Recouping wasted mechanical energy?

[Snowy]

BMW has a system called"efficient dynamics" that includes what seems to me to be a very mild hybrid system. It includes a heavy duty alternator that charges the battery only when the car is braking, coasting, or decelerating. You can feel the mechanical resistance (kind of like mild braking) when the alternator kicks on. My understanding is that BMW also installs a higher capacity battery to store the energy for use while the alternator is not running.

RVs, being heavy, seem like an natural place to install some sort of way to recuperate energy when stopping or coasting. We already have under-hood alternators and large house battery banks. It seems to me (maybe i just don't know any better) that all that would be necessary to be more recuperative in energy production would be to engage the under-hood alternator when coasting or stopping and disengage it when you apply gas (just like my car). Is there an output from one of the chassis systems that can tell an alternator to disengage when the gas pedal is pushed and engage when the driver takes their foot off the gas to coast or brake?

Does anyone know of anyone pursuing such technology for RVs?

Is there a way to DIY this?

Thanks.

[avanti]

The OM-651 4-cylinder engine that was available on the Sprinter for a few years starting in MY2014 has such a system. There are special sensors on the chassis battery to measure current and other parameters, and the ECU does the kinds of energy-saving things that you mention. These features are pretty common on modern vehicles. I am sure that the new Sprinter will have such.

The downside is that these systems make it increasingly problematic to attach external coach loads to the chassis electrical system. Coach batteries, etc, tend to confuse the ECU. This is one reason why the upfitters are going to second engine alternators--they allow the two electrical systems to be completely independent.

[Snowy]

avanti, you always make good, thoughtful posts...thanks. Perhaps I don't understand your answer. I was not thinking of using the chassis charge/battery system at all. Instead i was thinking of getting some output from the chassis and using that to modulate a second alternator.

[avanti]

Originally Posted by Snowy

avanti, you always make good, thoughtful posts...thanks. Perhaps I don't understand your answer. I was not thinking of using the chassis charge/battery system at all. Instead i was thinking of getting some output from the chassis and using that to modulate a second alternator.

Ah, now I see what were thinking. Sorry.

You could certainly do what you suggest. All the information you need is very likely available on the vehicle's CANbus. It isn't THAT hard to eavesdrop on the bus and figure out what you are looking for. One could start with throttle position, for example. I played around with our Sprinter's CANbus a bit. It definitely can be done. That plus an arduino could certainly control the second alternator. The Balmar regulator that folks use with the Nation's alternator has an input for this purpose, IIRC.

[peteco]

Originally Posted by Snowy

BMW has a system called"efficient dynamics" that includes what seems to me to be a very mild hybrid system. It includes a heavy duty alternator that charges the battery only when the car is braking, coasting, or decelerating. You can feel the mechanical resistance (kind of like mild braking) when the alternator kicks on. My understanding is that BMW also installs a higher capacity battery to store the energy for use while the alternator is not running.

RVs, being heavy, seem like an natural place to install some sort of way to recuperate energy when stopping or coasting. We already have under-hood alternators and large house battery banks. It seems to me (maybe i just don't know any better) that all that would be necessary to be more recuperative in energy production would be to engage the under-hood alternator when coasting or stopping and disengage it when you apply gas (just like my car). Is there an output from one of the chassis systems that can tell an alternator to disengage when the gas pedal is pushed and engage when the driver takes their foot off the gas to coast or brake?

Does anyone know of anyone pursuing such technology for RVs?

Is there a way to DIY this?

Thanks.

This would be a great way to setup a second alternator whose only job is to charge the house batteries. It could also disengage when the batteries are fully charged. Maybe such a control system already exists.

[booster]

The vehicle manufacturers are using that kind of system on most new stuff now. From all I have heard or read, the benefits are pretty small, but when you are trying to wring out every .001 MPG for CAFE compliance they do it, Probably lets them sell a few more poor mileage trucks, though.


One of the limiting factors of such a system, and a big difference when compared to a hybrid or full electric vehicle, is where the power is generated. The electric drive vehicles generate at the wheel motors, so they truly see all the available energy available because the are essentially connected to the ground. The alternator systems currently used, or the the one proposed, are on the engine so the power has to go backwards through the drivetrain to get there. By the time you look at the driveline parts in deceleration, you find lots of places to lose energy. The torque converter unlocks in deceleration and converters are designed to not be very efficient in backwards energy transfer by design to improve mileage and smoothness. Based on the engine braking we see in the newer vehicles, I think they are making the converters looser in backwards energy efficiency now than in the older ones, probably to improve mileage. When I let off the throttle on our Chevy, the rpm drop from power to coast is considerable. Of course, the only time you actually save any energy would be the amount of energy you would have used braking, you actually would not save anything just decelerating/coasting as you would be needing to add throttle sooner than if it was not charging.


It would be an easy thing to test, I think, as it could be done with a simple vacuum switch set to actuate only when deceleration level vacuum is seen in the engine. It could just interrupt the field of the alternator. A manual bypass switch on the vacuum switch would take care of getting back to full time charging. A concern may be having the alternator going on and off so much, especially if the batteries are pulling max output.


I think a smaller alternator that was run off the driveshaft like some of the rear axle lube pumps, might actually be a more affordable, simpler, thing to try as you get rid of nearly all the losses and you could run it off an air conditioner clutch which is designed to cycle a lot.

[booster]

[peteco]

Originally Posted by booster

Booster, when are you going to install this on your B

[booster]

Originally Posted by peteco

Booster, when are you going to install this on your B

I think I will leave this one to someone else


Based on how long our brakes are lasting, I don't think there is a whole lot of energy that would be available to justify the cost and hassle. Of course that is just a guess and I would certainly be interested in seeing one done!

[avanti]

It is true that the energy recovered by these systems is pretty small. However, they also improve perceived performance by off-loading the engine when the driver is trying to accelerate.