An electrically actuated brake booster capable of obtaining a desired boost ratio for a given input pressure when an electric actuator is activated as a boost source, so as to ensure a desired operability of a brake pedal. The electrically actuated brake booster comprises: an input piston 22 to whic
An electrically actuated brake booster capable of obtaining a desired boost ratio for a given input pressure when an electric actuator is activated as a boost source, so as to ensure a desired operability of a brake pedal. The electrically actuated brake booster comprises: an input piston 22 to which an input thrust is applied through an input rod 9 that moves in coordination with operation of a brake pedal 8; and a booster piston 21 to which a booster thrust is applied by an electric actuator 40 that uses an electric motor 41 as a drive source, such that the input piston 22 and the booster piston 21 are disposed to be movable relative to each other but are normally maintained in a neutral position of relative displacement by means of springs 34. While an amount of relative displacement between the pistons 21 and 22 is determined by the potentiometer 45, the electric motor 41 is controlled to adjust the amount of relative displacement to a predetermined value. At the same time, a reaction force acting on the input piston 22 resulting from a hydraulic brake pressure is offset by urging forces of the springs 34 to thereby obtain a desired level of boost ratio.
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What is claimed is: 1. An electrically actuated brake booster including: a first member adapted to move forward and backward in accordance with operation of a brake pedal; a second member disposed so as to be capable of moving relative to the first member; and an electric actuator for moving the se
What is claimed is: 1. An electrically actuated brake booster including: a first member adapted to move forward and backward in accordance with operation of a brake pedal; a second member disposed so as to be capable of moving relative to the first member; and an electric actuator for moving the second member forward and backward, wherein a hydraulic brake pressure is generated in a master cylinder by an input thrust applied to the first member by the brake pedal and a booster thrust applied to the second member by the electric actuator, such that a part of a reaction force resulting from the hydraulic brake pressure is transmitted to the first member, while another part of the reaction force is transmitted to the second member, the electrically actuated brake booster comprising: urging means disposed between the first member and the second member, wherein, when the first member and the second member are displaced relative to each other in at least one direction, an urging force of the urging means against the first member in a direction in which the second member is displaced relative to the first member becomes larger than that in a state prior to the relative displacement between the first and the second members. 2. An electrically actuated brake booster according to claim 1, wherein the first member is a shaft member, and the second member is a tubular member that is disposed outside the shaft member so as to be capable of moving relative to the shaft member. 3. An electrically actuated brake booster according to claim 2, wherein the shaft member and the tubular member serve as pistons of a master cylinder, front tip portions of the shaft member and the tubular member are disposed to face a pressure chamber of the master cylinder, such that a part of a reaction force resulting from a hydraulic brake pressure in the pressure chamber is transmitted to the shaft member, while another part of the reaction force is transmitted to the tubular member. 4. An electrically actuated brake booster according to claim 3, wherein the urging means is disposed in an interior of the tubular member. 5. An electrically actuated brake booster according to claim 2, wherein the urging means is disposed in an interior of the tubular member. 6. An electrically actuated brake booster according to claim 2, wherein a reaction member for transmitting a reaction force from a piston of the master cylinder to the shaft member and the tubular member is disposed between the shaft member/the tubular member and the piston. 7. An electrically actuated brake booster according to claim 1, wherein the urging means urges the first member relative to the second member towards a neutral position of relative displacement. 8. An electrically actuated brake booster according to claim 7, wherein the urging means comprises: a first spring for urging the first member relative to the second member in one direction; and a second spring for urging the first member relative to the second member in another direction, such that the neutral position is located in a position where spring forces of the first spring and the second spring are balanced. 9. An electrically actuated brake booster according to claim 1, wherein a forward urging force of the urging means acting on the first member, when the second member is displaced relative to the first member in a forward direction, becomes larger than that in a state prior to the relative displacement between the first and second members, so as to increase a boost ratio. 10. An electrically actuated brake booster according to claim 1, wherein a backward urging force of the urging means acting on the first member, when the second member is displaced relative to the first member in a backward direction, becomes larger than that in a state prior to the relative displacement between the first and second members, so as to decrease a boost ratio. 11. An electrically actuated brake booster according to claim 1, further comprising displacement-detecting means for detecting an amount of relative displacement between the first member and the second member, wherein the electric actuator is controlled on the basis of a detection signal output from the displacement-detecting means so as to adjust the amount of relative displacement to a predetermined value. 12. An electrically actuated brake booster according to claim 11, wherein the displacement-detecting means is disposed between the first member and the second member so as to detect an amount of relative displacement between the first and the second members. 13. An electrically actuated brake booster according to claim 11, wherein the displacement-detecting means comprises: first absolute-displacement-detecting means for detecting an absolute displacement of the first member relative to a vehicle body; and second absolute-displacement detecting means for detecting an absolute displacement of the second member relative to the vehicle body. 14. An electrically actuated brake booster according to claim 13, wherein the electric actuator is driven by a motor, and the second absolute-displacement detecting means comprises a rotation-detecting means for detecting a rotational displacement of the motor. 15. An electrically actuated brake booster including: a shaft member adapted to move forward and backward in accordance with operation of a brake pedal; a tubular member disposed outside the shaft member so as to be capable of moving relative to the shaft member; and an electric actuator for moving the tubular member forward and backward, the shaft member and the tubular member serving as pistons of the master cylinder, front tip portions of the shaft member and the tubular member being disposed to face a pressure chamber of a master cylinder, such that a hydraulic brake pressure is generated in the master cylinder by an input thrust applied to the shaft member by the brake pedal and a booster thrust applied to the tubular member by the electric actuator, the electrically actuated brake booster comprising: urging means for maintaining the shaft member and the tubular member in a neutral position of relative displacement, when brakes are not in operation; and displacement-detecting means for detecting an amount of relative displacement between the shaft member and the tubular member, wherein the electric actuator is controlled based on a detection signal output from the displacement-detecting means so as to adjust the amount of relative displacement to a predetermined value. 16. An electrically actuated brake booster according to claim 15, wherein the urging means comprises: a first spring for urging the shaft member relative to the tubular member in one direction; and a second spring for urging the shaft member relative to the tubular member in another direction, such that the neutral position is located in a position where spring forces of the first spring and the second spring are balanced. 17. An electrically actuated brake booster according to claim 15, wherein the displacement-detecting means is disposed between the shaft member and the tubular member so as to detect an amount of relative displacement between the shaft and tubular members.
Pfeiffer, Wolfgang; Nagel, Willi; Harter, Werner; Bolz, Martin-Peter; Bauer, Urs, Hydraulic brake system and method as well as control device for its operation.
Foitzik, Bertram; Schaefer, Patrick Christian, Hydraulic control unit for at least one hydraulic unit of a brake system and brake booster control unit for an electromechanical brake booster of a brake system.
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