Wheel assembly of rubber tyred gantry crane

Abstract

A wheel assembly for a gantry crane, comprising a vertical tube connectable to a frame of the gantry crane, a vertical axle pivotally connected to the vertical tube, two horizontal axles and each horizontal axle carrying a wheel, wherein each wheel is arranged to be independently driven by a drive motor connected to the corresponding wheel through a gear arrangement, and to form a force couple around the vertical axle.

Description

[0001] Wheel assembly of rubber tyred gantry crane

[0002] Background

[0003] The invention relates to a rubber tyred gantry (RTG] crane, and especially to a wheel assembly of the RTG crane.

[0004] A typical RTG crane comprises a frame with two main girders, a hoist arranged between thereof, two leg structures on each side of frame, and two upper beams and two lower beams connecting the leg structures. A wheel assembly is arranged at either end of each lower beam, resulting one wheel assembly at each corner of the RTG crane. Each wheel assembly comprises two substantially horizontal axles, each horizontal axle carrying at least one pair of crane supporting wheels, and the wheels of each pair are located at opposing ends of the horizontal axle. Each wheel assembly can be mounted to a lower beam about a vertical tube. The wheel assembly may be driven by traversing and steering means, which include an electric drive motor individually drivingly connected through gearing to one given wheel thereof. A locking device associated with each vertical tube may selectively prevent turning of the associated wheel assembly by locking the axle in a predetermined orientation, such that coordinated control of the individual drive motors and of the associated locking devices permit traversing and steering of the crane at will.

[0005] In the conventional pair of wheels, one wheel is a driving wheel and another wheel is an idle wheel. The wheels are supported by a heavy output shaft of the gear reducer mounted between the wheels. During travelling motion, the twisting of the wheels is prevented with the locking device, such as a locking pin. The turning is conducted by releasing the locking pin, which allows the wheels to turn around the vertical tube. As travelling motion is not possible without the locking pin in place, the angular positions of the RTG are predefined by holes in different angles for the locking pin allowing stepped turning of the wheel around the vertical tube.

[0006] One of the disadvantages of this arrangement is that turning is slow and difficult as the wheels must be turned one by one. The crane must be still for this purpose. It also causes extreme stresses for the output shaft of the gear reducer, as turning the rubber tyres generates major axial friction force between the tyre and the ground. This leads to uneven wear between the tyres and providing larger shaft diameter than necessary. As cranes get larger and heavier, more expensive gear reducers need to be developed. Brief disclosure

[0007] An object of the invention is thus to provide an arrangement that solves or at least alleviates the aforementioned problems. The invention is based on a wheel assembly where both wheels of the pair of wheels are driven separately.

[0008] Brief description of the drawings

[0009] The invention will now be described in more detail in connection with preferred embodiments and with reference to the accompanying drawings, in which:

[0010] Figure 1 illustrates a diagonal top view of a RTG crane according to an embodiment;

[0011] Figure 2 illustrates a cross-sectional view of a wheel assembly according to an embodiment;

[0012] Figure 3 illustrates a top view of the wheel assembly according to an embodiment;

[0013] Figure 4 illustrates a top view of the mutual position of a pair of wheels on wheel assemblies when the crane is steered to lateral direction;

[0014] Figure 5 illustrates a top view of the mutual position of a pair of wheels on wheel assemblies when the crane is steered to longitudinal direction;

[0015] Figure 6 illustrates a top view of the mutual position of a pair of wheels on wheel assemblies when the crane is steered in a circle;

[0016] Figure 7 illustrates a top view of the mutual position of a pair of wheels on wheel assemblies when the crane is steered in a slightly curved travelling motion;

[0017] Figure 8 illustrates a top view of the mutual position of a pair of wheels on wheel assemblies when the crane is steered to a curved right angle travelling motion.

