Transmission control system

In a vehicle having a transmission with separate fluid operated clutches for selecting a plurality of speed ratios as well as forward and reverse drive, a transmission control system including a source of pressurized fluid, a speed control cover including manually-actuated control means with a speed control valve for controlling the flow of fluid to said clutches and an automatic downshift system comprising an electronic speed sensing system in combination with downshift valve means, a method for automatically downshifting said transmission for one step from a higher speed ratio to a lower speed ratio when the setting of said speed control valve corresponds with said higher speed ratio, and subsequently automatically upshifting said transmission one step, said method comprising the steps of:

• a. producing an electronic pulse signal proportional to vehicle road speed;
• b. producing a continuous signal below a first predetermined vehicle road speed;
• c. actuating a solenoid valve, via said continuous signal, to provide an actuating pressure;
• d. closing a higher speed ratio clutch valve via said actuating pressure thereby disconnecting said higher speed ratio clutch;
• e. simultaneously diverting the fluid for pressurizing said higher speed ratio clutch valve to a lower speed ratio clutch valve;
• f. pressurizing said lower speed ratio clutch thereby effectively shifting said transmission said one step from said higher to said lower speed ratio;
• g. terminating said continuous signal at a second higher predetermined road speed;
• h. deactivating said solenoid valve thereby discontinuing said actuating pressure;
• i. opening said higher speed ratio clutch valve while simultaneously ceasing diverting of said pressurized fluid from said higher speed ratio clutch to said lower speed ratio clutch thereby disconnecting said lower speed ratio clutch;
• and
• j. pressurizing said high speed ratio clutch thereby effectively shifting said transmission said one step from said lower to said higher speed ratio.

In a transmission control system for a vehicle including a multiple speed ratio power shift transmission having a plurality of fluid pressure operated clutches, adapted to establish torque ratio changes, a source of pressurized fluid, a speed control cover including manually-actuated control means and a speed control valve, for controlling the flow of fluid to said clutches, wherein the improvement comprises an electronic speed sensing system and downshift valve means, for automatically shifting said transmission one step from a higher speed ratio to a lower speed ratio at a first predetermined ground speed by diverting the fluid for pressurizing a higher speed ratio clutch to a lower speed ratio clutch and automatically shifting said transmission said one step from said lower speed ratio back to said higher speed ratio at a second predetermined ground speed, differing from said first predetermined ground speed, by ceasing the diverting of said fluid, with the diverting of said fluid being possible only when the setting of said speed control valve corresponds with said higher speed ratio;

• said electronic speed sensing system including an electronic signal generator operatively connected with said transmission for producing an electronic pulse signal proportional to vehicle road speed, an electronic speed switch actuated via said electronic pulse signal for producing a continuous signal below a first predetermined vehicle road speed and terminating at a second higher predetermined vehicle road speed, and a solenoid valve actuated via said continuous signal from said electronic speed switch, said solenoid valve being hydraulically interconnected with said speed control cover only when the setting of said speed control valve corresponds with said higher speed ratio for providing a pressure for actuating at least a portion of said downshift valve means;
• and said downshift valve means including a sandwich valve interposed between said manually actuated control means and said transmission, said sandwich valve including first and second bores that serve to channel pressurized fluid from said speed control valve to said lower and higher speed ratio clutches, respectively, said sandwich valve further including third and fourth bores intersecting said first and second bores, respectively, a higher speed ratio clutch valve associated with said fourth bore for selectively closing off an entrance portion of said second bore, thereby interrupting the flow of pressurized fluid to said higher speed ratio clutch, means for actuating said higher speed ratio clutch valve to closed position, said actuating means being hydraulically interconnected with and controlled by said solenoid valve, and a lower speed ratio clutch valve associated with said third bore for selectively closing off an entrance portion of said first bore, while simultaneously selectively opening an exit portion of said first bore to said third bore.

For use with a vehicle having a transmission with separate fluid operated clutches for selecting a plurality of speed ratios, a transmission control system including a source of pressurized fluid, a transmission control cover with a speed control valve for controlling the flow of fluid to said speed ratio clutches wherein the improvement takes the form of a transmission automatic downshift system comprising an electronic speed sensing system in combination with downshift valve means for automatically shifting said transmission one step, which said speed control valve is set for a second speed ratio, to a lower first speed ratio, at a first predetermined ground speed by diverting pressurized fluid from a second speed ratio clutch to a first speed ratio clutch and thereafter, at a second higher predetermined ground speed, automatically shifting said transmission said one step back to said second speed ratio by ceasing the diverting of said fluid, with the diverting of said fluid being possible only while said speed control valve is set for said second speed ratio;

• and said electronic speed sensing system including an electronic signal generator operatively connected with said transmission for producing an electronic pulse signal proportional to vehicle road speed, an electronic speed switch actuated via said signal generator for producing a continuous signal below said first predetermined vehicle road speed and terminating at said second higher predetermined vehicle road speed, and a solenoid valve actuated via said signal from said electronic speed switch, said solenoid valve being hydraulically interconnected with said control cover only in said second speed ratio for providing a pressure for actuating said downshift valve means.

For use with a vehicle having a transmission with separate fluid operated clutches for selecting a plurality of speed ratios, a transmission control system including a source of pressurized fluid, a transmission control cover with a speed control valve for controlling the flow of fluid to said speed ratio clutches wherein the improvement takes the form of a transmission automatic downshift system comprising a speed sensing system in combination with downshift valve means for automatically shifting said transmission one step, while said speed control valve is set for a second speed ratio, to a lower first speed ratio, at a first predetermined ground speed by diverting pressurized fluid from a second speed ratio clutch to a first speed ratio clutch and thereafter, at a second higher predetermined ground speed, automatically shifting said transmission said one step back to said second speed ratio by ceasing the diverting of said fluid, with the diverting of said fluid being possible only while said speed control valve is set for said second speed ratio;

• and said speed sensing system including a signal generator operatively connected with said transmission for producing a signal proportional to vehicle road speed, a speed switch actuated via said signal generator for producing a continuous signal below said first predetermined vehicle road speed and terminating at said second higher predetermined vehicle road speed, and means for providing a pressure for actuating said downshift valve means, said pressure means actuated via said signal from said speed switch and hydraulically interconnected with said control cover only in said second speed ratio.