Master cylinder

Abstract

A master cylinder of the invention supplies a brake fluid from a large diameter pressurizing chamber 56 to a small diameter hydraulic chamber 49 by opening a reverse flow checking opening and closing portion 61 by sliding movement of a stepped piston 16 forwardly, that is, fast fill and when the hydraulic pressure of the large diameter pressurizing chamber 56 rises, a control valve 86 escapes the hydraulic pressure of the large diameter pressurizing chamber 56 to a reservoir 12 to gradually lower in accordance with rise of the hydraulic pressure of the small diameter hydraulic chamber 49, thereby capable of reducing a strange feeling in a pedal feeling caused by sudden pressure release of the large diameter pressurizing chamber 56.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to a master cylinder for supplying a brake fluid to a brake apparatus of an automobile or the like.[0003]2. Description of the Related Art[0004]As a conventional master cylinder, as described in a microfilm of A Japanese Utility Model Application No. 152602 / 1980 (Japanese Utility Model Laid-Open No. 73248 / 1982), there is provided a constitution in which by carrying out so-to-speak fast fill for supplying a large volume of a brake fluid at an initial stage of operation when the brake fluid is supplied to a brake apparatus such as a disk brake or a drum brake, an ineffective fluid amount at an initial stage of stroke is compensated for, and as a result, a pedal stroke can be shortened (fast fill type master cylinder).[0005]The fast fill type master cylinder is provided with a stepped cylinder having a large diameter cylinder portion and a small diameter cylinder portion, a stepped piston havi...

AI Technical Summary

Benefits of technology

[0015]The present invention has been made in view of the above-described situation and it is an object thereof to provide a master cylinder capable of reducing a strange feeling in a pedal operation brought when a hydraulic pressure of a large diameter pressurizing chamber is released while ensuring a fast fill function.

[0016]Further, it is another object of the invention to provide a master cylinder capable of shortening a pedal stroke while satisfying a high flow function needed in combining the master cylinder with a traction control apparatus and capable of reducing cost.

[0017]In order to achieve the above-described objects, according to an aspect of the invention, there is provided a master cylinder comprising a stepped cylinder having a large diameter cylinder portion and a small diameter cylinder portion; a stepped piston having a large diameter piston portion slidably inserted into the large diameter cylinder portion of the stepped cylinder and a small diameter piston portion slidably inserted into the small diameter cylinder portion of the stepped cylinder; and a reverse flow checking opening and closing portion for partitioning the inside of the stepped cylinder into a large diameter pressurizing chamber on the large diameter piston portion side and a small diameter hydraulic chamber on the small diameter piston portion side and permitting a brake fluid to flow only from the large diameter pressurizing chamber side to the small diameter hydraulic chamber side, the reverse flow checking opening and closing portion being opened by reducing a volume of the large diameter pressurizing chamber by sliding movement of the stepped piston toward the small diameter hydraulic chamber side to thereby supply the brake fluid from the large diameter pressurizing chamber side to the small diameter hydraulic chamber side, wherein the master cylinder is provided with a control valve for gradually reducing a hydraulic pressure of the large diameter pressurizing chamber in accordance with the rise of the hydraulic pressure of the small diameter hydraulic chamber.

Problems solved by technology

Meanwhile, there poses a problem that since the above-described master cylinder is provided with the notch, when the pressure is elevated slowly, the fluid of the large diameter pressurizing chamber flows to the reservoir and the fast fill cannot be carried out sufficiently.

However, when the ineffective stroke is simply set to be short, sectional areas of flow paths of the cut-off portion on the side of the small diameter hydraulic chamber and the cut-off portion on the side of the large diameter pressurizing chamber, are narrowed.

When the sectional areas of the flow paths are narrowed in this way, in the case that the master cylinder is used in a combination with a traction control apparatus, there poses a problem that when the brake fluid is forcibly sucked from the reservoir via the master cylinder in order to make the traction control apparatus operate the brake apparatus, the brake fluid cannot be made to flow at a sufficient flow rate, that is, in high flow.

However, when the above-described structure is applied to the cut-off portion on the small diameter hydraulic chamber side and the cut-off portion on the large diameter pressurizing chamber side, the control taper face are required in both of the cut-off portions, further, it is necessary to strictly control positional accuracy of both of the ports and therefore, there poses a problem that cost is increased.

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