are shown in the drawings.

[0048] It should be noted that, where there is no conflict, the embodiments and features described in this disclosure can be combined with each other. The technical solutions of this disclosure will now be described in detail with reference to the accompanying drawings and embodiments.

[0049] Unless otherwise stated, the exemplary implementations / embodiments shown are to be understood as providing exemplary features of various details that provide ways in which the technical concepts of this disclosure can be implemented in practice. Therefore, unless otherwise stated, the features of various implementations / embodiments may be additionally combined, separated, interchanged and / or rearranged without departing from the technical concepts of this disclosure.

[0050] Traditional lead screws suffer from high friction coefficients and strong lubrication dependence, as well as insufficient wear resistance leading to rapid accuracy decay.

[0051] To address the aforementioned technical problems, this embodiment provides a lead screw.

[0052] The lead screw in this embodiment includes a lead screw body 100, which includes a threaded section 110. The threaded section 110 is a trapezoidal threaded section used to cooperate with the lead screw nut 200.

[0053] The outer surface of the threaded section 110 is provided with a composite coating, namely, a chromium base bonding layer 300 and a tungsten carbide hardness support layer 400 are provided from the inside to the outside.

[0054] Among them, the chromium base bonding layer 300 refers to the chromium layer directly deposited on the surface of the threaded section 110 substrate of the lead screw body 100. As the innermost layer of the composite coating system, it undertakes the function of interface bonding. The tungsten carbide hardness support layer 400 refers to the tungsten carbide layer deposited on the surface of the chromium base bonding layer 300. It is also the outermost layer of the composite coating and is in direct contact with the lead screw nut 200. It undertakes the core function of reducing friction and inhibiting wear.

[0055] Understandably, the tungsten carbide hardness support layer 400 is made of tungsten carbide. Tungsten carbide (WC) is a typical high-hardness material (typically reaching HV1500-2500), far exceeding common substrates (such as steel, HV200-600). During friction, high hardness means its surface is less prone to plastic deformation. According to the "actual contact area theory" in tribology, when the hardness difference between two contact surfaces is large, the surface of the softer material will preferentially undergo plastic deformation, and the actual contact area is mainly determined by the deformation of the softer material. The high hardness of tungsten carbide makes it a "hard support," limiting the plastic deformation of the mating materials (such as the lead screw and nut 200), thereby significantly reducing the actual contact area. The reduction in contact area directly reduces frictional resistance (frictional force is positively correlated with contact area), achieving a low-friction effect.

[0056] Meanwhile, tungsten carbide exhibits a low inherent coefficient of friction (typically in the range of 0.1-0.3) when paired with common metals such as steel. This characteristic stems from the crystal structure of tungsten carbide (hexagonal close-packed or face-centered cubic structure) and its chemical bonding characteristics (a mixture of covalent and metallic bonds), resulting in weak interatomic interactions between the tungsten carbide and the paired material, thus reducing adhesive friction during the friction process. Furthermore, the low surface energy of tungsten carbide also inhibits the adsorption of organic matter (such as lubricating oil decomposition products) or wear particles during friction, further maintaining a low-friction state.

[0057] Tungsten carbide's high wear resistance inhibits wear through the following mechanisms: First, its high hardness reduces the tendency of mating materials to transfer to the tungsten carbide surface (adhesive wear is primarily characterized by material transfer), while its chemical inertness (it does not readily react with oxygen, water, etc.) reduces oxidative or corrosive wear. Second, even in the presence of small, hard particles at the friction interface (such as dust from the environment or wear debris), tungsten carbide's high hardness (far exceeding that of common abrasive particles like SiO2 and Fe2O3) effectively resists the cutting action of these particles, preventing surface ploughing or scratching. Equally important, its high hardness and high elastic modulus make the tungsten carbide layer less prone to fatigue cracking under cyclic stress, suppressing wear caused by surface fatigue spalling.

[0058] Tungsten carbide coatings are typically prepared using processes such as physical vapor deposition (PVD) or chemical vapor deposition (CVD), resulting in low surface roughness (Ra can reach below 0.1 μm), reducing frictional resistance caused by microscopic unevenness. Simultaneously, its high density (extremely low porosity) prevents the penetration of corrosive media or abrasive particles, maintaining long-term surface integrity. Furthermore, the chromium undercoat 300 ensures strong adhesion between the tungsten carbide layer and the substrate (chromium has excellent metallurgical bonding capabilities with both steel and tungsten carbide), preventing a sharp drop in frictional performance due to coating peeling.

