Shaft seal assembly having universal washer with bores for springs

A shaft seal assembly for an aircraft engine fuel pump has a seal housing (30) mounted upon the pump housing (32). A carbon face seal (42) is in wiping engagement with a seal face (40) on the drive shaft (36) of the pump. The carbon face seal has a recess (46) which receives a projection (44) for preventing face seal rotation. A universal washer (46), which is mounted in the seal housing in front of the carbon face seal, embodies four protuberances (48, 50, 52, 54) having bores (56, 58, 60, 62) which extend completely through the universal washer. Compression springs (64, 66) are contained in the bores and have their rear and front extremities in respective engagement with washers (70, 72) disposed on either side of the universal washer. The spring force, which is transmitted to the carbon face seal by the front washer, is overcome as pump pressure pushes the shaft toward the front of the pump. In the compressed condition, non-axial shaft alignments are accommodated by the universal washer.

TECHNICAL FIELD 
This invention relates to shaft seals, and more particularly, to shaft 
seals for aircraft engine fuel pumps. 
BACKGROUND ART 
While existing shaft seals assemblies for aircraft engine fuel pumps 
exhibit satisfactory performance, they have a relatively large number of 
parts which mandate a long length and a consequential tolerance stack-up 
which requires shimming to adjust the spring load to its operation range. 
In addition, certain shaft seal assemblies embody antirotation washers 
with bent tabs which may scar the carbon face seal. 
DISCLOSURE OF INVENTION 
A seal assembly of the invention may essentially comprise a carbon face 
seal and a relatively thick universal or gimbal washer, having springs 
extending therethrough at the bulges or protuberances thereof, sandwiched 
between two conventional washers. In a seal assembly of the invention the 
carbon face seal may incorporate one or more longitudinally extending 
recesses in its outer periphery for receiving a projection on the seal 
housing, thereby to prevent any rotation of the carbon face seal. 
A seal assembly of the invention is advantageous in that it is shorter than 
conventional seals and incorporates fewer parts, thereby obviating 
shimming to place the spring load in its operating range. In accordance 
with the invention, a seal assembly thereof does not mandate the inclusion 
of a thrust washer, an antirotation washer or cavities in the seal housing 
for mounting the springs. In contradistinction to a conventional seal 
assembly wherein the thrust washer is employed to minimize cycling of the 
springs during operating, it will be appreciated that in a seal assembly 
according to the invention the cycling of springs is also minimal because 
of their being disposed at the pivot points of the universal washer 
whereby the springs are essentially inoperative. 
Accordingly, it is a primary object of the invention to provide a 
relatively short shaft seal assembly having a minimal number of parts.

