High-precision sector gear for electric steering system and preparation method

Abstract

The invention provides a high-precision sector gear for an electric steering system and a preparation method, and belongs to the technical field of precision gear machining.The high-precision sector gear comprises a gear body, a fixing shaft hole is formed in the center of the gear body, and a plurality of weight reduction modules are arranged on the sector inner wall of the fixing shaft hole and the gear body and the sector of the gear body; tooth sections are distributed on the arc-shaped surface of the gear body, each tooth section comprises a middle tooth section, a transition tooth section and an edge tooth section which are sequentially connected, and the tooth pitches of the tooth sections are gradually distributed in the direction from the middle tooth sections to the edge tooth sections. The three-section tooth section structure with the gradually-changed tooth pitch is matched with the tooth pitch adjustable rack, the weight reduction module and the reinforcing ribs cooperate to achieve light weight and rigidity balance, self-adaptive compensation precision machining and the composite surface treatment technology are combined, smooth switching of the steering transmission ratio is achieved, steering is accurate and smooth, the structure is stable and resistant to abrasion, energy consumption is lower, and the service life of the steering system is prolonged. And the control performance and the service life of the electric steering system are obviously improved.

Description

Technical Field

[0001] This invention relates to the field of precision gear machining technology, and in particular to a high-precision sector gear for an electric steering system and its manufacturing method. Background Technology

[0002] With the rapid development of the automotive industry towards intelligence and energy conservation, electric power steering (EPS) systems have become the mainstream configuration for passenger car steering systems due to their advantages such as low energy consumption, sensitive response, and convenient operation. Their transmission accuracy and reliability directly affect the vehicle's driving safety and comfort. As a key transmission component of the EPS system, sector gears play a crucial role in transmitting steering torque and realizing steering angle conversion, and the industry continues to raise its requirements for their machining accuracy, structural stability, and service life.

[0003] Currently, sector gears on the market generally adopt a fixed tooth pitch design, and the processing technology is mainly traditional CNC hobbing. The hardness of the tooth surface is then improved by overall carburizing and quenching or tempering treatment.

[0004] However, the inherent problems of existing technologies have had several specific negative impacts on the performance of electric power steering systems: First, the fixed-pitch tooth structure results in a constant transmission ratio, which cannot adapt to the different needs of high-speed straight-line driving and low-speed large-angle steering (such as U-turns and parking). At high speeds, the vehicle is prone to instability due to excessively light steering, resulting in insufficient stability in straight-line driving; at low speeds, the excessive operating force reduces driving convenience, and the lack of transition in transmission ratio switching easily generates meshing impact, affecting steering smoothness. Second, the imbalance between lightweight design and structural rigidity directly affects transmission accuracy. Excessive weight reduction makes the gears prone to deformation during operation, resulting in increased steering clearance, obvious lag, and delayed response to steering commands; while simply increasing rigidity will increase the weight of the gears, increasing the load on the EPS motor. Third, the lack of real-time dynamic precision compensation in tooth profile machining easily leads to tooth pitch deviation and cumulative tooth direction error, resulting in inaccurate meshing between gears and racks, causing steering jamming or freewheeling. This not only reduces steering control precision but also exacerbates local wear on the tooth surface and causes meshing impact noise, affecting the vehicle's NVH (noise, vibration, and harshness) performance. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, the purpose of this invention is to provide a high-precision sector gear for electric power steering systems and its manufacturing method. By using a three-segment tooth structure with gradually changing tooth pitch and adapting it to an adjustable tooth pitch rack, a weight reduction module and reinforcing ribs work together to achieve a balance between lightweighting and rigidity. The invention also combines adaptive compensation precision machining and composite surface treatment processes to achieve smooth switching of steering transmission ratio, precise and smooth steering, stable and wear-resistant structure, and lower energy consumption, thus significantly improving the handling performance and service life of electric power steering systems.

[0006] To achieve the above objectives, the present invention provides the following solution: On one hand, the present invention provides a high-precision sector gear for an electric steering system, including a gear body, a fixed shaft hole at the center of the gear body, and several weight reduction modules provided on the fixed shaft hole, the inner wall of the sector of the gear body, and the sector of the gear body. Tooth segments are arranged on the arc-shaped surface of the gear body, and the tooth segments include intermediate tooth segments, transition tooth segments, and edge tooth segments connected in sequence. The tooth pitch of the tooth segments is gradually distributed along the direction from the intermediate tooth segment to the edge tooth segment.

