Abstract:
A wheeled transport device, such as luggage, a trash can, a garden cart or other hand cart configured to be manually wheeled in an inclined position by a pedestrian user, includes a collapsible handle at one end and wheels at the other end. The wheels are independently connected to the device by respective suspensions that exhibit a compliance, in response to forces applied to their respective wheels by the surface in a direction opposing wheel motion, selected to sufficiently alter suspension geometry to temporarily change an attitude, such as toe, camber or caster, of their respective wheels to counter a tendency of the device to overturn in response to the applied forces.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of U.S. Provisional Application No. 60/599,510, filed Aug. 6, 2004 and entitled “Suspensions for Wheeled Transport Devices,” which is incorporated by reference herein. 

   TECHNICAL FIELD 
   This invention relates to suspensions for wheeled transport devices such as luggage, carts or containers, configured to be manually pulled in an inclined position behind a pedestrian user. 
   BACKGROUND 
   Wheeled travel luggage and other hand pulled carts such as wheeled garbage cans and garden carts can create discomfort or injury to the user&#39;s hand or arm when the wheels inadvertently strike objects in their path or encounter uneven surfaces or sudden changes in elevation that send shock loads to the handle and into the arm, or in some cases flip over causing a twisting of the hand and arm. 
   Improvements to such hand-pulled, wheeled devices are desired. 
   SUMMARY 
   According to one aspect of the invention, a wheeled transport device, such as a piece of personal luggage configured to be manually wheeled in an inclined position by a pedestrian user, includes a main body defining a compartment for containing goods to be transported, a handle disposed at an upper end of the body when the transport device is in an operative, inclined position, the handle manually graspable by the pedestrian user while walking, and at least two wheels disposed at a lower end of the body when the transport device is in an operative, inclined position. Each of the two wheels is secured to the body by respective suspensions for independent rotation along a surface upon which the user is walking, and each suspension exhibits a compliance, in response to forces applied to its respective wheel by the surface in a direction opposing wheel motion, selected to sufficiently alter a geometry of the suspension to temporarily change an attitude of its respective wheel with respect to the main body to counter a tendency of the wheeled transport device to rotate about its axis of inclination in response to the applied forces. 
   Preferably, the suspension compliance is sufficient to maintain a center of gravity of the wheeled transport device disposed between contact areas between the wheels and the surface, as the suspension deflects and resumes an equilibrium state in response to an impact force imparted to its respective wheel by traversing a sharp step of 5.0 centimeters in height, at a walking speed of about 4.8 kilometers per hour. 
   In many cases, the temporarily changed attitude of the respective wheel is its rolling direction. For example, in some cases the suspension is geometrically configured to toe the respective wheel outward in response to the applied forces. 
   In some other cases, the temporarily changed attitude of the respective wheel is its camber or its caster. 
   In some configurations, each suspension and its respective wheel is detachable as a unit from the main body. 
   In some embodiments, each suspension includes a spring to store energy imparted by the applied forces, and a damper to dissipate energy imparted by the applied forces. The damper has an adjustable resistance to suspension deflection in some example, and in some cases the spring is adjustable. In some versions the spring is a leaf spring. 
   In some cases, the device is advantageously provided with multiple, interchangeable suspensions of differing properties. 
   In some embodiments, the suspension includes an elastomeric travel stop positioned to limit suspension deflection. 
   Some examples also include a wheel-driven electric generator that generates electrical power while the device is wheeled along the surface. 
   In some cases, the wheels themselves provide the suspension resilience, and the device may be provided with multiple, interchangeable wheels of differing properties. 
   In many versions, the handle is collapsible for storage, such as by telescoping motion. In some particularly advantageous embodiments, the wheels are interconnected to the collapsible handle, such that the wheels are automatically retracted when the handle is collapsed. 
   Various aspects of the invention feature a hand-pulled/pushed transport device, such as a suitcase, trash can, garden cart, hand cart or any other device, that is supported by at least two wheels connected to the transport device by a linkage system that allows wheel movement in response to impact loads to the wheels. The linkage system preferably has a pivoting attachment to the body of the transport device and the loads imparted to the wheel and linkage are transmitted to the body of the transport device by a spring and damper combination that dissipates at least some of the imparted energy. When a wheel of the transport device encounters an obstacle, the force of the impact is preferably absorbed and dissipated by a spring/damper system, such that less kinetic energy is transferred to the main body of the transport device, reducing the tendency to deviate from the travel path or turn about the long (i.e., inclined) axis of the device. To the extent that the energy of impact causes compression of the spring, the linkage preferably controls wheel movement in a deliberate way so that the wheel moves along a path that increases negative camber and increases toe-out which action causes the wheel to move the transport device in the direction that encourages the center of gravity of the device to stay within the wheelbase of the device, thus reducing the tendency toward overturning. 
