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Publication numberUS3005562 A
Publication typeGrant
Publication dateOct 24, 1961
Filing dateOct 29, 1959
Priority dateOct 29, 1959
Publication numberUS 3005562 A, US 3005562A, US-A-3005562, US3005562 A, US3005562A
InventorsWalter M Shaffer
Original AssigneeTowmotor Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Hydraulic drive for lift truck
US 3005562 A
Images(6)
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Description  (OCR text may contain errors)

Oct. 24, 1961 Filed Oct. 29, 1959 W. M. SHAFFER HYDRAULIC DRIVE FOR LIFT TRUCK 6 Sheets-Sheet l.

ww/MM Oct. 24, 1961 w. M. SHAFFER 3,005,562

HYDRAULIC DRIVE FOR LIFT TRUCK Filed Oct. 29, 1959 6 Sheets-Sheet 2 I pfsfeyo/P INVENTOR,

0d. 24, 1961 w. M.4sHAFFER 3,005,562

HYDRAULIC DRIVE FOR LIFT TRUCK Filed Oct. 29. 1959 6 Sheets-Sheet 3 y 6 INVENTOR.

Oct. 24, 1961 w. M. sHAFFER 3,005,562

HYDRAULIC DRIVE RoR LIFT TRUCK Filed oct. 29. 1959 6 Sheets-Sheet 4 Oct. 24, 1961 w. M. SHAFFER 3,005,562

HYDRAULIC DRIVE FOR LIFT TRUCK Filed Oct. 29. 1959 6 Sheets-Sheet 5 INVENTOR. 1%7'5? M 5644/5/55@ Oct. 24, 1961 w. M. sHAFFER HYDRAULIC DRIVE FOR LIFT TRUCK 6 Sheets-Sheet 6 Filed Oct. 29. 1959 United States Patent iiice 3,005,562 Patented Oct. 24, 1961 Gino Filed Oct. 29, 1959, Ser. No. 849,588 Claims. (Cl. 214-701) This invention relates to a hydraulic system and more particularly to a hydraulic drive system for a lift truck.

Numerous attempts have been made to provide a hydraulic system for a lift truck which would eiciently handle the loads imposed by the hoist cylinder and the tilt cylinders and at the same time maintain a smooth even controllable ow of hydraulic uid for propelling the vehicle through the desired speeds.

Some of such prior eiorts to provide a hydraulic system for a lift truck have included variable displacement motors for propelling the vehicle and wherein such motors were driven by a variable displacement pump driven by the engine. According to the present invention a hydraulic system for a lift truck is provided wherein a pair of fixed displacement gear pumps are driven by the engine and are connected to each other and to the tilt cylinders, the hoist cylinder and to variable displacement motors for propelling the vehicle so as to provide a more eiiicient, less complicated and less costly hydraulic drive system than has heretofore been provided for lift trucks.

It is among the objects of my invention to provide a lift truck having a power unit, variable displacement hydraulic motors to propel the lift truck, gear pumps driven by the power unit and tilt and hoist cylinders to tilt and hoist the lift truck load and wherein the gear pumps are connected to each other and to Valves for directing hydraulic iiuid so that during low speed drive of the vehicle the output of one pump is available for tilting and hoisting and the output of the other pump is available for propelling the vehicle and wherein under high speed drive of the lift truck the output of both pumps is available to propel the vehicle. In accordance with this object one pump is characterized by an output of about twice the output of the other pump and the larger pump is arranged to be connected to the tilt and hoist cylinders during low speed drive.

It is a further object of my invention to provide a hydraulic system in accordance with the preceding object wherein a valve housing having a pair of reciprocating plungers therein is connected to the output of the larger pump and wherein one of the plungers directs the output of the larger pump to one end or the other of the tilt cylinders to control the tilting of the mast on the lift truck and wherein the other of said plungers controls the raising and lowering of the hoisting cylinder for the lift truck.

It is a further object of my invention to provide a hydraulic system according to the preceding objects wherein a vehicle drive control valve housing is provided beneath the iioor of the lift truck and such housing includes a line connected to the output of the large gear pump and a line to the input side of the small gear pump and a line to the output of the small gear pump and to the drive motors whereby a foot pedal mounted on the oor of the lift truck controls a plunger in said valve housing controlling the flow of hydraulic iiuid to the motors yfor propelling the vehicle and wherein the displacement of the motors is varied in response to fluid pressure changes within a part of said housing.

It is a further object of my invention to provide an eicient and smooth manual control for the vehicle at any speed of the engine for maneuvering the vehicle in close quarters and without a time lag from the operation of the control to the motion of the truck. The control` here referred to is eicient for inching, which means moving the vehicle in small increments less than an inch at a time. The term creep, as referred to herein, means a slow controlled continuous motion of the vehicle in one direction.

It is a further object of my invention to provide a hydraulic system according to the preceding objects wherein the creep and inching control is obtainable at the same time a load is being lifted and/ or tilted on the lift truck mast.

It is a further object of my invention to provide a lift truck requiring a `single left foot control for the drive which leaves the operators right hand free to operate the lift, tilt and other accessories.

It is a further object of my invention to provide a hydraulic system according to the preceding object wherein the vehicle direction can be reversed without first stopping to operate a shifting lever or a clutch.

It is a further object of myl invention to provide a hydraulic system for a lift truck according to the preceding object wherein the relationship between the torque and the speed control is completely automatic `and wherein the input torque requirement of the drive stays within the engine torque capacity without requiring any thought or action by the operator of the vehicle.

It is a further object of my invention to provide a hydraulic system for a lift truck wherein the system provides an easily controlled and eiicient braking system for normal driving. In the lift truck according to my invention the conventional service brakes are utilized for emergency stops only.

Further objects and advantages relating to eiciency in operation, economies in manufacture and convenience for the lift truck operator will appear from the following description and the appended drawings wherein:

FIG. l is an elevation of a lift truck embodying the hydraulic drive made according to my invention;

FIG. 2 is a diagrammatic showing of the components of the hydraulic system and the conduit connections between the components;

FIG. 3 is an elevation with parts in section of a variable displacement hydraulic motor used for propelling the vehicle;

FIG. 3a is a draulic motor;

FIG. 4 is an elevation with parts in section of the Vehicle drive control valve;

FIG. 5 is a view of the vehicle drive control valve taken at right angles to the view of FIG. 4 and showing relief valve parts in section;

FIG. 6 is an elevation with control valve forming a part of my invention;

FIG. 7 is a sectional view of the tilt-hoist valve for operating the tilting and hoisting cylinders of the lift IL ruck;

(FIG: 8 is a plan view with parts in section showing the transmlssion and drive axle construction employed in the lift tru ck of my invention;

FIG. 9 is a side elevation showing the foot pedal control `for the vehicle drive control valve; and

FIG. l0 is an elevation of the foot pedal arrangement taken at right angles to the view of FIG. 9.

Referring to the drawings, the lift truck chassis 6 is supported by a pair of steering wheels 7 at the rear of the vehicle and a pair of drive wheels 8 at the front ofk the vehicle. A mast structure 9 is pivotally supported on the vehicle as at 10 and is provided with the carriage 11 which is adapted to be raised and lowered along the mast by the hoist cylinder 12 having the piston rod 13. It will. be understood that the mast may include slidable sections which may be elevated by the hoist cylinder 12.

plan view of a porting plate on the hyparts in section of a torque The mast 9 is adapted to be tilted about its pivotal mounting 10 by means of a pair of tilt cylinders 14 and 15.

The leftehand tilt cylinder 14 is illustrated in FIG. 1 and includes a piston rod 16 which is pivotally connected -as at 17 to the mast. The lower end of the left cylinder 14 is pivoted as at 18 lon the chassis 6 of the lift truck.

