Patent Description:
A motor driven compressor (MDC) can experience a thrust bearing failure mode. If left undetected, such a failure mode can result in moving surfaces impinging upon one another such that their surface temperatures increase. In some cases, these increases can lead to surface temperatures exceeding a predefined limit (e.g., a predefined limit of <NUM>°F in accordance with relevant requirements).

The issue of failure detection is often addressed in conventional MDCs through the presence of surface mounted thermal switches. The surface mounted thermal switches operate by detecting failures and causing a shutdown of the MDC. While such devices can be useful, inspections and field return units have shown that the surface mounted thermal switches can shift in position and cease to be fully operational.

<CIT> discloses a drive controller for a motor of a variable speed compressor. <CIT> discloses a method and device for controlling a hot restart of a centrifugal compressor driven by a turbine.

A motor driven compressor (MDC) with a control system is defined in claim <NUM>.

In accordance with additional embodiments, the actual and predicted minimum speeds are rotational speeds of a rotating element of the MDC.

In accordance with additional embodiments, the controller is configured to determine whether the actual speed of the MDC is below the predicted minimum speed for a first period of time and the controller is configured to restart the MDC following the shut down after a second period of time which is longer than the first period of time.

In accordance with additional embodiments, the controller is configured to cease the determining and the shutting down and then the restarting following a predefined number of consecutive restarts.

In accordance with additional embodiments, the predefined number of the consecutive restarts is reset in response to a conditional change.

In accordance with additional embodiments, the controller is configured to track a number of successful restarts.

In accordance with additional embodiments, the first period of time is shorter than the second period of time.

In accordance with additional embodiments, a common mode starter controller (CMSC) is configured to detect an MDC underspeed by which the controller detects if the restart of the MDC is successful.

In accordance with additional embodiments, the controller is configured to cease the determining, the causing and the restarting following a predefined number of consecutive restarts.

A method of controlling a motor driven compressor (MDC) is defined in claim <NUM>.

In accordance with additional embodiments, the determining, the causing and the restarting cease following a predefined number of consecutive restarts, the method further comprising resetting the number of the consecutive restarts in response to a conditional change.

In accordance with additional embodiments, the method further includes tracking a number of successful restarts.

As will be described below, thrust bearing failure modes are detected and acted upon by a system that will not shift in position over time and thus will not cease to be fully operational over time. The system involves the use of software-based detection of thrust bearing failures for use with a motor driven compressor (MDC) or another similar device.

<FIG> is a schematic diagram of MDC <NUM> in accordance with embodiments. The MDC <NUM> includes tie rod <NUM>, motor shafts 14a and 14b, stator winding <NUM>, rotor compressor stages 18a and 18b, thrust runner <NUM>, housing <NUM>, journal bearings 24a and 24b and thrust bearings 26a and 26b. In some cases, the stator winding <NUM> drives compressor stages 18a and 18b and, in other cases, rotating components may be driven by any rotating machine, such as a turbine. The motor shafts 14a and 14b rotate on the journal bearings 24a and 24b. The thrust runner <NUM> is utilized to prevent axial movement of the rotating components of the MDC <NUM>. The thrust bearings 26a and 26b prevent contact between the thrust runner <NUM> and the housing <NUM>. Failure modes can occur, for example, due to failures of any of the journal bearings 24a and 24b and the thrust bearings 26a and 26b. When a failure occurs at thrust bearing 26b, for example, heat is generated due to contact between the thrust runner <NUM> and the housing <NUM>. This heat is conducted to the surface of the housing <NUM> and can lead to above-normal temperatures relative to normal operating temperatures.

