Assembling device and assembling method for combined camshaft

Abstract

The invention discloses an assembling device and an assembling method for a combined cam shaft, which are characterized in that high-strength connection is realized, namely, the ultrahigh temperature difference between a cam sheet and a shaft tube is utilized to realize larger interference fit amount, so that the formed combined cam shaft can meet more stringent working conditions of an engine; due to the fact that the initial gap is large in the assembling process, a wider'operation time window 'is provided, the harshness of the operation rhythm is reduced, and the assembling process is more accurate and leisurely; no contact force or slight contact exists between the cam sheet and the shaft tube, so that the accurate grinding coating on the surface of the shaft tube is completely protected; full automation and high takt: automatic line production is suitable for large-scale production.

Description

Technical Field

[0001] This invention relates to the field of manufacturing technology for combined camshafts of internal combustion engines, and particularly to an assembly device and assembly method for a combined camshaft. Background Technology

[0002] Compared to camshafts made from a single material, modular camshafts divide the camshaft into several assemblable sub-parts. Based on different performance requirements, appropriate materials are selected and precision-machined before assembling them into a single camshaft. Due to their lightweight, high performance, and low cost, modular camshafts have maintained a promising market outlook. Currently used assembly processes include knurling, sintering, heat-shrinking (single-sided heating), and tube expansion. These traditional assembly methods mainly suffer from the following problems: Knurling (knurling the outer diameter of the shaft tube, slotting the inner hole of the cam plate, and pressing the cam sleeve onto the shaft tube axially; due to the interference fit between the outer diameter of the shaft tube and the diameter of the cam hole, the product undergoes plastic deformation after pressing, forming a strong mechanical connection); the knurling method has the following problems: Stress concentration: The tooth-like protrusions and grooves formed by knurling are stress concentration points at the root, which are prone to fatigue cracks under the periodic force of the cam. Limited and unstable connection strength: The tolerance fluctuations of the outer diameter of the shaft tube and the inner hole of the cam plate will directly affect the interference and the actual connection strength, which may lead to loosening of individual components or excessive assembly stress and damage to parts. The sintering method (pressing powdered cam plates onto a shaft tube, then placing them in a sintering furnace for formal sintering, during which the cam material shrinks and densifies while tightly connecting with the shaft tube); the sintering method has the following problems: Low precision: The cam shrinks during the sintering process, and the axial dimensions and angular position of the cam will change to a certain extent, making it difficult to control the precision. The heat-shrink method (traditional heat-shrink method involves heating the cam plate at room temperature so that its inner diameter is larger than the outer diameter of the shaft tube, and then installing the cam onto the shaft tube in a short time. After cooling, the cam plate shrinks, generating a huge bonding force with the shaft tube to form a strong integral connection); the heat-shrink method has the following problems: Weak connection strength: Limited by the initial clearance, the maximum interference between the cam and the shaft tube can be limited to a certain extent, and the theoretical assembly clearance is small. It is only suitable for camshafts with low load torque.

[0003] Therefore, it is necessary to develop a combined camshaft assembly device and assembly method to solve the above problems. Summary of the Invention

[0004] The purpose of this invention is to design a combined camshaft assembly device and assembly method to solve the above problems.

[0005] The present invention achieves the above objectives through the following technical solutions: An assembly device for a combined camshaft, comprising: First vertical moving mechanism; The first gripper; the first gripper is installed below the moving end of the first vertical moving mechanism; Liquid nitrogen tank; a first vertical moving mechanism is installed above the liquid nitrogen tank; a first gripper is positioned directly above the opening of the liquid nitrogen tank; A horizontal moving mechanism; the horizontal moving mechanism is installed on one side of the liquid nitrogen tank; the moving direction of the horizontal moving mechanism is perpendicular to the moving direction of the first vertical moving mechanism; The second gripper; the second gripper is mounted on the moving end of the horizontal moving mechanism; the horizontal moving path of the second gripper intersects the vertical moving path of the first gripper; A press-fitting mechanism used to press the shaft tube into the cam plate; Cam plate positioning device; the cam plate positioning device is installed inside the pressing mechanism; An industrial robot used to transfer shaft tubes to the pressing mechanism and transfer cam plates to the cam plate positioning device; the industrial robot is positioned between the pressing mechanism and the first vertical moving mechanism.