[0018] Detailed description of embodiments

[0019] Figure 1 illustrates a crane 1 according to an embodiment. The crane 1 comprises a frame 2 with two lower beams 3. Each end of the lower beam 3 is connected to a wheel assembly 5 so that the crane 1 has four wheel assemblies 5, one on each corner. The crane 1 may also be provided with a diesel generator 6, which supplies the crane 1 with power, and an electric distribution unit 7. The crane 1 can be a rubber tyred gantry (RTG) crane for lifting and moving containers 4, for example within a port area. Figure 2 illustrates a cross-sectional view of a wheel assembly 5 according to an embodiment, and Figure 3 illustrates a top view of the wheel assembly according to an embodiment. The wheel assembly 5 comprises a vertical tube 9 connectable to a frame 2 of the crane 1. The vertical tube 9 is typically a hollow structure having a cross-section of a circular or quadrangle design. A vertical axle

[0020] 10 is pivotally connected to the vertical tube 9 from their ends so that the vertical axle 10 is rotatable in relation to the vertical tube 9. Such pivotable connection may be implemented using a slewing bearing 12, for example. Other options include a king pin with an upper cylindrical bearing area for one bearing and a lower cylindrical bearing area for another bearing. The vertical axle 10 may have an upper flange 10a and a lower flange 10b for supporting a wheel support structure 13.

[0021] The wheel assembly 5 further comprises two horizontal axles 11 which are perpendicular to the vertical axle 10 and in such a way that the horizontal axles

[0022] 11 are located on opposite sides of the vertical axle 10 and each horizontal axle 11 carries a wheel 8a, 8b. The two horizontal axles 11 may be connected to the vertical axle 10 by the wheel support structure 13 which may also act as a gear housing for a gear arrangement 14. The wheel support structure 13 is arranged to protect the gear arrangement 14 and the horizontal axle 11 from dirt and water, for instance. The wheel support structure 13 can be rigidly secured to the vertical axle 10 by fasteners 15, for example bolts or screws. Especially, the wheel support structure 13 may have an upper edge 13a which is attached to the upper flange 10a of the vertical axle 10 and a lower edge 13b which is attached to the lower flange 10b of the vertical axle 10. Each horizontal axle 11 can be surrounded by the corresponding wheel support structure 13, which can be a mirror image of each other, thus providing a symmetric structure around the vertical axle 10.

[0023] Each wheel 8a, 8b is arranged to be independently driven by a drive motor 16a, 16b which is controlled with own motion controller and connected to the corresponding wheel 8a, 8b through the gear arrangement 14, and to form a force couple around the vertical axle 10. In this context, the force couple refers to a pair of opposite forces which creates a rotational effect without causing any translational motion. When the pair of wheels 8a, 8b are driven in straight line, the forces in the couple are equal in magnitude but opposite in direction. The torque is the turning effect produced by the force couple.

[0024] The first wheel 8a is arranged to be driven by a torque of a first drive motor 16a, and the second wheel 8b is arranged to be driven by a torque of a second drive motor 16b, wherein the first drive motor 16a and the second drive motor 16b may have different torques which enables the turning of the pair of wheels 8a, 8b. This means there is no need for a separate turning mechanism and instead the turning is enabled by the difference of the torques of the drive motors 16a, 16b. Especially, a torque of the first drive motor 16a and a torque of a second drive motor 16b may have opposite rotational directions.

[0025] Compared to the conventional RTG crane, which must be still when activating the turning of the wheels, this allows the wheel assembly 5 to be turned in a stepless manner by the difference of the torques of the first drive motor 16a and the second drive motor 16b. The turning motion can be actuated during the travelling motion which allows the wheel assembly 5 to be turned freely any angle -90 to 90 degrees during the drive. This has a massive effect on agility of the crane 1 as it allows travelling freely through any curve.

[0026] The vertical axle 10 may be located between the first drive motor 16a and the second drive motor 16b so that the first drive motor 16a and the second drive motor 16b are parallel to each other, and maybe parallel to the horizontal axles 11. When both wheels 8a, 8b are driven by independent drive motors 16a, 16b, the required torque is split between these two wheels 8a, 8b. This also allows the gear arrangement 14 to have a more compact size. For example, the gear arrangement 14 can comprise a fully helical gear reducer instead of a bevel-helical gear reducer. The gear ratio can be 75-110, and especially 80-95. For instance, when the RTG crane is driven without the load in full speed, the wheels 8a, 8b are rotated about 34 rpm and the motor about 3000 rpm. This change has a major effect on the noise emissions of the wheel assembly 5. Bevel gears can be manufactured efficiently only with lapping method, which is not as high accuracy final machining method as grinding or hard cutting which are used to manufacture fully helical gears.

