Abstract:
A method of using a magnetic fluid clutch for torque measurement comprises steps of modulating electric current through a coil of the magnetic fluid clutch to maintain a steady-state quasi-solid phase of a magnetic fluid medium contained within the magnetic fluid clutch when the magnetic fluid clutch is clutched to transmit torque from a torque input end of the clutch to a torque output end of the clutch, thereby ensuring that the torque output end rotates in response to the rotation of the torque input end without relative rotational slippage therebetween; and measuring a deflection value associated with the magnetic fluid clutch. The clutch is thereby used as a combined torque measurement and clutch apparatus.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is a continuation of U.S. patent application Ser. No. 09/991,220 filed Nov. 16, 2001 now U.S. Pat. No. 6,834,558, and allowed on Aug. 16, 2004, the contents of which are incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The present invention generally relates to torque measurement, and more particularly to a method of using a magnetic fluid clutch for torque measurement as well as to a combined torque measurement and clutch apparatus for use with this method. 
   BACKGROUND OF THE INVENTION 
   Engines which are utilized in single-engine helicopter applications typically incorporate a freewheeling clutch and a separate torque measuring device which is within or attached to the reduction gear box, or is attached to a drive system of the helicopter in order to establish torque transmission to the main rotor and to monitor the torque value transmitted to the main rotor, or facilitate auto-rotation in the event of a reduction or loss of engine power. 
   It is known that torque measurement can be achieved by a phase shift measuring device used to measure an angular deviation between two ends of a rotating shaft which transmits torque. One example of such a phase shift measuring device is described in U.S. Pat. No. 4,520,681, issued to Moore et al. on Jun. 4, 1985. The device of Moore et al. includes two slotted disks disposed on a rotating shaft a predetermined distance apart. A slot is formed in the periphery of each of the disks. A light source and a light sensor are mounted stationary with respect to the shaft and proximate to the periphery of each disk. The time duration between signals from the respective sensors is measured and the angular deviation of the two disks can be calculated therefrom. Measurement of this angular deviation determines the amount of twist on the shaft portion between the two disks. The torque can then be calculated from this angle of twist, by a computerized central processing device. 
   Another example of phase shift measuring devices is described in U.S. Pat. No. 5,918,286, which issued to Smith et al. on Jun. 29, 1999. Smith et al. describe a device for torque measurement of rotating shafts for the purpose of calculating the shaft power without using sensors mounted or glued to the shaft. Accuracy is increased by using only one single optical electronic sensor in the pulse receiver. The light is transmitted from the source/transmitter through optical fiber. The light beam is pulsed within two air gaps by coding disks/gear wheels mounted to the shaft at a convenient distance from each other. The time displacement between the vanes/teeth on the two disks/gear wheels is a measure on the shaft torque, enabling the shaft power to be calculated by a computer. To increase the accuracy in case of shaft vibration, the width modulated pulses are accumulated and averaged at convenient numbers of shaft turns. The accuracy is increased by detecting both rising and falling pulse edges in order to double the number of pulses of each shaft turn. 
   The angular deviation of the rotating shaft which transmits torque depends on both the torque value being transmitted through the rotating shaft and the resilient property in angle deviation of the rotating shaft, which is inherent in the nature of the shaft material and is further determined by the geometry of the shaft. Thus, the amount of torque transmitted through the rotating shaft can be calculated from the angular deviation of the rotating shaft because the geometry of the rotating shaft and the nature of the shaft material are not variable. Nevertheless, the rotating shaft is generally designed for full load torque transmission and therefore the angular deviation of the rotating shaft at a low torque level will be relatively small, resulting in inaccuracies in the torque measurement. However, such accuracy is needed for example, in helicopter rotor applications. 
   Therefore, there is a need for a method and apparatus for torque measurement which provide adequate measuring accuracy at various torque levels. 
   SUMMARY OF THE INVENTION 
   A primary object of the present invention is to provide a method of using a magnetic fluid clutch for torque measurement and transmission. 
