Lean-to-steer mechanisms with linear or non-linear steering responses

The present steerable wheel assembly incorporates a lean-to-steer mechanism into an inner race of a roller bearing, while a wheel is mounted to an outer race of the roller bearing. A shaft extending from the mechanism is attached to a body, and the mechanism acts to steer the outer race and the wheel about a vertical steering axis when the shaft is tilted about a horizontal axis. The mechanism can be a pivot joint, providing a linear steering response, or can be a lean-to-steer mechanism that provides a non-linear response where the steering action is not consistently responsive to tilting over the expected range of tilting. The present non-linear lean-to-steer mechanisms can also be incorporated into alternative lean-to-steer devices, and alternative mechanisms can employ tracking structures to coordinate tilting motion of a first moving element with steering motion of a second moving element to provide a non-linear lean-to-steer response.

FIELD OF THE INVENTION

The present system provides a lean-to-steer wheel assembly and a lean-to-steer mechanism which can be employed in the wheel assembly to provide a desired steering response.

BACKGROUND

Lean-to-steer devices allow an operator to steer a rolling device by shifting their weight from side to side. As the operator stands on a body of the device and shifts their weight, the body leans and a lean-to-steer mechanism pivots one or more wheels of the device to direct it along a curved path. U.S. Pat. No. 5,372,383 teaches various embodiments of a steerable wheel, one of which (FIGS. 15 and 16) employs an inner bearing race mounted on one link member and pivotably connected to a second link member at a central location within the wheel to steer the wheel in response to leaning. U.S. Pat. Nos. 4,138,127 and 7,073,799 teach roller skates having a pair of wheels that pivot on an axis slightly inclined away from horizontal; a similar steering scheme is frequently employed in skateboards. U.S. Pat. Nos. 5,169,166; 5,232,235; 5,330,214; 5,513,865; 6,755425; and 6,938,907 teach devices having a wheel assembly where the bearings of paired wheels tilt relative to horizontal, coordinated by a pair of parallel link members. U.S. Pat. No. 7,243,925 teaches a skateboard truck incorporating a pivot joint where the inclination of the pivot axis can be adjusted to alter the steering response of the skateboard.

SUMMARY OF THE INVENTION

The present invention provides a steerable wheel assembly that steers a wheel in response to tilting of a body supported by the wheel, as well as a lean-to-steer mechanism that can be employed in the steerable wheel assembly to provide a non-linear steering response. The invention has particular utility for “lean-to-steer” devices that steer in response to leaning motions by the operator, such as training skis employed to traverse a ground surface using a skiing motion, roller skates, skateboards, and similar devices. The device is typically equipped with at least two wheel assemblies attached to a body, and leaning the body to one side causes the wheels to steer into a turn in the direction in which the user is leaning. The front wheel assembly steers to turn so as to roll in the desired direction, while the rear wheel assembly steers the opposite direction to facilitate rolling in a tight turn radius. Alternatively, the device may be equipped only with a steerable wheel assembly in the front, and employ a conventional rear wheel assembly. For devices having more than two wheel assemblies, such as in-line roller skates, a series of steerable wheel assemblies can be employed, each adjusted to provide a steering response appropriate to its relative position in the series.

In the wheel assembly of the present invention, the steering action is provided by mounting the wheel to a shaft via a roller bearing, in combination with a motion-limiting mechanism that limits the range of motion between the shaft and an inner race of the roller bearing. The shaft is affixed with respect to the body of the ski or other device, such that leaning of the body causes the shaft to tilt (roll) about a longitudinal axis. Rotation of the wheel relative to the shaft is provided by the roller bearing. The roller bearing also has an outer race, to which the wheel is mounted; the races rotate freely with respect to each other about a roller bearing axis. The wheel has a rim with a substantially flat profile such that, when the assembly traverses a horizontal surface, the flat profile of the wheel rim maintains the roller bearing axis horizontal, parallel to and spaced apart from the surface being traversed. This profile prevents the wheel from leaning in response to leaning of the body, as might occur if a rounded rim were employed. In some cases, the wheel rim may have a slightly curved profile with a shoulder, so as to allow free leaning within a small angle. It may be possible to employ a more rounded rim profile in high-speed applications if the weight distribution of the wheel and speed of rotation allow gyroscopic stabilization to provide sufficient resistance to leaning of the wheel.

The motion-limiting structure, in combination with the effect of the wheel rim in limiting tilting of the roller bearing so as to maintain the roller bearing axis horizontal, controls the range of motion available to the inner race relative to the shaft in response to tilting of the shaft. This range of motion is restricted to generate the desired steering response of the inner bearing to tilting of the shaft, and thus the steering response of the wheel that results from leaning of the body to which the shaft is affixed. The ratio of the steering response to leaning can be either linear or non-linear in character. This approach, where limiting the motion between two elements constrains the available movement so as to require a steering action in order to accommodate tilting of one element relative to the other, can be employed to provide a non-linear steering response to various lean-to-steer devices. The operation of such limited motion in providing a steering response can be most readily understood in the simplest form, where a linear response is provided. This linear response is similar to that provided by prior art lean-to-steer mechanisms that employ pivot joints to control the steering response.

When a pivot joint is employed as the motion-limiting structure, it provides the steerable wheel assembly with a linear response of steering action when the shaft is tilted, where increased tilting of the shaft results in increased steering action of the wheel throughout the anticipated range of tilting during use. In the steerable wheel assembly, the pivot joint connects the shaft to the inner race of the roller bearing, and limits motion therebetween to pivotal motion about a pivot axis, which is inclined with respect to the horizontal plane and is normal to the roller bearing axis. Such a pivot joint can be provided by a spherical plain bearing with a pin inserted therethrough to limit relative motion of the bearing components to motion about the pivot axis. Alternatively, the same motion can be provided by a spherical bearing that is engaged by two pins extending from the inner race, one engaging a socket to define a pivot axis and the other slidably engaging a circumferential groove residing in a plane perpendicular to the pivot axis, or by mounting the shaft to a cross-bar that engages cylindrical recesses in the inner race via cross-bar bearings that serve to reduce friction in the pivotal motion under loads.

Because the pivot axis is inclined, the shaft cannot directly pivot about the longitudinal axis with respect to the roller bearing and the wheel when the user leans the body; instead, pivoting is limited to motion about the pivot axis. Thus, when a torque is applied by the user leaning the body, this torque forces the shaft (which is affixed relative to the body) to pivot with respect to the roller bearing and the wheel about the pivot axis, resulting in two components of rotational motion. One component allows the shaft to tilt away from a horizontal orientation to accommodate the leaning of the body (while the wheel rim remains engaged with the underlying surface, which in turn maintains the roller bearing axis horizontal), while the other component forces the roller bearing and the wheel to pivot about a vertical steering axis so as to cause the wheel to turn in the direction of the lean.

When a ski trainer or similar device is employed having a pair of steerable wheel assemblies, the assemblies are typically mounted such that their pivot axes intersect below the body when the shafts are horizontal. The result of this configuration is that, when the body is leaned to one side, the front wheel steers to turn in the direction of the lean to guide the body into a curve in that direction, while the rear wheel steers the opposite direction so as to allow the body to turn with a tighter curve radius. The device could employ more than two wheel assemblies, such as to provide an in-line roller skate, in which case the pivot axes of the assemblies should be oriented such that they intersect at a common point when the shaft is horizontal.

The responsiveness of the steering action to leaning of the shaft is dependent on the angle of the pivot axis with respect to the horizontal plane. The shaft could be affixed to the body in an adjustable manner so as to allow the inclination of the pivot axis to be adjusted, thereby adjusting the responsiveness of the steering action to suit the desired skiing technique being practiced.

In addition to the adjustment of the steering response in a linear manner as discussed above, it is possible to design the motion-limiting structure that connects the shaft to the inner race in such a manner as to provide a non-linear response to leaning. For example, in one application of a non-linear response, the range of steering action is limited such that only a certain range of tilting of the shaft can be accommodated by steering action of the inner race, and further tilting beyond the specified range results in tilting of the wheel rim relative to the underlying surface, allowing the wheel to more easily skid sideways rather than roll.

