Archive Article: 1997/10/18
Fendt is extending its revolutionary Vario hydro-mechanical drive system to a full range of four heavy cultivation tractors. Peter Hill reports.
AT 170hp, 200hp and 230hp, new versions of Fendts Favorit 900-series bring the Vario stepless transmission within the reach of more arable farmers.
"The concept has been proven to work and to be practical," maintains Ernst Weihele of Fendt.
The Favorit 900-series offers a step-up in performance from the semi-powershift 800-series by a hint of extra engine power; but the Vario transmission also helps, with more effective use of that power, as well as greater economy and operating versatility.
All four models are powered by MAN 6.9 litre, six-cylinder turbo diesels. Maximum outputs are delivered at 2,150rpm in the case of the 170hp and 200hp models, at 2,250rpm on the 230hp and 260hp machines.
Hydraulic lift, which is electronically controlled, is a substantial 9.18t, with up to 102 litres/min of oil available at the four standard auxiliary ports from a load and pressure sensing pump system.
The transmission, and its operational benefits, is the real focus of these tractors. By mixing hydraulic and mechanical drive, the transmission capitalises on the best characteristics of hydrostatic and powershift systems.
For one thing, hydraulic drive eliminates stepped gear ratios so drivers never find themselves without the right speed for the job. Mechanical drive, though, is more efficient at transmitting power at faster speeds. So, the transmission progressively changes the mix until at full speed – 50kph – drive is fully mechanical.
Scepticism about the ability of hydraulic pumps and motors to transmit the power and torque of a big six-cylinder turbo diesel is countered by independent German test results.
These show 81.1% of the Favorit 926 Varios engine power being delivered to the wheels, within a whisker of the 82.5% recorded in earlier tests on a 210hp Favorit 822 with four-speed powershift. Moreover, the Varios direct pto system, delivered 93.9% of engine power to the stub shaft.
Microprocessor control enables the driver to select a ground or pto speed, or an engine speed range, which the transmission will maintain (within reasonable limits) by adjusting ratios automatically under changing load. It means when ploughing through variable soil types or climbing inclines on the road, the driver has no need to change gear.
The driver can also regulate the rate at which the tractor accelerates and decelerates.