EP0489230B1 - Lifting mast, especially for lift trucks - Google Patents

Description

The invention relates to a lifting device according to the preamble of claim 1. Such a lifting device is known from US-A-2 456 320.

Height-adjustable masts, e.g. in connection with lifting vehicles have become known in a wide variety of designs. Due to the fact that the load-carrying means is mounted on one side of the mast, a bending moment is generated on the mast, the size of which depends on the load and the position of the center of gravity. The actual deflection of the mast depends on its spring properties. A load-related deflection is particularly noticeable in forklifts with large lifting heights, whose masts reach a considerable height in the fully extended position. The mast deflection causes a change in the position of the load, so that difficulties arise when loading and unloading loads, not least because of the vibrations that also occur.

From DE-OS 30 16 156 a mast has become known in which a boom is attached to the extendable mast part, on which a traction means acts to apply a counter-torque to the mast, which should approximately correspond to the load moment. With the aid of such a device, bending of the mast is largely prevented, the applied forces being introduced into the mast as pressure forces. The known construction requires a complex guide for the load chains and an additional considerable effort to generate the lifting forces. The effort is particularly high when masts are provided with a free lift. Another disadvantage is that due to the boom and the traction device, the depth of the mast is increased drastically.

In the known mast, it is also known to change the tension of the traction means with the aid of a pretensioning roller. The pretensioning roller can be actuated by an adjusting cylinder which is connected to the lifting cylinder for the mast via a pressure reducer. In this way, the load torque compensation is adjusted as a function of the pressure prevailing in the lifting cylinder. The tension pulley has to absorb considerable forces and is therefore expensive to store.

From DE-OS 31 01 953 a mast has become known in which, in a manner similar to the aforementioned known mast, also lateral load moments that occur with laterally displaceable load suspension means are compensated for. The disadvantages mentioned for the construction mentioned above apply equally to the load moment compensation described last.

From DE-OS 32 10 951 it has become known to provide an electronic path control on the load suspension device in order to use sensors to determine the position of the load suspension device relative to a fixed reflex mark in a stacking device and to correct it in the event of a deviation. The automatic positioning of the load handling device is relatively complex since it requires a measuring device and a drive control for the positioning. A reflex mark that is independent of the vehicle is also required. This must be attached to the stacking device directly next to the vehicle. The field of application of the known device is thus limited to so-called narrow aisle vehicles with a lateral stacking direction.

The invention has for its object to provide a lifting device of the type mentioned, in which the deformation in the mast and possibly in the mast holder or vehicle due to the load torque in each lifting range and including dynamic loads is compensated so that the situation with simple means the load does not change or only changes very slightly when lifting.

This object is achieved according to the invention by the features of the characterizing part of patent claim 1.

In the invention, the mast holder or the mast itself are adjustable and their position can be changed with the aid of the tilt drive. It is known to pivotally mount a mast in the scaffold holder, as a result of which, for example, the driver of a lifting vehicle can change the position of the load handler in order to change the unwanted position of the load handler caused by the mast bending. By swiveling the mast, the deflection of the mast is not canceled, but the extent remains. However, by pivoting the mast into a more or less backward inclined position, the load suspension device can be brought approximately into a position in which it would be without mast bending. Due to an arbitrary change in the inclination of the mast by the driver of the lifting vehicle, in particular in the case of large stack heights, only an insufficient compensation for deformation can be carried out. At least the change in incline made by the driver takes time. The invention therefore provides for the inclination drive to be actuated automatically as a function of the pressure in the lifting cylinder device. The tilt drive adjusts the mast regardless of its extended length by the amount resulting from the Load on the load handler results. The size of this load is reflected in the pressure in the lifting cylinder device.

The invention is based on the knowledge that there is a linearizable relationship between the lifting height and the resetting of the load in a large range. In other words, the adjustment path of the tilt drive depends solely on the pressure in the lifting cylinder, regardless of the height to which the mast is extended.

In the invention it was recognized that the position compensation of the load-bearing means on the mast does not require the deformation to be reversed, but rather that it is entirely sufficient to adjust the position of the mast according to the load. The design and control means required for this are very simple. If a tilt drive is available anyway, e.g. a corresponding lifting vehicle can be provided with a less complex additional hydraulic control in order to achieve the automatic deformation compensation. Vehicles already equipped with a tilt drive can therefore be converted easily.

