Testing fixture and method for measuring pitch diameter of spiral raceway of steering nut

Abstract

The invention discloses a testing fixture and method for measuring the pitch diameter of a spiral raceway of a steering nut, and belongs to the technical field of nut raceway detection. The gauge comprises a fixed measuring base, a movable measuring base, a guide pillar, a spring, a dial indicator, and a fixed steel ball assembly mounting block and a movable steel ball assembly mounting block which are arranged at the end parts of the two bases. Four steel ball assemblies and one steel ball assembly are arranged on the fixed installation block and the movable installation block respectively, and five steel balls form a three-raceway five-point space contact structure in the spiral raceway direction of the nut. The steel ball assembly adopts a floating structure limited by a flexible steel wire, so that the steel ball can freely and slightly move and automatically adjust the tangent angle with the raceway in the measurement process, and self-adaptive compensation for the form and position error of the raceway is realized. The movable measuring base achieves constant force resetting through guide column guiding and spring loading. Compared with traditional three-coordinate measurement, the device is short in measurement period, good in repeatability and suitable for efficient quantitative detection of the pitch diameter of the nut raceway of the electric power steering system.

Description

Technical Field

[0001] This invention relates to the field of steering nut testing technology, specifically to a measuring tool and method for the mean diameter of the helical raceway of a steering nut. Background Technology

[0002] In an electric power steering recirculating ball steering system, a helical raceway is provided on the inner side of the steering nut to guide the balls in their engagement with the screw. The pitch diameter of the nut raceway is one of the important parameters determining the accuracy of the ball-screw fit, clearance control, transmission stability, and lifespan. Inaccurate or untimely measurement of this pitch diameter may lead to assembly errors, poor transmission, or reduced lifespan.

[0003] Traditionally, the measurement of the pitch diameter of the helical raceway of a steering nut relies heavily on coordinate measuring machines (CMMs) or high-precision coordinate measuring equipment. While these methods offer high accuracy, they have the following drawbacks: The measurement cycle is long, which cannot meet the needs of rapid testing on the production line and is inefficient; the workpiece needs to be removed from the machining fixture for loading and measurement, which is complicated and prone to clamping errors; it has high requirements for operators and measurement environment and is not suitable for rapid testing on the workshop floor.

[0004] To address the aforementioned issues, some technical solutions have proposed online or semi-online measurement fixtures and methods. For example, patent document CN102322780A's basic principle involves using a fixed probe and a movable probe, each carrying a ball. The height difference between the two balls is adjusted to half the raceway pitch, and then inserted into the raceway of the nut being measured. The pitch diameter is determined by the difference in readings using a dial indicator. This structure achieves a certain degree of measurement of the nut raceway pitch diameter, but it only uses two-ball contact, lacking a multi-point contact structure, and its adaptability to raceway errors and measurement angles is weak. Patent document CN117387459B uses five steel balls arranged on a positioning post to detect the machining accuracy of the nut raceway. However, this device is mainly used for qualitative judgment of raceway machining errors, does not provide a quantitative measurement method for the pitch diameter, and the contact angle between the steel balls and the raceway is fixed, making it impossible to automatically compensate for nut manufacturing errors. Therefore, its measurement accuracy and applicability are limited, making it difficult to meet the online high-precision quantitative detection requirements for the nut raceway pitch diameter in electric steering systems.

[0005] Patent document CN110006308A discloses a method for detecting the center position of the screw shaft raceway using a slide table, probe, and dial indicator structure to control the coaxiality between the center of the screw R-groove and the raceway center. However, this solution mainly targets the detection of the screw shaft center position and does not address the measurement of the mean diameter of the internal helical raceway of the steering nut, nor does it incorporate an adaptive compensation structure with flexible floating steel balls. Therefore, this solution cannot achieve quantitative measurement and online detection of the nut raceway mean diameter, and differs significantly from this invention in both the detection object and measurement accuracy.

