Improvement of fastening connection of three-section type connecting rod of medium-speed diesel engine

Abstract

A fixed connection structure of a three-section type connecting rod of a medium-speed diesel engine comprises a connecting rod body, a connecting rod upper cover and a connecting rod lower cover, the connecting rod body and the connecting rod upper cover are connected through a connecting rod short stud and a nut, and the connecting rod upper cover and the connecting rod lower cover are connected through a connecting rod long stud and a nut. Reliable cooperation of the connecting rod threaded fastener bearing fatigue and impact loads is improved by optimizing the thread tolerance, the thread root radius and the stud outer diameter requirements of the connecting rod upper cover and the connecting rod short stud. By means of precise thread tolerance fit and optimized tooth bottom arc radius design, fatigue strength and impact resistance of threaded connection are remarkably improved, the problem that traditional connecting rod threaded connection is prone to loosening and failure is solved, and the connecting rod is suitable for the high-load working condition of a high-power medium-speed diesel engine.

Description

Technical Field

[0001] This utility model relates to the field of marine diesel engine technology, and in particular to the connection of a three-section connecting rod assembly for a medium-speed diesel engine. Background Technology

[0002] As a compression-ignition internal combustion engine, the diesel engine's working cycle includes four strokes: intake, compression, combustion-expansion, and exhaust. Among these, the connecting rod, as a key moving component, plays a crucial role in transmitting the piston's thrust to the crankshaft. The performance of the connecting rod directly affects the diesel engine's operating efficiency and reliability.

[0003] Three-section connecting rods are widely used in high-power medium-speed diesel engines due to their simple structure and ease of installation and maintenance. Typical four-stroke medium-speed diesel engines (such as those designed by the French Association for Thermal Engines) usually employ a parallel connecting rod layout, where two connecting rods are mounted side-by-side on the same crankpin, each connecting to a different piston bank. While this design is compact and efficient, it places higher demands on the connection strength of the connecting rods.

[0004] Traditional three-section connecting rods consist of a connecting rod body, an upper connecting rod cap, and a lower connecting rod cap, connected by studs and nuts. However, in actual operation, the threaded connections of the connecting rod often experience fatigue failure due to alternating and impact loads, leading to loosening or even breakage of the threads, seriously affecting the safety and service life of the diesel engine. The reliability issue of threaded connections is particularly prominent under high-load conditions.

[0005] Currently, industry optimization of connecting rod threaded connections mainly focuses on material selection and processing technology, but research on optimizing details such as thread tolerance fit and root radius is limited. Existing technologies exhibit relatively lenient thread tolerance design and insufficient attention to the root radius, leading to significant stress concentration at the threaded connection and reduced fatigue life. Utility Model Content

[0006] The purpose of this invention is to solve the problem of high-reliability connection of the three-section connecting rod of the diesel engine, and to ensure the safety of the diesel engine moving unit and the diesel engine.

[0007] An improvement to the fastening connection of a three-section connecting rod for a medium-speed diesel engine includes optimized thread design improvements for the connecting rod cap, the long connecting rod stud, and the connecting rod end stud.

[0008] To achieve the above objectives, the technical solution of this utility model is as follows:

[0009] A fixed connection structure for a three-section connecting rod of a medium-speed diesel engine, characterized in that it includes:

[0010] The main body of the connecting rod consists of the connecting rod body (4), the upper connecting rod cover (1), and the lower connecting rod cover (5).

[0011] The connecting rod short stud (2) and matching nut connect the connecting rod body (4) and the connecting rod cover (1);

[0012] The connecting rod long stud (3) and matching nut connect the upper cover (1) and the lower cover (5) of the connecting rod;

[0013] The small end of the connecting rod cover (1) is provided with an internal thread that mates with the short stud (2) of the connecting rod, and the large end of the connecting rod cover (1) is provided with an internal thread that mates with the long stud (3) of the connecting rod.

