Shinobi'sZ

Might be able to say the same for two-wheel drive vehicles as well. I am making 700whp with my C7Z and the launch control no longer works like it did at the stock hp level (550whp). I think on computer is wanting to see the OEM hp to brake, when I mash the brake and push the accelerator all the way to the floor it tries but then surges. I don't use launch control just was testing after the tune.

JerryU

Just recollecting my 1974 CJ5 V8 Jeep. In 4WD with the hubs locked, there was no torque converter or other element that could adjust front to rear. As I recall it was set up to have the front wheels be in control with a slightly different dif/Intermediate gear or whatever was in the Low gear FWD engagement case. My recollection was reinforced several times as it warned NOT to lock hubs and have in 4WD on dry pavement as it stressed the front universals. See side bar as I used a very high-tech solution to press the universals out to replace! 

I do recall the lengthy conversation by Tadge, Harlan Charles and Jess Holder in the ~1 hour Steve Garrette Podcase right after the last BASH. Tadge said they were starting from scratch when the E-Ray was being designed (probably 2012/2013) to deal with the complex issues in some situations coordinating front and rear wheel power with just computer control. He mentioned they are continually measuring "microslip" on all 4 tires to define how much power each wheel should receive in a turn (assume high "g.") He said there are certain situations where it is very difficult to decide what to do as when hitting a wet spot in a turn. They decided best to just shut the motor off and apply no load!

In another case he mentioned what became obvious to me in my 500-mile break-in drive. If cruising without coasting or braking the battery would get to a low state of charge (perhaps 30 to 40%.) When you did apply the brakes you saw -75+ hp as the motor turned generator tried to charge back to the 80% where it appears they want it to be. (Tadge in the Jay Leno video said it would charge with almost it's max 160 hp!) D Tagde mentioned that if going up a long snowy hill where the system would like to charge the battery that was prevented as the load on the front tires could affect stability.

So sounds like when i doubt- shut off the motor! May not happen often and I'm sure the programing with what if's is very complex!

SIDEBAR
When we moved our R&D Lab from Tarrytown NY to NE OH we could take anything we wanted as that portion of the Corporate Research Center was being shut down. We always had a machine shop where tensile and Charpy impact test specimens were made. Always tested on large devises like a Tinius Olsen Tensile Tester. It operated hydraulically and could break a flat bar tensile specimen from 100,000+ psi steel that was 5/8-inch-thick X one inch wide and heavier. After it was installed, we quickly decided it was cheaper to send test plates out to be machined and specimens set to a certified lab for many tests made that had to be certified, for the Navy, NRC, ASME vessels etc. So the Tinius Olsen sat unused.
However, with the salt on the roads in NE OH that Jeep front universal did not budge from the yoke with the very large vise we had in the Lab. So on a Saturday recall setting the tester up to press out that universal cap from the yoke. Remember cringing at the amount of force required and as the hydraulic pump groaned!

Similar to our tensile Tester.

3LZR21U

I would think with modern computing power, detecting wheel slip on each corner and cross referencing it against motor output, engine output, actual vehicle speed, etc--would result in the ability to precisely calibrate where to redirect power--even when well beyond stock power levels. Again, I am not an engineer. Just an enthusiast of technical progression.

RedLS6

2 wheel drive launch control is difficult enough to have been the topic for quite a few PhD doctoral thesis' and many published research papers. The C8 DCT is even harder since they're boosting the launch with both clutches and are trying to distribute the work (and heat) through both equally. You're probably at 700+ rw peak torque and a good bit more torque than the stock ~470 coming off idle, if you have a pulley - a good bit more than my car makes. The extra torque is what makes it difficult for the stock parameters -

rackemup

E-Ray low end torque will make it a ball to drive on the street.

JerryU

Curious, do you have a reference with info on what they do during Boost Shift? All I have seen "officially" is when Ed Piatek, (Chief Corvette Engineer at the time. Josh Holder's current job as Mary Barra pulled, Ed and half the Corvette engineers to work on EV's 4 years ago) QUOTING: “We found that during very aggressive launches we can drive torque through both shafts/clutches simultaneously which improves the 0 to 60 times.”

Assume they are slipping the clutches for XX milliseconds??

RedLS6

I can post some non proprietary DCT test clutch pressure graphs up, once the Guinness wears off and I can find them, quite a few manufacturers do this. It's more than a few milliseconds, more like a few hundred milliseconds. There are usually 3 stages, all at constant engine launch RPM; 1) Increasing clutch pressure on both clutches 1 and 2; Followed by 2) increasing clutch pressure on clutch 1 and decreasing pressure on clutch 2. Followed by 3) clutch 2 pressure goes to zero and then clutch 1 transitioning from slip to no slip (fully engaged). The idea is to split the slip work (and heat generation) evenly between both clutches, with a corresponding torque boost. This control scheme is difficult enough that some adjustability is a good thing.

NORTY

Nailed it.

mmthomas

Question for the experts!

Will the eray continuously attempt to charge the battery/drag brake tge front motor at all part throttle conditions up and until full throttle, where all power will be applied to all wheels?

JerryU

^^^
No expert, just a greadhead owner! BUT, Nope!
Tadge said it works this way (and I have felt want watched the power meter verifying.)

