Patent ID: 12240551

DETAILED DESCRIPTION

In the steering method according to the present invention, depending on the determined difference between the detected angular positions, at least one of the at least three steered wheels and the angle setpoint values provided by the steering computer are controlled by an electrical power electronics unit, and each steering motor is supplied with the electrical energy required to reduce the difference. According to the present invention, the steering motors are no longer driven hydraulically, but electrically.

The drive can, for example, also operated electrically. Each driven wheel can, for example, be assigned its own, electrically operated drive motor. The drive then comprises a number of electric motors that corresponds to the number of driven wheels.

A manually actuatable steering transmitter can, for example, be connected to the steering setpoint value transmitter. The angle setpoint values are thereby influenced when the steering transmitter is actuated. The steering transmitter can in particular be a steering wheel or a joystick.

In order to reduce the risk that an industrial truck steered with the aid of the steering method according to the present invention is not appropriately steered at the corresponding driving velocity, which could result in difficult or uncontrollable driving conditions, the traction motor or traction motors can, for example, also be powered with electrical power with the aid of the power electronics unit, which power is limited to the maximum permissible drive power depending on the angle setpoint values.

In a development of the steering method according to the present invention, the angular positions of the at least three motor-steerable wheels can, for example, be steered based on selectable steering programs.

In a development of the steering method according to the present invention, the drive of the industrial truck can, for example, be deactivated while a steering program is being selected. Alternatively or additionally, the steering transmitter can, for example, also be deactivated while a steering program is being selected, i.e., actuation of the steering transmitter, for example, turning the steering wheel, does not result in at least one of the steering motors being supplied with electrical power. The operational safety of the industrial truck is thereby increased.

In an embodiment of the steering method according to the present invention, the selectable steering programs can, for example, comprise a longitudinal travel program and a transverse travel program. The longitudinal and transverse travel programs differ in that the neutral positions of all wheels differ from one another by angular positions of 90°.

A choice can, for example, be made between the “front-axle steering,” the “rear-axle steering,” and the “all-wheel steering” steering sub-programs in the longitudinal travel program and/or in the transverse travel program. “Front-axle steering” is a steering sub-program in which only the wheels of the front axle in the forward direction of travel are steered due to an actuation of the steering transmitter, for example, a rotation of the steering wheel. Accordingly, “rear-axle steering” is a steering sub-program in which, when the steering transmitter is actuated, only the wheels of the rear axle viewed in the forward direction of travel are steered. In the “all-wheel steering” sub-program, all wheels of the industrial truck are accordingly steered when the steering transmitter is actuated.

A development of the steering method according to the present invention is, for example, where the selectable steering programs comprise a carousel travel program and/or a diagonal travel program and/or a parking program. In the carousel travel program, all wheels are brought into angular positions which, when the industrial truck is driven, result in a rotation of the wheels about a pivot point that lies within a base area of the industrial truck. In the so-called “parking program,” steered wheels of the industrial truck are brought into angular positions in which a shift of the industrial truck relative to the ground is not possible without overcoming the friction of the wheels on the ground, so the truck is prevented from shifting relative to the ground even without a braking effect due to the wheel positions.

In a development of the steering method according to the present invention, when the longitudinal travel program is selected, the steering angles of all steered wheels can, for example, be controlled to angular positions of 0°, when the transverse travel program is selected, they can, for example, be controlled to angular positions of 90°, and when the carousel travel program or the parking program are selected, the respective angular positions required by the steered wheels can, for example, be controlled directly.

In a development of the steering method according to the present invention, a steering pole, in which the axes of rotation of the wheels intersect when the industrial truck moves in a straight line, can, for example, be continuously displaceable with a control element provided in addition to the steering transmitter. In this steering method, the boundaries between longitudinal travel and transverse travel programs disappear and the industrial truck can be maneuvered in a particularly variable manner without interrupting the vehicle position.