[0007] Preferably, the weight reduction module includes a weight reduction groove and a weight reduction hole. The weight reduction groove is disposed on the fan surface of the gear body, and the weight reduction hole is disposed between the fixed shaft hole and the inner wall of the fan surface of the gear body.

[0008] Preferably, the weight-reducing groove is provided with a plurality of reinforcing ribs, and the reinforcing ribs are fixedly connected to the inner wall of the gear body.

[0009] Preferably, the intermediate tooth segment has 10-14 teeth, the tooth pitch between two adjacent teeth in the intermediate tooth segment is 6.28-6.35mm, the intermediate tooth segment is used to form a meshing engagement with the close-tooth working area of ​​the adjustable tooth rack, and the transmission ratio corresponding to the intermediate tooth segment is 14-16 to meet the steering stability requirements of the vehicle when driving straight at high speed.

[0010] Preferably, the transition tooth segment has 6-8 teeth, and the tooth pitch between two adjacent teeth in the transition tooth segment gradually increases along the direction from the middle tooth segment to the edge tooth segment, with the tooth pitch gradient controlled at 0.03-0.05 mm / tooth. The transition tooth segment is used to adapt to the tooth pitch transition zone of the tooth pitch adjustable rack, and the transmission ratio corresponding to the transition tooth segment is 12-14, so as to achieve a smooth and shock-free switching of the transmission ratio between the middle tooth segment and the edge tooth segment.

[0011] Preferably, the edge tooth segment has 6-10 teeth, the tooth pitch between two adjacent teeth in the edge tooth segment is 6.45-6.60mm, the edge tooth segment is used to mesh with the sparse tooth working area of ​​the tooth pitch adjustable rack, and the transmission ratio corresponding to the edge tooth segment is 10-12, so as to reduce the operating force of the steering system when turning at a large angle.

[0012] On the other hand, the present invention also provides a method for manufacturing the above-mentioned high-precision sector gear for electric steering systems, comprising the following steps: S1. High-strength quenched and tempered structural steel or powder metallurgy gear steel are selected as raw materials. A gear blank with a fan-shaped outer contour and a reserved area for a central fixed shaft hole is prepared by CNC forming milling or closed mold precision forging. The gear blank is subjected to a normalizing treatment to eliminate stress and improve the uniformity of the structure. S2. Mill weight reduction grooves on the fan surface of the gear body using a five-axis CNC milling machine. Prepare several weight reduction holes between the fixed shaft hole and the inner wall of the fan surface of the gear body using CNC drilling or laser drilling. Process reinforcing ribs in the bottom area of ​​the weight reduction grooves. S3. On the curved surface of the blank, mark the area of ​​the middle tooth segment, the transition tooth segment and the edge tooth segment. Use a CNC gear hobbing machine to cut the initial tooth with a uniform reference tooth pitch of 6.30mm. Simultaneously detect the tooth segment curvature and the tooth tip circle, and control the tooth direction error to be less than 0.01mm. S4. The tooth pitch control parameters are set in segments using an adaptive CNC tooth pitch compensation system. A dual-axis linkage CNC gear shaping machine is used in conjunction with a fine-tuning servo compensation system to perform cumulative tooth pitch adjustment. The tooth surface contact error is monitored in real time and the gradual tooth pitch is continuously transitioned without jump points through dynamic servo displacement micro-compensation. S5. The gear body is subjected to vacuum carburizing and quenching and low-temperature tempering. After heat treatment, a low-temperature aging treatment is performed to release residual stress. S6. Use a CNC profile grinding machine to perform synchronous fine grinding of the tooth surface of each tooth segment with gradually changing tooth pitch. The grinding path is programmed and controlled according to the actual tooth pitch distribution curve. The tooth pitch distribution, tooth profile error, transmission ratio consistency and meshing overlap are jointly checked by a laser interferometer and a coordinate measuring machine. S7. The surface of the gear body is treated with a sulfur-nitrogen composite diffusion layer to prepare a high-precision sector gear for electric steering system.

[0013] Preferably, in S2, the depth of the weight-reducing groove is controlled at 0.5-1.2mm, and the edge of the groove is rounded; the diameter of the weight-reducing hole is controlled at 0.01-0.03mm; the reinforcing rib is integrally connected to the inner wall of the gear body through one-time forming or EDM forming, so as to realize the restoration of rigidity after the weight reduction of the gear body.

