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Testing network characteristics of ECUs

Posted: 17 Jul 2013     Print Version  Bookmark and Share

Keywords:Electronic control units  ECU  CAN  LIN  FlexRay 

Electronic control units (ECUs) in modern vehicles are all connected through various communication interfaces. The information, which each ECU needs to function correctly, is received from other system components. For example, an instrument cluster can read the current speed or engine RPM from ESP and engine ECUs, respectively. In addition, the ECU puts data about its own status on the network for reception and evaluation by other control units.

The CAN bus is the most common data network in modern vehicles. However, as the trend continuously moves towards an increasing number of ECUs per additional communication networks have found their ways into new vehicle designs. The LIN bus, for example, is a sub-system of the CAN network and is used to relieve the bus load of the supervising CAN network and to reduce overall costs.

On the other hand, FlexRay communication between ECUs has become popular for safety critical applications, such as drive-by-wire. All the different networks within vehicles are connected via gateway ECUs that require special test cases like routing and transmission time.

Figure 1: Functional test system for testing network characteristics of control units.

Modern vehicle ECU's also support overall vehicle safety features on a system level. It is therefore of paramount importance that the ECU works faultlessly under all operating conditions. It is furthermore required that an ECU will not affect the overall communication in the vehicle environment or goes out of control in the event of a communications breakdown if the unit is connected to the vehicle bus.

For the purposes of test the ECU's system functions can be divided into physical, i.e. usually electrical, and communication characteristics. The test system measures electrical characteristics without a network connection. In order to measure the communication characteristics it is necessary to simulate the vehicle environment via one or more bus nodes.

Furthermore, failure simulations are yet other test tasks not to be neglected. The scope of failure simulation includes hardware faults as well as failures of the communication protocol written into the software.

System architecture requirements
The development of the test system started already 15 years ago, originally developed and implemented around the specifications for high speed and low speed CAN buses, CAN transport protocols and CAN diagnosis (KWP 2000) requirements. Further developments have added the ability to test K-line functions and LIN bus systems. Meanwhile, the test system is already in its fourth generation. It has been continuously enhanced, containing all current requirements in networking vehicle ECUs up to applications, such as network management, subnetwork operations or gateway test.

Figure 2: Block diagram of the hardware architecture.

Basic test needs were drawn from car manufacturers design specifications which define the interface conditions of the communication networks in the vehicle. These specifications determine the purpose and content of individual test steps and define the stimuli and measurements which must be made as well as the precision required. Next, a test requirements matrix was constructed to ensure that the tester configuration encompassed all of these highly complex test needs. Detailed analysis resulted in a number of mandatory core test components and so the base configuration of the tester for checking network characteristics was derived:
 • Oscilloscope and multi-meter functions for electrical measurements
 • CAN interfaces—the controllers' onboard software must support measuring functions and also be able to generate fault protocols
 • Integration of rest bus simulation for each UUT
 • Programmable and expandable unit under test (UUT) power supplies
 • The ability to simulate line faults
 • Diagnostic interface to access the UUT's internal fault memory

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