Since diesels produce more torque and don't have a wide useable RPM range, wouldn't it make more sense to add produce diesel cars with CVT transmissions?
Why don't we see diesel/CVT cars in the US?
Why don't we see diesel/CVT cars in the US?
CVT on diesel cars?
- Thread starter DrRoughneck
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Originally Posted By: d00df00d
Isn't torque capacity a relative weakness of CVTs?
Diesel cars have more torque than non-turbo cars, but less torque than SUVs (usually) and since CVTs are used in some SUVs, they should hbe able to handle a diesel car engine.
The advantage of CVT that I'm alluding to is its ability to varry speed at constant engine RPM. So from my understanding it would overall give a diesel car the ability to accelerate like a turbo-gas car.
Isn't torque capacity a relative weakness of CVTs?
Diesel cars have more torque than non-turbo cars, but less torque than SUVs (usually) and since CVTs are used in some SUVs, they should hbe able to handle a diesel car engine.
The advantage of CVT that I'm alluding to is its ability to varry speed at constant engine RPM. So from my understanding it would overall give a diesel car the ability to accelerate like a turbo-gas car.
Diesel has huge torque range, so it is much easier to use fewer speeds to get the efficiency than gas engine. Putting a CVT (low toque input, relatively speaking) in it doesn't do much other than reduce reliability and increase cost.
I think I read the new Chevy Cruze diesel is supposed to have a 9 speed auto. I'm not sure how much that helps with acceleration and performance but seems with that many gears who needs a CVT.
Despite the ravings of a few die hard diesel fans, diesel cars simply aren't that popular in the US. There are a couple manufacturers who are doing diesel, but in 2014 the diesel passenger car sales were only about 3% of total sales. Compare that to plug-in electric vehicles which were at .75%, and you can see that diesel cars only sell slightly more vehicles than electric plug-ins. The market dictates what manufacturers will do, and there simply isn't much of a market for diesel cars in the US.
If I remember correctly, the Subaru Forester has a diesel and CVT, just not available in the US.
If I remember correctly, the Subaru Forester has a diesel and CVT, just not available in the US.
Originally Posted By: DrRoughneck
Originally Posted By: d00df00d
Isn't torque capacity a relative weakness of CVTs?
Diesel cars have more torque than non-turbo cars, but less torque than SUVs (usually) and since CVTs are used in some SUVs, they should hbe able to handle a diesel car engine.
The advantage of CVT that I'm alluding to is its ability to varry speed at constant engine RPM. So from my understanding it would overall give a diesel car the ability to accelerate like a turbo-gas car.
I don't agree that an petrol engine has more torque than a comparable Diesel engine. Power in the petrol will be better I would expect but not torque.
The reason I think a CVT would be a bad fit for a CVT is that it would tend to rev the engine past peak torque when you hit the throttle hard.
In the same way as a manual truck can be a bit better at pulling heavy loads in difficult conditions (steep hills and twisty roads for example) than an automatic truck.
It is not as easy to keep the engine in peak torque with an automatic as it is in a manual, at least that is what I have been told by a truck driver as I have never driven an LGV.
I always felt that my diesel Pathfinder would have been better with a manual box, as when you tried to accelerate hard it would Rev the engine well past peak torque. I would expect that would be fine in the petrol engine versions.
Originally Posted By: d00df00d
Isn't torque capacity a relative weakness of CVTs?
Diesel cars have more torque than non-turbo cars, but less torque than SUVs (usually) and since CVTs are used in some SUVs, they should hbe able to handle a diesel car engine.
The advantage of CVT that I'm alluding to is its ability to varry speed at constant engine RPM. So from my understanding it would overall give a diesel car the ability to accelerate like a turbo-gas car.
I don't agree that an petrol engine has more torque than a comparable Diesel engine. Power in the petrol will be better I would expect but not torque.
The reason I think a CVT would be a bad fit for a CVT is that it would tend to rev the engine past peak torque when you hit the throttle hard.
In the same way as a manual truck can be a bit better at pulling heavy loads in difficult conditions (steep hills and twisty roads for example) than an automatic truck.
It is not as easy to keep the engine in peak torque with an automatic as it is in a manual, at least that is what I have been told by a truck driver as I have never driven an LGV.
I always felt that my diesel Pathfinder would have been better with a manual box, as when you tried to accelerate hard it would Rev the engine well past peak torque. I would expect that would be fine in the petrol engine versions.
Originally Posted By: czbrian
I think I read the new Chevy Cruze diesel is supposed to have a 9 speed auto. I'm not sure how much that helps with acceleration and performance but seems with that many gears who needs a CVT.
Hopefully they got that 9 speed right. I read over 500,000 of the ZF 9 speeds used in Jeeps, Honda, Acura, and a few others are being recalled. Probably old news to some, I stumbled upon it the other day.
I would imagine a diesel would tear up a CVT with the torque it puts out.
I think I read the new Chevy Cruze diesel is supposed to have a 9 speed auto. I'm not sure how much that helps with acceleration and performance but seems with that many gears who needs a CVT.
Hopefully they got that 9 speed right. I read over 500,000 of the ZF 9 speeds used in Jeeps, Honda, Acura, and a few others are being recalled. Probably old news to some, I stumbled upon it the other day.
I would imagine a diesel would tear up a CVT with the torque it puts out.
gathermewool
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I know it's not astronomical, but my FXT:
High-torque CVT
258 ft-lbs torque
//
Regarding a CVT (or any auto revving past the usable power band): it's all in the programming. A lot have posited that my Forester is actually faster at 3/4 throttle than wide-open 100%) throttle. I agree. 3/4 throttle is 3-4k RPM and 14-16# boost. 100% throttle results in less boost, more noise, and what feels like less power, since it's probably beyond its peak power band. This, I feel, is for those who need to HEAR their engine scream when they hit the 'go' pedal; the same people who would scream at the dealer if they mashed the 'go' pedal and only saw 3-4k RPM, even if that was the point of max power...
//
I don't know why diesels aren't offered with CVT's, but pop-rivit's post seems to sum it up pretty nicely.
High-torque CVT
258 ft-lbs torque
//
Regarding a CVT (or any auto revving past the usable power band): it's all in the programming. A lot have posited that my Forester is actually faster at 3/4 throttle than wide-open 100%) throttle. I agree. 3/4 throttle is 3-4k RPM and 14-16# boost. 100% throttle results in less boost, more noise, and what feels like less power, since it's probably beyond its peak power band. This, I feel, is for those who need to HEAR their engine scream when they hit the 'go' pedal; the same people who would scream at the dealer if they mashed the 'go' pedal and only saw 3-4k RPM, even if that was the point of max power...
//
I don't know why diesels aren't offered with CVT's, but pop-rivit's post seems to sum it up pretty nicely.
Originally Posted By: Pop_Rivit
If I remember correctly, the Subaru Forester has a diesel and CVT, just not available in the US.
Correct. The Subaru Forester and Outback diesels use a CVT. Some others I know of are the Audi A5, Nissan Qashqai and Nissan X-Trail (Rogue in the US?). So yeah, there definitely aren't many CVT diesels, but they do exist.
If I remember correctly, the Subaru Forester has a diesel and CVT, just not available in the US.
Correct. The Subaru Forester and Outback diesels use a CVT. Some others I know of are the Audi A5, Nissan Qashqai and Nissan X-Trail (Rogue in the US?). So yeah, there definitely aren't many CVT diesels, but they do exist.
Originally Posted By: gathermewool
I know it's not astronomical, but my FXT:
High-torque CVT
258 ft-lbs torque
//
Regarding a CVT (or any auto revving past the usable power band): it's all in the programming. A lot have posited that my Forester is actually faster at 3/4 throttle than wide-open 100%) throttle. I agree. 3/4 throttle is 3-4k RPM and 14-16# boost. 100% throttle results in less boost, more noise, and what feels like less power, since it's probably beyond its peak power band. This, I feel, is for those who need to HEAR their engine scream when they hit the 'go' pedal; the same people who would scream at the dealer if they mashed the 'go' pedal and only saw 3-4k RPM, even if that was the point of max power...
//
I don't know why diesels aren't offered with CVT's, but pop-rivit's post seems to sum it up pretty nicely.
Pretty interesting... I'd think max hp would be at 5k or so, which is where I'd think a CVT would sit for max acceleration.
I wonder if they had to detune. I mean, in a conventional stepped transmission, it's pretty hard to stay at any given rpm for very long while at full throttle. Either it's a momentary thing, or eventually you let up and torque drops.
I wonder if any 0-60 times (well maybe 0-100) times were checked to see if this is real.
I know it's not astronomical, but my FXT:
High-torque CVT
258 ft-lbs torque
//
Regarding a CVT (or any auto revving past the usable power band): it's all in the programming. A lot have posited that my Forester is actually faster at 3/4 throttle than wide-open 100%) throttle. I agree. 3/4 throttle is 3-4k RPM and 14-16# boost. 100% throttle results in less boost, more noise, and what feels like less power, since it's probably beyond its peak power band. This, I feel, is for those who need to HEAR their engine scream when they hit the 'go' pedal; the same people who would scream at the dealer if they mashed the 'go' pedal and only saw 3-4k RPM, even if that was the point of max power...
//
I don't know why diesels aren't offered with CVT's, but pop-rivit's post seems to sum it up pretty nicely.
Pretty interesting... I'd think max hp would be at 5k or so, which is where I'd think a CVT would sit for max acceleration.
I wonder if they had to detune. I mean, in a conventional stepped transmission, it's pretty hard to stay at any given rpm for very long while at full throttle. Either it's a momentary thing, or eventually you let up and torque drops.
I wonder if any 0-60 times (well maybe 0-100) times were checked to see if this is real.
It's all about the ratio spread, that's what the design engineers are looking for with all these multi speed slushboxes.
As used in cars the typical CVT signs off before 300 foot pounds or so. They do indeed lack torque capacity at this time.
All the many speed slushboxes need to be delightful is correct programming. Our ZF 8 speed is delightful as it runs through the gears, shifting precisely at 6 grand and delivering the power we paid for. I'm sure a CVT programmed properly would also be a fun vehicle to drive. The problem is no one seems to have gotten it right yet...
As used in cars the typical CVT signs off before 300 foot pounds or so. They do indeed lack torque capacity at this time.
All the many speed slushboxes need to be delightful is correct programming. Our ZF 8 speed is delightful as it runs through the gears, shifting precisely at 6 grand and delivering the power we paid for. I'm sure a CVT programmed properly would also be a fun vehicle to drive. The problem is no one seems to have gotten it right yet...
I have heard that the harmonics of diesel engines is a problem. That in mind, with newer diesels that have lower compression ratios and multiple injection events this might not be such a big problem.
Originally Posted By: d00df00d
Originally Posted By: artificialist
I have heard that the harmonics of diesel engines is a problem.
Interesting! How so?
The transition from power stroke to exhaust stroke is so dramatic that on some diesels, the serpentine belt squeals the moment the engine shuts off. This can happen even if the belt and tensioner have very few miles on them. One thing that somewhat helps is having a bigger and heavier crankshaft pulley/harmonic balancer.
The harmonics also have an effect on manual transmissions. Often the diesel variant of a car or truck will get a dual mass flywheel to control the harmonics, but at the same time, the gasoline variant may have a conventional flywheel.
Originally Posted By: artificialist
I have heard that the harmonics of diesel engines is a problem.
Interesting! How so?
The transition from power stroke to exhaust stroke is so dramatic that on some diesels, the serpentine belt squeals the moment the engine shuts off. This can happen even if the belt and tensioner have very few miles on them. One thing that somewhat helps is having a bigger and heavier crankshaft pulley/harmonic balancer.
The harmonics also have an effect on manual transmissions. Often the diesel variant of a car or truck will get a dual mass flywheel to control the harmonics, but at the same time, the gasoline variant may have a conventional flywheel.
Originally Posted By: DrRoughneck
Since diesels produce more torque and don't have a wide useable RPM range, wouldn't it make more sense to add produce diesel cars with CVT transmissions?
Why don't we see diesel/CVT cars in the US?
GM ruined the idea of mass diesels in the 1980's. Now VW has ruined the idea for years to come.
Diesel for passenger vehicles I think is done....
Since diesels produce more torque and don't have a wide useable RPM range, wouldn't it make more sense to add produce diesel cars with CVT transmissions?
Why don't we see diesel/CVT cars in the US?
GM ruined the idea of mass diesels in the 1980's. Now VW has ruined the idea for years to come.
Diesel for passenger vehicles I think is done....
Stick to gas engine.
From riding in city busses it seems diesels do well with a fairly loose torque converter, right at torque peak. Shifts are firm but the job gets done. But they'll rev, build speed without additional revs, then shift and repeat.
Apparently the older models only had one or two forward speeds!
Apparently the older models only had one or two forward speeds!
Originally Posted By: Mr Nice
Stick to gas engine.
In the US, where petrol is dirt cheap, I'd agree. For the rest of the world though, diesel makes a lot more sense.
Stick to gas engine.
In the US, where petrol is dirt cheap, I'd agree. For the rest of the world though, diesel makes a lot more sense.
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