Infinitely variable transmission for differentially steered vehicles

Abstract

An infinitely variable transmission system for differentially steered vehicles comprises two planetary gearboxes, each coupled to drive, as output, a driving component, such as track or wheel, on either side of a vehicle. The planetary gearboxes are drivingly coupled to a power source, such as an engine or motor, via fixed gear ratio driver and via belt drive system of two or more variable ratio belt drive pulleys. Each of the two outputs of the transmission can independently and simultaneously be controlled to revolve in forward, neutral (stop), and reverse directions in a manner of continuously and infinitesimally variable speed and torque.

Claims

1. An infinitely variable transmission system for differentially steered vehicles comprising; a driver pulley, which is drivingly connected to a power source; two variable ratio driven pulleys, each of which is controllably varied to control the speed and direction of rotation of each transmission output and hence each driving component; a single belt extending around the two driven pulleys and the driver pulley, forming a variable ratio belt drive system; and two planetary gearboxes, where gear sets of each are drivingly connected to the power source, a respective variable ratio driven pulley, and a respective driving component as output.

2. An infinitely variable transmission system for differentially steered vehicles as in claim 1, in which; ring gears of both planetary gearboxes are drivingly connected to the power source; planet gear carrier element of each planetary gearbox is drivingly connected to a respective driving component as a transmission output; and sun gear of each planetary gearbox is drivingly connected to a respective variable ratio driven pulley, to be driven in the opposite direction of rotation of the respective ring gear.

3. An infinitely variable transmission system for differentially steered vehicles as in claim 1, in which the driver pulley comprises a variable ratio pulley, comprising a means for continually exerting force on its flanges towards each other.

4. An infinitely variable transmission system for differentially steered vehicles as in claim 1, in which the driver pulley comprises a fixed ratio pulley, and the transmission further comprises a tensioner pulley for maintaining the tension of the belt.

5. An infinitely variable transmission system for differentially steered vehicles as in claim 1, in which the driver pulley comprises a variable ratio pulley, controllably varied along with the driven pulleys to control the operations of the transmission.

6. An infinitely variable transmission system for differentially steered vehicles comprising; a variable ratio driver pulley, comprising a means for continually exerting force on its flanges towards each other, that is drivingly connected to a power source; a variable ratio driven pulley with its flanges disconnected from each other; a belt extending around the driver and driven pulleys, forming a variable ratio belt drive system; a means for; controllably and independently moving each flange of the driven pulley along a respective straight path, established by the contact line between the belt and the respective flange face, established at the cross sectional view formed by the sectioning plane that passes through the axes of rotation of driver pulley and driven pulley flanges; and allowing for rotational motion of each flange about its respective axis; two planetary gearboxes, where gear sets of each are drivingly connected to the power source, a respective variable ratio driven pulley flange, and a respective driving component as output.

7. An infinitely variable transmission system for differentially steered vehicles as in claim 6, in which; ring gears of both planetary gearboxes are drivingly connected to the power source; planet gear carrier element of each planetary gearbox is drivingly connected to a respective driving component as a transmission output; and sun gear of each planetary gearbox is drivingly connected to a respective variable ratio driven pulley flange, to be driven in the opposite direction of rotation of the respective ring gear.

8. An infinitely variable transmission system for differentially steered vehicles as in claim 6, in which; planet gear carrier elements of both planetary gearboxes are drivingly connected to the power source; ring gear of each planetary gearbox is drivingly connected to a respective driving component as a transmission output; and sun gear of each planetary gearbox is drivingly connected to a respective variable ratio driven pulley flange, to be driven in the same direction of rotation of the respective planet gear carrier element.

