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A braking system including: a pressure control cylinder having a housing, a piston displaceable by activation of a drive source, and a pressure controlling chamber so that a working fluid can be supplied from the pressure controlling chamber to a brake cylinder, by displacement of the piston; and a

A braking system including: a pressure control cylinder having a housing, a piston displaceable by activation of a drive source, and a pressure controlling chamber so that a working fluid can be supplied from the pressure controlling chamber to a brake cylinder, by displacement of the piston; and a braking pressure control device operable to control the activation of the drive source, for controlling a pressure of the working fluid in the pressure controlling chamber or in the brake cylinder. The braking-pressure control device includes: a piston-bottoming-state detecting portion operable to detect a piston-bottoming state of the pressure control cylinder and/or a possibility of occurrence of the piston-bottoming state; and a drive-source control portion operable to control the activation of the drive source on the basis of result of detection made by the piston-bottoming-state detecting portion.

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1. A braking system comprising:a hydraulically operated brake cylinder capable of operating a brake; a pressure control cylinder having a housing, a piston which is received in said housing and which is displaceable relative to said housing between front and rear stroke end positions by activation o

1. A braking system comprising:a hydraulically operated brake cylinder capable of operating a brake; a pressure control cylinder having a housing, a piston which is received in said housing and which is displaceable relative to said housing between front and rear stroke end positions by activation of a drive source, and a pressure controlling chamber which is located on a front side of said piston and which is connected to said brake cylinder, so that a working fluid can be supplied from said pressure controlling chamber to said brake cylinder, by displacement of said piston in a direction away from the rear stroke end position toward the front stroke end position; and a braking-pressure control device operable to control the activation of said drive source, for controlling a pressure of the working fluid in said pressure controlling chamber, so that a pressure of the working fluid in said brake cylinder can be controlled, wherein said braking-pressure control device includes: a piston-bottoming-state detecting portion operable to detect at least one of a piston-bottoming state in which said piston has reached almost in the front stroke end position while the pressure of the working fluid in said brake cylinder has not yet reached a predetermined level, and a possibility of occurrence of said piston-bottoming state; and a drive-source control portion operable to control the activation of said drive source on the basis of result of detection made by said piston-bottoming-state detecting portion. 2. A braking system according to claim 1, wherein said drive-source control portion of said braking-pressure control device includes a piston-displacement control portion operable to displace said piston in a reverse direction that is opposite to said direction as a forward direction and to displace said piston in said forward direction, when at least one of said piston-bottoming state and said possibility of occurrence of said piston-bottoming state is detected by said piston-bottoming-state detecting portion,said braking system further comprising a working-fluid-flow permitting device capable of permitting flow of said working fluid to said pressure controlling chamber from a portion of said braking system other than said brake cylinder, when said piston is displaced in said reverse direction. 3. A braking system according to claim 2, wherein said piston-displacement control portion includes a reverse-displacement-distance determining portion operable to determine a distance by which said piston is to be displaced in said reverse direction, on the basis of a relationship between the pressure of the working fluid in said pressure controlling chamber and a distance from the rear stroke end position to a position of said piston.4. A braking system according to claim 2, wherein said piston-displacement control portion includes a reverse-displacement-distance determining portion operable to determine a distance by which said piston is to be displaced in said reverse direction, on the basis of at least one of the pressure of the working fluid in said pressure controlling chamber upon detection of said piston-bottoming state or said possibility of occurrence by said piston-bottoming-state detecting portion, and a distance from the rear stroke end position to a position of said piston upon detection of said piston-bottoming state or said possibility of occurrence by said piston-bottoming-state detecting portion.5. A braking system according to claim 2, wherein said piston-displacement control portion includes a reciprocation-number determining portion operable to determine a required number of times of reciprocations of said piston, on the basis of at least one of the pressure of the working fluid in said pressure controlling chamber, and a distance from the rear stroke end position to a position of said piston.6. A braking system according to claim 2, further comprising a brake-cylinder cut-off valve disposed between said pressure controlling chamber and said brake cylinder, and having an open state in which said pressure controlling chamber and said brake cylinder are communicated with each other, and a closed state in which said pressure controlling chamber and said brake cylinder are isolated from each other,wherein said braking-pressure control device includes a brake-cylinder-cut-off-valve control portion operable to place said brake-cylinder cut-off valve in said closed state when said piston of said pressure control cylinder is displaced in said reverse direction. 