A balance piston and an automatic transmission using it

Abstract

This invention discloses a balance piston for an automatic transmission (AT) and an AT including the same, belonging to the field of automatic transmission technology. The balance piston has a ring structure with a splined inner ring for spline engagement with the drive hub of the AT, allowing the balance piston to rotate synchronously with the drive hub. The balance piston has multiple arc-shaped holes for engaging with a push block on the first piston in the shift actuator. The balance piston directly drives the first piston to rotate synchronously through the connection between the arc-shaped holes and the push block. This invention, by adding a balance piston that rotates synchronously with the drive hub and using this balance piston to forcibly drive the first piston to rotate synchronously, fundamentally eliminates the speed difference between the first piston and the clutch drum, effectively solving the problem of uneven hydraulic oil distribution and pressure imbalance in the piston chamber caused by centrifugal force.

Description

Technical Field

[0001] This invention relates to the field of automatic transmission technology, specifically to a balance piston for an automatic transmission (AT), and also to an AT automatic transmission using the balance piston. Background Technology

[0002] Automatic transmissions (AT) achieve gear shifting through the engagement and disengagement of clutches and brakes, which is crucial for ensuring smooth power transmission and precise gear shifting. In the shifting mechanism of an AT, the actions of both the clutch and brake are driven by pistons. The movement of the pistons is powered by pressurized oil supplied by a hydraulic system. When the transmission is in operation, the clutch drum rotates at high speed along with the power input shaft, and the pistons, located inside the clutch drum, rotate at high speed along with it.

[0003] During the high-speed rotation of the piston and clutch drum, the hydraulic oil in the piston chamber is subjected to a strong centrifugal force. This centrifugal force causes uneven distribution of the hydraulic oil in the piston chamber, resulting in an imbalance of hydraulic pressure inside the piston chamber. If this centrifugal force cannot be effectively balanced, it will directly affect the piston's motion response speed and the pressure stability of the clamping friction plate, ultimately leading to slow shifting and shifting shock in the transmission, and may even reduce the service life of components such as friction plates and pistons, affecting the overall reliability of the transmission.

[0004] To address the hydraulic imbalance caused by centrifugal force, existing technologies mainly employ two solutions: the first is to create an oil drain hole on the piston, using the flow through the drain hole to regulate the distribution of hydraulic oil within the piston chamber, thereby counteracting the effects of centrifugal force; the second is to install a balance plate inside the piston chamber, using the structure of the balance plate to block and guide the hydraulic oil, thus achieving centrifugal force balance.

[0005] However, both of the aforementioned existing technical solutions have significant technical defects and are difficult to meet the working requirements of AT automatic transmissions over a wide speed range: For the solution with an oil drain hole, the flow capacity of the drain hole is a fixed value. When the transmission is running at low speeds, the centrifugal force is small, and the fixed drain hole will cause excessive pressure relief in the piston chamber, resulting in insufficient piston driving pressure, a significant decrease in piston response speed, and prominent shift lag. At high speeds, the centrifugal force increases sharply, and the flow capacity of the drain hole cannot meet the hydraulic oil balance requirements, resulting in poor centrifugal force balancing. For the solution with a balance plate, the balance plate has a complex structural design and requires precise matching with the piston chamber and clutch drum in multiple parts. This not only increases the overall manufacturing cost and assembly difficulty of the transmission shift actuator, but also the balancing effect of the balance plate is greatly affected by the speed. It has poor adaptability in different speed ranges (low, medium, and high), and the balancing effect over a wide speed range is not ideal. At the same time, the complex balance plate structure will also increase energy loss inside the transmission and reduce power transmission efficiency.

[0006] In summary, existing solutions for centrifugal force balancing in the piston chamber of automatic transmissions (AT) suffer from problems such as unreasonable structural design, poor balancing effect over a wide speed range, and impact on piston response speed or increased energy loss. They are unable to simultaneously ensure the precision of shifting, the efficiency of power transmission, and the reliability of operation of AT automatic transmissions. Therefore, a new centrifugal force balancing structure is urgently needed to address the aforementioned shortcomings of existing technologies. Summary of the Invention

[0007] The primary objective of this invention is to provide a balance piston for an automatic transmission (AT), thereby solving the technical problems of poor centrifugal force balance, low wide speed range adaptability, affected piston response speed, and high energy loss in the existing AT automatic transmission shift actuator.

[0008] Another objective of this invention is to provide an automatic transmission (AT) that utilizes this balance piston, thereby achieving more precise shift control, reducing energy loss during power transmission, and improving the overall reliability and service life of the transmission.

[0009] To achieve the above objectives, in a first aspect, the present invention proposes a balance piston for an automatic transmission (AT). The balance piston has an annular structure and is adapted to be installed inside the shift actuator of the AT automatic transmission. The inner ring of the balance piston has a spline structure, which is used to engage with the drive hub of the AT automatic transmission, allowing the balance piston to rotate synchronously with the drive hub. The balance piston has multiple arc-shaped holes, which are used to engage with push blocks on the first piston in the shift actuator. The balance piston directly drives the first piston to rotate synchronously through the connection between the arc-shaped holes and the push blocks. The balance piston, together with the clutch drum, the first piston, the piston spring, and the second piston, constitutes the shift actuator of the AT automatic transmission, balancing the centrifugal force on the hydraulic oil in the piston chamber by driving the first piston to rotate synchronously.

[0010] Preferably, the number of arc-shaped holes is 4 to 8, and all arc-shaped holes are evenly distributed in a ring around the center of the balance piston. This even distribution ensures that the driving force is uniform when the balance piston drives the first piston to rotate, preventing uneven wear or jamming of the first piston.

[0011] Preferably, at least one sealing ring mounting groove is provided on the outer circumferential surface of the balance piston for mounting a sealing element to achieve a dynamic seal between the seal element and the inner wall of the second piston. This ensures a tight seal between the balance piston and the second piston.

[0012] Preferably, an annular groove is provided on one side surface of the balance piston, the annular groove being used to install and position one end of the piston spring. This annular groove provides stable support and positioning for the spring.

[0013] Preferably, multiple limiting protrusions are evenly distributed in the annular groove to circumferentially limit the piston spring installed in the annular groove, prevent it from circumferentially moving during operation, and ensure the stability of the spring force.

[0014] Preferably, the spline structure of the inner ring of the balance piston is an involute spline with a module ranging from 1.0 to 2.5, a pressure angle of 20°, and a fit accuracy grade of not less than 7. Splines within this parameter range have the advantages of high load-bearing capacity, good centering accuracy, and smooth transmission, ensuring sufficient connection strength and rotational synchronization between the balance piston and the drive hub, and avoiding problems such as key slippage or key disengagement at the spline fit.

[0015] Preferably, the balance piston is made of high-strength alloy steel or high-strength aluminum alloy. When alloy steel is used, it undergoes heat treatment and surface carburizing and quenching to obtain a high-strength core and a wear-resistant surface. When aluminum alloy is used, it undergoes solution treatment and artificial aging to achieve lightweight and sufficient strength.

[0016] Preferably, all mating working surfaces of the balance piston, including the outer circumferential surface, sidewalls, and spline structure, are precision polished, with a surface roughness Ra value of no more than 0.8 μm after polishing. This high-precision surface treatment can significantly reduce the coefficient of friction, decrease wear and energy loss of moving parts, and improve response speed.

[0017] Secondly, the present invention proposes an automatic transmission (AT), comprising a power input shaft, a power output shaft, a clutch drum, a first piston, a piston spring, a second piston, a drive hub, and a shift actuator. The shift actuator includes a balance piston as described above and cooperates with the clutch drum, the first piston, the piston spring, and the second piston. The power output shaft is connected to the clutch drum and drives the clutch drum to rotate. The drive hub is drively connected to the power input shaft.

