Abstract:
A sensor for detecting a position of a transducer magnet in a movement direction, including: —a coil carrier extending in the movement direction, —a first coil extending in the movement direction that is wound onto the coil carrier and—a second and a third coil oriented according to the first coil, which are wound onto the coil carrier such that the second and third coils accordingly form a first and second transformer with the first coil, the transformation ratio of which is dependent on the position of the transducer magnet, —wherein at least the second coil or the third coil is arranged between the coil carrier and the first coil.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. National Phase Application of PCT International Application No. PCT/EP2014/053506, filed Feb. 24, 2014, which claims priority to German Patent Application No. 10 2013 203 586.1, filed Mar. 1, 2013, the contents of such applications being incorporated by reference herein. 
     FIELD OF THE INVENTION 
     The invention relates to a sensor for detecting a position of a transducer magnet and to a device for actuating a brake system of a vehicle with the sensor. 
     BACKGROUND OF THE INVENTION 
     EP 238 922 B1, which is incorporated by reference, discloses a position sensor that operates on the principle of measuring linear displacement on the basis of a permanent magnetic linear contactless displacement, known as PLCD. Such a position sensor is also referred to as a linear inductive position sensor, known as a LIPS. 
     SUMMARY OF THE INVENTION 
     An aspect of the invention is an improvement over the known position sensors. 
     According to one aspect of the invention, a sensor for detecting a position of a transducer magnet in a direction of movement comprises:
         a coil carrier, which extends in the direction of movement,   a first coil, which extends in the direction of movement and is wound up on the coil carrier, and   a second and a third coil, which are aligned according to the first coil and are wound up on the coil carrier, so that the second and third coils correspondingly form with the first coil a first and a second transformer, the transformation ratio of which is dependent on the position of the transducer magnet,   at least the second or third coil being arranged between the coil carrier and the first coil.       

     The sensor specified is based on the idea that the aforementioned first coil could be wound directly on the coil carrier, while the second and third coils could be wound over the first coil, when seen from the coil carrier. However, the second and third coils generally require delimiting elements, which hold the second and third coils together and define their position. For efficient use of material, these delimiting elements should be produced so as to be as thin as possible, for which reason webs would appear to be most appropriate here as delimiting elements. However, in the aforementioned setup, the webs would have to pass through the first coil and would thus restrict the space available for winding the first coil on the coil carrier. The situation is complicated further by the fact that the webs cannot be made as thin as desired, because they would otherwise be too sensitive and could be damaged during production or in use. The situation is complicated still further by the fact that the coil carrier is generally produced by an injection-molding process, in the course of which the webs must likewise have a certain thickness in order not to be damaged during production. 
     This is where the invention comes in, with the proposal not to wind the first coil onto the coil carrier first, but to wind the second and third coils onto the coil carrier first. In this way, the first coil can be wound not only over the second and third coils but also over the delimiting elements that can be formed by way of example as webs, whereby the delimiting elements themselves scarcely restrict the winding space of the first coil any more, or do not restrict it at all. Consequently, the overall space available for the specified sensor can be used more efficiently. 
     In a development of the specified sensor, the coil carrier comprises a main body which extends in the direction of movement and has a first and a second slot, which runs at least in certain regions in the circumferential direction around the direction of movement and in which the second and the third coil is correspondingly accommodated. The present development is based on the idea of using slots instead of webs as delimiting elements. Even if this involves increased material expenditure, the walls of these slots offer sufficient mechanical retention for the second and third coils and can also withstand high mechanical loads during the production of the coil carrier in comparison with the aforementioned webs. 
     In an additional development of the specified sensor, the second and third coils fill their corresponding slot up to an outer lateral surface of the main body, so that the second and third coils finish flush with the outer lateral surface of the main body. In this way, the first coil can be wound over the second and third coils without abrupt changes and edges. 
     In another development, the main body comprises a recess, which runs at least in certain regions in the circumferential direction around the direction of movement and is formed between the first slot and the second slot when viewed in the direction of movement. In this way, the material consumption for the coil carrier can be set optimally to the mechanical strength, in that the width of this recess is chosen to be just enough for the delimiting elements that are formed by the slots and the recess to be just strong enough to withstand all of the mechanical loads to be expected. 
