Variable compliance wheel

A system for adjusting the compliance of a wheel is provided. In one embodiment, wheel segments are adjusted, causing the stiffness of the wheel to change. Such adjustments can be made while the wheel is rotating, allowing the wheel compliance to be changed while a vehicle is in motion.

BACKGROUND OF THE INVENTION

The present invention generally relates to a wheel with variable compliance having many applications, including ground vehicle wheels, printing press rollers, material processing and handling equipment. More particularly, the present invention relates to a wheel that includes a rim having a center axis of rotation and a plurality of wheel segments engaged with the rim and connecting to a radial band appropriate for the intended usage of the wheel, where the rim and plurality of wheel segments are adapted to rotate about the center axis, and where the attachment points to the rim of the plurality of wheel segments can be moved in the direction of the axis of rotation. In the example of a ground vehicle application, the radial band includes tread elements to improve vehicle traction in wet or rough road surfaces or in complex terrain. For material handling applications, the radial band may have a smooth surface to apply even pressure to a printing medium, for example, or may contain striations or tread elements as required.

Various mechanisms currently exist for varying the ground contact pressure of a tire while a vehicle is being driven. This capability allows a vehicle to traverse soft soils by lowering the pressure within the tire, without compromising on-road performance. This is commonly achieved by varying the pressure within the carcass of a tire through the control of an air valve mounted on the wheel that can vent the tire's internal air to atmospheric pressure or to the pressure produced by an onboard air compressor plumbed through an airtight rotary seal. The commercial term for such a system is Central Tire Inflation System (CTIS). One such system is U.S. Pat. No. 5,553,647, “Central tire inflation system,” (Miroslav), the contents of which are hereby incorporated by reference, that describes a pressure air source, plumbing, valve, pressure sensor, and control system for varying the internal air pressure of a tire while driving. The shortcomings of this design are complexity, sensitivity to the elements, cost, and inability of the system to maintain adequate tire pressure when the tire is badly damaged.

Several patents have addressed this latter concern of pneumatic tire vulnerability with runflat inserts (U.S. Pat. No. 6,263,935, “Radial ply pneumatic runflat tire,” (Oare, et. al.)) or tires that do not rely on fluidic pressure for load carrying, a.k.a. non-pneumatic tires, (U.S. Pat. No. 6,431,235, “Non-pneumatic tire and rim combination,” (Steinke, et. al.)), the contents of both of these patents hereby incorporated by reference. The shortcomings of this system are weight and fixed tire stiffness.

The present invention describes a novel way of combining the benefits of variable tire stiffness with a damage tolerant tire design.

SUMMARY OF THE INVENTION

The present invention provides a variable stiffness wheel that can be used in a variety of applications, such as for support of ground vehicle traverse over a variety of terrain or for conveying materials (e.g., airport baggage handling). In one preferred embodiment, the variable stiffness wheel includes a plurality of wheel segments whose attachments to the center rotating rim (inner and outer) can be moved in the direction of the axis of rotation, thereby changing the tension of these elements, which is convenient, in one example, for tuning the ground contact pressure of the tire for the terrain being traversed. The inner attachment being accommodated via a sliding flange located towards the vehicle and the outer being accommodated via another sliding flange located away from the vehicle. Additionally, this method can be used to vary other wheel stiffness parameters such as vertical stiffness, lateral stiffness, torsional stiffness (about the axis of rotation or about an axis perpendicular to the axis of rotation) each of which can affect overall behavior of the system the wheel is used in (e.g., vehicle performance).

With the inner and outer wheel segment attachment points close together tensioning the spokes, the vertical stiffness of the wheel is increased. In the example of the vehicle wheel, this increased stiffness generally provides excellent on-road performance (cornering, steering feel, low rolling resistance, etc.) and increased payload carrying capacity and increased durability at high speeds.

