Interesting CVT transmission patent

[greycloud]

Hi

I was online reading about CVT types and stumbled upon attached Patent application for a unique CVT idea from 1983!

it looks feasible but I don't seem to find any actual application for it. This is surprising as it seems to solve common problem with current CVTs especially regarding high torque handling.

anyone has any idea why such idea wasn't adopted in the automotive or heavy equipment industries?

below is link to patent for anyone interested

EP0108577A1 - Power transmission apparatus - Google Patents

Power transmission apparatus for driving an output shaft (3) from an input shaft (2) comprising a fluid cylinder (36) secured to the output shaft (3) and a piston (35) slidably mounted in the cylinder. The piston (35) is driven in reciprocal movement in the cylinder (36) in response to rotation...

patents.google.com

 

[XR250]

Probably way too inefficient for automobile use. Maybe could be used in heavy equipment but I suppose current hydrostatic transmissions are adequate enough.

 

[BrianPetersen]

This sounds suspiciously like a Honda motorcycle CVT transmission from some years ago: https://global.honda/en/newsroom/news/2007/2071004-eng.html

Back when this was introduced to the market, it showed up in a peculiar model called the DN01. Friend of mine worked in a Honda powersports dealer at the time. They joked that those initials (well, close enough ...) stood for "do not order one" ... It was a failure in the marketplace, and Honda has not followed it up in other models.

Honda now builds some models with a dual-clutch-automatic, and others with automated manual layouts, but not that hydraulic CVT.

 

[greycloud]

This sounds suspiciously like a Honda motorcycle CVT transmission from some years ago: https://global.honda/en/newsroom/news/2007/2071004-eng.html

Back when this was introduced to the market, it showed up in a peculiar model called the DN01. Friend of mine worked in a Honda powersports dealer at the time. They joked that those initials (well, close enough ...) stood for "do not order one" ... It was a failure in the marketplace, and Honda has not followed it up in other models.

Honda now builds some models with a dual-clutch-automatic, and others with automated manual layouts, but not that hydraulic CVT.

that indeed looks very similar indeed! any idea what was the problem with such transmission?

 

[greycloud]

Probably way too inefficient for automobile use. Maybe could be used in heavy equipment but I suppose current hydrostatic transmissions are adequate enough.

why do you think it would be inefficient?

 

[BrianPetersen]

why do you think it would be inefficient?

Hydraulic pumps and motors typically don't make for efficient power transmission. There's just too many sources of energy loss. Fluid leaks, flow restriction when passing through multiple sets of valves and passageways, friction between plungers and cylinders, viscous pumping losses, etc.

The Honda CVT mentioned above, mostly got around this by having a split torque path. When operating in reduction mode (e.g. starting off from a stop), most of the power goes through the hydraulic path, then as the road speed increases, it splits through the hydraulic and mechanical paths, and at high road speed when it is in the tallest (lowest engine revs, lowest mechanical multiplication) ratio, it's all mechanical and the hydraulic part of it is just along for the ride.

For that matter, automotive torque converters are kinda-sorta like that, too. When in torque-multiplication mode (starting off from a stop), the efficiency is pretty terrible (and zero, when it is actually stalled, with the output turbine stopped). At higher speeds, due to the various centrifugal forces increasing with the square of pump and turbine speeds, it comes closer to locking up, and the modern ones actually have a mechanical lock-up clutch which bypasses all torque transmission around the torque converter and transmits it all mechanically. Basically it's only at high efficiency when the hydraulic part of it is no longer doing anything ... (bypassed, locked up via the external mechanical lock-up clutch)

 

[BrianPetersen]

that indeed looks very similar indeed! any idea what was the problem with such transmission?

I'm not aware of any actual "problems" with it, but Honda sold so few examples of that bike that there's not exactly a large user-base to report on.

I suspect the bigger issue is a combination of poorer efficiency than a gear-to-gear transmission, and unfavourable driveability characteristics, and probably, higher cost than gear-to-gear transmissions, of which Honda makes many millions every year. Premium-market motorcycles are enthusiast vehicles, and most enthusiasts (including myself) hate the way CVT-equipped vehicles drive, and sound. Some newer CVT-equipped vehicles have (partly) gotten around this by selecting fixed ratios within the transmission to emulate, let's say, "third gear" (by assigning it a fixed ratio within the CVT and emulate the operation of a normal multi-gear transmission with a selection of predetermined ratios), but then, why bother?

 

[KiwiME]

It looks like a swash plate hydrostatic pump in principle. What am I missing?

 

[greycloud]

I'm not aware of any actual "problems" with it, but Honda sold so few examples of that bike that there's not exactly a large user-base to report on.

I suspect the bigger issue is a combination of poorer efficiency than a gear-to-gear transmission, and unfavourable driveability characteristics, and probably, higher cost than gear-to-gear transmissions, of which Honda makes many millions every year. Premium-market motorcycles are enthusiast vehicles, and most enthusiasts (including myself) hate the way CVT-equipped vehicles drive, and sound. Some newer CVT-equipped vehicles have (partly) gotten around this by selecting fixed ratios within the transmission to emulate, let's say, "third gear" (by assigning it a fixed ratio within the CVT and emulate the operation of a normal multi-gear transmission with a selection of predetermined ratios), but then, why bother?

I read several reviews about this bike and indeed they report that its very reliable; however like u said their issue was the steep price indeed and that many felt like it was a scooter due to absence of a clutch. however, I believe any CVT would be good on effiecency side especially if compared to automatic transmission. then again like you said many poeple don't like how CVT feels.