BEST MODE OF CARRYING OUT THE INVENTION 
With reference to FIGS. 1 and 2, it would be profitable to briefly examine 
the construction of a typical conventional shaft seal assembly for an 
aircraft engine fuel pump before describing a seal of the invention. The 
seal assembly of FIGS. 1 and 2 includes a seal housing 2 secured to a pump 
housing 4 by means of bolts 6. A pump drive shaft 8, having a flange 10 
with a seal face 12 formed thereupon, extends into the housing away from 
its splined end where it is in driving connection with a rotating pump 
component such as a gear or the like. When the pump is operating normally, 
pressure forces urge the shaft 8 to the left or toward its splined end. 
The necessary sealing action is furnished by the engagement of a carbon 
face seal 14 and the seal face 12 during engine starting and normal engine 
operation. 
To the rear or left of the carbon face seal 14 is an antirotation washer 16 
which is cutaway on its periphery to receive a rotation preventing pin 18 
mounted in the seal housing 2. The washer 16 also incorporates a bent tab 
20 which is contained in a peripheral recess at the rear of the carbon 
face seal 14. Washer 16 basically serves to transfer torque from the 
carbon face seal 14 to the pin 18 whereby the face seal will not undergo 
any rotational movement. Behind the washer 16, a universal or gimbal 
washer 22 (sometimes termed a dimpled washer) is mounted in the seal 
housing 2 for accommodating non-axial shaft alignments. Interposed between 
the universal washer 22 and a plurality of springs 24 is a thrust washer 
26 which urges the universal washer forwardly. It will be noted that each 
of the springs 24 is mounted in a cavity 28 in the seal housing 2. After 
pressure forces build to an extent sufficient to urge the thrust washer 26 
to the rear against the seal housing 2, the springs 24 will only extend 
when the shaft is no longer axially aligned with the seal axis. 
A shaft seal assembly of the invention is shown in FIGS. 3 and 4. With 
reference thereto, a seal housing 30 is secured to a pump housing 32 by 
bolts 34. A pump drive shaft 36, having a flange 38 with a seal face 40 
formed thereupon, extends into the pump housing 32 into driving connection 
with a rotating pump component. During normal operation, pressure forces 
urge the shaft 36 to the right. A carbon face seal 42, mounted for axial 
movement within the seal housing 30, engages the seal face 40 during 
engine starting and normal engine operation whereby sealing engagement is 
thereby provided in a manner similar to that of the shaft seal of FIG. 1. 
From FIGS. 3 and 4, it may be seen that rotation of the carbon face seal 42 
is prevented by a rounded projection 44 on the inner periphery of the seal 
housing 30 which is received within a similarly shaped rounded recess 46 
in the carbon face seal 42. It will be appreciated that such an 
antirotation feature will not trammel the axial movement of the carbon 
face seal. An alternative approach (not illustrated) to the aforedescribed 
antirotation arrangement would be the provision of a steel ball half 
contained in a hemispherical recess in the outer surface of the carbon 
face seal and half contained in an axially extending recess on the inner 
periphery of the seal housing 30. Another alternative design would be that 
shown in FIG. 1 wherein a conventional antirotation washer is employed. 
With regard to the latter mentioned antirotation arrangement, it will 
become apparent from the ensuing description that such an arrangement will 
not occasion an increase in seal length since a washer or spring set of 
some sort must in any event be placed against the front or non-wiping face 
of the carbon face seal 42. 
The heart of the illustrated seal assembly is a universal or gimbal washer 
46 mounted in the seal housing 30. The universal washer 46 is generally 
identical in shape to that shown in FIG. 2 save for increased thickness. 
The washer 46 has four protuberances or dimples 48, 50, 52 and 54 
thereupon, whereby the washer 46 is pivotable about any axis orthoginal to 
the axis of the shaft 36 in the manner of a conventional universal washer. 
It will be noted that the protuberances 48 and 50 are diametrically 
opposed on the rear face of the washer 46 and that the protuberances 52 
and 54 are diametrically opposed on the front face of the washer 46 and 
are spaced ninety degrees from the protuberances on the rear face thereof. 
Bores 56, 58, 60 and 62 are centrally disposed in the respective 
protuberances 48, 50, 52 and 54 and extend from the front to the rear face 
of the washer 46. 
Compression springs 64 and 66 are contained within the respective bores 56 
and 58 and have their extremities extending well beyond the front and rear 
faces of the washer 46. Bores 60 and 62 contain similar springs (not 
shown). Preferably, four springs should be utilized although it will be 
understood that two could suffice for certain applications. On either side 
of the universal washer 46, washers 68 and 70 are mounted in the seal 
housing 30. Washer 68, which serves as a spring seat, abuts the front 
inner wall 72 of the seal housing whereas washer 70 abuts the front face 
of the carbon face seal 42. The front extremities of the springs seat 
against the washer 70 whereby the carbon face seal 42 is biased into 
engagement with the seal face 42. 
During engine starting, the carbon face seal 42 will be held in engagement 
with the seal face 40 by the urging of the springs in the seal assembly. 
As engine speed increases, fuel pressure acting on the rear or left side 
of the flange 38 will correspondingly increase until it overcomes the 
spring force, whereby the shaft 36 will move to the right when viewed in 
FIG. 3. Movement of the shaft 36 to the right results in rightward axial 
movement of the carbon face seal 42 and washer 70 in the seal housing 30. 
During such axial movement, washer 70 will engage the protuberances 48 and 
50 whereupon the universal washer 46 will be axially displaced rightwardly 
or toward the front of the pump until protuberances 52 and 54 contact the 
washer 58 whereby the seal assembly will be fully compressed. After 
compression of the seal assembly, alignment variations in the shaft will 
be accommodated by the universal washer 46. Because the springs are 
located at the points of rotation of the universal washer, minimum cycling 
of the springs will be engendered. It will be appreciated that although 
the universal washer embodies bores in the protuberances which beget 
higher stresses therein, the additional thickness of the universal washer 
renders such stresses acceptable. 
Obviously, many variations and modifications are possible in light of the 
above teachings without departing from the scope or spirit of the 
invention as defined in the appended claims: