US3757899A

US3757899A - Double mast side loader lift truck and double actuator balancing

Info

Publication number: US3757899A
Application number: US00123792A
Authority: US
Inventors: R Smith
Original assignee: C AND M MANUF CO
Current assignee: C AND M MANUF CO
Priority date: 1971-03-12
Filing date: 1971-03-12
Publication date: 1973-09-11
Anticipated expiration: 1990-09-11

Abstract

A side loader lift truck has a carriage which moves vertically between fore and aft spaced and unconnected masts. Forks on the carriage move laterally to either side of the masts through the open space between the masts. To prevent carriage tilting and jamming caused by a lift cylinder at one end of the carriage overrunning its opposite counterpart, a supply valve for the overrunning actuator is cut off until the other actuator catches up. The balancing or overrunning prevention is effected by connecting valve bodies to pistons, movable mast portions, or the carriage. Control spools moving within the valve bodies are interconnected by parallel chains and sprockets which move with an interconnecting shaft. The shaft is biased initially in an up or down direction, biasing the valve spools in the up or down position. When the carriage is being raised, excessive upward motion of one valve body carries the body over the spool, cutting off further supply through that valve to the actuator until the synchronizing shaft and chain return the valve spool to its predetermined position.

Description

I Sept. 11, 1973 United States Patent Smith, Jr.

[57 ABSTRACT A side loader lift truck has a carriage which moves ver- DOUBLE MAsT sIDE LOADER LIFT TRUCK AND DOUBLE ACTUATOR BALANCING [75] Inventor: Raym nd L- h, J Southbury, tically between fore and aft spaced and unconnected COIIIL masts. Forks on the carriage move laterally to either side of the masts through the open space between the masts. To prevent carriage tilting and jamming caused by a lift cylinder at one end of the carriage overrunning its opposite counterpart, a supply valve for the overrunning actuator is cut off until the other actuator catches up. The balancing or overrunning prevention is effected by connecting valve bodies to pistons, movable mast portions, or the carriage. Control spools moving within the valve bodies are interconnected by parallel chains and sprockets which move with an interconnecting shaft. The shaft is biased initially in an up or down direction, biasing the valve spools in the up or down position. When the carriage is being raised, excessive up- H m 9 Hl7 V. U41 n l m 2%6 P 79 m H9 0 07 9 3 C 8 g 7 9 .l 7 r 7 8 NM 8 .l c 9 l n 8 l mm M n mm 1 I Ma n m m M m. L s m & a u m A Cm M l m mm a m we a 0 m m N u a E d L d .1 w m D. mH A F A U IF 1 1 1] 3 2 l 2 8 7 2 2 5 55 ..l [l .1. ll.

References Cited UNITED STATES PATENTS ward motion of one valve body carries the body over the spool, cutting off further supply through that valve 214/161 EB to the actuator until the synchronizing shaft and chain 91/171 return the valve spool to its predetermined position. 91/171 2,785,809 3/1957 Riblet 2,932,171 4/1960 Ranson......... 2,602,298 7/1952 5 Claims, 6 Drawing Figures Primary Examiner-Gerald M. Forlenza Assistant Examiner-Lawrence J. Oresk AttorneyLittlepage, Quaintance, Wra

y y & Aisenberg pmmgnsm 1 ms SHEE! 1 0F 5 mvnmon RAYMOND L. SMITH JR.

ATTORNEYS PAIENTEUSEH 1 I973 SHEET 2 0i 5 wvsmon RAYMOND L. SMITH JR.

ATTORNEYS PATENTED 1 3. 757. 899 sum 3 0f 5 INVENTOR RAYMOND L. SMITH JR.

fiff/kfyg pan/b7000 j ilyfqiffilzy ATTORNEYS PAIENIEnsm I I975 SHEEI M 5 wig ATTORNEYS PATENIED I 3.757. 899

sum 5 or 5 mvsu'ron RAYMOND L. SMITH JR.

ATTOR N EYS DOUBLE MAST SIDE LOADER LIFT TRUCK AND DOUBLE ACTUATOR BALANCING BACKGROUND OF THE INVENTION Stacker retriever trucks have long been in use. Most such trucks are modifications of conventional fork lift trucks. When configured for narrow aisle warehouse use, the trucks have attachments which may move to the side for picking up and depositing loads. One problem has persisted. When the side moving attachments and loads are cantilevered forwardly on the conventional lift forks or on attachments which replace the standard lift forks, the capacities of the trucks are limited. Greater limits are imposed by the necessity of cantilevering the load laterally as well as forwardly. Thus, standard lift trucks are rated far below their standard capacities when using them as side loaders. The unique bending and twisting loads imposed on the mast structure require either mast reinforcement or the carrying of reduced loads. That is particularly critical in modern narrow aisle warehouses where clearances between loads and storage racks are limited, where accurate load positioning is required, and where excessive mast deflections cannot be tolerated.

Many warehousing systems employ fixed rails and cranes which move along the rails to service the storage racks. Costs of such fixed rail and crane systems are high as compared with stacker truck systems. 'The cranes have no versatility and are limited to movement along the predetermined fixed rail paths. Movement in an open area is impossible.

Crane systems do not have the deflection problems of stacker trucks. The tendency of loads to bend or defiect masts is limited by a pendulum effect. In the case of stacker trucks, deflected loads moving off center have increased tendency to stress the masts, thus the problems in fixed rail crane systems and in stacker truck systems are unique. 4

It has been suggested that fixed rail crane-like extractor systems be constructed WItI'L fOI'B, and aft masts which span a load moving in a narrow aisle. Such devices have been constructed simply as a vertically oriented rectangular frame having top, bottom and sides with an aligned pair of wheels at the top and an aligned pair of wheels at the bottom for moving in upper and lower tracks. Chains or cables lift the elevator between the side members of the frame. Inherently, the elevator is unstable, and lateral support is provided only by the upper and lower tracks. This system has the lack of versatility which is noted with all fixed rail crane systems. Because of the top member and rail which are necessary for that configuration, that system is not able to use the full floor to ceiling area of the warehouse. The construction of the system with rails at uniform fixed vertical distances causes great expense.

One of the drawbacks which has prevented development of a lift truck with fore and aft masts is the difficulty of coordinating the lift rate of cylinders associated with the masts. The conventional lift truck is constructed with side by side masts which are close to each other and which are interconnected in a single unit by cross pieces. Because of the closeness of the masts, and

that they tend to be self equalizing. Thus, if one piston tends to lead the piston of the other cylinder, the one piston tends to pull the other piston along. Such a self equalization cannot be present where pistons are far apart. In that case, there is no tendency of one piston to pull the other piston along.

In constructing a truck with two masts which are widely spaced so that a carriage may operate in an open space between the masts, the lift cylinders must be p0- sitioned adjacent the masts. Thus, the lift cylinders are wide apart. Variation in the extension of the parallel pistons produces a tilting of the carriage which can have several bad effects. In excessive variations, the carriage may jam. A tilted carriage creates the possibility of a sliding load which endangers the operator and the apparatus. A tilted carriage'cannot be positioned accurately opposite a storage area for inserting or retrieving a load.

The unevenness of the piston movement may have several causes. Commercially available flow dividers have accuracy errors which are intolerable for the fine control demanded in the present system. Experience indicates that 10 percent error is not unusual in the best commercial flow dividers. Unevenness of loading may cause variations in resistance to lift or exhaust pressure from the cylinders. The piston which supports the greater weight will tend to move upward slower and downward faster than its counterpart piston. I

The prior art has recognized the problem of balancing the advance or retraction of several parallel and spaced pistons which are subjected to varied loading. Many attempts have been made at maintaining an even piston advance or retraction. The previous approaches to the problem have used flow dividers such as mechanically coupled hydraulic motors, extensible valves which are connected between upper ends of pistons and complex servo systems which direct flow to a single piston or a group of pistons at a time. None of the prior art systems has provided the accuracy, simplicity and dependability which is necessary for use with a narrow aisle stacker retriever truck having widely spaced mast such as in the present invention.

