Centrifugal hydraulic head relief valve

A pressure responsive relief valve closing responsive to clutch actuating pressure and opening responsive to centrifugal forces and a spring force to relieve residual pressure in the hydraulic actuator of a rotating clutch to avoid clutch drag.

This invention relates to a friction clutch, and, more particularly, to a 
centrifugal hydraulic head relief valve in a rotating clutch in 
communication with a hydraulic actuator for closing in response to clutch 
actuating pressure and opening responsive to centrifugal force and a 
spring force acting on the valve to relieve residual pressure in the 
hydraulic actuator to avoid drag when the clutch is normally released. 
Hydraulic clutches in a rotating clutch assembly are normally actuated by 
pressurizing fluid in the pressurizing chamber of the hydraulic actuator 
which applies a force to a clutch disk stack to engage the clutch. When 
the pressure to the clutch is released, the clutch is only partially 
released because a portion of hydraulic fluid is retained in the supply 
passage and the pressurizing chamber in which centrifugal forces due to 
the rotation of the clutch produces a residual pressure in the 
pressurizing chamber. This force can be sufficient to cause a drag on the 
clutch disks which is objectionable. To relieve the residual pressure, 
valves have been provided in communication with the pressurizing chamber 
which act to relieve the hydraulic fluid. These relief valves operate to 
relieve the residual pressure in the pressurizing chamber of the hydraulic 
actuator but are not always completely satisfactory. The servicing of 
these valves can present a problem and because of inconvenience, the 
mounting of the valve within the clutch assembly may cause a contamination 
problem in the hydraulic oil and may require undue servicing. U.S. Pat. 
No. 2,642,844, Flinn, illustrates a valve assembly mounted within the 
rotating clutch for relieving of residual pressure in the hydraulic 
actuator. U.S. Pat. No. 3,534,840, Snoy, also discloses a relief valve in 
a clutch assembly for relieving the residual pressure in the hydraulic 
actuator. The relief valve shown in U.S. Pat. No. 2,642,844 is difficult 
to service and includes a spring biasing the valve radially inwardly to 
relieve residual pressure in the hydraulic actuator. Inertia forces 
operate on the valve in a radially outward direction and tend to operate 
against the spring. U.S. Pat. No. 3,534,840 shows a similar arrangement 
and is not provided with a means to assist the valve in moving to the 
release position other than centrifugal force. Contamination in the valve 
can cause ineffective relief of the residual pressure. The vent to the 
valve is in communication through a passage with the pressurizing chamber 
inwardly from the outer most portion of the pressurizing chamber. 
The applicant has provided a valve which is easily assembled, easily 
serviced and positive in operation. The valve is positioned in a radial 
opening in the clutch housing and is fastened with a cover which 
threadedly engages the threaded outer portion of the opening to maintain 
the valve in the assembled position. The valve is in communication with 
the radially outer portion of the hydraulic actuating chamber to assure 
that all of the fluid is vented from the chamber and avoid any residual 
pressure in the actuating chamber which may tend to produce a drag on the 
clutch disks. 
It is an object of this invention to provide a centrifugal hydraulic head 
relief valve for a rotating clutch. 
It is another object of this invention to provide a hydraulically actuated 
friction clutch having a relief valve for relieving centrifugal hydraulic 
head in the pressurizing chamber of the hydraulic actuator when the clutch 
is disengaged. 
It is a further object of this invention to provide a friction clutch 
having a relief valve for centrifugal hydraulic head opening responsive to 
centrifugal forces and a spring when the clutch is disengaged for closing 
responsive to clutch actuating pressure from the pressurizing chamber of 
the hydraulic actuator when the clutch is engaged. 
The objects of this invention are accomplished in a rotating clutch having 
a hydraulic actuator to apply a load to frictionally engaging disks when 
the clutch is engaged. Centrifugal hydraulic head normally produced by 
inertia forces on the hydraulic fluid in the supply passage and 
pressurizing chamber is released by the relief valve in response to a 
spring force and inertia forces on the valve to overcome fluid pressure on 
a predetermined area of the valve to relieve the pressure in the hydraulic 
actuator when the clutch is disengaged. The forces can be controlled by 
design to operate independent of speed of rotation. This prevents the 
hydraulic fluid from causing a drag on the clutch normally due to residual 
pressure in the conventional hydraulic clutch. The relief valve is closed 
in response to pressure of the clutch actuating fluid in the pressurizing 
chamber of the hydraulic actuator when the clutch is engaged. The valve is 
positioned radially in a radial position of the clutch housing and in 
communication with the radially outer portion of the pressurizing chamber 
of the hydraulic actuator to assure venting of all fluid in the chamber 
and avoid any residual pressure in the chamber. The valve can be easily 
assembled or disassembled for servicing to avoid any malfunctions which 
may be caused due to contamination of the hydraulic fluid.

