Ball screw pair and rack and pinion type electric power steering gear

Abstract

This invention discloses a ball screw assembly, including a ball nut and a return ball tube assembly. The return ball tube assembly is located outside the ball nut and includes a first return ball tube and a second return ball tube. Both have mating connecting rods and connecting holes. The end of the connecting rod has a guide structure and is interference-fitted with the connecting hole. The first return ball tube has a first inner tube, and the second return ball tube has a second inner tube. The ball nut has two return ball tube holes for inserting the two inner tubes. The holes have a communicating first groove and a second groove, with the first groove guiding the insertion of the inner tube. This invention's ball screw assembly, through a large-thread connection design, has a reasonable interference fit between the connecting rod and the connecting hole, and includes a guiding angle, making the return ball tube assembly convenient and the connection secure, avoiding the loosening or assembly difficulties encountered in traditional connection methods. This invention also discloses a rack and pinion type electric power steering system.

Description

Technical Field

[0001] This invention belongs to the technical field of vehicle steering systems. Specifically, this invention relates to a ball screw pair and a rack and pinion type electric power steering system. Background Technology

[0002] Ball screw assemblies, as key transmission components that convert rotary motion into linear motion, are widely used in modern industry. External circulation ball screw assemblies, with their advantageous ball circulation path layout, have potential in high-load, high-speed transmission scenarios. However, traditional external circulation ball screw assemblies suffer from problems such as ball return tube circulation jamming, significant impact of heat treatment on ball nut machining accuracy, and large taper in the grinding of rack and pinion screw raceways. These issues limit transmission efficiency, easily lead to loss of accuracy, and have short service life, making it difficult to meet the high-efficiency, precise, and reliable transmission requirements of high-end equipment such as new energy vehicles. Therefore, improving and optimizing their key components is of urgent practical significance. With the increasing demands for "high speed, high precision, and high reliability" in high-end equipment, the shortcomings of traditional external circulation ball screw assemblies in core component structural design and manufacturing process stability are becoming increasingly apparent.

[0003] Currently, the external circulation ball screw pair used in rack and pinion electric power steering systems has the following problems:

[0004] 1. The traditional ball return tube structure design is inconvenient to assemble, and the balls are prone to collision and jamming during circulation, resulting in increased transmission noise, accelerated ball wear, and consequently affecting transmission accuracy and service life.

[0005] 2. Ball nuts are the core carrier of transmission accuracy. Often, heat treatment deformation is difficult to control, which in turn affects assembly compatibility, ball jamming, and connection reliability. Secondly, the irregular hole that matches the return tube is difficult to process, which directly affects the matching with the return tube and may even affect the smoothness of ball movement.

[0006] 3. The flange is press-fitted onto the ball nut. Its function is to connect with the large pulley in the R-EPS, transmit torque to drive the ball nut to rotate, and convert the ball nut's return motion into linear motion. However, the secondary press-fit has several drawbacks. First, the short connection length of the flange makes it easy for the press-fit to be unreliable. Second, if the interference fit is too large, the nut will deform, resulting in increased friction between the steel ball and the inner and outer raceways, and even jamming. Third, if the interference fit is too small, there is a risk of the flange falling off, which could damage the entire R-EPS.

[0007] This invention provides an external circulation ball screw pair for a rack and pinion type electric power steering system, particularly concerning how to facilitate the assembly and secure connection of the return ball tube, improve operational stability, and reduce noise generated during operation. Summary of the Invention

[0008] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the present invention provides a ball screw pair for a rack and pinion type electric power steering system, the purpose of which is to facilitate the assembly of the return ball tube and ensure a firm connection.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a ball screw assembly, including a rack screw, a ball nut, and a return ball tube assembly. The return ball tube assembly is located outside the ball nut. The return ball tube assembly includes a first return ball tube and a second return ball tube. The first return ball tube and the second return ball tube are respectively provided with a matching connecting rod and a connecting hole. The end of the connecting rod is provided with a guide structure. The connecting rod and the connecting hole are interference fit.

[0010] The first return tube is provided with a first inner tube, and the second return tube is provided with a second inner tube. The ball nut has two return tube holes for the first inner tube and the second inner tube to be inserted respectively. The return tube holes are provided with a first groove and a second groove, which are connected. The first groove is an arc groove, and the second groove is an oblong groove. The first groove is used to guide the first inner tube and the second inner tube when they are inserted into the return tube holes.

