Abstract: The present invention enables a reliable radio communication between a plurality of dump trucks and loaders, improves operability, and can flexibly cope with movement of the dump truck during the loading operation. To this end, a loader selecting means (2) is provided for each dump truck, and a plurality of channels are provided for each dump truck controller (6) and each loader controller (35), the dump truck controller (6) inputs a loader selection signal from the loader selecting means (2), and selects, from a plurality of channels, a channel available for communicating with the loader controller (35) corresponding to the loader selection signal to transmit a load weight value, and the selected loader controller (35) receives the load weight value on the channel available for communications, and displays the received load weight value on a weight display means (32).

Abstract: A full hydraulic type steering control system is provided with a steering control valve for outputting a flow of a pressurized discharge fluid of a hydraulic pump in proportion to an amount of steering at a steering wheel, and a directional control valve for delivering the pressurized discharge fluid of the hydraulic pump into a steering control cylinder, with the output flow of pressurized fluid of the steering control valve being switched as a pilot fluid pressure. The directional control valve comprises a spool adapted to be slidably inserted in a spool bore of a valve body.

Abstract: In a four-wheel drive traveling system for a tipper, an output side of an engine is connected to rear wheels via a power transmission, at least one variable hydraulic motor for driving the front wheels and a hydraulic pump driven by the engine are provided, and the variable hydraulic pump and the variable hydraulic motor are connected into a closed circuit. The system includes arrangements for controlling displacement of the variable hydraulic pump, for detecting slippage of the rear wheels, for setting a discharge pressure of the hydraulic pump between a high pressure and a low pressure, and for controlling the displacement of the variable hydraulic pump so that the discharge pressure is a low pressure while slippage is not caused for the rear wheels and so that the discharge pressure is a high pressure while slippage is caused for the rear wheels.

Abstract: A hydraulic drive system of a steerable wheel of a dump truck facilitates the attaching and detaching of a hydraulic motor and allows for a large hydraulic motor to be used. In the drive system, a wheel axle is rotatably supported within a receptacle seat supported on a yoke. The steerable wheel is rotatably mounted on the outer periphery of the receptacle seat. The steerable wheel and one end of the wheel axle are connected via a speed reducer. A motor casing 33 of a hydraulic motor is connected by bolts to the receptacle seat at an end of the seat remote from the steerable wheel so that the hydraulic motor can be attached to and detached from the receptacle seat by tightening and loosening the bolts.