Beyond leaf springs: it doesn't matter if they're used in the most mundane of cargo roles, or as a platform for the latest high-tech electronic equipment, the vast majority of military trucks remain a relatively crude and technology-free zone.

However, things could be changing. With the experience of two Gulf wars and numerous ongoing global peacekeeping style deployments supporting those arguing for a more sophisticated logistic supply train, technology is all but assured a place in the next generation of trucks. And it should not be overlooked that more than ever armed forces are--voluntarily or otherwise--fielding equipment that complies with civilian legislation; legislation that can only be met by employing technology.

Without doubt, leading the field in the search for military-suitable technologies that will enhance the performance and maintainability of the next generation of military trucks are the Americans. The Operational Requirements Document is currently being drawn up for the Future Tactical:Fruck System (FTTS), a proposed two vehicle modular family that will replace the HMMWV, FMTV Hemtt, PLS (in certain echelons), and all remaining M35, M809 and M939 series trucks. The FTTS-UV (Utility Vehicle) will replace the HMMWV, while the FTTS-MSV (Manoeuvre Sustainment Vehicle) will replace all other types. Current funding has the FCS first fielding in 2012.

A major goal for the FTTS is to extend average operational range from the current 300 miles to 600 miles per vehicle, but with no increase ill fuel payload. The reasoning behind this goal becomes clear when it is realised that 70 per cent of the logistic burden on a battlefield is fuel, and that fuel delivery can cost between $ 30 (by Hemtt tanker) and $ 400 (by CH-47, as in Afghanistan) per gallon.

Going Hybrid

Conventional drive train technology alone will never provide close to the required savings, leaving truck manufacturers to look elsewhere for answers. This usually means hybrid drive systems, normally involving electric power. That said, the US Army's Tank Automotive Research Development and Engineering Centre (Tardec) is currently evaluating a Stewart & Stevenson FMTV fitted with a hybrid hydraulic drive system supplied by Permo-Drive of Australia.

Options for the more technology mature hybrid electric driveline are extensive and a feature in their own right, but common benefits associated with this type of drive are: greater fuel economy and reduced emissions as the engine can run at peak efficiency, a reduction in unladen weight due to the replacement of heavy, complex gearing systems with high power density electric drives and improved mobility brought about by the torque delivery characteristics of electric motors, with mobility being further improved by utilising individual wheel motors that provide a torque-managed traction control system. Furthermore, having dual-function engine/generator powerpacks gives hybrid electric designs the option to furnish power to service mobile or stationary battlefield electrical requirements, in some situations negating the need for separate field generators. Additionally. when the vehicle brakes, electric drive motors become generators and provide reverse torque, not only replenishing any energy storage system but also reducing brake wear by over 60 per cent.

Britain's QinetiQ (formerly Dera) was awarded a 40-month contract by the British Ministry of Defence, DEC (Director Equipment Capability) in August 2002 to fully evaluate hybrid electric drives for military applications and a concept demonstration/evaluation Hybrid Electric Demonstrator (Hed) is currently under construction. QinetiQ has developed sophisticated simulation models which allow control systems to be developed for managing traction distribution to individual wheels as well as the relative power flows between generators and batteries. QinetiQ is integrating all of the power system components with its vehicle management unit and the drivers' display panel.

Trials are due to commence in September 2004. The vehicle is being designed to mirror the mobility footprint of QinetiQ's earlier High Mobility Demonstrator (HMD), which will serve as a reference vehicle for the hybrid design.

Twin Volkswagen diesel engines of 80 kW each will power an electric generator providing direct power to individual hub-mounted electric drive motors each capable of delivering 50 kW of continuous power, 100 kW peak. Having no gearbox, transfer box, propshafts or drive axles, the hybrid, as a straight diesel-electric (no battery pack), will weigh 2.93 tonnes less than the HMD, even with a 214-litre increase in fuel capacity.

