ECU Command Synchronization Across Multiple Vehicle Buses
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Solution Overview
Problem
In vehicle communication systems, the use of CAN or CAN-FD with passive communication methods limits the number of devices and transmission path length, leading to deviations in operation timing between zone ECUs connected to different buses, affecting turn lamp lighting and brake actuator control.
Innovation Solution
A communication system employing a multi-master CSMA/CA protocol with prioritized signal transmission on multiple buses, where the central ECU transmits count signals with the highest priority and control signals with lower priority, ensuring synchronized operation timing across ECUs connected to different buses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If multiple buses are provided to connect central ECU and zone ECUs in different vehicle areas, then the communication coverage and number of connected devices are improved, but transmission timing deviation occurs between buses leading to operation timing variations
Solution Approach 1:
The system transmits a count signal before the control signal to establish a common time reference. Each ECU counts the clock cycles from the start of the count signal reception, and the control signal includes a start count value that synchronizes the operation start timing across all ECUs connected to different buses.
Solution Approach 2:
The system uses a multi-master CSMA/CA protocol where ECUs monitor the bus status and adjust their transmission timing based on feedback from the bus environment. The arbitration mechanism provides feedback about bus occupancy, allowing ECUs to coordinate their transmissions and maintain synchronization.
2Device complexity
If CAN or CAN-FD passive communication method is used, then device complexity is reduced, but the number of devices and transmission path length are limited
Solution Approach 1:
The communication system is segmented into multiple independent buses, each capable of connecting a limited number of ECUs. This segmentation allows the overall system to support a larger number of devices by distributing them across multiple buses while maintaining the simplicity of passive CAN/CAN-FD communication on each bus.
Solution Approach 2:
The CSMA/CA protocol and count signal synchronization mechanism are designed to be universally applicable across multiple buses and ECUs. The same protocol and synchronization method work on each bus, providing a scalable solution that can accommodate varying numbers of devices and buses without increasing system complexity.
3Productivity
If control signals are transmitted on buses with high load, then communication functionality is maintained, but transmission delay occurs causing operation timing deviation
Solution Approach 1:
The count signal is transmitted beforehand to establish a time reference before the actual control signal transmission. This preliminary action allows ECUs to synchronize their operation start timing based on the start count value included in the control signal, compensating for variations in transmission delay caused by bus load.
Data Source
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AI summary
A communication system includes a central, zone ECUs capable of communicating with the central ECU via a communication bus, and zone ECUs capable of communicating with the central ECU via a communication bus. The central ECU periodically transmits, to the communication buses, a count signal including a count value counted up every time the count signal is transmitted, transmits a control signal including a start count value and control content to the communication buses, and sets a transmission priority of the count signal to be higher than a transmission priority of the control signal. The zone ECUs receive the count signal and the control signal, after the control signal is received, when the count value included in the received count signal becomes equal to the start count value included in the control signal, an operation corresponding to the control content included in the control signal is started.