Abstract:
A measuring instrument for contactless detection of a path c is comprised of a two-part ( 14, 15 ) base plate ( 11 ), a side plate ( 16 ), and a movable part ( 12 ). The movable part ( 12 ) has a support plate ( 25 ) which is guided through a slot ( 26 ) in the side plate ( 16 ). At one end ( 27 ) of the support plate ( 25 ), there is a permanent magnet ( 28 ) which is embodied as smaller than the path (c). The magnet ( 28 ) can be embodied in one piece or in several pieces. Through the disposition of the magnet ( 28 ), it is possible to produce different sections, e.g. plateaus or sections deviating form the linear measurement line, in the measurement curve detected by the measuring instrument.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a measuring instrument. DE 29 23 644 C2 has disclosed a sensor which has a cylindrically embodied frame comprised of ferromagnetic material. A permanent magnet is moved in sliding fashion in the frame and its movement is proportional to the movement of a component. In addition, a magnetic field-sensitive element is disposed in a gap in the frame and is consequently enclosed in the magnetic circuit produced by the magnet and its output signal is proportional to the movement of the magnet. However, since the magnet slides directly on the inside of the frame, high friction losses can occur which distort the output signal. 
     SUMMARY OF THE INVENTION 
     The measuring instrument according to the invention has the advantage over the prior art that in a particularly simple manner, the support of the magnet serves to transmit the movement to be measured and serves as a support for the magnet and simultaneously also contributes to the conduction of the magnetic flux. By varying the length of the magnet and/or dividing it into individual sections, it is easy to produce a measurement curve with one or more plateaus. 
     Because of its simple design the sensor can be integrated into various systems for a relatively low installation cost, e.g. a throttle measuring instrument, a pedal module for a brake and gas pedal sensor, or can be used as a separate sensor in throttle valve sensors or a vehicle body deflection device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments of the invention are shown in the drawings and will be explained in detail in the subsequent description. 
     FIGS. 1 and 2 show a longitudinal section and a top view of a first exemplary embodiment. 
     FIG. 3 shows a graph of the course of the magnetic induction B over the entire measurement range c (c=a+b) and the position of the magnet in relation to the magnetic field-sensitive measuring element in three positions I to III shown in the graph. 
     FIGS. 4 to  9  show longitudinal sections and top views of modifications to the exemplary embodiment. 
     FIG. 10 shows a graph of the course of the magnetic induction B over the path c to be measured, with a plateau region X in the middle of the measurement curve. The position of the magnet in relation to the magnetic field-sensitive element is shown above it in three positions I to III. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1, a sensor is labeled  10 , which has a stator  11  and a movable part  12 . The stator  11  is comprised of a base plate comprised of two parts  14 ,  15 , and a side plate  16 , which is disposed approximately perpendicular to the base plate. The two parts  14 ,  15  of the base plate and the side plate  16  are comprised of magnetically conductive material, for example soft iron. Between the two parts  14 ,  15  of the base plate, there is a gap  18  in which a magnetic field-sensitive element  20  is disposed. For example a photoresistance cell, a magnetic transistor, coils, magnetoresistive elements, or a Hall element can be used as the magnetic field-sensitive element  20 . In this connection, it is important that the output signal of the magnetic field-sensitive component have as linear as possible a dependence on the magnetic induction B. The Figs. respectively show a measurement with the aid of a single magnetic field-sensitive element, a Hall element. In this instance, the element should be disposed as close to the center of the gap  18  as possible. However, it would also be possible, for example, to dispose additional magnetic field-sensitive elements in order, for example, to be able to execute a so-called redundant measurement (safety measurement). Lines lead from the magnetic field-sensitive element  20  to a printed circuit board  21  disposed on the underside of the parts  14 ,  15  of the base plate. 
     The movable part  12  is comprised of a support plate  25 , which is likewise comprised of a magnetically conductive material such as soft iron. The support plate  25  protrudes through a recess  26  embodied in the side plate  16 . The end  27  of the support plate  25  protruding into the sensor  10  has a magnet, i.e. a permanent magnet  28 . The other end  29  of the support plate  25  is disposed outside the sensor  10 . On this end  29 , there is a component, not shown, whose movement is to be detected. 
