Automatic transmission gear system for vehicles

Claim 1

An automatic transmission gear system for vehicles comprising a plurality of advance gears, a oneway clutch for achieving a gear shift at a lower speed and a friction engagement device provided in parallel with said oneway clutch and operated by oil pressure, a manual valve connected to a source of oil pressure, which is a characterized in that it is provided with detecting means which detect at least one parameter indicating the operating or driving conditions of the vehicle, and an oil pressure control device which is fluidly interposed between the manual valve and the friction engagement device and which supplies said friction engagement device with a high pressure oil when the engine brake is necessary at said gear shift at the lower speed and with a low pressure oil at which said friction engagement device is substantially released when the engine brake is not necessary in correspondence with the signals transmitted from said detecting means, said oil pressure control device including first and second valve means fluidly coupled together and to the manual valve, said first and second valve means cooperating so that when one valve means is controlling oil pressure, the other valve means is inoperative, each valve means also being an oil pressure pulse accumulator when it is not controlling oil pressure, and a solenoid valve means connected to said detecting means and to said first and second valve means for detecting different driving conditions to control operation of said first and second valve means, and a speed shifting valve connected to said first and second valve means and to said friction engagement device to supply oil to that friction engagement device from said first and second valve means.