Application: Hardware-in-the-loop (HIL) Testing, Durability Testing
Improving test automation and control functionality of an existing hybrid HIL test stand for electric parking brakes.
Akebono Brake Corporation is a global supplier of foundation brakes and brake friction materials for automotive OEM customers such as Audi, Chrysler, General Motors, Honda, Toyota, and many more. One of the new technologies they are focused on is electric parking brakes – a type of electro-mechanical brake that uses traditional hydraulic actuation for braking while driving and then switches to an electro-mechanical actuator for braking when parking. Pressing the parking brake switch causes the brake caliper to electrically clamp the brake pads onto the brake rotor and then the clamping force is maintained mechanically. The advantages to electric parking brakes include more space available in the car interior, better fuel efficiency from reduced system mass, and new features like automatic parking brake release when you drive off.
Akebono produces automotive brakes, including electric parking brakes that take up less space and automatically disengage when driving – useful for driving in heavy traffic and parking on hills. (Source: Carwow)
The Akebono R&D department for electric parking brakes previously used a mid-height tester for improving the braking control software. The hybrid HIL test stand consisted of:
- Prototype brake control software embedded on an electronic control unit (ECU)
- Control and data acquisition cabinet
- Mechanical test bench with a motor gear unit (MGU) and brake caliper
The mid-height tester is called a hybrid HIL system because of the mechanical components in the loop. In an actual vehicle, the MGU is directly connected to the brake caliper. In Akebono’s mechanical test bench, the MGU is on one side of the table, the caliper is on the other side, and in the middle they are connected to a torque box (that measures torque and position) via a drive shaft.
Updating the Mid-Height HIL Tester
The ECU software has logic algorithms for estimating the state of the brake and controlling the electronic actuation of the brakes. Using the performance data collected by the HIL tester, the Akebono engineers can refine and optimize the braking control algorithms in the ECU software. They wanted to update the control and data acquisition component of the HIL mid-height tester to accomplish the following goals:
- Integrate all functionality within a single development environment written in National Instruments (NI) LabVIEW
- Improve test automation
- Add additional control functionality
For efficiency’s sake, Akebono decided to focus its engineering resources on developing the ECU software for the electric parking brake, while contracting out the test stand development to an experienced test systems integrator. LabVIEW was chosen as the preferred programming environment because of its popularity in the test, measurement, and control industry. Genuen (formerly WTI) was found through the NI Alliance Partner Network and selected because of their in-depth expertise in NI technology, first-class customer support, and competitive pricing.
While Genuen was initially brought in to create software for the existing mid-height tester, a thorough evaluation of the system revealed other areas of improvement for greater functionality, usability, and efficiency. The decision was made to retrofit the existing tester's Emerson servo drives and the programmable power supply, and add an NI real-time CompactDAQ (cDAQ) system for increased test capabilities. CompactDAQ has an open, modular architecture that allows users to pick and choose from a whole suite of C Series I/O modules. For this application, eight C Series modules were selected for analog input and output, digital input and output, counter input, and thermocouple input.
Delivering a mid-height HIL tester with mechanical brake simulation and a full-height durability tester for 24-hour testing of multiple brakes.
The HIL test stand runs in three modes: assembly mode and two simulation modes. The assembly mode is responsible for assembly level testing or integration testing where multiple components are tested all together. In this mode, the entire mechanical test bench (with the MGU, caliper, and servo actuators) is used to provide real-world performance data. The CompactDAQ system serves as data acquisition equipment that monitors the environment, measures the load and position from the torque box, and verifies current and voltage values. It also triggers the MGU to start the beginning of each test cycle. The ECU software, which controls the MGU, makes its own estimations about the environmental measurements and then predicts what state the brake is in. The ECU controller sends its estimated measurements and the CompactDAQ sends its actual measurements to the host computer for comparison to evaluate how well the ECU software is performing and make adjustments as needed.
The HIL and durability testers were built on LabVIEW software, real-time CompactDAQ hardware, and mix-and-match C Series I/O modules because of their high performance features and flexible use in different applications.
