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At any speed, the motor slows the car first until the demand for deceleration exceeds its ability and the hydraulic brakes add deceleration. The motor is quite capable of moderate deceleration at any speed short of emergency or really brisk braking. Belief systems (not sure what you are trying to prove) are quite powerful, but here is a test you can easily do to demonstrate this. Set your cruise control say at 70 mph on an empty road. Now use the steering wheel controls to drop the set speed to say 40 mph. I think you would agree that that is pretty brisk slowing, probably brisker than you do on a daily basis (it is for me although I will do exactly that if I exit too hot). That is all motor. You can duplicate the same effect with just the brake lever. Where belief comes into play is that you are arguing that the hydraulic brakes are also activated in moderate deceleration scenarios (apparently you think a number on the speedometer matters). That is not how hybrids work or are designed, and would lead to less energy recovery and faster wear on brake components.

Any hydraulic valving and systems are irrelevant until hydraulic braking is activated after deceleration needs exceed that which the motor can provide alone. If you want to puzzle out braking engineering from diagrams, that's fine, but that has nothing to do with initial deceleration provided by the motor.

You can easily access thousands of articles that detail how hybrids work, again, kind of a silly debate here. They work by recovering energy from slowing, brakes work against that main goal.
You seem to be implying that the cruise control will only use regenerative braking and not hydraulic braking when it wants to slow down. Forgive me if you've already explained why think this is the case in a prior post that maybe I missed. Or maybe I'm misunderstanding your current post. When I look at that schematic, it suggests to me that the computer is potentially able to use both kinds of braking, and surely the AEB system is capable of using both kinds of braking (it would be a pretty lame system if it couldn't do that), so I don't know why the cruise control wouldn't also be able to use both in the test you've suggested.

On a slightly tangential note, I've observed that the cruise control accelerates and decelerates more aggressively than I usually do. I chock part of that up to "short sightedness" - it clearly doesn't see everything I see (like the guy in front of me in an adjacent lane getting ready to pull in front of me) and it doesn't anticipate as well, so if I'm letting it manage the speed in heavy traffic, there are times when it waits longer than I would to decelerate, and then it has to decelerate more quickly. Ditto for acceleration: I was driving this past weekend in EV mode with a nearly full battery, but with CC dialed in at 70 MPH. We hit a hill and I was annoyed that it started the ICE for a few seconds to get up the hill; pretty sure that if I'd been running the throttle, I might have slowed down a bit, but the ICE would not have started.
 

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You seem to be implying that the cruise control will only use regenerative braking and not hydraulic braking when it wants to slow down.
As I predicted, this group is denying that the smallest speed correction is using the motor only and brakes are being applied even in cruise control. Giving up. No way to prove the truth to deniers. Go ahead and deny engineering goals, actual use, power recovery meters, lack of heat of the disks after normal stops, and lack of wear on the pads. The brakes are used in every slowing situation!!!

On another note, talking about slowing from 70 mph versus 40 mph is a red herring. Slowing 10 mph from any speed takes exactly the same energy and is easily handled by the motor at most moderate deceleration rates. Sure, slowing from 70 to zero takes more energy than 40 to zero, but slowing from 70 to 60 is the same as 40 to 30 mph at the same rate of deceleration. By the way, slowing at a moderate rate 70 to zero mph is not enough energy to saturate the battery (even on the HEV), so that is also not a reason why physical brakes would be needed.
 

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As I predicted, this group is denying that the smallest speed correction is using the motor only and brakes are being applied even in cruise control. Giving up. No way to prove the truth to deniers. Go ahead and deny engineering goals, actual use, power recovery meters, lack of heat of the disks after normal stops, and lack of wear on the pads. The brakes are used in every slowing situation!!!

On another note, talking about slowing from 70 mph versus 40 mph is a red herring. Slowing 10 mph from any speed takes exactly the same energy and is easily handled by the motor at most moderate deceleration rates. Sure, slowing from 70 to zero takes more energy than 40 to zero, but slowing from 70 to 60 is the same as 40 to 30 mph at the same rate of deceleration. By the way, slowing at a moderate rate 70 to zero mph is not enough energy to saturate the battery (even on the HEV), so that is also not a reason why physical brakes would be needed.
CC does slow the car without using the friction brakes. Who is arguing otherwise?

NO. Kinetic energy is 1/2mv^2. 1/2m70^2-1/2m60^2 does not equal 1/2m40^2-1/2m30^2.

49-36=13
16-9=7
 

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Discussion Starter #64
I've been measuring brake temps with little conclusive evidence but some quick calculations.....

A 4000lb car requires dissipation of 223 or so BTU to slow from 70 to 60 mph. From 20 to 10 requires about 52 BTU.

While the battery may well not be saturated at the higher speeds, I suspect charging is, thus the chart's apparent use of the combination of friction and regenerative braking at the higher speeds.

