Road-to-rig testing brings real-world emissions testing into a precision lab setting and is generally regarded as the future of vehicle development.
JOSH ISRAEL | HORIBA AUTOMOTIVE TEST SYSTEMS
In 1995, the Environmental Protection Agency (EPA) created Rover—a first-of-its-kind on-board mass emissions measurement system. In the 25 years since the creation of that first unit, the automotive testing world has been applying and refining on-board test equipment, ultimately known as Portable Emissions Measurement Systems (PEMS).
On-board, real-world emissions testing is best characterized by how it contrasts to traditional vehicle certification testing. Traditional laboratory test programs apply precision instrumentation and testing methods to measure highly variable exhaust emissions. Vehicle manufacturers and regulators run lab tests in climate-controlled facilities and apply loads to the vehicle via a full-vehicle chassis dynamometer that simulates driving. The traditional laboratory approach tests vehicle emissions with sophisticated and precision equipment and methods under a narrow set of possible operating conditions that may not be generally representative of real-world emissions.
As has been found in the past few decades, real vehicle emissions often depend upon operating conditions that may not be reproduced during traditional lab testing. The invention of PEMS systems and their application to real-world testing has been a significant mitigating factor in this regard. PEMS testing measures representative real-world emissions with accurate measurement equipment under actual real-world operating conditions.
PEMS have now become standard equipment for regulatory bodies. In 1999 the EPA and the heavy-duty engine industry entered into a consent decree with a total cost estimated at over $1 billion, including fines, on heavy-duty diesel engine manufacturers. This action paved the way for new regulations such as 40 CFR Part 1065 (June 2005) and led to the establishment of PEMS test protocols for the heavy-duty engine industry. In 2015, following the “dieselgate” emissions scandal, the EPA warned all OEMs that their light-duty vehicles would undergo PEMS testing during certification (without disclosing their specific test methods). Also, in the wake of the “dieselgate” findings, European regulatory bodies finalized EURO VI test standards within the WLTP On-Board Test procedures, requiring PEMS testing for all vehicles sold in Europe.
Despite a lack of formal in-use U.S. regulation that requires PEMS testing for light-duty vehicles, North American OEMs have embraced this technology for both R&D and pre-certification. Real-time on-board testing has become a vital tool for all OEMs and engine calibration and a common part of the emissions testing process. Labs currently use PEMS for a variety of reasons— including in-use compliance assurance, engine optimization, calibration development, and platform harmonization for global sale.
PEMS and road-to-rig
While on-road testing has become universal, the focus has shifted to identifying discrepancies, and ultimately closing the gaps, between real-world test results and certification-quality data. One such gap is the repeatability of results. In real-world PEMS testing, test-to-test repeatability is difficult because it is impossible to repeat a road test under the same traffic, driving, and ambient conditions. Thus the test method lacks precision. Test-to-test comparisons aren’t possible for evaluating the effects of alternative powertrain calibrations or small changes to exhaust after-treatment systems.
What OEMs currently need is the ability to conduct realistic and representative real-world testing that is repeatable, in a precision laboratory, over a wide range of operating conditions. Such capabilities let OEMs build and tune vehicles that comply with future regulatory requirements on feasible timelines without excessive prototyping and design iteration.
A process commonly referred to as road-to-rig testing (R2R) brings real-world PEMS testing into a precision laboratory setting and is generally regarded as the future of vehicle testing and development. In essence, R2R combines accurate, repeatable, controlled-environment lab testing with the real-world on-road PEMS testing. It uses the results of on-road PEMS tests as inputs and, in some cases, for model validation. R2R also uses advanced chassis dynamometer techniques combined with real-time environmental control as well as, in many cases, hardware and software-in-the-loop.
