Hydraulic transmission control device

In a transmission system utilizing a differential gear set having a high speed transmission path and a low speed transmission path for coupling power from an input shaft to an output shaft, said gear set being operably connected to selectively controllable, variable displacement hydraulic pump-motor speed control means constructed and arranged to supply a selectively variable speed control input to said differential gear set to adjust the speed ratio thereof, the combination comprising:

• a. first clutch means operable when engaged to couple said speed control means to said gear set to control the speed ratio of said high speed transmission path;
• b. second clutch means operable when engaged to couple said speed control means to said gear set to control the speed ratio of said low speed transmission path;
• c. means for producing speed signals representative of the rates of rotation of said output shaft and said input shaft, respectively;
• and
• d. control means responsive to said speed signals for controlling the engagement and disengagement of said first and second clutch means, said control means being constructed and arranged to cause one of said clutch means to engage and the other of said clutch means to disengage when said speed signals attain a predetermined ratio indicating that the components of said high and low speed transmission paths are operating at a common speed;
• and
• e. retarding means for delaying the disengagement of said disengaging clutch means so that both said first and second clutch means are temporarily engaged for a period of time immediately following the time when said speed signals attain said predetermined ratio.