Load wheel with heat dissipating hub

Abstract

A load wheel for a vehicle is provided having a cylindrical hub with an axis, a first sidewall, a second sidewall, an outer surface, a central core extending coaxially within the hub, and a plurality of passageways extending in an axial direction between the first and second sidewall. A solid, non-pneumatic tire is bonded to the outer surface of the hub, and a set of bearing is mounted in the central core of the hub. The hub is characterized by a heat factor equal to the (hub masshub specific heat)/surface area exposed. The heat factor for a hub comprising passageways is compared to the heat factor for a solid hub to derive a heat factor ratio, which is used to select the exposed surface area of the hub and maintain the operating temperature of the wheel below the failure temperature.

Claims

1. A load wheel for a material handling vehicle, comprising: (a) a cylindrical hub having an axis, a first sidewall, a second sidewall, an outer surface, an inner surface, a central core defining an opening within the hub extending coaxially with the hub axis from the first sidewall to the second sidewall, and a plurality of passageways open at either end for exposure to the environment positioned between the outer surface and the inner surface and extending in an axial direction between the first sidewall and the second sidewall, and wherein the hub has a heat factor ratio of 0.7 or less, wherein the cylindrical hub has a diameter from about 3 inches to 12 inches and a width from 1.5 inches to 10 inches, wherein the hub is constructed of a material selected from the group consisting of aluminum, aluminum alloys, magnesium and magnesium alloys; (b) a solid, non-pneumatic tire bonded to the outer surface of the hub, wherein the outer surface of the cylindrical hub is free from projections designed to mechanically engage the tire; and (c) a set of bearings press fit into bearing bores in the inner surface of the hub, wherein the bearings comprise a center opening for receiving an axle of a vehicle.

2. The load wheel of claim 1, wherein the hub has a heat factor ratio of 0.5 or less.

3. The load wheel of claim 1, wherein the hub is constructed from a material having a thermal conductivity of 50 BTU/(hr-ft- F.) or greater.

4. The load wheel of claim 1, wherein the hub is constructed from a material having a density of O.26 lbs/in.sup.3 or less.

5. The load wheel of claim 1, wherein the hub is characterized by an exposed surface area comprising the area of the first and second sidewalls and the internal area of the plurality of passageways, and the ratio of the exposed surface area to the area of the outer surface of the hub that is bonded to the tire is 1 or greater.

6. The load wheel of claim 1, wherein the tire is bonded to the outer surface of the hub with a chemical adhesive.

7. The load wheel of claim 1, wherein the tire is a polyurethane elastomer.

8. The load wheel of claim 7, wherein the polyurethane elastomer is a thermosetting material.

9. The load wheel of claim 8, wherein the polyurethane elastomer is selected from the group consisting of toluene diisocyanate, methylenediphenyl diisocyanate, naphthalene diisocyanate, and phenylene diisocyanate based polyurethanes.

10. The load wheel of claim 1, wherein the hub is manufactured by extrusion.

11. The load wheel of claim 10, wherein the hub is constructed of a material selected from the group consisting of aluminum and aluminum alloys.

12. A material handling vehicle comprising a load wheel for a material handling vehicle according to claim 1.

13. The load wheel of claim 1, wherein the bearings abut shoulders formed in the inner surface, wherein the shoulders maintain the position of the outer face of the bearings near the sidewall of the hub.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is side perspective view of the hub of the present invention.

(2) FIG. 2 is a side perspective view of the load wheel assembly.

(3) FIG. 3 is a side sectional view of the load wheel of FIG. 2.

(4) FIG. 4 is a graph of the temperature of the load wheel versus time of operation for a solid hub (comparative) and a hub of the present invention.

(5) FIG. 5A is a perspective view of a prior art load wheel, with no passageways through the hub.

(6) FIG. 5B is a perspective view of a load wheel of the present invention having four passageways through the hub.

(7) FIG. 5C is a perspective view of a load wheel of the present invention having six passageways through the hub.

(8) FIG. 5D is a perspective view of a load wheel of the present invention having eight passageways through the hub.

(9) FIG. 5E is a perspective view of a load wheel of the present invention having ten passageways through the hub.

(10) FIG. 5F is a perspective view of a load wheel of the present invention having twelve passageways through the hub.

(11) FIG. 5G is a perspective view of a load wheel of the present invention having fourteen passageways through the hub.

(12) FIG. 5H is a perspective view of a load wheel of the present invention having sixteen passageways through the hub.