An engine housing 19 is carried by the chassis of the vehicle and supports a seat cushion 20 for the driver of the lift truck. The engine 21, indicated in phantom outline in FIG. l, is provided with a large gear pump 22 coupled to the engine at the forward end thereof. A smaller gear pump 23 is -mounted at the other end of the engine drive shaft and driven thereby. The particular arrangement of engine and pumps is not an essential part of the invention and other pump locations may be ernployed.

A counterweight 24 at theV rear of the vehicle surrounds the radiator 2S for the engine 21. The counterweight 24 is formed with a centralopening for discharge of cooling air from the radiator 25.

A steering wheel 26 is operatively connected to the dirigible wheels 7 and mounted adjacent the steering column 27 is a housing for the tilt-hoist valve 2S. `Conveniently arranged for manipulation by the oper-ator are valve levers 29 and 30 which are operatively connected to tilt plunger 31 and hoist plunger 32 of the tilt-hoist valve 28 A vehicle drive control valve 33 is mounted on the chassis 6 `beneath the door 34 of the lift truck. The vehicle control valve 33 is provided with a reciprocating plunger 35 which is operatively connected to a foot pedal 36 mounted above the floor 34 of the lift truck in a position convenient to the left foot of the operator. Y

As will appear from the following description, the operator vof the lift truck employing a hydraulic drive according to my invention may determine the direction and condition of drive by tilting his left foot and the foot pedal 36. The load carriage 11 on the mast of the vehicle may be raised and lowered and the mast 9 tilted by manual manipulation of the levers 29 and 30 mounted on the steering column. The operators right foot is used in the usual manner to control the throttle position for the engine 21 and the operators left hand is available for steering the vehicle during the right-hand manipulation of the levers 29 and 3).

Two motors 40 and 41 are provided to drive the vehicle. The left-hand motor 40 is shown in FIG. 1 as connected to the transmission 42 arranged to transmit the motor .drive Yto the drive wheels 8 of the vehicle. The motors 40 and 41 are identic-al in structure and one of the motors is shownin section in FIG. 3 `and will vbe described in detail. It will be understood that a single tmotor of larger size may be used Vinstead of the two ymotors 40 and 41. Two motors eliminate the need for a mechanical differential in the' drive axle.

The motor 4i! is provided with a rotor 43 which is in turn provided with a plurality of cylindrical bores. Each bore in the rotor 43 is provided with a piston 44. Referring vto FIG. 2, the motor-41 has been turned 90 with respect to the motor 40 to facilitate the illustration of the hydraulic lines going to and from the motors. Each piston 44 is provided with a bronze slipper 45 which isV mounted on the ball 46 at the end of the piston 44. The slippers are slidable along the'wobble plate 47 which is tiltable but non-rotatably mounted. The underside of each slipper 45 is provided Vwith a shallowrecess 48. Fluid pressure from within the piston 44 is effective through the hole 49 in the ball 46 andv through a mating hole in the slipper 45 to provide a body of iluid balancing out the thrust of the pistons 44 against the highly polished wobble plate 47. Springs 44a inside of each piston 44 bias the cylinder block or rotor V43 towards the boss 51 having the ports 51a and Sib. lPhe result of this arrangement is that there is comparatively little mechanical force exerted laterally between the sliding surface of the slippers and the highly polished surface of the wobble plate 47.

The openings 48 and 49 result in an arrangement wherein the slippers 45 slide on a lm of oil and there is little or no metal-to-metal contact between 4the slippers 45 and the wobble plate 47. The end 50 of the rotor 43 opposite the wobble plate 47 bears against an annular boss 51 on the end of the motor housing 5?.. The boss 51 (see FIG. 3a) is provided with t-wo crescent-shaped ports 51a and 51b which cooperate with the ports 53 through the end of the rotor 43. Each cylinder in the rotor is provided with a port 53 through which hydraulic fluid under pressure enters. As the pistons 44 move in response to iluid pressure the piston motion is converted to rotary motion of the rotor 43. The return stroke of the piston discharges the spent `fluid out port 53. The crescent-shaped ports 51a and Slb at the boss 5l open into the lines 5,4 and 55 of the motor housing. Depending upon the direction of -fluid llow in the lines 54 and 55, the directional rotation of the output shaft 56 is determined.

The rotor 43 is splined to the shaft 56 as at 57. The splined connection permits the end of the rotor adjacent the port boss 51 to align itself in response to springs 44a with the surface of the port boss 51. The wobble plate holder 5S is preferably trunnioned within the housing on a plate offset slightly from the axis of the shaft 56 :and toward the control piston 60. Accordingly the trunnion mounting for the wobble plate holder 58 provides an unbalanced moment urging the wobble plate to a minimum displacement position.

The motor is designed so that the maximum tilt angle of the wobble plate holder 53 is about 19 and in such maximum displacement position the volume output is preferably characterized by 3.2 cubic inches per revolution. The maximum tilt of the wobble plate holder 58 occurs when the back of the wobble plate holder 58 abuts the surface at the interior of the housing indicated at V59.V

Thertilting of the wobble plate holder 58 is effected by apparatus within the rotor housing at the left-hand side of the motor as viewed in FIG. 3. The tilting apparatus includes a cup-shaped piston 66 having a rounded head portion 62 arranged to bear against a boss 63 at one side of the wobble plate holder 58. Arranged within the piston is a spacer rod 64 having a reduced diameter portion 65 mounted for reciprocation in a sealing plug V66. The lower end of the reduced portion 65 bears against a hollow adjusting screw 67 having a hex socket 67a. The screw 67 may be adjusted axially in the cap 52 of the motor housing and thus limit the minimum tilt position of the piston 69 and of the wobble plate holder 58.

When fluid under pressure entering by way of line 69 moves through the hollow screw 67 and around the clearance between stem 65 and plug 66, such pressure is effective against the cross-section of the walls of the cup-like piston 60 to move the piston 60 axially away from the endof the hollow screw 67 and thus tilt the wobble plate holder. The plug or stationary sleeve 66 is preferably provided with O-rings to prevent the joint between the cover or end cap 52 and the housing of the motor 4t) from being subjected to high pressure. By adjusting the screw 67 the minimum displacementposition of the wobble plate holder 58 may be determined. y

The springs 44a within each ofthe pump pistons 44' of the rotor 43 also tend to bias the wobble plate holder 58 to a neutral or minimum displacement position. Such springs 44 also bias the rotor 43 axially toward the boss 51 of the end cap 52. The threaded sleeve 67 is provided lwith an Allen socket 67a to adjust thev sleeve axially and thereby limit the minimum displacement position of the wobble plate 47 Referring to the hydraulic system shown diagrammatically in FIG. 2, a reservoir 71 provides a supply of hydraulic fluid. The large gear pump 22 draws hydraulic fluid from the reservoir along conduit 72 in the direction of the arrow 73 and thence to the inlet 74 of the large pump 22. The output side of the pump 22 is connected to conduit 75 which enters the tilt-hoist valve housing 2S as at 76. The pumps 22 and 23 are preferably rated at 2000 pounds per square inch for continuous duty. They are gear pumps and are suited for use at 2500 pounds per square inch intermittently which is the type of service occurring in a lift truck. The larger pump 22 preferably has an output of 1.71 cubic inches displacement per revolution, and the smaller pump 23 has an output of a little less than half the output of the larger pump 22, namely, about .78 cubic inch per revolution. The output of the larger pump 22 enters the tilt-hoist valve at 76 and such hydraulic fluid as is not being used in tilting or hoisting exits from the valve body 28 as at port 77 4by way of 'line 7S which enters the vehicle drive control valve 33 at port 79.

The high pressure output of the smaller pump 23 leaves the pump 23 by way of conduit 80 and enters the vehicle drive control valve 33 at port 81. The input side or inlet for pump 23 is by way of conduit 82 which leads from port 83 in the vehicle drive control valve 33. The port 83 on the valve body 33 opens into a low pressure chamber 84 (FIG. 4).

