Attachment assembly for tandem wheeled vehicles

Abstract

An attachment assembly for tandem wheeled vehicles comprises a double caster unit that is releasably coupleable to a frame element of a forward vehicle of the tandem wheeled vehicles and an arm assembly which is releasably coupleable to the double caster unit and to a frame element of a rear vehicle of the tandem wheeled vehicles, wherein the double caster unit is configured with two swiveling caster wheels that are alignable with one other along a direction of travel.

Description

[0001] - 1 - ATTACHMENT ASSEMBLY FOR TANDEM WHEELED VEHICLES

[0002] Field of the Invention

[0003] The present invention relates to the field of attachment devices. More particularly, the invention relates to an attachment assembly for use in guiding a second wheeled vehicle that is attached to a first wheeled vehicle in tandem fashion.

[0004] Background of the Invention

[0005] Wheelchairs designed for manual propulsion by a user with limited walking ability have large nonpivoting rear wheels and smaller front caster wheels, allowing the wheelchair user to access the rear wheel and propel himself while being seated by rotating the rear wheels. A turn is made possible by applying a force on one of the rear wheels to cause the caster wheels to swivel about a vertical axis and the wheelchair to rotate about a rotation center located approximately equidistantly between the two non-pivoting rear wheels and with a turning radius defined by the arc traced by the outer caster wheel with respect to the center of rotation.

[0006] Wheelchair users are occasionally required to independently guide another wheeled vehicle, such as a shopping cart or a baby carriage, in tandem fashion. However, these tandem guiding wheelchair users often have difficulty in guiding the two vehicles when turning since each of the two vehicles may have a set of non-pivoting rear wheels. Although the wheelchair is able to be easily turned by the wheelchair user as described above, the turning motion is restricted or is rendered impossible when the front caster wheels are attached to the rear non-rotating wheels of the second wheeled vehicle. A successful turning operation can be successfully completed only if the wheelchair user overcomes the unwanted braking force exerted by the non-pivoting wheels of the second wheeled vehicle. Often the wheelchair user, or any other unimpaired user, lacks the required stamina to perform such a tiring activity.

[0007] Another difficulty encountered by tandem guiding wheelchair users is one of stability. Stability of a wheelchair is able to be achieved when the gravity-influenced line of action applied at the combined center of mass of the wheelchair and user remains between the point of contact of each wheel and the underlying ground surface. When one of the wheels traverses a small obstacle, the line of action generally remains between the points of contact as the wheelchair is caused to tilt only slightly. However, the wheelchair and wheelchair user are significantly tilted when uneven terrain is traversed, causing their stability to become compromised. This problem of instability is exacerbated when a second wheeled vehicle attached to the wheelchair also traverses the uneven terrain.- 2 -

[0008] It is an object of the present invention to provide an attachment assembly for tandem wheeled vehicles that facilitates an easy to perform turning operation.

[0009] It is an additional object of the present invention to provide an attachment assembly for tandem wheeled vehicles that has improved stability relative to prior art apparatus.

[0010] It is an additional object of the present invention to provide an attachment assembly for tandem wheeled vehicles that facilitates connection to the rear non-rotating wheels of the second wheeled vehicle without having to lift the rear wheels of the second wheeled vehicle off the ground.

[0011] Other objects and advantages of the invention will become apparent as the description proceeds.

[0012] Summary of the Invention

[0013] An attachment assembly for tandem wheeled vehicles comprises a double caster unit that is releasably coupleable to a frame element of a forward vehicle of the tandem wheeled vehicles and an arm assembly which is releasably coupleable to said double caster unit and to a frame element of a rear vehicle of the tandem wheeled vehicles, wherein said double caster unit is configured with two swiveling caster wheels that are alignable with one other along a direction of travel.

[0014] The rear vehicle may be a wheelchair or a different type of wheeled vehicle.

[0015] In one aspect, the arm assembly comprises a mounting member which is releasably coupleable to the double caster unit, and an elongated arm pivotally mounted at a first end on the mounting member so as to be pivotally displaceable about a horizontal axis and pivotally attached at a second end to a bracket that is fixedly attached to the frame element of the rear vehicle of the tandem wheeled vehicles.

[0016] In one aspect, the double caster unit comprises a first latch unit for facilitating releasable engagement with the mounting member of the arm assembly and a second latch unit for facilitating releasable engagement with the frame element of the forward vehicle of the tandem wheeled vehicles.

