Electromechanical actuator
By using steel materials and processing techniques of specific components, threaded spindles and planetary parts with martensite precipitation and strain hardening are formed, which solves the wear problem of screw drivers in the prior art, and improves wear resistance and machinery under impact loads. strength.
Patent Information
- Application Number
- CN202380045384.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2023-07-07
- Filing Date
- 2023-07-10
- Publication Date
- 2025-01-03
AI Technical Summary
There are problems with screw drivers in existing electromechanical actuators in wear, and it is difficult to effectively solve the wear resistance requirements under impact or impact loads.
Steel materials with specific compositions are used (C: 0.4% to 1.5%, Mn: 12.0% to 22.0%, Cr: 4.0%, Ni: 0.5%, Cu: 0.3%, V: 0.3%, S: 0.3%, P : 0.1%, Si: 4.0%, Al: 0.05%, the rest are iron and impurities) planetary rolling screw driver, forming threaded spindles and planetary parts through martensite precipitation and strain hardening, combining stretching and heat treatment technology, Improve material wear resistance.
High wear resistance under impact or impact loads is achieved, the mechanical strength and surface hardness of threaded spindles and planetary parts are significantly improved, and can withstand large axial forces and extend the service life of the equipment.
Smart Images
Figure CN119256107A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to an electromechanical actuator having a screw drive and a threaded spindle. Background Art
[0002] WO 2012 / 048917 A1 discloses a tempered steel and its use as a rod material, in particular for producing threaded spindles. WO 2012 / 048917 A1 assumes that the material Cf53 is a widely used steel suitable for surface hardening or edge hardening and can be used in particular for producing screws, worms, gears, shafts or spindles. The composition of the steel Cf53 is suitable for producing a fully load-bearing martensitic hardened surface layer in terms of rolling bearing technology.
[0003] Based on this, WO 2012 / 048917 A1 describes a further developed tempered steel Cf53B, with which a hardening portion (600 HV) of between 4 mm and 6 mm measured from an end face of a case hardened specimen can be achieved. The structure in the core generally comprises a mixture of pearlite and ferrite. The tempered steel according to WO 2012 / 048917 A1 comprises, among other things, 0.0031% to 0.005% boron and at least 3.5 parts of titanium per part of nitrogen. The tempered steel Cf53B is particularly suitable for the production of threaded spindles for ball screw drives.
[0004] A ball screw drive known from DE 10 2017 121 942 A1, which is intended for use in a brake booster, has a threaded nut made of a martensitic hardened steel which does not rust in the presence of brake fluid. The steel comprises at least 12% by weight of chromium. In addition, the steel may comprise, among other things, 0.4% to 1.3% of carbon, up to 2% of silicon, up to 2% of manganese and up to 2% of molybdenum. In particular, this may be a steel with material number 1.4108. DE 10 2017 121 942 A1 specifies that the achievable hardness of the threaded nut is 55 HRC.
[0005] EP 2 832 876 A1 describes a high-strength stainless steel wire which is said to have excellent heat deformation resistance. The steel wire is particularly suitable for producing high-strength springs. The springs are made of cast steel, wherein the deformation-induced martensite formation index must be within a specified range. The matrix of the steel wire forming the high-strength spring may include NiAl-based composite particles having a particle size of 50 nm or less.
[0006] EP 2 465 964 A1 describes a Hadfield steel composition comprising 0.9 to 1.35% by weight carbon, 11 to 14% by weight manganese, up to 0.8% by weight silicon, up to 0.07% by weight phosphorus, up to 0.05% by weight sulfur, at least 0.01% by weight hafnium, and the remainder iron and impurities. This steel is non-magnetic, has low electrical conductivity, and shows an increase in its impact toughness by cold deformation.
[0007] EP 0 142 873 A1 discloses an austenitic manganese hard steel having 0.8% to 1.8% by weight of carbon, 6% to 18% by weight of manganese, 0% to 3% by weight of chromium, 0% to 2% by weight of nickel, 0% to 2.5% by weight of molybdenum, 0% to 1% by weight of silicon, at least 0.01% by weight of titanium, at least 0.01% by weight of vanadium, 0.05% to 0.08% by weight of titanium and vanadium in total, and the remainder being iron, wherein the ratio of carbon to manganese is in the range of 1:8 to 1:14. This steel has the ability to harden during cold deformation.
