Patent Publication Number: US-6209899-B1

Title: Bicycle with passenger lift system

Description:
This is a continuation-in-part application of the U.S. patent application having the Ser. No. 09/146,809, filed Sep. 4, 1998 the contents of which are hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention is directed to improvements in bicycles and, in particular, to a bicycle having a rider-controlled system that raises and lowers a rider-supporting section during transit. 
     BACKGROUND OF THE INVENTION 
     Bicycles are a popular and efficient form of transportation that allow riders to travel over long distances with relative ease. Bicycles are also environmentally friendly and allow riders to exercise while they travel. As bicycle designs have progressed, numerous improvements have been implemented to enhance various aspects of bicycle performance. 
     Some modifications, like multi-gear drive systems, make bicycles easier to operate over hills and during periods of heavy wind. Additionally, new seat designs have made bicycles more comfortable, increasing the distance they may be ridden. Some bicycles, like recumbents, even allow riders to assume a reclined orientation during travel. Other bicycles include provisions to accommodate more than one rider simultaneously. Still other bicycles, like those of U.S. Pat. No. 4,400,003 and U.S. Pat. No. 5,052,706 have components that are selectively collapsible to promote easy storage and safe shipping. 
     In addition to providing a practical means of transportation and a convenient source of exercise, bicycles are often used as a source of entertainment. For example, many riders explore rocky terrain on so-called “mountain bikes.” This type of bicycle typically includes a shock absorbing suspension system that improves control over uneven surfaces. Suspension systems reduce rider fatigue by absorbing impacts that would otherwise be transmitted directly to the rider. An example of a suspension-including bicycle is disclosed in U.S. Pat. No. 5,658,001. 
     Mountainous terrain is not the only location traversed by thrill-seeking bicycle riders, however. Many riders choose the bicycle as a means of simulating temporary flight. Typically, this flight experience involves riding a bicycle at high speed up, onto, and over an inclined ramp. The bicycle&#39;s momentum carries the bicycle and rider through the air. 
     Ramp jumping, although thrilling, can be very dangerous; a wide variety of variables affect the outcome of a given jump. For example, approach speed, ramp angle, and even tire pressure must all be within given acceptable ranges for a jump to be successful. Misjudgment, lack of concentration, or poorly maintained equipment may all lead to a failed jump, resulting in possible injury or even death. As a result, ramp jumping is not an activity that is safe for all riders. 
     Regardless of the dangers involved, many bicycle riders attempt ramp jumping as a pastime. In addition, television promotes such events making it alluring to even the most unsophisticated riders. Unfortunately, few riders have the requisite knowledge and skill to jump ramps successfully. Many riders are injured because they perform jumps without understanding the dynamics involved. To make matters worse, most bicycle modifications do not make ramp jumping safer. 
     U.S. Pat. No. 5,301,969 is one known disclosure that provides a dual frame bicycle for purposes of jump simulation. The bicycle converts rotational energy from the bicycle back wheel into translational energy used to make the bicycle leap. The &#39;969 device is formed from two frames and employs a hooked pole that selectively engages a pin affixed to the bicycle rear wheel. The two bicycle frames are spaced apart by elastic members, and using the hooked pole to engage the rear wheel pin draws the two frames together, storing potential energy in the elastic members. The pole remains hooked to the wheel pin while until the wheel has rotated a predetermined distance, at which point the hook is released. When the hook is released, the energy stored in the elastic members is released, forcing the bicycle frames apart and causing the bicycle to jump. 
     The &#39;969 requires a two-frame construction that is cost prohibitive and, once the bicycle begins to store energy, a jump is unavoidable. Even if it were possible to wrench the hook free from the wheel pin before the wheel had rotated through the hook-releasing distance, the already-stored energy would still be released. As a result, a rider attempting to abort a jump will still be lifted before coming to rest. This design also makes it difficult for a rider to increase or decrease the amount of lift, as needed. The &#39;969 produces consistent amounts of lift which may not be appropriate for all situations during a given bicycle ride. 
