Abstract: A fluid pressure boosting device of the present invention performs jumping action at a higher servo ratio until fluid pressure in a power chamber (25) reaches a first predetermined value and a rear end (20e) of a reaction piston (20)comes in contact with a step of an input shaft (18). Since a switching valve is set in a first position I until the fluid pressure in the power chamber (25) reaches a second predetermined pressure, a reaction chamber (41) is connected to the reservoir (33) so as to be at atmospheric pressure. In this state, the normal brake control at a lower servo ratio is performed. As the fluid pressure in the power chamber (25) reaches a second predetermined value, the switching valve is set in a second position II by the fluid pressure so that the pressurized fluid in the power chamber is introduced into the reaction chamber (41). The fluid pressure in the reaction chamber 41 acts on the step between the reaction piston (20) and the input shaft (18) so that the servo ratio becomes higher.

Abstract: In a brake boosting system the present invention, as it is decided that brake assist is necessary, a pump 53 is driven, and a solenoid valve 72 is switched to its communication position, and a solenoid shut-off valve 75 is opened. Then, the pump 53 sucks brake fluid from a reservoir 9 through the solenoid valve 72 and sends out the brake fluid to the pressure intensifying chamber 21 through the solenoid shut-off valve 75. At this point, an output shaft 11 has already advanced and a radial hole 38 is positioned ahead of a seventh cup sealing member 31 so that the pressure intensifying chamber 21 and the reaction chamber 33 are shut off from the reservoir 9 so as to be in the sealed state. Therefore, pump discharge pressure is supplied to the pressure intensifying chamber 21 and the reaction chamber 33 so that the pressure in these chambers is intensified. Since the intensified pressure acts on the primary piston 12, the master cylinder pressure is intensified to a value greater than that of normal braking.

Abstract: The collar 13 for slidably supporting and guiding a valve body of the control valve 55 of the hydraulic pressure type booster 1 is press-fitted into the small diameter portion 9a of the stepped hole 9 of the power piston 8. The valve seat member 10 of the control valve 55 is also press-fitted into the small diameter portion 9a. Further, the small diameter protrusion 6b of the stepped cylindrical protrusion 6a of the plug 6, which divides the power chamber 25, is also press-fitted into the small diameter portion 4a of the stepped hole 4 of the housing 3. In the cylindrical member 17 in which the second valve seat 17a of the control valve 55 is formed, the stopper 17b to restrict a limit of retraction of the input shaft 18 is integrally formed. Further, the cylindrical fixing member 11 to fix the flange 10a of the valve seat member 10 is fixed to the power piston 8 with C ring 12 in the axial direction.

Abstract: In a hydraulic boosting device of the present invention, when the pressure stored in an emergency accumulator is less than a set pressure, a stepped piston 70 moves downward, a throttle valve 72 is set in a first position where the throttle valve 72 is seated in a valve seat 71, and hydraulic fluid flowing from a pump through an inlet path 14 is restricted by a flow limiting valve 68 so as to develop a fluid pressure in an annular path 73. The fluid pressure is stored in the emergency accumulator through a path 69, an accumulator valve 27, and an accumulator path 31. When the pressure stored in the emergency accumulator exceeds the set pressure, the stepped piston 70 moves upward, the throttle valve 72 is set in a second position where the throttle valve 72 is apart from the valve seat 71, and the hydraulic fluid from the pump is not restricted by the flow limiting valve 68 at all so as to flow freely toward a control valve. In this state, no fluid pressure is developed in the annular path 73.

Abstract: In a brake-pressure producing device of the present invention, a power piston 10 of a hydraulic booster 2 comprises a stepped piston including a large-diameter portion 10a on which fluid pressure of a power chamber 30 is exerted and a small-diameter portion 10b having the same diameter as the master cylinder piston 53. Both the pistons 10, 53 are interlocked with each other through an aligning rod 62. The pressurized fluid of the power chamber 30 is introduced into an annular chamber 51 formed on the circumference of the small-diameter portion 10b and the fluid pressure of the pressurized fluid is exerted on a stepped portion 10c between the large-diameter portion 10a and the small-diameter portion 10b in the direction opposite to the direction of the fluid pressure of the power chamber 30.

Abstract: In a hydraulic brake system of the present invention, the communication between a power chamber 30 of a hydraulic booster 2 and wheel cylinders (WCY) 58, 59 is allowed by a switching valve 64 when fluid pressure of an accumulator (ACC) 46 exceeds predetermined pressure. During braking operation, the fluid pressure of the ACC 46 introduced in the power chamber 30 is introduced directly to the WCYs 58, 59, thereby rapidly actuating brakes and thus improving the response. When the fluid pressure of the ACC 46 is less than the predetermined pressure, the communication between a fluid chamber 57 of a master cylinder (MCY) 3 and the WCYs 58, 59 is allowed by the switching valve 64. During braking operation, MCY pressure developed by a MCY piston 53 operated by an input shaft 21 through a power piston 10 is introduced into the WCYs 58, 59 through the switching valve 64. The brakes can securely work even when the fluid pressure of the ACC 46 is less than the predetermined pressure.

Abstract: A braking unit includes an intensifier mechanism for intensifying a braking liquid pressure of a master cylinder upon failure of a liquid pressure booster. The braking unit comprises the intensifier mechanism for intensifying the braking liquid pressure of the master cylinder when actuated, and a control valve which makes the intensifier mechanism operable upon failure of the liquid pressure booster. The control valve comprises a valve member which is urged by a spring tensioned with a given load and which is urged in the opposite direction from the spring by a liquid pressure of a power chamber of the liquid pressure booster. The valve member makes the intensifier mechanism operable whenever the resilience of the spring exceeds the urging force produced by the liquid pressure in the power chamber of the liquid pressure booster. This prevents an operational lag of the intensifier mechanism in the event the liquid pressure booster fails.