Medium truck differential reducer low resistance bearing

Abstract

This invention discloses a low-resistance bearing for a medium-sized truck differential reducer, relating to the field of vehicle transmission system bearing technology. It includes a housing, an inner bearing ring, a cage, and rollers. By creating a reverse pre-offset angle difference between the trapezoidal bearing ramp of the inner bearing ring, the inclined fitting hole of the cage, and the axis of the rollers, and by creating a radial clearance difference between the cage and the rollers where the driving force side is greater than the reverse drag force side, the rollers, under the driving load of the differential reducer, shift from an edge offset tendency to a load-bearing return state. Under the reverse drag load, they are pre-limited to avoid reverse wedging. This solves the problems of existing differential reducer bearings where the rolling elements are prone to skewing and tightening, end slippage, and increased local temperature rise under alternating driving and reverse drag loads.

Description

Technical Field

[0001] This invention relates to the field of bearing technology for vehicle transmission systems, and in particular to a low-resistance bearing for a differential reducer in a medium-sized truck. Background Technology

[0002] In medium-duty truck differential reducers, under conditions such as starting, full-load climbing, rapid acceleration, and downhill reverse dragging, the bearings not only bear radial loads but also simultaneously experience axial forces generated by gear meshing and alternating impact loads. Existing differential reducer bearings typically reduce friction by increasing raceway hardness, optimizing surface roughness, increasing lubrication, or adjusting assembly clearance. However, their structural design is mostly based on contact stability under static assembly conditions, with little constraint and compensation for the attitude changes of the rolling elements under alternating driving and reverse drag loads.

[0003] In actual operation, when the gear meshing load is transmitted to the bearing position, the rolling elements tend to deflect along the inner bearing ramp, causing the contact area to move towards the edge of the ramp. Under driving conditions, this deflection will cause end slippage and edge clamping. Under reverse drag conditions, it may form reverse wedging due to the reverse load direction. The above phenomena will lead to an increase in local frictional resistance of the bearing, an increase in operating temperature, and aggravated wear on the ends of the rolling elements and the edges of the bearing ramp.

[0004] The urgent problem to be solved is how to enable the rolling elements in the differential reducer bearing to shift from a skewed tendency to a stable bearing state under driving load without adding an extra complex adjustment mechanism, and to prevent them from continuing to shift towards the wedge tightening direction under reverse drag load, thereby reducing the end slippage, frictional resistance and operating temperature rise of the bearing. Summary of the Invention

[0005] The present invention provides a low-resistance bearing for a medium-duty truck differential reducer, comprising a housing, an inner bearing ring, a cage, and rollers. The inner bearing ring is fitted inside the housing, the cage is disposed between the housing and the inner bearing ring, and the rollers are fitted into the cage and overlap with corresponding surfaces of the housing and the inner bearing ring, respectively. The inner ring of the bearing has a trapezoidal cross-section, which forms a bearing ramp for overlapping with the roller; the cage has a fitting hole that is inclined relative to the bearing ramp, and the roller is fitted into the fitting hole in an oblique posture; The inclination angle of the bearing slope, the inclination angle of the fitting hole, and the axial inclination angle of the roller form a reverse pre-clinch angle difference. The direction of the reverse pre-clinch angle difference is opposite to the deflection direction of the roller under the differential reducer drive load. The deflection direction is the direction in which the roller deflects toward the edge of the bearing slope when it is subjected to the combined action of radial and axial forces. The side on which the roller generates a posture return displacement under the forward driving condition of the vehicle is designated as the drive return side, and the side on which the roller generates a wedging offset tendency under the reverse drag condition is designated as the reverse drag limiting side. The fitting hole forms a first limiting sidewall on the drive return side and a second limiting sidewall on the reverse drag limiting side. A first radial gap is formed between the first limiting sidewall and the outer peripheral surface of the roller, and a second radial gap is formed between the second limiting sidewall and the outer peripheral surface of the roller. The first radial clearance is used to allow the roller to return to its correct orientation along the mating hole under the driving load; the second radial clearance is used to limit the roller from continuing to wedge and deflect towards the edge of the bearing ramp under the reverse drag load; the first radial clearance is greater than the second radial clearance.

[0006] Furthermore, the inclination angle of the bearing inclined surface is denoted as α, the inclination angle of the inclined guide reference line used to define the assembly posture of the roller is denoted as β, and the inclination angle of the roller axis is denoted as γ. α, β and γ are all based on the central axis of the housing as the angular reference. A first angular difference is formed between β and α, and a second angular difference is formed between γ and α. The bias direction of at least one of the first angular difference and the second angular difference is opposite to the bias direction of the roller under the differential reducer drive load. The absolute value of the first angle difference is 0.3° to 2.5°, and the absolute value of the second angle difference is 0.2° to 1.8°.

[0007] Furthermore, a radial clearance difference is formed between the first radial clearance and the second radial clearance, the radial clearance difference being 0.01 mm to 0.08 mm.

[0008] Furthermore, the width ratio of the first radial gap to the second radial gap is 1.2 to 3.0; An angular offset is formed between β and γ, the angular offset being 0.2° to 1.5°, causing the roller to transition from a pre-offset overlapping state to a loaded return overlapping state within the range defined by the radial clearance difference.

[0009] Furthermore, a first axial end gap and a second axial end gap are respectively formed between the two ends of the cage and the roller, the first axial end gap being located on the large end side of the inner ring of the bearing, and the second axial end gap being located on the small end side of the inner ring of the bearing. The first axial end clearance is greater than the second axial end clearance, and is used to provide axial clearance space when the roller generates end displacement toward the large end side of the inner ring of the bearing after being subjected to a driving load, and to limit the axial movement of the roller toward the small end side of the inner ring of the bearing by the second axial end clearance.

[0010] Furthermore, the roller has a central bearing surface and end unloading surfaces located on both sides of the central bearing surface; The central bearing surface is used to form the main contact area with the bearing ramp when the roller is in the loaded and lapped state. The end unloading surface recedes away from the bearing ramp relative to the central bearing surface, so that the end of the roller avoids wedge contact with the edge of the bearing ramp after being loaded.

[0011] Furthermore, the yielding amount of the end unloading surface relative to the middle bearing surface is 0.005mm to 0.05mm; The central bearing surface and the end unloading surface are connected by a continuous transition surface, so that the main contact area migrates from the end region to the central region during the roller's return to center under load.

[0012] Furthermore, the bearing ramp includes an inlet ramp, a main bearing ramp, and a release ramp arranged sequentially along the contact migration direction of the roller relative to the bearing ramp. The inlet ramp is located on the side where the roller enters the main contact area, the release ramp is located on the side where the roller leaves the main contact area, and the main bearing ramp is located between the inlet ramp and the release ramp. The guide ramp is used to guide the roller into the pre-offset overlap state; the main bearing ramp is used to form a load-bearing return overlap with the central bearing surface; the release ramp is used to reduce the end drag generated when the roller leaves the main contact area after the roller has an end displacement towards the large end side of the inner ring of the bearing.

[0013] Furthermore, a micro-oil wedge gap is formed between the bearing inclined surface and the roller in the pre-offset overlapping state; The micro-oil wedge gaps converge along the inner ring of the bearing from the small end to the large end. The end of the micro-oil wedge gap closer to the small end of the inner ring of the bearing is the inlet side, and the end closer to the large end of the inner ring of the bearing is the outlet side. The width of the inlet side is greater than the width of the outlet side. When the roller changes from the pre-offset overlap state to the load-aligned overlap state, the inlet side is still located near the small end of the inner ring of the bearing, and the outlet side is still located near the large end of the inner ring of the bearing, so that the lubricating oil enters the micro-oil wedge gap from the inlet side and enters the main contact area as the roller returns to its original position under load.