[0011] The interference fit between the connecting rod and the connecting hole is 0.1 mm, and the interference fit length is 0.5 mm to 1 mm.

[0012] Both the first and second return ball tubes are provided with oil return grooves for storing lubricating grease.

[0013] The first bead return tube has a first protrusion on its end face facing the second bead return tube. The height of the first protrusion is 0.1mm, and multiple first protrusions are provided.

[0014] The ball return tube assembly has a flared opening at both the ball inlet and the ball outlet. The flared opening is an flared structure located at the ball inlet and the ball outlet, and its inner diameter gradually increases along the direction in which the steel ball enters and exits the ball return tube assembly.

[0015] The guide structure includes a first conical section and a second conical section. A cylindrical mating section is provided on the connecting rod. The second conical section is located between the cylindrical mating section and the first conical section. The inner surface of the connecting hole includes a first cylindrical surface, an inner conical surface, and a second cylindrical surface arranged sequentially along the axial direction. The second cylindrical surface is in contact with the cylindrical mating surface. The diameter of the first cylindrical surface is larger than the diameter of the first conical section and the second cylindrical surface.

[0016] The end face of the ball return tube assembly is positioned and fitted against the outer wall of the ball nut. The inner side of the second ball return tube is provided with a second boss, and the second boss and the two ball return tube end faces of the ball return tube assembly form a triangular positioning structure.

[0017] The ball nut is provided with an internal thread, which is formed before the ball nut is carburized and quenched. When machining the internal thread, a tap with a diameter 0.05 larger than the design size is selected.

[0018] A flange is provided on the ball nut, and the ball nut and the flange are an integral structure.

[0019] The present invention also provides a rack and pinion type electric power steering system, including the aforementioned ball screw pair.

[0020] The ball screw assembly of the present invention features a large-thread connection design with a reasonable interference fit between the connecting rod and the connecting hole, and a guide angle. At the same time, a guide groove is provided in the return ball tube hole, which makes the return ball tube easy to assemble and the connection firm, avoiding the loosening or assembly difficulties that occur in traditional connection methods. Attached Figure Description

[0021] This manual includes the following figures, which illustrate the following:

[0022] Figure 1 This is a schematic diagram of the structure of the ball screw assembly of the present invention;

[0023] Figure 2 yes Figure 1 Sectional view of AA;

[0024] Figure 3 This is an exploded view of the bead return assembly;

[0025] Figure 4 This is a schematic diagram of the internal structure of the return bead tube;

[0026] Figure 5 This is a schematic diagram of the connecting rod structure;

[0027] Figure 6 This is a schematic diagram of the internal structure of the connection hole;

[0028] Figure 7 This is a schematic diagram of the bead return assembly structure;

[0029] Figure 8 This is the front view of the ball nut;

[0030] Figure 9 This is a side view of a ball nut;

[0031] Figure 10 This is a schematic diagram of the structure of a ball nut;

[0032] Figure 11 This is a schematic diagram of the contact area between the ball nut and the return ball tube assembly;

[0033] Figure 12 This is a schematic diagram showing the fit between the two return bead tubes and the return bead tube opening.

[0034] Figure 13 This is a schematic diagram of the assembly of the card plate and the two return ball tubes;

[0035] The markings in the diagram are as follows: 1. Rack and pinion screw; 2. Flange; 3. First ball return tube; 4. Second ball return tube; 5. Four-point contact ball bearing; 6. Clamping plate; 7. Ball nut; 8. Ball; 9. First inner tube; 10. Second inner tube; 11. Connecting rod; 12. Connecting hole; 13. Flared mouth; 14. First boss; 15. Oil return groove; 16. First cylindrical surface; 17. Inner conical surface; 18. Second cylindrical surface; 19. First conical section; 20. Second conical section; 21. Cylindrical mating section; 22. Second boss; 23. Ball return tube end face; 24. Internal thread; 25. First groove; 26. Second groove. Detailed Implementation

[0036] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings, in order to help those skilled in the art to have a more complete, accurate and in-depth understanding of the concept and technical solutions of the present invention, and to facilitate its implementation.

[0037] It should be noted that in the following embodiments, the terms "first," "second," and "third" do not represent an absolute distinction in structure and / or function, nor do they represent the order of execution; they are merely for the convenience of description.

