Adding rear hub motors to a fwd gas powered vehicule ?

Jeff23spl

10 mW
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May 22, 2023
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Quebec
I was looking at possible use of hub motors to put in the rear of a front drive thermal car to make some kind of hybrid.
Using both energy to take off at a red light, use electric around town and run on gas for the highway.

Qs motors seem to have 12kw nominal hub held by a single shaft that could make a somewhat easy install.

I wonder what would happen to a bldc motor if you pull it with the thermal engine at higher speed than it is made for.
Assuming the bearing and rotor can handle that speed, what would happen electrically when we go above the kv RPM ?
Let say for exemple: the hub spec claim it can reach 100-120kmh with a standard 17inch tire but if the ice engine bring it up to 140-145kmh, what would happen ?
 
I would avoid hubmotors in the wheels. I think this is a good idea. Dodge made a successful prototype when there was talk of all vehicles switching to 48V instead of 12V. Of course it didn't go into production.

I'd like a temporary AWD on occasion if I was stuck in slippery conditions. I now believe the best candidate would be a small and light vehicle that can be bought as FWD or AWD. Then you take the FWD version, remove the rear suspension assembly, and swap-in the rear differential from a salvaged AWD.

In theory, all the parts should bolt right up. I'd get th 102V system and motor from a wrecked Zero motorcycle to hook up to the rear diff.

I believe the Toyota RAV has a FWD version plus an AWD version, and the mix of parts should work. It may be possible for an AWD version to simply have the driveshaft removed to disconnect the front transmission from the rear differential, but I fear the stock ECU and other sensors would not function because of the electronics for traction control and ABS.
 
I was looking at possible use of hub motors to put in the rear of a front drive thermal car to make some kind of hybrid.
Using both energy to take off at a red light, use electric around town and run on gas for the highway.
What's a "thermal car"? The only direct reference I found online in a quick google search uses the phrase but does not explain it even by implication or context.

If it is a specific model / brand of car, knowing which one you have will help us help you find a specific solution.




Qs motors seem to have 12kw nominal hub held by a single shaft that could make a somewhat easy install.

QSMotors is one of a number of companies that make hubmotors for cars that could bolt to the existing spindle mounts or have the spindle mounts adapted to do so. Some examples
Etc.

You'd need to know the specifics of your vehicle's design to determine which option is easiest to setup for it and/or best suited to it.

You'll also need to know how much power it will take to do the job you want it to do. You can use various simulators and calculators around the web to guesstimate that, given the specifics of your job and your driving conditions.


I wonder what would happen to a bldc motor if you pull it with the thermal engine at higher speed than it is made for.
Assuming the bearing and rotor can handle that speed, what would happen electrically when we go above the kv RPM ?
Let say for exemple: the hub spec claim it can reach 100-120kmh with a standard 17inch tire but if the ice engine bring it up to 140-145kmh, what would happen ?

A motor is also always a generator. The reason it will only spin up to a certain speed at a certain battery voltage is that the BEMF (generated voltage from spinning) reaches the same as the voltage from the controller, so no more current flows. (simplified, it's more complicated than that)

So if the motor, under the voltage you will run it at, can only reach a certain speed, and you then go over that speed by whatever means, the generated voltage (BEMF) is now higher than the controller's voltage, and the controller's FETs will uncontrollably act as a three-phase rectifier*** and begin feeding current back into the battery (uncontrollably charging it even if it is already full****), which creates drag in the motor and braking action on the vehicle. This also creates significant heat as in *** below.


***If the BEMF is higher voltage than the FETs can handle, they'll fail, usually failing shorted and suddenly braking the motor, causing significant heat in the motor, it's phase wires, the FETs, etc., which can quickly damage more things, and probably vaporize the FETs (which removes the short and releases the braking action and stops the heat), destroying the controller.


****If the battery has a BMS that is capable of detecting this condition, and disconnecting the battery from the controller under HVC conditions while charging is occuring, then it will protect the battery, but then the voltage on the controller FETs will spike way beyond what it had been as the load is removed by current flow ceasing, and then the above *** scenario will probably occur even if it hadn't been a problem before disconnect.