[0014] Preferably, in S4, the parameters of the adaptive CNC pitch compensation system are specifically set as follows: the pitch of the intermediate tooth segment is set to 6.28-6.35mm, the pitch of the transition tooth segment increases gradually by 0.03-0.05mm / tooth, and the pitch of the edge tooth segment is controlled at 6.45-6.60mm; after the gradual pitch precision trimming, the pitch error is controlled at 2-4μm, and the cumulative tooth direction error is controlled at 4-6μm.

[0015] Preferably, after the vacuum carburizing quenching and low-temperature tempering treatment, the hardness of the gear body is controlled at HRC58-62; the thickness of the sulfur-nitrogen composite carburizing layer is 3-8μm, which is used to improve the wear resistance and corrosion resistance of the gear tooth surface after treatment.

[0016] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects: (1) This invention adopts a three-segment pitch gradient structure consisting of an intermediate tooth segment, a transition tooth segment, and an edge tooth segment. By matching different working areas of the pitch-adjustable rack, it achieves full-condition optimization of steering performance. Among them, the intermediate tooth segment has 10-14 teeth with a tooth pitch of 6.28-6.35mm and a corresponding transmission ratio of 14-16. It can provide stable steering feedback when the vehicle is traveling at high speed and straight, effectively suppressing high-speed drifting and significantly improving straight-line driving stability. The transition tooth segment increases the tooth pitch gradually by 0.03-0.05mm / tooth. The structure of 6-8 transition teeth creates a smooth transition channel from a transmission ratio of 14-16 to 10-12, completely eliminating the meshing impact when switching traditional fixed-pitch gears. This design seamlessly integrates high-speed stability with low-speed lightness in steering feel, eliminating any jerking during steering. The 6.45-6.60mm tooth pitch structure with 6-10 teeth on the edge teeth adapts to the sparse tooth area of ​​the rack while reducing steering effort, making large-angle steering scenarios such as U-turns and parking easier and greatly improving steering convenience. This fundamentally solves the defects of inconsistent steering feel and obvious switching shocks in existing fixed-pitch gears, allowing the steering transmission ratio to dynamically adapt to driving conditions, significantly improving handling precision and smoothness.

[0017] (2) This invention solves the design contradiction of traditional gears where weight reduction inevitably leads to a loss of stiffness and maintaining stiffness inevitably leads to an increase in weight by integrating the weight reduction module and the reinforcing rib. The weight reduction groove on the fan-shaped surface of the gear body and the weight reduction hole around the fixed shaft hole form a three-dimensional weight reduction structure. Under the premise of ensuring the strength of the main transmission area, the weight of the gear is reduced to the maximum extent, which effectively reduces the load on the electric steering system motor and reduces energy loss. At the same time, the reinforcing rib in the weight reduction groove is firmly connected to the inner wall of the gear body through one-time forming or EDM, which builds a mechanical balance system of weight reduction and reinforcement. It can effectively resist the structural deformation under the action of steering torque and avoid problems such as increased steering clearance and delayed command response caused by gear deformation. Thus, this invention not only achieves the goal of lightweighting, but also ensures the structural stability of the gear during operation, so that the transmission accuracy is not affected by weight reduction, and ensures the accurate transmission of steering commands, taking into account both energy saving and control reliability.

[0018] (3) In the manufacturing process of this invention, the adaptive CNC pitch compensation system works in conjunction with the dual-axis linkage gear shaper to achieve precise pitch adjustment through real-time dynamic servo displacement compensation, control the cumulative error of pitch and tooth direction, and completely solve the problems of meshing jamming and idle running caused by pitch deviation in traditional processing, reduce local wear on the tooth surface, reduce meshing impact noise, and optimize vehicle NVH performance. In the surface treatment and heat treatment process, vacuum carburizing and quenching makes the gear hardness reach HRC58-62. Combined with the composite treatment of sulfur-nitrogen composite diffusion layer, it not only significantly improves the wear resistance of the tooth surface and effectively resists wear and pitting caused by long-term meshing, but also enhances the corrosion resistance, which can adapt to complex working conditions such as humid and dusty conditions and avoid meshing problems caused by tooth surface corrosion. At the same time, this invention also reduces the thermal deformation difference of different parts of the gear, ensures assembly accuracy, and further extends the service life of the gear. Thus, this method combination enables the gear to have stronger wear resistance and corrosion resistance on the basis of high-precision transmission, and the service life is improved, which greatly reduces the maintenance cost and failure risk of the electric steering system. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the structure of a high-precision sector gear for an electric steering system according to the present invention; Figure 2 This invention relates to a method for manufacturing a high-precision sector gear for an electric steering system; flowchart.

