Patent Application
20140331639
This application claims priority under 35 U.S.C. §119 to European Patent Application No. 13167305.5, filed 10 May 2013, titled “Turbomachine Lubrication System with an Anti-Siphon Valve for Windmilling,” which is incorporated herein by reference for all purposes.
1. Field of the Application
The present application relates to a circuit for distributing oil to an aircraft turbomachine. More specifically, the present application relates to one or more hydraulic circuits for actuating, cooling and/or lubricating the devices in an aircraft turbine engine. The present application relates also to an axial turbomachine in accordance with the present application.
2. Description of Related Art
An A turbomachine uses oil for different functions. This oil can be used both to lubricate moving parts and to cool them. The oil may also be used to actuate or feed devices because of its pressure. For example, it can be used to adjust the pitch of the fan blades of a turboprop or for damping movement transferred by the bearings (squeeze film). The oil may also be used to heat or cool certain parts of the turboprop or even the aircraft.
To carry out these functions, the oil is piped into a circuit with a pump for circulating it. Since different devices are connected in common to the circuit, there are usually several pumps in the circuit. Each can deliver or scavenge the oil at different rates and/or pressures so as to feed individual devices or groups of devices. Advantageously, these pumps are driven by a power takeoff on the shaft of the turbomachine in order to simplify the drive mechanism.
This drive mechanism ensures circulation of oil in a turboprop on an aircraft, even when it is cut off but the rotor is still spinning. In flight, the aircraft can fulfil its mission by cutting fuel to one of its engines. The blast of air created by the aircraft's speed is able to rotate the fan and thus the pumps connected to it.
Furthermore, an aircraft must obey safety rules associated with engine fires. The circuit must be able to cut off the flow of oil where it is likely to fuel the fire, and permit circulation in the devices requiring lubrication or mechanical energy. The circulating oil remains beneficial for certain devices which it can cool to a certain extent.
To provide these modes, control valves are associated with different pumps. However, the number of devices to be controlled, and the various modes to be taken into account necessitate a large number of control valves and a plurality of controls and sensors. Their number increases the cost of such an oil circuit, and its reliability is reduced.
Patent GB 2042649A discloses an oil feed system for the bearings of a turbomachine. The bearings are fed directly or via a distributor to which parallel loops are connected. The bearing oil is scavenged by means of pumps and is then sent to an auxiliary gearbox. The system has several non-return valves, one of which is located upstream of the distributor. Different pumps scavenge or inject oil from/into the bearings. A bypass valve with a programmable valve allows direct feed from an auxiliary gearbox when the turbomachine is idling and the non-return valve is closed. The system allows the flow of oil to be controlled very precisely. However, it requires complex control mechanisms.
Patent US2008/0178833 A1 discloses a turbomachine lubricating system. It has a feed for the turbomachine's devices and a scavenge pump for recovering the oil from the said devices, the two pumps being driven by the rotor shaft. For safety reasons, the circuit is provided with calibrated valves located at the outlet of each pump. They are configured to cut off the flow of oil in the event of windmilling. The system also includes a bypass loop to the oil at the outlet of the oil feed pump. The safety of this system when windmilling is based on calibrated valves, the latter being subject to attack by flames in the event of a turbomachine fire. In addition, this system does not meet the specific needs of certain devices in terms of safety, as these devices must remain supplied with oil in the event of windmilling.
Although great strides have been made in the area of lubrication for axial turbomachines, many shortcomings remain.
The present application aims to solve at least one of the technical problems presented by the prior art. The present application also aims to improve the safety of operating an oil feed system for a turbomachine. The present application also aims to simplify the operation of an oil feed system of a turbomachine while maintaining a given level of safety.
The present application relates to an oil feed system for a turbomachine comprising: a tank designed to contain a volume of oil; a feed pump for at least one device in the turbomachine, the said pump being connected to the tank and the said one or more devices; means of closure of the flow from the feed pump to the device or devices when the pump speed is less than a speed R1; wherein the means of closure are located hydraulically upstream of the pump, between the said pump and the tank.
According to an advantageous embodiment of the present application, the means of closure comprises an anti-siphon valve designed to close when the suction level of the feed pump is lower than a given threshold.
