GB2073821A - A hydraulic circuit for a fork-lift truck - Google Patents
A hydraulic circuit for a fork-lift truck Download PDFInfo
- Publication number
- GB2073821A GB2073821A GB8109366A GB8109366A GB2073821A GB 2073821 A GB2073821 A GB 2073821A GB 8109366 A GB8109366 A GB 8109366A GB 8109366 A GB8109366 A GB 8109366A GB 2073821 A GB2073821 A GB 2073821A
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- United Kingdom
- Prior art keywords
- control valve
- hole
- operating oil
- tilt
- spool
- Prior art date
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B66—HOISTING; LIFTING; HAULING
- B66F—HOISTING, LIFTING, HAULING OR PUSHING, NOT OTHERWISE PROVIDED FOR, e.g. DEVICES WHICH APPLY A LIFTING OR PUSHING FORCE DIRECTLY TO THE SURFACE OF A LOAD
- B66F9/00—Devices for lifting or lowering bulky or heavy goods for loading or unloading purposes
- B66F9/06—Devices for lifting or lowering bulky or heavy goods for loading or unloading purposes movable, with their loads, on wheels or the like, e.g. fork-lift trucks
- B66F9/075—Constructional features or details
- B66F9/20—Means for actuating or controlling masts, platforms, or forks
- B66F9/22—Hydraulic devices or systems
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- Engineering & Computer Science (AREA)
- Transportation (AREA)
- Structural Engineering (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Civil Engineering (AREA)
- Life Sciences & Earth Sciences (AREA)
- Geology (AREA)
- Mechanical Engineering (AREA)
- Forklifts And Lifting Vehicles (AREA)
- Fluid-Pressure Circuits (AREA)
Abstract
The hydraulic circuit (43) comprises a reservoir (44); a suction conduit (45); a hydraulic pump (47); a discharge conduit (49) having one end connected to the hydraulic pump (47) and the other end connected to the reservoir (44) for returning oil to the reservoir (44); at least one tilt cylinder (36) for forwardly and backwardly tilting the mast structure (33); a lift cylinder (39) for lifting and lowering the fork carriage (34); a tilt control valve (52) provided on the discharge conduit (49) for controlling actuation of the tilt cylinder (36), the tilt control valve (52) having two throttled passageways (95, 96) which allow a part of the operating oil to be discharged to the discharge conduit (49) downstream of the tilt control valve (52) only when the tilt control valve is changed to feed the operating oil to the tilt cylinder (36); and a lift control valve (97) provided on the discharge conduit (49) downstream of the tilt control valve (52) for controlling actuation of the lift cylinder (39). <IMAGE>
Description
SPECIFICATION
A hydraulic circuit
The present invention relates to a hydraulic circuit for use in a fork lift truck which has an upright mast structure, and a forked carriage mounted on the mast structure and movable upwardly and downwardly along the mast structure.
There have thus far been proposed a wide variety of such hydraulic circuits one of which is illustrated in Fig. 1. The hydraulic circuit comprises a reservoir tank 1 holding an operating oil and a suction conduit 2 which is connected at one end to the reservoir tank 1 through a filter 3. The suction conduit 2 is further connected at the other end to an inlet of a fixed displacement type hydraulic pump 5 which is in turn operatively connected to an electric motor 4 so that the operating oil is sucked from the reservoir tank 1 through the suction conduit 2 by the hydraulic pump 5. The hydraulic pump 5 has an outlet connected to one end of a discharge conduit 6 having the other end connected to the reservoir tank 1 so that the operating oil is returned to the reservoir tank 1 through the discharge conduit 6 by the hydraulic pump 5.On the discharge conduit 6 is provided a tilt control valve 8 operatively connected to a pair of tilt cylinders 7. On the discharge conduit 6 downstream of the tilt control valve 8 is provided a lift control valve 10 operatively connected to a lift cylinder 9 which is larger in volume than each of the tilt cylinders 7.
The lift control valve 10 is further connected to the discharge conduit 6 upstream of the tilt control valve 8 through a bypass conduit 11. First and second discharge conduits 12 and 13 respectively communicate with the tilt control valve 8 and the lift control valve 10. The bypass conduit 11 and the discharge conduit 6 downstream of the lift control valve 10 are connected by a relief valve 14 which serves to discharge the operating oil from the bypass conduit 11 to the discharge conduit 6 downstream of the lift control valve 10 when the pressure of the operating oil exceeds a predetermined pressure value in the bypass conduit 11 and the discharge conduit 6 upstream of the tilt control valve 8 and the lift control valve 10.
