Using NI VeriStand to Implement HIL Testing of Automotive ECUs

challenge:

Develop a modular hardware-in-the-loop (HIL) test system for real-time simulation of engines and vehicles based on commercial off-the-shelf (COTS) hardware to reduce the number of physical tests required during embedded software validation.

Solution:

The test system based on NI VeriStand real-time test software and NI PXI hardware provides the computing power required by users, and can achieve high-speed control using field-programmable gate array (FPGA) hardware. At the same time, a variety of different I/Os can not only ensure that the HIL system can meet current needs, but also can be expanded to meet future application needs.

Alma Automotive is a company based in northern Italy that provides customized solutions for the calibration, control and testing of vehicles. Depending on the needs of the customer, Alma Automotive provides pure software (models or model-based analysis) or integrated hardware and software solutions. Eldor provides automotive electronic components such as coils, sensor systems and electronic control units (ECUs).

HIL systems are the standard for ECU testing because they can be used to automate and standardize tests. Most HIL systems available on the market offer standard functionality that cannot be expanded or customized. Eldor chose the HIL solution proposed by Alma Automotive because the hardware and software are open and can be fully customized to their needs.

The HIL system simulates the device controlled by the ECU. All actual signals entering the ECU must be replaced by signals generated by the HIL test system. Because the goal is to test the functionality of the ECU, the simulation must run in real time. The model must respond accurately to ECU commands to test the entire embedded control system. For some types of signals, it is difficult to reproduce a correct time base because the high-frequency signal needs to be synchronized with the instantaneous position of the crankshaft. Typical examples include in-cylinder pressure, accelerometer, ion current, and intake pressure signals.

There are many HIL systems available on the market. The main disadvantage of most systems is the lack of tools to customize the basic function library provided by the HIL vendor. It is difficult to access the underlying (FPGA-like) functions, so these systems cannot meet customer needs.

The combination of NI VeriStand and the NI PXI platform meets the user's needs for I/O, computing power, signal simulation, and data analysis, and is completely open and modular. The two key factors that determine the success of this application are: taking full advantage of the NI LabVIEW FPGA module's ability to create complex FPGA code and creating a custom device to output camshaft, crankshaft, intake valve, sensor current, and cylinder pressure signals.

The HIL system proposed by Alma Automotive (Figure 1) integrates the following hardware and software components:

A complete engine/vehicle (motorcycle)/driver model developed using a PXI real-time controller with a step time of 500μs and a single-core CPU load of 20%; a high-bandwidth signal generator implemented using a custom device to generate model-based crankshaft, camshaft, intake valve, cylinder pressure and ion current signals, and also to obtain all ECU output commands, including ignition, injection, H-bridge and interrupt light commands. The custom device is implemented using a 7852R board .

A custom I/O signal conditioning board designed and produced by Alma Automotive converts the ECU analog output signals to TTL digital signals and enhances the PXI 6723 analog output signals (variable reluctance signals, VRS) when necessary.

A custom actuator and sensor Fault Insertion Unit (FIU) and an external junction box that provides 96 signals were designed and produced by Alma Automotive.

Figure 1 HIL system integration

The vehicle simulation mode can be used for open loop (user drives the vehicle) or closed loop simulation (driver follows the vehicle speed trajectory). The dynamometer mode can also simulate the operating conditions of the test bench. The engine is modeled using a multivariable torque map, and this sub-model outputs the engine torque, air/fuel ratio and other parameters. These outputs are sent to a custom device to generate high frequency signals, such as the intake pressure signal. The engine torque is used to feed the vehicle and transmission sub-models, the drivetrain components. The engine and vehicle speeds are calculated based on the engine torque, clutch position, interposed gears, tire operation and actual loads on the front and rear wheels.

The driver submodel manipulates the steering, brakes, clutch, and gear shifting via torque-based control logic, while the dynamometer submodel calculates the torque provided to keep the engine running at the required speed and load operating conditions. There is also a heat exchange submodel to evaluate the engine's coolant temperature; the electrical system submodel allows users to simulate the starter and battery voltage levels during starting. [page]

The core of the system is an NI VeriStand custom device plug-in designed by Alma Automotive. The plug-in is an engine I/O subsystem simulator that generates two channels of VRS/Hall sensor signals with conditioned voltages up to 120V p-p, configurable angle-based waveforms, and four channels of wheel signals. It also acquires 12 channels of conditioned high-voltage ECU excitation signals; 16 channels of common high-voltage ECU output signals such as on/off, frequency, and PWM ; and 8 channels of analog input signals conditioned to 120V p-p. Figure 2 shows the setup interface for the custom device. The number of sensor wheel teeth and sensor wheel type are fully configurable.

Figure 2 Customized crankshaft reference signal generator device

The FIU developed by Alma Automotive is also FPGA-based, using FPGAs to process more than 400 signals required to operate switches. The determinism of the FPGA allows safety features to be set in the system, including user-defined fault timeouts, global FIU disable, and overcurrent monitoring on the fault bus. Make-before-break FIU operation prevents ambiguous states in fault channels with user-configurable load release delays.

The FIU developed by Alma Automotive can handle 64 channels with a maximum current limit of 2A for the power supply, and has access to four common fault buses. Open circuits GND, Vcc and VBATT can be used as power supplies. Feedback information on the switch status is available through 320 LEDs.

The user can connect either real loads or simulated loads. When using real loads, such as a throttle valve, the simulation system reads the information from the feedback sensor, such as the throttle valve potentiometer, and feeds it to the model. When using simulated loads, such as a virtual throttle valve, the feedback signal is generated by the simulator, such as an analog output channel, and sent to the ECU. Switching between real and simulated loads is done by moving the jumper on the external terminal block.

The system was successfully connected to the target ECU. Figure 3 shows a typical NI VeriStand interface for HIL testing.

Figure 3 HIL test control panel

Users can use existing methods and bench test modes to focus on verifying the software and hardware functions of all ECUs. It is very easy to use and configure, and users can directly reconfigure the system without requesting customer support. The NI PXI platform is suitable for integration with third-party custom development boards.

It is important that the hardware and software of the HIL test system can be continuously updated as needs change. Because NI PXI hardware is modular and based on COTS components, it can be easily upgraded, which ensures that the system will operate and remain technologically advanced in the future. NI VeriStand has an open architecture and is easily integrated with LabVIEW and other development software, thus providing the necessary flexibility to meet any challenges that may arise as test requirements change.