Pressure control apparatus for the automatic transmission of automotive vehicles

Claim 1

Apparatus for controlling the supply pressure of the control members of an automatic transmission for vehicle power units, said apparatus comprising a control generator element supplying an electrical command voltage which is directly proportional to said supply pressure as a function of electrical signals representing information relative to the functioning of said transmission and of the vehicle power unit, said information comprising the state of the transmission, whether in engagement or between engagements due to inherent circuit delay, the ratio engaged or about to be engaged, the rotational speed of a transmission member, and the load of the vehicle power unit, said apparatus comprising in combination therewith: first means for supplying a first voltage which is a decreasing linear function of the said rotational speed and whose gradient is a function of the state of the transmission ratio, second means for supplying, starting from the said first voltage, a second voltage which is a decreasing linear function analogous to said first voltage but whose position is displaced as a function of the said load, third means for supplying, starting from said second voltage and from the information relative to the state of the transmission ratio, a third voltage which is a decreasing function of the rotational speed and comprises two linear portions connected by a point of discontinuity, the respective gradients of each of said linear portions being a function of the state of the transmission ratio, and fourth means supplying, starting from said third voltage and from the information relative to the said load, a fourth voltage which is a decreasing function of the rotational speed and comprises two linear portions connected by a point of discontinuity whose position is a function of the load, said control generator element being responsive to said four voltages for supplying said command voltage.