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Old 08-02-2022, 07:28 AM   #1 (permalink)
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MHEV retrofit - Motorhome

Hi all,

I've this idea for a more fuel efficient motorhome, and it has led me to a lot of places, including here for aero design and a hybrid drivetrain maybe?

Now, it seems like one of the big challenges of motorhomes besides being motorized bricks is that the drivetrain tends to be hugenormous because of the expected use and performance.

i'm looking at probably converting something like the GMC savana with a 4.3 since the 2.8 duramax is pretty pricey.

i've been reading on MHEV components that are 48 or 72 volts and it looks like many of the drivetrain components exist, but, i don't know how to get my hands on them without being an OEM

I feel like a P1/P4 combo would be pretty effective - giving me a start/stop and electric output axle, but, P2 is kinda enticing because it'd act as a motor assist and give engine brake regen in what seems like a relatively straight forward control scheme.

i haven't been able to find what i'm looking for online - i'm guessing it is a combo of my google-fu being weak and not using the right terminology.

The reason this seems to make sense to me a motorhome will have a relatively large house battery anyhow so the battery pack could probably pull double duty and possibly even work as a PHEV - charging when plugged in to shore power.

Thoughts?

thanks,

Jared

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Old 08-04-2022, 08:42 AM   #2 (permalink)
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a long wheelbase transit with the diesel cab/chassis looks like it is ~2000 - 2500 pounds as a rwd only, standard cab - the "light" class B transit based motorhomes are mostly 8000+ GVWR, granted they are figuring in liquid weights but even with large liquid storage tanks they add less than 1000 pounds total which suggests that easily the camper portion is 5000+ pounds.

now, most of them use similar construction on the exterior to what i'm proposing so, there aren't going to be amazing weight savings there - but, on the interior they tend to use traditional wood frame and heavy materials, which i hope to save on.

i'm hoping i can end up at ~6000-7000 pounds GVRW so not amazing savings. i think most of my best savings are going to come from aero.
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Old 08-04-2022, 08:49 AM   #3 (permalink)
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Most of your savings will come from aero. Chassis mods, not so much.
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Old 08-04-2022, 02:48 PM   #4 (permalink)
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Quote:
i'm hoping i can end up at ~6000-7000 pounds GVRW so not amazing savings. i think most of my best savings are going to come from aero.
The lightest structure possible is a geodesic dome. The trick is to fit into the box of allowable dimensions.



This could be built similar to the NASA van, with an overshell.
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Old 08-05-2022, 06:36 AM   #5 (permalink)
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I've been reading up more on integrated assist - i found a neat little write up about a study here:

https://www.epri.com/research/products/1008761

this is pretty much along the lines of what i've been thinking of - like the integrated assist from the insight, but, beefier for a larger vehicle.

now, this is 350V which is higher than i was hoping to work with - but the concept is the same (And i'm not completely opposed to it, just wary)

i'm also not really sure about the water cooling - it isn't something i've dealt with before in an automotive application so i'm not sure what needs to be done for sizing, routing, etc - though glycol is popular in HVAC so i should be able to figure that out.

Having a motorhome body should help simplify running the electrics and liquid lines as well, because i won't have to tuck them into the space that is available, i can make dedicated and accessible space. (pretty much picturing whatever the automotive equivalent of a pipe chase is..)

i'm having no luck finding anything by that model number presumably because it was developed for the program.

i also spent quite some time looking into hub drive motors yesterday - thinking an older chassis/cab would likely be rear wheel drive and this these might be able to be retrofit into the front hubs, but, it sounds like those are not ready for prime time - especially on wheels that steer, given some challenges with unsprung weight, longevity of the motor exposed to elements and robust water cooling that maintains flexibility for steering and suspension travel.

now, the unsprung weight thing is not something i fully understand, so, i may be able to overcome that to some extent, especially with using a heavy duty chassis, but, i suspect even if i were quality hub motors used are probably not particularly available, and the new ones that appear reputable don't publish a price which is almost never a good sign.

Is there a site like this one that is more focused on the electric side of things?

Also - i ran across several college or open source studies that talked about DIY-able hub motors, but, i was unable to find real specifics anywhere.. i dunno if my google fu is weak or if they are tight lipped?

Thanks again for listening to my rambling!

Jared
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Old 08-05-2022, 10:10 AM   #6 (permalink)
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Diyelectriccars.com?

Hub motors are still considered of flakey longevity and dubious handling effects.

