Machine design slide 20

Machine design slide 20 - ENGR 3220 – Machine Design ENGR...

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Unformatted text preview: ENGR 3220 – Machine Design ENGR 3220 – Machine Design April 4th, 2011 Brakes and Clutches Internal Expanding Brakes An internal expanding centrifugal-acting rim clutch. Internal Friction Shoe Geometry The Geometry Associated with an Arbitrary Point on the Shoe Pressure Distribution pa p = sin θ sin θ a Forces on the Shoe fpa br 2 Mf = ∫ sin θ (r − a cosθ )dθ sin θ a θ1 pa bra θ 2 2 MN = ∫θ1 sin θdθ sin θ a θ F= Rx = M N M f c For clockwise rotation pa bra ( A − fB ) − Fx sin θ a p bra Ry = a ( fA + B ) − Fy sin θ a A = ∫ sin θ cos θdθ θ1 θ2 B = ∫ sin 2 θdθ θ1 θ2 fpa br 2 (cos θ1 − cos θ 2 ) T= sin θ a Notation of External Contracting Shoes c fpa br θ 2 Mf = sin θ (r − a cos θ )dθ sin θ a ∫θ1 pa bra θ 2 2 MN = sin θdθ sin θ a ∫θ1 Rx = Ry = pa bra ( A + fB ) − Fx sin θ a pa bra ( fA − B) + Fy sin θ a θ2 θ1 F= MN + M f A = ∫ sin θ cos θdθ B = ∫ sin 2 θdθ θ1 θ2 fpa br 2 (cos θ1 − cos θ 2 ) T= sin θ a Brakes with Symmetrical Pivoted Shoe Mf =0 a= pa bra θ 2 2 MN = sin θ dθ sin θ a ∫θ1 T = afN 4r sin θ 2 2θ 2 + sin 2θ 2 pa br (2θ 2 + sin 2θ 2 ) 2 p brf Ry = a (2θ 2 + sin 2θ 2 ) 2 Rx = Example 1 The figure shows a 400-mm-diameter brake drum with four internally expanding shoes. Pins A and B each supports a pair of shoes. The actuating mechanism is to be arranged to produce the same force F on each shoe. The face width is 75 mm. The material used permits a coefficient of friction of 0.24 and a maximum pressure of 1000 kPa. Given a=150, c=165, R=200, d=50 Determine the actuating force ...
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Machine design slide 20 - ENGR 3220 – Machine Design ENGR...

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