[0008] DE 28 53 582 A1 describes a non-magnetic steel alloy having not more than 1.5% by weight of carbon, 0.1% to 1.5% by weight of silicon, 5% to 30% by weight of manganese, 0.005% to 0.5% by weight of nitrogen and at least one element from the group consisting of 0.05% to 1% by weight of sulfur, 0.05% to 1% by weight of lead, 0.05% to 1% by weight of selenium, 0.01% to 0.5% by weight of tellurium, 0.001% to 0.05% by weight of calcium, and the remainder being iron.
[0009] GB 276 048 A describes another Hadfield manganese steel having at least 11% by weight of manganese and at most 1.6% by weight of carbon.
[0010] "Material Data Sheet 1.3401 / X120Mn12" published by Team Edelstahl in 2020 discloses a composition of a manganese steel having 1.1% to 1.3% carbon by weight, 12% to 13% manganese by weight, 0.3% to 0.5% silicon by weight, a maximum of 0.1% phosphorus by weight, a maximum of 0.04% sulfur by weight, and a maximum of 1.5% chromium by weight.
[0011] In his 2010 paper “Höchstfestenichtrostende austenitische CrMn-Stähle” (“High-strength stainless austenitic CrMn steels”), Sascha Riedner of Ruhr-Universität Bochum describes, among other things, a study of an austenitic steel of the X120Mn12 type that achieved a surface hardness of up to 700 HV by local work hardening under impact or shock loads.
[0012] Furthermore, reference is made to the following paper, which relates in particular to sheet metal forming for automotive applications:
[0013] “Deformation-induced martensite formation during multi-stage forming and its use to optimize the HCF and VHCF properties of austenitic stainless steel sheets”, Dipl.-Wirt.-Ing., Carsten Müller-Bollenhagen, Department of Mechanical Engineering, Faculty IV, University of Siegen, April 2011.
[0014] Among other things, the paper deals with phase transformations of metastable austenite.
[0015] With regard to the known composition and properties of manganese steels, reference is made by way of example to the documents DE 28 46 930 A1, EP 2 803 736 A1, DE 866 893 B, WO 2017 / 021459 A1 and EP 0 205 869 A1. In general, manganese steels are characterized by a high wear resistance, in particular under impact or shock loads. Summary of the invention
[0016] The invention is based on the object of achieving a material advancement of electromechanical actuators compared to the aforementioned prior art, wherein, in particular, the wear aspects occurring in spindle drives, for example in electric actuators, are to be taken into account.
[0017] According to the invention, this object is achieved by an electromechanical actuator having the features of claim 1, which is operated using a screw drive. The electromechanical actuator comprises a screw drive in the form of a planetary rolling screw drive, wherein the planetary rolling screw drive provided is a true pitch screw drive having a driven cage guiding a plurality of planets and having a threaded spindle, wherein the threaded spindle and / or the planets are formed from a steel having the following composition: ○ C: 0.4% to 1.5% by weight, ○ Mn: 12.0% to 22.0% by weight, ○ Cr: 4.0% by weight, ○ Ni: up to 0.5% by weight, ○ Cu: up to 0.3% by weight, ○ V: 0.3% by weight, ○ S: 0.3% by weight, ○ P: up to 0.1% by weight, ○ Si: 4.0% by weight, ○ Al: up to 0.05% by weight, ○ The rest: iron and impurities resulting from smelting, On the surface of the steel, at least in the region of the threads produced by the forming process on the threaded spindle and / or the planets, there are the results of martensite precipitation and strain hardening.
[0018] A steel with the following composition is selected as the starting material for producing the threaded spindles and / or planets: ○ C: 0.4% to 1.5% by weight, ○ Mn: 12.0% to 22.0% by weight, ○ Cr: 4.0% by weight, ○ Ni: up to 0.5% by weight, ○ Cu: up to 0.3% by weight, ○ V: 0.3% by weight, ○ S: 0.3% by weight, ○ P: up to 0.1% by weight, ○ Si: 4.0% by weight, ○ Al: up to 0.05% by weight, ○ Rest: Iron and impurities resulting from smelting.
[0019] In particular, the manganese content is in the range of 12.0 to 14.0% by weight, and the chromium content is at most 1.8% by weight.