SUMMARY OF THE INVENTION The present invention provides a floor-supported lift truck with two spaced free standing masts supported only by the base with a space therebetween through which pallet engaging forks may be reciprocated. Pref erably, the free-standing masts are mounted fore and aft on the truck, and the pallet-engaging forks are positioned for lateral movement transverse to the forward direction of the truck. The forks and carriage structure are configured so that the forks may be shifted to either side of a truck to pick up or deposit loads.

As is customary in stacker retrievers, the operators platform is moved with the carriage so that the operator is opposite the storage station to observe the storage or retrieval operations. So that the operators view is completely unobstructed on both sides of the truck, both the load carrying forks and the operators platform are supported on the carriage between the fore and aft free-standing masts.

The great expanse between the masts makes imperative the coordinated driving of the lift cylinders. Excessive relative movement of one piston with respect to the other, multiplied by the advantage of the lifting chains would cause a caught carriage. Sloping of the carriage creates an inherent danger of load slippage as well as the danger of jamming the carriage against the masts.

To prevent relative overrun between lifting pistons, the present invention provides a synchronizing system. First parts of two-part valves are connected to similar moving parts of the lift actuator systems. The moving parts to which the first valve parts are connected may be the pistons, the movable masts, the carriage or connecting chains. The valves are in the main supply lines to their respective cylinders, and the valves control both the raising and lowering of the pistons, masts and carriage.

The second parts of the two-part valves are connected to operators which are in turn interconnected by a synchronizer. The synchronizer permits the operators and the second valve parts to move at equal speeds along with the first valve parts. Thus, the setting on the valves remains equal. When one of the pistons moves faster than the opposite piston, the first valve part associated with the faster moving piston is moved with respect to the associated second valve part. The latter is constrained by the operators and synchronizer from movement faster than the other second valve part. This relative movement between the first and second valve part in the supply line to the fast moving piston causes the valve setting to be changed toward a reduction in flow in that supply line. If the pistons are moving upward, the valve condition changes toward a reduction in flow and causes less fluid to flow toward the cylinder or temporarily interrupts the flow to the cylinder to permit the other piston to catch up with the faster moving piston.

When the pistons and carriage are being lowered, the fluid is flowing out of the cylinders through the valves. Relative movement of first and second valve parts changes the valve condition toward less flow or no flow and slows or stops the downward movement of the fast moving piston until the other piston tends to catch up.

The synchronizer which connects the two operators is biased in one direction or the other so that both valves are initially placed in an inward or outward flow permitting condition for advancing or retracting the pistons. In one preferred form of the preloading or biasing system, a three-way solenoid valve provides fluid pressure to a preload motor to run the motor in one direction or the other direction. A fluid operated clutch connects the preload motor to a sprocket for driving a chain and a preload gear keyed to the synchronizer shaft.

The bias provided to the synchronizer by the preload motor always tends to pull the second valve part in the intended direction of travel, up or down, ahead of the first valve part which is attached to the piston or to apparatus that moves with the piston. As the first valve part moves relative to the second valve part, which is characteristic of an overrun of that particular piston, the second valve part moves toward the central or neutral flow blocking position to retard the movement of that piston.

In the preferred embodiment of the invention, the valves associated with the cylinders are three-way valves having a central neutral position of the valve elements and having opposite extreme positions with internal check valves oriented for opposite flow. Setting the valve in one terminal position permits flow toward the cylinder. Setting the valve in the other terminal position permits flow away from the cylinder. ln the central position, no flow is permitted. The valves may have tapered bodies or cores which restrict flow in intermediate settings between the extreme position and the central position.

