Abstract:
A bi-dimensional position sensor that can be advantageously used in the turn system controlled from the steering wheel of a vehicle. The sensor includes a permanent magnet fixed to a control lever so as to move in a plane along first and second directions and to rotate about a third direction orthogonal to the preceding ones. The permanent magnet is movable with respect to an integrated device including a first group of sensor elements arranged spaced along the first direction, a second group of sensor elements arranged spaced along the second direction and a third group of sensor elements detecting the angular position of the permanent magnet. Electronics integrated with the sensor elements generate a code associated with each position which the permanent magnet may assume and generate a control signal corresponding to the desired function.

Description:
TECHNICAL FIELD 
     The present invention relates to a bi-dimensional position sensor of magnetic type, particularly for motor vehicle applications. 
     BACKGROUND OF THE INVENTION 
     As is known, at the present time the auxiliary functions controlled on the steering wheel (turn systems) of a motor vehicle, such as switching on the parking lights, full beam, dipped headlights, and direction indication, are performed by means of mechanical sliding contacts, the manufacture of which is particularly burdensome and affected by problems associated with the contacts (wear, aging etc.). 
     Control systems for these functions which do not require mechanical sliding contacts are therefore desirable. 
     In general, this problem is also encountered in applications which provide for the sending of a plurality of commands or signals by movement of a control element which acts on sliding contacts and in which there are a large number of operations of the control element. 
     SUMMARY OF THE INVENTION 
     According to principles of the present invention, a magnetic bi-dimensional position sensor is provided which includes a magnetic field generator having alternate areas of a first magnetic direction and a second magnetic direction. The magnetic field generator is translatable in a plane along first and second directions and is rotatable around an axis orthogonal to the first and second directions. The magnetic field generator may be a permanent magnet having quadrants with alternately north and south magnetic field directions. The magnetic field is detected by a plurality of magnetic field sensitive elements, which may be Hall effect sensors or magneto-resistors. The magnetic field generator may be fixed to a lever in a motor vehicle. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows an arrangement of sensor elements on a component of a sensor in diagrammatic form according to an embodiment of the present invention. 
     FIG. 2 shows a transverse section through part of the component shown in FIG. 1 according to an embodiment of the present invention. 
     FIG. 3 shows a second component of the sensor shown in FIG. 1 according to an embodiment of the present invention. 
     FIG. 4 shows a side view of a control device using the sensor shown in FIG. 1 according to an embodiment of the present invention. 
     FIG. 5 shows a block diagram of a component of the sensor shown in FIG. 1 according to an embodiment of the present invention. 
     FIGS. 6 and 7 show two diagrams of cooperation between components of the sensor shown in FIG. 1 in diagrammatic form according to other embodiments of the invention. 
     FIGS. 8 and 9 show tables relating to codes obtainable for different relative positions of the components of the sensor shown in FIG. 1 according to other embodiments of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in FIGS. 1-5, a sensor  1  according to several embodiments of the invention comprises an integrated device  2  and a permanent magnet  3  with four quadrants which is movable with respect to the integrated device  2 , parallel to it (in proximity or in contact) so as to move along a plane defined by two different coordinates X and Y and to rotate about an axis Ω perpendicular to the plane XY. In its turn the integrated device  2  is formed by a plurality of sensor elements  10  sensitive to a magnetic field and by a coding system. 
     In an embodiment of the invention, shown in FIG.  2  and described below, the sensor elements  10  are formed by Hall effect sensors. Alternatively, as shown diagrammatically in FIG. 5, the sensor elements  10  may be magneto-resistors produced by means of special magnetic films (such as Co—Fe, Ni—Fe, Ni—Co) having the property of variable resistance as a function of the magnetic field in which they are placed (see for example R A McCurrie “Ferromagnetic Materials: Structure and Properties”, Academic Press, vol. 2, page 93). The magneto-resistors have the advantage of being more sensitive to the magnetic field than Hall effect sensors, but require the deposition on the silicon, by sputtering or by evaporation, of magnetic films not generally used in the microelectronics industry and so they are more expensive to produce. 
     FIG. 1 shows a possible arrangement of the sensor elements  10  for the detection of 3×4 positions of the permanent magnet  3  in the plane XY and of the rotation by ±45° about the axis Ω (or, overall, of three different angular positions of the magnet  3 ). As will be noted, three sensor elements  10   1 - 10   3  are spaced along a first direction (direction X), four sensor elements  10   4 - 10   7  are spaced along a second direction (direction Y) perpendicular to the first direction X and two further sensor elements  108  and  10   9  are present arranged at a distance from the sensor elements  10   1 - 10   7  to detect an angle of rotation. 
     In general, therefore, to detect M positions along the direction X and N positions along the direction Y, at least M+N sensor elements are required, whilst two sensor elements serve to detect rotation in the case of rotations of ±45° and four sensor elements in the case of rotations of ±30° with respect to a nominal zero-angle position. 
     FIG. 2 shows a transverse section of a portion of a silicon slice  12  in which the integrated device  2  is integrated, in correspondence with a Hall effect sensor element  10 . In detail, the silicon slice  12  comprises a P-type substrate  13 , an N-type epitaxial layer  14  and P + -type junction insulation regions  15 , extending from a surface  16  of the slice  12  to the substrate  13  and surrounding each sensor element  10 . A contact region  18  can be seen on the surface  16  of the slice  12 , which region, together with a similar contact region which is not shown, is used to supply a current I, whilst contact regions  19 , also on the surface  16 , enable a potential difference generated by the sensor element  10  to be detected. A more complex version of the sensor element  10  which can be advantageously used in the sensor  1  is also described in U.S. Pat. No. 5,530,345 which is incorporated herein by reference. 