     What is lacking in the prior art is a single frame bicycle that allows a rider to experience the thrill of jumping, without requiring the rider to undergo the equipment preparation and skill set development associated with jumping over a ramp. The bicycle should provide a rider-controlled positioning means for raising the rider from a standard position to an elevated position and then safely returning him to the standard position. The bicycle should be able to elevate the rider without requiring that the bicycle become airborne. The bicycle should be customizable to provide varying degrees of lift to suit riders of different stature. The bicycle should also be customizable to provide different lifting characteristics, including varied lift rates and lift heights. 
     SUMMARY OF THE INVENTION 
     The instant invention is a bicycle having a user-controlled selective positioning system that allows the rider to adjust the height of a rider-supporting portion of the bicycle frame, with respect to the remainder of the bicycle. The bicycle includes a passenger support construction linked to a front and rear tire by wheel mounting assemblies located at opposite end of the support construction. A seat is mounted on the passenger support construction, and the height of the entire passenger support construction is adjustable with respect to the remainder of the bicycle during transit. Appropriate brakes are included in each embodiment, to slow the bicycle as needed. 
     The height of the passenger support construction is temporarily adjusted by a rider-controlled selective positioning system. The positioning system includes an energy transfer construction that converts rotational energy from the bicycle wheels into translational energy capable of lifting the rider. A network of cables directs the converted energy to lifting assemblies that operatively link the passenger support construction to the above-mentioned wheel mounting assemblies. As a result, the positioning system produces relative motion between the passenger support construction and the bicycle wheels. With this arrangement, the instant invention will elevate a rider without requiring the entire bicycle to become airborne. 
     Thus, an objective of the instant invention is to provide a single frame bicycle that selectively elevates, and subsequently lowers, a rider without requiring that the entire bicycle become airborne. 
     Another objective of the instant invention is to provide a bicycle that allows a rider to enjoy the thrill of ramp jumping without requiring a ramp or other additional equipment. 
     A further objective of the instant invention is to provide a bicycle that allows a rider to simulate a ramp jumping experience without requiring the preparation and skill set development associated with successful ramp jumping. 
     Still an additional objective of the instant invention is to provide a bicycle that provides a rider-controlled positioning means for raising the rider from a standard position to an elevated position and then safely returning him to the standard position. 
     Yet a further objective of the instant invention is to provide a bicycle that is customizable to provide varying degrees of lift to suit riders of different stature. 
     An additional objective of the instant invention is to provide a bicycle that is customizable to provide different lifting characteristics, including varied lift rates and lift heights. 
     Still another objective of the instant invention is to provide a bicycle that includes a positioning system which does not interfere with the steering of the bicycle. 
     Other objectives and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a side elevation view of an improved bicycle according to the present invention, with the included passenger support construction in a standard orientation; 
     FIG. 2 is a side elevation view of the bicycle shown in FIG. 1, with the passenger support construction in an elevated orientation; 
     FIG. 3 is a pictorial view of the bicycle shown in FIG. 1; 
     FIG. 4 is a close-up pictorial view of the bicycle shown in FIG. 1; 
     FIG. 5 is a close-up pictorial view of the first wheel mounting assembly of the bicycle shown in FIG. 1; 
     FIG. 6 is a side elevation view of an alternate embodiment of the bicycle of the present invention, with the included passenger support construction in a standard orientation; showing the motor in phantom lines 
     FIG. 7 is a side elevation view of the bicycle shown in FIG. 6, with the passenger support construction in an elevated orientation; 
     FIG. 8 is a close-up pictorial view of the energy transfer construction of the bicycle shown in FIG. 6; 
     FIG. 9 is a front elevation view of the bicycle shown in FIG. 6, with the drive sprocket in a disengaged position; and 
     FIG. 10 is a front elevation view of the bicycle shown in FIG. 6, with the drive sprocket in an engaged position. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     It is to be understood that while a certain form of the invention is illustrated, it is not to be limited to the specific form or arrangement of parts herein described and shown. It will be apparent to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not to be considered limited to what is shown in the drawings and described in the specification. 