   Another object of the present invention is to provide a method and apparatus for torque measurement which provides adequate accuracy at various torque levels. 
   A further object of the present invention is to provide a combined torque measurement and clutch apparatus and a method for using the apparatus for torque transmission and torque measurement. 
   The present invention is generally directed to a method of using a magnetic fluid clutch for torque measurement. The method comprises: modulating electric current through a coil of the magnetic fluid clutch to maintain a steady-state quasi-solid phase of a magnetic fluid medium contained within the magnetic fluid clutch when the magnetic fluid clutch is clutched to transmit torque from a torque input end of the clutch to a torque output end of the clutch, thereby ensuring that the torque output end rotates in response to the rotation of the torque input end without relative rotational slippage therebetween; and measuring a deflection value associated with the magnetic fluid clutch. 
   The deflection value associated with the magnetic fluid clutch is preferably measured by way of a phase shift measurement between the torque input end and the torque output end of the magnetic fluid clutch. The deflection value associated with the magnetic fluid clutch is also preferably measured by way of distortion measurement of a magnetic field applied to the magnetic fluid medium and then, a torque value can be calculated from the measured deflection value associated with the magnetic fluid clutch. 
   The viscosity/solidity of the magnetic fluid medium which is maintained in the steady-state quasi-solid phase, according to one embodiment of the present invention, can be varied to a level which matches a level of torque being transmitted through the magnetic fluid clutch so that the deflection value being measured is optimized within an adequate measuring range of a measuring device used for the measurement. For example, electric current through the coil of the magnetic fluid clutch can be modulated to increase the viscosity/solidity of the magnetic fluid medium when the level of torque being transmitted is relatively large; and the electric current through the coil of the magnetic fluid clutch can be modulated to decrease the viscosity/solidity of the magnetic fluid medium when the level of torque being transmitted is relatively small. Nevertheless, the change of the viscosity/solidity of the magnetic fluid medium should not change the no slippage work condition of the magnetic fluid clutch when the magnetic fluid clutch is used for torque measurement. 
   In accordance with another aspect of the present invention, an apparatus is provided including a magnetic fluid clutch which has a torque input end and a torque output end. The magnetic fluid clutch further includes a magnetic fluid medium therein and a coil for generating a magnetic field and applying the magnetic field to the magnetic fluid medium. The torque input end is adapted to be connected to a torque supply source, an engine of a helicopter for example, and the torque output end is adapted to be connected to a rotational work device, the main rotor of the helicopter for example. The apparatus further includes a first detector positioned at the torque input end and a second detector positioned at the torque output end. A processor is provided for controlling current through the coil of the magnetic fluid clutch and for processing signals from the first and second detectors to calculate an angular deviation between the torque input end and the torque output end. 
   The processor is preferably incorporated into a controller of an engine, or incorporated into a controller of an aircraft. 
   In one embodiment of the present invention, the magnetic fluid clutch comprises a rotating shaft having a first end and a second end. One of the ends forms the torque output end of the magnetic fluid clutch. A casing surrounding the rotating shaft is rotatable relative to the rotating shaft, and contains the magnetic fluid medium therein. The rotating casing forms the torque input end of the magnetic fluid clutch. Rotating members such as blades are affixed to the respective rotating shaft and the inside surface of the casing in order to increase the frictional contact of the respective rotating shaft and the rotating casing with the magnetic fluid medium. 
   In another embodiment of the present invention, the magnetic fluid clutch comprises a stationary casing containing the magnetic fluid medium therein. A first rotating shaft and a second rotating shaft form the respective torque input end and torque output end. The respective rotating shafts extend oppositely and outwardly from the inside of the casing and are rotatable relative to each other and relative to the casing. A first plate and a second plate are affixed to the first and second rotating shafts respectively, and are axially spaced apart. The first plate and second plate are disposed in the magnetic fluid medium so that torque can be transmitted from the first plate to the second plate through the magnetic fluid medium when the viscosity/solidity of the magnetic fluid medium reaches a certain level. 
