Hydraulic control system for automatic transmission, and method of controlling hydraulic pressure

A hydraulic control system for an automatic transmission, the automatic transmission including a plurality of friction elements, at least one of the friction elements being supplied with a hydraulic pressure which is so increased as to switch the friction element from a disengagement state to an engagement state, thus transmitting a revolution of an input element of the friction element to an output element of the friction element, the hydraulic control system controlling the hydraulic pressure as a standby pressure in a period from an engagement start point at which an engagement instruction for engaging the friction element is started to an abutment start point at which an abutment between the input element and the output element is started, the hydraulic control system comprising:

• a speed sensor for sensing a speed of the friction element;
• and
• a standby pressure increase section for increasing the standby pressure in accordance with the speed of the friction element sensed with the speed sensor,
• wherein the standby pressure increase section comprises:
• a means for determining speed state which determines whether the speed of the friction element sensed with the speed sensor is higher than a predetermined speed;
• wherein the standby pressure includes:
• a first standby pressure in a low speed state where the speed is not higher than the predetermined speed, and
• a second standby pressure in a high speed state where the speed is higher than the predetermined speed;
• and
• wherein, when the means for determining speed state determines that the speed of the friction element is in the high speed state, the standby pressure is made into the second standby pressure which is a hydraulic pressure higher than the first standby pressure.

A hydraulic control system for an automatic transmission, the automatic transmission including a plurality of friction elements, at least one of the friction elements being supplied with a hydraulic pressure which is so increased as to switch the friction element from a disengagement state to an engagement state, thus transmitting a revolution of an input element of the friction element to an output element of the friction element, the hydraulic control system controlling the hydraulic pressure as a standby pressure in a period from an engagement start point at which an engagement instruction for engaging the friction element is started to an abutment start point at which an abutment between the input element and the output element is started, the hydraulic control system comprising:

• a speed sensor for sensing a speed of the friction element;
• and
• a standby pressure increase section for increasing the standby pressure in accordance with the speed of the friction element sensed with the speed sensor,
• wherein the standby pressure includes:
• a first standby pressure increased with the standby pressure increase section, and
• a second standby pressure which is a hydraulic pressure still higher than the first standby pressure;
• and
• wherein the hydraulic control system further comprises:
• a fluid temperature sensor for sensing a fluid temperature of an operation fluid supplied to the friction element;
• and
• a standby pressure corrector for correcting the standby pressure from the first standby pressure to the second standby pressure, the correction with the standby pressure corrector being made in accordance with a decrease in the fluid temperature sensed with the fluid temperature sensor.

A method of controlling a hydraulic pressure with a hydraulic control system for an automatic transmission, the automatic transmission including a plurality of friction elements, at least one of the friction elements being supplied with the hydraulic pressure which is so increased as to switch the friction element from a disengagement state to an engagement state, thus transmitting a revolution of an input element of the friction element to an output element of the friction element, the hydraulic control system controlling the hydraulic pressure as a standby pressure in a period from an engagement start point at which an engagement instruction for engaging the friction element is started to an abutment start point at which an abutment between the input element and the output element is started, the method of controlling the hydraulic pressure comprising the following steps of:

• sensing a speed of the friction element with a speed sensor;
• and
• increasing the standby pressure, with a standby pressure increase section, in accordance with the speed of the friction element sensed at the sensing step with the speed sensor,
• wherein the increasing step with the standby pressure increase section comprises the following step of:
• determining, with a means for determining speed state, whether the speed of the friction element sensed with the speed sensor is higher than a predetermined speed;
• wherein the standby pressure includes:
• a first standby pressure in a low speed state where the speed is not higher than the predetermined speed, and
• a second standby pressure in a high speed state where the speed is higher than the predetermined speed;
• and
• wherein, when the means for determining speed state determines at the determining step that the speed of the friction element is in the high speed state, the standby pressure is made into the second standby pressure which is a hydraulic pressure higher than the first standby pressure.

A method of controlling a hydraulic pressure with a hydraulic control system for an automatic transmission, the automatic transmission including a plurality of friction elements, at least one of the friction elements being supplied with the hydraulic pressure which is so increased as to switch the friction element from a disengagement state to an engagement state, thus transmitting a revolution of an input element of the friction element to an output element of the friction element, the hydraulic control system controlling the hydraulic pressure as a standby pressure in a period from an engagement start point at which an engagement instruction for engaging the friction element is started to an abutment start point at which an abutment between the input element and the output element is started, the method of controlling the hydraulic pressure comprising the following steps of:

• sensing a speed of the friction element with a speed sensor;
• and
• increasing the standby pressure, with a standby pressure increase section, in accordance with the speed of the friction element sensed at the sensing step with the speed sensor,
• wherein the standby pressure includes:
• a first standby pressure increased at the increasing step with the standby pressure increase section, and
• a second standby pressure which is a hydraulic pressure still higher than the first standby pressure;
• and
• wherein the method of controlling the hydraulic pressure further comprises the following steps of:
• sensing, with a fluid temperature sensor, a fluid temperature of an operation fluid supplied to the friction element;
• and
• correcting, with a standby pressure corrector, the standby pressure from the first standby pressure to the second standby pressure, the correcting step being made in accordance with a decrease in the fluid temperature sensed at the sensing step with the fluid temperature sensor.