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Example20 SpringsThe valves of a diesel engine are to be opened 16mm by the valve mechanism.Eachspring s to exert a force of 300N when the valves are closedand 670Nwith the valvesopen.

a) Design a suitablespring with squaredand ground ends. The solid height of thespring shouldbe 10mm ess han the lengthwith the valves openand the outsidediametershould not exceed45mm. Use standard hromevanadiumsteelwire andassumehatthemaximumallowableshearstress s not to exceed600MPa.b) Determine the spring diameter and the free length if the spring index is 7 andG: 80GPa.

8/8/2019 Consider Example 18

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8/8/2019 Consider Example 18

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Example 18 SpringsThe return spring mechanismshown in the diagram s loaded by means of a helicaltension spring which is pre-tensionedby extendingthe spring by 15 mm to hold themechanism gainst he stop.The followingspecifications pply o the spring:Spring wire diameter : 20 mmNumber of work ing coi ls : 6.5Ins ide diameterof spr ing 130mmModulus of rigidity : 80GPaDetermine he maximum forceF which may be applied o the lever arm ABC to extendthe spring a further 40 mm. Estimate also the initial stress and he final stressnthe spring.

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n[}m(}grarnorclesehelicalpringsThisnomogramor closecoiledhetical pringsof roundwire sderivedrom he ormula' 8 P g . r '! = -' adrIn this data sheet he nomogram s given in Sf units as shown.

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Example28 Clutches

A disc clutch of the automotive ype has 2 pairs of friction faceseach 250mm outsidediameter nd 170mm nsidediameter.Whenpower s being ransmitted,he clutch s heldin engagementy 6 closecoiledhelicalspringswhich havesquared ndgroundends.Todisengagehe clutch hepressure late s withdrawn 1.5mm.Assuminguniformwearconditions, eterminehe following:a) The maximumallowable orceon the clutch if the maximum allowablepressures0.13MPa;b) Thepower capacityof the clutch at 4200 /min if the coefficient of friction is 0.3;c) Themaximumforceon eachspringwhenthe clutch is engaged.

CLUTCH SNGAGSD OISENGAGEO

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Example29 ClutchesA multiple disc clutch comprises 8 pairs of friction. surfaces' The clutchplatediameters re 150mmo.D. and 100mm .b. The co-efficientof friction

p:0't2 and heaxial force on the plates is 1350NprorriJ.d iy S iO"nticalspringsarranged'n the clutchhousing.

a) what is the torque capacity of this clutch? (consider uniform wear conditionsonlY). , r oUl Wftatpower canbe transmittedat 157 revs/min?

DRIVEH

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