Abstract:
A control panel comprising a cover that is equipped with at least one zone for detecting tactile contact forming a control button, in which a force sensor comprising a pressure-sensitive zone is arranged between the cover and the support so as to detect actuation of the control button, the force of the tactile contact being transmitted axially to the sensitive zone via a spacer plate made of an elastically compressible material that is inserted between the sensor and the cap, characterized in that the internal surface of the cap comprises a series of protruding elements that are distributed over the internal surface of the cap opposite the sensitive zone so as to form a number of regularly distributed zones of localized overpressure.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit under 35 U.S.C. §371 of published PCT patent application number PCT/EP 2011/063301, filed Aug. 2, 2011, claiming priority to French patent application number FR1056578 filed on Aug. 12, 2010, and published as WO2012/019944 on Feb. 16, 2012, the entire contents of which is hereby incorporated by reference herein. 
     TECHNICAL FIELD OF INVENTION 
     The present invention relates to a control panel, in particular for a motor vehicle, having resistive keys. 
     BACKGROUND OF INVENTION 
     The present invention relates more particularly to a control panel intended to be arranged in the passenger space of a motor vehicle, in particular on the dashboard, and which includes at least one control button in the form of a resistive key designed to control a determined function, for example to control starting or stopping of the air-conditioning function. 
     The control panel includes a cover which is mounted on a support and which is provided with at least one detection zone designed to form a control button. A force sensor is arranged between the cover and the support, behind the detection zone, so as to produce an electrical control signal when a user applies a sufficient pressure force to the detection zone. 
     To compensate for the mechanical plays between the force sensor and the detection zone, it is known to arrange a spacing plate made of elastomeric material between the force sensor and the cover that must allow a direct transmission of the tactile pressure force to the force sensor via the spacing plate to be ensured under all circumstances. To this end, the spacing plate is mounted axially compressed between the force sensor and the cover. 
     To allow the detection of the tactile pressure, it is necessary for the thickness of the cover in the detection zone to be relatively small so as to allow a slight elastic deformation of the cover towards the sensor on tactile pressure. Now, the mounting of the spacing plate in compression between the sensor and the cover tends to cause a permanent outward deformation of the cover at the level of the spacing plate that degrades the external appearance of the cover. Moreover, the distribution of the pressure over the spacing plate is not even, the pressure generally being mainly on the outer peripheral edge of the spacing plate. 
     These disadvantages are particularly prejudicial in applications subject to large temperature variations, as in a motor vehicle, which can result in a loss of pressure on the spacing plate. 
     SUMMARY OF THE INVENTION 
     The present invention is intended to remedy the disadvantages mentioned above by proposing a simple, effective and economic solution. 
     To this end, the invention proposes a control panel, in particular for a motor vehicle, including a cover which is mounted on a support and which is provided with at least one zone for detection of a tactile pressure forming a control button, in which a force sensor having a zone sensitive to pressure is arranged between the cover and the support, behind the detection zone, so as to detect the actuation of the control button to produce an electrical control signal when a user applies a determined tactile pressure force to the detection zone, the tactile pressure force being transmitted axially to the sensitive zone via a spacing plate made of elastically compressible material which is inserted between the sensor and the cover, characterised by the fact that the inside surface of the cover includes a series of relief elements which are distributed over the inside surface of the cover opposite the sensitive zone so as to form a plurality of localised zones of increased pressure on the spacing plate, the said localised zones of increased pressure being uniformly distributed so that the spacing plate applies a substantially even pre-stressing force over the sensitive zone. 
     The invention is particularly advantageous as it allows mounting to be effected in which the residual axial pressure applied to the force sensor at rest, i.e. in the absence of tactile pressure, is lesser. Thus, the force sensor is mounted without excessive compression between its support and the cover with the spacing plate, which reduces the risks of distortion of the materials forming the assembly. 
     In the case of a force sensor operating with a prestress, the prestress produced by the pressure of the spacing plate on the sensitive zone of the sensor can be appropriately adjusted over the whole surface of the spacing plate by means of the relief elements, without having to apply a high pressure to guarantee that the prestress is sufficient. 
