![]() A brake valve is integrated into this piston which, depending on the actuating direction, couples a pressure proportional to the pedal force exerted by the driver, which pressure is derived from the high outlet pressure of an auxiliary pressure source, either into the actuating pressure space delimited axially in a fixed manner by the end wall of the cylinder housing and movably by the piston or-in case of a retraction movement of the brake pedal-into the space which is delimited axially movably by the piston of the actuating cylinder and fixedly by the partition wall which delimits the primary outlet pressure space of the master cylinder against this space of the actuating cylinder.This actuating piston and together with the same the primary piston of the master cylinder is displaceable in the sense of a brake pressure build-up both when the brake servo unit is intact as also when the brake servo unit fails. The pedal plunger is supported at this piston rod, by way of which the force exerted by the driver is introduced into the piston of the actuating cylinder. ![]() Description of the Prior ArtSuch a brake apparatus is known from the DE 34 44 828 A1.In the known brake apparatus, a tandem master cylinder is coordinated to the static brake circuit of the primary outlet pressure space, along the central axis of which a linear hydrocylinder is arranged separated from the primary outlet pressure space by a partition wall, whose piston is provided on the side of the master cylinder with a plunger which passes through a central bore of the partition wall, sealed off with respect to the same, and is axially supported at the primary piston of the master cylinder.The actuating cylinder piston has a piston rod on the side of the pedal which passes through an end wall of the cylinder housing also displaceably sealed pressure-tight with respect to the same. Field of the InventionThe present invention relates to a brake apparatus for the pressure supply of the brakes of a hydraulic two-circuit brake installation of a road vehicle, in which at least one brake circuit is constructed as static brake circuit which is connected to an outlet pressure space, in which the brake pressure build up takes place by unidirectional displacement of the servo piston and of a master cylinder piston, whereby the servo piston experiences a pressure build-up displacement only when the brake servo unit operates properly and whereby the master cylinder piston experiences a pressure build-up displacement when the brake force servo unit is intact, as also when the brake force servo unit has failed, whereby in that case, in relation to a predetermined amount of the residual actuating force engaging at the master cylinder piston, an increase of the piston displacement travel and therewith a correlated pressure translation occurs.2. The servo piston displaceable only with an intact brake force servo unit includes an annular piston which by pressure actuation of its actuating surface with the outlet pressure of a brake valve of the brake force servo unit, is urged into unilateral abutment with an entrainment flange of a plunger piston extending through the annular piston in the axial direction, which plunger piston, in its turn, is coupled for movement with a force-transmitting element, by way of which also the component of the actuating force resulting from the pedal actuation and acting on the master cylinder piston in the sense of a brake pressure build up displacement is introduced into the same.īACKGROUND OF THE INVENTION1. In a brake apparatus for a hydraulic two-circuit brake installation of a road vehicle with static brake circuits, an outlet pressure space is provided for one of these brake circuits in which the brake pressure that is coupled into a static brake circuit of the vehicle, is adapted to be built up by the displacement in the same direction of a master cylinder piston which is also displaceable by the pedal force alone, and of a servo piston which is displaceable only when the brake force servo unit is intact.
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