[0014] Furthermore, at least one of the end unloading surface and the bearing inclined surface in the edge bearing region opposite to the end unloading surface is provided with a shear friction reducing layer; The central bearing surface and the area corresponding to the main contact area in the bearing slope retain the hardened bearing matrix, so that the roller maintains the bearing strength in the main contact area, and the shear friction reduction layer reduces the sliding friction between the roller end and the edge of the bearing slope.

[0015] The beneficial effects of this invention are as follows: by making the trapezoidal bearing slope of the inner ring of the bearing, the inclined fitting hole of the cage, and the axis of the roller form a reverse pre-offset angle difference, and by making the radial clearance difference between the cage and the roller greater on the driving force side than on the reverse drag force side, the roller is transformed from the edge offset tendency to the load return state under the driving load of the differential reducer, and is pre-limited under the reverse drag load to avoid reverse wedging. This solves the problems of the existing differential reducer bearings being prone to skew and clamping of the rolling elements, end slippage, and increased local temperature rise under the alternating driving and reverse drag loads. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a bottom view of the bearing body structure of the present invention; Figure 2 This is a top view schematic diagram of the bearing body structure of the present invention; Figure 3 This is a partial cross-sectional view of the bearing body of the present invention; Figure 4 This is a schematic diagram of the longitudinal section structure of the bearing body of the present invention; Figure 5 This is a schematic diagram of the bearing body of the present invention after the housing is removed.

[0018] In the diagram: 1. Housing; 2. Inner ring of the bearing; 3. Cage; 4. Roller. Detailed Implementation

[0019] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0020] Example 1 Reference Figures 1-5This is the first embodiment of the present invention. This embodiment provides a low-resistance bearing for a medium-duty truck differential reducer, including a housing 1, an inner bearing ring 2, a cage 3, and rollers 4. The inner bearing ring 2 is sleeved inside the housing 1, the cage 3 is disposed between the housing 1 and the inner bearing ring 2, and the rollers 4 are fitted into the cage 3 and overlap with the corresponding surfaces of the housing 1 and the inner bearing ring 2 respectively. The inner ring 2 of the bearing has a trapezoidal section, which forms a bearing ramp for overlapping with the roller 4; the cage 3 has a fitting hole that is inclined relative to the bearing ramp, and the roller 4 is fitted into the fitting hole in an inclined position. The inclination angle of the bearing slope, the inclination angle of the fitting hole and the axial inclination angle of the roller 4 form a reverse pre-clinch angle difference. The direction of the reverse pre-clinch angle difference is opposite to the deflection direction of the roller 4 under the driving load of the differential reducer. The deflection direction is the direction in which the roller 4 deflects toward the edge of the bearing slope when it is subjected to the combined action of radial and axial forces. The side of the roller 4 that generates a posture return displacement under the forward driving condition of the vehicle is called the drive return side, and the side of the roller 4 that generates a wedging offset tendency under the reverse drag condition is called the reverse drag limiting side. The fitting hole forms a first limiting sidewall on the drive return side and a second limiting sidewall on the reverse drag limiting side. A first radial gap is formed between the first limiting sidewall and the outer peripheral surface of the roller 4, and a second radial gap is formed between the second limiting sidewall and the outer peripheral surface of the roller 4. The first radial clearance is used to allow the roller 4 to return to its correct position along the mating hole under the driving load; the second radial clearance is used to limit the roller 4 from continuing to wedge and deflect towards the edge of the bearing ramp under the reverse drag load; the first radial clearance is greater than the second radial clearance.

[0021] In this embodiment, the driving force side and the anti-drag force side are both lateral limiting positions set relative to the outer peripheral surface of the roller 4 within the fitting hole of the cage 3, and are not the large or small end positions of the housing 1 or the inner ring 2 of the bearing; wherein, the driving force side is the side on which the roller 4 generates attitude return displacement when the vehicle accelerates, climbs a hill or is fully loaded and towed, and the anti-drag force side is the side on which the roller 4 generates wedging offset toward the edge of the bearing slope when coasting with the throttle released, when braking with the engine or when anti-dragring down a slope.

[0022] In this embodiment, a low-resistance bearing for a differential reducer of a medium-duty truck drive axle is provided, which is suitable for trucks with a total mass of 8t to 18t. The low-resistance bearing is installed between the differential reducer housing and the drive bevel gear shaft to bear the radial load, axial load and alternating load generated during the meshing of the drive bevel gear, as well as the load generated during vehicle acceleration, full-load climbing, coasting with the throttle released and downhill reverse dragging.

[0023] During assembly, housing 1 is pressed into the bearing seat hole of the differential reducer housing, and the inner ring 2 of the bearing is pressed onto the outer circumference of the drive bevel gear shaft, forming an annular bearing space between housing 1 and the inner ring 2. Then, a cage 3 containing multiple rollers 4 is installed into this annular bearing space, allowing the rollers 4 to roll and bear loads between housing 1 and the inner ring 2. After assembly, gear oil is added to the differential reducer housing, with the oil level controlled according to the normal operating oil level of the drive axle, ensuring that the rollers 4 are in a state of combined splash lubrication and localized oil lubrication during operation.

[0024] In this embodiment, the bearing inner ring 2 adopts a trapezoidal cross-sectional structure, with an inclined bearing surface formed on the side near the roller 4, denoted as the bearing inclined surface. This inclined bearing surface is not machined in a normal fully fitted manner, but is pre-biased in conjunction with the axial thrust direction generated by the active bevel gear in the driving state. For a set of samples, using the central axis of the housing 1 as the angle measurement reference, the inclination angle of the inclined bearing surface of the bearing inner ring 2 is machined to 12.0°, the inclined position (fitting hole position) in the cage 3 for accommodating the roller 4 is machined to 11.3°, and the axial inclination angle of the assembled roller 4 is controlled at about 11.6°. Thus, the roller 4 will not be completely pressed against the edge of the inclined bearing surface of the bearing inner ring 2 when unloaded, but will maintain a slightly reverse pre-biased state.

[0025] When a medium-sized truck is starting, accelerating, or climbing a hill under full load, the axial force generated by the meshing of the drive bevel gear will cause the roller 4 to tend to shift towards the edge of the inclined bearing surface of the inner ring 2 of the bearing. If the roller 4 is already arranged in a fully fitted state when unloaded, it is easy to further tighten towards the edge after being loaded, resulting in local slippage, heat generation, and increased wear. In this embodiment, through the above-mentioned angle pre-deflection, the skew tendency caused by the load of the roller 4 when the driving load increases is canceled out by the pre-set reverse pre-deflection amount, so that the roller 4 gradually returns to a more stable bearing position, and the contact mark moves from the edge area to the middle area of ​​the inclined bearing surface.

[0026] To enable roller 4 to perform the aforementioned minute attitude adjustments, a non-uniform clearance fit is used between the cage 3 and roller 4. In the prototype, the radial clearance on the side of roller 4 closest to the drive return side is designated as the first radial clearance and controlled to be approximately 0.06 mm; the radial clearance on the side of roller 4 closest to the anti-drag limit side is designated as the second radial clearance and controlled to be approximately 0.03 mm. The drive return side is the side where roller 4 generates attitude return displacement under forward drive conditions, and the anti-drag limit side is the side where roller 4 exhibits a wedging offset tendency under anti-drag conditions and needs to be restricted in advance. With the large end face of the bearing inner ring 2 facing upwards as a reference, the left side of the mating hole along the radial direction of the roller 4 is the driving force side. When the vehicle is accelerating, climbing, or fully loaded with traction, the roller 4 will produce a slight attitude return displacement towards the large end face of the bearing inner ring 2 under the action of the axial component force of the gear meshing. The right side of the mating hole along the radial direction of the roller 4 is the reverse drag force side. When the vehicle is coasting with the accelerator released, under engine braking, or in a downhill reverse drag state, the roller 4 is subjected to a reverse load and has a tendency to wedge and shift towards the small end face of the bearing inner ring 2. The above radial clearance can be measured between the corresponding side walls of the cage 3 and the roller 4 by feeler gauge, coordinate measuring machine, or partial sectioning inspection after assembly.