7. A braking system according to claim 6, wherein said hydraulically operated brake cylinder consists of a plurality of brake cylinders,said braking system further comprising: a low-pressure source which stores the working fluid under a pressure substantially equal to an atmospheric pressure; a plurality of individual pressure-control valve devices each including a pressure increasing valve and a pressure reducing valve, said pressure increasing valve being disposed between a corresponding one of said plurality of brake cylinders and said pressure controlling chamber, said pressure reducing valve being disposed between the corresponding one of said plurality of brake cylinders and said low-pressure source; wherein said braking-pressure control device further includes an anti-lock braking control portion operable to control the pressure of the working fluid in each of said plurality of brake cylinders such that a degree of wheel slipping is held within a predetermined range, by controlling at least one of said pressure increasing valve and said pressure reducing valve; and wherein said brake-cylinder cut-off valve is provided by said pressure increasing valve. 8. A braking system according to claim 2, further comprising a working fluid source,wherein said working-fluid-flow permitting device includes an inlet valve which is disposed between said working fluid source and said pressure controlling chamber and which is capable of permitting flow of said working fluid from said working fluid source toward said pressure controlling chamber when said piston is displaced in said reverse direction. 9. A braking system according to claim 2, further comprising:a master cylinder operable according to an operation of a brake operating member, to pressurize the working fluid; and a master-cylinder cut-off valve disposed between said pressure controlling chamber and said master cylinder, and having an open state in which said pressure controlling chamber and said master cylinder are communicated with each other, and a closed state in which said pressure controlling chamber and said master cylinder are isolated from each other, wherein said braking-pressure control device includes a master-cylinder-cut-off-valve control portion operable to place said master-cylinder cut-off valve in said open state when said piston is displaced in said reverse direction, and wherein said working-fluid-flow permitting device is provided by said master-cylinder cut-off valve. 10. A braking system according to claim 6, wherein said pressure control cylinder further has a rear pressure chamber which is located on a rear side of said piston,said braking system further comprising: a working-fluid-supply permitting device which is capable of permitting supply of the working fluid from said rear pressure chamber toward said brake cylinder without passage of the working fluid through said brake-cylinder cut-off valve when said piston is displaced in said reverse direction; and a working-fluid-flow inhibiting device which is capable of inhibiting flow of the working fluid from said rear pressure chamber toward a portion of said braking system other than said brake cylinder when said piston is displaced in said reverse direction. 11. A braking system according to claim 10, wherein said working-fluid-flow inhibiting device includes a flow permitting portion which is capable of permitting flow of the working fluid toward said rear pressure chamber when said piston is displaced in said forward direction.12. A braking system according to claim 10, wherein said working-fluid-supply permitting device includes a check valve which is capable of permitting flow of the working fluid from said rear pressure chamber toward said brake cylinder and inhibiting flow of the working fluid from said brake cylinder toward said rear pressure chamber.13. A braking system according to claim 10, wherein said piston of said pressure control cylinder has a rear pressure-receiving surface partially defining said rear pressure chamber and a front pressure-receiving surface partially defining said pressure controlling chamber, and wherein said rear pressure-receiving surface has an area that is smaller than an area of said front pressure-receiving surface.14. A braking system according to claim 2, wherein said pressure control cylinder further has a rear pressure chamber which is located on a rear side of said piston,said braking system further comprising: a working fluid source; and an inlet valve which is disposed between said working fluid source and said rear pressure chamber, and which is capable of permitting flow of the working fluid from said working fluid source toward said rear pressure chamber and inhibiting flow of the working fluid from said rear pressure chamber toward said working fluid source. 15. A braking system according to claim 14, further comprising an outlet valve which is disposed between said rear pressure chamber and said pressure controlling chamber, and which is capable of permitting flow of the working fluid from said rear pressure chamber toward said pressure controlling chamber and inhibiting flow of the working fluid from said pressure controlling chamber toward said rear pressure chamber,wherein said working-fluid-flow permitting device is provided by said outlet valve. 