With the inner and outer wheel segment attachment points spread apart from one another, the vertical stiffness of the wheel is reduced, enlarging the contact patch of the wheel with, for example, the ground, baggage, or other material. In the example of a printer, the stiffness of the print roller can be modulated to compensate for plate wear, extending the life of the plate and improving the throughput of the press. In the example of the vehicle wheel, the tire/terrain enveloping performance is improved, while the lower ground pressure gives the vehicle better off-road mobility on soft soils like mud, sand, and snow.

Continuing with the example of the vehicle, the inner and outer wheel segment attachment points spread far apart from one another which allows the vehicle to be lowered, thereby facilitating transportation in low clearance vehicles like aircraft. The lower ground pressure of this configuration is also beneficial to ramps and cargo floors that have strict limits on floor loading pressure due to floor structure limitations imposed by weight constraints, as is the case with many aircraft.

The inner and outer wheel segment attachment points can be varied from the maximum and minimum spacing while driving to suit the immediate needs of the vehicle.

Multiple inner and outer wheel segments can be stacked to produce a wheel with varying radial stiffness across the width of the wheel. This is beneficial for improving the lateral performance of the wheel by controlling the wheel's dynamic camber. In the example of wheels supporting a conveyer belt, this varying stiffness across the wheel width may help direct or steer baggage in a desired direction. In the example of a printer, the varying radial stiffness of a printer roller may direct paper in a desired direction or area, such as continuously adjusting the registration of multicolor press runs. This reduces the waste and rework associated with misregistered press output.

In the example of the vehicle, the dynamic camber can adjusted during cornering to improve maneuvering performance. This can also be beneficial for changing the heading of the vehicle while driving with little or no steering of the tire. By making the stiffness of the innermost pair of inner and outer wheel segments stiffer than the outermost pair, resulting forces at the wheel/road contact patch will serve to pull the vehicle in the direction of the outermost pair of wheel segments. Further, by reversing the relative stiffness between the two sections, the wheel can force the vehicle in the opposite direction. This has the potential of simplifying the steering system, reducing cost and weight, improving the durability of the suspension/steering system by eliminating vulnerable steering links, and reclaiming the swept volume lost to the tire as it steers for other vehicle components or cargo. Additionally, the radial wheel stiffness, when modulated at a high rate, can be used to counteract vehicle pitch and heave vibrations, augmenting or even replacing the vibration isolation functions of the vehicle's suspension system.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1A,1B,2, and3illustrate a first preferred embodiment of a variable stiffness wheel10. The variable stiffness wheel10includes a rim11, fixed flanges12band13band movable flanges12aand13a(also referred to as rings, plates and collars in this specification), and a plurality of wheel segments17,18(e.g., two oppositely angled spokes20) engaged with the flanges12a,12b,13a,13band an outer traction element16.

The rim11includes an inner flange (not shown) which locates an adaptor plate and thereby allows the wheel10to be mounted on a spindle (not shown) which allows the variable stiffness wheel to rotate about the center axis. Preferably the spindle and mounting mechanism is similar to wheel mounting mechanism of present vehicles (e.g., secured by lug nuts). While the variable stiffness wheel10, as well as other embodiments of the present invention, are described as being used on a vehicle, it should be understood that these embodiments can be used on almost any device that may utilize a wheel, such as to support a conveyer belt or as a roller for a printer.

As best seen inFIGS. 2 and 3, the wheel segments17,18are distributed evenly around the rim11. In the illustrated preferred embodiment, the wheel10includes about one hundred and twenty wheel segments17and18containing four different wheel segment planes (i.e., the planes formed by each spoke20of the segment17and18). It should be obvious to anyone skilled in the art that the variable stiffness wheel10may include fewer or more wheel segments17,18and fewer or more wheel segment planes.

The variable stiffness wheel10also includes sliding guides15engaged with the rim11and flanges12a,12b,13a,13b(the flanges12aand13adefining the movable wheel segments and the flanges12band13bdefining the nonmoving wheel segments) which affix the base of the plurality of wheel segments17,18(i.e., the base of the spokes20) to the rim11. Flanges13band12bare positively affixed to the wheel to restrict linear movement along the axis of rotation. Flanges12a,13aslide along the guides15and are loaded (i.e., their position is changed) with preload adjusters14that are in contact with the flanges12a,13aand the rim11. In this respect, as the preload adjusters14(which move via actuators, not shown in these Figures) pull on the flange13a, force is transferred through guides15to flange12a, causing both flanges12aand13ato move towards the preload adjuster14. Similarly, the preload adjusters14release their load, causing the flanges12aand13ato move away from the preload adjusters14.