In another example of a non-linear response, the motion can be limited to simulate the response of an alpine ski, where curving action increases with increasing tilt up to a certain degree of tilt, and thereafter remains relatively constant. To achieve this effect, the motion-limiting structure restricts the motion of the inner race relative to the shaft such that tilting within a certain range results in increasing steering action of the inner race (as discussed above for the embodiments employing a pivot joint), but allowing greater tilting of the shaft outside that range without causing further steering action of the inner race. Such actions can be provided by an inner spherical element affixed to the shaft engaged with an outer spherical socket in the inner race, in combination with guide elements and associated motion-limiting elements that restrict the motion between the spherical elements, where at least one of the motion-limiting elements guides its associated guide element along a non-linear path. To provide an alpine ski-type steering response, the non-linear path can have a linear response segment, in which the guide element is directed so as to provide the effect of a pivot joint between the inner spherical element and the outer spherical socket, and end segments bracketing the linear response segment and directing the guide element so as to allow tilting of the shaft without causing a steering response.

In a typical example, the inner spherical element is provided with two guide elements, each slidably and rotatably engaging a motion-limiting element in the outer spherical socket, one of which limits the motion of its associated guide element to allow rotation of the elements about the steering axis, and the other of which guides its associated guide element along a non-linear path to provide the desired steering response to tilting. Adjustment of the steering response can be provided by allowing the inclination and/or position of one or more of the motion-limiting elements to be adjustable, and/or by providing one or more of the motion-limiting elements on a component of the outer spherical socket that can be to be replaced with a similar component having a different motion-limiting element configuration.

For either linear or non-linear lean-to-steer mechanisms, further adjustment of the steering response can be provided by the use of resilient elements between components to bias their motion with respect to each other. Adjustment of the steering response can also be provided by mounting the lean-to-steer mechanism(s) to a body so as to provide a limited degree of flexibility (or providing a degree of flexibility in the body itself), where the flexibility allows the user to further adjust the response by shifting their weight forward or rearward to slightly adjust the inclination of the lean-to-steer mechanism.

The steerable wheel assembly of the present invention provides great flexibility in adjusting the steering performance of the wheels in response to leaning, and does so while placing minimal restrictions on the structure for mounting the wheel assemblies to the body of the device, making the wheel assemblies well-suited for adaptation to a variety of lean-to-steer devices.

Additionally, the lean-to-steer mechanism providing a non-linear response could be incorporated into other lean-to-steer devices. For example, the outer spherical socket could be incorporated into a fork to which a wheel is rotatably mounted, allowing a greater range of tilting without interference between the components. Similarly, the lean-to-steer mechanism could be incorporated into a skateboard truck, with a pair of wheels mounted to the shaft of the mechanism, with the shaft extending from an inner spherical element that pivots within an outer spherical socket that is mounted to the body of the device.

Alternative structures can be employed to provide similar non-linear steering responses. Lean-to-steer mechanisms of the present invention have a first moving element, which is affixed with respect to a body of a lean-to-steer device, and a second moving element, to which one or more wheels are rotatably mounted. The moving elements are movably connected together such that the second moving element can pivot with respect to the first moving element about a central point that resides at the intersection of a horizontal longitudinal axis and a vertical steering axis. The movable connection is configured to allow the first moving element to pivot about the longitudinal axis, to allow tilting of the body, and to allow the second moving element to pivot about the steering axis, to allow the steering response. Means for limiting the motion of the first moving element with respect to the second moving element are provided, and are configured to coordinate the combined tilting and steering pivoting such that tilting of the first moving element about the longitudinal axis can only be accommodated by causing the second moving element to pivot about the steering axis to maintain the axis of rotation of the wheel(s) horizontal.

The means for limiting the motion to provide the non-linear steering response typically employ a first element tracking structure mounted with respect to the first moving element and a corresponding second element tracking structure mounted with respect to the second moving element. The first element tracking structure can have one or more guide elements which engage corresponding track elements that provide the second element tracking structure, the track elements each being configured to direct the corresponding guide element along a non-linear path.

DETAILED DESCRIPTION

FIGS. 1-19illustrate embodiments of steerable wheel assemblies that provide what can be characterized as a linear steering response to tilting, where increased tilting results in increased steering action throughout the expected range of tilting.FIGS. 20-22 and 37 & 38illustrate some examples of non-linear steering responses, where increased tilting does not necessarily result in a corresponding increase in steering action; this non-linear response can be employed in steerable wheel assemblies, such as shown inFIGS. 20-22, but can also provide a benefit when employed in alternative lean-to-steer mechanisms, such as shown inFIGS. 23-36.

FIGS. 1-3illustrate a steerable wheel assembly10for use in a lean-to-steer device having a body12(one example being shown inFIG. 6). When the device traverses a nominally horizontal surface14, the assembly10provides steering about a nominally vertical steering axis16in response to leaning of the body12when the user supported on the body12shifts their weight; this weight shift creates a torque L about a nominally horizontal longitudinal axis18. The assembly10has a shaft20that is maintained in a fixed position relative to the body12so as to extend perpendicular to the longitudinal axis18. Typically, the shaft20is affixed to a mounting fork21(shown inFIG. 6), which in turn is affixed to the body12. The shaft20extends generally horizontally, and is tilted about the longitudinal axis18away from horizontal when the user leans the body12.

The assembly10employs a combination of a roller bearing22with a pivot joint23. The roller bearing22has a roller bearing axis24, about which an inner race26and an outer race28are free to rotate with respect to each other. Preferably, the roller bearing22is provided by a ball bearing to reduce friction, and a double row angular contact bearing is felt to be particularly suitable. The inner race26is mounted to the shaft20via the pivot bearing23, as discussed below, while a wheel30is mounted to the outer race28. The wheel30illustrated has a flat rim32that rests upon the horizontal surface14, thereby maintaining the roller bearing axis24essentially parallel to the horizontal surface14regardless of the speed of the device.

The pivot joint23of the assembly10is formed from a spherical plain bearing with its motion limited by a pivot pin33. As better shown inFIGS. 2 and 3, the spherical plane bearing has an inner spherical element34affixed onto the shaft20and an outer spherical socket35that is provided on the inner race26. The pivot pin33limits motion between the spherical element34and the spherical socket35to pivotal motion about a pivot axis36, and the pivot pin33is oriented such that the pivot axis36is perpendicular to the roller bearing axis24and inclined with respect to both the horizontal surface14and the longitudinal axis18by a pivot angle Θ. Because the orientation of the pivot pin33is set by the inner spherical element34, the magnitude of the pivot angle Θ is set by the orientation of the shaft20when it is fixed with respect to the body12.

By limiting the motion between the shaft20and the roller bearing22, the pivot joint23constrains the motion of the shaft20such that tilting of the shaft20about the longitudinal axis18(indicated by the arrow L) forces the entire the roller bearing22to turn about the steering axis16axis (indicated by the arrow S). Because the pivot axis36is inclined, the shaft20cannot simply pivot about the longitudinal axis18when the user leans the body12. The pivoting action is limited to movement about the pivot axis36(indicated by the arrow P), and thus the tilting movement of the shaft20can only be accommodated as a component of rotation about the pivot axis, with an additional component being motion about the steering axis16, since motion of the roller bearing22and the wheel30is limited by the engagement of the flat wheel rim32with the underlying surface14, which serves to maintain the roller bearing axis horizontal.

One visual representation of the effect of the pivot joint23is shown inFIGS. 4 and 5, where the constraint on the motion of the shaft20is represented by a slot48in a cylinder50, where the cylinder50is symmetrical about the pivot axis36and the slot48extends in a plane that is perpendicular to the pivot axis36. Thus, engagement with the slot48limits the shaft20to movement P about the pivot axis36. When the user leans the body12(indicated by the arrow L), causing the shaft20to tilt about the longitudinal axis18away from horizontal (as shown inFIG. 5), it can be seen that this tiling is only possible if the shaft20applies a camming force against the slot48, forcing the cylinder50to rotate about the pivot axis36(indicated by the arrow P), as illustrated by the change in position of a slot end52and a reference mark54. However, the motion of the cylinder50is constrained, since the cylinder50represents the pivot joint23that is limited in motion by the engagement of the wheel30(shown inFIG. 1) with the surface14. To accommodate the movement, the cylinder50must pivot about the steering axis16(indicated by the arrows S), thereby turning the wheel30to steer in the desired direction to turn the body12in the direction that the user is leaning. The rotation of the cylinder50also correspond to rotation of the pivot axis36(about which the cylinder is symmetrical) about the steering axis16, as indicated by the arrows SA.

The steerable wheel assembly10can be employed in a variety of lean-to-steer devices, including ski trainers, roller skates, skateboards, wheelbarrows, etc. Because the steering action is provided by the combination of the roller bearing22and the pivot joint23that are both centrally located within the wheel30, the assembly10can be readily incorporated into a variety of devices; all that is required is a structure to which the shaft20can be affixed. This simplicity is in contrast to various prior art devices, where the wheel rotates on an axle that is attached with complex mounting structures to provide the steering action. One example of a device employing the assembly10is a ski trainer100shown inFIG. 6.

