My Leaf roll back and almost kill a kid!

[cwerdna]

^^^
I'm not advocating people shift to neutral as a normal part of their driving, but I'm suggesting (where safe) shifting to neutral and then braking to test the friction brakes. If that doesn't work reliably, I think the OP needs to go back to the/a dealer.

 

[lemketron]

12.3 volts on "new" battery? i think next thing to do is get your voltmeter checked. it probably needs batteries too

Just checked my 18mo old battery (~12K miles) and it says 12.36V on my Fluke DVMM.

What voltage would you expect to see? Or are you implying that a new battery should read even higher?

 

[Herm]

Charge the battery, disconnect the negative terminal so there is absolutely no load, wait about 20 minutes and measure with your DVM.. this will give you an approximation of the condition of the battery, note it must be measured at room temperature:

http://www.digikey.com/us/en/techzone/energy-harvesting/resources/articles/battery-fuel-gauges.html" onclick="window.open(this.href);return false;

 

[Smidge204]

Are you completely sure about this? That one ABS valve being in "relief mode" would "block further fluid from leaving the master cylinder"?

Yes. Otherwise lowering pressure for one wheel would bleed pressure off of all the other wheels, and you'd lose breaking altogether. Even if the ABS unit fails (other than physically splitting open and leaking), at worst is becomes extra volume in the system. The whole point of "fail safe" is if it fails, you're still safe.

There's a fairly good explanation of how it all works here though the diagrams are poorly resized and hard to read.
=Smidge=

 

[RegGuheert]

The very notion that there is a possible scenario where an electrical/electronic fault can result in total brake failure is unforgivable, IMO.

There's a fairly good explanation of how it all works here though the diagrams are poorly resized and hard to read.

It seems clear from the diagrams in the link you provided that an electrical/electronic failure can cause the ABS to allow the pedal to move completely to the floor as reported by the OP by relieving all the pressure from the master cylinder. Why do I say this? Because the pressure holding valve and the pressure relief valve are two *separate* valves with two *independent* electrical controls. As such, a fault in programming or in communication could result in the pressure relief valve being opened while the pressure holding valve is also still open.

I would cede the point in your first quote above if and only if the pressure relief valve and the pressure holding valve were controlled by the same electrical actuator or the mechanical design was such that the solenoid could only start to open the pressure relief valve once the pressure holding valve was closed. However, it is clear from the theory of operation that there are three different operating modes present, meaning that two separate electrical actuators are used for the two valves. No mechanical interlock mechanism is shown preventing both valves from being opened simultaneously. Given two independently-operated valves, there are four distinct operating modes possible and it is up to the electrical/electronic controls to prevent the fourth mode from ever occurring.

 

[Smidge204]

Why do I say this? Because the pressure holding valve and the pressure relief valve are two *separate* valves with two *independent* electrical controls. As such, a fault in programming or in communication could result in the pressure relief valve being opened while the pressure holding valve is also still open.

Okay, let's examine that scenario: Both holding and relief valves are open. What happens?

Absolutely nothing. The holding valve only lets fluid flow into the pump mechanism, which has a tiny reservoir but is otherwise already filled with fluid. Nothing can flow through that channel because the pressure at the pump discharge is equal to the applied brake pressure. The purpose of the pump, after all, is to increase the pressure and cause flow from the reservoir back into the system... this increase in pressure goes back up the system and is is felt at the pedal as a vibration.

You might be a little bit of squish as that reservoir - which is only a few cubic centimeters in volume - fills but it will immediately firm up again. There is no bypass return to the master cylinder anywhere. Fluid goes into the unit and has no way of getting out except through to the brake caliper.
=Smidge=

 

[RegGuheert]

Okay, let's examine that scenario: Both holding and relief valves are open. What happens?

Absolutely nothing. The holding valve only lets fluid flow into the pump mechanism, which has a tiny reservoir but is otherwise already filled with fluid. Nothing can flow through that channel because the pressure at the pump discharge is equal to the applied brake pressure. The purpose of the pump, after all, is to increase the pressure and cause flow from the reservoir back into the system... this increase in pressure goes back up the system and is is felt at the pedal as a vibration.

