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An intelligent idea
02-JAN-2006

How stored hydraulic power could cut fuel costs in waste collection

Can new waste collection vehicles be designed
to offer real environmental advantages while actually saving money? An Ohio-based
company is about to start marketing the Intelligent Hydraulic Drive system,
which claims to do just that.

Should we look for revolutionary new technologies to improve the environmental
performance of the transport market or more incremental improvements on what
we already have? This argument is at the heart of the hybrid drive debate. A
diesel power unit is still the most fuel-efficient method we have of shifting
loads of anything from just the few tonnes right up to the 10, 20 or more tonnes
expected from a refuse collection vehicle (RCV), recyclable materials unit or
a refuse bulker. And that situation looks set to be the case for at least a
couple of `vehicle generations¿ ahead. In a global waste market that expects
a `vehicle generation¿ to last at least eight years and quite possibly 10 or
more, that¿s surely a good enough reason to continue to try and improve fuel
efficiency.

A key area of exploration has been the idea of matching up diesel power with
electric motors and/or battery packs. Indeed, a number of `hybrid¿ solutions
are already in limited production. But despite the use of phrases such as `zero
emissions¿ by the proelectric vehicle lobby when promoting battery electric
power as the only true path to `environmental righteousness¿, the electric vehicle
is handicapped by the weight, performance limitations and initial cost of batteries.

A SIMPLE ALTERNATIVE

How about a diesel or petrol engine driving a charging system that can, when
required, turn into a means of propulsion? The idea of a regenerative braking
system, where the energy normally lost when service brakes are used to slow
a vehicle is instead converted back into stored power, starts to make sense
on any commercial vehicle engaged on constant stop¿start operations. One thing
is certain ¿ apart from a city bus, an RCV is required to stop and start more
than any other commercial vehicle.

You might not have previously seen any synergy between a vehicle used to pick
up waste and one used to pick up people, but the similarities have not been
lost on suppliers such as Mercedes Benz and MAN. Mercedes drew on ideas from
the passenger coach sector for the design of its Econic range cab, while the
new MAN TGA low-entry cab can be specified with an automatic ZF gearbox, which
features a system known as `bus brakes¿. These bring the vehicle to a controlled
halt as soon as the driver¿s foot is removed from the accelerator.

To those, we can now add another major supplier ¿ automotive industry component
supplier, Dana Corporation. What Dana refers to as Intelligent Hydraulic Drive
(IHD) combines many of the arguments above. But unlike the electric hybrid alternatives,
IHD has been designed to be mechanically simple without being too bulky or weighing
any more than necessary. And the system is robust enough to stand everyday use
without constant servicing or downtime. On the face of it, Intelligent Hydraulic
Drive could have been made for waste sector applications.

MADE FOR WASTE APPLICATIONS?

It might come as something of a shock to learn that it wasn¿t. What started
out as an idea called `regenerative drive system¿ by designers working for a
specialist Australian company, Permo-Drive Pty Ltd, ended up being licensed
for production as an emergency power booster for military applications by the
Dana Corporation, based in Ohio, US. And if you can¿t readily see any connection
between the demands of the military and the need to keep our planet free from
garbage, then neither could I. But as I¿ve recently discovered, Dana¿s product
specialists did spot the wider benefits for civilian applications, and as a
result, a whole new set of operational benefits are about to come your way.

So how does IHD work? Why would you want to specify it on your next generation
of RCVs? The theory goes something like this. An RCV, especially on domestic
household collections, spends most of its time accelerating and braking. This
translates into increasingly expensive fuel costs and higher-than-average brake
repair costs compared with other truck-related operations. Add in the fact that
many cities around the world are suffering increasing traffic congestion, while
the authorities are demanding greater efficiency from their staff, yet also
want to be seen to be reducing emissions. Suddenly, the energy lost by heavy
braking becomes worth reclaiming. Especially as it¿s `for nothing¿ ¿ except,
that is, for the cost of the system needed to reclaim it.

`That¿s why we see Intelligent Hydraulic Drive as being so suitable for waste
collection applications,¿ explains Edward J. Greif, Vice President of IHD Products
at Dana Corporation. `We estimate that the payback time on waste collection
vehicles will be within two to three years.¿ Payback? Yes, that¿s the exciting
bit; according to Ed and his team, here¿s an environmental solution that claims
to actually save money. And to prove it, I was recently invited to try out a
prototype unit at a Dana Corporation test track facility deep in the Michigan
countryside.

It works like this. After starting out from the depot, the IHD system is `charged¿
by the regenerative braking effort created when the vehicle is brought to a
halt from around 30 miles/hour (50 km/hour). As Edward Greif explains, while
exhaust brakes are now a standard option on most truck chassis, turning the
engine back into a `pump¿ merely wastes the energy even though it saves on service
brake wear.

In contrast, IHD stores that braking energy in an accumulator until the power
can be utilized as a boost to the truck¿s normal diesel engine. So IHD in effect
`pumps¿ that reserve power back into the truck¿s driveline as the driver hits
the accelerator again ¿ see Figures 1 and 2.

While the system in its current form is basically a `one shot¿ system that¿s
either switched on or off, it does put back a significant proportion of the
energy scrubbed off when braking. It¿s not only the energy that¿s `for nothing¿,
because IHD also does the job of a retarder. Thus, a retarder doesn¿t need to
be specified with IHD ¿ giving a cost saving.

