[Sutripta]

^^^
Hi,
By inherently unstable, I mean something else.

Assume (for simplicity) that the brake is exactly that - a brake. Its retarding torque is essentially independent of rpm.

Assume that the brake has been adjusted, engine at WOT, and rpm as desired. This means that the retarding force (brake torque) is exactly equal to the driving force (engine torque).
Now superpose a small perturbation. Say for whatever reason engine drops a few rpm. Immediately the torque produced is less than the brake torque. Which will cause a further drop in speed. And this will continue till the engine stalls. Similar reasoning (and maths) if the speed increases.
This reasoning will hold good as long as the load torque/ rpm curve is less steep than the engine torque/ rpm curve.

So how was the rpm held constant?

Regards
Sutripta

[sapl]

Originally Posted by Sutripta

^^^
Hi,
By inherently unstable, I mean something else.

Now superpose a small perturbation. Say for whatever reason engine drops a few rpm. Immediately the torque produced is less than the brake torque. Which will cause a further drop in speed. And this will continue till the engine stalls. Similar reasoning (and maths) if the speed increases.
This reasoning will hold good as long as the load torque/ rpm curve is less steep than the engine torque/ rpm curve.

So how was the rpm held constant?

Regards
Sutripta

I understand your point. The fact remains that with the primitive control systems that were prevalent, you had to live with the speed accuracy that those systems could achieve. The only job of the person managing the brake control was to be as responsive as possible to vary the braking to hold the rpm as constant as possible.

Obviously the quality of the tune and the accuracy of the readings were far less that what are achievable today.

Even today if you go to the heat power labs of engineering colleges, you may be able to see some brake drum engine dynos in operation.

The brake consists of a drum with a flat belt around it. (Older ones even had a rope!) One end of the belt/rope is connected to a spring balance and the other to an adjustable screw. You tighten the screw to increase the load and loosen to lessen the load.

"Those were the days..."

For a more technical description of such dynos, please see

http://nptel.iitm.ac.in/courses/IIT-...gy/pdf/4_4.pdf

Regds.

[Sutripta]

Originally Posted by sapl

The only job of the person managing the brake control was to be as responsive as possible to vary the braking to hold the rpm as constant as possible.

Obviously the quality of the tune and the accuracy of the readings were far less that what are achievable today.
So you are saying it was entirely dependent on operator skill, not an aspect of machine design?


Even today if you go to the heat power labs of engineering colleges, you may be able to see some brake drum engine dynos in operation.

The brake consists of a drum with a flat belt around it. (Older ones even had a rope!) One end of the belt/rope is connected to a spring balance and the other to an adjustable screw. You tighten the screw to increase the load and loosen to lessen the load.
Band brake. Very powerful, highly nonlinear. Very difficult to fine control.

For a more technical description of such dynos, please see

http://nptel.iitm.ac.in/courses/IIT-...gy/pdf/4_4.pdf

Regds.

Thanks for the link. But nothing of interest to our discussion there. Basic stuff.

Regards
Sutripta

[sapl]

Well the old machines were indeed completely dependent on operator skill.

It is possible that some designs would have had a watts type governor too adjust the band brake tension to maintain the rpm, but I have not come across any literature or seen one.

I would think thaat if at all there was a mechanism to automatically regulate speed,it could have been a centrifugal watts type governor with appropriate reduction through linkages to adjust the band.

I agree band brakes are completely non linear and difficult to adjust.

Before electronically controlled dynos cams, the dynos were basic and the paper for which I sent you a link just about describes the dynos of the day.

All they could give you was a force reading on the band. The torque and the power had to be derived mathematically using this figure.

Regds.

[Arjun Reddy]

What BHP is it that your ride has on paper and what are the actuals.

Was at Race Dynamics headquarters at Bangalore yesterday and put my Fiat Punto Multijet 76 Hp on the DynaRD 400.

Karthik one of the Directors of RD was around with what looks a laptop from another planet and a million other things and was more than enthusiastic to put the car up on the dyno.

The car has already been fitted with the Diesel Tronics from RD when it had covered around 10k Kms. The car has now covered 48k Kms.

I am attaching the graph for both the torque and BHP figures and will wait for the experts to comment on.

Power 0 is the stock mode.
Power 1 is the P1 mode on the Diesel Tronics and
Power 2 is the full power mode on Diesel Tronics.

The Fiat generates around a max of 68 BHP in stock form at the wheels against the 76 claimed by the Fiat.

In P2 mode the car almost generated 80 BHP at the wheels.

The balance I guess is lost in transmission and other factors.

What was astonishing is the torque generated in the P2 mode compared to the stock mode at around 3000 RPM. I guess this is where the RD Diesel Tronics comes into play and makes city driving such a pleasure.



Pls note that the test was conducted with no aerodynamic assistance and the figures might vary based on road conditions.

Over to the experts.



Mods: pls merge if such a thread already exists.

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