In the PatBox CVT an auxiliary thin belt rides around the conventional V-belt and around rollers mounted on a lever.
The displacement of the lever varies the transmission ratio:
1 is a drive shaft (the crankshaft in most cases).
2 is a drive pulley comprising two conical halves.
3 is a driven shaft.
4 is a driven pulley comprising two conical halves.
5 is a V-belt.
6 is an auxiliary belt; it surrounds and abuts on the V-belt at the
drive pulley side.
7 is a lever comprising free rollers (12, 13) around which the auxiliary belt runs; a restoring spring (not shown) pulls the lever 7 to the left and keeps the auxiliary belt in tension; the linear speed of the inner side of the auxiliary belt 6 equals the linear speed of the external side of the V-belt 5.
In the following GIF animation, a pedal (15) having cuts (17 to 22) has been added to block the lever 7 at six distinct positions and to provide six additional distinct gear ratios to the CVT.
To shift to the next gear, the rider has to press slightly the pedal 15. The end 14 of the lever 7 leaves the cut wherein it was previously blocked and goes to the next one (shifts to the next gear ratio).
It is characteristic that in all the above gear shifts the driver / rider does not provide energy to the PatBox CVT; he just triggers the shifting; the required energy comes from the engine (like having a built-in servo).
In the following stereoscopic drawing (the one conical half of each pulley is removed; click here to enlarge):
the previously mentioned pedal 15 (the cyan part with the cuts) is shown blocked by a lock (magenta) allowing the free motion of the lever 7 (blue); by unlocking the cyan pedal (all it takes is a light press on the front finger of the lock), the transmission turns to manual with seven distinct gear ratios (six from the cyan pedal, plus the longest transmission ratio of the CVT).
When the rider wants to return to infinite ratios, he has just to press deeply the cyan pedal and then to release it; at its return (under the action of its restoring spring) the cyan pedal gets blocked again by the lock and the transmission returns either to the automatic infinite-ratios mode, or to the manual infinite-ratios mode.
By blocking or pressing the front end of the blue lever, the rider selects manually a transmission ratio from the infinite available.
By completely releasing the blue lever (the restoring spring of the blue lever, at the back, keeps the auxiliary belt in tension) the rider leaves the transmission to operate automatically.
Strengthening (or weakening) the restoring force that acts on the blue lever (by shifting the anchoring end of the restoring spring of the blue lever, for instance), the characteristic curve of the CVT varies: in order to increase the effective diameter of the drive pulley, the variator has to compress (by means of the V-belt) the spring of the driven pulley as usual, but it has also to displace angularly the lever 7 overcoming a stronger (or weaker) restoring force.
It is like replacing "on the fly" the rollers of the variator by lighter or heavier ones.
In a two-mode version the rider shifts from the "touring" to the "sport" mode by pushing a pin (a button) to anchor a middle point of the blue lever restoring spring: the restoring spring becomes stiffer, a stronger restoring force acts on the blue lever and the variator keeps the revs higher.
As the SECVT (Suzuki Electronically-controlled Continuously Variable Transmission, of Suzuki, used in the Suzuki Burgman and in the Aprilia Mana, and regarded as the state-of-the-art CVT for scooters), similarly the PECVT (PatBox Electronically-controlled Continuously Variable Transmission) can, optionally, operate in a "manual" mode, too, wherein the driver / rider selects, by a button or lever, a specific gear ratio (from a set of allowable "manual" gear ratios).
Compare the complication, the cost, the loads on the parts and the functionally of the above two electronically-controlled CVT's (SECVT vs. PECVT).
The problem:
With the current low-cost CVT's the rider has not the option to select the transmission ratio of his desire.
The tuning of the CVT in the factory (geometry of the pulleys / belt / variator, mass of the variator's weights, springs used etc) is a compromise for:
relatively acceptable fuel efficiency (mileage),
relatively acceptable acceleration,
relatively acceptable final speed,
relatively acceptable reliability,
relatively acceptable climbing ability,
relatively acceptable NVH (noise vibrations harshness) properties etc.
However the user of the CVT may have different priorities, or
priorities that vary depending on the instant conditions (traffic, gradient of the road, "with or without" a passenger (total weight), opposite wind, need for quiet operation, need for top acceleration etc).
