Abstract:
A touch switch for controlling accessory equipment of a vehicle in such a manner that malfunctions caused by factors such as changes in atmospheric conditions, receipt of an electromagnetic impulse, or the like can be avoided. A vehicle accessory touch switch comprises a touch section having a sensor conductor plate which is touched by an operator, a capacitance measurement section which measures a change in electrostatic capacity of the sensor conductor plate to a ground conductor as a sensor conductor plate capacity change, and a control section which controls accessory equipment according to comparison between the sensor conductor plate capacity change and a control judgment value, wherein the vehicle accessory touch switch controls the accessory equipment according to an operator touching the touch section, a sub-conductor plate is disposed, the capacitance measurement section measures a change in electrostatic capacity between the sub-conductor plate and the ground conductor as a sub-conductor plate capacity change, and the control section decides the control judgment value according to the sub-conductor plate capacity change measured by the capacitance measurement section.

Description:
PRIORITY INFORMATION 
   This application claims priority to Japanese Patent Application No. 2007-159189 filed on Jun. 15, 2007, which is incorporated herein by reference in its entirety. 
   BACKGROUND OF THE INVENTION 
   (a) Field of the Invention 
   The present invention relates to a touch switch for controlling accessory equipment of a vehicle according to a change in electrostatic capacitance caused when touched by a user. 
   (b) Description of the Prior Art(s) 
   Generally, an inner-door panel of a vehicle has a door pocket in which items such as maps or the like are stored by a vehicle occupant. It is, however, often difficult to retrieve a desired item from such a door pocket because usually light does not fully reach into the door pocket interior. As one attempt to provide a solution, door pockets provided with a lamp which can be turned on and off with a touch switch are sometimes provides.  FIG. 8  shows the structure of such a door pocket according to a related technology. 
   In this example, the door pocket is comprised of mutually opposed side walls  10 A and  10 B, a main wall  10 C which is connected to the side walls  10 A and  10 B to form a U-shaped wall, and a bottom plate  10 D which makes the bottom of the door pocket. The door pocket is fitted to an interior panel  12  such that an opening on the opposite side of the main wall  10 C comes into contact with the door interior panel  12 . A lamp  14  is attached to the inside surface of the side wall  10 A of the door pocket. A touch plate  16  which configures a vehicle accessory touch switch is fixed to the inside surface of the main wall  10 C of the door pocket. When the touch plate  16  is touched by a human hand to turn on the vehicle accessory touch switch, the lamp  14  is supplied with power and turned on. 
   By configuring as described above, the lamp  14  can be turned on when the vehicle occupant inserts his or her hand into the door pocket and touches the touch plate  16 . Thus, the occupant can easily retrieve an item stored in the door pocket. 
     FIG. 9  shows a structure of a vehicle accessory touch switch  18  applied to a door pocket. The touch plate  16  is formed of a dielectric material such as a synthetic resin or the like. A sensor conductor plate  20  is bonded to one surface of the touch plate  16  and connected to a capacitance measurement/control unit  24 . The capacitance measurement/control unit  24  is connected to a ground conductor  26  having electric potential as reference. 
   A switch  28  is controlled to be in ON or OFF state by the capacitance measurement/control unit  24 . One of the terminals of the switch  28  is connected to a negative terminal of a battery  30 . The other terminal of the switch  28  is connected to one of terminals of the lamp  14 . The other terminal of the lamp  14  is connected to the positive terminal of the battery  30 . 
   The capacitance measurement/control unit  24  measures the electrostatic capacitance between the sensor conductor plate  20  and the ground conductor  26  (hereinafter, the electrostatic capacitance or capacity between the conductor plate and the ground conductor  26  is simply referred to as “the capacitance to ground”) and controls the switch  28  if the measured value has a change which exceeds a prescribed control judgment value. 
   According to the above-described configuration, the capacitance to ground of the sensor conductor plate  20  can be changed when a surface of the touch plate  16 , which is opposite to a surface to which the sensor conductor plate  20  is bonded, is touched with a human hand having electrostatic capacity with respect to the ground conductor  26 . Thus, lighting of the lamp  14  can be controlled by touching the touch plate  16  with a hand. 
   A related technology of the present invention is described in JP-A 2006-196395. 
