Abstract: To avoid skidding of the driving wheels of a tractor (1) which runs on tires and which is fitted with hydraulic lifting devices (3, 4) on which are mounted working tools (35, 45) which are buried in the ground (in this case ploughs), the apparatus includes detector structure for determining the force for forward movement of the tractor, comparing that force to a reference value and producing pulses of less than one second, for alternately raising the two lifting devices (3, 4), the amplitude of the pulses being proportional to the excess of the forward movement force, up to a limit amplitude of centimeters approximately. The pulses are too short for the tools (35, 45) to lift with respect to the ground and the amplitude of the raising movement appears as squashing of the tires, which increases grip in order to overcome the excess of forward movement force.

Abstract: The tractor vehicle comprises a chassis supported by at least two sets of driving and steering wheels. A cab is fixed to the chassis and encloses the devices for driving the vehicle and the devices controlling tools coupled to the power take-off of the vehicle. The two sets of driving and steering wheels are driven in pairs located on the same side of the chassis by an independent drive. The two drives are interconnected by variator-inverter devices which act selectively on either of the two drives or on both thereof in a symmetrical or unsymmetrical manner. The vehicle may be employed not only in the agricultural field but in any other application such as public works.