Patent Description:
Some aircraft engines have propellers with variable pitch, referred to as propeller blade (or beta) angle. In such engines, accurate control of the beta angle is important for proper engine operation. For example, control of the beta angle may allow the blade angle to be controlled according to the desired engine power set-point. Accurate measure of the blade angle also ensures that the propeller is not inadvertently commanded to transition into low or reverse beta angles, which would cause a potentially serious failure condition for the aircraft.

A propeller may form part of an assembly having numerous components. For example, a propeller may be mounted to a propeller shaft, which may itself be received in a gear box. Further components may also be present. Each component of the propeller assembly may be manufactured to a specific nominal size and tolerance. The dimensional configuration of a particular propeller assembly may be influenced by the tolerance stack-up. That is, the propeller position may depend on whether parts in the assembly are over or under their nominal sizes, and by how much. Accurate control of the propeller and propeller assembly may depend on the tolerance stack-up. Moreover, safe and efficient operation may require that the tolerance stack-up is within specification.

<CIT> discloses a system for blade angle position feedback, which comprises an annular member operatively connected to rotate with a propeller and a sensor fixedly mounted adjacent the annular member and configured for detecting a passage of singularities as the annular member is rotated and axially displaced and for generating a sensor signal accordingly.

The present invention provides a propeller control system for an aircraft propeller as defined in claim <NUM>.

In some embodiments, the warning signal is a first warning signal and said controller is configured to produce a second warning signal if said longitudinal position is outside an intermediate range within said first threshold range.

The first threshold range corresponds to a dimensional tolerance of the propeller assembly and said intermediate range may correspond to measurement repeatability of said sensor.

In some embodiments, the controller is configured to store a calibration value indicative of said longitudinal position if said longitudinal position is within said first threshold range and to continuously measure intervals between consecutive ones of said signals, and to provide an output indicative of a propeller angle, based on said intervals and said calibration value.

In some embodiments, the position markers comprise ferrous teeth on said feedback ring and said sensor comprises a hall effect sensor that produces a voltage signal when one of said ferrous teeth passes proximate thereto.

In some embodiments, the controller is configured to measure said longitudinal position while said propeller is in a feather condition.

In some embodiments, the controller is configured to measure said longitudinal position while said propeller is in a maximum thrust condition.

In some embodiments, the controller is configured to measure said longitudinal position at engine startup.

The present invention further provides a method of monitoring an operating condition of an aircraft propeller as defined in claim <NUM>.

In some embodiments, the measuring is performed while said propeller is in a feather condition. In some embodiments, the measuring is performed while said propeller is in a maximum thrust condition.

In some embodiments, the method further comprises storing a calibration value from said measuring at engine startup and continuously measuring a longitudinal position of said feedback device based on a circumferential distance between adjacent ones of said position markers and said calibration value, and outputting a signal indicative of said blade angle based on said measuring.

In some embodiments, the measuring comprises producing a voltage by a Hall effect sensor in response to passing of a position marker.

An aircraft engine, which is not part of the claimed subject-matter, is also described, the engine comprising: a propeller rotatable about a longitudinal axis, the propeller having blades with adjustable blade angle; a feedback ring mounted for rotation with the propeller, and for movement along the longitudinal axis along with adjustment of the blade angle, the feedback ring comprising a plurality of position markers spaced around its circumference such that a circumferential distance between at least some adjacent ones of the position markers varies along the longitudinal axis; a propeller shaft extending from a gearbox for driving the propeller; a sensor fixedly mounted to the gearbox proximate the feedback ring, the sensor operable to produce a signal when passed by a feedback marker, such that an interval between ones of the signals is indicative of a circumferential distance between adjacent ones of the position markers; and a controller in communication with the sensor to measure an interval between consecutive ones of the signal on engine startup and compute a corresponding longitudinal position of the feedback ring, the controller configured to produce a warning signal if the longitudinal position is outside a threshold range.

In some embodiments, the warning signal is a first warning signal and said controller is configured to produce a second warning signal if said interval is outside an intermediate range within said threshold range.

In some embodiments, the threshold range is associated with a tolerance range and said intermediate range is associated with a measurement repeatability.

In some embodiments, the controller is configured to measure said interval while said propeller is in a feather condition.

In the drawings, which illustrate examples:.

<FIG> illustrates a gas turbine engine <NUM>, of a type typically provided for use in subsonic flight, comprising an inlet <NUM>, through which ambient air is propelled, a compressor section <NUM> for pressurizing the air, a combustor <NUM> in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section <NUM> for extracting energy from the combustion gases. The turbine section <NUM> illustratively comprises a compressor turbine <NUM>, which drives the compressor assembly and accessories, and at least one power or free turbine <NUM>, which is independent from the compressor turbine <NUM> and rotatingly drives a rotor shaft <NUM> about a propeller shaft axis A through a reduction gearbox <NUM>. Hot gases may then be evacuated through exhaust stubs <NUM>. The gas generator (not shown) of the engine <NUM> illustratively comprises the compressor section <NUM>, the combustor <NUM>, and the turbine section <NUM>. A rotor <NUM>, in the form of a propeller through which ambient air is propelled, is hosted in a propeller hub <NUM>. Rotor <NUM> may, for example, comprise a propeller of a fixed-wing aircraft or a main (or tail) rotor of a rotary-wing aircraft such as a helicopter. The rotor <NUM> may comprise a plurality of circumferentially-arranged blades (not shown) connected to a hub (not shown) by any suitable means and extending radially therefrom. The blades are also each rotatable about their own radial axes through a plurality of blade angles, which can be changed to achieve modes of operation, such as feather, full reverse, and forward thrust.