The ski trainer100employs two of the steerable wheel assemblies10shown inFIG. 1, attached to the body12which is formed in the shape of a snow ski. Each of the wheel assemblies (10F,10R) is attached to the body12by a rigid fork bracket (21F,21R), to which the shaft (20F,20R) is affixed. The simple structures of the attachment allows considerable freedom in the structure of the devices on which the assembly10can be employed, making it readily adaptable for training skis, skates, wheelbarrows, etc.

To provide the desired steering action for the trainer ski100, the shaft20F of the front assembly10F is affixed to the front fork bracket21F so as to set the inclination angle ΘFof the front pivot axis36F in the orientation as shown inFIGS. 2-3(pivot axis inclined downwards with increasing distance from the observer), while the shaft20R of the rear assembly10R is affixed to the rear fork bracket21R so as to set the inclination angle Θr of the rear pivot axis36R in the orientation as shown inFIG. 1(pivot axis inclined upwards with increasing distance from the observer). When the body12is leaned as indicated by the arrow L, both the shafts (20F,20R) also lean. In the front assembly10F, the leaning of the front shaft20F causes it to pivot about the front pivot axis36F as indicated by the arrow PF, causing a steering pivot of the front wheel30F relative to the front shaft20F as indicated by the arrow SF, turning the front wheel30F into the direction of the lean to guide the ski trainer100into a curve in that direction. This motion also causes rotation of the front pivot axis36F about the front steering axis16F, as indicated by the arrow SFA. In the rear assembly10R, leaning of the rear shaft20R causes it to pivot about the rear pivot axis36R as indicated by the arrow PR; because the inclination of the rear pivot axis36R is opposite that of the front pivot axis36F, this pivoting action causes a steering pivot of the rear wheel30R that is opposite that of the front wheel30F, as indicated by the arrow SR, this motion also causing rotation of the rear pivot axis36R about the rear steering axis16R, as indicated by the arrow SRA. Thus, the rear wheel30R is turned away from the direction of the lean, allowing the ski trainer100to curve in the direction guided by the front wheel30F with a smaller turning radius. As discussed below with regard toFIGS. 8 and 9, in some cases the rear inclination angle Θr measured from horizontal is set somewhat less the front inclination angle ΘFsuch that the front wheel30F turns more than the rear wheel30R for a particular amount of leaning of the body12. Additionally, both inclination angles (ΘF, Θr) can be adjusted to provide a desired degree of steering response to suit the intended use. Since the inclination angles (ΘF, Θr) are set simply by the attachment of the shafts20to the fork brackets21, no complex structure is required to provide such adjustability. For typical skiing applications, setting each of the pivot axes (36F,36R) at an angle (ΘF, Θr) of about 30°-60° from horizontal is preferred, depending on the distance between the wheel assemblies (10F,10R).

In addition to adjusting the steering response of the wheel30by mounting the shaft20so as to adjust the inclination angle Θ of the pivot axis36, the response to leaning of the body12can be further adjusted by providing means to bias the shaft20to a neutral position where it extends along the roller bearing axis24. One example of such biasing means is shown inFIG. 7, which illustrates two resilient bushings104that can be installed on the shaft20. The bushings104are made of a resilient material such as a urethane elastomer, such as is conventionally used for bushings in skateboards.

Each of the bushings104has a shaft passage106therethrough, and terminates at a bushing inner face108and a bushing outer face110. The bushing106is placed onto the shaft20with the bushing inner face108positioned to abut against the inner race26of the roller bearing22. A bushing washer112is then placed onto the shaft20against the bushing outer face110, and tightened against the bushing106by a bushing nut114, which threadably engages the shaft20. As the bushing nut114is tightened, the bushing106is compressed between the inner race26and the bushing washer112. When the shaft20is moved away from its neutral position by leaning of the body12(as indicated by arrow L inFIG. 6), the bushing106is resiliently deformed, and provides a reaction force urging the shaft20back to its neutral (horizontal) position. The magnitude of the reaction force to the increasing tilt of the shaft20can be adjusted by the configuration and composition of the bushing106and, to a lesser degree, by the degree of compression of the bushing106between the inner race26and the bushing washer112. Thus, the response can be readily adjusted to suit the desired conditions by replacing the resilient bushings106with alternative bushings having a different shape and/or composition. For some applications, it may be desirable to provide a time-dependent response by employing a bushing filled with a viscous material or which employs hydraulic control of its deformation; such a bushing should provide a stiff resistance to sudden deformation, but a softer response to more gradual deformation of the bushing. Similarly bushings that are keyed with respect to the shaft so as to have a defined orientation thereon could be employed, in which case the bushings can be provided with a face for engaging the inner race that is inclined with respect to a plane normal to the roller bearing axis. Such an inclined face would allow some variation in the steering action in response to weight distribution on the body, such that a deweighted body could be made to steer slightly to the outside of a curve.

As noted above in the discussion ofFIG. 6, the steering response of a device such as the ski trainer100can be adjusted by altering the inclination angles (ΘF, Θr) of the front and rear pivot axes.FIGS. 8 and 9illustrate two examples of typical adjustments that could be made to the ski trainer100to suit different skiing actions. As shown inFIG. 8, the ski trainer100has been set for a slalom-type skiing action, where tight turning in response for leaning is desirable. The front wheel assembly10F has been attached to the front fork bracket21F to set a relatively steep front inclination angle ΘFSfor the front pivot axis36F. In this case, to simulate a snow ski with greater carving action at the front, the rear wheel assembly10R has been attached to the rear fork bracket21R to set a somewhat less steep rear inclination angle ΘRSfor the rear pivot axis36R. Because of the steep angle ΘFS, the front assembly10F provides a strong steering action of the front wheel30F in response to leaning of the body12, thereby guiding the ski trainer100into a tight curve, while the response of the rear wheel30R is somewhat less. It should be noted that some snow skis are designed to provide a greater carving effect of the rear of the ski, and to simulate the action of such skis, the pivot angles of the front and rear may be the same. Alternatively, in some applications the steering action of the rear wheel may not be needed, in which case the rear wheel could be mounted conventionally rather than being a part of a wheel assembly of the present invention.

In contrast,FIG. 9shows the ski trainer100when set for a general downhill skiing action, where a more gradual turning action is desired. To achieve this, the front wheel assembly10F is attached to set a shallower front inclination angle ΘFG(where ΘFG<ΘFS) for the front pivot axis36F, and the rear wheel assembly10R has been attached to set a still less steep rear inclination angle ΘRGfor the rear pivot axis36R. Because of the smaller angle ΘFG, steering response of the front assembly10F is less than that when configured as shown inFIG. 8, providing a more gradual steering action of the front wheel30F in response to leaning of the body12. In some cases, the user may wish to deactivate one or both of the assemblies (typically the rear assembly), in which case a removable clip that can be temporarily attached to prevent motion between the shaft and the inner race could be provided.

FIG. 10illustrates a series of steerable wheel assemblies10employed in an alternative application, in-line roller skate150. In the skate150, the wheel assemblies10are all mounted to a common bracket152and oriented such that their pivot axes (36a-36e) are arranged to steer the wheels (30a-30e) such that they are aligned along the circumference of a circle in response to leaning of a skate body154. This action of the wheels (30a-30e) is similar to that of the wheels of the skate taught in U.S. Pat. No. 5,398,949, incorporated herein by reference. With this arrangement, the pivot axes (36a-36e) appear to radiate from a common point located below the skate150.

FIG. 11illustrates one issues that can arise when a user employs a pair of ski trainers100. Frequently, due to the stance of the user, the bodies12of the ski trainers100are canted with respect to the underlying surface14when the user is not leaning. As shown inFIG. 11, if this canting is not compensated, it results in the shafts20being inclined from their neutral horizontal orientation, and thus results in the wheels30steering in directions that impede the ability of the user to travel straight. Similarly, when leaning to one side to turn into a curve, the shafts20of the ski trainer100in the direction of the lean will be tilted at less of an angle than those on the side the user is leaning away from, resulting in the wheels30on the outside of the curve steering to track along a sharper curve than the wheels30on the inside of the curve. To avoid these problems, it is desirable for the ski trainer100to allow the shafts20of the steerable wheel assemblies10to be mounted such that the shafts20remain horizontal when the user is not leaning to one side, but has a stance such that the bodies12of the ski trainers100are canted while the user remains upright.