[0014] The structure is suitable for medium-speed diesel engines with a parallel connecting rod layout, where two of the three-section connecting rods are mounted on the same crank pin.

[0015] The connecting rod top cover is made of CrMo4 series vacuum degassed chromium-molybdenum alloy steel, and its upper and lower surfaces are in contact with the connecting rod body and the connecting rod bottom cover, respectively.

[0016] The connecting rod cap serves as a carrier for the various internal threads of the connecting rod long stud and connecting rod short stud.

[0017] The thread connecting the connecting rod cap and the connecting rod body is M48x3. This internal thread is obtained by machining. In order to achieve a better fit with the stud, the thread is optimized and the tolerance fit is increased. The optimized version is M48*3-6H, and the radius of the thread root arc is machined to R0.4 (0, -0.03).

[0018] The thread connecting the upper and lower connecting rod caps is M56x4. This internal thread is obtained through machining. In order to achieve a better fit with the studs, the thread connecting the lower connecting rod cap is optimized to M56x4, and the tolerance fit is increased to M56x4-6H. The radius of the thread root arc is machined to R0.5 (+0.08, 0).

[0019] The connecting rod short stud, which connects the connecting rod cap to the connecting rod body, is a forging with rolled threads at both ends. The external thread is M48x3, but to increase the tolerance requirement, it was optimized to M48x3-4g. The external thread was then ground to a diameter that meets the specified tolerance. (-0.698, -0.934).

[0020] The connecting rod stud connecting the upper and lower connecting rod caps is a forging with rolled threads at both ends. The thread used on the upper connecting rod cap is M56x4. To increase the tolerance, it was optimized to M56*4-4g, and the external threads were ground to a specific diameter. (-0.926, -1.2).

[0021] Compared with the prior art, the beneficial effects of this utility model are as follows:

[0022] By optimizing the tolerance of the inner thread of the connecting rod cover to grade 6H and the external thread of the stud to grade 4g, and strictly controlling the grinding dimensions of the outer diameter, the thread fit clearance is precisely controlled within the range of 0.05-0.08mm, which significantly improves the tightness and stability of the threaded connection and effectively prevents loosening.

[0023] The optimized root radius design (R0.4 and R0.5) effectively reduces stress concentration at the thread root, increasing fatigue life by more than 40%, and is particularly suitable for high-frequency alternating load conditions of diesel engines.

[0024] By using CrMo4 series vacuum degassing chromium-molybdenum alloy steel, combined with rolling thread technology and precision grinding, the impact load resistance of the threaded parts is increased by 35%, enabling them to withstand the severe vibrations and impacts during diesel engine operation. Attached Figure Description

[0025] Figure 1 This is the overall installation diagram of the three-section connecting rod.

[0026] Figure 2 It is the connection between the connecting rod cover and the connecting rod body.

[0027] Figure 3 It is the connection between the upper cover and the lower cover of the connecting rod.

[0028] Figure 4 Thread optimization diagram of connecting rod cover 1

[0029] Figure 5 Thread optimization diagram for connecting rod short stud 2

[0030] Figure 6 Optimization diagram of connecting rod long stud 3 threads

[0031] In the diagram: 1-Connecting rod upper cover, 2-Connecting rod short stud, 3-Connecting rod long stud, 4-Connecting rod body, 5-Connecting rod lower cover, 6-Nut one, 7-Nut two. Detailed Implementation

[0032] To enable those skilled in the art to better understand and implement this utility model, the specific embodiments of this utility model are described in detail below with reference to the accompanying drawings. The embodiments of this utility model can be implemented in many different forms and should not be construed as limited to the embodiments described herein.

[0033] like Figure 1 As shown, the three-section connecting rod mainly consists of a connecting rod body 4, a connecting rod upper cover 1, and a connecting rod lower cover 5. The connecting rod body 4 and the connecting rod upper cover 1 are connected by a connecting rod short stud 2 and a nut 6, while the connecting rod upper cover 1 and the connecting rod lower cover 5 are connected by a connecting rod long stud 3 and a nut 7. This three-section structure facilitates installation and maintenance, and is particularly suitable for high-power, medium-speed diesel engines.

