2当0<a≤死/时: IA IB Ic d (57/6)+a 2U2p sinad(at 2n/l(x/6)+a ISSS t =1.17Up cosa d NA N/B Wt 3当7<a≤57时 Igl lg? Wgr Igl U d z/1(/6)+a 2U2P sinad(at) wtl wt2 wt3 1+ cos 30 +a 1.17U 12P        . U cos U U sin td( t ) P ( ) ( ) d P 2 5 6 6 2 1 17 2 3 2 1 = =  + + 当 时： 6 2. 0    当 时6 5 6 3.     ( ) 3 1 30 1 17 2 3 2 1 0 2 6 2        + + = =  + cos . U U U sin td( t ) P ( ) d P