According to an advantageous embodiment of the present application, the system comprises a heat exchanger such as a cooler that is designed to contain a volume of oil; preferably the cooler essentially forms a closed chamber.
According to an advantageous embodiment of the present application, the means of closure are accommodated in the tank. The tank may be designed such that the valve can be immersed in the oil in the tank.
According to an advantageous embodiment of the present application, the means of closure are mechanically controlled by the suction level of the pump and preferably also by the pressure in the tank.
According to an advantageous embodiment of the present application, the pump is a first pump, the means of closure are the first means of closure; the system further comprising a second feed pump for which the mechanical drive is coupled to that of the first pump connected to the tank and one or more other devices in the turbomachine, the second means of closure of the flow from the second pump when the speed of the first feed pump falls below a speed R2, the said means being located upstream of the said pump, the speed R2 being different from speed R1.
According to an advantageous embodiment of the present application, speeds R1 and R2 have predetermined values.
According to an advantageous embodiment of the present application, speeds R1 and R2 differ by greater than 5%, more preferably by greater than 10%, more preferably by greater than 30%, even more preferably by greater than 100%.
According to an advantageous embodiment of the present application, the feed pump(s) has or have internal bypasses designed to reduce its or their suction level when the corresponding means of closure cuts off the flow.
According to an advantageous embodiment of the present application, the system includes a control pipe connecting the outlet(s) of the feed pump(s) to the corresponding means of closure to allow an oil flow when the discharge pressure of the said pump(s) exceeds a pressure P1.
The present application also relates to a turbojet comprising devices and an oil feed system, wherein the feed system is in accordance with the present application.
According to an advantageous embodiment of the present application, the turbojet includes a fan, the drive from which is coupled to that of the or one of the supply pumps, the rotating fan driving the said feed pump at a speed R3 when the turbojet is in flight and is not being supplied with fuel, corresponding to an autorotation flight mode, the speed R3 being less than the speed R1, so that the feed pump(s) do not operate when the turbojet is in autorotation flight mode.
According to an advantageous embodiment of the present application, the pump is a first pump, the means of closure are the first means of closure; the system further comprising a second feed pump for which the mechanical drive is coupled to that of the first pump and connected to the tank and one or more of the other devices on the turbomachine, the second means of closure of the feed from the second feed pump when the speed of the first feed pump falls below a threshold R2, the said means being arranged upstream of the said pump, the speed R2 differing from R1, wherein the turbojet comprises a fan which is coupled to drive the first and second feed pumps, the rotating fan driving the first feed pump at a speed R3 when the turbojet is in flight and not being supplied with fuel, corresponding to an autorotation flight mode, wherein the speed R3 lies between speeds R1 and R2, such that one of the first and second feed pumps discharges to its/their corresponding devices and the other of the said pumps does not discharge when the turbojet is in autorotation flight mode.
According to an advantageous embodiment of the present application, the drive speed R3 is less than 50%, preferably 30%, more preferably 10% of the drive speed when the turbojet is at its rated operational speed.
According to an advantageous embodiment of the present application, the speed R3 covers a range of values.
According to an advantageous embodiment of the present application, the devices supplied by the feed pump(s) comprise at least one rotor bearing lubrication chamber.
According to an advantageous embodiment of the present application, the oil feed system further comprises an oil scavenge loop for at least one of the devices, the loop being provided with a scavenge pump for which the drive is preferably coupled to the drive for the feed pump(s).
According to an advantageous embodiment of the present application, the oil feed system comprises a control pipe connecting the recovery loop downstream of the recovery pump with corresponding means of closure, the said means being designed to allow a flow of oil when the pressure in the control channel is higher than a pressure P2.
The present application also relates to an aircraft comprising an oil feed system and/or a turbojet, wherein the oil feed system is in accordance with the present application and/or the turbojet complies with the present application.
The feed system is independent and operates automatically. The actuators are very quick and particularly safe.
The present application enables the oil flow in the feed system to be cut off or opened with simple means of closure. The opening of the supply at the means of closure is carried out proportional to the pump's, and hence the fan's, rotational speed, which enables the opening to be simply related to the turbojet's actual operating condition.
