Circulating ball steering gear and structure for improving strength of steering nut

Abstract

The utility model discloses a recirculating ball steering gear and a structure for improving the strength of a steering nut, the recirculating ball steering gear comprises the steering nut and a sector on a rocker arm shaft, the steering nut is provided with a straight tooth rack meshed with the sector, the sector is a thickened sector of which the displacement coefficient is increased along the axial direction, and the overlap ratio of all sections of the sector is reduced along with the increase of the displacement coefficient. The overlap ratio of the small end of the gear sector is large, the overlap ratio of the large end of the gear sector is small, the tooth total height of the rack is gradually reduced from the end meshed with the large end of the gear sector to the end meshed with the small end of the gear sector, the tooth crest thickness is gradually increased from the end meshed with the large end of the gear sector to the end meshed with the small end of the gear sector, and therefore the strength of the steering nut can be effectively improved, and the service life of the steering nut can be effectively prolonged. The reliability of the steering gear can be effectively improved.

Description

TECHNICAL FIELD

[0001] The utility model belongs to the technical field of automobile parts, and particularly relates to a recirculating ball steering gear. BACKGROUND

[0002] The working principle of the recirculating ball steering gear (taking a hydraulic power-assisted recirculating ball steering gear as an example) is as follows: the steering angle and torque of a driver acting on a steering wheel are transmitted to an input shaft, a rotary valve controls the pressure difference on both sides of a steering nut according to the size and direction of the input steering angle and torque, the steering nut moves linearly, the toothed sector on a rocker shaft meshes with the rack on the steering nut, the axial movement of the steering nut causes the rocker shaft to rotate, and the rotation of the rocker shaft drives the steering arm to swing and is transmitted to the steering knuckle arm through a steering drag link, so that the steering wheel rotates.

[0003] The steering nut is an important transmission part in the recirculating ball steering gear, and its structure is shown in Figure 2 The rack on the steering nut meshes with the toothed sector on the rocker shaft. Since the toothed sector and the rack will be worn during operation, a meshing gap is generated. Therefore, in the constant-ratio steering gear, the toothed sector is a variable-thickness involute toothed sector with a variable coefficient along the axial direction, and the rack is a straight-toothed rack. After the tooth surfaces of the rack and the toothed sector are worn, the meshing gap is adjusted by adjusting the axial position of the rocker shaft. The installation of the steering nut and the rocker shaft is shown in Figure 3 Since the variable coefficient of the toothed sector increases along the axial direction, the coincidence degree of each section decreases with the increase of the variable coefficient. Therefore, the load on the teeth is unevenly distributed when the rack meshes with the toothed sector. The coincidence degree of the small end of the toothed sector is large, and the coincidence degree of the large end is small. Therefore, the load on one end of the rack meshing with the small end of the toothed sector is larger, the tooth root stress is larger, and the risk of fatigue fracture at the tooth root is larger.

[0004] During the wear test of a certain hydraulic recirculating ball steering gear, the steering was heavy. At this time, the test was performed 18000 times, the test steering gear was disassembled, and it was found that the tooth root of the steering nut was fractured. The fractured steering nut was cut along the crack, and obvious tear ridges could be seen, indicating that the failure mode was low-cycle fatigue fracture. The metallographic analysis result shows that the crack source is at the tooth root where the rack meshes with the small end of the rocker shaft, and then continuously extends to cause the tooth to fracture. This result also shows that the tooth root position where the rack meshes with the small end of the toothed sector is a dangerous position. In order to improve the strength and life of the rack, the stress at this position needs to be reduced.

[0005] The test method of the wear test is as follows: the steering gear assembly is installed on a test bench, the test oil pressure is the rated pressure of the steering gear, and the steering arm reaches the maximum input torque during the test; the input end rotates at a speed of 30 r / min, the input end angle is not less than 90% of the total angle, and 50000 cycles are completed. UTILITY MODEL CONTENTS

[0006] The utility model provides to solve the technical problem that the rack on the current structure's steering nut breaks due to insufficient strength, and provides a recirculating ball steering gear and improve the steering nut strength structure of steering gear.

[0007] To solve the above technical problems, the utility model adopts the following technical scheme:

[0008] First, a kind of improve the steering nut strength structure of recirculating ball steering gear is provided, including steering nut and the tooth fan on rocker shaft, the straight-toothed rack that the steering nut is equipped with is engaged with tooth fan, the tooth fan is thickening tooth fan that the coefficient of axial displacement increases, the coincidence of each section of tooth fan decreases with the increase of coefficient of axial displacement, the coincidence of small end of tooth fan is big, and the coincidence of big end is small, the full height of the tooth of rack gradually reduces from the one end engaged with the big end of tooth fan to the one end engaged with the small end of tooth fan, and the addendum thickness gradually increases from the one end engaged with the big end of tooth fan to the one end engaged with the small end of tooth fan.