[0006] Specifically, the pressing mechanism includes a vertically arranged second linear motor, a third cylinder, and a positioning center. The moving end of the second linear motor is connected to the side wall of the third cylinder. The third cylinder is installed vertically upside down. The positioning center is set vertically. The output end of the third cylinder is connected to the upper end of the positioning center. The lower end of the positioning center is connected to the upper end of the shaft tube. The cam plate positioning device is placed directly below the positioning center.

[0007] Furthermore, the pressing mechanism also includes a vertically arranged third linear motor and a guide rod. The second linear motor is located directly below the third linear motor, the guide rod is vertically arranged, the lower end of the guide rod is connected to the moving end of the third linear motor, and the upper end of the guide rod passes upward through the cam plate positioning device and presses against the lower end of the shaft tube.

[0008] Furthermore, preferably, the positioning tip is set on the same axis as the guide rod.

[0009] Furthermore, the first vertical moving mechanism is a first linear motor, which includes a first bearing, a first lead screw, a first servo motor, a lifting platform, and a first guide rail. The first end of the first lead screw is rotatably placed in the first bearing, and the second end of the first lead screw is connected to the shaft of the first servo motor. A screw hole is vertically provided in the middle of the lifting platform, and the lifting platform is threadedly engaged with the first lead screw through the screw hole. The lifting platform is circumferentially limited and vertically guided by the first guide rail.

[0010] Furthermore, the second linear motor includes an upper bearing, a second lead screw, a second servo motor, and an upper lifting platform; the third linear motor includes a lower bearing, a third lead screw, a third servo motor, and a lower lifting platform. The second and third linear motors share a second guide rail. The upper end of the second lead screw is rotatably placed inside the upper bearing, and the lower end of the second lead screw is connected to the shaft of the second servo motor. A screw hole is vertically provided in the middle of the upper lifting platform, and the upper lifting platform is threadedly engaged with the second lead screw through the screw hole. The lower end of the third lead screw is rotatably placed inside the lower bearing, and the upper end of the third lead screw is connected to the shaft of the third servo motor. A screw hole is vertically provided in the middle of the lower lifting platform, and the lower lifting platform is threadedly engaged with the third lead screw through the screw hole. Both the upper and lower lifting platforms are circumferentially limited and vertically guided by the second guide rail.

[0011] Furthermore, the horizontal moving mechanism includes a fourth linear motor and a support arm, with the support arm mounted on the moving end of the fourth linear motor and the second gripper mounted on the support arm.

[0012] An assembly method for a combined camshaft assembly device includes the following steps: S1. Incoming material inspection: Determine whether the dimensions, form and position tolerances, surface roughness, material and heat treatment status of the cam plate and shaft tube are qualified. S2. Cleaning and matching of parts; use ultrasonic cleaning to thoroughly remove oil, debris and impurities from the surface of parts; then perform 100% re-inspection of the inner diameter of the cam plate and the outer diameter of the shaft tube to ensure that the interference fit between each set of cam plates and the shaft tube is within the set range. S3, Temperature difference treatment; including heating cam plates and cooling shaft tubes; S4. Rapid transfer and positioning; After the cam plates are heated, the industrial robot quickly grabs a group of multiple cam plates into the cam plate positioning device within 8 seconds, fixing the cam plate phase and the axial distance between the cam plates. The heating wire ensures that the temperature of the cam plates is between 90℃ and 100℃. After the cam plates are positioned, the cooled shaft tube leaves the liquid nitrogen tank through the action of the first vertical moving mechanism. The industrial robot quickly grabs the shaft tube to the bottom of the positioning tip, so that the center hole at the head end of the shaft tube contacts the conical surface of the positioning tip. At the same time, the third linear motor drives the guide rod to move upward through the lower lifting platform until it hits the center hole at the tail end of the shaft tube. At this time, the shaft tube is clamped, and the axis of the shaft tube is collinear with the axis of the inner hole of multiple cam plates. S5, Press-fitting; Under the action of the second and third linear motors, the positioning center and guide rod drive the shaft tube to be sent from top to bottom at a constant and low speed to the precise axial positioning position to cooperate with multiple cam plates, and hold for 3-5 seconds; S6, Natural Delay; The press-fitted modular camshaft is transferred to a specific workstation by an industrial robot to cool to room temperature, allowing the temperature of each part to become completely uniform, the internal stress to be redistributed, and a uniform interference fit between the cam plate and the shaft tube to be achieved.

