Continuous drive

11 September 2012

Caterpillar's 966K XE wheeled loader features a continuously variable transmission (CVT) which the company says can deliver as much as 25% fuel savings. The system features a traditional mechanical drive in parallel with a hydraulic pump and motor (variator), and the outputs of the two are combined via a planetary gearbox.

This not only smoothes out gear changes, but at low machines speeds and/or under heavy loads the engine can be run at a higher, more efficient speed, while the variator translates this into drive, without the heat losses you would get from a mechanical system.

Thierry Brasseur, Caterpillar's medium wheeled loaders product and application specialist in Europe, Africa and the Middle East, said, "It provides significant advantages in all applications. Compared to a traditional loading cycle, you get torque at any speed - including very low engine speeds, so it is easy and faster to load the bucket. Travelling is much smoother because there is no shift - well they are synchronous, so you don't feel them, and in load & carry work, it is better than the conventional lock-up torque converter."

This sophistication comes at a price of course, and the pay-back period will depend on fuel costs. "In high cost fuel countries like Germany, where off-highway fuel is taxed at the same rate as road diesel, the return on investment is about two years, based on 1800 hours per year on an average duty application. In lower price fuel countries, where 'red' diesel is available at a lower tax rate, you need a bit more time - about three years at 2200 hours," said Mr Brasseur.

He added, "But the machine is also much more productive, because it is easier to load and travels faster. You have the additional benefits of reduced noise and vibration, because the machine is working at better engine speeds."

According to Mr Brasseur, the CVT is a technology that would work well with what Caterpillar categorises as medium wheeled loaders, which is to say from about 20 to 30 tonnes operating weight. "For a smaller machine, the return on investment would be much longer. On a much larger machine, you have other technologies such as electric drive or hybrids, which might produce better returns," he said.

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