# Patent

## Title
Solenoid transient variable resistance feedback for effecter position detection

## Abstract

Feedback from a solenoid is achieved by adding at least one variable resistance in parallel with the solenoid current feedback circuit for position detection. The resistance has current flowing therethrough when a switching device actuated by the solenoid is in one position or transitions from one position to at least one other position. A feedback current may be measured in the current feedback circuit and the position of the switching device in response to actuation thereof by the solenoid may be determined from the measured feedback current.

## Background
TECHNICAL FIELD
The application relates generally to a system and method for detecting the position of a switching device actuated by a solenoid.
BACKGROUND OF THE ART
Solenoids may be used to actuate switching devices in a variety of applications, such as fuel transmission systems or vehicle brake systems. As the response of the switching device to the actuation command of the solenoid may be of primary importance for a given application, it is desirable to monitor the operation of the solenoid and of the switching device. For this purpose, a variety of external sensing devices may be used to detect electrical or mechanical faults preventing operation of the solenoid or to provide feedback as to whether the switching device has operated as commanded by the solenoid. However, the use of such devices typically increases the weight, complexity and cost of the overall system.
There is therefore a need for an improved system and method for detecting the position of a switching device actuated by a solenoid.
SUMMARY
In one aspect, there is provided a switching device position detection system comprising a solenoid adapted to generate mechanical energy from an energizing current supplied thereto; a switching device coupled to the solenoid and adapted to be driven by the mechanical energy to move between a first position and at least one second position; at least one measuring element coupled to the switching device, the at least one measuring element adapted to be engaged by the switching device and to have a measuring current flowing therethrough when the switching device moves to the at least one second position; and a solenoid driver coupled to the solenoid and to the at least one measuring element and adapted to supply the energizing current to the solenoid and to detect the measuring current to determine whether the switching device has moved to the at least one second position.
In another aspect, there is provided a switching device position detection method comprising energizing a solenoid by supplying an energizing current from a solenoid driver coupled thereto, thereby actuating a switching device coupled to the solenoid to move between a first position and at least one second position; generating a measuring current through at least one measuring element coupled to the switching device when the switching device moves between the first position and the at least one second position; and detecting the measuring current at the solenoid driver to determine whether the switching device has moved to the at least one second position.
In a further aspect, there is provided a switching device position detection system comprising means for energizing a solenoid by supplying an energizing current from a solenoid driver coupled thereto, thereby actuating a switching device coupled to the solenoid to move between a first position and at least one second position; means for generating a measuring current through at least one measuring element coupled to the switching device when the switching device moves between the first position and the at least one second position; and means for detecting the measuring current at the solenoid driver to determine whether the switching device has moved to the at least one second position; and means for determining whether the switching device has moved to the at least one second position.



DESCRIPTION OF THE DRAWINGS
Reference is now made to the accompanying figures in which:
FIG. 1 is a schematic side cross-sectional view of a gas turbine engine;
FIG. 2a is a schematic diagram of a switching device position detection system in accordance with a first illustrative embodiment;
FIG. 2b is a schematic diagram of the switching device position detection system of FIG. 2a comprising a switch and a resistor;
FIG. 3 is a schematic diagram of an exemplary embodiment of the solenoid driver of FIG. 2a; 
FIG. 4 is a schematic diagram of a position detection system for a multi-position switching device in accordance with a second illustrative embodiment;
FIG. 5 is a schematic diagram of a position detection system for a multi-position switching device adapted to pass through a transient position in accordance with a third illustrative embodiment;
FIG. 6 is a graph of an exemplary transient current profile of the solenoid of FIG. 5;
FIG. 7 is a schematic diagram of a position detection system for a multi-position switching device adapted to pass through a plurality of transient positions in accordance with a fourth illustrative embodiment; and
FIG. 8 is a flowchart of a method for detecting the position of a switching device in accordance with an illustrative embodiment.