With reference to <FIG>, a system <NUM> is provided for monitoring and controlling an MDC, such as the MDC <NUM> of <FIG>. The system <NUM> includes one or more sensing elements <NUM>, a first servo control element <NUM>, a second servo control element <NUM> and a controller <NUM>. The one or more sensing elements <NUM> are disposable on at least one of the rotating components of the MDC <NUM>, such as the motor shafts 14a and 14b, and at least one of the stationary components of the MDC <NUM>, such as the housing <NUM>. In either case, the one or more sensing elements <NUM> may be disposed and configured to sense an operational parameter of the MDC <NUM> and, in accordance with embodiments, this operational parameter includes a rotational speed of the rotational components of the MDC <NUM> relative to the stationary components of the MDC <NUM> (e.g., a rotational speed in revolutions per minute (RPM) of the motor shafts 14a and 14b relative to the housing <NUM>). The first servo control element <NUM> is operably coupled with the MDC <NUM> and configured to start up, shut down and restart the MDC <NUM> in accordance with commands or instructions received by the first servo control element <NUM>. The second servo control element <NUM> may be provided as a component of the controller <NUM> or as a standalone component. In either case, the second servo control element <NUM> is configured to time certain events related to the monitoring and controlling of the MDC <NUM> as will be described below. The controller <NUM> is coupled to the one or more sensing elements <NUM>, the first servo control element <NUM> and the second servo control element <NUM>.

In accordance with embodiments, the system <NUM> may further include a common mode start controller (CMSC) <NUM>. In such cases, the CMSC <NUM> may be configured to detect an underspeed condition of the MDC <NUM> by which the controller <NUM> would be able to detect if a restart of the MDC <NUM> is or is not successful as will be described below.

With continued reference to <FIG> and with additional reference to <FIG>, the controller <NUM> includes a processing unit <NUM>, a memory unit <NUM> and a networking unit <NUM> by which the processing unit <NUM> is communicative with the one or more sensing elements <NUM>, the first servo control element <NUM> and the second servo control element <NUM>. The processing unit <NUM> may be provided as a central processing unit (CPU) and is coupled with the memory unit <NUM> and the networking unit <NUM>. The memory unit <NUM> has executable instructions stored thereon, which, when executed, cause the processing unit <NUM> to operate as described herein.

For example, when executed, the executable instructions cause the processing unit <NUM> to either calculate a predicted minimum speed of the MDC <NUM> based on current conditions or to access data reflective of the predicted minimum speed in the memory unit <NUM>, to receive signals from the one or more sensing elements <NUM> which are reflective of and derived from readings of an actual speed of the MDC <NUM> that are generated by the one or more sensing elements <NUM> and to determine from those signals whether the readings of the one or more sensing elements <NUM> are indicative of the actual speed of the MDC <NUM> falling below the predicted minimum speed (again, the predicted minimum and actual speeds of the MDC are, for example, rotational speeds of a rotating component thereof relative to a stationary component thereof).

In addition, in an event that is can be determined that the actual speed of the MDC <NUM> falls or has fallen below the predicted minimum speed, the executable instructions further cause the processing unit <NUM> to determine whether the actual speed of the MDC <NUM> falls or has fallen below the predicted minimum speed for a first period of time as timed by the second servo control element <NUM>. In an event it can be determined that the actual speed of the MDC <NUM> falls or has fallen below the predicted minimum speed for the first period of time, the executable instructions cause the processing unit <NUM> to in turn cause the first servo control element <NUM> to shut down the MDC <NUM> for a second period of time as timed by the second servo control element <NUM> following an end of the first period of time and to attempt to restart the MDC <NUM> following an end of the second period of time. Following the attempted restart, the executable instructions also cause the processing unit <NUM> to determine whether the attempted restart was or was not successful.

In accordance with embodiments, the first period of time may be shorter than the second period of time. In accordance with further embodiments, the first period of time may be about <NUM> seconds and the second period of time may be about <NUM> seconds. In accordance with still further embodiments, the determination of whether the attempted restart was or was not successful may be accomplished by the CMSC <NUM> being configured to directly sense whether the restart was or was not successful based on the CMSC <NUM> identifying that an incidence of the MDC <NUM> exhibiting or experiencing an underspeed condition is in effect and by the processing unit <NUM> communicating with the CMSC <NUM> to be receptive of a corresponding indication from the CMSC <NUM> of whether the restart was or was not successful.

