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. Through precise thread tolerance fit and optimized tooth bottom arc radius design, the 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] The present invention relates to the technical field of marine diesel engines, and particularly to the connection of a three-piece connecting rod assembly of a medium-speed diesel engine. Background Art

[0002] As a compression-ignition internal combustion engine, the working cycle of a diesel engine includes four strokes: intake, compression, combustion expansion, and exhaust. Among them, the connecting rod, as a key moving part of the diesel engine, undertakes the important function of transmitting the thrust of the piston to the crankshaft. The performance of the connecting rod directly affects the operating efficiency and reliability of the diesel engine.

[0003] The three-piece connecting rod is widely used in high-power medium-speed diesel engines due to its simple structure, convenient installation and maintenance, etc. A typical four-stroke medium-speed diesel engine (such as the model designed by the French Thermal Engine Society) usually adopts a side-by-side connecting rod layout, that is, two connecting rods are installed side by side on the same crankpin and are respectively connected to pistons in different rows. Although this design is compact and efficient, it places higher requirements on the connection strength of the connecting rod.

[0004] The traditional three-piece connecting rod consists of a connecting rod body, a connecting rod upper cover, and a connecting rod lower cover, and is connected by studs and nuts. However, in actual operation, the threaded connection part of the connecting rod often suffers from fatigue failure due to alternating loads and impact loads, resulting in thread loosening or even fracture, seriously affecting the safety and service life of the diesel engine. Especially under high-load working conditions, the reliability problem of the threaded connection is more prominent.

[0005] At present, the optimization of the connecting rod threaded connection in the industry mainly focuses on material selection and processing technology, but there is less research on the optimization of details such as thread tolerance fit and root radius of the thread. In the prior art, the thread tolerance design is relatively loose, and the root radius of the thread is not fully emphasized, resulting in obvious stress concentration at the threaded connection part and reducing the fatigue life of the connection. Summary of the Invention

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

[0007] An improvement in the fastening connection of a three-piece connecting rod of a medium-speed diesel engine includes an optimized improvement in the thread design of the connecting rod upper cover, the connecting rod long stud, and the connecting rod end stud.

[0008] To achieve the above object, the technical solution of the present invention is as follows:

[0009] A fixed connection structure of a three-piece connecting rod of a medium-speed diesel engine, characterized by comprising:

[0010] A connecting rod main body composed of a connecting rod body (4), a connecting rod upper cover (1), and a connecting rod lower cover (5)

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

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

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

[0014] The structure is applicable to medium-speed diesel engines with a parallel connecting rod layout, and two of the said three-piece connecting rods are installed on the same crankpin.

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

[0016] The connecting rod upper cover is the carrier of various internal threads of the long connecting rod stud and the short connecting rod stud.

[0017] The thread for connecting the connecting rod upper cover and the connecting rod body is M48x3. This internal thread is obtained by machining. In order to obtain better fit with various studs, the thread is optimized, the tolerance fit is increased, and it is optimized to M48*3-6H. The root radius of the thread is machined to R0.4(0,-0.03).

[0018] The thread for connecting the connecting rod upper cover and the connecting rod lower cover is M56x4. This internal thread is obtained by machining. In order to obtain better fit with various studs, the thread for connecting the connecting rod lower cover, which is M56x4, is optimized, the tolerance fit is increased, to M56x4-6H. The root radius of the thread is machined to R0.5(+0.08,0);

[0019] The short connecting rod stud for connecting the connecting rod upper cover and the connecting rod body is a forging, and the threads at both ends are rolled threads. The external thread is M48x3. The tolerance requirement is increased, and it is optimized to M48x3-4g, and the external thread is polished so that the outer diameter of the thread is polished to (-0.698, -0.934).

[0020] The long connecting rod stud for connecting the connecting rod upper cover and the connecting rod lower cover is a forging, and the threads at both ends are rolled threads. Among them, the thread for planting on the connecting rod upper cover is M56x4. The tolerance requirement is increased for it, and it is optimized to M56*4-4g, and the external thread is polished so that the outer diameter of the thread is polished to (-0.926, -1.2).

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] By optimizing the internal thread tolerance of the connecting rod upper cover to 6H grade, the external thread of the stud to 4g grade, and strictly controlling the outer diameter grinding size, the thread fit clearance is accurately controlled within the range of 0.05 - 0.08 mm, significantly improving the tightness and stability of the thread connection and effectively preventing loosening.

