Halfshaft having ball spline structure

Abstract

A half shaft according to an embodiment of the present invention comprises an inboard constant velocity joint; an outboard constant velocity joint; and a connecting shaft that interconnects the inboard constant velocity joint and the outboard constant velocity joint. A ball spline structure that guides axial displacement is formed on a drive shaft line between at least one of the inboard constant velocity joint and the outboard constant velocity joint and the connecting shaft. The ball spline structure comprises a plurality of outer ball spline grooves and inner ball spline grooves that face each other radially and are aligned axially, and a plurality of spline balls interposed between the outer ball spline grooves and the inner ball spline grooves. When actual balls selected according to dimensional grades are applied as the plurality of spline balls, the actual BCD gap, defined as the difference between the diameter of the ball center circle of the outer ball spline groove and the diameter of the ball center circle of the inner ball spline groove, is formed to satisfy a range of 0.1 mm to 0.14 mm, thereby eliminating ball jamming and preload caused by the combination of dimensional tolerances during the axial stroke operation of the ball spline structure, and reducing high-frequency plunge resistance caused by idle vibration.

Description

Technology Field

[0001] The present disclosure relates to a halfshaft configured to transmit the driving force of a vehicle. Background Technology

[0002] Generally, the drivetrains of vehicles, including eco-friendly vehicles and internal combustion engine vehicles, are equipped with half shafts to transmit driving torque output from a transmission or reduction gear to the wheels at a constant speed. Such half shafts must be capable of simultaneously accommodating longitudinal displacement and angular motion depending on driving conditions. To this end, a conventional half shaft includes an inboard constant velocity joint positioned on the inboard side, an outboard constant velocity joint positioned on the wheel side, and a connecting shaft connecting them.

[0003] Conventional general half-shaft structures employ a mechanism that simultaneously performs axial plunge movement and angle cutting functions within the inboard constant velocity joint. However, this structure is susceptible to relative sliding friction between internal joint components, making it prone to causing NVH issues due to frictional resistance. Furthermore, as the allowable axial movement becomes significantly restricted as the constant velocity joint reaches the maximum angle cutting state, there are limitations that make it difficult to apply to SUVs or off-road vehicles with large suspension movements.

[0004] To solve these problems, a ball spline halfshaft structure has been proposed in which the joint's angular cutting function and axial motion function are independently separated into respective regions. This separated structure adopts a layout in which the ball spline unit is either built-in integrally at a specific location on the drive shaft line, for example, within the inner race of an inboard constant velocity joint, or positioned between the inner and outer diameters of a tubular connecting shaft region.

[0005] This ball spline half-shaft structure has structural advantages that allow for a wide stroke range and improved wobble by reducing internal friction through the ball's rolling motion.

[0006] However, even with a half-shaft structure incorporating such an independent ball spline unit, NVH performance degradation still occurs under micro-vibration conditions induced in the idle state when the vehicle is stopped or in specific low-speed driving environments. Specifically, in environments where a fine sinusoidal reciprocating motion with a stroke of ±0.15 mm is applied at a high frequency of 30 Hz, there is a mechanical limitation in which High Frequency Plunge Resistance (HFPR) is actually significantly induced due to the combination of dimensional tolerances within the ball spline, the geometric contact state of the groove, and the imbalance in dynamic load distribution. This high frequency plunge resistance rises irregularly due to preload within the ball spline, micro-ball jamming during movement, and changes in the elastic deformation area when torque is applied, and this becomes a direct cause of idle vibrations in the vehicle body and steering wheel.

[0007] Therefore, there is a need for optimal universal numerical limiting design technology capable of organically controlling the dimensional gaps and groove geometric parameters of the ball spline section so that high-frequency plunge resistance in high-frequency micro-behavior environments can be dramatically reduced regardless of where the ball spline unit is positioned on the half-shaft drive axis.

[0008] The matters described in the technical background section of this invention are written to enhance understanding of the background of the invention and may include matters that are not prior art already known in the field to which this technology belongs. The problem to be solved

[0009] The present invention is based on a half shaft having an independent ball spline structure on the drive shaft line of the half shaft to accommodate length displacement due to the suspension behavior and steering of a vehicle, and is devised to overcome the technical limitations of such an independent, separate ball spline structure in a specific dynamic operating environment.

[0010] Specifically, regardless of whether the ball spline structure is directly integrated into the inner diameter of the inner race of the inboard constant velocity joint or formed in the inner diameter of the connecting shaft area in a tubular form, the vehicle is exposed to a special high-frequency micro-movement environment, such as high frequency of about 30 Hz and a micro-stroke of about 0.15 mm, when the vehicle is idle after stopping. Under such specific conditions, the combination of fine dimensional tolerances inside the ball spline unit, the geometric contact state of the groove, and the imbalance of load distribution can cause the High Frequency Plunge Resistance (HFPR) to be significantly increased, which can cause vibrations in the vehicle body and steering wheel. Accordingly, the problem that the present invention aims to solve is to provide a half shaft capable of dramatically reducing high-frequency plunge resistance by relieving ball preload and preventing spline ball jamming during high-frequency micro-movements, by deriving an optimal numerical range in which design parameters consisting of actual BCD clearance, ball groove conformity, ball groove vertex radius, and ball groove contact angle are organically linked so that the ball spline structure can be commonly applied regardless of the position and layout of the half shaft.

[0011] In addition, the present invention has another objective of providing a half shaft that can significantly reduce frictional resistance and ensure the structural strength and durability life required by a half shaft drive system by optimizing the dynamic contact area between the ball and the ball groove and alleviating stress concentration through precise control of four parameters under a dynamic stroke situation in which torque is continuously applied.