As depicted in <FIG>, the rotor <NUM> is part of a propeller assembly <NUM>. Rotor <NUM> is mounted to a propeller shaft <NUM> with a mounting flange <NUM>. The propeller shaft <NUM> is received in reduction gear box <NUM>. Reduction gear box <NUM> receives power from an input shaft <NUM> which rotates and drives propeller shaft <NUM> by way of a gear train <NUM>. Propeller shaft <NUM> and rotor <NUM> rotate around a longitudinal propeller axis A. As used herein, references to the longitudinal direction refer to a direction parallel to longitudinal propeller axis A.

Gear train <NUM> may reduce angular velocity such that rotor <NUM> turns at a lower speed than input shaft <NUM>. As depicted, gear train <NUM> includes two sets of reduction gears. However, gear train <NUM> could have any number of reduction gears. Alternatively or additionally, gear train <NUM> may include one or more planetary gear sets.

Reduction gear box <NUM> has a housing <NUM> with a front wall <NUM>. Propeller shaft <NUM> is received through an opening in front wall <NUM> and carried by a bearing <NUM> which fixes the longitudinal position of propeller shaft <NUM> relative to housing <NUM>.

Referring to <FIG>, an electronic beta feedback system <NUM> will now be described. The system <NUM> provides for accurate detection and measurement of propeller blade angle on propeller systems, such as the engine <NUM> of <FIG>. The system <NUM> may interface to existing mechanical interfaces of typical propeller systems to provide a digital detection for electronic determination of the propeller blade angle.

The system <NUM> illustratively comprises an annular member <NUM> and one or more sensors <NUM> positioned proximate the annular member <NUM>. Annular member <NUM> (referred to herein as a propeller beta feedback ring) has a plurality of position markers <NUM> provided thereon for detection by sensor <NUM>. In accordance with the present invention, sensor <NUM> is mounted for rotation with propeller <NUM> and to move axially with adjustment of the blade angle. The beta feedback ring <NUM> may be fixedly mounted, e.g. to housing <NUM> of reduction gearbox <NUM>. The following description provides examples of the system <NUM> with the feedback ring <NUM> mounted for rotation with propeller <NUM> and to move axially with adjustment of the blade angle, and the sensor <NUM> fixedly mounted. However, this configuration does not fall within the wording of the claims.

As depicted in <FIG>, the beta feedback ring <NUM> is supported for rotation with the propeller <NUM>, which rotates about the longitudinal axis A. The beta feedback ring <NUM> is also supported for longitudinal sliding movement along the axis A, e.g. by support members, such as a series of circumferentially spaced beta feedback rods <NUM> that extend along the longitudinal axis A. A compression spring <NUM> surrounds an end portion of each rod <NUM>.

As depicted in <FIG>, the propeller <NUM> comprises a plurality of angularly arranged blades <NUM> each of which is rotatable about a radially-extending axis R through a plurality of adjustable blade angles, the blade angle being the angle between the chord line (i.e. a line drawn between the leading and trailing edges of the blade) of the propeller blade section and a plane perpendicular to the axis of propeller rotation. The propeller <NUM> may be a reversing propeller <NUM> having a plurality of modes of operation, such as feather, full reverse, and forward thrust. In some modes of operations, such as feather, the blade angle is positive. The propeller <NUM> may be operated in a reverse mode where the blade angle is negative.

Feedback ring <NUM> is mounted to move along the longitudinal direction as the beta angle of the propeller blades is adjusted. Specifically, adjustment of the beta angle causes a corresponding axial movement of the rods <NUM>, and accordingly of the feedback ring <NUM>, parallel to axis A. Conversely, adjustment of the beta angle in a first direction causes feedback ring <NUM> to move forwardly, and adjustment of the beta angle in the opposite direction causes feedback ring <NUM> to move rearwardly. In an example, rods <NUM> and feedback ring <NUM> are moved to a maximally-forward position when blades <NUM> are at their smallest (or most negative) beta angle, and are moved to a maximally-rearward position when blades <NUM> are at their largest (or most positive) beta angle. As will be apparent, in other examples, this orientation may be reversed.