When the lift control valve 10 is changed to assume a first operational position I for actuating the lift cylinder 9 and raising the forked carriage of the fork lift truck at its desired level, the operating oil is fed by the hydraulic pump 5 to the lift cylinder 9 through the discharge conduit 6, the bypass conduit 11 and the lift control valve 10 so that the lift cylinder 9 is actuated to raise the forked carriage to its desired level. If the forked carriage is loaded in excess of a predetermined weight, the relief valve 14 allows the operating oil to pass through the relief valve 14 to the reservoir tank 1. On the other hand, if the forked carriage is loaded within the predetermined weight, the relief valve 14 prevents the operating oil from passing through the relief valve 14.
When the lift control valve 10 and the tilt
control valve 8 are then changed to assume a second operational position lI and a first operational position Ill, respectively, for the purpose of actuating the tilt cylinders 7 and of backwardly tilting the mast structure of the fork lift truck, the bypass conduit 11 is closed by the lift control valve 10 so that the operating oil discharged from the hydraulic pump 5 is fed to the tilt cylinders 7 through the discharge conduit 6 and the tilt control valve 8. As a result, the tilt cylinders 7 are actuated to cause the mast structure to be backwardly tilted.The flow of the operating oil is regulated while being fed to the tilt cylinders 7 by a throttle valve 15 provided in the tilt control valve 8 so as to decrease the operational speed of the tilt cylinders to a predetermined level. This results in the pressure of the operating oil being raised in the discharge conduit 6 upstream of the tilt control valve 8 up to the predetermined pressure level of the relief valve
14 at which the relief valve 14 is operated, thereby causing a part of the operating oil discharged from the hydraulic pump 5 to be returned to the reservoir tank 1.From the reason that such a prior art hydraulic circuit for a fork lift truck is, however, so designed and constructed that a part of the operating oil discharged from the hydraulic pump 5 is returned to the reservoir tank
1 through the relief valve 14, the pressure of the operating oil is raised in the discharge conduit 6 upstream of the tilt control valve 8 up to the predetermined pressure level of the relief valve 14, resulting in a large amount of electric power consumed by the motor 4 being wasted. In addition, there occurs offensive noise caused by the operating oil passing through the relief valve 14.
It is therefore an object of the present invention to provide an improved hydraulic circuit which reduces wasteful electric power consumed by the electric motor.
It is another object of the present invention to provide an improved hydraulic circuit which prevents offensive noise from being caused by the operating oil passing through the relief valve.
In order to accomplish the above objects, there is proposed a hydraulic circuit of the present invention for use in a fork lift truck having an upright mast structure, and a fork carriage mounted on the mast structure and movable upwardly and downwardly along the mast structure, comprising; a reservoir tank for holding an operating oil; a suction conduit having one end connected to the reservoir tank; a hydraulic pump connected to the other end of the suction conduit; a discharge conduit having one end connected to the hydraulic pump and the other end connected to the reservoir tank for returning the operating oil discharged by the hydraulic pump to the reservoir tank; at least one tilt cylinder for forwardly and backwardly tilting the mast structure; a lift cylinder for lifting and lowering the fork carriage; a tilt control valve provided on the discharge conduit for controlling actuation of the tilt cylinder, the tilt control valve having two throttled passageways which allow a part of the operating oil to be discharged to the discharge conduit downstream of the tilt control valve only when the tilt control valve is changed to feed the operating oil to the tilt cylinder; and a lift control valve provided on the
discharge conduit downstream of the tilt control valve for controlling actuation of the lift cylinder.
The features and advantages of the hydraulic
circuit according to the present invention will be
more clearly understood from the following
description in which like reference numerals and
characters designate corresponding or similar
members and structures throughout the figures
and in which::
Fig. 1 is a diagrammatic view showing the
general construction of a prior art hydraulic circuit;
Fig. 2 is a schematic side view of a fork lift truck
which has an upright mast structure to be tilted by
tilt cylinders present in the hydraulic circuit of the
present invention and which has a forked carriage
movable upwardly and downwardly along the
mast structure by a lift cylinder also present in the
hydraulic circuit of the present invention;
Fig. 3 is a diagrammatic view showing the general construction of the hydraulic circuit according to the present invention;
Fig. 4 is a cross sectional view of a tilt control valve present in the hydraulic circuit shown in
Fig. 3 and showing a neutral operational position of the tilt control valve;
Fig. 5 is a cross sectional view similar to Fig. 4 but showing the first operational position of the tilt control valve shown in Fig. 4;;
Fig. 6 is a cross sectional view similar to Fig. 4 but showing the second operational position of the tilt control valve shown in Fig. 4;
Fig. 7 is a fragmentary cross sectional view similar to Fig. 6 but showing a condition under which the operating oil is not fed to the tilt control valve during forward tilting of the mast structure;
Fig. 8 is a cross sectional view similar to Fig. 4 but showing another embodiment of the hydraulic circuit of the present invention;
Fig. 9 is a cross sectional view of the tilt control valve shown in Fig. 8 but showing a condition under which the mast structure is held backwardly tilted;
Fig. 10 is a cross sectional view of the tilt control valve shown in Fig. 8 but showing a condition under which the mast structure is held forwardly tilted; and
Fig. 11 is a fragmentary cross sectional view similar to Fig. 10 but showing a condition under which the operating oil is not fed to the tilt control valve during forward tilting of the mast structure.