[0012] The technical problems that the present invention aims to solve are not limited to those mentioned above, and other technical problems not mentioned will be understood by those skilled in the art from the description below. means of solving the problem

[0013] A half shaft according to an embodiment of the present invention comprises an inboard constant velocity joint; an outboard constant velocity joint; and a connecting shaft that interconnects the inboard constant velocity joint and the outboard constant velocity joint. A ball spline structure that guides axial displacement is formed on a drive shaft line between at least one of the inboard constant velocity joint and the outboard constant velocity joint and the connecting shaft. The ball spline structure comprises a plurality of outer ball spline grooves and inner ball spline grooves that face each other radially and are aligned axially, and a plurality of spline balls interposed between the outer ball spline grooves and the inner ball spline grooves. When actual balls selected according to dimensional grades are applied as the plurality of spline balls, the actual BCD gap, defined as the difference between the diameter of the ball center circle of the outer ball spline groove and the diameter of the ball center circle of the inner ball spline groove, is formed to satisfy a range of 0.1 mm to 0.14 mm, thereby eliminating ball jamming and preload caused by the combination of dimensional tolerances during the axial stroke operation of the ball spline structure, and reducing high-frequency plunge resistance caused by idle vibration.

[0014] In one example, the ball spline structure is directly integrally provided in the inner diameter portion of the inner race of the inboard constant velocity joint, and one end of the connecting shaft can be inserted into the inner diameter portion of the inner race and coupled to allow for sliding displacement.

[0015] In another example, the connecting shaft is a hollow connecting shaft, and the ball spline structure may be integrally formed on one side of the connecting shaft. A stub shaft extending axially from the inner race of the inboard constant velocity joint may be inserted into the inner diameter of the connecting shaft and coupled to allow for sliding displacement.

[0016] The outer ball spline groove and the inner ball spline groove may have a Gothic arch cross-sectional shape. When the radius of a gauge ball, which is a reference measuring ball, is called the gauge ball radius, and the radius of curvature of the outer and inner ball spline grooves forming a surface contact boundary with the gauge ball is called the ball groove contact radius, the ball groove fit, defined as the ratio of the ball groove contact radius to the gauge ball radius, may be formed to satisfy a range of 1.1 to 1.16.

[0017] The outer ball spline groove and the inner ball spline groove may have a Gothic arch cross-sectional shape. The ball groove apex radius, which is a rounded fillet radius at the vertex area formed by the outer and inner ball spline grooves meeting at the center, may be formed to satisfy a range of 60% to 90% of the radius of the gauge ball, which is a reference measuring ball.

[0018] The ball groove contact angle of the outer ball spline groove and the inner ball spline groove is the angle formed by the line connecting the contact points where the gauge ball and the surfaces of the outer and inner ball spline grooves physically meet each other, with respect to the center of the gauge ball which is the reference measuring ball, with respect to the radial normal, and can be formed to satisfy a range of 37° to 43°. Effects of the invention

[0019] According to the present invention, by separating the axial displacement (stroke) function and the articulation function of the joint, smooth rolling motion of the spline ball is ensured under torque application conditions, and internal frictional resistance is drastically reduced. As a result, the chronic wobble phenomenon that occurred during conventional inboard joint driving can be drastically prevented and improved.

[0020] Furthermore, the present invention limits the actual BCD clearance when applying graded balls to a range of 0.1 mm to 0.14 mm, thereby eliminating excessive preload of spline balls that may occur due to combinations of dimensional tolerances in the manufacturing process and resolving ball jamming during fine operation. Through this, the High Frequency Plunge Resistance (HFPR), which is the main cause of vibration transmitted to the vehicle body in high-frequency fine motion environments such as the vehicle's idle state, can be reduced, thereby maximizing the vehicle's NVH performance.

[0021] Furthermore, the present invention significantly reduces shear friction by reducing the dynamic contact area between the ball and the ball groove even under elastic deformation occurring when high torque is applied, by controlling the ball groove conformity—which is the ratio of the ball groove contact radius to the gauge ball radius—to an optimal range of 1.1 to 1.16. In particular, when the conformity is controlled to 1.12, which is within the critical region of the present invention, it is possible to achieve the effect of significantly reducing the high-frequency plunge resistance (HFPR) to an average level of about 30% across the entire stroke range compared to the conventional method (conformity 1.08).

[0022] Furthermore, the present invention provides a ball groove apex radius (RC) corresponding to 60% to 90% of the gauge ball radius at the deepest apex of a spline groove having a Gothic arch shape. BGV By forming a fillet, the phenomenon of stress concentration at a specific point when driving torque is applied is perfectly dispersed, thereby dramatically improving the durability and strength performance of the part. At the same time, the interference area with the ball during elastic deformation is eliminated, thereby blocking factors that increase resistance.

[0023] Furthermore, the present invention provides a ball groove contact angle (A CP By limiting the angle to 37° to 43°, the normal contact force (Ball Force) itself is mathematically reduced, thereby further lowering the stroke resistance. At the same time, under the set actual BCD clearance conditions, the dynamic contact angle becomes excessively large, preventing behavioral defects where the spline ball climbs up the edge of the groove and deviates or gets damaged, thereby increasing the driving reliability of the system.

[0024] Furthermore, as the axial movement and angle cutting functions are operated separately in independent areas, a wide range of stroke volume of up to 80mm can be fully secured without tight length constraints, even when the joint's angle of motion is large. Accordingly, it is possible to perfectly absorb and accommodate the undercarriage behavior of off-road vehicles or SUVs, where sudden and rough movements of the suspension system are frequent.