[0021] Explanation of reference numerals in the attached figures: 1. Gear body; 2. Fixed shaft hole; 3. Intermediate tooth section; 4. Transition tooth section; 5. Edge tooth section; 6. Weight reduction groove; 7. Reinforcing rib; 8. Weight reduction hole. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] Example 1 like Figure 1 As shown, this embodiment provides a high-precision sector gear for an electric power steering system. As a main transmission component of the electric power steering (EPS) system, it can achieve precise transmission of steering torque and dynamic adaptation of the transmission ratio. In this embodiment, the main body of the sector gear is the gear body 1, which has a fixed shaft hole 2 at its center. The inner wall of the fixed shaft hole 2 is adapted to the motor output shaft of the electric power steering system, which can stably transmit the steering torque output by the motor and ensure accurate response to steering commands. Several weight-reducing grooves 6 are arranged in the fan-shaped area of ​​the gear body 1. At the same time, several weight-reducing holes 8 are provided between the fixed shaft hole 2 and the inner wall of the fan-shaped area of ​​the gear body 1. The depth of the weight-reducing grooves 6 is controlled between 0.5-1.2mm and the edges are rounded. The diameter of the weight-reducing holes 8 is maintained at 0.01-0.03mm. The combination of the two can effectively reduce the overall weight of the gear body 1, reduce the load on the electric steering system motor, and meet the energy-saving design requirements of the system. Inside the weight-reducing grooves 6, several reinforcing ribs 7 are also provided. The reinforcing ribs 7 are fixedly connected to the inner wall of the gear body 1. On the basis of achieving lightweight, they can make up for the stiffness loss caused by the weight reduction structure, so that the gear body 1 is not easy to deform when subjected to steering torque, ensuring the stability of the transmission clearance and the smooth transmission of steering commands.

[0025] On the arc-shaped surface of the gear body 1, there are sequentially connected intermediate tooth segments 3, transition tooth segments 4, and edge tooth segments 5, forming a transmission structure with gradually changing tooth pitch. Assuming a symmetrical structure for the sector gear, the intermediate tooth segment 3 has 5 teeth, with a tooth pitch of 6.32mm between adjacent teeth, corresponding to a transmission ratio of 15. This tooth segment can precisely mesh with the closely spaced working area of ​​the adjustable-pitch rack. When the vehicle is traveling at high speed in a straight line, a small angle turn of the steering wheel can transmit torque through this tooth segment, providing stable steering feedback and effectively preventing steering drift at high speeds, significantly improving the stability of straight-line driving. The transition tooth segment 4 has 4 teeth, with the tooth pitch between adjacent teeth gradually decreasing. The gear ratio increases progressively from the intermediate tooth segment 3 to the edge tooth segment 5 in a gradient of 0.04 mm / tooth, corresponding to a transmission ratio of 13. This tooth segment is adapted to the tooth pitch transition zone of the adjustable pitch rack, enabling a smooth switching of the transmission ratio between the intermediate tooth segment 3 and the edge tooth segment 5. This completely eliminates the meshing impact during the switching of traditional fixed pitch gears, making the change in steering feel smoother and avoiding steering jerking. The edge tooth segment 5 has 3 teeth, with a tooth pitch of 6.52 mm between adjacent teeth, corresponding to a transmission ratio of 11. This tooth segment meshes with the sparse tooth working area of ​​the adjustable pitch rack. When the vehicle performs large-angle steering operations such as U-turns and parking, it can significantly reduce steering effort and improve the convenience of low-speed steering.

[0026] The working principle of this sector gear is as follows: When the vehicle is traveling at high speed in a straight line, the steering wheel only needs to be turned at a small angle. At this time, the middle tooth segment 3 of the gear body 1 meshes with the closely spaced working area of ​​the adjustable-pitch rack. The larger transmission ratio makes the steering feedback more stable, ensuring the stability of the vehicle's straight-line driving. When a large-angle steering operation is required, the steering wheel rotation angle gradually increases, and the transition tooth segment 4 of the gear body 1 meshes with the pitch transition area of ​​the rack. The gradual change in pitch, combined with the smooth change of the corresponding transmission ratio, makes the transmission of steering torque shock-free and without jerking. As the steering wheel rotation angle further increases, the edge tooth segment 5 meshes with the sparse-pitch working area of ​​the rack. The smaller transmission ratio significantly reduces the force required for steering operation, making large-angle steering easier. During this process, the fixed shaft hole 2 stably transmits the torque output by the motor. The weight-reducing groove 6 and weight-reducing hole 8 reduce the weight of the gear, while the reinforcing rib 7 ensures the structural rigidity of the gear body 1, preventing gear deformation from affecting transmission accuracy. Ultimately, the electric steering system achieves precise, smooth, and effortless operation under different working conditions.