The total displacement of the two pumps results A:from a design on the basis of the engine being capable of sustaining a speed of 300 or 400 revolutions per minute above the peak torque speed of the engine. The displacement of the small pump 23 is selected on a basis of an eiicient creep speed of the vehicle. This displacement, however, is such that with all of the hydraulic iiuid from the pump 23 going to the motors 40 and 41, the creeping speed will be suciently high so that there will be no tendency or inclination for the operator of the vehicle to go beyond the small pump or creeping range with the foot pedal 36 while creeping and lifting a load at the same time. If the operator were to go into the large pump or higher speed traveling range of the pedal 36, the truck would lurch at the time that the lift was completed.

The drive control valve 33 includes ra displacement control valve S5 as shown in FIGS. 5 and 6. FIG. 6 is a sectional view of the displacement control valve 85. The displacement control valve S5 operates to control the displacement of the motors 40 and 41 in accordance with the torque demand in the `drive wheels 8 of the vehicle.

The sensing means for the 'operation of the displacement control valve 85 includes the output pressure of the larger pump 22. Within the vehicle drive control valve body 33 a chamber 86 communicates with port 79 connected to line 78 coming from the tiltdhoist valve in the direction of the arrow 78a. The fluid pressure in space 86 is that Huid pressure derived from the large pump at its output side by way of line 7S and through valve 28.

'I'he displacement control valve 85 is provided with a passageway 87 which is in communication with the space 86 (in valve 33) and accordingly is subjected to the output pressure coming from the large pump through line 78. The displacement control valve 85 is provided with a plunger indicated in its entirety as at 88. The plunger 88 is mounted for reciprocation within `a bore transverse to the passageway 87. The valve 85 includes a chamber 89 at the lower end thereof as viewed in FIG. 6 and within the chamber 89 a spring 90 is arranged to bias the plunger 88 upwardly as viewed in FIG. 6 by means of a cup 91 and pin 92 which bears against the underside of the plunger-88.

The upper section SSb of the plunger S8 lits snugly within the vertical bore for the plunger in the valve body 85. This portion 88 of the plunger, however, is provided with a vertical groove 88C. Annular grooves on the plunger `form parallel sections indicated at 88d which are slightly small (about 21/2 thousandths) in diameter than the bore for the plunger. Such sections do not have any grooves such as the groove 88C. The lower sections 88e formed by the annular grooves have a sealing t with the bore and the lowermost portion SSf of the plunger 8S is provided with a longitudinal groove 88g so as to provide drainage from the bore 93 down into the chamber 89.

When the fluid pressure entering the displacement control valve by Iway of passage 87 reaches a predetermined value such, for example, as 1600 pounds per square inch, the plunger 88 is moved downwardly by fluid pressure in chamber 88a against the bias of the spring 90. This motion of the plunger is effective to open the space 88h of the plunger 88 into the passageway 93. Thus the space 88a above the plunger is placed in communication with the passageway 93 through the groove 83C and through the small annular space ybetween the sections 88]) and the bore. The small annular passage around the section 88d provides a fixed amount of restriction to slow up the ow of oil going to the control plunger 60 in the motor. This restriction is effective regardless of the extent to which the space 88h is opened with respect to passageway 93 during the displacement increasing phase of the operation. This prevents the occurrence of a hunting action in the wobble plate holder 58. The fluid under pressure thus admitted by way of passageway 93 enters the annular chamber 94 around a spring-pressed plunger 95. As viewed in FIG. 6 the plun-ger 95 is biased upwardly by means of spring 96 arranged in a chamber 57 which opens into the chamber 89. Fluid under pressure in the annular chamber 94 around the plunger 95 may leave the displacement valve body by way of port 9S, which opens into conduit 99 having one branch 69 leading to the control chamber of motor 40 and the other branch 100I leading to the control chamber of the motor 41.

As described above, the fluid under pressure entering the control chamber in the motor housing determines the angle of tilt of the wobble plate in each of the motors and thus determines the displacement of each motor. The greater the pressure in the lines 69' and 100, the greater the motor displacement. Such displacement will increase only as far as necessary to meet the tractive eiort re quired by the drive wheels S.

If the tractive effort requirement is high enough the displacement of the motors will go to its maximum at which time the pressure will start increasing beyond the 1600 pounds per square inch to a relief pressure of 2000 pounds per square inch for maximum torque. From zero to 1600 pounds per square inch corresponds to the range of zero to 23 foot pounds torque at each motor and the ratio between the pump and motor displacement is constant. Above that range, that is, from 23 to 60 foot pounds torque requirement at each motor, the pressure remains substantially constant at 1600 pounds per square inch and the ratio between the pump and motor displacements is infinitely varia'ble. For a torque requirement at each motor between 60 and 76 foot pounds, the pressure increases from 1600 to 2000 pounds per square inch and the ratio between the pump and motor displacement is again constant. The pressure and torque values given here are those found satisfactory for a certain lift truck having other characteristics given and are given for the purposes of example. Manifestly different sizes of lift trucks require different sizes of pumps and motors.

The relief ilow sensing valve plunger is arranged to cause the motors to go to a minimum displacement position when the flow through the relief valve (see FIG. 5) is greater than the combined maximum ow of both pumps 22 and 23. Such a greater flow condition would occur when the manually actuated plunger 35 is reversed while the truck is moving. Until the truck comes to a stop and is ready to reverse its direction, the motors 40 and 41 are being driven as pumps by reason of the 7 motion of the vehicle. The discharge of the motors when driven as pumps goes through the relief valve 160 so that in etect for a short time (until the vehicle stops) there are four pumps in the system.

A passageway 102 (see FIG. 5) is provided between the chamber 103 into which the relief valve 10i) discharges and thence into the low pressure space 84. The low pressure space 84 extends around to the lower end of the plunger 35 as viewed in FIG. 4.` The chamber 103 into which the relief valve 180 discharges communicates with the chamber 95C at the end of the plunger 95 through a line 184 leading to a port 105 in the displacement control valve 85. The relief valve 188' is pilot operated.

The hydraulic iluid in the space 193 is normally at reservoir return pressure and communicates with chamber 188s (lower portion of FIG. by way of the slanting passageway 100b. The chamber 108:1 provides a housing for a heavy spring 186e which normally presses the pilot valve 100d upwardly into a seat and thus closes off the passageway between the chamber 111011 and the cha'm'ber 1560 thereabove. A relatively light spring 156:1 normally biases the plunger 1561? upwardly against a stop ring. The pressure in space 156a is substantially the same as in the space 156 thereabove because of the small orilice 156e. The small oriiice 156e provides for fluid pressure transmission. In the event, however, that the pressure in 156 reaches the relief pressure of 2000 pounds per square inch and this 2000 pounds per square inch is transmitted into the space 15651, it unseats the pilot valve ltld. This results in a flow of oil through the orilice 156e past the pilot valve 10de and thence through the passageway 113% and into the space 13.3. Because of the pressure drop through the orifice 156e, the fluid pressure in the chamber 156e is suddenly reduced below that in space 156 and the resulting unbalanced condition is effective to move the plunger 156b downward in opposition to spring156d to open the ports 156C. The space 97 and the space 89 which communicates therewith at the lower end of the valve 8S are open to the space 84 in the valve 33 (see FIG. 4) by way of passageway 106 in the valve 85. A difference in iluid pressure between the space 163 and the space 84 is effective through line 134 against the plunger 35 and moves said plunger against the bias of the spring 96.

When pressure in the space 183 is approximately 35 pounds per square inch higher thanrin the space 84 due to the pressure drop through the passageway 182, this pressure dilierence is effective to move the plunger 9S against the force of the spring 96 so that the shoulder 95a on plunger 95 cioses the passageway 93. When this occurs the lower shoulder 95!) on the plunger 95 opens the space 94 around the plunger into the short passageway 108. As a result of this movement of plunger 95 iluid pressure in the line 99 is drained. Accordingly the wobble plate holder 58 is moved to its minimum dispiacernent position.