In addition, there are no constructive and structural difficulties to make the mast or its holder adjustable and to couple it with a corresponding drive. The functionality of the mast is not impaired, nor is the external dimensions enlarged.

Various solutions are conceivable for controlling the inclination drive depending on the pressure in the lifting cylinder device. One provides according to the invention that a pressure sensor is assigned to the mast lift cylinder device and the output signal of the pressure sensor is used to generate the control signal for the inclination drive. The pressure sensor can be, for example, a load cell. A motor with a spindle drive can serve as the adjustment drive. However, the use of at least one adjusting cylinder is particularly advantageous. It can engage on the mast or on the scaffold bracket of the mast. The pressure side of the mast lifting cylinder device can preferably be connected directly to the adjusting cylinder via a throttle. Optionally, a pressure translation can be interposed.

Even when unloaded, the considerable weight of the movable mast parts and the load-bearing part creates a considerable pressure in the mast lifting cylinder. So that this pressure does not already lead to an adjustment of the mast, an embodiment of the invention provides that a biasing force directed opposite the adjusting force acts on the tilt drive, which approximately corresponds to the adjusting force that the tilt drive generates when the load-carrying means is not loaded. Only when the pressure in the mast lift cylinder exceeds the value in the unloaded state, is the tilt drive used to adjust the mast for the purpose of compensating for deformation.

According to a further embodiment of the invention, a compression spring can act on the piston of the adjusting cylinder for the purpose of applying a prestressing force. In an alternative embodiment of the invention, the adjusting cylinder is connected to a hydraulic accumulator in order to apply the prestressing force. In the latter case, the mast lift cylinder is preferably connected to the adjustment cylinder via a pressure relief valve. The pressure relief valve maintains a certain pressure in the amount of the preload force in the adjustment cylinder. The biasing force is expediently adjustable so that an adjustment of the pressure prevailing in the mast lift cylinder is obtained in the unloaded state. If the pretensioning force is applied by a spring force, a spring behavior adapted to the spring characteristic of the mast can be achieved. The bending of the mast at a given load depends on its spring behavior. The adjustment path of the adjustment cylinder at a given pressure depends on the counter tension or the spring stiffness of the counter spring. In order to adapt the adjustment of the mast to the deformation actually taking place, the spring characteristics of the mast and preload spring are matched accordingly.

If, according to an embodiment of the invention, a paired arrangement of inclination cylinders is provided in parallel and at a distance on one side of the mast, torsional vibrations of the mast can also be damped. If there is a connection between the lifting cylinder and the tilt cylinder via a throttle, vibrations of the mast are also damped, which result in operation due to the working speed and when starting or stopping the movable mast and due to the movement of the load handler.

It is understood that an inclination of the mast for the purpose of compensating for deformation can also be obtained in that the vehicle changes its position. This can be done, for example, in that an inclination drive is connected between the chassis and the mast holder, which is operated in the manner described above.

• Fig. 1 bis 1 c zeigt ein Hubfahrzeug mit ausfahrbarem Hubgerüst in verschiedenen Betriebszuständen.
• Fig. 2 zeigt schematisch den unteren Bereich eines Hubgerüsts mit einem Antrieb zum Verformungsausgleich.
• Fig. 3 zeigt die Rückseite der Darstellung nach Fig. 3 in richtung Pfeil 3.
• Fig. 4 zeigt eine ähnliche Darstellung wie Fig. 2 mit einer abgewandelten Kraftübertragung zwischen Neigungsantrieb und Hubgerüst.
• Fig. 5 zeigt die Ansicht der Darstellung nach Fig. 4 in Richtung Pfeil 5.
• Fig. 6 zeigt schematisch eine hydraulische Schaltung eines Hubzylinders und eines Neigungszylinders für das Hubgerüst.
• Fig. 7 zeigt eine alternative Ausführungsform zum Betrieb eines Hub- und Neigungszylinders.
• Fig. 8 zeigt äußerst schematisch eine andere Möglichkeit zur Verstellung des Hubgerüsts.
• Fig. 9 zeigt schematisch eine Möglichkeit der Verstellung eines verfahrbaren Hubgerüsthalters.
• Fig. 10 zeigt einen Schnitt durch die Darstellung nach Fig. 9 nach der Linie 10-10.
• Fig. 11 zeigt schematisch ein Hubgerüst mit zwei Verstellzylindern zur Neigungsverstellung.
• Fig. 12 zeigt schematisch ein Hubgerüst mit einer abgewandelten Regelung zur Neigungsverstellung.
• Fig. 13 zeigt schematisch ein Hubfahrzeug mit Hubgerüst und Neigungsverstellung des Fahrzeugs.