In the two simulation modes, either the MGU or the caliper are disconnected from the test loop and replaced with simulation profiles running on the real-time CompactDAQ controller. The CompactDAQ system is still responsible for all measurements used in assembly mode, but now it also runs the caliper profile or MGU profile. Using a simulation model allows the tester to push the boundaries in evaluating hypothetical conditions or worst case scenarios. By varying different theoretical parameters in the simulation models, the CompactDAQ causes the servo actuators to react accordingly and apply different loads to test the system. The models were originally written using The MathWorks, Inc. Simulink® software, but Genuen recreated them with the LabVIEW Real-Time Module for simplicity’s sake.
Creating a New Full-Height Durability Tester
Due to the success of the HIL mid-height tester, Genuen was also called upon to create a brand-new full-height tester for running system-level durability testing. Unlike the mid-height tester, there is no HIL simulation component in this machine. Instead, this machine is capable of testing three electric parking brake systems simultaneously, using three ECUs with six actuators.
By utilizing the highly adaptable NI hardware and software platform, there was a substantial savings in non-recurring engineering (NRE) costs when moving from the HIL tester to the durability tester. The same commercial off-the-shelf (COTS) hardware and software from the mid-height test stand could be used and scaled up to meet the requirements of the full-height tester. Not many COTS architectures are capable of covering both HIL and durability applications, which is why Genuen specializes in building test systems with NI technology.
In this new test stand, two real-time CompactDAQ and USB CompactDAQ systems are loaded with C Series I/O modules for analog input and output, digital input and output, thermocouple input, strain/bridge input, and synchronization. The test stand is programmed with LabVIEW and the LabVIEW Real-Time Module, while using Python scripting for test automation.
This new system allows Akebono to verify the estimated durability of the braking system over the lifetime of the actuator. A typical test might include 150,000 cycles of applying and releasing the brake, while monitoring the internal software estimations and different benchmarks. The tester also has a built-in fail-safe functionality that causes it to enter a safe state in the case of an error. This ability gives Akebono the confidence to perform 24-hour, round-the-clock durability testing, increasing overall test efficiency of the lab.
Saving Time with CANalytics Software for CAN Communication
Both the retrofitted mid-height HIL tester and new full-height durability tester use ECUs that communicate through the CAN bus. Genuen developed a CAN interface software called CANalytics that helps engineers to quickly and cost-effectively add CAN monitoring and communication capabilities without having to reinvent the wheel every time. This standalone tool works with a wide variety of CAN hardware and makes all the benefits of CAN accessible in one cohesive application.
The engineers at Akebono use CANalytics to set up the communication database, map signals and scaling, and manage configurations for every test. The CANalytics software also pulls measurements, messages, and other data from the ECU controller to the host computer for analysis. Finally, CANalytics is used to pass simulated data back to the ECU, replicating various messages that the ECU would expect from the vehicle in different theoretical situations.
"The CANalytics platform has provided beneficial return on investment within our laboratory test environment. Using our HIL test stand, we are able to easily configure both our hardware and software components from a single development environment. As compared to competitive market packages, CANalytics provides all required functions for database configuration and signal monitoring while maintaining a highly competitive cost structure."–George Ritter, Controls Engineer, Akebono Brake Corporation
Genuen's smooth project management process ensured that the system requirements were well-defined, milestones were achieved on schedule, and the delivered stands perform as desired. Akebono also appreciated Genuen's excellent engineering support and immediate responses to all questions and concerns. In the end, Akebono’s R&D department for electric parking brakes received the following two test stands:
- A mid-height HIL tester used to improve prototype ECU software
- A full-height lifetime durability tester for verification and validation (V&V) testing
Building the stands with high performance real-time CompactDAQ controllers means the test systems are capable of faster closed loop control and monitoring. The improved test functionality ultimately decreases development time and speeds up time to market. Pleased with the results, Akebono has since ordered another test stand from Genuen to further the capabilities of their test laboratory.
Todd VanGilder - Genuen
George Ritter - Akebono Brake Corporation
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