The space 84 in the vehicle drive control valve 33 opens into line 110 which exits from the valve body at port 111. The line 110 runs through a filter 112 land thence to port 113 in the housing for the tilt-hoist valve 2S. The space 114 within the valve 28 opens into an exit port 115 connected to line 116 leading to the reservoir 71.

The discharge from the large pump 22 comes into the tilt-hoist valve 28 by way of line 75 kand port 76. The discharge thus enters a chamber 118. With the tilt-hoist valve in neutral position the hydraulic fluid in the chamber 118 moves through the path indicated by the arrows' 119 into the chamber 120. With the tilt plunger 31 in the neutral position shown in FIG. 7 and the hoist plunger 32 in the neutral position shown in FIG. 7, hydraulic fluid moves out of thel chamber 120 into the chamber 121 and thence into exit port 122 to line 78 leading to the port 79 in the vehicle drive control valve 33. Thus with the plungers 31 and 32 in the neutral position yillustrated .in

8 FIG. 7, the discharge from the large pump goes through thek valve body 28 and thence to the space 86 in the vehicle drive control valve 33.

The plunger 31 for the tilt cylinders 14 and 15 includes four spaced lands 123, 124, 125 and 126 spaced' from each other by reduced diameter portions 127, 128 and 129. An exit port 130 is located in a chamber 131 adjacent the reduced diameter portion 129 on the tilt cylinder plunger 32. The exit 130 leads by way of conduit 133 to the top of tilt cylinder 14 by way of branch 134 and to tilt cylinder 15 by way of branch 135. The exit port 130 is also shown in the diagrammatic view of FIG. 2. Near the lower end of the plunger 31 as viewed in FIG. 7 there is an exit port 136 adjacent the reduced diameter portion 127 of the plunger `and the exit port 136 leads by way of conduit 137 to the bottom tilt cylinder 14 through branch 138 and tothe tilt cylinder 15 by way of branch 139.

The chamber 114 within the valve 28 is open to the reservoir by way of line 116 and port 115. Accordingly this chamber which surrounds the pluugers 31 and 32 and their cooperating ports may be referred to as a lowrpressure chamber. It will be observed that moving the tilt plunger 31 downwardly as viewed in FIG. 7 will bring the upper edge of the land 123 to a position to open the port 136 into the chamber 114 and this would open the lower end of the tilt cylinders 14 and 15 into the lowv pressure chamber and discharge the hydraulic fluid therefrom into the reservoir 71. AtV the same time the uppermost exit port 130 cooperating with the reduced diameter portion 129 will open the upper ends of the tilt cylinders 14 and -15 to the hydraulic fluid coming into the valve body 28 from the large pump 22 by way of the line 75. Fluid under pressure in chamber 118 moves through passageway 118a into chamber 131 and thence outrto the tilt cylinders by way of port 130 and line 133. In this way the tilt cylinders are loaded with hydraulic iiuid under high pressure at one end of the tilt cylinders and open to the reservoir or low pressure at the other end of the tilt cylinders. Moving the plunger 31 in an opposite direction to the limit of its movement will reverse the operation just described. In other Words, the lower edge of the land 126 will be moved upwardly away from the position shown in FIG. 7 so as to permit hydraulic liuid coming from the line 133 and port 130 to ow into the low pressure chamber 114. High pressure fluid from space 118 moves to line 137 by way of passageway 118b. The chamber 114 is exhausted in 4the usual manner by way of port and line 116 leading to the reservoir 71.

The hoist cylinder 12 is a single acting cylinder. As viewed in FIG. 1, it will be understood that the weight of the masts and the carriage 11 moved upwardly by the hoist cylinder 12 will be effective to lower the carriage and masts when the cylinder 12 is exhausted. Accordingly the plunger 32 for the hoist cylinder comprises but three `lands 140, 141 and 142. When the plunger 32 .is movedupwardly as viewed in FIG. 7, the lower edge of the land 142 opens the chamber 143 into the low pressure chamber 114. This results in hydraulic fluid in the hoist cylinder coming back to the valve 2S by way of line -144 and into the port 145 in the chamber 143. Thevplunger 32 includes reduced diameter portions 146 and 147. When the .plunger 32 is moved Vdownwardly as viewedii'n FIG. 7, hydraulic fluid under high pressure from the large pump 22 is 'admitted to the chamber 143 and Vthence out through port 145 to line 144 and to the 'hoist cylinder 12. This admission of hydraulic liuid to the hoist cylinder 12 raises the carriage and masts in the usual manner. The fluid ow path to the hoist cylinder 12 from space 118 is through passageway 118a, through chamber a, thence through passageway .141a into chamber 141b.

Referring to the sectional view of the tilt-hoist valve 28 shown .in FIG. 7, it will be observed that -the output from the large pump enters the chamber 118 by way of line 75 and that a relief valve assembly 210 is arranged in the chamber 118 adjacent the line 75. It is desirable to provide a relief valve such as that indicated in its entirety as at 210 to protect the large pump 22 against overloads such as might occur if an attempt were made to lift a load on the load carriage that was too heavy for the hydraulic system including the pump 22. Similarly an attempt may be made by the operator to tilt the mast when the mast is subjected to a load or resistance against tilting greater than the capacity of the pump 22 and the associated hydraulic system parts.

The relief valve 210 comprises a cylindrical portion 211 extending through space 118. At any time the pump 22 is in operation hydraulic iluid can flow around portion 211 but such hydraulic uid has access to the relief valve poppet 225 only through the holes 212. Integrally formed with the cylindrical portion 211 is an upwardly extending cylindrical portion 213. A valve plunger 214 having a piston 215 and a valve closure 225 is mounted for reciprocation within the cylindrical portion 211 of the relief valve 210. A chamber is provided as at 216 above the piston 215 and passageways 217 lead upwardly from the chamber 216. The passageways 217 are closed at their upper end during normal operation of the lift truck by a spring-pressed valve member 218. The underside of the valve member 21S is pointed and seats in a recess in a section 219 having a bore 220 therein. The bore 220 is normally open to the fluid pressure in the chamber 118.

The spring above the Valve member 218 biases the member 218 downwardly and the bias of the spring 221 is adjusted by a screw 223. The spring bias is adjusted by the screw 223 to maintain the plunger in its lowered position when the pressure in the chamber 118` is Within the safe operating pressure of the large pump 22. When, however, the pressure in chamber 118` exceeds the adjustment eiected by screw 223 and spring 221, the plunger 218 is raised from Iits seat and fluid under pressure entering the opening 22,0 is conducted downwardly through passageways 217 into the chamber 216 above the piston 215. In response to piston movement the plunger 214 is carried downwardly against the bias of the spring 2214 and the valve closure 225 opens to relieve the pressure in the chamber 118 into space 114 and line 116 going to reservoir 71.

The plunger 35 of the drive control valve 33 is formed to provide a series of spaced lands 150, 151, 152 and 153. The plunger is shown in #its neutral position in FIG. 4 and when the plunger 35 is moved downwardly the uppermost land 153 closes the port 154 between the chamber 86 and the chamber 84. Hydraulic fluid from the large pump continues to move into the chamber 86.

Hydraulic fluid from the large pump being prevented from owing out to the port -154 and into the low pressure chamber 84 moves from the chamber 86 through a passageway 155a and past the check valve 155 into chamber 156 to supplement the hydraulic fluid under pressure coming into the chamber 156 from the small pump 23 by way of the line 88 and port 81. When the plunger 35 is moved upwardly a similar result occurs. Hydraulic fluid coming into the chamber 86 from the large pump 22 by way of the line 78 goes through the check valve 155 and supplements the hydraulic iluid coming into the chamber from the small pump 23. When all of the uid from the large pump 22 supplements the lluid coming from the small pump 23, the drive unit is in a normal drive condition which is faster than the creeping range of the vehicle.

