CA1105894A - Pallet truck - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A pallet truck for moving articles is disclosed having a load bearing chassis which can be elevated or Lowered.
A hydraulic lifting mechanism is provided for lifting the chassis. The lifting mechanism comprises at least one piston which is fully immersed in the hydraulic fluid employed and a pump with at least one pump piston for actuating the lifting piston. Valve control means are provided in the steering head base which also carries the steering handle. The steering handle is used to actuate the pump piston. The valve control means can be manipulated by the operator for the pallet truck so as to select lowering or raising of the chassis. A neutral position in which the pump is disconnected from the lifting mechanism is also provided. A second valve control means permits the pump circuit to adapt to various loads. The truck in accordance with the present invention is of particularly durable construction and can easily be controlled by the operator.

Description

~1~5~4 TITI,E: PAI.LET TR~CK
r~ _ck3ro nd o~ the n entron This invention relates to improvements in pallet trucks and more particularly to improvements in or relating to raising and lowering of the load-bearing platform or pla-tforms of such pallet trucks.
Palle-t trucks are well known in the material handling field. They usually comprise a load-supporting can-ti]evered platform or chassis moveable upon a plurality of supporting rollers or wheels. The chassis can be raised by rneans of a jack or lifting mechanism which is actuated by a steering handle to raise the i-tem or ltems carried on the chassis.
Lowering of the chassis is carried out by releasing the hydraulic fluid from the lifting cylinder associated with -the lifting mechanism. These pallet trucks are normally rated a-t a capacity of about 5 me-tric tonnes and, thus, are useEul in moving pallets, containers, crates and the like From one location to another where heavy-duty equipment, such as fork-lifts, cannot economically be cmployed.
Review of the Prior Art _ _ _ _ _ _ _ _ _ _ _ Pallet trucks as briefly described in the foregoing are known and have been described in the patent literature.
U.S. Patent 3,567,240 issued March 2, ]971, to Brassington discloses a dual lifting system for pallet trucks.
In accordance with the proposal by Brassington, lowering of the chassis of a pallet truck is carried out at a faster rate than that used for raising of the chassis.
According to the patent of Brassington, there is provided a lifting mechanism with an inner lift piston joined to an outer lift piston having a larger diameter than the inner lift piston, each piston being associated with a corresponding piston chamber. A-t a predetermined pressure, a check valve associated with the inner lift piston permits entry of ~ I

3 ~58~4 h~dralllic fluid throuc3h communication passayes from the inner lift chamber to the outer liEt charnber. The proposal by Brassing-ton includes siphon means to ensure that the outer lift chamber is sufficiently filled with hydraulic fluid. Membrane medns are also provicled to prevent leakaye of any hydraulic fluid from -the outer piston chamber.
U.S. Patent 3,608,922 issued Septcmber 28, 197], to Best et al discloses a foot operated pump -to force hydraulic fluid from a reservoir into a pis-ton chamber, thereby raising the frame or chassis of the truck. A manually operable release rnechanism is disposed near the s-teering handle of the truck.
This mechanism includes an obliquely disposed wedge member attached to the lowermost end of an actuating rod. The wedge member serves to actuate, via an in-termediate finger, the plunger for the fluid control valve. Moveme-nt of the plunger of the valve in this manner causes opening of the valve, there-by draining the hydraulic fluid from the piston chamber, so that the chassis of the truck will be lowered.
U.S. Patent 3,940,338 issued February 2~, 1976, to Bryntse discloses a lifting mechanism for a pallet truck in which a pivotally moun-ted control lever may be moved frorn a neutral locked position, in which the chassis is at rcst, to one oE two further positions to cause lowering or raising of the chassis, respectively. With the control lever in the neutral position the steeriny handle can be used for pulling and steering of the pal]et truck.
U.S. Patent 3,959,970 issued ~une l, 1976, to Bos et al is concerned with a hydraulic lift mechanism or jack for lifting vehicles therewith and, particularly, with the provision of a jack having a base plate on which there are disposed a jack cylinder and a pump cylinder, bo-th equipped with respective pistons, and in which there are provided communication passages and control valves. The advantaye of 3~3a~