Description will be hereinafter made regarding the embodiments of the hydraulic circuit according to the present invention.
Before going into the detailed description, the terms "upper" and "lower" which will appear in the following description are intended to mean in the illustrations of the drawings the "upper" and "lower" portions of parts or elements involved in the tilt control valve and the lift control valve only for the purpose of simplicity and better understanding thereof, but may of course be varied depending upon the arrangements of the tilt control valve and the lift control valve forming the hydraulic circuit of the present invention.
Likewise, the terms "upwardly" and "downwardly" which will also appear in the following description are intended to mean in the illustrations of the drawings the "directions" of the movements of the parts or elements involved in the tilt control valve and the lift control valve, but may of course be varied depending upon the arrangements of the tilt control valve and the lift control valve forming the hydraulic circuit of the present invention.
Referring now to the drawings and in particular to Fig. 2, there is shown a fork lift truck, generally indicated by the reference numeral 31, which comprises a truck body 32, an upright mast structure 33 having a lower end portion pivotally connected to the truck body 32 so as to be forwardly and backwardly tilted, a carriage 34 having a fork 35 and mounted on the mast structure 33 so as to be movable upwardly and downwardly along the mast structure 33. A pair of tilt cylinders 36 are pivotally connected to the truck body 32 by pins 37 and have piston rods 38, the leading ends of which are also pivotally connected to the mast structure 33 so that the mast structure 33 is tilted forwardly and backwardly when the tilt cylinders 36 are actuated to project and retract the piston rods 38.A lift cylinder 39 is securely mounted on the mast structure 33 and has a piston rod 40 on the leading end of which a sprocket wheel 41 is freely rotatably mounted. A chain 42 is passed over the sprocket wheel 41, having one end anchored to the lift cylinder 39 and the other end anchored to the fork carriage 34 so that the carriage 34 is moved upwardly and downwardly by way of the chain 42, when the lift cylinder 39 is actuated to project and retract the piston rod 40.
A hydraulic circuit 43 embodying the present invention is illustrated in Fig. 3 as comprising a reservoir tank 44 which holds an operating oil for operation of the hydraulic circuit 43. A suction conduit 45 has one end connected to the reservoir tank 44 through a filter 46 and the other end connected to an inlet of a fixed displacement type hydraulic pump 47 which is operatively connected to an electric motor 48. A discharge conduit 49 is connected at one end with the outlet of the hydraulic pump 47 and at the other end to a filter 50 which is in turn connected to the reservoir tank 44 through a first conduit 51. On the discharge conduit 49 is provided a tilt control valve 52 which is connected through second and third conduits 53 and 54 to front chambers 55 and rear chambers 56, respectively, forming in combination the tilt cylinders 36 which function to forwardly and backwardly tilt the mast structure 33.
The particular structure of the tilt control valve 52 will be seen in Fig. 4. The tilt control valve 52 comprises a valve body 57 which is formed with a hole 58 extending axially of the valve body 57. In the valve body 57 are formed annular grooves 59, 60, 61,62, 63, 64, 65, 66 and 67 which are arranged in this order from the upper end of the valve body 57 to the lower end thereof in coaxial relationship to the hole 58 so that the annular grooves 59 to 67 are in communication with the hole 58. Each of the grooves 59 to 67 has a crosssection larger in daimeter than that of the hole 58.
The outer peripheral surface of the valve body 57 is communicated at a port a with the annular grooves 62 and 64. In a similar manner, the outer peripheral surface of the valve body 57 is communicated at ports b, c, d, e, f, g and h with the annular grooves 59, 60, 61, 63, 65, 66 and 67, respectively. In the previously mentioned hole 58 is slidably received a spool 68 which has an upper end connected with a lever 69 as seen in
Fig. 3.