The land 151 located in the chamber 156 is provided with a groove 157 along the upper edge of the land. A similar groove 158 is formed along the lower edge of the land 151. When the plunger is moved upwardly (as viewed in FIG. 4) so that the land 15-1 just closes the port 159, the groove 157 is open but the land 150 therebelow is closed with respect to the port v160 so that the only access for iiow to the low pressure space 84 is through the groove 157, thence to chamber 163 and port 164. At this point the restriction offered by the groove 157 causes pressure to be built up against the small pump 23 and inthe spaces 156, 81, 18 and line 54b to the motors. The check valve 155 prevents ilow out through 1.55a, 86 and 154 to the space 8\4 since land 152 is still Open with respect to port 154. The pressure due to this amount of restriction is not high enough for any motion ofthe llifttruck even though it may be unloaded and there is no ilow in line 54b.

If the plunger 35 is moved slightly further upward (as viewed in FIG. 4), the groove 157 will oer suilicient restriction t-oV build up enough pressure against the pump 22 and in the spaces 156, 81, 162, -line 54b and also against the motors 40 and 411 to just overcome the resistance of the drive wheels. A very slow creeping motion will result with a minor portion of the fluid from chamber 156 going to the motor supply line 54b and the major portion of the uid escaping through groove 157 into chamber 163, out port 164 and thence into the space 84. As the upper edge of the land 1571 reaches the lower edge ofthe port 159 there is no motion of the vehicle. As the land continues to be raised the escape through the groove 157 of hydraulic fluid is decreased which means that more of the hydraulic lluid from the small pump entering chamber 156 is directed to the drive motors 40 and 41.

When the plunger 35 is raised to the point that the groove 157 is just closed, the vehicle is at its upper limit with respect to the creeping range and all of the oil from the small pump 23 is going to the motors 40 and 41. Land 152 and the cushioning groove 161 are open with respect to the port 154 so that the pressure level in the chamber 86 is not as high as the pressure in chamber 156 and accordingly there is n-o flow through the check valve 155 and the pump 22 is not acting to propel the vehicle. When, however, the plunger 35 is moved upward to the full extent of its travel and the land 152 as well as the groove 161 are closed with respect to the port 154, the large pump output 22 combines with the output of the small pump 23 as previously described and the vehicle is in full speed or high speed operating range. Under this full drive range or high speed condition of operation the output of both pumps is directed to the drive motors.

During the creep condition of drive, as above described, the motors 40 and 41 are at a position of minimum displacement since the pressure in the space 86 is low and will not cause the displacement control valve to function. Also for the creep condition of drive it will be understood that the engine is held at a constant speed by the accelerator pedal and that the creep speed of the vehicle is controlled entirely by the foot pedal 36 moving the plunger 35. When the foot pedal 36 is pushed down at the toe portion 181 thereof so as to move the plunger 35 into the Valve body 33 to its maximum, the

upper edge of the land 150 closes the port 1160 and the groove 157 at the upper edge of the land 151 is completely closed by being positioned Within the port 159.

A cushioning groove 161 at the upper edge'of land 152 may be disposed entirely within the port 154. Accordingly the only path forV oil in space 156 is down through chamber 162 and thence out through line 54b leading to the motors. The only route for hydraulic uid coming into the valve body 33 by line 78 from large pump 22 tis through the check valve 155 and thence into space 156 where it combined with the fluid from the smaller pump 23. Under the condition of drive just described both pumps are driving the motors. This is the normal travel condition of the vehicle. The maximum travel speed will be reached after a short period of acceleration if the accelerator pedal (not shown) is fully down and the engine throttle is wide open.

Vannesse At the start of the acceleration the system pressure goes to relief pressure of about 2000 pounds per square inch for :an instant and this is effective through the displacement control valve 85 to put the motors in their maximum displacement position. The system pressure then quickly drops to the shifting level of about 1600 pounds per square inch and, as the accelerating torque requirement at the driving wheels gradually decreases, the displacement of the motors also gradually decreases to a minimum displacement. Thereafter the system pressure f drops to about 900 to 1000 pounds per square inch for normal level travel.

With the hydraulic drive of my invention and While driving the vehicle forward, the position of the plunger 35 may be fully reversed. The relief iiow sensing valve plunger 95 operates as described above to keep the motors in minimum displacement until the vehicle approaches a complete stop. This is a maximum braking condition which is not severe until the truck is down to a very low speed. The braking action, however, can be easily and softly -controlled by using the opposite direction creep range of thefdrive control pedal.

While the truck is traveling forward the hydraulic.

fluidl moves from chamber 156 into chamber 162 and thence 'to the motors 48 and 41. Similarly during. this time the spent hydraulic iluid from the motors is returning by way of line 55h into chamber 163, thence out through port 164 into the low pressure space 84. lf the plunger 35 is pulled out, however, so that the lower edge -of the land 152 restricts the exit of this returning oil from chamber 153 through port 164, a back pressure is fbuilt up in chamber 163 against lthe oil returning from the motors. `The amount of restriction with the resultant back pressure determines how severe the braking will be. Since there is relatively low pressure in space 86, the motors will stay at -a minimum displacement regardless of Whether the plunger 35 is' moved rapidly or slowly as thevehicle approaches a completely stopped position.

If the vehicle is traveling with a full forward drive position of the plunger and the operators foot is removed from the accelerator, the engine speed slows down at a faster rate than the truck slows down. There is, therefore, 'not enough oil .to `supply the motors 46 and 41 when they are'acting as pumps. Under this condition 'of operation a make-up check valve 165 allows the difference between the volume the pumps supply andthe volume the motors need 'as pumps Vto enter space 156 from the space 84.

` It will be observed that the drive control valve is symmetrical in action and the functioning in reverse is substantially `the same as for forward drive except `that Adifferent lands and lshoulders and grooves operate to 'direct the hydraulic fluid. 'In forward drive hydraulic iiuid 'from space 156 moves into the chamber 162 and thence out to the motors 49 and 41 by way of line 54h. .During forward drive spent oil from vthe motors 40 and 41 returns by way of line 55b.YV On reverse drive an opposite condition obtains. Hydraulic liuid under pressure in space 156 is directed into chamber 163 and thence -to line 55b to reverse the drive of the motors 40 and 41. VUnder reverse drive the spent hydraulic uid is returned -by way of line'54b.

The 'pedal 36 for controlling themovement of the plunger 35 in the drive control valvev 33 isV preferably arranged as best `shown in FIG. 9. A bracket 175 supports a pedal pivot pin 176 and a depending arm 177 on the pedal 36 is connected through a link 1787to lever 179.

fThe lever 179 is iiXed to a shaft 18tlljournalled as at v186:2. When the toe portion 181 Vof the pedal36 is ,pressed downwardly the plunger 35 Yis pushed inwardiy of the valve body 33 by depending arm 185thv fixed to shaft '180. When the heel portion 182 of the pedal 36 is pushed down the plunger 35.is lwithdrawn'from the valve body 33. Integrally 'formed with thelever 179 12 is a-boss 183 having a :flattened portion 184 at its lower periphery which is adapted to bear against a liat upper edge of the switch lever 185.

A wiring diagram is superimposed on the showing of FIG. 9 for the engine starting motor circuit. The circuit includes a storage battery 186, a starting motor 187, a starter switch 188 and a switch indicated in its entirety as at 189. The lever 185 mounted on the switch 189 is effective to maintain a circuit across terminals 198 and 191 when the lever 185 is in the neutral position shown in FiG. 9. The lever 185 is biased to bear against the liat 184 on the boss 183.

