Method and clamp for manufacturing gear with directionally limited main bearing tooth surface

Abstract

The invention discloses a method for manufacturing a gear with a directionally limited main bearing tooth surface. The method comprises the following steps of: cutting a metal blank into a plurality of independent cake-shaped blanks through a cutting or sawing process; performing preprocessing operation on each cake-shaped blank to form a primary outer diameter, an axial end face and a central hole used for being mounted on a core shaft; the cake-shaped blanks are fixed to a core shaft structure, and the multiple cake-shaped blanks are fixed to a core shaft body; the fixed cake-shaped blank is subjected to gear hobbing operation through a hobbing cutter, and gear teeth are generated according to the standard involute tooth shape; after gear hobbing operation is completed, the gear and the mandrel structure are moved out of the gear hobbing station and transferred to a post-processing station; in the post-processing stage, the gear is subjected to angle indexing relative to the directional reference on the mandrel or the special indexing fixture; the orientation reference corresponds to a preset torque direction in actual use of the gear, and one tooth surface of each gear tooth is defined as a main bearing tooth surface; based on the angular indexing, a selective finish machining operation is performed on the primary bearing tooth surface.

Description

Technical Field

[0001] This invention relates to the field of mechanical transmission components, and particularly to a method and fixture for manufacturing gears with directionally defined main load-bearing tooth surfaces. More specifically, this invention relates to a noise-reducing and cost-optimized gear for an electronic parking brake (EPB) actuator, and a manufacturing method that significantly reduces processing costs while maintaining high reliability and acoustic performance. Background Technology

[0002] Electronic parking brake (EPB) systems are widely used in modern vehicles due to their advantages in integration efficiency, automation capabilities, and compatibility with vehicle control systems. In a typical EPB actuator, an electric motor drives a reduction gear mechanism to generate a large output force for engaging the parking brake.

[0003] The gears used in EPB actuators must meet several stringent requirements: First, the gears must operate reliably for a long time under low-speed, high-torque conditions; second, since the EPB actuators are installed close to the crew compartment, they must meet strict noise, vibration, and harshness (NVH) requirements; third, given the mass production characteristics of the EPB system, the gears must have economical manufacturing advantages, low unit cost, and stable quality.

[0004] Currently, the small-module gears used in EPB actuators are typically manufactured from copper alloys (such as C3604 brass) through full-profile machining, including hobbing, shaping, or milling. While these gears offer good noise reduction and wear resistance, the manufacturing process involves significant material removal, resulting in long machining cycles, severe tool wear, and increased production costs. In mass production, machining costs can account for a substantial proportion of the total gear cost.

[0005] To reduce costs, powder metallurgy (PM) gears have been proposed as an alternative. However, powder metallurgy gears inherently possess internal porosity, which can lead to increased noise, reduced fatigue strength, and uncertain long-term reliability. In safety-critical systems like EPB, customers often have safety concerns regarding the use of powder metallurgy gears, thus limiting their practical application.

[0006] Therefore, there is an urgent need for a new method for manufacturing gear structures that can reduce processing costs without relying on traditional powder metallurgy technology, while still meeting the stringent NVH and durability requirements of EPB actuators. Summary of the Invention

[0007] To overcome the shortcomings of the prior art, the present invention provides a gear manufacturing method and fixture with a directionally defined main bearing tooth surface. The gear structure reduces the amount of cutting while maintaining the low noise performance of the gear, and the manufacturing method minimizes the amount of material removed during machining and shortens the machining time.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a gear manufacturing method with a directionally defined main bearing tooth surface, comprising the following steps: cutting a metal blank into multiple independent disc-shaped blanks by a cutting or sawing process; pre-processing each disc-shaped blank to form a preliminary outer diameter, axial end face, and a center hole for mounting on a mandrel; fixing the disc-shaped blanks onto a mandrel structure, and fixing multiple disc-shaped blanks onto the mandrel shaft body; performing a hobbing operation on the fixed disc-shaped blanks using a hob, wherein all gear teeth (including the two opposing tooth surfaces of each tooth) conform to a standard involute tooth profile. After the hobbing operation is completed, the gear and mandrel structure are removed from the hobbing station and transferred to the post-processing station. In the post-processing stage, the gear is indexed at an angle relative to the orientation reference on the mandrel or a special indexing fixture. This orientation reference corresponds to the preset torque direction in actual use of the gear, thereby defining one of the tooth surfaces of each tooth as the main load-bearing tooth surface. Based on this angle indexing, selective finishing operations are performed on the main load-bearing tooth surface to specifically improve the working accuracy of the main load-bearing tooth surface and avoid finishing of non-load-bearing tooth surfaces, thereby reducing the number of finishing operations and shortening the tool cutting time.