DETAILED DESCRIPTION
FIG. 1 illustrates a gas turbine engine 10 of a type typically provided for use in subsonic flight, generally comprising in serial flow communication a fan 12 through which ambient air is propelled, a compressor section 14 for pressurizing the air, a combustor 16 in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section 18 for extracting energy from the combustion gases. High pressure rotor(s) 20 of the turbine section 18 are drivingly engaged to high pressure rotor(s) 22 of the compressor section 14 through a high pressure shaft 24. Low pressure rotor(s) 26 of the turbine section 18 are drivingly engaged to the fan rotor 12 and to other low pressure rotor(s) 28 of the compressor section 14 through a low pressure shaft 30 extending within the high pressure shaft 24 and rotating independently therefrom.
Referring to FIG. 2a and FIG. 2b, the engine 10 may comprise a plurality of switching devices 32, such as two-way switching valves, bypass valves, proportional valves, switches, or the like, used for controlling an operation thereof. For example, such switching devices 32 may include valves (not shown) used as part of a fuel system for enabling fuel, such as diesel oil pressurized by a suitable pump, to flow into the engine 10. During the starting of the gas turbine engine 10, the valve may be opened so that a portion of the fuel may flow through a starter manifold to combustion equipment (not shown) for the initiation of combustion. As soon as combustion has been initiated and sustained, the valve may be closed so that all the fuel may pass through a main manifold to burners. Still, it should be understood that the switching devices 32 may be used in applications other than fuel control systems, such as in engine health monitoring systems.
The switching device 32 may be driven by a solenoid 34 coupled to a solenoid driver 36, such as a microprocessor having preprogrammed logic (not shown). As illustrated in FIG. 2b, the solenoid 34 may comprise a coil 38 wrapped around a movable plunger 40 normally occupying a first physical position and displaced to a second physical position when the coil 38 is energized. For this purpose, the solenoid driver 36, which may be coupled to a power source (not shown), may generate a current command IC and send the current command IC to the solenoid 34 for supplying electrical energy to the coil 38. As a result, a current IS may flow through the solenoid 34, thereby energizing the coil 38 and generating mechanical energy to displace the plunger 40 from the first position to the second position. The solenoid driver 36 may use a variety of methods for directing the current command IC to the solenoid 34. For example, a constant electrical current may be turned on or off according to a desired position to be achieved by the solenoid 34. A pulse width modulation electrical current may also be used, with the pulse width modulations being set at a predetermined frequency so that the solenoid 34 may be activated and deactivated at desired time periods.
The movable plunger 40 of the solenoid 34 is illustratively connected to contacts of the switching device 32, such that the movement of the movable plunger 40 through the coil 38 actuates the switching device 32. When actuated, the switching device 32 may then move between at least a first, e.g. open, position A and a second, e.g. closed, position B. More positions may be provided depending on whether the switching device 32 is a single-position or a multi-position switching device, as will be discussed below.
A current feedback IF, equal to the sum of the current IS flowing through the solenoid 34 and the current, if any, flowing through the switching device 32, may be measured by a suitable sensor (not shown) and received at the solenoid driver 36 for monitoring the state of the solenoid 34 and of the switching device 32. On the basis of the value of such a current feedback IF, the solenoid driver 40 may adjust the magnitude of a new solenoid current command IC generated to sustain the energization of the coil 38 or alternatively de-energize the coil 38 if a desired operation, e.g. opening or closing of the switching device 32, has been fully achieved. For instance, the solenoid driver 36 may measure the current feedback IF and compare the current feedback IF to a threshold predetermined according to the physical characteristics of the solenoid 34 and the switching device 32. If the current feedback IF is below the threshold, the solenoid driver 36 may generate a current command IC that keeps the coil 38 energized. In this manner, the current IS flowing through the solenoid 34, and thereby the operation of the solenoid 34, may be regulated in a closed loop fashion by the solenoid driver 36.
