Speed change control device of automatic transmission

A speed change control device for an automatic transmission having four forward speeds and one reverse and including a torque converter, a main speed change mechanism and an auxiliary speed change mechanism, said speed change control device comprising:

• a band brake installed in said main speed change mechanism, said band brake including a servo-apply chamber which, when fed with a hydraulic pressure, can induce the second speed of the transmission and a servo-release chamber which, when fed with the hydraulic pressure, can induce the third speed of the transmission;
• 1-2, 2-3 and 3-4 shift valves, each having two switching positions for selectively carrying out application and releasing of hydraulic pressure to and from an oil chamber of a corresponding hydraulically-operated friction element, said 1-2 shift valve having a position in which the servo-apply chamber of said band brake is supplied with a hydraulic pressure;
• electrically-actuated first and second solenoid valves, said first solenoid valve outputting a hydraulic pressure which is applied to said 2-3 shift valve to control the switching operation of said 2-3 shift value, said second solenoid valve outputting a hydraulic pressure which is applied said 1-2 shift valve to control the switching operation of said 1-2 shift valve;
• and
• passage means for feeding said 3-4 shift valve with the hydraulic pressure from said second solenoid valve to control the switching operation of said 3-4 shift valve only when said 2-3 shift valve assumes a given position in which said servo-release chamber of said band brake is supplied with the hydraulic pressure.

A speed change control device for an automatic transmission having four forward speeds and one reverse and including a torque converter, a main speed change mechanism and an auxiliary speed change mechanism, said speed change control device comprising:

• a band brake installed in said main speed change mechanism, said band brake including a servo-apply chamber which, when fed with a hydraulic pressure, can induce the second speed of the transmission, and a servo-release chamber which, when fed with the hydraulic pressure, can induce the third speed of the transmission, said servo-release chamber having a pressure receiving area which is larger than that of said servo-apply chamber;
• 1-2, 2-3 and 3-4 shift valves each having two switching positions for selectively carrying out application and releasing of hydraulic pressure to and from an oil chamber of a corresponding hydraulically-operated friction element, said 1-2 shift valve having a position in which the servo-apply chamber of said band brake is supplied with a hydraulic pressure,
• electrically-actuated first and second solenoid valves, said first solenoid valve outputting a hydraulic pressure which is applied to said 2-3 shift valve to control the switching operation of said 2-3 shift valve, said second solenoid valve outputting a hydraulic pressure which is applied said 1-2 shift valve to control the switching operation of said 1-2 shift valve;
• and
• passage means for feeding said 3-4 shift valve with the hydraulic pressure from said second solenoid valve to control the switching operation of said 3-4 shift valve only when said 2-3 shift valve assumes a given position in which said servo-release chamber of said band brake is supplied with the hydraulic pressure;
• said passage means including:
• first means for defining a first passage which extends between said second solenoid valve and said 2-3 shift valve, said first passage having a portion exposed to one end of said 1-2 shift valve;
• and
• second means for defining a second passage which extends between said 2-3 shift valve and said 3-4 shift valve, said first and second passages being connected when said 2-3 shift valve assumes said given position;
• wherein said 1-2 shift valve is arranged so as to selectively carry out and stop a hydraulic pressure feeding to a low-and-reverse clutch, said 2-3 shift valve is arranged so as to selectively carry out and stop a hydraulic pressure feeding to a high clutch, and said 3-4 shift valve is arranged so as to selectively carry out and stop a hydraulic pressure feeding to both a direct clutch and a reduction brake.

A gear change control device for an automatic transmission having four forward speeds and one reverse, comprising:

• 1-2, 2-3 and 3-4 shift valves, each having two switching positions for selectively carrying out application and releasing of hydraulic pressure to and from an oil chamber of a corresponding hydraulically-operated friction element;
• first and second solenoid valves, each outputting a hydraulic pressure which is controlled in accordance with an electric signal applied thereto, said first solenoid valve outputting a hydraulic pressure to said 2-3 shift valve to control the switching operation of said 2-3 shift valve, and said second solenoid valve outputting a hydraulic pressure to said 1-2 shift valve to control the switching operation of said 1-2 shift valve;
• a friction element for the second speed, said friction element including a servo-apply chamber which, when fed with a hydraulic pressure, induces an engaged condition of the second speed friction element, and a servo-release chamber which, when fed with the hydraulic pressure, induces a disengaged condition of the second speed friction element, said servo-release chamber having a pressure receiving area larger than that of said servo-apply chamber;
• first passage means for feeding said servo-apply chamber with a hydraulic pressure through said 1-2 shift valve when said second solenoid valve stops the output of a hydraulic pressure therefrom;
• second passage means for feeding said servo-release chamber with a hydraulic pressure through said 2-3 shift valve when said first solenoid valve stops the output of a hydraulic pressure therefrom;
• and
• third passage means for permitting application of a hydraulic pressure from said second solenoid valve to said 3-4 shift valve to control the switching operation of said 3-4 shift valve only when said 2-3 shift valve assumes a position in which the servo-release chamber of said second speed friction element is fed with the hydraulic pressure.