[0038] Firstly, such as Figures 1 to 10 As shown, this embodiment of the invention provides a ball screw assembly for a rack and pinion type electric power steering system, including a rack and pinion screw 1, a ball nut 7, a retaining plate 6, a return ball tube assembly, and a four-point contact ball bearing. The return ball tube assembly is located outside the ball nut 7 and includes a first return ball tube 3 and a second return ball tube 4. The first return ball tube 3 and the second return ball tube 4 are respectively provided with a matching connecting rod 11 and a connecting hole 12. The end of the connecting rod 11 is provided with a guide structure, and the connecting rod 11 and the connecting hole 12 are interference fit. Through the large-thread connection design, the interference between the connecting rod 11 and the connecting hole 12 is reasonable and has a guide angle, which makes the return ball tube easy to assemble and the connection firm, avoiding the loosening or assembly difficulties that occur in traditional connection methods.

[0039] Meanwhile, a first inner tube 9 is provided on the first return tube 3, and a second inner tube 10 is provided on the second return tube 4. The first inner tube 9 and the second inner tube 10 are tubes with open ends and hollow interiors. The first inner tube 9 and the second inner tube 10 are used to allow the balls to pass through. The ball nut 7 has two return tube holes, which are through holes provided in the annular sidewall of the ball nut 7. The first inner tube 9 and the second inner tube 10 are respectively inserted into the two return tube holes. The return tube holes are provided with a first groove 25 and a second groove 26, which are connected. The first inner tube 9 and the second inner tube 10 have the same shape and size. The first groove 25 is an arc-shaped groove, and its diameter is the same as that of the first inner tube 9 and the second inner tube 10. The second groove 26 is an oblong groove, and its length is greater than the diameters of the first inner tube 9 and the second inner tube 10. The width of the second groove 26 is approximately equal to the diameters of the first inner tube 9 and the second inner tube 10. The first groove 25 is located at one edge of the width direction of the second groove 26 and is recessed in a direction away from the center of the width direction of the second groove 26 to form an arc structure. The recessed direction of the arc structure is adapted to the radial direction of the inner tube to fit the outer wall of the inner tube inserted into the return tube hole. The first groove 25 forms a guide angle in the return tube hole. The first groove 25 in the two return tube holes is used to guide the first inner tube 9 and the second inner tube 10 into the two return tube holes respectively during the assembly of the first return tube 3 and the second return tube 4, increasing the width of the return tube hole at the intersection of the first groove 25 and the second groove 26. The two inner tubes are inserted into the first groove 25 and the second groove 26 at the same time to avoid scratching the inner tubes.

[0040] The return ball hole is used to fix the inner tube of the return ball assembly. The return ball assembly is an injection molded part. The improved ball nut 7 has a circular arc groove milled at the return ball hole with a suitable ball end mill to avoid the position where the inner tube enters. The first circular arc groove 25 can cleverly wrap the inner tube, so that the inner tube can be smoothly installed into the return ball hole. At the same time, a waist-shaped groove is milled at the corresponding position. On the one hand, it is to avoid the inner tube, so that after assembly, the inner tube will not be squeezed or deformed due to interference with the nut, ensuring the normal working state of the return ball. On the other hand, the hole forms a guide angle to ensure that the inner tube is installed smoothly.

[0041] like Figure 1As shown, one end of the rack screw 1 is a rack segment for meshing with the steering gear, and the other end is a ball screw segment with an outer raceway. The ball nut 7 is fitted onto the ball screw segment of the rack screw 1. Its working principle is to achieve linear motion of the ball screw pair and apply axial push-pull assistance by circulating a certain number of balls within the raceway formed between the screw and the nut. The outer raceway of the rack screw 1 and the inner raceway of the ball nut 7 together form a helical channel for the movement of the balls. The helical channel contains the balls, which are the link for transmitting the relative motion between the screw and the nut. The screw and the nut achieve threaded transmission through the balls. The balls are arranged sequentially along the raceway in the nut. The return ball tube assembly is located on the outside of the ball nut 7 and is used to guide the balls to form a closed loop. The return ball tube hole establishes a return circulation channel, which is a necessary measure to ensure that the ball chain forms a closed loop and that the balls return. Therefore, the form of the return circulation channel directly affects the accuracy and performance of the entire ball screw pair.

[0042] In embodiments of the present invention, such as Figure 1 and Figure 13 As shown, two clamping plates 6 are provided, namely the left clamping plate and the right clamping plate. The left clamping plate and the right clamping plate fix the first return ball tube 3 and the second return ball tube 4 to the ball nut 7.