[0013] Specifically, S1 also includes laser shaping the inner wall of the cam plate to form a cross-striped pit structure.

[0014] Further, in S3, the heating cam plate includes: heating in an induction heating device, with a set temperature of 230°C and a heating time of 490 seconds. During the heating process, the inner diameter of the cam plate expands by 0.05 mm due to heat. The cooling shaft tube includes: picking up the qualified shaft tube from the material tray through the second gripper, sending the shaft tube to the underside of the first gripper of the cryogenic cooling device through the horizontal moving mechanism, clamping the shaft tube with the first gripper, releasing the second gripper and removing it through the horizontal moving mechanism, and then transferring the shaft tube to a liquid nitrogen tank with a set temperature of -196°C through the first vertical moving mechanism, and keeping it immersed for 300 seconds to fully cool it to the target temperature, with the outer diameter of the shaft tube shrinking by 0.05 mm due to cryogenic cooling.

[0015] The beneficial effects of this invention are as follows: High-strength connection: By utilizing the ultra-high temperature difference between the cam plate and the shaft tube, a larger interference fit is achieved, enabling the formed composite camshaft to meet more demanding engine operating conditions.

[0016] High assembly precision and consistency: Due to the large initial gap during assembly, a wider "operation time window" is provided, reducing the rigor of the operation rhythm, thus making the assembly process more precise and relaxed.

[0017] "Zero-damage" assembly: Since there is no contact force or only slight contact between the cam plate and the shaft tube, the finely ground coating on the surface of the shaft tube is completely protected.

[0018] Fully automated and high-speed: Automated assembly line operation, suitable for large-scale production. Attached Figure Description

[0019] Figure 1 This is a front view of the first vertical moving mechanism and the horizontal moving mechanism in this application; Figure 2 This is a side view of the first vertical moving mechanism and the horizontal moving mechanism in this application; Figure 3 This is the front view of the pressing mechanism in this application; Figure 4 This is a side view of the pressing mechanism in this application; Figure 5 This is a schematic diagram of the microstructure of the inner surface of the cam.