9. An infinitely variable transmission system for differentially steered vehicles as in claim 6, in which said means for moving flanges of the driven pulley comprises; two telescopic extending shafts, each coupled with two universal joint couplings on either ends, with further shafts extending from those universal joints to drivingly connect each flange to a respective sun gear; two housing elements being positioned on the back side of each flange, each comprising; a thrust bearing positioned in contact with the back side of each respective flange; an opening through the body of housing element for each respective flange's shaft to pass through, and to provide radial bearing support for each said shaft; a back face machined to be parallel to the path of motion of each respective flange; a set of straight cut grooves on said back face, running parallel to the path of motion of each respective flange; two guide blocks, stationarily positioned within the body of transmission, each comprising; a front face, machined to match and be in contact with the back face of a respective housing element; raised grooves on said front face to match and slidingly engage with the cut grooves of a respective housing element; a through opening to allow each respective flange's shaft to pass through; a means for controllably and independently moving each housing element, slidingly along the face of a respective guide block, to control the operations of the transmission.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG. 1 is a simplified illustration from a top view of a tracked vehicle, illustrating an embodiment of a transmission presented in this invention with respect to engine and driving components, tracks.

[0029] FIG. 2 is a top view illustration of a first embodiment of a transmission presented in accordance with this invention.

[0030] FIG. 3 is a front perspective view of the first embodiment.

[0031] FIG. 4 is a front view illustration of a second embodiment of a transmission presented in accordance with this invention.

[0032] FIG. 5 is a front perspective view of the second embodiment.

[0033] FIG. 6 is a front view illustration of a third embodiment of a transmission presented in accordance with this invention.

[0034] FIG. 7 is a front perspective view of the third embodiment.

[0035] FIG. 8 is a top view illustration of a fourth embodiment of a transmission presented in accordance with this invention.

[0036] FIG. 9 is a front perspective view of the fourth embodiment.

[0037] FIG. 10 is a front exploded perspective view of the variable ratio pulley belt drive system of the fourth embodiment.

[0038] FIG. 11 is a layout of the various principal modes of operation of the transmission in the fourth embodiment.

[0039] FIG. 12 is a front perspective view of an alternative form of the variable ratio pulley belt drive system of the fourth embodiment, illustrating the use of idler pulleys.

[0040] FIG. 13 is a top view illustration of a fifth embodiment of a transmission presented in accordance with this invention.

[0041] FIG. 14 is a front perspective view of the fifth embodiment.

DETAILED DESCRIPTION OF THE INVENTION

[0042] References to the accompanying figures are made hereinafter to better describe and illustrate some of the embodiments of the invention. References to position and orientation are made throughout the context to better describe various embodiments of the disclosure to the reader. These references such as left, up, middle are with respect to the appropriate viewing orientation of the respective page of the Figure, as can be deduced by the orientation of the reference numbers and characters of the Figure.

[0043] FIG. 1 illustrates a simplified, representative view of a tracked 24a 24b vehicle 25 utilizing an embodiment of a transmission 23 presented in accordance with this invention as a drive source. An engine 22 is drivingly connected to a transmission 23 of the form illustrated in FIG. 4, which is configured to drive the two output shafts. In this embodiment, beveled gear sets 26a 26b are utilized to couple the transmission output shafts with the respective shafts 27a 27b of the drive sprockets 28a 28b of the tracks 24a 24b. This figure illustrates the purpose of the transmission within a differentially steered application. It is to be appreciated that the actual implementation may differ from this illustration, but still fall within the scope of the disclosed invention.