[0043] Two independently moving ball chains are installed on the ball nut 7. The function of the return ball tubes is to guide the balls to form a circulating loop. The number of return ball tubes corresponds to the number of ball chain columns. Each return ball tube has one inlet and one outlet. The ball nut 7 has four return ball tube mounting holes, which are arranged in pairs to form a closed external circulation chain for continuous transmission. The return ball holes on the return ball tubes force the balls to roll along the raceway. After passing through the return ball holes, the balls return to the initial raceway, forming a circulating ball chain (i.e., one column).

[0044] like Figures 3 to 6 As shown, multiple connecting rods 11 are provided on both the first return ball tube 3 and the second return ball tube 4. The length direction of the connecting rod 11 is parallel to the axis of the first return ball tube 3 and the second return ball tube 4. The first return ball tube 3 and the second return ball tube 4 are sleeved on the ball nut 7. The first return ball tube 3 is provided with connecting holes 12 for inserting the connecting rods 11 on the second return ball tube 4. The second return ball tube 4 is provided with connecting holes 12 for inserting the connecting rods 11 on the first return ball tube 3. The number of connecting holes 12 is the same as the number of connecting rods 11.

[0045] In this embodiment of the invention, the interference fit between the connecting rod 11 and the connecting hole 12 is 0.1 mm, and the interference fit length is 0.5 mm to 1 mm. If the interference fit is large and the length of the interference fit is long, the pressing force during assembly will be large, and the connecting rod 11 may be easily broken. This large buckle design can meet the requirements of repeated disassembly and assembly, providing convenience for the after-sales service market. In the prior art, many such large buckles are press-fitted only once, and after disassembly, the buckle is subjected to pull-out force and becomes rough and deformed.

[0046] like Figures 3 to 6As shown, the guide structure includes a first conical section 19 and a second conical section 20, both of which are conical. A cylindrical mating section 21, also conical, is provided on the connecting rod 11. The cylindrical mating section 21 is conical, and the axes of the cylindrical mating section 21, the first conical section 19, and the second conical section 20 are also the axes of the connecting rod 11. The second conical section 20 is located between the cylindrical mating section 21 and the first conical section 19. The diameter of the small-diameter end of the first conical section 19 is smaller than that of the large-diameter end. The diameter of the first conical segment 19 is such that the small diameter end and the large diameter end are opposite ends of the first conical segment 19 in the axial direction. The diameter of the small diameter end of the second conical segment 20 is smaller than the diameter of the large diameter end. The small diameter end and the large diameter end of the second conical segment 20 are opposite ends of the second conical segment 20 in the axial direction. The diameter of the large diameter end of the first conical segment 19 is the same as the diameter of the small diameter end of the second conical segment 20. The diameter of the large diameter end of the second conical segment 20 is the same as the diameter of the cylindrical mating segment 21. The inner surface of the connecting hole 12 includes a first cylindrical surface 16, an inner conical surface 17, and a second cylindrical surface 18 arranged sequentially along the axial direction. The axis of the first cylindrical surface 16, the inner conical surface 17, and the second cylindrical surface 18 is also the axis of the connecting hole 12. The second cylindrical surface 18 is in contact with the cylindrical mating surface. The first cylindrical surface 16 and the second cylindrical surface 18 are cylindrical surfaces, and the inner conical surface 17 is a conical surface. The diameter of the first cylindrical surface 16 is larger than the diameter of the first conical section 19 and the second cylindrical surface 18. The diameter of the first cylindrical surface 16 is larger than the diameter of the cylindrical mating section 21. The cylindrical mating section 21 is the part with the largest diameter on the connecting rod 11. The diameter of the small diameter end of the inner conical surface 17 is smaller than the diameter of the large diameter end. The small diameter end and the large diameter end of the inner conical surface 17 are opposite ends in the axial direction of the inner conical surface 17. The distance between the small diameter end of the inner conical surface 17 and the second cylindrical surface 18 is smaller than the distance between the large diameter end of the inner conical surface 17 and the second cylindrical surface 18. The diameter of the large diameter end of the inner conical surface 17 is the same as the diameter of the first cylindrical surface 16, and the edge of the large diameter end of the inner conical surface 17 is connected to one end edge of the first cylindrical surface 16. During the process of inserting the connecting rod 11 into the connecting hole 12, the first conical segment 19 first enters the connecting hole 12. The first conical segment 19 passes through the center holes of the first cylindrical surface 16, the inner conical surface 17, and the second cylindrical surface 18 in sequence. Then, the first conical segment 19 also passes through the center holes of the first cylindrical surface 16, the inner conical surface 17, and the second cylindrical surface 18 in sequence. The first conical segment 19 and the second conical segment 20 cooperate with the inner conical surface 17 to play a guiding role. Finally, the cylindrical mating segment 21 is fully inserted into the connecting hole 12. The diameter A of the cylindrical mating segment 21 is larger than the diameter B of the second cylindrical surface 18. The outer circular surface of the cylindrical mating segment 21 is tightly fitted with the second cylindrical surface 18 to achieve a tight fit.