300+ volts are in the range of standard 220 electric service since the 220 is RMS, peak is about 340
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Old 08-10-2022, 02:18 AM   #7 (permalink)
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Quote:
Originally Posted by Piotrsko View Post
Hub motors are still considered of flakey longevity and dubious handling effects.
The handling effects would render it more tempting to fit the motors internally, in a way similar to how the front brakes of a CitroŽn 2CV were mounted. IIRC the BYD electric buses which were tested in my hometown had the rear electric motors mounted internally, one driving each rear wheel like hub-motors would.
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Old 08-10-2022, 09:34 AM   #8 (permalink)
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If they have massive bearings at both ends I have no difficulty. Bolting the wheels to an unsupported bell not so much.
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Old Yesterday, 07:32 PM   #9 (permalink)
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Hello Jerod,

In mild hybrids the electric motor is generally sandwiched between the engine and transmission or connects to the engine through the accessory belt. The way to get components is to look in junkyards or buy them as service parts from automakers. - you aren't going to get new ones from tier 1 suppliers.

I don't understand what you mean by P1/P4 and P2.

I have 2 Chevy vans. The first is an 2004 Astro van with a 4.3L V6 and 4 speed automatic. I converted it to a campervan about 6 years ago and added 2 inches of lift. The 2nd is a 2011 Chevy Express 4500 with a 6.6L Duramax , six speed auto and an ambulance body. It is getting converted to an RV.

I spent some time thinking about how to make the Astro a hybrid and the easiest way I could think of was to connect the electric motor through a 4x4 transfer case. The 4.3L was used for a bunch of 4x4 or AWD applications so a 4x4 transfer case is cheap and easy to find and bolts right up. Attach the electric motor of your choice to the output spline of the transfer case and you have a hybrid.

I'm not good at coding or controls so I was thinking of a simple stand-alone system to control the electric motor with an off-the-shelf controller and a simple lever for throttle. Push it forward and you add electric power, center is nothing, pull it back for regen. I'd add a gate to the shifter lever so the lever couldn't be accidentally knocked out of neutral.

Engage 4x4 and put the transmission in neutral and you could run the vehicle at low speeds on electric power alone without turning the engine.

Engage 4x2 and the vehicle runs just like stock with the electric motor disconnected from the transmission.



The concept of unsprung weight is pretty simple when you break it down. Sprung weight is anything on the body side of the suspension's spring. Unsprung is anything on the wheel side of the spring. The actual suspension components are partially sprung but there is no need to complicate things when talking about hub motors.




EDIT: XL Hybrids has a hybrid conversion for the Express / Savanna

https://media-exp1.licdn.com/dms/ima...sRs1Qqxu1fgenw


Last edited by JSH; Yesterday at 07:42 PM..
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Old Today, 07:04 AM   #10 (permalink)
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Quote:
Originally Posted by JSH View Post
Hello Jerod,

In mild hybrids the electric motor is generally sandwiched between the engine and transmission or connects to the engine through the accessory belt. The way to get components is to look in junkyards or buy them as service parts from automakers. - you aren't going to get new ones from tier 1 suppliers.
yeah, i'm finding that. i was hoping that having a big 10 university email and hinting that i might be doing research persuade them to discuss, but no bueno so far.

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Originally Posted by JSH View Post

I don't understand what you mean by P1/P4 and P2.


Quote:
Originally Posted by JSH View Post
The 2nd is a 2011 Chevy Express 4500 with a 6.6L Duramax , six speed auto and an ambulance body. It is getting converted to an RV.
i'm actually thinking of the same basic idea - trying to find a suitable donor.

I was really looking for something like a Trans Van, but so far they've all been in pretty poor shape so i think it is time to abandon that idea.

Quote:
Originally Posted by JSH View Post
I'm not good at coding or controls so I was thinking of a simple stand-alone system to control the electric motor with an off-the-shelf controller and a simple lever for throttle. Push it forward and you add electric power, center is nothing, pull it back for regen. I'd add a gate to the shifter lever so the lever couldn't be accidentally knocked out of neutral.
it sounds like you might not have to have any kind of manual interface - a lot of parallel systems seem to just "do their thing" with a throttle input that it sounds like can be captured from the OBD2 port. then it could be full time electric assist - ala honda insight integrated motor assist.

Quote:
Originally Posted by JSH View Post
EDIT: XL Hybrids has a hybrid conversion for the Express / Savanna
been trying to get ahold of them too

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