Undesirably uncontrolled driving conditions can be prevented if the steering method is, for example, designed so that, in the event of an unexpected difference between the angular position thereof and the angle setpoint value thereof determined on one wheel of the steerable wheels, the electrical power electronics unit is controlled so that the steering of this steerable wheel and possibly any other steerable wheel belonging to the same axle is switched off and the industrial truck is braked in a controlled manner. This development of the steering method increases the operational safety of an appropriately equipped industrial truck.

To further improve the operational safety of the industrial truck, it is further advantageous to design the steering method thereof so that, in the event of an unexpected difference between the angular position thereof and the angle setpoint value thereof, which difference is determined on one wheel of the steerable wheels and could result in a critical driving state, the drive of the industrial truck is switched off, for example, by interrupting the application of the electric traction motors with electrical power.

In the steering system for an industrial truck for carrying out the steering method described above, the steering motors are designed according to the present invention as electric motors, for example, as AC motors or as synchronous motors.

A power electronics unit that applies electrical power to the steering motors can then, for example, be designed so that it is suitable for controlling both AC motors and synchronous motors. A modular structure of a steering system is thus possible without having to provide different power electronics units for this purpose. Irrespective thereof, the power electronics unit can, for example, be designed so that it also serves to apply electrical power to at least one traction motor of the industrial truck, it being possible to influence the power level via an accelerator, for example, an “accelerator pedal.”

In order to provide the steerability of each steered wheel even when the assigned traction motor is subjected to maximum electrical power, the maximum power (“nominal power”) of the corresponding steering motor can, for example be between 10% and 50%, for example, between 20% and 40%, for example, between 25% and 35%, of the maximum power (“nominal power”) of the drive motor. In the case of an industrial truck with four steerable wheels, two of which are driven with the aid of a drive motor each and which has a dead weight of around seven tons when ready for operation, each steering motor can, for example, have a power output of around 1 kW and each traction motor can, for example, have a power output of around 4 kW.

The steering computer can, for example, comprise a device for storing a plurality of steering programs.

A steering angle sensor, for example, designed as an electrical or electronic steering angle sensor, can, for example, be assigned to each steerable wheel. This allows the angular position of each wheel to be detected in a particularly simple and reliable manner.

The steering setpoint value transmitter can, for example, comprise a pulse output at which electrical pulses are generated, the number of which depends on the actuation of the steering transmitter, in particular the angle of rotation of a steering wheel, and possibly on a control element provided in addition to the steering transmitter, for example, a joystick.

In a development of the steering system according to the present invention, angular positions of the steered wheels of at least 0°≤angular position≤360° can, for example, be achieved; i.e., the steerable wheels are provided to be steerable by at least 360° about a corresponding steering axle.

In the steering system according to the present invention, the steering motors can, for example, be designed as rotation motors, each with a drive shaft, the drive shaft being operatively connected via a flexible traction means or a gear drive with a steering shaft that defines a steering axle. In a steering system designed in this way, it is technologically comparatively simple to be able to turn each steerable wheel by at least 360° about its associated steering axle.

The present invention also relates to an industrial truck having a steering system as described above.

The present invention will be explained in greater detail below under reference to embodiments as shown in the drawings.

FIG.1schematically shows an industrial truck100, which comprises a frame1, which is approximately U-shaped in plan view, and three wheels2,3,4which are mounted thereon so as to be steerable about steering axles A. All wheels2,3,4are aligned inFIG.1so that their wheel axles B extend parallel to one another. These wheel positions correspond to a straight travel of the industrial truck100in the longitudinal direction of travel, which is symbolized by the arrow P1.

The steering axles A of the wheels2,3,4are formed by steering shafts6,7,8, with which each wheel is non-rotatably connected with respect to the steering axles A via a wheel carrier (which is not shown in the drawings).