In an example, actuators <NUM> engage with a piston assembly <NUM> for adjusting the beta angle of the blades. Specifically, piston assembly <NUM> moves back and forth along the longitudinal axis and cause rotation of blades <NUM> by sliding engagement with actuators <NUM>. In the depicted example, forward motion of piston assembly <NUM> reduces the beta angle of blades <NUM> and rearward motion increases the beta angle. However, in other examples, this may be reversed. Piston assembly <NUM> also engages rods <NUM> as it adjusts the beta angle. During a portion of the forward motion of piston assembly <NUM>, it bears against a stop <NUM> mounted to rod <NUM>, pulling rod <NUM> and feedback ring <NUM> forwardly and compressing spring <NUM> as shown in <FIG>. As piston assembly <NUM> moves rearwardly, spring <NUM> urges rod <NUM> and feedback wheel <NUM> rearwardly as shown in <FIG>. In the depicted example, feedback wheel <NUM> reaches its maximally-rearward position before piston assembly <NUM> reaches its maximally-rearward position. After feedback ring <NUM> reaches is maximally-rearward position, piston assembly <NUM> moves out of contact with stop <NUM> as shown in <FIG>, after which further rearward movement of piston assembly <NUM> does not cause movement of feedback ring <NUM>.

Other suitable configurations for adjusting beta angle and causing corresponding longitudinal movement of feedback wheel <NUM> will be apparent to skilled persons.

The feedback ring <NUM> is illustratively used to provide blade (or beta) angle position feedback. During rotation of the propeller (reference <NUM> in <FIG>), the feedback ring and plurality of position markers <NUM> rotate about longitudinal axis A and their passage is detected by at least one sensor <NUM> provided in a fixed relationship relative to the rotating propeller components. The sensor <NUM> may be any sensor (e.g. a speed transducer) configured to continuously detect passage of the position markers <NUM> during rotation of the propeller <NUM>. In one example, the sensor <NUM> is an electrically robust and environmentally sealed non-contact sensor suited for harsh environments and offering superior reliability. The sensor <NUM> may be any suitable inductive sensor having a varying reluctance or a Hall effect. In one example, the sensor <NUM> is implemented as a transducer comprising a coil wound around a permanent magnet (not shown). The position markers 102A, 102B, 102C may then be made of a magnetically conductive material, e.g. a ferrous metal, to enable the sensor <NUM> to detect the passage thereof.

<FIG> depicts a side view of a portion of beta feedback ring <NUM> and sensor <NUM>. The sensor <NUM> is illustratively mounted to a flange <NUM> of housing <NUM> of reduction gearbox <NUM> so as to be positioned adjacent the plurality of position markers <NUM>. In particular, the sensor <NUM> is illustratively secured to the propeller <NUM> so as to extend away from the flange <NUM> (and towards the position markers <NUM>) along a radial direction, identified in <FIG> as direction R. Sensor <NUM> and flange <NUM> may be fixedly mounted. In one example, a single sensor <NUM> is mounted in close proximity to the beta feedback ring <NUM> and the position markers <NUM>. In another example, in order to provide redundancy, one or more additional sensors <NUM> may be provided. For example, an additional sensor <NUM> may be mounted in a diametrically opposite relationship relative to the position markers <NUM>, which illustratively extend away from the feedback ring <NUM> and towards the sensor(s) <NUM>. In yet another example, several position markers <NUM> may be spaced equiangularly about the perimeter of the feedback ring <NUM>. Other examples may apply.

A controller <NUM> including a detection unit <NUM> is illustratively electrically connected to the sensor(s) <NUM> and configured to receive output signal(s) therefrom, the output signal(s) generated upon the sensor(s) <NUM> detecting the passage of a given position marker <NUM> adjacent thereto, as will be discussed further below. Controller <NUM> is configured to provide, on the basis of the signal(s) received from the sensor(s) <NUM>, a blade angle position feedback for the propeller (reference <NUM> in <FIG>), as will be discussed further below. For this purpose, as depicted in <FIG>, the controller <NUM> may comprise one or more a processors <NUM> (e.g. a microprocessor), a memory <NUM>, a non-volatile storage <NUM>, and one or more input-output (I/O) interfaces <NUM>. I/O interfaces <NUM> may interconnect with detection unit <NUM> for receiving data and may also interconnect with instrumentation of the aircraft, e.g. dials or displays in the cockpit. The detection unit <NUM> may further determine from the received output signal(s) the rotational speed of the propeller <NUM> as well as achieve propeller blade synchrophasing and propeller speed synchronization. Other applications will be readily understood by a person skilled in the art.

<FIG> is a schematic view of the toothed face <NUM> of feedback ring <NUM> (in the example of <FIG>, the inner face). <FIG> is a schematic front view of a portion of feedback ring <NUM>. As shown in <FIG>, in one example, the position markers <NUM> comprise a plurality of spaced protrusions or teeth mounted (using any suitable attachment means, such as screws, bolts, and the like) to inner face <NUM> of the feedback ring <NUM> or integrally formed with the feedback ring <NUM>. A first set of teeth, illustratively at least two first teeth 102A and 102C, and at least one second tooth, which is referred to herein as a detection tooth 102B, are provided, with the detection tooth 102B being positioned between two consecutive ones of the first teeth 102A and 102C. In one example, a total of three (<NUM>) teeth 102A, 102B, 102C, is provided about the perimeter of the feedback ring <NUM>, as illustrated. It should however be understood that more than three (<NUM>) teeth may be provided. In particular, more than one detection tooth as in 102B may be provided for propeller phase detection (e.g. to implement missing tooth detection, as discussed further below) and to maintain operation of the system. The number of teeth in turn drives the size of the digital counters provided in the detection unit (as discussed further below).

