Abstract: An automatic brake control apparatus includes a pressure intensifying solenoid valve in a hydraulic brake line connecting a source of hydraulic pressure with a brake, as well as a pressure reducing solenoid valve in a relief line branched from the brake line and connected to a low pressure reservoir. A pressure sensor is positioned to sense a hydraulic pressure in the brake line at a position downstream of a point where the relief line branches from the brake line. A controller receives a signal from the pressure sensor and determines desired brake pressure for producing a desired speed reduction rate. The controller outputs control signals to the pressure intensifying solenoid valve and the pressure reducing solenoid valve such that the detected brake pressure corresponds to the desired brake pressure. The apparatus may be incorporated into a brake pressure control valve having first and second stages.

Abstract: A hydraulic transmission coupling apparatus for transmitting a driving force to a front wheel driving shaft and a rear wheel driving shaft of a four-wheel drive vehicle, which is provided with a pump to generate hydraulic pressure corresponding to a rotation speed difference between both driving shafts, a reserving part for reserving hydraulic fluid, a fluid room disposed in the circulation passage of hydraulic fluid, and a piston located in the fluid room and sliding while subjected to the hydraulic pressure in the reserving part at one side thereof. When the volume of hydraulic fluid varies with the variation in fluid temperature, the piston slides and, as a result, the internal volume of the fluid room varies so as to absorb the volume variation of hydraulic fluid.