[0044] FIG. 2 and FIG. 3 illustrate the first embodiment of an Infinitely Variable Transmission in accordance with this invention. The engine shaft 101, driven by the engine, drives the ring gears 106a 106b of both planetary gearboxes via the respective fixed gear ratio drivers 102a 102b. Hence, both ring gears 106a 106b are driven at the same speed relative to each other. The engine shaft 101 is also coupled with the two spring loaded 113a 113b variable ratio driver pulleys 111a 111b, each of which is coupled with a respective variable ratio driven pulley 109a 109b via a respective belt 110a 110b, to form two variable ratio belt drive systems. The springs 113a 113b maintain a force load on one or both flanges of both of the driver pulleys 111a 111b, pushing the flanges towards each other. Within each variable ratio belt drive system, the gearing ratio of the driven pulley 109a(109b) is controllably varied, while the ratio of the driver pulley 111a(111b) is, in response, controlled by the spring 113a(113b) load, to maintain the belt tension, as well as to vary the overall belt drive system gear ratio. For instance, when the flanges of the controlled driven pulley 109a(109b) are set further apart from each other, moving the belt 110a(110b) to a smaller radius on that pulley, the flanges of the driver pulley 111a(111b) are set closer to each other by the spring load 113a(113b) to maintain the tension on the belt 110a(110b) and move the belt to a larger radius on that pulley. This action of adjusting the flange distances varies the gearing ratio through the belt drive system. As aforementioned, various apparatuses are commercially available for controllably varying the flange distances, hence the pulley gearing ratio, that can be utilized within these embodiments. In this illustration, driven pulleys 109a 109b are chosen as the controlled pulleys, while the driver pulleys 111a 111b are spring loaded 113a 113b. It is also chosen that only one flange of each pulley is movable along the shaft. For the driven pulleys 109a 109b, the flanges towards the center of the embodiment, and for the driver pulleys 111a 111b, the outer flanges are movable, hence maintaining belt alignment. It is to be appreciated that in alternative embodiments, the opposing flange sets or even both flanges for either or both driven and driver pulleys may be utilized to move along their shafts to achieve the same functionality. If the spring loaded pulley was preferred to have both of its flanges movable, spring load on both flanges may be used. In another alternative embodiment the driver pulleys 111a 111b may be utilized as the controlled pulley, while the driven pulleys 109a 109b may be utilized as the spring loaded 113a 113b pulleys. Also in another embodiment, the spring load 113a 113b may be eliminated by utilizing both driver 111a 111b and driven 109a 109b pulleys as controlled pulleys. Accordingly, flanges of both pulleys would controllably be moved along their shafts in opposing directions, to maintain the belt tension and vary the gearing ratio. A rubber style belt is suitable for this embodiment as it is common for many applications of variable ratio belt drive systems, such as CVT systems; however metal based belts may also be utilized as well.

[0045] Each driven pulley 109a 109b is then coupled with the respective sun gear 103a 103b via a respective shaft 108a 108b. The output shafts 107a 107b are driven by the travel of the respective planet gears 104a 104b around the respective sun gears 103a 103b via the respective planet gear carrier elements 105a 105b. Each planet gear 104a(104b) is free to rotate about the respective shaft that couples it to the respective carrier element 105a(105b). The output shafts 107a 107b are ultimately connected to drive the respective tracks of the vehicle.

[0046] The following speed relationship holds true for a planetary gearbox and a variable ratio belt drive system, coupled according to embodiment one, as well as according to embodiments two, three and four, where the belt drive system is coupled with the sun gear, the fixed ratio driver is coupled with the ring gear and the planet gear carrier element is utilized as the output shaft.

[00003]$w_o=w_e.Math.\left(\frac{\mathrm{fgr}-R.Math..Math.1.Math.\mathrm{vgr}}{\left(1+R.Math..Math.1\right).Math.\mathrm{vgr}.Math.\mathrm{fgr}}\right)$

[0047] Where w.sub.o is the output shaft 107a(107b) speed, w.sub.e is the engine shaft 101 speed, R1, as aforementioned, is the gear ratio between ring gear 106a(106b) and sun gear 103a(103b), fgr is the gear ratio between engine driver gear 102a(102b) and the ring gear 106a(160b), such as the ring gear outside teeth count divided by the engine driver gear teeth count, and vgr is the gear ratio through the variable ratio belt drive system, such as the belt contact point radius on the driven pulley 109a(109b) divided by the belt contact point radius on the driver pulley 111a(111b), which is variable via controlling the flanges. Accordingly, by consideration of these ratios, desired gear and pulley sizes can be determined to produce the desired ranges of motion of the vehicle through this transmission. According to this arrangement, the output shaft 107a(107b) will be at neutral (stop) condition when fgr=R1.Math.vgr. By varying the vgr ratios higher or lower from this point, by controlling the flange distances of the driven pulleys 109a 109b in embodiment one, by the same magnitude for both planetary gearboxes, the output shafts 107a 170b would deviate from neutral, in terms of rotational speed, by the same magnitude and hence straight motion in forward or reverse directions would be achieved. By varying the vgr ratios in differential amounts between the two planetary gearboxes, the output shafts 107a 107b would rotate in differential speeds relative to each other and hence steering action would be achieved.