It will be noted that when the pedal 36 is rocked from its neutral position, shown in FIG. 9, the boss 183 will be effective to rock the lever 185 downwardly eti .the flat 184 and such motion is effective to open the circuit across the terminals 190 and 191. The result of this arrangement is that the pedal 36 and the drive control plunger 35 must be in a neutral position before the starter motor may be energized through the starter switch 188. Thus there is an interlock between the drive control pedal 36 and the engine of the vehicle which insures that there will be no motion of the vehicle at the time the engine is started.

VThe rotation of the driving shaft kof the motors 4i) and 41 is transmitted to a ring gear 195 in the drive to the front wheels as illustrated in FIG. 8.V Each of the drive shafts for the motors 40 and 41 is provided with a beveled gear (not shown) to mesh with the teeth 196v of the ring gear 195. The ring gear 195 is provided with a hub 197 which is splined to the axle 198. The drive wheels are journalled on a stub axle 199 mounted in the transmission housing 280. The outer end of the drive shaft 198 is provided with a spur gear 281 which is adapted to mesh with an internal ring gear carried by the drive wheels. No mechanical dilerential is required 'inasmuch as the lluid pressure directed to the motors 40 and 41 accommodates the torque dilerences at the drive wheels resulting from turning the vehicle.

Having thus described this invention in such full, clear, concise and exact terms as to enable any person skilled in the art to which it pertains to make and use the same, and having set forth the best mode contemplated of carrying out this invention, I state that the subject-matter which I regard as being my invention is particularly pointed out and distinctly claimed in what is claimed, it being understood vthat equivalents or modifications of, or substitutions for, parts of the above specifically described embodiment of the invention'may be made without departing from the scope of the invention as set forth in lwhat is claimed.

What is claimed is:

l. Hydraulic drive means for a litt truck having a tilt cylinder and a hoist cylinder, said lift truck having a pair of drive wheels, variable displacement hydraulic motor means operatively connected to said drive wheels, an internal combustion engine, a irst gear pump operatively connected to and driven by said engine, a second Y gea-r vpumphaving a capacity of about half the capacity of said first gear pump operatively connected to said engine to be driven thereby, a hydraulic liuid reservoir, a conduit connecting said reservoir to the input of said yfirst gear pump, a tilt-hoist valve, a conduit connecting kthe output 'of said irst .gear pump to said tilt-hoist valve, a tilt plunger mounted for reciprocation in said tilt-hoist valve, conduit means connecting said tilt-hoist valve to said tilt cylinder whereby in response to tilt plunger movement hydraulic uid from .said first gear pump is directed into saidrtilt cylinder, a hoist valve plunge mounted 'for reciprocation in said tilt-hoist valve, conduit -means connecting said tilt-hoist valve to said hoist cylinder whereby said Vhoist plunger may be moved to direct fluid from said vfirst gear pump into said hoist cylinder, a drive control valve having a movable plunger therein, conduit means connecting said tilt-hoist-valve to -said 13 drive control valve to lead hydraulic fluid from said tilthoist valve into said drive control valve, a conduit leading from said tilt-hoist valve through said drive control valve to the input side of said second gear pump, conduit means connecting the output of said second gear pump to said vehicle drive control valve, said drive control valve plunger and said drive control valve having cooperating passageways to direct the output of said second gear pump to said variable displacement motors, torque control valve means comprising means movable in response to changes in fluid pressure in the output of said first-named gear pump in said drive control valve, conduit means connecting said torque control means and said variable displacement motor to vary the displacement of said motors in response to variations in prsure in the hydraulic duid from the output side of said rstnamed gear pump as sensed in said drive control valve.

2. Hydraulic drive means for a lift truck having a tilt cylinder and a hoist cylinder, said lift truck having a pair of drive wheels, variable displacement hydraulic motor means operatively connected to said drive wheels, an internal combustion engine, a first fixed displacement pump operatively connected to be driven by said engine, a second xed displacement pump having a capacity of about half the capacity of said first pump operatively connected to said engine to be driven thereby, hydraulic fluid reservoir means, a conduit connecting said reservoir to the input of said first pump, a tilt-hoist valve casing, a conduit connecting the output of said first pump to said tilt-hoist valve casing, a manually ope-rated tilt plunger mounted for reciprocation in said tilt-hoist valve casing, conduit means connecting said tilt-hoist valve casing to said tilt cylinder, cooperating cavities on the tilt plunger and valve whereby in response to plunger movement hydraulic fluid from said irst pump may be directed into said tilt cylinder, a hoist valve plunger mounted for manual reciprocation in said tilt-hoist valve casing, conduit means connecting said tilt-hoist valve casing to said hoist cylinder, cooperating cavities on the hoist plunger and valve whereby said hoist plunger may be moved to direct fluid from said first pump into said hoist cylipder, a drive control valve having a movable plunger therein, conduit means connecting said tilt-hoist valve to said drive control valve to lead hydraulic uid from said iirst pump and from said tilt-hoist valve casing into said drive control valve, a conduit leading from said tilt-hoist valve casing to the input side of said second pump, conduit means connecting the output of said second pump to said vehicle drive control valve, said drive control valve plunger and said drive control valve having cooperating passageways to direct the output of said second pump to said variable displacement motors, control valve means comprising means movable in response to changes in pressure in the output of said rstnamed pump, conduit means connecting said control valve means and said variable displacement motor to increase the displacement of said motors in response to increases in pressure in the hydraulic fluid at the output side of said first-named pump.

3. Hydraulic drive means for a lift truck having tilt cylinders and a hoist cylinder, said lift truck having a pair of drive wheels, -a pair of variable displacement hydraulic motors, each of said motors being operatively connected to one of said drive wheels, an internal cornbustion engine, a rst gear pump operatively driven by said engine, a second gear pump having a capacity of about half the capacity of said iirst gear pump operatively connected to said engine, hydraulic fluid reservoir means, a conduit connecting said reservoir to the input of said iirst gear pump, a tilt-hoist valve, a conduit connecting the output of said first gear pump to said tilt- -hoist valve, a tilt plunger mounted for reciprocation in said tilt-hoist valve, rst conduitrmeans connecting said tilt-hoist valve to said tilt cylinder whereby hydraulic uid from said rst gear pump may be directed into said 14 tilt cylinder, second conduit means connecting said tilthoist valve and tilt cylinders to direct fluid from the tilt cylinders to the said reservoir, a hoist valve plunger mounted for reciprocation in said tilt-hoist valve, conduit means connecting said tilt-hoist valve to said hoist cylinder whereby said hoist plunger may be moved to direct fluid from said rst gear pump into said hoist cylinder, -by-pass means -in said tilt-hoist valve to conduct said first pump output out of said tilt-hoist Valve, a drive control valve having a movable plunger therein, conduit means connecting said tilt-hoist valve, by-pass means to said drive control valve to lead hydraulic fluid from said tilt-hoist valve by-pass means into said drive control valve, a conduit leading from said tilt-hoist valve to the input side of said second gea-r pump, conduit means connecting the output of said second gear pump to said vehicle drive control valve, said drive control valve plunger and said drive control valve having cooperating passageways to direct the output of said second gear pump to said variable displacement motors, torque responsive means including means movable in response to changes in pressure in the drive control valve of iluid coming thereinto from the output of said rst-named gear pump, conduit means connecting said torque responsive means and each of said variable displacement motors to vary the displacement of said motors in response to variations in pressure in the hydraulic fluid in the drive control valve coming from the output side of said lirst-named gear pump.