[0009] Preferably, the full height of the tooth of rack gradually reduces from the one end engaged with the big end of tooth fan to the one end engaged with the small end of tooth fan by cutting the addendum of rack, and the addendum thickness gradually increases from the one end engaged with the big end of tooth fan to the one end engaged with the small end of tooth fan.

[0010] Preferably, the steering nut includes a column body having a hollow inner hole, and a first protruding ring and a second protruding ring respectively arranged at a first end and a second end of the column body, and the rack is arranged on an outer circle of the column body and connected with the first protruding ring.

[0011] Preferably, the outer circle of the first protruding ring is provided with an equal-height surface with the same height as the addendum.

[0012] Preferably, the outer circle of the column body is provided with a reinforcing rib.

[0013] Preferably, the reinforcing rib includes a first reinforcing rib extending in the axial direction and connected with the second protruding ring at one end and connected with the rack at the other end.

[0014] Preferably, the reinforcing rib further includes a second reinforcing rib extending in the axial direction and connected with the first protruding ring at one end, and the second reinforcing rib is staggered with the rack in the circumferential direction.

[0015] Preferably, the first end of the hollow inner hole of the column body is open, and the second end is closed.

[0016] Preferably, the rocker shaft and the tooth fan are in an integrated structure.

[0017] In addition, a recirculating ball steering gear is also provided, which includes a screw rod and the above-mentioned steering nut strength structure of recirculating ball steering gear, and the screw rod is threadedly connected with the steering nut.

[0018] The utility model discloses the above-mentioned technical scheme has the following beneficial effects:

[0019] By cutting the addendum of the rack, the whole height of the rack teeth gradually decreases from the end engaging with the big end of the tooth fan to the end engaging with the small end of the tooth fan, and the addendum thickness gradually increases from the end engaging with the big end of the tooth fan to the end engaging with the small end of the tooth fan, which can effectively improve the strength and service life of the steering nut and the reliability of the steering gear.

[0020] The features and advantages of the utility model will be disclosed in detail in the following specific embodiments and drawings. BRIEF DESCRIPTION OF DRAWINGS

[0021] The utility model will be further explained in connection with the drawings as follows:

[0022] Figure 1 It is hydraulic pressure booster circulating ball steering gear structure schematic diagram;

[0023] Figure 2 It is steering nut structure schematic diagram;

[0024] Figure 3 It is Figure 2 It is E-E section view;

[0025] Figure 4 It is steering nut and rocker arm shaft installation schematic diagram;

[0026] Figure 5 It is rack tooth force schematic diagram;

[0027] Figure 6 It is the steering nut structure schematic diagram of the utility model after improvement;

[0028] Figure 7 It is the comparative structure schematic diagram of the steering nut before and after improvement;

[0029] Figure 8 It is the three-dimensional model schematic diagram of the steering nut after improvement of the utility model. DETAILED DESCRIPTION

[0030] The technical scheme of the utility model embodiment will be explained and described in connection with the drawings of the utility model embodiment as follows, but the following embodiment is only the preferred embodiment of the utility model, and not all.Based on the embodiment in the embodiment, other embodiments obtained by the person skilled in the art without making creative labor all belong to the protection scope of the utility model.

[0031] The person skilled in the art can understand that the features in the following embodiment and embodiment can be combined mutually without conflict.

[0032] In the utility model, unless another definite provision and limitation, first feature is in second feature "on" or "under" can include first and second feature direct contact, also can include first and second feature is not direct contact but is through additional feature between them contact.Also, first feature is in second feature "on", "above" and "on" include first feature is in second feature directly above and oblique above, or only indicate first feature horizontal height higher than second feature.First feature is in second feature "under", "below" and "under" include first feature is in second feature directly below and oblique below, or only indicate first feature horizontal height less than second feature.

[0033] Furthermore, the terms "first", "second", etc. are used only for descriptive purposes and should not be construed as indicating or implying relative importance or an indicated number of technical features. Thus, features defined with "first", "second" can explicitly or implicitly include at least one of the features.

