Abstract:
A transmission clutch position sensor includes two Hall sensors located at opposite ends of a flux concentrator outside the casing of the transmission to sense a magnetic field generated by a magnet attached to the clutch piston. To reduce sensitivity to magnet-to-sensor gap tolerances, a ratio of the voltage of one Hall sensor to the sum of the voltages from both Hall sensors is used to correlate to the piston and, hence, clutch position.

Description:
I. FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to clutch position sensors for automotive vehicle transmissions. 
       II. BACKGROUND OF THE INVENTION 
       [0002]    Modem automotive vehicles employ an engine transmission system having gears of different sizes to transfer power produced by the vehicle&#39;s engine to the vehicle&#39;s wheels based on the speed at which the vehicle is traveling. The engine transmission system typically includes a clutch mechanism which may engage and disengage these gears. The clutch mechanism may be operated manually by the vehicle&#39;s driver, or automatically by the vehicle itself based on the speed at which the driver wishes to operate the vehicle. 
         [0003]    In automatic transmission vehicles, a need arises for the vehicle to sense the position of the clutch for smooth, effective shifts between gears in the transmission and for overall effective transmission control. Therefore, a clutch-position sensing component for sensing the linear position of the clutch must be used by automatic transmission vehicles to facilitate gear shifting and transmission control. 
         [0004]    Current clutch-position sensing components utilize magnetic sensors. One advantage to using magnetic sensors is that the sensor need not be in physical contact with the object being sensed, thereby avoiding mechanical wear between the sensor and the object. However, actual linear clutch measurement accuracy may be compromised when the sensor is not in physical contact with the sensed object because of a necessary gap or tolerance that exists between the sensor and the object. Moreover, current sensing systems addressing this problem use coils and certain application-specific integrated circuits which are relatively expensive. 
       SUMMARY OF THE INVENTION 
       [0005]    Accordingly, an apparatus has a magnet disposable inside an engine transmission casing and movable by an engine clutch mechanism in the casing as the engine clutch mechanism moves. A flux concentrator is disposable outside the engine transmission casing to concentrate magnetic flux from the magnet, and a first Hall sensor is juxtaposed with the flux concentrator for generating a first signal in response to a magnetic field. Additionally, a second Hall sensor is juxtaposed with the flux concentrator for generating a second signal in response to a magnetic field. A position determination circuit receives the first and second signals and based thereon outputs a signal representative of a linear position of the engine clutch mechanism. 
         [0006]    In some embodiments the flux concentrator is elongated and defines first and second ends, with the first Hall sensor being juxtaposed with the first end and the second Hall sensor being juxtaposed with the second end. If desired, a first magnetic booster and a second magnetic booster can be provided. The first Hall sensor may be disposed between the first end of the flux concentrator and the first magnetic booster, and the second Hall sensor may be disposed between the second end of the flux concentrator and the second magnetic booster. 
         [0007]    The flux concentrator can be made of a soft magnetic material. The magnet is disposed inside the transmission casing and is coupled to the engine clutch mechanism. On the other hand, the flux concentrator and Hall sensors typically are disposed outside the casing. In non-limiting implementations the flux concentrator tapers inwardly to the first and second ends as do the boosters. 
         [0008]    In another aspect, an apparatus has a position sensor disposed outside a transmission casing and bearing a distance within a tolerance from a moving part in the transmission whose position is sought to be measured with a desired degree of accuracy regardless of where in the tolerance the sensor is located relative to the part. The position sensor includes plural sensing elements whose individual outputs representing position of the part are affected by the location of the sensor within the tolerance. The sensor also includes a position determination member receiving the signals from the sensing elements and combining the signals in a way that produces a signal representative of the position of the part that is less affected by the location of the sensor within the tolerance than are the signals from the sensing elements. 