You might be a little bit of squish as that reservoir - which is only a few cubic centimeters in volume - fills but it will immediately firm up again. There is no bypass return to the master cylinder anywhere. Fluid goes into the unit and has no way of getting out except through to the brake caliper.
=Smidge=

Thanks! Makes sense.

So the question becomes the ratio of the volume of fluid pushed by a single pump of the brake pedal versus the volume of the four anti-lock reservoirs plus the volumes of the wheel cylinders between their static position and when braking occurs. Is there any way to determine what those volumes are to see how far the pedal would travel in this scenario?

 

[DaveinOlyWA]

12.3 volts on "new" battery? i think next thing to do is get your voltmeter checked. it probably needs batteries too

Just checked my 18mo old battery (~12K miles) and it says 12.36V on my Fluke DVMM.

What voltage would you expect to see? Or are you implying that a new battery should read even higher?

so lead acid battery held at just over 50% SOC? according to chart posted by Herm. not sure I can say that this is recommended.

i think the battery is sized too small for the load its handling. should really have changed this one to LI where it can better handle greater variations in SOC

 

[dgpcolorado]

Also, if you shift to neutral and use the brakes, is it relying solely on the friction brakes and there's no regen? That's the way it is on the Prius.

Unlike a number of others here, I never use neutral while the car is moving. But the Owners Manual is very clear:

Starting and driving
. Driving vehicle
. . Electric shift control system
. . . Shifting
. . . . N (Neutral)
<snip>
The regenerative brake system does not operate in the N (Neutral) position. However, the vehicle brakes will still stop the car.

I will note that I carefully trimmed off the first sentence in that paragraph, since I didn't want to bias the pro-neutral folks against the part I quoted. :|

Ray

If one is going to coast a long way—a half mile or more, say—it is more convenient in neutral. However, I found out early on that if I forgot I was in neutral all I had was the mechanical brakes—like most ICE cars—and the feel is very different from the usual LEAF braking, not to mention wasteful of energy. The solution was easy: remember to shift back to D for gentle slowing or Eco for more rapid slowing prior to approaching the Stop sign at the end of the run. For short stretches of coasting it is easier to just use Eco and feather the "A pedal" to keep the energy screen at 0 kW.

I realize that flatlanders or those who drive in traffic will have few opportunities to coast a long way safely. But it is routine for me at the bottom of my hill (if the Sheriff's officers don't have it staked out...)

 

[DaveinOlyWA]

i started coasting because most of the top performers here do it. plus its easier when you are trying to "glide" than trying to hold the power display to zero. when above say 30 mph, it feels different than eco or drive (unless you have a full charge) and I do feel that I coast farther and maintain more speed when I do.

maybe a psychological thing but i rather enjoy constantly shifting from eco to D to N to D to Eco. have completed many trips this way only touching brakes to stop at my destination

 

[oscar]

12.3 volts on "new" battery? i think next thing to do is get your voltmeter checked. it probably needs batteries too

Just checked my 18mo old battery (~12K miles) and it says 12.36V on my Fluke DVMM.

What voltage would you expect to see? Or are you implying that a new battery should read even higher?

ok measure with another voltmeter at work. The new reading is 12.47volts. This battery is brand new; replacement just 2 days ago.

Also had a chance to park at 3 different locations on uneven pavement. I couldn't repeat the brake lock symptom anymore.

So I'm going to conclude all my problems that I have listed is due to the 12Volts battery running low in range of 10.7 to 11.3 volts. I hope in near future someone post issues relating to car error. Ask them check the 12volts battery.

Also I agree with one of the post that Nissan should send an email or letter or warning that our 12volts is below the requirement level. I though Nissan download our car information when we hit agreement for information download or I'm mistaking that information download each time we start the car is tracking milage?

Anyway if Nissan can manage to measure the 12volts an display "Warning 12 volts battery replacement or check". It can save lots of headache for future Nissan Leaf owner!