FIG. 12illustrates a pair of ski trainers100′ that employ one scheme for accommodating the canting effect shown inFIG. 11. In the ski trainers100′, the fork brackets21are attached to ski bodies12with shims170interposed between the fork brackets21and the bodies12; these shims170serve to angle the fork brackets21relative to the bodies12, thereby providing a desired degree of cant for the bodies12relative to the shafts20, and allowing the shafts20to remain horizontal while the bodies12are canted to match the stance of the user. While shims170are shown for purposes of illustration, it should be appreciated that the fork brackets could be formed so as to incorporate a cant angle when affixed directly to the bodies12, or shims could be incorporated into the bindings that secure ski boots worn by the user onto the body12. While this approach accommodates the cant of the bodies12for the stance of a particular user, the lack of adjustability makes this scheme poorly suited for applications where the ski trainers100may be used by multiple users, such as in a rental situation.

To allow the cant angle to be adjusted to suit multiple stances, the degree of cant should be adjustable.FIG. 13illustrates a pair of ski trainers100″ that employ fork brackets21′ that allow the shafts20′ to be affixed thereto at an angle, thereby providing the effect of a bracket that incorporates an adjustable degree of shimming. One simple structure for providing this range of angles in the attachment is for at least one end of the shaft20′ to pass through a vertically-elongated slot200on the fork bracket21′, as better shown inFIG. 14. The vertically-elongated slot200allows the point of attachment of the shaft20′ to the fork bracket21′ to be adjusted. When such a vertically-elongated slot200is provided, the fork bracket21′ should be slightly arced to avoid off-axis forces when the nuts201are tightened to secure the shaft20′ to the fork bracket21′.

As shown inFIGS. 14 and 15, the fork bracket21′ also includes bracket index marks202that aid the user in setting a desired inclination angle Θ of the pivot axis36to provide a desired steering response appropriate for the intended type of skiing. As shown inFIG. 15, the bracket index marks202correspond to three different inclination angles (Θ1, Θ2, Θ3) to suit three different steering responses; for example, the first pivot inclination Θ1may be provide a gradual steering response well suited for general downhill skiing, the somewhat steeper pivot inclination Θ2may provide a steering response well suited for giant slalom skiing, and the third pivot inclination Θ3may be steeper to provide a sharp steering response well suited for slalom skiing. The inner race26′ is provided with a pivot index mark204that is aligned with the pivot axis36; when the shaft20is affixed to the fork bracket21′, the user can match the pivot index mark204to the desired bracket index mark202for the type of steering action desired, or to any intermediate position. An adjustment mechanism could be added to aid the user in setting the pivot angle to provide the desired steering response with greater precision and repeatability.

FIG. 14also shows bushing nuts206and bushing washers208that are employed to secure resilient bushings210on the shaft20′. When tightened, the bushing nut206and bushing washer208forcibly engage the resilient bushing210against the inner race26′ of the roller bearing22′ to provide a centering action that biases the shaft20′ to a position where it is horizontal and extends along the roller bearing axis24. The degree of the centering force can be adjusted by tightening or loosening the bushing nuts206to change the degree of compression of the resilient bushing210.

FIGS. 16 and 17illustrate components of a steerable wheel assembly300that forms another embodiment of the present invention, and which employs an alternative structure for providing a pivot joint302between a shaft304and a roller bearing inner race306of a roller bearing308.FIG. 16shows the components assembled, whileFIG. 17shows the components exploded and partially sectioned. The shaft304of this embodiment is affixed to a trunnion member310that extends perpendicular to the shaft304and has ends that are provided with trunnion member bearings312. As shown inFIG. 17, the trunnion member bearings312are aligned and provide free rotation between the trunnion member bearing inner race314, which can be fixed to the trunnion member310, and a trunnion member bearing outer race316about a pivot axis318. The roller bearing inner race306is formed with a pair of bearing seats320(better shown inFIG. 17) that are configured to receive the trunnion member bearing outer races316, and position them such that the pivot axis318is perpendicular to a roller bearing axis322, which is the axis of rotation between the roller bearing inner race306and a roller bearing outer race324. The shaft304is affixed to a fork bracket or similar fixture to position the trunnion member310so as to set the pivot axis318at a desired inclination angle Θ with respect to the horizontal. The reduced friction provided by the trunnion member bearings312is expected to provide greater freedom of motion between the shaft304and the inner roller bearing race306to provide smoother steering action under heavy loads.

FIG. 18illustrates components of a steerable wheel assembly400that forms another embodiment of the present invention, and which employs an alternative motion-limiting structure for providing a pivoting action between a shaft402and an inner race404of a roller bearing having and outer race (not shown) to which a wheel is attached. The motion-limiting structure again employs a spherical plain bearing having an inner spherical element406affixed onto the shaft402and an outer spherical socket408that is provided on the inner race404. A first pin410extending inwardly from the spherical socket408engages a circular recess412on the inner spherical element406, defining a first pin axis414in a similar manner to the pivot pin33and pivot axis36shown inFIGS. 2 and 3. The shaft402is affixed to the body of the device so as to position the circular recess412such that it sets the first pin axis414inclined with respect to the underlying horizontal surface and to a longitudinal axis416by a first pin angle Θ.

A second pin418also extends inwardly from the spherical socket408, and engages a guide groove420on the inner spherical element406; the guide groove extends circumferentially, residing in a plane to which the first pin axis414is perpendicular. The guide groove420is also shown inFIG. 19. The motion of the steerable wheel assembly400in response to leaning of a body to which the shaft402is affixed is similar to that of the steerable wheel assembly10discussed above.

In the embodiments discussed previously, the steering response of the wheel to leaning of the shaft can be characterized as linear; in such cases, as the tilting of the shaft increases, the rotation of the wheel about the vertical steering axis increases. While this provides a desirable response for many applications, there are some applications where a non-linear response is preferable, such that the steering action of the wheel is not directly responsive to the tilting of the shaft.

One situation where a non-linear response may be desirable is to provide a rear wheel that is limited in the degree of tilting of the shaft that it can accommodate while retaining its wheel rim on the surface being traversed.

FIG. 20illustrates an inner spherical element406′ that employs an alternative guide groove420′ that is truncated, having groove ends422that engage the second pin418to limit the range of pivoting motion about the first pin axis414. When the shaft402is tilted far enough to bring the second pin418into engagement with one of the groove ends424, the engagement limits further steering motion of the inner race404. At such point, further tilting of the shaft402cannot be accommodated by the steering motion while retaining a roller bearing axis424(shown inFIG. 18) horizontal, and thus the roller bearing axis424must be tilted off horizontal to accommodate further leaning. This results in a wheel rim (not shown) mounted to rotate about the inner race404being tilted with respect to the underlying surface, rather than remaining flat. The reduced contact area of the wheel rim reduces friction and allows the tilted wheel rim to more easily skid over the underlying surface, rather than rolling across it. This skidding action is frequently desirable for the rear wheel of a two-wheeled device, to allow the operator to turn more tightly than if the rear wheel were to track the path of the front wheel only through steering action. An alternative scheme to providing limited tilting may be to provide skid elements on the body or on the shaft that are brought into engagement with the ground surface when the body has been leaned sufficiently far; however, this scheme may provide unreliable response when employed on uneven ground surfaces.

Another situation where a non-linear response may be desirable is to provide a lean-to-steer device that more closely simulates the action of snow skis which are designed to carve at a specified turn radius; such skis are shaped such that they curve increasingly with increased leaning up to a point, and thereafter track along a specified radius of curvature independently of the degree of leaning. The steerable wheel assembly of the present invention can be designed such that the motion-limiting structure that connects the inner race to the shaft provides such a non-linear steering response, where the response to increased leaning is essentially linear up to a set point, and thereafter increased leaning is accommodated without a corresponding increase in steering action.

FIG. 21provides a visual representation of such a response, in a manner similar to the visual representation of the linear response shown inFIGS. 4 and 5. The constraint on motion of a shaft450is represented by a slot452in a cylinder454. Unlike the slot48shown inFIGS. 4 and 5, which is a linear slot, the slot452is a segmented slot having a central segment456and two vertical end segments458, only one of which is visible.

The central segment456extends in a plane that is perpendicular to a pivot axis460about which the cylinder454is symmetrical (the same relationship as the slot48in the cylinder50). When the shaft450is within a specified range of inclination to horizontal, it engages the central segment456and is limited to movement P about the pivot axis460. As the body to which the shaft450is affixed is tilted, the resultant tilting of the shaft450can only be accommodated if the shaft450applies a camming force against the central segment456, forcing the cylinder454to rotate about the pivot axis460(indicated by the arrow P). Again, since the motion of the cylinder454is constrained by the engagement of a wheel rim with the underlying surface, this rotation of the cylinder454causes the cylinder454to pivot about a vertical steering axis462(indicated by the arrows S). The steering action when the shaft engages the central segment456is the same as that discussed above with regard toFIGS. 4 & 5. Because the steering action provided is a linear response, the central segment456is considered to guide the shaft450along a functionally linear path, even though the central segment456itself is curved by its being formed on the surface of a cylinder. Similarly, arcuate guide slot segments formed on spherical surfaces can be considered as guiding an element engaged therewith along a functionally linear path.