         [0009]    In another aspect, a method includes receiving first and second signals from first and second Hall sensors, respectively. The signals represent a position of a moving part. The method includes determining a ratio in which a numerator is derived from only one of the signals, or from a difference between the signals, and the denominator is a sum derived from both of the signals. Position of the moving part is indicated using the ratio. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic view of a vehicle that can use the present clutch position sensor; 
           [0011]      FIG. 2  is a schematic view of a transmission, showing parts related to present principles; 
           [0012]      FIG. 3  is a schematic view an example embodiment of the sensor; 
           [0013]      FIG. 4  is a perspective view of an example embodiment of the sensor; and 
           [0014]      FIG. 5  is a graph showing voltage ratios versus clutch positions. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0015]    The present invention is intended for application in automotive transmission systems and will be described in that context. It is to be understood, however, that the present invention may also be applied to other applications and contexts requiring non-contact linear position sensors. 
         [0016]    Beginning initially with  FIG. 1 , a schematic view of an automotive vehicle is shown. The automotive vehicle  10  has an engine  12  and an engine transmission  14 . It is to be understood that the engine transmission  14  has a clutch capable of engaging transmission gears by means known within the art. Further, the engine transmission  14  is understood to employ a clutch position sensor described further below. The vehicle  10  also has plural wheels  16  so that the vehicle  10  may be mobile. 
         [0017]    Now referencing  FIG. 2 , a schematic view of an engine transmission is shown. The engine transmission  14  is surrounded by an engine transmission casing  16 , the casing  16  being made of a metal such as aluminum (or any non-magnetic material) in non-limiting embodiments. Additionally, the engine transmission  14  includes a clutch mechanism  18 . 
         [0018]    A magnet  20  is also shown in  FIG. 2 . The magnet  20  is disposed inside the casing  16  and is coupled to the engine clutch mechanism  18 . The magnet  20  can be particularly coupled to a moving part  22  of the clutch mechanism  18 . The moving part  22  may be a transmission clutch component such as a piston that moves a transmission clutch in non-limiting embodiments. Moreover, the clutch component may have a movement range in excess of 25 millimeters in non-limiting embodiments. However, it is to be understood herein that the magnet  20  may be placed on any acceptable moving part of the clutch mechanism  18  as determined by those skilled in the art. 
         [0019]    Continuing with  FIG. 2 , a transmission clutch position sensor  24  is disposed outside the casing  16  and is capable of sensing a magnetic field generated by the magnet  20 . It is to be understood that the sensor  24  is relatively inexpensive and preferably does not include a coil, including any type of electro-magnetic coil. The sensor  24  will be described in greater detail in  FIGS. 3 and 4 . 
         [0020]    The position sensor  24  disposed outside a transmission casing  16  bears a gap distance  26  within a tolerance from the moving part  22 . In non-limiting embodiments, the normal gap  26  may be anywhere from 5 millimeters up to 30 millimeters. After the sensor being calibrated at the normal gap, the sensor  24  may still output relatively constant measurements of the relatively large linear position of the moving part  22  at particular times based on the magnetic field generated by the magnet  20  regardless of where in the few millimeters tolerance of the gap the sensor is disposed. Further, the position sensor  24  may include plural sensing elements that will be functionally described in greater detail in  FIGS. 3 and 4 . 
         [0021]    Still in reference to  FIG. 2 , the position sensor  24  is electrically connected at least one position determining circuit  28 . The circuit  28  receives signals from the position sensor  24  and outputs a signal to an engine control module  30  indicating the linear position of the engine clutch mechanism  18 . The method of calculation for the linear position of the mechanism  18  will be described in greater detail below. The engine control module  30  is understood to be electronically connected to the circuit  28  and may use the linear position information in conjunction with vehicle operation in non-limiting embodiments to establish demanded clutch positions. 
         [0022]    Now referencing  FIG. 3 , a schematic view of an example embodiment of a position sensor is shown. It is to be understood that a sensor  32  may be disposable outside an engine transmission casing and is substantially similar in function and configuration to the sensor  24  described above. Thus,  FIG. 3  shows particular elements of a sensor  32  for the current embodiment. 
