australian-motor

am GP Tech
cn Honda’s RC212V gearbox
story ben Purvis
Photography gold & goose and ben purvis
seamless
n
tra siti n
Seamless-shift gearboxes will appear in roadbikes by 2012 –
the technology straight off Honda’s RC212V MotoGP machine
amcn /70
1
1. Darren Mescall operates a
small hand-wound model of the
seemless-shift transmission
2. First gear fully engaged – notice
the left dog teeth merging with the
bullet ring
3. Second gear fully engaged –
notice bullet ring on right
now fully engaged
2
3
H
onda’s 2011 RC212V MotoGP
bike was already looking hard
to beat even before the first
round of the championship,
with all fingers pointing
towards the firm’s ‘mystery’
seamless-shift transmission system as the
reason for the bike’s new-found pace.
While details of Honda’s gearbox are still a
closely guarded secret, several experts have
suggested that British gearbox specialists
Zeroshift could be behind the technology. So
we thought we’d pay them a visit to see just
what’s going on and discovered that, far from
being a purely race-oriented technology,
seamless-shift gearboxes are on the verge of
appearing on production machines.
Although confidentiality agreements
mean Zeroshift won’t mention the names of
the companies it’s working with, it’s clear
that Honda’s MotoGP transmission, which
is estimated to be worth between 0.3 to
0.5 seconds per lap, is either a Zeroshiftdesigned system or something very similar.
More surprising is the fact that, far from
being a race-only set-up, Zeroshift says
its already working with more than one
major manufacturer with the intention of
introducing exactly the same technology
on production bikes.
Zeroshift design engineer Darren Mescall
said: “We’re just on the verge. It’s taken
five years to develop an operating system
and in the last year we’ve had at least two
customers who are willing to go further.
They’re in the late prototype stages, so
they’re testing at present and, certainly by
the end of the year, we should have a large
announcement to make to say ‘we’re going
into production’.”
So it appears that seamless-shift
gearboxes will be in showrooms soon, maybe
even as early as next year, but what are they?
Whenever you change gear – regardless of
how fast you do it and whether or not you use
the clutch – you’re disengaging one gear and
creating a momentary gap in power delivery
before the next ratio is engaged.
Basically, for a brief moment, your bike
is free-wheeling. If you’re accelerating
that means there’s a moment where the
acceleration stops, resuming again when the
next gear takes up drive. If you’re changing
down it means you’re losing the enginebraking effect for a moment. On the road it’s
relatively easy to paper over these cracks in
power delivery with a bit of deft clutch and
throttle control, but that’s not addressing
the basic problem – and on the track those
moments with no power add up over a lap,
resulting in a significant loss in pace.
Seamless-shift transmissions solve the
problem, switching between ratios without
ever cutting drive to the rear wheel.
how it works
There are several firms developing seamlessshift transmissions but Zeroshift’s design is
probably the best contender for use in bikes
thanks to its ability to replace a conventional
transmission with minimal changes to the
transmission casing or the gear linkage.
Taking just two gears as an example
– say first and second – both can spin
freely on the output shaft of the gearbox
and are permanently meshed with their
counterparts, which are firmly fixed to the
input shaft. On a normal “dog” gearbox,
a “dog ring”, sliding along a spine on the
output shaft, sits between the two gears.
Slide it one way and lumps on the side of the
adjacent gear (called “dogs”) will engage
with matching notches in the dog ring, so the
dog ring locks the gear to the output shaft.
Now the input and output shafts are both
spinning; you’re in first gear.
Slide the dog ring the other way and
another set of dogs engage the second gear
ratio. In between will be a space where the
dog ring can spin, engaging neither gear –
the “neutral” position.
Zeroshift’s system allows the changeover
from one gear to the next without having to
go through that neutral position.
Between the gears it has two bullet rings,
each holding three bullets – specially shaped
dogs that can engage onto teeth on the sides
of the gears. To select first gear, one ring is
moved until its bullets hook onto the drive
teeth on the side of first gear. The second
ring is then moved the same direction, its
bullets filling in the gaps between the teeth
so there’s no slack, or backlash, if you
come off the throttle.
The clever bit is that this second set of
bullets isn’t under any load, the ring holding
them can be easily slid across towards the
second gear. Because second will be turning
faster than first, the teeth on the side of
that gear will hook onto the dogs, in turn
accelerating the output shaft’s speed. The
bullets that were taking the load from first
gear will therefore be unloaded and the ring
holding them will be able to slide across,
taking up the backlash on second gear.
Don’t worry if you don’t get it – if you need
to see how it works there are animations on
the Zeroshift website that make it clear as
day (www.zeroshift.com).
Mescall said: “One of the major benefits
is that not only is it seamless on an upshift,
for acceleration, but also during a downshift,
which is critical for fast cornering or late
braking. You can even change gear midcorner without upsetting the vehicle.”
71/ amcn
Neutral selected, with first gear about
to be engaged
All three bullet teeth now meshed with
first gear
Drive continues to first gear as the
bullet starts to move in readiness for
the second gear selection
Bullet has now reached second gear ring,
however drive continues to be transferred
to first gear
Second gear has now been fully engaged
with first gear bullet now merging into
second gear ring
One of the major benefits is that not only is it seamless on
an upshift, for acceleration, but also during a downshift
What are the
advantages?
Of course, having the ability to change gear
without any loss of drive is a serious bonus
– as shown by Honda in MotoGP. But it’s by
no means the only thing that the Zeroshift
transmission has got going for it.
Another is the system’s versatility since it
gives manufacturers the option to introduce
automatic gearboxes or semi-autos with
minimal expense or complexity.
Mescall said: “We have various options,
for an automated or manual system. That’s
the beauty of having low actuation forces.
“A lot of motorcycle riders want to be
able to feel the mechanical connection,
to feel the gear changing, and we can still
maintain that with this system, using just
the power of the rider’s foot to change gear.
“With systems that are automated, you
can take the element of rider error out of
1
2
the equation, so you have advantages of
safety, fuel economy and emissions.
Bill Martin, managing director of
Zeroshift, adds: “What you get from it is the
benefit of an automatic bike if you want it.
You just put it in ‘drive’ – and most people
probably would just do that, even if they
think they’d prefer to use the manual mode.
You know on cars they often have paddles
on the steering wheel to change gear? Most
people use those for the first two days, then
they just rely on the fully automatic mode.
“The performance is there. The fuel
economy gain is there. You’re always in the
right gear if you put it in ‘drive’. It’s good for
emissions and it’s good for the stability of
the bike – you’re not interrupting the
torque so you’re less likely to lose
control during a shift.
“You can operate it
via shift by wire,
with either no
clutch lever
or with a clutch-by-wire system, and that
means there’s no way of damaging the
system – the software protects it regardless
of what the rider does. Better for the bike
owner, and better for the manufacturer
and their warranty.”
Martin is keen to point out that, while
the attention might be on racing and highperformance bikes, even scooters could
benefit from the system.
“The belt CVT system is not efficient,”
Martin says. “We’ve heard figures ranging
from a 20 percent loss to a 35 percent loss.
That’s simply not sustainable. Switching
over from CVT to seamless shift means
it’s basically the same experience for the
scooter rider, but with 20 percent more
acceleration and 20 percent less fuel
consumption. And made in big enough
numbers we may be able to bring the
price down to match the cost of a CVT.”
In terms of how much the
system will cost
Main: The componentry is
very similar to a standard gearbox
1. Stoner’s Honda has been a
revelation with the gearbox technology
2. A digital diagram showing
first gear on the left, second on the right
when added to a bike, as usual the defining
factor will be the level of production.
“If it’s an extra, and a niche extra, then
it’s always going to be more expensive,”
Martin says. “But if that’s the only way the
bike comes then it’s going to be the same
price as the bike used to be.”
Scooters may be something that
the future holds for Zeroshift, but if a
production machine appears in the near
future it’s likely to be something more
expensive – probably a superbike or
a tourer. Client confidentiality means
the firm can’t name which companies
are experimenting with the system, but
Zeroshift is expecting at least one of the
manufacturers to make its involvement with
the company public before the end of 2011.
What’s wrong
with a dual-clutch
gearbox instead?
There is, of course, one bike already on the
market that offers many of the advantages
amcn /72
First gear has been fully disengaged, with
second gear now transmitting all the power
of a seamless-shift gearbox – Honda’s dualclutch, semi-automatic VFR1200F.
The dual-clutch box is derived from
similar systems that are already proving
popular in cars. It is effectively like having
two gearboxes. The first has its own clutch
and deals with 1st, 3rd and 5th gears. The
second, again with its own clutch, deals with
2nd, 4th and 6th. That way two gears can be
engaged simultaneously and shifts up or
down the ’box are done by disengaging one
clutch and engaging the other.
Sounds simple(ish), but it does add a
fair bit of complexity, including the need
for hydraulics to actually shift the gears
and some very sophisticated electronics
to make the transition between the two
clutches as seamless as possible.
While it works, and works well, Honda
hasn’t been able to transfer its dualclutch transmission to MotoGP thanks to
regulations specifically banning the use of
dual-clutch gearboxes. They don’t, however,
ban seamless-shift transmissions. That
instantly gives Zeroshift an advantage, but
so does the relative simplicity of its system.
Mescall says: “A lot of manufacturers like
the fact it’s not too dissimilar to a standard
gearbox. It’s not completely unknown
territory. It uses the same manufacturing
principles, the same actuation principles
and the same assembly principles.
Manufacturing-wise, it doesn’t deviate from
standard production methods.”
Riders may well feel the same way.
Zeroshift’s ability to provide seamless
shifts while still having the option of being
mechanically operated – you can still use a
foot lever, physically shifting the gear drum
just as on a conventional bike, and you can
still use a conventional clutch – might give
it another advantage: that of familiarity.
It’s clear that whatever seamless-shift
transmission Honda is using in MotoGP, it’s
operated just like a normal transmission,
adding fuel to the speculation that there
may even be some Zeroshift internals hiding
inside those HRC cases.
With announcements about production
Zeroshift machines expected before the end
of the year, it’s unlikely Honda’s secret will
remain under wraps for very long.
73/ amcn