This explains the great demand for aftermarket variators.
With a different, or a modified, variator the CVT operates/behaves
differently.
By putting heavier weights (heavier "rollers") in the same variator, the revs of engagement drop, the vehicle runs quieter at lower revs, the mileage increases, the CVT is more reliable; however the acceleration drops, an opposite wind or a steep uphill may become significant problems, etc.
By putting lighter weights (lighter "rollers") in the same variator, the revs of engagement increase, the vehicle accelerates faster, the climbing on a steep uphill is easy, the strong opposite wind is not a problem; on the other hand the noise increases, the mileage drops, the time between overhauls drops.
Replacing the original variator by an aftermarket "sport" one is, more or less, like replacing the original camshaft of a car engine by an aftermarket "wild" one. With the wild camshaft the power at high revs increases in expense of a worse engine at medium-low revs (in terms of mileage, emmisions, smoothness, response, driver friendly operation etc). With the "sport" variator the CVT keeps the engine at different (higher in general) revs even when this is bad.
A long ride in the highway at 50mph (80Km/h) constant speed (wherein the "original" variator keeps the engine revving at, say, 5000rpm) is exhausting (NVH) as compared to the case wherein with a "mild" variator at the same speed the engine is revving at only 4000rpm. In the second case the engine runs at a heavier load (more open throttle) that decreases the specific fuel consumption and increases the mileage.
With a "sport" variator things get even worse: at the same 50mph (80Km/h) the engine is revving at, say, 6000rpm and the throttle is even more closed (even lighter engine load): more noise, more vibrations, reduced mileage.
In a fast ride, on the other hand, wherein the time and the acceleration is what counts, the "sport" variator is the winner.
The low cost automatic CVT's of the art are of the type: "take it, or leave it"; the user / rider has to compromise with the characteristics of the CVT.
Case study: "Application on a bicycle"
Replacing the variator by a spring that pushes close to each other the two conical halves of the drive pulley, the PatBox CVT is ready for use in bicycles.
The drive pulley replaces the front sprocket of the bicycle, the driven pulley (with its spring) replaces the rear sprocket of the bicycle and the V-belt replaces the chain.
An auxiliary belt rides around, and abuts on, the V-belt (at the side of the pulley with the stronger spring); the auxiliary belt rides, also, around rollers on a lever.
If the spring of the drive pulley is the strongest, when the lever 7 is released, the PatBox CVT restores at its longest transmission ratio (the two halves of the drive pulley are close to each other).
If the spring of the driven pulley is the strongest, when the lever 7 is released, the PatBox CVT restores at its shortest transmission ratio (the two halves of the drive pulley are apart from each other).
The rider by displacing the lever varies continuously the transmission ratio.
The rider starts pedaling as usual.
When the rider needs a shorter (or longer) transmission ratio, the rider turns (or releases) the lever 7, the lever 7 rotates for a few degrees and then is secured till the next gearshift.
In a few words:
The PatBox is a simple, mechanical, lightweight, cheap and reliable
mechanism.
According the previous analysis, by modifying to PatBox the CVT of a scooter (all it takes is an auxiliary belt and a lever with some free rollers) the rider, besides the full automatic operation, gets an infinity of additional manually-selectable "gear ratios".
The rider can either vary, "on the fly", the characteristics of the
transmission in order to meet the instant needs for acceleration,
quiet operation, fuel efficiency, mileage etc, or the rider can leave alone the CVT to operate normally / automatically.
Instead of "moving" along a line of the "rpm vs speed" plot, with the PatBox the CVT can "move" along the same line, but it can also "move" outside it, in the area above the line (like moving in two dimensions instead of one).
With a variator engaging at lower revs (by replacing the "rollers" by heavier ones, for instance) this area extends providing additional useful and necessary modes (like: smoother, quieter and more economic highway trips) without any compromise in the acceleration, response, final speed etc.
While the PatBox CVT can provide infinite additional modes of operation, it actually adds no friction; instead, with the additional modes of operation, the overall efficiency (the mileage) improves, making the CVT greener.
Besides, the PatBox CVT can "replicate" any aftermarket variator; this means that with an aftermarket variator (any aftermarket variator) the vehicle cannot go faster than with the PatBox CVT.
