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Not ready for one pedal driving yet but..

23K views 79 replies 13 participants last post by  Super.gary 
#1 ·
I sure am ready to optomize hybrid driving. By that I mean off gas is coasting and on brake is regeneration. If we had a friction brake indicator, we could learn how to optomize slow downs and stops for max regeneration. I have to say, however, I like this car like it is more than any other new car I've ever bought.
 
#2 ·
I sure am ready to optomize hybrid driving. By that I mean off gas is coasting and on brake is regeneration. If we had a friction brake indicator, we could learn how to optomize slow downs and stops for max regeneration. I have to say, however, I like this car like it is more than any other new car I've ever bought.

You do. On the left side of your dash there is a ECO indicator. The lower part of the dial is for regenerative breaking. Optimum is the point where the line goes from thin to thick. Around that point the car is getting the most power from the electric motor without needing the breaks to slow down.
 
#3 ·
I think the key is like you said, "around that point", is it there or when it gets full scale or somewhere else? KIA did such a good job of making it seamless that, unlike some other EV's, I can't tell.

Do you KNOW that's where it is or have a reference?

I just want a little light that lights as the friction brakes are touching. I've even thought of rigging one up. When a bit younger, it would already be installed.
 
#4 ·
With normal "braking", the mechanical brakes don't engage. If you drive like you own a hybrid, the mechanical brakes will only engage in the last few feet of a full stop. Regen braking at speed can be amazing. Often coming to a stop, I will lower my set speed on cruise control by 30 mph, pretty brisk slowing (same effect as the brake pedal). Of course, I try to slow down earlier, but don't like to annoy traffic behind. I use the "hand throttle" (cruise control) for 90% of all driving above 20 mph.
 
#5 · (Edited)
I have to ask, how do you know that? KIA blends it so well that the friction brakes could engage when you first touch the pedal all the way to your post. If I knew how big the generator was I could guess by comparing it to the 60hp traction motor. I know that just prior to the "power" zone, the IC is not operating so if the generator was 60 hp equivalent, the deceleration might be the same as the acceleration with just the traction motor. Even that is not necessarily so.

I suppose cruise control deceleration is as good a guess as any as long as its not smart cruise as that has access to friction brakes.

Incidentally the physics of regenerative braking are such that a complete stop is impossible.
 
#12 ·
Talking about regen breaking, tried an EV on the last week end! very cool car.. liked the ride, all smooth and verrrryyy powerfull... You can stop the car with the left "paddle shift" behind the steering wheel. it's stop quick and easely without touching the breakes.! there is 4 regen mode on the model.


The only thing is if you are on the cruise system, it won't stop the car with the paddles..
 

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#14 ·
Regeneration is always totally separate from brakes by definition. There is an awful lot of quibbling on the Tesla boards as to whether one pedal driving uses nothing but regeneration or uses the brakes for a final stop. I suppose if the charge resistance is enough the last movement of rotor can be stopped by the stator.....and I stand corrected in practice. I know you realize that the brake pedal is near meaningless any more. Software has access to the friction brakes regardless of pedal operation.

The 60hp motor could be used for regeneration in Niro but I don't think it is. I believe it uses the HSG (hybrid starter generator) for regeneration and engine starting. I hope I'm wrong but all the simplified diagrams I see list them as two separate units. The motor I believe is in the transaxle and the HSG connected by a belt visable under the hood. I don't know how powerful the generator is.

Taking Niro on a 500 or so mile trip tomorrow and looking forward to playing with the IR thermometer in an attempt to see where friction and regeneration relate.
 
#15 ·
Regeneration is always totally separate from brakes by definition.
Um, no. Most hybrids and EVs (other than Tesla) blend the two when more deceleration is required. And most historically have done a bad job at this with strange braking feel. The Niro/Ioniq are better than most, which is why you are wondering when the hydraulic brakes add to deceleration.
 
