EP1046610A2

EP1046610A2 - Device and method for movement of a load carrier at an industrial truck

Info

Publication number: EP1046610A2
Application number: EP20000850068
Authority: EP
Inventors: Bengt Joelsson
Original assignee: BT Industries AB
Current assignee: BT Industries AB
Priority date: 1999-04-20
Filing date: 2000-04-18
Publication date: 2000-10-25
Also published as: SE9901408L; SE512652C2; SE9901408D0; EP1046610A3

Abstract

Device and method for movement of load carrying means of an industrial truck, in particular the pivot and lateral movement of a swing reach fork means. Hydraulic consumers (30, 32) provide the movements. A proportional valve (38, 40) is arranged in front each hydraulic consumer. The proportional flow valve (40) of the pivot movement has its inlet (58) connected to the outlet (56) of the other. At lateral movement the motor speed is controlled and the proportional flow valve (38) is held open. At pivot movement or simultaneous movement of both the motor speed is set so that the total flow somewhat surpasses a maximum value at the same time as the proportional flow valves (38, 40) are controlled to desired primary flow.

Description

This invention concerns a device for movement of a load carrier at an industrial truck in accordance with the preamble of claim 1 and a method for the movement of a load carrier at an industrial truck in accordance with the preamble of claim 7.

Prior art

At the handling of goods one often uses high storage racks with narrow aisles in order to minimize the area needed. This leads to the necessity of using so called narrow aisles or swing reach trucks. These trucks have a width that take almost the entire width of the aisle, and they are provided with so called swing fork means in order to be able to lift out loading pallets from the racks, which means that the fork carriage with the load forks can be moved laterally and pivot or swing 90° in each direction from a straight forward position. Goods can thus be collected and inserted without turning the truck itself as with other trucks.
This lateral movement and pivoting of the forks is however rather costly from an energy point of view since one often uses the same motor as for the lifting and lowering functions, where the lifting function require a considerably larger hydraulic flow than the pivot and lateral movements. As a result a large amount of hydraulic flow is just circulated and only a small part is used at the pivot and lateral movements, which leads to increased power consumption and the need of more powerful batteries or more frequent charging with corresponding drawbacks.
One way partly to solve this is to use two different hydraulic pumps for the two different groups of movements, but this leads to an increased number of components and thus increased costs.
It is also difficult to coordinate the pivot and lateral movement since the operator has to only partly open the valves in order to obtain the desired velocity. In narrow areas one has to be extra careful since severe consequences may occur if the load forks hit the rack.

Object of the invention

The object of the invention is to achieve a device and a method where the above problems are avoided and where pivot and lateral movements of the load forks of an industrial truck can be executed simply, safe and coordinated in an energy, environmentally and costwise efficient way.

Brief explanation of the invention

The object of the invention is achieved with a device according to the characterizing part of claim 1. Due to the speed controlled motor and an arrangement with proportional flow valves the waste flow and thereby also the energy consumption can be minimized.
The claims 2 and 3 concern preferred embodiments with efficient circuit solutions and designs of the movement providing hydraulic consumers.
A device according to the claims 4 and 6 allows the use of the same motor and pump for all hydraulic functions, while claim 5 concerns a device for optimized function and operator friendliness.
The method according to the invention is apparent from the characterizing part of claim 7. By controlling the motor, at lateral movement, so that only the necessary flow is obtained, the waste flow can be minimized thus optimizing the energy consumption. At the use of both consumers the motor is given a speed that with a certain margin surpass the added maximally allowed flows of the two consumers. The desired movement pattern is obtained by control of the proportional flow valves. It is impossible to control both functions by speed control of one and the same motor since all flow would go through the first consumer when coupled in series and through the one with the least resistance at coupling in parallel of the proportional flow valves, but with the above method the over all waste flow can be minimized.
Claim 8 concerns a preferred embodiment for the pivot movement. Since this movement has low flows in relation to the other ones the movement is technically difficult to control with motor speed control. This however leads to no impairing of the efficiency since the already low maximum flow result in less waste flows.
A method according to claims 9 - 11 gives optimized function and operator friendliness while the claim 12 enables safe efficient use of the same motor and pump for all hydraulic functions.
Further characteristics and advantages of the invention are apparent from the embodiment recited below, with reference to the enclosed figure that shows a schematic view of the hydraulic system of an industrial truck with swing reach fork means.

