| 主权项 |
1. A master cylinder device for supplying a pressurized brake fluid to a brake device provided in a wheel, comprising:
a housing whose front side end is closed and which includes a partition portion separating an interior of the housing into a front side chamber and a rear side chamber and having an opening through the partition portion, the partition portion of the housing including an annular separation wall portion projecting to inside the housing in a radial direction and an inner cylindrical portion having a hollow cylindrical shape and extending forward from an functioning as the opening, an interior of the inner cylindrical portion serving as a part of the rear side chamber; a pressure receiving piston which includes a main body portion having a flange on a rear end thereof and disposed in the front side chamber, and which is moved forward by receiving a force for pressurizing the brake fluid to be supplied to the brake device, the main body portion of the pressure receiving piston including a blind hole which is open rearward, whereby a rear side portion of the main body portion is a cylindrical portion having a hollow cylindrical shape, the main body portion having the flange at a rear end of the cylindrical portion; and an input piston which is disposed in the rear side chamber, which is connected to a brake operation member disposed behind the housing, and which can move forward by an operation force applied to the brake operation member, wherein the pressure receiving piston is disposed such that the main body portion of the pressure receiving piston is fitted, at the flange and a portion in front of the flange, in the housing with respective seals therebetween and such that the inner cylindrical portion of the partition portion is inserted in the cylindrical portion of the pressure receiving piston and the pressure receiving piston and the partition portion are fitted at an inner circumferential face of the cylindrical portion and an outer circumferential face of the inner cylindrical portion to each other with a seal, whereby: a pressurizing chamber in which the brake fluid to be supplied to the brake device is pressurized by a forward movement of the pressure receiving piston is defined in front of the main body portion of the pressure receiving piston; an input chamber into which a brake fluid from a high pressure source is introduced is defined between a rear end of the cylindrical portion and the separation wall portion of the partition portion; and an opposing chamber which opposes the input chamber with the flange being interposed between the opposing chamber and the input chamber is defined around the main body portion, wherein the input piston is fitted in the housing with a seal, whereby, between the input piston and the pressure receiving piston, there is defined an inter-piston chamber such that a bottom portion of the blind hole of the pressure receiving piston and the input piston face to each other with the opening formed in the partition portion being interposed between the bottom portion and the input piston in a state in which any seal is not present between the input piston and the pressure receiving piston, wherein an inter-chamber communication passage which allows a communication between the opposing chamber and the inter-piston chamber is provided, and a pressurized area of the pressure receiving piston on which a pressure of a brake fluid in the opposing chamber acts and a pressurized area of the pressure receiving piston on which a pressure of a brake fluid in the inter-piston chamber acts are equal, and wherein the master cylinder device further comprises a reaction force applying mechanism which allows a forward movement of the input piston relative to the housing by the operation force, and which applies, to the input piston, a reaction force against the forward movement and with a magnitude according to an amount of the forward movement, as an operation reaction force against an operation of the brake operation member. |
