Failsafe hydraulic control system for vehicle automatic transmission

A hydraulic control system for a vehicle automatic transmission which comprises first, second and third engaging means, said engaging means being combined to form a plurality of sets of pairs, the engaging means in each set being simultaneously engaged to enable shifting into a plurality of gear ratios corresponding in number to said sets to be achieved, hydraulic pressure supplying means for supplying hydraulic pressure to cause engagement of each of said first, second and third engaging means respectively, first hydraulic passage means for connecting said hydraulic pressure supplying means to said first engaging means, first shift means coupled to said first hydraulic passage means for switching supply and discharge of the hydraulic pressure to and from said first engaging means in accordance with running conditions of the vehicle, second hydraulic passage means for connecting said hydraulic pressure supplying means to said second engaging means, second shift means coupled to said second hydraulic passage means for switching supply and discharge of the hydraulic pressure to and from said second engaging means in accordance with the running conditions of the vehicle, third hydraulic passage means connecting said hydraulic pressure supplying means to said third engaging means, and third shift means coupled to said third hydraulic passage means for switching supply and discharge of the hydraulic pressure to and from said third engaging means in accordance with the running conditions of the vehicle, said hydraulic control system comprising:

• first pressure detecting means for detecting hydraulic pressure in said first hydraulic passage means between said first shift means and said first engaging means;
• second pressure detecting means for detecting hydraulic pressure in said second hydraulic passage means between said second shift means and said second engaging means;
• third pressure detecting means for detecting hydraulic pressure in said third hydraulic passage means between said third shift means and said third engaging means;
• valve means coupled to said first hydraulic passage means between said first pressure detecting means and said first engaging means and being movable between a supply position where said valve means opens said first hydraulic passage means for supplying the hydraulic pressure to be supplied to said first engaging means and a discharge position where said valve means discharges the hydraulic pressure supplied to said first engaging means;
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• switching means coupled to said valve means for switching said valve means to move said valve means to said discharge position when said first pressure detecting means detects that the hydraulic pressure in said first hydraulic passage means is higher than a first predetermined value, said second pressure detecting means detects that the hydraulic pressure in said second hydraulic passage means is higher than a second predetermined value, and said third pressure detecting means detects that the hydraulic pressure in said third hydraulic passage means is higher than a third predetermined value.

A hydraulic control system for a vehicle automatic transmission which comprises first, second and third engaging means respectively engagable for achieving three different forward gear ratios, fourth engaging means engagable when achieving each of said three forward gear ratios, hydraulic pressure supplying means for supplying hydraulic pressure to cause engagement of each of said first, second, third and fourth engaging means respectively, first hydraulic passage means for connecting said hydraulic pressure supplying means to said first engaging means, first shift means coupled to said first hydraulic passage means for switching supply and discharge of the hydraulic pressure to and from said first engaging means in accordance with running conditions of the vehicle, second hydraulic passage means for connecting said hydraulic pressure supplying means to said second engaging means, second shift means coupled to said second hydraulic passage means for switching supply and discharge of the hydraulic pressure to and from said second engaging means in accordance with the running conditions of the vehicle, third hydraulic passage means for connecting said hydraulic pressure supplying means to said third engaging means, third shift means coupled to said third hydraulic passage means for switching supply and discharge of the hydraulic pressure to and from said third engaging means in accordance with the running conditions of the vehicle, and fourth hydraulic passage means for connecting said hydraulic pressure supplying, means to said fourth engaging means, said hydraulic control system comprising:

• first pressure detecting means for detecting hydraulic pressure in said first hydraulic passage means between said first shift means and said first engaging means;
• second pressure detecting means for detecting hydraulic pressure in said second hydraulic passage means between said second shift means and said second engaging means;
• third pressure detecting means for detecting hydraulic pressure in said third hydraulic passage means between said third shift means and said third engaging means;
• fourth pressure detecting means for detecting hydraulic pressure in said fourth hydraulic passage means;
• first valve means provided in a portion of any one of said first, second and third hydraulic passage means, said portion thereof extending between the pressure detecting means coupled to the hydraulic passage means and the engaging means connected to the hydraulic passage means, said first valve means being movable between a supply position where said first valve means opens the hydraulic passage means for supplying the hydraulic pressure to be supplied to the engaging means and a discharge position where said first valve means discharges the hydraulic pressure supplied to the engaging means;
• second valve means provided in a portion of any one of said second, third and fourth hydraulic passage means in which hydraulic passage means said first valve means is not provided, said portion thereof extending between the pressure detecting means coupled to the hydraulic passage means and the engaging means connected to the hydraulic passage means, said second valve means being movable between a supply position where said second valve means opens the hydraulic passage means for supplying the hydraulic pressure to be supplied to the engaging means and a discharge position where said second valve means discharges the hydraulic pressure supplied to the engaging means;
• first switching means coupled to said first valve means for switching said first valve means to move said first valve means to said discharge position when the pressure detecting means coupled to the hydraulic passage means having provided therein said first valve means among said first, second and third hydraulic passage means detects that the hydraulic pressure in the hydraulic passage means is higher than a predetermined value and the pressure detecting means coupled to at least one of the remaining hydraulic passage means detects that the hydraulic pressure in the hydraulic passage means is higher than a predetermined value;
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• second switching means coupled to said second valve means for switching said second valve means to move said second valve means to said discharge position when the pressure detecting means coupled respectively to said second, third and fourth hydraulic passage means detect simultaneously that the hydraulic pressures in the respective hydraulic passage means are higher than their respective predetermined values.