[0020] In the diagram: 1-First vertical moving mechanism; 2-First guide rail; 3-First gripper; 4-Second gripper; 5-First lead screw; 6-First cylinder; 7-Horizontal moving mechanism; 8-Support arm; 9-Fourth linear motor; 10-Second cylinder; 11-Liquid nitrogen tank; 12-Liquid nitrogen tank opening; 13-Mounting bracket; 14-Second guide rail; 15-Upper lifting platform; 16-Lower lifting platform; 17-Cam plate positioning device; 18-Upper bearing; 19-Second lead screw; 20-Third cylinder; 21-Positioning center; 22-Second servo motor; 23-Third servo motor; 24-Guide rod; 25-Third lead screw; 26-Lower bearing. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0022] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0023] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0024] In the description of this invention, it should be understood that the terms "upper," "lower," "inner," "outer," "left," "right," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use, or the orientation or positional relationship commonly understood by those skilled in the art. They are only used to facilitate the description of this invention and to simplify the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0025] Furthermore, the terms "first," "second," etc., are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0026] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, terms such as "set" and "connection" should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0027] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0028] like Figure 1-4 As shown, an assembly device for a combined camshaft includes: First vertical moving mechanism 1; First gripper 3; First gripper 3 is installed below the moving end of the first vertical moving mechanism 1; First gripper 3 is driven by first cylinder 6; Liquid nitrogen tank 11; a first vertical moving mechanism 1 is installed above the liquid nitrogen tank 11; a first gripper 3 is positioned directly above the liquid nitrogen tank opening 12 of the liquid nitrogen tank 11; Horizontal moving mechanism 7; horizontal moving mechanism 7 is installed on one side of liquid nitrogen tank 11; the moving direction of horizontal moving mechanism 7 is perpendicular to the moving direction of first vertical moving mechanism 1. The second gripper 4 is mounted on the moving end of the horizontal moving mechanism 7; the horizontal moving path of the second gripper 4 intersects the vertical moving path of the first gripper 3; the second gripper 4 is driven by the second cylinder 10. A press-fitting mechanism used to press the shaft tube into the cam plate; Cam plate positioning device; the cam plate positioning device is installed inside the pressing mechanism; An industrial robot used to transfer shaft tubes to the pressing mechanism and transfer cam plates to the cam plate positioning device; the industrial robot is positioned between the pressing mechanism and the first vertical moving mechanism 1.

[0029] like Figure 3 and 4 As shown, the pressing mechanism includes a vertically arranged second linear motor, a third cylinder 20, and a positioning center 21. The moving end of the second linear motor is connected to the side wall of the third cylinder 20. The third cylinder 20 is installed vertically upside down. The positioning center 21 is set vertically. The output end of the third cylinder 20 is connected to the upper end of the positioning center 21. The lower end of the positioning center 21 is connected to the upper end of the shaft tube. The cam plate positioning device 17 is placed directly below the positioning center 21.

[0030] like Figure 3 and 4As shown, the pressing mechanism also includes a vertically arranged third linear motor and a guide rod 24. The second linear motor is positioned directly below the third linear motor. The guide rod 24 is vertically arranged, with its lower end connected to the moving end of the third linear motor. The upper end of the guide rod 24 passes upward through the cam plate positioning device 17 and presses against the lower end of the shaft tube. The positioning center 21 is coaxial with the guide rod 24. Both the second and third linear motors are mounted on the mounting bracket 13. like Figure 1 and 2 As shown, the first vertical moving mechanism 1 is a first linear motor (some structures are not shown in the figure). The first linear motor includes a first bearing, a first lead screw 5, a first servo motor, a lifting platform, and a first guide rail 2. The first end of the first lead screw 5 is rotatably placed in the first bearing, and the second end of the first lead screw 5 is connected to the shaft of the first servo motor. A screw hole is vertically provided in the middle of the lifting platform. The lifting platform is threadedly engaged with the first lead screw 5 through the screw hole. The lifting platform is circumferentially limited and vertically guided by the first guide rail 2.

[0031] like Figure 3 and 4 As shown, the second linear motor includes an upper bearing 18, a second lead screw 19, a second servo motor 22, and an upper lifting platform 15. The third linear motor includes a lower bearing 26, a third lead screw 25, a third servo motor 23, and a lower lifting platform 16. The second and third linear motors share a second guide rail 14. The upper end of the second lead screw 19 is rotatably placed inside the upper bearing 18, and the lower end of the second lead screw 19 is connected to the shaft of the second servo motor 22. A screw hole is vertically provided in the middle of the upper lifting platform 15, and the upper lifting platform 15 is threadedly engaged with the second lead screw 19 through the screw hole. The lower end of the third lead screw 25 is rotatably placed inside the lower bearing 26, and the upper end of the third lead screw 25 is connected to the shaft of the third servo motor 23. A screw hole is vertically provided in the middle of the lower lifting platform 16, and the lower lifting platform 16 is threadedly engaged with the third lead screw 25 through the screw hole. Both the upper lifting platform 15 and the lower lifting platform 16 are circumferentially limited and vertically guided by the second guide rail 14. The working principle of the second linear motor is as follows: When the second servo motor 22 is working, its shaft drives the second lead screw 19 to rotate. Because the upper lifting platform 15 is threadedly engaged with the second lead screw 19, and the upper lifting platform 15 is circumferentially limited and vertically guided by the second guide rail 14, the upper lifting platform 15 moves up and down along the second guide rail 14 when the second servo motor 22 is working. The working principles of the first, third, and fourth linear motors 9 are the same, and will not be elaborated here.

