Ball screw mechanism and vehicle power-assisted steering system

Abstract

The invention discloses a ball screw mechanism which comprises a rack screw, a ball nut and a reverser, the rack screw comprises a screw section, the screw section is provided with an outer spiral raceway for containing balls, the lead of the outer spiral raceway is at least 20, the outer spiral raceway comprises two semicircular raceways and an arc groove, and the arc groove is located between the two semicircular raceways. According to the ball screw mechanism disclosed by the invention, the screw section adopts a large-lead design, so that the transmission efficiency can be improved. The invention further discloses a vehicle power-assisted 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 mechanism and a vehicle power steering system. Background Technology

[0002] With the continuous development of commercial vehicles and influenced by the trend of new energy development, there is a demand for the electrification of components in vehicles. Drivers, with their high workload, require intelligent and electric steering systems, which also contribute to reducing energy consumption and emissions from fuel-powered vehicles. Currently, medium and heavy-duty commercial trucks use electro-hydraulic steering systems, lacking pure electric steering gears. This presents new challenges for traditional commercial vehicle component suppliers and the steering industry. The ball screw pair is a core functional component of R-EPS (Rack and Pinion Electric Power Steering) and is currently an irreplaceable key component. The working principle of R-EPS is that a motor drives the ball screw pair via a belt reduction mechanism, which in turn drives the rack shaft to achieve transmission. At the input end (the end connected to the steering wheel), it uses a rack and pinion transmission method, and a sensor transmits the steering wheel rotation signal to the motor, which then performs the power assist function. The ball screw pair is used to convert rotational motion into linear motion, enabling the steering system to accurately respond to the driver's operation and provide the required steering assistance. Furthermore, the application of ball screw assemblies is not limited to R-EPS; they play a crucial role in many other automotive systems, such as steering, braking, parking, and suspension systems. In Electric Power Steering (EPS) systems, the ball screw connects the electric power steering motor and the steering mechanism (such as a steering rack). When the driver operates the steering wheel, the EPS system controls the electric power steering motor to output corresponding torque based on the calculated optimal steering angle and force, while simultaneously transmitting the steering torque to the steering mechanism via the ball screw to ensure stability and controllability.

[0003] Currently, the ball screw assemblies used in R-EPS systems for commercial vehicles have the following problems:

[0004] 1. Currently, the lead of most ball screw pairs is 6, 7, or 8. A smaller lead in ball screw pairs affects system performance and efficiency, often resulting in insufficient sensitivity when steering. If the lead is too small, it means the nut moves less distance per revolution of the screw, leading to reduced transmission efficiency. Since power transmission efficiency is related to the number of force applications, a smaller lead means more force applications in the same amount of time, resulting in greater frictional losses and thus decreased efficiency.

[0005] 2. Noise issues with ball screw assemblies: The proper installation of each component directly affects noise levels. Improper installation can lead to unstable operation of the ball screw, resulting in noise problems. For example, if the return mechanism is not securely fixed, the balls may wobble or move around during their cyclical motion, causing obstructed ball movement and generating noise.

[0006] 3. In the existing steering gear recirculating ball structure, most adopt a separate structure of bearing and ball nut, which not only increases the number of parts, but also increases the error caused by processing and assembly. Summary of the Invention

[0007] 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 mechanism with the purpose of improving transmission efficiency.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a ball screw mechanism, including a rack screw, a ball nut and a return mechanism, wherein the rack screw includes a screw section, and an outer helical raceway for accommodating balls is provided on the screw section, the lead of the outer helical raceway is at least 20, and the outer helical raceway includes two semi-circular arc raceways and an arc groove, wherein the arc groove is located between the two semi-circular arc raceways.

[0009] The reversing device is provided with an insert, which is integrally injection molded with the reversing device. The insert is provided with a slot for the reversing device to be inserted.

[0010] The radius of the semi-circular raceway is greater than the radius of the circular groove, and the curvature of the semi-circular raceway is greater than the curvature of the circular groove.