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

[0024] By using CrMo4 series vacuum degassed chromium molybdenum alloy steel material, combined with the rolling thread process and precision grinding treatment, the impact load resistance of the thread part is increased by 35%, enabling it to withstand the severe vibration and impact during the operation of the diesel engine. Description of the Drawings

[0025] Figure 1 It is the overall installation drawing of the three-piece connecting rod.

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

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

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

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

[0030] Figure 6 Thread optimization diagram of the long stud 3 of the connecting rod

[0031] In the figure: 1 - connecting rod upper cover, 2 - short stud of the connecting rod, 3 - long stud of the connecting rod, 4 - connecting rod body, 5 - connecting rod lower cover, 6 - nut one, 7 - nut two. Detailed Implementation Modes

[0032] In order to enable those skilled in the art to better understand and implement the present invention, the following detailed description of the specific implementation modes of the present invention is provided in conjunction with the drawings. The implementation modes of the present invention can be realized in various different forms and should not be construed as limited to the implementation modes described herein.

[0033] As Figure 1 shown, the three-piece 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 is connected to the connecting rod upper cover 1 through a short stud 2 of the connecting rod and a nut one 6, and the connecting rod upper cover 1 is connected to the connecting rod lower cover 5 through a long stud 3 of the connecting rod and a nut two 7. This three-piece structure is convenient for installation and maintenance and is especially suitable for high-power medium-speed diesel engines.

[0034] The short connecting rod stud 2 is screwed into the small-end threaded hole of the upper connecting rod cover 1. The thread of the short connecting rod stud 2 is a rolled external thread, with an optimized value of M48x3-4g, and the external thread is polished; the thread of the upper connecting rod cover 1 that mates with it is M48x3-6H, and the bottom radius of its internal thread is R0.4(0,-0.03). In this way, the external thread of the short connecting rod stud 2 and the internal thread of the upper connecting rod cover 2 are in high-strength fit, meeting the high-strength use conditions of the three-piece connecting rod.

[0035] The long connecting rod stud 3 is screwed into the large-end threaded hole of the upper connecting rod cover 1. The thread of the long connecting rod stud 3 is a rolled external thread, with a design value of M56x4-4g, and the external thread is polished; the thread of the upper connecting rod cover 1 that mates with it is M56x4-6H, and the bottom radius of its internal thread is R0.5(+0.08,0). In this way, the external thread of the long stud 3 and the internal thread of the upper connecting rod cover 1 are in high-strength fit, meeting the high-strength use conditions of the three-piece connecting rod.

[0036] Tests have shown that the connection method of the three-piece connecting rod meets all the indicators for the use of the connecting rod, increasing the fatigue life of the threaded connection part by more than 40%, enhancing the anti-impact load capacity by 35%. After operating for 5000 hours under rated conditions, the thread fit still remains in good condition, effectively solving the problem of thread loosening that is prone to occur in the traditional structure.

[0037] The above is only the preferred embodiment of the present invention. Without departing from the principle of the present invention, those skilled in the art can also make several improvements and refinements, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A three-section connecting rod fixed connection structure of a medium-speed diesel engine, characterized in that: include: The connecting rod body (4), the connecting rod upper cover (1) and the connecting rod lower cover (5) are composed of a connecting rod body A connecting rod short stud (2) and a matching nut connecting the connecting rod body (4) and the connecting rod upper cover (1); A connecting rod long stud (3) and a matching nut connecting the connecting rod upper cover (1) and the connecting rod lower cover (5); The small end of the connecting rod upper cover (1) is provided with an internal thread that cooperates with the connecting rod short stud (2), and the large end of the connecting rod upper cover (1) is provided with an internal thread that cooperates with the connecting rod long stud (3).

2. The three-section connecting rod fixed connection structure of a medium-speed diesel engine according to claim 1, characterized in that: The internal thread of the small end of the connecting rod upper cover (1) is M48*3-6H, and the radius of the arc of the bottom of the thread is R0.4 (0,-0.03).

3. The three-section connecting rod fixed connection structure of a medium-speed diesel engine 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 radius of the arc at the bottom of the thread is R0.5 (+0.08,0).

4. The three-section connecting rod fixed connection structure of a medium-speed diesel engine according to claim 1, characterized in that: The external thread of the connecting rod short stud (2) is M48*3-4g, and its outer diameter is controlled by grinding.

5. The three-section connecting rod fixed connection structure 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 its outer diameter is controlled by grinding.

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

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