     In accordance with other advantageous characteristics of the invention: at least one of the relief elements has an axial thickness which varies in a transversal direction so as to compensate for the variations in intensity of the pressure force at rest of the cover on the spacing plate along the said transversal direction; the cover has a curved profile in the detection zone, and the axial thickness of the relief elements varies proportionally to the curvature of the cover relative to the support; the relief elements are separated from each other by interstitial spaces so as to allow sufficient flexion of the detection zone of the cover when a tactile pressure force is applied; the relief elements are formed of ribs; the relief elements are arranged in at least one line which is substantially parallel with the external outline of the sensitive zone; the relief elements are formed in one piece with the cover; the force sensor is of the type with detection of a variation in electrical resistance between conductive tracks; it includes a plurality of detection zones forming a plurality of control buttons associated with a plurality of force sensors, each force sensor including a spacing plate and a series of associated relief elements; the axial thickness of the relief elements is generally increasing in the transversal direction, from the periphery of the portion including the detection zones to a central part of the said portion; a small plate made of more rigid material than the material forming the spacing plate is inserted between the spacing plate and the sensitive zone of the sensor in order to contribute to even distribution of the prestressing force and the tactile pressure source over the sensitive zone of the sensor. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Other characteristics, aims and advantages of the invention will become apparent on reading the following detailed description and taking into account the attached drawings, given as a non-limiting example and in which: 
         FIGS. 1 and 2  are exploded perspective views which show diagrammatically a control panel fitted with resistive keys provided with force sensors and with spacing plates in accordance with a first embodiment of the invention; 
         FIG. 3  is a partial view in axial section which shows diagrammatically the structure of a force sensor with which the control panel of  FIGS. 1 and 2  is fitted; 
         FIG. 4  is a view from above which shows diagrammatically a film carrying a plurality of force sensors designed to be fitted to the control panel of  FIGS. 1 and 2 ; 
         FIG. 5  is an exploded perspective view which shows diagrammatically a second embodiment of a control panel in accordance with the teachings of the invention; 
         FIG. 6  is a view in axial section through the plane  6 - 6  of  FIG. 5  which shows diagrammatically the cover of the control panel of  FIG. 5  and the relief elements with which it is fitted; 
         FIG. 7  is a diagram showing the distribution of the pressure applied by the cover to the spacing plate of a force sensor within the framework of a control panel of the prior art; 
         FIG. 8  is a diagram similar to that of  FIG. 7  showing the distribution of the pressure applied by the cover to the spacing plate of a force sensor within the framework of a control panel in accordance with the second embodiment of the invention shown in  FIG. 5 ; 
         FIG. 9  is a perspective view from below of the cover of a control panel in accordance with a third embodiment in which the axial thickness of the relief elements varies; 
         FIG. 10  is a view in axial section through the plane  10 - 10  of  FIG. 9  which shows diagrammatically the cover of the control panel of  FIG. 9 ; 
         FIGS. 11 and 12  are perspective views from below of the cover of a control panel in accordance with modified embodiments in which the arrangement of the relief elements is different. 
     
    
    
     DETAILED DESCRIPTION 
     In the remainder of the description, identical or similar elements can be designated by identical references. 
       FIGS. 1 and 2  show a control panel  10  for a motor vehicle dashboard formed in accordance with a first embodiment in accordance with the teachings of the invention. It here includes a cover  12  which is mounted on a support  14 , the outside surface  16  of the cover  12  including a plurality of detection zones Z 1 , Z 2 , Z 3 , Z 4 , Z 5  of a tactile pressure forming a plurality of control buttons B 1 , B 2 , B 3 , B 4 , B 5 , or resistive keys. 
     In the remainder of the description, an axial orientation will be used in non-limiting manner along an axis X 1  substantially at right-angles to the general plane of the cover  12 , orientated from the bottom towards the top, i.e. from the support  14  towards the outside surface  16  of the cover  12 , which generally corresponds to an orientation from the bottom towards the top considering  FIGS. 1 and 2 . 
     Each control button B 1 , B 2 , B 3 , B 4 , B 5  here includes a force sensor  18  that is arranged between the cover  12  and the support  14 , behind and axially opposite the associated detection zone Z 1 , Z 2 , Z 3 , Z 4 , Z 5 . Each force sensor  18  is designed to detect the actuation of the associated control button B 1 , B 2 , B 3 , B 4 , B 5  to produce an electrical control signal when a user applies a tactile pressure force of sufficient intensity to the associated detection zone Z 1 , Z 2 , Z 3 , Z 4 , Z 5 . 
     In accordance with an advantageous characteristic of the invention, each force sensor  18  is of the type with resistance variable as a function of the force, for example of the FSR (force sensing resistor) type as described and illustrated in the documents US2006/0007172A1 and WO2009/070503A1 which are incorporated here by reference. 
     Preferably, a force sensor  18  mounted under mechanical prestress is used here, as has been shown in  FIGS. 3 and 4 . The force sensor  18  here includes a first  20  and a second  22  substrate at least one of which is flexible when a tactile pressure force is applied to the associated detection zone Z 1 , Z 2 , Z 3 , Z 4 , Z 5 . Electrical conductive tracks  24 ,  26  are arranged, for example in the form of interdigitated combs, on a face of the first substrate  20  opposite a resistive coating  28  arranged on the opposite face of the second substrate  22 , so as to define a zone sensitive to pressure  30  which is generally superimposed on the associated detection zone Z 1 , Z 2 , Z 3 , Z 4 , Z 5 . In the rest state of the force sensor  18 , in the absence of tactile pressure force, the resistive coating  28  is in electrical contact with portions of conductive tracks  24 ,  26 . 
     Advantageously, the five control buttons B 1 , B 2 , B 3 , B 4 , B 5  being positioned in substantially adjacent manner on the cover  12 , it is possible to arrange the five associated force sensors  18  on the same substrate  20 ,  22 . Thus, as shown in  FIGS. 1 ,  2 , and  4 , the force sensors  18  are in the form of a film  32  including an electrical connection ribbon  33  designed to allow the connection of the five sensors  18  to an electronic control unit (not shown). 
     In accordance with the embodiment shown, a spacing plate  34  made of elastically compressible material is mounted between each sensor  18  and the cover  12 , opposite the detection zone Z 1 , Z 2 , Z 3 , Z 4 , Z 5  so as to take up the mechanical plays between the sensor  18  and the cover  12 . Preferably, the five spacing plates  34  provided for the five sensors  18  are all formed by molding in a same plate  36  made of silicone or of elastomeric material. 
     It will be noted that, due to the rigidity of the cover  12  in the detection zone Z 1 , Z 2 , Z 3 , Z 4 , Z 5 , the operating plays, i.e. the axial displacements of the cover  12  in the detection zone, can be less than the mechanical plays. The spacing plate  44  therefore allows the mechanical plays to be taken up to allow the detection of the axial displacements X 1  of the cover  12  due to tactile pressures. 
     In accordance with the embodiment shown, an intermediate plate  38  is arranged between the support  14  of the cover  12  and the film  32  carrying the force sensors  18 . The intermediate plate  38 , which is fixed on the support  14 , forms a support for the force sensors  18 . It is preferably made from a sufficiently rigid material, for example polycarbonate (PC) or methyl polymethacrylate (PMMA) to allow the mounting of the force sensors  18  in prestress, i.e. to allow the force sensors  18  to be axially compressed between the intermediate plate  38  and the cover  12  with interposition of the small plate  36  between the force sensors  18  and the cover  12 . 
     In accordance with the teachings of the invention, the inside surface  40  of the cover  12  includes a series S 1 , S 2 , S 3 , S 4 , S 5  of relief elements  42  which are distributed over the inside surface of the cover  12 , opposite the sensitive zone  30 , so as to form a plurality of localized zones of increased pressure  44  on the spacing plate  34 , as will be explained in more detail in relation to  FIGS. 7 and 8  and with the second embodiment shown in  FIG. 5 . 
       FIGS. 5 and 6  show diagrammatically a second embodiment of the control panel  10  in accordance with the invention in which the mounting of the force sensors  18  is simplified because the film  32  provided with the force sensors  18  rests directly on the upper face of the support  14 . Moreover, the general shape of the control panel  10  is here generally parallelepipedal which allows the characteristics of the invention to be revealed. Of course, the control panel  18  could adopt any shape suited to its arrangement in the passenger space of a vehicle. 
     In the example embodiment shown, the control panel  10  includes six detection zones Z 1 , Z 2 , Z 3 , Z 4 , Z 5 , Z 6  and therefore six series S 1 , S 2 , S 3 , S 4 , S 5 , S 6  of associated relief elements  42 . The detection zones are here all identical and of rectangular shape. Of course, the control panel  10  could include detection zones of distinct shapes, these shapes having in particular to be suited to the ergonomic requirements of the controls. 
       FIG. 7  shows the distribution of the pressure applied by a conventional cover  12 , having no relief elements, on a spacing plate  34  and  FIG. 8  shows the distribution of the pressure applied by the cover  12  fitted with relief elements  42  in accordance with the invention on the spacing plate  34 . As can be seen, in the case of the prior art, the pressure is mainly applied to the periphery of the spacing plate  34  and at four localized points in the proximity of the center of the spacing plate  34 . Contrarily, in the case of the invention, the distribution of the pressure on the spacing plate  34  is better distributed due to the multiplicity of the relief elements  42  the positioning and distribution of which are so selected as to optimize the distribution of the pressure and thus allow the spacing plate  34  to apply a substantially even pressure over the sensitive zone  30  of the pressure sensor  18 . Thus, in the example shown, the relief elements  42  are made in the form of ribs spaced apart from each other and arranged in a rectangular line substantially parallel with the rectangular outline of the spacing plate  34  and of the sensitive zone  30 . Here there are eight ribs that produce eight localized zones of increased pressure  44 . 
