Anyway, I think that the newer buses with Voith gearboxs tend to
suffer from turbo lag... I've noticed that when I take a SBS
Transit Citaro or Wright with Voith gearbox, as well as SMRT's MAN
A24 (SMB388S), they tend to acclerate slowly before the turbo kicks
in and the bus gains pickup... It is different when you take a ZF
Wright or a MAN A22.
Whenever I take a ZF Wright or a MAN A22, the turbo kicks in
almost immediately, so the bus gains pickup quite quickly,
especially when the BC presses the acclerator down hard. I'm not
too sure about the Enviros though... However, I do find it
interesting that the older Volvo B10M MK IVs gain pickup easily,
which questions why the newer buses cannot gain pickup faster
despite more horsepower. Note that SMRT's O405s and O405G work on
the principal of using the turbo to pickup quickly.
I suspect the older buses do not suffer from turbo lag as much
as the newer buses today (Voith Wrights and Citaros), which
explains why these older buses with lesser horsepower acclerate
faster than the newer buses... Not trying to sound like an expert
here, but I just think turbo lag is responsible for slower new
buses today.
the gearbox has no relation to 'turbo lag', although power
transmission through the gearbox (through its design philosophy and
implementation) can amplify 'turbo lag'.
the bigger suspect, i believe, is the engine torque curve.
'turbo lag' kicks in when the engines enter the max rev band.
Pull the D9B and D2066 torque curves off the internet and it
becomes apparent why 'turbo lag' sets in. In comparison, the
OM447/457 engines have a much flatter torque curve (that gives you
fairly consistent torque across a very wide band).
Strictly speaking, its NOT turbo lag but engine torque
mapping that gives a STEPPED rather than FLAT torquer
curve prior the max torque rev band.
to quickly and briefly answer the topic matter -
ZF - during takeoff, TC (torque converter) non-lockup multiplies
torque on 1st gear, which hence masks 'any 'turbo
lag'. multiple lower mechanical gears (1 to 3) favour
acceleration once TC lockup is achieved.
Voith - TC operation radically differs as TC is not directly involved in
takeoff, but instead multiplies torque to faciltiate takeoff via
closing clutch on first mechanical gear (zf gear 3 equivalent).
the higher staroff gear ratio, coupled with a closing clutch
amplifies 'turbo lag' as torque multiplication is consistant
across the rev bands.
PS: Voiths are VERY CAPABLE of torque multiplication, to
the point torque multiplication can be as high as 5x input torque
during takeoff.