     In this case, the surface of the main body should preferably be formed at an obtuse angle when considered in the direction of movement. In an alternative embodiment, the surface of the main body could also be formed as round when considered in the direction of movement. 
     The second coil and the third coil are preferably arranged between the coil carrier and the first coil. However, it could likewise be appropriate to arrange only one of the second and third coils between the coil carrier and the first coil and to wind the other of the two coils onto the first coil. In this case, the specified displacement sensor could be provided with an asymmetry when seen in the direction of movement that can be influenced application-dependently with the characteristic curve of the specified displacement sensor. 
     In an additional development of the specified sensor, the coil carrier is produced from plastic, in particular by means of an injection-molding process. 
     In a particular development of the specified sensor, the second and third coils are compactly wound coils in comparison with the first coil. This compact winding makes it possible to measure the flux at one location of the core, for which many windings have to be concentrated at the location concerned in comparison with the primary winding. 
     This can be countered by compact winding. However, compact winding necessitates mechanically strong delimiting elements that can be provided as part of the specified sensor. 
     In a preferred development, the specified sensor is formed as a linear inductive position sensor, known as a LIPS. 
     According to a further aspect of the invention, a device for actuating a brake system of a vehicle comprises a brake pedal for setting a braking force by displacing the brake pedal in a direction of movement and a sensor according to one of the preceding claims for detecting the position of the brake pedal in the direction of movement and for outputting a signal indicating the braking force to be set, in dependence on the detected position of the brake pedal. 
     According to a further aspect of the invention, a method for producing a specified sensor comprises winding the second and third coils onto the coil carrier and winding the first coil onto the coil carrier over the second and third coils wound onto the coil carrier. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The properties, features and advantages of this invention that are described above and also the manner in which they can be achieved become clearer and more easily understandable in connection with the following description of the exemplary embodiments, which are explained more specifically in conjunction with the drawings, in which: 
         FIG. 1  shows a tandem main cylinder with a displacement sensor, 
         FIG. 2  shows the displacement sensor from  FIG. 1 , 
         FIG. 3  shows a perspective representation of part of the displacement sensor from  FIG. 2 , 
         FIG. 4  shows a sectional representation of a first embodiment of the displacement sensor from  FIG. 3  and 
         FIG. 5  shows a sectional representation of a second embodiment of the displacement sensor from  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the figures, the same technical elements are provided with the same designations and are described only once. 
     Reference is made to  FIG. 1 , which shows a tandem main cylinder  2  with a displacement sensor  4 . 
     The tandem main cylinder  2  also has a pressure piston  6 , which is arranged movably in a direction of movement  8  in a housing  10 , the movement of the pressure piston  6  being controlled by a foot pedal that is not shown. The pressure piston  6  is itself divided into a primary piston  12  and a secondary piston  14 , the primary piston  12  closing an inlet of the housing  10  and the secondary piston  12  dividing the interior space of the housing  10  into a primary chamber  16  and a secondary chamber  18 . Arranged on the primary piston  12  in the region of the inlet of the housing  10  is a secondary sleeve  20 , which isolates the interior space of the housing  10  from the ambient air. Seen looking into the interior space of the housing  10 , the secondary sleeve  20  is followed by a primary sleeve  22 , which seals off a gap between the primary piston  12  and a wall of the housing  10 . A pressure sleeve  24  on the secondary piston  14  isolates the pressure of the primary chamber  16  from the pressure of the secondary chamber  18 . Furthermore, a further primary sleeve  26  on the secondary piston  14  seals off a gap between the secondary piston  14  and the wall of the housing  10 . The primary piston  12  is supported against the secondary piston  14  by way of a first spring  28 , while the secondary piston is supported against a housing base by way of a second spring  30 . The primary chamber  16  and the secondary chamber  18  can be correspondingly supplied with hydraulic fluid, not shown, by way of a first and a second connection  32 ,  34 . 
     Since a person skilled in the art is familiar with the way in which a tandem main cylinder functions, it is intended to dispense with a more detailed representation of this. 