   The apparatus according to the present invention combines a clutch device with a torque measurement device and can have broad application potential, because of not only providing a new option for machine structure design, but also providing a new torque measurement method which provides more measurement accuracy. The latter is advantageous, particularly at low torque levels compared to a full load torque level of the machine into which the apparatus is incorporated. 
   Other advantages and features of the present invention will be better understood with reference to preferred embodiments of the present invention described hereinafter. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Having thus generally described the nature of the present invention, reference will now be made to the accompanying drawings, showing by way of illustration, the preferred embodiments thereof, in which: 
       FIG. 1  is a schematic illustration of a combined torque measurement and clutch apparatus according to one embodiment of the present invention showing a direct drive application in which the apparatus is directly coupled to an engine; and 
       FIG. 2  is a schematic illustration of the combined torque measurement and clutch apparatus according to another embodiment of the present invention, showing a reduction gearbox application in which the apparatus is incorporated into a reduction gear box of an engine. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   With reference to  FIG. 1 , an apparatus of the present invention generally designated at numeral  10 , includes a magnetic fluid clutch  12  which is directly coupled to an engine  14 , and thereby forms a torque output end of the engine  14 . The magnetic fluid clutch  12  includes a casing  16  supported on a stationary structure (not shown) of the engine  14 . A torque input shaft  18  extends outwardly from the inside of the casing  16  and is rotatable relative to the casing  16 . A first plate  20  is attached to the inner end of the torque input shaft  18  and is rotatable together with the shaft  18 . The magnetic fluid clutch  12  further includes a torque output shaft  22  which extends, oppositely with respect to the torque input shaft  18 , outwardly from the inside of the casing  12  and is rotatable relative to the casing  12 . A second plate  24  is attached to the inner end of the torque output shaft  22  and is rotatable together with the shaft  22 . The torque input and output shafts  18 ,  22  are positioned co-axially and the first and second plates  20 ,  24  are axially spaced apart from each other. 
   The magnetic fluid clutch  12  further includes a first core material  26  and a coil  28  wound around the first core material  26 . The two ends of the coil  28  are connected to an electronic controller  30  which is incorporated into a control system of the engine  14 , for example, a control system of a helicopter which is equipped with the engine  14 . A second core material  32  likewise has a coil  34  wound therearound. The two ends of the coil  34  are connected to the electronic controller  30  which is the same one controlling the coil  28 , but is illustrated separately. 
   Both the first and second plates  20 ,  24  are immersed in a magnetic fluid medium which is generally designated by numeral  36  and is contained within the casing  16 . The core materials  26 ,  32  are preferably positioned within the casing  16  and the magnetic fluid medium  36  is contained by an interior surface of the core materials  26 ,  32 . Alternatively, an inner casing (not shown) may be provided to protect coils  28  and  34 . The first and second plates  20 ,  24  and the first and second core materials  26 ,  32  preferably have a circular cross-section. The size of the first and second plates  20 ,  24  and the volume of the magnetic fluid medium  36  are determined by the specific properties of the magnetic fluid medium chosen, as well as performance specifications of the magnetic fluid clutch  12 . The torque input shaft  18  and the torque output shaft  22  pass through axially aligned openings  38 ,  40  defined by core materials  26 ,  32 . Seals  42 ,  44  are also preferably placed between openings  38 ,  40  and the magnetic fluid medium  36 , in order to prevent leakage thereof. 
   The electronic controller  30  provides current through coils  28 ,  34  in a controlled manner in order to apply an electric magnetic field to the magnetic fluid medium  36 . 
   The torque input shaft  18  is coupled at its outer end directly to the engine  14  by means of a coupler  46 . The torque output shaft  22  is adapted to be connected at its outer end to a rotational work device, for example, the main rotors of the helicopter. 