[0027] Example 2 like Figure 2 As shown, the present invention also provides a method for preparing a sector gear based on Embodiment 1, comprising the following steps: S1. High-strength quenched and tempered structural steel or powder metallurgy gear steel are selected as raw materials. A gear blank with a fan-shaped outer contour and a reserved area for a central fixed shaft hole is prepared by CNC forming milling or closed die precision forging. The gear blank is subjected to a normalizing treatment to eliminate stress and improve the uniformity of the structure.

[0028] The above step S1 specifically includes: if closed-mold precision forging is used, the raw material is first heated to 1100-1150℃ to the austenitic state, placed in the pre-formed sector gear mold, and forged by a press at a pressure of 800-1000MPa. After the blank cools to room temperature, the flash is removed to obtain a blank with a sector outer contour and a reserved area for the fixed shaft hole. This method can make the metal structure of the blank more compact, effectively improve the load-bearing strength of the gear body, and avoid cracks under subsequent steering torque.

[0029] If CNC forming milling is used, the raw material blank is clamped on the CNC milling machine worktable, the CAD model of the fan-shaped outer contour and the reserved area of ​​the fixed shaft hole is imported, and the carbide end mill is called to complete the contour milling with a spindle speed of 500r / min and a feed rate of 0.1mm / tooth. This method can accurately control the contour accuracy of the blank and provide a stable reference for subsequent processing.

[0030] Furthermore, during the normalizing process, the blank is placed in a box-type resistance furnace and heated to 870°C at a rate of 10°C / min. After holding at this temperature for 2 hours, it is cooled to 600°C in the furnace and then removed from the furnace and air-cooled to room temperature. This process can completely eliminate the forging / cutting internal stress of the blank, improve the uniformity of the microstructure, avoid deformation caused by stress release during subsequent processing, and ensure the final dimensional accuracy of the gear.

[0031] S2. A weight reduction groove is milled on the sector surface of the gear body using a five-axis CNC milling machine. Several weight reduction holes are prepared between the fixed shaft hole and the inner wall of the sector surface of the gear body using CNC drilling or laser drilling. Reinforcing ribs are processed in the bottom area of ​​the weight reduction groove.

[0032] The above step S2 specifically includes: clamping the gear blank on the four-axis rotary table of a five-axis CNC milling machine, using a 3mm diameter carbide ball end mill, importing the CAD path of the weight reduction groove, and machining it in a layered milling manner: each layer has a cutting depth of 0.2mm, and after milling to the target depth of 0.5-1.2mm, the groove edge is milled with a radius of 0.8mm. Layered milling can avoid blank deformation caused by excessive single cutting load, while the radius of 0.8mm can eliminate stress concentration at the groove edge, thereby reducing the risk of cracking in the groove area when the gear is working.

[0033] Furthermore, when preparing the weight-reduction holes, if laser drilling is used, a 50W fiber laser is selected, and the hole is positioned according to the CAD coordinates of the hole position, with a drilling speed of 0.5mm / s. The hole diameter is monitored in real time by a laser displacement sensor to ensure an accuracy between 0.01-0.03mm. If CNC drilling is used, a high-speed steel drill bit is selected, with a drilling speed of 800r / min and a feed rate of 0.05mm / r. This precision control can achieve weight reduction while avoiding hole position deviations that weaken the strength of the gear torque transmission area. Furthermore, if the reinforcing rib is machined in a single step, the contour connecting to the bottom of the groove and the inner wall of the main body is milled simultaneously during the milling of the weight-reducing groove. If electrical discharge machining (EDM) is used, the blank is clamped in an EDM machine, and copper electrodes are used to machine the rib according to its shape. A pulse width of 20μs and a peak current of 5A are set to integrate the reinforcing rib with the inner wall of the main body. This integrated structure allows the reinforcing rib and the gear body to simultaneously bear the steering torque, restoring the stiffness of the gear after weight reduction to more than 95% of its original state, and avoiding increased transmission clearance due to deformation.

