The present invention relates to a multiplex transmission apparatus comprising a plurality of communication networks, and a gateway node, interposed between the plurality of communication networks, for transmitting data.
According to remarkable development of electronics for vehicles, a large number of electrical components such as switches, sensors, actuators, and the like tend to be mounted therein, thus posing a serious problem associated with enlarged and complicated wiring harnesses for connecting the electrical components. In order to solve this problem, a multiplex transmission system in which a transmission path is commonly used by a large number of electrical components is adopted. In this system, communication nodes for the various electrical components, and communication nodes for control systems of, e.g., engine control (EGI) , four-wheel steering control (4WS) , anti-lock brake control (ABS) , and the like are connected to a multiplex transmission path to constitute a time-divisional multiplex transmission network.
In addition, a multiplex transmission apparatus is known. In this apparatus, a large number of communication nodes are classified into a first group consisting of communication nodes for control systems such as EGI, which require high-speed transmission, and a second group consisting of communication nodes for, e.g., electrical components such as switches, which do not require relatively high-speed transmission, and communication nodes for, e.g., an audio system, an air conditioner, and the like, which are not directly related to travel performance. The communication nodes in the first group are connected to a high-speed multiplex transmission path to constitute a first network, and the communication nodes in the second group are connected to a low-speed multiplex transmission path to constitute a second network. A gateway node is arranged between the high- and low-speed multiplex transmission paths, and performs data transfer between the communication nodes in the first and second groups, thereby constituting two multiplex transmission network systems, which can perform intercommunications.
A frame as a unit of a transmission signal of each node has a data field, an ID code field indicating a transmission source, and a priority code field indicating the priority order of transmission. The ID code designates a reception destination of the frame, and each node identifies based on the ID code whether or not a frame on the multiplex transmission path, to which the node is connected, is addressed to the node. The gateway node checks based on the ID codes whether or not data transfer is required. The priority code aims at preventing collision of frames on the multiplex transmission path of each network. If a high-priority node is executing transmission, transmission of a low-priority node is not executed and waits until transmission of the high-priority node is completed.
The gateway node always monitors the ID codes of frames on the first and second networks. When a frame having an ID code requiring data transfer is transmitted onto the multiplex transmission path of either network, the gateway node fetches the frame, and transmits data onto a reception-side network at an adjusted transmission speed after the multiplex transmission path of the reception-side network is ready. When the gateway node is set in a transmission standby state since the multiplex transmission path of the reception-side network is busy due to communications among the communication nodes in the network, and when the gateway node receives additional transfer data, the standby transfer data is lost, and a function to be realized based on the lost data cannot be realized.
However, in the multiplex transmission path comprising the gateway node, a data stack has a one-dimensional structure based on time, and reads out and transmits data in a storage order. Therefore, when low-priority data is stored before high-priority data, the low-priority data is read out and transmitted, and then, the high-priority data is transmitted, thus delaying transmission of the high-priority data.