[0018] Preferably, both the first piston and the second piston are mounted on the clutch drum, and the first piston and the balance piston are respectively disposed in two coaxial but radially different stepped holes of the second piston; a first sealing ring is embedded on the outer circumferential surface of the first piston for dynamic sealing with the corresponding inner hole wall of the second piston; a second sealing ring is embedded on the outer circumferential surface of the balance piston for dynamic sealing with the corresponding inner hole wall of the second piston; the two ends of the piston spring respectively abut against the spring seat surface of the first piston and the bottom surface or side wall of the annular groove of the balance piston; a plurality of push blocks on the first piston pass through a plurality of arc-shaped holes on the balance piston in a one-to-one correspondence, and the push blocks slide in engagement with the hole walls of the arc-shaped holes to transmit torque and allow the two to move relative to each other in the axial direction.

[0019] Due to the adoption of the above technical solution, the beneficial effects of the present invention are as follows: (1) Root-cause solution to the centrifugal force problem: Traditional solutions attempt to "counteract" centrifugal force under the premise of "relative rotation," while this invention forces the first piston to rotate synchronously with the drive hub (i.e., the power input part) through a balancing piston, so that there is no longer a speed difference between the first piston and the clutch drum. Since centrifugal force is proportional to the square of the rotational angular velocity, when the piston itself no longer rotates relative to the hydraulic oil, the hydraulic oil in its working chamber will not be subjected to the additional centrifugal force generated by the piston rotation. This fundamentally eliminates the root cause of centrifugal hydraulic pressure generated in the piston chamber due to the speed difference, and achieves "active prevention" rather than "passive cancellation" of centrifugal force.

[0020] (2) Excellent performance over a wide speed range: Since the speed difference is eliminated, no significant centrifugal hydraulic pressure is generated in the first piston chamber regardless of whether the input shaft speed is low or high. Therefore, the balancing effect of the present invention is independent of the speed, which perfectly solves the problem of excessive pressure relief at low speed and insufficient balance at high speed in the prior art. It can ensure the stability of piston drive pressure and response speed throughout the entire speed range.

[0021] (3) Compact structure and easy integration: The balance piston of the present invention ingeniously integrates multiple functions such as drive spline, transmission arc hole and spring mounting groove, and is itself an independent ring component. It can directly replace or integrate into the existing shift actuator, and is coaxially mounted with the first piston, second piston and other components. The axial and radial dimensions increase by a very small amount, the structure is very compact, and it is easy to improve and apply on the existing transmission platform.

[0022] (4) Fast response and low energy loss: Since the first piston is no longer affected by centrifugal hydraulic pressure, its movement is determined only by the control oil pressure and spring force. Therefore, when a shift command is received, the piston can respond quickly, achieving precise clamping and disengagement, eliminating shift lag. At the same time, by eliminating the drag caused by centrifugal force and reducing unnecessary oil churning and friction, the energy loss of the transmission is effectively reduced, and the power transmission efficiency is improved. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. 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 the structures shown in these drawings without creative effort.

[0024] Figure 1 This is a front view of the balance piston provided by the present invention.

[0025] Figure 2 The figure shows a sectional view of AA.

[0026] Figure 3 The three-dimensional balance piston provided by the present invention Figure 1 .

[0027] Figure 4 The three-dimensional balance piston provided by the present invention Figure 2 .

[0028] Figure 5 This is a partial view of the shift actuator in the automatic transmission (AT) provided by the present invention.

[0029] Explanation of reference numerals: 1-Balance piston; 1a-Spline structure; 1b-Arc-shaped hole; 1c-Sealing ring mounting groove; 1d-Annular groove; 1e-Limiting protrusion; 2-Clutch drum; 3-First piston; 3a-Push block; 4-Piston spring; 5-First sealing ring; 6-Second sealing ring; 7-Second piston; 8-Drive hub; 9-First friction plate assembly; 10-Second friction plate assembly. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0032] Furthermore, the use of terms such as "first" and "second" in this invention is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. Additionally, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. When the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed by this invention.

[0033] Example 1 Combination Figures 1 to 5 As shown, the present invention provides a balance piston 1 for an automatic transmission (AT), which is an overall annular rotating body structure and is adapted to be installed inside the shift actuator of the automatic transmission.