[0017] In one aspect, a latch of each of the first and second latch units is capable of being manipulated by a finger and is spring loaded so as to return to an original position after being manipulated.-3 -

[0018] In one aspect, the double caster unit comprises the two caster wheels each of which having a horizontal axle, a fork unit to which the horizontal axle of a corresponding caster wheel is rotatably mounted and provided with a surface overlying the corresponding caster wheel, two swivel joint mounts, and a rod protruding upwardly from the overlying surface, inserted within a corresponding swivel joint mount and rotatably secured therein to facilitate 360-degree rotation of the fork unit and to ensure contact with an underlying ground surface.

[0019] In one aspect, the double caster unit is advanceable in a sideways direction relative to a previous forward or rearward direction when the two caster wheels have swiveled 90 degrees during a maneuver from the forward or rearward direction to the sideways direction.

[0020] A carriage constituting the forward vehicle of the tandem wheeled vehicles and guidable by a user of the rear vehicle of the tandem wheeled vehicles comprises two of the attachment assemblies, each double caster unit of the two attachment assemblies being coupled to a corresponding carriage frame element in such a way so as to rearwardly support a corresponding lateral side of the carriage while traversing an underlying ground surface.

[0021] In one aspect, each double caster unit of the two attachment assemblies is releasably coupled to the corresponding carriage frame element.

[0022] In one aspect, each of the double caster units is replaceable with a dedicated non-pivoting wheel that is rotatably mountable to the corresponding carriage frame element.

[0023] In one aspect, the carriage is directly guidable by an unimpaired ambulatory user when each of the double caster units is coupled to the corresponding carriage frame element and is disengaged from a corresponding arm assembly.

[0024] In one aspect, the carriage is advanceable in a sideways direction relative to a previous forward direction or rearward direction when all caster wheels of the two attachment assemblies have swiveled 90 degrees during a maneuver from the forward or rearward direction to the sideways direction.

[0025] A set of tandem wheeled vehicles comprising the carriage and a wheelchair that constitutes the rear vehicle of the tandem wheeled vehicles.-4 -

[0026] The wheelchair may be designed for manual propulsion, a motorized wheelchair, or a wheelchair that is controllable by a joystick.

[0027] In one aspect, the second end of the arm is vertically displaceable while pivoting about a bar of the bracket when one or both of the carriage and wheelchair traverses an obstacle to ensure that at least one of the caster wheels of each attachment assembly remains in stable contact with an underlying ground surface.

[0028] Brief Description of the Drawings

[0029] In the drawings:

[0030] - Fig. 1 is a perspective view of tandem wheeled vehicles, showing two attachment assemblies according to an embodiment for interconnecting the tandem wheeled vehicles, when advancing forwardly;

[0031] - Fig. 2 is a perspective view of the attachment assembly of Fig. 1, when detached from each of the tandem wheeled vehicles;

[0032] - Fig. 3 is an exploded view of the attachment assembly of Fig. 2;

[0033] - Figs. 4A and 4B are a vertical cross section of the attachment assembly of Fig. 3 cut through the bores in the double caster unit adapted to receive an arm-associated lock pin, shown prior to, and following, respectively, the engagement of the arm assembly and double caster unit;

[0034] - Figs. 5A and 5B are a horizontal cross section of the double caster unit of Fig. 3, showing two positions of a latch which prevent and permit, respectively, the disengagement of the arm assembly and double caster unit;

[0035] - Figs. 6A and 6B are two exploded views, respectively, of the double caster unit of Fig. 3;

[0036] - Fig. 7 is a vertical cross section of the attachment assembly of Fig. 2 cut through the casing of the double caster unit, showing a spacer of a carriage-latch unit when engaged with a positioning element;

[0037] - Figs. 8A and 8B are another perspective view of the attachment assembly of Fig. 2, showing the carriage facing side of female and male double caster units, respectively;

[0038] - Fig. 9A is a vertical cross section of the attachment assembly of Fig. 2 and of a carriage frame element prior to being coupled together;

[0039] - Fig. 9B is a vertical cross section of the attachment assembly of Fig. 2 and of a carriage frame element after being coupled together;

[0040] - Fig. 9C is a perspective view of the attachment assembly of Fig. 2 and of the carriage frame element after being coupled together;-5 - - Figs. 10A and 1OB are a vertical cross section of the double caster unit of Fig. 3, showing a brake actuator in first and second pivotal positions, respectively;

[0041] - Fig. 11 is a perspective view of a carriage, shown mounted with rear wheels that have replaced corresponding attachment assemblies of Fig. 2;

[0042] - Fig. 12 is a side view of an attachment assembly, showing a circle traced about a double caster unit that is set to a decreased-size configuration, to indicate the geometrical similarity to the rear wheel of Fig. 11; and

[0043] - Figs. 13A-E is a side view of the double caster unit of Fig. 3, showing five combinations, respectively, of the orientation of the two caster wheels that are rotatably mounted thereto.