[0006] In summary, under the current technological state, no publicly available literature or existing technology can simultaneously meet the following requirements: multi-point contact to improve measurement stability and anti-interference capability; free-floating steel ball structure to adapt to raceway errors and automatically find the contact angle; and online rapid measurement without removing the nut from the clamping station, resulting in short cycle time and high efficiency. Based on this, there is a technical need to develop a new measuring fixture and method to overcome the shortcomings of existing technologies in terms of efficiency, accuracy, and applicability. Summary of the Invention

[0007] The technical problem this invention aims to solve is to overcome the shortcomings of existing methods and provide a measuring fixture and method for the pitch diameter of the helical raceway of steering nuts. This fixture and method are simple in structure, easy to operate, and enable rapid online testing of the pitch diameter of the helical raceway of steering nuts. The device achieves high-precision measurement of the pitch diameter of the helical raceway of steering nuts through a multi-point contact floating measuring structure, effectively improving testing efficiency and repeatability, meeting the online testing needs of electric power steering system production sites, and effectively solving the problems in the background art.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a measuring fixture and method for the mean diameter of the helical raceway of a steering nut, comprising a base, a fixed steel ball assembly mounting block, a movable steel ball assembly mounting block, and a dial indicator. The base includes a fixed measuring base and a movable measuring base. The middle portion of a stepped cylinder is removed to obtain two bases. A guide post is provided between the fixed measuring base and the movable measuring base, allowing the movable measuring base to slide up and down along the guide post between the two bases. A spring is provided on the guide post, which is used to drive the movable measuring base to separate from or reset with the fixed measuring base during measurement. A fixed steel ball assembly mounting block and a movable steel ball assembly mounting block are respectively provided on the fixed measuring base and the movable measuring base. Four steel ball assemblies are provided on the fixed steel ball assembly mounting block. A steel ball assembly is mounted on the movable steel ball assembly mounting block. The steel ball assembly is distributed along the helical raceway of the nut to form a five-point contact measurement structure. The steel ball assembly includes a steel ball, a steel ball fixing seat, and a flexible steel wire passing through the steel ball. The two ends of the flexible steel wire are fixed to both sides of the steel ball fixing seat. The flexible steel wire is used to restrict the free floating of the steel ball within the steel ball fixing seat and prevent the steel ball from falling out. The steel ball can move and roll freely within the steel ball fixing seat to achieve adaptive tangential contact with the helical raceway of the steering nut. A dial indicator is mounted above the movable measuring base to read the displacement change when the two bases are separated and to calculate the mean diameter value of the nut helical raceway. The dial indicator is used to read the measured displacement value when the fixed measuring base and the movable measuring base are separated, so as to calculate the mean diameter value of the nut helical raceway.

[0009] Furthermore, a handle mounting base is provided on the other side of the fixed measuring base, and a fixed handle is provided on the handle mounting base. A movable lever is provided below the fixed handle. A pull rod is provided on the other side of the movable measuring base, and the lower end of the pull rod is located in the handle mounting base. The movement of the pull rod can drive the movable measuring base to move up and down. A movable pin is provided at the lower end of the pull rod. The movable lever is hinged to the handle mounting base through the fixed pin. The fixed pin serves as the hinge fulcrum, allowing the movable lever to rotate around the fixed pin as the origin. A U-shaped groove is provided at one end of the movable lever, and the movable pin is located in the end U-shaped groove. When the movable lever is subjected to force and moves, the movement of the pull rod is realized through the cooperation of the U-shaped groove and the movable pin, thereby realizing the linkage control of the movable measuring base to move along the guide column direction through the movable lever.

[0010] Furthermore, a dial indicator mounting bracket is provided at the top of the guide post, and the dial indicator is mounted on the dial indicator mounting bracket.

[0011] Furthermore, the inner hole of the steel ball holder is slightly larger than the diameter of the steel ball. A threaded hole is provided at the bottom of the steel ball, through which a flexible steel wire passes. Side holes are provided on both sides of the steel ball holder. The two ends of the flexible steel wire are knotted and fixed to the side holes of the steel ball holder with solder. The steel ball holder is fixed on the mounting block. The two mounting blocks are arranged opposite each other. The steel ball holder is located on the arc-shaped surface of the mounting block, and the mounting block has a groove for fixing the steel ball holder. The specific arrangement is set according to the actual situation. This fixing structure is a conventional technology. The steel ball can move inside the steel ball holder, but due to the constraint of the flexible steel wire, the steel ball will not fall out of the steel ball holder. Since the steel ball can move freely inside the steel ball holder, during measurement, the contact angle between the steel ball and the nut raceway can be freely contacted.