     The permanent magnet  28  has a polarization direction perpendicular to the movement direction R of the support plate  25 , i.e. its polarization is aligned perpendicular to the base plate and parallel to the side plate  16 . In FIG. 1, the permanent magnet  28  is embodied as shorter than its total measurement range c. This also means that the permanent magnet  28  is not as long as the part  15  of the base plate. The permanent magnet  28  is disposed on the side of the support plate  25  oriented toward the base plate. In addition, a small gap is disposed between the permanent magnet  28  and the surface of the base plate in order to permit a slight mobility of the movable part  12  in relation to the stator  11 . This gap, however, should be kept as small as possible and should be constant during the measurement. 
     If the permanent magnet  28  is smaller than the total measurement range c, then a plateau region is produced, as shown in FIG.  3 . If the permanent magnet  28  is then disposed close to the end  27 , then the plateau region is produced at the end of the measurement curve. However, if the permanent magnet  28  is disposed on the support plate  25 , spaced apart from the end  27  of the support plate  25 , then the plateau region would be produced at the beginning of the measurement curve. 
     The graph in FIG. 3 shows the course of the characteristic curve of the magnetic induction B in the element  20 , for example a Hall element, over the path c of the support plate  25  and the component disposed on it. It is clear that with a path c=0, the induction B is likewise equal to zero, whereas after a travel distance a, it reaches the maximal induction value B=Max at position II. The position at path c=0 is labeled I in the graph and the entire path c is labeled III. The path c is comprised of path a and the plateau region b. Above the graph, the respective position of the movable part  12 , i.e. of the magnet  28 , in relation to the element  20  is shown for the three positions I, II, and III. In position I, the magnetic flux of the magnet  28  travels from the magnet  28  through the air gap to the part  15  of the base plate. In part  15 , the magnetic flux flows to the side plate  16  and from there via the support plate  25 , back to the permanent magnet  28 . It is clear that in position I, no magnetic flux occurs via the gap  18  and consequently through the magnetic field-sensitive element  20 . In position II, the support plate  25  together with the magnet  28 , is slid past the gap  18  toward the part  14  of the support plate  11  so that after a travel distance a, the end of the permanent magnet  28  has just passed the gap  18  and the permanent magnet  28  is consequently disposed only in the vicinity of the part  14  of the base plate  11  an no longer in the vicinity of the part  15  of the base plate  11 . The position II is the position in which the magnetic flux of the permanent magnet  28  travels completely by means of the gap  18  and consequently travels through the element  20  and the maximal possible magnetic induction B=Max is produced in the element  20 . The magnetic flux in position II consequently travels from the permanent magnet  28  via the gap into the part  14  of the base plate. From there, the magnetic flux flows via the gap  18  and the element  20  into the part  15  of the base plate and from there, via the side plate  16  and the support plate  25 , back into the magnet  28 . If the movable part  12 , i.e. the permanent magnet  28 , is slid further toward the left in the Fig., i.e. the magnet  28  is moved in the vicinity of the part  14  of the base plate  11  further away from the gap  18 , then the magnetic flux in the element  20  does not change. Furthermore, the maximal possible magnetic flux flows through the element  20 , in which the maximal possible magnetic flux induction B=Max is produced. As a result, a plateau region is produced between position II and position III, which has a length b. The plateau region b or, as in FIGS. 6 and 7, regions with different slopes in the measurement graph, are necessary in order to be able to control different events. 
     It is essential to the invention that the length a of the permanent magnet  28  is smaller than the total measurement range c and is smaller than the part  15  of the base plate  11  serving as a flux conducting part. In the prior exemplary embodiment, the permanent magnet  28  was embodied of one part and thus was disposed on the support plate  25  so that the beginning of the permanent magnet was also disposed at the beginning of the measurement range. In the exemplary embodiment according to FIGS. 4 and 5 and the graph according to FIG. 10, the permanent magnet  38  is now comprised of two parts  36 ,  37 . Due to this two-part design, the plateau region P, which corresponds to the path x of the sensor  10 , can be shifted between two linearly extending curve sections (FIG.  10 ). The two permanent magnet parts  36 ,  37  can be of different sizes or can also be the same size. This depends on how long the path a or b of the measurement curve is intended to be. In any case, though, the total length c, which is composed of the length a+×+b, must be less than or equal to the total length c. 
