Talk:Continuously variable transmission
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[edit] Infinigear-CVT
I was concerned about the former Infinigear entry, which as someone flagged, looked like an advertisement. Fair enough, if they describe how it works, but neither the entry nor the site referenced does. An encyclopedia entry should, if nothing else, be informative. The reference to my own CVT, directly above Infinigear's, gives full details on the referenced site and reasonable detail in the short entry. The same with Larry Anderson's CVT site - you can see exactly how it works, indeed he even has a video. What is the policy on this? I emailed Infinigear for information on their device, but though they replied pleasantly enough were unwilling to disclose details at this stage. -- ChrisYonge 15:55 PST, 3 October 2006
Someone's deleted their entire entry. Extreme but effective. I would be happy to see it remain - with the advertising verbiage reduced - if they just showed how the thing works on their site. Secrecy always implies something to hide. If it's not protected they shouldn't be talking about it. If it is protected then they shouldn't be doing anything except talking about it. -- ChrisYonge 20:25 PST, 3 October 2006
[edit] Copyright Violations
I added the attention flag.
The bit in the History section about the Renault/Williams car with the V10 and CVT is lifted directly from this site. This makes me question how legitimate the other bits are. That part ought to be reprased or rewritten, but the writing is so clear, I can't think of a much better way of saying it. -- Huddlebum 20:32, 12 February 2006 (UTC)
I agree - it's almost a direct duplicate of the forix text - be bold - so it's history - and so is the attention flag. If whoever originally inserted it has better text to offer - or can offer an explanation for the near identical phrasing...you know what to do. SteveBaker 03:10, 4 April 2006 (UTC)
[edit] Prius CVT
The Toyota Prius is perhaps incorrectly listed here as having a CVT. The Prius and other Hybrid Synergy Drive equipped cars do not have a CVT in the conventional sense of the term. They do not have a mechanical transmission with variable ratio. Rather, they use a combination of 2 motors generators and a planetary gearset to achieve the same effect.
- I've added explicit discussion of the Prius' system here. It's still a CVT in the sense that the ratio of engine-to-wheel speed is continuously variable. Toyota themselves call it an E-CVT (electronically-controlled CVT). --KJBracey 09:21, 13 November 2005 (UTC)
I agree with the following statement (shown above): 'The Toyota Prius is perhaps incorrectly listed here as having a CVT. The Prius and other Hybrid Synergy Drive equipped cars do not have a CVT in the conventional sense of the term. They do not have a mechanical transmission with variable ratio. Rather, they use a combination of 2 motors generators and a planetary gearset to achieve the same effect.'
The Toyota Prius drive system should be termed 'Power Split System' as opposed to CVT. The term 'CVT' should be narrowly defined as a stand-alone device with only one input and only one output.
The CVT is a transmission in which the ratio of the rotational speeds of two shafts, as the input shaft and output shaft of a vehicle or other machine, can be varied continuously within a given range, providing an infinite number of possible ratios. The Prius drive does not fit this definition because it uses more than one input shaft.
