Abstract:
A measuring travel instrument has a frame composed of a permeable material, a magnet situated inside the frame in a movable fashion, a magnetosensitive sensor situated in a slot of the frame that is situated in a closed magnetic circuit in such a fashion that a size of a magnetic flux of the magnet changes in it depending on a position of the magnet, a sled composed of a magnetically impermeable material and executing a sliding movement, the magnet being located in the sled, a guide member extending through a recess in the frame and connecting the sled with a component a movement of which is to be determined, the guide member composed of a permeable material and arranged in such a way that it forms a part of the frame conducting the magnetic flux of the magnet.

Description:
BACKGROUND OF THE INVENTION 
     The invention is based on a measuring instrument. A sensor is made known in DE 29 23 644 C2 that comprises a cylindrical frame produced out of ferromagnetic material. A permanent magnet is cylindrical frame produced out of ferromagnetic material. A permanent magnet is moved in sliding fashion in the frame, the movement of which is proportional to the movement of a component. Moreover, a magnetosensitive element is arranged in a gap of the frame and, therefore, in the closed magnetic circuit created by the magnet, the output signal of which magnetosensitive element is proportional to the movement of the magnet. Since the magnet slides directly on the inside of the frame, however, high frictional losses can occur that corrupt the output signal. Since the housing is closed, a varying magnetic flux is produced. 
     In contrast the measuring instrument according to the invention has the advantage that the magnet-since it is attached to a sled—can execute a sliding movement with relatively low frictional losses. The sled can be designed to be relatively slideable by way of its construction as well as by way of the materials used. Moreover, the sled can be incorporated in the closed magnetic circuit of the magnet in a simple fashion. Due to the conical seating of the sled, the magnet can be inserted and moved without play. The air gap is not affected by the force of the magnet, but rather kept constant during the measuring motion. Fluctuations in the output signal are thereby avoided. The guidance of the support and the attractive forces of the magnet are decoupled. No offset voltage is required with this measuring instrument. The measuring instrument can be easily integrated in systems to be measured, or it can be used as an independent sensor. It is therefore feasible that it can be used in transmission controls, or for measuring pedal travel or valve lift, for example. 
     Advantageous further developments and improvements of the measuring instrument indicated in Claim 1 are possible as a result of the measures described in the subclaims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention are presented in the diagram and are explained in greater detail in the description below. FIGS. 1 and 2 show different views and sections through a first embodiment. 
     FIG. 1 shows a longitudinal section, and 
     FIG. 2 shows a section II—II according to FIG.  1 . 
     FIGS. 3 through 5 present variants of the sled shown in FIG.  2 . 
     FIG. 6 shows the magnetic flux in an initial position and an induction B=0, 
     FIG. 7 shows the corresponding magnetic flux at maximum displacement and an induction B=max, and 
     FIG. 8 shows the corresponding course of induction B across the path S. 
     FIGS. 9 through 11 show a second embodiment, whereby FIG. 10 shows a section in the direction X—X according to FIG. 9, and FIG. 11 shows a section in the direction XI—XI of FIG.  9 . 
     FIG. 12 shows an alternative driver for the embodiment according to FIGS. 9 through 11. 
     FIGS. 13 through 15 show a third embodiment, whereby FIG. 14 shows a section in the direction XIV—XIV according to FIG. 13, and FIG. 15 shows a section in the direction XV—XV of FIG.  13 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIGS. 1 and 2, a measuring instrument is shown as  10  that has a frame made of magnetically soft material and comprising a multipart baseplate  11 ,  12 , and a side wall  13 . The baseplate  11 ,  12  has a passing slot  15  in which at least one magnetosensitive element  16  is situated. A magnetoresistor, magnet transistor, coils, magnetoresistive elements, or a Hall element, for example, can be used as the magnetosensitive element  16  here. A recess  18  is formed in the side wall  13 , through which a supporting plate  19  comprised of magnetically soft, i.e., permeable, material extends. A component is attached directly or indirectly to the end of the supporting plate  19  located outside the frame, the movement or travel of which is to be determined. A magnetic holder  21  comprised of magnetically impermeable material is attached to the end of the supporting plate  19  extending into the frame. A permanent magnet  22  is inserted in the magnetic holder  21  in a recess on the side facing the baseplate  11 ,  12  of the frame. The direction of polarization of the permanent magnet is arranged at right angles to the supporting plate  19  and the baseplate  11 ,  12 . A gap L 1  with magnetically impermeable material is formed between the permanent magnet  22  and the baseplate  11 ,  12 . This can be an air gap with the size L 1 , or the gap can be filled with another magnetically impermeable material. It is possible here, for example, that the permanent magnet  22  is completely enclosed by the magnetic holder  21 . In the embodiment according to FIG. 1, the gap  15 , in which the magnetosensitive element  16  is located, is closed by a cover  24  on its side facing the supporting plate  19 . The frame, i.e., the baseplate  11 ,  12  and the side wall  13  are enclosed by a housing  25  comprised of magnetically impermeable material. The housing  25  extends upward to just below the slit  18  in the side wall  13 . The housing  25  also has a slit in the region of the slit  15 , through which the connections of the magnetosensitive element  16  can be fed to a printed circuit board  27  situated on the outside of the housing  25 . 
