On a 4-wheel drive vehicle, the force transmitted by each wheel depends on the soil characteristics and the wheel load. This last depends on the slope (Figure 1) and on the external forces (Figure 2) coming from a winch, a bucket for a work loader, a blade for a snowplow or a bulldozer, etc.…. and on the payload. On a conventional 4-wheel drive, the force transmitted by each wheel is limited by the force transmitted by the weakest wheel according to the differential gears law.
To improve the vehicle grip, the following arrangement is proposed (Figure 3). A main motor MM, electric or thermal, drives two CVTs (Dr and Df) which each one drives an axle shaft. The Motors - Generators MGr and MGf independently control the torque on each axle. Thus, the weakest wheel only limits the torque of its opposite wheel on the axle and not the torque on the other three wheels simultaneously.
The gear ratios of the two epicycloid trains of the two CVTs are so that the MGr and MGl operate in engine-generator opposition over a wide range of vehicle speeds (patent FR3114055). A Control Unit MCU optimizes the torque on each axle until its wheel slippage and taking into account the battery state of charge and the electrical balance.
The system has other advantages: the regulation is only on 1/3 of the vehicle power, the electric motors occasionally increase the power of the main engine or serve as its auxiliaries, the vehicle can operate silently in electric mode, the narrow speed range of the main engine can be chosen at its best performances.