In recent years, both domestic and international passenger car markets have experienced a significant rise in self-owned brands. As gasoline engines continue to evolve, their replacement cycles are becoming shorter, and the performance gap between domestic and global advanced engine technologies is narrowing, with some domestic models even surpassing their foreign counterparts. As a critical component of the engine, the design and development of the cylinder block have become increasingly important.
The cylinder block serves as the skeleton and outer casing of the internal combustion engine, housing most of its major components. Inside, it contains the crankshaft mechanism, while externally, it supports the drive train, including the starter, generator, power steering pump, and air conditioning compressor. The upper part is mounted with the cylinder head assembly, and the lower side connects to the oil pan and oil collector. Additionally, the engine mount bracket is also integrated into the cylinder block, playing a vital role in the combustion chamber, cooling system, and lubrication system.
Due to its function, the cylinder block must have a complex shape, thin walls, and a box-like structure. It needs sufficient strength and rigidity to maintain the geometric shape of the components and ensure proper alignment. Effective cooling is essential to reduce thermal stress and maintain temperature within acceptable limits. Moreover, the overall dimensions should be compact to minimize weight, and all seams must be tightly sealed to prevent water, air, or oil leaks.
**Concept Design**
The design process begins with defining the main structural parameters of the engine, followed by modularizing components based on function or system. The vehicle model and related boundary conditions are determined. To accommodate engine vibrations, there must be a certain clearance between engine parts and front compartment components. Typically, the minimum clearance is 25mm front and rear, 25mm top and bottom, and 19mm left and right.
Based on benchmark engine analysis and thermodynamic software, feasibility studies are conducted to determine key parameters such as cylinder form, number of cylinders, bore, stroke, cylinder spacing, connecting rod length, piston compression height, burst pressure, and more. Parameters like cylinder height, center distance, front and rear surfaces, width, main cover bolts, and cylinder head bolts are then defined. Further analysis determines the cylinder structure (bisector, gantry), material selection (cast iron, cast aluminum, magnesium alloy), casting process (high/low pressure, gravity casting), and the use of cylinder liners and shaft seat inserts.
These identified parameters, structures, materials, and boundary conditions are reflected in the SKL model, serving as a reference for subsequent modeling.
**Layout Design**
After completing the concept design, the layout stage refines the design parameters. This includes:
1. Structural and dimensional design of specific engine components: front and rear end surfaces, intake and exhaust sides, oil sump, connecting rods, and crankshaft.
2. System design related to the cylinder itself, such as the cooling system, lubrication system, timing rail, ventilation system, and attachment systems (starter, transmission, etc.).
3. Consideration of the design reference points, clamping points, machining feasibility, and casting simulation.
The SKL skeleton line is updated accordingly to reflect these inputs.
**Detailed Design Stage**
Engine design is an iterative process, with no clear boundaries between layout and detailed design. These stages focus on parameterization into 3D models using software like PROE or UG. Forward design typically follows casting or die-casting principles, offering advantages like clear structure, easy updates, and improved efficiency. The digital model includes modules like the front end, rear end, intake and exhaust sides, top (with water core and ventilation), and bottom (crankcase core). Main oil passages and inter-cylinder ventilation are integrated into the front and rear modules.
**Water Jacket and Oil Return**
Once the crankcase shape is set, the water jacket is designed, considering bolt placement and adequate cooling. Gasoline engine blocks often use open water jackets. The water jacket height is generally from the first piston ring to the fire surface, with oblique water holes often used between cylinders. A water pump is usually placed at the front to circulate coolant through the cylinder and into the cylinder head.
Oil return and ventilation systems are crucial. Oil return holes allow lubricant from the cylinder head to flow back to the oil pan, while ventilation holes balance pressure in the valve chamber and crankcase.
**Bottom Module and Timing Components**
The crankcase shape is determined based on the link motion trajectory, with at least 5mm clearance. The front and rear modules house the timing drive and transmission, respectively. Sealing bands, bolt arrangements, and structural strength of flanges are considered. The inlet and exhaust side modules focus on support structures, accessory mounting, and rib arrangement.
**Main Bearing Cap**
The main bearing cap withstands forces from the crank-link mechanism. It is typically made of cast iron and undergoes finite element analysis. In aluminum alloy blocks, the cap is embedded in a frame to enhance strength. Crankshaft hole sizing ensures accurate positioning and avoids issues with mixed materials during processing.
Designers must follow strict clearance, wall thickness, flange thickness, boss size, sealing tape width, draft angles, and thread depth guidelines.
**CAE Analysis**
Modern CAE tools are now essential in engine development. Water jacket CFD analysis helps evaluate coolant flow, pressure loss, and heat transfer. These results feed into structural analysis, which considers thermal, assembly, and working loads. This helps assess cooling effectiveness and cylinder bore deformation.
**Test Verification**
Testing is critical to reduce costs and speed up development. Engine bench tests focus on cooling, lubrication, and deformation during prototyping, while tooling tests evaluate reliability and durability. Vehicle tests include high-temperature, high-load, and road trials. If failures occur, design modifications are made iteratively.
**Cylinder Mold Shaping**
After passing tests, the mold is prepared for mass production. This includes OTS approval, PPAP, small batch trials, and SOP implementation.
**Conclusion**
Cylinder block design is a complex system engineering task that requires comprehensive consideration of multiple factors. A holistic application of technical knowledge is essential to achieve optimal performance and reliability.
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