As tilting of the body increases, the cylinder454eventually rotates far enough for the shaft450to reach one of the vertical end segments458. At this point, the vertical end segment454allows the shaft450to simply tilt to accommodate further leaning, without causing further rotation of the cylinder454and thus without further steering motion about the steering axis462.

FIG. 22illustrates a steerable wheel assembly500that provides one example of a motion limiting structure for providing a non-linear steering response such as visually represented inFIG. 21. The assembly500has an inner race502of a roller bearing and a shaft504, where the shaft504has an inner spherical element506affixed thereon, which engages an outer spherical socket508that is provided on the inner race502. A pin510serving as a first guide element extends inwardly from the spherical socket508and engages a groove512in the inner spherical element506, the groove serving as a first motion-limiting element. The engagement of the pin510in the groove512limits the motion between the shaft504and the inner race502, preventing rotation of the inner race502about the shaft504. However, the inner race502is free to rotate about the pin510, and is free to rotate in such a manner as to move the pin510along the groove512; these combined rotational motions provide freedom for the inner race502to pivot with respect to the shaft504so as to accommodate a wide range of motion, rather than being limited to only pivoting about a single axis.

To limit the motion between the inner race502and the shaft504to provide the desired steering response, a guide plate514is affixed to the inner race502. The guide plate514has a guide slot516therein, which serves as a second motion-limiting element that engages the shaft504to limit the relative motion of the inner race502with respect to the shaft502, the shaft502serving as a second guide element. The guide slot516shown has a central segment518and two vertical end segments520. The central segment518is inclined with respect to the horizontal, and is maintained in such orientation by the engagement of the pin510on the inner race502with the groove512in the inner spherical element506. This engagement prevents rotation of the inner race502(to which the guide plate514is affixed) about the shaft504, and the shaft504in turn is affixed to the body of the device to which the steerable wheel assembly500is mounted.

The inclined central segment518limits motion between the inner race502and the shaft504to pivoting motion that moves the shaft504along the central segment518, which effectively limits the motion to pivoting about a central segment pivot axis522that is perpendicular to a roller bearing axis524of the inner race502and is inclined with respect to both the underlying horizontal surface and a longitudinal axis526by a central segment pivot angle Θ. This limitation on the relative motion of the inner race502and the shaft504causes the inner race502to steer about a vertical steering axis528in order to move the shaft504along the central segment518to accommodate tilting of the shaft502due to leaning.

However, when tilting of the shaft504is sufficient to reach the end of the central segment518, the shaft504engages one of the vertical end segments520, and becomes free to tilt without causing any steering motion of the inner race502about the steering axis528. Thus, the angular position of the inner race about the steering axis528remains constant when the shaft504is in the vertical end segment520. Thus, the guide slot516engages the shaft502so as to direct the shaft502along a segmented path, rather than a linear path.

It should be appreciated that the steering response of the inner race502to tilting of the shaft504in this embodiment is controlled by the configuration of the guide slot516in the guide plate514, and thus the response can be altered by replacing the guide plate514affixed to the inner race502with an alternative guide plate having a different guide slot configuration. The response could also be altered by allowing the position and/or inclination of the guide plate on the inner race to be adjusted. While the guide slot shown is provided in a plate, the slot could be provided in an alternative structure, such as a semi-spherical member affixed to the inner race.

An alternative scheme to providing guide elements and corresponding motion-limiting elements to provide a desired steering response between spherical bearing elements is illustrated inFIGS. 23 and 24, withFIG. 23illustrating a linear response lean-to-steer mechanism, andFIG. 24illustrating a non-linear response lean-to-steer mechanism. In these embodiments, ball-bearing guide elements are provided on the inner spherical element, and engage guide tracks provided on the spherical socket which serve as motion-limiting elements; this is a reverse of the embodiments shown inFIGS. 18-20where pins extending from the spherical socket engage grooves in the spherical element.

FIG. 23shows a linear response steering mechanism600having an inner spherical element602rotatably mounted in an outer spherical socket604, and affixed onto a shaft606. The inner spherical element602is provided with an opposed pair of guide bearings608, which engage a pair of bearing seats610in the spherical socket604, limiting motion of the spherical element602with respect to the spherical socket604to pivoting motion about a pivot axis612. This limitation to pivotal motion provides a linear lean-to-steer response similar to that provided by the steering mechanism300shown inFIGS. 16 and 17.

In contrast to the steering mechanism600,FIG. 24shows a steering mechanism650that provides a non-linear steering response to leaning. The steering mechanism650again has an inner spherical element652rotatably mounted in an outer spherical socket654, and affixed onto a shaft656. However, in this embodiment the inner spherical element652is provided with a first guide bearing658, and a pair of opposed second guide bearings660, while the spherical socket654is provided with a corresponding first guide tracks662and pair of second guide tracks664. The first guide bearing658moves in the first guide track662to limit motion of the spherical element652with respect to the spherical socket654to motion that moves the first guide bearing658along the first guide track662, which in this embodiment is oriented to direct the first guide bearing658along a linear (arcuate) path that allows rotation of the inner spherical element652and the outer spherical socket654about a vertical steering axis666. In addition to pivotal motion about the steering axis666, rotational motion about the axis of rotation of the first guide bearing658is allowed; in the mechanism650, the first guide bearing is positioned on the inner spherical element652such that its axis of rotation is also a longitudinal axis668about which the shaft656tilts.

The second guide bearings660move in their respective second guide slots664; however, the second guide slots664direct the second guide bearings along non-linear paths, such that the allowed motion between the inner spherical element652and the outer spherical socket654differs depending on the location of the second guide bearings660in the second guide slots664. Each of the second guide slots664has a linear response segment670, which allows motion about a pivot axis672; to provide this response, each of the linear response segments670resides along an arc that forms a portion of a diameter of the outer spherical socket654which is intersected by a shaft axis674along which the shaft656extends. While the second guide bearings660move in the liner response segments670of the second guide tracks664, the motion of the spherical element652with respect to the spherical socket654is limited to pivotal motion about the pivot axis672, and thus tilting of the spherical element652about the longitudinal axis668causes rotation of the spherical socket654about a vertical steering axis666. The linear response segment670of each second guide slot664joins at each end to a tilt-accommodating end segment676, which is directed at an angle to the linear response segment670. The end segments676are angled to direct the second guide bearings660in a direction that allows further free tilting of the inner spherical element652with respect to the spherical socket654without causing a further steering response about the steering axis666. It should be appreciated by one skilled in the art that alternative arrangements of guide elements and guide tracks could be employed to provide a similar response, or to provide a different non-linear response. The particular configuration of the guide tracks depends on the steering response desired, and could be determined mathematically or experimentally; in the latter case, the desired path of the tracks could be modeled by mounting a router to an inner spherical element and cutting the guide tracks in the outer spherical socket while the shaft is moved through the desired response motions.

The steering mechanism650can be adapted for a variety of applications for lean-to-steer devices. For example, shaft656could be affixed to a body and the spherical socket654incorporated into the inner race of a roller bearing of a wheel, to provide a steerable wheel assembly such as those discussed above. However, it has been found that lean-to-steer devices employing steerable wheel assemblies where the lean-to-steer mechanism resides inside the hub of the wheel may be limited in the degree of tilt which they can accommodate, due to interference of the components. One approach to allowing a greater degree of tilt is to offset the wheel from the shaft.FIG. 25illustrates a lean-to-steer assembly700that incorporates elements of the steering mechanism650; in the assembly700, a spherical socket702is extended to provide a fork member704, to which a wheel706is rotatably mounted. The shaft656of this embodiment is affixed to a body (not shown) in a manner similar to that of the steerable wheel assemblies discussed above. In the assembly700, tilting of the shaft656causes the fork member704and the wheel706mounted thereto to both pivot about the steering axis666.

