Transmission Pumps Up

New Page 1TECHNOLOGY FOCUSTransmission Pumps Up
Mild Hybrids' Fuel Efficiency

LANCASHIRE, UK (Dec. 30, 2005) - Torotrak PLC, which developed the Infinitely Variable Transmission (IVT), continues to work on placing its technology not just in conventional automobiles, but also in new mild parallel-hybrid systems. Mild hybrids are commonly defined as those in which the electric motor assists acceleration, but cannot drive the vehicle on its own.

In conventional transmissions, both the engine and transmission are independently controlled. In automatic transmission, gear ratios are fixed as well, resulting in engines only being able to operate at their most efficient mode for short times.

The IVT technology allows control of the complete powertrain to facilitate optimal engine efficiency, says Torotrak, because the IVT is torque-controlled rather than ratio-controlled. Software determines the torque needed at the wheels, and then the necessary torque is requested from the transmission, rather than setting a specific ratio. The engine can then be used to deliver the power efficiently, based on continuous available torque. In addition, the technology enables vehicle control to be maintained, even at slower speeds.

Inside the IVT.
(Photo: Torotrak)

One of the gains of IVT powertrain optimization, says Torotrak, is improved fuel efficiency. According to the company, engines are able to run at a higher overdrive speed of 74 mph/1,000 rpm. The IVT's geared neutral allows the engine to maintain a connection to the wheels even when a vehicle is stationary. This removes the requirement for a distinct torque converter. As well, because the IVT lacks defined ratio steps, it is able to operate the engine under conditions that lower emissions and improve fuel efficiency.

In a recent development, Torotrak, in cooperation with Newage International Inc., Cranfield University and the U.K. government program Foresight Vehicle, is developing a mild parallel-hybrid drive IVT that will be applied in a Ford Expedition.

Torotrak CEO Dick Elsy said, "We are able to offer a 20 percent fuel economy improvement from the fitment of IVT to a conventional vehicle, growing to more than 35 percent improvement with the parallel hybrid IVT derivative. Our results also show that the hybrid IVT is capable of producing very significant fuel economy gains whilst the vehicle is cruising at speed-an area where many current generation hybrid vehicles perform relatively poorly. These results bode well for real-world fuel economy improvement."

The parallel hybrid layout, incorporating IVT.
(Photo: Torotrak)

The company says that when built with an IVT, engine control would be optimized such that a mild parallel-hybrid could achieve the more complex and expensive full series-parallel hybrid drive's increased fuel efficiency benefit, but at lower cost and far less complexity.

"In other words, Torotrak is suggesting that although its IVT hybrid wouldn't have an all-electric mode, its increased base engine efficiency combined with the boost from the electric motor would match the fuel efficiency of series-parallel hybrids on the market and be less expensive," Elsy explained.

This advantage, when applied to a parallel-hybrid, allows car companies to provide the primary benefits of more complex hybrid configurations, but within a conventional vehicle layout. The system also allows for a modular approach by automakers, wherein the same vehicle could be offered with an IVT alone or with the IVT mild hybrid electric version. Besides the cost savings to both manufacturer and consumer, this will allow automakers to monitor and respond quickly to the changing customer demand for hybrids.

More information on how IVT technology works can be found at http://www.torotrak.com/IVT/action.htm.

(Source: Torotrak PLC)