So I'd recommend ensuring your electric system can achieve the same speeds as any other system, and any downhill runs you have, might potentially achieve.

If you can't do that, I'd recommend setting up a system (contactors, etc) to shutdown the controller and disconnect the phase wires of the motor from the controller before you attempt to acclerate beyond the limits of the electric system.
 
I would avoid hubmotors in the wheels. I think this is a good idea. Dodge made a successful prototype when there was talk of all vehicles switching to 48V instead of 12V. Of course it didn't go into production.

I'd like a temporary AWD on occasion if I was stuck in slippery conditions. I now believe the best candidate would be a small and light vehicle that can be bought as FWD or AWD. Then you take the FWD version, remove the rear suspension assembly, and swap-in the rear differential from a salvaged AWD.

In theory, all the parts should bolt right up. I'd get th 102V system and motor from a wrecked Zero motorcycle to hook up to the rear diff.

I believe the Toyota RAV has a FWD version plus an AWD version, and the mix of parts should work. It may be possible for an AWD version to simply have the driveshaft removed to disconnect the front transmission from the rear differential, but I fear the stock ECU and other sensors would not function because of the electronics for traction control and ABS.
Why do you suggest to avoid wheel hub ? is it for the salt during winter ?

But yes, using the awd parts on a fwd seem a good idea. i agree you would need an older model that don't have stability control because usually there is no easy way to disable it. For ABS it could make the ecm go crazy if the rear wheel spin on a fwd during winter....At worse you can remove the fuse but you will get a code...

on a differential you could have a 2-3000rpm motor and be good to go but you would need a larger motor and controler to drive both wheel by 1 motor. Maybe not from an ebike parts source....Someday we may get salvaged ev part for cheap.

The other problem could be to keep it street legal...One could keep it quiet but if involved in an accident, it can be tricky too...
 
What's a "thermal car"? The only direct référence I found online in a quick google search uses the phrase but does not explain it even by implication or context.
I should have said a thermal combustion engine car (I.C.E.) or usual gas or diesel powered car.

Thanks for explaining the regen effect.
that was my assumption that something bad could happen but i wasn't aware of exactly what....
Is an ebike going downhill can run into the same issue with a non regen controler ?

So i would need either higher kv motor with less torque or a more powerfull drive train?
A 3phases contactor large enough to handle this won't be cheap/small.....(Above 500a price get expotential)

On the other hand, if i would couple an electric motor to a car rear differential, i could keep the electric clutch (visco coupler) that is sometimes in the back with the differential. This could be used to mechanoically disconnect the motor from the wheel at higher speed. This way, a small electric motor could be used to get temporary awd for winter but i would prefer to get one large enough to propel the car at normal speed for fuel saving.
 
yrs ago golden motor dot com had electric axles along with water cooled mid drive engines up to 20-30kw.
I dont remember what the width of the axle was, it could have been go kart track width, or suzuki sidekick/jeep track width.
I bet you could fab something up from a $100 Suzuki Sidekick/Geo-Tracker axle differential from the junk yard, weld on a big ass chained gear to the yoke and go from there.
 
Also lots of cars do similar right now, though they use an AC motor attached to a diff and not in-wheel hubs. The Mitsubishi Outlander's electric motor is the rear diff which allows for junkyard options.
 
The easiest way IMO is to add a small bldc motor to the front crankshaft pulley.
I have done it once on a small car, I'm thinking on adding one to my vw.

The next best way I have seen is to take something like a Audi quattro and replace the front gearbox with a fwd one, or weld the middle diff.
A 4-8kw bldc motor can be adapted to the rear diff without expensive metal fabrication.
 
The easiest way IMO is to add a small bldc motor to the front crankshaft pulley.
I have done it once on a small car, I'm thinking on adding one to my vw.
Do you have a thread on this somewhere? i'd like to see it.

My Mazda 2 achieves >50mpg on the regular but it could use a couple extra ft-lbs of torque down low.. i'd be interested in a low power crank or belt attached electric motor, versus who know what is required to get rear hub motors working.
 
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Do you have a thread on this somewhere? i'd like to see it.
I may have like 1 pic from the top of the engine bay somewhere, I'll see if I can find it.
It wasn't anything fancy, the original alternator was replaced with a 4kw denzel motor, it ran on a 48v battery with a dc dc for 12V
Problem was the inspection, customer got scared so we unmounted it and he hasn't reinstalled it since then.
 
I may have like 1 pic from the top of the engine bay somewhere, I'll see if I can find it.
It wasn't anything fancy, the original alternator was replaced with a 4kw denzel motor, it ran on a 48v battery with a dc dc for 12V
Problem was the inspection, customer got scared so we unmounted it and he hasn't reinstalled it since then.
So your option is more like a torque booster but the engine keep running at all time and the electric motor can follow maximum thermal engine rpm ? 4kw if designed to run 6-7000rpm at 48v it would mean just few pound of torque unless you send it 12-16kw for few seconds ?
 
I may have like 1 pic from the top of the engine bay somewhere, I'll see if I can find it.
It wasn't anything fancy, the original alternator was replaced with a 4kw denzel motor, it ran on a 48v battery with a dc dc for 12V
Problem was the inspection, customer got scared so we unmounted it and he hasn't reinstalled it since then.
I'd like to know more for sure.

Was this motor part of a kit, or something you cooked up as a one-off?
4kw ( ~5.3hp ) sounds pretty good to me considering i have a 106 HP motor. Almost a 10% power upgrade, lol..
 
My Mazda 2 achieves >50mpg on the regular but it could use a couple extra ft-lbs of torque.. i'd be interested in a low power crank or belt attached electric motor, versus who know what is required to get rear hub motors working.
not bad 50mpg since this car is rated far less than that. My original idea was to add hubs on the back off a mazda3 skyactive fwd.
My driving habbits are a bit more reckless to get first in front of a red light than making mpg reccords but i found the idea interresting enought to dig into it. It won't make a dragster but on a dayly basis against other economy car it could be fun.
For the 3, I would just need special designed spindell to replace the original ones to take motor shaft. The spindell bearing is held by 4 bolts making it easy to revert back if needed. Brake caliper and ABS sensor would need extra work too. A special disk and large wheel with low profile tire could probably make it.
i was checking 2x 12kw nominal motors that can peak at 24kw to add significan torque. Rated at more than 350nm that would mean an extra temporary 500 foot pound to the rear wheels. It lwould probably add an extra 30% initial torque (13.8:1 first gear with above 1500p/f) and once the second gear shifted at 8:1, the e-motor would keep helping but probably start to drop in torque by gaining RPM but overall it would reach a well faster 0-100km/h....And 24kw continius should be enough to move the car around town since factory EV seems to use 15-25kw to maintain 100km/h in general....
 
The Mazda 2 was totally misrated. I've been a hypermiler since 2008; and my top fuel economy record was 68mpg at 60mph over a long duration. Amazing car but needs some extra horsepower for sure. 1.5L motor and all.

The missing piece was a hybrid motor. Of course they made a hybrid for Japan, but not for the USA, because we don't buy fuel efficient vehicles over here.

12kw motors can peak higher than 2x their rating for a very short period of time. The advantage for a car would be that a lot of the electric motor power is made in the range where the gas engine is making very little, even if you weren't hot rodding the motor.
 
Was this motor part of a kit, or something you cooked up as a one-off?
It was off the shelf stuff like this Motor D5500
The throttle was cable actuated so we used a hall box similar to this: Throttle PB-6 Type 0-5V Hall Effect Throttle Box generic | eBay
Battery was made from a VW Passat GTE hybrid battery, about 4KWh were used.
The pulley used a classic V Belt, really easy to turn on a lathe.
Controller was from Aliexpress.

So your option is more like a torque booster but the engine keep running at all time and the electric motor can follow maximum thermal engine rpm ? 4kw if designed to run 6-7000rpm at 48v it would mean just few pound of torque unless you send it 12-16kw for few seconds ?
It sure is way simpler and cheaper! My custom solution cost less than $1K back then. I'm sure I could come close with some used parts.
The car was pretty light, less than a metric ton for sure.
I've looked into those QS hub motors and it's pretty dam expensive + lots of fabrication.
That's why I said the second best option (price/fabrication wise) would be a awd car that gets converted to fwd.
 
