Powder metallurgical hollow camshaft with brazed inner nose and method of manufacturing

Abstract

This invention discloses a powder metallurgy hollow camshaft with a brazed inner end and its manufacturing method, belonging to the technical field of engine valve train mechanisms. The camshaft includes a hollow substrate, powder metallurgy functional components mounted on its outer wall, an inner end inserted into one end of the substrate, and an outer end insert nested outside the same end. The powder metallurgy components and the substrate are metallurgically bonded by combined sintering diffusion welding, and the inner end is brazed to the substrate. The manufacturing method includes blank preparation, substrate pretreatment, assembly, combined sintering, end brazing, and finishing steps. The product of this invention reduces weight by 30%-50%, the inner cavity also serves as an oil passage for improved lubrication and heat dissipation, and the material utilization rate is >95%. The manufacturing method has short steps, high connection strength, and a cam phase angle accuracy ≤0.15°, making it suitable for high-speed water-cooled diesel engines and hybrid turbocharged engines.

Description

Technical Field

[0001] This invention relates to the field of manufacturing technology of core components of engine valve train, and in particular to a powder metallurgy hollow camshaft with brazed inner end and its manufacturing method. Background Technology

[0002] The camshaft is the core actuator of the engine's valve train, responsible for precisely controlling the valve opening and closing timing and lift, directly determining the engine's power output, fuel consumption, and emissions. In a four-stroke engine, the camshaft rotates at half the crankshaft speed, pushing tappets and rocker arms through the cam profile to achieve precise control of the cylinder's intake and exhaust processes.

[0003] The camshafts of existing water-cooled diesel engines are generally manufactured using a solid forging process with 45# steel, which presents several technical bottlenecks: First, the material utilization rate is extremely low. A large amount of machining is required to remove excess material from the solid blank, resulting in an overall material utilization rate of less than 40%, and the procurement and processing costs of large-diameter bars are high. Second, the excessive weight leads to high rotational inertia, poor valve following at high speeds, and sluggish engine transient response, failing to meet the performance requirements of hybrid and high-boost engines. Third, heat treatment deformation is difficult to control. Large-diameter solid shafts experience significant internal and external temperature differences during quenching, easily leading to defects such as warping and excessive ovality, increasing costs for subsequent straightening processes. Fourth, there is no built-in lubrication channel; lubricating oil can only lubricate through the surface gap of the journal, resulting in high frictional losses and low heat dissipation efficiency. Fifth, dynamic balancing is difficult, leading to significant noise and vibration during high-speed operation.

[0004] Existing combined camshaft technologies (such as CN104551288A and CN113958685B) have attempted to adopt a split structure, but they have not solved the problems of insufficient connection strength and poor reliability of the inner end of the hollow camshaft. Moreover, the manufacturing process is complex, and defects such as loosening and cracking are prone to occur at the joint interface, which cannot meet the usage requirements of diesel engines under high torque conditions. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a powder metallurgy hollow camshaft with brazed inner end and its manufacturing method. While ensuring the mechanical properties and reliability of the camshaft, it achieves lightweight design, integrated lubrication and heat dissipation functions, simplifies manufacturing processes, reduces production costs, and improves product precision.

[0006] The technical solution adopted in this invention, which relates to a powder metallurgy hollow camshaft with brazed inner end and its manufacturing method, is as follows: A powder metallurgical hollow camshaft with a brazed inner end cap includes a hollow substrate, a plurality of powder metallurgical functional components assembled on the outer wall of the hollow substrate, an inner end cap inserted into one end of the hollow substrate, and an outer end cap nested outside the same end of the hollow substrate; wherein, the powder metallurgical functional components and the hollow substrate are metallurgically bonded by combined sintering diffusion welding, the inner end cap is fixedly connected to the hollow substrate by brazing, and the outer end cap is fixedly connected to the hollow substrate by brazing or diffusion welding.

[0007] A further improvement to the technical solution of this invention is that the hollow matrix comprises a high-strength seamless steel pipe with an outer diameter of 38mm, an inner diameter of 29mm, a wall thickness of 4.5mm, and a theoretical torque ≥1300. The end furthest from the inner end is machined with a 60° inner chamfer as a positioning hole.

[0008] A further improvement of the technical solution of the present invention is that: the powder metallurgy functional component includes a common journal, a common cam and a combined journal, and both sides of the common journal, the common cam and the combined journal are provided with concave weight reduction structures, which are made of alloyed powder metallurgy material with a density of 7.5-7.7 g / cm³ and a surface hardness of HRC 56-63.

[0009] A further improvement of the technical solution of the present invention is that: the axial compression force between the powder metallurgy functional component and the hollow matrix is ​​≥80KN, and the connection torque is >1400. Both the inner end and the outer end insert are made of 45# steel with a hardness of HRB 80-100, and the inner end connection torque is ≥1500. External end insert connection torque ≥1000 .