[0011] The axis of the two semi-circular raceways is at a certain distance from the pitch circle center, and the pitch circle center is located in the middle of the axis of the two semi-circular raceways.

[0012] The ball nut is provided with an inner helical raceway to accommodate the balls and a return ball elongated hole that forms a circulation loop with the return device. The diameter of the return ball elongated hole is set to 1.06 to 1.08 times the diameter of the balls.

[0013] The ball nut has a first mounting groove at both ends for mounting the return device. An eccentric positioning hole is provided in the first mounting groove. The return device has a boss that cooperates with the eccentric positioning hole for positioning.

[0014] The ball nut has a retaining ring groove inside to accommodate the elastic retaining ring. The retaining ring groove has a first contact surface and a second contact surface that fit against the outer circular surface of the elastic retaining ring. The first contact surface is a conical surface.

[0015] The ball nut has a second mounting groove inside to accommodate the oil baffle plate. The second mounting groove is adjacent to the retaining ring groove, and the oil baffle plate is located between the return device and the elastic retaining ring.

[0016] The oil baffle plate is provided with protrusions that contact the ball nut and oil return ribs that match the outer spiral raceway. Multiple protrusions are provided, and annular grooves are provided on the inner side of the protrusions.

[0017] The present invention also provides a vehicle power steering system, including the aforementioned ball screw mechanism.

[0018] The ball screw mechanism of the present invention adopts a large lead design in the screw section, which can improve the transmission efficiency. Attached Figure Description

[0019] This manual includes the following figures, which illustrate the following:

[0020] Figure 1 This is a schematic diagram of the ball screw mechanism of the present invention;

[0021] Figure 2 yes Figure 1 Sectional view of AA;

[0022] Figure 3 This is the normal cross-sectional view of the outer helical raceway;

[0023] Figure 4 This is a schematic diagram of the rough-machined "V" shaped raceway;

[0024] Figure 5 This is the front view of the ball nut;

[0025] Figure 6 This is a side view of a ball nut;

[0026] Figure 7 This is a schematic diagram showing the position of the first mounting groove and the inner spiral raceway;

[0027] Figure 8 This is a schematic diagram of the internal structure of the return switch;

[0028] Figure 9 yes Figure 8 Sectional view of AA;

[0029] Figure 10 This is a schematic diagram of the ball's rolling path;

[0030] Figure 11 This is the front view of the oil baffle;

[0031] Figure 12 This is a side view of the oil baffle.

[0032] The markings in the diagram are as follows: 1. Rack and pinion screw; 2. Ball nut; 3. Ball; 4. Return mechanism; 5. Bearing; 6. Oil baffle; 7. Elastic retaining ring; 8. Screw; 9. Semi-circular raceway; 10. Circular groove; 11. Chamfer; 12. Return ball elongated hole; 13. First mounting groove; 14. Eccentric positioning hole; 15. Retaining ring groove; 16. Flat square; 17. Inner helical raceway; 18. Insert; 19. Protrusion; 20. Oil return rib; 21. Annular groove; 22. Marking point; 23. Positioning protrusion. Detailed Implementation

[0033] 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.

[0034] 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.

[0035] like Figures 1 to 12 As shown, this invention provides a ball screw mechanism, including balls 3, a rack screw 1, a ball nut 2, and a return mechanism 4. The rack screw 1 includes a screw section with an outer helical raceway for accommodating the balls 3. The ball nut 2 has an inner helical raceway 17 for accommodating the balls. The lead of the outer helical raceway is at least 20, and the lead of the outer helical raceway is the same as the lead of the inner helical raceway 17. The rack screw 1 and the inner and outer raceways of the ball nut 2 form a receiving space, and a certain number of balls 3 circulate in the helical raceway groove. This converts the rotational motion of the ball nut 2 into the linear motion of the rack screw 1.

