| 摘要 |
A mobile load-carrying unit has ground-engaging wheels and a body which is supported upwardly spaced from the ground by these wheels. A self-propelled vehicle unit is also provided with wheels on which it can travel in a given path on the ground and is dimensioned to fit beneath the body of the load-carrying unit. Cooperative force-transmitting portions are provided on the two units and so act with one another as to exert downwardly directed pressure upon the vehicle unit when the latter is beneath the load-carrying unit and travels in its predetermined path, so that the conveying force exerted by the vehicle unit upon the load-carrying unit in a sense propelling the latter is in part converted into a component of force acting on the vehicle unit in direction toward the ground to increase frictional engagement of the wheels of the vehicle unit with the same.
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