FIGS. 26 and 27illustrate a lean-to-steer mechanism750with a simplified structure which offers greater flexibility in mounting to a body;FIG. 26shows the mechanism assembled, andFIG. 27shows it partially exploded. The mechanism750again employs a fork member752provided with a spherical socket754, and an inner spherical element756that is affixed to a support shaft758, which in turn is affixed to a body bracket760. In the mechanism750, the fork member752is provided with a guide passage762that is formed as a horizontal slot that is slidably engaged by a shaft bearing764mounted onto the support shaft758; the shaft bearing serves as a first guide element, while the guide passage762serves as a first motion-limiting element. The engagement of guide passage762and the shaft bearing764limits the rotational motion between the spherical element756and the socket754to either tilting motion about a longitudinal axis766along which the support shaft758extends, limited pivoting motion about a vertical steering axis768, or a combination of these motions.

The desired lean-to-steer action is achieved by coordinating the two pivoting motions by use of a guide bearing770, mounted to the spherical element756, and a guide track772provided in the spherical socket754. The engagement of the guide bearing770with the guide track772limits the rotation of the spherical element756in the socket754to motion that moves the guide bearing770along the guide track772; the guide bearing770serves as a second guide element, while the guide track772serves as a second motion-limiting element. When the operator tilts the body of the device employing the mechanism750, the bracket760and support shaft758are tilted about the longitudinal axis766. Because the motion of the spherical element756relative to the socket754is limited by the guide bearing770and guide track772, the tilting motion can only be accommodated by movement of the guide bearing770along the guide track772.

When the guide bearing770is in an inclined central active response segment774of the guide track772(shown inFIG. 27), movement of the guide bearing770along the guide track772requires rotation of the spherical element756relative to the socket754about the steering axis768. The active response segment774could be directed along a circumference of the spherical socket754to provide a linear steering response, or could deviate from following a circumference to provide a slightly variable steering response when the guide bearing770traverses the active response segment774. The guide passage762must be sized relative to the shaft bearing764to allow sufficient pivoting about the steering axis768to allow the guide bearing770to fully traverse the active response segment774.

The guide track772also has two end segments776that bracket the active response segment774and which, in the mechanism750illustrated, are directed along vertically-directed arcs that allow tilting of the spherical element756about the longitudinal axis766without rotation about the steering axis768when the guide bearing770is in one of the end segments776. The result of the illustrated configuration of the guide slot772is that leaning within a specified range, when the guide bearing770travels along the active response segment774, results in a steering response of the fork752about the steering axis768where the degree of steering rotation increases with increased leaning. Once the leaning exceeds the specified range, when the guide bearing770enters one of the end segments776, then further leaning does not result in further increase of the steering action. It should be appreciated that alternative response schemes could be achieved by employing a different guide slot configuration, or a similar response could be achieved by employing a guide groove in the inner spherical element that is engaged by a guide element protruding inward from the spherical socket.

FIG. 28illustrates a portion of one example of a lean-to-steer device780that employs one or more lean-to-steer mechanisms such as the mechanism750. The device780is formed as a training ski, having an elongated body782. The shaft758of the mechanism750is affixed to a front end784of the body782.

FIG. 29illustrates a lean-to-steer mechanism750′ that allows alternative second guide slots (772,772′) to be employed to provide different steering responses. Each of the second guide slots (772,772′) is provided on an interchangeable guide block (790,790′) that attaches to the remainder of the fork member752′ and contains a portion of the spherical socket754′. The guide slots (772,772′) each have an active response segment (774,774′), where the inclination of the active response segment774relative to the longitudinal axis766differs from the inclination of the active response segment774′. The difference in inclination results in a different steering response for the guide slots (772,772′) when the steering mechanism750′ is subjected to the same amount of leaning about the longitudinal axis266.

FIG. 30illustrates a lean-to-steer mechanism750″ that provides an alternative scheme for adjusting the steering response. In the mechanism750″, the guide slot772is provided on a pivoting block792that is pivotably attached to the remainder of the fork member752″ so as to pivot about a horizontal transverse axis794that is perpendicular to the longitudinal axis766and to the steering axis768. The pivoting block792also provides a portion of the spherical socket754″. The angular position of the pivoting block792is set by an adjustment mechanism796, which can be adjusted to change the angle of the guide slot772. In the mechanism750″, the angle of the active response segment774and the end segments776are both changed when the orientation of the pivot block792is adjusted, and thus some slight steering action may occur when the guide bearing770traverses one of the end segments776, depending on the current orientation of the pivot block792. It should be appreciated that a similar adjustment could be achieved with a fork member designed such that the angle of the entire spherical socket relative to the remainder of the fork member can be adjusted.

FIG. 31illustrates a lean-to-steer mechanism800which employs the fork752(only partially shown) and related elements, but which employs an alternative body bracket802to provide adjustment of the steering response. The body bracket802has a bracket housing804in which a tilting block806is pivotably mounted. The angular position of the tilting block806relative to the bracket housing804is adjusted by an adjustment mechanism808. The support shaft758is affixed to the tilting block806in the same manner as it is affixed to the body bracket760shown inFIG. 26, and thus adjusting the angle of the tilting block806serves to also adjust the angle of the shaft758and the spherical element756that is affixed thereto. Since the position of the fork752relative to the shaft758is constrained by the engagement of the guide passage762with the shaft bearing764, tilting the shaft758also tilts the fork752, including the guide slot772that is formed therein, thereby changing the angle of the guide slot772relative to the longitudinal axis766. It should be appreciated that a similar effect might be achieved by forming the guide slot with the ability to be vertically adjusted with respect to the remainder of the fork, thereby changing the angle of the support shaft relative to the fork and the guide slot.

Slight adjustment of the steering response can also be provided by incorporating a degree of flexibility into the device to provide additional control of the motion by the operator. Such flexibility could be incorporated into the body of the device, or could be provided by mounting each lean-to steer mechanism to the body via a flexible member. Such flexibility provides a subtle steering action in response to shifting of the operator's weight towards the front or back along the body, as the flexing acts to slightly alter the inclination of the lean-to-steer mechanism in response to shifting of the user's weight forward and backward, which causes greater or lesser flexing in response to the longitudinal weight distribution on the body.

FIG. 32illustrates a lean-to-steer mechanism850that has many features in common with the mechanism750shown inFIGS. 26 and 27and discussed above. The mechanism850again employs a fork member852provided with a spherical socket854, and an inner spherical element856that is affixed to a support shaft858, which in turn is affixed to a body bracket860. The interaction between the spherical element856and the spherical socket854is essentially the same as the interaction of the spherical element756in the spherical socket754discussed above.

In the mechanism850, a resilient element862is interposed between the fork member852and the body bracket860to provide a resistance to leaning of the body bracket860about a longitudinal axis864. The resilient element862has a shaped cross-section with four protrusions866, and a central passage868through which the support shaft858passes. The fork member852is provided with a fork member shaped recess870that is configured to non-rotatably engage a first end872of the resilient element862, and the body bracket860is provided with a similar bracket shaped recess874configured to non-rotatably engage a second end876of the resilient element862. When the mechanism850is assembled, the ends (872,876) of the resilient element862respectively engage the shaped recesses (870,874), preventing rotation between each of the ends (872,876) and the shaped recesses (870,874) that it engages. When the user of a device employing the mechanism850shifts their weight to lean a body (not shown) affixed to the body bracket860, such leaning can only be accommodated by twisting the second end876of the resilient element862relative to the first end872, thereby generating a resilient reaction force that attempts to return the resilient element862to its untwisted rest state where the ends (872,876) are aligned. The force of resistance to leaning could be adjusted by employing softer or stiffer resilient elements, which provide a different amount of resistant to twisting, or by including an adjustment mechanism to vary the compressive load on the resilient element.

FIGS. 33 & 34illustrate a lean-to-steer mechanism900that again employs an inner spherical element902and outer spherical socket904; rather than employing a fork member to mount a single wheel, the mechanism900has a pair of wheels906mounted onto a shaft908that extends from the inner spherical element902, and is well suited for use as a skateboard truck. The outer spherical socket904is provided in a body bracket910that is positioned between the wheels906. The inner spherical element902has a first guide bearing912mounted thereto, and a second guide bearing914is mounted to the shaft908. The first guide bearing912engages a first guide slot916provided in the outer spherical socket904, while the second guide bearing914engages a second guide slot918that is provided on a guide plate920. The second guide slot918communicates with an access opening922, allowing it to be installed without requiring the wheel906to be removed from the shaft908. The guide plate920is provided with a pair of arcuate slots924that are engaged by plate bolts926, allowing the guide plate920to be mounted to the body bracket910with a desired inclination of the second guide slot918. The guide plate920can be replaced with a supplemental guide plate928having a supplemental plate guide slot930configured differently than the second guide slot918on the guide plate920.

