Johan31270

Strong regen without press brake

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Hi,

 

I have my IS300H for 2 years now. I drove more than 25K miles and love it but :

Could you please make any suggestion for the followings things : (sorry for my english, I'm french)

1/

Sometimes, once a week or less, I have a strong regen even if i don't press the brake pedal. It happend at every speed !

I mean, the blue level indicates it regen at the maximum when for exemple I take of my foot to the throttle pedal at 90kmh, and I can clearly feel it brakes strong ! Like a Tesla..!

And later somehow, it disappears and the car has normal behavior again with  strong regen only with foot pedal... 

 

2/

Again, sometimes, I have a big lag in acceleration, just like if it was only the ICE is moving the car... It is very frustating, it is like I have no power from the Battery/electric engine. And the SOC doesn't move as usual even if the arrow shows it works normally... 

 

3/ EV MODE !

 

I love use EV mode when i leave my home in the morning. But it works only in the morning ! Several times I want to go to EV mode, and it says it is impossible ! 

Any suggestion ?

 

Thank you !!

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The only time that I have felt strong regen is when dropping down a gear or two using the paddle for example when descending a hill. Could your effect be due to the traction Battery running low  and requiring charging?

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11 hours ago, 200h said:

this is the pedal box that i've used its brilliant , lag is reduced making the car more drivable

https://www.diesel-performance.co.uk/tuning/car/lexus/is-iii/300h-ave30_-181ps133kw-2494-ccm/#go

Ok thanks ! It is plugged to the OBD ?

 

9 hours ago, reeac said:

The only time that I have felt strong regen is when dropping down a gear or two using the paddle for example when descending a hill. Could your effect be due to the traction battery running low  and requiring charging?

I don't touch the paddle in this case... I don't know why the car does that sometimes, its a mystery. It can happen when the Battery is low, or charged...

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I have noticed a similar thing with my GS450H, but I have found this happens if i have set the cruise speed at say 30 mph. If I then accelerate to a higher speed and then remove my foot from the accelerator pedal the car will coast for a short distance then decelerate strongly with lots of regen.

John.

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17 minutes ago, Britprius said:

I have noticed a similar thing with my GS450H, but I have found this happens if i have set the cruise speed at say 30 mph. If I then accelerate to a higher speed and then remove my foot from the accelerator pedal the car will coast for a short distance then decelerate strongly with lots of regen.

John.

Oh this is maybe the reason !! That's why i noticed that only on highway !!! I love the big regen, so i will try to set the cruise control to the minimum to see if it does something...

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13 hours ago, reeac said:

The only time that I have felt strong regen is when dropping down a gear or two using the paddle for example when descending a hill. Could your effect be due to the traction battery running low  and requiring charging?

That's not regen - that's using the eCVT to slow you down. In fact, it uses less / no regen; much better off using the brakes if you want the make use of the otherwise wasted energy.

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26 minutes ago, route66 said:

That's not regen - that's using the eCVT to slow you down. In fact, it uses less / no regen; much better off using the brakes if you want the make use of the otherwise wasted energy.

Incorrect using the paddles to give an effective lower ratio increases regen by speeding up MG1. In doing so producing more current for the Battery, and slowing the vehicle. Braking has much the same effect unless the braking is sufficient to operate the friction brakes that does waste energy.

John.

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From what i experienced, using the paddle increase the ICE breaking like a conventential car, but not the electic regen

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1 hour ago, route66 said:

That's not regen - that's using the eCVT to slow you down. In fact, it uses less / no regen; much better off using the brakes if you want the make use of the otherwise wasted energy.

 

6 minutes ago, Johan31270 said:

For what i experienced, using the paddle increase the ICE breaking like a conventential car, but not the electic regen

This is my experience also. I have a fairly long steep hill down to my home and using the paddles to restrict the gear range has no effect on regen just spins up the ICE. I just keep a gentle pressure on the brakes for max regen and can pretty much fully recharge the traction Battery.