[0036] Specifically, such as Figure 1 As shown, the rack and pinion screw 1 includes a rack section, a lead screw section, and a toothless section. The toothless section is located between and fixedly connected to the rack and lead screw sections. The rack section has multiple continuously distributed rack teeth that mesh with the steering gear. The outer surface of the lead screw section has an outer helical raceway. The lead screw section and the ball nut 2 together form a helical drive. One rack section and one lead screw section are provided, and the two ends of the toothless section are fixedly connected to the rack and lead screw sections respectively. The toothless section does not have rack teeth and is a cylinder of a certain length. The toothless section is coaxial with the rack and lead screw sections and is also located between the steering gear and the power assist pinion. The rack section has a certain length, and all rack teeth are arranged sequentially and equidistantly along the length of the rack section. The rack teeth are used to engage with the slots of the steering gear located between adjacent teeth.

[0037] like Figure 1 and Figure 3 As shown, in the normal (perpendicular to the axial direction of the rack screw 1) section of the outer helical raceway, the outer helical raceway includes two semi-circular arc raceways 9 and a circular arc groove 10. Both the semi-circular arc raceways 9 and the circular arc groove 10 are circular arc structures. The circular arc groove 10 is located in the middle of the two semi-circular arc raceways 9, and its two ends are connected to the two semi-circular arc raceways 9 respectively. The axis of the circular arc groove 10 is parallel to the axis of the semi-circular arc raceway 9. The radius of the semi-circular arc raceway 9 is larger than the radius of the circular arc groove 10, and the arc of the semi-circular arc raceway 9 is larger than the arc of the circular arc groove 10. The arc of the two semi-circular arc raceways 9 is the same, and the two semi-circular arc raceways 9 are symmetrically arranged.

[0038] like Figure 3 As shown, preferably, the axes of the two semi-circular arc raceways 9 are at a certain distance from the pitch circle of the outer helical raceway. Compared with the traditional single-circular arc raceway, this design is more conducive to the contact between the ball and the raceway, enabling the ball and raceway to achieve the optimal contact state, thereby improving the rotational flexibility and contact stiffness of the ball screw pair. The pitch circle is located in the middle of the axes of the two semi-circular arc raceways 9, and there is a certain distance between the axes of the two semi-circular arc raceways 9. The pitch circle and the axis of the arc groove 10 are on the same straight line perpendicular to the line connecting the axes of the two semi-circular arc raceways 9.

[0039] In the outer helical raceway, the ball 3 contacts the two semi-circular raceways 9, but does not contact the circular groove 10. The circular groove 10 in the outer helical raceway serves two purposes: firstly, it stores a certain amount of grease; secondly, it stores a certain amount of foreign matter, thus reducing raceway wear caused by foreign matter. The circular groove 10 forms a space for storing grease and / or foreign matter.

[0040] In this embodiment, the lead of the outer helical raceway is 20, and the screw section adopts a large lead design of 20, increasing the transmission efficiency to over 95%, marking its first application in the commercial vehicle field. Existing EPS (Electric Power Steering) systems use a worm gear structure for the power assist section, which relies on sliding friction and has a transmission efficiency of approximately 85%. In contrast, the R-EPS power assist section of this application uses a large lead ball screw structure, transmitting power through the rolling contact between the balls and the threaded grooves. This rolling method significantly reduces the coefficient of friction, thereby increasing transmission efficiency. When transmitting the same torque, the large lead ball screw can more effectively convert power and reduce energy loss. The large lead design aims for good load-bearing capacity and fast response, making it suitable for medium and large commercial vehicles and capable of meeting a front axle load of 2.5 tons.