the proposal to sest resides in ~he elimination of a separate valve housing and in the provision of a base plate made of substantially uni~orm material thickness.
U.S. Patent 3,982,767 issued September 28, 1976 to Larsson e-t al discloses a hand operated pallet truck having a release arrangement for actuating an outlet valve of a lifting piston chan~er, to lower the chassis of the pallet -truck. The primary advantage of the truck in accordance wi-th the Larsson reference resides ln the provision of a palle-t truck wherein the axis of the steering wheel intersects the vertical axis about which the wheel and the jack assembly rotate.
U.S. Patent 4,010,609 issued March 8, 1977, to Bou-troy et al discloses a pump piston arranged to face a jack piston, both pistons being arranged in a common, double-walled cylinder and having disposed between them a fixed, transverse partition. The device proposed by Bou~roy is particularly useful for adjusting the height of components in machinery, ror moving parts of seats, for office chairs and the like.
Pallet trucks are also disclosed in the following 20U.S. Patents:-ls ued

2,424,417 Quayle July 22, 1947 2,439,781 Quayle ~pril 14, 1948 2,681,202 Germond June ]5, 1954 2,940,767 Quayle June 14, 1960

3,136,128 Suter June 9, 1964 3,183,989 Trusock et al May 18, 1965 3,188,107 Quayle June 8, 1955 3,202,233 Dolphin et al August 24, 1965 303,249,170 Quayle May 3, 1966 3,260,534 Knights July 12, 1966 3,261,617 Becker et al July 19, 1966 S8~4 .
3,2~f.,9~5 Edera November 22, 1966 3,455,211 Du(~elay July 15, 1969 Summary of the rresent Invention , _ _ _ _ _ It is an object o~ tlle presen-t invention to provide a pallet truck wherein lowering and raising of the chassis of the truck are readily controlled.
t is also an object of the presen-t invention to provide a fluid actua-ted piston and piston chamber arrangement which is especially suitable for controlling the raising and lowering of a chassis oE a palLet truck.
In accordance with -the presellt invention, there is provided a pallet truck comprising a chassis moveable between at least one load bearing position and at least one load releasiny position; a fluid actuated piStOII and piston chamber arrangement disposed adjacent one end of said chassis whereby said piston operatively engac3es said chassis for movement thereof between the said positions; pump means for circulating fluid flow to said piston; passage means for com~unicating said piston chamber with said pump means; and valve means disposed in said passage means for controlling the fluid flow between said pump means and said piston, said valve means selectively initiating and terminating fluid flow to move said chassls between the said positions.
~ lso in accordance with -the present lnvention, there is provided a fluid actuated piston and piston chamber arrangement comprising a base member having an aperture passing therethrough;
sealing means mounted in said aperture; a hydraulic fluid reservoir housing above said base member and carried thereby; a piston chamber housing extending downwardly from said base member;

