Having CVT anyone?

I am pretty intrigued by the Constantly Variable Transmission that Subaru's got into and I hope some of you are already experienced with it. I am mainly interested how that thing behaves on downhill when with a conventional manual or A/T one would shift down the gear to engage the engine brake. Since CVT does not have gears, how would engine brake work there? TIA

Reply to
cameo
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A CVT doesn't have gears, but it has rollers that fulfill the same role as gears do.

Yousuf Khan

Reply to
Yousuf Khan

And if I understand Subaru's website correctly, the CVT in the Outback and Forester also has a manual mode where you can modify the gearing via paddles on the steering wheel, right?

I'm not happy about some of the shifting being on the steering wheel instead of the console, but there's no choice if I want a new Outback...

Patty

Reply to
Patty Winter

Back in the 50's and 60's, almost all shifters, both manual and auto, were on the steering rather than the console. What's old is new again.

Yousuf Khan

Reply to
Yousuf Khan

Anyone know the answer to this? Like Cameo, I'm curious whether you can slow down the car by downshifting. There's a steep hill near Yosemite where I routinely do that with my current Subie.

Maybe. I had a stick shift in the late '60s and a fully shiftable automatic after that, both shifted from the console. Then I inherited my mom's Mustang, which was not fully shiftable but did have the shifter on the console. Then I got the two cars I have now, one manual, one automatic, both shiftable from the console. I've never had an ordinary sedan or coupe, so I'm probably out of touch with what they offer.

Patty

Reply to
Patty Winter

It should be possible with a CVT, but no shifting required. The CVT will simply adjust itself to maintain whatever speed you desire. When going downhill, if you want to maintain a speed of X mph, with gravity pulling you faster, the engine is not as necessary, so the CVT should just adjust to a ratio that'll cause the engine to do less work pushing the car forward.

I remember my dad's old 60's Toyota Corona had a column shifter. And he told me that most cars he had before that were column-mounted too. Mustangs and stuff were sporty cars, so it's likely they would be console mounted. If you drove a family car, it was likely column-mounted.

Yousuf Khan

Reply to
Yousuf Khan

Yeas, but how would the CVT "know" what your desire is withouth those explicit gear ratios you can select?

Even my '72 Olds Cutlass had column shifter A/T.

Reply to
cameo

Well, how does an auto transmission know what gear you want, prior to the days of the computer? It used mechanical sensors, such as speed governors, engine vacuum, etc. Likely something similar in CVT, it uses sensors, the most important of which would be engine RPM.

Yup.

Yousuf Khan

Reply to
Yousuf Khan

And the auto transmission is going to select the gear *it* considers best for that engine speed. If I'm going downhill in Drive, my Legacy will happily choose third gear. The only way I use the engine to slow the car is by throwing it into first or second gear myself. Can you do that in the manual mode of a CVT?

Patty

Reply to
Patty Winter

Well, this is exactly what I am getting at, but you seem to be the only one understanding it. What Yousuf is saying applies to the normal acceleration and steady speed driving but hardly to downhill where a car could speed up beyond the speed limit if you don't ride the brakes or you don't shift down to engage the motor brake. On long down slopes you don't want to use the brake pedal only.

Reply to
cameo

You can speculate all day long here. But short of a test drive at the dealer I don't know how you gonna find if you'd like cvt programming and operation.

It looks once way on paper and once you get behind the wheel it's usually quite another world.

Reply to
AD
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Cameo and I weren't "speculating." We were asking a question in hopes that someone here actually has a Subaru with CVT and could answer the question from experience. But apparently no one does.

I'd have to drive about 20 minutes from a dealership to find a hill steep enough to try it myself, so I'm actually going to ask them first and see whether they know the answer.

Patty

Reply to
Patty Winter

The CVT has an infinite gear range, there is no single lower gear it can select to go slower, but it can select any gear ratio (or rather roller ratio) very smoothly to maintain the same speed. It should work the same uphill, downhill, or level.

Yousuf Khan

Reply to
Yousuf Khan

I understood it. But then, I'm a mechanical engineer so I have a professional responsibility to understand things like that.

I have no idea, however, how a Subaru CVT works. Swash plate? Variable diameter pulleys? Torque converter?