   The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 

   
     DESCRIPTION OF DRAWINGS 
       FIG. 1A  is a side views of a wheeled transport device as pulled by a person. 
       FIGS. 1B and 1C  are top and rear views, respectively, showing movement of the near wheel of  FIG. 1A  in response to hitting a bump. 
       FIG. 1D  illustrates retracting luggage wheels by collapsing an extendable luggage handle. 
       FIG. 2  is an exploded view of a first wheel suspension configuration. 
       FIG. 3  is a perspective view of a second wheel suspension configuration. 
       FIG. 4  is an exploded view of a third wheel suspension configuration, with means for retracting the wheel. 
       FIG. 4A  illustrates a wheel-driven generator. 
       FIG. 5  is an exploded view of a fourth wheel suspension configuration, with means for retracting the wheel. 
       FIG. 6  is an exploded view of a fifth wheel suspension configuration, with means for retracting the wheel. 
   

   Like reference symbols in the various drawings indicate like elements. 
   DETAILED DESCRIPTION 
   Referring to  FIG. 1A , many two-wheeled, human-powered, pull/push carts, luggage or the like can be rendered unsteady, uncomfortable or overturned by impacts to the wheels caused by rough surfaces, obstructions and/or sudden changes in elevation, such as stairs and curbs, particularly when the impact is to one wheel only, causing an upward motion on that corner and a torque around the pulling axis of the device, which can cause overturning. In the two-wheeled luggage  8  shown, as one wheel  10  hits a bump, the spring and damper  12  of the suspension connecting that wheel to the main luggage body  9  absorb some of the impact load imparted to the device by the bump. Furthermore, referring also to  FIG. 1B , when the spring  12  is compressed and the single-pivot axle moves rearward, rotating about axle pivot  11  along the plane of inclination, perpendicular to line  14 , the suspension is configured to move the wheel to toe the wheel outward, increasing the wheel&#39;s toe-out angle  18 . The plane of inclination is defined as the plane passing through the wheel/ground contact patch and the handle, in side view, forming an inclination angle  16  with respect to the ground plane of about 45 degrees plus or minus 15 degrees, depending upon luggage dimensions and handle height during rolling. As depicted in  FIG. 1C , the wheel is controlled to provide negative camber angle  20  as viewed from the rear. This change in wheel attitude helps to prevent overturning of the device by redirecting the wheels under the center of gravity. The change of wheel attitude occurs on both sides of the device, as the uplift created by the force of the bump on one wheel transfers weight to the opposite wheel, compressing that spring as well. As the device rolls about the longitudinal pulling axis, the negative camber of the wheel that remains in contact with the ground has the positive effect of keeping the wheel more perpendicular to the ground surface  22 , while the toe-out moves the whole device away from the point of upward deflection and in the surface direction corresponding to the angular direction of the torque couple, thereby keeping the center of gravity between the wheels, whereas if it moves outside either wheel the device will overturn. The illustrated embodiment depicts the plane of the axle movement as parallel to the bottom side of the luggage, which makes for an advantageously compact configuration, helping to minimize reductions in cargo space to accommodate suspension components and movement. 
     FIG. 1D  shows the preparation of a piece of luggage for storage, where collapsing the handle  21  of the luggage retracts the wheels  10  inside the outer faces of the luggage, making for a more compact storage configuration that permits more space internal to the luggage. 
     FIG. 2  shows one of many possible solutions to supporting a range of loads imposed on the luggage or other transport device, by interchangeable spring/damper units. The axle  24  that carries the wheel is mounted on the luggage body to pivot about a pivot axis  26 . Axle  24  has mounting bosses  28  to which one of multiple interchangeable spring/damper units, including a light spring/damper  32  and a heavy spring/damper  34 , can be selectively mounted for rotation about an axis perpendicular to axis  26 , but that also allow for some movement about other axes so as to allow the misalignment caused by motion through an arc as dictated by the overall geometry. The body of the luggage or other transport device provides a similarly misalignment-tolerant pivot  30  at which an opposite end of the spring/damper is mounted. Thus, springs/damper units may be originally selected, replaced or interchanged to configure the luggage for a particular loading and/or intended use. 
     FIG. 3  shows another of many possible solutions to supporting a range of loads imposed on the luggage or other transport device, by interchangeable spring/damper units. In this case, the axle  36  that carries the wheel  10  pivots on a sub-frame  44  secured to the luggage body  9 . Sub-frame  44  is modular and may be fitted to numerous variations of transport devices. The spring/damper  38  includes a bump stop device  40  that provides a resilient overload stop, and is mounted to a carrier  42  that can be selectively positioned in any of several spaced-apart positions along the axle, so as to provide greater or lesser mechanical advantage to the spring of the spring/damper assembly, thus providing tuneability of the system to accommodate a large range of loads. 
