Abstract:
A capacitive lock can include various circuits that allow it to operate more efficiently and with greater accuracy. For example, when a user continuously touches a door handle for a certain time duration, a sensor can be configured to retain a variation in capacitance. When the door handle is continuously touched, a time constant circuit (timer) can be provided inside the entry system and measures the contact time and unlocks a door on the assumption that the user has a will to unlock and/or operate the vehicle or other apparatus.

Description:
[0001]     This application claims the priority benefit under 35 U.S.C. § 119 of Japanese Patent Application No. 2005-221150 filed on Jul. 29, 2005, which is hereby incorporated in its entirety by reference.  
       BACKGROUND  
       [0002]     1. Technical Field  
         [0003]     The disclosed subject matter relates to a key named smart entry capable of locking/unlocking without directly operating the key when it is carried. More particularly, it is associated with an arrangement of the smart entry system for use in vehicles.  
         [0004]     2. Description of the Related Art  
         [0005]     In a smart entry key having a simple arrangement, an electromagnetic wave is always transmitted from the vehicle to the smart entry key carried by the user. When the user carrying the smart entry key approaches a locked door, trunk, or the like, the key receiving the electromagnetic wave from the vehicle transmits a code number. In this case, the door is unlocked if the code number matches.  
         [0006]     When the user moves away from the vehicle and it becomes impossible to receive a respondent electromagnetic wave from the smart entry key carried by the user, the vehicle automatically locks the door. In such a system, the vehicle tends to transmit the electromagnetic wave for a long time, and sometimes infinitely, easily resulting in battery exhaustion and/or other inconveniences.  
         [0007]      FIG. 10  shows a conventional system that is thought to improve upon this point. In accordance with typical use, when a door is opened/closed, a door handle is usually touched. Accordingly, as shown in  FIG. 10 , a sensor electrode  91  formed of a conductor such as a metal is provided inside a door handle body  90  formed of a resinous member. When the user touches the door handle body  90  with his/her hand, a variation occurs in a capacitance between the sensor electrode  91  assembled in the door handle body  90  and the earth/ground.  
         [0008]     This variation is converted into a voltage through a detector circuit, for example, including an AC amplifier  93  and a rectifier  94  as shown in  FIG. 11 . When the output from a voltage comparator  95  reaches a certain voltage, it is used as a trigger to operate a transceiver (not shown) provided in the vehicle. The transceiver transmits an electromagnetic wave to send a signal to the entry key carried by the user to confirm the ID code of the entry key.  
         [0009]     When the ID code matches, the vehicle is prepared for operation by doing things such as unlocking the door(s), moving the seats, and starting the engine, etc. In this case, if the vehicle parks in a well-trafficked place, passersby may unconsciously (or consciously) touch the door handle body  90 . In such a case, the transceiver operates and emits the electromagnetic wave, which uselessly consumes power and places a burden on the battery. Therefore, a portion of the door handle body  90  outside the vehicular body is provided with a grounded capacitive shield plate  92  to prevent the sensor electrode  91  from causing a variation in capacitance when it is touched from outside.  
         [0010]     Accordingly, the sensor electrode  91  causes a required variation in capacitance when the user extends his/her hand around the door handle body  90  to the inside thereof and grasps it. When the door handle is touched in such a state, the user is determined to have a will to ride on the vehicle, and a trigger operation allows the transceiver provided on the vehicle to perform certain operations.  
         [0011]     On termination of the use of the vehicle, the transmitter on the vehicle continues transmission in principle and, when the vehicle can not receive the respondent signal from the entry key carried by the driver, the door is locked. In this method, the transmitter on the vehicle tends to operate longer, and results in an increase in battery consumption. Therefore, a mechanical lock switch  96  may be located at an appropriate position in the door handle body  90 , an example of which is shown in  FIG. 12 . In this case, when the lock switch is pressed upon getting off the vehicle, the door is locked and the engine is immediately stopped. Alternatively, a lock sensor electrode  97  may be provided as shown in  FIG. 13  instead of the mechanical lock switch  96 . The lock switch  96  and the lock sensor electrode  97  require corresponding control circuits, though they are not shown in the figures (see JP-A 2002-295093).  
         [0012]     In the above-described conventional capacitive sensors, when an outsider operates the door handle body  90  or leans against the vehicle with an interest in the vehicle or the like, a large capacitance may arise in the vicinity of the door handle body  90 . In addition, a rainfall or snowfall may allow a dielectric such as water to exist in the vicinity of the door handle. In such cases, a variation may occur in capacitance associated with the sensor electrode  91 , and possibly result in a trigger operation to the transceiver provided on the vehicle.  