[0020] The starting product, which is present as a rod-shaped material, is deformed during the production of the threaded spindle and / or the planet, so that martensite precipitation and work hardening occur on the surface of the starting product, at least in the region of the thread produced using the forming process.
[0021] Austenitic manganese steel with the material number 1.3401 (X120Mn12) has proven to be particularly suitable for the production of threaded spindles and / or planetary parts. This austenitic manganese steel is a steel comprising 1.1% to 1.3% carbon, 12% to 13% manganese, 0.3% to 4.0% silicon, up to 0.1% phosphorus, up to 0.04% sulfur and up to 1.5% chromium, and the remainder iron and impurities resulting from the smelting process, each given in weight percentages, and has a high wear resistance, in particular when subjected to impact or shock. The manganese steel mentioned - also known as manganese hard steel - has otherwise proven itself as a material for the production of, for example, excavator teeth or jaw crushers and is particularly suitable for hot forming in a temperature range of 850°C to 1050°C.
[0022] Surprisingly, it has been shown that a reduced carbon content has a positive effect compared to steel with material number 1.3401. For example, a carbon content in the lower range of the specified interval, for example in the range of 0.4% to 0.8%, in the range of 0.4% to 0.6%, or in a narrower range of min. 0.4% and max. 0.5% C content (expressed in % by weight) ensures that hardening is less abrupt and therefore a greater degree of deformation can be achieved. In these cases, such steels are also referred to as weakened manganese steels.
[0023] The deformation of the rod-shaped starting material, which leads to the precipitation of martensite and work hardening, can initially involve a drawing process. In this drawing process, the rod-shaped part can be stretched as a pre-product and does not yet have a thread structure. This has the advantage that an intermediate product of uniform shape and quality can be obtained as a result of the drawing process for further processing into different end products, in particular threaded spindles and / or planets with different thread profiles. In the case of a spindle with a non-pitch profile, i.e. a groove-shaped profile, it is also referred to as a threaded spindle.
[0024] In all cases, the initial drawing process contributes to the mechanical strength of the final product, i.e. the threaded spindle and / or the planet. In the actuator, the threaded spindle is subjected to considerable axial forces during interaction with an existing counterpart, in particular in the form of a nut, roller or screw, wherein a sharp increase in force may occur.
[0025] In both the method variant with an initial drawing process and in the method variant without such plastic elongation of the rod-shaped starting material, the thread can be formed by thread rolling. Optionally, in addition to work hardening, a heat treatment can also be considered, wherein, in any case, the formation of the thread plays a crucial role in martensite precipitation and work hardening. The heat treatment can be designed in multiple stages and can in particular include subsequent temperature applications, i.e. tempering. Deep cooling of the rod-shaped material can also be provided in an intermediate step.
[0026] These steps, after heating the material to temperatures above 1000° C. and quenching, can reduce stresses in the forming area and stabilize the structure. With regard to the forming of the rod-shaped starting material, forging, in particular forging of the end sections of the material, can also be provided. At least the thread can be completed by machining in a manner known in principle.
[0027] The plastic forming process described is particularly suitable in its various variants for producing threaded spindles and planetary parts with barely perceptible, very low deformations. Core strengths of 800 MPa to 1080 MPa and surface hardnesses of 650 HV and above can be achieved for the workpiece. This applies both when the workpiece is a threaded spindle and when components that interact directly or indirectly with the threaded spindle, such as nuts, bolts, rollers or planetary parts, are to be machined as workpieces.
[0028] The threaded spindle is the spindle of a planetary rolling screw drive, wherein the planets of the planetary rolling screw drive also represent profiled shafts, which can be produced from a rod-shaped starting material having the composition specified above.
[0029] The electromechanical actuator is preferably used as a steering actuator for a motor vehicle, i.e. as an actuator for a front axle or rear axle steering device. In this case, reference is made by way of example to publications DE 10 2019 103 385 A1 and DE 10 2011 082 514 A1. Alternatively, the actuator according to the present application can be used, for example, in an actuating mechanism of a stationary industrial device.