[0025] In addition to this, various effects that can be obtained or predicted by the embodiments of the present invention are disclosed directly or implicitly in the detailed description of the embodiments of the present invention. Brief explanation of the drawing

[0026] The drawings attached below are intended to aid in understanding the present invention and provide embodiments of the invention together with the detailed description. However, the technical features of the present invention are not limited to specific drawings, and the features disclosed in each drawing may be combined with one another to form new embodiments. The embodiments of this specification may be better understood by referring to the following description in conjunction with the attached drawings, in which similar reference numerals refer to identical or functionally similar elements. FIG. 1 is a drawing illustrating the overall configuration of a half shaft according to one embodiment of the present invention. FIG. 2 is an axial cross-sectional view illustrating the connection structure of the inboard joint of the half shaft of FIG. 1. FIG. 3 is a cross-sectional view showing the shape of the outer ball spline groove formed on the inner circumference of the inner race according to the present invention and the BCD (Ball Center Diameter) when a gauge ball is applied. FIG. 4 is a cross-sectional view showing the shape of the inner ball spline groove formed on the outer surface of the connecting shaft according to the present invention and the BCD when a gauge ball is applied. FIG. 5 is a cross-sectional view showing detailed parameters of an outer ball spline groove according to the present invention. Figure 6 is a graph showing the test results of high-frequency plunge resistance (HFPR) according to stroke position according to the change in actual BCD clearance according to the present invention. Figure 7 is a graph showing the results of the analysis (CAE) of high-frequency plunge resistance (HFPR) according to the ball groove conformity and changes in contact angle according to the present invention. FIG. 8 is a graph showing the test results of high-frequency plunge resistance (HFPR) according to stroke position under ball groove conformity conditions according to the present invention. FIG. 9 is a graph showing the theoretical correlation between the ball groove contact angle and the contact force applied to the ball according to the present invention. FIG. 10 is a schematic diagram showing the vector decomposition relationship of the force acting between the ball and the ball groove by the ball groove contact angle according to the present invention. FIG. 11 is a partial cross-sectional view showing the overall configuration of a half shaft in which a ball spline structure is integrally formed on the connecting shaft side according to another embodiment of the present invention. FIG. 12 is an enlarged partial longitudinal section view of the connecting shaft side ball spline structure and the inboard constant velocity joint connection part of FIG. 11. The drawings referenced above are not necessarily drawn to scale and should be understood as providing a simplified representation of various features illustrating the basic principles of the invention. For example, specific design features of the invention, including specific dimensions, orientations, positions, and shapes, will be partially determined by specific intended applications and usage environments. Specific details for implementing the invention

[0027] Embodiments of the present invention are described below with reference to the attached drawings so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the described embodiments.

[0028] The terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the invention. As used herein, the singular form is intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising” and / or “comprising” as used herein indicate the presence of the specified features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, components, and / or groups thereof. As used herein, the term “and / or” includes any one or all combinations of one or more items listed in association. The term “combined” indicates a physical relationship between two components where the components are directly connected to each other or indirectly connected through one or more mediating components. In describing the components of the present invention, where it is stated that one component is "connected," "coupled," or "connected" to another component, it should be understood that the component may be directly connected, coupled, or connected to the other component, but that another component may also be "connected," "coupled," or "connected" between each component.

[0029] Hereinafter, a half shaft having an inner race ball spline structure according to a preferred embodiment of the present invention will be described in detail with reference to the attached drawings. In this process, the thickness of the lines or the size of the components shown in the drawings may be exaggerated for clarity and convenience of explanation. Furthermore, the terms described below are defined considering their functions in the present invention, and since these may vary depending on the intention or convention of the user or driver, the definitions of these terms should be based on the content throughout this specification.

[0030] A half shaft equipped with a ball spline structure according to the present invention is provided with an independent ball spline structure (40, 63) on the drive line of the half shaft to independently accommodate the axial displacement (stroke) of the drive shaft according to the suspension behavior and steering operation of the vehicle. At this time, the half shaft according to one aspect of the present invention can be implemented in two main forms depending on the purpose of optimizing driving efficiency and layout and the characteristics of the vehicle's lower suspension.

[0031] First, according to the first embodiment of the present invention, the ball spline structure (40) guiding the axial displacement may be directly built into the inner diameter portion of the inner race (22) of the inboard constant velocity joint (13). Specific geometric coupling relationships and design parameter definitions thereof will be described later with reference to FIGS. 1 to 10. Meanwhile, according to the second embodiment of the present invention, the ball spline structure (63) guiding the axial displacement may be integrally implemented in the inner diameter portion of a connecting shaft (53) formed in a tubular shape, and a separate stub shaft (54) extending from the inboard constant velocity joint (51) side is inserted into the connecting shaft (53) to allow sliding displacement. Specific configurations thereof will be described in detail with reference to FIGS. 11 and 12, which will be described later.

[0032] As such, the present invention, regardless of where the independent ball spline structures (40, 63) are positioned on the half-shaft drive axis line, the actual BCD clearance, ball groove conformity, ball groove vertex radius, and ball groove contact angle (A) described later CP Through organic numerical limit control of ), high-frequency plunge resistance (HFPR) during high-frequency micro-behavior can be reduced and structural reliability can be ensured.

[0033] FIG. 1 is a partial cross-sectional view showing the overall configuration of a half shaft having a ball spline structure integrally formed according to one embodiment of the present invention, and FIG. 2 is an enlarged partial longitudinal cross-sectional view of the inboard joint and ball spline structure of FIG. 1.

[0034] Referring to FIGS. 1 and 2, a half shaft (10) according to one embodiment of the present invention performs the function of transmitting a driving torque output from a vehicle's power source, such as a transmission or a reduction gear, to the wheel at a constant speed. In addition, the half shaft (10) is configured to absorb the vertical movement of the wheel due to terrain changes or road surface conditions while driving, and to actively accommodate the rotation angle (angle of rotation) of the wheel according to steering operation.