[0044] Detailed Description of the Invention

[0045] A wheelchair user who is impaired and has limited walking ability is able to independently and effortlessly guide another wheeled vehicle in tandem fashion, which may be referred to as the "forward wheeled vehicle", "forward vehicle" or "guided vehicle", in conjunction with an attachment assembly attached to the wheelchair that comprises a double caster unit adapted to replace each of the conventional rear non-pivoting wheels of the forward wheeled vehicle. By replacing each of the conventional rear non-pivoting wheels of the forward wheeled vehicle with freely rotating 360-degree caster wheels, the rear wheels of the forward vehicle no longer apply a braking force during a turning motion and enable the wheelchair user to guide the forward vehicle along relatively smallradius turns. Also, the two opposed sets of double caster units ensure increased contact with the underlying ground surface, even when uneven, relative to the conventional rear wheels to provide increased stability.

[0046] The following description relates to an arrangement whereby a wheelchair is attached to a baby carriage or stroller in tandem fashion, but it will be appreciated that the attachment assembly can be used in conjunction with other suitable tandem wheeled vehicles, mutatis mutandis.

[0047] As an introduction, Fig. 1 illustrates a baby carriage 5 that is attached to a wheelchair 15 in tandem fashion using a pair of attachment assemblies 20 according to one embodiment. Each attachment assembly 20 comprises a double caster unit 25 that is releasably coupled to a lower carriage frame element 7 by a corresponding carriage-latch unit 21, and a pivotal arm assembly 35 which is attached to both a corresponding double caster unit 25 and a frame element 19 of wheelchair 15, for example a substantially vertical frame element that extends to a footrest.-6 - Baby carriage 5 may advantageously be directly wheeled by a user, such as an unimpaired ambulatory user, when each double caster unit 25 is separated from the corresponding frame element 7 and is replaced with a dedicated non-pivoting wheel, which is capable of being rotatably mounted to frame element 7. For purposes of brevity, the term "carriage" is interchangeable with "stroller". Alternatively, carriage 5 may be directly wheeled by the user when the two caster units 25 are coupled to a corresponding frame element 7 instead of the non-pivoting wheels, but when the arm assemblies 35 are detached.

[0048] An enlargement of an assembled attachment assembly 20 is illustrated in Fig. 2. As shown, double caster unit 25 is configured with an upper casing 22, to an upper surface 23 of which mounting member 31 of arm assembly 35 is removably attached. Casing has two parallel vertical walls 27a-b between which upper surface 23, which is rounded at the sides, is interposed. Casing 22 is attached to a concealed support member, to which carriage-latch unit 21 is operatively connected and to which a swivel joint of each of the two caster wheels 32a-b enabling 360-degree directional movement is rotatably mounted. A manual brake actuator 28 is rotatably mounted on the two forks 26 of one of the caster wheels.

[0049] Mounting member 31 has a thickened element through which vertical lock pin 33 for releasable attachment with casing upper surface 23 is introduced, and two horizontally spaced and apertured vertical support elements 36 by which the carriage-end of elongated arm 37 is pivotally mounted. The carriage-end 37a of arm 37 is pivotally displaceable about horizontal pin 38 introduced through the corresponding aperture of each support element 36, allowing the wheelchair-end 37b of arm 37 to be vertically displaced when one or both of the carriage and wheelchair traverses a small obstacle while ensuring that at least one of caster wheels 32a-b of each attachment assembly 20 remains in stable contact with the underlying ground surface. The wheelchair-end 37b of arm 37 is pivotally connected to a bracket 17 that is adapted to be fixedly connected to a tubular frame element of the wheelchair. A handle 39, which may be curved and spring loaded, is attached to wheelchair-end 37b of arm 37, and assists in manipulation of arm 37 when being coupled to bracket 17.

[0050] Attachment assembly 20 when disassembled is illustrated in Fig. 3.

