A servo seal mechanism for inhibiting semi-suspended rudder gap cavitation

Abstract

The application belongs to the technical field of semi-suspension rudder anti-cavitation processing, and particularly relates to a follow-up sealing mechanism for inhibiting gap cavitation of a semi-suspension rudder. The follow-up sealing mechanism comprises two sealing assemblies arranged on the left and right sides of a rudder blade socket. Each sealing assembly comprises a rigid central shaft connected to the upper and lower inner walls of the rudder blade socket, and a roller sleeved on the rigid central shaft. The diameter of the roller matches the distance between the inner wall of the rudder blade socket and the rudder suspension arm. The follow-up sealing mechanism is installed on the rudder blade and can automatically and continuously dynamically seal the key gap as the rudder angle changes. The mechanism converts the traditional open high-speed drainage channel, which changes with the rudder angle, into a nearly closed or small constant gap limited space in real time through a pure mechanical physical method, thereby greatly weakening or even eliminating the conditions for generating gap cavitation, and has reliable, low-cost and simple structure design characteristics, and good compatibility with existing rudder systems.

Description

Technical Field

[0001] This invention belongs to the field of anti-cavitation technology for semi-suspended rudders, and particularly relates to a follow-up sealing mechanism for suppressing cavitation in the gaps of semi-suspended rudders. Background Technology

[0002] Semi-suspended rudders, a widely used type of rudder in ships, have their upper rudder blades connected to the rudder arm on the hull via a rudder pin, creating an inherent structural gap between them. When a ship travels at medium to high speeds, water flows through this narrow gap at extremely high velocity, causing the local pressure to drop sharply below the saturated vapor pressure of water, thus triggering cavitation in the gap. The continued occurrence of gap cavitation leads to cavitation damage to the surfaces of the rudder blades and rudder arm, significantly reducing structural lifespan. It also generates broadband noise and may induce rudder vibration, posing a serious threat to the ship's stealth, maneuverability, and safety.

[0003] Existing technologies for mitigating cavitation in semi-suspended rudder clearances primarily focus on passive defense and static optimization. A common approach is to optimize the geometry of the clearance area, such as by adding guide surfaces or ramps to the upper edge of the rudder arm or blade to improve local flow pressure distribution. Another method is to weld or spray anti-cavitation materials onto easily corroded areas. However, the effectiveness of geometric modifications heavily relies on pre-set operating conditions. In actual ship operation, changes in speed, draft, and trim can cause the flow field to deviate significantly from the design, leading to a substantial reduction or even failure of the cavitation mitigation effect. Material protection is merely a remedial measure and cannot eliminate the root cause of cavitation, thus having limited effectiveness in controlling noise and vibration. Summary of the Invention

[0004] The purpose of this invention is to provide a follow-up sealing mechanism that, based on practical needs, can directly act on key flow areas and continuously and effectively intervene in the gap flow field under varying operating conditions to suppress cavitation and cavitation in the gap of the semi-suspended rudder.

[0005] To achieve the above objectives, the present invention adopts the following technical solution.

[0006] A follow-up sealing mechanism for suppressing cavitation in the clearance of a semi-suspended rudder includes two sealing assemblies disposed on the left and right sides of the rudder blade bearing socket 3a; the sealing assembly includes: a rigid central shaft 1 with both ends connected to the inner walls of the upper and lower sides of the rudder blade bearing socket 3a, and a roller 2 sleeved on the rigid central shaft 1, wherein the diameter of the roller 2 matches the distance between the inner wall of the rudder blade bearing socket 3a and the rudder arm.

[0007] In a further improved or preferred embodiment of the aforementioned follow-up sealing mechanism for suppressing cavitation in the semi-suspended rudder clearance, two positioning shaft holes 1a are provided on the upper and lower inner walls of the rudder blade bearing socket 3a, and the rigid central shaft 1 is inserted into the positioning shaft holes 1a.

[0008] In a further improved or preferred embodiment of the aforementioned follow-up sealing mechanism for suppressing cavitation in the semi-suspended rudder clearance, an arc-shaped positioning shaft hole 1b is provided on the upper and lower inner walls of the rudder blade bearing socket 3a, and the upper and lower ends of the two rigid central shafts 1 are respectively inserted into the arc-shaped positioning shaft hole and located at both ends of the arc-shaped positioning shaft hole 1b; it also includes an elastic element provided in the arc-shaped positioning shaft hole 1b for supporting both ends of the rigid central shaft 1.

[0009] A further improvement or preferred embodiment of the aforementioned follow-up sealing mechanism for suppressing cavitation in the semi-suspended rudder clearance also includes a bearing disposed between the inner wall of the roller 2 and the rigid central shaft 1.

[0010] In a further improved or preferred embodiment of the aforementioned follow-up sealing mechanism for suppressing cavitation in the semi-suspended rudder clearance, the bearing refers to a self-lubricating sliding bearing made of polytetrafluoroethylene composite material, or a corrosion-resistant deep groove ball bearing equipped with a sealing structure.

[0011] A further improvement or preferred embodiment of the aforementioned follow-up sealing mechanism for suppressing cavitation in the semi-suspended rudder clearance also includes a sealing structure located in the contact area between the two ends of the roller 2 and the rigid central shaft 1.

[0012] In a further improvement or preferred embodiment of the aforementioned follow-up sealing mechanism for suppressing cavitation in the semi-suspended rudder clearance, the outer side of the sealing structure is sealed to block external seawater or impurities; the inner side is sealed to prevent leakage of bearing lubricating medium.

[0013] In a further improved or preferred embodiment of the aforementioned follow-up sealing mechanism for suppressing cavitation in the semi-suspended rudder clearance, the outer side of the sealing structure is close to the inner walls of the upper and lower sides of the rudder blade bearing socket 3a.

[0014] In a further improvement or preferred embodiment of the aforementioned follow-up sealing mechanism for suppressing cavitation in the semi-suspended rudder clearance, the rigid central shaft 1 is made of a high-strength, corrosion-resistant, and cavitation-resistant material.

[0015] In a further improvement or preferred embodiment of the aforementioned follow-up sealing mechanism for suppressing cavitation in the semi-suspended rudder clearance, the high-strength, corrosion-resistant, and cavitation-resistant material includes martensitic stainless steel or nickel-aluminum bronze; the roller is made of a cavitation-resistant and wear-resistant copper alloy or stainless steel that has undergone surface hardening treatment.

[0016] Its beneficial effects are as follows:

[0017] To address the inherent shortcomings of existing semi-suspended rudder clearance cavitation suppression methods, such as poor adaptability to operating conditions, passive protection, and inability to eliminate cavitation at its source, this application proposes a follow-up sealing mechanism installed on the rudder blade that automatically and continuously seals critical clearances dynamically as the rudder angle changes. This mechanism, through purely mechanical means, transforms the traditional, open, high-speed discharge channel that changes with the rudder angle into a nearly closed or confined space with a very small, constant gap in real time. This significantly weakens or even eliminates the conditions that cause clearance cavitation at its source, achieving wide-condition, adaptive, efficient, and stable cavitation suppression. This invention features a reliable, low-cost, and simple structural design, while also exhibiting good compatibility with existing rudder systems. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a semi-suspended rudder including a follow-up sealing mechanism;

[0019] Figure 2 It is a side perspective view of a semi-suspended rudder including a follow-up sealing mechanism;

[0020] Figure 3 This is a front perspective view of a semi-suspended rudder including a follow-up sealing mechanism;

[0021] Figure 4 yes Figure 2 BB section view;

[0022] Figure 5 yes Figure 2 Partial schematic diagram of area A in the middle;

[0023] Figure 6 yes Figure 2 Enlarged view of area A in the middle;

[0024] Figure 7 It is a cross-sectional view of a follow-up seal with an arc-shaped positioning shaft hole;

[0025] Figure 8 It is a cross-sectional view of a follow-up seal with multiple positioning axes;

[0026] Figure 9 This is a cavitation test diagram of a conventional semi-suspended rudder (left) and a semi-suspended rudder with a follow-up sealing mechanism at a rudder angle of 0° under the same operating conditions.

[0027] Figure 10 This is a cavitation test diagram of a conventional semi-suspended rudder (left) and a semi-suspended rudder with a follow-up sealing mechanism at a rudder angle of 5° under the same operating conditions.