Description of an embodiment

The figure shows a schematic view of the hydraulic system of an industrial truck with pivot fork means. The general design of the truck is in accordance with some known concept. All components as valves etc that are shown in the figure and related to the invention are known per se and exist on the market today. The invention thus concerns the use of the components, their mutual arrangement and their control.
The hydraulic system of the truck includes a speed controlled AC-motor 2 that drives an hydraulic pump 4. The inlet 3 of the pump has a connection 8 to a reservoir 6 for hydraulic fluid. The hydraulic consumers can be divided into two sub or part systems 10, 12. The first part system 10 is used for vertical movement in the form of lifting and lowering of the load carrying means of the truck, which means preferably comprise a normal fork carriage with two load forks (not shown here). The second part system 12 is used for horizontal movement in the form of lateral movement and pivoting of the fork carriage around a vertical axis.
The first part system includes three lifting cylinders 14, 16, 18 that are connected to the outlet 5 of the pump via a hydraulic conduit 15. The cylinders 14, 16, 18 are activated in sequence in the normal manner that automatically occurs due to the relation between pressure area and lifted load.
At lifting a directional valve 20 in the conduit 15 opens and at lowering another directional valve 22 opens. A filter is also arranged in the conduit to prevent dirt from the cylinders to reach the pump. At lowering the pump 4 works as motor and the motor 2 as generator in order regeneratively to feed back energy to a battery, not shown. A pressure limiting valve 24 opens at a prescribed maximum pressure that otherwise may be surpassed when the fork carriage reach the top or if the lift movement is obstructed by something. There is also a manually maneuverable emergency lowering valve 25 that is coupled in parallel with the directional valves 20, 22.
The second part system 12 includes two hydraulic consumers 30, 32. The first consumer 30 is a hydraulic motor cooperating with a frame mounted rack 33 for obtaining a lateral movement of the fork carriage. The hydraulic motor 30 is in accordance with the invention connected to the outlet 5 of the pump via a conduit 50 to the inlet 52 of a first proportional flow valve 38 and a conduit 62 from its primary flow outlet 54 via a 4/3 directional valve 42 and a load holding valve 46. The hydraulic motor 30 can be driven in both directions and the direction of the driving depends on the position of the directional valve 42.
The second consumer 32 is constituted by two cylinders 34, the pistons of which are connected with a chain or the like which cooperates with wheels 37 causing the pivoting of the fork carriage around a vertical axle. This second consumer 32 is in accordance with the invention connected to the outlet 5 of the pump via a conduit 50 and the return outlet 56 of the first three way proportional flow valve 38, a conduit 64 to the inlet 58 of a second three way proportional valve 40 and a conduit 66 from its primary flow outlet 60 via a 4/3 directional valve 44 and a load holding valve 48. Which cylinder 34 that is pressurized and with this the movement direction of the chain 36 and the wheel 37 depends on the position of the directional valve 44.
If the valve block of the second part system is prepared with conduits 70, 72 additional hydraulic functions may be connected for special applications, for instance for a fork tilt. A directional valve 31 is arranged on the exit conduit of the outlet conduit 50 of the pump 4.
The system includes an electronic control unit 80 that receives signals from controls 82, 84, 86, 88 influenceable by the operator for lifting and lowering, lateral movement of the fork carriage, pivoting of the fork carriage and auto rotation. The driver may via the controls 82, 84, 86, 88 choose desired travel direction and speed. Dependant on these incoming signals the control unit 80 delivers signals to the motor 2, the directional valves 20, 22, 31, the proportional flow valves 38, 40 and the directional valves 42, 44 via signal cables (here unnumbered). All valves have in uninfluenced condition the closed positions shown in the drawing as rest positions.
The control system 80 may of course if so desired be connected to more operator controls, further it may be advantageous to generate incoming signals from different components in order to allow control and detection of different end positions.
The fork carriage is controlled in the following manner:
