Cut-back pressure control device for multi-speed automatic transmission

A cut-back pressure control device for an automatic transmission, comprising:

• a sub-transmission unit through which power is transmitted in a respective one of power transmitting paths defined therethrough, the sub-transmission unit shiftable between a high-speed mode at which power is transmitted through one of said paths and a low-speed mode at which power is transmitted through another of said paths;
• a main transmission unit through which power is transmitted in one of at least two power transmitting paths, the main transmission unit shiftable between at least two shifting stages at which power is transmitted through respective ones of said at least two power transmitting paths,
• said main transmission unit operatively connected in series to said sub-transmission unit with engine torque being input to only one of the transmission units for driving said one of the transmission units and only the output of said one of the transmission units being input to the other of the transmission units for driving the other of the transmission units so that the effective output of the main transmission unit is combined with the effective output of the sub-transmission unit to provide a plurality of successively higher speeds that are capable of being output by the transmission;
• frictional engagement elements for selecting the power transmitting paths through which power is transmitted in the sub-transmission unit and the main transmission unit;
• hydraulic servomotors for actuating said frictional engagement elements;
• a thorttle valve for establishing throttle pressure,
• a cut-back valve operatively hydraulically connected to said throttle valve for applying cut-back pressure to said throttle valve to regulate the throttle pressure;
• said hydraulic servomotors including a first hydraulic servomotor disposed in said sub-transmission unit and operatively hydraulically connected to said cut-back valve, said first hydraulic servomotor for operating one of the frictional engaging elements with hydraulic pressure that varies when the sub-transmission unit is shifted between the high-speed mode and the low-speed mode, and
• a second hydraulic servomotor disposed in said main transmission unit and operatively hydraulically connected to said cut-back valve, said second hydraulic servomotor for operating another of the frictional engaging elements with hydraulic pressure when the main transmission unit is shifted to the second of said at least two shifting stages and any of higher ones of said at least two shifting stages at which the main transmission unit outputs a speed that is higher than that output by the main transmission unit when shifted to the first of said at least two shifting stages;
• and
• said cut-back valve having a spool for moving between a first position at which the cut-back valve does not apply said cut-back pressure to the throttle valve in response to the hydraulic pressure transmitted from said first hydraulic servomotor when said main transmission unit is shifted to the first shifting stage and the sub-transmission unit is shifted to said low-speed mode and a second position at which the cut-back valve applies said cut-back pressure to the throttle valve when said sub-transmission unit is shifted to said high-speed mode or when said main transmission unit is shifted to the second or the higher ones of said shifting stages.