Circuit and a method for feeding oil to rolling bearings in a turbomachine

1. A circuit for feeding oil to rolling bearings in a turbomachine, the circuit comprising:

an oil supply;

an oil duct connecting the oil supply to a plurality of lubrication enclosures connected in parallel and each of the lubrication enclosures containing at least one rolling bearing;

an oil feed pump disposed in the oil duct between the oil supply and the lubrication enclosures in order to take oil from the oil supply and deliver the oil to the rolling bearings; and

an oil recovery pump connected downstream from each lubrication enclosure in order to recover the oil that has been fed to the rolling bearings and return the oil to the oil supply;

a pressurizing valve placed in the oil duct between the oil feed pump and the lubrication enclosures, said pressurizing valve being adapted to open when a pressure at an inlet of the pressurizing valve exceeds a predetermined threshold pressure;

a branch connection duct in direct fluid communication with the inlet of the pressurizing valve and one of the lubrication enclosures, the one of the lubrication enclosures being always fed with oil via the branch connection duct even when the pressure at the inlet of the pressurizing valve has not reached the predetermined threshold; and

means for feeding the lubrication enclosures at a small oil flow rate when the pressure at the inlet of the pressurizing valve has not reached the predetermined threshold pressure,

wherein an inlet of the branch connection duct is placed in the oil duct upstream of the inlet of the pressurizing valve and an outlet of the branch connection duct is placed in the one of the lubrication enclosures, and

wherein the pressurizing valve is in direct fluid communication with the one of the lubrication enclosures.

2. A circuit according to claim 1 , further comprising a bypass duct connecting the inlet of the pressurizing valve to an outlet of the pressurizing valve and having a flow section that is calibrated to allow lubrication enclosures to be fed with oil at a low flow rate.

3. A circuit according to claim 2 , wherein the bypass duct is separate from the pressurizing valve, an inlet of the bypass duct is placed in the oil duct upstream of the inlet of the pressurizing valve, and an outlet of the bypass duct is placed in the oil duct downstream of the outlet of the pressurizing valve.

4. A circuit according to claim 1 , wherein the pressurizing valve presents a calibrated leakage rate so as to enable lubrication enclosures to be fed with oil at a low flow rate.

5. A circuit according to claim 1 , wherein the pressurizing valve is a check valve type having a rated spring.

6. A circuit according to claim 1 , further comprising an accessory gearbox and a transfer gearbox connected to the oil supply by the oil duct and connected in parallel with the rolling bearings.

7. A circuit according to claim 1 , including one lubrication enclosure situated at a front of the turbomachine and two lubrication enclosures situated at a rear of the turbomachine, the branch connection duct connecting the inlet of the pressurizing valve to the lubrication enclosure situated at the front.

8. A turbomachine including a circuit for feeding oil to rolling bearings according to claim 1 .

9. A circuit according to claim 1 , wherein said pressurizing valve is opened when a pressure of the one of the lubrication enclosures exceeds the predetermined threshold pressure.

10. A method of feeding oil to rolling bearings in a turbomachine, the bearings being connected in parallel in an oil circuit, the method comprising:

taking oil from an oil supply and delivering the oil to lubrication enclosures each containing at least one rolling bearing via an oil duct; and

recovering the oil that has been fed to the lubrication enclosures and returning the oil to the supply;

wherein a flow rate of oil fed to certain lubrication enclosures is reduced when an oil feed pressure to one of the lubrication enclosures is less than a predetermined threshold pressure,

wherein a pressurizing valve placed in the oil duct between the oil supply and the lubrication enclosures, said pressurizing valve being adapted to open when a pressure at an inlet of the pressurizing valve exceeds the predetermined threshold pressure,

wherein a branch connection duct is placed in direct fluid communication with the inlet of the pressurizing valve and the one of the lubrication enclosures, the one of the lubrication enclosures being always fed with oil via the branch connection duct even when the pressure at the inlet of the pressurizing valve has not reached the predetermined threshold,

wherein an inlet of the branch connection duct in placed in the oil duct upstream of the inlet of the pressurizing valve and an outlet of the branch connection duct is placed in the one of the lubrication enclosures, and

wherein the pressurizing valve is in direct fluid communication with the one of the lubrication enclosures.

11. A method according to claim 10 , further comprising opening said pressurizing valve when a pressure of the one of the lubrication enclosures exceeds the predetermined threshold pressure.

12. A method according to claim 10 , further comprising providing a bypass duct connecting the inlet of the pressurizing valve to an outlet of the pressurizing valve and having a flow section that is calibrated to allow lubrication enclosures to be fed with oil at a low flow rate.

13. A method according to claim 12 , wherein the bypass duct is separate from the pressurizing valve, an inlet of the bypass duct is placed in the oil duct upstream of the inlet of the pressurizing valve, and an outlet of the bypass duct is placed in the oil duct downstream of the outlet of the pressurizing valve.