FIGS. 35 & 36illustrate an lean-to-steer mechanism950having an alternative configuration suitable for use as a skateboard truck. Again, the mechanism950has an inner spherical element952and an outer spherical socket954, with a wheel shaft956extending from the inner spherical element952, and a pair of wheels958are mounted to the wheel shaft956. The outer spherical socket954in the mechanism950is mounted to a body bracket960via a support shaft962, and a first guide bearing964(shown inFIG. 35) is mounted on the support shaft962. A first guide slot966(also shown inFIG. 35) is provided in the outer spherical socket954. A second guide bearing968is mounted on the wheel shaft956, and a second guide slot970is provided in a guide plate972that can be attached to the outer spherical socket954. The guide plate972has a number of positioning holes974that allow it to be affixed to the outer spherical socket954in a number of different inclinations to adjust the steering response. The response is also affected by a resilient centering bushing976that is placed on the support shaft962, interposed between the outer spherical socket954and the body bracket960. Pivoting of the outer spherical socket954about a steering axis978acts to compress the centering bushing976, creating a reaction force that biases the outer spherical socket954back to a central position. It should be noted that positioning the resilient bushing to respond to the steering action, rather than responding to the tilting action (as is the case with the bushings104shown inFIG. 7and the bushings210shown inFIG. 14), allows a greater range of motion, as the tilting motion is frequently of greater angular magnitude than the steering motion.

A greater range of motion while providing a resilient centering force can also be provided by employing a resilient tensioning element, rather than a compression bushing.FIGS. 37 & 38are partially sectioned view that illustrate a steerable wheel assembly1000that is functionally similar to the assembly500shown inFIG. 22, having a lean-to-steer mechanism1002that controls the motion between an inner spherical element1004and an outer spherical socket1006, where the outer spherical socket1006serves as the inner race of a roller bearing. A shaft1008extending from the inner spherical element1004engages a guide slot1010that guides the shaft along a non-linear path to provide a desired steering response. The guide slot1010is formed on a hemispherical slot member1012, and has a central linear response segment1014that extends along an arc on a diameter of the inner spherical element1004; the arcuate linear response segment1014guides the shaft1008along a path that provides a linear steering response, and thus provides a functionally linear path.

The outer spherical socket1006is formed with a pair of inner mounting grooves1016, and a pair of tension adjustment elements1018(one of which is shown in phantom inFIG. 37) having outer mounting grooves1020are provided. A pair of resilient tension members1022(only one of which is shown inFIG. 37) are provided, each having a tension member inner lip1024and a tension member outer lip1026. When installed on the assembly1000, the tension member inner lip1024seats into one of the inner mounting grooves1016on the outer spherical socket1006, while the tension member outer lip1026seats into the outer mounting groove1020on the tension adjustment element1018on the same side. The tension adjustment elements1020threadably engage the shaft1008, allowing their position along the shaft1008to be adjusted relative to the outer spherical socket1006, thereby adjusting the tensile forces on the tension member1022. When the shaft1008is tilted by the operator leaning a body attached to the shaft1008, the tension members1022must stretch to accommodate the tilting, generating a reaction force that biases the shaft1008back to a level position. It should be appreciated that the tension members1022can accommodate a significantly greater range of tilting motion compared to compression bushings, such as the bushings104shown inFIG. 7or the bushings210shown inFIG. 14. When formed to enclose the elements (1004,1006,1012) of the lean-to-steer mechanism1002, the tension members1022provide an additional benefit in keeping these elements (1004,1006,1012) free of debris.

While the lean-to-steer mechanisms discussed above for providing a non-linear response employ a ball-and-socket connection in combination with guide members and corresponding guide slots to control the response action, alternative structures for providing the same non-linear response can be employed. Examples of such mechanisms are shown inFIGS. 39-44.

FIGS. 39-41illustrate a lean-to-steer mechanism1100suitable for use in a skateboard or similar lean-to-steer device.FIG. 39illustrates the mechanism1100when assembled, whileFIG. 40shows the components exploded, andFIG. 41is a detail view showing the components that define the non-linear response. The mechanism1100has a first moving element1102that can be mounted a body (not shown) and a second moving element1104to which a pair of wheels1106are mounted, so as to rotate about a horizontal wheel axis1108.

To provide the non-linear steering response, the first moving element1102is provided with a first tracking structure1110(labeled inFIGS. 40 and 41), which has a pair of guide bearings1112that serve as first structure tracking elements. The second moving element1104has a corresponding second tracking structure1114having a pair of guide ramps1116that serve as second structure tracking elements. The interaction of the guide bearings1112and the guide ramps1116to limit the motion of the second moving element1104in response to tilting of the first moving element1102is discussed in greater detail below with regard toFIG. 41.

To maintain the first tracking structure1110engaged with the second tracking structure1114and limit motion therebetween, a connecting structure1118is provided that limits the relative motion between the first moving element1102and the second moving element1104and also applies a compressive force to maintain engagement between the tracking structures (1110,1114). The connecting structure1118of this embodiment employs a trunnion member1120that is rotatably mounted in the second moving element1104so as to rotate about a vertical steering axis1122, and a shaft1124that passes through the trunnion member1120and extends substantially along a longitudinal axis1126about which the first moving element1102tilts. The longitudinal axis1126intersects the steering axis1122at a central point1128. The trunnion member1120serves as a shaft retaining element that connects the shaft1124to the second moving element1104, while the first moving element1102is provided with a shaft passage1130sized to slidably engage the shaft1124so as to limit the motion of the first moving element1102to pivoting on the shaft1124about the longitudinal axis1126or to sliding along the shaft1124. Since the shaft1124is in turn connected to the second moving element1104via the trunnion member1120, the relative rotational motions between the first moving element1102and the second moving element1104are limited to rotation about the steering axis1122, rotation about the longitudinal axis1126, or a combination of these motions.

The shaft1124has a shaft head1131and a shaft threaded end1132, which can be engaged by a nut1134that serves as a clamping element. In use, the shaft1124passes through the trunnion member1120as well as through a pair of resilient bushings1136,1138(shown in phantom inFIG. 39) that serve as resilient retaining elements. Washers1140are interposed between the shaft head1131and the resilient bushing1136, and between the nut1134and the resilient bushing1138. The resilient bushing1136in turn engages a second moving element bearing surface1142on the second moving element1104, while the resilient bushing1138engages a thrust bearing1144that in turn engages a first moving element bearing surface1146on the first moving element1102. When the nut1134is tightened on the shaft threaded end1132, the resilient bushings1136,1138become compressed between the nut1134and the shaft head1131, and apply a compressive load to the second moving element1104and the first moving element1102to force them towards each other, thereby maintaining the guide bearings1112on the first moving element1102forcibly engaged against the guide ramps1116on the second moving element1104. It should be noted that the engagement of the resilient bushing1136against the second element bearing surface1146provides resistance to pivoting of the trunnion member1120and the shaft1124relative to the second moving element1104, and thus provides a centering bias for the lean-to-steer mechanism1100.

The trunnion member1120engages the second moving element1104via a pair of trunnion bearings1148that allow pivoting of the second moving element1104about the steering axis1122relative to the shaft1124, while the thrust bearing1144and the slidable engagement of the shaft passage1130with the shaft1124allows tilting of the first moving element1102about the longitudinal axis1126relative to the shaft1124. Since the shaft1124is connected intermediate between the first moving element1102and the second moving element1104, the first moving element1102is movable relative to the second moving element1104about the longitudinal axis1126(allowing the first moving element1102and the body affixed thereto to tilt) and about the steering axis1122(allowing the steering action of the second moving element1104relative to the body attached to the first movable element1102).

As better shown inFIG. 41, the steering response of the second moving element1104to tilting of the first moving element1102is controlled by the engagement of the guide bearings1112on the guide ramps1116, in a similar manner to the motion-limiting action of the guide bearings and guide slots shown inFIGS. 24-36and discussed above. The guide bearings1112are mounted to the first moving element1102(omitted for clarity inFIG. 41) and the guide ramps1116are configured such that, when the guide bearings1112are forcibly engaged against the guide ramps1116by compressive forces (as discussed above), each of the guide bearings1112rotates about an individual guide bearing axis1150that intersects the central point1128regardless of the rotational position of the first moving element1102relative to the second moving element1104.

