Importance

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Abstract

A parking brake system is provided in which a parking brake state is obtained by forward movement of a parking piston (44) slidably fitted into a casing (23) with the rear side of the parking piston (44) facing a parking control fluid pressure chamber (47), and the forwardly moved state of the parking piston (44) is mechanically locked by a lock mechanism (31). An insertion shaft (59) and a casing (23), which form part of the lock mechanism (31), are formed so as to position spheres (58) radially inward when the parking piston (44) is at a retreat limit and position the spheres (58) radially outward when a lock piston (56) moves to a forward position in response to forward movement of the parking piston (44) from the retreat limit, and a plurality of guide grooves extending in the axial direction of the insertion shaft (59) are provided on the outer face of the insertion shaft (59), the guide grooves having a concavely curved cross-sectional shape with a diameter that is equal to or larger than the diameter of the spheres (58). This enables an automatic parking brake state to be obtained by a simple structure without consuming power.

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First Claim