#18 ·
Power brake unit is hydraulic and assists braking power. When car fails, it no longer adds power, but the brakes still work, the hydraulic system is still manually activated by foot pressure. Obviously, it takes a lot more pressure than when the power brake system is working. I can promise you the car manufacturers would be facing billions of dollars of lawsuits if deaths occur because a lack of redundant braking circuits. It would be nuts to remove them on cars. Even plane manufacturers where it makes for better engineering resist taking out mechanical systems. On the 737 Max, there were mechanical safeties in place, but the ESU apparently did not allow the pilots to operate them - the last crash the pilots are documented taking the proper steps to correct the electronic controls. Do you want that to be the case in the Niro when all systems go out? Picture driving at 70 mph and your drive by wire brakes and steering no longer work.
 
#19 ·
Sadly you are wrong with this car. There is no hydraulic piston that connects the break pedal to the breaks. Take a look at the parts and how they are connected. This is becoming more common inside of more vehicles these days as electronics gets more prevalent. The Toyota Prius hasn't had a mechanical break pedal for its entire existance. I think you are confusing the emergency mechanical break that is a wire that connects the emergancy break to the rear hydraulic break system. That is mechanical. But the hydraulic break pedal parts are purely computer controlled.
 
#24 ·
KIA has, like many others, gone to great lengths to make the car behave like a standard IC car. In gear, it creeps forward as if in idle, release the throttle and it decelerate as if compression braking but it's all artificial...... Why not use the throttle to go and the brake (pedal, that is) to slow or stop and use max regeneration prior to friction braking and tell the driver when the friction brakes are used.

Please don't mention the 737 Max crashes unless you have, at the minimum, reviewed the flight data traces and have 3000 hrs PIC time in the 737...
 
#25 ·
No manufacturer will tell you when the mechanical disk brakes are being used. The goal is to make a hybrid seem like a normal car behaves for braking and overcome the well known strange brake blending in hybrids. To do otherwise makes hybrids appear weirder and will cost sales.

Why does it matter when? You already know how to drive the car for greatest efficiency. If you do drive this way, physical brake use is minimized automatically. This is proven by how long the brake pads last on other hybrids. You can do this on manual shift cars as well. It was 140,000 miles on my last car before I had to replace pads. But if you are into jerky driving, your pads will not last as long.
 
#28 ·
I suppose it's the geek in me. Always wanting to know how and why. I could see KIA starting friction braking as soon as you touch the brake, all the way to only using them when regen is exhausted. The brake light is similar; is it certain regen braking, brake pedal, brake hydraulics pressurized, certain deceleration rate, some combination or what?

Does it matter? To my wife, for whom I bought the car; absolutely not, but to an auto enthusiast on a car forum, it does.

The marketing aspects, specifically making the car seem as "normal" with respect to the purely IC engine car; I understand but I don't have to like it. It just seems illogical but for one small consideration.......people don't buy weird cars.

On the other hand, it's all software anymore so why not? Coasting is more efficient than regen, regen is more efficient than friction so why not let the driver use that if he wants.

The pure EV's are going that way in all sorts of ways
 
#26 ·
Physics please

Quick correction to an earlier post- it is very much possible for regen braking to be effective down to and including 0 rpm. A classic physics class demo is to short circuit the input of an electric motor and then try to turn it. You can't. Since the resistance is zero, it would take an infinite force to generate an electric field (the motor operating as a generator). There are practical limitations due to the electronic brake controller having to dissipate too much current as you approach zero, but there is no theoretical reason why it isn't possible.
 
#27 ·
Quick correction to an earlier post- it is very much possible for regen braking to be effective down to and including 0 rpm. A classic physics class demo is to short circuit the input of an electric motor and then try to turn it. You can't. Since the resistance is zero, it would take an infinite force to generate an electric field (the motor operating as a generator). There are practical limitations due to the electronic brake controller having to dissipate too much current as you approach zero, but there is no theoretical reason why it isn't possible.
I think the resistance to turning with a shorted winding is the same as the maximum starting torque.
 