Each first tooth 102A or 102C is illustratively positioned along a direction D, which is substantially parallel to the axis A. The detection tooth 102B is positioned along a direction E angled to the direction D, such that the tooth 102B is offset relative to the teeth 102A and 102C. A range of angles may be used to design the detection tooth 102B. The angle between directions E and D may be selected based on optimization of development test data and may include compound angles, e.g. angles comprising a first component providing a radial component and a second component providing a tangential component. Illustratively, the angle between directions E and D is between <NUM> and <NUM> degrees. In one preferred example, the angle is set to <NUM> degrees so as to maximize the signal change (as detected by the sensor <NUM> in <FIG>) for a given axial movement of the propeller (reference <NUM> in <FIG>) resulting from the offset of tooth 102B relative to teeth 102A and 102C.

In some examples, teeth <NUM> may be provided in pairs. For example, <FIG> depict an example feedback ring <NUM> with a plurality of pairs of teeth 102A', 102B'. Each pair of teeth 102A', 102B' are angled relative to one another and to longitudinal axis A so as to diverge from one another and from axis A. As shown, teeth 102A', 102B' diverge in a rearward direction and converge in a forward direction. However, in other examples, this orientation may be reversed. Teeth 102A', 102B' may be angled to longitudinal axis A by the same angle, or by different angles. In an example, each of teeth 102A', 102B' is positioned approximately at a <NUM> degree to longitudinal axis A and teeth 102A', 102B' are positioned approximately at a <NUM> degree angle to each other.

Pairs of teeth 102A', 102B' are spaced at even intervals around the circumference of feedback ring <NUM>. One or more discontinuities may be provided in the spacing pattern. For example, as shown in <FIG>, an extra tooth 102C' may be placed between a pair of teeth 102A', 102B'. In some examples, extra teeth 102C' may be provided between multiple pairs of teeth 102A', 102B', provided that a discontinuity exists in the pattern of tooth spacing around the circumference of feedback ring <NUM>.

In some examples, a discontinuity may be provided in the form of a missing tooth or pair of teeth. For example, <FIG> depict a feedback ring <NUM> with diverging pairs of teeth 102A', 102B'. The pairs of teeth 102A', 102B' are evenly spaced, but a discontinuity is provided in the form of a gap <NUM> between pairs of teeth. Other examples may apply.

As illustrated in <FIG>, each sensor <NUM> may be mounted to the flange <NUM> adjacent the inner face <NUM> of the feedback ring <NUM>, i.e. inside the feedback ring <NUM>. In an alternate example, the teeth 102A, 102B, 102C may be mounted to (e.g. extend away from) an outer face <NUM> of the beta feedback ring <NUM> and each sensor <NUM> may accordingly be positioned adjacent the outer face <NUM>, about a perimeter of the feedback ring <NUM>. In yet another example, the position markers may comprise slots (not shown) rather than teeth, with the slots being machined or otherwise formed in the feedback ring <NUM> and made of a magnetically conductive material, e.g. a ferrous metal. It should be understood that the number of position markers 102A, 102B, 102C of the beta feedback ring <NUM> may be adjusted according to the desired application. For instance, the number of position markers 102A, 102B, 102C may be increased to provide low speed detection frequency for controller <NUM>.

Referring now to <FIG> and <FIG>, in operation, the feedback ring <NUM> rotates (e.g. in the direction of arrow F) during rotation of the propeller (reference <NUM> in <FIG>). The sensor <NUM> then detects the passage of each one of the position markers 102A, 102B, 102C and accordingly generates an output voltage signal (also referred to herein as a variable mark/space signal), illustrated by waveform <NUM> in <FIG>. In particular, as the position markers 102A, 102B, 102C are displaced by movement of the propeller <NUM>, each one of the position markers (e.g. position marker 102A) approaches the sensor <NUM>. This changes the sensor's reluctance and causes a magnetic field to be generated and current to flow in the sensor's coil. An increase in the sensor's output voltage signal <NUM> (e.g. a single pulse causing a positive voltage transition) is then produced. When the given position marker (e.g. position marker 102A) moves away from the sensor <NUM>, the pulse shape is inverted and the sensor's output voltage signal <NUM> is returned to zero.