[0027] Consequently, this provides enough available space in a wheel hub 17. Wheel hub 17 may be connected to the horizontal axle 11 and provides a housing for wheel bearings 19. The wheel hub 17 can comprise a fastening bush 20 and a fastening flange 21 fixed to the perimeter of the fastening bush 20. The wheel 8a, 8b is fastened at its rim 23 to the fastening flange 21 with bolts 24, so that the wheel 8a, 8b is rotated together with the wheel hub 17. The fastening bush 20 may be hollow and may have on the inner surface spaces arranged to receive wheel bearings 19 encircling part of the wheel support structure 13. To prevent dirt from entering the wheel bearings 19, the open end of the bush 20 may be sealed with a cover 22 with slightly protruding centre section. The wheel hub 17 may be supported with wheel bearings 19 to the wheel support structure 13, so that the vertical axle 10 supports the wheel support structure 13 and the wheel support structure 13 supports wheel hub 17 which supports the wheels 8a, 8b. The horizontal axle 11 is located inside the wheel support structure 13 and is supported by a gear wheel of the gear arrangement 14. The wheel support structure 13 may have a forged or a cast design. In the conventional RTG cranes, the wheel support structure may be rotatable. When the wheel support structure 13 is not rotating, as explained herein, it sees only pulsating stress instead of fully reversed stress when wheel support structure is a rotating shaft. Using forging or casting enables efficient use of material compared to solid round bars, and geometry can be optimized easily to minimize stress levels. Due to these reasons, fixed wheels support structure is superior to rotating shaft wheel support structure when it comes to load carrying capacity related to mass.

[0028] In addition to the gear arrangement 14, the wheel assembly 5 may further comprise a planetary gear stage 18 connected to a wheel hub 17. In the embodiment illustrated in Figure 2, the wheel hub 17 also provides housing for the planetary gear stage 18 between the horizontal axle 11 and the cover 22. The planetary gear stage 18 comprises a sun gear, three or more planet gears and a ring gear. The horizontal axle 11 rotates the sun gear while the planet gears are arranged around the sun gear. The planet gears may be rigidly fixed to the wheel support structure 13 so that they remain stationary and only rotate around their own axis. Due to this, the ring gear may be part of the wheel hub 17 and rotates the wheels 8a, 8b.

[0029] Figures 4-8 illustrate top views of the mutual positions of the pair of wheels on the wheel assemblies 5, wherein each crane has four wheel assemblies 5, one on each corner of the crane 1. Figure 4 illustrates the pair of wheels on the wheel assemblies 5 when the crane is steered to lateral direction. Figure 5 illustrates the pair of wheels on wheel assemblies 5 when the crane is steered to longitudinal direction. Figure 6 illustrates the pair of wheels on wheel assemblies 5 when the crane is steered in a circle. Figure 7 illustrates the pair of wheels on wheel assemblies 5 when the crane is steered in a slightly curved travelling motion. Figure 8 illustrates the pair of wheels on wheel assemblies 5 when the crane is steered to a curved right angle travelling motion.

[0030] Figure 4 illustrates a typical travelling direction in the port area. The crane 1 travels above the container stacks and moves the container to their assigned location. The lower beam 3 is arranged to connect the shorter distance between two wheel assemblies 5. As compared to the position of wheels in Figure 4, the pairs of wheels in Figure 5 have been turned 90 degrees, which allows the crane 1 to move longitudinally. This may be necessary when there are several rows of the container stacks, and the crane 1 is needed to move from one row to another.

[0031] Figure 6 illustrates steering in a circle, which is also possible by the invention. To enable steering in a circle, every outer wheel of the four wheel assemblies 5 must rotate faster than the inner wheels.

[0032] The present invention further enables slight turning or a complete 90 degrees turning. This is especially convenient for port areas with container stack layout which does not have a typical quadrangle area. For example, some the port area may be expanded due to increased shipping activity and the only way to expand is in diagonal direction. This causes challenges to conventional cranes which are not possible to steer in such a way because the conventional crane wheel assemblies are not designed to enable slight turning or 90 degrees turning while traveling. In the port, the efficiency can be improved by the following means: The existing port terminal area can be used more frequently filled with containers, because the turning radii of the travel path can be smaller. Efficiency will improve in terms of time, because turning can take place while driving, and the crane 1 does not have to be stopped while the wheels are turning. The wear of the wheels 8a, 8b will be much less thanks to the force couple that is effective in turning. As a result of this there is no need to change the wheels 8a, 8b as often, thus improving the utilization rate which is a significant advantage.

