Gearshift timing control arrangement for automatic power transmission

In an automatic power transmission having at least two forward drive range ratios consisting of lower and higher forward drive gear ratios and including a transmission mechanism having a fluid operated first frictional unit contributive to the shifting to the higher forward drive gear ratio when it is engaged and a fluid operated second frictional unit contributive to the shifting to the higher gear ratio when it is disengaged and a hydraulic control system including actuating fluid pressure generating means for producing an actuating fluid pressure to be supplied selectively to the first and second frictional units, control pressure generating means for producing a control fluid pressure, first passageway means for passing said actuating fluid pressure toward said first frictional unit for causing engagement of the first frictional unit, second passageway means for passing said actuating fluid pressure therethrough toward said second frictional unit for causing disengagement of the second frictional unit, a gear shift valve means for permitting said actuating fluid pressure through said first passageway and through said second passageway means in accordance with a predetermined schedule which is determined in response to said control fluid pressure, a gearshift timing control arrangement for incorporation into said hydraulic control system, comprising:

• first and second one-way flow restriction means arranged in series between said first passageway means and said second frictional unit, the first one-way flow restriction means intervening between the first passageway means and the second one-way flow restriction means and operative to pass fluid away from the second one-way flow restriction means toward said first passageway means without flow restriction therethrough and restrict the flow rate of the fluid to be passed in the opposite direction therethrough, the second one-way flow restriction means intervening between the first one-way flow restriction means and said second frictional unit and operative to restrict the flow rate of the fluid to be passed therethrough toward said second frictional unit,
• bypass passageway means bypassing the second one-way flow restrictor means of the series combination of said first and second one-way flow restriction means;
• and
• a gearshift timing valve provided in said bypass passageway means and responsive to said control fluid pressure for allowing said bypass passageway means to open when the control fluid pressure is lower than a predetermined value and closing the bypass passageway means when the control fluid pressure is higher than the predetermined value.