Extending Land Vehicle Fleet Life
CHRIS MACLEAN
© 2009 FrontLine Defence (Vol 6, No 6)

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The ECASS Difference
A short little ride in a ­passive suspension HMMWV (humvee), on the test track shown below, almost ended FrontLine’s plans to video a demonstration of L-3’s new suspension system.

We arrived at the RCMP test facility in Ottawa’s east end, on a sunny November day. Snow had fallen on the previous day’s demonstrations, but this sunshine resulted in lots of mud for us to slosh through during our demo – great fun for drivers Cedric and Dan (who moonlight as engineers for L-3 Electronic Systems).
 
Passive Suspension
Robert Matthews of L-3 Electronic Systems provided some background information before we got into the first humvee. Current vehicle suspensions in Canadian military vehicles are the conventional “passive” systems – this means shock loads are partially absorbed by the suspension system and the rest is passed into the vehicle. This, of course, causes tremendous wear and tear on the vehicles, not to mention the soldiers themselves, depending on how extreme the terrain is or the speeds with which they must be traversed.

As vehicle weight is increased (from up-armouring for example) a passive ­suspension system transfers more of the shock load directly into the vehicle. This affects everything in contact with the vehicle – the driver, passengers, mission equipment and the vehicle structure itself.

Increased payload from up-armouring or other additions also results in a certain lack of stability because of the higher centre of gravity. This factor may have contributed to some of the LAV rollovers that have been experienced in Afghanistan. To mitigate this, safety restrictions have been imposed on tactical fleets, forcing drivers to reduce speeds and exercise extreme caution when driving in unfamiliarly terrain. They are advised to avoid turret operations and restrict manoeuvers while on the move, which significantly limits tactical options.

During today’s L-3 demo of the passive system, Veronica, FrontLine’s videographer, was strapped into the back seat of the humvee. The intense shaking of the vehicle (the word ‘vibration’ doesn’t come close to describing the intensely jolting ride that Cedric subjected us to) shook screws and other pieces right out of the video camera. My SLR camera also plunged from my grip to the floor and it was all I could do to pin it against the door with my foot to avoid further damage – reaching down was out of the question (check out video footage on our web site). I can only imagine the physical effects of having to drive this vehicle, albeit not often in quite this bad of terrain, for the number of hours our soldiers must travel during missions.

Vehicle wear and crew fatigue clearly pose both safety and combat ­performance concerns. Industry has been diligently working on solutions to reduce some of the worst effects, and military groups have taken notice. The Electronically Controlled Active Suspension System (ECASS) is designed to easily scale from light to medium wheeled tactical vehicles and tracked combat vehicles.

Shock loads transferred into the vehicle, by passive systems, significantly increases life cycle costs, especially during high operational tempo in difficult terrain. According to L-3’s research, military vehicles subjected to rough terrain can require significant repairs as often as every 5,000 miles.
 
Active vs Semi-Active
The fully active system differs from semi-active suspensions in that the ECASS involves separately powered motors that dynamically raise and lower the vehicle’s wheels during operation. In both passive and semi-active systems, the force of a vehicle impacting an obstacle is dampened by the shock absorber. Semi-active systems can vary their dampening rate, however, the principle of dampening shock impacts remains the same. As these semi-active systems only dampen shock loads, body roll and shock is still transferred into the vehicle, with the accompanying center of gravity shifts, rollover risks and increased vehicle wear.

According to Scott Memmer, a Tech Center vehicle specialist in the USA, “an active suspension system has the capability to adjust itself continuously to changing road conditions. It ‘artificially’ extends the design parameters of the system by constantly monitoring and adjusting itself, thereby changing its character on an ongoing basis. It’s schizophrenic, if you will, but with a purpose. With advanced sensors and microprocessors feeding it information all the time, its identity remains fluid, contextual, amorphous. By changing its character to respond to varying road conditions, active suspension offers superior handling, road feel, responsiveness and safety.”

He goes on to say a “passive system cannot compensate for situations beyond its design parameters, thus shock absorbers bottom out, struts overextend, springs get sluggish and torsion bars get tweaked.”

 
 
Active Suspension Solution
An active suspension system replaces conventional shock absorbers with powered actuators at each wheel station. An L-3 Electronics Systems whitepaper explains the ECASS as “a three-axis sensor package [that] detects vehicle pitch, roll and yaw motions, and sends commands to the appropriate wheel station actuator to dynamically position the wheel in both jounce and rebound to keep the vehicle body level and to minimize shock loads transferred into the vehicle.”

The proven theory is that keeping the vehicle level will eliminate center of gravity shifts, improve overall stability, and thus reduce vehicle rollovers.

Active Suspension Advantages:

  • Reduces vehicle roll-over by eliminating adverse center of gravity shifts that accompany body roll.   
  • Minimizes shock and vibration failures of the vehicle, mission equipment, and system components.   
  • Reduces crew fatigue.
  • Restores Payload capacity, lost to inherent and supplemental armour, while maintaining vehicle stability, ride quality and mobility.   
  • Improves tactical agility through restoration of vehicle manoeuverability and performance in urban, off-road, trail, and cross-country operations.    

Testing of the L-3 System
Showing great interest, the Marine Corps Warfighting Lab asked the Office of the Naval Research to sponsor testing of L-3’s Electronically Controlled Active Suspension System.

According to the L-3 whitepaper, the “Nevada Automotive Test Center (NATC) recently completed performance and durability testing of an L-3 configured USMC “fleet” M1043, with a placard gross weight of 10,500 lbs, that was MAK-armored and pay-loaded to 14,500 lbs. The final test report was released in February 08. The current production model M-1151, ECASS equipped HMMWV, completed a second round of durability testing at NATC in March 2009, to validate the initial Life Cycle Cost data collected conducted in Phase 1 testing.”

ECASS Stability
For the safety and security of our soldiers, the ability to provide a stable platform for driver control and weapon operation while on the move is a capability that should receive top priority. This stability factor will offer soldiers a buffer from the jarring effects of difficult terrain, and will improve the effective operation of communication, sensor, computer and medical equipment while on the move.

Even though we kept pace with Cedric’s “passive” vehicle up ahead, the second half of the demo, in the ECASS-equipped armoured humvee driven by Dan, was quite safe for Veronica’s video camera. Not only did it remain intact, I was able to write in my notebook – unthinkable in the previous vehicle. The claim that the ECASS stablizes the operating platform and provides a consistent ride quality was impossible to refute.

Just like cell phones and unmanned vehicles, I predict it won’t be long before we wonder how we ever operated without fully-active suspension systems.

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Chris MacLean is the Editor-in-Chief of FrontLine Defence magazine.
© FrontLine Defence 2009

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