Fluid handling – Self-proportioning or correlating systems – Self-proportioning flow systems
Reexamination Certificate
1999-12-06
2001-04-24
Buiz, Michael (Department: 3753)
Fluid handling
Self-proportioning or correlating systems
Self-proportioning flow systems
C137S087010, C303S009630
Reexamination Certificate
active
06220270
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a vehicle brake system, and more particularly, to a vehicle brake system which includes a secondary (emergency) brake function and a hydraulic valve which closes off a failed brake circuit and permits the other circuit to function normally.
The John Deere 8000T tractor has a hydraulic braking system which includes a velocity fuse spool valve which is located downstream of the brake valves. The velocity fuse valve includes a spool which is normally held in an open flow position by centering springs. The centering springs, in conjunction with the pilot areas on the spool define a differential pressure which must exist between the two brake circuits before a lock-out of one circuit occurs. The lockout occurs due to low pressure in the failed circuit. Once the low pressure in the failed circuit is low enough to produce the predetermined pressure differential, the pressure differential will shuttle the spool and close off the failed circuit. After the spool has shuttled, the other circuit is allowed to function normally. However, typically such a valve will shuttle at a pressure differential which is low enough such that normal, intermittent, short duration variations in brake pressure may cause undesired shuttling of the velocity fuse valve spool. It would be desirable to control or limit the sensitivity of such a velocity fuse valve and prevent undesired shuttling of the velocity fuse valve spool in such situations.
SUMMARY OF THE INVENTION
Accordingly, an object of this invention is to provide velocity fuse valve for a hydraulic braking system which reduces or prevents undesired activation of the velocity fuse valve.
Another object of this invention is to provide such a velocity fuse valve which minimizes circuit complexity and which requires no adjustments to set a cut-off pressure.
These and other objects are achieved by the present invention, wherein an improved the velocity fuse valve controls communication between first and second brake valves and first and second brake lines. The velocity fuse valve includes a valve housing having a valve bore which slidably receives a valve spool. The spool moves in response to pressure in first and second pilot chambers, each communicated with a corresponding first and second outlet. The first pilot chamber is communicated with the first outlet via a first dashpot passage and a first orifice, and the second pilot chamber is communicated with the second outlet via a second dashpot passage and a second orifice. The orifices reduce or control how fast the spool will move in response to the pressure differential between the pilot chambers.
REFERENCES:
patent: 3774974 (1973-11-01), Braun
patent: 3914736 (1975-10-01), Nakamura et al.
patent: 4227746 (1980-10-01), Schopper et al.
patent: 4313642 (1982-02-01), Berisch
patent: 4691795 (1987-09-01), Wehmeyer et al.
patent: 4717208 (1988-01-01), Kubota
Dunbar Scott David
Valentin Timothy Lloyd
Buiz Michael
Deer & Company
Krishnamurthy Ramesh
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