[0012] Furthermore, three guide pillars are provided in a triangular arrangement. Two of them are located between the movable measuring base and the fixed measuring base, and the other is located between the fixed steel ball assembly mounting block and the movable steel ball assembly mounting block. This structure facilitates the relatively stable movement of the movable and fixed measuring bases. Countersunk holes are provided on both the movable and fixed measuring bases, and a second spring is provided between the countersunk holes. This second spring is used to enhance the reset force and can be provided or not provided depending on the actual situation.

[0013] Furthermore, the five steel ball assemblies are distributed on the nth, n-1th, and n+1th raceways of the nut raceway, with the steel ball assembly on the movable steel ball assembly mounting block positioned at the apex of the nth raceway; the four steel ball assemblies on the fixed steel ball assembly mounting block are symmetrically distributed along the axis on the n-1th and n+1th raceways, forming an isosceles triangle arrangement with the steel ball assembly on the movable steel ball assembly mounting block.

[0014] When designing the mounting holes, the spatial position where the steel ball is tangent to the raceway is determined based on the three-dimensional digital model of the nut. The diameter D1 of the circle tangent to the steel ball and the distance A1 to A5 between the steel ball and the end face are calculated. Based on this, the mounting hole coordinates of the fixed steel ball assembly mounting block and the movable steel ball assembly mounting block are determined.

[0015] Furthermore, the flexible steel wire is made of high-strength stainless steel wire or nickel-titanium alloy wire with a diameter of 0.2 to 0.5 mm to ensure the free floating and fatigue resistance of the steel ball.

[0016] Furthermore, the dial indicator can be an electronic meter head, which outputs digital signals through a signal acquisition module to realize electronic acquisition and automatic conversion of measurement data.

[0017] Furthermore, a method for measuring the pitch diameter of the helical raceway of a steering nut includes the following steps: Calibration steps: Insert the measuring head of the measuring gauge into the calibration gauge, press down the movable lever to move the movable measuring base down, so that the measuring steel ball assembly contacts the inner wall of the calibration gauge, and then zero the dial indicator; Measurement steps: Hold the movable lever and insert the probe into the raceway inside the steering nut. Slowly release the movable lever. Under the action of spring one, the fixed measuring base and the movable measuring base will separate, and the five measuring steel balls will make tangential contact with the three spiral raceways respectively. Reading and Conversion: Read the change value of the dial indicator pointer, compare it with the zero point during calibration, and calculate the mean diameter of the helical raceway of the steering nut based on the known dimensions of the calibration gauge; Error compensation: By utilizing the characteristic that the steel ball floats freely within the steel ball holder, the contact angle between the steel ball and the raceway is adaptively aligned, thereby compensating for the manufacturing error of the nut and improving measurement accuracy.

[0018] During measurement, the dial gauge value is read three times after each release of the handle and the average value is taken. The resulting mean diameter measurement error does not exceed ±0.01mm.

[0019] The measurement process can be performed online without removing the nut from the clamping station, and the measurement cycle takes no more than 5 minutes.

[0020] Compared with the prior art, the beneficial effects of the present invention are: 1. The steel ball assembly of the present invention adopts a floating structure with flexible steel wire limiting. The steel ball can move freely within the steel ball fixing seat and automatically find the tangential contact angle with the raceway, thereby automatically compensating for the machining error and assembly deviation of the nut raceway. Through the five-point three-raceway contact layout formed by the fixed and movable measuring base, the measuring points are evenly distributed in space, significantly reducing the influence of local shape and position errors on the measurement results. Experiments have shown that this structure ensures small error in the mean diameter measurement, good repeatability, and more stable and reliable measurement results.

[0021] 2. This invention adopts a guide post-spring-pull rod linkage structure to achieve rapid separation and reset of the movable measuring base. Combined with a dial indicator or electronic meter, it can achieve rapid reading and data conversion. The entire measurement process does not require removing the nut from the clamping station, and the measurement cycle does not exceed 5 minutes. Online inspection can be completed directly on the production line or inspection station. Compared with the traditional coordinate measuring machine method, the inspection efficiency is increased by more than 10 times, significantly shortening the production inspection cycle and improving the overall efficiency of the production line.