   The magnetic fluid clutch  12  provides a magnetically controlled fluid coupling between the first and second plates  20 ,  24 . Magnetic fluid medium  36  contains magnetically polarized particles. When a magnetic field which can be generated and controlled by the current through the coils  28 ,  34  is applied to the magnetic fluid medium  36 , particle chains form. In effect, magnetic fluid medium  36  changes from a free flowing state (steady-state liquid phase) to a highly viscous state (steady-state quasi-solid phase) when electric current is steadily increased through coils  28 ,  34 . Various intermediate levels of viscosity/solidity can be obtained by varying the magnetic field applied to the magnetic fluid medium  36 . Advantageously, the response time for the magnetic fluid medium  36  to change between a steady-state quasi-solid phase and a steady-state liquid phase is in the millisecond range. Therefore, torque transfer control changes can be performed very quickly. The property of the magnetic fluid medium  30  is described in more detail in U.S. Pat. No. 5,779,013, issued to Bansbach on Jul. 14, 1998, which is incorporated herein by reference. 
   A first disk  48  is affixed to the torque input shaft  18  at the outside of the casing  16  and is rotatable together with the shaft  18 . A second disk  50  is affixed to the torque output shaft  22  at the outside of the casing  16  and is rotatable together with the shaft  22 . The first disk  48  has a plurality of slots or holes  52  on the periphery thereof. The holes  52  extend through the disk  48 , adjacent to the periphery thereof, and are circumferentially and equally spaced apart from one another. A light source  54  is disposed on one side of the first disk  48  at a right angle thereto, such that the light emitted therefrom will pass through the holes  52  when the respective holes  52  are aligned with the light source  54 . A detector  56  is disposed on the other side of the first disk  48  at a right angle thereto. The detector  56  is disposed such that light emitted by the light source  54  impinges thereon when the respective holes  52  pass thereby. The light source  54  and the detector  56  are both stationary with respect to the rotating torque input shaft  18 . The second disk  50  has a plurality of slots or holes  58  disposed on the periphery thereof. The holes  58  extending through the second disk  50  are disposed adjacent to the periphery thereof and are circumferentially and equally spaced apart from one another. A light source  60  is disposed on one side of the second disk  50  adjacent to the periphery thereof, such that light emitted therefrom passes through the respective holes  58  when the respective holes  58  are rotated past the light source  60 . A detector  62  is disposed on the opposite side of the second disk  50  from the light source  60 , such that light passing through the respective holes  58  impinges upon the detector  62 . The light source  60  and the detector  62  are stationary with respect to the rotating torque output shaft  22 , as described above with reference to the light source  54  and the detector  56 . 
   When the magnetic fluid clutch  12  is required to be declutched to terminate torque transmission from the engine  14 , to the main rotor (not shown) for example, the electronic controller  30  supplies no current or only a small amount of current through the coils  28 ,  34 , thereby maintaining the magnetic fluid medium  36  in a substantially steady-state liquid phase. The first plate  20  which is driven by the engine  14  can rotate freely in the magnetic fluid medium  36  and the friction between the magnetic fluid medium  36  and the first and second plates  20 ,  24  is so small that the second plate  24  cannot be driven to rotate by the first plate  20  by means of the magnetic fluid medium  36 . 
   When a full load torque transmission is required, the electronic controller  30  provides an increased current through the coils  28 ,  34  above a predetermined level so that the magnetic fluid medium  36  is in a substantially steady-state quasi-solid phase. Thus, the friction between the magnetic fluid medium  36  and the first and second plates  20 ,  24  reaches a significant level such that the second plate  24  can be driven to rotate by the first plate  20  by means of the magnetic fluid medium  36 , without rotational slippage relative to the first plate  20 . 
   It is noted that the steady-state quasi-solid phase of the magnetic fluid medium  36  is not only determined by the viscosity/solidity of the magnetic fluid medium  36  but also depends on the level of torque transmitted therethrough. The magnetic fluid medium  36  with a predetermined viscosity/solidity level permits a maximum level of torque to be transmitted therethrough. When torque transmission is below the permitted level, no rotational slippage will occur between the first and second plates  20 ,  24 . Therefore, the magnetic fluid medium  36  with the predetermined viscosity/solidity is in a steady-state quasi-solid phase with respect to the torque transmission level which is below the permitted maximum level. However, the magnetic fluid medium  36  with the same predetermined viscosity/solidity is not in a steady-state quasi-solid phase with respect to torque levels to be transmitted which are equal to or above the permitted maximum level, because rotational slippage between the first and second plates  20 ,  24  will occur. In fact, the slippage between the first and second plates  20 ,  24  make torque transmission above the permitted maximum level impossible. This feature of the magnetic fluid medium also provides advantages for torque measurement using the magnetic fluid clutch  12  which will be further described below. 