A turntable10,11,12is non-rotatably fastened to each steering shaft6,7,8. For each of the wheels2,3,4, a steering motor14,15,16is provided, each with a drive shaft which likewise carry a turntable18,19,20. To transmit torque for the purpose of steering each wheel2,3,4, the turntables18,19,20of the steering motors14,15,16are each connected to the turntables10,11,12via flexible traction device22,23,24. The flexible traction device22,23,24can, for example, be chains or toothed belts. The turntables10,11,12;18,19,20are adapted to each flexible traction device22,23,24.

The steering motors14,15,16are designed as electric motors, in particular as AC motors or as synchronous motors, and form part of a steering system of the industrial truck100.

The steering system also comprises a steering computer26to which a steering setpoint value transmitter30, an input field31, and a control element32which is designed as a joystick, are connected via data lines27,28,29. The steering setpoint value transmitter30is coupled to a steering wheel60.

Each wheel2,3,4is assigned a steering angle sensor33,34,35(which is not shown in detail in the drawings) which is designed as an electronic steering angle sensor and which detects the current steering angle position α of each wheel2,3,4. In the longitudinal travel illustrated inFIG.1, the steering angle positions are α=0°, and, in the transverse travel shown inFIG.2, they are α=90°. The steering angles detected by the steering angle sensors33,34,35are provided to the steering computer26via data lines37,38,39.

The steering computer26is connected to a power electronics unit41via a control line40.

The steering motors14,15,16are connected to the power electronics unit41via electrical power lines42,43,44.

In the embodiment shown inFIGS.1and2, each of the steerable wheels2,3,4is assigned a separate, electric traction motor45,46,47, which cannot be seen in detail in the drawings. The traction motors45,46,47are connected to the power electronics unit41via power lines48,49,50. It is also, however, possible to assign a drive motor only to some of the steerable wheels, for example, only to the center wheel4, and to design the remaining wheels2,3to run freely. To influence the electrical power with which the traction motors are applied, an accelerator pedal58is provided, which is connected to the steering computer26via a data line.

A wheel speed sensor51,52,53(which again cannot be seen in the drawings) is assigned to each of the wheels2,3,4. Each wheel speed sensor51,52,53is connected to the steering computer via a data line54,55,56.

As set forth above, the industrial truck100is shown inFIG.1in the longitudinal direction of travel thereof symbolized by the arrow P1. In order to initiate the longitudinal direction of travel P1, a “longitudinal travel program” stored in the steering computer26is activated with the input field31.

FIG.2shows the same industrial truck100after a “transverse travel program” stored in the steering computer26is selected with the aid of the input field31. As can be seen by comparingFIGS.1and2, the wheels2,3,4were rotated by a steering angle α of 90° with the aid of the steering motors14,15,16about the respective longitudinal axis A so that the industrial truck100, if it is driven, now moves in the transverse direction of travel which is symbolized by the arrow P2.

FIG.3shows a view of the arrangement of steering motors and wheel arrangements of a four-wheeled industrial truck in a schematic plan view. In contrast to the industrial truck described with reference toFIGS.1and2, the industrial truck200according to this embodiment comprises, in addition to the three wheels2,3,4, a fourth wheel5, which is rotatably mounted on the frame1via steering shaft9about a steering axle A. The wheels2,3,4,5are arranged on this four-wheeled industrial truck200at the corners of a rectangle. A turntable13is in turn non-rotatably fastened to the steering shaft9. A fourth steering motor17is provided with a turntable21which is non-rotatably fastened to a drive shaft of the steering motor17. A flexible traction device25is again provided for the transmission of torques between the turntable21and the turntable13. A steering angle sensor36is also assigned to the fourth wheel5.