[0034] The connecting rod short stud 2 is screwed into the small end threaded hole of the connecting rod upper cover 1. The thread of the connecting rod short stud 2 is a rolled external thread with an optimized value of M48x3-4g, and the external thread has been ground. The thread of the connecting rod upper cover 1 that it mates with is M48x3-6H, and the root radius of its internal thread is R0.4 (0, -0.03). This allows the external thread of the connecting rod short stud 2 and the internal thread of the connecting rod upper cover 2 to have a high-strength fit, meeting the high-strength use conditions of the three-section connecting rod.

[0035] The connecting rod long stud 3 is screwed into the large end threaded hole of the connecting rod upper cover 1. The thread of the connecting rod long stud 3 is a rolled external thread with a design value of M56x4-4g, and the external thread has been ground. The thread of the connecting rod upper cover 1 that it mates with is M56x4-6H, and the root radius of its internal thread is R0.5 (+0.08,0). This allows the external thread of the long stud 3 to have a high-strength fit with the internal thread of the connecting rod upper cover 1, which meets the high-strength use conditions of the three-section connecting rod.

[0036] Tests have shown that the three-section connecting rod connection method meets all the requirements for connecting rod use, increasing the fatigue life of the threaded connection by more than 40% and the impact load resistance by 35%. After running for 5,000 hours under rated conditions, the thread fit still maintains a good condition, effectively solving the problem of thread loosening that is prone to occur in traditional structures.

[0037] The above description is only a preferred embodiment of the present utility model. Those skilled in the art can make several improvements and modifications without departing from the principle of the present utility model, and these improvements and modifications should also be considered within the protection scope of the present utility model.

Claims

1. An improvement in the secure connection of a three-piece connecting rod of a medium speed diesel engine, characterised in that, Comprise: Connecting rod body (4), connecting rod upper cover (1) and connecting rod lower cover (5) make up connecting rod main body Connecting rod short stud (2) and matched nut connecting connecting rod body (4) and connecting rod upper cover (1); Connecting rod long stud (3) and matched nut connecting connecting rod upper cover (1) and connecting rod lower cover (5); Wherein, the small end of the connecting rod upper cover (1) is provided with internal thread matched with the connecting rod short stud (2), and the large end of the connecting rod upper cover (1) is provided with internal thread matched with the connecting rod long stud (3).

2. The improvement in the fastening connection of a three-piece connecting rod for medium speed diesel engines according to claim 1, characterized in that The internal thread of the small end of the connecting rod upper cover (1) is M48x3-6H, and the tooth bottom arc radius is R0.4(0,-0.03).

3. The improvement in the fastening connection of a three-piece connecting rod for medium speed diesel engines according to claim 1, characterized in that The internal thread of the large end of the connecting rod upper cover (1) is M56x4-6H, and the tooth bottom arc radius is R0.5(+0.08,0).

4. The improvement of the fastening connection of a three-piece connecting rod of a medium speed diesel engine according to claim 1, characterized in that The external thread of the connecting rod short stud (2) is M48x3-4g, and the outer diameter is controlled at Ø48(-0.698,-0.934) after polishing.

5. The improvement of the fastening connection of a three-piece connecting rod of a medium speed diesel engine according to claim 1, characterized in that The external thread of the connecting rod long stud (3) is M56x4-6H, and the outer diameter is controlled at Ø56R0.5(+0.08,0) after polishing.

6. The improvement of the fastening connection of a three-piece connecting rod of a medium speed diesel engine according to claim 1, characterized in that The structure of the three-section connecting rod is suitable for medium-speed diesel engine with parallel connecting rod layout, and two three-section connecting rods are installed on the same crank pin.

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