     Now with reference to FIG. 1, the bicycle  10  of a first embodiment is shown. By way of overview, the bicycle  10  includes a passenger support construction  12  having a first wheel mounting assembly  14  disposed at a first end  16  thereof. A second wheel mounting assembly  18  is disposed at a second end  20  of the passenger support construction  12 . The bicycle  10  also includes a selective positioning system  22  that maneuvers the support construction  12  into a user-selected orientation with respect to the bicycle support surface. The details of the bicycle  10  will now be discussed. 
     With additional reference to FIG. 3, the passenger support construction  12  is an essentially-triangular truss characterized by a top tube  26 , a seat tube  28 , and a down tube  30 . The top tube  26  abuts the seat tube  28 , and the down tube  30  extends between the top tube and the seat tube. A seat post  32  extends upward from within the seat tube  28 , and a passenger-supporting seat  34  is disposed on a free end of the seat post. The juncture of the top tube  26  and the down tube  30  is characterized by a substantially-hollow head tube  36 . The head tube  36 , which is essentially a cylindrical sleeve, accommodates a standard handlebar support post  38 . In a preferred embodiment, the juncture of the down tube  30  and the seat tube  28  is characterized by a bottom bracket  40  in which a pedal crankset  42  is rotatably mounted. 
     As shown in FIGS. 1 and 2, the bicycle  10  also includes wheel mounting assemblies  14 , 18  mounted at opposite ends  16 , 20  of the passenger support construction  12 . The first wheel mounting assembly  14  includes a steering fork  44  having a first end  46  that is rigidly linked to the handlebar support post  38 . A wheel fork  48  is slidably attached to the legs of the steering fork  44 . More particularly, the wheel fork  48  and steering fork  44  are joined by a linking sleeve  50  attached to the wheel fork. The linking sleeve  50  allows relative motion between the steering fork  44  and the wheel fork  48 ; the steering fork slides within the linking sleeve. A front wheel  52  is rotatably secured to the wheel fork  48  via front mounting flanges  54  that extend from the bottom of the wheel fork. 
     As seen with joint reference to FIGS. 3 and 4, the second wheel mounting assembly  18  includes a pair of congruent, triangular trusses  56  having an attachment vertex  58 , a wheel engaging vertex  60 , and a control vertex  62 . The second wheel mounting assembly  18  is pivotally joined to the passenger support construction  12  via a pair of rigid joint plates  64  extending from the bottom bracket  40 . More specifically, the attachment vertex  58  is rotatably mounted on a support cylinder  66  that extends orthogonally between the joint plates  64 . The rear wheel  68  is mounted on a rear axle  69  that extends between the wheel engaging vertex  60  of each truss  56 . As a result, during lifting of the passenger support construction  12 , the second wheel mounting assembly  18  and the rear wheel  68  pivot as a unit with respect to the passenger support construction second end  20 . The second wheel attachment assembly  18  may include trusses of various geometry, as desired. 
     As mentioned above, the bicycle  10  also includes a selective positioning system  22  that allows a rider to raise and lower the passenger supporting construction  12  with respect to the wheels  52 , 68 . In keeping with the objects of the present invention, the selective positioning system  22  advantageously converts rotational energy form the front wheel  52  into translational energy capable of raising the passenger support construction  12 . 
     As shown in FIG. 3, the selective positioning system  22  includes an energy transfer construction  70  that is operatively linked to a first lifting assembly  72  and a second lifting system  74 . The first and second lifting assemblies  72 , 74  are responsible for vertical motion of the front and rear  16 , 20  portions of the passenger support construction  12 , respectively. 
     As seen in FIG. 5, the energy transfer construction  70  employs a pivot yoke  76  mounted on the front wheel axle  78 , a caliper-type clamp  80  mounted on the yoke, and a network of cables  82 , 84 , 86  that transmit energy throughout the bicycle  10 . The pivot yoke  76 , which resembles an inverted “U,” straddles the front wheel  52 , but does not interfere with the rotation of thereof. 