In order to monitor the operation of the switching device 32 and therefore detect potential faults, a sensing or measuring element 42, such as a resistor as illustrated in FIG. 2b, may be placed in parallel with the solenoid current feedback circuit comprising the solenoid 34 and the solenoid driver 36. It should be understood that although the description refers to a resistor 42, any other suitable measuring element known to those skilled in the art may be coupled to the switching device 32 to monitor a position thereof. When the switching device 32 is in the first, i.e. open, position A, no current may flow therethrough and the current feedback IF entering the solenoid driver 36 equals the current IS flowing through the solenoid 34, with the current IS flowing through the solenoid 34 being illustratively equal to the current command IC previously sent by the solenoid driver 36 to the solenoid 34 to actuate the solenoid 34. Measurements made while the switching device 32 is in position A correspond to time t=t1. When the switching device 32 moves to the second, i.e. closed, position B shown in dotted line, the switching device 32 engages the resistor 42. This results in a current IR flowing through the resistor 42 as long as the switching device 32 remains in the second position B, and thus in an increase in the solenoid current feedback IF at a time t=t2 compared to the previously measured IF at time t=t1.
Referring to FIG. 3, the current increase IR may be detected by the solenoid driver 36, which monitors the current feedback IF. For this purpose, the solenoid driver 36 may comprise a comparison module 44, a position detection module 46, and a command generation module 48. The comparison module 44 is illustratively adapted to receive the reading of the current feedback IF and compare the reading to the predetermined threshold, such as the current command IC at time t=t1. The result of the comparison may then be sent to the position detection module 46, which may be adapted to determine the position of the switching device 32 according to the comparison. Indeed, if the received reading of the current feedback IF at time t=t2 is equal to the previously issued current command IC at time t=t1, the solenoid driver 36 may determine that the switching device 32 is in the first position A. Alternatively, if the reading at time t=t2 is greater than the previously issued current command IC at time t=t1 by a value equal to the value of the current increase IR, which may be retrieved from a database (not shown) coupled to the solenoid driver 36, the current increase IR may be detected. The resistive value of the resistor 42 may indeed be stored in the database and retrieved by the solenoid driver 36 to determine a corresponding value of the current increase IR. As a result, the solenoid driver 36 may detect that the switching device 32 has moved to the second position B.
The position detection module 46 may then send the position estimate to the command generation module 48, which may generate a new current command IC to be sent to the solenoid 34 for controlling a movement of the plunger 40 relatively to the coil 38 and therefore adjust a position of the switching device 32. For example, if the position estimate indicates that the switching device 32 is in position A while it is desired to move the switching device 32 to position B, the value of the current command IC may be adjusted accordingly so that the solenoid 34 may remain energized and further actuate the switching device 32 to the desired position.
Referring to FIG. 4, according to an alternate embodiment, the switching device 32 may be adapted to move among a plurality of closed positions, e.g. two positions A, B. Accordingly, a plurality of resistors, e.g. two resistors 421, 422, having different resistive values may be provided in the solenoid current feedback circuit, with each resistor 421, 422 adapted to be engaged by the switching device 32 when the switching device 32 is in a given closed position A, B. For example, the switching device 32 may be adapted to move between a first closed position A and a second closed position B and, as such, a first resistor 421 and a second resistor 422 may be respectively provided for each position A, B. In this manner, when in the position A, the multi-position switching device 32 may engage the first resistor 421, thus leading to a current IR1 flowing therethrough as long as the switching device 32 remains in position A. When the multi-position switching device 32 moves to the position B, the resistor 422 may be engaged, thus leading to a current IR2 flowing therethrough as long as the switching device 32 remains in position B. The current IR1 or IR2 flowing through either resistor 421 or 422 engaged by the switching device 32 may then add to the current IS (equal to the previously issued current command IC) flowing through the solenoid 34 to form the current feedback IF sent to the solenoid driver 36.
