Lightweight integrated hollow shaft forging

Abstract

The utility model relates to motor drive part technical field especially a kind of lightweight integrated hollow shaft forge piece, connecting section is used to connect with reducer input shaft;Intermediate slender section is equipped with the inner hole for reducing weight and oil storage along the axial extension;Mounting section is used to cooperate with motor rotor core, and mounting section is equipped with the through hole being set along the axial direction, the through hole is coaxial through between inner hole, to supply cooling medium to flow into inner hole by the through hole, inflow hole of through hole is sealed by sealing block;Connecting section, intermediate slender section and mounting section are the integrated structure of no connection interface integrally forged into shape between;By the through hole inflow hole design is sealed by the structure of sealing block, and combine the tapered sealing surface of mounting section end, for temporary physical sealing to inner hole before heat treatment, effectively isolate external oxygen to enter inner hole in heat treatment process, so that shaft body can be directly placed into to air as heating medium Conventional normalizing furnace is handled.

Description

Technical Field

[0001] This utility model relates to the field of motor drive component technology, and in particular to a lightweight one-piece hollow shaft forging. Background Technology

[0002] The hollow shaft of the drive motor in new energy vehicles is a core torque transmission component connecting the motor rotor and the reducer, and its performance directly affects the efficiency, reliability, and durability of the drive system. To achieve lightweight design and integrated cooling, existing technologies generally employ a hollow shaft structure. However, this structure faces significant technical challenges in manufacturing, especially in the heat treatment stage.

[0003] Currently, for hollow shafts with deep and long inner holes, the mainstream manufacturing approach is to use a "segmented manufacturing and reassembly" process. This involves machining the connecting sections, intermediate sections, and mounting sections separately, and then assembling them into a whole through welding, interference fits, and connecting parts. While this split structure reduces the difficulty of machining individual sections, it inevitably introduces connection interfaces, leading to inherent problems such as stress concentration and difficulty in ensuring dynamic balance accuracy in the overall structure, thus affecting product reliability and lifespan.

[0004] A more prominent pain point lies in the oxidation and decarburization of the inner bore during heat treatment. Due to the deep and long inner bore and small diameter of the hollow shaft, when using a conventional normalizing furnace for air heating, oxygen in the furnace easily forms a "local oxygen-rich environment" within the inner bore, leading to severe oxidation and oxide scale formation on the inner bore surface, accompanied by the loss of surface carbon (decarburization). This defect directly degrades the surface quality of the inner bore, not only violating the technical requirements for forgings to have a smooth, defect-free inner wall, but also triggering a series of chain problems: the decarburized layer leads to a significant decrease in surface hardness and fatigue strength; the oxide scale falls off during subsequent service, clogging precision cooling channels and affecting the motor's heat dissipation efficiency. Currently, to avoid this problem, the industry is often forced to use controlled atmosphere normalizing furnaces or rely on outsourced heat treatment, but this significantly increases production costs and supply chain complexity, restricting the large-scale, economical manufacturing of products.

[0005] Therefore, there is an urgent need for an innovative hollow shaft design and manufacturing solution that can overcome the limitations of existing processes by starting from the product structure itself, so that it can be adapted to conventional heat treatment equipment, while fundamentally ensuring that the inner hole surface is free from oxidation and decarburization, and has high reliability, lightweight and excellent comprehensive performance. Utility Model Content

[0006] The technical problem to be solved by this utility model is: in order to solve the problems existing in the prior art in the background art, to provide a lightweight one-piece hollow shaft forging that fundamentally eliminates the oxidation and decarburization of the inner hole, achieves low-cost and high-quality heat treatment, and achieves the unity of extreme lightweight structure and high reliability performance.

[0007] The technical solution adopted by this utility model to solve its technical problem is: a lightweight one-piece hollow shaft forging, including a hollow shaft body, wherein the hollow shaft body includes... Connecting section, used for connection to the input shaft of the reducer; The middle section is slender and has an axially extending inner hole for weight reduction and oil storage. The mounting section is used to mate with the motor rotor core. The mounting section has an axially arranged through hole that is coaxially connected with the inner hole, allowing the cooling medium to flow into the inner hole through the through hole. This integrates an efficient and smooth cooling path, eliminating the need for additional connecting pipes. It has high heat dissipation efficiency, helps the motor maintain high power output continuously, and prevents thermal decay. The inlet hole of the through hole is sealed by a block, thereby preventing oxygen from entering the inner hole. This facilitates heat treatment in a normalizing furnace where the heating medium is air, thus improving the oxidation-free and decarburization-free inner wall of the hollow shaft. The connecting section, the slender middle section, and the installation section are integrally forged into a seamless structure, eliminating the need for welding, bolts, and other connection interfaces.

[0008] Furthermore, the lightweight one-piece hollow shaft forging installation section is formed by local heating and hot spinning, which concentrates energy, has a small heat-affected zone, and high forming precision, effectively ensuring the dimensional accuracy and surface quality of the installation section and the rotor core. The connection between the mounting section and the slender middle section is transitioned by a multi-step stepped shoulder. The outer surface of the mounting section is provided with a circular shaft section to support the bearing, providing a precise radial mounting reference and reliable axial positioning.

[0009] Furthermore, the inner hole includes a connected straight section and a tapered transition section. The tapered transition section is located close to the through hole in the mounting section, and its inner diameter gradually expands from the inside to the outside, forming a flow guide structure that facilitates the smooth introduction of cooling medium through the through hole.

[0010] Furthermore, the tapered transition section of the inner hole is connected to the through hole by a smoothly connected arc-shaped transition section.

[0011] Furthermore, the end face of the installation section and the corresponding outer peripheral surface of the sealing block form a matching conical sealing surface; the projection shape of this conical sealing surface on the vertical section passing through the axis is an inverted "eight" shape. Before or during heat treatment, the inlet is temporarily sealed to prevent external air from directly entering the deep inner hole, providing a convenient interface and serving as an auxiliary process to prevent oxidation of the inner hole.

[0012] Furthermore, the wall thickness of the slender middle section is less than that of the installation section, which not only reduces weight but also helps reduce internal stress and uneven cooling caused by abrupt changes in cross-section, thereby reducing the risk of accelerated oxidation and decarburization induced by differences in bamboo transformation.

[0013] Furthermore, the diameter of the connecting section is smaller than that of the middle slender section, and the two are connected by a sloping section to reduce dead zones of gas stagnation during heat treatment, which is conducive to the uniform flow and coverage of the protective atmosphere.

[0014] Furthermore, the matrix metallographic structure of the hollow shaft body consists of uniformly distributed ferrite and pearlite, with a bainite volume content of ≤10%, thereby ensuring the strength and toughness of the hollow shaft body.

[0015] Furthermore, the Brinell hardness of the hollow shaft body is 143–240 HBW, which gives the hollow shaft sufficient resistance to torsion, wear, and plastic deformation.

[0016] Furthermore, the depth of the decarburized layer on the surface of the hollow shaft body is ≤0.5mm, thereby ensuring the surface hardness and fatigue strength of the hollow shaft.

[0017] The beneficial effects of this utility model are: 1. By designing the inlet hole of the through hole as a structure that can be sealed by the sealing block, and combining it with the conical sealing surface at the end of the installation section, the inner hole is temporarily physically sealed before heat treatment, effectively preventing external oxygen from entering the inner hole during the heat treatment process. This allows the shaft to be directly placed into a conventional normalizing furnace with air as the heating medium for treatment, without relying on expensive and complex controlled atmosphere equipment. While significantly reducing production costs and process difficulty, it ensures that the inner wall of the inner hole is smooth and free from oxidation and decarburization, fundamentally eliminating oxidation and decarburization of the inner hole, and achieving low-cost, high-quality heat treatment. 2. The connecting section, the slender middle section, and the installation section are forged into a single unit, completely eliminating the connection interface and weak points of the traditional split structure, and significantly improving the overall strength and fatigue life. The slender middle section has the thinnest wall thickness, and the connecting section has a smaller diameter and a transition through an inclined section. This design precisely implements the principles of equal strength and lightweight, minimizing weight and rotational inertia while ensuring load-bearing capacity, achieving a balance between extreme lightweight structure and high reliability. 3. The installation section adopts local heating and hot spinning forming, which realizes near-net-shape forming of complex shapes in this area, with little thermal impact on other areas of the part, greatly improving plasticity, significantly reducing rheological stress, and good fluidity. 4. The metallographic structure, Brinell hardness, and surface decarburization layer depth ensure that the forgings have excellent strength, toughness, wear resistance, and fatigue performance. Attached Figure Description

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0019] Figure 1 This is a schematic diagram of the structure of this utility model; Figure 2This is a cross-sectional view of the present invention along direction AA; In the diagram: 1. Connecting segment, 2. Slender middle section; 21. Inner hole; 211. Straight section; 212. Tapered transition section; 213. Arc-shaped transition section. 3. Mounting section; 31. Through hole; 32. Circular shaft section. Detailed Implementation

[0020] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, illustrating only the basic structure of the present invention, and therefore only show the components relevant to the present invention.