[0047] The ball return tube assembly consists of a first ball return tube 3 and a second ball return tube 4. The connection between the first ball return tube 3 and the second ball return tube 4 uses a large-clip design. Two connecting rods 11 and two connecting holes 12 are respectively provided on the first ball return tube 3 and the second ball return tube 4. The end of the connecting rod 11 has a guide angle, a clever design that guides the connecting rod 11 and the connecting hole 12 during assembly. From a mechanical perspective, the guide angle guides the connecting rod to accurately enter the hole, avoiding additional stress caused by deviation during assembly, reducing assembly difficulty and the risk of damage. In the production assembly line of new energy vehicles, efficient and precise assembly is the foundation for ensuring the consistency and reliability of the entire vehicle. This guiding design of the ball return tube meets the needs of large-scale, high-quality production of new energy vehicles.

[0048] In embodiments of the present invention, such as Figure 3 and Figure 4 As shown, two connecting rods 11 are provided on both the first return bead tube 3 and the second return bead tube 4.

[0049] In embodiments of the present invention, such as Figure 4 As shown, both the first ball return tube 3 and the second ball return tube 4 are equipped with oil return grooves 15 for storing lubricating grease. In the power transmission system of new energy vehicles, the lubrication status of the ball screw directly affects the transmission efficiency and wear level. The design of the oil return grooves 15 can continuously provide lubrication to the contact area between the steel balls and the screw and nut, reduce friction loss, and improve energy transmission efficiency, which is of positive significance for improving the driving range of new energy vehicles.

[0050] In embodiments of the present invention, such as Figure 3 and Figure 4As shown, a first boss 14 is provided on the first end face of the first return bead tube 3 facing the second return bead tube 4. The height of the first boss 14 is 0.1mm. The height direction of the first boss 14 is parallel to the axis of the first return bead tube 3. Multiple first bosses 14 are provided, mainly to control the gap between the first end face of the first return bead tube 3 and the second end face of the second return bead tube 4 when the first return bead tube 3 and the second return bead tube 4 are pressed together. The first end face of the first return bead tube 3 and the second end face of the second return bead tube 4 are arranged opposite to each other. Connecting rods 11 and connecting holes 12 are provided on the first end face and the second end face. A first boss 14 is provided between two adjacent connecting rods 11 and two adjacent connecting holes 12. The first boss 14 fits against the second end face. The first boss 14 acts as a physical barrier between the first return ball tube 3 and the second return ball tube 4. During the pressing process of the upper and lower return ball tubes, it contacts other parts of the tube body first, thus strictly limiting the maximum pressing depth. This prevents the pressure from reaching the limit position when the force cannot be precisely controlled or is improperly controlled, which could cause deformation of the return ball tube inlet and outlet, indirectly resulting in poor ball movement. Furthermore, the 0.1mm height of the first boss 14 structurally prevents deformation of the ball running channel due to uncontrolled assembly pressure, ensuring the stable operation of the ball screw system and reducing vehicle performance fluctuations caused by mechanical failures.

[0051] In embodiments of the present invention, such as Figure 4 As shown, both the ball inlet and outlet of the ball return tube assembly are provided with flared openings 13. The flared openings 13 are flared structures located at the ball inlet and outlet, with their inner diameter gradually increasing along the direction of the steel ball entering and exiting the ball return tube assembly. The first ball return tube 3 and the second ball return tube 4 have positioning and anti-deviation designs. The flared openings 13 at the inlet and outlet are designed to allow the steel ball to enter and exit more smoothly. Without the flared openings 13, the first ball return tube 3 and the second ball return tube 4 would be injection molded parts. Such materials are prone to deformation, causing the inlet and outlet openings to narrow inwards. This results in the inner wall of the ball return tube being higher than the ball groove, or simply higher than the raceway on the ball nut 7, forming a ledge. The steel ball must first overcome this ledge, creating a fluctuation that can cause fluctuations and even noise in the ball screw assembly. The flared opening 13 design, from the perspective of fluid mechanics and kinematics, optimizes the entry and exit channels of the steel ball, reducing the resistance and impact of the steel ball's movement. In the frequent start-stop, acceleration, and deceleration conditions of new energy vehicles, the smoothness of the ball screw's movement directly affects the smoothness and comfort of power transmission. If the return ball tube deforms and produces noise due to structural defects, it will not only affect the driving experience, but long-term abnormal impacts may also accelerate component wear, reduce the service life of the ball screw, and increase the overall vehicle maintenance costs.

