Lead screw and lead screw nut assembly

Abstract

The present disclosure provides a screw rod and a screw rod nut assembly, the screw rod comprising: a screw rod body, the screw rod body comprising a threaded section, an outer surface of the threaded section sequentially provided from inside to outside with: a metal chromium base bonding layer, a tungsten carbide hardness support layer, and a DLC functional layer, the DLC functional layer being a diamond-like carbon coating layer; wherein a total thickness T1 of the metal chromium base bonding layer and the tungsten carbide hardness support layer is not less than 0.5 microns, and a thickness T2 of the DLC functional layer is not less than 1.5 microns. The screw rod nut assembly of the present disclosure comprises the above-mentioned screw rod.

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 transmission component, ball screws are used in the rear-wheel steering system of vehicles, and their performance directly affects the positioning accuracy, operating efficiency, and service life of the rear-wheel steering system. Traditional ball screws typically employ surface treatment processes such as chrome plating, nitriding, or phosphating to improve their surface hardness and wear resistance, but some shortcomings still exist in operation.

[0003] Firstly, while traditional surface treatment processes for lead screws can temporarily increase hardness, under long-term high-load, high-frequency reciprocating motion, the thread surface is prone to frictional wear, leading to increased clearance and consequently reduced transmission accuracy and shortened service life. Wear is particularly pronounced in critical load-bearing areas such as trapezoidal thread sections, directly impacting the reliability and stability of equipment operation.

[0004] Secondly, traditional lead screws have a high surface roughness. Under high-speed or high-load conditions, the fretting friction between the threaded pairs can easily cause vibration and noise, which can easily lead to NVH problems.

[0005] Equally important, traditional lead screws have a high coefficient of friction, resulting in significant energy loss during transmission. This is especially true in scenarios requiring long-term continuous operation, where the heat generation problem is significant, further limiting the improvement of transmission efficiency.

[0006] Finally, traditional lead screws rely on external lubricants to reduce friction, but lubricants are prone to failure under high temperature or high speed conditions and require regular maintenance and replacement, which increases the cost of product use.

[0007] These defects severely restrict the reliability of lead screws, and there is an urgent need for a lead screw solution that can simultaneously address the problems of friction, wear, transmission efficiency, and lubrication. Utility Model Content

[0008] This disclosure provides a lead screw and a lead screw nut assembly.

[0009] 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, a tungsten carbide hardness support layer and a DLC functional layer from the inside to the outside; wherein, the total thickness T1 of the chromium base bonding layer and the tungsten carbide hardness support layer is not less than 0.5 micrometers, and the thickness T2 of the DLC functional layer is not less than 1.5 micrometers.

[0010] According to one aspect of the technical solution disclosed herein, the lead screw solves the aforementioned problems of traditional lead screws through a multi-layer composite coating structure. Specifically, a chromium-based undercoat layer is directly attached to the surface of the threaded section substrate, significantly improving coating adhesion by utilizing the metallurgical bonding properties of chromium and the metal substrate; a tungsten carbide hardness support layer serves as an intermediate transition layer, buffering the contact stress between the balls and the threads through its high hardness, thus suppressing surface fatigue cracks caused by fretting wear; and a DLC functional layer, as the outermost layer, significantly reduces the sliding friction resistance between the threaded pairs through the low inherent friction coefficient of the diamond-like carbon structure, reducing energy loss and heat generation. The synergistic effect of these upper layers allows the thread surface to maintain a low wear rate under long-term high load and high-frequency reciprocating motion, effectively suppressing the problem of decreased transmission accuracy caused by increased mating clearance, while simultaneously reducing NVH (noise, vibration, and harshness) levels and decreasing dependence on lubricants, thereby extending the lead screw's service life and improving transmission efficiency.

[0011] According to at least one embodiment of the lead screw of the present disclosure, the ratio T1:T2 of the total thickness T1 of the chromium base bonding layer and the tungsten carbide hardness support layer to the thickness T2 of the DLC functional layer is 1:3±0.1.

