I have found that the THD102KF isn't as good as previous
generations. The THD100D (used on Volvo B58s, B59s and early
model B10Ms) was the best.
In normal everyday traffic, how often does one push a bus engine
to 1,800rpm? The answer is generally rarely ever unless the
transmission is ill-suited to the task at hand. An engine
with high torque at low engine speeds as well as a suitable
transmission with suitable programming are therefore required for
good in-traffic acceleration characteristics. In order to
calculate the optimal up-shifting engine speed, it is necessary to
investigate passenger comfort levels (read: shifting comfort) as
well as specific fuel consumption of the engine at various
speeds. Up-shifting at 1,800rpm is unnecessary - operating an
engine at or above it's 'rated' speed (yellow to red on the
tachograph) results in high fuel consumption and unnecessary engine
wear. It is therefore wise to ensure that the engine operates
within its 'green zone' as much as possible. At the same
time, it is also unwise to operate an engine at speeds below the
'green zone', as again fuel economy, performance, engine life and
smoothness suffers. Allowing an engine to run below the
'green zone' also promotes 'hunting' - where the transmission is
constantly 'between gears' - resulting in poor passenger comfort
levels.
In order to understand why new buses may not perform the same as
older buses, it is necessary to understand the concept of torque
reduction. Many new engines are fitted with OBD (On-Board
Diagnostics) systems that monitor the health of the engine as well
as the exhaust output. In order to guarantee low emissions
levels, some engines are 'cut back' at low speeds under full
load. If the OBD system detects an engine fault, the torque
output of the engine is also reduced. From experience, newer
buses require more frequent servicing to ensure reliable
operation.
Remember, official engine power and torque figures are
measured under ideal circumstances.
As above, there are more variables than you think. Modern
buses, with all their creature comforts, safety and emissions
control gear will almost always be significantly heavier than
previous generations of buses.
Regards,
Dave
The THD102KF is more fuel efficient and torquey than the THD101.
I draw my comparisons purely from driving experience. It was
also quieter and briskier, though now age is starting to show in
most THD102.
I have not had the chance to get behind the wheel powered by a
THD100. I have got behind a B57 with an Allison box.
Please describe to me about the THD100?
It is true that most drivers, even myself drive along the green
band. But there will be times high acceleration power is
needed; heavy load and taking on a steep slope. What most city
drivers need is acceleration, even braking effect and a firm
steering. These features will greatly reduce driver fatigue.
Except for current generations of buses with Euro IV or V
engines which are paired with closely spaced gears, there was no
difference in the ZF gearbox used in the THD101 and THD102. Even
the Nissan Diesel U31 of 1980s uses the same ZF4HP500 (correct me
if I am wrong).
I will love the hear more of your sharings on the newer Euro V
engines. You must have kept abreast on the developments over the
years.