[0051] Bracket 17 is shown to be configured with two portions 18a and 18b of semicircular cross section that are engageable with the tubular frame element of the wheelchair and define a tubular recess 16 therebetween that are capable of being brought closer to and further away from each other without being completely separated. In addition to the semicircular surface that faces recess 16, each of the-7 -two portions 18a and 18b has a substantially planar exterior wall. Bracket 17 also has a wall 14 substantially parallel to the exterior wall of semicircular portion 18a and a bar 13 extending from semicircular portion 18a to wall 14. The wheelchair-end 37b of arm 37 is configured with a semielliptical groove 41 within which bar 13 is receivable when arm 37 is being coupled with bracket 17 and which defines a terminal wall 43, which may be curved. To prevent disengagement of arm 37 from bracket 17, wheelchair-end 37b may be configured with an interior provided between two spaced end plates within which handle 39 is pivotally displaceable. In addition to the arcuate portion 39a that extends upwardly from wheelchair-end 37b, the handle may be configured with a C-shaped portion 39b extending downwardly and in an opposite rotational direction to portion 39a, as shown in Fig. 4B. When handle 39 is pivoted in a counterclockwise direction according to the illustrated orientation, C-shaped portion 39b is pivoted towards, and is engaged with, terminal wall 43. Bar 13 is thus firmly embraced by C-shaped portion 39b at one side and by terminal wall 43 at the other side. A spring (not shown) is biased to urge C-shaped portion 39b in engagement with terminal wall 43, and is forced to expand when handle is pivoted in the opposite rotational direction, i.e. the clockwise direction according to the illustrated orientation.

[0052] Casing upper surface 23 is configured with a bored raised member 47, and lock pin 33 is adapted to be releasably received and engaged in the vertical bore 49 (Fig. 4A) formed therethrough. Lock pin 33, such as one that is spring loaded, may be configured with an internal cylindrical spindle that is surrounded by a cylindrical shaft formed with one or more circumferential passages. A spring fitted in a passage may be compressed within the shaft when engaged by a surrounding engaging element. Upon releasing lock pin 33 from the engaging element, one arm assembly 35 may be replaced with another, such with an arm of a different length. Additionally, disengagement of the two arm assemblies 35 from the corresponding double caster unit 25 facilitates direct wheeling of the stroller, while unconnected to a wheelchair and without encountering interference from a protruding arm assembly. Fig. 4A illustrates arm assembly 35 when disengaged from double caster unit 25, and Fig.

[0053] 4B illustrates arm assembly 35 when coupled with double caster unit 25.

[0054] Reference is now made to Fig. 6A, which illustrates the support member 42 of double caster unit 25, when separated from casing 22. Support member 42 has a horizontal plate 44 from which two tubular swivel joint mounts 46 for use in rotatably mounting the swivel joint of a corresponding caster wheel 32a-b shown in Fig. 6B and two spaced mounting posts 48 upwardly protrude. Horizontal plate 44 is divided into two sections, and a semicircular rim 51 for abutment with a circular carriage-latch unit protective cover 53 extends downwardly between the two spaced horizontal plate sections. Recessed from the outer edge of rim 51 is a vertical support plate 56 that is- 8 -delimited by the rim below horizontal plate 44 and that also vertically extends thereabove, which for example assumes a truncated triangular configuration above the horizontal plate. A plan view of horizontal plate 44, swivel joint mounts 46 and mounting posts 48 is shown in Figs. 5A-B.

[0055] As shown in Fig. 6B, the horizontal axle 57 of each caster wheel 32a-b is mounted in a fork unit 30 comprising two opposed curved forks 26, an upper planar interconnecting element 34 that interconnects the two forks, and rod 52 protruding upwardly from interconnecting element 34. Rod 52 is inserted within corresponding swivel joint mount 46 and is rotatably secured therein by bearing elements 69 to facilitate the 360-degree rotation of fork unit 30. Brake actuator 28 may be pivotally connected to the two forks 26 of caster wheel 32b, which may be the rear caster wheel of the double caster unit. Alternatively, the fork unit may interface with another type of swivel joint well known to those skilled in the art.

[0056] As shown in Figs. 10A-B, mechanical brake actuator 28 comprises a first component 143 that includes an elongated substantially planar pedal portion 141 protruding rearwardly from interconnecting element 34 of the fork unit and a triangular toothed portion 144 pointing away from the pedal portion, and a second component 146 configured as a triangular toothed portion. Both first component 143 and second component 146 are pivotally displaceable about pin 149, which extends between both forks 26 of the fork unit and below interconnecting element 34, and are generally in engagement with each other as a result of the mutual contact provided by adjacent sides.

