Gated 6 Speed Manual. . . CVT?
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This is your morning reminder that you may have driven a vehicle with a gated 6 speed manual continuously variable transmission. Plus it has a rear-mid engine layout and a staggered wheel setup. Surely this is the most Jalop riding mower in existence.
The way these work is just wacky.
The air cooled carbureted gasoline piston engine spins a clutch disk at a constant RPM. There is no gas pedal. There is a single combination clutch/brake pedal that triples as a parking brake via a hilariously rudimentary pin setup.
The speed is varied when you move a lever (barely visible in the previous photo) along a gated metal shift pattern that allows for 5 forward speeds and reverse. The individual niches push the drive disk into contact with the clutch disk, sending power to the rear wheels. Depending on how far towards the center or edge of the clutch disk it is, it changes the drive ratio resulting in different speeds.
Since the disk is always spinning when the mower is on and there is no gas pedal, you have exactly 6 speeds at which you can go. There is no throttle to modulate. As a result, if you happen to fall off one of the earlier ones from before they had weight sensors in the seat, it'll just keep going until it runs into something. Happened to my brother once.
Also of note is the fact that the clutch/brake pedal is only used as a clutch pedal when setting off from a standstill. It'll jump and shudder a little if you let off it jerkily or too fast. If you have enough clutch material left (most of these are rolling around with extremely worn clutches from misuse and abuse) you can actually get the front wheels entirely off the ground by a good inch or two with a hard launch. At higher speeds, I usually give a dab of brake/clutch but it's not exactly necessary.
Oh, and these are designed to be stored upright over the winter if you care to drain the fuel tank.
Who knew riding mowers could be so interesting? I'd be really curious how a manual CVT with no throttle pedal could work in a car. I think you'd have to ditch the gated shifter to make it work and you'd probably want larger disks for greater range of speeds available.
Color enthusiast, Citroën fanatic, and Cruze driver
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That friction disc setup was a bit of a thing on some car designs in the 1920s, IIRC.
(I'll just go ahead and tag @Cé-hé-sin here rather than try to find examples myself.)
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@bhtooefr said in Gated 6 Speed Manual. . . CVT?:
That friction disc setup was a bit of a thing on some car designs in the 1920s, IIRC.
(I'll just go ahead and tag @Cé-hé-sin here rather than try to find examples myself.)
https://www.wikiwand.com/en/Lambert_friction_gearing_disk_drive_transmission
I like big boost and I cannot lie.
But mostly I drive tractors. -
Snowblowers use this same set up too. -
Neat.
I think it would be cool to have a manual CVT in a road car. Variable pulley diameter style, the "shifter" moves a pushrod to move the cones together or apart.
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@jawzx2 That's really interesting. I remember a Jason Drives episode where he drives a 1913 Metz that had a nearly identical setup. Those of course had a proper three pedal setup with a separate clutch and it didn't have a gated shifter. It really was a continuously variable transmission while the one in the Snapper has been locked into a set number of ratios so I guess it's not technically a CVT. I don't think you could really give a car a one pedal setup like a Snapper but it sure would be interesting.
I wonder why those simple disk drive units didn't stick around? They were extremely simple, easily repairable, and pretty durable.
Color enthusiast, Citroën fanatic, and Cruze driver
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@onlytwowheels said in Gated 6 Speed Manual. . . CVT?:
Snowblowers use this same set up too.I don't think I've ever seen a snowblower. Ever. So can't really comment on what I'm looking at herer.
Color enthusiast, Citroën fanatic, and Cruze driver
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@qaaaaa said in Gated 6 Speed Manual. . . CVT?:
Neat.
I think it would be cool to have a manual CVT in a road car. Variable pulley diameter style, the "shifter" moves a pushrod to move the cones together or apart.
It has been done before in the early days of motoring. It would be interesting as manually selecting your drive ratio is very different than controlling the throttle and you'd need to do both.
Color enthusiast, Citroën fanatic, and Cruze driver
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@whoistheleader said in Gated 6 Speed Manual. . . CVT?:
I wonder why those simple disk drive units didn't stick around? They were extremely simple, easily repairable, and pretty durable.
Efficiency and torque transmission. Also packaging. You can make one that transmits enough torque for modern applications, but then it has to be big, and doesn't lend itself to modern automobile packaging. The modern Allison/Torotrak IVT works on the same general principle, but with novel materials and two-stage reduction.
I like big boost and I cannot lie.
But mostly I drive tractors. -
@jawzx2 said in Gated 6 Speed Manual. . . CVT?:
Efficiency and torque transmission. Also packaging. You can make one that transmits enough torque for modern applications, but then it has to be big, and doesn't lend itself to modern automobile packaging. The modern Allison/Torotrak IVT works on the same general principle, but with novel materials and two-stage reduction.
"Unlike continuously variable transmissions (CVT) found in snowmobiles and some cars already on the market, the IVT can handle much more torque."
That's very interesting. It's an infinitely variable transmission that's kind of like two different CVTs joined together? How exactly is it infinite? Seems like of the disks available you'd eventually run out of final drive ratio. I think the fact that this is basically two CVTs smooshed together helps with packaging.
Color enthusiast, Citroën fanatic, and Cruze driver
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@whoistheleader I don't think it would be much different than driving a flappy paddle car. Just a different control interface.
As with driving a flappy paddle car, a computer would be able to do it more seamlessly.
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@whoistheleader I can imagine a theoretically infinitely variable transmission, it would not be so infinite in practice. Lots of CVTs are based around connecting a pair of truncated cones with their axes in opposite directions. If you merely continued the taper of each cone all the way to a point, the drive ratio would vary from zero to infinity. Good luck getting the belt to grip and to maintain a perfect zero radius pointed end.
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@qaaaaa You'd have to design an instrument to tell you the drive ratio you're currently in. I feel like that would be really fun as a needle in a dial rather than a digital readout (ugly decimals). The real odd thing I think would be the range of movement needed to get fine control of the drive ratio but allow for 0 mph and top speed.
Color enthusiast, Citroën fanatic, and Cruze driver
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@whoistheleader said in Gated 6 Speed Manual. . . CVT?:
@jawzx2 said in Gated 6 Speed Manual. . . CVT?:
Efficiency and torque transmission....
That's very interesting. It's an infinitely variable transmission that's kind of like two different CVTs joined together? How exactly is it infinite? Seems like of the disks available you'd eventually run out of final drive ratio. I think the fact that this is basically two CVTs smooshed together helps with packaging.
theoretically it has infinite ratios, but only if you consider the contact area of the drive disks as an actual one-dimensional point. There are of course physical limitations due to the size of the mechanism and requirements of frictional surface and drive oil adhesion... by packaging two units back to back, the range of available ratios becomes practically infinite, if not actually infinite.
I like big boost and I cannot lie.
But mostly I drive tractors. -
@bhtooefr I'm not Ce He Sin, but the notable one was the GWK.
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@just-a-scratch said in Gated 6 Speed Manual. . . CVT?:
Good luck getting the belt to grip and to maintain a perfect zero radius pointed end
How useful would that be anyways? I suspect not very. I don't think their IVT is infinite however as there seems to be a clear limit to their final drive ratio.
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@jawzx2 said in Gated 6 Speed Manual. . . CVT?:
by packaging two units back to back, the range of available ratios becomes practically infinite, of not actually infinite
The domain still seems like it would have a clear hard cutoff point if you multiplied the two final drive ratios of the individual units. Not a practically reachable limit, but still a limit. It's clever for sure but I'm not so sure about infinite.