[0027] When the vehicle is in driving mode, the larger drive force side clearance provides a small amount of positioning space for roller 4, allowing roller 4 to slightly return to its original position along the inclined position of cage 3 under load, without being rigidly locked by cage 3. When the vehicle is in reverse towing mode, the load direction changes in the opposite direction, and the smaller reverse towing force side clearance limits the reverse offset of roller 4 in advance, preventing roller 4 from continuing to be squeezed towards the inclined bearing surface edge of the inner ring 2 and forming a wedging. Thus, roller 4 can be released and return to its original position in driving mode, and can be restricted and prevented from jamming in reverse towing mode.

[0028] After assembly, a low-speed pre-rotation test is performed on the differential reducer assembly. The differential reducer housing is fixed on the test bench, and a specified amount of gear oil is added to the housing. The drive bevel gear shaft is continuously rotated at 100 r / min to 200 r / min for 5 to 10 minutes. During the pre-rotation, the initial rotational resistance is recorded to ensure it is stable. After stopping the machine, the contact marks between the roller 4 and the bearing inner ring 2 are observed. In qualified samples, the contact marks are mainly distributed in the middle area of ​​the inclined bearing surface of the bearing inner ring 2, and no continuous shiny linear scratches appear at the edge. If obvious linear scratches appear at the edge, it indicates that the roller 4 is edge-tight, and the pressing depth of the housing 1 in the housing bearing seat hole, the pressing position of the bearing inner ring 2 on the drive bevel gear shaft, or the clearance between the cage 3 and the roller 4 needs to be rechecked.

[0029] In bench tests simulating full vehicle operating conditions, the prototype of this embodiment was installed in the differential reducer assembly of a medium-duty truck drive axle. The test oil temperature was controlled at approximately 85°C, the input speed was set to 1200 r / min, and the output torque was set to 600 N·m, 1200 N·m, and 1800 N·m, respectively, to simulate light-load drive, normal-load drive, and full-load drive conditions. A reverse-drag loading condition was also set to simulate coasting with the throttle released and engine braking on a downhill slope. During the test, the additional friction torque of the differential reducer was recorded by an input torque sensor, and the operating temperature rise was recorded by a temperature sensor attached near the bearing housing.

[0030] When using a standard isometric bonding sample as a comparative example, after 2 hours of continuous operation, the contact marks between roller 4 and the inner ring 2 of the bearing were biased towards the edge area of ​​the oblique bearing surface. Some samples showed continuous polished bands at the corresponding positions on the ends of roller 4, and the temperature rise near the bearing housing was 28°C to 32°C. When using the sample of this embodiment, the contact marks were mainly located in the middle area of ​​the oblique bearing surface, the polished bands at the ends were significantly reduced, and the temperature rise near the bearing housing was 21°C to 25°C. Under a loading condition of 1200 N·m, the average additional frictional torque of the comparative example sample was 5.6 N·m, while the average additional frictional torque of the sample of this embodiment was 4.7 N·m.

[0031] As can be seen from the above assembly and testing process, this embodiment does not simply change the tilting placement of roller 4, but rather combines the actual force direction of the medium-duty truck differential reducer, enabling roller 4 to transition from a slightly pre-biased state to a stable load-bearing state under driving load, and preventing further offset towards the wedging direction under reverse drag load. Through the angular fit and unequal radial clearance fit between the bearing inner ring 2, cage 3, and roller 4, the frictional resistance, end slippage, and operating temperature rise of the differential reducer bearing position can be reduced without adding an additional adjustment mechanism.

[0032] Example 2 Please see Figures 1-5 The inclination angle of the bearing inclined surface is denoted as α, the inclination angle of the inclined guide reference line used to limit the assembly posture of the roller 4 in the fitting hole position is denoted as β, and the inclination angle of the axis of the roller 4 is denoted as γ. α, β and γ are all based on the central axis of the housing 1 as the angle reference. A first angular difference is formed between β and α, and a second angular difference is formed between γ and α. The offset direction of at least one of the first and second angular differences is opposite to the skew direction of the roller 4 under the differential reducer drive load. The absolute value of the first angular difference is 0.3° to 2.5°, and the absolute value of the second angular difference is 0.2° to 1.8°.

[0033] A radial clearance difference is formed between the first radial clearance and the second radial clearance, which is 0.01 mm to 0.08 mm; the width ratio of the first radial clearance to the second radial clearance is 1.2 to 3.0; an angular offset is formed between β and γ, which is 0.2° to 1.5°, so that the roller 4 changes from a pre-offset overlapping state to a loaded return overlapping state within the range defined by the radial clearance difference.

[0034] A first axial end gap and a second axial end gap are formed between the two ends of the cage 3 and the roller 4, respectively. The first axial end gap is located on the large end side of the inner ring 2 of the bearing, and the second axial end gap is located on the small end side of the inner ring 2 of the bearing. The first axial end gap is larger than the second axial end gap and is used to provide axial clearance space when the roller 4 produces a small end displacement towards the large end side of the inner ring 2 of the bearing after being subjected to a driving load, and to limit the excessive axial movement of the roller 4 towards the small end side of the inner ring 2 of the bearing by the second axial end gap.

[0035] In this embodiment, based on embodiment 1, the angular fit and clearance fit between the bearing inner ring 2, the cage 3 and the roller 4 are further defined to ensure that the roller 4 has a defined return path under the differential reducer drive load and is subject to advance limit under the reverse drag load, so as to avoid knocking due to excessive clearance or the roller 4 being unable to complete the attitude adjustment due to insufficient clearance.

[0036] Before machining the prototype, the main force direction is determined based on the gear meshing direction of the differential reducer in the drive axle of a medium-duty truck. Taking the support position of the drive bevel gear shaft as an example, when the vehicle is in driving mode, the axial component force generated by the meshing of the drive bevel gear causes the roller 4 to tend to deflect towards the outer edge of the oblique bearing surface of the inner ring 2 of the bearing. Therefore, this tendency is determined as the deflection direction that needs to be counteracted. Subsequently, using the central axis of the housing 1 as the angular reference, the oblique bearing surface of the inner ring 2 of the bearing, the position of the inclined fitting hole of the cage 3, and the assembly angle of the working axis of the roller 4 are machined respectively, so that the three form a slightly non-coincident angular relationship during cold assembly.

[0037] In a set of prototypes suitable for 10t-class medium-duty truck drive axles, the inclined bearing surface (bearing ramp) of the bearing inner ring 2 is machined to an angle of 12.0°, with a machining tolerance controlled within ±0.05°; the inclined fitting hole position (fitting hole position) of the cage 3 is machined to an angle of 11.3°, with a machining tolerance controlled within ±0.06°; and the axis inclination of the assembled roller 4 is controlled at 11.6°, with an assembly tolerance controlled within ±0.08°. At this point, the inclined fitting hole position of the cage 3 forms a 0.7° reverse offset relative to the inclined bearing surface of the bearing inner ring 2, and the axis of the roller 4 forms a 0.4° reverse offset relative to the inclined bearing surface of the bearing inner ring 2. This angular relationship allows the roller 4 to slightly avoid the outer edge area of ​​the inclined bearing surface of the bearing inner ring 2 when unloaded, rather than forming edge clamping in the assembled state.