     Due to the distribution of the relief elements  42  and therefore the optimized distribution of the localized zones of increased pressure  44 , the prestressing force applied by the spacing plate  34  to the sensitive zone  30  of the force sensor  18  is more even. The elasticity and the flexibility of the material forming the spacing plate  34  contribute to transmission and substantially even distribution of the prestressing force from the cover  12  and its relief elements  42  to the sensitive zone  30 . 
     Advantageously, the interstitial spaces  46  between the relief elements  42  are designed to allow sufficient flexion of the detection zone Z 1 , Z 2 , Z 3 , Z 4 , Z 5 , Z 6  of the cover  12  when a tactile pressure force is applied, preventing the relief elements  42  from making the cover  12  excessively rigid in the detection zone Z 1 , Z 2 , Z 3 , Z 4 , Z 5 , Z 6 . 
     The number and the dimensions of the relief elements  42  and of the interstitial spaces  46  can be adjusted depending on the pressure distribution and flexibility requirements of the detection zone Z 1 , Z 2 , Z 3 , Z 4 , Z 5 , Z 6 . 
     As can be seen in  FIG. 6 , the cover  12  includes a thin portion  48 , here defining a rectangular zone in which the adjacent detection zones Z 1 , Z 2 , Z 3 , Z 4 , Z 5 , Z 6  are arranged. This thin portion  48  offers a greater flexibility than the other zones of the cover  12  to allow the detection of the tactile pressures by the force sensors  18 . 
     Due to the location of the fixing points of the cover  12  on the support  14  on the periphery of the thin portion  48  and due to the flexibility of this thin portion  48  which deforms, the pressure applied by the cover  12  to the spacing plates  34  tends to be higher at the periphery of the thin portion  48  relative to the center of the thin portion  48 . 
     Also, to further improve the evenness of the prestressing force on the force sensors  18 , the invention proposes in a third embodiment shown in  FIGS. 9 and 10 , adjustment of the axial thickness of the relief elements  42  depending on their position relative to the periphery of the thin portion  48 . Thus, considering the view in axial section of  FIG. 10 , it is found that in each series S 1 , S 3 , S 5 , the axial thickness of the ribs  42  is increasing in a transversal direction X 2  from the periphery of the thin portion  48  to its center. This arrangement in accordance with the invention allows compensation for the pressure differences applied by the cover  12  to the spacing plates  34 . 
     In accordance with a modified embodiment (not shown), the thickness of the relief elements  42  can also be adjusted so as to compensate for the effects of a curvature of the cover  12  in the case of a cover  12  having a particular non-rectilinear transversal profile. 
     Preferably, the relief elements  42  are made in one piece with the cover  12 , for example by molding. 
     In accordance with modified embodiments, shown in particular in  FIGS. 11 and 12 , the relief elements  42  can have different forms, for example the form of ribs arranged in a circle, as in  FIG. 11 , or ribs arranged in a cross, as in  FIG. 12 . 
     The relief elements  42  could adopt forms other than ribs. However, the choice of ribs has the advantage of allowing easy manufacture, including by molding, while permitting a certain precision and great freedom in the positioning of the localized zones of increased pressure  44 . Moreover, the ribs allow these effects to be obtained without causing detrimental stiffening of the cover  12  in the detection zones Z 1 , Z 2 , Z 3 , Z 4 , Z 5 , Z 6 . 
     Advantageously, to obtain a yet more uniform distribution of the pressure over the sensitive zone  30 , each spacing plate  34  can be provided on its lower surface with a small plate made of material more rigid than the elastomeric material forming the spacing plate  34 . The small plate is for example made of relatively rigid thermoplastic material, compared to the elastomeric material forming the spacing plate  34 . The small plate can be made by over molding with the said spacing plate  34 . Each small plate extends generally over the whole area of the associated sensitive zone  30  to distribute the pressure over the whole of the sensitive zone  30 . 
     The control panel  10  has been described here with a plurality of control buttons B 1 , B 2 , B 3 , B 4 , B 5 . Of course, the invention applies to the modified embodiments that would include a single control button or a different number of control buttons. 
     While this invention has been described in terms of the preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow.