Patent ID: 7922610

Claim:
A line pressure control device for a belt type continuously variable transmission in which a belt is wrapped around a primary pulley connected to an input side of a vehicle drive system and a secondary pulley connected to an output side, a groove width of the primary pulley and the secondary pulley is varied in accordance with an oil pressure supplied by a hydraulic pump, and a speed ratio is varied in accordance with the groove width, wherein the transmission comprises: a first pressure regulating valve which comprises a solenoid and regulates the oil pressure supplied by the hydraulic pump as a line pressure by varying a valve opening in accordance with a solenoid current supplied to the solenoid; a second pressure regulating valve which regulates an oil pressure supplied to the primary pulley on the basis of the line pressure; and a third pressure regulating valve which regulates an oil pressure supplied to the secondary pulley on the basis of the line pressure, and the device comprising a controller which is configured to calculate a target line pressure which is equal to or greater than the larger of the oil pressures supplied to the primary pulley and the secondary pulley; calculate the solenoid current supplied to the solenoid required to realize the target line pressure by looking up a table showing a relationship between the solenoid current and the target line pressure, the table is set such that the target line pressure decreases as the solenoid current increases and the table has an inflection point in which a decrease rate of the target line pressure in a high current value region beyond the inflection point is smaller than a decrease rate of the target line pressure in a low current value region below the inflection point; feedback-control the line pressure to equal the target line pressure by controlling the solenoid current; determine that a divergence between the target line pressure and the actual line pressure occurs when the target line pressure has fallen below a first low pressure which is a line pressure at the inflection point during the feedback-control; and restrict the target line pressure, when the divergence is determined to have occurred during the feedback-control, such that the target line pressure does not fall below a lower limit value, the lower limit value being set to the line pressure at the time of a determination in which the divergence occurs.