   However, because the capacitance to ground of the sensor conductor plate  20  is variable depending on a change in humidity or the like of air around the vehicle accessory touch switch  18 , the vehicle accessory touch switch  18  may not function properly when the capacitance to ground is varied due to a change in atmospheric conditions. Also, a noise voltage may be induced in the conductor plate  20  by an unnecessary electromagnetic wave generated by other electric equipment, and an error occurs in the electrostatic capacitance measured by the capacitance measurement/control unit  24 , possibly causing a malfunction of the vehicle accessory touch switch  18 . 
   The present invention was achieved in view of the above-noted problems. Specifically, the present invention provides a touch switch for controlling accessory equipment of a vehicle that a malfunction which is caused by a factor due to changes in the environment such as a change of atmospheric conditions, receipt of an unrelated electromagnetic impulse, or the like can be avoided. 
   SUMMARY OF THE INVENTION 
   The present invention relates to a vehicle accessory touch switch, and may be configured to comprise a touch section having a sensor conductor plate which may be touched by a user, a capacitance measurement section which measures a change in electrostatic capacity of the sensor conductor plate to a ground conductor as a sensor conductor plate capacity change, and a control section which controls accessory equipment mounted on a vehicle according to comparison between the sensor conductor plate capacity change and a control judgment value, wherein the vehicle accessory touch switch controls the accessory equipment according to a user touch of the touch section, a sub-conductor plate is disposed independent of the sensor conductor plate, the capacitance measurement section measures a change in electrostatic capacity between the sub-conductor plate and the ground conductor as a sub-conductor plate capacity change, and the control section decides the control judgment value according to the sub-conductor plate capacity change measured by the capacitance measurement section. 
   According to the present invention, a vehicle accessory touch switch capable of avoiding a malfunction caused by an environmental change can be realized. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded view of a vehicle accessory touch switch. 
       FIG. 2  is a diagram showing a vehicle accessory touch switch. 
       FIG. 3  is a flowchart showing a processing performed by a capacitance measurement/control unit. 
       FIG. 4  is an exploded view of a vehicle accessory touch switch with a sub-conductor plate disposed on a bottom plate of a door pocket. 
       FIG. 5  is a diagram showing a touch plate with a sub-conductor plate disposed in a vicinity of a lower end of a touch plate. 
       FIG. 6  is a diagram showing a touch plate having a sensor conductor plates disposed on a touch surface. 
       FIG. 7  is a diagram showing a vehicle accessory touch switch for controlling accessory equipment. 
       FIG. 8  is a diagram showing a door pocket in which a vehicle accessory touch switch is incorporated. 
       FIG. 9  is a diagram showing a structure of a general vehicle accessory touch switch. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  shows an exploded view of a vehicle accessory touch switch  32  according to an embodiment of the invention which is incorporated into a door pocket.  FIG. 2  shows a structure of the vehicle accessory touch switch  32 . Component parts corresponding to those of  FIG. 8  and  FIG. 9  are denoted by the same reference numerals, and their descriptions will not be repeated. The vehicle accessory touch switch  32  has a touch plate  16  provided with a sensor conductor plate  20 , and a sub-conductor plate  22  disposed on a side surface of a bottom plate  10 D to which a main wall  10 C is affixed. 
   The sensor conductor plate  20  and the sub-conductor plate  22  are connected with conductor wires  20 L and  22 L, respectively, and the conductor wires  20 L and  22 L are connected to a capacitance measurement/control unit  24  which is built into the side wall  10 B. The touch plate  16  is fixed to the inside surface of the main wall  10 C of the door pocket. The vehicle accessory touch switch  32  controls to turn on a lamp  14  disposed within the door pocket. 
   The structure and operation of the vehicle accessory touch switch  32  will be described with reference to  FIG. 2 . The sensor conductor plate  20  is disposed on a surface opposite to the touch plate  16  having a touch surface  16 T which can be touched by a human hand. The sub-conductor plate  22  is disposed at a position where its capacitance to ground is not markedly changed even if the touch plate  16  is touched. Additionally, the sub-conductor plate  22  is disposed near the sensor conductor plate  20 . A distance between the sub-conductor plate  22  and the sensor conductor plate  20  is such a distance that a change (an environmental change in the vicinity of the vehicle accessory touch switch  32 ) due to an environmental change of the capacitance to ground of the sub-conductor plate  22  becomes equal to a change due to an environmental change of the capacitance to ground of the sensor conductor plate  20 . 
   The capacitance measurement/control unit  24  is connected to a ground conductor  26 . As the ground conductor  26 , the vehicle body may be suitably used. 