Exemplary embodiments of the invention are explained in more detail below with reference to drawings.

• 1 to 1 c shows a lifting vehicle with a retractable mast in different operating states the.
• Fig. 2 shows schematically the lower area of a mast with a drive to compensate for deformation.
• FIG. 3 shows the back of the illustration according to FIG. 3 in the direction of arrow 3.
• Fig. 4 shows a similar representation as Fig. 2 with a modified power transmission between the tilt drive and mast.
• FIG. 5 shows the view of the illustration according to FIG. 4 in the direction of arrow 5.
• Fig. 6 shows schematically a hydraulic circuit of a lifting cylinder and an inclination cylinder for the mast.
• 7 shows an alternative embodiment for operating a lifting and tilting cylinder.
• Fig. 8 shows very schematically another way of adjusting the mast.
• Fig. 9 shows schematically one way of adjusting a movable mast holder.
• Fig. 10 shows a section through the representation of FIG. 9 along the line 10-10.
• Fig. 11 shows schematically a mast with two adjustment cylinders for tilt adjustment.
• Fig. 12 shows schematically a mast with a modified regulation for the inclination adjustment.
• 13 schematically shows a lifting vehicle with a mast and inclination adjustment of the vehicle.

In Fig. 1, a lifting vehicle 10 can be seen with a mast holder 12 which receives a mast 14, which is adjustable in height and holds a sled-like load-carrying means 16. Details of the lifting vehicle 10 and the lifting frame 14 need not be explained, since they are generally state of the art.

In Fig. 1 it can be seen that by lifting a load 18 on the load-bearing means 16, the mast 14 bends due to the load moment applied on one side. The starting position is shown in dashed lines. In Fig. 1 it can be seen that a readjustment of the mast 14 in the direction of the driver of the vehicle 10 from the position shown in Fig. 1 a position of the load-carrying means 16 is obtained, which corresponds approximately to that of FIG. 1 a. A pivoting of the mast 14 thus enables a compensation of deformation and the stacking of the load 18 in the correct position regardless of the deformation of the mast 14.

From Fig. 3 it can be seen that the lower part of the mast 14, also called the mast, consists of two profiles 20, 22. The profiles 20, 22 are suspended in bearings at 24 and 26, respectively. The bearings are e.g. Components of the mast holder 12 according to FIG. 1. The extendable mast part of the mast 14, not shown, is actuated with the aid of the lifting cylinder 28. The hydraulic supply to the lifting cylinder 28 is not shown. The pressure section of the lifting cylinder 28 is connected via a hydraulic line 30, a throttle 32 and a pressure relief valve 34 to an inclination cylinder 36, the piston 38 of which is articulated via a rod 40 to a crossbar 42 which is connected to both profiles 20, 22 of the mast 14 is. A valve arrangement 44 in the line 30, which leads to a hydraulic source, serves as a lowering brake when the mast 14 is retracted.

On the other side of the piston 38, a hydraulic pressure accumulator 46 is connected to the cylinder 36. The gas volume 48 in the accumulator 46 generates a pressure in the corresponding cylinder space which corresponds to the pressure in the other cylinder space which is derived from the pressure space of the lifting cylinder 28 when the mast is supported by the lifting cylinder 28 but the load-bearing part is not loaded.

The pressure relief valve 34 maintains the pressure in the associated cylinder space, which is built up in the unloaded state. This pressure therefore withstands the back pressure due to the hydraulic accumulator 46. Actuation of the mast 14, i.e. a corresponding pivoting therefore does not take place. However, if the pressure in the lifting cylinder 28 rises due to a predetermined load, the pressure in the corresponding cylinder space also increases. It leads to a pivoting of the mast in the bearings 24, 26 in order to bring about a deformation compensation in the manner described with reference to FIG. 1. The displacement of the piston 38 caused at a certain pressure in the inclination cylinder 38 is dependent on the characteristic curve which has the gas volume 48. It is matched to the spring characteristic of the mast 14. The throttle 32 ensures that pressure fluctuations in the lifting cylinder do not lead to an oscillating adjustment of the inclination cylinder 36 and causes damping in the event of vibrations of the lifting frame.