Diesel-electric vehicles have been around for some time, large quarry dump trucks being a prime example. However, it is only recently that technology has allowed for the development of smaller more compact military suitable motors, and units capable of providing sufficient power to at least equal the power-to-weight ratio for high-mobility classification in contemporary vehicles are now available to fit the standard 20-inch (50.8 cm) military rim. 25-inch (63.5 cm) wheel rims will be fitted to the Hed, allowing combat vehicle power-to-weight ratios to be achieved.

While capable of operating as a diesel-electric, QinetiQ's Fled will be fitted with a battery system, initially high temperature nickel sodium chloride. The addition of batteries to a diesel-electric driveline gives a further increase in economy and reduction in emissions, brought about by stored battery energy eliminating or reducing transient loads being transferred to the engine. Additional power becomes available for burst acceleration and so on, plus there is an ability to drive stealthily off-road or operate battlefield equipment in a 'silent watch' mode.

Battery technology has improved over recent years, however concerns do remain within most military circles regarding their susceptibility to environmental extremes, weight, management and to some extent, end-of-life disposal. QinetiQ opted for a nickel sodium chloride solution as this type of battery is not adversely affected by environmental temperature extremes, is reliable, cost effective and has the required power-to-energy balance for truck applications. Weight of the batteries is approximately one tonne.

Military vehicle manufacturers looking at hybrid electric drive solutions specifically for wheeled vehicles currently include AM General, GM Defense, Oshkosh Truck Corporation and Stewart & Stevenson.

Shown in 1998, the first hybrid electric Hummers were developed by PEI Electronics. Under a contract awarded by Tacom in May 2002, AM General is currently acting as systems integrator for eight prototype vehicles. It is understood that if the technologies are proven the US Army could request between 15,000 and 20,000 (but no more than 20 per cent of the fleet) hybrid electric Hummers, primarily for their power generation and stealth characteristics.

Call on Cells

In January 2003, GM Defense unveiled a hybrid electric militarised Silverado pick-up (the base for the LSSV (Light Service Support Vehicle)). This vehicle was also equipped with a five kW proton exchange membrane (Peru) regenerative fuel cell system auxiliary power unit (APU). When the vehicle is driven, the Pem electrolyser uses diesel engine-provided electricity to break down water into hydrogen and oxygen, with the hydrogen stored for later use. Later, and with the engine switched off, the stored hydrogen together with oxygen from the air is then fed into the fuel cell to produce electricity, returning pure water as a byproduct. The water is stored allowing the cycle to be repeated. Fuel cells for military vehicles remain some years away. and questions still remain as to whether they can offer any real benefits.

Stewart & Stevenson has produced three hybrid electric FMTVs. The first was in conjunction with Lockheed Martin. the second in conjunction with BAE Systems. Both were series hybrids. In a series hybrid the diesel engine turns the generator, the generator powering the electric motors, there being no mechanical transmission linking engine speed to road wheel speed. The third vehicle, in conjunction with Allison, was a parallel hybrid. In a parallel hybrid both the diesel engine and electric motor can provide propulsion power, both being connected directly to the transmission.

For its hybrid work Oshkosh has opted for ultra capacitors and not batteries for energy storage. Ultra capacitors have the benefit of providing a lot of power over a short timeframe, unlike most batteries that tend to store more energy, but release it at a lower power. Stated benefits for ultra capacitors include the ability to be fully discharged during vehicle maintenance, they are environmentally friendly, resistant to temperature extremes and contain no precious metals, so should have no associated cost premium. Other benefits include weight: there being a four to five times saving over lead acid batteries for comparable applications. Ultra capacitors will also survive many more charge cycles than lead acid: the life of the vehicle, as opposed to an average of three years. Nickel sodium chloride batteries of the type to be fitted to the QinetiQ demonstrator should also last the life of the vehicle.

On a negative note, the limited energy storage capacity of ultra capacitors restricts stealthy or 'silent watch' applications to minutes, opposed to potentially hours with batteries.

