System and method for minimal draindown in cvt

Abstract

A hydraulic control system for a transmission is provided. The hydraulic control system provides a latching system to retain CVT clutch pressure and/or pulley pressure for one or more CVT torque transmitting mechanisms and/or CVT pulleys in a CVT transmission. Components of the hydraulic control system of the present disclosure may include blow off valves, such as ball check-valves, on the exhaust of the pulley control valves and the exhaust of the CVT clutch control valve(s), and a one-way valve, such as a supply ball check-valve, disposed adjacent to each of the fluid supply inlets of the pulley control valves and the fluid supply inlet of the CVT clutch control valve(s).

What is claimed is: 
     
         1 . 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, the accumulator circuit being in downstream fluid communication with the inlet valve; and   a clutch control circuit configured to fill a 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 clutch.   
     
     
         2 . The hydraulic control circuit of  claim 1 , wherein the inlet valve is a one-way valve configured to allow fluid to flow from the supply line to the pulley control circuit, the one-way valve being configured to prevent fluid from flowing from the pulley control circuit to the supply line. 
     
     
         3 . The hydraulic control circuit of  claim 2 , wherein the pulley valve outlet is a first pulley valve outlet, the pulley control valve assembly further comprising a second pulley valve outlet, the second pulley valve outlet being in upstream fluid communication with a pulley exhaust circuit, the pulley exhaust circuit fluidly communicating with a pulley blow-off valve. 
     
     
         4 . The hydraulic control circuit of  claim 3 , the accumulator circuit comprising an accumulator and an on-off valve, the on-off valve being configured to open to allow the accumulator to pressurize the pulley control circuit. 
     
     
         5 . The hydraulic control circuit of  claim 3 , wherein the pulley blow-off valve is a minimum pressure blow-off valve. 
     
     
         6 . The hydraulic control circuit of  claim 5 , wherein the pulley blow-off valve is configured to open at a minimum pressure from about 3 psi to about 5 psi. 
     
     
         7 . The hydraulic control circuit of  claim 2 , the one-way valve being a first one-way valve, the accumulator circuit further comprising a second one-way valve in upstream fluid communication with the accumulator, the second one-way valve being configured to open to charge the accumulator from the source of pressurized hydraulic fluid, the second one-way valve being configured to trap hydraulic fluid in the accumulator when fluid pressure in the accumulator exceeds fluid pressure in the supply line. 
     
     
         8 . The hydraulic control system of  claim 1 , the clutch valve outlet being a first clutch valve outlet, the clutch regulator valve assembly having a second clutch valve outlet in fluid communication with a clutch exhaust circuit, the clutch exhaust circuit fluidly communicating with a clutch blow-off valve. 
     
     
         9 . The hydraulic control system of  claim 8 , the clutch control circuit being in downstream fluid communication with the accumulator circuit. 
     
     
         10 . The hydraulic control circuit of  claim 9 , the clutch control circuit further comprising a third one-way valve in upstream fluid communication with the clutch and in downstream fluid communication with the clutch regulator valve assembly, the clutch control circuit further comprising a restricting orifice disposed in fluid communication between the first clutch valve outlet and the clutch. 
     
     
         11 . 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.   
     
     
         12 . The hydraulic control system of  claim 11 , the clutch valve outlet being a first clutch valve outlet, the clutch regulator valve assembly having a second clutch valve outlet in fluid communication with a clutch exhaust circuit, the clutch exhaust circuit fluidly communicating with a clutch blow-off valve. 
     
     
         13 . The hydraulic control system of  claim 11 , the clutch control circuit being in downstream fluid communication with the accumulator circuit. 
     
     
         14 . The hydraulic control circuit of  claim 11 , wherein the pulley valve outlet is a first pulley valve outlet, the pulley control valve assembly further comprising a second pulley valve outlet, the second pulley valve outlet being in upstream fluid communication with a pulley exhaust circuit, the pulley exhaust circuit fluidly communicating with a pulley blow-off valve. 
     
     
         15 . The hydraulic control circuit of  claim 14 , wherein the pulley blow-off valve is a minimum pressure blow-off valve. 
     
     
         16 . The hydraulic control circuit of  claim 14 , wherein the pulley blow-off valve is configured to open at a minimum pressure from about 3 psi to about 5 psi. 
     
     
         17 . The hydraulic control circuit of  claim 11 , wherein the clutch valve outlet is in fluid communication with a second clutch. 
     
     
         18 . The hydraulic control circuit of  claim 11 , wherein the first clutch is a drive clutch and the second clutch is a reverse clutch. 
     
     
         19 . 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.   
     
     
         20 . The hydraulic control system of  claim 17  wherein the first clutch is a drive clutch and the second clutch is a reverse clutch.