   A switch  28  is controlled by a control signal output by the capacitance measurement/control unit  24 . For the switch  28 , a semiconductor device circuit which is controlled by inputting a pulse signal indicating a high electric potential with respect to an electric potential of the ground conductor  26  for a prescribed time length is suitably used. For the switch  28 , a switch which is changed to an OFF state if it is in an ON state, and to an ON state if it is in an OFF state, each time the control signal is input can be used. 
   According to the structure of the vehicle accessory touch switch  32  shown in  FIG. 1  and  FIG. 2 , the sub-conductor plate  22  is disposed at a position where its capacitance to ground is not markedly changed even if the touch plate  16  is touched with a human hand. Therefore, the capacitance to ground of the sub-conductor plate  22  is changed by an environmental change which can be detected by detecting that the capacitance to ground of the sub-conductor plate  22  has changed. 
   The sub-conductor plate  22  is disposed near the sensor conductor plate  20 . Therefore, when the capacitance to ground of the sub-conductor plate  22  is changed, the capacitance to ground of the sensor conductor plate  20  is also changed by the environmental change which has changed the capacitance to ground of the sub-conductor plate  22 . Therefore, the change in the capacitance to ground of the sensor conductor plate  20  due to the environmental change can be detected by detecting that the capacitance to ground of the sub-conductor plate  22  has changed. 
   Accordingly, the vehicle accessory touch switch  32  according to this embodiment determines a control judgment value with respect to the capacitance to ground of the sensor conductor plate  20  based on the change in the capacitance to ground of the sub-conductor plate  22  and adjusts control sensitivity. 
   Processing performed by the vehicle accessory touch switch  32  when adjusting the control sensitivity will next described.  FIG. 3  shows a flowchart of the processing. The capacitance measurement/control unit  24  measures a change in the capacitance to ground of the sub-conductor plate  22  as a sub-conductor plate capacity change ΔCB (S 1 ). The change in electrostatic capacity can be measured by, for example, measuring electrostatic capacity at intervals of a prescribed time Δt and determining a difference obtained by subtracting from the measured electrostatic capacity value obtained at a prescribed time the measured electrostatic capacity value which is obtained earlier by the time Δt than the time when the measured value is obtained. The electrostatic capacity is preferably measured by impedance measurement, measurement based on a charging time constant or the like. 
   The capacitance measurement/control unit  24  judges whether the absolute value of the sub-conductor plate capacity change ΔCB exceeds a prescribed threshold value T (S 2 ). If the absolute value of the sub-conductor plate capacity change ΔCB exceeds the threshold value T, a control judgment value D is set to a low-sensitivity judgment value DL (S 3 ). Meanwhile, if the absolute value of the sub-conductor plate capacity change ΔCB is equal to the threshold value T or less, the control judgment value D is set to a high-sensitivity judgment value DH (S 4 ). The low-sensitivity judgment value DL is determined to be a value larger than the high-sensitivity judgment value DH. 
   The capacitance measurement/control unit  24  processes in the same manner as that for measurement of the sub-conductor plate capacity change ΔCB to measure a change in the capacitance to ground of the sensor conductor plate  20  as a sensor conductor plate capacity change ΔCR (S 5 ). 
   The capacitance measurement/control unit  24  judges whether the absolute value of the sensor conductor plate capacity change ΔCR exceeds the control judgment value D set in the step S 4  or S 5  (S 6 ). If the absolute value of the sensor conductor plate capacity change ΔCR is not larger than the control judgment value D, the processing returns to the processing of the step S 1 . Meanwhile, if the absolute value of the sensor conductor plate capacity change ΔCR exceeds the control judgment value D, a control signal instructing the switching of the switch  28  is output (S 7 ). As the control signal, a pulse signal may be suitably used. 
   If the switch  28  is in an OFF state when the control signal is input, the switch  28  is changed to an ON state to turn on the lamp  14 . And, if the switch  28  is in the ON state, it is changed to the OFF state to turn off the lamp  14 . 
   By the above processing, the control judgment value D is set to a high-sensitivity judgment value DH if the environment around the vehicle accessory touch switch  32  is stable and the absolute value of the sensor conductor plate capacity change ΔCR is not larger than the threshold value T. Meanwhile, if the environment around the vehicle accessory touch switch  32  changes and the absolute value of the sensor conductor plate capacity change ΔCR exceeds the threshold value T, the control judgment value D is set to the low-sensitivity judgment value DL. 