Proposed fuel savings for hybrid electric drive systems vary widely depending on who answers the question. With most engines using less than 20 per cent of their available horsepower when highway cruising, the savings in long haul work are clearly limited. However, once off-highway and in an environment where the engine is working far harder and power levels are varying considerably, between a 20 and 50 per cent reduction in fuel consumption are regularly stated as attainable. Smaller horsepower engines can, in certain situations, be employed in battery hybrids for additional savings, the downside of this being an underpowered vehicle when the batteries are exhausted.

With little exception, all diesel engines fitted to current generation trucks are of commercial design, the days of purpose-designed military special multi-fuel engines are gone. With fuel costs being the bane of a commercial operators' life. engine manufacturers are pushing technology to its limits to improve economy, so no significant breakthroughs can be expected in this area. The real problem facing engine manufacturers is making what are now sophisticated pieces of engineering with complex electronic management systems suitable for military applications, while still meeting emission standards.

To meet the North American EPA02 emissions standard introduced in October 2002, the majority of manufacturers adopted Exhaust Gas Recirculation (EGR) technology. This system is self-contained, primarily dealing with emission issues in the cylinder. However, as the exhaust gases require cooling, EGR requires a larger cooling system, with possible packaging implications for military applications. EPA02 is currently the most stringent emissions standard.

Equally as capable as EGR but with different characteristics is the SCR (Selective Catalytic Reduction) exhaust after-treatment route that most manufacturers (for the majority of engines) have selected in Europe to meet the October 2005 introduction of Euro 4. SCR works by injecting liquid urea (at around five per cent of fuel consumption) into the exhaust stream ahead of the catalyst, The resulting catalytic reaction releases ammonia from the urea solution that enables emissions (according to figures provided by Cummins) of nitrogen oxides to reduce by 30 per cent and particulate matter by 80 per cent compared to Euro 3 levels. A further major advantage of the SCR post-combustion process is that it can meet the projected Euro 4 standard with an engine running at Euro 1 emissions levels. This gives around a five per cent increase in fuel economy and ten per cent in power density (hp per litre) compared to the same engine running at Euro 3. On the negative side, militarily speaking-and packaging aside-is the support burden of yet another system employed purely for legislative appeasement and one that serves no useful military purpose.

Caterpillar. whose engines power the Oshkosh MTVR and the Stewart & Stevenson FMTV, has developed the Acert (Advanced Combustion Emission Reduction Technology), a system that combines both EGR and SCR technologies.

Sophistic electronics (despite their apparent shortcomings in the most hostile of operating environments) now control more and more functions on trucks. All modern engines are now so controlled, as are automatic transmissions, brakes and traction control systems, to name but a few. And there is more to come.

As part of the FTTS programme the US Army is planning to move away from its current four--level maintenance system to a two--level system, with the operator/maintainer being capable of carrying out 60 per cent of field maintenance tasks, the remaining 40 per cent being done at sustainment level. To achieve this each FTTS will be equipped with an embedded prognostic and diagnostic programme with read-outs for the operator. Integrated Electronic Technical Manuals (IETM) capable of audio and visual presentations will be used. as will 'plug and play' technologies on major components allowing for an innovative 'replace forward, fix rear' style of maintenance concept to be employed.

Some earlier generation systems requiring a laptop interface and with limited prognostic capabilities are already in use. Oshkosh's MTVR is fitted with the OBDS (On-Board Diagnostic System), while the FMTV A1 is fitted with Stewart 8,: Stevenson's IETM system. Oshkosh has also recently introduced Command Zone. a diagnostic/prognostic system based around multiplexing technology. Command Zone is fitted to the most recent wrecker variant of the MTVR that entered production in March 2003.