[0059] To improve coating uniformity, a chromium undercoat bonding layer 300 and a tungsten carbide hardness support layer 400 are sequentially deposited on the outer surface of the threaded section 110 using magnetron sputtering. During the deposition process, the magnetron sputtering process allows chromium atoms and tungsten carbide particles to be uniformly embedded in the diamond-like carbon network, ensuring a functional layer of uniform thickness on the threaded surface and avoiding the uneven thickness problem of traditional coatings on complex curved surfaces.

[0060] In this embodiment, the thickness ratio of the chromium base bonding layer 300 to the tungsten carbide hardness support layer 400 is approximately 1:3, with a deviation range of about ±0.1. That is, the thickness ratio of 1:3±0.1 means that the thickness of the chromium layer is equal to the thickness of the tungsten carbide layer (1):(3±0.1), which is a ratio range of 1:2.9 to 1:3.1. The lead screw solves the defects of traditional lead screws by constructing a double-layer coating structure with a thickness ratio of 1:3±0.1 between the chromium base bonding layer 300 and the tungsten carbide hardness support layer 400 on the surface of the thread section 110. Among them, the chromium base bonding layer 300 serves as a transition layer, forming a metallurgical bond with the lead screw body 100, thereby enhancing the bonding strength between the coating and the substrate; the tungsten carbide hardness support layer 400 enhances the wear resistance of the coating through tungsten carbide particles, slows down the wear of the thread flank under alternating loads, delays the accumulation of lead error, and thus extends the lead screw accuracy retention period; at the same time, the tungsten carbide hardness support layer 400 has a low coefficient of friction, reducing the dependence on continuous grease / oil mist lubrication.

[0061] In some embodiments, the thickness ratio of the chromium base adhesive layer 300 to the tungsten carbide hardness support layer 400 is 1:3. This thickness ratio is an optimized proportion that has been experimentally verified: the chromium base adhesive layer 300 provides sufficient interfacial bonding force, while the tungsten carbide hardness support layer 400 achieves a balance between wear resistance and flexibility.

[0062] For example, the thickness of the chromium base adhesive layer 300 is 0.5 micrometers, and the thickness of the tungsten carbide hardness support layer 400 is 1.5 micrometers. This thickness combination is suitable for light-load, high-precision applications. The 0.5-micrometer chromium base adhesive layer 300 effectively matches the thermal expansion coefficient of the substrate, avoiding interface stress concentration; the 1.5-micrometer tungsten carbide hardness support layer 400 maintains the coating's flexibility while ensuring wear resistance.

[0063] For example, to adapt to heavy-load conditions, the lead screw has a 1-micron thick chromium underlay bonding layer 300 and a 3-micron thick tungsten carbide hardness support layer 400. The 1-micron chromium underlay bonding layer 300 strengthens the interfacial bonding strength, while the 3-micron tungsten carbide hardness support layer 400 provides longer wear tolerance, slows down the thread profile wear rate, extends the accuracy retention time of the lead screw under heavy alternating loads, and reduces the maintenance frequency caused by wear.

[0064] It is understandable that as the total thickness of the composite coating increases, the thickness of each individual coating can increase in the same proportion as described above.

[0065] For example, the total thickness of the chromium base bonding layer 300 and the tungsten carbide hardness support layer 400 is 2 to 4 micrometers. Since the coating is too thin, its wear resistance is insufficient, and it is too thick, its internal stress increases and it is prone to peeling. The composite coating balances its functionality and reliability through thickness control. This range allows the composite coating to maintain structural integrity under various working conditions.

[0066] In some embodiments, the threaded section 110 is located in the middle of the lead screw body 100, and cylindrical journals 120 are provided at both ends of the lead screw. A transition section 140 is provided between the journals 120 and the threaded section 110, and the outer diameter of the transition section 140 gradually increases in the direction toward the threaded section 110. The outer surface of the transition section 140 is provided with a chromium base bonding layer 300 and a tungsten carbide hardness support layer 400 from the inside to the outside. The journals 120 are used to connect the bearings, and the tapered structure of the transition section 140 smoothly connects the journals 120 and the threaded section 110, reducing stress concentration. At the same time, the transition section 140 is simultaneously provided with a composite coating to avoid coating peeling caused by stress abrupt changes in the thread initiation area of ​​traditional lead screws.

