US 3600851 A
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Description (OCR text may contain errors)
UnitedStates Patent 2,704,395 3/1955 Heidegger 3,l02,363 9/1963 Ferriot 46/244 D 3,361,005 1/1968 Carpenter 74/436 3,481,072 I 12/1969 Stohrer 46/244 D 3,482,352 12/1969 Heim r 46/244 D Primary Examiner-Louis G. Mancene Assistant Examiner-Robert F. Cutting AttomeyAmster & Rothstein ABSTRACT: A battery-operated toy vehicle with a programmed automatic mechanism. The vehicle includes a chassis with an insert plate mounting a motor cradle and a battery cradle, a motor and batteries for driving the vehicle, a gear train for imparting motion to the rear wheels of the vehicle, a front-wheel assembly and drive train means for programming and providing steering action to the front-wheel assembly from the motion of the rear wheels.
front-wheel assembly steering,
SHEET 2 [IF 2 EDWIN NIELSEN BY 2 E TOY VEHICLE The present invention relates generally to toys, and in particular, to a chassis therefor including an automatic steering mechanism. I
Battery-powered toy vehicles or the like are easily operated on a track having a usual guide groove therein by permitting a depending guide or track follower on such a vehicle to extend into the guide groove and thus cause the vehicle to follow the guide groove curvature and otherwise perform on the track. To increase the play value of the vehicle, it is desirable that provision be made for operating the vehicle on a floor, table or other such conventional riding surface which, of course, does not have a guide groove. Thus, it is customary for use on conventional riding surfaces to provide the vehicle with appropriate steering structure to hold the front wheels in one of several positions and to move them between those positions. In this manner the vehicle is forced to follow a prescribed path, either circular or straight on the conventional riding surface. ln known toy vehicles, designed for use without a track, the play value of the toy vehicle is somewhat restricted in that the steering structure on the vehicle holds the front wheels in only one position and changes of that position usually involve removing the vehicle from its riding surface and manually altering the position or, in the alternative, the manual substitution of different cams in an'involved mechanism to selectively choose and hold a different position for the front wheels.
, Broadly, it is an object of the present invention to provide a toy vehicle having an improved steering mechanism overcoming the foregoing and other shortcomings of the prior art.
Specifically, it is an object to provide an improved steering mechanism for a toy vehicle which is primarily adapted to provide a multiplicity of front-wheel positions in a programmed, prescribed path, either circular or straight, or both, on a conventional riding surface.
lt is a further specific object of the present invention to provide an improved steering mechanism including steering control structure adapted to providing a plurality of complex paths for the vehicle by the inclusion of a plurality of complex, path-providing, interchangeable elements, with each forcing the vehicle to follow a prescribed path including both left-circular, right-circular, and straight-path segments on a conventional riding surface.
A toy vehicle demonstrating objects and advantages of the present invention includes a usual chassis with an insert plate having a front-wheel assembly mounted adjacent 1 one end thereof and a rear-wheel assembly including right and left rear wheels and a rear axle adjacent the other end, the rear axle being driven by a conventional toy vehicle motor. The insert plate mounts a motor, batteries, a gear train between the motor and rear axle, a front-wheel assembly and a drive train for programming and providing motion for the steering action of the front-wheel assembly. The drive train includes a worm gear on the rear axle for driving a pinion gear having an upstanding pin and collar. The upstanding pin and collar are arranged and constructed to drive a Geneva wheel, upon which is mounted a removable main cam, secured to the Geneva wheel by a cap. A cam follower assembly is pivoted on a bottom plate of the vehicle, underlying the insert plate. The rear end of the cam follower assembly engages the main cam. At its other or forward end, the cam follower assembly engages a tie rod of the front-wheel assembly such that movement of the cam follower assembly will cause side motion of the tie rod and attendant turning motion of the front wheels. The cam follower assembly further includes a spring for biasing the cam follower against the main cam. Thus, by providing a toy vehicle structure including conventional rear-wheel driving means, a front-wheel assembly including a usual pair of left and right wheels and a tie rod connected therebetween to provide pivotal movement of the pair of front wheels in unison, a Geneva mechanism having a programming main cam operatively connected to the rear wheels and a cam follower astrunk region of the vehicle, there is provided a motor cradle,
sembly for controlling the motion of the tie rod, a my, vehicle withincreased play value is provided. The main cam of the structure is attached in a removable fashion so that it is interchangeable with other main cams for altering the steering program.
