Simulation and testing of armored off-road vehicles based on NI VeriStand real-time platform

"We chose NI VeriStand as our real-time platform. This solution is based on industry-standard hardware and helped us achieve a high-performance system at a low cost."
– Andreas Abel, ITI

The Challenge: Design a holistic verification strategy for the built systems of an Armored Multi-Purpose Vehicle (AMPV).

The Solution: Design a series of experiments using real-time test tools built with NI VeriStand software and TraceTronic ECU-TEST automation software to create a hardware-in-the-loop (HIL) test bench to more quickly and completely validate the built system.

Figure 1: These armored vehicles exceed current protection standards and achieve good weight optimization

Author(s):Andreas Abel - ITI René Müller - TraceTronic ITI is one of the world's leading system simulation software and engineering companies. The SimulationX standard tool is used to evaluate the interaction of all components in technical systems and supports the Modelica language. ITI cooperates with subsidiaries, distributors and partners worldwide and is also a member of the National Instruments Alliance Partner in the United States.

TraceTronic provides innovative solutions, services and software products for the development and validation of complex embedded systems. The company's services range from software function development and testing of electronic control units (ECUs) to the full development of HIL systems.

Developing a validation framework for multi-purpose vehicles

To equip the defense sector as well as the police and security forces with more advanced mobility, modularity and protection, Kraus-Maffei Wegmann (KMW) and other companies took on the challenge of developing a new generation of armored multi-purpose vehicles (AMPVs) that not only offer good mobility but also the highest level of protection. They set new standards for armored vehicles by using armored steel and composite armor to create a self-supporting safety element. The vehicles exceed current protection standards and are significantly lighter. The vehicles are easy to operate and their optimized human-machine interface (HMI) allows the driver and other personnel to focus on the mission, further increasing the level of protection. The easier it is to drive the AMPV, the safer it is for people and equipment. We worked closely with experienced software and hardware manufacturers to develop a comprehensive validation strategy for the systems built into the vehicle.

Developing a combined HIL test platform

The project started with the realization of a HIL test bench. First, we analyzed the customer requirements and the electronic controller units (ECUs). The results formed the basis for the technical concept and test bench specifications. Market research on existing HIL simulators showed that there were no standard solutions that met the specific project requirements in terms of flexibility, integration and price, so we developed a custom system based on existing and dedicated components.

We chose NI VeriStand as our real-time platform. This NI solution is based on industry-standard hardware, which enabled us to achieve a high-performance system at a very reasonable cost. In addition, we were able to scale the system’s computing power in a flexible and cost-effective manner in response to growing test needs.
For fast calculations of the real-time model, we chose a standard server with two 2.53 GHz Intel Xeon processors. The two processors have a total of 8 cores. The relatively low load caused by the current real-time model provides sufficient scalability, even without the need to upgrade the hardware.

The I/O hardware is connected to the PC via a PXI expansion chassis. This occupies only one PCI Express slot, and the PXI backplane provides enough slots to plug in other I/O boards. The test platform uses NI PXI controller area network (CAN) communication cards as well as analog and digital I/O. For time-critical signals such as analog speed sensor signals, we added an NI PXI-7831R field-programmable gate array (FPGA) module. We used NI LabVIEW FPGA software to develop the FPGA program.

In addition, we have selected a signal conditioning unit with integrated fault simulation to reduce the complex wiring of the test bench and not to reduce the signal quality unnecessarily. In order to meet the requirements of two on-board voltage level vehicles, we have integrated two controllable power supplies in the test bench. The display shows the current load of the processor core and relevant information about the real-time system and the real-time model.

Test platform hardware layout

All components and wiring of the combined HIL test bench are fully integrated in a 19-inch rack. In addition to validating the ECU software, we can also use the test bench layout to test small series of modules, such as carriers with ECUs. This has also proven to be possible because we can connect the vehicle wiring harness directly to the test bench.

Real-time model

Require

As controllers become more complex, the demands on real-time plant models in terms of capabilities and level of detail are increasing. In particular, actuators in modern vehicles are increasingly constrained to operate in more ways than just switching on and off. For this purpose, we choose ITI SimulationX. [page]

Test system ECU interaction with the model

In this project, we used SimulationX to model all physical elements that interact with the vehicle controller, mainly including the following aspects:
Engine
Reduction box with torque converter and two-stage shiftable gearbox
Drivetrain with lockable and self-unlocking differentials, four-wheel drive, wheel speed steering model for cornering with ABS and steering sensors connected
Braking and ABS systems
Tire pressure monitoring system

Ensuring real-time performance

Compared to pre-configured black box solutions designed for real-time capabilities, physical models that are customized for specific tasks or derived from other real-time models are generally not capable of performing real-time tasks. Their real-time performance is guaranteed by the modeler when developing the model.