4 and 5 are the same parts as in FIGS. 2 and 3 with the same reference numerals ver see. It will only deal with differences.

4, the piston rod 40 is articulated on a lever 50 which is connected to an eccentric 52. The eccentric cooperates with a facing surface of the cross member 42. An alternative position of the lever 50 is shown in dashed lines. Lever 50 and eccentric represent a transmission gear to transmit the force from the tilt cylinder 36 to the mast 40. As a result, the hydraulic power of the tilt cylinder 36 can be reduced.

6, a lifting cylinder 60 for a lifting frame, not shown, which is connected via a line 62 to a hydraulic source, not shown, is connected via a line 64 with throttle 66 and pressure relief valve 68 to the pressure side of an inclination cylinder 70. The opposite side of the piston is acted upon by a compression spring 72. The biasing force of the spring 72 is counteracted by a corresponding pressure on the opposite side of the piston, which corresponds to the pressure in the lifting cylinder 60 in the unloaded state of the load-bearing part. The pressure limiting valve 68 ensures that a predetermined pressure is maintained in the inclination cylinder 70. The adjustable throttle 66 is used for damping purposes.

As far as the same parts are shown in the hydraulic circuit according to FIG. 7 with FIG. 6, the same reference numerals are also used. A control valve 74 is arranged in line 64 of the hydraulic circuit according to FIG. 7, with which the connection between the cylinders 60, 70 can be blocked. The valve 74 also controls the connection between a hydraulic accumulator 76 and the other side of the tilt cylinder 70. A pressure relief valve 80 is arranged in a corresponding line 78. A switching valve, not shown, is connected to the line 78 for the arbitrary actuation of the tilt cylinder 70, e.g. by the driver of a lifting vehicle. The line 64 is also connected to a line 82, which likewise leads to a switching valve (not shown) for actuating the tilt cylinder 70. The tilt cylinder 70 is automatically actuated as a function of the pressure in the lifting cylinder 60 when the valve 74 is open, the pressure in the hydraulic accumulator 76 determines the bias in the tilt cylinder 70.

In the embodiments 1 to 4, the mast was pivotally mounted in a holder. From Fig. 8 it can be seen that the holder can also be adjusted in order to compensate for deformation. In Fig. 8, the mast is designated 90, which is held in a holder 92. If the mast 90 is deformed when a load 94 (dashed line) is received, a deformation compensation takes place in that the holder 92 is pivoted about a pivot point 96 with the aid of an inclination drive (not shown).

In Fig. 9, the mast 98 of an otherwise not shown mast is indicated, which is received in a right-angled mast holder 100. In the present case, the mast holder 100 is designed to be movable. Lifting vehicles with movable masts are known per se. For this purpose, the horizontal leg of the mast holder 100 has two rollers 102, 102a, which roll on a track not shown in FIG. 9. An inclination cylinder 104 is also held on the horizontal leg, e.g. corresponds to the tilt cylinder 70 according to FIG. 6. Its rod 106 is articulated on an arm 108 which is connected to an eccentric 110. The eccentric 110 rotatably supports the roller 102a, which rolls on a raceway 112 (FIG. 10). The height of the axis of the roller 102a relative to the holder 100 can be adjusted by pivoting the arm 108 and thus rotating the eccentric 110. As a result, the mast holder 100 is pivoted slightly about the axis of the second roller 102, with the result that the mast 98 is also pivoted. In this way, a pivoting of the mast can also be achieved for the purpose of the desired deformation compensation. The tilt cylinder 104 is connected to the lifting cylinder, not shown, for the mast.

The stand mast of a mast according to FIG. 11 with the profiles 120, 122 of a mast 126 is pivotally mounted about an axis 124 in the mast holder, not shown. An adjusting cylinder 126, 128 acts on the profiles, which are hydraulically connected via throttles 130, 134 and connected to mast lifting cylinders 136, 138. The hydraulic circuit corresponds e.g. the embodiment according to Figures 6 or 7, so that there is no need to go into detail. With the aid of the tilt cylinders 126, 128 and the throttles 130, 134, torsional vibrations of the mast 126 can also be damped.