Various profiles for the guide ramps1116could be employed; as illustrated, each of the guide ramps1116has a central linear response segment1152bracketed by two end segments1154,1156. When the guide bearings1112are initially rolled across the guide ramps1116by tilting of the first moving element1102away from an upright neutral position, each of the linear response segments1152directs the associated guide bearing1112along an inclined path. Tilting the body and the first moving element1102in a clockwise direction, as indicated by the arrow CW, causes the guide bearing1112′ to force the linear response segment1152′ backwards as it rotates downwards, while the corresponding upwards movement of the guide bearing1112″ allows the linear response segment1152″ to move forwards to compensate, resulting in a pivot of the second moving element1104about the steering axis1122, as indicated by the arrow S′. However, when the guide bearings1112reach the end segments1154, further movement along the guide ramps1116does not result in any steering response. Similarly, tilting of the body and first moving element1102in a counter-clockwise direction, as indicated by the arrow CCW, causes the guide bearing1112″ to force the linear response segment1152″ backwards, and the guide bearing1112′ allows the linear response segment1152′ to move forwards, resulting in a steering response in the other direction as indicated by the arrow S″. Again, once the tilting is sufficient to bring the guide bearings1112to the end segments1156, the guide ramps1116are configured to allow further tilting without a steering response.

Since the steering response is controlled by the guide ramps, providing guide ramps having a different configuration allows one to change the steering response to provide a desired action.FIG. 42illustrates a second moving element1170that is designed to allow a user to readily replace a pair of guide ramps1172with an alternative configuration, and can be substituted for the second moving element1104discussed above. The guide ramps1172are provided on a guide clip1174that snaps onto a second moving element base portion1176, and can be readily removed and replaced by a similar guide clip having a different guide ramp configuration. Because the forces on the guide ramps1172are primarily compressive forces normal to the second moving element base portion1176, it may be practical to make the guide clip1174from a plastic material for greater ease of fabrication.

FIG. 42also illustrates an alternative trunnion member1178, which is formed integrally with a shaft1180, thereby simplifying construction and reducing the overall size of the resulting lean-to-steer mechanism. However, this mechanism lacks the centering bias provided by the resilient bushing1136.

FIGS. 43 and 44illustrate an alternative lean-to-steer mechanism1200that employs a ball-and-socket connection to mount a shaft1202to a second moving element1204, rather than employing a trunnion member. The shaft1202passes through an inner spherical element1206, which in turn is mounted in a spherical socket1208provided in the second moving element1204so as to pivot about a central point1210, and thus provides for pivotal motion about a vertical steering axis1212and a longitudinal axis1214, both of which intersect the central point1210.

A first moving element1216is provided, and in this embodiment has three guide bearings1218, each mounted to rotate about an individual guide bearing axis1220that intersects the central point1210. The use of three guide bearings1218, arranged at 120° from each other, avoids creating an effective horizontal axis of tilting that might result from using a pair of opposed guide bearings such as shown inFIGS. 39-41, since the motion of the inner spherical element1206in the spherical socket1208does not provide the resistance to such motion that is provided by the trunnion member1120shown inFIGS. 39-41. Because the shaft1202is rotatable with respect to the second moving element1204about the longitudinal axis1214, a resilient bushing1222can directly engage a first moving element bearing surface1224to apply a compressive load, and no thrust bearing is needed.

The second moving element1204is provided with three guide ramps1226, each positioned and configured to engage one of the guide bearings1218and to direct the guide bearing1218along a non-linear path in response to tilting of the first moving element1216to which the guide bearings1218are mounted. The exact configuration of the guide ramps1226can be determined experimentally or though CAD modeling to obtain the desired response, and there may be more than one configuration that can be employed to provide a particular desired response.

Variations of the lean-to-steer mechanism can be made to suit particular applications. For example,FIGS. 45 and 46illustrate a lean-to-steer mechanism1300that is functionally similar to the mechanism750shown inFIGS. 26-28, but which is designed to provide more balanced forces for greater strength.

The lean-to-steer mechanism1300has a first moving element1302, to which an inner spherical element1304(best shown inFIG. 46) is affixed via a support shaft1306. The mechanism1300illustrated is particularly well suited for use in a skateboard or similar device.

In the mechanism1300, the shaft1306extends on either side of the inner spherical element1304and is engaged by the first moving element1302at both ends of the shaft1306, providing balanced support and reducing bending moments on the shaft1306that would result from support at only one end, as in the mechanism750discussed above. The first moving element1302is formed as a bracket that can be readily affixed to a body (not shown).

The mechanism1300also has a second moving element1308that is provided with a spherical socket1310. A pair of wheels1312are mounted to the second moving element1308. The spherical socket1310engages the inner spherical element1304so as to limit motion between the first moving element1302and the second moving element1308to rotation about a central point1314, which resides at the intersection between a horizontal longitudinal axis1316and a vertical steering axis1318(shown inFIG. 45).

The motion between the moving elements (1302,1308) is further limited by engagement between a first tracking structure, provided by a pair of guide bearings1320mounted to the first moving element1302, and a second tracking structure provided by a pair of guide slots1322formed in the second moving element1308, and in which the guide bearings1320can move. The guide bearings1320are mounted to the inner spherical element1304and extend on either side thereof to provide balanced forces. The guide bearings1320serve as first structure tracking elements. The guide slots1322are provided in a pair of guide inserts1324that are fastened to a second element body1326of the second moving element1308. The guide slots1322serve as second structure tracking elements.

The engagement of the guide bearings1320with the guide slots1322limits the rotation of the spherical element1304in the socket1310to motion that moves the guide bearings1320along the guide slots1322. When the mechanism1300is tilted by action of the user, the first moving element1302, inner spherical element1304, and support shaft1306are tilted about the longitudinal axis1316. Because the motion of the spherical element1304relative to the socket1310is limited by the guide bearings1320and guide slots1322, the tilting motion can only be accommodated by movement of the guide bearings1320along the guide slots1322.

Each of the guide slots1322has a linear response segment1328bracketed by end segments1330(labeled inFIG. 46). The linear response segment1328is inclined such that movement of the guide bearing1320along the linear response segment1328, responsive to tilting about the longitudinal axis1316, can only be accommodated by pivoting of spherical socket1310about the steering axis1318. As the tilt of the inner spherical element1304increases, the pivot of the spherical socket1310increases in proportion, until such time as the guide bearing1320reaches one of the end segments1330. The end segments1330are configured to allow the guide bearing1320to move therein to accommodate further tilting without any steering response.

It should be appreciated that alternative lean-to-steer responses could be provided by employing a different configurations of the guide slots1322. If the guide slots1322are provided on interchangeable guide inserts1324as shown, the guide inserts1326can be removably fastened to the second element body1326to allow them to be readily replaced by guide inserts having a different configuration to provide a different response. Matching pairs of guide inserts can be color coded or otherwise visually matched to allow the user to readily select a pair of guide inserts that have corresponding guide slots.

The mechanism1300is provided with a tie rod1332that serves as a diagonal brace to provide further strength. The tie rod1332has a spherical plain bearing1334,1336mounted in each end (labeled inFIG. 46). The spherical plain bearing1334is fastened to the first moving element1302, while the spherical plain bearing1336is fastened to the second element body1326. The location of the spherical plain bearing1334is selected such that it rotates with respect to the remainder of the tie rod1332about a first end bearing pivot point1338(shown inFIG. 45) that resides either on or in close proximity to the longitudinal axis1316, thereby allowing tilting movement of the first moving element1302about the longitudinal axis1316. Similarly, the location of the spherical plain bearing1336is selected such that it rotates relative to the remainder of the tie rod1332about a second end bearing pivot point1340(also shown inFIG. 45) that resides either on or in close proximity to the steering axis1318, thereby allowing the second moving element1308to pivot about the steering axis1318relative to the tie rod1332.

FIG. 47illustrates a lean-to-steer mechanism1300′ that is similar to the mechanism1300discussed above, but which employs a dedicated diagonal brace1332′ rather than employing a conventional tie rod, to simplify fabrication. The diagonal brace1332′ has a first end pivot structure1334′ that pivotably engages a first element pivot structure1342on the first moving element1302′, this engagement allows pivoting between the brace1332′ and the first moving element1302′ about the longitudinal axis1316. Similarly, the brace1332′ has a second end pivot structure1336′ that pivotably engages a second element pivot structure1344provided on the second moving element1308′ to allow pivoting about the steering axis1318. The brace1332′ also differs in being positioned so as to extend forward of the second moving element1308′.

While the novel features of the present invention have been described in terms of particular embodiments and preferred applications, it should be appreciated by one skilled in the art that substitution of materials and modification of details can be made without departing from the spirit of the invention. To the extent that the appended claims have been drafted without multiple dependencies, this has been done only to accommodate formal requirements in jurisdictions which do not allow such multiple dependencies. It should be noted that all possible combinations of features which would be implied by rendering the claims multiply dependent are explicitly envisaged and should be considered part of the invention.