[0012] In the technical solution of this embodiment, when T1:T2 is controlled within the range of 1:3±0.1, the tungsten carbide hardness support layer can effectively disperse the contact load transmitted by the DLC functional layer, avoid local stress concentration caused by the support layer being too thin or insufficient flexibility caused by the support layer being too thick, thereby reducing the risk of coating cracking. While ensuring that the DLC functional layer has sufficient thickness to exert low friction characteristics, the support layer provides stable mechanical support, further suppresses thread surface wear, and alleviates the problem of transmission accuracy decay caused by accelerated wear of traditional lead screws.

[0013] According to at least one embodiment of the lead screw of this disclosure, the ratio of T1 to T2 is 1:3.

[0014] In the technical solution of this embodiment, T1:T2 is precisely set to 1:3 (i.e., T1:T2=1:3). Under this ratio, the thickness of the support layer can not only adequately buffer the load impact, but also avoid excessively increasing the rigidity of the coating and reducing its flexibility and fatigue resistance.

[0015] 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 2:3±0.1.

[0016] In the technical solution of this embodiment, at this ratio, the metallic chromium layer provides sufficient interfacial diffusion depth to enhance adhesion, while the tungsten carbide layer retains sufficient thickness to bear the hardness support role, avoiding the increase in brittleness caused by excessive chromium layer thickness or the interface peeling caused by excessive thin chromium layer thickness.

[0017] 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 2:3.

[0018] In the technical solution of this embodiment, under the above ratio, the thickness of the chromium base bonding layer ensures reliable bonding with the substrate, and the tungsten carbide hardness support layer provides sufficient hardness to disperse contact stress. This effectively suppresses the fretting wear of the thread surface at the moment of start-up and stop, reduces surface damage caused by lubrication failure of traditional lead screws, thereby reducing NVH problems and extending the maintenance cycle.

[0019] According to at least one embodiment of the lead screw of the present disclosure, the thickness of the chromium base bonding layer is 0.2 to 0.4 micrometers, the thickness of the tungsten carbide hardness support layer is 0.3 to 0.6 micrometers, and the thickness of the DLC functional layer is 1.5 to 3.0 micrometers.

[0020] In the technical solution of this embodiment, the thickness range covers typical working condition requirements: the chromium layer thickness ensures a balance between adhesion and flexibility, the tungsten carbide layer thickness provides resistance to deformation, and the DLC functional layer thickness ensures the durability of low friction characteristics.

[0021] According to at least one embodiment of the lead screw of the present disclosure, the total thickness of the chromium base bonding layer, the tungsten carbide hardness support layer and the DLC functional layer is 2.0 to 4.0 micrometers.

[0022] In the technical solution of this embodiment, the total thickness range takes into account both wear resistance and stress control. A total thickness of 2.0 micrometers is suitable for light-load conditions, while 4.0 micrometers is suitable for heavy-load conditions. The wear depth and coating life are matched by adjusting the overall thickness.

[0023] 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. The end face of the journal is provided with a positioning stop perpendicular to the axis of the lead screw. A transition section is provided between the positioning stop 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, a tungsten carbide hardness support layer and a DLC functional layer from the inside to the outside.

[0024] 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; the positioning stop ensures assembly coaxiality, and the cylindrical journal provides a bearing installation reference; at the same time, the transition section is synchronously coated with a composite coating to avoid coating peeling caused by stress abrupt changes in the thread initiation area of ​​traditional lead screws.

[0025] 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.

[0026] In the technical solution of this embodiment, a multi-layer coated lead screw is applied to the rear wheel steering mechanism of a vehicle. The low friction characteristics of the DLC functional layer reduce steering resistance, and the high hardness of the tungsten carbide support layer resists steering load impact. This can reduce the energy loss caused by the high friction coefficient of traditional steering lead screws and improve steering response speed. At the same time, the wear resistance of the coating extends the maintenance-free cycle and solves the maintenance cost problem caused by the reliance on regular lubrication in traditional solutions.

