Integral dust cover and pump drive

A chain saw having an outboard mounted centrifugal clutch adapted to drive an automatic lubricating pump. A cavity is formed in the portion of the housing from which the drive shaft protrudes. A worm gear for activating the lubrication pump is mounted in the cavity. A combination seal and worm gear drive member is slidably fit with the adapter of the clutch cup with a worm gear driver portion engaged with the worm gear. A disc shaped seal portion includes a lip that fits into a groove surrounding the cavity, held in place through engagement of the worm gear driver with the worm gear.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to chain saws having automatic lubricating systems 
wherein the lubrication is pumped to the saw chain and guide bar in 
reaction to engagement of the clutch for driving the saw chain, and more 
particularly it relates to a member that combines the functions of 
generating the drive for the lubricating pump and providing a seal around 
the pump to protect against dust and dirt contamination. 
2. Background Information 
On motorized chain saws, an endless saw chain is propelled by a drive 
sprocket coupled to a centrifugal clutch and is guided and travels in a 
formed groove in an elongated guide bar. The saw chain is guided and 
travels in the groove of the guide bar in a sliding metal-to-metal 
contact. To prevent heat build up, which could damage both the saw chain 
and guide bar, caused by the sliding metal-to-metal contact and also to 
reduce friction, a lubricating system is incorporated within the chain saw 
housing. 
The lubricating system has a reservoir that provides a supply of oil to a 
pump mechanism. When driven, the pump mechanism delivers oil to an 
aperture in the side wall of the groove of the guide bar via a connecting 
passageway, thereby providing lubricant to the saw chain and the groove of 
the guide bar. 
The lubricating systems on most chain saws are automatic. That is, oil is 
supplied to the saw chain and guide bar only when the saw chain is 
propelled by the engagement of the centrifugal clutch. To provide this 
automatic feature, the pump drive is therefore also coupled to the 
centrifugal clutch that propels the saw chain. 
In a common embodiment, the lubricating pump drive is coupled to the 
centrifugal clutch by utilizing a worm gear drive in the form of a 
threaded hub that is in turn driven by the shaft of the driven clutch cup. 
(This shaft is commonly referred to as the adapter in that it adapts a 
particular drive sprocket to the standard chain saw drive.) The worm gear 
driver is in mesh with a worm gear, and when rotated by the clutch cup, it 
in turn provides rotation to the worm gear which drives the pump 
mechanism. 
Since chain saws are operated in an environment where wood chips, sawdust 
and other debris are always present, a seal is provided to protect the 
pump drive components from these elements. The seal is typically a plastic 
cylindrical disc that is mounted and rotates with the adapter of the 
clutch cup. It has a protruding lip on its periphery. A metal washer is 
sometimes used between the seal and the face of the housing. The face of 
the housing has a circular groove or recess and the lip of the seal is 
designed to rotate inside the groove of the housing to cooperatively seal 
out the debris. 
The mounting of the seal in the above-described fashion has some 
shortcomings. The adapter and the clutch cup to which it is rigidly 
attached, by design, is permitted some axial float on the drive shaft of 
the chain saw. The seal being attached to the adapter will float or move 
away from the housing when the adapter and hub move axially away from the 
housing face. Movement of the seal away from the housing face provides a 
space for the entrance of wood chips, dust, etc. into the pump drive 
mechanism. The seal could also become partially dislodged from its 
frictional mount and therefore would wobble during rotation and provide an 
opening for entrance of wood chips, etc. 
SUMMARY 
Providing an effective seal for the oil pump drive mechanism is necessary 
due to the operating environment that is present during the operation of 
chain saws. 
The present invention provides an improved retention of the rotary seal 
that protects the pump drive mechanism from the contaminants of the 
operating environment. The improvement in seal retention is accomplished 
by integrating the worm driver and seal into a unit and thereby utilizing 
the axial force caused by the rotational resistance of the worm gear 
acting on the helix of the worm driver. The result is improved operation 
while reducing cost. The single member is believed to be less expensive to 
produce than the combination of elements of the prior art, and it is 
easier to assemble into the chain saw.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
With reference to the drawings, FIG. 1 is an exploded view of a chain saw 
housing 10. A cavity 11 in face 17 of the housing has an output or drive 
shaft 12 protruding outwardly therefrom. Rotatably mounted above and 
transverse to the output shaft 12, but within cavity 11, is an oil pump 
worm gear 14. An annular groove 16 that is concentric to the rotational 
axis of output shaft 12 (and surrounds the cavity 11) is formed in face 17 
of the housing 10. 
The above components of a chain saw are typical of conventional chain saws 
having outboard clutch mechanism. FIG. 2 illustrates the conventional 
components utilized in the prior art (shown in exploded view) that 
interconnect to the drive shaft 12 for driving the saw chain. They include 
a worm gear driver 18 that fits loosely over shaft 12 and engages worm 
gear 14 of the housing shown in FIG. 1. A metal washer 20 surrounds the 
worm gear driver 18 and a plastic seal 22 also surrounds the worm gear 
driver 18 and metal washer 20 in a manner that permits the annular lip 23 
of the seal 22 to ride in the groove 16 of the housing face 17. The 
adapter 30 of the clutch cup 32 is configured with external splines 33 
engaging spline grooves 35 of the rearwardly protruding flange 29 of the 
seal 22. The seal 22 is thus caused to be rotated with rotation of the 
clutch cup 32. Lug portions 31 on the end of adapter 30 are configured to 
project into receiving slot 19 in the worm gear driver 18. 