There's a couple of threads around here somewhere about an "altermotor" hybrid where someone is reusing one from a Buick or something like that. Was it by Elinx? I can't remember the right words used in it to find it in a search. :(
 
It sure is way simpler and cheaper! My custom solution cost less than $1K back then. I'm sure I could come close with some used parts.
The car was pretty light, less than a metric ton for sure.
I've looked into those QS hub motors and it's pretty dam expensive + lots of fabrication.
That's why I said the second best option (price/fabrication wise) would be a awd car that gets converted to fwd.
You are right. it is a costly projet to go with those Qs (about the price of the car if we add used batteries) but options seems limited in my area. I can go dismantle a used gas engine in a junkyard for few hundred bucks but they won't have salvaged EV yet.....i think most of them are sold to specialised shops that repair EV or some that swap expensives cars for $$$$. But it isn't a project i plan to start tomorow, i'm looking at options and when i will found one looking good enough, i will start.
Electric and mechanic stuff aren't a problem but i probably should find a local machinist friend that like projects and need an electric oriented buddy to exchange services....
The other problem is to get it approved by loacal agency. I should better stay quiet and manage risks of losses in a crash than trying to get it approved. I did just ask what it could involve to convert my other E-motocross project into an electric scooter (0-70km/h) and i got scared of all the requierements involved......
 
There's a couple of threads around here somewhere about an "altermotor" hybrid where someone is reusing one from a Buick or something like that. Was it by Elinx? I can't remember the right words used in it to find it in a search. :(
few times i did read about using an alternator as a motor, peoples were complaining about bad efficiency. is it when they try to re-use the wound rotor as is as a synchronous one or still after rebuildind/rewinding it? I'm curious because i have some and or it can be found for cheap.
 
AW is refering to a “altermotor”… a purpose designed dual function production unit that acts as an alternator and as a motor to add power ( usually about 15 kW) to the driveline when requested by the hybrid controls.
They are not modified alternators, but much more complex units normally operating at 48 v
GM used them on various. “Mild Hybrid” vehicles in the US, whilst VW, Audi, and Mercedes sold versions in Europe .
 
The "altermotor" I'm referring to isn't converted from an alternator, it's a purpose built system from Buick or some other car manufacturer I can't recall. There's at least two threads on it if I could find them.... :(
 
Over 10 years ago when we were racing buggies with VV motors I stuck an electric motor with a relatively small battery on one of the cars controlled by a button on the steering wheel. We were already pretty fast so only used on the start and when leaving corners when needed. Worked great until the other teams bitched about it. :mrgreen:
 
I was looking at possible use of hub motors to put in the rear of a front drive thermal car to make some kind of hybrid.
Using both energy to take off at a red light, use electric around town and run on gas for the highway.

Qs motors seem to have 12kw nominal hub held by a single shaft that could make a somewhat easy install.

I wonder what would happen to a bldc motor if you pull it with the thermal engine at higher speed than it is made for.
Assuming the bearing and rotor can handle that speed, what would happen electrically when we go above the kv RPM ?
Let say for exemple: the hub spec claim it can reach 100-120kmh with a standard 17inch tire but if the ice engine bring it up to 140-145kmh, what would happen ?

I has thinking about that idea too: 2-4 large, as in 5000W+ hub drives in car wheels would by far be the easiest to convert a car to electrical power, or make a hybrid. But to even be worth it, each hub would need to add at least 50 horsepower. That's around 40,000 watts. Each. The Qs could maybe make what, 10 horsepower? That's not worth the cost, effort, and any added power to a 3000-4000 lb car. Maybe to a 1200 lb dune buggy or Ariel Atom, something like that.

For 40,000 watts, how heavy is that hub going to be!?! 100 lbs? Or more? Once you start adding more than 10 lbs or more to a car wheel, even a rear wheel, it will not behave properly. It's not going to handle and brake the way it was designed to do. That's dangerous. Biking with an extra 20 lbs of motor and battery offroad is one thing. Driving in traffic with super heavy wheels that can't handle and brake properly...that's a deadly combination. And removing the hub drives away from the wheel will add a huge level of complexity. As in back to what they are currently doing now for EV's and hybrids anyway. So it would be a great thing...if it didn't add so much unsprung weight to the wheels.
 