In accordance with further embodiments, the executable instructions of the memory unit <NUM> may, when executed, cause the processing unit <NUM> to maintain a count of consecutive restarts of the MDC <NUM> and to cease the determining, the causing and the restarting following a predefined number of consecutive restarts (which may be stored in the memory unit <NUM>), to reset the predefined number of the consecutive restarts in response to a conditional change, such as a flight mission phase change, and to track and store in the memory unit <NUM> a total number of consecutive and non-consecutive successful restarts for the generation of a report.

With reference to <FIG>, a method of controlling an MDC, such as the MDC <NUM> of <FIG> is provided and may be executed, for example, by the system <NUM> and the controller <NUM> of <FIG> and <FIG>. As shown in <FIG>, the method includes determining from readings of the one or more sensing elements <NUM> whether an actual (rotational or other) speed of the MDC <NUM> falls below a predicted minimum (rotational or other) speed (block <NUM>) and, if so, determining whether a first period of time as timed by the second servo control element <NUM> has elapsed (block <NUM>).

In an event the actual speed of the MDC <NUM> falls or has fallen below the predicted minimum speed and the first period of time has elapsed, the method further includes causing the first servo control element <NUM> to shut down the MDC <NUM> (block <NUM>), then waiting for a second period of time as timed by the second servo control element <NUM> (block <NUM>) and restarting the MDC <NUM> following an end of the second period of
time (block <NUM>). At this point, the method includes detecting if the restart of the MDC <NUM> is or is not successful (block <NUM>) and tracking and storing a total number of consecutive or non-consecutive restarts for later use in a generated report (block <NUM>).

As noted above, the first period of time may be shorter than the second period of time and, more particularly, the first period of time may be about <NUM> seconds and the second period of time may be about <NUM> seconds.

With reference to <FIG>, a method of executing the detecting of whether the restart of the MDC <NUM> is or is not successful will now be described. As shown in <FIG>, the method includes detecting, at the CMSC <NUM>, that an underspeed condition of the MDC <NUM> is or is not in effect (block <NUM>), issuing an interrogative signal from the processing unit <NUM> to the CMSC <NUM> which requests a response signal that is reflective of the detecting (block <NUM>), receiving, at the processing unit <NUM>, the response signal from the CMSC <NUM> (block <NUM>) and determining, at the processing unit <NUM>, from the response signal whether the restart is or is not successful based on the content of the response signal (block <NUM>).

With reference to <FIG>, a further method of monitoring and controlling the MDC <NUM> of <FIG> which is executable by the system <NUM> and the controller <NUM> of <FIG> and <FIG> will now be described. As shown in <FIG>, each successful restart is counted (block <NUM>) and it is determined whether the count has or has not reached a predefined number of consecutive restarts which may, in some cases, be stored in the memory unit <NUM> (block <NUM>). If the predefined number of consecutive restarts has been reached, the determining, the causing and the restarting are ceased (block <NUM>). Subsequently, the method further includes identifying whether a conditional change, such as a change in a flight mission phase or status, has occurred (block <NUM>) and, if so, resetting the number of the consecutive restarts (block <NUM>) and resuming the determining, the causing and the restarting (block <NUM>).

Claim 1:
A motor driven compressor (MDC) (<NUM>) comprising rotating components, stationary components and a control system, the control system (<NUM>) comprising:
sensing elements (<NUM>);
a controller (<NUM>) coupled to the sensing elements, wherein the controller (<NUM>) is configured to determine whether an actual speed of the MDC (<NUM>) sensed by the sensing elements is below a predicted minimum speed for a first period of time and configured to:
shut down and then restart the MDC (<NUM>), and
detect if the restart of the MDC (<NUM>) is successful from the detection of an MDC underspeed condition, and characterized in that:
said sensing elements are disposed on at least one of the rotating components and at least one of the stationary components to sense said actual speed of the MDC.