         [0023]    The sensor  32  has at least one elongated flux concentrator  34  which may concentrate magnetic flux generated by a magnet  36  coupled to a moving part inside a transmission casing, the magnet  36  being substantially similar in function and configuration to the magnet  20  described in  FIG. 2 . Moreover, the flux concentrator  34  may be made of a soft magnetic material such as ferrite ceramic, magnet annealed NiFe, etc. 
         [0024]      FIG. 3  also shows plural sensing elements  38  which are closely juxtaposed with respective ends  40  of the flux concentrator  34 . It is to be understood that the sensing elements may be, without limitation, Hall sensors. It is to be further understood that each of the sensing elements  38  is capable of generating a signal or output in response to a magnetic field generated by the magnet  36  and concentrated onto the sensors by the flux concentrator. 
         [0025]    Thus, the plural sensing elements  38 , which may be Hall sensors in non-limiting embodiments, may each yield a signal or output representing the linear position a moving part, similar to the moving part  22  described in  FIG. 2 , which is measured based on the magnetic field created by movement of the magnet  36 . Accordingly, the individual outputs are received by the position determination circuit, which combines the signals in a way (described below) that produces a signal representative of the actual position of a moving part that is relatively unaffected by the location of the sensor  32  within a gap or tolerance. 
         [0026]    Still describing  FIG. 3 , the sensor  32  may also have plural magnetic boosters  42  which have respective ends  44  facing each booster&#39;s respective sensing element  38  in non-limiting embodiments. Accordingly, each of the sensing elements  38  may be disposed between a respective end  40  of the flux concentrator  34  and a respective end  44  of a magnetic booster  42 . The relative position of the sensing elements  38  between ends  40  and  44  will be described further in  FIG. 4 . 
         [0027]    Now referencing  FIG. 4 , a perspective view of an example embodiment of the sensor  32  also described in  FIG. 3  is shown. From the perspective view shown in  FIG. 4 , it may be appreciated that the flux concentrator  34  tapers inwardly toward the ends  40 . It may be further appreciated that the magnetic boosters  42  taper inwardly toward their respective ends  44  that face their respective sensing elements  38 . These inward tapers may increase the ability of the sensing elements  38  to sense a magnetic field strength. 
         [0028]    Continuing now in reference to  FIG. 5 , a graph showing magnetic field intensity ratios versus clutch positions is shown. The graph  46  shows magnetic field intensity ratios which are based on the magnetic field intensity from one position sensor divided by the sum of the magnetic field intensity from both sensors. Also, the ratio could be that the magnetic field intensity difference between the two sensors over the sum of the magnetic field intensity of both sensors. 
         [0029]    In other words, the ratios used in the graph  46  are determined by a numerator which is derived from only one of the signals of a position sensor or the difference between both sensors and a denominator which is the sum derived from both signal of the position sensors. This ratio may then be used to indicate the position of a moving part to within a certain degree of accuracy (preferably 3-5% of the actual position of the moving part) such as the piston of a clutch mechanism inside a vehicle transmission in non-limiting embodiments. The ratio thus allows an accurate measurement of the position of the moving part irrespective of where in the tolerance a position sensor may be, such as sensor  24  referenced in  FIG. 1  (i.e. despite a gap such as the gap  26  in  FIG. 1 ). 
         [0030]    The position indicated by the ratio may then be used by a vehicle, particularly by an engine control module in a vehicle, to control a subsequent position of the moving part in non-limiting embodiments. Thus, the graph shows voltage ratios ranging from 0 to 1.2 in the vertical column  48  and magnet positions ranging within a 50 millimeter range in the horizontal column  50 . The graph line  52  represents the sensor output when the Hall sensors are 26 mm from the magnet, whereas graph line  54 , which is nearly coterminous with graph line  52 , shows sensor output when the Hall sensors are 29 mm from the magnet. 
         [0031]    While the particular CLUTCH POSITION SENSOR FOR VEHICLE TRANSMISSION is herein shown and described in detail, it is to be understood that the subject matter which is encompassed by the present invention is limited only by the claims.