[0035] To this end, the half shaft (10) according to the present invention includes an inboard constant velocity joint (13) connected to a drive system on the transmission or reduction gear side, an outboard constant velocity joint (14) connected to a drive system on the wheel side, and a connecting shaft (11) that physically mediates between the inboard constant velocity joint (13) and the outboard constant velocity joint (14) to transmit torque. In addition, to prevent leakage of grease for internal lubrication and to block the ingress of external foreign matter, an inboard boot (15) is provided on the side of the inboard constant velocity joint (13), and an outboard boot (16) is connected on the side of the outboard constant velocity joint (14).

[0036] The inboard constant velocity joint (13) includes an outer race (21) connected to the output shaft of a transmission or reduction gear, an inner race (22) accommodated in the inner space of the outer race (21), a ball cage (23) interposed between the outer race (21) and the inner race (22) to restrict the movement of the ball, and a plurality of torque transmission balls (24) rotatably accommodated within a window (29) provided in the ball cage (23) to mediate driving torque. The plurality of torque transmission balls (24) are aligned on the joint center plane (P) in a non-angled state.

[0037] At this time, an outer ball groove (25) is formed along the axial direction on the inner surface of the outer race (21), and an inner ball groove (27) is formed on the outer surface of the inner race (22) to face the outer ball groove (25), and a torque transmission ball (24) is seated on the track formed by the outer ball groove (25) and the inner ball groove (27). The inboard constant velocity joint (13) of the present invention performs the function of accommodating the angle of bending of the drive shaft, i.e., articulation, that occurs during driving. Although the shapes of the outer ball groove (25) and the inner ball groove (25) are illustrated exemplarily in FIGS. 1 and FIGS. 2, their shapes can be varied.

[0038] Meanwhile, in the half shaft (10) according to the present invention, in order to structurally separate the angle cutting function and the axial displacement (Stroke / Plunge) function according to the movement of the suspension device, a ball spline structure (40) that guides axial movement between the inner diameter portion of the inner race (22) and the connecting shaft (11) is integrally formed.

[0039] Specifically, referring to FIG. 2, a receiving space is provided in the center of the inner diameter portion of the inner race (22) in a hollow form along the axial direction, and a plurality of outer ball spline grooves (41) are formed along the inner surface of the receiving space in alignment parallel to the axial direction (X). Correspondingly, on the outer surface of the connecting shaft (11) into which one end is inserted into the inner diameter portion of the inner race (22), a plurality of inner ball spline grooves (42) are formed along the axial direction (X) to form a ball track facing the outer ball spline grooves (41) in the radial direction. That is, the connecting shaft (11) in the present invention serves as the inner part of the ball spline structure (40).

[0040] A plurality of spline balls (44) are aligned and interposed between the outer ball spline groove (41) of the inner race (22) and the inner ball spline groove (42) of the connecting shaft (11). The spline balls (44) limit the relative rotational play between the connecting shaft (11) and the inner race (22) to transmit the driving torque from the transmission to the wheel side without loss, while minimizing axial movement resistance by rolling or sliding within the groove when axial displacement occurs. Additionally, a sleeve (43) may be interposed between the inner race (22) and the connecting shaft (11) to maintain the smooth axial circulation and alignment of the spline balls (44), and a sleeve pocket (45) is formed through the sleeve (43) to accommodate a plurality of spline balls (44) and prevent them from falling out. Through this organic coupling structure, the change in length of the drive shaft due to the vertical movement of the suspension is accommodated by a straight stroke through the ball spline structure (40) between the inner diameter of the inner race (22) and the connecting shaft (11).

[0041] With reference to FIGS. 3 and 4, the definition of design parameters and detailed geometric shape conditions of the present invention for blocking High Frequency Plunge Resistance (HFPR) generated during idle vibration and high-frequency micro-movement of a vehicle will be described.

[0042] The numerical limitations defined in the present invention are organically combined to ensure strength reliability by minimizing the friction coefficient inside the ball spline structure (40) and eliminating stress concentration in the part when dynamic torque is applied. A gauge ball (51), which is a standard measuring ball with a constant radius, is applied as a reference body for measuring and defining each parameter.

[0043] The actual BCD gap is defined as the radial dimensional difference between the ball center diameter (BCD) of the outer ball spline groove (41) provided in the inner race (22) and the ball center diameter of the inner ball spline groove (42) provided in the connecting shaft (11) when an actual ball, which is a grade ball precisely classified in the production process, is applied to the ball spline structure (40). In the present invention, the actual BCD gap is formed to satisfy a range of 0.1 mm to 0.14 mm.

[0044] As illustrated in FIGS. 3 and 4, the ball center circle diameter (BCD) refers to the virtual circle diameter formed by the ball centers (CB) of the gauge ball (51) that are seated between a plurality of spline grooves. When the inner race (22) and the connecting shaft (11) are assembled, if the actual BCD gap is set too tightly to less than 0.1 mm, an excessive preload beyond what is necessary is applied to the spline ball (44) due to a combination of dimensional tolerances that occur during part machining. This constrains the rotational movement of the ball during fine high-frequency plunge behavior, causing ball jamming, and as a result, the high-frequency plunge resistance (HFPR) rises sharply, causing vehicle body vibration. Conversely, if the actual BCD gap is excessively loose to exceed 0.14 mm, a large backlash occurs during the vehicle's forward and reverse movement, or acceleration and deceleration, causing rattling noise and shock. Accordingly, the present invention limits the actual BCD gap to 0.1 mm to 0.14 mm, thereby preventing rotational play while also blocking dynamic ball jamming caused by the tolerance combination.

[0045] Ball Groove Conformity is the ball groove contact radius (RC) of the outer ball spline groove (41) and the inner ball spline groove (42) with respect to the radius (Gage Ball Radius) of the reference measurement ball, the gauge ball (51). BGC It is defined as the ratio of ). In the present invention, the ball groove fit is controlled to satisfy the range of 1.1 to 1.16.