[0048] Referring to FIG. 4 and FIG. 5 as a second embodiment of this invention, an engine 22 is drivingly connected to a fixed ratio driver pulley 211, and to a fixed gear ratio driver 202 via the engine shaft 201. A single belt 210 couples the fixed ratio pulley 211 with two variable ratio driven pulleys 209a 209b. The fixed ratio driver gear 202 is drivingly connected to the ring gears 206a 206b of both planetary gearboxes. Similar to embodiment one, planet gear sets 204a 204b of both planetary gearboxes are each coupled to drive the respective output shafts 207a 207b via the respective carrier elements 205a 205b, which in turn drive the respective tracks of the vehicle. Again similar to embodiment one, sun gears 203a 203b are drivingly connected to the respective driven pulleys 209a 209b via the respective shafts 208a 208b. Also operationally similar to embodiment one, by controllably varying the distances between the flanges, hence the gearing ratios, of both variable ratio driven pulleys 209a 209b in synchronization with each other, straight motion in forward and reverse directions would be achieved. By varying gearing ratios in differential amounts between the two driven pulleys 209a 209b, the steering action would be achieved. A tensioner idler pulley 212 (FIG. 5) maintains the belt tension as flange distances are varied among the driven pulleys 209a 209b, hence the slack of the belt 210. The tensioner pulley 212 may also be used controllably to engage and disengage the transmission for vehicle braking, towing or start-up purposes. By releasing the tension on the belt 210, the driven pulleys 209a 209b would be disengaged from the driver pulley 211, and hence the sun gears 203a 203b would be disengaged from the engine 22. The engine would then drive only the rings gears 206a 206b, which in turn would drive the sun gears 203a 203b in the opposite direction of the ring gears 206a 206b by way of least resistance path, leaving the planet gears 204a 204b, hence the carrier elements 205a 205b and the output shafts 207a 207b in freewheeling motion. Controllable spring loaded engagement/disengagement tensioner pulleys are commonly utilized in many belt drive applications such as riding lawn mowers.

[0049] A third embodiment as outlined in FIG. 6 and FIG. 7 is similar to embodiment two, however differs from embodiment two by the fact that it utilizes a spring loaded 313 variable ratio driver pulley 311, in place of the fixed ratio driver pulley 211 of embodiment two, and the tensioner pulley 212 is absent. Similar to the spring loaded 113a 113b driver pulleys 111a 111b in embodiment one, the spring load 313 for the driver pulley 311 maintains a force load on one or both flanges towards each other. As the gearing ratios of the driven pulleys 309a 309b are controllably varied, the ratio of the driver pulley 311 varies in response, under the spring load, to maintain the belt 310 tension. This spring loaded 313 ratio-varying function of the driver pulley 311 in response to the controlled ratio-varying function of the driven pulleys 309a 309b also allows for the overall belt drive pulley system to deliver a wider range of gearing ratio compared to embodiment two, for similarly sized pulleys. Accordingly, in a similar layout as in embodiment two, the engine 22 is drivingly coupled with the spring loaded 313 variable ratio driver pulley 311 and the fixed ratio driver gear 302 via the engine shaft 301. The driver pulley 311 is coupled with the two driven variable ratio pulleys 309a 309b via single belt 310. The driver gear 302 is coupled with the ring gears 306a 306b of the planetary gearboxes, hence both rings gears 306a 306b rotate at the same speed and direction. The driven pulleys 309a 309b are each drivingly connected with each of the respective sun gears 303a 303b via the respective shafts 308a 308b. The planet gear sets 304a 304b are free to rotate around their respective shafts that connect them to the respective planet gear carrier elements 305a 305b. The two output shafts 307a 307b are connected to each of the respective carrier elements 305a 305b, which are driven by the travel of the planet gears 304a 304b in between the respective ring 306a 306b and sun gears 303a 303b. The output shafts 307a 307b, in turn, are connected with the respective tracks on either side of the vehicle.

[0050] Operationally similar to embodiment two as well, straight motion of vehicle in forward and reverse directions is achieved by varying the gearing ratios of the two driven pulleys 309a 309b in synchronization with each other, while the steering is achieved by differential varying of the gearing ratios relative to each other.

[0051] In an alternative embodiment, the spring loaded 313 variable ratio driver pulley 311 of embodiment three may be replaced by a controllable pulley, just as the two driven pulleys 309a 309b. In this arrangement, straight motion in forward, reverse, and neutral (stop) directions would be achieved by varying the gear ratio of the controllable driver pulley, and the steering would be achieved by differentially varying the driven pulleys 309a 309b. A tensioner idler pulley as in embodiment two may be used to compensate for the changing slack of the belt due to varying of the pulley ratios, and so to maintain the tension. In another embodiment, the tensioner idler pulley may be eliminated by implementing a gearing ratio varying methodology that coordinatingly controls the driver and the driven pulleys to maintain the belt tension. For instance, when the distance between the flanges of the driver pulley is increased to achieve a straight motion, the distances between the flanges of the two driven pulleys can controllably be reduced, by the same amount between the two driven pulleys, to compensate for the slack and hence maintain the tension.

[0052] The upper flanges of the driven pulleys, and the lower flange of the driver pulley for embodiments two and three are designated as movable within the presented illustrations. In alternative embodiments, opposing flanges or both flanges of these pulleys may be utilized as movable, and still fall within the scope of the disclosed invention. Similarly, spring load may be utilized on both flanges of the driver pulley for embodiment three as well. Similar to embodiment one, various belt types, such as rubber based or metal based belts, may be utilized for the application.

[0053] FIG. 8, FIG. 9, and FIG. 10 illustrate a fourth embodiment of a transmission in accordance with this invention. The engine shaft 401, driven by the engine, drives the rings gears 406a 406b of both planetary gearboxes via the respective fixed gear ratio drivers 402a 402b. The engine shaft 401 is also drivingly coupled to a spring 413a 413b loaded variable ratio driver pulley 411. The springs 413a 431b maintain a force load on both flanges, towards each other, of the driver pulley 411. The driver pulley is coupled to a variable ratio driven pulley 409 via single belt 410. The driven pulley 409 comprises two flanges 418a 418b that are disconnected from each other. Each flange 418a 418b of the driven pulley 409 is connected to a respective shaft 417a 417b. Each flange shaft 417a 417b is coupled with a respective sun gear 403a 403b via a respective flexible and extending coupling arrangement comprising telescopic shafts 416a 416b, universal joints 415a 415b, and respective sun gear shafts 408a 408b. Each flange 418a 418b and shaft arrangement 417a 417b is secured to its position and orientation by a respective housing element 420a 420b. Each housing element 420a 420b provides rotational freedom to a respective flange 418a 418b and shaft 417a 417b arrangement via a thrust bearing 419a 419b against the respective flange 418a 418b and a radial bushing or bearing around the respective shaft 417a 417b. The rotational freedom is around the axis of each respective shaft 417a 417b. Each housing element 420a 420b is supported by a respective guide block 421a 421b. Each guide block 421a 421b, secures each respective housing element 420a 420b, and hence the respective flange 418a 418b and shaft 417a 417b arrangement, to its respective position and orientation, but allows only for one freedom of linear motion, via inter-engaging guides and grooves, that is along the contact surface between the respective block 421a 421b and the housing element 420a 420b. The guide blocks 421a 421b also allow for the respective shafts 417a 417b, to pass through a slot which allow for the rotational motion of the shafts 417a 417b, as well as the aforementioned linear motion. As also can be interpreted from FIG. 8, this linear motion for each housing element 420a 420b is parallel to the respective flange-belt contact surface angle determined by the cross-section of the driven pulley flanges 418a 418b created by the cutting surface extending through the center axes of the engine driver shaft 401 and the driven pulley flange shafts 417a 417b, as well as the output shafts 407a 407b. Guide blocks 421a 421b are secured to their positions such that their relative positions with respect to each other and with respect to driver pulley 411, engine shaft 401, and the planetary gearboxes are fixed. Hence the guide blocks 421a 421b are likely to be secured to the same body as these other components, such as the vehicle frame or transmission enclosure body. In a similar setup as to previous embodiments, the rings gears 406a 406b of both planetary gearboxes are driven at the same speed and direction, relative to each other, via the respective fixed ratio driver gears 402a 402b, while the sun gears 403a 403b can be driven at varying speeds through the variable ratio belt drive system. The planet gears 404a 404b are connected to a respective carrier element 405a 405b with a freedom of rotation around the axis of their shafts. The output shafts 407a 407b are also connected to each of the respective carrier elements 405a 405b. The resulting circular traveling motion of the planet gears 404a 404b, due to the differential rotational motions of respective sun 403a 403b and ring 406a 406b gears, rotate the carrier elements 405a 405b, and hence the output shafts 407a 407b, which ultimately drive the respective tracks of the vehicle.

[0054] FIG. 11 illustrates the principal modes of operation of the fourth embodiment as a result of the aforementioned movement of the flanges 418a 418b. Illustrations a, b, and c in FIG. 11 may represent the varying modes of straight motion of operation in forward, reverse and neutral directions. Illustration a is designated as the neutral (stop) position, where the axes of rotation of the driven pulley flanges' shafts 417a 417b are in line with each other, causing both flanges 418a 418b to rotate at the same speed, and the distance between the flanges 418a 418b are such that the resulting variable belt drive gearing ratio, vgr, for both planetary gearboxes provides for the aforementioned fgr=R1.Math.vgr equation to hold true. At this point, the ratio of the rotational speed of sun, to the rotational speed of ring gear equals to R1, .sub.sun gear/.sub.ring gear=R1, for both planetary gearboxes and hence the output shafts 407a 407b of both planetary gearboxes are held at neutral (stop) position. In illustration b, both flanges 418a 418b are moved upwardly, in a synchronized fashion, by the same amount, such that their axes of rotation are still in line, allowing the belt to ride the driven pulley 409 at a smaller radius than in illustration a. In response, the flanges of the spring loaded 413a 413b driver pulley 411 move closer to each other, to move the belt to a larger radius on the driver pulley, to maintain the belt tension, as well as to lower the vgr ratio by the same amount for both planetary gearboxes. As a result, the sun gears of both planetary gearboxes would rotate faster than in illustration a, and depending on the ratios utilized between other gear set components, this would result in a forward or reverse rotational movement by the same speed, on both output shafts, 407a 407b. In illustration c, both flanges are moved downwardly, again in a synchronized fashion, by the same amount, hence their axes of rotation are still in line. The flanges are closer to each other than in illustration a, hence the belt rides the driven pulley 409 at a larger radius than in illustration a. As a result, the increased belt tension pushes the flanges of the driver pulley 411 further apart from each other, moving the belt to a smaller radius on the driver pulley 411. The vgr ratio increases by the same amount for both planetary gearboxes, and hence the sun gears for both planetary gearboxes rotate slower than in illustration a. Accordingly, the output shafts 417a 417b rotate at the same speed relative to each other, but in the opposite direction than in illustration b.

