Grease loaded grapple dampener

A grease loaded dampener for the swivel link of a grapple skidder is mounted to the pivot pin of the swivel link. The dampener is provided with two sets of friction plates. The friction plates are compressed by an annular piston that is slidably mounted to a bushing that is secured to the pivot pin. A grease zerk supplies grease to the cylinder formed between the bushing and the annular piston. A pressure relief valve is in fluid communication with the cylinder and prevents the cylinder from becoming over pressurized unduly compressing the friction plates.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention is directed to a grease loaded dampener for a grapple skidder 
having a pressure relief valve to prevent over compressing the friction 
plates. 
2. Description of the Prior Art 
Grapple skidders are forestry work vehicles used to haul logs in rugged 
terrain. The skidder is typically provided with a boom that can be 
manipulated into a variety of positions. A grapple is mounted to the end 
of the boom by a swivel link. The swivel link is pivotally coupled to the 
boom by a first pivot connection and pivot pin, and to the grapple by a 
second pivot connection and pivot pin. 
Each pivot connection of the swivel link is typically provided with at 
least one dampener for dampening any excessive oscillations occurring in 
the swivel link by the swinging movement of the unloaded grapple. 
Typically the first pivot connection is provided with a first dampener 
that comprises a first set of friction plates located on a first pivot 
pin. The first set of friction plates are operatively coupled to the 
swivel link and the boom. Similarly, the second pivot connection is 
provided with a second dampener that comprises a second set of friction 
plates located on a second pivot pin. The second set of friction plates 
are operatively coupled to the swivel link and the grapple. 
The pivot pins may be stepped pins having an enlarged portion adjacent to 
the pivot connection and a smaller portion on which are mounted the 
friction plates. The smaller portion is also provided with a threaded 
surface for receiving a jam nut and a retaining washer for compressing the 
friction plates. The operator at selected intervals tightens the jam nut 
with a torque wrench compressing the friction plates to ensure proper 
braking force. Such dampeners are disclosed in U.S. Pat. No. 4,417,759, 
assigned to the assignee of the present application. 
Instead of a jam nut and a retaining washer to supply a compressing force 
on the friction plates, hydraulic and grease loaded dampeners have also 
been proposed. See U.S. Pat. Nos. 3,301,587 and 4,572,567. Grease loaded 
dampeners use pressurized grease to drive a piston against the friction 
plates to increase the braking force. Such a dampener is disclosed in U.S. 
Pat. No. 4,679,839. The operator when greasing the machine injects grease 
through a grease zerk into the dampener. This drives the piston towards 
the friction plates increasing the braking force. 
Operators must periodically adjust the compression force of the jam nut on 
the mechanical dampener, or apply grease to the grease dampener. Many 
times operators over-tighten the jam nut and over-pressurize the grease 
dampener. This excessive compression force on the friction plates leads to 
accelerated wear on the friction plates and their early replacement. 
SUMMARY 
It is an object of the present invention to provide a dampener that cannot 
be overly compressed. 
It is a feature of the present invention that the dampener of the present 
invention is a grease loaded dampener that is provided with a pressure 
relief valve. 
The present invention comprises a grease loaded dampener for a swivel link. 
The swivel link extends between a boom and a grapple on a grapple skidder. 
The swivel link is provided with two pivot connections, each of which are 
provided with pivot pins. Friction plates are mounted to the pivot pins. A 
first set of friction plates is mounted on the first pivot pin and 
operationally extend between the swivel link and the boom. A second set of 
friction plates is mounted to the second pivot pin and operationally 
extend between the swivel link and the grapple. 
The friction plates are compressed by first and second grease loaded 
dampeners mounted to the first and second pivot pins, respectively. Each 
of the grease loaded dampeners comprises a stationary bushing mounted to 
the pivot pin and an annular piston slidably positioned on the bushing. 
Grease is applied to the cylinder formed between the piston and bushing 
through a grease zerk. Also in fluid communication with the so-formed 
cylinder is a pressure relief valve which drains grease from the dampener 
if the cylinder becomes over-pressurized.

DETAILED DESCRIPTION 
FIG. 1 illustrates a grapple skidder 10 having a supporting frame 12 and 
wheels 14. The wheels comprise ground engaging means for supporting and 
propelling the supporting structure. The supporting structure is provided 
with an engine compartment 16 and an operator's cab 18. A dozer blade 20 
extends from the front of the supporting frame by a suitable linkage, not 
shown. 