The sensor's output voltage signal <NUM> is received at the detection unit <NUM>, which continuously monitors the signal to detect transitions of the voltage waveform. When a transition is detected, the detection unit <NUM> accordingly determines that the increase in voltage corresponds to detection by the sensor <NUM> of passage of a position marker (e.g. position marker 102A). A digital counter (not shown), such as a free-running <NUM> counter, provided in the detection unit <NUM> starts counting the number of digital clock cycles until the next position marker (e.g. position marker 102B) is detected by the sensor <NUM>, i.e. until the next transition in the output voltage <NUM>. In particular, the counter determines the number of clock cycles between detection of passage of the first teeth 102A, 102C and detection of passage of the detection tooth 102B of the modified beta feedback ring <NUM>. The interval of time between the passage of the first tooth 102A and the passage of the detection tooth 102B is indicated as Tm while the interval of time between the passage of the detection tooth 102B and the passage of the first tooth 102C is indicated as Ts. The detected time intervals Tm and Ts are then stored in the memory for subsequent processing by the detection unit <NUM>. As discussed above, the number of teeth 102A, 102B, 102C limits the size and/or number of counters within the detection unit <NUM>. In some examples, the size and/or number of the digital counters may be increased to provide low speed detection frequency for the EEC, assuming a fixed digital timebase within the detection unit <NUM>. It should be understood that slowing the fixed digital timebase may also achieve low speed detection frequency but penalizes system accuracy. As shown, detection unit <NUM> detects positive transitions, each of which occurs on the approach of a tooth. However, in other examples, depending on the wiring and polarization of sensor <NUM>, the approach of a tooth may cause a negative transition and detection unit <NUM> may detect such transitions.

Referring now to <FIG> in addition to <FIG>, the angled or offset positioning of the detection tooth 102B results in the sensor <NUM> seeing different portions of the detection tooth 102B as the propeller mode of operation is modified and the blade angle is varied. Indeed, in one example, the propeller <NUM> is a reversing (or reverse-pitch) propeller which may be operated in beta mode for ground reversing or taxis operation. As a result, the propeller blades (reference <NUM> in <FIG>) may be moved toward reverse pitch, as discussed above, and a negative blade angle can be allowed to produce a reducing or negative thrust in the aircraft. As the blade angle decreases, the feedback ring <NUM> is moved longitudinally forward (in the direction of arrow B in <FIG>) at the low blade angle setting by operation of actuator <NUM> and rods <NUM>. Forward movement continues until reaching reverse pitch stop. At blade angles higher than the low blade angle setting, the feedback ring <NUM> remains stationary.

During longitudinal displacement of the feedback ring <NUM>, the sensor <NUM> is successively exposed to different sections of the position markers <NUM>, the different sections being taken along the direction E. As illustrated in <FIG>, the sensor <NUM> is in a first position 124B relative to the feedback ring <NUM> prior to the propeller entering the reverse mode of operation (e.g. before the feedback ring <NUM> begins axial movement). In this position 124B, the sensor <NUM> is adjacent an upper edge 126U of the feedback ring <NUM> is exposed to and can accordingly detect the passage of the upper end portion 128U of the angled tooth 102B. As the propeller <NUM> enters the beta mode of operation and the blade angle is decreased, the feedback ring <NUM> is gradually displaced along longitudinal axis A in the direction of arrow B. When the propeller is in the full reverse condition, the feedback ring <NUM> has been fully axially displaced and reaches the position illustrated in solid lines in <FIG> (with the original position of the feedback ring <NUM> being shown in dashed lines). As a result, the sensor <NUM> is in a second position 124A relative to the displaced feedback ring <NUM>. In this position 124b, the sensor <NUM> is adjacent to a lower edge <NUM> of the feedback ring <NUM> such that the sensor <NUM> is exposed to and can accordingly detect the passage of the upper end portion 128U of the angled tooth 102B.

As can be seen from <FIG> and <FIG>, the circumferential distance between tooth 102A and tooth 102B (i.e. the distance measured along a circumferential line of ring <NUM>) decreases in direction B due to the angled configuration of the tooth 102B. That is, teeth 102A, 102B may converge in direction B such that the lower end portion <NUM> is positioned closer to tooth 102A (measured in the direction of rotation illustrated by arrow F) than the upper end portion 128U. As such, when the feedback ring <NUM> is in the initial position with the sensor <NUM> in position 124B relative to the feedback ring <NUM>, the sensor <NUM> detects the passing of the tooth 102B (e.g. the upper end <NUM> ) earlier (i.e. in less time) than when the feedback ring <NUM> is fully displaced with the sensor <NUM> in position 124a relative to the feedback ring <NUM> and the sensor <NUM> detects the passing of the tooth 102B (e.g. the upper end 128U thereof). As a result, the time taken by the sensor <NUM> to detect the passing of the tooth 102B varies as the feedback ring <NUM> is displaced axially in the direction of arrow B. Still, since the teeth 102A, 102C are not angled but all extend along the direction E, as the feedback ring <NUM> moves, the sensor <NUM> detects passing of each one of the teeth 102A, 102C at the same time, regardless of whether the sensor is in position 124a or position 124b.

Therefore, as can be seen in <FIG>, the timeframes Tm and Ts are varied as the feedback ring <NUM> moves axially along the propeller system and the position of the sensor <NUM> relative to the feedback ring <NUM> varies. In particular and as discussed above, as feedback ring <NUM> moves longitudinally in direction B (<FIG>), the section or area of the tooth 102B observed by the sensor <NUM> is gradually displaced along the direction E of <FIG>, <FIG>, <FIG> and more rearward (relative to direction of arrow B) tooth sections are observed until the most rearward section, e.g. the upper end 128U, is detected. Accordingly, the area of the tooth 102B observed by the sensor <NUM> is gradually moved rearward, i.e. from the lower (and most forward) end <NUM> being detected at first to the upper (and most rearward) end 128U being detected at last, and tooth sections in between being successively detected by the sensor <NUM>. Therefore, the time interval Tm is increased and the time interval Ts decreased. This in turn alters the spacing relationship between Tm (timeframe between detection by sensor <NUM> of teeth 102A and 102B) and Ts (timeframe between detection by sensor <NUM> of teeth 102B and 102C).