Referring to the drawings, the hydraulic clutch assembly includes a clutch 
2. The transmission housing 3 encloses the rotating clutch assembly which 
includes a clutch drum 4 and a clutch hub 5. The reaction plate 6 is 
mounted on the end of the drum. The force actuating the clutch from the 
pressurized fluid acts on the end disk as the disc stack 160 is loaded. 
The disk stack 160 includes disks 7 carried by slots 9 of clutch disk 4. 
The disks 10 are carried on the spline 11 of the clutch hub 5. Normally, 
the piston 12 reciprocates within the cylinder 13 for engagement and 
disengagement of the clutch. The piston 12 forms a pressurizing chamber 14 
with the cylinder 13. The supply passage 15 supplies pressurized fluid to 
the pressurizing chamber 14. A relief passage 16 communicates between the 
pressurizing chamber 14 and the relief valve 17. 
The valve 17 consists essentially of a hollow shaft 18 seated in the 
central cone 19 at the base of the opening 20. A threaded portion 21 in 
the upper end of the opening threadedly receives the cover 22 which is in 
the form of a nut and can be tightened down against the shaft 18. The 
cover 22 is formed with a centering recess 23 which aligns the hollow 
shaft 18 within the opening 20. The cover 22 also firmly seats the shaft 
18 within its operating position. 
The valve sleeve 24 encircles the upper end of the hollow shaft 18 and is 
normally biased to the position as shown in FIG. 2 by the spring 25. A 
recess portion 26 provides a clearance between the upper end of sleeve 24 
to allow fluid above the valve sleeve. A socket 27 is provided in the 
upper end of the cover 22 to allow easy assembly and disassembly of the 
valve. 
The relief passage 16 is formed between the pressurizing chamber 14 and the 
valve 17. A vent passage 28 is provided radially from the valve to vent 
fluid from the valve when the relief valve 17 is in a position shown in 
FIG. 2. Radial passages 30 through hollow shaft 18 radially connect the 
central opening 30 with the recess 26. The radial passage 29 extends 
radially through the hollow shaft 18 to vent fluid from the central 
opening 30. 
Pressurized fluid from the pressurizing chamber 14 is in communication 
through the relief passage 16 and the hollow center opening 30 of the 
relief valve 18. When hydraulic fluid is pressurized in the pressurizing 
chamber 14, the fluid is allowed to enter the recess 26 through passages 
31, which biases the relief valve 24 downwardly to the position shown in 
FIG. 3 against the spring 25. In this position, the radial exit passage 29 
is closed. The valve remains in this position as long as there is 
pressurized fluid in the pressurizing chamber 14. No fluid is allowed to 
flow through the vent 28. 
The operation of the device will be described in the following paragraphs. 
Referring to FIG. 1, the clutch assembly is rotatably mounted within the 
transmission housing 3. When the clutch 2 is disengaged, the spring 25 
biases the relief valve 24 upwardly to the position as shown in FIG. 2. 
Fluid in the pressurizing chamber 14 is allowed to pass through the relief 
passage 16, through the central opening 30 and the radial exit openings 29 
and also through the vent passage 28 to relieve the pressure in the 
pressurizing chamber 14. Normally, when the clutch drum 4 is rotating and 
the hydraulic clutch is disengaged, fluid in the pressurizing chamber is 
relieved to avoid partial engagement causing a drag on the clutch disks. 
When pressurized fluid is admitted through the supply passage 15 to the 
pressurizing chamber 14, the pressurized fluid also flows through the 
relief passage 16 and a central opening 30 of the hollow shaft 18. 
Pressurized fluid is allowed to flow through passages 31 into the recess 
26 which biases the valve downwardly as shown in FIG. 3. The downward 
movement of the relief valve 24 closes the radial exit opening 29. This 
closes the valve and prevents escape of pressurized fluid from the 
pressurizing chamber 14 as the clutch is actuated. The valve will remain 
in this position so long as the pressure is great enough to compress the 
spring 25 to the position as shown in FIG. 3. When the clutch is released, 
the spring 25 and the centrifugal force on the relief valve 24 again 
extend radially outward to the position as shown in FIG. 2. 
The relief valve closes at a predetermined pressure which moves the sleeve 
24 downwardly against the force of the spring 25. A special feature of 
this invention is the way the valve is mounted in the clutch housing. When 
the clutch rotates, a centrifugal force will act on the sleeve 24 causing 
it to be forced in the same direction as the spring force. Centrifugal 
force will also act on the fluid in the pressurizing chamber 16 and all 
other fluid chambers connected to chamber 16 that rotate with the clutch 
housing. It is understood that although the supply passage is illustrated 
schematically, a supply passage similar to that of passage 115 for the 
clutch 116 might also be used. This would cause a force on the hydraulic 
fluid in the supply passage as well. The centrifugal force that acts on 
the hydraulic fluid in the supply passage, pressurizing chamber and the 
relief valve fromthe clutch rotation produces a pressure that acts on the 
area of the piston to bias it against the force of the spring 25. By 
design, the pressure times the area of the piston can be made equal to the 
centrifugal force acting on the sleeve 24 but in the opposite direction. 
If these forces cancel each other, then the valve operating pressure can 
be predetermined by the area of the sleeve and the spring load so that the 
valve opening pressure when measured at the valve is for all practical 
purposes independent of clutch rotating speeds.