[0041] like Figure 1 and Figure 3As shown, the opening formed on the outer circular surface of the lead screw section of the outer helical raceway has a chamfer 11. The chamfer 11 and the bottom arc groove 10 are machined as a single unit. The bar stock raceway is machined using both rough and finish machining. In short, a V-shaped helical raceway is rough-machined on the outer circular surface of the bar, resulting in a small allowance for finish grinding and significantly improving machining efficiency. Furthermore, this rough-machined groove r naturally forms an arc groove 10 after finish grinding. The chamfer 11 and the two semi-circular raceways 9 are then formed in one step through finish grinding. While ensuring a certain finish machining allowance, a suitable roughing groove cutter is selected. Commonly used groove cutters include C-type 80° and S-type 90°. The cutter tip radius is typically R0.8 to R1.2, which is the groove radius r, while still meeting the groove depth requirements. This rough machining method is readily available and can be achieved with most equipment.

[0042] like Figure 1 and Figure 5 As shown, the ball nut 2 has an internal helical raceway 17 that cooperates with the outer raceway of the rack screw 1. The ball nut 2 also has a return ball elongated hole 12 that forms a loop with the return device 4. The ball 3 can pass through the return ball elongated hole 12, which is located near the edge of the internal helical raceway 17. Through this return ball elongated hole 12 and the return device 4, the ball 3 forms a closed loop between the screw and the nut, achieving continuous transmission. With the help of the return ball elongated hole 12 on the return device 4, the ball 3 is forced to roll along the raceway. After passing through the return ball elongated hole 12 at the center of the nut, it returns to the initial raceway, forming a circular ball chain (i.e., a column). Establishing a return loop channel on the nut using the return device 4 is a necessary measure to enable the balls to return and form a closed loop in the ball chain. Therefore, the form of the return loop channel directly affects the accuracy and performance of the entire ball screw pair.

[0043] Preferably, the diameter of the return ball long hole 12 is set to 1.06 to 1.08 times the diameter of the ball 3. The function of the return ball long hole 12 is to form a circulation loop with the return device 4. The purpose of setting the diameter of the return ball long hole 12 to be larger is to reduce the obstruction of the circulation loop caused by the machining error of the nut and the return device 4.

[0044] like Figure 1 and Figure 5As shown, the ball nut 2 has a first mounting groove 13 for mounting the reversing device 4 at both ends. An eccentric positioning hole 14 is provided in the first mounting groove 13 and is located at the bottom of the first mounting groove 13. The reversing device 4 has a boss that cooperates with the eccentric positioning hole 14 for positioning. The boss is embedded in the eccentric positioning hole 14. The ball nut 2 also has a positioning surface, which is a plane parallel to the axis of the ball nut 2. The positioning surface and the radial direction of the ball nut 2 have an angle, which is an acute angle. The outer surface of the reversing device 4 includes an outer wall surface that fits with the positioning surface, so that the reversing device 4 can be quickly positioned and aligned, which is convenient for assembly.

[0045] like Figure 1 and Figure 6 As shown, the ball nut 2 has a retaining ring groove 15 inside to accommodate the elastic retaining ring 7. The retaining ring groove 15 is an annular groove inside the ball nut 2. The retaining ring groove 15 has a first contact surface and a second contact surface that fit against the outer circular surface of the elastic retaining ring 7. The first contact surface is a conical surface (sloping design). The two ends of the first contact surface are a large diameter end and a small diameter end, respectively. The diameter of the large diameter end is larger than the diameter of the small diameter end. The large diameter end of the first contact surface is connected to the outer edge of the second contact surface. The second contact surface is an annular plane perpendicular to the axis of the ball nut 2. The first contact surface and the second contact surface are coaxial with the ball nut 2. The outer circular surface of the elastic retaining ring 7 is in contact with the first contact surface, and the axial end face of the elastic retaining ring 7 is in contact with the second contact surface. The outer diameter of the elastic retaining ring 7 is larger than the diameter of the small diameter end of the first contact surface. A slope design is formed at the first contact surface of the retaining ring groove 15 to reduce the axial deviation caused by machining errors, so that the edge of the elastic retaining ring 7 can be reliably positioned on the slope without loosening, thereby eliminating the axial movement of the oil baffle plate 6 and the return device 4, and thus avoiding affecting the smoothness of the ball movement.

