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Site visit: VIPER
The VIPER chassis test facility in Virginia is using its academic connections to keep its equipment and procedures at the cutting edge
by Graham Heeps
The Virginia Institute for Performance Engineering and Research in the USA, or VIPER, consists of two test facilities, one for powertrain and one for chassis, both located at Virginia International Raceway on the Virginia/North Carolina border. Earlier this year, we toured the Virginia Tech-affiliated chassis test labs to catch up with the latest developments at this innovative facility.
The centerpiece of the operation is the eight-post rig. When it was originally installed by Moog FCS, the rig was the first of its kind in the world. It remains unique, but for different reasons, explains Dr Steve Southward, director of VIPER Service, the facility’s commercial arm.
“After analyzing the rig performance over two years of commercial and research testing, we targeted a number of key areas for improvement and developed an aggressive upgrade strategy,” he says. “We have changed the hydraulic power supply, the cooling system, the data acquisition, the sensing, and many of the control parameters. For instance, we were not able to achieve what we wanted in terms of actuator bandwidth, so we developed an innovative approach to tuning the control loops, which can be applied to any similar rig.
“We’ve gone after everything that we were either unhappy with or felt could be better. The innovation capacity that we have through our research partnership with Virginia Tech is one of the real advantages we have versus other testing houses. We have the capability to push the state of the art.”
Another major innovation on the rig went live in September 2009. Dissatisfied with the way that artefact forces from the four pneumatic aero loaders mounted on a test chassis were undesirably influencing the chassis’ natural behavior, VIPER staff resolved to replace them with a bespoke alternative.
“What we found in our testing was that to really get rid of those artefact forces that could potentially negatively impact correlation to the real world, you needed an actuator with a much higher bandwidth than the [hydraulic] wheel loaders that input the disturbing forces,” Southward says.
“So what we now have are electromagnetic linear motors. To our knowledge these are the first in existence in this application. The motors were co-developed with Roehrig Engineering and each one is essentially a 4K-EMA shock dyno with some other bells and whistles, retasked as an aero loader. We’ve got the motors tuned to about 50Hz performance right now. They have a ±4,000lb force capability but have the bandwidth authority to cancel out artefact forces that may be created by other actuator technologies. They were installed in October/November 2009 and have performed very well since.”
Other developments to both the rig and the tests offered have been driven by the new types of customers VIPER has served since a major rationalization of stock car teams ahead of the 2009 season, precipitated by the global economic crisis, resulted in a substantial decline in the number of outfits buying third-party rig time.
Drag racing is one of the new markets for VIPER, and a 2009 Pro Stock chassis was on the eight-poster at the time of PMW’s visit, instrumented up with a number of sensors for an innovative test program to figure out how the team’s changes to the chassis for 2010 are affecting performance at the track. The eight-poster’s ability to measure flexure in a tubeframe chassis due to its additional aero loader makes it particularly suitable for such work, but VIPER has also extended the rig capability in order to support the unique requirements of drag car testing.
Earlier this year, VIPER also upgraded its Cruden driving simulator to support the drag race market. “Cruden has developed a specific drive profile to better suit drag racing,” says Southward. “Obviously we’re limited by the stroke of the actuators so they’re pre-loading the rig back, so that when the vehicle launches we get as much longitudinal acceleration as possible. We’ve simulated a drag strip so that a driver can come a day or two before competition and practice at the ‘Christmas tree’. The Christmas tree itself is externally controllable from the operator terminal so that it’s not just a program that the driver would intuitively learn – it’s just like the competition where we have the pre-stage, the stage, and then a wait for the tree to be activated.”
VIPER has also purchased a second simulator from Cruden, which is due for delivery in late 2010. This will facilitate side-by-side testing, training, and some other development work on the research side, where there are plans for Virginia Tech students to investigate the teleoperation of autonomous vehicles and train autonomous vehicles to drive more like humans would drive them.
Indeed, the grant-funded research projects of Southward’s students kept the utilization of VIPER’s testing assets high during challenging times for the commercial operation last year. Recent research has concerned magnetorheological (MR) dampers for motorsport testing purposes.
“One of the things we’re trying to do is create what we call a programmable shock absorber,” Southward explains. A small change in current changes the behavior of the MR damper; the trick is in how you control that current.
“What my students and I have been developing is a technique for modeling the characteristics of that highly non-linear behavior and inverting it, so that I can make this shock look like any passive shock you might construct.
“You create a database of passive shocks, which we’ve started doing with the standard Penske [stock car] dampers. Our database contains dynamic response information, including non-linear characteristics like hysteresis and temperature dependencies. The result is that we can make this [MR] shock look like any of those passive ones, just with a software switch.
“You couldn’t necessarily race with this, but it would certainly be convenient to have one set of shocks on the car,” he continues. “For seven- or eight-post testing you could change shocks just by switching the software, and iterate through different combinations a lot quicker than physically rebuilding the device and putting new shocks on each time.”
Southward adds that some of the algorithms under development require only shock-position feedback – a common sensor on a race car – rather than needing an expensive force-feedback sensor to be built in.
He acknowledges that even for a single damper, compiling a database of characteristics for every conceivable state of build is a huge task. But that might not be necessary as the research advances: “It would be nice to get to a point where we could model from the [limited] data we had and predict that if I changed a shim, or used a different piston, it would have a particular effect. But to begin with we just want to make the MR damper look like ones we know; once we’ve solved that problem we can move on to the next one.”
It was always intended for VIPER to be part of a wider hub of automotive and motorsport testing and research in Virginia. The first steps were the creation of the labs at VIR and securing commercial access to two wind tunnels at NASA’s Langley Research Center in Hampton.
The economic crisis and political decisions put the brakes on some of the initial momentum when new investment was put on hold, delivery of a new MTS ‘rolling road’ test cart for the ‘14x22’ wind tunnel was delayed and the historic Langley Full Scale Tunnel was closed pending demolition. But now it seems the master plan is moving forward once more. In August 2010, Virginia Tech announced the establishment of the National Tire Research Center (NTRC), an advanced tire research and test facility to be created at VIR.
The facility is a partnership between Virginia Tech Transport Institute, GM, the Department of Mechanical Engineering in Virginia Tech’s College of Engineering, the Institute for Advanced Learning and Research in Danville (of which VIPER is part), the Southside Virginia community, and the Virginia Tobacco Indemnification and Community Relations Revitalization Commission.
NTRC will conduct independent testing, research, and assessments to complement R&D performed by tire and automakers, with a focus on increasing research on green technology. Funding for the center will total US$14 million, with US$5 million from GM, US$5 million from the Tobacco Commission, and US$4 million from Virginia Tech.
Its creators expect the NTRC to generate more than US$12 million in testing and research expenditures within five years and create up to 183 new jobs in the local economy by 2020. In addition, NTRC will generate research and teaching opportunities for the Virginia Tech faculty.
The NTRC will house a newly designed force and moment machine, designed for passenger car, light truck and race car tires. The center will also incorporate the latest rolling resistance machinery (with a goal to develop a new passenger tire that will increase fuel economy by 3-5mpg), reproduce real-world emergency events, and improve highway safety.
Nor is the wind tunnel situation a closed book. There’s still an MTS rolling road balance in storage at the NASA ‘14x22’ wind tunnel (left), while preliminary engineering studies for an all-new facility are nearing completion. The dream is a state-of-the-art wind tunnel that could be sited alongside VIPER and the NTRC at VIR.
This article was submitted in September 2010