[0034] S3. On the curved surface of the blank, mark the area of ​​the middle tooth segment, the transition tooth segment and the edge tooth segment. Use a CNC gear hobbing machine to perform initial tooth cutting with a uniform reference tooth pitch of 6.30mm. Simultaneously detect the tooth segment curvature and the tooth tip circle, and control the tooth direction error to be less than 0.01mm.

[0035] Step S3 specifically includes: using a scribing instrument in conjunction with CAD coordinates to mark the dividing points of the intermediate tooth segment, transition tooth segment, and edge tooth segment on the arc-shaped surface of the blank; clamping the blank on the worktable of the CNC hobbing machine, selecting a hob with a module of 2.5, setting the hob speed to 300 r / min and the axial feed to 0.2 mm / r, and completing the initial tooth cutting with a reference tooth pitch of 6.30 mm. A unified reference tooth pitch provides a consistent initial state for subsequent tooth pitch gradual dressing, avoiding tooth pitch connection deviations caused by segmented initial teeth; during the cutting process, using a dial indicator to detect the tooth segment arc and tooth tip circle in real time, and controlling the tooth direction error within 0.01 mm by adjusting the radial feed of the hobbing machine. This accuracy can ensure that when the subsequent tooth segments mesh with the tooth pitch adjustable rack, the tooth surface contact area is increased and the overload wear of the local tooth surface is reduced.

[0036] S4. The tooth pitch control parameters are set in segments using an adaptive CNC tooth pitch compensation system. A dual-axis linkage CNC gear shaper is used in conjunction with a fine-tuning servo compensation system to perform cumulative tooth pitch adjustment. The tooth surface contact error is monitored in real time, and the gradual tooth pitch is continuously transitioned without jump points through dynamic servo displacement micro-compensation.

[0037] Step S4 specifically includes: first, inputting parameters into the adaptive CNC tooth pitch compensation system: tooth pitch of the intermediate tooth segment 6.28-6.35mm, tooth pitch of the transition tooth segment increasing in a gradient of 0.03-0.05mm / tooth, and tooth pitch of the edge tooth segment 6.45-6.60mm; clamping the blank after initial tooth machining onto a dual-axis linkage CNC gear shaper, selecting a gear shaper cutter with a module of 2.5, setting the gear shaper cutter speed to 200r / min and the radial feed rate to 0.02mm / r. During machining, after every 3 teeth are cut, the system collects tooth surface contact error data through a contact displacement sensor, and the fine-tuning servo compensation system immediately outputs a displacement compensation amount of 0.001-0.003mm to correct the feed position of the gear shaper cutter until all tooth segments are finished, ultimately ensuring a tooth pitch error of 2-4μm and a cumulative tooth direction error of 4-6μm. This dynamic compensation mechanism enables continuous and gradual changes in tooth pitch, reducing the impact force during transmission ratio switching. At the same time, the minimal tooth pitch error ensures precise meshing between each tooth segment and the corresponding area of ​​the rack, resulting in a smoother steering feel.

[0038] S5. The gear body is subjected to vacuum carburizing and quenching and low-temperature tempering. After heat treatment, a low-temperature aging treatment is performed to release residual stress.

[0039] Step S5 specifically includes: clamping the gear in a vacuum carburizing furnace with zoned temperature control, setting the heating tube temperature of the gear ring area to 930℃ and carbon potential to 0.9%, and the heating tube temperature of the hub area to 890℃ and carbon potential to 0.7%, holding at these temperatures for 7 hours to complete carburizing. Zoned temperature control allows for a higher carbon concentration in the main areas of the gear ring drive, improving tooth surface hardness, while avoiding excessive carburizing in the assembly area that could lead to increased brittleness. Subsequently, the gear is transferred to a quenching oil bath and quenched at a cooling rate of ≥20℃ / s. During low-temperature tempering, the gear is placed in a tempering furnace, heated to 190℃, held for 2 hours, and then air-cooled. Next, a low-temperature aging treatment is performed: the gear is placed in a constant temperature chamber, held at 120℃ for 1 hour, and then naturally cooled to room temperature, stabilizing the gear hardness at HRC58-62, while also improving the residual stress relief rate, preventing gear deformation after subsequent precision grinding, and ensuring the long-term stability of tooth profile accuracy.