[0038] After the angle machining is completed, the radial clearance between the cage 3 and the roller 4 is controlled on both sides. Specifically, a radial clearance of 0.06mm to 0.07mm is formed on the side of the roller 4 closest to the driving force side, and a radial clearance of 0.03mm to 0.035mm is formed on the side of the roller 4 closest to the reverse drag force side. In this embodiment, the radial clearance on the driving force side is preferably machined to 0.064mm, and the radial clearance on the reverse drag force side is machined to 0.032mm, forming a radial clearance difference of 0.032mm, with a clearance width ratio of 2.0. This dimensional fit allows the roller 4 sufficient space to complete a slight self-alignment under driving conditions, while preventing excessive reverse movement under reverse drag conditions.

[0039] To ensure that the clearance difference is not simply an assembly error, the same positioning datum is used for control during the machining process. First, the inner positioning surface of the cage 3 is used as the clamping datum to machine the inclined fitting hole position. Then, a special inspection tool is used to measure the clearance difference between the two sides of the fitting hole position and the standard roller bar. After passing the test, the actual roller 4 is installed for retesting. During measurement, the standard roller bar or the actual roller 4 is placed in the inclined fitting hole position of the cage 3, and the minimum clearance on the driving force side and the reverse drag force side is measured radially. The measurement position is selected in the middle area of ​​the axial length of the roller 4 to avoid the end chamfer from affecting the measurement results. For batch samples, the radial clearance on the driving force side is controlled between 0.055mm and 0.075mm, the radial clearance on the reverse drag force side is controlled between 0.025mm and 0.040mm, and the radial clearance difference is controlled between 0.020mm and 0.045mm.

[0040] Regarding the angular fit between the cage 3 and the roller 4, an angular offset of approximately 0.8° is further established between the center line of the inclined fitting hole of the cage 3 and the axis of the roller 4. This angular offset is not intended to cause the roller 4 to operate at an angle for an extended period, but rather to allow the roller 4 to retain a pre-offset amount that can be offset by the driving load during cold assembly and low-load operation. When the vehicle is in normal driving condition, the gear meshing load causes the roller 4 to shift towards the outer edge of the inclined bearing surface of the inner ring 2 of the bearing. This shift trend is opposite to the direction of the pre-set angular offset. As the load increases, the roller 4 undergoes a slight attitude adjustment within the larger radial clearance on the driving force side, causing the actual contact area to gradually return from near the outer edge to the central region of the inclined bearing surface.

[0041] To reduce the tightness of the roller 4 end during the return process, this embodiment also controls the axial end clearance between the cage 3 and the two ends of the roller 4. Specifically, a larger first axial end clearance is provided between the end face of the roller 4 near the large end of the bearing inner ring 2 and the axial limiting surface of the large end corresponding to the fitting hole on the cage 3, and a smaller second axial end clearance is provided between the end face of the roller 4 near the small end of the bearing inner ring 2 and the axial limiting surface of the small end corresponding to the fitting hole on the cage 3. In the sample, the first axial end clearance is 0.12 mm and the second axial end clearance is 0.07 mm. When the vehicle is under driving load, the roller 4 generates a small end displacement towards the large end of the bearing inner ring 2. The first axial end clearance is used to provide axial clearance for this end displacement, reducing the sliding and tightness between the end of the roller 4 near the large end of the bearing inner ring 2 and the bearing inclined surface. When the vehicle is under reverse drag load, the second axial end clearance is used to limit the excessive axial movement of the roller 4 towards the small end of the bearing inner ring 2. The combined effect of this axial clearance difference and the aforementioned radial clearance difference restricts the attitude adjustment of roller 4 to a small range, preventing free wobbling.

[0042] During assembly, the cage 3 with the aforementioned angle and clearance relationship is combined with multiple rollers 4 and placed between the housing 1 and the inner ring 2 of the bearing. First, the drive bevel gear shaft is manually rotated 3 to 5 times to confirm that there is no jamming or periodic rubbing noise. Then, a low-speed run-in is performed. The low-speed run-in conditions are: speed 150 r / min, gear oil temperature 50℃ to 60℃, and duration 8 minutes. After the run-in, the contact marks between the rollers 4 and the inner ring 2 of the bearing are inspected. The contact marks of a qualified sample should be located in the middle area of ​​the oblique bearing surface of the inner ring 2 of the bearing. The width of the contact marks is continuous along the circumference but should not extend to the outer edge. If the contact marks are close to the outer edge and accompanied by a shiny end, it indicates that the angle offset is too small or the clearance on the reverse drag force side is too large. If the rotational resistance increases significantly and there are no obvious positioning marks of the rollers 4 in the cage 3, it indicates that the clearance on the drive force side is too small.

[0043] To verify the influence of angular and clearance differences on the load condition, a comparative test was conducted on three sets of samples. Comparative Example 1 used a perfectly equal angular fit, with a clearance of 0.045 mm on both the driving force side and the reverse drag force side; Comparative Example 2 used a reverse angular offset, but the radial clearances on both sides were equal; the sample in this embodiment used both a reverse angular offset and unequal radial clearances. The test conditions were: oil temperature 85℃, input speed 1200 r / min, output torque 1200 N·m, continuous operation for 2 hours, and the additional frictional torque, temperature rise near the bearing housing, and contact mark location were recorded after operation, as shown in Table 1.

[0044] Table 1: Comparison of bearing performance under different angular fit and radial clearance fit conditions

[0045] The test results show that when only a perfect angular fit is used, the roller 4 tends to shift towards the outer edge of the inclined bearing surface of the inner ring 2 after loading, resulting in higher frictional torque and temperature rise. When only an angular offset is set but the radial clearances on both sides are equal, the roller 4 has a certain tendency to return to center, but the anti-dragging side lacks early limiting, and the contact marks will still expand to the outer edge. In this embodiment, after controlling the angular offset, radial clearance difference and axial end clearance difference at the same time, the roller 4 can obtain a more stable return space under driving load, and will not continue to shift towards the wedging direction under anti-dragging load. Therefore, the contact marks are concentrated in the middle area, and the frictional torque and temperature rise are reduced.

[0046] This embodiment uses the combined setting of angular difference, radial clearance difference, angular offset and axial end clearance difference to limit the attitude change path of roller 4 to a controllable range.

[0047] In drive mode, roller 4 can achieve slight self-alignment by utilizing the larger drive force side clearance; in reverse drag mode, the smaller reverse drag force side clearance and smaller axial end clearance can limit reverse offset in advance; therefore, this structure does not rely on loose fit to reduce friction, but rather reduces edge clamping and end slippage by restricting posture adjustment under specific force directions. Example 3 Please see Figure 1-5 Roller 4 has a central bearing surface and end unloading surfaces located on both sides of the central bearing surface; The middle bearing surface is used to form the main contact area with the bearing slope when the roller 4 is in the loaded and straightened overlapping state. The end unloading surface recedes away from the bearing slope relative to the middle bearing surface, so that the end of the roller 4 avoids wedge contact with the edge of the bearing slope after being loaded. The allowable clearance between the end unloading surface and the middle bearing surface is 0.005 mm to 0.05 mm. The middle load-bearing surface and the end unloading surface are connected by a continuous transition surface, so that the main contact area migrates from the end area to the middle area during the process of roller 4 being loaded and returning to center.

