Driveshaft Angular Acceleration

[thomps22]

Hi all, does anyone have a concrete explanation for limiting driveshaft angular acceleration?

I'm assuming that high angular accelerations will lead to premature bearing life in the joint itself due to having to accelerate and decelerate the shaft inertia and the resulting bearing forces will grow with high accels. The larger the inertia, the more conscious you would have to be about max angular acceleration, correct?

The SAE handbook recommends some limits. 1000 rad/s for passcar and 2000 rad/s for large truck. I assume for large truck they mean typically smaller diameter shafts, shorter shafts and therefore less inertia to worry about?

Is there any concern about vibration or is the main concern joint life, or do they go hand in hand (I suspect so).

Thanks in advance.

 

[GMIracing]

quote:
"The SAE handbook recommends some limits. 1000 rad/s for passcar and 2000 rad/s for large truck."

rad/s is the unit for Rotational (angular) Velocity. Acceleration is rad/s^2 and is the rate at which the shaft increases rotational velocity.

For the same input force, more inertia will decrease the rate of rotational acceleration and also decrease your max rotational velocity... i.e. the critical velocity where the centrifugal force on the mass causes catastrophic failure. Additional mass will also make the shaft balancing process more difficult and also increase the effect centerline offset has on the assembly balance.
-Ryan

 

[rmw]

The u-joints-the gadgets that create the angular acceleration of a drive shaft in the first place-have specific limitations and within their safe range the shaft should be OK if designed properly. If you exceed the u-joint angle limits, then start worrying about the driveshaft.

rmw

 

[Tmoose]

"For the same input force, more inertia will decrease the rate of rotational acceleration and also decrease your max rotational velocity... i.e. the critical velocity where the centrifugal force on the mass causes catastrophic failure. "

The speed (rotational velocity) variation (angular acceleration) of a driveshaft operating at an angle with non-CV type joints at each end is a few percent. Not much risk that the shaft will reach the critical speed for an instant.

I think the limit has probably been set empirically, and sets the limit of the ( constantly reversing with frequency = 2X driveshaft rpm) angular acceleration based on noise and vibration issues at .

This section of the SAE manual refers to it as a "disturbance" and declares "automotive .... installations are extremeley sensitive to this type of excitation and to the the disturbance it creates"