The above brief description, as well as further objects, ,fea-
tures and advantages of the present invention will be more fully appreciated by reference to the following I detailed description of a presently preferred, but nonetheless illustrative embodiment in accordance with the present invention, when taken in conjunction with the accompanying drawings, wherein:
FIG. 1 is a side elevational view, with parts broken away, showing a chassis embodying features of the present invention;
FIG. 2 is a top view of the chassis of FIG. '1 with parts broken away to illustrate a portion of the Geneva mechanism according to the present invention;
FIG. 3 is a side elevational sectional view taken along the line 3-3 ofFIG. 2;
FIG. 4 is a bottom view, with parts broken away, showing the mechanism of the present invention and particularly the main cam of the Geneva mechanism and its cam follower assembly;
FIG. 5 is a top view of the electrical system'useful with a toy vehicle according to the present invention;
FIG. 6 is an isometric exploded view of a drive train including a Geneva mechanism useful in the present invention; and
FIG. 7 is a schematic representation of a typical path programmed and controlled by a drive train according to the present invention with the main cam and cam follower shown diagrammatically along the path at characteristic locations to illustrate the programming action thereof.
Reference is now made to the drawings and in-particular FIGS. 1 through 6, wherein there is shown a vehicle chassis embodying features of the present invention, the chassis being generally designated by the reference numeral 10. The chassis 10 is constructed to be detachably secured to any one of a number of small-scale or miniature replicas of a wide variety of vehicle bodies. The scale in the illustrative drawings is approximately twice that contemplated for vehicles embodying features of the present invention. In a typical construction, the overall length of the chassis will be of the order of inches. Notwithstanding such miniaturization, the chassis 10 will have the necessary functional attributes to enable the provision of a self-contained battery drive and the capability of steering the vehicle in a preprogrammed manner.
Referring now specifically to FIGS. 1 through 4, the chassis 10 is seen to include an elongated insert plate 12 having front and rear ends. A front-wheel assembly, generally designated by the reference numeral 14 and having left and right front steerable wheels 16, 18, is mounted on the insert plate 12 adjacent to the front end thereof. Disposed rearwardly of the front-wheel assembly 14 is a rear-wheel assembly, generally designated by the reference numeral 20, which includes nonsteerable left-and right rear wheels 22, 24. The reference throughout the specification to left and right components is intended to orient such components as viewed from the position of the driver when seated in the vehicle.
Intermediate the front and rear-wheel assemblies 14, 20, and in a position corresponding to the'main body of the vehicle, there is provided'a battery cradle, generally designated by the reference numeral 26, which in this illustrative assembly is constructed to receive side-by-side batteries 28, 30. The batteries extend lengthwise of the insert plate 12 and are substantially hidden from view by the vehicle body (not shown) when it is assembled with the chassis l0.
Disposed rearwardly of the rear-wheel assembly 20 in the subsequently described, the motor 34 is operatively connected 2 to the right rear wheeli24 of the rear-wheel assembly 20 for I, Circuit controlis provided by anon-off switch 15 (shown in its off position in FIG. 4), the switch 15 being movable in the direction designated by the arrow 15 to provide the on position. The switch 15 is coaxially attachedto switchplate 15a (FIGS. 2 and 5) to complete the motor-battery circuit. Motion of the switch in direction 15' provides corresponding motion 15' to the plate 15a as shown in FIG. 5 to electrically complete the circuit.
A bottom plate, generally designated 13, defines a lower housing for the chassis l0 and further defines an opening 13a for the on-off switch 15 and an opening 17 for the main cam 46 '(FIG. 4) to be described subsequently. Therefore, it may be seen that the entire chassis 10 including front and rearwheel assemblies 18, 20, motor 34, the drive train, and the batteries 28, 30, are carried on the insert plate 12 with only the cam follower 48 being mounted externally on the bottom plate 13.
As best seen in FIGS. 2 through 4 and 6, the features leading to the improved play value of a vehicle constructed according to the present invention reside in the cooperative provision with the foregoing generally conventional structures, a drive trainincluding a Geneva mechanism, generally designated 36, and acam follower assembly, generally designated 38. The
,1, Geneva mechanism-includes a worm gear 86 on the rear axle 78, a pinion gear 40, from which is upstanding a Geneva pin I 42 and a collar 42a for engagement with a Geneva wheel 44.
Removably mounted on the Geneva wheel is a main cam 46 protruding through bottom plate 13. The cam follower assembly 38 includes a cam follower 48 whose respective ends are for engagement with the main cam 46, and tie rod 50 of the front-wheel assembly, a cam follower pivot 48' for mounting the cam follower 48 on bottom plate 13, and a spring 52 for biasing the cam follower 48 in the direction of engagement with the main cam 46.
As the descriptionproceeds and from the foregoing explanation of the general arrangement, it will be appreciated that there is provided an exceptionally compact construction lending itself to programmed steering of a toy vehicle along a multiposition path, the program of the steering being selectively changeable by selective replacement of a single element of the vehicle drive train mechanism.
As seen best in FIGS. 1 through 4, the front-wheel assembly 14 includes left and right front mounting and contacting members 54, 56 which are of nearly identical construction and are fabricated of an electrically conductive material, such as bronze stampings. The left front mounting and contacting member 54 includes a planar base 540 which rests against and .is secured to the underlying portion of the insert plate 12 and is secured thereto as by rivet 58. The member 54 further includes an upstanding resilient left front battery contact 54b which is positioned at the corresponding forward end of the battery cradle 26 in position to engage the center terminal of the battery 28. Similarly, the right front mounting and contacting member 56 is secured to the insert plate 12 by rivet 60 and includes a planar base 56a and an upstanding resilient rightflfront batterycontact 56b located at the corresponding forward end of the battery cradle 26 in position to contact the center terminal of the battery 30.
The left front wheel 16 of the front'wheel assembly 14 is journaled on a left front axle 62 which extends horizontally and is attached to a knuckle 64 (FIG 3) journaled on a left front kingpin 66. Thus, the wheel-l6 is capable of rotating about its corresponding horizontal wheel axis, and may be turned about the vertical steering axis defined by the kingpin 66 (which also serves to avoid rotation of member 54). Similarly, the right front wheel 18 is. journaled on a right front axle 68 which is secured to a right front knuckle 70 (not shown) journaled on a right front kingpin 72. Provision is made for coordinating the front wheels I6, 18 for adjustment about the steering axes defined by the kingpins 66, 72 so that '50 extending transversely of the insert plate 12 across the front end thereof. One end of the tie rod 50 is connected to the knuckle arm 64a by the tie rod pin 74 and the other end of the tie rod 50 is connected to the knuckle arm Illa-by tie rod pin 76. Thus, the attitude of the wheels l6,;l8 iri relat ion to the chassis can be changed by moving theftiertid' fl irileitherfa left or right direction and itis thereby possibleztdhave the vehicle move on a straight path, traverse a course to the left, ortraverse acourse to the right; I
The wheels 16, 18 0f thefront-wheel assembly 16 and the wheels 22, 24 of the'rear-wheelassembly 20 are all substantially identical in construction and conventional for toy vehicles of this type. v
The rear-wheel assembly 20 includes a rear axle 78 which extends transversely of the chassis intermediate the battery cradle 26 and the motor cradle 32. The axle 78 is retained on the chassis by integral bearings 79 or journals, such as are conventional for vehicles of this type. The left and right rear wheels 22, 24 are journaled on the rear axle 78 with at least the left rear wheel 22 being arranged to freewheel.
The battery cradle 26, details of which are best seenin FIGS. 1, 2, and 3, is defined by flanges molded integrally with the insert'plate 12 of the chassis including a left marginal flange 12c, a right marginal flange 12f and a transverse flange 12g. With reference to FIG. 2, it will be seen that the insert plate 12 is provided with a central, longitudinally extending reinforcing rib 12! which medially partitions the battery cradle 26 into two side-by-side compartments adapted to receive the batteries 28, 30. The batteries 28, 30 are releasably secured in the battery cradle 26 by battery holddown and motor-contacting clips 80, 82 which are fabricated of electrically conducting material, preferably bronze stampings. The clips 80, 82 in cooperation with side clip 83 serve to releasably secure the motor 34 to the chassis, orient the motor 34' relative to the rear-wheel assembly 20 to establish drive thereto, and establish electrical connections between the batteries 28, 30 and the motor 34 as shown in FIG. 5. The motor 34 is of the fractional horsepower battery-operated type and is of generally known construction. Such motors are commercially available from a number of sources.
