Abstract: A self-tapping screw type fastener of the present invention is characterized in that an external thread 7 of an adjusting rod (self-tapping screw) 5 is screwed into and fastened to an output rod 1 with tapping an internal thread 3 in an inner peripheral surface of a smooth prepared hole 2 of the output rod 1. The adjusting rod 5 has a threaded shaft 13 with the external thread 7 formed thereon and a smooth guide shaft 14 projecting from an end of the threaded shaft 13. The outer diameter R1 of the smooth guide shaft 14 is set to be smaller than the major diameter R4 of the external thread 7 and to be slightly larger than the minor diameter R2 of the external thread 7 or the minor diameter R3 of the internal thread 3. Because of the diameter difference “t” between the diameter R1 and the diameter R2 or R3, a step 20 is formed so that the step comes in contact with the nearest ridge of the internal thread 3, thereby preventing the adjusting rod 5 from getting loose.

Abstract: An improvement of a reaction disc 25 and a valve plunger 8 disposed in a booster is provided. A recess 25a is formed in a rear end face 25b of the reaction disc while a projection 31a from the valve plunger 8 is loosely fitted into the recess 25a. When the break booster 1 is operated, the peripheral surface and the bottom of the recess 25a abut against the projection 31a, and the rear end face 25b abuts against the end face 31c of a plunger 31, whereby a brake reaction is transmitted to an input shaft 21. When an input or a force of depressing a brake pedal is reduced during the operation, a resistance is applied to a rearward retracting movement of the valve plunger 8 by the peripheral surface of the recess 25a. The invention allows the hysteresis to be increased without increasing the hardness of the reaction disc 25.

Abstract: A plurality of axially extending ribs are formed in the inner periphery of a valve body at its front end for slidably supporting the outer peripheral surface of the output shaft at its rear end. With this arrangement, any dimensional error which may occur in the region of the ribs can be suppressed small during the manufacturing of the valve body if a diameter shrinkage occurs in the inner periphery thereof. Accordingly, when the rear end of the output shaft is slidably fitted into the ribs, the output shaft is less likely to be askew with respect to the axis of the valve body. Accordingly, a biased abrasion of an annular seal member which is disposed between an opening formed in the front portion of a shell and the outer periphery of the output shaft at its front end to maintain a hermetic seal therebetween can be suppressed.

Abstract: A key member has an engaging portion, which is engaged with an annular groove formed in a valve plunger to prevent the valve plunger from coming off from a valve body. On the rear side of the key member, the valve body has a guide portion which is adapted to slidably guide the valve plunger. Axial passages are formed around the guide portion which form a variable pressure passage together with a radial passage. The key member is inserted in the radial passage in such a manner that its rear end face abuts against the end face of the guide portion. The distance between the engaging region of the key member and the valve plunger and the abutting portion of the key member and the valve body is decreased, so that the bending moment applied to the key member is decreased. This feature makes it possible to decrease the thickness of the key member and accordingly the weight of the latter.

Abstract: A valve mechanism for a brake or clutch booster, and more particularly, an improvement of a valve element used therein is disclosed. The valve element includes a seat which is located at the front end, a connection located at the rear end and connected to the inner periphery of a valve body, and a curved portion which is axially collapsible and interconnecting between the seat and the connection. An annular groove is formed in the inner peripheral surface of the connection at its front end. With this arrangement, the provision of the annular groove is effective to prevent any reduction in the flexibility of the curved portion if the diameter of the seat of the valve element is increased in order to increase the flow rate of the atmosphere into the booster. Thus, if the diameter of the seat 10a of the valve element 10 is increased, there is no need to increase the diameter of the connection 10b of the valve element 10.

Abstract: A reaction disc used in a brake booster, in particular, an improvement of an air vent formed in the outer periphery of the reaction disc is disclosed. The reaction disc is provided with a circumferentially discontinous bulge on its external peripheral surface, and a discontinuity in the bulge provides an air vent passage. A burr is formed on the external peripheral surface of the reaction disc as displaced from the bulge. The bulge has a height which is chosen to be greater than the height of the burr. When a reaction disc thus constructed is fitted into a recess of a push rod, the air vent passage provides a positive venting action for the air trapped in the recess. Accordingly, no deburring operation is required during the manufacture of the reaction disc.

Abstract: An improvement of a constant pressure passage formed within a valve body of a brake booster is disclosed. A notch of a given size is formed in the internal peripheral surface of the valve body at a location rearward of the rear end of the constant pressure passage. The provision of the notch allows the diameter of a reaction disc to be increased over the prior art by an amount corresponding to the depth of the notch, thus allowing the durability of the reaction disc to be improved.