In order to identify the resistor 421 or 422, which has been engaged by the switching device 32, and accordingly the position thereof, the current increase IR1 or IR2 may be detected by the solenoid driver 36 using the comparison module 44 to compare the reading of the current feedback IF at time t=t2 to the previously issued current command IC at time t=t1. In particular, if the result of the comparison indicates that the current feedback IF at time t=t2 is greater than the previously issued current command IC at time t=t1 by a value of IR1, the position detection module 46 may determine that the resistor 421 has been engaged by the switching device 32 and that the switching device 32 is therefore in position A. If the result of the comparison indicates that the current feedback IF at time t=t2 is greater than the previously issued current command IC at time t=t1 by a value of IR2, the position detection module 46 may identify that the resistor 422 has been engaged by the switching device 32 and that the switching device 32 is therefore in position B. If no resistor 421 or 422 has been engaged, no current increase IR1 or IR2 will illustratively be detected and the position of the switching device 32, i.e. the open position (not shown), will be determined accordingly.
Referring to FIG. 5, according to an alternative embodiment, the switching device 32 may be adapted to pass through a transient position T when moving between a first steady state position A and a second steady state position B. Accordingly, a resistor 50 may be coupled to the switching device 32 and adapted to be temporarily engaged by the switching device 32 when the switching device 32 passes through the transient position T.
When the resistor 50 is engaged, a current IT may flow through the resistor 50, resulting in a momentary current spike in the current feedback IF monitored by the solenoid driver 36. Thus, the solenoid driver 36 may identify the current spike IT as being representative of the switching device 32 transitioning from the first position A to the second position B, and vice versa. According to the monitored current feedback IF, the solenoid driver 36 may therefore determine the position of the switching device 32.
FIG. 6 shows the transient current profile of the current feedback IF versus time as the solenoid 34 moves between steady state positions A and B. At time 0, the solenoid 34 is illustratively energized. From time 0 to time 1, the current profile thus increases until a steady state current ISS is reached when the switching device is in steady state position A. An inflection point X may occur in the current profile due to a back electro-motive force generated by the movement of the plunger 40 through the coil 38. At time 1, the switching device 32 may move from position A to position B by passing through the transient position T, in which the resistor 50 is temporarily engaged. As a result, the current spike IT occurs and the current feedback IF reaches a peak value IPEAK. At time 2, the switching device 32 may move out of the transient position T towards the steady state position B. The resistor 50 is therefore no longer engaged and the current feedback IF decreases to eventually reach the steady state value ISS when the switching device 32 is in steady state position B.
In this embodiment, the solenoid driver 36 may receive at the comparison module 44 a reading of the current feedback IF and identify a momentary peak current IPEAK during the transition of the solenoid 34 from position A to position B, or vice versa. The comparison module 44 may then compare the peak current IPEAK to a predetermined threshold or current feedback trip point ITRIP. The current feedback trip point ITRIP may be set to a value greater than the value of the current command IC in order to take into account the increase in resistance, and in turn the increase in current IS flowing through the solenoid 34, as the solenoid 34 ages regardless of the current command IC supplied thereto. If the peak current IPEAK is equal to or greater than the current feedback trip point ITRIP, the comparison module 44 may determine that the current spike IT has occurred and the position detection module 46 may identify, on the basis of the comparison, that the switching device 32 has successfully moved positions. Otherwise, it may be determined that no current spike has occurred and that the switching device 32 has not moved positions despite a current command IC having been previously sent by the command generation module 48 to the solenoid 34 for energizing the solenoid 34. The position detection module 46 may therefore identify that a fault has occurred.