[0034] Referring to Figure 1 As shown in the figure, the hydraulic power circulating ball steering gear in the prior art comprises an input shaft 1, an input shaft dust-proof oil seal 2, an input shaft oil seal 3, an upper cover nut 4, an upper cover O-shaped ring 5, an upper seat circle four-point contact ball bearing 6, a steel ball four-point contact ball bearing 7, a lower seat circle four-point contact ball bearing 8, an outer oil channel O-shaped ring 9, an upper stroke valve bolt assembly 10, a steering nut 11, a shell 12, a stroke unloading valve assembly 13, a steering nut sealing ring 14, a steering nut O-shaped ring 15, a lower stroke valve bolt assembly 16, a screw rod pin 17, a torsion bar O-shaped ring 18, a rocker shaft 19, a first steel ball 20, a torsion bar 21, a screw rod 22, a valve body O-shaped ring 23, a valve body 24, a valve body O-shaped ring 25, a valve body sealing ring 26, an input shaft pin 27, a damping ring 28, an input shaft O-shaped ring 29, a second steel ball 30.

[0035] As shown in Figures 1 to 8 The steering nut 11 is provided with a straight-toothed rack 112, which is engaged with the tooth fan 191 on the rocker shaft 19. The tooth fan 119 is a variable-thickness tooth fan with an axial displacement coefficient increasing. The coincidence degree of each section of the tooth fan decreases with the increase of the displacement coefficient. The coincidence degree of the small end of the tooth fan is large, and the coincidence degree of the large end is small. Therefore, when the rack is engaged with the tooth fan, the load distribution on the teeth is uneven. The end of the rack engaged with the small end of the tooth fan bears a larger load, and the corresponding tooth root stress is larger.

[0036] The teeth on the rack can be regarded as cantilever beams. The force condition when engaged is shown in Figure 5 According to engineering experience, the maximum tooth root stress of the rack can be calculated according to the following formula:

[0037]

[0038] In the formula, F t— Tangential force, N;

[0039] h—Total height of rack teeth, mm;

[0040] B – Rack tooth width, mm;

[0041] S – Thickness of the rack tooth root, mm.

[0042] When the meshing point is at the tooth tip of the rack, the root stress of the rack is at its maximum. The maximum tangential force is the force transmitted by the steering nut when the steering gear output torque reaches its maximum value. The rack on the steering nut is a spur rack with a constant tooth height and root thickness, therefore the tooth thickness at the tooth tip is uniform. Generally, the uneven load distribution on the rack teeth is not considered in the design. Since the actual load distribution on the gear teeth is larger at the end meshing with the small end and smaller at the end meshing with the large end, the maximum root stress on the rack occurs at the end where the rack meshes with the small end of the gear sector, and fracture is prone to occur at this location.

[0043] According to formula (1), under the condition that other factors remain unchanged, reducing the total height of the teeth at the end meshing with the small end of the rocker arm shaft can reduce the root stress at that end. Figures 6 to 8 As shown, the end of the rack that meshes with the large end of the sector is designated as the first end A1, and the end that meshes with the small end of the sector is designated as the second end A2. The total height of the rack teeth gradually decreases from the end that meshes with the large end of the sector (i.e., the total height of the first end H1) to the end that meshes with the small end of the sector (i.e., the total height of the second end H2), and the tooth tip thickness gradually increases from the end that meshes with the large end of the sector (i.e., the tooth tip thickness L1) to the end that meshes with the small end of the sector (i.e., the tooth tip thickness L2). Figure 7 A comparison was made between the steering nuts before and after the improvement. The rack tooth tip C1 before the improvement and the rack tooth tip C2 after the improvement showed significant changes, namely, the corresponding change in the total tooth height.

[0044] To make the total height of the rack teeth gradually decrease from the end that meshes with the large end of the rocker arm shaft to the end that meshes with the small end of the rocker arm shaft, the rack tooth tips are cut along a straight line based on a general steering nut. This reduces the total height of the rack teeth at the end that meshes with the small end of the rocker arm shaft, thereby reducing the root stress at that point and improving the rack strength.

[0045] Based on a standard steering nut, the rack tooth tip can be cut along a straight line or curve, so that the total tooth height gradually decreases from the end that meshes with the large end of the rocker arm shaft to the end that meshes with the small end of the rocker arm shaft, while the tooth tip thickness gradually increases from the end that meshes with the large end of the rocker arm shaft to the end that meshes with the small end of the rocker arm shaft. This can improve the strength and lifespan of the steering nut rack.

