CVT and engine braking

[supton]

On my 2021 Corolla’s CVT (conventional, not hybrid), it has an engine braking shifter position “B”. Raises engine rpm, as expected. Works as expected. I realize someone will point out that brakes are cheaper than transmissions—duly noted, thank you—but I’m curious, with these transmission and their steel belts that push or pull, how does that work for wear? Do the belts that are push types do just fine when asked to pull? Does wear go up when used for engine braking, is extra heat generated, or is it a big nothing?

I am assuming that engine braking is less force than acceleration, that’s a variable too.

And so far, after the second D&F on my K313, the oil looks as red as could be. Probably shouldn’t be surprised, there’s hardly any clutch material in there to be shed (just the torque convertor, and I believe that is aggressive on lockup, once locked, it likely stays locked, until below a certain speed).

 

[dumkid]

The push belt can't pull. It will just push on the other side and be slack on the side where it normally pushes. I've never owned a cvt but on long hills I will use engine braking to help keep my brakes cool.

 

[eljefino]

Off topic, but my Dad had a 2005 Matrix AWD with conventional automatic that he used for engine braking on the hills of Vermont. It blew, and it blew because of this, and the transmission gurus knew about it. IIRC there was a service bulletin or recall about it.

I would not heavily use engine braking in a Toyota more than you need to even though your tranny is completely different.

 

[supton]

Off topic, but my Dad had a 2005 Matrix AWD with conventional automatic that he used for engine braking on the hills of Vermont. It blew, and it blew because of this, and the transmission gurus knew about it. IIRC there was a service bulletin or recall about it.

I would not heavily use engine braking in a Toyota more than you need to even though your tranny is completely different.

Interesting! never heard of that. Probably never will again either, probably some one-off, but something else for me to poke around into.

 

[benjy]

first off i would NEVER own a CVT + they are usually REPLACED costing as much as some engines its a NO BRAINER IMO!!

 

[supton]

first off i would NEVER own a CVT + they are usually REPLACED costing as much as some engines its a NO BRAINER IMO!!

Ok, but that answers the question how?

 

[IndyIan]

On my 2021 Corolla’s CVT (conventional, not hybrid), it has an engine braking shifter position “B”. Raises engine rpm, as expected. Works as expected. I realize someone will point out that brakes are cheaper than transmissions—duly noted, thank you—but I’m curious, with these transmission and their steel belts that push or pull, how does that work for wear? Do the belts that are push types do just fine when asked to pull? Does wear go up when used for engine braking, is extra heat generated, or is it a big nothing?

I am assuming that engine braking is less force than acceleration, that’s a variable too.

And so far, after the second D&F on my K313, the oil looks as red as could be. Probably shouldn’t be surprised, there’s hardly any clutch material in there to be shed (just the torque convertor, and I believe that is aggressive on lockup, once locked, it likely stays locked, until below a certain speed).

Good question, I never really thought about it, but I suppose it must be at least as much wear and heat as as when the transmission is being driven by the engine for the hp transmitted? Which I guess is true of any transmission.
Ours can use quite aggressive engine braking to maintain the cruise control speed when going down a hill, but there must be lots of subaru's out west that spend 1/4 of their mileage engine braking in cruise control, so I doubt it will be an issue for me.

 

[IndyIan]

first off i would NEVER own a CVT + they are usually REPLACED costing as much as some engines its a NO BRAINER IMO!!

Around here a lower mileage one for my car, at the wreckers is $1500-2000, which is a bit less than a AWD RAV4 trans, which is a good indicator that the two vehicles have about the same transmission failure rate.
Some of the many speed conventional transmissions have quite high prices at the wreckers, which says to me the demand is exceeding supply...

 

[haggler]

Admittedly I'm no expert on cvts but if the simulated downshift increases the gear ratio, wouldn't it be locked at that ratio? I.e. if you're going downhill and downshift it's holding a fixed ratio in that gear. I just don't see how that would wear more than downshift a regular AT. Its doing something similar in the cvts but I guess it would depend how that ratio is being preserved. I could see it putting more wear on the fluid though

 

[KrisZ]

As was mentioned already about the push belts, they cannot pull, they simply start pushing on the opposite side when engine braking. The same is true for pull belts, they cannot push, but instead pull the other side.

As far as extra wear and such, absent some design flaw, there should be no difference. If Toyota specifically included a gear selector for engine braking, then at least they think it’s safe to do this.

