Gearing down for the new year - Kia Niro Forum
 
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post #1 of 10 (permalink) Old 01-06-2019, 12:24 AM Thread Starter
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Gearing down for the new year

I thought I would try using Sport mode and “bumping” down gears to get the car to slow.... a strategy I liked to employ with my former Subaru in snow. Well it seems the car decouples the drive (likely only using the Electric motor to cause deccelleration) and the engine simply races... the end result is not satisfactory for geared slowing.

I must admit I was a bit disappointed. The regenerative braking is weak forcing me to use the brakes in snow when simply gearing down would be far safer.
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post #2 of 10 (permalink) Old 01-06-2019, 07:29 AM
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Originally Posted by biffidum View Post
I thought I would try using Sport mode and “bumping” down gears to get the car to slow.... a strategy I liked to employ with my former Subaru in snow. Well it seems the car decouples the drive (likely only using the Electric motor to cause deccelleration) and the engine simply races... the end result is not satisfactory for geared slowing.

I must admit I was a bit disappointed. The regenerative braking is weak forcing me to use the brakes in snow when simply gearing down would be far safer.
I had a whole post full of details on how regen braking is effectively the same as engine braking and then I read your post again and noticed something.

If the engine is racing with no throttle input that means it's not decoupled from the drive. It is being driven by the car's momentum. I think the big thing is that the little 1.6L Atkinison cycle ICE is just completely incapable of providing effective compression braking. Basically, it is doing exactly what you want it to do to the limits of it's capability, which is not much.

Also, keep in mind that just because you press the brake pedal doesn't mean you are engaging the service brakes. The car will increase regen force in order to slow the car until you request more braking than can be provided by regen alone. Most people find that with a little planning they can avoid using the service brakes at all during normal driving. I would think that same would be true in snow.

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post #3 of 10 (permalink) Old 01-06-2019, 10:51 AM Thread Starter
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Fair enough. Using a brake pedal in snow for those of us who have grown up with snow, is a last resort thing. It simply means retraining. I had simply hoped that the car would behave more like a standard ICE vehicle when in sport mode.

BTW, the end is not running in Atkinson mode when in sport mode... so the reving has likely more to do with disengaging the ICE from the drive once when down shifting. The engine sounds very much like it is free revving.
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post #4 of 10 (permalink) Old 01-06-2019, 02:20 PM
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BTW, the end is not running in Atkinson mode when in sport mode... so the reving has likely more to do with disengaging the ICE from the drive once when down shifting. The engine sounds very much like it is free revving.
Pretty sure that's not correct about sport mode.

An even if it was, the only way for the engine to rev if the drive is disconnected and there is no throttle input is for the ECU to increase the fuel on its own for some reason. I can't think of why they would do that. If the drive is disconnected and the ICE on at all, I would expect it to be at idle. Sort of like when you are in EV mode (at least in the PHEV) with the cabin heat on. The ICE runs to produce heat, but it's not driving the wheels, it's just idling.

I have driven a lot of diesel cars and they have the same behavior when coasting in gear. There's very little engine braking due to the lack of a throttle plate. I think the Atkinson cycle shows similar behavior because of the effectively shorter compression stroke. Less compression, less engine braking.

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post #5 of 10 (permalink) Old 01-06-2019, 06:46 PM Thread Starter
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You are likely correct, although it is still not quite what I had hoped for in snow. Can’t have it all 🙂
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post #6 of 10 (permalink) Old 01-07-2019, 04:05 PM
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Quote:
Originally Posted by biffidum View Post
I thought I would try using Sport mode and “bumping” down gears to get the car to slow.... a strategy I liked to employ with my former Subaru in snow. Well it seems the car decouples the drive (likely only using the Electric motor to cause deccelleration) and the engine simply races... the end result is not satisfactory for geared slowing.

I must admit I was a bit disappointed. The regenerative braking is weak forcing me to use the brakes in snow when simply gearing down would be far safer.

The engine stays engaged when downshifting as you describe, though it's pretty wimpy for any sort of compression braking. I'm not complaining about that as the motor-generator is supposed to handle that function for the most part.


You can tell it's engaged by blipping the throttle a little. The only purpose for the engine to spool up like that is because it's a manual transmission shifted by a robot and it's matching engine speed to transmission speed to make things as smooth as possible and reduce clutch wear. There'd be no point revving the engine if it wasn't being engaged, so unless I'm feeling a little aggressive or know I'm going to need power out of a corner, I've resorted to only up-shifting in sport mode, and letting the computer decide when to downshift. It's certainly not as fun, but this is the new paradigm. Pure EVs at least have regen-strength control.
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post #7 of 10 (permalink) Old 01-09-2019, 12:23 AM
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Fair enough. Using a brake pedal in snow for those of us who have grown up with snow, is a last resort thing. It simply means retraining.
Umm, I grew up in snow country too. So I have to ask, why do you think that engine braking is superior to using the brakes in slippery conditions? Because my own experiences indicate the opposite is true. Driving around in low gear might be a good way to stay out of trouble if you would otherwise be inclined to drive too fast, but if you're already going kind of fast and you want to slow down, it seems to me like the brake pedal has two advantages over down-shifting:


  1. It applies braking to all four wheels (although usually not equally) rather than just two. You're more likely to retain control when all four wheels are helping to slow down, rather than just two (assuming comparable braking force in both scenarios).
  2. If you start to skid, I think most people are wired to instinctively remove their foot from the brake pedal in order to regain control, without even having to think about it. But if you are skidding because of engine braking, my impression is that most people would not be able to count on their instinctive reactions to guide them through disengaging the transmission in order to regain steering control, unless they were really astute and also had a fair amount of time to think about it (or a whole lot of prior experience in that situation. Most people that have more than a little experience in that situation have had some pretty unfortunate experiences along the way).

I Googled this question before responding to your post, and was surprised to find that different sites recommend different approaches, there doesn't seem to be a clear consensus on this, but there should be. I drove a standard transmission for most of my driving years, and down-shifting was something I just automatically did as part of my standard approach to braking, regardless of road conditions. But there was one occasion a long time ago when I almost killed myself and three other people by downshifting on an icy road and completely losing control of the car as a result. I trained myself out of automatically down-shifting in slippery conditions after that experience.

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post #8 of 10 (permalink) Old 01-09-2019, 09:46 PM
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When in a situation that might cause the tires to lose traction, I try to coast to stop any force on the tires from brakes or engine. That is a bit harder in the Niro because a natural impulse to release the acceleration pedal may cause regen to break loose the tires.

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post #9 of 10 (permalink) Old 01-11-2019, 04:11 PM
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often when i downshift in sport mode the engine revs up quite a bit which is pretty noisy. but i assumed this was just the gearing not that the engine was decoupled. i compensate by shifting up so i know what gear i’m in before shifting down to keep the revs (noise) reasonable. i prefer my previous 4 speed auto where choosing 3 locked out 4 etc. i would use 3 and 2 to brake, 3 driving around town, and 2 for stop and go.
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post #10 of 10 (permalink) Old 02-02-2019, 10:40 AM
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Interesting discussion. You would think the stability control would help you out with regen braking and communicate with anti skid as well. All the information is certainly there. How and even if, I don't know but I'm fairly certain that anything you do on top of those systems will only complicate matters.
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