Patent Description:
Aircraft rely on electrical, pneumatic, and hydraulic systems for secondary power. A typical electrical system utilizes a <NUM>-stage, wound field synchronous (WFS) generator coupled to each engine to provide electric power to the distribution system and loads. One type of WFS generator includes a small permanent magnet generator (PMG) for control and excitation power, an exciter to energize the main field, and a main field generator arranged in a common housing. A primary benefit of the <NUM>-stage design is the ability to electrically turn off current flow in the main field windings during an electrical fault condition. A large single stage PMG offers the potential benefit of an appreciable weight reduction to the generator by eliminating the small PMG and exciter, but current flow in the PMG stator windings cannot be controlled in the same manner as in a <NUM>-stage WFS generator. PMG systems allow the generator to generate fault currents as long as it is rotating.

Conventional methods for stopping the rotation of WFS generators include a separable input shaft and generator rotor shaft. Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for improved disconnect mechanisms for disconnecting the drive train and avoiding fault currents accompanying spin down of single stage PMGs when conditions warrant. The present invention provides a solution for this need.

A disconnect mechanism according to the present invention is described herein and defined in claim <NUM>.

The disconnect ramp can include a first end and a second end, where engagement of the disconnect pawl with the first end of the disconnect ramp places the disconnect shaft in the first axial position, and where engagement of the disconnect pawl with the second end of the disconnect ramp places the disconnect shaft in the second axial position. A brake recess can include a friction disk and a biasing member seated within the brake recess to allow axial movement of disconnect shaft and the brake into the brake recess in the second axial position.

Engagement of the disconnect pawl at a position between the first end of the disconnect ramp and the second end of the disconnect ramp can place the disconnect shaft in intermediate axial position between the first axial position and the second axial position. The intermediate axial position can be a disengaged position such that the disconnect shaft is disengaged from both the input shaft and the brake.

A rotor and a biasing member can be included such that the disconnect shaft is seated in the rotor, and wherein the biasing member biases the disconnect shaft toward the first axial position. In embodiments, the rotor can be splined to the disconnect shaft. A pawl actuator can be operatively connected to drive the disconnect pawl to engage the disconnect ramp to move the disconnect shaft between the first axial position and the second axial position. In certain embodiments, the pawl actuator can be a linear solenoid actuator. In embodiments, a short detection unit can be operatively connected to the pawl actuator to actuate the pawl actuator in response to a detected short circuit.

In accordance with the present invention, an electric power generation system can include a generator housing, a stator within the generator housing, an input shaft defining a drive axis extending through the stator, a rotor mechanically connected to the input shaft to rotate about the drive axis, a disconnect mechanism having a disconnect ramp to selectively engage the input shaft to be driven about the drive axis by the input shaft, a brake seated in a brake recess selectively engaged with the disconnect mechanism.

In embodiments, the rotor can be splined to the disconnect shaft, and the disconnect shaft can be configured to disconnect from the input shaft in response to a detected short circuit in an electrical machine or in the electric power generation system. The disconnect ramp can be operatively connected to the disconnect shaft to axially move the disconnect shaft between at least a first axial position and a second axial position.

A disconnect pawl can selectively engaged with the ramp of the disconnect ramp, and a pawl actuator can be operatively connected to drive the disconnect pawl to engage the disconnect ramp to move the disconnect shaft between the first axial position and the second axial position. A short detection unit can be operatively connected to the generator system and the pawl actuator to actuate the pawl actuator in response to a short circuit in the electrical machine or in the electric power generation system.

In accordance with the present invention, a method for disconnecting and braking a rotating device includes, actuating a disconnect shaft to disengage the disconnect shaft from an input shaft, and engaging the disconnect shaft with a brake. In embodiments, the brake can engage an axial end of the disconnect shaft, and the method can further include monitoring the rotating device for short circuit faults, and actuating the disconnect shaft and engaging the disconnect shaft upon detection of a short circuit in the rotating device.

These and other features of the systems and methods of the subject invention will become more readily apparent to those skilled in the art from the following detailed description taken in conjunction with the drawings.

So that those skilled in the art to which the subject disclosure appertains will readily understand how to make and use the devices and methods of the subject invention without undue experimentation, embodiments thereof will be described in detail herein below with reference to certain figures, wherein:.

Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, a partial view of an embodiment of a system in accordance with the disclosure is shown in <FIG> and is designated generally by reference character <NUM>. Other embodiments of systems in accordance with the disclosure, or aspects thereof, are provided in <FIG>, as will be described. The systems and methods described herein can be used to reduce the risk of short circuits in rotating electrical devices.

Conventional aerospace electric power generators can be <NUM>-stage wound field devices. The <NUM>-stage design can be particularly beneficial due to the ability to de-excite, or electrically turn off current flow in the main field windings. In certain instances, permanent magnet generators (PMGs) can offer significant weight reductions over the conventional <NUM>-stage wound field generators. However, PMGs pose a challenge in stopping rotation in the event of an electrical fault condition. Conventional disconnect systems used in <NUM>-stage wound field devices provide for disconnection but may still allow the PMG to rotate and generate fault currents as it spins down to <NUM> rpm. To mitigate fault currents during inertial spin-down, system <NUM> provides the ability to rapidly decelerate the PMG rotor to <NUM> rpm after disconnect.

In accordance with at least one aspect of this invention, a generator system <NUM> can include a generator housing <NUM>. Within the housing <NUM>, an input shaft <NUM> defining a drive axis A extends through a stator <NUM>, and a rotor <NUM> is mechanically connected to the input shaft <NUM> to rotate about the drive axis A. A disconnect mechanism <NUM> can selectively engage the input shaft <NUM>, e.g. from a prime mover such as a gas turbine engine, at a first end <NUM> to be driven about the drive axis A by the input shaft <NUM>, and a brake <NUM> is seated in a brake recess <NUM> to selectively engage with the disconnect mechanism <NUM> at a second end <NUM>. The rotor <NUM> can be mechanically connected to the disconnect shaft <NUM> in any suitable manner, for example the rotor <NUM> can be splined to the disconnect shaft <NUM> via splines <NUM>.

