Reproducible test results with EtherCAT-based remote vehicle control
One of the largest commercial vehicle manufacturers is testing different powertrain configurations – diesel engines, fuel cells, and battery electric drives – on a roller test bench. Reproducible results are ensured by a vehicle remote control system designed by Softing Engineering & Solutions GmbH, which uses EtherCAT and an embedded PC from Beckhoff to access the trucks’ CAN bus systems directly and control functions such as gear changes.
The commercial vehicle manufacturer tests all model series sold worldwide under various brands on the Road-to-Rig (R2R) test bench in Wörth. This provides an initial indication of the conditions and dynamic driving situations that are simulated on the R2R test bench. A powerful fan and huge cooling units generate a wide variety of climatic conditions and air currents of around 100 km/h. “The commercial vehicle manufacturer uses its test bench to test how the various powertrain configurations interact with the other vehicle functions, superstructures, and driver cabs under realistic conditions,” says Jörg Rottkord, automotive industry manager at Beckhoff. Typical tests include range studies of various battery types and hydrogen-powered fuel cells, as well as consumption and exhaust gas measurements for trucks with diesel engines.
Since the vehicles are already equipped with measuring technology when they arrive at the test bench, all the test bench personnel have to do is set up the trucks – which means securing them with chains and preparing them for the various tests. This work also includes installing the remote control and connecting it to the on-board electronics.
Test bench electronics control gear changes and accelerator pedal position
The remote control allows important vehicle functions such as the driving mode, gear selection, cruise control, retarder, and accelerator pedal position to be remotely controlled from the control station via the test bench automation system. “This enables commercial vehicle manufacturers to carry out many complex measurements – of the kind that were previously only possible on the road – under realistic driving conditions and with a high degree of repeatability on the test bench,” says Dr. Tobias Kolb, who works in automotive test bench development at Softing Engineering & Solutions GmbH, highlighting the advantage of remote control.
The system consists of a compact control box in the vehicle, which is connected to the vehicle electronics via a vehicle-specific adapter cable set, plus another box in the control station and an embedded PC from Beckhoff as an interface with the test bench automation. The remote control box converts the setpoints of the test bench automation into corresponding messages for the vehicle’s CAN bus and feeds them into the on-board electronics. “To do this, we disconnect the CAN bus in the vehicle at a suitable point,” says Dr. Tobias Kolb.
Access to vehicle electronics with PC-based control
Simple though it may sound, the process actually requires a great deal of specific expertise. Data from the vehicle’s common power train controller is needed to control the test sequence. In addition, certain CAN messages – used for gear changes, for example – must be filtered, manipulated, and fed back into the telegram stream with the appropriate checksum. “To do this, Softing uses our CX20x0 Embedded PCs and several CAN interfaces – the EL6751 EtherCAT Terminals,” says Jörg Rottkord, automotive industry manager at Beckhoff.
“However, you have to take a smart approach to filtering the CAN messages from the entire vehicle,” says David Welsch from the commercial vehicle manufacturer, who is responsible for programming the remote control. For example, only the messages to be manipulated are extracted, modified, and fed back into the vehicle. The setpoints for a gear change, for instance, then come from the test bench automation. The Beckhoff TwinCAT software calculates the necessary data and copies it into the relevant CAN frames. “This frame is then sent back to the vehicle in real time with the correct CAN message number and checksum,” explains Dr. Tobias Kolb. The two main tasks of the remote control are to emulate the switching commands and the accelerator pedal sensor via two opposing PWM tracks generated by a 2-channel EL2502 EtherCAT Terminal.
PC-based control for reproducible test sequences
While drivers previously carried out test procedures manually in sometimes extreme temperatures, the commercial vehicle manufacturer can now use remote control to execute a wide range of scenarios with high precision and repeatability, either fully automatically according to the specified sequence or, if necessary, manually from the control station. “There is huge added value in the automated processes and the reproducible results,” emphasizes Jörg Rottkord.
Dr. Tobias Kolb, who developed the remote control, cites two reasons for choosing PC-based control: the modular and compact design of the embedded PCs and EtherCAT Terminals, and the low cost of hardware and software compared to typical rapid prototyping systems. “Since TwinCAT is available free of charge as a development environment, practically the only costs incurred are those for the runtime licenses,” Dr. Tobias Kolb continues. “We can also run the development system directly on the CX20x0 Embedded PC, which we operate with Windows,” adds David Welsch. Its performance is more than adequate for the cycle time of 1 ms and offers sufficient reserves in case further CAN messages need to be calculated in the future. “A major advantage of PC-based control is that the computing power can be easily adjusted as needed using an embedded PC with a different CPU – in the same form factor,” adds Jörg Rottkord.
The flexibility and openness of PC-based control helped Dr. Tobias Kolb solve a configuration problem: “Some vehicles operated at a transfer rate of 500 kBit, others at 667 kBit. Therefore, the CAN interfaces had to be able to switch between the two bit rates during runtimes when vehicles were changed. “Beckhoff’s support was very helpful in implementing this function with sample programs,” says David Welsch.
A total of four CAN interfaces are used for remote control: two for sending and receiving messages to and from the truck, and two for integrating a legacy system and configuring other CAN devices in asynchronous mode. “This is where the modularity and easy expandability of PC-based control technology proves to be a real advantage, especially thinking ahead to future vehicle generations that will use CAN FD as their communication system,” emphasizes Jörg Rottkord. Beckhoff supports CAN FD physics with the EL6753 EtherCAT Terminal, which can handle flexible data rates (FD) as well as extended data fields with up to 64 bytes. A powerful CANopen protocol implementation makes it possible to integrate any CANopen devices into the EtherCAT Terminal network.
Safe operation with TwinSAFE
Safety plays a major role in test bench technology and, in the case of the test bench remote control, takes the form of Safety over EtherCAT (FSoE) and TwinSAFE Terminals. The remote control is integrated into the emergency stop chain of the building automation system via contacts. Emergency stops are also installed in the vehicle and control station, and disconnect communication with the vehicle when activated. When this happens, the truck also enters emergency mode and the test bench goes into a safe state. In addition, communication is continuously monitored via a live cycle bit exchanged between the test bench and remote control via EtherCAT.
“We see the remote control as a blueprint for many other automotive projects,” says Dr. Tobias Kolb, highlighting the potential of the solution. With Beckhoff’s open and modular control technology in conjunction with EtherCAT, it is possible to implement cost-effective and powerful gateways between test benches and vehicles with a wide variety of peripherals.
