Method and apparatus for controlling line pressure in continuously variable transmission

A method for hydraulically controlling a continuously variable transmission of an automotive vehicle having an internal combustion engine, the transmission being adapted for shifting continuously between different reduction ratios and having a V-belt running over a drive pulley and a driven pulley, at least one of said pulleys having two conical discs engaging the V-belt and a cylinder chamber, one conical disc being axially fixed and the other conical disc being axially movable in response to an oil pressure in the cylinder chamber thereof to effect shifting between reduction ratios, the transmission having a line pressure regulator valve means for generating oil under a line pressure and having a pressure increase port, and a shift control valve having a pressure regulating spool means which is movable for regulating an oil supply flow communication between the cylinder chamber and the line pressure regulator valve means via which the oil is supplied to the cylinder chamber from the line pressure regulator valve means and an oil discharge flow communication via which oil is discharged from the cylinder chamber so as to determine the oil pressure in the cylinder chamber, the method comprising the steps of:

• detecting a state wherein a rapid shifting in reduction ratio is needed and generating a state indicative signal indicative of said state;
• causing a movement of the pressure regulating spool means of the shift control valve beyond a predetermined amount temporarily upon detecting said state so as to decrease said oil supply flow communication and increase said oil discharge flow communication beyond a predetermined degree;
• and
• causing the line pressure regulator valve means to increase the line pressure temporarily upon generation of said state indicative signal, thereby to decrease a drop in the flow rate of the oil supplied to the cylinder chamber via said oil supply flow communication which has been decreased, which drop is caused by the decrease in said oil supply flow communication.

An apparatus for hydraulically controlling a continuously variable transmission of an automotive vehicle having an internal combustion engine, the transmission being adapted for shifting continuously between different reduction ratios and having a V-belt running over a drive pulley and a driven pulley, at least one of which pulleys having two conical discs engaging the V-belt and a cylinder chamber, one conical disc being axially fixed and the other conical disc being axially movable in response to an oil pressure in the cylinder chamber thereof to effect shifting between reduction ratios, the apparatus comprising:

• a source of pressurized oil;
• a line pressure regulator valve communicating with said source of pressurized oil for generating oil under a line pressure, said line pressure regulator valve having a pressure increase port;
• a shift control valve communicating with said line pressure regulator valve and with the cylinder chamber of at least one pulley and having a pressure regulating spool means movable for an oil supply flow communication between the cylinder chamber and said line pressure regulator valve via which the oil under said line pressure is supplied to the cylinder chamber and an oil discharge flow communication via which the oil is discharged from the cylinder chamber in response to the position of said spool means;
• means for detecting a state where rapid shifting in reduction ratio is needed and generating a state indicative signal indicative of said state;
• means operatively connected with said spool means of said shift control valve for temporarily shifting said spool means of said shift control valve beyond a predetermined amount from the center position thereof upon detecting said state to a predetermined position wherein said oil supply flow communication is decreased and said oil discharge flow communication is increased beyond a predetermined degree;
• means for temporarily varying oil pressure at said pressure increase port of said line pressure regulator valve so as to cause said line pressure regulator valve to increase the line pressure upon generation of said state indicative signal, thereby to decrease a drop in flow rate of the oil supplied to the cylinder chamber via said oil supply flow communication which has been decreased, which drop is caused by the decrease in said oil supply flow communication.