The lever 69 is thus capable of moving the spool 68 upwardly and downwardly. The movement of the spool 68 is detected by a limit switch 70 which is engageable with a detent 71.
formed on the upper portion of the spool 68 when the tilt control valve 52 assumes its neutral position as shown in Fig. 3.
Returning to Fig. 4, the spool 68 is formed with spool lands 72, 73, 74, 75 and 76 which are arranged in this order from the upper end of the spool 68 to the lower end thereof. Each of the spool lands 72, 73, 75 and 76 is formed having an outer diameter substantially equal to the inner diameter of the hole 58, whereas only the spool land 74 is formed having an outer diameter somewhat smaller than the inner diameter of the hole 58. The spool land 75 is formed at its lower end with a cut-away portion 77. Likewise, the spool land 76 is formed at its upper end with a cut-away portion 78. In the lower half of the spool 68 is formed a bore 79 which extends axially of the spool 68 to slidably receive another spool 80 having an outer diameter smaller than the inner diameter of the bore 79.The spool 80 is formed with spool lands 81 and 82 each of which has an outer diameter substantially equal to the inner diameter of the bore 79. The outer peripheral surface of the spool land 75 is in communication with the bore 79 through a passageway 83, the outer peripheral surface of the spool 68 between the spool lands 75 and 76 is in communication with the bore 79 through a passageway 84, and the outer peripheral surface of the spool land 76 is in communication with the bore 79 through an orifice 85. A bolt 86 is screwed to the lower end of the spool 68 for closing the bore 79, and a compression coil spring 87 is interposed between the lower end of the spool 80 and the bolt 86 to upwardly bias the spool 80.
A spring casing 88 is formed with a concavity 89 which extends axially of the valve body 57 to be opened at the upper end of the spring casing 88. The spring casing 88 is secured to the lower end of the valve body 57 with the concavity 89 communicated with the hole 58 so as to allow the spool 68 to project into the concavity 89. The bolt 86 comprises a stem portion 90 downwardly projecting from the lower end of the spool 68 and an annular flange portion 91 integral with the stem portion 90 and larger in diameter than the stem portion 90.A pair of bell-mouth shaped spring retainers 92 and 92' respectively have flare portions 92a and 92a' and top portions 92b and 92b' formed with axial openings 92c and 92c' and are accommodated in the concavity 89 of the spring casing 88 with the top portions 92b and 92b' opposing each other in such a manner that the stem portion 90 of the bolt 86 passes through the axial openings 92c and 92c' of the spring retainers 92 and 92'. A compression coil spring 93 is housed in the concavity 89 of the spring casing 88 with the upper end engaging with the flare portion 92a of the spring retainer 92 and with the lower end engaging with the flare portion 92a' of the spring retainer 92'.It will therefore be understood that the top portion 92b of the spring retainer 92 is held in engagement with the lower end of the spool 68 while the top portion 92b' of the spring retainer 92' is also held in engagement with the annular flange portion 91 of the bolt 86 under such a condition that the spool 68 assumes its neutral position as indicated at I in Fig. 3 and shown in Fig. 4. In addition, the spool 68 is adapted to be moved upwardly until the top portion 92b' of the spring retainer 92' is brought into engagement with the top portion 92b of the spring retainer 92 against the compression coil spring 93 so as to assume its first operational position as indicated at 11 in Fig. 3 and shown in
Fig. 5.Likewise, the spool 68 is moved downwardly until the top portion 92b of the spring retainer 92 is brought into engagement with the top portion 92b' of the spring retainer 92' against the compression coil spring 93 so as to assume its second operational position as indicated at Ill in
Fig. 3 and shown in Fig. 6. When the tilt control valve 52 is changed from its neutral position as indicated at / in Fig. 3 and shown in Fig. 4 to its first operational position as indicated at 11 in Fig. 3 and shown in Fig. 5, a portion of the valve body 57 between the annular grooves 65 and 66 is located between the spool lands 75 and 76 to form an orifice passageway 94 in cooperation with the cut-away portions 77 and 78.Further, the spool land 74 is located between the annular grooves 62 and 63 so that a throttled passageway 95 is formed by the spool land 74 and a portion of the valve body 57 between the annular grooves 62 and 63. When the tilt control valve 52 is in turn changed to assume a second operational position as indicated atoll in Fig. 3 and shown in Fig. 6, the spool land 74 is disposed between the annular grooves 63 and 64 so that another throttled passageway 96 is formed by the spool land 74 and a portion of the valve body 57 between the annular grooves 63 and 64.