4. Hydraulic drive means for a lift truck comprising a pair of drive wheels, variable displacement hydraulic motor means connected to said drive wheels, a pair of tilt cylinders, a hoist cylinder, an internal combustion engine, a large fixed displacement pump operatively connected to said engine to be driven thereby and a small iixed displacement pump operatively connected to said engine to'be driven thereby, `said large pump having a capacity of about twice the capacity of the small pump, tilt-hoist valve means to direct the output of said large pump into said tilt `cylinders and direct the output of said large pump into said hoist cylinder, a hydraulic fluid reservoir, a conduit connecting said reservoir to the input of said large pump, a drive control valve, conduit means connecting said tilt-hoist valve to said drive control valve to direct the output of said large pump from the tilthoist valve to the drive control valve subsequent to operation of the tilt cylinders and the hoist cylinder, said small pump having an input line connected to said drive control valve whereby a portion of the output of said large pumpis available to supply the inlet of said small pump, conduit means connecting the output side of said small pump to said drive control valve, said drive control valve Aincluding metering means to direct a portion of the output of said small pump to said variable displacement drive motors under creep drive conditions, said drive control valve including means to direct the output of both of said pumps to said hydraulic drive motors under high speed drive conditions.

5. Hydraulic drive means for a lift truck comprising a pair of drive wheels, a variable displacement hydraulic motor connected to each of said drive wheels, said variable displacement motor having a tilting wobble plate t-ovary the motor displacement, a pair of tilt cylinders, a hoist cylinder, Van 'internal combustion engine, a large pump operatively connected to said engine to be driven thereby Vand a small pump operatively connected to said engine lto ybe driven thereby, said large pump having a capacity of about twice the capacity of the small pump, tilt-hoist valve means having manually reciprocable plungers to direct a part of the output of said large pump into said tilt cylinders and at the same time direct a part of the output of said large pump into said hoist cylinder, a hydraulic fluid reservoir, a conduit connecting said reservoir means to the input of said large pump, a drive control valve, conduit means connecting said tilt-hoist valve to said drive control valve to direct the entire output of said large pump from the tilt-hoist valve to the drive control valve subsequent to operation of the tilt cylinders and the hoist cylinder, Vsaid small pump having an input line connected to said drive control valve whereby a portion of the output of said large pump is directed to the inlet of said small pump, conduit means connecting the output side of said small pump to said drive control valve, said drive control valve including means to direct a part of the output `of said small pump to said variable` displacement drive motors under creep drive conditions, said drive control valve including means to direct the output of both of said pumps to said hydraulic drive motors under high speed drive conditions, a displacement control valve having means responsive to variations in the ouput of said large pump, a conduit connecting said displacement control valve and said hydraulic motor, said motor having pressure responsive means operatively connected to said wobble plate and to said conduit to vary the motor displacement.

6. Hydraulic drive means -for a lift truck having a mast provided with a hoist cylinder, said lift truck having tilt cylinders for tilting the mast, said lift truck having a pair of drive wheels at the forward end thereof and a pair of steering wheels at the rear end thereof, an internal combustion engine `mounted at the rear of said lift truck, a large gear pump driven by said engine and a small gear pump driven by said engine, said small gear pump having a capacity of about half the capacity of the large gear pump, means to direct the output of said large gear pump to said hoist cylinder and to said tilt cylinders for handling the load carried by the mast of the lift truck, a drive control valve mounted on the lift truck, said drive control vvalve having a reciprocating plunger therein, a foot pedal pivotally mounted on the lift truck and operatively connected to said drive ,control valve plunger, hydraulic reservoir means, conduit means connecting said hydraulic reservoir means to said large pump, valve and conduit means connecting the output of said said large gear pump to said drive control valve, conduit means connecting said drive control valve'to said small gear pump to provide input hydraulic iluid for said small gear pump from the output side of said large gear pump, valve and conduit means to direct a part of vthe output of said small Igear pump to said var-iablevolume displacement motors under creep drive conditions of the lift truck, and direct the output of both gear pumps to said hydraulic motors in response to high speed conditions of drive.

7. Hydraulic drive means for a lift truck having a mast provided lwith a hoist cylinder, said lift truck having tilt cylinders for tilting the mast, said lift truck having a pair of drive wheels at the forward end thereof and a pair of steering wheels at the rear end thereof, an internal combustion engine mounted at the rear of said lift truck, a large pump driven by said engine and a small pump driven by said engine, said small pump having a capacity of about half the capacity of the large pump, means to direct a part of the output of saidA large pump to said hoist cylinder, means to direct a part of the large pump output to said tilt cylinders for handling the load on the mast of said lift truck, ardrive control valve mounted on the lift truck, said drive control valve having a reciprocating plunger therein, a foot pedal pivotally mounted on the lift truck and operatively connected to said drive control valve plunger, said foot pedal and4 drive control Vplunger having neutral and forward and reverse positions, a starting motor for said engine, battery and cir- Vcuit means for energizing said starting motor, a switch in said circuit, means operatively connected to said foot pedal to open said switch in response to movement of the pedal from neutral `to either forward or reverse position.

8. 'Hydraulic drive means for a lift truck comprising a power unit, a first gear pump driven by said power unit, a second gear pump driven by said power unit, said second gear pump having an output corresponding'to about half of the output of said first gear pump, variable displacement rotary hydraulic traction motor means, a d-rive control valve, a fluid reservoir, conduit means connecting said reservoir to the input of said iirst gear pump, valve and conduit means connecting the output of said rst gear pump to said drive control valve, means directing a part of the output of said rst gear pump to the input of said second gear pump, conduit means connecting said drive control valve and the output of said second gear pump to said variable displacement hydraulic traction motor means for low speed drive of the vehicle, and means to supplement the output of said second gear pump with the output of said iirst gear pump for high speed drive of the vehicle.

9. Hydraulic drive means for a lift truck having a mast provided with a hoist cylinder, said lift truck having tilt cylinders for tilting the mast, said lift truck having a pair of drive wheels at the forward end thereof and a pair of steering wheels at the rear end thereof, variable displacement hydraulic motor means operatively connected to said drive wheels to provide traction for said lift truck, a p ower unit mounted at the rear of the lift truck, a large pump driven by said power unit and a small pump driven by said power unit, said small pump having a capacity of about half the capacity of the large pump, manual valve means to direct a part of the output of said large pump ,to said hoist cylinder and to direct a part of the large pump output to said tilt cylinders for handling the load on the mast of said lift truck, -a drive control valve mounted on the lift truck, said drive control valve having a reciprocating plunger therein, a foot pedal pivotally mounted on the lift truck and operatively connected to said drive control valve plunger, said foot pedal having a neutral position and adapted to be tilted forwardly therefrom for forward drive and rearwardly from said neutral ,position for reverse drive, means to adjust said traction motor to maximum displacement position yand, direct the output of both of said pumps to said traction motor means.

l0. Hydraulic drive means for a lift truck comprising a power unit, a first pump operatively connected to said power unit to be driven thereby, a second pump operatively connected to said power unit to be driven thereby, said first pump having an output volume of about twice the output volume of said second pump, a reservoir for hydraulic fluid, means to connect the input side of said tlrst Vpump to said reservoir to provide inlet iluid for said iirst pump, a tilt-hoist valve body, a drive control valve body, means to conduct the output from said rst pump through said tilt-hoist valve body to said drive control valve body, conduit means connected to said drive control Vvalve body and to the input side of said second pump whereby the inlet fluid for said second pump is supplied from said iirst pump after passage of said uid through both of Said valve bodies, variable displacement rotary hydraulic traction motor means, a manually operable drive control plunger mounted in said drive control valve body, cooperating cavities in said valve body and said plunger whereby movement of the plunger in one direction'conduits the iluid output of said second pump to said hydraulic traction motor means to rotate the traction motor in one direction and movement of said plunger in an opposite direction conducts the output of said second pump to said hydraulic traction motor means to drive the same in `an opposite direction, and torque-responsive means to vary the displacement of saidtraction motor means.