[0048] In this embodiment, based on Embodiments 1 and 2, the overlapping surface of the roller 4 and the oblique bearing surface of the inner ring 2 of the bearing are further processed so that after the roller 4 completes its return to center under load, the actual contact area can stably fall in the central bearing area, rather than remaining in the end edge area. This embodiment is mainly used to solve the problem that the ends of the roller 4 are prone to local tightness, edge scratches, and contact stress concentration during the switching of the differential reducer of a medium-duty truck when climbing hills under full load, accelerating rapidly, and towing backwards.

[0049] In a set of samples, the effective contact length of roller 4 is 15.0 mm, with the middle region being 10.5 mm and the two end regions each being 2.25 mm. During machining, the middle region of roller 4 is precision ground as the main load-bearing area, so that it preferentially forms stable contact with the inclined bearing surface of the inner ring 2 of the bearing after returning to center under load. The two end regions of roller 4 are machined to a slightly recessed state, with the maximum recess of the two ends relative to the middle region controlled at 0.018 mm. This recess should not be too large, as an excessive recess will reduce the transition support of the roller 4 ends to changes in posture; if the recess is too small, it is difficult to avoid the ends prematurely contacting the edge region of the inner ring 2 of the bearing under eccentric load.

[0050] To avoid abrupt changes between the central and end regions, a continuous transition is used between the central and end regions of roller 4. Specifically, the outer circumference of roller 4 is first precision ground, and then the slightly recessed areas at both ends are machined using CNC profile grinding, allowing a gradual transition from the central region to the end regions. The length of the transition section is controlled to be between 1.2 mm and 1.8 mm. In this embodiment, the transition section length is 1.5 mm. After machining, a profilometer is used to inspect the surface profile along the axial generatrix of roller 4. It is required that there be no visible abrupt changes in the central and end regions, and the profile deviation of the transition section is controlled within 0.003 mm.

[0051] The bearing ramp that mates with the roller 4 does not use a single-angle plane. The bearing ramp of the inner ring 2 includes an inlet ramp, a main bearing ramp, and a release ramp arranged sequentially along the direction from when the roller 4 enters the main contact area to when it leaves the main contact area. The inlet ramp is closer to the side where the roller 4 enters the main contact area, the release ramp is closer to the side where the roller 4 leaves the main contact area, and the main bearing ramp is located between the inlet ramp and the release ramp. In this embodiment, the side where the roller 4 enters the main contact area corresponds to the small end side of the inner ring 2, and the side where the roller 4 leaves the main contact area corresponds to the large end side of the inner ring 2. The release ramp is used to reduce end drag and end rubbing when the roller 4 leaves the main contact area after it has a slight end displacement toward the large end side of the inner ring 2.

[0052] In this embodiment, using the central axis of housing 1 as the angle measurement reference, the inclination angle of the entry area is machined to 11.8°, the inclination angle of the main load-bearing area is machined to 12.0°, and the inclination angle of the release area is machined to 12.2°. The three areas are connected by a grinding transition zone, the width of which is controlled to be between 0.8 mm and 1.5 mm. In this embodiment, the transition zone width is 1.0 mm. This angular change is not intended to alter the overall load-bearing direction, but rather to ensure that the roller 4 has a continuous attitude change path during entry, load-bearing, and exit, preventing momentary jamming of the roller 4 before and after the main load-bearing area.

[0053] After assembly, when the vehicle is under low load, roller 4 first makes slight contact with the guide area of ​​the inner ring 2 of the bearing. The guide area allows roller 4 to gradually transition from the pre-biased state in Embodiment 2 to the load-bearing state. After the vehicle enters the fully loaded driving state, roller 4 returns to the main load-bearing area under the combined action of radial and axial forces. At this time, the middle area of ​​roller 4 forms main contact with the main load-bearing area of ​​the inner ring 2 of the bearing. Since the ends of roller 4 have already formed a slight yield, even if there is a short-term impact load, the ends of roller 4 are not likely to push against the edge area of ​​the inner ring 2 of the bearing prematurely. When the vehicle releases the throttle and coasts or goes downhill and is dragged, roller 4 gradually transitions from the main load-bearing area to the release area. The release area can reduce the end drag of roller 4 when leaving the contact area and reduce the sudden increase in friction during the reverse drag switching.

[0054] To verify the fit between the curved surface and the segmented inclined surface, contact trace inspection was performed on the sample. During the inspection, a colorant was evenly applied to the inclined bearing surface of the bearing inner ring 2. The assembled differential reducer assembly was run at a low speed of 300 r / min for 10 minutes, and then the contact traces between the bearing inner ring 2 and the roller 4 were inspected. The contact traces of a qualified sample should be mainly concentrated in the main bearing area of ​​the bearing inner ring 2, continuously distributed circumferentially, and should not extend to the edge of the inclined bearing surface; intermittent slight contact traces are allowed at both ends of the roller 4, but should not form a continuous shiny scratch band.

[0055] Furthermore, a loading comparison test was conducted between the sample of this embodiment and the sample without the end-end relief treatment. The test conditions were: gear oil temperature 85℃, input speed 1200 r / min, output end loading torque 1200 N·m, continuous operation for 2 hours. After the test, the additional friction torque, temperature rise near the bearing housing, contact mark position and end polishing condition were recorded. The specific details are shown in Table 2.

[0056] Table 2: Comparison of the Influence of Curved Surface Recess and Segmented Inclined Surface Fit on Contact Area Migration and Operating Temperature Rise

[0057] As can be seen from Table 2, when only the two ends of roller 4 are treated to be in a recessed state, the end polishing is improved, but the contact marks are still easy to extend to the edge area of ​​the inner ring 2 of the bearing. When the middle bearing area and the end recessed area of ​​roller 4 cooperate with the lead-in area, main bearing area and release area of ​​the inner ring 2 of the bearing, the contact area of ​​roller 4 after being loaded can be more stably concentrated in the main bearing area, and the additional friction torque and the temperature rise of the bearing housing are further reduced.

[0058] The purpose of this embodiment is not simply to perform ordinary chamfering or smoothing on the roller 4, but to enable the roller 4 to bear the main load through its central area after returning to center under the action of the angle difference and clearance difference in embodiment 2, and to avoid edge wedging through the relief areas at both ends; at the same time, the segmented oblique bearing surface of the bearing inner ring 2 provides a continuous path for the roller 4 to be introduced, carried and released. Therefore, this structure can guide the contact area under driving load from the end edge to the central bearing area, reduce end slippage and local heat generation, thereby further improving the low-resistance operation stability of the differential reducer bearing position.

[0059] Example 4 Please see Figures 1-5 A micro-oil wedge gap is formed between the bearing inclined surface and the roller 4 in a pre-offset overlapping state; the micro-oil wedge gap is distributed in a converging direction along the inner ring 2 of the bearing from the small end side to the large end side. Specifically, the end of the micro-oil wedge gap near the small end side of the inner ring 2 of the bearing is the inlet side, and the end near the large end side of the inner ring 2 of the bearing is the outlet side, and the width of the inlet side is greater than the width of the outlet side.

[0060] When roller 4 changes from the pre-offset lap state to the load-aligned lap state, the inlet side is still located near the small end of the inner ring 2 of the bearing, and the outlet side is still located near the large end of the inner ring 2 of the bearing, so that the lubricating oil enters the micro-oil wedge gap from the inlet side and enters the main contact area with the load-aligned roller 4.

[0061] In this embodiment, based on embodiments 1 to 3, a specific method for forming a micro-oil wedge gap between the roller 4 and the inner ring 2 of the bearing is further disclosed to solve the problems of insufficient lubrication in the local contact area, increased end slip friction, and concentrated temperature rise in the contact area during the process of the roller 4 changing from the pre-deflection state to the load return state.