[0030] The screw drive is designed as a planetary roller gear and there is a rotational drive of the cage, which guides the planets of the screw drive. The planetary roller gear is designed as a screw drive with a precise pitch, in which very small transmission ratios are acceptable compared to planetary roller gears with a driven threaded spindle or with a driven spindle nut. BRIEF DESCRIPTION OF THE DRAWINGS
[0031] Hereinafter, exemplary embodiments of the present invention will be described in more detail with reference to the accompanying drawings. In the accompanying drawings:
[0032] Figure 1 A cross section of a steering actuator with a planetary rolling screw drive intended for use in a rear axle steering system is shown.
[0033] Figure 2 A flow chart is shown which illustrates the steps of manufacturing a threaded spindle for a steering actuator,
[0034] Figure 3 A graph showing the dependence of the hardness of the workpiece on the distance from the workpiece surface in a threaded spindle according to the present application and in a comparative example (not claimed),
[0035] Figure 4 Another graph is shown which illustrates data recorded during a tensile test on a threaded spindle.
[0036] The actuator, which is designated overall by the reference numeral 1 , is designed in the present case as an electromagnetic steering actuator for a rear axle steering system of a motor vehicle. DETAILED DESCRIPTION
[0037] The actuator 1 comprises a threaded spindle 2 which can be displaced in its longitudinal direction in order to change the steering angle of the rear wheels of a motor vehicle (not shown in detail). The threaded spindle 2 is aligned in the transverse direction of the vehicle. With regard to the basic structure and function of the actuator 1, reference is made to the cited prior art.
[0038] A plurality of planets 4 guided in a cage 5 roll on the thread of the threaded spindle 2, which thread is indicated as 3 and is a single-start thread in this case. The cage 5 comprises a cage disc 6 located on the two end faces of the planets 4 and a cage sleeve 7, which surrounds the entire planet 4 in an annular shape and is arranged concentrically with the central axis indicated as MA of the threaded spindle 2 and thus of the entire actuator 1. The planets 4 and the cage 5 are parts of a nut arrangement generally indicated as 8. External teeth 9 are formed on the outer peripheral surface of the cage sleeve 7, which make it possible to drive the entire cage 5 by means of a belt drive (not shown). The cage 5 serves as a rotary drive element, wherein the planetary rolling screw drive of the actuator 1 formed by the threaded spindle 2 and the nut arrangement 8 is designed as a planetary rolling screw drive with a precise pitch.
[0039] Each planet 4 has a central section 10 and two adjacent, relatively thin end sections 11. Each of the sections 10, 11 has a profile 12, 13 which is designed in the form of a non-pitch groove compared to the thread 3. Only the central section 10 of the planet 4 is in contact with the threaded spindle 2. On the other hand, the end sections 11 of the planet 4 are lifted off the thread 3 and engage in the profile 17 formed by the nut parts 14, 15. The nut parts 14, 15 assigned to the nut device 8 are adjusted so that a preload is provided between the nut parts 14, 15, the planet 4 and the threaded spindle 2.
[0040] The relative positioning of the nut parts 14, 15 with respect to each other is fixed by means of a locking nut 16. The inherently rigid arrangement of the screwed-together nut parts 14, 15 and the locking nut 16 is rotatably mounted in the cage 5 by means of two axial bearings 18. No driving force is fed into the nut parts 14, 15. The entire nut device 8 is mounted in a surrounding structure (not shown), i.e. the actuator housing, by means of two tapered roller bearings 19. Among other things, an electric motor is attached to the actuator housing, which drives a belt drive, which rotates the cage 5. Alternatively, the electric motor can be built into the actuator housing.
[0041] During operation of the electromechanical actuator 1, ie a steering actuator, rapidly increasing, almost sudden loads acting in the longitudinal direction of the threaded spindle 2 may occur. The thread 3 in particular must be able to withstand these loads.
[0042] In the following, reference is made to Figure 2 , wherein steps S1 to S5 represent individual manufacturing steps in the manufacture of the threaded spindle 2. Alternatively or additionally, the production of the planetary parts 4 can be realized similarly.
[0043] In step S1, a round steel bar is provided as a starting product. The round steel bar is a manganese steel X120Mn12 (material number 1.3401). Before the round steel bar is further processed, it can be plastically stretched in step S1, which has a positive effect on the desired hardening of the steel.
[0044] The initial product provided in step S1 is ground and rolled in steps S2 and S3. The rolling process produces in particular the thread 3. The precipitation of martensite during forming is essential for hardening.
