|Remote keyless entry system|
|Tuesday, 19 December 2006|
Remote keyless entry (RKE) systems include a receiver mounted in a motor vehicle and a portable hand held transmitter located remote from the receiver. The receiver has a memory that stores one or more security codes, each of which identifies a transmitter that is authorized entry into the vehicle. The remote vehicle entry transmitters are used for performing a wireless operation on a vehicle such as locking and unlocking a door, unlatching a trunk latch, or activating or deactivating an alarm system equipped on the vehicle. Each transmitter is provided with a plurality of manually actuatable switches allowing the driver to control different functions of the vehicle, such as lock and unlock the doors, arm a security system or open the trunk. These transmitters also have been proposed to control starting the vehicle engine. The transmitter includes circuitry that responds to the actuation of one of the switches to transmit a digital signal that includes a security code that uniquely distinguishes the transmitter from a plurality of similar transmitters and a function code representative of the control function to be performed, such as the unlocking of a door. When a given push button switch is operated, the transmitter sends an RF signal which carries a digital numerical code and a designation of the function to be performed. The receiver compares the received security code with each stored security code to determine whether the security code was transmitted by an authorized transmitter. If a match takes place, the receiver responds to the function code by causing performance of the control function requested, as by unlocking a vehicle door. A receiver in the vehicle receives the transmitter signal, verifies that the numerical code designates an authorized transmitter for that particular vehicle and if so, signals the vehicle control circuits to perform the prescribed function. In typical arrangements a receiver is mounted on the vehicle that receives wireless communication signals from a portable, hand held transmitter used by an owner of the vehicle. Typical transmitters are embodied in a key fob having switches that are activated by the vehicle owner to indicate a desired action on the part of the remote keyless entry system, such as unlocking the doors or the trunk. RKE transmitters usually use a phase locked loop (PLL) device as an RF transmission device. The receivers typically used in remote keyless entry systems are amplitude shift keying (ASK) receivers. Such receivers are effective for receiving the radio frequency signals typically generated by transmitters in remote keyless entry systems. Such RKE fobs generally utilize an antenna to transmit radio frequency (RF) signals to a vehicle in order to lock or unlock vehicle doors, open or close a vehicle sliding door, unlock a vehicle trunk, activate internal and/or external vehicle lights, and/or activate a "panic" alarm.
A keyless entry system has a keyless entry control unit which permits the remote control only when the ID code transmitted along with the command from the mobile transmitter is identical with the ID code registered therein. In such a keyless entry unit, inherent ID codes are allocated respectively to transmitters, and locking and unlocking information and the ID code information are transmitted from the transmitters. In keyless entry systems, one or more unique identifying codes are programmed into the transmitter. The transmitter and a receiver use a defined communication protocol. The communication protocol defines the timing of the bit stream and the tolerances. The transmitter can include a microprocessor that transmits according to a communication protocol. In receiving circuits used for a radio which receives a weak radio wave, such as a keyless entry system or simple data communications, a radio frequency (referred to as RF, hereinafter) is generally around 315 MHz or less. The RKE fob is typically a small rectangular or oval plastic housing with a plurality of depressible buttons for activating each one of the wireless operations. The outer surface of the housing is typically black in color. Each button is also typically black with a graphical display printed each of the buttons. To assist the operator in viewing the buttons of the RKE fob during poor lighting conditions, lighting schemes may be added to the RKE fob for illumination purposes. LEDs are typically used to illuminate more than one button or incorporate light piping to tunnel the light to the plurality of buttons. The key fob can be used within a fixed vicinity of the vehicle. The fob has a typical range of 10-20 meters from the vehicle. Special antennas and receivers can extend this to a practical limit of about 250-350 meters. The antenna is typically positioned on a circuit board and communicates with an electronic vehicle locking and unlocking system for locking and unlocking the vehicle doors. Lithium batteries are often used to power remote keyless entry systems.