#33 ·
The kniro.net site has a description of the braking system. The first graph on the page (see attachment) gives the impression that friction braking is used more frequently in normal driving than we might like to think. It also suggests that regenerative braking is doing most of the work of stopping the car at very low speeds close to zero, but that the last drop in speed to a full stop is managed primarily by hydraulic (friction) braking. One can imagine that if you limit yourself to a light press on the pedal, you can probably spend more time in the regen (light grey) than in the friction(dark grey) part of the graph.

This page also points out that in normal operation the braking is managed electrically, but "If the PSU or the IBAU is broken, IN valve and OUT valve are closed, and CUT valve is off. Therefore, the brake force is generated by only pressing a brake pedal manually by a driver. "
 

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#34 ·
Superb! The big news to me is that the motor is used to regenerate according to that. Units are not mentioned but if the graph is constant deceleration, it makes sense. At high speeds, the gen makes too much energy for the system to accept. As speed decreases, regen is capible of "that" level of deceleration until a very low speed then it's all friction.
 
#35 · (Edited)
Imagine a series of similar charts with ever decreasing levels of deceleration. The grey area would gradually retreat in speed until, at some level, it would be gone. I'm not really sure how this relates to the indicator, however.

Notice how regenerative braking rapidly goes to 0 at very low speeds.
 
#38 ·
Yeah, the lawyers are alive and well. The lane keep is another example. It is far better than the GM version I've driven but still disconnects without a bit of driver participation. Yticolev is correct in that there are few real world opportunities to use coast. With speed limits, traffic and cruise control; knowledge of friction braking is more a novelty than practical.

The geek in me still wants to know.

Niro has kindled a serious interest in a pure EV specifically a Tesla....
 
#43 ·
The brake pedal is NOT connected to a conventional master cylinder. It is "brake by wire" so the computer is responsible for braking and the pedal is just a vote. The park brake is purely mechanical and there is a failure mode. So far, I'd say a well done system.
 
#47 · (Edited)
The brake pedal is NOT connected to a conventional master cylinder. It is "brake by wire" so the computer is responsible for braking and the pedal is just a vote. The park brake is purely mechanical and there is a failure mode. So far, I'd say a well done system.

I am with you that I don't believe the car is running the brakes in the same method that a conventional ICE car works. Yes, I went out and took a better look and there is a piston that connects to the brake pedal, so mechanically the brake pedal does have a level of applying the breaks. What is up in the air though is how the system actually works.



Why do you think this is more interesting than all the other power assisted mechanical brakes that also do not push back against the pedal?

If you look at a standard master cylinder, the brakes have a piston that connects to the hydraulic lines and a reservoir tank. The first part of the pedal press pushes in extra fluid into the lines to move the brake pads closer to the rotors then the reservoir is closed off and the hydraulic oil is then forced to compress pushing the pads against the rotor that causes friction and stopping. It is a pretty simple mechanical process.


But with this car, you have a different system where there is a linked motor that is part of the transmission that will also be depending on a circuit to act as a resistance force by becoming a generator. All so far is pretty simple. But then you throw into this the graph that is put out by Kia (post#33) where if you read the chart, the friction breaks are engaging right at the beginning (assuming a higher speed stop) then lessen as the car starts to slow down at the very end engage fully.



If you look at the breaking as two separate systems with the hydraulic sperate from the regenerative electric, then model, a standard master cylinder design would not work, as it would just provide a logarithmic increasing force as the brake pedal is pressed, where the chart shows an initial higher pressure on the pad that lessens as the car slows. This would then require the addition of a total secondary piston in the hydraulic line that is computer controlled separately to the one connected to the brake pedal. So now you have a master cylinder system that had two pistons, that also require flowback protection between the two so that as the computer controlled piston doesn't just flood the reservoir tank depending on the position of the brake pedal piston. It is not a simple design.