[0021] like Figures 1-2 The lightweight, one-piece hollow shaft forging shown includes a hollow shaft body, which is an elongated rotating body, and the hollow shaft body comprises, along its axial direction, a series of components. Connecting section 1 is used to connect to the input shaft of the reducer; The middle slender section 2 has an axially extending inner hole 21 for weight reduction and oil storage. Mounting section 3 is used to mate with the motor rotor core. Mounting section 3 has an axially arranged through hole 31, which is coaxially connected with the inner hole 21, allowing the cooling medium to flow into the inner hole 21 through the through hole 31. The inner hole 21 mainly serves the dual function of weight reduction and storage and circulation channel for cooling oil (or coolant). The cooling medium is injected from the inlet of the through hole 31 at one end of mounting section 3 and flows smoothly into the inner hole 21 through the through hole 31, thereby forming an integrated, efficient and smooth cooling path inside the shaft, improving heat dissipation efficiency, helping the motor maintain high power output and preventing thermal decay. The inlet hole of the through hole 31 is sealed by a plug (not shown in the figure, such as a process plug); this seal can effectively prevent external oxygen from entering the deep and closed inner hole 21 during heat treatment, thereby creating a relatively isolated internal environment. This allows the hollow shaft to be directly placed into a conventional normalizing furnace with air as the heating medium for heat treatment, without relying on an expensive and complex controlled atmosphere furnace, ultimately achieving the technical requirements of a smooth inner surface, free of oxide scale and decarburized layer. Among them, the connecting section 1, the middle slender section 2 and the installation section 3 are integrally forged and formed without any connection interface. The sections are connected by a smooth geometric transition, forming a continuous whole without any mechanical connection interface such as welding or bolts.

[0022] Installation section 3 is formed by local heating and hot spinning. The connection between the mounting section 3 and the middle slender section 2 is transitioned by a multi-step stepped shoulder. The outer surface of the mounting section 3 is provided with a circular shaft section 32, which is used to support the bearing and provide a precise radial mounting reference and reliable axial positioning.

[0023] The inner hole 21 includes a connected straight section 211 and a tapered transition section 212. The tapered transition section 212 is located close to the through hole 31 in the mounting section 3, and its inner diameter gradually expands from the inside to the outside, forming a flow guide structure that facilitates the smooth introduction of cooling medium through the through hole 31.

[0024] like Figure 1 and Figure 2 As shown, the tapered transition section 212 of the inner hole 21 is connected to the through hole 31 by a smoothly connected arc-shaped transition section 213.

[0025] like Figure 2 As shown, the end face of the installation section 3 and the corresponding outer peripheral surface of the sealing block form a matching conical sealing surface; the projection shape of this conical sealing surface on the vertical section passing through the axis is an inverted "eight" shape, forming a funnel-shaped flow guiding structure.

[0026] The wall thickness of the slender middle section 2 is less than the wall thickness of the installation section 3.

[0027] The diameter of connecting section 1 is smaller than that of the middle slender section 2. The two are connected by a sloping section, which reduces the geometric dead angles where furnace gas may stagnate during the heat treatment process. This facilitates the uniform flow and coverage of the furnace atmosphere (or protective medium) along the outer surface of the parts, further improving the uniformity of the heat treatment process.

[0028] The matrix metallographic structure of the hollow shaft body consists of uniformly distributed ferrite and pearlite, with a bainite volume content of ≤10%. This metallographic structure ensures that the material has a good balance between strength and toughness.

[0029] The hollow shaft body has a Brinell hardness of 143 to 240 HBW, which ensures that the shaft has sufficient resistance to torsion, wear and plastic deformation to meet the stringent requirements of high torque transmission of the drive motor.

[0030] Ultimately, the depth of the decarburized layer on the surface of the hollow shaft body was ≤0.5mm, achieving a decarburized layer-free state.

