On 04/04/16 14:29, Roger Mills wrote:
On 04/04/2016 11:16, Dave Plowman (News) wrote:
In ,
Roger wrote:
On 03/04/2016 21:44, Vir Campestris wrote:
On 02/04/2016 18:01, Roger Mills wrote:
Of course there would. It would only be at its max value at the max
torque point itself - which may actually cover a range of speeds since
some engine torque curves are flatish rather than peaky at max torque.
We're talking about a dynamic rather than static situation anyway.
Acceleration is the RATE OF CHANGE of speed and is a continuously
variable function. If you're defining acceleration as a step change in
speed it's little wonder that you're living on a different cloud from
everyone else.

Maybe I need to change A1 for your benefit, thus:

A1: By using full throttle and allowing the car to accelerate over a
speed range which encompasses the max torque speed of the engine.
Maximum acceleration will occur as the engine passes through its max
torque point.

[In actual fact, it may not! As the car speed increases, the
aerodynamic
drag increases as the square of the speed. The effect of this -
which we
have so far ignored in this discussion - is that maximum acceleration
MAY occur slightly below the max torque speed because the increase in
drag may more than offset the increase in torque.]

I've given up on Plowman, he must be trolling. Or too embarrassed to
admit he's wrong.

Your A1 as it is written is perfectly true, but irrelevant for
performance.

Yes, I'm aware of that - and was simply trying to explain to Mr Plowman
that his assertion only applies if you restrict yourself to one gear.


If talking about the maximum accleration point in an engine's output over
its speed range, why would you not restrict it to one gear? Surely you
realise that what applies in one gear will also apply to another?

To get the greatest acceleration for a car you need to maximise the
amount of power that the engine generates.


Yes, indeed.

No it's ********. You need to maximise the torque. Not power.

You need to maximise the torque at the *wheels*. Don't forget, there's a
gearbox between the engine and the wheels. As you keep reminding us, a
gearbox magnifies the torque. But that comes at the expense of speed. So
- as should be obvious - you need a higher engine speed to maintain a
given road speed in a low gear than you would in a higher gear. And when
the engine is at its max power point you get the highest available
product of output speed and torque - which is what you want.


That's what I've been saying all along. That's why I gave
the example of using a continuously variable transmission to hold the
engine at its max power (*NOT* max torque) speed as the car accelerates.

Care to explain why a CVT holds the engine at maximum torque, then?


I'm not aware that it does. If I were to design one, it certainly wouldn't!

It's obvious when you consider that power = thrust x speed. At any given
speed, the higher the power the higher the thrust.

I've no idea what you mean by 'thrust' That's something usually
associated
with a jet engine. Power is a function of torque and RPM. And the higher
the power does *not* mean the higher the torque.


Newton's first law! A body remains at rest or moves at a constant speed
in a straight line unless acted upon by "forces".

In order to accelerate a car, you need an external force. That force is
imparted to the car through the contact patch. The torque imparted on
the wheels through the transmission manifests itself as a force at the
contact patch which tries to push the road backwards. But the road
usually wins, and pushes the car forwards instead. *That* is the thrust
to which I was referring.

And the point you and plowperson refuse to accept is that you will get
more thrust at the contact patch by running the engine at peak power and
using a deeper reduction ratio, than at peak (engine) torque with less
reduction ratio.


--
New Socialism consists essentially in being seen to have your heart in
the right place whilst your head is in the clouds and your hand is in
someone else's pocket.