[0009] As a preferred embodiment of the present invention, the gear is an integral structure made of a single fully dense copper alloy material.

[0010] As a preferred embodiment of the present invention, the finishing operation may be gear grinding, honing, or polishing.

[0011] As a preferred technical solution of the present invention, before completing the finishing operation, the fixed gear blank and mandrel structure are treated as a whole, and the angle between the orientation reference part and the gear teeth is kept fixed.

[0012] As a preferred embodiment of the present invention, the orientation reference part may be designed as a plane, keyway, groove, pin structure or indexing mark.

[0013] As a preferred embodiment of the present invention, one tooth surface of each tooth of the gear body serves as the main load-bearing tooth surface, while the opposite tooth surface mainly bears no load or secondary load as a non-load-bearing surface.

[0014] A gear clamp, wherein the gear clamp is a mandrel structure, the mandrel structure includes an end and a mandrel body disposed on the end, and an indexing block is disposed at the other end of the mandrel body, and an orientation reference part is provided on the indexing block, the orientation reference part serving as a positioning reference and used as an angle indexing positioning machining surface in finishing.

[0015] As a preferred embodiment of the present invention, the end portion includes a clamping part fixed to one side of the end block and a shoulder block disposed on the other side of the end block. The other side of the shoulder block is connected to a spindle body. The shoulder block serves as a reference surface. The gear blank is positioned against the shoulder block and fixed by a fixing member at one end of the spindle axis.

[0016] Compared with the prior art, the beneficial effects that this invention can achieve are: 1. Since the tooth profile is mainly obtained through near-net-shape forming, only the predetermined functional contact zone is micro-finished, and the total amount of cutting is greatly reduced; compared with fully machined copper alloy gears, the machining time can be shortened, directly reducing the unit part machining cost and tool consumption, and improving production efficiency; 2. Selective micro-finishing specifically targets the main load-bearing tooth surfaces and defined contact zones that actually engage under EPB operating torque. This concentrates surface quality improvements in critical areas, reducing meshing roughness excitation and improving repeatability. Therefore, operating noise is reduced, and more importantly, because functional areas are precisely controlled while non-functional areas do not introduce additional machining variations, noise differences between individual gears are reduced. 3. Near-net-shape construction provides consistent root transition fillets and tooth thickness, reducing stress concentration and lowering the likelihood of cracks caused by over-machining or sharp root transitions. Selective finishing fixtures further prevent over-machining, thereby reducing scrap rates and enabling stable mass production. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the gear manufacturing process of the present invention; Figure 2 This is a three-dimensional schematic diagram of a portion of the gear teeth of the present invention; Figure 3 This is a three-dimensional schematic diagram of gear honing according to the present invention; Figure 4 This is a schematic diagram of the three-dimensional structure of the gear teeth grinding of the present invention; Figure 5 This is a three-dimensional schematic diagram of the mandrel structure with gears installed according to the present invention; Figure 6 This is a three-dimensional schematic diagram of the mandrel structure of the present invention. The components are: 1. Gear body; 2. Gear teeth; 3. Main load-bearing tooth surface; 4. Non-load-bearing tooth surface; 5. Honing tool; 6. Grinding wheel; 7. Clamping part; 8. End block; 9. Shoulder block; 10. Fixing part; 11. Orientation reference part; 12. Indexing block; 13. Mandrel body. Detailed Implementation

[0018] To make the technical means, creative features, objectives, and effects of this invention easier to understand, the invention is further described below with reference to specific embodiments. However, the following embodiments are merely preferred embodiments of this invention and not all of them. Other embodiments obtained by those skilled in the art based on the embodiments described herein without creative effort are all within the protection scope of this invention.

