Automatic transmission control system with holddown device

For use with an automatic transmission for an automotive vehicle, comprising a gear transmission mechanism comprising a plurality of hydraulic fluid pressure actuated friction engaging mechanisms, and wherein a selective supply of actuating hydraulic fluid pressure to said friction engaging mechanisms selectively provides a plurality of speed stages from said gear transmission mechanism including an overdrive speed stage and a directly coupled speed stage which is the next speed stage below said overdrive speed stage;

• a hydraulic fluid pressure control system, comprising:
• (a) a manually operated selector valve which is manually selectable between a plurality of speed ranges including a "D" range, and at least one forward speed range which is not said "D" range, and which produces a forward pressure when any forward speed range is selected thereon, and a lower range pressure when any forward speed range except said "D" range is selected thereon;
• (b) a means for producing a kickdown pressure, which produces a kickdown pressure when and only when the value of a quantity representative of engine load is above a predetermined value;
• (c) an electrically operated hydraulic fluid pressure control device, which, according to a selective supply of actuating electrical energy thereto, selectively produces a holddown pressure;
• and which is controlled in accordance with operating conditions of the vehicle;
• (d) a direct/overdrive shift valve, comprising a sole override port;
• which, when no overriding hydraulic fluid pressure is supplied to said override port, controls the supply of hydraulic fluid pressure to at least one of said friction engaging mechanisms so as selectively to engage either said overdrive speed stage or said directly coupled speed stage of said gear transmission mechanism according to a balance relationship between a throttle pressure which is related to a quantity representative of engine load and a governor pressure which is related to vehicle road speed;
• and which, when overriding hydraulic fluid pressure is supplied to said override port, controls supply of hydraulic fluid pressure to said at least one friction engaging mechanism so as to definitely not engage said overdrive speed stage of said gear transmission mechanism, irrespective of said balance relationship between said throttle pressure and said governor pressure;
• and
• (e) a downshift fluid pressure selector valve, which has a single valve bore having four inputs ports adapted to be supplied with said forward pressure, said lower range pressure, said kickdown pressure and said holdown pressure, respectively, as input pressure signals, and one output port connected to said override port of said direct/overdrive shift valve, a single valve element slidably mounted in said valve bore, and a single bias spring, said output port delivering a substantial output pressure when either said lower range pressure is present or said kickdown pressure is present or said holddown pressure is absent.