Remember that any definition draws an outline around the subject of definition; description must include all relevant conditions and exclude all irrelevant conditions, much like a circled unit in a Venn diagram. The narrowest definitions allow us to describe relationships between elements of discussion in a discrete manner, as in a Venn diagram. Terms that are narrowly defined contain no implications that can confuse and obfuscate communication. Please be very careful about use of terms and definitions so that we can communicate clearly!Simbasat 20:33, 26 January 2007 (UTC)
[edit] BMW/Rover CVT
Lever positions: CVT does have PARK - (where the transmission is physically locked), - NEUTRAL where the engine is disengaged from the drive and the handbrake should be on. Engine could be revved as a normal gearbox. The German Sachs-ZF as fitted to BMW's and Rovers has six preset ratios in the software for manual 'sequential' changing, has a steel laminated oil-cooled belt (seperate oil cooler)and two 'wet' motorcycle style multiplate clutches (one for forward,one for reverse). The clutches work on oil pressure from an engine-driven pump, therefore as the rpm increases, oil pressure pushes the clutch plates together to provide a smooth pull away. Much better than the inefficient fluid flywheel of conventional automatics. To hold the car in low gear it simply has to be in manual position (in the case of the ZF this is with the lever to one side. It also has a 'sport' mode which simply lowers the ratio of the continuously variable range. In my bitter experience (I have driven more than 60,000 miles with one), whilst really smooth and relaxing to drive, the 'belt drive' type does not stand up to transmitting the torque of an engine of more than say, 100bhp despite claims that technology has now pushed through this limit. One problem is that the laminated steel belts have a tendency to overheat despite an external oil cooler. Cabinscooter 21:15, 7 June 2006 (UTC)
[edit] Honda City CVT
Q: I own a Honda City CVT. Right from the beginning, I have experienced side-to-side rocking at low speeds. I have verified the correctness of tyre pressure several times. Wheel alignment and balancing has also been done twice in total running of 10000km. But the car still rocks. Does this have to do anything with the fact that the car is CVT ? Are there any special points to be observed while driving a CVT car which can solve the rocking problem ? I shall be obliged for any suggestions.
A1: This probably does not have anything to do with the CVT. Please describe the rocking in more detail. Is it that the car "wanders" left to right, around the vertical axis? Or is it tilting left to right around the horizontal front-to-back axis? What are low speeds? Cruising at 30-50 km/h? Or very slow crawling in a parking lot or congested traffic? A CVT will probably exhibit "drive train oscillation" if it is (effectively) in a very low gear, going slowly, just like manual transmissions in first gear. That's experienced as foward-and-back rocking, rather than side to side, mind you: that wwOOwwOOwwOO jerking. Anyway, without knowing anything more, here are ideas: look into the suspension. Any car will rock if it has no shock absorbers. It is then just a mass resting on several springs. Mass + spring = harmonic motion. If an oscillator is driven at the right frequency, it will pick up amplitude. What else. Different bursts of power going to different wheels? Differential problems? Also, the tire pressure may be good, and the wheels may be balanced, but in what condition are the tires? Is there a bulge in any of the tires? Balancing won't compensate for the shape of the tire, only for its shifted center of mass.
Q : First of all, I thank you heartily for posting a reply. The car is normally smooth on smooth road. What I mean by rocking is that when I hit a pothole either on left or right side, the car bumps sideways excessively. To reply to your question objectively, the car tilts left to right around the horizontal front-to-back axis. But if I go on a speedbreaker (where right and left wheels are subject to SAME undulation), then the car doesn't rock. The dealership assures me that there is no problem in the shock absorbers even though I am not convinced. I had the car examined for shock absorbers by another agency and that too hasn't found any problem with shock absorbers. By low speed, I mean speeds below 20km/h. But even at higher speeds, the rough ride remains, albeit to smaller extent. I am sorry I am not competent enough to comment on your points whether different bursts of power is going to different wheels or whether there is differential problem. As regards the tyres (Bridgestone), they are new since the car itself is just 9 months old. There is no bulge visible to my untrained eyes. Neither was any doubt raised by wheel balancing agency in this respect. There are some more observations. Since I cannot measure the rocking, these are just my impressions and I hope these will not make the case more confusing. 1) The car exhibits less rocking when the boot is loaded to 5kg each on both right and left side. 2) Sometimes, even on relatively smooth roads, I feel as if I am driving on iron wheels (like a road roller). But, mysteriously enough, sometimes the ride is smooth. 3) If I run the car on neutral gear (like when going downhill), the car appears to have less rocking.
A2: This is caused by the design of your suspension. I think the problem is related to a torsion bar going from one side of the vehicle to the other. Yours might be too strong or too weak, or maybe even missing.
