Improved Crankshaft Design Reduces Weight and Increases Fuel Economy

Eco-friendliness and comfort (reduced emissions, lower fuel consumption, higher performance) are key objectives for automotive developers. To meet OEM and end consumer requirements, ThyssenKrupp Gerlach collaborates closely with its customers to develop solutions aimed at optimizing crankshaft weight and reducing friction.

Lighter webs

Once the initial design and sizing of the crankshaft is completed, work on optimizing the web geometry can begin. Weight reduction can be achieved by different measures:
• Reducing the web and counterweight surfaces to be machined: it must be ensured that the counterweights are designed in such a way that final balancing can be performed reliably.
• Alternative counterweight design: with optimized design, four counterweights can be enough to balance masses and reduce bending rather than eight.
• Optimizing web shoulder geometry under consideration of process requirements: an optimized design has a positive impact on material flow during forging and improves impression filling. This reduces the amount of material used and also lowers die wear.
• Recessing below the connecting rod bearings: during forging it is ensured that these weight reductions do not impede the material flow.

With reference to a four-cylinder passenger car diesel engine, ThyssenKrupp Gerlach has succeeded in reducing the weight of the unmachined part by 22 percent through optimized web geometry.

Reduced friction

To keep fuel consumption low and optimize vehicle performance, mechanical friction losses on the corresponding engine components must be minimized. ThyssenKrupp Gerlach is cooperating with its customers’ development engineers to exploit the potential for reducing bearing sizes on forged crankshafts.

As the crankshaft bearings are in direct contact with the friction bearings of the connecting rods and the bearing seats, smaller bearings will reduce the contact surfaces and thus lower friction. However, the lower-sized bearings also reduce the strength and stiffness of the crankshaft. These weaknesses can be offset by using alternative materials and production processes. It is also possible to modify web geometry in line with stresses so as to strengthen the crankshaft as a whole.

Whichever optimization approach is taken, it must be ensured that the crankshaft performs its function in the overall cranktrain and that it meets engine criteria in respect of performance, fuel consumption and acoustics.

Current development trends show that forged crankshafts offer the ideal opportunity for reducing bearing sizes due to the outstanding mechanical properties of the material.

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