Referring again to Fig. 3, a lift control valve 97 is provided on the discharge conduit 49 downstream of the tilt control valve 52 and is connected to a lower chamber 98 of the lift cylinder 39 which functions to raise or lower the fork carriage 34 (see Fig. 2) by a fourth conduit 99. A lever 100 is operatively connected to the upper end of a spool 101 of the lift control valve 97 so as to move the spool 101 upwardly and downwardly. The movement of the spool 101 is detected by a limit switch 102 which is engaged with a protrusion 103 formed on the upper portion of the spool 101 only when the spool 101 is raised to cause the lift control valve 97 to assume its first operational position V. On the fourth conduit 99 is provided a throttled passageway 104 which serves to restrict the flow of the operating oil from passing through the fourth conduit 99.A bypass conduit 105 is connected at one end with the fourth conduit 99 between the lift control valve 97 and the throttled passageway 104 and at the other end with the fourth conduit 99 between the lift cylinder 39 and the throttled passageway 104. On the bypass conduit 105 is provided a check valve 106 which allows the operating oil to pass through the bypass conduit 105 when the operating oil is fed to the lower chamber 98 of the lift cylinder 39 and which checks the operating oil when the operating oil is returned to the reservoir tank 44 from the lower chamber 98 of the lift cylinder 39. A bypass conduit 107 is connected at one end to the lift control valve 97 and at the other end to the ports d and fof the tilt control valve 52, while being in communication with the discharge conduit 49 upstream of the tilt control valve 52 at a junction 108.The discharge conduit 49 downstream of the lift control valve 97 is communicated with the lift control valve 97 through a first discharge conduit
109. A check valve 110 is provided on the bypass conduit 107 so as to allow the operating oil to be introduced into the lift control valve 97 while checking the operating oil from the lift control valve 97. A check valve 111 is provided on the
bypass conduit 108 between the junction 108 and the tilt control valve 52 so as to allow the operating oil to be introduced into the tilt control valve 52 while restricting the operating oil from
being discharged from the tilt control valve 52.
The bypass conduit 107 and the discharge conduit 49 downstream of the lift control valve 97 are connected by a relief valve 112 which is so designed as to discharge the operating oil from the bypass conduit 107 to the discharge conduit 49 downstream of the lift control valve 97 when the pressure of the operating oil in the bypass conduit 107 and the discharge conduit 49
upstream of the tilt control valve 52 exceeds a
predetermined pressure level of the operating oil
caused by loads mounted on the fork 35 (see
Fig. 2) of the carriage 34 (see Fig. 2).The ports b and h of the tilt control valve 52 communicate with the discharge conduit 49 downstream of the
lift control valve 97 through a second discharge
conduit 1 13, and the upper chamber 114 of the
lift cylinder 39 communicates with the reservoir
tank 44 through a third discharge conduit 11 5.
The operation of the present invention will now
be described.
When the lift control valve 97 is first changed to assume its first operational position Vfrom its neutral position !Vfor raising the carriage 34 with the tilt control valve 52 assuming its neutral position /, the lever 100 is raised upwardly so that the limit switch 102 is operated to cause the electric motor 48 to be started. The operating oil in the reservoir tank 44 is thus sucked through the suction conduit 45 and discharged by the hydraulic pump 47. The discharged operating oil is introduced into the lower chamber 98 of the lift cylinder 39 through the discharge conduit 49, the bypass conduit 107, the lift control valve 97 and the fourth conduit 99 and the bypass conduit 105, thereby operating the lift cylinder 39.The piston rod 40 is thus projected by the lifting cylinder 39 to cause the fork carriage 34 to be raised upwardly by the chain 42. While the operating oil is passing through the bypass conduit 107, the check valve 110 is forced open. The check valve 106 is similarly forced open while the operating oil is passing through the fourth conduit 99. When the lift control valve 97 is secondly changed to assume its second operational position VI from the first operational position Vfor lowering the fork carriage 34 with the tilt control valve 52 assuming its neutral position /, the lever 100 is lowered downwardly so that the limit switch 102 causes the electric motor 48 to be stopped, thereby bringing the fourth conduit 99 into communication with the first discharge conduit 109.As a consequence, the weight of the fork carriage 34 causes the operating oil in the lower chamber 98 of the lift cylinder 39 to be discharged to the reservoir tank 44 by way of the fourth conduit 99, the first discharge conduit 109, the discharge conduit 49, the filter 50 and the first conduit 51. While the operating oil is passing through the fourth conduit 99, the check valve 106 is closed so that the operating oil is passed through the throttled passageway 104 while being throttled.