[0046] Referring to FIG. 5, the spline grooves (41, 42) of the present invention take the shape of a Gothic arch rather than an arc to induce two-point contact with the ball (51). At this time, the radius of curvature of the portion forming a boundary surface substantially close to surface contact with the gauge ball (51) is the ball groove contact radius (RC). BGC...is. When the ball groove fit is less than 1.1 (i.e., when the radius of curvature of the groove is too close to the radius of the ball), the dynamic contact area between the ball and the groove surface becomes excessively wide due to the Hertzian elastic deformation of the material that occurs when the ball and the groove come into contact when a driving torque is applied. This excessive increase in the contact area amplifies viscosity and frictional resistance during axial sliding, significantly increasing the high-frequency plunge resistance (HFPR). On the other hand, when the fit exceeds 1.16 (i.e., when the groove is excessively flat compared to the ball), the contact area becomes too narrow, causing a significant increase in local contact pressure. This causes plastic deformation or fatigue delamination on the surface of the ball groove during torque transmission, severely reducing the durability strength of the drive system. Therefore, the present invention limits the fit to a range of 1.1 to 1.16 as the optimal point for achieving both friction reduction and strength maintenance.

[0047] Ball Groove Vertex Radius (RC) BGV ) is defined as a fillet radius rounded at the vertex (deepermost vertex) area of ​​the outer ball spline groove (41) and inner ball spline groove (42) formed in a Gothic arch shape. In the present invention, the ball groove vertex radius (RC) BGV ) is formed to have a range of 60% to 90% of the radius of the gauge ball (51).

[0048] As shown in FIG. 5, in a Gothic arch groove, two arcs meet at the central apex to form a cusp (i.e., a pointed apex). If a fillet does not exist at this apex or if the apex radius (RC) BGVIf the ) is formed too small, less than 60% of the gauge ball radius, severe stress concentration occurs around the apex when high torque is applied to the half shaft (10), causing cracks or breakage due to the notch effect. Conversely, the ball groove apex radius (RC) BGV If the apex fillet is formed to be excessively large, exceeding 90% of the gauge ball radius, the fillet at the apex becomes excessively enlarged, encroaching upon the concave space characteristic of a Gothic arch (the clearance space with the ball). In this case, during the dynamic elastic deformation of the ball due to torque application, the ball surface interferes with or is compressed against the apex fillet, linking the stroke operation frictional force and negatively affecting the High-Frequency Plunge Resistance (HFPR). Accordingly, to simultaneously achieve structural strength reinforcement and secure friction clearance space, the present invention [describes] the ball groove apex radius (RC). BGV ) indicates a range of 60% to 90% of the radius of the gauge ball (51).

[0049] Ball groove contact angle (Contact Angle, A CP ) is the ball center (C) of the gauge ball (51) when the gauge ball (51) is seated within the spline groove. B The line connecting the contact points (CP) where the ball groove surface and the ball groove surface physically meet is defined as the angle formed with the radial normal of the ball spline structure (40). In the present invention, the ball groove contact angle (A CP ) satisfies a range of 37° to 43°, and preferably is set to about 40°.

[0050] Referring to FIG. 5, the contact angle (A CP) is a geometric factor that determines the direction of the force component acting organically between the ball and the groove when torque is applied. If the contact angle becomes smaller than 37°, the radial component force pushing the ball from the groove surface under the same rotational torque is relatively reduced, and the normal contact force (Ball Force) applied to the ball itself increases mathematically. Since the increase in ball contact force increases rolling friction resistance during the stroke in direct proportion, it is difficult to expect a reduction effect in high-frequency plunge resistance (HFPR). Conversely, if the contact angle becomes too large exceeding 43°, while it may be advantageous for torque transmission efficiency and radial component force distribution, the dynamic contact angle exceeds a critical threshold when combined with the aforementioned actual BCD gap (0.1mm to 0.14mm) condition. As a result, a driving failure may occur in which the spline ball (44) climbs up the edge, which is the transverse edge boundary of the Gothic arch groove, during the dynamic stroke, causing the movement to deviate or damage the groove edge area.

[0051] Accordingly, the present invention controls the contact angle to a range of 37° to 43° as a boundary region that minimizes high-frequency plunge resistance by minimizing contact force while ensuring stable confinement behavior within the groove of the spline ball (44).

[0052] Figure 6 is a graph showing the measurement results of high-frequency plunge resistance (HFPR, N) according to stroke position (mm) as a function of actual BCD clearance. Here, high-frequency plunge resistance (HFPR) refers to the resistance force generated when a fine sine wave reciprocating motion with a stroke amount of ±0.15 mm is applied at a high frequency of 30 Hz to simulate the idle vibration of a vehicle. Referring to the graph above, it can be seen that the level of high-frequency plunge resistance and behavioral stability show a stark difference depending on the size of the actual BCD clearance.

[0053] In conditions where the gap is set too tightly, such as when the BCD gap is 0.02mm and 0.05mm, the HFPR value over the entire stroke range exhibits high resistance values ​​ranging from a minimum of 20N to a maximum of 45N. This is because an excessive preload is applied to the spline ball (44) due to the combination of dimensional tolerances within the ball spline structure (40), which hinders the organic rolling motion of the ball during fine strokes and causes ball jamming to occur frequently. Consequently, this high resistance is a major cause of worsening the vehicle's idle vibration.

[0054] On the other hand, under conditions where the actual BCD gap is set to 0.10 mm and 0.12 mm, which fall within the numerical limiting range of 0.1 mm to 0.14 mm according to the embodiment of the present invention, it can be seen that despite changes in stroke position, the HFPR value maintains very low and stable resistance performance at the level of approximately 12 N to 23 N. In particular, the best plunge resistance reduction effect is exhibited when the gap is 0.12 mm.