[0045] Furthermore, a heat treatment is performed in step S3. In step S4, the threaded spindle 2 is machined by turning. Machining can also include other machining techniques, in particular milling. In the last step S5, the workpiece, ie the threaded spindle 2, is cleaned.
[0046] exist Figure 3 and Figure 4 It is shown in Figure 2 Mechanical properties of the threaded spindle 2 manufactured by the method. Figure 3 The hardness curves in the work-hardened state (thick line) and in the work-hardened and heat-treated state (upper, thin line) are shown. For comparison, the hardness in the solution annealed state (300 HV) is shown. Figure 3 It can be seen that a surface hardness of about 550 HV can be achieved by work hardening alone. The dashed line shows work hardening with increasing deformation. Additional heat treatment increases the surface hardness to at least 650 HV.
[0047] Figure 4 The simplified diagram in Figure 2 shows the yield strength Ϭ E (related force: F) and tensile strength Ϭ B (related force: Z), which can be determined with the aid of a tensile test. Figure 4 It can be seen that the force increases with increasing elongation of the manganese steel from which the threaded spindle 2 is made. The core strength of the machined manganese steel used in the threaded spindle 2 is in the range of 800 MPa to 1080 MPa.
[0048] Reference numerals
[0049] 1 Actuator
[0050] 2 Threaded spindle
[0051] 3 Thread
[0052] 4 Planetary parts
[0053] 5 Cage
[0054] 6 Cage plate
[0055] 7 Cage sleeve
[0056] 8 Nut device
[0057] 9 External tooth system
[0058] 10 Center section of planet
[0059] 11 Planetary end section
[0060] 12 Contour of the central section
[0061] 13 Profile of end section
[0062] 14 Nut parts
[0063] 15 Nut parts
[0064] 16 Lock nut
[0065] 17 Profile of the nut component
[0066] 18 Thrust bearing
[0067] 19 Tapered roller bearings
[0068] Ϭ E Yield Strength
[0069] Ϭ B Tensile Strength
[0070] F-Force
[0071] MA Center Axis
[0072] Steps S1, ... S5
[0073] Z-Force
Claims
1. An electromechanical actuator (1) comprising a screw drive (2, 8) in the form of a planetary rolling screw drive (2, 8), wherein: The planetary rolling screw drive (2, 8) provided is a true pitch screw drive having a driven cage (5) for guiding a plurality of planetary elements (4) and having a threaded spindle (2), wherein the threaded spindle (2) and / or the planetary elements (4) are formed from a steel having the following composition: ○ C: 0.4% to 1.5% by weight, ○ Mn: 12.0% to 22.0% by weight, ○ Cr: 4.0% by weight, ○ Ni: up to 0.5% by weight, ○ Cu: up to 0.3% by weight, ○ V: 0.3% by weight, ○ S: 0.3% by weight, ○ P: up to 0.1% by weight, ○ Si: 4.0% by weight, ○ Al: up to 0.05% by weight, ○ The rest: iron and impurities resulting from smelting, On the surface of the steel, at least in the region of the thread (3) produced by a forming process on the threaded spindle (2) and / or the planet (4), there are results resulting from martensite precipitation and strain hardening.
2. The electromechanical actuator (1) according to claim 1, wherein: The threaded spindle (2) and / or the planetary element (4) are made of manganese steel (material number 1.3401).
3. The electromechanical actuator (1) according to claim 1 or 2, wherein: The threaded spindle is formed by a rod-shaped starting material made of steel.
4. The electromechanical actuator (1) according to claim 3, wherein: The rod-shaped starting material is formed during the drawing process.
5. An electromechanical actuator (1) according to claim 3 or claim 4, wherein: At least one section, in particular an end section, of the rod-shaped starting material is forged.
6. An electromechanical actuator (1) according to any one of claims 1 to 5, wherein: The work hardening of the threaded spindle (2) and / or the planetary parts (4) is at least partially produced by thread rolling.
7. An electromechanical actuator (1) according to any one of claims 1 to 6, wherein: The threaded spindle and / or the planetary element (4) are further heat treated.
8. The electromechanical actuator (1) according to any one of claims 1 to 7, which is designed as a steering actuator.