In an alternate preferred embodiment, all rings may be fixed in place, may slide relative to each other or may include some combination thereof. For example, the inner flanges13aand12bmay be fixed in place while the outer flanges12aand13bmay slide relative to the rim11. Further, each of the wheel segments17,18can be configured to nest between adjacent wheel segments17,18or be stacked in line with each other.

FIG. 2illustrates a detail isometric view of the variable stiffness wheel10with the traction element16sectioned away to illustrate the rim11, sliding rings12a,12b,13a,13b, and the plurality of wheel segments17,18.FIGS. 2 and 3illustrate the variable stiffness wheel10in one particular preload position, where the spacing between the rings12a,12b,13a,13bis at a nominal position. Where the ring pairs (12a,12band13a,13b) are closest together, the radial preload on the wheel segments17,18will be at its greatest. This results in the highest radial stiffness of the wheel. Where the ring pairs (12a,12band13a,13b) are furthest apart, the radial preload on the wheel segments17,18will be at its lowest and the angle of the wheel segments17,18is at their greatest angle with respect to the vertical applied load. Conversely, the lowest preload and weakest wheel segment angle provides the lowest radial stiffness of the wheel.

In the present preferred embodiment, each wheel segment17,18includes two oppositely angled spokes20which connect to one of the flanges12a,12b,13a,13band to the traction element16. Preferably the spokes20are coupled to the flanges12a,12b,13a,13band to the traction element16with either adhesive or mechanical fasteners, or by overmolding traction element16onto spokes20. The spokes20can comprise a variety of rigid or semi rigid materials such as polymer or composite material.

The preload adjusters14preferably include an actuator (not shown in these Figures) which may be controlled by the vehicle or manually adjusted by a user at the wheel itself. In one example, the linear actuator may be a pneumatic actuator driven by a CTIS. In another example, the linear actuator may be an electrical actuator that receives power through a slip ring connection (e.g., similar to the slip ring connections used for communication and power in the turret of a tank) to a chassis electrical system. In yet another example, a linear actuator may be a screw positioned through the rim11and connected to the flanges12a,12b,13a,13b, thereby causing the flanges to move axially.

Preferably, the vehicle includes a control system (e.g., a microprocessor and control software) for monitoring vehicle characteristics such as speed, wheel slippage (e.g., loss of traction on an icy terrain), roughness of terrain, etc., and adjusts the wheel firmness according to preset firmness profiles during vehicle operation. Preferably, a slip ring connection, as known in the art, can be used for communicating or controlling the mechanisms of the wheel10. In a more specific example, as the vehicle monitors the increasing speed, the microprocessor executing the control software of the vehicle then increases the firmness of the wheel to provide more desired vehicle handling at the higher speed. In an even more specific example, the control software of the control system may include multiple speed ranges so that when the vehicle is traveling at a speed within a predetermined speed range (e.g., between 1 and 20 MPH) the control system sets a predetermined tire firmness.

The control system may also be used for steering the vehicle by only modifying the firmness of a portion of the wheel (e.g., changing the firmness of half of the wheel). Similarly, the control system can adjust a portion of each wheel's firmness to improve handling characteristics of the vehicle, such as handling when cornering.

In other alternate preferred embodiments, the preload adjusters14may be actuated through other linear or rotary electromechanical, fluidic, magnetic, or other mechanisms of exerting a force at the base of the movable rings13a,12a. In another alternate preferred embodiment, the wheel segments17,18may be directly actuated radially or semi-radially, similar to a camera shutter.