   Under the condition of the magnetic fluid medium  36  being maintained in a steady-state quasi-solid phase which means no rotational slippage occurs between the first and second plates  20 ,  24 , and during rotation of the torque input shaft  18  and the torque output shaft  22  under a “no load” condition, the angular relationship of the first disk  48  with respect to the second disk  50  remains constant. However, if torque is transmitted through the clutch  12 , a corresponding torsional movement or twist between the first and second disks  48 ,  50  will result, and a relative angular deviation between the first disk  48  and the second disk  50  will occur. The amount of this angular deviation is a function of the torque, the properties of the magnetic fluid medium  36 , and the properties of the portions of the shafts  18 ,  22  between the two disks  48 ,  50 . 
   In order to measure the amount of angular deviation between the two disks  48 ,  50 , the output of the detectors  56 ,  62  is monitored to determine the angular position at which the respective holes  52 ,  58  pass by the detectors  56 ,  62 . By determining the points in time at which the light from the light source  54  impinges on the detector  56 , an indication can be obtained of the relative position of the holes  52  with respect to the rotation of the torque input shaft  18  about its longitudinal axis. In a similar manner, measurement of the output of the detector  62  also provides the relative position of the holes  58  with respect to the rotation of the output shaft  22 . By comparing the outputs of the detectors  56 ,  62  with respect to time, a relative angular position of the holes  52 ,  58  can be determined. In this manner, an angular deviation due to twist between the two disks  48 ,  50  can be determined with a high degree of precision. 
   The signals from the detectors  56 ,  62  are processed in the electronic controller  30 . The electric current through the coils  28 ,  34  is modulated at several predetermined levels in accordance with a series of permitted maximum torque levels. When the relative angular deviation between the two disks  48 ,  50  being detected by the detectors  56 ,  62  is relatively small, the electric current should be modulated to a lower level in order to decrease the viscosity/solidity of the magnetic fluid medium  36  so that the angular deviation between the two disks  48 ,  50  will increase, thereby resulting in a higher degree of measurement precision. As a general rule, the electric current level should be selected in accordance with a permitted maximum torque transmission level which is presumed to be greater than, but-close to the torque level being transmitted and measured, such that the magnetic fluid medium  36  is maintained in a relatively steady-state quasi-solid phase with respect to the torque level being transmitted and measured, in order to ensure that no slippage condition exists, while resulting in a relatively large amount of angular deviation between the two disks  48 ,  50 , which increases the measurement precision. 
     FIG. 2  illustrates another embodiment of the present invention, generally designated by numeral  10 ′ in which components similar to those of the apparatus  10  illustrated in  FIG. 1  are indicated by similar numerals and will not therefore be redundantly described in detail. 
   The combined torque measurement and clutch apparatus  10 ′ includes a magnetic fluid clutch  70  coupled to the engine  14  by means of a reduction gear box  72  (shown in broken lines) and is supported within the reduction gear box  72 . 
   The magnetic fluid clutch  70  includes a rotating shaft  74  rotatably supported by bearings  76  in the gear box  72 , and a cylindrical casing  78  surrounding and rotatable relative to the rotating shaft  74 . The cylindrical casing  78  includes a cylindrical wall  80  and two side walls  82 , defining in combination the casing therebetween and containing a magnetic fluid medium  84  therein. The cylindrical wall  80  of the casing  78  further includes extended sections at opposed ends. 