[0055] These test results demonstrate that by ensuring an actual BCD clearance of at least 0.1 mm, the preload inside the ball spline is effectively relieved, and the physical wedge phenomenon (squeezing) of the ball caused by the combination of tolerances during movement is resolved. However, since backlash and impact noise occur when the clearance exceeds 0.14 mm, the present invention limits the actual BCD clearance to a range of 0.1 mm to 0.14 mm as the optimal critical range that simultaneously satisfies the prevention of noise in the drive system and the reduction of high-frequency plunge resistance (improvement of NVH performance).

[0056] Figure 7 is a graph showing the computer analysis (CAE) results of high-frequency plunge resistance (HFPR, N) according to changes in ball groove conformity (B / G Conformity) for each contact angle condition (contact angles 30° and 40°). Referring to the graph in Figure 7, it is confirmed that geometric changes in ball groove conformity and contact angle have an organic effect on high-frequency plunge resistance.

[0057] At contact angles (30°, 40°) set as analysis conditions, the High-Frequency Plunge Resistance (HFPR) value tends to decrease proportionally as the magnitude of the ball groove fit increases from 1.04 to 1.40. This indicates that as the fit increases, the ball groove contact radius (RC) BGC This is because the gap (free space) between the gauge ball (51) is appropriately increased, so that the dynamic contact area between the ball and the ball groove is reduced even if elastic deformation occurs under conditions where dynamic torque is applied. As a result, the shear friction force during the ball spline stroke is minimized, and the high-frequency plunge resistance is reduced.

[0058] It can be seen that under the same fit conditions, the stroke resistance (HFPR) is significantly lower when the contact angle is 40° (Example), which is within the numerical limit range of the present invention, compared to when the contact angle is 30° (Comparative Example). This is because, as shown in the theoretical relationship described later (Figs. 9 and 10), as the contact angle increases, the normal contact force applied to the ball itself when torque is applied decreases, thereby effectively reducing the resistance during the stroke.

[0059] FIG. 8 is a graph showing the results of measuring the high-frequency plunge resistance (HFPR, N) by stroke position (mm) for two representative fit conditions (Conf. 1.08 and Conf. 1.12) in order to verify the analytical trend of FIG. 7 at the level of actual half-shaft parts. By referring to the test results of FIG. 8, the critical effect of limiting the fit value derived in the present invention can be specifically identified.

[0060] When the ball groove fit is set to 1.08, the high-frequency plunge resistance (HFPR) forms a high band of approximately 14N to 21N throughout the entire stroke behavior, exhibiting abrupt behavioral deviations. This implies that the friction drag is intensified as the surface contact area due to elastic deformation widens when torque is applied because the fit is too small. On the other hand, when the fit is set to 1.12, which falls within the numerical limiting range (1.1 to 1.16) of the present invention, it can be confirmed that the HFPR maintains a very low and flat resistance profile of approximately 12N to 15N throughout the entire stroke. Consequently, by optimizing the fit from 1.08 to 1.12, which is the implementation range of the present invention, a significant NVH reduction effect can be achieved in which the high-frequency plunge resistance (HFPR) is significantly reduced to an average of approximately 30% throughout the entire stroke. However, as the above suitability is too high, there is a concern that the structural durability performance of the ball groove may deteriorate due to increased surface pressure. Therefore, the present invention limits the ball groove suitability to a range of 1.1 to 1.16 as an optimal exclusive range that simultaneously satisfies securing durability and reducing idle vibration.

[0061] FIG. 9 is a graph showing the theoretical correlation between the ball groove contact angle and the contact force applied to the ball according to the present invention, and FIG. 10 is a schematic diagram showing the vector decomposition relationship of the force acting between the ball and the ball groove by the ball groove contact angle according to the present invention.

[0062] First, referring to FIG. 10, when examining the mechanical behavior of the force generated during torque transmission within the ball spline structure (40), the effective load (F) acting in the rotational direction (tangential direction) per spline ball (44) is determined by the total system torque (T) transmitted to the half shaft (10) and the total number (N) of spline balls (44). At this time, between the effective rotational load (F) and the actual normal ball contact force (F') applied perpendicularly to the surface of the Gothic arch-shaped spline groove, there is a ball center (C B Ball groove contact angle (A) formed based on ) CP According to )(θ), the following mathematical equation 1 holds.

[0063]

[0064]

[0065] Referring to the above mathematical formula 1 and the graph in Fig. 9, it can be seen that under normal torque conditions where the rotational load (F) per ball is constant, as the ball groove contact angle (θ) corresponding to the denominator term increases, the actual normal ball contact force (F') that the ball groove surface must bear decreases rapidly in inverse proportion. The reduction in the normal ball contact force (F') applied to the spline ball (44) acts as a factor that directly reduces the internal shear friction force generated when the ball spline structure (40) performs a fine stroke in the axial direction. Consequently, as the contact angle (θ) is controlled upward, the high-frequency plunge resistance (HFPR) can be effectively suppressed.

[0066] Ball groove contact angle (A) according to the present invention CP Computer-aided analysis (CAE) was performed to verify the quantitative effect of the control of ) on the actual high-frequency plunge resistance (HFPR) and ball contact force, and the results are shown in Table 1 below.

