U.S. patent application number 15/258430 was filed with the patent office on 2016-12-29 for pallet truck assembly.
The applicant listed for this patent is RYDER MATERIAL HANDLING ULC. Invention is credited to Mark Keen, Michael Novak, Thomas Ryder.
Application Number | 20160375920 15/258430 |
Document ID | / |
Family ID | 52274432 |
Filed Date | 2016-12-29 |
United States Patent
Application |
20160375920 |
Kind Code |
A1 |
Keen; Mark ; et al. |
December 29, 2016 |
PALLET TRUCK ASSEMBLY
Abstract
A powered pallet truck with a selectable effective reduced
turning radius, and an intermediate roller assembly for mounting on
the powered pallet truck, are provided. The intermediate roller
assembly can include a base, a linear actuator pivotably connected
at a base end to the base, a linkage pivotably connected to the
base, and at least one roller having an axis pivotably connected to
an actuating end of the linear actuator and to the linkage, the at
least one roller thus being movable between a retracted and an
engagement position. The assembly can be mounted to the underside
of a pallet truck fork having a load wheel. A turning radius
effectively defined by a drive wheel of the pallet truck and the
intermediate roller, or a turning radius effectively defined by the
drive wheel and the load wheel, can be selected.
Inventors: |
Keen; Mark; (Neustadt,
CA) ; Novak; Michael; (Hillsburgh, CA) ;
Ryder; Thomas; (Toronto, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
RYDER MATERIAL HANDLING ULC |
Mississauga |
|
CA |
|
|
Family ID: |
52274432 |
Appl. No.: |
15/258430 |
Filed: |
September 7, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14133953 |
Dec 19, 2013 |
9458001 |
|
|
15258430 |
|
|
|
|
Current U.S.
Class: |
280/43.12 |
Current CPC
Class: |
B62B 3/001 20130101;
B66F 9/22 20130101; B62B 3/008 20130101; B62B 3/0618 20130101; B62B
3/0612 20130101; B66F 9/065 20130101 |
International
Class: |
B62B 3/06 20060101
B62B003/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 10, 2013 |
CA |
2820695 |
Claims
1. An intermediate roller assembly for mounting on an underside of
a fork of a powered pallet truck, the powered pallet truck
comprising at least one load wheel mounted on the fork and a
hydraulic system including a first hydraulic actuator, the first
hydraulic actuator being coupled to an axle of the at least one
load wheel to move the at least one load wheel between a retracted
position and an extended position, the intermediate roller assembly
comprising: a base; a second hydraulic actuator pivotably connected
at a base end to the base; a linkage pivotably connected to the
base; at least one roller having an axis pivotably connected to an
actuating end of the second hydraulic actuator and to the linkage,
the at least one roller thus being movable between a retracted and
an engagement position; and a diverter valve adapted for connection
to the hydraulic system and the first and second hydraulic
actuators to selectively place either the first or second hydraulic
actuator in fluid communication with a hydraulic pressure source of
the hydraulic system.
2. The intermediate roller assembly of claim 1, wherein the base is
adapted for fastening to the underside of the fork.
3. The intermediate roller assembly of claim 1 installed on the
underside of the fork of the powered pallet truck and disposed
between at least one drive wheel of the powered pallet truck and
the at least one load wheel of the fork, such that when the at
least one roller is in the engagement position and in contact with
a work surface and the at least one load wheel is not in contact
with the work surface, a turning radius of the powered pallet truck
is determined by a distance between the at least one roller and the
at least one drive wheel.
4. An intermediate roller assembly for mounting on a powered pallet
truck, the intermediate roller assembly comprising: a base adapted
for mounting to the powered pallet truck; a linear actuator
pivotably connected at a base end to the base; a linkage pivotably
connected to the base; and at least one roller having an axis
pivotably connected to an actuating end of the linear actuator and
to the linkage, the at least one roller being movable between a
retracted and an engagement position by operation of the linear
actuator.
5. The intermediate roller assembly of claim 4, wherein the linear
actuator comprises a hydraulic cylinder.
6. The intermediate roller assembly of claim 5, further comprising
a diverter valve adapted for connection to the hydraulic cylinder
and a hydraulic system of the powered pallet truck.
7. The intermediate roller assembly of claim 6, wherein the
hydraulic system is operable to control at least one load wheel of
the powered pallet truck, and wherein the diverter valve, when
connected to the hydraulic system, permits the hydraulic system to
control the hydraulic cylinder.
Description
REFERENCE TO PRIOR APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 14/133,953, filed Dec. 19, 2013, which claims priority from
Canadian Patent Application No. 2,820,695, filed Jul. 10, 2013, the
entireties of which are incorporated herein by reference.
TECHNICAL FIELD
[0002] The present disclosure relates to pallet trucks and similar
conveyances, and in particular to powered pallet trucks with a
selectable turning radius.
TECHNICAL BACKGROUND
[0003] Pallet trucks, which are also commonly referred to as pallet
jacks, pump lifts, and pump trucks, are wheeled devices used to
lift and transport loaded and unloaded pallets on a fork assembly.
The construction and operation of pallet trucks is known in the
art. Both manual (hand-powered) and powered (motorized) pallet
trucks typically employ a lift mechanism employing a linear
actuator such as a hydraulic actuator, to raise the fork assembly
from a lowered position to provide sufficient clearance between the
lower surface of the pallet and the floor to permit travel. Each
fork of the fork assembly is supported by load wheels located near
the ends of the fork. Travel is controlled by the pallet truck
operator, typically by a steering assembly coupled to a drive
wheel; thus, the turning radius of the pallet truck is defined at
least in part by the wheelbase defined by the distance between the
load wheels and the drive wheel. The orientation of the load wheels
is typically fixed with respect to the pallet truck; accordingly,
the turning radius may be inconveniently large, with the result
that the pallet truck can be difficult to maneuver in a crowded or
constrained environment.
[0004] U.S. Pat. No. 8,336,913, issued to Aaseby et al., describes
a steering device for decreasing a turning radius of a manual
pallet jack. The steering device comprises a spring-biased wheel
mounted to the underside of the jack between an extensible roller
and a main wheel. When the pallet jack is in the lowered position
such that it is maneuverable to engage a pallet resting on the
ground, the spring-biased wheel contacts the ground and provides a
shorter turning radius between it and the main wheel of the jack.
When the pallet jack is moved to a raised position, however, a
larger turning radius is defined by the extensible roller and the
main wheel. However, it has been found that the selection of a
spring with suitable compressive force can be challenging, as too
weak a spring results in the spring-biased wheel losing contact
with the ground, while too much spring resistance makes it
difficult, but usually impossible, for the wheel to pass over the
lower stringer of a pallet. Furthermore, the steering device is
only capable of providing the shorter turning radius when the
pallet jack is unloaded (and in the lowered position), thus
limiting the utility of the steering device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] In drawings which illustrate by way of example only
embodiments of the present disclosure, in which like reference
numerals describe similar items throughout the various figures,
[0006] FIG. 1 is a perspective view of a powered pallet truck.
[0007] FIG. 2 is a top plan view of the powered pallet truck of
FIG. 1.
[0008] FIG. 3 is a perspective view of a powered pallet truck
provided with an intermediate roller assembly.
[0009] FIG. 4 is a plan view of the powered pallet truck of FIG.
3.
[0010] FIG. 5 is a perspective view of a first example of an
intermediate roller assembly.
[0011] FIG. 6 is a perspective view of a second example of an
intermediate roller assembly.
[0012] FIG. 7 is a bottom plan view of the intermediate roller
assembly of FIG. 6 mounted on a fork of the powered pallet truck of
FIG. 3.
[0013] FIG. 8 is a sectional view along the line AA indicated in
FIG. 4 showing intermediate roller assembly in an engagement
position mounted on a fork.
[0014] FIG. 9 is a sectional view of the mounted intermediate
roller assembly of FIG. 8 in a retracted position.
[0015] FIG. 10 is a side elevation of the pallet truck of FIG. 3
bearing a load with the intermediate roller assembly in the
engagement position.
[0016] FIG. 11 is a sectional view showing the mounted intermediate
roller assembly in a retracted position while the fork is in a
lowered position.
[0017] FIG. 12 is a sectional view showing the mounted intermediate
roller assembly in the retracted position while the fork is in a
raised position.
[0018] FIG. 13 is a sectional view showing the mounted intermediate
roller assembly in the engagement position while the fork is in a
raised position.
