Cooling arrangement and method for offset gearbox
An offset gearbox of an aircraft has a sump for a lubricant. A heat exchanger core extends through the sump in contact with the lubricant.
A fluid coolant for cooling an accessory such as an electrical power generating unit drivingly connected to the offset gearbox is circulated through the core in thermal communication but not mixed with the lubricant of the offset gearbox for cooling the lubricant. The cooling arrangement for the offset gearbox advantageously does not require a separate or dedicated heat exchanger which reduces system weight and cost. The single pump of the accessory can also be used for circulating the coolant. Increased reliability, independent oil change for maintenance and enhanced attitude performance are attained as gearbox performance does not affect power generating unit performance, and visa versa. An existing aircraft can be modified to include the offset gearbox with a minimum of modification and little additional weight and plumbing.
Offset gearboxes can be used in aircraft, as for adapting electrical power generating equipment or other accessories to the existing aircraft engines in a retrofit. Installed length, angular orientation and input speed of the accessory such as the electrical power generating equipment can be optimized by use of and offset gearbox. Offset gearboxes normally contain a lubricant, typically oil, for lubrication of the gears therein. Internal gearbox heat, created by bearings, gear meshes and pump(s) of the gearbox, must be dissipated to maintain acceptable oil operating temperatures within the gearbox. A cooling arrangement for an offset gearbox must be cost effective and not add undue weight to the aircraft.
An object of the present invention is to provide a cooling arrangement for a device, particularly an offset gearbox in an aircraft which requires both cooling and lubrication, the cooling arrangement overcoming the aforementioned problems and disadvantages in the prior art.
An additional object of the invention is to provide a cooling arrangement of the aforementioned type wherein the gearbox internal lubricant can be kept separate from the coolant of the electrical power generating component or other accessory. It is also an object of the invention to provide an aircraft having a reliable cooling arrangement which is cost effective and adds very little additional weight to an aircraft.
These and other objects of the invention are attained by the cooling arrangement of the invention for a device which requires both cooling and lubrication. The cooling arrangement comprises a first device with a lubricant therein for lubricating the first device, a second device, a fluid coolant for cooling the second device, and means for circulating the fluid coolant for cooling the second device in thermal communication with but not mixed with the lubricant of the first device for cooling the lubricant and thereby the first device. In the disclosed embodiment, the first device is an offset gearbox adapted to be driven by an aircraft engine through an aircraft engine gearbox. The accessory, which can be an electrical power generating unit, is drivingly connected to the offset gearbox.
The means for circulating the fluid coolant includes a core located in a sump of the offset gearbox. The core has a passage therein through which the coolant is circulated. Heat is transferred through the core from the lubricant in the sump to the coolant circulated through the core passage. In the disclosed embodiment both the gearbox lubricant and the coolant for the first and second devices, is oil. Since the gearbox internal oil is kept separate from the cooling oil of the electrical power generating component, increased reliability can be attained. The cooling arrangement also allows independent oil change as required for maintenance. Attitude performance (roll, climb, dive) is also enhanced as the working media of the devices are kept separate, e.g. gearbox performance does not affect power generating unit performance and vice-versa. Further, the offset gearbox does not require a separate or dedicated heat exchanger which reduces system weight and cost. In addition, the cooling arrangement of the invention involves very little additional weight and plumbing. Modification of an existing installation to include the cooling arrangement of the invention is also held to a minimum, as in a retrofit.
Another feature of the invention is that the core in the sump of the offset gearbox is formed integrally with a wall of sump, e.g. the bottom wall. Alternatively, the core can be separately formed and supported within the sump with support ribs. One or more fins may be added to the core to enhance heat exchange between the two fluids.
A method according to the invention for cooling an offset gearbox and an accessory such as an electrical power generating unit drivingly connected to the offset gearbox and having a passage for flowing a coolant therethrough, comprises the steps of providing the offset gearbox with a sump which contains a lubricant for lubricating and cooling the gearbox and a heat exchanger core extending in contact with the lubricant, the core having a passage therein for flowing a coolant, and circulating a coolant through both the accessory and the coolant passage of the core in the sump of the offset gearbox in thermal communication with but not mixed with the lubricant of the offset gearbox for cooling the lubricant.
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