A guide press fitting method of a worm assembly for an electric power steering system

Abstract

The application discloses a guiding and pressing assembly method of a worm assembly for an electric power steering system, which comprises the following steps: S1, placing the worm assembly into a worm cavity of a steering housing; S2, placing an auxiliary tool on the steering housing, and making a limiting flange of a guiding cylinder abut on an end face at a worm inlet; S3, applying a pressing force to a top end of a pressing column, and making the pressing column move downward, and making a ring surface abut on a top surface of a self-aligning bearing outer ring, and applying a flat pressing touch to the top surface of the self-aligning bearing outer ring to correct a skew state thereof; then, pushing the worm assembly to synchronously move downward in a whole vertical state, and making the self-aligning bearing and a deep groove ball bearing be pressed and assembled in place; and S4, releasing the pressing force on the pressing column, and removing the auxiliary tool. The application has the advantages of automatically correcting the skew state of the self-aligning bearing outer ring, solving the problems of difficult assembly and dependence on personal experience of an operator during the repair, improving the repair efficiency, shortening assembly repair beats and the like.

Description

Technical Field

[0001] This invention relates to the field of electric power steering system technology, specifically to a method for guiding and pressing a worm gear assembly for repair of an electric power steering system. Background Technology

[0002] The working principle of the electric column power steering system (CEPS) is as follows: the power steering motor outputs torque to drive the worm gear assembly to rotate, and the worm gear drives the worm wheel to rotate to achieve deceleration and torque increase, and provide assistance to the steering system.

[0003] Existing electric column power steering systems such as Figure 1-2 As shown, the steering housing 100 includes an output shaft rotatably mounted within the steering housing 100, a worm gear 300 press-fitted onto the output shaft, and a worm 200 meshing with the worm gear 300 press-fitted into the worm cavity 101 of the steering housing 100. A motor connector is coaxially mounted at the top of the worm 200. Large-end bearings and small-end bearings are respectively provided at the upper and lower ends of the worm 200. The large-end bearing is a self-aligning bearing 201, which can withstand a large worm impact force; the small-end bearing is a deep groove ball bearing 202, used to support the worm's rotation, and is circumferentially limited by a plastic bushing 400. The top of the worm cavity 101 has a bearing mounting hole 102 that is clearance-fitted with the outer ring of the self-aligning bearing 201. A worm inlet 103 is opened on the top surface of the steering housing 100 at the position corresponding to the bearing mounting hole 102.

[0004] In conventional production and assembly processes, the assembly sequence of the steering column assembly is typically as follows: first, the worm gear assembly is installed into the worm chamber of the steering housing; then, the worm wheel is fixed to the output shaft using an interference fit; and finally, the output shaft is locked to the housing with a nut. In this sequence, the worm wheel is not yet installed when the worm is inserted, and the tooth surface is in a free state with no external resistance. Therefore, the worm gear assembly can be smoothly inserted, making the operation simple.

[0005] However, after the assembly is completed, a no-load friction performance test is required. Because vehicle manufacturers have stringent requirements for steering feel and NVH performance, the worm gear teeth must be in a compressed state when produced to meet friction specifications. In actual production, the first-pass yield rate for this stage is approximately 90%–95%. When the test results show that the no-load friction exceeds the tolerance, the assembly needs to be reworked. At this point, the worm gear is firmly locked to the output shaft of the housing by a nut, making disassembly or adjustment inconvenient. The only way to rework is to disassemble and re-match the worm gear assembly.

[0006] In this rework scenario, the operator needs to manually screw the worm gear assembly back into the housing cavity where the worm wheel is already fixed. This process presents two overlapping technical difficulties: First, because the outer ring of the self-aligning bearing can swing freely, the operator cannot rely on feel to ensure that the axis of the worm gear and the upper bearing are aligned. This makes it easy for the outer ring of the self-aligning bearing to become misaligned, thus getting stuck at the entrance of the worm gear cavity and unable to enter smoothly. Second, the operator can only apply rotational force by holding the cylindrical outer wall of the motor connector. The lever arm is extremely short and the point of application is limited, resulting in the required manual torque far exceeding the ergonomic comfort range, further increasing the difficulty of installation. Therefore, the rework operation quality is highly dependent on personal experience, the worm gear assembly assembly process has poor stability, the rework operation is extremely time-consuming and laborious, and the rework cycle of the assembly is severely prolonged. Summary of the Invention