 

[lemketron]

... So I'm going to conclude all my problems that I have listed is due to the 12Volts battery running low in range of 10.7 to 11.3 volts. I hope in near future someone post issues relating to car error. Ask them check the 12volts battery.

Also I agree with one of the post that Nissan should send an email or letter or warning that our 12volts is below the requirement level. I though Nissan download our car information when we hit agreement for information download or I'm mistaking that information download each time we start the car is tracking milage?

Anyway if Nissan can manage to measure the 12volts an display "Warning 12 volts battery replacement or check". It can save lots of headache for future Nissan Leaf owner!

Indeed!! Seems ironic that we spend so much time worrying about the state of charge (and longevity, etc.) of our traction battery, and yet the achilles heel of the car may actually be the 12V battery.

Ideally, the car itself should warn us when the 12V battery gets low, and perhaps devices like WattsLeft and LeafScan could also monitor the voltage on the 12V bus for us...

 

[DaveinOlyWA]

... So I'm going to conclude all my problems that I have listed is due to the 12Volts battery running low in range of 10.7 to 11.3 volts. I hope in near future someone post issues relating to car error. Ask them check the 12volts battery.

Also I agree with one of the post that Nissan should send an email or letter or warning that our 12volts is below the requirement level. I though Nissan download our car information when we hit agreement for information download or I'm mistaking that information download each time we start the car is tracking milage?

Anyway if Nissan can manage to measure the 12volts an display "Warning 12 volts battery replacement or check". It can save lots of headache for future Nissan Leaf owner!

Indeed!! Seems ironic that we spend so much time worrying about the state of charge (and longevity, etc.) of our traction battery, and yet the achilles heel of the car may actually be the 12V battery.

Ideally, the car itself should warn us when the 12V battery gets low, and perhaps devices like WattsLeft and LeafScan could also monitor the voltage on the 12V bus for us...

the 12 volt battery was a sort of Achilles Heel on the Prius as well. twice, left door open (safe neighborhood i guess...) and dome light caused the battery to die. I then had to crawl into the back to pull the manual release to get hatch open to access the 12 volt battery to jump it.

 

[oscar]

Ideally, the car itself should warn us when the 12V battery gets low, and perhaps devices like WattsLeft and LeafScan could also monitor the voltage on the 12V bus for us...[/quote]

After thinking with all the pain I had to put up with in past few months. I realize get rid of the tree display and offer me a display to monitor the 12 Volts battery level!!!!!!!!!

We all agree the 12volts battery is the main component in the EV car( I consider the 12volts is a Heart like human body; Heart stop brain won't function anyway)! If 12volts low or dead many of the operation will be non functional! Can someone let Nissan know give us a 12volts display scale! Otherwise future Leaf owner got go buy a voltmeter. When Nissan can display it on the screen.

 

[davewill]

the 12 volt battery was a sort of Achilles Heel on the Prius as well. twice, left door open (safe neighborhood i guess...) and dome light caused the battery to die. I then had to crawl into the back to pull the manual release to get hatch open to access the 12 volt battery to jump it.

It's a little late to help, but I'm pretty sure although the battery itself is in back, there are jump contact points under the hood.

 

[planet4ever]

the 12 volt battery was a sort of Achilles Heel on the Prius as well. twice, left door open (safe neighborhood i guess...) and dome light caused the battery to die. I then had to crawl into the back to pull the manual release to get hatch open to access the 12 volt battery to jump it.

What? You never learned the right way to do that? My wife had a habit of switching the dome light to the ON position and forgetting it. I don't know how many times I've pulled the mechanical key out of the remote control so I could get in to pop the hood. Pry the plastic cover off the fuse box by the right wheel well and connect the red jumper cable to the special connector there which has a red cover. Grab the edge of the valve cover with the black cable. Much easier than crawling in the back. It's basically the same as with the LEAF except the hot connects to a real battery on the LEAF and a "virtual" battery on the Prius. (Well, OK, it does take a bit of practice on the Prius to learn how to squeeze the fuse box cover to disengage the projections that hold it in place.)