[0022] 3. The five-point contact measurement structure and mounting hole positions of the present invention can be adjusted according to the three-dimensional digital model parameters of nuts of different specifications, and have good versatility and reconfigurability; the flexible steel wire material can be high-strength stainless steel wire or nickel-titanium alloy wire, which has excellent elasticity and fatigue resistance, and is suitable for long-term use.

[0023] 4. Through the linkage mechanism between the fixed handle and the movable lever, the operator can complete the measurement operation with one hand without complicated clamping; the spring mechanism ensures constant measuring force and reduces reading errors caused by human operation differences; this device not only improves detection accuracy and efficiency, but also reduces the labor intensity and training requirements of operators. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a cross-sectional front view of the structure of the present invention; Figure 3 This is a schematic diagram of the steel ball structure of the present invention; Figure 4 This is a schematic diagram of the steel ball mounting structure of the present invention; Figure 5 This is a schematic diagram of the structure of the present invention with a nut; Figure 6 This is a schematic diagram of the axial position calculation structure for the nut raceway of the present invention.

[0025] In the diagram: 1. Dial indicator, 2. Dial indicator mounting bracket, 3. Guide post, 4. Movable measuring base, 5. Spring 1, 6. Pull rod, 7. Fixed handle, 8. Movable lever, 9. Handle mounting seat, 10. Fixed measuring base, 11. Steel ball fixing seat, 12. Fixed steel ball assembly mounting block, 13. Movable steel ball assembly mounting block, 14. Steel ball assembly, 15. Fixed pin, 16. Movable pin, 17. U-groove, 18. Steel ball, 19. Flexible steel wire, 20. Side hole, 21. Threaded hole, 22. Inner hole, 23. Spring 2, 24. Countersunk hole. Detailed Implementation

[0026] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention, 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, and therefore should not be construed as a limitation of this invention. Example 1

[0027] Please see Figure 1-6 This invention provides a technical solution: a measuring fixture and method for the mean diameter of the spiral raceway of a steering nut, comprising a base, a guide post 3, a spring 5, a dial indicator 1, a fixed steel ball assembly mounting block 12, a movable steel ball assembly mounting block 13, and five steel ball assemblies 14; the base consists of a fixed measuring base 10 and a movable measuring base 4, obtained by cutting off the middle part of a stepped cylinder, and the two bases are connected by the guide post 3; the movable measuring base 4 can slide up and down along the guide post 3; the spring 5 is provided on the guide post 3, which drives the movable measuring base 4 to separate from the fixed measuring base 10 during the measurement process and resets after release; the fixed steel ball assembly mounting block 12 and the movable steel ball assembly mounting block 13 are respectively installed on the opposite ends of the fixed measuring base 10 and the movable measuring base 4, with four steel ball assemblies 14 arranged on the fixed steel ball assembly mounting block 12 and one steel ball assembly 14 arranged on the movable steel ball assembly mounting block 13, and the five steel balls are distributed along the spiral raceway of the nut to form a five-point contact measuring structure.

[0028] Each steel ball assembly 14 includes a steel ball 18, a steel ball fixing seat 11, and a flexible steel wire 19. The inner hole 22 of the steel ball fixing seat 11 is slightly larger than the diameter of the steel ball 18. The lower part of the steel ball 18 is provided with a wire hole 21. The flexible steel wire 19 passes through the wire hole 21 and then passes through the side holes 20 on both sides of the steel ball fixing seat 11 and is fixed to limit the floating range of the steel ball 18 in the steel ball fixing seat 11 and prevent it from falling off. The steel ball 18 can move and roll freely in the steel ball fixing seat 11 and form tangential contact with the nut raceway in an adaptive manner. A dial indicator 1 is installed above the movable measuring base 4. The dial indicator 1 is installed on the dial indicator mounting bracket 2 at the top of the guide post 3 and is used to read the displacement value when the two measuring bases are separated and to convert the mean diameter of the nut helical raceway.