[0062] After roller 4 enters the loaded return-to-center overlapping state, the orientation of the inlet and outlet sides of the micro-oil wedge gap relative to the large and small ends of the bearing inner ring 2 remains unchanged. The inlet side is still close to the small end of the bearing inner ring 2, and the outlet side is still close to the large end of the bearing inner ring 2. At this time, the micro-oil wedge gap with a wide inlet and a narrow outlet formed in the pre-offset overlapping state is compressed by the loaded return-to-center action, and a lubricating oil inlet channel is formed at the leading edge of the main contact area, allowing the lubricating oil to enter the main contact area.

[0063] In this embodiment, the micro-oil wedge gap is not an additional independent component, nor is it simply formed by increasing the assembly clearance. Instead, it is formed by the combined use of the inclined bearing surface of the bearing inner ring 2, the central bearing area of ​​the roller 4, the end relief area of ​​the roller 4, and the angular pre-deflection relationship in Embodiment 2. When the vehicle is in a low-load or no-load rotating state, the roller 4 and the inclined bearing surface of the bearing inner ring 2 are not in full-width contact. Instead, a larger inlet-side gap is formed on the side where the roller 4 rolls into the main stress area, and a smaller outlet-side gap is formed on the side where the roller 4 rolls away from the main stress area. After the vehicle enters the driving loading state, the roller 4 gradually returns to the stable bearing position under the load. The gear oil in the inlet-side gap is carried into the main contact area, thereby forming a continuous oil film before the roller 4 completes its attitude return.

[0064] For ease of processing and inspection, this embodiment uses the rolling direction of roller 4 as the criterion for determining the inlet and outlet sides. Specifically, when the driving bevel gear shaft drives roller 4 to roll along the inclined bearing surface of the inner ring 2 of the bearing, the area where roller 4 first approaches the inclined bearing surface of the inner ring 2 is the inlet side, and the area where roller 4 leaves the main bearing area is the outlet side. During sample processing, with roller 4 in a pre-biased assembly state, the inlet side clearance is controlled to be 0.016 mm to 0.022 mm, and the outlet side clearance is controlled to be 0.004 mm to 0.009 mm; in this embodiment, the inlet side clearance is preferably 0.018 mm, and the outlet side clearance is 0.006 mm, so that a gradually narrowing wedge-shaped space is formed between the inlet and outlet sides.

[0065] The aforementioned gap dimensions can be confirmed through both cross-sectional sample inspection and replica film inspection. For cross-sectional sample inspection, without affecting the final assembly, the bearing inner ring 2, cage 3, and roller 4 from the same batch are used as inspection samples. Roller 4 is installed inside cage 3 and placed in the corresponding position of bearing inner ring 2. A coordinate measuring machine is used to measure the inlet and outlet distances between the outer circumference of roller 4 and the inclined bearing surface of bearing inner ring 2. For replica film inspection, a curable thin layer of replica material is coated on the inclined bearing surface of bearing inner ring 2. Roller 4 is pressed into the corresponding position in a pre-biased state and held for 30 to 60 seconds. After the replica film is removed, a profilometer is used to measure the film thickness change, thereby confirming whether the gap from the inlet to the outlet side gradually decreases. For formally assembled parts, the presence of micro-oil wedge gaps can be indirectly verified by the contact marks after low-speed running-in. The main contact marks of qualified samples should be concentrated in the middle bearing area of ​​the inner ring 2 of the bearing. There should be relatively uniform oil marks on the inlet side, and there should be no continuous dry friction polishing band on the outlet side.

[0066] During operation, 75W to 90 grade gear oil is added to the differential reducer housing, with the oil level controlled according to the normal operating oil level of the drive axle, ensuring that roller 4 receives splash lubrication during operation. When the vehicle starts at low speed or climbs a hill under full load, roller 4 has not yet fully entered the stable load-bearing position, and the larger gap on the inlet side can accommodate the gear oil carried in by roller 4. As roller 4 continues to roll, the gear oil on the inlet side is squeezed into the gradually narrowing gap, forming a certain amount of squeezed oil film at the smaller gap on the outlet side. This oil film can separate the local contact surfaces during the process of roller 4 transitioning from the pre-biased state to the loaded return state, reducing scratches caused by short-term slippage at the ends.

[0067] To avoid unstable load bearing due to excessively large micro-oil wedge clearance, this embodiment limits the clearance on both the inlet and outlet sides. When the inlet clearance is less than 0.012 mm, insufficient gear oil enters, and dry friction marks easily appear on roller 4 during the initial loading stage. When the inlet clearance is greater than 0.030 mm, roller 4 is prone to slight knocking sensation under low load conditions, and the contact marks are not continuous enough. When the outlet clearance is less than 0.003 mm, local compression and tightness easily form at the outlet. When the outlet clearance is greater than 0.012 mm, the oil film compression effect weakens, and the oil film stability in the main contact area decreases. Therefore, this embodiment preferably controls the inlet clearance to 0.016 mm to 0.022 mm and the outlet clearance to 0.004 mm to 0.009 mm, which can balance oil introduction, oil film formation, and load bearing stability.

[0068] During the processing, in order to make the micro-oil wedge clearance repeatable, the inclined bearing surface of the bearing inner ring 2 is first processed and then finely ground to control the surface roughness Ra between 0.16 μm and 0.32 μm; then the middle bearing area and the end relief area of ​​the roller 4 are processed to make the outer peripheral contour of the roller 4 form a continuous transition in the axial direction; then the roller 4 is installed in the cage 3, and by adjusting the tilt position of the cage 3 and the assembly angle of the roller 4, a clearance with a wide inlet and a narrow outlet is formed between the roller 4 and the inclined bearing surface of the bearing inner ring 2 in the pre-biased state.

[0069] This processing sequence ensures that the micro-oil wedge gap is consistent with the angular pre-bias relationship in Example 2, rather than randomly forming an unstable gap after assembly.

[0070] After assembly, the sample was tested for lubrication.

[0071] During the verification, the differential reducer assembly was fixed on the test bench, and the same batch of gear oil was added into the housing. The oil temperature was controlled at 80℃ to 90℃, and the input speed was set to 300 r / min for low-speed operation with oil for 10 minutes to allow the oil to fully enter between the roller 4 and the inner ring 2 of the bearing. Then the input speed was increased to 1200 r / min, the loading torque was set to 1200 N·m, and it was run continuously for 2 hours.

[0072] After the test, the oblique bearing surface of the inner ring 2 and the corresponding area of ​​the roller 4 were disassembled and inspected to observe the distribution of oil marks, dry friction polishing bands and contact marks, as shown in Table 3.

[0073] Table 3: Comparison of the Influence of Micro-Oil Wedge Clearance Size on Lubrication Condition and Bearing Performance

[0074] As shown in Table 3, when the inlet clearance is too small, gear oil cannot easily enter the space between the roller 4 and the inner ring 2 of the bearing in a timely manner, and a continuous polishing band is still easily generated in the end slip area. When both the inlet and outlet clearances are too large, although a large amount of gear oil enters, the bearing marks of the roller 4 in the main contact area are easily dispersed, and the low-resistance effect is not stable. In this embodiment, after controlling the inlet and outlet clearances to a gradually contracting micro-oil wedge shape, the gear oil can be carried in before the roller 4 rolls into the main bearing area and form a stable oil film during the return process of the roller 4. Therefore, the additional frictional torque and the temperature rise of the bearing housing are further reduced.