The relationship between the beta (blade angle) position and the measured values of Tm and Ts is then given by: <MAT>.

The expression (Ts - Tm) / (Ts + Tm) is also referred to as the mark-to-space ratio. The mark-to-space ratio is related to the feedback ring position by a function that is a characteristic of the ring and tooth geometry. The longitudinal position of the feedback ring is related to the propeller beta angle by a function specific to the propeller <NUM>.

The detection unit <NUM> can then apply equation (<NUM>) to compute the longitudinal position of the feedback ring <NUM> and the corresponding blade angle position for the propeller (reference <NUM> in <FIG>) and accordingly the axial position of the propeller system. The detection unit <NUM> can further detect axial movement of the feedback ring <NUM> by detecting a change in the spatial relationship between Ts and Tm. This could be done by comparing current values of Ts and Tm to previous values stored in memory and detecting the change in spatial relationship upon detecting a difference in the values.

In addition to beta position, the detection unit <NUM> can electronically decode the sensor's output voltage signal to determine the propeller's rotational speed. Indeed, the rotational speed can be computed on the basis of the sum of the timeframe values (Tm + Ts) and the number of position markers 102A, 102B, 102C, using known computation methods. Propeller synchrophasing and synchronization for multi-engine (e.g. twin engine) aircrafts and other applications may further be implemented by removing one or more of the position markers 102A, 102B, 102C from the beta feedback ring <NUM> to permit missing tooth pulse detection capability in the engine control electronics. It should be understood that either one of the position markers <NUM>, i.e. one of the first teeth 102A, 102B or one angled teeth 102B, may be removed from the feedback ring <NUM> to perform missing tooth detection. In particular, the angled tooth 102B may be removed such that a gap is created between successive first teeth 102A. Detection of the missing tooth may then provide a periodic (e.g., once per revolution) timing position signal. When several engines are provided in the aircraft, the timing position signal can then be used to keep the engines operating at the same revolutions per minute (RPM) and the propeller blades in phase with one another. As a result of such synchrophasing and synchronizing, noise and vibration can be reduced.

<FIG> illustrates a method <NUM> for electronic beta feedback. The method <NUM> comprises detecting the passage of a first non-offset position marker at step <NUM>. The next step <NUM> is then to count the clock cycles until the passage of an offset position marker is detected. The clock cycles until detection of the passage of a second non-offset position marker may then be counted at step <NUM>. Detection may be performed using a suitable sensor, such as a sensor <NUM> arranged on a beta feedback ring as discussed herein above with reference to <FIG>, with the non-offset and offset position markers arranged as discussed herein above with reference to <FIG>. The next step <NUM> may then be to compute the blade angle position on the basis of the counted clock cycles, e.g. by applying equation (<NUM>) discussed herein above. As discussed above, the rotation speed of the propeller may also be computed at step <NUM> using knowledge of the counted clock cycles and the number of position markers and propeller synchrophasing and synchronization may also be performed at step <NUM> by applying missing tooth detection.

As noted, sensor <NUM> is mounted to a flange <NUM> on housing <NUM> of reduction gearbox <NUM> (<FIG>). Thus, the longitudinal position of sensor <NUM> is fixed relative to reduction gearbox <NUM>. Conversely, feedback ring <NUM> is mounted for rotation with propeller <NUM> and its longitudinal location is dependent on the longitudinal location of propeller <NUM>. That is, actuators <NUM>, and rods <NUM> (<FIG>) cooperate to fix the longitudinal location of feedback ring <NUM> relative to that of propeller <NUM>.

Accordingly, the relative longitudinal position of feedback ring <NUM> and sensor <NUM> depends on that of propeller <NUM> and reduction gear box <NUM>. Design specifications may define known nominal positions of propeller <NUM> and reduction gear box <NUM>, and thus, of feedback ring <NUM> and sensor <NUM>. However, the actual relative positions of components may vary from their respective nominal design values. For example, variance may exist due to dimensional tolerances of components (the cumulative effect of which may be referred to as tolerance stack-up), variance in assembly, part wear or failure, or other factors.

As described above, the beta angle of propeller blades <NUM> is measured based on the relative longitudinal positions of feedback ring <NUM> and sensor <NUM>. Accurate control of beta angle during flight or ground operation may be crucial for safe and efficient operation. Moreover, operation of propeller assembly <NUM> within design specifications may likewise be crucial for safe and efficient operation.

Controller <NUM> may further be configured to monitor other operating conditions. For example, controller <NUM> may monitor relative longitudinal positions of feedback ring <NUM> and sensor <NUM> to verify that tolerances are within specifications, and to trim or calibrate beta angle measurement.

