Continuously Variable Transmissions

[Fanie]

Why aren't these used for marine apps ? You can run the drive motor at a constant speed where it produces most torque while the boat speed changes.

Here's a nice video of how it works.

http://www.karting1.co.uk/continuous...karts-test.htm

[Boston]

kinda makes me want to go rent a few beers and a cart
cool flicker Fanie
thanks

[alan white]

Infinite ratio drives have certain inherent inefficiencies which must be compensated for by allowing the engine to run, as said, at optimum speed. Then a 10% engine efficiency gain, for example, will be better than a 6% drive loss (and the loss due to extra transmisdsion cost)--- by 4%.
A typical boat will generally be capable of maintaining one optimum speed through the water, and it's assumed that the boat will run at that speed most of the time, so that the whole system (engine, trans, prop) can be optimized to that narrow speed range.
Of course, some boats might travel at variable speeds and it is possible that they could make better use of a variable speed transmission.
It's really a question of which usage would warrant the use of such a transmission. It would have to be a boat that spent a lot of the time at different speeds.
A good variable pitch propeller should be as or more efficient as any variable speed transmission. This is like being able to enlarge your car tires as you go faster. If a car could do that, it wouldn't need a transmission with gears.

[CDK]

Originally Posted by Fanie

Why aren't these used for marine apps ? You can run the drive motor at a constant speed where it produces most torque while the boat speed changes.

Here's a nice video of how it works.

http://www.karting1.co.uk/continuous...karts-test.htm

The CVT, invented by Huub van Doorne 30 years ago and improved numerous times, never got wide acceptance because the metal belt is very difficult to produce, especially when a lot of horsepowers are involved.
A few small Japanese cars use this system, the patented belt being supplied by the Dutch company. They still seem to be experimenting with larger ones.

[alan white]

Even further back, didn't the Dutch company Daf build a car with a CTV? the Subaru Justy can be had with ther CTV as an automatic transmission, as well as most snowmobiles built today. All of these had rubber belts though, I think. I didn't know about as metal belt.

[Fanie]

It seems the advantage of such a setup is that you can run the motor for most speed, for most torque or for best economy, all three usable for marine app.

Lots of cars have them nowadays.

[CDK]

Originally Posted by alan white

Even further back, didn't the Dutch company Daf build a car with a CTV? the Subaru Justy can be had with ther CTV as an automatic transmission, as well as most snowmobiles built today. All of these had rubber belts though, I think. I didn't know about as metal belt.

DAF stands for van Doorne's Automobiel Fabriek. The did manyfacture a passenger car with 2 giant V-belts as a transmission, but people got sick of having them changed every year and production facility was closed down several decades ago. They split up in a still successful truck factory and the CVT manufacturer who produces the metal "push-belt".

[FAST FRED]

"Of course, some boats might travel at variable speeds and it is possible that they could make better use of a variable speed transmission.
It's really a question of which usage would warrant the use of such a transmission. It would have to be a boat that spent a lot of the time at different speeds.
A good variable pitch propeller should be as or more efficient as any variable speed transmission."

I believe a 2 speed tranny would make most sense with a boat that has a Hi Cruise speed and a Low cruise speed.

While a CPP would allow the optomisation at EITHER speed , it could not do both.

A vessel that could shift to a higher shaft speed when running slowly would be able to keep the engine in a better more heavily loaded range , and would gain efficiency.

Weather that would be worth the cost of a 2 speed ZF and CPP , would depend on the annual hours of use.

FF

[Frosty]

It was Daf variomatic, the belts were not a prob as I remember. This idea is ubiquitous in small motorcycles I would say more than half the motorcycles made in Thailand are variamatic.

It works by weights on one hub expanding the two parts of the hub together so reducing the space for the belt making the V belt ride out. The driven hub would have similar 2 parts but have springs, the weights with centrifugal force over comes the springs. The belts were expensive so I used a B size V belt perfectly for a dollar.

The Daf would fail only due to vacuum pipes from the manifold that worked the drive hubs unlike the motorcycles. The vacuum pipes would often break and frighten the hell out of the owner . I bought quite few in Car auctions in my day.

I remember Ford making some auto transmission with a metal belt rather like a spandex wrist watch strap, it was unusual as the belt would push and not pull.

[Carioca]

Originally Posted by CDK

The CVT, invented by Huub van Doorne 30 years ago and improved numerous times, never got wide acceptance because the metal belt is very difficult to produce, especially when a lot of horsepowers are involved.
A few small Japanese cars use this system, the patented belt being supplied by the Dutch company. They still seem to be experimenting with larger ones.

I was unaware that DAF is only 30 years old, although the chronology of the CVT invention sounds about right !

I had always been under the impression that DAF was a Dutch re-start from post-WW II, similar to BMW and NSU.

[Frosty]

Bit more than 30 years,--45 at very least.

Daf are well known for heavy goods vehicles in Europe and are popular, even against Volvo etc

[Carioca]

Originally Posted by Frosty

Bit more than 30 years,--45 at very least.

Daf are well known for heavy goods vehicles in Europe and are popular, even against Volvo etc

If my memory is not failing me, I believe I saw DAF at the Earl´s Court Motor Show (London, UK) in the late 60´s - think it was ´69 - when NSU presented its Wankel-engined passenger car.

Prior to this, had heard/seen DAF as a heavy goods vehicle manufacturer. No DAF lorries in London in those days, though !

Originally Posted by FAST FRED

While a CPP would allow the optomisation at EITHER speed , it could not do both.FF

Fred the opposite, a CPP does exactly that. It optimizes the systems efficiency at ALL displ. speeds. (as long as the vessel is´nt operating at a narrow speed range all time).

And the Daffodil entered the market in 1961, so the system is older than Cornelis remembers, 50 years.

[marshmat]

Nissan is offering CVTs as an option in several of its cars right now.

The trouble with adapting them to marine use is the same problem that is encountered when adapting car engines to marine use. Namely, sustained transmission of high torque. It took many years and many millions of dollars to come up with a CVT that could handle the Nissan Murano's 265 hp or so. But the car (thing?) only ever produces full power for ten seconds or so at a time, and spends 98% of its operating life loafing along at much lower RPM and torque.

In a boat, the transmission is expected to handle the full power and torque of the engine, continuously, for thousands of hours before needing work. Think how long your car's gearbox would last if you drove it like a NASCAR racer, day in, day out. Would you get 250,000 km on it before needing any work? But we routinely expect that kind of duty cycle and lifespan from our marine gears.

Plus, we boaters can get a lot of the same benefits with a CPP or, in the case of heavy planing hulls, a two-speed gearbox. Both of which are mechanically simpler, easier to make really beefy, and easier to fix when they break.

[CDK]

Originally Posted by Frosty

Bit more than 30 years,--45 at very least.

Daf are well known for heavy goods vehicles in Europe and are popular, even against Volvo etc

DAF even existed in the 2nd world war, but under another name.
I nowhere wrote that DAF was 30 years old, only that van Doorne invented the present CVT that long ago.
They are separate companies now, DAF being a big player on the heavy lorry market in Europe.

The old Variomatic was the predecessor with V-belts. The Dutch called it a girder belt transmission. Most drivers were female, elderly and had a driving license restricted to this vehicle only (!)