Unfortunate that we don't have good labeling, numbers and units on the chart.
 

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By the way, slowing at a moderate rate 70 to zero mph is not enough energy to saturate the battery (even on the HEV), so that is also not a reason why physical brakes would be needed.

By your logic, an HEV should be able to then accelerate from 0 to 70mph and not have any problem with depleting the battery or starving the motor for power. And I know from trying that is impossible in this vehicle. Your logic is also massively flawed in your understanding of the HEV. The cruise control MUST have a means of using the brakes to slow down. There are many times when I am driving especially in the winter where the battery is up around the 80% charged. If I was in cruise control and needed to slow to even at a moderate rate that in your prior posts have stated is pretty fast, then where would all the power generated get dissipated to? The logic inside the car will be to protect the battery and trying to ram power into a battery that might already be warm as it's sitting at 80% charge, such voltage inrush would destroy the battery. So how could the car stop?


Please explain how you think it will work? Not all of us have a Plug-In with a massive battery yet we do have cruise control and regenerative braking.
 

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Discussion Starter #66 (Edited)
I'm pretty well satisfied that straight cruise uses nothing but regeneration with the possible exception of a fully charged battery. Also that smart cruise has access to friction brakes. Now that I know the motor is responsible for regeneration, I believe the theoretical limit is the same as the max acceleration it can deliver. In practice, however, the limit is almost certainly much less without dumping energy into a resistor, which I'm fairly certain it does not do. I think the max deceleration provided by normal cruise may be a good approximation of what regeneration is possible.

What little I've seen from my brake temp tests, though inconclusive, backs this up. At the higher speeds, at 1/2 beyond the notch in the charge area of the meter, there seems to be a fair amount of heating. 70 mph to 0 about 10 degrees. Nothing compared to what I would suspect from pure friction. Incidentally this was done on a rather steep hill with e brake used for the final stop.
 

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Discussion Starter #67
Braking at the notch resulted in only a few degrees of heating when started at 55 mph rather than 70 so I suspect it was regeneration only.

Around town, the front brakes got to 90 degrees so rusting won't be a problem.
 

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When I look at that schematic, it suggests to me that the computer is potentially able to use both kinds of braking, and surely the AEB system is capable of using both kinds of braking (it would be a pretty lame system if it couldn't do that), so I don't know why the cruise control wouldn't also be able to use both in the test you've suggested.
Semantics perhaps, but technically ACC does not use the brakes. The whole point of ACC is to not exceed traffic speed and to gently adjust speed. If emergency braking is required, then that is the AEB algorithm. And that is what I've observed happening during ACC, traffic turning (and no issue with an actual impact) will cause at least a maximum regen deceleration and probably brakes as well. It is so abrupt and disruptive (despite warning beeps less than one second before initiation) that I don't know which was activated, and never use ACC because of that. The same can happen in standard CC, but far far less frequently. Lower sensitivity in standard for some reason.
On a slightly tangential note, I've observed that the cruise control accelerates and decelerates more aggressively than I usually do. I chock part of that up to "short sightedness" - it clearly doesn't see everything I see (like the guy in front of me in an adjacent lane getting ready to pull in front of me) and it doesn't anticipate as well, so if I'm letting it manage the speed in heavy traffic, there are times when it waits longer than I would to decelerate, and then it has to decelerate more quickly.
I'm far smarter than the ACC algorithms and don't mind the extra attention needed for standard cruise control (which I'm in for perhaps 90 plus percent of all miles driven). Occasionally when I resume or change my CC setting to higher mph, the car does accelerate faster than I would manually. But it is not consistent (scary not to be I guess) and most of the time it accelerates at or slower than I would manually with no traffic following.

ACC is a luxury for those on congested commutes who want to arrive more relaxed. But it does cost efficiency by slowing and speeding up more than standard CC with a driver smarter than the driver and traffic ahead.
 

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A 4000lb car requires dissipation of 223 or so BTU to slow from 70 to 60 mph. From 20 to 10 requires about 52 BTU.
You could be right, but without looking at formulas, I'd say that scrubbing 10 mph at a constant rate is the same kinetic loss at any speed. That is assuming a vacuum and no frictional losses outside the brakes or motor deceleration. Same deal with accelerating. Change the rate of acceleration or deceleration during the process, and all bets are off. Infinite acceleration requires infinite power, right?
 

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Around town, the front brakes got to 90 degrees so rusting won't be a problem.
90 degrees is light braking to be sure. Even so, I suspect you were in stop and go situations with faster slowing than necessary. Rusting does seem to be a big issue for owners in Britain which is why some there recommend finding a parking lot to do some brisk braking to keep disks clean.
 

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Discussion Starter #72 (Edited)

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Discussion Starter #73
I find two things largely solve the glitches in smart cruise. If in a line passing in the left lane, use a lessor distance otherwise the longer distance is much smoother. Additionally smart cruise is easy to temporarily override with a touch on the throttle and/or the turn signal.
 