Abstract: A brake booster, and more particularly, an improvement of a coiled spring which is disposed within a valve body to return an input shaft to its inoperative position is disclosed. The coiled spring of the invention is generally cylindrical, and is disposed between a retainer secured to a tubular portion of the valve body and a step on the input shaft. The coiled spring includes a seat section which is disposed in abutment against the step on the input shaft and which has an inner diameter chosen to be less than the adjacent coil. Such arrangement enables an arcuate space 20d to be maintained radially between the seat section and its adjacent coil. The arcuate space is utilized as a pressure passage which allows the passage of the atmosphere. If the coiled spring is rapidly compressed upon operation of the booster, the described space is maintained, allowing an unhindered passage of the atmosphere through the space. This improves the response upon operation of the booster.

Abstract: An enclosed shell is divided by a center plate and a pair of front and rear diaphragms which are disposed on the opposite sides of the center plate into four chambers. A center body is fitted over a valve body which internally houses a valve mechanism. The center body slides relative to the central portion of the center plate with a seal member interposed therebetween. The inner periphery of the front diaphragm is inserted inside the center body, and is held between the valve body and the center body at a location rearward of the seal member, whereby the overall length of the brake booster is reduced.

Abstract: According to the present invention, a rotation preventive portion for preventing the rotation of bead portion, such as a stepped projection, is provided on the bead portion of diaphragm, which is squeezed between a front shell and a rear shell. When the front shell and the rear shell are assembled with such a diaphragm, the rotation of the bead portion is prevented by this rotation preventive portion (stepped bead). As the result, outer lip of the bead portion of diaphragm or the rolling portion of diaphragm are not squeezed between the front shell and the rear shell, and the front shell and the rear shell can be assembled without damaging or breaking the diaphragm.

Abstract: An improvement of a variable pressure passage formed in the valve body of a brake booster is disclosed. A variable pressure passage including a first radial passage in which a key member is inserted and a second radial passage continuing from and located rearward of the first radial passage is the basis of the invention. According to the invention, a third radial passage, which also forms the variable pressure passage, is located forwardly of and continues from the first radial passage, and has a circumferential width less than that of the key member. This allows a corresponding increase in the channel area of the variable pressure passage, thereby improving the operational response of the brake booster without the need to increase the axial size of the valve body since the third passage is formed forwardly of the key member.

Abstract: A brake booster is disclosed which reduces an idle stroke of an input shaft. A key member which is mechanically coupled to a valve plunger which forms part of a valve mechanism is provided with an elastic member so that when the brake booster is inoperative, the elastic member on the key member abuts against a shell and a valve body, respectively, thereby limiting a retracting movement of the valve body. Under this condition, a retracting movement of the key member is allowed by an elastic deformation of the elastic member if the input shaft is pulled rearward to cause a retracting movement of the valve plunger and the key member.

Abstract: A brake booster includes a key member coupled to a valve plunger. When the booster is inoperative, the key member is brought into abutment against an inner wall surface of a shell to limit a free retracting movement of a valve plunger and its connected input shaft so that a lost stroke of the input shaft can be reduced when the brake is operative for the next time. According to the invention, a shell includes a cylindrical extension which is circumferentially and integrally formed with an annular bulge which extends radially inward, with a seal member disposed on the rear side of the annular bulge.

Abstract: A brake booster is disclosed which reduces an idle stroke of an input shaft, by bringing a key member which is mechanically coupled to a valve plunger into abutment against an inner wall surface of a shell when the brake booster is inoperative. The shell includes a cylindrical projection which extends rearwardly from the center thereof, and the cylindrical projection is formed with a flange which extends radially inward, with its inner periphery cut away to define an opening. A valve body includes a cylindrical portion which extends through the opening to the outside thereof. By disposing the key member for abutment against the inner wall surface of the flange, a reduction in the length of the key member is enabled. A seal member seals the cylindrical portion of the valve body, and is located rearwardly of the flange and is received within a housing which is disposed outside the shell.

Abstract: A casing for use in a brake booster or clutch booster is provided. The casing includes a cylindrical portion which defines an outer periphery thereof, a flat central end wall which is disposed substantially perpendicular to the axis of the cylindrical portion, and a frustoconical portion which interconnects the cylindrical portion and the central end wall. According to the invention, a flat peripheral end wall is disposed between the cylindrical portion and the frustoconical portion so as to be substantially perpendicular to the axis of the cylindrical portion, thus increasing the rigidity of the casing.

Abstract: A shell connecting structure as used in a brake booster for holding a peripheral bead of a diaphragm between a front and a rear shell in a hermetically sealed manner. The front and the rear shell are connected together at a location radially outward of a power piston to thereby reduce an axial size of the shells while simultaneously minimizing a radial size of the connecting portion and hence the shells.

Abstract: A brake power servo booster including a stationary stop provided on the cylindrical projection of a rear shell, and a movable stop provided on an input shaft connected between a brake pedal and a valve mechanism, and operationally associated with the stationary stop to restrict the retracted position of the input shaft. An intermediate stop member is slidably provided in the cylindrical projection, and has its retraction restricted by the stationary stop. The input shaft extends slidably through the intermediate stop member. The movable stop is adapted for abutment on the intermediate stop member to restrict the retracted position of the input shaft.