If the operator gives a signal for lifting of the fork carriage via the control 82 the control unit 80 delivers a signal to the motor 2 to drive the pump 4 with the speed that corresponds to the velocity chosen by the operator. The directional valve 20 opens so that the hydraulic pressure reaches the cylinders 16, 18 via the conduit 15.
If the operator gives a signal for lowering of the fork carriage via the control 82 the control unit 80 delivers a signal to the directional valve 22, that opens, so that the hydraulic pressure caused by the load is returned through the pump 4 to the reservoir 6. The directional valve 20 is maintained closed. The pump 4 is in this case driven as motor while the motor 2 becomes a generator that is braked to the speed that corresponds to the velocity chosen by the operator. Regenerated energy is fed back to the battery in some known manner. From a purely practical standpoint it may be advantageous to mount the entire valve block of the first part system 10 directly on the pump 4.
If the operator gives a signal for lateral movement of the fork carriage via the control 84 the motor 2 is driven with a speed giving a flow corresponding to the desired velocity. The valve 31 opens and the first proportional flow valve 38 opens entirely and the directional valve 42 is placed in a position corresponding to the desired direction of the movement.
If the operator gives a signal for a pivot movement of the fork carriage via the control 86 the motor 2 is driven with a speed giving a flow corresponding to or slightly above a prescribed maximum flow for the second consumer 32. The valve 31 opens and the second proportional flow valve 40 opens so that the primary flow corresponds to the desired pivoting velocity. The directional valve 44 is placed in a position corresponding to desired direction of movement. As previously mentioned it is not wise to control this movement by motor speed control. The waste flow is returned via the return conduit 68 to the reservoir 6.
If the operator gives a signal simultaneous lateral movement and pivot movement via the controls 84, 86 the motor is driven with a speed giving a flow corresponding or slightly surpassing a given added maximum flow for both the consumers 30, 32. The valve 31 opens and the first proportional flow valve 38 opens so that the primary flow corresponds to the desired movement velocity. The remaining flow is taken from the return outlet via the conduit 64 to the second proportional flow valve 40 that opens so that the primary flow corresponds to the desired pivot velocity. The directional valves 42, 44 are put in positions corresponding to desired direction of movement. The waste flow is returned via the return conduit 68 to the reservoir 6.
The control 88 is used for auto rotation. This means that the load forks can be moved between two home positions, one for loading or unloading in a storage rack on one side of the aisle and one for the other side of the aisle. The auto rotation means that the control unit 80 automatically delivers a signal to the valves and the motor according to a predefined sequence where the indication of the operator result in the desired direction but with predefined velocity. The valves and the motor are aside from this controlled in the same way as in the previous paragraph.
The control unit 80 is further arranged to prevent the two part systems 10, 12 from being activated at the same time. This could lead to serious consequences since it at the handling of goods in narrow aisles otherwise is a risk for the load hitting the rack, which can lead to serious accidents. The control unit 80 therefor never deliver a signal for activation of vertical movement while horizontal movement is in progress, or vice versa.
If additional hydraulic consumers are connected they may be connected in series after the outlet 62 of the second proportional flow valve and controlled in the same manner with motor speeds corresponding to or surpassing total maximum value.
As a rough estimate of the flows that may be needed for different movements can be said 50 liters/minute for lifting, 8 liters/minute for lateral movement and 1,5 liters/per minute for pivot movement. From these rather great differences follow that the invention provide an optimized use of the motor 2 and the pump 4 and that large energy losses and waste flows can be avoided.
The invention may within the frame of the patent claims be used according to a number of alternative embodiments other than the above shown. Thus the hydraulic consumers may be replaced by others or completed with several. The valve arrangement may also be configured in other ways than the one shown in the drawing.