a piston mounted within said piston chamber housing and extending upwardly therefrom through said sealing means and through said 58~4 r~servoi r h~llsi.n(l to project llpwarclly therefromt said piston slidably engag.i.ng the sealin(l means; valve rneans mounted in said base member, pUlllp means connected to said valve means, fi.rst passage means extending from the reservoir through the base member . to the valve means, second passage means extending from the piston chamber to the valve means, said pump means and valve means being operable to pump fluid from the reservoir through the first passage means, thc va:Lve means and the second passage means to the piston chamber to raise the piston re]a-tive to the base member;
said valve means bei.ng operable to permi.t fluid to .return to the reservoir from the piston chamber throuc3h the secon,d passage means, .. the valve means and the first passage means and thereby permit lowering of the piston relative to the base member, said piston having a lower end portioll shaped to provide by-pass means permitting f].uid to pass from the pis-ton chamber to the reservoir past said seal means when said lower end portion of said piston traverses said seallng means.
Description of the Drawings .
Specific embodiments of the invention will now be described in more detail with reference to the accompanying , drawings, wherein:- ~
Figure 1 is a perspective vlew of a pallet truck in accordance with the present invention;
Figure 2 is a side elevation of -the pallet truck shown in Figure l;
Figure 3 i.s a perspective view of the components of the lifting mechan:ism arranged on -the steering.head base of the pallet truck;
Figure 4 is a perspective, exploded view of the components arranged on the steering head base 5~4 Figure 5 is a diagrammatic representation of the hydraulic circuit for the lifting mechanism of the pallet truck;
Figure 6 (on the same sheet as Figure 1) is a detail of the selecting handle of the truck in a first and a second position;
and Figure 7 (on the same sheet as Figure 1) is a detail of the selecting handle in a third position.
Specific Description A pallet truck incorporating the features of the present invention is generally illustrated in Figures 1 and 2. The truck has a main chassis 10 comprising two fork extensions 12 joined by a connecting arch 14 with a forwardly directed boss portion 16.
The fork extensions 12 of chassis 10 are supported by wheels or rollers 18 which are associated with linkage system 20, not shown in detail. The forward part of the linkage system is pivotally joined to the underside of transverse thrust plate 22.
A steering head base 24 is disposed in thrust plate 22. Steering head base 24 has a lowermost rod extension 26 (Figure 4) on which are mounted the forward two steering rollers or wheels 28. An upwardly extending clevis 30 is provided on the upper surface of steering head base 24 for mounting therebetween a steering handle 32.
The lower end of steering handle 32 (Figure 3) serves to actuate a pump assembly generally identified by numeral 33 for lifting mechanism, comprised of a lifting piston assembly generally designated by numeral 34; with a flow control means comprised of a flow control valve assembly 35 and check valve assembly 36 arranged between the pump and piston assemblies, all to be described in detail.
The lifting piston assembly 34 of the lifting mechanism is capable of raising, and can be controlled, by way of the flow control valve assembly 35, to lower the chassis 10.

~ D5~4 The raised position of chassis 10 is indicatéd in dash lines in Figure 2, while the lowered position of the chassis is shown in solid lines.
In response to actuation of the flow control valve assembly 35, the chassis 10 can be placed in a neutral position or condition. During this condition, -the chassis may be in the raised or lowered position or in a position between these two extremes. In this condition, the pump assembly 33 is effectively disconnected from the lifting piston assembly 34 and actuation of the steering handle 32 will not apply pumping pressure in the lifting mechanism. Thus, during this condition, the steering handle 32 is used to steer and move the truck from one location to another.
For the purpose of thls specification, the forward end of the pallet truck is that end having the steering head base 24 associated therewith.
Thus, thrust plate 22 has a vertical bore, not shown, through which the rod extension 26 of steering head base 24 passes, a collar 40 and an antifriction bearing 42 arranged between the respective facing walls of the steering head base 24 and the thrust plate 22. Bearing 42 is adapted to receive radial and axial loads. Collar 40 and bearing 42 are retained by a snap ring 44 in a suitable groove, as is known in the art.
Near its lowermost end, the rod extension 26 has a transverse bore 46 in which a wheel shaft 48 is journalled by a needle bearing 50. Wheels 28, of which only one is shown in Figure 4, are secured by washers 52 and pins 54; and bolt 56 fixes the wheel assembly in bore 46.
Steering handle 32, formed of square cross-section tubing has at its upper end a handle grip 58. Steering handle 32 is pivotally mounted with its lower end in clevis 30 by way of an inverted U-shaped brac]~et 60, rollers 62 and support bolts 64. The support bolts 64 also mount an actuating roller ~5~3~4 66 which transfers the pumping motion of the steering handle, i.e., movement of the handle 32 back and forth through a small arc as indicated in Figure 2, to pump piston 68. Pump piston 68 has a head portion 69 and is received with its rod end in the pump cylinder chamber 70 of steering head base 24, with a wiper ring 72 and a seal ring 74 being provided for the pump piston ~.
While the steering handle 32 can move the pump piston 68 into the pump cylinder chamber 70, when handle 32 is moved in pumping action, travel of the piston 68 is reversed by the action of coil spring 76 which is disposed between the upper face of the steering head base 24 and the pumping piston head 69.
A longitudinal roller 78 is supported on pin 79, mounted in the arms of clevis 30, for guiding parts of the actuating mechanism of the flow control valve assembly 35.
The actuating mechanism for the flow control valve assembly 35 firstly comprises a selecting handle 80 ex-tending within the handle grip 58 of steering handle 32. Selecting handle 80 is secured to or forms part of a guide end 82 slidingly disposed in the upper end of steering handle 32. A
finger tip lever 84 is rotatably secured on pin 86 which, in turn, is secured in guide end 82. Finger tip lever 84 has a circular, first cam section, eccentrically disposed with respect to the pin 86 and has a second cam section, somewhat paraboloid in shape.
As can best be seen with reference to Figures 6 and 7, the position of selecting handle 80 can be varied, depending on the position of finger tip lever 84. As shown in solid lines in Figure 6, the handle is in its lowermost position since the finger tip lever 84 rests with its side on the upper end of steering handle 32. For the sake of brevity, this position of the selecting handle 80, and of the finger tip lever 84, is 1~58~34 referred to as position 1. During this position, the pump assembly 33 of the lifting mechanism is effectively connected to the lifting piston assembly 34 so that the chassis 10 can be rais~ed in response to actuation of the steering handle 32 in pumping motion.
On repositioning of the finger tip lever 84, in clockwise direction, to the position shown insolid lines in ` Figure ~ the selecting handle 80 assumes the position indicated li~ewise in solid lines. This position is referred to as position 2. During this position, the pump assembly 33 of the lifting mechanism is effectively disconnected from the lifting piston assembly 34 so that the chassis 10 will remain in the prevailing position, and handle 32 can be used to steer and/or pull the truck without inadvertent use of the pump assembly 33.
The selecting handle 80 can be moved further in an q~s iq di~q ~e~ dD 7'f~d //,~
upward direction by the operator,~ this movement only being limited by the handle grip 58 (Figure 7). This action raises the finger tip lever 84 to position 3 and the flow control val.ve assembly 35 is thereby actuated so as to release the working pressure from the lifting piston assembly 34, thereby permitting lowering of the chassis, due to gravity.
Movement of the selecting handle 80 into one of the positions described is transmitted by rod 88 (Figures 3 and 4), a short chain section 90 and connecting pin 92 to a bell crank type operating lever 94, pivotally mounted on pin 96 in a trunnion 98 forming part of, or secured to, the side wall of steering head base 24. Pin 92 engages the bifurcated end 93 of operating lever 94 by way of a nut 100.
The vertically disposed arm ~ of operating lever 94 interacts with control piston 102 ~Figures 4 and 5~ forming part of the flow control valve assembly 35. Piston 102 has a sealing ring 104 associated therewith and a needle end 103 for receiving thereon spring 106.

SB~4 The piston 102 is moved in bore 108 in steering head base 24, in response to the positions assumed by the selecting handle 80 transmitted by the linkage system composed of rod 88, chain section 90 and connecting pin 92 and by operating lever 94.
Thus, when the sel.ecting handle 80 is in position 1, the vertically disposedl~d of lever 94 will just touch, but not displace, the control piston 102. When selecting handle 80 is moved to position 2, the operating lever 94 moves control piston 102 into the bore 108 in base 24. When the selecting handle 80 is brought to the position 3, piston 102 is still further moved into bore 108.
In order to best describe the various passages and other components of the hydraulic circuit, the description will now proceed with reference to Figure 5. This shows, sche-matically, on the right hand side of the page, the pump assembly 33, previously described with respect to Figure 4, and the flow control valve assembly 35 described thus far is shown alongside of the pump assembly 33.
Bore 108 narrows into control passage 110, which passage leads into ball chamber 112 having disposed -therein ball 114. Chamber 112 communicates with a ball valve bore 116 receiving therein a composite ball valve member 118 having longitudinal peripheral passages 119 and being sealed by seal ring 120. ~luid flow through the longitudinal cen-tral passage 122 and transverse bore ~ is controlled by a needle 126, ball 128 and spring 130. The ball valve bore 116 is closed by means of seal 132 and plug bolt.134.
sea~ /o,~ 5~
~ ~longsidc ~is-~osc,~ the flow control valve assembly 35 is check valve assembly 36 which is comprised of an adjustment screw 136 threadingly insertable in bore 138, the screw 136 being covered exteriorly by a cap 140 and washer 142. Screw 136 serves to compress a spring 144 thereby biasing a ball 146.

~S8~a The lifting piston assembly 34 will be described next.
It comprises lifting piston 150 disposed with its lower end in a bore 152 forming a lower cylinder chamber in rod extension 26 of steering head base 24. The upper end of the piston rod 150 extends in upper cy].inder chamber 154 extending above the upper face of the steering head base 24.
~s can best be seen in Figure 5, a seal 156 i5 arranged in a suitable groove in the walls of bore 158 in steering head base 24, approximately delineating the transition between lower cylinder chamber 152 and upper cylinder chamber 154. A reservoir nut 160 with an associated seal ring 162 and wiper ring 164 closes the upper cylinder chamber 154.
The following communications passages are provided between the main components of the hydraulic circuit shown in Figure 5. Passage 170 joins the upper cylinder chamber 154 with bore 138 of check valve assembly 36. Bore 138, in turn, is connected to bore 108 by passage 172. The ball chamber 112 is connected to pump cylinder 70 by passage 174 and passage 176 leads from ball valve bore 116 to lower cylinder chamber 152 near seal 156. Passage 178 connects the check valve assembly 36 with the passage 176.
At its lowermost end lifting rod 150 has in its circumference a planar depression 180. This depression allows hydraulic fluid to pass Erom lower cylinder chamber 152 to upper cylinder chamber 154 when the piston is displaced in upwardly direction until the depression 180 is bridged by the seal 156.
Lifting rod 150 is furnished at its upper end with a ball-receiving seat 182 for ball 184. sall 184 is received in a suitable depression in a corresponding ball seat, not shown, located in the boss portion 16, and serves as the friction-reducing joint between boss portion 16 and steering head base 24.

58~4 Operation of the pallet truck in accordance with the present invention is as follows:-In order to raise the chassis 10 of the truck, thefinger tip lever 84 is brought to position 1, shown in solid lines in Figure 6, if required. This will ensure that the operating lever 94 merely touches the control piston 102. When the handle is moved to actuate the pump piston 68 in a pump stroke, the hydraulic fluid, usually oil, is moved through passage 174 towards ball chamber 112 and ball 114 closes control passage 110; ball 128 is unseated and hydraulic fluid passes through transverse bore 124 into passage 176 and from thence into lower cylinder chamber 152, thereby raising the cylinder piston lS0. Pumping of hydraulic fluid can thus be continued until the chassis 10 is raised to the desired level.

The chassis can be lowered by moving the selecting 8~
handle~ to position 3. This action causes fullest inward movement of the control piston 102 into bore 108 by the inter-vention of operatlng lever 94. The ball 114 is moved by the needle extension 103 of control piston 102 to depress needle 126, which will unseat ball 128 in the central passage 122 of composite ball valve 118. The hydraulic fluid is now free to return from lower cylinder chamber 152 through passage 176, ball chamber ]12, control passage 110, bore 108 and passage 172, bore 138 and passage 170 into cylinder chamber 154. The piston 150 will thus be lowered in response to the load carried on the chassis, due to gravity.
The chassis will remain at rest in a prevailing position when the finger tip lever 84 is brought to position 2 (Figure 7) even though the handle 32 is moved in pumping motion. ~n this position operating lever 94 moves the needle end 103 of control piston 102 so as to keep the ball 114 unseated in ball chamber 112 and hydraulic fluid is merely moving back and forth through passages 170 and 172 and 174 ~58~4 without moving the piston 150 until a different position is selected.
Adjustment of -the screw 136 will permit regulation of the pressure rating of the truck. Thus, as the spring 144 is compressed, by turning the screw 136 so as to penetrate deeper into bore 138, the rating of the unit is increased. Turning of the screw in the opposite direction will reduce the pressure rating of the unit.
The check valve assembly is operative when the pressure in the system is excessive, i.e., the load to be carried on the chassis 10 is too great. This has the following effect:- hydraulic fluid is moved through the passage 176 and thence through passage 178, since the pressure in the system will maintain ball 128 in closing position in the composite ball valve member 118. The hydraulic fluid will thus unseat ball 146 and return to cylinder chamber 154 thereby permitting lowering of the piston rod 150.
Spring 106 is biasing the control piston 102 so that the system is ready for use, i.e., ready for raising the chassis by moving the handle 32 in pumping motion.
The upper limit of travel of piston 150 is conveni-ently controlled by the planar depression 160 near the lower-most end of piston 150. Thus, when reaching the seal 156, with this depression, the hydraulic fluid is free to pass from the cylinder chamber 152 to chamber 154 without a physical re-straint being placed of the piston 150 thus also adding to the longevity of the system.
It will be apparent from the foregoing that the pallet truck in accordance with the present invention has a number of important advantages.
For one, the lifting piston 150 with its associated - seal 156 in the lifting system is completely immersed in the hydraulic fluid, normally oil. This is in contradistinc-tion to ~L~,A~ 4 prior art proposals wherein oil is admitted to the piston from a separate oil reservoir, thereby giving rise to moisture accumulatiny and leading to damage by moisture, i.e., corrosion, of the piston and deterioration of the associated seal or seals when the piston is exposed to such conditions during long periods of rest.
Furthermore, the pallet truck in accordance with the present invention can easily be operated by the manipulation of a selecting handle that extends substantially coextens,ively within the main steering yrip. Easy control of position selection is afforded by finger tip lever 84.
Furthermore, the pressure rating of the system is readily adjusted to ensure that the pallet truck can accomodate different weights and pressures.
Selection of the neutral position or condition of the truck is useful in eliminating undue pressure in the system leading to possible breakage of components therein.

Claims (4)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A pallet truck comprising:
a chassis movable between at least one load bearing piston and at least one load releasing position;
front and rear ground-engaging wheel means for moving the pallet truck from place to place;
a base member supported by the front wheel means;
said base member having an aperture extending there-through;
sealing means mounted in said aperture;
a hydraulic fluid reservoir housing above said base member and carried thereby;
a piston chamber housing extending downwardly from the base member;
a piston mounted within the piston chamber housing and extending upwardly therefrom through said sealing means and through said reservoir housing to project upwardly therefrom into engagement with said chassis;
said piston slidably engaging said sealing means;
valve means mounted in the base member;
pump means mounted on the base member and connected to the valve means;
first passage means extending from the reservoir through the base member to the valve means;
second passage means extending from the piston chamber through the base member to the valve means;
said pump means and valve means being operable to pump fluid from the reservoir through the first passage means;

the valve means and the second passage means to the piston chamber to raise the piston relative to the base member and thereby raise the chassis from a load-releasing position to a load-bearing position;
said valve means being operable to permit fluid to return to the reservoir from the piston chamber through the second passage means, the valve means and the first passage means and thereby permit lowering of the piston relative to the abse member with consequent lowering of the chassis from a load-bearing position to a load-releasing position;
said pallet truck also including a steering handle pivotally connected to the base member for angular movement about a horizontal axis to effect operation of the pump means.

2. A pallet truck according to claim 1 wherein the pump means comprises a pump chamber housing carried by the base member and a piston slidably mounted in the pump chamber and projecting upwardly therefrom, and the steering handle has a lower end carrying actuating means for effecting downward movement of the pump psiton to cause fluid to be pumped from the pump chamber to the piston chamber, and a spring mounted in the pump chamber for effecting upward movement of the piston to cause fluid to be drawn into the pump chamber from the reservoir.

3. A pallet truck according to claim 1 wherein the valve means includes a pressure responsive valve operated by a predetermined hydraulic pressure in said second passage means to permit hydraulic fluid to flow from the second passage means through the pressure responsive valve into the first passage means.

4. A pallet truck according to claim 1 wherein said steering handle is elongated with a manually-grippable portion at an upper end, a manually-operable selecting handle adjacent the manually-grippable portion of the steering handle and linearly movable to and from lengthwise of the handle;
said selecting handle having a first position in which operation of the pump means effects raising of the chassis, spring means urging the selecting handle to the first position, a second position linearly beyond the first position in which operation of the pump means is ineffective to raise the chassis, said linearly-movable selecting handle carrying an angularly-movable cam operable to engage the steering handle in an operative position of said cam to retain the selecting handle in the second position;
said selecting handle having a third position linearly beyond the second position in which the valve means is actuated to permit flow of hydraulic fluid from the second passage means to the first passage means to effect lowering of the chassis.