andysinnh

HI there. Wife has an '18 RLX Sport Hybrid with about 7400 miles on the odometer. It's been pretty cold here lately, and as such the car tends to run a lot more in ICE mode than EV mode. We've started noticing an interesting behavior when cruising on rural roads (30-40 mph) when using the gas motor only. If you're cruising around and doing a slight acceleration, and then take your foot off the gas pedal, you get this slight feeling that's best described as a "skip" or "downshift" of the transmission. Basically, it feels like someone did a quick tug at the back of the car about 1/2 a second after you stop accelerating. I haven't looked to see whether the front electric motor is working when this happens, but it's definitely when the tach is showing rpm's in the 2k range. I know there's a TSB for the transmission for jerkiness on shifting, but not sure if this is related - or whether it's just sort of the way it is. Doesn't happen at higher speeds, and the behavior when going between ICE and EV modes is still smooth as silk. Anyone ever feel this?

thx - andy

psheu

Hi Andy,

I've been on the RLX hybrid for few years now. That kind of downshift don't normally occur. Was the "Sports" button engaged? The only time i notice the downshift is when that sports mode is active.

mrgold35

What are the outside temp ranges for you? I've noticed the colder it gets (like below 40 degrees), the more the hybrid acts like a regular I.C.E. vehicle. Maybe the electric motors were smoothing out that quick tug motion in warmer temps?

Triaque

Hi
I wanted to give you all my observations with my 2020 SH-SHAWD.

If we ignore the temperature component completely for a moment and look at the behavior only, I believe this affect of more aggressive deceleration may become clear for this vehicle.

With my vehicle decelerating on approximately 3% grade to flat pavement without Sport mode; the engine shuts off and the dual clutch completely decouples the engine from the transmission and front electric motor. From the instant of decoupling the electric motor becomes a generator with my foot completely off the pedal. In this situation, if I gently apply a feather pressure to the accelerator the electric motor will stop generating and allow the car to "free-wheel". If I alternate the slight pressure on the pedal with about 5 seconds between movements the vehicle will free wheel/decelerate-generate over and over. This is all with the ICE decoupled.


Now. If the vehicle is on a much steeper incline say 5% or greater.....the ICE is never shut down and remains coupled with the transmission thru the dual clutch. While performing a down hill grade movement while removing my foot from the accelerator pedal completely; the vehicle decelerates using the generator function of the electric motor AND uses engine braking AND it shifts on its own to a lower gear than would be required to free wheel. If during this set of conditions I feather a bit of pressure on the accelerator pedal, the engine shifts up into a higher gear. This doesn't apply any real torque to the drive train yet is allowing the vehicle to free wheel down the grade.

Ok. Circling back to the original quandary. If you add in VERY low temperatures....the engine will not shut down because it's better on the hybrid battery to supply loads to the front windshield glass heater/ice melting circuit/side view mirror de-ice circuit, rear windshield de-ice circuit, seat heaters, and heated fluid interior and transmission fluid heat exchanger ALL by burning fuel to heat water and spin the front generator. Any decelerations during low speed operation on flat road surfaces will create the feeling of significant engine braking with all this stuff energized on top of the effects that I described in prior paragraphs.

This vehicle is chocked full of software programming from the Japanese software engineers at Honda. If you really pay close attention, while driving, to this vehicle's behavior nuances.....you will see just how many compensations are taking place for every thing you can think of and some that you haven't yet.

andysinnh

Thanks, Triaque, for the detailed info on what you believe to be happening with the complex vehicle we all know/love. I believe that you're accurately describing what I'm feeling, in that the deceleration of the motor, and associated actions, is providing that small bit of "engine braking". Seems to make sense. Given this is the wife's car, I'll have to pay attention when I drive over the coming weeks to see if I can reproduce the behavior. I did notice last time that the deceleration feeling was more prominent when it was colder in the morning (teens Fahrenheit) and later in the day it wasn't noticeable as the temps rose into the 30's....

andy

Triaque

Andy

If you are living in Fahrenheit teens, then, every system is going to be sluggish till all fluids heat up. Acura made a block heater and dual clutch actuator assembly heater available for the 2020 model year due to the shudder feeling. With all the systems drawing electrical power to heat you and the wife plus de-ice.....I'm not surprised that you feel a good drag when decelerations occur in sub 30 deg F temps. Those de-ice systems do not auto time out in temperatures that low. Well ....the seat heater and steering wheel are under occupant control.

andysinnh

Thought I'd share another observation after driving the RLX last evening. I put the HUD into the mode showing the hybrid system, and worked to reproduce the situation. Again, it's during colder temps when the car is in ICE mode, and letting your foot off the gas results in a "pause" or "deceleration" feeling. I can safely say that the issue is the rear electric motors going into a regenerative mode. You can clearly see that the HUD shows the rear wheels turn green to show the regeneration process, and it's at that exact time that the feel of a deceleration happens. You don't notice it once the car is warmed up or the temps are higher, and once in the EV/ICE mode it returns to a more seamless feel.

Just another way the RLX SH SH-AWD behaves just a bit differently than my other non-SH SH-AWD's......

andy

mrgold35

I probably never noticed the downshift feeling since my MDX and RLX are hybrids. The rear electric motors are pretty much in regen mode almost everytime you lift off the gas pedal. The Acura Hybrids do a really good job of holding its downhill speed even on the steepest declines with rear regen braking.