out 02 ON 01P @in 01 O,N2 02P2 nTo =Const. 2T62 bp my= @out =02=1='1=Const. Oin 13Tb2 The fundamental law of gearing N The ratio of the driving gear radius to the driven gear radius remains constant as the teeth move into and out of mesh
. . 2 1 2 1 1 2 2 1 2 1 2 1 2 1 2 2 1 1 1 2 Const r r r r m Const r r r r r r O P O P O N O N m b b i n out V b b i n out V = = = = = = = = = = = = The fundamental law of gearing The ratio of the driving gear radius to the driven gear radius remains constant as the teeth move into and out of mesh. r1 r2
Important lines Tangency of the both base circles (基圆公切线)is the common K normal Line of action(力作用线) Axis of transmission(啮合线或传动线) Conclusion:these three lines are the same line
Important lines Conclusion: these three lines are the same line. Axis of transmission(啮合线或传动线) Line of action（力作用线） Tangency of the both base circles （基圆公切线）is the common normal . rbp rbg rp rg
3.Pressure angle(节圆压力角) Driving The pressure angle in a gearset is defined as the angle between the axis of transmission or line of action(common d normal)and the direction of velocity at n the pitch point. Meshing angle(啮合角) Standard value of the pressure angle are 14.5°，20°and25°.20°is the most Driven commonly used
The pressure angle in a gearset is defined as the angle between the axis of transmission or line of action(common normal) and the direction of velocity at the pitch point. Standard value of the pressure angle are 14.50, 200 and 250. 200 is the most commonly used. Meshing angle(啮合角) 3. Pressure angle（节圆压力角）
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4.Changing Center Distance 81 b2 分x03 0ow=} 2=2='b2=Const. a'cosa=rb +2 a"cosa"=ri+2 a cosa'=acosa=const
4. Changing Center Distance 1 2 'cos ' b b a = r + r 1 2 ''cos '' b b a = r + r a'cos' = a''cos'' = const. . 1 2 1 2 1 2 Const r r r r m b b i n out V = = = = =