Hydraulic servo unit with solenoid operated valves having variab

Details Hydraulic servo unit with solenoid operated valves having variab Hydraulic servo unit with solenoid operated valves having variab

1992-06-24

1994-10-18

Look, Edward K.

Motors: expansible chamber type

Differential

Motive fluid constantly applied to one working member face

91459, F15B 1517, F15B 13044

Patent

active

053557727

ABSTRACT:
A hydraulic servo unit for changing the swash plate angle of a continuously variable transmission to vary its speed reduction ratio comprises a cylinder whose chamber is divided into a rod-side chamber and a head-side chamber by a piston slidably fitted therein. The rod-side chamber is supplied with working oil under predetermined hydraulic pressure through a first hydraulic pressure supply passage. A second hydraulic pressure supply passage is connected to the head-side chamber through a duty-cycle-controlled first solenoid-operated valve, and a drain hydraulic passage is connected to the second hydraulic pressure supply passage through a second duty-cycle-controlled solenoid-operated valve. The first and second solenoid-operated valves are simultaneously actuated with different duty cycles. The difference between the different duty ratios is varied to vary the rate at which the working oil flows into or out of the head-side chamber through the second hydraulic pressure supply passage, in a wide range from a very low rate to a high rate. The working oil can accurately be controlled especially in a very low rate range for operating the hydraulic servo unit at very low speed. Therefore, continuously variable transmission can precisely and smoothly be controlled for varying the speed reduction ratio.

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