[0019] Example 1 — Near-net-shape forming + selective micro-finishing Gear structure This invention provides a gear for automotive actuators (especially electronic parking brake (EPB) actuators), designed to achieve low noise performance and reduced manufacturing costs. The processing method for the gear structure described in this application primarily targets gears, and the application of gears in automotive actuators is only one form; gears using this processing method can also be applied to other unidirectional rotation scenarios. The gear includes a gear body 1 with a central hole defining a rotation axis and a plurality of teeth 2 arranged circumferentially around the rotation axis. The gear body 1 is made of a fully dense copper alloy material (such as brass alloy), which was chosen for its good noise damping characteristics, wear resistance, and formability.

[0020] Each tooth 2 includes a root portion, a tip portion, and an opposing tooth surface. Unlike conventional gears where all tooth surfaces are fully machined to achieve the final geometry, the gear in this embodiment only requires specific functional areas of the tooth surface to meet high surface precision and surface roughness requirements. Specifically, this gear is suitable for EPB applications, where torque is primarily transmitted in a single direction during braking engagement. Therefore, one tooth surface of each tooth 2 serves as the primary load-bearing tooth surface 3, while the opposing tooth surface primarily bears no load or secondary load as the non-load-bearing tooth surface 4.

[0021] In this embodiment, the main load-bearing tooth surface 3 includes a defined functional contact area configured to mesh with the mating gear under working load. This functional contact area has sufficient axial width and circumferential length to ensure precise meshing, controllable backlash, and low-noise operation. The remainder of the tooth 2 (including the non-load-bearing tooth surface 4, part of the tooth tip, and the transition area near the tooth root) remains in a near-net-shape state, requiring no full-profile machining.

[0022] By designing the gear structure to require high precision only in predetermined functional areas, this embodiment significantly reduces machining requirements while maintaining the mechanical and acoustic properties necessary for EPB operation. This structural concept forms the basis for the related manufacturing methods and fixtures described below.

[0023] Manufacturing method of directional selective precision gears In Example 1, a method for manufacturing gears with oriented, defined main load-bearing tooth surfaces is provided. This method is particularly suitable for gears used in actuator systems (such as electronic parking brake mechanisms) where the torque transmission direction is substantially fixed during operation. The manufacturing method begins with a blank preparation step: S1, cutting a metal bar into multiple independent gear blanks using a cutting or sawing process; S2, subsequently performing a pre-machining operation (such as turning) on ​​each gear blank to form a preliminary outer diameter, axial end face, and a center hole for mounting on a mandrel. At this stage, the gear blanks have not yet formed the finished tooth profile; S3, After pre-machining, the gear blank is mounted onto the mandrel structure of the hobbing machine. This mandrel structure extends approximately horizontally and can support one or more gear blanks axially at intervals. During installation, the gear blank is axially positioned using axial stops or spacers. S4, Subsequently, the hob, arranged approximately vertically, performs the conventional hobbing operation. During the hobbing process, the mandrel drives the gear blank and the hob to rotate freely and synchronously, and all teeth (including the two opposing tooth surfaces of each tooth) are generated according to the standard involute tooth profile. No angle locking or orientation constraint is applied to the gear blank during the hobbing process, therefore it is compatible with conventional hobbing equipment and does not interfere with the generating motion. S5, After the hobbing operation is completed, the gear and mandrel structure are moved from the hobbing station to the post-processing station; S6, In the post-processing stage, the gear is indexed angularly relative to the orientation reference on the mandrel or a special indexing fixture; this orientation reference corresponds to the preset torque direction in actual use of the gear, thereby defining one tooth surface of each tooth as the main load-bearing tooth surface; S7, Based on this angular indexing, selective post-processing operations (such as finishing, polishing, honing, shaving, or local grinding) are performed, such as... Figure 3 and Figure 4 As shown, and Figure 3 and Figure 4 For illustrative purposes only; the actual processing method shall prevail.