[0032] like Figure 1 and 2 As shown, the horizontal moving mechanism 7 includes a fourth linear motor 9 and a support arm 8. The support arm 8 is mounted on the moving end of the fourth linear motor 9, and the second gripper 4 is mounted on the support arm 8.

[0033] An assembly method for a combined camshaft assembly device includes the following steps: S1. Incoming material inspection; determine whether the dimensions, form and position tolerances, surface roughness, material, and heat treatment status of the cam plate (material GCr15) and the shaft tube (material E355) are qualified; the inner wall of the cam plate is laser-shaped to form a cross-striped pit structure, such as... Figure 5 As shown, the cross-striped recessed structure on the inner wall of the cam plate forms a mechanical interlocking structure similar to "gear meshing" on the microscopic level of the final assembled camshaft. This structure not only increases the contact area but also distributes the torque load through physical interlocking, making the connection between the cam plate and the shaft tube more robust, able to withstand higher torque, and preventing slippage under extreme operating conditions. S2. Cleaning and matching of parts; use ultrasonic cleaning to thoroughly remove oil, debris and impurities from the surface of parts; then perform 100% re-inspection of the inner diameter of the cam plate and the outer diameter of the shaft tube to ensure that the interference fit between each set of cam plates and the shaft tube is within the set range. S3. Temperature difference treatment; including heating cam plate and cooling shaft tube; heating cam plate includes: heating in an induction heating device, the set temperature is 230℃, the heating time is 490 seconds, during the heating process, the inner diameter of the cam plate expands by 0.05mm due to heat; cooling shaft tube includes: the qualified shaft tube is picked up from the material tray by the second gripper 4, the shaft tube is sent to the first gripper 3 of the cryogenic cooling device by the horizontal moving mechanism 7, the first gripper 3 clamps the shaft tube, the second gripper 4 is released and removed by the horizontal moving mechanism 7, and then the shaft tube is transferred to the liquid nitrogen tank 11 with the temperature set at -196℃ by the first vertical moving mechanism 1, and kept immersed for 300 seconds to fully cool it to the target temperature, and the outer diameter of the shaft tube shrinks by 0.05mm due to cryogenic cooling.

[0034] S4. Rapid transfer and positioning; After the cam plates are heated, the industrial robot quickly grabs a group of multiple cam plates (8 in total) into the cam plate positioning device 17 within 8 seconds, fixing the cam plate phase and the axial distance between the cam plates. The heating wire ensures that the temperature of the cam plates is between 90℃ and 100℃, preventing the temperature from dropping too quickly after the cam leaves the induction heating device, which would cause the inner hole size of the cam to shrink. After the cam plates are positioned, the cooled shaft tube leaves the liquid nitrogen tank 11 through the action of the first vertical moving mechanism 1. The industrial robot quickly grabs the shaft tube and places it directly below the positioning tip 21, so that the center hole at the head end of the shaft tube contacts the conical surface of the positioning tip 21. At the same time, the third linear motor drives the guide rod 24 to move upward through the lower lifting platform 16 until it hits the center hole at the tail end of the shaft tube. At this time, the shaft tube is clamped, and the axis of the shaft tube is collinear with the axis of the inner hole of multiple cam plates. S5, Press-fitting; Under the action of the second and third linear motors, the positioning center 21 and guide rod 24 drive the shaft tube to be fed from top to bottom at a constant, low speed to the precise axial positioning position to engage with multiple cam plates, and hold for 3-5 seconds. During the pressing process, a monitoring system can record the pressing force-displacement curve in real time and compare it with the set acceptable range. Any abnormal curve (excessive or insufficient force, vibration) will trigger an alarm, achieving 100% online quality judgment.

