Controls for four-forward-speed automatic transmissions

In an automatic transmission for an automotive vehicle of the four-forward-speed type having shiftable gear means for changing the power transmission ratio of said transmission, said gear means being structured to provide a plurality of shift ranges including four forward speed ranges and a reverse range, gear shift means including means for setting a plurality of gear shift ranges and hydraulic servo means for controlling transmission clutch and brake means to effect shifting of said gear means in response to pressure fluid supplied to or drained from said hydraulic servo means, said hydraulic servo means including four hydraulic servo mechanisms for controlling shifting in said forward speed ranges and one hydraulic servo mechanism for providing reverse speed operation, a hydraulic fluid source, and a hydraulic control circuit for controlling flow of pressure fluid to and from said hydraulic servo mechanisms, a control system comprising:

• signal generating means for generating electrical signals representative of the operating condition of said vehicle;
• logic circuit means responsive to said gear shift means for emitting electrical signals in accordance with the signals received from said signal generating means, said emitted signals being representative of the shift range setting of said gear shift means and of the operating condition of said vehicle;
• a manual valve included in said hydraulic control circuit connected for flow communication with said hydraulic fluid source and including first and second port means, and means for selectively communicating said first and second port means with said fluid source;
• a first shift valve having said first port means of said manual valve connected thereto, and including a pair of output ports and means for selectively communicating said manual valve first port means with said pair of output ports;
• a second shift valve connected to said pair of output ports of said first shift valve, and including a first pair and a second pair of output ports and means for selectively individually communicating said pair of output ports of said first shift valve with said first and said second pair of output ports of said second shift valve;
• means individually connecting each of the ports of said first and second pair of output ports of said second shift valve with one each of said forward speed hydraulic servo mechanisms;
• said first and second shift valves operating to selectively supply pressure fluid from said first port of said manual valve to said four foward speed servo mechanisms to perform shifting within said four foward speed ranges in accordance with the shift range setting of said transmission;
• shift valve actuating means responsive to said logic circuit means to control operation of said first and second shift valves in accordance with signals emitted from said logic circuit means;
• and
• means for communicating said second port of said manual valve with said one reverse speed hydraulic servo mechanism by way of one of said first and second shift valves so that there may be obtained four forward speeds including a first forward speed capable of providing engine braking at all times and one reverse range.