     The wheel clamp  80  is operated by a handlebar-mounted clamp lever  88 . The handlebars  90 , themselves, are secured to the handlebar support post  38  and allow a rider to steer the bicycle  10  during transit. The clamp lever  88  is linked to the clamp  80  via a clamp cable  92 ; squeezing the clamp lever causes the clamp to engage the front wheel rim  94 . 
     The pivot yoke  76  is linked to other parts of the bicycle  10  by flexible cables  82 , 84 , 86 . With continued reference o FIG. 5, a pair of front lift cables  82  extends from yoke tethering posts  96  to distal ends  98  of the steering fork  44 . These front lift cables  82  are guided by a pair of front pulleys  100  that are rotatably mounted on the wheel fork  48 . As seen in FIG. 3, and with additional reference to FIG. 4, a single steering cable  84  extends from the yoke tethering posts  96 , continues over the front pulleys  100  and passes around a steering pulley  102  that is suspended below the passenger support construction  12 . The steering pulley  102  is, in turn, linked to the passenger support construction down tube  30  by a rear lift cable  86 . The rear lift cable  86  passes around a rear pulley  104  and is attached at opposite ends  106 , 108  to the steering pulley  102  and the passenger support construction down tube  30 , respectively. The rear pulley  104  is attached to the second wheel mounting assembly control vertex  62 . 
     During use, the pivot yoke  76 , wheel clamp  80 , pulleys  100 , 102 , 104  and pulleys  82 , 84 , 86  cooperate to raise and lower the passenger support construction  12  with respect to the bicycle wheels  52 , 68 . More specifically, squeezing the clamp lever  88  elevates the passenger support construction  12  from a standard position to an elevated, lifting position. Conversely, releasing the clamp lever  88  returns the passenger support construction  12  to the standard position. 
     The operation of the energy conversion construction  70  will now be described. When the clamp lever  88  is squeezed, the resultant tension produced in the clamp cable  92  causes the wheel clamp  80  to constrict, engaging the front wheel rim  94 . As the wheel clamp  80  engages the front wheel rim  94 , the pivot yoke  76  begins to rotate in tandem with the front wheel  52 . When the pivot yoke  76  travels about the front wheel axle  78 , the front lift, steering, and rear lift cables  82 , 84 , 86  are placed in tension. As the pivot yoke  76  continues to rotate around the front wheel axle  78 , the front lift cables  82  and the steering cable  84  translate with respect to the front pulleys  100 . The translation of the front lift cables  82  produces a concomitant upward translation of the steering fork  44  within the linking sleeve  50 . Similarly, the translation of the steering cable  84  causes the rear lift cable  86  to translate about the rear pulley  104  causing the second wheel mounting assembly  18  to rotate downward about the support cylinder  66 . 
     The above-described translation of the steering fork  44  and rotation of the second wheel mounting assembly  18  lifts the passenger support construction  12  with respect to the wheels  52 ,  68 . With joint reference to FIGS. 1 and 2, as the clamp lever  88  is released, the wheel clamp  80  disengages the front wheel rim  94  and allows the pivot yoke  76  to return to an equilibrium position. When the pivot yoke  76  comes to rest, tension in the positioning system cables  82 , 84 , 86  is released. As a result, the steering fork  44  and second wheel mounting assembly  18  return to their original positions, thus allowing the passenger support construction  12  to descend into its lowered, standard position. To increase the life of the cables  82 , 84 , 86 , the passenger support construction  12  rests upon bushings, not shown, when the passenger support construction is in the standard position. 
     The lift characteristics of the bicycle  10  are a product of the front and rear pulleys  100 , 104 . Although the pulleys  100 , 104  are round in the preferred embodiment, non-circular cams would also suffice. Using non-circular cams would produce lifting speeds that varied throughout the vertical travel of the passenger support construction  12 . 
