Vacuum booster, brake system equipped with the vacuum booster, and method of manufacturing plate plunger for vacuum booster

Abstract

A plate plunger 17 that determines a servo ratio SR of a vacuum booster 1 pertaining to the present invention has, on a corner portion between its outer peripheral surface and its surface that opposes a reaction disc 16, a servo ratio determination surface 17 c that is formed by an inclined surface and determines the servo ratio. The servo ratio determination surface 17 c comprises a reaction disc contact surface 17 f that determines the servo ratio and a reaction disc non-contact surface 17 g. Additionally, a variety of different servo ratios are obtained by performing secondary processing such as cutting or grinding on just the servo ratio determination surface 170 to change the outer peripheral diameter of the reaction disc contact surface 17 f.

1 . A vacuum booster comprising at least:
 an input shaft to which an input is applied;   a control valve that is operated by the input shaft;   a power piston that operates on atmospheric air introduced by the operation of the control valve;   an output shaft that puts out an output in which the input has been boosted by a servo ratio by the operation of the power piston;   a reaction disc to which a reaction force of the output of the output shaft is transmitted and which elastically deforms; and   a plate plunger with which the reaction disc that has elastically deformed comes into contact to transmit the reaction force to the input shaft and which determines the servo ratio,   wherein the plate plunger has, on a corner portion between an outer peripheral surface and a surface that opposes the reaction disc, a servo ratio determination surface that is formed by an inclined surface and determines the servo ratio, and   the servo ratio determination surface comprises a reaction disc contact surface that determines the servo ratio and a reaction disc non-contact surface.   
     
     
         2 . The vacuum booster according to  claim 1 , wherein the plate plunger is configured by a plate plunger base material in which an outer peripheral diameter of the reaction disc contact surface has been primarily processed to be equal to or greater than an outer peripheral diameter corresponding to the smallest servo ratio among a variety of different servo ratios and in which the servo ratio determination surface has been secondarily processed. 
     
     
         3 . The vacuum booster according to  claim 2 , wherein the primary processing is performed by mold forming or cut forming, and the secondary processing is performed by cutting or grinding. 
     
     
         4 . A brake system comprising at least:
 a brake pedal;   a brake booster that boosts a pedal force of the brake pedal by a predetermined servo ratio and outputs the boosted pedal force;   a master cylinder that operates on the output of the brake booster and generates hydraulic pressure; and   brake cylinders that generate brake force with the hydraulic pressure generated in the master cylinder to apply brakes to wheels, wherein the brake booster is the vacuum booster according to  claim 1 .   
     
     
         5 . A method of manufacturing a plate plunger with which a reaction disc comes into contact and which determines a servo ratio of a vacuum booster, the plate plunger manufacturing method comprising:
 primarily processing a plate plunger base material in such a way that an outer peripheral diameter of a reaction disc contact surface of the plate plunger with which the reaction disc comes into contact becomes equal to or greater than an outer peripheral diameter corresponding to the smallest servo ratio among a variety of different servo ratios; and   forming the reaction disc contact surface of the plate plunger in such a way that it has an outer peripheral diameter corresponding to a desired servo ratio by secondarily processing a servo ratio determination surface that determines the servo ratio on a corner portion between an outer peripheral surface of the plate plunger base material and a surface of the plate plunger base material that opposes the reaction disc.   
     
     
         6 . The plate plunger manufacturing method according to  claim 5 , further comprising
 secondarily processing the servo ratio determination surface in such a way that the servo ratio becomes the smallest servo ratio among the variety of different servo ratios to thereby obtain the plate plunger base material, and   using the plate plunger base material as is as the plate plunger in the case of obtaining a plate plunger with the smallest servo ratio and, in the case of obtaining a plate plunger with a larger servo ratio than the smallest servo ratio, forming the servo ratio determination surface of the plate plunger base material by further secondary processing to thereby obtain a plate plunger with the desired servo ratio.   
     
     
         7 . The plate plunger manufacturing method according to  claim 5 , wherein the primary processing is performed by mold forming or cut forming, and the secondary processing is performed by cutting or grinding. 
     
     
         8 . The brake system according to  claim 4 , wherein the plate plunger is configured by a plate plunger base material in which an outer peripheral diameter of the reaction disc contact surface has been primarily processed to be equal to or greater than an outer peripheral diameter corresponding to the smallest servo ratio among a variety of different servo ratios and in which the servo ratio determination surface has been secondarily processed. 
     
     
         9 . The brake system according to  claim 8 , wherein the primary processing is performed by mold forming or cut forming, and the secondary processing is performed by cutting or grinding.