[0028] Figure 11 This is a cavitation test diagram of a conventional semi-suspended rudder (left) and a semi-suspended rudder with a follow-up sealing mechanism at a rudder angle of 10° under the same operating conditions. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0030] To address the cavitation problem in the gap between the semi-suspended rudder arm and the rudder blade 3, traditional designs, in order to avoid motion interference, can only leave the gap open, completely lacking an effective sealing method. This invention innovatively proposes a follow-up sealing mechanism based on the rudder blade 3. Its core innovation lies in directly embedding the entire sealing unit within the dynamically moving rudder blade 3 body. When the rudder blade 3 rotates, the mechanism utilizes its relative motion with the stationary rudder arm to drive the sealing element to adaptively conform to the protruding outer surface of the rudder arm and the concave inner wall of the rudder blade 3, thereby achieving active sealing of the dynamic gap. This design fundamentally changes the technical approach to solving this problem, transforming passive gap acceptance into active dynamic sealing.

[0031] Specifically, the sliding rod follow-up sealing mechanism mainly includes the following core components, and its detailed structure, working principle and significant advantages are as follows:

[0032] (I) Detailed Composition

[0033] The implementation location of this invention is precisely defined in the mechanical engagement area between the rudder blade 3 and the rudder arm. The rudder blade 3 has a structure recessed towards the trailing edge (hereinafter referred to as "rudder blade recess 3a") in its middle, while the rudder arm has a columnar or shaft-like structure protruding towards the trailing edge of the rudder blade 3 and engaging with it (hereinafter referred to as "rudder arm pivot"). The two are hinged together by a vertical rudder pin. Between the inner wall of the rudder blade recess 3a and the outer wall of the rudder arm pivot, there exists an annular working gap surrounding the rudder pin. This mechanism is installed within this gap, specifically configured as follows... Figures 1-3 As shown, it includes two sealing assemblies disposed on the left and right sides of the rudder blade bearing socket 3a; the sealing assembly includes: a rigid central shaft (1) with both ends connected to the inner walls of the upper and lower sides of the rudder blade bearing socket 3a, and a roller (2) sleeved on the rigid central shaft (1), the diameter of the roller (2) being matched with the distance between the inner wall of the rudder blade bearing socket 3a and the rudder arm.

[0034] like Figure 4 , Figure 5 As shown, the core load-bearing component of this invention is a rigid central shaft. A key installation feature of this shaft is that its two ends are directly or via high-strength connecting members fixed to the inner walls of the left and right sides of the rudder blade bearing socket 3a. The installation position is symmetrical about the longitudinal section of the rudder, and the axis of the central shaft is parallel to the rotation axis of the rudder blade 3.

[0035] like Figure 6 The rigid central shaft 1 shown can be regarded as an inherent extension of the rudder blade 3 structure. Its spatial position is completely determined by the attitude of the rudder blade 3 and rotates synchronously with the rotation of the rudder blade 3.

[0036] like Figure 7 , Figure 8 As shown, as an optional improvement, the inner walls of the upper and lower sides of the rudder bearing socket are provided with arc-shaped positioning shaft holes (1b), and the upper and lower ends of the two rigid central shafts (1) are respectively inserted into the arc-shaped positioning shaft holes and located at both ends of the arc-shaped positioning shaft holes (1b); it also includes elastic elements provided in the arc-shaped positioning shaft holes (1b) for supporting the two ends of the rigid central shafts (1) or multiple roller structures, thereby enhancing the area rejection capability, or for better maintaining the cleanliness of the contact area in specific waters with many impurities.

[0037] In practice, the shaft is made of materials such as martensitic stainless steel or nickel-aluminum bronze, which have high strength, high corrosion resistance and good cavitation resistance, and is forged or precision machined as a whole. Its diameter must be such that the bending deformation under the maximum fluid load is negligible.

[0038] Roller 2, as a functional component that directly interacts with the stationary boundary, is concentrically mounted outside the central shaft via the aforementioned bearings. The inner bore of the roller is fixed to the outer ring of the bearing, and its outer cylindrical surface forms the working surface that creates a dynamic sealing interface with the outer surface of the stationary rudder arm pivot.

[0039] It is self-evident that the axial length of the drum must cover all paths that may be exposed when the rudder blade rotates at its full rudder angle. The drum is typically made of cavitation-resistant and wear-resistant copper alloy or surface-hardened stainless steel, and its outer surface may be coated with a low-friction, wear-resistant coating to optimize performance.