[0007] The technical problem this invention aims to solve is to overcome existing defects and provide a guiding press-fitting method for worm gear assemblies used in the rework of electric power steering systems. This method utilizes auxiliary tooling for guiding and press-fitting the worm gear assembly, automatically correcting the misalignment of the self-aligning bearing outer ring, ensuring the worm gear assembly remains vertical throughout the press-fitting process, and ensuring stable assembly. It also prevents the self-aligning bearing outer ring from getting stuck at the worm gear inlet, thus solving the problems of difficult assembly, poor process stability, and reliance on operator experience during rework. Furthermore, it eliminates the need for operators to manually apply rotational force to the motor connector, significantly reducing manual torque and operational difficulty, and alleviating operator workload. This method also improves rework efficiency and shortens the rework cycle time, effectively solving the problems in the background art.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a method for guiding and pressing a worm gear assembly for rework in an electric power steering system, comprising an auxiliary tooling, the auxiliary tooling including a guide cylinder, the bottom end of which is provided with a limiting flange for abutting against the end face of the worm gear inlet of the steering housing; the bottom surface of the limiting flange is also provided with a positioning ring that can be positioned and engaged with the worm gear inlet; a pressure post that can slide along its axial direction is sleeved inside the guide cylinder, the bottom surface of the pressure post having an axial inner hole, and the bottom annular surface of the pressure post forming an abutting annular surface for abutting against the outer ring of the self-aligning bearing; a compression spring is provided between the guide cylinder and the pressure post, the top end of the pressure post penetrating the guide cylinder; the method for guiding and pressing a worm gear assembly includes the following steps: S1. Place the re-matched worm gear assembly into the worm gear cavity of the steering housing, so that the deep groove ball bearing at the lower end of the worm is placed in the worm gear cavity, and the self-aligning bearing is placed at the opening of the bearing mounting hole. S2. Place the auxiliary tooling on the steering housing so that the limiting flange abuts against the end face at the worm gear inlet and is positioned and engaged with the worm gear inlet by the positioning ring. S3. Apply pressure to the top of the pressure column to make the pressure column overcome the elastic force of the compression spring and move downward along the guide cylinder; during the downward movement of the pressure column, the contact ring surface abuts against the top surface of the outer ring of the self-aligning bearing, and a flat pressure is applied to the top surface of the outer ring of the self-aligning bearing to correct its skew state; the pressure column continues to move downward, pushing the worm gear assembly to move downward synchronously while maintaining a vertical state, so that the self-aligning bearing is pressed into the bearing mounting hole, and the deep groove ball bearing is pressed into the plastic bushing; S4. After the worm gear assembly is pressed into place, release the pressing force on the pressure column. The pressure column slides upward and resets under the action of the pressure spring. Remove the auxiliary tooling and complete the rework operation.

[0009] Furthermore, the limiting flange is a ring-shaped structure, and the annular surface on the bottom surface of the limiting flange located outside the positioning ring is used to abut against the end face at the worm gear inlet.

[0010] Furthermore, the pressure column is a hollow stepped shaft structure, and the bottom surface of the guide cylinder is provided with a stepped hole that matches the pressure column; the top of the pressure column is provided with a cover plate, and the pressure spring is sleeved on the pressure column, with the upper and lower ends of the pressure spring abutting against the cover plate and the guide cylinder respectively.

[0011] Furthermore, the outer diameter of the abutting ring surface is smaller than the outer diameter of the self-aligning bearing outer ring, but larger than the inner diameter of the self-aligning bearing outer ring, and the abutting ring surface presses against the radial center region of the top surface of the self-aligning bearing outer ring.

[0012] Furthermore, the axial movement of the pressure column relative to the guide cylinder is not less than the downward movement distance required for the self-aligning bearing to be press-fitted into place from the bearing mounting hole opening.

[0013] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention uses a guide cylinder and a worm gear inlet positioning fit to guide the pressure column to move axially along the worm gear cavity, and uses the abutment ring to apply flat pressure to the top surface of the self-aligning bearing outer ring, which can automatically correct the misalignment of the self-aligning bearing outer ring, ensuring that the worm gear assembly remains vertical during the press-fitting process, and preventing the self-aligning bearing outer ring from getting stuck at the worm gear inlet. This solves the problems of difficult assembly during rework, poor process stability, and reliance on the operator's personal experience.

[0014] 2. Under the pressure of the pressing column, the worm gear assembly moves down synchronously, allowing the self-aligning bearing to be smoothly pressed into the bearing mounting hole. At the same time, the deep groove ball bearing is pressed into the plastic bushing. This eliminates the need for the operator to hold the motor connector and apply rotational force, significantly reducing the manual torque and operational difficulty, and alleviating the operator's labor intensity.