         [0013]     Accordingly, the transceiver mounted on the vehicle interprets the trigger operation as a request for unlocking or locking and performs transmission to the entry key, leading to consumption of the battery, or the power supply in the vehicle. When the owner carrying the entry key occasionally stands near the vehicle, another person may touch the handle body, or a rainfall may occur. Also in such a case, an erroneous operation may unlock the vehicle and start the engine or perform other functions, regardless of the will of the owner/driver.  
       SUMMARY  
       [0014]     The disclosed subject matter provides a capacitive lock switch that, in accordance with an aspect of the subject matter, can include: a metallic electrode arranged inside or in the vicinity of a door handle; a converter circuit operative to convert a variation in capacitance associated with the metallic electrode into an electrical parameter; a decision circuit operative to detect a level variation in the electrical parameter; and a time constant circuit operative to measure the time of the level variation to provide a lock signal on measurement of the variation in capacitance over a certain time.  
         [0015]     In the disclosed subject matter, after a certain level or higher variation is detected, continuity of this level variation over a certain time is computed, followed by providing a lock signal. Accordingly, the capacitive switch can achieve locking reliably, reflecting the will of the user. In addition, cost of the lock system can be kept down, there are few installation restrictions on the switches, and the system is very convenient in terms of its operation and use. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  is a block diagram illustrative of an embodiment associated with a capacitive lock switch made in accordance with principles of the disclosed subject matter;  
         [0017]      FIG. 2  is an illustrative view of shapes of waveforms among the blocks in the block diagram of  FIG. 1 ;  
         [0018]      FIG. 3  is a block diagram illustrative of another embodiment of a capacitive lock switch made in accordance with principles of the disclosed subject matter;  
         [0019]      FIG. 4  is an illustrative view of shapes of waveforms among the blocks in the block diagram of  FIG. 3 ;  
         [0020]      FIG. 5  is a block diagram illustrative of an arrangement of the high-pass filter of  FIG. 1 ;  
         [0021]      FIG. 6  is a waveform diagram illustrative of operation of the high-pass filter;  
         [0022]      FIG. 7  is a waveform diagram illustrative of operation of the tilt detector circuit of  FIG. 5 ;  
         [0023]      FIG. 8  is a block diagram illustrative of another embodiment of a capacitive lock switch made in accordance with principles of the disclosed subject matter;  
         [0024]      FIG. 9  is a waveform diagram illustrative of operation of another embodiment of a capacitive lock switch made in accordance with principles of the disclosed subject matter;  
         [0025]      FIG. 10  is a cross-sectional view illustrative of the structure of a door handle according to an example of related art;  
         [0026]      FIG. 11  is a block diagram illustrative of a detector circuit according to an example of related art;  
         [0027]      FIG. 12  is an illustrative view of a door handle according to another example of related art; and  
         [0028]      FIG. 13  is an illustrative view of a door handle according to yet another example of related art. 
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0029]     The disclosed subject matter will be described next in detail based on the exemplary embodiments shown in the figures. The basic detector circuit of the capacitive type lock switch can be configured as shown in  FIG. 1 . In this case, a capacitance  1  is the target capacitance provided, for example, in a door handle, latch, or the like of the vehicle. A converter  2  is a circuit operative to convert a value of the capacitance  1  into a voltage or a digital signal. A high-pass filter  3  is a circuit operative to remove a DC component from an output signal from the converter  2 . A comparator  4  is a circuit operative to binarize an output signal from the high-pass filter  3 .  
         [0030]     Consideration is now given to the case where a human body or the like touches the capacitance  1  to increase the capacitance  1  in  FIG. 1 . In this case, an output V 1  from the converter  2  also increases. If the rate of increase in the capacitance  1  is sufficiently higher than a time constant of the high-pass filter  3 , then the output V 1  from the converter  2 , an output V 2  from the high-pass filter  3 , and an output V 3  from the comparator  4  vary as shown in  FIG. 2 .  
         [0031]     In  FIG. 2 , Vth 1  and Vth 2  denote a threshold level for turning the output V 3  from the comparator from low level to high level, and a threshold level for turning it from high level to low level, respectively. In this way, an increase in the capacitance  1  can be detected.  
         [0032]     As an example of digitally detecting the variation in the capacitance  1 , the converter can be configured as shown in  FIG. 3 . In this example, a capacitance  5  determines the oscillation period of a reference oscillator  6  and is made invariable. The capacitance  5  is defined as a reference capacitance. A capacitance  8  determines the oscillation period of an oscillator  9 . The capacitance  8  is defined as a target capacitance.  
         [0033]     The reference capacitance  5  has a value of C 1  and the reference oscillator  6  has an oscillation period of T 1 . The oscillation period T 1  of the reference oscillator  6  is proportional to the value C 1  of the reference capacitance  5  and can be represented by the following expression. 
 
(T1=C1×R1)  (Expression 1) 
 
         [0034]     The target capacitance  8  has a value of C 2  and the oscillator  9  has an oscillation period of T 2 . A relation between the oscillation period T 2  of the oscillator  9  and the value C 2  of the target capacitance  5  can also be represented by the following expression that is similar to (Expression 1). 
 
(T2=C2×R2)  (Expression 2) 
 
         [0035]     A counter  7  is considered first. The counter  7  is given an achievable maximum of N 1  and has two outputs. The one output D 1  increases in response to a rising edge of the output from the reference oscillator  6 . The other output V 5  is a one-bit signal that turns high (H) when the value of D 2  reaches the achievable maximum N 1 . Thus, V 5  provides a pulse with a pulse width of T 1  and a period of (N 1 ×T 1 ).  
         [0036]     A counter  10  is considered next. The counter  10  counts rising edges of the output V 6  from the oscillator  9  and provides an output V 7  of high (H) when the count reaches N 2  or more certain times. The counter  10  is reset when the output V 5  from the counter  7  turns high (H).  
         [0037]     The output V 4  from the reference oscillator, the outputs D 1  and V 5  from the counter  7 , the output V 6  from the oscillator connected to the target capacitance, and the output V 7  from the counter have a relation as shown in  FIG. 4 . A falling edge of V 5 , or the reset signal to the counter  10 , and a rising edge of the signal V 6  fed from the oscillator  9  to the counter  10  immediately after that falling edge have a time difference of T 3  therebetween. The output D 1  from the counter  7  at a rising edge of the output V 7  from the counter  10  has a value of N 3 . In this case, the following expression is realized. 
 
( N 3× T 1)=( N 2 ×T 2+ T 3)  (Expression 3) 
 
         [0038]     As the achievable value of T 3  ranges from 0 to T 2 , (Expression 3) can be written as follows if N 2  is sufficiently larger than 1. 
 
(N3×T1=N2×T2)  (Expression 4) 
 
         [0039]     When T 1  and T 2  in (Expression 4) are substituted with (Expression 1) and (Expression 2), the value N 3  of the output D 1  from the counter  7  at a rising edge of the output from the counter  10  is represented by the following expression. 
 
 N 3={( C 2× R 2)/( C 1× R 1)}× N 2  (Expression 5) 
 
         [0040]     In the data latch  11  of  FIG. 3 , the value of input data D 1  is latched in response to a rising edge of V 7  and the latched value is output from D 2 . In this case, the value of N 3  is output from D 2 . Consideration is given to the case where the target capacitance C 2  varies from C 3  to C 3 +C 4 .  
         [0041]     When the target capacitance C 2  is equal to C 3 , D 2  has a value of N 4  and when the target capacitance C 2  is equal to C 3 +C 4 , D 2  has a value of N 5 . In this case, N 4  and N 5  are represented by the following respective expressions. 
 
 N 4={( C 3× R 2)/( C 1 ×R 1)}× N 2  (Expression 6) 
 
 N 5=[{( C 3+ C 4)× R 2}/( C 1× R 1)]× N 2  (Expression 7) 
 
         [0042]     From (Expression 6) and (Expression 7), a variation N 6  in N 3  when the target capacitance C 2  varies from C 3  to C 3 +C 4  is represented by the following expression. 
 
 N =( N 5− N 4)={( C 4× R 2)/( C 1× R 1)}× N 2  (Expression 8) 
 
         [0043]     C 1 , R 1 , R 2  and N 2  in (Expression 8) are previously given constants. Accordingly, measurement of the output D 2  from the data latch  11  allows the variation C 4  in the target capacitance to be derived independent of the initial value C 3  of the target capacitance. In the case of multiple channels, the channels can share the reference capacitance  5 , the reference oscillator  6  and the counter  7 .  
         [0044]     These operations make it possible to detect a variation in capacitance due to a touch of the human body or the like. In this case, though, a touch regardless of the will of the user may possibly cause the detector to respond. To reduce this possibility, a circuit is added such that the output from the comparator responds only to a touch over a certain time T 4 .  
         [0045]     A circuit having an arrangement shown in  FIG. 5  can be used for that purpose, and is used for the high-pass filter  3  and part of the comparator  4  in  FIG. 1 . In  FIG. 5 , a difference between an original signal and a signal passed through a low-pass filter  12  is used as the output from the high-pass filter  3  shown in  FIG. 1 .  
         [0046]     In  FIG. 5 , an input signal to the low-pass filter  12  is denoted with D 3  and an output signal from the low-pass filter  12  is denoted with D 4 . When the value of the input signal D 3  varies from N 7  to N 8 , the output signal D 4  from the low-pass filter  12  varies from N 7  to N 8  in accordance with a time constant thereof.  
         [0047]     In this case, subtraction of the signal that has passed through the low-pass filter  12  from the original signal yields a value of (D 3 −D 4 ). Therefore, when the value of the input D 3  to the low-pass filter  12  varies from N 7  to N 8 , the value (D 3 −D 4 ) from subtraction of the signal passed through the low-pass filter varies from 0 to (N 8 −N 7 ). Thereafter, it gradually approaches 0 in accordance with the time constant of the low-pass filter.  
         [0048]     The comparator  13  varies the output V 8  from low (L) to high (H) at a threshold level Vth 3  and high to low at a threshold level Vth 4 . In this case, when the variation (N 8 −N 7 ) in the input signal D is higher than Vth 3 , the comparator  13  varies the output V 8  from low to high.  
         [0049]     A timer  14  provides an output V 9  of high when the output V 8  from the comparator  13  is made low. In this state, the timer  14  is kept reset. Immediately after the comparator  13  varies the output V 8  from low to high, the output V 9  varies from high to low. When a time T 4  elapses immediately after the output V 9  turns low, the output V 9  turns high again.  
         [0050]     If the target capacitance returns to the original value when the output is high, that is, the input to the low-pass filter varies from N 8  to N 7 , D 4  takes a value from N 7  to N 8 . Therefore, the input (D 3 −D 4 ) to the comparator  13  has a value within a range between (−N 8 ) and 0. Accordingly, the output V 8  from the comparator  13  becomes low. In this case, the output V 9  from the timer  14  becomes high and the timer  14  is reset.  
         [0051]     As for the low-pass filter  12 , only when the output V 9  from the timer  14  is high, do clock signals V 9  for use in the low-pass filter  12  become effective. When the output V 9  from the timer  14  is low, the clock signals V 9  are ineffective.  
         [0052]     While the timer  14  keeps the output V 9  at low for the period of time T 4 , the low-pass filter  12  keeps the output unchanged. When the time T 4  elapses after the input D 3  to the low-pass filter  12  turns high, the low-pass filter  12  starts normal operation. When the output V 8  from the comparator and the output V 9  from the timer are both at high, the final detection signal V 11  exhibits high, which is regarded as an occurrence of the variation in capacitance.  
         [0053]     A variation in capacitance for a short time less than the time T does not vary the status of a circuit having a data retaining function, or the low-pass filter  12  and the timer  14 . This is equivalent to the case where such variation in capacitance did not arise. With respect to these operations, the states of the signals are as shown in  FIG. 6 .  
         [0054]     The above operations make it possible to realize a circuit operative to respond only to a variation in capacitance over a certain time T 4 . An occurrence of the variation in capacitance over the certain time T 4  increases the output V 8  from the low-pass filter  12 . Thereafter, when the target capacitance is not touched, that is, the capacitance returns to the pre-detection value V 7 , the output D 4  from the low-pass filter  12  approaches N 7  in accordance with the time constant thereof.  
         [0055]     During the process of approach of the output D 4  to N 7 , the value of D 4  is slightly higher than N 7 . Therefore, the level of the minus input to the comparator  13  increases to lower the sensitivity. To shorten the time of the lowered sensitivity, a tilt/slope detector circuit  16  can be provided.  
         [0056]     The output D 4  from the low-pass filter  12  is considered when the input D 3  varies from N 7  to N 8 . If the target capacitance is continuously touched, D 4  varies on a curve having an asymptote to N 8 , with a tilt/slope of 0 or more. Thereafter, when the target capacitance is not touched, the tilt/slope of D 4  reaches a value less than 0.  
         [0057]     A variation in the tilt/slope is detected at the tilt/slope detector  16  and, if it determines that the tilt/slope is below a certain value, data is set such that the output D 4  from the low-pass filter  12  reaches the value of the input D 3 . The longer the certain time T 4 , the better the erroneous operation can be prevented. In consideration of the general convenience to use, though, 0.3-1.5 seconds may be regarded as a desirable time.  
         [0058]      FIG. 8  shows a circuit arrangement according to another embodiment of the disclosed subject matter. This circuit includes a counter  1  configured to count reference signals, and a counter  2  configured to count the outputs from the counter  1 . The count in the counter  2  is sequentially stored in a memory at the timing of the output from the counter  1 . A microcomputer can determine when the count varies above a certain level, and provides an ON signal when a certain or more variation continues over a set time.  
         [0059]      FIG. 9  shows a timing chart for the embodiment of  FIG. 8 . When the count n 1 , n 2  during non-detection becomes a count lower than a certain level N (for example, as shown in n 3 , n 4 , n 5 , n 6 ) and the duration continues longer than t 1 , an output signal is generated.  
         [0060]     While there has been described what are at present considered to be exemplary embodiments of the invention, it will be understood that various modifications may be made thereto, and it is intended that the appended claims cover such modifications as fall within the true spirit and scope of the invention. All conventional art references described above are herein incorporated in their entirety by reference.