[0067] Ball groove contact angle (deg) HFPR(N) Ball contact force (N) 30 (Comparative Example) 122.2 840.9 40 (Examples of the present invention) 112.3 744.5 50 (Reference Example) 96.4 682.8

[0069] Analyzing the empirical data in Table 1 above shows that as the contact angle increases from 30° through 40°, which is a representative embodiment of the present invention, to 50°, the contact force applied to the ball groove is significantly reduced to 840.9N, 744.5N, and 682.8N. In conjunction with this, the high-frequency plunge resistance (HFPR), which is a measure of dynamic frictional resistance, is also significantly reduced to 122.2N, 112.3N, and 96.4N, proving that the mechanical component force mechanism described in FIGS. 9 and 10 is demonstrated.

[0070] However, while a contact angle of 50° in Table 1 above may be numerically the most advantageous in terms of resistance reduction, this condition causes structural limitations when combined with the dynamic behavior conditions under the actual BCD gap (0.01mm to 0.14mm), which is a parameter associated with the present invention. If the contact angle exceeds the critical threshold of 43° and becomes excessively large, the ball will move along the edge, which is the edge limit line of the Gothic arch groove, or cause driving failures that result in damage to the edge area, such as deviation from the behavior or damage to the edge area, during the process where the oscillation caused by the dimensional gap and the dynamic contact angle are shared during spline stroke operation. Therefore, the present invention ensures the behavioral stability of the spline ball (44) within the enclosure while lowering the ball contact force to derive the maximum high-frequency plunge resistance (HFPR) reduction effect, and the ball groove contact angle (A) is the optimal geometric critical region. CP ) is limited to a range of 37° to 43°.

[0071] Although an embodiment of the present invention has been described above with reference to the attached drawings, the present invention is not limited to the above embodiment and can be manufactured in various different forms, and those skilled in the art to which the present invention belongs will understand that it can be implemented in other specific forms without changing the technical concept or essential features of the present invention. For example, in the embodiment of the present invention, a Gothic Arch structure that induces two-point contact with a ball was described as a representative example of the cross-sectional shape of the outer ball spline groove (41) and the inner ball spline groove (42) of the ball spline structure (40), but it is obvious that various cross-sectional design variations, such as a composite arc shape or a multi-track shape, can be applied as long as they satisfy the geometric numerical limit range of the actual BCD gap, ball groove fit, ball groove apex radius, and ball groove contact angle presented in the present invention and can reduce high-frequency plunge resistance (HFPR). In addition, although the Jacobi geometric parameters of the outer and inner ball spline grooves (41, 42) in this specification are defined using a gauge ball (51) having a constant diameter as a reference measurement body, this is merely a means to clearly define the numerical range, and the spline ball (44) applied to the actual mass-produced product may be variably combined and selected from actual balls classified into appropriate diameter grades as needed. Furthermore, the spline portion of the inner race (22) and the connecting shaft (11) of the ball spline structure (40) according to the present invention can be implemented through various known metal processing processes such as cutting, precision cold / hot forging, or high-frequency heat treatment and finish grinding after a rolling process, and the scope of the present invention is not limited by the manufacturing method or surface treatment method.

[0072] Hereinafter, with reference to FIGS. 11 and 12, the coupling structure and operating mechanism of a half shaft having a ball spline structure according to the second embodiment of the present invention will be described. While the first embodiment described above is a layout in which the ball spline structure (40) is integrated within the inner race (22) of the inboard constant velocity joint (13), the second embodiment corresponds to a layout in which the ball spline structure (63) is configured as an independent sliding unit in the shaft line area outside the joint.

[0073] As illustrated in FIGS. 11 and 12, a half shaft according to a second embodiment of the present invention includes an inboard constant velocity joint (51), an outboard constant velocity joint (52), and a connecting shaft (53) connecting the inboard constant velocity joint (51) and the outboard constant velocity joint (52).

[0074] The inboard constant velocity joint (51) comprises an inner race (56) having an inner ball groove (58) formed in the inner diameter portion, an outer race (55) that surrounds the outer side of the inner race (56) and is connected to the outer diameter portion, a ball cage (62) that is interposed between the inner race (56) and the outer race (55) and has a plurality of windows, and a plurality of torque transmission balls (61) that are supported by the ball cage (62) and transmit torque. The torque transmission balls (61) are received between the outer ball groove (57) formed in the inner diameter of the outer race (55) and the inner ball groove (58) of the inner race (56) to accommodate the articulation behavior of the joint. Here, one end of a stub shaft (54), which is in the form of a separate solid shaft extending in the axial direction, is integrally fixedly connected to the inner diameter portion of the inner race (56) through a press-fit or spline connection method. The other end of the stub shaft (54) is extended axially toward the wheel side and inserted into the inside of the tubular connecting shaft (53).

[0075] The connecting shaft (53) is formed in the shape of a tubular pipe with an empty interior, and its other end is connected to the outboard constant velocity joint (52). Inside the inboard end of the connecting shaft (53), a ball spline structure (63) is integrally formed to accommodate the other end of the stub shaft (54) and guide the axial stroke displacement.

[0076] Specifically, the ball spline structure (63) includes a plurality of outer ball spline grooves (64) formed extending axially on one side of the inner diameter of the hollow connecting shaft (53), a plurality of inner ball spline grooves (65) formed extending axially on the outer circumference of the stub shaft (54) so ​​as to face the outer ball spline grooves (64) radially, and a plurality of spline balls (66) interposed between the outer ball spline grooves (64) and the inner ball spline grooves (65) to perform rolling motion. At this time, the plurality of spline balls (66) are rotatably supported within the pocket structure of a sleeve (67) interposed between the connecting shaft (53) and the stub shaft (54) to maintain axial alignment and prevent displacement. Additionally, a hollow portion (68) is formed in the internal space of the connecting shaft (53) to allow axial movement of the stub shaft (54).

[0077] According to the structure of the second embodiment, when a large axial displacement occurs due to the movement of the suspension system, the stub shaft (54) slides through the rolling behavior of the spline ball (66) in the inner diameter portion of the connecting shaft (53), thereby performing a smooth plunge stroke.