[0034] A spline structure 1a is provided on the inner ring of the balance piston 1, i.e., on the inner wall of its central hole. This spline structure 1a is preferably an involute spline, and its specific parameters can be designed according to the torque transmission requirements of the automatic transmission (AT). For example, its module can be selected in the range of 1.0 to 2.5, the pressure angle is a standard 20°, and the fit accuracy grade is typically required to be no less than grade 7 (GB / T 3478.1-2008). This spline structure 1a is used to mate with the external spline on the drive hub 8 in the AT automatic transmission. The drive hub 8 is connected to the power input shaft of the transmission (not shown in the figure). Therefore, when the power input shaft rotates, the drive hub 8 rotates accordingly, and through the spline connection, drives the balance piston 1 to achieve synchronous, non-slip rotation.

[0035] Multiple arc-shaped holes 1b are formed along the circumferential direction on the body of the balance piston 1. These arc-shaped holes 1b penetrate both axial sides of the balance piston 1 and are elongated arc-shaped holes extending in the circumferential direction. The main function of the arc-shaped holes 1b is to cooperate with the push blocks 3a on the first piston 3 in the shift actuator. Specifically, multiple push blocks 3a on the first piston 3 will pass through these arc-shaped holes 1b one by one. The push blocks 3a are used to act on the first friction plate assembly 9 of the AT automatic transmission. Since the push blocks 3a are in contact with the hole walls of the arc-shaped holes 1b in the circumferential direction, when the balance piston 1 is driven to rotate by the drive hub 8, the balance piston 1 pushes the push blocks 3a through the hole walls of the arc-shaped holes 1b, thereby forcibly driving the first piston 3 to rotate synchronously at the same speed. At the same time, since the arc-shaped holes 1b are through holes in the axial direction and have a certain radial width, the push blocks 3a are allowed to slide freely in the hole along the axial direction, which ensures that the first piston 3 will not be interfered with when it performs axial reciprocating motion under hydraulic pressure. The first friction plate assembly 9 is conventional existing technology and will not be described in detail here.

[0036] The number of arc-shaped holes 1b is preferably 4 to 8, and all arc-shaped holes 1b are evenly distributed in a ring along the central axis of the balance piston 1. For example, in this embodiment, 6 arc-shaped holes 1b are provided. This evenly distributed design can make the driving force of the balance piston 1 acting on the first piston 3 evenly distributed in the circumferential direction, avoiding the first piston 3 from tilting or jamming due to uneven force, and ensuring the smoothness of movement.

[0037] One or more sealing ring mounting grooves 1c are provided on the outer peripheral surface of the balance piston 1. The sealing ring mounting groove 1c is an annular groove for embedding sealing elements such as O-rings, rectangular rings, or lip rings (such as the second sealing ring 6 in a later embodiment). When the balance piston 1 is assembled into the corresponding inner hole of the second piston 7, the sealing element is used to achieve a dynamic seal between the two, preventing hydraulic oil from leaking from the mating clearance between them.

[0038] A concentric annular groove 1d is formed on one end face of the balance piston 1 (the side closer to the first piston 3 in the figure). The annular groove 1d is used to accommodate and position one end of the piston spring 4. The piston spring 4 is a helical spring, one end of which abuts against the spring seat surface of the first piston 3, and the other end is installed in the annular groove 1d, thereby providing a restoring force for the first piston 3.

[0039] Furthermore, to improve the stability of the spring operation and prevent circumferential movement or torsion of the spring when it rotates at high speed with the component, multiple limiting protrusions 1e are evenly distributed in the annular groove 1d. The end of the piston spring 4 is installed between two adjacent limiting protrusions 1e to circumferentially limit the piston spring 4.