The arrangements, design, and functionality of the fourth wheel5and the components described above correspond to those of the industrial truck100described with reference toFIGS.1and2, so that reference is made to the description thereof in order to avoid repetition. The industrial truck200also comprises the other components shown inFIGS.1and2, such as the steering setpoint value transmitter30, the steering wheel60, the input field31, the control element32, the steering computer26, and the power electronics unit41together with the associated data lines and power lines, wherein, in the case of the industrial truck200, additional data lines and power lines (which are not shown in the drawing) are provided for the arrangement of the fourth wheel5. Each of the wheels2,3,4,5in industrial truck200is also assigned a drive motor, which drive motor is configured in the same way as the traction motors45,46,47in the embodiment of the industrial truck100and which can be supplied with electrical power. In a four-wheeled industrial truck, it is again also possible to assign only some of the wheels, for example, the wheels4,5, to traction motors.

FIG.4is a basic illustration of a signal flow plan as it is implemented for each of the steered and driven wheels, using the example of wheel4.

FIG.5is a further basic illustration of a signal flow plan of a steered and driven wheel using the example of wheel4, which corresponds to the illustration according toFIG.4. The only difference is that the steering motor14is not coupled to the turntable10and thus to the corresponding steering shaft via a flexible traction device22, but rather via a spur gear57.

In the embodiment described, various steering programs are stored in the steering computer26, which can be selected, for example, with the aid of the input field31. The steering computer26is programmed so that a parameterized standard steering program is activated after the steering system has been switched on. The steered wheels remain in the angular position when the steering system is switched on and are only deflected after the direction of travel has been preselected.

The steering computer is also programmed so that the selection of a steering program, for example with the aid of the input field, can only be enabled under specific conditions. During such a programming of the steering computer, for example, the industrial truck must be stationary, the selected steering program must be enabled, the steering must be active, and any previous emergency shutdown must have been quitted.

After a steering program has been activated, the power electronics unit41is controlled by the steering computer26via the control line40so that the steered wheels are steered into the angular positions corresponding to the direction of travel. The angular positions of the steered wheels are detected with the steering angle sensors33,34,35,36and compared with that position given by the steering computer26depending on the selected steering program. The steering motors are controlled in order to minimize the setpoint/actual value difference.

During a steering program selection, the power electronics unit41is controlled by the steering computer26so that the traction motors are not activated. Any data transmitted by the steering setpoint value transmitter are also not taken into account. In other words, the steering wheel is not active in this state.

The steering computer can in particular have the following steering programs:a) Front-axle steering, transverse travel, shown inFIGS.6and7.

In the case of front-axle steering, only the wheels of the axle that forms the front axle V with respect to the forward direction PV are steered. The steering geometry is comparable to that of a four-wheeled car. For precise steering, the steering line L must run exactly through the rear axle H, as can be seen inFIGS.6and7. Depending on the actuation of the steering transmitter, the steered front wheels are shifted into angular positions so that their axes of rotation intersect in a steering pole X. This steering pole X is always on the steering line L.b) Transverse travel, all-wheel steering, shown inFIGS.8and9.

With this steering program, all wheels are steered depending on the steering transmitter. Their axes of rotation must all intersect in a common steering pole X hen cornering.c) Transverse travel, rear-axle steering, shown inFIGS.10and11.

In this steering program, only the wheels of the rear axle H that are on the rear with respect to the forward/transverse direction of travel are steered. The steering pole X lies on a steering line L which coincides with the front axle V.d) Transverse travel, diagonal steering, shown inFIGS.12and13.

Depending on the actuation of the steering transmitter, all wheels are steered in identical angular positions, so that the direction of travel of the vehicle changes without changing the orientation thereof.e) Front-axle steering, longitudinal travel, shown inFIGS.14and15.

This steering program corresponds to that of the front-axle steering, transverse drive steering program, but the direction of travel differs by 90° compared to the transverse travel.

The same applies analogously to the steering programs longitudinal travel, all-wheel steering, shown inFIGS.16and17, longitudinal travel, rear-axle steering, shown inFIGS.18and19, and longitudinal travel, diagonal direction, shown inFIGS.20and21.f) Carousel travel, shown inFIG.22.

In this steering program, the steering pole X, in which the axis of rotation of the wheels intersect, lies within a base area G of the industrial truck.g) Parking program shown inFIG.23.

