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Niro has kindled a serious interest in a pure EV specifically a Tesla....
That's your best option if you want to know when the mechanical brakes are in use. As far as I know, every other manufacturer uses blended braking. Of course, somewhat irrelevant with one pedal driving.
 

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I too would be shocked if there is no mechanical hydraulic failsafe brake.

I do notice the master brake cylinder on the firewall where it normally is in front of the brake pedal.

Update

Confirmed by inspection. Mechanical connection from pedal to master cylinder.

yticolev is correct

So from an engineering perspective, it is impossible for the Niro to not use the friction brakes as the brake pedal is directly connected to the master cylinder. And looking at the graphs and other provided anecdotal data, the master cylinder must be quite an engineering feat to have both a computer controlled system that will vary the force applied inside so that it can vary the amount of pressure given to the mechanical friction breaks without applying that force back to the person pushing the brake pedal.



I would love to see how the master cylinder is designed.
 

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Discussion Starter #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.
 

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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.
 

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the master cylinder must be quite an engineering feat to have both a computer controlled system that will vary the force applied inside so that it can vary the amount of pressure given to the mechanical friction breaks without applying that force back to the person pushing the brake pedal.
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?
 

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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.
 

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Discussion Starter #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.
 

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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.
 

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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.
 

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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.
 

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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.
 

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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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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.
 

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Discussion Starter #55
I think the chart is just a snapshot of one stop from some undefined high speed. This is combined with the fact that braking involves the reduction in momentum and momentum is proportional to velocity squared. At the higher speeds, the motor (generator) is incapable of using enough energy to provide the level of braking required so friction brakes suppliment regenerative braking. As the speed decreases so does the momentum at an exponential rate so regeneration braking is sufficient. That is, until very slow speeds where regenerative braking is practically impossible and it's all friction.

With no units given, it's just the general relationship of regenerative vs friction braking at ever decreasing speed with (probably) a given amount of driver pressure. I still wish it were related to the gauge.

As to back up brake hydraulics, what is the clevis pin depicted further down the pedal arm? Is it brake feel, back up brakes, both? The pedal feel in normal braking is superb until right at a stop and not terrible even there. It seems to me that there has to be a hydraulic connection to the pedal somewhere.
 

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At the higher speeds, the motor (generator) is incapable of using enough energy to provide the level of braking required so friction brakes suppliment regenerative braking.
43 HP and the 125 lb-ft of torque provides a lot of deceleration before hydraulic brakes are needed. Why not try the test yourself I suggested, slowing to 30 mph from 70 mph using only the cruise control.
It seems to me that there has to be a hydraulic connection to the pedal somewhere.
Yup. Only you have thrown doubt on that with your brake by wire only theory.
 

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My simple minded graph interpretation

I think the graph is actually quite clear if one takes a simple minded view.

The y axis is brake demand (driver pedal pressure) the x axis is car velocity.

The red line is a particular path of an infinite possible combinations of brake demand and velocity.

Regenerative braking as always used first regardless of velocity unless the velocity is zero.

Friction braking engages sooner at higher velocities at lower brake demand. At lower velocities, friction braking is only engaged at much higher brake demand. I think this is a safety margin strategy. At high velocity, the car will error on the side of providing more than enough braking. At higher velocities, don't push too hard on the brake pedal if you want to avoid friction braking.

Area around point I , regen only
Area around point II, both
Area around point III, both
Area around point IV, both
Area around point V, friction only

Kia Niro : Description and operation : AHB(Active Hydraulic Boost) System
 

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Discussion Starter #58 (Edited)
I think that's an excellent interpretation. Since momentum that must be overcome at higher speeds is proportional to velocity squared, friction brakes are required to reach a level of braking easily obtained by regenerative braking alone at lower speeds. At near stop where regenerative braking is practically impossible friction brakes are again, required.

I wonder if the clevis pin depicted further down the brake pedal arm is a hydraulic connection eather for artificial brake feel, back up brakes or both. I can't imagine brake feel done otherwise.
 

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Sorry, not buying these conjectures. I think if you try my test under just cruise control, you will see that deceleration (negative G force) is roughly the same from any speed using motor alone (at least that is the subjective effect in my car). It only backs off when you are within 10 mph of the new set point. In fact, deceleration may be higher at 70 mph as wind pressure is contributing a larger amount than at say 30 mph. Whereas acceleration will be lower at 70 versus 30 mph (motor or engine or both).

If anyone has an accelerometer you can rig, this could be some interesting objective data. But even so, it sounds like this group will now quibble if it is motor deceleration only. The power meter also gives you some indication of how hard the motor is working during deceleration and it is easier to get a high energy return result at a high speed than a low speed.
 

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I think the chart is just a snapshot of one stop from some undefined high speed. This is combined with the fact that braking involves the reduction in momentum and momentum is proportional to velocity squared. At the higher speeds, the motor (generator) is incapable of using enough energy to provide the level of braking required so friction brakes suppliment regenerative braking. As the speed decreases so does the momentum at an exponential rate so regeneration braking is sufficient. That is, until very slow speeds where regenerative braking is practically impossible and it's all friction.

With no units given, it's just the general relationship of regenerative vs friction braking at ever decreasing speed with (probably) a given amount of driver pressure. I still wish it were related to the gauge.

As to back up brake hydraulics, what is the clevis pin depicted further down the pedal arm? Is it brake feel, back up brakes, both? The pedal feel in normal braking is superb until right at a stop and not terrible even there. It seems to me that there has to be a hydraulic connection to the pedal somewhere.
actually momentum is mv and kinetic energy is 1/2mv^2 but your point is correct. Stopping from high speed requires dissipating a lot more energy than stopping from low speed.
 
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