     As one can see in FIG. 2, the side walls  28  of the housing  25  serve to guide the magnetic holder  21 . To this end, the surfaces  30  of the side walls  28  facing the inside of the housing  25  in FIG. 2 are trapezoidal in shape. The surfaces  32  of the magnetic holder  21  facing the surfaces  30  of the side walls  28  are also trapezoidal in shape. As a result of this design of the guide, a relatively frictionless sliding of the magnetic holder  21  in the housing  25  is made possible. Moreover, this trapezoidal shape determines the size of the air gap L 1 , and it makes a constancy of the air gap L 1  possible while the magnetic holder  21  moves in the housing  25 . 
     The permanent magnet  22  is magnetized at right angles to the axis of movement. This means that, depending on the direction of polarization, a magnetic flux is produced that emerges from the permanent magnet  22  and passes through the magnetic holder  21  to the supporting plate  19 . From the supporting plate  19 , the magnetic flux passes through the gap  18  and the side wall  13  to the part  11  of the baseplate. In the part  11  of the baseplate, the magnetic flux passes over the gap  15  and through the Hall element  16  to the part  12  of the baseplate and over the air gap L 1  back to the permanent magnet  22 , resulting in a closed magnetic circuit. In FIGS. 6 through 8, the magnetic flux is shown in an initial position (FIG. 6) and in maximum displacement (FIG.  7 ), and the course of the output voltage, i.e., the magnetic induction B in the magnetosensitive element  16  between the two extreme positions and across the path S, is shown. In FIG. 6, the magnetic holder  21  is located to the left in the diagram, i.e., the front side of the magnetic holder  21  almost touches the side wall  13 , out of which the support  19  extends. As one can see in FIG. 6, magnetic flux is not allowed to pass through the magnetosensitive element  16  in this initial position. To ensure that magnetic flux does not pass through the magnetosensitive element  16  in this position, the magnetic holder  21  must be comprised of magnetically impermeable material. In the base position, the magnetic flux therefore emerges from the magnet  22  and passes through the magnetic holder  21 , the support  19 , the gap  18 , the side wall  13  and the part  11  of the baseplate, and over the gap L 1  back to the magnet  22 . Since this magnetic flux does not pass through the magnetosensitive element  16 , the magnetic induction B=0 sketched in FIG. 8 results in this position. Since the sides of the measuring instrument  10  are open, magnetic flux cannot pass from the support  19  to the parts  11  and  12 . If the component to be measured, i.e., the support  19  with the magnetic holder  21 , is now slid to the right as viewed in the diagram, the magnetic flux that passes through the magnetosensitive element  16  increases continuously. This results in the linear measuring line  30  shown in FIG.  8 . At maximum extension, i.e., as shown in FIG. 7, when shifted to the right, i.e., when the magnet  22  is moved over and past the gap  15  and, therefore, the magnetosensitive element  16 , the maximum magnetic induction B=max is produced. In this position, the entire magnetic flux of the magnet  22  passes through the magnetosensitive element  16 , as illustrated in FIG.  7 . 
     Different designs of the magnetic holder are shown in FIGS. 3 through 5 that make the most frictionless sliding in the housing possible while ensuring constancy of the air gap L 1 . In FIG. 3, the magnetic holder  21   a  has vertical side walls  28   a . The magnetic holder  21   a  at least partially encloses the magnet  22  by way of extensions  31 ,  32 . The magnetic holder  21   a  also lies on the baseplate  11 ,  12  by way of the extensions  31 ,  32 . The thickness of these extensions  31 ,  32  also determines the size L 1  of the air gap between the magnet  22  and the baseplate. As a result, the air gap L 1  cannot be disturbed, i.e., corrupted, by the force of attraction F of the magnet  22  during measurement. The outsides of the magnetic holder  21   a  are bevelled in the region of the extensions  31 ,  32 , to ensure that the magnetic holder  21   a  slides as frictionlessly as possible in the housing  25   a  and on the baseplate. The internal walls of the housing  25   a  are designed to correspond to the shape of the magnetic holder  21   a.    