[0035] S6, Natural Delay; The press-fitted composite camshaft is transferred to a specific workstation by an industrial robot to cool to room temperature, allowing the temperature of each part to be completely uniform and the internal stress to be redistributed. This achieves a uniform interference fit between the cam plate and the shaft tube, ultimately achieving a static torque ≥150 N.M, an axial pull-out force ≥8000 N, and a dynamic torque ≥100 N.M (cycle count ≥8.3 x 1000000).

[0036] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An assembly device for a combined camshaft, characterized in that, include: First vertical moving mechanism; First gripper; The first gripper is installed below the moving end of the first vertical moving mechanism; Liquid nitrogen tank; a first vertical moving mechanism is installed above the liquid nitrogen tank; a first gripper is positioned directly above the opening of the liquid nitrogen tank; A horizontal moving mechanism; the horizontal moving mechanism is installed on one side of the liquid nitrogen tank; the moving direction of the horizontal moving mechanism is perpendicular to the moving direction of the first vertical moving mechanism; The second gripper; the second gripper is mounted on the moving end of the horizontal moving mechanism; the horizontal moving path of the second gripper intersects the vertical moving path of the first gripper; A press-fitting mechanism used to press the shaft tube into the cam plate; Cam plate positioning device; the cam plate positioning device is installed inside the pressing mechanism; An industrial robot used to transfer shaft tubes to the pressing mechanism and transfer cam plates to the cam plate positioning device; the industrial robot is positioned between the pressing mechanism and the first vertical moving mechanism.

2. The assembly device for a combined camshaft according to claim 1, characterized in that, The pressing mechanism includes a vertically arranged second linear motor, a third cylinder, and a positioning center. The moving end of the second linear motor is connected to the side wall of the third cylinder. The third cylinder is installed vertically upside down. The positioning center is set vertically. The output end of the third cylinder is connected to the upper end of the positioning center. The lower end of the positioning center is connected to the upper end of the shaft tube. The cam plate positioning device is placed directly below the positioning center.

3. The assembly device for a combined camshaft according to claim 2, characterized in that, The pressing mechanism also includes a vertically arranged third linear motor and a guide rod. The second linear motor is located directly below the third linear motor. The guide rod is vertically arranged, with its lower end connected to the moving end of the third linear motor. The upper end of the guide rod passes upward through the cam plate positioning device and presses against the lower end of the shaft tube.

4. The assembly device for a combined camshaft according to claim 3, characterized in that, The center line of the positioning tip and the guide rod is set to be coaxial.

5. The assembly device for a combined camshaft according to claim 1, characterized in that, The first vertical moving mechanism is a first linear motor, which includes a first bearing, a first lead screw, a first servo motor, a lifting platform, and a first guide rail. The first end of the first lead screw is rotatably placed in the first bearing, and the second end of the first lead screw is connected to the shaft of the first servo motor. A screw hole is vertically provided in the middle of the lifting platform, and the lifting platform is threadedly engaged with the first lead screw through the screw hole. The lifting platform is circumferentially limited and vertically guided by the first guide rail.