On the Ioniq forums, there are a number of advocates for regular emergency braking as the only way to clean the rust off the disk brakes from lack of use so they work well when you actually need them. There is no doubt that mechanical brakes are used far less on hybrid cars and EVs than ICE cars based on the longevity of the pads. There is also no doubt that the brakes will function in a total power loss so it is not brake by wire, at least not the mechanical braking action. It is also clear that activating the mechanical brakes requires a good bit of travel on the brake pedal no matter the circumstances. There is a lot of room in that travel length to activate regen deceleration without activating the mechanical brakes. There are a lot of possibilities on how this can be engineered but it clearly has been. Hate to say it, but this is a really foolish debate.

As with the post #33 in this thread, the way the hydraulic brakes function, it cannot be a simple mechanical brake system, and as you have pointed out with there being an actual connection to the brake pedal, not a simple by wire either. I guess that is why they call these cars a Hybrid, as there is quite a bit of combining both systems together.
 
#44 ·
On the Ioniq forums, there are a number of advocates for regular emergency braking as the only way to clean the rust off the disk brakes from lack of use so they work well when you actually need them. There is no doubt that mechanical brakes are used far less on hybrid cars and EVs than ICE cars based on the longevity of the pads. There is also no doubt that the brakes will function in a total power loss so it is not brake by wire, at least not the mechanical braking action. It is also clear that activating the mechanical brakes requires a good bit of travel on the brake pedal no matter the circumstances. There is a lot of room in that travel length to activate regen deceleration without activating the mechanical brakes. There are a lot of possibilities on how this can be engineered but it clearly has been. Hate to say it, but this is a really foolish debate.
 
#48 ·
Yes, it seems the hydraulics are transformed into an electric signal that blends regen with friction as required. With normal blending failed, the hydraulic pressure goes through a series of valves directly to friction brakes. I assume in normal braking, brake pedal feel is totally artificial.
 
#49 · (Edited)
Yes, it seems the hydraulics are transformed into an electric signal that blends regen with friction as required. With normal blending failed, the hydraulic pressure goes through a series of valves directly to friction brakes. I assume in normal braking, brake pedal feel is totally artificial.

No. There is a totally separate electrical sensor that is mounted on the brake pedal that senses the depression and amount of force (rotation angle) applied. This is what makes the whole system rather interesting from not only a functionality point of view (how it works) but also from an engineering perspective (how they made it work). So it would be sort of the other direction in the electrical is transformed into a hydraulic to operate the braking pads. It might be that the piston connected to the brake pedal is there for feedback pressure and had no actual connection to the actual braking system at all. Again, until someone actually tears down the system and comes up with a functionality diagram, I'd have no clue how it actually works. Think of when you hammer the brakes and ABS kicks in, you feel the pulses of the ABS working. That would not be possible if it was a total by wire system.
 
#50 ·
The posted graph is pretty difficult to read and misleading. A light press on the brake pedal does not activate the hydraulic brake, period. So something is wrong here. You are basing your theories on nothing concrete.

Even in ICE cars, it is a rare model that the first bit of travel on a brake pedal does anything (and if so, usually dangerously misadjusted). So on hybrids, there is plenty of room on the travel to initiate regen deceleration without the hydraulic brakes activating. The amount of deceleration power available versus slowing demand by driver (or AEB) will determine the blending of both. Power assist is completely separated by design on modern brakes as far as I'm aware. There are older mechanical assist systems (common in drum brakes but I've also seen designs for disk brakes) where the assist is part of the mechanical design, not a separate system. But this again is far removed from any reasonable misunderstanding of how hybrid brake systems work.
 
#51 ·
Yticolev. You are correct in the posted graph is difficult to read in you don't have any real indication as to what is being shown. To say it is misleading is a far stretch as since it doesn't say what the parameters of what is shown are, then it is only misleading if you make the wrong hypothesis as to what is being shown.