Claims

Device for the movement of load carrying means, in particular a fork carriage, at an industrial truck, which means are caused to move by a hydraulic system including a pump (4) driven by a motor (2), preferably an AC-motor, a reservoir (6) for hydraulic fluid connected to the inlet (3) of the pump, a first hydraulic consumer (30) for achievement of a lateral movement, and a second hydraulic consumer (32) for achievement of a pivoting movement, which consumers (30, 32) are connected to the outlet (5) of the pump, characterized in that the motor (2) is speed controlled, that the first consumer (30) is connected to the outlet (5) of the pump via a first three way proportional flow valve (38), that the second hydraulic consumer (32) is connected to the return outlet (56) of the first proportional flow valve via a second three way proportional flow valve (40), the return outlet (62) of which is connected to the reservoir (6) for the hydraulic fluid.
Device according to claim 1, characterized in that a directional valve (42, 44) and a load holding valve (46, 48) are arranged in series between the primary flow outlet (54, 60) of each proportional flow valve and its consumer (30, 32).
Device according to any of the claims 1 or 2, characterized in that the first hydraulic consumer (30) is constituted by an hydraulic motor and that the second consumer by two cylinders (34), the pistons of which are connected with each other via a driving chain (36) or corresponding.
Device according to any of the claims 1 - 3, characterized in that the pump is also connected to cylinders (14, 16, 18) for lifting and lowering of the load carrying means, that a directional valve (31) is arranged between the pump and the first proportional flow valve (38), and that the pump/motor (4/2) also can be driven as motor/generator for regenerative feeding to a battery at load lowering.
Device according to claim 1, characterized in that an electronic control unit (80) is connected to a number of controls (82, 84, 86, 88) for signals given by an operator, that the control unit (80) further is connected with the proportional flow valves (38, 40), the directional valves (42, 44) and the motor (2) for control of these in dependency of the signals given by the operator.
Device according to ny of the claims 1 - 5, characterized in that additional consumers are connected between the second proportional flow valve return outlet (62) and the hydraulic flow reservoir (6).
Method for the movement of load carrying means of the kind that is defined in claim 5, characterized in that the control unit (80) at a signal from the operator only for activation of the first hydraulic consumer (30) delivers control signals to the motor (2) to drive the pump (4) with a speed that gives the flow that corresponds to the movement velocity desired by the operator, and to open entirely the first proportional flow valve (38), that the control unit (80) at a signal from the operator for activation of both of the hydraulic consumers (30, 32) delivers control signals to the motor (2) to drive the pump (4) with a speed that gives a flow corresponding to or somewhat surpassing a given added maximum flow for said hydraulic consumers (30, 32), and to open the proportional flow valves (38, 40) to such a degree that the primary flow corresponds to the velocity desired by the operator.
Method according to claim 7, characterized in that the control unit (80) at a signal from the operator for activation of only the second hydraulic consumer (32) delivers control signals to the motor (2) to drive the pump (4) with a speed that gives a flow corresponding to or somewhat surpassing a maximum flow for said other hydraulic consumer (32), and to open the second proportional flow valve (40) to such a degree that the primary flow corresponds to the movement velocity desired by the operator.
Method according to claim 7 or 8, characterized in that the control unit (80) delivers a signal to the directional valve or valves (42, 44) to cause a position or positions corresponding to the direction of movement desired by the operator.
Method according to any of the claims 7 - 9, characterized in that each proportional flow valve (38, 40) is held closed when the control unit (80) is not receiving signals for movement of a connected consumer.
Method according to any of the claims 7 - 10, characterized in that the control unit (80) signals to the valves (38, 40, 42, 44) and the motor (2) to control the hydraulic consumers (30, 32) according to a preset sequence when the operator signals a movement from one home position to another home position of the load carrying means.
Method according to any of the claims 7 - 11 where the motor also is used for lifting and lowering of the load carrying means, characterized in that the control unit does not signal to cause movement containing these functions during the time that the first or second hydraulic consumer (30, 32) is activated, and vice versa.