[0033] The wheel assembly 5 may further comprise a brake mechanism 25 whose task is to prevent pivoting of the vertical axle 10 in relation to the vertical tube 9. This is especially important in emergency stop situations. The brake mechanism 25 can be for example a brake disk or a twist locking element. The brake mechanism 25 may comprise an open gear 26. The open gear 26 may be connected to the slewing bearing 12 or other pivotable connection between the vertical tube 9 and the vertical axle 10.

[0034] The wheel assembly 5 may further comprise an encoder (not shown), which is arranged to monitor angular position. The brake mechanism 25 may be connected to the encoder, which monitors vertical twist angle. As the wheels 8a, 8b maintain the direction of wheel assembly 5, twist locking element can have significant clearance to its contact surfaces and engage contact only when needed. As there is clearance the force to disengage and engage the locking is almost zero, so smaller and simpler mechanism can be used.

[0035] The brake mechanism 25 may comprise a locking mechanism or a locking pin mechanism (not shown). As both wheels 8a, 8b can be driven independently, the locking pin mechanism does not have to resist the eccentric drive force anymore. If the vertical twist angle is monitored by the encoder, it might be possible that pre-coded software and machinery can keep the wheel assemblies 5 aligned to desired travelling direction. This means that in normal operation the locking pin mechanism is not needed at all anymore in the present invention. Due to these points, the first drive motor 16a and the second drive motor 16b can share a common locking mechanism connected by a cardan shaft, for example. As the locking mechanism only moves a freely rotating “latch” and the torque requirement is low, a standard GES3 + MT06 machinery might be sufficient for this application, which is extremely cost-effective solution compared to the conventional locking pin mechanism. As the locking and unlocking of all machineries can be done within a second, the locking can be released always when the crane 1 is in standstill. This means the operator does not need to wait for the actuation of locking mechanisms when the wheel assemblies 5 need to be twisted. As locking and unlocking can be done frequently, seizing of locking pin mechanism is no longer an issue.

[0036] Instead of linear motion, the locking mechanism would now have only rotating motion, which is much easier to keep in flawless operation wish for example sealed bearings with relubrication possibility. As the wheel assemblies 5 do not need the locking pin anymore during travelling motion, the machineries can face any angle during travelling. This has a massive effect on the agility of the RTG crane, as it can travel freely through any curve. The wheel assembly 5 of the present invention may contain only two wheels 8a, 8b instead of four wheels but can still carry the same load as the 16-wheel RTG crane.

[0037] Since the wheel assembly 5 of the present invention is much smaller and lighter than the conventional solution with four wheels in one wheel assembly which are driven by two bigger drive motors, it is easier to separate from the frame 2 in need of maintenance and move to / from the maintenance area.

[0038] An example of the suitable RTG crane size can have following parame- ters / features: lifting height about 12 metres, lifting span about 15 metres, weight about 75 tons, loading body about 15 tons, maximum nominal load about 45 tons, maximum driving speed 65 m / min with the load and 130 m / min without the load, drive motor MT13XM200G 40 kW ED-60% 500V, 100Hz, brake about lOONm on the motor shaft, and size of the tyre 10-25 (D1615 mm).

[0039] Some of the benefits of the present invention include increased load capacity, reduced noise emissions, simplified locking pin mechanism, eight wheel pairs replaced with four wheel pairs with simpler machinery, increased performance and quality of the crane due to better agility, more time-saving operations due to less delays, and longer service time thanks to lighter components.

[0040] Direction of the wheel pair can be changed in the stepless manner by rotating each wheel independently with different speed or torque until the desired direction is achieved. No separated turning machinery is needed.

[0041] Parallel wheels can be driven with different speeds which allows wheel pair to turn around king pin or slew bearing axles. When all tyres are independently controlled, RTG cranes can do turning manoeuvres also on curved tracks and container stacks. Same design allows also fast wheel pair turning to other gantry crane operation modes like cross travelling, carousel turning and parking mode.