Referring to FIG. 7, the switching device 32 may be adapted to move among a plurality of steady state positions, as in A, B, and C, by passing through one of a plurality of transient positions, as in T1 and T2, when transitioning between a pair of the steady state positions. As such, a plurality of resistors, as in 501, 502, having different resistive values may be coupled to the transient positions T1, T2 and each adapted to be engaged by the switching device 32 when the switching device 32 passes through the corresponding transient position T1 or T2. For example, if the switching device 32 moves from the first steady state position A to the second steady state position B, the switching device 32 may pass through the first transient position T1 and temporarily engage the first resistor 501. As a result, a first current spike IT1 may occur. At this point, the first expected value of the current feedback IF is illustratively equal to the sum of the solenoid current IS, which is also equal to the previously issued current command IC, and the first current spike IT1. When the switching device 32 moves from the second steady state position B to the third steady state position C and passes through the second transient position T2, the switching device 32 may temporarily engage the second resistor 502, thus resulting in a second current spike IT2. In this case, the second expected value of the current feedback IF is equal to the sum of the previously issued current command IC and the second current spike IT2.
At any point during the transition of the switching device 32 from one position A, B, C to the next, the comparison module 44 may receive a reading of the current feedback IF and identify the peak value IPEAK of the current feedback IF. The comparison module 44 may then correlate the peak value IPEAK to the expected value of the current feedback IF. For instance, the comparison module 44 may determine that the peak value IPEAK is lower than either the first or the second expected value of the current feedback IF described above. The position detection module 46 may therefore identify that the switching device 32 has not passed through either transient position T1 or T2. In particular, assuming that the resistive value of the resistors 501, 502 is selected such that the first current spike IT1 is smaller than the second current spike IT2, if the peak value IPEAK is smaller than the first expected value of the current feedback IF, the position detection module 46 may detect that the switching device has not passed through transient position T1 and is therefore still in position A. If the peak value IPEAK is equal to or greater than the first expected value yet smaller than the second expected value, the position detection module 46 may identify that the switching device 32 has passed through the first transient position T1 but not through the second transient position T2 and is therefore in position B. If the peak value IPEAK is equal to or greater than the second expected value, the position detection module 46 may identify that the switching device 32 has passed through the second transient position T2 and is therefore in position C. Adjusting the resistive value of the resistors 501, 502 may allow to vary the current ranges used to determine the physical position of the driven switching device 32.
Feedback of the position of the switching device 32, and accordingly fault detection, may therefore be provided using the driving circuit of the solenoid 34 and without the need for discrete inputs to be received from an external sensing device, such as a discrete switch, temperature sensor, pressure sensor, Linear Variable Differential Transformer (LVDT), or the like, which may be coupled to the switching device 32. In addition, when the switching device 32 is in steady state operation, e.g. in position A, B, or C of FIG. 6, no added power consumption illustratively results from the presence of the resistors 501, 502 in the current feedback circuit. Thus, it may be possible to determine whether the switching device 32 has operated in response to the movement of the solenoid 34 using circuitry having reduced weight, cost, and complexity.
Referring to FIG. 8, a method 200 for detecting the position of a switching device 32 will now be described. The method 200 comprises at step 202 receiving the reading of the current feedback IF. Once the reading is received, the reading of the current feedback IF may be compared (step 204) to a predetermined threshold, such as the current command IC previously sent to the solenoid 34, the current feedback trip point ITRIP, or the expected value of the current feedback IF, as discussed above. The next step 206 is then to infer the position of the switching device 32 according to the result of the comparison. For example, in the case illustrated in FIG. 2a where a single resistor 42 may be engaged by the single position switch 32, if the current feedback IF is equal to the current command IC, it may be determined that the switching device 32 is in position A. Once the position of the switching device 32 has been inferred, a new solenoid current command IC may be generated to control the energization level, and therefore the operation, of the solenoid 34 so that the switching device 32 may be placed in a desired 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 invention disclosed. Modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.