As used herein, valves are broadly construed to include servo systems such as electrical, mechanical and hydraulic servo systems. Thus, the main flow controlling valve may be fixed in the supply line adjacent the cylinder, while a two-part servo element which controls the valve has a first part connected to move with the piston and a second part connected to move with a synchronizer. A similar two-part pilot valve or a two-part mechanical control for the main valve might replace the solenoid. Preferably, the solenoids, pilot valves or mechanical controls would all have three positions which would correspond with three positions of the main valve.

In a preferred embodiment of the invention, the truck is constructed with a rectangular open base having guide rollers at four corners for rolling along horizontal members of racks on opposite sides of a narrow aisle. A main propulsion and pump unit is mounted at one end of the rectangular frame. The pump unit is supported on tumable drive wheels in vertical independence from the frame for constant traction irrespective of loading. When the truck is in a narrow aisle, steering power is interrupted so that the truck is not steered toward the rack structure.

Telescoping masts are supported at opposite ends of the rectangular base. Preferably the masts are at one side of the frame.

The lower portions of the telescoping masts are rectangular tubes, which are employed as cooling reservoirs for the hydraulic fluid used in the system. Loading on the masts is primarily lateral, and the tubular portions are braced with lateral buttresses.

The top of the tubular fixed mast portions is configured as an uneven T with a long lateral cap portion extending across the truck and terminating in a roller for engaging a continuous horizontal member on the rack surface. A short portion of the T cap extends in the opposite direction and terminates in a roller for contacting a similar member on the opposite rack. A short parallel member is spaced fromthe long member,and between these members the extensible portion of the mast rides on rollers.

The movable mast sections are constructed of spaced outward opening channel sections having back-to-back webs parallel and spaced from each other and oriented transverse to the forward direction of the truck. Upper and lower ends of the channel members are connected together, and lower ends of the channel members have extensions which partially surround the fixed mast sections. Rollers in the extensions engage the fixed masts.

A carriage is supported between the movable mast sections. Support arms from the carriage extend through the space between the channel members and terminate rearwardly in supports for rollers which ride along opposite flanges of the channel member.

Chains connect the carriage and upper ends of the fixed mast section and overlie sheaves at upper extremities of the movable mast portions. In like manners, chains connect the fixed mast sections with lower portions of the movable mast sections and overlie sheaves on top of pistons. Vertical cylinders are connected to the fixed mast sections. Upward movement of the pistons drives the movable mast sections upward at a two to one ration and the carriage upward at a four to one ratio.

The carriage supports an operators platform and control station which moves up and down with the load. Mounted on the carriage is a rectangular frame which moves laterally to either side of the truck. Switches at opposite ends of the frame member are depressed when the frame touches a horizontal rack member which supports a pallet. Depressing of the switches enables a crosshead to move across the frame, carrying the load engaging forks outwardly into the rack.

When it is desired to reverse the direction of the forks, the forks are moved through the crosshead while the crosshead is moved across the frame.

In a preferred embodiment of the invention, at least one of the sideward extending members at the top of the fixed mast portion is configured with a trolley pick up for electrical power which is supplied at the rack face. When the truck is running within the narrow aisle, propulsion motors and pumps are' driven from power supplied through the trolleys. When the truck leaves the aisle, its power is supplied by batteries on the truck.

Preferably dual pumps of varied capacities are selectively coupled in parallel to provide high speed, low speed and inching operation of the carriage. In a preferred embodiment, one pump supplies power for steering control and for the clutch and preload motor through the main valve biasing system. When a solenoid is energized to supply power to the steering, the preload bias system is deenergized, returning the main valves to neutral so that the load can be neither raised nor lowered. When the solenoid is positioned to supply fluid pressure to the clutch and preload motor, the steering system is deenergized so that the truck cannot be turned. 5 v

' One object of the invention is the provision of narrow aisle warehousing stacker trucks with I spaced freestanding masts.

This invention has as another object the provision of a narrow aisle warehousing stacker truck with freestanding spaced fore and aft masts with an intermediately mounted carriage.

Another object of the invention is the provision of a lift piston synchronizing system for plural lift pistons in which valves in cylinder supply lines are shut off as pistons tend to overrun related pistons.

This invention has as a further objective the provision of synchronizing valve control means with preloading biasing systems for controlling the up and down valve configurations.

Another object of this invention is the provision of an interconnected steering and lift system whereby one function is discontinued as the other function is employed.

These and further objects of the invention will be apparent from the disclosure which includes the foregoing and ongoing specification, claims and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a perspective view of a floor supported narrow aisle warehousing stacker truck constructed according to the present invention.

FIG. 2 is a side elevation of a stacker truck similar to the stacker truck shown in FIG. 1, with a modified carriage having a single operators station.

FIG. 3 is a front elevation of the stacker truck shown in FIG. 2 with the power and propulsion portion removed for clarity.

FIG. 4 is a schematic representation of the dual cylinder synchronizing system.

FIG. 5 is a schematic hydraulic flow diagram for the dual cylinder synchronization system of FIG. 4.

FIG. 6 is a schematic representation of a hydraulic system for operating the biasing system shown in FIG. 4.

DETAILED DESCRIPTION OF THE DRAWINGS Referring to FIGS. 1, 2 and 3, a narrow aisle warehousing stacker truck is generally referred to by the numeral I. The truck comprises a rectangular base frame 2 with support rollers 4. Guidance wheels 6 are mounted at extremities of the frame for contacting horizontally elongated surfaces on rack structures adjacent the narrow aisles. Hydraulic power and propulsion unit 8 is connected to one end of frame 2 preferably by an elongated transverse pivot or hinge.

While the propulsion and pump section 8 is constrained against relative lateral motion with respect'to the frame, it is permitted vertical motion. Thus, the propulsion and steering wheels under section 8 are weighted only by section 8, rather than by the varying weight of the loaded and unloaded carriage.

In the embodiment shown in the drawings, masts 10 have fixed tubular sections 12 which are mounted on top of frame 2 near one sidethereof. Buttresses 14 are fixed to the tubular sections 12 to provide added lateral reinforcement. In a preferred embodiment, the tubes 12 hold hydraulic fluid and act as large cooling reservoirs. Hydraulic lines in base 2 connect the reservoir mast tube 12 with pumps in the power unit 8. I

The fixed mast sections 12 are capped by laterally extending brace members 16. Elongated horizontal arms 18 extend across the truck and terminate in wheels I9 which engage horizontally elongated surfaces on the rack structure adjacent the narrow aisles. In a similar manner, shorter extensions 20 extend laterally in the opposite direction and terminate in rollers 21 which engage rack surfaces.

Inner lateral extensions 22 are parallel to the elongated arms 18. Inward facing rollers 24, as shown in FIG. 3, are mounted on the

arms

18 and 22 for engaging inner surfaces of the flanges of I beams which form the movable mast portion 26. 7

Each movable mast section 26 is formed with two. I beams having parallel webs 28 oriently transverse to a forward direction of the truck and having flanges 29 parallel to a forward direction of the truck.

Lower ends of the movable masts are provided with horizontal extensions 30 which overlie the fixed tubular masts l2. Rollers 32 as shown in FIG. 3 are mounted in each support 30 for engaging opposite surfaces of fixed mast elements 12. As shown in FIG. 2, the l beams are held from spreading by interconnecting elements 34, which join the flanges 29 of the I beams on the side toward the fixed mast section.

Carriage 40 is supported on the movable mast bysupport extensions 42, which extend between the parallel I beams, and which carry wheels 44, shown in FIG. 3, for engagement against the inner surfaces of flanges 29.

In the embodiment shown in FIG. 1, an operators platform 46 has lift and drive controls which are omitted for clarity in the drawing. An overhead guard 48 protects the operator.

A helpers station 49 is similar to the operators sta tion 46. In FIGS. 2 and 3, the helpers station is omitted from that modification.

A double side loader capable of operating at either side of the truck is mounted on carriage 40. A rectangular frame 52 comprises two parallel interconnected I beams 54 mounted transverse to the forward direction of the truck. Frame 52 is capable of sliding laterally in either direction by operation of a cylinder Rollers fixed to the carriage and mounted within frame 52 for engaging flanges of the I beams 54 support the frame in its outward movement.

Feet

56 and 58, which are located at opposite ends of frame 52, engage pallet-supporting horizontal rack members. Foot 56 is fixed to frame 52. Foot 58 extends slightly outward and is depressible into alignment with foot 56. When foot 58 is depressed, indicating engagement with a rack member, head 60 is driven across frame members 54, carrying the forks 62 into the rack. Head 60 is supported on side pieces 64 with lower inward directed rollers 66, which ride on inner surfaces of outer flanges of I beams 54. An internal rotary hydraulic motor and gear drives head 60 across a rack which is connected to carriage 40.

Fork 62 extends through head 60. Racks are formed in lower surfaces of the forks, and pinions mounted on a common shaft drive the forks from a hydraulic rotary motor within head 60. Thus, the forks may be positioned on either side of the head, and the forks may be moved to either side of the aisle.

Parallel hydraulic cylinders 70 have pistons 72 which mount sheaves 74 at their upper extremities. Chains 76 have first ends connected to the fixed masts l2 and second ends connected to the lower ends of the movable mast portions. As the pistons 72 are driven upwardly, chains 76 carry the masts upward at twice the speed of the pistons.

In a similar manner, chains 78 are connected to upward extremities of the fixed masts and pass over sheave 79 mounted at upper portions of the movable masts and are connected to carriage 40. As the movable masts move upward, chain 78 carris the carriage upward at twice the speed of the movable masts.

Power to drive the pistons is supplied by pumps on power unit 8. Fluid lines within the base connect the pumps in the power unit with reservoirs in mast 12 and the pistons 70.

The greatest power requirement is in raising the carriage. The high speed raising of the carriage and movements over long distances are accomplished when the truck is in a narrow aisle. Propulsion of the truck over the horizontal surface requires far less power. Thus, in a preferred embodiment of the invention, one set of rollers 19 at the ends of horizontal arms 18 atop the fixed mast sections 12 is replaced with a trolley pick up for receiving power from power lines concealed in a side opening channel member mounted on one rack face in each aisle. Rectifiers on the power unit 8 convert the energy to DC for charging the truck batteries and for running the hydraulic pumps while the truck is an aisle. As the truck leaves the aisle, the trolley disengages, and battery power operates the hydraulic pumps.

As best shown in FIG. 2, the power unit 8 is hinged to base 2 by a single transverse bar 7. The weight on drive and steering wheels 9 is the constant weight of the power unit 8 rather than the variable weight of the en- .tire stacker truck and load.

In FIG. 4, a schematic representation of the dual cylinder 80 system is shown. Dual'pistons 82 are directly connected to movable mast sections 84. Carriage 86 moves upward along the movable mast 84 at twice the speed of piston 82 by the advantage imparted by cables 88. Valves 90, which may be main hydrualic valves, or master units of servo systems, have first parts 92 which are directly connected to movable masts 84. The parts 92 may be'connected to any similar movable parts of the system, such as the pistons 82, opposite sides of carriage 86 or cables 88.

Second valve parts 94 are movable with respect to the first valve parts. When valve parts 94 are moved downward, outward flow from cylinders 80 through supply lines is permitted, lowering pistons 82. When valve elements 94 are raised to their upper position, flow from supply line to cylinders 80 forces pistons 82 upward. In the central position as shown in the drawing, the supply line and cylinders are disconnected, cutting off the flow and stopping movement of piston 82. Valve elements 94 are controlled by operators which in this case are chains 96. Shafts 98 are fixed at a convenient location on the truck, for example near upper ends of the fixed masts. Sprockets 100 freely rotate on shafts 98. Sprockets 102 are keyed to synchronizer shaft 104. Thus, the chains 96, sprockets 102 and shaft 104 tend to keep valve elements 94 moving at the same speed.

Excessive movement of a first element 92 tends to draw that element over the second element 94. To bias valves 90 into a lowering or raising operating condition, a sprocket 106 is keyed on shaft 104. Chain 108 connects sprocket 106 with another sprocket 110. Clutch 112 operated by actuator 114 connects the sprocket 110. with a preload motor 116 which is operable in either direction to bias second valve elements either up or down.

The hydraulic flow diagram is schematically represented in FIG. 5.

Cylinders

120 and 122 respectively drive

pistons

124 and 126. Supply line 128 serves piston 120 through valve 130. Supply line 132 serves piston 122 through valve 134.

Fluid pressure is provided to supply lines 128 and 132 by parallel hydraulic pumps 136 and 138 of varied capacity. Either or both pumps may be operated to provide three varied speeds. The pumps supply fluid through check valve 140 and through flow divider 142 which is adjusted for maximum balance between the two cylinders. A return solenoid 144 may be energized to release pressure in supply lines 128 and 132 and to return fluid to sump 146. One-way variable flow restrictors 148 near

cylinders

120 and 122 control the lowering rates of the cylinders. Unrestricted flow in the up direction is provided, and restricted flow in the down direction is provided.

Using a servo system such as shown in FIG. 4, when

pistons

124 and 126 are being raised,

controllers

150 and 152 cause the pulling of

second valve parts

154 and 156 to the right, energizing switches 158 and 159 for connecting pumps.

If piston 124 tends to move faster than piston 126, controller 150 is deenergized and valve part 154 moves to its center position, cutting off flow to supply line 128 to cylinder 120, and deenergizing a pump by opening switch 158. As piston 126 catches up with piston 124, controller 150 is again energized, pulling second valve part 154 to the right and then closing switch 158 for supplying fluid pressure to cylinder 120.

When it is desired to lower the pistons, controllers I60 and 162 are energized, pulling

valve parts

154 and 156 to the left. At the same time, the pumps are shut off by switches 158 and 159, and valve 144 is open, allowing flow to reservoir 146. When piston 126 tends to overrun piston 124, controller 162 permits valve part 156 to be centered, preventing further flow from cylinder 122 until piston 124 catches up with piston 126.

.When the system is employed as a servo system, it is convenient to use solenoids as the control valves 90 in FIG. 4. Pulling second parts 94 upward with respect to first parts 92 has the effect of actuating solenoids such as 150 and 152 shown in FIG. 5. When a valve part 92 moves toward the center of part 94, such as in overrunning, the associated solenoid is deenergized, permitting the main control valve to return to its central neutral position. I

When the main

hydraulic control valves

130 and 134 are connected directly to the moving parts as shown at 90 in FIG. 4, the

controllers

150 and 152 are represented by the ends of chains 96 which tend to pull the second valve parts to their upper position as shown in FIG. 4 and to the right hand position as shown in FIG.

Controllers 160 and 162 are represented by the opposite ends of chains 96 which tend to pull the second valve parts 94 downward as shown in FIG. 4 or to the left as shown in FIG. 5. In a preferred embodiment of the biasing system which is shown in FIG. 6, a pump 170 supplies fluid to a steering system 172 or to a preload bias system generally indicated by numeral 174.

Solenoid 176 controls the output of pump 170. When solenoid 176 is in the preload mode as shown in the drawing, pressure is supplied to clutch cylinder 114 for engaging clutch 112 as shown in FIG. 4. When solenoid 178 is energized, valve 179 is drawn to its locking position l80'as shown in the drawing, and fluid is supplied through pressure relief valve 182 to the preload direction valve 184. In the central position of valve 184, no pressure is supplied to the preload motor 186. Valves 90 are in their central position, and no fluid flow is permitted to or from the lift cylinders. Energizing either solenoid 188 or 190 causes preload motor to turn in I thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. Lift truck apparatus comprising first and second spaced masts and first and second hydraulic actuators mounted adjacent said first and second masts, carriage means connected to the first and second masts for movement therealong and operatively connected to the actuators for being driven thereby, first and second valves connected to a common hydraulic power unit and mounted respectively adjacent the first and second actuators, each valve controlling the corresponding actuator during both upward and downward movement of the actuators, the valves having first portions connected to movable portions of the actuators, masts or carriage and having second portions movable with respect to the first portion, whereby movement of a second portion with respect to the first portion changes operational condition of a valve, first and second operator means connected respectively to movable portions of the first and second valves andsynchronizing means connected to the operators whereby relative movement of a first mast, first actuator or adjacent carriage portion with respect to the second mast, second actuator or a related carriage portion produces relative movement between first and second portions of at least one valve thereby changing operational condition of the valve. I I

2. Lift truck apparatus comprising first and. second spaced masts and first and second hydraulic actuators mounted adjacent said first and second masts, carriage means connected to the first and second masts for movement therealong and operatively connected to the actuators for being driven thereby, first and second valves mounted respectively adjacent the first and second actuators, the valves having first portions comprising spool valve bodies connected to movable portions ofthe actuators, masts or carriage and having second portions comprising spool valve pistons mounted within the bodies for movement therein, whereby movement of a second portion with respect to the first portion changes operational condition of a. valve, first and second operator means connected respectively to the spool valve pistons of the first and second valves and synchronizing means comprising a shaft having fixed radial extensions connected to the operators whereby relative movement of a first mast, first actuator or adjacent carriage portion with respect to the second mast, second actuator or a related carriage portion produces relative movement between first and second portions of at least one valve.

Claims

1. Lift truck apparatus comprising first and second spaced masts and first and second hydraulic actuators mounted adjacent said first and second masts, carriage means connected to the first and second masts for movement therealong and operatively connected to the actuators for being driven thereby, first and second valves connected to a common hydraulic power unit and mounted respectively adjacent the first and second actuators, each valve controlling the corresponding actuator during both upward and downward movement of the actuators, the valves having first portions connected to movable portions of the actuators, masts or carriage and having second portions movable with respect to the first portion, whereby movement of a second portion with respect to the first portion changes operational condition of a valve, first and second operator means connected respectively to movable portions of the first and second valves and synchronizing means connected to the operators whereby relative movement of a first mast, first actuator or adjacent carriage portion with respect to the second mast, second actuator or a related carriage portion produces relative movement between first and second portions of at least one valve thereby changing operational condition of the valve.

2. Lift truck apparatus comprising first and second spaced masts and first and second hydraulic actuators mounted adjacent said first and second masts, carriage means connected to the first and second masts for movement therealong and operatively connected to the actuators for being driven thereby, first and second valves mounted respectively adjacent the first and second actuators, the valves having first portions comprising spool valve bodies connected to movable portions of the actuators, masts or carriage and having second portions comprising spool valve pistons mounted within the bodies for movement therein, whereby movement of a second portion with respect to the first portion changes operational condition of a valve, first and second operator means connected respectively to the spool valve pistons of the first and second valves and synchronizing means comprising a shaft having fixed radial extensions connected to the operators whereby relative movement of a first mast, first actuator or adjacent carriage portion with respect to the second mast, second actuator or a related carriage portion produces relative movement between first and second portions of at least one valve.

3. The apparatus of claim 2 further comprising a biasing means connected to the synchronizing means for moving the synchronizing means in one of two directions thereby moving the second valve portions with respect to the first valve portions for creating a predetermined valve condition.

4. The apparatus of claim 1 wherein the first valve portions comprise spool valve bodies connected to move with respective actuators and where the second valve elements comprise spool valve pistons mounted within the bodies for movement therein, wherein the operators comprise flexible means connected to the spool valve pistons, and wherein the synchronizing means comprises a shaft having fixed sprockets connected to the flexible means for preventing excessive relative movement between the flexible means.

5. The apparatus of claim 2 further comprising a hydraulic pressure pump, a flow divider connected to the pressure pump for receiving hydraulic fluid therefrom and for dividing flow between first and second hydraulic lines which are connected through the first and second valves to the first and second actuators.