6. The assembly device for a combined camshaft according to claim 3, characterized in that, The second linear motor includes an upper bearing, a second lead screw, a second servo motor, and an upper lifting platform. The third linear motor includes a lower bearing, a third lead screw, a third servo motor, and a lower lifting platform. The second and third linear motors share a second guide rail. The upper end of the second lead screw is rotatably placed inside the upper bearing, and the lower end of the second lead screw is connected to the shaft of the second servo motor. A screw hole is vertically provided in the middle of the upper lifting platform, and the upper lifting platform is threadedly engaged with the second lead screw through the screw hole. The lower end of the third lead screw is rotatably placed inside the lower bearing, and the upper end of the third lead screw is connected to the shaft of the third servo motor. A screw hole is vertically provided in the middle of the lower lifting platform, and the lower lifting platform is threadedly engaged with the third lead screw through the screw hole. Both the upper and lower lifting platforms are circumferentially limited and vertically guided by the second guide rail.

7. The assembly device for a combined camshaft according to claim 1, characterized in that, The horizontal moving mechanism includes a fourth linear motor and a support arm. The support arm is mounted on the moving end of the fourth linear motor, and the second gripper is mounted on the support arm.

8. The assembly method of the assembly device for a combined camshaft according to any one of claims 1-7, characterized in that, Includes the following steps: S1. Incoming material inspection: Determine whether the dimensions, form and position tolerances, surface roughness, material and heat treatment status of the cam plate and shaft tube are qualified. S2. Cleaning and matching of parts; use ultrasonic cleaning to thoroughly remove oil, debris and impurities from the surface of parts; then perform 100% re-inspection of the inner diameter of the cam plate and the outer diameter of the shaft tube to ensure that the interference fit between each set of cam plates and the shaft tube is within the set range. S3, Temperature difference treatment; including heating cam plates and cooling shaft tubes; S4. Rapid transfer and positioning; After the cam plates are heated, the industrial robot quickly grabs a group of multiple cam plates into the cam plate positioning device within 8 seconds, fixing the cam plate phase and the axial distance between the cam plates. The heating wire ensures that the temperature of the cam plates is between 90℃ and 100℃. After the cam plates are positioned, the cooled shaft tube leaves the liquid nitrogen tank through the action of the first vertical moving mechanism. The industrial robot quickly grabs the shaft tube to the bottom of the positioning tip, so that the center hole at the head end of the shaft tube contacts the conical surface of the positioning tip. At the same time, the third linear motor drives the guide rod to move upward through the lower lifting platform until it hits the center hole at the tail end of the shaft tube. At this time, the shaft tube is clamped, and the axis of the shaft tube is collinear with the axis of the inner hole of multiple cam plates. S5, Press-fitting; Under the action of the second and third linear motors, the positioning center and guide rod drive the shaft tube to be sent from top to bottom at a constant and low speed to the precise axial positioning position to cooperate with multiple cam plates, and hold for 3-5 seconds; S6, Natural Delay; The press-fitted modular camshaft is transferred to a specific workstation by an industrial robot to cool to room temperature, allowing the temperature of each part to become completely uniform, the internal stress to be redistributed, and a uniform interference fit between the cam plate and the shaft tube to be achieved.

9. The assembly method of the assembly device for a combined camshaft according to claim 8, characterized in that, S1 also includes laser shaping the inner wall of the cam plate to form a cross-striped pit structure.

10. The assembly method of the assembly device for a combined camshaft according to claim 8, characterized in that, In S3, the heating cam plate includes: heating in an induction heating device, with a set temperature of 230℃ and a heating time of 490 seconds. During the heating process, the inner diameter of the cam plate expands by 0.05mm due to heat. The cooling shaft tube includes: picking up the qualified shaft tube from the material tray through the second gripper, sending the shaft tube to the underside of the first gripper of the cryogenic cooling device through the horizontal moving mechanism, clamping the shaft tube with the first gripper, releasing the second gripper and removing it through the horizontal moving mechanism, and then transferring the shaft tube to the liquid nitrogen tank with a set temperature of -196℃ through the first vertical moving mechanism, and keeping it immersed for 300 seconds to fully cool it to the target temperature. The outer diameter of the shaft tube shrinks by 0.05mm due to cryogenic cooling.

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