The present application enables several means of closure to be managed simply. In the event of windmilling and fire, the feed system has several modes of operation depending on the rotational speed of the fan. It enables the bearings to be lubricated and, at the same time, cuts off the circulation to where a leak may occur.
This is achieved without any means of external control. It enables the flow to be cut off completely when the turbojet is at rest and allows full flow when the jet engine operates at conventional speeds. The system cuts the feed when it becomes dangerous, and maintains it at the necessary level.
The central shaft 12 is rotatably mounted with respect to the housing of the turbomachine 2 by means of sets of bearings. These may include mechanical bearings that must be lubricated. This requirement is also necessary for the means of speed reduction. To meet these needs, the turbojet 2 includes an oil feed system that delivers oil to the different sets of bearings and the means of reduction.
The feed system may include a heat exchanger to cool the oil during operation. A quantity of oil is stored in a tank 16. This oil can then be used to cool the devices in the turbojet 2.
An intake fan, generally designated a fan, 18 is coupled to the rotor 14 and generates a flow of air which is divided into a primary flow 20 and secondary flow 22. The primary flow 20 follows a thermodynamic compression/expansion cycle. The secondary flow 22 provides the majority of the thrust of the jet engine via the fan 18. The fan 18 may be connected to the central shaft via a reduction gearbox which is lubricated by the feed system. Its speed can be set. This setting can be adjusted using the mechanical energy of the oil feed system.
The fan 18 is also capable of acting as an absorber of mechanical energy. During flight, at cruising speed, the turbojet 2 can be cut off so that it no longer generates any propulsive force. Due to the speed of the aircraft, a blast of air can turn the fan 18. This can also drive the devices and the equipment coupled thereto. This mode is commonly called “windmilling”, or autorotation. Generally speaking, the rotational speed of the fan 18 is then less than half its speed of rotation when operating at the rated speed of the turbojet 2, preferably less than a quarter, more preferably less than one tenth.
The oil is fed from the tank 16 to the various devices on the turbojet 2 via a primary feed 24. The devices may comprise a chamber for lubricating a bearing and a heat exchanger. The system includes a first feed pump 26 placed on the primary feed 24 and which draws oil from the tank 16. The pump's suction and discharge rates can be set according to its speed. That may be its rotational speed in the case of a rotary pump, or its frequency in the case of an oscillating pump. These pressures are also dependent on the viscosity of the oil at a given temperature.
The feed system further comprises a first means of closure, such as an anti-siphon valve 28, designed to prevent or enable the flow of oil from the tank 16 to the devices. It may be located at the lowest point of the tank 16. The valve 28 is located upstream of the first pump 26, and preferably upstream of any equipment or device connected to the primary feed 24.
The anti-siphon valve 28 is calibrated so as to remain closed in the presence of the column of oil held in the tank. When at a complete stop it prevents the tank emptying into the turbojet 2.
The valve 28 may include a sealing cap and an associated seat. When the sealing cap is on its seat, the valve is closed. The means of closure may include biasing or adjustment means to return the sealing cap to its seat in a closed position. The calibration means may include a pre-loaded spring which keeps the sealing cap on its seat provided it is subjected to a predetermined force. This force can be translated into a pressure applied to the sealing cap which corresponds to the opening pressure of the valve 28.
The operation of the valve 28 thus depends on the pressure difference to which it is subjected. This pressure difference depends mainly on the pressure in the tank 16, the geometry of the primary feed 24 and/or the suction pressure of the first pump 26. This depends on its speed. In this way, it is possible to adjust the opening of the valve depending on the rotational speed of the fan.
After reaching the devices, the oil can stay there or flow into the housing of the turbojet 2. It is sucked or drained as is the case by a scavenge pipe 30. This may comprise a scavenge pump 32 for scavenging the oil and then discharging it into the tank 16. A heat exchanger 34 may be located downstream of the scavenge pump 32. Thus the oil contained in the tank 16 remains at a low temperature relative to the temperature of the turbojet 2. The scavenge pipe 30 may comprise several pipes each equipped with a scavenge pump for scavenging the oil from different places at different rates.
