Hydraulic control device

Claim 1

An automatic transmission powered by an engine, for vehicles comprising means for initiating a downshift from a higher gear to a lower gear at time t1, means for engaging the lower gear at time t2 to complete the downshift, and means responsive to vehicle speed for unloading the engine by releasing the higher gear at a continuously variable release time between t1 and t2, the interval between the release time and time t2 being just sufficient to allow the unloaded engine to accelerate into synchronism with the lower gear, regardless of vehicle speed when the downshift is made.

Claim 3

An apparatus for controlling the automatic shifting of a planetary gear when downshifting the type of automatic transmission used in motor vehicles having a clutch controlling the higher gear, a brake-band controlling the lower gear, the brake-band being actuated by a brake-band piston which is double-acting and receives control pressure from a hydraulic medium on the application side through a brake application line by means of a pressure-reducing device causing a pressure reduction in the hydraulic medium, and a sleeve valve that shifts in response to certain conditions of vehicle speed and engine load to connect to atmospheric pressure (1) a clutch line used to carry control pressure to the application side of the clutch piston and (2) a brake release line used to carry control pressure to the release side of the brake-band piston, the improvement comprising means defining a fixed orifice restriction in the clutch line, an unrestricted bypass line that is vented to atmospheric pressure and connected in parallel to the fixed orifice restriction means, the bypass line having opening means having continuously variable dependence on vehicle speed, a pressure reservoir means connected in parallel to the clutch to cause a delay in the drop of the control pressure in the clutch line by discharging, initially through the fixed orifice restriction and subsequently through the bypass line, and a single fixed orifice restriction means acting as the pressure reducing device associated with the application side of the brake band piston to cause engagement of the lower gear in a fixed time, the drop in control pressure in the clutch line and the disengagement of the higher gear being made dependent on vehicle speed by the pressure reservoir means, the bypass line opening means and the clutch line fixed orifice restriction means to allow sufficient time for engine synchronism with the lower gear and to permit a smooth downshift at any vehicle speed.

Claim 4

An apparatus for controlling the automatic shifting of a planetary gear when downshifting the type of automatic transmission used in motor vehicles having a clutch controlling the higher gear, a brake-band controlling the lower gear, the brake-band being actuated by a brake-band piston which is double-acting and receives control pressure from a hydraulic medium on the application side through a brake application line by means of a pressure-reducing device causing a pressure reduction in the hydraulic medium, and a sleeve valve that shifts in response to certain conditions of vehicle speed and engine load to connect to atmospheric pressure (1) a clutch line used to carry control pressure to the application side of the clutch piston and (2) a brake release line used to carry control pressure to the release side of the brake-band piston, the improvement comprising means defining a fixed orifice restriction in the clutch line, an unrestricted bypass line that is vented to atmospheric pressure and connected in parallel to the fixed orifice restriction means, the bypass line having opening means having continuously variable dependence on vehicle speed, a pressure reservoir means connected in parallel to the clutch to cause a delay in the drop of the control pressure in the clutch line by discharging, initially through the fixed orifice restriction and subsequently through the bypass line, and a single fixed orifice restriction means acting as the pressure reducing device associated with the application side of the brake band piston to cause engagement of the lower gear in a fixed time, the drop in control pressure in the clutch line and the disengagement of the higher gear being made dependent on vehicle speed by the pressure reservoir means, the bypass line opening means and the clutch line fixed orifice restriction means to allow sufficient time for engine synchronism with the lower gear and to permit a smooth downshift at any vehicle speed.