[0010] A further improvement of the technical solution of the present invention is that: the end face of the powder metallurgy functional component is reserved for machining allowance, and the axial position tolerance after precision machining is ≤ ±0.3mm, and the cam phase angle accuracy is ≤0.15°.

[0011] A method for manufacturing a powder metallurgy hollow camshaft with brazed inner end, for manufacturing the aforementioned camshaft, includes the following steps: S1. Material preparation and pretreatment: Prepare hollow matrix and perform surface rust removal and degreasing, mold powder metallurgy functional component blanks and degrease them, and prepare inner end and outer end blocks. S2. Assembly and positioning: Fit the powder metallurgy compact onto the outer wall of the hollow matrix according to the design position; S3. Combined sintering diffusion welding: The assembled components are placed in a sintering furnace and sintered under a protective atmosphere to form a metallurgical bond between the powder metallurgy parts and the hollow matrix. S4. End connection: Insert the inner end into the interior of the hollow matrix end, and nest the outer end block outside the same end, and braze or diffusion weld the connection respectively. S5. Finishing and Inspection: The ends of the substrate, the end faces and ends of the powder metallurgy parts are finished, and the finished products are obtained after performance testing.

[0012] A further improvement of the above technical solution of the present invention is that: in step S3, the sintering temperature is 1120℃±10℃, the holding time is 1.5 hours, and during the sintering process, the alloying elements form a diffusion layer with a thickness ≥0.1mm at the interface.

[0013] A further improvement of the above technical solution of the present invention is that: in step S4, copper-based brazing filler metal is used for brazing, the brazing temperature is 850℃±20℃, and the welding is completed under a protective atmosphere.

[0014] A further improvement of the above technical solution of the present invention is that: in step S5, the powder metallurgy cam end face is ground, with a pre-machining allowance of 0.5-1mm, and the axial position tolerance after finishing is controlled within ±0.3mm.

[0015] The technological advancements achieved by this invention due to the adoption of the above technical solutions are as follows: Compared with traditional solid forged shafts, this invention reduces weight by 30%-50%, with a single shaft reducing weight by about 3.8Kg, significantly reducing rotational inertia and improving the engine's high-speed adaptability and transient response; the hollow inner cavity integrates lubrication channels, improving lubrication efficiency by more than 30%, while accelerating heat dissipation and stabilizing engine oil performance; the powder metallurgy cam has high surface hardness, extending wear life by more than 2 times.

[0016] The powder metallurgy near-net-shape forming process of this invention achieves a material utilization rate of >95%, far exceeding that of forging; the overall process is shortened to 6 steps, reducing a large number of turning and heat treatment straightening processes, and lowering manufacturing costs by 25%-35%; the combination of sintering diffusion welding and brazing processes ensures the connection strength and reliability of each component.

[0017] The present invention has controllable sintering shrinkage, cam phase angle accuracy ≤0.15°, axial position tolerance ≤±0.3mm, and product consistency is significantly better than traditional processes.

[0018] The lightweight design and reduced friction loss of this invention can reduce engine fuel consumption by 3%-5%. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of a camshaft manufactured using the solid forging process in the background art; Figure 2 This is a schematic diagram of the structure of a powder metallurgy hollow camshaft with a brazed inner end, according to the present invention. Figure 3 This is a schematic diagram of the left-end positioning structure of the present invention; Figure 4 This is a schematic diagram of the right end assembly connection structure of the present invention; Figure 5 This is a schematic diagram of the interface between the powder metallurgy functional component and the hollow matrix. Figure 6 This is a schematic diagram showing the machining allowance of the end face of a powder metallurgy cam.

[0020] In the attached diagram: 1. Hollow substrate; 2. Ordinary journal; 3. Ordinary cam; 4. Combined journal; 5. Inner end head; 6. Outer end insert; 7. 60° inner chamfer. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings. In the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessarily obscuring the concept of this invention. Example 1

[0022] like Figure 2-6 As shown in the figure, the powder metallurgy hollow camshaft with brazed inner end disclosed in this embodiment includes a hollow substrate 1. The outer wall of the hollow substrate 1 is equipped with 3 ordinary journals 2, 12 ordinary cams 3 and 1 combined journal 4. An inner end 5 is inserted into the right end of the hollow substrate 1, and an outer end insert 6 is nested on the outside of the right end.

[0023] Hollow matrix 1 is made of 40Cr high-strength seamless steel pipe with an outer diameter of 38mm, an inner diameter of 29mm, and a wall thickness of 4.5mm. After quenching and tempering, its tensile strength is ≥980MPa and its theoretical torque is ≥1300. The left end of the hollow substrate 1 is machined with a 60° internal chamfer 7, which serves as a positioning reference for subsequent finishing and replaces the internal center hole of the traditional solid shaft. The inner cavity of the hollow substrate 1 serves as a lubrication channel, supplying oil directly to the friction surface through the oil hole on the journal, thereby achieving forced lubrication and heat dissipation.