In another alternate preferred embodiment, each spoke20includes an inner lumen filled with pressurized media. The pressure of the media within the lumen is increased or decreased to respectively increase or decrease the stiffness of the spoke20, and therefore adjust the softness of the wheel10.

In another alternate preferred embodiment, each spoke may be composed of shape memory alloys to increase or decrease the firmness of the spoke20. For example, the shape memory alloy may include two predetermined shapes such as a straight and curved shape or two different radii of curve shapes. Applying power to the shape memory alloy distorts the spokes20between the two predetermined shapes or alternately to curves in between the two predetermined shapes. In this respect, the firmness of the wheel can be adjusted.

In another alternate preferred embodiment, artificial muscles or similar contracting materials (e.g., biomaterials) may be used as a linear actuator as part of the preload adjuster to move the flanges12a,12b,13a,13bbetween different positions.

Other mechanisms of adjusting preload tension/compression on the plurality of wheel segments may also include utilization of smart materials like artificial muscles biomaterials, or the replacement of wheel segments with linear or rotary actuators (e.g., as discussed in the preferred embodiment ofFIGS. 7A and 7B).

FIGS. 4,5A,5B, and6illustrate another preferred embodiment of the variable stiffness wheel110, comprising one or more toroid-shaped spoke rings114composed of a plurality of curved spokes124. One end of each spoke124of the spoke ring114is connected to a spoke collar116which slidably engages the wheel rim118. The other end of each spoke124is connected to the traction element112, preferably by adhesive, mechanical fasteners, or by overmolding (e.g., overmolding traction element112onto the spokes124).

As seen best inFIGS. 5A,5B and6, the wheel110includes spoke collars (similar to the flanges or rings described in previous embodiment of this specification) which slide in the direction of the axis of rotation of the rim118. As the spoke collars116slide, the end of the spokes124connected to the collar116also slides, thereby changing the curve of the spokes and modifying the firmness of the wheel110.

The wheel110is preferably mounted to a vehicle by a mechanism presently known in the art. For example, a wheel center120is affixed to a vehicle's wheel spindle (not shown), transmitting torque from the wheel spindle through wheel center120to the spoke collar116through the sliding guides122. Torque then is transmitted through the spoke ring114to traction element112which is in contact with the road surface, imparting braking and tractive forces to the vehicle. Wheel stiffness is increased by exerting a lateral force to the toroid-shaped spoke rings114in the direction of the axis of rotation of the wheel110, away from the plane of symmetry (shown inFIG. 4). Wheel stiffness is reduced by exerting a lateral force to spoke rings114towards the plane of symmetry.

FIG. 7AandFIG. 7Billustrate another preferred embodiment according to the present invention of a wheel for automatically increasing radial spoke stiffness according to increasing vehicle speed. Generally, this stiffness adjustment is achieved by harnessing the force of a mass210(or optionally a plurality of masses) which rotates with the wheel, thereby exerting force on the wheel as it rotates to change the configuration of the spokes.

At least one tension mass210is attached to outer spoke collar212by flexible cable214. The flexible cable214is routed over a reaction pulley216which is attached to wheel rim218. When the wheel rotates slowly (as seen inFIG. 7A), the force exerted on outer spoke collar212from the mass210is low, allowing outer spoke collar212(i.e., movable collar) to be pulled closer to inner spoke collar220(non movable collar) by the keeper spring226. This results in relatively low tension in each spoke ring222which maintains the wheel in a “soft” configuration with an enlarged ground contact patch size of traction element224. As the rotational speed of the wheel increases (as seen inFIG. 7B), the tension mass210exerts an increasingly larger force on flexible cable214, forcing the outer spoke collar212to move away from inner spoke collar220. The movement of outer spoke collar212increases the tension in each spoke ring222, increasing the wheel firmness and decreasing the ground contact patch size of traction element224.