The disconnect mechanism <NUM> comprises the input shaft <NUM>, a disconnect shaft <NUM>, and a disconnect ramp <NUM> operatively connected to the disconnect shaft <NUM> to axially move the disconnect shaft <NUM> between at least a first axial position (e.g. shown in <FIG>) and a second axial position (e.g. shown in <FIG>). The disconnect ramp <NUM> can be a worm gear, having any suitable number of threads <NUM>, for example, two or more threads 122a, 122b. A biasing member <NUM> can be engaged with the rotor <NUM> and the disconnect mechanism <NUM> to bias the disconnect shaft <NUM> toward the first axial position. The biasing member <NUM> also operates as a reset, to reset the disconnect shaft <NUM> into the first axial position after disconnect.

The disconnect mechanism <NUM> includes a disconnect pawl <NUM> selectively engaged with the ramp <NUM> of the disconnect mechanism <NUM>. The disconnect pawl <NUM> can selectively engage with the ramp <NUM> via a pawl actuator <NUM> (e.g. a linear solenoid actuator) operatively connected to drive the disconnect pawl <NUM> radially to engage the disconnect ramp <NUM> to move the disconnect shaft <NUM> between the first axial position and the second axial position. More specifically, the disconnect ramp <NUM> can include a first end <NUM> and a second end <NUM>, where engagement of the disconnect pawl <NUM> with the first end <NUM> of the disconnect ramp <NUM> places the disconnect shaft <NUM> in the first axial position.

As the disconnect shaft <NUM> continues to rotate, the disconnect pawl <NUM> will engage with the second end <NUM> of the disconnect ramp, placing the disconnect shaft <NUM> in the second axial position, by pulling the disconnect shaft <NUM> axially towards the brake recess <NUM> to contact the brake <NUM>. Engagement of the disconnect pawl <NUM> at a position between the first end <NUM> of the disconnect ramp <NUM> and the second end <NUM> of the disconnect ramp <NUM> places the disconnect shaft <NUM> in intermediate axial position between the first axial positon and the second axial position (e.g. as shown in <FIG>). The intermediate axial position can be a disengaged position such that the disconnect shaft <NUM> is disengaged from both the input shaft <NUM> and the brake <NUM>, where the disconnect shaft is no longer driven by the input shaft but is not actively engaged with the brake.

In embodiments, (e.g. as shown), the brake recess <NUM> can include a friction disc <NUM> and a disc biasing member <NUM> seated within the brake recess <NUM> to allow axial movement of disconnect shaft <NUM> and the disc <NUM> into the brake recess <NUM> in the second axial position. According to the invention, the brake <NUM> is axially spaced apart from the second <NUM> end of the disconnect shaft <NUM> in the first position, and the brake <NUM> engage the second end <NUM> of the disconnect shaft <NUM> in the second position. For example, compression spring <NUM> (or a plurality of compression springs) may be included in the recess <NUM> to bias the friction disc <NUM> towards the disconnect shaft <NUM>, but allow for the axial movement of the friction disc <NUM> and the disconnect shaft <NUM> together into the brake recess <NUM> in the second axial position. The deceleration rate of the disconnect shaft <NUM> by the brake <NUM> can be controlled by adjusting the spring force of the disc biasing members <NUM>, adjusting the contact area between the axial end <NUM> of the disconnect shaft <NUM> and the friction disc <NUM>, and/or adjusting the inertia of the rotor <NUM>.

A short detection unit <NUM> can be operatively connected to the generator system <NUM> and the pawl actuator <NUM> to actuate the pawl actuator <NUM> in response to a short circuit <NUM> in the generator system <NUM> or electric power distribution system. The short detection unit <NUM> may be a generator controller, an active or passive rectifier, or a stand-alone device. Actuating the pawl actuator <NUM> thus disconnects the disconnect shaft <NUM> and the rotor <NUM> from the input shaft <NUM> in response to the detected short circuit <NUM> in the generator system <NUM> or electric power distribution system.

In accordance with the present invention, a method for disconnecting and braking a rotating device <NUM> includes, actuating a disconnect shaft <NUM> to disengage the disconnect shaft <NUM> from an input shaft <NUM>, and engaging the disconnect shaft <NUM> with a brake <NUM>. In embodiments, the brake can engage an axial end <NUM> of the disconnect shaft <NUM>, and the method can further include monitoring the rotating device <NUM> for short circuit faults and actuating the disconnect shaft <NUM> and engaging the disconnect shaft <NUM> with the brake <NUM> upon detection of a short circuit in the rotating device <NUM> or in the electric power distribution system.

Claim 1:
A disconnect mechanism comprising:
an input shaft (<NUM>) defining a drive axis;
a disconnect shaft (<NUM>) selectively engaged with the input shaft (<NUM>) to be driven about the drive axis by the input shaft (<NUM>);
a disconnect ramp (<NUM>) operatively connected to the disconnect shaft (<NUM>) to axially move the disconnect shaft (<NUM>) between at least a first axial position and a second axial position; and
a disconnect pawl (<NUM>) selectively engaged with the disconnect ramp;
characterized by further comprising a brake (<NUM>) selectively engaged with the disconnect shaft (<NUM>) in the second axial position, wherein the brake (<NUM>) is axially spaced apart from an end of the disconnect shaft (<NUM>) in the axial first position and/or wherein the brake (<NUM>) engages the end of the disconnect shaft (<NUM>) in the second axial position.