One pumped-up automatic

Automotive Design & Production, March, 2004 by Christopher A. Sawyer

What Is It?

The Infinitely Variable Transmission (IVT), a hydro-mechanical replacement for conventional automatic transmissions in diesel-powered vehicles. "Our goal in creating the IVT was to manage a diesel engine in such a way that you could take advantage of its low-rpm torque capability," says Torvec, Inc. (Pittsford, NY) president Keith Gleasman, "to get fuel economy on par with a diesel/manual gearbox combination." The transmission displaces 12.7 in. (3), is capable of 300 hp., is 16.5-in. long and 7-in. in diameter, and weighs 78 lb. The hydraulic pump and motor are 80% interchangeable, with identical pistons (nine in each unit), cylinder blocks, housings and valving. A gearset reminiscent of the Torsen differential (invented by Gleasman and his father, Vernon), connects the pump and motor, and sends power to the driveshaft. The prototype is fitted to a Dodge Ram 4X4 with Cummins diesel power.

This Sounds Familiar ...

You're thinking of the Hydristor (http://www.autofieldguide.com/articles/100304.html), a variable-vane hydraulic pump automatic transmission. Though both Torvec's IVT and the Hydristor use hydraulic pressure to transfer power from the engine to the wheels, the IVT adds a gearset to the mix, and focuses mainly on improving city and urban fuel economy. The Hydristor is being developed to work with powertrains of all types and provide benefits at all speeds.

Isn't hydro-mechanical drive inefficient?

Gleasman says the noise and inefficiency of a conventional piston pump is due to its rotating cylinder block, and inefficient inlet and outlet port designs. The IVT uses a swash plate design that imparts reciprocating motion via the inclination of a faceplate on a shaft relative to the axis of rotation. This plate can be inclined up to 25[degrees] in either direction (for forward or reverse gears), or held at zero inclination at idle. Rotational mass is reduced, and the need for an outer casing eliminated. Overall efficiency hasn't been tested (a program to do this in conjunction with the EPA is under negotiation), but Gleasman says the volumetric efficiency of the IVT pump/motor is 99%.

[ILLUSTRATION OMITTED]

What about the real world?

In testing, the Torvec-equipped Dodge Ram 4X4 (test weight: 8,000 lb.) was driven continuously from 0 to 30 mph alongside a 4X2 Dodge Ram with a 5.7-liter gasoline engine and test weight of 6,000 lb. The half-ton 4X2 returned 9.9 mpg, while the IVT-equipped truck got 18.2 mpg, about what one would expect from a diesel/manual gearbox powertrain. However, the IVT version can do things a manual can't. "At one point, we had the IVT at a 70:1 reduction ratio," says Gleasman, "and were able to get out of the truck, walk around it, and get back in while it was moving." Yet, the truck can accelerate from 0 to 60 mph in 10 seconds with the engine never exceeding 1,850 rpm. This is an average speed increase of 110 rpm/second between the engine's 750 rpm idle speed and the 1,850 rpm seen at 60 mph.

Anything else?

The pump design can be used to power an energy recovery system that captures and stores energy during coast-down and braking. Another version plumbs a pump directly to the back of the engine that drives two half-size motors that send power to the front and rear axles. And the military is interested in the ability to bring a vehicle to a complete stop using only the IVT.

By Christopher A. Sawyer, Executive Editor