[0024] The ordinary journal 2, ordinary cam 3, and combined journal 4 are all made of HYHH-3 high wear-resistant powder metallurgy material, with the following chemical composition: C 0.8~1.0%, Cr 1.5~2.0%, Mo 0.5~0.8%, Cu 1.0~1.5%, and the balance being Fe. Each component has a 2mm deep concave weight-reduction structure on both sides, achieving a density of 7.6g / cm³ after sintering, a surface hardness of HRC 59, and a core hardness of HRC 35, thus balancing surface wear resistance and overall toughness.

[0025] The powder metallurgical functional component and the hollow substrate 1 are joined by combined sintering diffusion welding, forming a diffusion layer with a thickness of approximately 0.15 mm at the interface, achieving atomic-level bonding. Testing showed an axial release force of 92 kN and a connection torque of 1560 N. It has a strength far exceeding that of mechanical interference fits, and there is no risk of loosening or detachment under all engine operating conditions.

[0026] Both the inner end cap 5 and the outer end insert 6 are made of 45# steel, with a hardness of HRB 90 after heat treatment. The inner end cap 5 is inserted into the right end of the hollow substrate 1 and connected by brazing with copper-based solder, achieving a connection torque of 1680. The outer end is machined with an M20×1.5 drive thread; the outer end insert 6 is nested outside the right end of the hollow base 1 and is brazed with the same brazing filler metal, with a connection torque of 1120. It has φ8mm positioning pin holes machined on it.

[0027] The end face of the ordinary cam 3 is reserved with a machining allowance of 0.6mm. After sintering, it is precision machined by CNC end face grinding machine, and the final axial position tolerance is controlled within ±0.3mm. Example 2

[0028] This embodiment provides a method for manufacturing a powder metallurgy hollow camshaft with brazed inner end, including the following steps: S1. Material preparation and pretreatment: Cut φ38×4.5mm 40Cr seamless steel pipes to a length of 520mm as hollow matrix 1. Remove surface oxide scale by sandblasting and then remove oil stains by ultrasonic degreasing. Mix powder metallurgy raw materials according to the formula and press to form blanks of various functional parts. The blank density is 6.4g / cm³. Keep in a degreasing furnace at 400℃ for 1 hour to remove paraffin binder. Use 45# steel bar to process inner end 5 and outer end inserts, and heat treat to HRB 90.

[0029] S2. Assembly and positioning: Using a special phase angle tooling, the three ordinary journals 2, the twelve ordinary cams 3 and the one combined journal 4 are precisely fitted onto the outer wall of the hollow base 1 according to the design position. The fit clearance between each blank and the base is 0.05mm, and it is temporarily fixed by elastic clamps.

[0030] S3. Combined Sintering Diffusion Welding: The assembled components are placed in a mesh belt sintering furnace, and a decomposed ammonia protective atmosphere is introduced. The temperature is raised to 1120℃ at a rate of 10℃ / min, held at that temperature for 1.5 hours, and then cooled to room temperature with the furnace. During the sintering process, alloying elements such as Cr and Mo diffuse to the surface of the steel pipe, forming a continuous metallurgical bonding layer.

[0031] S4. End Connection: Insert the inner end 5 into the right end of the hollow substrate 1 with a clearance of 0.08mm. The outer end insert 6 is nested outside the substrate with a clearance of 0.05mm. Fill the connection surface with brazing foil. Place it in a vacuum brazing furnace and evacuate to 5×10⁻⁶ mm. -3 Pa, heat to 850℃ and hold for 20 minutes, then cool in the furnace to below 100℃ before removing from the furnace.

[0032] S5. Finishing and Inspection: Machining the 60° inner chamfer 7 on the left end of the hollow substrate 1 on a CNC lathe; grinding the cam end face using a CNC end face grinder to ensure an axial position tolerance of ±0.3mm; machining the M20×1.5 thread on the inner end 5 and the φ8mm pin hole on the outer end insert 6; finally, performing dimensional inspection, hardness testing, torsional strength testing, and dynamic balance correction. Once qualified, it is the finished product.