     As shown in a front view in FIG. 3 according to another embodiment of the invention, the permanent magnet  3  has four quadrants, alternately polarized South (quadrants  21  and  23 ) and North (quadrants  22  and  26 ), defining a center  24  and of dimensions such that, according to the position assumed by the permanent magnet  3  with respect to the integrated device  2 , each of the sensor elements  10  sees a specific quadrant  21 ,  22 ,  23 , or  26  and generates a voltage of corresponding value (positive in the case of the North quadrants  22  and  26  and negative in the case of the South quadrants  21  and  23 , for example). As shown in FIG. 4 according to another embodiment of the invention, the sensor  1  may be fitted to a control element, in this case a lever  4 , so as to define together therewith a control device  7  which can be controlled manually or by a machine and outputs an electrical control signal which can be used by an actuator. In particular, the permanent magnet  3  is fixed integrally with the lever  4  so as to follow its movements of translation according to the axes X and Y and of rotation about the axis Ω. According to this embodiment of the invention, the lever  4  is produced as a common control lever for a multifunctional switch system, fixed to a steering wheel of a motor vehicle with a joint (not shown) forming a turn system such as to transform the operations of the lever  4  on the driver&#39;s part into the rotational and translational movements provided for the permanent magnet  3 . In particular, a guide mechanism (not shown) permits only discrete movements of the permanent magnet  3  with respect to the integrated device  2 , as described in greater detail below with reference to FIGS. 6 and 7. 
     As shown in FIG. 5 according to another embodiment of the invention, the voltages generated by the sensor elements  10  are supplied to a coding system  11  comprising a code generator block  27 , a processing unit  28  and a memory  29  which stores an association between each code which can be generated by the generator block  27  and a respective control. 
     In particular, the code generator block  27  receives analog voltages generated by each sensor element  10  and transforms them into a digital code of several bits, generating, for example, a logic “1” when it receives a positive voltage (the sensor element  10  detects proximity to a North quadrant  22  or  26  of the permanent magnet) and a logic “0” in the opposite case. In practice, the code generator block  27  may be constituted by a battery of comparators each having an input connected to ground and an input receiving the voltage generated by a respective sensor element  10 . The binary code thus obtained (which has nine bits in the case of the integrated device  2  with nine sensor elements  10  shown in FIG. 1) is supplied to the processing unit  28  which, on the basis of the code received and the code stored in the memory  29 , determines the corresponding control (switching on parking lights, full beam or dipped headlights or another control) and generates an output signal S supplied, via the pins  25  of the integrated device  2  shown in FIG. 4, to the relative actuator (not shown) and/or to a central unit of the vehicle (not shown) to be processed. 
     Obviously, to distinguish the various positions of the permanent magnet  3  with respect to the integrated device  2  it is necessary that each position which the permanent magnet  3  can assume has an unambiguous code which does not coincide with that of any other position or that, in each position, at least one of the sensor elements  10  detects an opposite quadrant with respect to all the other positions. In particular, as regards translation, this requires, for each translation of the permanent magnet  3 , that the center  24  of the permanent magnet  3  is brought to a different side of at least one of the seven sensor elements  10   1 - 10   7 ; in the case of the sensor elements  10   1 - 10   9  of FIG. 1, the center  24  of the permanent magnet  3  may therefore roughly assume one of the positions shown in FIG.  6  and identified by the letters A-N according to another embodiment of the invention. 
     In particular, in FIG. 6, the horizontal and vertical lines are aligned, in each position A-N, with separation lines, denoted by  31 ,  32 , of the quadrants of the permanent magnet  3  and the permanent magnet  3  has been shown in the position centered on position A; consequently, movements of the permanent magnet  3  with respect to the integrated device  2  such as to bring its center  24  into correspondence with the positions A-N cause the generation of respective codes, as shown in the table of FIG. 8 for example and according to another embodiment of the invention. 
     As will be noted, the sensor elements  10   8  and  10   9  are unchanging for every translation in the plane XY and assume differing values. 
     Similarly, FIG. 7 shows according to another embodiment of the invention, the position of the permanent magnet  3  with respect to the integrated device  2  when the permanent magnet  3  is centered on position A and rotated by 45° clockwise with respect to the position shown in FIG.  6 . Also shown are the separation lines  31 ,  32  of the quadrants  21 ,  22 ,  23  and  26  of the permanent magnet  3  in the different positions A-N of the center  24 ; as will be noted, these separation lines  31 ,  32  are now inclined by ±45°. In this case, therefore, the code shown in the table of FIG. 9 is obtained according to another embodiment of the invention. 
     As will be noted, the sensor elements  10   8  and  10   9  are always associated with a logic“1”. 
     In a manner not shown, in view of the symmetry of the system a rotation of the permanent magnet  3  in the direction opposite to that shown in FIG. 7 (i.e., 45° anticlockwise with respect to FIG. 6) provides a table complementary to that of FIG.  9 . 
     The sensor  1  described has the following advantages. Primarily it is inexpensive, associated with the manufacturing costs of integrated devices; it is also highly reliable and durable, given that it does not comprise the use of sliding contacts and the permanent magnet  3  may also be at a slight distance from the integrated device  2 . Furthermore, it enables the number of controls that can be implemented to be extended with ease and it is not affected by surrounding light conditions. 
     Finally it will be clear that modifications and variants can be introduced to the sensor described and illustrated here without thereby departing from the protective scope of the invention, as defined in the accompanying claims. In particular, it is emphasized that the electronics for processing the signals generated by the sensor elements  10 , or at least part of them, could also not be integrated with the said sensor elements  10  were this to be desirable or appropriate for specific applications. 
     From the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as be the appended claims.