Volt's brake problem with the feel of sudden surge

Obviously sub standard. Let's have a full recall of all GM products and a witch hunt on their top management.

Ooops, sorry GM's an American company with a big union that pays into and supports the present US Government, so nothing will happen then.

 

Well doesn't this sound familiar? Physics strikes again.

There really isn't any way around this problem as long as braking systems are open loop, requiring the driver to modulate braking force to compensate for uneven braking. ABS helps retain control, but it does so by monitoring wheel rotation, not braking force. By the time the system notes lack of wheel rotation, the driver has already experienced the "surge".

The way to fix this problem is to go to closed loop braking control, where an accelerometer monitors braking effort. The driver presses on the brake pedal, telling the computer how hard he wants to brake. The computer increases braking effort and monitors the accelerometer until actual braking effort matches that requested. Regeneration and friction braking are blended seamlessly to provide the proper force. If regeneration is reduced friction is increased to compensate.

This sort of braking control can provide a uniform feel to the brakes over a variety of surfaces, up until the point when it is impossible to brake at the desired level. While it can control the braking effort, it can't create friction where it doesn't exist.

Tom

 

Tom,

Do you think it would require much more engineering and costs associated to make that change? I'd be surprised if the engineers weren't aware, but my guess is that economics takes over at some point?

 

The costs per vehicle aren't too bad, but when it comes to automobiles and other consumer products, costs are measured to the penny. Designers think long and hard about added even a few cents to the cost of a consumer product.

The engineering is considerable, but similar to the other drive-by-wire systems found in the Prius. I think it will happen eventually.

Tom

 

I've got over 10,500 miles now and have never experienced anything like that.

 

you, and the VAST majority of Prius owners. I say it's the unique part of driving any hybrid. Really, we can't seem to get past this? I'm all for a full GM investigation...since Toyota had to for a non-issue.

 

Thanks.

I would agree that it will happen eventually. Possibly as they get more and more hybrids on the road, the cost per vehicle may drop to a point they are willing to do it. I would be surprised if it isn't something already in the R&D area.

 

That report was quite unlike the prius brake software problem.

On the GM the complaint is when in L which introduces regen with foot off the accelerator, the braking skips when it loses traction. AFAIK there are not reports of brake problems when the driver actually puts their foot on the brake pedal. I would not put it past a software bug, as the prius problem was, but this is not a situation where new hardware is needed to close the loop. The driver is part of the loop and needs to hit the brakes when he wants to stop, just as he would using engine braking in a traditional car.

 

the volt is an expensive car... i would assume they would work to put in a lexus like equivalent of "even brake force distribution" and such.. since the lexus models really don't get the brake problems i've seen with the prius and now volt. i used to hot rod my parents rx400h... it acted like it was magnetically held to the ground.... sooo stable.

 

Even without accelerometer feedback (keeping the braking system "open loop"), I still don't see why Toyota or GM can not write the algorithm such that when the computer decides to reduce regen braking, it increases the friction braking accordingly to achieve a seamless transition.

 

I drive over speed bumps, and rough roads everyday and have not personally had this happen.. Will try to see if I cannot get it to happen on the way home though.. So far everything seems smooth to me. Maybe an issue isolated on the 2011's? I know the 2012's have a software update that is supposed to be back fitted to the 2011's to correct some issues.

 

Try to write one, you will find it nearly impossible with the current hardware.

 

+1

Yes it is quite straightforward. There are speed sensors at each wheel, the amount of regen energy can be monitored, and there is the speed sensor for the speedometer/odometer. Deceleration can be calculated from the current sensors. There is no need for new hardware, although accelerometers are now inexpensive. The toyota problem was a bug, that has been fixed. This has to do with regen in L, something meant to simulate engine braking not friction braking. I would not rule out a bug or lack of specification, but for all I know the software on the volt is operating the way the engineers intended it. This happens when the wheel sensors detect a slip and non-braking regen is removed from the comments. Without seeing the code, I would think a faster response to reengage brakes when an anti-lock event happens would be a possible solution.

 

I can't get it to happen on my car. I will try again in the morning. I was unaware there was even anything in the programming that affected regen braking as far as bumps and stuff are concerned. You would think that it would use the friction brakes to supplement the lost regen braking in a case like that since everything is done by wire. I have never had a problem with the braking feel on either car though.

 

The is deja vu, except affecting Volt folks. I wonder if they'll have the same pattern of many threads and arguments like we had over here...

Bwilson4web used to collect pictures of spots where this phenomena can be repro on Priuses. Pics at http://priuschat.com/forums/gen-iii-2010-prius-main-forum/67528-braking-problem-18.html#post1049963.

I've posted my known repro spot at http://priuschat.com/forums/gen-iii...99-poll-prius-brakes-problem.html#post1031776 but my Google Street View link there seems to have trouble. [ame="http://maps.google.com/maps?q=san+aleso+and+n+mathilda+ave,+sunnyvale,+ca&hl=en&ll=37.394119,-122.029264&spn=0.002474,0.001931&sll=37.393799,-122.029153&sspn=0.00007,0.004292&layer=c&cbp=13,236.12,,1,9.76&cbll=37.394282,-122.029212&hnear=N+Mathilda+Ave+%26+San+Aleso+Ave,+Sunnyvale,+Santa+Clara,+California+94085&t=h&z=19&vpsrc=0&panoid=-5crftgrV7BChonRx9VERA"]san aleso and n mathilda ave, sunnyvale, ca - Google Maps[/ame] should work.

I was last in that area within the past month or so and the pavement is still cruddy, like that.

 

Braking while running over a storm grate will cause it.

 

That is how it is presently done. The problem only occurs when traction is suddenly lost, not when the computer gently transitions from regeneration to friction braking.

Without an accelerometer to detect braking, the only way the computer knows when traction is lost is when one wheel stops turning as fast as the others. This, by necessity, involves some rotation of the other wheels, which means it takes time. The loss of braking effort during that time produces the "surge", or jerk.

Note that this is not unique to regenerative braking, but also happens with normal ABS brakes. This same issue has been reported with the Toyota FJ Cruiser, which is most definitely not a hybrid, but does use electrically assisted brakes.

Tom

 

I didn't with the "we're all going to die" braking in Prius either. It took quite a few tries to finally get it to trigger.

My commute takes me over train tracks. Despite smacking into them every day, nothing. Then I hit the brakes really hard just a moment before contact, it happened!

The reality of how much of an impact was required really stirred frustration with the magnitude of the smear campaign which resulted from it. Sure, a software update is good to encourage. But clearly, the issue didn't warrant the magnitude of the response & attention it got.

Now Volt has to deal with it. Think about how many don't want plug-in vehicles to gain any traction, who'd like to put a brake on them, perhaps a sudden surge of negative attention. (puns intended)
.

 

It does, but it takes a finite amount of time to detect the loss of regenerative braking and switch to friction brakes. The previous posts discuss the details.

Tom