Braking in the regenerative zone - no brake lights coming on

[Sven]

So, an intersting selection there ...!

Instant
2017 IS300h
2016 RC300h
2015 IS300h
2014 GS300h
2014 IS300h
2013 IS
2013 IS
2013 Is300h
2013 CT200h

Delay 
2015 IS300h
2014 GS300h
2010 RX450h

 

So, on the whole, we're looking like the lights should be coming on immediately but there's some exceptions, and it doesn't seem to be model/age related.  It's good to see that I'm not the only one though.

What I don't get then, is the mechanical switch.. I mean - why bother with it anymore?  If its only use is to light up the breaks, then why does the car slow down when they're not lit up?  There's some software going on that detects pressure on the pedal and starts the re-gen, then why not use that to turn them on?  I'm not a car software engineer by any mean, but it's almost like:

if(brakepressed==1 && pressure <10%)
then
 regen_brakes()
else if(brakepressed==1 && pressure >=10%)
then
 regen_brakes()
 enable_brake_system()
 enable_brake_lights()
endif

Of course the enable_brake_system() could be on with the <10% too.

This has been going on for a while and I'm waiting for a response from Lexus from my reply from the 29th of December, so watch this space.

 

[Sven]

On 03/01/2018 at 9:15 AM, TBi said:

In my view the regen braking is so slow that there is no need to put on the brake lights, it's equivalent of using engine braking. A driver who wouldn't notice you slowing down would either have to be very distracted or very bad and both should have no place on the road.

True - but we all know how many people can get distracted in rush hour traffic by the radio, a phone, a bird, an interesting looking cloud, someone in the back seat, checking someone elses car out in the next lane, thinking about the problems in the office/home etc... 

Like I said, it's happened more than a few times, and there will be more occasions where it could happen too. 

[Sven]

Hi all, 

I've had a reply from Lexus, and it wasn't quite what I was expecting. I've removed the names of anyone mentioned in the original email.

Quote

Since your initial contact we have reviewed your case with Lexus Bradford and they have confirmed that they have carried out back to back (comparison) tests with your vehicle and a similar one, and can confirm that they both perform in exactly the same way verifying that your vehicle is not faulty.

It is also worth noting that each and every model has to be homolgated for use on UK roads and, as you can imagine, the tests are extremely stringent.
Nevertheless, due to the serious nature of your query we asked Jason to log a technical report.

Our technical team have considered your concern and responded as follows;

As with all vehicles, when you come off the accelerator the vehicle will slow down gradually.  A Hybrid vehicle will slow down faster but active regenerative braking does not kick in until the brakes are applied, and at this point the brake lights will come on.  The light will come on between 1 & 6mm of depression depending on how the pedal has been adjusted, however until the lights come on the braking system is not fully engaged.

I trust that this clarifies the matter for you and illustrates that we have taken your concerns seriously.

Thoughts?

 

[ColinBarber]

1 hour ago, Sven said:

Hi all, 

I've had a reply from Lexus, and it wasn't quite what I was expecting. I've removed the names of anyone mentioned in the original email.

Thoughts?

 

I don't agree with Lexus. Whilst I said my brake light comes on before the mechanical brakes apply I can definitely apply the brakes lightly which increases the regen braking effort (as felt and seen on the power meter) before the brake light comes on.

[ColinBarber]

I also don't agree with

"As with all vehicles, when you come off the accelerator the vehicle will slow down gradually.  A Hybrid vehicle will slow down faster"

because Toyota design their system to replicate the feeling of an auto vehicle when coming off the accelerator (by applying a tiny amount of regen braking). Therefore they slow down around the same rate.

[sorcerer]

1 hour ago, Sven said:

The light will come on between 1 & 6mm of depression depending on how the pedal has been adjusted, however until the lights come on the braking system is not fully engaged.

Maybe I'm being a bit simplistic but surely, all you need to do now then is to adjust the mechanical brake light switch so that it switches the lights on at 1mm depression and that would be it sorted wouldn't it?

[wharfhouse]

My brake light (and the regen braking) come on pretty much immediately I touch the brake pedal with only a tiny fraction of "free play" when I first touch the brake pedal. I haven't looked at the Lexus brake pedal but in other cars as others have said the brake light switch is easily adjustable (in my Honda Accord it is was located up under the dash near the top of the brake pedal opposite the pivot point - the switch was closed when brakes not applied and opened when the brake was applied).

In most cars you can also adjust the brake pedal position so that it is slightly more "up" or "down" relative to the accelerator - again not sure how adjustable that is in the Lexus but if that is set wrong could be the problem too.

Another thought is that I would have thought the interlock for the auto shift is linked to the same brake pedal switch - I'm pretty sure mine is in that I don't have to put hardly pressure on the brake pedal to move from P to D - also the cruise control is I believe linked to the same switch - so if cruise is on and I just touch the brake pedal it disengages - if yours takes a push similar to getting the brake lights to come on for moving out of P and to disengage the cruise control then I would have thought it definitely points to either the switch and/or pedal being out of position relative to each other which should be easily rectified. 

[Sven]

Yeah, some of their technical comments don't ring true... the regen coasting doesn't cause it to slow down faster that any other automatic  car I've driven.  

I've had a reply to my reply... and this isn't what I was expecting :-(

My email to them:

Quote

thanks for the explanation.  I’ve had quite a few dealings with him, and he’s been a fantastic representative and makes it a pleasure to visit the Bradford branch.

 

I can very well image that the tests performed are to the highest of standards as one would come to expect from a premium brand such as yourselves.

 

Let me just reply to a few points in the technical teams response:

 

* As with all vehicles, when you come off the accelerator the vehicle will slow down gradually.  

 

Agreed.

 

* A Hybrid vehicle will slow down faster but active regenerative braking does not kick in until the brakes are applied,

 

Also agreed...

 

* and at this point the brake lights will come on.  

 

Not necessarily, and that was my original concern.

 

* The light will come on between 1 & 6mm of depression depending on how the pedal has been adjusted, however until the lights come on the braking system is not fully engaged.

 

During this 1-6mm travel the regeneration breaks are applied and the lights to not come on. It is only after the 6mm (assuming that it is 6mm) do the lights come on but the regeneration. 

 

From a technical point of view, I'm surprised that the break lights rely on a mechanical switch with a set travel amount given that the breaking system understands when the pedal is pressed - this appears to be a possible software correction.  

 

I guess that my pedal break light switch may need to be adjusted if that is the fault, and I do still believe that it is a fault.

 

I would love to know the tech teams thoughts on that too and I look forward to hearing from you in due course. 

however, this isn't quite the response from Lexus I expected, but I can see where they're coming from:

Quote

Thank you for your email and your positive comments about both you Lexus and Lexus Bradford.

We do not agree with you that there is a fault present as your car has been tested and found to perform exactly the same as similar vehicles.

However we do take on board your concerns and technical are happy that the brake pedal be adjusted within its 1-6mm tolerance.  I have asked Bradford to contact you to arrange this, and trust the results will provide you with peace of mind.

Just because similar vehicles do it, doesn't make it right. Just because mine will be fixed, doesn't mean that others will be.

I still think this issue can be fixed with a "simple" software fix (if brakepedal ==true then lights=on), but it looks like I've hit a bit of a dead end with lexus as they'll see it as "fixed" once mine has been complete.

 

Am I just being to picky here??