     In the preferred embodiment, the bicycle  10  is a bicycle, and the above-mentioned pedal crankset  42  is part of a drive system  110  used to motivate the bicycle  10  from one location to another. The drive system  110  also includes a flexible drive band  112 , such as a chain or belt, that operatively engages a front drive gear  114  and a rear drive gear  116 . As seen in FIG. 1, the front drive gear  114  is linked to the pedal crankset  42 , and the rear drive gear  116  is linked to the rear wheel  68 . A rider sitting upon the seat  34  operates the pedals  42 , thereby rotating the front drive gear  114 . This pedaling motion turns the flexible band, or chain  112  and causes rotation of the rear drive gear  115  and the attached rear wheel  68 ; rear wheel rotation propels the bicycle  10  forward. 
     A cable-actuated rear brake assembly  118  slows the bicycle  10  by engaging the bicycle rear wheel  68 , as directed by the rider. The drive system may also include a chain tensioner  120  to ensure that the drive band  112  remains taut, engaging the drive gears  114 , 116  as the passenger support construction  12  moves up and down. The drive system  110  may alternatively be a motor-driven chain or shaft. Motor  120 ′ is mounted on the passenger support construction  12  and is connected to the drive system  110  by chain or shaft (not shown). 
     An alternate embodiment of the bike  210  is seen in FIGS. 6 through 10. In this embodiment, the bike  210  includes an alternate selective positioning system  22 ′. The selective positioning system  22 ′ includes a first lifting assembly  72 ′ and a second lifting  74 ′ assembly. These lifting assemblies  72 ′,  74 ′ are operatively connected with an energy transfer construction  70 ′. The first lifting assembly  72 ′ is responsible for vertical motion of the front portion of the passenger support construction  12 ′. The second lifting assembly  74 ′ is responsible for vertical motion of the rear portion  20 ′ of the passenger support construction  12 ′. The energy conversion construction  70 ′ works with the lifting assemblies  72 ′,  74 ′ to convert rotational energy of the front wheel into vertical motion of the passenger support construction  12 ′. 
     The first lifting assembly  72 ′ is shown in FIGS. 8,  9  and  10 . By way of overview, the first lifting assembly  72 ′ employs a pair of sprockets  212 , 214  and a linking chain  216  that joins the sprockets. The first lifting assembly  72 ′ cooperates with the energy conversion construction  70 ′, which includes an actuator assembly  228  that cooperates with a linkage construction  215 . Together, the actuator assembly  228  and linkage construction  215  transfer motion from the rotating sprockets  212 , 214  to a steering fork  44 ′ that movably supports the front  16 ′ of the passenger support construction  12 ′. The first lifting assembly  72 ′ will now be described in more detail. 
     As seen in FIG. 8, the first lifting assembly  72 ′ includes a drive sprocket  212  mounted on the front wheel axle  78 ′. A front wheel fork  48 ′ includes front mounting flanges  54 ′ at the lower end to support the front wheel axle  78 ′. The front wheel fork  48 ′ also includes a linking sleeve  50 ′ that, as described below, joins the front wheel fork to an included steering fork  44 ′. The steering fork  44 ′ is slidably mounted within the linking sleeve  50 ′. A lift sprocket  214  is operatively joined to the drive sprocket  212  by a linking chain  216 . With this arrangement, because the drive sprocket  212  and lift sprocket  214  are connected by the linking chain  216 , rotation of the drive sprocket produces rotation of the lift sprocket. Moreover, since the drive sprocket  212  rotates with the front wheel  52 ′, rotating the front wheel will produce concomitant rotation of the lift sprocket  214 . 
     The lift sprocket  214  is movably mounted on a lift sprocket axle  218 ; the sprocket axle is, in turn, rotatably mounted within a lift sprocket axle housing  220 . As best seen in FIGS. 9 and 10, the lift sprocket axle housing  220  is rigidly fixed on a mounting arm  222  that extends upward from the front wheel fork  48 ′. The lift sprocket  214  rotates around the lift sprocket axle  218  and also slides axially therealong. A lift crank  224  is also rigidly mounted on the lift sprocket axle  218 . More specifically, as seen in FIGS. 9 and 10, the lift sprocket  214  is slidably disposed on the sprocket axle  218 , between the lift crank  224  and the lift sprocket axle housing  220 . 
     An engagement pin  226  extends orthogonally from the lift crank  224 , extending toward the lift sprocket  214 . As seen in FIG. 6, the lift sprocket  214  is characterized by a series of engagement apertures, or cutouts  232 . Interaction between the engagement pin  226  and the lift sprocket cutouts  232  produces movement of the passenger support construction  12 ′ and will be described further below. 
     With continued reference to FIGS. 9 and 10, the first lifting assembly  72 ′ cooperates with the energy conversion construction  70 ′. The energy conversion construction  70 ′ employs the actuator assembly  228  and the linkage construction  215  to convert rotational energy into vertical motion. The actuator assembly  228  moves the lift sprocket  214  between an engaging position, shown in FIG. 10, and a disengaging position, shown in FIG.  9 . With reference to FIG. 6, the actuator assembly  228  is controlled by a clamp lever  88 ′, which is linked to the actuator assembly via a control cable  92 ′. Squeezing the clamp lever  88 ′ causes a sprocket plunger  230  to push the lift sprocket  214  along the lift sprocket axle  218 , away from the lift sprocket axle housing  220 . When this occurs the lift sprocket  214  moves into the engaging orientation. A return spring  231  biases the lift sprocket  214  into the non-engaging position when the clamp lever  88 ′ is released. 
     In the engaging position, the lift sprocket  214  is forced against the lift crank  224 , and the engagement pin  226  passes through one of the lift sprocket cutouts  232 . With the lift sprocket  214  in the engaging position, wherein the engagement pin  226  passes through one of the cutouts  232 , the lift crank  224  will rotate in tandem with the lift sprocket. 
     As seen in FIGS. 6, and  7 , the steering fork  44 ′ is movably joined to the lift sprocket  214  by a linklage construction  215 . The linkage construction  215  includes the lift crank  224  and a rigid positioning arm  234 . The first end  236  of the positioning arm  234  is pivotally attached to the lift crank  224 , and the second end  238  of the positiong arm is pivotally attached to the steering fork apex  240 . 
     When the engagement pin  226  engages the lift sprocket  214 , rotation of the lift sprocket results in joint motion of the lift crank  224  and the positioning arm  234 . In turn, because the positioning arm  234  is connected to the steering fork  44 ′, movement of the positioning arm produces relative motion between the steering fork and the front wheel fork  48 ′. More particularly, and with respect to FIG. 7, as the lift sprocket  214  turns the lift crank  224 , the positioning arm  234  acts as a piston, forcing the steering fork  44 ′ to slide within the linking sleeve  50 ′. 
     By way of example, squeezing the clamp lever  88 ′ when the front wheel  52  is rotating forces the lift sprocket  214  into the engagement position and causes the lift crank  224  to rotate. As the front wheel  52 ′ continues to rotate, rotational energy from the front wheel is transferred to the steering fork apex  240  through the lift crank  224  and positioning arm  234  of the linkage construction  215 . As the lift crank  224  continues to rotate, the angle between the lift crank  224  and positioning arm  234  changes, and the steering fork translates within the linking sleeve  50 ′. Although other configurations are possible, FIG. 7 shows a preferred embodiment, wherein the passenger support construction  12 ′ is at a maximum lift position when the angle between the lift crank  224  and the positioning arm  234  is approximately one-hundred-eighty degrees. 
     As mentioned above, this embodiment of the selective positioning system  22 ′ includes a second lifting assembly  74  that lifts the rear portion  20 ′ of the passenger support construction  12 ′. As seen in FIGS. 6 and 7, the alternate second lifting assembly  74 ′ is similar to the primary embodiment of the second lifting assembly  74 , shown in FIG.  1 . As with the primary embodiment, the alternate embodiment of the second lifting assembly  74 ′ is responsible for producing rotational movement of the rear wheel mounting assembly  18 ′ with respect to the passenger support construction  12 ′. With particular reference to FIG. 6, the rear wheel mounting assembly  18 ′ included in this embodiment of the bicycle  210  is essentially the same as the primary embodiment of the second wheel mounting assembly  18 . 
