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Old 02-24-2022, 04:14 PM   #1 (permalink)
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Lightbulb DIYing Euro-style belt-alternator-assist hybrid - feasible?

Low-voltage hybrids (typically 48V) are all over the place in European countries, and they provide drivability improvements at low RPM, instant engine start-stop (without the risk of burning up the starter), and as much as a 15% fuel efficiency improvement in some cases.
I have a concept for a similar system as an eco-mod, and I'd appreciate it if you could help me figure some stuff out.

Preface: this system would be for automatic/CVT vehicles only. Manual transmissions would require more wiring to auto-stop effectively (you need to know if you're in neutral or not.)

I found a permanent magnet BLDC motor online, that is rated 72 volts, around 60 lb-ft peak torque, draws about 400 amps at full load. Torquiest one I could find in an alternator-like form factor and 72-volt.

The motor would be attached to the crankshaft via a belt, similar to a supercharger. My main concern would be belt slippage, especially at max assist (about 25kW). I'd guess I'd need one heck of a tensioner, or re-use an existing supercharger drive kit.

As far as control, an Arduino microcontroller board would be plugged into the OBDII port, a relay acting as an automated kill switch, the brake light switch on the pedal, and the motor controller. The control board (I'll call it the Hybrid ECU from now on) would calculate how much power assist or regenerative braking was required, based on the calculated engine load, speed, engine RPM, and brake-light switch.

Calibration question: at what load point should assist begin (to prevent an open-loop super-rich operating condition?) I did some data logging in my parents' Accord with a K24Z engine, and normal acceleration produced about 75-85% calculated load - should I be assisting at these load levels, or should I start earlier? Should I re-gen drag the engine at a low load to improve BSFC, or should I reserve re-gen drag for DFCO only?

When the driver's foot was on the brake, the ECU would wait until the vehicle was creeping (6 mph or below to avoid killing the automatic transmission) before effectively triggering an automated EOC. As with EOC, vehicle systems would continue to run, powered by the 12V battery. Could I safely cut the engine any higher than 6 mph?

When the driver lifted off the brake or the hybrid battery was low, the assist motor would kick back in, delivering its peak 25kW to spin the engine back up to idle speed quickly. Once the engine was at a workable RPM, the crankshaft position sensor would be reconnected and the combustion engine would take over.
Would about 60 lb-ft be enough for a quick restart of an average 4-cylinder engine? The system would not be tasked to handle cold starts, the 12-volt starter would do that. I saw a product called the E-Charger online, and they reportedly started a 6.0 Vortec V-8 with 150 lb-ft via a belt drive system.

Like OEM hybrids, this system would have specific conditions in which the engine would not stop when the vehicle did. For example, the engine would not stop if it was not at normal operating temperature, because cold starts would not be possible with the assist motor. The engine would also not stop if the ambient temperature was extremely low or extremely high, to ensure cabin comfort. The ECU may also be able to parse CAN data on supported vehicles to prevent an auto stop (or kick the engine back in) if the A/C needed to run.

An additional issue would be motor cooling. If the motor was in place of the alternator, its cooling fan would be sucking in hot air, limiting peak torque and possibly making it impossible to restart the engine after an auto stop. One could possibly use a hood scoop to feed cool air to the motor, so it wouldn't overheat. That would look quite interesting. A bystander would see a hood scoop, suggesting a ram-air intake or supercharger setup. When the hood was lifted, all they would see would be an alternator-looking thing with orange electrical cabling running to it.

As far as battery capacity goes, I'd be using LTO cells, and need enough capacity to supply about a minute of maximum assist. If the vehicle had to idle for any reason, it would charge the hybrid battery as much as it could unless it was full already (engine load optimization.) During catalytic-converter warm-up periods (fast idle), the motor would impart a bit more re-gen drag, to speed up the warm-up cycle (and produce electricity for more assist/engine spool-up in the future.)

Do you have any other questions? I'd be happy to answer them!

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Old 02-24-2022, 04:34 PM   #2 (permalink)
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Do you have any other questions? I'd be happy to answer them!
Do you know you are reinventing the [mild hybrid] wheel?

ecomodder.com/forum/showthread.php/controller-mods-build-e-assist-altermotor-35003

ecomodder.com/forum/showthread.php/gms-eassist-34290
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Old 02-24-2022, 07:21 PM   #3 (permalink)
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I admit I haven't read everything here or understand everything.

One thing, though is I don't see the need to know when a manual transmission is in neutral or not. Just shut off fuel and let the engine turn off, whether in gear or not. Of course, depending on the engine, it could shake a bit as it comes to a stop in gear. But many modern engines aren't as shaky as older ones. Also, taking off in gear from a stopped engine still makes sense with a manual transmission. Again, it just might be a bit shaky at first.
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Old 02-25-2022, 05:39 PM   #4 (permalink)
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Originally Posted by Isaac Zachary View Post
I admit I haven't read everything here or understand everything.

One thing, though is I don't see the need to know when a manual transmission is in neutral or not. Just shut off fuel and let the engine turn off, whether in gear or not. Of course, depending on the engine, it could shake a bit as it comes to a stop in gear. But many modern engines aren't as shaky as older ones. Also, taking off in gear from a stopped engine still makes sense with a manual transmission. Again, it just might be a bit shaky at first.
If the system was able to know if the gearbox was in neutral, it could stop the engine at high speeds (coasting down a hill, etc.) That would provide greater FE gains than just waiting for 6 mph.
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Old 02-25-2022, 05:53 PM   #5 (permalink)
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Do you know you are reinventing the [mild hybrid] wheel?
The Gen 2 eAssist is water-cooled and requires 100+ volts. The cooling and battery system for such a motor would be much more difficult to fit in an existing vehicle (especially the water cooling system.) One MIGHT be able to use PC water-cooling parts, but I'm not sure what the wattage-dissipated-as-heat figure is for that eAssist motor. No solid specs on current-draw or Kv ratings either = no-go IMO. One must know what kind of current a given electrical machine will draw before fitting it to a vehicle.
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Old 02-25-2022, 07:13 PM   #6 (permalink)
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Watercooled? I guess my Superbeetle is out.

The first link was to the HaroldinCR thread, which spun off from MPaul Holmes thread on Open Revolt.
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Old 02-25-2022, 07:36 PM   #7 (permalink)
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Originally Posted by The_Techie_Stirlingite View Post
If the system was able to know if the gearbox was in neutral, it could stop the engine at high speeds (coasting down a hill, etc.) That would provide greater FE gains than just waiting for 6 mph.
I still don't get it. I'd want fuel to be cut to the engine any time my foot is off the pedal, whether I'm coasting in neutral or engine braking. I don't see an advantage of keeping the engine idling at any speed. Why?
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Old 02-26-2022, 10:12 AM   #8 (permalink)
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Watercooled? I guess my Superbeetle is out.

The first link was to the HaroldinCR thread, which spun off from MPaul Holmes thread on Open Revolt.
Hozabout a wasserboxer cylinder kit from a 1 st generation engine. I hear they are hard to stop leaking but you get almost 2 liters displacement.
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Old 02-26-2022, 01:59 PM   #9 (permalink)
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Originally Posted by Isaac Zachary View Post
I still don't get it. I'd want fuel to be cut to the engine any time my foot is off the pedal, whether I'm coasting in neutral or engine braking. I don't see an advantage of keeping the engine idling at any speed. Why?
Safety: It you cut fuel and turn of the engine anytime you lift of the throttle you go to full engine braking. This is braking separate from the hydraulic braking system and the ABS system can't control it. In low traction situations engine braking alone can be enough to lock the wheels and cause the vehicle to lose control. (RWD truck, unloaded, downhill, on snow)

This is one of the reasons that you don't find high speed automatic emergency braking on manual transmission cars.

You also wouldn't want to car to lurch forward if someone hit the throttle with the car at a stop, in gear, with the clutch engaged. A manual car should only start when in neutral or when the clutch is disengaged.

Convenience. Shifting into neutral to turn off the engine gives the driver control of when it happens. There can be plenty of cases where the driver might not want the engine to turn off. A 95 degree day in humid Alabama stop and go traffic comes to mind from personal experience. (I didn't buy a Civic Hybrid because it didn't have an electric AC compressor and the AC turned off at stops)

Longevity: For long life you want your engine to come up to operating temperature quickly. Turn your engine off every time you lift the throttle could cause the engine never to come to operating temperature. (This is why hybrids don't turn off the engine until it comes up to temperature)
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Old 02-26-2022, 03:15 PM   #10 (permalink)
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Safety: It you cut fuel and turn of the engine anytime you lift of the throttle you go to full engine braking. This is braking separate from the hydraulic braking system and the ABS system can't control it. In low traction situations engine braking alone can be enough to lock the wheels and cause the vehicle to lose control. (RWD truck, unloaded, downhill, on snow)

This is one of the reasons that you don't find high speed automatic emergency braking on manual transmission cars.
Are there ABS systems that increase the throttle when the tires start to skid from engine braking so as to eliminate engine braking from the equasion?

If not, I still don't see the point. In the cars I've driven with a kill switch of some sort I've never felt a difference in engine braking between fuel on and fuel off, with the exception of putting around in 1st gear at idle speed. If your gearing is low enough to cause your tires to slide from engine braking with fuel off they will do the same with the fuel on, except in that 1st gear scenario.

Now is elimiating the chances of sliding at 5mph worth it? Maybe. But at those speeds I don't see engine-braking-sliding as being a problem that one couldn't easily control.

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You also wouldn't want to car to lurch forward if someone hit the throttle with the car at a stop, in gear, with the clutch engaged. A manual car should only start when in neutral or when the clutch is disengaged.
And what would be the difference between that and an automatic with or without stop start, or in an EV? In an automatic or an EV, if the car is in gear and you hit the throttle the car will lurch forwards. Why would the same thing in a manual transmission car be less safe?

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Originally Posted by JSH View Post
Convenience. Shifting into neutral to turn off the engine gives the driver control of when it happens. There can be plenty of cases where the driver might not want the engine to turn off. A 95 degree day in humid Alabama stop and go traffic comes to mind from personal experience. (I didn't buy a Civic Hybrid because it didn't have an electric AC compressor and the AC turned off at stops)
This is why a switch could be added. Obviously the driving style would have to change. But we are talking about a DIY project here, right? and not a car designed for the masses?

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Originally Posted by JSH View Post
Longevity: For long life you want your engine to come up to operating temperature quickly. Turn your engine off every time you lift the throttle could cause the engine never to come to operating temperature. (This is why hybrids don't turn off the engine until it comes up to temperature)
I can agree with this principle. But again, the reason why a simple switch could be added for the feature? A simple switch would be much easier than to make a complicated system that tracks engine temperature, engine speed, car speed, neutral position on the transmission, maybe catalytic converter efficiency, etc. so it can electronically decide when and when not to turn off th engine. Not that such a system wouldn't be nice in a way, but I don't see it as necessary when all you really need is just a switch on the dash.

I mean, ya, you could make a system that tracks thinks like if your AC is on or a system that tracks engine temperatures so it won't kill the engine during those moments. But then you also have to guess when the system is going to decide to do what it wants to do. For an example, you come up to a stop and the engine isn't warm enough, so it keeps idling. You come up to another and it decides it's warm enough so it shuts off. Then, of course, now you do need the system to only make those on and off transitions when the car is in neutral so it won't be doing it when you're doing something that an unexpected shut off could mess you up.

But that brings up another problem. What if you suddenly need to take off? Now you have to start the engine in neutral, then shift into gear and then release the clutch. Sure, we who like to hypermile have done that. But the nice thing of starting the car in gear, especially with an electric motor and clutch engaged, is that you can hit the accelerator and go just like in a typical hybrid or automatic or EV.

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