How Connecting Rod Bearings Work-A More Detailed Look At How These Bearings Transfer Power From the Pistons to the Crankshaft

Connecting rod bearings play a crucial role in the operation of internal combustion engines. Situated between the connecting rod and the engine’s crankshaft, these bearings help transfer the reciprocating motion of the pistons into the rotary motion that powers the crankshaft. The precision-engineered bearings must withstand tremendous loads and temperatures while minimizing friction. In this article, we take a more in-depth look at the function of connecting rod bearings and how they are designed and manufactured to meet the demanding conditions inside a modern engine.

Connecting Rod Bearing Basics

Here is an expanded introduction covering the basics of connecting rod bearings:

Connecting rod bearings are semi-circular pieces made of a steel or aluminum alloy backing lined with a layer of babbitt or copper lead alloy. They feature grooves to carry oil for lubrication and are precision-machined to fit with tight tolerances.

Location- Connecting rods are located between the piston wrist pin at the top end and the crankshaft journal on the bottom end, transferring power and motion between the two components. The bearings are fitted into the rod and end cap to surround the crank journal.

Purpose- The main job of connecting rod bearings is to smoothly transfer the reciprocating motion of the pistons into the rotating motion of the crankshaft while also withstanding tremendous pressure and heat. They must maintain a thin oil film along the shaft journals to separate surfaces and prevent metal-to-metal contact to reduce friction and prevent rapid wear or failure. Proper lubrication keeps friction low even with extremely heavy loads during combustion.

How Connecting Rod Bearings Transfer Power

The combustion of the air-fuel mixture in the cylinder applies downward pressure on the piston crown, causing the piston to move linearly down the bore during the power stroke. This vertical motion applies lateral force to the side of the connecting rod, bending the rod along its axis.

The connecting rod transmits this reciprocating energy to the crankshaft throw it is attached to, pushing the journal around in a circular path as the rod moves with the piston. This is where the connecting rod bearings play a pivotal role.

The thin layer of babbitt alloy lining of the bearings allows the journal to smoothly ride on a thin cushion of oil, greatly reducing metal-on-metal friction. Tight tolerances between the crank diameter and the bearing ensure stability with minimal play. The horseshoe shape of the bearing shells converges pressure evenly across the surface area of the journal.

As combustion forces alternately push and pull on the connecting rods, the bearings transfer this energy into the rotational motion of the crankshaft, which can then be used to drive other components. Good connecting rod bearings minimize losses due to friction while keeping wear to a minimum through proper lubrication. Their effectiveness is critical to efficient engine operation.

Dealing with Stress and Wear

To withstand thousands of cycles per minute under intense pressure and heat, connecting rod bearings must be extremely durable and resistant to fatigue. During combustion, they may experience compressive loads exceeding 20,000 psi. Additionally, inertial forces from the rapid changes of direction at the bottom and top dead centers apply bending stresses to the rods.

The thin oil film prevents the scrubbing away of the softer bearing alloy by the steel or cast iron crankshaft journals. But over time, heat and pressure can deform the babbitt surface layer, wearing down the interface between surfaces. High combustion pressures can also push bearing caps out of alignment, concentrating loads unevenly.

Manufacturing bearings within precise roundness and surface finish specifications provide stability with a consistent gap for oil passage. Proper prelubrication prevents dry starts, which rapidly wear surfaces. High-quality oil filters ensure contaminants are captured before they reach the bearings. Maintenance at normal engine operating temperatures gives the oil film the best viscosity under load.

The combination of using high-strength alloy backing, keeping tight tolerances, effective lubrication systems, and smooth, round journal surfaces enables connecting rod bearings to reliably endure many thousands of engine cycles without failure. However extreme stresses can still lead to wiped bearings or thrown rods, which require rebuilding damaged components.

Recent Advancements and Improvements

A. New bearing materials and coatings- Engine builders are now using improved copper beryllium alloys or applying advanced overlays like silicon graphite to enable higher load capacity and better embedability into the bearing surface. Some coatings reduce friction while also resisting corrosion.

B. Improved manufacturing processes and tolerances- Tighter quality controls during machining, grinding, heat treating, and assembly allow bearings to be made with less variability in the roundness and surface finish of mating parts. Precision tolerances prevent unwanted looseness under load or binding when cold.

C. Bearing innovations still being researched- Engineers continue studying new babbitt compositions with ceramic microparticles and reduced levels of lead and copper. Bearings with grooves, holes, or surface patterns that retain additional oil are also being tested. Dynamically adaptive designs that flex under pressure to optimize clearances are another emerging concept still under development.

The continuing evolution of the science behind connecting rod bearings enables them to reliably sustain ever-greater demands from more powerful and efficient engines. By incrementally improving their strength, consistency, lubrication, and precision, engine builders equip bearings to thrive under extreme stresses.

Conclusion

Connecting rod bearings play an integral yet unsung role in managing the intense forces inside combustion engines to smoothly transfer power to the crankshaft. As described in this MPA Power project, ongoing advances in bearing technology and precision manufacturing enable these components to withstand tremendous stresses and temperatures. The operation and longevity of high-performance engines depends on the quality of materials and processes applied to critical bearings. By bringing together durable alloys, fine tolerances, and effective lubrication, connecting rod bearings exemplify essential fastener solutions from MPA Power Project. As engine builders continue pushing limits, our bearings form a strong link between pistons and crankshafts.