[0042] This new solution will allow stepless turning of the RTG gantry crane wheels without any separate slewing or turning machinery. Turning of the wheel will be done using the gantry travelling machineries and speed difference of the two wheels in the wheel pair. Each wheel 8a, 8b may have its own drive motor 16a, 16b, which can be electric, so that each wheel 8a, 8b can be independently steered. Each drive motor 16a, 16b can be steered together so that the desired combined effect is obtained. Each drive motor 16a, 16b may have a frequency-controlled drive to have the control on the drive motors. Frequency controlled drives may operate independently on each drive motor 16a, 16b or have a combined control together to influence more than one drive motor 16a, 16b. Electric motors are preferrable AC motors. In a wheel block the drives may operate as a pair. With the combined effect, the crane’s 1 travel path can be curved as desired when driving forwards or backwards. In this way, the travelling motions and steering modes according to Figures 6-8 can be realized.

[0043] This will allow active steering while driving that RTG crane could operate on the curved track with or without load. The conventional RTG cranes do not allow stepless wheel turning. The curved track drive has done with speed difference between the crane ends in old design. With the standard RTG design we do not achieve small enough turning radius and operation with curved track is difficult. In the conventional solutions active steering is impossible with the wheel pair on the same shaft. This leads to the bigger wheel diameters and bigger wheel forces.

[0044] Reference numbers

[0045] 1 crane

[0046] 2 frame

[0047] 3 lower beam

[0048] 4 container

[0049] 5 wheel assembly

[0050] 6 diesel generator

[0051] 7 electric distribution unit

[0052] 8a first wheel

[0053] 8b second wheel

[0054] 9 vertical tube

[0055] 10 vertical axle

[0056] 10a upper flange

[0057] 10b lower flange

[0058] 11 horizontal axle

[0059] 12 slewing bearing

[0060] 13 wheel support structure

[0061] 13a upper edge

[0062] 13b lower edge

[0063] 14 gear arrangement

[0064] 15 fastener

[0065] 16a first drive motor

[0066] 16b second drive motor

[0067] 17 wheel hub

[0068] 18 planetary gear stage

[0069] 19 wheel bearing

[0070] 20 fastening bush

[0071] 21 fastening flange

[0072] 22 cover

[0073] 23 rim

[0074] 24 bolt brake mechanism open gear

Claims

Claims1. A wheel assembly for a gantry crane, comprising a vertical tube connectable to a frame of the gantry crane, a vertical axle pivotally connected to the vertical tube, two horizontal axles and each horizontal axle carrying a wheel, wherein each wheel is arranged to be independently driven by a drive motor connected to the corresponding wheel through a gear arrangement, and to form a force couple around the vertical axle.

2. The wheel assembly according to claim 1, wherein the first wheel is arranged to be driven by a torque of a first drive motor, and the second wheel is arranged to be driven by a torque of a second drive motor, wherein the first drive motor and the second drive motor have different torques.

3. The wheel assembly according to claim 1 or 2, wherein a torque of a first drive motor and a torque of a second drive motor have opposite rotational directions.

4. The wheel assembly according to claim 2 or 3, wherein the wheel assembly is arranged to be turned in a stepless manner by the difference of the torques of the first drive motor and the second drive motor.

5. The wheel assembly according to any one of claims 2-4, wherein the vertical axle is located between the first drive motor and the second drive motor so that the first drive motor and the second drive motor are parallel to each other, and preferably parallel to the horizontal axles.

6. The wheel assembly according any one of claims 1-5, wherein the gear arrangement comprises a fully helical gear reducer.

7. The wheel assembly according any one of claims 1-6, wherein the wheel assembly further comprises a planetary gear stage connected to a wheel hub.

8. The wheel assembly according to any one of claims 1-7, wherein the wheel assembly further comprises a wheel support structure, which is rigidly fastened to the vertical axle.

9. The wheel assembly according to claim 8, wherein the wheel hub is supported with wheel bearings to the wheel support structure.

10. The wheel assembly according any one of claims 1-9, wherein the wheel assembly further comprises a brake mechanism comprising an open gear.

11. The wheel assembly according to claim 10, wherein the open gear is connected to a slewing bearing.

12. The wheel assembly according to claim 10 or 11, wherein the brake mechanism is connected to an encoder, which monitors vertical twist angle.

13. The wheel assembly according to any one of claims 2-12, wherein the first drive motor and the second drive motor share a common locking mecha- nism connected by a cardan shaft.

14. The wheel assembly according to any one of claims 1-13, wherein the wheel assembly contains only two wheels.

15. A rubber tyred gantry crane, comprising a frame with two lower beams, a wheel assembly according to any one of claims 1-14 arranged at either end of each lower beam.

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