[0015] 3. The auxiliary tooling has a simple and compact structure. The pressure column is automatically reset by the compression spring, which is easy to operate and can be quickly placed and removed, which helps to improve the rework efficiency and shorten the rework cycle of the assembly. Attached Figure Description

[0016] Figure 1 This is a cross-sectional view of an existing electric power steering system. Figure 2 A schematic diagram of the worm gear assembly structure in an existing electric power steering system; Figure 3 This is a perspective view of the auxiliary tooling for the present invention; Figure 4 This is a front view of the auxiliary tooling for the present invention; Figure 5 This is a cross-sectional view of the auxiliary tooling for the present invention; Figure 6 This is a schematic diagram of the structure of the auxiliary tooling for pressing the worm gear assembly according to the present invention; Figure 7 This is a cross-sectional view of the worm gear assembly of the present invention before it is installed into the worm gear cavity and press-fitted. Figure 8 for Figure 7 Enlarged view of a specific area; Figure 9 This is a cross-sectional view of the worm gear assembly after it has been press-fitted into place according to the present invention.

[0017] In the picture: Electric power steering system: 100, Steering housing; 101, Worm gear chamber; 102, Bearing mounting hole; 103, Worm gear inlet; 200, Worm gear; 201, Self-aligning bearing; 202, Deep groove ball bearing; 300, Worm wheel; 400, Plastic bushing; Auxiliary fixtures: 6. Compression spring; 7. Guide cylinder; 71. Limiting flange; 711. Positioning ring; 8. Pressure column; 81. Abutting ring surface; 82. Cover plate. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Example Please see Figure 3-9A method for guiding and pressing a worm gear assembly for repair of an electric power steering system includes an auxiliary tooling. The auxiliary tooling includes a guide cylinder 7, and a limiting flange 71 is provided on the circumferential side wall at the bottom end of the guide cylinder 7. The limiting flange 71 is an annular structure, and a positioning convex ring 711 is also provided on the bottom surface of the limiting flange 71, which is coaxially arranged with it. The outer annular surface of the positioning convex ring 711 can be positioned and engaged with the worm gear inlet 103. The annular surface on the bottom surface of the limiting flange 71 located outside the positioning convex ring 711 is used to abut against the end face of the worm gear inlet 103. In this embodiment, in order to facilitate the quick abutment of the limiting flange 71 of the guide cylinder 7 against the end face of the worm gear inlet 103 of the steering housing 100, the outer diameter of the positioning convex ring 711 is slightly smaller than the inner diameter of the worm gear inlet 103.

[0020] The guide cylinder 7 is fitted with a pressure column 8 that can slide along its axial direction. The axial movement of the pressure column 8 relative to the guide cylinder 7 is not less than the downward movement distance required for the self-aligning bearing 201 to be pressed into place from the opening of the bearing mounting hole 102. The pressure column 8 is a hollow stepped shaft structure. The axial inner hole of the pressure column 8 is used to avoid the motor connector. The bottom end of the pressure column 8 forms an abutting ring surface 81 at the edge of the axial inner hole, and the abutting ring surface 81 is used to abut against the top surface of the outer ring of the self-aligning bearing 201. The outer diameter of the abutting ring surface 81 is smaller than the outer diameter of the outer ring of the self-aligning bearing 201, but larger than the inner diameter of the outer ring of the self-aligning bearing 201.

[0021] The bottom surface of the guide cylinder 7 is provided with a stepped hole that matches the pressure column 8; the top end of the pressure column 8 passes through the guide cylinder 7 and is fixedly provided with a cover plate 82; a compression spring 6 is sleeved on the pressure column 8, and the upper and lower ends of the compression spring 6 abut against the cover plate 82 and the guide cylinder 7 respectively; the compression spring 6 applies an upward elastic force to the cover plate 82 of the pressure column 8, so that the cover plate 82 is located above the guide cylinder 7.

[0022] The guide press-fitting method for worm gear assemblies includes the following steps: S1. Place the re-matched worm gear assembly into the worm cavity 101 of the steering housing 100, so that the deep groove ball bearing 202 at the lower end of the worm 200 is placed in the worm cavity 101, and the self-aligning bearing 201 is placed at the opening of the bearing mounting hole 102. S2. Place the auxiliary tooling on the steering housing 100 so that the annular surface on the bottom surface of the limiting flange 71, located outside the positioning ring 711, abuts against the end face at the worm gear inlet 103. The outer annular surface of the positioning ring 711 is positioned and engaged with the worm gear inlet 103 to ensure that the guide cylinder 7 is placed vertically on the steering housing 100. S3. Apply pressure to the cover plate 82 at the top of the pressure column 8, so that the pressure column 8 overcomes the elastic force of the compression spring 6 and moves downward along the guide cylinder 7; during the downward movement of the pressure column 8, the contact surface 81 abuts against the radial center area of ​​the top surface of the outer ring of the self-aligning bearing 201, and applies a flat pressure to the top surface of the outer ring of the self-aligning bearing 201 to correct its skew state; the pressure column 8 continues to move downward, pushing the worm gear assembly to move downward synchronously while maintaining a vertical state, so that the self-aligning bearing 201 is pressed into the bearing mounting hole 102, and at the same time the deep groove ball bearing 202 is pressed into the plastic bushing 400; S4. After the worm gear assembly is pressed into place, release the pressing force on the pressure column 8. The pressure column 8 slides upward and resets under the action of the pressure spring 6. Remove the auxiliary tooling and complete the rework operation.