[0024] The key is that this post-processing operation is applied only to the main load-bearing tooth surfaces, while the relatively non-load-bearing tooth surfaces remain in their post-hogging state. By applying high-precision and excellent surface finish treatment only to the functionally critical tooth surfaces, this manufacturing method reduces unnecessary over-machining, improves noise performance, and allows for more lenient tolerance control in non-critical areas, thereby reducing overall manufacturing and assembly costs without altering the basic hobbing process.

[0025] In traditional gear manufacturing processes, after hobbing, the two tooth surfaces of each gear tooth are typically subjected to the same finishing operations (such as grinding, honing, or polishing) to achieve symmetrical surface accuracy, regardless of the actual force direction experienced by the gear during operation. This results in additional machining time, increased tool wear, and higher manufacturing costs, even for tooth surfaces that do not significantly contribute to torque transmission.

[0026] In contrast, the manufacturing method of the present invention clearly distinguishes between the main load-bearing tooth surface 3 and the non-load-bearing tooth surface 4 based on the preset torque transmission direction during gear operation. After the initial hobbing process forms a complete tooth profile, only the main load-bearing tooth surface 3 is selectively subjected to post-finishing operations, while the corresponding non-load-bearing tooth surface 4 remains in a semi-finished state.

[0027] By intentionally omitting the high-precision finishing of the non-load-bearing tooth surface 4, the number of finishing processes is reduced, the tool cutting time is shortened, and unnecessary surface finishing is avoided. This selective finishing strategy, under actual working conditions (especially for gear systems with fixed or primarily unidirectional torque, such as electronic parking brake systems (EPB systems), effectively controls manufacturing costs while ensuring meshing accuracy and noise performance.

[0028] Material properties The gear is a monolithic structure made of a single, fully dense copper alloy material (such as brass). The selected copper alloy has good noise damping characteristics, wear resistance, and formability, making it suitable for automotive actuator applications (especially electronic parking brake systems). In this embodiment, the material composition of the gear is uniformly distributed throughout the gear body, including the teeth, tooth roots, and center bore area.

[0029] Although the materials themselves are not classified into multiple types, gears are functionally differentiated through surface finishes. Specifically, the pre-defined functional contact areas on the gear teeth, corresponding to the main load-bearing tooth surfaces during actuator operation, are selectively micro-finished and optionally subjected to surface densification treatments such as rolling or polishing. These functional areas have higher surface precision and lower roughness to ensure low-noise meshing performance.

[0030] In contrast, the non-functional areas of the gear teeth (including the non-load-bearing tooth surface, part of the tooth tip, and the transition area near the tooth root) retain the surface state produced by the near-net-shape forming process. By modifying the surface only in the functional areas while maintaining a uniform material composition, this embodiment reduces processing costs and material waste without affecting acoustic performance or mechanical reliability.

[0031] Example 2—Manufacturing fixture for directional control and selective machining In Embodiment 2, a manufacturing fixture is provided for implementing the above-described manufacturing method and achieving selective machining of gear tooth surfaces with directional limitations. This manufacturing fixture is based on a mandrel structure and is compatible with conventional gear hobbing and post-processing equipment. The fixture includes a mandrel body 13 extending along a longitudinal axis, which can be mounted on a machine tool jaw or between the jaw and the tailstock via a clamping portion 7 of the mandrel structure. The outer cylindrical surface of the mandrel body 13 supports the center hole of the gear, thereby ensuring concentric alignment of the gear with the rotation axis of the mandrel.

[0032] The mandrel structure also includes an indexing block 12 disposed at the end of the mandrel body 13 and an orientation reference portion 11 disposed on the indexing block 12. The orientation reference portion 11 can be designed as a plane, keyway, groove, pin structure, or indexing mark. This orientation reference portion 11 does not interfere with the free rotation of the gear during gear hobbing, but serves as an angular reference in the indexing operation after hobbing. The mandrel fixture also includes one or more axial fixing members 10 arranged along the mandrel body 13 (such as spacers, spacers, mandrel shoulders, or similar). Figure 5 and Figure 6 The bolt-fitted parts shown are used to fix the gear body 1, while the shoulder block 9 serves as a reference surface. These axial fasteners 10 prevent axial movement of the gear body 1 during processing and ensure consistent axial positioning of multiple workpieces. While ensuring the gear body 1 is fixed, other forms of fasteners 10 can be used to fix the gear blank, not limited to threaded connections.