     FIG. 4  shows a suspension system configured to provide a spring damper system for a piece of luggage as previously described, but that also retracts the entire wheel system when the handle of the luggage is collapsed to the stored position as shown in  FIG. 1D . As in the above embodiments, the luggage or other transport device with a collapsing handle is supported by two wheels  10  rotating on an axle  46  and has the wheels connected to the main body of the luggage by a pivoting knuckle  48  that allows wheel axle pivoting about a linear pivot axis  50  in response to impact loads to the wheels. Loads imparted to the wheel and knuckle are transmitted to the body of the transport device by a spring  60  and damper  62  combination that dissipates at least some of the imparted energy. When wheel  10  encounters an obstacle, force of the impact is absorbed and dissipated by the spring/damper system and less energy is imparted to the main body of the transport device, reducing the tendency to deviate from the travel path or turn on the long axis of the device. To the extent that the energy of impact causes compression of the spring, the linkage controls wheel movement in a way predetermined to cause the wheel to move along a path that increases negative camber and increases toe-out, causing the wheel to move the transport device in the direction that encourages the center of gravity of the device to stay within the wheelbase of the device. The spring/damper combination is contained by a seat  56  and a spindle  58  that pivots on the knuckle, extends through holes  62  defined in mounting block  68 , and is threaded into an adjusting wheel, allowing for adjustment of spring assembly preload. Mounting block  68  travels is free to travel along a track  72  defined in the main luggage body, and is pinned to locating arm  66  at hole  70 . Arm  66  is attached to an extendable telescoping arm  84  of the pulling handle assembly of the transport device. When this arm  84  is pushed inward to its storage position, the bottom of the arm pushes down on the platform end  80  of the locating arm, disengaging the detent pin  76  from its locked position  74  along pin track  75  and enabling the locating arm to slide rearward, permitting the carriage  68  to also move rearward, followed by the entire spring/damper assembly and axle  46 , such that the wheel  10  is retracted into a cavity of the transport device body. 
   Referring to  FIG. 4A , electrical generator  86  is mounted in the body of the pivoting knuckle  88  and is driven by a spur gear  89  that engages gear teeth  90  internal to road wheel  10   a . It is also possible to mount the generator within the body of the luggage or transport device and drive it by a rotating axle internal to the linkage. 
     FIG. 5  shows an alternative suspension system for a piece of wheeled luggage employing a leaf spring rather than a coil spring and providing the ability to tune the system for varying loads, as well as providing retraction of the entire wheel system when the handle of a piece of luggage is collapsed to the stored position. The luggage is supported by two wheels  10  rotating on respective axles  94  connecting the wheels to the transport device by leaf springs  96  that constrain wheel movement along a linear pivot axis by trapping the spring in carrier hub  98 . The leaf spring is located by a detent pin  102  that the user can engage in various holes in the spring to adjust the spring rate. The detent pin is held in engagement by a second leaf spring  100  or other similar mechanism. The entire wheel/hub assembly is positioned by a rigid rod  104  that has a pivoting attachment to the body of the transport device. The location of the wheel inboard or outboard of the body of the luggage is dependent on the angular position of the rigid rod linkage. With rod  104  releas ably engaged in a recess  105  in spring clip  106 , the wheel is outboard in the transit position. When the extendable telescoping arm  114  of the pulling handle assembly is pushed down, a cam block  112  disengages spring  106  and pushes the rigid rod  104  through an arc, retracting the wheel assembly. When the extendable telescoping arm is pulled out, a flexible cord  110  pulls up on the crank portion  108  of rod  104 , returning the rod into releasably engagement within recess  105  of spring  106  and pivoting the unloaded wheel assembly again into the outboard transit mode. 
     FIG. 6  shows an alternative suspension system for a piece of wheeled luggage, employing an elastomeric wheel  10   b  with molded internal ribs that resiliently deform when loaded, both providing effective springing of the load and providing damping of the system. These wheels are preferably interchangeable and each designed to accommodate a different load range. The luggage is supported by two such wheels, each rotating on an axle  118  connected to the transport device by a rigid rod linkage  124  that has a pivoting attachment to the body of the transport device. As with the embodiment of  FIG. 5 , the location of the wheel inboard or outboard of the body of the luggage is dependent on the angular position of the rigid rod linkage, and similar means are provided for extending and retracting the wheels. Electrical generator  120  is mounted on a square portion  122  of rigid rod linkage  124  and is driven by a spur gear  125  that engages a rigid gear (not shown) internal to the elastomeric wheel  116 . It is also possible to mount the generator within the body of the luggage or transport device and drive it by a rotating axle internal to the linkage. Further details of wheel-driven generators can be found in U.S. patent application Ser. No. 60/599,360, filed on Aug. 6, 2004 and entitled “ELECTRICAL POWER GENERATION,” the entire contents of which are incorporated herein by reference. 
   A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.