     The displacement sensor  4  has a test piece in the form of a slide  36  with a transducer magnet  37  at its head end, which can be pushed under a sensor circuit  38 , still to be described, when considered looking into the plane of the image. For sliding the slide  36 , the primary piston  12  has a flange  40 , against which the slide  36  is mounted. The flange  40  and the primary piston  12  consequently together form an object to be measured, the position of which is determined by the sensor circuit  38 , still to be described, of the displacement sensor  4 . The sensor circuit  38  is formed by a number of conductor tracks on a wiring carrier  42 , such as a lead frame, a printed circuit board or some other substrate. For protection, for example from dirt, a cover  46  may be placed on the printed circuit board  42  with the sensor circuit  38 . 
     Reference is made to  FIG. 2 , which shows the displacement sensor  4  from  FIG. 1 . 
     The circuit  38  of the displacement sensor comprises a transducer  48 , which in the present embodiment is formed as a linear inductive position sensor, known as a LIPS. The LIPS  48  detects a magnetic field  50  of the transducer magnet  37  and on the basis of this outputs an electrical transducer signal, not referred to any more specifically, to the circuit  38 . This transducer signal is transformed by a first signal processing chip  52  and a second signal processing chip  54  into a measuring signal, not referred to any more specifically, from which the position of the slide  36 , and consequently the position of the flange  40  and of the primary piston  12 , are obtained. The measuring signal generated in this way can finally be picked off at a transmitting interface  56  of the displacement sensor  4  by way of a cable that is not represented any further and be passed on to a higher signal processing unit that is not represented any further, such as for example an engine and/or brake control in a vehicle that is not represented any further. 
     The circuit  38  may comprise protective elements  58  for protecting the two signal processing chips  52 ,  54 , for example from an overvoltage. Furthermore, arranged between the circuit  38  and the LIPS  48  may be a shielding plate  60 , which shields from electromagnetic fields between the circuit  38  and the transducer  48  and thus avoids any influence of the circuit  38  on the LIPS  48 . 
     In the present embodiment, the LIPS  48  is arranged in a defined position on the wiring carrier  42  by way of a form fit  62 . In this case, a protective mass  64  surrounds the wiring carrier  42  and the transducer  48 . 
     In  FIG. 3 , a perspective view of the LIPS  48  is represented. The LIPS  48  comprises a coil carrier  66  with a winding space, which is divided by way of four webs  68  into a middle portion  70  and two side portions  72 . The coil carrier  66  carries a primary coil  74 , which extends along a core, which cannot be seen any further in  FIG. 3 , and in the present case is intended to be assumed as being of one layer. At the two opposite outer zones of the primary coil  74 , the coil carrier  66  carries densely wound secondary coils  76  for measuring an induction voltage. 
     That is to say that the coils  74 ,  76  in the LIPS  48  can be distinguished in two different ways. On the one hand, the coils interact as part of a measuring transformer, the primary coil  74  exciting a magnetic field and inducing the induction voltage in the secondary coils  76 . The choice of the primary and secondary coils  74 ,  76  is in principle as desired, and does not have to be implemented in the way shown in  FIG. 3 . The LIPS  48  of the present embodiment is intended to be able to be evaluated by radiometric signal processing, for which reason the choice of the primary coil  74  and the secondary coils  76  is made in the aforementioned way. The signal processing connected to such a LIPS  48  performs a measurement of the induction voltage at each of both secondary coils  76  and calculates the two measured induction voltages with a suitable algorithm, which has the aim of suppressing disturbances. In the simplest case, this can be performed by a suitable series connection of the secondary coils  76 . This is preferably performed by an analog or digital signal processing, which offers considerable freedom in the implementation of a mathematical model with which the position value is calculated from the two induction voltages. 
     Furthermore, the coils  74 ,  76  can be divided with regard to their geometrical form into coils  74  with a low winding density, which are wound almost along the entire length of the core (in the present exemplary embodiment of the primary coil  74 ), and also those that are wound compactly with a high winding density at a specific location of the core that is not shown (in the present exemplary embodiment the secondary coils  76 ). 
     Further details on the way in which a LIPS functions can be taken for example from the documents DE 44 259 03 C3, which is incorporated by reference and EP 238 922 B1, which is incorporated by reference. 
     In  FIG. 3 , the windings of the primary coil  74  in the middle portion  70  and the two side portions  72 , which are divided off by the webs  68 , lie on the same radius. As a result, the magnetic core, not shown any further, in the coil carrier  66  is enclosed as closely as possible by the individual coils  74 ,  76 . This is particularly advantageous since, with a predetermined number of windings, the coils  74 ,  76  have the smallest length of wire, and consequently also the smallest ohmic resistance, the least material consumption and also the smallest mass and the smallest volume. Furthermore, unnecessary stray flux through the likewise enclosed air volume (or volume of the diamagnetic or paramagnetic coil carrier) is minimized. The stray flux may impair the flux linkage and lead to external fields influencing the coils  74 ,  76  more than necessary. 
     Reference is made to  FIG. 4 , which shows a sectional representation of an alternative embodiment of the LIPS  48  from  FIG. 3 . 
     The LIPS  48  shown in  FIG. 4  is based on the realization that the sensor shown in  FIG. 3  entails technical disadvantages in terms of production that outweigh the electrotechnical advantages. 
     In  FIG. 4 , the secondary coils  76  are wound in slots  78  or pockets. When seen in the radial direction, the secondary coils  76  completely fill their slots here. It can be seen directly that there is no difference from the solution that is shown in  FIG. 3  with regard to the delimitation of the winding space of the secondary coils  76 . However, the coil carrier  66  in  FIG. 4  does not have narrow webs  78  that impair the robustness or durability of the workpiece or tool. When seen from the coil carrier  66 , here the primary coil  74  has been wound radially onto the secondary coils  76 , and thus comes to lie on the surface of the coil carrier  66  and the secondary coils  76 . The surface formed jointly by the coil carrier  66  and the secondary coils  76  has in this case virtually no contours, and therefore also no impediments for a uniform winding spacing. Although the arrangement shown in  FIG. 4  of the coil carrier  66 , the primary coil  74  and the secondary coil  76  is not advantageous for use for inductances or transformers in general applications, it has surprisingly been possible to demonstrate experimentally that the air or coil-carrier space additionally enclosed by the primary coil  74  only has a negligible influence on the technical measuring properties of the LIPS  48  thus formed. 
     Reference is made to  FIG. 5 , which shows a sectional representation of a further alternative embodiment of the LIPS  48  from  FIG. 3 . 
     In  FIG. 5 , the material consumption of the coil carrier is minimized, with otherwise the same properties of the LIPS  48  in comparison with the LIPS from  FIG. 4 . The greater radius of the primary coil  74  in  FIG. 4  in comparison with  FIG. 3  is reduced on average in  FIG. 5 , because ramps  80  of the winding of the primary coil  74  make it possible to adopt various radii. The slope of the ramps should in this case be made to match the winding process of the primary coil  74 . 
     To be certain of avoiding slipping or sliding away of the windings of the primary coil  74  into the range of smaller radii, a step-shaped structure could also be provided instead of the ramps  80 . Alternatively, the region of the ramps  80  may be embodied with a rough surface, in order that the windings can be supported locally on the unevennesses. 
     All of the variants of the LIPS  48  that are represented could optionally be embodied as bodies of revolution. An alternative would however be possible with a cross section of the magnetic core  82  shown in  FIGS. 4 and 5  in the form of a polygon, an ellipse or some other form for example of the coil carrier  66  to which a winding can be applied. 
     Moreover, the section represented in  FIGS. 4 and 5  could not be present over the entire circumference of the LIPS  48 , as  FIG. 3  already shows: to achieve the aim of a multi-layered winding for the secondary coils  76 , for example with a rectangular cross section of the winding assembly, it is enough if the webs  68 , and consequently also the slots  78  or pockets, are present in partial regions of the overall circumference of the LIPS  48 . The winding wires generally do not in any case allow the windings to deviate appreciably from the predetermined form if there is no delimitation in the form of webs  68  or slots  78  in partial regions of the circumference. 
     The sections shown in  FIGS. 4 and 5  should therefore only be regarded by way of example as a rotationally symmetrical form of the LIPS  48 . Alternatively, the LIPS  48  could also take the form shown in  FIGS. 4 and 5  when there is at least one section through the coil body  66  that corresponds to one of the forms represented, while all of the other possible sections through the coil body  66 , i.e. at other angles to the circumference, may have a differently contoured cross section, in particular an uncontoured body. 
     Only the possibility of the contour of the coil body  66  containing thin webs  68  at these other angles to the circumference should be ruled out, because this could stand in the way of a robust construction that is suitable for production.