During engine startup, propeller <NUM> may be idled, during which the beta angle of blades <NUM> may default to a feather condition, namely, maximum beta angle. In this condition, actuator <NUM> does not bias rods <NUM> rearwardly (<FIG>). Thus, in the feather condition, feedback ring <NUM> is in its maximally-forward position. Reduction of the beta angle would result in feedback ring <NUM> progressively being urged in the rearward direction.

While propeller <NUM> is idled with blades <NUM> in feather condition, feedback ring <NUM> turns along with propeller <NUM> and sensor <NUM> detects passage of teeth <NUM>. Detection unit <NUM> measures the interval Tm between passage of teeth 102A, 102B. As described above with reference to <FIG> and <FIG>, at a given rotational speed of propeller <NUM>, the duration Tm corresponds to a circumferential distance between teeth 102A, 102B, where they pass over or under sensor <NUM>. The measured circumferential distance is in turn associated with a specific longitudinal position of feedback ring <NUM> relative to sensor <NUM>. For simplicity, tolerance verification and beta-feedback calibration are described herein with reference to measurements of longitudinal position, based on the observed distance between position markers. However, as will be apparent, calculations may instead be performed directly based on measured circumferential distances, without conversion to corresponding longitudinal positions.

Since propeller <NUM> is known to be in its feather condition in which actuators <NUM> do not bias feedback ring <NUM> rearwardly, feedback ring <NUM> is known to be in its maximally-forward position. Thus, a particular relative longitudinal position, and a corresponding circumferential distance between position markers may be expected based on design specifications and the measured position should be within a specified tolerance depending on geometry and environmental conditions present during engine start up. However, the actual longitudinal position, and thus, the measured circumferential distance between markers, may differ from the expected position, due to dimensional tolerances, assembly variability, part wear or failure, or the like.

For example, feedback ring <NUM> may be expected, based on design specifications, to be positioned as indicated in <FIG>. However, feedback ring <NUM> may in fact be located forward of its expected position. In the expected position, teeth 102A, 102B would pass sensor <NUM> proximate their upper ends 128U, where the circumferential distance between teeth 102A, 102B is short. However, in the actual position, teeth 102A, 102B pass sensor <NUM> closer to their lower ends <NUM>, where the circumferential distance between 102A and102B is shorter. Conversely, if the actual position was rearward of the defined position, the time interval Tm between passage of teeth 102A and 102B would be shorter than expected, and the circumferential distance would likewise be shorter.

Controller <NUM> may be configured to receive a baseline measurement from detection unit <NUM> at startup and compare the measurement to a reference value for the feather condition. Any difference between the two may result from dimensional variance in components, etc..

Controller <NUM> may be configured to compare the measured position to a threshold range. For example, the reference feather value may be the measurement that would be obtained at the feather condition if all components had their nominal dimensions and locations, in accordance with design specifications. The upper and lower limits of the threshold range are measurements associated with the upper and lower tolerance limits of the propeller assembly. A measurement outside the tolerance thresholds may indicate an unsafe operating condition and may be associated with, for example, one or more parts being outside design specifications, a part failure, incorrect assembly, or other conditions. Controller <NUM> may therefore be configured to output a signal indicative of tolerance status. The signal may, for example, be provided for display on an aircraft instrument.

Controller <NUM> may store the baseline measurement in non-volatile memory <NUM> for use as a calibration value. Specifically, the controller may output a signal to an internal or external storage for storing the baseline measurement as a calibration value. Subsequent measurements taken using sensor <NUM> may be compared to the calibration value to account for dimensional variances, etc., thereby correcting beta angle measurements. Controller <NUM> may also output a signal for displaying the calibration status on an aircraft instrument.

In addition, on engine startup, controller <NUM> may further be configured obtain a new measurement in the feather condition and compare it to the previous stored baseline measurement. If the new measurement differs from the previous baseline measurement by more than a threshold value associated with repeatability of the measurement system, a change may have occurred in one or both of the propeller assembly or the measurement assembly. Accordingly, if a new measurement differs from the baseline measurement by more than a repeatability threshold, a warning (e.g. an alarm) may be enunciated and a maintenance procedure may be performed. For example, it may first be determined if maintenance had previously been performed without setting a new baseline value. If so, the deviation from the repeatability threshold may be associated with the previous maintenance. For instance, if a part of the propeller assembly was replaced, the dimensions of the assembly may change slightly, and the measured baseline value may be expected to change. Conversely, if no maintenance had previously been performed without adjusting the baseline value, the deviation from the repeatability tolerance may indicate a change in the propeller or measurement assembly, such as part wear, breakage or deformation. Accordingly, the warning may result in an inspection being performed.

<FIG> depicts a process <NUM> of calibrating a propeller control system. At block <NUM>, the aircraft engine is started. During engine starting, blades <NUM> of propeller <NUM> are in their feather condition, namely, maximum beta angle.

At block <NUM>, controller <NUM> obtains a baseline measurement indicative of the longitudinal position of feedback ring <NUM> relative to sensor <NUM> based on the circumferential distance between teeth 102A, 102B.