[0057] Brake actuator 28 is in a first pivotal position in Fig. 10A whereby pedal portion 141 is substantially parallel to the underlying ground surface, and the first and second components are configured such that the apex of toothed portion 144 of the first component is slightly spaced from caster wheel 32b and a second side 147 of the second component is angularly spaced from the underside of interconnecting element 34. Consequently, caster wheel 32b is unrestricted, and is free to rotate about axle 57 and to swivel about the axis of rod 52.

[0058] Brake actuator 28 is in a second pivotal position in Fig. 10B. In this second pivotal position, the apex of toothed portion 144 of the first component, and possibly the apex of the toothed second portion 146, engages the periphery of caster wheel 32b to prevent rotation of the caster wheel. Also, second side 147 of the second component frictionally engages the underside of interconnecting element 34 to prevent a swiveling action about the axis of rod 52.- 9 - In one embodiment, the first and second components of brake actuator 28 are able to be disengaged from each other, so that second component 146 is able to remain in the second pivotal position to prevent swivel wheel 32b from swiveling while first component 143 is able to set to the first pivotal position to permit rotation of the caster wheel.

[0059] Fig. 7 illustrates the connection of corresponding elements of casing 22 and support member 42. One vertical wall 24 of casing 22 is complementary to the truncated triangular vertical support plate 56 of support member 42, and is ensured of being in abutting relation therewith by means of the interconnection of each mounting post 48 of support member 42 and a corresponding upright 27 of casing 22.

[0060] As shown in Figs. 3, 4A-B, 6A, 7 and 9A, double caster unit 25 is also configured with an auxiliary bore 72 that is aligned with bore 49 when casing 22 and support member 42 are interconnected. Auxiliary bore 72 is formed in tube 74 that is fitted in the centerline of triangular vertical support plate 56 of support member 42 and in planar guide plate 77 provided at the top of tube 74, which coincides with the horizontal line of truncation of the triangular support plate. When an arm assembly 35 is engaged with double caster unit 25, lock pin 33 is inserted in both bore 49 and auxiliary bore 72. Horizontal interspace 64, within which arm latch 62 for releasably engaging lock pin 33 is receivable and displaceable, is defined between guide plate 77 and the bottom edge of vertically oriented posts 81a-b provided with raised member 47. Stroke-limiting walls 83a-b extend vertically upwardly from corresponding edges of guide plate 77.

[0061] The structure and operation of arm latch 62 are shown with reference to Figs. 3-5, 6A and 9A. Arm latch 62 is a rectangular finger-driven plate that is fitted in horizontal interspace 64 provided in a recessed portion 66 of casing wall 27a which is adjacent to casing upper surface 23, so as to be supported by, and slidable along, guide plate 77. The rectangular plate is formed with a main aperture 67, e.g. elliptical, and with a secondary aperture 68, e.g. circular, in communication with, and significantly smaller than, the main aperture. Two thin abutting elements 61 and 63 extend in opposite directions from a corresponding long edge of arm latch 62, at the end thereof closest to casing wall 27b.

[0062] Main aperture 67 is sized to movably receive lock pin 33, when introduced through bore 49, while secondary aperture 68 is sized to frictionally engage the spindle of lock pin 33. The outer diameter of lock pin 33 slightly protrudes outwardly from one or more recessed circumferential passages within each of which a corresponding spring (not shown) is fitted. When the lock pin is introduced through- 10-bores 49 and 72 and through main aperture 67, the internal edge of arm latch 62 that delimits the main aperture freely surrounds each circumferential passage. Following movement of arm latch 62 in one direction, the internal edge that delimits secondary aperture 68 is received within one of the recessed circumferential passages and sufficiently urges compression of the spring to maintain lock pin 33 in a locked condition. Movement of arm latch 62 in an opposite direction releases lock pin 33.

[0063] The long edges of rectangular arm latch 62 passing through horizontal interspace 64 extend between two opposed short edges 76 and 78 thereof. The first edge 76 is adapted to protrude from recessed portion 66 of casing wall 27a, as shown in Figs. 2 and 5A. The second edge 78 is engaged with a spring 73 that is in contact at the other end with casing wall 27b and supported from below. After protruding first edge 76 is finger driven, spring 73 is caused to become compressed by second edge 78. Spring 73 is biased such that, when relaxed as shown in Fig. 5A, lock pin 33 is engaged with secondary aperture 68 and unable to be removed from arm latch 62 and raised member 47, and when compressed as shown in Fig. 5B, the lock pin is unrestricted and able to be released from arm latch 62 and raised member 47. Following manipulation of lock pin 33, the force applied onto arm latch 62 is released and spring force return the arm latch to the position shown in Fig. 5A. The horizontal displacement of arm latch 62 is limited by abutting elements 61 and 63 upon contact with a projecting end surface of guide plate 77.