In FIG. 12, a mast, generally designated 140, is pivotably mounted about an axis 142 in a mast holder, not shown. Lifting cylinders 144, 146 act on the movable part of the mast 140 and are actuated by a hydraulic pressure source via a valve 148. A line 150 in which a pressure gauge 152 is arranged branches off from the lines to the lifting cylinders 144, 146. The signal from the pressure meter goes to a controller 154, the other input of which is connected via a functional line 156 to a distance meter 158, which measures the displacement of an inclination cylinder 160. Controller 154 generates a control signal for one Motor 162 that drives a hydraulic pump 164. In this way, an adjustment signal for the tilt cylinder 160 is generated as a function of the pressure measured in the lifting cylinder 144 or 146.

FIG. 13 shows a schematically illustrated lifting vehicle 170 with a lifting mast holder 172 which holds a lifting mast 174 which can be extended in height. The vehicle 170 e.g. two front wheels 176 and a single rear wheel 178. The bearing of the wheel 178 is mounted eccentrically, so that the axis of rotation of the wheel 178 can be changed at a distance from the vehicle by hydraulic actuation of the eccentric 180 with the aid of an adjusting cylinder 182. This also changes the inclination of the vehicle 170 and thus the inclination of the mast 174. The actuation of the inclination cylinder 182 can be carried out in the same way as for the inclination cylinders of the above-described embodiments.

Claims (15)

1. Lift apparatus including a lift frame, a lift frame holder and a sub-structure if desired, which lift frame is provided with a stand mast, at least one extendible mast member guided along the stand mast, a load receiving means guided along the extendible mast member so as to be displaceable in height, and a mast lift cylinder assembly for displacing the extendible mast member, the lift frame being pivotally mounted to the lift frame holder or the lift frame holder being displaceably mounted to the substructure, and an inclination drive being connected to the lift frame or the lift frame holder for varying the inclination of the lift frame, characterized in that the inclination drive (36,104), for compensating displacements of the load receiving means (16), the lift frame (14,19) or the lift frame holder (96,100) is displaceable automatically in response to the pressure in the mast lift cylinder assembly (28).

2. A lift apparatus according to claim 1, characterized in that the mast lift cylinder assembly has associated therewith a pressure sensor and the output signal of the pressure sensor serves to provide the control signal for the inclination drive.

3. A lift apparatus according to claim 1 or claim 2, characterized in that a biasing force opposite to the displacement force is acting upon the inclination drive (36,70,104), which biasing force corresponds approximately the displacement force which the inclination drive provides when the load receiving means (16) is unloaded.

4. A lift apparatus according to any of claims 1 to 3, characterized in that the inclination drive comprises a displacement cylinder (36,70,104).

5. A lift apparatus according to claim 4, characterized in that the displacement cylinder (36,70,104) engages the stand mast (22) or the frame holder (100).

6. A lift apparatus according to claim 5, characterized in that the pressure side of the mast lift cylinder assembly (28,60) communicates with the displacement cylinder (36,70), preferably via a throttle (32,66).

7. A lift apparatus according to claim 5 or claim 6, characterized in that the displacement cylinder (36,70,104) is pivotally mounted to the stand mast or frame holder.

8. A lift apparatus according to claim 5 or claim 6, characterized in that the displacement cylinder (36) is pivotally mounted to an excentric member (52) which co-operates with a counter- surface of the stand mast (20) or the frame holder.

9. A lift apparatus according to claim 3 or any of claims 4 to 8, characterized in that a compression spring (72) acts upon the piston of the displacement cylinder (70,104) for providing said biasing force.

10. A lift apparatus according to claim 3 and any of claims 4 to 9, characterized in that the displacement cylinder (36,70) communicates with a hydraulic reservoir (46,76) for providing said biasing force.

11. A lift apparatus according to claim 4 and claim 9 or claim 10, characterized in that the mast lift cylinder assembly (28,60) communicates with the displacement cylinder (36,70) via a pressure limiting valve (34,68).

12. A lift apparatus according to any of claims 3 to 11, characterized in that the biasing force is adjustable.

13. A lift apparatus according to any of claims 4 to 12, characterized in that a pair of displacement cylinders engages one side of the stand mast in a parallel and spaced relationship.

14. A lift apparatus according to claim 1, characterized in that the lift frame is mounted to a lift truck including a carriage, that the lift truck is mounted so that its inclination with respect to the carriage is adjustable, and the inclination drive operates between the lift truck and the carriage.

15. A lift apparatus according to any of claims 1 to 14, characterized in that a transmission is provided between the inclination drive and the lift frame or the lift frame holder.

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