Patent ID: 8183978

Claim:
An electronic key apparatus for a vehicle, comprising: an on-vehicle device mounted on a vehicle; a plurality of portable devices possessed by a user, each portable device having a unique ID code, a number and a transmission time period unique to the number; and a control device mounted on the vehicle, wherein: the electronic key apparatus for a vehicle activates the control device in a case where the on-vehicle device has verified ID codes for the portable devices through communication between the portable devices and the on-vehicle device; the on-vehicle device comprises: transmitter/receptor for communicating with the portable devices; a memory for storing a first answering signal, a second answering signal, and a third answering signal containing the ID codes for the plurality of portable devices, respectively; reception strength determiner for outputting a reception determination signal for determining that the first answering signal from the plurality of portable devices has been received, based on a reception strength of a reception signal; a driver for outputting a control signal to the control device of the vehicle; and a controller for: sequentially transmitting, to the plurality of portable devices through the transmitter/receptor, a first request signal for determining whether the plurality of portable devices approach a specific area, a second request signal for identifying a number of a registered portable device, and a third request signal for verifying an ID code for the registered portable device, according to a matching result of comparison between the request signals and the answering signals, sequentially receiving the first answering signal, the second answering signal, and the third answering signal from the plurality of portable devices based on the transmission, sequentially comparing the first answering signal, the second answering signal, and the third answering signal sent from the plurality of portable devices with the first answering signal, the second answering signal, and the third answering signal separately stored in the memory every time the first answering signal, the second answering signal, and the third answering signal are received from the plurality of portable devices, and controlling the driver in a case where the ID code for a portable device finally registered is verified based on the comparison result; and wherein the controller transmits the second request signal to the plurality of portable devices through the transmitter/receptor in a case where the reception determination signal is received from the reception strength determiner, even when the first answering signal cannot be normally detected, and the plurality of portable devices transmit the second answering signal at unique transmission timings for each portable device.