DETAILED DESCRIPTION OF THE INVENTION
[0019] The embodiments described herein provide a powered pallet
truck provided with an intermediate roller assembly permitting
operation of the pallet truck with a selectable turning radius, and
further provide an intermediate roller assembly that can be used to
retrofit a pallet truck.
[0020] There is accordingly provided an intermediate roller
assembly for mounting on an underside of a fork of a powered pallet
truck, the intermediate roller assembly comprising: a base; a
linear actuator pivotably connected at a base end to the base; a
linkage pivotably connected to the base; and at least one roller
having an axis pivotably connected to an actuating end of the
linear actuator and to the linkage, the at least one roller thus
being movable between a retracted and an engagement position.
[0021] In one aspect, the base is adapted for fastening to the
underside of the fork. In another aspect, the linear actuator
comprises a hydraulic cylinder. In still another aspect, the
intermediate roller assembly is installed on the underside of the
fork of the powered pallet truck and disposed between at least one
drive wheel of the powered pallet truck and at least one load wheel
of the fork, such that when the at least one roller is in the
engagement position and in contact with a work surface and the at
least one load wheel is not in contact with the work surface, a
turning radius of the powered pallet truck is determined by a
distance between the at least one roller and the at least one drive
wheel.
[0022] There is also provided a powered pallet truck, including: a
head section including a drive unit and at least one drive wheel; a
fork assembly comprising at least one fork, each fork comprising at
least one load wheel movable between a retracted position and an
extended position, a first turning radius of the powered pallet
truck on a work surface being determined by a distance between the
at least one drive wheel and the at least one load wheel when the
at least one load wheel is engaged with the work surface; and at
least one intermediate roller disposed on the at least one fork
between the at least one load wheel and the at least one drive
wheel, the at least one intermediate roller being movable between
an engagement position and a retracted position, a second turning
radius of the powered pallet truck being determined by a distance
between the at least one drive wheel and the at least one
intermediate roller when in the engagement position.
[0023] In one aspect, the fork assembly is movable between a
lowered position and a raised position, the at least one
intermediate roller being movable to the engagement position while
the fork assembly is in the raised position. In another aspect, the
at least one load wheel is engaged with the work surface when the
fork assembly is in the lowered position and the at least one load
wheel is in the retracted position; the at least one load wheel is
engaged with the work surface when the fork assembly is in the
raised position and the at least one load wheel is in the extended
position; and the at least one load wheel is not engaged with the
work surface when the fork assembly is in the raised position and
the at least one load wheel is in the retracted position.
[0024] In still a further aspect, the powered pallet truck
comprises: a first hydraulic actuator pivotably coupled to an axle
of the at least one load wheel to move the at least one load wheel
between a retracted position and an extended position; a second
hydraulic actuator pivotably coupled to an axle of the at least one
intermediate roller to move the at least one intermediate roller
between the retracted position and the engagement position; a
hydraulic system providing a hydraulic pressure source; and a
diverter valve in communication with the hydraulic system and the
first and second hydraulic actuators to selectively place either
the first or second hydraulic actuator in fluid communication with
the hydraulic pressure source.
[0025] In a further aspect, when the first hydraulic actuator is
selected and actuated, the at least one load wheel is moved to the
extended position and the at least one intermediate roller is in
the retracted position; and when the second hydraulic actuator is
selected and actuated, the at least one intermediate roller is in
the engagement position and the at least one load wheel is in the
retracted position. In still a further aspect, when neither the
first hydraulic actuator nor the second hydraulic actuator is
actuated, both the at least one load wheel and the at least one
intermediate roller is in the retracted position.
[0026] There is also provided a powered pallet truck, comprising: a
chassis comprising at least one drive wheel; a fork assembly
mounted on the chassis and comprising a pair of forks each
supported by at least one load wheel, the fork assembly having a
loaded state, wherein in the loaded state, a load is borne by the
fork assembly and the fork assembly is in a raised position; and an
intermediate roller assembly mounted on each fork between the at
least one load wheel and the at least one drive wheel, the
intermediate roller assembly comprising at least one intermediate
roller movable by a linear actuator between a retracted position in
which the at least one intermediate roller is not engaged with a
work surface and an engagement position in which the at least one
intermediate roller is engaged with the work surface while the fork
assembly is in the loaded state, a turning radius of the powered
pallet truck on the work surface being determined by a distance
between the at least one drive wheel and the at least one
intermediate roller when in the engagement position with the fork
assembly in the loaded state.
[0027] In one aspect, the intermediate roller assembly comprises: a
base; the linear actuator, pivotably connected at a base end to the
base; and a linkage pivotably connected to the base; the at least
one intermediate roller having an axis pivotably connected to an
actuating end of the linear actuator and to the linkage. In still
another aspect, the linear actuator is a hydraulic actuator. In yet
a further aspect, the powered pallet truck further comprises a
hydraulic system providing a hydraulic pressure source to the
hydraulic actuator. In still a further aspect, the at least one
load wheel is movable by a further hydraulic actuator between an
engagement position and a retracted position, the further hydraulic
actuator being connected to the hydraulic system; and the hydraulic
system comprising a diverter valve in communication with the
hydraulic actuator of the intermediate roller assembly and the
further hydraulic actuator to selectively place either hydraulic
actuator in fluid communication with the hydraulic pressure
source.
[0028] FIG. 1 illustrates a typical powered pallet truck 10
comprising a head or control section 20 and a fork assembly 30. The
head section 20 can include a frame or chassis housing the drive
unit for the pallet truck; this can include an AC drive unit and
motor. The head section also includes the steering assembly 26 used
by the operator to control travel by the pallet truck. The steering
assembly is operatively coupled to the drive wheel 24. In the
examples illustrated and described herein, a single drive wheel 24
is shown; however, it will be appreciated by those skilled in the
art that the head section 20 may include multiple wheels, for
example a drive wheelset; for ease of exposition, however, a single
drive wheel 24 is referenced in these examples. It will be
appreciated by those skilled in the art, though, that the concepts
and the intermediate roller assemblies may be adapted for use with
pallet trucks having more than one main wheel. The head section 20
also includes a mechanism for controlling one or more lift
mechanisms used to raise and lower the fork assembly 30. The
control mechanism may be a switch or toggle used to control the
motor driving the lift mechanism(s). An example of a powered pallet
truck is the Model WP 3000 distributed by Crown Equipment
Corporation of New Bremen, Ohio, U.S.A.
[0029] The fork assembly typically includes a pair of forks 32, and
is illustrated as such herein. Each fork 32 is provided with at
least one load wheel 36. Load wheels may be provided in sets,
rather than as the single load wheel illustrated here; again, those
skilled in the art will appreciate that the embodiments herein
extend to such configurations. When the load wheel 36 contacts the
floor or other work surface on which the pallet truck is
travelling, the load wheel 36 bears at least part of the load
carried by the forks 32. Thus, the load wheel 36 is typically
disposed at or near the distal end 33 of the fork 32. In the
example of FIG. 1, the wheels 36 are visible through apertures 35
provided in the fork surface that accommodate the wheels 36 while
still permitting free rotation when the wheels 36 are in a
retracted position. Again, the typical fork assembly includes a
plurality (usually two) forks; however, the concepts and
embodiments herein apply to alternative fork assembly
configurations.
[0030] The degree of extension or retraction of the load wheel 36,
the amount of clearance beneath the forks 32, and the length, width
and separation of the forks 32 of the fork assembly, are determined
generally by the application: namely, the size and type of the
pallets or other load the pallet truck is intended to lift and
transport. While standard dimensions of pallets have been more or
less established, pallet trucks may be customized as necessary to
accommodate specific job requirements. Regardless of individual
specifications, though, the handling of the pallet truck is
affected by the pallet trucks' effective turning radius or turning
circle, i.e., the smallest radius or diameter of the smallest
circular turn that the pallet truck can make. The turning radius is
determined at least in part by the size of the pallet truck's
wheelbase, or the distance between the load wheels and the drive
wheel. This is illustrated in the plan view of FIG. 2, which
illustrates the wheelbase d measured as the longitudinal distance
between the load wheels 36 (indicated by line b) and the drive
wheel 24 (indicated by line a), with the wheels shown in phantom.
The greater the wheelbase, the greater the turning radius; this
typically adversely affects the maneuverability of the pallet
truck.