     The design of the magnetic holder according to FIG. 4 makes an application possible using a housing enclosing the magnetic holder, as shown in the preceding figures, as well as an application in which only the bottom side of the magnetic holder rests on the baseplate or on a housing. As shown in the design according to FIG. 3, the magnetic holder  21   b  encloses the magnet  22  with two extensions  31   b  and  32   b . The magnetic holder  21   b  also rests on the baseplate by way of these extensions  31   b  and  32   b . Moreover, rails  41 ,  42  are formed on the magnetic holder  21   b , which extend parallel to the side wall of the baseplate. The rails  41 ,  42  hereby serve to guide the magnetic holder  21   b  on the baseplate; they can also be used—either simultaneously or as an alternative—as a support on a housing located beneath it. 
     A housing  25   c  is shown in FIG. 5 that completely encloses the magnetic holder  21   c . Additionally, in order to ensure the most frictionless sliding of the magnetic holder  21   c  possible in the housing  25   c , the upper edges  44 , i.e., the outside edges of the magnetic holder  21   c , are bevelled in the region of the support  19 . The magnetic holder  21   c  can also be used without an external housing, however, because it also rests on the baseplate at least partially by way of the extensions  31   c ,  32   c.    
     While, in the preceding embodiments, the component to be monitored was located on the end of the support  19  opposite to the magnetic holder  21 , the component is now situated at a right angle to the magnetic holder and its direction of movement, so that the direction of movement of the magnetic holder runs parallel to the movement of the component to be monitored. The frame  50  of the instrument according to FIG. 9 has a U-shaped cross-section, is made of magnetically soft material, and comprises the the side wall  13   a , a cover  51 , and the baseplate—which, in turn, is comprised of the two parts  11   a  and  12   a . A magnetic holder  52  is situated between the cover  51  and the baseplate  11   a ,  12   a , in which the magnet  22  is embedded, and which is shown further in FIGS. 10 and 11 in greater detail. A region of magnetically impermeable material is again located between the magnet  22  and the baseplate  11   a ,  12   a , which region can consist of the magnetic holder  52  as in FIG. 9, or it can be an air gap, as shown in FIG.  1 . As one can see in FIG. 10, the magnetic holder  52  comprises a flange-like extension  55  in which a driver  56  is situated that is connected to the component to be monitored, which is not shown. Extensions  58 ,  59  are formed on the magnetic holder  52  on the side facing the flange  25 , with which the magnetic holder  52  abuts against the baseplate or the cover  51 . A further extension  60  is also formed on the magnetic holder  52  on the opposite side, which abuts against the longitudinal side of the cover  51 . In order to make the sliding of the magnetic holder  52  against or on the baseplate  11   a ,  12   a  or against or on the cover  51  as frictionless as possible, undercuts are formed on the bridge to each of the extensions  58 ,  59 ,  60 . 
     A recess  61  is formed in the flange  55  of the magnetic holder  52  into which three extensions  62  arranged in the shape of a star extend, which make it possible to fix the driver  56  in the method of a press fit. In order to achieve a concentration of the magnetic flux in the region of the gap  15  between the parts  11   a  and  12   a  of the baseplate, the edges are bevelled, so that a concentration of the magnetic flux in the region of the magnetosensitive element  16  takes place. 
     A variant of the attachment of the driver on the magnetic holder is shown in FIG.  12 . To this end, a circular opening  64  is formed in the flange  55   a  of the magnetic holder, through which the driver  56   a  extends. The driver  56   a  comprises a slit  65  on its upper end that passes through approximately in the center, so that the segments produced when the driver  56   a  is guided into the opening  64  deform elastically and, in their end position, fix the driver  56   a  pressed in the opening  64 . 
     In the embodiment according to FIGS. 13 through 15, a measuring instrument is presented in which the component  70  to be monitored is connected to the magnetic holder  73  comprised of magnetically impermeable material. The magnetic holder  73  is brought into the position by way of at least one spacer ( 71 ,  72 ), in which the magnet lies approximately in the center between the cover  51  and the parts  11   a  and  12   a . The magnetic holder  73  with the magnets  22  is moved contactlessly between the U-shaped frame  50 . As in FIG. 9, the frame is designed with a U-shaped cross-section here as well, and is comprised of magnetically soft material. Two columns  71 ,  72  are situated on a substructure  70 , which enclose the baseplate  11   a ,  12   a . A plate  73  comprised of magnetically soft material rests on the columns  71 ,  72 , on which the magnet  22  is situated. The region between the plate  11   a ,  12   a  and the cover  51  is again filled by the magnetic holder  75  comprised of magnetically impermeable material.