The feed pump 26 and the scavenge pump 32 are mechanically coupled, directly or via gearboxes. They are also coupled to the fan 18 directly or via gearboxes. A shaft can engage the central shaft 12 to operate the pumps. This method of driving simplifies the system as it requires no external power to operate and no additional means of control. The rotation of the fan 18 and hence that of the central shaft 12 drives the feed and scavenge pumps (26, 32) during normal operation of the turbojet 2. If this latter is cut off, windmilling may occur, from which the fan 18 can drive the pumps (26, 32) and the various devices requiring lubrication. Cutting off the turbojet 2 means cutting its fuel supply.
The anti-siphon valve 28 is configured to open and permit the flow of oil in the event of windmilling. In this way, oil can be supplied to those devices that require lubrication because of their movement. The valve 28 has a dual function since it cuts off the flow of oil when the turbojet 2 comes to a complete stop, and reopens it in the event of windmilling when the rotational speed of the pump exceeds a speed R1. In the event of windmilling, the rotational speed of the fan 18 is substantially less than the nominal operating speed.
The present application can dispense with complex means of control that are both expensive and rather fragile.
To improve the reliability of the feed system or use a more straightforward operation, it may comprise a control pipe 36 connected to the outlet of the feed pump 26 and the valve 28. Its means of closure can be configured so as to allow flow when the delivery pressure of the feed pump 26 exceeds a pressure P1. Thus, when the rotational speed of the fan 18 is sufficiently high, the valve 28 opens, enabling the oil feed.
In the same way, the feed system may include a control pipe 38 connecting the scavenge loop 30 to the valve 28. The line 38 is advantageously located on the discharge side of the scavenge pump 32 in order to take advantage of the discharge pressure. This will be proportional to the rotational speed of the fan 18. The means of closure of the valve 28 may be configured to allow a flow of oil when the discharge pressure of the scavenge pump 32 exceeds a pressure P2. Thus, when the rotational speed of the fan 18 is sufficiently high, the valve 28 opens, enabling the oil feed. The pressures P1 and P2 may be different.
The feed system comprises a tank 116, a primary feed 124 and a secondary feed 125. They are both connected to the tank 116. The primary feed 124 comprises a first valve 128 and a first feed pump 126 downstream. The secondary feed 124 comprises a second valve 128 and a second feed pump 126 downstream. These feeds are advantageously in parallel. They each supply different devices For example, one may supply a bearing, and the other a heat exchanger.
The feed system comprises a scavenge pipe 130 with a scavenge pump 132. This scavenge pipe can be divided upstream and enables oil to be collected from different devices at different rates and pressures. The pumps (126, 127, 132) are mechanically coupled to the fan 118 and are therefore capable of circulating oil in the event of windmilling.
The valves (128, 129) are independent of one other. They are designed to cut the flow of oil from the tank 116 when the turbojet 102 has come to a complete stop. The first valve 128 is designed to open when the drive speed of the first feed pump 126 exceeds a speed R1, the second valve 129 is designed to open when the drive speed of the first feed pump 126 exceeds a speed R2, that is to say for different rotational speeds of the fan 118. The drive speeds R1 and R2 may differ by greater than 5%, preferably greater than 50%, more preferably greater than 100%, even more preferably greater than 300%.
This feed system provides power to various devices independently because of the rotation of the fan 118. One can be starved of a feed while another is fed. This configuration is particularly advantageous in the event of an engine fire and windmilling since the feed system enables, for example, a bearing to be supplied while cutting off the feed to a heat exchanger. In fact, in this mode, several devices are rotating and need to be lubricated. For its part, the heat exchanger can be damaged by fire and may release a significant amount of oil. This represents a fuel that could worsen the fire and further damage the aircraft. Being able to cut off the flow of oil to that device means that risks can be controlled.
The valves are located in the tank 116 or at its output. They are located upstream of any equipment or device. In this way, they can cut the flow in pipes that may be exposed to the fire. Thus they do not release any oil should these be damaged. The present application also enables the flow of oil to be cut off when there is insufficient oil in the pipes to cool them, thus allowing them to withstand the fire.
| Number | Date | Country | Kind |
|---|---|---|---|
| 13167305.5 | May 2013 | EP | regional |