Some 40 or 50 years ago a Dutch company called DAF imported to the US a small car with a CVT based on variable diameter pulleys. A friend had designed a transmission like that as a senior-year project in mechanical engineering, and bought a used DAF out of curiosity. The first lesson learned was that the DAF could be started while in gear; he learned this when his wife started it up and rammed it into the back of their other car. The DAF wound up sitting at the curb until the weeds grew up around it, the neighbors complained, and he had to have it towed away.

That has nothing to do with Subaru but I think it's a funny story. I doubt variable diameter pulleys could transmit the torque of a modern engine.

Reply to
John Varela

That's interesting, the only type of CVT I knew about were the variable diameter pulleys. I had no idea that there were other types available. Now I want to look it up.

Yousuf Khan

Reply to
Yousuf Khan

There's an animation about how engine RPM corresponds to road speed in a CVT vs. a manual transmission. It also includes a brief stretch where it shows how it reacts while going up a hill, you can then extrapolate how the same thing will react while going downhill too. You also see that the CVT is much more efficient than a manual transmission in every respect. You should be able to accelerate 25% faster with a CVT than with a manual transmission, because of the added efficiency in transmitting engine power curves to the road. They even talk about the old Subaru Justy being one of the first cars to feature CVT. Looks like Subaru are reintroducing it on more polished cars now.

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The rest of the article will also demonstrate how various designs of CVT work.

Yousuf Khan

Reply to
Yousuf Khan

**I was reading the new issue of Consumer Reports yesterday. They compared the new Impreza and Mazda 3. Here's a kinda relevant bit for you:

" Reduced weight, a new CVT, and a 148-hp, 2.0-liter four-cylinder engine helps the Impreza get slightly better acceleration and 3 more mpg than the previous model. But the CVT provides too much engine braking on downhills."

Under the term Lows: Noise, excessive engine braking.

kaboomie

Reply to
kaboom

Sorry to disagree again,this time on the extrapolation issue. Why would extrapolation from straight and uphill driving work to downhill situation when such extrapolation does not work for conventional A/Ts? You have to use manual downshifting on the latter for downhills even though you don't have to touch the stickshift going uphill. So where is the symmetry?

That's all nice, but this is not the issue I was getting at. As to actually doing a test drive at a dealership, that would be problematic for at least two reasons: first, I don't think a dealer would let me drive to the nearest ski area to test it on a long downhill and second, I don't like the typical hyena rush of half a dozen salesmen running toward me as I approach the showroom and then would not let me leave without a signed contract. OK, that's a bit of exaggeration in order to make my point. I think you know what I mean.

Reply to
cameo

Now THAT is and interesting and useful info in this topic. I just wonder how that excessive engine braking comes about. I suppose when a driver lets his/her foot off the gas pedal on a downhill which is probably not as doable with CVT as with conventional A/Ts. It appears that with CVT one would not want to take the foot off unless wanting to decelerate fast. To me excessive engine braking is still preferable to inadequate one. However, the noise is not something I would be looking for with a good engine brake.

Reply to
cameo

Maybe it's a Bay Area thing, but the dealers around here don't seem to do that any more. I would walk out the door if they tried.

Anyway, I had some free time between appointments today, so I went into a local Subaru dealership and chatted with a salesman. He confirmed that if you put the CVT into manual mode, you can then brake with the engine by repeatedly tapping the "-" paddle on the steering wheel column. He said it would only be in extreme situations that the car would refuse to do what you asked, such as if you tried to gear it really low at freeway speeds. In other words, the car will protect the engine from redlining. But he knew the hill I was referring to and said it should be no problem gearing down to slow down the car on it.

He also mentioned that you can gear down with the paddles even without going into manual mode, although in that case the car will go back into drive when it thinks it's good to do so. He says he sometimes does that to slow down on freeway exit clover- leafs. But if you do put the console shifter into manual mode first, then the car will not go back into drive until you tell it to.

He also pointed out that auto-transmission Outbacks (I didn't ask about the Forester) have a tachometer. That does say to me that Subaru's engineers believe in giving drivers control and information; that they aren't trying to appeal to drivers who want the car to do everything for them and not bother them unless there's a problem. I was driving the Porsche today, so he probably quickly got the idea that I'm the sort who wants a car to do what I say, not what it thinks is best. (Except on black ice; then I'm happy to let the Subie do its thing. :-))

I didn't have time to test drive an Outback today, but when I do get around to it, I'll give the manual mode a workout and let you all know what happens. Cameo, perhaps there's something closer than a ski area that you could try it on? Like a freeway onramp/offramp or some other manmade "hill"?

Patty

Reply to
Patty Winter

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