The engine cylinder block is the framework of the engine, around which all other components are assembled in a manner similar to how a subframe is assembled around a truck frame. The cylinder block houses the engine cylinders and the engine crankcase. North American on-highway medium and heavy-duty diesel engines all use in-line or V-type cylinder configurations, which require a single crankshaft and thus use a monolithic casting for the cylinder block. In all these engines, the cylinder block is made of various cast iron alloys. Although the oil pan may be made of aluminum, composites, or even plastic, due to the forces that diesel engines endure, iron-based alloys are often more suitable for cylinder block material than aluminum-based alloys. Currently, when aluminum alloy cylinder blocks are used, the cylinder liners must be treated with a plasma transferred arc cladding process. Although this situation may change, currently when diesel engines use aluminum alloy cylinder blocks, they are typically used in non-commercial, small-bore applications.
To reduce weight and enhance strength, most engine cylinder blocks have been cast with alloys in recent years, and special processes are often employed, usually in combination with surface cladding technology for the cylinder bores. Figure 9-1 shows the stripped cylinder block used in the MaxxForce 13 engine: this engine adopts a cylinder block structure of compacted graphite iron (CGI) to increase strength and reduce weight.
Figure 9–1 Navistar MaxxForce 13 compacted graphite iron (CGI) cylinder block.
In recent years, in pursuit of lighter, stronger, and more durable engines, the alloying of cylinder blocks has increased. The cylinder block typically needs to withstand the following forces:
Torque twist
Cylinder pressure
Thermal shock
Torque twist occurs when the torsional force of the crankshaft is anchored by the cylinder block. The cylinder block may be subjected to torque twist effects from either the input or output end of the crankshaft. This means that the situation may occur at high cylinder pressure or, conversely, be generated by the transmission system. Excessive cylinder pressure, especially in small engines without cylinder liners, can lead to failure. Thermal shock occurs when a hot cylinder block is suddenly cooled, such as when it is rinsed with cold water in a cleaning bay. Torque twist is more likely to be a factor in the damage of recent lightweight cylinder block models. The following methods are used to control the torque twist of the cylinder block:
Stiffening plates: Bolted to the flange at the bottom of the cylinder block to increase rigidity.
Supporting bolts: Bolts that pass laterally through the cylinder block and are screwed into the main bearing caps.
High section modulus cast oil pan: Bolted to the crankcase flange of the cylinder block and the flywheel housing.