[0046] Specifically, the steering nut comprises a column body 111 with a hollow inner hole, and a first convex ring 113 and a second convex ring 114 respectively arranged at the first end and the second end of the column body, and the rack 112 is arranged on the outer circle of the column body and connected with the first convex ring. The outer circle of the first convex ring is provided with an equal-height surface 117 which is equal in height to the tooth top. The outer circle of the column body is provided with a rib. The rib comprises a first rib 115 extending in the axial direction and connected with the second convex ring at one end and with the rack at the other end; and the rib further comprises a second rib 116 extending in the axial direction and connected with the first convex ring at one end, and the second rib is staggered with the rack in the circumferential direction. The rib enhances the overall structural strength of the steering nut. The first end of the hollow inner hole of the column body is open, and the second end is closed. The rocker shaft and the tooth fan are in an integrated structure.

[0047] According to the above technical solution, on the basis of the original steering nut, the tooth top of the rack is cut along a straight line, so that the full height of the teeth of the rack gradually decreases from one end engaged with the large end of the rocker shaft to one end engaged with the small end of the rocker shaft, and the tooth top thickness gradually increases from one end engaged with the large end of the rocker shaft to one end engaged with the small end of the rocker shaft. The steering gear equipped with the improved steering nut is subjected to wear test, and the test equipment and test conditions remain unchanged. It can meet the requirement of 50000 cycles. After the test is completed, the steering gear is disassembled, and the steering nut does not show failure phenomena such as cracking and breaking. Therefore, it can be concluded that the steering nut designed according to the above technical solution has higher strength and longer service life compared with the steering nut introduced in the technical background, and can effectively improve the reliability of the steering gear.

[0048] The above is only a specific embodiment of the utility model, but the protection scope of the utility model is not limited to this. Those skilled in the art should understand that the utility model includes but is not limited to the content described in the above specific embodiments and the drawings. Any modification which does not deviate from the function and structural principle of the utility model shall be included in the scope of the claims.

Claims

1. A structure for improving the strength of the steering nut of a recirculating ball steering gear, comprising a steering nut and a toothed sector on a rocker shaft, the steering nut being provided with a straight-toothed rack which engages with the toothed sector, the toothed sector being a variable-thickness toothed sector with an axial coefficient of displacement which increases, the degree of coincidence of each section of the toothed sector decreasing as the coefficient of displacement increases, the degree of coincidence being greater at the small end of the toothed sector and smaller at the large end, characterized in that, The tooth full height of the rack is gradually reduced from the end engaging with the large end of the tooth sector to the end engaging with the small end of the tooth sector, and the tooth crest thickness is gradually increased from the end engaging with the large end of the tooth sector to the end engaging with the small end of the tooth sector. ​ 2. The structure for increasing the strength of the rotation nut of the circulating ball steering gear according to claim 1, wherein The tooth full height of the rack is gradually reduced from the end engaging with the large end of the tooth sector to the end engaging with the small end of the tooth sector, and the tooth crest thickness is gradually increased from the end engaging with the large end of the tooth sector to the end engaging with the small end of the tooth sector by cutting the tooth crest of the rack.

3. The structure for increasing the strength of the rotation nut of the circulating ball steering gear according to claim 1, wherein The steering nut comprises a column body with a hollow inner hole and first and second convex rings respectively arranged at the first and second ends of the column body, and the rack is arranged on the outer circle of the column body and connected with the first convex ring.

4. The structure for increasing the strength of the rotation nut of the circulating ball steering gear according to claim 3, wherein The outer circle of the first convex ring is provided with an equal-height surface with the same height as the tooth crest.

5. The structure for increasing the strength of the rotation nut of the circulating ball steering gear according to claim 3, wherein The outer circle of the column body is provided with a stiffening rib.

6. The structure for increasing the strength of the rotation nut of the circulating ball steering gear according to claim 5, wherein The stiffening rib comprises a first stiffening rib extending in the axial direction and connected with the second convex ring at one end and with the rack at the other end.

7. The structure for increasing the strength of the rotation nut of the circulating ball steering gear according to claim 6, wherein The stiffening rib further comprises a second stiffening rib extending in the axial direction and connected with the first convex ring at one end, and the second stiffening rib is staggered with the rack in the circumferential direction.

8. The structure for increasing the strength of the rotation nut of the circulating ball steering gear according to claim 3, wherein The first end of the hollow inner hole of the column body is open, and the second end is closed.

9. The structure for increasing the strength of the rotation nut of the circulating ball steering gear according to claim 1, wherein The rocker arm shaft and the tooth sector are in an integrated structure.

10. A recirculating ball steering gear characterized by, The structure for improving the strength of the steering nut of the circulating ball steering gear comprises a screw rod and the structure for improving the strength of the steering nut of the circulating ball steering gear according to any one of claims 1 to 9, and the screw rod is threadedly connected with the steering nut.

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