The crankshaft is the core rotating component of the engine. Its function is to convert the reciprocating motion of the piston into rotational motion and drive the vehicle's transmission system, generator, compressor, and other accessories through output torque. It withstands cyclically varying gas pressure, inertial forces, and centrifugal forces, requiring high strength, rigidity, wear resistance, and good balance. It is a key component that determines engine performance and lifespan.
Crankshaft Classification
1. By structural form:
- Integral crankshaft: The main journal and connecting rod journal are formed as one piece, with a simple structure and high reliability, suitable for medium- to high-speed diesel engines.
- Built-up crankshaft: Manufactured in segments and then assembled, facilitating maintenance, commonly used in large low-speed diesel engines.
2. By engine type:
- Inline crankshaft (e.g., L-type): The number of connecting rod journals equals the number of cylinders, compact structure, mostly used in passenger cars.
- V-type crankshaft (e.g., V6, V8): The number of connecting rod journals is half the number of cylinders, suitable for high-power engines.
- Horizontally opposed crankshaft: Used in special layout engines (e.g., Porsche Boxer engine), with good balance.
3. By material and process:
- Forged crankshaft: Made of medium carbon steel (45 steel) or alloy steel (40CrMo), with high fatigue strength, used in high-performance engines.
- Cast crankshaft: Made of ductile cast iron (QT700-2), low cost, suitable for medium and small power engines.
Specifications
1. Dimensional parameters:
- Main journal diameter: φ50-φ300mm (increasing with power).
- Connecting rod journal diameter: φ40-φ280mm.
- Length: 0.3-3m (depending on the number and arrangement of cylinders).
2. Materials and performance:
- Hardness: Surface quenching HRC 50-62, core HRC 25-40.
- Fatigue strength: Forged steel ≥600MPa, ductile iron ≥400MPa.
3. Precision requirements:
- Journal roundness ≤0.01mm, coaxiality ≤0.03mm, surface roughness Ra ≤0.8μm.
Design Parameters
1. Mechanical design:
- Bending and torsional strength: Must meet 1.5 times the maximum engine torque safety factor.
- Transition fillet radius: R ≥3mm to reduce stress concentration and avoid fatigue cracks.
2. Dynamic balance:
- Counterweight design offsets centrifugal force, vibration amplitude ≤0.02mm (G6.3 dynamic balance grade).
3. Lubrication and cooling:
- Oil passage layout: Through the main journal and connecting rod journal to ensure high-pressure lubrication.
- Hollow structure: Reduces weight and optimizes heat dissipation.
Application Scope
1. Internal combustion engine field:
- Construction machinery (e.g., excavators), passenger cars, commercial vehicles, ships, generator sets.
2. Special applications:
- Aircraft engines, motorcycles, agricultural machinery (tractors).
3. Industry demands:
- High reliability (e.g., military vehicles), economy (commercial vehicles), high performance (racing engines).
Important Features
1. High strength and fatigue resistance:
- Forging process ensures continuous metal flow lines, surface strengthening improves lifespan.
2. Precision manufacturing:
- CNC grinding and online inspection technology achieve micron-level accuracy.
3. Lightweight design:
- Topology optimization or hollow structure reduces weight and improves fuel efficiency.
4. Modular design and maintainability:
- Built-up design facilitates replacement of worn parts, reducing maintenance costs.
5. Environmental adaptability:
- Surface coatings (e.g., nitriding, hard chrome plating) enhance corrosion resistance.
Process Introduction
1. Blank manufacturing:
- Forging: Hot die forging press forming, optimized metal flow lines.
- Casting: Ductile cast iron air impact molding, high precision, low cost.
2. Heat treatment:
- Quenching and tempering: Quenching plus high-temperature tempering to optimize strength and toughness.
- Surface induction hardening: Medium-frequency quenching forms a hardened layer (depth 1.5-3mm).
3. Machining process:
- External milling: CNC disc milling cutter intermittent cutting to improve efficiency.
- Tracking grinding: CNC coordinated grinding of main and connecting rod journals completed in one setup.
4. Strengthening technology:
- Rounded corner rolling: Roller pressing of rounded corners, lifespan increased by 120%-230%.
- Shot peening strengthening: Surface compressive stress layer enhances fatigue resistance.
5. Quality inspection:
- Ultrasonic flaw detection + magnetic particle inspection to check for cracks, dynamic balancing test to verify vibration.
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