(13) FIG. 6 is a graph of the temperature of the load wheel calculated at the bond line between the tire and outer surface of the hub versus time of operation.

(14) FIG. 7 is a graph of the operating temperature of the load wheel versus the Heat Factor Ratio of the wheel. The vertical Y axis shows the temperature after 2 hours (7,200 seconds) of operation.

DETAILED DESCRIPTION OF THE INVENTION

(15) Without intending to limit the scope of the invention, the preferred embodiments and features are hereinafter set forth. All of United States patents and published patent applications cited in the specification are incorporated herein by reference. The term polymer or polymeric as used in the present application denotes a material having a weight average molecular weight (M.sub.w) of at least 5,000. The term copolymer refers to a polymer derived from more than one species of monomer, and is intended to include, for example, terpolymers and quaterpolymers. Unless otherwise indicated, conditions are 25 C., I atmosphere of pressure, and 50% relative humidity. Unless otherwise indicated, average values are weight averages.

(16) Referring to FIG. 1-3, cylindrical hub 1 has a first sidewall 2 and a second sidewall 3, opposite the first sidewall. Hub 1 has an outer surface 4 and an inner surface 5 defining a central core within hub 1, which extends coaxially with axis 6. A plurality of passageways 7 extend axially between outer surface 4 and inner surface 5 of hub 1. Passageways 7 are open at either end, that is, at both sidewall 2 and sidewall 3. Together, the cumulative areas within each of passageways 7, as well as the area of sidewalls 2 and 3 (less openings for passageways 7) constitute the surface area of hub 1 exposed to the ambient air, during operation of the load wheel.

(17) Referring to FIGS. 2-3, load wheel 8 is made up of hub 1, bearings 9 and 10, which may be pressed into the central core of hub 1, defined by inner surface 5. Shoulders 11 and 12 are formed by recesses within the central core, and bearings 9 and 10, respectively, butt against the shoulders within inner surface 5 of hub 1. Tire 13 is bonded to outer surface 4 of hub 1 at interface 14 with a suitable adhesive, such as the Chemlok family of adhesives, or CONAP adhesives available from Elantas, or Cilbond adhesives available from H.B. Fuller Company. Tire 13 may be a thermosetting elastomer, such as a polyurethane elastomer, as is conventionally used in load wheels.

Example 1

(18) Sample 1A (Comparative). A prior art, standard 5 diameter by 3.875 wide polyurethane load wheel was produced using a conventional cast iron hub. The hub was machined from a grey iron casting using a CNC lathe. The hub was then prepped for adhesive using typical degreasing and blasting procedures to remove contaminants and apply a surface profile to improve elastomer adhesion. The hubs were then sprayed with adhesive and dried. After drying, the hubs were then pre-heated in an oven to activate the adhesive and placed into steel molds before being poured with a 2-part hot cast, MOCA-cured, TDI ether polyurethane that results in a 96 shore A hardness tire compound. After demolding, the parts were post-cured at temperature for 24 hrs.

(19) Sample 1B (Present Invention). A high-performance 5 diameter by 3.875 wide polyurethane load wheel was produced from extruded aluminum. An aluminum extrusion was designed with a web structure as shown and cut to width. The hub of the load wheel approximated the design shown in FIGS. 1-3. The bearing bores were then machined into the hub using a CNC lathe. The high performance hubs were then prepared and manufactured into load wheels following the same procedure as the comparative standard load wheels described in Sample 1A.

(20) Testing: Sample 1A and Sample 1B were both pressed with identical sets of 6305-2RS bearings and loaded onto a custom designed dynamometer test machine with a 36 rotating drum. The samples were placed into a pivoting fixture to allow even load distribution between the test samples as the samples are compressed against the drum to simulate loading and speeds that the tire and wheels would experience in field usage. Computer controlled hydraulics and drive motors were programmed to apply the following loading and speed program to the test wheels shown in Table 1, below.

(21) TABLE-US-00001 TABLE 1 Example 1, Load Program for Dynamometer Testing of Sample 1A and Sample 1B Load Wheels Total Load Load Per Test Applied Wheel Speed Duration 5000 lbs 2500 lbs 3 mph 2 hrs 5400 1bs 2700 lbs 3 mph 2 hrs

(22) During testing, thermal imaging of the side-by-side test samples was recorded using a FUR A325sc camera. Temperature versus time recordings were captured on the exterior surfaces of the bearings and polyurethane tire sidewalls from Sample 1A (Comparative) and Sample 1B (Present Invention). The results are presented graphically in FIG. 4.