   The disk  48  and a gear  86  are mounted on the respective extended sections of the cylindrical wall  80  of the casing  78  at the opposite ends thereof. The casing  78  is also rotatably supported in the gear box  72  by bearings  88  at the respective extended sections of the cylindrical wall  80  at the opposite ends thereof. 
   The second disk  50  is mounted at a first torque output end  90  of the rotating shaft  74  which is connected, for example, to the main rotor (not shown) of the helicopter. A second torque output end  92  of the rotating shaft  74  is provided and may be connected for example, for driving the tail rotor (not shown) of a helicopter. The gear  86  mounted on the casing  78  forms a torque input end of the magnetic fluid clutch  70  and engages gear  94  which is mounted on a torque output shaft  96  of the engine  14 . The torque output shaft  96  of the engine  14  is also rotatably supported within the gear box  72  by bearings  98 . 
   A coil  100  is wound around a first core material  102  and is connected to the electronic controller  30 . A coil  104  is wound around a second coil material  106  and is connected to the electronic controller  30 . Similar to those illustrated in  FIG. 1 , the controller  30  in  FIG. 2  is a single device but is illustrated as two separate blocks. The first and second core material  102  and  106  are supported on a stationary structure (not shown) of the gear box  72 , and preferably, in combination form a ring around the casing  78  and are radially apart therefrom so that the magnetic fluid field generated by current passing through the coils  100 ,  104  is applied to the magnetic fluid medium  84  within the casing  78 . 
   Similar to the apparatus  10  illustrated in  FIG. 1 , the light sources  54 ,  60  and detectors  56 ,  62  are disposed at the opposite sides of the respective disks  48 ,  50 , and are connected to the electronic controller  30 . The holes  52  and  58  of the respective disks  48  and  50  illustrated in  FIG. 1  are also provided in the respective disks  48 ,  50  of the embodiment  10 ′ but are not shown in  FIG. 2 . 
   When the casing  78  is rotated by the engine  14 , the rotating shaft  74  will remain immobile or will rotate in response to the rotation of the casing  78 , depending on the viscosity/solidity condition of the magnetic fluid medium  84 . In order to increase the frictional contact of the magnetic fluid medium  84  with the rotating casing  78  and the rotating shaft  74 , rotating members which include, for example, circumferentially spaced blades, are preferably attached to the respective rotating casing  78  and the rotating shaft  74  and are immersed in the magnetic fluid medium  84  within the casing  78 , as illustrated but not indicated with numerals in  FIG. 2 . 
   During operation, the apparatus  10 ′ performs the same functions as that of apparatus  10  which is illustrated in  FIG. 1  for both torque transmission and torque measurement. The method of using the apparatus  10 ′ for clutching, and declutching in torque transmission and for measuring torque in a selected measuring range is the same as described with reference to the apparatus  10  illustrated in  FIG. 1 , and will not therefore be described again herein. 
   The phase shift measuring devices which include the disks  48 ,  50 , light sources  54 ,  60  and detectors  56 ,  62 , used in apparatus  10  and  10 ′, in  FIGS. 1 and 2  for torque measurement, can be substituted by means for detecting distortion of the magnetic field applied to the magnetic fluid medium  36  or  84 . The magnetic field distortion is a function of the torque level transmitted through the magnetic fluid medium  36  or  84  to which the magnetic field is applied. Therefore, the torque value can be calculated by a processor from the result of the magnetic field distortion measurement. 
   Modifications and improvements to the above-described embodiments of the present invention may become apparent to those skilled in the art. The magnetic fluid clutch used in the embodiments of the present invention may be varied in configuration. For example, the rotating shaft  74  of the magnetic fluid clutch  70  can be used as a torque input end of the clutch, and the gear  86  mounted on the casing  78  can be used as a torque output end of the clutch. The light sources  54 ,  60  and the light detectors  56 ,  62  may also be replaced by various electric or electronic detectors, or transducers 
   The foregoing description is intended to be exemplary rather than limiting. The apparatus of the present invention can be used for helicopter engines, but also can be used in various other applications. The scope of the invention is therefore intended to be limited solely by the scope of the appended claims.