1) Field of the Invention
The present invention relates to a technology for notifying presence of a vehicle to a periphery of the vehicle appropriately.
2) Description of the Related Art
In recent years, in place of automobiles that use a gasoline engine (an internal combustion engine) as a power source, hybrid automobiles that include both a gasoline engine and an electric motor as power sources, fuel-cell-powered automobiles that travel while generating electric power with a fuel cell using a hydrogen gas as a fuel, electric automobiles that use a battery (an electric motor), which is charged by a charger, as a power source, and the like have started to be widely used.
An advantage in driving a vehicle with such an electric motor is that a traveling sound is small (a silence characteristic is high). However, a pedestrian or a bicycle rider may judge whether an automobile (a vehicle) is present around the pedestrian or the bicycle rider or assume a distance between the vehicle and the pedestrian or the bicycle rider according to an engine sound emitted from the vehicle.
Since the pedestrian or the bicycle rider makes his/her judgment based on a traveling sound of an engine driven vehicle, which has been generally used in the past, there is a problem in that the pedestrian or the bicycle rider may be slow in noticing presence of an electric motor driven vehicle (or a hybrid automobile or a fuel-cell-powered automobile) with a high silence characteristic or may make an error in assumption of a distance.
Usually, a pedestrian walking on a street or a bicycle rider can recognize approach or the like of an automobile (a vehicle) according to an engine sound or the like of the vehicle. However, in the case of the hybrid automobile, since the hybrid automobile is in a mode of traveling by an electric motor rather than traveling by an engine at the time of low-speed traveling, no engine sound is emitted, which causes a near collision or the like. Similarly, in the case of the electric automobile or the fuel-cell-powered automobile, the automobile is always in a mode of traveling by an electric motor. Thus, since a pedestrian cannot recognize approach of the electric automobile or the fuel-cell-powered automobile, which causes a near collision as in the case of the hybrid automobile.
Therefore, vehicle-presence notifying apparatuses for solving the problems caused by the silence characteristic provided in the hybrid automobiles, the fuel-cell-powered automobiles, the electric automobiles, and the like have been disclosed in patent documents.
Concerning this type of a conventional technique, for example, Japanese Patent Application Laid-open No. H11-27810 discloses a technique for an electric automobile that gives an alarm by voice using a speaker or the like to a pedestrian and a driver around its vehicle when the vehicle detects a human body (a pedestrian) with a photographing camera or a radar provided in the vehicle. Japanese Patent Application Laid-open No. H7-322403 discloses a technique for notifying a driving state of an electric automobile to a pedestrian or a driver with sound. Japanese Patent Application Laid-open No. H10-83187 discloses a technique for a hybrid automobile that emits different artificial sounds according to a driving mode at the time of traveling. Japanese Patent Application Laid-open No. H10-178704 discloses a technique for a hybrid automobile that reduces an engine sound When a road, on which a vehicle is traveling, is congested.
However, vehicle-presence notifying apparatuses according to the conventional techniques have problems as described below. In the case of the conventional technique disclosed in the Japanese Patent Application Laid-open No. H11-27810, it is necessary to provide a sound source for the speaker or the like anew in the electric automobile, which causes an increase in cost. In the case of the conventional techniques disclosed in Japanese Patent Application Laid-open No. H7-322403 and Japanese Patent Application Laid-open No. H10-83187, an artificial sound for notifying a driving state of the vehicle to a pedestrian or a driver is simply emitted or an artificial sound is emitted according to a driving mode, which only prevents a silence characteristic originally provided in the hybrid automobile and the fuel-cell-powered automobile. In addition, in the case of such conventional techniques, it is possible to notify approach of a vehicle to a pedestrian with an artificial sound or the like emitted from the speaker. However, in the notifying by such an artificial sound, since a pedestrian not in a traveling direction of the vehicle can also hear an alarm sound, the technologies are contrary to the silence characteristic originally provided in the hybrid automobile and the fuel-cell-powered automobile. In residential areas in the suburbs rather than a city where there is heavy traffic of pedestrians, noise caused by automobiles is a problem. Thus, notifying by an alarm sound using the speaker or the like is not so preferable in terms of the environment.