[0029] In another embodiment, a handle mounting base 9 is provided on one side of the fixed measuring base 10, with a fixed handle 7 mounted on the mounting base 9 and a movable lever 8 below it; a pull rod 6 is fixed on the other side of the movable measuring base 4, with the lower end of the pull rod 6 located inside the handle mounting base 9 and equipped with a movable pin 16; the movable lever 8 is hinged to the handle mounting base 9 via a fixed pin 15, with the fixed pin 15 serving as a fulcrum, and a U-shaped groove 17 provided at one end of the movable lever 8, with the movable pin 16 located in the groove; when the operator pushes or releases the movable lever 8, the U-shaped groove 17 drives the movable pin 16 and the pull rod 6 to move, thereby driving the movable measuring base 4 to slide up and down along the guide post 3, achieving rapid loading and resetting; this structure makes operation simple, measurement can be completed with one hand, and the direction of force application is constant, with good force repeatability.

[0030] To enhance structural stability, the guide posts 3 are preferably configured as three in a triangular arrangement, with two located between the movable measuring base 4 and the fixed measuring base 10, and the other located between the two steel ball assembly mounting blocks 12 and 13; the two bases are provided with countersunk holes 24, and springs 23 are installed between the countersunk holes to enhance the restoring force, so that the movable measuring base 4 can quickly return to its original position and maintain parallelism after measurement.

[0031] Five steel ball assemblies 14 are distributed along the nth, n-1th, and n+1th raceways of the nut being measured. The steel ball on the movable steel ball assembly mounting block 13 is located at the apex of the nth raceway, while the four steel balls on the fixed steel ball assembly mounting block 12 are symmetrically arranged along the axis on the n-1th and n+1th raceways, forming an isosceles triangle arrangement. The position of the mounting hole is determined by the three-dimensional digital model of the nut. The coordinates of the mounting hole are determined after calculating the diameter D1 of the tangent circle between the steel ball and the raceway and the end face distances A1 to A5. This layout ensures the geometric symmetry of the measurement space and improves the measurement stability and repeatability.

[0032] The flexible steel wire 19 can be made of high-strength stainless steel wire or nickel-titanium alloy wire with a diameter of 0.2 to 0.5 mm to ensure the floating and fatigue resistance of the steel ball 18; the steel ball fixing seat 11 can be made of stainless steel or high-hardness engineering plastic; the flexible steel wire 19 can be fixed by welding, snap ring or clamping; the presence of the steel wire not only prevents the steel ball 18 from falling off, but also allows it to float freely within a small range to adapt to the change of the nut raceway angle and achieve high-precision tangential contact.

[0033] The dial indicator 1 can be either mechanical or electronic. When using an electronic dial indicator, the signal is output as a digital signal through the acquisition module. The mean diameter value can be automatically calculated and recorded by the data acquisition system, enabling online automated detection. This system can be connected to the production line data management system to store measurement results in real time, facilitating traceability and statistical analysis.

[0034] When using it, the measurement method includes the following steps: (1) Calibration: Insert the measuring instrument into the standard calibration gauge, press down the movable lever 8 to move the movable measuring base 4 down to contact the inner wall of the calibration gauge, and adjust the dial indicator 1 to zero; (2) Measurement: Hold the movable lever 8, insert the probe into the raceway of the nut to be measured, and slowly release the lever 8. Under the action of spring 5, the two measuring bases will automatically separate, and the five steel balls 18 will make tangential contact with the three raceways respectively. (3) Reading and conversion: Record the reading of dial indicator 1, compare it with the zero point, and convert the mean diameter of the nut helical raceway according to the calibration gauge reference size; (4) Error compensation: The free floating of the steel ball 18 in the fixed seat 11 can automatically correct the manufacturing error of the nut raceway and realize the adaptive alignment of the contact angle, thereby improving the measurement accuracy and stability; the average value of three readings is taken for each measurement, and the error of the mean diameter measurement does not exceed ±0.01mm; the entire measurement process can be completed online without removing the workpiece from the clamping station, and the single measurement cycle does not exceed 5 minutes.

[0035] This invention achieves high-precision measurement of the helical raceway center diameter of a steering nut through the synergistic effect of guide post guidance, elastic loading, and multi-point floating contact structure; the fixed measuring base 10 and the movable measuring base 4 are precisely matched through guide post 3, enabling the movable base to slide smoothly along the nut axis; a spring 5 is provided on the outside of the guide post 3 to provide a constant elastic force during the measurement process, so that the movable base automatically resets after release and maintains loading stability.