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At the risk of stating the obvious, the regen operates when the traction Battery needs it.  Regen happens whenever foot off the throttle, at any speed, and especially when using the engine for braking, on a long downhill for example. 

Acceleration lag is normal and very frustrating.  My solution is to change down or switch to sport before accelerating. 

Pure EV only seems to operate for 4/5 kms.  Rest of the time it  'supports' the petrol engine. 

 

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19 minutes ago, BigChange said:

At the risk of stating the obvious, the regen operates when the traction battery needs it.  Regen happens whenever foot off the throttle, at any speed, and especially when using the engine for braking, on a long downhill for example. 

 

Not in my experience. if one invokes engine braking, by using the paddles/selector to restrict the gear range, increasing engine revs but no extra regen. 

Regen only with brake pedal application and yes, only if the traction Battery requires it (easily 90% of the time)

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On 8/23/2019 at 12:23 PM, Britprius said:

Incorrect using the paddles to give an effective lower ratio increases regen by speeding up MG1. In doing so producing more current for the battery, and slowing the vehicle. Braking has much the same effect unless the braking is sufficient to operate the friction brakes that does waste energy.

John.

Using the paddles in the IS300H is the same as using the "B" mode in a regular Prius - the main difference being the degree of control offered by the 6 "gears"; in the Prius it's really just a 1 gear equivalent. This article is a bit old but it does explain what is going on when you use the "B" mode (/ "Gears" in an IS300H): http://techno-fandom.org/~hobbit/cars/b-mode.html

This is what makes the Toyota/Lexus Hybrid installations so sophisticated - they are not just a bolt on, and the depth of integration in the design requires the engine to be started/stopped many times in normal driving to facilitate this. Unlike most engines, the Toyota/Lexus hybrid regularly keeps the vales open in the ICE to allow it to rotate with minimal pumping losses. The downside of this is poor engine braking. Using the "B" mode / "gears" to slow down returns the valves to normal ICE operation which help the car to slow down, and on the IS300H, the 6 "gears" allows control over the gearing. More revs with valves in normal operation = more engine braking.

So, as per the technical explanation in the above article and the experiences of drivers above, if you want regen, decelerate and/or use the brakes. The paddles do add to the fun (and their use wastes no energy if the Battery is already full) but doesn't do anything to charge up the Battery,

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30 minutes ago, route66 said:

Using the paddles in the IS300H is the same as using the "B" mode in a regular Prius - the main difference being the degree of control offered by the 6 "gears"; in the Prius it's really just a 1 gear equivalent. This article is a bit old but it does explain what is going on when you use the "B" mode (/ "Gears" in an IS300H): http://techno-fandom.org/~hobbit/cars/b-mode.html

This is what makes the Toyota/Lexus Hybrid installations so sophisticated - they are not just a bolt on, and the depth of integration in the design requires the engine to be started/stopped many times in normal driving to facilitate this. Unlike most engines, the Toyota/Lexus hybrid regularly keeps the vales open in the ICE to allow it to rotate with minimal pumping losses. The downside of this is poor engine braking. Using the "B" mode / "gears" to slow down returns the valves to normal ICE operation which help the car to slow down, and on the IS300H, the 6 "gears" allows control over the gearing. More revs with valves in normal operation = more engine braking.

So, as per the technical explanation in the above article and the experiences of drivers above, if you want regen, decelerate and/or use the brakes. The paddles do add to the fun (and their use wastes no energy if the battery is already full) but doesn't do anything to charge up the battery,

First of all let me state I was involved with the design of the Toyota hybrid system. Only a small part, but enough to know what goes on.
At no point in any of the now many iterations of the system is the ability in the engine design able to keep open the valves. The engines used are generally normal existing engines with modifications to valve timing.
The valve timing is altered so that some of the cylinder intake is returned to the inlet manifold by closing the inlet valves long after bottom dead centre, but this is done to reduce the effective compression ratio from around 13/1 "depending on the engine being used" to around 9/1. This in effect turns the engine from an Otto cycle engine " intake, and combustion stroke being equal" to a virtual Atkinson cycle engine "where the combustion stroke is longer than the compression stroke".

