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Old 02-26-2022, 05:37 PM   #11 (permalink)
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Yes, there are advanced stability control systems that incorporate throttle with braking. I really doubt the OP is going to do that kind of coding and controls with his home project

The difference between fuel on and fuel off engine braking is small - but it can be enough to make a difference in the right conditions. That is why you wouldn't want to set the engine to always turn off when the throttle is lifted fully.

When I lived in TN our neighborhood was up on a hill. It had an 18 degree drive up from the main road (yes, I measured it with an angle finder). With our truck in 2wd mode that hill was dangerous to go down in the snow. If you let off the gas too quick or too much the engine braking was enough to break the back loose and you wouldn't gain control again. Sideways slide down the hill into the main road. The only way to safely descend that hill was to go down in 4WD low and just let the truck idle down the hill or chain up and drive down - then unchain at the bottom.


A car with an automatic will only start the engine in neutral or park. It has an interlock to keep if from attempting to start in gear and having the starter propel the car forward. A car with a manual transmission will only start in neutral or if the clutch is disengaged. It has an interlock to keep from attempting to start in gear and having the starter propel the car forward.

Same with a homemade mild hybrid system. You wouldn't want it to start the car in gear with just a touch of the throttle unless it is in neutral or the clutch is disengaged.

You mention twice about adding a switch to decide when to active the stop / start. It would be easier to tie into to the neutral switch. Shift to neutral - the engine turns off. Shift back into to gear - the engine turns on when the clutch starts to release.

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Old 02-26-2022, 07:22 PM   #12 (permalink)
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Quote:
Originally Posted by JSH View Post
Yes, there are advanced stability control systems that incorporate throttle with braking. I really doubt the OP is going to do that kind of coding and controls with his home project

The difference between fuel on and fuel off engine braking is small - but it can be enough to make a difference in the right conditions. That is why you wouldn't want to set the engine to always turn off when the throttle is lifted fully.

When I lived in TN our neighborhood was up on a hill. It had an 18 degree drive up from the main road (yes, I measured it with an angle finder). With our truck in 2wd mode that hill was dangerous to go down in the snow. If you let off the gas too quick or too much the engine braking was enough to break the back loose and you wouldn't gain control again. Sideways slide down the hill into the main road. The only way to safely descend that hill was to go down in 4WD low and just let the truck idle down the hill or chain up and drive down - then unchain at the bottom.


A car with an automatic will only start the engine in neutral or park. It has an interlock to keep if from attempting to start in gear and having the starter propel the car forward. A car with a manual transmission will only start in neutral or if the clutch is disengaged. It has an interlock to keep from attempting to start in gear and having the starter propel the car forward.

Same with a homemade mild hybrid system. You wouldn't want it to start the car in gear with just a touch of the throttle unless it is in neutral or the clutch is disengaged.

You mention twice about adding a switch to decide when to active the stop / start. It would be easier to tie into to the neutral switch. Shift to neutral - the engine turns off. Shift back into to gear - the engine turns on when the clutch starts to release.
Maybe there's one thing that I'm thinking but isn't mentioned here: putting the swtich on the throttle system itself. Maybe I wasn't clear on the way I envision a DIY mild hybrid. With foot off accelerator fuel is shut off. With foot on accelerator fuel is turned on. That way the driving experience at a stop would be that when the accelerator pedal is touched, the car moves forward. Let off the pedal, and the car slows down and stops because fuel is cut off.

Hooking it up to the neutral switch and having it auto start when shifting out of neutral adds one more detail that would need to be addressed, the system knowing if starting is even necessary since you pass neutral every time you shift gears. You could add a system that when shifting out of neutral starts the engine if engine RPM is below a certain threshold, but again then you have the problem of it self starting when in gear unless you add the clutch switch to the system. But if your clutch cable fails then the system would try to start with it in gear again.

For it to start in neutral you would need a manual way of starting it in neutral before moving the shifter.

I still prefer the idea of a system that just starts if you touch the pedal and cuts fuel if you let off the pedal.

Also, if it's so steep that you can't engine brake down the hill in 2WD that's one of the few times I suggest coasting in neutral or keeping the car speed down to begin with since engine braking is only a problem at higher RPMs. I don't think everyone needs 4WD with low range so they can engine brake down extremely steep hills in the winter.
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Old 02-27-2022, 12:00 PM   #13 (permalink)
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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?
Modern engines already cut fuel during engine braking. When ecomodders discuss "DFCO" this is exactly what we mean. I would just supplement engine braking by putting drag on the engine with the assist motor (slowing you down a little more and regenerating the 72-volt battery.)
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Old 02-27-2022, 12:06 PM   #14 (permalink)
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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.
That's one of my questions - will the 60-lb-ft torque of the assist motor be enough to spool the engine up to idle speed quickly?
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Old 02-27-2022, 01:04 PM   #15 (permalink)
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That's one of my questions - will the 60-lb-ft torque of the assist motor be enough to spool the engine up to idle speed quickly?
What engine? That is a key piece of information you left out of your original post. What type of vehicle are you attempting to hybridize?

Hyundai's 48V hybrid motor is 12 kw / 55 Nm (16 HP / 40 lb-ft) That is enough to spin up their 1.6L turbo diesel.

Ram's eTorque 48V hybrid system adds 90 lb-ft to the V6 and 130 lb-ft to the V8.


To answer one of your original questions I would not wait for high load conditions to feed in electric power. I would add it in earlier. Maybe not just after idle speed but early enough it is working in your day to day driving. (You would need to instrument your car to find out your load patterns)

Also be careful with handling your electrical components. The limit for high voltage is 50V. (That is why automakers use 48V systems) With high voltage you get into situations were touching the wrong thing can kill you and even unplugging something under load can seriously injury or kill you. We got to see a sorts of gory stuff in our high-voltage training at work that allows us to enter HV areas and work on HV vehicles. Watch a video on arc flash.


Personally if I was trying to add hybrid power to regular car I wouldn't worry about stop / start. I would just use the electric motor to feed in power and regen. Some 1st generation Honda Insight owners did that with a lever on the center console. Forward is power / back is regen.
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Old 02-27-2022, 01:36 PM   #16 (permalink)
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What engine? That is a key piece of information you left out of your original post. What type of vehicle are you attempting to hybridize?
I would think a system like this would be most advantageous for 4-cylinder vehicles. Anything bigger would see negligible benefits from the assist. Maybe an utterly torque-less V6 might see a benefit, but generally speaking, the more low-end grunt the engine had, the less benefit the assist would give.

I've instrumented my grandparents' Accord to find out load patterns. Normal city acceleration is around 70-80% calculated load, and highway cruising is about 50-70% but rapidly spikes to near 100 climbing even a slight hill in top gear. I figured about 50% would be a good point to begin assisting, maybe biasing that up based on speed so I don't drain the entire battery cruising on the highway. Re-gen would be based on DFCO status, again maybe biased based on speed.

As for your point on start-stop, we need to move on from idling. I'm honestly puzzled why start-stop isn't mandatory (it's 2022.) It isn't just advantageous for FE, the lack of vibration, emissions, and noise is a great thing.

Last edited by The_Techie_Stirlingite; 02-27-2022 at 01:44 PM..
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Old 02-27-2022, 02:18 PM   #17 (permalink)
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Any ICE benefits from hybrid assist. Ram's eTorque reduces combined fuel consumption 15% in the 1500 full size pickup.

You still haven't said what vehicle YOU intend to modify and make a hybrid. Is your grandparent's Accord the vehicle? You (or your grandparents) are quite the leadfoot if you are maintaining 50-70% engine load cruising on flat ground. What is you cruise speed?

Stop / Start is not universal in the USA because our fuel economy standards are low and fuel is cheap. Automakers don't need to add stop/start to hit CAFE standards so they don't add it. The fine for missing CAFE targets is only $55 per 1 mpg. Fuel is cheap so fuel economy is not a priority for US drivers. Plenty will even disable stop / start on vehicles that come with it. If US drivers cared more about fuel economy car manufacturers would care more about fuel economy.

It is a different story in the EU were fuel economy standards are strict, fines are steep, and fuel is expensive. Stop / start is quickly becoming standard and I would expect it to be universal in 2025 when the next level of fleet CO2 standards hit.

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