[0040] S6. Use a CNC profile grinding machine to perform gradual pitch synchronous fine grinding on the tooth surface of each tooth segment. The grinding path is programmed and controlled according to the actual tooth pitch distribution curve. The tooth pitch distribution, tooth profile error, transmission ratio consistency and meshing overlap are jointly checked by a laser interferometer and a coordinate measuring machine.

[0041] Step S6 specifically includes: clamping the gear onto a CNC profile grinding machine, importing the tooth pitch distribution curve set in S4, calling a cubic boron nitride grinding wheel, setting the grinding wheel speed to 1500 r / min and the feed rate to 0.01 mm / r, and performing fine grinding on each tooth segment separately. The grinding path programmed according to the tooth pitch distribution curve can accurately preserve the gradual tooth pitch structure of each tooth segment, avoiding uniform grinding from destroying the preset transmission ratio characteristics. After fine grinding, the tooth surface is scanned with a laser interferometer to obtain the tooth pitch distribution curve; then, a coordinate measuring machine is used to select 3 teeth of each tooth segment, measure the tooth profile error (control ≤ 0.005 mm), calculate the transmission ratio (deviation ≤ 0.5), and simultaneously detect the meshing overlap (≥ 1.2). This joint verification step can ensure that the tooth profile error and transmission ratio deviation are within the design range, and the improvement of the meshing overlap can further reduce the tooth surface contact stress and extend the service life of the gear.

[0042] S7. The surface of the gear body is treated with a sulfur-nitrogen composite diffusion layer to prepare a high-precision sector gear for electric steering system.

[0043] Step S7 specifically includes: placing the gear in an ion nitriding furnace, introducing a mixed nitriding agent of hydrogen sulfide and ammonia at a volume ratio of 1:5, setting the furnace temperature to 520℃ and the pressure to 500Pa, and holding for 4 hours; after treatment, using an eddy current thickness gauge to check the thickness of the nitrided layer to ensure it is within the range of 3-8μm. This composite nitriding layer can simultaneously form a wear-resistant sulfide layer and a corrosion-resistant nitride layer on the gear surface, improving the wear resistance and salt spray corrosion resistance of the gear surface, effectively solving the defect that traditional single surface treatment cannot simultaneously achieve both wear resistance and corrosion resistance, and significantly extending the service life of gears under complex working conditions.

[0044] Therefore, by adopting the above-mentioned high-precision sector gear and manufacturing method for electric steering systems, a three-segment tooth structure with gradually changing tooth pitch is used, along with an adjustable tooth pitch rack, a weight reduction module, and reinforcing ribs to achieve a balance between lightweighting and rigidity. The combination of adaptive compensation precision machining and composite surface treatment processes enables smooth switching of steering transmission ratio, precise and smooth steering, stable and wear-resistant structure, and lower energy consumption, significantly improving the handling performance and service life of electric steering systems.

[0045] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A high-precision sector gear for an electric steering system, characterized in that, The gear body includes a fixed shaft hole at its center. Several weight-reducing modules are provided on the fixed shaft hole, the inner wall of the fan-shaped surface of the gear body, and the fan-shaped surface of the gear body. Tooth segments are arranged on the arc-shaped surface of the gear body. The tooth segments include intermediate tooth segments, transition tooth segments, and edge tooth segments connected in sequence. The tooth pitch of the tooth segments is gradually distributed along the direction from the intermediate tooth segment to the edge tooth segment.

2. The high-precision sector gear for an electric steering system according to claim 1, characterized in that, The weight reduction module includes a weight reduction groove and a weight reduction hole. The weight reduction groove is disposed on the sector surface of the gear body, and the weight reduction hole is disposed between the fixed shaft hole and the inner wall of the sector surface of the gear body.

3. A high-precision sector gear for an electric steering system according to claim 2, characterized in that, The weight-reducing groove is provided with several reinforcing ribs, which are fixedly connected to the inner wall of the gear body.

4. A high-precision sector gear for an electric steering system according to claim 1, characterized in that, The intermediate tooth segment has 10-14 teeth, and the tooth pitch between two adjacent teeth in the intermediate tooth segment is 6.28-6.35mm. The intermediate tooth segment is used to form a meshing fit with the close-tooth working area of ​​the adjustable tooth rack, and the transmission ratio corresponding to the intermediate tooth segment is 14-16 to meet the steering stability requirements when the vehicle is traveling at high speed in a straight line.

