An Orbitless PRIME drive is a novel fixed-ratio epi-cyclic drive which has been shown to have a higher speed rating and efficiency, but slightly less torque capacity than a Planetary drive. To reduce NVH in the highspeed noise generating 1st stage, while still maintaining torque capacity, it can be mated to a Planetary downstream stage to get the best of both technologies.
The Orbitless drive is a fundamentally new epi-cyclic gearing configuration that is similar to a Planetary drive, but uses a second carrier instead of a ring gear to provide its planets with reaction torque. It may be configured as a low-ratio drive (PRIME), as a high-ratio drive (PLUS), or as a combination of the two (HYBRID).
The low-ratio Orbitless PRIME has a number of properties that contribute to its low-noise characteristics.
- Half as many gear engagements
- Lower pitch velocity
- Uni-directional pressure angle force applied to the planets
- Housing that acts as a sound barrier rather than a sound source
Figure 1: Planet Vibration in Orbitless PRIME & Planetary Drives
Vibrations that are developed in a Planetary drive, and propagated by its toothed housing (illustrated in Fig. 1) are absent in an Orbitless PRIME drive, as shown by a SimulationX by ESIÔ model that compares two geometrically equivalent drives. An FFT of the radial planet force shows a distinct spike at the Planetary tooth engagement frequency, but no distinct spikes in the Orbitless audible frequency spectrum (see Fig. 2).
Figure 2: SimulationX Model & FFT of Orbitless PRIME & Planetary Drives
Like any engineering design, the low-NVH of an Orbitless PRIME drive, does come at a price. Internal forces are somewhat higher, and the reduction ratio is somewhat lower than a Planetary drive, so torque capacity and space efficiency are sacrificed. However, the relative strengths of both are combined by mating an Orbitless PRIME 1st stage with Planetary down-stream stages (Fig. 3). The high-speed Orbitless PRIME stage, armed with plastic planets, eliminates noise at its source, while metal low-speed Planetary stages amplify the ratio with maximum torque support.
Figure 3: Conceptual Multi-Stage Orbitless PRIME / Planetary Drive
A prototype 32mm Orbitless PRIME gear-head is constructed (Fig. 4) which is interchangeable with an off-the-shelf Planetary gear-head. It is constructed and noise measurements are taken, both for the stand-alone single-stage gear-head, and in series with an off-the-shelf 2-stage Planetary gear-head.
Figure 4: Prototype Orbitless PRIME Drive
No perceptible spikes are measured at the tooth engagement frequency, or anywhere else in the audible spectrum, and comparative sound measurements for a corresponding Planetary drive are shown to be higher. The flat frequency spectrum is consistent with prior simulated results and it is confirmed that the primary stage is the dominant noise source since downstream stages only appear to attenuate noise.
Currently, the Orbitless drive platform is being applied in a wide range of sizes and applications that include automotive power-trains, automotive automation, medical devices, and smart home technologies. Orbitless will be presenting more on this topic at the International Conference on Gears, held in Garching from Sept. 18-20, 2019.
To find out more about the latest developments or how an Orbitless Drive can address your noise-sensitive application, visit www.orbitless.com, come see us in Garching, or contact us by email.
Leo Stocco, PhD, PEng, CTO
Robert Eisses, CEO
+1 604 724 3719
Orbitless Drives Inc. Vancouver BC, Canada