CRANKSHAFT

CRANKSHAFT

CRANKSHAFT OPERATING CONDITIONS Variable forces and moments Variable forces and moments Alternating stresses (due to gas and inertia forces) Alternating stresses (due to gas and inertia forces)

CRANKSHAFT DIMENSIONS DEPEND ON 1.The number of main and crankpin bearings 2.The design of the cylinder block » separate cylinders or cylinder blocks » wet or dry liners

CRANKSHAFT OVERALL DIMENSIONS DIMENSIONS DEPEND ON 3.The design of the cylinder heads » common head for all cylinders » separate heads for 2 or 3 cylinders 4.The way of joining the connecting rods 5.The cranshaft material and method of manufacture (steel die-forged or cast- iron)

Ratios of L cen /D Design of Engine Carburettor Diesel In-Line with dry liners, crankshaft main sliding bearings every two main sliding bearings every two cylinders (double-span shaft) cylinders (double-span shaft) In-Line (single-span crankshaft) V-type with in-line arrngement of connecting rods on crankpin of connecting rods on crankpin With main roller bearings

COUNTERWEIGHTS THE MAIN BEARINGS IN HIGH SPEED. MULTICYLINDER ENGINES ARE RELIEVED BY MEANS OF COUNTERWEIGHTS. THE MAIN BEARINGS IN HIGH SPEED. MULTICYLINDER ENGINES ARE RELIEVED BY MEANS OF COUNTERWEIGHTS. THE USE OF COUNTERWEIGHS WILL INCREASE THE MOMENT OF INERTIA OF CRANK MASSES. THE USE OF COUNTERWEIGHS WILL INCREASE THE MOMENT OF INERTIA OF CRANK MASSES. THE NATURAL FREQUENCY OF THE CRANKSHAFT WILL BE REDUCED. THE NATURAL FREQUENCY OF THE CRANKSHAFT WILL BE REDUCED. THE MASS OF THE COUNTERWEIGHTS REACHES % OF THE TOTAL MASS OF THE REVOLVING PARTS THE MASS OF THE COUNTERWEIGHTS REACHES % OF THE TOTAL MASS OF THE REVOLVING PARTS COUNTERWEIGHTS SHOULD NEVER BE THICKER THEN THE WEB SO AS NOT TO REMOVE THE FORMER WHEN THE JOURNALS ARE REGROUND IN SERVICE. COUNTERWEIGHTS SHOULD NEVER BE THICKER THEN THE WEB SO AS NOT TO REMOVE THE FORMER WHEN THE JOURNALS ARE REGROUND IN SERVICE.

OPERATIONAL FACTORS THE CRANKSHAFT MUST EASILY MOVE AXIALLY TO ALLOW FOR ITS FREE THERMAL EXPANSION WITH RESPECT TO THE CRANKCASE. THE CRANKSHAFT MUST EASILY MOVE AXIALLY TO ALLOW FOR ITS FREE THERMAL EXPANSION WITH RESPECT TO THE CRANKCASE. AXIAL FIXATION IS DONE BY THRUST RINGS. AXIAL FIXATION IS DONE BY THRUST RINGS. TO INCREASE THE FATIGUE STRENGTH THE CRANKSHAFT IS MECHANICALLY AND THERMALLY TREATED. TO INCREASE THE FATIGUE STRENGTH THE CRANKSHAFT IS MECHANICALLY AND THERMALLY TREATED. DECREASING JOURNAL BEARING WIDTH AND INCREASING THE WEB THICKNESS IS A NEW TREND FOR INCREASING THE STIFFNESS OF CRANKSHAFTS. DECREASING JOURNAL BEARING WIDTH AND INCREASING THE WEB THICKNESS IS A NEW TREND FOR INCREASING THE STIFFNESS OF CRANKSHAFTS.

CRANSHAFT MATERIALS NITRALLOY STEEL, SURFACE HARDENED BY NITRIDING. NITRALLOY STEEL, SURFACE HARDENED BY NITRIDING. A HIGH-CARBON OR ALLOY STEEL SURFACE- HARDENED BY FLAME OR INDUCTION HARDENING. A HIGH-CARBON OR ALLOY STEEL SURFACE- HARDENED BY FLAME OR INDUCTION HARDENING. A HIGH-CARBON OR ALLOY STEEL, HEAT TREATED BUT NOT SURFACE-HARDENED A HIGH-CARBON OR ALLOY STEEL, HEAT TREATED BUT NOT SURFACE-HARDENED CAST IRON CAST IRON

CAST IRON CRANKSHAFT

STRENGTH ANALYSIS OF CRANKSHAFTS ACTING FORCES EXTERNAL FORCES AND MOMENTS INDUCED BY THEEXTERNAL FORCES AND MOMENTS INDUCED BY THE – FORCES OF GAS PRESSURE – INERTIA OF THE MOVING MASSES TORSIONAL AND BENDING VIBRATIONS TORSIONAL AND BENDING VIBRATIONSFAILURE THE STATISTICS OF DEFECTS SHOWS THAT THE CRANKSHAFTS USUALLY FAIL OWING TO FATIGUE CAUSED BY ALTERNATING BENDING AND TORSIONAL STRESSES

CRANKSHAFT

ANALYSIS OF A FULLY SUPPORTED CRANKSHAFT

BENDING STRESS IN CRANK PIN BENDING STRESS

BENDING STRESS IN JOURNAL BENDING STRESS

BENDING STRESS FOR CRANK WEB BENDING STRESS