The real-time capability of the model is achieved through two main mechanisms. On the one hand, a unique, thoroughly symbolic preprocessing is used. During code generation, SimulationX automatically preprocesses the physical and mathematical equations of the entire system model. The system is simplified by solving and substituting equations, simplifying expressions that appear multiple times in one calculation, and completely removing calculations that do not affect the quantities of the specified interface signals (such as internal result variables). All this is done without user involvement; in combination with other code optimization measures, a very efficient real-time code is obtained. On the other hand, several 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 so that all calculation time requirements are met.

In general, the SimulationX models developed for this project have excellent performance. For example, on one processor core, the entire powertrain model only requires 20% of the computing power, even though the model implements a relatively high sampling rate.

Drivetrain Model Example

The component models in the powertrain are implemented with different levels of detail according to the I/O requirements of the associated ECUs. From the engine perspective, the map-based model is sufficient to accurately describe the engine behavior. However, the injection system actuators require accurate device modeling from control inputs to position sensors and parameterization.

In this project, we validated this model part with a real injection control system. The gearbox and torque converter were physically modeled, including clutch and brake models, whose friction characteristics were parameterized. This made it possible to model gear changes and transition behaviors during gear changes, such as speed gradients and gear change times. This step is meaningful because the gearbox actuator can be operated not only in an on/off manner but also in intermediate steps with different brake and clutch torques. The remaining driveline model includes the elasticity of the driveshaft, so that it can carry out typical driveline vibrations. Depending on the steering angle, the curve radius of each wheel is different, so that during cornering, the sensor can detect the individual wheel speeds.

In addition to the controller output signals, the transmission model also processes the braking torque provided by the brake system model and applies it to the wheels. The transmission speed sensor outputs support the various ECUs, but their signal frequency is too high to be generated by the real-time model and is instead generated by the FPGA. The model can only provide the pulse frequency of the gear teeth passing through the sensor

The model shown is run on one processor core of a real-time system with a cycle time of 0.1 ms. Therefore, the model uses less than 20% of the computational resources of the processor core.

Test Automation

In order to fully utilize the HIL test bench, we need a flexible test automation environment. Since KMW internal development requires a variety of regression tests, automated testing is essential for quality and cost reasons.

For this application, we use the test automation environment of TraceTronic ECU-TEST. This tool is used to specify, implement, execute and document test results.

The reusability of test cases saves users valuable time by changing signal mapping at different development stages in the relevant test environment. Tests are designed visually without editing source code.

The regression tests implemented in ECU-TEST cover the entire bandwidth of the required verification level, ranging from low-level tests such as simulating ECU inputs and observing the relevant responses on the CAN, to tests of interactive and complex functions such as fault management and fault confirmation. This helps to reduce the test workload to 15% of the previous workload, and the test depth is significantly improved.

benefit

The production of advanced, highly protected, relatively lightweight, multi-purpose vehicles with a variety of new functions requires complex networked ECUs. The vehicle manufacturer is responsible for the entire system, including the vehicle, internally developed ECUs, and ECUs obtained from external suppliers. In order to complete the task well, the manufacturer will integrate and jointly test all ECUs to ensure that they can be installed in the vehicle correctly from the beginning.

The new HIL test platform is a unique combination of international standard hardware and software components. As a result, customers receive a pricing-optimized, highly scalable validation framework consisting of a HIL test platform, customized real-time models and a highly automated test environment. This combination helps manufacturers integrate different vehicle ECUs in an optimized and cost-effective way. This also enables customers to take advantage of scalability and I/O flexibility. With the real-time model in the loop, AMPV's ECU network can be quickly validated and provides an integrated approach to optimize the entire system. In this project, the test workload was reduced by 85% compared to non-HIL test methods, while the test depth was significantly improved.

result

Using NI real-time hardware and NI VeriStand software, we have been able to efficiently complete model development and HIL test bench integration. We took advantage of the clearly defined interfaces between the model, test bench software, and hardware to perform development activities in all three areas in parallel. The short learning curve of NI VeriStand helped us get the HIL test system up and running quickly. The scalable environment ensures that we can expand the HIL test system to meet future needs. NI VeriStand is easily reconfigurable so that the configuration can be changed when test requirements change, for example, when signals and models need to be rerouted for debugging. The inherent integration of NI VeriStand with real-time and FPGA hardware enables the test system to meet the required timing requirements and to accommodate future test expansions.