The valve timing is variable, but at no point are the valves kept open to reduce pumping losses. All that is required to remove any engine braking is to remove any electrical supply to MG1. The engine is then effectively disconnected from the transmission. This allows the engine to stop, and the car still to be powered by MG2 or be braked or give overrun regen by MG2 returning power to the Battery. Alternatively if the Battery is close to maximum charge level MG2 can power MG1 ,and spin the engine "without fuel" to give engine braking.

MG2 is always connected to the wheels "if the wheels are turning so is it". MG1 is effectively the engine starter, and device for engine braking, It has other functions that I will not go into.

John.

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I love these technical discussions, one learns something every day.

In my experience, as posted above, if I use the paddles to restrict the gear range (I'm in normal drive mode) going down the long steep hill to home, the engine revs rise but the regen meter shows minimal recovery. If I leave the transmission in D(again in normal mode) and gently apply the foot brake I can get maximum regen on the meter all the way down.

Does the regen meter not display recovery then, if the system works as @Britprius describes? Or is what John describes only true when the traction Battery is fully charged already?

 

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1 hour ago, NemesisUK said:

I love these technical discussions, one learns something every day.

In my experience, as posted above, if I use the paddles to restrict the gear range (I'm in normal drive mode) going down the long steep hill to home, the engine revs rise but the regen meter shows minimal recovery. If I leave the transmission in D(again in normal mode) and gently apply the foot brake I can get maximum regen on the meter all the way down.

Does the regen meter not display recovery then, if the system works as @Britprius describes? Or is what John describes only true when the traction battery is fully charged already?

 

The power meter does display energy recovered in both modes. What I believe is confusing the issue is that changing "down" will not slow the car as quickly as using the brakes. The rate of retardation directly affects the amount of regen. You can obviously brake harder to slow down than changing down will provide, but it is more efficient to regen over a long period at a lower rate than to get a high regen for a short period.

Braking beyond a certain threshold will bring in to operation the friction brakes reducing the amount of regen possible with a more gentle reduction in speed. There are many factors that are involved with regen including Battery charge level, and Battery temperature. If the Battery is fully charged "actually 80% charged" the system will not allow any more charge. Braking down a hill will cause the engine revs to rise, "any regen from MG2 going to MG1 to spin the engine" and conversely putting your foot on the accelerator the engine revs will fall "the system no longer is regening so will dump the high Battery charge by powering the car from the Battery, and engine revs will reduce or even stop because MG1 is no longer required to dump energy into spinning the engine.

John..

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2 hours ago, Britprius said:

First of all let me state I was involved with the design of the Toyota hybrid system. Only a small part, but enough to know what goes on.
At no point in any of the now many iterations of the system is the ability in the engine design able to keep open the valves. The engines used are generally normal existing engines with modifications to valve timing.
The valve timing is altered so that some of the cylinder intake is returned to the inlet manifold by closing the inlet valves long after bottom dead centre, but this is done to reduce the effective compression ratio from around 13/1 "depending on the engine being used" to around 9/1. This in effect turns the engine from an Otto cycle engine " intake, and combustion stroke being equal" to a virtual Atkinson cycle engine "where the combustion stroke is longer than the compression stroke".

The valve timing is variable, but at no point are the valves kept open to reduce pumping losses. All that is required to remove any engine braking is to remove any electrical supply to MG1. The engine is then effectively disconnected from the transmission. This allows the engine to stop, and the car still to be powered by MG2 or be braked or give overrun regen by MG2 returning power to the battery. Alternatively if the battery is close to maximum charge level MG2 can power MG1 ,and spin the engine "without fuel" to give engine braking.

MG2 is always connected to the wheels "if the wheels are turning so is it". MG1 is effectively the engine starter, and device for engine braking, It has other functions that I will not go into.

John.