[0040] Considering that the balance piston 1 needs to operate under high pressure, high speed, and high frequency reciprocating motion conditions, its materials and manufacturing processes have high requirements. As a preferred option, the balance piston 1 can be made of high-strength alloy steel (such as 20CrMnTi, 40Cr, etc.) or high-strength aluminum alloy (such as 7075 aluminum alloy). If alloy steel is used, the blank needs to undergo quenching and tempering heat treatment after forging to obtain good comprehensive mechanical properties. Then, the key mating surfaces such as splines and outer circles are subjected to surface carburizing and quenching treatment to improve surface hardness and wear resistance. If aluminum alloy is used, solution treatment and artificial aging (T6 treatment) are required to obtain high strength. Finally, all important mating working surfaces, such as the outer circumferential surface that mates with the second sealing ring 6, the wall of the arc-shaped hole 1b that mates with the push block 3a of the first piston 3, the tooth surface of the spline structure 1a, and the bottom surface of the annular groove 1d, need to be precision machined and polished so that the surface roughness Ra value is no greater than 0.8μm, in order to minimize the coefficient of friction and wear.

[0041] Example 2, Reference Figure 5 As shown, this embodiment provides an automatic transmission (AT) including the balance piston 1 described in Embodiment 1, particularly its shift actuator. The AT also includes a power input shaft (not shown), a power output shaft (not shown), a clutch drum 2, a first piston 3, a piston spring 4, a second piston 7, a drive hub 8, a first friction plate assembly 9, a second friction plate assembly 10, and other housings. The first friction plate assembly 9 and the second friction plate assembly 10 are conventional prior art and will not be described in detail here.

[0042] The clutch drum 2 is a rotating component with a cylindrical structure, one end of which is connected to the power output shaft of the transmission and can be driven to rotate. The first piston 3 and the second piston 7 are both annular pistons, coaxially fitted onto the outer circumference of the clutch drum 2. In this embodiment, the second piston 7 has two coaxial stepped holes with different radial dimensions inside. The first piston 3 and the balance piston 1 are respectively disposed within these two stepped holes. Specifically, the first piston 3 is disposed in the first inner hole with a smaller radial dimension, while the balance piston 1 is disposed in the second inner hole with a larger radial dimension.

[0043] A sealing ring groove is machined on the outer circumferential surface of the first piston 3, in which a first sealing ring 5 is embedded. The outer edge of the first sealing ring 5 is tightly fitted with the wall of the first inner hole of the second piston 7, achieving a dynamic seal between them. Similarly, a second sealing ring 6 is embedded in the sealing ring mounting groove 1c on the outer circumferential surface of the balance piston 1, and the outer edge of the second sealing ring 6 is tightly fitted with the wall of the second inner hole of the second piston 7, achieving a dynamic seal. Through the mutual cooperation of the first sealing ring 5, the second sealing ring 6, the clutch drum 2, the first piston 3, the second piston 7, and the balance piston 1, one or more controllable hydraulic working chambers are formed inside the gear shifting actuator.

[0044] One end of the piston spring 4 abuts against the dedicated spring seat surface of the first piston 3, while the other end extends into and abuts against the annular groove 1d of the balance piston 1. The limiting protrusion 1e in the annular groove 1d provides circumferential positioning for the end of the piston spring 4.

[0045] On the end face of the first piston 3, multiple push blocks 3a are integrally formed or fixedly connected along the circumferential direction. The number and position of these push blocks 3a correspond one-to-one with the arc-shaped holes 1b on the balance piston 1. In the assembled state, each push block 3a passes through a corresponding arc-shaped hole 1b. The two sides of the push block 3a maintain contact or a very small fit clearance with the hole wall of the arc-shaped hole 1b in the circumferential direction, thereby enabling the balance piston 1 to transmit torque to the first piston 3 through the push blocks 3a. The arc-shaped hole 1b and the push block 3a slide against each other, allowing the first piston 3 to move axially relative to the balance piston 1 under hydraulic pressure.

[0046] The pusher 3a on the first piston 3 acts on the first friction plate assembly 9. The second piston 7 acts on the second friction plate assembly 10.

[0047] The drive hub 8 is a component that is connected to the power input shaft for transmission. An external spline is provided on the outer circumferential surface of the drive hub 8, which meshes with the spline structure 1a of the inner ring of the balance piston 1, thereby realizing the fixed connection and synchronous rotation of the drive hub 8 and the balance piston 1.