As will be apparent, the worm gear driver 18 is rotatably driven by adapter 
30 and seal 22 is also rotatably driven by adapter 30, but the seal 22 and 
worm gear driver 18 are independent of each other. As previously 
mentioned, the clutch cup 32 and its adapter 30 are designed to have 
slight axial movement relative to shaft 12. The worm gear driver 18 is 
engaged with worm gear 14 (FIG. 1) so that it seeks to pull the worm gear 
toward the driver (or vice versa) by forcing rotation in a 
counter-clockwise direction as viewed in FIG. 1 (see arrow 41). Thus, gear 
driver 18 does not move with the axial movement of the adapter 30. As the 
adapter 30 is pulled away from the worm gear driver, lug portions 31 can 
become disengaged from slots 19, particularly as the tip of the lug 
portion 31 and/or the slots 19 become worn. As concerns seal 22, as the 
adapter 30 is pulled away from the housing, seal 22 will move away from 
the groove 16 to expose the cavity 11 and worm gear 14 to the debris 
generated during the cutting action. Both of these undesired occurrences 
are cured by the device of the present invention which will now be 
explained. 
An integral combination member 34, which includes a gear driver, seal and 
washer is illustrated in FIGS. 1, 3, 4, 5 and 7. The configuration of 
member 34 comprises a cylindrical disc having a hub 37 protruding axially 
from the inner face 42 of the cylindrical disc. The disc and hub are 
concentric to a common bore 36, with the bore 36 being sufficiently large 
to provide a loose fit of member 34 on output shaft 12. (see FIG. 1) 
Screw threads 38 are provided on the protruding hub 37 and provide the worm 
gear driver action of previously described member 18 of FIG. 2. The screw 
threads 38 mesh with the oblique grooves of the worm gear 14. There is a 
lip 40 at the periphery of the cylindrical disc of member 34. The lip 40 
protrudes beyond the inner face 42 and enters the annular groove 16 of the 
chain saw housing face 17 when member 34 is mounted on the output shaft 
12. The lip 40 is narrower and shallower than annular groove 16, 
therefore, the lip 40 enters the groove 16, but is not in physical contact 
with either the side edges or the bottom of the groove 16. 
Drive slots 48 as shown in FIGS. 4 and 5 are inset into the face of member 
34 opposite the protruding hub 37. The drive slots are configured and 
positioned to be aligned and positively engaged by the protruding drive 
lugs 39 (FIG. 1) of the clutch cup adapter 30. The drive slots 48 have a 
sufficient depth to permit the axial float of the driving lugs 39 of the 
clutch adapter 30, without changing the axial position of the member 34. 
The driving lugs 39 of the clutch adapter 30 are sufficiently long to 
provide positive engagement with the drive slots 48 within the limits of 
the axial float of the clutch adapter 30. 
With particular reference to FIGS. 1 and 7, the member 34 is placed on the 
output shaft 12, with the threads 38 of the worm gear driver hub 37 
engaging and meshed with the worm gear 14. When the worm gear driver (hub 
37 and threads 38) meshes with worm gear 14, the lip 40 of member 34 
simultaneously enters the annular groove 16 of the housing face 17, and 
also positions the inner face 42 in close proximity to the chain saw 
housing face 17. 
The overall assembly of the chain saw and driver components is shown in the 
perspective, exploded view of FIG. 6. A guide bar 28 is rigidly fastened 
to the chain saw housing by bolts protruded through the mounting slot 27. 
An endless saw chain 25 is positioned in the guide slot 21 on the 
periphery of the guide bar 28. A rim sprocket 24 is mounted to the adapter 
30 of the clutch cup, adjacent one end of the guide bar 28. The clutch cup 
32 with adapter 30 is positioned on the output shaft 12, with the rim 
sprocket 24 fitting in splined engagement on the adapter 30. The 
protruding drive lugs 39 of the adapter 30 are aligned and enter the drive 
slots 48 (not shown in FIG. 6) of the member 34. Rigidly attached to the 
output shaft 12 is a centrifugal clutch (inside the clutch cup 32) which 
engages and rotatively drives the clutch cup. 
When assembled, (see FIGS. 1 and 7) the clutch mechanism 44 located inside 
cup 32 is retained on shaft 12 by nut 46 (outboard of washer 50) screwed 
onto the screw threads 52 on the end of shaft 12. 
When the output shaft 12 exceeds a predetermined RPM, the centrifugal 
clutch mechanism 44 frictionally engages the wall of the clutch cup 32 to 
rotate the clutch cup, adapter, rim sprocket (which drives the saw chain) 
and the member 34. The rotation of member 34, through screw threads 38 on 
hub 37, provides rotary motion to the worm gear 14 which drives the oil 
pump mechanism (not shown). The interengagement of screw threads 38 with 
worm gear 14 also urges the member 34 axially toward the housing 10, 
thereby maintaining the sealing interconnection between lip 40 of member 
34 and groove 16 of housing 10. The member 34 is retained in position 
against the housing 10 regardless of the axial float of the clutch cup 32 
and adapter 30. 
The above embodiment is considered the preferred embodiment of the 
invention. Others having skill in the art will likely perceive of 
alternative embodiments, improvements or modifications without departing 
from the scope of the invention as defined in the following claims.