The analysis of principles of continuously variable transmission of tractors

BACKGROUND: Modern agricultural activity requires the use of high–tech equipment such as, in particular, a multifunctional tractor, which, according to actual trends, should be an autonomously controlled mobile power plant. In modern tractors, meeting current requirements, multiflow shaft-planetary gearboxes with cumulative effect are used.

AIMS: Comparison of the operation principles of two types of automatic tractor transmissions: with hydrostatic drive and with electromechanical drive.

METHODS: During the research, a literature review of printed and online publications with technical description of the transmissions of the considered design was carried out.

RESULTS: The operation principles of two types of automatic tractor transmissions were considered: with hydrostatic drive (Fendt VarioDrive) and with electromechanical drive (Ruselprom-electroprivod LLC).

The operation principle of the Fendt VarioDrive transmission (planetary multiflow transmission with mechanical and hydrostatic branches) consists in dividing the torque coming from the internal combustion engine by a planetary gearbox into mechanical and hydrostatic branches, followed by summation of flows by a collecting shaft. The change in the gear ratio and movement direction of the tractor is controlled by the ECU by means of controlling the hydrostatic branch of the transmission. The transmission is nominally continuously variable due to the absence of gears as such.

The set of traction electrical equipment of the transmission developed by Ruselprom- electroprivod LLC, installed on a tractor, includes:

– an synchronous motor generator with a power converter and a microprocessor control system;

– a traction asynchronous motor of the central drive with a power converter and a microprocessor control system;

– a DC-DC converter for energy supply of auxiliary equipment.

– power converters and a DC-DC converter are integrated into the power electronics unit;

– a top-level controller with controls and indicator panel in the driver’s cab.

The control system of the electromechanical transmission provides with full control of its operation and the functioning of the internal combustion engine. The operation principle of the system is based on the essentials of hybrid transport operation. Tractor movement is possible in one of two ranges: “range 1”, operational (0...18 km/h) and “range 2”, transport (0...42 km/h)

CONCLUSIONS: Due to the modern concept of electric drive units, layout solutions with an electromechanical drive having an electric generator in their design are more promising and applicable in the future, especially for trailed equipment.