When the tilt control valve 52 is changed to assume its first operational position as indicated at 11 in Fig. 3 and shown in Fig. 6 with the lift control valve 97 assuming its neutral operational position IVonly for the purpose of backwardly tilting the mast structure 33, the lever 69 is raised as shown in Fig. 3 so that the limit switch 70 is disengaged from the detent 71 to cause the electric motor 48 to be started. The operating oil is thus sucked through the suction conduit 45 and discharged by the hydraulic pump 47. The discharged operating oil is fed to the tilt control valve 52 through the discharge conduit 49. The discharged operating oil causes the check valve 111 on the bypass conduit 107 to be opened and is introduced into the annular groove 65 through the port fand then into the front chambers 55 of the tilt cylinders 36 through the orifice passageway 94, the annular groove 66, the port g and the second conduit 53. While the operating oil is passing through the orifice passageway 94, the operating oil is throttled thereby. The operating oil discharged by the hydraulic pump 47 in the rear chambers 56 of the tilt cylinders 36 is returned to the reservoir tank 44 by way of the third conduit 54, the port c, the annular groove 60, the annular groove 59, the port b, the second discharge conduit 11 3, the discharge conduit 49, the filter 50 and the first conduit 51.This results in the tilt cylinders 36 being operated at a predetermined speed to cause the mast structure 33 to be tilted backwardly. During tilting of the mast structure 33, a part of the operating oil is fed to the annular groove 62 through the port a and then is throttlingly discharged to the discharge conduit 49 through the throttled passageway 95, the annular groove 63 and the port e. The throttled passageway 95 is formed by the spool land 74 and a portion of the valve body 57 between the annular grooves 62 and 63 since the spool land 74 of the spool 68 is smaller in diameter than the hole 58 and the spool land 74 is located in the hole 58 between the-annular grooves 62 and 63.
Therefore, the pressure of the operating oil in the discharge conduit 49 upstream of the tilt control valve 52 can be reduced lower than in the prior art hydraulic circuit. More specifically, the pressure of the operating oil can be maintained lower than the predetermined pressure level of the relief valve 112, thereby decreasing the electric power consumed by the electric motor 48. Additionally, no noise occurs as the relief valve 112 is not operated.
When the tilt control valve 52 is then changed to assume its second operational position Ill as indicated at 111 in Fig. 3 and shown in Fig. 6 with the lift control valve 97 assuming its neutral operational position IVonly for the purpose of forwardly tilting the mast structure 33, the lever 69 is lowered downwardly in Fig. 3 so that the limit switch 70 is operated to start the electric motor 48. The operating oil is thus sucked through the suction conduit 45 and discharged by the hydraulic pump 47.The operating oil is fed to the tilt control valve 52 through the discharge conduit 49, the oil causes the check valve 111 on the bypass conduit 107 to be opened and is introduced into the annular groove 61 through the port d and then into the rear chambers 56 of the tilt cylinders 36 through the hole 58, the annular groove 60, the port c and the third conduit 54. On the other hand, the operating oil discharged from the hydraulic pump 47 enters the bore 79 through the port f, the annular groove 65 and the passageway 83 to urge the spool 80 downwardly against the compression coil 87, thereby bringing the annular groove 66 into communication with the annular groove 67 through the passageway 84, the bore 79 and the orifice 85. The check valve 111 is forced open by the operating oil when the operating oil passes through the bypass conduit 107.Accordingly, the operating oil in the front chamber 55 of the tilt cylinders 36 is introduced into the annular groove 66 through the second conduit 53 and the port g, and then is returned to the reservoir tank 44 through the passageway 84, the bore 79, the orifice 85, the annular groove 67, the port h, the second discharge conduit 11 3, the discharge conduit 49, the filter 50 and the first conduit 51. During passing through the orifice 85, the operating oil is throttled thereby. This results in the tilt cylinders 36 being operated at a predetermined speed to cause the mast structure 33 to be tilted forwardly.
During tilting of the mast structure 33, a part of the operating oil discharged from the hydraulic pump 47 is fed to the annular groove 64 through the port a and then is discharged to the discharge conduit 49 downstream of the tilt control valve 52 through the throttled passageway 96, the annular groove 63 and the port e. The throttled passageway 96 is formed by the spool land 74 and a portion of the valve body 57 between the annular grooves 63 and 64 since the spool land 74 of the spool 68 is smaller in diameter than the hole 58 and the spool land 74 is located in the hole 58 between the annular grooves 63 and 64.
Therefore, the pressure of the operating oil in the discharge conduit 49 upstream of the tilt control valve 52 can be reduced lower than in the prior art hydraulic circuit. More specifically, the pressure of the operating oil can be maintained lower than the predetermined pressure level of the relief valve 112, thereby decreasing the electric power consumed by the electric motor 48. Additionally, no noise occurs as the relief valve 112 is not operated.