[0031] Accordingly, an intermediate roller assembly (illustrated in
FIG. 5 and following figures) is provided to selectively alter the
wheelbase and thus the turning radius of the pallet truck. The
position of the intermediate rollers of the intermediate roller
assembly is shown in FIGS. 3 and 4. FIG. 3 provides a perspective
view of a pallet truck 100, which, as above, includes a head
section 120 and fork assembly 130. The head section 120 includes
the drive assembly 126, chassis or frame 122, and drive wheel 124.
The fork assembly includes forks 132, load wheels 136 positioned at
distal ends 134, and apertures 135. In addition, at least one
intermediate roller 240 is provided at an intermediate location
between the load wheel 135 and the drive wheel 124, on at least
one, but most advantageously all, forks of the fork assembly 130.
As will be described below, in certain states the intermediate
rollers 240, rather than the load wheels 135, bear the load of the
pallet truck 100. The intermediate location can be determined
according to the typical load distribution on the fork
assembly.
[0032] FIG. 4 is a plan view of the pallet truck 100 provided with
the intermediate roller assembly, showing the position of the
intermediate rollers 240 with respect to the load wheels 136 and
drive wheel 124 in phantom. When the intermediate rollers 240,
rather than the load wheels 136, bear the load on the fork assembly
130, the wheelbase d' is the distance between the intermediate
rollers 240 (indicated by line c) and the drive wheel (indicated by
line a), which is less than the wheelbase d when the load wheels
136 are bearing the load as in FIG. 2. In one example, a pallet
truck having an average turning circle of about 126'' was fitted
with intermediate rollers assemblies reducing the turning circle to
about 82'', or a reduction in the turning circle of about 35%.
[0033] The intermediate roller assembly 200 is illustrated in FIG.
5. The intermediate roller assembly 200 in this example is mounted
on a base 210, which can be a steel plate or other frame that is
adapted or adaptable for fastening to the underside of a fork 132.
A hydraulic strut or cylinder 220 or other suitable linear actuator
is pivotably mounted at its base end to the base 210. In the
example of FIG. 5, a bearing provided on the base end of the
hydraulic cylinder 220 is mounted on an axle 222, itself mounted to
the base 210 by a bracket 212 including a bearing 214 provided
therein. Other pivoting connections between the hydraulic cylinder
220 and the base 210 may be used.
[0034] The rod or actuating end of the hydraulic cylinder is
provided with a pivoting connection to an intermediate roller 240.
In this example, a linkage 226, here a bracket or clevis linkage,
extends from the cylinder rod and receives the axle 242 of the
intermediate roller 240 in a bearing 228. The axle 242 of the
intermediate roller 240 is thus displaced on actuation of the
hydraulic cylinder 220. Motion of the intermediate roller axle 242
is constrained by a linkage 230, which itself is pivotably
connected to both the intermediate roller 240 and the base 210. In
the example of FIG. 5, an axle 232 of the linkage 230 is mounted in
a bracket 216, which itself is fixed to the base 210. The axle 242
of the intermediate roller 240 is also mounted on the linkage 230.
The linkage 230 and the bracket 226 thus permit free rotation of
the intermediate roller 240, while controlling the displacement of
the axle 242 with respect to the base 210, and thus to the fork 132
when the assembly 200 is mounted thereto.
[0035] FIG. 5 also illustrates a spare bracket 216', which, as can
be seen in the example of FIG. 6 below, can be used in a dual
hydraulic cylinder embodiment of the intermediate roller assembly
200'. In this dual hydraulic cylinder version, a pair of hydraulic
cylinders 220, 220' is pivotably mounted via brackets 212, 212',
and to intermediate rollers 240, 240' via brackets 226, 226'. The
intermediate rollers 240, 240' are also rotatably mounted on their
corresponding linkage 230, 230' as described above, and the
linkages 230, 230' are pivotably mounted on brackets 216, 216'. In
these examples, the base 210 can be a steel plate, and the various
components described above used to connect the linear actuator and
the rollers can be machined metal components. However, the
manufacture of these components and the materials used can be
selected from any suitable technique and material known to those
skilled in the art. While specific examples of pivoting connections
are illustrated here, other pivoting connection arrangements may be
suitably employed and are also known to those skilled in the
art.
[0036] FIG. 7 depicts the example intermediate roller assembly 200'
mounted on the underside of a fork 132, thus illustrating the
relative position of the intermediate rollers 240, 240' with
respect to the load wheel 136. In this example, an actuator 140
used to control the position of the load wheel 136 is disposed
between the hydraulic cylinders 220, 220' of the assembly 200'. In
the case of a single hydraulic cylinder 220 as in the example
assembly 200, the hydraulic cylinder 220 would simply be positioned
alongside the load wheel actuator 140. The load wheel actuator 140
here is a hydraulic actuator, connected by a linkage 142 that is
pivotably mounted to the wheel brace 144 bearing the axle of the
load wheel 136. Actuation of the load wheel actuator 140 causes the
axle of the load wheel 136 to be displaced with respect to the fork
132, thus enabling the load wheel 136 to be raised or lowered with
respect to the work surface. In the following examples, reference
is had to the single-hydraulic cylinder variant of FIG. 5, but it
will be appreciated that these examples also apply to the
dual-hydraulic cylinder variant.
[0037] Since the positions of both the load wheel 136 and
intermediate roller 240 are controlled by linear actuators, the
mechanism used to control the load wheel actuator 140 can be
adapted to control the intermediate roller actuator 220 as well.
For instance, as both actuators 140, 220 in this example are
hydraulic cylinders, the same hydraulic system may be employed for
both actuators 140, 220, with a diverter valve (not shown)
interposed between the hydraulic pressure source and the cylinders
to select either the load wheel actuator 140 or the intermediate
roller actuator 220, or neither. Then, on actuation of a switch or
toggle provided for operator control and in operative communication
with the diverter valve, hydraulic pressure can be diverted from
one actuator to the other by altering the fluid communication
between the hydraulic system and the actuators 140, 220, and
pressure released on the other actuator. Alternatively, pressure
can be released on both actuators. The configuration of a typical
hydraulic system for a pallet truck will be known to those skilled
in the art. The diverter valve can be located in the system as the
last valve through which the hydraulic fluid passes through to
reach the load wheel and intermediate roller actuators, and thus
after any other filters or valves in the system. In this manner an
existing pallet truck's hydraulic system can be advantageously
fitted with an assembly 200 (or 200') after manufacture without
requiring installation of a separate hydraulic system. In some
examples, however, at least a final filter is interposed between
the diverter valve and the actuators 140, 220 to assist in removal
of any remaining particulate matter in the hydraulic fluid before
entry into the actuators 140, 220. Of course, in a further example
(not shown), independent hydraulic systems may be provided for
controlling the load wheel 136 and the intermediate roller 240.
[0038] FIGS. 8 and 9 illustrate the effect of actuation of the
hydraulic cylinder 220 on the intermediate roller 240 in a side
elevation view of the assembly 200 as mounted on the underside of
the fork 132. In these figures the fork 132 is shown in a sectioned
view as the fork typically includes depending side members (such as
the forward depending flange 138 shown in sectioned view in FIG. 8)
that provide rigidity to the fork structure and protect the load
wheel 136 and actuator 140, thus obscuring these components and the
assembly 200 from view. In the view of FIG. 8, it can be seen that
the fork 132 is in a lowered position with respect to the work
surface 300, with the load wheel 136 engaging the work surface. In
addition, the intermediate roller 240 is itself in contact with the
work surface 300, while the piston 222 (shown in phantom) of the
hydraulic cylinder 220 travels towards the cylinder's base as shown
by the arrow, indicating a return to a low pressure condition after
pressure is released from the hydraulic cylinder 220. As a result
of the release of pressure, the position of the axle 242 of the
intermediate roller 240 is able to move upwards as indicated by the
upwards arrow in FIG. 8. The intermediate roller 240 is thus
movable to the position shown in FIG. 9, where it is no longer in
contact with the work surface 300 and is thus in a retracted
position.
[0039] FIG. 10 illustrates the pallet truck 100 with the fork
assembly 130 (and thus the fork 132) in a raised position and in a
loaded state, in which the load wheel 136 is in a retracted
position and not in engagement with the work surface 300, and the
intermediate roller 240 is in an engagement position, in engagement
with the work surface 300. In this figure, the pallet truck 100 is
shown bearing a load 410 on a pallet 400. It will be appreciated by
those skilled in the art that as a result of diversion of hydraulic
pressure to the actuator 220 of the intermediate roller assembly,
the intermediate roller 240 is extended to the engagement position
and pressure is released on the actuator 140 (not shown in FIG. 10)
controlling the position of the load wheel 136; accordingly the
load wheel 136 is shown in the retracted position. It can also be
seen that in the raised position, while the lower edge of the
pallet 402 clears the work surface, the intermediate roller 240
remains in contact with the work surface 300 between the slats (not
shown) of the pallet 400. Conversely, when pressure is diverted
from the actuator 220 and to the actuator 140 of the load wheel
136, then the load wheel 136 will be extended and the intermediate
roller 240 retracted, similar to what is shown in FIG. 9. This can
occur while the fork assembly remains in a raised position as in
FIG. 10; thus, even in the raised position, the operator can select
between engaging the load wheels 136 and the intermediate rollers
240 and thereby select a larger or smaller turning radius while the
fork assembly 130 is in a raised and in a loaded condition.
[0040] FIGS. 11 to 13 illustrate a sequence of states of the fork
assembly (as represented by a single fork 132), intermediate roller
240, and load wheel 136. In FIG. 11, no hydraulic pressure is
applied to either the intermediate roller 240 or load wheel 136
actuators, and the fork 132 is in a lowered position. The load
wheel 136 is therefore engaged with the work surface 300, while
also in a retracted position, and the intermediate roller 240 is in
a retracted position and not in engagement with the work surface
300. In this state, the pallet truck 100 may be carrying a load,
but due to the minimal clearance between the fork 132 and the work
surface 300, the pallet truck 100 would typically not be travelling
with a pallet load. In this position, the pallet truck 100 would
typically be in an unloaded state, and is maneuverable to engage a
standard pallet resting on the work surface. In this state,
however, the pallet truck 100 could be steered with a larger
turning radius (as determined by the distance between the drive
wheel, not shown in FIGS. 11 to 13, and the load wheel 136).
[0041] In FIG. 12, hydraulic pressure is applied to the load wheel
actuator 140 and not to the intermediate roller actuator 220, and
the fork 132 is in a raised position. As a result, the load wheel
136 is in an extended position and is still engaged with the work
surface 300 while the intermediate roller 240, which remains in its
retracted position, is not. In this state, given the greater
clearance between the fork 132 and the work surface, when the
pallet truck 100 is loaded, the load is raised above the ground and
there would be sufficient distance between the lower surface of a
pallet and the work surface to permit travel while the pallet truck
100 is bearing a pallet load, as in FIG. 10. In this state, again,
the pallet truck 100 will have the larger turning radius.
[0042] In FIG. 13, the pallet truck 100 may still be in the loaded
state of FIG. 10 or 12. The fork 132 is in a raised position, so
again, there would be sufficient clearance underneath a loaded
pallet for the pallet truck to travel. Hydraulic pressure on the
load wheel actuator 140 is released, and hydraulic pressure is
applied to the intermediate roller actuator 220. The intermediate
roller 240 is therefore in an engagement position, in contact with
the work surface 300, and the load wheel 136 is in a retracted
position, and not in engagement with the work surface. In this
state, then, the turning radius is effectively reduced from the
states of FIGS. 1i and 12, as it is now determined by the distance
between the intermediate roller 240 and the drive wheel (not
shown).
[0043] It can be seen from the foregoing examples that the
selective engagement of the intermediate rollers 240 thus allows
the turning radius of the pallet truck 100 to be reduced, whether
or not the pallet truck is loaded, and even when the fork assembly
130 is in a raised position. The dimensions of the intermediate
roller 240, the linkage 230, and the extension of the piston of the
hydraulic actuator 220 can be selected according to the specific
application and dimensions of the fork assembly 130. It can further
be seen that the intermediate roller assembly 200 can function and
provide a shortened turning radius whether the pallet truck 100 is
in a loaded or empty condition, thus improving maneuverability of
the pallet truck 100 in any working condition.
[0044] Various embodiments of the present invention having been
thus described in detail by way of example, it will be apparent to
those skilled in the art that variations and modifications may be
made without departing from the invention. The invention includes
all such variations and modifications as fall within the scope of
the appended claims. Throughout the specification, terms such as
"may" and "can" are used interchangeably and use of any particular
term should not be construed as limiting the scope or requiring
experimentation to implement the claimed subject matter or
embodiments described herein.
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