[0075] Further observation of the contact state after disassembly reveals that, in this embodiment, the inner ring 2 of the bearing forms continuous but non-blackened contact marks in the central area of ​​the inclined bearing surface. Uniform oil marks are present on the inlet side, while no obvious dry friction scratches are observed on the outlet side. The roller 4 only shows a few intermittent shallow scratches at its end, without forming a continuous circumferential shiny wear band. This indicates that the micro-oil wedge gap can provide transitional lubrication during the roller 4's attitude return process, preventing localized dry friction before the roller 4 has fully entered the stable bearing position.

[0076] The purpose of this embodiment is to further transform the angle pre-deflection in Embodiment 2 and the contact area migration in Embodiment 3 into conditions for the formation of a lubricating oil film. The larger inlet side clearance is responsible for introducing gear oil, and the smaller outlet side clearance is responsible for forming an oil film compression. Together, they keep the roller 4 lubricated when it changes from the pre-deflection state to the stable load-bearing state. This structure does not require additional oil supply lines or oil pumps, nor does it rely on external control mechanisms. It can improve the lubrication state of the differential reducer bearing position in the initial stage of drive loading and the reverse drag switching process simply by controlling the geometric clearance between the bearing inner ring 2 and the roller 4, thereby reducing frictional resistance, operating temperature rise and end slip wear.

[0077] Example 5 Please see Figures 1-5 At least one of the end unloading surface and the edge bearing area opposite to the end unloading surface is provided with a shear friction reduction layer. The hardened bearing substrate is retained in the area corresponding to the main contact area in the middle bearing curved surface and the bearing inclined surface, so that the roller 4 maintains the bearing strength in the main contact area, and the sliding friction between the end of the roller 4 and the edge of the bearing inclined surface is reduced by the shear friction reducing layer.

[0078] In this embodiment, based on embodiments 1 to 4, a zoned friction-reducing treatment is applied to the area between the inner ring 2 and the roller 4 where end slippage is prone to occur. This ensures that the low-shear friction-reducing layer primarily acts on the high-risk end slippage area without covering the main load-bearing area. This treatment method is used to prevent the full-surface coating from crushing, peeling, or changing the contact stiffness of the main load-bearing area under high contact loads.

[0079] In this embodiment, the bearing inner ring 2 and roller 4 first undergo basic heat treatment. Specifically, the bearing inner ring 2 and roller 4 can be made of bearing steel material, and after quenching and low-temperature tempering, their surface hardness is controlled between 60HRC and 63HRC. The central bearing area of ​​roller 4 and the corresponding main contact area in the inner ring 2 of the bearing retain the hardened surface after heat treatment, without being covered by a low-shear friction-reducing layer, so that this area still relies on the hardened matrix to bear the main radial and axial loads under full-load driving conditions.

[0080] The low-shear friction-reducing layer is only applied to locations where end slippage is likely to occur. For roller 4, friction-reducing treatment is applied to the end unloading areas at both ends, with each end extending 1.8 mm to 2.5 mm from the end face to the center. For the bearing inner ring 2, friction-reducing treatment is applied to the corresponding edge band near the end unloading area of ​​roller 4 on its inclined bearing surface, with the edge band width controlled to be 1.5 mm to 2.2 mm. The main contact area outside the above areas remains in a hardened bearing substrate state, thereby forming a partitioned surface structure with compressive strength in the main bearing area and friction reduction in the end slip area.

[0081] In a set of samples, the effective contact length of roller 4 is 15.0 mm, the length of the central bearing area is 10.5 mm, and the unloading areas at both ends are 2.25 mm each. During processing, a low-shear friction-reducing layer is deposited within a 2.0 mm range at both ends of roller 4, and the same friction-reducing treatment is applied to a 1.8 mm range near the edge of the oblique bearing surface of the bearing inner ring 2; no friction-reducing layer is deposited in the 10.5 mm range in the middle of roller 4 and in the main contact zone in the middle of the oblique bearing surface of the bearing inner ring 2.

[0082] Before the friction reduction treatment, the area to be treated is first finely ground and cleaned to control the surface roughness Ra of the area to be deposited to 0.08 μm to 0.16 μm. Then, a masking fixture is used to cover the main contact area that does not need to be deposited, exposing only the end slip area. Plasma cleaning is then performed to remove surface oil and oxide film. During deposition, a metal transition layer with a thickness of 0.10 μm to 0.20 μm is first formed, followed by a carbon-based shear friction reduction layer with a thickness of 1.5 μm to 3.0 μm. In this embodiment, the transition layer thickness is 0.15 μm, the carbon-based shear friction reduction layer thickness is 2.0 μm, and the deposition temperature is controlled below 160℃ to avoid affecting the original heat treatment hardness of the bearing inner ring 2 and roller 4.

[0083] To avoid the coating boundary becoming a source of peeling, the shear friction reducing layer is not cut off at a right angle on the side near the main contact area, but instead forms a gradual transition boundary with a width of 0.3 mm to 0.6 mm. In this embodiment, the width of the gradual transition boundary is 0.5 mm, and the coating thickness gradually decreases from 2.0 μm at the end area to 0 μm at the boundary of the main contact area. With this treatment, even if the contact area slightly migrates during the return-to-center process under load, the roller 4 will not suddenly press against the edge of the coating step, thereby reducing the risk of coating peeling.

[0084] After the friction-reducing layer treatment is completed, the appearance, thickness, and adhesion status of the samples are inspected. Thickness can be measured using cross-sectional microscopic observation or ball mill pit thickness measurement; adhesion status can be determined through scratch loading test and low-speed pre-run-in test. In qualified samples, the shear friction-reducing layer should continuously cover the end unloading area and should not enter the central main load-bearing area; large-area sheet-like peeling should not be observed after scratch testing. After a low-speed pre-combination of 10 minutes, slight polishing marks may appear in the end area, but there should be no continuous peeling bands that penetrate the coating.

[0085] After the sample with the above-mentioned partitioned friction reduction treatment was installed into the differential reducer assembly, a loading test was conducted according to the lubrication conditions in Example 4. The test oil temperature was controlled at about 85℃, the input speed was 1200 r / min, and the output loading torque was 1200 N·m, running continuously for 2 hours; then the loading torque was increased to 1800 N·m and the operation continued for 1 hour to observe the surface condition of the main load-bearing area and the end slip area under higher load. After the test, the bearing inner ring 2 and roller 4 were disassembled and inspected, and the additional friction torque, bearing housing temperature rise, end wear width, and coating condition were recorded, as shown in Table 4.

[0086] Table 4: Comparison of the effects of partitioned shear friction-reducing layers on end slip wear and low-resistivity performance

[0087] As can be seen from Table 4, without the friction-reducing layer, a wide continuous wear band easily appears in the end area of ​​roller 4, indicating that the end slippage is still significant. Although the friction-reducing layer on the entire surface can reduce the initial friction torque, the main contact area is subjected to high contact stress, which easily leads to point indentations and local peeling after loading. In this embodiment, the shear friction-reducing layer is limited to the end slippage area, while the hardened bearing substrate of the main contact area is retained, so that the end slippage friction is reduced and the main contact area maintains high bearing stability.

[0088] The disassembly and inspection results showed that in the sample of Example 5, the contact marks in the bearing area of ​​the middle of roller 4 were continuous and there was no coating peeling problem; the shear friction reducing layer in the unloading area at the end remained continuously covered, with only slight polishing marks; the polishing marks on the edge of the inclined bearing surface of the inner ring 2 of the bearing were significantly shorter than those in Comparative Example 7. This indicates that the partitioning treatment can be combined with the aforementioned angle pre-offset, clearance release, curved surface return, and micro-oil wedge lubrication, so that roller 4 mainly relies on the hardened area in the middle to bear the load under driving load, and relies on the shear friction reducing layer to reduce friction during short-term slippage at the end.