[edit] Lever Positions
See BMW/Rover CVT Cabinscooter 21:30, 7 June 2006 (UTC)
Blonde2max 18:54, 26 March 2006 (UTC) I just wondered if CVT cars had lever positions like proper automatics? For example do they have
PARK - Where the transmittion is actually locked, and even removing the handbreak wont cause the car to roll NEUTRAL - Where the "Gearbox" and engine are completely disengadged; ie you can press the accelerator and let it rev to 5000RPM without anything exploding (assuming it's petrol) Something to hold the car in low gear/switch off overdrive?
I think they are quite interesting however I would never drive a CVT as it is still an automatic and they are evil =(
(PLease sign your comments by typing for tilde characters at the end of your posts (~~~~).
The CVT MINI Cooper has all of the usual automatic shifter positions - plus the ability to push the shifter sideways to force an up-shift or a down-shift. However, since the transmission doesn't really have discrete shift points, this is merely simulated in software. I also strongly dislike driving automatics - but I recognise that for some people they are a very good idea indeed. SteveBaker 20:19, 26 March 2006 (UTC)
- The CVT used in the Ford Five Hundred also has all the same positions as a traditional/geared automatic, so I would assume that most if not all modern CVTs use the standard positions. --SodiumBenzoate 03:09, 25 August 2006 (UTC)
The Rudge "Multi" motorcycle used a "DAF" type CVT from 1912 until the 1920s, including some racing success. So this predated the DAF by about 45 years! There were a few other older vehicles that also used one type of CVT or another, such as the Ner-a-car which used a CVT based on a mechanical integrator.
sorry i always put the ~ at the start. I am new at wiki - sorry peepole. thanks for your replys.Blonde2max 20:59, 30 April 2006 (UTC)
[edit] Illustrations Needed
Might be easy for you guys to visualize what's going on, but we need more illustrations for the rest of us! --Nil0lab 21:14, 4 April 2006 (UTC)
[edit] Variator
Link to Variator is not useful, as that entry is way to vague. Should it be expanded, or should there be a specialized article, e.g. "Variator (automatic continuously variable transmission)" --Nil0lab 21:19, 4 April 2006 (UTC)
[edit] ICE acronym not defined in E-CVT section
What does it mean? It just appears.
ICE = Internal Combustion Engine
[edit] Yonge CVT
Biased towards the advantages and uniqueness. Needs a re-write that doesn't sound like a patent application or investment brochure. 66.183.181.9 22:10, 2 December 2006 (UTC)
[edit] E-CVT?
Is it appropriate to use "E-CVT," which is basically a Toyota marketing term, as a generic descriptor of a type of transmission?
1. The term "ECVT" was used by Subaru to describe its Justy in 1989.review So, the term isn't exclusive to Toyota even in the marketing arena.
2. If the term "E-CVT" means "electronically controlled continuously variable transmission," that's an accurate description of many pulley designs manufactured today. The term is too generic to be meaningful, especially when every other section title is an accurate descriptor of a subclass within the CVT class; again, it seems like a Toyota attempt to make a simple coupling seem more technically advanced than it is.
3. The article itself states: "Although sold as a CVT it is in fact not such a device." So, why is it in the article at all? We're right back to Toyota's marketing being reported as fact. It goes on to say: "The response of the complete system (under computer control) is similar in feel to a CVT in that the ICE speed is relatively low and constant under low power or high and constant under high power." I will abstain from a rude analogy which explains that things which feel like they may belong in a class may not, in fact, belong to that class.
This transmission is a planetary gearset. It may give a CVT-like experience as part of a broader system, but the gearbox itself is clearly not a CVT and doesn't belong in this article. Maybe the way to handle it is to simply call the whole Toyota-style hybrid system a type of CVT, because if you take out any component of that system, even the CVT-like behavior of this gearset would disappear.
One more argument for deletion of the E-CVT section: the CVT article defines a CVT as an "automatic transmission." The automatic transmission article says: "An automatic transmission is an automobile gearbox that can change gear ratios automatically as the car or truck moves, thus freeing the driver from having to shift gears manually." The Toyota system has, according to the CVT article, a "fixed gear ratio." So, by that definition, the Toyota piece is not only not a CVT, it's not even an automatic, because it can't change gear ratios at all.