[0027] According to at least one embodiment of the lead screw of the present disclosure, the threaded section is a trapezoidal threaded section.

[0028] In this embodiment, the larger contact area of ​​the trapezoidal thread distributes the load, and the DLC functional layer reduces side friction. For the easily worn side areas of the trapezoidal thread, the DLC layer effectively suppresses fretting wear, alleviating the problem of increased clearance caused by side wear in traditional trapezoidal lead screws, thereby maintaining the long-term positioning accuracy of the steering mechanism.

[0029] 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.

[0030] 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

[0031] The accompanying drawings illustrate exemplary embodiments of the present disclosure and, together with the description thereof, serve to explain the principles of the present disclosure. These drawings are included to provide a further understanding of the present disclosure and are incorporated in and constitute a part of this specification.

[0032] Figure 1 This is a schematic diagram of the lead screw according to one embodiment of the present disclosure.

[0033] Figure 2 yes Figure 1 Sectional view of section A.

[0034] Figure 3 This is a schematic diagram of a coating area according to one embodiment of the present disclosure.

[0035] Figure 4This is a schematic diagram of the layer structure of a coating according to one embodiment of the present disclosure.

[0036] Figure 5 This is a schematic diagram of a lead screw layer structure according to one embodiment of the present disclosure.

[0037] Figure 6 This is a schematic diagram of the wear curves of a lead screw coating and other materials under dry conditions according to one embodiment of the present disclosure.

[0038] Figure 7 This is a schematic diagram of the corrosion of a DLC functional layer and titanium nitride in a salt spray breath test according to one embodiment of the present disclosure.

[0039] The specific labels in the attached figures are as follows:

[0040] 100 lead screw body

[0041] 110 threaded section

[0042] 120 journal

[0043] 130 Positioning Stop

[0044] 140 Transition Section

[0045] 200 screw nut

[0046] 210 Spiral Through Hole

[0047] 220 flange

[0048] 230 Cylindrical shaft segment

[0049] 240 boss

[0050] 300 metallic chromium base adhesive layer

[0051] 400 tungsten carbide hardness support layer

[0052] 500 DLC Function Layer Detailed Implementation

[0053] The present disclosure will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the disclosure. Furthermore, it should be noted that, for ease of description, only the parts relevant to the present disclosure are shown in the accompanying drawings.

[0054] 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.

[0055] 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.

[0056] In existing technologies, ball screws are used in vehicle rear-wheel steering systems, and their performance affects many aspects of the system's performance. Traditional ball screws employ various surface treatment processes, but still have shortcomings: First, the thread surface is prone to wear under long-term high-load motion, especially in critical areas, affecting reliability and stability; second, the high surface roughness easily leads to NVH problems under high speed or high load; third, the high coefficient of friction results in significant energy loss, and heat generation limits the improvement of transmission efficiency; fourth, they rely on external lubricants, are prone to failure under high temperature or high speed, and require regular maintenance and replacement, increasing operating costs.

[0057] To address the aforementioned technical problems, this embodiment provides a lead screw that can be used in the steering mechanism of the rear wheels of a vehicle.

[0058] Figure 1 This is a schematic diagram of the lead screw according to one embodiment of the present disclosure. Figure 2 yes Figure 1 Sectional view of section A in the middle. Figure 3 This is a schematic diagram of a coating area according to one embodiment of the present disclosure. Figure 4 This is a schematic diagram of the layer structure of a coating according to one embodiment of the present disclosure. Figure 5 This is a schematic diagram of a lead screw layer structure according to one embodiment of the present disclosure.

[0059] See Figures 1 to 5 As shown, the lead screw in this embodiment includes a lead screw body 100, and the lead screw body 100 includes a threaded section 110, which is a trapezoidal threaded section used to cooperate with the lead screw nut 200.