## Claims

1. A switching device position detection system comprising:
a solenoid adapted to generate mechanical energy from an energizing current supplied thereto;
a switching device coupled to the solenoid and adapted to be driven by the mechanical energy to move between a first position and at least one second position;
at least one measuring element coupled to the switching device, the at least one measuring element adapted to be engaged by the switching device and to have a measuring current flowing therethrough when the switching device moves to the at least one second position; and
a solenoid driver coupled to the solenoid and to the at least one measuring element and adapted to supply the energizing current to the solenoid, to detect the measuring current, and to determine on the basis of detection of the measuring current whether the switching device has moved to the at least one second position, wherein the solenoid driver is adapted to receive a feedback current comprising a sum of the energizing current and the measuring current when the at least one measuring element has moved to the at least one second position, and compare the feedback current to a predetermined threshold to detect the measuring current.

2. The system of claim 1, wherein, upon determining whether the switching device has moved to the at least one second position, the solenoid driver is adapted to update the energizing current for supply to the solenoid.

3. The system of claim 1, wherein the predetermined threshold corresponds to the energizing current at a time t=t1 preceding a time t=t2 at which the switching device has moved to the at least one second position.

4. The system of claim 1, wherein the at least one measuring element comprises at least one resistor.

5. The system of claim 1, wherein the switching device is adapted to move between the first position and a plurality of successive second positions.

6. The system of claim 5, wherein the at least one measuring element comprises a first measuring element, the first measuring element adapted to be engaged by the switching device and to have a first measuring current flowing therethrough when the switching device is in the first position, and a plurality of second measuring elements each adapted to be successively engaged by the switching device and to have a second measuring current flowing therethrough when the switching device is in a corresponding one of the plurality of successive second positions.

7. The system of claim 6, wherein the second measuring current flowing through a first one of the plurality of second measuring elements is different from the first measuring current and from the second measuring current flowing through a second one of the plurality of second measuring elements.

8. The system of claim 1, wherein the switching device is adapted to move between a plurality of successive steady state positions and to pass through a transient position when moving between each pair of the plurality of successive steady state positions.

9. The system of claim 8, wherein the at least one measuring element comprises a plurality of measuring elements each adapted to be temporarily engaged by the switching device and have the measuring current flowing therethrough when the switching device passes through the transient position.

10. A switching device position detection method comprising:
energizing a solenoid by supplying an energizing current from a solenoid driver coupled thereto, thereby actuating a switching device coupled to the solenoid to move between a first position and at least one second position;
generating a measuring current through at least one measuring element coupled to the switching device when the switching device moves between the first position and the at least one second position; and
detecting the measuring current at the solenoid driver by receiving a feedback current comprising a sum of the energizing current and the measuring current when the at least one measuring element has moved to the at least one second position and comparing the feedback current to a predetermined threshold, and determining, on the basis of detection of the measuring current, whether the switching device has moved to the at least one second position.

11. The method of claim 10, wherein comparing the feedback current to a predetermined threshold comprises comparing the feedback current to the energizing current at a time t=t1 preceding a time t=t2 at which the switching device has moved to the at least one second position.

12. The method of claim 10, further comprising, upon detecting the measuring current at the solenoid driver to determine whether the switching device has moved to the at least one second position, updating the energizing current for supply to the solenoid.

13. The method of claim 10, wherein energizing the solenoid actuates the switching device to move between the first position and a plurality of successive second positions.

14. The method of claim 13, wherein generating a measuring current comprises generating the measuring current through a first measuring element coupled to the switching device when the switching device is in the first position and generating the measuring current through each one of a plurality of second measuring elements coupled to the switching device when the switching device is in a corresponding one of the plurality of successive second positions.

15. The method of claim 10, wherein energizing the solenoid actuates the switching device to move between a plurality of successive steady state positions and to pass through a transient position when moving between each pair of the plurality of successive steady state positions.

16. The method of claim 15, wherein generating a measuring current comprises generating the measuring current through each one of a plurality of measuring elements coupled to the switching device when the switching device passes through the transient position.

17. A switching device position detection system comprising:
means for energizing a solenoid by supplying an energizing current from a solenoid driver coupled thereto, thereby actuating a switching device coupled to the solenoid to move between a first position and at least one second position;
means for generating a measuring current through at least one measuring element coupled to the switching device when the switching device moves between the first position and the at least one second position; and
means for detecting the measuring current at the solenoid driver by receiving a feedback current comprising a sum of the energizing current and the measuring current when the at least one measuring element has moved to the at least one second position and comparing the feedback current to a predetermined threshold, and determining, on the basis of detection of the measuring current, whether the switching device has moved to the at least one second position.