SWORDS INTO PLOUGHSHARES

In military applications, two options are available. When getting a laden vehicle
moving away from the rest mode, the extra power can be switched in to provide
a seamless boost to the tractive effort of the diesel engine. Alternatively,
the power can be used instead of full diesel power. In other words, in this
`conservation mode¿, the IHD electronics signal back to the truck¿s diesel injection
system that something less than full throttle is required.

This saves on fuel and increases operational range, while delivering the same
performance as the truck engine would normally provide on full throttle.

So if that¿s the theory, what¿s IHD like in practice? This project is so new
that it has not actually been fitted to any RCV yet; only three IHD systems
currently exist, all based on military truck-based prototypes. I was lucky to
be given full access to one of these ¿ a fully loaded 6 x 6 truck of the Austrian
Steyr design, now built under licence of Stewart & Stevenson of Sealey, Texas,
for the US military.

This might appear to have nothing in common with a typical RCV, but with some
300 horsepower driving through an Alison World Series transmission, it soon
became clear that while the application differed, the value of IHD suited both
applications perfectly. My mission was to simulate a series of stop¿start manoeuvres
around the test track in `supplementary mode¿, while trying out the `power boost¿
application when approaching steep slopes on awkward terrain.

IHD stores the braking energy until the power can be utilized as a boost to the truck¿s normal diesel engine

With IHD activated, we¿re talking about fuel savings estimated at up to 30%,
a virtual doubling of available engine torque up to 30 miles/hour or 50 km/hour
(by which time the accumulators will have been discharged), and a reduction
in brake repair costs that could be as much as 75% of current costs on drum-braked
trucks. All this is in exchange for a current payload penalty of less than 500
kg.

On the units produced to date, the electronics and what Dana refers to as
the `hydraulic service module¿ (the accumulator assemblies and related components)
are fitted behind the truck cab, storing hydraulic pressure at 5000 psi (240
kPa). These are connected by hydraulic hose connections to the regenerative
drive system (a hydraulic motor) inserted into the truck driveline. This offers
both a `drive¿ capability under acceleration and provides the regenerative braking
effect to `charge¿ the accumulator on deceleration.

My test vehicle was fitted out with a whole computer screen full of dials to
help me understand what was actually happening. As most waste collection operations
are done in something of a hurry, I was immediately amazed by how much energy
is wasted under braking even from as slow a speed as 30 miles/hour (40 km/hour).
With the IHD system `charged¿, we also need to accept that full power is nearly
always used to get the vehicle rolling again in a low gear ¿ even in urban areas.
In conservation mode, it was interesting to see how the fuel flow was dramatically
cut back as the hydraulic power from the accumulator was fed in. It might not
be `perpetual motion¿, but assuming each start was preceded by a charge-inducing
stop, that extra power was available automatically each time the accelerator
pedal was pressed. And if it wasn¿t? Well, it wouldn¿t matter. The truck would
just perform normally until the system was ready.

Though the need for a military vehicle to escape hostile fire (by moving away
from an incident as fast as possible) might not have a direct parallel with
a RCV, it could be argued that the power boost mode gives the driver an opportunity
to benefit from a short burst of power that might otherwise cause driveline
damage such as lugging at low revs. In this mode, the test truck sprinted up
to 30 miles/hour (40 km/hour) fully loaded in less time than would have expected
of an unladen vehicle. Typically, in addition to the extra torque, it is claimed
that IHD delivers upwards of the equivalent of extra 160 horsepower on demand.
This has a real safety bonus when lifting the laden vehicle out of deep wheel
ruts of the kind likely to be found on a landfill. The power delivery was from
almost zero revs and felt like a giant, invisible hand pushing the vehicle from
behind.

SUMMING UP

Intelligent Hydraulic Drive isn¿t going to dramatically change the way in which
RCVs work in the future. But the fact that it won¿t require extra design resources
(it can be easily retrofitted onto existing chassis) is a major advantage. But
unlike earlier ideas on dual-fuel vehicles, if something goes wrong, the whole
vehicle won¿t be unserviceable ¿ see Figure 3.

If there is a shortcoming, it¿s that in its current form, IHD doesn¿t enable
a diesel RCV to enter a low- or zero-emissions zone and work by switching over
completely to hydraulic drive. At present, there¿s only enough stored energy
for `one hit¿ and the diesel engine remains running at all times. Specialists
at Dana feel that a fuel saving in a stop¿start cycle is the best way forward
rather than opting for a greater capacity of stored power. This might enable
the vehicle to work with the diesel engine switched off ¿ though this is an
option on a project for lighter gross weight vehicles.

The future looks bright ¿ partly because IHD works, but also because it turns
a resource that would otherwise be wasted into a saving. If it really can repay
its installation costs within less than half the lifetime of the base vehicle,
as Edward Greif insists it can, I¿d say opting for IHD when it becomes available
(prices haven¿t been fixed yet) would be a pretty intelligent idea for a sector
where recycling is a core value.

The next phase involves equipping a number of RCVs with IHD customer demonstrations.
The process will start within the next 12¿18 months in the US, where commercial
waste haulers will be looking for cost savings. It will also involve units working
for local authorities in Europe and the Pacific Rim markets, where reduced fuel
costs and environmental gains are the priority.

 

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