[0046] like Figure 1 and Figure 5As shown, a flat square 16 is provided on the outer circumference of the ball nut 2. The flat square 16 and the center of the return ball elongated hole 12 form a machining and inspection reference. Machining uses the flat square 16 for clamping and positioning to determine the starting point position of the spiral raceway, so that the starting and ending spiral lines at both ends of the nut are consistent. This ensures that after the return device 4 is assembled, the inlet and outlet of the return ball groove correspond to the interface of the inner spiral raceway 17 of the ball nut 2, and that a smooth transition can be achieved. The inner spiral raceway 17 is located in the center of the opening of the first mounting groove 13. If the starting point position of the inner spiral raceway 17 is deviated, it will directly cause the raceway to mismatch with the raceways on the return devices 4 at both ends, resulting in misalignment. This will inevitably cause the balls to collide with the return devices 4, increasing noise and temperature. As a result, the ball movement will be obstructed or even jammed, and may even lead to the failure of the entire ball screw assembly. During the machining process, the detection of the thread starting point is also particularly important. Machining and inspection always use the flat square 16 on the nut as a reference, which can ensure reference consistency and reduce deviation. For thread start point detection, simply use a flat square 16 positioning clamp and a profilometer to accurately measure the thread start point position. This greatly solves the problems of early debugging and effective control during thread processing.

[0047] The return mechanism 4 is a special device with two main functions: first, to guide the balls 3 from one raceway to another; and second, to return the balls 3 to the space between the screw and nut after completing one cycle, so that they can re-enter the cycle. In the inner cycle, the balls 3 always maintain contact with the outer helical raceway surface of the screw section, which gives the inner cycle ball screw high rigidity and positioning accuracy.

[0048] A smooth raceway is provided on the return mechanism 4, with its raceway curve positioned tangent to the pitch circle diameter of the ball nut 2. This forms a smooth transition track with the helical raceway of the ball nut 2. The interface of the return mechanism 4 is tangent to the threaded raceway, thus guiding the balls into the return through-hole to form a closed loop. In an internal circulation ball screw, the ball circulation method directly affects its performance and efficiency. The design of the return mechanism 4 is a crucial aspect of internal circulation ball screws, responsible for guiding the balls to correctly return and re-enter the circulation loop during the circulation process. Tangency refers to the contact state between the ball and the screw surface in the return mechanism; that is, the ball is tangent to the screw surface at the edge of the return mechanism. This design helps ensure that the balls can smoothly pass through the return mechanism and continue their cyclical movement on the screw.

[0049] Preferably, the retroreflector 4 is made of a blend of materials such as nylon, glass fiber, and toughening agent. The addition of glass fiber and toughening agent to the nylon has a good noise reduction effect and also increases the wear resistance of the retroreflector 4.

[0050] like Figure 2 , Figure 8 and Figure 9As shown, the reversing device 4 has an insert 18 inside, which is integrally injection molded with the reversing device 4. The insert 18 has slots for the reversing device 4 to be inserted into, and these slots are annular grooves on the outer surface of the insert 18. Multiple slots are provided, all arranged sequentially along the axial direction of the insert 18. The reversing device 4 is fixedly mounted on the ball nut 2 by screws inserted into the insert 18, which has internal threads that mate with the screws. The insert 18 and the reversing device 4 are injection molded together, ensuring that a portion of the reversing device 4 is evenly embedded in the slots of the insert 18. This structure has a high pull-out force, effectively preventing the insert 18 from falling out, thereby indirectly fixing the reversing device 4.