Ray

 

[DaveinOlyWA]

This was on the 06 and I was not the primary driver. I as far as the hood jump option it was pretty tight fit. A bunch of people connected a tab to the contact point that made it easy to grab. I never did. I also was not lucky enough to ha e any help in these situations

 

[garygid]

I am planning to add display of the 12v battery voltage
to the next version of the GID-Meter's firmware.

A small addition to the hardware will also be necessary,
possibly requiring one solder connection.

However, adding the hardware to older GID-Meters
should be relatively easy, I expect.

 

[RegGuheert]

ok measure with another voltmeter at work. The new reading is 12.47volts. This battery is brand new; replacement just 2 days ago.

That's about 80% SOC by some tables. It depends on the temperature and the battery chemistry, of course. My guess is they did not charge the battery before inserting it into the LEAF since most cars will quickly charge up the battery to 100%. Simply put, the LEAF does not put a lot of effort into fully recharging the 12V battery like most cars. Perhaps that is because it is a deep-cycle battery rather than a starting battery, but either will experience hardening-of-the-sulfate if left below 100% SOC for long. I've read that in very hot weather the lead sulfate can harden in as few as three days. I don't know about that, but leaving a lead-acid battery not fully charged does reduce its capacity over time.

There have been a couple of other threads where I and others have made some measurements of LEAF 12V battery voltage that you can use for comparison. This post has a plot I made showing the voltage of the battery for a LEAF when it is sitting unplugged in between being driven. There is a seven-day period in there (between days 14 and 21) when I did not touch the car at all. You can see the voltage of our LEAF battery got below what you are seeing.

For reference, here is another thread which includes some 12V battery measurements.

In any case, I don't think the LEAF's propensity to leave the 12V battery below 100% SOC is the cause of your battery failure. You apparently just had a bad battery and one of the cells shorted prematurely. I doubt you will ever experience this problem again.

 

[aqn]

Are you completely sure about this? That one ABS valve being in "relief mode" would "block further fluid from leaving the master cylinder"?

Yes. Otherwise lowering pressure for one wheel would bleed pressure off of all the other wheels, and you'd lose breaking altogether.

There are four hydraulic channels from the ABS controller (LEAF service manual, pages BRC-214, BRC-215), one to each caliper. I should hope that "bleeding off" of hydraulic pressure is done independently in each channel. Hydraulic pressure being relieved in one channel should not affect the other channels.

If fluid is prevented from leaving the master cylinder as soon as one wheel locks up and the ABS activates, then the three remaining calipers will not receive any additional hydraulic pressure and therefore their braking power are limited to the level it was at as soon as one wheel loses traction and the ABS comes on. For instance, what if one wheel was on a patch on ice and the other three on dry pavement at the moment I step on the brakes? The wheel on ice would lock up the moment hydraulic pressure increases and the ABS would activate. If the ABS blocks fluid from leaving the master cylinder, the other three brake pistons will not get the full dose of hydraulic pressure and not be doing their job.

That is why I was skeptical of your statement.

Even if the ABS unit fails (other than physically splitting open and leaking), at worst is becomes extra volume in the system. The whole point of "fail safe" is if it fails, you're still safe.

There's a fairly good explanation of how it all works here though the diagrams are poorly resized and hard to read.
=Smidge=

The diagram shows one ABS channel for one wheel. Braking and ABS action at one wheel should be independent of the others.

Also, that diagram shows a "closed ABS system" where a pump maintains hydraulic pressure in the affected hydraulic path. In an open system, the affected wheel simply has its pressure bled off into a reservoir. "A disadvantage of the open systems is that the brake pedal will drop during a long ABS stop as fluid flows from the brake lines."

I can certainly see how a software bug, or sensors malfunctioning, can cause all four channels to activate, bleeding off hydraulic pressure from each channel back into the ABS reservoir and/or back into the brake fluid reservoir, the net result being the brake pedal sinking to the floor. (I have not researched the service manual so I do not know whether the LEAF has a return path for excess hydraulic pressure back to the brake reservoir.)