Power plants – Pressure fluid source and motor – Pulsator
Reexamination Certificate
2001-05-16
2002-07-16
Ryznic, John E. (Department: 3745)
Power plants
Pressure fluid source and motor
Pulsator
C060S555000
Reexamination Certificate
active
06418716
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a hydraulic brake booster for operating wheel brakes with a magnified or boosted hydraulic pressure, and more particularly to an improvement of a hydraulic brake booster comprising a primary master cylinder for outputting a hydraulic pressure corresponding to an input from a brake pedal for the operation thereof, a hydraulic pressure source, a proportional pressure booster valve for drawing from the hydraulic pressure source a boost pressure corresponding to the hydraulic pressure outputted from the primary master cylinder for outputting and a secondary master cylinder for operating wheel brakes with a hydraulic brake pressure corresponding to the boost pressure outputted from the proportional pressure booster valve.
2. Description of the Related Art
The applicant has proposed before a hydraulic pressure booster described in JP-A-2000-177572, in which a primary master cylinder, a proportional pressure booster valve and a secondary master cylinder can be laid out individually and freely without interfering with one another, this making the hydraulic pressure booster advantageous in that the booster can easily be installed even in a limited narrow space.
In a case, however, where a tandem master cylinder is used for the primary master cylinder of the above hydraulic pressure booster, pairs of proportional pressure booster valves and secondary master cylinders are provided, respectively, in such a manner as to correspond to a pair of output ports provided in the primary master cylinder, this increasing the number of components involved in the booster, thereby making it difficult to reduce the production cost. In addition, scattering of sliding resistance of respective operating members of the pair of proportional pressure booster valves may cause a slight variation in timing at which the pair of secondary master cylinders are activated.
In addition, it is desirable for the proportional booster valve to output boost hydraulic pressure in accordance with pressure characteristics in which the pressure is drastically enhanced as if it were to jump in an initial operating stage of the primary master cylinder based on a viewpoint of eliminating a play portion from a hydraulic system extending from the proportional booster valve to the wheel brakes via the secondary master cylinders and thereafter is enhanced relatively moderately, and in order to obtain such pressure characteristics, it is considered to use as a reaction member the elastic material such as rubber used in the hydraulic booster which is disclosed in JP-A-11-20663. With the elastic material, however, since the elastic properties thereof vary depending upon temperatures, it is difficult with elastic material to obtain the aforesaid pressure characteristics in a stable fashion.
SUMMARY OF THE INVENTION
The invention was made in view of these situations, and an object thereof is to provide a hydraulic brake booster in which in addition to achieving the reduction in the number of components involved therein, a pair of secondary master cylinders can be made at all times to output hydraulic brake pressure simultaneously.
Further, another object of the invention is to provide a hydraulic brake booster which can stably obtain the hydraulic pressure characteristics in which the output from the proportional booster valve is jumped in an initial operating stage of the primary master cylinder.
With a view to attaining the object of the invention, according to a first aspect thereof, there is provided a hydraulic brake booster comprising a primary tandem master cylinder having a pair of output ports for outputting hydraulic pressure to an input to a brake pedal for the operation thereof, a hydraulic pressure source for outputting a hydraulic pressure which is higher than the hydraulic pressure outputted from the primary master cylinder, a plurality of secondary master cylinders each having an input pressure chamber and an output pressure chamber for outputting hydraulic pressure corresponding to the hydraulic pressure outputted from the input pressure chamber which is connected to wheel brakes, and a proportional pressure booster valve having a control piston facing at one end thereof a primary control pressure chamber to which one of both the output ports is connected, a free piston facing at both ends thereof a secondary control pressure chamber to which the other of both the output ports is connected and the primary control pressure chamber, respectively, and adapted to apply a direct pressing force to the control piston at the one end as the hydraulic pressure of the primary control pressure chamber decreases below the hydraulic pressure of the secondary control pressure chamber, a reaction unit for applying to the other end of the control piston a reaction force corresponding to the hydraulic pressure of a boost pressure chamber connected in common to the plurality of input pressure chambers, and a valve unit adapted to be activated as the control piston moves in an axial direction to there by draw from the hydraulic pressure source a hydraulic pressure proportional to the hydraulic pressure outputted from the primary master cylinder for introduction into the boost pressure chamber.
According to this construction, the hydraulic pressure outputted from both the output ports in the primary master cylinder which is operated by the input to the brake pedal to operate the same is applied to the ends of the free piston in the proportional pressure booster valve, and the free piston then operates such that the hydraulic pressure in the primary control pressure chamber between the control piston and the free piston balances with the hydraulic pressure in the secondary control pressure chamber which is located on the opposite side of the primary control pressure chamber and toward which the free piston faces at the one end thereof. Then, the proportional pressure booster valve outputs the boost pressure which is proportional to the hydraulic pressures of the primary and secondary control pressure chambers which balance with each other, and this hydraulic pressure so outputted from the proportional pressure booster valve then operates the plurality of secondary master cylinders, whereby the wheel brakes are applied strongly. Namely, since the plurality of secondary master cylinders are operated by virtue of the boost pressure outputted from the single common proportional pressure booster valve, the respective secondary master cylinders are always made to operate simultaneously with the boosted force without being affected by the sliding resistance that would occur on the operating members within the proportional pressure booster valve, whereby all the wheel brakes are applied simultaneously. According to this construction, the single proportional pressure booster valve suffices for the simultaneous operation of the plurality of secondary master cylinders and hence the number of components involved in the booster can be reduced, whereby the construction of the booster can be simplified, this contributing to the reduction in the production cost thereof. Moreover, even if there occurs a failure in the hydraulic system communicating with the primary control pressure chamber for some reason, the control piston can be pushed to operate directly with the hydraulic pressure in the secondary control pressure chamber, while there occurs a failure in the hydraulic system communicating with the secondary control pressure chamber for other reason, as long as the hydraulic pressure in the primary control pressure chamber remains normal, the control piston still can be pushed therewith, whereby the pressure boosting function of the proportional pressure booster valve can be maintained.
According to a second aspect of the invention, there is provided a hydraulic brake booster as set forth in the first aspect of the invention, wherein the output port of both the output ports of the primary master cylinder which is adapted to output at an earlier timing is connected to t
Matsuno Isao
Mizusaki Yoshinobu
Nakano Joichi
McGuireWoods LLP
Nissin Kogyo Co. Ltd.
Ryznic John E.
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