Excavating – Snow or ice removing or grooming by portable device – Including specific hydraulic control system to position...
Reexamination Certificate
2003-01-07
2004-03-02
Pezzuto, Robert E. (Department: 3671)
Excavating
Snow or ice removing or grooming by portable device
Including specific hydraulic control system to position...
Reexamination Certificate
active
06698113
ABSTRACT:
FIELD OF THE INVENTION
This disclosure concerns an invention relating generally to actuators for heavy machinery, and more specifically to fluid actuators (i.e., hydraulic and/or pneumatic actuators) used in snowplows to reposition plow moldboards with respect to the plowing vehicle.
BACKGROUND OF THE INVENTION
In machinery wherein heavy components are repositioned with respect to the remainders of the machines—for example, in plows where plow moldboards are repositioned with respect to the plowing vehicle—it is often useful to have some form of means for decelerating the heavy component as it approaches the remainder of the machine to reduce the chance of collision between components. As an example, consider
FIG. 1
, which illustrates an exemplary snowplowing vehicle at
100
. The snowplowing vehicle
100
has a front moldboard
102
, and a side moldboard
104
(commonly referred to as a wing plow because it is unfoldable from the plowing vehicle
100
like a wing). The wing plow
104
is hingedly affixed to the plowing vehicle
100
at an inner end
106
, and a fluid actuator
108
(generally a hydraulic actuator) extends between the plowing vehicle
100
and the midsection of the wing plow
104
to move the wing plow
104
between the folded and unfolded positions. When standard hydraulic actuators are used at
108
, problems sometimes arise when the actuator
108
is retracted. The wing plow
104
is pulled towards the plowing vehicle
100
, and depending on the fastening arrangement between the wing plow
104
and the plowing vehicle
100
, its retraction speed may increase as the wing plow
104
approaches the plowing vehicle
100
. This may lead to collision between the wing plow
104
and the plowing vehicle
100
, particularly when the wing plow
104
is more flexible and/or when the retraction speed is high. Even where the wing plow
104
is withdrawn at constant or diminishing speed, the inertia of the heavy wing plow
104
generally causes it to overshoot its standard at-rest folded position during retraction, and thereby causes it to collide with a plowing vehicle
100
.
Because of the size and weight of the wing plow
104
, it is capable of inflicting thousands of dollars of damage on the plowing vehicle
100
if the impact is significant. Such damage often occurs owing to the speed of plowing operations. Cities and counties necessarily try to limit their fleets of plowing vehicles
100
to no more than the minimum number of plows necessary because each plowing vehicle
100
involves a significant capital investment which is only used during a small portion of the year. However, during periods of heavy snow, public safety demands that the roads be cleared as soon as possible. Thus, the operator of each plowing vehicle
100
is concerned with clearing as much snow as possible, as soon as possible. The plowing vehicles
100
are therefore operated at slow driving speeds, generally 20-30 mph in residential areas, though faster speeds may be used on highways and on highly-traveled thoroughfares where fast clearance is needed for safety. During operation, the plow moldboards must often be rapidly repositioned for effective road clearance and/or to avoid obstacles, and the need for rapid repositioning may increase where there are driving conditions of low visibility. As an example, the wing plow
104
may need to be rapidly folded adjacent the plowing vehicle
100
when the operator of the vehicle
100
suddenly sees a mailbox or other object within the path of the wing plow
104
. The wing plow
104
may then be retracted at such a speed that it strikes the cab of the vehicle
100
, which may cause significant damage. The problem cannot be avoided by driving more slowly owing to the aforementioned need for rapid plowing; additionally, the operator cannot simply allow the wing plow
104
to strike objects in its path, since this will rapidly destroy the wing plow
104
(as well as the vehicle hydraulics owing to the shock to actuator
108
).
A number of modifications have been made to plow actuators (such as actuator
108
) to attempt to allow more rapid actuation without impact on the plowing vehicle
100
. A first approach is illustrated in
FIG. 2
, wherein a cross-sectional view of a modified wing plow fluid actuator
200
is shown. The fluid actuator
200
includes an actuator arm
202
which is driven by a piston
204
moving within a cylinder casing
206
. One of the piston
204
and the cylinder casing
206
is affixed to the plowing vehicle
100
or associated structure, while the other is affixed to the plow moldboard or associated structure, so that extension and retraction of the piston
204
within the cylinder casing
206
actuates the plow moldboard with respect to the plowing vehicle
100
. Within the cylinder casing
206
, the piston
204
is driven by fluid pumped into (or from) a face port
208
situated in front of the face of the piston
204
, and a tail port
210
situated on the opposite side of the piston
204
. Hydraulic lines
212
are shown connected to each of the face port
208
and tail port
210
. A restrictor
214
containing an orifice with reduced flow area is situated between the face port
208
and its hydraulic line
212
. Thus, when the actuator arm
202
is retracted within the cylinder casing
206
by pumping hydraulic fluid into the tail port
210
and/or out of the face port
208
, the restrictor
214
causes the piston
204
to travel more slowly owing to the decreased flow area it presents for withdrawal of hydraulic fluid. While this works well in helping to deter harsh impact of the wing plow
104
on the plowing vehicle
100
, it is disadvantageous in that folding and unfolding of the wing plow
104
is slowed throughout the entire range of motion of the actuator arm
202
. Therefore, this modification is disadvantageous where the wing plow
104
needs to be rapidly deployed or withdrawn.
Owing to this problem, the fluid actuator
300
shown in
FIGS. 3-4
was developed. Such a fluid actuator
300
is commonly referred to in the industry as a “cushion cylinder” or “decel” (deceleration) cylinder because retraction is initially fast, but it slows in the latter part of retraction to avoid the shock of moldboard impact. Fluid actuator
300
is similar to the fluid actuator
200
in that it has an actuator arm
302
driven by a piston
304
within a cylinder casing
306
by fluid being pumped into or out of a face port
308
and a tail port
310
via hydraulic lines
312
. However, the piston
304
is modified so that it will decelerate during retraction. This is done by providing a cavity
316
in the sides of the piston
304
adjacent the cylinder casing
306
, and an aperture
318
in the face of the piston
304
which opens onto the cavity
316
. Thus, as the piston
304
is retracted, it will initially block the face port
308
(as shown in FIG.
3
). Once the piston
304
is sufficiently retracted that the face port
308
opens onto the cavity
316
(as shown in FIG.
4
), hydraulic fluid in front of the face of the piston
304
will flow through the aperture
318
, into the cavity
316
, and then through the face port
308
. The aperture
318
is formed with smaller flow area than the face port
308
. Therefore, once the piston
304
moves rearwardly of the face port
308
, the effective flow area for escape of hydraulic fluid from in front of the face of the piston
304
is reduced, causing the piston to retract at slower speed. The piston
304
therefore has a higher retraction speed over a first portion of its retraction, and a slower retraction speed over the latter portion of its retraction. An optional restrictor
314
having a function similar to that of restrictor
214
is also shown, and may be omitted if desired.
This arrangement works very well to avoid collision between the wing plow
104
and the plowing vehicle
100
, but is subject to certain disadvantages. The fluid actuator
300
is not well suited for mass manufacture because different plowing vehicles
100
have hydraulic pumps of different capaciti
Gagnon Martin
Jones Jayson D.
DeWitt Ross & Stevens S.C.
Fieschko, Esq. Craig A.
Pezzuto Robert E.
LandOfFree
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