Integration of FlexRay-based control units in existing test benches

Transcription

1 Integration of FlexRay-based control units in existing test benches Authors: Roland Bacher, BMW Group Munich Herbert Haas, BMW Group Munich Martin Simons, IXXAT Automation Weingarten Today, measuring and control technology in vehicle test benches is connected to the control units via CAN interfaces. With the increasingly use of FlexRay, the BMW Group has developed and successfully implemented a universal concept for integrating FlexRay into existing test benches. This new concept enables FlexRay users and developers to build upon their existing platforms instead of replacing them. The BMW Group is the first car maker to introduce FlexRay as a very powerful, real-time communication system, in the BMW X5. Model ranges planned for the future will also include FlexRay. FlexRay is a deterministic communication system with a bandwidth of 20 times greater than CAN and is able to meet the growing requirements of data transmission between control units, sensors and actuators in vehicles. The introduction of FlexRay has considerable effects on test bench technology in the various departments of the BMW Group. Today s test bench automation is CAN-based, in which the electrical systems in the vehicle and the automation unit in the test bench communicate via CAN interfaces. However, in the new BMW X5, for example, the control units of the variable shock absorber adjustment already communicate via the FlexRay bus. In order to test these control units as well as the vehicle components involved on the existing test benches, the

2 messages transmitted on the FlexRay network had to be converted to CAN-interfaces. It was thus possible to continue to use the existing test benches with their specific measuring and control technology. To achieve this, the concept of a freely configurable gateway was developed at the BMW Group that converts FlexRay messages to CAN messages and vice versa. Fig. 1 shows an example of the integration of the FlexRay-CAN gateway in a test bench. The automation unit defines the target values for the servo cylinders and controls via the sensors. The servo cylinders simulate the load of the vehicle components involved. The control units react to the load registered by their sensors with their related actuators and send messages on the FlexRay bus, which the automation unit typically receives via the CAN bus. This is carried out via the FlexRay-CAN gateway, which receives the messages of the control unit on the FlexRay bus and forwards them to the automation unit via the CAN bus. Fig. 1: Integration of FlexRay-based control units via gateway on existing test bench The main requirements of the FlexRay-CAN gateway are: The ability to integrate the automation technology equipped with CAN interfaces Configurability for use on various control units Stand-alone operation, i.e. operation without PC after configuration Automatic start-up with the last configuration saved Generation of messages with the necessary data security information Command/status interface compatible with the automation unit Defined time response for the conversion of the bus signals of FlexRay to CAN bus and vice versa Configuration of the unit from the PC via the Ethernet interface

3 The graphical user interface of a configuration tool should enable simple assignment of signals on the FlexRay bus to signals on the CAN bus (and vice versa). For this, the tool should read in the description files of the message traffic on the FlexRay bus (normally using FIBEX) and CAN bus (using FIBEX or CANdb). For CAN busses without a description file, this is optional. The tool should check all inputs of the user for consistency (e.g. bit length, data type). All files of a configuration should be contained in one project. The FlexRay CCM from IXXAT was used as the hardware and software platform (Fig. 2). This unit already complies with most of the requirements for the gateway. Due to the robust housing, the wide temperature range and the wide range of supply voltage, it is especially suitable for use in a test bench and in a vehicle. Analysis and diagnostics tools of various vendors and the residual bus simulation originally developed by the BMW Group already run on the FlexRay CCM. With all these applications, functions are implemented on the hardware of the FlexRay CCM via loadable software modules. IXXAT was able to implement the FlexRay-CAN gateway with another loadable software module and a corresponding PC-based configuration tool, with relatively low development costs. Fig. 2: Gateway platform FlexRay CCM In general, users work with process variables that are transmitted in FlexRay and CAN messages and not the messages themselves. For this reason, the conversion of messages from the assignment of signals is calculated on the PC and provided as a loadable table. The gateway configuration tool (Fig. 3) allows the assignment of signals via simple "drag and drop". It supports the user s inputs by suggesting signals with relevant names. If there is no description file for the CAN bus, the user can also enter the conversion of messages directly.

4 Fig. 3: User interface of the FlexRay/CAN gateway configuration tool The loadable gateway software module converts messages on the FlexRay bus to messages on the CAN bus and vice versa. The FlexRay bus is operated by an automatically generated code, which transmits the FlexRay messages in the specified cycles with the data back-up information expected by the control units. If the FlexRay-CAN gateway is configured accordingly, it starts the FlexRay bus automatically. The CAN bus is provided with messages: either event-controlled or cyclically. The cycle time is entered during configuration. Both CAN buses of the CCM can be used. In general, only some of the signals on the FlexRay bus are relevant, so that the bandwidth on the CAN bus is sufficient. If bandwidth is exceeded, the FlexRay-CAN gateway reports this with a message. With the download dialogue, the user loads the necessary files and the code onto the hardware of the FlexRay CCM. The FlexRay-CAN gateway then works in stand-alone mode. A connection to the PC is then no longer necessary. After switching on, the FlexRay-CAN gateway starts with the configuration last saved. The user only has to connect the unit to the PC and start the configuration tool to make changes. The command/status interface for the automation unit is implemented via one of the two CAN interfaces of the FlexRay-CAN gateway, which it receives via the reset command and transmits a cyclical status message.

5 The BMW Group now successfully uses the FlexRay-CAN gateway for various testing technologies. These are: Endurance strength test benches (Fig. 4) Engine and gear test benches Functional development drive Vehicle measurement technology to determine operating loads Measuring technology customer behavior Fig. 4: Endurance strength test benches The universal gateway is becoming increasingly widespread and is also used by the suppliers of the BMW Group for internal projects. If interested, the software license and support for the gateway is available to other suppliers from IXXAT. With the development of the FlexRay-CAN gateway, a solution was implemented with relatively low development costs that enable the continued use of comprehensive existing testing equipment and a fast conversion of test benches of CAN-based to FlexRay-based systems. In addition, the IXXAT CCM platform, already widely used is extended by yet another important area of application.