Section IV Glossary Of Terms

Resonance -  Resonance is the "natural frequency" of the drive train. This frequency is a result of the combination of the rotational inertias of the transmission, prop shafts, and axles sprung on the torsional springs of the clutch and axle shafts. This resonance will "ring" and cause huge dynamic, oscillatory torques and displacement when the engine and/or U-joints are operating at a speed where their pulses occur at "natural frequency".

U-Joint Working Angle -  The U-joint working angle is the absolute angle between the adjacent shafts at any U-joint in the system (i.e., between the output shaft of the transmission and the adjacent propeller shaft) or between the front axle output shaft and the inter-axle propeller shaft.

U-Joint Working Angle Cancellation -  U-Joint working angle cancellation is the extent to which adjacent working angles are equal. For example, the front axle output and the inter-axle propeller shaft might have a joint working angle of four degrees. The rear axle input and the inter-axle propeller shaft should ideally have the same angle of four degrees.

This would "cancel" the dynamic effect of the front axle output joint angle. This cancellation could either be done by a "broken back" or "parallel" setup. A large amount of "non-cancellation" is a direct cause of driveline pulsation. This is true for all adjacent driveline-working angles Multi-piece propeller shafts have a slightly more complex relation - ship, which is covered in RP 61OA.

Driveline Angularity -  Driveline angularity refers to all joint working angles in the driveline, individually and as a system.

Air Suspension Ride Height -  Air suspension ride height is defined by industry references as the centerline of axle to the bottom of the frame.

Soft Damped Clutches -  Soft damped clutches have torsional spring rates of 350 ft.-lbs. Per degree or less and in some cases hysteresis of greater than 80 ft.-lbs. These are available in 14 inch and larger sizes.

Viscous Driveline Dampers -  Viscous driveline dampers are devices with rotational masses that are coupled to the driveline by means of viscous fluid.

Damping -  Damping is the reduction of destructive dynamic torques at resonance through energy "dissipation". This can be accomplished through friction (hysteresis) or the "molasses" (viscous) action of thick fluids.

Drive train Torsional -  A drive train torsional is any dynamic oscillation in driveline torque or speed. This can be expressed in terms of torque (ft.-lbs.), displacement (degrees), speed (RPM), or acceleration (radians per second squared). Traditionally, the units of measure have been torsional acceleration (radians per second squared).

Half Firing Frequency -  The term half firing frequency refers to engine pulsations that occur at three times the camshaft rotational speed for all 6-cylinder engines.