Fixed block shaft inner bearing race for integrated drive generator

An inner bearing race has a body extending from a first end to a second end. An inner bearing race surface defined between a pair of lands extends radially outwardly of the inner bearing race surface, with one of the lands extending to the second end. The bearing race surface is defined by inner face surfaces of the lands. The inner bearing race surface extends for an axial distance between the inner facing surfaces along a central axis C of the body and defines a first distance. A second distance defines an outer diameter of the inner bearing race surface is defined as a second distance and a ratio of the first distance to the second distance being between 0.20 and 0.30. An integrated drive generator and a method are also disclosed.

BACKGROUND

This application relates to an inner bearing race for a fixed block shaft in a hydraulic unit of an integrated drive generator.

Integrated drive generators are known and often utilized in aircraft. As known, a gas turbine engine on the aircraft provides a drive input into a generator input shaft. The generator typically includes a disconnect shaft that can transmit the input into a gear differential. The gear differential selectively drives a main generator to provide electric power for various uses on the aircraft.

It is desirable that the generated power be of a desired constant frequency. However, the speed from the input shaft will vary during operation of the gas turbine engine. This would result in variable frequency.

Integrated drive generators are provided with speed trimming hydraulic units. Gears associated with the differential and, in particular, a ring gear portion, provide rotation from the differential back into the trimming unit. A carrier also rotates another portion of the trimming unit. The trimming unit is operable to result in the output speed of the differential being effectively constant, such that electric power of a desirable frequency is generated.

The generator is mounted between two housing portions and a seal plate is mounted between the two housing portions.

In addition, various accessory systems, such as various pumps, are driven by the output ring gear of the differential through an accessory drive gear.

A fixed block shaft in the hydraulic unit is supported on a bearing and an inner bearing race for this bearing raises design challenges.

SUMMARY

An inner bearing race for use in an integrated drive generator has a body extending from a first end to a second end. An inner bearing race surface defined between a pair of lands extends radially outwardly of the inner bearing race surface, with one of the lands extending to the second end. The bearing race surface is defined by inner face surfaces of the lands. The inner bearing race surface extends for an axial distance between the inner facing surfaces along a central axis of the body and defines a first distance. An outer diameter of the inner bearing race surface is defined as a second distance and a ratio of the first distance to the second distance being between 0.20 and 0.25.

In addition, an integrated drive generator and a method of replacing an inner bearing race from an integrated drive generator are disclosed.

DETAILED DESCRIPTION

FIG. 1shows an integrated drive generator20. As shown, housing portions18and19surround the integrated drive generator and a seal plate17sits between the housing portions18and19.

A gas turbine engine22may drive an input shaft23which selectively drives a disconnect assembly26. The disconnect assembly26, in turn, drives a carrier shaft28, which drives a carrier34in a gear differential30.

As the carrier shaft28rotates, planet gears36and38are caused to rotate. Gears38have a gear interface42with a first ring gear portion40. Gears36have a gear interface48with a second ring gear portion46.

Ring gear portion40has a gear interface50with a main generator drive gear52. When drive gear52is driven to rotate, it rotates a rotor56associated with a stator58of the main generator as well as an exciter rotor60. Electric power is generated for a use62, as known.

It is desirable that the frequency of the generated electric power be at a desired frequency. This requires the input speed to gear52to be relatively constant and at the desired speed. As such, the speed of the input shaft23is added to the speed of the speed trimmer66to result in a constant input speed to gear52.

A gear15that is part of the carrier has a gear interface16with a gear13driving a shaft14also within the speed trimmer.

As known, the speed trimmer66includes a variable unit72and a fixed unit76. The units72and76may each be provided with a plurality of pistons and a swash plate arrangement. If the input speed of the gear13is too high, the speed of the gear52will also be too high, and hence, the speed trimmer66acts to lower the speed of the trim gear46which will drop the speed of gear52. On the other hand, if the input speed is too low, the speed trimmer will increase the trim gear speed and he speed seen by gear52will increase.