Color enthusiast, Citroën fanatic, and Cruze driver
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@whoistheleader Nah, if the shifter was just a sliding handle, I think a tach and speedo would be sufficient, really
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@whoistheleader said in Gated 6 Speed Manual. . . CVT?:
@jawzx2 said in Gated 6 Speed Manual. . . CVT?:
by packaging two units back to back, the range of available ratios becomes practically infinite, if not actually infinite
The domain still seems like it would have a clear hard cutoff point if you multiplied the two final drive ratios of the individual units. Not a practically reachable limit, but still a limit. It's clever for sure but I'm not so sure about infinite.
sure, there is a physical limit, but when you are talking about speeds required of a vehicle on public roads and given the limitations of internal combustion power delivery they are practically infinite. I think the ones that actually made it to production have a clutch, but the idea is that with the engine in idle and both drives at maximum reduction the output ratio becomes millions or even billions to one and in practice it could spend days idling and only move a few fractions of an inch. "Infinitely variable transmission" is clearly a marketing name and a way to differentiate it from the CVTs already in the market, but again, if we look at this sentence: "theoretically it has infinite ratios, but only if you consider the contact area of the drive disks as an actual one-dimensional point." the concept is infinitely variable.
I like big boost and I cannot lie.
But mostly I drive tractors. -
@jawzx2 Marketing gonna market. Not that a truly infinitely variable transmission would be very practical.
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@qaaaaa said in Gated 6 Speed Manual. . . CVT?:
@whoistheleader Nah, if the shifter was just a sliding handle, I think a tach and speedo would be sufficient, really
But it's more boring that way. . .
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The biggest reason the Snapper has gating is that the transmission is always trying to force itself into more favorable (i.e. lower ratio) gearing.
One thing about this kind of design that makes it less ideal for auto use is the characteristics of the contact patch. Because it's disc to disc, the "ideal" transfer is between two points with an infinite capacity to transmit force. The one point of intersection. In reality, it's going to be a short line of contact that's sort of tangent to the two circles, and of a minimum width band where on one wheel the two sides of the band are at the same speed, and on the other, the outside is moving faster.
The more deformable the disk, the longer the "line" and the more power, but it starts having to curve and deform in two dimensions. Possibly setting up vibration. The wider the contact patch, the more power it can transmit, but the more scrubbing takes place and faster wear. The gear ratio at its lowest also corresponds to the least ideal contact patch, so the highest disc wear and the lowest efficiency.
A belt CVT can transfer more power in some applications because the "contact patch" can be much longer and closer to a continuous line of tiny finite width and limited scrubbing, but the belt is continually changing aspect, which robs efficiency in some other ways. Because you need a "big circle" making contact, it also means it's not that compact.
Some of these Snappers have the rubber disk bolted directly to the transaxle, but others have a friction lining inside the disk so it can soft-start without chipping the rubber. If you dump the clutch on these, the former kind is more fun.
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@ramblinrover said in Gated 6 Speed Manual. . . CVT?:
The biggest reason the Snapper has gating is that the transmission is always trying to force itself into more favorable (i.e. lower ratio) gearing.
One thing about this kind of design that makes it less ideal for auto use is the characteristics of the contact patch. Because it's disc to disc, the "ideal" transfer is between two points with an infinite capacity to transmit force. The one point of intersection. In reality, it's going to be a short line of contact that's sort of tangent to the two circles, and of a minimum width band where on one wheel the two sides of the band are at the same speed, and on the other, the outside is moving faster.
The more deformable the disk, the longer the "line" and the more power, but it starts having to curve and deform in two dimensions. Possibly setting up vibration. The wider the contact patch, the more power it can transmit....
This brings up one of the magic bits of the Torotrak/Allison design: there is no direct mechanical contact between the disks and drive plates, torque is transferred through a viscous oil adhesion layer.
I like big boost and I cannot lie.
But mostly I drive tractors. -
@jawzx2 Oh really, that is interesting. I suppose that increases durability and helps reduce wear and scrubbing. The dry friction disks in the Snapper definitely wear faster because of that.