A boom 22 is pivotally mounted to the rear of the supporting structure. It 
can be selectively positioned by boom positioning hydraulic cylinders 24. 
A grapple 26 having tongs 28 is supported from the boom by swivel link 30. 
The grapple may be rotated relative to the boom by a hydraulic motor 
located in the top of the boom at 32. It should be noted that the rotator 
motor could also be located in the head of the grapple. 
The swivel link is best illustrated in FIG. 2 and is provided with first 
and second orthogonal pivot connections 34 and 36, respectively. Each 
pivot connection is relatively conventional having two pivot pins located 
on opposite sides of the vertical centerline of the swivel link. In 
describing the present invention, the first pivot connection will be 
defined as having a first pivot pin, and the second pivot connection will 
be defined as having a second pivot pin. The first and second pivot pins 
are not necessarily the only pivot pins associated with each pivot 
connection, but are the ones to which the first and second grease loaded 
dampeners are mounted. 
The first pivot connection is provided with a first stepped pivot pin, not 
shown, which is identical to the second stepped pivot pin 38 located in 
the second pivot connection 36. The stepped pivot pin is provided with an 
enlarged portion 40 and a smaller portion 42. The enlarged portion of the 
first and second pivot pins carry the pivot journals for pivotally 
supporting the swivel link relative to the boom and the grapple relative 
to the swivel link respectively. The dampener is mounted to the smaller 
portion of the stepped pivot pins. 
It should be noted that the second grease loaded dampener of the second 
pivot connection will be discussed in detail as it is identical to the 
grease loaded dampener of the first pivot connection. 
The second grease loaded dampener illustrated in FIG. 2 is structurally 
identical to the first grease loaded dampener, except that it dampens 
oscillations between the swivel link and the grapple; whereas the first 
dampener reduces the oscillations between the boom and the swivel link. 
The second grease loaded dampener comprises a second set of friction 
plates 46. These plates are mounted to the smaller portion 42 of the 
second pivot pin. Two of the friction plates 48 are tanged to channel 50 
which is integral with the swivel link. The channel 50 is formed by two 
outwardly projecting members, and is provided with two bearing blocks 51 
which contact the side edges of the friction plates extending into the 
channel. The three remaining friction plates 52 are sandwiched around 
friction plates 48 and are tanged to U-shaped catch 54 which is bolted to 
the grapple. 
In the first pivot connection, some of the first set of friction plates 45 
are tanged to the swivel link by channel 47 having bearing blocks 49 and 
the remaining plates are tanged to the boom by U-shaped catch 53 which is 
bolted to the boom. It should be noted that U-shaped catches identical to 
the ones used for coupling the friction plates to the boom and grapple 
head can be used to couple the friction plates to the swivel link rather 
than the integrally formed channels. The remaining elements of the first 
pivot connection are identical to the second pivot connection and as such 
the numbers used for identifying these elements will be the same. 
The friction plates are contacted by Belleville springs 56. The Belleville 
springs in turn are contacted by annular piston 58 which is slidably 
mounted to bushing 60. The piston together with the Belleville springs 
forms a means for applying a compressing force to the friction plates. 
Bushing 60 is mounted to the pivot pin and restrained from outward 
movement by washer 62 and bolt 64. Bolt 64 is axially received in the end 
face of the pivot pin. A donut-shaped cylinder 66 is formed between the 
bushing and the annular piston. This cylinder is sealed by suitable seals 
68. Pressurized grease can be injected into this space by a grease gun 
through grease zerk 70. The cylinder forms a means for increasing the 
compressing force applied to the friction plates by the piston and 
Belleville washers. 
Pressure relief valve 72 is in fluid communication with cylinder 66 and is 
used to drain off excess grease when the cylinder becomes over-pressurized 
with grease. Such a pressure relief valve is supplied by Fluid Line 
Products, of Willoughby, Ohio. The pressure relief valve forms a means for 
limiting the amount of compressing force applied to the friction plates. 
The pressure setting on the pressure relief valve can be set so that it 
corresponds to the highest desired pressure applied to the friction 
plates. In this way an operator applies grease to the grease zerk until 
grease is expelled through the pressure relief valve. 
With this invention an operator of the cable skidder can grease the 
dampener whenever he is greasing the other joints of the skidder. The 
pressure relief valve insures that the dampener is properly pressurized at 
all times. 
The present invention should not be limited to the above described grease 
loaded dampener, but should be limited solely by the claims that follow.