Shift control method for automatic transmission

A shift control method for an automatic transmission which includes a plurality of power transmission paths provided between input and output members, a plurality of engaging elements for selectively establishing said power transmission paths, and engagement-controlling means for controlling engagement-actuation pressures of said engaging elements in response to pressure command signals;

• said engagement-controlling means carrying out a shift-up control from an off-going range to an on-coming range by releasing an off-going engagement element in response to a shift-up command;
• comprising the steps of
• releasing an off-going engaging element at an off-going-range controlling stage by generating a pressure command signal which quickly lowers the engagement-actuation pressure of said off-going engaging element,
• controlling said off-going element at an off-going-range controlling stage by generating a pressure command signal which controls the engagement-actuation pressure of said off-going engaging element such that said off-going engaging element is kept slipping within a predetermined range of input/output rotational speed ratio (=output rotational speed/input rotational speed), and
• clearing an invalid stroke of an on-coming engaging element at an oncoming-range invalid-stroke-clearing stage by generating a pressure command signal which sets the engagement-actuation pressure of said on-coming engaging element to a predetermined high-pressure necessary for said on-coming engaging element to clear an invalid stroke;
• and characterized by
• initiating said on-coming-range invalid-stroke-clearing stage in response to said shift-up command;
• proceeding through the shift-up control from said off-going-range releasing stage to said off-going-range controlling stage when the input/output speed ratio of said off-going engaging element reaches a first predetermined value in said off-going-range stage;
• generating a pressure command signal for engaging said on-coming engaging element in a predetermined engaging pattern when the input/output speed ratio of said off-going engaging element reaches a second predetermined value greater than said first predetermined value in said off-going-range controlling stage;
• and
• generating a pressure command signal for completely releasing said off-going engaging element when the input/output speed ratio of said off-going engaging element reaches a third predetermined value greater than said second predetermined value in said off-going-range controlling stage.