I'm reluctant to edit without getting other perspectives, so thanks in advance for any thoughts on this.Meersman 17:08, 8 December 2006 (UTC)
[edit] this seems more commentary
"CVT control computers often emulate the traditional abrupt gear changes, especially at low speeds, because most drivers expect the sudden jerks and will reject a perfectly smooth transmission as lacking in apparent power."
Without proper referencing the above sentence seems more of a predictive or commentary nature rather than informative. As such it should be relegated to the discussion page or another suitable section. Origen
[edit] IVT (Infinitely Variable Transmission)
The following definition for IVT is misleading:
'An extension to CVT design, sometimes known as the Infinitely Variable Transmission (IVT), allows the transmission to drive a vehicle backwards as well as forwards. Transmission input is connected to the engine, then it is split into 2 shafts with one connected to an epicyclic gear set. The output from the CVT shaft is connected to another shaft that connects to a different set of gears in the epicyclic. The gear that does not draw power from engine or CVT transfers torque to the transmission output. The gear set acts as a mechanical adding machine to subtract one speed from the other, allowing the car to go forwards, backwards, or neutral.'
The IVT is a subset of CVT's because it is a special case CVT. Most (if not all) IVT's result from the combination of a CVT with an epicyclic gear system (which is also known as a planetary gear system) that facilitates the aforementioned subtraction of one speed from another speed. This subtraction only needs to result in an infinite range of positive, non-backwards 'gear ratios' because reversal of output direction is trivial, in practice; the IVT definition should only include continuous output variability from zero output to any finite positive maximum output ratio because the maximum output ratio can be arbitrarily chosen (from infinite practical possibilities) through input or output gear, pulley or sprocket sizes without affecting the zero output or the continuity. Importantly, the IVT is distinguished as being 'infinite' in its bandgap, or range; high gear is infinite times higher than low gear.
Although it is true that an epicyclic gear system can produce positive and reverse (backward) output from a CVT, this is impractical because near-zero output (at the pos/neg transition) will produce exceedingly high torque values within any traction-based CVT, and will produce extreme vibration with any 'ratcheting' CVT. Practical constraints should exclude reverse operation from the IVT definition. —The preceding unsigned comment was added by 71.198.223.13 (talk) 02:15, 26 January 2007 (UTC).
[edit] IVT (infinitely Variable Transmission)
02:35, 26 January 2007 (UTC)71.198.223.13The following definition for IVT is misleading:
'An extension to CVT design, sometimes known as the Infinitely Variable Transmission (IVT), allows the transmission to drive a vehicle backwards as well as forwards. Transmission input is connected to the engine, then it is split into 2 shafts with one connected to an epicyclic gear set. The output from the CVT shaft is connected to another shaft that connects to a different set of gears in the epicyclic. The gear that does not draw power from engine or CVT transfers torque to the transmission output. The gear set acts as a mechanical adding machine to subtract one speed from the other, allowing the car to go forwards, backwards, or neutral.'
The IVT is a subset of CVT's because it is a special case CVT. Most (if not all) IVT's result from the combination of a CVT with an epicyclic gear system (which is also known as a planetary gear system) that facilitates the aforementioned subtraction of one speed from another speed. This subtraction only needs to result in an infinite range of positive, non-backwards 'gear ratios' because reversal of output direction is trivial, in practice; the IVT definition should only include continuous output variability from zero output to any finite positive maximum output ratio because the maximum output ratio can be arbitrarily chosen (from infinite practical possibilities) through input or output gear, pulley or sprocket sizes without affecting the zero output or the continuity. Importantly, the IVT is distinguished as being 'infinite' in its bandgap, or range; high gear is infinite times higher than low gear.
