There are six discs that change...
There are six discs that change pitch to transmit torque (two are shown).
It looks like the consumer pickup truck is about to get another shot in the arm from the medium- and heavy-duty industry. The last booster was the diesel engine, so this next infusion will surely be beneficial as well. In March of 2009, Torotrak, a British-based engineering company, announced it was partnering with Allison to offer infinitely variable transmissions (IVT) to the commercial truck market. If it is good enough for the latest severe-duty tractors and heavy earth moving equipment, it ought to hold up to anything we can dish out.
What is an IVT?
Instead of only having a few fixed gear ratios like conventional transmissions, the IVT uses a variator, effectively giving the transmission an infinite number of seamless speeds. The IVT uses computer software to determine the power required at the tires and then requests torque from the transmission.
A closer look at the variator...
A closer look at the variator shows four discs.
(A) The outer ones are connected to the crank-shaft of the engine.
(B) The inner ones spin freely on the shaft and are connected to the drive wheels. Notice the six rollers (three per side). They transfer the power from the outer discs to the inner discs. Each roller is connected to a hydraulic piston, and the amount of force it provides deter-mines the range of reaction torque within the variator. Going deeper into engineering jargon, this technology is formally called full-toroidal traction drive. Full-toroidal means doughnut and that is the shape created where the rollers meet the discs.
Unlike continuously variable transmissions (CVT) found in snowmobiles and some cars already on the market, the IVT can handle much more torque.
How This Benefits You
Fuel Economy: An IVT transmission is currently being demonstrated in a Ford Expedition with a 5.4L gas engine. Independently monitored tests show a 20 percent improvement compared to the four-speed automatic transmission. Computer-generated tests predict at least a 10 percent improvement compared to six-speed automatics.
Reduced Emissions: Since the gears aren't fixed, the transmission allows the engine to operate at its peak efficiency. According to Torotrak, the Ford we just mentioned, equipped with an IVT, produced the same level of emissions without exhaust gas recirculation (EGR) as the same engine and traditional transmission with EGR.
Geared Neutral Feature: The IVT is geared neutral, meaning the engine is connected to the tires even if the truck is stopped, without the need for a clutch or torque converter. So even if you stop the vehicle on a hill, the transmission will hold it stationary without the driver having touse the brakes.