System and method for minimal draindown in cvt

A hydraulic control system for a continuously variable transmission, the hydraulic control system comprising:

• a source of pressurized hydraulic fluid configured to communicate pressurized hydraulic fluid via a supply line;
• a pulley control circuit configured to fill a plurality of pulleys with pressurized hydraulic fluid and axially move at least one pulley of the plurality of pulleys to adjust a speed ratio, the pulley control circuit including a pulley control valve assembly having a pulley valve inlet and a pulley valve outlet, the pulley valve inlet being in downstream fluid communication with the supply line, the pulley valve outlet being in direct fluid communication with only one of the plurality of pulleys;
• an inlet valve disposed in downstream fluid communication with the supply line, the inlet valve configured to selectively communicate fluid from the supply line to the pulley control valve assembly, the inlet valve being further configured to close to keep fluid pressure in the pulley control circuit when fluid pressure in the pulley control circuit exceeds fluid pressure in the supply line;
• an accumulator circuit in upstream fluid communication with the pulley control valve assembly and downstream fluid communication with the inlet valve, the accumulator circuit having an accumulator, an on-off valve, and a second one-way valve, the on-off valve being configured to open to allow the accumulator to pressurize the pulley control circuit, and the second one-way valve in upstream fluid communication with the accumulator and configured to open to charge the accumulator from the source of pressurized hydraulic fluid and configured to trap hydraulic fluid in the accumulator when fluid pressure in the accumulator exceeds fluid pressure in the supply line;
• and
• a clutch control circuit configured to fill a first clutch with pressurized hydraulic fluid, the clutch control circuit including a clutch regulator valve assembly having a clutch valve inlet and a clutch valve outlet, the clutch valve inlet being in downstream fluid communication with the supply line and the inlet valve, the clutch valve outlet being in fluid communication with the first clutch.

A hydraulic control system for a continuously variable transmission, the hydraulic control system comprising:

• a source of pressurized hydraulic fluid configured to communicate pressurized hydraulic fluid via a supply line;
• a pulley control circuit configured to fill a plurality of pulleys with pressurized hydraulic fluid and axially move at least one pulley of the plurality of pulleys to adjust a speed ratio, the pulley control circuit including a pulley control valve assembly having a pulley valve inlet and a pulley valve outlet, the pulley valve inlet being in downstream fluid communication with the supply line, the pulley valve outlet being in direct fluid communication with only one of the plurality of pulleys;
• an inlet valve disposed in downstream fluid communication with the supply line, the inlet valve configured to selectively communicate fluid from the supply line to the pulley control valve assembly, the inlet valve being further configured to close to keep fluid pressure in the pulley control circuit when fluid pressure in the pulley control circuit exceeds fluid pressure in the supply line;
• an accumulator circuit in upstream fluid communication with the pulley control valve assembly and downstream fluid communication with the inlet valve, the accumulator circuit having an accumulator, an on-off valve, and a second one-way valve, the on-off valve being configured to open to allow the accumulator to pressurize the pulley control circuit, and the second one-way valve in upstream fluid communication with the accumulator and configured to open to charge the accumulator from the source of pressurized hydraulic fluid and configured to trap hydraulic fluid in the accumulator when fluid pressure in the accumulator exceeds fluid pressure in the supply line;
• and
• a clutch control circuit configured to fill a first clutch and a second clutch with pressurized hydraulic fluid, the clutch control circuit including a clutch regulator valve assembly having a clutch valve inlet and a clutch valve outlet, the clutch valve inlet being in downstream fluid communication with the supply line and the inlet valve, the clutch valve outlet being in fluid communication with the first clutch and the second clutch.