[0051] like Figure 1 and Figure 6 As shown, the ball nut 2 has a second mounting groove inside to accommodate the oil baffle 6. The second mounting groove and the retaining ring groove 15 are adjacent and coaxial. The second mounting groove is an annular groove inside the ball nut 2. The second mounting groove is located between the inner spiral raceway 17 and the retaining ring groove 15. The oil baffle 6 is located between the return device 4 and the elastic retaining ring 7. One end of the oil baffle 6 is in contact with the return device 4. The elastic retaining ring 7 applies axial pressure to the oil baffle 6. Under the action of the elastic retaining ring 7, the return device 4 is pressed tightly and does not loosen.

[0052] like Figure 11 and Figure 12 As shown, the oil baffle 6 has a circular structure. The oil baffle 6 is provided with protrusions 19 that contact the ball nut 2 and oil return ribs 20 that match the outer spiral raceway. Multiple protrusions 19 are provided on the outer circular surface of the oil baffle 6, all arranged circumferentially along the oil baffle 6. Annular grooves 21 are provided on the inner side of each protrusion 19. Each protrusion 19 and an annular groove 21 are located on the radial line of the oil baffle 6. The annular groove 21 is a groove extending axially through the end face of the oil baffle 6 and is arc-shaped. The protrusions 19 have a certain elasticity. When a force is applied to the protrusions 19 radially towards the axis of the oil baffle 6, the protrusions 19 can deflect towards the annular groove 21. After the force is removed, under the action of the protrusions 19's own elastic force, the protrusions 19 can deflect outwards towards the annular groove 21, allowing them to fit against the inner circular surface of the second mounting groove.

[0053] The outer circumference of the oil baffle 6 has multiple protrusions 19 at various locations, with two protrusions 19 at each location. An annular groove 21 is provided on the inner side of the two protrusions 19 at each location. The protrusions 19 and the oil baffle 6 are integrally injection molded.

[0054] In this embodiment, as Figure 11As shown, the outer circumference of the oil baffle 6 has four identical protrusions 19. An annular groove 21 is provided between two protrusions 19 at each location. The outer diameter of the protrusions 19 is designed to interference fit with the second mounting groove of the ball nut 2. In this case, the annular groove 21 serves to expand the four protrusions 19 and hold them tightly within the inner hole of the ball nut 2, making the oil baffle 6 easier to install and less prone to loosening. Furthermore, the annular groove 21 helps to prevent or reduce deformation of the plastic part during injection molding.

[0055] like Figure 11 and Figure 12 As shown, an oil return rib 20 is provided on the oil baffle 6. The oil return rib 20 matches the outer helical raceway, and a certain gap is left between the oil return rib 20 and the outer helical raceway. This effectively ensures that the lubricating grease is always within the raceway. During high-speed operation, this prevents the grease in the ball screw assembly from being thrown out. Otherwise, insufficient grease will cause dry friction of the steel balls, reducing their service life.

[0056] A suitable matching gap is set between the oil return rib 20 and the outer spiral raceway. The spiral line is consistent with the starting point of the spiral line of the rack screw 1. Otherwise, assembly will be difficult, and the oil return rib 20 will interfere with the screw raceway or even fail.

[0057] Therefore, a positioning protrusion 23 is provided on the circumference of the oil baffle 6. The positioning protrusion 23 is fixedly set on the outer circumference of the oil baffle 6, protruding outward from the oil baffle 6. The positioning protrusion 23 can be engaged in the positioning hole provided in the ball nut 2, accurately locating the position of the oil baffle 6. Through the cooperation between the positioning protrusion 23 and the positioning hole, the oil baffle 6 is prevented from rotating circumferentially within the ball nut 2. The positioning hole and the positioning surface are adjacent. Without the positioning protrusion 23, the oil baffle 6 can rotate within the hole of the ball nut 2, causing the position of the oil baffle 6 to shift. This can easily lead to a misalignment between the lead screw raceway and the oil baffle 6, resulting in jamming.

[0058] A mark point 22 is set on the oil baffle plate 6. The mark point 22 serves as the positioning point of the elastic washer during assembly. During the assembly process, the assembler can assemble the elastic retaining ring 7 according to the position of the mark point 22, ensuring that the opening direction of the elastic retaining ring 7 faces the mark point 22. In this way, the elastic retaining ring 7 can better press the return device 4, thereby ensuring that the return device 4 will not loosen.