[0052] In embodiments of the present invention, such as Figure 7 , Figure 11 and Figure 12As shown, the end face of the return tube of the return tube assembly is positioned and fitted with the outer wall of the ball nut 7. The inner side of the second return tube 4 is provided with a second boss 22, and the second boss 22 and the two end faces of the return tube of the return tube assembly form a triangular positioning structure. The two return tube end faces of the ball return tube assembly are the end faces of the first inner tube 9 and the second inner tube 10, respectively. The first inner tube 9 is mounted on the first return tube 3 and the two are integrally formed. The second inner tube 10 is mounted on the second return tube 4 and the two are integrally formed. The two return tube end faces and the second boss 22 are triangularly distributed. When the two return tubes are assembled onto the ball nut 7, the triangular positioning structure formed by the two return tube end faces and the second boss 22 limits the insertion depth of the first inner tube 9 and the second inner tube 10, which can relatively stably attach the two return tubes to the outer wall of the ball nut 7. Without the limiting effect of the second boss 22, the return tube end faces of the first inner tube 9 and the second inner tube 10 could easily push against the bottom plane of the two return tube holes of the ball nut 7, which could easily cause extrusion deformation. Secondly, the triangular positioning structure utilizes the stability principle of triangles to establish a stable spatial positioning relationship during the assembly of the return tubes and the ball nut 7. During operation, new energy vehicles face complex road conditions and vibrations. This stable positioning structure effectively prevents relative misalignment between the ball screw assembly and the ball nut 7, ensuring the transmission accuracy of the ball screw system. Misalignment not only increases transmission errors and affects vehicle handling precision (such as in the application of ball screws in steering and braking systems), but may also cause additional stress concentration, accelerating component damage.

[0053] In this embodiment of the invention, the ball nut 7 has an internal thread, which is machined before carburizing and quenching. A tap with a pitch diameter 0.05 larger than the design dimension is used when machining the internal thread. The ball nut 7 is made of carburized steel. After carburizing and quenching, the ball nut 7 deforms after heat treatment, and the thread will typically fail to pass through the go gauge 100%. If the thread is machined after heat treatment, the high hardness makes machining difficult and results in significant tap wear, leading to substantial waste. To overcome deformation due to heat treatment, a tap with a pitch diameter 0.05 larger is used before heat treatment. After heat treatment, the thread can pass through the go gauge and stop the no-go gauge. The core of this process improvement lies in balancing the impact of heat treatment on thread accuracy and machining difficulty. In the production of new energy vehicles, the thread accuracy of the ball nut 7 directly affects the transmission efficiency and positioning accuracy of the ball screw. By rationally adjusting the sequence of heat treatment and thread machining, and combining this with the flexible application of tap specifications, both the machining difficulty and cost are reduced (by minimizing tap wear), while ensuring the thread precision requirements are met, satisfying the high precision and high reliability demands of new energy vehicles for their power transmission systems. In the powertrain and chassis control systems of new energy vehicles, the thread precision of the ball nut 7 determines the smoothness of power transmission and the accuracy of control command execution. For example, in electric power steering systems, the transmission precision of the ball screw directly affects the vehicle's steering feel and response speed. By optimizing the thread machining process of the ball nut 7, the accuracy of the transmission system is ensured, improving vehicle handling stability and driving experience. Simultaneously, it helps reduce energy loss caused by transmission errors, indirectly improving the overall vehicle's energy efficiency.

[0054] In embodiments of the present invention, such as Figure 8 As shown, a flange 2 is mounted on the ball nut 7. The ball nut 7 and flange 2 are an integral structure. The flange 2 is used to connect the drive device, which generates driving force to rotate the ball nut 7. In existing technology, the flange is a separate, secondary press-fit type, with the connecting plate serving as the transmission connection. When the interference fit between the flange's center hole and the outer diameter of the ball nut is too large, the ball nut is prone to deformation during press-fitting, leading to increased frictional resistance in the entire ball screw pair and even ball jamming. Due to structural limitations, the interference fit length is only about 3mm. If the interference fit is insufficient, the flange is prone to detachment. In this embodiment of the invention, through structural optimization, the flange 2 and ball nut 7 are designed as an integral unit. This not only eliminates the control difficulties of separate processing and simplifies the assembly process, but more importantly, it reduces the risk of flange 2 detachment to zero.

