Classifications

• • 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
  • B66F9/24—Electrical devices or systems

Definitions

• the present invention relates to an electrically driven fork lift truck comprising a fork lift platform for carrying loads and fork lifting means for adjusting the height of the fork lift platform.
• the fork lifting means are driven by an electric motor which drives a hydraulic pump.
• the pressurized hydraulic fluid is used to operate the hydraulic fork lift cylinders.
• German patent application DE-A-199 34 994 describes an electrically driven fork lift truck, in which the lift platform is driven using a hydraulic cylinder provided with hydraulic fluid from a pump driven by an electric motor, hi other known fork lift trucks, the hydraulic pump may also be driven by a combustion engine.
• the hydraulic actuators as used in present electrically driven fork lift trucks have the disadvantage that the efficiency of the actuators is less than fifty percent. Because of this, the electric capacity required for driving the electric motor for the hydraulic pump is large, requiring large batteries and frequent charging or changing of the batteries.
• the present invention seeks to provide an improved fork lift truck which has a better efficiency than present fork lift trucks. This is achieved by a fork lift truck according to the preamble defined above, in which the fork lifting means comprise an electromechanical actuator connected to the fork lift platform for directly driving the fork lift platform.
• the electromechanical actuator comprises an assembly of an electric motor and a screw/nut assembly for converting the motor rotary motion in a linear motion.
• the screw/nut assembly may comprise a ball screw or roller screw to allow efficient and friction free translation of the rotary motion in a linear movement.
• the ball or roller screw may be implemented as a planetary gear, in which the thread is arranged to eliminate ball or roller recirculation and permit a true planetary movement of the balls or rollers (no axial movement).
• the fork lift truck further comprises fork tilting means for tilting the fork lift platform, the fork lift tilting means comprising an electromechanical actuator.
• the specifications of this electromechanical actuator may be less stringent as the one for the lifting function, as smaller forces are required.
• fork side shifting means for side shifting the fork lift platform may be present, the fork lift side shifting means comprising an electromechanical actuator, i this case the specifications of the electromechanical actuator maybe even less stringent, possibly allowing to use a simple DC electric motor.
• the fork lift truck may in an even further embodiment comprise drive means for driving at least one wheel of the fork lift truck, the drive means comprising at least one electromechanical actuator, e.g. an electric motor.
• the fork lift truck may further comprise steering means for steering steerable wheels of the fork lift truck, the steering means comprising an electromechanical actuator directly driving the steering angle of the steerable wheels of the fork lift truck.
• the fork lift truck may also comprise brake means for slowing down the fork lift truck, the brake means comprising an electromechanical actuator for directly applying a brake force on one or more wheels of the fork lift truck.
• the fork lift truck comprises a battery package having at least one battery for driving the electromechanical actuators.
• the battery package may be removeable to allow easy replacement of the battery, e.g. when it is depleted.
• the fork lift track may comprise a combustion engine and a generator for providing electrical power to the electromechanical actuators and for charging the at least one battery.
• This hybrid embodiment will e.g. allow to operate the fork lift truck inside a building using only the battery for supply of energy, while outside the combustion engine may be used for operation of the fork lift track and charging the battery.
• further comfort and safety related functions are also implemented using electromechanical actuators.
• the fork lift truck may comprise a tiltable cabin for providing maintenance access, and cabin tilting means for tilting the tiltable cabin, the cabin tilting means comprising an electromechanical actuator.
• the fork lift truck may comprise a rotatable seating arrangement or rotatable cabin and seating rotation means for rotating the seating arrangement or rotatable cabin with respect to the fork lift truck, the seating rotation means comprising an electromechanical actuator.
• the viewing direction of the operator may be rotated over e.g. 90 or 180°.
• Fig. 1 shows a schematic view of an electrically driven fork lift truck
• Fig. 2 shows a schematic view of an electromechanical actuator as used in the present invention
• Fig. 3 shows a schematic electrical block diagram of the electrically driven fork lift truck.
• an electrically driven fork lift track 10 according to an embodiment of the present invention is shown. It comprises a fork lift truck body 4 with two steerable back wheels 2 and two fixed wheels 3. Furthermore, the fork lift truck 10 comprises a fork lift platform 1 for carrying loads, which can be controlled in three directions: up and down (indicated by arrow A), tilting forward and backward (indicated by arrow B) and moving left and right (indicated by arrow C). In Fig. 1, also the possible turning direction of the fork lift truck 10 is indicated by arrow D, and the driving direction is indicated by arrow E. The fork lift truck 10 is operated using a number of controls, of which a steering wheel 5 for steering, joystick 6 for operating the fork 1, accelerator pedal 7 and brake pedal 8 are indicated schematically in Fig. 1.
• the lifting operation of the fork 1 is executed using an electromechanical actuator 20, an embodiment of which is shown schematically in Fig. 2.
