Harmonic damper
Encyclopedia
A harmonic damper is a device fitted to the free (accessory drive) end of the crankshaft
of an internal combustion engine
. It is essential in engines with long crankshafts (such as straight-8
engines) and is present on most engines as it reduces torsional vibrations that tend to peak at certain speeds.
s will tend to "wind" this spring, which will respond (as a spring-mass system) by unwinding and re-winding in the opposite direction. This will usually be damped out naturally, but at certain crankshaft rotational speeds the impulses from the cylinder firing can be in synchronization with the natural resonant frequency. (Some aircraft engines are restricted from continuous operations at specific RPM to avoid the danger of metal fatigue
causing a break in the crankshaft.) In an automotive engine there is little control over operation in such specific speed bands and furthermore there may be uncomfortable vibrations as the engine is operated through such speeds, even if not a problem for engine durability.
Many small block V8 engines, such as Ford Windsor and Cleveland, Chevrolet small block 400 and big block 454, and certain Chrysler V8s, a portion of the crankshaft system's overall balancing may be provided by an unbalanced damper.
or transmission
, just beyond the cover of the timing chain, gears, or belt, and behind the accessory drive pulley (which may carry one or more V-belts or a single serpentine cog-belt. In older vehicles there will usually be an inscribed timing mark, there for purposes of setting the ignition timing.
Crankshaft
The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation...
of an internal combustion engine
Internal combustion engine
The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...
. It is essential in engines with long crankshafts (such as straight-8
Straight-8
The straight-eight engine or inline-eight engine is an eight-cylinder internal combustion engine with all eight cylinders mounted in a straight line along the crankcase...
engines) and is present on most engines as it reduces torsional vibrations that tend to peak at certain speeds.
Need
Without the presence of a damper a long crankshaft will tend to act as a torsional spring to some extent. Impulses applied to the crankshaft by the connecting rodConnecting rod
In a reciprocating piston engine, the connecting rod or conrod connects the piston to the crank or crankshaft. Together with the crank, they form a simple mechanism that converts linear motion into rotating motion....
s will tend to "wind" this spring, which will respond (as a spring-mass system) by unwinding and re-winding in the opposite direction. This will usually be damped out naturally, but at certain crankshaft rotational speeds the impulses from the cylinder firing can be in synchronization with the natural resonant frequency. (Some aircraft engines are restricted from continuous operations at specific RPM to avoid the danger of metal fatigue
Metal Fatigue
Metal Fatigue , is a futuristic science fiction, real-time strategy computer game developed by Zono Incorporated and published by Psygnosis and TalonSoft .-Plot:...
causing a break in the crankshaft.) In an automotive engine there is little control over operation in such specific speed bands and furthermore there may be uncomfortable vibrations as the engine is operated through such speeds, even if not a problem for engine durability.
Many small block V8 engines, such as Ford Windsor and Cleveland, Chevrolet small block 400 and big block 454, and certain Chrysler V8s, a portion of the crankshaft system's overall balancing may be provided by an unbalanced damper.
Construction
The damper consists of an inner hub affixed usually by a key and keyway to the outer end of the crankshaft. An outer circular mass is attached to the hub by an integral rubber or other elastomeric section. This crankshaft and damper together become (in its torsional response) a spring-mass-damper system. By selection of the damping section material and the size of the outer mass the damper may be made to resist and thus quiet the specific torsional vibrations. These vibrations will not be at the same frequency as originally since additional mass has been added to the resonant system, so the damper must be tuned for the resultant circumstances. The overall appearance is that of a thick disk.Identification
The damper will be fitted at the front of the engine (opposite the clutchClutch
A clutch is a mechanical device which provides for the transmission of power from one component to another...
or transmission
Transmission (mechanics)
A machine consists of a power source and a power transmission system, which provides controlled application of the power. Merriam-Webster defines transmission as: an assembly of parts including the speed-changing gears and the propeller shaft by which the power is transmitted from an engine to a...
, just beyond the cover of the timing chain, gears, or belt, and behind the accessory drive pulley (which may carry one or more V-belts or a single serpentine cog-belt. In older vehicles there will usually be an inscribed timing mark, there for purposes of setting the ignition timing.