To accurately replicate real-world conditions in the lab, R2R mimics them using PEMS combined with advanced testing techniques such as a driving robot, advanced dynamometers, and dynamic temperature and pressure control. The Horiba road-to-rig approach is rooted in HORIBA Torque Matching (HTM). The torque matching method matches each parameter that affects the emissions of a vehicle during laboratory testing with the value recorded during a prior real-world drive. In this way, the vehicle does not distinguish between a dynamometer test in the lab and the corresponding real-world drive.
The overall HTM test method can be considered a three-step process:
Step 1 is a road test in which baseline route, vehicle, and weather data is collected to establish a reference for replication in the lab. A data logger, weather station, and an optional PEMS system log certain basic, real-world vehicle operating parameters and mass emissions over a road route.
Step 2 is a validation test of the vehicle in the laboratory under the same precisely-controlled conditions as the road test. The replication employs the coordinated use of a robot driver, an altitude simulator, and the dynamometer to continuously match the operating state of the vehicle emissions control system.
Step 3 consists of lab simulation tests in which different powertrain calibrations, emissions control components, environmental conditions, or other driving conditions are substituted or simulated for the purpose of measuring the “real world emissions” to determine the impact of the change.
The ultimate goal of R2R is to shorten development cycles while meeting the goal of fielding cleaner, more efficient vehicles. With a robust R2R toolset, manufacturers can push development efforts farther upstream to reduce prototyping and the number of testing iterations both in the lab and on the road. Reductions in testing and prototyping have become critical for manufacturers as they grapple with the diversity of powertrain systems in electric and hybrid-electric vehicles. Complex drive systems, such as those with hybrid transmissions, previously required extensive tests and a long series of on-road trials. The testing of complete powertrains is shifting to the test bed at every stage of development, thereby improving the quality of development services, reducing costs, and shortening development time.
EiL paired with PEMS
Parallel testing is a major area of focus as manufacturers push to shorten development cycles. Users are pairing PEMS testing with various simulation methods, among them EiL (engine in the loop). EIL is an advanced simulation method used by HORIBA-Mira’s engineering consultancy team. Along with simulation of the driver, environment, and road, this method accelerates vehicle development by allowing laboratory testing to more accurately represent real-world performance.
Rooted in testing automation software, HORIBA’s RDE+ solution includes a novel R2R testing method known as HORIBA Torque Matching. This method has been developed and evaluated for replicating and simulating different real-world conditions, e.g. changes in weather, while measuring emissions with laboratory precision. The software coordinates the control of the complex R2R tools necessary to replicate real-world conditions in a laboratory while also coordinating the workflow of the R2R test routine to optimize lab efficiency.
RDE CoDriver is a mobile app tool that helps drivers navigate complex on-road tests. During each test, the RDE CoDriver app calculates and presents real-time information related to the progress and validity of the test. It uses data from a wirelessly connected PEMS app which continuously gives feedback about the status of the test and immediately informs the driver about failures, reducing wasted test time and minimizing resources.
To help lab managers boost test efficiency, reduce down time, and increase control over the testing process, HORIBA has developed STARS Enterprise. This app-based laboratory automation system handles testing workflow and data management in the interest of efficiency.
Accurate testing at various altitudes and temperatures, paired with other real-driving conditions, is essential to ensure internal combustion engines meet emissions and performance standards. Altitude chambers have been the typical solution—but they are costly, inflexible, and often don’t represent real-world conditions. They also take up a large footprint and consume appreciable power. Mobile Multi-Function Efficient Dynamic Altitude Simulation (Medas) from HORIBA dynamically controls engine intake air and exhaust back pressure to simulate desired altitudes and seasonal temperature changes. Medas also provides temperature and humidity conditioning to the engine or powertrain to duplicate real-world testing conditions.
The methods and uses of PEMS-based testing will evolve as automakers continually experience more stringent emissions standards and diverse technology accompanying the rise of connected autonomous vehicles. R2R solutions will be an important part of that process, and it is easy to imagine a future where designers complete significant design milestones in a lab using on-road testing results as inputs to the simulation and validation process. Thus the use of PEMS and R2R test methods is an art that will continue to be refined.