[0033] In the above embodiments, a powder metallurgy hollow camshaft with brazed inner end and its manufacturing method are provided. Compared with traditional solid forged camshafts, the present invention reduces weight by 30%-50%, with a single shaft weight reduction of approximately 3.8 kg, significantly reducing rotational inertia and improving the engine's high-speed adaptability and transient response. The hollow inner cavity integrates lubrication channels, improving lubrication efficiency by more than 30%, while accelerating heat dissipation and stabilizing engine oil performance. The powder metallurgy cam has high surface hardness, extending wear life by more than 2 times. The powder metallurgy near-net-shape forming process of the present invention achieves a material utilization rate of >95%, far exceeding that of forging processes. The overall process is shortened to 6 steps, reducing a large number of turning and heat treatment straightening processes, and reducing manufacturing costs by 25%-35%. The combination of sintering diffusion welding and brazing processes ensures the connection strength and reliability of each component. The sintering shrinkage rate of the present invention is controllable, the cam phase angle accuracy is ≤0.15°, and the axial position tolerance is ≤±0.3mm, with product consistency significantly better than traditional processes. The lightweight and reduced friction loss of the present invention can reduce engine fuel consumption by 3%-5%.

[0034] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the concept and scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the inventive concept should fall within the protection scope of the present invention. All technical contents for which protection is sought in this invention are fully described in the claims.

Claims

1. A powder metallurgy hollow camshaft with brazed inner end, characterized in that: It includes a hollow substrate (1), multiple powder metallurgy functional components assembled on the outer wall of the hollow substrate (1), an inner end head (5) inserted into one end of the hollow substrate (1), and an outer end block (6) nested outside the same end of the hollow substrate (1); wherein, the powder metallurgy functional components and the hollow substrate (1) are metallurgically bonded by combined sintering diffusion welding, the inner end head (5) is fixedly connected to the hollow substrate (1) by brazing, and the outer end block (6) is fixedly connected to the hollow substrate (1) by brazing or diffusion welding.

2. The powder metallurgy hollow camshaft with brazed inner end as described in claim 1, characterized in that: The hollow matrix (1) comprises a high-strength seamless steel pipe with an outer diameter of 38mm, an inner diameter of 29mm, a wall thickness of 4.5mm, and a theoretical torque ≥1300. The end away from the inner end (5) has a 60° inner chamfer (7) as a positioning hole.

3. The powder metallurgy hollow camshaft with brazed inner end as described in claim 1, characterized in that: The powder metallurgical functional components include ordinary journals (2), ordinary cams (3) and combined journals (4). Both sides of the ordinary journals (2), ordinary cams (3) and combined journals (4) are provided with concave weight reduction structures. They are made of alloyed powder metallurgy materials with a density of 7.5-7.7 g / cm³ and a surface hardness of HRC 56-63.

4. The powder metallurgy hollow camshaft with brazed inner end as described in claim 1, characterized in that: The axial pressure release force between the powder metallurgy functional component and the hollow matrix (1) is ≥80KN, and the connection torque is >1400. Both the inner end (5) and the outer end insert (6) are made of 45# steel with a hardness of HRB 80-100. The connecting torque of the inner end (5) is ≥1500. The connecting torque of the outer end insert (6) is ≥1000. .

5. A powder metallurgy hollow camshaft with brazed inner end as described in claim 1, characterized in that: The end face of the powder metallurgy functional component has a pre-machining allowance, and the axial position tolerance after precision machining is ≤ ±0.3mm, and the cam phase angle accuracy is ≤0.15°.

6. A method for manufacturing a powder metallurgy hollow camshaft with brazed inner ends, characterized in that, For manufacturing the camshaft according to any one of claims 1-5, the following steps are included: S1. Material preparation and pretreatment: Prepare hollow matrix (1) and remove rust and grease from the surface, mold the powder metallurgy functional component blank and degrease it, and prepare inner end (5) and outer end block (6). S2. Assembly and positioning: The powder metallurgy compact is fitted onto the outer wall of the hollow matrix (1) according to the design position; S3, Combined sintering diffusion welding: The assembled components are placed in a sintering furnace and sintered under a protective atmosphere to form a metallurgical bond between the powder metallurgy components and the hollow matrix (1). S4. End connection: Insert the inner end (5) into the interior of the hollow substrate (1) and the outer end insert (6) nested outside the same end, and braze or diffusion weld the connection respectively. S5. Finishing and Inspection: The ends of the substrate, the end faces and ends of the powder metallurgy parts are finished, and the finished products are obtained after performance testing.

7. The manufacturing method of a powder metallurgy hollow camshaft with brazed inner end according to claim 6, characterized in that: In step S3, the sintering temperature is 1120℃±10℃, the holding time is 1.5 hours, and during the sintering process, alloying elements form a diffusion layer with a thickness ≥0.1mm at the interface.

8. The method for manufacturing a powder metallurgy hollow camshaft with brazed inner end according to claim 6, characterized in that: In step S4, copper-based brazing filler metal is used for brazing at a temperature of 850℃±20℃, and the welding is completed under a protective atmosphere.

9. A method for manufacturing a powder metallurgy hollow camshaft with brazed inner end according to claim 6, characterized in that: In step S5, the powder metallurgy cam end face is ground, with a machining allowance of 0.5-1mm, and the axial position tolerance after finishing is controlled within ±0.3mm.

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