[0055] As a key component of the ball screw, the precision of the rack and pinion screw 1 directly affects the trajectory of the steel balls and the transmission efficiency. In the power transmission and control links of new energy vehicles (such as electric braking systems and electric seat adjustment systems), the precision of the ball screw determines the action accuracy and response speed of the actuator. By ensuring the machining precision of the rack and pinion screw 1, the overall performance of the ball screw system can be improved, making the various electric control functions of the vehicle more precise and stable, and improving the intelligence and comfort level of the whole vehicle. Precision grinding of the raceway is a method for online detection and verification of the straightness of the center lines of the two centers of the grinding machine, ensuring the precision of the precision-machined raceway. In this embodiment of the invention, the specific implementation process is as follows: a long bar of the same length as the machined rack and pinion screw 1 is made, and the two ends of the long bar shaft are precision-milled with composite center holes, the outer circle is ground with a centerless grinder, and then the center holes are ground. The straightness and runout of the long bar shaft are detected by a three-coordinate measuring machine to meet the calibration requirements. Before the equipment debugging of the precision-ground outer raceway of the rack and pinion screw 1, the long bar shaft needs to be used to calibrate and verify whether the two centers of the equipment are on the same center line. A dial indicator is used to check the runout and straightness of the outer diameter of the long bar shaft. If both runout and straightness are within 0.002, it can be determined that the centers of the two center holes at both ends of the equipment are on a straight line. The core of this testing method lies in calibrating the precision of the grinding machine by simulating the machining state of the rack screw 1. In the production of ball screws for new energy vehicles, the machining precision of the rack screw 1 directly determines the transmission precision and performance of the ball screw. Through this precise equipment calibration method, the consistency of precision of the rack screw 1 during the machining process can be guaranteed, laying the foundation for the high-performance performance of the ball screw after it is assembled into a system. If the center of the equipment itself has a large eccentricity, then even fine grinding of the raceway cannot guarantee the machining precision of the raceway.

[0056] The ball screw pair with the above structure has the following advantages:

[0057] 1. Robust and reliable ball return tube connection: The large buckle connection design ensures a reasonable interference fit between the connecting rod and the connecting hole, and features a guide angle, making the ball return tube easy to assemble and securely connected, avoiding the loosening or assembly difficulties that occur in traditional connection methods.

[0058] The limiting boss design at one end of the return ball tube makes the return ball tube more stable after it is assembled onto the nut, avoiding squeezing deformation caused by the end face of the return ball tube hitting the end face of the nut.

[0059] 2. Smooth ball circulation: The flared design at the inlet and outlet of the return ball tube effectively avoids the problem of ball obstruction caused by tube deformation; the protrusion on the end face of the return ball tube prevents tube deformation caused by excessive pressing, further ensuring smooth ball circulation.

[0060] 3. Excellent lubrication: The ball return groove on the ball return tube can store lubricating grease, providing continuous lubrication for the balls, reducing wear between the balls and the ball return tube and nut raceway, and extending the service life of the ball screw.

[0061] 4. Reduced processing cost of ball nuts: By improving the processing technology before heat treatment of internal threads, the difficulties in thread processing after heat treatment and the large amount of tap wear are avoided, thus reducing production costs while ensuring thread accuracy.

[0062] The ball screw nut and return tube are properly assembled: the arc groove and waist-shaped groove design of the return tube orifice of the ball screw nut avoids interference between the return tube and the nut, prevents the return tube from being squeezed and deformed, and ensures the normal operation of the ball screw. The flange connection is reliable: through improvements to the flange structure, the problems of easy detachment and deformation of the ball screw nut caused by traditional split flanges are avoided, ensuring the reliable connection and transmission of the ball screw.

[0063] 5. Improved machining accuracy of rack and pinion screws: The method of online detection and verification of the straightness of the center lines of the two centers on the grinding machine ensures the machining accuracy of the rack and pinion screw raceway, thereby improving the transmission accuracy and stability of the ball screw.

[0064] 6. Good operational stability and low noise: Due to the smooth circulation of the balls and the reasonable assembly of each component, the ball screw pair has small fluctuations and low noise during operation, which improves the overall performance of the equipment.