[0023] Test verification: Ten sets of steering gear assemblies and worm gear components awaiting rework were taken from each group and assembled using both manual installation and the guided press-fit method described in this embodiment; the cycle time was then recorded. The test data are as follows: As can be seen from the table above, the manual installation method is time-consuming and the worm gear assembly process is unstable, which greatly prolongs the rework cycle of the assembly. In contrast, the guide press-fit method of this embodiment is time-saving and the worm gear assembly process is stable, which shortens the rework cycle of the assembly.

[0024] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for guiding and pressing a worm gear assembly for repair of an electric power steering system, characterized in that, The system includes auxiliary tooling, which includes a guide cylinder with a limiting flange at its bottom end. The limiting flange abuts against the end face of the worm gear inlet of the steering housing. The bottom surface of the limiting flange also has a positioning ring that can be positioned and engaged with the worm gear inlet. A pressure post, which can slide axially along the guide cylinder, is fitted inside the guide cylinder. The pressure post has an axial inner hole on its bottom surface, and its bottom annular surface forms an abutment annular surface for abutting against the outer ring of the self-aligning bearing. A compression spring is provided between the guide cylinder and the pressure post, with the top end of the pressure post penetrating the guide cylinder. The guiding and pressing method for the worm gear assembly includes the following steps: S1. Place the re-matched worm gear assembly into the worm gear cavity of the steering housing, so that the deep groove ball bearing at the lower end of the worm is placed in the worm gear cavity, and the self-aligning bearing is placed at the opening of the bearing mounting hole. S2. Place the auxiliary tooling on the steering housing so that the limiting flange abuts against the end face at the worm gear inlet and is positioned and engaged with the worm gear inlet by the outer ring surface of the positioning ring. S3. Apply pressure to the top of the pressure column to make the pressure column overcome the elastic force of the compression spring and move downward along the guide cylinder; during the downward movement of the pressure column, the contact ring surface abuts against the top surface of the outer ring of the self-aligning bearing, and a flat pressure is applied to the top surface of the outer ring of the self-aligning bearing to correct its skew state; the pressure column continues to move downward, pushing the worm gear assembly to move downward synchronously while maintaining a vertical state, so that the self-aligning bearing is pressed into the bearing mounting hole, and the deep groove ball bearing is pressed into the plastic bushing; S4. After the worm gear assembly is pressed into place, release the pressing force on the pressure column. The pressure column slides upward and resets under the action of the pressure spring. Remove the auxiliary tooling and complete the rework operation.

2. The guide press-fitting method for a worm gear assembly used in the repair of an electric power steering system according to claim 1, characterized in that: The limiting flange is a ring-shaped structure, and the annular surface on the bottom surface of the limiting flange located outside the positioning ring is used to abut the end face at the worm gear inlet.

3. The guide press-fitting method for a worm gear assembly for repair of an electric power steering system according to claim 1, characterized in that: The pressure column is a hollow stepped shaft structure, and the bottom surface of the guide cylinder has a stepped hole that matches the pressure column; the top of the pressure column is provided with a cover plate, and the pressure spring is sleeved on the pressure column, with the upper and lower ends of the pressure spring abutting against the cover plate and the guide cylinder respectively.

4. The guide press-fitting method for a worm gear assembly for repair of an electric power steering system according to claim 1, characterized in that: The outer diameter of the abutting ring is smaller than the outer diameter of the self-aligning bearing outer ring, but larger than the inner diameter of the self-aligning bearing outer ring, and the abutting ring presses against the radial center region of the top surface of the self-aligning bearing outer ring.

5. The guide press-fitting method for a worm gear assembly for repair of an electric power steering system according to claim 1, characterized in that: The axial movement of the pressure column relative to the guide cylinder is not less than the downward movement distance required for the self-aligning bearing to be press-fitted into place from the bearing mounting hole opening.

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