Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Reexamination Certificate
1999-10-15
2001-08-07
Look, Edward K. (Department: 3745)
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
Reexamination Certificate
active
06269732
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a pneumatic booster which is used in a brake system for a vehicle.
In many vehicles, use is made of a brake system comprising: a pneumatic booster for boosting a depressing force applied to a brake pedal; a master cylinder for generating a fluid pressure in accordance with an output of the pneumatic booster; and a disk brake which receives the fluid pressure from the master cylinder by means of a piston within a caliper and generates a predetermined braking force. Conventionally, for larger vehicles, a tandem type pneumatic booster having two power pistons arranged in tandem is employed in the brake system, because a tandem type pneumatic booster is capable of generating a high output. In recent years, however, study has been made of using a single-type pneumatic booster having a single power piston, with a view to reducing the size of a brake system.
In order to enable the use of a single-type pneumatic booster, it is necessary to increase a ratio of a pressure-receiving area of a cylinder within the caliper in the disk brake to a pressure-receiving area of the master cylinder. That is, efficiency of the master cylinder must be increased by reducing the diameter of the master cylinder to a level which is as low as possible. However, when a single-type pneumatic booster is applied simply by reducing the diameter of the master cylinder, the amount of fluid for operating the disk brake becomes insufficient. This insufficiency of the amount of fluid can be compensated for by increasing the stroke in each of the master cylinder and the pneumatic booster. However, when the stroke in the pneumatic booster is increased, the stroke of the brake pedal is also increased. This lowers brake operability. Therefore, in order to ensure the same brake operability as obtained in conventional brake systems, it is necessary to reduce a pedal ratio (a ratio of a distance between a pivot for the brake pedal and a point at which an input force is applied to a distance between the pivot and a point at which an output is obtained).
When the pedal ratio becomes small, the depressing force applied to the brake pedal becomes large. As a measure for preventing such an increase in the depressing force, it is known to increase a fluid force for advancing a plunger in the booster, which force is generated due to a difference between negative pressure and positive pressure acting on the booster. However, no effective mechanisms have been developed to increase the above-mentioned fluid force.
SUMMARY OF THE INVENTION
In view of the above, the present invention has been made. It is an object of the present invention to provide a pneumatic booster which generates a large fluid force for advancing a plunger therein so as to reduce a resistance thrust force at the time of depressing the brake pedal, and therefore can be easily applied even when the stroke in the booster is large.
The pneumatic booster of the present invention comprises a shell body, a power piston dividing an interior of the shell body into a constant-pressure chamber and a variable-pressure chamber, a valve body supported by the power piston and a plunger provided within the valve body. In order to achieve the above-mentioned object, an annular atmospheric valve seat at an end portion of the plunger which portion is connected to an input shaft has a larger diameter than that of a plunger in a conventional pneumatic booster. The atmospheric valve seat is located in a position forward in a direction of propelling of the power piston relative to a negative pressure valve seat. The atmospheric valve seat is positioned so as to substantially correspond with the negative pressure valve seat in an axial direction. In other words, the atmospheric valve seat is positioned so as to radially overlap the negative pressure valve seat. In a poppet valve mechanism including seal surfaces capable of abutting against the above-mentioned valve seats, the seal surfaces are spaced apart from each other in the axial direction.
By this arrangement, since the atmospheric valve seat of the plunger is larger in diameter than that in a conventional pneumatic booster, a fluid force generated due to a differential pressure acting on the plunger becomes large, thereby reducing a resistance thrust force at the time of depressing the brake pedal. Further, since the atmospheric valve seat and the negative pressure valve seat are spaced apart from each other in the axial direction, a sufficient flow path area can be ensured, so that the plunger can be advanced and returned without any delay.
REFERENCES:
patent: 5651300 (1997-07-01), Ikeda et al.
patent: 8-67239 (1996-03-01), None
Ando Hiromi
Endo Mitsuhiro
Koshu Atsuya
Leslie Michael
Look Edward K.
Tokico Ltd.
Wenderoth , Lind & Ponack, L.L.P.
LandOfFree
Pneumatic booster does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Pneumatic booster, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pneumatic booster will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2445508