*As Featured on NI.com
Original Authors: Andreas Abel, ITI
Edited by Cyth Systems
The Challenge
Designing a holistic validation strategy for the embedded systems in an armored multipurpose vehicle (AMPV).
The Solution
Designing a series of tests using real-time testing tools built with NI VeriStand software and TraceTronic ECU-TEST automation software to create a test bench to validate embedded systems more quickly and completely.
Developing a Validation Framework for Multipurpose Vehicles
To equip defense units as well as police and security forces with new levels of mobile, modular, and protective technologies for their current operations, Krauss-Maffei Wegmann (KMW) and a number of other companies took on the challenge of developing a new generation of AMPVs that have high mobility and provide maximum protection at the same time. They also created a self-supporting safety cell made from armored steel and composite armor that set new benchmarks for these vehicles. The vehicles exceed the current protection standards and achieve significant weight optimizations.
Simple vehicle handling and optimized human-machine interfaces (HMIs) inside the vehicle further contribute to the high protection level because the driver and crew can focus on mission-related tasks. The simpler it is to drive the AMPV, the safer it is for vehicle occupants and the equipment. In cooperation with experienced software and hardware manufacturers, we designed a holistic validation strategy for the embedded systems in the vehicle.
Left: The Combination Test Bench, Right: A schematic of the system architecture.
Developing a Combination Test Bench
The project started with implementing a test bench to test both hardware and software. First, we analyzed the customer requirements and the electronic control units (ECUs). The resulting analysis formed the foundation for the technical concept and the test bench specification. Market research on existing simulators quickly revealed that there is not a standard solution that meets the specific project requirements concerning flexibility, degree of integration, and price, so we developed a custom system based on both off-the-shelf and specialized components.
We selected NI VeriStand as the real-time platform. This NI solution is based on industry-standard hardware, which helps us implement a high-performance system at a very reasonable cost. Also, we can scale the system’s computational power with growing testing requirements in a flexible and cost-effective manner.
To quickly compute real-time models, we selected a standard server with two Intel Xeon processors, both clocked at 2.53 GHz. The two processors have eight total cores. The comparatively low load caused by the current real-time models provides sufficient capacity for future extensions, even without hardware upgrades.
The I/O hardware is connected to the PC through a PXI expansion chassis. This occupies just one PCI Express slot, and the PXI chassis offers a sufficient number of free slots for additional I/O boards. The test bench uses NI PXI boards for controller area network (CAN) communication as well as analog and digital I/O. For certain time-critical signals, such as emulating speed sensor signals, we added an NI PXI-R Series field-programmable gate array (FPGA) module. We developed an FPGA program using NI LabVIEW FPGA software.
We also chose a signal conditioning unit with integrated fault simulation. This reduces the wiring complexity in the test bench without unnecessary signal quality degradation. To meet the requirements of a vehicle with two onboard voltage levels, we integrated two controllable power supplies into the test bench. A display shows the current load of the processor cores as well as relevant messages of the real-time system and the real-time models.
The Hardware Layout of the Test Bench
Alongside ECU software, we can use the test bench to test small-batch series modules such as carriers with ECUs. This is possible because we can connect the vehicle wiring harness directly to the test bench.
Real-Time Models
Requirements
The increasing complexity of controller functions also leads to increasing requirements on real-time plant models with respect to their capabilities and the modeled degree of detail. In particular, actuators in modern vehicles are increasingly operated in a controlled way rather than just in an on/off fashion. For this reason, we chose SimulationX from ITI.
In this project, we modeled all physical components interacting with vehicle controllers in SimulationX, including the following:
Engine
Gearbox with torque converter and two-stage shiftable transfer gearbox
Driveline with lockable and self-unlocking differentials, four-wheel drive, a steering model for wheel speed variations when cornering that couples to the ABS and steering sensors
Brake and ABS systems
Tire pressure monitoring and control system
Ensuring Real-Time Capability
In contrast to preconfigured black-box solutions that are designed for real-time capabilities, physical models that are tailored for a particular task or derived from other real-time models are not generally capable of performing real-time tasks. Instead, their real-time capabilities are ensured by the modeler during model development.
The real-time capability of the models is achieved based on two main mechanisms. In one instance, a unique and thorough symbolic preprocessing is used. During code generation, SimulationX automatically preprocesses the physical and mathematical equations of the complete system model. It simplifies the system by resolving and substituting equations, reducing expressions that occur multiple times to one computation, and completely removing the computation of quantities that do not affect the specified interface signals (such as internal result variables). All this takes place without requiring user interaction and, in combination with further code optimization measures, results in very efficient real-time code. On the other hand, a number of analysis methods such as natural frequencies and vibration modes as well as energy distribution and performance analysis, assist the user in the model-performance optimization process and thus contribute to the fulfillment of all computation-time requirements.
Test Automation
To fully take advantage of the test bench, we needed a flexible test automation environment. Due to the extensive regression tests required for KMW’s in-house development, automated tests are indispensable for quality and cost reasons.
For this application, we used the test automation environment from TraceTronic, ECU-TEST. This tool is used to specify, implement, execute, and document the test case results.
The reusability of test cases saves valuable time for the user and is achieved by altering signal mappings for different development stages in the respective test environment. Tests are designed graphically without editing any source code manually.
Regression tests implemented in ECU-TEST cover the full bandwidth of required validation levels, ranging from low-level tests such as stimulating an ECU input and observing the respective response on the CAN, up to testing heavily interacting and complex functions such as fault management and fault recognition.
Benefits
Producing state-of-the-art, highly protected, and comparably lightweight multipurpose vehicles with a lot of new functionality was only possible when using complex networked ECUs. The vehicle manufacturer bears the responsibility for the overall system, which consists of the vehicle, ECUs developed in-house, and ECUs obtained from external suppliers. In order to fully master this responsibility, all ECUs must be integrated and tested in combination so that they can be installed to the vehicle correctly the first time.
The novel test bench is a unique combination of internationally established standard hardware and software components. As a result, the customer receives an optimally priced, highly scalable validation framework composed of the test bench, tailored real-time models, and a highly automated test environment. This combination helps the manufacturer integrate the different vehicle ECUs in an optimal and cost-efficient way. Thus, the customer can fully exploit the scalability and I/O flexibility advantages. With real-time models, the AMPV’s ECU network can be validated quickly, providing an integrated approach to optimize the whole system.
Results
Using NI real-time hardware and NI VeriStand software, we performed the model development and test bench integration very efficiently. We used the well-defined interfaces between models, test bench software, and hardware to develop activities in parallel on all three fields. The short learning curve of NI VeriStand helped us get our test system up and running very quickly. The extensible environment provides assurance that we can scale our test system to meet future needs. The native integration of NI VeriStand with real-time and FPGA hardware enabled the test system to meet necessary timing requirements and allows for future test expansion.
Original Authors:
Andreas Abel, ITI
Edited by Cyth Systems