Rotary Valves

Rotary engines have been under investigation for decades now, with a view to eliminating reciprocating pistons. However, such engines never managed to provide durable results mainly due to sealing problems as experienced by many NSU Ro 80 and Mazda car owners. Rotary applications now have a tendency to be restricted to smaller engines such as those used to power drones. Another sector of an engine that could also see its reciprocating elements being eliminated is the cylinder head where the traditional valves could be replaced by rotary valves. Bocanegra Motor in Spain has recently demonstrated an engine that uses such an arrangement in which the valves, their rockers and rods are replaced by ported shafts. Because both ends of the ports are used alternatively, the shaft rotates twice as slowly as the camshaft it replaces, i.e. four times slower than the crankshaft. Another advantage of the set up is that the opening thus afforded is larger. It also allows for ideal timing in respect to the top dead centre position of the pistons and there are no restrictions on 'crossing' the timing since there are no valves to collide either with another or with the piston. Finally, the design requires no oil and is better cooled due to the fact that there is no constant exposure of the same surface with the chamber in the 'closed' position (in fact the unused face is enabled to cool). The absence of lubricant also reduces the pollution normally caused by worn valve stems or guides.

Bocanegra is also developing a 'flat-configured' engine that uses a linear transmission system that deletes the traditional crankshaft and therefore the propensity of pistons to 'ovalise' the cylinders.

Suspension

Suspension systems are an area likely to see considerable changes in the near future, with independent systems finally seemingly poised to make the breakthrough into heavier trucks they have so long been threatening. Since trucks first appeared on to the battlefield leaf springs have been the norm, and while having few moving parts to create major maintenance issues, it has long been acknowledged that the more complex independent suspension set-up does offer considerable mobility advantages. Ireland's Timoney Technology promotes its coil-spring independent system as offering (vehicle dependant) a two- to three-fold increase in speed across rough ground when compared to an identical leaf-sprung vehicle. Timoney suspensions have been fitted to numerous airfield crash tenders and armoured vehicles and have been fitted to two prototype Volvo 8 x 8 high mobility trucks, as well as being the original suspension fit for QinetiQ's HMD. The Timoney suspension has also been licence-produced by Arvin Meritor. However, it was Oshkosh who 'cracked' the military truck market with its Tak-4 system as fitted to the MTVR, currently in production for US and British armed forces.

The often stated weight penalty for an independent suspension set-up is a myth, the only current negative being one of cost: an independent set-up having a procurement cost premium of around 60 per cent per wheel. This premium is purely a volume issue and costs are likely to be comparable with leaf spring systems when mass production is achieved.

Certain Tatra trucks can be fitted with an independent suspension set-up, but one unique to Tatra, whose trucks feature a backbone torque tube-style chassis and swinging half-axle suspension system. On certain models individual half-axles are sprung by airbags with internal coil springs. Airbags, despite offering ride quality superior to even coil springs, have generally not proven ideal for military applications. Aside from vulnerability to damage issues, the concept of an airbag is generally not suited to the amounts of suspension travel required in a high mobility vehicle. However. Tatra has found the solution by mounting the airbags inwards and above the torque tube to minimise the risk of damage and in a position where small degrees of bag expansion/compression relate to high degrees of wheel travel.

QinetiQ's demonstrator will be fitted with air suspension, the hub drives allowing the air bags to be mounted high in the chassis, out of harms way and where the ratio of expansion/compression to wheel travel is favourable. QinetiQ has also developed a system that prevents bag deformation at wheel travel extremes. Without the restriction of conventional drive shafts total wheel travel has increased 15 per cent compared to the earlier HMD's independent coil spring suspension. A 400 kg weight saving has also been achieved.

The next improvement in suspension technology looks set to be active, or at least, semi-active hydragas strut suspension. A passive hydragas strut carries a premium of around $ 600 per wheel with a limited increase in ride quality compared to coil springs, but at a premium of around $1000 per wheel a semi-active system can be fitted. QinetiQ's HMD and Oshkosh's Hemtt ProPulse demonstrator are fitted with semi-active suspension, the benefits of which include ride-height control, self-levelling and lock when static, or on more sophisticated systems, self-levelling during travel. Fully active suspension with independent wheel control and the ability to automatically adapt spring rates to suit payload and prevailing road/terrain conditions is on the horizon for high mobility trucks, but the required software is not yet fully proven.

