Brake booster with compressible air valve for braking speed...

Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type

Reexamination Certificate

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Reexamination Certificate

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06209442

ABSTRACT:

TECHNICAL FIELD
The technical field of this invention is differential brake boosters for vehicles.
BACKGROUND OF THE INVENTION
Power brake boosters of the differential pressure type using engine vacuum are well known in the motor vehicle industry. A brake booster of this type has a diaphragm separating a vacuum chamber open to a source of vacuum, such as created in an engine intake passage, and a working chamber normally provided with vacuum or atmospheric air by a valve apparatus responsive to input brake pedal actuation to provide brake assist force as required through a power piston fixed to the diaphragm and coupled to the booster output.
The valve apparatus may have a vacuum valve seat on the power piston that is engageable with a floating control valve as well as an air valve that also has a seat engageable with the same side of the floating control valve and is coupled to a brake input rod. In the rest position (no brake apply) the air valve is engaged with the floating control valve, and the vacuum valve is slightly separated therefrom to guarantee vacuum on both sides of the diaphragm and thus no brake boost assist. A brake input to the air valve moves the air valve seat axially past the vacuum valve seat, whereupon the floating control valve moves against the vacuum valve seat to shut off the flow of vacuum into the working chamber and allow the air valve seat to disengage and admit air at atmospheric pressure into the working chamber. The increase in air pressure in the working chamber produces a differential pressure across the diaphragm to move it axially; and the power piston move with it to provide an assist force to the brake fluid in the master cylinder. Movement of the power piston allows the floating control valve to move toward the air valve seat; and the level of boost assist is thus matched to the driver's input force. The opening of the air valve is calibrated to provide smooth brake apply in normal and typical driving situations.
Occasionally a driver may wish or need to stop the vehicle as quickly as possible. In such a situation, it might be possible to provide slightly quicker brake application by admitting air to the working chamber of the brake booster at a faster rate. But this faster air admittance should not be provided except in such situations, since it would not produce appropriate braking behavior in normal driving.
SUMMARY OF THE INVENTION
The apparatus of this invention provides a braking speed of application enhancement by increasing the air valve opening in a vacuum brake booster when a vehicle operator applies braking force quickly and forcefully. This is accomplished with a two part air valve which is normally expanded axially to a normal length by an internal spring but which may be shortened to open the air valve by a greater amount when the brake pedal input force is sufficient to move the air valve axially against another spring into contact with a shoulder of the power piston. The internal spring has a much higher preload than the other spring so that the booster operates with a fully axially expanded air valve in normal, low force brake activation. Once the air valve axially engages the power piston, however, the increase in air valve opening is immediate and substantial with any further increase in braking force. The air valve has an air valve input element having a pin projecting radially outward into an opening in a side wall of an air valve output element surrounding the air valve input element so as to axially engage a side of the opening to limit expansion of the air valve by the spring and thus define the normal axial length of the air valve.


REFERENCES:
patent: 3049099 (1962-08-01), Price
patent: 3109282 (1963-11-01), Price
patent: 3110031 (1963-11-01), Price
patent: 3143927 (1964-08-01), French et al.
patent: 3279327 (1966-10-01), French
patent: 4729285 (1988-03-01), Harrison
patent: 5040450 (1991-08-01), Jakobi
patent: 5884548 (1999-03-01), Ando et al.
patent: 1550970 (1969-07-01), None
patent: 2152610 (1985-08-01), None

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