11. Hydraulic drive means for a Vlift truck comprising a power unit, a first gear pump operatively connected to said power unit to be driven thereby, a second gearpump operatively connected to said power unit to be driven thereby, said first gear pumphaving an output capacity oi about twice the output capacity of .said second gear pump, afreservoir for hydraulic fluid, means to connect the input side of said first pump to said reservoir to provide inlet iluid for said first pump, a tiltcylinder, a hoi-st cylinder, a tilt-hoist valve casing, adrive control valve casing, means to conductthe output of said lirst pump through Said tilt-hoist Valve `casing to said drive control valve casing, conduit means to connect said drive control valve casing to the input side of said second gear pump to provide hydraulic fluid for the inlet of said second gear pump whereby the hydraulic iiuid supply for said second gear pump is obtained from said iirst gear pump output, variable displacement rotary hydraulic traction motor means, said traction motor means having la wobble plate therein to vary the displacement of the motor, a manually operable drive control plunger mounted for reciprocation in said drive control valve casing, cooperating cavities in said drive control valve casing and in said plunger whereby movement of the plunger in one direction conducts the lluid output ofthe second gear pump to said traction motor means to rotate the motor in one direction and movement of said plunger in an opposite direction conducts the output of said second gear pump to said hydraulic motor means to drive the same in an opposite direction, and means to tilt the wobble plate and move the wobble plate to maximum displacement position.

12. Hydraulic drive means for a lift truck comprising an internal combustion engine, a irst gear pump driven by said engine, a second gear pump driven by said engine, said second gear pump having an output corresponding to about half the output of said iirst gear pump, variable displacement hydraulic motor means for driving the traction wheels of the lift truck, said gear pumps each having a lluid supply inlet, a source of iluid supply connected to the inlet of each of said gear pumps, a tilthoist valve, tilt cylinder means and hoist cylinder means, a conduit connecting the output of said iirst pump to said tilt-hoist valve to supply fluid under pressure for said tilt cylinder and hoist cylinder, a vehicle drive control valve, a conduit connecting said tilt-hoist valve to said drive control valve, means connecting the output of said second gear pump to said drive control valve, said drive control valve including means to combine the output of said second gear pump with the output of said first gear pump coming into the drive control valve from the tilthoist valve, and conduit means connecting the drive control valve to said variable displacement hydraulic motor means.

13. Hydraulic drive means for a lift truck comprising a frame, an internal combustion engine on the frame, traction wheels and steering wheels supporting the frame, a first gear pump driven by said engine, a second gear pump driven by said engine, said second gear pump having an output corresponding to about half the output of said first gear pump, variable displacement hydraulic motor means for driving said traction wheels of the lift truck, a fluid pressure responsive displacement control for said hydraulic motor means, said gear pumps each having a liuid supply inlet, a source of fluid supply connected to the inlet of each of said gear pumps, a tilt-hoist Valve, tilt cylinder means and hoist cylinder means, a conduit connecting the output of said irst pump to said tilthoist valve to supply iluid under pressure to said tilthoist valve for actuating said tilt cylinder and hoist cylinder, a vehicle drive control valve, a conduit connecting said tilt-hoist valve to said drive control valve, means connecting the output of said second gear pump to said drive control valve, said drive control valve including means to combine the output of said second gear pump with the output of said first gear pump coming into the drive control valve from the tilt-hoist valve, and conduit means connecting the drive control valve to said variable displacement hydraulic motor means, a displacement valve, conduit means connecting the displacement control for the hydraulic motor and the drive control valve to vary the displacement of the hydraulic motor means.

14. Hydraulic drive means for a lift truck comprising an internal combustion engine, traction wheels for the lift truck, a first pump coupled to said engine to be driven thereby, a second pump driven by said engine, fluid supply means for said pumps connected to the input side of each pump, a tilt cylinder, a hoist cylinder, a tilt-hoist valve casing, a tilt plunger mounted for reciprocation in said casing, said casing and said tilt plunger having cooperating passageways to direct the iiow of hydraulic fluid through said tilt-hoist valve, conduit means connecting the output of said iirst gear pump to said tilt-hoist valve, a conduit leading from said tilt-hoist valve to one end of said tilt cylinder, a conduit leading from said tilthoist valve to an opposite end of said tilt cylinder whereby movement of said tilt plunger in one direction directs the output of said iirst gear pump into one end of said tilt cylinder and at the same time the conduit leading from the other end of said tilt cylinder is discharged into said tilt-hoist valve, a hoist plunger mounted for reciprocation in said tilt-hoist valve, said hoist plunger and said valve casing having cooperating passageways therein to direct uid from said first gear pump to said hoist cylinder, a drive control valve adapted to be manually moved by the operator of the lift truck, conduit means connecting the tilt-hoist valve to said drive control valve, Iconduitl means to direct the output of said second pump to said drive control valve, said drive control valve having means to combine the output of the lirst pump coming thereto from the tilt-hoist valve with the output of the second pump coming thereto, variable displacement rotary hydraulic motor means for driving the said traction wheels of the lift truck and conduit means to direct the combined output of the two pumps to said hydraulic motor means.

l5. Hydraulic drive means for a lift truck comprising an internal combustion engine, traction wheels for the lift truck, a iirst pump coupled to said engine to be driven thereby, a second pump driven by said engine, iluid supply means for said pumps connected to the input side of each pump, a tilt cylinder, a hoist cylinder, a tilt-hoist valve casing, a tilt plunger mounted for reciprocation in said casing, said casing and said tilt plunger having cooperating passageways to direct the ow of hydraulic uid through said tilt-hoist valve, conduit means connecting the output of said first gear pump to said tilthoist valve, a conduit leading from said tilt-hoist valve to one end of said tilt cylinder, a conduit leading from said tilt-hoist valve to an opposite end of said tilt cylinder whereby movement of said tilt plunger in one direction directs the output of said first gear pump into one end of said tilt cylinder and at the same time the conduit leading from the other end of said tilt cylinder is discharged into said tilt-hoist valve, a hoist plunger mounted for reciprocation in said tilt-hoist valve, said hoist plunger and said valve casing having cooperating passageways therein to direct fluid from said rst gear pump to said hoist cylinder, a drive control valve adapted to be manually moved by the operator of the lift truck, `conduit means connecting the tilt-hoist valve to said drive control valve, conduit means to direct the output of said second pump to said drive control valve, said drive control valve having means to combine the output of the iirst pump coming thereto from the tilt-hoist valve with the output of the second pump coming thereto, variable displacement rotary hydraulic motor means for driving the said traction wheels of the lift truck and conduit means to direct the combined output of the two pumps to said hydraulic motor means, said hydraulic motor means having a fluid pressure responsive member for varying the motor displacement, a displacement valve, conduit means connecting said uid pressure responsive member and said displacement valve and conduit means connecting said displacement valve and said drive control valve.

References Cited in the le of this patent UNITED STATES PATENTS 1,814,857 Rosle July 14, 1931 2,255,560 Fieber et al. Sept. 9, 1941 2,842,273 Granryd July 8, 1958

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Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3135357 *Dec 22, 1961Jun 2, 1964Clark Equipment CoLift truck control system
US3148502 *Jun 28, 1961Sep 15, 1964Hough Co FrankHydrostatic transmission arrangement for tractor loaders
US3163008 *Apr 9, 1963Dec 29, 1964Elmer K HansenHydraulic drive system
US3165775 *Sep 13, 1961Jan 19, 1965Tennant Co G HPower sweeper drive, vacuum and propulsion
US3187497 *May 4, 1962Jun 8, 1965Hough Co FrankHydrostatic arrangement for tractor loaders
US3208221 *Sep 30, 1963Sep 28, 1965Drott Mfg CorpHydraulic operating apparatus
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Classifications
U.S. Classification414/635, 60/421, 187/224, 180/307
International ClassificationB66F9/075, B60K17/10, F15B11/17, B66F9/22
Cooperative ClassificationF15B2211/20584, F15B11/17, B60K17/10, F15B2211/7142, F15B2211/78, F15B2211/761, F15B2211/3116, B66F9/22, B66F9/07595, B66F9/07572
European ClassificationB66F9/075U, B66F9/075P, B66F9/22, F15B11/17, B60K17/10