This infinitely variable transmission has the gearing range of an 11-speed automotive transmission.

July 7, 2011
The Telam CVT has both forward and reverse rotation as well as a geared neutral inherent in the design, making it what’s called an infinitely variable transmission (IVT).

The Telam constant-gear-mesh infinitely variable transmission (IVT) from Tom Troester is a special type of continuously variable transmission (CVT). In contrast to standard transmissions, which have only finite or step gear ratios producing three, four, or five speeds, CVTs additionally have all ratios available between the gears. This lets the engine run at its most efficient rpm while varying the vehicle speed.

It has been known for decades in the automotive industry that a CVT increases fuel mileage. In fact, several are in use today. All — excluding ones with supplemental motor planetary systems — are variations of the Van Doorne design. The Van Doorne design is essentially a belt drive with two pulleys, each of which has a variable diameter. The simple belt drive relies on friction, which limits its use in automobiles as well as its ratio range. Refinements such as steel belts and push belts improved the drives’ torque capacity, but it is still necessary to increase the normal force via the pulleys to further increase torque capacity, which reduces efficiency. Additionally, pending CAFÉ standards to boost vehicle mpg are pushing automotive manufacturers to develop six, seven, eight, and nine-speed transmissions. These are either dual-clutch transmissions (DCT) or conventional multistage planetary gear transmissions with a torque converter. Both types are complex, heavy, and expensive to manufacture.

In contrast, the Telam’s constant-gear-mesh design is unique in CVTs. The scalable design is lightweight and efficient because it needs no high parasitic loadings to increase the normal force. The Telam CVT has both forward and reverse rotation as well as a geared neutral inherent in the design, making it what’s called an infinitely variable transmission (IVT). The design uses special cone gears in one planetary stage. The cone gears incorporate an involute gear geometry that provides constant gear meshing. The cones are planet gears, meaning they rotate about the input shaft and also about their own axis as in conventional planetary gearing. The cone planet gears mesh with an adjustable internal ring gear on different cone diameters, which varies the output ratio and direction of rotation.

To better understand the geared neutral and reverse rotation, consider a normal two-stage planetary transmission. Like the Telam IVT, the output shaft receives two inputs. One comes from the input shaft/cone carrier rotation. The other comes from the gear cone rotation about its axis, which spins in the opposite direction of the cone carrier/input shaft. When the rotation of the cone gears about their axis, from one rotation of the input shaft/cone carrier, imparts one rotation of the output shaft, this is defined as geared neutral. Because the cones rotate in the opposite direction of the input shaft, the gear train yields a zero output-shaft rotation. This feature also explains the integral reverse, which is just the adjustable internal ring gear moving along the gear cone to a different diameter. Prototypes have demonstrated a forward ratio range of over 18:1 and a reverse ratio range of over 5:1. This is equivalent to an 11-speed conventional automotive transmission.

The Telam IVT’s wide ratio range lets it interface to a flywheel battery for a simple practical hybrid vehicle that could recover 70% of the braking energy of every-day type local driving.

The flywheel hybrid vehicle consists of two lightweight Telam IVTs. The first IVT connects to the engine and differential. The other IVT connects to the differential and flywheel battery. During normal driving with input from the accelerator pedal, the first IVT controls vehicle speed by varying the IVT ratio — while letting the engine run at optimum efficiency with low emissions and low fuel consumption. During this time, the other IVT tracks the differential speed and adjusts the ratio to match the current flywheel battery rpm. In other words, the driver determines the acceleration rate and the IVT gets the feedback from the accelerator pedal to use the energy from the flywheel battery. When the driver brakes, the other IVT controls vehicle deceleration by adjusting the IVT ratio to charge the flywheel battery. Concurrently, the first IVT tracks the differential speed and adjusts the IVT ratio to match engine rpm.

Tracking engine rpms in this manner also allows recovering the normal engine braking energy down to zero vehicle speed or zero differential rpm. This is possible because both Telam IVTs have a geared neutral. The Telam brake regenerative system is the primary vehicle-brake system. Note that this is not possible with current hybrid-electric-braking regenerative systems because they are severely limited by the charging rate of the battery, the difficulty of generating electrical energy at low rpms, and the efficiency of the mechanical-electrical conversion process.

Also, the Telam IVT flywheel-battery system inherently functions as a start-stop device, which most experts say provides a 10 to 15% mpg increase in city driving. The software shuts downs the engine at zero vehicle speed or zero differential rpm. When the driver releases the brake pedal and pushes the accelerator pedal, an IVT adjusts the IVT ratio to match the vehicle acceleration, which is determined by the stored energy from the flywheel battery. The other IVT tracks the differential speed and adjusts the IVT to the engine starting rpm, which enables engine ignition and fuel. Control of the vehicle’s speed switches to the first IVT when the engine is running and the accelerator produces a constant speed instead of acceleration. This switch would happen sooner when the flywheel battery is depleted of stored energy.

In addition to automobiles, Telam IVTs target applications presently using hydrostatic transmissions such as lawn tractors, skid-steering vehicles, and recreation vehicles. Other applications might include wind generators, which could be controlled for 60 cycles at various blade speeds. Similarly, stationary generator engines under low loads could run at idle rpm while the generator runs at 60-cycle speed. This would save fuel at low electrical loads.

Troester’s Telam IVT is patented. Watch a motion animation of it. He is looking for development partners and can be reached at [email protected].

© 2011 Penton Media, Inc.

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