• the electromechanical actuator 20 comprises an electric motor 21 , a drive axle 22, a resolver 23, external tube 24 and drive rod 25 having a mounting hole 26.
• the external tube 24 encloses a planetary roller screw which is driven directly by the drive axle 22 which is coupled to the electric motor 21, e.g. a brushless motor.
• the roller screw converts the rotary motion of the drive axle 22 into a linear movement of the drive rod 25.
• a nut extends and retracts the drive rod 25.
• the roller screw is held by a combination of angular contact ball bearings which allow for high speed and high rigidity.
• Electromechanical actuator 20 in general have a power consumption efficiency of more than 80 %, as compared to 50 % for hydraulic actuators.
• Fig. 3 a schematic view is shown of the electrical system of the fork lift track
• the operator inputs 5-8 are shown, and on the right side the respective electromechanical actuators inputs 12-17 for the various functions of the fork lift track 10.
• The, preferably electrical, signals from the operator inputs 5-8 are input to a control unit 11.
• Feedback signals may be received from the electromechanical actuators 20 to allow feedback control loop implementation in the control unit 11.
• the control unit 11 may comprise separate control subunits 1 la-d associated with the operator inputs 5-8.
• the fork 1 is driven up and down (direction A) using one, but preferably two electromechanical actuators 20 (via inputs 13).
• the specifications of the ball screw type actuators 20 may allow a dynamic carrying capacity of 66 kN and a static carrying capacity of 189 kN using a stroke of 1500 mm.
• the electric motor 21 is rated at approximately 10 kW. This arrangement will allow lifting a load of 2000 kg at 0.5 m/s.
• the tilting of the fork 1 may be driven using an electromechanical actuator 20 of the roller screw type (preferably two actuators 20 are used to allow symmetric loading), allowing a dynamic carrying capacity of 51 kN and a static carrying capacity of 80 kN and a stroke of 200 mm.
• the side shift actuation of the fork 1 does not require very large forces to be provided by the electromechanical actuator 20 via actuator input 15, and may e.g. be implemented using a DC motor providing about 9 kN over a stroke of 200 mm.
• the steering function of the fork lift track 10 may also be implemented using electromechanical actuation, possibly using steer-by-wire techniques via steering actuator input 12.
• the steering function may be implemented using two electromechanical actuators 20 directly driving the two steered wheels 2.
• the steered wheels 2 may be synchronised using software control, e.g. using an Ackermann algorithm.
• the propulsion of the fork lift track 10 may be implemented using electric actuation means, such as electric motors driving each of the front wheels 3 directly via actuator inputs 16.
• the brake function of the fork lift track 10 may also be implemented using electromechanical actuators co-operating with friction discs attached to the wheels 2, 3 of the fork lift track 10 and receiving inputs from the control unit 11 via actuator input 17.
• actuators may be of the brake-by- wire type, in which electrical signals are sent from the brake pedal 8 to the brake actuators 28.
• the electromechanical actuators 20 are supplied by a battery 30, which is a relative high voltage type, e.g. 48 V, to allow driving all the electromechanical actuators 20.
• the battery 30 may be a removeable battery, allowing changing a depleted battery by a fully charged or recharged battery.
• the fork lift truck 10 further comprises an engine 32, such as a combustion engine, and a generator 31 mechanically coupled to the engine 32.
• the generator 31 provides electrical energy to the electromechanical actuators 20 directly, or via charging of the battery 30.
• This hybrid arrangement allows e.g. to use the combustion engine 32 outdoors and only the battery 30 indoors to drive the forklift truck 10.
• an electrically driven fork lift truck may be envisaged addressing comfort and safety issues.
• the cabin of the fork lift truck 10 may be tiltable to provide access to the battery pack 30, or the engine 32 and generator 31, e.g. for maintenance.
• the cabin tilt function may be provided using an electromechanical actuator 20.
• the cabin of the fork lift track, or at least a seating arrangement for the operator of the fork lift track 10 may be rotatable around a vertical axis, such that the operator may change its viewing direction depending on the operating and/or driving direction of the fork lift truck 10 (e.g. 90° rotation or 180° rotation).
• the seating arrangement or the complete cabin may be mounted in the fork lift track 10 using a slew bearing, and the rotation function may be implemented using an electromechanical actuator 20, e.g. in the form of a worm wheel attached to the slew bearing and a threaded shaft driven by an electric motor.
• electromechanical actuators 20 instead of conventional hydraulic actuators and the required hydraulic fluid supplies, an efficiency gain of over 30 % may be achieved.
• direct electrical drive to the front wheels 3 instead of an electric motor and a gearbox, an additional 5 to 30 % may be gained in efficiency.

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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)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

Family

ID=29244979

Family Applications (1)

Country Status (3)

Cited By (4)

Citations (8)

• 2002
  • 2002-04-11 NL NL1020371A patent/NL1020371C2/nl not_active IP Right Cessation
• 2003
  • 2003-04-11 AU AU2003230449A patent/AU2003230449A1/en not_active Abandoned
  • 2003-04-11 WO PCT/NL2003/000280 patent/WO2003086944A1/en not_active Application Discontinuation

Patent Citations (8)

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