[0036] During measurement, five steel ball assemblies 14 are distributed along the nut raceway direction, forming a spatial tangential contact layout of three raceways and five points. The single steel ball on the movable measuring base 4 is located at the apex of the middle raceway, and the four steel balls on the fixed measuring base 10 are respectively arranged at symmetrical positions on the two adjacent raceways. This arrangement ensures that the measuring points are evenly distributed in space, which can effectively offset local shape and position errors.

[0037] During operation, the operator moves the lever 8 to pull the rod 6, causing the movable measuring base 4 to move downward along the guide post 3, pressing the probe into the nut. When the lever 8 is released, the spring 5 pushes the movable base to reset, and the five steel balls form a stable tangential contact with the nut raceway. At this time, the displacement of the movable measuring base 4 is directly read by the dial indicator 1, reflecting the geometric difference between the raceway diameter of the nut being measured and the standard calibration gauge.

[0038] Because the guide post is strictly coaxial with the measurement direction, the steel ball can float freely under the constraint of the flexible steel wire and automatically find the optimal contact angle, thus maintaining a stable geometric contact relationship even when there are manufacturing errors or clamping deviations in the raceway. During the measurement process, there is a linear correspondence between the small displacement of the movable base and the change in the raceway pitch diameter, and its proportionality constant is determined by the steel ball arrangement angle, helix angle and guide structure. By establishing a calibration curve in advance using a standard calibration gauge, the accurate conversion between the reading and the pitch diameter can be achieved.

[0039] In electronic measurement mode, the displacement signal output by dial gauge 1 is transmitted to the calculation unit through the signal acquisition module. The system automatically completes data conversion and recording, realizing digital and automated measurement of the pitch diameter. The entire device does not require disassembling the nut or changing the clamping station during the measurement process. A single measurement can be completed within a few minutes, and the measurement accuracy can reach ±0.01mm, meeting the online detection requirements of the pitch diameter of the nut raceway in the electric steering system production line.

[0040] The mounting hole positions are determined based on the three-dimensional digital model of the nut being measured. The five steel balls are made tangent to the nth, n−1th, and n+1th raceways, respectively. The diameter D1 of the circle tangent to the steel ball and the distances A1 to A5 between the steel ball and the end face are calculated. Based on this, the mounting hole coordinates of the fixed steel ball assembly mounting block and the movable steel ball assembly mounting block are determined.

[0041] In summary, this invention transforms the complex measurement of the helical raceway's center diameter into single-axis displacement detection through the collaborative working principle of "guide post guidance + elastic loading + five-point floating contact + displacement conversion." This not only improves measurement accuracy and stability but also achieves the goals of structural simplification, convenient operation, and rapid on-site detection.

[0042] The foregoing has shown and described the basic principles, main features and advantages of the present invention. Various changes and modifications can be made to the present invention without departing from the spirit and scope thereof, and all such changes and modifications fall within the scope of the present invention as claimed.

Claims

1. A measuring tool and method for the pitch diameter of the helical raceway of a steering nut, comprising a base, a fixed steel ball assembly mounting block (12), a movable steel ball assembly mounting block (13), and a dial indicator (1), characterized in that: The base includes a fixed measuring base (10) and a movable measuring base (4). A guide post (3) is provided between the fixed measuring base (10) and the movable measuring base (4). The movable measuring base (4) can slide up and down along the guide post (3) between the two bases. A spring (5) is provided on the guide post (3). A fixed steel ball assembly mounting block (12) and a movable steel ball assembly mounting block (13) are respectively provided on the fixed measuring base (10) and the movable measuring base (4). Four steel ball assemblies (14) are provided on the fixed steel ball assembly mounting block (12). The movable steel ball assembly is mounted on the fixed steel ball assembly mounting block (12). A steel ball assembly (14) is provided on the mounting block (13). The steel ball assembly (14) is distributed along the spiral raceway of the nut to form a five-point contact measurement structure. The steel ball assembly (14) includes a steel ball (18), a steel ball fixing seat (11), and a flexible steel wire (19) passing through the steel ball (18). The two ends of the flexible steel wire (19) are fixed to both sides of the steel ball fixing seat (11). The flexible steel wire (19) is used to restrict the steel ball (18) from floating freely in the steel ball fixing seat (11) and prevent the steel ball from falling out. A dial indicator (1) is installed above the movable measuring base (4).

