Lol. There are clutches within the gearbox. However, the main
connection between the engine and the gears isnt the clutch like
the manual gearbox, but rather, the torque converter. And its
impossible to stall an auto vehicle unless the gearbox is gone
case. The solenoid/mechanical valves will downshift in a manner
that the engine's rpm is ALWAYS higher than the output speed. Even
if the output speed is higher than the engine's rpm, the engine
will not stall.
Lets take this for example: A fan(A) blowing a max speed at about
1800rpm against some fan blades(B). The B started moving and spins
at 1600rpm(due to power loss, their speed will NEVER be the same).
However B is attached to this high speed motor. Now B is turned by
the motor at 2000rpm, however, A remains at 1800rpm. I dont know
how to explain this physics and mechanics behind these, but its
nearly impossible to stall an auto vehicle.
Another scenario is , vehicle's tire loss traction and gained
traction suddenly. In a manual vehicle this normally leads to a
engine stall. My cousin last time park car in carpark encountered
this situation, and his engine ALWAYS stall, due to drivetrain
system shock when the tires gained traction suddenly, which the
engine isnt designed to withstand. Try taking a VO3x on svc 25, 22,
etc. when they enter AMK Int on a wet day.
There this row of steel gratings on the road which becomes
extremely slippery when wet. So whenever it rains and the VO3x
slowly enter, the bus will stall abit when the driving wheels went
over these gratings as the tires spin uncontrollably. However when
the tire hits the concrete surface the tire is forced to slow down
to normal speed ALMOST instantenously. In a manual vehicle this
would have stalled the engine. However, in a VO3x, theres a strong
rattling coming from the engine and drivetrain, which i know it
suffered some shock within the system.
The lock-up clutch connects the gearbox and axle when the bus
gets up to speed.
This way saves fuel and cuts efficiency loss of the torque
converter to zero upon connection.
Ever heard of the VOs or MKIVs whose lock-up clutch has been
disabled? That's what you were referring to. Utterly horrible to
listen to. And no...its not 1800 and 1600, the difference is really
more in the range of 2100 and 1700 for VOs.
Yes. You can stall the auto bus if the clutch doesnt react to
road conditions fast enough. I've experienced that on emergency
brakings for buses twice already.
The VOs at AMK won't stall bcos by default, the clutch for the
ZF4 usually disengages rather early, unlike the later generation
gearboxes which emphasise engine braking, the application of which
is only possible because of the presence of the clutch. You can't
do that with a torque converter only auto vehicle. Personally I
don't like the use of engine braking for the new buses, they make
for jerky and noisy rides, especially for the already jerky
K230UBs, but they reduce the reliance on contact braking, together
with the retarder. But I'm also pretty sure we'll be seeing higher
incidences of worn-out clutches, so that should negate the
advantages somewhat.