[0064] The coupling of a double caster unit with an existing corresponding lower carriage frame element 7 is illustrated in Figs. 6-9.

[0065] The double caster unit may be a female double caster unit 25A shown in Fig. 8A wherein its carriagelatch unit 21A is configured with a central tubular cavity 92 for receiving a horizontal lock pin 98 protruding from a male carriage frame element 7A shown in Fig. 9A.

[0066] Alternatively, the double caster unit may be a male double caster unit 25B shown in Fig. 8B wherein its carriage-latch unit 21B is configured with a central protruding tubular rod 96 for insertion within the central tubular cavity provided with a female carriage frame element.

[0067] If so desired, female double caster unit 25A may be converted to a male double caster unit by coupling tubular rod 96 within central tubular cavity 92.

[0068] The following description of a carriage-latch unit by which a double caster unit is coupled with a corresponding carriage frame element will be made with respect to a female double caster unit, but- 11 -it will be appreciated that the structure is also applicable to a male double caster unit, mutatis mutandis.

[0069] As shown in Fig. 8A, central cavity 92 of female carriage-latch unit 21A is delimited by horizontal-axis tube 93, which is secured by two laterally extending horizontal plate sections 44, two vertical plates 91 each downwardly extending from the connection of a corresponding plate 44 and tube 93, a vertical plate 94 upwardly extending from the periphery of tube 93, and two oblique plates 97 each positioned between vertical plate 94 and a corresponding horizontal plate 44. Plates 44, 91, 94 and 97 are integrated with circular boundary 99, which axially protrudes from vertical support plate 56 (Fig. 6A).

[0070] As shown in Figs. 6A-B, walls 27a-b of casing 22 are each configured with a semicircular opening 29 for engagement from above with circular boundary 99 and with circular carriage-latch unit protective cover 53, respectively. The two semicircular openings 29 may have identical dimensions.

[0071] Carriage-latch unit 21A comprises positioning element 106 axially protruding from support plate 56 in a direction away from circular boundary 99 that is configured for example with orthogonal elements defining the illustrated rectangular boundary within which cavity 92 is included, angled latch 103, protective cover 53, and spacer 102 axially protruding from planar protective cover 53 and configured to be engaged with two or more boundary elements of positioning element 106, to ensure correct positioning of the spacer. It will be appreciated that spacer 102 may be configured in other ways as well, as long as it is suitably peripherally engaged by a complementary positioning element.

[0072] Latch 103 has a first planar wall 101 that is adapted to be engaged with vertical support plate 56 and that is configured with a variably shaped aperture 107, and a second planar wall 108 that is considerably shorter than first wall 101 and angled, e.g. perpendicularly angled, with respect to the first wall. The bottom of first wall 101 may be provided with a spring 104.

[0073] Protective cover 53 may be integrally formed with spacer 102 and with two laterally spaced mounting pegs 109. Each mounting peg 109 is adapted to be securely received in a corresponding hole 58 formed in vertical support plate 56 below horizontal plate 44 and laterally spaced from positioning element 106, such as by frictional engagement. Protective cover 53 is also formed with a central finger-insertable recess 59 that has a sufficient depth and width to allow a finger inserted within the recess to access the second latch wall.- 12-

[0074] Fig. 7 illustrates an exemplary configuration of spacer 102, which is shown for illustrative purposes when separated from the protective cover but which is, as explained above, formed integrally with the protective cover. Spacer 102, which is shown without the latch, has a vertical length shorter than the protective cover.

[0075] The straight periphery of spacer 102 is shown to be engaged with boundary elements of positioning element 106, while pegs 109 are shown to be engaged with corresponding holes formed in vertical support plate 56, such that each is laterally spaced from positioning element 106. An upper end of spacer 102 is formed with an aperture 111 within which second latch wall 108 (Fig. 6B) is receivable and vertically displaceable.

[0076] When the protective cover provided with the integrally formed spacer 102 is coupled by pegs 109 with vertical support plate 56, a thin vertical interspace is defined between vertical support plate 56 and spacer 102. This interspace is sized to allow first latch wall 101 to be received and vertically displaceable therewithin while being maintained in an essentially vertical disposition as a result of secured contact with both vertical support plate 56 and spacer 102.