2. The measuring tool and method for the mean diameter of the helical raceway of a steering nut according to claim 1, characterized in that: A handle mounting base (9) is provided on the other side of the fixed measuring base (10). A fixed handle (7) is provided on the handle mounting base (9). A movable hand lever (8) is provided below the fixed handle (7). A pull rod (6) is provided on the other side of the movable measuring base (4). The lower end of the pull rod (6) is located in the handle mounting base (9). A movable pin (16) is provided at the lower end of the pull rod (6). The movable hand lever (8) is hinged to the handle mounting base (9) through the fixed pin (15). A U-shaped groove (17) is provided at one end of the movable hand lever (8). The movable pin (16) is located in the end U-shaped groove (17).

3. The measuring tool and method for the mean diameter of the helical raceway of a steering nut according to claim 1, characterized in that: The top of the guide post (3) is provided with a dial indicator mounting bracket (2), and the dial indicator (1) is mounted on the dial indicator mounting bracket (2).

4. The measuring tool and method for the mean diameter of the helical raceway of a steering nut according to claim 1, characterized in that: The inner hole (22) of the steel ball fixing seat (11) is slightly larger than the diameter of the steel ball (18). The lower part of the steel ball (18) is provided with a wire hole (21). The flexible steel wire (19) is inserted through the wire hole (21). The two sides of the steel ball fixing seat (11) are respectively provided with side holes (20). The two ends of the flexible steel wire (19) are tied together and fixed in the side holes (20) of the steel ball fixing seat (11) by soldering.

5. The measuring tool and method for the pitch diameter of the helical raceway of a steering nut according to claim 1, characterized in that: Three guide pillars (3) are arranged in a triangular pattern. Two of them are located between the movable measuring base (4) and the fixed measuring base (10), and the other is located between the fixed steel ball assembly mounting block (12) and the movable steel ball assembly mounting block (13). The movable measuring base (4) and the fixed measuring base (10) are respectively provided with countersunk holes (24), and a spring (23) is provided between the countersunk holes (24).

6. The measuring tool and method for the pitch diameter of the helical raceway of a steering nut according to claim 1, characterized in that: The five steel ball assemblies (14) are distributed on the nth, n-1th and n+1th raceways of the nut raceway, with the steel ball assembly (14) on the movable steel ball assembly mounting block (13) arranged at the vertex of the nth raceway; the four steel ball assemblies on the fixed steel ball assembly mounting block (12) are symmetrically distributed along the axis on the n-1th and n+1th raceways, forming an isosceles triangle arrangement with the steel ball assembly (14) on the movable steel ball assembly mounting block (13).

7. The measuring tool and method for the pitch diameter of the helical raceway of a steering nut according to claim 1, characterized in that: The flexible steel wire (19) is made of high-strength stainless steel wire or nickel-titanium alloy wire with a diameter of 0.2 to 0.5 mm.

8. The measuring tool and method for the pitch diameter of the helical raceway of a steering nut according to claim 1, characterized in that: The dial indicator (1) can be an electronic meter head, which outputs digital signals through the signal acquisition module to realize electronic acquisition and automatic conversion of measurement data.

9. A method for measuring the mean diameter of the helical raceway of a steering nut, characterized in that, The measuring fixture for the pitch diameter of the helical raceway of a steering nut, as described in any one of claims 1-8, comprises the following steps: (1) Calibration steps: Insert the measuring head of the measuring gauge into the calibration gauge, press down the movable lever (8) to move the movable measuring base (4) down, and let the measuring steel ball assembly (14) contact the inner wall of the calibration gauge before zeroing the dial indicator (1); (2) Measurement steps: Hold the movable hand lever (8) and insert the probe into the inner raceway of the steering nut. Slowly release the movable hand lever (8). Under the action of spring 1 (5), the fixed measuring base (10) and the movable measuring base (4) are separated. The five measuring steel balls (18) are in tangential contact with the three spiral raceways respectively. (3) Reading and conversion: Read the pointer change value of the dial indicator (1), compare it with the zero point during calibration, and calculate the mean diameter of the spiral raceway of the steering nut based on the known calibration gauge dimensions; (4) Error compensation: By utilizing the characteristic that the steel ball (18) floats freely in the steel ball fixing seat (11), the contact angle between the steel ball (18) and the raceway is adaptively aligned, thereby compensating for the manufacturing error of the nut and improving the measurement accuracy.

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