[0089] The above-mentioned approach does not simply involve adding a wear-resistant coating, but rather, based on the contact distribution of the roller 4 after it returns to center under load, the surface treatment area is limited to the high-slippage location at the end. Therefore, this not only avoids the main load-bearing area from peeling off due to excessive coating pressure, but also reduces the slippage friction in the end unloading area during the initial stage of drive loading and the reverse drag switching process. Through the above-mentioned zoned friction reduction treatment, the low-resistance bearing can maintain a low friction torque, a low temperature rise, and a small end wear width during long-term operation in the differential reducer of a medium-duty truck.

[0090] It should be noted that the data in Tables 1 and 4 are the average values ​​obtained after testing three samples under the same bench conditions. The test oil temperature was controlled at around 85℃, the input speed was 1200 r / min, and the output torque was 1200 N·m.

[0091] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A low-resistance bearing for a medium-sized truck differential reducer, comprising a housing (1), an inner bearing ring (2), a cage (3), and rollers (4), wherein the inner bearing ring (2) is fitted inside the housing (1), the cage (3) is disposed between the housing (1) and the inner bearing ring (2), and the rollers (4) are fitted into the cage (3) and overlap with corresponding surfaces of the housing (1) and the inner bearing ring (2), characterized in that, The inner ring (2) of the bearing has a trapezoidal cross section, which forms a bearing ramp for overlapping with the roller (4); the cage (3) has a fitting hole that is inclined relative to the bearing ramp, and the roller (4) is fitted into the fitting hole in an oblique posture; The inclination angle of the bearing slope, the inclination angle of the fitting hole and the axial inclination angle of the roller (4) form a reverse pre-clinch angle difference. The direction of the reverse pre-clinch angle difference is opposite to the deflection direction of the roller (4) under the differential reducer drive load. The deflection direction is the direction in which the roller (4) deflects toward the edge of the bearing slope when it is subjected to the combined action of radial and axial forces. The side on which the roller (4) generates a posture return displacement under the forward driving condition is taken as the driving return side, and the side on which the roller (4) generates a wedge-tightening offset tendency under the reverse drag condition is taken as the reverse drag limiting side. The fitting hole forms a first limiting sidewall on the driving return side and a second limiting sidewall on the reverse drag limiting side. A first radial gap is formed between the first limiting sidewall and the outer peripheral surface of the roller (4), and a second radial gap is formed between the second limiting sidewall and the outer peripheral surface of the roller (4). The first radial clearance is used to allow the roller (4) to return to its correct position along the fitting hole under the driving load; the second radial clearance is used to limit the roller (4) from continuing to wedge and deflect towards the edge of the bearing slope under the anti-drag load; the first radial clearance is greater than the second radial clearance.

2. The low-resistance bearing for a medium-duty truck differential reducer as described in claim 1, characterized in that, The inclination angle of the bearing inclined surface is denoted as α, the inclination angle of the inclined guide reference line used to limit the assembly posture of the roller (4) is denoted as β, and the inclination angle of the axis of the roller (4) is denoted as γ. α, β and γ are all based on the central axis of the housing (1) as the angle reference. A first angular difference is formed between β and α, and a second angular difference is formed between γ and α. The bias direction of at least one of the first angular difference and the second angular difference is opposite to the bias direction of the roller (4) under the differential reducer drive load. The absolute value of the first angle difference is 0.3° to 2.5°, and the absolute value of the second angle difference is 0.2° to 1.8°.

3. The low-resistance bearing for a medium-duty truck differential reducer as described in claim 2, characterized in that, A radial clearance difference is formed between the first radial clearance and the second radial clearance, the radial clearance difference being 0.01 mm to 0.08 mm.

4. The low-resistance bearing for a medium-duty truck differential reducer as described in claim 3, characterized in that, The width ratio of the first radial gap to the second radial gap is 1.2 to 3.0; An angular offset is formed between β and γ, the angular offset being 0.2° to 1.5°, causing the roller (4) to change from a pre-offset overlapping state to a loaded return overlapping state within the range defined by the radial clearance difference.

5. The low-resistance bearing for a medium-duty truck differential reducer as described in claim 1, characterized in that, A first axial end gap and a second axial end gap are formed between the two ends of the cage (3) and the roller (4), respectively. The first axial end gap is located on the large end side of the inner ring (2) of the bearing, and the second axial end gap is located on the small end side of the inner ring (2) of the bearing. The first axial end gap is greater than the second axial end gap, and is used to provide axial clearance space when the roller (4) generates end displacement toward the large end side of the inner ring (2) of the bearing under the action of driving load, and to restrict the axial movement of the roller (4) toward the small end side of the inner ring (2) of the bearing by the second axial end gap.

6. The low-resistance bearing for a medium-duty truck differential reducer as described in claim 1, characterized in that, The roller (4) has a central bearing surface and end unloading surfaces located on both sides of the central bearing surface; The central bearing surface is used to form a main contact area with the bearing ramp when the roller (4) is in the loaded and lapped state. The end unloading surface recedes away from the bearing ramp relative to the central bearing surface, so that the end of the roller (4) avoids wedge contact with the edge of the bearing ramp after being loaded.

7. The low-resistance bearing for a medium-duty truck differential reducer as described in claim 6, characterized in that, The yield of the end unloading surface relative to the middle bearing surface is 0.005 mm to 0.05 mm; The middle bearing surface and the end unloading surface are connected by a continuous transition surface, so that the main contact area migrates from the end area to the middle area during the loading and straightening process of the roller (4).

8. The low-resistance bearing for a medium-duty truck differential reducer as described in claim 6, characterized in that, The bearing slope includes an inlet slope, a main bearing slope, and a release slope arranged sequentially along the contact migration direction of the roller (4) relative to the bearing slope. The inlet slope is located on the side where the roller (4) enters the main contact area, the release slope is located on the side where the roller (4) leaves the main contact area, and the main bearing slope is located between the inlet slope and the release slope. The guide ramp is used to guide the roller (4) into the pre-offset overlap state; the main bearing ramp is used to form a load-bearing return overlap with the middle bearing surface; the release ramp is used to reduce the end drag generated when the roller (4) leaves the main contact area after the roller (4) generates end displacement towards the large end side of the bearing inner ring (2).

9. The low-resistance bearing for a medium-duty truck differential reducer as described in claim 8, characterized in that, A micro-oil wedge gap is formed between the bearing inclined surface and the roller (4) in the pre-eccentric overlap state; The micro-oil wedge gap is distributed in a converging manner along the inner ring (2) of the bearing from the small end side to the large end side. The end of the micro-oil wedge gap near the small end side of the inner ring (2) of the bearing is the inlet side, and the end near the large end side of the inner ring (2) of the bearing is the outlet side. The width of the inlet side is greater than the width of the outlet side. When the roller (4) changes from the pre-offset lap state to the load return lap state, the inlet side is still located near the small end of the inner ring (2) of the bearing, and the outlet side is still located near the large end of the inner ring (2) of the bearing, so that the lubricating oil enters the micro-oil wedge gap from the inlet side and enters the main contact area with the load return of the roller (4).

10. The low-resistance bearing for a medium-duty truck differential reducer as described in claim 6, characterized in that, At least one of the end unloading surface and the bearing slope, in the edge bearing region opposite to the end unloading surface, is provided with a shear friction reduction layer; The central bearing surface and the area corresponding to the main contact area in the bearing slope retain the hardened bearing matrix, so that the roller (4) maintains the bearing strength in the main contact area, and the shear friction reduction layer reduces the sliding friction between the end of the roller (4) and the edge of the bearing slope.

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