Continuously variable transmission and its hydraulic pressure control method

A hydraulic pressure control method in a continuously variable transmission that includes a primary pulley, a secondary pulley, a power transmission member wound between the pulleys, and a shift control hydraulic circuit for regulating a primary pressure supplied to the primary pulley and a secondary pressure supplied to the secondary pulley by using a line pressure as an original pressure, and that shifts by changing the primary pressure and the secondary pressure and by changing widths of grooves of the pulleys, the hydraulic pressure control method comprising:

• setting a target primary pressure as a target value of the primary pressure and a target secondary pressure as a target value of the secondary pressure, based on a speed ratio;
• deciding a cross-point region as a region where an absolute value of a deviation, obtained by subtracting the target primary pressure from the target secondary pressure, is smaller than a predetermined deviation;
• setting a target line pressure as a target value of the line pressure to be a value obtained by adding an offset amount, as a positive value, to either one having a higher value out of the target primary pressure and the target secondary pressure, when decision of the cross-point region is made or when decision of the cross-point region is made and in a region where the deviation increases to a positive side;
• and
• controlling the primary pressure, the secondary pressure, and the line pressure to be the target primary pressure, the target secondary pressure, and the target line pressure, respectively.

A continuously variable transmission that includes a primary pulley, a secondary pulley, a power transmission member wound between the pulleys, and a shift control hydraulic circuit for regulating a primary pressure supplied to the primary pulley and a secondary pressure supplied to the secondary pulley by using a line pressure as an original pressure, and that shifts by changing the primary pressure and the secondary pressure and by changing widths of grooves of the pulleys, the continuously variable transmission comprising:

• means for setting a target pulley pressure that sets a target primary pressure as a target value of the primary pressure and a target secondary pressure as a target value of the secondary pressure, based on a speed ratio;
• means for deciding a cross-point region that decides the cross-point region as a region where an absolute value of a deviation, obtained by subtracting the target primary pressure from the target secondary pressure, is smaller than a predetermined deviation;
• and
• means for setting a target line pressure that sets the target line pressure as a target value of the line pressure to be a value obtained by adding an offset amount, as a positive value, to either one having a higher value out of the target primary pressure and the target secondary pressure,
• wherein, when decision of the cross-point region is made or when decision of the cross-point region is made and in a region where the deviation increases to a positive side, the shift control hydraulic circuit controls the primary pressure, the secondary pressure, and the line pressure to be the target primary pressure, the target secondary pressure, and the target line pressure, respectively.