In the parking program, the wheels are brought into a pre-programmed angular position completely independently of one another so that the industrial truck is secured against rolling away even without the use of the brakes.h) Variable all-wheel steering, shown inFIGS.24-26.

This steering program initially corresponds to the steering program all-wheel steering. With the aid of the additional control element32connected to the steering computer26, which can be designed as a joystick, for example, the steering pole can now, for example, be shifted continuously so that the industrial truck can be maneuvered in a particularly variable manner without interrupting the driving state. All wheels can be rotated by 360° about the steering axles A for this purpose.

In the embodiments described, the steering computer can be designed so that different devices can be selected as steering setpoint value transmitters, however, they must always have a pulse output (apart from operation via a radio remote control in which the steering setpoint value transmitter would not be activated). The following parameters can, for example, be selected:

1. Pulse output Clock/UpDown or A/B track:

If the parameter “Pulse output Clock/UpDown” is selected, the steering computer is adapted to a steering setpoint value transmitter, the pulses of which contain information about the steering direction, for example, the direction of rotation of the steering wheel.

If the “A/B-track” parameter is selected, the steering computer is adapted to a steering setpoint value transmitter that generates pulses on two tracks A and B that are offset by 90°. The steering computer recognizes the steering direction, for example, the direction of rotation of the steering wheel, on the basis of the signal sequence received from the steering setpoint value transmitter.

2. Number of pulses generated by the steering setpoint value transmitter per steering wheel turn.

3. Direction of rotation.

The steering computer is also designed so that, when the steering transmitter is actuated, for example, when the steering wheel is turned, the generated pulses are counted by the steering computer and processed into an absolute steering setpoint value. From the parameters of the axle coordinates and the selected steering program, the steering computer calculates the required angle setpoint values of the steered wheels to achieve the desired change in direction.

The angular positions of the wheels steered with the aid of electric AC motors or synchronous motors are detected via the steering angle sensors33,34,35,36, which can be designed as potentiometric steering angle sensors. The actual angle of each steered wheel is calculated from the potentiometric signals and stored adjustment values. The steering computer compares the angular position (actual angle) thus determined with the angle setpoint value determined for each selected steering program based on the steering setpoint value determined angle setpoint with the angular position. On the basis of the setpoint/actual value difference, the power electronics unit41is controlled by the steering computer26so that it actuates the steering motor in the sense of a setpoint/actual value compensation.

If an error occurs with a steered wheel of a steering axle, for example, no angular position is transmitted, the steering operations of the steered wheels of this axle are deactivated and the steered wheels can, for example, be set into a neutral position by a corresponding routine stored in the steering computer, which correspond, for example, to their starting angular positions or straight-ahead driving positions. The steered wheels of the other, unaffected axles, however, remain active and allow steering corrections to be carried out in this way. The steering computer also contains a routine that controlled the power electronics unit in the event of every critical error in the steering so that the industrial truck is completely stopped.

The present invention is not limited to embodiments described herein; reference should be had to the appended claims.

LIST OF REFERENCE NUMERALS

100,200Industrial truck

1Frame

2,3Wheel

4Center wheel/Wheel

5Fourth wheel

6,7,8,9Steering shaft

10,11,12,13Turntable

14,15,16,17Steering motor

18,19,20,21Turntable

22,23,24,25Flexible traction means

26Steering computer

27,28,29Data lines

30Steering setpoint value transmitter

31Input field

32Control element

33,34,35,36Steering angle sensor

37,38,39Data lines

40Control line

41Power electronics unit

42,43,44Power lines

45,46,47Traction motor

48,49,50Power lines

51,52,53Wheel speed sensors

54,55,56Data lines

57Spur gear

58Accelerator pedal

59Data line

60Steering wheel

A Steering axles

B Wheel axles

G Base area

H Rear axle

P1Longitudinal direction of travel

P2Transverse direction of travel

PV Forward direction of travel

L Steering line

V Front axle

X Steering pole

α Angle