If the operating oil is not fed to the rear chambers 56 of the tilt cylinders 36 during forward tilting of the mast structure 33, resulting from such a certain cause as, for example, stopping of the electric motor 48, the spool 80 is moved upwardly by the action of the compression coil spring 87, thereby causing the orifice 85 to be closed by the spool land 82 of the spool 80 as shown in Fig. 7. This means that the operating oil in the front chambers 55 of the tilt cylinders 36 cannot be discharged and thus the forward tilting motion of the mast structure 33 is stopped.
When the tilt control valve 52 is then changed to assume its neutral operational position I with the lift control valve 97 assuming its neutral operational position IV, the lever 69 is returned to its original position as shown in Fig. 3 whereupon the limit switch 70 is brought into engagement with the detent 71 of the spool 68, thereby causing the electric motor 48 to be stopped. The operating oil is not fed to the tilt control valve 52 so that the mast structure 33 is held at a desired angle with respect to the truck body 32.
According to the present invention, throttled passageways 11 6 and 117 may be formed in the second embodiment as shown in Figs. 8 to 10 in lieu of the previously mentioned throttled passageways 95 and 96.
In Fig. 8 to 10, a spool land 74' is formed on the spool 68 in place of the spool land 74 to have a diameter substantially equal to the hole 58. A pair of throttling lands 73' and 75' are formed on the spool 68 at opposite sides of the spool land 74' and have respective opposing end portions 63a' and 75a' smaller in diameter than the hole 58. As shown in Fig. 9, the throttled passageway 116 is formed by the end portion 75a' of the throttling land 75' and a portion of the valve body 57 between the annular grooves 63 and 64 when the end portion 75a' of the throttling land 75' is located in the hole 58 between the annular grooves 63 and 64 for tilting the mast structure 33 backwardly.As shown in Fig. 10, the other throttling passageway 117 is formed by the end portion 73a' of the throttling land 73' and a portion of the valve body 57 between the annular grooves 62 and 63 when the end portion 73a' of the throttling land 73' is located in the hole 58 between the annular grooves 62 and 63 for tilting the mast structure 33 forwardly.
The construction and functions of remaining elements or parts in the second embodiment are substantially the same as those of the first embodiment as shown in Figs. 4 to 7, and will not be described hereinafter to avoid tedious repetition.
Fig. 11 shows an operational condition under which the operating oil is not fed to the rear chambers 56 of the tilt cylinders 36 during forward tilting of the mast structure 33, resulting from such a certain cause, for example, stopping of the electric motor 48. Under these conditions, the spool 80 is moved upwardly by the action of the compression coil spring 87, thereby causing the orifice 85 to be closed by the spool land 82 of the spool 80. This means that the operating oil in the front chambers 55 of the tilt cylinders 36 cannot be discharged and thus the forward tilting motion of the mast structure 33 is stopped.
Although it is has been described in the above that a pair of tilt cylinders 36 are provided to tilt the mast structure 33 forwardly and backwardly, only one tilt cylinder may be provided according to the present invention. However, a pair of guide rods are preferably provided on the truck body 32 so as to guide the mast structure 33 while the mast structure is being tilted forwardly and backwardly.
Claims (4)
1. A hydraulic circuit for a fork lift truck having an upright mast structure, and a fork carriage mounted on said mast structure and movable upwardly and downwardly along said mast structure, comprising:
a reservoir tank for holding an operating oil;
a suction conduit having one end connected to said reservoir tank;
a hydraulic pump connected to the other end of said suction conduit;
a discharge conduit having one end connected to said hydraulic pump and the other end connected to said reservoir tank for returning said operating oil discharged by said hydraulic pump to said reservoir tank;
a tilt cylinder for forwardly and backwardly tilting said mast structure;
a lift cylinder for lifting and lowering said fork carriage;;
a tilt control valve provided on said discharge conduit for controlling actuation of said tilt cylinder, said tilt control valve having two throttled passageways which allow a part of said operating oil to be discharged to said discharge conduit downstream of the tilt control valve when said tilt control valve is changed to feed said operating oil to said tilt cylinder; and
a lift control valve provided on said discharge conduit for controlling actuation of said lift cylinder.
