Method and apparatus for controlling speed changing unit

An apparatus for controlling a speed changing unit comprising:

• a transmission including a plurality of auxiliary speed changing clutches at a first stage and a plurality of main speed changing clutches at a second stage as viewed from an input shaft of said transmission,
• a plurality of pressure control valves individually connected to said plural clutches in the transmission to generate in a pertinent clutch a hydraulic pressure corresponding to an electrical signal inputted therein,
• a hydraulic pump for feeding pressurized hydraulic oil to said plural pressure control valves,
• means for detecting an amount of hydraulic oil delivered from said hydraulic pump,
• a plurality of means associated with the plural clutches for detecting the termination of filling of a respective clutch with hydraulic oil,
• means for determining, during speed changing, whether clutches to be engaged comprise both an auxiliary speed changing clutch and a main speed changing clutch and also determining whether an output from said means for detecting an amount of hydraulic oil by the hydraulic pump below a predetermined value, and
• means selecting an auxiliary clutch and a main clutch corresponding to a desired speed stage during speed changing and for controlling the respective pressure control valves corresponding to the auxiliary speed changing clutch and the main speed changing clutch thus selected in such a manner that when results derived from determinations made by said determining means are identified as yes, feeding of hydraulic oil to the auxiliary speed changing clutch thus selected is first started, and thereafter feeding of hydraulic oil to the main speed changing clutch thus selected and gradual increasing of clutch pressure for the auxiliary speed changing clutch thus selected are started at the time point when the termination of filling of the auxiliary speed changing clutch is detected by an output from said filling detecting means.