• First and I have observed, it mostly charges the battery when coasting and braking - saving energy. After I have been driving at a steady speed, I see it get go negative 75+ hp as I brake! He also said in the Jay Leno video it can charge with almost it's 160 hp output.
• Tadge said IF the battery gets low, (I find it stays close to the max 80% charge) the LT2 will "push the front wheels, motor tuned generator" IF you are not demanding full power from the LT2. He said you won't notice as it will increase the throttle via wire so you will not detect it is happening. (Can feel a little.)
• So at WOT it won't happen.
• Now I have not tried Charge+ (no need) and don't recall if he said what occurs there, BUT logic would say if Tracking and you're at WOT unlikely it would try to charge the battery. BUT guess if charge got lower than 20% it might. It had been said they won't let it get lower than ~20% so if you are expecting "help" from Torque Vectoring in an apex of a turn- it will be there!
• Don't know their algorithms. But there is a graph on the center display that shows state of charge and looks like the band is from as low as 20% to as high as 80% no higher. Never saw it get close to 20%. It sure charges fast when braking.

3LZR21U

I don't know, but I would assume so. Not the regen braking part, but the charging off part throttle. I don't know for certain. Just from my layperson perspective, if you need say 300hp to get you through a corner at the limits of physics, then there should be ~100hp+ that the ICE can provide, which isn't being used (unneeded). So in conditions like this, it should be easy to squeeze a little more out of the ICE to charge the batteries--without negatively impacting performance. Just my $.02.

PRE-Z06

How does the regeneration affect braking, does it feel any different for those that have one. It was very noticeable in the Plaid I drove on track, but with the E-Ray only having a front motor Im curious if it is just dragging the front wheels when recharging?

JerryU

If the Battey is say at 60% versus the normal 80% when braking you can feel something but it's not like the BMW EV I just drove. Most of the time just feels like good braking (after I bedded the brakes!)

Funny when I wrote my PDF re C8 hybrids the December 2019 after the leaked article re C8 Hybrid in November 2919 I had written this below, which I had seen prior in Road & Track:An R&T article by Jason Cammisa had an interesting comment re the brake by-wire assist related to the C8 Hybrid:
"Once you start thinking about a hybrid Corvette (by-wire assist) really starts to pay dividends. Hybrids use blended brake systems that continually shift braking duties between regenerative braking and conventional friction braking. This leads to inconsistent and unusual pedal feel that a by-wire assist eliminates!"
I recall F1 drivers having to balance how much friction brake they used for a turnintegrating“if” their KERS would be aggressively charging their small battery. Sounds like “by-wire assist” can help compensate for that variability."

Yep, brake by wire can composite your foot brake force by knowing how much generator braking is occurring! Have not heard the issue in F1 in the last few years. Perhaps they have compesating software as well!

PRE-Z06

So is the brake by wire compensating with the brake bias when the front is regenerating braking? If you just lift off the throttle in a corner is it enough to cause weight to be transferred?

3LZR21U

I'd guess that the electronic means has a lot more response and ability to change rapidly than conventional mechanical (hydraulic) means.

JerryU

Yep, appears to operate just a Jason Cammica speculated in that R&T article in ~2019! Doubt if making a high "g" turn they allow it to change the car balance. Tadge has said the algorithms that control front/rear and side to side balance (like Torque Vectoring) are very complex. As he noted in the case of a front wheel hitting a slick wet spot in a turn they don't try to manage front wheel power, they shut the motor off and let the open dif coast!

SIDEBAR
BTW, been following the fact that the C8 would be a hybrid after I read the 1174 page government report (written 2012) that cars would be required to ~double EPA test mpg by 2025 (to cut CO2 emissions in half.) That was reinforced in a EPA Press Release that said following the new requirements would have the "average car" achieving 54.5 mpg! Note that report showed the Corvette Family (and other 2 seat sports cars) would be required to achieve ~39 mpg in 2025. The long, detailed report said most cars would use hybrid technology. I have continually updated that Doc and waiting for the next show to drop. Although the early EPA plan was stopped with a pen in January 2017 the current pen reinstated in April 2022 stating the average car will be required to achieve 49 mpg in 2026. We'll see just how it will be measured! Here is the updated PDF Doc: http://netwelding.com/C8_FWD_Hybrid.pdf

RedLS6

Was talking to a buddy here about the E-Ray dyno, and he pointed out that he suspected the E-Ray's electric motor was being driven to put out more than its 125 ft-lb rating. I think it's putting out right around its 125 ft-lb rating. The dyno measures directly at the rollers, and then refers the roller values back to the engine via the DCT transmission gearing. So, the dyno is combining both the ICE wheel output and electric wheel output to determine an equivalent output at the ICE flywheel, by referring back through the DCT gear ratios.

Here's the math: I'm assuming the dyno was done in 4th gear.
Motor makes 125 ft-lb at motor shaft
Motor gear reduction is 8.16 : 1
Motor makes 1020 ft-lb at wheels

Dyno refers the 1020 ft-lb back to the engine flywheel through the 4th DCT gear (0.88) and final drive (4.89)

(1020) / (0.88 * 4.89) equals 237 ft-lb added by the motor. Approximately equal to the dyno graph deltas.

This just means that the 125 ft-lb added by the motor "feels" like an additional ~230 ft-lb at the LT2.

dw886

There's a new E-ray Dyno video that popped up on YouTube from a few days ago that I just bumped into. These guys Dyno'd it at 499 miles, and then again at 501 miles after the "break in" period to see if there was any difference.

PRE-Z06

Thanks for sharing, so it appears they limit torque down low regardless and then there is ~50hp drop up top when battery is drained which makes sense in the lower trap speeds we’ve seen in the drag race videos.