Believing mobility to be a major issue, for FTTS the US Army is looking at a potential increase between 50 and 100 per cent in cross-country mobility. A conventional leaf sprung vehicle has been modelled travelling at 25.7 km/h cross-country. Independent suspension increases that speed to 38.6 km/h, fully active suspension further increasing speed to 51 km/h. Active suspension can be fitted to beam axles and is not restricted to use with independent suspension set-ups.

In the future it appears that strategic mobility will be as important as tactical mobility and certainly with FTTS achieving the desired levels of strategic mobility it seems certain to push available technology, to the limit.

At present it is projected that the FTTS-MSV will be an LHS-equipped design with a required 1:1 payload to unladen weight ratio (the current Hemtt is around 0.6:1). The intelligent LHS will operate both as an LHS arm and materials handling crane. The system will also be capable of loading/unloading 20 ft ISO containers directly into/out of a C-130. The modular two-section flatracks will weigh one tonne (currently close to two tonnes) each section capable of carrying a 5.5-tonne load. The MSV will be capable of carrying an eleven-tonne payload on and off-road, but must be air transportable by C-130 with a 5.5-tonne load. Unladen it must be capable of transport underslung by a CH-53E helicopter, this to meet the US Marine Corps sea-basing strategy requirement.

The US Army is currently procuring matching trailers for its FMTV fleet, but in utilising trailers with tactical trucks is the exception to the rule since, as lift multipliers, trailers are often seen as parasitic mobility restrictors. FTTS-MSV will have a companion eleven-tonne payload trailer, but unlike current generation trailers it will be powered. Air transportability could be desirable, laden into a C-130 or high-capacity helicopter.

Propshaft drive for trailers has been tried on several occasions but with limited success due to adverse effects on handling, leaving an extension of any hybrid drive system fitted to the prime mover as the likely option for any future driven trailer projects. QinetiQ recently concluded a programme for the Ministry of Defence that examined the benefits of driven trailers. A Leyland Drops 8 X 6 logistic support truck was modified to provide hydraulic drive to its companion Drops trailer.

Multidrive in Britain has approached the truck/trailer mobility problem by the development of the Pulse Propulsion Trailer (PPT). Coupled to Multidrive's purpose-designed, four-wheel drive, four-wheel steer, Future Cargo Vehicle (FCV) an FCV/PPT combination can carry two 20 ft ISO containers, or 15 tonnes legally. The combination has a curb-to-curb turning radius of just 10.7 metres. The standard PPT incorporates the ability to load/ unload itself and the towing vehicle without the need for additional winches or cranes. It also has the ability to assist in the self-recovery of the towing vehicle, being fitted with a ground spade and hydraulic drawbar. The PPT will accept hybrid drive system. An FCV/PPT combination is currently on loan to the National Automotive Centre in the US.

Multidrive believes the FCV/PPT combination meets a large proportion of the emerging FTTS-MSV requirement, and in conjunction with technologies from the company's Flex Frame concept is currently bidding (teamed with Stewart & Stevenson and QinetiQ) for part of the FTTS development programme.

While appearing to be a truck/trailer combination at first glance, the Flex Frame concept is in fact that of an articulated combination that allows movement between its two sections within three planes while at the same time transferring drive to the rear section. The basic design leverages Multidrive's experience with ADTs (Articulated Dump Trucks), but unlike an ADT (or the tracked Alvis Hagglunds Bv 206) the Flex Frame does not steer by articulation, steering being achieved in a conventional manner and by the front axle of the tractor section. The two sections can be split in less than 30 minutes.

I.C. Young inputs from Eric H. Biass