From my way of reading it, I am thinking it is more how the brake system works in respect to speed and not really how hard you are pressing on the brake pedal. As those items are also variables, it does make the graph less meaningful as likely those factors will change how the system work. But the logic would go that if you are braking at a high speed, say 70mph, the hydraulic breaks would initially be needed to slow you down about equal to the regenerative braking by the motor. But as the vehicle slows, the amount of force needed by the hydraulic brakes will drop off quite aggressively as most of the braking power can be done by the motor. It is at the very end of the braking process that the motor stops regenerative braking and the hydraulic brakes kick in.


I don't know how you are interpreting the graph. As I said, the way the system actually works isn't cut and dry and until someone starts to take the car apart and publish how things really work, we are just speculating based on opinions and not real facts.
 
#54 ·
But the logic would go that if you are braking at a high speed, say 70mph, the hydraulic breaks would initially be needed to slow you down about equal to the regenerative braking by the motor. But as the vehicle slows, the amount of force needed by the hydraulic brakes will drop off quite aggressively as most of the braking power can be done by the motor. It is at the very end of the braking process that the motor stops regenerative braking and the hydraulic brakes kick in.
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.
 
#52 ·
I agree that graph I posted leaves some things to be desired. My impression is that it's trying to portray more information than can be reliably portrayed in a two dimensional graph, and it's probably more of a hypothetical portrayal of a typical sequence of events than anything else.

The other diagrams on the page required some study before I felt like I could understand them. It helps to recognize that there are three sets of valves represented in those schematics, described as "In", "Out" and "Cut". In the absence of electrical supply, the In and Out valves are closed and the Cut valves are open, leading to the arrangement that appears in the diagram labeled "3.Brake malfunction". This appears to portray a conventional hydraulic/mechanical braking system, and it's what you would have if a fuse blew at 60 MPH and you needed to use the brakes to stop (one hopes that all of these valves will be 100% reliable in opening and closing for the lifetime of the car, or things might not go so well in a power-out condition).

My take after studying the diagrams is that when everything is working correctly, it is 100% "brake by wire" and only diagrams #1 and #2 come into play. The computer regulates the In and Out valves to modulate the pressure, based on some sort of "Driver's demand" pressure signal, the sensor for which I could not confidently determine from the schematic. But in a power failure scenario, we have diagram 3 and it's a conventional braking system.

As for rust on brakes: I live in an arid climate so don't have many opportunities to investigate this, but I recall an occasion years ago where I happened to be looking at the rotors of two cars that had been parked out in the rain, on grass, overnight. Both cars had been driven the previous night and I was checking them out in the morning. One had rotors without a spec of rust, the other had rotors that had already acquired surface rust, in the perhaps 10 hours since they had both been parked in a damp environment. The former was a BMW, the latter was a Mazda RX7. Both nice cars, but the BMW clearly had higher grade steel than the Mazda with respect to the material that the rotors were made of. Which begs the question: what happens to a Niro's rotors if you leave it outside over night in warm weather and damp conditions? And if they do develop surface rust as quickly as that Mazda did, then that might actually be an interesting way to discover how much you are using your friction brakes in the course of driving, in that if you drive and stop a few times and it's all polished off, then you're probably using the friction brakes a fair bit, and if it isn't, then perhaps you haven't used them much at all. Not quantitative, but still possibly offering insights.
 
#53 ·
The Niros rotors rust in an 8 hour work day. I can drive to work and when I leave (if it has been heavy raining), there will be surface rust on the rotors.

One thing to remember, rust has very little to do with the "quality" of the metal used. Extremely high purity cast iron will rust in minutes. High dollar steel can also rust in hours. Even the lowest grade of stainless steel is not going to rust under normal conditions.

Perhaps the BMW mentioned above was engineered with stainless steel rotors and not iron or steel rotors. Either metal stops the vehicle just as well as the other metals.
 
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