(23) The side-by-side testing of Sample 1A, the standard offer load wheel currently used in the material handling industry, and Sample 1B, the inventive high performance load wheel, shows that the two wheels perform differently under the same operating conditions. Initially during start-up and low operating times, the high performance wheel Sample 1B increases in temperature more rapidly than the standard wheel Sample 1A. Surprisingly, Sample 1A quickly becomes higher temperature than Sample 1B as steady-state operation is achieved. At the higher loading state, Sample 1A continues to run hotter than Sample 1B. Sample 1B's low mass, high surface area, and good thermal conductivity allow heat to be quickly transferred from the bearings and the tire to the hub, where it can effectively dissipate to the environment. Sample 1A's relatively large mass, low surface area, and lower thermal conductivity traps heat inside of the bearings and the elastomer and causes them to operate at a higher temperature.

Example 2

(24) Several different hubs were modeled using CAD software and thermal simulation software was used to analyze the effects of hub mass, specific heat, surface area, work or power applied to the hub, and different convective coefficients. The hubs were modeled with an elastomer tire to match industry standard 5 diameter wheels with a width of 3.875 and an elastomer cross-section of approximately 0.5, such as described in Example 1, herein. The tire and wheel assemblies that were modeled are shown in Table 2, below, and in FIG. 5. Samples 2A-2H are shown in FIGS. 5A-5H, respectively.

(25) TABLE-US-00002 TABLE 2 Example 2 - tire and wheel assemblies 2A through 2H Specific Hub Exposed Tire Heat Dia- Hub Hub Bond Sample (BTW/ meter Width Area Area Hub Mass Material lb- F.) (in) (in) (in.sup.2) (in.sup.2) 2A 3.153 Aluminum 0.215 4 3.875 16.483 48.694 2B 2.856 Aluminum 0.215 4 3.875 39.2602 48.694 20 2.707 Aluminum 0.215 4 3.875 50.648 48.694 2D 2.559 Aluminum 0.215 4 3.875 62.036 48.694 2E 2.411 Aluminum 0.215 4 3.875 73.425 48.694 2F 2.262 Aluminum 0.215 4 3.875 84.8132 48.694 2G 2.114 Aluminum 0.215 4 3.875 96.201 48.694 2H 1.965 Aluminum 0.215 4 3.875 107.589 48.694

(26) The elastomer tire was modeled such that power could be applied in the thermal simulation from a center cross-section within the tire mass in order to simulate the internal heat build-up due to hysteresis during cyclic loading from tire operation. The cross section within the tire to which was applied power is approximately 3.0 by 0.13, centered within the tire elastomer in a ring shape.

(27) Samples 2A through 2H were then modeled using SolidWorks Simulation Professional using the thermal simulation tool. A power of 20 watts was applied to the central section of the tire elastomer as described. A convection of 10 Watts/m.sup.2 was applied to the exposed surfaces which include the tire tread surface and sidewalls and the exposed hub sidewalls. The bearing bores and internal surfaces between the bores were excluded from convection since these spaces would be occupied or concealed from air flow when fitted with bearings and a shaft during operation. The initial temperatures of the materials were set to 72 F. and the ambient air temperature was also set to 72 F. The simulation was run for 7200 seconds, recording data points every 60 seconds for a total of 120 data points. The temperature readings were probed from the simulation at the interface between the tire elastomer and the metal hub, which is the location of the thermally sensitive and application critical adhesion area between the tire and the hub.

(28) The temperature of the load wheel at the bond line between the tire and outer surface of the hub over time of operation, for each of the sample load wheels 2A-2H is shown in FIG. 6.

(29) The simulation results show that, initially, the heavier mass and lower surface area hubs produce a lower temperature experience by the bond between the tire and the hub. Surprisingly, however, at longer times which are more representative of continuous operation, the higher mass and lower surface area hubs operate at higher temperatures. The rate of initial temperature increase is related to the power (load and speed of the tire operation), the hub mass, and its specific heat based on its material of construction. The operating temperature, however, is related to its ability to remove excess thermal energy from the system and dissipate it to the environment. Because convective loss depends, in part, on the temperature differential between the object and the ambient air, a relationship between the hubs mass, specific heat, and exposed surface area can be used to define the desired performance range of a high performance hub. The Heat Factor is defined herein as the hubs mass multiplied by its specific heat, divided by the total exposed surface area of the tire and wheel system, exclusive of bearing bores and internal surfaces:
Heat Factor=(hub masshub specific heat)/surface area exposed

(30) For a given tire elastomer and hub material, a desired Heat Factor Ratio can be found between a high performance design and a standard solid design by taking the ratio of the Heat Factors of a given tire and wheel design versus a design using solid hub wheel of the same material. A design with a solid hub such as an industry standard load wheel would have a Heat Factor Ratio of 1 by definition. In order to operate in a region that provides high performance and extend the life of the bearings, a ratio less than 1 is desired and lower is better. Table 3, below contains the Heat Factor and the Heat Factor Ratio calculated for load wheel assemblies 2A-2H.

(31) TABLE-US-00003 TABLE 3 Specific Total Heat Wheel Heat Sample (BTW/ Surface Heat Factor Hub Mass Material lb- F.) Area (in.sup.2) Factor Ratio 2A 3.153 Aluminum 0.215 86.443 0.007842 1 2B 2.856 Aluminum 0.215 109.2202 0.005622 0.716904 2C 2.707 Aluminum 0.215 120.608 0.004826 0.615344 2D 2.559 Aluminum 0.215 131.996 0.004168 0.531515 2E 2.411 Aluminum 0.215 143.385 0.003615 0.460998 2F 2.262 Aluminum 0.215 154.7732 0.003142 0.400685 2G 2.114 Aluminum 0.215 166.161 0.002735 0.348804 2H 1.965 Aluminum 0.215 177.549 0.003927 0.303424

(32) Based on the simulation data, the temperature after 2 hours of operation can be plotted as a function of the Heat Factor Ratio, and is shown in FIG. 7.

Example 3

(33) To illustrate the effectiveness of the Heat Factor Ratio in determining a high performance hub design, simulations were run in the same manner as Example 2, but switching the hub designs out to a low Heat Factor Ratio design in 3 different materials. The hub has a diameter of 4 and a width of 3.875. Bearing bores are designed for 6305 sized bearings (62 mm OD). The hub design is illustrated FIGS. 1-3.

(34) Samples 3A, 3B, and 3B were modeled in CAD and put through the same simulation parameters used in Example 2. The hub materials were aluminum for 3A, mild steel for 3B, and copper for 3C. Their properties were calculated as shown in Table 4, below.

(35) TABLE-US-00004 TABLE 4 Exposed Total Hub Wheel Bonded Specific Heat Temp Surface Surface Surface Heat Factor at Mass Area Area Area (BTU/ Heat Ratio To 7200 Sample Material (lbs) (in.sup.2) (in.sup.2) (in.sup.2) lb- F.) Factor Solid sec 3A Aluminum 1.555 132.342 202.302 48.694 0.215 0.001653 0.210735 127.74 3B Mild Steel 4.493 132.342 202.302 48.694 0.122 0.00271 0.345512 129.23 3C Copper 5.127 132.342 202.302 48.694 0.0923 0.002339 0.298286 128.27

(36) As shown in Table 4, the Heat Factor Ratio of samples 3A-3C predicts the lower operating temperatures of the bond surface, even though the hubs have identical design dimensions and differ only in material of construction.

Example 4

(37) The most common failures for small diameter tires are often bond failures, due to thermal degradation of the bond between the tire and the hub. This is caused by bearing heat generation and dynamic heating from elastomer hysteresis under cycling loading during high duty cycle operation. To test the ultimate performance of the high performance load wheel design, a test to failure was performed. 5 OD by 3.875 width load wheels with either an industry standard solid cast iron hub or a high performance, low Heat Factor Ratio hub of extruded aluminum (both as produced in example 1) were individually tested on a dynamometer using the following test conditions outlined in Tables 5 and 6, below.

(38) TABLE-US-00005 TABLE 5 Load Load Initial Increase Time Test Loading Amount Intervals Speed (lbs) (lbs) (hrs) (3 mph) 2500 200 2 3

(39) TABLE-US-00006 TABLE 6 Heat Factor Sample Description Ratio 4A Solid Cast Iron Hub 1 4B Aluminum Extruded 0.211 Hub

(40) The samples, 4A (standard wheel, comparative) and 4B (inventive), were each loaded onto the test dynamometer for their respective runs after being fitted with identical 6305-2RS bearings. The wheels were tested at 2500 lbs. loading at 3 mph, with the loading increased every two hours by 200 lbs. The test was run until failure. Temperature was recorded using an infrared temperature probe positioned to record temperatures at the external bond/hub interface line where the tire sidewall meets the hub. After the test the wheels were examined to determine the type of failure (bond, material, bearing, etc.).

(41) TABLE-US-00007 TABLE 7 4A Running External Time Load Temp. (hrs) (lbs) F. 2 2500 134 2 2700 140 2 2900 145 2 3100 149 2 3300 154 2 3500 159 2 3700 164 2 3900 173 0.8 4100 198

(42) TABLE-US-00008 TABLE 8 4B Running External Time Load Temp. (hrs) (lbs) F. 2 2500 131 2 2700 136 2 2900 141 2 3100 147 2 3300 151 2 3500 155 2 3700 161 2 3900 166 2 4100 172 2 4300 182 2 4500 190 2 4700 198 2 4900 203 2 5100 205 0.5 5300 206

(43) The failure of 4A was categorized as bond failure, which is when the tire material remains essentially intact but separates from the hub during operation. Although the failure load for this size standard wheel is excellent for industry standards, bond failure is considered an early failure in that the elastomer material still had remaining dynamic load carrying capacity at failure and could not be tested until material degradation.

(44) The failure mode of sample 4B was found to be material failure, which is defined as material degradation with the adhesive bond layer still intact between the hub and the tire elastomer. This is observed in this case as a bubble where material degraded and became molten, forming a bulge in the tire that tripped the failure switch of the test. This is considered a full life test in that the material was run until its load carrying capacity is reached. While well above design limits for field use and no material failure would be expected in the field, the high performance hub design allowed the bond and the material to function together to achieve significantly higher performance than the standard wheel in 4A. This could allow industrial equipment to operate at higher loads and/or speeds while maintaining adequate safety factors for the tire and wheel performance.

(45) The load wheels of the present invention may be provided for use in the following applications.

(46) Material handling vehicles including fork trucks, pallet trucks, reach trucks, order picker trucks, and automated material handling equipment (automated or autonomous guided vehicles or AGV's) used in warehousing, food distribution, food processing, e-commerce, and industrial facilities. The load wheels of the present invention are particularly useful for electric fork trucks and pallet trucks including class I electric motor rider trucks, class II electric motor narrow aisle trucks, and class III electric motor hand or hand/rider trucks. The load wheels of the present invention for these applications generally range in diameter from about 2 to about 10 and generally have widths from about 1.5 to 8.

(47) The load wheels of the present invention may also be useful in floor/pavement maintenance applications such as floor cleaning equipment and industrial sweepers, scrubbers, burnishers, polishers, etc. as drive and idler wheels. These units may be walk behind or especially ride-on units which carry heavier loads at higher speeds to cover large facilities such as factories, warehouses, parking garages, campuses, etc. The load wheels of the present invention for these applications generally range in diameter from about 3 to about 12 and generally have widths from about 1.5 to 10.

(48) The load wheels of the present invention may also be useful for load wheels used in high speed dynamic applications such as amusement rides including roller coasters, monorails, trams, cable cars, etc. due to the very high speeds, intense dynamic loadings, and repetitive motions required, which would benefit from the higher performance of these inventive load wheels. The load wheels of the present invention for these applications generally range in diameter from about 1 to about 12 and generally have widths from about 1.5 to 6.

(49) The inventive load wheels may also be useful in autonomous vehicle or robotic vehicles (AGV's) as the lower temperatures and higher performance afforded by the inventive wheels will reduce failures and maintenance issues that could cause machine operation interruption in the absence of a human operator and could enable the vehicles to operate at higher speeds and loads than otherwise would be safe as compared to operations with human operators/passengers. The load wheels of the present invention for these applications generally range in diameter from about 3 to about 12 and generally have widths from about 1.5 to 10.

(50) The inventive wheels may also be useful in heavy duty continuously loaded operations requiring roller type wheel motion within such equipment as conveyors and trommels, as the rollers to support the loads and drive the belts or support and/or drive the trommel drums and components. These applications require extended continuous use and heavy loads in harsh environments and higher performance load wheels which run cooler will provide improved performance of the equipment and efficiency of the operations as compared to standard wheels. The load wheels of the present invention for these applications generally range in diameter from about 2 to about 18 and generally have widths from about 2 to 48.

(51) There are, of course, many alternative embodiments and modifications, which are intended to be included in the following claims.