In recent years, both domestic and international passenger car markets have experienced a significant rise in self-owned brands. This growth is driven by the rapid replacement of gasoline engines, as their inherent characteristics lead to shorter lifecycles. The gap between domestic and international engine technologies has been narrowing, with some domestic models even surpassing foreign counterparts. As a critical component of the engine, the cylinder block has become increasingly important in design and development.
The cylinder block serves as the skeleton and outer casing of the internal combustion engine. It houses almost all major engine components, including the crankshaft mechanism inside and various drive systems like the starter, generator, power steering pump, and air conditioning compressor on the outside. The top part is mounted with the cylinder head assembly, while the bottom connects to the oil pan and oil collector. Additionally, engine mount brackets are integrated into the cylinder block, playing a vital role in the combustion chamber, cooling system, and lubrication system.
Due to its functional requirements, 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 integrity of the components and ensure proper fit and alignment. Efficient cooling is essential to reduce thermal stress and maintain optimal temperatures. The overall dimensions should be compact to minimize weight, and all seams must be tightly sealed to prevent leaks of water, air, or oil.
**Concept Design**
The design process begins with defining key engine parameters and modularizing components based on function or system. The vehicle model and boundary conditions are determined, ensuring adequate clearance between engine parts and front compartment components. Typically, minimum clearances are set at 25mm for front and rear, 25mm for top and bottom, and 19mm for left and right.
Based on benchmark engine analysis and thermodynamic performance software, feasibility studies are conducted to determine cylinder form, number of cylinders, bore, stroke, cylinder spacing, connecting rod length, piston compression height, and other thermodynamic parameters. These parameters guide the determination of cylinder height, center distance, end surfaces, width, main cover bolts, and cylinder head bolts. Further analysis defines the cylinder structure (e.g., bisector, gantry), material selection (cast iron, cast aluminum, magnesium alloy), casting processes (high pressure, low pressure, gravity casting), and the use of cylinder liners and shaft seat inserts.
These parameters, along with structural, process, and boundary conditions, are reflected in the SKL model, which serves as a reference for subsequent modeling.
**Layout Design**
After completing the concept design, the layout phase refines key parameters, including:
1. Specific structures and dimensions of the front and rear ends, intake and exhaust sides, oil sump, connecting rods, and crankshaft.
2. Cooling, lubrication, timing, and ventilation systems integrated into the cylinder block, along with attachments such as starters, transmissions, and suspension.
3. Consideration of the cylinder block’s design reference points, clamping points, machining feasibility, and casting simulation.
The SKL skeleton line is updated accordingly.
**Detailed Design Stage**
Engine design is an iterative process with no clear boundaries between layout and detailed design. It involves continuous refinement and parameterization using 3D software like PROE or UG. Forward design typically follows casting or die-casting principles, offering clear structure, easy updates, and improved efficiency. The cylinder digital model includes modules such as the front, rear, intake, exhaust, top, and bottom, with main oil passages and inter-cylinder ventilation integrated into the front and rear modules.
**Water Jacket and Oil Return System**
Once the crankcase shape is determined, the water jacket design is established. It must accommodate cylinder head bolt placement and provide sufficient cooling. Open water jackets are commonly used in high-pressure cast aluminum gasoline engines. The water jacket height is typically from the first piston ring to the fire surface, with oblique water holes often used between cylinders for compactness. A water pump is usually placed at the front end to circulate coolant through the cylinder and into the cylinder head.
Oil return and ventilation holes are essential to return lubricating oil from the cylinder head to the oil pan and balance air pressure in the valve chamber and crankcase.
**Crankcase Shape and Structural Design**
The basic parameters of the cylinder block define the crankcase shape. The inclusion line of the link motion trajectory is crucial for determining the inner wall shape, with a minimum clearance of 5mm. This ensures proper movement of the crankshaft and connecting rod without interference.
**Front and Rear Modules**
The front end of the crankcase houses the timing drive train, while the rear end accommodates the transmission. The front module must consider clearance, seal bands, and bolt arrangements. The rear module focuses on flange strength, rib arrangement, and positioning of the starter and output shaft.
**Inlet and Exhaust Side Modules**
These modules handle the support and extension of the intake and exhaust systems, as well as the placement of accessories like air compressors, boosters, generators, and starter bosses. Structural strength and rib arrangement are also critical in this area.
**Main Bearing Cap**
The main bearing cap supports the crank-link mechanism and requires high mechanical properties. Cast iron is commonly used, with finite element analysis for structural integrity. In aluminum alloy crankcases, the main bearing caps are embedded within a frame to enhance strength.
**Design Principles**
Key design considerations include clearance requirements, wall thickness, flange thickness, process bosses, sealing tape widths, draft angles, and thread connections. These ensure structural integrity, manufacturability, and performance.
**CAE Integration**
Computer-Aided Engineering (CAE) plays a crucial role in modern engine development. Water jacket CFD analysis, temperature field analysis, and structural analysis help evaluate cooling efficiency, deformation, and load distribution, leading to optimized designs.
**Test Verification**
Testing is essential to validate performance and reliability. Engine bench tests focus on cooling, lubrication, and deformation, while tooling tests assess durability and fatigue resistance. Vehicle tests include high-temperature, high-load, and road trials. If failures occur, design modifications are made iteratively.
**Mold Shaping and Production**
Once the cylinder passes testing, mold production is initiated, followed by OTS, PPAP, small batch trials, and SOP implementation for mass production.
**Conclusion**
Cylinder block design is a complex, multidisciplinary task requiring comprehensive consideration of technical, structural, and manufacturing factors. Effective integration of knowledge across disciplines is essential for successful development.
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