I has thinking about that idea too: 2-4 large, as in 5000W+ hub drives in car wheels would by far be the easiest to convert a car to electrical power, or make a hybrid. But to even be worth it, each hub would need to add at least 50 horsepower. That's around 40,000 watts. Each. The Qs could maybe make what, 10 horsepower? That's not worth the cost, effort, and any added power to a 3000-4000 lb car. Maybe to a 1200 lb dune buggy or Ariel Atom, something like that.

For 40,000 watts, how heavy is that hub going to be!?! 100 lbs? Or more? Once you start adding more than 10 lbs or more to a car wheel, even a rear wheel, it will not behave properly. It's not going to handle and brake the way it was designed to do. That's dangerous. Biking with an extra 20 lbs of motor and battery offroad is one thing. Driving in traffic with super heavy wheels that can't handle and brake properly...that's a deadly combination. And removing the hub drives away from the wheel will add a huge level of complexity. As in back to what they are currently doing now for EV's and hybrids anyway. So it would be a great thing...if it didn't add so much unsprung weight to the wheels.
Unsprung weight is a good remark but ''deadly'' seem a bit much?

the weight of rear hub on ebike vs the ebike ratio is probably worse and some goes faster on 2 wheels than i'm planing.....
i used to survive driving cars from 80s without much brakes nor handling, or hauling trailer/rv so it is hard to believe it can be that worse?

The Qs i was looking at is 12kw nominal each and 24kw peak but 70pounds (32kg)
2 would brings 24kw/48 peak (64hp) added to 155hp thermal for 2750pounds + batteries and stuff (30-3200maybe).
215hp isn't huge power but probably enough for a nice 0-50kmh
Good chances 48kw will need help from the thermal engine on highway to accel or climb hill but it should be enough to move the car around town at lower speeds.

Yes 160kw/320 peak or even more would be ideal but the cost and battery needs would follow and unfortunately, i have manny hobbies with just a common limited budjet. :)

I will look at a common motor option also, as i said i'm not ready to start this project yet.
 
Unsprung weight is a good remark but ''deadly'' seem a bit much?

the weight of rear hub on ebike vs the ebike ratio is probably worse and some goes faster on 2 wheels than i'm planing.....
i used to survive driving cars from 80s without much brakes nor handling, or hauling trailer/rv so it is hard to believe it can be that worse?

The Qs i was looking at is 12kw nominal each and 24kw peak but 70pounds (32kg)
2 would brings 24kw/48 peak (64hp) added to 155hp thermal for 2750pounds + batteries and stuff (30-3200maybe).
215hp isn't huge power but probably enough for a nice 0-50kmh
Good chances 48kw will need help from the thermal engine on highway to accel or climb hill but it should be enough to move the car around town at lower speeds.

Yes 160kw/320 peak or even more would be ideal but the cost and battery needs would follow and unfortunately, i have manny hobbies with just a common limited budjet. :)

I will look at a common motor option also, as i said i'm not ready to start this project yet.

Yes, the older cars, especially ones with drum brakes on the front, were horrible to drive.

As the owner of a 13 lb front hub & wheel, I will tell you that the bike is fine on pavement and gravel, fine on level surfaces and for climbing (as long as it's not too loose), but really not fun downhill. It understeers and I really need to be careful. Imagine multiplying that weight by at least 10x on both front or even rear wheels, and then wondering how the car is going to handle and brake. Crashing a bike is one thing. Crashing a car is quite another! Hub motors by definition fit inside of a wheel's hub. It would take such a heavy wheel to be worth the electricity generation for a car that I would just be shocked if someone could do it and the car's power, performance, and overall CO2 footprint would be worth the addition of the hub drives. They would absolutely need to be on the rear. So front wheel drive for gas, and rear wheels would be electrical driven. If someone could pull it off, it would be huge, because for example in the State of California, there could be a mass-transfer of older gas-driving FWD cars to hybrid hub-drive cars. It could make millons, because the conversion is so easy. You just swap out the wheels and add the battery and wiring/controller.
 
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