[0078] In particular, the ball spline structure (63) is controlled to satisfy the geometric numerical limitation conditions of the four design parameters of the present invention, in the same way as the first embodiment described above. That is, when assembled by applying an actual ball precisely classified as a plurality of spline balls (66), the actual BCD clearance, defined as the radial dimensional difference between the BCD of the outer ball spline groove (64) and the BCD of the inner ball spline groove (65), is precisely formed to satisfy the range of 0.1 mm to 0.14 mm.

[0079] In addition, matching the geometric criteria illustrated in FIG. 5, the ball groove conformity applied to the Gothic arch section of the outer and inner ball spline grooves (64, 65) satisfies the range of 1.1 to 1.16, and the ball groove apex radius (RC), which is the fillet radius of the deepest vertex of the groove, is BGV ) has a range of 60% to 90% of the gauge ball radius, and the ball groove contact angle (A CP ) is mutually controlled to maintain a range of 37° to 43°.

[0080] Consequently, in the layout structure of the inner diameter sliding type of the connecting shaft (53) according to the second embodiment, the initial preload and ball jamming phenomenon according to the combination of dimensional tolerances are effectively blocked through critical numerical control of the four design parameters mentioned above. Therefore, the high-frequency plunge resistance (HFPR) can be drastically reduced by more than 30% on average under the high frequency of 30Hz and fine stroke environment of 0.15mm, which are the idle vibration conditions of the vehicle, and stress concentration is relieved when high torque is applied and the phenomenon of the ball climbing up the groove edge is prevented, thereby achieving a universal and significant NVH reduction effect and structural durability reliability that is not limited to the drive system layout.

[0081] Although embodiments of the present invention have been described above, the scope of the present invention is not limited thereto and includes all changes and modifications within the scope recognized as equivalents that can be easily changed by a person skilled in the art from the embodiments of the present invention. Explanation of the symbols

[0082] 10 half shafts 11 connecting shaft 13 Inboard constant velocity joint 14 outboard constant velocity joint 15 Inboard Boot 16 Outboard Boot 21 Outer Lace 22 inner lace 23 ball cage 24 torque transmission balls 25 outer ball grooves 27 Inner Ball Groove 29 Windows 40 ball spline structure 41 Outer ball spline groove 42 inner ball spline groove 43 sleeves 44 spline balls 45 sleeve pockets 51 gauge ball CP contact point C B ball center A CP contact angle RC BGV Ball groove apex radius RC BGC Ball groove contact radius 51 Inboard constant velocity joint 52 outboard constant velocity joint 53 connecting shaft 54 stub shaft 55 Outer Lace 56 Inner Lace 57 Outer Ball Groove 58 inner ball grooves 61 Torque transmission ball 62 ball cage 63 Ball Spline Structure 64 outer ball spline groove 65 inner ball spline groove 66 spline balls 67 sleeves 68 Chinese Ministry

Claims

Claim 1 Inboard constant velocity joint; outboard constant velocity joint; The apparatus includes a connecting shaft that interconnects the inboard constant velocity joint and the outboard constant velocity joint, and a ball spline structure that guides axial displacement is formed on a drive shaft line between at least one of the inboard constant velocity joint and the outboard constant velocity joint and the connecting shaft. The ball spline structure includes a plurality of outer ball spline grooves and inner ball spline grooves that face each other radially and are aligned axially, and a plurality of spline balls interposed between the outer ball spline grooves and the inner ball spline grooves. When actual balls selected according to dimensional grade are applied as the plurality of spline balls, the actual BCD gap, defined as the difference between the ball center circle diameter of the outer ball spline groove and the ball center circle diameter of the inner ball spline groove, is formed to satisfy a range of 0.1 mm to 0.14 mm, thereby preventing ball jamming according to the combination of dimensional tolerances during the axial stroke operation of the ball spline structure. A half shaft that reduces high-frequency plunge resistance caused by idle vibration by eliminating preload generation. Claim 2 In claim 1, the ball spline structure is directly integrally provided in the inner diameter portion of the inner race of the inboard constant velocity joint, and a half shaft is coupled such that one end of the connecting shaft is inserted into the inner diameter portion of the inner race and slides. Claim 3 In claim 1, the connecting shaft is a hollow connecting shaft, the ball spline structure is integrally formed on one side of the connecting shaft, and a half shaft is coupled such that a stub shaft extending axially from the inner race of the inboard constant velocity joint is inserted into the inner diameter of the connecting shaft and slides. Claim 4 A half shaft according to claim 1, wherein the outer ball spline groove and the inner ball spline groove have a Gothic arch cross-sectional shape, and the radius of a gauge ball, which is a reference measuring ball, is called the gauge ball radius, and the radius of curvature of the outer and inner ball spline grooves forming a surface contact boundary with the gauge ball is called the ball groove contact radius, and the ball groove fit, defined as the ratio of the ball groove contact radius to the gauge ball radius, is formed to satisfy a range of 1.1 to 1.

16. Claim 5 A half shaft according to claim 1, wherein the outer ball spline groove and the inner ball spline groove have a Gothic arch cross-sectional shape, and the ball groove apex radius, which is a rounded fillet radius at the vertex area formed by the outer and inner ball spline grooves meeting at the center, is formed to satisfy a range of 60% to 90% of the radius of a gauge ball, which is a reference measuring ball. Claim 6 A half shaft according to claim 1, wherein the ball groove contact angle of the outer ball spline groove and the inner ball spline groove is the angle formed by the line connecting the contact points where the gauge ball and the surfaces of the outer and inner ball spline grooves physically meet each other, with respect to the center of the gauge ball which is the reference measuring ball, with respect to the radial normal, and is formed to satisfy a range of 37° to 43°.

Images