   Here, the low-sensitivity judgment value DL is a value larger than the high-sensitivity judgment value DH. Therefore, if the environment around the vehicle accessory touch switch  32  changes, a value larger than the value which is set when the environment is stable is set as the control judgment value D. At step S 6  the control judgment value D indicates a level of change in the capacitance to ground of the sensor conductor plate  20  required for control of the switch  28 . 
   Therefore, if the environment around the vehicle accessory touch switch  32  changes, a change in the capacitance to ground of the sensor conductor plate  20  required for control of the switch  28  becomes larger than when the environment is stable. Thus, the capacitance to ground of the sensor conductor plate  20  is changed by the environmental change, and malfunctioning of the vehicle accessory touch switch  32  can be avoided. 
   The low-sensitivity judgment value DL is determined under a condition that it is less than the absolute value of the sensor conductor plate capacity change ΔCR at the time when a human hand touches the touch surface  16 T in addition to the condition that it is a value sufficient to avoid a malfunction. When the low-sensitivity judgment value DL is determined in this manner, the absolute value of the sensor conductor plate capacity change ΔCR exceeds the control judgment value D when the touch surface  16 T is touched by a human hand. Thus, a human touch will cause the capacitance measurement/control unit  24  (S 6 , S 7 ) to output the control signal, and the switch  28  can be controlled. 
   Meanwhile, it is preferable that the high-sensitivity judgment value DH is decided according to the operability of the vehicle accessory touch switch  32 . In other words, a distance between the human hand and the touch surface  16 T when the control signal is output in the step S 7  is set, and the high-sensitivity judgment value DH is determined such that the control signal is output when a human hand comes closer than the preset distance to the touch surface  16 T. It is preferable that the low-sensitivity judgment value DL and the high-sensitivity judgment value DH are decided through experimental evaluation, simulation, or the like. 
   Although an example in which the sub-conductor plate  22  is disposed on the side surface of the bottom plate  10 D was described above, the present invention may also be configured such that the sub-conductor plate  22  is disposed on the outside surface of the bottom plate  10 D of the door pocket as shown in  FIG. 4 . 
   As shown in  FIG. 5 , the sub-conductor plate  22  may be disposed near a lower end of the touch plate  16 . The sub-conductor plate  22  is disposed at a position separated as much as possible from the portion which is touched by a human hand. In the structure of  FIG. 5 , the sensor conductor plate  20  and the sub-conductor plate  22  are disposed on the same flexible substrate  16 T and affixed to the touch plate  16 . 
   In addition, the touch plate  16  may be configured such that the sensor conductor plate  20  is provided on the touch surface  16 T as shown in  FIG. 6 . The capacitance measurement/control unit  24  measures a change in the capacitance to ground of the sensor conductor plate  20  due to a contact or approach of the human hand to the sensor conductor plate  20  and controls the switch  28  according to the measured result. The sub-conductor plate  22  may be disposed on a surface opposite to the touch surface  16 T, a side surface of the bottom plate  10 D to which the main wall  10 C is bonded, an outer side surface of the bottom plate  10 D of the door pocket, or the like. 
   For the switch  28  provided on the vehicle accessory touch switch  32 , a switch which is changed from an OFF state to an ON state when a control signal is input and then changed to the OFF state after maintaining the ON state for a prescribed time period may be employed. When such a switch is used, the lamp  14  is lit for a prescribed time period after the touch plate  16  is touched by a human hand and goes off automatically. Thus, a person operating the lamp  14  can be freed from the burden of touching the touch plate  16  again in order to turn off the lamp  14 . 
   The vehicle accessory touch switch can be applied to the control of accessory equipment installed on the vehicle, such as automatic windows, an interior light, a radio, an air conditioner, and the like, in addition to the control of the switch  28 . An example vehicle accessory touch switch  38  for controlling such accessory equipment  36  is shown in  FIG. 7 . In this figure, component parts corresponding to those of  FIG. 2  are denoted by the same reference numerals, and their description will not be repeated. The capacitance measurement/control unit  24  controls the accessory equipment  36  in  FIG. 7 . Generally, an accessory equipment control circuit is provided with a semiconductor device circuit which can control according to a pulse signal. Therefore, it can also control, for example, opening/closing of an automatic window, adjustment of an interior light, tuning of a radio, temperature setting of an air conditioner, and the like.