Abstract:
Accessible at both sides of this toy vehicle is a shifter element that enables a user to control the vehicle using only one hand, and without picking the vehicle up or even obstructing its forward travel. The shifter element may be used to turn the vehicle on or off. If the vehicle has two or more operating modes the shifter may be used to select between the modes. The shifter thus enhances the play fantasy, since &#34;real&#34; vehicles start and stop without being raised from the street by their drivers. The shifter element moves transversely relative to the vehicle. In one position the element protrudes at one side of the vehicle, and if pushed inwardly there the element moves toward the other side of the vehicle. In the other position the element protrudes at the other side of the toy; if pushed inwardly it moves toward the first side. In operation, laterally protruding wheels at the corners of the vehicle protect the shifter element from actuation by nearby objects; yet the element is readily operated by squeezing either of its ends against the opposite side of the vehicle.

Description:
RELATED APPLICATIONS 
     This application is a continuation of copending U.S. patent application Ser. No. 438,510, which was filed Nov. 2, 1982, and which issued Apr. 16, 1985, as U.S. Pat. No. 4,511,343. That application was itself a continuation-in-part of application No. 417,544, filed Sept. 13, 1982, and which issued Jan. 8, 1985, as U.S. Pat. 4,492,058. Application 417,554 was in turn a continuation-in-part of application 233,495, filed Feb. 11, 1981, and now abandoned. The latter application was in turn a continuation-in-part of application 121,645, filed Feb. 14, 1980, and issued Dec. 22, 1981, as U.S. Pat. No. 4,306,375. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     This invention relates generally to toy vehicles. It particularly relates to control of such toy vehicles in mechanically very simple ways that nevertheless enhance the illusion of realism, which is to say the fantasy, of play with such vehicles. By &#34;control&#34; is meant turning such vehicles on or off, as well as selecting between plural alternative operating modes (when available) depending upon the operating surface and upon the preference of the user. 
     2. Other Toy Vehicles 
     Other toys, even those operating at selectable plural speeds, have in essence provided only a single mode of operation. 
     For example, the U.S. Pat. No. 4,306,375 mentioned above describes a toy vehicle which has startling climbing characteristics. It is able (traction permitting) to climb any grade on which it will not tip over backward--grades up to about 40°--and to negotiate a vertical step taller than its tire radius. Its chassis is only slightly longer than, and less than twice as wide as, a &#34;penlight&#34; battery. 
     That toy, however, by virtue of its relatively low operating speed, is particularly intended for use in its very unusual operating mode as a special-purpose climbing toy. The phrase &#34;climbing toy&#34; as used in this document means a toy, such as is described in the aforementioned patent, which has extraordinary climbing characteristics and certain features that are aimed at enhancing and maximizing those characteristics. 
     On the other hand, some earlier toys may have had two or more speeds, but to the best of our knowledge there have been no toys in which such plural speeds were provided for corresponding plural and essentially different operating purposes. As far as we know, prior miniature toy vehicles (other than the &#34;climbing toy&#34; described in the aforementioned patent) have been intended for and capable of self-propulsion across a generally level surface such as the floor or rug in a home, and at relatively low torques and high speeds. For purposes of verbal shorthand in this document we refer to such toys as &#34;generally conventional toys,&#34; and to their operation as &#34;generally conventional-toy operation.&#34; 
     Further, we know of no plural-speed powered toys whose speeds can be selected without picking up the entire toy vehicle to manipulate a selector of some kind underneath or inside the vehicle, and/or without using both hands to manipulate the selector. This limitation interferes with the free sway of illusion and fantasy in the use of a powered toy vehicle, by providing an obstacle to a toy user&#39;s native imagination. A &#34;real&#34; vehicle would not be raised from the street by its operator for speed changes, and a &#34;real&#34; vehicle is shifted using just one hand, so the illusion of playing with a &#34;real&#34; vehicle is dampened by the necessity to pick up the toy vehicle and to use both hands when changing speeds. 
     Yet another type of earlier toy, which undoubtedly antedates by centuries those toys just discussed, is the free-rolling vehicle which the user pushes, or allows to roll downhill. Ironically, such a primitive and simple use is not within the capabilities of many modern powered toys, because the motors and particularly the gear trains in many such toys are always engaged with the wheels. In the case of relatively large gear reductions, it can be very difficult to turn the wheels of such a vehicle: the gear train intrinsically resists being operated from its low-mechanical-advantage end. 
     In the toy vehicle of the earlier-mentioned patent, for instance, an extremely large mechanical-advantage value is obtained by use of a worm and worm gear. As is commonly known, the pitch of a worm is so shallow that it is quite impossible to rotate the worm by turning the worm gear: the worm gear simply binds against what is, in all practical effect, a stop. This effect is somewhat extreme in the toy vehicle of the earlier-mentioned patent, because of the use of a worm and worm gear, but it remains true that many or most powered toys cannot be freely rolled. 
     Again, we know of no powered toys whose wheels can be disengaged from their gear trains, to permit free rolling use, without picking the toy vehicle up and/or without using both hands to manipulate a selector. This too is an interference with the effectiveness of illusion in the use of a powered toy vehicle, as already described with respect to speed changes. 
     SUMMARY OF THE DISCLOSURE 
     A primary objective of our invention is to permit a user to convert a toy between free-rolling use and powered use--and, in fact, between generally conventional-toy operation and climbing-toy operation as well--with just one hand and without picking up the vehicle. 
     We believe that this three-mode operation of a single toy, available to the user without the necessity of lifting the toy vehicle from the surface on which it rests or operates, and without the necessity of using both hands, is an entirely new result. 
     This invention provides a toy vehicle that is adapted for (1) generally conventional-toy operation at at least one speed on a generally flat surface, (2) climbing-toy operation at at least one reduced speed with greater torque on a steep and/or irregular surface, and (3) free-rolling unpowered miniature &#34;hand toy&#34; vehicle use--all depending upon the setting of a single one-hand-operable control that is accessible to a user without the user&#39;s picking the vehicle up. 
     More specifically, a preferred embodiment of our invention provides a plural-speed miniature toy vehicle that is intended for use with &#34;electrical battery means&#34;. Such means include an elongated dry-cell battery preferably of the penlight type--that is to say, a quite small one having a pronounced longitudinal axis--as well as necessary cladding, and such other features as may come to be associated with such batteries. &#34;Electrical battery means&#34; also include more than one battery in a single vehicle. 
     To obtain the climbing-toy features of our prior invention, the preferred embodiment of our invention advantageously has, when the battery means are in use, major weight components positioned to provide a generally symmetrical, compact, balanced and relatively low arrangement--particularly when considered in relation to wheeled vehicles that have exaggerated ground clearance between the front and rear wheels. 
     A preferred embodiment of our toy-vehicle invention has a chassis, preferably with walls that define an interior compartment. 
     It also advantageously has &#34;wheel means&#34;--which may include not only wheels but various forms and types of tires, cleating, paddling structures, half-track- or tank-style endless belts, and/or even skids at one end in combination with rotary driving structures at the other. The wheel means are mounted to the chassis for rolling rotation (of at least some member, such as the driving rollers in the case of a half-track belt) about laterally extending axes. Certain embodiments of our invention have both &#34;front wheel means&#34; and &#34;rear wheel means&#34; whose rotation axes are respective mutually parallel but spaced-apart front and rear axes. The distance between the front and rear axes is generally about two inches in one preferred embodiment of our invention. 
     Mounted in the interior compartment are means to releasably support the electrical battery means in the compartment. The longitudinal axis of the battery means when thus supported is preferably to extend substantially front-to-back of the vehicle, and substantially the full distance between the front and rear axes. 
     An electric motor is mounted in the interior compartment. The motor, of course, has a driveshaft. Also on the chassis are means for electrically connecting the battery means (when the battery means are in place) to the motor, so that the battery means power the motor driveshaft. 
     It is important that, when the battery means are supported in the supporting means, at least major portions of the motor and of the battery means be at approximately the same height as the front and rear wheel means. This feature provides much of the favorable weight distribution mentioned earlier, particularly enhancing the operation of the toy vehicle in its climbing-toy mode. 
     Additionally mounted in the interior compartment is a speed-reduction mechanism connecting the motor driveshaft to both the front- and the rear-wheel means mentioned earlier, to transmit rotation from the driveshaft to the wheel means with a mechanical advantage. Associated with this speed-reduction mechanism are means for selecting among a plurality of values of the mechanical advantage. These features, speaking broadly to encompass equivalent detailed arrangements for accomplishing the same purposes, may be called means for &#34;establishing and selecting&#34; a mechanical advantage between the motor shaft and the wheel means. 
     Included among the plural values of mechanical advantage is at least one value that provides a combination of relatively high speed and relatively low torque. With this value selected, the vehicle is operable as a generally conventional toy on generally flat surfaces. 
     Also included is at least one other value that provides a combination of relatively lower speed and relatively higher torque--sufficiently higher that the vehicle is operable as a climbing toy on surfaces that are steeper and/or more irregular. 
     Also included, preferably, is what might be regarded as a &#34;mechanical advantage of zero&#34;--that is to say, a setting of the speed-reduction mechanism in which the motor driveshaft is fully disengaged from the wheel means. When such a setting is provided it is particularly advantageous that it be obtained by use of a gear-train configuration in which the wheel means rotate freely relative to the gearing (or at least relative to the high-stepdown stages of the gearing), yielding a &#34;rolling neutral.&#34; 
     The toy vehicle should also have electrical contact means for completing an electrical connection between the motor and the battery means, when the battery means are within the housing and the worm gear is engaged. These contact means should also interrupt the electrical connection when the worm gear is not engaged, so that the motor and the high-speed end of the reduction mechanism are disabled when the toy vehicle is shifted into &#34;rolling neutral.&#34; 
     The motor, the speed-reduction mechanism, the selecting means, and the battery means, when the battery means are supported in the supporting means, substantially fully occupy the interior compartment. Thus the entire assemblage is extremely small, providing a truly miniature vehicle whose performance is thereby rendered all the more droll and appealing for toy users. 
     In a preferred embodiment the speed-reduction mechanism includes a worm that is adapted to be powered by the motor shaft, a worm gear adapted to engage and be driven by the worm, and an axle positioned at the front or rear axis. This entire mechanism is preferably duplicated at the front and rear ends of the chassis; and the front wheel means are mounted to the axle that is mounted to the front end of the chassis, and the rear wheel means are mounted to the axle that is mounted to the rear end of the chassis. 
     The front and rear wheel means are powered respectively by the worm gears that are mounted to the front and rear ends of the chassis. We prefer to accomplish this powering by driving the axle from the worm gear, and the wheel means from the axle, but this geometry is not the only one that is within the scope of certain embodiments of our invention. 
     We also prefer that the speed-reduction mechanism have a driver gear mounted to or otherwise powered from the motor shaft, and two gear clusters powered by the driver gear. Each of these two gear clusters advantageously consists of a spur-gear section and a worm section, in a one-piece integral assembly. In this document these clusters are called &#34;spur-gear-and-worm clusters.&#34; The worm mentioned earlier is provided selectably by the worm section of either one of these two spur-gear-and-worm clusters. 
     The worm gear in our preferred embodiments is shiftable relative to the spur-gear-and-worm clusters, so that it engages and is driven by the worm section of either of the two clusters. We find it particularly convenient and effective to provide both the shifting of the worm gear and its driving of the axle by giving the worm gear a square-shaped central hole and positioning it to slide along a mating square-cross-section axle, laterally with respect to the chassis, between positions in which the worm gear engages the two worm sections respectively. In this way the worm gear is always in position to drive the axle via their mating square geometries. 
     In preferred embodiments the worm gear has an intermediate position between those in which it engages the two worms. In this intermediate position the worm gear engages neither worm, thus permitting the worm gear and attached axle and wheel means to rotate freely independent of the worms. This feature provides the &#34;rolling neutral&#34; capability already mentioned. 
     Again, this entire mechanism is duplicated at the two ends of the chassis. 
     The &#34;establishing and selecting&#34; means mentioned earlier should also include means for actually effectuating the selection. A user should be able to manipulate these effectuating means manually, by simple finger pressure, to operate the vehicle either as a generally conventional toy or as a climbing toy--or in rolling neutral as an unpowered hand toy. We consider it important to make the manually manipulable effectuating means accessible to the user at the side of the toy vehicle housing, while the vehicle rests upon any of its various kinds of operating surfaces, without the necessity for removing the vehicle from such surfaces. We consider it equally important to make the effectuating means operable with the fingers of just one hand. 
     We have found two embodiments of the mechanism described above to be particularly advantageous, although several others are operable and yield most of the advantages of the preferred embodiments. In both of our preferred embodiments, at each end of the chassis the two spur-gear-and-worm clusters are--as previously noted--powered from a driver gear on the motor shaft. 
     In one of these embodiments the spur-gear section of a first one of the two clusters is driven by the driver gear directly, and the spur-gear section of the other cluster is driven by the spur-gear section of the first cluster. In this configuration the two clusters consequently rotate in opposite directions, and the two worms are therefore of opposite pitch. 
     In the other preferred embodiment the spur-gear sections of both of the two clusters are driven by the driver gear directly (as is only one in the first preferred embodiment). In this second preferred embodiment the clusters rotate in the same direction, so the worms have the same &#34;handedness&#34; (rather than opposite as in the first preferred embodiment). 
     The choice as between these two embodiments or versions is largely a matter of preference, but the two versions do have several advantages in common: 
     First, we have found that it is desirable to place the gear-train stage at which disengagement is effected (for the purpose of selecting a value of mechanical advantage) &#34;downstream&#34; from the worm. By using this order of elements, we are able to provide the &#34;rolling neutral&#34; capability without any extra point of disengagement and without adding undue complexity to the mechanism. 
     Second, we have found that it is desirable to place the worm &#34;downstream&#34; in the gear train from any additional reduction stage that is used. By using this order of elements we cause the worm itself to rotate more slowly than the motor driveshaft, and we believe that the efficiency and longevity of the worm are improved by avoiding high-speed rotation of the worm. 
     Third, we consider it desirable to effect the selection of mechanical-advantage values at a stage in the gear train where the gears are rotating relatively slowly. Doing so minimizes clashing of the gears upon engagement, and gear wear upon both engagement and disengagement, thus extending the life of the mechanism. 
     The foregoing three advantages are all possessed by the &#34;establishing and selecting&#34; means that have been described above, and whose details are presented later. 
    
    
     All of the foregoing operational principles and advantages of the present invention will be more fully appreciated upon consideration of the following detailed description, with reference to the appended drawings, of which: 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a toy vehicle which is a preferred embodiment of our invention, shown without a scale-model vehicle body in place. 
     FIG. 2 is a generalized elevation of the embodiment of FIG. 1 in use on an accompanying toy terrain, particularly illustrating the dual (climbing and conventional) capabilities of the toy and also illustrating the appearance of the toy with a scale-model vehicle body in place. 
     FIG. 3 is a plan view of the embodiment of FIGS. 1 and 2, shown without the mechanism cover that appears in FIG. 1. 
     FIG. 4 is a side elevation view, partly in section, of the embodiment of FIGS. 1 through 3, taken along the line 4--4 of FIG. 3. 
     FIG. 5 is an end elevation view, partly in section, of the same embodiment--taken along the line 5--5 of FIG. 4. In this view the worm gear is shown disengaged from both worms. 
     FIG. 6 is a plan view of the same embodiment, partly in section, taken along the line 6--6 of FIG. 4. 
     FIGS. 7 and 8 are fragmentary end elevations of a portion of the apparatus as shown in FIG. 5, but with the worm gear engaging the low-speed high-torque worm in Fig. 7, and engaging the high-speed low-torque worm in FIG. 8. 
     FIG. 9 is an exploded perspective view showing a part of the mechanism for effectuating the selection of mechanical-advantage values, along with the electrical contact means, for the embodiments of FIGS. 1 through 8. 
     FIG. 10 is a fragmentary elevation, partly in section and taken along the line 10--10 of FIG. 6, showing operating details of some of the FIG. 9 elements as assembled. 
     FIG. 11 is an end elevation of the exterior of the embodiments of FIGS. 1 through 10, taken from the right foreground as seen in FIG. 1. 
     FIGS. 12 through 14 show an alternative preferred embodiment to the detailed drive mechanism of FIGS. 1, 3, 4, 5, 7 and 8. In particular, whereas the latter six drawings depict a first spur-gear-and-worm cluster driven directly from a driver gear on the motor shaft, and the other spur-gear-and-worm cluster driven from the spur-gear section of that first cluster, FIGS. 12 through 14 show both clusters driven directly from the driver gear. 
     FIG. 12 is a perspective drawing comparable to FIG. 1 though from a different vantage (namely, the equivalent of the far left foreground in FIG. 1) and showing only the drive details. 
     FIG. 13 is a fragmentary plan of the FIG. 12 mechanism. 
     FIG. 14 is a fragmentary side elevation taken along the line 14--14 of FIG. 13. 
     FIG. 15 is a fragmentary end elevation taken along the line 15--15 of FIG. 13. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in FIGS. 1, 3 through 8, and 11 through 14, preferred embodiments of our invention are built in and around a chassis 10 consisting of upstanding left and right side walls 11, front end wall 12 and rear end wall 13, all erected about the periphery of an extended horizontal floor 19. 
     The front end wall has a forward protrusion 14 which supports and contains functional connections for a small light bulb 26, and which also supports a transparent light distributor 51. Details of the bulb 26, distributor 51, and related features are presented in the above-mentioned patent and will not be repeated here. 
     The front end wall 12 also has a generally rectangular slot 15, 16 formed in it. The rear end wall 3 has a similar slot 17, 18. These slots are for use in aligning the mechanism cover 60, which also is discussed in detail in the previously mentioned patent and will not be further discussed here, although some minor differences may arise--principally due to the greater width of the present mechanism. The slots 15, 16, and 17, 18 also function in journaling certain rotating portions of the mechanism. This too is accomplished substantially as described in the previous patent, though the number of rotating parts is larger. 
     The chassis 10 serves both as a frame to support and as a partial enclosure to conceal and protect the power source and train. 
     Mounted below the chassis for rolling rotation with respect to it are two mutually parallel but spaced-apart axles, an axle 36 near the front and an axle 46 near the rear of the chassis. Secured to the ends of these two axles 36 and 46 are respective pairs of wheels--front wheels 237 and rear wheels 247, with corresponding tires 37 and 47, which are thus in effect mounted to the frame for rolling rotation about respective mutually parallel but spaced-apart axes (the centerlines of the axles 36 and 46), one such axis being in front of the other. 
     The wheels 237 and 247, with tires 37 and 47 and other paraphernalia such as treads or paddles which may be added for other purposes not here significant, are in this document identified for convenience as &#34;wheel means.&#34; 
     Mounted atop the chassis floor 19 at a position between the two axles (or wheel rotation axes) is an electric motor with housing 27. The motor housing 27 is located against one of the side walls 11, and oriented so that its driveshaft 283 (FIGS. 3 and 4) is perpendicular to the two wheel-rotation axes. This motor is of a type whose driveshaft extends both fore and aft from the motor housing. The motor housing 27 is secured against longitudinal motion by two blocks 319, which are integral with the chassis floor 19 and the adjacent side wall. 
     Mounted to the two ends of the motor driveshaft 283 are respective &#34;drive pinions&#34; or &#34;drive gears&#34; (we mean these terms to be interchangeable) 31 at the front and 41 at the rear, which are firmly secured for rotation with the driveshaft. 
     Below and to the left (taking the direction of vehicle motion as &#34;straight ahead&#34;) of the drive pinions 31 and 41 and meshed with them are respective spur gears 32 and 42, which rotate on corresponding shafts 35 and 45 oriented parallel to the driveshaft. The spur-gear shafts 35 and 45 are each journalled at one of their respective ends into one of the motor blocks 319, and at the other of their respective ends into the corresponding end wall 12 or 13. 
     Sharing the spur-gear shafts 35 and 45 with the spur gears 32 and 42, and firmly secured to those spur-gear shafts to rotate with them, are respective worms 33 and 43. We prefer to make the spur gears 32 and 42 and the corresponding worms 33 and 43 as respective integral assemblies, or spur-gear-and-worm clusters: one such cluster 32-33 thus has a spur-gear section 32 and worm section 33, and the other cluster 42-43 has a spur-gear section 42 and worm section 43. 
     Similar spur-gear-and-worm clusters 32a-33a and 42a-43a are also provided. These additional clusters are respectively positioned adjacent and parallel to the already discussed spur-gear-and-worm clusters 32-33 and 42-43. Each of the additional clusters 32a-33a and 42a-43a is journalled at one of its ends into one of the motor blocks 319, and at the other of its ends into the corresponding end wall 12 or 13. 
     With the addition of these additional clusters 32a-33a and 42a-43a, the fore and aft ends of the drive mechanism remain symmetrical. It may be noted, however, that they are not identical to each other but rather are mirror images: the first-mentioned (high mechanical advantage) clusters 32-33 and 42-43 are &#34;outboard&#34; or toward the left in both ends of the mechanism, while the additional (low mechanical advantage) clusters 32a-33a and 42a-43a are &#34;inboard&#34; or toward the right. 
     The spur-gear sections 32a and 42a of these additional clusters 32a-33a and 42a-43a are driven from the respective adjacent spur-gears 32 and 42 of the outboard clusters 32-33 and 42-43. This drive arrangement causes the inboard clusters 32a-33a and 42a-43a to rotate in the opposite direction from the first-mentioned or outboard clusters 32-33 and 42-43. 
     Accordingly, since the object of the inboard clusters 32a-33a and 42a-43a is to drive the respective worm gears 34 and 44 in the same direction though with different mechanical advantages, the worm sections 33a and 43a are opposite in &#34;handedness&#34;--that is, they are of opposite pitch--relative to the outboard clusters 33 and 43 respectively. 
     Below these pairs of clusters, and oriented and disposed to mesh with the worm sections 33 and 43, are respective worm gears 34 and 44--each oriented to rotate about axes parallel to the axes of wheel rotation. The worm gears 34 and 44 and the respective wheel pairs 237 and 247 are mounted conaxially (that is, together on the same respective axles 36 and 46). 
     Whereas the wheel pairs 237 and 247 are fixed to their respective axles 36 and 46, however, the worm gears 34 and 44 are keyed to their respective axles 36 and 46. This may be accomplished, for example, by providing the gears 34 and 44 with respective hubs 434 and 444 (FIGS. 5 and 6) that have square central holes (FIG. 4), and providing the axles 36 and 46 with matching square cross-sections. Thus the worm gears 34 and 44 rotate with, but can slide along, the axles 36 and 46. 
     The worm gears 34 and 44 in fact can slide along their respective axles 36 and 46 into engagement with either of the respective worms: the front-end worm gear 34 can engage either the worm section 33 of cluster 32-33, or the worm section 33a of cluster 32a-33a; while the rear-end worm gear 44 can engage either the worm section 43 of cluster 42-43, or the worm section 43a of cluster 42a-43a. 
     The result of sliding the worm gears 34 or 44 between worm sections in this way is to select different values of mechanical advantage between the motor driveshaft 238 and the wheels 237 and 247. The difference may be regarded as derived from the additional gear-train stages represented by mutually engaged spur-gear sections 32 and 32a, at one end of the chassis, and mutually engaged spur-gear sections 42 and 42a at the other end of the chassis. 
     Thus each of the worm gears 34 and 44 drives a respective pair 237 or 247 of wheels, but with mechanical-advantage values that depend upon the positions along the axles 36 and 46 of the worm gears 34 and 44, relative to the worm sections 33 and 33a at the front of the chassis, and 43 and 43a at the rear. 
     FIGS. 6 and 9 show a detent mechanism consisting of an arm 491 extending from the shifting element 425-425a, and dimensioned to be &#34;springy&#34; in the direction fore and aft of the vehicle, and a triple-notched structure 492 formed in the housing floor 19 and positioned to engage the arm 491. This mechanism is dimensioned and located to provide three stable positions for the shifting element 425-425a, in which positions, respectively, the worm gears are (1) engaged with the low-mechanical-advantage worms, or (2) engaged with the high-mechanical-advantage worms, or (3) disengaged entirely. It is to be understood that the three positions in our preferred embodiment do not exist in the order just stated, the disengaged position being the middle one; and that it is within the scope of our invention to provide the three positions in any order. 
     The wheels 237 and 247, as well as the axles 36 and 46 themselves, must rotate relative to the housing walls 11--even though the axles 36 and 46 are square. If desired, the wheels 237 and 247 may be provided with externally cylindrical but internally square bushings, fitted snugly over the square ends of the axles 36 and 46, but rotating smoothly in cylindrical holes formed in downward extensions of the chassis walls 11 (see FIGS. 5 through 8). We have found, however, that such bushings need not be provided, and an economy can therefore be realized, if the axles 36 and 46 and the housing walls 11 are made of suitable materials and suitably configured. In particular, we have found that with drawn steel axles--having smooth, rounded corners--and with housing walls 11 made of hard plastic such as the materials known commercially as ABS or &#34;Delrin,&#34; there is insignificant wear of the housing walls, the loads involved being quite light. 
     In this way the wheels may be driven by a symmetrical power train having only two or three stages and yet providing a choice between very high mechanical advantage and only moderate mechanical advantage, between the motor driveshaft and the axles. This versatile power train occupies a narrow space along one side of the chassis 11--and thus leaves the greater width of the chassis for a &#34;penlight&#34; battery 21 (whose positive pole appears at 23) and the appropriate electrical connectors 22 and 24. 
     As to the battery polarity, the motor connections, and the &#34;handedness&#34; or pitch direction of the worms used in our invention, it is to be understood that any two of these factors may be reversed and the toy vehicle will operate in the same direction. For instance, if the battery polarity is reversed and the handedness of the worms is also reversed, the vehicle will still move &#34;forward&#34; as defined by the front/rear terminology used in this document. 
     From the fact that the dry-cell battery 21 appearing in FIG. 1 is only a size-AA penlight type, the remarkably small overall size of the vehicle may be seen dramatically. Yet, due to the simplicity of the novel drive train, it is possible to obtain the two modes of operation described earlier, and without highly miniaturized or high-precision gears. 
     The point at which shifting and disengagement is effected in the described mechanism--that is, the functional location of the shiftable and disengageable worm gears 34 and 44--is &#34;downstream&#34; in the power train from the worms 33, 33a and 43, 43a respectively. Hence the mechanism has the added advantage, noted earlier, of providing a freely operable &#34;rolling neutral.&#34; 
     The worms 33, 33a and 43, 43a are respectively &#34;downstream&#34; in the power train from additional gear-reduction stages composed of the drive pinions or spur gears 31 and 41 in combination with the spur-gear sections 32, 32a and 42, 42a of the spur-gear-and-worm clusters. Hence the mechanism has the further advantage, also noted earlier, of operating the worms 33, 33a and 43, 43a at relatively low speeds for better operating efficiency. 
     The disengageable and shiftable worm gears 34 and 44, moreover, are at the final, lowest-rotational-velocity point in the power train. Hence the mechanism has the yet further advantage of &#34;shifting&#34; the lowest-speed gears available, and thereby minimizing clash and wear. 
     FIGS. 12 through 14 illustrate another embodiment of the power-train features of our invention. This embodiment too has all of the foregoing advantages. Subject to slight reservations it may be regarded as a variant that is equally preferred with the embodiment already discussed. These drawings are representative of both ends of the mechanism, though with a mirror-image form of duplication as encountered in the previously discussed embodiment. 
     Here the pinion or driver gear 741 is lengthened so that it can engage continuously both (1) the spur-gear section 742 of the low-speed spur-gear-and-worm cluster 742-743 and (2) the spur-gear section 742a of the high-speed spur-gear-and-worm cluster 742a-743a. Both clusters are thus driven in common directly from the driver 741, whereas in the previously described embodiment the corresponding high-speed cluster 42a-43a was driven from the spur section 42 of the low-speed cluster 42-43 as an intermediate. 
     Examination of the drawings will reveal that the resulting speeds of the respective high-speed clusters 42a-43a and 742a-743a (i.e., their angular velocities) are identical. They are identical because the intermediate spur 42 transmits the pinion rotation &#34;1:1&#34;--that is, without any gearing change--to the high-speed cluster. 
     Since the intermediate spur 42 introduces a reversal of rotational sense, however, the directions of high-speed cluster rotation are opposite for the two configurations. In the embodiment of FIGS. 12 through 15 the worms 743a and 743 consequently rotate in the same direction, rather than in opposite directions as do the worms 43 and 43a of the first-discussed embodiment. The handedness or pitch of the two worms 743a and 743, therefore, is the same rather than opposite. 
     The various other elements of the variant embodiment in FIGS. 12 through 15 are essentially the same as those in the drawings relating to the first-discussed embodiment. Accordingly the detailed discussion of these other features is not repeated here. 
     Some preference for the first-discussed embodiment may arise from the slight protrusion of the low-speed spur section 742, in the variant embodiment, toward the battery compartment; however, this may well be overcome by minor rearrangements of the parts. 
     A miniature scale-model vehicle body (such as 74 in FIG. 2) is fitted to the chassis 10. The body 74 snaps on and off to permit easy changing of the battery 21, as generally described in the previously mentioned patent. The body style typically is derived from a real vehicle body, with some adjustment of proportions to fit the chassis. 
     The toy vehicle of the previously mentioned patent was uniquely adapted for operation on steep surfaces such as portion 83 of the toy terrain shown in FIG. 2, and over vertical steps taller than its own wheel radius, such as that at 86 in FIG. 2, and on surfaces that are irregular, or both steep and irregular. The toy vehicle of our present invention is also operable on all such surfaces, by virtue of its plural selectable mechanical-advantage values. The toy vehicle of our present invention, however, is also operable in a satisfying mode of play on generally flat and regular surfaces such as portion 85 of the terrain in FIG. 2. 
     To obtain excellent traction, the tires 37 and 47 can be made of rubber foam or plastic foam, or other soft material--with special characteristics as described in the earlier-mentioned patent--or can be replaced by cleated wheels, tractor-type tracks, or other types of surface-engaging propulsive structures, all within the scope of our present invention. 
     Some details of the construction of this preferred embodiment of our invention include protective worm-gear wells, such as the rear well 73, encasing the worm gears 34 and 44 respectively, and drive-mechanism cover 60. The wells such as rear well 73 must be wider than the corresponding structures appropriate to the invention of the earlier-mentioned patent, because the wells in the present case must accommodate the lateral motion of the worm gears 34 and 44 along their axles. 
     The journalling of the spur-gear-and-worm clusters into the chassis, at the ends of the clusters that are remote from the motor housing, may be accomplished as indicated in the previously mentioned patent, or in other convenient ways. 
     The electrical switching mechanism of our present invention is in part novel. Battery 21 applies power through contacts 22 and 24 (FIGS. 3, 6, 9, and 10) to the light bulb 26 and motor 27 in parallel. The rear-end metal contact 22 is fixed to the housing floor 19 by means of a self-tapping screw 22a. This contact 22 is extended along the side of the battery to metallic contact 422, which contacts the bottom of the motor housing 27 to complete the circuit, but only (as will be described in detail) when the worm gear is engaged with one of the worms. 
     The other metal contact 24 is similarly secured to the housing floor by a similar screw 24a; soldered at 24b to this contact 24 is the bared conductive end of an insulated length of wire 224, whose remote end engages an appropriate contact point on the motor. 
     The novel aspect of this mechanism resides in the use of a single manual control to effectuate (1) selection of mechanical advantage, or (2) disengagement of the wheel means from the gearing entirely, and (3) completion or interruption of the electrical connections, depending upon whether the control is in position to select a nonzero value of mechanical advantage in accordance with choice number (1), or in position to disengage the wheels in accordance with choice number (2). 