[0067] Furthermore, the journal 120 end face is provided with a locating stop 130 perpendicular to the lead screw axis, and a transition section 140 is located between the locating stop 130 and the threaded section 110. The locating stop 130 ensures assembly coaxiality, the cylindrical journal 120 provides a bearing mounting reference, and by extending the coating to the transition section 140, continuous protection is formed from the adjacent area of ​​the locating stop 130 to the threaded section 110.

[0068] The aforementioned threaded section 110 is a trapezoidal threaded section. The tooth angle (30°) of the trapezoidal thread generates a large lateral force during sliding. The composite coating can alleviate the problem of increased fit clearance caused by lateral wear in traditional trapezoidal lead screws, thereby maintaining the long-term accuracy of the lead screw nut 200 assembly.

[0069] This embodiment provides a lead screw and nut assembly, including the aforementioned lead screw and a nut 200 threadedly connected to a threaded section 110. The nut 200 has a helical through-hole 210 at its center, adapted to the threaded section. One end of the nut 200 has a flange 220, and the other end has a cylindrical shaft section 230. A boss 240 is provided on the side of the cylindrical shaft section 230 near the flange 220. This lead screw and nut assembly converts rotational force into linear thrust through the rotational movement of the lead screw body 100 engaging with the thread of the helical through-hole 210 inside the nut 200. The flange 220 connects to the load, moving the load and preventing its own rotation. The boss 240 at the other end can constrain the travel of the nut 200, thereby achieving precise and reliable linear reciprocating motion.

[0070] This embodiment provides a vehicle steering mechanism, such as a rear wheel steering mechanism, which includes the lead screw and nut assembly described in the above embodiment. By using the lead screw, the steering mechanism can reduce frictional resistance during steering and improve steering feel; at the same time, it reduces wear on the threaded section 110, extends the maintenance-free cycle of the steering mechanism, and is suitable for vehicle scenarios requiring frequent steering.

[0071] In the description of this specification, the references to terms such as "one embodiment / mode," "some embodiments / modes," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment / mode or example is included in at least one embodiment / mode or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment / mode or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments / modes or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments / modes or examples described in this specification, as well as the features of different embodiments / modes or examples.

[0072] Those skilled in the art should understand that the above embodiments are merely for illustrating the present disclosure and are not intended to limit the scope of the disclosure. Those skilled in the art can make other changes or modifications based on the above disclosure, and these changes or modifications still fall within the scope of the present disclosure.

Claims

1. A lead screw, characterized in that, include: The lead screw body includes a threaded section, and the outer surface of the threaded section is provided with the following from the inside to the outside: Chromium-based adhesive layer; as well as Tungsten carbide hardness support layer; The thickness ratio of the chromium base adhesive layer to the tungsten carbide hardness support layer is 1:3±0.

1.

2. The lead screw according to claim 1, characterized in that, The thickness ratio of the chromium base adhesive layer to the tungsten carbide hardness support layer is 1:

3.

3. The lead screw according to claim 1, characterized in that, The thickness of the chromium base adhesive layer is 0.5 micrometers, and the thickness of the tungsten carbide hardness support layer is 1.5 micrometers.

4. The lead screw according to claim 1, characterized in that, The thickness of the chromium base adhesive layer is 1 micrometer, and the thickness of the tungsten carbide hardness support layer is 3 micrometers.

5. The lead screw according to claim 1, characterized in that, The total thickness of the chromium base adhesive layer and the tungsten carbide hardness support layer is 2 to 4 micrometers.

6. The lead screw according to claim 1, characterized in that, The threaded section is located in the middle of the lead screw body. The two ends of the lead screw are provided with cylindrical journals. A transition section is provided between the journals and the threaded section. The outer diameter of the transition section gradually increases in the direction toward the threaded section. The outer surface of the transition section is provided with a chromium base bonding layer and a tungsten carbide hardness support layer from the inside to the outside.

7. The lead screw according to claim 6, characterized in that, The journal end face is provided with a positioning stop perpendicular to the lead screw axis, and the transition section is located between the positioning stop and the threaded section.

8. The lead screw according to claim 1, characterized in that, The chromium base bonding layer and the tungsten carbide hardness support layer are sequentially deposited on the outer surface of the threaded section by magnetron sputtering.

9. The lead screw according to claim 1, characterized in that, The threaded section is a trapezoidal threaded section.

10. A lead screw and nut assembly, characterized in that, The screw includes any one of claims 1 to 9, and further includes a nut threaded to the threaded section, wherein the nut has a helical through hole at its center that is adapted to the threaded section, one end of the nut has a flange, and the other end of the nut has a cylindrical shaft section, wherein the cylindrical shaft section has a boss on the side near the flange.

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