     Now with continued reference to FIG. 6, although similar to the primary embodiment of the second lifting assembly  74 , the alternate second lifting assembly  74 ′ is different from the primary embodiment in several ways. The second lifting assembly  74 ′ includes a single lift cable  242  that is securely fixed at a first end  244  to the wheel fork vertex  246  and at a second end  248  to the passenger support construction down tube  30 ′. The path of the lift cable  242  is guided by a front pulley  250  mounted just below the steering fork apex  240  and a rear pulley  252  that is affixed to the rear wheel mounting assembly control vertex  62 ′. With this arrangement, the above-described translational motion of the steering fork  44 ′ within the linking sleeve  50 ′ produces pivotal motion of the rear wheel mounting assembly  18 ′ with respect to the passenger support construction  12 ′. As a result, squeezing the clamp lever  88 ′ to place the lift sprocket  214  in the engagement position not only causes the linkage construction  215  to force the front  16 ′ of the passenger support construction  12 ′ upward, it also causes the rear wheel mounting assembly  18 ′ to pivot with respect to the passenger support construction  12 ′, thereby forcing the rear  20 ′ of the passenger support construction upward. 
     Operation of this embodiment of the selective positioning system  22 ′ will now be described. When the bicycle  210  is in motion, both the front wheel  52 ′ and the rear wheel  68 ′ rotate. The drive sprocket  212  rotates along with the front wheel  52 ′. Rotation of the drive sprocket  212  causes the linking chain  216  to turn the lift sprocket  214 , thereby causing the lift sprocket to rotate about the lift sprocket axle  218 . 
     When a rider, not shown, wishes to lift the passenger support construction  12 ′, he squeezes the clamp lever  88 ′. As the clamp lever  88 ′ is squeezed, the control cable  92 ′ tightens, causing the sprocket plunger  230  to pivot, thereby forcing the lift sprocket  214  toward the lift crank  224 . As the lift sprocket  214  moves toward the lift crank, and into the engaging position, the engagement pin  226  passes into one of the lift sprocket cutouts  232 , resulting in tandem motion of the lift crank  224  and lift sprocket  214 . As discussed above, because the drive sprocket  212  and lift sprocket  214  are joined via the linking chain  216 , rotating the drive sprocket will rotate the lift sprocket. 
     As the lift sprocket  214  and lift crank  224  continue to rotate, the angle between lift crank  224  and positioning arm  234  changes, and the positioning arm forces the steering fork  44 ′ to slide within the linking sleeve  50 ′, thereby moving the passenger support construction upward with respect to the front wheel  52 ′. In keeping with the objectives of the present invention, raising the steering fork  44 ′ causes the lift cable  242  to travel along the front and rear pulleys  252 , 252 , thereby causing the rear wheel mounting assembly  18 ′ to pivot downward with respect to the passenger support construction  12 ′. 
     The steering fork  44 ′ translation and rear wheel support  18 ′ rotation occur at essentially the same time. Together, these motions cooperatively lift the passenger support construction  12 ′ with respect to the wheels  52 ′,  68 ′, from a standard position, shown in FIG. 6, into an elevated position, shown in FIG.  7 . When the clamp lever  88 ′ is released, the return spring  231  urges the sprocket plunger  230  into the disengaging position, thereby allowing gravity-assisted return of the passenger support construction  12 ′ into the standard position. If the rider squeezes the clamp lever  88 ′ for an extended period of time, the passenger support construction  12 ′ will alternately move up and down, in response to the changing angle between the lift crank  224  and positioning arm  234 . 
     Although the invention has been described in terms of a specific embodiment, it will be readily apparent to those skilled in this art that various modifications, rearrangements and substitutions can be made without departing from the spirit of the invention. The scope of the invention is defined by the claims appended hereto.