 

[atikovi]

Ok, but that answers the question how?

Maybe just venting? Comment should read,

first off i would NEVER own a NISSAN CVT + they are usually REPLACED costing as much as some engines its a NO BRAINER IMO!!

Have a Corolla with over 250,000 miles and a Subaru with over 350,000 miles and their CVTs are still fine.

 

[nascarnation]

Maybe just venting? Comment should read,

Have a Corolla with over 250,000 miles and a Subaru with over 350,000 miles and their CVTs are still fine.

That's impressive. There's no doubt billions of miles of field experience in the last two decades has improved the breed. Including fluids and electronics.

 

[SwampSurvivor]

As was mentioned already about the push belts, they cannot pull, they simply start pushing on the opposite side when engine braking. The same is true for pull belts, they cannot push, but instead pull the other side.

As far as extra wear and such, absent some design flaw, there should be no difference. If Toyota specifically included a gear selector for engine braking, then at least they think it’s safe to do this.

I do kinda wish our Nissan didn't go right to the rev limiter when but in L or "overdrive" is turned off. Mild engine braking by turning off "overdrive" would be nice, but it acts like you have lost all brakes. I played around with that a bit on our 2017 before it was trade don the 2019.

 

[GSCJR]

I've said this before, my Maxima was a beast when it came to engine braking. It was a blast to drive through the mountains on our way to South Florida with a full trunk and the family on board. With every negative there's a positive when it comes to CVTs. I was able to get my current DD due to a bad CVT, so there's that. $2000 for a car which I've been driving around with a used CVT for years. The CVT alone goes for $2500 right now.

2012 Subaru Legacy 2.5 N/A CVT 266k Kms

This is going to be my new DD. I've never owned a Subaru, so I'm looking for some advice and tips. I'm going over it to get it road worthy and so far it needs, ball joints, pads and rotors, tires, LCA bushings and the LF window won't go down. The car has been sitting for two years after the CVT...

bobistheoilguy.com

 

[Delta]

The CVT in the '19 Subaru we had was horrible at engine braking. Even when you selected a range it still went too darn fast down the mountain. Finally just left it in normal mode and used the stab brake method.

 

[97prizm]

Maybe just venting? Comment should read,

Have a Corolla with over 250,000 miles and a Subaru with over 350,000 miles and their CVTs are still fine.

Nissan traditionally used Jatco cvts. What does Toyota and Subaru use, and how are they different. I know early on a I remember seeing a handful of nissan cubes in salvage yards due to the cvt transmission going bad and the repair price was astronomical.

 

[MolaKule]

On my 2021 Corolla’s CVT (conventional, not hybrid), it has an engine braking shifter position “B”. Raises engine rpm, as expected. Works as expected. I realize someone will point out that brakes are cheaper than transmissions—duly noted, thank you—but I’m curious, with these transmission and their steel belts that push or pull, how does that work for wear? Do the belts that are push types do just fine when asked to pull? Does wear go up when used for engine braking, is extra heat generated, or is it a big nothing?

I am assuming that engine braking is less force than acceleration, that’s a variable too.

And so far, after the second D&F on my K313, the oil looks as red as could be. Probably shouldn’t be surprised, there’s hardly any clutch material in there to be shed (just the torque convertor, and I believe that is aggressive on lockup, once locked, it likely stays locked, until below a certain speed).

I see engine braking as similar to hard acceleration.

Both put loads on the belt that are above straight and level cruise.

 

[Oliveoil2]

I see engine braking as similar to hard acceleration.

Both put loads on the belt that are above straight and level cruise.

This^^^. This goes for everything. The harder you drive there is an increase in wear.

 

[supton]

Sure, but what is "too much"?

Just driving the car creates wear. Not driving the car lets seals dry out and things rust up; not driving will cause a car to age out.

But is hard engine braking the same force as hard engine acceleration? and is the belt under a different stress in each case?

Guess I'll find out in a few years.

 

[MolaKule]

But is hard engine braking the same force as hard engine acceleration? and is the belt under a different stress in each case?

Guess I'll find out in a few years.

I am defining Stress here as the pressure or tension exerted on a material object. I certainly don't think you'll see much if any compressive forces in a CVT belt/chain.

In acceleration the "Driving Member," which is connected to the engine, will be applying the tension forces to the belt to turn the "Driven" member which is connected to the wheels.

In braking, the situation is reversed in the sense that the Driven member now becomes the Driving member. Tension is still applied in both cases.