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Semantics perhaps, but technically ACC does not use the brakes. The whole point of ACC is to not exceed traffic speed and to gently adjust speed. If emergency braking is required, then that is the AEB algorithm. And that is what I've observed happening during ACC, traffic turning (and no issue with an actual impact) will cause at least a maximum regen deceleration and probably brakes as well. It is so abrupt and disruptive (despite warning beeps less than one second before initiation) that I don't know which was activated, and never use ACC because of that. The same can happen in standard CC, but far far less frequently. Lower sensitivity in standard for some reason.

I'm far smarter than the ACC algorithms and don't mind the extra attention needed for standard cruise control (which I'm in for perhaps 90 plus percent of all miles driven). Occasionally when I resume or change my CC setting to higher mph, the car does accelerate faster than I would manually. But it is not consistent (scary not to be I guess) and most of the time it accelerates at or slower than I would manually with no traffic following.

ACC is a luxury for those on congested commutes who want to arrive more relaxed. But it does cost efficiency by slowing and speeding up more than standard CC with a driver smarter than the driver and traffic ahead.
Thanks for explaining your thoughts. My experience with ACC is that it doesn't accelerate gently and it's capable of decelerating aggressively too, but it's an open question in my mind as to whether it limits itself to regen or readily uses friction too. My first guess is that it employs a mix of both, just as the car presumably does when a human driver brakes with equal abruptness.

Prior to purchasing my Niro, I longed for ACC because I found myself getting highly annoyed when I came up behind a driver on a freeway that wasn't holding a constant speed (for no apparent reason): ACC defuses some of that frustration, some of the time. But your comments have planted the seed that I should do a little driving with ACC disabled and just using the standard CC to see if I'm happier with the acceleration/deceleration logic. On the other hand, I'll be turning off a safety feature when I do that (standard CC only decelerates when going down a hill and the dialed-in speed is exceeded, whereas ACC decelerates in an attempt to maintain a safe following distance under changing conditions... it's just not as good at this job as I would like).
 

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Hey yticoley, gave your trick of using cruise control for regen braking a try. WOW! What a difference in the amount of battery charge you get coming to a stop. Just started and seems to make a difference in gas mileage. What mileage are you averaging? Why cant we get this amount of regen without cruise?
 

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You can get the same amount of regen, in fact more, by using the brakes (you can see that on the charge meter). But in a given stop, it should be close to a zero sum game as the lost momentum can only regen a certain amount in total. Slowing slowly is best bang for your buck, avoid any chance of using the disk brakes, and gaining a chance of preserving momentum if traffic or the lights change before a full stop. Mind you, I try not to do that if I'll annoy traffic behind me. The major advantage of cruise control, especially standard cruise control, is less variance in speed over manual control, and obviously less unintended heavy pedal presses, especially when accelerating (I use CC to get up to speed on highway ramps and going into higher speed zones).

I don't think my mpg is spectacular. In the Niro, I'm getting a little over 52 mpg annual average in four season weather (every drop of gasoline calculated). That's only about 6% better than the EPA estimate. Some of that is due to removing roof rails from my LX, and some due to some changes to driving habits (cruise control not being one of them). My mpg is substantially better than the more real world Fuelly results of 45 mpg for all Niros, but still inside the bell curve of Fuelly results.
Kia Niro MPG - Actual MPG from 576 Kia Niro owners

I'd probably average over 53 mpg annually if I didn't cherry pick the best summer days to use my motorcycle instead (69 mpg). Those days reduce the number of highest car mpg days - I can usually do 60 mpg on such days (in fact, not sure I can justify using the motorcycle to save money). Rainy days drop mpg substantially and I don't ride my motorcycle on those days either so the car mpg takes the hit.
 

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My mpg is substantially better than the more real world Fuelly results of 45 mpg for all Niros, but still inside the bell curve of Fuelly results.
Kia Niro MPG - Actual MPG from 576 Kia Niro owners.

Sadly the Fuelly results are very badly skewed. There are quite a number of PHEV drivers that are loggin into Fuelly and reporting their fuel economy that reduces the real world average as they plug in EV mode that us HEV (hybrid only) drivers can't get. So when you see the drivers with the over 70mpg reduce the average to the detrement of reality. I have pointed this out in another thread. What good does saying you get 125mpg just because you work less than 20 miles from where you live and can charge your car every night so driving to work pretty much uses zero gas, so the only time you really do use fuel is on longer trips over the weekend.
 

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If there was a significant number of PHEV owners on Fuelly, I would agree. Not sure you have it right though, PHEV owners getting 70 mpg and posting same to Fuelly would increase the fleet mpg for all. In any case, you can filter PHEV owners out of the results. I tried Niro FE and again got about 45 mpg.
Kia Niro FE MPG - Actual MPG from 40 Kia Niro FE owners
 
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