Truck & Off-Highway Engineering - February 2022 - 21

ORIGINAL EQUIPMENT
" Once you play around with the methodology to
get the lowest possible weight, you can then
manipulate where you apply that weight to
take best advantage. "
pack, some competitor vehicles would
need a 400-kWh battery pack.
" We have spent a whole host of time
looking at the best possible build methJohn
Randerson,
Mellor Bus chief
technology officer
for the Woodall
Nicolson Group.
something that is entirely different, "
Randerson said. Entirely different in this
case includes the design, appearance,
size and battery capacity of the vehicle,
while maintaining a competitive range.
Lightweight build methodology
" If we can make this vehicle 3-tonnes
lighter than competitor vehicles of the
same size, then what can we do with
that 3 tonnes? " he said. " Well, it's what
you don't do with it; you don't carry it
around day after day, night after night,
charging it up. " Randerson noted that
while the new Sigma 10 range is powered
with a 210-kWh CATL battery
odology for these vehicles, " he said.
" Already within the business, we use
quite exotic stainless steel throughout
the construction of our existing vehicles,
and the same is used in the Sigma
range. I would say for the past 20 to 30
years, larger buses have used aluminium,
quite a lot of it and structural stress
panels. This build is entirely different in
that we use an integral stainless-steel
welded fabricated structure, which although
it is stainless steel, there is less
of it and it saves weight.
" The chassis technology uses exactly
the same methodology, " Randerson
continued. " You'll see on these vehicles,
there is not just a decorative finish on
the outside - that is indeed carbon
fiber. The floor structure is not a traditional
18- or 15-mm birch-faced plywood;
it's a composite and it's one that
we have been using in our vehicles for
probably the last 10 years. We have actually
got such a degree of experience
in how to do this from the smaller buses
that we've been able to adapt and
tweak it into these kinds of platforms to
make them as light as possible.
" You take those three items and we
save weight significantly, " he said. " We
go out of our way to fit lightweight
seats, we've got 17.5-inch alloy wheels.
Once you start on that journey towards
light weight, a 17.5-inch tire and alloy is
a lot lighter than a 22.5-inch or a 19inch,
so there is an increasing payback.
If you don't need an eight-tonne rear
axle, you need a six-tonne rear axle, it's
a lighter axle, it has a smaller motor, so
the payback from just some, on the face
of it, minor tweaks to a build methodology
and a body design continue right
the way through. "
The front axles on Sigma 8, 9 and 10
models all are rated at 5.5-tonnes
(12,125 lb). " It's far lighter than an
8-tonne [17,637-lb] axle. So, once you
play around with the methodology to
get the lowest possible weight, you can
then manipulate where you apply that
weight to take best advantage, "
Randerson said.
Mellor Bus has adopted a similar approach
to the drive axle. Sigma 7, 8 and
9 models will be driven by a Dana eaxle.
" The 10 and 11 will use a ZF portal
rear axle with a traditional short propshaft
and motor setup, and the Sigma
12 is different again in that it will have a
ZF hub drive, " Randerson said. " So, we
have selected the best possible solution
for each of the applications, instead of
saying, 'We have an axle, we can buy it
in volume, it goes in everything.' "
The vehicles will be equipped with a
A CCS-type charging socket enabling DC charging will allow a Sigma 7 to be re-charged in about 1.5
hours and a Sigma 10 in 2.25 hours.
TRUCK & OFF-HIGHWAY ENGINEERING
CCS-type charging socket enabling DC
charging. This will enable a Sigma 7 to
be re-charged in about 1.5 hours and a
Sigma 10 in around 2.25 hours. Mellor
Bus quotes a range of about 160 miles
(257 km) on a full charge.
John Kendall
February 2022 21

Truck & Off-Highway Engineering - February 2022

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