A GOVERNOR FOR TKLIOPHONE DIALS 1281 



tion and the loads imposed by the i)ulsing mechanism result in an 

 average torciue oi 7,500 dyne-cm at the governor. Over the life of a dial 

 this input torcjue at the governor will vary as the dial efficiency varies. 

 Initially the dial mechanism is lubricated and the bearings and gears 

 turn freely. With time and continued operation, the accumulation of 

 dirt and wear products affect the dial so that more torc^ue is needed to 

 dn\-e the mo\-ing parts. This causes a decrease in the remainder toi-(iue 

 going to the gON'ernor. 



Another aspect of torciue riMiuiring consideration is that resulting from 

 forcing of the finger-wheel during run-down. This action can produce 

 torque values at the go\'ernor of the order of 1 10,000 dyne-cm or a tortiue 

 of approximately fifteen times that which appears at the governor during 

 normal operation. 



The second factor, which can vary during dial life, is the value of the 

 stud-to-case coefficient of friction, fx. Both the drive-bar and fly-bar 

 governors have studs of Ebonite compounded with 40 per cent by 

 weight of hard rubber dust and cases of ASTM B16 brass. Actual service 

 tests show the satisfactory wearing ability of these materials. 



Each governor is initially adjusted for speed by changing the tension 

 of the governor spring. At the time this adjustment is made, a particular 

 friction condition exists between the governor studs and case. With time 

 or continued operation there is always the possibility of a change oc- 

 curring in this friction value. Such factors as very high humidity, lubri- 

 cation products traveling to the stud operating region, or the accumula- 

 tion of foreign-material or wear particles may produce different values of 

 friction and hence result in variation in governor and dial speed from the 

 initially adjusted value. 



The range of coefficient of friction values (jl expected for rubber on 

 brass is from 0.05 to 0.35. These are the extreme conditions produced by 

 oil in the governor case for the 0.05 value and very low unit pressure on 

 a scored brass surface for the 0.35 value. For this study a representative 

 figure for the average stud-to-case friction value was taken to be 0.25. 



The problem of variation in steady state governor speed with changes 

 in the coefficient of friction and mput torque can be analyzed by con- 

 sidering the derivatives of speed with respect to these values. This is done 

 by operating on the equations for terminal speed. 



Speed with Respect to Coefficient of Friction 



For the drive-bar governor, the partial derivative of speed, with respect 

 to coefficient of friction, is as follows: 