... and let me state I wasn't involved in any aspect of the design of the Toyota Hybrid system! I'm just interested in technology and have read extensively on the Toyota hybrid system.

I've just googled "b mode toyota hybrid engine "valve timing"" - as I first did when we introduced a Prius+ into the family fleet 4 years ago - and now realise that I got carried away when I first read about the altering of the valve timing. For no reason whatsoever (!), I read altered valve timing to mean that the valves were held open. The google results prove what you say: the valve timing is just changed with B mode, they are not held open:

  • From a blog in Toyota's UK site (link) :
    Incidentally, when you move the transmission selector in to the B position, to get engine braking, the Prius alters its valve timing and pretends to be an Otto engine as Atkinson engines have useless engine braking.
  • From the Priuschat site (link) :
    B mode primarily changes the valve timing to create engine braking
  • Toyotanation (link) :
    B mode is much simpler than it has been described. It is simply an engine brake mode. Because the Atkinson cycle has poor engine braking, the intake timing is temporarily moved back to Otto cycle when in B mode. On all fuel injected engines fuel is cut off when you back off on the accelerator. No fuel is used in engine braking. You are just pumping air. Like an air compressor the engine gets hot from pumping and energy is wasted as heat. The source of energy for engine braking is the wheels, and the kinetic energy of the vehicle, not the Battery.
  • Hybridcars (link) :
    The "B", engine Brake mode for the Prius uses a change in valve timing to turn the engine into an air compressor to increase the compression braking effect.
  • Geekswithblogs (link) :
    When you go into B mode, it stars opening the air intake valves at the least efficient time. This causes the engine to push around a lot of air, which uses up energy, and helps slow you down, taking work off of the brakes.

I'm still confused however.. If the change to engine timing increases engine braking, then surely (& backed up by some of the above links) that means less regen?

 

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On our GS450h, using the paddles will bring the ICE into play (as I can get a bit more info on the GS because I can have a rev meter in the HUD while having the hybrid power-gauge in the cluster). 

Foot-off-throttle will only give very mild regen (about 10% of the regen sector of the power gauge). Very gentle pressure on the brake pedal will bring the needle down to 100% regen without bringing friction brakes into play.

Pulling the paddle (with foot on neither accelerator or brake) will cause the regen needle to jump to around 75%, but within about 2 seconds it will have reduced to 20% or so. Pulling the paddle again will cause another regen jump, but as the road speed and "gear" (ie D4, D3, D2) get more and more mismatched then the ICE revs climb and you're into the realms of traditional ICE engine braking. 

Very gentle brake pedal pressure is the best way to maximise use of regen braking, but max regen (at least on the GS) is pretty weak (but bear in mind that I had a Nissan Leaf and am picking up a Tesla this week - I'm familiar with the regen that can come from much bigger Battery packs). 

Also bear in mind that different vehicles will regen differently. I suspect that the GS has relatively weak regen because the regen is only applying deceleration torque to the rear wheels (and suddenly applying lots of braking torque to only the rear axle is not ideal), whereas FWD hybrid drivetrains (inc RX) can apply rather more regen because they are applying braking torque to the front axle (and this variance applies to EVs as well - AWD Teslas have quite a lot more regen than RWD Teslas do. Expect the new breed of RWD EVs (eg Honda e, VW ID3, etc) to have less regen than AWD/FWD EVs)

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10 minutes ago, route66 said:

I'm still confused however.. If the change to engine timing increases engine braking, then surely (& backed up by some of the above links) that means less regen?

 

From reading Lexus-EU-Tech docs (specifically for the RC300h) regen is only a function of the (foot) braking system. If one uses the paddles to induce engine braking one only achieves the same level of regen as if one simply lifts of the throttle. But as you discovered at each down-shift the car will invoke regenerative braking to bring down the engine revs to within the optimal for that gear range.

When using regenerative braking (by applying the foot brake) the engine is stopped and effectively de-coupled from the drivetrain by operating MG1 to relieve MG2 of any engine drag, thereby maximising the regen efficiency 

It's a fiendishly clever and complex system,.. 