[0059] like Figure 1As shown, a bearing is mounted on the ball nut 2. The bearing is a four-point contact ball bearing with an increased ball diameter and a denser arrangement of steel balls, resulting in high impact resistance and a load capacity of 60 kN. A four-point contact ball bearing is an angular contact ball bearing capable of withstanding bidirectional axial loads. It features guaranteed transmission accuracy and increased transmission torque. This type of bearing has a high limiting speed, making it suitable for high-speed, precision applications. Four-point contact ball bearings can provide a large load capacity and axial and radial support within a compact space. Its rated load is almost identical to that of two paired single-row angular contact ball bearings, but it saves 50% of axial space. These characteristics make four-point contact ball bearings an ideal choice for ball screw assemblies.

[0060] The ball screw mechanism with the above structure has the following advantages:

[0061] 1. High transmission precision, smooth movement, and no crawling phenomenon. Low frictional resistance and long service life; the transmission efficiency of commercial ball screw pairs in new energy is very high, typically reaching over 95%. This is because sliding friction is converted into rolling friction, eliminating transmission backlash and thus improving efficiency and precision;

[0062] 2. The ball screw pairs for new energy commercial applications have a long service life and minimal wear on parts, which greatly reduces system downtime for maintenance and thus effectively reduces maintenance costs.

[0063] 3. The ball screw assembly is particularly outstanding for its low frictional resistance and low noise characteristics. Through advanced design and manufacturing processes, frictional resistance has been successfully reduced, noise generation has been minimized, and operational comfort has been improved. Steering wheel shifts are smooth and without any impact noise, resulting in a good driving experience and high comfort. Steering noise is also low. In new energy commercial vehicles without engines, where vehicle noise is already low, low-noise steering systems are even more suitable.

[0064] 4. New energy commercial ball screw assemblies can effectively reduce energy consumption, lower system operating costs, and provide strong support for the sustainable development of intelligent systems. With no hydraulic oil circuits, there are no oil leakage problems, and no environmental pollution is caused.

[0065] 5. The nut, using a four-point contact ball bearing, can withstand a large axial reciprocating load;

[0066] 6. High Strength: The rack screw 1 is made of SCM440 chromium-molybdenum alloy steel. After high-frequency quenching, the surface hardness of the rack screw 1 can reach 60-65 HRC, making it suitable for applications requiring high hardness and wear resistance. The ball nut 2 is made of 20CrMnTi, and after heat treatment, its surface hardness can reach 58-64 HRC. It exhibits minimal machining deformation and excellent fatigue resistance. During production, the rack screw 1 is manufactured using advanced processes such as double-head turning and cyclone milling. These processes effectively improve the machining accuracy and surface finish of the rack screw 1, thereby increasing its load-bearing capacity and service life.

[0067] 7. High Sensitivity: The ball recirculation curve is designed so that the ball movement direction is tangential to the raceway rather than intersecting it. This reduces impact loss and noise, improving the smoothness and sensitivity of the ball screw pair's movement. The raceway tooth profile is designed with two semi-circular arcs and a contact angle of 45°. Through precision grinding of the screw helical raceway, tooth profile deviation can be well controlled. While ensuring the contact angle deviation on both sides of the raceway is within 2°, the contact angle is maintained close to 45°, achieving high sensitivity. Furthermore, a specific proportion of the raceway radius is designed to reduce Hertzian elastic stress and elastic deformation, thereby reducing wear.

