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I've been using the regen braking paddles very actively for the past 2 months (since I bought my Insight). I use it when I am approaching to a full stop (traffic light, intersection) regardless if it's a downhill or not. And I will say it's helping with the mpg, not a lot but quiet enough to make you smile to see the difference!

However, I realized, if I am over certain speed like 50mph, and then try to apply the regen braking paddles, I hear a roaring sound from the engine, and it kinda makes me wonder why. If this paddles are only acting as brakes, why the engine struggles and makes the noise? Almost same noise as if you're trying to floor it after a full stop, anyone else experiencing this? Or am I not supposed to use paddles above certain speed?
 

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I realized, if I am over certain speed like 50mph, and then try to apply the regen braking paddles, I hear a roaring sound from the engine, and it kinda makes me wonder why. If this paddles are only acting as brakes, why the engine struggles and makes the noise? Almost same noise as if you're trying to floor it after a full stop, anyone else experiencing this? Or am I not supposed to use paddles above certain speed?
I've heard a sound like you described, though for me it was when accelerating while in a high-regen setting. I think the sound relates to the "engine-to-generator" transition happening as regen is added. To help the transition, I try to apply or release regen gradually at higher speeds.

The electric motor becomes a generator by running backwards as regen is applied. The level of regen (and paddle use) controls the degree of the motor being "generator" rather than engine. More regen means more "back-torque" applied in the reverse direction of the drive shaft, creating a net feeling of braking. It's really a complex set of transitions that are more technical than 'acting like brakes.'

It gets kind of technical, but the following are some video descriptions I've found, plus a simpler link/attachment with description of regen:
[0:21 - 2:23] Regen Braking1 - youtube.com/watch?v=BhOEoXfxHMc
[1:00 - 3:40] Induction Motor - youtube.com/watch?v=EWZkFX48vu0
[1:52 - 4:00] Regen Braking2 - youtube.com/watch?v=0b2i5ufN7k0
[see #4 - snapshot attached] autobytel.com/hybrid-cars/car-buying-guides/weird-noises-your-hybrid-makes-and-why-126954/
 

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I realized, if I am over certain speed like 50mph, and then try to apply the regen braking paddles, I hear a roaring sound from the engine, and it kinda makes me wonder why. If this paddles are only acting as brakes, why the engine struggles and makes the noise? Almost same noise as if you're trying to floor it after a full stop, anyone else experiencing this? Or am I not supposed to use paddles above certain speed?
The engine roar on deceleration occurs when the rate of charge is exceeded and the ICE needs to kick in (not using gas - just the clutch lock-up) to take the load off. This occurs during a very fast slowdown from high speed or when the battery is full and there's no place left to store the energy. At that point, engine braking kicks in. It's totally normal, but was scary the first time I had it happen! The engine isn't really struggling - it's helping you bleed off speed!
 

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I bought a 2007 Acura TSX used in 2010. The first time I was driving down a steep hill (on the middle and east of America you would call it a mountain) in the rain, it suddenly downshifted and the car started to skid. It happened more than once that winter and it was pretty scary. I was told there was some computerized system in it that decided that lower gear would be better. I guess that's similar to our regen braking kicking in.
 

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So I just did a trip from dc to Pittsburgh lastnight and the engine noise was let's say...less favorable. I had the car in sport mode mostly but that was because I enjoyed the immediate regen down hills. The strange thing was once the battery was full and I was going down a long hill without any throttle the engine freaking roared like I was engine braking down the hill the entire way. I thought that was so strange. I'm hoping on the way back Normal mode won't do that. I also like sport mode because it maintains a higher soc on the battery than normal or econ.

I'm wondering if some heavy duty sound dampening material on the engine firewall would reduce some of the low frequency noise...
 

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If your battery gets topped off, the Insight needs to put the regen energy somewhere, and that's through engine braking. It will get noticeably worse of the battery is topped off and you use the paddles to jack up regen - there's no place for it to go.
 

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So I just did a trip from dc to Pittsburgh lastnight and the engine noise was let's say...less favorable. I had the car in sport mode mostly but that was because I enjoyed the immediate regen down hills. The strange thing was once the battery was full and I was going down a long hill without any throttle the engine freaking roared like I was engine braking down the hill the entire way. I thought that was so strange. I'm hoping on the way back Normal mode won't do that. I also like sport mode because it maintains a higher soc on the battery than normal or econ.

I'm wondering if some heavy duty sound dampening material on the engine firewall would reduce some of the low frequency noise...
It was!! Hit the gas "feather foot will keep you in EV" and make a free mph run at the next hill !! :smile_big:
 

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So I just did a trip from dc to Pittsburgh last night and the engine noise was let's say...less favorable. I had the car in sport mode mostly but that was because I enjoyed the immediate regen down hills. The strange thing was once the battery was full and I was going down a long hill without any throttle the engine freaking roared like I was engine braking down the hill the entire way. I thought that was so strange. I'm hoping on the way back Normal mode won't do that. I also like sport mode because it maintains a higher soc on the battery than normal or econ.
As hasarad mentioned, it's kind of a pseudo-engine braking condition. I like and reference the explanation of it provided in a prior post - Engine Braking / Noise when HV Battery is Full. The electric motor is likely spinning the engine rather than consuming gas in this condition - Engine Noise Complaints

This is admittedly super geeky, but now owning a hybrid, I map out drives by terrain so I can avoid (or anticipate) where the engine would work hard and/or to pre-plan and optimize what modes to use when.

In terms your drive, the terrain from DC to Pittsburgh looks mostly uphill until a decline from Mt. Pleasant on. Sport mode maintained high SOC, and left little room for regen for the downhill stretch, triggering the high battery charge and engine/energy bleed-off. On next outbound trip, getting to a low battery level (turning off Sport?) before the downhill run would help maximize energy recovery (though the total decline looks steep enough that you'd max out battery charge anyhow).

Your return trip from Pittsburgh to DC looks mostly be downhill (after Somerset?), so Sport mode shouldn't be necessary since you'll naturally capture charge from the downhill stretches. Normal or EV mode will be better choices, to keep the battery level low enough to accept more/new charge.
 

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I was driving on the freeway and there was a downhill grade. I used my left paddle shift to slow down and regen. I noticed the battery level was pretty high and heard a high rpm from the engine, meaning it is also engine braking the vehicle.

My question is: Does the single speed transmission that engages at high speeds have variable ratios?

I read from many places saying that it is a single ratio direct connection. But then engine braking wouldn’t be possible.

Any thoughts? Thanks!
 

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I was driving on the freeway and there was a downhill grade. I used my left paddle shift to slow down and regen. I noticed the battery level was pretty high and heard a high rpm from the engine, meaning it is also engine braking the vehicle.

My question is: Does the single speed transmission that engages at high speeds have variable ratios?

I read from many places saying that it is a single ratio direct connection. But then engine braking wouldn’t be possible.

Any thoughts? Thanks!
The engine braking is from the main traction motor energy being dumped into the generator motor that will then use the engine as friction to electrically brake the traction motor. It's basically turning the engine into a resistor electrically. There's not transmission involved. The lockup clutch (direct engine clutch is only one ratio) essentially an overdrive gear - if you were to try using that to slow down the car it would never work.
 

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Thanks @Mobilcams that answers it!
What's interesting about it is in the morning when the engine and electrical system is not warmed up or ready, I have heard the engine braking when coming up to a stop sign at relatively low speeds. Pretty interesting way to bleed off excess power. I wonder how big of a resistor they would have to make to mimic the resistance the engine/battery offers.
 
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