[0060] like Figure 4 and Figure 5 As shown, the outer surface of the threaded section 110 is provided with a DLC composite coating, which consists of a chromium base bonding layer 300, a tungsten carbide hardness support layer 400, and a DLC functional layer 500 arranged sequentially from the inside to the outside.

[0061] The chromium-based undercoat layer 300 is a chromium layer directly deposited on the surface of the lead screw thread section 110 substrate. As the innermost layer of the composite coating system, it serves as the interface bonding layer. The tungsten carbide hardness support layer 400 is a tungsten carbide layer deposited on the surface of the chromium-based undercoat layer 300. As the intermediate layer of the composite coating system, it provides mechanical support. The DLC functional layer 500 is a diamond-like carbon coating, such as hydrogen-containing amorphous carbon (aC:H), deposited on the surface of the tungsten carbide hardness support layer 400. As the outermost layer of the composite coating system, it directly contacts the lead screw nut 200 and performs the core functions of reducing friction and inhibiting wear.

[0062] Understandably, the carbon atoms within the DLC functional layer 500 exist in a hybrid form of SP² (graphite bonds) and SP³ (diamond bonds), with SP² bonds accounting for approximately 55%–65%, SP³ bonds for approximately 25%–35%, and hydrogen content for approximately 5%–15%. This structure allows the coating to possess both the lubricity of graphite and the hardness of diamond—SP² bonds form layered slip surfaces, generating a self-lubricating effect during friction; SP³ bonds provide high hardness support, resisting contact stress. In other words, a higher proportion of SP³ bonds results in a harder DLC functional layer 500 but poorer lubricity; conversely, a higher proportion of SP² bonds results in a lower hardness but better lubricity. A standard functional layer typically contains approximately 60% SP² bonds, 30% SP³ bonds, and 10% hydrogen.

[0063] The total thickness T1 of the chromium base adhesive layer 300 and the tungsten carbide hardness support layer 400 is not less than 0.5 micrometers, and the thickness T2 of the DLC functional layer 500 is not less than 1.5 micrometers.

[0064] For example, a chromium-based underlay bonding layer 300 is formed on the surface of the threaded section 110 using a physical vapor deposition (PVD) process, with a thickness t1 of 0.2 micrometers. A tungsten carbide hardness support layer 400 is formed on the surface of the chromium-based underlay bonding layer 300 using a plasma-assisted chemical vapor deposition (PACVD) process, with a thickness t2 of 0.3 micrometers. A DLC functional layer 500 is formed on the surface of the tungsten carbide hardness support layer 400 using unbalanced magnetron sputtering technology, with a thickness of 1.5 micrometers. The total thickness T1 of the chromium-based underlay bonding layer 300 and the tungsten carbide hardness support layer 400 is 0.5 micrometers, and the thickness T2 of the DLC functional layer 500 is 1.5 micrometers.

[0065] In some implementations, T1:T2 = 1:3, t1:t2 = 2:3. When the total thickness of the chromium base adhesive layer 300, the tungsten carbide hardness support layer 400, and the DLC functional layer 500 increases, the thickness of each coating layer can be increased in the above proportions. For example, when the total thickness of the chromium base adhesive layer 300, the tungsten carbide hardness support layer 400, and the DLC functional layer 500 is 4 micrometers, t1 is 0.4 micrometers, t2 is 0.6 micrometers, T1 is 1 micrometer, and T2 is 3 micrometers. The lead screw adapts to the usage requirements of different working conditions by adjusting the thickness of each coating layer.

[0066] Understandably, in actual production, the ratio of T1:T2 is approximately 1:3, with some deviation possible, ranging from ±0.1. That is, a thickness ratio of 1:3 ±0.1 means the thickness of the chromium layer : the thickness of the tungsten carbide layer = (1):(3 ±0.1), i.e., a ratio range of 1:2.9 to 1:3.1. Similarly, the ratio of t1:t2 is approximately 2:3, which may also have some deviation, ranging from ±0.1.