In essence, the variable unit72receives an input through gear13that is proportional to the speed of the input shaft23. The variable unit72also receives a control input from a control monitoring the speed of the generator rotor56. The position of the swash plate in the variable unit72is changed to in turn change the speed and direction of the fixed unit76. The fixed unit76can change the speed, and direction of rotation of the shaft70, and this then provides control back through the trim ring gear46to change the speed reaching the generator. In this manner, the speed trimmer66results in the frequency generated by the generator being closer to constant, and at the desired frequency.

A permanent magnet generator32rotates with the ring gear40.

An accessory drive shaft29rotates with the carrier shaft28and drives a plurality of accessory gears31.

The operation of the integrated drive generator20is generally as known in the art. A worker of ordinary skill would recognize that the desired frequency and speed at use62would dictate a number of design functions.

FIG. 2shows that there are a pair of hydraulic or speed trimming units66associated with a single ring gear46and a single carrier15.

FIG. 3shows details of the hydraulic unit66. A speed into the gear13will be proportional to the speed from the input shaft23. The gear13rotates with a shaft92. The shaft92has a surface95supported on bearing93. The shaft, through splined teeth121, drives a cylinder block104to rotate.

The shaft90is called a fixed block shaft, although it rotates. It is called “fixed” as it is driven by the displacement half of the pump and motor assembly. The shaft90is supported on a bearing132received on a bearing race130on the fixed shaft90. In addition, an inner race134for the bearing132is mounted on a housing19. The inner race134includes a race surface136.

A control91changes the position of a swash plate100based upon the input speed seen at the generator. As the cylinder block104rotates, pistons102within the cylinder block cam off a surface of the swash plate100. As the position of the swash plate100is changed by control91, the amount of hydraulic fluid driven by the pistons102, through a port plate106, and against piston110in a cylinder block112changes. As the pistons110move, they cam off a surface of fixed swash plate108. This results in a control of a speed and direction of rotation of cylinder block112. Cylinder block112has a spline connection at121to a shaft94. Thus, the hydraulic unit66results in a desired speed and direction of rotation of the shaft94, ultimately based upon the input speed seen at the generator. The shaft94drives the shaft90through a spline connection at137/180to in turn drive the gear68. The gear68interacts with the trim ring gear64such that the ultimate speed leaving the differential30to the gear52is controlled to achieve a constant desired speed at the generator.

The cylinder blocks104and112are effectively identical. In addition, there are similar cylinder blocks104/112in both of the hydraulic units66.

FIG. 4Ashows the inner bearing race134having inner bearing race surface150.

As shown inFIG. 4B, the inner bearing race has a body140extending between a first end142and a second end144. A pair of lands146and148extend radially outwardly of the bearing race surface150. The land146has an outer peripheral surface152. Inner faces151of the lands146and148define an axial length of the bearing race d1along a central axis C. A boss160extends to the first end142from the land148and has an outer surface162. A diameter of the bearing race surface150is defined as d2. An outer diameter to an outer surface152of the land146is defined as d3. An inner bore153is positioned inwardly of the bearing race surface150and has an inner diameter of d4.

A method of replacing an inner bearing race in an integrated drive generator includes the steps of removing an existing inner bearing race from an integrated drive generator having an input shaft connected to a differential. The differential is connected to a generator, and is also being connected to a hydraulic unit, which includes a variable swash plate and a fixed swash plate. Each of the swash plates are associated with a set of pistons. A fixed shaft is associated with the fixed swash plate, and connected to a cylinder block associated with the fixed swash plate. The fixed shaft includes a spline connection to drive a fixed block shaft, the fixed block shaft has gear teeth engaged to a ring gear in the differential. The fixed block shaft is supported on a bearing, and the existing inner bearing race supports the bearing. The existing inner bearing race is replaced with a replacement inner bearing race having a body extending from a first end to a second end. An inner bearing race surface is defined between a pair of lands extending radially outwardly of the inner bearing race surface, with one of the lands extending to the second end, and the bearing race surface defined by inner face surfaces of the lands, and the inner bearing race surface extending for an axial distance between the inner facing surfaces along a central axis of the body, and defining a first distance, and a second distance defined to an outer diameter of the inner bearing race surface being defined as a second distance and a ratio of the first distance to the second distance being between 0.20 and 0.30.