[0033] During the gear hobbing operation, the fixture supports the gear body 1 so that the spindle structure and hob can rotate synchronously via the machine tool. At this stage, the orientation reference 11 does not function. In the subsequent post-processing stage, the fixture cooperates with the indexing mechanism, which in turn cooperates with the orientation reference 11, thereby fixing the gear body 1 at an angle relative to the machining tool. In this fixed-angle state, selective post-processing operations can be performed on the preset main bearing tooth surface 3.

[0034] This fixture, by separating the rotary support function during gear hobbing from the angular indexing function during post-processing, can precisely control which tooth surfaces undergo high-precision finishing. This fixture structure ensures repeatability, improves process stability, and allows for the selective application of strict tolerances only where functional requirements necessitate, thus balancing manufacturing efficiency and product performance.

[0035] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for manufacturing a gear having a directionally defined main load-bearing tooth surface, characterized in that: The gear manufacturing method includes the following steps: S1, cutting the metal billet into multiple independent disc-shaped blanks through cutting or sawing processes; S2, perform pre-processing on each disc-shaped blank to form the initial outer diameter, axial end face and center hole for mounting on the mandrel; S3, fix the disc-shaped blank on the mandrel structure, and fix multiple disc-shaped blanks on the mandrel body 13; S4, the fixed disc-shaped blank is hobbed by a hob, and all gear teeth (including the two opposing tooth surfaces of each tooth) are generated according to the standard involute tooth profile; S5. After the gear hobbing operation is completed, the gear and mandrel structure are removed from the gear hobbing station and transferred to the post-processing station. S6, In the post-processing stage, the gear will be indexed at an angle relative to the orientation reference on the spindle or special indexing fixture; the orientation reference corresponds to the preset torque direction in actual use of the gear, thereby defining one of the tooth surfaces of each tooth as the main bearing tooth surface (3). S7. Based on this angle division, selective finishing operation is performed on the main bearing tooth surface (3), which improves the working accuracy of the main bearing tooth surface (3) in a targeted manner, avoids finishing of the non-bearing tooth surface (4), reduces the number of finishing operations, and shortens the tool cutting time.

2. The gear manufacturing method with a directionally defined main load-bearing tooth surface according to claim 1, characterized in that: The gear is an integral structure made of a single, fully dense copper alloy material.

3. The gear manufacturing method with a directionally defined main load-bearing tooth surface according to claim 1, characterized in that: The finishing operations can be gear grinding, honing, and polishing.

4. The gear manufacturing method with a directionally defined main load-bearing tooth surface according to claim 3, characterized in that: Before completing the finishing operation, the fixed gear blank and mandrel structure are treated as a whole, and the angle between the orientation reference part (11) and the gear tooth (2) is kept fixed.

5. The gear manufacturing method with a directionally defined main load-bearing tooth surface according to claim 4, characterized in that: The orientation reference part (11) can be designed as a plane, keyway, groove, pin structure or indexing mark.

6. The gear manufacturing method with a directionally defined main load-bearing tooth surface according to claim 1, characterized in that: One tooth surface of each tooth (2) of the gear body (1) serves as the main load-bearing tooth surface (3), while the opposite tooth surface mainly bears no load or secondary load as the non-load-bearing surface (4).

7. A gear fixture, applied to any one of the gear manufacturing methods according to claims 1-6, characterized in that: The gear clamp is a spindle structure, which includes an end and a spindle body (13) disposed on the end. The other end of the spindle body (13) is provided with an indexing block (12). An orientation reference part (11) is provided on the indexing block (12). The orientation reference part (11) serves as a positioning reference and is used as an angle indexing positioning machining surface in finishing.

8. The gear clamp according to claim 2, characterized in that: The end portion includes a clamping part (7) fixed on one side of the end block (8) and a shoulder block (9) provided on the other side of the end block (8). The other side of the shoulder block (9) is connected to the spindle body (13). The shoulder block (9) serves as a reference surface. The gear blank is positioned against the shoulder block (9) and fixed by a fixing member at one end of the spindle axis (13).

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