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RatioZero is a prototype concept for a continuously variable transmission (CVT) that uses toothed gears instead of belts, chains, or traction rollers. Its geometry changes the speed ratio continuously while gears hand off the torque, aiming to combine the smooth ratio control of a CVT with the positive engagement of a geared transmission. Donald Papp introduced the prototype in Hackaday on December 14, 2024; the underlying mechanism is also described in U.S. Patent 8,534,146, issued to the Iowa State University Research Foundation on September 17, 2013.
What a geared CVT is
A conventional geared gearbox selects from fixed ratios. A belt CVT or traction CVT varies its ratio continuously, but relies on friction contact and therefore must manage clamping force, heat, and possible slip. A geared CVT tries to vary the ratio without making the power path depend on friction.
The patent describes the objective directly: “The present invention provides continuously variable speeds using gears rather than friction elements.” That is a design description, not proof that every implementation will outperform a production belt or traction CVT.
How RatioZero transfers power
Three rotating elements
In the RatioZero presentation, the outer ring is the input and the inner ring is the output. Three small, marked gears sit between them. As the assembly rotates, those gears take turns transferring power—acting like relay runners. Their changing engagement positions alter the relationship between input and output speed without a stepped gear change.
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Why the ratio can change continuously
The ratio is controlled by geometry rather than by selecting one gear pair from a set. As the relative positions of the toothed members change, the active path through the small gears changes smoothly. Because the teeth remain engaged, the concept can provide a stepless ratio adjustment while retaining positive mechanical engagement.
Hackaday describes the intended result as “a smooth, stepless adjustment of gear ratios with the best of both worlds.” The phrase captures the goal; the published material does not include an independent dynamometer test confirming that result under load.
What the patent adds to the concept
Adjustable-angle members and guideways
U.S. Patent 8,534,146 discloses two guideways, toothed members, and a gear. The speed ratio is set by the angle between the members, with adjustment described over a 0-to-90-degree range. The patent’s detailed description gives example velocity ratios of 3.732:1, 1:1, and 0.4142:1 for illustrated orientations.
Rank #2
- Meets the challenging demands of most belt and chain-driven continuously variable transmissions
- Ensures smooth shifting and maximizes power transfer with enhanced anti-shudder protection
- Anti-wear technology improves durability to help extended the life your transmission
- Exceptional metal-metal friction protection helps maximize cvt service life and avoid costly repairs
- Full synthetic formula with advanced additives protects against transmission breakdown better than conventional fluids
Those three figures are patent embodiment examples calculated for the disclosed configurations. They are not measured efficiency, torque, durability, or range figures for a finished RatioZero transmission.
Alternative mechanisms in the disclosure
Other patent embodiments show ways to turn the geometric idea into a controllable machine:
- A vertical input rack and horizontal output racks driven by spur gears.
- One-way clutches to manage the alternating transfer of motion between members.
- Slider-crank conversion for translating rotary and linear motion.
- Linear bearings and lubrication for guided, moving components.
- A twin-lead screw assembly for synchronous ratio adjustment.
These are disclosed implementation options, not confirmation that every item appears in the RatioZero prototype shown publicly.
Rank #3
- For use in all CVT transmissions
- Corrects and prevents problems caused by worn-out, degraded fluid
- Reduces noise
- Provides anti-shudder durability
- Protects belt/chain, pulleys and other components from excessive wear
Is it really continuously variable?
Yes, in the engineering sense intended by the design: the control geometry can move through a range of positions instead of choosing only discrete gear pairs. The patent specifies an adjustable angle, and the RatioZero explanation describes relay gears handing off power as the geometry changes.
“Continuously variable” does not mean unlimited ratio range or perfectly constant torque capacity. The published sources do not state a complete operating range, control speed, torque limit, backlash specification, or whether the prototype maintains uninterrupted torque during every transition.
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The comparison below separates the mechanisms from claims that would require testing. “Not established” means the two published sources do not provide a verified value.
Rank #4
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| Question | Geared CVT concept | Belt or traction CVT |
|---|---|---|
| How torque is transmitted | Meshing toothed members and gears; the patent states that tooth engagement eliminates slip as a loss mechanism. | Friction contact between a belt and pulleys or between traction elements and rollers; slip and contact losses must be controlled. |
| Ratio control | Continuous adjustment of member geometry, including the patent’s 0-to-90-degree angle range. | Continuous adjustment of pulley diameter or roller contact geometry. |
| Published efficiency result for RatioZero | Not stated; no independent efficiency test is reported. | No head-to-head result against RatioZero is reported. |
| Load capacity and durability | Not established for the prototype; tooth stress, bearings, clutches, and synchronization would determine practical limits. | Depends on the specific production design, materials, clamping force, cooling, and duty cycle. |
| Control and hardware | May require synchronized adjustment, one-way clutches, bearings, lubrication, and a twin-lead screw or equivalent actuator. | Requires ratio actuators and friction management; exact hardware varies by design. |
| Packaging and production readiness | Not established; the available material presents a prototype and patent embodiments. | Production packaging and service practices are established for existing commercial CVTs, but that does not validate RatioZero. |
Would it improve efficiency over a belt CVT?
It could reduce one class of loss: the patent argues that toothed engagement has no tooth slip, so there would be no losses due to slip at that interface. A geared path can still lose energy through tooth friction, bearing drag, lubricant churning, clutch operation, alignment error, backlash, and the repeated handoff among moving gears.
Continuous ratio control could also help an engine remain nearer an efficient operating point. That benefit depends on the controller, ratio range, response time, and the transmission’s own losses. Neither Hackaday’s article nor the patent reports an independently measured efficiency map, fuel-economy result, torque test, or comparison with a belt CVT. It is therefore accurate to describe efficiency as the design rationale, not a demonstrated advantage.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What would have to be proven in testing
- Input-output efficiency across speed, torque, temperature, and ratio.
- Maximum continuous and peak torque, including tooth, rack, bearing, and clutch loads.
- Backlash, noise, vibration, and smoothness during gear handoffs.
- Durability of the one-way clutches, linear guides, lubrication system, and ratio actuator.
- Control behavior when changing ratio under load and during startup or braking.
- Packaging, cooling, service intervals, and manufacturing cost compared with a production CVT.
Until those measurements are published, the patent examples should be read as kinematic demonstrations rather than performance benchmarks.
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Can you buy a RatioZero transmission?
Hackaday’s December 14, 2024 article presents RatioZero as a prototype, not as a documented mass-market product. Neither that article nor U.S. Patent 8,534,146 provides a production catalog listing, price, order channel, volume announcement, or independent commercialization data. A reader should not assume that a vehicle-ready unit is available simply because the concept has a patent and a public prototype.
The practical takeaway
RatioZero is a credible mechanical idea for a geared CVT: toothed gears provide the power path, while adjustable geometry changes the ratio continuously. The patent supplies a range of mechanisms and example ratios, including the 0-to-90-degree control concept and 3.732:1, 1:1, and 0.4142:1 illustrative configurations. What remains unknown is exactly what matters for a road-going transmission—measured efficiency, torque capacity, durability, cost, packaging, and production status.
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