At block <NUM>, controller <NUM> receives an instruction from an operator to store the baseline measurement as a calibration value in non-volatile memory. The instruction may be input, for example, using a switch or button in the cockpit, a software control or any other suitable input device and method.

At block <NUM>, controller <NUM> determines if the difference between the measured value and the reference value is greater than a tolerance threshold range. In an example, the tolerance threshold is +/- <NUM> thousandths of an inch (<NUM>) from nominal. If so, at block <NUM>, controller <NUM> outputs a warning signal for display on an aircraft instrument. The warning signal may, for example, be a prompt for maintenance to be performed and a "no dispatch" indication that the aircraft should not be flown. Alternatively, if the measured value is within the threshold, at block <NUM>, the measured value is stored in non-volatile memory. The ring position baseline value stored in non-volatile memory may subsequently be used in beta angle control functions of the aircraft. Such functions may include beta limiting (minimum blade angle limiting) and governing in reverse. Specifically, subsequent measurements may be compared to the baseline value to determine the beta angle.

<FIG> depicts a process <NUM> of checking the propeller assembly. At block <NUM>, the aircraft engine is started. During engine starting, blades <NUM> of propeller <NUM> are in their feather condition, namely, maximum beta angle.

At block <NUM>, controller <NUM> compares the baseline measurement to a reference threshold range for the feather condition.

At block <NUM>, controller <NUM> determines if the difference between the measured value and the refer value is greater than a tolerance threshold range. In an example, the tolerance threshold is +/- <NUM> thousandths of an inch (<NUM>) from nominal. If so, at block <NUM>, controller <NUM> outputs a warning signal for display on an aircraft instrument. The warning signal may, for example, be a prompt for maintenance to be performed and a "no dispatch" indication that the aircraft should not be flown. Alternatively, if the measured value is within the threshold, at block <NUM>, the measured value is compared to the previous baseline, if any. At block <NUM>, controller <NUM> determines if the new measured value differs from the previous baseline by more than a repeatability threshold. The repeatability threshold may be an intermediate range within the tolerance threshold range. In an example, the repeatability threshold is +/- <NUM> thousandths of an inch (<NUM>). The measured value may differ from the previous baseline by more than the repeatability threshold if, for example, a maintenance procedure is performed, such as replacement of a component, or if a failure occurs. At block <NUM>, a warning may be enunciated to perform a maintenance procedure. The warning produced at block <NUM> may differ from those produced at block <NUM> and at block <NUM> of <FIG>. The maintenance procedure may include determining whether the measurement system should be re-calibrated based on previous maintenance and performing an inspection.

Process <NUM> may be initiated automatically based, e.g. on a timer or trigger condition at controller <NUM>. Alternatively, process <NUM> may be initiated by operation of a control input, e.g. by a pilot or technician.

Process <NUM> may be initiated by operation of a control input, e.g., by a pilot or technician. Process <NUM> may be repeated at least following assembly of an engine or propeller assembly, or after servicing such as replacement of a part. Process <NUM> may further be repeated periodically and automatically, e.g. on each startup. This may allow for verification that the propeller assembly is within design specifications. Moreover, accuracy of beta angle measurement may be maintained. For example, if a part is replaced, dimensions of the propeller assembly and the relative locations of feedback ring <NUM> and sensor <NUM> may change, yet remain within tolerance specifications. Nevertheless, controller <NUM> may be recalibrated to correct for the changed dimensions.

As described above, tolerance monitoring and calibration of the beta angle feedback system is performed based on expected values in the feather condition of propeller <NUM>. Alternatively, the above-described process may be performed based on obtaining measurements at another known blade angle and comparing those measurements to reference values associated with that blade angle. For example, measurements may be obtained with the aircraft propeller blades in a maximum thrust condition, with a small positive beta angle. In such a condition, the feedback ring <NUM> is known to be in its maximally-forward position. The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the appended claims.

Claim 1:
A propeller control system for an aircraft propeller (<NUM>) rotatable about a longitudinal axis and having an adjustable blade angle, the control system comprising:
a blade angle feedback ring (<NUM>) and a sensor (<NUM>), wherein the sensor (<NUM>) is couplable to the propeller (<NUM>) to rotate with the propeller (<NUM>) and to move along the longitudinal axis (A) along with adjustment of the blade angle, said blade angle feedback ring (<NUM>) comprising a plurality of position markers (<NUM>) spaced around its circumference such that a circumferential distance between at least some adjacent ones of said position markers (<NUM>) varies along said longitudinal axis (A);
the sensor (<NUM>) positioned adjacent said blade angle feedback ring (<NUM>) for producing signals indicative of passage of said position markers (<NUM>), such that an interval between ones of said signals is indicative of a circumferential distance between adjacent ones of said position markers (<NUM>); and
a controller (<NUM>) in communication with said sensor (<NUM>) to measure a longitudinal position of the sensor (<NUM>) couplable to the propeller (<NUM>) based on an interval between consecutive ones of said signal, said controller (<NUM>) configured to produce a warning signal if said longitudinal position is outside a first threshold range, wherein the propeller (<NUM>) forms part of a propeller assembly and said first threshold range corresponds to upper and lower dimensional tolerance limits of the propeller assembly.