16. A braking system comprising:a hydraulically operated brake cylinder capable of operating a brake; a pressure control cylinder having a housing, a piston which is received in said housing and which is displaceable relative to said housing between front and rear stroke end positions by activation of a drive source, and a pressure controlling chamber which is located on a front side of said piston and which is connected to said brake cylinder, so that a working fluid can be supplied from said pressure controlling chamber to said brake cylinder, by displacement of said piston in a direction away from the rear stroke end position toward the front stroke end position; a braking-pressure control device operable to control the activation of said drive source, for controlling a pressure of the working fluid in said pressure controlling chamber, so that a pressure of the working fluid in said brake cylinder can be controlled; and a master cylinder having a master-cylinder housing, and a master-cylinder piston which is displaceably received in said master-cylinder housing and which is connected to a brake operating member, said master cylinder being connected to said brake cylinder so that the working fluid can be supplied from said master cylinder to said brake cylinder, by forward displacement of said master-cylinder piston relative to said master-cylinder housing in response to an operation of said brake operating member; wherein said braking-pressure control device includes a fast-filling control portion operable to control amount of flow of the working fluid from said master cylinder toward said brake cylinder such that a ratio of said amount of flow of the working fluid to an amount of the forward displacement of said master-cylinder piston is made larger when said pressure of the working fluid in said brake cylinder is not larger than a predetermined threshold value, than when said pressure of the working fluid in said brake cylinder is larger than said predetermined threshold value, and wherein said braking-pressure control device controls the activation of said drive source for thereby controlling said pressure of the working fluid in said pressure controlling chamber, while said brake cylinder is isolated from said master cylinder. 17. A braking system according to claim 16, further comprising a master-cylinder cut-off valve which is disposed between said pressure controlling chamber and said master cylinder, said master-cylinder cut-off valve having an open state in which said pressure controlling chamber and said master cylinder are communicated with each other, and a closed state in which said pressure controlling chamber and said master cylinder are isolated from each other,wherein said fast-filling control portion of said braking-pressure control device switches said master-cylinder cut-off valve from said open state to said closed state when said pressure of the working fluid is increased to said predetermined threshold value. 18. A braking system according to claim 16, wherein said master-cylinder piston of said master cylinder includes a large-diameter portion and a small-diameter portion, and cooperates with said master-cylinder housing to define first and second pressurizing chambers, such that the working fluid can be supplied from said first and second pressurizing chambers to said brake cylinder, by the forward displacement of said master-cylinder piston relative to said master-cylinder housing,said braking system further comprising: a working fluid source; and an outflow inhibiting valve which is disposed between said working fluid source and said first pressurizing chamber, and which is controlled by said fast-filling control portion of said braking-pressure control device, such that said outflow inhibiting valve inhibits flow of the working fluid from said first pressurizing chamber toward said working fluid source when said pressure of the working fluid in said brake cylinder is not larger than said predetermined threshold value, and such that said outflow inhibiting valve permits said flow of the working fluid from said first pressurizing chamber toward said working fluid source when said pressure of the working fluid in said brake cylinder is larger than said predetermined threshold value. 19. A braking system according to claim 18, further comprising a master-cylinder cut-off valve which is disposed between said pressure controlling chamber and said master cylinder, said master-cylinder cut-off valve having an open state in which said pressure controlling chamber and said master cylinder are communicated with each other, and a closed state in which said pressure controlling chamber and said master cylinder are isolated from each other,wherein said braking-pressure control device includes a valve control portion operable to place said master-cylinder cut-off valve in said closed state and to place said outflow inhibiting device in a flow-permitting state for permitting said flow of the working fluid from said first pressurizing chamber toward said working fluid source, when said pressure of the working fluid in said brake cylinder is larger than said predetermined threshold value. 20. A braking system according to claim 16, wherein said fast-filling control portion of said braking-pressure control device includes:a piston-bottoming-state detecting portion operable to detect at least one of a piston-bottoming state in which said piston of said pressure control cylinder has reached almost in the front stroke end position while the pressure of the working fluid in said brake cylinder has not yet reached a predetermined level, and a possibility of occurrence of said piston-bottoming state; and a pressure-threshold-value determining portion operable to determine said threshold value such that said threshold value is larger when said at least one of said piston-bottoming state and said possibility of occurrence of said piston-bottoming state is detected, than when neither said piston-bottoming state nor said possibility of occurrence of said piston-bottoming state is detected. 