2. A hydraulic circuit as set forth in claim 1, wherein said tilt control valve comprises a valve body formed with a hole axially extending therein, two annular inlet grooves formed in said valve body in axially spaced relationship to each other and communicated with said hole, an annular outlet groove formed in said valve body between said inlet grooves and communicated with said hole, a spool slidably received in said hole and having a throttling land smaller in diameter than said hole, said throttled passageways being formed by said throttling land and portions of said valve body between said outlet groove and said inlet grooves when said throttling land is located in said hole between said outlet groove and one of said inlet grooves and when said throttling land is located in said hole between said outlet groove and the other of said inlet grooves.
3. A hydraulic circuit as set forth in claim 1, wherein said tilt control valve comprises a valve body formed with a hole axially extending therein, two annular inlet grooves formed in said valve body in axially spaced relationship to each other, and communicated with said hole, an annular outlet groove formed in said valve body between said inlet grooves and communicated with said hole, a spool slidably received in said hole and having a spool land substantially equal in diameter to said hole of said valve body, a pair of throttling lands formed on said spool at opposite sides of said spool land and having respective opposing end portions smaller in diameter than said hole, said throttled passageways being formed by said end portions of said throttling lands and portions of said valve body between said outlet groove and said inlet grooves when the end portion of one of said throttling lands is located in said hole
between said outlet groove and one of said inlet grooves and when the end portion of the other of said throttling lands is located in said hole
between said outlet groove and the other of said
inlet grooves.
4. A hydraulic circuit substantially as described with reference to, and as illustrated in, Figs. 2 to 7 or Figs. 8 to 11 of the accompanying drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP3849680A JPS56136799A (en) | 1980-03-25 | 1980-03-25 | Oil pressure circuit for fork lift |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2073821A true GB2073821A (en) | 1981-10-21 |
| GB2073821B GB2073821B (en) | 1983-10-26 |
Family
ID=12526865
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8109366A Expired GB2073821B (en) | 1980-03-25 | 1981-03-25 | Hydraulic circuit for a fork-lift truck |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JPS56136799A (en) |
| DE (1) | DE3111765A1 (en) |
| FR (1) | FR2479169A1 (en) |
| GB (1) | GB2073821B (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2569786A1 (en) * | 1984-08-31 | 1986-03-07 | Vickers Systems Sa | HIGH PRESSURE HYDRAULIC DISPENSER WITH PILOT PRESSURE GENERATOR |
| FR2840293A1 (en) * | 2002-06-04 | 2003-12-05 | Linde Ag | Hydraulic lifting device has bypass valve which bypasses control valve unit in lowering operation to make connection of lift cylinder to reservoir and which is loaded in throughflow position during lowering operation with lower load |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH01104599A (en) * | 1987-10-16 | 1989-04-21 | Toyota Autom Loom Works Ltd | Cargo-handling controller |
| JP2599775B2 (en) * | 1988-11-17 | 1997-04-16 | 株式会社クボタ | Backhoe working vehicle hydraulic circuit |
| AT409856B (en) * | 1999-10-25 | 2002-12-27 | Mht Mechhydtronic Ges M B | Lifting unit for a generally torsion-resistant frame, specifically for a container |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5266847A (en) * | 1975-11-29 | 1977-06-02 | Mitsui Shipbuilding Eng | Cooling method and device for welding |
| JPS6054238B2 (en) * | 1977-10-12 | 1985-11-29 | ティー・シー・エム株式会社 | Cargo handling control device for electric cargo handling vehicles |
-
1980
- 1980-03-25 JP JP3849680A patent/JPS56136799A/en active Pending
-
1981
- 1981-03-24 FR FR8105866A patent/FR2479169A1/en not_active Withdrawn
- 1981-03-25 GB GB8109366A patent/GB2073821B/en not_active Expired
- 1981-03-25 DE DE19813111765 patent/DE3111765A1/en not_active Withdrawn
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2569786A1 (en) * | 1984-08-31 | 1986-03-07 | Vickers Systems Sa | HIGH PRESSURE HYDRAULIC DISPENSER WITH PILOT PRESSURE GENERATOR |
| EP0176381A1 (en) * | 1984-08-31 | 1986-04-02 | Vickers Systems Sa | High-pressure hydraulic directional control valve with a pilot pressure generator |
| FR2840293A1 (en) * | 2002-06-04 | 2003-12-05 | Linde Ag | Hydraulic lifting device has bypass valve which bypasses control valve unit in lowering operation to make connection of lift cylinder to reservoir and which is loaded in throughflow position during lowering operation with lower load |
Also Published As
| Publication number | Publication date |
|---|---|
| FR2479169A1 (en) | 1981-10-02 |
| JPS56136799A (en) | 1981-10-26 |
| DE3111765A1 (en) | 1982-02-11 |
| GB2073821B (en) | 1983-10-26 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |