Abstract:
A portable device for receiving and sending a signal to an automotive device control system includes a communication means for receiving and sending the signal to the automotive device control system, a control means for controlling the communication means, a potential detection means for detecting electrical potential of a battery used to energize the communication means and the control means, and a detection control means for controlling detection operation of the potential detection means. The detection control means operates the potential detection means either in a continuous monitor mode or in an intermittent monitor mode in order to detect potential of the battery. The intermittent monitor mode is used when potential of the battery is equal to or higher than a predetermined potential, and the continuous monitor mode is used when potential of the battery is lower than a predetermined potential.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application is based on and claims the benefit of priority of Japanese Patent Application No. 2004-127930 filed on Apr. 23, 2004, the disclosure of which is incorporated herein by reference.  
       FIELD OF THE INVENTION  
       [0002]     The present invention relates to a portable device for an automotive device control system and, more specifically, to a portable device for controlling access to automobile and automotive devices based on communication between the portable device and the automotive device control system.  
       BACKGROUND OF THE INVENTION  
       [0003]     In recent years, remote access control systems for automobile such as SMARTKEY SYSTEM (registered trademark) is known and used for controlling access to an automotive device control system. This type of system controls access to an automobile by locking and unlocking doors, starting an engine, unlocking a steering wheel and opening a trunk lid through a radio communication between a portable device carried by a user and a main part of the system disposed in an automobile.  
         [0004]     The portable device generally uses a battery for electrical power supply. Therefore, portable device continuously monitors voltage potential of the battery by using a voltage monitor circuit and initializes its internal setting in order to prevent malfunction of the portable device because of a low voltage potential. An operation scheme described above for a conventional portable device is disclosed in Japanese Patent Document JP-A-2002-247656.  
         [0005]     However, the operation scheme for the conventional portable device suffers from decreased battery life because the conventional portable device continuously consumes electricity of the battery to operate the voltage monitor circuit.  
       SUMMARY OF THE INVENTION  
       [0006]     In view of the above-described problems, it is an object of the present invention to provide a portable device for an automotive device control system that has an extended battery life by reducing electricity consumption.  
         [0007]     The portable device for the automotive device control system of the present invention includes a communication means for sending and receiving a signal from a main body of the automotive device control system, a control means for controlling the communication means, a potential detection means for detecting electrical potential of a battery used to energize the communication means and the control means, and a detection control means for controlling operation of the potential detection means. Operation mode of the potential detection means is chosen from a continuous monitor mode and an intermittent monitor mode, based on a detected electrical potential of the battery. The detection control means chooses the intermittent monitor mode when the electrical potential of the battery is equal to or higher than a predetermined electrical potential, and it chooses the continuous monitor mode when the battery potential is lower than the predetermined electrical potential.  
         [0008]     The potential detection means operated in the above described manner consumes less electricity of the battery in the intermittent monitor mode than in the continuous monitor mode for the operation of the potential detection means because the potential detection means uses electrical power intermittently in the intermittent monitor mode while the battery potential is higher than the predetermined electrical potential. Therefore, electricity consumption for detecting electrical potential decreases and the battery of the portable device has an extended life.  
         [0009]     The potential detection means operates in the continuous monitor mode when the electrical potential of the battery is lower than the predetermined electrical potential. In this manner, the portable device can prevent malfunction caused by an insufficient electrical potential.  
         [0010]     The detection control means puts the portable device in a sleep state that stops monitoring of a battery potential while the portable device is waiting for a transmission signal from the main body of the automotive device control system in the intermittent monitor mode. The detection control means switches to a resume state for detecting the battery potential when the portable device has received the transmission signal from the main body of the automotive control system. The detection control means returns to the sleep state when the portable device has sent a response signal to the transmission signal.  
         [0011]     The detection control means detects battery potential of the portable device after sending the response signal to the main body of the automotive device control system when potential detection means operates in the intermittent monitor mode. This is because sending the response signal consumes electrical power of the battery and lowers the battery potential. In this manner, the battery potential is detected appropriately in the intermittent monitor mode. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     Other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings, in which:  
         [0013]      FIG. 1  is a block diagram of a portable device and a main body of an automotive device control system according to an embodiment of the present invention;  
         [0014]      FIG. 2  is a flowchart of a battery potential detection method used in the portable device; and  
         [0015]      FIG. 3  is a time chart that illustrates the battery potential detection method in relation to a series of changes in the battery potential. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]     An embodiment of the present invention is described with reference to FIGS.  1  to  3 .  
         [0017]      FIG. 1  shows a block diagram of an automotive device control system having a portable device. The automotive device control system includes an automotive device control apparatus  10  installed on an automobile, a door lock controller  20  and a portable device  30 . The automotive device control apparatus  10  and the portable device  30  communicates with each other.  
         [0018]     The automotive device control apparatus  10  includes a transmitter  11 , a receiver  12 , and a control ECU  13 . The transmitter  11  and the receiver  12  are disposed in a compartment of the automobile or on the outside of the compartment. For example, the transmitter  11  and the receiver  12  are disposed in a part close to a door handle. The transmitter  11  transmits a transmission signal to the outside of the compartment upon receiving a transmission control signal from the control ECU  13 . The receiver  12  receives an ID code signal from the portable device  30  and outputs the ID code signal to the control ECU  13 .  
         [0019]     The control ECU  13  is installed on the automobile and controls the transmitter  11  and the receiver  12 . The control ECU  13  has a memory for storing a transmitter control program, an ID code of the portable device  30  and the like. The control ECU  13  compares the ID code transmitted from the portable device  30  with the ID code stored in the memory, and determines if those two codes are the same. The control ECU  13  re-transmits a transmission signal based on the comparison result and outputs an operation signal to the door lock controller  20 . The door lock controller  20  locks or unlocks doors upon receiving the operation signal from the control ECU  13 .  
         [0020]     The portable device  30  includes a receive portion  31 , a transmit portion  32 , a controller  33 , and a battery  34 . The receive portion  31 , the transmit portion  32  and the controller  33  in this embodiment are implemented as an IC chip respectively. The receive portion  31  receives the transmission signal from the transmitter  11  of the automobile device control apparatus  10  and the transmit portion  32  transmits a signal back to the receiver  12  of the automobile device control apparatus  10 . The controller  33  is implemented as a microcomputer of well-known type including a CPU, a memory and the like. The portable device  30  has its own ID code and the ID code is stored in the memory of the controller  33 . The controller  33  is programmed to transmit an ID code signal including the ID code to the receiver  12  on the apparatus  10  through the transmit portion  32  when it receives the transmission signal from the transmitter  11  of the apparatus  10  through the receive portion  31 .  
         [0021]     The battery  34  supplies electricity to the receive portion  31 , the transmit portion  32  and the controller  33 . The controller  33  has an electrical potential monitor circuit  33   a  to detect an electrical potential of the battery  34 . In this embodiment, a source potential Vdd of the battery  34  is specified as 3 volt, and a reset potential Vret is specified as 1.8 volt. The reset potential is used as a threshold for initializing the portable device  30  in order to avoid malfunction of the portable device  30 .  
         [0022]     The portable device  30  monitors the potential of the battery  34  in an intermittent monitor mode or in a continuous monitor mode. The intermittent monitor mode is further defined as an alternating operation of a sleep state and a resume state, that is, the sleep state for stopping operation of potential detection and the resume state for resuming operation of potential detection. The continuous monitor mode continuously monitors the electrical potential of the battery  34 . The two modes of potential detection are switched based on a switch potential Vdet. In this embodiment, the switch potential Vdet is determined as a higher potential, i.e., 1.9 volt, than the reset potential Vret.  
         [0023]     Potential monitor operation of the portable device  30  is described with reference to  FIGS. 2 and 3 .  
         [0024]      FIG. 2  shows a flowchart of potential monitor operation controlled by the controller  33  based on a program stored therein. The operation starts with step S 10  where the potential monitor mode is set to the intermittent monitor mode. In the intermittent monitor mode, an initial state of monitoring is the sleep state that stops potential detection of the battery  34 . Then, the portable device  30  waits for a reception of the transmission signal transmitted from the transmitter  11  of the apparatus  10  on the automobile (step S 11 ). The state of monitor operation is changed to the resume state upon receiving (step S 11 : yes) the transmission signal (step S 12 ) and the potential detection circuit  33   a  detects the potential of the battery  34  (step S 13 ). Step  11  repeats itself (step S 11 : no) until the transmission signal is received.  
         [0025]     The detected potential is compared with the switch potential Vdet in step S 14 . When the detected potential is lower than the switch potential Vdet (step S 14 : yes), the ID code signal including low potential warning (step S 15 ) is transmitted to the receiver  12  on the automobile (step S 16 ). When the detected potential is not lower than the switch potential Vdet (step S 14 : no), the ID code signal transmitted to the receiver  12  does not include low potential warning (step S 15  skipped).  
         [0026]     The potential of battery  34  is detected again by the potential detection circuit  33   a  after the ID code signal is transmitted to the receiver  12  (step S 17 ). The detected potential is compared with the switch potential Vdet (step S 18 ). When the detected potential is equal to or higher than the switch potential Vdet (step S 18 : no), the resume state of the intermittent monitor mode is switched to the sleep state (step S 19 ). When the detected potential is lower than the switch potential Vdet (step S 18 : yes), the intermittent monitor mode is switched to the continuous monitor mode (step S 20 ).  
         [0027]      FIG. 3  shows a time chart that illustrates battery potential detection method in relation to a series of changes in the potential of the battery  34  along the time parameter t. The initial state of the monitor operation is the sleep state as shown in  FIG. 3 .  
         [0028]     The potential of the battery  34  lowers because of the ID code signal transmission operation after the portable device  30  receives the transmission signal from the transmitter  11  of the apparatus  10  on the automobile (time t 1 ). The potential of the battery  34  is detected upon receiving the transmission signal. The monitor operation is switched from the sleep state to the resume state according to the program. The ID code signal does not include low potential warning at this point, because the potential is not lower than the switch potential Vdet.  
         [0029]     The potential of the battery  34  gradually regains after transmission of the ID code signal (time t 2 ). The potential of the battery  34  is detected just before the monitor operation is switched from the resume state to the sleep state (time t 3 ). The monitor operation is switched from the resume state to the sleep state because the detected potential is not lower than the switch potential Vdet at time t 3 .  
         [0030]     Next, the potential of the battery  34  is detected upon receiving the transmission signal from the transmitter  11 . The monitor operation is switched from the sleep state to the resume state according to the program (time t 4 ). The ID code signal includes low potential warning, because the potential is lower than the switch potential Vdet at time t 4 .  
         [0031]     The ID code transmission ends at time t 5 . The potential of the battery  34  is detected just before the monitor operation is switched from the resume state to the sleep state (time t 6 ). The monitor operation is switched from the resume state to the sleep state because the detected potential is not lower than the switch potential Vdet at time t 6 .  
         [0032]     Next, the potential of the battery  34  is detected upon receiving the transmission signal from the transmitter  11 . The monitor operation is switched from the sleep state to the resume state according to the program (time t 7 ). The ID code signal includes low potential warning, because the potential is lower than the switch potential Vdet at time t 7 .  
         [0033]     The ID code transmission ends at time t 8 . The potential of the battery  34  is detected just before the monitor operation is switched from the resume state to the sleep state (time t 9 ). The monitor operation is changed from the intermittent monitor mode to the continuous monitor mode because the detected potential is lower than the switch potential Vdet at time t 9 .  
         [0034]     The above-described scheme of the potential detection saves battery energy used by potential detection because operation of the detection circuit stops intermittently in the intermittent monitor mode while the detected potential of the battery  34  is equal to or higher than the switch potential Vdet. Therefore, the battery life of the portable device  30  is extended.  
         [0035]     The monitor operation is changed from the intermittent monitor mode to the continuous monitor mode when the detected potential of the battery  34  is lower than the switch potential Vdet. The change of the monitor modes serves as a preparation for further decrease of the battery potential. In this manner, malfunction of the portable device  30  can be prevented because detection circuit is operated continuously for potential detection.  
         [0036]     The battery potential of the portable device decreases when it transmits the ID code signal to the automotive device control apparatus  10 . Therefore, the battery potential is preferably monitored when the ID code signal is transmitted.  
         [0037]     Although the present invention has been fully described in connection with the preferred embodiment thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art.  
         [0038]     For example, though the present invention is applied to the portable device  30  of the automotive device control system, the invention can also be applied to a portable device for two-way communication between a system and a portable device that requires extended battery life for continuous operation.  
         [0039]     Such changes and modifications are to be understood as being within the scope of the present invention as defined by the appended claims.