Structures of Connecting Rods in Diesel Engines

Connecting rods are key components in diesel engines, which can be categorized into ordinary connecting rods and V-type connecting rods. Each type features unique structural designs tailored to different engine configurations. This article will delve into the specific structures of these two types of connecting rods.

Structure of V-type Connecting Rods in Diesel Engines

For V-type diesel engines, the connecting rods corresponding to the two cylinders on the left and right sides can be divided into the following three forms based on their connection methods:

1.Side-by-side connecting rods: The connecting rods of the corresponding left and right cylinders are mounted on the same crankpin one after another. The connecting rod of one cylinder bank is installed on the neck of the crankshaft, while the connecting rod of the other cylinder bank is connected to the lug pin of the main connecting rod through a cylinder pin.

2.Master-and-slave connecting rods: Among the two connecting rods corresponding to the left and right cylinders, one acts as the master connecting rod, directly installed on the crankpin. The other is the slave connecting rod, which is attached to the master connecting rod through a special pin structure. This design effectively reduces the space occupied by the connecting rod assembly, making it suitable for V-type engines with a narrow included angle between cylinder banks.

3.Fork-type connecting rods: In this structure, the big end of one connecting rod is made into a fork shape, and the big end of the other connecting rod is inserted into the opening of the fork-type connecting rod. The wing plate of the fork-type connecting rod extends to the big end part, forming a fork shape. This design reduces the height of the reshaped connecting rod body, which helps in lowering the overall height of the engine and improving its compactness.

In large-bore and multi-cylinder V-type internal combustion engines, master-and-slave connecting rods and fork-type connecting rods are mainly used due to their better load-bearing capacity and compact structure. In general V-type internal combustion engines, side-by-side connecting rods are mostly adopted because of their simpler structure and lower manufacturing cost.

Structure of Ordinary Connecting Rods in Diesel Engines

An ordinary connecting rod is mainly composed of the following components:

1.Small end of connecting rod: It is usually in the shape of a short circular tube, used to install the piston pin. Generally, a large-radius arc is used to connect smoothly with the rod body to reduce stress concentration at the transition. A wear-resistant thin-wall bushing made of tin bronze or iron-based powder metallurgy is pressed into the small end hole to reduce the wear of the piston pin. To lubricate the mating surface between the bushing and the fully floating piston pin, holes or grooves are drilled or milled on the upper part of the small end of the connecting rod and the bushing to collect the splashed oil mist. For connecting rods with pressure lubrication, an oil passage is drilled in the rod body, through which lubricating oil flows from the crankshaft connecting rod journal to the friction surface of the small end bushing.

2.Connecting rod body: The connecting rod body usually adopts an I-shaped cross-section. Under the condition of the same material and cross-sectional area, the I-shaped cross-section has the largest bending section modulus. Therefore, the connecting rod can achieve maximum structural rigidity and strength with the lightest weight, which is crucial for reducing the inertia force of the connecting rod during engine operation and improving the engine's working efficiency and service life.

3. Big end of connecting rod: The big end of the connecting rod is the part that connects with the crankshaft connecting rod journal and also serves as the bearing part of the connecting rod journal. The big end of the connecting rod is generally divided into two parts by the center of the hole for easy disassembly and assembly. During assembly, the two parts are connected by two or four connecting rod bolts. Since the accuracy requirement of the big end hole is very high, the hole must be processed after the two parts are combined and cut. After the hole processing is completed, a positioning device must be used to fix the relative position between the connecting rod big end cover and the connecting rod big end to prevent misalignment during assembly. In addition, marks should be made on the side surfaces of the big end and the big end cover to avoid misalignment during reassembly.

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