The vehicles now-a-days contain many circuits, sensors and other electrical components related to the modern technology. All these parts are to be communicated with each other to perform functions among the available networks. For example communication is needed in between the dash board switch and front of the vehicle, for the head lights to react when the driver presses its switch. In the vehicle systems this communication is done by point to point connections. If the entire vehicle features as sensors, motors, switches and electrical devices are accumulated that results in accumulation of enormous wire connections. The present day networks provide a more efficient method for today’s in vehicle communication easily.
This networking is a multiplexing that is used to transfer data and distribute the data among all the electronic modules with a serial bus. Without the serial networking the in vehicle communication will require a dedicated wiring from point to point that results in bulky, expensive and very complex harness of wiring that is much difficult. The serial bus application will reduce the number of wires with the combination of signals on a single wire. The information is sent to individual modules to control each and every function as Anti-lock braking, turn signals and the display of the dash boards. The present day vehicle needs the increase in the networking facility more evidently.
Standardized protocols will enable the expansion of the higher volume economy class vehicles. Many standards have been developed but SAE and CAN (controlled area network) are the most predominant standards.
With regards to classification SAE has defined three basic categories as:
Class A (low speed)
Class B (medium speed)
Class C (high speed)
The high speed CAN (Class c) network is used commute to work at 200miles per hour whereas Class B protocol is 2 miles per hour. The travel is very much lesser for Class C network.
The functioning multiple of Class A functions requires an inexpensive, low speed communication and unique generic UARTs. These functions are not been standardized by the international organizations.
JI850 is adopted as a standard protocol for Class B networks by SAE. It has been used as a most recommended practice for more than seven years that got acceptance throughout the North America. It is implemented in many production vehicles for data share and diagnostic purposes. It is a low cost implementation as body electronics, diagnostics and instrumentation. It is a big effort that is a combination for GM Class 2 and Ford SCP. This class is the result of the two wire differential bus. OBD-II will specify the stored default codes to be available through a diagnostic port with the help of a standard protocol.
It is a predominant multiplexing protocol that is targeted at high speed, real time control and it can operate up to 1 Mb/s. It is developed in the early 1980s by Robert Bosch GmbH that worked with Intel on the first silicon implementation 82526 controller. The initial implementation of version 1.2 allows 11-bit message identifier with limited number of distinct messages. ISO in Europe has adopted this CAN as the high speed network protocol. It expressed an immediate need for the CAN protocol especially for the luxury models because of this advantage offered to the highly distributed nature of the electronic sub systems. CAN acceptance is growing. The SAE bus and truck subcommittee for control and communications selected this as the basis for J1939, a Class C network for truck and bus applications.
Intel and Multiplexing:
It has been a key player for standardized automotive in vehicle networking from past 20 years. Intel is now integrated with J1850 functionality. The development of 82526 and the stand lone versions that are integrated with 82527 CAN architecture. The controllers will handle and communicate the functions where transmission, reception, error detection and its confinement are included. The communication supports the functions the network where access, arbitration, error detection etc. is made easy. In order to minimize CPU overhead three interrupts and byte level message buffers that provide the efficient message handling.
More functions and multiple networks:
The main key feature that has much benefit is the ability to add functions without any new hardware or any decreased reliability. The capability of networking will become common on mid and low priced automobiles where the manufacturers are able to offer the functionality that is found on high end vehicles.
The need for speed and low latency are very critical for the power train and vehicle dynamics. Definitely a gate way would transfer the required diagnostic information in between the multiple networks.
Advantages of networking:
It provides the system benefits that are realized at the beginning of in vehicle network.
- It decreased the number of wires that are required for each function.
- The system quality, serviceability and installation are improved along with system cost and weight.
- Common sensor data such as vehicle speed, temperatures etc. are available on the network so as to share the data in order to eliminate the need of reluctant sensors.