5. A high-precision sector gear for an electric steering system according to claim 1, characterized in that, The transition tooth segment has 6-8 teeth. The tooth pitch between two adjacent teeth in the transition tooth segment gradually increases from the middle tooth segment to the edge tooth segment. The tooth pitch gradient is controlled at 0.03-0.05 mm / tooth. The transition tooth segment is used to adapt to the tooth pitch transition area of ​​the tooth pitch adjustable rack. The transmission ratio corresponding to the transition tooth segment is 12-14 to achieve a smooth and shock-free switching of the transmission ratio between the middle tooth segment and the edge tooth segment.

6. A high-precision sector gear for an electric steering system according to claim 1, characterized in that, The edge tooth segment has 6-10 teeth, and the tooth pitch between two adjacent teeth in the edge tooth segment is 6.45-6.60mm. The edge tooth segment is used to mesh with the sparse tooth working area of ​​the tooth pitch adjustable rack, and the transmission ratio corresponding to the edge tooth segment is 10-12, so as to reduce the operating force when the steering system is turned at a large angle.

7. A method for manufacturing a high-precision sector gear for an electric steering system according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. High-strength quenched and tempered structural steel or powder metallurgy gear steel are selected as raw materials. A gear blank with a fan-shaped outer contour and a reserved area for a central fixed shaft hole is prepared by CNC forming milling or closed mold precision forging. The gear blank is subjected to a normalizing treatment to eliminate stress and improve the uniformity of the structure. S2. Mill weight reduction grooves on the fan surface of the gear body using a five-axis CNC milling machine. Prepare several weight reduction holes between the fixed shaft hole and the inner wall of the fan surface of the gear body using CNC drilling or laser drilling. Process reinforcing ribs in the bottom area of ​​the weight reduction grooves. S3. On the curved surface of the blank, mark the area of ​​the middle tooth segment, the transition tooth segment and the edge tooth segment. Use a CNC gear hobbing machine to cut the initial tooth with a uniform reference tooth pitch of 6.30mm. Simultaneously detect the tooth segment curvature and the tooth tip circle, and control the tooth direction error to be less than 0.01mm. S4. The tooth pitch control parameters are set in segments using an adaptive CNC tooth pitch compensation system. A dual-axis linkage CNC gear shaping machine is used in conjunction with a fine-tuning servo compensation system to perform cumulative tooth pitch adjustment. The tooth surface contact error is monitored in real time and the gradual tooth pitch is continuously transitioned without jump points through dynamic servo displacement micro-compensation. S5. The gear body is subjected to vacuum carburizing and quenching and low-temperature tempering. After heat treatment, a low-temperature aging treatment is performed to release residual stress. S6. Use a CNC profile grinding machine to perform synchronous fine grinding of the tooth surface of each tooth segment with gradually changing tooth pitch. The grinding path is programmed and controlled according to the actual tooth pitch distribution curve. The tooth pitch distribution, tooth profile error, transmission ratio consistency and meshing overlap are jointly checked by a laser interferometer and a coordinate measuring machine. S7. The surface of the gear body is treated with a sulfur-nitrogen composite diffusion layer to prepare a high-precision sector gear for electric steering system.

8. The method for manufacturing a high-precision sector gear for an electric steering system according to claim 7, characterized in that, In S2, the depth of the weight-reducing groove is controlled between 0.5 and 1.2 mm, and the edge of the groove is rounded. The diameter of the weight-reducing hole is controlled between 0.01 and 0.03 mm. The reinforcing rib is integrally connected to the inner wall of the gear body through one-time forming or EDM forming to restore the rigidity of the gear body after weight reduction.

9. A method for manufacturing a high-precision sector gear for an electric steering system according to claim 7, characterized in that, In S4, the parameters of the adaptive CNC pitch compensation system are specifically set as follows: the pitch of the intermediate tooth segment is set to 6.28-6.35mm, the pitch of the transition tooth segment increases gradually by 0.03-0.05mm / tooth, and the pitch of the edge tooth segment is controlled at 6.45-6.60mm; after the gradual pitch precision trimming, the pitch error is controlled at 2-4μm, and the cumulative tooth direction error is controlled at 4-6μm.

10. A method for manufacturing a high-precision sector gear for an electric steering system according to claim 7, characterized in that, After vacuum carburizing, quenching, and low-temperature tempering, the hardness of the gear body is controlled at HRC58-62; the thickness of the sulfur-nitrogen composite carburizing layer is 3-8μm, which is used to improve the wear resistance and corrosion resistance of the gear tooth surface after treatment.

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