[0055] Illustration d and e represents two of the various modes of steering operation. Accordingly, in illustration d, the left flange 418a is moved upwardly, while the right flange 418b is moved downwardly. At this point, the axes of rotation of both flanges 418a 418b are offset from each other but still parallel to each other, and the belt contacts the two flanges 418a 418b over different contact profiles, such that the belt rides the left flange 418a over an average contact profile of smaller radius, and the right flange 418b over an average contact profile of larger radius. Accordingly, the left flange 418a provides for a lower vgr ratio for the left planetary gearbox and rotates with a faster rotational speed than the right flange 418b, which provides for a larger vgr ratio for the right planetary gearbox. Resultantly, the output shafts 407a 407b rotate in opposing directions relative to each other, providing the steering action. In illustration e, the flanges are moved in a similar fashion but in opposing directions than in illustration d. Accordingly, the output shafts rotate in opposing directions than in illustration d, hence achieving steering in the opposing direction than in illustration d.

[0056] In modes of operation, where the flanges 418a 418b are moved differentially, two of which are presented in FIG. 11, illustrations d and e, the belt 410 possesses different contact profiles between the two flanges 418a 418b, as well as varying contact radii along the arc of contact on each flange 418a 418b, which may result in additional belt 410 behavior characteristics such as slip, flex or twist. Hence, an optimum arc of belt 410 contact may be preferred, particularly over the driven pulley flanges 418a 418b, to limit the extent of such additional belt 410 behavior. Hence an alternative embodiment, as presented in FIG. 12, may be employed where one or more idler pulleys 430 431 may be utilized between the driver 411 and the driven 409 pulleys, stationary or dynamic, to provide such desired arc of belt 410 contact, particularly over the driven pulley 409.

[0057] A belt engagement and disengagement mechanism may also be implemented by moving the flanges 418a 418b of the driven pulley 409 apart from each other beyond the extent that the driver pulley 411 can compensate, rendering the belt 410 loose. This may be achieved by limiting the travel of the flanges of the driver pulley 411 either within the spring 413a 413b load system or simply by letting the flanges of the driver pulley 411 abut each other. Another means of disengaging the belt 410 maybe possible by controllably moving the flanges of the driver pulley 411 apart from each other, against the spring loads 413a 413b. Moving the flanges 418a 418b of the driven pulley 409 apart from each other to the point where the belt 410 can fit through the gap in between may also be used as a means for belt replacement.

[0058] In an alternative embodiment, the controlling of the gearing ratio through the belt drive system may also be achieved by replacing the spring loaded 413a 413b driver pulley 411 by a controllable variable ratio pulley. Similar modes of operation can be achieved by controllably varying the ratio of the driver pulley, in coordination with the aforementioned controlled varying of the driven pulley 409, such that the belt 410 tension is maintained during the operation.

[0059] In the embodiment presented here, the controlled moving of the flanges 418a 418b can be achieved by moving the housing elements 420a 420b along the guide blocks 421a 421b. For instance, to use this transmission in a zero-turn lawnmower application, two handlebar controls may be coupled via linkage arms to the housing elements 420a 420b to resemble the control style of common hydraulically driven zero-turn lawnmowers. However, the significance of the embodiment is the aforementioned linear movement of the flanges 418a 418b, hence it is to be appreciated that the mechanism introduced in this specification for the desired movement of the flanges 418a 418b may also be achieved by alternative methods, such as different bracket or housing designs, and still fall within the scope of the disclosed invention. Similarly, alternative forms of flexible and extending couplings between the flanges 418a 418b and the respective sun gears 403a 403b, such as CV joints, may also be employed.