[0067] See Figures 1 to 3 As shown, in some embodiments, cylindrical journals 120 are provided at both ends of the lead screw body 100. The end face of the journal 120 is machined with a locating stop 130 perpendicular to the lead screw axis. A transition section 140 is provided between the locating stop 130 and the trapezoidal threaded section 110. The outer diameter of the transition section 140 gradually increases from the journal 120 towards the threaded section 110, forming a certain taper angle. The outer surface of the transition section 140 is also covered with the same DLC composite coating as the threaded section 110, such as... Figure 3 As shown in the figure, the area within the dashed box represents the area covered by the DLC composite coating on the lead screw body 100.

[0068] Figure 6 This is a schematic diagram of the wear curves of a lead screw coating and other materials under dry conditions according to one embodiment of the present disclosure.

[0069] like Figure 6 As shown, the DLC composite coating disclosed herein has a lower coefficient of friction than other materials (such as uncoated bearing steel, hard chrome, nitrided alloy steel, electroplated nickel, copper alloy, nickel alloy Teflon and other DLC materials), with almost no wear, no scratches and cold welding, and its coefficient of friction changes significantly less with test time than other materials, and its performance is reliable.

[0070] Figure 7 This is a schematic diagram of the corrosion of a DLC functional layer and titanium nitride in a salt spray breath test according to one embodiment of the present disclosure.

[0071] like Figure 7As shown, the DLC functional layer 500 has stronger corrosion resistance than titanium nitride. Therefore, the lead screw with the DLC functional layer 500 has better corrosion resistance than the traditional lead screw.

[0072] The above technical solution addresses the core problem of traditional lead screws under high-load conditions through a multi-layer composite coating structure. Specifically, a chromium-based adhesive layer 300 is directly attached to the surface of the thread section 110 substrate. Utilizing the metallurgical bonding properties of chromium with the metal substrate, it significantly improves coating adhesion, avoiding the peeling defects of traditional chromium plating or nitriding layers during reciprocating motion. A tungsten carbide hardness support layer 400 serves as an intermediate transition layer, using its high hardness to buffer the contact stress between the balls and the threads, suppressing surface fatigue cracks caused by fretting wear. The outermost layer, the DLC functional layer 500, significantly reduces the sliding friction resistance between the threaded pairs through its low inherent friction coefficient of diamond-like carbon structure, reducing energy loss and heat generation. The synergistic effect of these layers maintains a low wear rate on the thread surface during long-term high-load, high-frequency reciprocating motion, effectively suppressing the decrease in transmission accuracy caused by increased clearance, while also reducing NVH levels and dependence on lubricants, thereby extending the lead screw's service life and improving transmission efficiency.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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; Tungsten carbide hardness support layer; as well as DLC functional layer, wherein the DLC functional layer is a diamond-like carbon coating; The total thickness T1 of the chromium base adhesive layer and the tungsten carbide hardness support layer is not less than 0.5 micrometers, and the thickness T2 of the DLC functional layer is not less than 1.5 micrometers.

2. The lead screw according to claim 1, characterized in that, The ratio of T1:T2 is 1:3±0.

1.

3. The lead screw according to claim 2, characterized in that, The ratio of T1 to T2 is 1:

3.

4. 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 2:3±0.

1.

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

3.

6. The lead screw according to claim 1, characterized in that, The thickness of the chromium base adhesive layer is 0.2 to 0.4 micrometers, the thickness of the tungsten carbide hardness support layer is 0.3 to 0.6 micrometers, and the thickness of the DLC functional layer is 1.5 to 3.0 micrometers.

7. The lead screw according to claim 1, characterized in that, The total thickness of the chromium base bonding layer, the tungsten carbide hardness support layer, and the DLC functional layer is 2.0–4.0 micrometers.

8. 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. The end face of the journal is provided with a positioning stop perpendicular to the axis of the lead screw. A transition section is provided between the positioning stop 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, from the inside out, a chromium base bonding layer, a tungsten carbide hardness support layer, and a DLC functional layer.

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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