     As can be seen from FIGS. 9 and 10, the contact strip 22, 422 is pinned to the chassis floor 19 by means of another self-tapping screw 428, which is threaded into a hole 419 formed in the floor 19. The floor 19 is thickened at this point, to provide sufficient thread length for secure attachment of the screw 428, by formation of a boss 429--which extends both downward and upward relative to the nearby portions of the floor 19. 
     The upper extension of the boss 429 also forms a standoff and guide pin. The boss functions as a standoff in that it holds the contact strip 422 up away from the floor 19 proper. In the space thus formed between the strip 422 and the floor 19 fits the shifting element 425, 425a. This shifting element defines a slot 526, which is dimensioned to accept the guide-pin/standoff/boss 429. The shifting element is retained between the floor 19 and the contact 422. As shown, the shifting element 425, 425a is made slightly thinner than the height of the upward extension of the boss 429, so that the shifting element can slide smoothly between the floor 19 and the contact 422. 
     The shifting element extends and slides through apertures 411 (FIG. 1) in both side walls 11, and has manually manipulable ends 425 and 425a that are--when the shifting element is installed in the chassis 10--thus user-accessible near the bottom of the outside of the chassis 10, at the left and right sides of the toy vehicle respectively. The shifting element also has shifting forks 534 and 544 (FIGS. 6 and 9) that are sized and disposed to engage the worm gears 34 and 44 respectively, to drive the worm gears laterally (along their respective square axles) into engagement with the respective worms 33, 33a and 43, 43a--or into an entirely disengaged intermediate position, for &#34;rolling neutral,&#34; for the objectives previously indicated. 
     The &#34;dogleg&#34; structure 525 of the shifting element is an advantageous arrangement for obtaining access to the worm gears 34 and 44, to shift them, while clearing the bottom ends of the motor mounts 319. 
     The effectuating means mentioned earlier include all the provisions described in the foregoing three paragraphs. The overall result of these combined provisions is that a user may shift between the three modes of operation of the toy vehicle without picking the vehicle up, and using just one hand to move the shift element leftward or rightward between the stable positions of the detent mechanism. 
     In particular, to shift the element from its leftward or central position toward the right, the user can: 
     (1) place her or his left thumb (or right index finger, if it is preferred to use the right hand) against the right side of the vehicle body, above or next to the shift element end 425 but not obstructing the shift element end 425; 
     (2) place the left index finger (or right thumb, if the right hand is to be used) against the left end 425a of the shift element; and 
     (3) squeeze the thumb and index finger together to complete the shifting. 
     Similarly, to shift the element from its rightward or central position toward the left, the user can place the left index finger (or right thumb) against the left side of the vehicle body, but positioned to avoid obstructing the shift element end 425a, and the left thumb (or right index finger) against the right end 425 of the shift element, and squeeze to complete the shifting. 
     It is also possible to operate the shifting mechanism by holding the vehicle down with the palm of the hand or with one or more fingers, while pushing the shifting element laterally with one finger. We do not prefer this way of using the mechanism, because it does not yield the same degree of control as the way described in the preceding paragraphs. 
     These ways of using the shifting element thus provide relative motion between that element and the other parts of the shifting mechanism, to actually effectuate the selection of mechanical advantage--or, in other words, to actually effectuate the selection among plural operating modes. The word &#34;manipulable&#34; and the phrase &#34;manipulable . . . with one hand only&#34; are used in the appended claims to describe the suitability of the shifting element for use in this way--that is, not merely that the shifting element can be manipulated, but that when it is manipulated it is effective; it can be manipulated with only one hand to obtain the relative motion required for selection of a mechanical advantage or operating mode. 
     A dimple 523 (FIGS. 6, 9, and 10) formed in the top surface of the shifting element 425, 425a accommodates a mating dimple 423 formed in the contact element 22, 422, when the two are in alignment, permitting the motor-contact end 422 of the contact element to descend out of contact with the bottom of the motor housing 27. This is the condition of the shifting and contact elements when the shifting element is in position to disengage the worm gears 34 and 44 from both of their respective mating worms, as previously described. 
     When the shifting element is in position to engage the worm gears 34 and 44 with either of their respective mating worms, however, the dimple 523 in the top surface of the shifting element 425, 425a is moved out of alignment with the dimple 423 in the contact element 22, 422, forcing the upturned end 422 of the contact element upward into contact with the bottom of the motor housing 27. 
     It is to be understood that all of the foregoing detailed descriptions are by way of example only, and not to be taken as limiting the scope of our invention--which is expressed only in the appended claims.