 

[greycloud]

It looks like a swash plate hydrostatic pump in principle. What am I missing?

well, pump is directly connected to motor so that changes everything. other variations included in the patent replace the swashplate with an accentric cam or a crank arm.

 

[greycloud]

Hydraulic pumps and motors typically don't make for efficient power transmission. There's just too many sources of energy loss. Fluid leaks, flow restriction when passing through multiple sets of valves and passageways, friction between plungers and cylinders, viscous pumping losses, etc.

The Honda CVT mentioned above, mostly got around this by having a split torque path. When operating in reduction mode (e.g. starting off from a stop), most of the power goes through the hydraulic path, then as the road speed increases, it splits through the hydraulic and mechanical paths, and at high road speed when it is in the tallest (lowest engine revs, lowest mechanical multiplication) ratio, it's all mechanical and the hydraulic part of it is just along for the ride.

For that matter, automotive torque converters are kinda-sorta like that, too. When in torque-multiplication mode (starting off from a stop), the efficiency is pretty terrible (and zero, when it is actually stalled, with the output turbine stopped). At higher speeds, due to the various centrifugal forces increasing with the square of pump and turbine speeds, it comes closer to locking up, and the modern ones actually have a mechanical lock-up clutch which bypasses all torque transmission around the torque converter and transmits it all mechanically. Basically it's only at high efficiency when the hydraulic part of it is no longer doing anything ... (bypassed, locked up via the external mechanical lock-up clutch)

by fluid leaks I believe you mean leaks between cylinder and plungers which should be low if I'm not mistaken. flow restrictions and viscous pumping losses well be present in an auto tranmission as well cause u still have a trans pump running all time with passage ways to deliver the oil pressure. In addition to that u don't have the losses from all the gears constantly turning around in auto transmission to make the different gear ratios and u can more freely select more suitable engine rpm since its a CVT. though to be honest without actual design Its difficult to know the weight and magnitude of losses from each component without actual design

 

[BrianPetersen]

In a regular (geared) automatic transmission, although it relies upon hydraulics in order to function, the actual power delivery is not transmitted by the hydraulics (aside from inside the torque converter, which nowadays is locked up most of the time) ... it's gear-to-gear. There is a pump to produce the hydraulic pressure that is used to engage the various clutches and brakes, and it does eat some power, but it's a tiny fraction of the power being transmitted through the transmission as a whole.

Hydrostatic transmissions transmit ALL of the engine's power through the pump and hydraulics.

The Honda transmission uses a pump actuated by the difference between the input shaft speed and the output shaft speed. If the swash plate on the hydraulic motor on the output shaft is set to zero displacement then that blocks fluid flow through the hydrostatic part of the transmission, and then the pump's output speed is forced to match the input speed due to the hydraulic fluid not having anywhere to go, and thus, power transmission is mechanical when it is in direct drive. The fluid isn't being pumped in that situation - it's trapped under pressure between the pump and motor, but it isn't flowing, because the output motor is set to zero displacement. It's a rather clever design.

 

[LionelHutz]

All the big tractors are now using transmissions that employs hydrostatic drive in them, not directly but basically as a coupling between gear sets that forces input vs output speed changes. They must be very efficient since big operators are looking at the fuel used per acre (or 100 acres) of field coverage when purchasing their equipment. You can tell which ones have it because they have a hydrostatic whine when they go past on the road.

I believe the AGCO (Fendt) system runs through the full speed range without any gear changes and the CNH (Case) system changes though 3-4 gears with the hydraulic part speed matching the gear changes so it's a bump less change the operator doesn't even notice.

 

[greycloud]

All the big tractors are now using transmissions that employs hydrostatic drive in them, not directly but basically as a coupling between gear sets that forces input vs output speed changes. They must be very efficient since big operators are looking at the fuel used per acre (or 100 acres) of field coverage when purchasing their equipment. You can tell which ones have it because they have a hydrostatic whine when they go past on the road.

I believe the AGCO (Fendt) system runs through the full speed range without any gear changes and the CNH (Case) system changes though 3-4 gears with the hydraulic part speed matching the gear changes so it's a bump less change the operator doesn't even notice.

if you are referring to different gears being engaged by hydraulic clutch then that is the norm in entire automotive industry as well as construction equipment

 

[greycloud]

The Honda transmission uses a pump actuated by the difference between the input shaft speed and the output shaft speed. If the swash plate on the hydraulic motor on the output shaft is set to zero displacement then that blocks fluid flow through the hydrostatic part of the transmission, and then the pump's output speed is forced to match the input speed due to the hydraulic fluid not having anywhere to go, and thus, power transmission is mechanical when it is in direct drive. The fluid isn't being pumped in that situation - it's trapped under pressure between the pump and motor, but it isn't flowing, because the output motor is set to zero displacement. It's a rather clever design.

though it should be hydraulic in overdrive

 

[BrianPetersen]

though it should be hydraulic in overdrive

The Honda transmission does not provide an overdrive. Direct-drive is the tallest ratio that it can provide. It will also be the ratio that provides the highest efficiency ... because there are (almost, aside from leakage) no hydraulic pumping losses.

 

[greycloud]

The Honda transmission does not provide an overdrive. Direct-drive is the tallest ratio that it can provide. It will also be the ratio that provides the highest efficiency ... because there are (almost, aside from leakage) no hydraulic pumping losses.

any idea where I can read more about this transmission?

 

[BrianPetersen]

The link provided earlier is all I've got. The motorcycle in question was a failure in the marketplace, and the transmission it used was never used again in another model, so there's not a lot about it.