     The two parts  36 ,  37  of the permanent magnet  38  are magnetized in the same direction, i.e. they have a magnetization direction and/or polarization direction perpendicular to the movement direction of the moved part  12 , i.e. the polarization direction of the permanent magnet  28  is perpendicular to the base plate and parallel to the side plate  16 . Because the measurement range x is now disposed between the two permanent magnet parts  36 ,  37 , the plateau region P is shifted into the course of the measurement line so that a characteristic curve is produced analogous to the one shown in FIG.  10 . FIG. 10 now shows a characteristic curve in which the two permanent magnet parts  36 ,  37  are the same size. In FIG. 4, the permanent magnet part  36  is larger than the permanent magnet part  37 , which would mean that the measurement path a would be greater than the measurement path b. Moreover, it would also be possible to provide more than two permanent magnet parts, i.e. three, four, etc. It would thus be possible to produce a correspondingly desirable number of plateaus in the measurement line. Instead of a permanent magnet, it would also be possible to produce magnetized regions on the support plate  25 , as depicted in FIGS. 8 and 9. This design could be used for all of the exemplary embodiments mentioned here and is shown by way of example in FIGS. 8 and 9. Particular controls can be carried out with the aid of the plateau or plateaus and/or sections that deviate from the original measurement curve. 
     The graph in FIG. 10, in turn, shows the course of the magnetic induction B over the path c. Shown for the three positions I (path c=0) and III (path c=max, i.e. c=a+×+b) and for position II, which is disposed in the plateau region P, i.e. in the measurement path x. In position I, both of the parts  36 ,  37  of the permanent magnet  38  are disposed in the vicinity of the part  15  of the base plate. In this position I, there is no magnetic flux via the gap  18  and consequently through the magnetic field-sensitive element  20 . This means that no magnetic induction B is produced in the element  20 . The magnetic flux of both the part  36  and the part  37  takes place via the gap into the part  15  of the base plate and from there via the side plate  16  and the support plate  25 , back into the two parts  36 ,  37  of the permanent magnet  38 . If, as in position II, the one permanent magnet part  36  is disposed in the vicinity of the part  14  and the other part  37  of the permanent magnet  38  is disposed in the vicinity of the part  15  of the base plate, then the gap  18  and consequently the element  20  are disposed in the region x between the two magnet parts  36 ,  37 . This means that in position II in the graph according to FIG. 10, there is a plateau region P which has the length x, i.e. the length between the two permanent magnet parts  36 ,  37 . FIG. 2 shows the magnetic flux of each of the parts  36 ,  37  of the permanent magnet  38 . The magnetic flux of the permanent magnet  37  which is associated with the plate  15  still does not travel via the element  20 . The magnetic flux of the part  37  still travels from the part  37 , via the gap to the part  15  of the base plate  11 , and via the side plate  16  and the support plate  25 , back to the part  37  of the permanent magnet  38 . The magnetic flux of the other part  36  of the permanent magnet  38  travels from the part  36 , via the gap into the part  14  of the support plate  11 . From there, the magnetic flux travels through the gap  18  and consequently through the element  20  into the part  15  of the base plate  11  and via the side plate  16  and the support plate  25 , back to the magnet part  36 . Consequently, the magnetic flux does not change during the travel distance x. 
     In position III, after the travel distance c (c=a+×+b), both permanent magnet parts  36  and  37  are now associated with the part  14  of the base plate  11 . This means that the magnetic flux of both the part  36  and the part  37  travels through the element  20  and the maximal magnetic induction B=Max is consequently produced there. The depiction of position III shows that the magnetic flux of both the part  36  and the part  37  travels from the respective part, via the gap, into the part  14  of the base plate. From there, the magnetic field travels via the gap  18  and through the element  20  into the part  15  and via the side plate  16  and the support plate  25 , back to the respective parts of the permanent magnet  38 . 
     Whereas in the preceding exemplary embodiments, there is a division of the two permanent magnet parts  36  and  37 , the parts can also be connected to each other with a small intermediary piece. A corresponding exemplary embodiment is shown in FIGS. 6 and 7. In FIG. 6, the intermediary piece  40  is embodied as resting against the support plate  25 , i.e. it connects the surface of the two parts  36   a  and  37   a  of the permanent magnet resting against the support plate  25 . Naturally it would also be possible to dispose the connecting piece  40  on the outer edge, i.e. in the region of the magnet which is oriented toward the base plate  11 , or in the center, or laterally toward the back and/or front. Because of this connecting piece  40 , the measurement curve in the vicinity of the travel path x no longer extends flat in the form of a plateau, as in the preceding exemplary embodiments and as shown in FIG. 10; instead, the measurement curve has a slope in region x that is a function of the width of the connecting piece  40 . The slope can be influenced by the size, in particular the width. This means that it is also possible for there to be an intermediary piece which is wider than the permanent magnet parts and consequently, a steeper curve course can be achieved in this region than in the vicinity of the permanent magnet parts.