Anti-locking brake modulator with independent input and output solenoid actuated valves including check valve and pressure relief valve

An anti-locking modulator, comprising:

• a pressure source of pressurized fluid;
• a control chamber receiving said pressurized fluid;
• a brake pressure cylinder for supplying braking pressure to a brake;
• pressure reduction means for reducing said braking pressure during an anti-locking operation depending on the pressure level of said pressurized fluid in said control chamber;
• an input solenoid valve connecting said pressure source and said control chamber and including a fixed first valve seat, a movable first valve element seating on said first valve seat, an armature operatively engaging said first valve element to the side of said first valve element opposite said valve seat, a first spring on the side of said armature and said movable first valve element opening to said control chamber for biasing said first valve element towards said first valve seat, and a first solenoid operatively positioned with respect to said armature such that when electrically powered further forces said first valve element against said first valve seat to prevent said pressurized fluid from flowing into said control chamber, and wherein when said first solenoid is electrically deenergized, said pressurized fluid from said pressure source is applied against said first spring to unseat said movable first valve element and permits pressurized fluid flow into said control chamber;
• and said first spring acts on said movable first valve element such that said first solenoid valve functions as a check valve to prevent pressurized fluid from flowing from said control chamber to said pressure source;
• and
• an output solenoid valve independent of said input solenoid valve connecting said control chamber to a reduced pressure region and including a fixed second valve seat, a second movable valve element and an armature on the side of said second valve seat proximate to said reduced pressure region, and a second solenoid which when energized moves said second valve element away from said second valve seat, a second spring engaging said armature and biasing said second valve element against said pressurized fluid in said control chamber to maintain said second movable valve element closed against said second valve seat when said second solenoid is electrically deenergized, and wherein said biasing force of said second spring is in excess of that of said first spring so that said second valve element functions as a pressure relief valve with said pressurized fluid maintained in said control chamber at a pressure no higher than a prescribed pressure determined by said second spring, and wherein said second solenoid, when electrically energized, is of sufficient power to move said second valve element out of sealing contact with said second valve seat against the bias of said second spring to drain said pressurized fluid from said control chamber.