A hydraulic control system for a vehicle automatic transmission which comprises first, second, third and fourth engaging means for establishing different forward gear ratios, hydraulic pressure supplying means for supplying hydraulic pressure to cause engagement of each of said first, second, third and fourth engaging means respectively, first hydraulic passage means for connecting said hydraulic pressure supplying means to said first engaging means, first shift means coupled to said first hydraulic passage means for switching supply and discharge of the hydraulic pressure to and from said first engaging means in accordance with running conditions of the vehicle, second hydraulic passage means for connecting said hydraulic pressure supplying means to said second engaging means, second shift means coupled to said second hydraulic passage means for switching supply and discharge of the hydraulic pressure to and from said second engaging means in accordance with the running conditions of the vehicle, third hydraulic passage means for connecting said hydraulic pressure supplying means to said third engaging means, third shift means coupled to said third hydraulic passage means for switching supply and discharge of the hydraulic pressure to and from said third engaging means in accordance with the running conditions of the vehicle, fourth hydraulic passage means for connecting said hydraulic pressure supplying means to said fourth engaging means, and fourth shift means coupled to said fourth hydraulic passage means for switching supply and discharge of the hydraulic pressure to and from said fourth engaging means, the arrangement being such that a first gear ratio is achieved when said first and fourth engaging means are simultaneously engaged, a second gear ratio is achieved when said second and fourth engaging means are simultaneously engaged, a third gear ratio is achieved when said third and fourth engaging means are simultaneously engaged, a fourth gear ratio is achieved when said second and third engaging means are simultaneously engaged, said hydraulic control system comprising:

• first pressure detecting means for detecting hydraulic pressure in said first hydraulic passage means between said first shift means and said first engaging means;
• second pressure detecting means for detecting hydraulic pressure in said second hydraulic passage means between said second shift means and said second engaging means;
• third pressure detecting means for detecting hydraulic pressure in said third hydraulic passage means between said third shift means and said third engaging means;
• fourth pressure detecting means for detecting hydraulic pressure in said fourth hydraulic passage means between said fourth shift means and said fourth engaging means;
• first valve means provided in a portion of any one of said first, second and third hydraulic passage means, said portion thereof extending between the pressure detecting means coupled to the hydraulic passage means and the engaging means connected to the hydraulic passage means, said first valve means being movable between a supply position where said first valve means opens the hydraulic passage means for supplying the hydraulic pressure to be supplied to the engaging means and a discharge position where said first valve means discharges the hydraulic pressure supplied to the engaging means;
• second valve means provided in a portion of any one of said second, third and fourth hydraulic passage means in which hydraulic passage means said first valve means is not provided, said portion thereof extending between the pressure detecting means coupled to the hydraulic passage means and the engaging means connected to the hydraulic passage means, said second valve means being movable between a supply position where said second valve means opens the hydraulic passage means for supplying the hydraulic pressure to be supplied to the engaging means and a discharge position where said second valve means discharges the hydraulic pressure supplied to the engaging means;
• first switching means coupled to said first valve means for switching said first valve means to move said first valve means to said discharge position thereof when the pressure detecting means coupled to the hydraulic passage means having provided therein said first valve means detects that the hydraulic pressure in the hydraulic passage means is higher than a predetermined value and the pressure detecting means coupled to at least one of the remaining hydraulic passage means detects that the hydraulic pressure in the hydraulic passage means is higher than a predetermined value;
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• second switching means coupled to said second valve means for switching said second valve means to novel said second valve means to said discharge position when the pressure detecting means coupled respectively to said second, third and fourth hydraulic passage means simultaneously detect that the hydraulic pressures in the respective hydraulic passage means are higher than their respective predetermined values.