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CVT: a potted history of a transmission

By: Muck-shifter1
On: May 31, 2017
In: Tech Blog
Tagged: Liebherr, wheel loader

Continuously Variable Transmissions (CVT) for off-road vehicles have been around since the 1990s, but are only now beginning to appear on construction equipment (wheel loaders being the first application; Caterpillar & Liebherr with Doosan next). There may be a concern about the durability of this combined hydrostatic and mechanical driveline, so let me tell you a story.
By the mid 1990s Fendt had introduced the first such transmission in a premium agricultural tractor, followed by Steyr. When Case took over Steyr this was going to be the first time a CVT was going to be offered by one of the big boys (in terms of unit sales).
Many hundreds of service folk around Europe where trained on in-field repairs, spare transmission parts were stocked in every region, 24 hour hot lines established. The field fix was to take off one of the rear wheels then unbolt the access panel to get to the CVT. Then undo the end plate, withdraw the gear pack and replace it with new set.
The point of the story being that the CVT box proved to be spectacularly reliable, with this over the top support structure a waste of time and money.
CVTs now dominate high end European tractors, not just because of their controllability, but because then can save huge amount of diesel and are comfortable to operate.
The point of the tractor history lesson being that Steyr worked with ZF to develop the CVT. ZF then launched their own version of the CVT design, which has gone on to dominate the industry. For example, modern Liebherr wheel loaders use a version of this box.

JCB has come up with an interesting variation on the theme, a sequential hydrostatic and mechanical transmission for telehandlers. This contrasts with the power being constantly divided between the two pathways in a CVT.

2017-05-31
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