[0077] Fig. 9A illustrates latch 103 after its first wall has been placed in abutting relation with vertical support plate 56 and with spacer 102, and protective cover 53 has been coupled with the vertical support plate. Spacer 102 is shown to be formed with a secondary cavity 112 that is axially aligned with cavity 92 when protective cover 53 is coupled with vertical support plate 56. The default position of latch 103 is as shown whereby the second latch wall is in contact with the bottom wall of aperture 111 (Fig. 7). At this default position, spring 104 is in contact with the lower surface of spacer 102. The length of the second latch wall is sufficiently long to be accessed by a finger within recess 59.

[0078] Immediately prior to coupling protective cover 53 with vertical support plate 56, latch 103 is positioned between vertical support plate 56 and spacer 102 to assume its default position. At this default position, the small-width portion of variably shaped aperture 107 of latch 103 is aligned with both cavity 92 and secondary cavity 112 and male carriage frame element 7A is able to be coupled with female double caster unit 25A. In order to insert lock pin 98 through latch 103, the large-width portion of variably shaped aperture 107 should be aligned with cavities 92 and 112 by pushing latch 103 upwards.- 13- As shown in Figs. 9A and 9C, carriage frame element 7A comprises bifurcated bracket 123 connected at the bottom of an oblique support bar 131 of carriage 5, generally at the intersection with a horizontal rear frame bar 136 when employed, planar extension 126 that extends away from support bar 131, i.e. in a rearward direction when carriage 5 is the forward vehicle, horizontal lock pin 98 that is fixedly and perpendicularly connected to extension 126 close to a terminal end thereof, and an abutment 128, e.g. annular, which surrounds horizontal lock pin 98.

[0079] Since horizontal lock pin 98 protrudes from abutment 128, frame element 7A is easily coupled with double caster unit 25A. Lock pin 98 is inserted through cavities 92 and 112 and the small-width portion of variably shaped aperture 107 of latch 103, as shown in Fig. 9B, until abutment 128 contacts boundary 99 (Fig. 8A). A circumferential passage of lock pin 98 is engaged by an edge of the small-width portion of variably shaped aperture 107 of latch 103 to prevent additional displacement of the latch. When latch 103 is raised within aperture 111 upon contacting its second wall such as with a finger, the edge of the small-width portion of variably shaped aperture 107 is disengaged from the circumferential passage and the large-width portion of variably shaped aperture 107 is caused to surround lock pin 98. Consequently, lock pin 98 is free to be displaced and removed from cavities 92 and 112.

[0080] After double caster unit 25A is separated from frame element 7A, a removable non-pivoting rear wheel 65a for use with carriage 65 shown in Fig. 11 may be mounted on lock pin 98 of frame element 7A. Wheel 65a may be provided with a bearing to facilitate wheel rotation when mounted on lock pin 98.

[0081] As shown in Fig. 12, removable non-pivoting wheel 65a is geometrically similar to, and has the same diameter as, a circle traced along the radially outwardly curved periphery of casing 22 and of the corresponding fork 26 of caster wheels 32a-b, when cavity 92 (Fig. 9A) is the center of the circle and the double caster unit is urged to a decreased-size configuration such as during a turning operation whereby the two forks are provided with mirror symmetry following a swiveling action. The geometrical similarity between a decreased-size double caster unit and non-pivoting wheel 65a is of much significance when the carriage is being transported as the double caster unit will be ensured of not interfering with a folded carriage frame element. The ground-engaging peripheral portion of caster wheels 32a-b is sized to be slightly more spaced from the central cavity than that of removable wheel 65a to ensure increased contact with the underlying ground surface.- 14- Since caster wheels are self-aligning while swiveling in accordance with the direction of travel, there are many combinations of the orientation of the two caster wheels of a double caster unit while the guided vehicle on which the double caster unit traverses an underlying ground surface.

[0082] Figs. 13A-E illustrate five combinations, respectively, of the orientation of caster wheels 32a-b rotatably mounted to a double caster unit 25.

[0083] Fig. 13A illustrates double caster unit 25 when both caster wheels 32a-b are advancing forwardly, the two caster wheels being aligned along the direction of travel. In Fig. 13B, the double caster unit has reversed its direction and both caster wheels 32a-b are advancing rearwardly with respect to the original direction of travel. In Fig. 13C, the double caster unit is undergoing a turning operation whereby caster wheel 32b is at the center of the turn and caster wheel 32a is urged to change its orientation. Alternatively, brake actuator 28 is operated to prevent caster wheel 32b from swiveling while allowing it to rotate about axle 57, or caster wheel 32a is unloaded, urging the double caster unit to a decreased-size configuration. In Fig. 13D, the double caster unit is advancing in a sideways direction relative to a previous forward direction, and both of caster wheels 32a-b have swiveled 90 degrees. In Fig. 13E, the double caster unit is undergoing a turning operation whereby caster wheel 32a is at the center of the turn and caster wheel 32b is urged to change its orientation.