[0068] 8. High Precision: The precision grades of this type of rack and pinion screw are divided into 1, 2, 3, 4, 5, 7, and 10, with grade 1 being the highest. Precision is mainly reflected by the average stroke error / e within the effective stroke, the variation within the effective stroke / Vu, the stroke variation within any 300mm stroke / V300, and the stroke variation within any 2π stroke / V2π. Currently, the industry standard is generally around grade 5, while the ball screw mechanism of this invention achieves a manufacturing precision of grade 2. Furthermore, the axial clearance of the rack and pinion screw pair is controlled within 0.02mm, resulting in a small transmission clearance and faster, more precise dynamic response of the system.

[0069] The present invention also provides a vehicle power steering system, including a steering mechanism and a power steering mechanism. The steering mechanism mainly includes a steering torsion bar mechanism connected to the steering wheel and a steering gear connected to the steering torsion bar mechanism. The power steering mechanism includes a power steering motor, a power steering pinion, a power steering gear, and a ball screw mechanism with the above-mentioned structure. The steering gear meshes with a rack segment.

[0070] In the vehicle power steering system of the present invention, a two-stage transmission mechanism of gear mechanism + ball screw is adopted. The output speed and torque of the power steering motor are applied to the ball nut 2 after being reduced and increased in torque by the power steering pinion and the power steering gear. Then, through the ball screw, the rotational motion of the ball nut 2 is converted into the linear motion of the rack screw 1, and at the same time, the applied power steering torque is converted into the linear moving force of the rack screw 1.

[0071] The vehicle power steering system provided by this invention is for commercial vehicles and belongs to the category of R-EPS.

[0072] The present invention has been described above by way of example with reference to the accompanying drawings. Obviously, the specific implementation of the present 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 protection scope of the present invention.

Claims

1. Ball screw mechanism, characterized by: The rack screw includes a screw segment, an outer spiral raceway for accommodating balls is arranged on the screw segment, the lead of the outer spiral raceway is at least 20, the outer spiral raceway includes two semicircular arc raceways and a circular arc groove, and the circular arc groove is located between the two semicircular arc raceways.

2. The ball screw mechanism according to claim 1, characterized by: The reverser is provided with an insert which is integrally injection molded with the reverser, and the insert is provided with a clamping groove for embedding the reverser.

3. The ball screw mechanism according to claim 1, characterized by: The radius of the semicircular arc raceway is greater than the radius of the circular arc groove, and the radian of the semicircular arc raceway is greater than the radian of the circular arc groove.

4. The ball screw mechanism according to any one of claims 1 to 3, characterized by: The axis of the two semicircular arc raceways is a certain distance from the center of the pitch circle, and the center of the pitch circle is located between the axes of the two semicircular arc raceways.

5. The ball screw mechanism according to any one of claims 1 to 4, characterized by: The ball nut is internally provided with an inner spiral raceway for accommodating balls and a ball returning long hole forming a circulation loop with the reverser, and the diameter of the ball returning long hole is set to be 1.06-1.08 times the diameter of the ball.

6. The ball screw mechanism according to claim 5, characterized by: The ball nut is provided at both ends with a first mounting groove for mounting the reverser, the first mounting groove is internally provided with an eccentric positioning hole, the reverser is provided with a boss for cooperating with the eccentric positioning hole for positioning.

7. The ball screw mechanism according to claim 5, characterized by: The ball nut is internally provided with a retainer groove for accommodating an elastic retainer, the retainer groove is internally provided with a first contact surface and a second contact surface which are in contact with the outer cylindrical surface of the elastic retainer, and the first contact surface is a conical surface.

8. The ball screw mechanism according to claim 7, characterized by: The ball nut is internally provided with a second mounting groove for accommodating an oil baffle, the second mounting groove is adjacently arranged with the retainer groove, and the oil baffle is located between the reverser and the elastic retainer.

9. The ball screw mechanism according to claim 8, characterized by: The oil baffle is provided with a protrusion in contact with the ball nut and an oil return rib matched with the outer spiral raceway, the protrusion is provided with multiple protrusions, and the inner side of the protrusion is provided with an annular groove.

10. A vehicle power assisted steering system characterised in that: The ball screw mechanism includes any one of claims 1-9.

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