[0060] FIG. 13 and FIG. 14 illustrate a fifth embodiment of a transmission in accordance with this invention. This embodiment is similar to embodiment four, however, utilizes the sun gear sets 503a 503b and the planet gear sets 504a 504b along with the carrier elements 505a 505b of the planetary gearboxes as inputs, and the ring gear sets 506a 506b as outputs. Accordingly, the engine shaft 501, driven by the engine, drives the planet gear carrier elements 505a 505b of both planetary gearboxes via the respective fixed ratio driver pulleys 502a 502b and belts 529a 529b. The planetary gearboxes utilized in this embodiment have same size sun 503a 503b and ring 506a 506b gears, also commonly known as differential system. The planet gears 504a 504b are free to rotate about the axes of their respective shafts that couple them to their respective carrier elements 505a 505b, and are placed in between the respective sun 503a 503b and the rings gears 506a 506b in a beveled fashion to achieve the aforementioned same size structure. Following the same structure as in embodiment four for the rest of embodiment five, the engine shaft 501 is also drivingly coupled with the spring loaded 513a 513b variable ratio driver pulley 511, which in turn is coupled via a belt 510 with a variable ratio driven pulley 509. The flanges 518a 518b of the driven variable ratio pulley 509 is disconnected from each other and each is connected to a respective shaft 517a 517b. Each shaft 517a 517b is then coupled with the respective sun gear 503a 503b of each planetary gearbox via flexible and extending coupling arrangement comprising telescopic shafts 516a 516b and universal joints 515a 515b, as well as the respective shafts 508a 508b of the sun gears 503a 503b. Each flange 518a 518b of the driven pulley 509, and each respective shaft 517a 517b are secured to its position and orientation, and guided in the same fashion of linear movement as in embodiment four via the respective housing elements 520a 520b, thrust bearings 519a 519b and the guide blocks 521a 521b. The ring gears 506a 506b are drivingly connected to the respective output shafts 507a 507b.

[0061] In this arrangement of inputs and output, in order for the output shaft 507a(507b), and hence the ring gear 506a(506b) of a planetary gearbox to be at neutral (stop) position, the sun gear 503a(503b) and the planet gear carrier element 505a(505b) need to rotate in the same direction, but with the planet gear carrier element 505a(505b) rotating at half the rotational speed of the sun gear 503a(503b). Hence, consideration has to be given accordingly in selecting the appropriate gearing ratios among the inputs to the planetary gearbox system to achieve the desired range of motion. Following the same operational modes as in embodiment four, the straight driving motion in forward, reverse and neutral directions are achieved by moving the flanges 518a 518b in synchronization with each other in the same direction and magnitude, while the steering is achieved by moving the flanges 518a 518b in differential amounts and directions relative to each other. Embodiment five would benefit from all the alternative embodiment considerations as outlined for embodiment four, due to the similar structure.

[0062] For all the embodiments presented here, various reasons such as the layout of the system within the vehicle, required arc of belt contact over the pulleys, required gearing ratios between components and hence the required gear and pulley sizes, and serviceability considerations may require the position and orientation of the components of the transmission to vary from the illustrations presented in this context. For instance, a belt coupling, as illustrated in embodiment five, chain drive or worm gear may be utilized between the engine and the utilized gear set of the planetary gearboxes for the fixed gear ratio coupling. Idler gears may be utilized in between gear couplings, such as in between the engine driver gear and the ring gear sets in embodiments one, two, three and four, to vary the position and orientation of the engine shaft with respect to planetary gearboxes. Similarly, other forms of couplings between the variable ratio belt drive system, the engine, as well as the gear sets of the planetary gearbox, such as flexible couplings or beveled gearing, chain drive may be employed. It is, therefore, to be appreciated by the reader to consider these alternative forms of coupling between the components of the transmission, and still fall within the scope of the disclosed invention, so long as the required directions of motion of components and the gear ratios are maintained. Other forms of planetary gearboxes, such as the one illustrated within embodiment five, may also be employed. Also, other forms of biasing elements to provide the function of the spring in spring loaded pulleys may also be employed, such as hydraulic pressure, or other forms of springs.

[0063] Depending on the implementation, various methodologies of controlling the variable ratio pulleys may be utilized. For instance, to use this transmission in a common zero-turn lawnmower application, two handlebar controls may be coupled via linkage arms to control each of the apparatuses that control the flange distances for the driven pulleys for embodiments one, two and three, or as aforementioned, each of the housing elements for embodiment four and five, to resemble the control style of common hydraulically driven zero-turn lawnmowers. In another instances, where enhanced control is desired, computerized logic based control systems may be implemented that may control the pulleys via actuators, as well as controlling the other components such as the engine throttle.