[0048] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A balance piston for an automatic transmission (AT), characterized in that, The balance piston (1) is an annular structure and is adapted to be installed inside the shift actuator of the AT automatic transmission; The inner ring of the balance piston (1) is provided with a spline structure (1a), which is used to engage with the drive hub (8) of the AT automatic transmission, so that the balance piston (1) rotates synchronously with the drive hub (8). The balance piston (1) is provided with multiple arc-shaped holes (1b). The arc-shaped holes (1b) are used to cooperate with the push block (3a) on the first piston (3) in the shift actuator. The balance piston (1) directly drives the first piston (3) to rotate synchronously through the connection between the arc-shaped holes (1b) and the push block (3a). The balance piston (1), together with the clutch drum (2), the first piston (3), the piston spring (4), and the second piston (7), constitute the shift actuator of the AT automatic transmission. The centrifugal force on the hydraulic oil in the piston chamber is balanced by driving the first piston (3) to rotate synchronously.

2. The balance piston for an automatic transmission according to claim 1, characterized in that, The number of the arc-shaped holes (1b) is 4 to 8, and all the arc-shaped holes (1b) are evenly distributed in a ring around the center of the balance piston (1).

3. The balance piston for an automatic transmission according to claim 1, characterized in that, At least one sealing ring mounting groove (1c) is provided on the outer peripheral surface of the balance piston (1) for mounting a sealing element to achieve a dynamic seal with the inner wall of the second piston (7).

4. The balance piston for an automatic transmission according to claim 1, characterized in that, An annular groove (1d) is provided on one side surface of the balance piston (1), the annular groove (1d) being used to install and position one end of the piston spring (4).

5. The balance piston for an automatic transmission according to claim 4, characterized in that, A limiting protrusion (1e) is provided in the annular groove (1d) to circumferentially limit the piston spring (4).

6. The balance piston for an automatic transmission according to claim 1, characterized in that, The inner ring of the balance piston (1) has an involute spline structure (1a), with a module of 1.0-2.5, a pressure angle of 20°, and a spline fit accuracy of grade 7.

7. The balance piston for an automatic transmission according to claim 1, characterized in that, The balance piston (1) is made of alloy steel or aluminum alloy. When alloy steel is used, it is strengthened by tempering heat treatment and surface carburizing treatment. When aluminum alloy is used, it is strengthened by solution treatment and artificial aging treatment.

8. The balance piston for an automatic transmission according to claim 1, characterized in that, All mating working surfaces of the balance piston (1), including the outer circumferential surface, side wall and spline structure (1a), are precision polished, and the surface roughness Ra value after polishing is no greater than 0.8μm.

9. An automatic transmission (AT), comprising a power input shaft, a power output shaft, a clutch drum (2), a first piston (3), a piston spring (4), a second piston (7), a drive hub (8), and a shift actuator, characterized in that, The shifting actuator adopts the balance piston (1) of any one of claims 1 to 8, and is configured in conjunction with the clutch drum (2), the first piston (3), the piston spring (4), and the second piston (7); the output shaft is connected to the clutch drum (2) and drives the clutch drum (2) to rotate; the drive hub (8) is connected to the power input shaft.

10. The automatic transmission according to claim 9, characterized in that, The first piston (3) and the second piston (7) are both mounted on the clutch drum (2), and the first piston (3) and the balance piston (1) are respectively disposed in two coaxial but radially different stepped holes of the second piston (7); a first sealing ring (5) is embedded on the outer circumferential surface of the first piston (3) for dynamic sealing with the corresponding inner hole wall of the second piston (7); a second sealing ring (6) is embedded on the outer circumferential surface of the balance piston (1) for dynamic sealing with the corresponding inner hole wall of the second piston (7); a plurality of push blocks (3a) on the first piston (3) pass through a plurality of arc-shaped holes (1b) on the balance piston (1) in a one-to-one correspondence, and the push blocks (3a) slide with the hole wall of the arc-shaped holes (1b) to transmit torque and allow the two to move relative to each other in the axial direction.

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