FIG. 8AandFIG. 8Billustrate another preferred embodiment according to the present invention for pneumatically adjusting the stiffness of spokes320. An air spring310(and optionally a plurality of air springs) is affixed to wheel rim312and to the outer spoke collar314. All air springs310are in fluid communication with a central pressurized air source (not shown) via pneumatic tubing316. When air is supplied to pneumatic tubing316, the air springs310inflate and force the outer spoke collar314to move closer to the inner spoke collar318(i.e., moving from the position illustrated inFIG. 8Ato the position illustrated inFIG. 8B). As with previously described embodiments, this movement of the outer spoke collar314decreases the tension in spoke ring320and increases the ground contact patch size of traction element322(i.e., decreases firmness of the wheel).

When a pressure relief valve (not shown) is opened, air flows out of air springs310and into pneumatic tubing316and is exhausted to atmosphere through pressure relief valve (not shown). The deflated air springs310allow the outer spoke collar314to move away from inner spoke collar318(to the position seen inFIG. 8A), increasing the tension in spoke ring320and decreasing the ground contact patch size of traction element322. This relationship may appear counterintuitive when compared with a pneumatic time, however this preferred embodiment of the wheel remains stiff if left in its native shape and will become more compliant by pushing the spoke rings inward to decrease the spoke tension.

Preferably, the pressurized air for the air springs310is provided through a hollow, pressurized vehicle axle spindle which couples and thereby seals to the wheel similar to currently known central tire inflation systems. This sealed region of the wheel is in communication with pneumatic tubing316, allowing the vehicle (e.g., a computer and software within the vehicle) to pneumatically control the air springs310and thus the firmness of the wheel.

It should be understood that many of the elements described in the embodiments of this specification can be mixed or incorporated with other embodiments set forth in this specification without departing from the present invention.

Referring toFIG. 9, a conveyor device400consists of a plurality of rollers402with a variable lateral compliance capability, as described in various embodiments of the present specification. However, since the rollers402typically have a greater relative width compared with wheels, a plurality of spoke segments may be included along the length of rollers402. The rollers402may be configured to freely spin or may be motorized for propelling luggage404in the direction shown with the arrow.

When a sensor (not shown) detects a piece of luggage404which should be routed to the leftmost conveyor chute406, or alternately a user wishes to change the route of the luggage, the lateral compliance of rollers402is modulated. In this respect the course or direction of luggage404is changed. Similarly, the lateral compliance of rollers402may be modulated to direct luggage to the rightmost conveyor chute408.

FIGS. 10A,10B,10C,11,12A and12B illustrate another preferred embodiment according to the present invention for manually adjusting the stiffness of spokes510. Generally, a handle530rotates a central cable spool522which increases or decreases a cable tension on outboard inner spoke collar524and inboard inner spoke collar520, thereby adjusting the tension of the spokes510.

The inboard inner spoke collar520is connected to the cable spool522by a flexible cable512(or optionally a plurality of flexible cables). The flexible cable512is routed over reaction pulleys514between the wheel rim516and wheel center518. Similarly, the outboard inner spoke collar524is connected to cable spool522by a flexible cable512(or optionally a plurality of flexible cables). The flexible cable512is routed over additional reaction pulleys514between wheel rim516and wheel center518.

In this respect, as the spool522winds the cable512, the pulleys514support the increased cable tension that moves both inner spoke collars520and524toward the center of the wheel. Thus, the tension of the spokes510is modified, similar to the previously described embodiments of this specification.

Referring toFIGS. 11-12B, the cable spool522is attached to the wheel center518by fastener526and prevented from rotating with respect to wheel center518by engagement of a shear pin528(or optionally a plurality of shear pins) with wheel center518. The shear pin528is attached to handle530and is prevented from disengaging from wheel center518by helical spring532.

When the user wishes to increase spoke tension, the operator pulls the handle530laterally outward, disengaging the shear pin528from the wheel center518. After shear pin528is disengaged, the operator rotates the handle530, causing the cable spool522to rotate. When the cable spool522rotates, the flexible cable512is pulled onto the cable spool522, drawing the outboard inner spoke collar524and the inboard inner spoke collar520towards each other and increasing the tension in the spokes510. When a desired spoke tension is reached, the operator pushes the handle530laterally inwards, re-engaging shear pin528with the wheel center518.