[0084] While some embodiments of the invention have been described by way of illustration, it will be apparent that the invention can be carried out with many modifications, variations and adaptations, and with the use of numerous equivalents or alternative solutions that are within the scope of persons skilled in the art, without exceeding the scope of the claims.

Claims

- 15- CLAIMS1. An attachment assembly for tandem wheeled vehicles, comprising a double caster unit that is releasably coupleable to a frame element of a forward vehicle of the tandem wheeled vehicles and an arm assembly which is releasably coupleable to said double caster unit and to a frame element of a rear vehicle of the tandem wheeled vehicles, wherein said double caster unit is configured with two swiveling caster wheels that are alignable with one other along a direction of travel.

2. The attachment assembly according to claim 1, wherein the arm assembly comprises a mounting member which is releasably coupleable to the double caster unit, and an elongated arm pivotally mounted at a first end on the mounting member so as to be pivotally displaceable about a horizontal axis and pivotally attached at a second end to a bracket that is fixedly attached to the frame element of the rear vehicle of the tandem wheeled vehicles.

3. The attachment assembly according to claim 2, wherein the double caster unit comprises a first latch unit for facilitating releasable engagement with the mounting member of the arm assembly and a second latch unit for facilitating releasable engagement with the frame element of the forward vehicle of the tandem wheeled vehicles.

4. The attachment assembly according to claim 3, wherein a latch of each of the first and second latch units is capable of being manipulated by a finger and is spring loaded so as to return to an original position after being manipulated.

5. The attachment assembly according to claim 1, wherein the double caster unit comprises the two caster wheels each of which having a horizontal axle, a fork unit to which the horizontal axle of a corresponding caster wheel is rotatably mounted and provided with a surface overlying the corresponding caster wheel, two swivel joint mounts, and a rod protruding upwardly from the overlying surface, inserted within a corresponding swivel joint mount and rotatably secured therein to facilitate 360-degree rotation of the fork unit and to ensure contact with an underlying ground surface.

6. The attachment assembly according to claim 5, wherein the double caster unit is advanceable in a sideways direction relative to a previous forward or rearward direction when the two caster wheels have swiveled 90 degrees during a maneuver from the forward or rearward direction to the sideways direction.- 16- 7. A carriage constituting the forward vehicle of the tandem wheeled vehicles and guidable by a user of the rear vehicle of the tandem wheeled vehicles, the carriage comprising two of the attachment assemblies of claim 3, each double caster unit of the two attachment assemblies being coupled to a corresponding carriage frame element in such a way so as to rearwardly support a corresponding lateral side of the carriage while traversing an underlying ground surface.

8. The carriage according to claim 7 , wherein each double caster unit of the two attachment assemblies is releasably coupled to the corresponding carriage frame element.

9. The carriage according to claim 8, wherein each of the double caster units is replaceable with a dedicated non-pivoting wheel that is rotatably mountable to the corresponding carriage frame element.

10. The carriage according to claim 7 , which is directly guidable by an unimpaired ambulatory user when each of the double caster units is coupled to the corresponding carriage frame element and is disengaged from a corresponding arm assembly.

11. The carriage according to claim 10, which is advanceable in a sideways direction relative to a previous forward direction or rearward direction when all caster wheels of the two attachment assemblies have swiveled 90 degrees during a maneuver from the forward or rearward direction to the sideways direction.

12. A set of tandem wheeled vehicles, comprising the carriage of claim 7 and a wheelchair that constitutes the rear vehicle of the tandem wheeled vehicles.

13. The set of tandem wheeled vehicles according to claim 12, wherein the wheelchair is selected from the group of a manual propelled wheelchair, a motorized wheelchair, and a wheelchair that is controllable by a joystick.

14. The set of tandem wheeled vehicles according to claim 12, wherein the second end of the arm is vertically displaceable while pivoting about a bar of the bracket when one or both of the carriage and wheelchair traverses an obstacle to ensure that at least one of the caster wheels of each attachment assembly remains in stable contact with an underlying ground surface.

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