Although it is true that an epicyclic gear system can produce positive and reverse (backward) output from a CVT, this is impractical because near-zero output (at the pos/neg transition) will produce exceedingly high torque values within any traction-based CVT, and will produce extreme vibration with any 'ratcheting' CVT. Practical constraints should exclude reverse operation from the IVT definition. 71.198.223.13 02:35, 26 January 2007 (UTC)
[edit] Copied from talk:Infinitely Variable Transmission
The Infinitely Variable Transmission (IVT) is a specific type of Continuously Variable Transmission (CVT). The Wikipedia definition of the CVT is flawed, and should be corrected before the definition of the IVT is produced. As an early inventor of both a CVT and an IVT, I feel that I'm qualified to define both terms.
Note that any definition should include only essential conditions, and therefor it should not include anything else. For example, a CVT is not necessarily an automatic transmission because its ratio can be continuously adjusted manually, so it should not be defined as an automatic transmission! The CVT does not require reverse operation either. The only conditions for a CVT are that it is continuously variable in its essential control (ratio) of shaft speeds within a given range, and that it is a transmission, and nothing else. I suggest the following replacement Wikipedia definition of the CVT:
The Continuously Variable Transmission (CVT) is a transmission in which the ratio of the rotational speeds of two shafts, as the input shaft and output shaft of a vehicle or other machine, can be varied continuously within a given range, providing an infinite number of possible ratios.
The Infinitely Variable Transmission (IVT) definition is more challenging because it contains the word 'infinitely', which is sometimes confused with the infinite choice of ratios in any CVT. Prevalent usage of the term IVT refers to the infinite range of ratios with certain CVT's, as opposed to infinite choice. This distinction about infinite range is critical to the definition of the IVT because it implies either that the highest output/input ratio is infinitely higher than the lowest ratio, or conversely that the lowest output/input ratio is infinitesimal. No transmission can have an infinitely high output/input ratio, but a transmission can have an infinitesimally low (including zero) output/input ratio, so the IVT must be continuously variable in selection of ratios that include zero output. So, I offer the following Wikipedia definition of the IVT:
The Infinitely Variable Transmission (IVT) is a CVT in which the ratio of output shaft rotation speed to input shaft rotation speed can be varied continuously within a given range that includes zero.
Users of the terms CVT and IVT as defined above should not confound their discussions by misuse. CVT's and IVT's can have additional features, such as automatic operation, disengageability and reversibility. Please note that such discussions can use adjectives that preface these terms, e.g. 'Automatic CVT', 'Disengageable CVT', or 'Reversible IVT', etc.71.198.223.13 00:50, 27 January 2007 (UTC)
[edit] Anderson A+CVT
Is it me or does the section on the Anderson A+CVT seem like original research? Considering that the guy who uploaded the photo took it himself and is called Fred Anderson. In my opinion it is in breach of the Wikipedia:No original research policy, any other opinions? Mumby 16:39, 5 March 2007 (UTC)
[edit] Naudic Incremental CVT (iCVT)
I pulled the entire section on the Naudic Incremental CVT (iCVT) for the same reason as the Anderson system. It had basically turned into an advert for the naudic system; it is not neutral and I think it is in breach of wikipedia's policies on advertising and original research. Consider this: the Naudic CVT was invented by a guy called Dr. J. Naude, and all the info is being added by a user called JNaude. The article should describe the difffernt types of CVT, not the different brands. Mumby 17:37, 22 March 2007 (UTC)
[edit] Leonardo da Vinci
The page indicates that "Leonardo da Vinci, in 1490, conceptualized a stepless continuously variable transmission" and has two external links immediately after that. However, neither of those links provides any substantive information about Leonardo, much less about that particular conceptualization. I have not found any evidence for this assertion; in fact, everything I've found (via Google, etc.) uses an almost identical phrase, with no additional information nor evidence. Unless someone can produce a valid reference, this should be removed from the page. 152.17.54.23 01:56, 1 April 2007 (UTC)