[0031] In summary, this effectively ensures the consistency of surface hardness and fatigue strength of the parts, thereby ensuring the long lifespan and high reliability of the product.

[0032] Working principle and process: First, the billet after descaling undergoes cold forging in a rotary forging mill to reduce its wall thickness and length. Then, the thinner section of the billet is locally heated, followed by spinning to achieve the desired shape. Figure 1 , 2The one-piece hollow shaft blank shown; Subsequently, a special process sealing block was installed at the entrance of the through hole 31 using a conical sealing surface to seal it; Next, the sealed shaft is placed in a conventional normalizing furnace with air as the heating medium for heat treatment, during which the sealing structure effectively isolates the inner hole from the oxidizing furnace gas.

[0033] After heat treatment, the sealing block is removed, and key parts such as the inner hole 21 are precision machined to the final size.

[0034] During motor assembly, the cooling pipes are connected to the inlet of the through hole 31, through which the cooling medium is injected, flows through the through hole 31, the arc-shaped transition section 213, and the conical transition section 212, and finally enters the main channel of the inner hole 21, achieving effective cooling of the rotor system. The connecting section 1 is connected to the input shaft of the reducer, and the mounting section 3 is fitted with the motor rotor core, thereby completing the power transmission function.

[0035] Based on the above-described preferred embodiments of this utility model, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the technical concept of this utility model. The technical scope of this utility model is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A lightweight, one-piece hollow shaft forging, characterized in that: Includes a hollow shaft body, the hollow shaft body comprising Connecting section (1) is used to connect to the input shaft of the reducer; The middle slender section (2) has an axially extending inner hole (21) for weight reduction and oil storage. The mounting section (3) is used to cooperate with the motor rotor core. The mounting section (3) is provided with a through hole (31) arranged along the axial direction. The through hole (31) is coaxially connected with the inner hole (21) so that the cooling medium can flow into the inner hole (21) through the through hole (31). The inlet hole of the through hole (31) is sealed by the block block. Among them, the connecting section (1), the middle slender section (2) and the mounting section (3) are integral structures with no connecting interface formed by integral forging.

2. The lightweight one-piece hollow shaft forging according to claim 1, characterized in that: The installation section (3) is formed by local heating and hot spinning; The connection between the mounting section (3) and the middle slender section (2) is transitioned by a multi-stage stepped shoulder; The outer surface of the mounting section (3) is provided with a round shaft section (32) to support the bearing and provide a precise radial mounting reference and reliable axial positioning.

3. The lightweight one-piece hollow shaft forging according to claim 1, characterized in that: The inner hole (21) includes a connected straight section (211) and a tapered transition section (212). The tapered transition section (212) is located close to the through hole (31) in the mounting section (3), and its inner diameter gradually expands from the inside to the outside, forming a flow guide structure that facilitates the smooth introduction of cooling medium through the through hole (31).

4. A lightweight, one-piece hollow shaft forging according to claim 3, characterized in that: The tapered transition section (212) of the inner hole (21) is connected to the through hole (31) by a smoothly connected arc-shaped transition section (213).

5. A lightweight, one-piece hollow shaft forging according to claim 1, characterized in that: The end face of the installation section (3) and the corresponding outer peripheral face of the sealing block form a matching conical sealing surface; the projection shape of the conical sealing surface on the vertical section passing through the axis is an inverted "eight" shape.

6. A lightweight, one-piece hollow shaft forging according to claim 1, characterized in that: The wall thickness of the intermediate slender section (2) is less than the wall thickness of the mounting section (3).

7. A lightweight, one-piece hollow shaft forging according to claim 1, characterized in that: The diameter of the connecting segment (1) is smaller than the diameter of the middle slender segment (2), and the two are connected by a sloping transition segment.

8. A lightweight, one-piece hollow shaft forging according to claim 1, characterized in that: The matrix metallographic structure of the hollow shaft body is uniformly distributed ferrite and pearlite, and the bainite volume content is ≤10%.

9. A lightweight, one-piece hollow shaft forging according to claim 1, characterized in that: The Brinell hardness of the hollow shaft body is 143-240 HBW.

10. A lightweight, one-piece hollow shaft forging according to claim 1, characterized in that: The depth of the decarburized layer on the surface of the hollow shaft body is ≤0.5mm.

Images