The motor cradle 32 further mounts a gear train 84 from the motor 34 to the right rear wheel 24. The gear train includes gears of various diameters well known in the art in order to provide drive from the motor shaft 84a to a wheel gear. 84b coaxial with the right wheel 24.
Referring particularly to FIGS. 2 through 4and 6, a drive train for programming and controlling the front wheel as; sembly steering mechanism according to the present invention is shown as including a Geneva mechanism 36 and a cam follower assembly 38. The.G,eneva mechanism 36 includes a worm gear 86 disposed approximately centrally of the rearwheel axle 78, the worm gear 86 meshing with pinion gear 40 in approximately a 30:1 reduction to provide rotation thereof. The pinion gear 40 includes an upstanding pin 42 and an upstanding collar 42a for engaging a Geneva wheel 44. Removably secured to and coaxial with the Geneva wheel is a main cam 46 which is retained in place by a retaining cap 44a extending from the Geneva wheel 44. The retaining cap 44a has retaining cap lugs 44b, 44c extending laterally thereof for accomplishing the retaining function. The main cam 46 defines at its centralportion an opening 46a, the opening including lug-receiving slots 46b, 46c and lug tracks 46d, 46e. It may be seen therefore, that the lugs 44b, 440 are intended for insertion to the lug-receiving slots 46b, 46c and for movement of the cam follower defines a tie rod slot 48c for receiving a downwardly protruding pin 50a from the tie rod 50.
Operation of the entire Geneva mechanism 36 and the motion imparted thereby to the cam follower assembly 38 may be described as follows with particular reference to FIG. 6: As the worm gear 86 rotates with the rear-wheel axle 78 in the direction 77 shown, a motion designated by the arrow 94 is imparted to the pinion gear 40. As the pinion gear 40 rotates in direction 94, a similar motion is assumed by the pinion gear collar 42a and the pin 42. The Geneva wheel 44 is constructed to define both dwell slots 44d and index slots 44e, the collar 42a of the pinion gear riding in successive dwell slots 44d and the pin 42 of the pinion gear 40 intended for insertion to successive indexing slots 44e. As the pinion gear 40 rotates, the collar 42a rotates in a dwell slot 44d until the pin 42 is rotated to a position for insertion to an indexing slot 44e. When the pin 42 arrives at the entrance position of an indexing slot 44e, it may be seen that the partially truncated collar 42a will be in a position out of the dwell slot 44d. At this pint, a rapid indexing (approximately 45 of the Geneva wheel 44 will take place as the pinion gear 40 continues to rotate. Such indexing imparts rapid motion in the direction 96 to the Geneva wheel 44 until the pin 42 has rotated to a position where it passes out from the indexing slot 44e. At this point, the collar 42a will again be passed into the next successive dwell slot 44d, at which point the Geneva wheel 44 will cease moving until the pin 42 is inserted to the next successive indexing slot 442. Repetitions of such motions continue to occur with alternate dwell periods and rapid indexing periods provided to. the Geneva wheel 44. Since the main cam 46 is attached to the Geneva wheel 44 with lugs 44b, 44c bearing against lug walls 46f, 463, the alternating dwell and rapid indexing motion of the Geneva wheel 44 is imparted positively to the main cam 46'. It may be seen further from FIG. 6 that the main cam 46 defines edge surface portions 100, 200, 300 of varying depth and length for producing the follower actions labeled 100', 200', and 300' in FIG. 7. The timing of such action by the cam follower tip 48a is programmed by the alternate motion and timing in direction 98 of the main cam 46 as dictated by the motion of the Geneva wheel 44 and the balance of the Geneva mechanism 36.
To further describe the Geneva mechanism 36, the structure of the Geneva mechanism elements in the illustrative embodiment are shown with the pinion 40 having a dwell ratio of approximately 2 to 1. That is, the dwell-causing-collar 42a is in contact with a dwell slot 44d for twice as much of the pinion gear rotation as the pin 42 is in contact with an indexing slot 442. Stated differently, the collar 42a is active for 240 of a single rotation of the pinion gear 40 and the pin 42 is active for 120. Construction of the Geneva wheel 44 is such that the indexing slots 442 occur every 45 along the periphery of the Geneva wheel. Also, the main cam 46 is designed to include edge surface portions 100, 200, and 300 with the portions 100 subtending an arc of 30 along the periphery of the main cam, portions 200 subtending an arc of 15 and the portions 300 subtending an arc of 30, Particular reference to FIGS. 4, 6, and 7 indicate that the closest edge surface portions to the center of the main cam 46 are portions labeled 100, the furthest portions from the center are those labeled 300 and the intermediate surface portions are labeled 200. When the cam follower tip 480 is contacting the deepest surface portions 100, the cam follower tip 48awill be at its furthest extent to the left of the vehicle. The tie rod arm 48b of the cam follower 48 will therefore be at the position B denoted by ghost lines in the drawing of FIG. 4. This B position is the furthest right position for the tie rod arm 48b and the tie rod 50. In this position. therefore, the vehicle front-wheel assembly will be steered to the right since the rightward motion of tie rod 50 pivots the knuckle arms 70a and 64a about the kingpin's 72 and 66. respectively. Likewise, the wheels I8, 16 are thereby turned to a rightwardly steering position for the vehicle.
Conversely, when the cam follower tip 48a is contacting the surface portions 300 (furthestaway from the center of'the main cam 46), the tie rod arm 48b of the cam follower 48 is moved to the position denoted by ghost lines C in'FIG. 4. Such action produces leftward motion of the tie rod 50 causing the vehicle to turn to the'left. It may be seen clearly that the straight-ahead position of the tie rod arm 48b of the'cam follower 48 is the position shown in FIG. 4 and denoted by the label A. 'Such straight-ahead orientation of the elements shown is assumed when the cam follower tip 48a is contacting an intermediate depth portion 200 on the main cam 46.
In order to provide a clear understanding of the construction of a toy vehicle according to the present invention, a brief description of the operation will now be provided. At the beginning of the operational cycle it is assumed that the collar 42a is inserted to a dwell slot 44d of the Geneva wheel 44 and in the midposition thereof, so that the pinion gear 40 is rotating without imparting any motion to the Geneva wheel. This is considered, therefore, the midposition of the dwell period since the collar 42a rotates with a clearance relationship to the dwell slot 44d. At that point, the pin is on the opposite side of the axis of the pinion gear 40 from the structural center of the collar 42a. Also, in the assumed initial position, the toy vehicle chassis 10 is at the midpoint of its straight path as shown at point A,, in the lower right segment of the total path 150 pro grammed for the vehicle. The, initial position for the cam follower tip 48a relative to the main cam 46 is at the middle of an edge portion 200 designated A,'.
As the motor continues to operate through gear train 84 to rotate the rear-wheel axle 78, the worm gear 86 will rotate in direction 77 and cause, with a 30-to-1 reduction, the rotation of pinion gear 40 in direction 94. Since the pin 42 is 60 from insertion to an indexing slot 442, or one-third rotation I therefrom, it will require approximately 10 full rotations of the rear-wheel axle 78 to reach that insertion point. During that one-third rotation of the pinion gear 40, the Geneva wheel 44 will remain stationary, thus maintaining a straight path for the vehicle, which was its orientation initially.
As soon as the pin 42 enters the indexing slot 446, the Geneva wheel 44 begins rapid indexing for approximately 45 of its rotation. During the rapid indexing, the main cam 46 also rapidly rotates 45, thus moving the cam follower tip 48a (relative to the main cam 46) past the midpoint C, of the next successive edge surface portion 300 to the midpoint A of the following edge portion 200. As discussed previously, the edge portion 300 defines a left-turn orientation for the front wheels l6, 18. The positions of the main cam 46 and cam follower tip 48a, as shown in the position labeled 300 in the drawing of FIG. 7, are therefore passed quickly during indexing and the vehicle chassis l0 quickly proceeds past position c,, in the path 150.
After the rapid indexing of 45 rotation by the main cam 46 and the Geneva wheel 44, the pin 42 will be in a position to exit from the indexing slot 44e which it had entered. During the indexing period, the pinion gear 40 had rotated by an amount equal to of rotation which corresponds to 10 full rotations of the rear wheels 22, 24. As the pin 42 exits from the indexing slot 44e, the vehicle chassis 10 is in the position A of the total vehicle path in FIG. 7. The Geneva mechanism now assumes a period of dwell as the collar 42a enters a dwell slot 44d, causing the vehicle chassis, and particularly the front wheels thereof to maintain a straight position for 20 full rotations of the rear wheels and two-thirds of a rotation of the pinion gear 40, The vehicle maintains the straight position until the pin 42 again enters an indexing slot 44e causing the main cam 46 to rapidly index approximately 45 to point A,,' in FIG. 6. During the indexing, the cam follower tip 48a passes the midposition B, of an edge portion I00, which dictates a right turn for the chassis 10. The chassis, therefore, quickly traverses a right run through point B, of path 150 (cam follower tip 48a and main cam 46 positions for B, shown in FIG. 7 as 100). With point A contacting the cam follower tip 48a at the end of the indexing, the vehicle will then assume a straight path and hold the straight path during the ensuing dwell period of the Geneva mechanism. The
straight path will be maintained during the dwell period for approximately 20 full rotations of the rear wheels. The path '150 of the vehicle chassis then continues through points C A etc. corresponding to main cam surface portion midpoints C,', A], etc. in the same manner with alternate dwell and indexing periods.
In accordance with the foregoing description of structure and operation, a toy vehicle chassis 10 has been described as using programmed and controlled steering operation. By interchanging main cam 46 with others of various designs and edge surface configurations, the path 150 may be altered almost without limit. For instance,the illustrative main cam 46 described herein provided intermediate-depth edge portions i 200 to correspond with dwell periods. It may be seen that arcs of turn having much greater extent than those shown in path 150 may be obtained by synchronizing dwell periods of the Geneva wheel with other edge surface portions 100, 300. Also, the Geneva wheel can be replaced by a mutilated gear or other programming means to provide intermittent motion.
Furthermore, it should be understood that the toy vehicle may be used to simulate typical city driving where long straight runs and rapid turns are the rule. Also, the simulation of toyboats and planes is accomplished with the present invention by merely using a different body configuration for attachment to the chassis shown.
What I claim is:
1. For use in programming the direction of movement of a toy vehicle of the type including a chassis, drive means mounted on the chassis for propelling the vehicle and a steering member, mounted on the chassis for movement between a plurality of steering positions, a programming means comprising: a programming cam, a Geneva mechanism for providing interrupted, rotative movement for said cam including dwell periods and indexing periods, a cam follower operatively connected to said cam and said Geneva mechanism for translating said interrupted, rotative movement with said periods into movement for positioning said steering member for a long period in one of its steering positions and for a short period in another of its steering positions.
2. For use in programming the direction of movement of a toy vehicle of the type including a chassis, drive means mounted on the chassis for propelling the vehicle and a steering member mounted on the chassis for movement between a number of steering positions, a steering mechanism comprising: a programming means, means for driving said programming means, which provides interrupted rotative movement including dwell periods and indexing periods and cam means translating said interrupted rotative movement with said periods into movement for positioning said steering member for a long period in one of its steering positions and for a short period in another of its steering positions, said cam means including a cam follower and said programming means including a replaceable cam and a Geneva mechanism having a Geneva wheel, said Geneva wheel and said cam being coaxial and removably attached for rotating together and for replacement of said cam, said cam follower being operatively connected to said steering mechanism at one of its ends and contacting said cam at the other of its ends.
3. A drive train for a vehicle chassis having a front-wheel turning assembly, a rear-wheel assembly, a motor and a drive connection between said motor and one of said wheel assemblies, said drive train comprising a Geneva mechanism operatively connected to the motor and a cam follower assembly operatively connected to turn said front-wheel turning assembly and operable therewith to alter the orientation of the vehicle chassis, said cam follower assembly including a cam follower and said Geneva mechanism including a cam for contacting and rotating relative to said cam follower and thereby imparting motion thereto said Geneva mechanism further including a Geneva wheel attached to said cam and rotatable therewith.
4. The invention according to claim 3 wherein a pinion gear is provided to impart motion to said Geneva wheel, said pinion gear having a pin and 'collar upstanding therefrom and said Geneva wheel defining pinreceiving index slots and collarreceiving dwell slots, said dwell slots and said collar defining a clearance therebetween.
5. The invention according to claim 4 wherein the rearwheel assembly is driven by the motor and said Geneva mechanism further includes a rear-wheel axle worm gear for driving said pinion gear.