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This weekend I saw that if i set the cruise control to 90kmh, and i push the throttle to 130 or 140kmh, the car will then use maximum regen to come back to the previous set speed, without touching the brake...

Why Lexus didn't let choice for the dirver about level of regen ? Like Tesla does...

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Toyota are aiming the cars at ICE drivers. Also the small Battery packs in hybrids are not ideal for trying to sink very large regen currents (reprents a very large C rate for the cells). In general, bigger Battery pack = more current (due to more cells in parallel) = higher total charge/regen/discharge currents for a given cell C rate. I've found that the GS450h gives best results if you don't mess with it - use the brake pedal for regen, drive around it, don't mess with paddles or "EV mode" - just let it get on with it.

Tesla have taken a different approach to everyone else with regard regen and braking. In a Tesla the brake pedal is just that - a brake pedal, like in a regular non-hybrid ICE car. There is no blended regen/brake, and as a result you get a much keener, more consistent (and confidence inspiring) brake-pedal feel*. They do offer two regen settings (Standard, which is just that - what they expect you to use, and "Low" - much less regen, meant to not alienate ICE drivers too much. Many new tesla owners use "low" for a week or two, then switch to standard and forget about it). Tesla are taking very much a simple and predictable approach so that the car will always behave as consistently as possible (but if you charge the car to 100% then you do lose regen braking, as in all EVs). Tesla expect you to select a regen level and live with it (and it's certainly not set up to be changed on the fly). 

Many other EV makers now (esp Mercedes EQC, Audi E-tron, Hyundai Kona, Kia e-Niro) are putting paddles into their cars to allow quick adjustment of regen on the fly, from none at all ("sailing mode" in mercedes parlance) to bringing a car to a stop (Hyundai/Kia - keep left paddle pulled until car stops), by 2-3 intermediate levels of regen. This tends to appeal to "petrolheads" and "enthusiasts", but actually most experienced EV drivers just find it irrelvant (and in fact annoying, if it defaults back to a standard level each time you start the car, rather than remembering what level you choose).

My Nissan leaf had 2 levels of regen, but I basically always used the higher level and it was actually just annoying having it set up as it was on the drive selector (because the higher level required a second manipulation of the drive selector, and if you went into reverse would need 2 manipulations to get back to high regen mode). 

* In my Leaf and in the GS, the "blended" brake-pedal does result in inconsistency as to how the car slows down for a given brake pedal pressure. The Leaf would occasionally just decide not to really bother. In the GS if you apply moderate pressure from ~70mph (ie max regen but minimal/zero friction) then as you get to about 30mph then all of a sudden it stops decelerating (despite continuing constant pressure on the pedal. And no, it's not because the Battery got full - 2-3 empty bars remaining), requiring a step change in pedal pressure to maintain a given level of retardation. At best it's simply not smooth, at worst it's unpredictable. The power is there, in the pedal.... you just don't always know how far or hard you have to press to get it. 

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As said above there is a difference between front, AWD, and rear wheel drive cars. It is obvious that with rear wheel drive the amount of regen is limited because of the risk of locking the rear wheels particularly in wet or freezing conditions. With all versions any slippage on any wheel will instantly cancel regen braking, and normal friction brakes take over.
Four wheel drive systems have the higher regen capability because all four wheels contribute to the regen input. Front wheel drive also gives a high level of regen as braking transfers weight to the front wheels making slip less likely.


With the GS450H, and all Toyota hybrids with Nimh cells they are all wired in series. There being 240 cells giving a nominal voltage of 288 volts against the Prius that uses the same cells has a Battery made of fewer cells "168", and has a nominal voltage of 201.6 volts. The cell capacity and therefore the Battery capacity remains the same 6.5 AH as does the maximum charge, and discharge rate in amps.

John. 

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How is the IS300H equivalent of B-mode (switch to "normal" timing to enhance engine braking) triggered? I'm sure the paddles have something to do with it, but not clear what exactly causes the switch on and off?

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