[0065] Secondly, embodiments of the present invention also provide a rack and pinion type electric power steering system, including a ball screw assembly with the above-described structure. This ball screw assembly can be referred to... Figures 1 to 13 The details will not be elaborated further here. Since the rack and pinion type 1 electric power steering system of the present invention includes the ball screw pair in the above embodiments, it has all the advantages of the above ball screw pair.

[0066] The invention has been described above with reference to the accompanying drawings, but this is not an exhaustive list. Clearly, the specific implementation of the invention is not limited to the above-described manner. Any non-substantial improvements made using the inventive concept and technical solution, or the direct application of the inventive concept and technical solution to other situations without modification, are all within the scope of protection of this invention. In a ball screw system, components such as the ball return tube, ball nut, and rack and pinion screw do not work independently but rather collaborate and influence each other. The ball return tube ensures smooth circulation and precise guidance of the steel balls, the ball nut realizes threaded transmission and power conversion, and the rack and pinion screw 1 provides a high-precision transmission foundation. In the actual operation of new energy vehicles, these components need to work collaboratively under complex operating conditions (such as different driving speeds, load changes, temperature fluctuations, etc.), and performance fluctuations of any component may affect the performance of the entire system. Therefore, in-depth research into the collaborative mechanism between components and optimization of system integration schemes are key to ensuring the high performance and high reliability of the ball screw system.

Claims

1. A ball screw assembly, comprising a rack and pinion screw, a ball nut, and a ball return tube assembly, wherein the ball return tube assembly is disposed outside the ball nut, characterized in that, The bead return tube assembly includes a first bead return tube and a second bead return tube. The first bead return tube and the second bead return tube are respectively provided with a matching connecting rod and a connecting hole. The end of the connecting rod is provided with a guide structure. The connecting rod and the connecting hole are interference fit. The first return tube is provided with a first inner tube, and the second return tube is provided with a second inner tube. The ball nut has two return tube holes for the first inner tube and the second inner tube to be inserted respectively. The return tube holes are provided with a first groove and a second groove, which are connected. The first groove is an arc groove, and the second groove is an oblong groove. The first groove is used to guide the first inner tube and the second inner tube when they are inserted into the return tube holes.

2. The ball screw assembly according to claim 1, characterized in that, The interference fit between the connecting rod and the connecting hole is 0.1 mm, and the interference fit length is 0.5 mm to 1 mm.

3. The ball screw assembly according to claim 1, characterized in that, Both the first and second return ball tubes are provided with oil return grooves for storing lubricating grease.

4. The ball screw assembly according to any one of claims 1 to 3, characterized in that, The first bead return tube has a first protrusion on its end face facing the second bead return tube. The height of the first protrusion is 0.1mm, and multiple first protrusions are provided.

5. The ball screw assembly according to any one of claims 1 to 3, characterized in that, The ball return tube assembly has a flared opening at both the ball inlet and the ball outlet. The flared opening is an flared structure located at the ball inlet and the ball outlet, and its inner diameter gradually increases along the direction in which the steel ball enters and exits the ball return tube assembly.

6. The ball screw assembly according to any one of claims 1 to 3, characterized in that, The guide structure includes a first conical section and a second conical section. A cylindrical mating section is provided on the connecting rod. The second conical section is located between the cylindrical mating section and the first conical section. The inner surface of the connecting hole includes a first cylindrical surface, an inner conical surface, and a second cylindrical surface arranged sequentially along the axial direction. The second cylindrical surface is in contact with the cylindrical mating surface. The diameter of the first cylindrical surface is larger than the diameter of the first conical section and the second cylindrical surface.

7. The ball screw assembly according to any one of claims 1 to 3, characterized in that, The end face of the ball return tube assembly is positioned and fitted against the outer wall of the ball nut. The inner side of the second ball return tube is provided with a second boss, and the second boss and the two ball return tube end faces of the ball return tube assembly form a triangular positioning structure.

8. The ball screw assembly according to any one of claims 1 to 3, characterized in that, The ball nut is provided with an internal thread, which is formed before the ball nut is carburized and quenched. When machining the internal thread, a tap with a diameter 0.05 larger than the design size is selected.

9. The ball screw assembly according to any one of claims 1 to 3, characterized in that, A flange is provided on the ball nut, and the ball nut and the flange are an integral structure.

10. A rack and pinion type electric power steering system, characterized in that, Includes the ball screw pair as described in any one of claims 1 to 9.

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