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by **The7** » Tue Sep 25, 2007 9:24 am

Engine braking in car = regen braking in ebike!?

Engine braking is not permitted for trucks (over a certain weight) for long decending downhill. Why?
If so, should we use regen braking in ebike? Why?

by **safe** » Tue Sep 25, 2007 10:00 am

The7 wrote:Engine braking in car = regen braking in ebike!?

Engine braking is not permitted for trucks (over a certain weight) for long decending downhill. Why?
If so, should we use regen braking in ebike? Why?

I proved over in the Induction Motor Braking thread that if you want to equal the braking force of high quality disc brakes (that can skid the tires) you would need to be able to create a regenerative braking force of:

:arrow:

8 horsepower

The problem is that the laws are designed so that the maximum forward motion force is supposed to be 1 horsepower. So you have a factor of eight difference between the way the motor is supposed to be designed for forward motion verses how the motor needs to work in braking motion.

So I just don't see regenerative braking as a serious idea... you could recapture a sliver of energy if you regen as you go downhill, but it's not a really powerful braking force... at least not compared to something that can skid the FRONT tire. (the rear tire can often skid at very low braking forces because the weight gets shifted forwards)

The permanent magnet type of motor has a higher intitial braking force, but it ends up becoming somewhat of a constant.

Here's a thought.... what if you could somehow "downshift" your permanent magnet motor so that it's forced to overrev WAAAAAAY past it's no load peak area. That way the motor is being slowed down by the permanent magnet backemf. While at low speeds the permanent magnets backemf would only be 1 horsepower but if you could seriously overrev the motor (like 3-4 times) then the back emf would shoot through the roof...

by **Rassy** » Tue Sep 25, 2007 7:48 pm

The7 said

Engine braking is not permitted for trucks (over a certain weight) for long decending downhill. Why?
If so, should we use regen braking in ebike? Why?

I think "unmuffled" engine braking is not allowed because it is a noise maker. I.e., it has nothing to do with safety and is usually posted in populated areas.

IMO regen braking on an ebike is a great thing to do. I am just watching for a good and inexpensive way to deal with the electricity produced.

by **OneEye** » Wed Sep 26, 2007 10:12 am

That's what I thought, too, Rassy. You WANT trucks to be able to engine brake on the long hills, it saves the brake pads from overheating and failing or locking up. The Jake Brake is quite noisy though, so populated areas will often post no engine braking as you move through the city/town.

by **The7** » Wed Sep 26, 2007 10:32 am

Wonder if there is any safety issue of engine braking for trucks besides noise?

by **OneEye** » Wed Sep 26, 2007 11:03 am

Primarily it's an engine/transmission wear and noise issue. Using the jake brake is safer as it leaves the regular drum & disk brakes cool and ready for use. As friction brakes heat up they provide less braking power.

In this white paper (from Australia) they are discussing whether the safety risk of PROHIBITING engine braking in certain areas is acceptable. The underlying (unstated) assumption/fact is engine brakes are a safe option, particularly for long downhill decents.

http://www.ntc.gov.au/filemedia/Reports ... an2006.pdf

4 Contribution of Engine Brakes to Safe Braking

4.1 General Considerations

Auxiliary brakes can contribute to both road safety and transport efficiency by taking the load off the service brakes. The safety implications of operating a vehicle with and without an engine compression brake will be assessed.

by **fechter** » Wed Sep 26, 2007 12:31 pm

On steep grades, the friction brakes on a large truck can easily fade and result in a runaway. Using the engine brake allows the friction brakes to cool and regain their effectiveness (or prevent them from getting hot in the first place). Noise is the main problem as far as I can tell.