21. A braking system according to claim 20, wherein said pressure-threshold-value determining portion includes a bottoming-information-basis determining portion operable to determine said threshold value on the basis of at least one of said pressure of the working fluid in said pressure controlling chamber upon detection of said piston-bottoming state or said possibility of occurrence by said piston-bottoming-state detecting portion, and a distance from the rear stroke end position to a position of said piston upon detection of said piston-bottoming state or said possibility of occurrence by said piston-bottoming-state detecting portion.22. A braking system according to claim 16, further comprising a stroke simulator which is allowed to be operable when said brake cylinder is isolated from said master cylinder.23. A braking system comprising:a hydraulically operated brake cylinder capable of operating a brake; a pressure control cylinder having a housing, a piston which is received in said housing and which is displaceable relative to said housing between front and rear stroke end positions by activation of a drive source, and a pressure controlling chamber which is located on a front side of said piston and which is connected to said brake cylinder, so that a working fluid can be supplied from said pressure controlling chamber to said brake cylinder, by displacement of said piston in a direction away from the rear stroke end position toward the front stroke end position; a braking-pressure control device operable to control the activation of said drive source, for controlling a pressure of the working fluid in said pressure controlling chamber, so that a pressure of the working fluid in said brake cylinder can be controlled; a master cylinder operable according to an operation of a brake operating member, to pressurize the working fluid; and a master-cylinder cut-off valve disposed between said pressure controlling chamber and said master cylinder, and having an open state in which said pressure controlling chamber and said master cylinder are communicated with each other, and a closed state in which said pressure controlling chamber and said master cylinder are isolated from each other, wherein said braking-pressure control device includes: a working-fluid-deficiency detecting portion which is operable to detect at least one of a deficiency of the working fluid within said pressure controlling chamber and a possibility of occurrence of said deficiency, while the pressure of the working fluid in said brake cylinder is controlled by said pressure control cylinder, with said master-cylinder cut-off valve being held in said closed state; and a piston-displacement control portion operable to displace said piston in a reverse direction that is opposite to said direction as a forward direction and to displace said piston in said forward direction, when at least one of said deficiency of the working fluid and said possibility of occurrence of said deficiency is detected by said working-fluid-deficiency detecting portion. 24. A braking system comprising:a hydraulically operated brake cylinder capable of operating a brake; a pressure control cylinder having a housing, a piston which is received in said housing and which is displaceable relative to said housing between front and rear stroke end positions by activation of a drive source, and a pressure controlling chamber which is located on a front side of said piston and which is connected to said brake cylinder, so that a working fluid can be supplied from said pressure controlling chamber to said brake cylinder, by displacement of said piston in a direction away from the rear stroke end position toward the front stroke end position; a braking-pressure control device operable to control the activation of said drive source, for controlling a pressure of the working fluid in said pressure controlling chamber, so that a pressure of the working fluid in said brake cylinder can be controlled; a master cylinder operable according to an operation of a brake operating member, to pressurize the working fluid; and a master-cylinder cut-off valve disposed between said pressure controlling chamber and said master cylinder, and having an open state in which said pressure controlling chamber and said master cylinder are communicated with each other, and a closed state in which said pressure controlling chamber and said master cylinder are isolated from each other, wherein said braking-pressure control device includes: a master-cylinder-cut-off-valve control portion operable to switch said master-cylinder cut-off valve from said open state to said closed state when said pressure of the working fluid in said brake cylinder is increased to a predetermined threshold value; a piston-bottoming-state detecting portion operable to detect at least one of a piston-bottoming state in which said piston of said pressure control cylinder has reached almost in the front stroke end position while the pressure of the working fluid in said brake cylinder has not yet reached a predetermined level, and a possibility of occurrence of said piston-bottoming state; and a pressure-threshold-value determining portion operable to determine said threshold value such that said threshold value is larger when said at least one of said piston-bottoming state and said possibility of occurrence of said piston-bottoming state is detected, than when neither said piston-bottoming state nor said possibility of occurrence of said piston-bottoming state is detected.