[0040] A set of high-precision bearings is installed between the inner bores at both ends of the roller and the rigid shaft. These bearings are key components ensuring the core function of the mechanism, ensuring that the roller's rotational motion is independent of the central shaft's rotation. The inner ring of the bearing forms a fixed fit with the central shaft, while its outer ring supports and positions the roller. The bearings must possess the characteristic of stable operation in seawater environments or under long-term lubrication conditions, specifically exhibiting extremely low starting and running frictional torque, high radial load capacity, and excellent corrosion resistance. In terms of material and configuration selection, self-lubricating sliding bearings with engineering plastic substrates, such as PTFE composite bearings, or corrosion-resistant deep groove ball bearings equipped with special sealing structures, are ideal implementation options. This bearing configuration ensures that the roller can achieve free rotational motion with minimal resistance relative to the central shaft, i.e., relative to the rotating rudder blade 3.

[0041] On the outer side of each bearing, that is, at a position immediately adjacent to the upper and lower end faces of the roller, a set of sealing knots is arranged. The function of these sealing knots is to achieve bidirectional isolation and protection: the outer main seal is used to prevent external seawater, suspended sediment, marine organisms and other pollutants from entering the bearing cavity axially; the inner negative seal is used to prevent the bearing lubricating medium from leaking outward and to limit the crosstalk of fluids between different cavities.

[0042] (II) Working Principle

[0043] The working principle of the slide rod follow-up sealing mechanism described in this invention is a passive adaptive process based on contact sealing and hydrodynamic drive response. Its core lies in the fact that the roller, as a floating sealing body, has its motion state entirely determined by its surrounding hydrodynamic environment and contact friction, thereby achieving real-time sealing of dynamic gaps.

[0044] When the ship is sailing straight and the rudder blade 3 is in the zero position, the outer cylindrical surface of the roller of the sliding rod follow-up sealing mechanism, under the designed assembly state without external load intervention, simultaneously maintains contact with the inner wall of the rudder blade bearing socket 3a and the outer wall of the rudder arm pivot, thus forming a complete static mechanical seal interface. Under this condition, the flow field in the gap region is stable, the fluid load acting on the roller is small, and the torque generated is insufficient to overcome the inherent static friction resistance torque within the system. Therefore, the roller remains stationary relative to the central axis.

[0045] When steering, taking a right turn as an example, the central axis fixed to the rudder blade 3 rotates synchronously to the right. Since the outer surface of the roller is simultaneously in contact with and constrained by the rudder blade bearing 3a and the rudder arm pivot, its motion is determined by the mechanical balance of these two contact points. Driven by contact friction, the roller will rotate around its own axis, generating a rotational motion coordinated with the direction of rotation of the rudder blade 3. This transforms the relative motion between the roller and the inner wall of the rudder blade bearing 3a, and the relative motion between the roller and the outer wall of the rudder arm pivot, from harmful sliding friction into low-resistance rolling friction or a composite motion with minimal slip.

[0046] Once a stable rudder angle is reached and maintained, the flow field stabilizes. If the steady-state fluid force is still greater than the dynamic friction of the system, the drum will maintain a corresponding constant low-speed rotation; if the steady-state fluid force decreases to an insufficient level to overcome the dynamic friction, the drum's rotation will gradually stop, and it will continue to maintain a static seal by relying on the contact pressure of its surface. Whether the drum is rotating slowly or stationary, its physical structure has occupied and sealed most of the fluid passage.

[0047] When the rudder angle changes, the geometry and hydrodynamic environment of the gap region change accordingly, leading to a significant alteration in the fluid load acting on the drum. This changing fluid load, through fluid-structure interaction, generates a new driving torque on the drum. When this torque exceeds the system's current static frictional resistance torque, it drives the drum to undergo adaptive rotation around its central axis until it reaches a new dynamic or static equilibrium. This process is entirely passively driven by the interaction between the fluid and the structure, achieving a sealing mechanism that adaptively adjusts the mechanism's state according to changes in flow conditions.

[0048] like Figures 9-11 As shown, the test diagrams show the cavitation results of a conventional semi-suspended rudder (left) and a semi-suspended rudder with a follow-up sealing mechanism at rudder angles of 0°, 5°, and 10° under the same operating conditions. It can be seen that at different rudder angles, the cavitation degree of the semi-suspended rudder with a follow-up sealing mechanism of this application is significantly lower than that of the conventional semi-suspended rudder, which can produce intuitive and effective cavitation improvement.

[0049] This invention offers several significant advantages. Compared to traditional passive optimization schemes, this invention achieves a fundamental improvement in technical principles by introducing an adaptive follow-up sealing mechanism. This mechanism can transform dynamically changing gaps into a controlled sealing interface in real time, thereby suppressing the conditions for gap cavitation at its source.

[0050] In terms of performance, this mechanism demonstrates outstanding adaptability to all operating conditions. Its working mechanism is entirely driven by the interaction between rudder angle changes and the hydrodynamic environment, representing an autonomous physical response. Therefore, its effectiveness is unaffected by changes in ship speed, loading status, and attitude, maintaining a stable and consistent sealing effect under all design conditions, completely solving the performance degradation problem of traditional static design methods at non-design points.

[0051] In terms of engineering practicality, this mechanism possesses outstanding reliability. Its core is based on the classic shaft support principle, featuring a simple and clear structure that does not rely on external energy or control systems, achieving a high degree of mechanical autonomy. This purely mechanical, passive design enables it to exhibit extremely high operational stability, long service life, and low maintenance requirements in harsh marine environments.

[0052] This invention also boasts excellent engineering compatibility and ease of implementation. Its modular and symmetrical design allows it to function as a compact functional unit, embedded within the structural gaps of existing rudder systems, with minimal impact on the original system's load-bearing path, weight, and inertia. This enables its easy integration into new designs and its application as an efficient retrofit solution to existing vessels.

[0053] Finally, 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 the scope of protection of the present invention. 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 essence and scope of the technical solutions of the present invention.

Claims

1. A follower-type sealing mechanism for suppressing cavitation in the clearance of a semi-suspended rudder, characterized in that, It includes two sealing assemblies disposed on the left and right sides of the rudder blade bearing socket; the sealing assembly includes: a rigid central shaft (1) with both ends connected to the inner walls of the upper and lower sides of the rudder blade bearing socket, and a roller (2) sleeved on the rigid central shaft (1), the diameter of the roller (2) being matched with the distance between the inner wall of the rudder blade bearing socket and the rudder arm.

2. The follow-up sealing mechanism for suppressing cavitation in the semi-suspended rudder clearance according to claim 1, characterized in that, Two positioning shaft holes (1a) are provided on the inner walls of the upper and lower sides of the rudder bearing socket, and the rigid central shaft (1) is inserted into the positioning shaft hole (1a).

3. The follow-up sealing mechanism for suppressing cavitation in the semi-suspended rudder clearance according to claim 1, characterized in that, The upper and lower inner walls of the rudder bearing socket are provided with arc-shaped positioning shaft holes (1b), and the upper and lower ends of the two rigid central shafts (1) are respectively inserted into the arc-shaped positioning shaft holes and located at both ends of the arc-shaped positioning shaft holes (1b); it also includes elastic elements provided in the arc-shaped positioning shaft holes (1b) for supporting both ends of the rigid central shafts (1).

4. The follow-up sealing mechanism for suppressing cavitation in the semi-suspended rudder clearance according to claim 1, characterized in that, It also includes a bearing located between the inner wall of the drum (2) and the rigid central shaft (1).

5. The follow-up sealing mechanism for suppressing cavitation in the semi-suspended rudder clearance according to claim 4, characterized in that, The bearing refers to a self-lubricating sliding bearing made of polytetrafluoroethylene composite material, or a corrosion-resistant deep groove ball bearing equipped with a sealing structure.

6. The follow-up sealing mechanism for suppressing cavitation in the semi-suspended rudder clearance according to claim 4, characterized in that, It also includes a sealing structure located in the contact area between the two ends of the roller (2) and the rigid central shaft (1).

7. The follow-up sealing mechanism for suppressing cavitation in the semi-suspended rudder clearance according to claim 6, characterized in that, The outer side of the sealing structure is sealed to block external seawater or impurities; the inner side is sealed to prevent the bearing lubricating medium from leaking out.

8. The follow-up sealing mechanism for suppressing cavitation in the semi-suspended rudder clearance according to claim 6, characterized in that, The outer side of the sealing structure is close to the inner walls of the upper and lower sides of the rudder bearing socket.

9. The follow-up sealing mechanism for suppressing cavitation in the semi-suspended rudder clearance according to claim 1, characterized in that, The rigid central shaft (1) is made of a high-strength, corrosion-resistant, and cavitation-resistant material.

10. The follow-up sealing mechanism for suppressing cavitation in the semi-suspended rudder clearance according to claim 8, characterized in that, The high-strength, corrosion-resistant, and cavitation-resistant material includes martensitic stainless steel or nickel-aluminum bronze; the roller is made of cavitation-resistant and wear-resistant copper alloy or stainless steel that has undergone surface hardening treatment.

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